2,104 research outputs found
System Design for a Long-Line Quantum Repeater
We present a new control algorithm and system design for a network of quantum
repeaters, and outline the end-to-end protocol architecture. Such a network
will create long-distance quantum states, supporting quantum key distribution
as well as distributed quantum computation. Quantum repeaters improve the
reduction of quantum-communication throughput with distance from exponential to
polynomial. Because a quantum state cannot be copied, a quantum repeater is not
a signal amplifier, but rather executes algorithms for quantum teleportation in
conjunction with a specialized type of quantum error correction called
purification to raise the fidelity of the quantum states. We introduce our
banded purification scheme, which is especially effective when the fidelity of
coupled qubits is low, improving the prospects for experimental realization of
such systems. The resulting throughput is calculated via detailed simulations
of a long line composed of shorter hops. Our algorithmic improvements increase
throughput by a factor of up to fifty compared to earlier approaches, for a
broad range of physical characteristics.Comment: 12 pages, 13 figures. v2 includes one new graph, modest corrections
to some others, and significantly improved presentation. to appear in
IEEE/ACM Transactions on Networkin
Supercoherent states and physical systems
A method is developed for obtaining coherent states of a system admitting a supersymmetry. These states are called supercoherent states. The presented approach is based on an extension to supergroups of the usual group-theoretic approach. The example of the supersymmetric harmonic oscillator is discussed, thereby illustrating some of the attractive features of the method. Supercoherent states of an electron moving in a constant magnetic field are also described
Infrasonic observations of large-scale HE events
The Los Alamos Infrasound Program has been operating since about mid-1982, making routine measurements of low frequency atmospheric acoustic propagation. Generally, the authors work between 0.1 Hz to 10 Hz; however, much of the work is concerned with the narrower range of 0.5 to 5.0 Hz. Two permanent stations, St. George, UT, and Los Alamos, NM, have been operational since 1983, collecting data 24 hours a day. For the purposes of this discussion, the authors concentrate on their measurements of large, high explosive (HE) events at ranges of 250 km to 5330 km. Because their equipment is well suited for mobile deployments, they can easily establish temporary observing sites for special events. The measurements are from the permanent sites, as well as from various temporary sites. A few observations that are typical of the full data set are given
Asymptotic enumeration of correlation-immune boolean functions
A boolean function of boolean variables is {correlation-immune} of order
if the function value is uncorrelated with the values of any of the
arguments. Such functions are of considerable interest due to their
cryptographic properties, and are also related to the orthogonal arrays of
statistics and the balanced hypercube colourings of combinatorics. The {weight}
of a boolean function is the number of argument values that produce a function
value of 1. If this is exactly half the argument values, that is,
values, a correlation-immune function is called {resilient}.
An asymptotic estimate of the number of -variable
correlation-immune boolean functions of order was obtained in 1992 by
Denisov for constant . Denisov repudiated that estimate in 2000, but we will
show that the repudiation was a mistake.
The main contribution of this paper is an asymptotic estimate of
which holds if increases with within generous limits and specialises to
functions with a given weight, including the resilient functions. In the case
of , our estimates are valid for all weights.Comment: 18 page
Arithmetic on a Distributed-Memory Quantum Multicomputer
We evaluate the performance of quantum arithmetic algorithms run on a
distributed quantum computer (a quantum multicomputer). We vary the node
capacity and I/O capabilities, and the network topology. The tradeoff of
choosing between gates executed remotely, through ``teleported gates'' on
entangled pairs of qubits (telegate), versus exchanging the relevant qubits via
quantum teleportation, then executing the algorithm using local gates
(teledata), is examined. We show that the teledata approach performs better,
and that carry-ripple adders perform well when the teleportation block is
decomposed so that the key quantum operations can be parallelized. A node size
of only a few logical qubits performs adequately provided that the nodes have
two transceiver qubits. A linear network topology performs acceptably for a
broad range of system sizes and performance parameters. We therefore recommend
pursuing small, high-I/O bandwidth nodes and a simple network. Such a machine
will run Shor's algorithm for factoring large numbers efficiently.Comment: 24 pages, 10 figures, ACM transactions format. Extended version of
Int. Symp. on Comp. Architecture (ISCA) paper; v2, correct one circuit error,
numerous small changes for clarity, add reference
Long slit spectroscopy of NH2 in comets Halley, Wilson, and Nishikawa-Takamizawa-Tago
Long-slit spectra of comets Halley, Wilson and Nishikawa-Takamizawa-Tago were obtained with the 3.9 meter Anglo-Australian Telescope. Spectra of comets Halley and Wilson were obtained with the IPCS at a spectral resolution of 0.5 A and a spatial resolution of 10(exp 3) km. Spectra of comets Wilson and Nishikawa-Takamizawa-Tago were obtained with a CCD at a spectral resolution of 1.5 A and a spatial resolution of approximately 3 x 10(exp 3) km. Surface brightness profiles for NH2 were extracted from the long-slit spectra of each comet. The observed surface brightness profiles extend along the slit to approximately 6 x 10(exp 4) km from the nucleus in both sunward and tailward directions. By comparing surface distribution calculated from an appropriate coma model with observed surface brightness distributions, the photodissociation timescale of the parent molecule of NH2 can be inferred. The observed NH2 surface brightness profiles in all three comets compares well with a surface brightness profile calculated using the vectorial model, an NH3 photodissociation timescale of 7 x 10(exp 3) seconds, and an NH2 photodissociation timescale of 34,000 seconds
Mach number and wall thermal boundary condition effects on near-wall compressible turbulence
We investigate the effects of thermal boundary conditions and Mach number on
turbulence close to walls. In particular, we study the near-wall asymptotic
behavior for adiabatic and pseudo-adiabatic walls, and compare to the
asymptotic behavior recently found near isothermal cold walls (Baranwal et al.
