Influence of the contacts on the conductance of interacting quantum wires

We investigate how the conductance G through a clean interacting quantum wire is affected by the presence of contacts and noninteracting leads. The contacts are defined by a vanishing two-particle interaction to the left and a finite repulsive interaction to the right or vice versa. No additional single-particle scattering terms (impurities) are added. We first use bosonization and the local Luttinger liquid picture and show that within this approach G is determined by the properties of the leads regardless of the details of the spatial variation of the Luttinger liquid parameters. This generalizes earlier results obtained for step-like variations. In particular, no single-particle backscattering is generated at the contacts. We then study a microscopic model applying the functional renormalization group and show that the spatial variation of the interaction produces single-particle backscattering, which in turn leads to a reduced conductance. We investigate how the smoothness of the contacts affects G and show that for decreasing energy scale its deviation from the unitary limit follows a power law with the same exponent as obtained for a system with a weak single-particle impurity placed in the contact region of the interacting wire and the leads.Comment: 10 page, 4 figures included, minor changes in the summary, version accepted for publication in PR

Software Architecture Improvement through Test-Driven Development

This research involves empirical software engineering studies applied in academic and professional settings to assess the influence of test-driven development on software quality. Particular focus is given to internal software design quality. Pedagogical implications are also examined. Initial results and the study protocol and plans will be presented

From RS-232 to Object Request Brokers: Incremental Object-Oriented Networking Projects

Selecting an appropriate set of laboratory experiences and projects for a Data Communications and Computer Networks course can be difficult due to the broad and deep nature of the topics. Emphasis may be placed on many networking aspects including design, evaluation, efficiency, security, protocols, tools, and applications. This paper presents a set of projects that attempt to integrate software engineering and systems administration topics. The projects emphasize network application programming. Particular attention will be given to a sequence of incremental projects using an object-oriented approach including the use of the Unified Modeling Language (UML) and a design pattern

Joining Inventory by Parataxonomists with DNA Barcoding of a Large Complex Tropical Conserved Wildland in Northwestern Costa Rica

BACKGROUND: The many components of conservation through biodiversity development of a large complex tropical wildland, Area de Conservacion Guanacaste (ACG), thrive on knowing what is its biodiversity and natural history. For 32 years a growing team of Costa Rican parataxonomists has conducted biodiversity inventory of ACG caterpillars, their food plants, and their parasitoids. In 2003, DNA barcoding was added to the inventory process. METHODOLOGY/PRINCIPAL FINDINGS: We describe some of the salient consequences for the parataxonomists of barcoding becoming part of a field biodiversity inventory process that has centuries of tradition. From the barcoding results, the parataxonomists, as well as other downstream users, gain a more fine-scale and greater understanding of the specimens they find, rear, photograph, database and deliver. The parataxonomists also need to adjust to collecting more specimens of what appear to be the "same species"--cryptic species that cannot be distinguished by eye or even food plant alone--while having to work with the name changes and taxonomic uncertainty that comes with discovering that what looked like one species may be many. CONCLUSIONS/SIGNIFICANCE: These career parataxonomists, despite their lack of formal higher education, have proven very capable of absorbing and working around the additional complexity and requirements for accuracy and detail that are generated by adding barcoding to the field base of the ACG inventory. In the process, they have also gained a greater understanding of the fine details of phylogeny, relatedness, evolution, and species-packing in their own tropical complex ecosytems. There is no reason to view DNA barcoding as incompatible in any way with tropical biodiversity inventory as conducted by parataxonomists. Their year-round on-site inventory effort lends itself well to the sampling patterns and sample sizes needed to build a thorough barcode library. Furthermore, the biological understanding that comes with barcoding increases the scientific penetrance of biodiversity information, DNA understanding, evolution, and ecology into the communities in which the parataxonomists and their families are resident

Retraction Note: An apoptosis-enhancing drug overcomes platinum resistance in a tumour-initiating subpopulation of ovarian cancer.

