bluuebunny/crossref_metadata_2025 huggingface dataset:
CRYSTALLOGRAPHY OF SPIRAL LATTICES
Authors: RIVIER N.
Published: November 2004

Spiral lattices, beautifully illustrated in composite flowers such as daisies and discussed in a recent letter by Bursill, Peng and Fan, have concentric crystalline grains separated by quasicrystalline grain boundaries. They are generated by a simple algorithm parametrized by one golden (or noble) angle. The topology of the patterns and their crystallographic properties (floret shape, lattice planes) are set by Voronoi construction. Golden or noble angle, and thus Fibonacci or Lucas numbers of visible spirals in each grain, correspond to maximal uniformity of the pattern so that their ubiquity in nature is the consequence of a variational principle. Existing results are reviewed here, which answer some questions raised by Bursill et al.
SUPERCONDUCTING Bi-Sr-Ca-Cu-O THIN FILMS PREPARED BY THE PULSED-LASER EVAPORATION
Authors: ZHANG F.M. , ZHANG Y.C. , GU S.J. , ZHOU Y.L. , CHEN Z.H. , YANG B.Y. , YUAN S.L. , WANG W. , ZHENG G.G. , ZHENG J.Q. , GUAN W.Y.
Published: November 2004

We report here the preparation of the superconducting Bi-Sr-Ca-Cu-O thin films on SrTiO 3(100) substrates by a Nd:YAG laser, which provides laser pulses with wavelength of 1.06µm and pulse width of 200ns. After the heat treatment at 850°C for half an hour in oxygen flow, the samples exhibit superconductivity with the zero resistance at 66.8K and the onset temperature around 84K. X-ray diffraction analyses show that the samples have the preferred orientation with the c-axis perpendicular to the substrate.
MODEL FOR OXYGEN ABSORPTION AND STRUCTURAL PHASE TRANSITION IN YBa2Cu3O7−y
Authors: VAREA C. , ROBLEDO A.
Published: November 2004

We reproduce, quantitatively, the observed dependence with temperature and O 2 partial pressure of the ordering of oxygen and the concommitant structural transition in YBa 2 Cu 3 O 7−y by means of a layered oxygen lattice gas model in equilibrium with an external source of O 2. The free energy considers, in addition to Cu -mediated oxygen-oxygen interactions, the elastic energy of the crystal. Depending on the coupling between these two terms the transition may turn into 1st order and further ordering along the Cu-O chains may appear for low oxygen content.
MAGNETIC FLUX QUANTIZATION EFFECTS IN DISORDERED BISMUTH
Authors: RAJASEKHARAN K. , BOUGHTON R.I. , YIN FANG-FANG , SUMANASEKERA GAMINI
Published: November 2004

Measurements have been carried out on the oscillatory part of the low field magnetoresistance of thin disordered bismuth films. Observations of the flux quantization oscillations and their harmonics yield values for the electron diffusion length in this material, Lϕ. The results are discussed in terms of the implications of the weak localization theory of Altshuler, Aronov and Spivak.
DEFORMATION POTENTIALS IN WURTZITE-TYPE SEMICONDUCTORS
Authors: HERNÁNDEZ-CABRERA A.
Published: November 2004

A simple tight-binding scheme gives satisfactory results for the deformation potentials of wurtzite-type semiconductors by connecting them with the interactions in the unperturbed semiconductors.
EFFECT OF ELECTRON IRRADIATION ON HIGH Tc SUPERCONDUCTORS
Authors: SWELGARD E.L. , BUSKIRK F.R. , NEIGHBOURS J.R. , MARUYAMA X.K. , DRIES L.J. , HUANG C.Y. , JUNGA F.A. , HOR P.H. , MENG R.L. , CHU C.W.
Published: November 2004

High T c bulk superconductors, YBa 2 Cu 3 O 6.7 and GdBa 2 Cu 3 O 6.7, were irradiated with 67.5 MeV electrons at dose levels from 0.3 Mrad to 150 Mrad. Resistance versus temperature data show little change in T c after irradiation but significant structural degradation was observed.
TRANSPORT AND LOW FIELD MAGNETIC PROPERTIES OF HIGH TcBi2CaSr2Cu2O8−δ AND Tl0.8Ca2Ba2Cu3O8+δ COMPOUNDS
Authors: TAI M.F. , HSU S.W. , KU H.C. , WANG W.N.
Published: November 2004

Electrical resistivity, low field diamagnetic susceptibility (constant field-cooled in various magnetic fields) and low field magnetization measurements on new high T c superconducting copper oxides Bi 2 CaSr 2 Cu 2 O 8−δ (2122) (T c =89 K ) and thallium-deficient Tl 0.8 Ca 2 Ba 2 Cu 3 O 8+δ (0.8,2,2,3) (T c =117 K ) were reported. Meissner diamagnetic signal decreases with increasing magnetic field of these new superconducting copper oxides.
SUBSOLIDUS PHASE RELATIONS OF Nd2O3-BaO-CuO SYSTEM AND SUPERCONDUCTIVITY OF Nd1+xBa2−xCu3Oy (0≤x≤1)
Authors: FU SUJIA , XIE SHISHENG , LIANG JINGKUI , CHE GUAUNGCHANG , ZHAO ZONGXIANG
Published: November 2004

The 930°C subsolidus phase relationships of Nd 2 O 3- BaO-CuO system ( CuO -rich region) have been determined by means of X-ray diffraction method. The superconductivity of Nd 1+x Ba 2−x Cu 3 O y have been studied. These compounds are superconducting provided they have orthorhombic distorted perovskite structures. The results show that the superconductivity mechanism is related to the Cu-O low dimensional network which may be dependent on the orthorhombic distorted structure, oxygen content and distribution. The result also shows that the amorphous content will influence their superconductivity; but it seems independence on the (Ba,Nd) order-disorder arrangements. Unlike in the other systems, the best superconducting compound in this system does not limit to the ideal (123) composition.
FLUCTUATION PAIRING AND HEAT CAPACITY OF HIGH Tc SUPERCONDUCTORS
Authors: THOMPSON R.S. , KRESIN V.Z.
Published: November 2004

The leading correction due to thermodynamic fluctuations to the dependence of the heat capacity on temperature and applied magnetic field is calculated for anisotropic high T c superconductors.
ON THE GAUGE THEORY OF THE RESONATING VALENCE BOND STATES
Authors: BASKARAN G. , SHANKAR R.
Published: November 2004

