24,011 research outputs found
History state formalism for Dirac's theory
We propose a history state formalism for a Dirac particle. By introducing a
reference quantum clock system it is first shown that Dirac's equation can be
derived by enforcing a timeless Wheeler-DeWitt-like equation for a global
state. The Hilbert space of the whole system constitutes a unitary
representation of the Lorentz group with respect to a properly defined
invariant product, and the proper normalization of global states directly
ensures standard Dirac's norm. Moreover, by introducing a second quantum clock,
the previous invariant product emerges naturally from a generalized continuity
equation. The invariant parameter associated with this second clock
labels history states for different particles, yielding an observable evolution
in the case of an hypothetical superposition of different masses. Analytical
expressions for both space-time density and electron-time entanglement are
provided for two particular families of electron's states, the former including
Pryce localized particles.Comment: 9 pages, 2 figures, final versio
Prostaglandin E2-EP1 and EP2 receptor signaling promotes apical junctional complex disassembly of Caco-2 human colorectal cancer cells
<p>Abstract</p> <p>Background</p> <p>The apical junctional complex (AJC) is a dynamic structure responsible to maintain epithelial cell-cell adhesions and it plays important functions such as, polarity, mechanical integrity, and cell signaling. Alteration of this complex during pathological events leads to an impaired epithelial barrier by perturbation of the cell-cell adhesion system. Although clinical and experimental data indicate that prostaglandin E<sub>2 </sub>(PGE<sub>2</sub>) plays a critical function in promoting cell motility and cancer progression, little is known concerning its role in AJC disassembly, an event that takes place at the beginning of colorectal tumorigenesis. Using Caco-2 cells, a cell line derived from human colorectal cancer, we investigated the effects of prostaglandin E<sub>2 </sub>(PGE<sub>2</sub>) treatment on AJC assembly and function.</p> <p>Results</p> <p>Exposition of Caco-2 cells to PGE<sub>2 </sub>promoted differential alteration of AJC protein distribution, as evidenced by immunofluorescence and immunoblotting analysis and impairs the barrier function, as seen by a decrease in the transepithelial electric resistance and an increase in the permeability to ruthenium red marker. We demonstrated the involvement of EP1 and EP2 prostaglandin E<sub>2 </sub>receptor subtypes in the modulation of the AJC disassembly caused by prostanoid. Furthermore, pharmacological inhibition of protein kinase-C, but not PKA and p38MAPK significantly prevented the PGE<sub>2 </sub>effects on the AJC disassembly.</p> <p>Conclusion</p> <p>Our findings strongly suggest a central role of Prostaglandin E2-EP1 and EP2 receptor signaling to mediate AJC disassembly through a mechanism that involves PKC and claudin-1 as important target for the TJ-related effects in human colorectal cancer cells (Caco-2).</p
One More Step Towards Well-Composedness of Cell Complexes over nD Pictures
An nD pure regular cell complex K is weakly well-composed
(wWC) if, for each vertex v of K, the set of n-cells incident to v is
face-connected. In previous work we proved that if an nD picture I is
digitally well composed (DWC) then the cubical complex Q(I) associated
to I is wWC. If I is not DWC, we proposed a combinatorial algorithm
to “locally repair” Q(I) obtaining an nD pure simplicial complex PS(I)
homotopy equivalent to Q(I) which is always wWC. In this paper we give
a combinatorial procedure to compute a simplicial complex PS(¯I) which
decomposes the complement space of |PS(I)| and prove that PS(¯I) is also
wWC. This paper means one more step on the way to our ultimate goal:
to prove that the nD repaired complex is continuously well-composed
(CWC), that is, the boundary of its continuous analog is an (n − 1)-
manifold.Ministerio de Economía y Competitividad MTM2015-67072-
Path Integrals from Spacetime Quantum Actions
We present a spacetime Hilbert space formulation of Feynman path integrals
(PIs). It relies on a tensor product structure in time which provides extended
representations of dynamical quantum observables through a spacetime quantum
action operator. As a consequence, the ``sum over paths'' of the different PI
formulations naturally arise within the same Hilbert space, with each one
associated with a different quantum trajectory basis. New insights on PI-based
results naturally follow, including exact discretizations and a non-trivial
approach to the continuum limit.Comment: 8 pages, 1 figur
Spacetime quantum and classical mechanics with dynamical foliation
The conventional phase space of classical physics treats space and time
differently, and this difference carries over to field theories and quantum
mechanics (QM). In this paper, the phase space is enhanced through two main
extensions. Firstly, we promote the time choice of the Legendre transform to a
dynamical variable. Secondly, we extend the Poisson brackets of matter fields
to a spacetime symmetric form. The ensuing "spacetime phase space" is employed
to obtain an explicitly covariant version of Hamilton equations for
relativistic field theories. A canonical-like quantization of the formalism is
then presented in which the fields satisfy spacetime commutation relations and
the foliation is quantum. In this approach, the classical action is also
promoted to an operator and retains explicit covariance through its
non-separability in the matter-foliation partition. The problem of establishing
a correspondence between the new noncausal framework (where fields at different
times are independent) and conventional QM is solved through a generalization
of spacelike correlators to spacetime. In this generalization, the Hamiltonian
is replaced by the action, and conventional particles by off-shell particles.
