42,620 research outputs found

### Outline of the Mu radar

A middle and upper atmospheric radar system is described. The antenna array consists of 25 groups each of which consists of 19 crossed-Yagis with three elements; each antenna has semiconductor transmitter and receiver, called a module, and each group of 19 antennas works as an independent small radar steering its radar beam under the control of a microcomputer. Thus, the total system consists of 25 small radars of this kind, enabling one to do various sophisticated operations with the system. The system is controlled by two other computers, one for radar controlling (HP9835A) and the other for data taking and on-line analysis (VAX11/750). The computer-controlled system is simple in operation for users and reliable in observation. Very quick beam steering (as quick as in a msec) is also possible because of electronic phase-changing of each module output under control of the microcomputer which is further controlled by the radar controller

### Japanese contributions to MAP

Japan contributed much to MAP in many branches. The MU (middle and upper atmosphere) radar, in operation during the MAP period, produced various novel possibilities in observations of middle atmosphere dynamics; possibilities which were fairly well realized. Gravity wave saturation and its spectrum in the mesosphere were observed successfully. Campaign observations by radars between Kyoto and Adelaide were especially significant in tidal and planetary wave observations. In Antarctica, middle atmosphere observation of the dramatic behavior of aerosols in winter is well elucidated together with the ozone hole. Theoretical and numerical studies have been progressing actively since a time much earlier than MAP. Now it is pointed out that gravity waves play an important role in producing the weak wind region in the stratosphere as well as the mesosphere

### The X-ray Outburst of H1743-322: High-Frequency QPOs with a 3:2 Frequency Ratio

We observed the 2003 X-ray outburst of H1743-322 in a series of 130 pointed
observation with RXTE. We searched individual observations for high-frequency
QPOs (HFQPOs) and found only weak or marginal detections near 240 and 160 Hz.
We next grouped the observations in several different ways and computed the
average power-density spectra (PDS) in a search for further evidence of HFQPOs.
This effort yielded two significant results for those observations defined by
the presence of low-frequency QPOs (0.1-20 Hz) and an absence of
``band-limited'' power continua: (1) The 9 time intervals with the highest 7-35
keV count rates yielded an average PDS with a QPO at $166 \pm 5$ Hz. ($4.1
\sigma$; 3--35 keV); and (2) a second group with lower 7-35 keV count rates (26
intervals) produced an average PDS with a QPO at $242 \pm 3$ Hz ($6.0 \sigma$;
7--35 keV). The ratio of these two frequencies is $1.46 \pm 0.05$. This finding
is consistent with results obtained for three other black hole systems that
exhibit commensurate HFQPOs in a 3:2 ratio. Furthermore, the occurrence of
H1743-322's slower HFQPO at times of higher X-ray luminosity closely resembles
the behavior of XTE J1550-564 and GRO J1655-40. We discuss our results in terms
of a resonance model that invokes frequencies set by general relativity for
orbital motions near a black-hole event horizon.Comment: 12 pages, 3 figures, submitted to Ap

### A Matrix Kato-Bloch Perturbation Method for Hamiltonian Systems

A generalized version of the Kato-Bloch perturbation expansion is presented.
It consists of replacing simple numbers appearing in the perturbative series by
matrices. This leads to the fact that the dependence of the eigenvalues of the
perturbed system on the strength of the perturbation is not necessarily
polynomial. The efficiency of the matrix expansion is illustrated in three
cases: the Mathieu equation, the anharmonic oscillator and weakly coupled
Heisenberg chains. It is shown that the matrix expansion converges for a
suitably chosen subspace and, for weakly coupled Heisenberg chains, it can lead
to an ordered state starting from a disordered single chain. This test is
usually failed by conventional perturbative approaches.Comment: 4 pages, 2 figure

