Effect of electrode material on thermally stimulated discharge and dark current in polystyrene

Thermally stimulated discharge (TSD) currents excited at 110°C by 117 V in 20 μm thick polystyrene (PS) films in contact with Al, Zn, Pb, Cd, Cu and Ni have been measured keeping the other electrode as Al. TSC parameters are observed to change with the choice of electrode material. Maximum charge is stored by PS films in contact with Cu. The observed polarization is explained in terms of detrapping of charges injected from the electrodes with subsequent space-charge formation. The dependence of dark current at 50°C in metal-PS-Al systems on applied voltage in the range 3–117 V has also been investigated. Current density-square root voltage plots are observed to have straight portions at high field values. Zero field current density extrapolated from these plots and TSC activation energy are found to vary with metal work function qualitatively in a similar manner.     

Photo-polarisation in pure and doped polystyrene

Depolarisation currents have been measured of the photo-electrets of pure and copperphthalocyanine doped polystyrene films using UV-radiation. A hyperbolic decay law is observed suggesting bimolecular recombination process. Doped films show strong saturation with the applied field supporting a trap filling mechanism.     

Thermally stimulated discharge current studies in copper phthalocyanine - doped polystyrene films

To improve the electret characteristics, TSD current studies of copper phthalocyanine - doped polystyrene films of about 20 microns thickness have been made as a function of doping concentration, poling temperature and field. Generally the thermograms observed exhibit α and ρ peaks. The activation energy is found to decrease as the concentration of the dopant in the polymer is increased. It is established that keeping the forming field constant and by increasing the concentration of the dopant, the same polarisation can be obtained at a lower poling temperature. A Maxwell-Wagner two-phase model with space - charge build-up seems to provide a possible mechanism for the polarisation.     

VELOCITY PROFILES OF NEWTONIAN AND NON-NEWTONIAN TOROIDAL FLOWS MEASURED BY A LDA TECHNIQUE

Laser Doppler Anemomeiry was used to measure the primary (axial) and secondary (recirculating) velocity profiles in laminar flows of Newtonian (ethylene glycol) and non-Newtonian (aqueous solutions of CMC and PAA) liquids in curved tubes. Rheological characteristics of these liquids were measured using standard viscometric techniques (Haake and Mechanical Spectrometer). The effect of the shear-thinning viscosity is to flatten the axial velocity profile while enhancing the circulating flow close to the walls. On the other hand, the viscoelasticity reduces the extent of the secondary flow for all Dean numbers. This fact explains the reduction of laminar friction reported in the literature.

The primary and secondary velocity profiles, which appear to be the first ones ever published for the toroidal flows, are compared with the predictions of numerical simulation. The agreement is good when comparing the profiles of the axial flow but it is unsatisfactory for the secondary flows.     

Exact train pathing

Suppose we are given a schedule of train movements over a rail network into which a new train is to be included. The origin and the destination are specified for the new train; it is required that a schedule (including the path) be determined for it so as to minimize the time taken without affecting the schedules for the old trains. In the standard formulations of this single train pathing problem, the time taken by the train to traverse any block (track segment guarded by a signal) in the network is deemed to be a fixed number, independent of how the train arrived onto that block. In other words, the standard formulations of train pathing do not accurately model the acceleration/deceleration restrictions on trains. In this paper we give an algorithm to solve the single train pathing problem, while taking into account the maximum allowed acceleration and deceleration as well as explicitly modeling signals. For trains having ‘large’ maximum acceleration and deceleration, our algorithm runs in polynomial time. On the other hand, if the train to be pathed is capable of only very small acceleration so that it must take a long time to reach full speed, our algorithm takes exponential time. However, we prove that the pathing problem is NP-complete for small acceleration values, thus justifying the time required by our algorithm. Our algorithm can be used as a subroutine in a heuristic for multiple train pathing. If all trains have large (but possibly different) accelerations this algorithm will run in polynomial time. V. Nagarajan is supported in part by NSF grant CCF-0728841.     

Role of AgNPs in the enhancement of seed germination and its effect on plumule and radicle length of Pennisetum glaucum

