2,079 research outputs found
Nonexponential Relaxations in a Two-Dimensional Electron System in Silicon
The relaxations of conductivity have been studied in a strongly disordered
two-dimensional (2D) electron system in Si after excitation far from
equilibrium by a rapid change of carrier density n_s at low temperatures T. The
dramatic and precise dependence of the relaxations on n_s and T strongly
suggests (a) the transition to a glassy phase as T->0, and (b) the Coulomb
interactions between 2D electrons play a dominant role in the observed
out-of-equilibrium dynamics.Comment: 5 pages, 5 figure
Kinematic differences between NLS1 and BLAGN sources
It is well-known that the higher policyclic aromatic hydrocarbon (PAH)
abundance, lower black hole mass, higher accretion rate and lower luminosities
are among the major characteristics of Narrow-Line Seyfert galaxies (NLS1),
when they are compared to Broad line Seyfert galaxies (BLS1). NLS1s may be
normal Seyfert galaxies at an early stage of evolution, their black holes may
still be growing and/or they could be special for some other reason. In this
work we discuss the findings that NLS1s have most of line and continuum
luminosities correlated with FWHM(H), which may be the trace of their
rapid black hole mass grow. BLS1 do not show such trends. Also, PAHs may be
destroyed as the black hole grows and the starbursts are removed, for NLS1
objects.Comment: Revisiting narrow-line Seyfert 1 galaxies and their place in the
Universe - NLS1 Padov
Photo-centric variability of quasars caused by variations in their inner structure: Consequences on Gaia measurements
We study the photocenter position variability due to variations in the quasar
inner structure. We consider variability in the accretion disk emissivity and
torus structure variability due to different illumination by the central
source. We discuss possible detection of these effects by Gaia. Observations of
the photocenter variability in two AGNs, SDSS J121855+020002 and SDSS
J162011+1724327 have been reported and discussed. With investigation of the
variations in the quasar inner structure we explore how much this effect can
affect the position determination and whether it can be (or not) detected with
Gaia mission. We used (a) a model of a relativistic disk, including the
perturbation that can increase brightness of a part of the disk, and
consequently offset the photocenter position, and (b) a model of a dusty torus
which absorbs and re-emits the incoming radiation from accretion disk. We
estimated the value of the photocenter offset due to these two effects. We
found that perturbations in the inner structure can significantly offset the
photocenter. It depends on the characteristics of perturbation and accretion
disk and structure of the torus. In the case of two considered QSOs the
observed photocenter offsets cannot be explained by variations in the accretion
disk and other effects should be considered. We discussed possibility of
exploding stars very close to the AGN source, and also possibility that there
are two variable sources in the center of these two AGNs that may indicate a
binary super-massive black hole system on a kpc (pc) scale. The Gaia mission
seems to be very perspective, not only for astrometry, but also for exploring
the inner structure of AGNs. We conclude that variations in the quasar inner
structure can affect the observed photocenter (up to several mas). There is a
chance to observe such effect in the case of bright and low-redshifted QSOs.Comment: 12 pages, 8 figures, 3 tables. Accepted for publication in Astronomy
and Astrophysics. Language improved, typos correcte
DETERMINING THE ACTUAL REDUCTION FACTOR OF DISTRIBUTION CABLE LINES WITH APPLIED CROSS-BONDING
The considered problem appears as the consequence of the fact that many metal installations surrounding power lines in urban areas are situated under the surface of the ground and cannot be visually determined or verified. This paper presents the methodological version that enables solving the problem in the case of cable lines with cross-bonding, but it can also be applied with higher accuracy to cable lines with no applied cross-bonding than the existing one. It is based on the test measurement of currents appearing in two cable line phase conductors during a simulated ground fault in the supplied HV substation. By using the here-presented methodology it is possible to put the grounding problem of high-voltage distribution substations into realistic frameworks. Its application in practice shows that the actual conditions for solving this problem are much more favorable than was considered before
Diagnostics of plasma in the ionospheric D-region: detection and study of different ionospheric disturbance types
Here we discuss our recent investigations of the ionospheric plasma by using
very low and low frequency (VLF/LF) radio waves. We give a review of how to
detect different low ionospheric reactions (sudden ionospheric disturbances) to
various terrestrial and extra-terrestrial events, show their classification
according to intensity and time duration, and present some methods for their
detections in time and frequency domains. Investigations of detection in time
domain are carried out for intensive long-lasting perturbations induced by
solar X-ray flares and for short-lasting perturbations caused by gamma ray
bursts. We also analyze time variations of signals used in the low ionospheric
monitoring after earthquake events. In addition, we describe a procedure for
the detection of acoustic and gravity waves from the VLF/LF signal analysis in
frequency domain. The research of the low ionospheric plasma is based on data
collected by the VLF/LF receivers located in Belgrade, Serbia
A 100-MESFET planar grid oscillator
A 100-MESFET oscillator which gives 21 W of CW effective radiated power (ERP) with a 16-dB directivity and a 20% DC-to-RF conversion efficiency at 5 GHz is presented. The oscillator is a planar grid structure periodically loaded with transistors. The grid radiates and the devices combine quasi-optically and lock to each other. The oscillator can also be quasi-optically injection-locked to an external signal. The planar grid structure is very simple. All of the devices share the same bias, and they can be power and frequency tuned with a mirror behind the grid or dielectric slabs in front of it. An equivalent circuit for an infinite grid predicts the mirror frequency tuning. The planar property of the oscillator offers the possibility of a wafer-scale monolithically integrated source. Thousands of active solid-state devices can potentially be integrated in a high-power source for microwave or millimeter-wave applications
Mesoscopic Behavior Near a Two-Dimensional Metal-Insulator Transition
We study conductance fluctuations in a two-dimensional electron gas as a
function of chemical potential (or gate voltage) from the strongly insulating
to the metallic regime. Power spectra of the fluctuations decay with two
distinct exponents (1/v_l and 1/v_h). For conductivity , we find a third exponent (1/v_i) in the shortest samples, and
non-monotonic dependence of v_i and v_l on \sigma. We study the dependence of
v_i, v_l, v_h, and the variances of corresponding fluctuations on \sigma,
sample size, and temperature. The anomalies near
indicate that the dielectric response and screening length are critically
behaved, i.e. that Coulomb correlations dominate the physics.Comment: Revised according to referee remark
- …