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Diesel soot powder generated under idle and load engine conditions was pressed into pellets at pressures ranging up to approximately 8.5 GPa. Soot powder was also immersed in acetone in order to obtain soot aggregates without agglomeration. Small-angle x-ray scattering was carried out on the powder, the pellets, and on the acetone-immersed soot. Powder and pellets show characteristic aggregate structure at small scattering vectors. Scattering curves of the pellets show a shift of the aggregate size-related scattering feature towards larger scattering vectors for increasing pressure. For the highest pressures, this aggregate structure vanished, while the suspected primary particle scattering became visible as the asymptote of the aggregate scattering structure. Soot was immersed and ultrasonicated in acetone to prevent agglomeration of aggregates, which naturally occurs in powders. This can be considered as the simulation of asymptotic behavior for vanishing pressure. Aggregate size of powder was about 290 nm for the idle soot and 240 nm for the load soot. Primary particle sizes were 14.3 and 10.2 nm, respectively. The idle soot showed a higher compressibility (0.9 GPa/nm) than the load soot (12.0 GPa/nm). Pressing the soot into pellets eliminates scattering structures from aggregation of primary particles and provides a good route to reveal the otherwise inaccessible primary particle scattering. In addition, studying the aggregate structure as a function of pellet pressure allows us to derive compacticity data of the soot. [ABSTRACT FROM AUTHOR]

This study examined the ability of older children to integrate spatial information across sequential observations of bandpass noise. In experiment I, twelve adults and twelve 8–14 yr olds localized 1–5 sounds, all presented at the same location along a 34° speaker array. Rate of gain in response precision (as a function of N observations) was used to measure integration efficiency. Children were no worse at localizing a single sound than adults, and—unexpectedly—were no less efficient at integrating information across observations. Experiment II repeated the task using a Reverse Correlation paradigm. The number of observations was fixed (N = 5), and the location of each sound was independently randomly jittered. Relative weights were computed for each observation interval. Distance from the ideal weight-vector was used to index integration efficiency. The data showed that children were significantly less efficient integrators than adults: only reaching adult-like performance by around 11 yrs. The developmental effect was small, however, relative to the amount of individual variability, with some younger children exhibiting greater efficiency than some adults. This work indicates that sensory integration continues to mature into late childhood, but that this development is relatively gradual. [ABSTRACT FROM AUTHOR]

Eight normal-hearing listeners practiced a tone-detection task in which a 1-kHz target was masked by a spectrally unpredictable multitone complex. Consistent learning was observed, with mean masking decreasing by 6.4 dB over five sessions (4500 trials). Reverse-correlation was used to estimate how listeners weighted each spectral region. Weight-vectors approximated the ideal more closely after practice, indicating that listeners were learning to attend selectively to the task relevant information. Once changes in weights were accounted for, no changes in internal noise (psychometric slope) were observed. It is concluded that this task elicits robust learning, which can be understood primarily as improved selective attention. [ABSTRACT FROM AUTHOR]

This paper examines what mechanisms underlie auditory perceptual learning. Fifteen normal hearing adults performed two-alternative, forced choice, pure tone frequency discrimination for four sessions. External variability was introduced by adding a zero-mean Gaussian random variable to the frequency of each tone. Measures of internal noise, encoding efficiency, bias, and inattentiveness were derived using four methods (model fit, classification boundary, psychometric function, and double-pass consistency). The four methods gave convergent estimates of internal noise, which was found to decrease from 4.52 to 2.93 Hz with practice. No group-mean changes in encoding efficiency, bias, or inattentiveness were observed. It is concluded that learned improvements in frequency discrimination primarily reflect a reduction in internal noise. Data from highly experienced listeners and neural networks performing the same task are also reported. These results also indicated that auditory learning represents internal noise reduction, potentially through the re-weighting of frequency-specific channels. [ABSTRACT FROM AUTHOR]

Automatic tuning of double-crystal monochromators presents an interesting challenge in software. The goal is to either maximize, or hold constant, the throughput of the monochromator. An additional goal of the software feedback is to disable itself when there is no beam and then, at the user’s discretion, re-enable itself when the beam returns. These and other routine goals, such as adherence to limits of travel for positioners, are maintained by software controls. Many solutions exist to lock in and maintain a fixed throughput. Among these include a hardware solution involving a wave form generator, and a lock-in amplifier to autocorrelate the movement of a piezoelectric transducer (PZT) providing fine adjustment of the second crystal Bragg angle. This solution does not work when the positioner is a slow acting device such as a stepping motor. Proportional integral differential (PID) loops have been used to provide feedback through software but additional controls must be provided to maximize the monochromator throughput. Presented here is a software variation of the PID loop which meets the above goals. By using two floating point variables as inputs, representing the intensity of x rays measured before and after the monochromator, it attempts to maximize (or hold constant) the ratio of these two inputs by adjusting an output floating point variable. These floating point variables are connected to hardware channels corresponding to detectors and positioners. When the inputs go out of range, the software will stop making adjustments to the control output. Not limited to monochromator feedback, the software could be used, with beam steering positioners, to maintain a measure of beam position. Advantages of this software feedback are the flexibility of its various components. It has been used with stepping motors and PZTs as positioners. Various devices such as ion chambers, scintillation counters, photodiodes, and photoelectron collectors have been ... [ABSTRACT FROM AUTHOR]