EDIT: I am not speaking of IO bound processes. I am speaking of CPU bound process. But, here I do not want my process to keep on hogging CPU. If i have a 4 core machines and if i run four simple loops within a process, the CPU consumption shoots up to 400% till the application/process is running.
I am seeking here some experience on the topic which everyone would have faced some time or other. e.g. I debugged once an application was hogging CPU on Windows as it was looping continuously to search for a non-existent file.
How can I write my program in a way that two different CPU bound applications run smoothly (give a good response)?
It is easier to rewrite/redesign/refactor code than profiling and fixing it.
These suggestions go a long way for the beginner to understand the concepts.
Find the parts where it is spending the most time.
Do not fall into the trap of perverting your code up front in the name of optimization.
Remember Amdhal's Law. You aren't going to get noticeable improvements by speeding up something that is already only consuming 1% of your program's time. You get the best bang for your optimization buck by speeding up the part your program spends the most of its time doing.
Do as little work as possible.
Since you have edited your original question I'll add some more thoughts here to address the specific situation that you have described.
Assuming that you don't know where your process is blocking (since you were asking for debugging tips) you can start by just pausing the debugger, this will stop the application whatever it is doing and from there you can investigate the current location of all the threads and see if any of them are in a tight loop.
Secondly any decent profiler will easily help catch situations like this. Attach the profiler and run the application to the blocked point look at the calls that are dramatically getting a greater percentage of your total runtime. From there you can work your way back out to find the blocking loop.
Once you have located your problem ideally rethink the algorithm to avoid the situation completely. If this isn't possible then introduce sleep commands on the thread. This will allow other threads to get onto the CPU and increase the responsiveness of the application and the OS as a whole at the expense of increasing the operations runtime. The trick to multicore programming is ensuring that all your threads compromise between performance and consideration to the other waiting tasks.
Without knowing the specific language or operating system your targeting I can't advise on the but debugger/profiler combination for the problem, but I'd imagine there are good solutions out there for most mature languages.
Use a profiler religiously. Don't rely on common sense when searching for bottlenecks.
Learn big-O notation, remember big-O for common algorithms.
Avoid busy wait loops at all costs.
In case of embedded, learn how to make code fit into code cache, that can make a tenfold speedup sometimes on tight loops.
When doing high-level layered development, learn how to cache data efficently (for example, to minimize the number of DB statements).
If its purely CPU usage gain you're after then it's big-O notation you need. You need to work out how to get your algorithms to work in the least computations possible.
However, as for general performance, I find CPU usage to be one of the lesser bottlenecks.
Data binding, do you get all the data up front or just get it as required. Choosing one of these methods can be key to the performance of your app.
Can you reduce the data you're working on? If you can get it all to fit in memory easily, you can gain performance here. On a side note, if you put too much in memory it can have an opposite effect.
I think to sum up, there is no generic solution to performance. Write your code (with some intelligence), then look at where it is struggling.
I am speaking of CPU bound process. But, here I do not want my process to keep on hogging CPU. If i have a 4 core machines and if i run four simple loops within a process, the CPU consumption shoots up to 400% till the application/process is running.
Under normal circumstances, your code will even consume CPU cycles when it doesn't have to do anything (i.e. "busy wait").
For example, an empty infinite loop will simply run as fast as it possibly can, if it doesn't have to do anything else.
However, in some circumstances, you don't want to busy wait, or on some platforms you may want to avoid it at all.
One established way of doing this is to use sleep calls when idling, so that the system scheduler can reschedule all running threads. Similarly, you could use timers to determine your function's actual update rate and simply avoid calling your code if it doesn't have to be run (this is a mechanism that is sometimes used by games or simulators).
In general, you'll want to avoid polling and instead use intelligent data structures (for example a job queue) that provide for a possibility to automatically adjust your runtime behavior accordingly, without having to check the data structure itself permanently.
calculate memory of your operations.
calculate time of each operations.
It's not quite clear to me whether you're looking for ways to make the most efficient use of CPU, or ways to avoid bogging down a machine when you've got a lot of CPU-intensive stuff to do.
For the former, you ideally want an OS that will simply let you take over the CPU(s) completely for as long as you like, so you don't have to waste CPU cycles on the OS itself, not to mention any other processes that might be running.
For the latter, well, I've been writing some some code lately that uses poorly designed CPU-bound algorithms, and the new Intel I7 processor has been my saviour. Given four cores each able to run two threads, I merely try to limit my OS thread usage to five or six per application, and I've still got CPU available to switch to another window to run the kill command. At least until I drive the system into swap with space leaks.
Good suggestions here. The simpler you write the code, the more time you will save yourself.
I look at performance tuning as an extension of debugging. People say measure, measure, measure, but I don't. I just let the program tell me exactly what the problem is, by dropping in on it unannounced, several times if needed. It's usually a surprise, and it's never wrong.
The usual history of this, depending on how big the program, is finding and fixing a series of performance problems, each giving anywhere from 10% to 50% speedup (more if there is a bad problem). This gives an overall speedup of maybe 10 times.
Then the samples tell me exactly what it is doing, but I can't think of how to fix it without a basic redesign, realizing that if I had done the design differently in the first place, it would have been a lot faster to start with.
Supposing I can do the redesign, then I can do a few more rounds of performance find-and-fix. After this, when I hit the point of diminishing returns, I know it is about as fast as physically possible, and I can single-step it at the assembly level and watch every instruction "pulling its weight" in getting to the answer.
There is real satisfaction in getting to that point.
Not the answer you're looking for? Browse other questions tagged performance cpu-usage cpu-speed or ask your own question.


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Researchers use 3-D printing to guide human face transplants
by Radiological Society of North America
3-D print model used in surgical planning. Credit: RSNA
Researchers are using computed tomography (CT) and 3-D printing technology to recreate life-size models of patients' heads to assist in face transplantation surgery, according to a study presented today at the annual meeting of the Radiological Society of North America (RSNA).
Physicians at Brigham and Women's Hospital in Boston performed the country's first full-face transplantation in 2011 and have subsequently completed four additional face transplants. The procedure is performed on patients who have lost some or all of their face as a result of injury or disease.
In the study, a research team led by Frank J. Rybicki, M.D., radiologist and director of the hospital's Applied Imaging Science Laboratory, Bohdan Pomahac, M.D., lead face transplantation surgeon, and Amir Imanzadeh, M.D., research fellow, assessed the clinical impact of using 3-D printed models of the recipient's head in the planning of face transplantation surgery.
"This is a complex surgery and its success is dependent on surgical planning," Dr. Rybicki said. "Our study demonstrated that if you use this model and hold the skull in your hand, there is no better way to plan the procedure."
Each of the transplant recipients underwent preoperative CT with 3-D visualization. To build each life-size skull model, the CT images of the transplant recipient's head were segmented and processed using customized software, creating specialized data files that were input into a 3-D printer.
"In some patients, we need to modify the recipient's facial bones prior to transplantation," Dr. Imanzadeh said. "The 3-D printed model helps us to prepare the facial structures so when the actual transplantation occurs, the surgery goes more smoothly."
Although the entire transplant procedure lasts as long as 25 hours, the actual vascular connections from the donor face to the recipient typically takes approximately one hour, during which time the patient's blood flow must be stopped.
"If there are absent or missing bony structures needed for reconstruction, we can make modifications based on the 3-D printed model prior to the actual transplantation, instead of taking the time to do alterations during ischemia time," Dr. Rybicki said. "The 3-D model is important for making the transplant cosmetically appealing."
The researchers said they also used the models in the operating room to increase the surgeons' understanding of the anatomy of the recipient's face during the procedure.
"You can spin, rotate and scroll through as many CT images as you want but there's no substitute for having the real thing in your hand," Dr. Rybicki said. "The ability to work with the model gives you an unprecedented level of reassurance and confidence in the procedure."
Senior surgeons and radiologists involved in the five face transplantations agreed that the 3-D printed models provided superior pre-operative data and allowed complex anatomy and bony defects to be better appreciated, reducing total procedure time.
"Less time spent in the operating room is better for overall patient outcomes," Dr. Pomahac added.
Based on the results of this study, 3-D printing is now routinely used for surgical planning for face transplantation procedures at Brigham and Women's Hospital, and 3-D printed models may be implemented in other complex surgeries.
Provided by Radiological Society of North America
Citation: Researchers use 3-D printing to guide human face transplants (2014, December 1) retrieved 29 January 2023 from https://medicalxpress.com/news/2014-12-d-human-transplants.html
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redpajama_set_name: RedPajamaCommonCrawl


