Integrated investigation of the mixed origin of lunar sample 72161,11

Sample 72161,11 (dark mantle at LRV-3) has a graphic mean grain size (M _z) of 3.88 ø, inclusive graphic standard deviation (σ _I) of 1.29, and a total carbon content of 204µg C g^?1 sample, and is, therefore, quite mature. However, the agglutinate content is only 30% in the 90–177µm particles, indicating an apparent departure from steady state. Analyses of C, CH₄, and H₂ concentrations in size fractions larger than 149µm show that the volume correlated component of these species increases with increasing grain size. In a homogeneous agglutinate population the volume correlated component is expected to be independent of grain size. The observed increase can be interpreted in terms of the mixing of a dominant local population of coarser agglutinates, with high carbon and hydrogen, with an imported population of finer agglutinates relatively poor in carbon and hydrogen. When analyses of size-fractions from the bulk sample are considered, these effects are apparently obliterated by the admixture of coarse-grained material low in agglutinates. It seems likely that this low agglutinate content is a consequence of the breakdown of the fragile, large agglutinates in the imported material during their movement to the sample site.     

Recurrent explosions in the nuclei of galaxies

High-velocity ejection of gas from the central region of galaxies is now an observationally established phenomenon. Such ejections have been attributed to some kind of activities in the nuclei of galaxies. It has been suggested that conditions leading to explosive events periodically prevail in the centre of galaxies causing recurrent explosions and driving the gas thereby outward with sufficiently high velocities. The magnitude of the ejection velocity and the amount of gas driven out will actually depend on the intensity of the activity at the centre. Remnants of recurrent activity have been discovered in the inner region of our Galaxy. The ‘3-kpc’ arm, the 2.4 kpc arm, the molecular ring at 270 pc and some other features are believed to have been caused by periodic activity at the centre of our Galaxy. We have outlined a model that can explain the recurrent explosions in the centre of a galaxy. The boundary of the nucleus of the Galaxy is considered here as a stationary shock front where high velocity gas coming from the outer regions impinges and gets heated and condensed. This condensed, hot gas then flows inwards by intense gravitational pull, but in course of its passage inward it loses its velocity due to radiation pressure and frictional retardation. A layer of dense, hot gas is therefore formed some distance (typically 0.001 pc) away from the centre where short radio and microwaves are trapped. As the density of gas in this layer is enhanced by the inflowing gas, shorter-wave radiation is trapped. The pressure of radiation therefore gradually builds up in the layer which ultimately overcomes the gravitational pull and the layer is blown off violently. The whole process may be completed over and over again at intervals of 10⁶–10⁷ yr.     

Role of Coulomb collisions in the equatorial F-region plasma instabilities

The effect of collisions on electrostatic instabilities driven by gravity and density gradients perpendicular to the ambient magnetic field is studied. Electron collisions tend to stabilize the short wavelength (k_y?_i ? 1, where k_y is the perpendicular wavenumber of the instability and ?_i is the ion Larmor radius) kinetic interchange mode. In the presence of weak ion-ion collisions, this mode gets converted into an unmagnetized ion interchange mode which has maximum growth rate one order smaller than that of the collisionless mode. On the other hand, electron collisions can excite a long wavelength resistive interchange mode in a wide wavenumber regime ($\text{10}{}^{\mathrm{?}}\text{3 ? k}{}_{\mathrm{y}}\text{?}{}_{\mathrm{i}}\text{? 0.3}$) with growth rates comparable to that of the collisional Rayleigh-Taylor mode. The results may be relevant to some of the spread F irregularities.     

Wind dependence of quasi-specular sea scatter

Earlier investigations have shown that a power law relationship of the typeσ=aW ^b exists between the scattering coefficientσ and sea surface wind speedW at microwave frequencies. The coefficientsa andb are usually quoted for different frequencies, look angles, polarizations etc. This paper attempts to define the angular dependence using such a power law relationship in the quasi-specular range.     

SH waves in a semi-infinite elastic space due to torsional disturbance

Summary The paper concerns the finding of displacement in a semi-infinite elastic space due to torsional disturbance produced by an expanding source. A formal solution has been derived by the integral transform technique and the modified Cagniard method in two different cases, viz. velocity of expansion is less than or greater than the velocity of shear waves in the medium.     

