15,216 research outputs found
Determination of biaxial creep strength of T-111 tantalum alloy
Biaxial creep strength of T-111 tantalum alloy tubing in high temperature, high vacuum environmen
Bartonella apis sp. nov., a honey bee gut symbiont of the class Alphaproteobacteria.
Here, we report the culture and characterization of an alphaproteobacterium of the order Rhizobiales, isolated from the gut of the honey bee Apis mellifera. Strain PEB0122T shares >95 % 16S rRNA gene sequence similarity with species of the genus Bartonella, a group of mammalian pathogens transmitted by bloodsucking arthropods. Phylogenetic analyses showed that PEB0122T and related strains from the honey bee gut form a sister clade of the genus Bartonella. Optimal growth of strain PEB0122T was obtained on solid media supplemented with defibrinated sheep blood under microaerophilic conditions at 35-37 °C, which is consistent with the cultural characteristics of other species of the genus Bartonella. Reduced growth of strain PEB0122T also occurred under aerobic conditions. The rod-shaped cells of strain PEB0122T had a mean length of 1.2-1.8 μm and revealed hairy surface structures. Strain PEB0122T was positive for catalase, cytochrome c oxidase, urease and nitrate reductase. The fatty acid composition was comparable to those of other species of the genus Bartonella, with palmitic acid (C16 : 0) and isomers of 18- and 19-carbon chains being the most abundant. The genomic DNA G+C content of PEB0122T was determined to be about 45.5 mol%. The high 16S rRNA gene sequence similarity with species of Bartonella and its close phylogenetic position suggest that strain PEB0122T represents a novel species within the genus Bartonella, for which we propose the name Bartonella apis sp. nov. The type strain is PEB0122T ( = NCIMB 14961T = DSM 29779T)
Pinning modes and interlayer correlation in high magnetic field bilayer Wigner solids
We report studies of pinning mode resonances in the low total Landau filling
(\nu) Wigner solid of a series of bilayer hole samples with negligible
interlayer tunneling, and with varying interlayer separation d. Comparison of
states with equal layer densities (p,p) to single layer states (p,0) produced
{in situ} by biasing, indicates that there is interlayer quantum correlation in
the solid at small d. Also, the resonance frequency at small d is decreased
just near \nu=1/2 and 2/3, indicating the importance in the solid of
correlations related to those in the fractional quantum Hall effects
Asymmetric Quantum Shot Noise in Quantum Dots
We analyze the frequency-dependent noise of a current through a quantum dot
which is coupled to Fermi leads and which is in the Coulomb blockade regime. We
show that the asymmetric shot noise as function of frequency shows steps and
becomes super-Poissonian. This provides experimental access to the quantum
fluctuations of the current. We present an exact calculation for a single dot
level and a perturbative evaluation of the noise in Born approximation
(sequential tunneling regime but without Markov approximation) for the general
case of many levels with charging interaction.Comment: 5 pages, 2 figure
Quantum oscillations observed in graphene at microwave frequencies
We have measured the microwave conductance of mechanically exfoliated
graphene at frequencies up to 8.5 GHz. The conductance at 4.2 K exhibits
quantum oscillations, and is independent of the frequency
Measurement efficiency and n-shot read out of spin qubits
We consider electron spin qubits in quantum dots and define a measurement
efficiency e to characterize reliable measurements via n-shot read outs. We
propose various implementations based on a double dot and quantum point contact
(QPC) and show that the associated efficiencies e vary between 50% and 100%,
allowing single-shot read out in the latter case. We model the read out
microscopically and derive its time dynamics in terms of a generalized master
equation, calculate the QPC current and show that it allows spin read out under
realistic conditions.Comment: 5 pages, 1 figur
Giant microwave photoresistance of two-dimensional electron gas
We measure microwave frequency (4-40 GHz) photoresistance at low magnetic
field B, in high mobility 2D electron gas samples, excited by signals applied
to a transmission line fabricated on the sample surface. Oscillatory
photoresistance vs B is observed. For excitation at the cyclotron resonance
frequency, we find an unprecedented, giant relative photoresistance (\Delta
R)/R of up to 250 percent. The photoresistance is apparently proportional to
the square root of applied power, and disappears as the temperature is
increased.Comment: 4 pages, 3 figure
AC Magnetotransport in Reentrant Insulating Phases of Two-dimensional Electrons near 1/5 and 1/3 Landau fillings
We have measured high frequency magnetotransport of a high quality
two-dimensional electron system (2DES) near the reentrant insulating phase
(RIP) at Landau fillings () between 1/5 and 2/9. The
magneto\textit{conductivity} in the RIP has resonant behavior around 150 MHz,
showing a \textit{peak} at 0.21. Our data support the interpretation
of the RIP as due to some pinned electron solid. We have also investigated a
narrowly confined 2DES recently found to have a RIP at 1/31/2 and we
have revealed features, not seen in DC transport, that suggest some intriguing
interplay between the 1/3 FQHE and RIP.Comment: 4 pages and 1 figure (amsart format), 16th International Conference
on High Magnetic Fields in Semiconductor Physics (SemiMag16), August 2-6,
2004, Tallahasse
Mesoscopic Spin-Hall Effect in 2D electron systems with smooth boundaries
Spin-Hall effect in ballistic 2D electron gas with Rashba-type spin-orbit
coupling and smooth edge confinement is studied. We predict that the interplay
of semiclassical electron motion and quantum dynamics of spins leads to several
distinct features in spin density along the edge that originate from
accumulation of turning points from many classical trajectories. Strong peak is
found near a point of the vanishing of electron Fermi velocity in the lower
spin-split subband. It is followed by a strip of negative spin density that
extends until the crossing of the local Fermi energy with the degeneracy point
where the two spin subbands intersect. Beyond this crossing there is a wide
region of a smooth positive spin density. The total amount of spin accumulated
in each of these features exceeds greatly the net spin across the entire edge.
The features become more pronounced for shallower boundary potentials,
controlled by gating in typical experimental setups.Comment: 4 pages, 4 figures, published versio
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