Collisions of small ice particles under microgravity conditions (II): Does the chemical composition of the ice change the collisional properties?

Context: Understanding the collisional properties of ice is important for understanding both the early stages of planet formation and the evolution of planetary ring systems. Simple chemicals such as methanol and formic acid are known to be present in cold protostellar regions alongside the dominant water ice; they are also likely to be incorporated into planets which form in protoplanetary disks, and planetary ring systems. However, the effect of the chemical composition of the ice on its collisional properties has not yet been studied. Aims: Collisions of 1.5 cm ice spheres composed of pure crystalline water ice, water with 5% methanol, and water with 5% formic acid were investigated to determine the effect of the ice composition on the collisional outcomes. Methods: The collisions were conducted in a dedicated experimental instrument, operated under microgravity conditions, at relative particle impact velocities between 0.01 and 0.19 m s^-1, temperatures between 131 and 160 K and a pressure of around 10^-5 mbar. Results: A range of coefficients of restitution were found, with no correlation between this and the chemical composition, relative impact velocity, or temperature. Conclusions: We conclude that the chemical composition of the ice (at the level of 95% water ice and 5% methanol or formic acid) does not affect the collisional properties at these temperatures and pressures due to the inability of surface wetting to take place. At a level of 5% methanol or formic acid, the structure is likely to be dominated by crystalline water ice, leading to no change in collisional properties. The surface roughness of the particles is the dominant factor in explaining the range of coefficients of restitution

The oral-aboral axis of a sea urchin embryo is specified by first cleavage

Several lines of evidence suggest that the oral-aboral axis in Strongylocentrotus purpuratus embryos is specified at or before the 8-cell stage. Were the oral-aboral axis specified independently of the first cleavage plane, then a random association of this plane with the blastomeres of the four embryo quadrants in the oral-aboral plane (viz. oral, aboral, right and left) would be expected. Lineage tracer dye injection into one blastomere at the 2-cell stage and observation of the resultant labeling patterns demonstrates instead a strongly nonrandom association. In at least ninety percent of cases, the progeny of the aboral blastomeres are associated with those of the left lateral blastomeres and the progeny of the oral blastomeres with the right lateral ones, respectively. Thus, ninety percent of the time the oral pole of the future oral-aboral axis lies 45 degrees clockwise from the first cleavage plane as viewed from the animal pole. The nonrandom association of blastomeres after labeling of the 2-cell stage implies that there is a mechanistic relation between axis specification and the positioning of the first cleavage plane

Macromere cell fates during sea urchin development

This paper examines the cell lineage relationships and cell fates in embryos of the sea urchin Strongylocentrotus purpuratus leading to the various cell types derived from the definitive vegetal plate territory or the veg_2 tier of cells. These cell types are gut, pigment cells, basal cells and coelomic pouches. They are cell types that constitute embryonic structures through cellular migration or rearrangement unlike the relatively non-motile ectoderm cell types. For this analysis, we use previous knowledge of lineage to assign macromeres to one of four types: VOM, the oral macromere; VAM, the aboral macromere, right and left VLM, the lateral macromeres. Each of the four macromeres contributes progeny to all of the cell types that descend from the definitive vegetal plate. Thus in the gut each macromere contributes to the esophagus, stomach and intestine, and the stripe of labeled cells descendant from a macromere reflects the re-arrangement of cells that occurs during archenteron elongation. Pigment cell contributions exhibit no consistent pattern among the four macromeres, and are haphazardly distributed throughout the ectoderm. Gut and pigment cell contributions are thus radially symmetrical. In contrast, the VOM blastomere contributes to both of the coelomic pouches while the other three macromeres contribute to only one or the other pouch. The total of the macromere contribution amounts to 60% of the cells constituting the coelomic pouches

Competence, specification and induction of Pax-3 in the trigeminal placode

Placodes are discrete regions of thickened ectoderm that contribute extensively to the peripheral nervous system in the vertebrate head. The paired-domain transcription factor Pax-3 is an early molecular marker for the avian ophthalmic trigeminal (opV) placode, which forms sensory neurons in the ophthalmic lobe of the trigeminal ganglion. Here, we use collagen gel cultures and heterotopic quail-chick grafts to examine the competence, specification and induction of Pax-3 in the opV placode. At the 3-somite stage, the whole head ectoderm rostral to the first somite is competent to express Pax-3 when grafted to the opV placode region, though competence is rapidly lost thereafter in otic-level ectoderm. Pax-3 specification in presumptive opV placode ectoderm occurs by the 8-somite stage, concomitant with robust Pax-3 expression. From the 8-somite stage onwards, significant numbers of cells are committed to express Pax-3. The entire length of the neural tube has the ability to induce Pax-3 expression in competent head ectoderm and the inductive interaction is direct. We propose a detailed model for Pax-3 induction in the opV placode

