Twin-Photon Confocal Microscopy

A recently introduced two-channel confocal microscope with correlated detection promises up to 50% improvement in transverse spatial resolution [Simon, Sergienko, Optics Express {\bf 18}, 9765 (2010)] via the use of photon correlations. Here we achieve similar results in a different manner, introducing a triple-confocal correlated microscope which exploits the correlations present in optical parametric amplifiers. It is based on tight focusing of pump radiation onto a thin sample positioned in front of a nonlinear crystal, followed by coincidence detection of signal and idler photons, each focused onto a pinhole. This approach offers further resolution enhancement in confocal microscopy

How river rocks round: resolving the shape-size paradox

River-bed sediments display two universal downstream trends: fining, in which particle size decreases; and rounding, where pebble shapes evolve toward ellipsoids. Rounding is known to result from transport-induced abrasion; however many researchers argue that the contribution of abrasion to downstream fining is negligible. This presents a paradox: downstream shape change indicates substantial abrasion, while size change apparently rules it out. Here we use laboratory experiments and numerical modeling to show quantitatively that pebble abrasion is a curvature-driven flow problem. As a consequence, abrasion occurs in two well-separated phases: first, pebble edges rapidly round without any change in axis dimensions until the shape becomes entirely convex; and second, axis dimensions are then slowly reduced while the particle remains convex. Explicit study of pebble shape evolution helps resolve the shape-size paradox by reconciling discrepancies between laboratory and field studies, and enhances our ability to decipher the transport history of a river rock.Comment: 11 pages, 5 figure

QPOs in microquasars: the spin problem

In the Galactic microquasars with double peak kHz quasi-periodic oscillations (QPOs), the ratio of the two frequencies is 3:2. This supports the suggestion that double peak kHz QPOs are due to a non-linear resonance between two modes of accretion disk oscillations. For the microquasars with known mass, we briefly compare the black hole spin estimates based on the orbital resonance model with the recently reported spin predictions obtained by fitting the spectral continua. Results of these two approaches are not in good agreement. We stress that if the spectral fit estimates are accurate and can be taken as referential (which is still questionable), the disagreement between the predicted and referential values would represent a rather generic problem for any relativistic QPO model, as no spin influence would appear in the observed 1/M scaling of the QPO frequencies. The epicyclic frequencies relevant in these models are often considered to be equal to those of a test particle motion. However modifications of the frequencies due to the disc pressure or other non-geodesic effects may play an important role, and the inaccuracy introduced in the spin estimates by the test particle approximation could be crucial.Comment: 3 pages, proceedings of the IAU XXVIth General Assembl

Quasiperiodic oscillations in a strong gravitational field around neutron stars testing braneworld models

The strong gravitational field of neutron stars in the brany universe could be described by spherically symmetric solutions with a metric in the exterior to the brany stars being of the Reissner-Nordstrom type containing a brany tidal charge representing the tidal effect of the bulk spacetime onto the star structure. We investigate the role of the tidal charge in orbital models of high-frequency quasiperiodic oscillations (QPOs) observed in neutron star binary systems. We focus on the relativistic precession model. We give the radial profiles of frequencies of the Keplerian (vertical) and radial epicyclic oscillations. We show how the standard relativistic precession model modified by the tidal charge fits the observational data, giving estimates of the allowed values of the tidal charge and the brane tension based on the processes going in the vicinity of neutron stars. We compare the strong field regime restrictions with those given in the weak-field limit of solar system experiments.Comment: 26 pages, 6 figure

Protonation and ring closure of stereoisomeric alpha-substituted cinnamic acids in superacidic media studied by 13C NMR spectroscopy and computations

Five alpha-substituted cinnamic acids [(E)- and (Z)-2,3-diphenyl-, (E)- and (Z)-3-(2-methoxyphenyl)-2-phenyl- and (E)-2-(2-methoxyphenyl)-3-phenyl-propenoic acids] have been protonated in fluorosulfonic acid at -78 degrees C, Protonation of the carboxylic group and a second protonation on the methoxy group at -78 degrees C or the ring bearing the methoxy group at 0 degrees C have been observed by C-13 NMR spectroscopy Upon protonation (Z)-alpha-phenylcinnamic acid is transformed to a protonated indenol derivative, Dehydrative ring closure begins at -78 degrees C and goes to completion at 0 degrees C, Similar transformations of the other studied Z-acid are suppressed by the deactivating effect of the protonated methoxy group. Only protonation has been observed for the E-acids at -78 degrees C as well as 0 degrees C, Calculations at the HF/3-21G level provide the equilibrium structures of the corresponding cations, Results of IGLO/C-13 NMR shift calculations are in good agreement with the experimental findings

The Aschenbach effect: unexpected topology changes in motion of particles and fluids orbiting rapidly rotating Kerr black holes

Newton's theory predicts that the velocity $V$ of free test particles on circular orbits around a spherical gravity center is a decreasing function of the orbital radius $r$, $dV/dr < 0$. Only very recently, Aschenbach (A&A 425, p. 1075 (2004)) has shown that, unexpectedly, the same is not true for particles orbiting black holes: for Kerr black holes with the spin parameter $a>0.9953$, the velocity has a positive radial gradient for geodesic, stable, circular orbits in a small radial range close to the black hole horizon. We show here that the {\em Aschenbach effect} occurs also for non-geodesic circular orbits with constant specific angular momentum $\ell = \ell_0 = const$. In Newton's theory it is $V = \ell_0/R$, with $R$ being the cylindrical radius. The equivelocity surfaces coincide with the $R = const$ surfaces which, of course, are just co-axial cylinders. It was previously known that in the black hole case this simple topology changes because one of the ``cylinders'' self-crosses. We show here that the Aschenbach effect is connected to a second topology change that for the $\ell = const$ tori occurs only for very highly spinning black holes, $a>0.99979$.Comment: 9 pages, 7 figure

Térbe zárt kert = Enclosed garden

The archetype of the enclosed garden is the medieval hortus conclusus, which make the perfect type from the former types. The enclosed gardens of nowadays have developed from the hortus conclusus, which behave like a prism. Peter Zumthor's Serpentine Gallery Pavilion is the best example for the contemporary hortus conclusus. The purpose of our study to make a typological collection about contemporary enclosed gardens. The base of the typology is the borderline of the garden, the wall of the garden. We based the study of borderline to Dom Hans van der Laan's architectural theory and his monastery building in Vaals. We analyze the typology by six contemporary enclosed gardens from the simple wall to the building volume through the volumes of the wall. The openings of the walls can be the next way of our analysis.A bezárt kertek kiérlelt archetípusa a hortus conclusus, a középkori kolostorudvarok kertjei. A hortus conclusus, mint egy prizma összegyűjti az összes megelőző bezárt kert változatot, tökéletes típust hoz létre, majd belőle fejlődnek tovább napjaink bezárt kertjeinek végtelen variációi. A hortus conclusus kortárs beteljesülése Peter Zumthor Serpentine Gallery pavilonja. A kutatásunk célja a kortárs kertek tipológiai gyűjteményének elkészítése, melynek alapja a kert határa, a kertet határoló fal vizsgálata. A kert határát Dom Hans van der Laan építészetelmélete és vaalsi kolostorbővítése alapján közelítettük meg. A tipológiát hat kortárs bezárt kert elemzésével mutatjuk be, az egyszerű tömör falas bekerített tértől, a fal teresedései által tömeggé vált határon át, amíg a fal teljesen eltűnik és az udvart meghatározó épülettömeg jelenti a határt. A tipológia továbbvitele, amikor a falak alaprajzi és a falban lévő nyílások szerinti megnyitását vizsgáljuk