Vol. 52, No. 6 (2003)
2003, 52 (6): 1313-1318. doi: 10.7498/aps.52.1313
A variable separation approach is used to obtain exact solutions of the Nizhnik-Novikov-Veselov equation.One of the exact solutions of this model is analysed t o study the interaction between two dromions,dromion and “solitoff” both analytically and graphically.Some new interacting properties are reaveled.
Iterative layering approach to multiple scattering and emission from inhomogenou s random scatter media
2003, 52 (6): 1319-1325. doi: 10.7498/aps.52.1319
Taking into account the multiple scattering of vector radiative transfer (VRT), an iterative layering method is developed by stratifying the random media into m ulti-slabs and employing the lower-order Mueller matrix solution to derive high- order scatterings. This approach is applied to the simulation of polarized brigh tness temperature from an inhomogeneous snowpack of randomly and densely distrib uted spherical particles with nonuniform profiles of particle size, fractional v olume and physical temperature. Numerical results are compared with conventional eigen-analysis approach for a uniform scatter medium. The functional dependence of multiple scattering and emission upon the characteristic parameters such as particle size, fractional volume, physical temperature etc. are discussed, and a re also compared with the microwave remote sensing measurements of the multi-lay ers snowpack.
Effects of non-conservative forces and nonholonomic constraints on Lie symmetrie s of a Hamiltonian system
2003, 52 (6): 1326-1331. doi: 10.7498/aps.52.1326
The effects of non-conservative forces and nonholonomic constraints on Lie symmetries and conserved quantities of a Hamiltonian system are studied. When non-conservative forces or nonholonomic constraints are inserted in the Hamiltonian system, we obtain the conditions under which Lie symmetries, structure equation and conserved quantities of the system will remain present. The famous Emden equation and Appell-Hamel model are taken as examples to illustrate the application of the results.
Nonlinear elementary excitations in a monoatomic chain with second nearest neigh bour anharmonic interaction
2003, 52 (6): 1332-1336. doi: 10.7498/aps.52.1332
By using a multiple scales method,we study the lattice vibration of a monoatomic chain taking into account the nearest neighbour and the second next nearest neighbour harmonic and anharmonic interactions.It is shown that nonpropagating solitons exist in any position of the Brillouin zone.Compared with that of a soliton in monoatomic chains with only nearest-neighbour interactions,the group velocity at the centre of the Brillouin zone is enhanced but attenuates more rapidly.I n addition,a new position of zero velocity for the soliton is found in the first Brillouin.Our results show that the amplitude of this kind of soliton increases and the location of the soliton with the largest amplitude is close to the cent re of the Brillouin zone.
2003, 52 (6): 1337-1339. doi: 10.7498/aps.52.1337
Kadomtsev-Petviashvili(KP) equation is derived for unmagnetized,relativistic and hot ion plasmas.The result suggests that the nonlinear ion acoustic solitary waves in a relativistic hot ion plasma are stable even when there are some higher-order transverse perturbations.There are only compressive solitary waves in the relativistic hot ion plasmas,this has been vertified analytically in this paper.
Hawking radiation of Weyl neutrinos in a rectilinearly nonuniformly accelerating Kinnersley black hole
2003, 52 (6): 1340-1345. doi: 10.7498/aps.52.1340
The quantum thermal effect of Weyl neutrinos in a rectilinearly nonuniformly accelerating Kinnersley black hole is investigated by using a method of generalized tortoise coordinate transformation.The equation that determines the location,the Hawking temperature of the event horizon and the thermal radiation spectrum of neutrinos are derived.Our results show that the location and the temperature of the event horizon depend not only on the time but also on the angle.
2003, 52 (6): 1346-1349. doi: 10.7498/aps.52.1346
The quantum corrections to the entropy of the Barriola-Vilenkin black hole due to the massless gravitational field are calculated by using the brick-wall model.It is shown that the quantum corrections consist of two parts:One is a quadratic divergent term at the event horizon and is proportional to the surface area of the event horizon.The other is two logarithmically divergent terms which not only depend on the characteristics of the black hole but also on the spin of the field.The whole expression does not take the form of the scalar field.
