Browse Issues:

ARTICLES

Temporal fluctuations in wave propagation in random media

Michael J. Stephen

Phys. Rev. B 37, 1 (1988) - Published 1 January, 1988

Atomic relaxations around vacancy clusters in molybdenum and their effects on trapped-positron lifetime

S. N. Khanna, B. K. Rao, P. Jena, D. Esterling, and M. J. Puska

Phys. Rev. B 37, 6 (1988) - Published 1 January, 1988

Jahn-Teller effect in the emission and excitation spectra of the Sb3+ ion in LPO4 (L=Sc,Lu,Y)

E. W. J. L. Oomen, W. M. A. Smit, and G. Blasse

Phys. Rev. B 37, 18 (1988) - Published 1 January, 1988

Mössbauer effect used to study rare-earth oxides synthesized by a high-pressure method

Su Wenhui, Liu Xiaoxiang, Jin Mingzhi, Xu Weiming, Wu Daiming, and Liu Milan

Phys. Rev. B 37, 35 (1988) - Published 1 January, 1988

Low-temperature ion-beam mixing in metals

S.-J. Kim, M-A. Nicolet, R. S. Averback, and D. Peak

Phys. Rev. B 37, 38 (1988) - Published 1 January, 1988

Ginzburg-Landau parameters for an ErRh4B4 single crystal

F. Behroozi, G. W. Crabtree, L. N. Hall, and D. G. Hinks

Phys. Rev. B 37, 50 (1988) - Published 1 January, 1988

X-ray-absorption fine-structure study of the A15 superconductors Nb3(Sn,Sb)

J. B. Boyce, F. Bridges, T. Claeson, T. H. Geballe, G. W. Hull, N. Kitamura, and F. Weiss

Phys. Rev. B 37, 54 (1988) - Published 1 January, 1988

Superconductivity and structure in sputtered Nb-Ta multilayers

P. R. Broussard and T. H. Geballe

Phys. Rev. B 37, 60 (1988) - Published 1 January, 1988

Critical currents in sputtered Nb-Ta multilayers

P. R. Broussard and T. H. Geballe

Phys. Rev. B 37, 68 (1988) - Published 1 January, 1988

Resonantly enhanced quantum decay: A time-dependent Wentzel-Kramers-Brillouin approach

Matthew P. A. Fisher

Phys. Rev. B 37, 75 (1988) - Published 1 January, 1988

Consequences of resonant impurity scattering in anisotropic superconductors: Thermal and spin relaxation properties

P. J. Hirschfeld, P. Wölfle, and D. Einzel

Phys. Rev. B 37, 83 (1988) - Published 1 January, 1988

I-V characteristics of coupled ultrasmall-capacitance normal tunnel junctions

K. Mullen, E. Ben-Jacob, R. C. Jaklevic, and Z. Schuss

Phys. Rev. B 37, 98 (1988) - Published 1 January, 1988

Electronic behavior of oxygen-deficient YBa2Cu3O7δ

W. K. Kwok, G. W. Crabtree, A. Umezawa, B. W. Veal, J. D. Jorgensen, S. K. Malik, L. J. Nowicki, A. P. Paulikas, and L. Nunez

Phys. Rev. B 37, 106 (1988) - Published 1 January, 1988

Resistivity of nonmetallic La2ySryCu1xLixO4δ single crystals and ceramics

M. A. Kastner, R. J. Birgeneau, C. Y. Chen, Y. M. Chiang, D. R. Gabbe, H. P. Jenssen, T. Junk, C. J. Peters, P. J. Picone, Tineke Thio, T. R. Thurston, and H. L. Tuller

Phys. Rev. B 37, 111 (1988) - Published 1 January, 1988

Theory of the Hall coefficient of polycrystals: Application to a simple model for La2xMxCuO4 (M=Sr,Ba)

Ting -Kang Xia and D. Stroud

Phys. Rev. B 37, 118 (1988) - Published 1 January, 1988

Valence bands and electron correlation in the high-Tc superconductors

J. C. Fuggle, P. J. W. Weijs, R. Schoorl, G. A. Sawatzky, J. Fink, N. Nücker, P. J. Durham, and W. M. Temmerman

Phys. Rev. B 37, 123 (1988) - Published 1 January, 1988

Magnetoresistance as a probe of superconducting islands in La-Sr-Cu-O

C. Uher and A. B. Kaiser

Phys. Rev. B 37, 127 (1988) - Published 1 January, 1988

Dependence of magnetic properties of pellets of nominal composition YBa2Cu3O7x on processing conditions

