Magnetic-field-modulated microwave-absorption detection in a Bi-Sr-Ca-Cu-O superconductor

Superconducting transitions are observed at 110 K, 100 K, and 72 K in a nominally BiSrCaCu₂O _x ceramic using the novel technique of magnetic-field-modulated microwave-absorption detection. The response of the BiSrCaCu₂O _x ceramic to an external magnetic field differs markedly from that of YBa₂Cu₃O and, in particular, -dT _c /dH is much greater in the bismuth sample.     

Switching of domains and domain walls in Fe<Subscript>50</Subscript>Mn<Subscript>50</Subscript>/Ni<Subscript>81</Subscript>Fe<Subscript>19</Subscript> bilayers with non-180° ferromagnetic domains

We have studied FeMn/Ni₈₁Fe₁₉ bilayers using vectorial vibrating-sample magnetometry (VSM) and the magnetooptic-indicator-film (MOIF) technique and observed stationary antiferromagnetic (AF) domain walls throughout the hysteresis process. The FeMn/Ni₈₁Fe₁₉ bilayer was demagnetized at 450 K and then cooled to 300 K in a zero field. The resultant hysteresis loop at 300 K clearly shows two loops, one shifted to the left of the origin and the other, to the right. Moreover, one loop is slanted and the other is square, indicating that the two sets of ferromagnetic (FM) domains have noncollinear magnetizations. At the zero applied field, the MOIF images clearly reveal the FM domains and domain walls. These domain walls, however, are hybrid domain walls connecting both FM and AF domain walls. With the application of a magnetic field, the FM domain walls can be swept. But, regardless of the applied field, including the case where the FM layer has been made into a single domain, domain walls at the original locations are still visible. Of the two sets of the FM domains with different magnetic-anisotropy axes, one set becomes reversed by rotation during magnetization reversal, while the other set becomes reversed by domain-wall nucleations and propagations.     

Characterization of Capacitive Array for NDE Applications

Abstract

We have developed a capacitive array sensor which responds to the complex dielectric constant of an interrogated material. The sensor requires only single-sided access and operates in a differential mode for detection of discontinuities in the relative dielectric constant, ε _r , or in the absolute mode where the interest is in absolute quantities. The device in general is noncontacting but can be fabricated as an embedded sensor.

Various proof-of-concept studies have been performed to explore possible applications of the device. In the differential mode, small surface features (notches) were detected in a conductor; in dielectrics, both surface and subsurface features were detected. The probe was sensitive to change in impedance caused by a curing epoxy, viewed through a graphite-epoxy composite panel.

A study was performed to assess the use of the probe for noncontact characterization of sintering of ceramics. In this (absolute) mode, the effects of liftoff and dielectric constant must be separated. We propose a scheme based on the ability to multiplex the capacitive array probe to accomplish this. Preliminary investigation shows that the effect of parasitic capacitance between the probe and ground points in the environment must be suppressed.     

Phenotype resembling Gitelman's syndrome in mice lacking the apical Na+-Cl- cotransporter of the distal convoluted tubule

Mutations in the gene encoding the thiazide-sensitive Na+-Cl- cotransporter (NCC) of the distal convoluted tubule cause Gitelman's syndrome, an inherited hypokalemic alkalosis with hypomagnesemia and hypocalciuria. These metabolic abnormalities are secondary to the deficit in NaCl reabsorption, but the underlying mechanisms are unclear. To gain a better understanding of the role of NCC in sodium and fluid volume homeostasis and in the pathogenesis of Gitelman's syndrome, we used gene targeting to prepare an NCC-deficient mouse. Null mutant (Ncc-/-) mice appear healthy and are normal with respect to acid-base balance, plasma electrolyte concentrations, serum aldosterone levels, and blood pressure. Ncc-/- mice retain Na+ as well as wild-type mice when fed a Na+-depleted diet; however, after 2 weeks of Na+ depletion the mean arterial blood pressure of Ncc-/- mice was significantly lower than that of wild-type mice. In addition, Ncc-/- mice exhibited increased renin mRNA levels in kidney, hypomagnesemia and hypocalciuria, and morphological changes in the distal convoluted tubule. These data indicate that the loss of NCC activity in the mouse causes only subtle perturbations of sodium and fluid volume homeostasis, but renal handling of Mg2+ and Ca2+ are altered, as observed in Gitelman's syndrome.     

