4,564 research outputs found
A Study of starless dark cloud LDN 1570: Distance, Dust properties and Magnetic field geometry
We wish to map the magnetic field geometry and to study the dust properties
of the starless cloud, L1570, using multi-wavelength optical polarimetry and
photometry of the stars projected on the cloud. We made R-band imaging
polarimetry of the stars projected on a cloud, L1570, to trace the magnetic
field orientation. We also made multi-wavelength polarimetric and photometric
observations to constrain the properties of dust in L1570. We estimated a
distance of 394 +/- 70 pc to the cloud using 2MASS JHKs colours. Using the
values of the Serkowski parameters namely , ,
{\lambda}max and the position of the stars on near infrared color-color
diagram, we identified 13 stars that could possibly have intrinsic polarization
and/or rotation in their polarization angles. One star, 2MASS
J06075075+1934177, which is a B4Ve spectral type, show the presence of diffuse
interstellar bands in the spectrum apart from showing H{\alpha} line in
emission. There is an indication for the presence of slightly bigger dust
grains towards L1570 on the basis of the dust grain size-indicators such as
{\lambda}max and Rv values. The magnetic field lines are found to be parallel
to the cloud structures seen in the 250{\mu}m images (also in 8{\mu}m and
12{\mu}m shadow images) of L1570. Based on the magnetic field geometry, the
cloud structure and the complex velocity structure, we believe that L1570 is in
the process of formation due to the converging flow material mediated by the
magnetic field lines. Structure function analysis showed that in the L1570
cloud region the large scale magnetic fields are stronger when compared with
the turbulent component of magnetic fields. The estimated magnetic field
strengths suggest that the L1570 cloud region is sub-critical and hence could
be strongly supported by the magnetic field lines.Comment: 26 pages, 22 figures, and 7 tables; Accepted for its publication in
A&
The Universal Edge Physics in Fractional Quantum Hall Liquids
The chiral Luttinger liquid theory for fractional quantum Hall edge transport
predicts universal power-law behavior in the current-voltage (-)
characteristics for electrons tunneling into the edge. However, it has not been
unambiguously observed in experiments in two-dimensional electron gases based
on GaAs/GaAlAs heterostructures or quantum wells. One plausible cause is the
fractional quantum Hall edge reconstruction, which introduces non-chiral edge
modes. The coupling between counterpropagating edge modes can modify the
exponent of the - characteristics. By comparing the fractional
quantum Hall states in modulation-doped semiconductor devices and in graphene
devices, we show that the graphene-based systems have an experimental
accessible parameter region to avoid the edge reconstruction, which is suitable
for the exploration of the universal edge tunneling exponent predicted by the
chiral Luttinger liquid theory.Comment: 7 pages, 6 figure
Spin Waves in Disordered III-V Diluted Magnetic Semiconductors
We propose a new scheme for numerically computing collective-mode spectra for
large-size systems, using a reformulation of the Random Phase Approximation. In
this study, we apply this method to investigate the spectrum and nature of the
spin-waves of a (III,Mn)V Diluted Magnetic Semiconductor. We use an impurity
band picture to describe the interaction of the charge carriers with the local
Mn spins. The spin-wave spectrum is shown to depend sensitively on the
positional disorder of the Mn atoms inside the host semiconductor. Both
localized and extended spin-wave modes are found. Unusual spin and charge
transport is implied.Comment: 14 pages, including 11 figure
Nonequilibrium Dynamics and Aging in the Three--Dimensional Ising Spin Glass Model
The low temperature dynamics of the three dimensional Ising spin glass in
zero field with a discrete bond distribution is investigated via MC
simulations. The thermoremanent magnetization is found to decay algebraically
and the temperature dependent exponents agree very well with the experimentally
determined values. The nonequilibrium autocorrelation function shows
a crossover at the waiting (or {\em aging}) time from algebraic {\em
quasi-equilibrium} decay for times to another, faster algebraic
decay for with an exponent similar to one for the remanent
magnetization.Comment: Revtex, 11 pages + 4 figures (included as Latex-files
Concept of Nabhi – A Review Study
The central point of body in between Amashaya (location of undigested food) and Pakvashaya (location of digested food) is termed as Nabhi. In classical texts of Ayurveda; scattered references regarding Nabhi are available like Nabhi is mentioned as a vital spot (Marma) of body. Nabhi is also included among the fifteen Koshthangas of body. In Sharirasthana of Sushruta Samhita; Acharya Sushruta mentioned that Sira and Dhamani are originated from Nabhi. Acharya Vagbhatta has quoted Nabhi as a dominant place of Pitta Dosha. Nabhi is an abode of Pranas (vital energy). Available literature and commentary on Nabhi interprets it as a Navel but practically it doesn’t make a sense to stick with this interpretation. Therefore; it is need to review classical texts of Ayurveda and contemporary literature to get clear and unambiguous meaning of the word “Nabhi” now a day. After thoroughly reading and interpreting the literature available regarding Nabhi; core of physiological process would be considered by the term Nabh
