Spectrophotometric determination of silicate in natural waters by formation of α-molybdosilicic acid and reduction with a tin(IV)-ascorbic acid-oxalic acid mixture

Reaction of dissolved silicate with molybdate at pH 3.8–4.8 in acetate buffer yields only the α-molybdosilicic acid. Treatment of this acid with a solution containing tin(IV) chloride, ascorbic acid and oxalic acid rapidly gives the blue reduced acid without reducing the excess of molybdate reagent. In the recommended procedure, Beer's Law is followed at 740 nm over the range 0–2000 μg Si l^-1 with a coefficient of variation of 0.34% at 400 μg Si l^-1 and 0.52% at 40 μg Si l^-1. The sensitivity of the method is not affected by ionic strength.     

The nih-epa chemical information system in support of structure elucidation2

Progress in the development of the NIH—EPA chemical information system is reviewed.     

The probability of MgO surface excitations with fast electrons

A scanning Transmission Electron Microscope has been used to investigate the probability of exciting surface modes in MgO cubes when fast electrons pass a certain distance outside the specimen. The experimental results give reasonable agreement with the classical theory of dielectric excitation by a moving charge providing relativistic effects are included.     

Poloidal E x B drift used as an effective rotational transform to achieve long confinement times in a toroidal electron plasma

Electron plasmas with mean densities of 5.0 x 10(6) cm(-3) have been confined for as long as 18 ms in a partially toroidal trap with a purely toroidal magnetic field (B(0)=196 G, R(o)=43 cm, a=5 cm). Confinement is limited to 2.0 ms unless feedback is employed to suppress the growth of a toroidal version of the m=1 diocotron mode. The confinement time is much longer than all characteristic single-particle drift time scales and therefore confirms the existence of an equilibrium in which the space-charge-generated E x B drift acts as an effective rotational transform.     

Heritability of Stroop and flanker performance in 12-year old children

Background  

There is great interest in appropriate phenotypes that serve as indicator of genetically transmitted frontal (dys)function, such as ADHD. Here we investigate the ability to deal with response conflict, and we ask to what extent performance variation on response interference tasks is caused by genetic variation. We tested a large sample of 12-year old monozygotic and dizygotic twins on two well-known and closely related response interference tasks; the color Stroop task and the Eriksen flanker task. Using structural equation modelling we assessed the heritability of several performance indices derived from those tasks.     

The contribution of high frequencies to human brain activity underlying horizontal localization of natural spatial sounds

Background  

In the field of auditory neuroscience, much research has focused on the neural processes underlying human sound localization. A recent magnetoencephalography (MEG) study investigated localization-related brain activity by measuring the N1m event-related response originating in the auditory cortex. It was found that the dynamic range of the right-hemispheric N1m response, defined as the mean difference in response magnitude between contralateral and ipsilateral stimulation, reflects cortical activity related to the discrimination of horizontal sound direction. Interestingly, the results also suggested that the presence of realistic spectral information within horizontally located spatial sounds resulted in a larger right-hemispheric N1m dynamic range. Spectral cues being predominant at high frequencies, the present study further investigated the issue by removing frequencies from the spatial stimuli with low-pass filtering. This resulted in a stepwise elimination of direction-specific spectral information. Interaural time and level differences were kept constant. The original, unfiltered stimuli were broadband noise signals presented from five frontal horizontal directions and binaurally recorded for eight human subjects with miniature microphones placed in each subject's ear canals. Stimuli were presented to the subjects during MEG registration and in a behavioral listening experiment.