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Showing papers by "Argonne National Laboratory published in 1987"


Book
01 Jan 1987
TL;DR: This chapter discusses Primal Method Primal-Dual Methods, Path-Following Algorithm, and Infeasible-Interior-Point Algorithms, and their applications to Linear Programming and Interior-Point Methods.
Abstract: Preface Notation 1. Introduction. Linear Programming Primal-Dual Methods The Central Path A Primal-Dual Framework Path-Following Methods Potential-Reduction Methods Infeasible Starting Points Superlinear Convergence Extensions Mehrotra's Predictor-Corrector Algorithm Linear Algebra Issues Karmarkar's Algorithm 2. Background. Linear Programming and Interior-Point Methods Standard Form Optimality Conditions, Duality, and Solution Sets The B {SYMBOL 200 \f "Symbol"} N Partition and Strict Complementarity A Strictly Interior Point Rank of the Matrix A Bases and Vertices Farkas's Lemma and a Proof of the Goldman-Tucker Result The Central Path Background. Primal Method Primal-Dual Methods. Development of the Fundamental Ideas Notes and References 3. Complexity Theory. Polynomial Versus Exponential, Worst Case vs Average Case Storing the Problem Data. Dimension and Size The Turing Machine and Rational Arithmetic Primal-Dual Methods and Rational Arithmetic Linear Programming and Rational Numbers Moving to a Solution from an Interior Point Complexity of Simplex, Ellipsoid, and Interior-Point Methods Polynomial and Strongly Polynomial Algorithms Beyond the Turing Machine Model More on the Real-Number Model and Algebraic Complexity A General Complexity Theorem for Path-Following Methods Notes and References 4. Potential-Reduction Methods. A Primal-Dual Potential-Reduction Algorithm Reducing Forces Convergence A Quadratic Estimate of \Phi _{\rho } along a Feasible Direction Bounding the Coefficients in The Quadratic Approximation An Estimate of the Reduction in \Phi _{\rho } and Polynomial Complexity What About Centrality? Choosing {SYMBOL 114 \f "Symbol"} and {SYMBOL 97 \f "Symbol"} Notes and References 5. Path-Following Algorithms. The Short-Step Path-Following Algorithm Technical Results The Predictor-Corrector Method A Long-Step Path-Following Algorithm Limit Points of the Iteration Sequence Proof of Lemma 5.3 Notes and References 6. Infeasible-Interior-Point Algorithms. The Algorithm Convergence of Algorithm IPF Technical Results I. Bounds on u _k \delimiter "026B30D (x^k,s^k) \delimiter "026B30D Technical Results II. Bounds on (D^k)^{-1} \Delta x^k and D^k \Delta s^k Technical Results III. A Uniform Lower Bound on {SYMBOL 97 \f "Symbol"}k Proofs of Theorems 6.1 and 6.2 Limit Points of the Iteration Sequence 7. Superlinear Convergence and Finite Termination. Affine-Scaling Steps An Estimate of ({SYMBOL 68 \f "Symbol"}x, {SYMBOL 68 \f "Symbol"} s). The Feasible Case An Estimate of ({SYMBOL 68 \f "Symbol"} x, {SYMBOL 68 \f "Symbol"} s). The Infeasible Case Algorithm PC Is Superlinear Nearly Quadratic Methods Convergence of Algorithm LPF+ Convergence of the Iteration Sequence {SYMBOL 206 \f "Symbol"}(A,b,c) and Finite Termination A Finite Termination Strategy Recovering an Optimal Basis More on {SYMBOL 206 \f "Symbol"} (A,b,c) Notes and References 8. Extensions. The Monotone LCP Mixed and Horizontal LCP Strict Complementarity and LCP Convex QP Convex Programming Monotone Nonlinear Complementarity and Variational Inequalities Semidefinite Programming Proof of Theorem 8.4. Notes and References 9. Detecting Infeasibility. Self-Duality The Simplified HSD Form The HSDl Form Identifying a Solution-Free Region Implementations of the HSD Formulations Notes and References 10. Practical Aspects of Primal-Dual Algorithms. Motivation for Mehrotra's Algorithm The Algorithm Superquadratic Convergence Second-Order Trajectory-Following Methods Higher-Order Methods Further Enhancements Notes and References 11. Implementations. Three Forms of the Step Equation The Cholesky Factorization Sparse Cholesky Factorization. Minimum-Degree Orderings Other Orderings Small Pivots in the Cholesky Factorization Dense Columns in A The Augmented System Formulat