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Computed_tomography
It has been suggested that Synchrotron X-ray tomographic microscopy, X-ray tomography be merged into this article or section. (Discuss)
Computed tomography (CT), was originally known as "EMI scan" as it was developed at a research branch of EMI, a company best known today for its music and recording business. It was later known as computed axial tomography (CAT or CT scan) and body section roentgenography. It is a medical imaging method employing tomography where digital geometry processing is used to generate a three-dimensional image of the internals of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation. The word "tomography" is derived from the Greek tomos (slice) and graphein (to write). CT produces a volume of data which can be manipulated, through a process known as windowing, in order to demonstrate various structures based on their ability to block the X-ray beam. Although historically (see below) the images generated were in the axial or transverse plane (orthogonal to the long axis of the body), modern scanners allow this volume of data to be reformatted in various planes or even as volumetric (3D) representations of structures.
Although most common in healthcare, CT is also used in other fields, for example nondestructive materials testing. Another example is the DigiMorph project at the University of Texas at Austin which uses a CT scanner to study biological and paleontological specimens.
Additional recommended knowledge
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Correct Test Weight Handling Guide: 12 Practical Tips
Safe Weighing Range Ensures Accurate Results
2 Previous studies
2.1 Tomography
2.2 Tomosynthesis
3 Types of Modern CT acquisition
3.1 Scout/Pilot/Topogram
3.2 Axial
3.3 Cine
3.4 Helical/Spiral
3.5 DRR
4.1 Electron Beam CT
4.2 Helical or Spiral CT
4.3 Multislice CT
4.4 Dual Source CT
4.5 256+ Slice CT
4.6 Inverse geometry CT
5 Diagnostic use
5.1 Cranial
5.2 Chest
5.3 Pulmonary Angiogram
5.3.1 Diagnostic use
5.3.2 Acquisition
5.3.3 Interpretation
5.4 Cardiac
5.5 Abdominal and pelvic
5.6 Extremities
6 Advantages and hazards
6.1 Advantages over projection radiography
6.2 Radiation exposure
6.2.1 Typical scan doses
6.3 Adverse reactions to contrast agents
7.1 Windowing
9 Three dimensional (3D) Image Reconstruction
9.1 The principle
9.2 Multiplanar reconstruction
9.3 3D rendering techniques
9.4 3D rendering software
9.5 Image segmentation
9.6 Example
In the 1930s the Italian radiologist Alessandro Vallebona proposed a method to represent a single slice of the body on the radiographic film. This exam was known as tomography. The idea is based on simple principles of projective geometry: moving synchronously and in opposite directions the radiogen tube and the film, the image created by the points on the focal plane appears sharper, while the images of the other points annihilate as noise.
Tomography has been one of the pillars of radiologic diagnostics until the early 80's, when the advent of computer and of the circular methodic, this last due to Godfrey Newbold Hounsfield and Allan McLeod Cormack, gradually supplanted it in favour of CT.
The first commercially viable CT scanner was invented by Sir Godfrey Newbold Hounsfield in Hayes, United Kingdom at EMI Central Research Laboratories using X-rays. Hounsfield conceived his idea in 1967, and it was publicly announced in 1972. Allan McLeod Cormack of Tufts University, Massachusetts, USA independently invented a similar process, and both Hounsfield and Cormack shared the 1979 Nobel Prize in Medicine.
The original 1971 prototype took 160 parallel readings through 180 angles, each 1° apart, with each scan taking a little over five minutes. The images from these scans took 2.5 hours to be processed by algebraic reconstruction techniques on a large computer.
The CT scanner was "the greatest legacy" of the Beatles, with the massive profits resulting from their record sales enabling EMI to fund scientific research[1], including into computerised tomography. The first production X-ray CT machine (in fact called the "EMI-Scanner") was limited to making tomographic sections of the brain, but acquired the image data in about 4 minutes (scanning two adjacent slices) and the computation time (using a Data General Nova minicomputer) was about 7 minutes per picture. This scanner required the use of a water-filled Perspex tank with a pre-shaped rubber "head-cap" at the front, which enclosed the patient's head. The water-tank was used to reduce the dynamic range of the radiation reaching the detectors (between scanning outside the head compared with scanning through the bone of the skull). The images were relatively low resolution, being composed of a matrix of only 80 x 80 pixels. The first EMI-Scanner was installed in Atkinson Morley's Hospital in Wimbledon, England, and the first patient brain-scan was made with it in 1972. In the U.S., the first installation was at the Mayo Clinic. As a tribute to the impact of this system on medical imaging the Mayo Clinic has an EMI scanner on display in the Radiology Department.
The first CT system that could make images of any part of the body, and did not require the "water tank" was the ACTA scanner designed by Robert S. Ledley, DDS at Georgetown University.
Tomography
CT's primary benefit is the ability to separate anatomical structures at different depths within the body. A form of tomography can be performed by moving the X-ray source and detector during an exposure. Anatomy at the target level remains sharp, while structures at different levels are blurred. By varying the extent and path of motion, a variety of effects can be obtained, with variable depth of field and different degrees of blurring of 'out of plane' structures.
Although largely obsolete, conventional tomography is still used in specific situations such as dental imaging (orthopantomography) or in intravenous urography.
Digital tomosynthesis combines digital image capture and processing with simple tube/detector motion as used in conventional radiographic tomography - although there are some similarities to CT, it is a separate technique. In CT, the source/detector makes a complete 360 degree rotation about the subject obtaining a complete set of data from which images may be reconstructed. In digital tomosynthesis, only a small rotation angle (e.g. 40 degrees) with a small number of discrete exposures (e.g. 10) are used. This incomplete set of data can be digitally processed to yield images similar to conventional tomography with a limited depth of field. However, because the image processing is digital, a series of slices at different depths and with different thicknesses can be reconstructed from the same acquisition, saving both time and radiation exposure.
Because the data acquired is incomplete, tomosynthesis is unable to offer the extremely narrow slice widths that CT offers. However, higher resolution detectors can be used, allowing very-high in-plane resolution, even if the Z-axis resolution is poor. The primary interest in tomosynthesis is in breast imaging, as an extension to mammography, where it may offer better detection rates, with little extra increase in radiation exposure.
Reconstruction algorithms for tomosynthesis are significantly different from conventional CT, as the conventional filtered back projection algorithm requires a complete set of data. Iterative algorithms based upon expectation maximization are most commonly used, but are extremely computationally intensive. Some manufacturers have produced practical systems using commercial GPUs to perform the reconstruction.
Types of Modern CT acquisition
Scout/Pilot/Topogram
A Scout image is used in planning the exam and to establish where the target organs are located. The beginning and end of the scan are set by the target region and the location of the patient on the table. Once the Scout image is created it is used to determine the extent of the desired Axial/Helical scan. During the Scout scan the gantry is rotated to a fixed position and the table is translated as x-ray is delivered. The image appears similar to a radiograph.
In axial "step and shoot" acquisitions each slice/volume is taken and then the table is incremented to the next location. In multislice scanners each location is multiple slices and represents a volume of the patient anatomy. Tomographic reconstruction is used to generate Axial images.
A cine acquisition is used when the temporal nature is important. This is used in Perfusion applications to evaluate blood flow, blood volume and mean transit time. Cine is a time sequence of axial images. In a Cine acquisition the cradle is stationary and the gantry rotates continuously. Xray is delivered at a specified interval and duration.
Helical/Spiral
Helical is a very fast way to examine the target anatomy. The volume is scanned very quickly because the table is in constant motion as the gantry rotates continuously. There is no interscan delay between slices as in a Axial acquisition.
A Digitally Reconstructed Radiograph (DRR) is used to help plan the treatment. The DRR is corrected for the fan beam effect. This is the prime difference from the Scout/Pilot image.
It has been suggested that Digitally Reconstructed Radiograph be merged into this article or section. (Discuss)
Since the introduction of the first clinical system by Hounsfield, several generations of scanners have been produced, with distinguishing tube-detector configuration and scanning motion (Canadian Association of Medical Radiation Technologists CT Imaging 1-Theory textbook).
min scan time
First translate-rotate 1~2 pencil thin 2.5 min
Second translate-rotate 3~52 narrow fan 10 sec
Third Rotate-rotate 256~1000 wide fan 0.5 sec
Fourth Rotate-fixed 600~4800 wide fan 1 sec
Fifth electron beam 1284 detectors wide fan electron beam 33 ms
Although numbered sequentially, the 3rd and 4th generation designs developed at approximately the same time. The concept of electron beam CT, which some authors have called 5th generation, followed later. Some authors have described up to 7 generations of CT design. However, it is only generations one to four that are widely, and consistently, recognised.
In the first and second generation designs, the X-ray beam was not wide enough to cover the entire width of the 'slice' of interest. A mechanical arrangement was required to move the X-ray source and detector horizontally across the field of view. After a sweep, the source/detector assembly would be rotated a few degrees, and another sweep performed. This process would be repeated until 360 degrees (or 180 degrees) had been covered. The complex motion placed a limit on the minimum scan time at approximately 20 seconds per image.
In the 3rd and 4th generation designs, the X-ray beam is able to cover the entire field of view of the scanner. This avoids the need for any horizontal motion; an entire 'line' can be captured in an instant. This allowed simplification of the motion to rotation of the X-ray source. Third and fourth generation designs differ in the arrangement of the detectors. In 3rd generation, the detector array is as wide as the beam, and must therefore rotate as the source rotates. In 4th generation, an entire ring of stationary detectors are used.
The third generation design suffers because it is highly sensitive to detector performance. Because of the fixed relationship of a detector to a specific part of the beam, any miscalibration or malfunction of an individual detector will appear as a ring in the final reconstructed image. As the detectors moved and were exposed to physical stress, loss of calibration and subsequent 'ring artifacts' were commonplace. The fourth generation, with its fixed detectors benefited not just from improved reliability of the detectors, but because the detectors could be automatically calibrated as the X-ray beam approached, and because the different reconstruction geometry meant that a malfunction would lead only to subtle loss of image contrast (fogging) rather than a visible ring.
Solving the issue of detector stability has led 3rd generation designs to the dominant position in contemporary designs. 4th generation designs suffered very high cost (due to the large number of detectors) and had very high susceptibility to 'streak artifacts' (due to compton scattering). All current CT scanners are of the 3rd generation design.
Electron Beam CT
Electron beam tomography (EBCT) was introduced in the early 1980s, by medical physicist Andrew Castagnini, as a method of improving the temporal resolution of CT scanners. Because the X-ray source has to rotate by over 180 degrees in order to capture an image the technique is inherently unable to capture dynamic events or movements that are quicker than the rotation time.
Instead of rotating a conventional X-ray tube around the patient, the EBCT machine houses a huge vacuum tube in which an electron beam is electro-magnetically steered towards an array of tungsten X-ray anodes arranged circularly around the patient. Each anode is hit in turn by the electron beam and emits X-rays that are collimated and detected as in conventional CT. The lack of moving parts allows very quick scanning, with single slice acquisition in 50-100 ms, making the technique ideal for capturing images of the heart. EBCT has found particular use for assessment of coronary artery calcium, a means of predicting risk of coronary artery disease.
The very high cost of EBCT equipment, and its poor flexibility (EBCT scanners are essentially single-purpose cardiac scanners), has led to poor uptake; fewer than 150 of these scanners have been installed worldwide. EBCT's role in cardiac imaging is rapidly being supplanted by high-speed multi-detector CT, which can achieve near-equivalent temporal resolution with much faster z-axis coverage.
Helical or Spiral CT
See main article Helical cone beam computed tomography
Helical, also called spiral, CT was introduced in the early 1990s, with much of the development led by Willi Kalender and Kazuhiro Katada. In older CT scanners, the X-ray source would move in a circular fashion to acquire a single 'slice', once the slice had been completed, the scanner table would move to position the patient for the next slice; meanwhile the X-ray source/detectors would reverse direction to avoid tangling their cables.
In helical CT the X-ray source (and detectors in 3rd generation designs) are attached to a freely rotating gantry. During a scan, the table moves the patient smoothly through the scanner; the name derives from the helical path traced out by the X-ray beam. It was the development of two technologies that made helical CT practical: slip rings to transfer power and data on and off the rotating gantry, and the switched mode power supply powerful enough to supply the X-ray tube, but small enough to be installed on the gantry.
The major advantage of helical scanning compared to the traditional shoot-and-step approach, is speed; a large volume can be covered in 20-60 seconds. This is advantageous for a number or reasons: 1) often the patient can hold their breath for the entire study, reducing motion artifacts, 2) it allows for more optimal use of intravenous contrast enhancement, and 3) the study is quicker than the equivalent conventional CT permitting the use of higher resolution acquisitions in the same study time. The data obtained from spiral CT is often well-suited for 3D imaging because of the lack of motion mis-registration and the increased out of plane resolution. These major advantages led to the rapid rise of helical CT as the most popular type of CT technology.
Despite the advantages of helical scanning, there are a few circumstances where it may not be desirable - there is, of course, no difficulty in configuring a helical capable scanner for scanning in shoot-and-step mode. All other factors being equal, helical CT has slightly lower z-axis resolution than step-and-shoot (due to the continual movement of the patient). Where z-resolution is critical but where it is undesirable to scan at a higher resolution setting (due to the higher radiation exposure required) e.g. brain imaging, step-and-shoot may still be the preferred method.
Multislice CT
