The effects of dams on longitudinal variation in river food webs

We examined the effects of two dams on longitudinal variation of riverine food webs using stable isotope and gut contents analyses along four rivers in the Hunter Valley in eastern Australia. Longitudinal 15N enrichment was observed in most invertebrate taxa and food sources but significant longitudinal variation was rare for 13C, and composition of gut contents of invertebrate taxa did not vary significantly with longitudinal position. Most invertebrates and food sources were more 15N-enriched at sites immediately downstream of the dams than expected from their upstream longitudinal position, a result not mirrored by gut contents and 13C. Enrichment of 15N downstream may be attributed to altered water quality as a result of impoundment but further research is necessary to elucidate whether physico-chemical riverine processes or trophic mechanisms are responsible. Our observations regarding the influence of dams on isotope ratios are contrary to the few existing studies, suggesting the small volumes relative to annual inflows of dams in the present study limit downstream impacts by maintaining aspects of flow variability. © 2013 © 2013 Taylor & Francis

Barrier tuning of atomic layer deposited Ta2O5 and Al2O3 in resonant tunnelling diodes for terahertz applications

The performance of double dielectric (MIIM) resonant tunneling diodes using atomic layer deposited oxides of low (Al2O3) and high (Ta2O5) electron affinity (χ) is investigated. Varying the individual layer thickness of Ta2O5 with a 1 nm thick Al2O3, evidence for resonant tunneling is observed and related to the bound states in the quantum well established between the oxide layers. The results show good rectifying capability of resonant tunneling diodes at low turn-on voltage enabling their potential use for terahertz applications

The e!ects of a non-intervention HACCP implementation on process hygiene indicators on bovine and porcine carcasses

Four sites on each of 720 dressed carcasses (360 bovine and 360 porcine) were sampled (2,880 samples in total) in a single commercial abattoir slaughtering cattle and pigs using two separate slaughterlines. The carcasses were sampled before HACCP (pre-HACCP; 960 samples) and after HACCP implementation (post-HACCP; 1,920 samples) and Total Viable Count (TVC), Enterobacteriaceae count (EC) and Salmonella spp. prevalence were determined. During the pre-HACCP period, mean TVC levels on four tested sites varied on bovine carcasses between 3.03 and 4.19 log10 cfu/cm2 and on porcine carcasses between 3.73 and 3.99 log10 cfu/cm2. During the post-HACCP period, TVC levels on all tested sites on carcasses were further signicantly reduced, by 0.33-1.64 log and 1.13-2.04 log on bovine and porcine carcasses, respectively, compared to the pre-HACCP period. Both the EC occurrence in samples and EC levels in EC-positive samples somewhat decreased during post-HACCP as compared to pre-HACCP period, but the reductions were not statistically signicant due to large proportion of EC-negative samples and very low counts in EC-positive samples. Salmonella spp. was not detected in any of bovine or porcine carcass samples, regardless of whether they were taken pre- or post-HACCP. Overall, the processhygiene- improving eects of non-intervention HACCP have been proven through reduction of TVC on carcasses, but could not be veried in the present study through similar reductions in EC and/or Salmonella, because of their low levels and/or absence

Corrosion Behavior of the As-cast and Heat-treated ZA27 Alloy

Corrosion behaviour of the as-cast and heat-treated ZA27 alloy was examined. The alloy was prepared by conventional melting and casting route and then thermally processed by applying T4 heat treatment regime (solutionizing at 370 °C for 3 hours followed by water quenching and natural aging). Corrosion rate of the as-cast and heat-treated ZA27 alloy was determined in 3.5 wt. % NaCl solution through immersion test using both weight loss method and polarization resistance measurements. It was shown that applied thermal treatment resulted in increased ductility of the heat-treated alloy and had a small beneficial effect on the corrosion resistance of ZA27 alloy

