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Creator | Title | Description | Subject | Date |
| 526 |
 |
Davidson, Diane W. | Evolutionary ecology of symbiotic ant-plant relationships | Abstract.--A tabular survey of ant-plant symbioses worldwide summarizes aspects of the evolutionary ecology of these associations. Remarkable similarities between ant-plant symbioses in disjunct tropical regions result from convergent and parallel evolution of similarly preadapted ants and plants. ... | Symbioses; Evolution; Taxonomic | 1993 |
| 527 |
 |
Golden, Kenneth M. | Exact result for the effective conductivity of a continuum percolation model | A random two-dimensional checkerboard of squares of conductivities 1 and 8 in proportions p and 1 - p is considered. Classical duality implies that the effective conductivity obeys o* = V8 at p = 1/2. It is rigorously found here that to leading order as 8--0, this exact result holds for all p in the... | Particles; Matrix; Checkerboard | 1994 |
| 528 |
 |
Mattis, Daniel C. | Exact solution of a many-fermion system and its associated boson field | Luttinger's exactly soluble model of a one-dimensional many-fermion system is discussed. We show that he did not solve his model properly because of the paradoxical fact that the density operator commutators [p(p), p(-p')], which always vanish for any finite number of particles, no longer vanish in ... | Many-electron problem; Fermi surface; Boson field; Dirac sea | 1965 |
| 529 |
 |
Mattis, Daniel C. | Exact wave functions in superconductivity | The ground-state wave function and some of the excited states of the BCS reduced Hamiltonian are found. In the limit of large volume, the boundary and continuity conditions on the exact wave function lead directly to the equations which Bardeen, Cooper, and Schrieffer found by a variational techniqu... | Ground states | 1961 |
| 530 |
 |
Mattis, Daniel C. | Exactly soluble model of interacting electrons | We diagonalize a many-fermion Hamiltonian consisting of terms quadratic as well as quartic in the field operators. A dual spectrum of eigenstates is an interesting result. We also derive a formula for obtaining the free energy at finite temperature. | Eigenstates; Free energy; Excitation spectrum | 1972 |
| 531 |
 |
Mattis, Daniel C. | Exactly solvable model of a magnetic impurity | A slight modification of the "mixing" term in Anderson's model of a magnetic impurity produces an exactly solvable model. Results of some preliminary calculations are given, and upper and lower bounds on Anderson's model are obtained by means of the exact solutions. . | Magnetic impurity; Ground-state energy; Free energy | 1971-11 |
| 532 |
 |
Symko, Orest George | Exchange interactions and magnetic dimension in Cu(L-alanine)2 | A study of the magnetic properties of the copper (II) complex of the amino acid L-alanine [CU(Lalanine) 2] is reported. The susceptibility of a powder sample has been measured between 0.013 and 240 K. A linear-spin-chain model with antiferromagnetic exchange coupling J = -0.52 K fits well the susce... | Cu(L-alanine)2; Exchange interactions; Magnetic dimension | 1991-01 |
| 533 |
 |
Vardeny, Zeev Valentine; Ehrenfreund, Eitan A. | Excitation dynamics in disubstituted polyacetylene | We studied the excitation dynamics in films of disubstituted polyacetylene, a degenerate ground-state conjugated polymer, using psec transient and steady-state spectroscopies. The polymer is found to support charged and neutral topological soliton excitations concurrent with a strong intrinsic p... | Excitation dynamics; Disubstituted polyacetylene; Laser action | 1999-05 |
| 534 |
 |
Vardeny, Zeev Valentine | Excitation dynamics in single molecular crystals of α-hexathiophene from femtosecond to millisecond | We identify odd- and even-parity states and measure transient photomodulation spectra of Frenkel excitons in a-hexathiophene single crystals. The lowest Frenkel excitons are characterized by a stimulated emission band at ~2 eV and an absorption band at 1.3 eV. Intramolecular internal conversion go... | Excitation dynamics; alpha-hexathiophene; Frenkel excitons; pi-conjugated polymers; Photoexcitation | 2001-04 |
