31 research outputs found
Higher order contributions to Rashba and Dresselhaus effects
We have developed a method to systematically compute the form of Rashba- and
Dresselhaus-like contributions to the spin Hamiltonian of heterostructures to
an arbitrary order in the wavevector k. This is achieved by using the double
group representations to construct general symmetry-allowed Hamiltonians with
full spin-orbit effects within the tight-binding formalism. We have computed
full-zone spin Hamiltonians for [001]-, [110]- and [111]-grown zinc blende
heterostructures (D_{2d},C_{4v},C_{2v},C_{3v} point group symmetries), which
are commonly used in spintronics. After an expansion of the Hamiltonian up to
third order in k, we are able to obtain additional terms not found previously.
The present method also provides the matrix elements for bulk zinc blendes
(T_d) in the anion/cation and effective bond orbital model (EBOM) basis sets
with full spin-orbit effects.Comment: v1: 11 pages, 3 figures, 8 table
The ACOS CO_2 retrieval algorithm – Part 1: Description and validation against synthetic observations
This work describes the NASA Atmospheric CO_2 Observations from Space (ACOS) X_(CO_2) retrieval algorithm, and its performance on highly realistic, simulated observations. These tests, restricted to observations over land, are used to evaluate retrieval errors in the face of realistic clouds and aerosols, polarized non-Lambertian surfaces, imperfect meteorology, and uncorrelated instrument noise. We find that post-retrieval filters are essential to eliminate the poorest retrievals, which arise primarily due to imperfect cloud screening. The remaining retrievals have RMS errors of approximately 1 ppm. Modeled instrument noise, based on the Greenhouse Gases Observing SATellite (GOSAT) in-flight performance, accounts for less than half the total error in these retrievals. A small fraction of unfiltered clouds, particularly thin cirrus, lead to a small positive bias of ~0.3 ppm. Overall, systematic errors due to imperfect characterization of clouds and aerosols dominate the error budget, while errors due to other simplifying assumptions, in particular those related to the prior meteorological fields, appear small
Avaliação da resistência ao cisalhamento da união entre duas ligas a base de CoCr e uma cerâmica
INTRODUCTION: Based on the importance of the integrity of the metal/ceramic interface, the purpose of this work was to
evaluate the shear bond strength of the metal-ceramic union of two Co-Cr alloys (Wirobond C, Bego; Remanium 2000, Dentaurum)
combined with Omega 900 ceramic (Vita Zahnfabrik). MATERIAL and METHOD: Eleven cylindrical matrixes were made for
each alloy, and the metallic portion was obtained with the lost wax casting technique with standardized waxing of 4mm of height
and of 4mm of diameter. The ceramic was applied according to the manufacturer’s recommendations with the aid of a teflon
matrix that allowed its dimension to be standardized in the same size as the metallic portion. The specimens were submitted to
the shear bond test in an universal testing machine (EMIC), with the aid of a device developed for such intention, and constant
speed of 0.5mm/min. RESULTS and CONCLUSIONS: The mean resistance was 48.387MPa for Wirobond C alloy, with standard
deviation of 17.718, and 55.956MPa for Remanium 2000, with standard deviation of 17.198. No statistically significant difference
was observed between the shear strength of the two metal-ceramic alloys. ______________________________________________________________________________________________________________ RESUMOINTRODUÇÃO: Baseados na importância da integridade da interface metal-cerâmica, este trabalho tem como objetivo
avaliar a resistência ao cisalhamento da união metal-cerâmica de duas ligas de Co-Cr (Wirobond C, Bego; Remanium 2000,
Dentaurum) combinadas com a cerâmica Omega 900 (Vita Zahnfabrik). MATERIAIS E MÉTODOS: Foram confeccionados 11
corpos-de-prova cilÃndricos para cada liga utilizada, sendo que a porção metálica foi obtida por fundição pela técnica da cera
perdida, através de enceramentos padronizados com 4mm de altura por 4mm de diâmetro. A aplicação da cerâmica foi realizada
segundo recomendações do fabricante, com auxÃlio de uma matriz de teflon que permitia sua padronização com as mesmas
dimensões da porção metálica. Os corpos-de-prova foram submetidos ao ensaio de resistência ao cisalhamento em máquina de
ensaios universal (EMIC), com auxÃlio de dispositivo desenvolvido para tal propósito, sob velocidade constante de 0,5mm/
min. RESULTADOS E CONCLUSÕES: As médias de resistência obtidas foram 48,387 MPa para a liga Wirobond C, com desvio
padrão de 17,718, e 55,956 MPa para a Remanium 2000, com desvio padrão de 17,198. Após análise de variância foi possÃvel
observar que não há diferença estatisticamente significante entre os valores de resistência ao cisalhamento das duas ligas
metalocerâmicas
Improved retrievals of carbon dioxide from Orbiting Carbon Observatory-2 with the version 8 ACOS algorithm
Since September 2014, NASA's Orbiting Carbon Observatory-2 (OCO-2)
satellite has been taking measurements of reflected solar spectra and using
them to infer atmospheric carbon dioxide levels. This work provides details
of the OCO-2 retrieval algorithm, versions 7 and 8, used to derive the
column-averaged dry air mole fraction of atmospheric CO2
(XCO2) for the roughly 100 000Â cloud-free measurements recorded
by OCO-2 each day. The algorithm is based on the Atmospheric Carbon
Observations from Space (ACOS) algorithm which has been applied to
observations from the Greenhouse Gases Observing SATellite (GOSAT) since
2009, with modifications necessary for OCO-2. Because high accuracy,
better than 0.25 %, is required in order to accurately infer carbon
sources and sinks from XCO2, significant errors and regional-scale
biases in the measurements must be minimized. We discuss efforts to filter
out poor-quality measurements, and correct the remaining good-quality
measurements to minimize regional-scale biases. Updates to the radiance
calibration and retrieval forward model in version 8 have improved many
aspects of the retrieved data products. The version 8 data appear to have
reduced regional-scale biases overall, and demonstrate a clear improvement
over the version 7 data. In particular, error variance with respect to TCCON
was reduced by 20 % over land and 40 % over ocean between versions 7
and 8, and nadir and glint observations over land are now more consistent.
