39,459 research outputs found
Geological evaluation of Nimbus vidicon photography, Chesapeake Bay-Blue Ridge
Geological evaluation of Nimbus vidicon photography of Chesapeake Bay to Blue Ridge are
Power of unentangled measurements on two antiparallel spins
We consider a pair of antiparallel spins polarized in a random direction to
encode quantum information. We wish to extract as much information as possible
on the polarization direction attainable by an unentangled measurement, i.e.,
by a measurement, whose outcomes are associated with product states. We develop
analytically the upper bound 0.7935 bits to the Shannon mutual information
obtainable by an unentangled measurement, which is definitely less than the
value 0.8664 bits attained by an entangled measurement. This proves our main
result, that not every ensemble of product states can be optimally
distinguished by an unentangled measurement, if the measure of
distinguishability is defined in the sense of Shannon. We also present results
from numerical calculations and discuss briefly the case of parallel spins.Comment: Latex file, 18 pages, 1 figure; published versio
Convex probability domain of generalized quantum measurements
Generalized quantum measurements with N distinct outcomes are used for
determining the density matrix, of order d, of an ensemble of quantum systems.
The resulting probabilities are represented by a point in an N-dimensional
space. It is shown that this point lies in a convex domain having at most d^2-1
dimensions.Comment: 7 pages LaTeX, one PostScript figure on separate pag
Coral symbiodinium community composition across the Belize Mesoamerican barrier reef system is influenced by host species and thermal variability
Accepted manuscrip
Stellar and Molecular Gas Kinematics of NGC1097: Inflow Driven by a Nuclear Spiral
We present spatially resolved distributions and kinematics of the stars and
molecular gas in the central 320pc of NGC1097. The stellar continuum confirms
the previously reported 3-arm spiral pattern extending into the central 100pc.
The stellar kinematics and the gas distribution imply this is a shadowing
effect due to extinction by gas and dust in the molecular spiral arms. The
molecular gas kinematics show a strong residual (i.e. non-circular) velocity,
which is manifested as a 2-arm kinematic spiral. Linear models indicate that
this is the line-of-sight velocity pattern expected for a density wave in gas
that generates a 3-arm spiral morphology. We estimate the inflow rate along the
arms. Using hydrodynamical models of nuclear spirals, we show that when
deriving the accretion rate into the central region, outflow in the disk plane
between the arms has to be taken into account. For NGC1097, despite the inflow
rate along the arms being ~1.2Msun/yr, the net gas accretion rate to the
central few tens of parsecs is much smaller. The numerical models indicate that
the inflow rate could be as little as ~0.06Msun/yr. This is sufficient to
generate recurring starbursts, similar in scale to that observed, every
20-150Myr. The nuclear spiral represents a mechanism that can feed gas into the
central parsecs of the galaxy, with the gas flow sustainable for timescales of
a Gigayear.Comment: accepted by Ap
Are There Magnetars in High Mass X-ray Binaries? The Case of SuperGiant Fast X-Ray Transients
In this paper we survey the theory of wind accretion in high mass X-ray
binaries hosting a magnetic neutron star and a supergiant companion.
We concentrate on the different types of interaction between the inflowing
wind matter and the neutron star magnetosphere that are relevant when accretion
of matter onto the neutron star surface is largely inhibited; these include the
inhibition through the centrifugal and magnetic barriers. Expanding on earlier
work, we calculate the expected luminosity for each regime and derive the
conditions under which transition from one regime to another can take place. We
show that very large luminosity swings (~10^4 or more on time scales as short
as hours) can result from transitions across different regimes.
The activity displayed by supergiant fast X-ray transients, a recently
discovered class of high mass X-ray binaries in our galaxy, has often been
interpreted in terms of direct accretion onto a neutron star immersed in an
extremely clumpy stellar wind. We show here that the transitions across the
magnetic and/or centrifugal barriers can explain the variability properties of
these sources as a results of relatively modest variations in the stellar wind
velocity and/or density. According to this interpretation we expect that
supergiant fast X-ray transients which display very large luminosity swings and
host a slowly spinning neutron star are characterized by magnetar-like fields,
irrespective of whether the magnetic or the centrifugal barrier applies.
Supergiant fast X-ray transients might thus provide a new opportunity to
detect and study magnetars in binary systems.Comment: Accepted for publication in ApJ. 16 pages, 6 figure
Geological Evaluation of Nimbus Vidicon Magery - Northwest Greenland
Geological evaluation of Nimbus satellite vidicon imagery of northwest Greenlan
Optimal distinction between non-orthogonal quantum states
Given a finite set of linearly independent quantum states, an observer who
examines a single quantum system may sometimes identify its state with
certainty. However, unless these quantum states are orthogonal, there is a
finite probability of failure. A complete solution is given to the problem of
optimal distinction of three states, having arbitrary prior probabilities and
arbitrary detection values. A generalization to more than three states is
outlined.Comment: 9 pages LaTeX, one PostScript figure on separate pag
The Fulling-Davies-Unruh Effect is Mandatory: The Proton's Testimony
We discuss the decay of accelerated protons and illustrate how the
Fulling-Davies-Unruh effect is indeed mandatory to maintain the consistency of
standard Quantum Field Theory. The confidence level of the Fulling-Davies-Unruh
effect must be the same as that of Quantum Field Theory itself.Comment: Awarded "honorable mention" by Gravity Research Foundation in the
2002 Essay competitio
The spin vector of Venus determined from Magellan data
A control network of the north polar region of Venus has been established by selecting and measuring control points on full-resolution radar strips. The measurements were incorporated into a least-squares adjustment program that improved initial estimates of the coordinates of the control points, pole direction, and rotation rate of Venus. The current dataset contains 4206 measurements of 606 points on 619 radar strips. The accuracy of the determination is driven by spacecraft ephemeris errors. An accurate estimate of the rotation period of Venus was obtained by applying an ephemeris improvement technique. The second cycle closure orbits improved ephemeris solutions for 40 orbits (376-384, 520-528, 588-592, 658-668, 1002-1010, 1408-1412, 1746-1764, and 2166-2170) are included and fixed in the geodetic control computations, thus trying the network to the J2000 coordinate system
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