Neuronal spatial learning

Neurons are electrically active structures determined by the evolution of ion-specific pumps and channels that allow the transfer of charges under the influence of electric fields and concentration gradients. Extensive studies of spike timing of neurons and the relationship to learning exist. However, the properties of spatial activations during action potential in the context of learning have to our knowledge not been consistently studied. We examined spatial propagation of electrical signal for many consecutive spikes using recorded information from tetrodes in freely behaving rats before and during rewarded T-maze learning tasks. Analyzing spatial spike propagation in expert medium spiny neurons with the charge movement model we show that electrical flow has directionality which becomes organized with behavioral learning. This implies that neurons within a network may behave as “weak learners” attending to preferred spatial directions in the probably approximately correct sense. Importantly, the organization of spatial electrical activity within the neuronal network could be interpreted as representing a change in spatial activation of neuronal ensemble termed “strong learning.” Together, the subtle yet critical modulations of electrical flow directivity during weak and strong learning represent the dynamics of what happens in the neuronal network during acquisition of a behavioral task.     

Seismic Behavior of Cantilever Retaining Walls with Liquefiable Backfills

A series of centrifuge tests were conducted to investigate the seismic behavior of fixed-base, cantilever, retaining walls supporting saturated, liquefiable, cohesionless backfills. Accelerations, bending strains, deflections, and lateral earth pressures were measured on the walls. Accelerations, pore pressures, and surface settlements were measured in the soil. Parametric studies investigating effects of wall stiffness and magnitude of shaking on the wall-soil behavior were conducted. The magnitude and distribution of lateral earth pressures were determined. Experimental results demonstrated that excess pore pressures in liquefiable backfills contribute significantly to seismic, lateral, earth pressures. It was shown that the average rise in the dynamic thrust is well correlated to the excess pore pressures in the backfill but is insensitive to the range of wall stiffness. It was found that simple calculations, based on Coulomb's active earth pressure theory, can be used to estimate the dynamic thrust at the end of shaking, when backfill liquefies completely. The location of the line of action of the total static lateral thrust was approximately two-thirds of the wall height from the top. During shaking, this distance varied between 0.6 and 0.8 of the wall height.     

Effect of machining parameters on surface roughness and material removal rate in finish turning of ±30° glass fibre reinforced polymer pipes

This paper studies the effect of varying machining parameters in turning on surface roughness and material removal rate (m.r.r.) for ±30° filament wound glass fibre reinforced polymers (GFRP) in turning operations using coated tungsten carbide inserts under dry cutting conditions. The paper describes the development of an empirical model for turning GFRP utilising factorial experiments. Second order predictive model covering speed, feed, depth of cut and tool nose radius has been developed at 95% confidence interval for surface roughness and material removal rate. Contour plots of the surface roughness and m.r.r. for different machining conditions have been generated from the empirical equations. Overlaid contour graph help in obtaining iso-value of roughness for different values of m.r.r.     

Electrochemical sensing of sulphur dioxide: a comparison using dodecanethiol and citrate capped gold nanoclusters

A comparison of cyclic voltammograms of dodecanethiol (DDT) capped Au nanoclusters (5.0 0.5 nm) and trisodium citrate (Cit) capped Au nanoclusters (approximately 10-15 nm) modified glassy carbon electrode shows a dramatic variation in the current when exposed to a small amount of sulphur dioxide. This is explained using the electrocatalytic properties of Au nanoclusters towards the oxidation of SO2, thus facilitating the fabrication of electrochemical sensors for the detection of SO2. The intrinsic redox changes observed for gold nanocluster-modified glassy carbon electrodes disappear on passing SO2, despite a dramatic current increase, which indeed scales up with the amount of dissolved SO2. Interestingly, a complete rejuvenation of the redox behavior of gold is also observed on subsequent removal of SO2 from the solution by passing pure nitrogen for 15 minutes. Further, these nanoclusters when characterized with X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) after SO2 passage reveal a variety of SO2 adsorption modes on gold surface. XP spectra also show a shift of 1.03 eV towards higher binding energy indicating a strong adsorption of SO2 gas, while FTIR gives conclusive evidence for the interaction of SO2 with gold nanoparticles.     

