502 research outputs found
Superconducting Quantum Interference in Fractal Percolation Films. Problem of 1/f Noise
An oscillatory magnetic field dependence of the DC voltage is observed when a
low-frequency current flows through superconducting Sn-Ge thin-film composites
near the percolation threshold. The paper also studies the experimental
realisations of temporal voltage fluctuations in these films. Both the
structure of the voltage oscillations against the magnetic field and the time
series of the electric "noise" possess a fractal pattern. With the help of the
fractal analysis procedure, the fluctuations observed have been shown to be
neither a noise with a large number of degrees of freedom, nor the realisations
of a well defined dynamic system. On the contrary the model of voltage
oscillations induced by the weak fluctuations of a magnetic field of arbitrary
nature gives the most appropriate description of the phenomenon observed. The
imaging function of such a transformation possesses a fractal nature, thus
leading to power-law spectra of voltage fluctuations even for the simplest
types of magnetic fluctuations including the monochromatic ones. Thus, the
paper suggests a new universal mechanism of a "1/f noise" origin. It consists
in a passive transformation of any natural fluctuations with a fractal-type
transformation function.Comment: 17 pages, 13 eps-figures, Latex; title page and figures include
Does the Red Queen reign in the kingdom of digital organisms?
In competition experiments between two RNA viruses of equal or almost equal
fitness, often both strains gain in fitness before one eventually excludes the
other. This observation has been linked to the Red Queen effect, which
describes a situation in which organisms have to constantly adapt just to keep
their status quo. I carried out experiments with digital organisms
(self-replicating computer programs) in order to clarify how the competing
strains' location in fitness space influences the Red-Queen effect. I found
that gains in fitness during competition were prevalent for organisms that were
taken from the base of a fitness peak, but absent or rare for organisms that
were taken from the top of a peak or from a considerable distance away from the
nearest peak. In the latter two cases, either neutral drift and loss of the
fittest mutants or the waiting time to the first beneficial mutation were more
important factors. Moreover, I found that the Red-Queen dynamic in general led
to faster exclusion than the other two mechanisms.Comment: 10 pages, 5 eps figure
Fundamental limits of electron and nuclear spin qubit lifetimes in an isolated self-assembled quantum dot
Combining external control with long spin lifetime and coherence is a key challenge for solid state spin qubits. Tunnel coupling with electron Fermi reservoir provides robust charge state control in semiconductor quantum dots, but results in undesired relaxation of electron and nuclear spins through mechanisms that lack complete understanding. Here, we unravel the contributions of tunnelling-assisted and phonon-assisted spin relaxation mechanisms by systematically adjusting the tunnelling coupling in a wide range, including the limit of an isolated quantum dot. These experiments reveal fundamental limits and trade-offs of quantum dot spin dynamics: while reduced tunnelling can be used to achieve electron spin qubit lifetimes exceeding 1âs, the optical spin initialisation fidelity is reduced below 80%, limited by Auger recombination. Comprehensive understanding of electron-nuclear spin relaxation attained here provides a roadmap for design of the optimal operating conditions in quantum dot spin qubits
Multi-layered Ruthenium-modified Bond Coats for Thermal Barrier Coatings
Diffusional approaches for fabrication of multi-layered Ru-modified bond coats for thermal
barrier coatings have been developed via low activity chemical vapor deposition and high activity
pack aluminization. Both processes yield bond coats comprising two distinct B2 layers, based on
NiAl and RuAl, however, the position of these layers relative to the bond coat surface is reversed
when switching processes. The structural evolution of each coating at various stages of the
fabrication process has been and subsequent cyclic oxidation is presented, and the relevant
interdiffusion and phase equilibria issues in are discussed. Evaluation of the oxidation behavior of
these Ru-modified bond coat structures reveals that each B2 interlayer arrangement leads to the
formation of α-Al 2 O 3 TGO at 1100°C, but the durability of the TGO is somewhat different and in
need of further improvement in both cases
Gallium(III) chelates of mixed phosphonate-carboxylate triazamacrocyclic ligands relevant to nuclear medicine: structural, stability and in vivo studies
Three triaza macrocyclic ligands, H6NOTP (1,4,7-triazacyclononane-N,NâČ,Nâł-trimethylene phosphonic acid),
H4NO2AP (1,4,7-triazacyclononane-N-methylenephosphonic acid-NâČ,Nâł-dimethylenecarboxylic acid), and
H5NOA2P (1,4,7-triazacyclononane-N,NâČ-bis(methylenephosphonic acid)-Nâł-methylene carboxylic acid), and
their gallium(III) chelates were studied in view of their potential interest as scintigraphic and PET (Positron
Emission Tomography) imaging agents. A 1H, 31P and 71Ga multinuclear NMR study gave an insight on the
structure, internal dynamics and stability of the chelates in aqueous solution. In particular, the analysis of 71Ga
NMR spectra gave information on the symmetry of the Ga3+ coordination sphere and the stability of the chelates towards hydrolysis. The 31P NMR spectra afforded information on the protonation of the non-coordinated oxygen atoms from the pendant phosphonate groups and on the number of species in solution. The 1H NMR spectra allowed the analysis of the structure and the number of species in solution.
