Wave loads on large vertical cylinders: A design method

The finite element method based on linear diffraction theory proposed by Zienkiewicz and Bettess (1977) has been used to compute wave loads and moments about the bed of surface piercing cylinders of circular, square, rectangular and elliptical sections for different angles of wave incidence. On the basis of the results obtained, a design method is presented in the form of simple design charts for estimating wave forces and moments on large cylinders of arbitrary sections. The numerical solutions obtained have been checked for their validity by comparing with other theoretical solutions and experimental data. Further the application of the design method to a case study shows good correlation with experimental and other theoretical solutions.     

A comparison of intracrystalline deformation in naturally and experimentally deformed quartzites

A relatively undeformed quartzite sample from the Weverton formation was experimentally deformed in plane strain at a temperature of 700° C, a confining pressure of 15 kb and a constant strain rate of 10⁻⁶/sec, in a modified Griggs apparatus. A comparison of the known experimental strain for the sample with that measured from deformed rutile needles within the quartz grains shows fairly close agreement between the two values. This confirms the validity of using the needles as intracrystalline strain markers. A comparison has been made of the microstructures and preferred orientations in the experimentally deformed sample and a naturally deformed sample of the same quartzite which has undergone the same strain. The experimentally deformed sample exhibits more inhomogeneous intragranular deformation and a “double funnel” pattern of c axes, while the naturally deformed sample exhibits more homogeneous intragranular deformation and a broad great circle girdle of c axes normal to the foliation and lineation.     

Seeing coal‐seam top ahead of the drill bit through seismic‐while‐drilling

Blast damage to the tops of coal seams due to incorrect blast standoff distances is a serious issue, costing the industry in Australia about one open‐cut mine for every ten operating mines. The current approach for mapping coal‐seam tops is through drilling and pierce‐point logging. To provide appropriate depth control with accuracy of ±0.2 m for blast hole drilling, it is typically necessary to drill deep reconnaissance boreholes on a 50 m x 50 m grid well in advance of overburden removal. Pierce‐point mapping is expensive and can be inaccurate, particularly when the seam is disturbed by rolls, faults, and other obstacles.Numerical modelling and prototype‐field testing are used in this paper to demonstrate the feasibility of two seismic‐while‐drilling‐based approaches for predicting the approach to the top of coal during blast hole drilling: (i) reverse “walk‐away” vertical seismic profiling recording, in which the drill bit vibration provides the source signal and the geophones are planted on the surface near the drill rig, and (ii) in‐seam seismic recording, in which channel waves, driven by the coupling to the coal of the seismic signal emitted by the approaching drill bit, are guided by the seam to geophones located within the seam in nearby or remote boreholes.     

Climatic periodicities recorded in lake sediment magnetic susceptibility data: Further evidence for solar forcing on Indian summer monsoon

The Indian summer monsoon exhibits considerable spatio-temporal variability.It is therefore important to understand its dynamics and the inherent periodicities.In this study,we have performed spectral and wavelet analyses of magnetic susceptibility data for sediments from Thimmannanayakanakere(TK)-a small lake in southern India.The main objective of this investigation is to identify and explain the possible origin of the prominent periodicities present in the magnetic susceptibility data.Significant periodicities in the TK χ_(lf)data are centered at 906,232,147,128,96,61,54 and 44 years,which might have a solar origin.The wavelet power spectrum of the raw and detrended χ_(lf)data confirms the findings of spectral analysis and also provides temporal variations of the significant cyclicities during the past3700 cal.years B.P.Positive correlation is documented between sunspot activity and TK xif data;crossspectral analysis of the reconstructed sunspot data and TK xif data suggest that there is a strong coherence between the two datasets as significant periodicities are documented in both.There is a good match between the TK xif and the reconstructed total solar irradiance data for the past 1200 years.However,an out-of-phase relationship is documented at certain time-intervals,which may be attributed to uncertainties in the age-depth model.The results obtained from this study show that solar variations are the main controlling factor of the southwest monsoon and,like other archives from different regions in India,the TK lake sediments have also recorded these solar signatures.     

Characterization of fluid inclusions encaged in quartz veins of Parsoi Formation,central India

The study focuses on analysis of primary and secondary fluid inclusions present in quartz veins hosted in the phyllites to explore the stress and temperature conditions at the time of formation of metasediment sequences of the of Parsoi Formation, central India. The results reveal the two-phase liquid-rich fluid inclusions that indicate that the intrusions of quartz veins in phyllite may have taken place between the temperature from 168.8°C to 256.3°C with an average of 205.55°C from a magmatic moderately saline fluid (3.7 to 18.29 wt. % NaCl equiv.). The final ice-melting temperatures ranges from -14.6°C to -2.2°C which indicate that the aqueous fluids are mainly H₂O-NaCl. The density distribution of fluid inclusions rich in liquid H₂O only are unimodel and low in natures and appears to be entrapped between pressure 1.666 to 2.125 kbar at depth of 200m. The study supports epithermal nature of fluid inclusions. The characteristic of fluid inclusions along with lithological and structural peculiarities, nature of structural features may be helpful in exploring the future potential zone of gold mineralization in similar types of area.     

High-speed bubble sizing using the double frequency technique foroceanographic applications

A high-speed bubble sizing technique that should have the capability of accurately determining bubble populations in breaking waves has been developed. The system was able to acquire an average bubble spectrum from 2.5 to 6 kHz in 0.1 s. Through the use of a double frequency technique, there would be very little or no contribution from nonresonant bubbles at each frequency of interest. The results of the system were compared to the data obtained by listening to ambient bubble noise with a transducer and from photographic population counts     

A modified algorithm for CLEANing wide-field maps with extended structures

A simple but effective modification to the conventional CLEAN algorithm is suggested. This modification ensures both stability and speed when CLEAN is applied to maps containing a mixture of point sources and extended structures. The method has been successfully applied to the recently-completed sky survey at 34.5 MHz (Dwarakanath & Udaya Shankar 1990). This survey was made using the Gauribidanur T array (GEETEE)1 in 1-D aperture synthesis mode. Since in this case the ‘dirty beam’ (point spread function) cannot be directly computed, a method to obtain this is discussed in detail. The results of this deconvolution procedure have been encouraging in terms of reduced computing time and improved dynamic range in our maps. This algorithm should find wider application in deconvolving maps which have both extended structures and point sources This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore & the Raman Research Institute, Bangalore.     

A digital correlation receiver for the GEETEE radio telescope

A 128-channel digital correlation receiver has been built for the GEETEE 1, the low-frequency radio telescope situated at Gauribidanur, South India, (latitude 13°36′12′′ N). The receiver uses a modified doublesideband (DSB) technique. The quadrature samples required for a DSB system are obtained by sampling the digitized intermediate frequency (I.F.) signals by two clocks which are separated in time by one quarter of the period of the I.F. The visibilities required for one-dimensional synthesis are measured using one-bit correlators. A technique to measure amplitude information for the signal using a threshold detector and a one-bit correlator has been developed. The receiver has been successfully used for continuum, spectral-line and pulsar observations. The antenna system of GEETEE and its configuration for one dimensional synthesis are also described in this paper This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore and the Raman Research Institute, Bangalore.