Distribution and Density of Vegetative Hydrilla Propagules in the Sediments of Two New Zealand Lakes

The distribution and density of hydrilla (Hydrilla verticillata (L.f.)Royle) turions and tubers in two New Zealand lakes were assessed by sampling cores of sediment from Lakes Tutira and Waikapiro each year from 1994 to 1997. Turion and tuber density differed with water depth, with maximum numbers of tubers and turions found in the 1-2 m and 1.5-4m water depth ranges respectively. A high turion to tuber ratio was observed, with turions accounting for over 80% of propagules. The relatively low numbers of turions and tubers compared with other reports, and the distribution of most tubers within the shallow water is likely to be associated with black swan grazing (Cygnus atratus Latham), with maintains a canopy of hydrilla consistently 1 m below the water surface

MODELING AND TEST OF THE EFFICIENCY OF ELECTRONIC SPEED CONTROLLERS FOR BRUSHLESS DC MOTORS

Small electric uninhabited aerial vehicles (UAV) represent a rapidly expanding market requiring optimization in both efficiency and weight; efficiency is critical during cruise or loiter where the vehicle operates at part power for up to 99% of the mission time. Of the four components (battery, motor, propeller, and electronic speed controller (ESC)) of the electric propulsion system used in small UAVs, the ESC has no accepted performance model and almost no published performance data. To collect performance data, instrumentation was developed to measure electrical power in and out of the ESC using the two wattmeter method and current sense resistors; data was collected with a differential simultaneous data acquisition system. Performance of the ESC was measured under different load, commanded throttle, bus voltage, and switching frequency, and it was found that ESC efficiency decreases with increasing torque and decreasing bus voltage and does not vary much with speed and switching frequency. The final instrumentation was limited to low-voltage systems and error propagation calculations indicate a great deal of error at low power measurements; despite these limitations, an understanding of ESC performance appropriate for conceptual design of these systems was obtained. MODELING AND TEST OF THE EFFICIENCY OF ELECTRONIC SPEED CONTROLLERS FOR BRUSHLESS DC MOTOR

Dusty Disks Around Central Stars of Planetary Nebulae

Only a few percent of cool, old white dwarfs (WDs) have infrared excesses interpreted as originating in small hot disks due to the infall and destruction of single asteroids that come within the star's Roche limit. Infrared excesses at 24 micron were also found to derive from the immediate vicinity of younger, hot WDs, most of which are still central stars of planetary nebulae (CSPN). The incidence of CSPN with this excess is 18%. The Helix CSPN, with a 24 micron excess, has been suggested to have a disk formed from collisions of Kuiper belt-like objects (KBOs). In this paper, we have analyzed an additional sample of CSPN to look for similar infrared excesses. These CSPN are all members of the PG 1159 class and were chosen because their immediate progenitors are known to often have dusty environments consistent with large dusty disks. We find that, overall, PG 1159 stars do not present such disks more often than other CSPN, although the statistics (5 objects) are poor. We then consider the entire sample of CSPN with infrared excesses, and compare it to the infrared properties of old WDs, as well as cooler post-AGB stars. We conclude with the suggestion that the infrared properties of CSPN more plausibly derive from AGB-formed disks rather than disks formed via the collision of KBOs, although the latter scenario cannot be ruled out. We finally remark that there seems to be an association between CSPN with a 24 micron excess and confirmed or possible binarity of the central star.Comment: 11 pages, 5 figures, AJ, in pres

Hyperinsulinism in short-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency reveals the importance of beta-oxidation in insulin secretion

A female infant of nonconsanguineous Indian parents presented at 4 months with a hypoglycemic convulsion. Further episodes of hypoketotic hypoglycemia were associated with inappropriately elevated plasma insulin concentrations. However, unlike other children with hyperinsulinism, this patient had a persistently elevated blood spot hydroxybutyrylcarnitine concentration when fed, as well as when fasted. Measurement of the activity of L-3-hydroxyacyl-CoA dehydrogenase in cultured skin fibroblasts with acetoacetyl-CoA substrate showed reduced activity. In fibroblast mitochondria, the activity was less than 5% that of controls. Sequencing of the short-chain L-3-hydroxyacyl-CoA dehydrogenase (SCHAD) genomic DNA from the fibroblasts showed a homozygous mutation (C773T) changing proline to leucine at amino acid 258. Analysis of blood from the parents showed they were heterozygous for this mutation. Western blot studies showed undetectable levels of immunoreactive SCHAD protein in the child's fibroblasts. Expression studies showed that the P258L enzyme had no catalytic activity. We conclude that C773T is a disease-causing SCHAD mutation. This is the first defect in fatty acid beta -oxidation that has been associated with hyperinsulinism and raises interesting questions about the ways in which changes in fatty acid and ketone body metabolism modulate insulin secretion by the beta cell. The patient's hyperinsulinism was easily controlled with diazoxide and chlorothiazide

A complementary compact laser based neutron source

Several experiments of neutron generation using high intensity laser sources, with a power exceeding 10^19W/cm^2 via TNSA (Target Normal Sheath Acceleration) or other similar methods, have been performed in the past years in different laboratories. However, so far there is no one running neutron source based on such a technology. In the framework of the Conceptual Report Design of a new accelerator in the Eupraxia project we are studying the possibility to have a laser-based neutron source, not only by TNSA but also from self-injection schemes. We focus our attention on the applications in cultural heritage studies as well also on the complementary role that such a source can have in the framework of large facilities devoted to radiation production.Comment: 4 pages, two figures, 3rd European Advanced Accelerators Concept

Probabilistic expert systems for handling artifacts in complex DNA mixtures

This paper presents a coherent probabilistic framework for taking account of allelic dropout, stutter bands and silent alleles when interpreting STR DNA profiles from a mixture sample using peak size information arising from a PCR analysis. This information can be exploited for evaluating the evidential strength for a hypothesis that DNA from a particular person is present in the mixture. It extends an earlier Bayesian network approach that ignored such artifacts. We illustrate the use of the extended network on a published casework example

Dust Formation and Survival in Supernova Ejecta

The presence of dust at high redshift requires efficient condensation of grains in SN ejecta, in accordance with current theoretical models. Yet, observations of the few well studied SNe and SN remnants imply condensation efficiencies which are about two orders of magnitude smaller. Motivated by this tension, we have (i) revisited the model of Todini & Ferrara (2001) for dust formation in the ejecta of core collapse SNe and (ii) followed, for the first time, the evolution of newly condensed grains from the time of formation to their survival - through the passage of the reverse shock - in the SN remnant. We find that 0.1 - 0.6 M_sun of dust form in the ejecta of 12 - 40 M_sun stellar progenitors. Depending on the density of the surrounding ISM, between 2-20% of the initial dust mass survives the passage of the reverse shock, on time-scales of about 4-8 x 10^4 yr from the stellar explosion. Sputtering by the hot gas induces a shift of the dust size distribution towards smaller grains. The resulting dust extinction curve shows a good agreement with that derived by observations of a reddened QSO at z =6.2. Stochastic heating of small grains leads to a wide distribution of dust temperatures. This supports the idea that large amounts (~ 0.1 M_sun) of cold dust (T ~ 40K) can be present in SN remnants, without being in conflict with the observed IR emission.Comment: MNRAS accepte