text:
Journal of Glaciology
Volume 14 Issue 70
Deducing Thickness Changes Of A...
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Deducing Thickness Changes Of An Ice Sheet From Radio-Echo And Other Measurements
The effect of thinning of the layers by lateral flow
Journal of Glaciology, Volume 14, Issue 70
1975 , pp. 49-56
J. F. Nye and H. H. Wills (a1)
(a1)
Physics Laboratory, University of Bristol, Bristol, England
Copyright: © International Glaciological Society 1975
Published online by Cambridge University Press: 30 January 2017
Figures:
Fig. 1. P is a marker buried in the firn, in the time interval Δt it moves to P′. PQ is drawn parallel to the surface
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The displacement of the surface of an ice sheet and of markers set in its top layers can be measured geodetically, and also, it is expected, by radio-echo methods. The paper discusses how such measurements could be interpreted as showing long-term changes in the thickness of the ice sheet; in particular it discusses how one might design an experiment so as to avoid unwanted effects due to short-term changes in rate of accumulation. The analysis is similar to that of Federer and others (1970), but it corrects an error, so that when applied to their results for central Greenland it gives a different result for the lowering of the surface. Federer and others have already concluded that the average accumulation rates during the past 100 years have been below those needed to keep in balance with the velocity of the ice sheet as a whole. Using a particular model, it is found that this has resulted in the surface lowering at a mean rate of 0.050 m a−1 between 1871 and 1968, and a mean rate of 0.140 m a−1 between 1959 and 1968.
The proposed radio-echo method of measuring the movement of an ice sheet (Nye and others, 1972[b]; Walford, 1972; Nye and others, 1972[a]) works in essence by enabling one to set up a horizontal and vertical coordinate system, fixed relative to the rock bed, precise to a few centimetres, and independent of visible landmarks. It has been suggested that the displacement of features such as the surface of the snow, a particular firn layer, or a marker set in the snow, could be measured relative to this fixed frame. This paper discusses how such displacement measurements could be interpreted, and, in particular, to what extent they could be interpreted as showing long-term changes in the thickness of the ice sheet. Federer and others (1970) analyse a similar problem in relation to the measurements of horizontal and vertical displacement made by the repeated geodetic surveys of the Expedition Glaciologique Internationale au Groenland (EGIG 1 and 2) in central Greenland. The topic is not as straightforward as it may at first appear.
If an ice sheet is in a steady state, with a certain rate of accumulation, and if the accumulation rate is suddenly changed, the new steady state is approached asymptotically with a time constant of the order of 103 to 104 years (Nye, 1960; Haefeli, 1961). Thus, even with a rapidly varying accumulation rate, the velocity pattern of the ice sheet as a whole is expected to change rather slowly with time; this is in contrast to the accumulation rate itself, which is expected to show fluctuations on a wide variety of time scales, from single storms, through seasonal changes to long-term climatic changes.
The direct approach to the problem of discovering long-term changes in the thickness of an ice sheet would be simply to measure the change in height of the surface over a certain time interval. The difficulty with this method is that the result would obviously be very sensitive to the particular values taken by the accumulation rate during the interval; one does not want the experiment to be merely a complicated way of discovering that it has recently been snowing exceptionally hard. To distinguish the long-term trend from short-term "noise" of this sort one might try to measure the change in height, not of the horizon of age zero, which is the surface, but of the firn horizon which is, say, ten years old. Such a horizon of course moves relative to the firn; and so the method would involve identifying the ten-year-old horizon by stratigraphic studies at the beginning and at the end of the time interval. Even if the identification were correct, the measured height changes would still be far from steady, for they would still reflect short-term fluctuations in accumulation rate, such as single storms or single years with high accumulation. Thus a direct approach of this sort would only be successful if the measurement interval were very long.
Rather than trying to identify repeatedly a firn horizon of given age, which moves relative to the firn, it is much easier to use markers which are fixed relative to the firn. At the same time it will be noticed that the direct method just described does not make use of the extensive information on the history of the rate of accumulation which has been the main result of the many stratigraphic studies carried out in Greenland and Antarctica. But, although it provides a much better method, the use of markers fixed in the firn, together with information on accumulation rate, brings its own problems. For example, the downward velocity of markers set in the upper layers of the firn is only partly due to the velocity of the ice sheet as a whole; a large part is due to the compaction of the firn. The latter component is affected by fluctuations in accumulation rate, and this must be taken into account. Knowing the velocity of the markers, and with information from stratigraphy about the history of accumulation rate, we can try to answer the question: by how much is the velocity of the ice sheet as a whole out of balance with the current long-term accumulation rate? When the question is put in this form it is obvious that the precise answer must depend on the time period over which one chooses to average the accumulation rate. The direct method would measure the rate of increase of thickness of the ice sheet averaged simply over the period of observation; by contrast, the method which uses markers in the firn in conjunction with the accumulation rate effectively makes the averaging period equal to the length of the stratigraphic record; this will usually be much longer, and the result will be correspondingly better.