In this brief report we review some of the basic concepts involved in the gauge theory approach to the Resonating Valence Bond State of strongly correlated electronic systems. Some general consequences of the local gauge symmetry on the nature of excitations are also discussed.
INTERACTING ORDER PARAMETER MODEL FOR INCREASED Tc IN POLYTYPES OF THE Cu-O SYSTEMS
Authors: BIRMAN JOSEPH L. , LU J.P.
Published: November 2004

We introduce a simple phenomenological model with coupled order parameters for polytypes of multilayer copper-oxide systems. Polytypism increases the transition temperature from the [Formula: see text] of a single layer. For polytypes of a single layer of CuO2 we obtain the maximum T c of ~ 140 K using reasonable values of parameters.
EVIDENCE FOR ANOMALOUS FLUCTUATIONS IN SUPERCONDUCTING Bi1.75Pb0.25Ca2Sr2Cu3O10
Authors: AUSLOOS M. , LAURENT CH. , PATAPIS S.K. , GREEN S.M. , LUO H.L. , POLITIS C.
Published: November 2004

We report very precise measurements of the electrical resistivity of granular Bi 1.75 Pb 0.25- Ca 2 Sr 2 Cu 3 O 10 superconducting ceramics from room temperature down to the superconducting percolating temperature. We analyze the temperature behavior of the excess conductivity and of the temperature derivative variation in electrical resistivity in order to extract the superconductivity fluctuation dimensionality regimes. We obtain unusual power law behaviors which do not correspond to predictions based on Aslamazov and Larkin theory (nor to its generalizations) nor to the regimes found in YBa 2 Cu 3 O 7, e.g., here, dR/dT≃E−11/6 for ln E in [−4,0] with E=|T−T c |T c , where T c is the critical temperature.
POSSIBLE COEXISTENCE OF ANTIFERROMAGNETISM AND SUPERCONDUCTIVITY IN THE HUBBARD MODEL
Authors: JUE-LIAN SHEN , ZHAO-BIN SU , JIN-MING DONG , LU YU
Published: November 2004

The Hubbard model in the nearly half-filled case was studied in the mean field approximation using the effective Hamiltonian approach. Both antiferromagnetic order parameter and condensation of singlet pairs were considered. In certain parameter range the coexistence of antiferromagnetism and superconductivity is energetically favorable. Relations to the high temperature superconductivity and other theoretical approaches are also discussed.
VOLUMETRIC MEASUREMENT OF LABILE IONS THROUGH CORROSION OF YBa2Cu3O7−x
Authors: DOU S.X. , LIU H.K. , BOURDILLON A.J. , TAN N.X. , ZHOU J.P. , SORRELL C.C. , EASTERLING K.E.
Published: November 2004

The stability of sintered YBa2Cu3O7−x {123} in various aqueous solutions was investigated. It was found that all aqueous solutions have detrimental effects on superconduction in {123}. Based on the evolution of O2 through the reaction of {123} with acid, the volumetric measurement technique has been established for determining the quantity of Cu3+ in {123} with excellent reproducibility. In nitric acid the sintered {123} is much more stable than Ag, Cu or Ni metals, which are sometimes used in processing {123}, for example as cladding in wire drawing. {123} tends to passivate in concentrated acid. Impurity-doped and multiphase specimens generally suffer enhanced corrosion in water due to the formation of micro-electrochemical cells. Material with the tetragonal crystal structure is more stable in water than that with the orthorhombic structure, indicating that the sensitivity of {123} to water can be attributed to the presence of Cu3+ which is the driving force for rapid oxidation and reduction reactions in water.
GROWTH AND PROPERTIES OF YBCO SUPERCONDUCTING THIN FILMS PREPARED BY DC MAGNETRON SPUTTERING FROM A PAIR OF SUPERCONDUCTING STOICHIOMETRIC YBCO TARGETS
Authors: YAN S.L. , LIANG C.G. , HAN R.X. , YU B.X. , LIU W.Y. , LIU B.R. , SUN F.T. , ZHOU D.M. , BAI H.X. , YAN J. , YANG X.M. , ZHANG Q.M. , ZHOU X.D.
Published: November 2004

Superconducting YBCO thin films have been fabricated by dc magnetron sputtering from a pair of stoichiometric YBCO superconducting targets on polycrystalline ZrO 2 substrates. The post-annealing superconducting films exhibit the properties with the critical onset temperature of 95 K and zero resistivity temperature at 83 K. The relation between the composition of the film and the radial position of the substrate is investigated. The XRD analysis proved that the films are mainly orthorhombic polycrystalline structure.
TlBa2NdCu2O7 AND TlBa2YCu2O7 TWO NON-SUPERCONDUCTIVE OXIDES WITH THE “1212” STRUCTURE
Authors: MARTIN C. , BOURGAULT D. , MICHEL C. , HERVIEU M. , RAVEAU B.
Published: November 2004

Two new thallium cuprates isostructural with the “1212” superconductors were synthesized. These materials do not exhibit any superconductivity in spite of the presence of Tl(III), contrary to the oxides such as Tl 2 Ba 2 CaCu 2 O 8 or Tl 2 Ba 2 Ca 2 Cu 3 O 10. Their X-ray powder diffraction study confirms their close relationships with the superconductor TlBa 2 CaCu 2 O 7, i.e., their structure is built up from distorted double rock salt-type layers [(TIO) (BaO)] intergrown with oxygen deficient double perovskite layers [ BaY ( CuO 2.5)2] or [ BaNd ( CuO 2.5)2]. Although the determination of the positions of the oxygen atoms cannot be considered as accurate, one significant difference with respect to TlBa 2 CaCu 2 O 7 must be pointed out: the oxygen atoms forming the basal planes of the CuO 5 pyramids are brought closer together along c, leading to an almost cubic environment for Y and Nd, whereas the CaO 8 prisms are elongated along c in the thallium superconductors.
ORDER OF PHASE TRANSITION IN HIGH TEMPERATURE SUPERCONDUCTIVITY
Authors: LEE T.D.
Published: November 2004

We present arguments that the phase transition in some of the newly discovered high temperature superconductors is first-order, unlike the usual Λ-transition.
CONSERVATION LAWS AND EXACT SOLUTIONS OF THE BOLTZMANN EQUATION
Authors: MATTIS DANIEL C. , SZPILKA ANTHONY M. , CHEN HUA
Published: November 2004

