有限学时背景下中药药理学实验教学现状探析

实验教学是中药药理学不可或缺的教学环节,学时减少和课程培养目标不变的矛盾是实验教学中的关键问题。从教师与学生的角度探析有限学时背景下中药药理学实验教学现状,提出合理的教学对策。初步实践结果表明教学效果良好,为进一步提高中药药理学实验教学质量、提升学生专业素养提供一定的参考。

有限学时下药理学实验教学质量现状及其对策

药理学是一门理论性和实践性很强的学科,药理学实验是药理学教学中的重要环节。文章基于药理学实验学时缩减的背景下,从学生和授课教师角度探析药理学实验教学质量并提出可行的改进措施,为进一步提高药理学实验教学质量、提升学生专业素养提供一定的参考。

有限学时下化工设计中物料衡算教学改革探索──以直接推算法为例

为了适应有限学时下化工设计课程理论教学,探索解决新工科背景下基于OBE理念“应用型”人才的培养目标。以化工设计中物料衡算的直接推算法为例,从基本原理与概念、计算步骤,计算示例3个方面进行了重新编排,同时引入Excel辅助计算以提高授课效率,促进与提升学生的设计能力与工程意识。

关于富里哀级数的教学注记

富氏级数在自然科学和工程技术中有广泛的应用,但讲授学时较少。如何在有限学时内,在不超出大纲知识范围的前提下讲授得深入浅出,表达出它的主要性质和特征,这是值得下功夫的教研题目。我们认为,在尊重数学严谨性的基础上,多从物理含义进行解释,有助于学生直观理解富氏级数的特点和条件,其效果较好。富氏级数主要是研究工程中的周期现象的,因此它的引入可从简谐振动开始。当一个质点M,在以A为半径的圆上,从初相角ψ开始,以圆频率ω转动时,M在y轴上的投影是一个简谐振动y(t)=Ash(ωt+ψ),也就是由振幅A,圆频率ω和初相角ψ确定一个简谐振动。又因为y(t)满足(d^2y)╱)(dt^2)+ω~2y=0,这说明只要物体受到一个与位移相反的力的作用。

OPTIMAL PERFORMANCE OF THERMOELECTRIC REFRIGERATION SYSTEM USING ENTROPY GENERATION MINIMIZATION METHOD

With the entropy generation minimization （EGM） method, the thermodynamical performance optimization in a thermoelectric refrigeration system is studied. The optimization is affected by the irreversibility of heat transfer caused by finite temperature differences, the heat leak between external heat reservoirs and the internal dissipation of working fluids. EGM is taken as an objective function for the optimization. The objective function and design parameters are obtained. Optimal performance curves are presented by thermal and electronic parameters. Effects of these parameters on general and optimal performances are investigated. Results are helpful in determining optimal design conditions in real thermoelectric refrigeration systems.

试论《电工学》课程的改革及其教材的建设

当今电技术,发展迅猛,应用广泛,渗透深远,因此电工学课程在工科教学中愈显重要。然而,长期以来,电工学课程内容“多、杂、浅”,不仅与有限学时的矛盾十分严重,而且也严重脱离非电专业对电技术的实际要求。尽管目前电工学课程已分为电工技术和电子技术,但其内容实质基本未变,上述两问题依旧存在,因此,电工学课程必须从根本上进行改革,否则,上述两问题将会愈演愈烈……,为此,笔者从该课程及其教材建设的原则、体系和内容这三个方面,发表如下浅见,以期抛砖引玉。

The optimal performance of a generalized Carnot cycle for a generalized heat transfer law

The finite time thermodynamic performance of a generalized Carnot cycle, in which the heat transfer between the working fluid and the heat reservoirs obeys the generalized law Q∝( Δ T) m , is studied. The optimal configuration and the fundamental optimal relation between power and efficiency of the cycle are derived. Some special examples are discussed. The results can provide some theoretical guidance for the design a practical engine.

Thermodynamic optimization for a quantum thermoacoustic refrigeration micro-cycle

A model of quantum thermoacoustic refrigeration micro-cycle(QTARMC)is established in which heat leakage is considered.A single particle contained in a one-dimensional harmonic potential well is studied,and the system consists of countless replicas.Each particle is confined in its own potential well,whose occupation probabilities can be expressed by the thermal equilibrium Gibbs distributions.Based on the Schrodinger equation,the expressions of coefficient of performance(COP)and cooling rate for the refrigerator are obtained.Effects of heat leakage on the optimal performance are discussed.The optimal performance region of the refrigeration cycle is obtained by the using ofΩobjective function.The results obtained can enrich the thermoacoustic theory and expand the application of quantum thermodynamics.

