A survey of nulling pulsars using the Giant Meterwave Radio Telescope

Several pulsars show sudden cessation of pulsed emission, which is known as pulsar nulling. In this paper, the nulling behaviour of 15 pulsars is presented. The nulling fractions of these pulsars, along with the degree of reduction in the pulse energy during the null phase, are reported for these pulsars. A quasi-periodic null-burst pattern is reported for PSR J1738-2330. The distributions of lengths of the null and the burst phases as well as the typical nulling time scales are estimated for eight strong pulsars. The nulling pattern of four pulsars with similar nulling fraction are found to be different from each other, suggesting that the fraction of null pulses does not quantify the nulling behaviour of a pulsar in full detail. Analysis of these distributions also indicate that while the null and the burst pulses occur in groups, the underlying distribution of the interval between a transition from the null to the burst phase and vice verse appears to be similar to that of a stochastic Poisson point process.Comment: 10 pages, 7 figures, accepted for publication in MNRA

Nuclear DNA and protein content evaluation in Taxus plant cell cultures using multiparameter flow cytometry

Plant cell cultures of Taxus provide the most reliable production methods for the anti-cancer drug paclitaxel. In order to comprehend the inherent culture heterogeneity and production variability in cell cultures, it is essential that the cellular metabolism is studied at the genomic level. Genomic stability in plant cell cultures is crucial as it affects cell growth and division, metabolite accumulation and protein synthesis. A rapid and efficient method to prepare nuclei suspensions from aggregated cell cultures of Taxus was employed. Methods were subsequently developed to simultaneously stain them for DNA and protein content using Propidium Iodide and Fluorescein Isothiocyanate respectively. Flow cytometry was used to analyze and quantify the DNA content and genome size of Taxus using known reference species as standards. Furthermore, their genomic stability was evaluated by correlating DNA content and genome size with cell size and complexity, protein content, and elicitation effects using multiparameter flow cytometry. These techniques to evaluate and correlate various culture characteristics can be very useful in designing superior bio processes for enhanced production.


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Recovery from visual dysfunction following mild traumatic brain injury is associated with adaptive reorganization of retinal inputs to lateral geniculate nucleus in the mouse model utilizing central fluid percussion injury.

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality nationwide. Prevalence of mild TBI (mTBI) vastly outnumbers more severe forms however the associated morbidity has only recently gained public attention. Visual dysfunction is a significant component of mTBI associated morbidity with recovery of function linked with improvement in global outcomes. Examination of sensory and motor pathways in other brain injury paradigms support that recovery is largely dependent on adaptive plasticity of remaining connections. Current examinations of visual function recovery following mTBI is limited to identifying evidence for recovery and objective evidence for adaptive plasticity is limited. Therefore, to understand the mechanisms behind visual recovery in mTBI, we utilize a mouse model to examine the changes in the downstream target of retinal ganglion cells (RGC) in the formed vision pathway, the lateral geniculate nucleus (LGN). Using techniques designed to identify structural changes as well as electrophysiologic connectivity we aimed to identify if deafferentation due to experimental mTBI is met with adaptive structural and electrophysiologic reorganization of inputs to LGN relay cells, to determine if they may contribute to recovery of vision over time. Examination of ensuing deafferentation in LGN was performed using a combination of anterograde tract tracing with cholera toxin B conjugated fluorescent probes, immunohistochemistry targeting retinal ganglion cell axon terminals, and a transgenic mouse in which a subpopulation of retinal ganglion cells are labelled with green fluorescent protein. Our studies were designed to capture structural reorganization in specific subpopulations of retinal ganglion cells and determine if ensuing reorganization violated projection patterns established during normal development and refinement of the retinal geniculate pathway. Additionally, our studies examined the electrophysiologic responses of relay neurons in the lateral geniculate nucleus to stimulation of the optic tract as a function of time following injury. Using ex-vivo patch clamp recording of LGN relay neurons, we examined responses of these cells to stimulation of the optic tract following mTBI. Our findings demonstrated intact short-term depression at the retinal geniculate synapse following injury, which is a mechanism through which LGN relay neurons establish functional connectivity from retinal inputs. This innate mechanism of short-term plasticity likely uncovers latent connectivity between the remaining retinal inputs and LGN relay neurons to provide new connectivity for functional recovery. These studies support the premise that recovery of function in the visual axis following mild TBI is dependent on adaptive structural and electrophysiologic reorganization within the lateral geniculate nucleus

Transient compressible flow in a compliant viscoelastic tube

Motivated by problems arising in the pneumatic actuation of controllers for micro-electromechanical systems (MEMS), labs-on-a-chip or biomimetic soft robots, and the study of microrheology of both gases and soft solids, we analyze the transient fluid--structure interaction (FSIs) between a viscoelastic tube conveying compressible flow at low Reynolds number. We express the density of the fluid as a linear function of the pressure, and we use the lubrication approximation to further simplify the fluid dynamics problem. On the other hand, the structural mechanics is governed by a modified Donnell shell theory accounting for Kelvin--Voigt-type linearly viscoelastic mechanical response. The fluid and structural mechanics problems are coupled through the tube's radial deformation and the hydrodynamic pressure. For small compressibility numbers and weak coupling, the equations are solved analytically via a perturbation expansion. Three illustrative problems are analyzed. First, we obtain exact (but implicit) solutions for the pressure for steady flow conditions. Second, we solve the transient problem of impulsive pressurization of the tube's inlet. Third, we analyze the transient response to an oscillatory inlet pressure. We show that an oscillatory inlet pressure leads to acoustic streaming in the tube, attributed to the nonlinear pressure gradient induced by the interplay of FSI and compressibility. Furthermore, we demonstrate an enhancement in the volumetric flow rate due to FSI coupling. The hydrodynamic pressure oscillations are shown to exhibit a low-pass frequency response (when averaging over the period of oscillations), while the frequency response of the tube deformation is similar to that of a band-pass filter.Comment: 27 pages, 11 figures; v2 revision removes Knudsen number effects and clarifies a few points; accepted for publication in Physics of Fluid