166 research outputs found
Effects of velocity profile and inclination on dual-jet-induced pressures on a flat plate in a crosswind
An experimental study was conducted to determine surface pressure distributions on a flat plate with dual subsonic, circular jets exhausting from the surface into a crossflow. The jets were arranged in both side-by-side and tandem configurations and were injected at 90 deg and 60 deg angles to the plate, with jet-to-crossflow velocity ratio of 2.2 and 4. The major objective of the study was to determine the effect of a nonuniform (vs uniform) jet velocity profile, simulating the exhaust of a turbo-fan engine. Nonuniform jets with a high-velocity outer annulus and a low-velocity core induced stronger negative pressure fields than uniform jets with the same mass flow rate. However, nondimensional lift losses (lift loss/jet thrust lift) due to such nonuniform jets were lower than lift losses due to uniform jets. Changing the injection angle from 90 deg to 60 deg resulted in moderate (for tandem jets) to significant (for side-by-side jets) increases in the induced negative pressures, even though the surface area influenced by the jets tended to reduce as the angle decreased. Jets arranged in the side-by-side configuration led to significant jet-induced lift losses exceeding, in some cases, lift losses reported for single jets
Inbreeding alters intersexual fitness correlations in Drosophila simulans.
PublishedJournal ArticleIntralocus sexual conflict results from sexually antagonistic selection on traits shared by the sexes. This can displace males and females from their respective fitness optima, and negative intersexual correlations (r mf) for fitness are the unequivocal indicator of this evolutionary conflict. It has recently been suggested that intersexual fitness correlations can vary depending on the segregating genetic variation present in a population, and one way to alter genetic variation and test this idea is via inbreeding. Here, we test whether intersexual correlations for fitness vary with inbreeding in Drosophila simulans isolines reared under homogenous conditions. We measured male and female fitness at different times following the establishment of isofemale lines and found that the sign of the association between the two measures varied with time after initial inbreeding. Our results are consistent with suggestions that the type of genetic variation segregating within a population can determine the extent of intralocus sexual conflict and also support the idea that sexually antagonistic alleles segregate for longer in populations than alleles with sexually concordant effects.Foundation for Polish Science (FNP)NER
Tight lower bound to the geometric measure of quantum discord
Dakic, Vedral and Brukner [Physical Review Letters \tf{105},190502 (2010)]
gave a geometric measure of quantum discord in a bipartite quantum state as the
distance of the state from the closest classical quantum (or zero discord)
state and derived an explicit formula for a two qubit state. Further, S.Luo and
S.Fu [Physical Review A \tf{82}, 034302 (2010)] obtained a generic form of this
geometric measure for a general bipartite state and established a lower bound.
In this brief report we obtain a rigorous lower bound to the geometric measure
of quantum discord in a general bipartite state which dominates that obtained
by S.Luo and S.Fu.Comment: 10 pages,2 figures. In the previous versions, a constraint was
ignored while optimizing the second term in Eq.(5), in which case, only a
lower bound on the geometric discord can be obtained. The title is also
consequently changed. Accepted in Phys.Rev.
Multipartite entanglement in fermionic systems via a geometric measure
We study multipartite entanglement in a system consisting of
indistinguishable fermions. Specifically, we have proposed a geometric
entanglement measure for N spin-1/2 fermions distributed over 2L modes (single
particle states). The measure is defined on the 2L qubit space isomorphic to
the Fock space for 2L single particle states. This entanglement measure is
defined for a given partition of 2L modes containing m >= 2 subsets. Thus this
measure applies to m <= 2L partite fermionic system where L is any finite
number, giving the number of sites. The Hilbert spaces associated with these
subsets may have different dimensions. Further, we have defined the local
quantum operations with respect to a given partition of modes. This definition
is generic and unifies different ways of dividing a fermionic system into
subsystems. We have shown, using a representative case, that the geometric
measure is invariant under local unitaries corresponding to a given partition.
We explicitly demonstrate the use of the measure to calculate multipartite
entanglement in some correlated electron systems. To the best of our knowledge,
there is no usable entanglement measure of m > 3 partite fermionic systems in
the literature, so that this is the first measure of multipartite entanglement
for fermionic systems going beyond the bipartite and tripartite cases.Comment: 25 pages, 8 figure
Sexual selection drives the evolution of male wing interference patterns.