Numerical Study of Thermoelectric Generation within a Reciprocal Flow Porous Media Burner

A numerical study based on direct thermal to electric energy conversion was performed in a reciprocal flow porous media burner embedded with two layers of thermoelements. The burner lean combustibility limit was sought in order to maximize global efficiency of thermal to electrical energy conversion by minimizing fuel consumption. Once the pairs of operational variables, composition and filtrational velocity of gas inlet mixture were found, the optimal length and placement of thermoelectric elements within the reactor high thermal gradients were sought to maximize the electric current, thermoelements and system overall efficiency. A two temperature-resistance model for finite time thermodynamics was developed for the thermoelectric elements energy fluxes. Results indicate a distribution of current and efficiencies that presents a maximum at different themoelements length. Maximum values for current and system efficiency obtained were 44.3 m A and 2.5%, respectively.

Dynamic Multi-class Network Loading Problem

The dynamic network loading problem (DNLP) consists in determining on a congested network, time-dependent arc volumes, together with arc and path travel times, given the time varying path flow departure rates over a finite time horizon. The objective of this pap er is to present the formulation of an analytical dynamic multi-class network loading model. The mo del does not require the assumption of the FIFO condition. The existence of a solution to the model is shown.

Variation of Two-photon Absorption Cross Sections and Optical Limiting of Compounds Induced by Static Electric Field

By numerically solving the Maxwell-Bloch equations using an iterative predictor-corrector finite-difference time-domain technique, we investigate propagating properties of a few-cycle laser pulse in a 4,4＇-bis（di-n-butylamino） stilbene （BDBAS） molecular medium when a static electric field exists. Dynamical two-photon absorption （TPA） cross sections are obtained and optical limiting （OL） behavior is displayed. The results show that when the static electric field intensity increases, the dynamical TPA cross section is enhanced and the OL behavior is improved. Moreover, both even- and odd-order harmonic spectral components are generated with existence of the static electric field because it breaks the inversion symmetry of the BDBAS molecule. This work provides a method to modulate the nonlinear optical properties of the BDBAS compounds.

Progress in optimization of mass transfer processes based on mass entransy dissipation extremum principle

The mass entransy and its dissipation extremum principle have opened up a new direction for the mass transfer optimization. Firstly, the emergence and development process of both the mass entransy and its dissipalion extremum principle are reviewed. Secondly, the combination of the mass entransy dissipation extremum principle and the finite-time thermodynamics for opti- mizing the mass transfer processes of one-way isothermal mass transfer, two-way isothermal equimolar mass transfer, and iso- thermal throttling and isothermal crystallization are summarized. Thirdly, the combination of the mass entransy dissipation ex- tremum principle and the constructal theory for optimizing the mass transfer processes of disc-to-point and volume-to-point problems are summarized. The scientific features of the mass entransy dissipation extremam principle are emphasized.

Optimal Performance Characteristics of Subcritical Simple Irreversible Organic Rankine Cycle

Based on the theory of finite time thermodynamics, a subcritical simple irreversible organic Rankine cycle(SSIORC) model considering heat transfer loss and internal irreversible losses is established in this paper. The total heat transfer surface area is taken as a constraint, and R245fa is adopted as working fluid of the cycle in the performance optimization. The evaporator heat transfer surface area and mass flow rate of the working fluid are optimized to obtain the maximum power output and thermal efficiency of the SSIORC, respectively. In addition, the influences of the internal irreversibilities on the optimal performances are also investigated. The results show that when the evaporator heat transfer surface area is varied, the relationship between power output and thermal efficiency is a loop-shaped curve, and there exist maximum power output and thermal efficiency points, respectively. However, the two maximum points are very close to each other. When the mass flow rate of the working fluid is varied, the relationship between power output and thermal efficiency is a parabolic-like curve. With the decreases of expander and pump irreversible losses, the performances of the irreversible SSORC are close to those of the endoreversible SSORC with the only loss of heat transfer loss.

