Parthasarathy Srinivasan

Third-order effect in solid-state NMR of quadrupolar nuclei

Abstract The theory and experimental observation of the third-order effect in solid-state NMR of quadrupolar nuclei are presented. The third-order effect consists of spherical harmonic terms up to rank l =6 and shifts NMR frequencies between two spin states that are not symmetric such as satellite transitions. Two-dimensional satellite transition magic-angle spinning experiment averages both the first and the second-order quadrupolar interactions making the quantitative measurement of the third-order effect possible. The third-order quadrupolar effect in andalusite has been measured at 11.7 T and its powder patterns are fitted with numerical simulations.

Satellite transition rotational resonance of homonuclear quadrupolar spins: magic-angle effect on spin-echo decay and inversion recovery

Abstract Satellite transition rotational resonance and magic-angle effects on central-transition spin-echo decay and inversion recovery of half-integer quadrupolar nuclei are presented. Small magic-angle offsets can change the satellite transition rotational resonance condition and consequently lead to dramatic effects on line width, spin-echo decay and inversion recovery. An half degree magic-angle offset lengthens α-Al 2 O 3 spin-echo decay by 50% and inversion-recovery by nearly two orders of magnitude. The theory of satellite transition rotational resonance is presented and the origin of these magic-angle effects is explained.

Oxygen regulates the effective diffusion distance of nitric oxide in the aortic wall.

Endothelium-derived nitric oxide (NO) is critical in maintaining vascular tone. Accumulating evidence shows that NO bioavailability is regulated by oxygen concentration. However, it is unclear to what extent the oxygen concentration regulates NO bioavailability in the vascular wall. In this study, a recently developed experimental setup was used to measure the NO diffusion flux across the aortic wall at various oxygen concentrations. It was observed that for a constant NO concentration at the endothelial surface, the measured NO diffusion flux out of the adventitial surface at [O(2)]=0 microM is around fivefold greater than at [O(2)]=150 microM, indicating that NO is consumed in the aortic wall in an oxygen-dependent manner. Analysis of experimental data shows that the rate of NO consumption in the aortic wall is first order with respect to [NO] and first order with respect to [O(2)], and the rate constant k(1) was determined as (4.0+/-0.3) x 10(3) M(-1) s(-1). Computer simulations demonstrate that NO concentration distribution significantly changes with oxygen concentration and the effective NO diffusion distance at low oxygen level ([O(2)] < or =25 microM) is significantly longer than that at high oxygen level ([O(2)]=200 microM). These results suggest that oxygen-dependent NO consumption may play an important role in dilating blood vessels during hypoxia by increasing the effective NO diffusion distance.

The neighborhood method and its coupling with the wavelet method for signal separation of chaotic signals

Signal separation, i.e., the elimination or suppression of extraneous components from measured signals, is an essential module of modern signal analysis. We report the development of two novel signal separation methods--(i) the neighborhood method (NM) and (ii) a modified wavelet method (MWM)--that seem to be aptly suited for signals acquired from machining process sensors, i.e., for chaotic signals with small, uniform Lyapunov exponents. For the NM, a variant of shadowing signal separation methods used for signal separation of chaotic signals, we establish theoretical bounds on performance under various noisy conditions and analyze its algorithmic complexity. Our MWM is an adaptation of Donohos wavelet method to nonlinear, and possibly chaotic, signals with multiplicative noise. It incorporates certain features of the NM and it has lower algorithmic complexity than the NM, and is, therefore, more suitable for on-line implementation. Both methods were tested on chaotic signals corresponding to the reconstructed Rossler attractor. A discussion on the application of both methods to signals obtained from actual machining process sensors is provided in order to motivate their suitability to real-world nonlinear processes.

On the relation between the WRT invariant and the Hennings invariant

The purpose of this paper is to provide a simple relation between the Witten–Reshetikhin-Turaev SO (3) invariant and the Hennings invariant associated to quantum .