2,277 citations


Journal ArticleDOI
TL;DR: In situ neutron powder diffraction measurements show that the orthorhombic-to-tetragonal phase transition in YBa/sub 2/Cu/sub 3/O/sub 7-//sub x/ is an order-disorder transition in which the disordering of oxygen atoms into a normally vacant site destroys the one-dimensional Cu-O chains present in the room-temperature orthorHombic structure.
Abstract: In situ neutron powder diffraction measurements show that the orthorhombic-to-tetragonal phase transition in $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$, which occurs near 700\ifmmode^\circ\else\textdegree\fi{}C in a pure oxygen atmosphere, is an order-disorder transition in which the disordering of oxygen atoms into a normally vacant site destroys the one-dimensional Cu-O chains present in the room-temperature orthorhombic structure. For both structures, the oxygen stoichiometry decreases monotonically with increasing temperature. The transition temperature depends on the oxygen partial pressure and occurs when the stoichiometry is near Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.5}$. The tetragonal structure has a partially occupied, nearly octahedral Cu-O arrangement, in contrast to the orthorhombic structure which has one-dimensional Cu-O chains. The observed depression of the superconducting transition temperature in tetragonal $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$, which has been quenched from high temperature, could result either from the disordering of oxygen atoms which destroys the one-dimensional chains or from the absence of ${\mathrm{Cu}}^{3+}$ ions.

908 citations


Journal ArticleDOI
TL;DR: It is shown that it is possible to develop a finite terminating quadratic programming algorithm without non-degeneracy assumptions and to apply these results to algorithms for linearly constrained problems.
Abstract: The aim of this paper is to study the convergence properties of the gradient projection method and to apply these results to algorithms for linearly constrained problems. The main convergence result is obtained by defining a projected gradient, and proving that the gradient projection method forces the sequence of projected gradients to zero. A consequence of this result is that if the gradient projection method converges to a nondegenerate point of a linearly constrained problem, then the active and binding constraints are identified in a finite number of iterations. As an application of our theory, we develop quadratic programming algorithms that iteratively explore a subspace defined by the active constraints. These algorithms are able to drop and add many constraints from the active set, and can either compute an accurate minimizer by a direct method, or an approximate minimizer by an iterative method of the conjugate gradient type. Thus, these algorithms are attractive for large scale problems. We show that it is possible to develop a finite terminating quadratic programming algorithm without non-degeneracy assumptions.

582 citations


Journal ArticleDOI
TL;DR: The role of Ba is to suppress the instability and stabilize a higher-symmetry tetragonal, I4/mmm structure which is metallic and superconducting.
Abstract: ${\mathrm{La}}_{1.85}$${\mathrm{Ba}}_{0.15}$${\mathrm{CuO}}_{4}$ exhibits high-${\mathrm{T}}_{\mathrm{c}}$ superconductivity with an onset temperature near 33 K as measured by resistivity and magnetic susceptibility. The nonsuperconducting end-member compound, ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$, which has an orthorhombic, Cmca structure, exhibits semiconducting behavior. The orthorhombic distortion is proposed to result from a Peierls 2${\mathrm{k}}_{\mathrm{F}}$ instability or a soft zone-boundary phonon mode. The role of Ba is to suppress the instability and stabilize a higher-symmetry tetragonal, I4/mmm structure which is metallic and superconducting.

