4,368 research outputs found
Landauer formula without Landauer's assumptions
The Landauer formula for dissipationless conductance lies at the heart of modern electronic transport, yet it remains without a clear microscopic basis. We analyse the Landauer formula microscopically and give a straightforward quantum kinetic derivation for open systems. Some important experimental implications follow. These lie beyond the Landauer result as popularly received
Anomalies in one-dimensional electron transport: Quantum point contacts and wires
Over the last several decades, interest in quasi-one dimensional charge transport has progressed from the seminal discoveries of Landauer quantization of conductance as a function of carrier density, to significant finer-scale phenomena. Those include: (i) fractional conductance, or '0.7 anomaly'; (ii) zero-bias anomaly; (iii) Rashba-effect anomalies; and (iv) apparent violation of the Landauer upper bound on conductance. In this work we present a very short summary of the first three items. The last anomaly, which remained theoretically unexamined until recently, is discussed in detail with emphasis on novel low-dimensional physics
Magnetic hard-direction ordering in anisotropic Kondo systems
We present a generic mechanism that explains why many Kondo materials show
magnetic ordering along directions that are not favoured by the crystal-field
anisotropy. Using a renormalization-group (RG) analysis of single impurity
Kondo models with single-ion anisotropy, we demonstrate that strong
fluctuations above the Kondo temperature drive a moment re-orientation over a
wide range of parameters, e.g. for different spin values and number of
Kondo channels . In tetragonal systems this can happen for both easy-plane
or easy axis anisotropy. The characteristic crossing of magnetic
susceptibilities is not an artefact of the weak-coupling RG treatment but can
be reproduced in brute-force perturbation theory. Employing numerical
renormalization group (NRG), we show that for an under-screened moment (,
) with easy-plane anisotropy, a crossing of magnetic susceptibilities can
also occur in the strong-coupling regime (below the Kondo temperature). This
suggests that collective magnetic ordering of such under-screened moments would
develop along the magnetic hard axis
Semiautomated text analytics for qualitative data synthesis
Approaches to synthesizing qualitative data have, to date, largely focused on
integrating the findings from published reports. However, developments in text
mining software offer the potential for efficient analysis of large pooled primary
qualitative datasets. This case study aimed to (a) provide a stepâbyâstep guide to
using one software application, Leximancer, and (b) interrogate opportunities
and limitations of the software for qualitative data synthesis. We applied
Leximancer v4.5 to a pool of five qualitative, UKâbased studies on transportation
such as walking, cycling, and driving, and displayed the findings of the
automated content analysis as intertopic distance maps. Leximancer enabled
us to âzoom outâ to familiarize ourselves with, and gain a broad perspective
of, the pooled data. It indicated which studies clustered around dominant topics
such as âpeople.â The software also enabled us to âzoom inâ to narrow the
perspective to specific subgroups and lines of enquiry. For example, âpeopleâ
featured in men's and women's narratives but were talked about differently,
with men mentioning âkidsâ and âold,â whereas women mentioned âthingsâ
and âstuff.â The approach provided us with a fresh lens for the initial inductive
step in the analysis process and could guide further exploration. The limitations
of using Leximancer were the substantial data preparation time involved and the
contextual knowledge required from the researcher to turn lines of inquiry into
meaningful insights. In summary, Leximancer is a useful tool for contributing
to qualitative data synthesis, facilitating comprehensive and transparent data
coding but can only inform, not replace, researcherâled interpretive work
A therapeutic potential for marine skeletal proteins in bone regeneration
A vital ingredient for engineering bone tissue, in the culture dish, is the use of recombinant matrix and growth proteins to help accelerate the growth of cultivated tissues into clinically acceptable quantities. The skeletal organic matrices of calcifying marine invertebrates are an untouched potential source of such growth inducing proteins. They have the advantage of being ready-made and retain the native state of the original protein. Striking evidence shows that skeleton building bone morphogenic protein-2/4 (BMP) and transforming growth factor beta (TGF-ÎČ) exist within various marine invertebrates such as, corals. Best practice mariculture and the latest innovations in long-term marine invertebrate cell cultivation can be implemented to ensure that these proteins are produced sustainably and supplied continuously. This also guarantees that coral reef habitats are not damaged during the collection of specimens. Potential proteins for bone repair, either extracted from the skeleton or derived from cultivated tissues, can be identified, evaluated and retrieved using chromatography, cell assays and proteomic methods. Due to the current evidence for bone matrix protein analogues in marine invertebrates, together with the methods established for their production and retrieval there is a genuine prospect that they can be used to regenerate living bone for potential clinical use. © 2013 by the authors; licensee MDPI