Modeling and performance analysis of energy selective electron (ESE) engine with heat leakage and transmission probability

A model of an energy selective electron (ESE) engine with linear heat leakage and Lorentzian transmission probability is established in this paper.The expressions for the main performance parameters of the ESE engine operating as a heat engine or a refrigerator are derived by using the theory of finite time thermodynamics.The optimum performances of the ESE engine are explored and the influences of the heat leakage,the central energy level of the resonance,and the width of the resonance on the performance of the ESE engine are analyzed by using detailed numerical examples.The optimal operation regions of power output and efficiency (or cooling load and coefficient of performance (COP)) are also discussed.Moreover,the performances of the ESE engine with Lorentzian transmission probability are compared with those with rectangular transmission probability.It is shown that the power output versus efficiency (or cooling load versus COP) characteristic curves with and without heat leakage are all closed loop-shaped ones.The efficiency (or COP) of the ESE engine decreases as the heat leakage increases.It is found that as the resonance width increases,the power output and efficiency (or cooling load and COP) increase to a maximum and then decrease due to the finite range of energies which contribute positively to the power generation or refrigeration in the electron system.Especially,when heat leakage is taken into account,the characteristic curves of maximum efficiency (or maximum COP) versus half resonance width are parabolic-like ones,which are quite different from the monotonic decreasing characteristic curves obtained in previous analyses without considering heat leakage.The results obtained in this paper can provide some theoretical guidelines for the design and operation of practical electron energy conversion devices such as solid-state thermionic refrigerators.

Modeling, Experimental Study on the Heat Transfer Characteristics of Thermoelectric Generator

This paper investigates the heat transfer characteristics of a thermoelectric generator. The influence of heat dissipation intensity to the sub-thermal resistances distribution is experimentally studied. Based on the thermal network analysis and finite time thermodynamics, an analytical model including all thermal resistances (in both thermocouples and external heat exchangers) is developed to predict the performance of the generator. The results show that the computed values of output power agree well with the experimental values. The heat transfer enhancement on the generator cold side greatly reduces the cold side temperature and thermal resistance, and obviously improves the output power. Compare with air natural convection cooling, the main thermal resistance changes from the resistance between the fins and the ambient to the thermal contact resistances between the generator and the heat sink at the conditions of forced convection and water cooling. This study may be guide the optimization of generator structure.

Power output analyses and optimizations of the Stirling cycle

Based on the finite time thermodynamics theory,the entransy theory and the entropy theory,the Stirling cycles under different conditions are analyzed and optimized with the maximum output power as the target in this paper.The applicability of entransy loss(EL),entransy dissipation(ED),entropy generation(EG),entropy generation number(EGN) and modified entropy generation number(MEGN) to the system optimization is investigated.The results show that the maximum EL rate corresponds to the maximum power output of the cycle working under the infinite heat reservoirs whose temperatures are prescribed,while the minimum EG rate and the extremum ED rate do not.For the Stirling cycle working under the finite heat reservoirs provided by the hot and cold streams whose inlet temperatures and the heat capacity flow rates are prescribed,the maximum EL rate,the minimum EG rate,the minimum EGN and the minimum MEGN all correspond to the maximum power output,but the extremum ED rate does not.When the heat capacity flow rate of the hot stream increases,the power output,the EL rate,the EG rate and the ED rate increase monotonously,while the EGN and the MEGN decrease first and then increase.The EL has best consistency in the power output optimizations of the Stirling cycles discussed in this paper.

Efficiency at Maximum Power Output of a Quantum-Mechanical Brayton Cycle

The performance in finite time of a quantum-mechanical Brayton engine cycle is discussed, without intro- duction of temperature. The engine model consists of two quantum isoenergetic and two quantum isobaric processes, and works with a single particle in a harmonic trap. Directly employing the finite-time thermodynamics, the efficiency at maximum power output is determined. Extending the harmonic trap to a power-law trap, we find that the efficiency at max/mum power is independent of any parameter involved in the model, but depends on the confinement of the trapping potential.

Science Letters:Finite time-horizon Markov model for IEEE 802.11e

We model wireless local area network channel utilization over a finite interval through a finite time-horizon Markov(FTHM) model.By accurately capturing time-varying utilization,the FTHM model allows for generally distributed transmis-sion-opportunity(TXOP) duration,which most existing models do not account for.An absorbing state is introduced to limit the lifetime of the counting process,resulting in a non-ergodic Markov chain that is solved via transient analysis.The model predic-tions for time-varying utilization are validated by simulation with errors of no more than 0.1% after eight beacon intervals.Moreover,we show that the FTHM model prediction error is below 4% for Poisson distributed and uniformly distributed TXOP durations.

Fabricating scheme and optical properties of a flexible semiconductor micro-laser

A new scheme for fabricating a kind of flexible semiconductor micro-laser is put forward.And the optical properties of this kind of flexible semiconductor laser are investigated by the finite difference time domain(FDTD) method.The results show that the light should be localized by photonic crystals(PCs),and the interaction between light and gain medium should be enhanced,while the mode of laser should be modulated.These results indicate that the PCs could control the spontaneous emission,and lead the radiation emission to the needed frequency.