The classical multicomponent nucleation theory for cavitation in water with dissolved gases

The Classical Nucleation Theory (CNT) in its multicomponent form is presented as a reliable tool for the investigation of homogeneous nucleation in cavitation processes in aqueous systems. Several cases are considered, starting form the most simple case of a void cavity emerging at negative pressure, then treating the case of a bubble composed of water vapor only, and finally investigating the influence of various gases dissolved in water on the nucleation rate and the composition of the critical cluster. Aqueous systems related to cavitation in hydraulic machinery and to cavitation in carbonated beverages are discussed.http://deepblue.lib.umich.edu/bitstream/2027.42/84298/1/CAV2009-final120.pd

Laser-induced Precession of Magnetization in GaMnAs

We report on the photo-induced precession of the ferromagnetically coupled Mn spins in (Ga,Mn)As, which is observed even with no external magnetic field applied. We concentrate on various experimental aspects of the time-resolved magneto-optical Kerr effect (TR-MOKE) technique that can be used to clarify the origin of the detected signals. We show that the measured data typically consist of several different contributions, among which only the oscillatory signal is directly connected with the ferromagnetic order in the sample.Comment: 4 pages, 5 figure

Test-​Photostability of pulsed laser deposited amorphous thin films from Ge-​As-​Te system

International audienc

Terrestrial lichen response to partial cutting in lodgepole pine forests on caribou winter range in west-central British Columbia

In west-central British Columbia, terrestrial lichens located in older, lodgepole pine (Pinus contorta) forests are important winter forage for woodland caribou (Rangifer tarandus caribou). Clearcut harvesting effectively removes winter forage habitat for decades, so management approaches based on partial cutting were designed to maintain continuous lichen-bearing habitat for caribou. This study tested a group selection system, based on removal of 33% of the forest every 80 years in small openings (15 m diameter), and two irregular shelterwood treatments (whole-tree and stem-only harvesting methods) where 50% of the stand area is cut every 70 years in 20 to 30 m diameter openings. The abundance of common terrestrial lichens among the partial cutting and no-harvest treatments was compared across five replicate blocks, pre-harvest (1995) and post-harvest (1998, 2000 and 2004). The initial loss of preferred forage lichens (Cladonia, Cladina, Cetraria and Stereocaulon) was similar among harvesting treatments, but there was greater reduction in these lichens in the openings than in the residual forest. After eight years, forage lichens in the group selection treatment recovered to pre-harvest amounts, while lichen in the shelterwood treatments steadily increased from 49 to 57% in 1998 to about 70% of pre-harvest amounts in 2004. Although not part of the randomized block design, there was substantially less lichen in three adjacent clearcut blocks than in the partial cuts. Regression analysis pre- and post-harvest indicated that increased cover of trees, shrubs, herbs, woody debris and logging slash corresponded with decreased forage lichen abundance. In the short-term, forestry activities that minimize inputs of woody debris, control herb and shrub development, and moderate the changes in light and temperatures associated with canopy removal will lessen the impact on lichen. Implementation of stand level prescriptions is only one aspect of caribou habitat management. A comprehensive approach should consider all factors and their interactions to maintain a viable population of woodland caribou in west-central British Columbia

Arboreal forage lichen response to partial cutting of high elevation mountain caribou range in the Quesnel Higland of east-central British Columbia

Group selection silvicultural systems have been recommended for managing mountain caribou (Rangifer tarandus caribou) habitat in high elevation Engelmann spruce – subalpine fir forests in east-central British Columbia. We measured the response of arboreal lichen (a key winter forage) to harvesting of 30% of the forested area using three partial cutting treatments, which created small (0.03 ha), medium (0.13 ha), and large (1.0 ha) openings, and a no-harvest treatment. Treatments were replicated on four sites, and monitored over a ten year post-harvest period. The short-term loss of lichen associated with removal of approximately one third of the trees was partially offset by a significant (P=0.01) increase in lichen abundance on trees in the caribou feeding zone (up to 4.5 m) in the three partial cutting treatments relative to trees in the uncut forest. Differences among treatments in the change in lichen composition, as measured by the percentage of Alectoria sarmentosa and Bryoria spp., were marginally significant (P=0.10). The partial cutting treatments showing a greater likelihood of shifting towards more Bryoria spp. than no-harvest treatment (P=0.04). In the year of harvest (1993), larger trees were found to hold more lichen than smaller trees (P=0.04), and live trees supported more lichen than dead trees (P=0.01), but lichen loading was similar among tree species (P=0.51). Tree fall rates were similar among treatments, based on the ten year average (0.6–0.8% of sample trees per year). The results indicate that caribou foraging habitat is maintained in the residual forest when group selection systems that remove only 30% of the trees are applied. Information on the distribution of lichen is useful for developing stand level prescriptions. Providing lichen bearing habitat meets just one of the needs of caribou. A comprehensive approach that considers all factors and their interactions is essential to maintain and recover the threatened mountain caribou

Cavitation processes in binary systems – the effect of a dissolved gas on the nucleation rate described by the classical nucleation theory

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.The Classical Nucleation Theory (CNT) is applied to nucleation in cavitation processes in binary mixtures of a liquid component and a dissolved gas component. The multi-component form of the CNT allows to study the influence of the dissolved gas concentration on the resulting nucleation rate. Four binary mixtures are studied, diethylether – nitrogen, propane – carbon dioxide, isobutane – carbon dioxide, and chlorodifluoromethane – carbon dioxide, whose experimental nucleation rates are available in the literature. The nucleation rates and their dependence on concentration of the dissolved gas calculated according to the CNT show good agreement with the experimental data.pm201

The Star Formation History of the Carina Dwarf Galaxy

We have analyzed deep B and V photometry of the Carina dwarf spheroidal reaching below the old main-sequence turnoff to about V = 25. Using simulated color-magnitude diagrams to model a range of star formation scenarios, we have extracted a detailed, global star formation history. Carina experienced three significant episodes of star formation at about 15 Gyr, 7 Gyr, and 3 Gyr. Contrary to the generic picture of galaxy evolution, however, the bulk of star formation, at least 50%, occured during the episode 7 Gyr ago, which may have lasted as long as 2 Gyr. For unknown reasons, Carina formed only 10-20% of its stars at an ancient epoch and then remained quiescent for more than 4 Gyr. The remainder (~30%) formed relatively recently, only 3 Gyr ago. Interest in the local population of dwarf galaxies has increased lately due to their potential importance in the understanding of faint galaxy counts. We surmise that objects like Carina, which exhibits the most extreme episodic behavior of any of the dwarf spheroidal companions to the Galaxy, are capable of contributing to the observed excess of blue galaxies at B = 24 only if the star formation occurred instantaneously.Comment: 23 pages of text, 20 figures, 8 tables. AJ, in pres