An investigation op the electrical resistance of thin films of rare earth metals

Measurements have been made of the electrical resistivity in the film plane of rare earth metal films over a thickness range of 130 A to 250O A. The films are deposited onto glass substrates by high vacuum evaporation at pressures better than 10(^-6) torr and are protected by an over coating of silicon monoxide. The resistivity has been examined between 4.2 K and room temperature; the magnetoresistance has also been studied in the presence of applied transverse fields up to 15 KOe and longitudinal fields up to 10 KOe. The variation of resistance with temperature is similar in form to that obtained for bulk specimens for all film thicknesses. However, in films less than about 400 A thick, the spin-disorder resistivity shows a pronounced decrease in magnitude but the degree of variation did not appear to be consistent with thickness. The spin-disorder resistivity is obtained by computing a least-squares fit to the linear high temperature part of the resistance curve and extrapolating to 0 K. The results show that in the temperature region where spin-wave theory is applicable, at very low temperatures pspin ɚ T(^2) in accordance with spin-wave theory but at higher temperatures, this falls off, so that It is found that pspin ɚ T(^2) in the first case, the variation of Pspin(T) can be better explained in terms of an anisotropy energy gap and the change to a T(^3/2) proportionality has been related to the behaviour of the spontaneous magnetization and the anomalous Hall effect. In addition, the variation of pSpin of dysprosium is examined in detail and it is suggested that the observed fall off of spin resistivity with thickness, which can be extrapolated to zero at zero thickness, is related to the variation of magnetization with thickness in the film. Finally, magnetoresistive studies detected negative effects with fields applied transversely to the electric field. The anomalous peak at the Neel point is suppressed in dysprosium and terbium and a small demagnetizing field effect is observed in dysprosium

Exports and Externalities: the other side of trade and ecological risk and Technology Diffusion in a Competitive World

This paper develops a general equilibrium model to measure welfare effects of taxes for correcting environmental externalities caused by domestic trade, focusing on exter- nalities that arise through exports. Externalities from exports come from a number of sources. Domestically owned ships, planes, and automobiles can become contaminated while visiting other regions and bring unwanted pests home, and species can be in- troduced by contaminated visitors that enter a region to consume goods and services. The paper combines insights from the public finance literature on corrective environ- mental taxes and trade literature on domestically provided services. We find that past methods for measuring welfare effects are inadequate for a wide range of externalities and show the most widely used corrective mechanism, taxes on the sector imposing the environmental externality, may often do more harm than good. The motivation for this paper is the expansion of invasive species' ranges within the United States. We apply our analytical model to the specifc example of quagga and zebra mussel (Dreissena polymorpha and Dreissena rostiformis bugenis) invasion into the U.S Pacific Northwest.environmental regulation, tax interactions, invasive species, environment and trade

The pros and cons of using SDL for creation of distributed services

In a competitive market for the creation of complex distributed services, time to market, development cost, maintenance and flexibility are key issues. Optimizing the development process is very much a matter of optimizing the technologies used during service creation. This paper reports on the experience gained in the Service Creation projects SCREEN and TOSCA on use of the language SDL for efficient service creation

Stepping stones for biological invasion: A bioeconomic model of transferable risk

Herein we model the widespread dispersal and management of an invasive species as a weak-link public good. The risk of introduction is driven in part by economic activity, is influenced by policies directed at the risk, and economic activity responds/adapts to the risk. Framed around recent introductions and rapid spread of dreissenid mussels in the Western United States, we find three key results. First, partial equilibrium estimates of welfare loss are significantly overestimated relative to general equilibrium estimates. If ecosystem services and market goods are substitutes the partial equilibrium bias is greater than if they are compliments. Second, well-intended policies do not necessarily reduce overall risk; risk reduction actions can transfer risk to another time or location, or both, which may increase total risk. Third, policies of quotas and inspections have to be extreme to improve welfare, with inspections having advantages over quotas.bioeconomic, invasive species, risk, weak-link, welfare, Environmental Economics and Policy, Risk and Uncertainty, Q2, Q26, Q57,

Calculus Made Easy

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Loss of solutions in shear banding fluids in shear banding fluids driven by second normal stress differences

Edge fracture occurs frequently in non-Newtonian fluids. A similar instability has often been reported at the free surface of fluids undergoing shear banding, and leads to expulsion of the sample. In this paper the distortion of the free surface of such a shear banding fluid is calculated by balancing the surface tension against the second normal stresses induced in the two shear bands, and simultaneously requiring a continuous and smooth meniscus. We show that wormlike micelles typically retain meniscus integrity when shear banding, but in some cases can lose integrity for a range of average applied shear rates during which one expects shear banding. This meniscus fracture would lead to ejection of the sample as the shear banding region is swept through. We further show that entangled polymer solutions are expected to display a propensity for fracture, because of their much larger second normal stresses. These calculations are consistent with available data in the literature. We also estimate the meniscus distortion of a three band configuration, as has been observed in some wormlike micellar solutions in a cone and plate geometry.Comment: 23 pages, to be published in Journal of Rheolog

Prevalence of subclinical cardiac abnormalities in patients with metal-on-metal hip replacements