458 citations


Journal ArticleDOI
TL;DR: In this paper, a model for polarized EPR spectra generated in radical pair reactions in micelles is proposed, based on electron spin-spin interactions which remain observable because of limited diffusion.
Abstract: A model for polarized EPR spectra generated in radical pair reactions in micelles is being proposed. The model is based on electron spin-spin interactions which remain observable because of limited diffusion in micelles. The experimental observable is a doubling of hyperfine transitions, split by the magnitude of the interaction. The polarization is generated by the nonadiabatic generation of the radical pair with a triplet or singlet precursor. The time evolution of the wave function leads to a non-Boltzmann distribution of the populations among the four energy levels. The theory is tested by comparison with experiments, previously reported and repeated in this laboratory, obtained by laser flash photolysis of benzophenone in sodium dodecyl sulfate (SDS) micelles. Simulations of the shape of the spectra and their time dependence give excellent agreement with experiment. The model is further supported by experiments in micelles modified by different salt concentrations as well as different chain lengths of the micelle-forming molecules.

411 citations


Journal ArticleDOI
01 Aug 1987-Nature
TL;DR: In this paper, the authors present the results of a study of the structure and transport properties of the series of compounds Y1−xPrxBa2Cu3O7−δ (x = 0−1.0), in which they observe a monotonic decrease in Tc and eventually a metal-nsulator transition with increasing Pr concentration.
Abstract: Considerable excitement has been generated by the report of superconductivity above 90 K in a multi-phase Y–Ba–Cu oxide1. The superconducting phase was subsequently identified as YBa2Cu3O7−δ2,3. The complete replacement of Y by the trivalent rare-earths La–Lu, with the exception of Ce, Pr and Tb, yields a superconducting phase with a critical temperature (Tc) almost identical to that reported for the yttrium compound4–7. This is somewhat surprising as most of these ions carry significant magnetic moments, the presence of which rapidly decreases Tc in ordinary superconductors. The three exceptions noted, Ce, Pr and Tb, are the rare-earth ions which have a stable tetravalent state. Here we present the results of a study of the structure and transport properties of the series of compounds Y1−xPrxBa2Cu3O7−δ (x = 0−1.0), in which we observe a monotonic decrease in Tc and eventually a metal–nsulator transition with increasing Pr concentration. To date, this is the only rare-earth ion which has been found substantially to alter Tc upon partial substitution for Y.

406 citations


Journal ArticleDOI
TL;DR: For cascade energies of 3 and 5 keV in Cu, which are the highest energies (in reduced units) yet treated by fully dynamical simulations, it is found that local melting occurs and persists for several picoseconds.
Abstract: The role of thermal spikes in energetic displacement cascades has been investigated by molecular-dynamics computer simulation. For cascade energies of 3 and 5 keV in Cu, which are the highest energies (in reduced units) yet treated by fully dynamical simulations, it is found that local melting occurs and persists for several picoseconds. The implications of this behavior for atomic mixing, Frenkel-pair production, and point-defect clustering are discussed.

355 citations



Journal ArticleDOI
01 May 1987-Nature
TL;DR: In this article, high-resolution neutron powder diffraction data for this phase with x = 0.15(7) were presented, and the results agree with ref. 4 with respect to cation positions, but the location of one set of oxygen defects is substantially different and necessitates the lowering of lattice symmetry from tetragonal to orthorhombic (space group Pmmm).
Abstract: Materials within the phase diagram Y2O3–BaO–CuO have recently generated great interest because of the observation of superconductivity with a critical temperature (Tc ) of ≳90 K1,2; the current consensus is that YBa2Cu3O7−x (x ≈ 0.2) is the superconducting phase (see, for example ref. 3). Hazen et al.4 concluded, from a single-crystal X-ray diffraction experiment, that its structure is based on the corner-linked octahedral perovskite structure: the tetragonal unit cell (space group P&4bar;m2) arises from a tripling of the c-axis resulting from the ordering of yttrium and barium cations and associated oxygen defects. Here we present high-resolution neutron powder diffraction data for this phase with x = 0.15(7). Our results agree with ref. 4 with respect to cation positions, but the location of one set of oxygen defects is substantially different and necessitates the lowering of lattice symmetry from tetragonal to orthorhombic (space group Pmmm), in agreement with separate findings5–8. In contrast to the 35-K superconductor, La1.85Ba0.15CuO4, the corner-linked CuO4 planar groups are connected not only as sheets in the a–b plane but also as chains parallel to the ft-axis. The average copper valence is 2.23 (5). From bond valence arguments we infer that the Cu2+ and Cu3+ ions preferentially occupy square pyramidal and square planar sites respectively. Crystal chemical considerations suggest that these structural features may be involved in the superconducting mechanism.