Multislice CT scanners are similar in concept to the helical or spiral CT but there are more than one detector ring. It began with two rings in mid nineties, with a 2 solid state ring model designed and built by Elscint (Haifa) called CT TWIN, with one second rotation (1993): It was followed by other manufacturers. Later, it was presented 4, 8, 16, 32, 40 and 64 detector rings, with increasing rotation speeds. Current models (2007) have up to 3 rotations per second, and isotropic resolution of 0.35mm voxels with z-axis scan speed of up to 18 cm/s.[2]. This resolution exceeds that of High Resolution CT techniques with single-slice scanners, yet it is practical to scan adjacent, or overlapping, slices - however, image noise and radiation exposure significantly limit the use of such resolutions.
The major benefit of multi-slice CT is the increased speed of volume coverage. This allows large volumes to be scanned at the optimal time following intravenous contrast administration; this has particularly benefitted CT angiography techniques - which rely heavily on precise timing to ensure good demonstration of arteries.
Computer power permits increasing the postprocessing capabilities on workstations. Bone suppression, volume rendering in real time, with a natural visualization of internal organs and structures, and automated volume reconstruction really change the way diagnostic is performed on CT studies and this models become true volumetric scanners. The ability of multi-slice scanners to achieve isotropic resolution even on routine studies means that maximum image quality is not restricted to images in the axial plane - and studies can be freely viewed in any desired plane.
Dual Source CT
Siemens introduced a CT model with dual X-ray tube and dual array of 64 slice detectors, at the 2005 Radiological Society of North America (RSNA) medical meeting. Dual sources increase the temporal resolution by reducing the rotation angle required to acquire a complete image, thus permitting cardiac studies without the use of heart rate lowering medication, as well as permitting imaging of the heart in systole. The use of two x-ray units makes possible the use of dual energy imaging, which allows an estimate of the average atomic number in a voxel, as well as the total attenutaion. This permits automatic differentiation of calcium (e.g. in bone, or diseased arteries) from iodine (in contrast medium) or titanium (in stents) - which might otherwise be impossible to differentiate. It may also improve the characterization of tissues allowing better tumor differentiation.
256+ Slice CT
At RSNA 2007, Philips announced a 256 slice scanner, while Toshiba announced a "dynamic volume" scanner based on 320 slices. The majority of published data with regard to both technical and clinical aspects of the systems have been related to the prototype unit made by Toshiba Medical Systems. The recent 3 month Beta installation at Johns Hopkins Press Release using a Toshiba system tested the clinical capabilities of this technology JHU Gazette. The technology currently remains in a development phase but has demonstrated the potential to significantly reduce radiation exposure by eliminating the requirement for a helical examination in both cardiac CT angiography and whole brain perfusion studies for the evaluation of stroke.
Inverse geometry CT
Inverse geometry CT (IGCT) is a novel concept which is being investigated as refinement of the classic third generation CT design. Although the technique has been demonstrated on a laboratory proof-of-concept device, it remains to be seen whether IGCT is feasible for a practical scanner. IGCT reverses the shapes of the detector and X-ray sources. The conventional third-generation CT geometry uses a point source of X-rays, which diverge in a fan beam to act on a linear array of detectors. In multidetector computed tomography (MDCT), this is extended in 3 dimensions to a conical beam acting on a 2D array of detectors. The IGCT concept, conversely, uses an array of highly collimated X-ray sources which act on a point detector. By using a principle similar to electron beam tomography (EBCT), the individual sources can be activated in turn by steering an electron beam onto each source target.
The rationale behind IGCT is that it avoids the disadvantages of the cone-beam geometry of third generation MDCT. As the z-axis width of the cone beam increases, the quantity of scattered radiation reaching the detector also increases, and the z-axis resolution is thereby degraded - because of the increasing z-axis distance that each ray must traverse. This reversal of roles has extremely high intrinsic resistance to scatter; and, by reducing the number of detectors required per slice, it makes the use of better performing detectors (e.g. ultra-fast photon counting detectors) more practical. Because a separate detector can be used for each 'slice' of sources, the conical geometry can be replaced with an array of fans, permitting z-axis resolution to be preserved.
Diagnostic use
Since its introduction in the 1970s, CT has become an important tool in medical imaging to supplement X-rays and medical ultrasonography. Although it is still quite expensive, it is the gold standard in the diagnosis of a large number of different disease entities. It has more recently begun to also be used for preventive medicine or screening for disease, for example CT colonography for patients with a high risk of colon cancer. Although a number of institutions offer full-body scans for the general population, this practice remains controversial due to its lack of proven benefit, cost, radiation exposure, and the risk of finding 'incidental' abnormalities that may trigger additional investigations.
Diagnosis of cerebrovascular accidents and intracranial hemorrhage is the most frequent reason for a "head CT" or "CT brain". Scanning is done with or without intravenous contrast agents. CT generally does not exclude infarct in the acute stage of a stroke. However, CT is useful to exclude an intra-cranial hemorrhage as a cause, or complication of the stroke. For the detection of acute hemorrhage, especially subarachnoid hemorrhage, CT is the test of choice as it is more sensitive than MRI.
For detection of tumors, CT scanning with IV contrast is occasionally used but is less sensitive than magnetic resonance imaging (MRI).
CT has an important role in evaluation of the functioning of a ventriculoperitoneal shunt by demonstrating the volume of the ventricular system. Although CT cannot assess intracranial pressure, it can demonstrate several important causes of raised intracranial pressure. Despite the limitation that CT may not detect raised intracranial pressure, it may help in the clinical decision to perform lumbar puncture and is often performed in this context.
CT is also useful in the setting of trauma for evaluating facial and skull fractures.
In the head/neck/mouth area, CT scanning is used for surgical planning for craniofacial and dentofacial deformities, evaluation of cysts and some tumors of the jaws/paranasal sinuses/nasal cavity/orbits, diagnosis of the causes of chronic sinusitis, and for planning of dental implant reconstruction.
CT is excellent for detecting both acute and chronic changes in the lung parenchyma. A variety of different techniques are used depending on the suspected abnormality. For evaluation of chronic interstitial processes (emphysema, fibrosis, and so forth), thin sections with high spatial frequency reconstructions are used - often scans are performed both in inspiration and expiration. This special technique is called High resolution CT (HRCT)....... Note: HRCT is normally done with thin section with skipped areas between the thin sections. Therefore it produces a sampling of the lung and not continuous images. Continuous images are provided in a standard CT of the chest.
For detection of airspace disease (such as pneumonia) or cancer, relatively thick sections and general purpose image reconstruction techniques may be adequate. IV contrast may also be used as it clarifies the anatomy and boundaries of the great vessels and improves assessment of the mediastinum and hilar regions for lymphadenopathy; this is particularly important for accurate assessment of cancer.
CT angiography of the chest is also becoming the primary method for detecting pulmonary embolism (PE) and aortic dissection, and requires accurately timed rapid injections of contrast (Bolus Tracking) and high-speed helical scanners. CT is the standard method of evaluating abnormalities seen on chest X-ray and of following findings of uncertain acute significance.
Pulmonary Angiogram
CT pulmonary angiogram (CTPA) is a medical diagnostic test used to diagnose pulmonary embolism (PE). It employs computed tomography to obtain an image of the pulmonary arteries.
It is a preferred choice of imaging in the diagnosis of PE due to its minimally invasive nature for the patient, whose only requirement for the scan is a cannula (usually a 20G). Before this test is requested, it is usual for the referring clinician to have carried out a D-dimer blood test and requested a chest X-Ray to rule out any other possible differential diagnosis.
MDCT (multi detector CT) scanners give the optimum resolution and image quality for this test
Images are usually taken on a 0.625mm slice thickness, although 2mm is sufficient.
50 - 100 mls of contrast is given to the patient at a rate of 4 ml/s.
The tracker/locator is placed at the level of the Pulmonary Arteries, which sit roughly at the level of the carina.
Images are acquired with the maximum intensity of radio-opaque contrast in the Pulmonary Arteries. This is done using bolus tracking.
CT machines are now so sophisticated that the test can be done with a patient visit of 5 minutes with an approximate scan time of only 5 seconds or less.
A normal CTPA scan will show the contrast filling the pulmonary vessels, looking bright white. Ideally the aorta should be empty of contrast, to reduce any partial volume artefact which may result in a false positive. Any mass filling defects, such as an embolus, will appear dark in place of the contrast, filling / blocking the space where blood should be flowing into the lungs.
With the advent of subsecond rotation combined with multi-slice CT (up to 64-slice), high resolution and high speed can be obtained at the same time, allowing excellent imaging of the coronary arteries (cardiac CT angiography). Images with an even higher temporal resolution can be formed using retrospective ECG gating. In this technique, each portion of the heart is imaged more than once while an ECG trace is recorded. The ECG is then used to correlate the CT data with their corresponding phases of cardiac contraction. Once this correlation is complete, all data that were recorded while the heart was in motion (systole) can be ignored and images can be made from the remaining data that happened to be acquired while the heart was at rest (diastole). In this way, individual frames in a cardiac CT investigation have a better temporal resolution than the shortest tube rotation time.
Because the heart is effectively imaged more than once (as described above), cardiac CT angiography results in a relatively high radiation exposure around 12 mSv. For the sake of comparison, a chest X-ray carries a dose of approximately 0.02[3] to 0.2 mSv and natural background radiation exposure is around 0.01 mSv/day. Thus, cardiac CTA is equivalent to approximately 100-600 chest X-rays or over 3 years worth of natural background radiation. Methods are available to decrease this exposure, however, such as prospectively decreasing radiation output based on the concurrently acquired ECG (aka tube current modulation.) This can result in a significant decrease in radiation exposure, at the risk of compromising image quality if there is any arrhythmia during the acquisition. The significance of radiation doses in the diagnostic imaging range has not been proven, although the possibility of inducing an increased cancer risk across a population is a source of significant concern. This potential risk must be weighed against the competing risk of not performing a test and potentially not diagnosing a significant health problem such as coronary artery disease.
It is uncertain whether this modality will replace invasive coronary catheterization. Currently, it appears that the greatest utility of cardiac CT lies in ruling out coronary artery disease rather than ruling it in. This is because the test has a high sensitivity (greater than 90%) and thus a negative test result means that a patient is very unlikely to have coronary artery disease and can be worked up for other causes of their chest symptoms. This is termed a high negative predictive value. A positive result is less conclusive and often will be confirmed (and possibly treated) with subsequent invasive angiography. For the record, the positive predictive value of cardiac CTA is estimated at approximately 82% and the negative predictive value is around 93%.
Dual Source CT scanners, introduced in 2005, allow higher temporal resolution by acquiring a full CT slice in only half a rotation, thus reducing motion blurring at high heart rates and potentially allowing for shorter breath-hold time. This is particularly useful for ill patients who have difficulty holding their breath or who are unable to take heart-rate lowering medication.
The speed advantages of 64-slice MSCT have rapidly established it as the minimum standard for newly installed CT scanners intended for cardiac scanning. Manufacturers are now actively developing 256-slice and true 'volumetric' scanners, primarily for their improved cardiac scanning performance.
The latest MSCT scanners acquire images only at 70-80% of the R-R interval (late diastole). This prospective gating can reduce effective dose from 10-15mSv to as little as 1.2mSv in follow-up patients acquiring at 75% of the R-R interval. Effective doses at a centre with well trained staff doing coronary imaging can average less than the doses for conventional coronary angiography.
Abdominal and pelvic
CT is a sensitive method for diagnosis of abdominal diseases. It is used frequently to determine stage of cancer and to follow progress. It is also a useful test to investigate acute abdominal pain. Renal/urinary stones, appendicitis, pancreatitis, diverticulitis, abdominal aortic aneurysm, and bowel obstruction are conditions that are readily diagnosed and assessed with CT. CT is also the first line for detecting solid organ injury after trauma.
Oral and/or rectal contrast may be used depending on the indications for the scan. A dilute (2% w/v) suspension of barium sulfate is most commonly used. The concentrated barium sulfate preparations used for fluoroscopy e.g. barium enema are too dense and cause severe artifacts on CT. Iodinated contrast agents may be used if barium is contraindicated (e.g. suspicion of bowel injury). Other agents may be required to optimize the imaging of specific organs: e.g. rectally administered gas (air or carbon dioxide) for a colon study, or oral water for a stomach study.
CT has limited application in the evaluation of the pelvis. For the female pelvis in particular, ultrasound and MRI are the imaging modalities of choice. Nevertheless, it may be part of abdominal scanning (e.g. for tumors), and has uses in assessing fractures.
CT is also used in osteoporosis studies and research along side DXA scanning. Both CT and DXA can be used to assess bone mineral density (BMD) which is used to indicate bone strength, however CT results do not correlate exactly with DXA (the gold standard of BMD measurement). CT is far more expensive, and subjects patients to much higher levels of ionizing radiation, so it is used infrequently.
CT is often used to image complex fractures, especially ones around joints, because of its ability to reconstruct the area of interest in multiple planes. Fractures, ligamentous injuries and dislocations can easily be recognised with a 0.2 mm resolution.[citation needed]
Advantages and hazards
Advantages over projection radiography
