141 research outputs found
Aspects of finite electrodynamics in D=3 dimensions
We study the impact of a minimal length on physical observables for a
three-dimensional axionic electrodynamics. Our calculation is done within the
framework of the gauge-invariant, but path-dependent, variables formalism which
is alternative to the Wilson loop approach. Our result shows that the
interaction energy contains a regularised Bessel function and a linear
confining potential. This calculation involves no theta expansion at all. Once
again, the present analysis displays the key role played by the new quantum of
length.Comment: 12 pages, 2 figures; reference list updated and extended; new
aknowlegments; removed line after eq.(1) erroneously inserte
Remarks on Screening in a Gauge-Invariant Formalism
In this paper we display a direct and physically attractive derivation of the
screening contribution to the interaction potential in the Chiral Schwinger
model and generalized Maxwell-Chern-Simons gauge theory. It is shown that these
results emerge naturally when a correct separation between gauge-invariant and
gauge degrees of freedom is made. Explicit expressions for gauge-invariant
fields are found.Comment: 13 pages, 1 figure, to appear in PR
Effect of Prenatal Exposure to Lead on Estrogen Action in the Prepubertal Rat Uterus
Lead is a widely spread environmental pollutant known to affect both male and female reproductive systems in humans and experimental animals and causes infertility and other adverse effects. The present paper investigated the effects of prenatal exposure to lead on different parameters of estrogen stimulation in the uterus of the prepubertal rat. In prenatally and perinatally exposed rats, estrogen-induced endometrial eosinophilia, endometrial stroma edema, and eosinophil migration towards the endometrium, and uterine luminal epithelial hypertrophy are enhanced while several other responses to estrogen appear unchanged. These effects may contribute to decrease in fertility following prenatal exposure to lead. The striking difference between most of these effects of prenatal exposure and the previously reported effects of chronic exposure to lead suggests that prenatal exposure to lead may neutralize the effects of chronic exposure to lead, providing partial protection of cell function against the adverse effects of chronic exposure to lead. We propose that the mechanism involved, named imprinting or cell programming, persisted through evolution as a nongenetic adaptive mechanism to provide protection against long-term environmental variations that otherwise may cause the extinction of species not displaying this kind of adaptation
Solutions for f(R) gravity coupled with electromagnetic field
In the presence of external, linear / nonlinear electromagnetic fields we
integrate f(R) \sim R+2{\alpha}\surd(R+const.) gravity equations. In contrast
to their Einsteinian cousins the obtained black holes are non-asymptotically
flat with a deficit angle. In proper limits we obtain from our general solution
the global monopole solution in f(R) gravity. The scale symmetry breaking term
adopted as the nonlinear electromagnetic source adjusts the sign of the mass of
the resulting black hole to be physical.Comment: 7 pages no figure, final version for publication in European Physical
Journal
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Prevalence of psychotic symptoms in children needing inpatient care: Relationship to diagnosis
Hiding and Confining Charges via "Tube-like" Wormholes
We describe two interesting effects in wormhole physics. First, we find that
a genuinely charged matter source may appear neutral to an external observer -
a phenomenon opposite to the famous Misner-Wheeler "charge without charge"
effect. This phenomenon takes place when coupling a bulk
gravity/nonlinear-gauge-field system to a charged lightlike brane as a matter
source. The "charge-hiding" effect occurs in a wormhole solution which connects
a non-compact "universe", comprising the exterior region of
Schwarzschild-(anti-)de-Sitter (SdS) or purely Schwarzschild black hole beyond
the Schwarzschild horizon, to a Levi-Civita-Bertotti-Robinson-type (LCBR)
"tube-like" "universe" via a wormhole "throat" occupied by the brane. In this
solution the whole electric flux produced by the brane is expelled into the
"tube-like" "universe" and the brane is detected as neutral by an observer in
the non-compact "universe". Next, we find a truly charge-confining wormhole
solution when we couple the bulk gravity/nonlinear-gauge-field system to two
oppositely charged lightlike branes. The latter system possesses a "two-throat"
wormhole solution, where the "left-most" and the "right-most" "universes" are
two identical copies of the exterior region of SdS black hole beyond the
Schwarzschild horizon, whereas the "middle" "universe" is of LCBR "tube-like"
form with geometry dS_2 x S^2. It comprises the finite-extent intermediate
region of dS_2 between its two horizons. Both "throats" are occupied by the two
oppositely charged lightlike branes and the whole electric flux produced by the
latter is confined entirely within the middle "tube-like" "universe". A crucial
ingredient is the special form of the nonlinear gauge field action, which
contains both the standard Maxwell term as well as a square root of the latter.
