470 research outputs found
Cotreatment with a novel phosphoinositide analogue inhibitor and carmustine enhances chemotherapeutic efficacy by attenuating AKT activity in gliomas
On the Effect of Quantum Interaction Distance on Quantum Addition Circuits
We investigate the theoretical limits of the effect of the quantum
interaction distance on the speed of exact quantum addition circuits. For this
study, we exploit graph embedding for quantum circuit analysis. We study a
logical mapping of qubits and gates of any -depth quantum adder
circuit for two -qubit registers onto a practical architecture, which limits
interaction distance to the nearest neighbors only and supports only one- and
two-qubit logical gates. Unfortunately, on the chosen -dimensional practical
architecture, we prove that the depth lower bound of any exact quantum addition
circuits is no longer , but . This
result, the first application of graph embedding to quantum circuits and
devices, provides a new tool for compiler development, emphasizes the impact of
quantum computer architecture on performance, and acts as a cautionary note
when evaluating the time performance of quantum algorithms.Comment: accepted for ACM Journal on Emerging Technologies in Computing
System
Reducing reflections from mesh refinement interfaces in numerical relativity
Full interpretation of data from gravitational wave observations will require
accurate numerical simulations of source systems, particularly binary black
hole mergers. A leading approach to improving accuracy in numerical relativity
simulations of black hole systems is through fixed or adaptive mesh refinement
techniques. We describe a manifestation of numerical interface truncation error
which appears as slowly converging, artificial reflections from refinement
boundaries in a broad class of mesh refinement implementations, potentially
compromising the effectiveness of mesh refinement techniques for some numerical
relativity applications if left untreated. We elucidate this numerical effect
by presenting a model problem which exhibits the phenomenon, but which is
simple enough that its numerical error can be understood analytically. Our
analysis shows that the effect is caused by variations in finite differencing
error generated across low and high resolution regions, and that its slow
convergence is caused by the presence of dramatic speed differences among
propagation modes typical of 3+1 relativity. Lastly, we resolve the problem,
presenting a class of finite differencing stencil modifications, termed
mesh-adapted differencing (MAD), which eliminate this pathology in both our
model problem and in numerical relativity examples.Comment: 7 page
Consistency of post-Newtonian waveforms with numerical relativity
General relativity predicts the gravitational wave signatures of coalescing
binary black holes. Explicit waveform predictions for such systems, required
for optimal analysis of observational data, have so far been achieved using the
post-Newtonian (PN) approximation. The quality of this treatment is unclear,
however, for the important late-inspiral portion. We derive late-inspiral
waveforms via a complementary approach, direct numerical simulation of
Einstein's equations. We compare waveform phasing from simulations of the last
cycles of gravitational radiation from equal-mass, nonspinning black
holes with the corresponding 2.5PN, 3PN, and 3.5PN orbital phasing. We find
phasing agreement consistent with internal error estimates based on either
approach, suggesting that PN waveforms for this system are effective until the
last orbit prior to final merger.Comment: Replaced with published version -- one figure removed, text and other
figures updated for clarity of discussio
Quantum Estimation of Parameters of Classical Spacetimes
We describe a quantum limit to measurement of classical spacetimes.
Specifically, we formulate a quantum Cramer-Rao lower bound for estimating the
single parameter in any one-parameter family of spacetime metrics. We employ
the locally covariant formulation of quantum field theory in curved spacetime,
which allows for a manifestly background-independent derivation. The result is
an uncertainty relation that applies to all globally hyperbolic spacetimes.
Among other examples, we apply our method to detection of gravitational waves
using the electromagnetic field as a probe, as in laser-interferometric
gravitational-wave detectors. Other applications are discussed, from
terrestrial gravimetry to cosmology.Comment: 23 pages. This article supersedes arXiv:1108.522
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
Toward faithful templates for non-spinning binary black holes using the effective-one-body approach
We present an accurate approximation of the full gravitational radiation
waveforms generated in the merger of non-eccentric systems of two non-spinning
black holes. Utilizing information from recent numerical relativity simulations
and the natural flexibility of the effective-one-body (EOB) model, we extend
the latter so that it can successfully match the numerical relativity waveforms
during the last stages of inspiral, merger and ringdown. By ``successfully''
here, we mean with phase differences < 8% of a gravitational-wave cycle
accumulated by the end of the ringdown phase, maximizing only over time of
arrival and initial phase. We obtain this result by simply adding a
4-post-Newtonian order correction in the EOB radial potential and determining
the (constant) coefficient by imposing high-matching performances with
numerical waveforms of mass ratios m1/m2 = 1, 3/2, 2 and 4, m1 and m2 being the
individual black-hole masses. The final black-hole mass and spin predicted by
the numerical simulations are used to determine the ringdown frequency and
decay time of three quasi-normal-mode damped sinusoids that are attached to the
EOB inspiral-(plunge) waveform at the EOB light-ring. The EOB waveforms might
be tested and further improved in the future by comparison with extremely long
and accurate inspiral numerical-relativity waveforms. They may already be
employed for coherent searches and parameter estimation of gravitational waves
emitted by non-spinning coalescing binary black holes with ground-based
laser-interferometer detectors.Comment: 15 pages, 9 figure
Binary black hole late inspiral: Simulations for gravitational wave observations
Coalescing binary black hole mergers are expected to be the strongest
gravitational wave sources for ground-based interferometers, such as the LIGO,
VIRGO, and GEO600, as well as the space-based interferometer LISA. Until
recently it has been impossible to reliably derive the predictions of General
Relativity for the final merger stage, which takes place in the strong-field
regime. Recent progress in numerical relativity simulations is, however,
revolutionizing our understanding of these systems. We examine here the
specific case of merging equal-mass Schwarzschild black holes in detail,
presenting new simulations in which the black holes start in the late inspiral
stage on orbits with very low eccentricity and evolve for ~1200M through ~7
orbits before merging. We study the accuracy and consistency of our simulations
and the resulting gravitational waveforms, which encompass ~14 cycles before
merger, and highlight the importance of using frequency (rather than time) to
set the physical reference when comparing models. Matching our results to PN
calculations for the earlier parts of the inspiral provides a combined waveform
with less than half a cycle of accumulated phase error through the entire
coalescence. Using this waveform, we calculate signal-to-noise ratios (SNRs)
for iLIGO, adLIGO, and LISA, highlighting the contributions from the
late-inspiral and merger-ringdown parts of the waveform which can now be
simulated numerically. Contour plots of SNR as a function of z and M show that
adLIGO can achieve SNR >~ 10 for some intermediate-mass binary black holes
(IMBBHs) out to z ~ 1, and that LISA can see massive binary black holes (MBBHs)
in the range 3x10^4 100 out to the earliest epochs
of structure formation at z > 15.Comment: 17 pages, 20 figures. Final published versio
Modeling kicks from the merger of generic black-hole binaries
Recent numerical relativistic results demonstrate that the merger of
comparable-mass spinning black holes has a maximum ``recoil kick'' of up to
\sim 4000 \kms. However the scaling of these recoil velocities with mass
ratio is poorly understood. We present new runs showing that the maximum
possible kick perpendicular to the orbital plane does not scale as
(where is the symmetric mass ratio), as previously proposed, but is more
consistent with , at least for systems with low orbital precession.
We discuss the effect of this dependence on galactic ejection scenarios and
retention of intermediate-mass black holes in globular clusters.Comment: 5 pages, 1 figure, 3 tables. Version published in Astrophys. J. Let
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