Hybrid turbidite-drift channel complexes: An integrated multiscale model

The interaction of deep-marine bottom currents with episodic, unsteady sediment gravity flows affects global sediment transport, forms climate archives, and controls the evolution of continental slopes. Despite their importance, contradictory hypotheses for reconstructing past flow regimes have arisen from a paucity of studies and the lack of direct monitoring of such hybrid systems. Here, we address this controversy by analyzing deposits, high-resolution seafloor data, and near-bed current measurements from two sites where eastward-flowing gravity flows interact(ed) with northward-flowing bottom currents. Extensive seismic and core data from offshore Tanzania reveal a 1650-m-thick asymmetric hybrid channel levee-drift system, deposited over a period of ∼20 m.y. (Upper Cretaceous to Paleocene). High-resolution modern seafloor data from offshore Mozambique reveal similar asymmetric channel geometries, which are related to northward-flowing near-bed currents with measured velocities of up to 1.4 m/s. Higher sediment accumulation occurs on the downstream flank of channel margins (with respect to bottom currents), with inhibited deposition or scouring on the upstream flank (where velocities are highest). Toes of the drift deposits, consisting of thick laminated muddy siltstone, which progressively step back into the channel axis over time, result in an interfingering relationship with the sandstone-dominated channel fill. Bottom-current flow directions contrast with those of previous models, which lacked direct current measurements or paleoflow indicators. We finally show how large-scale depositional architecture is built through the temporally variable coupling of these two globally important sediment transport processes. Our findings enable more-robust reconstructions of past oceanic circulation and diagnosis of ancient hybrid turbidite-drift systems

Supersymmetric Model of a 2D Long-Range Bose Liquid

The model Hamiltonian of a two-dimensional Bose liquid (proposed earlier by Kane, Kivelson, Lee and Zhang as the Hamiltonian which has Jastrow-type wavefunctions as the ground-state solution), is shown to possess nonrelativistic supersymmetry. For the special value of the coupling constant $\alpha=1/2$ the quantum mechanics described by this Hamiltonian is shown to be equivalent to the dynamics of (complex) eigenvalues of random Gaussian ensemble of normal complex matrices. For general $\alpha$, an exact relation between the equal-time current-current and density-density correlation functions is obtained, and used to derive an asymptotically exact (at low wavevectors q) spectrum of single-particle excitations beyond the superfluid ground-state (realized at low $\alpha$'s). The ground-state at very large $\alpha$ is shown to be of ``Quantum Hexatic" type, possessing long-range orientational order and quasi-long-range translational order but with zero shear modulus. Possible scenaria of the ground-state phase transitions as function of $\alpha$ are discussed.Comment: Revtex; 12 pages, 1 Postscript figur

Quantum Monte Carlo simulation for the conductance of one-dimensional quantum spin systems

Recently, the stochastic series expansion (SSE) has been proposed as a powerful MC-method, which allows simulations at low $T$ for quantum-spin systems. We show that the SSE allows to compute the magnetic conductance for various one-dimensional spin systems without further approximations. We consider various modifications of the anisotropic Heisenberg chain. We recover the Kane-Fisher scaling for one impurity in a Luttinger-liquid and study the influence of non-interacting leads for the conductance of an interacting system.Comment: 8 pages, 9 figure

Tests of Higgs and Top Effective Interactions

We study the possibility to detect heavy physics effects in the interactions of Higgs bosons and the top quark at future colliders using the effective Lagrangian approach. The modification of the interactions may enhance the production of Higgs bosons at hadron colliders through the mechanisms of gluon fusion and associated production with a W boson or $t\bar{t}$ pairs. The most promising signature is through the decay of the Higgs boson into two photons, whose branching ratio is also enhanced in this approach. As a consequence of our analysis we get a bound on the chromomagnetic dipole moment of the top quark.Comment: 14 pages, Latex, two figures available by fax under request. To be published in Phys. Lett

Book Reviews

Book 1 Book Title: Basic EpidemiologyBook Authors: R. Beaglehole, R. Bonita & T. KjellströmPp. viii + 174. (in English, French and Spanish in preparation). $19,40. Geneva: WHO. 1993. Order No. 1150395. ISBN 92-4-154446-5.Book 2Book Title: A Pocket Book of Social and Community PaediatricsBook Author: Jo SibertPp. viii + 164. London: Edward Arnold. 1992. ISBN 0-340-54929-7.Book 3Book Title: Knowledge Beats CancerBook Author: Albert Stegmann AlbertsPp. 226. Illustrated. R55,45. Pretoria: Haum Tertiary. 1993. ISBN 0-7986-3196-1.Book 4Book Title: AIDS and Your ResponsePp. vi + 226. R49,50. ISBN 0-620-17319-X.Book 5Book Title: Principles for Evaluating Chemical Effects on the Aged Population. Enviromnental Health Criteria. No. 144Book Author: W.H.O.Pp. 159. (English only).$20,50. Geneva: WHO. 1993. Order No. 1160144. ISBN 92-4-1571446.Book 6Book Title: The Guide to Heart Sounds: Normal and AbnormalBook Authors: Donald W. Novey, Marcia Pencak & John M. StangAudio-cassette narrated by: Donald W. Novey. pp. xi + 74. Illustrated. Florida: CRC Press. 1988. ISB J 0-8493-0153X.Book 7Book Title: Propachlor. Enviromnental Health Criteria. No. 147Book Author: W.H.O.Pp. 110. (English, French and Spanish summaries). $17,30. Geneva: WHO. 1993. Order TO. 1160147. ISBN 92-4-157147-0.Book 8Book Title: Quality Assurance in Health Care: A HandbookBook Authors: Roger Ellis & Dorothy WhittingronLondon: Edward Arnold. 1993. ISBN 0-340-55273-5.Book 9Book Title:  Rehabilitation after Cardiovascular Diseases, with Special Emphasis on Developing CountriesReport of a WHO expert committee. Technical Report Series No 831. Pp. viii + 122 (available in English, French and Spanish in preparation). Geneva: WHO. 1993. ISBN 92-4-120831-7

