236 research outputs found

    Linking Adult Reproduction and Larval Density of Invasive Carp in a Large River

    Get PDF
    Identifying how temporal variation in the environment affects reproductive success of invasive alien species will aid in predicting future establishment and tracking dynamics of established populations. Asian carp Hypophthalmichthys spp. have become a nuisance in recent years in the Mississippi River basin. Their populations are apparently expanding, indicating favorable conditions for reproduction. During 2004 and 2005, we quantified mean density of Asian carp larvae, mean monthly gonadosomatic index (GSI) of adult males and females, and number of eggs within mature females in the lower Illinois River, a major tributary of the Mississippi River. A flood (water velocity ≥ 0.7 m/s) and drought (\u3c0.2 m/s) occurred during apparent spawning in 2004 and 2005, respectively. During 2004, Asian carp larvae were found during 32% of sampling weeks; mean GSI and fecundity were relatively low for adults, probably reflecting partially spawned individuals and perhaps low reproductive investment. During the drought of 2005, larval stages were present during only one (5%) of the sampling weeks, whereas mean GSI and fecundity of adults were high through summer. Females resorbed their eggs instead of spawning during this year. Spawning conditions during low water periods appear to be unsuitable for Asian carps, inhibiting adult spawning and yielding few larvae. Spawning conditions during 2004 were better but still yielded low densities of larvae relative to native fishes. Reproduction in the lower Illinois River appears to be linked to river flow and its impact on adult spawning decisions, but conditions for strong year-class production (i.e., high larval densities) may be rarer than previously expected

    The routinisation of management controls in software.

    Get PDF
    Author's post-print version. Final version published by Springer; available online at http://link.springer.com/Our paper aims to explore management control as complex and intertwining process over time, rather than the (mainstream) fixation on rational, optimising tools for ensuring business success. We set out to contribute towards our understanding of why and how particular management controls evolve over time as they do. We discuss how the management control routines of one organisation emerged and reproduced (through software), and moved towards a situation of becoming accepted and generally unquestioned across much of the industry. The creativity and championing of one particular person was found to be especially important in this unfolding change process. Our case study illuminates how management control (software) routines can be an important carrier of organisational knowledge, both as an engine for continuity but also potentially as a catalyst for change. We capture this process by means of exploring the ‘life-story’ of a piece of software that is adopted in the corrugated container industry

    The MAJORANA DEMONSTRATOR: A Search for Neutrinoless Double-beta Decay of Germanium-76

    Full text link
    The {\sc Majorana} collaboration is searching for neutrinoless double beta decay using 76^{76}Ge, which has been shown to have a number of advantages in terms of sensitivities and backgrounds. The observation of neutrinoless double-beta decay would show that lepton number is violated and that neutrinos are Majorana particles and would simultaneously provide information on neutrino mass. Attaining sensitivities for neutrino masses in the inverted hierarchy region, 155015 - 50 meV, will require large, tonne-scale detectors with extremely low backgrounds, at the level of \sim1 count/t-y or lower in the region of the signal. The {\sc Majorana} collaboration, with funding support from DOE Office of Nuclear Physics and NSF Particle Astrophysics, is constructing the {\sc Demonstrator}, an array consisting of 40 kg of p-type point-contact high-purity germanium (HPGe) detectors, of which \sim30 kg will be enriched to 87% in 76^{76}Ge. The {\sc Demonstrator} is being constructed in a clean room laboratory facility at the 4850' level (4300 m.w.e.) of the Sanford Underground Research Facility (SURF) in Lead, SD. It utilizes a compact graded shield approach with the inner portion consisting of ultra-clean Cu that is being electroformed and machined underground. The primary aim of the {\sc Demonstrator} is to show the feasibility of a future tonne-scale measurement in terms of backgrounds and scalability.Comment: Proceedings for the MEDEX 2013 Conferenc

    Status of the MAJORANA DEMONSTRATOR experiment

    Full text link
    The MAJORANA DEMONSTRATOR neutrinoless double beta-decay experiment is currently under construction at the Sanford Underground Research Facility in South Dakota, USA. An overview and status of the experiment are given.Comment: 8 pages, proceeding from VII International Conference on Interconnections between Particle Physics and Cosmology (PPC 2013), submitted to AIP proceeding

    Design Optimization of the graded AlGaN/GaN HEMT device performance based on material and physical dimensions

    Get PDF
    Design optimization of the traditional AlGaN/GaN HEMT device has been comprehensively conducted in achieving improved performance and current handling capability using the Synopsys’ Sentaurus TCAD tool. Varying material and physical considerations, specifically investigating the effects of graded barriers, spacer interlayer, material selection for the channel as well as study of the effects in the physical dimensions of the HEMT have been extensively carried out. Critical figure-of-merits (FOMs) specifically the DC characteristics, 2DEG concentrations and mobility of the heterostructure device have been evaluated. Significant observations include enhancement of maximum current density by 63% while the electron concentration was found to propagate by 1020 cm-3 in the channel. This work aims to provide tactical optimization to traditional HFETs, rendering its application as power amplifiers, MMICs and RADAR, which requires low noise performance and very high RF design operations. Analysis in covering the breadth and complexity of heterostructure devices has been carefully executed through extensive TCAD modelling and the end structure obtained has been optimized to provide best performance

