Transient visually evoked potential.

A light delivered to the human eye will instigate changes in electrical potentials recorded over the visual cortex that last for some finite time, at least several hundred milliseconds. If the rate of stimulation is sufficiently low, the response is completed before the next visual stimulus arrives; the cortical potential is then called a transient evoked response. This review of the transient evoked potential describes the techniques by which the response is obtained, the problems inherent in its use, and procedures by which these difficulties can be overcome or minimized. A summary of the research results from the field enumerates those findings which have been well established and replicated by many investigators, those that are more controversial or as yet inconclusive, and the many practical applications of the technique for science and medicine. Finally, the needs for an underlying physiological theory and for future research are discussed.     

内燃机瞬时转速测量误差的研究

对内燃机瞬时转速测量进行研究 ,从ω(°CA)和n(r/min)两方面分析产生误差的原因 ,并进一步给出提高测量精度的方法     

Power Transient Monitor

The power transient monitor is a specialized electric equipment developed to provide the capability of automatically and unattendedly recording randomly occurring power transients and disturbances in electric power systems. Twelve magnetic data channels record power waveforms and 14 pulse-voltage counters register the occurrence of pulse-voltage transients according to magnitude and duration. The power waveforms are continuously recorded and erased from a rotating magnetic drum. When a transient is sensed, a record signal is provided to a quick-start magnetic tape whereupon pretransient, transient, and post-transient waveforms are transcribed from the drum onto the tape. The time of each recording is also indicated on the tape. The waveform recordings can be viewed on an oscilloscope or reproduced on an oscillograph. Representative transient recordings made with the monitor at six widely separated continental and overseas field installations are presented.     

光纤瞬变电流传感器

本文介绍了一种适用于瞬变电流测量的光纤传感器。它具有响应速度快、绝缘强度高、抗电磁干扰能力强等特点,是电力系统测量交流暂态大电流的一种潜在的具有很大实用价值的电流传感器     

Transient infrared transmission spectroscopy

Transient infrared transmission spectroscopy is a new method that can acquire analytically useful transmission spectra from moving, optically thick solids. No sample preparation is required. The spectra are of sufficient quality for accurate quantitative compositional analysis. The method works by the creation of a thin, short-lived, chilled layer at the sample surface. Blackbody-like thermal emission from the bulk of the sample is selectively absorbed as it passes through the chilled layer, so the transmission spectrum of the layer is superimposed on the observed thermal emission. Spectra of polycarbonate, beeswax, and copolymers of methyl and butyl methacrylate are presented. Compositional analysis of the methacrylate copolymers with a standard error of prediction of only 0.87 mol % is demonstrated.     

Thermal Transient Test Apparatus

An apparatus for evaluating the thermal transient behavior of an electroexplosive device is described. The thermal response provides nondestructive testing insight with respect to device design and behavior. Abnormal responses may be indicative of imminent failure and the apparatus provides a rapid evaluation method for quality control.     

Transient Nonequilibrium Molecular Dynamic Simulations of Thermal Conductivity: 1. Simple Fluids

Thermal conductivity has been previously obtained from molecular dynamics (MD) simulations using either equilibrium (EMD) simulations (from Green--Kubo equations) or from steady-state nonequilibrium (NEMD) simulations. In the case of NEMD, either boundary-driven steady states are simulated or constrained equations of motion are used to obtain steady-state heat transfer rates. Like their experimental counterparts, these nonequilibrium steady-state methods are time consuming and may have convection problems. Here we report a new transient method developed to provide accurate thermal conductivity predictions from MD simulations. In the proposed MD method, molecules that lie within a specified volume are instantaneously heated. The temperature decay of the system of molecules inside the heated volume is compared to the solution of the transient energy equation, and the thermal diffusivity is regressed. Since the density of the fluid is set in the simulation, only the isochoric heat capacity is needed in order to obtain the thermal conductivity. In this study the isochoric heat capacity is determined from energy fluctuations within the simulated fluid. The method is valid in the liquid, vapor, and critical regions. Simulated values for the thermal conductivity of a Lennard-Jones (LJ) fluid were obtained using this new method over a temperature range of 90 to 900 K and a density range of 1–35 kmol · m^-3. These values compare favorably with experimental values for argon. The new method has a precision of ±10%. Compared to other methods, the algorithm is quick, easy to code, and applicable to small systems, making the simulations very efficient.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22--27, 2003, Boulder, Colorado, U.S.A.     

