Aerodynamic properties of fractal grains: Implications for the primordial solar nebula

Under conditions in the primordial solar nebula and dense interstellar clouds, small grains have low relative velocities. This is the condition for efficient sticking and formation of fractal aggregates. A calculation of the ratio of cross section, sigma, to number of primary particles, N, for fractal clusters yielded 1n sigma/N = 0.2635 + 0.5189N sup (-0.1748). This ratio decreases slowly with N and approaches a constant for large N. Under the usual assumption of collisions producing spherical compact, uniform density aggregates, sigma/N varies as N sup -1/3 and decreases rapidly. Fractal grains are therefore much more closely coupled to the gas than are compact aggregates. This has a significant effect on the aerodynamic behavior of aggregates and consequently on their evolution and that of the nebula

The comprehension revolution : a twenty-year history of process and practice related to reading comprehension

Includes bibliographie

Is there a Jordan geometry underlying quantum physics?

There have been several propositions for a geometric and essentially non-linear formulation of quantum mechanics. From a purely mathematical point of view, the point of view of Jordan algebra theory might give new strength to such approaches: there is a ``Jordan geometry'' belonging to the Jordan part of the algebra of observables, in the same way as Lie groups belong to the Lie part. Both the Lie geometry and the Jordan geometry are well-adapted to describe certain features of quantum theory. We concentrate here on the mathematical description of the Jordan geometry and raise some questions concerning possible relations with foundational issues of quantum theory.Comment: 30 page

The relationship between chronic alcohol abuse and information processing ability in older adults

The issue of alcohol use and abuse among older adults is one that is gaining attention in current literature. Although it is an important issue, empirical evidence within the domain of alcohol, aging, and cognition, is sparse. Thus, the proposed preliminary study was designed to examine the relationship between chronic alcohol consumption and information processing speed in older adults. Eight matched participants (4 per group, mean age 56 years) were divided into two groups: Alcoholic or non-alcoholic. Participants were assigned to their respective group and matched based on the information provided on a health questionnaire. All participants completed a series of information processing measures. A 2 (Group) x 3 (Test) ANOVA with repeated measures on the last factor was used to compare reaction times of three separate tests of information processing ability. Unfortunately, the analysis suffered from lack of statistical power. However, data trends strongly suggested a difference between the alcoholic and non-alcoholic participants on all measures of information processing. Further, interactive trends of the data were noted with the alcoholics showing more deficits as a result of the more complex processing requirements. Future suggestions are to continue the work with more participants of more diverse socio-economic status, health, and alcohol behavior, as assessed through the a priori health questionnaire

Development of the visual pathway in Xenopus laevis (Daudin)

Aspects of the development and distribution of the primary retinal afferent projection to the contralateral optic tectum were studied by light microscopy, electron microscopy, and microelectrode recording from adult and tadpole optic nerves and optic tecta of the toad Xenopus laevis (Daudin). The adult tectum was found to be innervated by four populations of optic nerve afferents with different conduction velocities and retinal receptive field properties. Current source density analysis of the postsynaptic potentials recorded extra cellularly from tectal cell populations revealed the spatial distribution of optic nerve afferent synapses. The dendrites of cells that constitute tectal cell layer 8 were found to receive the majority of retinal afferent fibre input. The earliest time at which ganglion cell terminal activity was recorded in the tectum was tadpole Stage 46, at which time the optic nerve was entirely composed of unmyelinated fibres. The excitatory receptive fields of these units were large, and these units were easily habituated. Stage 46 was also the earliest time at which postsynaptic field potentials ('u' waves) could be recorded in the tectum and synapses observed morphologically. Evoked potentials ('m' waves), characteristic of a myelinated fibre innervation of the tectum, were first seen at tadpole Stage 59, as was the appearance and development of optic nerve myelination. No obvious correlations, other than the division of optic nerve axons into my elimated and unmyelinated fibre populations, could be made between optic nerve fibre conduction velocity groups and fibre diameter histograms. However, an obvious correlation between optic nerve conduction velocity groups and postsynaptic field potentials recorded in the tectum was observed. In addition, - a clear correlation was discovered between the distributions of the current sinks of postsynaptic activity and the location of recording sites of ganglion cell axon terminals having known receptive field properties, A gradual emergence of the adult pattern of tectal innervation by optic nerve afferents, during the time at which the tadpole undergoes metamorphosis, was observed