| 535 |
 |
Vardeny, Zeev Valentine; Taylor, P. Craig | Excitation energy dependence of photoinduced absorption in intrinsic a-Si:H | We have studied subgap absorption of intrinsic a-Si:H induced by below- and above-gap photoexcitation. We find very similar photoinduced subgap absorption spectra when excited with 2.4 eV or 1.2 eV light. Both spectra exhibit a power-law dependence on laser intensity ?T ~ 1a, where a is 0.5 and 0.7... | Intrinsic a-Si:H; Subgap absorption; Photoinduced absorption; Gap photoexcitation; Photomodulation; Electronic states | 1998 |
| 536 |
 |
Vardeny, Zeev Valentine; Raikh, Mikhail E. | Excitations in opal photonic crystals infiltrated with polarizable media | Photonic crystals (PC) are a class of artificial structures with a periodic dielectric function. PCs can be a laboratory for testing fundamental processes involving interactions of radiation with matter in novel conditions. We have studied the optical properties of opal PCs that are infiltrated with... | Opal photonic crystals; Polarizable media; Bragg gap; Polaritonic gap; Photonic stop band | 2002 |
| 537 |
 |
Vardeny, Zeev Valentine; Raikh, Mikhail E. | Excitations in photonic crystals infiltrated with polarizable media | Light propagation in a photonic crystal with incomplete band gap, infiltrated with polarizable molecules is considered. We demonstrate that the interplay between the spatial dispersion caused by Bragg diffraction and polaritonic frequency dispersion gives rise to alternative propagating excitation... | Polarizable media; Light propagation; Bragg diffraction; Excitations | 2001-06 |
| 538 |
 |
DeTar, Carleton | Excited states in staggered meson propagators | We report on preliminary results from multi-particle fits to meson propagators with three flavors of light dynamical quarks. We are able to measure excited states in propagators with pion quantum numbers, which we interpret as the pion 2S state, and argue is evidence of locality of the action. In t... | Excited states; Meson propagators | 2004-03 |
| 539 |
 |
Vardeny, Zeev Valentine | Excited-state relaxation in ∏-conjugated polymers | We study ultrafast relaxation processes of odd- (Bu) and even-parity (Ag) exciton states in poly(p-phenylene vinylene) derivatives. The Bu states are studied using a regular two-beam pump-and-probe spectroscopy, which can monitor vibronic relaxation and exciton diffusion. In order to observe the A... | Ultrafast relaxation; Excited-state relaxation; pi-conjugated polymers; PPV | 2002-05 |
| 540 |
 |
Lupton, John Mark | Exciton confinement in organic dendrimer quantum wells for opto-electronic applications | Organic dendrimers are a fascinating new class of materials for opto-electronic applications. We present coupled electronic oscillator calculations on novel nanoscale conjugated dendrimers for use in organic light-emitting diodes. Strong confinement of excitations at the center of the dendrimers is ... | Exciton confinement; Opto-electronic applications; Coupled electronic oscillator | 2002 |
| 541 |
 |
Vardeny, Zeev Valentine | Exciton dynamics in single-walled nanotubes: transient photoinduced dichroism and polarized emission | Ultrafast relaxation of photoexcitations in semiconducting single-walled carbon nanotubes (S-NTs) were investigated using polarized pump-probe photomodulation (with 150 fs time resolution) and cw polarized photoluminescence (PL). Both annealed and unannealed thin NT films and D2O solutions of isola... | Exciton dynamics; Single-walled carbon nanotubes; SWNT; Transient photoinduced dichroism; Polarized emission; Ultrafast relaxation; Photoexcitations | 2005-03 |
| 542 |
 |
