Cortical surface shape analysis based on spherical wavelets

In vivo quantification of neuroanatomical shape variations is possible due to recent advances in medical imaging and has proven useful in the study of neuropathology and neurodevelopment. In this paper, we apply a spherical wavelet transformation to extract shape features of cortical surfaces reconstructed from magnetic resonance images (MRIs) of a set of subjects. The spherical wavelet transformation can characterize the underlying functions in a local fashion in both space and frequency, in contrast to spherical harmonics that have a global basis set. We perform principal component analysis (PCA) on these wavelet shape features to study patterns of shape variation within normal population from coarse to fine resolution. In addition, we study the development of cortical folding in newborns using the Gompertz model in the wavelet domain, which allows us to characterize the order of development of large-scale and finer folding patterns independently. Given a limited amount of training data, we use a regularization framework to estimate the parameters of the Gompertz model to improve the prediction performance on new data. We develop an efficient method to estimate this regularized Gompertz model based on the Broyden-Fletcher-Goldfarb-Shannon (BFGS) approximation. Promising results are presented using both PCA and the folding development model in the wavelet domain. The cortical folding development model provides quantitative anatomic information regarding macroscopic cortical folding development and may be of potential use as a biomarker for early diagnosis of neurologic deficits in newborns.     

System for Precise Control of Volumetric Flow Rate during Sampling with a Cascade Impactor

Calculations were made with efficiency curves developed for the micro-orifice impactor (MOI) to estimate errors in mass collected on individual stages due to fluctuations in the flow rate during sampling of submicrometer particles. The sizes of these errors depend on the size distribution of the sampled aerosol and the level of flow rate fluctuation. For a log-normally distributed particle population, mass errors due to flow rate fluctuations were bimodally distributed about stages with cutpoints near the aerosol Mass Median Aerodynamic Diameter (MMAD). The largest errors occurred uniformly on the stage with the smallest cutpoint (here, 0.059 w m). These errors were asymmetric with respect to sign, which leads to a net error for a randomly fluctuating flow rate. In general, mass errors increased with decreasing geometric standard deviation ( σ g ) and were substantially greater for populations with 0.5 w m MMADs than for those with 0.2 w m MMADs. The largest net errors for the former were 4, 110, and 560% for σ g of 1.2 and flow rate fluctuations of - 1, - 5, and - 10%, respectively, but decreased to 0.03, 0.9, and 4%, respectively, for a σ g of 1.9. Flow rate fluctuations, therefore, lead to a positive bias in the geometric standard deviation inferred from the measured masses and reduce the user's ability to interpret differences in size distributions. To minimize these effects, we developed and tested a system for controlling the volumetric sampling rate through a MOI at 30 LPM with a precision of 0.06% (600 ms averaging; 0.67% for 5 ms averaging), a level of precision that allows for accurate relative calibration between flow systems and for which errors from flow rate fluctuations are reduced to <1%, even for a very narrow aerosol ( σ g 1.2). Mass errors for an uncontrolled field test were as large as -60%, but these were reduced to <0.22% in a comparable controlled field test. In two replicate tests of the system, agreements between stage masses collected on MOI stage 7 ( D 50 = 0.173 w m) of two simultaneously operated flow-controlled impactors sampling 0.2 w m diameter monodisperse test particles were 0.997 and 0.996, although differences as large as 4% were observed for some stages. The system is suitable for use with standard "Federal Reference Method" samplers.     

On the forced convective heat transport in a droplet-laden flow in microchannels

Recently, a great deal of attention has been focused on development of microfabricated devices for manipulating minute amounts of liquids. In particular, an extensive experimental work is devoted to generation, motion and manipulation of drops in microfluidic channels, or digital microfluidics. In the present work the numerical approach based on volume-of-fluid method, combined with the piece-wise linear interface reconstruction scheme, is implemented for modeling of droplet motion and forced heat transport in a droplet-laden laminar flow in a circular microchannel. The simulations show a very good agreement with asymptotic results concerning the motion of spherical and slender drops in confined laminar flows. The effective rates of the forced heat transfer in a droplet-laden flow are found to be superior over that in single-phase Poiseuille flow. The enhancement is anticipated to be a result of the flow disturbance in the carrier fluid due to propagation of a train of translating drops and efficient convective transport within drops due to internal circulation.

Incremental deployment of network monitors based on Group Betweenness Centrality

In many applications we are required to increase the deployment of a distributed monitoring system on an evolving network. In this paper we present a new method for finding candidate locations for additional deployment in the network. This method is based on the Group Betweenness Centrality (GBC) measure that is used to estimate the influence of a group of nodes over the information flow in the network. The new method assists in finding the location of k additional monitors in the evolving network, such that the portion of additional traffic covered is at least (1−1/e) of the optimal.     