Preventive, promotive and curative aspect of Dhumapana in Urdhvajatrugata Roga
Dhumapana is very effective treatment for upper clavicular diseases (Urdhvajatrugata Roga). It is also effective in coughing (Kasa Roga) and in induction of emesis. However it is not widely practiced. The curative aspect of Dhumapana is somewhat known in clinicians but its preventive and promotive aspect is neither much known nor practiced. Different types of Dhumapana are mentioned in Ayurvedic classics, made from different Dhumavarti, using different drugs; according to the need of action. It works on Vata and Kapha Dosha. It can be used for Shamana and Shodhana Karma. It can be advised at different stages of treatment to achieve these Karma. In this article an effort has been made to elaborate the preventive, promotive and curative aspect of Dhumapana
Processing-Related Issues for the Design and Lifing of SiC/SiC Hot-Section Components
For successful SiC/SiC engine components, numerous process steps related to the fiber, fiber architecture, interphase coating, and matrix need to be optimized. Under recent NASA-sponsored programs, it was determined that many of these steps in their initial approach were inadequate, resulting in less than optimum thermostructural and life properties for the as-fabricated components. This presentation will briefly review many of these process issues, the key composite properties they degrade, their underlying mechanisms, and current process remedies developed by NASA and others
Strong Griffiths singularities in random systems and their relation to extreme value statistics
We consider interacting many particle systems with quenched disorder having
strong Griffiths singularities, which are characterized by the dynamical
exponent, z, such as random quantum systems and exclusion processes. In several
d=1 and d=2 dimensional problems we have calculated the inverse time-scales,
t^{-1}, in finite samples of linear size, L, either exactly or numerically. In
all cases, having a discrete symmetry, the distribution function, P(t^{-1},L),
is found to depend on the variable, u=t^{-1}L^{z/d}, and to be universal given
by the limit distribution of extremes of independent and identically
distributed random numbers. This finding is explained in the framework of a
strong disorder renormalization group approach when, after fast degrees of
freedom are decimated out the system is transformed into a set of
non-interacting localized excitations. The Frechet distribution of P(t^{-1},L)
is expected to hold for all random systems having a strong disorder fixed
point, in which the Griffiths singularities are dominated by disorder
fluctuations.Comment: 11 pages, 11 figure
Effects of dissipation on disordered quantum spin models
We study the effects of the coupling to an Ohmic quantum reservoir on the
static and dynamical properties of a family of disordered SU(2) spin models in
a transverse magnetic field using a method of direct spin summation. The
tendency to form a glassy phase increases with the strength of the coupling of
the system to the environment. We study the influence of the environment on the
features of the phase diagram of the various models as well as the stability of
the possible phases.Comment: 24 pages, 8 fig
Bound Magnetic Polaron Interactions in Insulating Doped Diluted Magnetic Semiconductors
The magnetic behavior of insulating doped diluted magnetic semiconductors
(DMS) is characterized by the interaction of large collective spins known as
bound magnetic polarons. Experimental measurements of the susceptibility of
these materials have suggested that the polaron-polaron interaction is
ferromagnetic, in contrast to the antiferromagnetic carrier-carrier
interactions that are characteristic of nonmagnetic semiconductors. To explain
this behavior, a model has been developed in which polarons interact via both
the standard direct carrier-carrier exchange interaction (due to virtual
carrier hopping) and an indirect carrier-ion-carrier exchange interaction (due
to the interactions of polarons with magnetic ions in an interstitial region).
Using a variational procedure, the optimal values of the model parameters were
determined as a function of temperature. At temperatures of interest, the
parameters describing polaron-polaron interactions were found to be nearly
temperature-independent. For reasonable values of these constant parameters, we
find that indirect ferromagnetic interactions can dominate the direct
antiferromagnetic interactions and cause the polarons to align. This result
supports the experimental evidence for ferromagnetism in insulating doped DMS.Comment: 11 pages, 7 figure
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