17,132 research outputs found
Equilibrium relationships for non-equilibrium chemical dependencies
In contrast to common opinion, it is shown that equilibrium constants
determine the time-dependent behavior of particular ratios of concentrations
for any system of reversible first-order reactions. Indeed, some special ratios
actually coincide with the equilibrium constant at any moment in time. This is
established for batch reactors, and similar relations hold for steady-state
plug-flow reactors, replacing astronomic time by residence time. Such
relationships can be termed time invariants of chemical kinetics
Debt Financing and Financial Flexibility Evidence from Pro-active Leverage Increases
Firms that intentionally increase leverage through substantial debt issuances do so primarily as a response to operating needs rather than a desire to make a large equity payout. Subsequent debt reductions are neither rapid, nor the result of pro-active attempts to rebalance the firm’s capital structure towards a long-run target. Instead, the evolution of the firm’s leverage ratio depends primarily on whether or not the firm produces a financial surplus. In fact, firms that generate subsequent deficits tend to cover these deficits predominantly with more debt even though they exhibit leverage ratios that are well above estimated target levels. While many of our findings are difficult to reconcile with traditional capital structure models, they are broadly consistent with a capital structure theory in which financial flexibility, in the form of unused debt capacity, plays an important role in capital structure choices.
Incoherent quantum feedback control of collective light scattering by Bose-Einstein condensates
It is well known that in the presence of a ring cavity the light scattering
from a uniform atomic ensemble can become unstable resulting in the collective
atomic recoil lasing. This is the result of a positive feedback due to the
cavity. We propose to add an additional electronic feedback loop based on the
photodetection of the scattered light. The advantage is a great flexibility in
choosing the feedback algorithm, since manipulations with electric signals are
very well developed. In this paper we address the application of such a
feedback to atoms in the Bose-Einstein condensed state and explore the quantum
noise due to the incoherent feedback action. We show that although the feedback
based on the photodetection does not change the local stability of the initial
uniform distribution with respect to small disturbances, it reduces the region
of attraction of the uniform equilibrium. The feedback-induced nonlinearity
enables quantum fluctuations to bring the system out of the stability region
and cause an exponential growth even if the uniform state is globally stable
without the feedback. Using numerical solution of the feedback master equation
we show that there is no feedback-induced noise in the quadratures of the
excited atomic and light modes. The feedback loop, however, introduces
additional noise into the number of quanta of these modes. Importantly, the
feedback opens an opportunity to position the modulated BEC inside a cavity as
well as tune the phase of scattered light. This can find applications in
precision measurements and quantum simulations.Comment: 7 pages, 7 figure
Applicability of Rydberg atoms to quantum computers
Applicability of Rydberg atoms to quantum computers is examined from
experimental point of view. In many theoretical proposals appeared recently,
excitation of atoms into highly excited Rydberg states was considered as a way
to achieve quantum entanglement in cold atomic ensembles via dipole-dipole
interaction that could be strong for Rydberg atoms. Appropriate conditions to
realize a conditional quantum phase gate have been analyzed. We also present
the results of modeling experiments on microwave spectroscopy of single- and
multi-atom excitations at the one-photon 37S-37P and two-photon 37S-38S
transitions in an ensemble of a few sodium Rydberg atoms. The microwave spectra
were investigated for various final states of the ensemble initially prepared
in its ground state. The quantum NOT operation with single atoms was found to
be affected by the Doppler effect and fluctuations of the microwave field. The
spectrum of full excitation of several Rydberg atoms was much narrower than
that of a single atom. This effect might be useful for the high-resolution
spectroscopy. The results may be also applied to the studies on collective
laser excitation of ground-state atoms aiming to realize quantum gates.Comment: 12 pages, 8 EPS figures, Revtex4. Old references corrected, new adde
Evaluation of different sources of uncertainty in climate change impact research using a hydro-climatic model ensemble
The international research project QBic3 (Quebec-Bavarian Collaboration on Climate Change) aims at investigating the potential impacts of climate change on the hydrology of regional scale catchments in Southern Quebec (Canada) and Bavaria (Germany). Yet, the actual change in river runoff characteristics during the next 70 years is highly uncertain due to a multitude of uncertainty sources. The so-called hydro-climatic ensemble that is constructed to describe the uncertainties of this complex model chain consists of four different global climate models, downscaled by three different regional climate models, an exchangeable bias correction algorithm, a separate method to scale RCM outputs to the hydrological model scale and several hydrological models of differing complexity to assess the impact of different hydro model concepts. This choice of models and scenarios allows for the inter-comparison of the uncertainty ranges of climate and hydrological models, of the natural variability of the climate system as well as of the impact of scaling and correction of climate data on mean, high and low flow conditions. A methodology to display the relative importance of each source of uncertainty is proposed and results for past runoff and potential future changes are presented
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