29,450 research outputs found
Efficiency of autonomous soft nano-machines at maximum power
We consider nano-sized artificial or biological machines working in steady
state enforced by imposing non-equilibrium concentrations of solutes or by
applying external forces, torques or electric fields. For unicyclic and
strongly coupled multicyclic machines, efficiency at maximum power is not
bounded by the linear response value 1/2. For strong driving, it can even
approach the thermodynamic limit 1. Quite generally, such machines fall in
three different classes characterized, respectively, as "strong and efficient",
"strong and inefficient", and "balanced". For weakly coupled multicyclic
machines, efficiency at maximum power has lost any universality even in the
linear response regime
Regional VARs and the channels of monetary policy
We find that the magnitudes of the regional effects of monetary policy were considerably dampened during the Volcker-Greenspan era. Further, regional differences in the depths of monetary-policy-induced recessions are related to the concentration of the banking sector, whereas differences in the total cost of these recessions are related to industry mix.Monetary policy
Structural breaks and regional disparities in the transmission of monetary policy
Using a regional VAR, we find large differences in the effects of monetary policy shocks across regions of the United States. We also find that the region-level effects of monetary policy differ a great deal between the pre-Volcker and Volcker-Greenspan periods in terms of their depth and length. The two sample periods also yield very different rankings of the regions in terms of the effects of monetary policy. Our regional VAR also suggests that aggregate VARs that ignore regional variations can suffer from severe aggregation bias. We use the results of our regional VAR to find evidence that recession depth related to the banking concentration and that the total cost of recession is related to the industry mix. Finally, we demonstrate that the differences between the two sample periods are due to changes in the mechanism by which monetary policy shocks are propagated.Monetary policy ; Regional economics ; Economic conditions
Waveguide physical modeling of vocal tract acoustics: flexible formant bandwidth control from increased model dimensionality
Digital waveguide physical modeling is often used as an efficient representation of acoustical resonators such as the human vocal tract. Building on the basic one-dimensional (1-D) Kelly-Lochbaum tract model, various speech synthesis techniques demonstrate improvements to the wave scattering mechanisms in order to better approximate wave propagation in the complex vocal system. Some of these techniques are discussed in this paper, with particular reference to an alternative approach in the form of a two-dimensional waveguide mesh model. Emphasis is placed on its ability to produce vowel spectra similar to that which would be present in natural speech, and how it improves upon the 1-D model. Tract area function is accommodated as model width, rather than translated into acoustic impedance, and as such offers extra control as an additional bounding limit to the model. Results show that the two-dimensional (2-D) model introduces approximately linear control over formant bandwidths leading to attainable realistic values across a range of vowels. Similarly, the 2-D model allows for application of theoretical reflection values within the tract, which when applied to the 1-D model result in small formant bandwidths, and, hence, unnatural sounding synthesized vowels
Regularity of Horizons and The Area Theorem
We prove that the area of sections of future event horizons in space-times
satisfying the null energy condition is non-decreasing towards the future under
any one of the following circumstances: 1) the horizon is future geodesically
complete; 2) the horizon is a black hole event horizon in a globally hyperbolic
space-time and there exists a conformal completion with a ``H-regular'' Scri
plus; 3) the horizon is a black hole event horizon in a space-time which has a
globally hyperbolic conformal completion. (Some related results under less
restrictive hypotheses are also established.) This extends a theorem of
Hawking, in which piecewise smoothness of the event horizon seems to have been
assumed. No assumptions about the cosmological constant or its sign are made.
We prove smoothness or analyticity of the relevant part of the event horizon
when equality in the area inequality is attained - this has applications to the
theory of stationary black holes, as well as to the structure of compact Cauchy
horizons. In the course of the proof we establish several new results
concerning the differentiability properties of horizons.Comment: final version to appear in Annales Henri Poincare, various changes as
suggested by a referee, in particular a section on Krolak's area theorems
adde
Compressive force generation by a bundle of living biofilaments
To study the compressional forces exerted by a bundle of living stiff
filaments pressing on a surface, akin to the case of an actin bundle in
filopodia structures, we have performed particulate Molecular Dynamics
simulations of a grafted bundle of parallel living (self-assembling) filaments,
in chemical equilibrium with a solution of their constitutive monomers.
Equilibrium is established as these filaments, grafted at one end to a wall of
the simulation box, grow at their chemically active free end and encounter the
opposite confining wall of the simulation box. Further growth of filaments
requires bending and thus energy, which automatically limit the populations of
longer filaments. The resulting filament sizes distribution and the force
exerted by the bundle on the obstacle are analyzed for different grafting
densities and different sub- or supercritical conditions, these properties
being compared with the predictions of the corresponding ideal confined bundle
model. In this analysis, non-ideal effects due to interactions between
filaments and confinement effects are singled out. For all state points
considered at the same temperature and at the same gap width between the two
surfaces, the force per filament exerted on the opposite wall appears to be a
function of a rescaled free monomer density . This
quantity can be estimated directly from the characteristic length of the
exponential filament size distribution observed in the size domain where
these grafted filaments are not in direct contact with the wall. We also
analyze the dynamics of the filament contour length fluctuations in terms of
effective polymerization () and depolymerization () rates, where again it
is possible to disentangle non-ideal and confinement effects.Comment: 24 pages, 7 figure
Newly-Discovered Planets Orbiting HD~5319, HD~11506, HD~75784 and HD~10442 from the N2K Consortium
Initially designed to discover short-period planets, the N2K campaign has
since evolved to discover new worlds at large separations from their host
stars. Detecting such worlds will help determine the giant planet occurrence at
semi-major axes beyond the ice line, where gas giants are thought to mostly
form. Here we report four newly-discovered gas giant planets (with minimum
masses ranging from 0.4 to 2.1 MJup) orbiting stars monitored as part of the
N2K program. Two of these planets orbit stars already known to host planets: HD
5319 and HD 11506. The remaining discoveries reside in previously-unknown
planetary systems: HD 10442 and HD 75784. The refined orbital period of the
inner planet orbiting HD 5319 is 641 days. The newly-discovered outer planet
orbits in 886 days. The large masses combined with the proximity to a 4:3 mean
motion resonance make this system a challenge to explain with current formation
and migration theories. HD 11506 has one confirmed planet, and here we confirm
a second. The outer planet has an orbital period of 1627.5 days, and the
newly-discovered inner planet orbits in 223.6 days. A planet has also been
discovered orbiting HD 75784 with an orbital period of 341.7 days. There is
evidence for a longer period signal; however, several more years of
observations are needed to put tight constraints on the Keplerian parameters
for the outer planet. Lastly, an additional planet has been detected orbiting
HD 10442 with a period of 1043 days.Comment: Accepted for publication in Ap
Business cycle phases in U.S. states
The U.S. aggregate business cycle is often characterized as a series of distinct recession and expansion phases. We apply a regime-switching model to state-level coincident indexes to characterize state business cycles in this way. We find that states differ a great deal in the levels of growth that they experience in the two phases: Recession growth rates are related to industry mix, whereas expansion growth rates are related to education and age composition. Further, states differ significantly in the timing of switches between regimes, indicating large differences in the extent to which state business cycle phases are in concord with those of the aggregate economy.Business cycles ; Regional economics
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