5,421 research outputs found
Proto-clusters in the Lambda CDM Universe
We compare the highly clustered populations of very high redshift galaxies
with proto-clusters identified numerically in a standard CDM universe
() simulation. We evolve 256^3 dark matter
particles in a comoving box of side 150h^{-1}Mpc. By the present day there are
63 cluster sized objects of mass in excess of 10^{14}h^{-1}Mo in this box. We
trace these clusters back to higher redshift finding that their progenitors at
z=4--5 are extended regions of typically 20--40 Mpc (comoving) in size, with
dark halos of mass in excess of 10^{12}h^{-1}Mo and are overdense by typically
1.3--13 times the cosmological mean density. Comparison with the observation of
Lyman alpha emitting (LAEs) galaxies at z=4.86 and at z=4.1 indicates that the
observed excess clustering is consistent with that expected for a proto-cluster
region if LAEs typically correspond to massive dark halos of more than
10^{12}h^{-1}Mo. We give a brief discussion on the relation between high
redshift concentration of massive dark halos and present day rich clusters of
galaxies.Comment: 4 pages, 5 figures, Accepted for publication in ApJ Letter
Demonstration of deterministic and high fidelity squeezing of quantum information
By employing at recent proposal (R. Filip, P. Marek and U.L. Andersen, Phys.
Rev. A {\bf 71}, 042308 (2005) \cite{Filip05.pra}), we experimentally
demonstrate a universal, deterministic and high-fidelity squeezing
transformation of an optical field. It relies only on linear optics, homodyne
detection, feedforward and an ancillary squeezed vacuum state, thus direct
interaction between a strong pump and the quantum state is circumvented. We
demonstrate three different squeezing levels for a coherent state input. This
scheme is highly suitable for the fault-tolerant squeezing transformation in a
continuous variable quantum computer.Comment: 5 pages, 4 figure
Quantum error correction beyond qubits
Quantum computation and communication rely on the ability to manipulate
quantum states robustly and with high fidelity. Thus, some form of error
correction is needed to protect fragile quantum superposition states from
corruption by so-called decoherence noise. Indeed, the discovery of quantum
error correction (QEC) turned the field of quantum information from an academic
curiosity into a developing technology. Here we present a continuous-variable
experimental implementation of a QEC code, based upon entanglement among 9
optical beams. In principle, this 9-wavepacket adaptation of Shor's original
9-qubit scheme allows for full quantum error correction against an arbitrary
single-beam (single-party) error.Comment: realization of a Gaussian error correction protocol suitable for
non-Gaussian error correctio
Ultraviolet Line Emission from Metals in the Low-Redshift Intergalactic Medium
We use a high-resolution cosmological simulation that includes hydrodynamics,
multiphase star formation, and galactic winds to predict the distribution of
metal line emission at z~0 from the intergalactic medium (IGM). We focus on two
ultraviolet doublet transitions, OVI 1032,1038 and CIV 1548,1551. Emission from
filaments with moderate overdensities is orders of magnitude smaller than the
background, but isolated emission from enriched, dense regions with
T~10^5-10^5.5 K and characteristic sizes of 50-100 kpc can be detected above
the background. We show that the emission from these regions is substantially
greater when we use the metallicities predicted by the simulation (which
includes enrichment through galactic winds) than when we assume a uniform IGM
metallicity. Luminous regions correspond to volumes that have recently been
influenced by galactic winds. We also show that the line emission is clustered
on scales ~1 h^-1 Mpc. We argue that although these transitions are not
effective tracers of the warm-hot intergalactic medium, they do provide a route
to study the chemical enrichment of the IGM and the physics of galactic winds.Comment: replaced by version to appear in ApJ (conclusions unchanged, one new
figure), 16 pages (emulateapj), 11 figures, version with higher resolution
figures available at
http://www.tapir.caltech.edu/~sfurlane/metals/coverpage.htm
A Numerical Method for Calculating the Wave Drag of a Configuration from the Second Derivative of the Area Distribution of a Series of Equivalent Bodies of Revolution
