52,621 research outputs found
Modification of an astronaut's mock up tool kit Final report
Design and tests of astronauts tool kit and tools for in-flight space maintenanc
Aharonov-Casher oscillations of spin current through a multichannel mesoscopic ring
The Aharonov-Casher (AC) oscillations of spin current through a 2D ballistic
ring in the presence of Rashba spin-orbit interaction and external magnetic
field has been calculated using the semiclassical path integral method. For
classically chaotic trajectories the Fokker-Planck equation determining
dynamics of the particle spin polarization has been derived. On the basis of
this equation an analytic expression for the spin conductance has been obtained
taking into account a finite width of the ring arms carrying large number of
conducting channels. It was shown that the finite width results in a broadening
and damping of spin current AC oscillations. We found that an external magnetic
field leads to appearance of new nondiagonal components of the spin
conductance, allowing thus by applying a rather weak magnetic field to change a
direction of the transmitted spin current polarization.Comment: 16 pages, 6 figure
Equilibrium states of a test particle coupled to finite size heat baths
We report on numerical simulations of the dynamics of a test particle coupled
to competing Boltzmann heat baths of finite size. After discussing some
features of the single bath case, we show that the presence of two heat baths
further constraints the conditions necessary for the test particle to
thermalize with the heat baths. We find that thermalization is a spectral
property in which the oscillators of the bath with frequencies in the range of
the test particle characteristic frequency determine its degree of
thermalization. We also find an unexpected frequency shift of the test particle
response with respect to the spectra of the two heat baths. Finally, we discuss
implications of our results for the study of high-frequency nanomechanical
resonators through cold damping cooling techniques, and for engineering
reservoirs capable of mitigating the back-action on a mechanical system.Comment: Strongly related to arXiV:0810.3251 (appeared in European Physical
Journal B 61, 271 (2008
Ac hopping conduction at extreme disorder takes place on the percolating cluster
Simulations of the random barrier model show that ac currents at extreme
disorder are carried almost entirely by the percolating cluster slightly above
threshold; thus contradicting traditional theories contributions from isolated
low-activation-energy clusters are negligible. The effective medium
approximation in conjunction with the Alexander-Orbach conjecture leads to an
excellent analytical fit to the universal ac conductivity with no nontrivial
fitting parameters
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Cancer cell lines show high heritability for motility but not generation time
Tumour evolution depends on heritable differences between cells in traits affecting cell survival or replication. It is well established that cancer cells are genetically and phenotypically heterogeneous; however, the extent to which this phenotypic variation is heritable is far less well explored. Here, we estimate the broad-sense heritability (H2) of two cell traits related to cancer hallmarks––cell motility and generation time––within populations of four cancer cell lines in vitro and find that motility is strongly heritable. This heritability is stable across multiple cell generations, with heritability values at the high end of those measured for a range of traits in natural populations of animals or plants. These findings confirm a central assumption of cancer evolution, provide a first quantification of the evolvability of key traits in cancer cells and indicate that there is ample raw material for experimental evolution in cancer cell lines. Generation time, a trait directly affecting cell fitness, shows substantially lower values of heritability than cell speed, consistent with its having been under directional selection removing heritable variation
All-sky Measurements of Short Period Waves Imaged in the OI (557.7 nm), Na(589.2 nm) and Near Infrared OH and O2(0,1) Nightglow Emissions During the ALOHA-93 Campaign
As part of the ALOHA‐93 campaign a high performance all‐sky CCD imaging system was operated at Haleakala Crater, Maui, to obtain novel information on the properties and sources of short period gravity waves over an extended height range ∼80–100 km. Sequential observations of the near infrared OH and O2(0,1) bands and the visible wavelength OI(557.7 nm) and Na(589.2 nm) line emissions have enabled a unique comparison of the morphology and dynamics of the wave motions and their occurrence frequency at each emission altitude to be made. Two major findings are: (a) the detection of significantly higher amounts of wave structure at OI altitudes (∼96 km) compared with that in the OH emission (∼87 km) and (b) the discovery of an unusual morphology, small‐scale wave pattern that was most conspicuous in the OI emission and essentially absent at OH heights. These data provide strong evidence for the presence of ducted wave motions in the lower thermosphere
The 2nd order renormalization group flow for non-linear sigma models in 2 dimensions
We show that for two dimensional manifolds M with negative Euler
characteristic there exists subsets of the space of smooth Riemannian metrics
which are invariant and either parabolic or backwards-parabolic for the 2nd
order RG flow. We also show that solutions exists globally on these sets.
Finally, we establish the existence of an eternal solution that has both a UV
and IR limit, and passes through regions where the flow is parabolic and
backwards-parabolic
Transferring elements of a density matrix
We study restrictions imposed by quantum mechanics on the process of matrix
elements transfer. This problem is at the core of quantum measurements and
state transfer. Given two systems \A and \B with initial density matrices
and , respectively, we consider interactions that lead to
transferring certain matrix elements of unknown into those of the
final state of \B. We find that this process eliminates the
memory on the transferred (or certain other) matrix elements from the final
state of \A. If one diagonal matrix element is transferred, , the memory on each non-diagonal element
is completely eliminated from the final density operator of
\A. Consider the following three quantities \Re \la_{a\not =b}, \Im
\la_{a\not =b} and \la_{aa}-\la_{bb} (the real and imaginary part of a
non-diagonal element and the corresponding difference between diagonal
elements). Transferring one of them, e.g., \Re\tir_{a\not = b}=\Re\la_{a\not =
b}, erases the memory on two others from the final state of \A.
Generalization of these set-ups to a finite-accuracy transfer brings in a
trade-off between the accuracy and the amount of preserved memory. This
trade-off is expressed via system-independent uncertainty relations which
account for local aspects of the accuracy-disturbance trade-off in quantum
measurements.Comment: 9 pages, 2 table
Vacuum polarization of massive scalar fields in the spacetime of the electrically charged nonlinear black hole
The approximate renormalized stress-energy tensor of the quantized massive
conformally coupled scalar field in the spacetime of electrically charged
nonlinear black hole is constructed. It is achieved by functional
differentiation of the lowest order of the DeWitt-Schwinger effective action
involving coincidence limit of the Hadamard-Minakshisundaram-DeWitt-Seely
coefficient The result is compared with the analogous result derived
for the Reissner-Nordstr\"om black hole. It is shown that the most important
differences occur in the vicinity of the event horizon of the black hole near
the extremality limit. The structure of the nonlinear black hole is briefly
studied by means of the Lambert functions.Comment: 22 pages, 10 figure
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