Significance of the Sm-Nd isotopic systematics of the Akilia Association

Samarium-Neodymium analyses were carried out on fourteen samples of basic to ultrabasic metavolcanics from several enclaves of the Amitsoq gneisses (T = to or approximately 3,700 Ma). Field observations suggest that all the analyzed rocks belong to the pre-Amitsoq Akilia Association. Consequently, a minimum age of 3,700 Ma is postulated for the emplacement of their protoliths. When all the data points are put together in a conventional isochron diagram, no clear isochron relationship can be discerned. However, the points seem to fall within a band broadly corresponding to an age of 3,600 Ma. The isotopic results are difficult to interpret satisfactorily. Two contrasting interpretations are offered and summarized: (1) data scatter as a result of open system behavior; and (2) data scatter due to a melange of data sets defining two distinct isochrons

Jahn-Teller instability in C6H6+ and C6H6- revisited

The benzene cation (C6H6+) has a doublet (e_{1g}) ground state in hexagonal ring (D_{6h}) geometry. Therefore a Jahn-Teller (JT) distortion will lower the energy. The present theoretical study yields a model Huckel-type Hamiltonian that includes the JT coupling of the e_{1g} electronic ground state with the two e_{2g} vibrational modes: in-plane ring-bending and C-C bond-stretching. We obtain the JT couplings from density functional theory (DFT), which gives a JT energy lowering of 970 cm^{-1} in agreement with previous quantum chemistry calculations. We find a non-adiabatic solution for vibrational spectra and predict frequencies shifts of both the benzene cation and anion, and give a reinterpretation of the available experimental data.Comment: 6 pages, 3 figure

Pentaquark state in pole-dominated QCD sum rules

We propose a new approach in QCD sum rules applied for exotic hadrons with a number of quarks, exemplifying the pentaquark Theta^{+} (I=0,J=1/2) in the Borel sum rule. Our approach enables reliable extraction of the pentaquark properties from the sum rule with good stability in a remarkably wide Borel window. The appearance of its valid window originates from a favorable setup of the correlation functions with the aid of it chirality of the interpolating fields on the analogy of the Weinberg sum rule for the vector currents. Our setup leads to large suppression of the continuum contributions which have spoiled the Borel stability in the previous analyses, and consequently enhances importance of the higher-dimensional contributions of the OPE, which are indispensable for investigating the pentaquark properties. Implementing the OPE analysis up to dimension 15, we find that the sum rules for the chiral-even and odd parts independently give the Theta^{+} mass of 1.68 pm 0.22 GeV with uncertainties of the condensate values. Our sum rule indeed gives rather flat Borel curves almost independent of the continuum thresholds both for the mass and pole residue. Finally, we also discuss possible isolation of the observed states from the KN scattering state on view of chiral symmetry.Comment: 8 pages, 7 figure

On the discrepancy principle for stochastic gradient descent

Stochastic gradient descent (SGD) is a promising numerical method for solving large-scale inverse problems. However, its theoretical properties remain largely underexplored in the lens of classical regularization theory. In this note, we study the classical discrepancy principle, one of the most popular a posteriori choice rules, as the stopping criterion for SGD, and prove the finite-iteration termination property and the convergence of the iterate in probability as the noise level tends to zero. The theoretical results are complemented with extensive numerical experiments

An exact Riemann solver based solution for regular shock refraction

We study the classical problem of planar shock refraction at an oblique density discontinuity, separating two gases at rest. When the shock impinges on the density discontinuity, it refracts and in the hydrodynamical case 3 signals arise. Regular refraction means that these signals meet at a single point, called the triple point. After reflection from the top wall, the contact discontinuity becomes unstable due to local Kelvin-Helmholtz instability, causing the contact surface to roll up and develop the Richtmyer-Meshkov instability. We present an exact Riemann solver based solution strategy to describe the initial self similar refraction phase, by which we can quantify the vorticity deposited on the contact interface. We investigate the effect of a perpendicular magnetic field and quantify how addition of a perpendicular magnetic field increases the deposition of vorticity on the contact interface slightly under constant Atwood number. We predict wave pattern transitions, in agreement with experiments, von Neumann shock refraction theory, and numerical simulations performed with the grid-adaptive code AMRVAC. These simulations also describe the later phase of the Richtmyer-Meshkov instability.Comment: 21 pages, 17 figures in 41 ps-files, accepted by J. Fluid Mec

