Vol. 49, No. 10 (2000)
2000-05-20
GENERAL
2000, 49 (10): 1901-1903.
doi: 10.7498/aps.49.1901
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In this paper, a system of first order ordinary differential equations is expressed in the form of first order Lagrange equations.The determining equations of L ie symmetries are established by the invariance of the ordinary differential equ ations under the infinitesimal transformations. The condition under which a Lie symmetry can lead to a conserved quantity is obtained and the form of the conser ved quantities is given.
2000, 49 (10): 1904-1908.
doi: 10.7498/aps.49.1904
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Some soliton solutions for a class of nonlinear coupled equations are obtained by double parameter hypothesis. Many well-known equations in physics are special cases of the coupled equations presented in this paper. Some incorrect conclusio n in the literature are corrected.
2000, 49 (10): 1909-1911.
doi: 10.7498/aps.49.1909
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In this paper we present the numerical solutions of neutral atoms with attractive interaction in a harmonic trap. The calculated result shows the bistability curve of the number of condensate atoms versus the energy eigenvalues. The maximum number of atoms in and attractive Bose-Einstein condensate deduced hereby is in agreement with the experimental on the whole.
2000, 49 (10): 1912-1918.
doi: 10.7498/aps.49.1912
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The vector representation of density matrix is given in this paper. Any density matrix can be expanded in a real linear Hilbert space. The criteria for insepara bility of mixed states can be expressed in the geometrical picture. Such express ion is concise and perceptible. The neighborhood of the maximal mixed state is analyzed and a stronger result about the volume measure of the neighborhood is obtained.
2000, 49 (10): 1919-1921.
doi: 10.7498/aps.49.1919
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In this paper the design of observers of a class of chaotic systems is discussed. By means of scalar nonlinear signal one can construct a control law to implement the synchronization between the investigated chaotic system and its observer.
2000, 49 (10): 1922-1925.
doi: 10.7498/aps.49.1922
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A new nonlinear feedback following controlling method of chaotic systems is presented to stabilize chaotic systems and follow a deteministic motion. Theory and experiments show this controlling method is strongly robust.
2000, 49 (10): 1926-1932.
doi: 10.7498/aps.49.1926
Abstract +
A new traffic flow cellular automaton (CA) model situated between Nagel-Schrecke nberg (NS) type and Fukui-Ishibashi (FI) type is defined and studied. This new m odel adopes the gradual acceleration scenario for all cars as NS model and the s tochastic delay scenario for only the car with speed limit as FI model. It is pr oved that the fundamental diagram of the average traffic flow speed as the funct ion of the car density for the new model is exactly the same as for FI model. Th is means that if the acceleration scenario of the FI traffic flow model in which a car may increase in velocity rapidly from zero to the velocity limit M or the maximum velocity permitted by empty spacing ahead, is changed to a gradual way in which the velocity of a car may increase by only one unit at most in one time step, the asymptotic steady state behavior of traffic flow will not be changed by interaction between cars and the self-organization evolution of the traffic flow.
2000, 49 (10): 1933-1937.
doi: 10.7498/aps.49.1933
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A brief description of the systematic theory for X-ray transmission through a cy linder capillary is proposed. Based on the description, a calculation model for X-ray transmission through a cylinder capillary is suggested and a corresponding computer program is worked out. The numerical results of X-ray transmission thr ough a cylinder capillary given by the computer program fit the corresponding ex perimental results very well.
NUCLEAR PHYSICS
2000, 49 (10): 1938-1946.
doi: 10.7498/aps.49.1938
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The electromagnetic dissociations (EDs) of 60 A GeV16O in nuclear emu lsion is investigated with high statistics for the first time. It is found that the interaction cross section for EDs increases with increasing beam energy, and the charge distribution of projectile fragments is the same as the results at 2 00 A GeV, but the production probability of projectile fragments with charge 3≤ Z≤5 is smaller than that of the results at 200 A GeV. These results can be expl ained by use of the Weizscker-Williams method for calculating the EDs contributi ons. The percentage abundances of various decay modes for EDs at 60 A GeV is the same as the results at 200 A GeV,but different from the results at 14.6 A GeV. The EDs of 60 A GeV16O is mainly caused by the giant dipole and quadr upole resonance of E1 and E2 and by the quasi deuteron effect, which can be qual itatively explained by the multiplicity distribution of projectile fragmentation proton in EDs. The multiplicity distribution of α fragments in EDs and nuclear events have different functional forms. This difference may be a consequence of the different reaction mechanisms involved in EDs and nuclear events.