A method based on linearized and slender-body theories, which is easily adapted to electronic-machine computing equipment, is developed for calculating the zero-lift wave drag of single- and multiple-component configurations from a knowledge of the second derivative of the area distribution of a series of equivalent bodies of revolution. The accuracy and computational time required of the method to calculate zero-lift wave drag is evaluated relative to another numerical method which employs the Tchebichef form of harmonic analysis of the area distribution of a series of equivalent bodies of revolution. The results of the evaluation indicate that the total zero-lift wave drag of a multiple-component configuration can generally be calculated most accurately as the sum of the zero-lift wave drag of each component alone plus the zero-lift interference wave drag between all pairs of components. The accuracy and computational time required of both methods to calculate total zero-lift wave drag at supersonic Mach numbers is comparable for airplane-type configurations. For systems of bodies of revolution both methods yield similar results with comparable accuracy; however, the present method only requires up to 60 percent of the computing time required of the harmonic-analysis method for two bodies of revolution and less time for a larger number of bodies
Dynamic Innate Immune Responses of Human Bronchial Epithelial Cells to Severe Acute Respiratory Syndrome-Associated Coronavirus Infection
Human lung epithelial cells are likely among the first targets to encounter invading severe acute respiratory syndrome-associated coronavirus (SARS-CoV). Not only can these cells support the growth of SARS-CoV infection, but they are also capable of secreting inflammatory cytokines to initiate and, eventually, aggravate host innate inflammatory responses, causing detrimental immune-mediated pathology within the lungs. Thus, a comprehensive evaluation of the complex epithelial signaling to SARS-CoV is crucial for paving the way to better understand SARS pathogenesis. Based on microarray-based functional genomics, we report here the global gene response of 2B4 cells, a cloned bronchial epithelial cell line derived from Calu-3 cells. Specifically, we found a temporal and spatial activation of nuclear factor (NF)κB, activator protein (AP)-1, and interferon regulatory factor (IRF)-3/7 in infected 2B4 cells at 12-, 24-, and 48-hrs post infection (p.i.), resulting in the activation of many antiviral genes, including interferon (IFN)-β, -λs, inflammatory mediators, and many IFN-stimulated genes (ISGs). We also showed, for the first time, that IFN-β and IFN-λs were capable of exerting previously unrecognized, non-redundant, and complementary abilities to limit SARS-CoV replication, even though their expression could not be detected in infected 2B4 bronchial epithelial cells until 48 hrs p.i. Collectively, our results highlight the mechanics of the sequential events of antiviral signaling pathway/s triggered by SARS-CoV in bronchial epithelial cells and identify novel cellular targets for future studies, aiming at advancing strategies against SARS
Low-latency adiabatic quantum-flux-parametron circuit integrated with a hybrid serializer/deserializer
Adiabatic quantum-flux-parametron (AQFP) logic is an ultra-low-power
superconductor logic family. AQFP logic gates are powered and clocked by
dedicated clocking schemes using ac excitation currents to implement an
energy-efficient switching process, adiabatic switching. We have proposed a
low-latency clocking scheme, delay-line clocking, and demonstrated basic AQFP
logic gates. In order to test more complex circuits, a serializer/deserializer
(SerDes) should be incorporated into the AQFP circuit under test, since the
number of input/output (I/O) cables is limited by equipment. Therefore, in the
present study we propose and develop a novel SerDes for testing
delay-line-clocked AQFP circuits by combining AQFP and rapid
single-flux-quantum (RSFQ) logic families, which we refer to as the AQFP/RSFQ
hybrid SerDes. The hybrid SerDes comprises RSFQ shift registers to facilitate
the data storage during serial-to-parallel and parallel-to-serial conversion.
Furthermore, all the component circuits in the hybrid SerDes are clocked by the
identical excitation current to synchronize the AQFP and RSFQ parts. We
fabricate and demonstrate a delay-line-clocked AQFP circuit (8-to-3 encoder,
which is the largest delay-line-clocked circuit ever designed) integrated with
the hybrid SerDes at 4.2 K up to 4.5 GHz. Our measurement results indicate that
the hybrid SerDes enables the testing of delay-line-clocked AQFP circuits with
only a few I/O cables and is thus a powerful tool for the development of very
large-scale integration AQFP circuits.Comment: 7 pages, 6 figure
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