234 research outputs found
Size Differential Growth And Uptake Kinetics Of Inorganic Phosphate In Some Marine Diatoms
The marine diatoms such as Amphiprora gigantea O'Meara, Amphora coffeaeformis (Agardh) Kütz., Cocconeis heteroidea Hantz and Cyclotella meneghiniana Kütz. isolated from the coastal waters were made axenic and investigated for their growth, kinetics of phosphate uptake and assimilation. Phosphate-phosphorus at higher concentration depressed growth and division rates of all the diatoms. The uptake and assimilation of phosphate-phosphorus followed the classic Michaelis-Menten kinetics. Dark uptake was 37-71% when compared to light saturated uptake. Amphiprora gigantean, the largest diatom showed the low Ks and Km values whereas the smallest diatom Cyclotella meneghiniana exhibited high Ks and Km values for phosphate uptake and assimilation. DCMU inhibited phosphate uptake even at 2.5µM concentration indicated that the phosphate uptake is mediated mainly by the energy derived from photosynthesi
Source Radiation Patterns In Cased Boreholes
Source radiation from open and cased boreholes are well documented. The effect of
an unbonded casing on the radiation patterns of volume, radial stress and axial stress
sources in a borehole has received less attention and is modeled and analyzed here in
the context of performing single well imaging. Radiation patterns were evaluated using
a global matrix approach and wavenumber integration. 'While a borehole with a bonded
casing has a single propagating mode at low frequencies, the stoneley mode, the borehole
with unbonded casing has three propagating modes. Of the two additional modes that
are due to the unbonded casing, one is present mainly in the cross-section of the casing
and has a phase speed close to the speed of longitudinal waves in steeL Because of
its large phase speed (~ 5400 m/s), this mode radiates into almost all formations and
influences the radiation pattern of all source types. Test data and the predicted radiation patterns were used to identify the annulus material behind the casing.Massachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation
Consortiu
Cement Bond Evaluation Using Early Refracted Arrivals
The cement bond evaluation tool is a device used to examine the integrity of cement
bonding to the casing. A conceptual tool operating between 80-200 kHz is considered
here, with a transmitter and two receivers, oriented parallel to the axis of the borehole
and next to the casing. The compressional head wave in the casing, excited by
the transmitter, will be the first arrival to be measured by the two receivers in most
situations. With both receivers on the same side of the transmitter, the attenuation of
this wave in traveling between the two receivers is dependent on the properties of the
medium immediately outside the casing. The radially layered borehole was modeled as a
layered plane medium for large operating frequency. A spectral integral approach (complete wave synthesis) was used to compute the response at the receiver locations, which then provided attenuations. Different parameters, such as transducer separation (1-12 in), annulus thickness (0-6 in), annulus impedance (free pipe to good cement), casing thickness (0.25-0.45 in), standoff distance (0.5-1 in) and source frequency (80-200 kHz) were varied in the evaluation of the operation of the tool. The parameter studies based on the theoretical computations revealed that free pipe could be distinguished from the presence of cement in a variety of situations. Additionally, lower bounds on receiver separations are given for reliable operation of the tool.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumGas Research Institut
Specific heat study of single crystalline Pr Ca MnO in presence of a magnetic field
We present the results of a study of specific heat on a single crystal of
PrCaMnO performed over a temperature range 3K-300K in
presence of 0 and 8T magnetic fields. An estimate of the entropy and latent
heat in a magnetic field at the first order charge ordering (CO) transition is
presented. The total entropy change at the CO transition which is 1.8
J/mol K at 0T, decreases to 1.5 J/mol K in presence of 8T magnetic
field. Our measurements enable us to estimate the latent heat
235 J/mol involved in the CO transition. Since the entropy of the
ferromagnetic metallic (FMM) state is comparable to that of the charge-ordered
insulating (COI) state, a subtle change in entropy stabilises either of these
two states. Our low temperature specific heat measurements reveal that the
linear term is absent in 0T and surprisingly not seen even in the metallic FMM
state.Comment: 8 pages (in RevTEX format), 12 figures (in postscript format)
Submitted to Phys. Rev.