First, CT completely eliminates the superimposition of images of structures outside the area of interest. Second, because of the inherent high-contrast resolution of CT, differences between tissues that differ in physical density by less than 1% can be distinguished. Third, data from a single CT imaging procedure consisting of either multiple contiguous or one helical scan can be viewed as images in the axial, coronal, or sagittal planes, depending on the diagnostic task. This is referred to as multiplanar reformatted imaging.
Radiation exposure
CT is regarded as a moderate to high radiation diagnostic technique. While technical advances have improved radiation efficiency, there has been simultaneous pressure to obtain higher-resolution imaging and use more complex scan techniques, both of which require higher doses of radiation. The improved resolution of CT has permitted the development of new investigations, which may have advantages; e.g. Compared to conventional angiography, CT angiography avoids the invasive insertion of an arterial catheter and guidewire; CT colonography may be as useful as a barium enema for detection of tumors, but may use a lower radiation dose.
The greatly increased availability of CT, together with its value for an increasing number of conditions, has been responsible for a large rise in popularity. So large has been this rise that, in the most recent comprehensive survey in the UK, CT scans constituted 7% of all radiologic examinations, but contributed 47% of the total collective dose from medical X-ray examinations in 2000/2001.[4] Increased CT usage has led to an overall rise in the total amount of medical radiation used, despite reductions in other areas.
The radiation dose for a particular study depends on multiple factors: volume scanned, patient build, number and type of scan sequences, and desired resolution and image quality. Additionally, two helical CT scanning parameters that can be adjusted easily and that have a profound effect on radiation dose are tube current and pitch.[5] CT scans of children have been estimated to produce non-negligible increases in the probability of lifetime cancer mortality leading to calls for the use of reduced current settings for CT scans of children.[6] A 2007 report in the New England Journal of Medicine suggested that the radiation from current CT-scan use may cause as many as 1 in 50 future cases of cancer.[7]
According to the USAToday, and members of the American Heart Association, an average CT scan can expose a patient to between 1,000 to 10,000 millirems of radiation, depending on the exact machine and the examination being performed. However, Japanese people who were 1 mile from ground zero received only 3,ooo millirems of radiation, on average. [8]
Typical scan doses
Typical effective dose (mSv)
(milli rem)
Chest X-ray 0.1 10
Head CT 1.5[9] 150
Abdomen CT 5.3[9] 530
Chest CT 5.8[9] 580
Chest, Abdomen and Pelvis CT 9.9[9] 990
Cardiac CT angiogram 6.7-13[10] 670 - 1300
CT colonography (virtual colonoscopy) 3.6 - 8.8 360 - 880
Adverse reactions to contrast agents
Because CT scans rely on intravenously administered contrast agents in order to provide superior image quality, there is a low but non-negligible level of risk associated with the contrast agents themselves. Certain patients may experience severe and potentially life-threatening allergic reactions to the contrast dye.
The contrast agent may also induce kidney damage. The risk of this is increased with patients who have preexisting renal insufficiency, preexisting diabetes, or reduced intravascular volume. In general, if a patient has normal kidney function, then the risks of contrast nephropathy are negligible. Patients with mild kidney impairment are usually advised to ensure full hydration for several hours before and after the injection. For moderate kidney failure, the use of iodinated contrast should be avoided; this may mean using an alternative technique instead of CT e.g. MRI. Perhaps paradoxically, patients with severe renal failure requiring dialysis do not require special precautions, as their kidneys have so little function remaining that any further damage would not be noticeable and the dialysis will remove the contrast agent.
X-ray slice data is generated using an X-ray source that rotates around the object; X-ray sensors are positioned on the opposite side of the circle from the X-ray source. Many data scans are progressively taken as the object is gradually passed through the gantry. They are combined together by the mathematical procedure known as tomographic reconstruction.
Newer machines with faster computer systems and newer software strategies can process not only individual cross sections but continuously changing cross sections as the gantry, with the object to be imaged, is slowly and smoothly slid through the X-ray circle. These are called helical or spiral CT machines. Their computer systems integrate the data of the moving individual slices to generate three dimensional volumetric information (3D-CT scan), in turn viewable from multiple different perspectives on attached CT workstation monitors.
In conventional CT machines, an X-ray tube and detector are physically rotated behind a circular shroud (see the image above right); in the electron beam tomography (EBT) the tube is far larger and higher power to support the high temporal resolution. The electron beam is deflected in a hollow funnel shaped vacuum chamber. X-rays are generated when the beam hits the stationary target. The detector is also stationary.
The data stream representing the varying radiographic intensity sensed reaching the detectors on the opposite side of the circle during each sweep is then computer processed to calculate cross-sectional estimations of the radiographic density, expressed in Hounsfield units. Sweeps cover 360 or just over 180 degrees in conventional machines, 220 degrees in EBT. CT is used in medicine as a diagnostic tool and as a guide for interventional procedures. Sometimes contrast materials such as intravenous iodinated contrast are used. This is useful to highlight structures such as blood vessels that otherwise would be difficult to delineate from their surroundings. Using contrast material can also help to obtain functional information about tissues.
Pixels in an image obtained by CT scanning are displayed in terms of relative radiodensity. The pixel itself is displayed according to the mean attenuation of the tissue(s) that it corresponds to on a scale from -1024 to +3071 on the Hounsfield scale. Pixel is a two dimensional unit based on the matrix size and the field of view. When the CT slice thickness is also factored in, the unit is known as a Voxel, which is a three dimensional unit. The phenomenon that one part of the detector cannot differ between different tissues is called the "Partial Volume Effect". That means that a big amount of cartilage and a thin layer of compact bone can cause the same attenuation in a voxel as hyperdense cartilage alone. Water has an attenuation of 0 Hounsfield units (HU) while air is -1000 HU, cancellous bone is typically +400 HU, cranial bone can reach 2000 HU or more (os temporale) and can cause artifacts. The attenuation of metallic implants depends on atomic number of the element used: Titanium usually has an amount of +1000 HU, iron steel can completely extinguish the X-ray and is therefore responsible for well-known line-artifacts in computed tomograms.
Windowing
Windowing is the process of using the calculated Hounsfield units to make an image. The various radiodensity amplitudes are mapped to 256 shades of gray. These shades of gray can be distributed over a wide range of HU values to get an overview of structures that attenuate the beam to widely varying degrees. Alternatively, these shades of gray can be distributed over a narrow range of HU values (called a "narrow window") centered over the average HU value of a particular structure to be evaluated. In this way, subtle variations in the internal makeup of the structure can be discerned. This is a commonly used image processing technique known as contrast compression. For example, to evaluate the abdomen in order to find subtle masses in the liver, one might use liver windows. Choosing 70 HU as an average HU value for liver, the shades of gray can be distributed over a narrow window or range. One could use 170 HU as the narrow window, with 85 HU above the 70 HU average value; 85 HU below it. Therefore the liver window would extend from -15 HU to +155 HU. All the shades of gray for the image would be distributed in this range of Hounsfield values. Any HU value below -15 would be pure black, and any HU value above 155 HU would be pure white in this example. Using this same logic, bone windows would use a "wide window" (to evaluate everything from fat-containing medullary bone that contains the marrow, to the dense cortical bone), and the center or level would be a value in the hundreds of Hounsfield units. Processing will most likely take between five minutes and one hour.
Although CT is a relatively accurate test, it is liable to produce artifacts, such as the following.
Aliasing Artifact or Streaks
These appear as dark lines which radiate away from sharp corners. It occurs because it is impossible for the scanner to 'sample' or take enough projections of the object, which is usually metallic. It can also occur when an insufficient mA is selected, and insufficient penetration of the x-ray occurs. These artifacts are also closely tied to motion during a scan.
Partial Volume Effect
This appears as 'blurring' over sharp edges. It is due to the scanner being unable to differentiate between overlying structures and respective HU's. The processor tries to average out the two densities or structures. This can be partially overcome by scanning using thinner slices.
Ring Artifact
Probably the most common mechanical artifact, the image of one or many 'rings' appears within an image. This is due to a detector fault.
Noise Artifact
This appears as gaining on the image and is caused by a low signal to noise ratio. This occurs more commonly when a thin slice thickness is used. It can also occur when the kV or mA is too low.
Motion Artifact
This is seen as blurring which is caused by movement of the object being imaged.
Streaking appearances can occur when the detectors intersect the reconstruction plane. This can be reduced with filters or a reduction in pitch.
Beam Hardening
This can give a 'cupped appearance'. It occurs when there is more attenuation in the center of the object than around the edge. This is easily corrected by filtration and software.
Three dimensional (3D) Image Reconstruction
Some statements in this article may be misleading.
Please help clarify this article. Suggestions may be on the talk page.
The principle
Because contemporary CT scanners offer isotropic, or near isotropic, resolution, display of images does not need to be restricted to the conventional axial images. Instead, it is possible for a software program to build a volume by 'stacking' the individual slices one on top of the other. The program may then display the volume in an alternative manner.
Multiplanar reconstruction
Multiplanar reconstruction (MPR) is the simplest method of reconstruction. A volume is built by stacking the axial slices. The software then cuts slices through the volume in a different plane (usually orthogonal). Optionally, a special projection method, such as maximum-intensity projection (MIP) or minimum-intensity projection (mIP), can be used to build the reconstructed slices.
MPR is frequently used for examining the spine. Axial images through the spine will only show one vertebral body at a time and cannot reliably show the intervertebral discs. By reformatting the volume, it becomes much easier to visualise the position of one vertebral body in relation to the others.
Modern software allows reconstruction in non-orthogonal (oblique) planes so that the optimal plane can be chosen to display an anatomical structure. This may be particularly useful for visualising the structure of the bronchi as these do not lie orthogonal to the direction of the scan.
For vascular imaging, curved-plane reconstruction can be performed. This allows bends in a vessel to be 'straightened' so that the entire length can be visualised on one image, or a short series of images. Once a vessel has been 'straightened' in this way, quantitative measurements of length and cross sectional area can be made, so that surgery or interventional treatment can be planned.
MIP reconstructions enhance areas of high radiodensity, and so are useful for angiographic studies. mIP reconstructions tend to enhance air spaces so are useful for assessing lung structure.
3D rendering techniques
Surface rendering
A threshold value of radiodensity is chosen by the operator (e.g. a level that corresponds to bone). A threshold level is set, using edge detection image processing algorithms. From this, a 3-dimensional model can be constructed and displayed on screen. Multiple models can be constructed from various different thresholds, allowing different colors to represent each anatomical component such as bone, muscle, and cartilage. However, the interior structure of each element is not visible in this mode of operation.
Volume rendering
Surface rendering is limited in that it will only display surfaces which meet a threshold density, and will only display the surface that is closest to the imaginary viewer. In volume rendering, transparency and colors are used to allow a better representation of the volume to be shown in a single image - e.g. the bones of the pelvis could be displayed as semi-transparent, so that even at an oblique angle, one part of the image does not conceal another.
Some examples of CT 3D surface rendering software include
VGStudio, Mimics, 3D doctor, Amira....etc
Main article: Segmentation (image processing)
Where different structures have similar radiodensity, it can become impossible to separate them simply by adjusting volume rendering parameters. The solution is called segmentation, a manual or automatic procedure that can remove the unwanted structures from the image.
Some slices of a cranial CT scan are shown below. The bones are whiter than the surrounding area. (Whiter means higher radiodensity.) Note the blood vessels (arrowed) showing brightly due to the injection of an iodine-based contrast agent.
A volume rendering of this volume clearly shows the high density bones.
After using a segmentation tool to remove the bone, the previously concealed vessels can now be demonstrated.
^ The Beatles greatest gift... is to science. Whittington Hospital NHS Trust. Retrieved on 2007-05-07.
^ Supplement to Applied Radiology, "Cardiac CT: Where are we today and where are we going?".
^ Hart, D; Wall B F (2002). "Radiation exposure of the UK population from Medical and Dental X-ray examinations". NRPB report W-4.
^ Hart, D.; Wall (2004). "UK population dose from medical X-ray examinations". European Journal of Radiology 50 (3): 285-291.
^ Donnelly, Lane F.; et al (February 2001). "Minimizing Radiation Dose for Pediatric Body Applications of Single-Detector Helical CT". American Journal of Roentgenology 176 (2): 303-6.
^ Brenner, David J.; et al. (2001). "Estimated Risks of Radiation-Induced Fatal Cancer from Pediatric CT". American Journal of Roentgenology (176): 289-296.
^ Template error: argument title is required.
^ a b c d Shrimpton, P.C; Miller, H.C; Lewis, M.A; Dunn, M. Doses from Computed Tomography (CT) examinations in the UK - 2003 Review
^ Radiation Exposure during Cardiac CT: Effective Doses at Multi–Detector Row CT and Electron-Beam CT
Categories: Medical imaging | Radiography
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Computed_tomography". A list of authors is available in Wikipedia.
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text:
Q: Why is my hashable object not found in a set of that hashable object, the set being an attribute of another object? I have a recursive relationship between objects of two classes: Foo has a set of Bar objects (in its bars attribute) and every Bar has a list of Foo objects (in its foos attribute). I've implemented is as shown in the MWE below, but the test fails. Why?
According to the Python Glossary, a set can only contain hashable objects and hashable objects:

An object is hashable if it has a hash value which never changes during its lifetime (it needs a __hash__() method), and can be compared to other objects (it needs an __eq__() method).

I don't really know if my MWE below satisfies that the objects have a hash that never changes, because the hash depends on the the other object(s) in the list and set attributes. Is there a way to solve this problem?
Minimal working example:
import unittest

class Test(unittest.TestCase):
    def test_foo_bar(self):
        foo = Foo()
        bar = Bar()
        bar.add_foo(foo)

        print(bar)
        print(foo.bars)
        print(hash(bar))
        for bar in foo.bars:
            print(hash(bar))
        # The previous print lines print the following:
        # <mwe2.Bar object at 0x105ba8080>
        # {<mwe2.Bar object at 0x105ba8080>}
        # -9223096319794529578
        # -9223096319794529578

        # The following assertion is OK
        self.assertTrue(bar in {bar})

        # The following assertion fails with AssertionError: False is not true
        self.assertTrue(bar in foo.bars)

class Foo:
    def __init__(self):
        self.bars = set()

    def __hash__(self) -> int:
        return hash(self.__dict__.values())

class Bar:
    def __init__(self):
        self.foos = list()

    def __hash__(self) -> int:
        return hash(tuple(self.foos))

    def add_foo(self, foo: "Foo"):
        foo.bars.add(self)
        self.foos.append(foo)

if __name__ == '__main__':
    unittest.main()

I use CPython, Python 3.6.x.