A full analysis of the motion of the markers would require a theory of the snow compaction process with a varying accumulation rate and temperature, which is a very difficult matter. The theory that follows avoids this by stating conclusions entirely in terms of steady accumulation rates, although a model involving a sudden change from one steady rate to another is also considered.
If there were a perfectly steady state, snow would fall in a given location at a steady rate and the velocity of the ice sheet would be just sufficient to ensure that the surface remained fixed in space. The compaction of the snow into firn would result in a density: depth relation that was constant with time. But we may expect that, provided the accumulation rate and the atmospheric conditions remain steady, even if the velocity of the ice sheet is out of balance with the accumulation rate. the physics of the compaction process will still be essentially the same; and therefore the density: depth relation will be constant, provided the depth is measured relative to the surface. This is Sorge's Law (Bader, 1960,1963).
The first model we use is thus as follows. The accumulation rate is constant. The movement of the ice sheet as a whole is out of balance with this accumulation rate, and so the thickness h at the place in question changes. Over a time interval short compared with 103 to 104 years, ∂h/∂t will be constant, to a sufficient approximation. We wish to relate ∂h/∂t to the motion of a marker in the firn. P in Figure 1 is a marker put at a certain depth in the firn at time t. The age, at time t, of the firn layer in which the marker lies is T. At a later time t+Δt the marker (assumed fixed in the medium) is at P' and is now in firn of age t+Δt PQ, is a line drawn parallel to the surface of the ice sheet and P'Q, is perpendicular to it.
P'Q, equals VΔ t, where V is the downward velocity component of P normal to the surface. At time t+Δt the firn layer of age V is above the marker by an amount a Δt, measured parallel to P'Q, where a is the average rate of accumulation measured normal to the surface as thickness of firn per unit time between the depths of P and P'. Let us assume that the water equivalent is fully preserved in a vertical column; there is no thinning of the layers by lateral flow. Then a is related to the rate of accumulation a∗ measured normal to the surface as thickness of water equivalent by
where ρw is the density of water and ρ is the density at the depth concerned (the mean density between the depths of P and P'). Hence the horizon of age V has moved up parallel to its normal by a distance aΔ—VΔt. But, according to the model underlying Sorge's Law, the firn layer of age V is always to be found at the same depth below the surface. Hence the upward displacement of the horizon of age V is identical with the upward displacement of the surface, which, in turn, is equal to the increase ΔΑh in thickness of the ice sheet measured normal to its surface. Hence
or, taking the limit,
In this equation both a and Г vary with depth z, but their difference is constant. In terms of a density: depth profile ρ(z) we have
For an alternative derivation of Equation (3), consider an imaginary parallel-sided slab of constant thickness z whose top surface coincides with the moving top surface of the ice sheet. The slab is not fixed in space, neither is it fixed within the medium; it moves up along the normal to the surface with velocity ∂h/∂t. The mass flux through the top surface is the rate of accumulation of mass a∗ρw; the mass flux through the bottom surface is (∂h/∂t + V)ρ where ρ is the density at depth z; and, by Sorge's Law, the mass within the slab is constant. Equation (3) follows.
These derivations neglect the thinning of the layers by lateral flow. This effect gives a correction term in Equation (3) which, for the Greenland measurements referred to later, amounts to about 2% of the individual terms on the right-hand side. So as not to obscure the main issue we shall neglect this term in what follows. It is discussed in the Appendix.
The radio-echo method essentially enables one to relocate the point P at the later time t+Δt, when the marker has reached P'. Hence it gives the vector PP', from which the component P'Q., equal to VΔt, may be deduced. This is emphasized because from one point of view the method measures horizontal and vertical displacements separately—horizontal displacement by observing the fading pattern of the envelope of the echo, and vertical displacement by observing the phase of the echo. This would make it seem as if the results should be referred to a coordinate system parallel and perpendicular to the bed of the ice sheet, with the difficulty that the slope of the bed is not known with any accuracy. The difficulty is avoided when it is realized that the method simply relocates P; one can then measure the components of the vector PP' in whatever coordinate system happens to be convenient.
