33 research outputs found
Effect of Distributed Particle Magnetic Moments on the Magnetization of NiO Nanoparticles
Magnetization of nanoparticles of NiO are measured and analyzed taking into
account a distribution in particle magnetic moment. We find that disregarding
this distribution in the analysis is the reason for the many anomalous
observations reported on this system in the literature.Comment: 4 pages, 2 figure
Non-equilibrium effects in the magnetic behavior of Co_3O_4 nanoparticles
We report detailed studies on non-equilibrium magnetic behavior of
antiferromagnetic Co_3O_4 nanoparticles. Temperature and field dependence of
magnetization, wait time dependence of magnetic relaxation (aging), memory
effects and temperature dependence of specific heat have been investigated to
understand the magnetic behavior of these particles. We find that the system
shows some features characteristic of nanoparticle magnetism such as
bifurcation of field cooled (FC) and zero field cooled (ZFC) susceptibilities
and a slow relaxation of magnetization. However, strangely, the temperature at
which the ZFC magnetization peaks coincides with the bifurcation temperature
and does not shift on application of magnetic fields up to 1 kOe, unlike most
other nanoparticle systems. Aging effects in these particles are negligible in
both FC and ZFC protocol and memory effects are present only in FC protocol. We
estimate the N\'eel temperature by using Fisher's relation as well as directly
by measurement of specific heat, thus testing the validity of Fisher's relation
for nanoparticles. We show that Co3O4 nanoparticles constitute a unique
aniferromagnetic system which develops a magnetic moment in the paramagnetic
state because of antiferromagnetic correlations and enters into a blocked state
above the N\'eel temperature.Comment: 6 pages,7 figure
Seismology of the Sun : Inference of Thermal, Dynamic and Magnetic Field Structures of the Interior
Recent overwhelming evidences show that the sun strongly influences the
Earth's climate and environment. Moreover existence of life on this Earth
mainly depends upon the sun's energy. Hence, understanding of physics of the
sun, especially the thermal, dynamic and magnetic field structures of its
interior, is very important. Recently, from the ground and space based
observations, it is discovered that sun oscillates near 5 min periodicity in
millions of modes. This discovery heralded a new era in solar physics and a
separate branch called helioseismology or seismology of the sun has started.
Before the advent of helioseismology, sun's thermal structure of the interior
was understood from the evolutionary solution of stellar structure equations
that mimicked the present age, mass and radius of the sun. Whereas solution of
MHD equations yielded internal dynamics and magnetic field structure of the
sun's interior. In this presentation, I review the thermal, dynamic and
magnetic field structures of the sun's interior as inferred by the
helioseismology.Comment: To be published in the proceedings of the meeting "3rd International
Conference on Current Developments in Atomic, Molecular, Optical and Nano
Physics with Applications", December 14-16, 2011, New Delhi, Indi
THE RATE OF BINARY BLACK HOLE MERGERS INFERRED FROM ADVANCED LIGO OBSERVATIONS SURROUNDING GW150914
A transient gravitational-wave signal, GW150914, was identi
fi
ed in the twin Advanced LIGO detectors on 2015
September 2015 at 09:50:45 UTC. To asse
ss the implications of this discovery,
the detectors remained in operation with
unchanged con
fi
gurations over a period of 39 days around the time of t
he signal. At the detection statistic threshold
corresponding to that observed for GW150914, our search of the 16 days of simultaneous two-detector observational
data is estimated to have a false-alarm rate
(
FAR
)
of
<
́
--
4.9 10 yr
61
, yielding a
p
-value for GW150914 of
<
́
-
210
7
. Parameter estimation follo
w-up on this trigger identi
fi
es its source as a binary black hole
(
BBH
)
merger
with component masses
(
)(
)
=
-
+
-
+
mm
M
,36,29
12
4
5
4
4
at redshift
=
-
+
z
0.09
0.04
0.03
(
median and 90% credible range
)
.
Here, we report on the constraints these observations place on the rate of BBH coalescences. Considering only
GW150914, assuming that all BBHs in the universe have the same masses and spins as this event, imposing a search
FAR threshold of 1 per 100 years, and assuming that the BBH merger rate is constant in the comoving frame, we infer a
90% credible range of merger rates between
–
--
2
53 Gpc yr
31
(
comoving frame
)
. Incorporating all search triggers that
pass a much lower threshold while accounting for the uncerta
inty in the astrophysical origin of each trigger, we estimate
a higher rate, ranging from
–
--
13 600 Gpc yr
31
depending on assumptions about the BBH mass distribution. All
together, our various rate estimat
es fall in the conservative range
–
--
2
600 Gpc yr
31
Traditional Indian memory enhancer herbs and their medicinal importance
International audienc