6,871 research outputs found
A method to find quantum noiseless subsystems
We develop a structure theory for decoherence-free subspaces and noiseless
subsystems that applies to arbitrary (not necessarily unital) quantum
operations. The theory can be alternatively phrased in terms of the
superoperator perspective, or the algebraic noise commutant formalism. As an
application, we propose a method for finding all such subspaces and subsystems
for arbitrary quantum operations. We suggest that this work brings the
fundamental passive technique for error correction in quantum computing an
important step closer to practical realization.Comment: 5 pages, to appear in Physical Review Letter
Development of a high-sensitivity torsion balance to investigate the thermal Casimir force
We report development of a high-sensitivity torsion balance to measure the
thermal Casimir force. Special emphasis is placed on experimental
investigations of a possible surface electric force originating from surface
patch potentials that have been recently noticed by several experimental
groups. By gaining a proper understanding of the actual contribution of the
surface electric force in real materials, we aim to undertake precision force
measurements to resolve the Casimir force at finite temperature in real metals,
as well as in other semiconducting materials, such as graphene.Comment: Proceedings of the 10th International Conference "Quantum Field
Theory Under the Influence of External Conditions"; 11 pages and 4 figure
Fiber-top atomic force microscope
We present the implementation of an atomic force microscope (AFM) based on fiber-top design. Our results demonstrate that the performances of fiber-top AFMs in contact mode are comparable to those of similar commercially available instruments. Our device thus represents an interesting\ud
alternative to existing AFMs, particularly for applications outside specialized research laboratories, where a compact, user-friendly, and versatile tool might often be preferred
Parametrical optimization of laser surface alloyed NiTi shape memory alloy with Co and Nb by the Taguchi method
Different high-purity metal powders were successfully alloyed on to a nickel titanium (NiTi) shape memory alloy (SMA) with a 3 kW carbon dioxide (CO2) laser system. In order to produce an alloyed layer with complete penetration and acceptable composition profile, the Taguchi approach was used as a statistical technique for optimizing selected laser processing parameters. A systematic study of laser power, scanning velocity, and pre-paste powder thickness was conducted. The signal-to-noise ratios (S/N) for each control factor were calculated in order to assess the deviation from the average response. Analysis of variance (ANOVA) was carried out to understand the significance of process variables affecting the process effects. The Taguchi method was able to determine the laser process parameters for the laser surface alloying technique with high statistical accuracy and yield a laser surface alloying technique capable of achieving a desirable dilution ratio. Energy dispersive spectrometry consistently showed that the per cent by weight of Ni was reduced by 45 per cent as compared with untreated NiTi SMA when the Taguchi-determined laser processing parameters were employed, thus verifying the laser's processing parameters as optimum
Causality-Violating Higgs Singlets at the LHC
We construct a simple class of compactified five-dimensional metrics which
admits closed timelike curves (CTCs), and derive the resulting CTCs as analytic
solutions to the geodesic equations of motion. The associated Einstein tensor
satisfies all the null, weak, strong and dominant energy conditions. In
particular, no negative-energy "tachyonic" matter is required. In
extra-dimensional models where gauge charges are bound to our brane, it is the
Kaluza-Klein (KK) modes of gauge-singlets that may travel through the CTCs.
From our brane point of view, many of these KK modes would appear to travel
backward in time. We give a simple model in which time-traveling Higgs singlets
can be produced by the LHC, either from decay of the Standard Model (SM) Higgs
or through mixing with the SM Higgs. The signature of these time-traveling
singlets is a secondary decay vertex pre-appearing before the primary vertex
which produced them. The two vertices are correlated by momentum conservation.
