Vol. 52, No. 9 (2003)
2003, 52 (9): 2105-2108. doi: 10.7498/aps.52.2105
A form invariance for mechanical systems with second_order reducible differential constraints is studied．Two methods to study the form invariance of the systems are used．In the first method，the system is considered as a nonholonomic system with second_order and in the second method it is considered as a system after reduction．The relation between the two methods is obtained．The result proves that it is possible that some symmetries are lost in the second method．
2003, 52 (9): 2109-2113. doi: 10.7498/aps.52.2109
A subalgerbra 1, which is equivalent to the subalgebra of the loop al gebra 2 in “1997 Acta Math. Sin. 40 801”, is constructed by making use of algebraic t ransformation. Then a high-dimensional loop algebra is presented in terms of 1. An isospectral problem is established following by the use of direc t sum ope rators and isomorphic relations among subalgebras. It follows that a type of exp anding integrable system for the NLS_mKdV hierarchy of evolution equations is ob tained. As in reduction cases, the integrable couplings of the famous Schrding er equation and mKdV equation are presented.
2003, 52 (9): 2114-2120. doi: 10.7498/aps.52.2114
Two statistical quantities are proposed in this paper,that is Q and R,Q is calle d the exponent of dynamical autocorrelation factor, and R is called the exponent of dynamical cross_correlation factor. Using Q and R,we can identify the dynami cal property of time series or their implicative dynamical structural levels and complexity by estimating the “distance” between diffierent time series or dif fierent segments of same time series.This method has been verified to be valid b y some typical instances.
2003, 52 (9): 2121-2126. doi: 10.7498/aps.52.2121
Based on the NaSch cellular automaton traffic model, a new one_dimensional cellular automaton model (called SDNaSch model, for short) is proposed through prefer entially considering the sensitive behaviour of drivers, in which the randomizat ion brake is arranged before the deterministic deceleration. According to the ne w update rules of the evolution of vehicles, numerical simulation is conducted a nd leads to some new results. The fundamental diagram obtained by the simulation shows that the traffic capacity of a road is enhanced and closer to the observe d data compared with that of the NaSch model. It is found from the fundamental d iagram that there exist two branches in some density regions, which illustrates the existence of the metastable state near the critical point and the phase sepa ration. According to the evolution pattern of the vehicle speed in space and tim e, the wide moving jams is reproduced with the phase transitions between free fl ow and wide moving jams. With the consideration of the actual traffic situation, i.e., some drivers being sensitive and following the new rules, while others be ing not and following the original NaSch rules, the corresponding simulation ver ifies the remarkable effect of the sensitive driving factor on the characteristi cs of traffic flows. The traffic capacity rises along with the increase in the f raction of sensitive drivers.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2003, 52 (9): 2127-2130. doi: 10.7498/aps.52.2127
In this letter, we investigated random lasing phenomenon in ZnO powder using the pump_probe technique. Under 267nm laser pumping, supernarrow single_mode emission and multi_mode emission were observed by precisely controlling the pumping intensity and the excitation beam size on the sample. The supernarrow emission peaks are much narrower than the normal luminescence and ASE spectra. The time_resolved pump_probe measurement shows that the lifetime of the emission state above the lasing threshold is only a few picoseconds which demonstrates that the formation of supernarrow random lasing bandwidth is due to stimulated emission.
Study on the 16O(p,pα)12C and 16O (α，2α) 12C knockout reactions according to the independent α-cluster mode l
2003, 52 (9): 2131-2134. doi: 10.7498/aps.52.2131
According to the independent α-cluster model, the reaction cross sections and s pectroscopic factors of the reactions 16O(p,pα)12 C and 16O(α，2α)12C at the energies of 101.5,90 and 140 Me V have bee n calculated by means of distorted wave impulsion approximation. Reaction cross sections and spectroscopic factors calculated are in agreement with experimental data, and are better than the results by using shell model. This indicates that the independent α_cluster model can describe the mechanism of the reactions be tter.
Structural transformation of nanocrystalline titania grown by sol-gel technique and the growth kinetics of crystallites
2003, 52 (9): 2135-2139. doi: 10.7498/aps.52.2135
Structural transformation of nanocrystalline titania prepared by sol_gel method with hydrolysis precursor titanium isopropoxide was investigated. At the same ti me, the growth kinetics of titania powders was also studied. It was found that t he grain size of the powders increased slowly with autoclave heating temperature up to 503K, when hydrolysis pH value was 0.9, but grew rapidly when heating tem perature was higher than 503K. The activation energies for growth of anatase cry stallites in two temperature regions were calculated to be 18.5kJ/mol and 59.7 k J/mol respectively. The x_ray diffraction results show that the transformation f rom anatase phase to rutile phase starts at 503K and structural transformation f inished when temperature raises to 543K, which is a temperature much lower than that of the transformation reported in the literature.