2003, 52 (6): 1350-1353. doi: 10.7498/aps.52.1350
The quantum corrections to the entropy of the Vaidya-Bonner-de Sitter black hole due to gravitational fields are investigated by using the brick-wall model.When the event horizon of the black hole does not depend upon the advanced-time,the results coincide with that of the Reissner-Nordstrm-de Sitter black hole.
Ordered structure and system development of the force dissipation system(Ⅱ),Minimal value principle of generalized energy and system development
2003, 52 (6): 1354-1359. doi: 10.7498/aps.52.1354
The minimal value principle of the generalized energy is demonstrated using the atmosphere nonlinear dynamics. It is demonstrated more theoretically that the mi nimal value principle is coincident to the principle of least entropy production in the nonequilibrium thermodynamics of atmosphere. The minimal value principle shows that the generalized energy at the final state of a force dissipation dyn amic system reaches a minimal value. However,the principle of least entropy prod uction shows that the irreversible process inside a system is weakest at the fin al state of an open system far from the thermodynamic equilibrium state. Further more, the final state in which the generalized energy of the system reaches the minimal value and the entropy production of the system reaches the minimum value is generally a stable stationary state. It is corresponding to a certain system ic ordered structure. This means that it is an ordered stationary state of “low consumption but high effect”.In the atmosphere,as a typical complex system in nature, the principle of least entropy production and the minimal energy value p rinciple imply a universal principle for complex systems, which always tend to t he ordered stationary state of “low consumption but high effect”.
A method of controlling chaos by employing a dynamical nonlinear feedback controller is developed to guide chaotic motions towards regular motions.The controller is an active feedback controller without affecting the original system parameters,and is piecewise-quadratic function in the form of x|x|.In addition,it is quite simple and easy to implement in circuit.Numerical simulation shows the effectiveness and applicability of this method.
2003, 52 (6): 1365-1371. doi: 10.7498/aps.52.1365
Stochastic bifurcation of the Duffing-van der Pol oscillators under both additive and multiplicative random excitations is studied in detail by the generalized cell mapping method using digraph.As an alternative definition,stochastic bifurcation may be defined as a sudden change in character of a stochastic attractor when the bifurcation parameter of the system passes through a critical value.It is found that under certain conditions stochastic bifurcation mostly occurs when a stochastic attractor collides with a stochastic saddle.Our study reveals that the generalized cell mapping method with digraph is also a powerful tool for global analysis of stochastic bifurcation.By this global analysis ,the mechanism of development,occurrence,and evolution of a stochastic bifurcation can be explored clearly and vividly.
2003, 52 (6): 1372-1378. doi: 10.7498/aps.52.1372
The perturbative evaluation of the time-dependent quantum transport is investigated by making use of the Lewis-Riesenfeld invariant theory and the invariant-related unitary transformation formulation in this paper.We obtain the complete set of solutions of the time-dependent Schrdinger equation governing the behaviour of electrons in a double-well structure. Based on these exact solutions,we obtain the first-order quantum rate equation by regarding the interaction Hamiltonian between the double-well structures and the heat reservoirs as the perturbative Hamiltonian.An approach to the geometric phase factor (Berry's phase factor) in the adiabatic quantum transport process is briefly discussed in this paper.We hold that the formulation presented here has advantages in dealing with transport problem over the method proposed by Gurvitz et al.
Ordered structure and system development of the force dissipation system(Ⅰ),Principle of minimum entropy production and ordered structure
2003, 52 (6): 1379-1384. doi: 10.7498/aps.52.1379
Development of a system is always driven by the thermodynamic irreversible process and also the nonlinear dynamics process.The entropy equilibrium equation,which combines the equation set of atmosphere dynamics and the Gibbs relation in which kinetic energy change is taken into account,can describe the thermodynamic irreversible process and the nonlinear dynamics process.Up to now,the principle of minimum entropy production has been demonstrated only using the Onsager linear phenomenological relation in the nonequilibrium state thermodynamics.This paper demonstrates the principle of minimum entropy production by using the new entrop y equilibrium equation that is established with the atmosphere kinetic equation. As a result the principle of minimum entropy production is universal in the line ar and nonlinear regions of thermodynamics.A system arrives at a state of minimu m entropy production with the weakest irreversible process,when it is in heat tr ansportation balance;vapor transportation balance and momentum transportation ba lance.This minimum-entropy-production state is a stationary state,when the syste m is also in dynamic equilibrium and with out advection.This stationary state co rresponds to a certain ordered structure of the atmosphere system, when it devia tes from the equilibrium state.
