PubMed Health⌕ Search

Biomedical subjects

R S Sethi

Publications and source records attributed to R S Sethi.

At least 19 recordsLinked to original sources
PubMed2005

Planar coil excitation of multifrequency shear wave transducers.

A transducer format that replaces the electrode of an acoustic resonator with a planar spiral coil is used to extract multifrequency spectral information from adsorbed protein films. Both amorphous silica and crystalline piezoelectric resonators are driven to resonance by forces induced across an air gap by magnetic direct generation and piezoelectric excitation induced by the electromagnetic field of the coil. Inspection of the harmonic frequencies between 6 MHz and 0.6 GHz indicates that the response of these two resonator types is described by different families of shear acoustic standing waves, with similar acoustic features to the quartz crystal microbalance. Exposure of the devices to protein solutions results in reproducible shifts of their harmonic frequencies, up to a maximum of 15 kHz and increasing linearly with frequency and operating mode. The gradient, determined from the ratio of the frequency change to the operating frequency was determined as 21.5 x 10(-6) for the quartz device and 60.9 x 10(-6) for the silica device. Consistency with the Sauerbrey equation for the piezoelectric linear shear mode was comparable at a predicted value of 22.5 x 10(-6), but not for the radial shear mode of the silica device at 12.7 x 10(-6). Opportunities resulting from the wide bandwidth of the planar coil excitation and choice of acoustic mode are discussed with respect to acoustic fingerprinting of adsorbed proteins.

Electronics↗
PubMed2003

The acoustic spectrophonometer: a novel bioanalytical technique based on multifrequency acoustic devices.

A measurement technique similar to optical absorption spectroscopy but based on evanescent acoustic waves is described in this paper. This format employs a planar spiral coil to vibrate a single crystal of quartz from 6 to 400 MHz, in order to measure multifrequency acoustic spectra. Consistency with the defined Sauerbrey and Kanazawa terms K1 and K2 when applied to multiple frequencies was found for these specific operating conditions in terms of a significant fit between the measured and calculated values: For an IgG surface density of 13.5 ng mm(-2) the measured value of K1 is 22.5 x 10(-6) and the calculated value is 20.4 x 10(-6), whilst for glycerol viscous loadings of 5.131 cP the measured value of K2 is 0.47 and the calculated value is 0.54. Thus for these specific surface loadings the multifrequency data fits to the predictions of the Sauerbrey model to within 10% and to Kanazawa model within 13%. However collective frequency shifts for 5.131 cP solutions of sucrose, dextran and glucose were found to exhibit an unanticipated additional variability (R2 < 0.4) with frequency, but retained a square root of frequency dependency within a factor 2 of the interpolated K2 values. The response to the 5.131 cP dextran solution was found to be significantly below the other isoviscous solutions, with a substantially reduced frequency shift and K2 value than would be expected from its bulk viscosity. In comparison with these viscous solutions, IgG protein films consistently produced linear frequency shifts with little scatter (R2 > 0.96) that were proportional to the operating frequency, and fully consistent with the Sauerbrey model under these specific conditions. A t-test value of 14.52 was calculated from the variance and mean of the two groups, and demonstrates that the acoustic spectrophonometer can be used to distinguish between the acoustic impedance characteristics of two chemical systems that are not clearly differentiable at a single operating frequency.

Acoustics↗
PubMed2003

Hypersonic evanescent waves generated with a planar spiral coil.

A planar spiral coil has been used to induce hypersonic evanescent waves in a quartz substrate with the unique ability to focus the acoustic wave down onto the chemical recognition layer. These special sensing conditions were achieved by investigating the application of a radio frequency current to a coaxial waveguide and spiral coil, so that wideband repeating electrical resonance conditions could be established over the MHz to GHz frequency range. At a selected operating frequency of 1.09 GHz, the evanescent wave depth of a quartz crystal hypersonic resonance is reduced to 17 nm, minimising unwanted coupling to the bulk fluid. Verification of the validity of the hypersonic resonance was carried out by characterising the system electrically and acoustically: Impedance calculations of the combined coil and coaxial waveguide demonstrated an excellent fit to the measured data, although above 400 MHz a transition zone was identified where unwanted impedance is parasitic of the coil influence efficiency, so the signal-to-noise ratio is reduced from 3000 to 300. Acoustic quartz crystal resonances at intervals of precisely 13.2138 MHz spacing, from the 6.6 MHz ultrasonic range and onto the desired hypersonic range above 1 GHz, were incrementally detected. Q factor measurements demonstrated that reductions in energy lost from the resonator to the fluid interface were consistent with the anticipated shrinkage of the evanescent wave with increasing operating frequency. Amplitude and frequency reduction in contact with a glucose solution was demonstrated at 1.09 GHz. The complex physical conditions arising at the solid-liquid interface under hypersonic entrainment are discussed with respect to acceleration induced slippage, rupture, longitudinal and shear radiation and multiphase relaxation affects.

Biophysical Phenomena↗
PubMed1980

Nezelof syndrome.

Explore the source record for details and available documents.

Child, Preschool↗
PubMed1975

Histochemical studies in stomatal apparatus of Phaseolus mungo Linn. I. Localization of enzymes and structural material.

In the present investigations, the localization of several enzymes (Acid Phosphatase, Peroxidase, succinic dehydrogenase, Phosphorylase, alkaline phosphatase, ATP-ase) and other substances in the guard and subsidiary cells as well as trichomes of the leaves of Phaseolus mungo, was carried out. Attempts were also made to follow the sequence of developmental stages starting with meristemoids and culminating in differentiated structures. The basic information thus obtained is used in interpreting the developmental physiology of stomatal differentiation as well as their cellular organisation. Histochemical observations made in the present studies are compared with the electron microscopical observations of Whatley (1972). It is proposed that mitochondria played a basic role in the functioning of the guard cells. The present studies also demonstrated activity of acid phosphatase in the guard cells and was localized in spherosomes. The latter varied in the activity for acid phosphatase and was dependent on the turgid level of the cell. Interestingly, enough localization of phosphatase could only be observed in spherosomes when the osmotic pressure in the cell was relatively low, once the osmotic pressure increased, the activity disappeared.

Acid Phosphatase↗
PubMed1975

Histochemical studies in stomatal apparatus of Phaseolus mungo linn. IV. Mechanism of stomatal action.

The histochemical studies were carried out in the open and closed stomata of Phaseolus mungo leaves. Several enzymes like, Acid phospatase peroxidase, succinic dehydrogenase, phosphorylase, alkaline phosphatase, ATP-ase etc. were localized in the guard and subsidiary cells of epidermal peel. On the basis of cytochemical localization, enzyme activity was precisely interpreted. In the light of fluctuations in the localization, activities of different enzymes, an attempt is made to provide the functional interpretation of stomatal mechanism. We have attempted to correlat our observations in relation to diurnal metabolisms. Our studies suggest that starch-sugar inter-changes played a vital role in the stomatal regulation. We are also inclined to believe that besides guard cells, subsidiary cells also influenced the turgid conditions. A model based on available facts in collaboration with our own studies is presented which tends to explain the stomatal regulation.

Acid Phosphatase↗
PubMed1975

Histochemical studies in stomatal apparatus of Phaseolus mungo Linn. II. Localization of phosphorylase.

Using histochemical techniques the presence of phosphorylase in the guard cells and subsidiary cells of Phaseolus mungo leaf has been demonstrated. The intensity of reaction is intense in the material collected at night while during the day collected leaves, both chloroplastic and cytoplasmic starch was absent. The functional significance of chloroplastic starch in the subsidiary cells in relation to the stomatal mechanism is discussed.

Chloroplasts↗