16,647 research outputs found
Dicarba-closo-dodecarborane-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium : biological relevance and synthetic strategies
This review describes how the incorporation of dicarba-closo-dodecarboranes into half-sandwich complexes of ruthenium, osmium, rhodium and iridium might lead to the development of a new class of compounds with applications in medicine. Such a combination not only has unexplored potential in traditional areas such as Boron Neutron Capture Therapy agents, but also as pharmacophores for the targeting of biologically important proteins and the development of targeted drugs. The synthetic pathways used for the syntheses of dicarba-closo-dodecarboranes-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium are also reviewed. Complexes with a wide variety of geometries and characteristics can be prepared. Examples of addition reactions on the metal centre, BâH activation, transmetalation reactions and/or direct formation of metalâmetal bonds are discussed (103 references)
New Internal Stress Driven on-Chip Micromachines for Extracting Mechanical Properties of Thin Films
A new concept of micromachines has been developed for measuring the
mechanical properties of thin metallic films. The actuator is a beam undergoing
large internal stresses built up during the deposition process. Al thin films
are deposited partly on the actuator beam and on the substrate. By etching the
structure, the actuator contracts and pulls the Al film. Full stress strain
curves can be generated by designing a set of micromachines with various
actuator lengths. In the present study, the displacements have been measured by
scanning electronic microscopy. The stress is derived from simple continuum
mechanics relationships. The tensile properties of Al films of various
thicknesses have been tested. A marked increase of the strength with decreasing
film thickness is observed.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Non-Existence of Time-Periodic Solutions of the Dirac Equation in a Reissner-Nordstrom Black Hole Background
It is shown analytically that the Dirac equation has no normalizable,
time-periodic solutions in a Reissner-Nordstrom black hole background; in
particular, there are no static solutions of the Dirac equation in such a
background field. The physical interpretation is that Dirac particles can
either disappear into the black hole or escape to infinity, but they cannot
stay on a periodic orbit around the black hole.Comment: 24 pages, 2 figures (published version
An alternative approach to efficient simulation of micro/nanoscale phonon transport
Starting from the recently proposed energy-based deviational formulation for
solving the Boltzmann equation [J.-P. Peraud and N. G. Hadjiconstantinou, Phys.
Rev. B 84, 2011], which provides significant computational speedup compared to
standard Monte Carlo methods for small deviations from equilibrium, we show
that additional computational benefits are possible in the limit that the
governing equation can be linearized. The proposed method exploits the
observation that under linearized conditions (small temperature differences)
the trajectories of individual deviational particles can be decoupled and thus
simulated independently; this leads to a particularly simple and efficient
algorithm for simulating steady and transient problems in arbitrary
three-dimensional geometries, without introducing any additional approximation.Comment: 4 pages, 2 figure
Protecting clean critical points by local disorder correlations
We show that a broad class of quantum critical points can be stable against
locally correlated disorder even if they are unstable against uncorrelated
disorder. Although this result seemingly contradicts the Harris criterion, it
follows naturally from the absence of a random-mass term in the associated
order-parameter field theory. We illustrate the general concept with explicit
calculations for quantum spin-chain models. Instead of the infinite-randomness
physics induced by uncorrelated disorder, we find that weak locally correlated
disorder is irrelevant. For larger disorder, we find a line of critical points
with unusual properties such as an increase of the entanglement entropy with
the disorder strength. We also propose experimental realizations in the context
of quantum magnetism and cold-atom physics.Comment: 5 pages, 3 figures; published versio
A quantum de Finetti theorem in phase space representation
The quantum versions of de Finetti's theorem derived so far express the
convergence of n-partite symmetric states, i.e., states that are invariant
under permutations of their n parties, towards probabilistic mixtures of
independent and identically distributed (i.i.d.) states. Unfortunately, these
theorems only hold in finite-dimensional Hilbert spaces, and their direct
generalization to infinite-dimensional Hilbert spaces is known to fail. Here,
we address this problem by considering invariance under orthogonal
transformations in phase space instead of permutations in state space, which
leads to a new type of quantum de Finetti's theorem that is particularly
relevant to continuous-variable systems. Specifically, an n-mode bosonic state
that is invariant with respect to this continuous symmetry in phase space is
proven to converge towards a probabilistic mixture of i.i.d. Gaussian states
(actually, n identical thermal states).Comment: 5 page
Soft-tissue specimens from pre-European extinct birds of New Zealand
We provide the first complete review of soft tissue remains from New Zealand birds that became extinct prior to European settlement (c. AD 1800). These rare specimens allow insights into the anatomy and appearance of the birds that are not attainable from bones. Our review includes previously unpublished records of âlostâ specimens, and descriptions of recently discovered specimens such as the first evidence of soft tissues from the South Island goose (Cnemiornis calcitrans). Overall, the soft tissue remains are dominated by moa (with specimens from each of the six genera), but also include specimens from Finsch's duck (Chenonetta finschi) and the New Zealand owlet-nightjar (Aegotheles novaezealandiae). All desiccated soft tissue specimens that have radiocarbon or stratigraphic dates are late Holocene in age, and most have been found in the semi-arid region of Central Otago
Scaling of Entanglement Entropy in the Random Singlet Phase
We present numerical evidences for the logarithmic scaling of the
entanglement entropy in critical random spin chains. Very large scale exact
diagonalizations performed at the critical XX point up to L=2000 spins 1/2 lead
to a perfect agreement with recent real-space renormalization-group predictions
of Refael and Moore [Phys. Rev. Lett. {\bf 93}, 260602 (2004)] for the
logarithmic scaling of the entanglement entropy in the Random Singlet Phase
with an effective central charge . Moreover we
provide the first visual proof of the existence the Random Singlet Phase thanks
to the quantum entanglement concept.Comment: 4 pages, 3 figure
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