(2022)). This is done by analyzing a new large database of highly-resolved
direct numerical simulations of turbulent channels with different wall thermal
conditions and centerline Mach numbers. We observe that the asymptotic
power-law behavior of Reynolds stresses as well as heat fluxes does change with
both centerline Mach number and thermal-condition at the wall. Power-law
exponents transition from their analytical expansion for solenoidal fields to
those for non-solenoidal field as the Mach number is increased, though this
transition is found to be dependent on the thermal boundary conditions. The
correlation coefficients between velocity and temperature are also found to be
affected by these factors. Consistent with recent proposals on universal
behavior of compressible turbulence, we find that dilatation at the wall is the
key scaling parameter for this power-law exponents providing a universal
functional law which can provide a basis for general models of near-wall
behavior.Comment: 24 pages, 15 figures, Under consideration for publication in Journal
of Fluid Mechanic
Quantum Repeater with Encoding
We propose a new approach to implement quantum repeaters for long distance
quantum communication. Our protocol generates a backbone of encoded Bell pairs
and uses the procedure of classical error correction during simultaneous
entanglement connection. We illustrate that the repeater protocol with simple
Calderbank-Shor-Steane (CSS) encoding can significantly extend the
communication distance, while still maintaining a fast key generation rate.Comment: 11 pages, 5 figures (add new section III with an explicit example and
new appendix A
TGF beta 1 attenuates expression of prolactin and IGFBP-1 in decidualized endometrial stromal cells by both SMAD-dependent and SMAD-independent pathways
Background: Decidualization (differentiation) of the endometrial stromal cells during the secretory phase of the menstrual cycle is essential for successful implantation. Transforming Growth Factor beta 1 (TGF beta 1) canonically propagates its actions via SMAD signalling. A role for TGF beta 1 in decidualization remains to be established and published data concerning effects of TGF beta 1 on markers of endometrial decidualization are inconsistent.
Methodology/Principal Findings: Non-pregnant endometrial stromal cells (ESC) and first trimester decidual stromal cells (DSC) were cultured in the presence or absence of a decidualizing stimulus. Incubation of ESCs with TGF beta 1 (10 ng/ml) down-regulated the expression of transcripts encoding the decidual marker proteins prolactin (PRL), insulin-like growth factor binding protein-1 (IGFBP-1) and tissue factor (TF). TGF beta 1 also inhibited secretion of PRL and IGFBP-1 proteins by ESCs and surprisingly this response preceded down-regulation of their mRNAs. In contrast, DSCs were more refractory to the actions of TGF beta 1, characterized by blunted and delayed down-regulation of PRL, IGFBP-1, and TF transcripts, which was not associated with a significant reduction in secretion of PRL or IGFBP-1 proteins. Addition of an antibody directed against TGF beta 1 increased expression of IGFBP-1 mRNA in decidualised cells. Knockdown of SMAD 4 using siRNAs abrogated the effect of TGF beta 1 on expression of PRL in ESCs but did not fully restore expression of IGFBP-1 mRNA and protein.
Conclusions/Significance: TGF beta 1 inhibits the expression and secretion of decidual marker proteins. The impact of TGF beta 1 on PRL is SMAD-dependent but the impact on IGFBP1 is via an alternative mechanism. In early pregnancy, resistance of DSC to the impact of TGF beta 1 may be important to ensure tissue homeostasis
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