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

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