Vardeny, Zeev Valentine | Exciton dynamics in soluble poly(p-phenylene vinylene) | We report studies of poly(2,5-dioctyloxy paraphenylene vinylene) thin films and solutions by a variety of transient, steady state, and nonlinear optical techniques. The energy states and optical absorption of the dominant even and odd parity excitons have been determined. Photogenerated singlet exci... | Exciton dynamics; Poly(p-phenylene vinylene); PPV; Pi-conjugated polymers | 1997 |
| 543 |
 |
Vardeny, Zeev Valentine; Gellermann, Werner | Exciton dynamics in soluble poly(p-phenylene-vinylene): toward an ultrafast excitonic switch | We have applied a variety of ps transient and cw optical techniques to elucidate the dynamics, absorption, and emission properties of excitons in soluble derivatives of poly(p-phenylene vinylene) neat films and dilute solutions. We found that the photogenerated singlet excitons in both films and sol... | Exciton dynamics; Excitonic switch | 1997-06 |
| 544 |
 |
Lupton, John Mark | Exciton storage in CdSe/CdS tetrapod semiconductor nanocrystals: electric field effects on exciton and multiexciton states | CdSe/CdS nanocrystal tetrapods are interesting building blocks for excitonic circuits, where the flow of excitation energy is gated by an external stimulus. The physical morphology of the nanoparticle, along with the electronic structure, which favors electron delocalization between the two semicond... | | 2012-01-01 |
| 545 |
 |
Vardeny, Zeev Valentine | Excitons in poly(para-phenylenevinylene) | We show that one-electron band theory fails to describe optical absorption in PPV and the absorption spectrum can be described only within a Coulomb-correlated model. The lowest optical state is an exciton, whose binding energy is estimated theoretically to be 0.90 ± 0 . 1 5 e V Measurements of the... | Poly(para-phenylenevinylene); PPV | 1994-11 |
| 546 |
 |
Vardeny, Zeev Valentine | Excitons, polarons, and laser action in poly(p-phenylene vinylene) films | We have used a multitude of linear and nonlinear cw optical spectroscopies to study the optical properties of water precursor poly(p-phenylene vinylene) (PPV) thin films. These spectroscopies include absorption, photoluminescence, photoinduced absorption and their respective optically detected magne... | PPV films; Excitons; Laser action; Poly(p-phenylene vinylene) | 2003 |
| 547 |
 |
Mattis, Daniel C. | Existence of two phase transitions in Hubbard model | We solve the Hubbard model, for one electron per atom in a simple cubic structure, using one-particle Green's functions. We determine the accuracy of this calculation to be good by comparison with an exact solution by Lieb and Wu of a one-dimensional limiting case. | Critical temperature | 1969-12 |
| 548 |
 |
DeTar, Carleton | Exotic hybrid mesons from improved Kogut-Susskind fermions | We summarize our measurement of the mass of the exotic 1−+ hybrid meson using an improved Kogut-Susskind action. We show results from both quenched and dynamical quark simulations and compare with results from Wilson quarks. Extrapolation of these results to the physical quark mass allows compar... | Chromomagnetic field; Kogut-Susskind fermions; Wilson quarks | 2003-05 |
| 549 |
 |
DeTar, Carleton | Exotic hybrid mesons with light quarks | Hybrid mesons, made from a quark, an antiquark and gluons, can have quantum numbers inaccessible to conventional quark-antiquark states. Confirmation of such states would give information on the role of "dynamical" color in low energy QCD. We present preliminary results for hybrid meson masses using... | Hybrid mesons; Kogut-Susskind quarks; Wilson quarks | 1997-02 |
| 550 |
 |
DeTar, Carleton | Exotic meson spectroscopy from the clover action at β = 5.85 and 6.15* | We repeat our original simulations of the hybrid meson spectrum using the clover action, as a check on lattice artifacts. Our results for the 1−+ masses do not substantially change. We present preliminary results for the wave function of the 1−+ state in Coulomb gauge. | Clover action; Quark spectroscopy | 1999-03 |