S. S. P. Parkin, E. M. Engler, V. Y. Lee, and R. B. Beyers

Phys. Rev. B 37, 131 (1988) - Published 1 January, 1988

Magnetic form factor of Cu in La2CuO4

T. Freltoft, G. Shirane, S. Mitsuda, J. P. Remeika, and A. S. Cooper

Phys. Rev. B 37, 137 (1988) - Published 1 January, 1988

Lattice-instability-enhanced high-temperature superconductivity for the perovskite-family oxides

Mitsuo Kataoka

Phys. Rev. B 37, 143 (1988) - Published 1 January, 1988

Homogeneous nucleation temperature of liquid He3

D. Lezak, L. C. Brodie, J. S. Semura, and E. Bodegom

Phys. Rev. B 37, 150 (1988) - Published 1 January, 1988

Variational theory of superconductivity and application to the low-density electron gas

Yasutami Takada

Phys. Rev. B 37, 155 (1988) - Published 1 January, 1988

Domain growth and topological defects in an Ising model with competing interactions

T. Ala-Nissila, J. D. Gunton, and K. Kaski

Phys. Rev. B 37, 179 (1988) - Published 1 January, 1988

Monte Carlo study of growth in the two-dimensional spin-exchange kinetic Ising model

Jacques G. Amar, Francis E. Sullivan, and Raymond D. Mountain

Phys. Rev. B 37, 196 (1988) - Published 1 January, 1988

Mean-field model of the Verwey transition in magnetite

Ricardo Aragón and Jurgen M. Honig

Phys. Rev. B 37, 209 (1988) - Published 1 January, 1988

Concentration inhomogeneities in random magnets. I. Characterization using optical birefringence

A. R. King, I. B. Ferreira, V. Jaccarino, and D. P. Belanger

Phys. Rev. B 37, 219 (1988) - Published 1 January, 1988

Concentration inhomogeneities in random magnets. II. Effects on critical-phenomena studies

D. P. Belanger, A. R. King, I. B. Ferreira, and V. Jaccarino

Phys. Rev. B 37, 226 (1988) - Published 1 January, 1988

Molecular-dynamics simulation of the structural phase transition in Rb2CaCl4

D. P. Billesbach, P. J. Edwardson, and J. R. Hardy

Phys. Rev. B 37, 236 (1988) - Published 1 January, 1988

Magnetic field dependence of the spin dynamics in the reentrant spin glass Fe70.4Al29.6

P. Böni, S. M. Shapiro, and K. Motoya

Phys. Rev. B 37, 243 (1988) - Published 1 January, 1988

Finite-temperature behavior of the Anderson lattice

B. H. Brandow

Phys. Rev. B 37, 250 (1988) - Published 1 January, 1988

Static critical behavior of annealed disordered alloys: Fe1xVx

X. S. Chang and C. Hohenemser

Phys. Rev. B 37, 261 (1988) - Published 1 January, 1988

Neutron-diffraction study of the magnetic ordering in EuAs3, Eu(As1xPx)3, and β-EuP3

T. Chattopadhyay, P. J. Brown, P. Thalmeier, W. Bauhofer, and H. G. von Schnering

Phys. Rev. B 37, 269 (1988) - Published 1 January, 1988

First-principles study of the pressure-induced bcc-hcp transition in Ba

Y. Chen, K. M. Ho, and B. N. Harmon

Phys. Rev. B 37, 283 (1988) - Published 1 January, 1988

Paramagnetic form factors for cubic itinerant electron systems

J. F. Cooke, S. H. Liu, and A. J. Liu

Phys. Rev. B 37, 289 (1988) - Published 1 January, 1988

Random-field effects on the kinetics of a magnetic system with continuous symmetry

Ferdinando de Pasquale, Gene F. Mazenko, Piero Tartaglia, and Marco Zannetti

Phys. Rev. B 37, 296 (1988) - Published 1 January, 1988

Highly efficient algorithm for percolative transport studies in two dimensions

D. J. Frank and C. J. Lobb

Phys. Rev. B 37, 302 (1988) - Published 1 January, 1988

Direct numerical solution of the master-equation transport on disordered lattices via the Lanczos algorithm

