Time-energy Distribution Research Articles

Resonant Diurnal Oscillations and Mean Alongshore Flows Driven by Sea/Land Breeze Forcing in the Coastal Southern California Bight

Abstract This study presents observations of the cross-sectional structure of resonant response to sea/land breezes (SLBs) off Huntington Beach (HB) in the Southern California Bight (SCB). A resonant response to local diurnal wind stress fluctuations associated with SLB forcing occurs intermittently and produces strong diurnal oscillations of flow and temperature resulting from enhanced work of the diurnal local wind on the sea surface. At nighttime (daytime), a coherent cross-sectional circulation with offshore (onshore) currents in the surface layer (upper 15 m) and onshore (offshore) currents in the intermediate layer around 20 m are generated, with a three-layered vertical structure on the outer shelf. The authors find a net cross-shore eddy heat flux (net cooling of nearshore water) during the period of strong response to SLB, that is, a rectified mean heat flux and steeper isotherms resulting from the diurnal SLB fluctuations. The steepened mean isotherms are also found to be in thermal–wind balance with intensified mean equatorward flow, which thus can also be generated by the resonant SLB dynamics. Similar rectified onshore transport of other quantities is expected, relevant for biogeochemical processes. The distribution of maximum diurnal kinetic energy in time and across the shelf supports the concept that subinertial shears create the sufficient condition for resonant response to SLB forcing.

Simulation and Optimization of Dual-Coil Discharge Ignition System

In order to improve discharge characteristics of engine ignition, a dual-coil ignition was designed. Simulation models of ignition energy, secondary voltage and spark duration of this ignition were established. The influence of discharge time interval and energy distribution method on discharge characteristics of the dual-coil ignition was studied. Compared with single-coil ignition, the results show that dual-coil ignition produced higher secondary voltage, ignition energy and extended spark duration. When total ignition energy remains constant, the dual-coil coupled discharge mode can improve energy conversion efficiency. The ignition can achieve flexible switching of discharge modes and optimal control of discharge characteristics，which is beneficial for improving fuel economy and reducing exhaust emissions.

Microflares to megaflares: Solar observations and modeling

AbstractThe observationally determined properties of solar flares such as overall energy budget and distribution in space, time and energy of flare radiation, have improved enormously over the last cycle. This has enabled precision diagnostics of flare plasmas and nonthermal particles in large and small events, informing and driving new theoretical models. The theoretical challenges in understanding flare are considerable, involving MHD and kinetic processes operating in an environment far from equilibrium. New observations have also provided some challenges to long-standing models of flare energy release and transport. This talk overviewed recent observational and theoretical developments, and highlighted some important questions for the future

Effects of temporal shapes of sound markers on the perception of interonset time intervals

This study investigated how the temporal characteristics, particularly durations, of sounds affect the perceived duration of very short interonset time intervals (120-360ms), which is important for rhythm perception in speech and music. In four experiments, the subjective duration of single time intervals marked by two sounds was measured utilizing the method of adjustment, while the markers' durations, amplitude difference (which accompanied the duration change), and sound energy distribution in time were varied. Lengthening the duration of the second marker in the range of 20-100ms increased the subjective duration of the time interval in a stable manner. Lengthening the first marker tended to increase the subjective duration, but unstably; an opposite effect sometimes appeared for the shortest time interval of 120ms. The effects of varying the amplitude and the sound energy distribution in time of either marker were very small in the present experimental conditions, thus proving the effects of marker durations per se.

Size measurement of carbon and iron nanoparticles by laser induced incadescence

Application of the laser-induced incandescence method for instant size measurements of nanoparticles is considered. Laser heating and subsequent cooling processes of carbon and iron nanoparticles suspended in a gas medium are simulated. The process of laser energy absorption by nanoparticles in Releigh limit is thoroughly analyzed, taking into account time and spatial energy distribution in the laser beam, as well as the cooling of nanoparticles, by collisions with ambient gas molecules of in the free-molecular regime and in the course of evaporation. On the basis of this model, software has been created for analyzing and interpreting the heat radiation signals of laser-heated nanoparticles (laser-induced incandescence) obtained in experiments, as well as for determining their sizes. Using the developed approach, data on the sizes of carbon nanoparticles formed in the course of C2H2 pyrolysis, as well as the time profiles of iron nanoparticles produced in the course of laser photolysis of Fe(CO)5, are obtained and are in good agreement with transmission electron microscopy data.

