A short proof of an index theorem, II

We introduce a slight modification of the usual equivariant $KK$-theory. We use this to give a $KK$-theoretical proof of an equivariant index theorem for Dirac-Schrodinger operators on a non-compact manifold of nowhere positive curvature. We incidentally show that the boundary of Dirac is Dirac; generalizing earlier work of Baum and coworkers, and a result of Higson and Roe.Comment: Corrected typo in abstract. No changes to conten

Generalized second law of thermodynamics in f(T) gravity

We investigate the validity of the generalized second law (GSL) of gravitational thermodynamics in the framework of f(T) modified teleparallel gravity. We consider a spatially flat FRW universe containing only the pressureless matter. The boundary of the universe is assumed to be enclosed by the Hubble horizon. For two viable f(T) models containing $f(T)=T+\mu_1{(-T)}^n$ and $f(T)=T-\mu_2 T(1-e^{\beta\frac{T_0}{T}})$, we first calculate the effective equation of state and deceleration parameters. Then, we investigate the null and strong energy conditions and conclude that a sudden future singularity appears in both models. Furthermore, using a cosmographic analysis we check the viability of two models. Finally, we examine the validity of the GSL and find that for both models it is satisfied from the early times to the present epoch. But in the future, the GSL is violated for the special ranges of the torsion scalar T.Comment: 16 pages, 10 figures, accepted by JCAP 201

Identification of distribution of Macrobrachium nipponense in freshwater ecosystems and coastal waters of Golestan Province, Caspian Sea

Distribution of freshwater shrimp (Macrobrachium nipponense) in the freshwater ecosystems such as Alagol, Almagol, Ajigol lagoons, Gomishan lagoon and Gorganrud River. Sampling were done from may 2009 to my 2010 parameters such as, length frequency, growth rate, sampling, feeding, environmental factors and sedimentation were investigated. 3689 females and 8551 males were collected and biometrical parameters were recorded. Total length ranged between 3.2 to 98.7 mm. The parameters b of length-weight relationship in Alagol, Almagol, Ajigol were 3.49, 3.15, 3.45, 3.22 and 3.22, 3.28 for male and female, respectively. It shows in all lagoons for male and female growth is positive Allometric. Spawning period was from May to June. The length first at maturity (total and/or carapace) for three lagoons was 50.5 mm and 133 mm, respectively. The minimum and maximum of egg volume were 0.12 mm3 in Ajigol and 0.07 mm3 Alagol, respectively. The relationship between fecundity and length was found to be linear regression models for Alagol, Ajigol and nonlinear regression models for Almagol lagoon. Result showed that this species is omnivorous. The minimum and maximum temperature was 6.5ْ C in fall and 33ْ C in summer. The lowest and highest fluctuations of pH level in Ajigol and alagol lagoons were 8.2-9.2 and 7.2-9.8. Among three lagoons, the most EC was 5.9 Ms/c in Alagol lagoon. The Gorganrud River shows the maximum EC, 16.7 Ms/c

Existence of relativistic stars in f(T) gravity

We examine the existence of relativistic stars in f(T) modified gravity and explicitly construct several classes of static perfect fluid solutions. We derive the conservation equation from the complete f(T) gravity field equations and present the differences with its teleparallel counterpart. Firstly, we choose the tetrad field in the diagonal gauge and study the resulting field equations. Some exact solutions are explicitly constructed and it is noted that these solutions have to give a constant torsion scalar. Next, we choose a non diagonal tetrad field which results in field equations similar to those of general relativity. For specific models we are able to construct exact solutions of these field equations. Among those new classes of solutions, we find negative pressure solutions, and an interesting class of polynomial solutions.Comment: 19 pages; substantially revised and extended version, off diagonal tetrad discussion adde

QCD ghost f(T)-gravity model

Within the framework of modified teleparallel gravity, we reconstruct a f(T) model corresponding to the QCD ghost dark energy scenario. For a spatially flat FRW universe containing only the pressureless matter, we obtain the time evolution of the torsion scalar T (or the Hubble parameter). Then, we calculate the effective torsion equation of state parameter of the QCD ghost f(T)-gravity model as well as the deceleration parameter of the universe. Furthermore, we fit the model parameters by using the latest observational data including SNeIa, CMB and BAO data. We also check the viability of our model using a cosmographic analysis approach. Moreover, we investigate the validity of the generalized second law (GSL) of gravitational thermodynamics for our model. Finally, we point out the growth rate of matter density perturbation. We conclude that in QCD ghost f(T)-gravity model, the universe begins a matter dominated phase and approaches a de Sitter regime at late times, as expected. Also this model is consistent with current data, passes the cosmographic test, satisfies the GSL and fits the data of the growth factor well as the LCDM model.Comment: 19 pages, 9 figures, 2 tables. arXiv admin note: substantial text overlap with arXiv:1111.726

The generalized second law of gravitational thermodynamics on the apparent horizon in f(R)-gravity

We investigate the generalized second law (GSL) of thermodynamics in the framework of $f(R)$-gravity. We consider a FRW universe filled only with ordinary matter enclosed by the dynamical apparent horizon with the Hawking temperature. For a viable modified gravity model as $f(R)=R-\alpha/R+\beta R^{2}$, we examine the validity of the GSL during the early inflation and late acceleration eras. Our results show that for the selected $f(R)$-gravity model minimally coupled with matter, the GSL in the early inflation epoch is satisfied only for the special range of the equation of state parameter of the matter. But in the late acceleration regime, the GSL is always respected.Comment: 10 pages, accepted by Europhys. Lett. 201

Study of Shovier and Mirzakhanlo dam reservoirs in Zanjan province in order to aquaculture activity

Inland water aquaculture activity have been known as an important approach for protein production while reservoir lakes recognized to have a significant potential for this purpose. Zanjan province in Iran with several dam reservoirs is suitable for aquaculture development. This study was conducted on biotic and abiotic factors of two lakes Shovir and Mirzakhanlo in order to determine aquaculture potentially of reservoirs. This two lakes located on different climatic region; Shovir located in region of semi arid area with very cold weather in winter, while Mirzakhanlo is in semi humid area and warm weather characteristic. In this study the plankton, benthos and fishes were assessed and the 15 hydrochemical factors were measured in order to determine the fisheries potential for fish introduction or release. The results showed that the phytoplankton abundance of Mirzakhanlo varied between 1.6 to 45.2 million cell/l. with 32 identified genus. The zooplankton abundance varied between 48 to 632 n/l. and 22 identified genus. The abundance plankton in shovir varied between 1.350 to 34.2 million cell/l. and 240 to 4500 n/l. for phyto and zooplankton respectively. Macrobenthos biomass were 21.4 and 0.34 g/m^2 in Shovir and Mirzakhanlo lakes respectively while Chironomidae and Tubificidae families were dominant groups. The lake sediment organic matter were 4.3 and 3.2 % respectively. In ichtiology survey identified 5 and 7 species in Mirzakhanlo and Shovir lakes respectively. The hydro-chemical results indicated no restriction for aquaculture activity and according to trophic model both lakes are recognized as meso-eutrophic and eutrophic. Despite of climatic restrictions, the potential for fish production was estimated about 321 and 151 kg/ha for Shovir and Mirzakhanlo lakes respectively that can be improved by using agricultural and the other native facilities