2003, 52 (9): 2140-2144. doi: 10.7498/aps.52.2140
In order to extend the scope of application of BaF2 scintillators in the diagnosis of the fast-pulse-radiation-field, an ultraviolet-light-filter has been dev eloped for the modification of the scintillation spectrum. The experimental resu lts reveal that the filter, which is composed of Al2O3, Mg F2, and Al, has a very low transmittance to the slow component light emitted by BaF2 in the in cident angles from 0°to 45° with respect to the surface normal, but has a rela tively high transmittance to the fast component light also emitted by it. The pr operty of the temporal response curve has been obtained by use of a pulse x-rays source, and the damage effect induced by the irradiation of the neutron with an energy of 14.1 MeV is also introduced in this paper.
ATOMIC AND MOLECULAR PHYSICS
2003, 52 (9): 2145-2148. doi: 10.7498/aps.52.2145
Three types of state-to-state dielectronic recombination processes for Be-like i ons Au75+ have been investigated. Based on multi-configuration Hartre e-Foc k-Relativistic and distorted wave approaches, state-to-state dielectronic recomb ination rate coefficients have been calculated at electron temperatures 0.6-10.0 keV. Variations of the coefficient with electron temperature, recombination type s and up-or down-states have also been discussed in detail.
CLASSICAL AREA OF PHENOMENOLOGY
Studies on the analytical propagation equations of Gaussian beams through a mult i-apertured imaging system of B=0
2003, 52 (9): 2149-2154. doi: 10.7498/aps.52.2149
By using the method of matrix decomposition and expanding the aperture function into a finite sum of complex Gaussian functions, the closed-form propagation equ ations of Gaussian beams through a multi-apertured imaging system of B=0 are der ived and are illustrated with a few typical numerical examples. The advantages o f our treatment are pointed out.
2003, 52 (9): 2155-2158. doi: 10.7498/aps.52.2155
The periodic disturbance in transmittance of the polystyrene photonic crystal with a diameter of 3μm is observed in our experiment. According to the peak-to-peak intervals of the periodic disturbance, it can be seen that the periodic disturbance does not come from Mie scattering or Bragg diffraction, but from the propagation of whispering gallery mode in polystyrene spheres. The results show new potential applications of phtonic crystals.
2003, 52 (9): 2159-2164. doi: 10.7498/aps.52.2159
Novel multi-wavelength laser, based on semiconductor optical amplifier (SOA) and cascaded two-stage sampled fibre gratings, is theoretically and experimentally investigated in this paper. The reflection spectrum of the sampled fibre grating and lasing output spectrum are calculated. Exploiting SOA and sampled fibre grating manufactured by our laboratory,a multi-wavelength laser with 11 wavelengths, in which the output power difference is smaller than 1dB, is achieved. Compared with the scheme based on the ordinary sampled fibre grating, more lasing wavelengths and more uniform lasing output power can be achieved in the novel scheme, which can be concluded from both theoretical calculation and experimental analysis.
2003, 52 (9): 2165-2169. doi: 10.7498/aps.52.2165
Brillouin amplifier was numerically simulated by the theoretic model of transient stimulated Brillouin scattering including depleted pump. Pulse waveform versus power density of the pump and the energy ratio of the seed to the pump was given. Experiment was done so as to verify the theory. The theoretical calculation was in good agreement with the experimental result.
Theoretical and numerical investigation for propagation of ultrashort intense l aser pulse in plasma channel
2003, 52 (9): 2170-2175. doi: 10.7498/aps.52.2170
Characteristics of propagation of ultrashort intense laser pulses in a partially stripped pre-formed plasma channel, assumed to be parabolic and unperturbed, are discussed. From Maxwell equations the refractive index equation and Hamilton-Jacobi equation, which describe the evolution of the electric field, are derived including the effects of the diffraction, the third-order intensity-dependent nonlinearity, plasma defocusing, the self-focusing of the plasma channel, and t he relativistic self-focusing. The envelope equation of laser propagating in the plasma channel, and the general expression relating the laser spot size with th e propagation distance and the width of the plasma channel etc., are derived bas ed on the Hamilton-Jacobi equation and the refractive index equation.