ATOMIC AND MOLECULAR PHYSICS
2003, 52 (6): 1385-1389. doi: 10.7498/aps.52.1385
The model-potential method including correlation effects is applied to the computation of lifetimes of high s series Rydberg states of Na atom.This theoretical model does not depend on the experimental results.In comparison,the results agree well with experiments and provide the evidence of the validity of this theoretical method.
CLASSICAL AREA OF PHENOMENOLOGY
2003, 52 (6): 1390-1395. doi: 10.7498/aps.52.1390
A new kind of even and odd coherent states i.e.the photon-added and photon-deple ted states,can be obtained from acting boson inverse operators on the usual even and odd coherent states.The new states are the eigenstates of the operators a^ -ka^k+2 and a^+-ka2a^+k,r espectively.The results show that these states may reveal the anti-bunching and quantum squeezing effects.
2003, 52 (6): 1396-1402. doi: 10.7498/aps.52.1396
Resonator parameters and thermo-stability conditions for plane-plane resonator o f multi-rod series connection solid-state lasers were investigated by means of m atrix optics.Stability areas of six-rod-connection solid-state lasers in a plane -plane resonator were calculated.The results show that stability areas and non-s tability areas of the multi-rod series-connection solid-state lasers distribute alternately.If the length of the resonator,the number(n) of laser rods and the s pacing (L) between two neighbouring laser rods are given and a symmetry configur ation (L1=L2) is adopted,then every stability area reaches a largest extent. If the condition (L1=L2=L/2) is supposed in plane-plane re sonator and the th ermo focus length (f) is greater than a lower limit value (fm),the st ability c ondition (01G2m),the resonator come into a deep non-stability area.The lower limit va lue (fm) is determined by the number (n) of laser rods and the spacin g (L) between two rods,the formula is fm=0.25L(if 2≤n≤10).
2003, 52 (6): 1403-1407. doi: 10.7498/aps.52.1403
Using a free-electron laser source,we have studied the nonlinear absorption in I nSb,Hg1-xCdxTe and InAs semiconductors.By measuring the tr ansmission,two -photon-absorption(TPA)has been investigated as a function of the input power.In two cases,a distinct saturation of TPA coefficients has been observed.Using an extension of these methods,we demonstrated that the reduced transmission at high intensities is primarily due to free-carrier-absorption(FCA) of the electrons a nd holes generated by TPA,not directly due to the TPA process.Furthermore,by car eful calculation,we have extracted the convincing cross section of FCA.
2003, 52 (6): 1408-1411. doi: 10.7498/aps.52.1408
Cavity mode matching principles of end-pumped solid-state lasers are analyzed th eoretically.The analyses in this article can be important references for designi ng end-pumped solid-state lasers.
2003, 52 (6): 1412-1417. doi: 10.7498/aps.52.1412
Using the moving mirror model,we studied analytically the harmonic generation from solid targets illuminated by intense laser pulses.Comparison of the results o f the moving mirror model with those of particle-interaction computor simulations and experiments reveals the shortcomings of this model though it can really give many useful characters of the process of high-order harmonic generations.
2003, 52 (6): 1418-1421. doi: 10.7498/aps.52.1418
The effects of Kerr nonlinearity on the band-gap structure of one-dimensional ph otonic crystals was investigated. The photonic band-gap in the nonlinear region can be modulated by changing the intensity. It was found that due to the nonline ar modulation, the electromagnetic eigenmodes of cosine function type go into th e linear gap and become soliton-like modes of hyperbolic secant function type. A number of novel soliton-like electromagnetic modes are found in the gap.