Absorption of Light in the Okoboji Lakes

In August 1938 the absorption of light was measured at various depths in the Okoboji Lakes by means of a photronic cell and a tungsten filament lamp which were mounted behind glass windows in separate metal housings so that a parallel beam of light passed through one half meter of water before striking the photronic cell. This apparatus could be lowered to any desired depth, and the transmission at that depth could be measured with a microammeter. This was converted to percentage transmission through one meter by comparison with a similar reading taken with the apparatus in air. After the formation of the thermocline in Lake West Okoboji the transmission per meter \Vas about 30 per cent for the upper 10 meters, rose sharply between 12 and 13 meters to 46 per cent, remained about constant to 17 meters, rose sharply to 74 per cent at 18 meters, then gradually to 81 per cent between 22 and 28 meters. Below 28 meters the transmission dropped to about 70 per cent. These data are being studied in relation to the distribution of plankton. The average transmission of Lake East Okoboji was about 0.0002% per meter and varied only slightly with depth

Gastric Ulceration, Appetite and Feeding Practices in Standardbred Racehorses in the Czech Republic

The objective of our study was to determine the prevalence of poor appetite and its correlation with the prevalence of gastric ulceration, and to evaluate relation between feeding management (feeding frequency and feeding regularity) and gastric ulceration in a group of 54 Standardbred racehorses in training. Prevalence of gastric ulceration in the group of horses with poor general appetite was 94.8%. Prevalence of gastric ulceration in the group of horses with good general appetite was 48.6%. Significant association between poor general appetite and squamous gastric ulcer presence was observed (p < 0.001). Gastric ulceration was found in 75.0% of horses fed twice daily and in 57.9% horses fed three times a day. Fifty seven point nine per cent of regularly fed horses had gastric ulcers. Irregularly fed horses were ulcer-positive in 75.0%. Thus no significant association between feeding frequency or regularity and the occurrence of gastric ulcers was found

FREKUENSI TRAIT THALASSEMIA-b DI AMBON, MALUKI

Genetic screening for D-thalassemia trait was carried out in Ambon population of the Moluccas, a population genetically related with other eastern Indonesian populations with strong Melanesian influence where HbE gene frequency is very low. Blood specimens were collected from 92 adult healthy unrelated individuals consists of 32 males and 60 females mostly student nurses participated in the study. Three blood indices, hemoglobin concentration, packed cell volume and MCHC were normal. However, increase of HbA2 concentration was observed in six individuals (6.5%). Unlike the previous study, not even single individual with abnormally structural hemoglobin was found in this study. The occurrence of carrier of this genetic traits comparable with previous studies in Java, again confirms the interaction of 13-thalassemia and HbE distribution in malaria endemic region. Further measures include premarital genetic counseling should be considered to avoid public health problem that may be created in the future. Key words : genetic screening, B-thalassemia trait, malaria endemic, premarital genetic counselin

An overview of the synaptic vesicle lipid composition

Chemical neurotransmission is the major mechanism of neuronal communication. Neurotransmitters are released from secretory organelles, the synaptic vesicles (SVs) via exocytosis into the synaptic cleft. Fusion of SVs with the presynaptic plasma membrane is balanced by endocytosis, thus maintaining the presynaptic membrane at steady-state levels. The protein machineries responsible for exo- and endocytosis have been extensively investigated. In contrast, less is known about the role of lipids in synaptic transmission and how the lipid composition of SVs is affected by dynamic exo-endocytotic cycling. Here we summarize the current knowledge about the composition, organization, and function of SV membrane lipids. We also cover lipid biogenesis and maintenance during the synaptic vesicle cycle