Thus, to apply Equation (3), one measures ľ at a number of depths and one also needs to know ρ at these depths and the steady accumulation rate a∗; ∂h/∂t is then deduced for each depth. If the model were correct, a∗; ∂h/∂t should be a constant. In fact we know that the accumulation rate fluctuates, and so ∂h/∂t as deduced in this way, using an average a∗ and an average ρ(z) curve, will fluctuate with depth. But we expect the irregularities to diminish with depth, for the following reason. Suppose there is one year with an unusually high accumulation. A marker set in the surface at the beginning of that year will show a larger value of V than usual because the consolidation of the firn beneath it is taking place under a load that is higher than usual. A marker set at depth at the beginning of the same year will also show a larger value of V than usual, but now the effect will be smaller, because the consolidation of the firn beneath this deeper marker is taking place under a load that is made up of several annual layers, and the unusually thick one at the top is only one of many, the rest of which are of the normal thickness. So the abnormality in V will diminish with depth. a∗ and ρ(z), being long-term averages, are only slightly altered by the single bad year, and therefore we expect that the values of ∂h/∂t deduced using Equation (3) from the deeper layers will be the most reliable; a plot of ∂h/∂t versus depth should approach a steady value. In this way the effect of short-term fluctuations of accumulation rate on the rate of consolidation should be smoothed out. One is left with the question of what long-term average to take for a∗ in Equation (3), but, as we have already said, this problem is inherent in the original question: how much is the velocity of the ice sheet as a whole out of balance with the current long-term accumulation rate?
An advantage of the method described, using Equation (3), is that the measurements to be made are essentially simple. It is not necessary to find the age of particular firn layers; the only stratigraphy needed is that necessary to establish the long-term accumulation rate.
The measurements described give the change of thickness at the site; they do not of themselves disclose whether it is characteristic of the ice sheet as a whole, or whether, for example, it is cause by the horizontal movement through the measuring site of a bulge in thickness. These effects could only be separated by measuring at a number of different sites.
Radio-echo observations to measure V, and hence ∂h/∂t are being planned at South Pole Station, Antarctica, but the result will probably not be known for some 5 to 10 years. However, closely related observations have already been analysed for Jarl-Joset station in central Greenland by Federer and others (1970); see also Quer vain (1969, p. 135–41). The height ofa point in an inclined shaft 40 m below the surface was surveyed on two occasions, in 1960 and 1968, and the vertical velocity was deduced. The horizontal eastward component of the velocity at the station was also measured. The authors deduce the resultant lowering of the surface, but the calculation contains an error, of a confusing kind. Apart from this their analysis is basically the same as ours. To relate the two approaches we divide Equation (2) by cos α, where a (≈ 0.003 raa) is the slope of the surface, and express V in terms of u and v, the horizontal and vertical components of the total velocity, thus
We use a subscript v for quantities measured vertically, rather than normal to the surface; thus
and hence, multiplying by ρ/ρ.w,
where Vr ∗ = (ρ/ρw)(v—u tan α) as defined by Federer and others (1970) in their Equations (1) and (2). Thus
Vr ∗ is the downward velocity normal to the surface, V, converted to water equivalent and multiplied by sec α.
Federer and others (1970) find Vr ∗ =0.29 m a−1 in the period 1960 to 1968; they compare this with the corresponding 9-year mean accumulation rate aV ∗, equal to 0.19 m a−1, to obtain a deficit of o.10 m a−1 water equivalent over this period. To obtain the resultant lowering of the surface they multiply this water equivalent by ρw and divide by a mean density value of the material between the surface in 1968 and the layer of the year 1960, namely 480 kg m−3. But Equation (4) shows that to obtain ∂hv/∂t the water equivalent (av ∗— Vr ∗) should be multiplied by ρw/ρ, where ρ is the density measured at the depth of the marker, 40 m below the surface, namely 690kg m−3. Thus
which gives a lowering of the surface between 1960 and 1968 of 1.16 m (rather than 1.67 m). The measured lowering of the surface was 1.74 m, which agrees less well than before. The reason for the difference must either be errors of measurement or that the model used for calculation, which assumes a constant rate of accumulation, is inadequate.
Table I of Federer and others (1970) shows measured rates of accumulation for different periods and is reproduced, in part, in Table I. Weighting the measured values in column 3 of Table I according to the time intervals, we see that, while the average accumulation rate for 1871–1959 was 0.262 ma−1, during 1959–68 it was only 0.193 ma−1. This suggests a model in which the accumulation rate is a step function falling suddenly from 0.262 to 0.193 ma−1 in 1959. We can no longer use Sorge's Law, and a complete analysis would involve considering the details of the snow compaction process. However, as an approximation we might proceed as follows. Suppose first that the accumulation rate had continued steadily at 0.262 ma−1. The expected lowering of the surface from 1960 to 1968 can then be estimated from Equation (4) by using the values of Vr ∗ and ρ measured at 40 m depth (the actual values Vr ∗ and ρ in this hypothetical situation would be slightly different). The lowering would have been 0.32 m. In fact the accumulation rate from 1959-68 was 0.069 ma−1 lower than the value just assumed, a deficit of 0.621 m of water. Suppose that the only effect of this is that a corresponding layer of firn of density 480kg m−3 is missing; we are assuming that, despite the thinner-than-usual top strata, the compaction below proceeded unaltered. It is then as if a layer 1.29 m thick had been sliced off. The total lowering would be 0.32 m + 1.29 m = 1.61 m. This is evidently an overestimate because in fact the compaction rate would be slowed down. Nevertheless it is still less than the observed value of 1.74 m (but an improvement on the value of 1.16 m obtained by assuming a steady accumulation rate of 0.19 ma−1). By making the step occur in 1958 instead of 1959 the total calculated lowering would be 1.76 m, virtually as observed. If the step occurred in 1957 the calculated lowering would be 1.90 m. Again, these are both overestimates.
