Biomedical subjects

T Venkatesan

Publications and source records attributed to T Venkatesan.

At least 19 recordsLinked to original sources

PubMed2026

Ultrastructural Insights Into the Reproductive Anatomy and Eggs of Cotton Pink Bollworm, Pectinophora gossypiella Saunders (Lepidoptera: Gelechiidae).

The pink bollworm, Pectinophora gossypiella Saunders is a major pest of cotton, notorious for its high reproductive potential and rapid evolution of resistance to Bacillus thuringiensis (Bt) toxins. Despite its economic significance, detailed knowledge of its reproductive anatomy and egg ultrastructure has remained limited, constraining the development of advanced molecular control strategies such as CRISPR/Cas9-based genome editing. The present study provides the first comprehensive characterization of the reproductive system and egg surface morphology of P. gossypiella using stereomicroscopy and scanning electron microscopy (SEM) techniques. The male reproductive system consists of fused, bean-shaped testes, seminal vesicles, duplex and simplex ejaculatory ducts, and paired accessory glands. The female reproductive system comprises paired ovaries with four polytrophic ovarioles per ovary, lateral and common oviducts, accessory glands, corpus bursae, and spermathecal glands. Eggs are oval, dorsoventrally flattened, exhibit a reticulated chorion with distinct micropylar and aeropylar regions. SEM images revealed 6-9 rosette cells encircling a circular micropylar plate, 14-19 first order and 17-23 s order ribs, and 250-291 polygonal surface cells. The structural features of P. gossypiella eggs reveal key sites for sperm entry, aeropylar respiration, and candidate zones for microinjection in gene editing applications. These findings establish a morphological baseline critical for optimizing embryo manipulation and ribonucleoprotein (RNP) delivery in lepidopteran genome editing. This study represents a pioneering effort to integrate classical egg morphology with molecular entomology, thereby advancing precision genetic interventions aimed at resistance management and population suppression in P. gossypiella.

Animals↗

PubMed2001

Do superconductors have zero resistance in a magnetic field?

We show that dc voltage versus current measurements of a YBa(2)Cu(3)O(7-delta) film in a magnetic field can be collapsed onto scaling functions proposed by Fisher et al. [Phys. Rev. B 43, 130 (1991)] as is widely reported in the literature. We find, however, that good data collapse is achieved for a wide range of critical exponents and temperatures. These results strongly suggest that agreement with scaling alone does not prove the existence of a phase transition. We propose a criterion to determine if the data collapse is valid, and thus if a phase transition occurs. To our knowledge, none of the data reported in the literature meet our criterion.

Journal Article↗

PubMed2001

Electroresistance and electronic phase separation in mixed-valent manganites.

The sensitivity of transport in colossal magnetoresistance (CMR) manganites to external electric and magnetic fields is examined using field effect configurations with La(0.7)Ca(0.3)MnO(3) (LCMO), Na(0.7)Sr(0.3)MnO(3), La(0.7)Ba(0.3)MnO(3), and La(0.5)Ca(0.5)MnO(3) (0.5-doped LCMO) channels, and ferroelectric PbZr(0.2)Ti(0.8)O(3) (PZT) or dielectric (SrTiO(3)) gates. A large electroresistance (ER) of approximately 76% at 4 x 10(5) V/cm is found in LCMO with PZT-ferroelectric gate, but the magnitude of the effect is much smaller (a few percent) in the other three channels. The ER and CMR effects are remarkably complimentary. The size and systematics of the effect strongly favor a percolative phase separation picture.

Journal Article↗

PubMed2001

Recurrent acute pancreatitis: an algorithmic approach to identification and elimination of inciting factors.

Recurrent acute pancreatitis represents a challenging clinical problem associated with significant morbidity, impairment in quality of life, and expense. If unchecked, recurrent episodes of acute pancreatitis may lead to chronic pancreatitis. In this work we have combined the opinion of experts in pancreatology and an extensive review of the literature to develop a logical algorithm that facilitates the stepwise identification and elimination of inciting factors using current technology. The approach taken in recurrent acute pancreatitis is clearly dependent on adequate and appropriate evaluation and treatment of the patient with an initial episode of acute pancreatitis. Future advances in the treatment of these patients will almost certainly depend on improved imaging modalities, prospective clinical trials assessing the efficacy of endoscopic and surgical intervention, a better understanding of mutations and pathophysiologic mechanisms responsible for recurrent acute pancreatitis, and the development of novel, effective preventive and therapeutic strategies.