While this paper documents the significant improvements in the ACOS
algorithm, it will continue to evolve and improve as the CO2 data
record continues to expand.</p
Profile of patients with Baggio-Yoshinari Syndrome admitted at "Instituto de Infectologia Emilio Ribas"
Analysis of Saturn’s thermal emission at 2.2-cm wavelength: Spatial distribution of ammonia vapor
This work focuses on determining the latitudinal structure of ammonia vapor in Saturn’s cloud layer near 1.5 bars using the brightness temperature maps derived from the Cassini RADAR (Elachi et al. [2004], Space Sci. Rev. 115, 71–110) instrument, which works in a passive mode to measure thermal emission from Saturn at 2.2-cm wavelength. We perform an analysis of five brightness temperature maps that span epochs from 2005 to 2011, which are presented in a companion paper by Janssen et al. (Janssen, M.A., Ingersoll, A.P., Allison, M.D., Gulkis, S., Laraia, A.L., Baines, K., Edgington, S., Anderson, Y., Kelleher, K., Oyafuso, F. [2013]. Icarus, this issue). The brightness temperature maps are representative of the spatial distribution of ammonia vapor, since ammonia gas is the only effective opacity source in Saturn’s atmosphere at 2.2-cm wavelength. Relatively high brightness temperatures indicate relatively low ammonia relative humidity (RH), and vice versa. We compare the observed brightness temperatures to brightness temperatures computed using the Juno atmospheric microwave radiative transfer (JAMRT) program which includes both the means to calculate a tropospheric atmosphere model for Saturn and the means to carry out radiative transfer calculations at microwave frequencies. The reference atmosphere to which we compare has a 3× solar deep mixing ratio of ammonia (we use 1.352 × 10^(−4) for the solar mixing ratio of ammonia vapor relative to H_2; see Atreya [2010]. In: Galileo’s Medicean Moons – Their Impact on 400 years of Discovery. Cambridge University Press, pp. 130–140 (Chapter 16)) and is fully saturated above its cloud base. The maps are comprised of residual brightness temperatures—observed brightness temperature minus the model brightness temperature of the saturated atmosphere.
The most prominent feature throughout all five maps is the high brightness temperature of Saturn’s subtropical latitudes near ±9° (planetographic). These latitudes bracket the equator, which has some of the lowest brightness temperatures observed on the planet. The observed high brightness temperatures indicate that the atmosphere is sub-saturated, locally, with respect to fully saturated ammonia in the cloud region. Saturn’s northern hemisphere storm was also captured in the March 20, 2011 map, and is very bright, reaching brightness temperatures of 166 K compared to 148 K for the saturated atmosphere model. We find that both the subtropical bands and the 2010–2011 northern storm require very low ammonia RH below the ammonia cloud layer, which is located near 1.5 bars in the reference atmosphere, in order to achieve the high brightness temperatures observed. The disturbances in the southern hemisphere between −42° and −47° also require very low ammonia RH at levels below the ammonia cloud base. Aside from these local and regional anomalies, we find that Saturn’s atmosphere has on average 70 ± 15% ammonia relative humidity in the cloud region. We present three options to explain the high 2.2-cm brightness temperatures. One is that the dryness, i.e., the low RH, is due to higher than average atmospheric temperatures with constant ammonia mixing ratios. The second is that the bright subtropical bands represent dry zones created by a meridionally overturning circulation, much like the Hadley circulation on Earth. The last is that the drying in both the southern hemisphere storms and 2010–2011 northern storm is an intrinsic property of convection in giant planet atmospheres. Some combination of the latter two options is argued as the likely explanation