Experimental Electronic Structure and Interband Nesting in BaVS_3

The correlated 3d sulphide BaVS_3 is a most interesting compound because of the apparent coexistence of one-dimensional and three-dimensional properties. Our experiments explain this puzzle and shed new light on its electronic structure. High-resolution angle-resolved photoemission measurements in a 4eV wide range below the Fermi level explored the coexistence of weakly correlated a_1g wide-band and strongly correlated e_g narrow-band d-electrons that is responsible for the complicated behavior of this material. The most relevant result is the evidence for a_1g--e_g inter-band nesting condition.Comment: 4 pages, 3 figure

Thermally activated charge carriers and mid-infrared optical excitations in quarter-filled CDW systems

The optical properties of the quarter-filled single-band CDW systems have been reexamined in the model with the electron-phonon coupling related to the variations of electron site energies. It appears that the indirect, electron-mediated coupling between phase phonons and external electromagnetic fields vanishes for symmetry reasons, at variance with the infrared selection rules used in the generally accepted microscopic theory. It is shown that the phase phonon modes and the electric fields couple directly, with the coupling constant proportional to the magnitude of the charge-density wave. The single-particle contributions to the optical conductivity tensor are determined for the ordered CDW state and the related weakly doped metallic state by means of the Bethe--Salpeter equations for elementary electron-hole excitations. It turns out that this gauge-invariant approach establishes a clear connection between the effective numbers of residual, thermally activated and bound charge carriers. Finally, the relation between these numbers and the activation energy of dc conductivity and the optical CDW gap scale is explained in the way consistent with the conductivity sum rules.Comment: 12 pages, 9 figure

Crowdsourcing Content Creation for SQL Practice

Crowdsourcing refers to the act of using the crowd to create content or to collect feedback on some particular tasks or ideas. Within computer science education, crowdsourcing has been used -- for example -- to create rehearsal questions and programming assignments. As a part of their computer science education, students often learn relational databases as well as working with the databases using SQL statements. In this article, we describe a system for practicing SQL statements. The system uses teacher-provided topics and assignments, augmented with crowdsourced assignments and reviews. We study how students use the system, what sort of feedback students provide to the teacher-generated and crowdsourced assignments, and how practice affects the feedback. Our results suggest that students rate assignments highly, and there are only minor differences between assignments generated by students and assignments generated by the instructor.Peer reviewe

Progressor: Social navigation support through open social student modeling

The increased volumes of online learning content have produced two problems: how to help students to find the most appropriate resources and how to engage them in using these resources. Personalized and social learning have been suggested as potential ways to address these problems. Our work presented in this paper combines the ideas of personalized and social learning in the context of educational hypermedia. We introduce Progressor, an innovative Web-based tool based on the concepts of social navigation and open student modeling that helps students to find the most relevant resources in a large collection of parameterized self-assessment questions on Java programming. We have evaluated Progressor in a semester-long classroom study, the results of which are presented in this paper. The study confirmed the impact of personalized social navigation support provided by the system in the target context. The interface encouraged students to explore more topics attempting more questions and achieving higher success rates in answering them. A deeper analysis of the social navigation support mechanism revealed that the top students successfully led the way to discovering most relevant resources by creating clear pathways for weaker students. © 2013 Taylor and Francis Group, LLC

Theory of Magnetic Field Induced Spin Density Wave in High Temperature Superconductors

The induction of spin density wave (SDW) and charge density wave (CDW) orderings in the mixed state of high $T_c$ superconductors (HTS) is investigated by using the self-consistent Bogoliubov-de Gennes equations based upon an effective model Hamiltonian with competing SDW and d-wave superconductivity interactions. For optimized doping sample, the modulation of the induced SDW and its associated CDW is determined by the vortex lattice and their patterns obey the four-fold symmetry. By deceasing doping level, both SDW and CDW show quasi-one dimensional like behavior, and the CDW has a period just half that of the SDW along one direction. From the calculation of the local density of states (LDOS), we found that the majority of the quasi-particles inside the vortex core are localized. All these results are consistent with several recent experiments on HTS