3,201 research outputs found

    Chirality Dependence of the KK-Momentum Dark Excitons in Carbon Nanotubes

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    Using a collection of twelve semiconducting carbon nanotube samples, each highly enriched in a single chirality, we study the chirality dependence of the KK-momentum dark singlet exciton using phonon sideband optical spectroscopy. Measurements of bright absorptive and emissive sidebands of this finite momentum exciton identify its energy as 20 - 38 meV above the bright singlet exciton, a separation that exhibits systematic dependencies on tube diameter, 2n+m2n+m family, and semiconducting type. We present calculations that explain how chiral angle dependence in this energy separation relates to the Coulomb exchange interaction, and elaborate the dominance of the KA1K_{A_1'} phonon sidebands over the zone-center phonon sidebands over a wide range of chiralities. The Kataura plot arising from these data is qualitatively well described by theory, but the energy separation between the sidebands shows a larger chiral dependence than predicted. This latter observation may indicate a larger dispersion for the associated phonon near the KK point than expected from finite distance force modeling.Comment: 24 pages, 12 figures, 1 table; slight title change, Figures 1 and 11 added, reference added, presentation improved throughout documen

    Customised Alloy Blends for In-Situ Al339 Alloy Formation Using Anchorless Selective Laser Melting

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    The additive manufacturing process Selective Laser Melting (SLM) can generate large thermal gradients during the processing of metallic powder; this can in turn lead to increased residual stress formation within a component. Metal anchors or support structures are required to be built during the process and forcibly hold SLM components to a substrate plate and minimise geometric distortion/warpage due to the process induced thermal residual stress. The requirement for support structures can limit the geometric freedom of the SLM process and increase post-processing operations. A novel method known as Anchorless Selective Laser Melting (ASLM) maintains processed material within a stress relieved state throughout the duration of a build. As a result, metal components formed using ASLM do not develop signification residual stresses within the process, thus, the conventional support structures or anchors used are not required to prevent geometric distortion. ASLM locally melts two or more compositionally distinct powdered materials that alloy under the action of the laser, forming into various combinations of hypo/hyper eutectic alloys with a new reduced solidification temperature. This new alloy is maintained in a semi-solid or stress reduced state for a prolonged period during the build with the assistance of elevated powder bed pre-heating. In this paper, custom blends of alloys are designed, manufactured and processed using ASLM. The purpose of this work is to create an Al339 alloy from compositionally distinct powder blends. The in-situ alloying of this material and ASLM processing conditions allowed components to be built in a stress-relieved state, enabling the manufacture of overhanging and unsupported features

    Nuclear factor-kappa B localization and function within intrauterine tissues from term and preterm labor and cultured fetal membranes

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    Abstract Background The objective of this study was to quantify the nuclear localization and DNA binding activity of p65, the major transactivating nuclear factor-kappa B (NF-kappaB) subunit, in full-thickness fetal membranes (FM) and myometrium in the absence or presence of term or preterm labor. Methods Paired full-thickness FM and myometrial samples were collected from women in the following cohorts: preterm no labor (PNL, N = 22), spontaneous preterm labor (PTL, N = 21), term no labor (TNL, N = 23), and spontaneous term labor (STL, N = 21). NF-kappaB p65 localization was assessed by immunohistochemistry, and DNA binding activity was evaluated using an enzyme-linked immunosorbent assay (ELISA)-based method. Results Nuclear p65 labeling was rare in amnion and chorion, irrespective of clinical context. In decidua, nuclear p65 labeling was greater in the STL group relative to the TNL cohort, but there were no differences among the TNL, PTL, and PNL cohorts. In myometrium, diffuse p65 nuclear labeling was significantly associated with both term and preterm labor. There were no significant differences in ELISA-based p65 binding activity in amnion, choriodecidual, and myometrial specimens in the absence or presence of term labor. However, parallel experiments using cultured term fetal membranes demonstrated high levels of p65-like binding even the absence of cytokine stimulation, suggesting that this assay may be of limited value when applied to tissue specimens. Conclusions These results suggest that the decidua is an important site of NF-kappaB regulation in fetal membranes, and that mechanisms other than cytoplasmic sequestration may limit NF-kappaB activation prior to term

    Modeling the impact of battery degradation within lifecycle cost based design optimization of heavy-duty hybrid electric vehicles

