On the absence of the usual weak-field limit, and the impossibility of embedding some known solutions for isolated masses in cosmologies with f(R) dark energy

This version deposited at arxiv 02-10-12 arXiv:1210.0730v1. Subsequently published in Physical Review D as Phys. Rev. D 87, 063517 (2013) http://link.aps.org/doi/10.1103/PhysRevD.87.063517. Copyright American Physical Society (APS).11 pages11 pages11 pages11 pagesThe problem of matching different regions of spacetime in order to construct inhomogeneous cosmological models is investigated in the context of Lagrangian theories of gravity constructed from general analytic functions f(R), and from non-analytic theories with f(R)=R^n. In all of the cases studied, we find that it is impossible to satisfy the required junction conditions without the large-scale behaviour reducing to that expected from Einstein's equations with a cosmological constant. For theories with analytic f(R) this suggests that the usual treatment of weak-field systems may not be compatible with late-time acceleration driven by anything other than a constant term of the form f(0), which acts like a cosmological constant. For theories with f(R)=R^n we find that no known spherically symmetric vacuum solutions can be matched to an expanding FLRW background. This includes the absence of any Einstein-Straus-like embeddings of the Schwarzschild exterior solution in FLRW spacetimes

A Landau fluid model for warm collisionless plasmas

A Landau fluid model for a collisionless electron-proton magnetized plasma, that accurately reproduces the dispersion relation and the Landau damping rate of all the magnetohydrodynamic waves, is presented. It is obtained by an accurate closure of the hydrodynamic hierarchy at the level of the fourth order moments, based on linear kinetic theory. It retains non-gyrotropic corrections to the pressure and heat flux tensors up to the second order in the ratio between the considered frequencies and the ion cyclotron frequency.Comment: to appear in Phys. Plasma

Multiferroic coupling in nanoscale BiFeO3

Using the results of x-ray and neutron diffraction experiments, we show that the ferroelectric polarization, in ~22 nm particles of BiFeO3, exhibits a jump by ~30% around the magnetic transition point T_N (~635 K) and a suppression by ~7% under 5T magnetic field at room temperature (<<T_N). These results confirm presence of strong multiferroic coupling even in nanoscale BiFeO3 and thus could prove to be quite useful for applications based on nanosized devices of BiFeO3.Comment: 4 pages including 4 figures and supplementary data; accepted for publication in Appl. Phys. Let

Clean-up of Contaminated Indoor Air Using Photocatalytic Technology

A number of Sick Building Syndrome studies have concluded that microorganisms, endotoxins and VOCs in indoor air are involved in the development and/or aggravation of allergies and illnesses in buildings. The phototcatalytic indoor air disinfection and detoxification technology provides one of the most viable solutions to the growing need to remediate and purify contaminated indoor air. The experiments were conducted in a stainless steel environmental chamber to quantitatively measure the photocatalytic VOC destruction using Acetone as a representative VOC. While monitoring the VOC destruction, carbon dioxide (C02) levels were also measured. By performing a mass balance between the VOC destruction and C02 production, the photocatalytic technology was found to be completely effective. Dark control experiments were performed for each condition to confirm the validity of each experiment. The photocatalytic technology tested in these experiments was demonstrated to completely oxidize acetone at normal indoor air atmospheric conditions

Surface Geometry of 5D Black Holes and Black Rings

We discuss geometrical properties of the horizon surface of five-dimensional rotating black holes and black rings. Geometrical invariants characterizing these 3D geometries are calculated. We obtain a global embedding of the 5D rotating black horizon surface into a flat space. We also describe the Kaluza-Klein reduction of the black ring solution (along the direction of its rotation) which relates this solution to the 4D metric of a static black hole distorted by the presence of external scalar (dilaton) and vector (`electromagnetic') field. The properties of the reduced black hole horizon and its embedding in \E^3 are briefly discussed.Comment: 10 pages, 9 figures, Revtex

A homomorphism theorem and a Trotter product formula for quantum stochastic flows with unbounded coefficients

We give a new method for proving the homomorphic property of a quantum stochastic ow satisfying a quantum stochastic differential equation with unbounded coefficients, under some further hypotheses. As an application, we prove a Trotter product formula for quantum stochastic ows and obtain quantum stochastic dilations of a class of quantum dynamical semigroups generalizing results of [5

Conservation amidst political unrest: the case of Manas National Park,India

Across the world there exists a large overlap of biodiversity hotspots with areas experiencing high levels of sociopolitical and ethnic conflicts, making the impacts of such activities a critical factor for long-term conservation of biodiversity in these regions1. India is no exception with many forested areas, including protected areas, experiencing conflicts of varying intensity owing to numerous complicated issues ranging from cultural identity to socio-political and environmental security. Such conflicts not only act as a major impediment to scientific monitoring, protection and management in the biodiversity-rich areas, but also lead to abuse of wildlife and natural areas by conflict parties and opportunistic elements in the absence of adequate protection and monitoring forces. Therefore, in the collective interest of biodiversity conservation, a greater challenge perhaps lies in devising new ways and methods to conserve landscapes in strifetorn areas, where emotions are often charged up and conservation of biodiversity does not figure among the immediate priorities

Optical Biosensors: A Revolution Towards Quantum Nanoscale Electronics Device Fabrication

The dimension of biomolecules is of few nanometers, so the biomolecular devices ought to be of that range so a better understanding about the performance of the electronic biomolecular devices can be obtained at nanoscale. Development of optical biomolecular device is a new move towards revolution of nano-bioelectronics. Optical biosensor is one of such nano-biomolecular devices that has a potential to pave a new dimension of research and device fabrication in the field of optical and biomedical fields. This paper is a very small report about optical biosensor and its development and importance in various fields

Quantum isometries and noncommutative spheres

We introduce and study two new examples of noncommutative spheres: the half-liberated sphere, and the free sphere. Together with the usual sphere, these two spheres have the property that the corresponding quantum isometry group is "easy", in the representation theory sense. We present as well some general comments on the axiomatization problem, and on the "untwisted" and "non-easy" case.Comment: 16 page