Table. I. Measured hates of accumulation at jarl-joset station, greenland
Let us return to the original question: by how much is the velocity of the ice sheet as a whole out of balance with the current long-term accumulation rate? From Equation (4), using values from the 40 m depth level, we find that, if the "current long-term accumulation rate" is interpreted as meaning the mean value for the 97 year period 1871–1968 (av ∗= 0.255 m of water per year), the rate of fall of the surface is 0.050 m a−1. Strictly interpreted, this is the rate at which the surface would have fallen if the accumulation rate had been steady at its measured average value during the period, and if, under these hypothetical conditions, ρ and Vr ∗ at 40 m depth had taken their measured values. Table II shows the results if the "current long-term accumulation rate" is taken instead as the mean for 1871–1959 or for 1959–68.
The final column in Table II gives 1 — (av ∗/Vr ∗) as a percentage, the amount by which the accumulation rate is below the balance value.
I should like to thank Dr R. G. Oakberg for helpful discussions of the problem, and Dr M. R. de Quervain for kindly reading and commenting on a draft of the paper.
Bader, H. 1960 Theory of densification of dry snow on high polar glaciers. U.S. Snow, Ice and Permafrost Research stablishment. Research Report 69,
Bader, H. 1963 Theory of densification of dry snow on high polar glaciers. II. (In Kingery, W.D., ed. Ice and now; properties, processes, and applications: proceedings of a conference held at the Massachusetts Institute of Technology, February 12–16,1962 Cambridge, Mass., M.I.T. Press p. 351–76.)
Federer, B. 1970 Outflow and accumulation of ice in Jarl–Joset station, Greenland, by Federer, B.,v[on] Sury, H.[–V.],Philberth, K., Quervain., M. [R] de Journal of Geophysical Research, Vol. 75, No. 24, p. 4567–69.
Haefeli, R. 1961 Contribution to the movement and the form of ice sheets in the Arctic and Antarctic. Journal of Glaciology, Vol. 3, No. 30, p. 1133–51.
Nye, J.F. 1960 The response of glaciers and ice–sheets to seasonal and climatic changes. Proceedings of the Royal Society of London, Scr. A, Vol. 256, No. 1287 p. 559–84.
Nye, J.F. 1972[a]. Measuring the change in thickness of the Antarctic ice sheet, by Nye, F.J.,Berry, M.,Walford, E.M. Nature, Physical Science, Vol. 240, No. 97, p. 7–9.
Nye, J.F. 1972[b]. Proposal for measuring the movement of a large ice sheet by observing radio echoes, by Nye, J.F.,Kyte, R.G.,Threlfall, D.C. Journal of Glaciology, Vol. 11, No. 63, p. 319–25.
Quervain de, M.R.. 1969 Schneekundliche Arbeiten der Internationalen Glziologischen Grönlandexpedition (Nivologie). Meddleleser om Gronland, Bd. 177, Nr. 4.
Walford, M.E.R.. 1972 Glacier movement measured with a radio echo technique. Nature, Vol. 239, No. 5367 P. 93–95.
The lateral spreading of the ice sheet causes a thinning of the annual layers which is in addition to the effect of compaction; at sufficient depth, where the density has become nearly constant, this is the dominant effect. The lateral spreading rate will be almost uniform with depth in the upper layers, but for the sake of generality we will use a model in which it varies with depth. To derive the appropriate correction term to Equation (3) we first examine Surge's Law a little more carefully.
Consider a model in which the accumulation rate is steady in time but variable in space. The spreading rate likewise varies in space, both vertically and horizontally, but measured relative to the surface of the ice sheet it is steady in time; that is to say, it depends on horizontal position and on depth. The spreading rate is out of balance with the accumulation rate and so the thickness of the ice sheet changes steadily with time, but non-uniformly in space. Such a condition obviously could not persist for all time (because the thickness cannot be negative) but we could imagine it persisting for a period of, say, 103 years. So we adopt this model, but with the proviso that we must not draw conclusions from it about the state of layers older than 103 years, because such layers experienced an unspecified spreading before our steady spreading rate started. With this proviso and provided atmospheric conditions are steady, we assert that the density: depth curve will be constant in time.
Now we repeat the mass flux argument which follows Equation (3) in the main part of the paper, but paying attention to the lateral flux. Take as the control volume a parallel-sided slab of constant thickness z whose moving top surface, of area S°, coincides with the moving top surface of the ice sheet. The sides of the slab are normal to the top and bottom faces and are fixed in space (that is, they only move perpendicular to the surface). The lateral spreading rate is measured by specifying the proportional rate of change e(z) of a test area S fixed in the firn and parallel to the surface, namely
If there was no change of density, e would also be the compressive strain-rate normal to the surface. Thus e may be thought of as the compressive strain-rate normal to the surface that acts in addition to compaction. The mass flux through the sides of the slab is then
, where the bar denotes the average value between the surface and depth z. By the generalization of Sorge's Law asserted above, the mass within the slab remains constant. Hence
and thus
where ρ, V and
are all functions of z. The last term is the required correction to Equation (3). To estimate its magnitude, neglect all density variations and put ē ≈ V/h. The term is then V(z/h), which for the Greenland example is 1.6% of V.
The correction can also be expressed in terms of the age of the layer at depths z, but the form of Equation (3a) has the advantage of involving quantities which can be measured without stratigraphy.
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text:
package org.springframework.boot.autoconfigure.jta;