Transient processes in shear flows of viscoelastic fluids. I. Propagation of a shear wave

A theoretical investigation is made of the initial stage of a transient process in the shear flow of a viscoelastic fluid having a relaxation-time spectrum.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 6, pp. 992–1000, June, 1982.     

Transient virulence of emerging pathogens

Should emerging pathogens be unusually virulent? If so, why? Existing theories of virulence evolution based on a tradeoff between high transmission rates and long infectious periods imply that epidemic growth conditions will select for higher virulence, possibly leading to a transient peak in virulence near the beginning of an epidemic. This transient selection could lead to high virulence in emerging pathogens. Using a simple model of the epidemiological and evolutionary dynamics of emerging pathogens, along with rough estimates of parameters for pathogens such as severe acute respiratory syndrome, West Nile virus and myxomatosis, we estimated the potential magnitude and timing of such transient virulence peaks. Pathogens that are moderately evolvable, highly transmissible, and highly virulent at equilibrium could briefly double their virulence during an epidemic; thus, epidemic-phase selection could contribute significantly to the virulence of emerging pathogens. In order to further assess the potential significance of this mechanism, we bring together data from the literature for the shapes of tradeoff curves for several pathogens (myxomatosis, HIV, and a parasite of Daphnia) and the level of genetic variation for virulence for one (myxomatosis). We discuss the need for better data on tradeoff curves and genetic variance in order to evaluate the plausibility of various scenarios of virulence evolution.     

Transient volume holograms in polymethylmethacrylate

New transient volume holographic recording materials are described in this report. These consist of either coronene or 1,2;5,6-dibenzanthracene incorporated into polymethylmethacrylate. The largely amplitude, volume holograms formed as a result of triplet-state absorption have lifetimes of 6.4 and 0.9 s respectively and diffraction efficiencies close to the predicted values of 10⁻⁴. Production of permanent holograms has been prevented by careful control of the polymerization conditions to produce a matrix of sufficient rigidity to prevent reactions between the triplet states and the polymer. By using spectrally well separated write and read wavelengths, erasure of the holograms by the read beam is avoided.     

Transient reliability of ceramic structures

Present capabilities of the NASA Ceramic Analysis and Reliability Evaluation of Structures/Life (CARES/Life) code include probabilistic life prediction of ceramic components subjected to fast fracture, slow crack growth (SCG) (stress corrosion), and cyclic fatigue failure modes. Currently, this code has the capability to compute the time-dependent reliability of ceramic structures subjected to simple time-dependent loading. For example, in SCG type failure conditions CARES/Life can handle the cases of sustained and linearly increasing time-dependent loads, whereas for cyclic fatigue applications, it can account for various types of repetitive constant amplitude loads. In real applications applied loads are rarely that simple, but rather vary with time in more complex ways such as engine start up and shut down and dynamic and vibrational loads. In addition, when a given component is subjected to transient environmental and/or thermal conditions, the material properties also vary with time. The objective of this paper is to demonstrate a methodology capable of predicting the time-dependent reliability of components subjected to transient thermomechanical loads that take into account the change in material response with time. In this article, the dominant delayed failure mechanism is assumed to be SCG. This capability has been added to the NASA CARES/Life code, which has also been modified to have the ability of interfacing with commercially available finite element analysis codes executed for transient load histories. An example involving a ceramic exhaust valve subjected to combustion cycle loads is presented to demonstrate the viability of this methodology and the CARES/Life program.     

Transient moisture effects in materials

The paper reviews transient moisture effects in various materials with emphasis on their viscoelastic properties and durability. The first part of the review is dedicated to the phenomenological aspects of the effects in materials such as whole wood, plywood, particleboard, fibreboard, paper, natural and synthetic fibres and composite materials. Creep, creep recovery, dynamic response and failure as influenced by various transient moisture conditions are discussed in relation to the materials system, the extent and rate of moisture change, loading modes, temperature levels, specimen sizes, type of solvent and preventive measures. The second part is devoted to the discussion of mechanistic models. Explanations of the phenomenon from a molecular and materials standpoint are assessed, compared and discussed in depth so that one can gain deeper insight into the phenomenon as discussed in the first part. The main mechanisms discussed include: (i) hydrogen bonding, (ii) slip planes and (iii) crystallite slippage and rotation.     

