Conductance fluctuations in quasi-two-dimensional systems: a practical view

The universal conductance fluctuations of quasi-two-dimensional systems are analyzed with experimental considerations in mind. The traditional statistical metrics of these fluctuations (such as variance) are shown to have large statistical errors in such systems. An alternative characteristic is identified, the inflection point of the correlation function in magnetic field, which is shown to be significantly more useful as an experimental metric and to give a more robust measure of phase coherence.Comment: 9 pages, 7 figure

Overlapping of Ranges of Eastern and Western Hognose Snakes in Southeastern Iowa

Overlapping of ranges of the eastern hognose snake (Heterodon platyrhinos Latreille) and the western hognose snake (Heterodon nasicus nasicus Baird and Girrard) is reported from a sand prairie in Muscatine County, Iowa

Previous attentional set can induce an attentional blink with task-irrelevant initial targets

Identification of a second target is often impaired by the requirement to process a prior target in a rapid serial visual presentation (RSVP). This is termed the attentional blink. Even when the first target is task-irrelevant an attentional blink may occur providing this first target shares similar features with the second target (contingent capture). An RSVP experiment was undertaken to assess whether this first target can still cause an attentional blink when it did not require a response and did not share any features with the following target. The results revealed that such task-irrelevant targets can induce an attentional blink providing that they were task-relevant on a previous block of trials. This suggests that irrelevant focal stimuli can distract attention on the basis of a previous attentional set

Electrical generation of pure spin currents in a two-dimensional electron gas

Pure spin currents are measured in micron-wide channels of GaAs two-dimensional electron gas (2DEG). Spins are injected and detected using quantum point contacts, which become spin polarized at high magnetic field. High sensitivity to the spin signal is achieved in a nonlocal measurement geometry, which dramatically reduces spurious signals associated with charge currents. Measured spin relaxation lengths range from 30 to 50 microns, much longer than has been reported in GaAs 2DEG's. The technique developed here provides a flexible tool for the study of spin polarization and spin dynamics in mesoscopic structures defined in 2D semiconductor systems

Fluctuations of g-factors in metal nanoparticles: Effects of electron-electron interaction and spin-orbit scattering

We investigate the combined effect of spin-orbit scattering and electron-electron interactions on the probability distribution of $g$-factors of metal nanoparticles. Using random matrix theory, we find that even a relatively small interaction strength %(ratio of exchange constant $J$ and mean level %spacing \spacing $\simeq 0.3$) significantly increases $g$-factor fluctuations for not-too-strong spin-orbit scattering (ratio of spin-orbit rate and single-electron level spacing 1/\tau_{\rm so} \spacing \lesssim 1), and leads to the possibility to observe $g$-factors larger than two.Comment: RevTex, 2 figures inserte

Free and protein-conjugated polyamines in mouse epidermal cells. Effect of high calcium and retinoic acid.

We have investigated polyamine metabolism in primary cultures of mouse epidermal cells. These cells, which grow at low Ca2+ levels as a monolayer with characteristics of basal cells, terminally differentiate when the extracellular Ca2+ level is raised above 1 mM. The cellular levels of free polyamines were measured, and, after incubation of cell cultures with [3H]putrescine, the distribution of label in both acid-soluble and acid-insoluble cellular components was examined. Free polyamine levels were reduced in cells induced to differentiate. Treatment with retinoic acid, which prevents differentiation and causes increased proliferation, resulted in an increase in free putrescine. Upon adjustment of the calcium concentration to a level that induces differentiation, the enzyme transglutaminase was activated, and a concomitant increase in the level of both protein-bound mono- and bis-gamma-glutamyl derivatives of putrescine and spermidine was observed. Isolation of a material of apparent molecular weight about 6000 which contains only mono-gamma-glutamylpolyamines and the finding of both mono- and bis-gamma-glutamylpolyamines in the protein fraction containing cornified cell envelopes provided the basis for speculation on polyamines in envelope formation. Our data suggest that polyamines play a role during epidermal cell differentiation through transglutaminase-mediated post-translational modification

Numerical study of resonant spin relaxation in quasi-1D channels

Recent experiments demonstrate that a ballistic version of spin resonance, mediated by spin-orbit interaction, can be induced in narrow channels of a high-mobility GaAs two-dimensional electron gas by matching the spin precession frequency with the frequency of bouncing trajectories in the channel. Contrary to the typical suppression of Dyakonov-Perel' spin relaxation in confined geometries, the spin relaxation rate increases by orders of magnitude on resonance. Here, we present Monte Carlo simulations of this effect to explore the roles of varying degrees of disorder and strength of spin-orbit interaction. These simulations help to extract quantitative spin-orbit parameters from experimental measurements of ballistic spin resonance, and may guide the development of future spintronic devices

Activation of transglutaminase and production of protein-bound gamma-glutamylhistamine in stimulated mouse mast cells

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Spin orbit effects in a GaAs quantum dot in a parallel magnetic field

We analyze the effects of spin-orbit coupling on fluctuations of the conductance of a quantum dot fabricated in a GaAs heterostructure. We argue that spin-orbit effects may become important in the presence of a large parallel magnetic field B_{||}, even if they are negligble for B_{||}=0. This should be manifest in the level repulsion of a closed dot, and in reduced conductance fluctuations in dots with a small number of open channels in each lead, for large B_{||}. Our picture is consistent with the experimental observations of Folk et al.Comment: 5 page

Electron transport through single Mn12 molecular magnets

We report transport measurements through a single-molecule magnet, the Mn12 derivative [Mn12O12(O2C-C6H4-SAc)16(H2O)4], in a single-molecule transistor geometry. Thiol groups connect the molecule to gold electrodes that are fabricated by electromigration. Striking observations are regions of complete current suppression and excitations of negative differential conductance on the energy scale of the anisotropy barrier of the molecule. Transport calculations, taking into account the high-spin ground state and magnetic excitations of the molecule, reveal a blocking mechanism of the current involving non-degenerate spin multiplets.Comment: Accepted for Phys. Rev. Lett., 5 pages, 4 figure