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Articles 1 - 11 of 11

Full-Text Articles in Physics

Orientational Phases For M3C60, Taner Yildirim, Suklyun Hong, A. Brooks Harris, Eugene J. Mele Oct 1993

Orientational Phases For M3C60, Taner Yildirim, Suklyun Hong, A. Brooks Harris, Eugene J. Mele

Department of Physics Papers

The mechanism of the orientational ordering of C60 in alkali-metal-doped fullerenes M3C60 is studied. Since the M-C60 (M=K,Rb) interactions cause the C60 molecules to assume one of two standard orientations, this model is equivalent to a generalized Ising model on a fcc lattice. The Ising interactions depend on two type of energies: (1) the direct interaction, i.e., the orientationally dependent part of interactions between nearest-neighboring C60 molecules (each carrying charge -3e), and (2) the band energy of the electrons transferred from M+ ions to the C603- ...


Renormalization Of Chiral Couplings In Tilted Bilayer Membranes, Philip C. Nelson, Thomas Powers Oct 1993

Renormalization Of Chiral Couplings In Tilted Bilayer Membranes, Philip C. Nelson, Thomas Powers

Department of Physics Papers

We study the effects of chiral constituent molecules on the macroscopic shapes attained by lipid bilayer membranes. Such fluid membranes are beautiful examples of statistical ensembles of random shapes~ sometimes coupled to in-plane order. We analyze them with methods of continuum elasticity theory, generalizing the well-known Canham-Helfrich model, and in particular incorporate the effects of thermal fluctuations. The condition that coordinate choice be immaterial greatly constrains the possible forms of the statistical weights in these systems, leading to very few independent couplings and hence physically simple models. Thermal fluctuations effectively reduce the chirality of a membrane at long scales leading ...


Evidence For Two Exponent Scaling In The Random Field Ising Model, Michael Gofman, Joan Adler, Amnon Aharony, A. Brooks Harris, Moshe Schwartz Sep 1993

Evidence For Two Exponent Scaling In The Random Field Ising Model, Michael Gofman, Joan Adler, Amnon Aharony, A. Brooks Harris, Moshe Schwartz

Department of Physics Papers

Novel methods were used to generate and analyze new 15 term high temperature series for both the (connected) susceptibility χ and the structure factor (disconnected susceptibility) χd for the random field Ising model with dimensionless coupling K=J/kT, in general dimension d. For both the bimodal and the Gaussian field distributions, with mean square field J2g, we find that (χd-χ)/K2gχ2=1 as TTc(g), for a range of [h2]=J2g and d=3,4,5. This confirms the exponent relation γ¯=2γ (where χ ...


Orientational Phase Transition In Naxc60 (1 < X < 3), Taner Yildirim, John E. Fischer, A. Brooks Harris, Peter W. Stephens, Dan Liu, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii Aug 1993

Orientational Phase Transition In Naxc60 (1 < X < 3), Taner Yildirim, John E. Fischer, A. Brooks Harris, Peter W. Stephens, Dan Liu, Laurent Brard, Robert M. Strongin, Amos B. Smith Iii

Department of Physics Papers

X-ray diffraction and calorimetry data on cubic NaxC60(1<xTm above that of pure C60, e.g., Tm(x=1.3)=325 K. The ordered phases are the same as in pure C60: simple cubic, space group Pa3¯, but the orientations in the disordered phase are more restricted. We explain how Na stabilizes the ordered phase to rather high T, while K and Rb do not, in terms of Coulomb interactions between C60 molecules and and Na ions which we calculate from the local density approximation charge density of C ...


Multipole Approach To Orientational Interactions In Solid C60, Taner Yildirim, A. Brooks Harris, Steven C. Erwin, Mark R. Pederson Jul 1993

Multipole Approach To Orientational Interactions In Solid C60, Taner Yildirim, A. Brooks Harris, Steven C. Erwin, Mark R. Pederson

Department of Physics Papers

We calculate electrostatic multipole moments of C60 up to l=18 using the quantum-mechanical charge distribution with icosahedral symmetry obtained from ab initio calculations. It is found that the second nonzero moment (l=10) is comparable to the first nonzero moment (l=6). The values of several low-order multipole moments are almost 10 times smaller than those found from the charge distribution of recently proposed potential models and thus the actual Coulomb interaction between C60 molecules is much smaller than previously predicted. Much better agreement with calculated multipoles is obtained from a model which introduces point charges at ...