Vibration-Based Damage Detection of Pipeline System by HHT Method

Pipelines are regarded as the most cost-effective and the safest choice for transporting oil in bulk. In this study, the significance and necessity of conducting damage detection for onshore pipelines is firstly stated. Then, the limitations of current measures in use in pipeline industry and the inherent difficulty of applying vibration-based damage detection techniques (VBDT) to pipeline structures are addressed. This study focuses on exploring the applicability of an advanced VBDT method, HHT method, to the condition assessment of onshore pipelines. The feasibility and effectiveness of HHT method is verified through numerical study. The result shows that for the cases with single or multi segments of damage which are of the same type or of different types coexist in the structure, the HHT method is capable of providing very good results for the damage detection of pipeline system under ambient excitations. The obtained Hilbert spectrum gives very explicit presentation of the structural response’s energy distribution in both time and frequency domain, the marginal spectrum offers satisfactory result not only for locating the damaged area but also for a rough estimate of damage severity.

Time–frequency characteristics of blasting vibration signals measured in milliseconds

In order to study the time–frequency characteristics of blasting vibration signals, measured in milliseconds, we carried out site blasting vibration tests at an open pit of the Jinduicheng Mine. Based on recorded field data and applying a combination of RSPWVD and wavelet, we analyzed the time–frequency characteristics of recorded field data, summarized the time–frequency characteristics of blasting vibration signals in different frequency bands and present detailed information of blasting vibration signals in milliseconds of high time–frequency resolutions. Because RSPWVD can be seen as of definite physical significance to signal energy distribution in time and frequency domains, we studied the energy distribution of blasting vibration signals for various milliseconds intervals from a perspective of energy distribution. The results indicate that the effect of milliseconds intervals on time–frequency characteristics of blasting vibration signals is significant; the length of delay time directly affects the energy distribution of blasting vibration signals as well as the duration of energy in frequency bands.

Temperature effects in the sputtering of a molecular solid by energetic atomic and cluster projectiles.

Temperature effects in the sputtering of an organic molecule were investigated by subjecting a well defined film of coronene to Au1 and C60 primary ions at 100 and 300 K. Strong field photoionization of the sputtered neutral flux was employed to monitor the change in flight time and kinetic energy distributions of intact and fragmented species.

Time-energy analysis of above-threshold ionization

A Wigner-distribution-like function is proposed for analysis of the time-energy distribution of photoelectron emitted from an atom in intense laser fields. For the first time, the time-energy distribution of the photoelectron spectrum in above-threshold ionization is present. The interference pattern in the above-threshold ionization process in laser fields with different frequencies are investigated using the proposed method.

The effect of energy concentration of earthquake ground motions on the nonlinear response of RC structures

Usually different nonlinear time responses due to earthquake ground motion are distinguished by non-localized spectra, such as the response or power spectra. However, these spectra are often not able to explain the large discrepancy among structural responses caused by different earthquake records. The local spectrum, obtained by the wavelet transform, shows the energy distribution in the time-frequency domain, and helps to understand the very different structural responses. By changing the energy distribution in time of several earthquake records, the effect of energy concentration on the structural nonlinear response is demonstrated. This paper proposes the use of the characteristic peak ground acceleration, which is the peak of the signal constructed by only a few special wavelet components of an earthquake record, to quantify the difference between earthquake records, since this measure indicates the magnitude of the energy concentrated around the fundamental period of a structure.