A: The problem is that your Bar's hash changes immediately after you add it to Foo.bars. You can see this if you add some print statements in the add_foo method:
def add_foo(self, foo: "Foo"):
    foo.bars.add(self)
    print(hash(self))
    self.foos.append(foo)
    print(hash(self))

Output:
3527539
957074234

This is because the hash is calculated based on self.foos, so any modification of self.foos also changes the object's hash.
(Side note: Contrary to what's stated in the question, bar in {bar} evaluates to True as you'd expect. There is no reason why it wouldn't. I suspect that there was some kind of mistake while debugging.)

A simple way to make the unittest work is to swap the two lines of code in add_foo:
def add_foo(self, foo: "Foo"):
    self.foos.append(foo)  # append first
    foo.bars.add(self)  # add to the set with the new hash

Output:
Ran 1 test in 0.000s

OK

However, this isn't a real fix: It won't help if you call add_foo more than once. If you ever call add_foo after adding a Bar object to a set or a dict, you'll get the same problem again.
I think it's clear that having interdependent classes with inconsistent hashes is a bad design choice. Possible solutions include

*

*Removing the Foo -> Bar -> Foo dependency cycle

*Finding a consistent hash method

redpajama_set_name: RedPajamaStackExchange


text:
Erkin Koray is the first studio album by Turkish rock musician Erkin Koray. The album is a collection of singles dating from 1967 - 1973. In 2006 the album was rereleased on CD, with 8 bonus tracks, by World Psychedelia Ltd.

'Çiçek Dagi' (Mountain of Flowers) was originally performed by the Erkin Koray Dörtlüsü Quartet at the Altin Mikrofon (Golden Microphone) contest in 1968, at which, they won fourth place. 'Sana Birşey Olmuş' (Something Has Happened to You) is a cover of the song "Land of a Thousand Dances" in Turkish.  The songs 'Nihansin Dideden' (You are Hidden From Sight), 'Istemem' (I Don't Want), and 'Köperüden Geçti Gelin' (The Bride Crossed Over The Bridge) were recorded by Koray and his band Yeralti Dörtlüsü (The Underground Quartet).  'Yagmur' and 'Aska Inanmiyorum' were recorded by the Erkin Koray Süper Group. 'Züleyha' was recorded by Erkin Koray & Ter. 'Mesafeler' and 'Silinmeyen Hatiralar' were recorded by [Erkin Koray's group] Stop. The group never got to the recording stage. 'Mesafeler' and 'Silinmeyen Hatiralar' were the only two songs from Stop's rehearsals to be released.

