3,111 research outputs found
The impact of two-dimensional elastic disk
The impact of a two-dimensional elastic disk with a wall is numerically
studied. It is clarified that the coefficient of restitution (COR) decreases
with the impact velocity. The result is not consistent with the recent
quasi-static theory of inelastic collisions even for very slow impact. The
abrupt drop of COR is found due to the plastic deformation of the disk, which
is assisted by the initial internal motion.(to be published in J. Phys. Soc.
Jpn.)Comment: 6 Pages,2 figure
Dynamic buckling and fragmentation in brittle rods
We present experiments on the dynamic buckling and fragmentation of slender
rods axially impacted by a projectile. By combining the results of Saint-Venant
and elastic beam theory, we derive a preferred wavelength lambda for the
buckling instability, and experimentally verify the resulting scaling law for a
range of materials including teflon, dry pasta, glass, and steel. For brittle
materials, buckling leads to the fragmentation of the rod. Measured fragment
length distributions show two clear peaks near lambda/2 and lambda/4. The
non-monotonic nature of the distributions reflect the influence of the
deterministic buckling process on the more random fragmentation processes.Comment: 4 pages, 5 figures, submitted to Physical Review Letter
Liver Resection for Primary Hepatic Neoplasms.
Subtotal hepatic resection was performed in 356 patients; 87 had primary hepatic malignancies, 108 had metastatic tumors, and 161 had benign lesions including 8 traumatic injuries. The global mortality was 4.2%. The experience has elucidated the role of subtotal hepatic resection both for benign and malignant neoplasms
Simulation for the oblique impact of a lattice system
The oblique collision between an elastic disk and an elastic wall is
numerically studied.
We investigate the dependency of the tangential coefficient of restitution on
the incident angle of impact.
From the results of simulation, our model reproduces experimental results and
can be explained by a phenomenological theory of the oblique impact.Comment: 30 pages, 9 figures, submitted to J. Phys. Soc. Japa
Determining the Parameters of Massive Protostellar Clouds via Radiative Transfer Modeling
A one-dimensional method for reconstructing the structure of prestellar and
protostellar clouds is presented. The method is based on radiative transfer
computations and a comparison of theoretical and observed intensity
distributions at both millimeter and infrared wavelengths. The radiative
transfer of dust emission is modeled for specified parameters of the density
distribution, central star, and external background, and the theoretical
distribution of the dust temperature inside the cloud is determined. The
intensity distributions at millimeter and IR wavelengths are computed and
quantitatively compared with observational data. The best-fit model parameters
are determined using a genetic minimization algorithm, which makes it possible
to reveal the ranges of parameter degeneracy as well. The method is illustrated
by modeling the structure of the two infrared dark clouds IRDC-320.27+029 (P2)
and IRDC-321.73+005 (P2). The derived density and temperature distributions can
be used to model the chemical structure and spectral maps in molecular lines.Comment: Accepted for publication in Astronomy Report
A spectral line survey of Orion KL in the bands 486-492 and 541-577 GHz with the Odin satellite I. The observational data
Spectral line surveys are useful since they allow identification of new
molecules and new lines in uniformly calibrated data sets. Nonetheless, large
portions of the sub-millimetre spectral regime remain unexplored due to severe
absorptions by H2O and O2 in the terrestrial atmosphere. The purpose of the
measurements presented here is to cover wavelength regions at and around 0.55
mm -- regions largely unobservable from the ground. Using the Odin
astronomy/aeronomy satellite, we performed the first spectral survey of the
Orion KL molecular cloud core in the bands 486--492 and 541--576 GHz with
rather uniform sensitivity (22--25 mK baseline noise). Odin's 1.1 m size
telescope, equipped with four cryo-cooled tuneable mixers connected to broad
band spectrometers, was used in a satellite position-switching mode. Two mixers
simultaneously observed different 1.1 GHz bands using frequency steps of 0.5
GHz (25 hours each). An on-source integration time of 20 hours was achieved for
most bands. The entire campaign consumed ~1100 orbits, each containing one hour
of serviceable astro-observation. We identified 280 spectral lines from 38
known interstellar molecules (including isotopologues) having intensities in
the range 80 to 0.05 K. An additional 64 weak lines remain unidentified. Apart
from the ground state rotational 1(1,0)--1(0,1) transitions of ortho-H2O, H218O
and H217O, the high energy 6(2,4)--7(1,7) line of para-H2O and the
HDO(2,0,2--1,1,1) line have been observed, as well as the 1,0--0,1 lines from
NH3 and its rare isotopologue 15NH3. We suggest assignments for some
unidentified features, notably the new interstellar molecules ND and SH-.
