30,521 research outputs found
Dynamic model for failures in biological systems
A dynamic model for failures in biological organisms is proposed and studied
both analytically and numerically. Each cell in the organism becomes dead under
sufficiently strong stress, and is then allowed to be healed with some
probability. It is found that unlike the case of no healing, the organism in
general does not completely break down even in the presence of noise. Revealed
is the characteristic time evolution that the system tends to resist the stress
longer than the system without healing, followed by sudden breakdown with some
fraction of cells surviving. When the noise is weak, the critical stress beyond
which the system breaks down increases rapidly as the healing parameter is
raised from zero, indicative of the importance of healing in biological
systems.Comment: To appear in Europhys. Let
Initial Observations of Sunspot Oscillations Excited by Solar Flare
Observations of a large solar flare of December 13, 2006, using Solar Optical
Telescope (SOT) on Hinode spacecraft revealed high-frequency oscillations
excited by the flare in the sunspot chromosphere. These oscillations are
observed in the region of strong magnetic field of the sunspot umbra, and may
provide a new diagnostic tool for probing the structure of sunspots and
understanding physical processes in solar flares.Comment: 10 pages, 6 figures, ApJL in pres
The Strength and Nature of Bequest Motives in the United States
In this paper, we analyze the strength and nature of bequest motives in the United States using data from the 2000 Health and Retirement Study (HRS). The results of our analysis suggest that bequest motives are very strong in the United States and that they are altruistically motivated. This suggests that the altruism (or dynasty) model applies in the United States and that the selfish life cycle model does not apply. Moreover, our results also suggest that older, wealthier, married, more highly educated, Caucasian, healthy, and non-religious individuals are more likely to leave a bequest than other individuals.Bequests, Bequest Motives, Altruism, Life Cycle Model, Household Behavior
Velocity selection problem for combined motion of melting and solidification fronts
We discuss a free boundary problem for two moving solid-liquid interfaces
that strongly interact via the diffusion field in the liquid layer between
them. This problem arises in the context of liquid film migration (LFM) during
the partial melting of solid alloys. In the LFM mechanism the system chooses a
more efficient kinetic path which is controlled by diffusion in the liquid
film, whereas the process with only one melting front would be controlled by
the very slow diffusion in the mother solid phase. The relatively weak
coherency strain energy is the effective driving force for LFM. As in the
classical dendritic growth problems, also in this case an exact family of
steady-state solutions with two parabolic fronts and an arbitrary velocity
exists if capillary effects are neglected. We develop a velocity selection
theory for this problem, including anisotropic surface tension effects. The
strong diffusion interaction and coherency strain effects in the solid near the
melting front lead to substantial changes compared to classical dendritic
growth.Comment: submitted to PR
Study of Resistive Micromegas in a Mixed Neutron and Photon Radiation Field
The Muon ATLAS Micromegas Activity (MAMMA) focuses on the development and
testing of large-area muon detectors based on the bulk-Micromegas technology.
These detectors are candidates for the upgrade of the ATLAS Muon System in view
of the luminosity upgrade of Large Hadron Collider at CERN (sLHC). They will
combine trigger and precision measurement capability in a single device. A
novel protection scheme using resistive strips above the readout electrode has
been developed. The response and sparking properties of resistive Micromegas
detectors were successfully tested in a mixed (neutron and gamma) high
radiation field supplied by the Tandem accelerator, at the N.C.S.R. Demokritos
in Athens. Monte-Carlo studies have been employed to study the effect of 5.5
MeV neutrons impinging on Micromegas detectors. The response of the Micromegas
detectors on the photons originating from the inevitable neutron inelastic
scattering on the surrounding materials of the experimental facility was also
studied
Large Amplitude Dynamics of the Pairing Correlations in a Unitary Fermi Gas
A unitary Fermi gas has a surprisingly rich spectrum of large amplitude modes
of the pairing field alone, which defies a description within a formalism
involving only a reduced set of degrees of freedom, such as quantum
hydrodynamics or a Landau-Ginzburg-like description. These modes are very slow,
with oscillation frequencies well below the pairing gap, which makes their
damping through quasiparticle excitations quite ineffective. In atomic traps
these modes couple naturally with the density oscillations, and the
corresponding oscillations of the atomic cloud are an example of a new type of
collective mode in superfluid Fermi systems. They have lower frequencies than
the compressional collective hydrodynamic oscillations, have a non-spherical
momentum distribution, and could be excited by a quick time variation of the
scattering length.Comment: 4 pages, 3 figures, published version, updated figures and a number
of change
- …