### Time variability of accretion flows: effects of the adiabatic index and gas temperature

We report on next phase of our study of rotating accretion flows onto black
holes. We consider hydrodynamical (HD) accretion flows with a spherically
symmetric density distribution at the outer boundary but with spherical
symmetry broken by the introduction of a small, latitude-dependent angular
momentum. We study accretion flows by means of numerical two-dimensional,
axisymmetric, HD simulations for variety of the adiabatic index, $\gamma$ and
the gas temperature at infinity, $c_\infty$. Our work is an extension of work
done by Proga & Begelman who consider models for only $\gamma=5/3$. Our main
result is that the flow properties such as the topology of the sonic surface
and time behavior strongly depend on $\gamma$ but little on $c_\infty$. In
particular, for $1 < \gamma < 5/3$, the mass accretion rate shows large
amplitude, slow time-variability which is a result of mixing between slow and
fast rotating gas. This temporal behavior differs significantly from that in
models with \gamma\simless 5/3 where the accretion rate is relatively
constant and from that in models with \gamma\simgreat 1 where the accretion
exhibits small amplitude quasi-periodic oscillations. The key parameter
responsible for the differences is the sound speed of the accretion flow which
in turn determines whether the flow is dominated by gas pressure, radiation
pressure or rotation. Despite these differences the time-averaged mass
accretion rate in units of the corresponding Bondi rate is a weak function of
$\gamma$ and $c_\infty$.Comment: 31 pages, 14 figures, accepted for publication in ApJ, for full
resolution version goto http://users.camk.edu.pl/mmosc/ms.pd

### String tension and glueball masses of SU(2) QCD from perfect action for monopoles and strings

We study the perfect monopole action as an infrared effective theory of SU(2)
QCD. It is transformed exactly into a lattice string model. Since the monopole
interactions are weak in the infrared SU(2) QCD, the string interactions become
strong. The strong coupling expansion of string model shows the quantum
fluctuation is small. The classical string tension is estimated analytically,
and we see it is very close to the quantum one in the SU(2) QCD. We also
discuss how to calculate the glueball mass in our model.Comment: LATTICE99(Confinement), 3 pages and 1 EPS figure

### Monitoring of the MU radar antenna pattern by Satellite Ohzora (EXOS-C)

As the first attempt among MST (mesosphere stratosphere troposphere) type radars, the MU (middle and upper atmosphere) radar features an active phased array system. Unlike the conventional large VHF radars, in which output power of a large vacuum tube is distributed to individual antenna elements, each of 475 solid state power amplifier feeds each antenna element. This system configuration enables very fast beam steering as well as various flexible operations by dividing the antenna into independent subarrays, because phase shift and signal division/combination are performed at a low signal level using electronic devices under control of a computer network. The antenna beam can be switched within 10 microsec to any direction within the zenith angle of 30 deg. Since a precise phase alignment of each element is crucial to realize the excellent performance of this system, careful calibration of the output phase of each power amplifier and antenna element was carried out. Among various aircraft which may be used for this purpose artificial satellites have an advantage of being able to make a long term monitoring with the same system. An antenna pattern monitoring system for the MU radar was developed using the scientific satellite OHZORA (EXOS-C). A receiver named MUM (MU radar antenna Monitor) on board the satellite measures a CW signal of 100 to 400 watts transmitted from the MU radar. The principle of the measurement and results are discussed

### Unusual Phase Reversal of Superhumps in ER Ursae Majoris

We studied the evolution of superhumps in the peculiar SU UMa-type dwarf
nova, ER UMa. Contrary to the canonical picture of the SU UMa-type superhump
phenomena, the superhumps of ER UMa show an unexpected phase reversal during
the very early stage (~5 d after the superoutburst maximum). We interpret that
a sudden switch to so-called late superhumps occurs during the very early stage
of a superoutburst. What had been believed to be (ordinary) superhumps during
the superoutburst plateau of ER UMa were actually late superhumps. The
implication of this discovery is briefly discussed.Comment: 4 pages, 5 figures, submitted to Publ. Astron. Soc. Japa

### Relativistic Diskoseismology. I. Analytical Results for 'Gravity Modes'

We generalize previous calculations to a fully relativistic treatment of
adiabatic oscillations which are trapped in the inner regions of accretion
disks by non-Newtonian gravitational effects of a black hole. We employ the
Kerr geometry within the scalar potential formalism of Ipser and Lindblom,
neglecting the gravitational field of the disk. This approach treats
perturbations of arbitrary stationary, axisymmetric, perfect fluid models. It
is applied here to thin accretion disks. Approximate analytic eigenfunctions
and eigenfrequencies are obtained for the most robust and observable class of
modes, which corresponds roughly to the gravity (internal) oscillations of
stars. The dependence of the oscillation frequencies on the mass and angular
momentum of the black hole is exhibited. These trapped modes do not exist in
Newtonian gravity, and thus provide a signature and probe of the strong-field
structure of black holes. Our predictions are relevant to observations which
could detect modulation of the X-ray luminosity from stellar mass black holes
in our galaxy and the UV and optical luminosity from supermassive black holes
in active galactic nuclei.Comment: 31 pages, 6 figures, uses style file aaspp4.sty, prepared with the
AAS LATEX macros v4.0, significant revision of earlier submission to include
modes with axial index m>

- …