225 research outputs found
Vital Functions Contribute to the Spread of Extracellular Fluids in the Brain: Comparison Between Life and Death
Vascular pulsations, contractions of vascular smooth muscle cells and breathing have
been reported to foster movement and clearance of interstitial and cerebrospinal
fluids from the brain. The aim of this study was to estimate the contribution of
these vital functions. We compared the spread of an injected hydrophilic tracer
(Fluoro-Emerald, a 10 kDa fluorescein-coupled dextran amine) in the brains of live
anesthetized and sacrificed rats at 30 and 90 min after injection. To determine the
overall pattern of distribution of tracers, we created 3D-reconstructions of the horizontal
transections of the whole brain. Immunofluorescence staining with laminin and collagen
IV was performed to determine the pattern of distribution of tracer in relation to the
cerebrovascular basement membranes. We found that diffusion was widely restricted
to the periventricular region in sacrificed rats with no spread to the contralateral
hemisphere, while the bulk flow occurred along the vasculature and reached the
surface and the contralateral hemisphere as soon as 30 min after injection in live
anesthetized animals. The tracer appeared to be localized along the vascular basement
membranes and along fiber tracts as reported previously. Thus, our data indicate that
vital functions are essential for the remote movement of extracellular fluids within the
cerebral parenchyma
Black Hole--Scalar Field Interactions in Spherical Symmetry
We examine the interactions of a black hole with a massless scalar field
using a coordinate system which extends ingoing Eddington-Finkelstein
coordinates to dynamic spherically symmetric-spacetimes. We avoid problems with
the singularity by excising the region of the black hole interior to the
apparent horizon. We use a second-order finite difference scheme to solve the
equations. The resulting program is stable and convergent and will run forever
without problems. We are able to observe quasi-normal ringing and power-law
tails as well an interesting nonlinear feature.Comment: 16 pages, 26 figures, RevTex, to appear in Phys. Rev.
No-go theorem for false vacuum black holes
We study the possibility of non-singular black hole solutions in the theory
of general relativity coupled to a non-linear scalar field with a positive
potential possessing two minima: a `false vacuum' with positive energy and a
`true vacuum' with zero energy. Assuming that the scalar field starts at the
false vacuum at the origin and comes to the true vacuum at spatial infinity, we
prove a no-go theorem by extending a no-hair theorem to the black hole
interior: no smooth solutions exist which interpolate between the local de
Sitter solution near the origin and the asymptotic Schwarzschild solution
through a regular event horizon or several horizons.Comment: 16 pages, 1 figure, Latex, some references added, to appear in
Classical and Quantum Gravit
Fidelity trade-off for finite ensembles of identically prepared qubits
We calculate the trade-off between the quality of estimating the quantum
state of an ensemble of identically prepared qubits and the minimum level of
disturbance that has to be introduced by this procedure in quantum mechanics.
