extfieldsofstudy:
Materials Science
Physics

text:
SIW Based Wideband Horn Antenna

In this paper, we have proposed CSRR (complementary split ring resonator) loaded Substrate Integrated Waveguide (SIW) horn antenna. The whole system is designed on a single substrate, having advantages of small size, low profile, and low cost, etc. The design process and simulation results of a CSRR-loaded SIW horn antenna at K-band and Ka-band are presented. The proposed antenna is an outstanding choice for K, Ka bands and even higher frequency synthesis. It has well-behaved gain and suitable reflection coefficient value less than 1.5 (-10dB S11 and VSWR<1.5). The simulated gain of antenna attains 7.48±1dB over majority of the bandwidth and with radiation efficiency of 85%. The simulation has been done using full-wave package, High Frequency Structure Simulator Software (HFSS) based on Finite element method (FEM).

INTRODUCTION
To facilitate enrich the demands of a wider bandwidth in support of exploding data transmission, the operating frequency of satellite and wireless communication systems have been increasing to the high range frequencies [1]. To migrate from low frequency bands to high frequency bands provide wider bandwidth and low atmospheric absorption. It also gives the capability of long range wireless data transmission for point to point communication. There are various applications, such as Imaging and communication satellites, uplink in the Ka band and downlink between Ku-band. All these type of applications require light weight, low cost, and high gain antennas, which constitute most critical parts of such systems.
Most suitable antennas for such kind of applications are from planar structure. However, this type of antennas like microstrip antennas suffers from serious losses particularly at bends and discontinuities by increasing frequency [2]. Although numerous planar antennas have been studied for Ka band communication and radar systems in which the increasing of frequency accompanied with the decreasing of radiation efficiency due to the inherent losses on the microstrip feeding network. Non-planar structure is the alternate for planar structure that provides low losses and high power handling capacity. However, it is difficult to configure the non-planar structure to planar active components. So, SIW was proposed to overcome the mentioned hurdles [3]. It enjoys not only the advantages of non-planar features, but also other benefits, namely, compact, low cost, light weight, easy to manufacture using PCB technique and other planar processing technologies, and also being easily connected to coplanar waveguide utilizing a wideband and uni-planar transition [4].
SIW structure consists of arrays of metallic posts created in a planar substrate. There various devices are designed and fabricated using these techniques. One of the vital application of this technique is horn antenna. It has numerous of applications because of its simplicity, wide bandwidth, and high gain. However, the dimension of the antenna becomes smaller with increased frequency (due to the shorter wavelength). It required a micromachining fabrication process [5].
SIW based horn antennas are less costly and can easily be interfaced with CPW or microstrip line [6][7][8]. However, its bandwidth is not wider and they radiates in parallel to the substrate that is not suitable for many practical applications [9]. So it is required to make a structure having wider bandwidth and better gain. Recently, it is found that the inclusion of SRR (Split Ring Resonator) and CSRR (Complementary Split Ring Resonator) not only improve the gain, it also increases the bandwidth of filters as well as antenna [10][11][12]. This type of structures is based on metamaterial concepts. In this paper, CSRRs structure is first cut from the ground plane in order to increase the bandwidth of a simple microstrip patch antenna. The sub-wavelength resonances can be chosen to realize an electrically small antenna. On the other hand, the higher modes of the CSRRs are selected to merge with the main resonance of the patch antenna. For this, the CSRRs rings are embedded to the boundary of the patch. On account of the wider bandwidth the right-handed resonance will yield to the design. Then, the CSRRs structure is modified with crossovers that are installed in the structure of a traditional MA. More details of the design principles of the proposed antennas are described and their simulation results are shown.

ANTENNA CONFIGURATION
As shown in fig. 1, it contains the basic horn antenna configured using planar technology (SIW technique). Integration of rectangular waveguide and horn antenna using SIW technology provide compact structure and ease of fabrication [13]. It shows that the horn antenna is created with the use of metallic vias (It connects top and bottom plane of the structure). Taper type of microstrip feed line is use for the microstrip to waveguide transition [13][14][15][16]. In this design, the dominant mode is TE10 and we have taken the center frequency 21.5GHz. For the propagation of fundamental mode, the width a and thickness b should be selected from, where is free space wavelength and is permittivity of dielectric medium.  This structure is simulated by using HFSS, it is full 3D EM solver based on FEM (finite element method). The Scattered parameter of this structure is shown in fig. 2. As shown in fig. 2, this structure is resonant at three different frequencies 21.28GHz (21.2 GHz to 21.82 GHz) , 24.2GHz (24.00 GHz to 24.30 GHz) and 26.4GHz (26.2 GHz to 27 GHz) respectively. It gives -10dB bandwidth is more than 250MHz. Fig. 3 show the gain plot of the antenna that contains more than 7dB gain. The radiation pattern in E-plane and H-plane is also shown in fig. 4. In this pattern, there is few side-lobes generated which is happened due to air gap between two posts of the SIW structure.  (1)If the equivalence capacitance of the CSRR is increased, the resonant frequency shifts towards the lower frequency. Fig. 6 shows the simulated scattering parameter of CSRR loaded SIW antenna. As shown in fig. 6, this proposed antenna resonates three different frequencies 21.7 GHz (K-band), 24.2 GHz (K-band) and 27.13 GHz (Ka-band) respectively. Inclusion of CSRR in ground plane is shifted the resonant frequency to the lower resonant frequency while it increased bandwidth around 600 MHz at first resonant frequency in K-band and 400MHz at 3rd resonant frequency in Ka-band. However, inclusion of CSRR in ground plane also reduces the radiation efficiency and return loss. Figure 6: S11 of Single CSRR-loaded SIW horn Antenna Figure 7: 3D plot Gain of CSRR-loaded SIW horn Antenna Finally, we have introduced another split ring into CSRR for improving response, the structure of 3 CSRR is shown in fig. 8a and its equivalent circuit is shown in fig. 8b. Fig. 9a, 9b and 9c shows the top, bottom and side view of the proposed antenna.    Gain in dB 7.07 6.7 6

CONCLUSION:
It is concluded from the proposed designs that inclusion of CSRR in SIW based horn antenna provides better gain, wider bandwidth (four times the without CSRR in SIW horn antenna) and multiple resonant frequencies. This type of structure is very compact and will be used in LEO to LEO satellite communication where more than one antenna is required for tracking to other satellite.


In vitro quality evaluation of leading brands of ciprofloxacin tablets available in Bangladesh

Background Ciprofloxacin is a broad-spectrum antibiotic that acts against a number of bacterial infections. The study was carried out to examine the in vitro quality control tests for ten leading brands of ciprofloxacin hydrochloride 500 mg tablet formulation, registered in Bangladesh by Directorate General of Drug Administration. The quality control parameters of ten different brands of ciprofloxacin hydrochloride 500 mg tablets were determined by weight variation, friability, hardness, disintegration, dissolution and assay tests. All the tablets were evaluated for conformity with United States Pharmacopoeia-National Formulary (USP-NF) and British Pharmacopoeia (BP) standards. Results Among ten brands of tablets Brand C had lower mean weight variation of 1.59% and Brand E had highest mean weight variation of 3.32%. For friability test Brand F had lowest mean friability (0.27%) and Brand G had highest mean friability (0.54%). Among ten brands mean lowest and highest hardness were founded in Brand G (4.49 kg/cm2) and Brand F (7.13 kg/cm2) respectively. The disintegration time for ten brands of ciprofloxacin tablet obtained were in the subsequent order: Brand G (8.19 min) < Brand C (9.25 min) < Brand E (9.61 min) < Brand D (10.11 min) < Brand B (11.07 min) < Brand A (12.15 min) < Brand H (13.68 min) < Brand I (14.59 min) < Brand J (16.32 min) < Brand F (17.49 min). Among ten brands for dissolution test mean percentages of drug release were not less than 80% in 45 min for four tablets (Brand E, 81.52%; Brand D, 86.44%; Brand G, 86.82% and Brand C, 94.12%), consequently they met BP standard and as per USP-NF standard six brands (Brand B, 75.62%; Brand A, 76.18%; Brand E, 81.52%; Brand D, 86.44%; Brand G, 86.82% and Brand C, 94.12%) had released not less than 75% drugs, so they also complied with the standard. The percentages of the drug content of the ten brands of ciprofloxacin tablet were obtained in the following sequence: Brand H (96.84%) < Brand J (97.34%) < Brand D (98.15%) < Brand I (98.47%) < Brand E (99.37%) < Brand F (100.28%) < Brand B (100.38%) < Brand A (100.54%) < Brand G (101.39%) < Brand C (101.46%). All of the brands met the BP and USP-NF specifications for assay. First-order, Higuchi and Korsmeyer–Peppas kinetics model fit for all of the mentioned ten brands. Conclusion The present study revealed that all of the leading brands of this tablet met the quality control parameters as per pharmacopoeial specifications except dissolution test for four brands (Brand J, Brand H, Brand I, and Brand F).

