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Slow Cooling (slow + cooling)
Terms modified by Slow Cooling Selected AbstractsEFFECT OF RAPID COOLING ON THE GROWTH AND PENETRATION OF SALMONELLA ENTERITIDIS INTO EGG CONTENTSJOURNAL OF FOOD SAFETY, Issue 4 2002HAIQIANG CHEN ABSTRACT Shell eggs were inoculated internally with approximately 10 cells of Salmonella enterica serovar enteritidis (S. enteritidis) and subjected to three different cooling treatments. Eggs were cooled from an initial temperature of 27C to approximately 7.2C. After cooling, eggs were stored at approximately 7.2C for 36 days, or stored at 5.7,9.5C for 30 days plus 6 days at 37C to simulate temperature abuse. Rapid cooling and subsequent storage of eggs at approximately 7.2C inhibited the growth of S. enteritidis in eggs. Slow cooling, and/or temperature abuse promoted growth of S. enteritidis in eggs. The penetration study indicated that rapid cooling and subsequent storage at 7.2C for 30 days did not affect the penetration of S. enteritidis into egg contents. The S. enteritidis isolated from the eggshell with shell membranes was significantly higher (P < 0.05) than from the internal egg contents, indicating that most of the S. enteritidis cells were trapped within the shell pores and/or shell membranes. [source] Nucleation kinetics and growth of nonlinear optical bis (dimethyl sulfoxide) manganese mercury thiocyanate single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2008C. M. Raghavan Abstract Nonlinear optical (NLO) material of bis (dimethyl sulfoxide) manganese mercury thiocyanate (MMTD) was synthesized by two step reaction method. The solubility and metastable zonewidth were experimentally determined in order to optimize the growth parameters. Bulk crystals of MMTD were grown by slow cooling and slow evaporation methods. The structure of the grown crystal was confirmed by X-ray diffraction analysis. Presence of functional groups and the coordination of Lewis base ligand of dimethyl sulfoxide (DMSO) were confirmed by FT-IR analysis. Optical transparency of the grown crystals was studied by UV-Vis spectroscopy. Nonlinear optical property of the grown crystal was confirmed by Kurtz powder method. Etching studies reveal the formation of triangular hillock etch patterns, indicative of 2D nucleation mechanism. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of Cooling Rate on Glass Transition Temperature of Sucrose Solutions and Rice Starch GelJOURNAL OF FOOD SCIENCE, Issue 6 2003C.-L. Hsu ABSTRACT: The study's objectives were to determine the influence of cooling rate through the primary zone of freezing on Tg in sucrose solutions and rice starch gels. The influence of cooling rate, water content, and annealing on Tg were evaluated. Results indicated that the observed Tg values for sucrose solutions were lower after rapid cooling (70% solids: rapid cooling ,66.7°C; slow cooling ,64.6 °C; 30% solids: rapid cooling ,34.6 °C; slow cooling ,33.3 °C). The Tg values of annealed samples are higher than the Tg of both rapidly and slowly cooled samples (70%: ,44.2 °C; 30%: ,32.7 °C). The Tg of the rice starch gel was ,9.0 °C after rapid cooling and ,7.5 °C after slow cooling. [source] Petrology of Martian meteorite Northwest Africa 998METEORITICS & PLANETARY SCIENCE, Issue 5 2008Allan H. TREIMAN This 456-gram, partially fusion-crusted meteorite consists of (by volume) ,75% augite (core composition Wo39En39Fs22), ,9% olivine (Fo35), ,7% plagioclase (Ab61An35) as anhedra among augite and olivine, ,3.5% low-calcium pyroxenes (pigeonite and orthopyroxene) replacing or forming overgrowths on olivine and augite, ,1% titanomagnetite, and other phases including potassium feldspar, apatite, pyrrhotite, chalcopyrite, ilmenite, and fine-grained mesostasis material. Minor secondary alteration materials include "iddingsite" associated with olivine (probably Martian), calcite crack fillings, and iron oxide/hydroxide staining (both probably terrestrial). Shock effects are limited to minor cataclasis and twinning in augite. In comparison to other nakhlites, NWA 998 contains more low-calcium pyroxenes and its plagioclase crystals are blockier. The large size of the intercumulus feldspars and the chemical homogeneity of the olivine imply relatively slow cooling and chemical equilibration in the late- and post-igneous history of this specimen, and mineral thermometers give subsolidus temperatures near 730 °C. Oxidation state was near that of the QFM buffer, from about QFM-2 in earliest crystallization to near QFM in late crystallization, and to about QFM + 1.5 in some magmatic inclusions. The replacement or overgrowth of olivine by pigeonite and orthopyroxene (with or without titanomagnetite), and the marginal replacement of augite by pigeonite, are interpreted to result from late-stage reactions with residual melts (consistent with experimental phase equilibrium relationships). Apatite is concentrated in planar zones separating apatite-free domains, which suggests that residual magma (rich in P and REE) was concentrated in planar (fracture?) zones and possibly migrated through them. Loss of late magma