16,928 research outputs found
Consequences of inter-population crosses on developmental stability and canalization of floral traits in Dalechampia scandens (Euphorbiaceae)
Genetic regulatory pathways of splitâhand/foot malformation
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146859/1/cge13434-sup-0001-EditorialProcess.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146859/2/cge13434_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146859/3/cge13434.pd
Relativistic electrons from sparks in the laboratory
Discharge experiments were carried out at the Eindhoven University of
Technology in 2013. The experimental setup was designed to search for electrons
produced in meter-scale sparks using a 1 MV Marx generator. Negative voltage
was applied to the high voltage (HV) electrode. Five thin (1 mm) plastic
detectors (5 each) were distributed in various configurations close
to the spark gap. Earlier studies have shown (for HV negative) that X-rays are
produced when a cloud of streamers is developed 30-60 cm from the negative
electrode. This indicates that the electrons producing the X-rays are also
accelerated at this location, that could be in the strong electric field from
counterstreamers of opposite polarity. Comparing our measurements with modeling
results, we find that 300 keV electrons produced about 30-60 cm from the
negative electrode are the most likely source of our measurements. A
statistical analysis of expected detection of photon bursts by these fiber
detectors indicates that only 20%-45% of the detected bursts could be from soft
(10 keV) photons, which further supports that the majority of detected
bursts are produced by relativistic electrons
Measuring Sizes of Marginally Resolved Young Globular Clusters with HST
We present a method to derive sizes of marginally resolved star clusters from
HST/WFPC2 observations by fitting King models to observations. We describe
results on both simulated images and on observations of young compact clusters
in NGC 3597 and NGC 1275. From the simulations, we find that we can measure
King model concentrations (c) to an accuracy of about a factor of two for all
combinations of c and King radius (r_0) of interest if the data have high S/N
(>~ 500 for the integrated brightness). If the concentration is accurately
measured, we can measure the King radius accurately. For lower S/N, marginally
resolved King profiles suffer from a degeneracy; different values of the
concentration give different r_0 but have comparable reduced chi-squared
values. In this case, neither the core radius nor the concentration can be
constrained individually, but the half-light radius can be recovered
accurately.
In NGC 3597, we can only differentiate between concentrations for the very
brightest clusters; these suggest a concentration of ~ 2. Assuming a
concentration of 2 for the rest of the objects, we find an average King radius
for the clusters in NGC 3597 of 0.7 pc, while the clusters in NGC 1275 have an
average radius of 1.1 pc. These are similar to the average core radii for
Galactic globular clusters, 0.92 pc. We find average half-light radii of 5.4 pc
and 6.2 pc for the young clusters in NGC 3597 and NGC 1275, respectively, while
the average half-light radii of Galactic globulars is 3.4 pc. The spread in the
derived radial parameters in each cluster system is comparable to that observed
in the Galactic globular cluster system.Comment: 38 pages, 19 figures, accepted for publication in PAS
On the Nucleon Distribution Amplitude: The Heterotic Solution
We present a new nucleon distribution amplitude which amalgamates features of
the Chernyak-Ogloblin-Zhitnitsky model with those of the Gari-Stefanis model.
This "heterotic" solution provides the possibility to have asymptotically a
small ratio \hbox{}, while fulfilling
most of the sum-rule requirements up to the third order. Using this nucleon
distribution amplitude we calculate the electromagnetic and weak nucleon form
factors, the transition form factor and the decay widths
of the charmonium levels , , and into .
The agreement with the available data is remarkable in all cases.Comment: 15 pages, RUB-TPII-21/92 Preprin
Approach to Perturbative Results in the N-Delta Transition
We show that constraints from perturbative QCD calculations play a role in
the nucleon to Delta(1232) electromagnetic transition even at moderate momentum
transfer scales. The pQCD constraints, tied to real photoproduction data and
unseparated resonance response functions, lead to explicit forms for the
helicity amplitudes wherein the E2/M1 ratio remains small at moderately large
momentum transfer.Comment: 4 pages, 2 figures, ReVTe
Masses of the 70- Baryons in Large Nc QCD
The masses of the negative parity 70-plet baryons are analyzed in large N_c
QCD to order 1/N_c and to first order in SU(3) symmetry breaking. The existing
experimental data are well reproduced and twenty new observables are predicted.
The leading order SU(6) spin-flavor symmetry breaking is small and, as it
occurs in the quark model, the subleading in 1/N_c hyperfine interaction is the
dominant source of the breaking. It is found that the Lambda(1405) and
Lambda(1520) are well described as three-quark states and spin-orbit partners.
New relations between splittings in different SU(3) multiplets are found.Comment: 11 pages; references were added and a couple of improvements to the
text were mad
On Effect of Equilibrium Fluctuations on Superfluid Density in Layered Superconductors
We calculate suppression of inter- and intralayer superconducting currents
due to equilibrium phase fluctuations and find that, in contrast to a recent
prediction, the effect of thermal fluctuations cannot account for linear
temperature dependence of the superfluid density in high-Tc superconductors at
low temperatures. Quantum fluctuations are found to dominate over thermal
fluctuations at low temperatures due to hardening of their spectrum caused by
the Josephson plasma resonance. Near Tc sizeable thermal fluctuations are found
to suppress the critical current in the stack direction stronger, than in the
direction along the layers. Fluctuations of quasiparticle branch imbalance make
the spectral density of voltage fluctuations at small frequencies non zero, in
contrast to what may be expected from a naive interpretation of Nyquist
formula.Comment: 5 pages, LaTeX, RevTeX, Submitted to PR
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