2003, 52 (9): 2176-2184. doi: 10.7498/aps.52.2176
For BiB3O6(BIBO) crystals the refractive index on the main optical axis was measured. A systematic research was performed on the frequency-doubling property of the BIBO crystal. When the fundamental light was supplied by a Nd:YAG laser (λ=1064nm), the largest effective nonlinear optical coefficient was found in th e Type-Ⅰ phase-matching direction (168.9°, 90°). We measured the angular acce ptance, temperature acceptance, laser damage threshold, and the ultra-cavity as well as the intro-cavity frequency-doubling characteristics of the BIBO crystal. In our experiments, the largest ultra-cavity frequency-doubling conversion effi ciency was 68%, and the intro-cavity frequency doubling output power reached 1.0 6W.
The Bragg reflection characteristics of the fibre grating formed by chirped ultr ashort laser pulses
2003, 52 (9): 2185-2189. doi: 10.7498/aps.52.2185
Under the illumination of 800 nm femtosecond laser pulse, two-photon absorption phenomenon can occur in the photosensitive glass As2S3. When a chirped femtosecond laser pulse meets with another femtosecond laser pulse in an As2S3 fibre, the interference pattern can be recorded permanently as a chirped grating. In this paper, the relation between the structure of the chirped fibre grating and the parameters of the incident femtosecond pulse is described. Numerical calculations show that the chirped fibre grating has a broad Bragg reflection spectrum.
2003, 52 (9): 2190-2193. doi: 10.7498/aps.52.2190
A gain-switched laser diode (LD) was used as an external pulse injection source to reduce the timing jitter of gain-switched Fabry-Perot and DFB LDs. The low j itter and frequency-independent optical pulse can be achieved using this techniq ue. Phase noise measurement shows that with external pulse injection, the timing jitter of gain-switched FP LD was reduced from 1.2ps to 830fs and the timing ji tter of gain-switched DFB was reduced from 12ps to 1.2ps.
2003, 52 (9): 2194-2199. doi: 10.7498/aps.52.2194
We report that when the density at the centre of a cohesionless granular pile is slightly smaller than the density at its sides, such that the elastic strength at the centre is evidently smaller than the strength at the sides, the pressure distribution under the pile will show a dip at the centre. For the conical (or w edge-shaped) piles formed by slowly pouring grains from a point (or a line), the small density variation may be due to the phenomenon that the pile is slightly tapped by the down-rolling grains along the pile surfaces. The computation shows that the observed pressure distribution can be well reproduced by the elastic t heory with a spatial-varying bulk modulus.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2003, 52 (9): 2200-2205. doi: 10.7498/aps.52.2200
The plasma conditions of Ni-like Ag, Cd, In, Sn, Sb, and Ne-like Fe, Co, Ni, Cu, Zn x-ray lasers are numerically simulated, using a one-dimensional hydrodynamic code. The results suggest that there is a correspondence of plasma conditions b etween some Ni-like x-ray lasers and Ne-like x-ray lasers by comparing the hydro dynamic characteristics of electron temperature, ion abundance and ion populatio n density. For example, the plasma condition of the Ni-like Ag x-ray laser is si milar to that of the Ne-like Fe x-ray laser and the Ni-like Cd x-ray laser is si milar to that of Ne-like Co, etc. Due to this correspondence, we can use the sim ulation of those Ne-lie x-ray lasers to give suggestions of performance of this partner Ni-like x-ray lasers.
General procedure to formulate Hamiltonian theory of the completely integrable n onlinear equations and its application to the sine-Gordon equation
2003, 52 (9): 2206-2212. doi: 10.7498/aps.52.2206
For a completely integrable nonlinear equation, the Poisson bracket of monodramy matrix is known to be expressed in a form of integral with respect to x. The in tegrand is found to be an x-differential of a linear combination of direct produ ct of two pairs of Jost solutions definitely, and the coefficients can be determ ined by comparing the corresponding elements of direct product matrices on two s ides. Hence a general procedure for constructing Hamiltonian formalism is given for a completely integrable nonlinear equation. As an example, the Hamiltonian t heory of sine-Gordon equation is re-examined, which shows the essence of the lin ear combination method for its very complicated Poisson bracket. And the previou s works involve, as is known, some inappropriate violating simultaneity of varia bles in Poisson bracket, which is also revised now.
