24,774 research outputs found
Charm production in deep inelastic and diffractive scattering
We consider the production of charm by real and virtual photons. Special
attention is paid to diffractive charm production, which provides information
on the gluonic content of the Pomeron. Our calculations are based on the gluon
distributions of the CKMT-model, which is shown to lead to agreement with the
data on open charm production in deep inelastic scattering. We compare
predictions for diffractive charm production of different models for the
distribution of gluons in the Pomeron. Experiments at HERA should be able to
discriminate between them. Predictions for beauty production in diffractive and
non-diffractive interactions of photons are also given.Comment: 14 pages REVTEX and 24 figures include
Ultrafast magnetophotoconductivity of semi-insulating gallium arsenide
The speed of opto-electronic switches is increased or decreased by the application of a magnetic field. This is achieved by inducing a carrier drift toward or away from the semiconductor surface, resulting in the enhancement or suppression of surface recombination. We establish that surface recombination plays a major role in determining the speed of the opto-electronic switch
The Be-test in the Li-rich star \#1657 of NGC 6397: evidence for Li-flash in RGB stars?
The Li-rich turn-off star in the globular cluster NGC 6397 could represent
the smoking gun for some very rare episode of Li enrichment in globular
clusters. We aim to understand the nature of the Li enrichment by performing a
spectroscopic analysis of the star, in particular of its beryllium (Be)
abundance, and by investigating its binary nature. We observe the near UV
region where the Beii resonance doublet and the NH bands are located. We could
not detect the Beii lines and derive an upper limit of log (Be/H)< -12.2, that
is consistent with the Be observed in other stars of the cluster. We could
detect a weak G-band, which implies a mild carbon enhancement
[C/Fe]. We could not detect the UV NH band, and we derive an upper
limit [N/Fe]. For oxygen we could notdetect any of the near UV OH lines,
which implies that oxygen cannot be strongly enhanced in this star. This is
consistent with the detection of the Oi triplet at 777nm, which is consistent
with [O/Fe]~0.5. Combining the UVES and Mike data, we could not detect any
variation in the radial velocity greater than 0.95 kms over 8 years. The
chemical composition of the star strongly resembles that of `first generation'
NGC6397 stars, with the huge Li as the only deviating abundance. Not detecting
Be rules out two possible explanations of the Li overabundance: capture of a
substellar body and spallation caused by a nearby type II SNe. Discrepancies
are also found with respect to other accretion scenarios,except for
contamination by the ejecta of a star that has undergone the RGB Li-flash.Comment: Accepted for publication in A&
Classical integrability of chiral and classical curves
In this letter, classical chiral is studied in the lightcone gauge
. The once integrated equation of motion for the current is shown to
be of the Lax form, which demonstrates an infinite number of conserved
quantities. Specializing to gauge group SU(2), we show that solutions to the
classical equations of motion can be identified with a very large class of
curves. We demonstrate this correspondence explicitly for two solutions. The
classical fermionic fields associated with these currents are then obtained.Comment: Final version to appear in Mod. Phys. Lett. A. A reference and two
footnotes added. 6 pages revte
Stink Bugs (Hemiptera: Heteroptera: Pentatomidae) of Minnesota: An Annotated Checklist and New State Records
Pentatomidae have been relatively poorly documented in Minnesota. Based on literature and museum records, an annotated checklist of the Pentatomidae of Minnesota was created. State-level and county-level records for Minnesota and the distribution of each species in North America are provided. Fifty-one species of Pentatomidae (12 Asopinae, 37 Pentatominae, and 2 Podopinae) are recorded for Minnesota. Of this total, 15 species are newly recorded for the state. Knowledge of the fauna of Pentatomidae in Minnesota will be important for providing baseline data for monitoring of potential shifts in the fauna resulting from the invasions of exotic Pentatomidae. Furthermore, a list of native Pentatomidae will be necessary for monitoring non-target impacts, if classical biological control is implemented for management of exotic Pentatomidae
The effects of newly measured cross sections in hydrogen on the production of secondary nuclei during the propagation of cosmic rays through interstellar H
The cross sections of six important cosmic ray source nuclei in hydrogen at several energies between 300 and 1800 MeV/nuc were measured. Significant differences, sometimes exceeding 50%, exist between these new measurements and the earlier semiempirical predictions, and a new set of semiempirical formulae are being determined that better describe this fragmentation. New cross sections were obtained so that the systematics of their effects on cosmic ray propagation through interstellar hydrogen can be examined
Charge and energy dependence of the residence time of cosmic ray nuclei below 15 GeV/nucleon
The relative abundance of nuclear species measured in cosmic rays at Earth has often been interpreted with the simple leaky box model. For this model to be consistent an essential requirement is that the escape length does not depend on the nuclear species. The discrepancy between escape length values derived from iron secondaries and from the B/C ratio was identified by Garcia-Munoz and his co-workers using a large amount of experimental data. Ormes and Protheroe found a similar trend in the HEAO data although they questioned its significance against uncertainties. They also showed that the change in the B/C ratio values implies a decrease of the residence time of cosmic rays at low energies in conflict with the diffusive convective picture. These conclusions crucially depend on the partial cross section values and their uncertainties. Recently new accurate cross sections of key importance for propagation calculations have been measured. Their statistical uncertainties are often better than 4% and their values significantly different from those previously accepted. Here, these new cross sections are used to compare the observed B/C+O and (Sc to Cr)/Fe ratio to those predicted with the simple leaky box model
Efficient one- and two-qubit pulsed gates for an oscillator stabilized Josephson qubit
We present theoretical schemes for performing high-fidelity one- and
two-qubit pulsed gates for a superconducting flux qubit. The "IBM qubit"
consists of three Josephson junctions, three loops, and a superconducting
transmission line. Assuming a fixed inductive qubit-qubit coupling, we show
that the effective qubit-qubit interaction is tunable by changing the applied
fluxes, and can be made negligible, allowing one to perform high fidelity
single qubit gates. Our schemes are tailored to alleviate errors due to 1/f
noise; we find gates with only 1% loss of fidelity due to this source, for
pulse times in the range of 20-30ns for one-qubit gates (Z rotations,
Hadamard), and 60ns for a two-qubit gate (controlled-Z). Our relaxation and
dephasing time estimates indicate a comparable loss of fidelity from this
source. The control of leakage plays an important role in the design of our
shaped pulses, preventing shorter pulse times. However, we have found that
imprecision in the control of the quantum phase plays the major role in the
limitation of the fidelity of our gates.Comment: Published version. Added references. Corrected minor typos. Added
discussion on how the influence of 1/f noise is modeled. 36 pages, 11 figure
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