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    The optimal design of hybrid electric vehicle (HEV) powertrains from a systems perspective is critical to realize the maximum benefits for a given application. This is particularly true in the heavy-duty vehicle space where the major challenges are: (i) greater emphasis on economic viability, (ii) reluctance to take on risk associated with new technologies, and (iii) numerous diverse applications that preclude a one-size-fits-all approach to hybrid-electric powertrain design. Past studies on HEV powertrain design have either ignored battery degradation, or failed to holistically capture its impact from a lifecycle cost perspective. The focus of this effort is the development of a model-based framework that enables parametric optimization of the design and control of hybrid electric vehicles while accounting for the degradation of the lithium-ion battery and its impact on the total cost-of-ownership of the vehicle. Two different implementations of such a framework are described. The first implementation explores a very high-fidelity approach to enable engineering design optimization across a small parameter space. It captures the impact of battery degradation on fuel consumption and battery replacements over the vehicle life by incorporating a high-fidelity electrochemical battery model capable of predicting degradation, and degraded performance, into the powertrain simulation. An electric motor and battery size optimization problem is studied for a parallel HEV transit bus application. Results show that different optimal component sizes are obtained when different optimization objectives, such as net present value, payback period, internal rate of return, or simply the day 1 fuel consumption, are considered. Accounting for the battery degradation in the powertrain simulations shows fuel consumption increasing by up to 10% from day 1 to end-of-life of the battery. These results highlight the utility of the proposed implementation in enabling better design decisions as compared to methods that do not capture the evolution of vehicle performance and fuel consumption as the battery degrades. However, the high-fidelity electrochemical battery degradation model and the interval-by-interval simulation approach used in this implementation are computationally too expensive for a large-scale design study. In contrast, the second implementation uses a simpler empirical battery model to enable a large-scale study over a 10-parameter design space, over multiple architectures and vehicle applications. This implementation is designed to aid heavy-duty vehicle and powertrain component manufacturers in identifying market opportunities and planning future products. The design space explored in this work includes three powertrain component sizing parameters, four control strategy parameters and three vehicle uncertainty parameters. Multiple drive cycles were simulated across the Class 5-7 medium-duty truck and Class 7-8 transit bus applications for both parallel and series plug-in hybrid electric vehicle (PHEV) powertrain architectures with charge depleting and charge sustaining modes of operation. These simulation results were then evaluated for real-world economic viability under different economic assumptions corresponding to the 2015, 2020, 2025 and 2030 time frames. Sensitivity of the economic viability of solutions was also studied with respect to the vehicle uncertainty parameters, economic assumptions and vehicle utilization assumptions. (Abstract shortened by ProQuest.

    Working capital management of trading houses in India

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    Capital formation is of crucial importance in the process of economic development. Experience of development in other countries suggests that a high rate of capital formation was achieved to trigger rapid economic growth. The Indian planning commission puts this idea correctly when it states: "The level of production and the material well-being a community can attain depends, in the main, on the stock of capital and its disposal, i.e., on the amount of land per capital and of productive equipment in the shape of machinery, buildings, tools and implements factories, locomotives, engines, irrigation facilities, power installations and communications. The large stock of capital, the greater trend to be the productivity of labour and therefore, the volume of commodities and services that can be turned out with same effort." The investment in the working capital is decisive to any financial manager as it is important as the investment in the fixed capital. The management of current assets is similar to that of fixed assets in a sense that in both cases the firm analyses their effects on its return and risk. Working capital management focuses on firm's investment in current assets and current liabilities. Excessive investment in current assets impairs firm's profitability, as idle investment earns nothing while inadequate amount of working capital can threaten the solvency of the firm, if it fails to meet its current obligations

    Metaproteomic evidence of changes in protein expression following a change in electrode potential in a robust biocathode microbiome

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    Microorganisms that respire electrodes may be exploited for biotechnology applications if key pathways for extracellular electron transfer (EET) can be identified and manipulated through bioengineering. To determine whether expression of proposed Biocathode-MCL EET proteins are changed by modulating electrode potential without disrupting the relative distribution of microbial constituents, metaproteomic and 16S rRNA gene expression analyses were performed after switching from an optimal to suboptimal potential based on an expected decrease in electrode respiration. Five hundred and seventy-nine unique proteins were identified across both potentials, the majority of which were assigned to three previously defined Biocathode-MCL metagenomic clusters: a Marinobacter sp., a member of the family Chromatiaceae, and a Labrenzia sp. Statistical analysis of spectral counts using the Fisher's exact test identified 16 proteins associated with the optimal potential, five of which are predicted electron transfer proteins. The majority of proteins associated with the suboptimal potential were involved in protein turnover/turnover, motility, and membrane transport. Unipept and 16S rRNA gene expression analyses indicated that the taxonomic profile of the microbiome did not change after 52 hours at the suboptimal potential. These findings show that protein expression is sensitive to the electrode potential without inducing shifts in community composition, a feature that may be exploited for engineering Biocathode-MCL

    Complete analysis of the B-cell response to a protein antigen, from in vivo germinal centre formation to 3-D modelling of affinity maturation

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    Somatic hypermutation of immunoglobulin variable region genes occurs within germinal centres (GCs) and is the process responsible for affinity maturation of antibodies during an immune response. Previous studies have focused almost exclusively on the immune response to haptens, which may be unrepresentative of epitopes on protein antigens. In this study, we have exploited a model system that uses transgenic B and CD4<sup>+</sup> T cells specific for hen egg lysozyme (HEL) and a chicken ovalbumin peptide, respectively, to investigate a tightly synchronized immune response to protein antigens of widely differing affinities, thus allowing us to track many facets of the development of an antibody response at the antigen-specific B cell level in an integrated system <i>in</i> <i>vivo</i>. Somatic hypermutation of immunoglobulin variable genes was analysed in clones of transgenic B cells proliferating in individual GCs in response to HEL or the cross-reactive low-affinity antigen, duck egg lysozyme (DEL). Molecular modelling of the antibody–antigen interface demonstrates that recurring mutations in the antigen-binding site, selected in GCs, enhance interactions of the antibody with DEL. The effects of these mutations on affinity maturation are demonstrated by a shift of transgenic serum antibodies towards higher affinity for DEL in DEL-cOVA immunized mice. The results show that B cells with high affinity antigen receptors can revise their specificity by somatic hypermutation and antigen selection in response to a low-affinity, cross-reactive antigen. These observations shed further light on the nature of the immune response to pathogens and autoimmunity and demonstrate the utility of this novel model for studies of the mechanisms of somatic hypermutation
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