The distribution function f which satisfies the time-dependent Boltzmann equation (BE) for a Lorentz model with perfectly elastic random scatterers is proved nonnegative, and is computed exactly when backscattering dominates. Joule heating and Ohm’s law are recovered, although f has no steady-state limit, contrary to the relaxation-time approximation. (The conventional approximation to the time-independent BE also yields Ohm’s law but not the Joule heating and, worse, it unphysically predicts f<0.) The exact solution is compared with various effective-temperature approximations, and is shown to remain very nearly unchanged over a wide range of times even in the presence of a small amount of inelastic scattering.
THE OCCURRENCE OF SUPERCONDUCTIVITY IN THE Ho (Ba2−xSrx) Cu3O7−δ SYSTEM
Authors: TAI M.F. , HWANG J.R. , KU H.C.
Published: November 2004

Electrical, magnetic and crystallographic measurements have been carried out for the pseudoquaternary Ho ( Ba 2−x Sr x) Cu 3 O 7−δ system in order to check the systematic variation of superconducting transition temperature T c , normal state electrical resistivity and phase boundary. T c decreases monotonically with the increasing Sr substitution and drops sharply to zero for x≥1.6. No resisitivity anomaly was observed.
Bi-Sr-Ca-Cu-O SURFACE STUDIED BY MEANS OF SCANNING TUNNELLING MICROSCOPE
Authors: WITEK A. , DABKOWSKI A. , RAULUSZKIEWICZ J.
Published: November 2004

Surface topography of the high-T c superconductor BiSrCaCu 2 O x has been investigated by means of scanning tunnelling microscope. The measurements were performed on the natural surface of ceramics material in air at room temperature. It can be deduced from the surface images, that bulk orthorhombic crystal structure extends to the surface. The surface seems to be uniform metallic in character and not drastically contaminated. Regular steps observed on the surface correspond to the dimension of the unit cell in z direction or its multiples.
SOME PROPERTIES OF VANADIUM DOPED Y-Ba-Cu-O SUPERCONDUCTOR
Authors: DING S.Y. , YU Z. , GAO P. , SHI K.X.
Published: November 2004

Samples of YBa 2 Cu 3−x V x O y with various x values were made to study the effects of doping element on properties of Y-Ba-Cu-O superconductor. The doped samples show an almost unchanged T c value. Whereas the volume fraction of superconducting phase decreases with the increase of the value of x. The sizes of granule in the doped samples are smaller than that of the undoped ones. The doped samples are also denser and harder. Dependence of J c on T for x=0.6 was also measured at H=510 G and in T>50 K . All of the results made one speculate that the vanadium appears mainly at interface as a kind of impurity. It was considered that improving the connectedness of interface is more important than increasing the fraction of superconducting phase at some conditions for enhancing J c of oxide superconductors.
JOSEPHSON MICROSTRIP MIXER USING SUPERCONDUCTOR AT LIQUID NITROGEN TEMPERATURES
Authors: CAI S.Z. , HOU Y.S. , YU E.X. , QIU J.W. , MIAO B.C.
Published: November 2004

Matching between waveguide and Josephson junction is a very important problem for making a Josephson mixer. In this paper this problem is solved by putting the junction in a microstrip circuit. The Josephson microstrip mixer is easy to adjust, small dimension and light weight. Some new results are also presented.
OBSERVATION OF THE ESR FOR HIGH-Tc SUPERCONDUCTORS Bi-Sr-Ca-Cu-O
Authors: YUAN S.L. , HOU B.H. , JIN S.Z. , WANG W. , ZHENG G.G. , RAN Q.Z. , GUAN W.Y. , ZHENG J.Q.
Published: November 2004

The preliminary study on the electron spin resonance (ESR) for the Bi-Sr-Ca-Cu-O system with different superconducting transition temperatures has been made at room temperature. It is found that the Lande factor g-values are increased with increasing zero resistance temperature T c0 but width between peaks ΔH pp of the ESR spectrum decreased with increasing T c0 . These might be attributed to the spin-orbit coupling of the magnetic ions and the Jahn-Teller distortion in the perpendicular component.
SQUID OPERATING AT LIQUID NITROGEN TEMPERATURES
Authors: BOBRAKOV V.F. , POLUSHKIN V.N. , VASILIEV B.V.
Published: November 2004

A two-hole rf-squid fabricated from high-temperature superconducting yttrium-based ceramic is described. Squid operates at liquid nitrogen temperatures and demonstrates all principal features of rf-squid signal. At high frequency, the noise level of the high-T c squid is only three times as much as the corresponding level of the commercial helium rf-squid. The 1/f-noises begin from 100 Hz approximately so that at low frequencies, the high-T c squid sensitivity is by 1.5 order less than the helium squid sensitivity.
DEPENDENCE OF CRITICAL CURRENT ON TEMPERATURE FOR DIRTY TYPE-II SUPERCONDUCTORS
Authors: YU Z. , DING S.Y. , SHI K.X. , YAN J.L.
Published: November 2004

Based on the non-ideal planar defect model developed by the authors earlier and electron scattering flux pinning mechanism, we have derived a temperature dependence of critical current which predicts a same relation for both of I c and H c2 in dirty type-II superconductors. In order to test the prediction, the I c (T) and H c2 (T) were measured on PbBi-SiO multilayer films. The agreement between the theoretical and experimental results is satisfactory.
ELASTICITY BEHAVIOR (5°C−350°C) AND SUPERCONDUCTIVITY IN YBa2Cu3O7−δ
Authors: ZHU J.S. , WANG Y.N. , GU M. , KUI J.S.
Published: November 2004

Elasticity behavior (5°C−350°C) and the relationship between elasticity and superconductivity in YBa 2 Cu 3 O 7−δ have been studied. Oxygen content in the sample plays an important role in both properties. Sample dependent variations in elastic modulus were observed.
ZERO RESISTANCE NEAR 80 K IN THE BISMUTH LEAD CUPRATES Pb2−xBixSr2(YCa)1Cu3O8
Authors: RETOUX R. , MICHEL C. , HERVIEU M. , RAVEAU B.
Published: November 2004