This is the author accepted manuscriptThe seemingly transparent wings of many insects have recently been found to display unexpected structural coloration. These structural colours (wing interference patterns: WIPs) may be involved in species recognition and mate choice, yet little is known about the evolutionary processes that shape them. Furthermore, to date investigations of WIPs have not fully considered how they are actually perceived by the viewers' colour vision. Here, we use multispectral digital imaging and a model of Drosophila vision to compare WIPs of male and female Drosophila simulans from replicate populations forced to evolve with or without sexual selection for 68 generations. We show that WIPs modelled in Drosophila vision evolve in response to sexual selection and provide evidence that WIPs correlate with male sexual attractiveness. These findings add a new element to the otherwise well-described Drosophila courtship display and confirm that wing colours evolve through sexual selection.Natural Environment Research Council (NERC)Leverhulme Trus
Thermal quantum and classical correlations in two qubit XX model in a nonuniform external magnetic field
We investigate how thermal quantum discord (QD) and classical correlations
(CC) of a two-qubit one-dimensional XX Heisenberg chain in thermal equilibrium
depend on the temperature of the bath as well as on nonuniform external
magnetic fields applied to two qubits and varied separately. We show that the
behavior of QD differs in many unexpected ways from the thermal entanglement
(EOF). For the nonuniform case (B1 = -B2), we find that QD and CC are equal for
all values of (B1 = -B2) and for different temperatures. We show that, in this
case, the thermal states of the system belong to a class of mixed states and
satisfy certain conditions under which QD and CC are equal. The specification
of this class and the corresponding conditions are completely general and apply
to any quantum system in a state in this class satisfying these conditions. We
further find that the relative contributions of QD and CC can be controlled
easily by changing the relative magnitudes of B1 and B2. Finally, we connect
our results with the monogamy relations between the EOF, CC and the QD of two
qubits and the environment.Comment: 8 pages, 13 figures. We connect our results with the monogamy
relations between the EOF, CC and the QD of two qubits and the environmen
Calculation of quantum discord for qubit-qudit or N qubits
Quantum discord, a kind of quantum correlation, is defined as the difference
between quantum mutual information and classical correlation in a bipartite
system. It has been discussed so far for small systems with only a few
independent parameters. We extend here to a much broader class of states when
the second party is of arbitrary dimension d, so long as the first, measured,
party is a qubit. We present two formulae to calculate quantum discord, the
first relating to the original entropic definition and the second to a recently
proposed geometric distance measure which leads to an analytical formulation.
The tracing over the qubit in the entropic calculation is reduced to a very
simple prescription. And, when the d-dimensional system is a so-called X state,
the density matrix having non-zero elements only along the diagonal and
anti-diagonal so as to appear visually like the letter X, the entropic
calculation can be carried out analytically. Such states of the full bipartite
qubit-qudit system may be named "extended X states", whose density matrix is
built of four block matrices, each visually appearing as an X. The optimization
involved in the entropic calculation is generally over two parameters, reducing
to one for many cases, and avoided altogether for an overwhelmingly large set
of density matrices as our numerical investigations demonstrate. Our results
also apply to states of a N-qubit system, where "extended X states" consist of
(2^(N+2) - 1) states, larger in number than the (2^(N+1) - 1) of X states of N
qubits. While these are still smaller than the total number (2^(2N) - 1) of
states of N qubits, the number of parameters involved is nevertheless large. In
the case of N = 2, they encompass the entire 15-dimensional parameter space,
that is, the extended X states for N = 2 represent the full qubit-qubit system.Comment: 6 pages, 1 figur
An Experimentally accessible geometric measure for entanglement in -qubit pure states
We present a multipartite entanglement measure for -qubit pure states,
using the norm of the correlation tensor which occurs in the Bloch
representation of the state. We compute this measure for several important
classes of -qubit pure states such as GHZ states, W states and their
superpositions. We compute this measure for interesting applications like one
dimensional Heisenberg antiferromagnet. We use this measure to follow the
entanglement dynamics of Grover's algorithm. We prove that this measure
possesses almost all the properties expected of a good entanglement measure,
including monotonicity. Finally, we extend this measure to -qubit mixed
states via convex roof construction and establish its various properties,
including its monotonicity. We also introduce a related measure which has all
properties of the above measure and is also additive.Comment: 23 pages, 6 figures, presented in part at ISCQI (Bhubaneswar, India),
comments are welcom
Separability and Entanglement of Quantum States Based on Covariance Matrices
We investigate the separability of quantum states based on covariance
matrices. Separability criteria are presented for multipartite states. The
lower bound of concurrence proposed in Phys. Rev. A. 75, 052320 (2007) is
improved by optimizing the local orthonormal observables.Comment: 11 page
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Ex vivo HIV entry into blood CD4+ T cells does not predict heterosexual HIV acquisition in women.
CAPRISA, 2018.Abstract available in pdf
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