Background Metal-on-metal (MOM) hip prostheses have a higher failure rate than conventional prostheses and leaching of cobalt and chromium has been linked to cardiomyopathy. We screened MOM subjects to evaluate if cobalt and chromium are related to subclinical cardiac dysfunction. Methods A single centre, non-randomised, observational study using echocardiography in 95 patients who had undergone MOM hip prostheses, and 15 age matched controls with non-MOM hip replacement. Serial plasma cobalt and chromium levels were recorded, and data compared by tertiles of cobalt exposure. Results Indexed left ventricular (LV) end-diastolic and end-systolic volumes (EDVi and ESVi) increased with tertile of cobalt (omnibus p = 0.003 for EDVi and ESVi), as did indexed left atrial (LA) volumes (p = 0.003). MOM subjects had 25% larger EDVi than controls, 32% larger ESVi (40 ml vs. 32 ml, and 15 ml vs. 11 ml, p = 0.003 for both) and 28% larger indexed LA (23 ml vs. 18 ml, p = 0.002). There were no differences in LV systolic or diastolic function, including ejection fraction, tissue velocity and mitral E/e′. Estimated glomerular filtration rate was 18% lower in the highest tertile compared with the lowest (p = 0.01) and correlated inversely with LA volume (r = −0.36, p < 0.001) and LV EDV (r = −0.24, p = 0.02). Conclusions No correlations between sensitive measures of systolic or diastolic cardiac function or serum cobalt/chromium levels were observed in this study. However, there was a relationship between increasing left ventricular and left atrial volumes and declining renal function with high cobalt levels which requires further evaluation in MOM patients

A systematic examination of preoperative surgery warm-up routines

Recent evidence indicates that a preoperative warm-up is a potentially useful tool in facilitating performance. But what factors drive such improvements and how should a warm-up be implemented?In order to address these issues, we adopted a two-pronged approach: (1) we conducted a systematic review of the literature to identify existing studies utilising preoperative simulation techniques; (2) we performed task analysis to identify the constituent parts of effective warm-ups. We identified five randomised control trials, four randomised cross-over trials and four case series. The majority of these studies reviewed surgical performance following preoperative simulation relative to performance without simulation.Four studies reported outcome measures in real patients and the remainder reported simulated outcome measures. All but one of the studies found that preoperative simulation improves operative outcomes-but this improvement was not found across all measured parameters. While the reviewed studies had a number of methodological issues, the global data indicate that preoperative simulation has substantial potential to improve surgical performance. Analysis of the task characteristics of successful interventions indicated that the majority of these studies employed warm-ups that focused on the visual motor elements of surgery. However, there was no theoretical or empirical basis to inform the design of the intervention in any of these studies.There is an urgent need for a more rigorous approach to the development of "warm-up" routines if the potential value of preoperative simulation is to be understood and realised. We propose that such interventions need to be grounded in theory and empirical evidence on human motor performance

Performance assessment of a NaI(Tl) gamma counter for PET applications with methods for improved quantitative accuracy and greater standardization

BACKGROUND: Although NaI(Tl) gamma counters play an important role in many quantitative positron emission tomography (PET) protocols, their calibration for positron-emitting samples has not been standardized across imaging sites. In this study, we characterized the operational range of a gamma counter specifically for positron-emitting radionuclides, and we assessed the role of traceable (68)Ge/(68)Ga sources for standardizing system calibration. METHODS: A NaI(Tl) gamma counter was characterized with respect to count rate performance, adequacy of detector shielding, system stability, and sample volume effects using positron-emitting radionuclides (409- to 613-keV energy window). System efficiency was measured using (18)F and compared with corresponding data obtained using a long-lived (68)Ge/(68)Ga source that was implicitly traceable to a national standard. RESULTS: One percent count loss was measured at 450 × 10(3) counts per minute. Penetration of the detector shielding by 511-keV photons gave rise to a negligible background count rate. System stability tests showed a coefficient of variation of 0.13% over 100 days. For a sample volume of 4 mL, the efficiencies relative to those at 0.1 mL were 0.96, 0.94, 0.91, 0.78, and 0.72 for (11)C, (18)F, (125)I, (99m)Tc, and (51)Cr, respectively. The efficiency of a traceable (68)Ge/(68)Ga source was 30.1% ± 0.07% and was found to be in close agreement with the efficiency for (18)F after consideration of the different positron fractions. CONCLUSIONS: Long-lived (68)Ge/(68)Ga reference sources, implicitly traceable to a national metrology institute, can aid standardization of gamma counter calibration for (18)F. A characteristic feature of positron emitters meant that accurate calibration could be maintained over a wide range of sample volumes by using a narrow energy window centered on the 511-keV peak

The Sagnac Phase Shift suggested by the Aharonov-Bohm effect for relativistic matter beams

The phase shift due to the Sagnac Effect, for relativistic matter beams counter-propagating in a rotating interferometer, is deduced on the bases of a a formal analogy with the the Aharonov-Bohm effect. A procedure outlined by Sakurai, in which non relativistic quantum mechanics and newtonian physics appear together with some intrinsically relativistic elements, is generalized to a fully relativistic context, using the Cattaneo's splitting technique. This approach leads to an exact derivation, in a self-consistently relativistic way, of the Sagnac effect. Sakurai's result is recovered in the first order approximation.Comment: 18 pages, LaTeX, 2 EPS figures. To appear in General Relativity and Gravitatio