Rice paddies as a methane source

Rice fields are considered to be among the highest sources of atmospheric methane, an important source of global warming. In order to meet the projected rice needs of the increasing world population, it is estimated that the annual world's rough rice production must increase to 760 million tons (a 65% increase) in the next 30 years. This will increase methane emissions from ricefields if current technologies are kept. Methane emissions from ricefields are affected by climate, water regime, soil properties, and various cultural practices like irrigation and drainage, organic amendments, fertilization, and rice cultivars. Irrigated rice comprises 50% of the world-harvested rice area and contributes 70% to total rice production. Because of assured flooding during the growing period it is the primary source of methane. Rainfed rice emits less methane due to periods of droughts. Upland rice, being never flooded for a significant period of time, is not a significant source of methane. There is great potential to develop no regret mitigation options that are in accordance with increasing rice production.     

Stellar irradiance variations due to surface temperature inhomogeneities

Observations of rotational modulation of continuum brightness and photospheric and chromospheric spectral-line profiles of late-type stars indicate the presence of very inhomogeneous surface temperature distributions. We present three stellar examples (VY Ari, HR 7275, HU Vir) where time-series photometry is used to trace the evolution of spotted regions. Simultaneous spectroscopy and Doppler imaging for one of the three stars (HU Virgo, Fig. 1) makes it possible to compute the temperature distribution of the photosphere and the relative intensity distribution of parts of the chromosphere (from CaII K and H line profiles). The combination of time-series spot modeling and Doppler imaging enabled us to determine thesign and amount of differential surface rotation on HU Vir. We found a big, cool polar spot (see figure below) and a differential (surface) rotation law where higher-latitude regions rotate faster than lower-latitude regions (opposite to what we see on the Sun). Currently, this ensemble of techniques - time-series photometry and photospheric and chromospheric Doppler imaging - is only applicable to stars overactive by approximately a factor of 100 as compared to the active Sun, e.g. the evolved components in RS CVn-type binaries and some rapidly-rotating, single, pre-main sequence stars or giant stars. Stellar rotation is a fundamental parameter for (magnetic) activity. Starspots, or any other surface inhomogeneities, allow one to derive very precise stellar rotation rates and, if coupled with seismological observations of solar-type stars, could provide information on the internal angular momentum distribution in overactive late-type stars.To be published in Astronomy & Astrophysics.     

Effect of perturbed potentials on the non-linear stability of libration pointL 4 in the restricted problem

The non-linear stability of the libration pointL ₄ in the restricted problem has been studied when there are perturbations in the potentials between the bodies. It is seen that the pointL ₄ is stable for all mass ratios in the range of linear stability except for three mass ratios depending upon the perturbing functions. The theory is applied to the following four cases:

The effect of Antarctic O3 decline on night airglow intensity of Na5893Å, O5577Å, OH emissions and its correlation with total solar flare numbers

The paper presents the effect of O₃ depletion on different night airglow emission lines. Calculations based on chemical kinetics show that the airglow intensity of Na5893Å, O5577Å and OH band emissions will also be affected due to the depletion of O₃ concentration. Intensity of Na5893Å is calculated theoretically for Halley Bay (76° S,27° W), British Antarctic Survey Station, during the period 1973 to 1984. It is concluded from the covariation of different emission lines that O5577Å and OH emissions also follow the same trend of variation. A study has been made to find the correlation between the depletion of O₃ concentration and total solar flare numbers. Important results are as follows:

Adsorption of fluoride on goethite surfaces-implications on dental epidemiology

Fluoride ion interaction with synthetically prepared goethite has been investigated over a range of pH values (4–9) and F^– concentrations (10^–3–10^–5 M). The amount of F^– retained by goethite suspensions was found to be a function of pH, media ionic strength, F^– concentration, and goethite concentration. The lowest ionic strength (0.001 M KNO₃) gave the highest adsorption medium. Uptake was minimal at pH >7 and increased with decreasing pH. Thermodynamic properties for fluoride adsorption at 298 K and 323 K were investigated. The isosteric heat of adsorption (H _r) was calculated and the heterogeneity and homogeneity of the surface examined for goethite. In view of the importance of fluoride in dental health, the interaction of fluoride on goethite in the physical environment has important implications on dental epidemiology.     

