10,104 research outputs found
Unbounded-Error Classical and Quantum Communication Complexity
Since the seminal work of Paturi and Simon \cite[FOCS'84 & JCSS'86]{PS86},
the unbounded-error classical communication complexity of a Boolean function
has been studied based on the arrangement of points and hyperplanes. Recently,
\cite[ICALP'07]{INRY07} found that the unbounded-error {\em quantum}
communication complexity in the {\em one-way communication} model can also be
investigated using the arrangement, and showed that it is exactly (without a
difference of even one qubit) half of the classical one-way communication
complexity. In this paper, we extend the arrangement argument to the {\em
two-way} and {\em simultaneous message passing} (SMP) models. As a result, we
show similarly tight bounds of the unbounded-error two-way/one-way/SMP
quantum/classical communication complexities for {\em any} partial/total
Boolean function, implying that all of them are equivalent up to a
multiplicative constant of four. Moreover, the arrangement argument is also
used to show that the gap between {\em weakly} unbounded-error quantum and
classical communication complexities is at most a factor of three.Comment: 11 pages. To appear at Proc. ISAAC 200
Unbounded-error One-way Classical and Quantum Communication Complexity
This paper studies the gap between quantum one-way communication complexity
and its classical counterpart , under the {\em unbounded-error}
setting, i.e., it is enough that the success probability is strictly greater
than 1/2. It is proved that for {\em any} (total or partial) Boolean function
, , i.e., the former is always exactly one half
as large as the latter. The result has an application to obtaining (again an
exact) bound for the existence of -QRAC which is the -qubit random
access coding that can recover any one of original bits with success
probability . We can prove that -QRAC exists if and only if
. Previously, only the construction of QRAC using one qubit,
the existence of -RAC, and the non-existence of
-QRAC were known.Comment: 9 pages. To appear in Proc. ICALP 200
Comparison of Bond in Roll-bonded and Adhesively Bonded Aluminums
Lap-shear and peel test measurements of bond strength have been carried out as part of an investigation of roll bonding of 2024 and 7075 aluminum alloys. Shear strengths of the bonded material in the F temper are in the range of 14 to 16 ksi. Corresponding peel strengths are 120 to 130 lb/inch. These values, which are three to five times those reported in the literature for adhesively bonded 2024 and 7075, are a result of the true metallurgical bond achieved. The effects of heat-treating the bonded material are described and the improvements in bond strength discussed relative to the shear strength of the parent material. The significance of the findings for aerospace applications is discussed
High-mass star formation in southern disk galaxies
As part of a major study of the physical processes of star formation and the evolution of galactic discs, the detailed distribution of high-mass star formation within southern late-type spirals and Magellanic-type galaxies is being measured by means of narrow-band imaging in Ha and the continuum, spectroscopic studies of prominent HII regions identified in the Ha images, and by radio mapping in neutral hydrogen and the continuum. The radio mapping will be undertaken with the Southern Hemisphere's first large, multi-frequency synthesis array, the Australia Telescope. Some optical imaging and spectroscopic data has already been acquired; the optical data and some preliminary results are described
Improved electromechanical master-slave manipulator
Electric master-slave manipulator uses force multiplication and allows the operator to remotely control the slave arm. Both the master and slave arms execute seven distinct motions by a specially designed force-reflecting servo having a one to one correspondence between the motion at the master and slave
The Detection of Outflows in the IR-Quiet Molecular Core NGC 6334 I(North)
We find strong evidence for outflows originating in the dense molecular core
NGC 6334 I(North): a 1000 Msol molecular core distinguished by its lack of HII
regions and mid-IR emission. New observations were obtained of the SiO 2-1 and
5-4 lines with the SEST 15-m telescope and the H2 (1-0) S(1) line with the ESO
2.2-m telescope. The line profiles of the SiO transitions show broad wings
extending from -50 to 40 km/s, and spatial maps of the line wing emission
exhibit a bipolar morphology with the peaks of the red and blue wing separated
by 30". The estimated mass loss rate of the outflow is comparable to those for
young intermediate to high-mass stars. The near-IR images show eight knots of