2003, 52 (6): 1422-1426. doi: 10.7498/aps.52.1422
Based on theory analysis, we have demonstrated experimentally how to use cascaded wideband fibre Bragg grattings (FBGs) as reflectors in the superfluorescent fi bre sources (SFS) configuration. In the experiment, we investigated the output c haracteristcs of the set-up with cascaded wideband FBGs, and compared it with th ose of the set-up with fibre ring reflector or without any reflector. From what we have achieved in the experiment, we find that the cascaded wideband FBGs is p romising to be used as reflectors in SFS.
2003, 52 (6): 1427-1431. doi: 10.7498/aps.52.1427
Time- and space- resolved x-ray spectrum diagnostic system has been established by coupling flat-field grating and gated-MCP (micro-channel plate) with an optic al CCD. A series of experimental investigations on the characterization of the d iagnostic system have been carried out to develop quantitative measurement techn ology of x-ray absorption spectrum. This diagnostic technology has been successf ully applied to the measurements of absorption.
2003, 52 (6): 1432-1437. doi: 10.7498/aps.52.1432
In this paper, we report novel long-period fibre gratings (LPFGs) written by focused high-frequency CO2 laser pulses. A number of unique characteri stics of such a LPFG, such as stroin, temperature, bend, torsion and transverse-load, etc., are observed by experiment, for the first time to our knowledge. These uni que features are mainly due to the asymmetrical distribution of the refractive i ndex on the cross section of the LPFG induced by high-frequency CO2 l aser puls es. Based on these unique characteristics, we have proposed a novel bend-insensi tive LPFG sensor that could solve the problem of cross-sensitivity between bend and other measurements, a novel torsion sensor that can realize absolute measure ment of twist rate and a load sensor that can achieve simultaneous measurement o f transverse load and temperature using a single LPFG element.
First-order statistical properties of ultrasonic speckles back-scattered from a kind of weak scattering interface
2003, 52 (6): 1438-1443. doi: 10.7498/aps.52.1438
First-order statistical properties of ultrasonic speckles back-scattered from an interface with tiny pints on, which is considered as one kind of weak scatterin g interface, are studied in this paper. Based on four assumptions, theoretical a nalyses indicate that the amplitude of ultrasonic speckles in space is in the fo rm of Rice distribution, and the phase probability density function of the ultra sonic speckles is a compound function of Gauss distribution function and Gauss p robability integral function. When the density of the pits on the interface is v ery high, the amplitude of ultrasonic speckles becomes Rayleigh distributed. To verify the theoretical analysis conclusion, the amplitude probability distributi on of ultrasonic speckles is measured by using a set of experimental systems wit h step scanning controlled by a computer, which is built by the authors. The exp erimental results are in good agreement with the theoretical predicted results. So, the assumptions proposed in this paper are suitable for the theoretical anal yses.
2003, 52 (6): 1444-1449. doi: 10.7498/aps.52.1444
The heat conduction behaviour in a nanofluid fluid medium has many abnormal properties. Combined with the analysis based on microscale heat transfer theory and the physicochemical behaviours of nanofluid, the mechanism of heat conduction in nanofluid has been studied. The effects of nonlinear heat transfer in nanoparticle, micro convection are caused by the Brownian movement of nanoparticles, congregation of nanoparticles, and orderly array of liquid molecules at the interface between the nanoparticle surface and the base fluid.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2003, 52 (6): 1450-1454. doi: 10.7498/aps.52.1450
In this paper, the electron motion in a submillimeter level microhollow cathode discharge(MHCD) is investigated under high pressures by Monte Carlo simulation. Some swarm parameters have been obtained such as the electron density distribu tion in the field direction for a steady state, the energy and spatial distribut ion under different pressures.The result shows that MHCD under high pressures c an reflect in more detail the essence of the 'oscillating' effect of the hollow cathode discharge.When electrons oscillate in MHC,most of them are scattered st ill forward.With increasing pressure,the effect of lateral scattering will exhib it gradually.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2003, 52 (6): 1455-1460. doi: 10.7498/aps.52.1455
Cu-MgF2 nanoparticle cermet films with the copper volume fraction of vol.10%-30% were prepared by rf magnetron co-sputtering deposition and analyzed by x-ray diffraction, x-ray photoelectron spectroscopy and temperature-varying four-wi re technique. Microstructure analysis shows that the cermet films are made of m ainly amorphous MgF2 matrix with embedded fcc-Cu nanoparticles. The a verage si ze of Cu nanoparticles increases from 11.9nm to 17.8nm as Cu content rises fro m vol.10% to vol.30%. The results of electrical conductivity from 50 to 300K sho w that when Cu volume fraction is between 15 and 20%, the film shows a percolati on threshold qCM, and the electric conductivity changes～e ight orders. T he active energies of doping and the intrinsic conductivity of the cermet films and their contributions to the film electrical conductivity are discussed. Based on the percolation theory, the percolation threshold of Cu-MgF2 cerm et film is discussed as well.
