2,813 research outputs found
Low temperature hopping magnetotransport in paramagnetic single crystals of cobalt doped ZnO
Long needle-shaped single crystals of Zn1-xCoxO were grown at low
temperatures using a molten salt solvent technique, up to x=0.10. The
conduction process at low temperatures is determined to be by Mott variable
range hopping. Both pristine and cobalt doped crystals clearly exhibit a
crossover from negative to positive magnetoresistance as the temperature is
decreased. The positive magnetoresistance of the Zn1-xCoxO single crystals
increases with increased Co concentration and reaches up to 20% at low
temperatures (2.5 K) and high fields (>1 T). SQUID magnetometry confirms that
the Zn1-xCoxO crystals are predominantly paramagnetic in nature and the
magnetic response is independent of Co concentration. The results indicate that
cobalt doping of single crystalline ZnO introduces localized electronic states
and isolated Co2+ ions into the host matrix, but that the magnetotransport and
magnetic properties are decoupled.Comment: 7 pages, 9 figures, submitted to Physical Review
Transbasin water transfers
Presented at the 2001 USCID water management conference, Transbasin water transfers on June 27-30, 2001 in Denver, Colorado.Includes bibliographical references.To utilise the waters of the rivers Sutlej, Beas and Ravi flowing through Punjab, and which come to the exclusive share of India, as per the Indus Waters Treaty-1960 between the Governments of India and Pakistan, a number of projects have been planned, constructed or are under construction on these rivers. These projects have helped in gainfully diverting the waters of river Beas in Sutlej and of river Ravi to Beas, in addition to providing multi-purpose benefits. The projects have brought an agricultural and industrial revolution to the states of Punjab, Haryana and the desert areas of Rajasthan and transformed them into granaries of India. The paper briefly describes the various projects and their salient features. The impacts of the projects on the economy, environment, health, tourism and recreation etc. have been highlighted. Since these projects have enabled the diversion of surplus waters of one river to another, studies for integrated operation and management of waters of these rivers have been carried out for deriving optimum benefits. The paper also describes the real time integrated operation techniques, factors necessitating their adoption, and computer models used for integrated operation of the Bhakra Beas system of reservoirs. It is recommended that for effective utilization of the available waters, and implementation of the real time integrated operation techniques, an automatic data collection and transmission system be installed
Chronic Mountain Sickness-Phobrang Type
Clinical0 features of 27 cases of Chronic Mountain Sickness (CMS) from the Himalayas are reported. They are compared with 75 native highlanders (NH). All CMS patients were immigrants to high altitude. Mean duration of stay at high altitude was seven years. Mean values for haematocrit and haemoglobin were 80% and 23 G% respectively for the CMS group and 40% and 17.9 G% respectively for the native highlande group. Mean QRS axis in the former was +118 and in the latter +76. Incidence and quantum of protienuria were significantly higher in the CMS group. Cardiac catheteri -sation studies done in eight CMS cases showed elevated Pulmonary Artery (PA) pressures even after a mean of 14.2 days at sea level. The disease which has four diagnostic elements-hypoxemia and polycythemia, pulmonary hypertension, right ventricular enlargement and nephropathy with dense proteinuria-is a variant of 'Monge's Disease' and a name CMS Phobrang Type is suggested, along with a new approach to clinical classification which may help in diagnosis before cor pulmonale sets in. Limited therapeutic trials conducted at highaltitude seem to indicate that yogic deep breathing exercises, low-dose aspirin and diamox may be beneficial in the prevention and therapy of CMS Phobrang Type at high  altitude
XMM-Newton observations of HD189733 during planetary transits
We report on two XMM-Newton observations of the planetary host star HD189733.
The system has a close in planet and it can potentially affect the coronal
structure via interactions with the magnetosphere. We have obtained X-ray
spectra and light curves from EPIC and RGS on board XMM-Newton which we have
analyzed and interpreted. We reduced X-ray data from primary transit and
secondary eclipse occurred in April 17th 2007 and May 18th 2009, respectively.