320 citations


Journal ArticleDOI
TL;DR: In this paper, the drift velocity in a pool system depends upon vessel diameter, system pressure, gas flux and fluid physical properties, and the results show that the relative velocity and void fraction can be quite different from those predicted by conventional correlations.

316 citations


Journal ArticleDOI
TL;DR: In this article, the electronic structure of the high T c superconductor, YBa 2 Cu 3 O 7-δ, determined from highly precise all-electron local density calculations yields a relatively simple highly 2D electronic band structure consisting of two 2D Cu2-O and two 1D Cu1-O bands (one almost empty and one almost full at δ = 0, becoming full at ≥ 0.1) near E F.

Journal ArticleDOI
TL;DR: Etude realisee sur une large plage de compositions, Tc decroit lentement quand x croit, et atteint 0 a la transition d'orthorhombique a tetragonal.
Abstract: The structural and superconducting properties of orthorhombic and tetragonal $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ have been determined for a wide range of stoichiometries ($0.3lxl0.7$). In the orthorhombic phase, ${T}_{c}$ decreases smoothly as $x$ increases and reaches zero at the orthorhombic-to-tetragonal transition. Tetragonal $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ is not superconducting at any stoichiometry. This systematic depression of ${T}_{c}$ is correlated with the decrease in the oxygen content which alters the electronic structure of the Cu-O networks.

Journal ArticleDOI
TL;DR: In this paper, a current transfer model is proposed in which weak conduction along the c axis plays a role in limiting critical-current density at grain boundaries, and the effect of intrinsic conduction anisotropy is discussed.
Abstract: Measurements of the transport critical‐current density (Jc), magnetization Jc, and magnetoresistance in a number of bulk sintered samples of Y1Ba2Cu3Ox from several different laboratories indicate that the transport Jc is limited by weak‐link regions between high Jc regions. The weak‐link Jc has a Josephson character, decreasing by two orders of magnitude as the magnetic field is increased from 0.1 to 10 mT at 77 K. An examination of the grain‐boundary region in Y1Ba2Cu3Ox shows no observable impurities or second phases to the scale of the [001] lattice planes (∼12 A). The effect of intrinsic conduction anisotropy is discussed. A current‐transfer model is proposed in which weak conduction along the c axis plays a role in limiting Jc at grain boundaries. Orienting the grains in the powder state during processing may result in enhanced transport Jc in bulk conductors.

Journal ArticleDOI
TL;DR: In this paper, the conductivity of porous Ni/ZrO/sub 2-/Y/Sub 2/O/Sub 3/ cermets at 1000/sup 0/C was determined as a function of Ni content between 15 and 50 volume percent (v/o) of total solids for two different zirconia particle sizes.
Abstract: The conductivity of porous Ni/ZrO/sub 2-/Y/sub 2/O/sub 3/ cermets at 1000/sup 0/C was determined as a function of Ni content between 15 and 50 volume percent (v/o) of total solids for two different zirconia particle sizes (23 and 47 m/sup 2//g). Below Ni contents of 30 v/o, ionic conduction through the zirconia phase dominated. At 30 v/o Ni, a greater than three order of magnitude increase in the conductivity was observed, corresponding to a change in mechanism to electronic conduction through the Ni phase. The conductivity of cermets made with a Ni content greater than 30 v/o Ni was found to decrease with increasing temperature between 700/sup 0/ and 1000/sup 0/C. While the conductivity of the cermets with the larger particle size zirconia was higher by more than a factor of four, all the samples studied had the same activation energy, 5.7 +- 0.1 kJ/mol. The increase in conductivity with zirconia particle size is attributed to improved Ni particle-to-particle contact, resulting from the Ni phase being able to cover more completely the surface of the zirconia matrix where it resides.