Background
Ciprofloxacin is an antibiotic in a group of drugs called fluoroquinolones [1]. In 1981 it was discovered by Bayer, Germany. The Food and Drug Administration (FDA) approved this drug in 1987 for uses in the United States as first oral broad-spectrum antibiotic [2]. It is one of the most important medications needed in the basic health care system and available on the World Health Organization's (WHO) list of essential medicines [3]. It is available as a generic medication and not very expensive [4,5]. Generic drugs must be chemically and biopharmaceutically equivalent in comparison to the innovator drug. Quality parameters such as strength, purity, content uniformity, disintegration time (DT) and dissolution rate must be identical for pharmaceuticals that are chemically and biopharmaceutically equivalent [6]. Generic drugs are not only decreasing the health care costs [2] but also the quality of the drugs. The qualities of generic drugs are in doubt in case of poor, developing as well as industrialized countries.
There are a number of cases related to substandard and counterfeit drugs. Composition and ingredients of substandard drugs don't meet the correct scientific specifications for these reasons they are ineffective and often dangerous to the patient. Counterfeit drugs may include products with the correct ingredients but fake packaging, with the wrong ingredients, without active ingredients or with insufficient active ingredients [7]. It is believed that the health hazard effects of counterfeit drugs are greater than substandard drugs [8]. Substandard and counterfeit drugs are a major cause of morbidity, mortality and loss of public confidence in drugs and health structures [9]. WHO has estimated that approximately 10% of the global pharmaceuticals market consists of counterfeit drugs, but this estimate increases to 25% in developing countries, and may exceed 50% in certain countries [10]. FDA estimates that up to 25% of the drugs consumed in poor countries are substandard or counterfeit [11]. China and India are recognized as the leading countries in the production of counterfeit drugs and bulk active ingredients used for counterfeiting worldwide [12]. Several studies showed that counterfeits of pharmaceuticals sourced in China and India were detected in 42 and 33 countries respectively [13]. Almuzaini et al. showed that prevalence of substandard or counterfeit medicines in Lao PDR, Tanzania, Cambodia and Uganda are 12.2-44.5%, followed by Indonesia, Nigeria, Cameroon 18-48% and in Myanmar, Cambodia, Lao PDR, Ghana, Kenya, Tanzania, Uganda, Madagascar, Mali, Mozambique, Zimbabwe 11-44% [14]. In 2009, 25 children were dying after taking paracetamol syrup due to the presence of poisonous diethylene glycol in Bangladesh [15,16]. Substandard and counterfeit drugs are not only limited to poor and developing countries but also intensely noticeable in developed countries. In 2007-2008, due to the uses of adulterated blood thinner, heparin 149 Americans were dying that was legally imported. In 2012, contaminated steroids killed 11 people and sickened another 100 people in the US. In another case, vials of the cancer medicine, avastin were found to contain no active ingredients [17]. In a study of WHO found that 28% of antibiotic and 20-90% of antimalarial drugs were failed quality specifications [18].
Pharmaceuticals must satisfy certain standards to claim it to be a quality drug. The main criteria for the quality of any drug in dosage form are its safety, potency, efficacy, stability, patient acceptability and regulatory compliance [19]. To ensure the safety and efficacy of pharmaceutical products, the quality of pharmaceutical must be reliable and reproducible from batch to batch [20]. To ensure the requisite quality, drug manufacturers are required to test their products during and after manufacturing at various intervals during the shelf-life of the product [21]. WHO supports the practice of prescribing of generic medicines to reduce the cost of the health care system, but this should be supported with adequate evidence for the substitution of one brand for another [22]. Comparison of bioequivalence study between the generic products versus the innovator product is one of the major challenges and prime factors for a generic marketing authorization [23]. Several studies showed that switching from branded to generic medicine might result in changes of pharmacokinetics/pharmacodynamics profile, leading to subtherapeutic concentration or therapeutic failure and or adverse reactions [24]. It is very essential to do bioequivalence studies for generic products on account of any significant difference in the rate and extent by which the therapeutic ingredients become available at the site of drug action, administered under uniform conditions in an adequately designed study [25]. To identify bioavailability problems dissolution testing serves as an indicator [26]. Biopharmaceutically as well as chemically equivalent drug products must have the same quality, strength, purity, content uniformity, disintegration and dissolution rates [27]. In vitro quality control (QC) of pharmaceutical products is a fixed set of investigation started during production by in-process quality control tests and after production by finished product quality control tests as per official pharmacopoeias and different regulatory agencies. QC tests help in avoiding the confusion regarding safety, potency, efficacy and stability of pharmaceuticals [28].
The prevalence of substandard and or counterfeit medicines is significantly higher in poor and developing countries. As ciprofloxacin is widely used antibiotic in Bangladesh, the objective of this study was to assess the quality of different leading brands of ciprofloxacin hydrochloride 500 mg tablet formulation commercially available in the market of Bangladesh.

Drugs and chemicals
Ten commercially available leading brands of ciprofloxacin hydrochloride tablet each with a label claim 500 mg were purchased from the various retail pharmacies of Dhaka city in Bangladesh. Details information about the brands are shown in Table 1

In vitro quality control tests Weight variation test
For this test according to the USP-NF weight variation test was run by weighting 20 tablets for each of the ten brands individually using an electronic balance, then calculating the average weights and comparing the individual tablet weights to the average. The difference in the two weights was used to calculate weight variation by using the following formula [19,29,30]: where, I w = Individual weight of the tablet and A w = Average weight of the tablet.
The tablet complies with the test if not more than 2 of the individual weights deviate from the average weight by more than the 5% [19,29,30].

Friability test
For this test Roche friabilator was used. Twenty tablets from each of the ten brands were weighed and placed in the friabilator and then operated at 25 rpm for 4 min. The tablets were then dedusted and weighed. The difference in the two weights was used to calculate friability by using the following formula [19,31]: where, I w = Total Initial weight of the tablets and F w = Total final weight of the tablets.
The tablet complies with the test according to USP-NF if tablets loss less than 1% of their weight [19,31].

Hardness test
For this test Monsanto hardness tester was used. Ten tablets were randomly selected from each of the ten brands and tested. This test measures the pressure required to break diametrically placed tablets by applying pressure with coiled spring [19,32]. In-house acceptable limit for this test is 6 ± 2 kg/cm 2 .

Disintegration test
For this test USP disintegration apparatus was used. To test for DT, one tablet was placed in each tube for each brand and the basket rack was positioned in a 1000 ml vessel containing 900 ml of water maintained at 37 ± 2 °C, so that the tablets remained 2.5 cm below the surface of the liquid on their upward movement and descent not closer than 2.5 cm from the bottom of the beaker. A standard motor driven device was used to move the basket assembly containing the tablets up and down through a distance of 5-6 cm at a frequency of 28-32 cycles per minute. Perforated plastic discs were used to prevent the floating of tablets. The apparatus was operated for 30 min [19,29].
To comply with the USP-NF standards, the tablets must disintegrate and all particles must pass through the 10-mesh screen within 30 min. If any residue remains, it must have a soft mass with no palpably firm core [25,29].

Dissolution test
For this test USP dissolution apparatus was used. To test for dissolution, one tablet was placed in each vessel (6 vessels) for each brand, containing 900 ml of 0.1 M hydrochloric acid (HCl) as a dissolution medium maintained at 37 ± 0.5 °C. The rotational speed of the apparatus was held constant at 50 rpm. A sample of 5 ml was withdrawn at a fixed time intervals (15,30,45 and 60 min) and this was immediately replaced with the same volume of fresh test media [25,29,33]. The sample was filtered and 1 ml of filtrate was taken and diluted to 50 ml with distilled water. So the solution was 50 times diluted. The absorbance of the diluted filtrate was determined spectrophotometrically at the wavelength of 276 nm, using 0.1 M HCl as blank. The percentage of drug release at each interval was calculated by using standard ciprofloxacin. As per USP-NF tablets meet with this test if not less than 75% dissolves in 45 min. According to BP tablet comply with this test if not less than 80% dissolves in 45 min [19,29,33].

Assay test
Analysis of drug potency in tablets helps to determine the strength or content of drug in a dosage form. 100 mg of standard ciprofloxacin hydrochloride powder was weighed and dissolved in 10 ml of distilled water and diluted up to 100 ml to get 1000 µg/ml concentration of standard stock solution. From this stock solution 10 ml was taken to another 100 ml volumetric flask and diluted to get 100 µg/ml of drug concentration. Then, using this stock solution various other concentrations were prepared like 5, 10, 15, 20, 25 and 30 µg/ml. Absorbance values of these concentrations were measured at 276 nm by using UV spectrophotometer and standard graph was plotted by taking absorbance values on Y-axis and concentration values on X-axis. For this test tablets from each brand were crushed into fine powder and sufficient amount of powder was weighed so that the amount contains 100 mg of active ciprofloxacin and dissolved in 100 ml 0.1 M HCl and further dilution was made to obtain 100 µg/ml for each brand. Then 4 ml of each brand made up to 100 ml with 0.1 M HCl and the absorbance of each brand was taken at 276 nm against the blank [21].
The USP-NF specification is that the content of ciprofloxacin hydrochloride should not be less than 90% and not more than 110%, while BP specifies that the content should not be less than 95% and not more than 105% [29,33].

