12,997 research outputs found
Derivation of the Blackbody Radiation Spectrum from a Natural Maximum-Entropy Principle Involving Casimir Energies and Zero-Point Radiation
By numerical calculation, the Planck spectrum with zero-point radiation is
shown to satisfy a natural maximum-entropy principle whereas alternative
choices of spectra do not. Specifically, if we consider a set of
conducting-walled boxes, each with a partition placed at a different location
in the box, so that across the collection of boxes the partitions are uniformly
spaced across the volume, then the Planck spectrum correspond to that spectrum
of random radiation (having constant energy kT per normal mode at low
frequencies and zero-point energy (1/2)hw per normal mode at high frequencies)
which gives maximum uniformity across the collection of boxes for the radiation
energy per box. The analysis involves Casimir energies and zero-point radiation
which do not usually appear in thermodynamic analyses. For simplicity, the
analysis is presented for waves in one space dimension.Comment: 11 page
Control of erythroid differentiation: asynchronous expression of the anion transporter and the peripheral components of the membrane skeleton in AEV- and S13-transformed cells
Chicken erythroblasts transformed with avian erythroblastosis virus or S13 virus provide suitable model systems with which to analyze the maturation of immature erythroblasts into erythrocytes. The transformed cells are blocked in differentiation at around the colony-forming unit- erythroid stage of development but can be induced to differentiate in vitro. Analysis of the expression and assembly of components of the membrane skeleton indicates that these cells simultaneously synthesize alpha-spectrin, beta-spectrin, ankyrin, and protein 4.1 at levels that are comparable to those of mature erythroblasts. However, they do not express any detectable amounts of anion transporter. The peripheral membrane skeleton components assemble transiently and are subsequently rapidly catabolized, resulting in 20-40-fold lower steady-state levels than are found in maturing erythrocytes. Upon spontaneous or chemically induced terminal differentiation of these cells expression of the anion transporter is initiated with a concommitant increase in the steady- state levels of the peripheral membrane-skeletal components. These results suggest that during erythropoiesis, expression of the peripheral components of the membrane skeleton is initiated earlier than that of the anion transporter. Furthermore, they point a key role for the anion transporter in conferring long-term stability to the assembled erythroid membrane skeleton during terminal differentiation
Incremental Distance Transforms (IDT)
A new generic scheme for incremental implementations of distance transforms (DT) is presented: Incremental Distance Transforms (IDT). This scheme is applied on the cityblock, Chamfer, and three recent exact Euclidean DT (E2DT). A benchmark shows that for all five DT, the incremental implementation results in a significant speedup: 3.4×−10×. However, significant differences (i.e., up to 12.5×) among the DT remain present. The FEED transform, one of the recent E2DT, even showed to be faster than both city-block and Chamfer DT. So, through a very efficient incremental processing scheme for DT, a relief is found for E2DT’s computational burden
Quantum computers can search rapidly by using almost any transformation
A quantum computer has a clear advantage over a classical computer for
exhaustive search. The quantum mechanical algorithm for exhaustive search was
originally derived by using subtle properties of a particular quantum
mechanical operation called the Walsh-Hadamard (W-H) transform. This paper
shows that this algorithm can be implemented by replacing the W-H transform by
almost any quantum mechanical operation. This leads to several new applications
where it improves the number of steps by a square-root. It also broadens the
scope for implementation since it demonstrates quantum mechanical algorithms
that can readily adapt to available technology.Comment: This paper is an adapted version of quant-ph/9711043. It has been
modified to make it more readable for physicists. 9 pages, postscrip
Ordering kinetics of stripe patterns
We study domain coarsening of two dimensional stripe patterns by numerically
solving the Swift-Hohenberg model of Rayleigh-Benard convection. Near the
bifurcation threshold, the evolution of disordered configurations is dominated
by grain boundary motion through a background of largely immobile curved
stripes. A numerical study of the distribution of local stripe curvatures, of
the structure factor of the order parameter, and a finite size scaling analysis
of the grain boundary perimeter, suggest that the linear scale of the structure
grows as a power law of time with a craracteristic exponent z=3. We interpret
theoretically the exponent z=3 from the law of grain boundary motion.Comment: 4 pages, 4 figure
Grover's Quantum Search Algorithm for an Arbitrary Initial Mixed State
The Grover quantum search algorithm is generalized to deal with an arbitrary
mixed initial state. The probability to measure a marked state as a function of
time is calculated, and found to depend strongly on the specific initial state.
The form of the function, though, remains as it is in the case of initial pure
state. We study the role of the von Neumann entropy of the initial state, and
show that the entropy cannot be a measure for the usefulness of the algorithm.
We give few examples and show that for some extremely mixed initial states
carrying high entropy, the generalized Grover algorithm is considerably faster
than any classical algorithm.Comment: 4 pages. See http://www.cs.technion.ac.il/~danken/MSc-thesis.pdf for
extended discussio
Ab Initio Calculation of Spin Gap Behavior in CaV4O9
Second neighbor dominated exchange coupling in CaV4O9 has been obtained from
ab initio density functional (DF) calculations. A DF-based self-consistent
atomic deformation model reveals that the nearest neighbor coupling is small
due to strong cancellation among the various superexchange processes. Exact
diagonalization of the predicted Heisenberg model yields spin-gap behavior in
good agreement with experiment. The model is refined by fitting to the
experimental susceptibility. The resulting model agrees very well with the
experimental susceptibility and triplet dispersion.Comment: 4 pages; 3 ps figures included in text; Revte
Energy properness and Sasakian-Einstein metrics
In this paper, we show that the existence of Sasakian-Einstein metrics is
closely related to the properness of corresponding energy functionals. Under
the condition that admitting no nontrivial Hamiltonian holomorphic vector
field, we prove that the existence of Sasakian-Einstein metric implies a
Moser-Trudinger type inequality. At the end of this paper, we also obtain a
Miyaoka-Yau type inequality in Sasakian geometry.Comment: 27 page
Gamma-ray diagnostics of Type Ia supernovae: Predictions of observables from three-dimensional modeling
Besides the fact that the gamma-ray emission due to radioactive decays is
responsible for powering the light curves of Type Ia supernovae (SNe Ia), gamma
rays themselves are of particular interest as a diagnostic tool because they
provide a direct way to obtain deeper insights into the nucleosynthesis and the
kinematics of these explosion events. Focusing on two of the most broadly
discussed SN Ia progenitor scenarios - a delayed detonation in a
Chandrasekhar-mass white dwarf (WD) and a violent merger of two WDs - we use
three-dimensional explosion models and perform radiative transfer simulations
to obtain synthetic gamma-ray spectra. Both chosen models produce the same mass
of 56Ni and have similar optical properties that are in reasonable agreement
with the recently observed supernova SN 2011fe. In contrast to the optical
regime, the gamma-ray emission of our two chosen models proves to be rather
different. The almost direct connection of the emission of gamma rays to
fundamental physical processes occuring in SNe Ia permits additional
constraints concerning several explosion model properties that are not easily
accessible within other wavelength ranges. Proposed future MeV missions such as
GRIPS will resolve all spectral details only for nearby SNe Ia, but hardness
ratio and light curve measurements still allow for a distinction of the two
different models at 10 and 16 Mpc for an exposure time of 10^6 s, respectively.
The possibility to detect the strongest line features up to the Virgo distance
will offer the opportunity to build up a first sample of SN Ia detections in
the gamma-ray energy range and underlines the importance of future space
observatories for MeV gamma rays.Comment: 10 pages, 8 figures, accepted for publication by A&
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