Journal ArticleDOI
01 May 1987-Science
TL;DR: Research applications of accelerator mass spectrometry have been concentrated in the earth sciences, and in physics, and may become an important tool for the materials and biological sciences.
Abstract: Particle accelerators, such as those built for research in nuclear physics, can also be used together with magnetic and electrostatic mass analyzers to measure rare isotopes at very low abundance ratios. All molecular ions can be eliminated when accelerated to energies of millions of electron volts. Some atomic isobars can be eliminated with the use of negative ions; others can be separated at high energies by measuring their rate of energy loss in a detector. The long-lived radioisotopes (10)Be, (14)C,(26)A1, 36Cl, and (129)1 can now be measured in small natural samples having isotopic abundances in the range 10(-12) to 10(- 5) and as few as 10(5) atoms. In the past few years, research applications of accelerator mass spectrometry have been concentrated in the earth sciences (climatology, cosmochemistry, environmental chemistry, geochronology, glaciology, hydrology, igneous petrogenesis, minerals exploration, sedimentology, and volcanology), in anthropology and archeology (radiocarbon dating), and in physics (searches for exotic particles and measurement of halflives). In addition, accelerator mass spectrometry may become an important tool for the materials and biological sciences.

Journal ArticleDOI
TL;DR: The largest increases in the critical magnetization current occurred at 77 K and 79 K, and there was a slight linear decrease in the transition temperature with neutron fluence.
Abstract: Magnetization measurements were performed on single crystals of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ to study the effect of fast neutron irradiation on flux pinning and the critical magnetization current. Neutron irradiation up to a fluence of 8.16\ifmmode\times\else\texttimes\fi{}${10}^{17}$ n/${\mathrm{cm}}^{2}$ systematically enhanced the magnitude and reduced the anisotropy of the critical magnetization current compared to unirradiated samples. The largest increases in the critical magnetization current occurred at 77 K. There was a slight linear decrease in the transition temperature with neutron fluence.

Journal ArticleDOI
TL;DR: A large collection of public-domain mathematical software is now available via electronic mail, and a library catalog to be sent by return mail.
Abstract: A large collection of public-domain mathematical software is now available via electronic mail. Messages sent to "netlibcanl-mcs" (on the Arpanet/CSNET) or to "research!netlib" (on the UNIX® network) wake up a server that distributes items from the collection. The one-line message "send index" causes a library catalog to be sent by return mail.

Journal ArticleDOI
TL;DR: In this article, the authors present a parallel algorithm for the symmetric algebraic eigenvalue problem, which is based upon a divide and conquer scheme suggested by Cuppen for computing the eigensystem of a symmetric tridiagonal matrix.
Abstract: In this paper we present a parallel algorithm for the symmetric algebraic eigenvalue problem. The algorithm is based upon a divide and conquer scheme suggested by Cuppen for computing the eigensystem of a symmetric tridiagonal matrix. We extend this idea to obtain a parallel algorithm that retains a number of active parallel processes that is greater than or equal to the initial number throughout the course of the computation. We give a new deflation technique which together with a robust root finding technique will assure computation of an eigensystem to full accuracy in the residuals and in the orthogonality of eigenvectors. A brief analysis of the numerical properties and sensitivity to round off error is presented to indicate where numerical difficulties may occur. The algorithm is able to exploit parallelism at all levels of the computation and is well suited to a variety of architectures.Computational results are presented for several machines. These results are very encouraging with respect to both...

Journal ArticleDOI
01 Aug 1987
TL;DR: This note compares the performance of different computer systems while solving dense systems of linear equations using the LINPACK software in a Fortran environment.
Abstract: This note compares the performance of different computer systems while solving dense systems of linear equations using the LINPACK software in a Fortran environment. About 100 com puters, ranging from a CRAY X-MP to the 68000-based systems such as the Apollo and SUN Workstations to IBM PC's, are compared.

Journal ArticleDOI
TL;DR: In this paper, a magnetic isolation of the Y ions is found to explain the existence of high Tc superconductivity of the RBa2Cu3O7-δ compounds (where R = magnetic heavy lanthanides).