H2 emission. Five of the knots form a linear chain which is displaced from the
axis of the SiO outflow; these knots may trace shock excited gas along the path
of a second, highly collimated outflow. We propose that I(N) is a rare example
of a molecular core in an early stage of cluster formation.Comment: 4 pages, LaTeX, 3 ps figures, accepted by ApJ
A parsec-scale flow associated with the IRAS 16547-4247 radio jet
IRAS 16547-4247 is the most luminous (6.2 x 10^4 Lsun) embedded young stellar
object known to harbor a thermal radio jet. We report the discovery using
VLT-ISAAC of a chain of H_2 2.12 um emission knots that trace a collimated flow
extending over 1.5 pc. The alignment of the H_2 flow and the central location
of the radio jet implies that these phenomena are intimately linked. We have
also detected using TIMMI2 an isolated, unresolved 12 um infrared source
towards the radio jet . Our findings affirm that IRAS 16547-4247 is excited by
a single O-type star that is driving a collimated jet. We argue that the
accretion mechanism which produces jets in low-mass star formation also
operates in the higher mass regime.Comment: Accepted for publication in ApJL, 10 pages, 2 figure
The Formaldehyde Masers in Sgr B2: Very Long Baseline Array and Very Large Array Observations
Observations of two of the formaldehyde (H2CO) masers (A and D) in Sgr B2
using the VLBA+Y27 (resolution ~0.01") and the VLA (resolution ~9") are
presented. The VLBA observations show compact sources (<10 milliarcseconds, <80
AU) with brightness temperatures >10^8 K. The maser sources are partially
resolved in the VLBA observations. The flux densities in the VLBA observations
are about 1/2 those of the VLA; and, the linewidths are about 2/3 of the VLA
values. The applicability of a core-halo model for the emission distribution is
demonstrated. Comparison with earlier H2CO absorption observations and with
ammonia (NH3) observations suggests that H2CO masers form in shocked gas.
Comparison of the integrated flux densities in current VLA observations with
those in previous observations indicates that (1) most of the masers have
varied in the past 20 years, and (2) intensity variations are typically less
than a factor of two compared to the 20-year mean. No significant linear or
circular polarization is detected with either instrument.Comment: 20 pages, 3 figures, 5 tables, accepted to Ap
1/f spectrum and memory function analysis of solvation dynamics in a room-temperature ionic liquid
To understand the non-exponential relaxation associated with solvation
dynamics in the ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate,
we study power spectra of the fluctuating Franck-Condon energy gap of a
diatomic probe solute via molecular dynamics simulations. Results show 1/f
dependence in a wide frequency range over 2 to 3 decades, indicating
distributed relaxation times. We analyze the memory function and solvation time
in the framework of the generalized Langevin equation using a simple model
description for the power spectrum. It is found that the crossover frequency
toward the white noise plateau is directly related to the time scale for the
memory function and thus the solvation time. Specifically, the low crossover
frequency observed in the ionic liquid leads to a slowly-decaying tail in its
memory function and long solvation time. By contrast, acetonitrile
characterized by a high crossover frequency and (near) absence of 1/f behavior
in its power spectra shows fast relaxation of the memory function and
single-exponential decay of solvation dynamics in the long-time regime.Comment: 10 pages, 4 figure
Apparent hysteresis in a driven system with self-organized drag
Interaction between extended defects and impurities lies at the heart of many
physical phenomena in materials science. Here we revisit the ubiquitous problem
of the driven motion of an extended defect in a field of mobile impurities,
which self-organize to cause drag on the defect. Under a wide range of external
conditions (e.g. drive), the defect undergoes a transition from slow to fast
motion. This transition is commonly hysteretic: the defect either moves slow or
fast, depending on the initial condition. We explore such hysteresis via a
kinetic Monte Carlo spin simulation combined with computational
coarse-graining. Obtaining bifurcation diagrams (stable and unstable branches),
we map behavior regimes in parameter space. Estimating fast-slow switching
times, we determine whether a simulation or experiment will exhibit hysteresis
depending on observation conditions. We believe our approach is applicable to
quantifying hysteresis in a wide range of physical contexts.Comment: 11 pages (preprint format), 4 color figures in separate file
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