31P and 1H NMR titrations combined with potentiometry afforded the measurement of the protonation
constants (log KHi) and the microscopic protonation scheme of the triaza macrocyclic ligands. The remarkably
high thermodynamic stability constant (log KGaL =34.44 (0.04) and stepwise protonation constants of Ga
(NOA2P)2â were determined by potentiometry and 69Ga and 31P NMR titrations. Biodistribution and gamma
imaging studies have been performed on Wistar rats using the radiolabeled 67Ga(NO2AP)â and 67Ga
(NOA2P)2âchelates, having both demonstrated to have renal excretion. The correlation of the molecular
properties of the chelates with their pharmacokinetic properties has been analysed.The authors thank the financial support from the Fundação para a CiĂȘncia e Tecnologia
(F.C.T., Portugal, projects RREQ/481/QUI/2006 and RECI/QEQ-QFI/0168/2012), the Rede Nacional de RMN (RNRMN), the Hungarian Scientific Research Fund (OTKA grants K-109029 and K-120224), the JĂĄnos Bolyai Research Scholarship (Gy.T.) of the Hungarian Academy of Sciences and the EU COST Action TD1004 âTheragnostics Imaging and Therapyâ. The research was also supported by the EU and co-financed by the European Regional Development Fund (FEDER) under the projects CENTRO-07-CT62-FEDER) and
GINOP-2.3.2-15-2016-00008.info:eu-repo/semantics/publishedVersio
Asteroseismology from multi-month Kepler photometry: the evolved Sun-like stars KIC 10273246 and KIC 10920273
Energy and system size dependence of \phi meson production in Cu+Cu and Au+Au collisions
We study the beam-energy and system-size dependence of \phi meson production
(using the hadronic decay mode \phi -- K+K-) by comparing the new results from
Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4
and 200 GeV measured in the STAR experiment at RHIC. Data presented are from
mid-rapidity (|y|<0.5) for 0.4 < pT < 5 GeV/c. At a given beam energy, the
transverse momentum distributions for \phi mesons are observed to be similar in
yield and shape for Cu+Cu and Au+Au colliding systems with similar average
numbers of participating nucleons. The \phi meson yields in nucleus-nucleus
collisions, normalised by the average number of participating nucleons, are
found to be enhanced relative to those from p+p collisions with a different
trend compared to strange baryons. The enhancement for \phi mesons is observed
to be higher at \sqrt{s_NN} = 200 GeV compared to 62.4 GeV. These observations
for the produced \phi(s\bar{s}) mesons clearly suggest that, at these collision
energies, the source of enhancement of strange hadrons is related to the
formation of a dense partonic medium in high energy nucleus-nucleus collisions
and cannot be alone due to canonical suppression of their production in smaller
systems.Comment: 20 pages and 5 figure
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fbâ1 of protonâproton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
Seismic analysis of four solar-like stars observed during more than eight months by <i>Kepler</i>
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