Drug release kinetics
To evaluate the kinetics of drug release from the tablets the results of in vitro drug release study of formulations were fitted with various kinetic equations like zeroorder, first-order, Higuchi and Korsmeyer-Peppas model [34]. The equations of different release kinetics are given below: Zero-order kinetics: Q t = Q 0 + K 0 t where, K 0 , K 1 and K h indicates zero-order, first-order and Higuchi rate constants respectively, Q t /Q 0 means fraction of drug released at time t, K means rate constant and n means release exponent. The kinetics that gives high regression coefficient (R 2 ) value is considered as the best fit model [34][35][36].

Statistical analysis
All the results were expressed as mean ± SD. The results of dissolution test were analyzed by one-way analysis of variance (ANOVA) followed by Post Hoc t test. Microsoft Excel 2010 (Roselle, IL, USA) was used for the statistical and graphical evaluations. A probability of P < 0.05 was considered as significant.

Results
The tablet complies with the weight variation test if not more than 2 of the individual weights deviate from the average weight by more than the 5 percent. The mean results for weight variation for ten brands obtained were in the following order:  Fig. 1. Among all tablets mean highest weight variation was found in Brand E, 3.32% and the lowest was found in Brand C, 1.59%. This means that all the brands complied with the compendial specifications. Figure 2 showed the mean results of friability for ten brands of ciprofloxacin tablet in the subsequent First-order kinetics: log Q t = log Q 0 + K 1 t/2.303 Higuchi kinetics: Q t = K h t 1/2 Korsmeyer−Peppas kinetics: Q t /Q 0 = Kt n  54%). Thus, the brand most likely to lose particles during handling was Brand G, 0.54%, while the least likely to lose particles was Brand F, 0.27%. Friability for all the brands was below 1% and they complied with the compendial specifications. The mean hardness results (Fig. 3) for ten brands obtained were in the specified order: Brand G (4.49 kg/ cm 2 ) < Brand C (5.12 kg/cm 2 ) < Brand E (5.94 kg/ cm 2 ) < Brand B (6.35 kg/cm 2 ) < Brand D (6.45 kg/ cm 2 ) < Brand H (6.55 kg/cm 2 ) < Brand A (6.64 kg/ cm 2 ) < Brand J (6.73 kg/cm 2 ) < Brand I (7.06 kg/ cm 2 ) < Brand F (7.12 kg/cm 2 ). From Fig. 3, it can be seen that Brand F, 7.12 kg/cm 2 had the highest hardness value while Brand G, 4.49 kg/cm 2 had the lowest value.
Disintegration could be directly related to dissolution and subsequent bioavailability of a drug. The DT for ten brands of ciprofloxacin tablet obtained were in the succeeding order: Brand G (8.19 min) < Brand C (9.25 min) < Brand E (9.61 min) < Brand D (10.11 min) < Brand B (11.07 min) < Brand A (12.15 min) < Brand H (13.68 min) < Brand I (14.59 min) < Brand J (16.32 min) < Brand F (17.49 min). Highest DT was found in Brand F, 17.49 min and lowest was found in Brand G, 8.19 min. All the brands complied with the compendial specifications for this test given in Fig. 4.
The calibration curve of standard ciprofloxacin is given in Fig. 5   The statistical evaluation (ANOVA) of dissolution test given in Table 2 showed that there was significant variation (P < 0.05) found among ten brands of ciprofloxacin tablets. The kinetics of drug release of the proposed brands (Brand A, Brand B, Brand C, Brand D, Brand E, Brand F, Brand G, Brand H, Brand I and Brand J) were treated in different kinetics model such as zero-order, first-order, Higuchi and Korsmeyer-Peppas mentioned in Table 3.

Discussion
Quality is not an accident, it is the result of intelligent effort [37]. The quality of pharmaceuticals is under great risks in developing countries especially in Bangladesh. There are several factors related to bad quality among these uses of substandard raw material and lacks of facility are most prominent. Therefore, it is necessary to check the quality. Pharmacopeial testing confirms these properties according to fixed standards. Different brands of ciprofloxacin hydrochloride tablets were obtained from different retail pharmacy outlets within Dhaka City and were subjected to weight variation, friability, hardness, disintegration, dissolution and assay tests.
The weight of the tablet is the amount of granules which contains the labeled amount of the therapeutic ingredient. A large weight variation precludes good content uniformity. Due to a variety of reasons tablets may be excessively overweight or underweight. Patients receiving the overdose or underdose tablet, experiences unpredictable therapeutic response [38]. The tablet complies with this test if not more than 2 of the individual weights deviate from the average weight by more than the 5 percent. The mean results of weight variation for ten brands obtained were in the following order: Brand C (1.59%) < Brand I (1.95%) < Brand G (2.12%) < Brand H (2.34%) < Brand D (2.36%) < Brand A (2.39%) < Brand J (2.44%) < Brand F (2.79%) < Brand B (2.99%) < Brand E (3.32%) revealed in Fig. 1. Among ten brands of ciprofloxacin tablet, all of the brands met the specification, highest weight variation was seen in Brand E and the lowest was in Brand C. In the study of quality control and in vitro bioequivalence studies on four brands of ciprofloxacin tablets commonly sold in Uyo Metropolis, Nigeria, Jackson et al. also reported similar results [6].
Friability of tablet is the capacity to withstand shock and abrasion in packaging, handling and shipping. Friable tablets no longer have sharp edges, consequent pharmaceutical elegance and patient acceptance. Tablet friability results in weight loss of tablets which may affect the therapeutic response [39]. The mean results of friability for ten brands obtained were in the subsequent order: Brand  Fig. 7 Results of drug content of ten leading brands of ciprofloxacin tablets. Results were expressed as mean ± SD (n = 20/brand) (0.54%) exposed in Fig. 2. The results for friability were below 1% for ten brands of ciprofloxacin tablets, which met the specification. Salih and Hamam in the study of comparative in vitro evaluation of generic ciprofloxacin hydrochloride tablets showed that all the four different manufacturing brands of ciprofloxacin tablets complied with USP-NF requirements for this test [40]. Tablets require a certain amount of hardness to withstand mechanical shocks of handling in manufacturing, packaging and shipping. In addition, tablets should be able to withstand reasonable abuse when in the hands of consumers. Adequate tablet hardness and resistance to powdering are necessary requisites for consumer acceptance. More recently, this relationship of hardness to tablet disintegration and perhaps more significantly, to the drug dissolution release rate, has become apparent [41]. Tablet hardness can be attributed to the difference in properties of excipients employed in the manufacture of the different brands. Hardness values did not correlate with friability values [42]. The mean results of hardness for ten brands obtained were in the resulting order: Brand G (4.49 kg/cm 2 ) < Brand C (5.12 kg/cm 2 ) < Brand E (5.94 kg/cm 2 ) < Brand B (6.35 kg/cm 2 ) < Brand D (6.45 kg/cm 2 ) < Brand H (6.55 kg/cm 2 ) < Brand A (6.64 kg/cm 2 ) < Brand J (6.73 kg/cm 2 ) < Brand I (7.06 kg/ cm 2 ) < Brand F (7.12 kg/cm 2 ) exhibited in Fig. 3. But the Figs. 2 and 3 showed that highest friable brand, Brand G has lowest hardness and lowest friable brand, Brand F has highest hardness. All of the tablets met the in-house specification for this test. In the bioequivalence studies on some selected brands of ciprofloxacin hydrochloride tablets in the Nigerian market with ciproflox ® as innovator brand Ayodeji et al. showed that all of the brands comply with the specification for this test [43].
Before absorption of drug takes place in the body, it must be in solution form. For most tablets the first important step toward solution is the breakdown of the tablet into smaller particles or granules, a process known as disintegration [44]. Disintegration must be directly related to dissolution and subsequent bioavailability of a drug [45]. The DTs for ten brands were under 30 min. The mean results of DT for ten brands obtained were in the aforementioned order: Brand G (8.19 min) < Brand C (9.25 min) < Brand E (9.61 min) < Brand D (10.11 min) < Brand B (11.07 min) < Brand A (12.15 min) < Brand H (13.68 min) < Brand I (14.59 min) < Brand J (16.32 min) < Brand F (17.49 min) shown in Fig. 4. As per results shown, Brand G has lowest DT and Brand F has highest DT, but all of the brands meet the compendial requirements. Similar findings were reported by Kahsay and Egziabher [46].
When a drug is administered orally in the form of the tablet, the absorption of the tablet depends on how fast it goes into solution, i.e., absorption of a drug is totally dependents on the dissolution of the tablet. Dissolution is a rate limiting step prior to absorption. The rate of dissolution is directly related to the efficacy of the tablet products, as well as to bioavailability difference between formulations [47]. To meet the BP standard the percentages of drug release at 45 min must be not less than 80 and 75% according to USP-NF standard. The percentages of drug release for ten brands of ciprofloxacin tablet in 45 min were in the succeeding order: Brand F (61.87%) < Brand I (65.77%) < Brand H (69.36%) < Brand J (72.86%) < Brand B (75.62%) < Brand A (76.18%) < Brand E (81.52%) < Brand D (86.44%) < Brand G (86.82%) < Brand C (94.12%), presented in Fig. 6. Among ten brands the percentages of drug release were more than 80% for four brands (Brand E, Brand D, Brand G and Brand C) and less than 80% for six brands (Brand F, Brand I, Brand H, Brand J, Brand B and Brand A) as   Fig. 6. In the study on in vitro quality assessment and bioequivalence studies on four brands of ciprofloxacin tablets, marketed in Ambo, Ethiopia, Fereja et al. stated that out of four brands of ciprofloxacin tablets one brand failed to meet the dissolution profile [48]. Analysis of the assay of the drug is very important to determine the presence, absence, or quantity of one or more components in the dosage form [19]. In this study ciprofloxacin hydrochloride tablets were assayed by using UV spectroscopic technique due to lack of instrumentation. A number of literatures suggest the UV spectroscopy for the analysis of ciprofloxacin hydrochloride tablet [49]. In fact there is no major problem in the assay of ciprofloxacin tablet by UV spectroscopic technique instead of high performance liquid chromatography technique. The percentages of the drug content of the ten brands of ciprofloxacin tablet were obtained in the following sequence: Brand H (96.84%) < Brand J (97.34%) < Brand D (98.15%) < Brand I (98.47%) < Brand E (99.37%) < Brand F (100.28%) < Brand B (100.38%) < Brand A (100.54%) < Brand G (101.39%) < Brand C (101.46%) displayed in Fig. 7. All of the brands were complied with the BP and USP-NF specification for assay test. The highest percentage of drug content was obtained for Brand C (101.46%), whereas the lowest percentage of drug content was obtained from Brand H (96.84%) given in Fig. 7. Usman et al., in the evaluation of dissolution testing for ciprofloxacin (500 mg) tablets: post market surveillance of different brands available in Ras Al Khaimah (UAE) showed that all ciprofloxacin tablets comply with the content assay test [34].
To compare the quality of all the ten brands used in the study ANOVA was performed. Results presented in Table 2 indicate that there are no significant differences in the release pattern of different brands at P < 0.05 and the F value (2.660375) is higher than F crit value (2.124029). Table 3 shows the different kinetics model that was used to plot various parameters for considering the determination of R 2 . It shows that the all of the mentioned kinetics fit for all brands. However the first-order kinetics, described the drug dissolution with R 2 approximately 1 for Brand F and Brand H, Higuchi kinetics model for Brand F and Brand G and Korsmeyer-Peppas kinetics model for Brand A, Brand B and Brand D respectively. Zero-order kinetics did not best fit to any brands. Among ten brands only Brand F and Brand H were best fit model for first-order kinetics. In case of Brand F and Brand G, Higuchi kinetics model was the best fit model.
Korsmeyer-Peppas kinetics model was the best fit model for Brand A, Brand B and Brand D among ten brands.