Journal ArticleDOI
TL;DR: Analysis of the relative efficiencies for the induction of SSBs revealed a spectrum that coincided closely with nucleic acid absorption below 313 nm, and at longer wavelengths, the plot of relative efficiency vs. wavelength contained a minor shoulder in the same wavelength region as that observed in a previously obtained action spectrum for stationary phase Bacillus subtilis cells.
Abstract: — An action spectrum for the immediate induction in DNA of single-strand breaks (SSBs, frank breaks plus alkali-labile sites) in human P3 teratoma cells in culture by monochromatic 254-, 270-, 290-, 313-, 334-, 365-, and 405-nm radiation is described. The cells were held at +0.5dC during irradiation and were Iysed immediately for alkaline sedimentation analysis following the irradiation treatments. Linear fluence responses were observed over the fluence ranges studied for all energies. Irradiation of the cells in a D2O environment (compared with the normal H2O environment) did not alter the rate of induction of SSBs by 290-nm radiation, whereas the D2O environment enhanced the induction of SSBs by 365- and 405-nm irradiation. Analysis of the relative efficiencies for the induction of SSBs, corrected for quantum efficiency and cellular shielding, revealed a spectrum that coincided closely with nucleic acid absorption below 313 nm. At longer wavelengths, the plot of relative efficiency vs. wavelength contained a minor shoulder in the same wavelength region as that observed in a previously obtained action spectrum for stationary phase Bacillus subtilis cells. Far-UV radiation induced few breaks relative to pyrimidine dimers, whereas in the near-UV region of radiation, SSBs account for a significant proportion of the lesions relative to dimers, with a maximum number of SSBs per lethal event occurring at 365-nm radiation.

Journal ArticleDOI
TL;DR: High-resolution electron microscopy shows the coexistence of several distinct core structures for coincident-site lattice boundaries in NiO bicrystals and suggests the presence of a high concentration of Schottky pairs in the grain boundaries.
Abstract: High-resolution electron microscopy shows the coexistence of several distinct core structures for coincident-site lattice boundaries in NiO bicrystals near $\ensuremath{\Sigma}=5, (310)$, and $\ensuremath{\Sigma}=13, (510)$, where $\ensuremath{\Sigma}$ is the reciprocal density of coincident lattice sites. Lattice expansion perpendicular to the $\ensuremath{\Sigma}=5$ grain boundaries is considerably smaller than calculated theoretically. Structural units in boundaries near $\ensuremath{\Sigma}=13, (510)$ exhibit translations normal to the grain-boundary plane, resulting in a rumpling of the interface on an atomic scale. Our observations suggest the presence of a high concentration of Schottky pairs in the grain boundaries.

Journal ArticleDOI
TL;DR: In this article, the authors evaluated digital Landsat thematic mapper (TM) data for lithologic mapping capabilities over the Meatiq dome area in the hyper-arid Eastern Desert of Egypt.
Abstract: Digital Landsat thematic mapper (TM) data were evaluated for lithologic mapping capabilities over the Meatiq dome area in the hyper-arid Eastern Desert of Egypt Bi-directional spectral reflectance data (04–25 µm) for powders of the major rock types exposed in the dome and published spectral reflectance data were used as guides in selecting TM band reflectance ratios that maximize discrimination of individual rock types on the basis of their respective mineralogies Comparison of TM data with field and petrographic observations shows (1) increasing amounts of magnetite and other opaque minerals, with low, flat spectral reflectances, decrease the ratio of TM band 5 (155 to 175) to band 1 (045 to 052 µm); (2) increasing amounts of hydroxyl-bearing minerals, with hydroxyl ion vibrational absorptions in TM band-7 wavelength region (208 to 235 µm), increase the ratio of TM band 5 to band 7; (3) increasing amounts of Fe-bearing aluminosilicates that absorb in the band-4 wavelength region (076 to 09 µm) increase the product of the following two TM ratios: band 5 to band 4 and band 3 (063 to 069 µm) to band 4; and (4) thin (≤5 µm), desert varnish that covers many outcrops modulates, but does not obscure, the spectral reflectance signatures of the Meatiq rocks The varnish consists of amorphous to poorly crystalline dioctahedral smectite, iron oxides, and/or oxyhydroxides Serpentinite, mafic mylonite, massive amphibolite, quartzofeldspathic mylonite, biotite schist, and quartz phyllonite were mapped on the basis of their unique values in one or more of the three ratio images, whereas coarse- and fine-grained granites, granite gneiss, and tonalite, with similar mineralogies and TM band ratios, were mapped as a group Finer subdivisions were made where field traverses provided local verification Results demonstrate that appropriate processing and presentation of Landsat TM data can significantly augment field observations for lithologic mapping of large areas in arid regions

Journal ArticleDOI
TL;DR: In this article, a detailed high temperature X-ray diffraction was performed to study the structural phase of YBa 2 Cu 3 O 7−δ, and the results indicated the existence of a reversible orthorhombic to tetragonal phase transition at a temperature close to 750°C.