When the foliation is quantized, the previous map is recovered by conditioning
on foliation eigenstates, in analogy with the Page and Wootters mechanism. We
also provide an interpretation of the correspondence in which the causal
structure of a given theory emerges from the quantum correlations between the
system and an environment. This idea holds for general quantum systems and
allows one to generalize the density matrix to an operator containing the
information of correlators both in space and time.Comment: 25 pages, 4 figure
Spacetime Quantum Actions
We propose a formulation of quantum mechanics in an extended Fock space in
which a tensor product structure is applied to time. Subspaces of histories
consistent with the dynamics of a particular theory are defined by a direct
quantum generalization of the corresponding classical action. The
diagonalization of such quantum actions enables us to recover the predictions
of conventional quantum mechanics and reveals an extended unitary equivalence
between all physical theories. Quantum correlations and coherent effects across
time and between distinct theories acquire a rigorous meaning, which is encoded
in the rich temporal structure of physical states. Connections with modern
relativistic schemes and the path integral formulation also emerge.Comment: 16 pages, 3 figures, accepted for publication in Phys. Rev.
Renormalization Group and Grand Unification with 331 Models
By making a renormalization group analysis we explore the possibility of
having a 331 model as the only intermediate gauge group between the standard
model and the scale of unification of the three coupling constants. We shall
assume that there is no necessarily a group of grand unification at the scale
of convergence of the couplings. With this scenario, different 331 models and
their corresponding supersymmetric versions are considered, and we find the
versions that allow the symmetry breaking described above. Besides, the allowed
interval for the 331 symmetry breaking scale, and the behavior of the running
coupling constants are obtained. It worths saying that some of the
supersymmetric scenarios could be natural frameworks for split supersymmetry.
Finally, we look for possible 331 models with a simple group at the grand
unification scale, that could fit the symmetry breaking scheme described above.Comment: 18 pages. 3 figures. Some results reinterpreted, a new section and
references added. Version to appear in International Journal of Modern
Physics
Optical detection of the radio supernova SN 2000ft in the circumnuclear region of the luminous infrared galaxy NGC 7469
SN 2000ft is detected in two independent Planetary Camera images (F547W and
F814W) taken May 13, 2000, about two months before the predicted date of the
explosion (July 19, 2000), based on the analysis of its radio light evolution
by Alberdi and collaborators. The apparent optical magnitudes and red color of
SN 2000ft indicate that it is observed through an extinction of at least A=
3.0 magnitudes. The extinction corrected lower limit to the absolute visual
magnitude (M 18.0), identifies SN 2000ft as a luminous supernova
in the optical, as other luminous radio supernovae before. SN 2000ft exploded
in a region located at only 0.1 arcsec (i.e. 34 +/- 3 pc) west of a faint
cluster (C24). No parent cluster is identified within the detection limits of
the HST short exposures. The unambiguous detection of SN 2000ft in the visual
shows that multi-epoch sub-arcsecond (FWHM less than 0.1 arcsec) optical
imaging is also a valid tool that should be explored further to detect
supernovae in the dusty (circum)nuclear regions of (U)LIRGs
Giant and Broadband THz and IR Emission in Drift-biased Graphene-Based Hyperbolic Nanostructures
We demonstrate that Cherenkov radiation can be manipulated in terms of
operation frequency, bandwidth, and efficiency by simultaneously controlling
the properties of drifting electrons and the photonic states supported by their
surrounding media. We analytically show that the radiation rate strongly
depends on the momentum of the excited photonic state, in terms of magnitude,
frequency dispersion, and its variation versus the properties of the drifting
carriers. This approach is applied to design and realize miniaturized,
broadband, tunable, and efficient terahertz and far-infrared sources by
manipulating and boosting the coupling between drifting electrons and
engineered hyperbolic modes in graphene-based nanostructures. The broadband,
dispersive, and confined nature of hyperbolic modes relax momentum matching
issues, avoid using electron beams, and drastically enhance the radiation rate
- allowing that over 90% of drifting electrons emit photons. Our findings open
a new paradigm for the development of solid-state terahertz and infrared
sources.Comment: 4 figure
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