Low-frequency electric field fluctuations excited by ring current protons

Energetic protons haying ring type distributions are shown to generate low-frequency electrostatic waves, propagating nearly transverse to the geomagnetic field lines, in the ring current region by exciting Mode 1 arid Mode 2 nonresonant instabilities and a resonant instability. Mode 1 nonresonant instability has frequencies around ~4 Hz with transverse wavelengths of ~(8–80) km, and it is likely to occur in the region L = (7–8). Mode 2 nonresonant instability can generate frequencies ~(850–1450) Hz with transverse wavelengths ~(2–20) km. The typical frequencies and transverse wavelengths associated with the resonant instability are (950–1250) Hz and (30–65) km. Both the Mode 2 nonresonant instability and the resonant instability can occur in the ring current region with L = (4–6). The low-frequency modes driven by energetic protons could attain maximum saturation electric field amplitude varying from 0.8 mV/m to 70 mV/m. It is suggested that the turbulence produced by the low-frequency modes may cause pitch angle scattering of ring current protons in the region outside the plasmapause resulting in the ring current decay.     

Effects of Different Diets on the Dietary Attractability and Selectivity of Chinese Shrimp, Fenneropenaeus chinensis

Attractabilities of different diets and dietary selectivity of Chinese shrimp, Fenneropenaeus chinensis were studied through behavior observation and feeding experiment, respectively. The five diets used in the experiment are: Fish Flesh (FF), Shrimp Flesh (SF), Clam Foot (CF), Polychaete Worm (PW), and Formulated Diet (FD). No significant differences of attractability exist between any two different diets when every two natural diets or all five diets are provided simultaneously. On the other hand, significant differences of attractability exist between FD and every single natural diet when they are provided simultaneously. Results of behavioral observation indicate that natural diets are more attractive than FD. In feeding experiment, Chinese shrimp has distinct selectivity on different diets. It positively selects CF and PW, negatively selects FF and SF, and excludes FD absolutely. The results of the present studies indicate that the dietary selectivity of shrimp was based not only on the attractabilities of the diets, but also on the responses such as growth and food conversion.     

Extreme Rainfall Events and Associated Natural Hazards in Alaknanda Valley, Indian Himalayan Region

Introduction The Himalaya is considered to be the youngest mountains on the earth, and is tectonically very active, and hence inherently (geologically) vulnerable to hazards. Extreme rainfall events, landslides, debris flows, torrents and flash floods due…     

Deuterium on Venus: Model comparisons with pioneer Venus observations of the predawn bulge ionosphere

A model of the predawn bulge ionosphere composition and structure is constructed and compared with the ion mass spectrometer measurements from the Pioneer Venus Orbiter during orbits 117 and 120. Particular emphasis is given to the identification of the mass-2 ion which we find unequivocally due to D⁺ (and not H₂⁺). The atmospheric D/H ratio of 1.4% and 2.5% is obtained at the homopause (～ 130 km) for the two orbits. The H₂⁺ contribution to the mass-2 ion density is less than 10%, and the H₂ mixing ratio must be <0.1 ppm at 130 km altitude. The He⁺ data require a downward He⁺ flux of ～2 × 10⁷ cm^?2 sec^?1 in the predawn region which suggest that the light ions also flow across the terminator from day to night along with the observed O⁺ ion flow.     

Kinematic wave modelling in water resources: a historical perspective

The history of the kinematic wave theory and its applications in water resources are traced. It is shown that the theory has found its niche in water resources and its applications are so widespread that they may well constitute what may be termed ‘kinematic wave hydrology’. Few theories have been applied in hydrology and water resources as extensively as the kinematic wave theory. This theory, however, is not without limitations and when it is applied they must be so recognized. Copyright © 2001 John Wiley & Sons, Ltd.     

Spectra of quasiperiodic oscillations of galactic X-ray sources–dynamical regimes from a simple model

We suggest that the dynamical regime(s) underlying quasi-periodic oscillations observed in the spectra of bright galactic-bulge X-ray sources are nonlinear with a mixed phase space. The important feature of such regimes is that they are generic among nonlinear Hamiltonian and nearly Hamiltonian systems of more than two degrees of freedom. We give a simple example of such chaotic (deterministic) systems whose spectra share a number of features with those observed for quasiperiodic oscillations of such sources.     