Conclusion
From the present study it was clearly demonstrated that all of the leading brands of the ciprofloxacin hydrochloride tablet met the criteria laid in the official monographs for in vitro quality control tests except dissolution test for four brands (Brand F, Brand I, Brand H and Brand J). But each brand should meet dissolution criteria to be therapeutically effective. So the healthcare professionals should focus on quality rather gift items to ensure better health of people. It will ultimately force the pharmaceutical industry to invest more in quality to ensure better pharmaceuticals for the betterment of the health sector of the country.


extfieldsofstudy:
Engineering
Computer Science

text:
Real-Time Contingency Analysis with Corrective Transmission Switching - Part I: Methodology

Transmission switching (TS) has gained significant attention recently. However, barriers still remain and must be overcome before the technology can be adopted by the industry. The state of the art challenges include AC feasibility and performance, computational complexity, the ability to handle large-scale real power systems, and dynamic stability. This two-part paper investigates these challenges by developing an AC TS-based real-time contingency analysis (RTCA) tool that can handle large-scale systems within a reasonable time. The tool proposes multiple corrective switching actions, after detection of a contingency with potential violations. To reduce the computational complexity, three heuristic algorithms are proposed to generate a small set of candidates for switching. Parallel computing is implemented to further speed up the solution time. Furthermore, stability analysis is performed to check for dynamic stability of proposed TS solutions. Part I of the paper presents a comprehensive literature review and the methodology. The promising results, tested on the Tennessee Valley Authority (TVA) system and actual energy management system (EMS) snapshots from Pennsylvania New Jersey Maryland (PJM) and the Electric Reliability Council of Texas (ERCOT), are presented in Part II. It is concluded that RTCA with corrective TS significantly reduces potential post-contingency violations and is ripe for industry adoption.

