1,458 research outputs found
Heating without heat: thermodynamics of passive energy filters between finite systems
Passive filters allowing the exchange of particles in a narrow band of energy
are currently used in micro-refrigerators and energy transducers. In this
letter, we analyze their thermal properties using linear irreversible
thermodynamics and kinetic theory, and discuss a striking phenomenon: the
possibility of increasing or decreasing simultaneously the temperatures of two
systems without any supply of energy. This occurs when the filter induces a
flow of particles whose energy is between the average energies of the two
systems. Here we show that this selective transfer of particles does not need
the action of any sort of Maxwell demon and can be carried out by passive
filters without compromising the second law of thermodynamics. The phenomenon
allows us to design cycles between two reservoirs at temperatures
that are able to reach temperatures below or above .Comment: 5 pages, 3 figure
A Cutoff Procedure and Counterterms for Differential Renormalization
Explicit divergences and counterterms do not appear in the differential
renormalization method, but they are concealed in the neglected surface terms
in the formal partial integration procedure used. A systematic real space
cutoff procedure for massless theory is therefore studied in order to
test the method and its compatibility with unitarity. Through 3-loop order, it
is found that cutoff bare amplitudes are equal to the renormalized amplitudes
previously obtained using the formal procedure plus singular terms which can be
consistently cancelled by adding conventional counterterms to the Lagrangian.
Renormalization group functions and obtained in the
cutoff theory also agree with previous results.Comment: 28 pages, CTP#2099-DTP/92/40-UBECMPF/92/13, 2 figures (not included).
(Tex problems solved and information about number of pages and figures added
Relative states, quantum axes and quantum references
We address the problem of measuring the relative angle between two "quantum
axes" made out of N1 and N2 spins. Closed forms of our fidelity-like figure of
merit are obtained for an arbitrary number of parallel spins. The asymptotic
regimes of large N1 and/or N2 are discussed in detail. The extension of the
concept "quantum axis" to more general situations is addressed. We give optimal
strategies when the first quantum axis is made out of parallel spins whereas
the second is a general state made out of two spins.Comment: 6 pages, no figure
Price dynamics, informational efficiency and wealth distribution in continuous double auction markets
This paper studies the properties of the continuous double auction trading mechanishm using an artificial market populated by heterogeneous computational agents. In particular, we investigate how changes in the population of traders and in market microstructure characteristics affect price dynamics, information dissemination and distribution of wealth across agents. In our computer simulated market only a small fraction of the population observe the risky asset's fundamental value with noise, while the rest of agents try to forecast the asset's price from past transaction data. In contrast to other artificial markets, we assume that the risky asset pays no dividend, so agents cannot learn from past transaction prices and subsequent dividend payments. We find that private information can effectively disseminate in the market unless market regulation prevents informed investors from short selling or borrowing the asset, and these investors do not constitute a critical mass. In such case, not only are markets less efficient informationally, but may even experience crashes and bubbles. Finally, increased informational efficiency has a negative impact on informed agents' trading profits and a positive impact on artificial intelligent agents' profits
Optimal scheme for estimating a pure qubit state via local measurements
We present the optimal scheme for estimating a pure qubit state by means of
local measurements on N identical copies. We give explicit examples for low N.
For large N, we show that the fidelity saturates the collective measurement
bound up to order 1/N. When the signal state lays on a meridian of the Bloch
sphere, we show that this can be achieved without classical communication.Comment: Version to appear in PRL (minor changes, title changed
Buturi Solar
The village of Makongoro in the Buturi community of Tanzania lacks the resources to bring any form of energy to power the local school. The most reliable source of energy we could bring to the school is in the form of a photovoltaic system, as the climate of Buturi provides an ideal location for the implementation of such system. We have designed a solar microgrid specifically for Buturi and the needs of the school, that has the capability to power laptops, cell phones, and lighting throughout the school building. The system is fully detailed and explained in this report, with the final goal of implementation in the near future
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