4,349 research outputs found
Factors of Micromanipulation Accuracy and Learning
Micromanipulation refers to the manipulation under a microscope in order to
perform delicate procedures. It is difficult for humans to manipulate objects
accurately under a microscope due to tremor and imperfect perception, limiting
performance. This project seeks to understand factors affecting accuracy in
micromanipulation, and to propose strategies for learning improving accuracy.
Psychomotor experiments were conducted using computer-controlled setups to
determine how various feedback modalities and learning methods can influence
micromanipulation performance. In a first experiment, static and motion accuracy
of surgeons, medical students and non-medical students under different
magniification levels and grip force settings were compared. A second experiment
investigated whether the non-dominant hand placed close to the target can contribute
to accurate pointing of the dominant hand. A third experiment tested a
training strategy for micromanipulation using unstable dynamics to magnify motion
error, a strategy shown to be decreasing deviation in large arm movements.
Two virtual reality (VR) modules were then developed to train needle grasping
and needle insertion tasks, two primitive tasks in a microsurgery suturing
procedure. The modules provided the trainee with a visual display in stereoscopic
view and information on their grip, tool position and angles. Using the
VR module, a study examining effects of visual cues was conducted to train tool
orientation. Results from these studies suggested that it is possible to learn and
improve accuracy in micromanipulation using appropriate sensorimotor feedback
and training
Quarkonium formation time in quark-gluon plasma
The quarkonium formation time in a quark-gluon plasma (QGP) is determined
from the space-time correlator of heavy quark vector currents using the
quarkonium in-medium mass and wave function obtained from heavy quark
potentials extracted from the lattice QCD. It is found that the formation time
of a quarkonium increases with the temperature of the QGP and diverges near its
dissociation temperature. Also, the quarkonium formation time is longer if the
heavy quark potential is taken to be the free energy from lattice calculations
for a heavy quark pair, compared to that based on the more negative internal
energy.Comment: 5 pages, 4 figure
Quarkonium formation time in relativistic heavy-ion collisions
We calculate the quarkonium formation time in relativistic heavy-ion
collisions from the space-time correlator of heavy quark vector currents in a
hydrodynamics background with the initial nonequilibrium stage expanding only
in the longitudinal direction. Using in-medium quarkonia properties determined
with the heavy quark potential taken to be the free energy from lattice
calculations and the fact that quarkonia can only be formed below their
dissociation temperatures due to color screening, we find that (1S),
(2S), (3S), and are formed,
respectively, at 1.2, 6.6, 8.8, 5.8, and 11.0 fm/c after the quark pair are
produced in central Au+Au collisions at the top energy of Relativistic Heavy
Ion Collider (RHIC), and these times become shorter in semi-central collisions.
We further show, as an example, that including the effect of formation time
enhances appreciably the survivability of (1S) in the produced hot
dense matter.Comment: 6 pages, 4 figure
production and elliptic flow in relativistic heavy-ion collisions
Using a two-component model for charmonium production, which includes
contributions from both the initial hard nucleon-nucleon scattering and from
the regeneration in the quark-gluon plasma, we study the nuclear modification
factor and elliptic flow of in relativistic heavy ion
collisions. For the expansion dynamics of produced hot dense matter, we
introduce a schematic fireball model with its transverse acceleration
determined from the pressure gradient inside the fireball and azimuthally
anisotropic expansion parameterized to reproduce measured of light
hadrons. We assume that light hadrons freeze out at the temperature of 120 MeV
while charmonia at 160 MeV, similar to the kinetic and chemical freeze-out
temperatures in the statistical model, respectively. For the properties of
charmonia in the quark-gluon plasma, we use the screening mass between their
charm and anticharm quarks and their dissociation cross sections given by the
perturbative QCD (pQCD) in the leading order and up to the next-to-leading
order, respectively. For the relaxation time of charm and anticharm quarks in
the quark-gluon plasma, we also use the one calculated in the leading order of
pQCD. Modeling the effect of higher-order corrections in pQCD by introducing
multiplicative factors to the dissociation cross section of charmonia and the
elastic scattering cross sections of charm and anticharm quarks, we find that
this effect is small for the of as they suppress the number
of initially produced but enhance the number of regenerated ones. The
higher-order corrections increase, however, the of . Our results
suggest that the of can play an important role in discriminating
between production from the initial hard collisions and from the
regeneration in the quark-gluon plasma.Comment: 15 pages, 14 figure
Heavy baryon/meson ratios in relativistic heavy ion collisions
Heavy baryon/meson ratios and in
relativistic heavy ion collisions are studied in the quark coalescence model.
For heavy baryons, we include production from coalescence of heavy quarks with
free light quarks as well as with bounded light diquarks that might exist in
the strongly coupled quark-gluon plasma produced in these collisions. Including
the contribution from decays of heavy hadron resonances and also that due to
fragmentation of heavy quarks that are left in the system after coalescence,
the resulting and ratios in midrapidity
() from central Au+Au collisions at GeV are
about a factor of five and ten, respectively, larger than those given by the
thermal model, and about a factor of ten and twelve, respectively, larger than
corresponding ratios in the PYTHIA model for collisions. These ratios are
reduced by a factor of about 1.6 if there are no diquarks in the quark-gluon
plasma. The transverse momentum dependence of the heavy baryon/meson ratios is
found to be sensitive to the heavy quark mass, with the
ratio being much flatter than the ratio. The latter peaks at
the transverse momentum GeV but the peak shifts to GeV in the absence of diquarks.Comment: 11 pages, 2 figure
Contributions of hyperon-hyperon scattering to subthreshold cascade production in heavy ion collisions
Using a gauged flavor SU(3)-invariant hadronic Lagrangian, we calculate the
cross sections for the strangeness-exchange reactions YY to N\Xi (Y=\Lambda,
\Sigma) in the Born approximation. These cross sections are then used in the
Relativistic Vlasov-Uehling-Uhlenbeck (RVUU) transport model to study \Xi
production in Ar+KCl collisions at incident energy of 1.76A GeV and impact
parameter b=3.5 fm. We find that including the contributions of hyperon-hyperon
scattering channels strongly enhances the yield of \Xi, leading to the
abundance ratio \Xi^{-}/(\Lambda+\Sigma^{0})=3.38E-3, which is essentially
consistent with the recently measured value of by the HADES collaboration at GSI.Comment: 8 pages, 5 figure
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