Sixteen new IR laser dyes

Sixteen new IR laser dyes are reported. All lased successfully under excitation from a simple linear flashlamp of about 700-ns rise time. Untuned lasing wavelengths ranged from 810 to 972 nm. Laser output pulse energies from the four best of these dyes were 5-15 times greater than from diethylthiatricarbocyanine iodide (DTTC), with peak output of about 50 mJ obtained from 128-J excitation. Solvent effects with four selected laser dyes are also discussed.     

A point process model for auditory neurons considering both their intrinsic dynamics and the spectrotemporal properties of an extrinsic signal

We propose a point process model of spiking activity from auditory neurons. The model takes account of the neuron's intrinsic dynamics as well as the spectrotemporal properties of an input stimulus. A discrete Volterra expansion is used to derive the form of the conditional intensity function. The Volterra expansion models the neuron's baseline spike rate, its intrinsic dynamics-spiking history-and the stimulus effect which in this case is the analog of the spectrotemporal receptive field (STRF). We performed the model fitting efficiently in a generalized linear model framework using ridge regression to address properly this ill-posed maximum likelihood estimation problem. The model provides an excellent fit to spiking activity from 55 auditory nerve neurons. The STRF-like representation estimated jointly with the neuron's intrinsic dynamics may offer more accurate characterizations of neural activity in the auditory system than current ones based solely on the STRF.     

Alteration of Fatty Acid Profile in Fragile X Syndrome

Fragile X Syndrome (FXS) is the most prevalent monogenic cause of Autism Spectrum Disorders (ASDs). Despite a common genetic etiology, the affected individuals display heterogenous metabolic abnormalities including hypocholesterolemia. Although changes in the metabolism of fatty acids (FAs) have been reported in various neuropsychiatric disorders, it has not been explored in humans with FXS. In this study, we investigated the FA profiles of two different groups: (1) an Argentinian group, including FXS individuals and age- and sex-matched controls, and (2) a French-Canadian group, including FXS individuals and their age- and sex-matched controls. Since phospholipid FAs are an indicator of medium-term diet and endogenous metabolism, we quantified the FA profile in plasma phospholipids using gas chromatography. Our results showed significantly lower levels in various plasma FAs including saturated, monosaturated, ω-6 polyunsaturated, and ω-3 polyunsaturated FAs in FXS individuals compared to the controls. A decrease in the EPA/ALA (eicosapentaenoic acid/alpha linoleic acid) ratio and an increase in the DPA/EPA (docosapentaenoic acid/eicosapentaenoic acid) ratio suggest an alteration associated with desaturase and elongase activity, respectively. We conclude that FXS individuals present an abnormal profile of FAs, specifically FAs belonging to the ω-3 family, that might open new avenues of treatment to improve core symptoms of the disorder.     

An Optimum Combination of Power Levels and Combiner Weighting for Generating 64-QAM from Three 4-PSK Signals

64 state quadrature amplitude modulation (64-QAM) can be generated by combining three 4-PSK signals, thereby allowing nonlinear amplifiers with smaller power ratings to be used. An optimum combination of amplifier power levels and combiner weighting is described which results in no lost power when the peak power state of the 64-QAM signal is being keyed.     

Peptides Derived from Growth Factors to Treat Alzheimer’s Disease

Alzheimer’s disease (AD) is a devastating neurodegenerative disease characterized by progressive neuron losses in memory-related brain structures. The classical features of AD are a dysregulation of the cholinergic system, the accumulation of amyloid plaques, and neurofibrillary tangles. Unfortunately, current treatments are unable to cure or even delay the progression of the disease. Therefore, new therapeutic strategies have emerged, such as the exogenous administration of neurotrophic factors (e.g., NGF and BDNF) that are deficient or dysregulated in AD. However, their low capacity to cross the blood–brain barrier and their exorbitant cost currently limit their use. To overcome these limitations, short peptides mimicking the binding receptor sites of these growth factors have been developed. Such peptides can target selective signaling pathways involved in neuron survival, differentiation, and/or maintenance. This review focuses on growth factors and their derived peptides as potential treatment for AD. It describes (1) the physiological functions of growth factors in the brain, their neuronal signaling pathways, and alteration in AD; (2) the strategies to develop peptides derived from growth factor and their capacity to mimic the role of native proteins; and (3) new advancements and potential in using these molecules as therapeutic treatments for AD, as well as their limitations.     

On properties of royalty and tax regimes in Alberta’s oil sands

Simulation models that include royalty and tax provisions are used to examine the distribution between developers and governments of net returns from the development of Alberta’s oil sands deposits. A specific focus is to assess the effects on the level and distribution of net revenues associated with a number of changes in assumed revenue and expenditure conditions. Developers typically bear a greater share of the consequences of variations in capital expenditures than they do of changes in operating expenditures, prices, and exchange rates. A comparison across royalty and tax regimes suggest that there is a positive relationship between the level of net revenues estimated to accrue to either developers or governments and the share of the consequences of changes in conditions borne by that party. Some differences across production technologies are noted. The role of the federal government as a fiscal player in oil sands development has shrunk over time. In contrast, under the current regime, the Government of Alberta captures a higher share of net returns and typically bears a greater proportion of the consequences of changes in conditions than at any time since the introduction of an explicit royalty and tax regime in 1997.     

Pore network simulations of drying of capillary porous media. Influence of thermal gradients

A pore network model of drying with heat transfer is developed. The model is applied to study the influence of surface tension gradients induced by thermal gradients on the phase distribution within a capillary porous medium. The numerical simulations show that surface tension gradients can lead to invasion percolation in a destabilizing gradient (IPDG) patterns or invasion percolation in a stabilizing gradient patterns depending on the sign of thermal gradient. The surface tension gradient effect is shown to be significant for sufficiently weakly disordered porous media. The results are summarized on a phase diagram delineating the various patterns that can be expected as functions of thermal gradient and disorder parameter. This diagram is pertinent to situations where occupation probability gradients induced by viscous or gravity effects are negligible.The results also indicate the possibility of a somewhat paradoxical convective drying situation when thermal gradients and disorder are such that a IPDG pattern develops. In this case, contrary to more conventional situations, it may be much more efficient to blow an air colder than the porous medium initial temperature.     

Nanostructured Superconductors With Asymmetric Pinning Potentials: Vortex Ratchets

Ratchets formed from spatially asymmetric confining potentials can rectify an oscillatory driving force and generate directed motion. Such devices can probe the fundamental nature of particle transport in nanoscale systems, both solid state and biological. Vortices in superconductors form an ideal system for exploring ratchet phenomena. Various techniques are available for producing nanostructured pinning landscapes that can provide tailored asymmetries for vortex ratchets. Progress in the theory and experimental implementations of vortex ratchets will be reviewed. In many cases, intervortex interactions in ratchet structures result in intriguing collective effects in the vortex transport, such as reversals in the sense of the rectification. Future vortex ratchet investigations may probe possible quantum mechanical ratchet effects, explore the dynamics of single vortices in ratchets, and test vortex devices based on ratchet phenomena.