Analysis of the vertexes ΞQ∗ΞQ′V\Xi_Q^*\Xi'_Q V, ΣQ∗ΣQV\Sigma_Q^*\Sigma_Q V and radiative decays ΞQ∗→ΞQ′γ\Xi_Q^*\to \Xi'_Q \gamma, ΣQ∗→ΣQγ\Sigma_Q^*\to \Sigma_Q \gamma

In this article, we study the vertexes $\Xi_Q^*\Xi'_Q V$ and $\Sigma_Q^* \Sigma_Q V$ with the light-cone QCD sum rules, then assume the vector meson dominance of the intermediate $\phi(1020)$, $\rho(770)$ and $\omega(782)$, and calculate the radiative decays $\Xi_Q^*\to \Xi'_Q \gamma$ and $\Sigma_Q^*\to \Sigma_Q \gamma$.Comment: 28 pages, 4 tables, revised versio

Investigation of continuous-time quantum walk on root lattice AnA_n and honeycomb lattice

The continuous-time quantum walk (CTQW) on root lattice $A_n$ (known as hexagonal lattice for $n=2$) and honeycomb one is investigated by using spectral distribution method. To this aim, some association schemes are constructed from abelian group $Z^{\otimes n}_m$ and two copies of finite hexagonal lattices, such that their underlying graphs tend to root lattice $A_n$ and honeycomb one, as the size of the underlying graphs grows to infinity. The CTQW on these underlying graphs is investigated by using the spectral distribution method and stratification of the graphs based on Terwilliger algebra, where we get the required results for root lattice $A_n$ and honeycomb one, from large enough underlying graphs. Moreover, by using the stationary phase method, the long time behavior of CTQW on infinite graphs is approximated with finite ones. Also it is shown that the Bose-Mesner algebras of our constructed association schemes (called $n$-variable $P$-polynomial) can be generated by $n$ commuting generators, where raising, flat and lowering operators (as elements of Terwilliger algebra) are associated with each generator. A system of $n$-variable orthogonal polynomials which are special cases of \textit{generalized} Gegenbauer polynomials is constructed, where the probability amplitudes are given by integrals over these polynomials or their linear combinations. Finally the suppersymmetric structure of finite honeycomb lattices is revealed. Keywords: underlying graphs of association schemes, continuous-time quantum walk, orthogonal polynomials, spectral distribution. PACs Index: 03.65.UdComment: 41 pages, 4 figure

Universal Quantum Computation using Exchange Interactions and Teleportation of Single-Qubit Operations

We show how to construct a universal set of quantum logic gates using control over exchange interactions and single- and two-spin measurements only. Single-spin unitary operations are teleported instead of being executed directly, thus eliminating a major difficulty in the construction of several of the most promising proposals for solid-state quantum computation, such as spin-coupled quantum dots, donor-atom nuclear spins in silicon, and electrons on helium. Contrary to previous proposals dealing with this difficulty, our scheme requires no encoding redundancy. We also discuss an application to superconducting phase qubits.Comment: 4.5 pages, including 2 figure

Decoherence of electron spin qubits in Si-based quantum computers

Direct phonon spin-lattice relaxation of an electron qubit bound by a donor impurity or quantum dot in SiGe heterostructures is investigated. The aim is to evaluate the importance of decoherence from this mechanism in several important solid-state quantum computer designs operating at low temperatures. We calculate the relaxation rate $1/T_1$ as a function of [100] uniaxial strain, temperature, magnetic field, and silicon/germanium content for Si:P bound electrons. The quantum dot potential is much smoother, leading to smaller splittings of the valley degeneracies. We have estimated these splittings in order to obtain upper bounds for the relaxation rate. In general, we find that the relaxation rate is strongly decreased by uniaxial compressive strain in a SiGe-Si-SiGe quantum well, making this strain an important positive design feature. Ge in high concentrations (particularly over 85%) increases the rate, making Si-rich materials preferable. We conclude that SiGe bound electron qubits must meet certain conditions to minimize decoherence but that spin-phonon relaxation does not rule out the solid-state implementation of error-tolerant quantum computing.Comment: 8 figures. To appear in PRB-July 2002. Revisions include: some references added/corrected, several typos fixed, a few things clarified. Nothing dramati