2003, 52 (9): 2213-2218. doi: 10.7498/aps.52.2213
Using the new inner surface modification technique named GEPSⅡ(grid-enhanced pl asma source ion implantation), which is designed for inner surface modification of tubular work piece, has successfully produced TiN coating on 0.45% C steel (4 5# steel). By comparing with the uncoated 45# steel sample, the electrochemical corrosion test on the coated 45# steel samples presents about 5—10 times improv ement in their corrosion resistance. Structural analysis shows that the TiN coat ings have preferred crystal orientation(111) and (2000). And the depth of coatin gs is about 20 nm, with part of which embedding in the substrate.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2003, 52 (9): 2219-2222. doi: 10.7498/aps.52.2219
The structural relaxation of Zr55Cu30Al10Ni5 bulk amorphous alloy during annealing at 360 and 380℃ have been investigated by in-situ synchrotron radiation x-ray small angle scattering (SAXS). The experimental results o btained show that the fluctuations of electron density during the annealing proc ess are due to structural relaxations of bulk amorphous alloy before cyrstalliza tion. It is found that a homogenization in electron density takes place during a nnealing, which is attributed to the change from topological short-range order (TSRO) structural relaxation to chemical short-range order (CSRO) structural relaxation. The annealing time required for this change becomes shorter as the annealing temperature increases.
2003, 52 (9): 2223-2228. doi: 10.7498/aps.52.2223
Based on the principle of x-ray fluorescence holography, we numerically simulate d an iron single crystal model of a body-centred cubic lattice. From the fluores cence hologram produced numerically, the Fe atomic images were reconstructed. Th e atomic images of the (001),(100),(010) crystallographic planes were consistent with the corresponding atomic positions of the model. The result indicates that one can obtain internal structure images of single crystals at atomic-resolutio n by using x-ray fluorescence holography.
2003, 52 (9): 2229-2234. doi: 10.7498/aps.52.2229
The LiAl is a typical intermetallic compound which has many important applications. We have employed the first-principles pseudopotentials and the plane wave energy band method to calculate the vacancy formation energies of Li and Al vacancies in LiAl intermetallic compound as well as the atomic relaxations around the vacancies. The charge redistribution around the vacancies, electronic densi ty of states and their band structures are also discussed.
2003, 52 (9): 2235-2238. doi: 10.7498/aps.52.2235
Mechanism of irradiation effects is analyzed for floating gate read only memorie s (ROMs). Phenomena in experiments are reasonably explained. It is proposed that failures in devices result from oxide trapped charge and interface trapped char ge generated by radiation in memory cells and peripheral circuitry. The neutron, proton and 60Co γ irradiation effects in FLASH ROM and EEPROM a re total dose effects.
2003, 52 (9): 2239-2243. doi: 10.7498/aps.52.2239
In this paper the characteristics of isothermal and isochronal annealing for post-radiated MOS transistor were studied. The results show that 100℃ isothermal a nnealing is the most effective treatment, while the time of isochronal annealing is the shortest. Secondly, the recovery of threshold voltage under the +5V bias is the fastest and biggest, compared to that under 0V and float bias. These predictied results by using isochronal annealing data were compared with the ex periment curve obtained from isothermal annealing, and the agreement is good.
2003, 52 (9): 2244-2248. doi: 10.7498/aps.52.2244
In a vertically vibrated binary granular mixture, sandwich-like segregation pattern is observed; a layer of large heavy particles is sandwiched in between two layers of small particles. This pattern is different from the double-layer structure, known as the “Brazil nut” effect, where the large heavy particles populate on the top. Our experiments show that such a three-layer structure is a stable pattern. It occurs when the vibration acceleration is beyond a critical threshold. Two different segregation processes are observed. The mechanisms for these two segregation processes are discussed. The dependence of the segregation pr ocesses on the driving frequency f and acceleration Γ, and the size ratio and volume ratio of the particles are also experimentally studied.
2003, 52 (9): 2249-2253. doi: 10.7498/aps.52.2249
3ω method has been investigated and its applications are analyzed. A wide appli cations in measuring the thermal conducti-vity and specific heat of material s are discussed. Here we discuss the mechanism of this method and introduce some basic applications. With some calculations in the two dimensional tunnel juncti on arrays and applications of 3ω method, a fast, primary Coulomb blockade therm ometer can be realized with a super-high precision in measuring temperatures in the Coulomb blockade regime.