The trade-off is quantified using two mean fidelities: the operation fidelity
which characterizes the average resemblance of the final qubit state to the
initial one, and the estimation fidelity describing the quality of the obtained
estimate. We analyze properties of quantum operations saturating the
achievability bound for the operation fidelity versus the estimation fidelity,
which allows us to reduce substantially the complexity of the problem of
finding the trade-off curve. The reduced optimization problem has the form of
an eigenvalue problem for a set of tridiagonal matrices, and it can be easily
solved using standard numerical tools.Comment: 26 pages, REVTeX, 2 figures. Few minor corrections, accepted for
publication in Physical Review
Neuronal damage in autoimmune neuroinflammation mediated by the death ligand TRAIL
Here, we provide evidence for a detrimental role of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in neural death in T cell-induced experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Clinical severity and neuronal apoptosis in brainstem motor areas were substantially reduced upon brain-specific blockade of TRAIL after induction of EAE through adoptive transfer of encephalitogenic T cells. Furthermore, TRAIL-deficient myelin-specific lymphocytes showed reduced encephalitogenicity when transferred to wild-type mice. Conversely, intracerebral delivery of TRAIL to animals with EAE increased clinical deficits, while naive mice were not susceptible to TRAIL. Using organotypic slice cultures as a model for living brain tissue, we found that neurons were susceptible to TRAIL-mediated injury induced by encephalitogenic T cells. Thus, in addition to its known immunoregulatory effects, the death ligand TRAIL contributes to neural damage in the inflamed brain
Quantum Distribution of Gaussian Keys with Squeezed States
A continuous key distribution scheme is proposed that relies on a pair of
canonically conjugate quantum variables. It allows two remote parties to share
a secret Gaussian key by encoding it into one of the two quadrature components
of a single-mode electromagnetic field. The resulting quantum cryptographic
information vs disturbance tradeoff is investigated for an individual attack
based on the optimal continuous cloning machine. It is shown that the
information gained by the eavesdropper then simply equals the information lost
by the receiver.Comment: 5 pages, RevTe
Parity proofs of the Bell-Kochen-Specker theorem based on the 600-cell
The set of 60 real rays in four dimensions derived from the vertices of a
600-cell is shown to possess numerous subsets of rays and bases that provide
basis-critical parity proofs of the Bell-Kochen-Specker (BKS) theorem (a
basis-critical proof is one that fails if even a single basis is deleted from
it). The proofs vary considerably in size, with the smallest having 26 rays and
13 bases and the largest 60 rays and 41 bases. There are at least 90 basic
types of proofs, with each coming in a number of geometrically distinct
varieties. The replicas of all the proofs under the symmetries of the 600-cell
yield a total of almost a hundred million parity proofs of the BKS theorem. The
proofs are all very transparent and take no more than simple counting to
verify. A few of the proofs are exhibited, both in tabular form as well as in
the form of MMP hypergraphs that assist in their visualization. A survey of the
proofs is given, simple procedures for generating some of them are described
and their applications are discussed. It is shown that all four-dimensional
parity proofs of the BKS theorem can be turned into experimental disproofs of
noncontextuality.Comment: 19 pages, 11 tables, 3 figures. Email address of first author has
been corrected. Ref.[5] has been corrected, as has an error in Fig.3.
Formatting error in Sec.4 has been corrected and the placement of tables and
figures has been improved. A new paragraph has been added to Sec.4 and
another new paragraph to the end of the Appendi
Parity proofs of the Kochen-Specker theorem based on the 24 rays of Peres
A diagrammatic representation is given of the 24 rays of Peres that makes it
easy to pick out all the 512 parity proofs of the Kochen-Specker theorem
contained in them. The origin of this representation in the four-dimensional
geometry of the rays is pointed out.Comment: 14 pages, 6 figures and 3 tables. Three references have been added.
Minor typos have been correcte
Controlling passively-quenched single photon detectors by bright light
Single photon detectors based on passively-quenched avalanche photodiodes can
be temporarily blinded by relatively bright light, of intensity less than a
nanowatt. I describe a bright-light regime suitable for attacking a quantum key
distribution system containing such detectors. In this regime, all single
photon detectors in the receiver Bob are uniformly blinded by continuous
illumination coming from the eavesdropper Eve. When Eve needs a certain
detector in Bob to produce a click, she modifies polarization (or other
parameter used to encode quantum states) of the light she sends to Bob such
that the target detector stops receiving light while the other detector(s)
continue to be illuminated. The target detector regains single photon
sensitivity and, when Eve modifies the polarization again, produces a single
click. Thus, Eve has full control of Bob and can do a successful
intercept-resend attack. To check the feasibility of the attack, 3 different
models of passively-quenched detectors have been tested. In the experiment, I
have simulated the intensity diagrams the detectors would receive in a real
quantum key distribution system under attack. Control parameters and side
effects are considered. It appears that the attack could be practically
possible.Comment: Experimental results from a third detector model added. Minor
corrections and edits made. 11 pages, 10 figure
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