154 research outputs found
Development of a time series-based methodology for estimation of large-area soil wetness over India using IRS-P4 microwave radiometer data
Soil moisture is a very important boundary parameter in numerical weather prediction at different spatial and temporal scales. Satellite-based microwave radiometric observations are considered to be the best because of their high sensitivity to soil moisture, apart from possessing all-weather and day-night observation capabilities with high repetitousness. In the present study, 6.6-GHz horizontal-polarization brightness temperature data from the Multifrequency Scanning Microwave Radiometer (MSMR) onboard the Indian Remote Sensing Satellite IRS-P4 have been used for the estimation of large-area-averaged soil wetness. A methodology has been developed for the estimation of soil wetness for the period of June-July from the time series of MSMR brightness temperatures over India. Maximum and minimum brightness temperatures for each pixel are assigned to the driest and wettest periods, respectively. A daily soil wetness index over each pixel is computed by normalizing brightness temperature observations from these extreme values. This algorithm has the advantage that it takes into account the effect of time-invariant factors, such as vegetation, surface roughness, and soil characteristics, on soil wetness estimation. Weekly soil wetness maps compare well to corresponding weekly rainfall maps depicting clearly the regions of dry and wet soil conditions. Comparisons of MSMR-derived soil wetness with in situ observations show a high correlation (R>0.75), with a standard error of the soil moisture estimate of less than 7% (volumetric unit) for the surface (0-5 cm) and subsurface (5-10 cm) soil moisture
Role of many-body entanglement in decoherence processes
A pure state decoheres into a mixed state as it entangles with an
environment. When an entangled two-mode system is embedded in a thermal
environment, however, each mode may not be entangled with its environment by
their simple linear interaction. We consider an exactly solvable model to study
the dynamics of a total system, which is composed of an entangled two-mode
system and a thermal environment, and also an array of infinite beam splitters.
It is shown that many-body entanglement of the system and the environment plays
a crucial role in the process of disentangling the system.Comment: 4 pages, 1 figur
Meteorite falls over India during 2003: Petrographic and chemical characterization and cosmogenic records
Two meteorite falls observed over India in 2003 led to the recovery of surviving fragments. The Kasauli meteorite that fell in northern India is a single fall, while Kendrapara meteorite is a multiple fall that covered a large coastal region of Orissa. Data for petrographic characteristics and chemical composition suggest that the two meteorites belong to the H group of chondrites, with Kasuali suffering a lesser degree of thermal metamorphism than Kendrapara during their residence in their parent bodies. Cosmogenic records indicate a large size (≥1 m) for the Kendrapara meteoroid that has spent ~5 million years in interplanetary space following its ejection from its parent body until its fall on the Earth. On the other hand, the Kasauli meteoroid spent an unusually long time (~37 Ma) in interplanetary space before its fall and lost ~80% of its original mass during atmospheric ablation
Evidence for Bound Entangled States with Negative Partial Transpose
We exhibit a two-parameter family of bipartite mixed states , in a
Hilbert space, which are negative under partial transposition
(NPT), but for which we conjecture that no maximally entangled pure states in
can be distilled by local quantum operations and classical
communication (LQ+CC). Evidence for this undistillability is provided by the
result that, for certain states in this family, we cannot extract entanglement
from any arbitrarily large number of copies of using a projection
on . These states are canonical NPT states in the sense that any
bipartite mixed state in any dimension with NPT can be reduced by LQ+CC
operations to an NPT state of the form. We show that the main
question about the distillability of mixed states can be formulated as an open
mathematical question about the properties of composed positive linear maps.Comment: Revtex, 19 pages, 2 eps figures. v2,3: very minor changes, submitted
to Phys. Rev. A. v4: minor typos correcte
Multipartite pure-state entanglement and the generalized GHZ states
We show that not all 4-party pure states are GHZ reducible (i.e., can be
generated reversibly from a combination of 2-, 3- and 4-party maximally
entangled states by local quantum operations and classical communication
asymptotically) through an example, we also present some properties of the
relative entropy of entanglement for those 3-party pure states that are GHZ
reducible, and then we relate these properties to the additivity of the
relative entropy of entanglement.Comment: 7 pages, Revtex, type error correcte
Classification of multi-qubit mixed states: separability and distillability properties
We give a complete, hierarchic classification for arbitrary multi-qubit mixed
states based on the separability properties of certain partitions. We introduce
a family of N-qubit states to which any arbitrary state can be depolarized.
This family can be viewed as the generalization of Werner states to multi-qubit
systems. We fully classify those states with respect to their separability and
distillability properties. This provides sufficient conditions for
nonseparability and distillability for arbitrary states.Comment: 12 pages, 2 figure
Non-local Operations: Purification, storage, compression, tomography, and probabilistic implementation
We provide several applications of a previously introduced isomorphism
between physical operations acting on two systems and entangled states [1]. We
show: (i) how to implement (weakly) non-local two qubit unitary operations with
a small amount of entanglement; (ii) that a known, noisy, non-local unitary
operation as well as an unknown, noisy, local unitary operation can be
purified; (iii) how to perform the tomography of arbitrary, unknown, non-local
operations; (iv) that a set of local unitary operations as well as a set of
non-local unitary operations can be stored and compressed; (v) how to implement
probabilistically two-qubit gates for photons. We also show how to compress a
set of bipartite entangled states locally, as well as how to implement certain
non-local measurements using a small amount of entanglement. Finally, we
generalize some of our results to multiparty systems.Comment: 15 pages, no figure
Scheme for the generation of an entangled four-photon W-state
We present a scheme to produce an entangled four-photon W-state by using
linear optical elements. The symmetrical setup of linear optical elements
consists of four beam splitters, four polarization beam splitters and four
mirrors. A photon EPR-pair and two single photons are required as the input
modes. The projection on the W-state can be made by a four-photon coincidence
measurement. Further, we show that by means of a horizontally oriented
polarizer in front of one detector the W-state of three photons can be
generated.Comment: titile is changed, to appear in PR
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