22,085 research outputs found
Transition from Icosahedral to Decahedral Structure in a Coexisting Solid-Liquid Nickel Cluster
We have used molecular dynamics simulations to construct a microcanonical
caloric curve for a 1415-atom Ni icosahedron. Prior to melting the Ni cluster
exhibits static solid-liquid phase coexistence. Initially a partial icosahedral
structure coexists with a non-wetting melt. However at energies very close to
the melting point the icosahedral structure is replaced by a truncated
decahedral structure which is almost fully wet by the melt. This structure
remains until the cluster fully melts. The transition appears to be driven by a
preference for the melt to wet the decahedral structure.Comment: 7 pages, 6 figure
Implementable Quantum Bit-String Commitment Protocol
Quantum bit-string commitment[A.Kent, Phys.Rev.Lett., 90, 237901 (2003)] or
QBSC is a variant of bit commitment (BC). In this paper, we propose a new QBSC
protocol that can be implemented using currently available technology, and
prove its security under the same security criteria as discussed by Kent. QBSC
is a generalization of BC, but has slightly weaker requirements, and our
proposed protocol is not intended to break the no-go theorem of quantum BC.Comment: To appear in Phys. Rev. A., 9 pages, 2 figure
Classical Concepts in Quantum Programming
The rapid progress of computer technology has been accompanied by a
corresponding evolution of software development, from hardwired components and
binary machine code to high level programming languages, which allowed to
master the increasing hardware complexity and fully exploit its potential.
This paper investigates, how classical concepts like hardware abstraction,
hierarchical programs, data types, memory management, flow of control and
structured programming can be used in quantum computing. The experimental
language QCL will be introduced as an example, how elements like irreversible
functions, local variables and conditional branching, which have no direct
quantum counterparts, can be implemented, and how non-classical features like
the reversibility of unitary transformation or the non-observability of quantum
states can be accounted for within the framework of a procedural programming
language.Comment: 11 pages, 4 figures, software available from
http://tph.tuwien.ac.at/~oemer/qcl.html, submitted for QS2002 proceeding
Serum Concentration and Chemotactic Activity of E-selectin (CD62E) in Inflammatory Bowel Disease
E-selectin (CD62E) is an endothelial specific glycoprotein belonging
to the selectin family of adhesion molecules. Because a high
expression of this molecule at intestinal mucosal surfaces in
inflammatory bowel disease (IBD) has been described earlier, the aim
was to assess serum levels of E-selectin (sE-selectin) and to
correlate it to disease activity, and further to evaluate its
chemotactic properties at physiological concentrations. Levels of
sEselectin were measured by a sandwich ELISA technique in 31 IBD
patients together with 15 healthy volunteers. In ulcerative colitis
the median value was 0.46 nM (0.16–0.75), in Crohn’s disease
0.47 nM (0.22–1.24), and in healthy controls 0.34 nM
(0.22–0.83). No statistically significant differences in
sE-selectin were revealed between these groups (p > 0.05). The in vitro chemotactic capabilities of E-selectin (in the
concentration range of 0.10–31.4 nM) were assessed using the
leading front technique. A significantly increased migratory
response was found at concentrations of 1.00 (p < 0.05) and 3.14 nM (p < 0.02). It is concluded that sE-selectin in
contrast to sICAM-1 does not act as a sensitive indicator of local
immune activation in IBD. However, E-selectin may be important for
recruitment and accumulation of neutrophilic granulocytes and other
phagocytes involved in the inflammatory process seen in IBD. Future
investigations are encouraged in order to reveal its in
vivo effects
Soluble interleukin-2 receptors in ulcerative colitis