Acute Disease↗

PubMed2001

Toxicity analysis of N- and C-terminus-deleted vegetative insecticidal protein from Bacillus thuringiensis.

A vegetative insecticidal protein (VIP)-encoding gene from a local isolate of Bacillus thuringiensis has been cloned, sequenced, and expressed in Escherichia coli. The expressed protein shows insecticidal activity against several lepidopteran pests but is ineffective against Agrotis ipsilon. Comparison of the amino acid sequence with those of reported VIPs revealed a few differences. Analysis of insecticidal activity with N- and C-terminus deletion mutants suggests a differential mode of action of VIP against different pests.

Animals↗

PubMed2000

Phase transitions in the incoherent lattice fluctuations in YBa2Cu3O(7-delta)

The growing body of experimental evidence for the existence of complex textures of charges and spins in the high-temperature superconductors has drawn attention to the so-called 'stripe-phase' models as a possible basis for the mechanism of superconductivity in these materials. Such observations have until now been restricted to systems where the texture dynamics are slow or suppressed altogether, and do not include the important case of YBa2Cu3O(7-delta). It seems likely that the dynamic behaviour of stripes, which has been suggested to undergo several phase transitions as a function of temperature, should also be reflected in the lattice properties of the host materials, and this forms the motivation for our present experiments. Specifically, we use MeV helium ion channelling, an ultrafast real-space probe of atomic displacements (with sub-picometre resolution), to probe incoherent lattice fluctuations in YBa2Cu3O(7-delta) as a function of temperature and oxygen doping. We detect lattice fluctuations that are larger than the expected thermal vibration component, and which show anomalies characteristic of the phase transitions anticipated for a dynamic stripe phase. Comparison of our lattice results with single-particle-tunnelling and photoemission data highlights the importance of spin-charge separation phenomena in the copper oxide superconductors.

Journal Article↗

PubMed1999

Prevalence and predictors of severe acute pancreatitis in patients with acquired immune deficiency syndrome (AIDS).

OBJECTIVE: Recent case control data suggested that a severe course of acute pancreatitis in HIV+ patients was 1) common (50% of cases), 2) poorly predicted by Ranson's criteria (sensitivity 41%), and 3) accurately predicted by a diagnosis of AIDS (positive predictive value 67%). However, the definition of severity included length of stay in hospital and excluded commonly accepted markers (local complications, systemic complications, and need for surgery). The aim of this study was to determine 1) the prevalence of severity and 2) the value of these predictors with regard to severity, as defined by commonly accepted standardized criteria in patients with AIDS and acute pancreatitis. METHODS: A retrospective review identified 50 patients with AIDS exhibiting clinical, laboratory, and/or radiological features of acute pancreatitis. RESULTS: Only five patients followed a severe course as defined by accepted markers. Of these patients, 29 had values available for at least nine of 11 of Ranson's criteria (sensitivity 80%, specificity 54%). Points were awarded most commonly for decreased serum Ca2+ (n = 14) and elevated serum LDH (n = 7). CONCLUSIONS: In patients with AIDS and acute pancreatitis at our institutions, 1) the prevalence of severity and 2) the sensitivity of Ranson's criteria with regard to severity is comparable to that reported in large historical case series of immunocompetent patients. Pseudohypocalcemia and/or elevation in LDH are frequent, likely due to the catabolic infectious disease state.

Acquired Immunodeficiency Syndrome↗

PubMed1997

Ferroelectric Field Effect Transistor Based on Epitaxial Perovskite Heterostructures

Ferroelectric field effect devices offer the possibility of nonvolatile active memory elements. Doped rare-earth manganates, which are usually associated with colossal magnetoresistive properties, have been used as the semiconductor channel material of a prototypical epitaxial field effect device. The carrier concentration of the semiconductor channel can be "tuned" by varying the manganate stochiometry. A device with La0.7Ca0.3MnO3 as the semiconductor and PbZr0.2Ti0.8O3 as the ferroelectric gate exhibited a modulation in channel conductance of at least a factor of 3 and a retention loss of 3 percent after 45 minutes without power.

Journal Article↗

PubMed1996