Light Curves for Rapidly-Rotating Neutron Stars

We present raytracing computations for light emitted from the surface of a rapidly-rotating neutron star in order to construct light curves for X-ray pulsars and bursters. These calculations are for realistic models of rapidly-rotating neutron stars which take into account both the correct exterior metric and the oblate shape of the star. We find that the most important effect arising from rotation comes from the oblate shape of the rotating star. We find that approximating a rotating neutron star as a sphere introduces serious errors in fitted values of the star's radius and mass if the rotation rate is very large. However, in most cases acceptable fits to the ratio M/R can be obtained with the spherical approximation.Comment: Accepted by the Astrophysical Journal. 13 pages & 7 figure

Spin-orbital Kondo decoherence by environmental effects in capacitively coupled quantum dot devices

Strong correlation effects in a capacitively coupled double quantum-dot setup were previously shown to provide the possibility of both entangling spin-charge degrees of freedom and realizing efficient spin-filtering operations by static gate-voltage manipulations. Motivated by the use of such a device for quantum computing, we study the influence of electromagnetic noise on a general spin-orbital Kondo model, and investigate the conditions for observing coherent, unitary transport, crucial to warrant efficient spin manipulations. We find a rich phase diagram, where low-energy properties sensitively depend on the impedance of the external environment and geometric parameters of the system. Relevant energy scales related to the Kondo temperature are also computed in a renormalization-group treatment, allowing to assess the robustness of the device against environmental effects.Comment: 13 pages, 13 figures. Minor modifications in V

Mapping individual electromagnetic field components inside a photonic crystal

We present a method to map the absolute electromagnetic field strength inside photonic crystals. We apply the method to map the electric field component Ez of a two-dimensional photonic crystal slab at microwave frequencies. The slab is placed between two mirrors to select Bloch standing waves and a subwavelength spherical scatterer is scanned inside the resulting resonator. The resonant Bloch frequencies shift depending on the electric field at the position of the scatterer. To map the electric field component Ez we measure the frequency shift in the reflection and transmission spectrum of the slab versus the scatterer position. Very good agreement is found between measurements and calculations without any adjustable parameters.Comment: 12 pages, 7 figure

Universal and wide shear zones in granular bulk flow

We present experiments on slow granular flows in a modified (split-bottomed) Couette geometry in which wide and tunable shear zones are created away from the sidewalls. For increasing layer heights, the zones grow wider (apparently without bound) and evolve towards the inner cylinder according to a simple, particle-independent scaling law. After rescaling, the velocity profiles across the zones fall onto a universal master curve given by an error function. We study the shear zones also inside the material as function of both their local height and the total layer height.Comment: Minor corrections, accepted for PRL (4 pages, 6 figures

Timing jitter in photon detection by straight superconducting nanowires: Effect of magnetic field and photon flux

We studied the effect of the external magnetic field and photon flux on timing jitter in photon detection by straight superconducting NbN nanowires. At two wavelengths 800 and 1560 nm, statistical distribution in the appearance time of the photon count exhibits Gaussian shape at small times and exponential tail at large times. The characteristic exponential time is larger for photons with smaller energy and increases with external magnetic field while variations in the Gaussian part of the distribution are less pronounced. Increasing photon flux drives the nanowire from quantum detection mode to the bolometric mode that averages out fluctuations of the total number of nonequilibrium electrons created by the photon and drastically reduces jitter. The difference between Gaussian parts of distributions for these two modes provides the measure for the electron-number fluctuations. Corresponding standard deviation increases with the photon energy. We show that the two-dimensional hot-spot detection model explains qualitatively the effect of magnetic field

Elastic precession of electronic spin states in interacting integer quantum Hall edge channels

We consider the effect of Coulomb interactions in the propagation of electrons, prepared in arbitrary spin states, on chiral edge channels in the integer quantum Hall regime. Electrons are injected and detected at the same energy at different locations of the Hall bar, which is modeled as a chiral Tomonaga-Luttinger liquid. The current is computed perturbatively in the tunneling amplitudes, within a non-crossing approximation using exact solutions of the interacting Green's functions. In the case of different channel velocities, the spin precession effect is evaluated, and the role of interaction parameters and wavevectors is discussed.Comment: 5 pages, 3 figure

Les paléoenvironnements sédimentaires au Wisconsinien moyen et supérieur, île d’Anticosti, golfe du Saint-Laurent, Québec

