Scintillation Caustics in Planetary Occultation Light Curves

We revisit the GSC5249-01240 light curve obtained during its occultation by Saturn's North polar region. In addition to refractive scintillations, the power spectrum of intensity fluctuations shows an enhancement of power between refractive and diffractive regimes. We identify this excess power as due to high amplitude spikes in the light curve and suggest that these spikes are due to caustics associated with ray crossing situations. The flux variation in individual spikes follows the expected caustic behavior, including diffraction fringes which we have observed for the first time in a planetary occultation light curve. The presence of caustics in scintillation light curves require an inner scale cut off to the power spectrum of underlying density fluctuations associated with turbulence. Another possibility is the presence of gravity waves in the atmosphere. While occultation light curves previously showed the existence of refractive scintillations, a combination of small projected stellar size and a low relative velocity during the event have allowed us to identify caustics in this occultation. This has led us to re-examine previous data sets, in which we have also found likely examples of caustics.Comment: 4 pages, 3 figures; ApJL submitte

Observation of a temperature dependent electrical resistance minimum above the magnetic ordering temperature in Gd2_2PdSi3_3

Results on electrical resistivity, magnetoresistance, magnetic Results on electrical resistivity, magnetoresistance, magnetic susceptibility, heat capacity and Gd Mossbauer measurements on a Gd-based intermetallic compound, Gd$_{2}$PdSi$_{3}$ are reported. A finding of interest is that the resistivity unexpectedly shows a well-defined minimum at about 45 K, well above the long range magnetic ordering temperature (21 K), a feature which gets suppressed by the application of a magnetic field. This observation in a Gd alloy presents an interesting scenario. On the basis of our results, we propose electron localization induced by s-f (or d-f) exchange interaction prior to long range magnetic order as a mechanism for the electrical resistance minimum.Comment: 4 pages, 4 figure

Double Charge Exchange And Configuration Mixing

The energy dependence of forward pion double charge exchange reactions on light nuclei is studied for both the Ground State transition and the Double-Isobaric-Analog-State transitions. A common characteristic of these double reactions is a resonance-like peak around 50 MeV pion lab energy. This peak arises naturally in a two-step process in the conventional pion-nucleon system with proper handling of nuclear structure and pion distortion. A comparison among the results of different nuclear structure models demonstrates the effects of configuration mixing. The angular distribution is used to fix the single particle wave function.Comment: Added 1 figure (now 8) corrected references and various other change

A Perturbative/Variational Approach to Quantum Lattice Hamiltonians

We propose a method to construct the ground state $\psi(\lambda)$ of local lattice hamiltonians with the generic form $H_0 + \lambda H_1$, where $\lambda$ is a coupling constant and $H_0$ is a hamiltonian with a non degenerate ground state $\psi_0$. The method is based on the choice of an exponential ansatz $\psi(\lambda) = {\rm exp}(U(\lambda)) \psi_0$, which is a sort of generalized lattice version of a Jastrow wave function. We combine perturbative and variational techniques to get succesive approximations of the operator $U(\lambda)$. Perturbation theory is used to set up a variational method which in turn produces non perturbative results. The computation with this kind of ansatzs leads to associate to the original quantum mechanical problem a statistical mechanical system defined in the same spatial dimension. In some cases these statistical mechanical systems turn out to be integrable, which allow us to obtain exact upper bounds to the energy. The general ideas of our method are illustrated in the example of the Ising model in a transverse field.Comment: 27 pages, three .ps figures appended, DFTUZ 94-2

Eimeria collieie n. sp. (Apicomplexa:Eimeriidae) from the western long-necked turtle (Chelodina colliei)

A new species, Eimeria collieie n. sp., is described from the western long-necked turtle (Chelodina colliei). Sporulated oocysts (n = 35) are spherical to subspherical, with colourless single layer oocyst wall, 0.6 ± 0.2 (0.4-0.7) μm thick. Oocyst with elongated ellipsoid sporocysts. Oocyst length, 29.8 ± 0.4 (28.2-31.0) μm; oocyst width, 29.4 ± 0.3 (28.0-30.8) μm; oocyst length/width (L/W) ratio, 1.0 ± 0.03 (1.0-1.05). Micropyle, oocyst residuum and polar granule were absent. Sporocysts with sporocyst residuum and 2 sporozoites. Sporocyst length, 21.6 ± 0.4 (21.2-22.0) μm; sporocyst width, 6.0 ± 0.3 (5.7-6.3) μm; sporocyst L/W ratio, 3.6 ± 0.2 (3.4-3.8). Stieda, parastieda and substieda bodies were absent. Sporozoite length, 14.0 ± 0.2 (13.8-14.2) μm; sporozoite width, 2.6 ± 0.2 (2.4-2.8) μm; sporozoite L/W ratio, 5.46 ± 0.10 (5.4-5.6). Molecular analysis was conducted at three loci: the 18S and 28S ribosomal RNA (rRNA), and the mitochondrial cytochrome oxidase gene (COI). At the 18S rRNA locus, E. collieie n. sp. shared 96.4% and 98.3% genetic similarity to E. ranae (GenBank accession number: EU717219) and E. arnyi (AY613853) respectively. At the 28S rRNA locus, E. collieie n. sp. shared 91.6% genetic similarity to E. papillata (GenBank accession number: GU593706) and phylogenetic analysis at this locus placed E. collieie n. sp. in aseparateclade. At the COI locus, E. collieie n. sp. shared 92.7% genetic similarity to Eimeria setonicis (GenBankaccession number: KF225638) from a quokka (Setonix brachyurus) in Western Australia. Reptile-derived sequences were not available for the 28S rRNA and the COI loci. Based on morphological and molecular data, this isolate is a new species of coccidian parasite that, to date, has only been found in western long-necked turtles