New superconductors Pb 2−x Bi x Sr 2 Y 1−x Ca x Cu 3 O 8(0≤x≤0.60) and Pb 2−x Bi x Sr 2 Y 1−y Ca y Cu 3 O 8 (x=0.6, y=0.5 and y+1) have been isolated. They are isostructural with Pb 2 Sr 2 Y 0.5 Ca 0.5 Cu 3 O 8. Their structure consists of a double intergrowth of oxygen deficient perovskite layers (A CuO 3−x)m(A′O)n (m=1.5, n=1), with A= Bi , Ca, Pb, Sr, Y and A′=Bi, Pb, Sr. The superconducting properties of this phase are greatly improved with respect to Pb 2 Sr 2 Y 0.5 Ca 0.5 Cu 3 O 8(Tc=46 K), since a Tc of 79 K (zero resistance) can be reached.
SUPERCONDUCTIVITY OF Bi1−xPbxSrCaCu2Oy(0≤x≤0.5) OXIDES
Authors: CHEN C. , YAO Y.S. , HUANG X.M. , CUI C.G. , LI S.L. , JIAN S.L. , WANG W.K.
Published: November 2004

The superconducting ceramics Bi 1−x Pb x SrCaCu 2 O y(0≤x≤0.5) have been prepared by conventional powder solid state reaction. A zero resistance transition temperature at 105 K has been observed in the sample with composition x=0.2. The effect of Pb content on the superconductivity of the ceramics has been studied. The results indicate that partial substitution of Pb (x≤0.3) for Bi enhances the superconductivity of Bi-oxide.
STRUCTURE MODIFICATION OF BiSrCaCuO SUPERCONDUCTORS DUE TO Pb-SUBSTITUTION
Authors: ZHU XING , FENG SUNQI , ZHANG JIAN , LU GUO , CHEN KAIXUAN , WU KE , GAN ZIZHAO
Published: November 2004

Pb-substitution to BiSrCaCuO superconductors has modified the crystallographic structure, in addition to the enhancement of the superconducting properties.
RANDOM WALK ON ANISOTROPICALLY GENERATED PERCOLATION CLUSTER AND ANISOTROPIC RANDOM WALK ON PERCOLATION CLUSTER
Authors: KIM C.S. , LEE MIN-HO
Published: November 2004

We studied two subjects related to anisotropy: random walk on percolation cluster having anisotropy (RWAC) and direction dependent (anisotropic) random walk on percolation cluster (AWIC). We find that the anisotropy of the cluster has only time-delaying effect on asymptotic convergence of the spectral dimensionality ds and fractal dimensionality of walk dw, however, the anisotropy of the walk results in lower spectral dimensionality and higher fractal dimensionality, as anisotropy grows larger.
ELECTRICAL CONDUCTIVITY AND STRUCTURAL INVESTIGATION OF THE SYSTEM Zn1−xCuxMnxFe2−xO4
Authors: KHAN M.N. , AL-DALLAL S. , MEMON A. , AHMED ASHFAQ , DARSHANE V.S.
Published: November 2004

X-ray, electrical conductivity and infrared absorption studies for the system Zn 1−x Cu x Mn x Fe 2−x O 4 have been carried out. All the compounds in the range 0≤x≤1 show cubic symmetry. It is found that all the compounds of the system possess low mobility values in the order of 10−9 cm 2/ Vsec and conduction is due to hopping process. The electrical conductivity measurements show that the activation energy decreases with increasing concentration of Cu 2+ and Mn 3+ in the crystal lattice. X-ray intensity calculations and IR studies indicated the presence of Zn 2+ at tetrahedral sites, Cu 2+ and Mn 3+ at octahedral sites, and Fe 3+ distributed both tetrahedral and octahedral sites. The probable ionic configuration for the system is suggested as [Formula: see text]
PECULIARITIES OF ELECTRONIC PARAMAGNETISM IN ANTIFERROMAGNETS
Authors: BRAZOVSKII S. , LUKJANCHUK I. , RAMAZASHVILI R.
Published: November 2004

The continuous and localized states of electrons in antiferromagnets (AFM) are studied in the presence of the magnetic field or the intrinsic magnetization. Peculiar features of both the Pauli and Curie susceptibilities are found. They may be tested in all intrinsic AFM with residual carriers like spin density wave (SDW) compounds, superconducting cuprates and also in s-f systems if their relevant electronic states are close to the reduced magnetic zone boundary (MZB).
PREPARATION OF YBaCuO THIN FILMS BY MULTILAYER DEPOSITION
Authors: GARCÍA-VÁZQUEZ VALENTÍN , POWERS KIM D. , LEAVITT J. A. , McINTYRE L. , FALCO CHARLES M.
Published: November 2004

We report the fabrication of YBa 2 Cu 3 O 7−x thin films by a combination of dc triode sputtering from Y and Cu targets, and simultaneous thermal evaporation from a BaF 2 source. A composition near the ideal 1:2:3 stoichiometry, with a resistive transition onset at 92 K and zero resistance at 80 K have been obtained by deposition on SrTiO 3 substrates, followed by furnace annealing.
A DYNAMICAL SYSTEM WITH CHAOTIC BEHAVIOR
Authors: SEIMENIS J.
Published: November 2004

We develop a method to find solutions of the equations of motion in Hamiltonian Dynamical Systems. We apply this method to the system [Formula: see text] We study the case a → 0 and we find that in this case the system has an infinite number of period dubling bifurcations.
SPIN-MONOPOLES AND ANYON STATISTICS IN EFFECTIVE GAUGE THEORIES OF HIGH Tc SUPERCONDUCTORS
Authors: AITCHISON I. J. R. , MAVROMATOS N. E.
Published: November 2004

In the presence of monopole configurations of the spin (or "statistical") gauge field arising in effective theories of systems may be relevant to high T c superconductivity, the coefficient of the Chern-Simons term, which determines the statistics of the anyons, is quantized in such a way that, in the superconducting state, the electromagnetic flux quantum is restricted to the values 2π/2qe, q = integer . This result is achieved by requiring U(1) gauge invariance on manifolds of the form R2 × S1 where S1 is the compactified Matsubara time of quantum statistics. A brief discussion on the role of holes in the cancellation of the bare Chern-Simons term, and the consequences thereof, is also presented.
X-RAY DIFFRACTION AND ELECTRON PARAMAGNETIC RESONANCE STUDIES OF A Bi4Sr2.5Ca2.5Cu4Ox SUPERCONDUCTING PHASE
Authors: LEVENTOURI TH. , GUSKOS N. , CALAMIOTOU M. , PAPAGEORGIOU O. , PARASKEVAS S. , PERDIKATSIS V.
Published: November 2004

