4,653 research outputs found
The influence of the jet opening angle on the appearance of relativistic jets
We reinvestigate the problem of the appearance of relativistic jets when
geometrical opening is taken into account. We propose a new criterion to define
apparent velocities and Doppler factors, which we think being determined by the
brightest zone of the jet. We numerically compute the apparent velocity and the
Doppler factor of a non homokinetic jet using different velocity profiles. We
argue that if the motion is relativistic, the high superluminal velocities
beta_{app} ~ gamma, expected in the case of an homokinetic jet, are only
possible for geometrical collimation smaller than the relativistic beaming
angle 1/gamma. This is relatively independent of the jet velocity profile. For
jet collimation angles larger than 1/gamma, the apparent image of the jet will
always be dominated by parts of the jet traveling directly towards the observer
at lorentz factors < gamma resulting in maximal apparent velocities smaller
than gamma}. Furthermore, getting rid of the homokinetic hypothesis yields a
complex relation between the observing angle and the Doppler factor, resulting
in important consequences for the numerical computation of AGN population and
unification scheme model.Comment: Accepted in MNRAS, 12 pages and 9 Figure
Was the Cosmic Web of Protogalactic Material Permeated by Lobes of Radio Galaxies During the Quasar Era?
Evidence for extended active lifetimes (> 10^8 yr) for radio galaxies implies
that many large radio lobes were produced during the `quasar era', 1.5 < z < 3,
when the comoving density of radio sources was 2 -- 3 dex higher than the
present level. However, inverse Compton losses against the intense microwave
background substantially reduce the ages and numbers of sources that are
detected in flux-limited surveys. The realization that the galaxy forming
material in those epochs was concentrated in filaments occupying a small
fraction of the total volume then leads to the conclusion that radio lobes
permeated much of the volume occupied by the protogalactic material during that
era. The sustained overpressure in these extended lobes is likely to have
played an important role in triggering the high inferred rate of galaxy
formation at z > 1.5 and in the magnetization of the cosmic network of
filaments.Comment: 5 pages, 0 figures, submitted to ApJ Letters; uses emulateapj
Pattern of drug use in the management of psoriasis in a tertiary care hospital: a prospective study
Background: Psoriasis is a chronic skin disease, characterized by chronic and recurrent scaly plaques with itching. The treatment modalities for psoriasis include topical, systemic, and phototherapy (PT). The pattern of therapy may vary depending upon the type, severity, and duration of the disease. As there are few reports in the Indian literature regarding the pattern of drug use in psoriasis and evaluating the efficacy and patient compliance to treatment, the present study was conducted.Methods: This was a prospective, observational study conducted on121 newly diagnosed and untreated patients with psoriasis, who attended Dermatology outpatient department of a tertiary care hospital. The severity of the disease was assessed by baseline psoriasis area severity index (PASI) score. Most of the patients were treated with topical therapy consisting of glucocorticoids (GC) monotherapy or combination with, salicylic acid, calcitriol and coal tar. Systemic therapy and PT were considered only for severe cases of psoriasis with baseline PASI score >4. The patients were monitored every 2 weeks for 3 months.Results: The topical medications induced effective resolution of lesions in most of the patients, along with adequate symptomatic relief. The response to GC monotherapy was found significant (90.47%; p4. Regular follow-up is required not only to monitor the treatment response, but also to ensure good patient compliance by proper counseling
Influence of nutrients and plant growth regulators on growth parameters and yield of Pigeonpea (Cajanus cajan (L.) Millsp.)
Pigeonpea is the second most important pulse crop after chickpea in India. The yield of pigeonpea is very low due to indeterminate growth habit and poor source-sink relationship. Plant growth regulators are known to influence the source-sink relationship and stimulate the translocation of photo-assimilates thereby helping in effective flower formation, fruit and seed development and ultimately enhance productivity of the crops. With this background, a field experiment was conducted with pigeonpea (CO Rg 7) under irrigated condition in Tamil Nadu Agricultural University, Coimbatore. An experiment was aimed at determining the effect of various nutrients and growth-promoting hormones on the growth parameters and yield of pigeonpea (Cajanus cajan (L.) Millsp.). The Factorial Randomised Block Design was used in the field trial and was replicated three times. At the vegetative stage, the treatments included foliar sprays of growth inhibitors such as M2-Mepiquat chloride (MC) @ 500 pp, M3-Chlormequat chloride (CC) @ 500 ppm and M1- Control. At flower initiation and 15 days later, various plant growth regulators, such as T2-SA (100 ppm), T3-BR (0.1 ppm), T4-Napthyl acetic acid (40 ppm), T5-Nutrients (ZnSO4 @ 0.5 percent + H3BO3 @ 0.3 percent, T6-Mono Ammonium Phosphate @ 2 percent, and T7-TNAU Pulse Wonder @ 1 percent), T8-Nutrient consortia I (1%) and T9-Nutrient consortia II (1%), were used. Among the treatments, the combination of Chlormequat chloride and nutrient consortia treatments (M3T8&M3T9) had better performances in growth parameters and yield of pigeonpea (CO Rg 7). Foliar application of M3T8-Chlormequat chloride and Nutrient consortia I (1%) resulted significantly (P<0.05) in the highest Total dry matter production (64.85; 82.96 g plant-1), Leaf area (1629; 1873 cm-2 plant-1), Leaf area index (1.358; 1.561), Specific leaf weight (7.29; 10.34 mg cm-2) and Seed yield (1133 kg ha-1) when compared to other treatments. The present study that the application of a combined formulation of hormones and nutrients present in the nutrient consortia at the flowering and pod formation stages influenced the growth parameters and resulted in higher seed yield