T-Cell activation results in the release or shedding of a soluble form (45 kDa) of the cellular (55 kDa) low-affinity interleukin-2 receptor (α-chain) (slL-2R). The present study was performed to investigate if the serum concentration of sIL-2R is a marker of disease activity in patients with ulcerative colitis (UC), a chronic inflammatory bowel disease. Twenty-seven UC patients (about half of them in remission) and 13 healthy volunteers were studied, sIL-2R concentrations were measured by an enzyme-linked immunosorbent assay, and significantly elevated median sIL-2R values were found in clinically active UC (150 pg/ml; range 100–420), compared to inactive UC (145 pg/ml; range 110–255), and healthy controls (110 pg/ml; range 80–165) (p < 0.01). There was no correlation between sIL-2R concentrations and extent of the disease. Due to the overlap of serum sIL-2R concentrations between different disease stages and controls, the general diagnostic value seems to be limited. However, since slL-2R release is an IL-2 dependent phenomenon, we conclude that the demonstration of increased serum sIL-2R concentrations in UC suggests the existence of an enhanced T-cell activation in vivo in this disease. Further longitudinal studies are required to elucidate if repeated measurements of sIL-2R levels provide an additional way of monitoring UC disease activity in individual patients
On some non-conformal fractals
This paper presents a simple method of calculating the Hausdorff dimension
for a class of non-conformal fractals
Entanglement Patterns in Mutually Unbiased Basis Sets for N Prime-state Particles
A few simply-stated rules govern the entanglement patterns that can occur in
mutually unbiased basis sets (MUBs), and constrain the combinations of such
patterns that can coexist (ie, the stoichiometry) in full complements of p^N+1
MUBs. We consider Hilbert spaces of prime power dimension (as realized by
systems of N prime-state particles, or qupits), where full complements are
known to exist, and we assume only that MUBs are eigenbases of generalized
Pauli operators, without using a particular construction. The general rules
include the following: 1) In any MUB, a particular qupit appears either in a
pure state, or totally entangled, and 2) in any full MUB complement, each qupit
is pure in p+1 bases (not necessarily the same ones), and totally entangled in
the remaining p^N-p. It follows that the maximum number of product bases is
p+1, and when this number is realized, all remaining p^N-p bases in the
complement are characterized by the total entanglement of every qupit. This
"standard distribution" is inescapable for two qupits (of any p), where only
product and generalized Bell bases are admissible MUB types. This and the
following results generalize previous results for qubits and qutrits. With
three qupits there are three MUB types, and a number of combinations (p+2) are
possible in full complements. With N=4, there are 6 MUB types for p=2, but new
MUB types become possible with larger p, and these are essential to the
realization of full complements. With this example, we argue that new MUB
types, showing new entanglement characteristics, should enter with every step
in N, and when N is a prime plus 1, also at critical p values, p=N-1. Such MUBs
should play critical roles in filling complements.Comment: 27 pages, one figure, to be submitted to Physical Revie
Entropy inequalities from reflection positivity
We investigate the question of whether the entropy and the Renyi entropies of
the vacuum state reduced to a region of the space can be represented in terms
of correlators in quantum field theory. In this case, the positivity relations
for the correlators are mapped into inequalities for the entropies. We write
them using a real time version of reflection positivity, which can be
generalized to general quantum systems. Using this generalization we can prove
an infinite sequence of inequalities which are obeyed by the Renyi entropies of
integer index. There is one independent inequality involving any number of
different subsystems. In quantum field theory the inequalities acquire a simple
geometrical form and are consistent with the integer index Renyi entropies
being given by vacuum expectation values of twisting operators in the Euclidean
formulation. Several possible generalizations and specific examples are
analyzed.Comment: Significantly enlarged and corrected version. Counterexamples found
for the most general form of the inequalities. V3: minor change
Teleportation in a noisy environment: a quantum trajectories approach
We study the fidelity of quantum teleportation for the situation in which
quantum logic gates are used to provide the long distance entanglement required
in the protocol, and where the effect of a noisy environment is modeled by
means of a generalized amplitude damping channel. Our results demonstrate the
effectiveness of the quantum trajectories approach, which allows the simulation
of open systems with a large number of qubits (up to 24). This shows that the
method is suitable for modeling quantum information protocols in realistic
environments.Comment: 9 pages, 2 figure
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