2000, 49 (10): 1947-1952.
doi: 10.7498/aps.49.1947
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The neutron diffusion equation is usually solved in a symmetric region.For a non-rectangular symmetric region,the nonphysical singular problem arises when the c onventional method of deriving nodal solution is employed.In this paper,a new me thod based on both symmetries of the problem and an analytic representation of t he nodal flux distribution is presented.The method is effective for the solution of multigroup diffusion equation in the symmetric region,especially for the non -rectangular problem.It can be applied in 2-D or 3-D problems and its applicatio n in hexagonal geometry is introduced as an example.The only approximations used in deriving the method are the treatment of unknown functions.The efficiency of the proposed method is demonstrated by results of various 2-D and 3-D benchmark problems using the GTDIF-H code.
ATOMIC AND MOLECULAR PHYSICS
2000, 49 (10): 1953-1958.
doi: 10.7498/aps.49.1953
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A fully relativistic multiconfiguration Dirac-Fock method with Breit and QED cor rections is used to calculate the spin-forbidden 2s2 1S0—2s2p 3P1 (Z=10—103) transition energy level se parations and transition probabilities for the Be-like ions. The results are in good agreements with recent experimental data and other theoretical values. The results show that the spin-forbidden transition probabilities are in corresponde nce with these of E1 transitions and cannot be ignored in the laser plasma of hi gh temperature in ICF and MCF fusions.
CLASSICAL AREA OF PHENOMENOLOGY
2000, 49 (10): 1959-1964.
doi: 10.7498/aps.49.1959
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The light intensity distribution near the fiber probe of the Transmission Scanning Near Field Optical Microscopy(SNOM) was calculated by the model of R.D.Grober.The resolution,transmission depth and transmittance of the light intensity were discussed.The imaging process of excited biological fluorescent molecules was simulated,and it was found that the dipole direction of fluorescent molecules and he polarization of incident light influenced the detected signals.Both the pol arization direction of incident light and the dipole direction of fluorescent mo lecules would affect the fluorescent molecules imaging.
2000, 49 (10): 1965-1968.
doi: 10.7498/aps.49.1965
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The enhanced ionization(EI) behavior of multiatomic molecular ions is studied in intense laser fields by the numerical solution of time-dependent Schrodinger eq uation with the symmetrical splitting of the short-time exponential propagator a nd fast fourier transformation(FFT).The influence of the intensity and the frequ ency of the laser on EI is given.With the laser frequency increasing,the criticl a value of bond length for EI decreases and the ionization probability decreases too.The ionization probability increases with increasing laser intensity.The EI disappeares when the intensity reaches a certain value.
2000, 49 (10): 1969-1972.
doi: 10.7498/aps.49.1969
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It is predicted in this paper that incoherently coupled screening-photovoltaic s oliton pairs are possible in biased photovoltaic-photorefractive crystals under steady-state conditions.These soliton pairs are established by the solitary beam s which have the same polarization,wavelength,and are mutually incoherent.The sc reening-photovoltaic soliton pairs can be considered as the united form of scree ning soliton pairs and closed-circuit photovoltaic soliton pairs.They reduce to screening soliton pairs in the absence of photovoltaic effect,whereas they becom e photovoltaic soliton pairs under the closed-circuit condition when the bias fi eld is not applied.
2000, 49 (10): 1973-1977.
doi: 10.7498/aps.49.1973
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Concentric diffraction rings with bright center in the far field and dark center in the near field of the probe beam were experimentally observed when a strong pump laser beam (526nm) and a weak probe laser beam (632.8nm) cross under the no nlinear medium film (Polypyrrylarylenemethine/polyvinyl film).Based on Fresnel-K irchhoff diffraction integral equation,this phenomenon can be explained by the d iffraction effect of the probe beam from the laser-induced phase-hole in the non linear medium caused by the pump beam.The numeric calculations give good agreeme nt with the experimental results.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2000, 49 (10): 1978-1981.
doi: 10.7498/aps.49.1978
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In ion cyclotron resonance heating,a 2-dimension antenna model is used for the c avity loop antenna with comparatively complex bounding conditions,neglecting the influence of loop antenna parallel component for simplicity.The detailed calculation process of a 3-dimension antenna model is given in this paper.This model i s closer to the practical antenna,its calculation results can be used for the re ference of antenna design.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2000, 49 (10): 1982-1987.