Investigation of magnetic properties at low temperatures on permanent magnetic N d60Al10Fe20Co10 bulk metallic glass
2003, 52 (6): 1461-1464. doi: 10.7498/aps.52.1461
The temperature dependence of magnetic properties for Nd60Al10 Fe20Co10 bulk metallic glass is investigated. The re sults indicate that th e Nd60Al10Fe20Co10 bulk metallic gla ss exhibits permanen t magnetic behaviour at room temperature. The coercive force and the shape of hy steresis loops change markedly when temperature decreases. AC magnetic susceptib ility is measured and a peak at about 18K is found. The peak moves torwards high temperatures when the frequency is increased. This indicates that there are spi n glass structures in the bulk metallic glass.
2003, 52 (6): 1465-1468. doi: 10.7498/aps.52.1465
High-quality nc-Si/a-Si:H diphasic films with improved stability were prepared b y using the plasma-enhanced chemical vapor deposition technology. In comparison with typical amorphous silicon, the diphasic silicon films possess higher photoc onductivity (two orders larger than that of the amorphous silicon film) and fair ly good photosensitivity(the ratio of the photo-to dark-conductivity is about 10 4) and higher stability (the degradation of the photoconductivity is less than 10% after 24h long light soaking with 50 mW/cm2 intensity at room te mperature ). In addition, the diphasic silicon film has a better light spectra response in the longer wavelength range. The improvement in photoelectronic properties may be attributed to: the existence of the disorder within the amorphous matrix, whi ch breaks the momentum selection rule in the optical transition and, consequentl y, results in the large light absorption coefficient and high photosensitivity; the improved medium range order and low gap states density. Excess carriers gene rated in the amorphous matrix tend to recombine in the embedded crystallites, wh ich suppresses nonradiative recombination within the amorphous matrix and reduce s the subsequent defect creation.
2003, 52 (6): 1469-1473. doi: 10.7498/aps.52.1469
The magnetic/nonmagnetic p-n junction was prepared by implanting gadolinium into the n-type silicon with low-energy dual-ion-beam epitaxy technology.The magnet ic layer GdxSi1-x shows excellent magnetic properties at r oom temperature. High magnetic moment 10μB per Gd atom is observed, which is interpreted by RKKY mechanism. Magnetic/nonmagnetic p-n junctions show rectifying behaviour, but no magnetoresistance is observed.
2003, 52 (6): 1474-1478. doi: 10.7498/aps.52.1474
A series of solid electrolytes KNb1-xMgxO3-δ (x=0.0—0.3) with an orthorhombic perovskite structure was synthesized under high temperature and high pressure（4.0GPa，870℃）. The effect of Mg-doping on the structure transformation and electrical properties was systematically studied in this paper. The Raman spectra at different temperatures and differential thermal analysis results indicate that the structure of the samples transforms from ferroelectric orthorhombic to tetragonal phase, and finally to paraelectric cubic phase with increasing temperature. Weakening of the coupling effect of A-site cation on BO6 octahedra and the B-site cation contribution to spontaneous polarization, as a result of the Mg2+ doping in KNbO3, leads to th e decrease of Curie temperature.The Curie point of KNb0.85Mg0.15 O2.775,decreasing by about 40℃ in comparison with KNbO3 ,is 392℃.Impedance spectroscopic data show that the conductivity of the samples is ionic, the grai n-boundary effect is very significant, and the conductivity of the samples is de termined mainly by the grain-boundary. Mg-doping increases the oxygen ion conduc tivity of the samples. KNb0.9Mg0.1O2.85 has the highest conduc tivity of 1.2×10-3S/cm at 700℃ in all of the samples,which makes it a kind of promising oxygen ionic conduction materials.
