National Space Development Agency of Japan

About: National Space Development Agency of Japan is a based out in . It is known for research contribution in the topics: Satellite & Communications satellite. The organization has 944 authors who have published 1111 publications receiving 18958 citations. The organization is also known as: National Space Development Agency of Japan & NASDA.

A Radiation Hydrodynamic Model for Protostellar Collapse. II. The Second Collapse and the Birth of a Protostar

Abstract: We carry out radiation hydrodynamic calculations to study physical processes in the formation of a 1 M☉ protostar. Following our previous work, calculations pursue the whole evolution from the beginning of the first collapse to the end of the main accretion phase. The adiabatic core formed after the initial collapse (i.e., the first core) experiences further gravitational collapse triggered by dissociation of molecular hydrogen, which leads to the formation of the second core, i.e., the birth of a protostar. The protostar grows in mass as accreting the infalling material from the circumstellar envelope, while the protostar keeps its radius at ~4 R☉ during the main accretion phase. These typical features in the evolution are in good agreement with previous studies. We consider two different initial conditions for the density distribution: homogeneous and hydrostatic cloud cores with the same central density of 1.415 × 10-19 g cm-3 . The homogeneous core has the total mass of 1 M☉ while the hydrostatic core has 3.852 M☉. For the initially homogeneous model, the accretion luminosity rapidly rises to the maximum value of 25 L☉ just after the birth of a protostar, and declines gradually as the mass accretion rate decreases. In contrast, the luminosity increases monotonically with time for the initially hydrostatic model. This difference arises because the mass accretion rate varies depending on the inward acceleration at the initial stage, which affects the luminosity curve. A less massive hydrostatic core would possess the similar properties in the luminosity curve to the 3.852 M☉ case, because a hydrostatic cloud core with mass lower than 3.852 M☉ can be shown to provide a smaller mass accretion rate after the birth of a protostar and a more gradual rise in the luminosity curve. Our numerical code is designed to provide the evolution of the spectral energy distribution (SED) along with the dynamical evolution in our spherically symmetric calculations. We confirm that the SED evolves from a 10 K graybody spectrum to hotter spectra typical for class I and flat spectrum sources. The SED for the class 0 sources corresponds to the age of 2 × 104 yr, which is smaller by an order of magnitude than the typical age of class I objects. Considering possible nonspherically symmetric effects, we suggest that observed class 0 sources should consist of the "genuine" class 0 objects, which are as young as 104 yr, and more evolved protostars on edge-on view ("class 0-like class I" objects). The contamination of edge-on class I objects into class 0 sources are not negligible because they are more abundant than genuine class 0 objects. Since observations indicate that the class 0 sources are typically more luminous than class I sources, the initially hydrostatic model, where the luminosity increases monotonically with time, does not match the observations. The initially homogeneous model, in contrast, shows a tendency consistent with the observations. Compiling our results and other theoretical and observational evidence, we illustrate an evolutionary picture of protostar formation. In terms of the evolutionary time and the inclination to an observer, we find that protostellar objects are clearly categorized.

The Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E), NASDA's contribution to the EOS for global energy and water cycle studies

Abstract: The Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) was developed and provided to the National Aeronautics and Space Administration's EOS Aqua satellite by the National Space Development Agency of Japan, as one of the indispensable instruments for Aqua's mission. AMSR-E is a modified version of AMSR that was launched December 2002 aboard the Advanced Earth Observing Satellite-II (ADEOS-II). It is a six-frequency dual-polarized total-power passive microwave radiometer that observes water-related geophysical parameters supporting global change science and monitoring efforts. The hardware improvements over existing spaceborne microwave radiometers for Earth imaging include the largest main reflector of its kind and addition of 6.925-GHz channels. These improvements provide finer spatial resolution and the capability to retrieve sea surface temperature and soil moisture information on a global basis. This paper provides an overview of the instrument characteristics, mission objectives, and data products.

