Isotope selective laser enhancement of the Li+H2 reaction

The enhancement of the Li+H₂LiH+H reaction due to laser excitation of the Li atom to the2p state has been investigated using absorption techniques. Using a rate equation model we obtain from our data a reaction cross-section [Li(2p)+H₂LiH+H]=(0.10±0.03)Ų at 515°C. By selectively exciting one Li isotope the reaction is made isotope selective, suggesting an efficient means of isotope separation.     

Polarization of the secondary nucleons in thepp → ppπ 0 andpp→npπ+ reactions at 1000 MeV

The calculation of the secondary nucleons polarization in thepppp⁰ andppnp⁺ reactions at 1000 MeV is effected in the framework of the one-pion exchange model. It is shown that polarization is due to the interference of the resonant amplitude with the non-resonant amplitudes of theN virtual scattering. The angular dependence of the polarization is sensitive to the behaivour of theN scattering amplitudes off the mass shell.Submitted to the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.     

Rate equations in the hopping transport

The usual kinetic equations for the site occupation probabilities in an external field are solved exactly in a simple one-dimensional periodic model with two kinds of atoms using a) free boundary conditions and order of limitsN, 0 needed for a proper treatment of the dc conductivity here b) boundary conditions with metallic contacts and order of limitsN, 0 and c) the same boundary conditions but reversed order of limiting processes 0,N typical of e.g. numerical and percolation treatments. (N and are the number of sites and frequency.) It is demonstrated that though the bulk dc conductivity is the same in all three cases, local bulk properties of the material are strongly dependent on the régime used. The role of the order of all three limiting processes 0,N+ andn+ (N–n+) for local shifts of the chemical potential _n in the dc limit is examined (n is the number of the relevant site calculated from a boundary of the chain). It is shown especially that the rate equation treatment (régime a) on the one hand and numerical or percolation treatments (régime c) on the other hand never yield the same bulk values of _r.     

Combinations of Observables

This article begins with a review of the framework of fuzzy probability theory.The basic structure is given by the -effect algebra of effects (fuzzy events) E(,A) and the set of probability measures M ⁺ ₁ (, A) on a measurable space (,A). An observable X: B E(, A) is defined, where (, B) is the value spaceof X. It is noted that there exists a one-to-one correspondence between states onE(, A) and elements of M ⁺ (, A) and between observables X: B E(,A) and -morphisms from E(, B) to E(, A). Various combinations ofobservables are discussed. These include compositions, products, direct products,and mixtures. Fuzzy stochastic processes are introduced and an application toquantum dynamics is considered. Quantum effects are characterized from amonga more general class of effects. An alternative definition of a statistical map T:M ⁺ ₁ (, A) M ⁺ ₁ (, B) is given.     

The neon-like yttrium collisional laser

We have investigated the Ne-like yttrium collisionally pumped laser using a detailed time dependent collisional radiative model within a fluid code (EHYBRID), and post-processors to investigate the effects of refraction and saturation. We conclude that, in addition to that on the twoJ = 2 1 lines, gain is generated on theJ = 0 1 transition and that this line very closely overlaps theJ = 2 1 transition at 155 . A 50% reduction in the calculated monopole excitation rate which pumps theJ = 0 1 line (a notoriously uncertain quantity) is required to obtain satisfactory agreement with experiment — the same modification as was required for the germanium laser.     

TheK S 0 →π0 l + l − andK L 0 →π0 l + l − decays in the standard model and the extended Nambu-Jona-Lasinio model

TheK _S ^{0 0} l ⁺ l ^– andK _L ^{0 0} l ⁺ l ^– decays are considered within the framework of the Standard model in the one-photon exchange approximation, i.e.K _S,L ^{0 0}+ *⁰ +l ⁺ l ^–. To evaluate the low-energy matrix elements of theK ⁰(¯K ⁰)⁰+ * transitions, the constituentquark-loop approximation, based on the extended Nambu-Jona-Lasino (NJL) model, is used. The obtained results are compared with other theoretical estimates and the experimental bounds.     

830 nm emission in sodium vapor

We demonstrate that the intriguing 830 nm coherent emission, which is observed when sodium vapor is pumped with a high-power pulsed laser tuned near the 3S4D two-photon transition, is due to an axially phase-matched six-wave mixing process. This conclusion is based upon the observation of emission near 584 nm, which is coupled to the 830 nm emission in the six-wave mixing process: ₁+₂=2_L–_4D4P –_4P3D . In addition, we have observed coherent emission near 1.16 m, which is due to an analogous process involving cascade through the 4S (as opposed to the 3D) state. We calculate the wavelengths of all photons involved in these processes using the standard formulas of parametric wave-mixing theory, and show that they can be predicted to within experimental uncertainties. Finally we report observations of significant blue shifts of the 830 nm and 1.16 m emissions in a mixed sodium-potassium vapor. These shifts can be readily understood by considering the effect of the potassium on the frequency-dependent refractive index of the vapor. Due to these results, other recent interpretations of the 830 nm emission as stimulated excimer emission on the Na₂ 1³ _g ⁺ 1³ _u ⁺ band must now be rejected.     

