Ascertaining the Ideality of Photometric Stereo Datasets under Unknown Lighting

The standard photometric stereo model makes several assumptions that are rarely verified in experimental datasets. In particular, the observed object should behave as a Lambertian reflector, and the light sources should be positioned at an infinite distance from it, along a known direction. Even when Lambert’s law is approximately fulfilled, an accurate assessment of the relative position between the light source and the target is often unavailable in real situations. The Hayakawa procedure is a computational method for estimating such information directly from data images. It occasionally breaks down when some of the available images excessively deviate from ideality. This is generally due to observing a non-Lambertian surface, or illuminating it from a close distance, or both. Indeed, in narrow shooting scenarios, typical, e.g., of archaeological excavation sites, it is impossible to position a flashlight at a sufficient distance from the observed surface. It is then necessary to understand if a given dataset is reliable and which images should be selected to better reconstruct the target. In this paper, we propose some algorithms to perform this task and explore their effectiveness

VLA Observations of H I in the Helix Nebula (NGC 7293)

We report the detection of 21-cm line emission from H I in the planetary nebula NGC 7293 (the Helix). The observations, made with the Very Large Array, show the presence of a ring of atomic hydrogen that is associated with the outer portion of the ionized nebula. This ring is most probably gas ejected in the AGB phase that has been subsequently photodissociated by radiation from the central star. The H I emission spreads over about 50 km/s in radial velocity. The mass in H I is approximately 0.07 solar masses, about three times larger than the mass in molecular hydrogen and comparable with the mass in ionized hydrogen.Comment: 19 pages, 9 figure

Full Aging in Spin Glasses

The discovery of memory effects in the magnetization decays of spin glasses in 1983 began a large effort to determine the exact nature of the decay. While qualitative arguments have suggested that the decay functions should scale as $t_{w}$, the only time scale in the system, this type of scaling has not yet been observed. In this letter we report strong evidence for the scaling of the TRM magnetization decays as a function of $t_{w}$. By varying the rate and the profile that the sample is cooled through its transition temperature to the measuring temperature, we find that the cooling plays a major role in determining scaling. As the effective cooling time decreases, $\frac {t}{t_{w}}$scaling improves and for $t_{c}^{eff}<20s$ we find almost perfect $\frac{t}{t_{w}}$ scaling. We also find that subtraction of a stationary term from the magnetization decay has a small effect on the scaling but changes the form of the magnetization decay and improves overlap between curves produced with different $t_{w}$.Comment: 4 pages, 3 figure

Superintegrability on N-dimensional spaces of constant curvature from so(N+1) and its contractions

The Lie-Poisson algebra so(N+1) and some of its contractions are used to construct a family of superintegrable Hamiltonians on the ND spherical, Euclidean, hyperbolic, Minkowskian and (anti-)de Sitter spaces. We firstly present a Hamiltonian which is a superposition of an arbitrary central potential with N arbitrary centrifugal terms. Such a system is quasi-maximally superintegrable since this is endowed with 2N-3 functionally independent constants of the motion (plus the Hamiltonian). Secondly, we identify two maximally superintegrable Hamiltonians by choosing a specific central potential and finding at the same time the remaining integral. The former is the generalization of the Smorodinsky-Winternitz system to the above six spaces, while the latter is a generalization of the Kepler-Coulomb potential, for which the Laplace-Runge-Lenz N-vector is also given. All the systems and constants of the motion are explicitly expressed in a unified form in terms of ambient and polar coordinates as they are parametrized by two contraction parameters (curvature and signature of the metric).Comment: 14 pages. Based on the contribution presented at the "XII International Conference on Symmetry Methods in Physics", Yerevan (Armenia), July 2006. To appear in Physics of Atomic Nucle

Cooper-pair coherence in a superfluid Fermi-gas of atoms

We study the coherence properties of a trapped two-component gas of fermionic atoms below the BCS critical temperature. We propose an optical method to investigate the Cooper-pair coherence across different regions of the superfluid. Near-resonant laser light is used to induce transitions between the two coupled hyperfine states. The beam is split so that it probes two spatially separate regions of the gas. Absorption of the light in this interferometric scheme depends on the Cooper-pair coherence between the two regions.Comment: 10 pages, 5 figures. Submitted to J. Phys. B as a proceedings of the Salerno 2001 BEC worksho

A feature-rich transmission spectrum for WASP-127b

WASP-127b is one of the lowest density planets discovered to date. With a sub-Saturn mass ($M_{\rm p}=0.18 \pm 0.02 M_J$) and super-Jupiter radius ($R_{\rm p}= 1.37 \pm 0.04 R_J$), it orbits a bright G5 star, which is about to leave the main-sequence. We aim to explore WASP-127b's atmosphere in order to retrieve its main atmospheric components, and to find hints for its intriguing inflation and evolutionary history. We used the ALFOSC spectrograph at the NOT telescope to observe a low resolution ($R\sim330$, seeing limited) long-slit spectroscopic time series during a planetary transit, and present here the first transmission spectrum for WASP-127b. We find the presence of a strong Rayleigh slope at blue wavelengths and a hint of Na absorption, although the quality of the data does not allow us to claim a detection. At redder wavelengths the absorption features of TiO and VO are the best explanation to fit the data. Although higher signal-to-noise ratio observations are needed to conclusively confirm the absorption features, WASP-127b seems to posses a cloud-free atmosphere and is one of the best targets to perform further characterization studies in the near future.Comment: Accepted for Publication A&A Letters, May 22nd, 201

Ocorrência de Anastrepha fraterculus (Diptera:Tephritidae) em butiazeiro (Butia odorata) na região de Pelotas, RS.

O objetivo do trabalho foi registrar a presença de dípteros da família Tephritidae em pomares na área experimental da Embrapa Clima Temperado, em Pelotas, RS

Wigner Crystal State for the Edge Electrons in the Quantum Hall Effect at Filling ν=2\nu = 2

The electronic excitations at the edges of a Hall bar not much wider than a few magnetic lengths are studied theoretically at filling $\nu = 2$. Both mean-field theory and Luttinger liquid theory techniques are employed for the case of a null Zeeman energy splitting. The first calculation yields a stable spin-density wave state along the bar, while the second one predicts dominant Wigner-crystal correlations along the edges of the bar. We propose an antiferromagnetic Wigner-crystal groundstate for the edge electrons that reconciles the two results. A net Zeeman splitting is found to produce canting of the antiferromagnetic order.Comment: 22 pgs. of PLAIN TeX, 1 fig. in postscript, published versio