import java.io.File;
import java.net.InetAddress;
import java.net.UnknownHostException;

import javax.transaction.TransactionManager;
import javax.transaction.UserTransaction;

import org.junit.After;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.ExpectedException;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.boot.jta.XAConnectionFactoryWrapper;
import org.springframework.boot.jta.XADataSourceWrapper;
import org.springframework.boot.jta.atomikos.AtomikosDependsOnBeanFactoryPostProcessor;
import org.springframework.boot.jta.atomikos.AtomikosProperties;
import org.springframework.boot.jta.bitronix.BitronixDependentBeanFactoryPostProcessor;
import org.springframework.boot.test.EnvironmentTestUtils;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.jta.JtaTransactionManager;
import org.springframework.util.FileSystemUtils;

import com.atomikos.icatch.config.UserTransactionService;
import com.atomikos.icatch.jta.UserTransactionManager;

import static org.hamcrest.Matchers.equalTo;
import static org.hamcrest.Matchers.is;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertThat;
import static org.junit.Assert.assertTrue;
import static org.mockito.Mockito.mock;

/**
 * Tests for {@link JtaAutoConfiguration}.
 *
 * @author Josh Long
 * @author Phillip Webb
 * @author Andy Wilkinson
 */
public class JtaAutoConfigurationTests {

	@Rule
	public ExpectedException thrown = ExpectedException.none();

	private AnnotationConfigApplicationContext context;

	@Before
	public void cleanUpLogs() {
		FileSystemUtils.deleteRecursively(new File("target/transaction-logs"));
	}

	@After
	public void closeContext() {
		if (this.context != null) {
			this.context.close();
		}
	}

	@Test
	public void customPlatformTransactionManager() throws Exception {
		this.context = new AnnotationConfigApplicationContext(
				CustomTransactionManagerConfig.class, JtaAutoConfiguration.class);
		this.thrown.expect(NoSuchBeanDefinitionException.class);
		this.context.getBean(JtaTransactionManager.class);
	}

	@Test
	public void disableJtaSupport() {
		this.context = new AnnotationConfigApplicationContext();
		EnvironmentTestUtils.addEnvironment(this.context, "spring.jta.enabled:false");
		this.context.register(JtaAutoConfiguration.class);
		this.context.refresh();
		assertEquals(0, this.context.getBeansOfType(JtaTransactionManager.class).size());
		assertEquals(0, this.context.getBeansOfType(XADataSourceWrapper.class).size());
		assertEquals(0, this.context.getBeansOfType(XAConnectionFactoryWrapper.class)
				.size());
	}

	@Test
	public void atomikosSanityCheck() throws Exception {
		this.context = new AnnotationConfigApplicationContext(JtaProperties.class,
				AtomikosJtaConfiguration.class);
		this.context.getBean(AtomikosProperties.class);
		this.context.getBean(UserTransactionService.class);
		this.context.getBean(UserTransactionManager.class);
		this.context.getBean(UserTransaction.class);
		this.context.getBean(XADataSourceWrapper.class);
		this.context.getBean(XAConnectionFactoryWrapper.class);
		this.context.getBean(AtomikosDependsOnBeanFactoryPostProcessor.class);
		this.context.getBean(JtaTransactionManager.class);
	}

	@Test
	public void bitronixSanityCheck() throws Exception {
		this.context = new AnnotationConfigApplicationContext(JtaProperties.class,
				BitronixJtaConfiguration.class);
		this.context.getBean(bitronix.tm.Configuration.class);
		this.context.getBean(TransactionManager.class);
		this.context.getBean(XADataSourceWrapper.class);
		this.context.getBean(XAConnectionFactoryWrapper.class);
		this.context.getBean(BitronixDependentBeanFactoryPostProcessor.class);
		this.context.getBean(JtaTransactionManager.class);
	}