Emission properties of high-order harmonic generation

Reported are the emission properties (energy-time distributions) of high-order harmonic generation (HHG) calculated for lasers of different pulse durations (τL, in units of radian) in full width at half maximum (FWHM) and different carrier-envelope phases (CEPs,Φ). Calculations demonstrate that the cutoff energy of HHG spectrum produced by a few-cycle laser is less than that by an infinite duration laser (ωmax=3.17Up+Ip, where ωmax is the angular frequency of the photon, Up the ponderomotive potential of the laser field, and Ip the atomic ionization potential). A τL＝4π rad, Φ＝15° laser can produce a single distribution pulse peaked at 0.94 rad and spanning 1.29 rad with a cutoff energy ωmax=2.90Up+Ip and a bandwidth 0.86Up. For the same laser but with Φ＝-75°, double distribution pulses occur with equal amplitudes, cutoff energy ωmax=2.70Up+Ip and bandwidth 0.70Up. These two pulses are peaked at -0.58 rad and 2.43 rad，span 1.22 rad and 1.33 rad, respectively. Calculations also demonstrate that the bandwidth of a selected distribution pulse decreases much faster than its duration as the laser duration grows. The CEP dependence of the single distribution pulse parameters (its energy and time positions) show interesting 180° periodic structures. These features enable us to select attosecond pulse parameters and temporally control them by adjusting CEP. Theoretical analysis shows that the influences of CEP instability on the measured photoelectron spectra and the experimental results may be weakened to the maximum extent or even eliminated by choosing appropriate energy bandwidths of X-rays in attosecond measurements. All these results are helpful in realizing the HHG dynamic process. They can be used as new references in optimizing and selecting single and double attosecond pulses.

Unscented Kalman filter for time varying spectral analysis of earthquake ground motions

A novel parametric time-domain method for time varying spectral analysis of earthquake ground motions is presented. Based upon time varying autoregressive moving average (ARMA) modeling of earthquake ground motion, unscented Kalman filter (UKF) is used to estimate the time varying ARMA coefficients. Then, time varying spectrum is yielded according to the time varying ARMA coefficients. Analysis of the ground motion record El Centro (1940, N–S) shows that compared to Kalman filter (KF) based method, short-time Fourier transform (STFT) and wavelet transform (WT), UKF based method can more reasonably represent the distribution of the seismic energy in time–frequency plane, which ensures its better ability to track the local properties of earthquake ground motions and to identify the systems with nonlinearity. Analysis of the seismic response of a building during the 1994 Northridge earthquake shows that UKF based method can be potentially a useful tool for structural damage detection and health monitoring. Lastly, it is found that the theoretical frequency resolving power of ARMA models usually neglected in some studies has considerable effect on time varying spectrum and it is one of the key factors for ARMA modeling of earthquake ground motion.

Application of digital signal processing to architectural acoustics in the 1960s

Digital signal processing techniques in architectural acoustics were first used to investigate the acoustical properties of Philharmonic Hall at Lincoln Center for the Performing Arts in New York City in the early 1960s. The management of Lincoln Center invited the Acoustics Research Department of Bell Labs, headed by Manfred Schroeder, to assist in an evaluation of the Hall because conventional measurement methods were unable to explain its subjective performance. Computer‐generated specially shaped tone bursts were played and the sound pressures at different locations in the Hall were recorded and later converted into digital form for evaluation. Special filters were programmed to evaluate reverberation times based on different portions of the decay, and energy distribution in time, space, and frequency domains. Better insights into the relationships between subjective and physical measurements were made possible utilizing the power in digital signal processing.

