Dependence of sea surface drag coefficient on wind-wave parameters

The relationships between sea surface roughness z 0 and wind-wave parameters are analyzed,and spurious self-correlations are found in all of the parameterization schemes.Sea surface drag coefficient C D is fitted by four wind-wave parameters that are wave age,wave steepness,windsea Reynolds number R B and R H ,and the analyzed data are divided into laboratory,field and combined data sets respectively.Comparison and analysis of dependence of C D on wind-wave parameters show that R B can fit the C D most appropriately.Wave age and wave steepness are not suitable to fit C D with a narrow range data set.When the value of wave age has a board range,R H is not suitable to fit C D either.Three relationships between C D and R B are integrated into the bulk algorithm COARE to calculate the observational friction velocity,and the results show that the relationship between C D and R B which is fitted with field data set can describe the momentum transfer in the open ocean,under low-moderate wind speed condition,most appropriately.

Study on the Characteristics of the Gas Switch Electrode Erosion

Gas spark switch is one of the key parts in pulsed power technology.Electrode erosion has great influence on the switch performance and lifetime.In this paper,a field distortion gas switch is selected for the experiment and a great deal of discharging experiments have been conducted in different test conditions.The forming process of etch pit as well as its influencing factors is discussed briefly and surface roughness coefficient(SRC) of the electrode is put forward to evaluate the state of electrode erosion.Experimental results show that current peak plays an important role in electrode erosion when waveforms of discharge current are the same,and electric charge and oscillation frequency of discharge current also have great effect on the electrode erosion when waveforms of discharge current are different.With the increase of discharge times,SRC decreases slowly at first and then decreases quickly after three thousand of discharge times.

STUDY ON CLIMATIC FEATURES OF SURFACE TURBULENT HEAT EXCHANGE COEFFICIENTS AND SURFACE THERMAL SOURCES OVER THE QINGHAI-XIZANG PLATEAU

Using monthly mean of surface turbulent heat exchange coefficients calculated based on data from four automatic weather stations(AWS)for thermal equilibrium observation in July 1993— September 1996 and of surface conventional measurements,an empirical expression is established for such coefficients.With the expression,the heat exchange coefficients and the components of surface thermal source are computed in terms of 1961—1990 monthly mean conventional data from 148 stations over the Qinghai-Xizang(Tibetan)Plateau(QXP)and its adjoining areas,and the 1961—1990 climatic means are examined. Evidence suggests that the empirical expression is capable of showing the variation of the heat exchange coefficient in a climatic context.The monthly variation of the coefficients averaged over the QXP is in a range of 4×10^(-3)-5×10^(-3).The wintertime values are bigger in the mountains than in the valleys and reversal in summer.Surface effective radiation and sensible heat are the dominant factors of surface total heat.In spring surface sensible heat is enhanced quickly, resulting in two innegligible regions of sensible heat,one in the west QXP and the other in northern Tibet.with their maximums emerging in different months.In spring and summer sensible heat and surface effective radiation are higher in the west than in the east.The effective radiation peaks for the east in October—December and the whole QXP and in June and October for the west.The surface total heat of the plateau maximizes in May.minimizes in December and January,and shows seasonal variation more remarkable in the SW compared to the eastern part.In the SW plateau the total heat is much more intense than the eastern counterpart in all the seasons except winter.Under the effect of the sensible heat,the total heat on the SW plateau starts to considerably intensify in February,which leads to a predominant heating region in the west,with its center experiencing a noticeable westward migration early in summer and twice pronounced weakening in July and after October.However,the weakening courses are owing to different causes.The total heat over the north of QXP is greatly strengthened in March.thus generating another significant thermal region in the plateau.

CALCULATION OF COUPLED PROBLEM BETWEEN TEMPERATURE AND PHASE TRANSFORMATION DURING GAS QUENCHING IN HIGH PRESSURE

The gas quenching is a modern, effective processing technology. On the basis of nonlinear surface heat-transfer coefficient obtained by Cheng during the gas quenching, the coupled problem between temperature and phase transformation during gas quenching in high pressure was simulated by means of finite element method. In the numerical calculation, the thermal physical properties were treated as the functions of temperature and the volume fraction of phase constituents. In order to avoid effectual ＂oscillation＂ of the numerical solutions under smaller time step, the Norsette rational approximate method was used.

A THEORY OF DETERMINING MASS TRANSFERPARAMETERS FOR WOOD PARTICLE MATERIALS

The transient mass transter processes in the natural drying of wood particle materials were experimental;y studied A new theory tio determme the mass transfer parameters in the Materials was developed in terms of gradient transformation method(GTM).By making use of GTM.Thewater vapour diffusion coefficient and the surtaee emission coefficent of wood chip were expermentally determined both in air phase and in solid phase.It Was found that the internal resistance to water vapour diffusion in the air phase of wood partiele aggregates is around ten to the third power as large as that in common air The drag coefficient was given to quantify the effect The phenomenon of undersurface diffusion in wood partiele bed was quantitatively modelled.The dimensionless Fourier snumber and the Biot's number for mass transfer were theoretically derived.The study showed that Biot's number for the problem investigated was the ratio of the characteristie length of wood partiele bed to the penetrating depth of the undersurface.An analytical solution of the nonlinear goveming equation for water transport process in the aggregates of wood chip was obtained by introducing the variable coefficients measured in the study into the governing equation.The comparison between the analytical solution and the observed moisture content of wood chip showed that the deviation was less than ±7%.The thermophysieal properties of wood particle materials are little known at present.The knowledge provided in the paper will be and in the handling.researeh or engineering application of wood chip.wood shavingsete.

