Lot Splitting in Stochastic Flow Shop and Job Shop Environments

In recent years many firms have been implementing small lot size production. Lot splitting breaks large orders into smaller transfer lots and offers the ability to move parts more quickly through the production process. This paper extends the deterministic studies by investigating various lot splitting policies in both stochastic job shop and stochastic flow shop settings using performance measures of mean flow time and the standard deviation of flow time. Using a computer simulation experiment, we found that in stochastic dynamic job shops, the number of lot splits is more important than the exact fonn of splitting. However, when optimal job sizes are determined for each scenario, we found a few circumstances where the implementation of a small initial split, called a "flag," can provide measurable improvement in flow time performance. Interestingly, the vast majority of previous research indicates that methods other than equal lot splitting typically improves makespan performance. The earlier research, however, has been set in the static, deterministic flow shop environment. Thus, our results are of practical interest since they show that the specific method of lot splitting is important in only a small set of realistic environments while the choice of an appropriate number of splits is typically more important

Circumstellar grain extinction properties of recently discovered post AGB stars

The circumstellar grains of two hot evolved post asymptotic giant branch (post AGB) stars, HD 89353 and HD 213985 were examined. From ultraviolet spectra, energy balance of the flux, and Kurucz models, the extinction around 2175 A was derived. With visual spectra, an attempt was made to detect 6614 A diffuse band absorption arising from the circumstellar grains so that we could examine the relationship of these features to the infrared features. For both stars, we did not detect any diffuse band absorption at 6614 A, implying the carrier of this diffuse band is not the carrier of the unidentified infrared features not of the 2175 A bump. The linear ultraviolet extinction of the carbon-rich star HD 89353 was determined to continue across the 2175 A region with no sign of the bump; for HD 213985 it was found to be the reverse: a strong, wide bump in the mid-ultraviolet. The 213985 bump was found to be positioned at 2340 A, longward of its usual position in the interstellar medium. Since HD 213985 was determined to have excess carbon, the bump probably arises from a carbonaceous grain. Thus, in view of the ultraviolet and infrared properties of the two post AGB stars, ubiquitous interstellar infrared emission features do not seem to be associated with the 2175 A bump. Instead, the infrared features seem related to the linear ultraviolet extinction component: hydrocarbon grains of radius less than 300 A are present with the linear HD 89353 extinction; amorphous anhydrous carbonaceous grains of radius less than 50 A might cause the shifted ultraviolet extinction bump of HD 213985

Aging and Spectro-Temporal Integration of Speech

The purpose of this study was to determine the effects of age on the spectro-temporal integration of speech. The hypothesis was that the integration of speech fragments distributed over frequency, time, and ear of presentation is reduced in older listeners—even for those with good audiometric hearing. Younger, middle-aged, and older listeners (10 per group) with good audiometric hearing participated. They were each tested under seven conditions that encompassed combinations of spectral, temporal, and binaural integration. Sentences were filtered into two bands centered at 500 Hz and 2500 Hz, with criterion bandwidth tailored for each participant. In some conditions, the speech bands were individually square wave interrupted at a rate of 10 Hz. Configurations of uninterrupted, synchronously interrupted, and asynchronously interrupted frequency bands were constructed that constituted speech fragments distributed across frequency, time, and ear of presentation. The over-arching finding was that, for most configurations, performance was not differentially affected by listener age. Although speech intelligibility varied across condition, there was no evidence of performance deficits in older listeners in any condition. This study indicates that age, per se, does not necessarily undermine the ability to integrate fragments of speech dispersed across frequency and time

Gap Detection in School-Age Children and Adults: Center Frequency and Ramp Duration

The age at which gap detection becomes adultlike differs, depending on the stimulus characteristics. The present study evaluated whether the developmental trajectory differs as a function of stimulus frequency region or duration of the onset and offset ramps bounding the gap

Cochlear hearing loss and the detection of sinusoidal versus random amplitude modulation

This study assessed the effect of cochlear hearing loss on detection of random and sinusoidal amplitude modulation. Listeners with hearing loss and normal-hearing listeners (eight per group) generated temporal modulation transfer functions (TMTFs) for envelope fluctuations carried by a 2000-Hz pure tone. TMTFs for the two groups were similar at low modulation rates but diverged at higher rates presumably because of differences in frequency selectivity. For both groups, detection of random modulation was poorer than for sinusoidal modulation at lower rates but the reverse occurred at higher rates. No evidence was found that cochlear hearing loss, per se, affects modulation detection

