375 research outputs found
Waveform sampling using an adiabatically driven electron ratchet in a two-dimensional electron system
We utilize a time-periodic ratchet-like potential modulation imposed onto a
two-dimensional electron system inside a GaAs/AlGaAs
heterostructure to evoke a net dc pumping current. The modulation is induced by
two sets of interdigitated gates, interlacing off center, which can be
independently addressed. When the transducers are driven by two identical but
phase-shifted ac signals, a lateral dc pumping current results, which
strongly depends on both, the phase shift and the waveform of the
imposed gate voltages. We find that for different periodic signals, the phase
dependence closely resembles . A simple linear model of
adiabatic pumping in two-dimensional electron systems is presented, which
reproduces well our experimental findings.Comment: 3 figure
Electrical read-out of the local nuclear polarization in the quantum Hall effect
It is demonstrated that the now well-established `flip-flop' mechanism of
spin exchange between electrons and nuclei in the quantum Hall effect can be
reversed. We use a sample geometry which utilizes separately contacted edge
states to establish a local nuclear spin polarization --close to the maximum
value achievable-- by driving a current between electron states of different
spin orientation. When the externally applied current is switched off, the
sample exhibits an output voltage of up to a few tenths of a meV, which decays
with a time constant typical for the nuclear spin relaxation. The surprizing
fact that a sample with a local nuclear spin polarization can act as a source
of energy and that this energy is well above the nuclear Zeeman splitting is
explained by a simple model which takes into account the effect of a local
Overhauser shift on the edge state reconstruction.Comment: Submitted to Phys. Rev. Let
Ultracold Atoms as a Target: Absolute Scattering Cross-Section Measurements
We report on a new experimental platform for the measurement of absolute
scattering cross-sections. The target atoms are trapped in an optical dipole
trap and are exposed to an incident particle beam. The exponential decay of the
atom number directly yields the absolute total scattering cross-section. The
technique can be applied to any atomic or molecular species that can be
prepared in an optical dipole trap and provides a large variety of possible
scattering scenarios
Observation of two relaxation mechanisms in transport between spin split edge states at high imbalance
Using a quasi-Corbino geometry to directly study electron transport between
spin-split edge states, we find a pronounced hysteresis in the I-V curves,
originating from slow relaxation processes. We attribute this long-time
relaxation to the formation of a dynamic nuclear polarization near the sample
edge. The determined characteristic relaxation times are 25 s and 200 s which
points to the presence of two different relaxation mechanisms. The two time
constants are ascribed to the formation of a local nuclear polarization due to
flip-flop processes and the diffusion of nuclear spins.Comment: Submitted to PR
Performance Limitations of Flat Histogram Methods and Optimality of Wang-Landau Sampling
We determine the optimal scaling of local-update flat-histogram methods with
system size by using a perfect flat-histogram scheme based on the exact density
of states of 2D Ising models.The typical tunneling time needed to sample the
entire bandwidth does not scale with the number of spins N as the minimal N^2
of an unbiased random walk in energy space. While the scaling is power law for
the ferromagnetic and fully frustrated Ising model, for the +/- J
nearest-neighbor spin glass the distribution of tunneling times is governed by
a fat-tailed Frechet extremal value distribution that obeys exponential
scaling. We find that the Wang-Landau algorithm shows the same scaling as the
perfect scheme and is thus optimal.Comment: 5 pages, 6 figure
Manifestation of the bulk phase transition in the edge energy spectrum in a two dimensional bilayer electron system
We use a quasi-Corbino sample geometry with independent contacts to different
edge states in the quantum Hall effect regime to investigate the edge energy
spectrum of a bilayer electron system at total filling factor . By
analyzing non-linear curves in normal and tilted magnetic fields we
conclude that the edge energy spectrum is in a close connection with the bulk
one. At the bulk phase transition spin-singlet - canted antiferromagnetic phase
curve becomes to be linear, indicating the disappearance or strong
narrowing of the incompressible strip at the edge of the sample.Comment: 5 pages, 5 figure