Structural properties of sodium ion implanted poly(vinyl alcohol) films

Poly(vinyl alcohol) (PVA) films were implanted with sodium ions at various energies and total doses. Modified films were characterized by Fourier transform IR (FTIR), UV–visible (UV–vis), X‐ray diffraction (XRD), and scanning electron microscopy (SEM). From FTIR studies, it was evident that scission of the main chain occurred together with removal of hydrogen and hydroxyl groups. Sodium ions formed weak bonds with oxygen from the neighboring chains. UV–vis studies of implanted PVA showed increases in the absorbance values with the various energies and total doses. XRD studies revealed that, as the energy and total dose increased overall, the crystallinity decreased and new peaks at different 2θ values appeared. Changes in the crystallinity were also studied for thermally annealed PVA films in order to correlate and understand the phenomena of recrystallization due to ion implantation. The morphological features of the films were investigated by SEM. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 276–283, 2005     

Estimating manufacturing cycle time and throughput in flow shops with process drift and inspection

Process drift is a common occurrence in many manufacturing processes where machines become dirty (leading to more contamination) or processing parameters degrade, negatively affecting system performance. Statistical process control tracks process quality to determine when the process has gone out of control (has drifted beyond its specifications). This paper considers the case where parts examined at a downstream inspection station are used to determine when the upstream process is out of control. The manufacturing cycle time from the out of control process to the downstream inspection process influences the detection time that elapses until the out of control process is noticed and repaired. Because an out of control process produces more bad parts, the detection time affects the number of good parts produced and the throughput of the manufacturing system. This situation is common in many industries but no models of the phenomena exist. This paper presents a novel manufacturing system model based on queueing network approximations for estimating the manufacturing cycle time and throughput of such systems. These are important performance measures since they influence economic measures such as inventory costs and revenue. The model can be used for a variety of system design and analysis tasks. In particular, the model can be used to evaluate the placement of inspection stations in a process flow.     

Computing Information in Neuronal Spikes

This paper provides new insights regarding the transfer of information between input signal and the output of neurons. Simulations of the Hodgkin-Huxley (HH) model combined with computational techniques are used to estimate this transfer of information. Our analysis shows that comparatively, mutual information (MI) between input signal and sodium flux is about two times that between input signal and output spikes during each spike within a millisecond-level time domain. This higher transfer of information provided by ionic fluxes extends the working frequency domain of neural cells beyond those accessible to information transfer within spikes alone.     

Blending Validation and Content Uniformity of Low-Content, Noncohesive Powder Blends

Blending validation has become mandatory, partly through good manufacturing practice (GMP), partly through a court action (the Barr decision) in 1993. Although feasibly carried out with existing technology, there are situations where the methodology for sampling causes a suspected bias in the figures, and one such case is where the drug content (expressed as fraction in the following) is low. In particular, this dilemma is predominant where the blended materials are not cohesive. Possible explanations for this are voiced, as are suggestions on how to proceed rationally in such cases.     

A potential probiotic culture ST2 produces siderophore 2,3-dihydroxybenzoylserine under intestinal conditions

The aim of this study was to characterise siderophores of a culture bearing better probiotic qualities of human origin. In this direction, bacterial strain ST2 was isolated from faecal sample of 6-month-old healthy infant, which showed close similarity with Escherichia coli based on 16S r-RNA gene sequence analysis and biochemical characteristics. It was tested for siderophore production under in vitro iron limiting intestinal conditions. The siderophore produced was catecholate type of 2,3-dihydroxybenzoylserine on the basis of FTIR, NMR and mass spectra analysis. The strain obeyed probiotic properties as per WHO and FAO guidelines. It showed excellent tolerance in partially simulated gastro-intestinal tract conditions, non-haemolytic nature, susceptibility to many antibiotics tested and antimicrobial activity against enteric pathogens like Salmonella typhimurium, Streptococcus pyogenes, and Staphylococcus aureus. Hence, this culture could be a possible probiotic candidate in iron nutrition, but only after conducting proper animal and human trials.