We report a study of a low T c phase of the bismuth superconductor. A nominally Bi 4 Sr 2.5 Ca 2.5 Cu 4 O x compound was produced by the solid state reaction method with a T c = 80 K . X-ray diffraction studies show that the structure is very similar to the structure of the 4:3:3:4 composition with indications of small amounts of other phases. Electron paramagnetic resonance spectroscopy gives a strong Cu 2+ signal at temperatures above T c . We make a comparison between the local symmetry of the Cu 2+ ion complexes in this Bi sample and in the Y–Ba–Cu–O superconductor we had studied before.
INVESTIGATION OF rf SQUID BEHAVIOR AT LIQUID NITROGEN TEMPERATURES
Authors: POLUSHKIN V. N. , VASILIEV B. V.
Published: November 2004

An investigation of the performance of two hole Y–Ba–Cu–O rf-SQUID operating at liquid nitrogen temperatures are reported. The magnetic flux white noise level ~ 10−4Φ0 (Φ0 = 2.07 × 10−15 Wb ) is determined by amplifier noise since it is equal to the white noise level of a low-temperature SQUID with the same amplifier. Overall 1/f fluctuations develop at frequencies below 20 Hz. The measurement methods and the values of the main parameters are given.
MAGNETIC PROPERTIES OF Bi1.6Pb0.4Sr2Ca2Cu3Oy
Authors: WEI CHONGDE , LIN CHIN , ZHOU YAQIN , FENG QINGRONG , SUN YUNXI , LI GUOZHONG , WU KE , XUE LIXIN
Published: November 2004

Magnetic properties of Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O y were studied. Partial substitution of Pb for Bi results in a larger magnetic critical current. Possible explanation was discussed.
A RAMAN SPECTROSCOPIC STUDY OF RE2BaCuO5 WHERE RE = Y, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Lu
Authors: LOO B. H. , BURNS D. H. , XIDIS A. L.
Published: November 2004

We have prepared and determined the Raman spectra of a class of compounds of formula RE2 BaCuO 5, where RE = Y , Sm, Eu, Gd, Dy, Ho, Er, Tm, and Lu. Other rare-earth elements, Nd, Ce, Tb and Pr, are found not to form this class of compounds.
LOW FIELD PENETRATION AND INTRINSIC CRITICAL CURRENTS IN LAYERED SUPERCONDUCTORS
Authors: FEINBERG D. , VILLARD C.
Published: November 2004

Trapping of flux line cores between weakly coupled superconducting layers is considered. An estimate of the resulting high intrinsic critical current is given for field and current both parallel to the layers. The first flux penetration is studied as a function of the field direction. Each flux line takes the shape of a Sine-Gordon soliton lattice and encounters a lock-in transition towards the layers at a critical orientation.
ENHANCED EFFECTIVE MASS IN N-DOPED DEGENERATE SILICON
Authors: FERREIRA da SILVA A.
Published: November 2004

The effective mass of phosphorus-doped silicon has been calculated in the light of the Gutzwiller method for highly correlated system. The many-valley nature of the host conduction band minima with a variational impurity concentration dependence is taken into account in the calculation. The results show fair agreement when compared to previous work and available experimental data. Calculation of the density of states at the Fermi energy is also presented for the sake of comparison.
A MODEL FOR MODULATIONS IN Bi2Sr2CanCun+1O2n+6+d RELATED TO AURIVILLIUS OXYGEN
Authors: ZHU XING , YIN DAOLE , LIN BINGXIONG
Published: November 2004

In view of the difficulties encountered by the so far postulated structural models, a new model for the modulations in high T c bismuth superconducting compounds is proposed. In this model, the regions with and without the Aurivillius oxygen adjacent to Bi–O layers appear alternately along [010] with a fair or pseudo periodicity which results to commensurate or incommensurate modulations. The experimentally observed positions of cation atoms in modulated Bi compounds can be explained by this model without suffering from unreasonably short Bi–O bond lengths.
COMPLEX SUSCEPTIBILITY, MAGNETIZATION AND ELECTRICAL RESISTIVITY OF HIGH TEMPERATURE SUPERCONDUCTORS
Authors: CHEN KAI XUAN , LU GUO , DAI YUAN DONG , WEI CHONG DE , XUE LI XIN , WU KE , SUN YUN XI , LIU ZUN XIAO , LAN JIAN , LI GUO ZHONG
Published: November 2004

ac complex susceptibility, χ′ and χ″, dc magnetization and electrical resistivity of sintered superconductors Bi–Pb–Sr–Ca–Cu–O and Y–Ba–Cu–O have been measured. The results show two non-linear 2/3 power behaviors: field dependence of χ″ peak temperature, a quasi de Almeida-Thouless line, and a irreversibility line. The former corresponds to the property of intergrain material measured at low field, it can be interpreted by superconductive glass state in high-T c superconductor and/or the weakly connected loop model. The latter corresponds to the property of intragrain material measured at higher field, it can be interpreted by the thermally activated flux creep model. Moreover, the field dependences of width and height of χ″ peak are also exhibited. Finally, we have measured the I – V characteristics at 103.8 K for Bi–Pb–Sr–Ca–Cu–O sample and suggested the relation between the χ″ peak temperature and the zero dissipation temperature.
A CRITICAL STUDY FOR BRANCHED POLYMERS AND LATTICE ANIMALS: THERMAL AND PERCOLATIVE TRANSITIONS
Authors: GUJRATI P. D.
Published: November 2004

We investigate a field theory of a grand-canonical ensemble of branched polymers and lattice animals and show that the upper critical dimension for thermal phase transitions is du = 4. The transition in the dilute limit is first-order and there is no dimensional reduction. We suggest that the previous results in this limit correspond to a spinodal singularity and not to a physical singularity as the associated percolative transition is preempted by the first-order thermal transition.
HIGH TEMPERATURE SERIES ANALYSIS OF SUSCEPTIBILITY DATA OF La2CuO4
Authors: SZETO K. Y.
Published: November 2004

The zero-field magnetic susceptibility of La 2 CuO 4 is analyzed using high temperature series for five different magnetic Hamiltonians in two-dimensions: spin 1/2 Heisenberg model, spin 1/2 XY model, classical Heisenberg model, classical XY model, and the Ising model. The goodness of fit indicates that the quantum spin 1/2 Heisenberg model is best, with the classical XY model second.
CORRELATION AND LOCALIZATION OF TWO-DIMENSIONAL ELECTRONS IN A STRONG MAGNETIC FIELD
Authors: TSUI D. C.
Published: November 2004