	@Test
	public void defaultBitronixServerId() throws UnknownHostException {
		this.context = new AnnotationConfigApplicationContext(
				JtaPropertiesConfiguration.class, BitronixJtaConfiguration.class);
		String serverId = this.context.getBean(bitronix.tm.Configuration.class)
				.getServerId();
		assertThat(serverId, is(equalTo(InetAddress.getLocalHost().getHostAddress())));
	}

	@Test
	public void customBitronixServerId() throws UnknownHostException {
		this.context = new AnnotationConfigApplicationContext();
		EnvironmentTestUtils.addEnvironment(this.context,
				"spring.jta.transactionManagerId:custom");
		this.context.register(JtaPropertiesConfiguration.class,
				BitronixJtaConfiguration.class);
		this.context.refresh();
		String serverId = this.context.getBean(bitronix.tm.Configuration.class)
				.getServerId();
		assertThat(serverId, is(equalTo("custom")));
	}

	@Test
	public void defaultAtomikosTransactionManagerName() throws UnknownHostException {
		this.context = new AnnotationConfigApplicationContext();
		EnvironmentTestUtils.addEnvironment(this.context,
				"spring.jta.logDir:target/transaction-logs");
		this.context.register(JtaPropertiesConfiguration.class,
				AtomikosJtaConfiguration.class);
		this.context.refresh();

		File epochFile = new File("target/transaction-logs/"
				+ InetAddress.getLocalHost().getHostAddress() + ".tm0.epoch");
		assertTrue(epochFile.isFile());
	}

	@Test
	public void customAtomikosTransactionManagerName() throws BeansException, Exception {
		this.context = new AnnotationConfigApplicationContext();
		EnvironmentTestUtils.addEnvironment(this.context,
				"spring.jta.transactionManagerId:custom",
				"spring.jta.logDir:target/transaction-logs");
		this.context.register(JtaPropertiesConfiguration.class,
				AtomikosJtaConfiguration.class);
		this.context.refresh();

		File epochFile = new File("target/transaction-logs/custom0.epoch");
		assertTrue(epochFile.isFile());
	}

	@Configuration
	@EnableConfigurationProperties(JtaProperties.class)
	public static class JtaPropertiesConfiguration {

	}

	@Configuration
	public static class CustomTransactionManagerConfig {

		@Bean
		public PlatformTransactionManager transactionManager() {
			return mock(PlatformTransactionManager.class);
		}