Quantum Phases of Cold Polar Molecules in 2D Optical Lattices
We discuss the quantum phases of hard-core bosons on a two-dimensional square
lattice interacting via repulsive dipole-dipole interactions, as realizable
with polar molecules trapped in optical lattices. In the limit of small
tunneling, we find evidence for a devil's staircase, where solid phases appear
at all rational fillings of the underlying lattice. For finite tunneling, we
establish the existence of extended regions of parameters where the groundstate
is a supersolid, obtained by doping the solids either with particles or
vacancies. Here the solid-superfluid quantum melting transition consists of two
consecutive second-order transitions, with a supersolid as the intermediate
phase. The effects of finite temperature and confining potentials relevant to
experiments are discussed.Comment: replaced with published versio
Coronary artery disease-associated genetic variants and biomarkers of inflammation
Introduction: Genetic constitution and inflammation both contribute to development of coronary artery disease (CAD). Several CAD-associated single-nucleotide polymorphisms (SNPs) have recently been identified, but their functions are largely unknown. We investigated the associations between CAD-associated SNPs and five CAD-related inflammatory biomarkers. Methods: We genotyped 45 CAD-associated SNPs in 701 stable CAD patients in whom levels of high-sensitivity C-reactive protein (hsRCP), interleukin-6, calprotectin, fibrinogen and complement component 3 levels had previously been measured. A genetic risk score was calculated to assess the combined risk associated with all the genetic variants. A multiple linear regression model was used to assess associations between the genetic risk score, single SNPs, and the five inflammatory biomarkers. Results: The minor allele (G) (CAD risk allele) of rs2075650 (TOMM40/APOE) was associated with lower levels of high-sensitivity C-reactive protein (effect per risk allele: -0.37 mg/l [95%CI -0.56 to -0.18 mg/l]). The inflammatory markers tested showed no association with the remaining 44 SNPs or with the genetic risk score. Conclusions: In stable CAD patients, the risk allele of a common CAD-associated marker at the TOMM40/APOE locus was associated with lower hsCRP levels. No other genetic variants or the combined effect of all variants were associated with the five inflammatory biomarkers
Ukupna taložna tvar na području Primorsko-goranske županije u razdoblju 1975.-2008.
Dustfall measurements in Primorsko-goranska county started in 1975 in the Bakar Bay (Site 2 - Bakar and Site 3 - Kraljevica). The measurements were extended to the city of Rijeka (Site 1 - Rijeka) in 1982, to the nearby islands (Site 4 - Krk and Site 5 - Cres) in 1986, and inland to Gorski Kotar (Site 6 - Delnice and Site 7 - Lividraga) in 1995. This article brings the results of dustfall measurements from 1975 to 2008. Dustfall was low in the city, the nearby islands, and Gorski Kotar. Recommended and limit values
were occasionally exceeded in the Bakar Bay due to emissions from the coke plant and harbour at Site 2 (1979-1997) and from the shipyard at Site 3. Lead content in the dustfall was below the national limits, save for two occasions at Site 2. Deposition of sulphur and nitrogen at the inland sites were below the respective critical load values.Ispitivanja ukupne taložne tvari u Primorsko-goranskoj županiji započela su 1975. godine na području Bakarskog zaljeva. Mjerenja su se 1982. god proširila na grad Rijeku, 1986. na otoke Krk i Cres, a 1995. i na područje Gorskog kotara. U radu su prikazani rezultati mjerenja ukupne taložne tvari u razdoblju 1975.-2008. na sedam odabranih postaja: u gradu Rijeci, dvije na području Bakarskog zaljeva (Bakar i Kraljevica), dvije na otocima (Krk i Cres) te dvije u Gorskom kotaru (Delnice i Lividraga). Analizirano je kretanje prosječnih godišnjih vrijednosti ukupno istaloženih tvari te u njima prisutnih količina sagorivog pepela, sulfata, nitrata, amonija i olova. Na području grada Rijeke, otoka Krka i Cresa te Gorskog kotara
količina ukupne taložne tvari je niska. Količine ukupne taložne tvari povremeno su prelazile preporučenu graničnu vrijednost u Bakru (1979.-1994.), zbog emisija iz koksare i iz luke za rasuti teret te u Kraljevici, gdje se osamdesetih godina osjećao utjecaj koksare u Bakru, a od sredine devedesetih pojačani rad u brodogradilištu. Količine olova u taložnoj tvari su niske na svim postajama, osim povremenih skokova u Bakru, kada su prijeđene preporučene vrijednosti. Količine istaloženog sumpora i dušika na području
Gorskog kotara ispod su odgovarajućih vrijednosti kritičnog opterećenja za ispitivana područja
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