Parsing XML Using Parallel Traversal of Streaming Trees
Abstract. XML has been widely adopted across a wide spectrum of applica-tions. Its parsing efficiency, however, remains a concern, and can be a bottleneck. With the current trend towards multicore CPUs, parallelization to improve per-formance is increasingly relevant. In many applications, the XML is streamed from the network, and thus the complete XML document is never in memory at any single moment in time. Parallel parsing of such a stream can be equated to parallel depth-first traversal of a streaming tree. Existing research on parallel tree traversal has assumed the entire tree was available in-memory, and thus cannot be directly applied. In this paper we investigate parallel, SAX-style parsing of XML via a parallel, depth-first traversal of the streaming document. We show good scalability up to about 6 cores on a Linux platform.
Observation of the Smectic C -- Smectic I Critical Point
We report the first observation of the smectic C--smectic I (C--I) critical
point by Xray diffraction studies on a binary system. This is in confirmity
with the theoretical idea of Nelson and Halperin that coupling to the molecular
tilt should induce hexatic order even in the C phase and as such both C and I
(a tilted hexatic phase) should have the same symmetry. The results provide
evidence in support of the recent theory of Defontaines and Prost proposing a
new universality class for critical points in layered systems.Comment: 9 pages Latex and 5 postscript figures available from
[email protected] on request, Phys.Rev.Lett. (in press
Potentials of airborne hyperspectral aviris-ng data in the exploration of base metal deposit—a study in the parts of Bhilwara, Rajasthan
In this study, we have processed the spectral bands of airborne hyperspectral data of Advanced Visible Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) data for delineating the surface signatures associated with the base metal mineralization in the Pur-Banera area in the Bhilwara district, Rajasthan, India.The primaryhost rocks of the Cu, Pb, Zn mineralization in the area are Banded Magnetite Quartzite (BMQ), unclassified calcareous silicates, and quartzite. We used ratio images derived from the scale and root mean squares (RMS) error imagesusing the multi-range spectral feature fitting (MRSFF) methodto delineate host rocks from the AVIRIS-NG image. The False Color Composites (FCCs) of different relative band depth images, derived from AVIRIS-NG spectral bands, were also used for delineating few minerals. These minerals areeither associated with the surface alteration resulting from the ore-bearing fluid migration orassociated with the redox-controlled supergene enrichments of the ore deposit.The results show that the AVIRIS-NG image products derived in this study can delineate surface signatures of mineralization in 1:10000 to 1:15000 scales to narrow down the targets for detailed exploration.This study alsoidentified the possible structural control over the knownsurface distribution of alteration and lithocap minerals of base metal mineralizationusing the ground-based residual magnetic anomaly map. This observationstrengthens the importance of the identified surface proxiesas an indicator of mineralization. X-ray fluorescence analysis of samples collectedfromselected locations within the study area confirms the Cu-Pb-Zn enrichment. The sulfide minerals were also identified in the microphotographs of polished sections of rock samples collected from the places where surface proxies of mineralization were observed in the field. This study justified the investigation to uti-lize surface signatures of mineralization identified using AVIRIS-NG dataand validated using field observations, geophysical, geochemical, and petrographical data
Non-linear electrical response in a charge/orbital ordered CaMnO crystal : the charge density wave analogy
Non-linear conduction in a charge-ordered manganese oxide
PrCaMnO is reported. To interpret such a feature, it is
usually proposed that a breakdown of the charge or orbitally ordered state is
induced by the current. The system behaves in such a way that the bias current
may generate metallic paths giving rise to resistivity drop. One can describe
this feature by considering the coexistence of localized and delocalized
electron states with independent paths of conduction. This situation is
reminiscent of what occurs in charge density wave systems where a similar
non-linear conduction is also observed. In the light of recent experimental
results suggesting the development of charge density waves in charge and
orbitally ordered manganese oxides, a phenomenological model for charge density
waves motion is used to describe the non-linear conduction in
PrCaMnO. In such a framework, the non-linear conduction
arises from the motion of the charge density waves condensate which carries a
net electrical current.Comment: 13 pages, 6 figure
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