9,957 research outputs found
Determination of the interactions in confined macroscopic Wigner islands: theory and experiments
Macroscopic Wigner islands present an interesting complementary approach to
explore the properties of two-dimensional confined particles systems. In this
work, we characterize theoretically and experimentally the interaction between
their basic components, viz., conducting spheres lying on the bottom electrode
of a plane condenser. We show that the interaction energy can be approximately
described by a decaying exponential as well as by a modified Bessel function of
the second kind. In particular, this implies that the interactions in this
system, whose characteristics are easily controllable, are the same as those
between vortices in type-II superconductors.Comment: 8 pages, 8 figure
Single File Diffusion enhancement in a fluctuating modulated 1D channel
We show that the diffusion of a single file of particles moving in a
fluctuating modulated 1D channel is enhanced with respect to the one in a bald
pipe. This effect, induced by the fluctuations of the modulation, is favored by
the incommensurability between the channel potential modulation and the moving
file periodicity. This phenomenon could be of importance in order to optimize
the critical current in superconductors, in particular in the case where mobile
vortices move in 1D channels designed by adapted patterns of pinning sites.Comment: 4 pages, 4 figure
Recommended from our members
Dissociating visuo-spatial and verbal working memory: It’s all in the features
Echoing many of the themes of the seminal work of Atkinson and Shiffrin (1968), this paper uses the Feature Model (Nairne, 1988, 1990; Neath & Nairne, 1995) to account for performance in working memory tasks. The Brooks verbal and visuo-spatial matrix tasks were performed alone, with articulatory suppression, or with a spatial suppression task; the results produced the expected dissociation. We used Approximate Bayesian Computation techniques to fit the Feature Model to the data and showed that the similarity-based interference process implemented in the model accounted for the data patterns well. We then fit the model to data from Guérard and Tremblay (2008); the latter study produced a double dissociation while calling upon more typical order reconstruction tasks. Again, the model performed well. The findings show that a double dissociation can be modelled without appealing to separate systems for verbal and visuo-spatial processing. The latter findings are significant as the Feature Model had not been used to model this type of dissociation before; importantly, this is also the first time the model is quantitatively fit to data. For the demonstration provided here, modularity was unnecessary if two assumptions were made: (1) the main difference between spatial and verbal working memory tasks is the features that are encoded; (2) secondary tasks selectively interfere with primary tasks to the extent that both tasks involve similar features. It is argued that a feature-based view is more parsimonious (see Morey, 2018) and offers flexibility in accounting for multiple benchmark effects in the field
Spectral Features of the Proximity Effect
We calculate the local density of states (LDOS) of a superconductor-normal
metal sandwich at arbitrary impurity concentration. The presence of the
superconductor induces a gap in the normal metal spectrum that is proportional
to the inverse of the elastic mean free path for rather clean systems. For
a mean free path much shorter than the thickness of the normal metal, we find a
gap size proportional to that approaches the behavior predicted by the
Usadel equation (diffusive limit).Comment: LT22 proceeding
FTIR difference and resonance raman spectroscopy of rhodopsins with applications to optogenetics
Thesis (Ph. D.)--Boston UniversityThe major aim of this thesis is to investigate the molecular basis for the function
of several types of rhodopsins with special emphasis on their application to the new
field of optogenetics. Rhodopsins are transmembrane biophotonic proteins with 7
a-helices and a retinal chromophore. Studies included Archaerhodopsin 3 (AR3), a
light driven proton pump similar to the extensively studied bacteriorhodopsin (BR);
channelrhodopsins 1 and 2, light-activated ion channels; sensory rhodopsin II (SRII),
a light-sensing protein that modulates phototaxis used in archaebacteria; and squid
rhodopsins (sRho), the major photopigment in squid vision and a model for human
melanopsin, which controls circadian rythms.
The primary techniques used in these studies were FTIR difference spectroscopy
and resonance Raman spectroscopy. These techniques, in combination with site directed
mutagenesis and other biochemical methodologies produced new knowledge
regarding the structural changes of the retinal chromophore, the location and function
of internal water molecules as well as specific amino acids and peptide backbone.
Specialized techniques were developed that allowed rhodopsins to be studied in intact
membrane environments and in some cases in vivo measurements were made on
rhodopsin heterologously expressed in E. coli thus allowing the effects of interacting
proteins and membrane potential to be investigated.
Evidence was found that the local environment of one or more internal water
molecules in SRII is altered by interaction with its cognate transducer, Htrii, and is
also affected by the local lipid environment. In the case of AR3, many of the broad
IR continuum absorption changes below 3000 cm-1, assigned to networks of water
molecules involved in proton transport through cytoplasmic and extracellular portions
in BR, were found to be very similar to BR. Bands assigned to water molecules
near the Schiff base postulated to be involved in proton transport were, however,
shifted or absent. Structural changes of internal water molecules and possible bands
associated with the interaction with ,8-arrestins were also detected in photoactivated
squid rhodopsin when transformed to the acid Meta intermediate. Near-IR confocal
resonance Raman measurements were performed both on AR3 reconstituted into E.
coli polar lipids and in vivo in E. coli expressing AR3 in the absence and presence of
a negative transmembrane potential. On the basis of these measurements, a model
is proposed which provides a possible explanation for the observed fluorescence dependence of AR3 and other microbial rhodopsins on transmembrane potential
Accurate mass measurements of Ne, Na, Mg performed with the {\sc Mistral} spectrometer
The minuteness of the nuclear binding energy requires that mass measurements
be highly precise and accurate. Here we report on new measurements Mg
and Na performed with the {\sc Mistral} mass spectrometer at {\sc
Cern}'s {\sc Isolde} facility. Since mass measurements are prone to systematic
errors, considerable effort has been devoted to their evaluation and
elimination in order to achieve accuracy and not only precision. We have
therefore conducted a campaign of measurements for calibration and error
evaluation. As a result, we now have a satisfactory description of the {\sc
Mistral} calibration laws and error budget. We have applied our new
understanding to previous measurements of Ne, Na and
Mg for which re-evaluated values are reported.Comment: submitted to Nuclear Physics
Blow-up of the hyperbolic Burgers equation
The memory effects on microscopic kinetic systems have been sometimes
modelled by means of the introduction of second order time derivatives in the
macroscopic hydrodynamic equations. One prototypical example is the hyperbolic
modification of the Burgers equation, that has been introduced to clarify the
interplay of hyperbolicity and nonlinear hydrodynamic evolution. Previous
studies suggested the finite time blow-up of this equation, and here we present
a rigorous proof of this fact
- …