The authors have investigated beneficial effects of 1 mM of silver nanoparticles (AgNPs) on agriculturally important plant Pennisetum glaucum (Bajara). The extracellular AgNPs were synthesised using Bacillus subtilis spizizenni and characterised using ultraviolet–visible absorption spectroscopy, Fourier transform infrared spectroscopy (FT‐IR) and transmission electron microscopy (TEM). Optical absorption spectrum showed characteristic peak of AgNPs at 423 nm. FT‐IR analysis of AgNPs showed peak at 3435 cm⁻¹, which indicates the presence of N–H group (primary, secondary amines and amides) on the surface of AgNPs. TEM studies indicate that synthesised AgNPs have average size of ∼2 nm. Energy dispersive X‐ray spectroscopy showed strong signal of Ag at 3 keV. Treatment of 1 mM AgNPs to the bajara seeds was found to be sufficient for excellent germination of seeds within 3 days. There was also significant increase in radicle and plumule length as compared with control bajara seeds according to statistical analysis by one‐way analysis of variance, followed by Tukey''s test. The percentage of AgNPs detected in root samples was 0.003% (by inductively coupled plasma atomic emission spectroscopy), which is negligible. There is still need to study the bioavailability and the type of interaction of AgNPs with plants, necessary for application in agriculture.Inspec keywords: transmission electron microscopy, ultraviolet spectra, scanning electron microscopy, nanofabrication, X‐ray diffraction, nanoparticles, visible spectra, silver, atomic emission spectroscopy, X‐ray chemical analysis, Fourier transform infrared spectra, statistical analysis, agricultureOther keywords: ultraviolet–visible absorption spectroscopy, transmission electron microscopy, Pennisetum glaucum, Bacillus subtilis spizizenni, energy dispersive X‐ray spectroscopy, Fourier transform infrared spectroscopy, optical absorption spectrum, plumule length, radicle length, silver nanoparticles, Tukey''s test, inductively coupled plasma atomic emission spectroscopy, statistical analysis, Bajara seeds, scanning electron microscopy, X‐ray diffraction, analysis of variance, electron volt energy 3.0 keV, time 3.0 d, Ag     

Hydrodynamics and liquid phase residence time distribution in mesh microreactor

This paper is focused on the experimental analysis of residence time distribution and phase hold-up in a mesh microreactor. A microreactor, where a finely weaved mesh is sandwiched between two flat plates with specific inlets for gas and liquid, is proposed. The microvolumes formed upon sandwiching the mesh are totally connected and thus it yields a view of several interconnected microvolumes. This system is easy to build and does not need precision micromachining. A high-speed photographic analysis yielded the phase distribution for different mesh types over a wide range of operating gas and liquid flow rates. The RTD was studied by measuring the liquid phase conductivity at the outlet of the reactor. Channeling prevailed for mesh with smaller open area. The ADEM was used for fitting the tracer curves with tailing ends. The RTD and the image analysis for all the mesh types showed hysteresis when the gas flow rate was maintained constant and the liquid flow rate was gradually increased and then decreased.     

RAPD profile variation amongst provenances of neem

Neem, described as a tree for solving global problems, is an evergreen, long-lived, multipurpose tree of the tropics with a wide distribution range in India. It is believed to be highly cross-pollinated. Inter-provenance variations have been reported in neem in case of morphological and physiological characters. Yet no reports about the genetic determinism for these variations are available to our knowledge. In order to have an idea about the extent and/or nature of genetic (DNA) variation in neem, the powerful RAPD technique has been employed. RAPD profiles of 34 accessions/provenances of neem were generated with 200 decamer random primers, of which the data from the 49 primers, that resulted in reproducible amplification products, were considered for analysis. Based on the presence/absence of bands, a similarity matrix was computed. Dendrogram was constructed by UPGMA method based on the pairwise similarities amongst the RAPD profiles. The similarities in RAPD profiles amongst the different DNAs was more than that expected due to the cross-pollinated nature of the tree and furthermore, these more-than-expected similarities were not due to random chance. These results suggest that neem may have a narrow genetic base.     

Iron, zinc, copper, manganese and magnesium in malignant lymphomas

Lymph node and spleen tissues involved in malignant lymphomas were analysed for iron, manganese, copper, zinc and magnesium by atomic absorption spectrophotometry. The levels of iron are found to be significantly lower in the case of Hodgkin's lymphoma compared with non-Hodgkin's lymphoma and normal lymph nodes. However, they are elevated in Hodgkin's lymphoma when compared with the normal value for spleen tissues. Magnesium is significantly higher in lymph nodes of non-Hodgkin's lymphoma compared with Hodgkin's lymphoma and normal values, but is not altered significantly in spleen tissues. The distribution of the other elements examined is not altered significantly in malignant lymphomas. The importance of the in situ levels of these elements to NMR imaging is discussed.     

Temperature dependence and energetics of the equilibrium sorption of water vapor in glassy polyacrylonitrile

Equilibrium sorption isotherms for water vapor in commercial polyacrylonitrile film are presented. The data are discussed in terms of hte dual-mode sorption model at low vapor activities with cluster formation occuring at higher activities. The film samples were treated by a two-stage extraction process to remove a tenaciously held solvent present from the manufacturing process. Extraction of the residual had a minor effect on the equilibrium sorption of water in the film. The temperature dependence of the various sorption parameters is presented and discussed in detailed.