705 research outputs found
Towards the lattice study of M-theory
We propose the Wilson discretization of the supersymmetric Yang-Mills Quantum
Mechanics as a lattice version of the matrix model of M-theory. An SU(2) model
is studied numerically in the quenched approximation for D=4. A clear signal
for the existence of two different phases is found and the continuum
pseudocritical temperature is determined. We have also extracted the continuum
limit of the total size of the system in both phases and for different
temperatures.Comment: Lattice 2000 (Gravity and Matrix Models
A theorem for the beam splitter entangler
It is conjectured that the an entanglement output states from a beam splitter
requires the nonclassicality in the input state(M.S. Kim, W. Son, V. Buzek and
P. L. Knight, Phys. Rev. A, 65, 032323(2002)). Here we give a proof for this
conjecture.Comment: Two relevant literatures added. To appear in Phys. Rev.
Properties of a beam splitter entangler with Gaussian input states
An explicit formula is given for the quantity of entanglement in the output
state of a beam splitter, given the squeezed vacuum states input in each mode.Comment: To appear in Phys. Rev.
Excitable Scale Free Networks
When a simple excitable system is continuously stimulated by a Poissonian
external source, the response function (mean activity versus stimulus rate)
generally shows a linear saturating shape. This is experimentally verified in
some classes of sensory neurons, which accordingly present a small dynamic
range (defined as the interval of stimulus intensity which can be appropriately
coded by the mean activity of the excitable element), usually about one or two
decades only. The brain, on the other hand, can handle a significantly broader
range of stimulus intensity, and a collective phenomenon involving the
interaction among excitable neurons has been suggested to account for the
enhancement of the dynamic range. Since the role of the pattern of such
interactions is still unclear, here we investigate the performance of a
scale-free (SF) network topology in this dynamic range problem. Specifically,
we study the transfer function of disordered SF networks of excitable
Greenberg-Hastings cellular automata. We observe that the dynamic range is
maximum when the coupling among the elements is critical, corroborating a
general reasoning recently proposed. Although the maximum dynamic range yielded
by general SF networks is slightly worse than that of random networks, for
special SF networks which lack loops the enhancement of the dynamic range can
be dramatic, reaching nearly five decades. In order to understand the role of
loops on the transfer function we propose a simple model in which the density
of loops in the network can be gradually increased, and show that this is
accompanied by a gradual decrease of dynamic range.Comment: 6 pages, 4 figure
Quantum optical coherence tomography with dispersion cancellation
We propose a new technique, called quantum optical coherence tomography
(QOCT), for carrying out tomographic measurements with dispersion-cancelled
resolution. The technique can also be used to extract the frequency-dependent
refractive index of the medium. QOCT makes use of a two-photon interferometer
in which a swept delay permits a coincidence interferogram to be traced. The
technique bears a resemblance to classical optical coherence tomography (OCT).
However, it makes use of a nonclassical entangled twin-photon light source that
permits measurements to be made at depths greater than those accessible via
OCT, which suffers from the deleterious effects of sample dispersion. Aside
from the dispersion cancellation, QOCT offers higher sensitivity than OCT as
well as an enhancement of resolution by a factor of 2 for the same source
bandwidth. QOCT and OCT are compared using an idealized sample.Comment: 19 pages, 4 figure
Gene phylogenies and protein–protein interactions: possible artifacts resulting from shared protein interaction partners
The study of gene families critically depends on the correct reconstruction of gene genealogies, as for instance in the case of transcription factor genes like Hox genes and Dlx gene families. Proteins belonging to the same family are likely to share some of the same protein interaction partners and may thus face a similar selective environment. This common selective environment can induce co-evolutionary pressures and thus can give rise to correlated rates and patterns of evolution among members of a gene family. In this study, we simulate the evolution of a family of sequences which share a set of interaction partners. Depending on the amount of sequence dedicated to protein–protein interaction and the relative rate parameters of sequence evolution three outcomes are possible: if the fraction of the sequence dedicated to interaction with common co-factors is low and the time since divergence is small, the trees based on sequence information tend to be correct. If the time since gene duplication is long two possible outcomes are observed in our simulations. If the rate of evolution of the interaction partner is small compared to the rate of evolution of the focal protein family, the reconstructed trees tend towards star phylogenies. As the rate of evolution of the interaction partner approaches that of the focal protein family the reconstructed phylogenies tend to be incorrectly resolved. We conclude that the genealogies of gene families can be hard to estimate, in particular if the proteins interact with a conserved set of binding partners, as is likely the case for transcription factors
Bounded fitness landscapes and the evolution of the linguistic diversity
A simple spatial computer simulation model was recently introduced to study
the evolution of the linguistic diversity. The model considers processes of
selective geographic colonization, linguistic anomalous diffusion and mutation.
