87 research outputs found
Curvaton reheating and intermediate inflation in brane cosmology
In this paper, we study the curvaton reheating mechanism for an intermediate
inflationary universe in brane world cosmology. In contrast to our previous
work, we assume that when the universe enters the kination era, it is still in
the high-energy regime. We then discuss, in detail, the new cosmological
constraints on both the model parameters and the physical quantities.Comment: 15 pages, 4 figures. With some modifications to the text the version
published on Can. J. Phys. arXiv admin note: significant text overlap with
arXiv:1011.080
Noether symmetry in the higher order gravity theory
Noether symmetry for higher order gravity theory has been explored, with the
introduction of an auxiliary variable which gives the only correct quantum
desccription of the theory, as shown in a series of earlier papers. The
application of Noether theorem in higher order theory of gravity turned out to
be a powerful tool to find the solution of the field equations. A few such
physically reasonable solutions like power law inflation are presented.Comment: 9 page
Viability of Noether symmetry of F(R) theory of gravity
Canonization of F(R) theory of gravity to explore Noether symmetry is
performed treating R - 6(\frac{\ddot a}{a} + \frac{\dot a^2}{a^2} +
\frac{k}{a^2}) = 0 as a constraint of the theory in Robertson-Walker
space-time, which implies that R is taken as an auxiliary variable. Although it
yields correct field equations, Noether symmetry does not allow linear term in
the action, and as such does not produce a viable cosmological model. Here, we
show that this technique of exploring Noether symmetry does not allow even a
non-linear form of F(R), if the configuration space is enlarged by including a
scalar field in addition, or taking anisotropic models into account.
Surprisingly enough, it does not reproduce the symmetry that already exists in
the literature (A. K. Sanyal, B. Modak, C. Rubano and E. Piedipalumbo,
Gen.Relativ.Grav.37, 407 (2005), arXiv:astro-ph/0310610) for scalar tensor
theory of gravity in the presence of R^2 term. Thus, R can not be treated as an
auxiliary variable and hence Noether symmetry of arbitrary form of F(R) theory
of gravity remains obscure. However, there exists in general, a conserved
current for F(R) theory of gravity in the presence of a non-minimally coupled
scalar-tensor theory (A. K. Sanyal, Phys.Lett.B624, 81 (2005),
arXiv:hep-th/0504021 and Mod.Phys.Lett.A25, 2667 (2010), arXiv:0910.2385
[astro-ph.CO]). Here, we briefly expatiate the non-Noether conserved current
and cite an example to reveal its importance in finding cosmological solution
for such an action, taking F(R) \propto R^{3/2}.Comment: 16 pages, 1 figure. appears in Int J Theoretical Phys (2012
Chemokine receptor trio: CXCR3, CXCR4 and CXCR7 crosstalk via CXCL11 and CXCL12.
Although chemokines are well established to function in immunity and endothelial cell activation and proliferation, a rapidly growing literature suggests that CXC Chemokine receptors CXCR3, CXCR4 and CXCR7 are critical in the development and progression of solid tumors. The effect of these chemokine receptors in tumorigenesis is mediated via interactions with shared ligands I-TAC (CXCL11) and SDF-1 (CXCL12). Over the last decade, CXCR4 has been extensively reported to be overexpressed in most human solid tumors and has earned considerable attention toward elucidating its role in cancer metastasis. To enrich the existing armamentarium of anti-cancerous agents, many inhibitors of CXCL12-CXCR4 axis have emerged as additional or alternative agents for neo-adjuvant treatments and even many of them are in preclinical and clinical stages of their development. However, the discovery of CXCR7 as another receptor for CXCL12 with rather high binding affinity and recent reports about its involvement in cancer progression, has questioned the potential of "selective blockade" of CXCR4 as cancer chemotherapeutics. Interestingly, CXCR7 can also bind another chemokine CXCL11, which is an established ligand for CXCR3. Recent reports have documented that CXCR3 and their ligands are overexpressed in different solid tumors and regulate tumor growth and metastasis. Therefore, it is important to consider the interactions and crosstalk between these three chemokine receptors and their ligand mediated signaling cascades for the development of effective anti-cancer therapies. Emerging evidence also indicates that these receptors are differentially expressed in tumor endothelial cells as well as in cancer stem cells, suggesting their direct role in regulating tumor angiogenesis and metastasis. In this review, we will focus on the signals mediated by this receptor trio via their shared ligands and their role in tumor growth and progression
Revisiting Noether gauge symmetry for F(R) theory of gravity
Noether gauge symmetry for F(R) theory of gravity has been explored recently.
The fallacy is that, even after setting gauge to vanish, the form of F(R)
\propto R^n (where n \neq 1, is arbitrary) obtained in the process, has been
claimed to be an outcome of gauge Noether symmetry. On the contrary, earlier
works proved that any nonlinear form other than F(R) \propto R^3/2 is obscure.
