Search results for "Cooling"

Small ice particles at slightly supercooled temperatures in tropical maritime convection

2020

In this paper we show that the origin of the ice phase in tropical cumulus clouds over the sea may occur by primary ice nucleation of small crystals at temperatures just between 0 and −5 ∘C. This was made possible through use of a holographic instrument able to image cloud particles at very high resolution and small size (6 µm). The environment in which the observations were conducted was notable for the presence of desert dust advected over the ocean from the Sahara. However, there is no laboratory evidence to suggest that these dust particles can act as ice nuclei at temperatures warmer than about −10 ∘C, the zone in which the first ice was observed in these clouds. T…

2017

Abstract. During free fall in clouds, ice hydrometeors such as snowflakes and ice particles grow effectively by riming, i.e., the accretion of supercooled droplets. Volatile atmospheric trace constituents dissolved in the supercooled droplets may remain in ice during freezing or may be released back to the gas phase. This process is quantified by retention coefficients. Once in the ice phase the trace constituents may be vertically redistributed by scavenging and subsequent precipitation or by evaporation of these ice hydrometeors at high altitudes. Retention coefficients of the most dominant carboxylic acids and aldehydes found in cloud water were investigated in the Mainz vertical wind tu…

Natural Convection Cooling of a Hot Vertical Wall Wet by a Falling Liquid Film

2008

Abstract The system studied is a plane channel in which one of the two vertical walls is kept at an arbitrary temperature profile and may be partially or completely wet by a falling liquid film, while the opposite wall is adiabatic. Air from the environment flows along the channel with a mass flow rate which depends on the balance between hydraulic resistances and buoyancy forces. These latter, in their turn, depend on the distribution of temperature and humidity (hence, density) along the channel and eventually on the heat and mass transferred from wall and film to the humid air. A simplified computational model of the above system was developed and applied to the prediction of relevant qu…

Convectively driven vortex flows in the Sun

2008

We have discovered small whirlpools in the Sun, with a size similar to the terrestrial hurricanes (<~0.5 Mm). The theory of solar convection predicts them, but they had remained elusive so far. The vortex flows are created at the downdrafts where the plasma returns to the solar interior after cooling down, and we detect them because some magnetic bright points (BPs) follow a logarithmic spiral in their way to be engulfed by a downdraft. Our disk center observations show 0.009 vortexes per Mm^2, with a lifetime of the order of 5 min, and with no preferred sense of rotation. They are not evenly spread out over the surface, but they seem to trace the supergranulation and the mesogranulation. T…

An efficient proposal for the application of simulated annealing algorithms

2014

Complex nonlinear optimization problems require specific resolution techniques. These problems are often characterized by a solution space that presents many local optima. In these cases, local search algorithms, as the classical descent neighborhood search method, have a heavy drawback: the optimization algorithm generally converges towards a local minimum. To avoid getting trapped in a local minimum, the optimization algorithm must allow to accept worse solutions than the current one. Several kinds of algorithms have been ideated for this purpose and they differ for the acceptance criteria of a pejorative solution. Among such algorithms it is possible to remember the Taboo Search (TS) and…

Aging in a free-energy landscape model for glassy relaxation. II. Fluctuation-dissipation relations.

2006

Several fluctuation-dissipation relations are investigated for a simple free-energy landscape model designed to describe the primary relaxation in supercooled liquids. The calculations of the response and of the correlation functions are performed for a quench from a high temperature to a low temperature. In the model, all dynamical quantities reach equilibrium after long times, but for times shorter than the re-equilibration time they do not exhibit time-translational invariance and the fluctuation-dissipation theorem is violated. Two measures for these violations are considered. One such measure is given by the slope in a plot of the integrated response versus the correlation function and…

Spin-orbit, radial, and angular coupling effects in the NaRb excited states

2009

Spin-orbit, radial, and angular nonadiabatic matrix elements between the lowest excited states of NaRb are evaluated by quasi-relativistic ab initio methods, and the results accompanied by potential curves, permanent and transition moments are compared with experimental data and preceding calculations.

Dynamics of a supercooled polymer melt above the mode-coupling critical temperature: cage versus polymer-specific effects

2000

This paper reports results of molecular dynamics simulations for a glassy polymer melt consisting of short, non-entangled chains. The temperature region studied covers the supercooled state of the melt above the mode-coupling critical temperature. The analysis focuses on the interplay of simple-liquid and polymer-specific effects. One can clearly distinguish two regimes: a regime of small and one of large monomer displacements. The first regime corresponds to motion of a monomer in its local environment. It is dominated by the cage effect and well described by the idealized mode-coupling theory. The second regime is governed by the late-β/early-α process. In this regime the connectivity of …

Relations entre les variations climatiques, les perturbations du cycle du carbone et les crises de la production carbonatée : application au Crétacé …

2011

The Early Cretaceous is punctuated by carbon cycle perturbations, associated with organic matter burial episodes and carbonate production crises. These events coincide with short-term cooling (<1Ma), yet the mechanisms are still unclear, because of low resolution in sea surface temperature reconstructions. Recent climatic models suggest that carbonate-platform-collapse events may trigger a short-term ocean cooling episode (Donnadieu et al., accepted). In order to establish relations between climates and carbonate productions, we performed stratigraphic, palaeoecologic and geochemical analyses on Valanginian sediments from the La Charce-Vergol and the Ollioules sections (South-East France) a…

A comparative study of mechanical properties of fresh and frozen-thawed porcine intervertebral discs in a bioreactor environment

2016

Abstract Limited availability of fresh intervertebral discs (IVDs) necessitates the use of frozen-thawed samples in biomechanical investigations. Several authors have reported the mechanical properties of frozen-thawed IVDs, but few studies have investigated the effects of storage temperature and cooling rate. The validity and reliability of the applied freezing-thawing procedures are still relatively unknown. The study aims to compare the mechanical responses of fresh porcine IVDs and porcine IVDs, which were frozen at different freezing temperatures with a controlled-rate cooling process and then thawed. The specimens were obtained from pigs aged 6 months. A total of 18 functional spine u…