Severe blends have been detected in the line wings of the H218O, H217O and 13CO
lines changing the true linewidths of the outflow emission.Comment: 21 pages, 10 figures, 7 tables, accepeted for publication in
Astronomy and Astrophysics 30 August 200
Self-diffusion in granular gases
The coefficient of self-diffusion for a homogeneously cooling granular gas
changes significantly if the impact-velocity dependence of the restitution
coefficient is taken into account. For the case of a constant
the particles spread logarithmically slow with time, whereas the
velocity dependent coefficient yields a power law time-dependence. The impact
of the difference in these time dependences on the properties of a freely
cooling granular gas is discussed.Comment: 6 pages, no figure
Modeling of Protostellar Clouds and their Observational Properties
A physical model and two-dimensional numerical method for computing the
evolution and spectra of protostellar clouds are described. The physical model
is based on a system of magneto-gasdynamical equations, including ohmic and
ambipolar diffusion, and a scheme for calculating the thermal and ionization
structure of a cloud. The dust and gas temperatures are determined during the
calculations of the thermal structure of the cloud. The results of computing
the dynamical and thermal structure of the cloud are used to model the
radiative transfer in continuum and in molecular lines. We presented the
results for clouds in hydrostatic and thermal equilibrium. The evolution of a
rotating magnetic protostellar cloud starting from a quasi-static state is also
considered. Spectral maps for optically thick lines of linear molecules are
analyzed. We have shown that the influence of the magnetic field and rotation
can lead to a redistribution of angular momentum in the cloud and the formation
of a characteristic rotational velocity structure. As a result, the
distribution of the velocity centroid of the molecular lines can acquire an
hourglass shape. We plan to use the developed program package together with a
model for the chemical evolution to interpret and model observed starless and
protostellar cores.Comment: Accepted to Astronomy Report
New Mechanics of Traumatic Brain Injury
The prediction and prevention of traumatic brain injury is a very important
aspect of preventive medical science. This paper proposes a new coupled
loading-rate hypothesis for the traumatic brain injury (TBI), which states that
the main cause of the TBI is an external Euclidean jolt, or SE(3)-jolt, an
impulsive loading that strikes the head in several coupled degrees-of-freedom
simultaneously. To show this, based on the previously defined covariant force
law, we formulate the coupled Newton-Euler dynamics of brain's micro-motions
within the cerebrospinal fluid and derive from it the coupled SE(3)-jolt
dynamics. The SE(3)-jolt is a cause of the TBI in two forms of brain's rapid
discontinuous deformations: translational dislocations and rotational
disclinations. Brain's dislocations and disclinations, caused by the
SE(3)-jolt, are described using the Cosserat multipolar viscoelastic continuum
brain model.
Keywords: Traumatic brain injuries, coupled loading-rate hypothesis,
Euclidean jolt, coupled Newton-Euler dynamics, brain's dislocations and
disclinationsComment: 18 pages, 1 figure, Late
Simulation of cohesive head-on collisions of thermally activated nanoclusters
Impact phenomena of nanoclusters subject to thermal fluctuations are
numerically investigated. From the molecular dynamics simulation for colliding
two identical clusters, it is found that the restitution coefficient for
head-on collisions has a peak at a colliding speed due to the competition
between the cohesive interaction and the repulsive interaction of colliding
clusters. Some aspects of the collisions can be understood by the theory by
Brilliantov {\it et al.} (Phys. Rev. E {\bf 76}, 051302 (2007)), but many new
aspects are found from the simulation. In particular, we find that there are
some anomalous rebounds in which the restitution coefficient is larger than
unity. The phase diagrams of rebound processes against impact speed and the
cohesive parameter can be understood by a simple phenomenology.Comment: 10 pages, 12 figures, submitted to PRE; revised content and added
reference
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