5,960 research outputs found
Decreased myocardial injury and improved contractility after administration of a peptide derived against the alpha-interacting domain of the L-type calcium channel.
BackgroundMyocardial infarction remains the leading cause of morbidity and mortality associated with coronary artery disease. The L-type calcium channel (IC a-L) is critical to excitation and contraction. Activation of the channel also alters mitochondrial function. Here, we investigated whether application of a alpha-interacting domain/transactivator of transcription (AID-TAT) peptide, which immobilizes the auxiliary ÎČ2 subunit of the channel and decreases metabolic demand, could alter mitochondrial function and myocardial injury.Methods and resultsTreatment with AID-TAT peptide decreased ischemia-reperfusion injury in guinea-pig hearts ex vivo (n=11) and in rats in vivo (n=9) assessed with uptake of nitroblue tetrazolium, release of creatine kinase, and lactate dehydrogenase. Contractility (assessed with catheterization of the left ventricle) was improved after application of AID-TAT peptide in hearts ex vivo (n=6) and in vivo (n=8) up to 12 weeks before sacrifice. In search of the mechanism for the effect, we found that intracellular calcium ([Ca(2+)]i, Fura-2), superoxide production (dihydroethidium fluorescence), mitochondrial membrane potential (Κm, JC-1 fluorescence), reduced nicotinamide adenine dinucleotide production, and flavoprotein oxidation (autofluorescence) are decreased after application of AID-TAT peptide.ConclusionsApplication of AID-TAT peptide significantly decreased infarct size and supported contractility up to 12 weeks postcoronary artery occlusion as a result of a decrease in metabolic demand during reperfusion
Quantum nondemolition measurements of a particle in electric and gravitational fields
In this work we obtain a nondemolition variable for the case in which a
charged particle moves in the electric and gravitational fields of a spherical
body. Afterwards we consider the continuous monitoring of this nondemolition
parameter, and calculate along the ideas of the so called restricted path
integral formalism, the corresponding propagator. Using these results the
probabilities associated with the possible measurement outputs are evaluated.
The limit of our results, as the resolution of the measuring device goes to
zero, is analyzed, and the dependence of the corresponding propagator upon the
strength of the electric and gravitational fields are commented. The role that
mass plays in the corresponding results, and its possible connection with the
equivalence principle at quantum level, are studied.Comment: Accepted in International Journal of Modern Physics D, 14 page
Dynamical Generation of Noiseless Quantum Subsystems
We present control schemes for open quantum systems that combine decoupling
and universal control methods with coding procedures. By exploiting a general
algebraic approach, we show how appropriate encodings of quantum states result
in obtaining universal control over dynamically-generated noise-protected
subsystems with limited control resources. In particular, we provide an
efficient scheme for performing universal encoded quantum computation in a wide
class of systems subjected to linear non-Markovian quantum noise and supporting
Heisenberg-type internal Hamiltonians.Comment: 4 pages, no figures; REVTeX styl
Pulse Control of Decoherence in a Qubit Coupled with a Quantum Environment
We study the time evolution of a qubit linearly coupled with a quantum
environment under a sequence of short pi pulses. Our attention is focused on
the case where qubit-environment interactions induce the decoherence with
population decay. We assume that the environment consists of a set of bosonic
excitations. The time evolution of the reduced density matrix for the qubit is
calculated in the presence of periodic short pi pulses. We confirm that the
decoherence is suppressed if the pulse interval is shorter than the correlation
time for qubit-environment interactions.Comment: 5 pages, 2figure
Synchronized pulse control of decoherence
We present a new strategy for multipulse control over decoherence. When a
two-level system interacts with a reservoir characterized by a specific
frequency, we find that the decoherence is effectively suppressed by
synchronizing the pulse-train application with the dynamical motion of the
reservoir.Comment: 14 pages, 8 figure
Long-time electron spin storage via dynamical suppression of hyperfine-induced decoherence in a quantum dot
The coherence time of an electron spin decohered by the nuclear spin
environment in a quantum dot can be substantially increased by subjecting the
electron to suitable dynamical decoupling sequences. We analyze the performance
of high-level decoupling protocols by using a combination of analytical and
exact numerical methods, and by paying special attention to the regimes of
large inter-pulse delays and long-time dynamics, which are outside the reach of
standard average Hamiltonian theory descriptions. We demonstrate that dynamical
decoupling can remain efficient far beyond its formal domain of applicability,
and find that a protocol exploiting concatenated design provides best
performance for this system in the relevant parameter range. In situations
where the initial electron state is known, protocols able to completely freeze
decoherence at long times are constructed and characterized. The impact of
system and control non-idealities is also assessed, including the effect of
intra-bath dipolar interaction, magnetic field bias and bath polarization, as
well as systematic pulse imperfections. While small bias field and small bath
polarization degrade the decoupling fidelity, enhanced performance and temporal
modulation result from strong applied fields and high polarizations. Overall,
we find that if the relative errors of the control parameters do not exceed 5%,
decoupling protocols can still prolong the coherence time by up to two orders
of magnitude.Comment: 16 pages, 10 figures, submitted to Phys. Rev.
