1,951 research outputs found
Quiet engine program flight engine design study
The results are presented of a preliminary flight engine design study based on the Quiet Engine Program high-bypass, low-noise turbofan engines. Engine configurations, weight, noise characteristics, and performance over a range of flight conditions typical of a subsonic transport aircraft were considered. High and low tip speed engines in various acoustically treated nacelle configurations were included
The Bravyi-Kitaev transformation for quantum computation of electronic structure
Quantum simulation is an important application of future quantum computers
with applications in quantum chemistry, condensed matter, and beyond. Quantum
simulation of fermionic systems presents a specific challenge. The
Jordan-Wigner transformation allows for representation of a fermionic operator
by O(n) qubit operations. Here we develop an alternative method of simulating
fermions with qubits, first proposed by Bravyi and Kitaev [S. B. Bravyi, A.Yu.
Kitaev, Annals of Physics 298, 210-226 (2002)], that reduces the simulation
cost to O(log n) qubit operations for one fermionic operation. We apply this
new Bravyi-Kitaev transformation to the task of simulating quantum chemical
Hamiltonians, and give a detailed example for the simplest possible case of
molecular hydrogen in a minimal basis. We show that the quantum circuit for
simulating a single Trotter time-step of the Bravyi-Kitaev derived Hamiltonian
for H2 requires fewer gate applications than the equivalent circuit derived
from the Jordan-Wigner transformation. Since the scaling of the Bravyi-Kitaev
method is asymptotically better than the Jordan-Wigner method, this result for
molecular hydrogen in a minimal basis demonstrates the superior efficiency of
the Bravyi-Kitaev method for all quantum computations of electronic structure
Pole structure of the Hamiltonian -function for a singular potential
We study the pole structure of the -function associated to the
Hamiltonian of a quantum mechanical particle living in the half-line
, subject to the singular potential . We show that
admits nontrivial self-adjoint extensions (SAE) in a given range of values
of the parameter . The -functions of these operators present poles
which depend on and, in general, do not coincide with half an integer (they
can even be irrational). The corresponding residues depend on the SAE
considered.Comment: 12 pages, 1 figure, RevTeX. References added. Version to appear in
Jour. Phys. A: Math. Ge
Lifshitz fermionic theories with z=2 anisotropic scaling
We construct fermionic Lagrangians with anisotropic scaling z=2, the natural
counterpart of the usual z=2 Lifshitz field theories for scalar fields. We
analyze the issue of chiral symmetry, construct the Noether axial currents and
discuss the chiral anomaly giving explicit results for two-dimensional case. We
also exploit the connection between detailed balance and the dynamics of
Lifshitz theories to find different z=2 fermionic Lagrangians and construct
their supersymmetric extensions.Comment: Typos corrected, comment adde
Honey bee foraging distance depends on month and forage type
To investigate the distances at which honey bee foragers collect nectar and pollen, we analysed 5,484 decoded waggle dances made to natural forage sites to determine monthly foraging distance for each forage type. Firstly, we found significantly fewer overall dances made for pollen (16.8 %) than for non-pollen, presumably nectar (83.2 %; P < 2.2 × 10−23). When we analysed distance against month and forage type, there was a significant interaction between the two factors, which demonstrates that in some months, one forage type is collected at farther distances, but this would reverse in other months. Overall, these data suggest that distance, as a proxy for forage availability, is not significantly and consistently driven by need for one type of forage over the other
Why do house-hunting ants recruit in both directions?
To perform tasks, organisms often use multiple procedures. Explaining the breadth of such behavioural repertoires is not always straightforward. During house hunting, colonies of Temnothorax albipennis ants use a range of behaviours to organise their emigrations. In particular, the ants use tandem running to recruit naïve ants to potential nest sites. Initially, they use forward tandem runs (FTRs) in which one leader takes a single follower along the route from the old nest to the new one. Later, they use reverse tandem runs (RTRs) in the opposite direction. Tandem runs are used to teach active ants the route between the nests, so that they can be involved quickly in nest evaluation and subsequent recruitment. When a quorum of decision-makers at the new nest is reached, they switch to carrying nestmates. This is three times faster than tandem running. As a rule, having more FTRs early should thus mean faster emigrations, thereby reducing the colony’s vulnerability. So why do ants use RTRs, which are both slow and late? It would seem quicker and simpler for the ants to use more FTRs (and higher quorums) to have enough knowledgeable ants to do all the carrying. In this study, we present the first testable theoretical explanation for the role of RTRs. We set out to find the theoretically fastest emigration strategy for a set of emigration conditions. We conclude that RTRs can have a positive effect on emigration speed if FTRs are limited. In these cases, low quorums together with lots of reverse tandem running give the fastest emigration
Model of the best-of-N nest-site selection process in honeybees
The ability of a honeybee swarm to select the best nest site plays a fundamental role in determining the
future colony’s fitness. To date, the nest-site selection process has mostly been modelled and theoretically
analysed for the case of binary decisions. However, when the number of alternative nests is larger than two,
the decision process dynamics qualitatively change. In this work, we extend previous analyses of a valuesensitive
decision-making mechanism to a decision process among N nests. First, we present the decisionmaking
dynamics in the symmetric case of N equal-quality nests. Then, we generalise our findings to a
best-of-N decision scenario with one superior nest and N – 1 inferior nests, previously studied empirically
in bees and ants. Whereas previous binary models highlighted the crucial role of inhibitory stop-signalling,
the key parameter in our new analysis is the relative time invested by swarm members in individual discovery
and in signalling behaviours. Our new analysis reveals conflicting pressures on this ratio in symmetric and
best-of-N decisions, which could be solved through a time-dependent signalling strategy. Additionally,
our analysis suggests how ecological factors determining the density of suitable nest sites may have led to
selective pressures for an optimal stable signalling ratio
Discrete Symmetries in the Weyl Expansion for Quantum Billiards
We consider two and three-dimensional quantum billiards with discrete
symmetries. We derive the first terms of the Weyl expansion for the level
density projected onto the irreducible representations of the symmetry group.
As an illustration the method is applied to the icosahedral billiard. The paper
was published in J. Phys. A /27/ (1994) 4317-4323Comment: 8 printed pages Latex fil
Vanishing Viscosity Limits and Boundary Layers for Circularly Symmetric 2D Flows
We continue the work of Lopes Filho, Mazzucato and Nussenzveig Lopes [LMN],
on the vanishing viscosity limit of circularly symmetric viscous flow in a disk
with rotating boundary, shown there to converge to the inviscid limit in
-norm as long as the prescribed angular velocity of the
boundary has bounded total variation. Here we establish convergence in stronger
and -Sobolev spaces, allow for more singular angular velocities
, and address the issue of analyzing the behavior of the boundary
layer. This includes an analysis of concentration of vorticity in the vanishing
viscosity limit. We also consider such flows on an annulus, whose two boundary
components rotate independently.
[LMN] Lopes Filho, M. C., Mazzucato, A. L. and Nussenzveig Lopes, H. J.,
Vanishing viscosity limit for incompressible flow inside a rotating circle,
preprint 2006
The trace of the heat kernel on a compact hyperbolic 3-orbifold
The heat coefficients related to the Laplace-Beltrami operator defined on the
hyperbolic compact manifold H^3/\Ga are evaluated in the case in which the
discrete group \Ga contains elliptic and hyperbolic elements. It is shown
that while hyperbolic elements give only exponentially vanishing corrections to
the trace of the heat kernel, elliptic elements modify all coefficients of the
asymptotic expansion, but the Weyl term, which remains unchanged. Some physical
consequences are briefly discussed in the examples.Comment: 11 page
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