I. INTRODUCTION
AINTAINING a reliable power system is of utmost importance. The North American Electric Reliability Corporation (NERC) requires power systems to withstand the loss of a single bulk electric element (N-1) [1]. While various classes of reserves are acquired, reliable operation is not always achieved. Real-time contingency analysis (RTCA) is frequently repeated for this purpose.
In the Midcontinent Independent System Operator (MISO) system, the RTCA package simulates more than 11,500 contingency scenarios every four minutes [2]. RTCA utilizes data from the state estimator and contingency analysis is performed by successively solving AC power flows. Thermal and voltage violations corresponding to different contingencies are, then, determined [3] by analyzing the power flow results.
Pennsylvania New Jersey Maryland (PJM) operators simulate a full AC contingency analysis to identify the contingencies that cause violations in the system [4]. Approximately 6,000 contingencies are assessed every minute at PJM [4]. Although there is a list of all contingencies in PJM's database, not all contingencies in that list are evaluated at all times [5].
The Electric Reliability Council of Texas (ERCOT) uses a two-phase procedure to perform breaker-to-breaker contingency analysis [6]. A heuristic screening procedure is performed in the first phase to identify the most severe contingencies based on the post-contingency violations. Previously, ERCOT had approximately 3938 contingencies, including 2958 single branch contingencies, 375 double branch contingencies, and 605 generator contingencies, modeled in its system [7]. The RTCA in ERCOT executes every five minutes [7].
If a contingency with post-contingency violations is detected, appropriate actions will be taken to ensure reliability. These actions include:  Sending constraints to security-constrained economic dispatch to move away from a vulnerable state.  Commitment of fast-start units to improve availability of local reserves.  Transmission switching (TS) to enhance deliverability of reserves. Corrective transmission switching (CTS) is shown to be a viable solution [8]- [10] for handling contingencies, which is also significantly cheaper than its alternatives. CTS is already being used in normal and post-contingency operation, though to a very limited extent, at PJM [11]. Despite the vast body of literature that has been dedicated to TS over the last decade, important challenges remain for more systematic adoption of the technology. The challenges include computational complexity, unknown or poor AC performance, concerns regarding the stability of switching actions, and limited insight on performance of the technology on actual large-scale power system data. This paper closes an important gap in the literature by addressing these challenges for the RTCA application. An open source AC CTS-based RTCA tool, which is fast and works with actual power system data, is developed. The tool is tested on the Tennessee Valley Authority (TVA) system and actual energy management system (EMS) snapshots from PJM and ERCOT. High performance computing (HPC) is em-ployed to improve computational efficiency. The results, presented in Part II [12], are very promising and show that CTS can provide significant reliability benefits by drastically reducing the potential post-contingency violations. This will translate into significant savings due to substantially reduced need for expensive reliability-motivated generation redispatch and commitment. The tool is able to handle the PJM system in about five minutes with a standard desktop and parallel computing can be used to further reduce the solution time. Furthermore, stability analysis is performed on selected cases to test the switching solutions are dynamically stable.
The rest of this paper is organized as follows. Section II presents a literature review on TS and the challenges for its implementation. Section III explains the concept of corrective TS. Section IV presents the algorithm and methodology. Parallel computing details are presented in Section V. Stability analysis methodology is described in Section VI. Finally, Section VII concludes the paper.
II. LITERATURE REVIEW Currently, power system software does not utilize the flexibility of the transmission network and transmission elements are modeled as fixed assets. A single network topology is likely not optimal for different hours corresponding to different operating states of the system. Even though the flexibility in the transmission network is not modeled in optimal power flow and economic dispatch problems, it is well known that the system operators can and do change the network topology in practice [13]- [16].
Previous research has demonstrated that TS provides a variety of benefits including cost savings [17]- [18], active power loss reduction [19]- [20], thermal and voltage violation reduction [21]- [24], and enhancement of integration of renewable energy resources [25]. Furthermore, TS is shown to be beneficial in load shed recovery [26], enhancement of do-not-exceed limits [27]- [28], security and cost improvement in transmission and generation expansion planning [29], and potential cost saving in outage coordination [30].
It is illustrated in [31] that the optimal solution with TS will be at least as good as the solution obtained without TS. Cooptimization of unit commitment and TS is presented in [32]. Numerical studies show that the optimal network topology could be different for subsequent hours and that it is even possible to eliminate the need to commit additional generators as the deliverability of reserves is improved via TS. Tests conducted on the standard IEEE 118-bus test case demonstrate that 25% saving in system dispatch cost could be achieved by optimizing the transmission network topology [33]. It is a general concern that TS may compromise the reliability of the system. However, [34] shows that 15% of the overall cost can be reduced via optimizing the transmission topology, while still maintaining N-1 reliability.
TS is a power flow control technology that can improve the transfer capability and reduce the cost due to thermal and voltage limits. The total congestion costs in the PJM system in 2013 increased by $147.9 million, which amounts to a 28% increase compared to 2012 level of $529 million [35]. Therefore, there is a great opportunity for efficiency improvement through TS and other power flow control technologies, such as flexible AC transmission system (FACTS) devices [36]- [38].
A major advantage of TS is that it does not require installation of sophisticated hardware, such as expensive FACTS; TS can be performed with existing circuit breakers. Therefore, TS is a low cost power flow control technology that can significantly improve the efficiency of the power system. All the promising findings described above indicate that TS is an efficient and low-cost technology for building a smarter and more flexible electric grid.
Optimizing transmission line configurations is proposed as one of the advanced transmission technologies in the Energy Policy Act of 2005 [39]. The mathematical representation of optimal TS (OTS), with a DC set of assumptions, is a mixed integer linear program (MILP) with binary variables representing the status of the switchable transmission assets (line or transformer). Two different procedures, deterministic MILP and genetic algorithm, are proposed to find the best network topology for congestion management [40]. Results show that network reconfiguration could be used as an effective mechanism to relieve network congestion.
One of the main challenges facing industry adoption of TS is its computational complexity. MILPs are computationally expensive problems, specifically for the OTS application, considering the size of the power system. Thus, it is a challenge to get an exact solution for OTS with MILP-based within the limited available time. Therefore, many attempts to reduce the computational complexity of the problem have been pursued. In [41], a reduced MILP formulation is developed with power transfer distribution factors (PTDF) and line outage distribution factors [42]. Sensitivity analysis has been used as a way to overcome the computational complexity of the problem [43]- [46]. A greedy algorithm is proposed to quickly identify switching candidates using duals from a DC optimal power flow (DCOPF) [45] and an AC optimal power flow (ACOPF) [46]. However, [47] studies these algorithms on a large-scale Polish system and concluded that this heuristic may be inconsistent in performance. A cycle-based formulation for OTS is proposed in [48] to reduce the computational complexity by providing strong valid inequalities for the use of cutting-plane approach in a DC framework. Alternatively, high performance computing could be used to reduce the solution time for TS applications [49].
Due to the above mentioned reasons, as well as other concerns such as dynamic stability, implementation of TS has been very limited. Some system operators use TS as a corrective mechanism for improving voltage profiles and mitigating thermal overloads [14], [50]. TS is also being employed during planned outages, to make the transition smooth, and as a post-contingency corrective action [51]. California ISO (CAISO) is reported to perform TS on a seasonal basis and to relieve congestion in the system [14], [16], [52]. PJM has posted a list of potential transmission switching solutions that may reduce or eliminate violations for normal and postcontingency situations [11], [53]. However, these switching actions are not guaranteed to always provide benefits because they are identified offline; even when they do provide benefits, they may not be the best option [53]. The performance of a particular TS action is highly dependent on the operating state of the system. This paper develops an RTCA package that effectively incorporates TS as a corrective mechanism. The major bottle-necks to the implementation of TS are addressed by developing a RTCA tool with corrective TS. Prior work on CTS focuses on approaches that do not confirm with the modelling requirements or are based on algorithms that do not scale well. The majority of literature on this topic is based on small-scale test systems with DC power flow models.
While the developed RTCA tool with CTS is straightforward from an algorithmic sense, it is for that reason why the approach is innovative and ready to make a large impact in industry; it is not only scalable but it is also highly effective and, thus, it bridges the gap between the existing technology and actual implementation. The contributions of this paper are the following: 1. The algorithms developed are extremely fast. In fact, they can handle a snapshot of PJM in about five minutes with a standard desktop. Parallel computing would further improve the solution time. Therefore, this paper effectively tackles the computational complexity of CTS.
2. Full AC power flow is used for implementation of the method. Therefore, there will be no ambiguity on the performance of the solution in an AC setting.
3. The tool is able to handle large-scale systems. The TVA system and actual snapshots from the EMS of PJM and ERCOT are used to test the tool.
4. Stability analysis is performed on a subset of cases using standard industry software such as PSS/E to test the dynamic stability of proposed solutions.
This paper studies CTS with the details explained above and addresses the state of the art challenges of CTS. Therefore, the conclusions presented in this paper are more comprehensive compared to earlier studies. Preliminary results and conclusions related to this work were published in [54]. This paper elaborates on [54] and presents the algorithm development.
The paper also provides detailed information on high performance computing implementation as well as stability analysis. Part II of this paper presents detailed results obtained on the PJM, TVA, and ERCOT systems as well as stability analysis and high performance computing performance. Thus, this paper closes a significant gap in the literature by accomplishing the above-mentioned goals.

III. CONCEPT OF CORRECTIVE SWITCHING
This section presents two examples to show how CTS can reduce or eliminate post-contingency violations. Fig. 1 shows an example that CTS fully eliminates all the voltage violations caused by a transmission contingency. This example is from the authors' prior work in [24]. The network shown in Fig. 1 is a 500KV level portion of the TVA system. This particular case corresponds to a lightly loaded period. In the pre-contingency state, the switching candidate produces reactive power, which travels through the contingency line. In the post-contingency state, too much reactive power must stay in the affected area since the contingency line is now not available to deliver the excessive reactive power out of this area, which leads to over voltage. In the post-switching state, the source element of producing that excessive reactive power, which is the CTS solution itself, is removed from the system; hence, the over voltage violations are all eliminated.  IV. METHODOLOGY AND ALGORITHM The procedure for contingency analysis with CTS is presented in Fig. 3. The normal operating state of the system, which consists of AC power flow information, is first fed into RTCA. Contingency analysis is then performed and the contingencies that cause violations beyond a specific threshold are identified. The tolerances used in this paper are 0.005 per unit for voltage violation and 5 MVA for flow violations. Both metrics are based on an aggregate level across the entire system. Only those contingencies with violations beyond the thresholds are sent to the CTS routine. Five switching candidates, which would eliminate or reduce the violations, are identified for each of those contingencies.
Stability analysis, using a standard industry tool such as PSS/E, is performed on selected cases to test for dynamic stability after performing the corrective switching action.

A. Contingency Analysis
RTCA is a well-known and essential function in modern energy management systems. The RTCA package developed in this paper adopts the standard assumptions as given below: 1. For transmission element contingencies, all generators' active power outputs remain at the pre-contingency level except for the generators at the slack bus(es).
2. For generator contingencies, participation factor based on available capacity is used to redispatch generation [24].
3. The faulty element is isolated using circuit breakers. This paper utilizes OpenPA [55], an open source decoupled AC power flow [56], as the power flow engine of the RTCA.  If the right corrective actions are not implemented, contingencies may cause post-contingency voltage limit violations and line overloading. Such conditions may lead to a cascading outage. A possible result of cascading failures is a system blackout, with disastrous socio-economic consequences. Therefore, managing post-contingency violations appropriately is essential for secure operation of the system.
Operators have several options to maintain reliability after detection of a contingency with potential violations. The operator can move the dispatch away from the vulnerable state or commit additional units. These are common means of maintaining reliability. Note that reliability motivated commitments and redispatch create a significant economic burden. While such economic burdens are justifiable in order to prevent catastrophic blackouts, there are cheaper solutions.
CTS is shown to be an effective alternative to many preventive approaches. Not only is CTS effective, it is also drastically cheaper. CTS may completely eliminate the potential postcontingency violations or significantly reduce them. Thus, there will be substantially less need for expensive reliabilitymotivated commitments and redispatch. Taking everything into account, corrective transmission switching provides reliability benefits, through which significant cost savings will be achieved.
Note that system operators do not model all potential N-1 events in RTCA. Various contingencies are not likely to cause violations based on the immediate system condition. The operator may also have a predetermined strategy to alleviate post-contingency violations, e.g., switchable shunts, adjustment of transformer taps, bus splitting, FACTS devices, or a predetermined special protection scheme (SPS). To provide a comprehensive study, this paper simulates all the potential N-1 events, excluding radial lines.

