Local tunneling barrier height observations of NiAl(1 1 0)

Local work functions at individual atoms on a compound metal surface have been experimentally examined. The simultaneously obtained STM and local tunneling barrier height (LBH) images of NiAl(1 1 0) show that LBH at geometrically lower Ni sites is much higher than that at geometrically higher Al sites, indicating that each individual atom on the NiAl(1 1 0) surface has a specific potential barrier for relevant electrons.     

不同宽度和角度下木材表面火蔓延特性的实验研究

选取宽2～11 cm、厚3 mm的樟木、杉木和白木试样进行了一系列实验,测量了火蔓延速度、火焰高度、火焰温度和试样表面温度。结果表明,火焰高度随试样宽度增加而增大,并在宽度增加至某个值后不再增大;同宽度下,密度大的试样火焰高度大。放置角度为负时,不同密度试样的火蔓延速度差较小,角度为正时,火蔓延速度随角度增加而增大,且不同密度试样的火蔓延速度差变大.     

Characteristics and parameter extraction for NiGe/n-type Ge Schottky diode with variable annealing temperatures

Current transport mechanism in Ni-germanide/n-type Ge Schottky diodes is investigated using current--voltage characterisation technique with annealing temperatures from 300~\duto 500~\du. Based on the current transport model, a simple method to extract parameters of the NiGe/Ge diode is presented by using the $I$--$V$ characteristics. Parameters of NiGe/n-type Ge Schottky diodes fabricated for testing in this paper are as follows: the ideality factor $n$, the series resistance $R_{\rm s}$, the zero-field barrier height $\phi _{\rm b0}$, the interface state density $D_{\rm it}$, and the interfacial layer capacitance $C_{\rm i}$. It is found that the ideality factor $n$ of the diode increases with the increase of annealing temperature. As the temperature increases, the interface defects from the sputtering damage and the penetration of metallic states into the Ge energy gap are passivated, thus improving the junction quality. However, the undesirable crystallisations of Ni-germanide are observed together with NiGe at a temperature higher than 400~\du. Depositing a very thin ($\sim $1~nm) heavily Ge-doped $n^{+}$ Ge intermediate layer can improve the NiGe film morphology significantly.     

OSMAR2000探测海面风浪场原理与实现

从Barrick反演无向浪高谱的公式出发,在高频地波雷达OSMAR2000工作频率条件下,对反演均方浪高、浪周期的公式进行了修正,并将其应用于高频地波雷达OSMAR2000的风浪场的反演,将反演结果与同时进行现场工作的传统海洋探测设备输出结果比较,证明本文方法行之有效。     

Effect of graphene tunnel barrier on Schottky barrier height of Heusler alloy Co_2MnSi/graphene/n-Ge junction

We demonstrate that the insertion of a graphene tunnel barrier between Heusler alloy Co_2MnSi and the germanium(Ge) channel modulates the Schottky barrier height and the resistance–area product of the spin diode. We confirm that the Fermi level is depinned and a reduction in the electron Schottky barrier height(SBH) occurs following the insertion of the graphene layer between Co_2MnSi and Ge. The electron SBH is modulated in the 0.34 eV–0.61 eV range. Furthermore,the transport mechanism changes from rectifying to symmetric tunneling following the insertion. This behavior provides a pathway for highly efficient spin injection from a Heusler alloy into a Ge channel with high electron and hole mobility.     

高功率激光器喷雾冷却的实验研究

以水为冷却介质,采用Spray公司的TG0.3机械雾化实心圆锥喷嘴,在体积通量为0.044,0.049和0.053 m3/(m2·s)情况下,对刻有不同微结构槽道冷却面的无沸腾区换热性能进行实验研究。结果表明：刻有微结构的表面可明显增强换热效果;壁面刻有高为0.2 mm的微结构槽道且壁面温度为52 ℃时,体积通量为0.044 m3/(m2·s则热流可达260 W/cm2,通量为0.053 m3/(m2·s则散热功率高达376 W/cm2,完全可以满足当前高功率激光器的散热需求。对于光滑面以及槽肋高为0.1和0.2 mm的换热面,其换热能力随着体积通量的增加而增强;换热面高度为0.4 mm时,通量对换热的影响变得较微弱。微结构槽道不仅增加了换热面积,还有利于液膜扩散,减小液膜厚度,增强换热。在三种不同的流量通量下,高度为0.2 mm的微结构槽道换热性能最佳。     