Mark S. Friedrichs and Richard A. Friesner

Phys. Rev. B 37, 308 (1988) - Published 1 January, 1988

Effective force constant for a central-force random network

E. J. Garboczi

Phys. Rev. B 37, 318 (1988) - Published 1 January, 1988

Fractal model for disordered magnets

G. Gavoille and J. Hubsch

Phys. Rev. B 37, 321 (1988) - Published 1 January, 1988

Anderson localization and interactions in one-dimensional metals

T. Giamarchi and H. J. Schulz

Phys. Rev. B 37, 325 (1988) - Published 1 January, 1988

Coherent Kondo-lattice state and the crossover transitions in the Anderson-lattice model

H. Kaga, H. Kubo, and T. Fujiwara

Phys. Rev. B 37, 341 (1988) - Published 1 January, 1988

Phase transitions in a quasi-two-dimensional XY random magnetic system

K. Katsumata, J. Tuchendler, Y. J. Uemura, and H. Yoshizawa

Phys. Rev. B 37, 356 (1988) - Published 1 January, 1988

Formation of deep grooves in directional solidification

Douglas A. Kurtze

Phys. Rev. B 37, 370 (1988) - Published 1 January, 1988

Integrable spin-1 Heisenberg chain with impurity

Kong-Ju-Bock Lee and P. Schlottmann

Phys. Rev. B 37, 379 (1988) - Published 1 January, 1988

Band-theoretical study of magnetism in Sc2CuO4

T. C. Leung, X. W. Wang, and B. N. Harmon

Phys. Rev. B 37, 384 (1988) - Published 1 January, 1988

Glass and phase transitions in (KBr)1x(KCN)x

A. Loidl, K. Knorr, J. M. Rowe, and G. J. McIntyre

Phys. Rev. B 37, 389 (1988) - Published 1 January, 1988

Electron-electron interaction from the pressure dependence of the Mössbauer isomer shift of metallic tin

Paul A. Magill and Louis D. Roberts

Phys. Rev. B 37, 399 (1988) - Published 1 January, 1988

Monte Carlo evidence of a phase transition in the two-dimensional step model

Eduardo Sánchez-Velasco and Peter Wills

Phys. Rev. B 37, 406 (1988) - Published 1 January, 1988

Magnetic properties of Cu2Zn1xMnxGeS4: Antiferromagnetic interactions in the wurtz-stannite structure

Y. Shapira, E. J. McNiff, Jr., N. F. Oliveira, Jr., E. D. Honig, K. Dwight, and A. Wold

Phys. Rev. B 37, 411 (1988) - Published 1 January, 1988

Scaling and crossover in a fermion-boson mixture

K. K. Singh

Phys. Rev. B 37, 419 (1988) - Published 1 January, 1988

Exact-eigenstates study of the disordered Hubbard model

Avinash Singh

Phys. Rev. B 37, 430 (1988) - Published 1 January, 1988

Magnetic exchange in disordered metals

Anuradha Jagannathan, Elihu Abrahams, and Michael J. Stephen

Phys. Rev. B 37, 436 (1988) - Published 1 January, 1988

Finite-temperature contributions to the specific heat of the electron-phonon system

Dermot Coffey and C. J. Pethick

Phys. Rev. B 37, 442 (1988) - Published 1 January, 1988

Dielectric relaxation thermodynamics: Comparison with experiment

L. F. del Castillo and L. S. García-Colín

Phys. Rev. B 37, 448 (1988) - Published 1 January, 1988

Magnetic susceptibility of the Suzuki phase formed in NaCl:Mn2+ in the 0.074.2-K temperature range

J. C. Gómez Sal, F. Rodríguez, M. Moreno, and J. L. Tholence

Phys. Rev. B 37, 454 (1988) - Published 1 January, 1988

Orbital effects in magnetic dynamics of thulium iron garnets

A. Lehmann-Szweykowska, P. E. Wigen, L. Kowalewski, M. M. Kaczmarek, and T. B. Mitchell

Phys. Rev. B 37, 459 (1988) - Published 1 January, 1988

Analytic solution of the block-cluster theory of site and bond percolation in arbitrary dimension