This Article has been retracted; see accompanying Retraction Note

Empirical Software Engineering in Industry Short Courses

This paper reports on a pilot project that incorporated small empirical studies in three industry short courses. These laboratory experiments were one component of a larger leveled study on the effects of test-driven development (TDD) on internal software quality. The approach is proposed to have pedagogical value to student-developers by improving their understanding and appreciation for empirical evidence, to instructors by providing feedback through surveys and exercises, and to the community at large by reporting results of the studies. Pre-experiment surveys in the three pilot experiments revealed large differences in programmer opinions of TDD. Possible correlations to development environment and programmer experience will be proposed. Post-experiment surveys revealed improvements in programmer opinions of TDD following the experiment exercises. Crafting sufficiently small but interesting assignments proved to be challenging. Few complete solutions were submitted and some developers were unwilling to submit their partial solutions. Positive observations will be made regarding the use of experiments in short courses. For instance, participating in the study encourages analytical thinking, prompts developers to evaluate alternative approaches, and instills the value of empirical evidence. Ethical concerns regarding threats to validity are raised and addressed. The authors find that ethical considerations not only support performing such studies, but encourage it as the duty of software professionals

A Leveled Examination of Test-Driven Development Acceptance

Test-driven development (TDD) has garnered considerable attention in professional settings and has made some inroads into software engineering and computer science education. A series of leveled experiments were conducted with students in beginning undergraduate programming courses through upper-level undergraduate, graduate, and professional training courses. This paper reports that mature programmers who try TDD are more likely to choose TDD over a similar test-last approach. Additionally this research reveals differences in programmer acceptance of TDD between beginning programmers who were reluctant to adopt TDD and more mature programmers who were more willing to adopt TDD. Attention is given to confounding factors, and future studies aimed at resolving these factors are identified. Finally proposals are made to improve early programmer acceptance of TDD

On the Influence of Test-Driven Development on Software Design

Test-driven development (TDD) is an agile software development strategy that addresses both design and testing. This paper describes a controlled experiment that examines the effects of TDD on internal software design quality. The experiment was conducted with undergraduate students in a software engineering course. Students in three groups completed semester-long programming projects using either an iterative Test-First (TDD), iterative Test-Last, or linear Test-Last approach. Results from this study indicate that TDD can be an effective software design approach improving both code-centric aspects such as object decomposition, test coverage, and external quality, and developer-centric aspects including productivity and confidence. In addition, iterative development approaches that include automated testing demonstrated benefits over a more traditional linear approach with manual tests. This study demonstrates the viability of teaching TDD with minimal effort in the context of a relatively traditional development approach. Potential dangers with TDD are identified regarding programmer motivation and discipline. Pedagogical implications and instructional techniques which may foster TDD adoption will also be referenced

Electron‐Diffraction Structural Study of Polymeric Gaseous Hydrogen Fluoride

Electron diffraction patterns with molecular interference features extending beyond s  =  35Å−1s=35Å−1 were obtained for gaseous self‐associated HF introduced under its own vapor pressure at −19° and at +22°C through a conventional nozzle system into a 40‐kV electron beam. The diffraction patterns and their dependence on temperature are best explained with the hypothesis that the monomer and a puckered, cyclic hexamer were the only appreciable constituents of the scattering vapors. Mean FFF angles in the hexamer were found to be only about 104°, in contrast with the 120° angles reported for the infinite planar zigzag chains in crystalline HF at −125°C. This pucker may simply be a consequence of thermal bending of the extremely flexible ring. Indeed, the experimental radial distribution function is so smeared out by large ring‐bending amplitudes that the data cannot distinguish between boatlike and chair conformations. It is likely that the free (HF)6 molecules sweep randomly through both conformations in their thermal undulations. At the two temperatures studied the hydrogen‐bonded FF distances were 2.525 and 2.533 Å, with standard errors of 0.003 Å, in comparison with the solid‐state result of 2.49 ± 0.01 Å. Corresponding FF amplitudes of vibration were 0.089 and 0.101 Å (±0.003 Å), respectively. Perhaps 70% at −19° and 45% at 22° of the hydrogen bonds were asymmetric with covalent FH distances 0.040 Å longer than those in the monomer molecules. The data suggest, however, that the remainder of the ring protons migrate a substantial distance off‐axis to a more symmetrical disposition between the fluorines.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70108/2/JCPSA6-50-8-3611-1.pd