    High-isolation antenna array using SIW and realized with a graphene layer for sub-terahertz wireless applications

    Get PDF
    This paper presents the results of a study on developing an effective technique to increase the performance characteristics of antenna arrays for sub-THz integrated circuit applications. This is essential to compensate the limited power available from sub-THz sources. Although conventional array structures can provide a solution to enhance the radiation-gain performance however in the case of small-sized array structures the radiation properties can be adversely affected by mutual coupling that exists between the radiating elements. It is demonstrated here the effectiveness of using SIW technology to suppress surface wave propagations and near field mutual coupling effects. Prototype of 2x3 antenna arrays were designed and constructed on a polyimide dielectric substrate with thickness of 125 mu m for operation across 0.19-0.20 THz. The dimensions of the array were 20x13.5x0.125 mm(3). Metallization of the antenna was coated with 500 nm layer of Graphene. With the proposed technique the isolation between the radiating elements was improved on average by 22.5 dB compared to a reference array antenna with no SIW isolation. The performance of the array was enhanced by transforming the patch to exhibit metamaterial characteristics. This was achieved by embedding the patch antennas in the array with sub-wavelength slots. Compared to the reference array the metamaterial inspired structure exhibits improvement in isolation, radiation gain and efficiency on average by 28 dB, 6.3 dBi, and 34%, respectively. These results show the viability of proposed approach in developing antenna arrays for application in sub-THz integrated circuits

    Analyses of the mechanical, electrical and electromagnetic shielding properties of thermoplastic composites doped with conductive nanofillers

    Get PDF
    The purpose of this study is to observe effect of incorporating vapor-grown carbon nanofibers with various amounts in polyvinylidene fluoride matrix in terms of mechanical strength and electromagnetic shielding effectiveness. Thermoplastic conductive nanocomposites were prepared by heat-pressed compression molding. Vapor-grown carbon nanofibers were utilized at various weight ratios (1 wt.%, 3 wt.%, 5 wt.%, and 8 wt.%) as conductive and reinforcing materials. Polyvinylidene fluoride was used as a thermoplastic polymer matrix. Scanning electron microscopic analysis was conducted in order to characterize the morphology and structural properties of the nanocomposites and results revealed well dispersion of carbon nanofibers within the matrix for all concentrations. Mechanical characteristics were investigated according to standards. Findings proved that overall increments of 16%, 37.5%, and 56% were achieved in terms of tensile strength, elasticity modulus, and impact energy, respectively, where a total reduction of 44.8% was observed in terms of elongation for 8 wt.% vapor-grown nanofiber matrix compared to that of 0 wt.%. Electromagnetic shielding effectiveness's of the nanocomposites were determined by standard protocol using coaxial transmission line measurement technique in the frequency range of 15–3000 MHz. It was observed that resistance, sheet resistance, and resistivity of nanocomposites depicted substantial reduction with the increment in nanofiber content. Nevertheless, it was observed that nanofiber content, dispersion, and network formation within the composites were highly influent on the electromagnetic shielding effectiveness performance of the structures

    An international multicenter study of protocols for liver transplantation during a pandemic : a case for quadripartite equipoise

    Get PDF
    Background & Aims: The outbreak of COVID-19 has vastly increased the operational burden on healthcare systems worldwide. For patients with end-stage liver failure, liver transplantation is the only option. However, the strain on intensive care facilities caused by the pandemic is a major concern. There is an urgent need for ethical frameworks to balance the need for liver transplantation against the availability of national resources. Methods: We performed an international multicenter study of transplant centers to understand the evolution of policies for transplant prioritization in response to the pandemic in March 2020. To describe the ethical tension arising in this setting, we propose a novel ethical framework, the quadripartite equipoise (QE) score, that is applicable to liver transplantation in the context of limited national resources. Results: Seventeen large- and medium-sized liver transplant centers from 12 countries across 4 continents participated. Ten centers opted to limit transplant activity in response to the pandemic, favoring a “sickest-first” approach. Conversely, some larger centers opted to continue routine transplant activity in order to balance waiting list mortality. To model these and other ethical tensions, we computed a QE score using 4 factors – recipient outcome, donor/graft safety, waiting list mortality and healthcare resources – for 7 countries. The fluctuation of the QE score over time accurately reflects the dynamic changes in the ethical tensions surrounding transplant activity in a pandemic. Conclusions: This four-dimensional model of quadripartite equipoise addresses the ethical tensions in the current pandemic. It serves as a universally applicable framework to guide regulation of transplant activity in response to the increasing burden on healthcare systems. Lay summary: There is an urgent need for ethical frameworks to balance the need for liver transplantation against the availability of national resources during the COVID-19 pandemic. We describe a four-dimensional model of quadripartite equipoise that models these ethical tensions and can guide the regulation of transplant activity in response to the increasing burden on healthcare systems
    corecore