	}

}

redpajama_set_name: RedPajamaGithub


text:
How to Use a Laser Level?
Learn the best and most simplest method to use a laser level.
Laser LevelGuides
1. What is a Laser Level?
2. What Is a Laser Level Used For?
3. Types of Laser Level:
3.1. Cross-Line Laser Level:
3.2. Dot/Point Laser Level:
3.3. Rotary Laser Level:
3.4. Tile Laser Level:
4. How to Choose a Laser Level?
5. How to Use a Laser Level?
6. Frequently Asked Questions:
6.1. How to use a laser level to hang pictures?
6.2. How to use a laser level for grading?
6.3. How does a laser level work?
7. Conclusion:
Laser levels are mainstream devices mainly used in construction, survey, and renovation works. Since they entered the market, laser levels have quickly replaced several common leveling instruments at the bubble level. It is a multipurpose device that greatly eases any project and cuts off the time required for taking measurements.
Currently, there are four types of laser levels in the market. The automatic 360 laser levels allow you to survey any area without the need for an assistant. However, people are often confused about how to use a laser level? Well, this article is here to help you get started with all your projects.
What is a Laser Level?
A laser level is a special tool used by DIYers and construction workers to maintain perfect alignment throughout the job site. The device emits a straight laser beam in the horizontal and vertical directions, forming a virtual plane. Moreover, the 3-point laser levels also emit a laser in the third axis to form a 3D plane. Workers can use this laser plane to reference construction, surveying, and renovation projects.
Modern laser levels are very different from the first products. For instance, the first laser levels were bulky devices that required up to two people to operate them. Furthermore, these units were very expensive, and only the high-end companies could afford them. However, you can also find a laser level for home use at an affordable price nowadays.
What Is a Laser Level Used For?
Laser levels have become necessary for projects requiring a straight reference plane over a large distance. The laser plane acts as a virtual chalk line to guide you in perfectly aligning all the objects. Moreover, its use is not limited to professional workers only, and anyone can use them in indoor and outdoor projects.
You can use a laser level for common tasks like hanging pictures, fitting dado rails, and hanging curtains in your home. Similarly, the auto-leveling laser levels are used for outdoor projects like excavation, foundation works, and grading. Some automatic laser levels come with a tripod for outdoor stability. In short, laser levels are versatile devices that you can use across different projects according to your needs.
Types of Laser Level:
Laser levels are classified based on their use and the color of the laser beam. Generally, two types of laser levels are available based on the laser color, i.e., red and green. Similarly, there are four types of laser levels based on their usage and laser plane, they are:
Cross-line laser level
Dot/Point laser level
Rotary laser level
Tile laser level
Cross-Line Laser Level:
Line laser levels are the most advanced and common lasers used by professionals. These devices emit a laser beam in vertical and horizontal directions to form a 2D plane. The laser comes in handy when working on an elevated structure such as a wall. The line laser level is usually used for indoor projects by mounting it on a tripod stand. However, you can also use it for referencing the outside walls of a structure.
Hanging pictures
Indoor projects
Dot/Point Laser Level:
The dot or point laser level is commonly known as a plumb laser level. It is the simplest laser device that you can find in the market. The device is mainly used to check the alignment of various objects and plumbing the walls. Moreover, a dot laser level is also the cheapest laser device that you can purchase.
Installing power outlets
Installing light switches
Foundation works
Installation of heating and ventilation system
Rotary Laser Level:
The rotary laser levels are also the most advanced type of laser device in the world. Contractors and surveyors usually use them before starting any construction project. The best thing about these laser levels is that they are highly accurate over long distances. The best 360 laser levels have an accuracy of 1/16-inch for up to 50 feet. A rotary laser emits a straight laser line while rotating incredibly fast; thus, it forms a constant laser plane in every direction.
Best laser level for builders
Construction grading
Landscaping works
Tile Laser Level:
A tile laser level is not very different from a point laser level. The only difference is that it emits a straight laser plane at floor level. Interior design workers mostly use it to install tiles and other flooring types. However, it is also used for outdoor projects that require perfect ground alignment. The good thing about tile laser levels is that you don't need a tripod stand to use them.
Installation of flooring
Pipe installation
How to Choose a Laser Level?
Choosing the right laser level for the project is extremely important for professionals. There are many different types of laser levels in the market; each has its set of applications. Therefore, you must consider these factors before finalizing your purchase:
For indoor projects: All laser levels are suitable for indoor projects but with different applications. For example, you need a cross-line laser level for carpeting and hanging objects on the wall. Similarly, the dot or point is the best laser level for electricians and interior designers. Lastly, a tile laser level is perfect for flooring works.
For outdoor construction: You need the best laser level for daylight when working outside. A typical red laser is almost invisible beyond a few feet, while a powerful green laser is visible for up to 60 feet. Similarly, you will also need to use a laser level detector to establish reference points throughout the site.
For survey: Laser levels are perfect for surveying and construction grading. The laser forms a reference plane to help you with landscaping works. However, it is recommended to use a green laser level and a laser detector to avoid time wastage.
Mount the laser level on a tripod stand if you use one; otherwise, skip this step.
Calibrate the device's level by adjusting the tripod's clamps till the bubble is stabilized in the center of the circle. However, a self-leveling laser level doesn't require this step; give it time to adjust itself.
Adjust the laser height by aiming it at a reference point. Alternatively, you can also manually input the laser plane adjustments if you know the measurement.
Turn on the laser level and take the laser detector to the point where you want to take a reading.
The laser level will beep twice as soon as it detects the laser detector, so take your time.
Similarly, all you need is to turn on the laser level to form a virtual laser plane when working on indoor projects.
The laser beam packs an immense amount of energy. So, it is best to wear safety goggles when working to avoid any eye damage.
How to use a laser level to hang pictures?
1. Use a measuring tape to determine the height of the picture frame.
2. Calibrate the device's level by stabilizing the bubble inside the circle.
3. Turn on the laser level and aim it at the initial point.
4. Press the laser button to form a laser plane on the wall/walls.
5. Hammer a nail on the wall and hang your pictures.
How to use a laser level for grading?
1. Set up the laser level on a tripod stand on firm ground.
2. Calibrate the device's level or give it a moment to self-adjust.
3. Identify the initial height of the grade and pitch grade slopes from there.
4. Take the laser detector to the desired area and adjust it till you hear a beeping sound.
5. Measure the grade difference between the original height and the graded height.
6. Excavate the area if the grade is below the ground or fill the area if it is above the ground.
How does a laser level work?
A laser level is an advanced device that emits a laser beam on the wall. The beam forms a virtual laser plane that you can use as a reference for aligning various objects.
Laser levels are gradually replacing different types of leveling tools. They are used in construction projects, renovation works, and surveying. Moreover, you can also use a laser level for DIY projects. However, people are often confused about how to use a laser level. If you are also wondering the same, this article will surely help you a lot.
Wade Gilbert
I'm Wade Gilbert. I love laser engraving, cutting, etching, and marking on paper, acrylics, and plastics. I write tutorials and guides about engraving and cutting different materials. I also review different laser engravers and related products.
Laser CuttersGuides
How to Start a Laser Cutting Business?
Laser EngraversGuides
A Simple Guide to Laser Engraving Metal
Laser Engraving for Beginners
How to Etch Acrylic Sheets?