This paper gives a brief review of some recent experiments on the localization-delocalization transition in the integral quantum Hall effect and the new quantum liquid ground states giving rise to the fractional quantum Hall effect.
GENERAL 8-VERTEX MODEL ON THE HONEYCOMB LATTICE: EQUIVALENCE WITH AN ISING MODEL
Authors: LIN K. Y. , WU F. Y.
Published: November 2004

It is shown that the general 8-vertex model on the honeycomb lattice is always reducible to an Ising model in a nonzero but generally complex magnetic field. In the most general case of the staggered 8-vertex model characterized by 16 independent vertex weights, the equivalent Ising model has three anisotropic interactions and a staggered magnetic field which assumes two different values on the two sublattices.
EPITAXIALLY GROWN YBCO THIN FILMS ON LOW LOSS LaAlO3 SUBSTRATE
Authors: ZHANG Y. Z. , LI L. , ZHAO Y. Y. , ZHAO B. R. , WANG Y. G. , QIU X. G. , WANG Y. H. , XU P.
Published: November 2004

A planar dc magnetron sputtering device was used to prepare high T c and high J c YBCO thin films. Both single crystal and polycrystal thin films were successfully grown on (100) oriented LaAlO 3 substrates. Zero resistance temperature T c0 = 92.3 K and critical current density J c (0) = 3.82 × 106 A/cm 2 at 77 K was obtained. The films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).
EFFECT OF A TRANSVERSE MAGNETIC FIELD AT THE TRICRITICAL POINT IN CsCoCl32H2O
Authors: PADUAN-FILHO A. , BECERRA C. C.
Published: November 2004

In this letter we report the experimental investigation of the magnetic phase diagram of CsCoCl 3 2H 2 O near the tricritical point Tt in the (H‖, H⊥, T)-space. We determine the position of Tt by studying the frequency dependence of the ac magnetic susceptibility at the antiferro to paramagnetic transition. From our analysis, Tt is independent of a perpendicular field up to 20 kOe. In the (H‖, T)-plane, the tricritical point is located at Tt = 1.88 K and Ht = 2.85 kOe , in good agreement with neutron diffraction data obtained in the analogous deuterated compound.
THE EXAFS STUDY OF SUBSTITUTIONAL FE IN Y–Ba–Cu–O SYSTEM
Authors: DONG JUN , LU KUNQUAN , ZHAO BORU
Published: November 2004

Near neighboring structures around Fe in YBa 2( Cu 1−x Fe x)3 O 7−y with nominal values of x = 0.07 and 0.10, were determined using extended X-ray absorption fine structure measurements. The results show that substitutional Fe cations are located at Cu(1) site, and essential structures around Fe are similar to those around Cu(1) in YBa 2 Cu 3 O 7−y, but bond lengths of Fe–O(4) and Fe–O(1) are shrunk as compared with those of Cu(1)–O(4) and Cu(1)–O(1) in YBa 2 Cu 3 O 7−y due to the substitution of Cu by Fe. The interesting result is that extra oxygen anions are introduced located at O(5) sites near the substitutional Fe cation and the number of these oxygen anions apparently increases with the content of Fe in the compounds. It can be estimated that substitutional Fe in Y–Ba–Cu–O system has more than one coordination geometries, but has distorted octahedral coordination in a statistical sense. In combination with the superconductivity in these compounds, it is suggested that Cu–O structure on the basal plane of unit cell in YBa 2 Cu 3 O 7−y plays an important role in high-T c superconductivity.
OXYGEN pzπ VERSUS px,y FERMI-LIQUID STATES IN HIGH-Tc OXIDES AND VALENCE PHOTOEMISSION SPECTRA OF Bi2(Ca,Sr,La)3Cu2O8
Authors: JOHNSON K. H.
Published: November 2004

Recent angle-resolved photoemission studies of the valence-band states of the high-T c superconductor, Bi 2( Ca,Sr,La )3 Cu 2 O 8, have led workers to conclude that the electronic states at the Fermi energy (E F ) have mainly O 2px and 2py symmetry, while O 2pz-like states are not allowed by the C4υ(∆5) symmetry of these states. Nevertheless, a complete projection of the basis functions for the C4υ symmetry group ∆5 (or "E") representation indicates both O 2px, 2py and O 2pz orbital contributions at E F . The O 2px and 2py components are nonbonding, whereas the O 2pz orbitals overlap under the influence of significant Cu (dxz,yzπ*)− O (pzπ) antibonding hybridization to form spatially delocalized O (pzπ)− O (pzπ) bonding molecular orbitals parallel to the Cu–O x − y (a − b) planes. The doubly-degenerate O (pzπ)− O (pzπ) "bonds" and their associated shallow "double-well" potentials are the basis for Fermi-liquid character and a dynamic Jahn-Teller mechanism for Cooper pairing first proposed in 1983 and first applied to high-T c oxides in 1987.
NORMAL STATE RESISTIVITY OF A QUANTUM ANTIFERROMAGNET IN HIGH Tc CUPREOUS OXIDES
Authors: XU J. H. , TING C. S. , XING D. Y.
Published: November 2004

The normal state in-plane resistivity ρab and the out-of-plane resistivity ρc of high T c cupreous oxides are studied in terms of the interactions between the charged carries and the excitations including phonons in a doped quantum antiferromagnet which can be described by either a resonant valence bond (RVB) state or a quantum Néel state. We found that only in a properly doped quantum Néel state and when the renormalized the speed of spin wave becomes soft, ρab and σc = 1/ρc could have the desired experimental behaviors and depend linearly on T from T c up to room temperature if the quantum Néel state still, persists in high T c samples.
DEPOSITION TECHNIQUES FOR HIGH Tc THIN FILMS
Authors: MARITATO L. , FALCO CHARLES M.
Published: November 2004

Vapor deposition techniques successfully used for producing thin films of YBa 2 Cu 3 O 7−x are reviewed.
IMPURITY ADSORPTION INDUCED SURFACE CHARGE-DENSITY OSCILLATION AND INDIRECT ATOMIC INTERACTIONS
Authors: TSONG TIEN T. , CHEN CHONG-LIN
Published: November 2004