Uncertainty in TC Maximum Intensity with Fixed Ratio of Surface Exchange Coefficients for Enthalpy and Momentum

The classical tropical cyclone(TC)maximum intensity theory of Emanuel suggests that the maximum azimuthal wind of TC depends linearly on the ratio of surface exchange coefficients for enthalpy and momentum(C_(k)and C_(d)).In this study,a series of sensitivity experiments are conducted with the three-dimensional Cloud Model 1(CM1),by fixing the ratio of C_(k)/C_(d)but varying the specific values of C_(k)and C_(d)simultaneously.The results show significant variations in the simulated TC maximum intensity by varying C_(k)and C_(d),even if their ratio is fixed.Overall,the maximum intensity increases steadily with increasing C_(k)and C_(d)when their value is smaller than 1.00×10^(-3),and then this increasing trend slows down with further increases in the coefficients.Two previous theoretical frameworks—one based on gradient wind balance and the other incorporating the unbalanced terms-are applied to calculate the maximum potential intensity(PI).The calculated value of the former shows little variation when varying the specific values of C_(k)and C_(d),while the latter shows larger values with increases in both C_(k)and C_(d).Further examination suggests that the unbalanced effect plays a key role in contributing to the increasing intensity with increasing C_(k)and C_(d).

EXPERIMENTAL ANALYSIS OF THE TURBULENT TRANSFER COEFFICIENT FOR SENSIBLE HEAT IN THE SURFACE LAYER OVER THE QINGHAI-XIZANG PLATEAU

This study deals with the turbulent structure in the surface layer over the Qinghai-Xizang Plateau.Using gradient transfer and heat balance methods we have determined the nondimensional coefficient 1/(?)_m(?)h in the expression of turbulent transfer coefficient for sensible heat (K_h).It is found that the results are in good agreement with the 1/(?)_m(?)_h obtained by Pruitt,et al.The K_h at a height of 1m under cloudy and cloudless conditions is calculated.Finally,the ratio of K_h to momentum turbulent coefficient over the plateau is compared with those over plains.

AlN-based surface acoustic wave resonators on platinum bottom electrodes for high-temperature sensing applications

Surface acoustic wave（SAW） resonators with Pt/AlN/Si and Pt/AlN/Pt/Si configurations were fabricated by lift-off photolithography techniques. High-temperature performances of both configurations were investigated for temperature sensor applications. AlN films grown on Ptcoated Si substrates exhibit a lower（002） preferred orientation than those grown on Si substrates. The center frequencies of Pt/AlN/Si and Pt/AlN/Pt/Si configurations at room temperature are 424.1 and 456.4 MHz, respectively.The SAW was limited by Pt bottom electrodes to propagate in AlN layer. The temperature coefficient of frequency（TCF） values of Pt/AlN/Si and Pt/AlN/Pt/Si configurations are-51.6 × 10^-6 and-69.2 × 10^-6℃^-1, respectively.Compared with that of Pt/AlN/Si configuration, the TCF value of Pt/AlN/Pt/Si configuration decreases by 34.1 %.AlN resonator with the Pt floating bottom electrodes provides a large, quasi-constant temperature sensitivity which is suitable for temperature sensor applications.

Survey of deep sub-barrier heavy-ion fusion hindrance phenomenon for positive and negative Q-value systems using the proximity-type potential

A systematic survey of the accurate measurements of heavy-ion fusion cross sections at extreme sub-barrier energies is performed using the coupled-channels(CC)theory that is based on the proximity formalism.This work theoretically explores the role of the surface energy coefficient and energy-dependent nucleus-nucleus proxim-ity potential in the mechanism of the fusion hindrance of 14 typical colliding systems with negative Q-values,in-eluding ^(11a)B+^(197)AU,^(12)C+^(198)Pt,^(16)O+^(208)Pb,^(28)Si+^(94Mo),^(48)Ca+^(96)Zr,^(28Si+)^(64)Ni,^(58)Ni+^(58)Ni+,^(60)Ni+^(89)Y,^(12)C+^(204)Pb,^(36)S+^(64)Ni,^(36)S+^(90)Zr,^(40)Ca+^(90)Zr,^(40)Ca+^(40Ca)and ^(48)Ca+^(48)Ca,,as well as five typical colliding systems with positive Q-values,ineluding ^(12)C+^(30)Si,^24Mg+^(30)Si,^(36)Si+^(48)Ca, and ^(40)Ca+^(48)Ca.It is shown that the outcomes based on the proximity potential along with the above-mentioned physical effects achieve reasonable agreement with the experimentally observed data of the fusion cross sections(Tfus(£),astrophysical S(E)factors,and logarithmic derivatives L(E)in the energy region far below the Coulomb barrier.A discussion is also presented on the performance of the present theoretical approach in reproducing the experimental fusion barrier distributions for different colliding systems.

Chemical diffusion and oxygen exchange of LaNi_(0.4)Fe_(0.6)O_(3-δ)ceramics

Oxygen surface exchange and oxygen chemical diffusion coefficients of LaNi_(0.4)Fe_(0.6)O_(3-δ)ceramics are determined via conductivity relaxation method after stepwise change of temperature in the range of 700-950℃in air and Ar/O2 gas flow at oxygen partial pressures(p_(o2))of 4 Pa,18 Pa,37 Pa,47 Pa and 59 Pa.The highest conductivity(about 160 S·cm^(-1))is found at 950℃in air.No oxygen exchange(δ=0)below 700℃is observed in the investigated p_(o2) range.The oxygen exchange coefficients determined in reduction mode are higher than those determined in oxidation mode.This is explained by clusterization of oxygen vacancies on the surface of the sample investigated in oxidation mode.The opposite tendency is found for chemical diffusion coefficients.Unlike surface,the oxygen vacancies of the volume region are probably not clustered and have predetermined the higher oxygen diffusion mobility of the sample treated in oxidation mode.