Ear canal cross-sectional pressure distributions: mathematical analysis and computation.

Cross-sectional pressure distributions, natural acoustic modes, and associated cutoff frequencies are determined for real ear-canal geometries using an asymptotic theory in combination with a numerical method. The technique is particularly well suited to obtain the higher modes, which are trapped near both ends of the ear canal. Results detail the influence of the canal geometry and frequency on the spatial distribution of the pressure. Adult ear-canal geometries are determined near the concha from ear-mold sections using a light microscope interfaced to a video-data-acquisition system. Computed results compare favorably to the exact solutions for circular and square acoustic waveguides. The cutoff frequency of the two adult ear canals studied averaged 20% less than the cutoff frequency of a circular tube of identical cross-sectional area. Inserting a probe microphone into the canal decreases the rate of decay of circumferential nonplanar modes while increasing the rate of decay of radial modes. Relative to the pressure beyond the tube, insertion increases the plane-wave component of the pressure around the tube by a multiplicative factor approximately equal to the square root of the original area divided by the occluded area. Eccentric placement of the probe tube has a relatively small influence on the cutoff frequency. The transition of the pressure distribution at the entrance to a simple plane wave in the core region of the canal is calculated and shown graphically for the actual geometry of two adult subjects.     

Measurements of the Decay KL-->e+ e- mu+ mu-

The KTeV experiment at Fermilab has isolated a total of 132 events from the rare decay K(L)-->e+ e- mu+ mu-, with an estimated background of 0.8 events. The branching ratio of this mode is determined to be [2.69+/-0.24(stat)+/-0.12(syst)]x10(-9), with a radiative cutoff of M(2)(ee mu mu)/M(2)(K)>0.95. The first measurement using this mode of the parameter alpha from the D'Ambrosio-Isidori-Portolès (DIP) model of the K(L)gamma*gamma* vertex yields a result of -1.59+/-0.37, consistent with values obtained from other decay modes. Because of the limited statistics, no sensitivity is found to the DIP parameter beta. We use this decay mode to set limits on CP and lepton violation.     

Rate of Convergence to Equilibrium for the Spatially Homogeneous Boltzmann Equation with Hard Potentials

For the spatially homogeneous Boltzmann equation with hard potentials and Grad's cutoff (e.g. hard spheres), we give quantitative estimates of exponential convergence to equilibrium, and we show that the rate of exponential decay is governed by the spectral gap for the linearized equation, on which we provide a lower bound. Our approach is based on establishing spectral gap-like estimates valid near the equilibrium, and then connecting the latter to the quantitative nonlinear theory. This leads us to an explicit study of the linearized Boltzmann collision operator in functional spaces larger than the usual linearization setting.     

Visible cascade Higgs decays to four photons at hadron colliders

The presence of a new singlet scalar particle a can open up new decay channels for the Higgs boson, through cascades of the form h --> 2a --> X, possibly making discovery through standard model channels impossible. If a is CP odd, its decays are particularly sensitive to new physics. Quantum effects from heavy fields can naturally make h --> 4 g the dominant decay which is difficult to observe at hadron colliders, and is allowed by CERN LEP for m(h) > 82 GeV. However, there are usually associated decays, either h --> 2g2gamma or h --> 4gamma, which are more promising. The decay h-->4gamma is a clean channel that can discover both a and h. At the CERN LHC with 300 fb(-1) of luminosity, a branching ratio of order 10(-4) is sufficient for discovery for a large range of Higgs boson masses. With total luminosity of approximately 8 fb(-1), discovery at the Fermilab Tevatron requires more than 5 x 10(-3) in branching ratio.     

Bleaching of color centers in NaCl crystals with laser pulses

Abstract

Bleaching of F centers in gamma irradiated NaCl crystals at room temperature and elevated temperatures using laser pulses from pulsed laser systems is studied in this paper. The rate of decay of F centers is monitored and the decay constants are evaluated. A comparison on the decay kinetics is made for CW and pulsed bleaching with a He-Cd laser. F center to C center conversions using a thermo-optic scheme are carried out with nanosecond dye laser pulses in gamma irradiated NaCl crystals.     

