8,643 research outputs found
Modeling surface roughness scattering in metallic nanowires
Ando's model provides a rigorous quantum-mechanical framework for
electron-surface roughness scattering, based on the detailed roughness
structure. We apply this method to metallic nanowires and improve the model
introducing surface roughness distribution functions on a finite domain with
analytical expressions for the average surface roughness matrix elements. This
approach is valid for any roughness size and extends beyond the commonly used
Prange-Nee approximation. The resistivity scaling is obtained from the
self-consistent relaxation time solution of the Boltzmann transport equation
and is compared to Prange-Nee's approach and other known methods. The results
show that a substantial drop in resistivity can be obtained for certain
diameters by achieving a large momentum gap between Fermi level states with
positive and negative momentum in the transport direction.Comment: 25 pages, 11 figure
Linking eye design with host symbiont relationships in pontoniine shrimps (crustacea, decapoda, palaemonidae)
Symbiosis is prevalent in the marine environment with many studies examining the effects of such interactions between host and symbiont. Pontoniine shrimps are a group whose ecology is characterised by symbiotic interactions. This investigation examines the gross morphology of Pontoniinae compound eyes and superficial optical parameters with reference to their symbiotic relationship or lifestyle category; free-living, ectosymbiont, endosymbiont (bivalves) or endosymbiont (non-bivalves). The eye morphologies of free-living and ectosymbiotic species are very similar, yet differ from both forms of endosymbiotic species. Endosymbionts have significantly smaller and simpler eyes with larger facets and bigger interommatidial angles and eye parameters for increased sensitivity levels. However bivalve endosymbionts form an intermediary group between non-bivalve endosymbionts and ectosymbionts as a result of their more active lifestyle. The accessory eye or "nebenauge", although of uncertain function, commonly occurs in free-living Pontoniinae species but rarely in endosymbionts apart from in more primitive species. The variation in morphology reflects tensions between functional requirements and ecological pressures that have strongly influenced eye design in Pontoniinae. © 2014 Dobson et al
Transitions to Entrepreneurship and Industry-Specific Barriers
Drivers of entrepreneurial entry are investigated in this study by examining how entry into small-business ownership is shaped by industry-specific constraints. The human- and financial-capital endowments of potential entrepreneurs entering firms in various industries are shown to differ profoundly, depending on the type of venture entered. The educational credentials of highly educated potential entrepreneurs, in particular, predict avoidance of small-firm ownership in some industries as well as attraction to others. Recognizing that individuals choose an industry sector jointly with their decision to enter entrepreneurship, we find that the conventional practice of conflating different industry types in empirical analyses of transitions to entrepreneurship generates misleading findings about the determinants of entrepreneurship.entrepreneurship, self-employment, capital constraints, transitions, entry barriers, business start-ups
One evidence base; three stories: do opioids relieve chronic breathlessness?
Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/. The efficacy of low-dose systemic opioids for chronic breathlessness was questioned by the recent Cochrane review by Barnes et al We examined the reasons for this conflicting finding and re-evaluated the efficacy of systemic opioids. Compared with previous meta-analyses, Barnes et al reported a smaller effect and lower precision, but did not account for matched data of crossover trials (11/12 included trials) and added a risk-of-bias criterion (sample size). When re-analysed to account for crossover data, opioids decreased breathlessness (standardised mean differences -0.32; -0.18 to -0.47; I2=44.8%) representing a clinically meaningful reduction of 0.8 points (0-10 numerical rating scale), consistent across meta-analyses
Quasiperiodic localized oscillating solutions in the discrete nonlinear Schr\"odinger equation with alternating on-site potential
We present what we believe to be the first known example of an exact
quasiperiodic localized stable solution with spatially symmetric
large-amplitude oscillations in a non-integrable Hamiltonian lattice model. The
model is a one-dimensional discrete nonlinear Schr\"odinger equation with
alternating on-site energies, modelling e.g. an array of optical waveguides
with alternating widths. The solution bifurcates from a stationary discrete gap
soliton, and in a regime of large oscillations its intensity oscillates
periodically between having one peak at the central site, and two symmetric
peaks at the neighboring sites with a dip in the middle. Such solutions, termed
'pulsons', are found to exist in continuous families ranging arbitrarily close
both to the anticontinuous and continuous limits. Furthermore, it is shown that
they may be linearly stable also in a regime of large oscillations.Comment: 4 pages, 4 figures, to be published in Phys. Rev. E. Revised version:
change of title, added Figs. 1(b),(c), 4 new references + minor
clarification
Cohomology rings of almost-direct products of free groups
An almost-direct product of free groups is an iterated semidirect product of
finitely generated free groups in which the action of the constituent free
groups on the homology of one another is trivial. We determine the structure of
the cohomology ring of such a group. This is used to analyze the topological
complexity of the associated Eilenberg-Mac Lane space.Comment: 16 page
Breathlessness in the elderly during the last year of life sufficient to restrict activity
OBJECTIVES: Breathlessness is prevalent in older people. Symptom control at the end of life is important. This study investigated relationships between age, clinical characteristics and breathlessness sufficient to have people spend at least one half a day in that month in bed or cut down on their usual activities (restricting breathlessness) during the last year of life. DESIGN: Secondary data-analysis SETTING: General community PARTICIPANTS: 754 non-disabled persons, aged 70 and older. Monthly telephone interviews were conducted to determine the occurrence of restricting breathlessness. The primary outcome was the percentage of months with restricting breathlessness reported during the last year of life. RESULTS: Data regarding breathlessness were available for 548/589 (93.0%) decedents (mean age 86.7 years (range 71 to 106; males 38.8%). 311/548 (56.8%) reported restricting breathlessness at some time-point during the last year of life but no-one reported this every month. Frequency increased in the months closer to death irrespective of cause. Restricting breathlessness was associated with anxiety, (0.25 percentage point increase in months breathlessness per percentage point months reported anxiety, 95% CI 0.16 to 0.34, P<0.001), depression (0.14, 0.05 to 0.24, P=0.002) and mobility problems (0.07, 0.03 to 0.1, P=0.001). Percentage months of restricting breathlessness increased if chronic lung disease was noted at the most recent comprehensive assessment (6.62 percentage points, 95% CI 4.31 to 8.94, P<0.001), heart failure (3.34, 0.71 to 5.97, P<0.01), and ex-smoker status (3.01, 0.94 to 5.07, P=0.002), but decreased with older age (─0.19, ─0.37 to ─0.02, P=0.03). CONCLUSION: Restricting breathlessness increased in this elderly population in the months preceding death from any cause. Breathlessness should be assessed and managed in the context of poor prognosis
AutoEFT: Constructing and exploring on-shell bases of effective field theories
Effective Field Theories (EFTs) provide a framework for capturing the effects
of yet unseen heavy degrees of freedom in a model-independent manner. However,
constructing a complete and minimal set of operators, especially at higher mass
dimensions, is challenging. We present AutoEFT, an implementation of an
algorithm that systematically handles redundancies among operators due to
equations of motion, integration-by-parts identities, Fierz identities, and
repeated fields. This algorithm enables the construction of on-shell bases for
a broad range of EFTs. Additionally, it facilitates the exploration of various
aspects within this field, such as investigating higher mass dimensions or the
relationship between different operator bases. AutoEFT can be applied to
phenomenologically relevant theories like the Standard Model and its
extensions, including new light particles or additional symmetry groups.Comment: 7 pages, 1 figure; contribution to the proceedings of the European
Physical Society Conference on High Energy Physics (EPS-HEP2023), 21-25
August 2023, Hamburg, German
The independent association of overweight and obesity with breathlessness in adults: a cross-sectional, population-based study
Obesity is an independent risk factor for chronic breathlessness and should be assessed in people with this symptom
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