Determination of thermal parameters of one-dimensional nanostructures through a thermal transient method

We present an improved methodology for a thermal transient method enabling simultaneous measurement of thermal conductivity and specific heat of nanoscale structures with one-dimensional heat flow. The temporal response of a sample to finite duration heat pulse inputs for both short (1 ns) and long (5 μs) pulses is analyzed and exploited to deduce the thermal properties. Excellent agreement has been obtained between the recovered physical parameters and computational simulations through choosing an optimized pulse width.     

The analysis of structural defects in piezo and ferroelectric materials by the “heat pulse” method

We consider the “heat pulse” technique for the analysis of structural imperfections. This method is based on the propagation of a pulse or packet of pulses of non-equilibrium acoustic phonons with 10¹¹–10¹² Hz frequencies.     

Thermogenesis: Relative kinetic limits

This work presents kinetic limits for conduction calorimeters taken from experimental data and given in reduced units (ν τ₁). Two different criteria are proposed concerning either a full reconstruction of a rectangular heat pulse (used in calibration procedures) or a complete separation of elementary pulses to provide a fair reconstruction of the thermogenesis. These upper limits are given for several signal to noise ratios.     

Theoretical study of heating of spherical nanoparticle in media by short laser pulses

Theoretical investigation is made of heating of a small solid (metal) spherical particle in a liquid or gaseous medium on exposure to intense laser radiation pulse. The solutions are obtained for quasi-stationary distributions of temperature inside and around of a particle and conductive heat transfer between the particle and the surrounding medium with allowance for the temperature dependence of the transfer coefficients. The heating of spherical nanoparticle in medium on exposure to laser radiation pulse and following cooling is considered on the base of analytical solutions. The time dependencies of particle temperature are obtained. Comparison of some predicted results of the heating of gold spherical nanoparticle in liquid media with experimental data is given and agreement of theoretical results with experimental data validates the model and theory developed.     

Heat conduction in a two-dimensional spherulite

The anisotropy of thermal conduction in a spherulite is calculated for a two-phase model. The problem of the temperature distribution due to cooling of a spherulite suddenly heated at one point is solved. An analytical result is given and isothermal contours are calculated for wide ranges of thermal conduction anisotropy and cooling time. Experiments with spot-heated isotactic polypropylene (i-PP) and isotactic polystyrene (i-PS) spherulites were conducted using a laser pulse and a needle as heat sources. The isotherms were recorded using a thin coating of a heat-sensitive indicator substance, and then by comparison with theoretical isotherm patterns the heat conduction anisotropy of a PP spherulite was estimated. Additional measurements of heat conduction coefficients of at least two polymer films characterized by different crystallinity permit calculation of the thermal conductivity of the amorphous phase, and the conductivities of single crystals along chains and perpendicular to the chains. The results show that the heat is transferred mainly along the primary bonds of polymer chains. However, the morphology of sperulites and lamellas plays an important role.     

激光在电极处理中的应用

本文从实验方法、影响因素、处理后电极的性能等几个方面,对用激光处理电极这一新方法进行了评述。利用激光处理后的电极,具有周期性更新、寿命长、稳定性好等优点。     

Simulation of temperature-modulated DSC of transitions represented by abrupt changes in heat capacity

Computer simulations have been applied to elucidate the response of a sample to temperaturemodulated differential scanning calorimetry (tm-DSC) during transitions. Two cases have been simulated; a latent heat without supercooling (represented by an abrupt heat capacity pulse with perfect reversibility) and a latent heat with perfect supercooling or large hysteresis (an abrupt heat capacity change without reversibility, i.e. the change in heat capacity is seen on heating, but not on cooling). Because the simulation was applied to these well-characterized phenomena, the results are useful to reveal actual sample thermal responses during transitions. The non-reversible component was observed in both cases and has no distinct difference. Higher harmonics due to non-linearity of the transitions were also observed. Furthermore, by inspecting thermal response of the sample and the essential feature of tm-DSC, a new method of data analysis has been devised.     