2003, 52 (6): 1479-1483. doi: 10.7498/aps.52.1479
The microscopic structures of the diamond films generated on Si (100) substrates by chemical vapor deposition have been studied by x-ray wide angle diffraction spectroscopy, grazing incidence x-ray scattering spectra, positrons annihilation lifetime spectroscopy, and qualitative software and Positronfit program. The di ffraction x-ray spectra show a structure difference between the near substrate p art (NSP) and near free-surface part (NFP) of the diamond film specimens, which reflect the weak ［111］texture in NSP and the strong［220］ texture in NFP. The positron annihilation lifetime spectroscopy of the specirnens and the analyzing data indicate that the majority of positrons annihilate around 200 ps and 400 p s. The vacancies, vacancy clusters, and voids were found in the film specimens, depending on the processes in which the chemical vapor deposition is generated.
2003, 52 (6): 1484-1487. doi: 10.7498/aps.52.1484
Polycrystalline ZnO films with a good preferred orientation were deposited on sapphire, Si and quartz substrates by rf magnetron sputtering. A 356 nm Ultraviolet (UV) photoluminescence (PL) peak and a 446 nm blue peak were observed at room temperature when excited with 270 nm light. After high-temperature annealing in oxygen, the crystallinity of the films was improved. The intensity of the UV emission increased by 7 and 14 times, respectively, for the films on sapphire and quartz substrates respectively. We conclude that the UV emission originates from the inter-band transition of electrons and the blue emission is due to the transition of electrons from the shallow donor level of the oxygen vacancies to the valence band.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Theoretical studies of submillimeter radiation and near-infrared emission due to excitonic recombination in an asymmetric coupled-quantum-well structure
2003, 52 (6): 1488-1495. doi: 10.7498/aps.52.1488
In this paper the delocalized behaviours of an asymmetric coupled-quantum-well structure (a-CQWS) have been studied and the transfer process of the electrons between the two wells has been analyzed theoretically based on V-type system. We show that an electronic packet of coherent oscillation created by an ultrashort pulse can be viewed as a classical electronic dipole damping oscillator, whose lifetime depends strongly on both the electronic-tunneling transfer time and the carrier-longitudinal optial scattering time.The submillimeter radiative lifetime created by coherent oscillation of an electronic wave packet is related to the oscillation damping rate between the two wells but not to the exitonic recombination rate; the intensity in frequency domain has the Lorentzs profile.It is shown that the transiton frequency of near-infrared radiation generated by the excitonic recombination has a tunable characteristic.This result implys that the high-speed modulator and the tunable source in the near infrared-radiation region can be obtained from the asymmetric double-quantum well structure in the future optical communication.
Study of the current-voltage characteristics of n-on-p junction fabricated by pr oton-implanted molecular beam epitaxial Hg1-xCdxTe
2003, 52 (6): 1496-1499. doi: 10.7498/aps.52.1496
Large area n-on-p structures of p-n junction with different proton implantation doses are fabricated on the moleculer beam epitaxial grown HgCdTe films for mid-infrared wavelength region. Current-voltage characteristics of the p-n junction are measured at 77K. The zero-bias resistance-area product (R0A ) of 312.5Ω·cm2 is obtained when the proton implantation dose is 2×10 15cm-2， and R0A increases to 490Ω·cm2 after ann ealing at low temperatures.
2003, 52 (6): 1500-1504. doi: 10.7498/aps.52.1500
CaCu3Ti4O12 bulk and thin films are prepared su ccessfully by solid-state reaction and pulsed laser deposition (PLD). Dielectric constants ε′ (1kHz,300K) higher than 14000 are found in both types of CaCu3Ti4O12 materials, which is the best result in this system. We first report the c-axis-oriented epitaxial CaCu3Ti4O12 thin film and i ts dieletric properties.Such a high dielectric constant does not depend much upon temperature in the range of 100-300K,showing that this material has high thermal stability.The behaviour of dielectric conductivity σd against frequency can be well ex plained in terms of the hopping mechanism.