Studies of some diatomic molecules in the F- and early G-type dwarf stars

A critical analysis of CH, NH, OH, C₂, and CN molecules/radicals has been made in twenty-four F- and early G-type dwarfs at different effective temperature as well as in new constructed model atmosphere. Molecular indices of bandheads ofA-X system of CH, NH, OH, C₂, and CN have been obtained by using the data available in the literature (thirteen-colour and eight-colour photometry).Besides, some interesting plots of the molecular indices vs _eff, molecular abundances and molecular indices vs dissociation energy, reduced equivalent widths and FCF's vs dissociation energy for respective molecules have also been enumerated. It is found that the molecular indices at bandheads ofA-X system of CH, NH, OH, C₂, and CN are approximately constant (5810–6570 K). It is to be noted that the molecular indices decrease in the order OH, NH, CH, C₂, and CN at a given temperature.The dissociation equilibrium of CH, NH, OH, C₂, and CN is considered at 5810, 6570, and 7160 K phases in model atmosphere. At standard scale of abundance the molecular abundance and molecular index decrease in the order OH, NH, CH, C₂, and CN at any given phase, however, CN abundance and index increase (_eff=0.867-0.767). The amplitude of abundance and index variation decrease in the order NH, OH, CH, C₂, and CN (_eff=0.767-0.704).The reduced equivalent width decrease in the order OH, NH, CH, and C₂ and FCF's decrease in the order CH, OH, NH, CN, and C₂.The confrontation of models and observations of spectra of F- and early G-type dwarfs of parent molecules is of primary importance to investigate the physical conditions within atmospheres. Reliable excitation models are also requisite for interpreting spectroscopic observations of parent molecules and deriving molecular abundances.     

Spectrophotometric observations and evolutionary status of ten Be stars

The continuum energy distribution data of ten Be stars — namely, HR 1761, HR 1786, HR 1820, Ori, Ori, OT Gem, Lyr, HR 7983, Cyg, and 59 Cyg — have been presented in the wavelength range 3200–8000 Å. The observed energy distribution curve shows near infrared excess for majority of Be stars and a double Balmer jump for HR 8047 and HR 8146. Empirical effective temperatures of these stars have been estimated by comparing the observed continuum energy distributions with that of computed theoretical models given by Kurucz (1979).On the basis of an HR diagram with evolutionary tracks for different solar masses the masses of these Be stars have been estimated. Position of these studied stars on the HR diagram suggests that these Be stars may be in the stage of core contraction after exhausting hydrogen at the centre and have undergone hydrogen exhaustion in the thick shell.     

Anelasticity of the crust and upper mantle beneath north and central India from the inversion of observed Love and Rayleigh wave attenuation data

The fundamental mode Love and Rayleigh waves generated by earthquakes occurring in Kashmir, Nepal Himalaya, northeast India and Burma and recorded at Hyderabad, New Delhi and Kodaikanal seismic stations are analysed. Love and Rayleigh wave attenuation coefficients are obtained at time periods of 15–100 seconds, using the spectral amplitude of these waves for 23 different paths along northern (across Burma to New Delhi) and central (across Kashmir, Nepal Himalaya and northeast India to Hyderabad and Kodaikanal) India. Love wave attenuation coefficients are found to vary from 0.0003 to 0.0022 km^–1 for northern India and 0.00003 km^–1 to 0.00016 km^–1 for central India. Similarly, Rayleigh wave attenuation coefficients vary from 0.0002 km^–1 to 0.0016 km^–1 for northern India and 0.00001 km^–1 to 0.0009 km^–1 for central India. Backus and Gilbert inversion theory is applied to these surface wave attenuation data to obtainQ ^–1 models for the crust and uppermost mantle beneath northern and central India. Inversion of Love and Rayleigh wave attenuation data shows a highly attenuating zone centred at a depth of 20–80 km with lowQ for northern India. Similarly, inversion of Love and Rayleigh wave attenuation data shows a high attenuation zone below a depth of 100 km. The inferred lowQ value at mid-crustal depth (high attenuating zone) in the model for northern India can be by underthrusting of the Indian plate beneath the Eurasian plate which has caused a low velocity zone at this shallow depth. The gradual increase ofQ ^–1 from shallow to deeper depth shows that the lithosphere-asthenosphere boundary is not sharply defined beneath central India, but rather it represents a gradual transformation, which starts beneath the uppermost mantle. The lithospheric thickness is 100 km beneath central India and below that the asthenosphere shows higher attenuation, a factor of about two greater than that in the lithosphere. The very lowQ can be explained by changes in the chemical constitution taking place in the uppermost mantle.     

Free-convective flow of non-Newtonian fluid with heat sources

An analytical study is performed to examine the effects of temperature-dependent heat source on free-convective flow of non-Newtonian fluid (Walters's liquidB). The expression for the velocity field has been obtained by the Laplace transform technique. The influence of the various parameter entering into the problem is extensively discussed.