744 research outputs found
Micromachined Polycrystalline Sige-Based Thermopiles for Micropower Generation on Human Body
This paper presents a polycrystalline silicon germanium (poly-SiGe)
thermopile specially designed for thermoelectric generators used on human body.
Both the design of the single thermocouple and the arrangement of the
thermocouple array have been described. A rim structure has been introduced in
order to increase the temperature difference across the thermocouple junctions.
The modeling of the thermocouple and the thermopile has been performed
analytically and numerically. An output power of about 1 W at an output
voltage of more than 1 V is expected from the current design of thermopiles in
a watch-size generator. The key material properties of the poly-SiGe have been
measured. The thermopile has been fabricated and tested. Experimental results
clearly demonstrate the advantage of the rim structure in increasing output
voltage. In presence of forced convection, the output voltage of a non-released
thermopile can increase from about 53 mV/K/cm2 to about 130 mV/K/cm2 after the
rim structure is formed. A larger output voltage from the thermopile is
expected upon process completion.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
Optimizing dual energy cone beam CT protocols for preclinical imaging and radiation research
Objective: The aim of this work was to investigate whether quantitative dual-energy CT (DECT) imaging is feasible for small animal irradiators with an integrated cone-beam CT (CBCT) system.
Methods: The optimal imaging protocols were determined by analyzing different energy combinations and dose levels. The influence of beam hardening effects and the performance of a beam hardening correction (BHC) were investigated. In addition, two systems from different manufacturers were compared in terms of errors in the extracted effective atomic numbers (Z(eff)) and relative electron densities (rho(e)) for phantom inserts with known elemental compositions and relative electron densities.
Results: The optimal energy combination was determined to be 50 and 90kVp. For this combination, Z(eff) and r rho(e) can be extracted with a mean error of 0.11 and 0.010, respectively, at a dose level of 60cGy.
Conclusion: Quantitative DECT imaging is feasible for small animal irradiators with an integrated CBCT system. To obtain the best results, optimizing the imaging protocols is required. Well-separated X-ray spectra and a sufficient dose level should be used to minimize the error and noise for Z(eff) and rho(e). When no BHC is applied in the image reconstruction, the size of the calibration phantom should match the size of the imaged object to limit the influence of beam hardening effects. No significant differences in Z(eff) and rho(e) errors are observed between the two systems from different manufacturers.
Advances in knowledge: This is the first study that investigates quantitative DECT imaging for small animal irradiators with an integrated CBCT system
Policy search with high-dimensional context variables
Direct contextual policy search methods learn to improve policy
parameters and simultaneously generalize these parameters
to different context or task variables. However, learning
from high-dimensional context variables, such as camera images,
is still a prominent problem in many real-world tasks.
A naive application of unsupervised dimensionality reduction
methods to the context variables, such as principal component
analysis, is insufficient as task-relevant input may be ignored.
In this paper, we propose a contextual policy search method in
the model-based relative entropy stochastic search framework
with integrated dimensionality reduction. We learn a model of
the reward that is locally quadratic in both the policy parameters
and the context variables. Furthermore, we perform supervised
linear dimensionality reduction on the context variables
by nuclear norm regularization. The experimental results
show that the proposed method outperforms naive dimensionality
reduction via principal component analysis and
a state-of-the-art contextual policy search method
Expanded Iron UTA spectra -- probing the thermal stability limits in AGN clouds
The Fe unresolved transition array (UTAs) produce prominent features in the
15-17?A wavelength range in the spectra of Active Galactic Nuclei (AGN). Here
we present new calculations of the energies and oscillator strengths of inner-
shell lines from Fe XIV, Fe XV, and Fe XVI. These are crucial ions since they
are dominant at inflection points in the gas thermal stability curve, and UTA
excitation followed by autoionization is an important ionization mechanism for
these species. We incorporate these, and data reported in previous papers, into
the plasma simulation code Cloudy. This updated physics is subsequently
employed to reconsider the thermally stable phases in absorbing media in Active
Galactic Nuclei. We show how the absorption profile of the Fe XIV UTA depends
on density, due to the changing populations of levels within the ground
configuration.Comment: ApJ in pres
Thermal personalities of older people in South Australia: A personas-based approach to develop thermal comfort guidelines
Published: 13 November 2020An important consideration for future age-friendly cities is that older people are able to live in housing appropriate for their needs. While thermal comfort in the home is vital for the health and well-being of older people, there are currently few guidelines about how to achieve this. This study is part of a research project that aims to improve the thermal environment of housing for older Australians by investigating the thermal comfort of older people living independently in South Australia and developing thermal comfort guidelines for people ageing-in-place. This paper describes the approach fundamental for developing the guidelines, using data from the study participants’ and the concept of personas to develop a number of discrete “thermal personalities”. Hierarchical Cluster Analysis (HCA) was implemented to analyse the features of research participants, resulting in six distinct clusters. Quantitative and qualitative data from earlier stages of the project were then used to develop the thermal personalities of each cluster. The thermal personalities represent different approaches to achieving thermal comfort, taking into account a wide range of factors including personal characteristics, ideas, beliefs and knowledge, house type, and location. Basing the guidelines on thermal personalities highlights the heterogeneity of older people and the context-dependent nature of thermal comfort in the home and will make the guidelines more user-friendly and useful.Helen Bennetts, Larissa Arakawa Martins, Joost van Hoof and Veronica Soebart
An embedding scheme for the Dirac equation
An embedding scheme is developed for the Dirac Hamiltonian H. Dividing space
into regions I and II separated by surface S, an expression is derived for the
expectation value of H which makes explicit reference to a trial function
defined in I alone, with all details of region II replaced by an effective
potential acting on S and which is related to the Green function of region II.
