38 research outputs found
Functional bosonization with time dependent perturbations
We extend a path-integral approach to bosonization previously developed in
the framework of equilibrium Quantum Field Theories, to the case in which
time-dependent interactions are taken into account. In particular we consider a
non covariant version of the Thirring model in the presence of a dynamic
barrier at zero temperature. By using the Closed Time Path (Schwinger-Keldysh)
formalism, we compute the Green's function and the Total Energy Density of the
system. Since our model contains the Tomonaga Luttinger model as a particular
case, we make contact with recent results on non-equilibrium electronic
systems.Comment: 21 pages, 8 figure
Pumping current of a Luttinger liquid with finite length
We study transport properties in a Tomonaga-Luttinger liquid in the presence
of two time-dependent point like weak impurities, taking into account
finite-length effects. By employing analytical methods and performing a
perturbation theory, we compute the backscattering pumping current (I_bs) in
different regimes which can be established in relation to the oscillatory
frequency of the impurities and to the frequency related to the length and the
renormalized velocity (by the electron-electron interactions) of the charge
density modes. We investigate the role played by the spatial position of the
impurity potentials. We also show how the previous infinite length results for
I_bs are modified by the finite size of the system.Comment: 9 pages, 7 figure
Transient effects in the backscattered current of a Luttinger liquid
We study the backscattered current in a Luttinger liquid in the presence of a
point like weak impurity switched on at finite time, taking into account
finite-temperature effects. We show how the well-known results for a static
impurity are distorted. We derive a dimensionless parameter as
function of the electron-electron interaction and the temperature, such that
for ) the switching process is relevant (irrelevant). Our
results suggest the possibility of determining the value of the Luttinger
parameter through time measurements in transport experiments at fixed
voltage.Comment: 8 pages, 3 figures. To appear in Physical Review
Density Contrast Sedimentation Velocity for the Determination of Protein Partial-Specific Volumes
The partial-specific volume of proteins is an important thermodynamic parameter required for the interpretation of data in several biophysical disciplines. Building on recent advances in the use of density variation sedimentation velocity analytical ultracentrifugation for the determination of macromolecular partial-specific volumes, we have explored a direct global modeling approach describing the sedimentation boundaries in different solvents with a joint differential sedimentation coefficient distribution. This takes full advantage of the influence of different macromolecular buoyancy on both the spread and the velocity of the sedimentation boundary. It should lend itself well to the study of interacting macromolecules and/or heterogeneous samples in microgram quantities. Model applications to three protein samples studied in either H2O, or isotopically enriched H218O mixtures, indicate that partial-specific volumes can be determined with a statistical precision of better than 0.5%, provided signal/noise ratios of 50–100 can be achieved in the measurement of the macromolecular sedimentation velocity profiles. The approach is implemented in the global modeling software SEDPHAT
Revisão: ProteÃnas anticongelantes – uma tecnologia emergente para o congelamento de alimentos
Morphological and Electrophysiological Evidence for an Ionotropic GABA Receptor of Novel Pharmacology
Analytical Ultracentrifugation and Size-Exclusion Chromatography Coupled with Light Scattering for the Characterization of Membrane Proteins in Solution
International audienceAnalytical ultracentrifugation (AUC) sedimentation velocity (SV) with absorbance and interference detection and size-exclusion chromatography coupled with static and dynamic light scattering, absorbance, and refractive index detections (SEC/MALS) are two techniques that combine separation and analysis, in an absolute manner, of the mass and size of macromolecules in solution. We present here how they can be applied to the study of membrane proteins. We describe briefly the principles of the species separation, what the detection systems used measures, some theoretical background, the steps for data analysis with the example of the outer membrane protein FhuA, and emphasize the complementarity between these two techniques