Auroral Plasma Acceleration Above Martian Magnetic Anomalies

Aurora is caused by the precipitation of energetic particles into a planetary atmosphere, the light intensity being roughly proportional to the precipitating particle energy flux. From auroral research in the terrestrial magnetosphere it is known that bright auroral displays, discrete aurora, result from an enhanced energy deposition caused by downward accelerated electrons. The process is commonly referred to as the auroral acceleration process. Discrete aurora is the visual manifestation of the structuring inherent in a highly magnetized plasma. A strong magnetic field limits the transverse (to the magnetic field) mobility of charged particles, effectively guiding the particle energy flux along magnetic field lines.The typical, slanted arc structure of the Earth’s discrete aurora not only visualizes the inclination of the Earth’s magnetic field, but also illustrates the confinement of the auroral acceleration process. The terrestrial magnetic field guides and confines the acceleration processes such that the preferred acceleration of particles is frequently along the magnetic field lines. Field-aligned plasma acceleration is therefore also the signature of strongly magnetized plasma.This paper discusses plasma acceleration characteristics in the night-side cavity of Mars. The acceleration is typical for strongly magnetized plasmas – field-aligned acceleration of ions and electrons. The observations map to regions at Mars of what appears to be sufficient magnetization to support magnetic field-aligned plasma acceleration – the localized crustal magnetizations at Mars (Acuña et al., 1999). Our findings are based on data from the ASPERA-3 experiment on ESA’s Mars Express, covering 57 orbits traversing the night-side/eclipse of Mars. There are indeed strong similarities between Mars and the Earth regarding the accelerated electron and ion distributions. Specifically acceleration above Mars near local midnight and acceleration above discrete aurora at the Earth – characterized by nearly monoenergetic downgoing electrons in conjunction with nearly monoenergetic upgoing ions. We describe a number of characteristic features in the accelerated plasma: The “inverted V” energy-time distribution, beam vs temperature distribution, altitude distribution, local time distribution and connection with magnetic anomalies. We also compute the electron energy flux and find that the energy flux is sufficient to cause weak to medium strong (up to several tens of kR 557.7 nm emissions) aurora at Mars.Monoenergetic counterstreaming accelerated ions and electrons is the signature of field-aligned electric currents and electric field acceleration. The topic is reasonably well understood in terrestrial magnetospheric physics, although some controversy still remains on details and the cause-effect relationships. We present a potential cause-effect relationship leading to auroral plasma acceleration in the nightside cavity of Mars – the downward acceleration of electrons supposedly manifesting itself as discrete aurora above Mars.

Mixing in Unbaffled High-Throughput Experimentation Reactors

With the increasing implementation of high-throughput experimentation techniques within research laboratories throughout the chemicals industries, it is important that the flow regimes in such unbaffled vessels be fully characterized and the implications on mixing performance be understood. Particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques are used in this work to study the mixing and hydrodynamic behavior of low-viscosity fluids in small stirred vessels with diameters 60 and 88 mm. Baffled and unbaffled vessels are considered, and the difference in efficiency is quantified at a constant power input per unit volume. Positioning the impeller into an eccentric configuration is adopted as a means toward improving mixing efficiency in unbaffled vessels. Results show that the eccentric configuration provides equally efficient mixing as the traditional baffled vessel in terms of mixing time and turbulent kinetic energy distribution. PIV and PLIF measurements show that the ...

Behaviour of ohmic systems in cavities—a non-perturbative approach

We consider a system consisting of a particle in the approximation of a harmonic oscillator, coupled to an ohmic environment inside a spherical reflecting cavity of radius R. Starting from the solution of the confined problem, we study the behaviour of the system in free space understood as the limit of an arbitrarily large radius in the quantities describing the confined solution. From a mathematical point of view we show that this method to approach the problem is not equivalent to consider the system a priori embedded in unbounded space. In particular, the matrix elements of the transformation turning the system to principal axis do not tend to distributions in the limit of an arbitrarily large cavity as it should be the case if the two procedures were mathematically equivalent. By introducing dressed coordinates we define dressed states which allow a non-perturbative unified description of the time evolution process for the system, in both cases of a small or an arbitrarily large cavity, for weak and strong coupling regimes. In particular we perform a study of the time energy distribution in a small cavity, with the initial condition that the particle is in the first excited state. We conclude for the quasi-stability of the excited particle in the weak coupling regime, which is a well-known experimental fact. Also our study of a superposition of dressed states in a large cavity concludes that it obeys a statistical distribution for very large times, in other words, we find a kind of “spontaneous” decoherence in free space.

Measurements of the Thermal Diffusivity and Thermal Conductivity of Metals Near the Melting Point

A pulsed technique for measuring the thermal diffusivity a and thermal conductivity λ of spherical samples with an allowance for the spatial–time energy distribution over the laser-beam cross section is described. The measured temperature dependences а(Т) and λ(Т) for solid and liquid tin near the melting point of samples are presented. The a and λ measurement accuracies are 5 and 15%, respectively.