2003, 52 (6): 1505-1508. doi: 10.7498/aps.52.1505
MgB2 thick films were grown on metal substrates Ta, Mo and W using th e electrophoresis technique. The scanning electron microscopy and x-ray diffraction show that the grains in the MgB2 thick films are in random orientation wi th their size below 1μm. The onset temperatures of superconducting transition of MgB2/Ta，MgB2/Mo，MgB2/W are observed at 36.5, 34.8 and 33.4K, with the transition widths of 0.3, 1.5 and 2.0K, respectively. The critical current density of th e MgB2/Mo thick film at 5 K and 1T is more than 105 A/cm2. This n ew method provides a great potential for MgB2 in practical applicatio ns.
2003, 52 (6): 1509-1514. doi: 10.7498/aps.52.1509
An analytical formula for the free energy of two coupled π rings is presented.Using the formula, the free energy is calculated for equidirectional spontaneous magnetization and inverse spontaneous magnetization of the two coupled π rings. We found that the whole system has a lower free energy in the latter case.
2003, 52 (6): 1515-1519. doi: 10.7498/aps.52.1515
Quarter wave resonator (QWR) is the best choice of the acceleration cavity for heavy ion superconducting accelerator. Using dc bias-voltage sputtering system, w e can sputter niobium films of several microns on the oxygen-free high-conductiv ity copper(OFHC) substrate. Good superconducting properties and acceleration pro perties of the cavity can be obtained. But compared with niobium cavity, it has very low Q and Eacc. Niobium nitride (NbN) is a good superconducto r, and it has a higher superconducting transition temperature (Tc) th an pu re niobium. Through experiments, we find that the Tc transition point of n iobium films rises to about 9.6K by using NbN interlayer between OFHC substrate and niobium films. So using this method can improve the superconducting properti es and thus the acceleration properties.
2003, 52 (6): 1520-1523. doi: 10.7498/aps.52.1520
Structure, magnetic and transport properties of polycrystalline Nd0.5 Sr0.4Pb0.1Mn1-xFexO3 Com pounds were experimentally studies. Single-phase samples were obtained in the range x=0.0—0.1 of Fe Content. There are no appreciable structure changes for the introduction of Fe. Mn-site doping favous a reduction of magnetic/resistive transport, at a rate of ～16K for 6% Fe, and an elevated resistivity. Metal-insulator transition disappears when the content of Fe exceeds ～0.08. The enhanced doping effects in Nd0.5Sr0.4Pb0.1Mn1-xFexO3 can be ascribed to the presence of Fe, which influences the concentration of mobile electron eg and restrain the double exchange interaction in the compounds.
2003, 52 (6): 1524-1528. doi: 10.7498/aps.52.1524
Ceramic samples SrBi4-xLaxTi4O15 (x =0.00, 0.10, 0.25, 0.50, 0.75, 1.00), have been prepared by solid-state reaction method. T heir structure was analyzed by x-ray diffraction, and their dielectricity and fe rroelectricity were measured. It is found that La-doping does not change the cry stal structure of SrBi4Ti4O15. The remnant pola rization (2P4) in creases at first, then decreases with the increase of La content. The 2P4 reaches a maximum value of 24.2 μC·cm-2, when x is 0.25. The c oerc ive field of SrBi3.75La0.25Ti4O15 is 60.8 kV·cm-1 . The 2P4 increases by about 50% and the Ec decrease s near 25%, compa red with these of SrBi4Ti4O15. Obviously, the f erroelectricity of SrBi 4Ti4O15 is improved by lanthanum doping. The te mperature of p hase transition (Tc) decreased with La cloping. The Tc of SrBi3.75La0.25Ti4O15 is 451 ℃. When x=0.75 and 1.00, the SrBi4-xLaxTi4O15 exhibit the typical characteristics of relaxor ferro electrics.
2003, 52 (6): 1529-1532. doi: 10.7498/aps.52.1529
A simple method for measuring the optical non-homogeneity and growth layers in t he LiNbO3∶Fe crystal is reported. We can compute the change of refra ctive ind ex Δne at different positions in the crystal according to the distan ce be tween e—o light-spots, which vary with the change of the position of incident l ight-spot in crystal. Furthermore we can obtain the non-homogeneity and determin e the position and thickness of the growth layers in the crystal.
