Measured lifetime of SF6-

The lifetime of the SF6 anion was measured at the electrostatic ion storage ring ELISA, where decays in the time span from 100 mus to a few seconds were recorded. We find a nonexponential decay with an approximate t(-1.5) power-law dependence. The observed decay rate is accounted for by a model for thermionic emission that takes into account the initial energy spread of the SF6 molecule prior to electron capture as well as some kinetic energy of the captured electron in the applied plasma-ion source. The energy dependent decay rate is described by an Arrhenius decay constant with a pre-exponential factor and the electron affinity.     

Spread and Quote-Update Frequency of the Limit-Order Driven Sergei Maslov Model

We perform numerical simulations of the limit-order driven Sergei Maslov （SM） model and investigate the probability distribution and autocorrelation function of the bid-ask spread S and the quote-update frequency U. For the probability distribution, the model successfully reproduces the power law decay of the spread and the exponential decay of the quote-update frequency. For the autocorrelation function, both the spread and the quote-update frequency of the model decay by a power law, which is consistent with the empirical study. We obtain the power law exponent 0.54 for the spread, which is in good agreement with the real financial market.     

皮秒时间相关单光子计数光谱仪的核心技术

研制的皮秒时间相关单光子计数光谱仪利用时间相关单光子计数(TCSPC)技术,采用了具有分光时间弥散动态和静态补偿特性的光栅分光系统,解决了传统分光系统的光信号时间弥散问题;使用多道谱分析仪开设时间窗口,测量荧光衰减曲线和时间分辨光谱;用荧光衰减曲线的多指数拟合方法处理数据。给出了光谱仪的原理和总体方案,介绍了系统的集成和工作流程。通过各种标准样品的试验数据分析和对比,得出系统所测荧光寿命可达到ps量级,而且具有最高的灵敏度——单光子计数,时间分辨率达到8．8ps。     

Quantifying bid-ask spreads in the Chinese stock market using limit-order book data

The statistical properties of the bid-ask spread of a frequently traded Chinese stock listed on the Shenzhen Stock Exchange are investigated using the limit-order book data. Three different definitions of spread are considered based on the time right before transactions, the time whenever the highest buying price or the lowest selling price changes, and a fixed time interval. The results are qualitatively similar no matter linear prices or logarithmic prices are used. The average spread exhibits evident intraday patterns consisting of a big L-shape in morning transactions and a small L-shape in the afternoon. The distributions of the spread with different definitions decay as power laws. The tail exponents of spreads at transaction level are well within the interval (2,3) and that of average spreads are well in line with the inverse cubic law for different time intervals. Based on the detrended fluctuation analysis, we found the evidence of long memory in the bid-ask spread time series for all three definitions, even after the removal of the intraday pattern. Using the classical box-counting approach for multifractal analysis, we show that the time series of bid-ask spread do not possess multifractal nature.     

Dynamics of Quantum Correlation of Two Atoms with Photon Recoil

By taking into account spatial degrees of freedom of the atoms, we study the dynamics of the quantum correlation between the electronic states of two atoms, separately placed in two single-mode ring cavities. We show that the quantum correlation of the atomic electronic states can decay to almost zero in a finite time, and the quantum correlation between the cavities depends on the spatial spread of the atoms.     

Point spread functions of the T(2) decay in k-space trajectories with long echo train

T(2) decay during long echo trains of magnetic resonance (MR) imaging pulse sequences is known to cause a blurring effect, due to the peak broadening of the point spread function (PSF). In contrast, the simultaneous amplitude-loss effect, led by the peak reduction of the PSF, has gained much less attention. In this report, we analyzed the PSFs of both the truncation and T(2) decay for Cartesian (linear profile ordering and low-high ordering) and spiral trajectories, respectively. Then, we derived simple formulas to characterize both the blurring and amplitude-loss effects, which are functions of the ratios of the echo train duration (T(k)) over T(2) (T(k)/T(2)). Signal-to-noise ratio (SNR) per unit time was thus analyzed considering both the amplitude-loss effect induced by the T(2) decay and the SNR gain from the long acquisition duration based on MR sampling theory. Optimum T(k)/T(2) ratios to achieve maximum SNR per unit time were 1.2 for the Cartesian trajectory and 0.8 for the spiral trajectory.     

Decay distribution of spontaneous emission from an assembly of atoms in photonic crystals with pseudogaps

Spontaneous decay behaviors from an assembly of atoms (or molecules) in 3D photonic crystals (PC's) with pseudogaps are investigated. Theoretically, a lifetime distribution function for these atoms or molecules is defined to reveal decay kinetics. Our calculations show that quite wide or narrow lifetime distributions can occur for different spread configurations of the atoms (or molecules). The pure PC effect may lead to coexistence of both accelerated and inhibited decay processes. These results provide theoretical clarification for substantial discrepancies in the recent reported experiments.     