Heisenberg Antiferromagnet With A Low Concentration Of Static Defects, C. C. Wan, A. Brooks Harris, Deepak Kumar Jul 1993

Heisenberg Antiferromagnet With A Low Concentration Of Static Defects, C. C. Wan, A. Brooks Harris, Deepak Kumar

Department of Physics Papers

The static and dynamic response associated with a low concentration x of static defects in a Heisenberg antiferromagnet at zero temperature is analyzed within linearized spin-wave theory via a boson formalism involving a non-Hermitian potential. We obtain the dispersion relation for long-wavelength spin waves in the form ω(q)=c(x)q+iγ(x)qτ. Our results for c(x) agree with previous work and, in particular, give c(x)=c(0)[1-αx+O(x2)], where the coefficient α, which can be related to the helicity modulus and the uniform perpendicular susceptibility, diverges in the limit ...


Was Superlocalization Observed In Carbon-Black–Polymer Composites?, Amnon Aharony, A. Brooks Harris, Ora Entin-Wohlman Jun 1993

Was Superlocalization Observed In Carbon-Black–Polymer Composites?, Amnon Aharony, A. Brooks Harris, Ora Entin-Wohlman

Department of Physics Papers

A Comment on the Letter by van der Putten, Phys. Rev. Lett. 69, 494 (1992).


Interatomic Forces And Atomic Structure Of Grain Boundaries In Copper-Bismuth Alloys, Min Yan, Mojmír Šob, David E. Luzzi, Vaclav Vitek, Graeme J. Ackland, M. Methfessel, C. O. Rodriguez Mar 1993

Interatomic Forces And Atomic Structure Of Grain Boundaries In Copper-Bismuth Alloys, Min Yan, Mojmír Šob, David E. Luzzi, Vaclav Vitek, Graeme J. Ackland, M. Methfessel, C. O. Rodriguez

Departmental Papers (MSE)

The many-body empirical potentials that describe atomic interactions in the copper-bismuth system were constructed using both experimental data and physical quantities obtained by ab initio full-potential linear muffin-tin orbital calculations for a metastable Cu3Bi compound. These potentials were then used to calculate the structure of a grain boundary in copper containing bismuth, which was at the same time studied by high-resolution electron microscopy (HREM). Excellent agreement between the calculated and observed structures is shown by comparing a through-focal series of observed and calculated images. This agreement validates the constructed potentials, which can be used with a high confidence ...


Distribution Of The Logarithms Of Currents In Percolating Resistor Networks. Ii. Series Expansions, Joan Adler, Amnon Aharony, Raphael Blumenfeld, A. Brooks Harris, Yigal Meir Mar 1993

Distribution Of The Logarithms Of Currents In Percolating Resistor Networks. Ii. Series Expansions, Joan Adler, Amnon Aharony, Raphael Blumenfeld, A. Brooks Harris, Yigal Meir

Department of Physics Papers

We investigate the distribution of the logarithms, logi, of the currents in percolating resistor networks via the method of series expansions. Exact results in one dimension and expansions to thirteenth order in the bond occupation probability, p, in general dimension, for the moments of this distribution have been generated. We have studied both the moments and cumulants derived therefrom with several extrapolation procedures. The results have been compared with recent predictions for the behavior of the moments and cumulants of this distribution. An extensive comparison between exact results and series of different lengths in one dimension sheds light on ...


Distribution Of The Logarithms Of Currents In Percolating Resistor Networks. I. Theory, Amnon Aharony, Raphael Blumenfeld, A. Brooks Harris Mar 1993

Distribution Of The Logarithms Of Currents In Percolating Resistor Networks. I. Theory, Amnon Aharony, Raphael Blumenfeld, A. Brooks Harris

Department of Physics Papers

The distribution of currents, ib, in the bonds b of a randomly diluted resistor network at the percolation threshold is investigated through a study of the moments of the distribution P^(i2) and the moments of the distribution P(y), where y=-lnib2. For q>qc the qth moment of P^(i2), Mq (i.e., the average of i2q), scales as a power law of the system size L, with a multifractal (noise) exponent ψ̃(q)-ψ̃(0). Numerical data indicate that qc is negative, but becomes small for ...


Comment On "New Orientationally Ordered Low-Temperature Superstructure In High-Purity C60", A. Brooks Harris, Ravi Sachidanandam Jan 1993

Comment On "New Orientationally Ordered Low-Temperature Superstructure In High-Purity C60", A. Brooks Harris, Ravi Sachidanandam

Department of Physics Papers

A Comment on the Letter by G. Van Tendeloo et al. Phys. Rev. Lett. 69, 1065 (1992).