In the April 2007 observation only variability due to weak flares is
recognized. In 2009 HD189733 exhibited a X-ray flux always larger than in the
2007 observation. The average flux in 2009 was higher than in 2007 observation
by a factor of 45%. During the 2009 secondary eclipse we observed a softening
of the X-ray spectrum significant at level of ~3 sigma. Further, we observed
the most intense flare recorded at either epochs. This flare occurred 3 ks
after the end of the eclipse.The flare decay shows several minor ignitions
perhaps linked to the main event and hinting for secondary loops that emit
triggered by the main loop. Magneto-Hydro-Dynamical (MHD) simulations show that
the magnetic interaction between planet and star enhances the density and the
magnetic field in a region comprised between the planet and the star because of
their relative orbital/rotation motion. X-ray observations and model
predictions are globally found in agreement, despite the quite simple MHD model
and the lack of precise estimate of parameters including the alignment and the
intensity of stellar and planetary magnetic fields. Future observations should
confirm or disprove this hypothesis, by determining whether flares are
systematically recurring in the light curve at the same planetary phase.Comment: Accepted for publication on The Astrophysical Journa
Preparation and ultrasonic study of sodium potassium tantalate (Na1-xKxTaO3) mixed system
Ultrasonic velocity of the piezoelectric ceramic pellets of ferroelectric material Na1-xKxTaO3 (X=0, 0.2, 0.3, 0.4, 0.5, 0.6 and 1.0) have been investigated at temperature 32 ÂşC and frequency 5 MHz with the help of ultrasonic c-scan system developed at NPL, New Delhi. The samples have been prepared by the conventional solid-state reaction method and sintering process
Interactions of the magnetospheres of stars and close-in giant planets
Since the first discovery of an extrasolar planetary system more than a
decade ago, hundreds more have been discovered. Surprisingly, many of these
systems harbor Jupiter-class gas giants located close to the central star, at
distances of 0.1 AU or less. Observations of chromospheric 'hot spots' that
rotate in phase with the planetary orbit, and elevated stellar X-ray
luminosities,suggest that these close-in planets significantly affect the
structure of the outer atmosphere of the star through interactions between the
stellar magnetic field and the planetary magnetosphere. Here we carry out the
first detailed three-dimensional MagnetoHydroHynamics (MHD) simulation
containing the two magnetic bodies and explore the consequences of such
interactions on the steady-state coronal structure. The simulations reproduce
the observable features of 1) increase in the total X-ray luminosity, 2)
appearance of coronal hot spots, and 3) phase shift of these spots with respect
to the direction of the planet. The proximate cause of these is an increase in
the density of coronal plasma in the direction of the planet, which prevents
the corona from expanding and leaking away this plasma via a stellar wind. The
simulations produce significant low temperature heating. By including dynamical
effects, such as the planetary orbital motion, the simulation should better
reproduce the observed coronal heating
FK Comae Berenices, King of Spin: The COCOA-PUFS Project
COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast
spinning, heavily spotted, yellow giant FK Com (HD117555; G4 III). This single
star is thought to be a recent binary merger, and is exceptionally active by
measure of its intense ultraviolet and X-ray emissions, and proclivity to
flare. COCOA-PUFS was carried out with Hubble Space Telescope in the UV
(120-300 nm), using mainly its high-performance Cosmic Origins Spectrograph,
but also high-precision Space Telescope Imaging Spectrograph; Chandra X-ray
Observatory in the soft X-rays (0.5-10 keV), utilizing its High-Energy
Transmission Grating Spectrometer; together with supporting photometry and
spectropolarimetry in the visible from the ground. This is an introductory
report on the project.
FK Com displayed variability on a wide range of time scales, over all
wavelengths, during the week-long main campaign, including a large X-ray flare;
"super-rotational broadening" of the far-ultraviolet "hot-lines" (e.g., Si IV
139 nm (T~80,000 K) together with chromospheric Mg II 280 nm and C II 133 nm
(10,000-30,000 K); large Doppler swings suggestive of bright regions
alternately on advancing and retreating limbs of the star; and substantial
redshifts of the epoch-average emission profiles. These behaviors paint a
picture of a highly extended, dynamic, hot (10 MK) coronal magnetosphere around
the star, threaded by cooler structures perhaps analogous to solar prominences,
and replenished continually by surface activity and flares. Suppression of
angular momentum loss by the confining magnetosphere could temporarily postpone
the inevitable stellar spindown, thereby lengthening this highly volatile stage
of coronal evolution.Comment: to be published in ApJ
Observation of Replica Symmetry Breaking in the 1D Anderson Localization Regime in an Erbium-Doped Random Fiber Laser
The analogue of the paramagnetic to spin-glass phase transition in disordered
magnetic systems, leading to the phenomenon of replica symmetry breaking, has
been recently demonstrated in a two-dimensional random laser consisting of an
organic-based amorphous solid-state thin film. We report here the first
demonstration of replica symmetry breaking in a one-dimensional photonic system
consisting of an erbium-doped random fiber laser operating in the
continuous-wave regime based on a unique random fiber grating system, which
plays the role of the random scatterers and operates in the Anderson
localization regime. The clear transition from a photonic paramagnetic to a
photonic spin glass phase, characterized by the probability distribution
function of the Parisi overlap, was verified and characterized. In this unique
system, the radiation field interacts only with the gain medium, and the fiber
grating, which provides the disordered feedback mechanism, does not interfere
with the pump
Turbulence Hierarchy in a Random Fibre Laser
Turbulence is a challenging feature common to a wide range of complex
phenomena. Random fibre lasers are a special class of lasers in which the
feedback arises from multiple scattering in a one-dimensional disordered
cavity-less medium. Here, we report on statistical signatures of turbulence in
the distribution of intensity fluctuations in a continuous-wave-pumped
erbium-based random fibre laser, with random Bragg grating scatterers. The
distribution of intensity fluctuations in an extensive data set exhibits three
qualitatively distinct behaviours: a Gaussian regime below threshold, a mixture
of two distributions with exponentially decaying tails near the threshold, and
a mixture of distributions with stretched-exponential tails above threshold.
All distributions are well described by a hierarchical stochastic model that
incorporates Kolmogorov's theory of turbulence, which includes energy cascade
and the intermittence phenomenon. Our findings have implications for explaining
the remarkably challenging turbulent behaviour in photonics, using a random
fibre laser as the experimental platform.Comment: 9 pages, 5 figure
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