2003, 52 (9): 2254-2258. doi: 10.7498/aps.52.2254
The diffusion mechanisms of Gd adatom on Cu(110) surface are investigated by means of molecular dynamics.The simulation results show that along ［1 1 0］ direct ion the Gd adatom diffuses by hopping,and the frequency of long jumps is very hi gh.While along［0 0 1］direction,the Gd adatom diffuses by exchanging.The freque ncy of hopping is higher than that of exchanging.The frequency of hopping and ex changing can be described by Arrhenius equation.The calculated diffusion barrier of hopping is 0.097eV and that of exchanging is 0.33eV.Moreover the diffusion b arrier of hopping is calculated by energy relaxation method.
Phase transformation of AlN in AlN/VN nanomultilayers and its effect on the mech anical properties of films
2003, 52 (9): 2259-2263. doi: 10.7498/aps.52.2259
AlN/VN nanomultilayers were prepared by reactive magnetron sputtering method. Th e effect of modulation period on the microstructure and mechanical properties of AlN/VN nanomultilayers were studied in this work. The results show that AlN exi sts in metastable cubic structure (c-AlN) at small modulation period and forms c oherent epitaxial grown superlattice with VN. At larger modulation periods, AlN transforms from cubic structure to stable hexagonal structure (h-AlN),and the na nomultilayers form a “brick-wall” structure with nanometer grains. The discuss ion shows that the template effect of VN is beneficial to the growth of c-AlN, b ut cannot increase its critical thickness remarkably.
Electronic theoretical study on the modification mechanism of rare earth element s in zinc-aluminum cast alloys
2003, 52 (9): 2264-2267. doi: 10.7498/aps.52.2264
The atomic structural model of the α phase-liquid interface region in ZA27 allo ys was set up by combining molecular dynamics theory with computer programming.T he electronic structure of α phase solid solution with rare earth elements and that of crystal-liquid growth front enriched with rare earth elements in the ZA2 7 casing alloy were investigated by the recursion method.The calculated results show that rare earth elements are more stable in the phase interface region than in α phase.This explains the fact that the solid solubility of rare earth elem ents in α phase is very small,but large in the crystal-liquid growth front.The structural energy difference between the rare earth elements in the crystal-liqu id growth front and in the α phase is greater than that in Al,which support the view point that rare earth elements enriched in the crystal-liquid growth front can make α crystal-branch melt and break down,dissociate,and propagate.Calcula tions of bond order integrals (BOIs) also show that rare earth elements in the α phase-liquid growth front are not easier than Al to solidify on the surface o f α phase,so that the growth of α grains is blocked,and the alloy is refined,t hus illucidating the modification mechanism of rare earth elements from an elect ronic level for the zinc-aluminum cast alloys.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2003, 52 (9): 2268-2273. doi: 10.7498/aps.52.2268
There are three different structures of the α-Al2O3(0001) crystal surface b ecause different atoms are terminated on the outermost layer. Our calculations a re based on the density functional theory in local density approximation, and on ultra-soft pseudopotential methods, with the valence orbital expanded in plane- wave by using three-dimensional periodic boundary conditions in κ-space, first ly, the calculation result is that α-Al2O3(0001) crystal surface structure which the outermost layer is terminated by a single layer of Al atoms is much mo re stable than the other two structures. Secondly, a rhombohedral primitive cell is employed to perform cell optimizations, with ten atoms in the unit cell, and the calculated equilibrium parameters are:a0＝0.48178nm,γ＝120.16, which are in excellent agreement with recent experimental values(a0＝0.47591nm ),with a difference of less than 1.3%. Moreover, our calculations are performed with a su per-cell slab model in vacuum environment, in which the outermost layer is termi nated by single Al atoms. By investigating the four-layer relaxation and Al-O a toms population of the surface, we obtain results that the top single Al layer i s an inward relaxation of 0.0792 nm—0.098nm, that is, the second-layer O atoms are turned into the top layer,and the top O and Al atoms population analysis sho w that the valence electrons are concentrated on the surface oxygen ions with a greater probability,it is obvious that the α-Al2O3(0001) crystal surface ap pears in the O-surface state,which is discussed from the microstructure of α-Al 2O3(0001)crystals in details.
The electronic structures and binding energy of the defects related to Y3+ dopants in PbWO4 crystals have been investigated by the relativi stic self-consistent discrete variational embedded cluster method.The results show that ［2(Y3+Pb)-VPb”］ is more stable than the other Y3+ r elated defects.Using the transition state method,we find that the transition ene rgy of O2p→Y5d is about 3.9eV.This signifies that Y3+ ions will not res ult in the absorptions at 350nm and 420nm in the PbWO4 crystal.Moreov er,the ef fect on electronic structure in PbWO4 caused by Y dopants is differen t from that caused by La dopants.