在Fe-Zn-Mg-Cr尖晶石结构催化剂上丁烯-2氧化动力学

用玻璃外循环无梯度反应器研究了在Fe-Zn-Mg-Cr尖晶石结构催化剂上丁烯-2氧化脱氢动力学。丁烯-2氧化脱氢动力学服从三步骤Redox机理。用脉冲法研究了催化剂用丁烯-2还原及还原催化剂用氧再氧化步骤。用脉冲法测定了丁烯-2吸附热。丁烯-2及丁二烯深度氧化动力学服从经验速度方程。用正交设计法估计了动力学方程的参数。丁烯-2氧化脱氢速度比丁烯-1要快。     

Measurement and energy correction due to charge carrier lifetimes in large HPGe spectrometers

This work addresses the energy spectrum correction due to increased charge carrier collection times in larger HPGe spectrometers. The energy of the radiation interaction is expected to be proportional to the total collected charge. This is increasingly not true with larger HPGe spectrometers. Some charge is lost as the total charge travels from the interaction location to the collection electrode. This path dependent loss of charge results in decreased energy resolution. In HPGe spectrometers, this process is characterized by the charge carrier lifetime constant and is given as an exponential function of the charge carrier collection time divided by this constant. Thus large detectors can experience exponential decrease in energy resolution as charge carrier collection time increases. We studied the effect of charge carrier lifetime on energy resolution for a p-type point contact HPGe spectrometers using pulse shape analysis. We present a method using the rise time to correct for the charge carrier lifetime on a pulse by pulse basis for a given HPGe spectrometer.     

Control of harmonic generation by initial-state preparation

A procedure to control harmonic generation is proposed using initial state control. We show that an initial molecular state can be prepared before shining a strong laser pulse to maximize the output harmonic generation. We demonstrate the method by maximizing emission for the sixth harmonic on a given initial IR pulse in a model H₂⁺ system using five initial vibrational states.     

The use of DP polarography in the elucidation of organic electrode reactions

Differential pulse polarography (together differential pulse voltammetry) consists of a well-stated electroanalytical technique widely used for routine metal ion analysis. The equations obtained from rigorous treatments are difficult to handle to elucidate reaction mechanisms. In this paper the application of DP polarography to the elucidation of the mechanism of organic electrode reactions is presented. Approximate equations for a variety of electrode processes are given. Baseline subtraction and the case of ill-overlapped and close peaks are analyzed. The method is illustrated with experimental examples as the reductions of isonicotinamide and simazine at low pH values.     

脉冲加热-红外吸收光谱法测定钒铝合金中氢

对脉冲加热-红外吸收法测定钒铝合金中氢的分析方法进行了研究。通过实验对分析功率、称样量和校正标样等测试条件进行了讨论。实验表明钒铝合金中的氢易释放,对于AlV85样品中氢,热提取法和熔融法测定结果一致;但AlV50样品中氢,热提取法的结果略高于熔融法,故实验中选用热提取法测定钒铝合金中氢量。热提取法用0.75g金属锡作助熔剂,于4.0kW分析功率条件下测定钛标准样品中氢来确定氢工作曲线的校正系数,在1.5kW分析功率下测定钒铝合金中氢,测定结果与高频感应-热导法(用5g钢标准样品对氢的测定进行校正)结果吻合。对3个钒铝合金中氢量进行了测定,结果的相对标准偏差为2.2%～6.5%(n=8)。     

Electroporation of subcutaneous mouse tumors by rectangular and trapezium high voltage pulses