Geometry of isograds in metamorphic terrains

A simple mathematical relation among the dip of isograd surface (θ), dip of isotherm surface (α), temperature gradient (T_g), pressure gradient (P_g) and δT/gdP of reaction is given by:

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P_g is taken to be constant at 0.3 kb/km. Four major theoretical models for shapes and orientations of isograds are formulated on the basis of the parameters α, T_g and δT/δP. This offers a rational basis for studying the geometry of isograds, normal/reverse metamorphism and determination of temperature gradient. Two examples have been studied in the light of these models; in one case the domed shape of the isograd is best explained by a downwardly directed T_g; in the other case, reverse metamorphism is best explained as the result of a horizontal T_g of 18°C/km.     

Facies analysis of Pleistocene limestones from Neil West Coast Formation,Neil Island,Ritchie’s archipelago of South Andaman,India

Petrographic thin section analysis of the samples collected from the type section of Neil West Coast Formation, situated in the west coast of Neil Island yielded moderately preserved coralline red algae, benthic and planktic foraminifers, coral fragments, echinoid spines and gastropod shells. The coralline red algae are represented by both non-geniculate and geniculate forms. The non-geniculate forms belong to melobesids, lithophylloids and mastophoroides. The geniculate forms are represented by species of Amphiroa, Corallina, and Jania. However, the diversity and abundance of coralline algal forms are less in comparison to the benthic foraminifers those are represented by Amphistegina, Neorotalia, Ammonia, Elphidium, Operculina, Assilina, Amphisorus and texularids. Planktic foraminifers like Globigerinoides and other biogenic components viz., gastropod shells, echinoid spines and coral fragments are also common. A foraminiferal-algal grainstone facies has been recognized as observed in the field as well as in thin section analysis. The overall assemblage of the biogenic components and facies analysis indicate intertidal to near shore environment of deposition with high energy condition and increased hydrodynamic activity.     

Arsenic distribution along different hydrogeomorphic zones in parts of the Brahmaputra River Valley,Assam (India)

The spatial distribution of arsenic (As) concentrations along three classified hydrogeomorphological zones in the Brahmaputra River Valley in Assam (India) have been investigated: zone I, comprising the piedmont and alluvial fans; zone II, comprising the runoff areas; and zone III, comprising the discharge zones. Groundwater (150 samples) from shallow hand-pumped and public water supply wells (2–60 m in depth) was analysed for chemical composition to examine the geochemical processes controlling As mobilization. As concentrations up to 0.134 mg/L were recorded, with concentrations below the World Health Organization and the Bureau of Indian Standards drinking-water limits of 0.01 mg/L being found mainly in the proximal recharge areas. Eh and other redox indicators (i.e., dissolved oxygen, Fe, Mn and As) indicate that, except for samples taken in the recharge zone, groundwater is reducing and exhibits a systematic decrease in redox conditions along the runoff and discharge zones. Hydrogeochemical evaluation indicated that zone I, located along the proximal recharge areas, is characterized by low As concentration, while zones II and III are areas with high and moderate concentrations, respectively. Systematic changes in As concentrations along the three zones support the view that areas of active recharge with high hydraulic gradient are potential areas hosting low-As aquifers.     

A high-resolution seismic catalog for the 2021 MS6.4/MW6.1 Yangbi earthquake sequence,Yunnan, China: Application of AI picker and matched filter

We present a high-resolution seismic catalog for the 2021 M_S6.4/M_W6.1 Yangbi sequence. The catalog has a time range of 2021-05-01 to 2021-05-28, and contains ~8,000 well located events. It captures the features of the whole foreshock sequence and the early aftershocks. We designed a detection strategy incorporating both an artificial intelligent (AI) picker and a matched filter algorithm. Here, we adopt a hybrid AI method incorporating convolutional and recurrent neural network (CNN & RNN) for event detection and phase picking respectively (i.e. CERP), a light-weight AI picker that can be trained with small volume of data. CERP is first trained with detections from a STA/LTA and Kurtosis-based method called PAL, and then construct a rather complete template set of ~4,000 events. Finally, the matched filter algorithm MESS augments the initial detections and measures differential travel times with cross-correlation, which finally results in precise relocation. This process gives 9,026 detections, among which 7,943 events can be well relocated. The catalog shows as expected power-law distribution of frequency magnitude and reveals detailed pattern of seismicity evolution. The main features are: (1) the foreshock sequence images simple fault geometry with consistent strike, but also show a variable event depth along strike; (2) the mainshock ruptures the same fault of the foreshock sequence and activate conjugate faults further to the southeast; (3) complex seismicity are developed in the post-seismic period, indicating complex triggering mechanisms. Thus, our catalog provides a reliable basis for further investigations, such as b-value studies, rupture process, and triggering relations.