2003, 52 (9): 2280-2283. doi: 10.7498/aps.52.2280
GeFe2O4 is a spinel-type compound in which the neighborhoo d of a Fe2+ ion has a trigonal symmetry with respect to an axis which is parallel to one of the three 〈111〉 direction,and varies from site to site . The crystal-field and spin-orbit complete Hamiltonian matrix of 3d4/3d6 ions ha ve been establishe d by irreducible representation method, The zero-field splitting parameters D an d F-a of Fe2+ ions in GeFe2O4 crystal are prese nted by using the cryst al-field and spin-orbit interaction complete diagonalizing Hamiltonian matrix wi th the theory of electron paramagnetic resonance; at the same time, the contribu tions to zero-field splitting from spin-triplet state have been studied. The res ults show that the contributions to zero-field splitting from spin-triplet state are important and strong. The calculated results are in good agreement with the experimental data.
Electronic energy and life span probability distribution of the HgS/CdS/HgS sphe rical nanometer system
2003, 52 (9): 2284-2289. doi: 10.7498/aps.52.2284
The physical Model for the spherical HgS/CdS/HgS nanometer system and equations satistied by the electron motion are built. The energy and life span of s-electr on and the variation of the probability distribution with the width of the poten tial barrier and well are probed. Some important results indicate that the ener gy and life span of the electron increase with the increase of the potential bar rier width; electronic energy decreases with the increase of the potential well width, however the electronic life span is increased. The interaction between la yers has an important influence on the results.
2003, 52 (9): 2290-2292. doi: 10.7498/aps.52.2290
A one-dimensional integrable spin-orbital model is studied. In the large spin li mit, the degrees of freedom of the spin part can be described by the classical I sing spins. Without the external magnetic field, the ground state of the system is a connected orbital liquid with the background of Ising antiferromagnetic ord er of spins. The elementary excitations are the usual spinon-like orbital quanta . In an external magnetic field, flux phase exists in the system. The fluxes(two parallel ising spins)cut the system into disconnected orbital liquids(domains).
Linear optical absorption properties and internal electromagnetic field distribu tions of periodic multiple quantum wells
2003, 52 (9): 2293-2297. doi: 10.7498/aps.52.2293
Linear absorptive properties of the periodic multi-quantum well (MQW) structures are studied. It is found that the absorption is determined by the interplay of pulse widths, layer number N and periods. A threshold existing in N divides Bragg absorption into a rising and dropping regions. The corresponding maximum is an independent constant. Absorptions for non-Bragg arrangement keeps monoton ously increasing with its first part almost coinciding with the corresponding Br agg absorptions.This demonstrates a dramatic Bragg suppression,which never appea rs in the rising region. Further more, the Beer's law is proved to be still exac tly suitable for periodic structures.
A novel,yet direct,parameter-extraction method for heterojuction bipolar transis tors small-signal model
2003, 52 (9): 2298-2303. doi: 10.7498/aps.52.2298
An accurate and broad-band method for heterojuction bipolar transistors(HBT) small-signal model parameters is presented in this paper.This method differs from previous ones by extracting the equivalent-circuit parameters without using spec ial test structure or global numerical optimization techniques.The main advantag e of this method is that a unique and physically meaningful set of intrinsic par ameters is extracted from impedance and admittance representation of the measure d S-parameters in the frequency range of 0.5—12GHz under different bias conditi ons.An equivalent circuit for the HBT under a forward-bias condition is proposed for extraction of access resistance and parasitic inductance.The method yields a deviation of less then 5% between measured and modeled S-parameters.
2003, 52 (9): 2304-2308. doi: 10.7498/aps.52.2304
We have synthesized the pseudo-quaternary Heusler alloy Ni50Mn25 -xFe xGa25(x=0—25) by arc-melting and melt-spinning techniques .The structure ,magnetic properties,and martensitic phase transformation were investigated.The thermoelastic martensitic transformation characteristics and x-ray diffraction c onfirmed the high chemical ordering L21 structure of our samples in t he whole doping range.The dopant of iron decreases the martensitic transformation tempera ture and increases the Curie temperature for the doping level of x＜17.The ferro magnetic contribution of Fe atoms in Ni50.5Mn25-xFexGa24.5 h as been investigated in detail by precisely measuring the magnetization at 4K.It has been found that Fe atoms were indeed in Mn positions and contributed a loca lized moment up to 2.55—3.55μB.