Stationary solutions provide approximations to the eigenstates of H within I.
The Green function for the embedded Hamiltonian is equal to the Green function
for the entire system in region I. Application of the method is illustrated for
the problem of a hydrogen atom in a spherical cavity and an Au(001)/Ag/Au(001)
sandwich structure using basis sets that satisfy kinetic balance.Comment: 16 pages, 5 figure
Electrons in a ferromagnetic metal with a domain wall
We present theoretical description of conduction electrons interacting with a
domain wall in ferromagnetic metals. The description takes into account
interaction between electrons. Within the semiclassical approximation we
calculate the spin and charge distributions, particularly their modification by
the domain wall. In the same approximation we calculate local transport
characteristics, including relaxation times and charge and spin conductivities.
It is shown that these parameters are significantly modified near the wall and
this modification depends on electron-electron interaction.Comment: 10 pages with 4 figure
An In-Depth Spectroscopic Analysis of the Blazhko Star RR Lyr. I. Characterisation of the star: abundance analysis and fundamental parameters
The knowledge of accurate stellar parameters is a keystone in several fields
of stellar astrophysics, such as asteroseismology and stellar evolution.
Although the fundamental parameters can be derived both from spectroscopy and
multicolour photometry, the results obtained are sometimes affected by
systematic uncertainties. In this paper, we present a self-consistent spectral
analysis of the pulsating star RR Lyr, which is the primary target for our
study of the Blazhko effect. We used high-resolution and high signal-to-noise
ratio spectra to carry out a consistent parameter determination and abundance
analysis for RR Lyr. We provide a detailed description of the methodology
adopted to derive the fundamental parameters and the abundances. Stellar
pulsation attains high amplitudes in RR Lyrae stars, and as a consequence the
stellar parameters vary significantly over the pulsation cycle. The abundances
of the star, however, are not expected to change. From a set of available
high-resolution spectra of RR Lyr we selected the phase of maximum radius, at
which the spectra are least disturbed by the pulsation. Using the abundances
determined at this phase as a starting point, we expect to obtain a higher
accuracy in the fundamental parameters determined at other phases. The set of
fundamental parameters obtained in this work fits the observed spectrum
accurately. Through the abundance analysis, we find clear indications for a
depth-dependent microturbulent velocity, that we quantified. We confirm the
importance of a consistent analysis of relevant spectroscopic features,
application of advanced model atmospheres, and the use of up-to-date atomic
line data for the determination of stellar parameters. These results are
crucial for further studies, e.g., detailed theoretical modelling of the
observed pulsations.Comment: 12 pages, accepted for publication in Astronomy & Astrophysic
Energy Levels and Transition Probabilities for Nitrogen-Like Fe xx
Energies of the 700 lowest levels in Fexx have been obtained using the multiconfiguration Dirac-Fock method. Configuration interaction method on the basis set of transformed radial orbitals with variable parameters taking into account relativistic corrections in the Breit-Pauli approximation was used to crosscheck our presented results. Transition probabilities, oscillator and line strengths are presented for electric dipole (E1), electric quadrupole (E2) and magnetic dipole (M1) transitions among these levels. The total radiative transition probabilities from each level are also provided. Results are compared with data compiled by NIST and with other theoretical work
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