Total Collision Cross Sections for the Interaction of Atomic Beams of Alkali Metals with Gases

Total collision cross sections (Q) for the interaction of atomic beams of K and Cs with a number of molecules were measured with an apparatus of 30″ angular resolution. Although absolute determinations of Q are difficult, relative values are readily obtained (±3%). Results are reported as the ratio (Q*) of the cross section for a given molecule to that of argon for the same beam atom. Seventy‐seven molecules (of varied complexity and reactivity) were studied with K and 16 with Cs beams. Q* ranged from 0.29 to 2.8.The data were correlated using the Massey‐Mohr theory, assuming an attractive intermolecular potential V(r) = —C/r6. For this case Q=b(C/vr)2/5, where vr is the relative velocity and b a known constant. C was estimated from standard formulas for the London dispersion and dipole‐induced dipole forces, using known refraction and dipole moment data. The theoretical values of Q differ by a nearly constant factor from the experimental results; thus values of Q* are predicted with good accuracy. The deviation between Qcalc* and Qobs* was <±3% for 57% (and <±10% for 87%) of the molecules. Most of the large deviations occurred for the light gases.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70463/2/JCPSA6-31-6-1619-1.pd

Comparing teacher roles in Denmark and England

This article reports the findings of a comparative study of teaching in Denmark and England; its broader aim is to help develop an approach for comparing pedagogy. Lesson observations and interviews identified the range of goals towards which teachers in each country worked and the actions these prompted. These were clustered using the lens of Bernstein’s pedagogic discourse (1990; 1996) to construct teacher roles which provided a view of pedagogy. Through this approach we have begun to identify variations in pedagogy across two countries. All teachers in this study adopted a variety of roles; of significance was the ease with which competent English teachers moved between roles. The English teachers observed adopted roles consistent with a wider techno-rationalist discourse. There was a greater subject emphasis by Danish teachers whose work was set predominantly within a democratic humanist discourse, whilst the English teachers placed a greater emphasis on applied skills

Quantum rainbow scattering at tunable velocities

Elastic scattering cross sections are measured for lithium atoms colliding with rare gas atoms and SF6 molecules at tunable relative velocities down to ~50 m/s. Our scattering apparatus combines a velocity-tunable molecular beam with a magneto-optic trap that provides an ultracold cloud of lithium atoms as a scattering target. Comparison with theory reveals the quantum nature of the collision dynamics in the studied regime, including both rainbows as well as orbiting resonances

Total Collision Cross Sections for the Interaction of Molecular Beams of Cesium Chloride with Gases. Influence of the Dipole‐Dipole Force upon the Scattering

Total cross sections (Q) for the interaction of beams of CsCl with a number of molecules were measured using an apparatus of ca 4′ angular resolution in which the temperature of the scattering gas could be varied from 200°—735°K. The temperature dependence of Q was studied for Ar, CH4, CH2F2, CHF3, CF4, NO, H2S, NH3, and for cis‐ and trans‐CHCl☒CHCl. Relative values of Q at 300°K were measured for eight additional gases.The data were correlated using the Massey‐Mohr theory, assuming an intermolecular potential V(r) = —C/r6, so that Q=b(C/vr)2/5, where vr is the relative velocity and b a known constant; the potential constant C was estimated from formulas for the dispersion, dipole‐induced dipole, and dipole‐dipole forces.For the nonpolar gases the observed small temperature dependence of Q agrees within experimental error (±3%) with that expected from the temperature dependence of vr. The theoretical values of Q differ by a nearly constant factor from the experimental results; thus relative cross sections (Q*) are predicted with fair accuracy.For the polar gases the Q's are large, decreasing significantly with increasing temperature. Because of the large dipole‐dipole interaction, the approximate theoretical treatment (based on the limiting temperature‐dependent dipole‐dipole contribution to C) accounts only semiquantitatively for the observations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70830/2/JCPSA6-33-2-584-1.pd

Development Of Third Harmonic Generation As A Short Pulse Probe Of Shock Heated Material