2003, 52 (9): 2309-2313. doi: 10.7498/aps.52.2309
We have studied in this paper,by performing the Monte Carlo numerical simulation,both the hysteretic scaling and the dynamical phase transition of a three-dimen sional,(3D) classical X-Y model driven by an sinusoidally oscillating external m agnetic field.A scaling formula has been worked out which relates the hysteresis loop area with the amplitude h0 and frequency ω of the external fie ld as wel l as the reduced temperature T/Tc of the system in the form:Area～hα0ωβ(1-T/Tc)γ.The best-fit expo nents are α=0.57,β=0.34 and γ=0.9.The 3D X- Y model also characterizes a distinctive discrepancy in dynamical transition fea ture after short and long term evolution of magnetization,respectively.Our simul ation disclosed that the short-term evolution of magnetization (period number≤1 0) attains the symmetry-breaking of system with a nonzero dynamical order parame ter (Q≠0) at a either critical amplitude h0c or frequency ωc.The symme try-breaking in short term,however,evolves steadily into a symmetric disorder st ate (Q=0) after a longer term relaxation of system.The specific relaxation times at which the Q value becomes zero from nonzero increase evidently as the temper ature of system drops.
2003, 52 (9): 2315-2318. doi: 10.7498/aps.52.2315
The phase transformation and thermal expansion behaviour of (Pb0.97La 0.02(Zr0.65Sn0.35-xTix)O3 (PZST,0.1≤x≤0.14)antiferroelectric ceramics (AFEt)have been investigated as functions of temperature and Ti conte nt x.It was found that for the specimens with 0.1≤x≤0.12,the thermal expansion coefficient (α) curve showed an unusual “bending” at the temperature of T,wh ile the specimens remained a tetragonal phase.For 0.125≤x≤0.14,the specimens s howed a ferroelectric rhombohedral phase (FER) at room temperature.Wh en heated ,the FER phase was changed to an antiferroelectric tetragonal phase ( AFEt) a nd pareoelectroic cubic phase (PEc) at temperatures of TFA and Tc,resp ectively.In addition,T and TFA increased with the increase of Ti cont ent x , while Tc was decreased.The phases were detected by the XRD pattern at differ ent temperatures.The temperature-Ti content (x) phase diagram of (Pb0.97La 0.02)(Zr0.65Sn0.35-xTix)O3 was finally established.The the rmal expansion behaviour of (Pb0.97La0.02)(Zr0.65Sn0.35-xTix)O3 (0.1≤x≤0.14) have been expla ined based upon the nano-size phase s eparation of the PZST complex pervoskite compounds.
Study on principal refractive indices of the ferroelectric single crystal 0.62Pb (Mg1/3Nb2/3)O3-0.38PbTiO3
2003, 52 (9): 2319-2323. doi: 10.7498/aps.52.2319
The refractive indices and their dispersions in 0.62Pb(Mg1/3Nb2/ 3)O 3-0.38PbTiO3(PMNT62/38)single crystals were accurately mea sured with the min imum deviation method at 20℃.The parameters of modified Sellmeier's equation fo r both no and ne are obtained.We relate the refractive ind ices to energy-ban d structure of oxygen-octahedron ferroelectrics and the Sellmeier optical coeffi cients,E0=5.50eV,λ0=0.226μm，Ｓ０=1.004×1014m-2 and Ed=28 .10eV for n0 and Ｅ0=5.57eV,λ0=0.223μm，S0=1.017×1014m-2 and Ed=28.10eV for ne were obtained through fitting the si ngle-term oscillat or equation.For materials with ABO3 perovskite structure,the octahedr al BO6 unit governs the lower lying conduction bands and the upper valence bands and ma kes a substantial contribution to the refractive indices.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2003, 52 (9): 2324-2330. doi: 10.7498/aps.52.2324
Very high frequency (VHF) Plasma and its glow discharge mechanism during the deposition of μc-Si:H film have been studied by means of optical emission spectroscopy (OES) technique in this paper.From the measured OES spectra,where the valuable information on the Si,SiH,H and H2 intensities were provided,the influence of deposition conditions on the VHF plasma has been investigated.The intensitie s of SiH,H2 and H of VHF-gas deposition(GD) to deposit μc-Si:H were much high er than those of RF-GD to deposit a-Si:H.Under the experiment condition to depos it μc-Si:H,Si,SiH,the H and H2 intensities increased obviously with the excit ation frequency,and the variation of the deposition rate with the excitation fre quency was similar to that of SiH.The SiH intensity of VHF-GD became higher than its Si intensity as the hydrogen dilution ratio decreased.The influences of the hydrogen dilution ratio on the plasma optical emission spectra also depended on the reaction pressure,the excitation power as well as the excitation frequency. In the case of the hydrogen ratio (R=H2/SiH4)R=23,the SiH intensity decrease d monotonously against the excitation pressure at a low excitation power (e.g.5W ).But the SiH intensity increased at first, then decreased with the increase of the pressure at the high excitation power (e.g.11-55W).In the case of the hydrog en ratio R=5.7,the SiH intensity decreased monotonously against the excitation p ressure for all the excitation power.The Si,SiH,H and H2 intensities also incr eased with the excitation power and then trended to be saturated,and they are ea sier to saturate with the increase of the hydrogen dilution ratio.All the experi mental results demonstrated that the influences of the excitation frequency,the excitation power,the reaction pressure and the hydrogen dilution ratio were correlative,none of the deposition conditions is the critical factor to improve the deposition rate.
