1,362 research outputs found
Tet-On Systems For Doxycycline-inducible Gene Expression.
The tetracycline-controlled Tet-Off and Tet-On gene expression systems are used to regulate the activity of genes in eukaryotic cells in diverse settings, varying from basic biological research to biotechnology and gene therapy applications. These systems are based on regulatory elements that control the activity of the tetracycline-resistance operon in bacteria. The Tet-Off system allows silencing of gene expression by administration of tetracycline (Tc) or tetracycline-derivatives like doxycycline (dox), whereas the Tet-On system allows activation of gene expression by dox. Since the initial design and construction of the original Tet-system, these bacterium-derived systems have been significantly improved for their function in eukaryotic cells. We here review how a dox-controlled HIV-1 variant was designed and used to greatly improve the activity and dox-sensitivity of the rtTA transcriptional activator component of the Tet-On system. These optimized rtTA variants require less dox for activation, which will reduce side effects and allow gene control in tissues where a relatively low dox level can be reached, such as the brain
A model for interacting instabilities and texture dynamics of patterns
A simple model to study interacting instabilities and textures of resulting
patterns for thermal convection is presented. The model consisting of
twelve-mode dynamical system derived for periodic square lattice describes
convective patterns in the form of stripes and patchwork quilt. The interaction
between stationary zig-zag stripes and standing patchwork quilt pattern leads
to spatiotemporal patterns of twisted patchwork quilt. Textures of these
patterns, which depend strongly on Prandtl number, are investigated numerically
using the model. The model also shows an interesting possibility of a
multicritical point, where stability boundaries of four different structures
meet.Comment: 4 pages including 4 figures, page width revise
Condensation of the roots of real random polynomials on the real axis
We introduce a family of real random polynomials of degree n whose
coefficients a_k are symmetric independent Gaussian variables with variance
= e^{-k^\alpha}, indexed by a real \alpha \geq 0. We compute exactly
the mean number of real roots for large n. As \alpha is varied, one finds
three different phases. First, for 0 \leq \alpha \sim
(\frac{2}{\pi}) \log{n}. For 1 < \alpha < 2, there is an intermediate phase
where grows algebraically with a continuously varying exponent,
\sim \frac{2}{\pi} \sqrt{\frac{\alpha-1}{\alpha}} n^{\alpha/2}. And finally for
\alpha > 2, one finds a third phase where \sim n. This family of real
random polynomials thus exhibits a condensation of their roots on the real line
in the sense that, for large n, a finite fraction of their roots /n are
real. This condensation occurs via a localization of the real roots around the
values \pm \exp{[\frac{\alpha}{2}(k+{1/2})^{\alpha-1} ]}, 1 \ll k \leq n.Comment: 13 pages, 2 figure
Two Graviton Production at and Hadron Hadron Colliders in the Randall-Sundrum Model
We compute the pair production cross section of two Kaluza Klein modes in the
Randall-Sundrum model at and hadron hadron colliders. These processes
are interesting because they get dominant contribution from the graviton
interaction at next to leading order. Hence they provide a nontrivial test of
the low scale gravity models. All the Feynman rules at next to leading order
are also presented. These rules may be useful for many phenomenological
applications including the computation of higher order loop corrections.Comment: 24 pages, 11 figures, some typos correcte
Spin injection into a ballistic semiconductor microstructure
A theory of spin injection across a ballistic
ferromagnet-semiconductor-ferromagnet junction is developed for the Boltzmann
regime. Spin injection coefficient is suppressed by the Sharvin
resistance of the semiconductor , where is the
Fermi-surface cross-section. It competes with the diffusion resistances of the
ferromagnets , and in the absence of contact
barriers. Efficient spin injection can be ensured by contact barriers. Explicit
formulae for the junction resistance and the spin-valve effect are presented.Comment: 5 pages, 2 column REVTeX. Explicit prescription relating the results
of the ballistic and diffusive theories of spin injection is added. To this
end, some notations are changed. Three references added, typos correcte
Theory of spin-polarized bipolar transport in magnetic p-n junctions
The interplay between spin and charge transport in electrically and
magnetically inhomogeneous semiconductor systems is investigated theoretically.
In particular, the theory of spin-polarized bipolar transport in magnetic p-n
junctions is formulated, generalizing the classic Shockley model. The theory
assumes that in the depletion layer the nonequilibrium chemical potentials of
spin up and spin down carriers are constant and carrier recombination and spin
relaxation are inhibited. Under the general conditions of an applied bias and
externally injected (source) spin, the model formulates analytically carrier
and spin transport in magnetic p-n junctions at low bias. The evaluation of the
carrier and spin densities at the depletion layer establishes the necessary
boundary conditions for solving the diffusive transport equations in the bulk
regions separately, thus greatly simplifying the problem. The carrier and spin
density and current profiles in the bulk regions are calculated and the I-V
characteristics of the junction are obtained. It is demonstrated that spin
injection through the depletion layer of a magnetic p-n junction is not
possible unless nonequilibrium spin accumulates in the bulk regions--either by
external spin injection or by the application of a large bias. Implications of
the theory for majority spin injection across the depletion layer, minority
spin pumping and spin amplification, giant magnetoresistance, spin-voltaic
effect, biasing electrode spin injection, and magnetic drift in the bulk
regions are discussed in details, and illustrated using the example of a GaAs
based magnetic p-n junction.Comment: 36 pages, 11 figures, 2 table
Double quantum dot turnstile as an electron spin entangler
We study the conditions for a double quantum dot system to work as a reliable
electron spin entangler, and the efficiency of a beam splitter as a detector
for the resulting entangled electron pairs. In particular, we focus on the
relative strengths of the tunneling matrix elements, the applied bias and gate
voltage, the necessity of time-dependent input/output barriers, and the
consequence of considering wavepacket states for the electrons as they leave
the double dot to enter the beam splitter. We show that a double quantum dot
turnstile is, in principle, an efficient electron spin entangler or
entanglement filter because of the exchange coupling between the dots and the
tunable input/output potential barriers, provided certain conditions are
satisfied in the experimental set-up.Comment: published version; minor error correcte
Linking Backlund and Monodromy Charges for Strings on AdS_5 x S^5
We find an explicit relation between the two known ways of generating an
infinite set of local conserved charges for the string sigma model on AdS_5 x
S^5: the Backlund and monodromy approaches. We start by constructing the
two-parameter family of Backlund transformations for the string with an
arbitrary world-sheet metric. We then show that only for a special value of one
of the parameters the solutions generated by this transformation are compatible
with the Virasoro constraints. By solving the Backlund equations in a
non-perturbative fashion, we finally show that the generating functional of the
Backlund conservation laws is equal to a certain sum of the quasi-momenta. The
positions of the quasi-momenta in the complex spectral plane are uniquely
determined by the real parameter of the Backlund transform.Comment: 25 pages, 1 figur
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