Experimental investigations of changes in the rate of beta decay of radioactive elements

Changes in the rate of the beta decay of radioactive elements whose periods are about 24 h and 27 d are detected on the basis of long-term investigations performed with the aid of scintillation and germanium-lithium gamma detectors. The use of the scintillation procedure yields results whose level of significance is much higher than 5%, while the procedure based on germanium—lithium detectors gives a more than 1% deviation from the average value of fluxes of gamma rays accompanying, for example, ⁶⁰Co beta decay. With allowance for the rotation of the laboratory frame together with the Earth, deviations of the change in the rate of beta decay of radioactive elements single out three directions in the physical space.     

Sign of excited state nuclearg-factors using gamma detected NMR/ON

Integral nuclear orientation and conventional CW NMR/ON studies using parity conserving gamma radiation can yield the nuclear moment μ, g and hence the nuclear spin, I, of the radioactive parent nuclei, but not the sign of g. In principle, the sign of g is accessible using parity non conserving beta radiation but is technically difficult; also, some nuclei decay without particle emission. We describe a novel spin echo NMR/ON technique that overcomes these previous difficulties and allows determination of the sign of the g-factor using gamma radiation.     

X(3872) and Bound State Problem of D~0(D)*~0((D)~0D*~0)

We have performed a dynamical calculation of the bound state problem of D~0(D)~(*0) by considering the pion and sigma meson exchange potential.Our preliminary analysis disfavors the molecular interpretation of X(3872) if we use the experimental D~* Dπ coupling constant g=0.59 and a reasonable cutoff around 1 GeV,which is the typical hadronic scale.In contrast,there probably exists a loosely bound S-wave B (-B)~* molecular state.Such a molecular state would be rather stable since its dominant decay mode is the radiative decay through B~*→Bγ.     

Measurement of the decay rate of the negative ion of positronium (Ps-)

A new determination of the decay rate of the negative ion of positronium (Ps-), using a beam-foil method and a stripping-based detection technique, is reported. The measured result of gamma = 2.089(15) ns(-1) is a factor of 6 more precise than the previous experimental value of gamma = 2.09(9) ns(-1), and is in excellent agreement with the theoretical value of gamma = 2.086(6) ns(-1).     

Observation of radiative B-->phi K gamma decays

The radiative decay B-->phi K gamma is observed for the first time. The branching fraction for the charged B--->phi K- gamma decay mode is measured to be B(B--->phi K- gamma)=(3.4+/-0.9+/-0.4)x10(-6). The photon energy distribution for the B--->phi K- gamma decay is presented. The signal for the neutral B(0)-->phi K(0)gamma decay mode is not statistically significant and an upper limit, B(B(0)-->phi K(0)gamma)<8.3x10(-6) at 90% C.L., is set. The analysis is based on a data set of 90 fb(-1) collected by the Belle experiment at the e(+)e(-) asymmetric collider KEKB.     

Direct and statistical gamma decay of the giant quadrupole resonance of 208Pb

The gamma decay of the giant quadrupole resonance of ²⁰⁸Pb is discussed. The relative contribution of the decay via the compound nucleus is calculated from the statistical theory. It is found that the compound decay is as important as the direct decay. The summed contribution of the direct and compound decay modes, however, is a factor of 2 smaller than the observed gamma branching ratio GQR → gs.     

Coupled waves of linear velocity,angular velocity,and temperature in a liquid with internal rotation

Equations of motion for a locally nonequilibrium liquid with internal rotation are derived, and the thermospin effect is considered. It is demonstrated that high-frequency transverse coupled waves of linear velocity, angular velocity of internal rotation, and temperature may propagate a liquid with internal rotation. A dispersion relation and a frequency dependence of the damping ratio are deduced. Comparison between theoretical and experimental values of the transverse sound velocity dispersion shows their satisfactory agreement. Low-frequency transverse waves do not penetrate into the liquid: they decay over a distance on the order of the wavelength. It is shown that frequencies and their corresponding wavenumbers exist in a liquid with internal rotation at which either waves do not decay or a phase shift in the skin layer is absent. It is found that the excitation spectrum may contain a cutoff frequency or an energy gap due to interaction between the linear and angular velocity fields. The dispersion and damping ratio for the coupled waves near synchronism points, where uncoupled waves resonantly interact with each other, are determined.     

Coherent decay of positronium bose condensate

The rate of self-stimulated emission of photon pairs by pseudoscalar particles from Bose condensate is calculated. Growing with density, this rate exceeds the density-independent rate of spontaneous two-photon decay at plausible density values of positronium gas, thus opening, in principle, the way to the annihilation gamma ray laser realization.     

