135,771 research outputs found
Optimal Quantum Circuits for General Two-Qubit Gates
In order to demonstrate non-trivial quantum computations experimentally, such
as the synthesis of arbitrary entangled states, it will be useful to understand
how to decompose a desired quantum computation into the shortest possible
sequence of one-qubit and two-qubit gates. We contribute to this effort by
providing a method to construct an optimal quantum circuit for a general
two-qubit gate that requires at most 3 CNOT gates and 15 elementary one-qubit
gates. Moreover, if the desired two-qubit gate corresponds to a purely real
unitary transformation, we provide a construction that requires at most 2 CNOTs
and 12 one-qubit gates. We then prove that these constructions are optimal with
respect to the family of CNOT, y-rotation, z-rotation, and phase gates.Comment: 6 pages, 8 figures, new title, final journal versio
Developmental changes in foraging-predator avoidance trade-offs in larval lumpfish Cyclopterus lumpus
The 5-12 wk old larvae increased time spent clinging to a surface in the presence of a predator, trading-off time available for foraging in order to reduce the probability of attack. Overall, fewer fish fed in the presence of a predator, and of the fish that did feed, 12 wk old lumpfish also showed a significant decrease in feeding rate (bites per minute swimming) in the presence of a predator. -from Author
Determining the parameters in a social welfare function using stated preference data: an application to health
One way in which economists might determine how best to balance the competing objectives of efficiency and equity is to specify a social welfare function (SWF). This paper looks at how the stated preferences of a sample of the general public can be used to estimate the shape of the SWF in the domain of health benefits. The results suggest that it is possible to determine the parameters in a social welfare function from stated preference data, but show that people are sensitive to what inequalities exist and to the groups across which those inequalities exist
Z' mass limits and the naturalness of supersymmetry
The discovery of a 125 GeV Higgs boson and rising lower bounds on the masses
of superpartners have lead to concerns that supersymmetric models are now fine
tuned. Large stop masses, required for a 125 GeV Higgs, feed into the
electroweak symmetry breaking conditions through renormalisation group
equations forcing one to fine tune these parameters to obtain the correct
electroweak vacuum expectation value. Nonetheless this fine tuning depends
crucially on our assumptions about the supersymmetry breaking scale. At the
same time extensions provide the most compelling solution to the
-problem, which is also a naturalness issue, and allow the tree level
Higgs mass to be raised substantially above . These very well motivated
supersymmetric models predict a new boson which could be discovered at the
LHC and the naturalness of the model requires that the boson mass should
not be too far above the TeV scale. Moreover this fine tuning appears at the
tree level, making it less dependent on assumptions about the supersymmetry
breaking mechanism. Here we study this fine tuning for several
supersymmetric extensions of the Standard Model and compare it to the situation
in the MSSM where the most direct tree level fine tuning can be probed through
chargino mass limits. We show that future LHC searches are extremely
important for challenging the most natural scenarios in these models.Comment: 58 pages, 5 figures; typos corrected, references added; matches
version to be published in Phys. Rev.
Laboratory experiments on cohesive soil bed fluidization by water waves
Part I. Relationships between the rate of bed fluidization and the rate of wave energy dissipation, by Jingzhi Feng and Ashish J. Mehta and Part II. In-situ rheometry for determining the dynamic response of bed, by David J.A. Williams and P. Rhodri Williams.
A series of preliminary laboratory flume experiments were carried out to examine the time-dependent
behavior of a cohesive soil bed subjected to progressive, monochromatic waves. The bed was an aqueous,
50/50 (by weight) mixture of a kaolinite and an attapulgite placed in a plexiglass trench. The nominal bed
thickness was 16 cm with density ranging from 1170 to 1380 kg/m 3, and water above was 16 to 20 cm
deep. Waves of design height ranging from 2 to 8 cm and a nominal frequency of 1 Hz were run for
durations up to 2970 min. Part I of this report describes experiments meant to examine the rate at which
the bed became fluidized, and its relation to the rate of wave energy dissipation. Part II gives results on
in-situ rheometry used to track the associated changes in bed rigidity.
Temporal and spatial changes of the effective stress were measured during the course of wave action,
and from these changes the bed fluidization rate was calculated. A wave-mud interaction model developed
in a companion study was employed to calculate the rate of wave energy dissipation. The dependence of
the rate of fluidization on the rate of energy dissipation was then explored.
Fluidization, which seemingly proceeded down from the bed surface, occurred as a result of the loss
of structural integrity of the soil matrix through a buildup of the excess pore pressure and the associated loss of effective stress. The rate of fluidization was typically greater at the beginning of wave action and
apparently approached zero with time. This trend coincided with the approach of the rate of energy
dissipation to a constant value. In general it was also observed that, for a given wave frequency, the larger
the wave height the faster the rate of fluidization and thicker the fluid mud layer formed. On the other
hand, increasing the time of bed consolidation prior to wave action decreased the fluidization rate due to
greater bed rigidity. Upon cessation of wave action structural recovery followed.
Dynamic rigidity was measured by specially designed, in situ shearometers placed in the bed at
appropriate elevations to determine the time-dependence of the storage and loss moduli, G' and G", of
the viscoelastic clay mixture under 1 Hz waves. As the inter-particle bonds of the space-filling, bed
material matrix weakened, the shear propagation velocity decreased measurably. Consequently, G'
decreased and G" increased as a transition from dynamically more elastic to more viscous response
occurred. These preliminary experiments have demonstrated the validity of the particular rheometric
technique used, and the critical need for synchronous, in-situ measurements of pore pressures and moduli
characterizing bed rheology in studies on mud fluidization.
This study was supported by WES contract DACW39-90-K-0010.
(This document contains 151 pages.
A Very Large Array 3.6cm continuum survey of Galactic Wolf-Rayet stars
We report the results of a survey of radio continuum emission of Galactic
Wolf-Rayet stars north of declination -46 degrees. The observations were
obtained at 8.46 GHz (3.6cm) using the Very Large Array (VLA), with an angular
resolution of about 6 x 9 arcsec and typical rms noise of 0.04 mJy/beam. Our
survey of 34 WR stars resulted in 15 definite and 5 probable detections, 13 of
these for the first time at radio wavelengths. All detections are unresolved.
Time variations in flux are confirmed in the cases of WR98a, WR104, WR105 and
WR125. WR79a and WR89 are also variable in flux and we suspect they are also
non-thermal emitters. Thus, of our sample 20-30% of the detected stars are
non-thermal emiters. Average mass loss rates determinations obtained excluding
definite and suspected non-thermal cases give similar values for WN (all
subtypes) and WC5-7 stars, while a lower value was obtained for WC8-9 stars.
Uncertainties in stellar distances largely contribute to the observed scatter
in mass loss rates. Upper limits to the mass loss rates were obtained in cases
of undetected sources or for sources which probably show additional non-thermal
emission.Comment: 21 pages, Latex, 21 postscript figures, to be published in The
Astronomical Journal, May 200
Description of the Spacecraft Control Laboratory Experiment (SCOLE) facility
A laboratory facility for the study of control laws for large flexible spacecraft is described. The facility fulfills the requirements of the Spacecraft Control Laboratory Experiment (SCOLE) design challenge for a laboratory experiment, which will allow slew maneuvers and pointing operations. The structural apparatus is described in detail sufficient for modelling purposes. The sensor and actuator types and characteristics are described so that identification and control algorithms may be designed. The control implementation computer and real-time subroutines are also described
Effect of signal duration on detection for gated and for continuous noise
Effect of signal duration on detection for gated and continuous nois
- …