Energy conditions for Bianchi type I universe in f(G) gravity

In this paper, we discuss energy conditions in modified Gauss-Bonnet gravity for locally rotationally symmetric Bianchi type I universe model with perfect fluid. The matter contents are constructed to discuss the energy conditions bounds. We take two specific f(G) models along with present day values of Hubble, deceleration, jerk and snap parameters. It is found that weak and null energy conditions are satisfied while strong energy conditions are violated for both models which represents the accelerated expansion of the universe.     

Astronomical research activities with the 74 inch telescope at Kottamia observatory

Two topics of research, namely extragalactic and variable star studies represent the main attitudes of astronomical work at the Helwan Observatory.The 74 inch telescope at Kottamia (476 m, 2^h.12, 29^°.93 N) some 60 km to the east of Cairo is the main instrument. Some other auxiliary equipment (Cassegrain and echelle spectrographs, Westinghouse and Japanese cameras and photoelectric photometer) can be attached at both Cassegrain and Newtonian foci.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Application of data assimilation for improving forecast of water levels and residual currents in Singapore regional waters

Hydrodynamic models are commonly used for predicting water levels and currents in the deep ocean, ocean margins and shelf seas. Their accuracy is typically limited by factors, such as the complexity of the coastal geometry and bathymetry, plus the uncertainty in the flow forcing (deep ocean tide, winds and pressure). In Southeast Asian waters with its strongly hydrodynamic characteristics, the lack of detailed marine observations (bathymetry and tides) for model validation is an additional factor limiting flow representation. This paper deals with the application of ensemble Kalman filter (EnKF)-based data assimilation with the purpose of improving the deterministic model forecast. The efficacy of the EnKF is analysed via a twin experiment conducted with the 2D barotropic Singapore regional model. The results show that the applied data assimilation can improve the forecasts significantly in this complex flow regime.     

Molecular and distribution data on the poorly known,elusive, cave mysid Harmelinella mariannae (Crustacea: Mysida)

Mediterranean underwater marine caves harbour abundant populations of several species of mysids that are increasingly used as biological models in ecological and evolutionary studies. One exception is the species Harmelinella mariannae, described in 1989 and then hardly ever again reported in the literature. We here provide the first data on the distribution of this poorly known taxon that, contrary to expectations for a rare brooding cave dweller, we now report from Madeira Island in the nearby Atlantic, to the easternmost parts of the Mediterranean. Brief behavioural observations are added, particularly its atypical solitary habits and its feeding behaviour as a high trophic level carnivore. Molecular characterization of the different specimens captured provided three sorts of information. Mitochondrial COI and 16S haplotypes suggest different colonization waves in the Mediterranean, with one group in the Eastern Basin, two in the Marseille region in the NW part of this sea, and another group with a very wide extension from Madeira to Liguria and Malta. Mitochondrial data also support that one of the groups in Marseille might have diverged as a cryptic species of Harmelinella. 18S rRNA gene displays a single common sequence to all specimens from the four groups, and seems to confirm the original proposed placement of this taxon within the subfamily Heteromysinae, not Leptomysinae.     

Trace element geochemistry of CR chondrite metal

We report trace element analyses by laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) of metal grains from nine different CR chondrites, distinguishing grains from chondrule interior (“interior grains”), chondrule surficial shells (“margin grains”), and the matrix (“isolated grains”). Save for a few anomalous grains, Ni‐normalized trace element patterns are similar for all three petrographic settings, with largely unfractionated refractory siderophile elements and depleted volatile Au, Cu, Ag, S. All three types of grains are interpreted to derive from a common precursor approximated by the least‐melted, fine‐grained objects in CR chondrites. This also excludes recondensation of metal vapor as the origin of the bulk of margin grains. The metal precursors were presumably formed by incomplete condensation, with evidence for high‐temperature isolation of refractory platinum‐group‐element (PGE)‐rich condensates before mixing with lower temperature PGE‐depleted condensates. The rounded shape of the Ni‐rich, interior grains shows that they were molten and that they equilibrated with silicates upon slow cooling (1–100 K h^?1), largely by oxidation/evaporation of Fe, hence their high Pd content, for example. We propose that Ni‐poorer, amoeboid margin grains, often included in the pyroxene‐rich periphery common to type I chondrules, result from less intense processing of a rim accreted onto the chondrule subsequent to the melting event recorded by the interior grains. This means either that there were two separate heating events, which formed olivine/interior grains and pyroxene/margin grains, respectively, between which dust was accreted around the chondrule, or that there was a single high‐temperature event, of which the chondrule margin records a late “quenching phase,” in which case dust accreted onto chondrules while they were molten. In the latter case, high dust concentrations in the chondrule‐forming region (at least three orders of magnitude above minimum mass solar nebula models) are indicated.     

3‐D hydrodynamic simulations of the solar chromosphere

We present first results of three‐dimensional numerical simulations of the non‐magnetic solar chromosphere, computed with the radiation hydrodynamics code CO⁵BOLD. Acoustic waves which are excited at the top of the convection zone propagate upwards into the chromosphere where the waves steepen into shocks. The interaction of the waves leads to the formation of complex structures which evolve on short time scales. Consequently, the model chromosphere is highly dynamical, inhomogeneous, and thermally bifurcated.     

Simulation of the interaction of galactic cosmic‐ray protons with meteoroids: On the production of radionuclides in thick gabbro and iron targets irradiated isotropically with 1.6 GeV protons

Abstract— Thick spherical targets made of gabbro (R = 25 cm) and of steel (R = 10 cm) were irradiated isotropically with 1.6 GeV protons at the Saturne synchrotron at Laboratoire National Saturne (LNS)/CEN Saclay in order to simulate the interaction in space of galactic cosmic‐ray (GCR) protons with stony and iron meteoroids. Proton fluences of 1.32 × 10¹⁴ cm^?2 and 2.45 × 10¹⁴ cm^?2 were received by the gabbro and iron sphere, respectively, which corresponds to cosmic‐ray exposure ages of about 1.6 and 3.0 Ma. Both artificial meteoroids contained large numbers of high‐purity target foils of up to 28 elements at different depths. In these individual target foils, elementary production rates of radionuclides and rare gas isotopes were measured by x‐ and γ‐spectrometry, by low‐level counting, accelerator mass spectrometry (AMS), and by conventional rare gas mass spectrometry. Also samples of the gabbro itself were analyzed. Up to now, for each of the experiments, ～500 target‐product combinations were investigated of which the results for radionuclides are presented here. The experimental production rates show a wide range of depth profiles reflecting the differences between low‐, medium‐, and high‐energy products. The influence of the stony and iron matrices on the production of secondary particles and on particle transport, in general, and consequently on the production rates is clearly exhibited by the phenomenology of the production rates as well as by a detailed theoretical analysis. Theoretical production rates were calculated in an a priori way by folding depth‐dependent spectra of primary and secondary protons and secondary neutrons calculated by Monte Carlo techniques with the excitation functions of the underlying nuclear reactions. Discrepancies of up to a factor of 2 between the experimental and a priori calculated depth profiles are attributed to the poor quality of the mostly theoretical neutron excitation functions. Improved neutron excitation functions were obtained by least‐squares deconvolution techniques from experimental thick‐target production rates of up to five thick‐target experiments in which isotropic irradiations were performed. A posteriori calculations using the adjusted neutron cross sections describe the measured depth profiles of all these simulation experiments within 9%. The thus validated model calculations provide a basis for reliable physical model calculations of the production rates of cosmogenic nuclides in stony and iron meteorites as well as in lunar samples and terrestrial materials.