The artificial electrotransfer of bioactive agents such as drugs, peptides or therapeutical nucleic acids and oligonucleotides by membrane electroporation (MEP) into single cells and tissue cells requires knowledge of the optimum ranges of the voltage, pulse duration and frequency of the applied pulses. For clinical use, the classical electroporators appear to necessitate some tissue specific presetting of the pulse parameters at the high voltage generator, before the actual therapeutic pulsing is applied. The optimum pulse parameters may be derived from the kinetic normal mode analysis of the current relaxations due to a voltage step (rectangular pulse). Here, the novel method of trapezium test pulses is proposed to rapidly assess the current (I)/voltage (U) characteristics (IUC). The analysis yields practical values for the voltage U(app) between a given electrode distance and pulse duration t(E) of rectangular high voltage (HV) pulses, to be preset for an effective in vivo electroporation of mouse subcutaneous tumors, clamped between two planar plate electrodes of stainless steel. The IUC of the trapezium pulse compares well with the IUC of rectangular pulses of increasing amplitudes. The trapezium pulse phase (s) of constant voltage and 3 ms duration, following the rising ramp phase (r), yields a current relaxation which is similar to the current relaxation during a rectangular pulse of similar duration. The fit of the current relaxation of the trapezium phase (s) to an exponential function and the IUC can be used to estimate the maximum current at a given voltage. The IUC of the falling edge (phase f) of the trapezium pulse serves to estimate the minimum voltage for the exploration of the long-lived electroporation membrane states with consecutive low-voltage (LV) pulses of longer duration, to eventually enhance electrophoretic uptake of ionic substances, initiated by the preceding HV pulses.     

Square modulated differential thermal analysis

KMnF₃ and DKDP crystals have been studied around their phase transitions using a conduction calorimetry technique where a long periodical square thermal pulse (0.05 K in amplitude) is superposed to a heating or cooling ramp as low as 0.06 K h⁻¹. Specific heat data obtained in the dissipation and relaxation semiperiods of the square pulse become different inside the phase transition interval. The electromotive force developed by the heat fluxmeters at the end of the relaxation semiperiod (underlying signal) is compared with the DTA trace obtained in a second run with the same temperature ramp but without the modulated perturbation. The comparison between the DTA trace and specific heat data obtained in the first run allows us to determine the value of the latent heat and to obtain information about the kinetic of the phase transition.     

Theoretical analysis of the thermal effects during in vivo tissue electroporation

Tissue electroporation is a technique that facilitates the introduction of molecules into cells by applying a series of short electric pulses to specific areas of the body. These pulses temporarily increase the permeability of the cell membrane to small drugs and macromolecules. The goal of this paper is to provide information on the thermal effects of these electric pulses for consideration when designing electroporation protocols. The parameters investigated include electrode geometry, blood flow, metabolic heat generation, pulse frequency, and heat dissipation through the electrodes. Basic finite-element models were created in order to gain insight and weigh the importance of each parameter. The results suggest that for plate electrodes, the energy from the pulse may be used to adequately estimate the heating in the tissue. However, for needle electrodes, the geometry, i.e. spacing and diameter, and pulse frequency are critical when determining the thermal distribution in the tissue.     

高温下甲苯在不同去阳离子丝光沸石上的吸附性质和表面反应

用脉冲色谱法测量了不同交换度的NaHM上甲苯的吸附热,並用动态法测量了程序升温脱附和反应。结果表明:吸附量小于5微升/克,交换度小于32％时,主要显示Na⁺中心的吸附性质。其吸附热基本上不随交换度变化。交换度大于32％时,在H⁺中心上的吸附渐趋显著,吸附热也随交换度的增加而渐次下降。 比保留体积随交换度变化的曲线在交换度为32-41％处有极大值。通过吸附熵的计算认为这可能与交换过程中主孔道阳离子空间位阻的下降有关。     

A comparison of different evaluation methods in modulated temperature DSC

Modulated temperature-DSC is a new method for measuring the thermal behaviour of materials. In this method, the response of the sample to a time-dependent signal (sinusoidal temperature change) is measured. Two different methods are known for the evaluation of the measured data. The first is the separation of the measured data into reversing and non-reversing components of heat flow. The second is based on the linear response theory and yields a complex heat capacity with a real part (storage heat capacity) and an imaginary part (loss heat capacity).

The theoretical basis and the possibilities of interpretation of both evaluation methods are investigated. The results of both methods are compared theoretically for the case of simple time-dependent processes. Experimental results are given for the glass transition process.     

Theoretical fundamentals of multi-body method

The general heat balance equation for multi-body system represents a stable system, with different time constants. The mathematical basis of the multi-body method is also given.