1,475 research outputs found
Increased accuracy of ligand sensing by receptor internalization
Many types of cells can sense external ligand concentrations with
cell-surface receptors at extremely high accuracy. Interestingly, ligand-bound
receptors are often internalized, a process also known as receptor-mediated
endocytosis. While internalization is involved in a vast number of important
functions for the life of a cell, it was recently also suggested to increase
the accuracy of sensing ligand as the overcounting of the same ligand molecules
is reduced. Here we show, by extending simple ligand-receptor models to
out-of-equilibrium thermodynamics, that internalization increases the accuracy
with which cells can measure ligand concentrations in the external environment.
Comparison with experimental rates of real receptors demonstrates that our
model has indeed biological significance.Comment: 9 pages, 4 figures, accepted for publication in Physical Review
The equivalence principle, uniformly accelerated reference frames, and the uniform gravitational field
The relationship between uniformly accelerated reference frames in flat
spacetime and the uniform gravitational field is examined in a relativistic
context. It is shown that, contrary to previous statements in the pages of this
journal, equivalence does not break down in this context. No restrictions to
Newtonian approximations or small enclosures are necessary
Generalization of entanglement to convex operational theories: Entanglement relative to a subspace of observables
We define what it means for a state in a convex cone of states on a space of
observables to be generalized-entangled relative to a subspace of the
observables, in a general ordered linear spaces framework for operational
theories. This extends the notion of ordinary entanglement in quantum
information theory to a much more general framework. Some important special
cases are described, in which the distinguished observables are subspaces of
the observables of a quantum system, leading to results like the identification
of generalized unentangled states with Lie-group-theoretic coherent states when
the special observables form an irreducibly represented Lie algebra. Some open
problems, including that of generalizing the semigroup of local operations with
classical communication to the convex cones setting, are discussed.Comment: 19 pages, to appear in proceedings of Quantum Structures VII, Int. J.
Theor. Phy
Dynamics of Atom-Atom Correlations in the Fermi problem
We present a detailed perturbative study of the dynamics of several types of
atom-atom correlations in the famous Fermi problem. This is an archetypal model
to study micro-causality in the quantum domain where two atoms, the first
initially excited and the second prepared in its ground state, interact with
the vacuum electromagnetic field. The excitation can be transferred to the
second atom via a flying photon and various kinds of quantum correlations
between the two are generated during this process. Among these, prominent
examples are given by entanglement, quantum discord and nonlocal correlations.
It is the aim of this paper to analyze the role of the light cone in the
emergence of such correlations.Comment: 14 pages, 7 figure
Characterizing entanglement with global and marginal entropic measures
We qualify the entanglement of arbitrary mixed states of bipartite quantum
systems by comparing global and marginal mixednesses quantified by different
entropic measures. For systems of two qubits we discriminate the class of
maximally entangled states with fixed marginal mixednesses, and determine an
analytical upper bound relating the entanglement of formation to the marginal
linear entropies. This result partially generalizes to mixed states the
quantification of entaglement with marginal mixednesses holding for pure
states. We identify a class of entangled states that, for fixed marginals, are
globally more mixed than product states when measured by the linear entropy.
Such states cannot be discriminated by the majorization criterion.Comment: 6 pages, 5 color figures in low resolution due to oversizing
problems; to get the original high-resolution figures please contact the
authors. Minor changes, final versio
Scaling algebras and pointlike fields: A nonperturbative approach to renormalization
We present a method of short-distance analysis in quantum field theory that
does not require choosing a renormalization prescription a priori. We set out
from a local net of algebras with associated pointlike quantum fields. The net
has a naturally defined scaling limit in the sense of Buchholz and Verch; we
investigate the effect of this limit on the pointlike fields. Both for the
fields and their operator product expansions, a well-defined limit procedure
can be established. This can always be interpreted in the usual sense of
multiplicative renormalization, where the renormalization factors are
determined by our analysis. We also consider the limits of symmetry actions. In
particular, for suitable limit states, the group of scaling transformations
induces a dilation symmetry in the limit theory.Comment: minor changes and clarifications; as to appear in Commun. Math.
Phys.; 37 page
Optimal performance of endoreversible quantum refrigerators
The derivation of general performance benchmarks is important in the design of highly optimized heat engines and refrigerators. To obtain them, one may model phenomenologically the leading sources of irreversibility ending up with results that are model independent, but limited in scope. Alternatively, one can take a simple physical system realizing a thermodynamic cycle and assess its optimal operation from a complete microscopic description. We follow this approach in order to derive the coefficient of performance at maximum cooling rate for any endoreversible quantum refrigerator. At striking variance with the universality of the optimal efficiency of heat engines, we find that the cooling performance at maximum power is crucially determined by the details of the specific system-bath interaction mechanism. A closed analytical benchmark is found for endoreversible refrigerators weakly coupled to unstructured bosonic heat baths: an ubiquitous case study in quantum thermodynamics
Lectins from the Red Marine Algal Species Bryothamnion seaforthii and Bryothamnion triquetrum as Tools to Differentiate Human Colon Carcinoma Cells
The carbohydrate-binding activity of the algal lectins from the closely related red marine algal species Bryothamnion triquetrum (BTL) and Bryothamnion seaforthii (BSL) was used to differentiate human colon carcinoma cell variants with respect to their cell membrane glyco-receptors. These lectins interacted with the cells tested in a dose-dependent manner. Moreover, the fluorescence spectra of both lectins clearly differentiated the cells used as shown by FACS profiles. Furthermore, as observed by confocal microscopy, BTL and BSL bound to cell surface glycoproteins underwent intense internalization, which makes them possible tools in targeting strategies
Entanglement of two-mode Gaussian states: characterization and experimental production and manipulation
A powerful theoretical structure has emerged in recent years on the
characterization and quantification of entanglement in continuous-variable
systems. After reviewing this framework, we will illustrate it with an original
set-up based on a type-II OPO with adjustable mode coupling. Experimental
results allow a direct verification of many theoretical predictions and provide
a sharp insight into the general properties of two-mode Gaussian states and
entanglement resource manipulation
Association of Central Arterial Stiffness and Pressure Pulsatility with Mild Cognitive Impairment and Dementia: The Atherosclerosis Risk in Communities Study-Neurocognitive Study (ARIC-NCS)
The association of central arterial stiffness and pressure pulsatility with mild cognitive impairment and dementia is not well characterized in the population-based setting
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