Transient three-dimensional contact problems: mortar method. Mixed methods and conserving integration

The present work deals with the development of an energy-momentum conserving method to unilateral contact constraints and is a direct continuation of a previous work (Hesch and Betsch in Comput Mech 2011, doi:) dealing with the NTS method. In this work, we introduce the mortar method and a newly developed segmentation process for the consistent integration of the contact interface. For the application of the energy-momentum approach to mortar constraints, we extend an approach based on a mixed formulation to the segment definition of the mortar constraints. The enhanced numerical stability of the newly proposed discretization method will be shown in several examples.     

Transient Capillary Channel Flow Stability

Capillary channel techniques with free liquid surfaces provide very reliable means for liquid management in space. However, capillary channel flow is subject to limitation due to liquid surface instabilities when a critical flow rate is reached. Steady flow rate limitation is a consequence of the choking effect and well understood. Critical steady flow rate computation with a one-dimensional model is related to a numerical singularity which occurs at critical flow. For transient flow the singularity does not occur. Therefore, a new transient stability model is defined. It is based on the steady model, a simplified transient momentum balance, the consideration of the capillary pressure of typical observed surface shapes, and on a simplified dynamic inside the channel. The balance and dynamic are defined by liquid and geometrical properties only and therefore significantly easier to compute than a transient differential equation system. In 2011, experiments were performed in cooperation with NASA on the International Space Station (ISS) to confirm the model for steady flow and validate the new transient model. A new phenomenon is discussed, the flexibility effect, which provides significant additional transient stability for channels of sufficient length. An undesired feedback effect, provoked by the reuse of the liquid in a circular loop of the experimental setup, and which influenced the measurements, is compensated by a semi-empirical model for a feedback ratio.     

Transient conductivity in nanostructured films

The understanding of electron transfer across interfaces and nanostructures constitutes a major challenge in emerging nanodevices. Ultrafast injection of carriers through the interface at femtosecond scale has been reported in dye-TiO2 systems and in piezotronics devices based on ZnO nanotubes, followed by anomalous transport of the charges through the nanoporous network. These features which could not be expected on the basis of bulk models, motivated real-time theoretical studies of the injection dynamics and transport at the nanoscale to improving the overall efficiency. In this paper correlation functions are evaluated by the Fourier transform of the frequency-dependent conductivity of the system. Drude-Lorentz and Schmith models, fitted to experimental data, have been analyzed. We present results for TiO2 and ZnO oxides nanostructured films. It is found that the diffusion coefficient of carriers is usually very small, but can reach values comparable to the single crystal at early times after carriers are released, even in the presence of structural disorder, under conditions concerning the size of the nanoparticles, the strength of the coupling of the charges with the nanoparticles and the relaxation time. Our result for the current-current correlation function as a function of time is in agreement with the obtained result by ultrafast time THz spectroscopy.     

Transient two-dimensional fuel-concentration measurement technique

We propose a nonintrusive experimental technique, the transient fuel-concentration measurement technique (TFMT), that is capable of being used to measure two-dimensional profiles of transient fuel concentrations over an open liquid fuel surface. The TFMT is based on single-wavelength holographic interferometry; its response time is less than 1 mus and spatial resolution is 0.1 mol. %/0.1 mm. It was applied to measure both methanol vapor and n-propanol vapor concentrations. To assess the accuracy of the technique, our results were compared with steady-state methanol and n-propanol fuel-vapor concentrations measured by other researchers with a microsampling technique combined with gas chromatography. We found the TFMT to be accurate for on-line monitoring of two-dimensional profiles of fuel-vapor concentrations.     

Transient absorption in excimer-exposed silica

The transient absorption produced in high-purity fused silica by exposure to a 193-nm excimer laser is investigated as a function of exposure, dissolved molecular hydrogen content, and hydrogen-related processing. Long-term recovery of transmittance was found to correlate with the dissolved molecular hydrogen concentration, whereas short-term fade was due to geminate recombination of an E? center with an H radical. The redarkening process was shown to be the result of photolysis of SiH, which regenerates color centers. When the silica was processed in a hydrogen atmosphere at high temperature and subsequently exposed at 193 nm, the glass was found to produce an absorption spike, a fast, recoverable decrease in transmittance. The origin of the spike was linked to the creation of a precursor produced in the thermal reaction of silica with hydrogen. The precursor can be identified by its signal in the Raman spectrum. It is suggested that the precursor has absorption at 193 nm.