Light-Shift Imbalance Induced Blockade of Collective Excitations Beyond the Lowest Order
Current proposals focusing on neutral atoms for quantum computing are mostly
based on using single atoms as quantum bits (qubits), while using cavity
induced coupling or dipole-dipole interaction for two-qubit operations. An
alternative approach is to use atomic ensembles as qubits. However, when an
atomic ensemble is excited, by a laser beam matched to a two-level transition
(or a Raman transition) for example, it leads to a cascade of many states as
more and more photons are absorbed^1. In order to make use of an ensemble as a
qubit, it is necessary to disrupt this cascade, and restrict the excitation to
the absorption (and emission) of a single photon only. Here, we show how this
can be achieved by using a new type of blockade mechanism, based on the
light-shift imbalance (LSI) in a Raman transition. We describe first a simple
example illustrating the concept of light shift imbalanced induced blockade
(LSIIB) using a multi-level structure in a single atom, and show verifications
of the analytic prediction using numerical simulations. We then extend this
model to show how a blockade can be realized by using LSI in the excitation of
an ensemble. Specifically, we show how the LSIIB process enables one to treat
the ensemble as a two level atom that undergoes fully deterministic Rabi
oscillations between two collective quantum states, while suppressing
excitations of higher order collective states.Comment: 6 pages, 5 figure
Solving relativistic hydrodynamic equation in presence of magnetic field for phase transition in a neutron star
Hadronic to quark matter phase transition may occur inside neutron stars (NS)
having central densities of the order of 3-10 times normal nuclear matter
saturation density (). The transition is expected to be a two-step
process; transition from hadronic to 2-flavour matter and two-flavour to
equilibrated charge neutral three-flavour matter. In this paper we
concentrate on the first step process and solve the relativistic hydrodynamic
equations for the conversion front in presence of high magnetic field. Lorentz
force due to magnetic field is included in the energy momentum tensor by
averaging over the polar angles. We find that for an initial dipole
configuration of the magnetic field with a sufficiently high value at the
surface, velocity of the front increases considerably.Comment: 16 pages, 4 figures, same as published version of JPG, J. Phys. G:
Nucl. Part. Phys. 39 (2012) 09520
Understanding BL Lac objects Structural & kinematic mode changes in the BL Lac object PKS 0735+178
Context. We present evidence that parsec-scale jets in BL Lac objects may be
significantly distinct in kinematics from their counterparts in quasars. We
argued this previously for the BL lac sources 1803+784 and 0716+714, report
here a similar pattern for another well-known BL Lac object, PKS 0735+178,
whose nuclear jet is found to exhibit kinematics atypical of quasars. Aims. A
detailed study of the jet components' motion reveals that the standard AGN
paradigm of apparent superluminal motion does not always describe the
kinematics in BL Lac objects. We study 0735+178 here to augment and improve the
understanding of the peculiar motions in the jets of BL Lac objects as a class.
Methods. We analyzed 15 GHz VLBA (Very Long Baseline Array) observations
(2cm/MOJAVE survey) performed at 23 epochs between 1995.27 and 2008.91.
Results. We found a drastic structural mode change in the VLBI jet of 0735+178,
between 2000.4 and 2001.8 when its twice sharply bent trajectory turned into a
linear shape.We further found that this jet had undergone a similar transition
sometime between December 1981 and June 1983. A mode change, occurring in the
reverse direction (between mid-1992 and mid-1995) has already been reported in
the literature. These structural mode changes are found to be reflected in
changed kinematical behavior of the nuclear jet, manifested as an apparent
superluminal motion and stationarity of the radio knots. In addition, we found
the individual mode changes to correlate in time with the maxima in the optical
light curve. The last two transitions occurred before a (modest) radio flare.
The behavior of this pc-scale jet appears to favor a scenario involving
non-ballistic motions of the radio knots, produced by the precession of a
continuous jet within the ambient medium.Comment: Accepted for publication in A&A (Abstract reduced for astro-ph
Free volume study of poly(chlorotrifluoroethylene) using positron annihilation spectroscopy as a microanalytical tool
Positron lifetimes and X-ray diffraction measurements were carried out on poly(chlorotrifluoroethylene) films annealed between 25 and 215 degrees C. The positron lifetime results were used to determine the free volume and XRD data were used to determine the apparent crystallite size and crystallinity. The glass transition temperature (T-g) of 52 degrees C obtained from positron results is in agreement with that obtained by thermal analysis. The average free volume cell size is 74 Angstrom(3) in films annealed below T-g, and increases to 84 Angstrom(3) in samples annealed above T-g. Although the observed changes in positron lifetime parameters as a function of annealing temperature are small, they are significant for the kind of material investigated. Our observations are explained in terms of thermally activated chain mobility, local relaxations and long-range motions. We further estimate, for the first time, the activation energies in the amorphous and crystalline regions of the polymer using the Goldanskii kinetic relations. Copyright (C) 1996 Elsevier Science Ltd
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