1,009 research outputs found
USING BEM TO PREDICT THE EFFECTIVE THERMAL CONDUCTIVITY FOR HETEROGENEOUS MATERIALS
This work presents a study on the effective thermal conductivity in material with heterogeneous composition in two dimensions. The Boundary Elements Method (BEM) is used to solve the steady state potential equations. The sub regions technique was implemented in order to take into account the effects of these inclusions inside the domain. In the numerical implementation, the inclusions are randomly generated in a Representative Volume Element (RVE) domain. The Average Field Theory is used to predict the effective properties (macroscopic) of the material with heterogeneous composition. The material is characterized by a specified volume fraction as well as the inclusion’s size. The samples are composed of square domains with defined number of randomly distributed inclusions and submitted to a condition of unidirectional heat conduction. Each set of samples is analyzed several times in order to guarantee statistical stability of the result
Spin coherent quantum transport of electrons between defects in diamond
The nitrogen-vacancy color center in diamond has rapidly emerged as an
important solid-state system for quantum information processing. While
individual spin registers have been used to implement small-scale diamond
quantum computing, the realization of a large-scale device requires development
of an on-chip quantum bus for transporting information between distant qubits.
Here we propose a method for coherent quantum transport of an electron and its
spin state between distant NV centers. Transport is achieved by the
implementation of spatial stimulated adiabatic Raman passage through the
optical control of the NV center charge states and the confined conduction
states of a diamond nanostructure. Our models show that for two NV centers in a
diamond nanowire, high fidelity transport can be achieved over distances of
order hundreds of nanometres in timescales of order hundreds of nanoseconds.
Spatial adiabatic passage is therefore a promising option for realizing an
on-chip spin quantum bus
An evolutionary study of volatile chemistry in protoplanetary disks
The volatile composition of a planet is determined by the inventory of gas
and ice in the parent disk. The volatile chemistry in the disk is expected to
evolve over time, though this evolution is poorly constrained observationally.
We present ALMA observations of C18O, C2H, and the isotopologues H13CN, HC15N,
and DCN towards five Class 0/I disk candidates. Combined with a sample of
fourteen Class II disks presented in Bergner et al. (2019b), this data set
offers a view of volatile chemical evolution over the disk lifetime. Our
estimates of C18O abundances are consistent with a rapid depletion of CO in the
first ~0.5-1 Myr of the disk lifetime. We do not see evidence that C2H and HCN
formation are enhanced by CO depletion, possibly because the gas is already
quite under-abundant in CO. Further CO depletion may actually hinder their
production by limiting the gas-phase carbon supply. The embedded sources show
several chemical differences compared to the Class II stage, which seem to
arise from shielding of radiation by the envelope (impacting C2H formation and
HC15N fractionation) and sublimation of ices from infalling material (impacting
HCN and C18O abundances). Such chemical differences between Class 0/I and Class
II sources may affect the volatile composition of planet-forming material at
different stages in the disk lifetime.Comment: Accepted to Ap
Why do people fitted with hearing aids not wear them?
Objective: Age-related hearing loss is an increasingly important public health problem affecting approximately 40% of 55–74 year olds. The primary clinical management intervention for people with hearing loss is hearing aids, however, the majority (80%) of adults aged 55–74 years who would benefit from a hearing aid, do not use them. Furthermore, many people given a hearing aid do not wear it. The aim was to collate the available evidence as to the potential reasons for non-use of hearing aids among people who have been fitted with at least one. Design: Data were gathered via the use of a scoping study. Study sample: A comprehensive search strategy identified 10 articles reporting reasons for non-use of hearing aids. Results: A number of reasons were given, including hearing aid value, fit and comfort and maintenance of the hearing aid, attitude, device factors, financial reasons, psycho-social/situational factors, healthcare professionals attitudes, ear problems, and appearance. Conclusions: The most important issues were around hearing aid value, i.e. the hearing aid not providing enough benefit, and comfort related to wearing the hearing aid. Identifying factors that affect hearing aid usage are necessary for devising appropriate rehabilitation strategies to ensure greater use of hearing aids
Exploring the consequences of Mobility: Reclaiming jet lag as the state of travel disorientation
The c2d Spitzer spectroscopic survey of ices around low-mass young stellar objects II: CO2
This paper presents Spitzer-IRS spectroscopy of the CO2 15.2 micron bending
mode toward a sample of 50 embedded low-mass stars in nearby star-forming
clouds, taken mostly from the ``Cores to Disks (c2d)'' Legacy program. The
average abundance of solid CO2 relative to water in low-mass protostellar
envelopes is 0.32 +/- 0.02, significantly higher than that found in quiescent
molecular clouds and in massive star forming regions. It is found that a
decomposition of all the observed CO2 bending mode profiles requires a minimum
of five unique components. Roughly 2/3 of the CO2 ice is found in a water-rich
environment, while most of the remaining 1/3 is found in a CO environment.
Ground-based observations of solid CO toward a large subset of the c2d sample
are used to further constrain the CO2:CO component and suggest a model in which
low-density clouds form the CO2:H2O component and higher density clouds form
the CO2:CO ice during and after the freeze-out of gas-phase CO. It is suggested
that the subsequent evolution of the CO2 and CO profiles toward low-mass
protostars, in particular the appearance of the splitting of the CO2 bending
mode due to pure, crystalline CO2, is first caused by distillation of the
CO2:CO component through evaporation of CO due to thermal processing to ~20-30
K in the inner regions of infalling envelopes. The formation of pure CO2 via
segregation from the H2O rich mantle may contribute to the band splitting at
higher levels of thermal processing (>50 K), but is harder to reconcile with
the physical structure of protostellar envelopes around low-luminosity objects.Comment: Accepted for Ap
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