L'inlandsis laurentidien n'a jamais dépassé la côte sud de l'île d'Anticosti ni pénétré dans le golfe du Saint-Laurent après 36 000 ans BP. De plus, la corrélation entre les unités stratigraphiques, accompagnée de datations au 14C, permet la description des événements liés à trois avancées glaciaires du Quaternaire supérieur au centre-sud de l'île. En premier lieu, dans les vallées inondées par la transgression marine, l'avènement d'une masse de glace, au Wisconsinien moyen, met en place des dépôts glacio-marins datés de 36 000 ans BP. Par contre. Ia glace s'étend sur les interfluves élevés adjacents et abandonne un till daté de 30 000 ans BP. À la limite des secteurs côtiers, le vêlage intensif du front glaciaire provoque la mise en place, sur les côtes basses, de sédiments glacio-marins datés de 28 000 ans BP, définissant par le fait même les variations importantes de la dynamique d'écoulement glaciaire dans un milieu marin. En deuxième lieu, une récurrence au Wisconsinien supérieur s'arrête à la côte sud de l'île, comme en témoigne la présence, dans les embouchures de vallées et dans la zone côtière, de sédiments glacio-marins datés de 13 500 ans BP. La mise en place de cette deuxième unité de matériel glacio-marin confirme les perturbations importantes du front glaciaire que provoque à cette latitude une grande profondeur d'eau. En troisième lieu, lors de la phase de régression marine, une calotte résiduelle qui ne couvre que les interfluves et les vallées secondaires avance à la limite de la zone côtière et met en place un matériel glacio-marin daté de 12 000 ans BP. Cette récurrence est le résultat d'un réajustement gravitationnel relié au relèvement isostatique ainsi qu'à l'abaissement du niveau marin.Anticosti Island, Gulf of St. Lawrence, Québec. The Laurentide Ice Sheet did not extend beyond the south coast of Anticosti Island into the Gulf of St. Lawrence after 36 000 years BP. Correlation of stratigraphie units, supported by 14C dates, reveal the events associated with three glacial advances during the late Quaternary of the south-central part of the island. Firstly, during the mid-Wisconsinan the ice sheet advanced into drowned valleys and deposited glacial-marine sediments dated at 36 000 yrs BP. The ice also covered adjacent interfluves and deposited a till dated at 30 000 yrs BP. Subsequently, in the present coastal zones, intense calving at the ice front resulted in the deposition of glacial-marine sediments dated at 28 000 yrs BP. This illustrates the important variations in the flow dynamic of the ice sheet in a marine environment. Secondly, during the late-Wisconsinan the ice sheet read-vanced again to the south coast of the island but did not extend into the Gulf. This is revealed by the presence of glacial-marine sediments, dated at 13 500 yrs BP, at the mouths of river valleys and in the actual low coastal zones. Deposition of this second glacial-marine unit confirmes the influence, at this latitude, of a deep water marine environment on the extension of the glacial front. Thirdly, contemporaneously with the marine regression, a residual ice cap that covered the interfluves and certain small valleys advanced to the limit of the present coastal zone and deposited glacial-marine sediments dated at 12 000 yrs BP. This advance resulted from gravitational reajustments as a function of the crustal uplift and the lowered marine limit.Das Laurentische Inlandeis ist niemals ùber die Sùdkùste der Insel Anticosti hinausgekommen, noch ist es in den Golf des Sankt Lorenz-Stroms nach 36000 v.u.Z. eingedrungen. In den von der Meer-Transgression ùberschwemmten Tâlern hat das Vordringen einer Eismasse im mittleren Wisconsin glazial-marine Ablagerungen hinterlassen, die auf 36000 Jahre v.u.Z. datiert werden. Andererseits hat sich das Eis bis auf die erhôhten angrenzenden Interfluves ausgedehnt und Geschiebelehm abgelagert, der auf 30000 Jahre v.u.Z. datiert wird. An der Grenze der Kustengebiete hat das intensive Kalben der Eisfront die Ablagerung von glazial-marinen Sedimenten an den tiefliegenden Kùsten hervorgerufen, die auf 28 000 Jahre v.u.Z. datiert werden. Hierdurch werden die erheblichen Variationen in der Strômungs-Dynamik der Eisdecke im Meeres-Milieu illustriert. Zweitens hait ein VorstoB im spàten Wisconsin an der Sùdkùste der Insel an, wie es durch glazial-marine Sedimente bestàtigt wird, die sich in den Talmùndungen und im Kùstengebiet befinden und die auf 13 500 Jahre v.u.Z. datiert werden. Die Ablagerung dieser zweiten Einheit von glazial-marinem Material bestàtigt die erheblichen Stôrungen der Eisfront, die in dieser Zone durch eine betrachtliche Wassertiefe verursacht werden. Drittens stôBt wâhrend der Phase des Sinkens des Meeresspiegels eine Restkalotte, die nur die Interfluves und die Sekundârtâler bedeckt, bis zur Grenze des Kùstengebiets vor und lagert glazial-marines Material ab, das auf 12 000 Jahre v.u.Z. datiert wird. Dieser VorstoB ist das Ergebnis einer Schwere-Wiederanpassung, in Verbindung mit einer isostatischen Anhebung und dem Sinken des Meeresspiegels