The weakness of diffuse bands in nebular environments. Possible impact on thePAH+ hypothesis

It has been widely suggested that PAH cations (PAH+) may be the carriers of the diffuse interstellar bands, so it is of interest to probe diffuse behavior in regions suspected of having high abundances of PAHs. Here we examine the strengths of several of the visible-wavelength diffuse interstellar bands in two nebular environments where infrared emission and ultraviolet indicators show that PAHs are abundant. One might expect the PAHs to be predominantly positively ionized in these regions, yet the diffuse bands are systematically weak. This led us to examine the ionization balance for see whether the weakness of the diffuse bands might rule out PAH cations as the carriers. We find that this conclusion is ambiguous, however, due to the very rapid rates for recombination of PAHs: under conditions that may reasonably represent our observed nebulae, the PAHs might be in predominantly neutral form. If so, this would explain the weakness of the diffuse bands, but leaves open some very perplexing questions about where the PAHs might be dominantly in cation form, hence where the diffuse bands do arise if they are due to PAH+

The weakness of diffuse bands in nebular environments. Possible impact on thePAH+ hypothesis

It has been widely suggested that PAH cations (PAH+) may be the carriers of the diffuse interstellar bands, so it is of interest to probe diffuse behavior in regions suspected of having high abundances of PAHs. Here we examine the strengths of several of the visible-wavelength diffuse interstellar bands in two nebular environments where infrared emission and ultraviolet indicators show that PAHs are abundant. One might expect the PAHs to be predominantly positively ionized in these regions, yet the diffuse bands are systematically weak. This led us to examine the ionization balance for see whether the weakness of the diffuse bands might rule out PAH cations as the carriers. We find that this conclusion is ambiguous, however, due to the very rapid rates for recombination of PAHs: under conditions that may reasonably represent our observed nebulae, the PAHs might be in predominantly neutral form. If so, this would explain the weakness of the diffuse bands, but leaves open some very perplexing questions about where the PAHs might be dominantly in cation form, hence where the diffuse bands do arise if they are due to PAH+

Effects of Self-Generated Noise on Estimates of Detection Threshold in Quiet for School-Age Children and Adults

Detection thresholds in quiet become adult-like earlier in childhood for high than low frequencies. When adults listen for sounds near threshold, they tend to engage in behaviors that reduce physiologic noise (e.g., quiet breathing), which is predominantly low frequency. Children may not suppress self-generated noise to the same extent as adults, such that low-frequency self-generated noise elevates thresholds in the associated frequency regions. This possibility was evaluated by measuring noise levels in the ear canal simultaneous with adaptive threshold estimation

The uptake of selenium by perennial ryegrass in soils of different organic matter contents receiving sheep excreta

Background and Aims The intake of selenium, an essential element for animals and humans, in ruminants is largely determined by selenium concentration in ingested forages, which take up selenium mainly from soil. Ruminant excreta is a common source of organic fertilizer, which provides both nutrients and organic matter. This study aims to unentangle the unclear effect of applying different types of ruminant excreta in soils of different organic matter contents on selenium uptake by forage. Methods Perennial ryegrass (Lolium perenne) was grown in soils of different organic matter contents. Urine and/or feces collected from sheep fed with organic or inorganic mineral supplements, including selenium, were applied to the soils. The selenium in the collected samples were analyzed using ICP-MS. The associated biogeochemical reactions were scrutinized by wet chemistry. Results The application of urine and/or feces resulted in either the same or lower selenium concentrations in perennial ryegrass. The excreta type did not affect total selenium accumulation in grass grown in low organic matter soil, whereas in high organic matter soil, feces resulted in significantly lower total selenium accumulation than urine, which was attributed to a possible interaction of selenium sorption in soil and microbial reduction of Se. Conclusion This one-time excreta application did not increase, but further decrease in some treatments, selenium concentration and accumulation in the perennial ryegrass. Consequently, to increase ruminant selenium intake, supplementing selenium directly to animals is more recommended than applying animal manure to soil, which might drive selenium reduction and decrease selenium uptake by grass