This theory was previously shown to produce a QCD-like confining dynamics in
flat space-time.Comment: 26 pages, 2 figures; v.2 several references added, missing constant
factors in few equations inserted, acknowledgement added, results unchanged;
v.3 28 pages, several clarifying remarks, references and acknowledgements
added, version to appear in International Journal of Modern Physics
Finite axionic electrodynamics from a new noncommutative approach
Using the gauge-invariant but path-dependent variables formalism, we compute
the static quantum potential for noncommutative axionic electrodynamics (or
axionic electrodynamics in the presence of a minimal length). Accordingly, we
obtain an ultraviolet finite static potential which is the sum of a Yukawa-type
and a linear potential, leading to the confinement of static charges.
Interestingly, it should be noted that this calculation involves no theta
expansion at all. The present result makes manifest the key role played by the
new quantum of length in our analysis.Comment: 14 pages, 2 figures, final version to appear in J.Phys.A, added
comments, reference list update
Effective Action for QED with Fermion Self-Interaction in D=2 and D=3 Dimensions
In this work we discuss the effect of the quartic fermion self-interaction of
Thirring type in QED in D=2 and D=3 dimensions. This is done through the
computation of the effective action up to quadratic terms in the photon field.
We analyze the corresponding nonlocal photon propagators nonperturbatively in %
\frac{k}{m}, where k is the photon momentum and m the fermion mass. The poles
of the propagators were determined numerically by using the Mathematica
software. In D=2 there is always a massless pole whereas for strong enough
Thirring coupling a massive pole may appear . For D=3 there are three regions
in parameters space. We may have one or two massive poles or even no pole at
all. The inter-quark static potential is computed analytically in D=2. We
notice that the Thirring interaction contributes with a screening term to the
confining linear potential of massive QED_{2}. In D=3 the static potential must
be calculated numerically. The screening nature of the massive QED
prevails at any distance, indicating that this is a universal feature of % D=3
electromagnetic interaction. Our results become exact for an infinite number of
fermion flavors.Comment: Latex, 13 pages, 3 figure
Comparing development and regeneration in the submandibular gland highlights distinct mechanisms
A common question in organ regeneration is the extent to which regeneration reca- pitulates embryonic development. To investigate this concept, we compared the ex- pression of two highly interlinked and essential genes for salivary gland development, Sox9 and Fgf10, during submandibular gland development, homeostasis and regenera- tion. Salivary gland duct ligation/deligation model was used as a regenerative model. Fgf10 and Sox9 expression changed during regeneration compared to homeostasis, suggesting that these key developmental genes play important roles during regen- eration, however, significantly both displayed different patterns of expression in the regenerating gland compared to the developing gland. Regenerating glands, which during homeostasis had very few weakly expressing Sox9-positive cells in the stri- ated/granular ducts, displayed elevated expression of Sox9 within these ducts. This pattern is in contrast to embryonic development, where Sox9 expression was absent in the proximally developing ducts. However, similar to the elevated expression at the distal tip of the epithelium in developing salivary glands, regenerating glands dis- played elevated expression in a subpopulation of acinar cells, which during homeosta- sis expressed Sox9 at lower levels. A shift in expression of Fgf10 was observed from a widespread mesenchymal pattern during organogenesis to a more limited and pre- dominantly epithelial pattern during homeostasis in the adult. This restricted expres- sion in epithelial cells was maintained during regeneration, with no clear upregulation in the surrounding mesenchyme, as might be expected if regeneration recapitulated development. As both Fgf10 and Sox9 were upregulated in proximal ducts during regeneration, this suggests that the positive regulation of Sox9 by Fgf10, essential during development, is partially reawakened during regeneration using this model. Together these data suggest that developmentally important genes play a key role in salivary gland regeneration but do not precisely mimic the roles observed during development
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