B. Heuristic Approaches for Computational Tractability
To reduce the computational complexity of the problem, three heuristics are proposed to generate a limited set of switching candidates. This fairly small subset of switchable elements includes quality solutions and also can be processed within a reasonable time, making the method suitable for realtime applications. The three heuristics, which are proposed in this paper to generate the candidate switching list, are listed below. Complete enumeration (CE) is only used to gauge the performance of the heuristics.
 Closest branches to contingency element (CBCE),  Closest branches to violation elements (CBVE),  Data mining (DM). Based on the authors' prior experience, it is observed that most of the beneficial switching solutions lie within a close vicinity of the contingency element and/or the violations. Based on this observation, two heuristic approaches, CBCE and CBVE, are developed. CBCE searches for the 100 closest branches to the contingency element. CBVE heuristic searches for the 100 branches closest to the elements with violations.
For transmission contingencies, it is found that the network violations occur on the elements that are very close to the contingency element. Hence, the lists of transmission switching candidates generated by both the CBCE and CBVE would be very similar. For generator contingencies, since the generators are redispatched, the violations may not be that close to the contingency. In this case, it is very likely that the CBVE method provides better CTS solutions when compared with the CBCE heuristic.
The distance of one element to another element, used by both CBCE and CBVE in this paper, is defined as the number of branches in the shortest path connecting these two elements. Therefore, neither the electrical distance [57]- [58] nor the real distance (miles) is involved in this metric; the proximity of two elements is only determined by the topological characteristics of the network. Suppose the contingent element is a line; all other transmission assets that are directly connected to either of the two contingent line's buses, they are given a distance of zero. When the distance is listed as being zero for a line, the shortest path does not traverse across any other transmission asset to reach that specified line whose distance is zero. Lines that have a distance of one are connected to the far end bus of lines that have a distance of zero (for the corresponding shortest path). This process repeats to generate distances based purely on a topological structure and the shortest path.
For the data mining technique, it was first observed that many switching solutions come from a common subset of transmission assets. The system cases are split into two sets: training and test. Initially, complete enumeration of all the switchable branches is performed for each of the potential critical contingencies on the training set. The beneficial switching actions for each contingency in each scenario are identified and combined together. This combined list is a very small subset of all switchable elements. The combination of the beneficial switching actions for the training set is considered as the switching candidate list for the test set. The basic assumption behind this method is that, even if operational conditions change, previously determined beneficial switching solutions should be at least top candidates considered for the switching action. To be more specific, the training set can be considered historical information while the test set will consist of snapshots in real-time.
Different tolerances for identifying beneficial solutions with the DM method can result in different candidate list lengths. In Part II, three DM methods with different thresholds are studied. They are referred to as DM1, DM2, and DM3, respectively. There is no minimum threshold used in DM1 for identifying the beneficial switching solutions, which makes the list very long for this approach, since even the candidates produc-ing negligible improvements will be considered as potentially beneficial CTS solutions. Only the switching actions that provide a violation reduction of more than 5% comprise the candidates for CTS in DM2. DM3 has the smallest list length as it includes only those switching actions that provide a violation reduction of more than 10%.
Apart from the heuristic methods, a complete enumeration (CE) of all possible switching actions is also performed in order to estimate the best possible benefits that can be achieved with CTS. CE is obviously not a practical approach so it is merely used to confirm the optimal solution and to offer a basis for analysis of the quality of heuristic methods.

C. Metrics
Average violation reduction in percent is used to show the effectiveness of the method on an aggregate level: where, ∆ 0 denotes the total violations after contingency ; ∆ 1 denotes the total violations after corrective switching with contingency still present; and is the total number of critical contingencies identified.
Although the post-contingency violations may be reduced on an aggregate level by implementing a specific CTS action, it is important to analyze the impact of the switching action on individual elements. It is possible that a specific switching action, while reducing the overall violations, creates additional violations that did not exist before implementation of the CTS action. CTS may also increase the violation on one particular element, while reducing the overall violations. Therefore, solutions are checked for Pareto improvements (PI); the CTS solution provides a Pareto improvement when at least one post-contingency violation reduces without causing any additional violations on any other element of the system.
Depth is defined as the location of the identified beneficial CTS solution in the candidate list. Depth is proposed only as a metric to evaluate the efficiency of each heuristic. The average depth can be calculated as follows: where, , denotes the location or the index of the identified beneficial CTS solution in the ranking list for contingency ; is the number of critical contingencies for which a beneficial CTS solution exists.

D. N-1-1 Reliability
Meeting the N-1-1 reliability requirement is essential to ensure a reliable system. Thus, one major CTS concern is regaining N-1 reliability after the first contingency and the related CTS action. NERC's N-1-1 reliability criterion states that the system has to become N-1 reliable again within 30 minutes following the first contingency. In the case of a contingency leading to network violations, a corrective action is first implemented to relieve the violations and bring the system back to acceptable operational conditions in a very short time. This paper proposes CTS as an effective corrective action at this initial step. Subsequently, remedial actions will be taken to regain N-1 reliability in post-switching situations. The remedial actions can include a mixture of generation redispatch, further CTS actions, and putting the switched CTS line back in service. This paper focuses on the immediate corrective action taken right after the occurrence of the contingency and N-1-1 reliability is outside the scope of this paper.

E. Impacts of Switching Solutions on Circuit Breakers
The proposed corrective TS scheme is intended to provide operators with additional corrective control actions that are very cheap and effective; the only associated cost of CTS is the impact on circuit breakers. CTS provides the operator with a corrective switching solution that would be implemented only if the contingency occurs. One concern regarding transmission switching is the impact on circuit breakers; ABB gave a presentation at PJM on circuit breaker health in relation to transmission switching, [59]. Since the probability of the contingency is low, the great benefit of this corrective control technology is that it would rarely need to be implemented. Additionally, there are many beneficial switching solutions, see [12], which makes the likelihood of multiple CTS actions on the same circuit breakers very low. Thus, the wear and tear on the circuit breaker due to CTS is minor.

F. Multiple Switching Solutions
Only a single switching action will be implemented as a corrective mechanism in this paper for each contingency. Although switching multiple lines simultaneously is theoretically possible and would provide more flexibility, we focus on single switching solutions based on the request of industry and we leave the investigation of multiple switching solutions to future work.

V. HIGH PERFORMANCE COMPUTING
With the advancements in computer technology, high performance computing is increasingly gaining popularity. The hardware for implementation of HPC is easily available nowadays. Moreover, mature parallel programming models, such as message passing interface (MPI), make parallel programming attainable for real-world applications.
The nature of the CTS module within the developed RTCA is apt for parallel computing. Evaluation of each switching candidate is independent of other candidates and, thus, can be assigned to an independent processor. The problem is solved simultaneously with multiple threads by breaking it into independent sub-problems. Parallel computing enables such parallelizable problems to be solved significantly faster.
One metric to measure the effectiveness of parallel computing is the parallel efficiency as defined in (3), where denotes the number of threads, 1 denotes the computational time of the sequential program, and denotes the computational time of the parallel program with threads.
For RTCA with CTS, as presented in this paper, the parallel efficiency is close to one, suggesting significant room for computational efficiency gains via parallel computing.
The parallel computing tool used for the simulations performed in Part II of this paper is MPJ-Express [60], which is the message passing interface in JAVA. The hardware for parallel computing simulation used is "cab" cluster at Lawrence Livermore National Laboratory (LLNL).

VI. STABILITY ANALYSIS
Power system stability is of utmost importance. It is not practical, and certainly not economically efficient, to design a system to be stable for all possible N-k contingency scenarios. Hence, the system is always designed such that it maintains stability only for a subset of disturbances around any given operating state.
The system stability, which is subject to a particular disturbance, depends on its current operating state and the nature of the disturbance. It is possible that the power system operating at a given set of conditions (operating states) is stable for a particular disturbance; however, the same disturbance may cause the system to collapse when it is operating at another particular stressed operating state. Hence, it is not proper to classify a disturbance as small or large depending on its magnitude alone.
Contingencies, as well as switching actions, are generally associated with large changes to the operating steady-state equilibrium of the system. Since the focus of this paper is contingency analysis with CTS, stability analysis plays an important role in this work. Moreover, there is an overarching concern that CTS may introduce more vulnerability to the system leading to system instability. These important issues are addressed through this paper.
Power system stability has been defined as the ability of the system for a given initial operating state to regain a state of operating equilibrium after occurrence of a physical disturbance with system variables remaining bounded [61]. Maintaining dynamic stability is an essential requirement for secure operation of the power system. Power system instability has been reported to cause several major blackouts in the past, which emphasizes the need to focus more on the power system stability studies [62].
Part II presents stability analysis results for corrective TS in PJM. The dynamic data for the PJM system contains information about the different machine models in the system. Time domain simulation is performed using PSS/E to analyze the effect of the proposed CTS actions on the system stability. The stability studies are conducted on selected hours with different loading profiles and different number of contingencies leading to network violations.
Time domain simulations are performed on all critical contingencies for the selected hours to check the stability of the switching solutions. It is very essential to check the stability of TS actions as unstable switching solutions would weaken the system rather than reducing the violations. Two different methodologies are followed to perform the time domain simulation for transmission contingencies and generator contingencies. In case of transmission contingencies, generation redispatch is not performed. The generators at the slack bus(es) are used to pick up the change in losses. However, generation redispatch based on the available capacity is implemented following a generator contingency.
For transmission contingencies, the base case power flow is run for the initial 2 seconds after which a transmission contingency is simulated. At t=20s, the CTS action is implemented and the simulation is terminated at t=40s.
The time domain simulation is run for a total of 60 seconds in case of generator contingencies. The base case is run for the initial 2 seconds without any disturbance to the system. The generation contingencies are simulated at t=2s and the generation redispatch associated with the particular contingency is implemented at t=20s. This is followed by the switching action, which is implemented at t=40s and the simulation is terminated at t=60s.
The rotor angle, frequency, and voltage stability are checked for the selected switching actions. The relative rotor angles of all machines are monitored throughout the duration of the simulation to ensure that no single machine or group of machines swing away from the rest of the system and lose synchronism. If there is a relative rotor angle separation of any machine from the rest of the system such that it loses synchronism, the CTS action is categorized as unstable. The frequency of all the buses in the area of disturbance is monitored and it is checked that the frequency stays within the limits of 59.5Hz<f<60.5Hz [63]. For any bus in the system, if the frequency deviates beyond the specified threshold, the switching action is considered to be unstable. Similarly, a voltage threshold of 0.9<V<1.1 [63] is used to ensure that the switching action does not cause voltage instability.
Note that the objective of performing stability studies in this paper is to check if the switching solution is stable, assuming the system remains stable after the contingency. Hence, the emphasis of this study is on the stability of CTS action, not the dynamics of the contingency itself. The results presented in Part II show that the majority of the proposed switching candidates that are tested are stable, suggesting that TS is a viable corrective mechanism. This is consistent with how PJM views the stability issues in its footprint [64]. PJM concludes that stability has yet to become a significant system limitation [64].

