8,036 research outputs found
Manipulating the torsion of molecules by strong laser pulses
A proof-of-principle experiment is reported, where torsional motion of a
molecule, consisting of a pair of phenyl rings, is induced by strong laser
pulses. A nanosecond laser pulse spatially aligns the carbon-carbon bond axis,
connecting the two phenyl rings, allowing a perpendicularly polarized, intense
femtosecond pulse to initiate torsional motion accompanied by an overall
rotation about the fixed axis. The induced motion is monitored by femtosecond
time-resolved Coulomb explosion imaging. Our theoretical analysis accounts for
and generalizes the experimental findings.Comment: 4 pages, 4 figures, submitted to PRL; Major revision of the
presentation of the material; Correction of ion labels in Fig. 2(a
Pest management: Four years experience in a commercial apple orchard
Pest management in a 12-ha apple orchard from 1973 to 1976 resulted in a 50 percent reduction in the number of sprays that are normally applied to control insects and mites. Codling moth, <i>Laspeyresia pomonella</i> (L.), populations were monitored by sex pheromone traps and populations of other insects and mites were assessed by specific sampling techniques. Leafrollers were the most difficult pests to control and fruit injury was 1.5 to 2.0 percent in 3 of the 4 years. Mites were held below treatment levels by the predator, <i>Typhlodromus occidentalis</i> Nesbitt, except for the apple rust mite, <i>Aculus schlechtendali</i> (Nalepa) which required chemical control
Thermodynamics, strange quark matter, and strange stars
Because of the mass density-dependence, an extra term should be added to the
expression of pressure. However, it should not appear in that of energy
according to both the general ensemble theory and basic thermodynamic
principle. We give a detail derivation of the thermodynamics with
density-dependent particle masses. With our recently determined quark mass
scaling, we study strange quark matter in this new thermodynamic treatment,
which still indicates a possible absolute stability as previously found.
However, the density behavior of the sound velocity is opposite to the previous
finding, but consistent with one of our recent publication. We have also
studied the structure of strange stars using the obtained equation of state.Comment: 6 pages, 6 PS figures, REVTeX styl
Semiclassical two-step model for strong-field ionization
We present a semiclassical two-step model for strong-field ionization that
accounts for path interferences of tunnel-ionized electrons in the ionic
potential beyond perturbation theory. Within the framework of a classical
trajectory Monte-Carlo representation of the phase-space dynamics, the model
employs the semiclassical approximation to the phase of the full quantum
propagator in the exit channel. By comparison with the exact numerical solution
of the time-dependent Schr\"odinger equation for strong-field ionization of
hydrogen, we show that for suitable choices of the momentum distribution after
the first tunneling step, the model yields good quantitative agreement with the
full quantum simulation. The two-dimensional photoelectron momentum
distributions, the energy spectra, and the angular distributions are found to
be in good agreement with the corresponding quantum results. Specifically, the
model quantitatively reproduces the fan-like interference patterns in the
low-energy part of the two-dimensional momentum distributions as well as the
modulations in the photoelectron angular distributions.Comment: 31 pages, 7 figure
Charge and critical density of strange quark matter
The electric charge of strange quark matter is of vital importance to
experiments. A recent investigation shows that strangelets are most likely
highly negatively charged, rather than slightly positively charged as
previously believed. Our present study indicates that negative charges can
indeed lower the critical density, and thus be favorable to the experimental
searches in heavy ion collisions. However, too much negative charges can make
it impossible to maintain flavor equilibrium.Comment: 4 pages, LATeX with REVTeX style, one PS figure. To be published in
Phys. Rev. C 59(6), 199
A Cosmological Three Level Neutrino Laser
We present a calculation of a neutrino decay scenario in the early Universe.
The specific decay is \nu_{2} \to \nu_{1} + \phi, where \phi is a boson. If
there is a neutrino mass hierarchy, m_{\nu_{e}} < m_{\nu_{\mu}} <
m_{\nu_{\tau}}, we show that it is possible to generate stimulated decay and
effects similar to atomic lasing without invoking new neutrinos, even starting
from identical neutrino distributions. Under the right circumstances the decay
can be to very low momentum boson states thereby producing something similar to
a Bose condensate, with possible consequences for structure formation. Finally,
we argue that this type of decay may also be important other places in early
Universe physics.Comment: 7 pages, RevTex, due for publication in Phys. Rev. D, April 15 issu
Mass formulas and thermodynamic treatment in the mass-density-dependent model of strange quark matter
The previous treatments for strange quark matter in the quark
mass-density-dependent model have unreasonable vacuum limits. We provide a
method to obtain the quark mass parametrizations and give a self-consistent
thermodynamic treatment which includes the MIT bag model as an extreme. In this
treatment, strange quark matter in bulk still has the possibility of absolute
stability. However, the lower density behavior of the sound velocity is
opposite to previous findings.Comment: Formatted in REVTeX 3.1, 5 pages, 3 figures, to appear in PRC6
Colour-singlet strangelets at finite temperature
Considering massless and quarks, and massive (150 MeV) quarks in
a bag with the bag pressure constant MeV, a colour-singlet
grand canonical partition function is constructed for temperatures
MeV. Then the stability of finite size strangelets is studied minimizing the
free energy as a function of the radius of the bag. The colour-singlet
restriction has several profound effects when compared to colour unprojected
case: (1) Now bulk energy per baryon is increased by about MeV making the
strange quark matter unbound. (2) The shell structures are more pronounced
(deeper). (3) Positions of the shell closure are shifted to lower -values,
the first deepest one occuring at , famous -particle ! (4) The shell
structure at vanishes only at MeV, though for higher
-values it happens so at MeV.Comment: Revtex file(8 pages)+6 figures(ps files) available on request from
first Autho
Differential atom interferometry beyond the standard quantum limit
We analyze methods to go beyond the standard quantum limit for a class of
atomic interferometers, where the quantity of interest is the difference of
phase shifts obtained by two independent atomic ensembles. An example is given
by an atomic Sagnac interferometer, where for two ensembles propagating in
opposite directions in the interferometer this phase difference encodes the
angular velocity of the experimental setup. We discuss methods of squeezing
separately or jointly observables of the two atomic ensembles, and compare in
detail advantages and drawbacks of such schemes. In particular we show that the
method of joint squeezing may improve the variance by up to a factor of 2. We
take into account fluctuations of the number of atoms in both the preparation
and the measurement stage, and obtain bounds on the difference of the numbers
of atoms in the two ensembles, as well as on the detection efficiency, which
have to be fulfilled in order to surpass the standard quantum limit. Under
realistic conditions, the performance of both schemes can be improved
significantly by reading out the phase difference via a quantum non-demolition
(QND) measurement. Finally, we discuss a scheme using macroscopically entangled
ensembles.Comment: 10 pages, 5 figures; eq. (3) corrected and other minor change
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