IRAS observations of the ISM in the gamma CAS reflection nebula

Mid-infrared emission from other galaxies originates both from interstellar grains heated by diffuse starlight and local excitation of grains by hot OB stars. Thus, a detailed examination of the Infrared Astronomy Satellite (IRAS) data from a B star interacting with the interstellar medium (ISM) could provide insight into infrared (IR) emission processes in external galaxies. Researchers have therefore used IRAS data to study the B0 IVe star gamma Cas and its surroundings, which they find to exhibit evidence of grain heating, destruction, and possible star formation

The ultraviolet extinction in M-supergiant circumstellar envelopes

Using International Ultraviolet (IUS) archival low-dispersion spectra, ultraviolet spectral extinctions were derived for the circumstellar envelopes of two M supergiants: HD 60414 and HD 213310. The observed stellar systems belong to a class of widely-separated spectroscopic binaries that are called VV Cephei stars. The total extinction was calculated by dividing the reddened fluxes with unreddened comparison fluxes of similar stars (g B2.5 for HD 213310 and a normalized s+B3 for HD 60414) from the reference atlas. After substracting the interstellar extinctions, which were estimated from the E(B-V) reddening of nearby stars, the resultant circumstellar extinctions were normalized at about 3.5 inverse microns. Not only is the 2175 A extinction bump absent in the circumstellar extinctions, but the far-ultraviolet extinction rise is also absent. The rather flat, ultraviolet extinction curves were interpreted as signatures of a population of noncarbonaceous, oxygen-rich grains with diameters larger than the longest observed wavelength

Pseudo-distances on symplectomorphism groups and applications to flux theory

Starting from a given norm on the vector space of exact 1-forms of a compact symplectic manifold, we produce pseudo-distances on its symplectomorphism group by generalizing an idea due to Banyaga. We prove that in some cases (which include Banyaga's construction), their restriction to the Hamiltonian diffeomorphism group is equivalent to the distance induced by the initial norm on exact 1-forms. We also define genuine "distances to the Hamiltonian diffeomorphism group" which we use to derive several consequences, mainly in terms of flux groups.Comment: 21 pages, no figure; v2. various typos corrected, some references added. Published in Mathematische Zeitschrif

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

The origin of micrograins

Using ultraviolet and infrared techniques, researchers investigated the origins of the tiny (approx. 10A) grains whose presence in the interstellar medium (ISM) is inferred from near-infrared photometry (Sellgren, Werner, and Dinerstein 1983; Sellgren 1984). The authors consider two possibilities: (1) that the grains are formed by condensation in stellar atmospheres; or (2) that they are formed by fragmentation of larger grains in interstellar shocks. They searched for evidence of very small grains in circumstellar environments by analyzing ultraviolet extinction curves in binaries containing hot companions, and by searching for the 3.3-micron emission feature in similar systems. The ultraviolet extinction curve analysis could be applied only to oxygen-rich systems, where small carbonaceous grains would not be expected, so these results provide only indirect information. Researchers find a deficiency of grains smaller than 800A in oxygen-rich systems, consistent with theoretical models of grain condensation which suggest that grains grow to large sizes before injection into the interstellar medium. More direct information on carbonaceous micrograins was obtained from the search for the 3.3-micron feature in carbon-rich binaries with hot companions, whose ultraviolet flux should excite the tiny grains to emit in the infrared. No 3.3-micron feature was found, suggesting that the micrograins are absent in these systems. In addition to the negative search for micrograins in circumstellar environments, researchers have also studied the possible association of these grains with shocks in the diffuse interstellar medium. Using Infrared Astronomy Satellite (IRAS) colors as indicators of the presence or absence of the small grains (e.g., Ryter, Puget, and Perault 1987 and references cited therein), researchers systematically searched for them in regions (reflection nebulae) expected to have sufficient ultraviolet flux to make them glow in the infrared. They found that the distribution is not uniform. The researchers propose that production of micrograins by fragmentation of larger grains in shocks could explain this uneven distribution

