4,941 research outputs found
Molecular basis for modulation of the p53 target selectivity by KLF4
The tumour suppressor p53 controls transcription of various genes involved in apoptosis, cell-cycle arrest, DNA repair and metabolism. However, its DNA-recognition specificity is not nearly sufficient to explain binding to specific locations in vivo. Here, we present evidence that KLF4 increases the DNA-binding affinity of p53 through the formation of a loosely arranged ternary complex on DNA. This effect depends on the distance between the response elements of KLF4 and p53. Using nuclear magnetic resonance and fluorescence techniques, we found that the amino-terminal domain of p53 interacts with the KLF4 zinc fingers and mapped the interaction site. The strength of this interaction was increased by phosphorylation of the p53 N-terminus, particularly on residues associated with regulation of cell-cycle arrest genes. Taken together, the cooperative binding of KLF4 and p53 to DNA exemplifies a regulatory mechanism that contributes to p53 target selectivity
Exact infinite-time statistics of the Loschmidt echo for a quantum quench
The equilibration dynamics of a closed quantum system is encoded in the
long-time distribution function of generic observables. In this paper we
consider the Loschmidt echo generalized to finite temperature, and show that we
can obtain an exact expression for its long-time distribution for a closed
system described by a quantum XY chain following a sudden quench. In the
thermodynamic limit the logarithm of the Loschmidt echo becomes normally
distributed, whereas for small quenches in the opposite, quasi-critical regime,
the distribution function acquires a universal double-peaked form indicating
poor equilibration. These findings, obtained by a central limit theorem-type
result, extend to completely general models in the small-quench regime.Comment: 4 pages, 2 figure
Quantum phase transition in quantum wires controlled by an external gate
We consider electrons in a quantum wire interacting via a long-range Coulomb
potential screened by a nearby gate. We focus on the quantum phase transition
from a strictly one-dimensional to a quasi-one-dimensional electron liquid,
that is controlled by the dimensionless parameter , where is the
electron density and is the characteristic length of the transverse
confining potential. If this transition occurs in the low-density limit, it can
be understood as the deformation of the one-dimensional Wigner crystal to a
zigzag arrangement of the electrons described by an Ising order parameter. The
critical properties are governed by the charge degrees of freedom and the spin
sector remains essentially decoupled. At large densities, on the other hand,
the transition is triggered by the filling of a second one-dimensional subband
of transverse quantization. Electrons at the bottom of the second subband
interact strongly due to the diverging density of states and become
impenetrable. We argue that this stabilizes the electron liquid as it
suppresses pair-tunneling processes between the subbands that would otherwise
lead to an instability. However, the impenetrable electrons in the second band
are screened by the excitations of the first subband, so that the transition is
identified as a Lifshitz transition of impenetrable polarons. We discuss the
resulting phase diagram as a function of .Comment: 18 pages, 8 figures, minor changes, published versio
Quantum correlations in the temporal CHSH scenario
We consider a temporal version of the CHSH scenario using projective
measurements on a single quantum system. It is known that quantum correlations
in this scenario are fundamentally more general than correlations obtainable
with the assumptions of macroscopic realism and non-invasive measurements. In
this work, we also educe some fundamental limitations of these quantum
correlations. One result is that a set of correlators can appear in the
temporal CHSH scenario if and only if it can appear in the usual spatial CHSH
scenario. In particular, we derive the validity of the Tsirelson bound and the
impossibility of PR-box behavior. The strength of possible signaling also turns
out to be surprisingly limited, giving a maximal communication capacity of
approximately 0.32 bits. We also find a temporal version of Hardy's nonlocality
paradox with a maximal quantum value of 1/4.Comment: corrected versio
Kinematic dynamo wave in the vicinity of the solar poles
We consider a dynamo wave in the solar convective shell for the kinematic
-dynamo model. The spectrum and eigenfunctions of the
corresponding equations are derived analytically with the aid of the WKB
method. Our main aim here is to investigate the dynamo wave behavior in the
vicinity of the solar poles. Explicit expressions for the incident and
reflected waves are obtained. The reflected wave is shown to be relatively weak
in comparison to the incident wave. The phase shifts and the ratio of
amplitudes of the two waves are found.Comment: 20 pages, 2 EPS figure
Shear-Driven Dynamo Waves in the Fully Nonlinear Regime
Large-scale dynamo action is well understood when the magnetic Reynolds number (Rm) is small, but becomes problematic in the astrophysically relevant large Rm limit since the fluctuations may control the operation of the dynamo, obscuring the large-scale behavior. Recent works by Tobias & Cattaneo demonstrated numerically the existence of large-scale dynamo action in the form of dynamo waves driven by strongly helical turbulence and shear. Their calculations were carried out in the kinematic regime in which the back-reaction of the Lorentz force on the flow is neglected. Here, we have undertaken a systematic extension of their work to the fully nonlinear regime. Helical turbulence and large-scale shear are produced self-consistently by prescribing body forces that, in the kinematic regime, drive flows that resemble the original velocity used by Tobias & Cattaneo. We have found four different solution types in the nonlinear regime for various ratios of the fluctuating velocity to the shear and Reynolds numbers. Some of the solutions are in the form of propagating waves. Some solutions show large-scale helical magnetic structure. Both waves and structures are permanent only when the kinetic helicity is non-zero on average
Typical local measurements in generalised probabilistic theories: emergence of quantum bipartite correlations
What singles out quantum mechanics as the fundamental theory of Nature? Here
we study local measurements in generalised probabilistic theories (GPTs) and
investigate how observational limitations affect the production of
correlations. We find that if only a subset of typical local measurements can
be made then all the bipartite correlations produced in a GPT can be simulated
to a high degree of accuracy by quantum mechanics. Our result makes use of a
generalisation of Dvoretzky's theorem for GPTs. The tripartite correlations can
go beyond those exhibited by quantum mechanics, however.Comment: 5 pages, 1 figure v2: more details in the proof of the main resul
Probing Spin-Polarized Currents in the Quantum Hall Regime
An experiment to probe spin-polarized currents in the quantum Hall regime is
suggested that takes advantage of the large Zeeman-splitting in the
paramagnetic diluted magnetic semiconductor zinc manganese selenide
(ZnMnSe). In the proposed experiment spin-polarized electrons are
injected by ZnMnSe-contacts into a gallium arsenide (GaAs) two-dimensional
electron gas (2DEG) arranged in a Hall bar geometry. We calculated the
resulting Hall resistance for this experimental setup within the framework of
the Landauer-B\"uttiker formalism. These calculations predict for 100%
spininjection through the ZnMnSe-contacts a Hall resistance twice as high as in
the case of no spin-polarized injection of charge carriers into a 2DEG for
filling factor . We also investigated the influence of the equilibration
of the spin-polarized electrons within the 2DEG on the Hall resistance. In
addition, in our model we expect no coupling between the contact and the 2DEG
for odd filling factors of the 2DEG for 100% spininjection, because of the
opposite sign of the g-factors of ZnMnSe and GaAs.Comment: 7 pages, 5 figure
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