Neon field ion image spots of Ta impurities, deposited on the Ir (100) surface, show a halo-ring structure. This image structure is most probably produced by the impurity adsorption induced oscillatory electronic charge-density distribution at the surface. The oscillatory electronic charge-density modulation is the cause of electronic indirect interactions of atoms in alloys and on metal surfaces. Manifestations of these interactions can be found in the compositional variation in the near surface layers of alloys in surface segregation, and in the pair-interaction of adsorbed atoms.
NEUTRON DIFFRACTION STUDY ON (Bi−Pb)2Sr2Ca2Cu3O10
Authors: JI-LIAN YANG , CHUN-TANG YE , BAI-SHENG ZHANG , JI-ZHOU LI , JIAN KANG , YONG-FAN DING , YU-SHENG HE , JING-CANG ZHANG , AI-SHENG HE , JIONG XIANG
Published: November 2004

The polycrystalline sample of (Bi–Pb)2Sr2Ca2Cu3O10 with Tc=107 K was prepared. The X-ray diffraction proved that the sample is single phase. The crystal structure study on the sample has been carried out by neutron diffraction. The result shows that its structure is tetragonal body-centre structure with space group of I4/mmm, containing a few oxygen atoms at 4e site in Bi–Pb layers.
QUANTUM JUMPS IN OPTICAL DOUBLE RESONANCE
Authors: D’SOUZA RICHARD , JAYARAO ARUNDHATI S. , LAWANDE SURESH V.
Published: November 2004

We present some analytical results of quantum jumps in a cascade configuration. We study the two cascades with the upper or lower transition strongly driven. We discuss the temporal behaviour of the conditional probabilities and the response functions.
EFFECTS OF A PARTIAL SUBSTITUTION OF Cu ELEMENTS BY Nb ELEMENTS IN YBaCuO SYSTEM
Authors: HIGO S. , HAKURAKU Y. , OGUSHI T. , KAWANO I. , ISHIKAWA Y.
Published: November 2004

Samples of the YBaCuNbO system with different molecular ratios of YBa 2 NbO y to YBa 2 Cu 3 O 7−d, were prepared in air by the solid-state reaction method. The X-ray powder diffraction patterns showed that the sample was composed of two phases, one corresponding to the YBa 2 Cu 3 O 7−d phase and the other to the YBa 2 NbO y phase with a cubic lattice parameter of 8.425 Å to 8.436 Å depending on the Nb content. The superconducting zero resistivity temperature, T c 0, of the YBaCuNbO system increased with the increase of the molecular ratios, from 91.2 K up to a maximum temperature of 92.8 K, and then, by a further increase in the molecular ratio, the T c 0 was drastically reduced with a gradient of −1.94 K /%x.
SUPERCONDUCTING PROPERTIES AND NORMAL-STATE RESISTIVITY OF CaBaLaCu3Oy
Authors: LEE H.C. , LEE S.G. , KIM Y.C. , YI K.S. , JANG M.S.
Published: November 2004

The superconducting properties of CaBaLaCu 3 O y with Tc=76 K were reported. The X-ray diffraction pattern analysis shows that the CaBaLaCu3Oy compound has tetragonal structure at room temperature. The superconductivity of this compound was confirmed from the temperature dependence of electrical resistivity and self-inductance. We also examined the temperature dependence of the normal-state resistivity ρ(T) from 300 K to 900 K. From the linear behavior of ρ(T) in the range Tc<T<620 K, the strength of electron-phonon coupling constant λ and the electron mean free path l are obtained from the standard electron-phonon dissipation mechanism. Our estimated value of λ≃0.62 implies that the superconductivity of CaBaLaCu 3 O y is not to be interpreted only in terms of the phonon-mediated electron-electron interaction.
POSSIBLE STRUCTURAL PHASE TRANSITION OF SINGLE PHASE (Bi, Pb)2Sr2Ca2Cu3O10+y SUPERCONDUCTING CERAMIC: AN INFRARED STUDY
Authors: AISHENG HE , JINCANG ZHANG , FANGGAO CHANG , WEIQIN LU , JIONG XIANG , YUSHENG HE
Published: November 2004

The infrared spectra of single phase (Bi, Pb)2Sr2Ca2Cu3O 10+y polycrystalline samp were studied over a temperature range of 300–120 K. Three vibrational modes were found at ambient temperature. A new band appears at 900 cm −1 near 200 K and experi evidence proved that the appearance of the new band is actually through an isothermal-like process, indicating a structural phase transition taking place. Unstable fluctuations were also observed between 200 and 140 K. This phenomenon is consistent with our previously reported ultrasonic, specific heat and lattice constants anomalies of the same sample. A possible mechanism of this phase transition is also discussed.
POSITRON ANNIHILATION IN HIGH Tc SUPERCONDUCTOR Bi-Sr-Ca-Cu-O
Authors: HUANG H.C. , LI D.H. , ZHENG S.N. , LI A.L. , CHEN F. , SUN H.C. , ZHU S.Y. , YAN Y.F. , ZHAO Z.X.
Published: November 2004

The temperature dependences of the positron annihilation lifetime and Doppler broadening have been measured in the Bi-Sr-Ca-Cu-O superconducting system from 77 to 300 K. The results show the existence of two superconducting phases: Tc=90 K 2212 phase and Tc=107 K 2223 phase, with the latter being dominant. Two anomalies were detected around 145 and 250 K, respectively. The role of long-time sintering and adding Pb and Nb in Bi-Sr-Ca-Cu-O is demonstrated in stabilizing the 2223 phase.
THE RESTRICTED SPIN MODEL
Authors: FARACH H.A. , CRESWICK R.J. , POOLE C.P.
Published: November 2004

We present a novel anisotropic Heisenberg model in which the classical spin is restricted to a region of the unit sphere which depends on the value of the anisotropy parameter Δ. In the limit Δ→1, we recover the Ising model, and in the limit Δ→0, the isotopic Heisenberg model. Monte Carlo calculations are used to compare the critical temperature as a function of the anisotropy parameter for the restricted and unrestricted models, and finite-size scaling analysis leads to the conclusion that for all Δ>0 the model belongs to the Ising universality class. For small A the critical behavior is clearly seen in histograms of the transverse and longitudinal (z) components of the magnetization.
XANES STUDY OF Ni-DOPED Bi-Ca-Sr-Cu-O SYSTEM
Authors: RAO K.V.R. , SRIVASTAVA P. , SEKHAR B.R. , GARG K.B. , AGARWAL S.K. , AWANA V.P.S. , NARLIKAR A.V.
Published: November 2004