G. Ord, B. Payandeh, and M. Robert

Phys. Rev. B 37, 467 (1988) - Published 1 January, 1988

Two-magnon Raman scattering in CdxMn1xF2 mixed crystals

P. Ciepielewski, Z. Kalinski, I. Gregora, and V. Vorlicek

Phys. Rev. B 37, 472 (1988) - Published 1 January, 1988

Fluctuation and bifurcation of the path described by generalized random walks

Hiroaki Hara, Tsunehiro Obata, and Seung Joo Lee

Phys. Rev. B 37, 476 (1988) - Published 1 January, 1988

Anomalous logarithmic slow-dynamics behavior on hierarchical and random systems

Shlomo Havlin and Haim Weissman

Phys. Rev. B 37, 487 (1988) - Published 1 January, 1988

Quasi-one-dimensional solid-liquid phase transition in compounds containing iodine trimers

C. Noguera and P. Le Guennec

Phys. Rev. B 37, 492 (1988) - Published 1 January, 1988

BRIEF REPORTS

Estimation of expectation values formed with Jastrow wave functions

Michael A. Day and Robert J. Hardy

Phys. Rev. B 37, 503 (1988) - Published 1 January, 1988

Structure of icosahedral Al(M1xFex) alloys (M=Cr, Mn, or Fe)

P. J. Schurer, B. Koopmans, and F. van der Woude

Phys. Rev. B 37, 507 (1988) - Published 1 January, 1988

Cu-induced surface disruption of La1.85Sr0.15CuO4

D. M. Hill, Y. Gao, H. M. Meyer, III, T. J. Wagener, J. H. Weaver, and D. W. Capone, II

Phys. Rev. B 37, 511 (1988) - Published 1 January, 1988

Interface formation of semiconductors with high-Tc superconductors: Ge/La1.85Sr0.15CuO4

Y. Gao, T. J. Wagener, J. H. Weaver, and D. W. Capone, II

Phys. Rev. B 37, 515 (1988) - Published 1 January, 1988

Observation of alignment of superconducting YBa2Cu3O7 particles in a magnetic field using neutron diffraction

J. M. Tranquada, A. I. Goldman, A. R. Moodenbaugh, G. Shirane, S. K. Sinha, A. J. Jacobson, and J. T. Lewandowski

Phys. Rev. B 37, 519 (1988) - Published 1 January, 1988

Size of Josephson junctions in Ba-Y-Cu-O compounds

M. Perić, B. Rakvin, M. Prester, N. Brničević, and A. Dulčić

Phys. Rev. B 37, 522 (1988) - Published 1 January, 1988

Model for the role of oxygen defects in oxygen-defect superconductors

J. W. Halley and Herbert B. Shore

Phys. Rev. B 37, 525 (1988) - Published 1 January, 1988

Crystal structure of the oxides BaCuGd2O5 and Ba2Cu3GdO7x

J. A. Campá, J. M. Gómez de Salazar, E. Gutiérrez-Puebla, M. A. Monge, I. Rasines, and C. Ruíz-Valero

Phys. Rev. B 37, 529 (1988) - Published 1 January, 1988

Thermodynamic fluctuations in the high-Tc perovskite superconductors

Aharon Kapitulnik, M. R. Beasley, C. Castellani, and C. Di Castro

Phys. Rev. B 37, 537 (1988) - Published 1 January, 1988

Model for the order-disorder transition in YBa2Cu3Oy

J. M. Bell

Phys. Rev. B 37, 541 (1988) - Published 1 January, 1988

Evidence of low-energy tunneling excitations in the high-Tc superconductor YBa2Cu3O7x

P. Esquinazi, C. Durán, C. Fainstein, and M. Núñez Regueiro

Phys. Rev. B 37, 545 (1988) - Published 1 January, 1988

Time-dependent magnetization of a superconducting glass

M. Tuominen, A. M. Goldman, and M. L. Mecartney

Phys. Rev. B 37, 548 (1988) - Published 1 January, 1988

Heat capacity of the high-temperature superconductor Ba2DyCu3O7

Tooru Atake, Yoshiki Takagi, Tetsurō Nakamura, and Yasutoshi Saito

Phys. Rev. B 37, 552 (1988) - Published 1 January, 1988

Evidence for possible stable superconductivity at 500 K

A. Erbil, A. C. Wright, and E. P. Boyd

Phys. Rev. B 37, 555 (1988) - Published 1 January, 1988

Meissner effect up to 300 K in microscopic regions of Y-Ba-Cu-O

J. F. Riley, W. S. Sampath, K. Y. Lee, N. Mate, and J. W. Blake

Phys. Rev. B 37, 559 (1988) - Published 1 January, 1988

High-resolution x-ray-scattering study of charge-density-wave modulation in chromium

