Gamma-ray flares from black hole coronae

We present results of a study of non-thermal, time-dependent particle injection in a corona around an accreting black hole. We model the spectral energy distribution of high-energy flares in this scenario. We consider particle interactions with magnetic, photon and matter fields in the black hole magnetosphere. Transport equations are solved for all species of particles and the electromagnetic output is predicted. Photon annihilation is taken into account for the case of systems with early-type donor stars.Comment: 7 pages, 7 figures. Accepted for publication in the Proceedings of the 25th Texas Symposium on Relativistic Astrophysics, held in Heidelberg, December 06-10, 201

The neural correlates of phonological short-term memory: A repetitive transcranial magnetic stimulation study

Neuropsychological reports and activation studies by means of positron emission tomography anti functional magnetic resonance imaging have suggested that the neural correlates of phonological short-term memory are located in the left hemisphere, with Brodmann's area (BA) 40 being, responsible for short-term storage and BA 44 for articulatory rehearsal. However, a careful review of the literature on the role of left BA 40 shows that the data are equivocal. We tested We hypotheses by means of repetitive transcranial magnetic stimulation (rTMS). Participants performed four tasks: two phonological judgements, thought to require only articulatory rehearsal Without the contribution of short-term storage digit span, which involves both short-term storage and articudlatory rehearsal: and a pattern span, this last heing the control task. The sites of stimulation were left BA 40. left BA 44 anti the electrode location V-W plus a baseline without TMS. Reaction times increased and accuracy decreased in the case of the phonological judgement and digit span after stimulation of both left sites, suggesting that BA 40, in addition to BA 44. is involved in phonological judgements. Possible explanations are discussed, namely, the possibility that (i) the neural correlates of rehearsal are not limited to BA and (ii) phonological judgements invlove processes other than rehearsal. We also consider the effects of using different tasks and responses to resolve some of the descrepancies in the literature

Optical binding in nanoparticle assembly: Potential energy landscapes

Optical binding is an optomechanical effect exhibited by systems of micro- and nanoparticles, suitably irradiated with off-resonance laser light. Physically distinct from standing-wave and other forms of holographic optical traps, the phenomenon arises as a result of an interparticle coupling with individual radiation modes, leading to optically induced modifications to Casmir-Polder interactions. To better understand how this mechanism leads to the observed assemblies and formation of patterns in nanoparticles, we develop a theory in terms of optically induced energy landscapes exhibiting the three-dimensional form of the potential energy field. It is shown in detail that the positioning and magnitude of local energy maxima and minima depend on the configuration of each particle pair, with regards to the polarization and wave vector of the laser light. The analysis reveals how the positioning of local minima determines the energetically most favorable locations for the addition of a third particle to each equilibrium pair. It is also demonstrated how the result of such an addition subtly modifies the energy landscape that will, in turn, determine the optimum location for further particle additions. As such, this development represents a rigorous and general formulation of the theory, paving the way toward full comprehension of nanoparticle assembly based on optical binding

Strengthening constraints on Yukawa-type corrections to Newtonian gravity from measuring the Casimir force between a cylinder and a plate

We discuss possibility to obtain stronger constraints on non-Newtonian gravity from measuring the gradient of the Casimir force between a cylinder and a plate. Exact analytical expression for the Yukawa-type force in a cylinder-plate configuration is obtained, as well as its asymptotic expansions. The gravitational force is compared with the Casimir force acting between a cylinder and a plate. Numerical computations for the prospective constraints on non-Newtonian gravity are performed for recently proposed experiment using a microfabricated cylinder attached to a micromachined oscillator. Specifically, it is shown that this experiment is expected to obtain up to 70 times stronger constraints on the Yukawa-type force, compared with the best present day limits, over a wide interaction range from 12.5 to 630 nm.Comment: 17 pages, 2 figures; to appear in Phys. Rev.

Ermakov approach for the one-dimensional Helmholtz Hamiltonian

For the one-dimensional Helmholtz equation we write the corresponding time-dependent Helmholtz Hamiltonian in order to study it as an Ermakov problem and derive geometrical angles and phases in this contextComment: 6 pages, LaTe