A perception- and PDE-based nonlinear transformation for processing spoken words

Speech signals are often produced or received in the presence of noise, which is known to degrade the performance of a speech recognition system. In this paper, a perception- and PDE-based nonlinear transformation was developed to process spoken words in noisy environment. Our goal is to distinguish essential speech features and suppress noise so that the processed words are better recognized by a computer software. The nonlinear transformation was made on the spectrogram (short-term Fourier spectra) of speech signals, which reveals the signal energy distribution in time and frequency. The transformation reduces noise through time adaptation (reducing temporally slowly varying portions of spectra) and enhances spectral peaks (formants) by evolving a focusing quadratic fourth-order PDE. Short-term spectra of speech signals were initially divided into three (low, mid and high) frequency bands based on the critical bandwidth of human audition. An algorithm was developed to trace the upper and lower intensity envelopes of signal in each band. The difference between the upper and lower envelopes reflects the signal-to-noise (SNR) ratio of each band. Constant, low SNR signals in each band were adaptively decreased to reduce noise. Then evolution of the focusing PDE was used to enhance the spectral peaks, and further reduce noise interference. Numerical results on noisy spoken words indicated that the transformed spectral pattern of the spoken words was insensitive to noise for SNR ranging from 0 to 20 dB (decibel). The spectral distances between noisy words and original words decreased after the transformation. A numerical experiment was performed on 11 spoken words at SNR=5 dB . A noisy word is recognized numerically by computing the closest L 2 spectral distance from the clean template. The experiment reached a recognition rate as high as 100%. Analyses on the properties of the transformation are provided.

コーダ波エンベロープの解析による散乱強度非一様分布の検出

Deterministic analysis of coda waves has become one of the effective approaches to estimate inhomogeneous structure in the crust and uppermost mantle. Seismic array observation gives coherent wave trains, which are suitable for estimating scattering properties beneath the array. Local or regional seismographic network offers distribution of coda wave energy in space and time, which has an advantage of estimating scattering properties in a wide area below the station network. In this paper, several studies of the latter analysis are introduced. One of those analyses, proposed by Nishigami (1991), is to invert coda envelopes observed by a local seismographic network into spatial distribution of scattering coefficients. An observational equation is derived under the assumption of S to S single isotropic scattering and spherical source radiation, where observed data are the deviations of coda envelope from a master curve decaying smoothly. The unknown parameters are the relative scattering coefficients assigned to small blocks that divide the three-dimensional space. The observational equation can be solved by a recursive stochastic inversion. This analysis method applied to the central California data delineates deep structure of the San Andreas fault system as a structure with strong scattering. Several regions in central Japan were also analyzed by this method and detailed distribution of S wave reflectors was estimated below active volcanoes, Mt. Ontake and Mt. Nikko-Shirane. Weak scattering correlated with a seismic gap area was also recognized in the Hokuriku region. Revenaugh (1995a) proposed another method, callled Kirchhoff coda migration, which stacks the energy of single-scattered waves within the coda of teleseismic P waves observed by a local seismographic network. This method was applied to southern California and the following images were obtained, strong P to P scattering from the slab subducting beneath the Transverse Ranges at depths of 50-200km; P to Rg scattering correlated with topographic roughness; and P to S scattering from the aftershock area of the 1992 Landers earthquake. These two methods analyzing the seismic network data seem to be effective to estimate the heterogeneous structure in the crust and uppermost mantle. From the viewpoint of imaging the deep structure of active faults, the inversion analysis of coda envelopes from local earthquakes may be more effective. The variance reduction of the observed data, however, is low, for example, about 14% for the central California analysis. In the future, the simple models of scattering and source radiation assumed in the inversion analysis should be improved into more realistic ones to increase the model fitting. Forward modeling such as proposed by Obara (1997) will also be important to understand the whole shape of coda envelopes related to inhomogeneous distribution of scattering and attenuation intensity.

New parameter for the assessment of blasting efficiency

The efficiency of a blast depends very widely on three groups of parameters: rock mass, blast geometrical parameters and energy distribution in space (borehole bottom, column energy) and time (delays between holes and rows). According to the expected results from a blast, there are several definitions for the term efficiency. The criterion for the block size reduction in the muck pile is often considered as important, because generally it has a great influence on the efficiency of all the operations after the blast. In this paper, a new parameter for the assessment of the blast efficiency is proposed, based on the relative comparison of area delimited by the Rosin-Rammler curves of the in situ rock mass and of the muck pile. This parameter is then compared to others previously established, namely the fragmentation index (Aler et al. 1996) and the surface energy ratio (Hamdi et al. 2001).