doi: 10.7498/aps.49.1982
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The direct method was applied to the image processing for [001] simulated high-r esolution electron microscope images of protein streptavidin.The image deconvolu tion was carried out for two images of different defocus values such that the st ructural information loss due to the zero crosses of contrast transfer function could be compensated.It is shown that the determined defocus values based on two images combined are closer to the true ones than those based on a single image. The phase extension was also carried out for this protein.The initial structure factors were calculated from the theoretical structure model,with the phases of 0.30nm resolution and amplitudes of 0.25nm resolution.Both the deconvoluted imag e of 0.30nm resolution and projected crystal structure of 0.25nm resolution obta ined are in agreement with the projected potential distribution maps of theoreti cal structure model.
2000, 49 (10): 1988-1994.
doi: 10.7498/aps.49.1988
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XAFS technique has been used to quantitatively determine the local structure evo lutions of ultrafine Ni-P and Ni-Ce-P amorphous alloys prepared by chemical redu ction during the annealing process.Using an asymmetric atom distribution functio n model of convolution of a Gaussian function PG and an exponential f unction PE for XAFS data analysis,we obtained that the average bond l ength Ｒj,coordination N,thermal disorder factor σT,and s tatic disorder factor σS for the Ni-Ni first neighbor shell are 0.27 1nm,10.0,0.0060nm and 0.028nm in the Ni-P and 0.271nm,10.6,0.0070nm and 0.030nm in the Ni-Ce-P initial samples,respectively.It indicates that the σS is rather large and about three times larger than that of σT.The Ni -P sample crystallized under the annealing temperature of 573K,while the crystal lizing temperature of Ni-Ce-P sample is about 100K higher.The result suggests th at the thermal stability of Ni-Ce-P sample is significantly increased by the add ition of 2% Ce element.After being annealed at 773K,both Ni-P and Ni-Ce-P sample s are fully crystallized as metallic Ni and an amount of crystalline Ni3P.Furthermore,we have found that the static disorder σs of Ni-Ni coordination shell is 0.011nm for the Ni-P and still larger for the Ni-Ce-P samp les annealed at 773K,despite their radial distribution functions around Ni atoms are similar to that of Ni foil.It implies that the Ni lattice obtained from the crystallized Ni-P and Ni-Ce-P amorphous alloys is significantly distorted by th e interaction of P element.
2000, 49 (10): 1995-2000.
doi: 10.7498/aps.49.1995
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Four new bistable twisted nematic liquid crystal display (BTN-LCD) modes with no n crossed polarizers are developed for the first time. Most of them present high contrast ratio and high transmittance with high stability; some display between black and white states, the performance reaches the level of twist nematic liqu id crystal display device. They are better than those modes using crossed polari zers presented before.
2000, 49 (10): 2001-2006.
doi: 10.7498/aps.49.2001
Abstract +
The site occupancies of orientational angle 98° and 38° of C60 mole cules versus temperature is investigated by extremal dynamic model in the temper ature range between order-disorder phase transition and glassy transition.The oc cupancy of orientational angle 38° calculated by the model are precisely coinci dent with reported experimental values at T=85K,90K and 260K,respectively.The mo re precise agreement and second-order differential to temperature of site occupa ncy predict that the glassy transition point is at 84K.The relaxation process of two orientational states from non-equilibrium deduced by the new model is relat ed to the non-exponent factor β in KWW equation,and overall relaxation of C60 crystal is mainly attributed to the relaxation of the lowest energy le vel.Considering two energy levels and their energy difference,the calculated β value 0.9495 is near the experimental value 0.94±0.02.
2000, 49 (10): 2007-2010.
doi: 10.7498/aps.49.2007
Abstract +
The changes of defects in PbWO4 crystal caused by La dopant have been studied by means of positron annihilation lifetime and X-ray photoelectron spec trum (XPS).The results show that La dopant enhance the concentration of lead vac ancy (ＶPb) which can be described as the positron capture center in PbWO4 crystal,and lead vacancy will furthermore introduce low-valent oxygen center.We discuss the mechanism of La doped in PbWO4,and consi der that oxygen vacancy is restrained by doping of La,while lead vacancy density is increased by La dopant.
2000, 49 (10): 2011-2016.
doi: 10.7498/aps.49.2011
Abstract +
In this paper we determined 6 ordered structure types and 7 perfect ordered structures of hexagonal honeycomb lattice by using concentration-wave theory.And we proposed an explanation for the ordered structures of O atoms absorbed by (0001) surfaces of Ru crystal and Na ions in intercalation compound Nax TiS 2.