Doon Gibbs, K. M. Mohanty, and Jakob Bohr

Phys. Rev. B 37, 562 (1988) - Published 1 January, 1988

Phase diagram for a random mixture of competing Ising anisotropies

Rita M. Zorzenon dos Santos and Raimundo R. dos Santos

Phys. Rev. B 37, 569 (1988) - Published 1 January, 1988

Mooij correlation in disordered metals

A. M. Jayannavar and N. Kumar

Phys. Rev. B 37, 573 (1988) - Published 1 January, 1988

COMMENTS

Comment on "Time decay of the saturated remanent magnetization in a metallic spin glass"

J. J. Préjean and J. Souletie

Phys. Rev. B 37, 577 (1988) - Published 1 January, 1988

Reply to "Comment on `Time decay of the saturated remanent magnetization in a metallic spin glass' "

P. Granberg, P. Svedlindh, P. Nordblad, and L. Lundgren

Phys. Rev. B 37, 579 (1988) - Published 1 January, 1988

RAPID COMMUNICATIONS

Gauge theory of high-temperature superconductors and strongly correlated Fermi systems

G. Baskaran and P. W. Anderson

Phys. Rev. B 37, 580(R) (1988) - Published 1 January, 1988

Backscattering of high-energy electrons from disordered media: Antienhancement due to the spin-orbit interaction

R. Berkovits and M. Kaveh

Phys. Rev. B 37, 584(R) (1988) - Published 1 January, 1988

Observation of intense two-beam positron diffraction and the precise determination of the positron band gap in rare-gas crystals

E. M. Gullikson, A. P. Mills, Jr.,, and E. G. McRae

Phys. Rev. B 37, 588(R) (1988) - Published 1 January, 1988

Magnetic ordering of Gd and Cu in superconducting and nonsuperconducting GdBa2Cu3O7δ

B. D. Dunlap, M. Slaski, Z. Sungaila, D. G. Hinks, K. Zhang, C. Segre, S. K. Malik, and E. E. Alp

Phys. Rev. B 37, 592(R) (1988) - Published 1 January, 1988

Charged boson condensation in high-Tc superconductors

Xiao-Gang Wen and Rui Kan

Phys. Rev. B 37, 595(R) (1988) - Published 1 January, 1988

Electron-phonon interaction in Ba2 YCu3O7

W. Weber and L. F. Mattheiss

Phys. Rev. B 37, 599(R) (1988) - Published 1 January, 1988

High-Tc superconductor YBa2Cu3O7δ studied by positron annihilation

S. J. Wang, S. V. Naidu, S. C. Sharma, D. K. De, D. Y. Jeong, T. D. Black, S. Krichene, J. R. Reynolds, and J. M. Owens

Phys. Rev. B 37, 603(R) (1988) - Published 1 January, 1988

X-ray and neutron-diffraction study of La1Ba2Cu3O9δ: Influence of the Cu-O structure on Tc

Yi Song, J. P. Golben, S. Chittipeddi, S. I. Lee, R. D. McMichael, X. D. Chen, J. R. Gaines, D. L. Cox, and A. J. Epstein

Phys. Rev. B 37, 607(R) (1988) - Published 1 January, 1988

Thermodynamic fluctuations in the superconductor Y1Ba2Cu3O9y: Evidence for two-dimensional superconductivity

M. Ausloos and Ch. Laurent

Phys. Rev. B 37, 611(R) (1988) - Published 1 January, 1988

Millimeter-wave absorption in La-Ba-Cu-O and Y-Ba-Cu-O superconductors

A. T. Wijeratne, G. L. Dunifer, J. T. Chen, L. E. Wenger, and E. M. Logothetis

Phys. Rev. B 37, 615(R) (1988) - Published 1 January, 1988

Critical-magnetic-field anisotropy in single-crystal YBa2Cu3O7

J. S. Moodera, R. Meservey, J. E. Tkaczyk, C. X. Hao, G. A. Gibson, and P. M. Tedrow

Phys. Rev. B 37, 619(R) (1988) - Published 1 January, 1988

Magnetism and microstructure of YBa2Cu3O7x superconductors produced by rapid solidification

