7,334 research outputs found
Dynamic criticality far-from-equilibrium: one-loop flow of Burgers-Kardar-Parisi-Zhang systems with broken Galilean invariance
Burgers-Kardar-Parisi-Zhang (KPZ) scaling has recently (re-) surfaced in a
variety of physical contexts, ranging from anharmonic chains to quantum systems
such as open superfluids, in which a variety of random forces may be
encountered and/or engineered. Motivated by these developments, we here provide
a generalization of the KPZ universality class to situations with long-ranged
temporal correlations in the noise, which purposefully break the Galilean
invariance that is central to the conventional KPZ solution. We compute the
phase diagram and critical exponents of the KPZ equation with -noise
(KPZ) in spatial dimensions using the dynamic
renormalization group with a frequency cutoff technique in a one-loop
truncation. Distinct features of KPZ are: (i) a generically
scale-invariant, rough phase at high noise levels that violates
fluctuation-dissipation relations and exhibits hyperthermal statistics {\it
even in d=1}, (ii) a fine-tuned roughening transition at which the flow
fulfills an emergent thermal-like fluctuation-dissipation relation, that
separates the rough phase from (iii) a {\it massive phase} in (in
the interface is always rough). We point out potential connections to
nonlinear hydrodynamics with a reduced set of conservation laws and noisy
quantum liquids.Comment: 29 pages, 11 figures, 1 table, 54 references, v2 as publishe
New opportunities for future, small, General-Aviation Turbine Engines (GATE)
The results of four independent contracted studies to explore the opportunities for future small turbine engines are summarized in a composite overview. Candidate advanced technologies are screened, various cycles and staging arrangements are parametrically evaluated, and optimum conceptual engines are identified for a range of 300 to 600 horsepower applications. Engine improvements of 20 percent in specific fuel consumption and 40 percent in engine cost were forecast using high risk technologies that could be technically demonstrated by 1988. The ensuing economic benefits are in the neighborhood of 20 to 30 percent for twin-engine aircraft currently powered by piston engines
Fluctuations of imbalanced fermionic superfluids in two dimensions induce continuous quantum phase transitions and non-Fermi liquid behavior
We study the nature of superfluid pairing in imbalanced Fermi mixtures in two
spatial dimensions. We present evidence that the combined effect of Fermi
surface mismatch and order parameter fluctuations of the superfluid condensate
can lead to continuous quantum phase transitions from a normal Fermi mixture to
an intermediate Sarma-Liu-Wilczek superfluid with two gapless Fermi surfaces --
even when mean-field theory (incorrectly) predicts a first order transition to
a phase-separated "Bardeen-Cooper-Schrieffer plus excess fermions" ground
state. We propose a mechanism for non-Fermi liquid behavior from repeated
scattering processes between the two Fermi surfaces and fluctuating Cooper
pairs. Prospects for experimental observation with ultracold atoms are
discussed.Comment: as accepted to Phys. Rev. X; 10 pages, 10 figures, 75 reference
Umklapp Superradiance from a Collisionless Quantum Degenerate Fermi Gas
The quantum dynamics of the electromagnetic light mode of an optical cavity
filled with a coherently driven Fermi gas of ultracold atoms strongly depends
on geometry of the Fermi surface. Superradiant light generation and
self-organization of the atoms can be achieved at low pumping threshold due to
resonant atom-photon Umklapp processes, where the fermions are scattered from
one side of the Fermi surface to the other by exchanging photon momenta. The
cavity spectrum exhibits sidebands, that, despite strong atom-light coupling
and cavity decay, retain narrow linewidth, due to absorptionless transparency
windows outside the atomic particle-hole continuum and the suppression of
inhomogeneous broadening and thermal fluctuations in the collisionless Fermi
gas.Comment: Revised version, as accepted to Physical Review Letter
Continuois Time Contests
This paper introduces a contest model in which each player decides when to stop a privately observed Brownian motion with drift and incurs costs depending on his stopping time. The player who stops his process at the highest value wins a prize. Applications of the model include procurement contests and competitions for grants. We prove existence and uniqueness of the Nash equilibrium outcome, even if players have to choose bounded stopping times. We derive the equilibrium distribution in closed form. If the noise vanishes, the equilibrium outcome converges to - and thus selects - the symmetric equilibrium outcome of an all-pay auction. For two players and constant costs, each player’s profits increase if costs for both players increase, variance increases, or drift decreases. Intuitively, patience becomes a more important factor for contest success, which reduces informational rents
Gambling in Contests
This paper presents a strategic model of risk-taking behavior in contests. Formally, we analyze an n-player winner-take-all contest in which each player decides when to stop a privately observed Brownian Motion with drift. A player whose process reaches zero has to stop. The player with the highest stopping point wins. Contrary to the explicit cost for a higher stopping time in a war of attrition, here, higher stopping times are riskier, because players can go bankrupt. We derive a closed-form solution of the unique Nash equilibrium outcome of the game. In equilibrium, the trade-off between risk and reward causes a non-monotonicity: highest expected losses occur if the process decreases only slightly in expectation
Preliminary performance appraisal of Navy V/STOL transport and search-type airplanes using hydrogen fuel
First-cut estimates are given of the performance advantages of liquid-hydrogen-fueled, ejector wing, V/STOL aircraft designed for shipboard delivery and search-type missions. Results indicate that the use of LH2 could reduce gross weights 30 percent, empty weights 15 percent, and energy consumption 10 percent for a fixed payload and mission. If gross weight is fixed, the delivery range could be increased about 60 percent or the hover time during a search mission doubled. No analysis or discussion of the economic and operational disadvantages is presented
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