Probing the order-to-chaos region in superdeformed 151Tb and 196Pb nuclei with continuum gamma transitions

The gamma decay associated with the warm rotation of the superdeformed nuclei 151Tb and 196Pb has been measured with the EUROBALL IV array. Several independent quantities provide a stringent test of the population and decay dynamics in the superdeformed well. A Monte Carlo simulation of the gamma decay based on microscopic calculations gives remarkable agreement with the data only assuming a large enhancement of the B(E1) strength for 1-2 MeV gamma rays, which may be related to the evidence for octupole vibrations in both mass regions.     

Formation and relaxation of two-dimensional vortex crystals in a magnetized pure-electron plasma

Systematic examinations are carried out experimentally about the contribution of background vorticity distributions (BGVD's) to the spontaneous formation and decay of ordered arrays (vortex crystals) composed of strong vortices (clumps) by using a pure-electron plasma. It is found that the BGVD level needs to be higher for an increasing number of clumps to form vortex crystals and that the number of the clumps constituting the crystal decreases in time as proportional to gamma lnt in contrast to proportional to t (-xi) with xi approximately 1 as accepted well in turbulence models. The decay rate gamma increases with the BGVD level. The observed configurations of the clumps cover the theoretically predicted catalogue of vortex arrays in superfluid helium, suggesting a possible relaxation path of the crystal states.     

Heavy top quark decay into a charged Higgs scalar and a photon (gluon)

We consider the decay of a heavy top quark into a charged Higgs scalar and a hard photon (gluon)tH ⁺ b(g). We give the general result for fermions of arbitrary mass. Our results for the differential decay rate for these two processes are remarkably simple. The radiation amplitude zero (RAZ) factorization is explicit but there is no RAZ for these processes because of the presence of opposite-sign charges. We obtain a branching ratio of 0.063% for bH⁺ and 5.6% for bH⁺g. Thus both decays should be relatively easy to see at the SSC.     

Decay of ion acoustic wave in magnetized plasma

Ion acoustic wave at frequency smaller than ion cyclotron frequency is shown to decay due to effect of finite perpendicular wavelength. The decay rate is found to be independent of frequency and is considerably larger than the classic nonlinear Landau damping rate.     

On the problem of activation energy of thermal decay of color centers and similar non-stationary processes

Thermally stimulated process is discussed as a superposition of components with equal activation energy and a distribution of frequency factors. Changes of concentrations of individual components of this process proceed according to first order rate law. A relationship between Laplace transformation of the distribution of frequency factors and the law governing the resulting changes of the concentration is studied. An application on the thermal decay of F-centers indicates that actual activation energy tends to be greater than the energy resulting e.g. from Urbach analysis. Experimental procedures are proposed allowing the actual activation energy and the distribution of frequency factors to be determined.     

Reevaluation of the 22Na(p,gamma) reaction rate: implications for the detection of 22Na gamma rays from novae

Understanding the processes which create and destroy 22Na is important for diagnosing classical nova outbursts. Conventional 22Na(p,gamma) studies are complicated by the need to employ radioactive targets. In contrast, we have formed the particle-unbound states of interest through the heavy-ion fusion reaction, 12C(12C,n)23Mg and used the Gammasphere array to investigate their radiative decay branches. Detailed spectroscopy was possible and the 22Na(p,gamma) reaction rate has been reevaluated. New hydrodynamical calculations incorporating the upper and lower limits on the new rate suggest a reduction in the yield of 22Na with respect to previous estimates, implying a reduction in the maximum detectability distance for 22Na gamma rays from novae.     

Spike onset dynamics and response speed in neuronal populations

Recent studies of cortical neurons driven by fluctuating currents revealed cutoff frequencies for action potential encoding of several hundred Hz. Theoretical studies of biophysical neuron models have predicted a much lower cutoff frequency of the order of average firing rate or the inverse membrane time constant. The biophysical origin of the observed high cutoff frequencies is thus not well understood. Here we introduce a neuron model with dynamical action potential generation, in which the linear response can be analytically calculated for uncorrelated synaptic noise. We find that the cutoff frequencies increase to very large values when the time scale of action potential initiation becomes short.