10C continued: A deeper radio survey at 15.7 GHz
We present deep 15.7-GHz observations made with the Arcminute Microkelvin
Imager Large Array in two fields previously observed as part of the Tenth
Cambridge (10C) survey. These observations allow the source counts to be
calculated down to 0.1 mJy, a factor of five deeper than achieved by the 10C
survey. The new source counts are consistent with the extrapolated fit to the
10C source count, and display no evidence for either steepening or flattening
of the counts. There is thus no evidence for the emergence of a significant new
population of sources (e.g. starforming) at 15.7 GHz flux densities above 0.1
mJy, the flux density level at which we expect starforming galaxies to begin to
contribute. Comparisons with the de Zotti et al. model and the SKADS Simulated
Sky show that they both underestimate the observed number of sources by a
factor of two at this flux density level. We suggest that this is due to the
flat-spectrum cores of radio galaxies contributing more significantly to the
counts than predicted by the models.We thank the staff of the Mullard Radio Astronomy Observatory for maintaining and operating AMI. IHW and CR acknowledge Science and Technology Facilities Council studentships. IHW acknowledges support from the Square Kilometre Array South Africa project and the South African National Research Foundation. This research has made use of NASAâs Astrophysics Data System. We thank the referee for their careful reading of this manuscript.This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stv296
Tuberculosis/HIV/AIDS coinfection in Porto Alegre, RS/Brazil - invisibility and silencing of the most affected groups
OBJECTIVE: To analyze how belonging to certain social groups contributes to constituting the vulnerabilities associated with illnesses due to tuberculosis/HIV/AIDS coinfection. METHODOLOGYThis is a qualitative study carried out in the city of Porto Alegre, state of Rio Grande do Sul, in regions of high social vulnerability. Twenty coinfected people were interviewed in specialized health services between August and December 2016. The analysis was based on the frameworks The Sound of Silence and Vulnerability and Human Rights. RESULTS: Socioeconomic conditions were decisive for the constitution of the vulnerability conditions. Processes of people invisibilization, and the silencing of their voices, in a scenario marked by economic, racial and gender inequalities, contributed for their health needs not to be understood and effectively taken into account in the services actions. FINAL CONSIDERATIONS: The more effective strategies are to legitimize voices and to understand the needs of those affected by coinfection, the greater the chances that programmatic responses to the problem will be successful
Characterising hyperinsulinaemia induced insulin resistance in human skeletal muscle cells
Hyperinsulinaemia potentially contributes to insulin resistance in metabolic tissues, such as skeletal muscle. The purpose of these experiments was to characterise glucose uptake, insulin signalling and relevant gene expression in primary human skeletal muscle-derived cells (HMDCs), in response to prolonged insulin exposure (PIE) as a model of hyperinsulinaemia-induced insulin resistance. Differentiated HMDCs from healthy human donors were cultured with or without insulin (100 nM) for 3 days followed by an acute insulin stimulation. HMDCs exposed to PIE were characterised by impaired insulin-stimulated glucose uptake, blunted IRS-1 phosphorylation (Tyr612) and Akt (Ser473) phosphorylation in response to an acute insulin stimulation. Glucose transporter 1 (GLUT1), but not GLUT4, mRNA and protein increased following PIE. The mRNA expression of metabolic (PDK4) and inflammatory markers (TNF-α) was reduced by PIE but did not change lipid (SREBP1 and CD36) or mitochondrial (UCP3) markers. These experiments provide further characterisation of the effects of PIE as a model of hyperinsulinaemia-induced insulin resistance in HMDCs
A question of scale: Human migrations writ large and small
Several recent papers illustrate the importance of migration and gene flow in molding the patterns of genetic variation observed in humans today. We place the varied demographic processes covered by these terms into a more general framework, and discuss some of the challenges facing attempts to reconstruct past human mobility and determine its influence on our genetic heritage
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