redpajama_set_name: RedPajamaCommonCrawl


Bogoroch & Associated LLP is committed to litigating cases against disability insurers on behalf of our clients with an end to obtaining a declaration from the Court that they meet the test of disability as defined in their respective policies of insurance.The Court's conclusion that a claimant is disabled entitles him or her to arrears (or"back benefits") from the date the insurer terminated the benefits up to the date of trial, and the insurer must also reinstate the payment of benefits as of the date of the trial.Alternatively we will aim to settle a case before trial by persuading the insurance company to pay a lump sum to the claimant, thereby "cashing out" the policy. The advantage of cashing out is closure, no further requirement to deal with the insurance company, attend on medical assessments and take other steps required by the Insurer on an ongoing basis. Our goal is to attend a mediation, or settlement meeting, with the insurer early on in the litigation, in order to negotiate a settlement as soon as possible after a lawsuit is commenced.


Kyle Morgan owns and operates Mercantile Processing Inc., a credit card processing broker among other things. Morgan launched the company in 2007, and now has three employees and five independent sales agents. Morgan will be honored at the Small Business Administration's awards dinner on June 7 in Newark.
"Kyle demonstrated significant success in each of the evaluated areas, and shows great potential for the future growth of his business," says Jayne Armstrong, district director of SBA's Delaware District Office.


text:
Home Home and leisure Manchester Researchers find clouds filled with 'ice-lollies'
Manchester Researchers find clouds filled with 'ice-lollies'
Nigel Barlow
On sunny days like this, a cloud full of ice-lollies sounds like the ultimate treat and researchers from the University of Manchester have discovered such clouds, twice.
The researchers, led by Stavros Keppas, from The University of Manchester's School of Earth, Atmospheric and Environmental Science, describe their findings in the journal of the American Geophysical Union.
The team spotted a significant concentration of curious ice formations in the shape of a stick with a spherical head at the end, resembling an ice-lolly, during a research flight over the north-east Atlantic Ocean last September. But this wasn't the first time the team had spotted such phenomena. They had also seen the unusual ice particles over south-west of the UK on a similar flight back in 2009, meaning this wasn't just a freak event of nature first time around.
Then, by studying where the so-called ice-lollies appeared and using past research about ice particle formation, the researchers figured out the ice-lollies' origins and how they may even affect the weather.
Stavros Keppas, lead author, explains: "Ice-lollies are the product of the collision between an ice column and a liquid water droplet in the air. Ice splinters are created at temperatures between -3 and -8oC in the cloud and instantly freeze any water droplet they touch, creating these unusual ice-lolly shapes. The Ice crystals grow into distinctive and somewhat predictable shapes, depending on the temperature, amount of water vapour and humidity."
Stavros thinks this kind of ice-lolly particle form on a regular basis, especially at high latitudes. However, he concedes more research is needed in these kinds of clouds to see if it is a widespread phenomenon.
He added: "More measurements are needed in this region of a cloud system to see if this is a widespread phenomenon. But recent advances in measurement techniques allow us to see meteorological phenomena with more precision than ever before. Now we can identify unique formations such as these and begin to understand their complexity even more."
But if you're hoping to eat one of the ice-lollies, think again, the team says they are only around a millimetre long and found at altitudes between one and two kilometres in the air. So, it doesn't look like cloud-based ice-lollies will be replacing the more humble choc-ice and 99 cones just yet. In fact, the only chance of ever seeing one – if you don' have a research plane – could be if it falls to earth as rain, but even that isn't guaranteed.
Stavros added: "The ice-lollies slowly fall as precipitation to the ground. If the temperature increases above zero Celsius, then the lolly will melt and form a small rain drop. However, even if the temperature profile of the atmosphere is negative at all layers, ice-lollies might not reach the ground in their original shape or be deformed due to other microphysical processes occurring in the clouds. Also, even the temperature stays below zero Celsius, if the humidity drops below 100% then the particles could vanish."
But the ice-lollies do also have a purpose and could even affect the life-cycle of cloud. He added: "Ice-lollies can alter the balance between liquid water and ice in what we call mixed phase clouds, these are clouds which contain both liquid and ice. This may have a significant impact on the cloud lifetime. Ice-lollies can also impact on the precipitation formation."
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The Flexible 'I' Joint option allows for variance in the chamfers of the glass panels, resulting in the polished edge 'flat' dimension of glass becoming less critical.
The new Flexible I joint has been designed with the installer in mind and offers a greater ease of installation on site, whilst maintaining the minimal sight lines and overall finish required of the G2G range.
The G2G Flexible I joint maintains the strength and clarity of the G2G range. The flexible end sections produce a great contact between the seal and glass reducing any chance of the ingress of dust and fibres.
The G2G range provides an alternative to silicone sealant whilst still maintaining the traditional clear sight lines. The G2G profiles provide a demountable system which offers greater flexibility in the products application as it can be used in permanent and semi-permanent applications.