2000, 49 (10): 2017-2021.
doi: 10.7498/aps.49.2017
Abstract +
We have studied the semiconducting property of the Y1Ba2Cu 3O7-δ(δ≥05, abbreviated YBCO) thin film which is depo sited on Si substrate and the characteristics of the bolometer using the film to detect IR radiation. We measured TCR merit and Hall coefficient and analyzed th e microstructure and the responsive characteristics of the YBCO semiconducting t hin film through XRD and Raman spectrum. We believe that the thin film is a new sensing material which can be applied to uncooled infrared focal plane bolometers.
2000, 49 (10): 2022-2026.
doi: 10.7498/aps.49.2022
Abstract +
Exchange biasing and coercive field of molecular-beam-epitaxy-grown Fe/Fe50 Mn50 bilayers have been investigated by Surface Magneto-optical Kerr Effect(SMOKE) and ferromagnetic resonance measurements. The results indica te that there is no exchange biasing when the thickness of antiferromagnetic lay er is less than 55nm. The exchange biasing appears when the thickness of antif erromagnetic layer is greater than 55nm，and the maximum value is reached when the thickness is about 7nm. Exchange biasing and coercive field decrease with f urther increase of the thickness of the antiferr-magnetic layer. The ferromagnet ic resonance measurement results show that there exists unidirectional anisotrop y. The above results are discussed in the paper.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2000, 49 (10): 2027-2032.
doi: 10.7498/aps.49.2027
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In our calculations of lattice vibration, one acoustic and three optical branche s were found to compose the phonon vibrating spectrum. Some isolated modes with frequencies lying outside the continuum branches aise under the defect states. These localized modes result in the sharp peaks in the infrared absorption and Raman spectra.
2000, 49 (10): 2033-2036.
doi: 10.7498/aps.49.2033
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The nonlinear behavior of two kinds of arrays of two coupled quantum-dot cells w as examined. Each square cell composed of four quantum dots in the corners conta ins two electrons and couples with the neighboring cell by Coulomb interaction. The electrons in one cell tend to occupy antipodal dots which results in a cell “polarization”. In steady-state regime, we have investigated the evolution of the polarization of one cell under the switch of the polarization of the other c ell. Our results demonstrated that the response of the polarization of one cell to that of the other cell exhibits a good nonlinear characteristics with suitabl e parameters.
2000, 49 (10): 2037-2040.
doi: 10.7498/aps.49.2037
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Using frequency-dependent capacitance spectroscopy, we investigate the charging dynamics of silicon quantum dots embedded in oxide matrix through a SiO2/Si-quantum dots/SiO2/Si-substrate tunnel capacitor. Two resonance peaks both for capacitance and conductance in the inversion region are observed at room temperature, being attributed to the direct tunneling between the condu ctance band ofSi-substrate and the one-and two-electron ground-state level of th e Si quantum dot. The Coulomb charging energy of the dots is extracted from the experimental results.
2000, 49 (10): 2041-2046.
doi: 10.7498/aps.49.2041
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Hydrogenated amorphous carbon films were deposited using ECR plasma with benzene as carbon source at varying substrate temperature. The effects of deposition te mperature on the resistivity and the intensity of electric break down have been investigated. The results show these properties depend on their growth condition s. The experiment results are further investigated using Raman spectra analysis.
2000, 49 (10): 2047-2050.
doi: 10.7498/aps.49.2047
Abstract +
We have measured the resistance of some Bi2Sr2CaCu2O8 superconducting single crystals along ab plane and the c axis. In some single crystals, a remarkable resistivity anomaly near the superconduct ing transition temperature is observed in the ab plane. The peak is suppressed a nd vanishes gradually with increasing applied magnetic field (>100Gs) or transpo rt current. We proposed that the resistance peak is a quasi-reentrant behavior d ue to the inhomogeneous distribution of the superconducting phase.
2000, 49 (10): 2051-2054.
doi: 10.7498/aps.49.2051
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A dc-SQUID planar gradiometer has been fabricated with YBa2Cu3O7-δ step-edge Josephson junctions on a 10mm×10mm single crysta l SrTiO3 ［100］ substrate. The gradiometer has a pair of pickup loop s with an area of 33 mm2 and the baseline of 45mm. The system opera tes well in unshielded environment. A rejection of common mode fields of 14×1 02 in all directions and a field gradient sensitivity (white noise) b etter than 8pT/cmHz at 77K have been achieved.