M. E. McHenry, J. McKittrick, S. Sasayama, V. Kwapong, R. C. O'Handley, and G. Kalonji

Phys. Rev. B 37, 623(R) (1988) - Published 1 January, 1988

Neutral fermion, charge-e boson excitations in the resonating-valence-bond state and superconductivity in La2CuO4-based compounds

Z. Zou and P. W. Anderson

Phys. Rev. B 37, 627(R) (1988) - Published 1 January, 1988

High-Tc superconductivity at twin boundaries in a Landau-Ginzburg superconductor oxide model

A. Robledo and C. Varea

Phys. Rev. B 37, 631(R) (1988) - Published 1 January, 1988

Anisotropy in the near-edge absorption fine structure of YBa2Cu3O7δ

P. E. Batson and M. F. Chisholm

Phys. Rev. B 37, 635(R) (1988) - Published 1 January, 1988

Determination of the magnetic field penetration depth in superconducting yttrium barium copper oxide: Deviations from the Bardeen-Cooper-Schrieffer laws

J. R. Cooper, C. T. Chu, L. W. Zhou, B. Dunn, and G. Grüner

Phys. Rev. B 37, 638(R) (1988) - Published 1 January, 1988

Magnetic screening by a thin superconducting surface layer

Charles Kittel, S. Fahy, and Steven G. Louie

Phys. Rev. B 37, 642(R) (1988) - Published 1 January, 1988

Destruction of global superconductivity in quench-condensed metal films

R. S. Markiewicz

Phys. Rev. B 37, 644(R) (1988) - Published 1 January, 1988

Universal criterion for the onset of superconductivity in granular films

Richard A. Ferrell and Behzad Mirhashem

Phys. Rev. B 37, 648(R) (1988) - Published 1 January, 1988

Superconducting energy gap in MBa2Cu3O7δ-type materials

A. Wittlin, L. Genzel, M. Cardona, M. Bauer, W. König, E. García, M. Barahona, and M. V. Cabañas

Phys. Rev. B 37, 652(R) (1988) - Published 1 January, 1988

Ground state of the strong-coupling Hubbard Hamiltonian: A numerical diagonalization study

Efthimios Kaxiras and Efstratios Manousakis

Phys. Rev. B 37, 656(R) (1988) - Published 1 January, 1988

Quasi-two-dimensional behavior of the surface magnetization in a ferromagnet with softened surface exchange

J. Mathon and S. B. Ahmad

Phys. Rev. B 37, 660(R) (1988) - Published 1 January, 1988

Temperature-induced phase transitions in TlReO4: A Raman spectroscopic and x-ray diffraction study

A. Jayaraman, G. A. Kourouklis, R. M. Fleming, and L. G. Van Uitert

Phys. Rev. B 37, 664(R) (1988) - Published 1 January, 1988

Enhanced magnetoresistance of ultrathin (AuCo)n multilayers with perpendicular anisotropy

E. Vélu, C. Dupas, D. Renard, J. P. Renard, and J. Seiden

Phys. Rev. B 37, 668(R) (1988) - Published 1 January, 1988

Percolation and Cosserat elasticity: Exact results on a deterministic fractal

Laurent Limat

Phys. Rev. B 37, 672(R) (1988) - Published 1 January, 1988

Scenario for the Vogel-Fulcher "law"

W. M. Saslow

Phys. Rev. B 37, 676(R) (1988) - Published 1 January, 1988

Isotope effect and pressure dependence of the freezing temperature in proton glasses

B. Tadić, R. Pirc, and R. Blinc

Phys. Rev. B 37, 679(R) (1988) - Published 1 January, 1988

Internal modes of a soliton

P. Kumar and B. S. Thomas

Phys. Rev. B 37, 683(R) (1988) - Published 1 January, 1988

Dendritic solidification of krypton

J. H. Bilgram, M. Firmann, and W. Känzig

Phys. Rev. B 37, 685(R) (1988) - Published 1 January, 1988

Sign In to Your Journals Account

Filter

Filter

Article Lookup

Enter a citation