Evidence of Chemical Bonding at Biomaterial-Hard Tissue Interfaces:

Abstract: For many years, glass-polyalkenoate cements have been described as possessing the unique properties of self-adherence to human hard tissues, such as bones or teeth. However, direct experimental evidence to prove the existence of chemical bonding has not been advanced. X-ray Photoelectron Spectroscopy (XPS) was used to analyze the chemical interaction of a synthesized polyalkenoic acid with enamel and synthetic hydroxyapatite. For both enamel and hydroxyapatite, the peak representing the carboxyl groups of the polyalkenoic acid was detected to have significantly shifted to a lower binding energy. De-convolution of this shifted peak disclosed two components with a peak representing unreacted carboxyl groups and a peak suggesting chemical bonding to hydroxyapatite. On average, 67.5% of the carboxyl groups of the polyalkenoic acid were measured to have bonded to hydroxyapatite. XPS of hydroxyapatite also disclosed its surface to be enriched in calcium and decreased in phosphorus, indicating that phosphorus was extracted at a relatively higher rate than calcium. Analysis of these data supports the mechanism in which carboxylic groups replace phosphate ions (PO4(3-)) of the substrate and make ionic bonds with calcium ions of hydroxyapatite. It is concluded that an ultrathin layer of a polyalkenoic acid can be prepared on a hydroxyapatite-based substrate by careful removal of non-bonded molecules. With this specimen-processing method, XPS not only provided direct evidence of chemical bonding, but also enabled us to quantify the percentages of functional groups of the polyalkenoic acids that bonded to calcium of hydroxyapatite.

Development of precipitation radar onboard the Tropical Rainfall Measuring Mission (TRMM) satellite

Abstract: The precipitation radar (PR) onboard the Tropical Rainfall Measuring Mission (TRMM) satellite is the first spaceborne radar to measure precipitation from space. The PR, operating at 13.8 GHz, is a 128-element active phased array that allows a fast and sophisticated cross-track scanning over a swath width of 215 km with a cross-range spatial resolution of about 4.3 km. The PR has a minimum detectable rain rate of 0.5 mm/h with range resolution of 250 m. In order to achieve a reliable and accurate rain echo data for three years mission life, functions for internal and external calibrations are implemented. Through a series of PR flight-model tests on the ground and an initial checkout just after the TRMM launch, it is confirmed that the PR functions properly and meets the performance requirements to quantitatively measure three-dimensional (3D) precipitation distribution from space.

Study of the X-Ray Background Spectrum and its Large-Scale Fluctuation with ASCA

Abstract: We studied the energy spectrum and the large-scale fluctuation of the X-ray background with the ASCA GIS instrument based on the ASCA Medium Sensitivity Survey and Large Sky Survey observations. A total of 91 fields with Galactic latitude |b|> 10◦ were selected with a sky coverage of 50 deg2 and 4.2 Ms of exposure. For each field, non-X-ray events were carefully subtracted and sources brighter than ∼ 2× 10−13 erg cm−2 s−1 (2–10 keV) were eliminated. Spectral fits with a single power-law model for the individual 0.7–10 keV spectra showed a significant excess below ∼ 2 keV, which could be expressed by an additional thermal model with kT 0.4 keV or a steep power-law model with a photon index of Γsoft 6. The 0.5–2 keV intensities of the soft thermal component varied significantly from field to field by 1σ =52+4 −5%, and showed a maximum toward the Galactic Center. This component is considered to be entirely Galactic. As for the hard power-law component, an average photon index of 91 fields was obtained to be Γhard = 1.412± 0.007± 0.025 and the average 2–10 keV intensity was calculated as F hard X = (6.38± 0.04± 0.64)× 10−8 erg cm−2 s−1 sr−1 (1σ statistical and systematic errors). The Galactic component is marginally detected in the hard band. The 2–10 keV intensities show a 1σ deviation of 6.49+0.56 −0.61%, while deviation due to the reproducibility of the particle background is 3.2%. The observed deviation can be explained by the Poisson noise of the source count in the f.o.v. (∼ 0.5deg), even assuming a single logN–logS relation on the whole sky. Based on the observed fluctuation and the absolute intensity, an acceptable region of the logN– logS relation was derived, showing a consistent feature with the recent Chandra and XMM-Newton results. The fluctuation of the spectral index was also examined; it implied a large amount of hard sources and a substantial variation in the intrinsic source spectra (ΓS 1.1± 1.0).