Rapid determination of the RF pulse flip angle and spin-lattice relaxation time for materials imaging

For samples with T1s longer than 10s, calibration of the RF probe and a measurement of T1 can be very time-consuming. A technique is proposed for use in imaging applications where one wishes to rapidly obtain information about the RF flip angle and sample T1 prior to imaging. The flip angle measurement time is less than 1s for a single scan. Prior knowledge of the RF flip angle is not required for the measurement of T1. The resulting time savings in measuring the values of flip angle and T1 are particularly significant in the case of samples with very long T1 and short T2*. An imaging extension of the technique provides RF flip angle mapping without the need for incrementing the pulse duration, i.e., RF mapping can be performed at fixed RF amplifier output.     

Modelling of turbulent lifted jet flames using flamelets: a priori assessment and a posteriori validation

This study focuses on the modelling of turbulent lifted jet flames using flamelets and a presumed Probability Density Function (PDF) approach with interest in both flame lift-off height and flame brush structure. First, flamelet models used to capture contributions from premixed and non-premixed modes of the partially premixed combustion in the lifted jet flame are assessed using a Direct Numerical Simulation (DNS) data for a turbulent lifted hydrogen jet flame. The joint PDFs of mixture fraction Z and progress variable c, including their statistical correlation, are obtained using a copula method, which is also validated using the DNS data. The statistically independent PDFs are found to be generally inadequate to represent the joint PDFs from the DNS data. The effects of Z–c correlation and the contribution from the non-premixed combustion mode on the flame lift-off height are studied systematically by including one effect at a time in the simulations used for a posteriori validation. A simple model including the effects of chemical kinetics and scalar dissipation rate is suggested and used for non-premixed combustion contributions. The results clearly show that both Z–c correlation and non-premixed combustion effects are required in the premixed flamelets approach to get good agreement with the measured flame lift-off heights as a function of jet velocity. The flame brush structure reported in earlier experimental studies is also captured reasonably well for various axial positions. It seems that flame stabilisation is influenced by both premixed and non-premixed combustion modes, and their mutual influences.     

Emittance-dominated long bunches in dual harmonic RF system

The storage of long bunches for long time intervals needs flattened stationary buckets with a large bucket height. The longitudinal motion of the initially mismatched beam has been studied for both the single and dual harmonic RF systems. The RF amplitude is determined to be r.m.s wise matched. The bucket height of the single harmonic system is too small even for shorter bunch with only 20% increased energy spread. The Halo formation and even debunching can be seen after a few synchrotron periods for single particles with large amplitude. In the case of small energy spread for a cooled beam, Coulomb interaction cannot be ignored. The external voltage has to be increased to keep the r.m.s bunch length unchanged. The new voltage ratio R(N) simplifies physics for the emittance-dominated bunches with modest particle number N. For the single harmonic system, substantial amount of debunching occurs without increasing the external voltage, but very little if the RF amplitude is doubled. Results from the ORBIT tracking code are presented for the 1 GeV bunch in the HESR synchrotron, part of the GSI FAIR project.     

Origin bands of electronically forbidden spectra made allowed by centrifugal distortion

Watson’s theory of pure rotational spectra in nonpolar molecules is adapted to show that, if appropriate symmetry conditions are met, centrifugal distortion can lead to the appearance of the forbidden 0-0 origin band in an electronically forbidden spectrum. The intensity of such bands will be low; in the case of the benzene ùB_2u-¹A_1g system the maximum intensity of the forbidden origin is estimated to be about 10⁻⁷ of that of the 6¹₀ band in the main vibronic spectrum. The prospects for the experimental detection of such weak bands are discussed.