Synergistic Effects of 3D ECM and Chemogradients on Neurite Outgrowth and Guidance: A Simple Modeling and Microfluidic Framework

During nervous system development, numerous cues within the extracellular matrix microenvironment (ECM) guide the growing neurites along specific pathways to reach their intended targets. Neurite motility is controlled by extracellular signal sensing through the growth cone at the neurite tip, including chemoattractive and repulsive cues. However, it is difficult to regenerate and restore neurite tracts, lost or degraded due to an injury or disease, in the adult central nervous system. Thus, it is important to evaluate the dynamic interplay between ECM and the concentration gradients of these cues, which would elicit robust neuritogenesis. Such information is critical in understanding the processes involved in developmental biology, and in developing high-fidelity neurite regenerative strategies post-injury, and in drug discovery and targeted therapeutics for neurodegenerative conditions. Here, we quantitatively investigated this relationship using a combination of mathematical modeling and in vitro experiments, and determined the synergistic role of guidance cues and ECM on neurite outgrowth and turning. Using a biomimetic microfluidic system, we have shown that cortical neurite outgrowth and turning under chemogradients (IGF-1 or BDNF) within 3D scaffolds is highly regulated by the source concentration of the guidance cue and the physical characteristics of the scaffold. A mechanistic-driven partial differential equation model of neurite outgrowth has been proposed, which could also be used prospectively as a predictive tool. The parameters for the chemotaxis term in the model are determined from the experimental data using our microfluidic assay. Resulting model simulations demonstrate how neurite outgrowth was critically influenced by the experimental variables, which was further supported by experimental data on cell-surface-receptor expressions. The model results are in excellent agreement with the experimental findings. This integrated approach represents a framework for further elucidation of biological mechanisms underlying neuronal responses of specialized cell types, during various stages of development, and under healthy or diseased conditions.

Pediatric glioblastoma cells inhibit neurogenesis and promote astrogenesis, phenotypic transformation and migration of human neural progenitor cells within cocultures

Abstract Neural progenitor cell (NPC) fate is influenced by a variety of biological cues elicited from the surrounding microenvironment and recent studies suggest their possible role in pediatric glioblastoma multiforme (GBM) development. Since a few GBM cells also display NPC characteristics, it is not clear whether NPCs transform to tumor cell phenotype leading to the onset of GBM formation, or NPCs migrate to developing tumor sites in response to paracrine signaling from GBM cells. Elucidating the paracrine interactions between GBM cells and NPCs in vivo is challenging due to the inherent complexity of the CNS. Here, we investigated the interactions between human NPCs (ReNcell) and human pediatric GBM‐derived cells (SJ‐GBM2) using a Transwell® coculture setup to assess the effects of GBM cells on ReNcells (cytokine and chemokine release, viability, phenotype, differentiation, migration). Standalone ReNcell or GBM cultures served as controls. Qualitative and quantitative results from ELISA®, Live/Dead® and BrdU assays, immunofluorescence labeling, western blot analysis, and scratch test suggests that although ReNcell viability remained unaffected in the presence of pediatric GBM cells, their morphology, phenotype, differentiation patterns, neurite outgrowth, migration patterns (average speed, distance, number of cells) and GSK‐3&bgr; expression were significantly influenced. The cumulative distance migrated by the cells in each condition was fit to Furths formula, derived formally from Ornstein‐Uhlenbeck process. ReNcell differentiation into neural lineage was compromised and astrogenesis promoted within cocultures. Such coculture platform could be extended to identify the specific molecules contributing to the observed phenomena, to investigate whether NPCs could be transplanted to replace lesions of excised tumor sites, and to elucidate the underlying molecular pathways involved in GBM‐NPC interactions within the tumor microenvironment. HighlightsInteractions between human NPCs and human pediatric GBM‐derived cells investigated using a coculture setup.NPC morphology, phenotype, differentiation, neurite outgrowth, and migration patterns significantly influenced by GBMs.Cumulative migration distance fit to Furths formula derived formally from Ornstein‐Uhlenbeck process.Significant applications in NPC transplantation efforts to replace lesions of excised tumor sites.Cocultures helped elucidate the underlying pathways involved in GBM‐NPC interactions in a tumor microenvironment.