Frictional properties of light-activated antimicrobial polymers in blood vessels

The adhesion of microbes to catheter surfaces is a serious problem and the resulting infections frequently lead to longer hospitalisation and higher risk for the patient. Several approaches have been developed to produce materials that are less susceptible to microbial colonisation. One such approach is the incorporation of photoactivated compounds, such as Toluidine Blue O (TBO), in the polymeric matrix resulting in ‘light-activated antimicrobial materials’. The insertion and removal of catheters can cause tissue damage and patient discomfort through frictional forces; hence the lubricity of a catheter material is also very important. In this work the tribological performance of silicone and polyurethane containing TBO and gold nanoparticles were evaluated using two different surfaces, the inner part of the aorta and the superior vena cava of sheep. Static and kinetic friction coefficients of these materials were measured using a tribometric device developed for in vitro applications using dry materials and those lubricated with blood. It was found that neither the preparation process nor the presence of TBO or gold nanoparticles, had an effect on the friction factors in comparison to those of untreated materials. In all cases, static and kinetic friction coefficients on aorta tissue were higher than those on vena cava due to higher surface roughness of the aorta. The presence of blood as a lubricant resulted in lower friction coefficients.     

Novel method for the preparation of Cs-containing FAU(Y) catalysts for aniline methylation

Cs-containing FAU(Y)-type zeolite catalysts were prepared by conventional and novel ion exchange procedures followed by incipient wetness impregnation with CsOH. The novel ion exchange procedure involved hydrothermal treatment of NaY zeolite in aqueous solution of CsCl at 140–200 °C for 6–24 h. The samples were characterized by low-temperature nitrogen adsorption, X-ray fluorescence analysis, X-ray powder diffraction, scanning electron microscopy, ²³Na, ²⁷Al and ¹³³Cs magic angle spinning nuclear magnetic resonance, CO₂ and NH₃-Temperature programmed desorption. The results show that hydrothermal treatment at 200 °C allows to obtain higher degrees of ion-exchange (up to 83%) with respect to conventional method giving maximum 66%–69%. Catalytic properties of Cs-containing FAU(Y) were studied in aniline methylation. The yield of N-methylaniline is shown to correlate with catalyst’s basicity. The best catalyst performance was achieved over the catalyst with the highest ion-exchange degree impregnated with CsOH. The selectivity to N-methylaniline over this catalyst reached 96.4%.

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Testing the Role of Glutamate NMDA Receptors in Peripheral Trigeminal Nociception Implicated in Migraine Pain

The pro-nociceptive role of glutamate in the CNS in migraine pathophysiology is well established. Glutamate, released from trigeminal afferents, activates second order nociceptive neurons in the brainstem. However, the function of peripheral glutamate receptors in the trigeminovascular system suggested as the origin site for migraine pain, is less known. In the current project, we used calcium imaging and patch clamp recordings from trigeminal ganglion (TG) neurons, immunolabelling, CGRP assay and direct electrophysiological recordings from rat meningeal afferents to investigate the role of glutamate in trigeminal nociception. Glutamate, aspartate, and, to a lesser extent, NMDA under free-magnesium conditions, evoked calcium transients in a fraction of isolated TG neurons, indicating functional expression of NMDA receptors. The fraction of NMDA sensitive neurons was increased by the migraine mediator CGRP. NMDA also activated slowly desensitizing currents in 37% of TG neurons. However, neither glutamate nor NMDA changed the level of extracellular CGRP. TG neurons expressed both GluN2A and GluN2B subunits of NMDA receptors. In addition, after removal of magnesium, NMDA activated persistent spiking activity in a fraction of trigeminal nerve fibers in meninges. Thus, glutamate activates NMDA receptors in somas of TG neurons and their meningeal nerve terminals in magnesium-dependent manner. These findings suggest that peripherally released glutamate can promote excitation of meningeal afferents implicated in generation of migraine pain in conditions of inherited or acquired reduced magnesium blockage of NMDA channels and support the usage of magnesium supplements in migraine.     

In vitro dissolution of bioactive glass S53P4 microspheres

Static and dynamic in vitro dissolution studies showed large differences for various size-fractions of non-porous, flame-sprayed commercial microspheres (45–500 µm) of bioactive glass S53P4. The smaller the spheres, the more their composition deviated from the nominal glass. The dissolution studies were carried out in simulated body fluid and tris(hydroxymethyl) aminomethane buffer for seven days. The ion concentrations in solutions were analyzed using inductively coupled plasma optical emission spectrometry, and the pH was measured as a function of time. Also, changes in the sphere size distribution and mass losses were determined. The calcium phosphate and the silica-rich layers at the sphere surfaces were investigated using scanning electron microscopy after several immersion times. The smallest (45–90 µm) spheres appeared almost inert. In contrast, typical silica-rich and calcium phosphate layers were identified at the largest spheres after three days of static and dynamic dissolutions. During the past years, bioactive glass microspheres have been added to paste-like injectable bone grafting materials, putties to enhance their molding properties. The obtained results provide a better understanding of the dissolution patterns of bioactive glass microspheres.