Kinetics of the decelerated fluorescence of organic molecules in n-paraffins at 77 K and its mathematical model

Results of investigations into the kinetics of decelerated fluorescence decay for 1,2-benzpyrene in dodecane and coronene in n-octane at 77 K are presented in the paper. It is demonstrated that the reason for the nonexponential kinetics is a statistical spread of the triplet-triplet annihilation rate constant. A mathematical model is suggested which describes well the decelerated fluorescence decay in these systems. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 3–8, December, 2007.     

Baryon number violating nuclear decay

The expressions for baryon number violating nuclear partial decay widths are derived from the interactions as predicted by grand unified theories. Theory predicts that the baryon number violating proton decay inside the nucleus is hindered relative to the free proton decay rate. In the case of closed shell nuclei, the meson spin-isospin dependence of the partial width is the same as that for the nucleon decay. The branching ratios of decay amplitudes depend on the nuclear binding energies. Nuclear structure introduces lepton energy spread of ±49.5 MeV for light closed shell nuclei, while it does not affect the back to back emission of lepton-meson pair.     

Quantum diffusion in polaron model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers

We numerically investigate quantum diffusion of an electron in a model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with fluctuation of the parameters due to the impact of colored noise. The randomness is introduced by fluctuations of distance between two consecutive bases along the stacked base pairs. We demonstrate that in the model the decay time of the correlation can control the spread of the electronic wavepacket. Furthermore it is shown that in a motional narrowing regime the averaging over fluctuation causes ballistic propagation of the wavepacket, and in the adiabatic regime the electronic states are affected by localization.     

Observation of chaotic and regular dynamics in atom-optics billiards

We report on experimental observations of chaotic and regular motion of ultracold atoms confined by a billiard-shaped optical dipole potential induced by a rapidly scanning laser beam. To investigate the dynamics of the atoms confined by such an "atom-optics" billiard we measure the decay of the number of trapped atoms through a hole on the boundary. A fast and purely exponential decay, the clear signature of chaotic motion, is found for a stadium billiard, but not for a circular or an elliptical billiard, in agreement with theory. We also investigated the effects of decoherence, velocity spread, and gravity on regular and chaotic motion.     

Fluorescence decay time of single semiconductor nanocrystals

We present fluorescence decay measurements of single ZnS covered CdSe nanocrystals. It is shown that the fluorescence decay time is fluctuating during the investigation leading to a multiexponential decay even for a single nanocrystal. In combination with measurements of the fluorescence blinking behavior we find that a high fluorescence intensity is correlated with a long fluorescence decay time. This is consistent with a model of fluctuating nonradiative decay channels leading to variable dynamic quenching processes of the excited state.     

Auditory discrimination of rise and decay times in tone and noise bursts.

There are indications in the literature on speech perception that differences in rise and decay times of the amplitude envelope are relevant physical correlates in phonemic contrasts. Yet, little is known about the perception of rise and decay times as such. In the present study we have attempted to establish JND's for both rise and decay times of 1000-Hz sine waves as well as white noise bursts by means of an adjustment method. The rise and decay of stimulus amplitude were synthesized to be linear functions of time. Results show that the JND for a change in rise/decay time is generally about 25% of the duration of the rise/decay time. This Weber fraction is a minimum at rise/decay times of about 80 ms and increases significantly for rise/decay times below 20 ms. Of the four signal condition noise bursts were performed with the greatest accuracy (at moderate rise/decay times), while changes in onset time of sine waves were discriminated best at very short rise times (where energy splatter may have contributed an additional cue).     

Time dilations in bound muon decay

A number of experiments show that the decay lifetimes of muons bound to atomic nuclei are longer than the decay lifetimes of free muons. The special relativistic time dilation predicts decay lifetime dilations that are substantially smaller than the observed decay lifetime dilations. In this paper it is shown that adding a recently predicted electro-magnetic time dilation (analogous to the gravitational time dilation) to the special relativistic time dilation gives a total time dilation that agrees with the observed decay lifetime dilations.     

Determination of the scintillator decay time by the autocorrelation method

An autocorrelation method is developed for determining the composition and decay time of scintillators. This method also allows studying the spatial distribution of nuclear radiation and controlling the amount of the dopants introduced in the scintillator. The decay time is measured from a few nanoseconds to microseconds. It is found out that the decay time increases in plastic scintillators with a wavelength shifter and a Gd doped.     