KL,S → l+l− decays in the quark model of superconductivity type

The probabilities of K_L,S l⁺l^– decays are calculated by considering only the dominant two-lepton channel K_L,S ^{* *} l⁺l^–. The transitions K⁰ X, where X=⁰,, or (700) dominating in the K_L,S ^{* *}decay amplitudes, are described by the effective weak Lagrangian. The matrix elements of four-quark operators are calculated within the framework of the quark model of superconductivity type. It is shown that the leading contribution to matrix elements of K⁰ X transitions comes from the penguin operator matrix elements.     

Survival probability in one dimension for theA+B→B reaction with hard-core repulsion

We study the effect of hard-core repulsion (known as the bus effect) betweenB particles on the reaction-diffusion systemA+BB in the continuous-time random walk model in one dimension with theA particles stationary. We show rigorously that the survival probability of theA particles is asymptotically bounded asC ₁lim _t{[–logS(t)]/t ^0.5}C ₂, whereC ₁ andC ₂ are constants. We also do simulations to confirm our results.     

Studies on the microstructure of phase transitions in two kinds of liquid crystals by PAT and DSC

The positron lifetime and DSC measerments for EBBA and DOBAMBC have been made with heating and cooling clycles. The experimental results show that a shorter lifetime (₁) is essentially independent of temperature while the longer lifetime (₂) and the intensity (I ₂) change abruptly double or triple with temperature. Consequently, the EBBA has only nematic phases while the DOBAMBC has two liquid-crystalline phases (smectic C* and smectic A) with transition temperatures as follows: for EBBA, solid nematic (304.5 K), nematic isotropic (356.5 K), isotropic nematic (356.5 K), nematic solid (301 K); and for DOBAMBC, solid smectic C* (346 K), smectic C* smectic A (357.5 K), smectic A isotropic (389 K). These critical temperatures are in accordance with the transition temperatures measured by DSC. In addition, the difference in the solid-nematic transition temperature in the heating and cooling cycles was also observed. A discussion about the correlation of the observed changes in lifetime (₂) with the changes in molecular orientational order (S) and dielectric anisotropy () is presented.     

The form factors of the decays π− → e−¯veγ and K− → e−¯veγ

In the special type of the quark model we obtain the ratio=h _A/h_V of the axial (h_A) and vector (h_V) form factors for the decays ^– e^– ¯v_e and K^– e^–¯v_e different from unity. The low-energy theorem, relating the electric polarizability of the charged pion with the ratio, is analyzed. It is shown that < 1 corresponds to , calculated by accounting the contribution of the scalar meson(700) into the amplitude of the Compton effect on the pion. In the absence of the(700) contribution we have=1.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.     

Variance calculations and the Bessel kernel

In the Laguerre ensembleof n xN Hermitian matrices, it is of interest both theoretically and for applications to quantum transport problems to compute the variance of a linear statistic, denoted var_N f, asN . Furthermore, this statistic often contains an additional parameter a for which the limit is most interesting and most difficult to compute numerically. We derive exact expressions for both lim_N var_N f and lim , lim_N var_N f.     

A dual-polarization InSb receiver for 461/492 GHz

A dual-polarization InSb hot-electron bolometer-mixer receiver has been built for the James Clerk Maxwell Telescope, for operation at 461 and 492 GHz (the frequencies of theJ=43 rotational transition of CO and of the³ P ₁³ P ₀ transition of neutral carbon). Receiver noise temperatures of 500K have been obtained at 461 GHz, in observing bandwidths of 3 MHz. The receiver was designed as a common-user or facility instrument. Here we describe those aspects of the design and construction which enabled this goal to be realized.     

Energy-Momentum Properties and the Spin of Short-Lived Particles

The space–time translation property of a stable particle is characterized by a time-like Lorentz vector (E, _k ). We show in this contribution that unstable particles are, in addition, characterized by a space-like Lorentz 4-vector of uncertainties, or spreads, ( E, k). This is true for unstable states created in formation-, in production-, and in decay-experiments. The space-like nature of the spread vector causes a nonzero momentum spread to be present in all Lorentz frames so that there is no Lorentz frame in which the unstable particle is entirely at rest. With the space-like spreadvector ( E, k) in addition to the time-like (E, _k ), also the rotation property of an unstable particle is affected, and unstable states have an uncertainty in their spin. This means neighboring spin states are occupied in addition to the original spin. Experiments are discussed that show a principal limitation of the accuracy of spin measurement from finite lifetimes. Wave functions for unstable particles are discussed, and we show in the example of a short-lived spin-0 state that the appearance of a spin neighbor in the amplitude is proportional to the inverse lifetime.     