We demonstrate that pre-appearing vertices in the Higgs singlet-doublet mixing
model may well be observable at the LHC.Comment: 55 pages, 5 figures, v4: Version updated to include in single
manuscript the contents of Erratum [Phys. Rev. D 88, 069901(E) (2013)], Reply
[Phys. Rev. D 88, 068702 (2013)], Comment [Phys. Rev. D 88, 068701 (2013),
arXiv:1302.1711], and original published article [Phys. Rev. D 87, 045004
(2013), arXiv:1103.1373]. Positive conclusions remain unchange
SUMOylation inhibits FOXM1 activity and delays mitotic transition
The forkhead box transcription factor FOXM1 is an essential effector of G2/M-phase transition, mitosis and the DNA damage response. As such, it is frequently deregulated during tumorigenesis. Here we report that FOXM1 is dynamically modified by SUMO1 but not by SUMO2/3 at multiple sites. We show that FOXM1 SUMOylation is enhanced in MCF-7 breast cancer cells in response to treatment with epirubicin and mitotic inhibitors. Mutation of five consensus conjugation motifs yielded a SUMOylation-deficient mutant FOXM1. Conversely, fusion of the E2 ligase Ubc9 to FOXM1 generated an auto-SUMOylating mutant (FOXM1-Ubc9). Analysis of wild-type FOXM1 and mutants revealed that SUMOylation inhibits FOXM1 activity, promotes translocation to the cytoplasm and enhances APC/Cdh1-mediated ubiquitination and degradation. Further, expression of the SUMOylation-deficient mutant enhanced cell proliferation compared with wild-type FOXM1, whereas the FOXM1-Ubc9 fusion protein resulted in persistent cyclin B1 expression and slowed the time from mitotic entry to exit. In summary, our findings suggest that SUMOylation attenuates FOXM1 activity and causes mitotic delay in cytotoxic drug response
Local structures of free-standing AlₓGa₁ˍₓN thin films studied by extended x-ray absorption fine structure
Local structural information for the first two atomic shells surrounding Ga atoms in free standing AlₓGa₁ˍₓN alloy films has been obtained by extended x-ray absorption fine structure spectroscopy. For an AlN mole fraction ranging from 0 to 0.6, we found that the first shell Ga–N bond length had only a weak composition dependence, roughly one quarter of that predicted by Vegard’s Law. In the second shell, the Ga–Ga bond length was significantly longer than that of Ga–Al (Δ∼0.04–0.065 Å). A bond-type specific composition dependence was observed for the second shell cation–cation distances. While the composition dependence of the Ga–Ga bond length is ∼70% of that predicted by Vegard’s Law, the Ga–Al bond length was essentially composition independent. These results suggested that local strain in AlₓGa₁ˍₓN was also accommodated by lattice distortion in the Al cation sublattice.This
work was supported by the Director, Office of Science, Of-
fice of Basic Energy Sciences, Materials Science Division of
the U.S. Department of Energy under Contract No.
DE-AC03-76SF00098. The LLO work was performed at the
UC Berkeley Integrated Materials Laboratory which was
supported in part by the National Science Foundation. C.J.G.
and M.C.R. were supported by the Australian Synchrotron
Research Program, funded by the Commonwealth of Australia
via the Major National Research Facilities Program.
SSRL was supported by the Office of Basic Energy Sciences
of the U.S. Department of Energy
Reactive Turbulent Flow in Low-Dimensional, Disordered Media
We analyze the reactions and
occurring in a model of turbulent flow in two dimensions. We find the reactant
concentrations at long times, using a field-theoretic renormalization group
analysis. We find a variety of interesting behavior, including, in the presence
of potential disorder, decay rates faster than that for well-mixed reactions.Comment: 6 pages, 4 figures. To appear in Phys. Rev.
Spacetime Emergence and General Covariance Transmutation
Spacetime emergence refers to the notion that classical spacetime "emerges"
as an approximate macroscopic entity from a non-spatio-temporal structure
present in a more complete theory of interacting fundamental constituents. In
this article, we propose a novel mechanism involving the "soldering" of
internal and external spaces for the emergence of spacetime and the twin
transmutation of general covariance. In the context of string theory, this
mechanism points to a critical four dimensional spacetime background.Comment: 11 pages, v2: version to appear in MPL
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