2003, 52 (6): 1533-1539. doi: 10.7498/aps.52.1533
The absorption and emission properties of the concentrations and thickness of Yb3+-doped phosphate glasses have been investigated. The integrated cro ss section, absorption cross section, emission cross section, the spontaneous emission probability, and the effective line width of fluorescence of Yb3+- doped phosphate glasses were determined. The effect of the radiation trapping on spectroscopic properties was discussed. It was found that the effect of radiation trapping increases remarkably with the concentration and thickness of Yb3+-doped phosphate glasses. Radiation trapping causes significant lengthening of the measured fluorescence lifetime τf which is longer than the radia tive lifetime τrad. The error in measuring the fluorescence lifetime unde r low Yb3+ ion concentration (0.2mol%Yb2O3) is 3 0% and the error is 43% under high Yb3+ ion concentration (6mol%Yb2O3 ) 6mol%. Radiation trapping also significantly increases the effective line width Δλeff. I t will be increased by 14% and 30% larger under low and high Yb3+ ion concentration respectively.
The Mo-doped titania exhibits a visible broadband emission under a 978 nm laser diode excitation. The luminescence has been assigned to the transitions from the excited states 3T1, 3T2 to the ground state 1A1 of the ［MoO4］2- radical. In TiO2∶Mo system, the p ower dependence of the upconversion-luminescence intensity exceeds a quadratic dependence, and the time evolution of the upconversion luminescence after the onset of continuous wave excitation is characterized by a rise time of 63 ms. These properties show the typical fingerprints of a photon avalanche. No luminescence was observed from the sample when excited with a pulsed laser (1064 nm) from a Nd∶YAG or a pulsed Raman-shift laser (953.6nm) pumped by a second harmonic of the Nd∶YAG. Regardless of the energy mismatch between the pulsed laser and the continuous wave diode laser, another reason may be that the duration time of a single laser pulse (10 ns) is much shorter than the rise time of the photon avalanche. The fluorescence “transfer function” theory is used to study the luminescence dynamics, which provides a good description of the experimental data.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2003, 52 (6): 1545-1548. doi: 10.7498/aps.52.1545
Heat-electric properties at high temperatures were measured on tungsten trioxide (WO3) ceramics doped with Tb4O7 prepared by c onventional solid-sintering method. The results indicated that a phase transition occurred at 350℃ on heating and 270℃ on cooling with a large thermal hysteresis of about 80℃. And the samples can provide an electric energy output at a constant temperature of 500℃, which cannot be explained by the known thermoelectric or pyroelectric effect. We regard it as a new heat-electric effect, by which a new way of converting heat energy to electric energy may be found.
2003, 52 (6): 1549-1553. doi: 10.7498/aps.52.1549
Near-stoichiometric Er∶LiNbO3 has many properties superior to the co ngruent one and has aroused extensive interest. It was obtained by the technique of vapor transport equilibration (VTE), its optical properties, including OH- absorption spectra, transmission spectra, emission spectra and the position of absorption edge were studied. The higher transmittance, the narrower of the peak width, the “blueshift" of the optical absorption edge, as well as the significant reduction of the OH- absorption band are indicative of the VTE treatment having brought the crystal closer to the stoichiometric composition. We also observed the increase of Er3+ luminescent intensity, and predicted that the VTE treatment must lead to the increase of fluorescence lifetime. The possible modification of materials in amplifier, self-frequency doubling laser and waveguide laser etc were expected.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2003, 52 (6): 1554-1560. doi: 10.7498/aps.52.1554
microtubules are the important components and function units in cytoskeletal, an d filled with water inside it. In this paper, by using the quantum field theory, we study the interactions between the electric dipole field of water molecules confined within the hollow core of microtubules and the quantized electromagnetic radiation field, and the characteristic of collective electromagnetic radiation raised from water's electric dipoles. In addition, the coupling between the water molecule system confined within microtubules and the surrounding heatbath is discussed.