In the approach, we ascribe to each language a fitness function which depends
on the number of people that speak that language. Here we extend the
aforementioned model to examine the role of saturation of the fitness on the
language dynamics. We found that the dependence of the linguistic diversity on
the area after colonization displays a power law regime with a nontrivial
exponent in very good agreement with the measured exponent associated with the
actual distribution of languages on the Earth.Comment: 10 pages, 3 figure
Effect of replacing wheat bran with spineless cactus plus urea in sugarcane-based diets for sheep
In times of drought, the availability of feed is reduced, and the use of concentrate ingredients, such as wheat bran, becomes costly for animal production. Thus, the use of spineless cactus emerges as a potential solution to the shortage of feed and water during prolonged drought periods. The objective of this study was to evaluate the effects of replacing wheat bran with spineless cactus plus urea (0%, 25%, 50%, 75%, and 100%) in sugarcane-based diets for sheep on nutrient intake, feeding behaviour, nitrogen balance and microbial protein synthesis. Five male Santa Ines sheep with average initial bodyweight of 34.0 ± 3.6 kg were used in a 5 × 5 Latin square. The maximum intakes of dry matter (DM) (1414 g/day), organic matter (OM) (1281 g/day), crude protein (CP) (204 g/day), neutral detergent fibre corrected for ash and protein (NDFap) (425 g/day), and total digestible nutrients (TDN) (890 g/day) were estimated with replacement levels of 80.2%, 75.3%, 88.6%, 50.5%, and 79.3% respectively. Feeding behaviour was not altered by replacing wheat bran with spineless cactus plus urea. Nitrogen retention increased by 0.10 g/day, while plasmatic urea nitrogen increased by 0.20 mg/day for every 1% level of replacement. The maximum production of microbial nitrogen (15.9 g/day) and microbial protein synthesis (99.4 g/day) were estimated with replacement levels of 45.8 and 45.7%, respectively. It is concluded that up to 80% wheat bran could be replaced with spineless cactus plus urea in sugarcane-based diets for sheep.Keywords: Alternative feed, drought, feeding behaviour, intake, microbial protei
Creation of NOON states by double Fock-state/Bose-Einstein condensates
NOON states (states of the form where and
are single particle states) have been used for predicting violations of
hidden-variable theories (Greenberger-Horne-Zeilinger violations) and are
valuable in metrology for precision measurements of phase at the Heisenberg
limit. We show theoretically how the use of two Fock state/Bose-Einstein
condensates as sources in a modified Mach Zender interferometer can lead to the
creation of the NOON state in which and refer to arms of the
interferometer and is the total number of particles in the two condensates.
The modification of the interferometer involves making conditional ``side''
measurements of a few particles near the sources. These measurements put the
remaining particles in a superposition of two phase states, which are converted
into NOON states by a beam splitter. The result is equivalent to the quantum
experiment in which a large molecule passes through two slits. The NOON states
are combined in a final beam splitter and show interference. Attempts to detect
through which ``slit'' the condensates passed destroys the interference.Comment: 8 pages 5 figure
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