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A perceptual-statistics shading model
The process of surface perception is complex and based on several influencing factors, e.g., shading, silhouettes, occluding contours, and top down cognition. The accuracy of surface perception can be measured and the influencing factors can be modified in order to decrease the error in perception. This paper presents a novel concept of how a perceptual evaluation of a visualization technique can contribute to its redesign with the aim of improving the match between the distal and the proximal stimulus. During analysis of data from previous perceptual studies, we observed that the slant of 3D surfaces visualized on 2D screens is systematically underestimated. The visible trends in the error allowed us to create a statistical model of the perceived surface slant. Based on this statistical model we obtained from user experiments, we derived a new shading model that uses adjusted surface normals and aims to reduce the error in slant perception. The result is a shape-enhancement of visualization which is driven by an experimentally-founded statistical model. To assess the efficiency of the statistical shading model, we repeated the evaluation experiment and confirmed that the error in perception was decreased. Results of both user experiments are publicly-available datasets
Dynamical Decoupling Using Slow Pulses: Efficient Suppression of 1/f Noise
The application of dynamical decoupling pulses to a single qubit interacting
with a linear harmonic oscillator bath with spectral density is studied,
and compared to the Ohmic case. Decoupling pulses that are slower than the
fastest bath time-scale are shown to drastically reduce the decoherence rate in
the case. Contrary to conclusions drawn from previous studies, this shows
that dynamical decoupling pulses do not always have to be ultra-fast. Our
results explain a recent experiment in which dephasing due to charge
noise affecting a charge qubit in a small superconducting electrode was
successfully suppressed using spin-echo-type gate-voltage pulses.Comment: 5 pages, 3 figures. v2: Many changes and update
Tracing the evolution in the iron content of the ICM
We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies
at z>0.3, which cover a temperature range of 3>kT>15 keV. Our analysis is aimed
at measuring the iron abundance in the ICM out to the highest redshift probed
to date. We find that the emission-weighted iron abundance measured within
(0.15-0.3)R_vir in clusters below 5 keV is, on average, a factor of ~2 higher
than in hotter clusters, following Z(T)~0.88T^-(0.47)Z_o, which confirms the
trend seen in local samples. We made use of combined spectral analysis
performed over five redshift bins at 0.3>z>1.3 to estimate the average emission
weighted iron abundance. We find a constant average iron abundance Z_Fe~0.25Z_o
as a function of redshift, but only for clusters at z>0.5. The
emission-weighted iron abundance is significantly higher (Z_Fe~0.4Z_o) in the
redshift range z~0.3-0.5, approaching the value measured locally in the inner
0.15R_vir radii for a mix of cool-core and non cool-core clusters in the
redshift range 0.1<z<0.3. The decrease in Z_Fe with redshift can be
parametrized by a power law of the form ~(1+z)^(-1.25). The observed evolution
implies that the average iron content of the ICM at the present epoch is a
factor of ~2 larger than at z=1.2. We confirm that the ICM is already
significantly enriched (Z_Fe~0.25Z_o) at a look-back time of 9 Gyr. Our data
provide significant constraints on the time scales and physical processes that
drive the chemical enrichment of the ICM.Comment: 6 pages, 6 figures, to appear in the Proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching
(Germany
Pulse Control of Decoherence with Population Decay
The pulse control of decoherence in a qubit interacting with a quantum
environment is studied with focus on a general case where decoherence is
induced by both pure dephasing and population decay. To observe how the
decoherence is suppressed by periodic pi pulses, we present a simple method to
calculate the time evolution of a qubit under arbitrary pulse sequences
consisting of bit-flips and/or phase-flips. We examine the effectiveness of the
two typical sequences: bb sequence consisting of only bit-flips, and bp
sequence consisting of both bit- and phase-flips. It is shown that the
effectiveness of the pulse sequences depends on a relative strength of the two
decoherence processes especially when a pulse interval is slightly shorter than
qubit-environment correlation times. In the short-interval limit, however, the
bp sequence is always more effective than, or at least as effective as, the bb
sequence.Comment: 11 pages, 7 figure
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