Terminal Molybdenum Phosphides with d Electrons: Radical Character Promotes Coupling Chemistry

A terminal Mo phosphide was prepared via group transfer of both P- and Cl-atoms from chloro-substituted dibenzo-7λ^3-phosphanorbornadiene. This compound represents the first structurally characterized terminal transition metal phosphide with valence d electrons. In the tetragonal ligand field, these electrons populate an orbital of d_(xy) parentage, an electronic configuration that accommodates both metal d-electrons and a formal M≡P triple bond. Single electron oxidation affords a transient open shell terminal phosphide cation with significant spin density on P, as corroborated by CW and pulsed EPR characterization. Facile P-P bond formation occurs from this species via intermolecular phosphide coupling

Neonatal White Matter Maturation Is Associated With Infant Language Development

Background: While neonates have no sophisticated language skills, the neural basis for acquiring this function is assumed to already be present at birth. Receptive language is measurable by 6 months of age and meaningful speech production by 10-18 months of age. Fiber tracts supporting language processing include the corpus callosum (CC), which plays a key role in the hemispheric lateralization of language; the left arcuate fasciculus (AF), which is associated with syntactic processing; and the right AF, which plays a role in prosody and semantics. We examined if neonatal maturation of these fiber tracts is associated with receptive language development at 12 months of age. Methods: Diffusion-weighted imaging (DWI) was performed in 86 infants at 26.6 ± 12.2 days post-birth. Receptive language was assessed via the MacArthur-Bates Communicative Development Inventory at 12 months of age. Tract-based fractional anisotropy (FA) was determined using the NA-MIC atlas-based fiber analysis toolkit. Associations between neonatal regional FA, adjusted for gestational age at birth and age at scan, and language development at 12 months of age were tested using ANOVA models. Results: After multiple comparisons correction, higher neonatal FA was positively associated with receptive language at 12 months of age within the genu (p < 0.001), rostrum (p < 0.001), and tapetum (p < 0.001) of the CC and the left fronto-parietal AF (p = 0.008). No significant clusters were found in the right AF. Conclusion: Microstructural development of the CC and the AF in the newborn is associated with receptive language at 12 months of age, demonstrating that interindividual variation in white matter microstructure is relevant for later language development, and indicating that the neural foundation for language processing is laid well ahead of the majority of language acquisition. This suggests that some origins of impaired language development may lie in the intrauterine and potentially neonatal period of life. Understanding how interindividual differences in neonatal brain maturity relate to the acquisition of function, particularly during early development when the brain is in an unparalleled window of plasticity, is key to identifying opportunities for harnessing neuroplasticity in health and disease

Speech-evoked ABR: Effects of age and simulated neural temporal jitter

The speech-evoked auditory brainstem response (sABR) provides a measure of encoding complex stimuli in the brainstem, and this study employed the sABR to better understand the role of neural temporal jitter in the response patterns from older adults. In experiment 1, sABR recordings were used to investigate age-related differences in periodicity encoding of the temporal envelope and fine structure components of the response to a /da/speech token. A group of younger and a group of older adults (n = 22 per group) participated. The results demonstrated reduced amplitude of the fundamental frequency and harmonic components in the spectral domain of the recorded response of the older listeners. In experiment 2, a model of neural temporal jitter was employed to simulate in a group of young adults (n = 22) the response patterns measured from older adults. A small group of older adults (n = 7) were also tested under the jitter simulation conditions. In the young adults, the results showed a systematic reduction in the response amplitude of the most robust response components as the degree of applied jitter increased. In contrast, the older adults did not demonstrate significant response reduction when tested under jitter conditions. The overall pattern of results suggests that older adults have reduced neural synchrony for encoding periodic, complex signals at the level of the brainstem, and that this reduced synchrony can be modeled by simulating neural jitter via disruption of the temporal waveform of the stimulus