We report the results of X-ray absorption measurements on partial substitution of Ni in place of Cu in Bi 2 Ca 1 Sr 2 Cu 2−x Ni x O y with x varying from 0 to 10 at %. The XRD patterns of the samples confirm their single phase nature. The transition temperature Tc decreases monotonically with Ni doping and the rate of decrease of Tc is around 2.5 K at % of the nominal substitution. The XANES results show that Ni is incorporated in the lattice with Ni-O bonds substituting for Cu-O bonds. The progressive decrease in the ratio of Cu 2+/ Cu 1+ is examined.
LONG RANGE SURFACE EXCITON POLARITONS: NEW LONG RANGE SURFACE MODES
Authors: YANG FUZI , BRADBERRY G.W. , SAMBLES J.R.
Published: November 2004

The work on the recently discovered long range coupled surface mode, the long range surface exciton-polariton is reviewed. The basic simple analytic equations which describe its dispersion in the symmetric case are presented and discussed. Adding a coupling prism perturbs these equations but does not necessarily lead automatically to a broader resonance. It is shown how 100% coupling is achieved for the symmetrically surrounded layer by a coupling gap thickness which makes the resonance lie very close to the critical angle. The consequences of small changes of symmetry and a small amount of absorption in the surrounding dielectrics are discussed.
VECTOR PAIRING AND FLUCTUATION-INDUCED CHERN-SIMONS TERM IN ANYON SUPERCONDUCTIVITY
Authors: HO CHOON-LIN , HU BAMBI , YU HOI-LAI
Published: November 2004

Assuming some sorts of vector pairing in high-temperature superconductivity, we show how the topological Chern-Simons term can be generated dynamically due to quantum fluctuations in a BCS-type four-fermion model. This fluctuation-induced Chern-Simons term provides a natural way to incorporate fractional statistics and thus a more direct connection with anyon superconductivity.
GROWTH AND ANISOTROPIC RESISTIVITY OF Bi2Sr2CaCu2Oy SINGLE CRYSTALS WITH ZERO RESISTIVITY AT 90 K
Authors: YANG G. , ZHAO Z.X.
Published: November 2004

A Bi2Sr2CaCu2Oy single crystal with zero resistivity at 90 K was grown by self-flux method. The diffraction of TEM and X-ray showed that the crystals were in “2212” phase with c=3.07 nm. Diamagnetism appeared at 91.5 K. The anisotropic resistivity of the crystal has been measured using the Montgomery technique. The superconducting transition onset in resistivity occurred at about 95 K and zero resistivity at 90 K. The resistivity showed strong anisotropic characteristics, with typical metallic behavior above 122 K and a semiconducting-like temperature dependence before superconducting transition in the a-b plane, which is quite different from previous results. The resistivity in the c-direction showed semiconducting-like temperature dependence, like other high Tc oxide superconductors but only above 122 K. ρcT versus T2 could be quite well represented by a linear relation. At present, it is difficult to determine the temperature dependence of resistivity in-plane from data analysis. The structure instability may be responsible for the negative temperature dependence of resistivity below 122 K.
SPIN FLUCTUATION INDUCED PAIRING FOR HIGH Tc COMPOUNDS
Authors: BHATTACHARYYA P.
Published: November 2004

We show that measurements of the upper critical field can, within the context of the pairing hypothesis, distinguish between spin fluctuation dominated pairing and those that do not involve spin. Comparison with experiments supports the hypothesis that the dominant pairing interaction in high Tc compounds is spin fluctuation induced. We also show the existence of a new mode in the mixed state, the mid-gap state, which is an immediate consequence of gauge symmetry.
GROWTH OF YBCO AND NBCO SINGLE CRYSTALS
Authors: KUMAR P.S. , JAYAVEL R. , MURUGAKOOTHAN P. , RAO C.R.V. , SUBRAMANIAN C. , RAMASAMY P.
Published: November 2004

Platelet and bulk single crystals of YBCO have been grown from peritectic and partial melt respectively. A modified flux technique has been adopted to grow flux-free NdBa 2 Cu 3 O 7−δ single crystals. The grown crystals were characterised by X-ray diffraction studies and a.c. susceptibility measurements. Growth spirals were observed on the surface of the crystals.
THE IRREVERSIBILITY LINES OF YBa2Cu3Oy SUPERCONDUCTOR BY MELT-TEXTURED GROWTH METHOD
Authors: WEI C.D. , DAI Y.D. , LIU Z.X. , LAN J. , REN H.T. , HE Q. , XIAO L. , WANG R.K. , YU D.A.
Published: November 2004

The study of magnetization irreversibility line of a YBaCuO superconductor fabricated by melt-textured growth method with a critical temperature Tc of 89.3 K is presented. The sample exhibits obvious anisotropy similar to the behavior of single crystal. The thermal activation energy is an order of magnitude larger than that of YBaCuO single crystal and is also larger than that of polycrystal YBaCuO sample.
3-D OBJECT INSPECTION FROM MULTIPLE 2-D CAMERA VIEWS
Authors: CHANG KO-CHIANG , TSAI WEN-HSIANG
Published: November 2004

A new approach to 3-D object inspection using 2-D camera views is proposed. With input objects put on a turntable for inspection, a top view of the object is first taken by a top camera right above the table. The object shape boundary points are extracted, and the centroid as well as the principal axis of the shape are computed for top-view registration with the model shape, using the generalized Hough transform. The distance-weighted correlation is then used as the similarity measure for shape matching. Input objects with low similarity values are rejected. Non-rejected objects are inspected further from lateral views, using a lateral camera for image taking and the turntable for object rotation. Experimental results with a high inspection rate and a fast inspection speed show the feasibility of the proposed approach.
A NOTE OF CAUTION ON COMBINING CERTAINTIES
Authors: NEAPOLITAN RICHARD E.
Published: November 2004

In the case of expert systems, when premises from two different rules argue for the same conclusion, there exist a number of methods for combining the certainties in the conclusion, obtained from each premise individually, to yield a total certainty in the conclusion. When these certainties are interpreted as probability values, it is necessary in all these methods to make assumptions of independence concerning the premises and conclusion. It is proven here that there does not exist a procedure which yields, for all probability functions, meaningful bounds for the probability of the conclusion based on two premises in terms of the probabilities of the conclusion based on each premise individually. Additionally, it is proven that there does not even exist a procedure which yields, for all probability functions, meaningful bounds for the probability of the conclusion based on two premises in terms of the probabilities of all one- and two-member combinations of the premises and the conclusion.

Finally, suggestions are made as to when to make assumptions of independence and when to take other alternatives.