We are studying high-pressure laser produced shock waves in silicon (100). To examine the material dynamics, we are performing pump-probe style experiments utilizing 600 ps and 40 fs laser pulses from a Ti:sapphire laser. Two-dimensional interferometry reveals information about the shock breakout, while third harmonic light generated at the rear surface is used to infer the crystalline state of the material as a function of time. Sustained third harmonic generation (THG) during a similar to 100 kbar shock breakout indicate that the rear surface remains crystalline for at least 3 ns. However, a decrease in THG during a similar to 300 kbar shock breakout suggests a different behavior, which could include a change in crystalline structure.Mechanical Engineerin

Globular Cluster Abundances from High-Resolution Integrated Light Spectra, I: 47 Tuc

We describe the detailed chemical abundance analysis of a high-resolution (R~35,000), integrated-light (IL), spectrum of the core of the Galactic globular cluster 47 Tuc, obtained using the du Pont echelle at Las Campanas. We develop an abundance analysis strategy that can be applied to spatial unresolved extra- galactic clusters. We have computed abundances for Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Ba, La, Nd and Eu. For an analysis with the known color-magnitude diagram (cmd) for 47 Tuc we obtain a mean [Fe/H] value of -0.75 +/-0.026+/-0.045 dex (random and systematic error), in good agreement with the mean of 5 recent high resolution abundance studies, at -0.70 dex. Typical random errors on our mean [X/Fe] ratios are 0.07-0.10 dex, similar to studies of individual stars in 47 Tuc, although Na and Al appear enhanced, perhaps due to proton burning in the most luminous cluster stars. Our IL abundance analysis with an unknown cmd employed theoretical Teramo isochrones; however, we apply zero-point abundance corrections to account for the factor of 3 underprediction of stars at the AGB bump luminosity. While line diagnostics alone provide only mild constraints on the cluster age (ruling-out ages younger than ~2 Gyr), when theoretical IL B-V colors are combined with metallicity derived from the Fe I lines, the age is constrained to 10--15 Gyr and we obtain [Fe/H]=-0.70 +/-0.021 +/-0.052 dex. We find that Fe I line diagnostics may also be used to constrain the horizontal branch morphology of an unresolved cluster. Lastly, our spectrum synthesis of 5.4 million TiO lines indicates that the 7300-7600A TiO window should be useful for estimating the effect of M giants on the IL abundances, and important for clusters more metal-rich than 47 Tuc.Comment: 40 pages text & references, 4 tables, 19 figures (72 pages total). Changes include addition of B-V color to help constrain GC age. To appear in Ap

Irreducible characters of GSp(4, q) and dimensions of spaces of fixed vectors

In this paper, we compute the conjugacy classes and the list of irreducible characters of GSp(4,q), where q is odd. We also determine precisely which irreducible characters are non-cuspidal and which are generic. These characters are then used to compute dimensions of certain subspaces of fixed vectors of smooth admissible non-supercuspidal representations of GSp(4,F), where F is a non-archimedean local field of characteristic zero with residue field of order q.Comment: 48 pages, 21 tables. Corrected an error in Table 16 for type V* representations (theta_11 and theta_12 were switched

Anti-Proton Evolution in Little Bangs and Big Bang

The abundances of anti-protons and protons are considered within momentum-integrated Boltzmann equations describing Little Bangs, i.e., fireballs created in relativistic heavy-ion collisions. Despite of a large anti-proton annihilation cross section we find a small drop of the ratio of anti-protons to protons from 170 MeV (chemical freeze-out temperature) till 100 MeV (kinetic freeze-out temperature) for CERN-SPS and BNL-RHIC energies thus corroborating the solution of the previously exposed "ani-proton puzzle". In contrast, the Big Bang evolves so slowly that the anti-baryons are kept for a long time in equilibrium resulting in an exceedingly small fraction. The adiabatic path of cosmic matter in the phase diagram of strongly interacting matter is mapped out