215,538 research outputs found
Reexamining the "finite-size" effects in isobaric yield ratios using a statistical abrasion-ablation model
The "finite-size" effects in the isobaric yield ratio (IYR), which are shown
in the standard grand-canonical and canonical statistical ensembles (SGC/CSE)
method, is claimed to prevent obtaining the actual values of physical
parameters. The conclusion of SGC/CSE maybe questionable for neutron-rich
nucleus induced reaction. To investigate whether the IYR has "finite-size"
effects, the IYR for the mirror nuclei [IYR(m)] are reexamined using a modified
statistical abrasion-ablation (SAA) model. It is found when the projectile is
not so neutron-rich, the IYR(m) depends on the isospin of projectile, but the
size dependence can not be excluded. In reactions induced by the very
neutron-rich projectiles, contrary results to those of the SGC/CSE models are
obtained, i.e., the dependence of the IYR(m) on the size and the isospin of the
projectile is weakened and disappears both in the SAA and the experimental
results.Comment: 5 pages and 4 figure
Digital numerically controlled oscillator
The frequency and phase of an output signal from an oscillator circuit are controlled with accuracy by a digital input word. Positive and negative alterations in output frequency are both provided for by translating all values of input words so that they are positive. The oscillator reference frequency is corrected only in one direction, by adding phase to the output frequency of the oscillator. The input control word is translated to a single algebraic sign and the digital 1 is added thereto. The translated input control word is then accumulated. A reference clock signal having a frequency at an integer multiple of the desired frequency of the output signal is generated. The accumulated control word is then compared with a threshold level. The output signal is adjusted in a single direction by dividing the frequency of the reference clock signal by a first integer or by an integer different from the first integer
Crystal growth and in-plane optical properties of TlBaCaCuO (n=1,2,3) superconductors
Single crystals of thallium-based cuprates with the general formula
TlBaCaCuO(n=1,2,3) have been grown by the flux
method. The superconducting transition temperatures determined by the ac
magnetic susceptibility are 92 K, 109 K, and 119 K for n=1,2,3 respectively.
X-ray diffraction measurements and EDX compositional analysis were described.
We measured in-plane optical reflectance from room temperature down to 10 K,
placing emphasis on Tl-2223. The reflectance roughly has a linear-frequency
dependence above superconducting transition temperature, but displays a
pronounced knee structure together with a dip-like feature at higher frequency
below T. Correspondingly, the ratio of the reflectances below and above
T displays a maximum and a minimum near those feature frequencies. In
particular, those features in Tl2223 appear at higher energy scale than Tl2212,
and Tl2201. The optical data are analyzed in terms of spectral function. We
discussed the physical consequences of the data in terms of both clean and
dirty limit.Comment: 8 pages, 13 figures, to be published in Phys. Rev.
Gluon GPDs and Exclusive Photoproduction of a Quarkonium in Forward Region
Forward photoproduction of can be used to extract Generalized Parton
Distributions(GPD's) of gluons. We analyze the process at twist-3 level and
study relevant classifications of twist-3 gluon GPD's. At leading power or
twist-2 level the produced is transversely polarized. We find that at
twist-3 the produced is longitudinally polarized. Our study shows that
in high energy limit the twist-3 amplitude is only suppressed by the inverse
power of the heavy quark mass relatively to the twist-2 amplitude. This
indicates that the power correction to the cross-section of unpolarized
can have a sizeable effect. We have also derived the amplitude of the
production of at twist-3, but the result contains end-point
singularities. The production of other quarkonia has been briefly discussed.Comment: Discussions of results are adde
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