VII. CONCLUSIONS
Transmission switching is a low cost power flow control technology that would reduce the operational cost, improve system reliability, and enhance integration of intermittent renewable resources. Despite all these benefits, the industry adoption of the technology has been fairly limited due to the following barriers: computational complexity for large-scale systems, ambiguous AC performance, and stability concerns. This paper comprehensively addresses the state of the art challenges of transmission switching. An open source multithreaded AC-based RTCA package, which incorporates CTS as a corrective mechanism, is developed. When RTCA identifies a contingency with potential network violations, a separate routine finds effective CTS actions to relieve the violations. Thus, the need for reliability-motivated commitment and redispatch will be drastically reduced. This will translate into reliability benefits and also substantial cost savings.
The RTCA developed in this paper proposes multiple switching actions for each contingency. For each potential switching solution, the violation reduction and a flag indicating a Pareto improvement is communicated to the operator. The operator has the choice to implement any of the solutions based on the associated violation reductions, Pareto performance, or stability concerns.
Part II presents the performance of the developed RTCA with actual data from PJM, ERCOT, and TVA. The results demonstrate the effectiveness of CTS based on its ability to reduce post-contingency violations in an AC setting.


extfieldsofstudy: Physics Business

text:
Exploring Leadership Capability Team Leaders for Construction Industry in Malaysia: Training and Experience

It has been said that the construction industry must unleash its potential as a source of wealth creation and provide opportunity for the betterment of quality of life. In ensuring the quality of workmanship at construction sites, supervisory skills of site supervisors need to be enhanced. It stressed out that to match business growth and excellence overseas, we must recognize and act on the importance of continuously developing niche expertise and capabilities. Undoubtedly, the role of research in determining the specific leadership skills and the needed core capabilities cannot be over-emphasized. In ensuring the quality of workmanship at construction sites, leadership skills especially supervisory skill for site supervisors need to be enhanced. In this study, quantitative research design with survey questionnaire was used to collect the data and simple random sampling was employed in selecting 248 respondents involving team leaders in construction industry from whole of Malaysia. The data was analyzed using descriptive and inferential statistics; ANOVA in SPSS 21.0. Training and experience in leadership has been found to be significance to leadership capability of team leaders. The opinions from the respondents also indicated that they need the training of leadership and they had to enhance themselves to enable them to become better and more competitive leaders. The results of this assessment can pinpoint the areas needing improvement and therefore can be used as basis in designing and/or deciding development programmes. This study also found that generally the team leaders in construction industry needed more opportunities to expand their leadership capability to become the effective leaders in future.

Introduction
The pace of change today is fast and we are forced to face new challenges with a lot of uncertainties. The proposition that the economic and social wellbeing of society, and those in it, is substantially dependent on the effective and efficient performance of organisations of all kinds, which in turn depend on adequate or excellent leadership and management capability that can be learned and developed, would be accepted by many as likely to be true in common sense and everyday observation [1]. Developments in the construction industry such as the growing volume of activity, rising number of active stakeholders, technology advancement, global competition, and demand for fast-track completion, have created many distinct challenges.
It seems the construction sector is experiencing a gap in leadership capability, compared to other industry sectors generally. Research from [2] found that 54 % of managers in the construction sector rate the leadership skills of their line manager as good or very good, compared to 65 per cent of managers in other industry sectors. 12 % of managers go as far as to say the leadership skills of their line manager are 'bad' or 'very bad' (a similar number to respondents in other industry sectors). Managers rate senior leader skills and capability less positively. In terms of 'distant leadership' (senior business leaders), only 23 per cent of managers in the construction sector rate the leadership skills of senior leaders as good or very good (compared to 50 per cent of respondents from other industry sectors) and an equal number (23%) rate senior leader skills as poor or very poor. Although there are some positive indicators on the quality of leadership, given the investment in leadership development of the last decade, there is considerable room space for improvement and some questions remain unanswered about what makes for effective leadership development.
A locally derived concept of leadership and leadership capability is therefore important in developing tailor-fit leadership development programmes and reliable research instruments that could be used in the Malaysian context. Therefore, the purpose of this study is to explore leadership capability team leaders for construction industry in Malaysia focusing on training and experiences of leaders.

Leadership
Although there are many definitions and explanations for leadership, it "is one of the most observed and least understood phenomena on earth" [3]. Accordingly, explaining leadership itself is difficult because the nature of leadership is complicated [4]. They recognized the key components associated with the leadership phenomena and defined it as a process whereby a leader with his intelligence and willpower has a bearing on a group of subordinates or employees to be able them to develop their potentials so as to achieve the organizational objectives within granted time, funding, and quality. [5] defines leadership as a phenomenon that requires the process of influencing follower, whereby leaders with good personality and attitude, shares a vision in organisation. Leadership can be interpreted as the combination of ability and leaders' behaviour to influence other's perception consistent with the organisation's mission and vision.
[6] designated that leadership is still a dynamic concept for the development of communication channels toward others and influences the group for goal accomplishment. No ultimate leadership behaviour exists [7] and the many ways that leadership has been conceptualized will affect the relationship among leaders and followers who intend real changes and outcomes that reflect their shared purposes [8]. Therefore, dealing with rapid, complex, and often discontinuous change requires effective leadership. While the importance of leadership has long been recognized as a success factor for organizations, in regard to project context there have still not been enough empirical studies to support the association between leadership capability and project success of construction industry. However, overall project success consists of several dimensions that depend on the manager's leadership style [9,10] and competences [11].

Leadership Capability
Research from [12] forwarded a leadership capability framework with thirteen generic leadership capabilities in Australian Technical and Further Education (TAFE) institutions. Their research focused on developing a new generation of leaders with both generic organisational leadership qualities and strong business and commercial capabilities to develop leadership success. They proposed thirteen generic leadership capabilities to be included to TAFE leadership capability framework.
Callan's core capability for VET managers consists of: a) holding a corporate vision and direction; b) focusing strategically; c) achieving outcomes; d) developing and managing resources; e) demonstrating leadership in relation to change; f) developing interpersonal relationships, displaying a capacity for personal development and mastery; g) demonstrating business and entrepreneurial skills; and h) having the ability to develop and empower people [13]. More recently, [12] prepared another set of generic leadership capabilities which have many elements in common with those outlined by [13] The key exception is that [12] also suggest that generic leadership capability is combined with a set of sector-specific, contextual capability: providing educational leadership; understanding and working within industry and the community; and working with the VET system.
Research from [14] stressed that individual VET leaders must be able to respond to internal and external change through their character and alliance building skills; though risk taking, initiative and innovation; and capabilities around visioning (i.e. vision, future trends, proactively). As an extension of this point, it is clear that not all the leadership and management capabilities that exists with individuals is fully utilised in organisational settings [1]. This is because of mixture of motivational factors, revolving around whether people are recognised as having these abilities and are rewarded for using them, and structural issues concerning work planning, career development and organisation design affecting the extent to which individual capabilities can contribute to collective capabilities.