Track listing

World Psychedelia Bonus Tracks

References

Erkin Koray albums
1973 albums

redpajama_set_name: RedPajamaWikipedia


text:
Former Chief Stew Johanna Mueller dies
Mar 15, 2019 by Lucy Chabot Reed
By Lucy Chabot Reed
Johanna Mueller broke into yachting the old fashioned way. While working at a hardware store, her work ethic shone through and touched yacht owners shopping inside. It was the late 1970s and there were no such things as crew agencies.
Ms. Mueller, who would spend the next 40 years working on classic boats, died Feb. 27 of complications from lung cancer. She was 78.
Those yacht owners — Bill and Betty Remmert of St. Louis, Missouri — offered Ms. Mueller a job as chief stew on their 97-foot Burger M/Y Elizabeth R, and she traveled the Caribbean, Bahamas and northeast coast of the U.S. with them.
Her next boat was M/Y Big Dipper, the 80-foot Burger owned by Edwin Singer of Corpus Christi, Texas, where then-Mate Rick Rahm met her in the early 1980s. That yacht also traveled the Bahamas and the northeast, and she would work with them throughout the 80s.
Onboard M/Y Big Dipper, an 80-foot Burger, on the day before she sold, circa 1983. From left, then-Mate Rick Rahm, owner Edwin Singer, Chief Stew Johanna Mueller, Capt. Gus Rahm. Photos provided
"Johanna made a significant contribution to any vessel she served on," now-Capt. Rick Rahm said. "She was in charge of the interior of the vessel and the comfort of its owners, family, friends and guests. She made sure the vessel was always ready to entertain and serve its guests. Johanna had 'a place for everything and everything in its place'."
Ms. Mueller worked on another 80-foot Burger named M/Y Yankee Spirit.
Johanna Mueller, circa 1987
"Johanna and Burgers had a thing going on!" Capt. Rahm wrote.
Her last berth was on the 125-foot Burger known as Mimi/Kakapo owned by Stanley Hubbard of St. Paul, Minnesota. She retired from the Hubbards about five years ago after being with them for nearly two decades.
"Johanna was an amazing crew member, one of the hardest workers I have ever had the pleasure of working with," said Capt. Jeffrey Hardgrave, who joined M/Y Mimi in 2007 when Ms. Mueller was already aboard. "They broke the mold with Johanna; she was one of a kind."
Born in Bavaria, Germany, on Sept. 28, 1940, Ms. Mueller was the youngest of five children. She emigrated to America in the 1950s and worked as a nanny for a U.S. Army officer and his two young sons. She arrived in Fort Hood, Texas and stayed with the family until the boys graduated from high school. She then moved to Florida and worked as a waitress in Miami and in that hardware store in Hallandale Beach. She never married.
"She could varnish a handrail, handle lines, stand a watch, care for health issues, listen to your problems and be a friend when you needed one," Capt. Rahm said. "She had a good sense of humor, brightened lives, made guests welcome and loved walking in the evening. Those that knew her will always carry her memory in their hearts."
Ms. Mueller is survived by her brother, Heinrich, and family in Bavaria. No services are planned, per her last wishes, Capt. Rahm said.
Lucy Chabot Reed is publisher of The Triton. Comments are welcome below.
coast, Obituaries, Triton Exclusives
About Lucy Chabot Reed
Lucy Chabot Reed is publisher and founding editor of The Triton.
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From the Bridge: Crew dream of moving up, captains long to move down
From the Bridge: by Dorie Cox A group of yacht captains with experience at the helm of yachts from 100 feet to more than 250 feet gathered to address
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We are delighted to announce that London Festival Opera will be presenting A Feast of Opera in three enchanting historic settings - Amorbach Abbey for an Opera Gala featuring the works of the great German, French and Italian composers, Kloster Eberbach for a recital covering three centuries of great operatic repertoire, and Vollards Castle for a recreation of a 19th century Opera Soirée performed in period evening dress.
Day 1 - London/Manchester/Bristol/Edinburgh to Bucharest, Romania.
Fly by scheduled flight. On arrival transfer to the MS Royal Crown in Fetesti (approx. 2 hour drive). Sail this evening.
The vast Danube Delta is one of the most important wetlands left in Europe. We will access this unique region from Mila 35 at the entrance to the delta and explore by local boats. Return to the vessel and sail in the afternoon. Tonight join your fellow travellers for Welcome Drinks and Dinner.
Early this morning, arrive in Cernavoda at the entrance to the Black Sea Canal. Drive to nearby Constanta, a popular resort city. Its colourful history dates back to ancient Greek and Roman times. On a guided tour we will see the Museum of National History and Archaeology and the Museum of Ethnography.
Day 4 - Veliko Tarnovo, Bulgaria.
From Rousse, enjoy a full day tour to the city of Veliko Tarnovo, the capital of the second Bulgarian Kingdom from 1187 to 1393. The city formed a natural fortress, located on three hills surrounding the Yantra River. A palace, fortifications and churches were built into the terrain. Across the river, ancient stone houses seemingly perched on top of each other rise up the steep riverbank. After lunch in a local restaurant, visit the museum town of Arbanassi.
Day 5 - Belogradchick & Vidin.
Arrive this morning in the Bulgarian port of Vidin. After breakfast on board we will drive to Belogradchik which is located close to the Serbian border. The Belogradchik Rocks are a famous Bulgarian beauty spot. The sandstone has been weathered into all manner of bizarre shapes, and housed amongst the rocks is an Ottoman fort, built on the remains of a Roman structure. Return to the ship for lunch and this afternoon we visit Vidin for a performance of classical music by a string quartet from the wonderful Vidin Philharmonic.
Day 6 - Cruising Through the Iron Gates.
Day 7 - Belgrade, Serbia.
Spend the morning in this interesting city. A halfday tour highlights the city's main attractions, including the Kalemegdan fortress as it looms over the confluence of the Sava and Danube rivers, Saint Sava Cathedral, the largest Orthodox Church in the world, and Tito's Memorial. Your tour ends with a superb local folklore performance ashore. Sail this afternoon towards Hungary.
Day 8 - Pecs & Villany, Hungary.
This morning we arrive in the port of Mohacs, and depart after breakfast for a full day scenic tour of Pecs and Villany. The city of Pecs enjoys a fine position on the slopes of the Mecsek Hills and our tour will feature the sites associated with the city's Roman Ottoman Hapsburg past, as well as a short organ recital in the splendid Pecs Cathedral. Continue on to the town of Villany for lunch and wine tasting. Villany is one of Hungary's top wine regions, known for its reds and rosés. Thanks to the area's sub-Mediterranean climate, wines are full-bodied and spicy and of the highest quality. Sail in the evening towards Budapest.
We have the day to explore Hungary's elegant capital. Spend the morning on an excursion that will include the old quarter, the Matthias Church and the Fishermen's Bastion. Return to the ship for lunch and spend the afternoon at leisure, or you may wish to join our optional excursion to the fascinating Museum of Music History, with its wonderful collection of instruments and interactive displays. Tonight there will be a "Budapest by Night" cruise as we sail on towards Slovakia.
Day 10 - Bratislava, Slovakia.
Cruise through Hungary to Slovakia, arriving in the capital in the afternoon. Enjoy a walking tour of the city see the old quarter, the ornate Baroque Palace and the ancient city gates. Our tour will finish with a visit to the beautiful Klarissen Church where a string quartet will perform a concert of music by Dvorak and Mozart.
Day 11 - Vienna, Austria.
A morning city tour of Austria's elegant capital will take us around the famous Ringstrasse, and the Old Quarter including St Stephan's cathedral. Alternatively join a guided visit to the impressive Zentralfriedhof (Vienna Central Cemetery), the second largest in Europe, and with honorary graves of renowned Austrian musicians, historians and politicians. Mozart, Beethoven and other luminaries of the musical world (Schubert, Brahms, Strauss) are buried, or memorialized here. We also visit the Church of St. Charles Borromeo, a significant Art Nouveau church building. Return to the ship for lunch and this afternoon is at leisure to explore this majestic city further. Tonight there will be an optional evening of music ashore at the State Opera House or similar, subject to availability and depending on schedules.
After breakfast join our delightful tour to the Vienna Woods, including a visit to the Mayerling hunting lodge, where scandal once rocked the royal family, as well as the Cistercian Abbey of Heiligenkreuz. Return to the ship for lunch and enjoy an afternoon at leisure, or you may wish to join our optional excursion to Schonbrunn Palace and Gardens, the favourite summer residence of Maria Theresa. Sail overnight towards Melk.
Day 13 - Wachau Valley & Melk.
Enjoy a morning cruise as we sail through the beautiful Wachau Valley towards the great Baroque Abbey of Melk, situated high above the Danube. After lunch, depart for a guided tour of the abbey, including the Imperial Staircase, the Marble Hall and the abbey church.
Day 14 - Passau, Germany.
Arrive in the early afternoon in Passau, where the Inn and Ilz rivers join the Danube. After lunch on board join the tour that will include a scenic drive and a guided walk through the Old Town. Tour the breathtaking Cathedral of St. Stephan, which contains the world's largest church pipe organ. Return to your ship and sail on towards Regensburg.
Enjoy a morning guided stroll around historic Regensburg, Germany's largest and best preserved Medieval city. See the twin-spired cathedral Dom St Peter, the treasury and the tower houses. Return to the ship for lunch, and sail on towards Nuremberg.
Join a morning guided tour of this historic city, capital of Franconia. On our tour see the old city within the vast walls and visit Zeppelin Field and the site of the Nuremberg Trials, the Palace of Justice. We have the afternoon at leisure here to explore further.
Arrive in Bamberg in the morning and enjoy a tour of one of Germany's loveliest cities. Its relative geographical location, some 40 miles north of Nuremberg, was a key factor in preserving its architectural heritage from the ravages of war. Every single European style from the Romanesque onwards, has left its mark on Bamberg, each bequeathing at least one major building. This afternoon the ship remains in Bamberg, allowing you free time to explore further. Sail onwards in the late afternoon.
After a morning of scenic cruising, arrive in Wurzburg, the wine capital of Franconia. Tour this attractive town including the Prince Bishop's Residenz Palace and the old town with its impressive collection of churches. Your tour in this magnificent palace ends with a wine tasting in the Residenz Cellar. Return to the ship and sail in the early evening.
We arrive today in the pretty Franconian town of Miltenberg, renowned for its half-timbered Medieval houses. On a walking tour see the picturesque triangular shaped Marktplatz and the restored castle. Return to the vessel for lunch followed by a short drive to nearby Amorbach Abbey for an afternoon performance by London Festival Opera of celebrated opera arias and ensembles.
Day 20 - Eltville & Kloster Eberbach.
Arrive this afternoon into the small town of Eltville and transfer the short distance to nearby Kloster Eberbach, established in the 13th century by Cistercian monks from Clairvaux in France, and the outstanding backdrop to the film "The Name of the Rose". Our visit there will include a performance of popular repertoire by London Festival Opera and a chance to taste wine made from the world-famous Steinberg vineyard. Afterwards return to the MS Royal Crown and enjoy some free time in Eltville before we sail.
After breakfast today depart by coach to nearby Vollrads Castle. This grand estate has been the Greiffendau residence since the 14th century and the making of wine on this site can be traced back to 1211. We will enjoy a visit to the Vinothek to sample some of their splendid wines. Afterwards, enjoy the final concert in the company of London Festival opera with a performance in period costume for an added visual impact. Return to your ship for lunch and sail this afternoon through the scenic Rhine Gorge as we head towards Cologne.
We arrive this morning into Cologne, and take a tour to see the city's famous cathedral. The cathedral is the largest Gothic church in northern Europe with a total area of almost 8000 square metres and room for more than 20,000 people, and the second tallest spire and façade in the world. Return to your ship and spend a relaxing afternoon cruising towards Amsterdam.
Day 23 - Amsterdam, Netherlands.
Arrive into Amsterdam at lunch time and this afternoon visit one of the great art houses of Europe. Choose between the Rijksmuseum, with its splendid collection of old masters, including Rembrandt's famous "The Night Watch" which hangs in the Hall of Honour. Alternatively, you may prefer a visit to the Van Gogh Museum, which offers one of the world's largest collection of works by the artist, including "Almond Blossom" and "The Bedroom". Tonight join your fellow travellers for the Farewell Drinks and Dinner.
Day 24 - Amsterdam to London/Manchester/Bristol/Edinburgh.
Disembark this morning for the return scheduled flight to the UK.
PRICE INCLUDES: Economy class scheduled air travel • 23 nights aboard the MS Royal Crown on full board basis • House wine, beer and soft drinks with lunch and dinner • Shore excursions • Guest Speaker • Cruise Director • Performances by London Festival Opera • Tour Manager • Gratuities • Complimentary Wi-Fi on board • Transfers • Port taxes • Airport taxes.
Not Included: Travel insurance, optional tours on Days 9, 12 and music evening ashore in Vienna on day 11.
After studying History at Cambridge University Peter Williams spent more than 30 years in the British Army (Coldstream Guards) and enjoyed an unusually varied career. As an Infantryman he carried out ceremonial duties in London, spent two years in the mountains of Oman, served twice in Northern Ireland and commanded an armoured infantry battalion based in Münster, Germany. In the early 1990s he wrote speeches for the Supreme Allied Commander Europe, an American general.
During the Cold War he specialised in intelligence and studied Russian and German before spending more than four years in the 1980s in Berlin and East Germany as an officer in the British Commanders'-in-Chief Mission to the Group of Soviet Forces in Germany (known as BRIXMIS), in effect working as a military spy (MBE).
From 1993-94 he commanded his Coldstream Guards armoured infantry battalion in Bosnia-Herzegovina on UN peacekeeping operations during the civil war there (OBE). He went on to do two more tours of duty in the former Yugoslavia. The first was in 1995 as the Deputy Chief UN Military Observer; his boss there is now the President of Indonesia. Finally in 1998 he was the Chief Faction Liaison Officer in NATO's HQ in Sarajevo, dealing with the Bosnian Serb and Bosnian Federation Ministries of Defence and general staffs.
From 2001-02 he served first on the Western European Union Military Committee and then on the European Union Military Committee. His final military posting was from 2002-05 in Moscow where he started up and led NATO's Military Liaison Mission to the Russian Federation, working on military cooperation projects with the Russian armed forces (CMG). He retired from the Army in December 2005.
He now enjoys giving talks to schools, on cruise ships and to other audiences about Cold War and other current and historical issues and helps to train British military diplomats. He is a member of the international Guild of Battlefield Guides. He is also the editor of The Guards Magazine, the in-house journal of the British Army's Household Division (Household Cavalry and Foot Guards).
He is married to Anne, who was an Army education officer and language teacher; she now designs and makes jewellery. They live in Wiltshire and have three adult children and a very old black Labrador dog.
If you would like to spend some time in Bucharest before embarking the MS Royal Crown we are offering a three night pre-cruise extension.
Day 1 London to Bucharest, Romania. Fly by scheduled flight. On arrival transfer to your four star hotel for a three night stay. Tonight join your fellow travellers in the hotel restaurant for a Welcome Drink and Dinner.
Day 2 Discover Bucharest. After breakfast enjoy a panoramic city tour of the city's highlights, including the National Theatre, the University Square, the Romanian Athenaeum, the National Art Museum, the Opera House, the Military Academy, the Arch of Triumph, Victory Avenue, and the Free Press House. We complete the morning with a walking tour of the Old Town, including a visit to Stravropoleos Church, Lipscani Lane, Manuc's Inn and the Old Princely Court. Enjoy lunch in "Carul cu Bere", Bucharest's oldest beer house, with its colourful Belle Epoque interior, stained-glass windows and classic Romanian fare. This afternoon we will visit the Parliament Palace, the second largest administrative building in the world at 3.77 million square feet. This gargantuan construction is Ceausescu's most infamous creation, and makes for a fascinating tour. Return to your hotel, and dinner will be under your own arrangements this evening.
Day 3 Snagov & Mogosoaia. After breakfast at your hotel, depart for our visit to Snagov Monastery. This monastery was founded in 1408 by Mircea the Elder, Vlad Dracul's grandfather. Vlad, also known as Vlad Tepes is the historical character on whom Bram Stoker's book Dracula is based and is said to be buried here by the monks in 1476. After lunch in a local restaurant we continue on to visit Mogosoaia Palace, built in the 17th century in the Romanian Renaissance style. Return to Bucharest for an evening at leisure. Dinner will be under your own arrangements tonight.
Day 4 Bucharest to Fetesti. After breakfast there will be free time to relax, sightsee or shop at leisure before your afternoon departure for Fetesti (approx. 2 hour drive). On arrival embark the MS Royal Crown.
Price Includes: Three nights hotel accommodation on bed & breakfast basis, dinner & welcome drink on Day 1, lunch on Days 2 & 3, drinks with included meals (wine/beer/soft drinks), all sightseeing and entrances as described, transfers, services of a local English speaking guide throughout.
Not Included: Travel insurance, dinners on Days 2 and 3, lunch on Day 4.