Confirmation of Potential Cyprinid Hosts for a State Threatened Freshwater Mussel of East Texas

Previously suggested Cyprinid host-fish for the state threatened Texas pigtoe (Fusconaia askewi) and Louisiana pigtoe (Pleurobema riddelli) of East Texas were investigated. The Red shiner, Blacktail shiner, and Bullhead minnow were targeted as potential hosts. The viability of these fish as hosts was tested by collecting them from three different rivers of East Texas and housing them in an Aquatic Habitat Tank System (AHAB) to allow the natural development and release of glochidia or juvenile mussels that were attached to the fish in the wild. Juvenile mussels were molecularly identified with amplification of mitochondrial DNA (mtDNA) using the ND1 gene. The DNA was sequenced and compared to the NCBI database and cross-referenced with an adult molecular key that was created for all 37 mussel species that occur in East Texas. Fifteen juveniles were successfully sequenced. All 15 naturally released from both Red shiners and Blacktail shiners that were collected from all three rivers and were identified as F. askewi. The Red shiner and Blacktail shiner have been confirmed hosts for F. askewi and the Bullhead minnow was rejected as a host for F. askewi. In addition, glochidial release dates and the rate of metamorphosis for F. askewi was estimated

Movement patterns and athletic performance of leopards in the Okavango Delta

Although leopards are the most widespread of all the big cats and are known for their adaptability, they are elusive and little is known in detail about their movement and hunting energetics. We used high-resolution GPS/IMU (inertial measurement unit) collars to record position, activity and the first high-speed movement data on four male leopards in the Okavango Delta, an area with high habitat diversity and habitat fragmentation. Leopards in this study were generally active and conducted more runs during the night, with peaks in activity and number of runs in the morning and evening twilight. Runs were generally short (less than 100 m) and relatively slow (maximum speed 5.3 m s−1, mean of individual medians) compared to other large predators. Average daily travel distance was 11 km and maximum daily travel distance was 29 km. No direct correlation was found between average daily temperature and travel distance or between season and travel distance. Total daily energy requirements based on locomotor cost and basal metabolic rate varied little between individuals and over time. This study provides novel insights into movement patterns and athletic performance of leopards through quantitative high-resolution measurement of the locomotor, energetic, spatial and temporal movement characteristics. The results are unbiased by methodological and observational limitations characteristic of previous studies and demonstrate the utility of applying new technologies to field studies of elusive nocturnal species

Esophageal Involvement in Lymphoma

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75337/1/j.1572-0241.1985.tb02134.x.pd

Guidelines for physical weed control research: flame weeding, weed harrowing and intra-row cultivation

A prerequisite for good research is the use of appropriate methodology. In order to aggregate sound research methodology, this paper presents some tentative guidelines for physical weed control research in general, and flame weeding, weed harrowing and intra-row cultivation in particular. Issues include the adjustment and use of mechanical weeders and other equipment, the recording of impact factors that affect weeding performance, methods to assess effectiveness, the layout of treatment plots, and the conceptual models underlying the experimental designs (e.g. factorial comparison, dose response). First of all, the research aims need to be clearly defined, an appropriate experimental design produced and statistical methods chosen accordingly. Suggestions on how to do this are given. For assessments, quantitative measures would be ideal, but as they require more resources, visual classification may in some cases be more feasible. The timing of assessment affects the results and their interpretation. When describing the weeds and crops, one should list the crops and the most abundantly present weed species involved, giving their density and growth stages at the time of treatment. The location of the experimental field, soil type, soil moisture and amount of fertilization should be given, as well as weather conditions at the time of treatment. The researcher should describe the weed control equipment and adjustments accurately, preferably according to the prevailing practice within the discipline. Things to record are e.g. gas pressure, burner properties, burner cover dimensions and LPG consumption in flame weeding; speed, angle of tines, number of passes and direction in weed harrowing. The authors hope this paper will increase comparability among experiments, help less experienced scientists to prevent mistakes and essential omissions, and foster the advance of knowledge on non-chemical weed management