Conditional associative learning is impaired in cerebellar disease in humans.

Eight patients with lesions restricted to the cerebellum were compared with a total of 25 age-matched controls on an reaction time (RT) task allowing the recording of simple and choice RTs as well as RTs to abstract visual patterns signifying the particular movement to be performed. In all conditions the actual movements required (either a left or a right button press) remained the same, but the cognitive requirements of the task varied. In the abstract patterns condition, the significance of the various patterns with regard to the required movement had to be learned by the Ss. The patients with cerebellar lesions were particularly impaired in this condition. It is concluded that the cerebellum is involved not just in the timing of movements but also in the decision process as to which movement should be performed under particular circumstances. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanical properties of functionally graded 2-D cellular structures: A finite element simulation

Functionally graded cellular structures such as bio-inspired functionally graded materials for manufacturing implants or bone replacement, are a class of materials with low densities and novel physical, mechanical, thermal, electrical and acoustic properties. A gradual increase in cell size distribution, can impart many improved properties which may not be achieved by having a uniform cellular structure.The material properties of functionally graded cellular structures as a function of density gradient have not been previously addressed within the literature. In this study, the finite element method is used to investigate the compressive uniaxial and biaxial behavior of functionally graded Voronoi structures. Furthermore, the effect of missing cell walls on its overall mechanical (elastic, plastic, and creep) properties is investigated.The finite element analysis showed that the overall effective elastic modulus and yield strength of structures increased by increasing the density gradient. However, the overall elastic modulus of functionally graded structures was more sensitive to density gradient than the overall yield strength. The study also showed that the functionally graded structures with different density gradient had similar sensitivity to random missing cell walls. Creep analysis suggested that the structures with higher density gradient had lower steady-state creep rate compared to that of structures with lower density gradient.     

Plastic microfluidic devices modified with polyelectrolyte multilayers

Control of the polymer surface chemistry is a crucial aspect of development of plastic microfluidic devices. When commercially available plastic substrates are used to fabricate microchannels, differences in the EOF mobility from plastic to plastic can be very high. Therefore, we have used polyelectrolyte multilayers (PEMs) to alter the surface of microchannels fabricated in plastics. Optimal modification of the microchannel surfaces was obtained by coating the channels with alternating layers of poly(allylamine hydrochloride) and poly(styrene sulfonate). Polystyrene (PS) and poly(ethylene terephthalate) glycol (PETG) were chosen as substrate materials because of the significant differences in the polymer chemistries and in the EOF of channels fabricated in these two plastic materials. The efficacy of the surface modification has been evaluated using XPS and by measuring the EOF mobility. When microchannels prepared in both PS and PETG are modified with PEMs, they demonstrate very similar electroosmotic mobilities. The PEMs are easily fabricated and provide a means for controlling the flow direction and the electroosmotic mobility in the channels. The PEM-coated microchannels have excellent wettability, allowing facile filling of the channels. In addition, the PEMs produce reproducible results and are robust enough to withstand long-term storage.     

Quantitative X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry characterization of the components in DNA

The great diversity of techniques to synthesize and use DNA microarrays has made them extremely flexible for a variety of applications. This flexibility also has made standardization difficult, leading to problems comparing data from these different systems. In this work, we use the surface science techniques of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to analyze the components of DNA. The atomic ratios of the components of nucleobases, nucleosides, and nucleotides were characterized by XPS. The chemical shifts in the high-resolution XPS spectra allow for their relatively easy resolution. The unique positive and negative ions from the nucleobases, nucleosides, and nucleotides in their TOF-SIMS spectra were identified. This information was used to build a comprehensive table of all of the molecular ions. These standard spectra of DNA components can be used to predict the relative amounts of the bases within more complex molecules either by univariate analysis (i.e., by relating the base molecular ions to the sugar fragment ions within the nucleotides) or by multivariate analysis (e.g., principal component analysis). Our preliminary examination of four oligonucleotides shows promising results in that we can distinguish between two oligomers of similar composition using univariate and multivariate analysis, although additional studies are needed to expand this method to more complex oligomers.     

Geochemistry of trace metals in a fresh water sediment: field results and diagenetic modeling

Concentrations of Fe, Mn, Cd, Co, Ni, Pb, and Zn were determined in pore water and sediment of a coastal fresh water lake (Haringvliet Lake, The Netherlands). Elevated sediment trace metal concentrations reflect anthropogenic inputs from the Rhine and Meuse Rivers. Pore water and sediment analyses, together with thermodynamic calculations, indicate a shift in trace metal speciation from oxide-bound to sulfide-bound over the upper 20 cm of the sediment. Concentrations of reducible Fe and Mn decline with increasing depth, but do not reach zero values at 20 cm depth. The reducible phases are relatively more important for the binding of Co, Ni, and Zn than for Pb and Cd. Pore waters exhibit supersaturation with respect to Zn, Pb, Co, and Cd monosulfides, while significant fractions of Ni and Co are bound to pyrite. A multi-component, diagenetic model developed for organic matter degradation was expanded to include Zn and Ni dynamics. Pore water transport of trace metals is primarily diffusive, with a lesser contribution of bioirrigation. Reactions affecting trace metal mobility near the sediment-water interface, especially sulfide oxidation and sorption to newly formed oxides, strongly influence the modeled estimates of the diffusive effluxes to the overlying water. Model results imply less efficient sediment retention of Ni than Zn. Sensitivity analyses show that increased bioturbation and sulfate availability, which are expected upon restoration of estuarine conditions in the lake, should increase the sulfide bound fractions of Zn and Ni in the sediments.     

Potential effects of forest fire and storm flow on total mercury and methylmercury in sediments of an arid-lands reservoir

A study was conducted from July 1995 to June 1996 to examine the spatial and temporal changes of mercury concentrations in sediments of an arid-lands reservoir. Prior to the first sample collection in July, a forest fire burned 2930 ha of mixed conifer and ponderosa pine in the watershed of Caballo Reservoir in south-central New Mexico. The fire was eventually extinguished by summer rains and storm runoff resulting in the mobilization and transport of charred vegetative material into an intermittent tributary (Palomas Creek) that drains the watershed into Caballo Reservoir. Concentrations of total mercury (THg), monomethlymercury (MMHg), and total organic carbon (TOC) in surficial sediments revealed fire, followed by storm runoff, enhanced the transport of mercury and organic matter to the reservoir. Concentrations of THg in sediments increased from 7.5 etag/g in July to 46.1 etag/g by November 1995 at one site (Palomas) nearest the outflow of Palomas Creek. No other spatial or temporal trends were observed for THg at other sites throughout the remainder of the study. Concentrations of MMHg in sediments at the Palomas site increased from 0.428 etag/g in July to 12.46 etag/g by October 1995 compared to concentrations in sediments at the remaining sites which ranged from 0.11 to 1.50 etag/g throughout the study. The ratio of MMHg to THg (a gross index of methylation activity) was greatest in sediments from the Palomas site (5.4-33.8%) compared to the remaining sites (0.01-3.60%). The ratio was mirrored by elevated TOC in sediments at the Palomas site (2.5-11.8%) that remained elevated throughout the study. Fire and subsequent late-summer rains may have had a twofold effect on mercury concentrations in Caballo Reservoir. The storm-driven runoff following the forest fire carried mercury complexed to organic matter which resulted in elevated levels of mercury as well as providing a carbon source for microbial methylation processes in sediment.