Near-threshold production of the multistrange Xi- hyperon

The yield for the multistrange Xi(-) hyperon has been measured in 6A GeV Au+Au collisions via reconstruction of its decay products pi(-) and Lambda, the latter also being reconstructed from its daughter tracks of pi(-) and p. The measurement is rather close to the threshold for Xi(-) production and therefore provides an important test of model predictions. The measured yield for Xi(-) and Lambda are compared for several centralities. In central collisions the Xi(-) yield is found to be in excellent agreement with statistical and transport model predictions, suggesting that multistrange hadron production approaches chemical equilibrium in high baryon density nuclear matter.     

Comparison of source images for protons, pi-'s, and lambda's in 6A GeV Au+Au collisions

Source images are extracted from two-particle correlations constructed from strange and nonstrange hadrons produced in 6A GeV Au+Au collisions. Very different source images result from pp vs p Lambda vs pi(-)pi(-) correlations. Scaling by transverse mass can describe the apparent source size ratio for p/pi(-) but not for Lambda/pi(-) or Lambda/p. These observations suggest important differences in the space-time emission histories for protons, pions, and neutral strange baryons produced in the same events.     

Solid-state polymerization of a diacetylene crystal: Thermal,ultraviolet, and γ-ray polymerization of 2,4-hexadiyne-1,6-diol bis-(p-toluene sulfonate)

Results are presented for the thermal, ultraviolet, and γ-ray polymerization of 2,4-hexadiyne-1,6-diol bis-(p-toluene sulfonate) (PTS). Monomer extraction is used to obtain polymer conversion-vs.-time curves at 30, 50, and 80°C. In agreement with previous work over a narrower temperature range, the curves all display a dramatic autocatalytic effect with an onset at about 10% conversion to polymer. Although the polymerization rate undergoes a 200-fold change over this temperature range, the shape of the conversion curves does not change. These data yield an activation energy (E) of 22.2 ± 0.4 kcal/mole when interpreted in terms of the time required to reach 50% polymer. An annealing technique is used to provide a closer look at the autocatalytic region. In that case, E = 22.5 ± 0.8 kcal/mole is determined from measurements of the time required to go from 10 to 50% polymer at temperatures ranging from 23 to 80°C (a 500-fold change in rate). Thermal polymerization rates measured in the low-conversion limit using a spectroscopic method based on diffuse reflectance yield E = 22.8 ± 0.6 kcal/mole. Thus E is independent of polymer conversion and the autocatalytic effect can be best understood as arising from a large increase in the propagation length of the polymer chains. The autocatalytic effect is shown to be present in both UV and γ-ray polymerization. In the case of γ-ray polymerization, conversion-vs.-time and spectroscopic measurements are consistent with inhomogeneities in the polymer concentration caused by particle tracks. Activation energies for UV and γ-ray polymerization are quite low (2-3 kcal/mole) and confirm that the chain initiation event makes the major energetic contribution to E. The polymerization mechanism is discussed in detail. The photopolymerization experiments can be consistently interpreted with a model based on the triplet excited state of the diacetylene monomer as the chain initiation species.     

Wrap-around partitioning for block bidiagonal linear systems

A stable vector algorithm for the solution of block diagonallinear systems is obtained by a permutation of the unknownscalled wrap-around partitioning combined with standard QR factorization.Wrap-around partitioning uses blocking and selects the unknownsin the blocks in turns. After a suitable orthogonal eliminationstep one ends up with a reduced system which is again blockbidiagonal and so wrap-around partitioning can be applied again.Using a simple model for vectorization overhead it is shownthat small block sizes give best performance. The minimal blocksize 2, which corresponds to cyclic reduction, is suboptimaldue to memory bank conflicts.     

Q branches in the rotational spectrum of HOC1

We have obtained the far-i.r. rotational spectrm of HOCI from 70–263 cm^?1. The most prominent features of the rotational spectrum are the Q branches, for which we have measured positions. Statistical strengths for the Q branches ave been calculated and μβ, the component of the dipole moment that allows Q branch transitions has been determined from P and R branch line intensities. We find μβ = 1.4 ± 0.2 D. We also calculate Q branch strengths and shifts at stratospheric temperature.     

Comments on the optical properties of fully conjugated polymers: Analogy between polyenes and polydiacetylenes

The similarity of the π-electron backbones of the polyenes and the polydiacetylenes suggests an analogy between these two fully conjugated, linear polymers. The extent of the analogy is discussed through the examination of a series of model compounds: the polyenes and the polyenynes. The optical band gaps and the polarizabilities of polyenynes are compared to those of the polyenes and to the predictions of a modified free-electron model. It is concluded that the chain-dependent electronic properties of the polyenes may be extrapolated with some confidence to the polydiacetylenes.     

Absolute Intensities of the 10-µm Bands of (16)O(3)

Two hundred ninety experimental absolute intensities of nu(1) and nu(3) transitions of ozone have been measured, with good accuracy (<2%). They are used to derive the transition-moment parameters for these bands. The agreement between our observed and calculated line intensities is satisfactory. This work shows that the intensities of these two bands are on average 4% smaller than those used in the literature. In addition, 20 intensities of the nu(2) + nu(3) - nu(2) band confirm this value. Also, 42 line intensities of the 2nu(1)-nu(3) band are reported. Copyright 2001 Academic Press.     

Raman and resonance-Raman spectra of CsI/I−3

Raman and resonance-Raman spectra of the I^?₃ ion isolated within CsI crystals have been studied using 647 nm and 488 nm exciting radiation. Sample temperatures between 300 and 20 K have been used. Eleven overtones of the symmetric stretching mode (nν₁) have been observed in the resonance-Raman spectrum excited by the 488 nm Ar⁺ laser line. Bands centred at 153, 170, 264 and 304 cm^?1 have been assigned as ν₃, 2ν₂, ν₁+ν₃ and 2ν₃(Σ⁺) respectively. The remaining structure between the nν₁ lines has been assigned as due to combinations of these lines with the lattice vibrations of the CsI crystal.