7,579 research outputs found
Microvariability in BL Lacertae : "zooming'' into the innermost blazar regions
In this work, we present the results of our multi-band microvariability study of the famous blazar BL Lac. We performed microvariablity observations of the source in the optical VRI bands for four nights in 2016. We studied the intranight flux and spectral variability of the source in detail with an objective to characterize microvariability in the blazars, a frequently observed phenomenon in blazars. The results show that the source often displays a fast flux variability with an amplitude as large as ~0.2 magnitude within a few hours, and that the color variability in the similar time scales can be characterized as “bluer-when-brighter” trend. We also observed markedly curved optical spectrum during one of the nights. Furthermore, the correlation between multi-band emission shows that in general the emission in all the bands are highly correlated; and in one of the nights V band emission was found to lead the I band emission by ~13 min. The search for characteristic timescale using z-transformed auto-correlation function and the structure function analyses reveals characteristic timescale of ~50 min in one of the R band observations. We try to explain the observed results in the context of the passage of shock waves through the relativistic outflows in blazars
Generation of Magnetic Field in the Pre-recombination Era
We study the possibility of generating magnetic fields during the evolution
of electron, proton, and photon plasma in the pre-recombination era. We show
that a small magnetic field can be generated in the second order of
perturbation theory for scalar modes with adiabatic initial conditions. The
amplitude of the field is \la 10^{-30} \rm G at the present epoch for scales
from sub-kpc to \ga 100 \rm Mpc.Comment: 8 page
Influence of field-like torque in synchronization of spin torque oscillators
The magnetization dynamics of two parallelly coupled spin torque oscillators,
destabilization of steady states and removal of multistability, are
investigated by taking into account the influence of field-like torque. It is
shown that the existence of such torque can cancel the effect of damping and
can, therefore, cause the oscillators to exhibit synchronized oscillations in
response to direct current. Further, our results show that the presence of
field-like torque enhances the power and Q-factor of the synchronized
oscillations. The validity of the above results is confirmed by numerical and
analytical studies based on the stochastic Landau-Lifshitz-Gilbert-Slonczewski
equation.Comment: 10 pages, 10 figures, Accepted for Publication in IEEE Transactions
on Magnetic
Search for quantum criticality in a ferromagnetic system UNi1-xCoxSi2
Polycrystalline samples of the isostructural alloys UNi1-xCoxSi2 (0 <= x <=
1) were studied by means of x-ray powder diffraction, magnetization, electrical
resistivity and specific heat measurements, at temperatures down to 2 K and in
magnetic fields up to 5 T. The experimental data revealed an evolution from
strongly anisotropic ferromagnetism with pronounced Kondo effect, observed for
the alloys with x < 0.98 and being gradually suppressed with rising Co-content,
to spin-glass-like states with dominant spin fluctuations, seen for the sample
with x = 0.98. Extrapolation of the value of TC(x) yields a critical
concentration xc = 1, at which the magnetic ordering entirely disappears. This
finding is in line with preliminary data collected for stoichiometric UCoSi2.Comment: to appear in Phys. Rev.
Moving from Data-Constrained to Data-Enabled Research: Experiences and Challenges in Collecting, Validating and Analyzing Large-Scale e-Commerce Data
Widespread e-commerce activity on the Internet has led to new opportunities
to collect vast amounts of micro-level market and nonmarket data. In this paper
we share our experiences in collecting, validating, storing and analyzing large
Internet-based data sets in the area of online auctions, music file sharing and
online retailer pricing. We demonstrate how such data can advance knowledge by
facilitating sharper and more extensive tests of existing theories and by
offering observational underpinnings for the development of new theories. Just
as experimental economics pushed the frontiers of economic thought by enabling
the testing of numerous theories of economic behavior in the environment of a
controlled laboratory, we believe that observing, often over extended periods
of time, real-world agents participating in market and nonmarket activity on
the Internet can lead us to develop and test a variety of new theories.
Internet data gathering is not controlled experimentation. We cannot randomly
assign participants to treatments or determine event orderings. Internet data
gathering does offer potentially large data sets with repeated observation of
individual choices and action. In addition, the automated data collection holds
promise for greatly reduced cost per observation. Our methods rely on
technological advances in automated data collection agents. Significant
challenges remain in developing appropriate sampling techniques integrating
data from heterogeneous sources in a variety of formats, constructing
generalizable processes and understanding legal constraints. Despite these
challenges, the early evidence from those who have harvested and analyzed large
amounts of e-commerce data points toward a significant leap in our ability to
understand the functioning of electronic commerce.Comment: Published at http://dx.doi.org/10.1214/088342306000000231 in the
Statistical Science (http://www.imstat.org/sts/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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