Journal ArticleDOI
TL;DR: In this article, the authors measured the permeability coefficients of some metal species through selected supported liquid membranes (SLM) over extended periods of time, in the presence and absence of osmotic pressure gradients.

Journal Article
TL;DR: Flat colonic mucosa in familial polyposis is therefore markedly aberrant and may be highly dedifferentiated, suggesting several possible mechanisms for the very high incidence of cancer that develops in this epithelium.
Abstract: A computer-based scanning and image-processing system has been developed to quantitate the relative level of expression of each of 4000 cloned complementary DNA sequences in small biopsies routinely removed from the mucosa of normal and neoplastic human large intestine. Individuals have been studied from well-defined population groups in which colonic epithelial cells have progressed to increasingly advanced stages of neoplastic transformation. Comparison of normal colonic mucosa to colonic carcinomas demonstrated alterations in expression of approximately 7% of the cloned sequences; fewer changes were found between benign colonic adenomas and either normal colonic mucosa or carcinomas. A subset of the sequences which change in expression during progression from normal mucosa, to adenoma, to carcinoma showed complementary changes when colon carcinoma cells were induced to differentiate in vitro with sodium butyrate; quantitative correlations between in vivo and in vitro results were highly significant. Comparison of normal colonic mucosa with mucosa from patients with the autosomal dominant disease familial polyposis revealed more extensive alterations in gene expression involving approximately 25% of the clones screened. Flat colonic mucosa in familial polyposis is therefore markedly aberrant and may be highly dedifferentiated, suggesting several possible mechanisms for the very high incidence of cancer that develops in this epithelium.

Journal ArticleDOI
TL;DR: The results indicate that a first-order phase transformation triggered by an elastic instability occurs during solid-state amorphization of Zr/sub 3/Al by ion irradiation.
Abstract: Changes in shear elastic constant, long-range order, and lattice parameter were measured during disordering and eventual amorphization of ${\mathrm{Zr}}_{3}$Al by ion irradiation. Large (\ensuremath{\simeq}50%) elastic softening was observed during disordering, and anomalies occurred in all three measured parameters over a narrow range of ion doses. The results indicate that a first-order phase transformation triggered by an elastic instability occurs during solid-state amorphization. The changes reported here during disordering and amorphization are very similar to behavior observed previously in a large number of solids during heating to melting.

Journal ArticleDOI
TL;DR: It was found that the affinity of binding sites on intact IgG was underestimated by a factor of at least 2 and that the error was inversely related to the fraction of liganded binding sites, resulting in the calculation of valid association constants for intact IgGs without alteration of the experimental protocol.


Journal ArticleDOI
TL;DR: In this paper, Ab initio molecular orbital pair potentials for the interaction of Fe2+ and Fe3+ ions with H2O were used to calculate the three-body energies from the interactions of two water molecules with the cations.
Abstract: Ab initio molecular orbital pair potentials for the interaction of Fe2+ and Fe3+ ions with H2O are reported. Molecular dynamics calculations of the static structure of the solvation shell of Fe2+ and Fe3+ in water using the ab initio pair potentials gives physically incorrect results, i.e., the coordination numbers are eight instead of six as observed experimentally. This problem has also been encountered by other workers for divalent transition metal ions in water. By computing three‐body energies from the interaction of two water molecules with the cations, we show that the origin of the problem is most likely in the assumption of the additivity of the pair potentials, i.e., neglect of many‐body forces. Empirical potentials are reported which take approximate account of the three‐body forces and give coordination numbers of six for both Fe2+ and Fe3+ in water.