2000, 49 (10): 2055-2058.
doi: 10.7498/aps.49.2055
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X-ray diffraction and photoemission measurements have been carried out for Bi2Sr2CaCu2-xSnxO8+δ system. With Sn doping, lattice parameters a and c change somewhat, O1s and Cu2p core le vels shift differently in binding energy. From the experiment, we can deduce tha t the Sn ions are mostly in divalent state at small amount of doping, and in tet ravalent state at high doping level. Doping with Sn may have less influence on t he superconductivity than that with other elements. The results support the conc lusion that chemical environment plays a major role in the shifts of all core le vels in the high Tc superconducting samples.
2000, 49 (10): 2059-2065.
doi: 10.7498/aps.49.2059
Abstract +
The polar Kerr rotation, Kerr ellipticity and optical constant n and k change regularly with the increase of Mn doping in Pt layer of Pt/Co multilayers. Through calculation and analyses, in heavy Mn doping the change of the Kerr rotation is due to the off-diagonal elements of dielectric tensor. However, in light Mn dop ing the change of Kerr rotation results from the change in the magneto-optical a nd optical constants. The enhanced magneto-optical Kerr rotation is due to the e nhancement of Pt spin-orbit coupling. The variation of Pt spin-polarization resu lts in the change of diagonal and off-diagonal elements of dielectric tensor.
2000, 49 (10): 2066-2071.
doi: 10.7498/aps.49.2066
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In this article,the electrochromic (EC) properties of R.F.deposited NiOx thin films are investigated.It was found that non-stoichiometric NiOx(x>1) thin films which are rich in O element have EC activation.In NiOx thin films exist both Ni3+ and Ni2+ ions.The insert ion of H+ ions and their sequential occupation of Ni vacation render t2g energy levels of Ni3＋ ions completely filled.Thus,Ni3+ is reduce to Ni2+ ions and the NiOx films get light transparent.On the contrary,the extraction of H+ ions from NiO x films will produce vacancies in the t２g energy levels o f Ni２＋.Ni2+ ions are oxidized to Ni3+ ions,wh ich makes NiOx films absorb light.The film is then colored.
2000, 49 (10): 2072-2077.
doi: 10.7498/aps.49.2072
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Thermoluminescent 3D spectra of MgSO4 doped with Dy and Mn,P,Cu were measured.It is observed that the spectral wavelengths of MgSO4:Dy are related to the energy transitions of Dy3+ ions which play the role o f luminescent centers.The glow peaks at 140℃ and 190℃ about 660nm broad wavele ngth band were observed in MgSO4 doped with Mn.It means that Mn promo tes to form the new luminescent centers.When MgSO4 was co-doped with Dy and Mn,the main glow peak occurred at 380℃ in 480nm and 580nm wavelengths an d the glow peaks in 480nm and 580nm below 300℃ and all glow peaks in 660nm are strongly suppressed.The emission spectra of the MgSO4:Dy,Mn phosphor show the characteristic wavelengths of Dy3+ ions.Therefore,Dy3+ ions remain the major luminescent centers and Mn plays an important role f or energy transfer to the Dy ions in the MgSO4:Dy,Mn phosphor.Compari ng the 3D glow curves between MgSO4:Dy and MgSO4:Dy,P show s that the 260℃ glow peak of MgSO4:Dy shifts to 283℃ with high inte nsity while the temperature of glow peak at 360℃ remains unchanged.The relative intensities of glow peaks between 480nm band and 580nm band have been altered w hile the temperature of 283℃ glow peak is unchanged after MgSO4 was codoped with Dy and P,Cu.
2000, 49 (10): 2078-2082.
doi: 10.7498/aps.49.2078
Abstract +
In this article,we studied the thermoluminescence of pure PbWO4 and P bWO4:Y above room temperature (30℃—300℃).We found that Y3＋-doping reduces the intensity of thermoluminescence of PbWO4 and moves the peaks of thermoluminescence to higher temperature after γ-ray irradia tion about 1Mrad dose,which can improve the stability of PbWO4 lumine scence.We also calculated the parameters of the traps,namely the depth of traps, frequency factor and the time of release from the traps at 300K.Visible light ca n also influence thermoluminescence.The intensity of thermoluminescence below 24 0℃ increased after blue and green illumination for all samples.Furthermore,visi ble light can induce new thermoluminescence peaks in some samples,which is cause d either by that the carriers released by visible light are subsequently retrapp ed by some shallower traps,or the visible light illumination may possibly create new types of traps.