Radiative decay time of a nongray medium with arbitrary configurations

Based on the principle of conservation of energy, a simple analytical expression is presented for the radiative decay time of a nongray medium with arbitrary configurations. It is expressed explicity in terms of the mean beam length and the total band absorptance. In the high-pressure limit, where the decay time based on the harmonic thermal perturbation is available for two configurations, comparison is made with the present decay time. Good agreement is found.     

Effect of listening level and background noise on the subjective decay rate of room impulse responses: Using time-varying loudness to model reverberance

Room impulse responses (RIRs) are used very widely to characterize the acoustic conditions of rooms, such as in the derivation of reverberation time, early decay time and clarity index. This study investigates the subjective decay rate (or reverberance) of RIRs when directly listened to (rather than convolved with a dry signal such as speech or music). Through a subjective experiment, it investigates the effects of gain (or listening level) and background noise level on the reverberance of RIRs that had been measured in three concert auditoria. The task of the experiment was to match the decay rate of RIRs to that of a reference RIR by ear, by adjusting the RIRs’ exponential decay rate. Based on objective loudness modeling, gain should have a positive effect on reverberance, and background noise has a negative effect. This is confirmed in the results of the experiment. Furthermore, the objectively calculated loudness decay function provides an effective predictor of subjective decay rate, which performs better than conventional early decay time or reverberation time for the RIRs tested.     

A low-voltage decay time analyzer for monitoring ionizers

This paper presents a development of a low-voltage decay time analyzer to replace the charged plate monitor which works at the high-voltage level. The proposed low-voltage decay time analyzer is based on the measurement of the induced charges on a conductive plate via an ultra-high input impedance amplifier. A microcontroller with an Ethernet module is the central processing to control, calculate the decay time, and enable network communications. The test results show that the analyzed decay times correlate to the standard test method.     

Temperature dependence of radiative recombination in CdSe quantum dots with enhanced confinement

We studied in details the recombination dynamics and its temperature dependence in epitaxially grown neutral CdSe/ZnSSe quantum dots with additional wide-band gap MgS barriers. Such design allows to preserve a very high quantum yield and track the radiative recombination dynamics up to room temperature. A fast initial decay of ∼0.6 ns followed by a slow decay with a time constant ∼30–50 ns is observed at low temperature T < 50 K. The fast decay gradually disappears with increasing temperature while the slow decay shortens and above 100 K predominantly a single-exponential decay is observed with a time constant ∼1.3 ns, which is weekly temperature dependent up to 300 K. To explain the experimental findings, a two-level model which includes bright and dark exciton states and a temperature dependent spin-flip between them is considered. According to the model, it is a thermal activation of the dark exciton to the bright state and its consequent radiative recombination that results in the long decay tail at low temperature. The doubling of the decay time at high temperatures manifests a thermal equilibrium between the dark and bright excitons.     

Beam dynamics in an ultra-low energy storage rings (review of existing facilities and feasibility studies for future experiments)

Storage rings operating at ultra-low energies and in particular electrostatic storage rings have proven to be invaluable tools for atomic and molecular physics. Due to the mass independence of the electrostatic rigidity, these machines are able to store a wide range of different particles, from light ions to heavy singly charged bio-molecules. However, earlier measurements showed strong limitations on beam intensity, fast decay of ion current, reduced life time etc. The nature of these effects was not fully understood. Also a large variety of experiments in future generation ultra-low energy storage and decelerator facilities including in-ring collision studies with a reaction microscope require a comprehensive investigation of the physical processes involved into the operation of such rings. In this paper, we present review of non-linear and long term beam dynamics studies on example of the ELISA, AD Recycler, TSR and USR rings using the computer codes BETACOOL, OPERA-3D and MAD-X. The results from simulations were benchmarked against experimental data of beam losses in the ELISA storage ring. We showed that decay of beam intensity in ultra-low energy rings is mainly caused by ion losses on ring aperture due to multiple scattering on residual gas. Beam is lost on ring aperture due to small ring acceptance. Rate of beam losses increases at high intensities because of the intra-beam scattering effect adds to vacuum losses. Detailed investigations into the ion kinetics under consideration of the effects from electron cooling and multiple scattering of the beam on a supersonic gas jet target have been carried out as well. The life time, equilibrium momentum spread and equilibrium lateral spread during collisions with this internal gas jet target were estimated. In addition, the results from experiments at the TSR ring, where low intensity beam of CF⁺ ions at 93 keV/u has been shrunk to extremely small dimensions have been reproduced. Based on these simulations, conditions for stable ring operation with extremely low emittance beam are presented. Finally, results from studies into the interaction of ions with a gas jet target at 3–30 keV energy range are summarized.