through these zones is consistent with the low bulk REE content of NWA 998 compared with the calculated REE content of its parent magma. [source] Evaluating planetesimal bow shocks as sites for chondrule formationMETEORITICS & PLANETARY SCIENCE, Issue 11 2004Fred J. CIESLA The formation of such shocks is modeled using a piecewise parabolic method (PPM) code under a variety of conditions. The results of this modeling are used as a guide to study chondrule formation in a one-dimensional, finite shock wave. This model considers a mixture of chondrule-sized particles and micron-sized dust and models the kinetic vaporization of the solids. We found that only planetesimals with a radius of ,1000 km and moving at least ,8 km/s with respect to the nebular gas can generate shocks that would allow chondrule-sized particles to have peak temperatures and cooling rates that are generally consistent with what has been inferred for chondrules. Planetesimals with smaller radii tend to produce lower peak temperatures and cooling rates that are too high. However, the peak temperatures of chondrules are only matched for low values of chondrule wavelength-averaged emissivity. Very slow cooling (<,100s of K/hr) can only be achieved if the nebular opacity is low, which may result after a significant amount of material has been accreted into objects that are chondrule-sized or larger, or if chondrules formed in regions of the nebula with small dust concentrations. Large shock waves of approximately the same scale as those formed by gravitational instabilities or tidal interactions between the nebula and a young Jupiter do not require this to match the inferred thermal histories of chondrules. [source] 39Ar- 40Ar chronology of R chondritesMETEORITICS & PLANETARY SCIENCE, Issue 3 2003Eleanor T. DIXON The 39Ar- 40Ar ages were determined on whole-rock samples of four R chondrites: Carlisle Lakes, Rumuruti, Acfer 217, and Pecora Escarpment #91002 (PCA 91002). All samples are breccias except for Carlisle Lakes. The age spectra are complicated by recoil and diffusive loss to various extents. The peak 39Ar- 40Ar ages of the four chondrites are 4.35, ,4.47 ± 0.02, 4.30 ± 0.07 Ga, and 4.37 Ga, respectively. These ages are similar to Ar-Ar ages of relatively unshocked ordinary chondrites (4.52,4.38 Ga) and are older than Ar-Ar ages of most shocked ordinary chondrites («4.2 Ga). Because the meteorites with the oldest (Rumuruti, ,4.47 Ga) and the youngest (Acfer 217, ,4.30 Ga) ages are both breccias, these ages probably do not record slow cooling within an undisrupted asteroidal parent body. Instead, the process of breccia formation may have differentially reset the ages of the constituent material, or the differences in their age spectra may arise from mixtures of material that had different ages. Two end-member type situations may be envisioned to explain the age range observed in the R chondrites. The first is if the impact(s) that reset the ages of Acfer 217 and Rumuruti was very early. In this case, the ,170 Ma maximum age difference between these meteorites may have been produced by much deeper burial of Acfer 217 than Rumuruti within an impact-induced thick regolith layer, or within a rubble pile type parent body following parent body re-assembly. The second, preferred scenario is if the impact that reset the age of Acfer 217 was much later than that which reset Rumuruti, then Acfer 217 may have cooled more rapidly within a much thinner regolith layer. In either scenario, the oldest age obtained here, from Rumuruti, provides evidence for relatively early (,4.47 Ga) impact events and breccia formation on the R chondrite parent body. [source] Formation of mesosiderites by fragmentation and reaccretion of a large differentiated asteroidMETEORITICS & PLANETARY SCIENCE, Issue 7 2001Edward R. D. SCOTT To test whether impacts can excavate core iron and mix it with crustal material, we used a low-resolution, smoothed-particle hydrodynamics computer simulation. For 50,300 km diameter differentiated targets, we found that significant proportions of scrambled core material (and hence potential mesosiderite metal material) could be generated. For near-catastrophic impacts that reduce the target to 80% of its original diameter and about half of its original mass, the proportion of scrambled core material would be about 5 vol%, equivalent to ,10 vol% of mesosiderite-like material. The paucity of olivine in mesosiderites and the lack of metal-poor or troilite-rich meteorites from the mesosiderite body probably reflect biased sampling. Mesosiderites may be olivine-poor because mantle material was preferentially excluded from the metal-rich regions of the reaccreted body. Molten metal globules probably crystallized around small, cool fragments of crust hindering migration of metal to the core. If mantle fragments were much hotter and larger than crustal fragments, little metal would have crystallized around the mantle fragments allowing olivine and molten metal to separate gravitationally. The rapid cooling rates of mesosiderites above 850 °C can be attributed to local thermal equilibration between hot and cold