2000, 49 (10): 2083-2088.
doi: 10.7498/aps.49.2083
Abstract +
The construction of an organic microcavity with an organic light-emitting thin f ilm sandwiched between a porous silicon Bragg reflector and a silver film is dem onstrated.The peak widths of the PL spectra are greatly reduced from 83nm to 4nm as compared with those measured from non-cavity structures.The off-resonant opt ical modes are highly depressed.As is always observed from an optical microcavit y,the peak intensity is enhanced,and the peak position shows a blue shift with i ncreasing exit angles.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2000, 49 (10): 2089-2093.
doi: 10.7498/aps.49.2089
Abstract +
The optical absorption properties of BaO semiconductor thin films deposited by v acuum evaporation were measured when a vertical electric field was applied on th e surface of the thin films.Enhanced absorption in the near-ultraviolet band was observed.The absorption was increased with the increased intensity of applied e lectric field.Theoretical analysis indicates that the energy-band edges of BaO s emiconductor become bent on the application of electric field,and there is an in creased probability for electrons in the valence band to tunnel through the forb idden gap according to the quantum-mechanics.As a result,it becomes possible for the photons with energy less than Eg to be absorbed by the electrons ,and which leads to the enhanced photoabsorption of BaO thin films in the near-u ltraviolet band.Franz-Keldysh effect and Stark effect were used to explain the e lectroabsorption spectrum when metal oxide semiconductor was excited by the phot ons with energy less or more than Eg.
2000, 49 (10): 2094-2100.
doi: 10.7498/aps.49.2094
Abstract +
The wetting behavior of molten GaSb drops on the substrates of GaP,BN or GaAs in space has been investigated using Chinese recovered satellite.The interaction at the interface of the molten drop and the substrate has been analyzed and compared with the results on the earth.The experiment results show that the gravity has an effect on the wetting behavior of GaSb molten drop.The contact angle of GaSb drop with GaP and BN substrates in space is larger than that on the earth.The morphology of the interface between the concreted drop and the substrate indicates that on the earth the interaction at the liquid/solid interface is strong and a wider transition region exists.It is concerned that the gravity convection is of benefit to the transfer of matters.The experiment results also show that the morphology of the samples concreted in space is more uniform than that on the earth.
2000, 49 (10): 2101-2105.
doi: 10.7498/aps.49.2101
Abstract +
The ethylene (C2H4) adsorbed on Ru(1010) surface has been studied by X-ray photoelectron spectroscopy (XPS),thermal desorption spectroscop y (TDS) and ultraviolet photoelectron spectroscopy (UPS).The results show that e thylene absorbs in molecular state on Ru(1010) surface stably below 200K.The deh ydrogenation of ethylene occurs at 200K.The main product of the dehydrogenation of the absorbed ethylene is the acetylene (C2H2). After th e dehydrogenation of the absorbed ethylene,the C1s shifts 0.3eV to low binding e nergy level,and the binding energies of σCC and σCH bond have an increase of 0.5eV and 1.1eV respectively.
LETTERS
2000, 49 (10): 2106-2108.
doi: 10.7498/aps.49.2106
Abstract +
We have demonstrated a diode-pumped Q-switched Nd:YVO4 laser that pro duced ultraviolet output at 266nm by using BBO single pass fourth harmonic gener ation.When the incident pumping power was 7.9W,we obtained 63mW output and IR-UV energy conversion as great as 11% at 12.5kHz repetition rate with per pulse ene rgy of 5μJ and peak power of 252W.
2000, 49 (10): 2109-2112.
doi: 10.7498/aps.49.2109
Abstract +
CeNiSn is an interesting heavy fermion compound,with its ground state being a Kondo insulator.The effect of the substitution of Ni by Cu on the specific heat of CeNi1-xCuxSn polycrystal samples is studied through the m ethod of chemical element substitution.A series of samples (x=00,0.02,0.06,0.0 6) were prepared with an electric arc furnace in the atmosphere of flowing high purity argon gas.X-ray powder diffraction analysis shows that all the final samp les have single-phase structure,and that,with the increase of the substitution a mount of Ni,the crystal parameters of the samples become larger.The specific hea t measurements were performed with an adiabatic colorimeter.The results indicate that the doping of Cu increases the specific heat at low temperature,and that t he V-shape gap is gradually suppressed.The physical mechanism may be that the do ping of copper brings about the Kondo lattice discorder and the increase in 3d e lectrons.