Magnetic relaxation in metallic films: Single and multilayer structures

The intrinsic magnetic relaxations in metallic films will be discussed. It will be shown that the intrinsic damping mechanism in metals is caused by incoherent scattering of itinerant electron-hole pair excitations by phonons and magnons. Berger [L. Berger, Phys. Rev. B 54, 9353 (1996)] showed that the interaction between spin waves and itinerant electrons in multilayers can lead to interface Gilbert damping. Ferromagnetic resonance (FMR) studies were carried out using magnetic single and double layer films. The FMR linewidth of the Fe films in the double layer structures was found to always be larger than the FMR linewidth measured for the single Fe films having the same thickness. The increase in the FMR linewidth scaled inversely with the film thickness, and was found to be linearly dependent on the microwave frequency. These results are in agreement with Berger's predictions. (C) 2002 American Institute of Physics

The Hypanis Valles delta: The last highstand of a sea on early Mars?

One of the most contentious hypotheses in the geological history of Mars is whether the northern lowlands ever contained an oceanic water body. Arguably, the best evidence for an ocean comes from the presence of sedimentary fans around Mars' dichotomy boundary, which separates the northern lowlands from the southern highlands. Here we describe the palaeogeomorphology of the Hypanis Valles sediment fan, the largest sediment fan complex reported on Mars (area >970 km2). This has an extensive catchment (4.6 x 105 km2) incorporating Hypanis and Nanedi Valles, that we show was active during the late-Noachian/early-Hesperian period (∼3.7 Ga). The fan comprises a series of lobe-shaped sediment bodies, connected by multiple bifurcating flat-topped ridges. We interpret the latter as former fluvial channel belts now preserved in inverted relief. Meter-scale-thick, sub-horizontal layers that are continuous over tens of kilometres are visible in scarps and the inverted channel margins. The inverted channel branches and lobes are observed to occur up to at least 140 km from the outlet of Hypanis Valles and descend ∼500 m in elevation. The progressive basinward advance of the channellobe transition records deposition and avulsion at the margin of a retreating standing body of water, assuming the elevation of the northern plains basin floor is stable. We interpret the Hypanis sediment fan to represent an ancient delta as opposed to a fluvial fan system. At its location at the dichotomy boundary, the Hypanis Valles fan system is topographically open to Chryse Planitia – an extensive plain that opens in turn into the larger northern lowlands basin. We conclude that the observed progradation of fan bodies was due to basinward shoreline retreat of an ancient body of water which extended across at least Chryse Planitia. Given the open topography, it is plausible that the Hypanis fan system records the existence, last highstand, and retreat of a large sea in Chryse Planitia and perhaps even an ocean that filled the northern plains of Mars

The role of parental achievement goals in predicting autonomy-supportive and controlling parenting

Although autonomy-supportive and controlling parenting are linked to numerous positive and negative child outcomes respectively, fewer studies have focused on their determinants. Drawing on achievement goal theory and self-determination theory, we propose that parental achievement goals (i.e., achievement goals that parents have for their children) can be mastery, performance-approach or performance-avoidance oriented and that types of goals predict mothers' tendency to adopt autonomy-supportive and controlling behaviors. A total of 67 mothers (aged 30-53 years) reported their goals for their adolescent (aged 13-16 years; 19.4 % girls), while their adolescent evaluated their mothers' behaviors. Hierarchical regression analyses showed that parental performance-approach goals predict more controlling parenting and prevent acknowledgement of feelings, one autonomy-supportive behavior. In addition, mothers who have mastery goals and who endorse performance-avoidance goals are less likely to use guilt-inducing criticisms. These findings were observed while controlling for the effect of maternal anxiety