ejecta. Very slow cooling below 400 °C probably reflects the large size of the body and the excellent thermal insulation provided by the reaccreted debris. We infer that our model is more plausible than an earlier model that invoked an impact at ,1 km/s to mix projectile metal with target silicates. If large impacts cannot effectively strip mantles from asteroidal cores, as we infer, we should expect few large eroded asteroids to have surfaces composed purely of mantle or core material. This may help to explain why relatively few olivine-rich (A-type) and metal-rich asteroids (M-type) are known. Some S-type asteroids may be scrambled differentiated bodies. [source] Microstructures of metal grains in ordinary chondrites: Implications for their thermal historiesMETEORITICS & PLANETARY SCIENCE, Issue 3 2000Hugues LEROUX Three ordinary chondrites, Saint Séverin (LL6), Agen (H5), and Tsarev (L6) were selected because they display contrasting microstructures, which reflects different thermal histories. In Saint Séverin, the microstructure of the Ni-rich metal grains is due to slow cooling. It consists of a two-phase assemblage with a honeycomb structure resulting from spinodal decomposition similar to the cloudy zone of iron meteorites. Microanalyses show that the Ni-rich phase is tetrataenite (Ni = 47 wt%) and the Ni-poor phase, with a composition of ,25% Ni, is either martensite or taenite, these two occurring adjacent to each other. The observation that the Ni-poor phase is partly fcc resolves the disagreement between previous transmission electron microscopy (TEM) and Mössbauer studies on iron meteorites and ordinary chondrite metal. The Ni content of the honeycomb phase is much higher than in mesosiderites, confirming that mesosiderites cooled much more slowly. The high-Ni tetrataenite rim in contact with the cloudy zone displays high-Ni compositional variability on a very fine scale, which suggests that the corresponding area was destabilized and partially decomposed at low temperature. Both Agen and Tsarev display evidence of reheating and subsequent fast cooling obviously related to shock events. Their metallic particles mostly consist of martensite, the microstructure of which depends on local Ni content. Microstructures are controlled by both the temperature at which martensite forms and that at which it possibly decomposes. In high-Ni zones (>15 wt%), martensitic transformation started at low temperature (<300 °C). Because no further recovery occurred, these zones contain a high density of lattice defects. In low-Ni zones (<15 wt%), martensite grains formed at higher temperature and their lattice defects recovered. These martensite grains present a lath texture with numerous tiny precipitates of Ni-rich taenite (Ni = 50 wt%) at lath boundaries. Nickel composition profiles across precipitate-matrix interfaces show that the growth of these precipitates was controlled by preferential diffusion of Ni along lattice defects. The cooling rates deduced from Ni concentration profiles and precipitate sizes are within the range 1,10 °C/year for Tsarev and 10,100 °C/year for Agen. [source] Improvement in crystalline perfection, piezo-electric property and optical transparency of in-situ poled Fe,LiNbO3 single crystals by post growth annealing and polingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2005G. C. Budakoti Abstract Crystalline perfection, piezoelectric response and optical transparency of in-situ poled Fe,LiNbO3 single crystals was studied. Very low angle grain boundaries and the variations in the piezoelectric charge constant d33 were observed in the as-grown crystals. Grain boundaries were successfully removed at higher annealing temperatures but the d33 value was decreased. Low crystalline perfection and d33 were observed after poling the annealed specimen. These parameters were improved by low temperature annealing followed by very slow cooling. FTIR spectra revealed that OH, and CO32, ionic defects were present in the as-grown crystals. The OH, ion concentration was reduced, CO32, ions were removed and optical quality was improved after annealing at higher temperatures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic Properties and Crystal Structure of Solvent-Free Sc@C82 Metallofullerene MicrocrystalsCHEMPHYSCHEM, Issue 7 2007Yasuhiro Ito Abstract Magnetic properties of solvent-free crystals of the endohedral Sc@C82 are investigated by SQUID and X-ray powder diffraction. We find that the crystal is a paramagnet and the magnetic susceptibility decreases from 150 K with evidence of antiferromagnetic-like interactions by slow cooling. X-ray crystal analysis reveals the presence of a phase transition at 150 K, which is attributed to an orientational ordering transition of the fullerene molecules. At low temperatures we find a magnetic metastable state that can be controlled by the cooling rate. The metastable state can be formed by rapid cooling. The direction of Sc@C82 molecular axis in the crystals is disordered in the metastable state, and the susceptibility is higher than that in the slow cooling case at low temperature. [source] | |||||||||||||