1,943 research outputs found
Band-monitoring Payload for a CubeSat Satellite
During changing sun activity, the ionosphere is responding accordingly and therefore it is interesting to observe the propagation behavior of shortwave bands. For the above mentioned purpose we have designed a band-monitoring payload for an experimental CubeSat satellite. The payload consists of a receiver, which is able to receive SSB modulated narrowband signals in 28 MHz uplink band, and a transmitter with FM modulation in UHF downlink band. The receiver frequency is selected to be at the center of radio amateur activity with low data rate digital modulations
Coherent resistance of a disordered 1D wire: Expressions for all moments and evidence for non-Gaussian distribution
We study coherent electron transport in a one-dimensional wire with disorder
modeled as a chain of randomly positioned scatterers. We derive analytical
expressions for all statistical moments of the wire resistance . By means
of these expressions we show analytically that the distribution of the
variable is not exactly Gaussian even in the limit of weak
disorder. In a strict mathematical sense, this conclusion is found to hold not
only for the distribution tails but also for the bulk of the distribution
.Comment: Revised version, 8 pages, 4 figures, RevTeX
Spin-engineered quantum dots
Spatially nonhomogeneously spin polarized nuclei are proposed as a new
mechanism to monitor electron states in a nanostructure, or as a means to
createn and, if necessary, reshape such nanostructures in the course of the
experiment. We found that a polarization of nulear spins may lift the spin
polarization of the electron states in a nanostructure and, if sufficiently
strong, leads to a polarization of the electron spins. Polarized nuclear spins
may form an energy landscape capable of binding electrons with energy up to
several meV and the localization radius 100\AA.Comment: 9 pages, 1 figure, submitted to Physica E, Augist 31, 200
Massive Spin Collective Mode in Quantum Hall Ferromagnet
It is shown that the collective spin rotation of a single Skyrmion in quantum
Hall ferromagnet can be regarded as precession of the entire spin texture in
the external magnetic field, with an effective moment of inertia which becomes
infinite in the zero g-factor limit. This low-lying spin excitation may
dramatically enhance the nuclear spin relaxation rate via the hyperfine
interaction in the quantum well slightly away from filling factor equal one.Comment: 4 page
Stranger in a Strange Land: Old Chair, New University
There are opportunities and challenges associated with appointing a chair from within and from outside the organization. This discussion will consider multiple aspects and focus on considerations for changing institutions to assume the chair position
Localized states in 2D semiconductors doped with magnetic impurities in quantizing magnetic field
A theory of magnetic impurities in a 2D electron gas quantized by a strong
magnetic field is formulated in terms of Friedel-Anderson theory of resonance
impurity scattering. It is shown that this scattering results in an appearance
of bound Landau states with zero angular moment between the Landau subbands.
The resonance scattering is spin selective, and it results in a strong spin
polarization of Landau states, as well as in a noticeable magnetic field
dependence of the factor and the crystal field splitting of the impurity
levels.Comment: 12 pages, 4 figures Submitted to Physical Review B This version is
edited and updated in accordance with recent experimental dat
Nucleus-mediated spin-flip transitions in GaAs quantum dots
Spin-flip rates in GaAs quantum dots can be quite slow, thus opening up the
possibilities to manipulate spin states in the dots. We present here
estimations of inelastic spin-flip rates mediated by hyperfine interaction with
nuclei. Under general assumptions the nucleus mediated rate is proportional to
the phonon relaxation rate for the corresponding non-spin-flip transitions. The
rate can be accelerated in the vicinity of a singlet-triplet excited states
crossing. The small proportionality coefficient depends inversely on the number
of nuclei in the quantum dot. We compare our results with known mechanisms of
spin-flip in quantum dot.Comment: RevTex 4 pages, 1 figure, submitted to Phys. Rev.
Resolution of Conflicting Signals at the Single-Cell Level in the Regulation of Cyanobacterial Photosynthesis and Nitrogen Fixation
Unicellular, diazotrophic cyanobacteria temporally separate dinitrogen (N-2) fixation and photosynthesis to prevent inactivation of the nitrogenase by oxygen. This temporal segregation is regulated by a circadian clock with oscillating activities of N-2 fixation in the dark and photosynthesis in the light. On the population level, this separation is not always complete, since the two processes can overlap during transitions from dark to light. How do single cells avoid inactivation of nitrogenase during these periods? One possibility is that phenotypic heterogeneity in populations leads to segregation of the two processes. Here, we measured N-2 fixation and photosynthesis of individual cells using nanometer-scale secondary ion mass spectrometry (nanoSIMS) to assess both processes in a culture of the unicellular, diazotrophic cyanobacterium Crocosphaera watsonii during a dark-light and a continuous light phase. We compared single-cell rates with bulk rates and gene expression profiles. During the regular dark and light phases, C. watsonii exhibited the temporal segregation of N-2 fixation and photosynthesis commonly observed. However, N-2 fixation and photosynthesis were concurrently measurable at the population level during the subjective dark phase in which cells were kept in the light rather than returned to the expected dark phase. At the single-cell level, though, cells discriminated against either one of the two processes. Cells that showed high levels of photosynthesis had low nitrogen fixing activities, and vice versa. These results suggest that, under ambiguous environmental signals, single cells discriminate against either photosynthesis or nitrogen fixation, and thereby might reduce costs associated with running incompatible processes in the same cell
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