Biomedical subjects

N Chandrasekhar

Publications and source records attributed to N Chandrasekhar.

15 recordsLinked to original sources

PubMed2006

One-photon photodetachment of I- in glycerol: spectra and yield of solvated electrons in the temperature range 329<or=T<or=536 K.

Solvated electrons in glycerol were generated via a resonant one-photon photodetachment of the charge-transfer-to-solvent (CTTS) band of I- in glycerol (Gl) after irradiation with a 248 nm excimer laser. Optical absorption spectra of solvated electrons (esolv-) in Gl were recorded as a function of temperature (381<or=T<or=505 K). The observed redshift of the absorption maximum, homegamax, yields a temperature coefficient d(homegamax)/dT=-(2.67+/-0.07)x10(-3) eV K-1. For solutions with a concentration c(I-) approximately 10(-3)M, the absorbance of esolv- at homegamax increases by a factor of about 65 when the temperature is raised from 329 to 536 K. This effect can be partially explained by a temperature-dependent redshift of the CTTS spectrum of I- in Gl with respect to the laser wavelength. The main contribution to the increasing yield of esolv- is determined by diffusion controlled escape dynamics of the electron in the contact pair (I:e-)solv which is formed very fast during the detachment process. At room temperature no absorption of esolv- (absorbance<1.0x10(-3)) could be observed which is probably a result of an extremely small self-diffusion coefficient of Gl (a factor of 1250 lower than that of water at 298 K). The results are compared with a previous study of I- in ethylene glycol.

Journal Article↗

PubMed2006

Evidence for laser-induced formation of solvated electrons in room temperature ionic liquids.

The photolytic generation of solvated electrons was observed for the first time in two room temperature ionic liquids (RTILs), trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide (IL) and 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide (IL). A 70 fs UV-pulse was used to excite the RTILs, while the transient response was monitored in the visible and near-infrared spectral regions. Immediately after excitation, a pulse duration limited rise of the induced absorption indicated the formation of solvated electrons suggesting the existence of pre-formed traps in RTILs. A broad transient absorption spectrum with a full width at half maximum of about 0.9 eV, typical for solvated electrons, was reconstructed from the transient profiles. Wavelength-independent relaxation dynamics at longer delay times suggest a lifetime of solvated electrons in the ns regime in agreement with results from pulse radiolysis studies. Adding 1,1-dimethylpyrrolidinium iodide to IL led to an increase of the UV absorbance and consequently, to an increase of the yield of solvated electrons. Furthermore, this solute is an efficient electron scavenger causing the transients to decay within about 40 ps.

Absorption↗

PubMed2005

Switching in organic devices caused by nanoscale Schottky barrier patches.

We have identified a possible electronic origin of metal filaments, invoked to explain the switching behavior of organic devices. Interfaces of two representative organics polyparaphenylene (PPP) and poly(2-methoxy-5-2-ethyl-hexyloxy-1,4-phenylenevinylene) with Ag are investigated using ballistic emission microscopy. Nanometer scale spatial nonuniformity of carrier injection is observed in ballistic electron emission microscopy images of both interfaces. The measured Schottky barrier (SB) appears to be consistent with metal states tailing into the gap of the PPP. We find that the SB values exhibit a distribution, even for the diodes with low ideality factors. The implications of this distribution on the measured physical properties of the diode are discussed, in light of work on devices of similar geometry, published in the literature. We also demonstrate that patches of low SB are likely to nucleate current filaments which can cause local ionization and are reported to be responsible for the switching behavior observed in metal-organic, metal-CuS and Ag-AgSe structures.

Journal Article↗

PubMed2005

Population dynamics of the Teak defoliator (Hyblaea puera Cramer) in Nilambur teak plantations using Randomly Amplified Gene Encoding Primers (RAGEP).

BACKGROUND: The Teak defoliator (Hyblaea puera) is a pest moth of teak woodlands in India and other tropical regions (e.g. Thailand) and is of major economic significance. This pest is of major concern as it is involved in complete defoliation of trees during the early part of the growing season. Defoliation does not kill teak trees, but it results in huge amount of timber loss. Teak defoliator outbreaks are a regular annual feature in most teak plantations in India and it is extremely difficult to predict the exact time and place of occurrence of these outbreaks. Evidence from the study of the population dynamics of H. puera indicated habitual, short range movements of emerging moth populations, suggesting that these populations have spread to larger areas, generation after generation, affecting the entire teak plantations. We were therefore interested in investigating the temporal and spatial relationship among various population groups in Nilambur, Kerala (India) and address the cause of outbreak at the landscape level. RESULTS: The populations were classified into 'endemic', 'epicenter' and 'epidemic' populations based on the time of occurrence and size of infestation. We devised a novel method of screening nuclear and mitochondrial DNA polymorphisms using Randomly Amplified Gene Encoding Primers (RAGEP). We have used this method extensively to evaluate the species specificity, reproducibility and to discriminate among the three different characterised populations of teak defoliator. CONCLUSIONS: This method also allowed us to comment with some certainty that the endemic teak defoliator, H. puera do not play a major role in contributing to large-scale infestations. With respect to the hypotheses put forward regarding the origin of outbreaks of the moth, this study confirms the role of migration in outbreak causation, while negating the belief that endemic populations aggregate to cause an epidemic.

Animals↗

PubMed2005

Experimental study and numerical estimation of current changes in electroosmotically pumped microfluidic devices.

Electroosmotic flow (EOF) was investigated in microfabricated fluidic devices using the current monitoring technique. Current changes ranging from 50 to 130 pA/s were detected. These observations indicate that in microfluidic devices with small reservoir volumes, electrolysis of water influences the fluid transport, giving rise to changes in pH and increase in concentration of ionic species in the fluidic system. As a result of the electrolysis and associated increment in ion concentration, the thickness of the Debye layer and surface potential vary, affecting the overall migration behavior of the solution. The magnitude of EOF and the electrophoretic properties of molecules can no longer be treated as constant/invariant. These temporal anomalies are undesirable during analytical separations and in fluid control applications. A numerical analysis of the impact of the continuous ionic strength increase on the EOF dynamics is presented using well-established conduction and EOF theories. The numerical results are found to be in good agreement with the observed current changes. These results indicate that to improve assay reproducibility, monitoring the electric current is an effective tool to determine whether electrolytic reactions are taking place. Our work also serves to test the numerical accuracy of EOF theories and models.

Electric Conductivity↗

PubMed1996