Time-resolved resonance-Raman study of porphyrins and metalloporphyrins in the electronic excited states

Current developments of our Time-Resolved Resonance-Raman (TR³) studies on the (*) excited states of free-base porphyrins and (dd) excited state of Ni-OctaEthylPorphyrin (NiOEP) in solutions are described. A device for quasi-simultaneous measurements has been developed to obtain correct difference spectra for pump/probe spectra of various delay times and probe-only spectrum. This technique is practically powerful to obtain TR³ spectra of porphyrins and metalloporphyrins. An orbital-symmetry marker band ( ₂) exhibited upshifts alongS ₀S ₁T ₁ transitions for free-base octaethylporphyrin (H₂OEP), while downshifts along the same transitions for free-base TetraPhenylPorphyrin (H₂TPP). This is interpreted by the symmetry differences in the highest occupied molecular orbitals of H₂OEP (a _u-orbital) and H₂TPP (b _1u-orbital). An intensity-borrowing mode ( ₁₉) was enhanced by the AlbrechtC-term in resonance with theS ₁S _n transition, but not in resonance with theT ₁T _n transition for H₂OEP. This fact can be considered to be due to different vibronic couplings between the singlet and triplet manifolds. For the (dd) excited state of NiOEP, our TR³ study suggests the excess energy for the ( ^*) to (dd) transition was vibrationally cooled prior to the electronic relaxation from the (dd) state to the ground state with a relaxation time of ca. 300 ps. Comparison between Stokes- and anti-Stokes resonance Raman spectra for the delay time of 0 ps indicated that the lower limit of vibrational temperature in 0–40 ps time range is 750 K.     

On the asymptotics of occurrence times of rare events for stochastic spin systems

We consider translation-invariant attractive spin systems. LetT _,x ^v be the first time that the average spin inside the hypercube reaches the valuex when the process is started from an invariant measure with density smaller thanx. We obtain sufficient conditions for (1) ¦¦^–1 logT _,x ^v (x) in distribution as ¦¦ , and ¦¦^–1 logT _,x ^v (x) as ¦¦ , where (x):= –lim ¦¦^–1 log {(average spin inside ) x. And (2)T _,x ^v /ET _,x ^v converges to a unit mean exponential random variable as ¦¦ . Both (1) and (2) are proven under some type of rapid convergence to equilibrium. (1) is also proven without extra conditions for Ising models with ferromagnetic pair interactions evolving according to an attractive reversible dynamics; in this case is a thermodynamic function. We discuss also the case of finite systems with boundary conditions and what can be said about the state of the system at the timeT _,x ^v .On leave from São Paulo University.     

The influence of reabsorption on fluorescence spectra of NdxLa1−x P5O14

The influence of reabsorption on emission spectra of Nd_xLa_1–x P₅O₁₄ for the⁴F₃ ⁴I_9/2 and⁴F_3/2 ⁴I1_1/2 transitions was studied. The comparison of theoretical curves calculated with the reabsorption taken into account with experimental curves enabled us to explain so far observed spectra and prove the validity of the present model of fluorescence in these materials.Dedicated to Professor Miroslav Trlifaj on the occasion of his sixtieth birthday.The authors are indebted to M. Trlifaj for the suggestion to study high concentration rare earth compounds and deep interest in this work. The samples were kindly prepared by K. Blaek from Monokrystaly, Turnov.     

To the problem of KL→π0γγ decay

It is shown that the contribution of diagrams with intermediate state vector mesons to the K_L ⁰ amplitude, intensively discussed in literature in recent years, is close to zero provided that theSU(3) group breaking is taken into account. At the same time, the contribution of scalar mesons in the intermediate state is essential. The obtained estimates for Br(K_L ⁰) conform with the recent experimental data Br(K_L ⁰ )=(2·1 ± 0·6)×10^–6.Dedicated to the memory of our friend Prof. M. Gmitro.We wish to thank S. B. Gerasimov and A. B. Govorkov for useful discussions.     

Non-commutative spheres

LetA be the irrational rotation algebra, i.e. theC ^*-algebra generated by two unitariesU, V satisfyingVU=e ²ⁱ UV, with irrational, and consider the fixed point subalgebraB under the flip automorphismUU ^–1,VV ^–1. We prove thatB is an AF-algebra.Dedicated to Professor Huzihiro Araki on the occasion of his 60'th birthday     

Resonant coherent transients in a gas in the standing-wave field

Polarization decay in the presence of a standing electromagnetic wave field at a Doppler broadened transition is investigated theoretically and experimentally. It is shown that in the direction opposite to the propagation of an excited pulse the polarization decays at a transition frequency rather than at an exciting field frequency as usual. This permits the use of transients both in studies of relaxation processes and in Doppler-free super-high resolution spectroscopy. A resonant coherent transient has been used in measurements of relaxation decay constants of a dipole moment for collisions in SF₆ (=10.6m). This method has enabled one to resolve reliably the structure of theQ(38) transition (=10.6m) of theF ₁ ⁰ +E ₀=F ₂ ⁰ line of the 0v ₃ band in SF₆ within a Doppler absorption line.