Comparing four approaches for technical debt identification

Software systems accumulate technical debt (TD) when short-term goals in software development are traded for long-term goals (e.g., quick-and-dirty implementation to reach a release date versus a well-refactored implementation that supports the long-term health of the project). Some forms of TD accumulate over time in the form of source code that is difficult to work with and exhibits a variety of anomalies. A number of source code analysis techniques and tools have been proposed to potentially identify the code-level debt accumulated in a system. What has not yet been studied is if using multiple tools to detect TD can lead to benefits, that is, if different tools will flag the same or different source code components. Further, these techniques also lack investigation into the symptoms of TD “interest” that they lead to. To address this latter question, we also investigated whether TD, as identified by the source code analysis techniques, correlates with interest payments in the form of increased defect- and change-proneness. Comparing the results of different TD identification approaches to understand their commonalities and differences and to evaluate their relationship to indicators of future TD “interest.” We selected four different TD identification techniques (code smells, automatic static analysis issues, grime buildup, and Modularity violations) and applied them to 13 versions of the Apache Hadoop open source software project. We collected and aggregated statistical measures to investigate whether the different techniques identified TD indicators in the same or different classes and whether those classes in turn exhibited high interest (in the form of a large number of defects and higher change-proneness). The outputs of the four approaches have very little overlap and are therefore pointing to different problems in the source code. Dispersed Coupling and Modularity violations were co-located in classes with higher defect-proneness. We also observed a strong relationship between Modularity violations and change-proneness. Our main contribution is an initial overview of the TD landscape, showing that different TD techniques are loosely coupled and therefore indicate problems in different locations of the source code. Moreover, our proxy interest indicators (change- and defect-proneness) correlate with only a small subset of TD indicators.     

Eddy-current reflection probes: Theory and experiment

A general Z theory of reflection-type eddy-current probes was recently developed for new types of robotic proximity sensors. In this paper, the theory is applied to the characterization of surface-connected flaws. Flaw signals were calculated using a finite-difference implementation of the Z theory developed at Stanford University. A special air-core eddy-current reflection probe was fabricated at the National Institute of Standards and Technology (NIST) and used to obtain flaw signals for a number of rectangular-shaped electrical-discharge-machined (EDM) notches in aluminum. An automatic impedance analyzer was used to measure flaw signals as the probe was scanned over the length of the flaw. Experimental results were then compared to predictions of the theory.This paper is a contribution of the National Institute of Standards and Technology, not subject to copyright in the United States.     

Effect of technical grade pentachlorophenol on rumen microorganisms

The toxicity of technical grade pentachlorophenol to rumen microorganisms was tested by an in vitro fermentation procedure. Rumen fluid was collected from a fistulated mature steer fed a diet of all alfalfa hay. The compound was dissolved in absolute ethanol and added in vitro at concentrations ranging from 0 to 100 ppm. Digestion of cellulose and production of volatile fatty acids over 24 and 48 h of incubation was used to assess toxicity. Both cellulose digestion and propionic acid production were decreased at the 10 ppm concentration. The results suggest that technical grade pentachlorophenol has the potential to interfere with utilization of cellulose in ruminants.     

Simulating families of studies to build confidence in defect hypotheses

While it is clear that there are many sources of variation from one development context to another, it is not clear a priori what specific variables will influence the effectiveness of a process in a given context. For this reason, we argue that knowledge about software process must be built from families of studies, in which related studies are run within similar contexts as well as very different ones. Previous papers have discussed how to design related studies so as to document as precisely as possible the values of likely context variables and be able to compare with those observed in new studies. While such a planned approach is important, we argue that an opportunistic approach is also practical. The approach would combine results from multiple individual studies after the fact, enabling recommendations to be made about process effectiveness in context.

In this paper, we describe two processes with which we have been working to build empirical knowledge about software development processes: one is a manual and informal approach, which relies on identifying common beliefs or ‘folklore’ to identify useful hypotheses and a manual analysis of the information in papers to investigate whether there is support for those hypotheses; the other is a formal approach based around encoding the information in papers into a structured hypothesis base that can then be searched to organize hypotheses and their associated support. We test these processes by applying them to build knowledge in the area of defect folklore (i.e. commonly accepted heuristics about software defects and their behavior). We show that the formal methodology can produce useful and feasible results, especially when it is compared to the results output from the more manual, expert-based approach. The formalized approach, by relying on a reusable hypothesis base, is repeatable and also capable of producing a more thorough basis of support for hypotheses, including results from papers or articles that may have been overlooked or not considered by the experts.