15,765 research outputs found
A transceiver module of the Mu radar
The transceiver (TR) module of a middle and upper atmospheric radar is described. The TR module used in the radar is mainly composed of two units: a mixer (MIX unit) and a power amplifier (PA unit). The former generates the RF wave for transmission and converts the received echo to the IF signal. A 41.5-MHz local signal fed to mixers passes through a digitally controlled 8-bit phase shifter which can change its value up to 1,000 times in a second, so that the MU radar has the ability to steer its antenna direction quickly and flexibly. The MIX unit also contains a buffer amplifier and a gate for the transmitting signal and preamplifier for the received one whose noise figure is less than 5 dB. The PA unit amplifies the RF signal supplied from the MIX unit up to 63.7 dBm (2350 W), and feeds it to the crossed Yagi antenna
Quantum Larmor radiation in conformally flat universe
We investigate the quantum effect on the Larmor radiation from a moving
charge in an expanding universe based on the framework of the scalar quantum
electrodynamics (SQED). A theoretical formula for the radiation energy is
derived at the lowest order of the perturbation theory with respect to the
coupling constant of the SQED. We evaluate the radiation energy on the
background universe so that the Minkowski spacetime transits to the Milne
universe, in which the equation of motion for the mode function of the free
complex scalar field can be exactly solved in an analytic way. Then, the result
is compared with the WKB approach, in which the equation of motion of the mode
function is constructed with the WKB approximation which is valid as long as
the Compton wavelength is shorter than the Hubble horizon length. This
demonstrates that the quantum effect on the Larmor radiation of the order
e^2\hbar is determined by a non-local integration in time depending on the
background expansion. We also compare our result with a recent work by Higuchi
and Walker [Phys. Rev. D80 105019 (2009)], which investigated the quantum
correction to the Larmor radiation from a charged particle in a
non-relativistic motion in a homogeneous electric field.Comment: 12 pages, 4 figure, accepted for publication in Physical Review
NMR evidence for a strong modulation of the Bose-Einstein Condensate in BaCuSiO
We present a Cu and Si NMR study of the quasi-2D coupled
spin 1/2 dimer compound BaCuSiO in the magnetic field range 13-26 T and
at temperatures as low as 50 mK. NMR data in the gapped phase reveal that below
90 K different intra-dimer exchange couplings and different gaps
( = 1.16) exist in every second plane along
the c-axis, in addition to a planar incommensurate (IC) modulation. Si
spectra in the field induced magnetic ordered phase reveal that close to the
quantum critical point at = 23.35 T the average boson density
of the Bose-Einstein condensate is strongly modulated along the
c-axis with a density ratio for every second plane
. An IC modulation of the local
density is also present in each plane. This adds new constraints for the
understanding of the 2D value = 1 of the critical exponent describing
the phase boundary
Cosmic-Ray Ionization Rate in Protoplanetary Disks with Sheared Magnetic Fields
We investigate the effects of magnetic-field configurations on the ionization rate by cosmic rays in protoplanetary disks. First, we consider cosmic-ray propagation from the interstellar medium (ISM) to the protoplanetary disks and showed that the cosmic-ray density around the disk should be 2 times lower than the ISM value. Then, we compute the attenuation of cosmic rays in protoplanetary disks. The magnetic fields in the disk are stretched to the azimuthal directions, and cosmic rays need to detour while propagating to the midplane. Our results show that the detouring effectively enhances the column density by about two orders of magnitude. We employ a typical ionization rate by cosmic rays in diffuse ISM, which is considered too high to be consistent with observations of protoplanetary disks, and find that the cosmic rays are significantly shielded at the midplane. In the case of the disk around IM Lup, the midplane ionization rate is very low for r ≲ 100 au, while the value is as large as a diffuse ISM in the outer radii. Our results are consistent with the recent Atacama Large Millimeter/submillimeter Array observation that indicates the radial gradient in the cosmic-ray ionization rate. The high ionization rate in the outer radii of disks may activate the magnetorotational instability that was thought to be suppressed due to ambipolar diffusion. These results will have a strong influence on the dynamical and chemical evolutions of protoplanetary disks
Phase diagram of Nambu-Jona-Lasinio model with dimensional regularization
We investigate the phase diagram on temperature-chemical potential plane in
the Nambu-Jona-Lasinio model with the dimensional regularization. While the
structure of the resulting diagram shows resemblance to the one in the
frequently used cutoff regularization, some results of our study indicate
striking difference between these regularizations. The diagram in the
dimensional regularization exhibits strong tendency of the first order phase
transition.Comment: 9 pages, 9 figure
Existence of Heavy Fermions in the Antiferromagnetic Phase of CeIn3
We report the pressure-dependent optical conductivity spectra of a heavy
fermion (HF) compound CeIn3 below the Neel temperature of 10 K to investigate
the existence of the HF state in the antiferromagnetic (AFM) phase. The peak
due to the interband transition in the hybridization gap between the conduction
band and nearly localized 4f states (c-f hybridization) appears at the photon
energy of about 20 meV not only in the HF regime but also in the AFM regime.
Both the energy and intensity of the c-f hybridization peak continuously
increase with the application of pressure from the AFM to the HF regime. This
result suggests that the c-f hybridization, as well as the heavy fermions,
exists even in the AFM phase of CeIn3.Comment: 5 pages, 3 figure
Roles of Bond Alternation in Magnetic Phase Diagram of RMnO3
In order to investigate nature of the antiferromagnetic structures in
perovskite RMnO3, we study a Heisenberg J1-J2 model with bond alternation using
analytical and numerical approaches. The magnetic phase diagram which includes
incommensurate spiral states and commensurate collinear states is reproduced.
We discuss that the magnetic structure with up-up-down-down spin configuration
(E-type structure) and the ferroelectricity emerge cooperatively to stabilize
this phase. Magnetoelastic couplings are crucial to understand the magnetic and
electric phase diagram of RMnO3.Comment: 5 pages, 6 figure
D Numerical Simulation of Sediment Transport around Spurdikes under Various Installation Conditions
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
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