5,553 research outputs found
Multiscale models of colloidal dispersion of particles in nematic liquid crystals
We use homogenization theory to develop a multiscale model of colloidal dispersion of particles in nematic liquid crystals under weak-anchoring conditions. We validate the model by comparing it with simulations by using the Landauâde Gennes free energy and show that the agreement is excellent. We then use the multiscale model to study the effect that particle anisotropy has on the liquid crystal: spherically symmetric particles always reduce the effective elastic constant. Asymmetric particles introduce an effective alignment field that can increase the Fredericks threshold and decrease the switch-off time
Performing joint measurements and transformations on several qubits by operating on a single control qubit
An n-qubit quantum register can in principle be completely controlled by
operating on a single qubit that interacts with the register via an appropriate
fixed interaction. We consider a hypothetical system consisting of n spin-1/2
nuclei that interact with an electron spin via a magnetic interaction. We
describe algorithms that measure non-trivial joint observables on the register
by acting on the control spin only. For large n this is not an efficient model
for universal quantum computation but it can be modified to an efficient one if
one allows n possible positions of the control particle.
This toy model of measurements illustrates in which way specific interactions
between the register and a probe particle support specific types of joint
measurements in the sense that some joint observables can be measured by simple
sequences of operations on the probe particle.Comment: 7 pages, revtex, 3 figure
cis-6-Methoxycarbonyl-2,10-dioxa-1-phosphabicyclo[4.4.0]decane 1-Oxide
The crystal structure of the title compound, C9H1505P, is described. The molecule consists of two cis-fused six-membered rings, both in the chair conformation.
Recombinant Mitochondrial Transcription Factor A with N-terminal Mitochondrial Transduction Domain Increases Respiration and Mitochondrial Gene Expression in G11778A Leber's Hereditary Optic Neuropathy Cybrid Cells
Diseases involving mitochondrial defects usually manifest themselves in high-energy, post-mitotic tissues such as brain, retina, skeletal and cardiac muscle and frequently cause deficiencies in mitochondrial bioenergetics. We have developed a scalable procedure to produce recombinant human mitochondrial transcription factor A (TFAM) modified with an N-terminal protein transduction domain (PTD) and mitochondrial localization signal (MLS) that allow it to cross membranes and enter mitochondria through its "mitochondrial transduction domain" (MTD,=PTD+MLS). _In vitro_ studies in a classic mitochondrial disease cell model demonstrated that Alexa488-labeled MTD-TFAM rapidly entered the mitochondrial compartment. MTD-TFAM treatment of these cell lines reversibly increased oxygen consumption (respiration) rates 3-fold, levels of respiratory proteins and mitochondrial gene expression. _In vivo_ results demonstrated that respiration increased to lesser degrees in mitochondria from tissues of mice injected with MTD-TFAM. MTD-TFAM can alter mitochondrial bioenergetics and holds promise for treatment of mitochondrial diseases involving deficiencies of energy production
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Surface and interstitial Ti diffusion at the rutile TiO2(110) surface
Diffusion of Ti through the TiO2 (110) rutile surface plays a key role in the growth and reactivity of TiO2. To understand the fundamental aspects of this important process, we present an analysis of the diffusion of Ti adspecies at the stoichiometric TiO2(110) surface using complementary computational methodologies of density functional theory corrected for on-site Coulomb interactions (DFT+U) and a charge equilibration (QEq) atomistic potential to identify minimum energy pathways. We find that diffusion of Ti from the surface to subsurface (and vice versa) follows an intersticialcy exchange mechanism, involving exchange of surface Ti with the 6-fold coordinated Ti below the bridging oxygen rows. Diffusion in the subsurface between layers also follows an interstitialcy mechanism. The diffusion of Ti is discussed in light of continued attempts
to understand the re-oxidation of non-stoichiometric TiO2(110) surfaces
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Summary Hydrogeologic Assessment U.S. Department of Energy Pantex Plant, Carson County, Texas
In 1990, the Bureau of Economic Geology (BEG) and the Department of Geological Sciences (DOGS) at The University of Texas at Austin and the Water Resources Center (WRC) at Texas Tech University began a five-year program, funded by the Department of Energy (DOE) through the Governor's Office of the State of Texas, to characterize the geohydrology of Pantex Plant. The purpose of this work, which is summarized in this report, was to provide data and information that would assist in the remediation of contaminated sites at Pantex and support the State of Texas in its review of the Department of Energy's (DOE's) remediation program. The results of this investigation describe the physical setting and heterogeneities that control movement and distribution of contaminants and the processes that affect rates and fate of contaminants. The fate and distribution of contaminants, the selection and application of appropriate remediation approaches, the evaluation of the effectiveness of remediation technologies, and the proper monitoring of the affected environment all depend on knowledge of the controls and rates of active processes at Pantex Plant.Bureau of Economic Geolog
Economical quantum cloning in any dimension
The possibility of cloning a d-dimensional quantum system without an ancilla
is explored, extending on the economical phase-covariant cloning machine found
in [Phys. Rev. A {\bf 60}, 2764 (1999)] for qubits. We prove the impossibility
of constructing an economical version of the optimal universal cloning machine
in any dimension. We also show, using an ansatz on the generic form of cloning
machines, that the d-dimensional phase-covariant cloner, which optimally clones
all uniform superpositions, can be realized economically only in dimension d=2.
The used ansatz is supported by numerical evidence up to d=7. An economical
phase-covariant cloner can nevertheless be constructed for d>2, albeit with a
lower fidelity than that of the optimal cloner requiring an ancilla. Finally,
using again an ansatz on cloning machines, we show that an economical version
of the Fourier-covariant cloner, which optimally clones the computational basis
and its Fourier transform, is also possible only in dimension d=2.Comment: 8 pages RevTe
Complexity of decoupling and time-reversal for n spins with pair-interactions: Arrow of time in quantum control
Well-known Nuclear Magnetic Resonance experiments show that the time
evolution according to (truncated) dipole-dipole interactions between n spins
can be inverted by simple pulse sequences. Independent of n, the reversed
evolution is only two times slower than the original one. Here we consider more
general spin-spin couplings with long range. We prove that some are
considerably more complex to invert since the number of required time steps and
the slow-down of the reversed evolutions are necessarily of the order n.
Furthermore, the spins have to be addressed separately. We show for which
values of the coupling parameters the phase transition between simple and
complex time-reversal schemes occurs.Comment: Completely rewritten, new lower bounds on the number of time steps,
applications and references adde
The effectiveness of quantum operations for eavesdropping on sealed messages
A quantum protocol is described which enables a user to send sealed messages
and that allows for the detection of active eavesdroppers. We examine a class
of eavesdropping strategies, those that make use of quantum operations, and we
determine the information gain versus disturbance caused by these strategies.
We demonstrate this tradeoff with an example and we compare this protocol to
quantum key distribution, quantum direct communication, and quantum seal
protocols.Comment: 10 pages, 2 figures. Third Feynman Festival, 25 -- 29 August 2006,
University of Maryland, College Park, Maryland, U.S.
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