Carbon isotope systematics of individual hydrocarbons in hydrothermal petroleum from Escanaba Trough, northeastern Pacific Ocean

We submitted individual aliphatic and polycyclic aromatic hydrocarbons in samples of hydrothermal petroleum from Escanaba Trough to compound specific isotope analysis to trace their origins. The carbon isotope compositions of the alkanes and polycyclic aromatic hydrocarbons (means -27.5 and -24.7%, respectively) reflect a primarily terrestrial organic matter source.     

Powder- and single crystal Mössbauer spectroscopy on synthetic fayalite

Mössbauer measurements on synthetic iron orthosilicate Fe₂SiO₄ (fayalite) were carried out in the antiferromagnetic spin state below T _N 65 K. The Mössbauer parameters isomer shift , inner magnetic field H(0), angle between H(0) and the z-component of the electric field gradient (efg), quadrupole splitting QS and asymmetry parameter were determined as a function of temperature. These parameters could be attributed to the two crystallographic sites M1 and M2.The smaller isomer shift on M1 with respect to M2 displays the more covalent character of the Fe-O bond on M1, which is supported by previous neutron diffraction experiments. H(0) shows a Brillouin-type behaviour with different fields on the two crystallographic sites (stronger on M1) and a small discontinuity at T = 23 K which corresponds with previous magnetic measurements. The quadrupole splitting is equal on both sites within error bars, in agreement with previous theoretical results and in contradiction to previous Mössbauer refinements published elsewhere.     

Room temperature solid-state detectors for Gamma ray burst spectroscopy

We have evaluated several solid state detectors which offer excellent energy resolution at room temperature for soft X-rays. For soft X-rays (< 1 keV to 20 keV), silicon P-intrinsic-N (PIN) and avalanche-mode photodiodes (APD's) have been studied. Using commercially available charge sensitive pre-amplifiers, these photodiodes provide 1 keV resolution without cooling. Their detection efficiencies are limited to about 20 keV and 15 keV, respectively. To overcome this constraint, we have studied thick (1.5 mm) PIN detectors made by Micron Semiconductor Ltd., U.K., as well as compound semiconducting materials with high Z constituents such as CZT and PbI₂. PbI₂ allows high detection efficiencies of photons up to 100 keV with detectors 100–300 microns thick. These new detectors offer the capability to study the low-energy spectral evolution of Gamma ray bursts (GRBs). A matrix of these detectors could be used as an image plane detector with moderate spatial resolution for imaging.     

The effect of an optically thin region on stability of an accretion disk around a supermassive black hole

We analyse conditions of the innermost portion of an accretion disk and establish a set of equations for this region. A stable innermost region may exist, which can probably explain the observed UV and X-ray spectra, avoiding the unstable emission. We then discuss the detailed radial structure of a disk around a black hole for typical AGN parameters and obtain different kinds of- relationships for different regions of a disk. On the basis of this, we discuss the stability. A new type of cycle is present, which we call a double S shaped cycle. In this cycle, the extent of accretion rate variability is much larger than that in dwarf nova cycles. This probably solves the problem of violent variability of AGN. In the meantime, the very high accretion rate at the hottest state in limit cycles in the unstable region may provide continuous injection of matter to the jet and power the relativistic motion of the jet.     

On the internal structure and magnetic fields of

First, a sequence of four-zone models for the interior of Venus is constructed under the assumption of hydrostatic equilibrium. While the equation of state for each zone is taken to be the Bullen's relation with its coefficients consistent with the PREM Earth model (Dziewonski and Anderson, 1981), the position of core-mantle boundary is determined by matching solutions of the Emden's equation in different regions. The results of hydrostatic models indicate the presence of a reasonably large molten iron core in Venus, broadly similar to the Earth. It is also found that the position of the core-mantle interface is nearly model-independent. Second, we focus on the question why Venus does not possess a significant global magnetic field and on what we can learn from this fact. Solutions of magnetohydrodynamic equations appropriate for the molten core of Venus are discussed. It is argued that, because the Elsasser number measuring the relative importance of Coriolis and Lorentz forces satisfies 1, equations for the problem of thermal convection in the Venusian fluid core must be nearly uncoupled with the dynamo equation. The existence of a global magnetic field, though small, then suggests that the size of the magnetic Reynolds numberR _m must beR _m =O(10), sustaining a dynamo action near its marginal state but not an active dynamo in the Venusian molten core. On the basis of asymptotic relations for finite amplitude convection, a useful constraint on important physical parameters for the liquid core of Venus is derived and discussed.