13,429 research outputs found
Instrumentation of a high-sensitivity microwave vector detection system for low-temperature applications
We present the design and the circuit details of a high-sensitivity microwave
vector detection system, which is aiming for studying the low-dimensional
electron system embedded in the slots of a coplanar waveguide at low
temperatures. The coplanar waveguide sample is placed inside a phase-locked
loop; the phase change of the sample may cause a corresponding change in the
operation frequency, which can be measured precisely. We also employ a
double-pulse modulation on the microwave signals, which comprises a fast pulse
modulation for gated averaging and a slow pulse modulation for lock-in
detection. In measurements on real samples at low temperatures, this system
provides much better resolutions in both amplitude and phase than most of the
conventional vector analyzers at power levels below -65 dBm.Comment: 7 pages, 11 figures, 1 table, lette
New PbSnTe heterojunction laser diode structures with improved performance
Several recent advances in the state-of-the-art of lead tin telluride double heterojunction laser diodes are summarized. Continuous Wave operation to 120 K and pulsed operation to 166 K with single, lowest order transverse mode emission to in excess of four times threshold at 80 K were achieved in buried stripe lasers fabricated by liquid phase epitaxy in the lattice-matched system, lead-tin telluride-lead telluride selenide. At the same time, liquid phase epitaxy was used to produce PbSnTe distributed feedback lasers with much broader continuous single mode tuning ranges than are available from Fabry-Perot lasers. The physics and philosophy behind these advances is as important as the structures and performance of the specific devices embodying the advances, particularly since structures are continually being evolved and the performance continues to be improved
Investigation of nonlinear interaction phenomena in the ionosphere
Ionospheric phenomena as thermal radiation noise, propagation of naturally occurring radio noise through ionosphere, and generation of very low frequency emission
Dispersion Relations for a Magnetoactive Finite Temperature Plasma
Equations for dispersion relations of magnetoactive finite temperature plasm
Effect of Electrostatic Fields on the Propagation of Electromagnetic Waves in a Finite Temperature Magnetoactive Plasma
Electrostatic field effect on propagation of electromagnetic waves in finite temperature magnetoactive plasm
Study of HST counterparts to Chandra X-ray sources in the Globular Cluster M71
We report on archival Hubble Space Telescope (HST) observations of the
globular cluster M71 (NGC 6838). These observations, covering the core of the
globular cluster, were performed by the Advanced Camera for Surveys (ACS) and
the Wide Field Planetary Camera 2 (WFPC2). Inside the half-mass radius (r_h =
1.65') of M71, we find 33 candidate optical counterparts to 25 out of 29
Chandra X-ray sources while outside the half-mass radius, 6 possible optical
counterparts to 4 X-ray sources are found. Based on the X-ray and optical
properties of the identifications, we find 1 certain and 7 candidate
cataclysmic variables (CVs). We also classify 2 and 12 X-ray sources as certain
and potential chromospherically active binaries (ABs), respectively. The only
star in the error circle of the known millisecond pulsar (MSP) is inconsistent
with being the optical counterpart. The number of X-ray faint sources with
L_x>4x10^{30} ergs/s (0.5-6.0 keV) found in M71 is higher than extrapolations
from other clusters on the basis of either collision frequency or mass. Since
the core density of M71 is relatively low, we suggest that those CVs and ABs
are primordial in origin.Comment: 12 pages, 6 figures. Accepted for publication in Astronomy and
Astrophysic
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