7,977 research outputs found
On Rotation Curve Analysis
An analysis of analytical methods used for computing galactic masses on the
basis of rotation curves (Saari 2015) is shown to be flawed
Josephson Plasma Resonance in Solid and Glass Phases of BiSrCaCuO
Vortex matter phases and phase transitions are investigated by means of
Josephson plasma resonance in under-doped BiSrCaCuO
single crystals in a microwave frequency range between 19 and 70 GHz.
Accompanied by the vortex lattice melting transition, a jump of the interlayer
phase coherence extracted from the field dependence of the plasma frequency was
observed. In the solid phase, the interlayer coherence little depends on field
at a temperature region well below while it gradually decreases as field
increases toward the melting line up to just below . As a result, the
magnitude of the jump decreases with increasing temperature and is gradually
lost in the vicinity of . This indicates that the vortex lines formed in
the vortex solid phase are thermally meandering and the phase transition
becomes weak especially just below .Comment: 5pages and 4 figures. Submitted to Physica C (Proceedings of
Plasma2000, Sendai
Superconducting Plasma Excitation at Microwave Frequencies in Parallel Magnetic Fields in
Josephson plasma resonance has been studied in a wide microwave frequency
range between 10 and 52 GHz in a magnetic field parallel to the -plane in
under-doped \BI. Above about 30 GHz two resonance modes were observed: one
(LT mode) appears at low temperatures and another (HT mode) at higher
temperatures, leaving a temperature gap between two regions. These two
resonance modes exhibit a sharp contrast each other both on temperture and
magnetic field dependences and show distinct characters different entirely from
the c-axis Josephson plasma resonance. From temperature and field scan
experiments at various frequencies it is suggested that the LT mode can be
attributed to the coupled Josephson plasma mode with Josephson vortices, while
the HT mode is a new plasma mode associated possibly with the periodic array of
Josephson vortices.Comment: submitted to Physica C (Prceedings of Plasma2000, Sendai
Radiation from a Josephson STAR-emitter
We calculate the angular dependence of the radiation-zone output power and
electric polarization of stimulated terahertz amplified radiation (STAR)
emitted from a voltage applied across cylindrical and rectangular stacks
of intrinsic Josephson junctions. During coherent emission, a spatially uniform
Josephson current density in the stack acts as a surface electric current
density antenna source, leading to an harmonic radiation frequency spectrum, as
in experiment, but absent in all cavity modesl of cylindrical mesas. Spatial
fluctuations of the Josephson current cause its fundamental mode to lock
onto the lowest finite energy cylindrical cavity mode, causing it to resonate,
leading to a non-uniform magnetic surface current density radiation source, and
a non-trivial combined fundamental frequency output power with linear
polarization We also present a model of the superconducting substrate, and
present results for rectangular mesas.Comment: 18 pages, 26 figures, submitted to PR
Two Phase Collective Modes in Josephson Vortex Lattice in Intrinsic Josephson Junction BiSrCaCuO
Josephson plasma excitations in the high superconductor
BiSrCaCuO have been investigated in a wide microwave
frequency region (9.8 -- 75 GHz), in particular, in magnetic field applied
parallel to the plane of the single crystal. In sharp contrast to the case
for magnetic fields parallel to the c axis or tilted from the plane, it
was found that there are two kinds of resonance modes, which are split in
energy and possess two distinctly different magnetic field dependences. One
always lies higher in energy than the other and has a shallow minimum at about
0.8 kOe, then increases linearly with magnetic field. On the other hand,
another mode begins to appear only in a magnetic field (from a few kOe and
higher) and has a weakly decreasing tendency with increasing magnetic field. By
comparing with a recent theoretical model the higher energy mode can naturally
be attributed to the Josephson plasma resonance mode propagating along the
primitive reciprocal lattice vector of the Josephson vortex lattice, whereas
the lower frequency mode is assigned to the novel phase collective mode of the
Josephson vortex lattice, which has never been observed before.Comment: 11 pages and 10 figure
Spectroscopy of Ultra-diffuse Galaxies in the Coma Cluster
We present spectra of 5 ultra-diffuse galaxies (UDGs) in the vicinity of the
Coma Cluster obtained with the Multi-Object Double Spectrograph on the Large
Binocular Telescope. We confirm 4 of these as members of the cluster,
quintupling the number of spectroscopically confirmed systems. Like the
previously confirmed large (projected half light radius 4.6 kpc) UDG, DF44,
the systems we targeted all have projected half light radii kpc. As
such, we spectroscopically confirm a population of physically large UDGs in the
Coma cluster. The remaining UDG is located in the field, about Mpc behind
the cluster. We observe Balmer and Ca II H \& K absorption lines in all of our
UDG spectra. By comparing the stacked UDG spectrum against stellar population
synthesis models, we conclude that, on average, these UDGs are composed of
metal-poor stars ([Fe/H] ). We also discover the first UDG with
[OII] and [OIII] emission lines within a clustered environment, demonstrating
that not all cluster UDGs are devoid of gas and sources of ionizing radiation.Comment: 5 pages, 4 figure
Dimensional Crossover in Heavy Fermions
Recently we have shown that a one-parameter scaling, the Coherence
Temperature, describes the physical behavior of several heavy fermions in a
region of their phase diagram. In this paper we fully characterize this region,
obtaining the uniform susceptibility, the resistivity and the specific heat.
This allows for an explicit evaluation of the Wilson and the Kadowaki-Woods
ratios in this regime. These quantities turn out to be independent of the
distance to the critical point. The theory of the one-parameter scaling
corresponds to a zero dimensional approach. Although spatial correlations are
irrelevant in this case, time fluctuations are critically correlated and the
quantum hyperscaling relation is satisfied for . The crossover from
to is smooth. It occurs at a lenght scale which is inversely related to
the stiffness of the lifetime of the spin fluctuations.Comment: 4 pages, revtex, no figures, submitted to Physical Review
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