Here, we show that, setting gauge term zero, Noether equations are satisfied
only for n = 2, which again does not satisfy the field equations. Thus, as
noticed earlier, the only admissible form that Noether symmetry is F(R) \propto
R^3/2 . Noether symmetry with non-zero gauge has also been studied explicitly
here, to show that it does not produce anything new.Comment: 9 pages, To appear in Astrophysics Space Scienc
Noether symmetry for Gauss-Bonnet dilatonic gravity
Noether symmetry for Gauss-Bonnet-Dilatonic interaction exists for a constant
dilatonic scalar potential and a linear functional dependence of the coupling
parameter on the scalar field. The symmetry with the same form of the potential
and coupling parameter exists all in the vacuum, radiation and matter dominated
era. The late time acceleration is driven by the effective cos- mological
constant rather than the Gauss-Bonnet term, while the later compensates for the
large value of the effective cosmological constant giving a plausible answer to
the well-known coincidence problem.Comment: 17 pages, 5 figures, in press on GR
In vitro and in vivo evaluation of 2-chloroethylnitrosourea derivatives as antitumor agents
Aim: To evaluate potential of Naphthal-NU, Napro-NU and 5-Nitro-naphthal-NU, 2-chloroethylnitrosourea compounds with substituted naphthalimide in the pre-clinical studies. Materials and Methods: In vitro cytotoxicity of three nitrosoureas was determined in human and mouse tumor cell lines by MTT assays. In vivo anti-tumor potential was evaluated in Sarcoma-180 (S-180) and Ehrlich’s carcinoma (EC) solid tumors. Apoptosis in S-180 cells was analyzed by using Annexin V-Propidium Iodide (PI). Histological analysis of liver and kidney was performed at optimum dose (50 mg/kg). Expression status of CD4+, CD8+ and CD25+ cells in treated mouse were also examined. Results: Significant tumor growth retardation by the compounds was noted in early and advanced disease groups, as the life span of drug treated mice increased considerably. Drug induced killing was observed by induction of apoptosis. Naphthal-NU and 5-Nitro-naphthal-NU were effective to normalize the tumor induced structural abnormalities of liver and kidney. The compounds have no immunotoxic effect on CD4+ and CD8+ T cells and down regulate CD4+CD25+ regulatory T cells. Conclusion: Overall data holds promise for the antitumor activity with lower toxicity of the compounds that can be utilized for the treatment of human malignant tumors. Key Words: cytotoxicity, Naphthal-NU, Napro-NU, 5-Nitro-naphthal-NU, Sarcoma-180, Ehrlich’s carcinoma
Bianchi Type I Cosmology in Generalized Saez-Ballester Theory via Noether Gauge Symmetry
In this paper, we investigate the generalized Saez-Ballester scalar-tensor
theory of gravity via Noether gauge symmetry (NGS) in the background of Bianchi
type I cosmological spacetime. We start with the Lagrangian of our model and
calculate its gauge symmetries and corresponding invariant quantities. We
obtain the potential function for the scalar field in the exponential form. For
all the symmetries obtained, we determine the gauge functions corresponding to
each gauge symmmetry which include constant and dynamic gauge. We discuss
cosmological implications of our model and show that it is compatible with the
observational data.Comment: 13 pages, 2 figures, accepted for publication in 'European Physical
Journal C
LRS Bianchi type I universes exhibiting Noether symmetry in the scalar-tensor Brans-Dicke theory
Following up on hints of anisotropy in the cosmic microwave background
radiation (CMB) data, we investigate locally rotational symmetric (LRS) Bianchi
type I spacetimes with non-minimally coupled scalar fields. To single out
potentially more interesting solutions, we search for Noether symmetry in this
system. We then specialize to the Brans-Dicke (BD) field in such a way that the
Lagrangian becomes degenerate (nontrivial) and solve the equations for Noether
symmetry and the potential that allows it. Then we find the exact solutions of
the equations of motion in terms of three parameters and an arbitrary function.
We illustrate with families of examples designed to be generalizations of the
well-known power-expansion, exponential expansion and Big Rip models in the
Friedmann-Robertson-Walker (FRW) framework. The solutions display surprising
variation, a large subset of which features late-time acceleration as is
usually ascribed to dark energy (phantom or quintensence), and is consistent
with observational data.Comment: 25 pages, no figure, to appear in General Relativity and Gravitatio
Noether gauge symmetry for gravity in Palatini formalism
In this study, we consider a flat Friedmann-Robertson-Walker (FRW) universe
in the context of Palatini theory of gravity. Using the dynamical
equivalence between gravity and scalar-tensor theories, we construct a
point Lagrangian in the flat FRW spacetime. Applying {\em Noether gauge
symmetry approach} for this Lagrangian we find out the form of
and the exact solution for cosmic scale factor. It is shown that the resulting
form of yield a power-law expansion for the scale factor of the
universe.Comment: 7 pagese, no figures; Published in Astrophysics & Space Science. Some
minor corrections have been mad
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