2003, 52 (9): 2331-2336. doi: 10.7498/aps.52.2331
This paper describes the principle of flow-levitation method. An analytical mode l for preparation of nanometal powders in inert gases is presented. Associated w ith the relation between dynamics of gas flow and temperature, the process of th ermal diffusion, nucleation, condensation and crystallization of powders is stud ied. The results of theoretical analysis are in agreement with the practice.It i ndicates that we can control the particle-size distribution by choosing appropri ate characteristic technological parameters.
High-resolution electron-energy-loss spectroscopy study on the reaction of MgF2 with Alq3(8-hydroxy-quinoline)aluminum
2003, 52 (9): 2337-2341. doi: 10.7498/aps.52.2337
The reaction between MgF2 and tris (8-hydroxy-quinoline)aluminum (Alq 3)has b een studied using high-resolution electron-energy-loss spectroscopy (HREELS).The reaction between MgF2 and Alq3 occurs in the cases of MgF 2 deposited on A lq3 and Alq3 on MgF2.The shift of the loss peak corresponding to the out-o f-plane ring bend is observed to be similar to that for Mg deposited on Alq 3.T he HREELS spectra indicate that Mg is produced from MgF2 deposited on Alq3,a nd interacts with Al,O and N in Alq3.Analysis of the HREELS results s uggests that Mg is not in the Alq3 molecule plane.
2003, 52 (9): 2342-2346. doi: 10.7498/aps.52.2342
The free energy of the TIP4P water is computed by expanded ensemble method,which allows us to calculate absolute free energies with a high precision for arbitrary systems using a relative simple computational scheme.The free energy of NVT ensemble of TIP4P water is -21.485±0.035kJ/mol,which is in accordance with the r esults obtained by using other method.A method for choosing crucial parameters ( balance factors)is proposed.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
By viewing each integral process in the ensemble prediction as a locus of quasi-particle in the nonequilibrium statistical physics theory,numerical experiments of Lorenz model are performed,and under the circumstance that the initial value of the model is near the equilibrium state of different properties,the temporal evolution of the number of quasi-particles in the ground state and the first excited state is calculated in this paper.The results confirm that if the dynamic system has stable equilibrium states in the whole phase space,the long-range temporal evolutional behavior of the system in the vicinity of the stable equilibrium states is predictable.If the dynamic system has not any stable equilibrium state in the whole phase space and the initial value of the system is far away from the unstable equilibrium states,then most of the quasi-particles lie in the low-energy state within 1-2 weeks,i.e.it is most probable.If the initial value lies in the vicinity of the unstable equilibrium states,the temporal evolution of the system is almost unpredictable.This proves theoretically that the effect of the ensemble prediction obtained after performing a large number of integral processes in better than that from the single integral process of a single init ial value.This offers a physical explanation why the ensemble prediction has a h igher accuracy.
2003, 52 (9): 2354-2358. doi: 10.7498/aps.52.2354
By using the thin film model,which is based on the brick-wall method,the entropy of the Dirac field in a general spherically symmetric and charged evaporating black hole is calculated.The conclusion that black hole entropy is proportional to its horizon area can still be applied by regulating the cutoff,which is time dependent.