Traditional scoring of sleep provides little information about the process of transitioning between vigilance-states.
We hypothesized that chronic upper airway obstruction (UAO) will lead to sleep instability in the absence of frank obstructed apneas or hypopneas.
Using an approach similar to previous reports [1, 2] defined a 2-dimensional (2D) state space technique (SST) using 2 spectral amplitude ratios calculated by dividing integrated spectral amplitudes at selected frequency bands. We calculated two spectral amplitude ratios by integrating the spectral amplitude over specific frequencies: 0.5-20/0.5-40 Hz for ratio 1 and 0.5-4/0.5-9 Hz for ratio 2. Each second of this ratio was mapped into the 2D state space, ratio 2 vs. ratio 1 (Figure 1). State space analysis yields wake at low ratio 1 values and SWS at high ratio 1 values. We used the SST to explore whether the abnormal sleep in UAO reflects sleep instability, faster movements, and abnormal transitions between vigilance-states.
Spontaneous sleep in rats. Values of wake (W), light slow wave sleep (LSWS), deep slow wave sleep (DSWS) and paradoxical sleep (PS) are shown.
We analyzed whole day electroencephalography sleep/wake recordings of UAO and sham control juvenile Sprague-Dawley rats using SST. SST is a non-categorical approach allowing quantitative and unbiased examination of sleep/wake states and state transitions. Measurements of sleep/wake recordings were performed at baseline and following administration of ritanserin (5-HT2 receptor antagonist) the next day to stimulate sleep.
UAO rats spent less time in deep (delta-rich) slow wave sleep (SWS) and near transition zones between states. Sleep state transitions were more frequent and rapid in UAO rats, indicating that obstructed animals have more regions where vigilance-states are unstable. The number of microarousals and trajectories from light SWS to wake and vice versa increased in the UAO group. Ritanserin consolidated sleep in both groups by decreasing the number of microarousals and trajectories between wake to light SWS, and increasing deep SWS in UAO.
Traditional sleep scoring in 10-second epochs reveals little information about the process of transitioning between states, as cortical activity and behavior can change quite rapidly in rodents; the SST analysis provides second-by-second resolutions. Also, conventional scoring simply identifies discrete states, so it can overlook important variations within states, such as the distinctions between light and deep SWS or between sleep and wake states. We present evidence that SST enables visualization of vigilance-state transitions and velocities that were not evident by traditional scoring methods. These observations provide new insight on abnormal sleep and highlight the usefulness of SST in understanding the role of UAO on sleep dynamics.


I've never been involved in a church plant before. There's plenty of hope and excitement, but we don't even know all the challenges we will face.
Our multi-campus church is planning to open a new campus in Lorain, Ohio, a self-described "international city" of about 63,000 people on the shores of Lake Erie about 30 miles west of Cleveland. As of 2016, whites comprised 51.7 percent of the city's population, Hispanics 29.1 percent, blacks 14.5 percent and "two or more races" 3.1 percent.
I'm interested in this because my wife and I raised our three sons at an inner-city church in Saginaw, Michigan, with similar demographics to Lorain. Now that they are grown and on their own, I have more time to devote to this.
To learn more about planting a multi-ethnic church, the Lorain campus pastor and I attended a three-day conference on the topic in Chicago. It was eye-opening.
If we want to be a multi-ethnic church, then the dominant culture cannot be more than 80 percent of the church. Research shows that if visitors see at least 20 percent of people in their ethnic group attending, then they feel like "members" and not "visitors." We should be strategic about seeking 20 percent of an ethnic group if we truly want to be multi-ethnic.
For some people, society does not work – economically, medically, socially, religiously, etc. These people do not trust any institutions. Church plants will take a long time for these people to trust. They may reject institutionalism, even if they hunger for God. To reach them, we might need to change the way we do church – why 11 a.m. services? Why does communion happen weekly or monthly? Etc. These are not wrong, but they are not in the Bible. What's Biblical, and what's cultural?
The new national divide is achiever vs. non-achiever. Achievers value the individual; non-achievers value the society. Most non-whites (as well as whites) are achievers. Achievers are mainstream; non-achievers live in the sub-culture.
One speaker said white pastors are excellent at "three-point sermons with seven sub-points." That's fine, but that's not how black preachers preach. If we want to reach black people, this might become an issue. Another example: Hispanics will show up late, then they will stay late. That's their culture. We might need to re-think the way we do church.
The traditional church model: Meet Jesus, attend church, connect/serve/give, go into the world. This isn't working; it's too shallow.
The new model: Meet Jesus, attend church, deep change, go into the world.
How to accomplish deep change? We need to meet emotional, social, intellectual, physical and spiritual needs – all of them. Which means all of those needs in my life, as a leader, must be met as well, or I will not be an effective leader. The Mary-Martha struggle: When are we focused on our actions at the expense of spending time with Jesus?
This is not a quick fix. It's hard. It takes time.
Whites frequently will not get involved in a church (or any other organization) unless they lead it. Several speakers made this point. Whites often don't leave room for other ethnic groups to lead – or if they do, they must follow the examples of whites. We often do this unconsciously.
There is no assimilating into one true culture in heaven. All cultures are good. Faith brings out the best in all of them. Every culture has stories to tell.
How much of church planting is led by whiteness? Most of it. It's a strange mix of benevolence and oppression. This has become the only story. How do we liberate from whiteness (or any dominant culture)? According to the Bible, we die to it. We are not to assimilate, but to create a new story.
Jesus' blood is the new story, for all cultures. His death and resurrection is the great equalizer for all of us. Jesus didn't ask us to become Him. Instead, He became one of us.
Those of us in the dominant culture often forget that we have a culture. Everybody speaks with an accent except me, for example.
Marginalization happens when people are minimized in different ways. Marginalization often leads to oppression, which is defined as sin plus power.
Jesus went to the margins. He was surrounded by sinners and tax collectors and prostitutes and women and children. All of us need to go there, too.
Jesus gave us a table, and all the chairs around it are on the same level. No high chairs and low chairs. Everybody drinks from the same cup, and we share germs. All ethnic groups are equal before God.
Blacks' history is slavery. No other immigrant group can say that. We heard first-person testimonies from several ethnic minorities who have experienced racism in their lifetimes. My wife has a co-worker whose boyfriend is black. He recently was talking with several friends in the parking lot of the apartment complex in Lorain where he lives. Another resident of the apartment complex called the cops on him. His crime? Being black and talking with his friends. It happens still today, even in Lorain.
As white people, we cannot deny that these things happened, and are still happening. If we want to reach this population for Christ, we need to meet them where they are.
Another cultural difference: Whites often see themselves as a collection of individuals. Blacks see themselves as a community. This is crucial to understanding how we communicate differently.
For example, a white police officer in Houston recently killed a black man in his own apartment. Blacks wanted the world to feel his suffering and pain. They wanted pastors to talk about that the following Sunday. Our reaction as whites? We want more facts. Give us the details of what happened before we react.
This is huge. We must understand this difference.
Cities – with density and proximity – amplify the opposition to the gospel.
How do we evangelize in this setting?
We must critique the culture. The standards our culture offers don't work. If your career is your primary motivator in life, what happens when – not if, but when – you lose it? If it's to be a good person, you'll never be good enough (maybe you haven't committed adultery, but have you lusted? This is Jesus' standard.) If it's freedom, you aren't, and you know it. If you live for money, you'll never have enough. If you seek beauty, you'll never feel beautiful. And on and on.
But if you serve Jesus, you'll get forgiveness when you fail.
There are no merit-based scholarships in heaven. Only grace.
Wise application of the word of God to your concerns.


PPMS has pioneered the art of surface mobility solutions to handle mass transit operations in a proficient way.
We have an array of mobility solutions like City Bus, Intercity, Corporate rentals, Hop on Hop off service and Family tour planner. We understand the concept of human logistics and have mastered it over these past 25 years.
Today we operate around 500 vehicles of different categories to cater 3 lac. passenger daily. Staff training at all levels across the organization and environment, health, safety measures are a priority practice at the company.
City bus Operations in 5 state capitals and 10 cities within next two years.
Business Network and geographical presence at strategic locations throughout the country in next three years.
Positioning our company as undisputed leader in India in the field of Public transport having a fleet size of more than 1000 buses in next 3 years.
Recognition as a professional organization having a very capable team, goodwill of customer & other stakeholders with a brand equity spreading across society it serves, within the next 3 years.