Method of statistical filtering

Minimal formula for bounding the cross correlation between a random forcing function and the state error when this correlation is unknown is used in optimal linear filter theory applications. Use of the bound results in overestimation of the estimation-error covariance

Visualisation of fingermarks and grab impressions on fabrics. Part 1: gold/zinc vacuum metal deposition

Vacuum metal deposition (VMD) is a highly sensitive technique originally introduced for detecting latent fingermarks on smooth non-porous surfaces such as carrier bags, plastics and glass. The current study explores whether VMD can be used in the examination of clothing from physical and sexual assault cases in order to visualise identifiable fingermark ridge detail and/or palmar flexion crease detail, thus allowing potential areas to be indicated for DNA swabbing and/or to determine the sequence of events. Four different fabrics were utilised during this study – nylon, polyester, polycotton and cotton, along with 15 donors who ranged in their age and propensity to leave fingermarks, from good to medium to poor as determined by results obtained from test runs using paper and plastic carrier bags processed with VMD. Once samples were collected they were kept for a determined time (1, 2, 3, 4, 5, 6, 7, 14, 21 or 28 days) and then treated using the gold/zinc metal VMD process. From the results, it appears that greater ridge detail is visible on the smoother non-porous fabrics, such as nylon whereas on rougher porous fabrics, such as cotton, only empty prints and impressions, rather than any ridge details, were visible. All fabrics did however allow the development of touch marks that could be targeted for DNA taping thus potentially leading to a DNA profile and possible identification of a suspect

Visualisation of fingermarks and grab impressions on dark fabrics using silver vacuum metal deposition

Vacuum metal deposition (VMD) involves the thermal evaporation of metal (silver) in a vacuum, resulting in a uniform layer being deposited on the specimen being treated. This paper examines the use of silver on dark fabrics, thus offering a simpler operation and more obvious colouration to that of the traditional use of gold and zinc metals which must be evaporated separately. The aim of this study was to investigate the effect of fabric type, donor, mark age and method of fingermark deposition on the quality of marks visualised using silver VMD. This was achieved by collecting fingermark deposits from fifteen donors, of both sexes and various ages, by a grab or a press method. Four different fabrics: satin, polyester, polycotton and cotton were studied over a 10 day timeline of 1, 2, 3, 4, 5, 6, 7, 14, 21 and 28 + days. It was found that satin and polyester gave the most positive results, with polyester often producing excellent ridge detail. Cotton and polycotton were less successful with no ridge detail being observed. The donors also had an observable effect on the results obtained probably due to variations in secretions produced or pressures applied during specimen collection. The age of the mark or the method of mark deposition had little influence on the results obtained. Silver VMD is a viable process for visualising marks on certain dark fabrics and has the advantage over gold/zinc VMD in that the marks visualised are light in colour which contrasts well against the dark background

Thermal Desorption of Water-Ice in the Interstellar Medium

Water (H2O) ice is an important solid constituent of many astrophysical environments. To comprehend the role of such ices in the chemistry and evolution of dense molecular clouds and comets, it is necessary to understand the freeze-out, potential surface reactivity, and desorption mechanisms of such molecular systems. Consequently, there is a real need from within the astronomical modelling community for accurate empirical molecular data pertaining to these processes. Here we give the first results of a laboratory programme to provide such data. Measurements of the thermal desorption of H2O ice, under interstellar conditions, are presented. For ice deposited under conditions that realistically mimic those in a dense molecular cloud, the thermal desorption of thin films (~50 molecular layers) is found to occur with zero order kinetics characterised by a surface binding energy, E_{des}, of 5773 +/- 60 K, and a pre-exponential factor, A, of 10^(30 +/- 2) molecules cm^-2 s^-1. These results imply that, in the dense interstellar medium, thermal desorption of H2O ice will occur at significantly higher temperatures than has previously been assumed.Comment: 9 pages, 4 figures, accepted for publication in MNRA

Teaching Excellence: A Reaction to the Smith Commission Report and its Effects

This paper has been written partially in response to the Smith Commission Report, and partially in response to the reactions the report has elicited already. The Smith Commission Report voiced many valid concerns about teaching excellence; however, many of the so-called "innovations" that have been developed in answer to Stuart Smith's call for teaching excellence are, in fact, little different from those techniques implemented under the auspices of the Ontario Universities Program for Institutional Development (OUPID) in the 1960's and early 1970's. This being the case, the authors feel that the most likely result will be a similar lack of success. It is, therefore, our suggestion that an attempt ought to be made to change the infrastructure of the university sys- tem so that it supports good teaching and research with equal measure. This, above all else, should lead to real improvements in the quality of teaching