Leadership Capability in Construction Industry
From the viewpoint of [15], there are no poor engineers or scientists, only poor leaders. If leaders have excellent resources but manage them poorly, they will get nothing but poor results. It can be noted that leadership skills are crucial at the leadership level in any industry. Thus, partaking actively in the organization to ensure the strategy is linked to the overall business strategy is the first sign of the leadership. The findings from [16] concluded that with a big question of how applicable are leadership models and approaches developed in settings other than construction when applied to the construction industry. They also argued that construction industry's basis in selecting and employing the supervisors, should be more systematically researched to ensure its applicability to construction industry.
Construction industry faces major leadership challenges such as those relating to the workforce including lack of quality people owing to difficulty in attracting talent, ageing workforce, dealing with issues, teamwork and communication, training and education [17]. They further stated that the economic challenges include funding difficulties, uncertain economic conditions and technological challenge include increased of information and communication technology used, technology gap between developed and developing countries and matters of technology transfer need to be studied.
Recent publications also propose that the construction industry needs to develop individuals who are not only good managers but also have genuine and authentic passion to lead the project. Such leaders are not self-centred and project-stereotype rather they are motivated by the well-being of their subordinates, organisations and society [18]. Continued theory building and systematic testing for existing propositions on authentic leadership will improve the understanding, prediction and application of the positive impact of authentic leadership development [19].
Leaders help the team break boundaries to build relationships and support one another, scouting for the necessary information to accomplish objectives and achieve success [20]. In this regard, a transformational leader has been found to promote project effectiveness. Transformational leaders aim to transform individuals so that go beyond the status quo with the purpose of improving the ability to innovate and adapt in the team environment [21]. On the grounds that the aim of the study is centred on sustainable development and hence one of the variables of sustainability is social concerns, therefore, transformational leadership as a humanistic way to manage the subordinates [21] has been regarded to be assessed among the project managers in sustainable building projects. [22] contends that leadership capability will not undergo drastic changes rather, the organisations should expect a sharpened focus on current skills necessary to accommodate intensified conditions in business and society The organisation therefore need to be more sensitive about leadership qualities and capabilities, besides fulfilling growing needs by creating diverse workforces and implementing technology improvements.

Methodology
Quantitative method using survey questionnaire was employed in this study. The purpose of using the quantitative method in this research was to predict and explain the phenomena through focused collection of numerical data. In this research, questionnaire was used to gather the required data and was adapted from the items used by [15].
Construction Project Managers and Construction Site Managers were chosen as respondents for this study. They were selected because those were the posts closest to construction sites, while Civil & Structural Supervisors were chosen as representative of the supervisory position because they are the posts with the largest number of members. Simple random sampling was used to identify the respondents this research. This type of sampling was employed as the random sampling works on the principle of randomisation. In simple random sampling, every individual in the population has the same probability of being selected as respondent. The respondents were drawn from the list of team leaders (consisting of 683 individuals) obtained from CIDB. As per Krejcie and Morgan's Table of Statistically Determination of Sample Size (S) Required for a Given Population (N) Based on the Three Sample Factors, for a population of 683, the sample taken was 248. The researcher wrote down the numbers from 1 to 683 in pieces of paper to represent the population. All the numbered papers were placed in a bowl and 248 numbers were drawn to ensure that every individual in the population had equal chance to be selected. Of the 248 respondents throughout Malaysia including Sabah and Sarawak, only 171 questionnaires were sent back by the respondents, thus generating a retrieval rate of 69%. According [23], the response rate of 50%-60% or greater is optimal because non-response bias is thought to be minimal with that high response rate. The data derived from the survey questionnaire, descriptive and inferential statistics using SPSS version 21.0 was used to analyse all the items. Table 1 presents the respondents' demographic characteristics. The table shows the distribution and percentage of respondents according to their gender, age, leadership courses attended, and years in leadership positions of the respondent. More than half (57.3%) respondents were male and 42.7% were female. Respondents with the age below 20 years old accounted for 0.6%, 41.5% were 21-30 years old, 24% were 31-40 years old, 41-50 years old were 16.4% of the total respondents, and 7.5% belonged to age range of 51-60 years. This table also illustrates the respondents' distribution and percentage according to the leadership courses they had attended. A large majority (51.5%) of them had attended between 1-3 courses. Only (8.8%) of the respondents had attended more than 10 courses. The table also shows the distribution and percentage of respondents according to the number of years in leadership positions. A little less than half (45.6%) of the respondents has 6-10 years of working experience as a leader, while there were only 2.3% of respondents with 16-20 years of working experience.

Leadership Training and Experience
Inferential statistics allow the findings from research to be generalised. One-way ANOVA was used to define the significant difference between leadership courses and team leader position with leadership capability. Table 2 shows the results of one-way ANOVA analysis of number of leadership courses attended and years in leadership position. A statistically significant difference was found between number of leadership courses attended and leadership capability with F(5, 4) = 0.81, p < 0.05 and between team leader position and leadership capability with F( 5, 4)=3.09, p<0.05 . Thus, there were significant difference between leadership courses with leadership capability, and between years in leadership position with leadership capability. These findings showed that the core leadership capability is influenced by number of leadership courses attended and years in leadership position.
Thus, post hoc test were used to obtain a significant omnibus F-test with a leadership courses group and years in position group that consists of four and five means. Additional explorations of the differences among means in these groups are needed to provide specific information on which means are significantly different from each other. Table 3 shows the result of Post Hoc test on leadership courses attended. and Group 3 (4-6 times; M=2.63, SD= 1.63) with p= 0.002. In other words the number of leadership courses attended by team leaders is statistically significant between Group 2 (1-3 times) and Group 3 (4-6 times). Group 1 (no related courses attended), Group 4 (7-9 times) did not relate significantly with each other or either Group 2 or 3. This result shows that the moderate times of training leadership courses affected leadership capability of team leaders. Table 4 shows the results of Post Hoc test on years in leadership position by team leader. Tukey HSD test in Post Hoc test were conducted on all possible pairwise contrasts. The following pairs groups were found to have significant relationship, p<0.05; Group 3 (6-10 years; M=2.36, SD= 1.56) and Group 4 (11-15 years; M=1.79, SD= 1.86) with p= 0.006. In other words the number of leadership courses attended by team leaders is statistically significant between Group 3 and Group 4. Group 1 (less than a year), Group 2 (1-5 years), Group 5 (16-20 years) and Group 6 (more than 20 years) did not relate significantly with each other or either Group 3 or 4. This result shows that the moderate times of experience in leadership affected leadership capability of team leaders.

Discussion
With regards to the number of courses attended and number of years in leadership position, the findings showed that there were significant differences on leadership capabilities. The researchers labelled the number of course attended as leadership training and development while number of years in leadership position as leadership experience. Team leaders need leadership training and development to improve their capability in leadership. This finding reaffirms the previous study by [23] that points out that it is important for leaders to attend leadership training and development programme rather than attending management training programme. This is because leadership training provides more information and knowledge about leadership compared to management issues. Organisations often offer leadership training because they think it is a step to developing leaders in their organisation.
The respondents believe that training and development programmes will enable them to acquire new and enhanced skills that will later make them better leaders. These findings are also similar with the previous study of [24]. Their study showed that middle-position employees as with the respondents of this study see leadership training as beneficial and they are willing to invest personal, unpaid time to participate in leadership courses just to improve their efficiency in their current job. In order for leadership training and development to be effective, the training providers should make use of variety of learning methods. [25]  simulation, in-basket training, case study, incident process, and assessment centres. [26] further pointed out that the most common training techniques used are lectures, case studies, discussion groups, reading assignments, and simulations. The varieties of training technique are to affirm the same lesson or information in a variety of ways so that leaders can internalize the information and put it into action.
The findings of this research also indicate that leadership experience contributes to the improvement in leadership capabilities. The number of years in leadership position has significant relationship with leadership capabilities. This is similar with previous research of [27] who found that experience is among the key influencers in leadership development. They report that only about 30% of the sample of successful vocational education administrator leaders placed emphasis on when the experiences should occur. They recognise, however, that it certainly might be helpful to provide experiences in a person's administrative career as early as possible. Finding from [28] also emphasised that leaders must have experience in their industry and leadership to develop knowledge-based vision and direction that contribute to leadership credibility and capabilities. The finding from [29] emphasize that the real-time experienced leaders have been proven to affect leadership effectiveness perceived by subordinates and peers.
The importance of experience in leadership capability was recognised by the respondents in open ended section of questionnaire. They stated that construction industry needs project manager or site supervisor with leadership and working experience. Scholars in leadership development field have long considered challenging work experience as a key in the process of developing team leader's leadership capabilities [30,31]. One with leadership experience has better leadership ability than one without leadership experience. In addition, leadership ability is obtained from leadership experience and not only through working experience [32].
Leaders learn from their experience to deal with interpersonal and organisational issues. From the feedback of respondents, the results indicated that leaders should have experience in their field and in leadership [33]. Both components contribute to the success of organisation performance to reach the objectives and mission of the team. Respondents also stated that leaders with leadership and work experiences are valuable to the company. With these experiences, they will be able to face and solve the problems that arise at the site and the organisation handily.

Conclusion
Leadership training has been seen as one of the personal attributes. Leadership training can maximize productivity, shape a positive culture and promote harmony. Training provided should be able to help people gain crucial skills and allows the organizations to attack relevant, crucial, real-time issues. Leadership training program should be designed to increase effectiveness of leaders' professions by cultivating their leadership capabilities. Leader with experience exudes more credibility during their leadership tenure. Credibility therefore is an important component of leader's personal attributes. Credible leaders' are able to influence followers; leaders are seen as a credibility model to employees.
The result suggested that the integration of leadership experiences and leadership training can and will greatly influence the core leadership capabilities of team leaders. This study also found that generally the team leaders in construction industry needed more opportunities to expand their leadership capability. The findings of this study therefore be of vital use in charting their leadership development. In like manner, the framework could be a useful tool in assessing the team leaders' leadership potentials and performance.