2,713 research outputs found
Mass transfer and chemical reaction in gas-liquid-liquid systems
Gas-liquid-liquid reaction systems may be encountered in several important fields of application as e.g. hydroformylation, alkylation, carboxylation, polymerisation, hydrometallurgy, biochemical processes and fine chemicals manufacturing. However, the reaction engineering aspects of these systems have only been considered occasionally. For systems with very slow reaction kinetics this is not surprising, as the three phases will be at physical equilibrium. In reaction systems with fast parallel and consecutive reactions the effects of mass transfer and mixing on the product yield can be significant. A fascinating example of such a reaction system is the Koch synthesis of Pivalic Acid. In this work this reaction system was chosen as model system to study these effects
London dispersion forces without density distortion: a path to first principles inclusion in density functional theory
We analyse a path to construct density functionals for the dispersion
interaction energy from an expression in terms of the ground state densities
and exchange-correlation holes of the isolated fragments. The expression is
based on a constrained search formalism for a supramolecular wavefunction that
is forced to leave the diagonal of the many-body density matrix of each
fragment unchanged, and is exact for the interaction between one-electron
densities. We discuss several aspects: the needed features a density functional
approximation for the exchange-correlation holes of the monomers should have,
the optimal choice of the one-electron basis needed (named "dispersals"), and
the functional derivative with respect to monomer density variations.Comment: 12 pages, 4 figure
Statins and the vasculopathy of systemic sclerosis: potential therapeutic agents?
It has been postulated that endothelial cell injury is the initiating event in the pathogenesis of systemic sclerosis, causing attraction, attachment, migration and infiltration of activated T-cells and subsequent production of cytokines and growth factors. As a result of the action of these cytokines and growth factors, chemoattraction of fibroblasts into the vessel wall and transdifferentiation of resident fibroblasts and smooth muscle cells into myofibroblasts occur leading to fibrosis and exaggerated collagen deposition in the vessel wall. To date, the therapeutic options for the vasculopathy of systemic sclerosis have been limited to drugs that cause vasodilation and inhibit platelet aggregation and only a few agents have shown vascular remodeling effects. Therapeutic agents that could potentially modify the course of this vasculopathy may have a disease-modifying effect, particularly, if instituted in the early stages of the disease. Extensive recent studies have shown that statins display numerous effects independent of their well-established lipid-lowering effect that may be of potential benefit in preventing vascular injury and ischemic vascular events. Here, we review the current literature, which suggests that statins may have a modifying effect on the vasculopathy of systemic sclerosis
A new method to determine the skin thickness of asymmetric UF-membranes using colloidal gold particles
In this paper a new method is presented for the determination of the skin thickness of asymmetric ultrafiltration membranes. The method is based on the use of well-defined, uniformly sized colloidal gold particles, permeated from the sublayer side of the membrane, combined with electron microscopic analysis of the membrane afterward. Using this method poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and polysulfone (PSf) membranes were investigated. PPO membranes appeared to have a well-defined skin layer with a thickness of about 0.2 μm and a pore size distinctly different from that in the macroporous layer underneath. In the case of PSf such a distinct skin layer cannot be defined. The size of the pores in these membranes gradually increases from skin to sublayer
Systemic sclerosis: current views of its pathogenesis.
Systemic sclerosis (SSc) is an autoimmune disorder of unknown etiology characterized by severe and often progressive cutaneous and visceral fibrosis, pronounced alterations in the microvasculature, and numerous cellular and humoral immune abnormalities. Clinically, SSc is very heterogeneous, encompassing a spectrum ranging from mild limited forms of skin sclerosis with minimal internal organ involvement to severe skin and multiple internal organ fibrosis. Mortality and morbidity in SSc are very high and are directly related to the extent of the fibrotic and microvascular alterations. A better understanding of the pathogenesis of this incurable disorder will help to better target and design effective therapy in the future
Noise in (double) relaxation oscillation SQUIDs
We have modelled the effect of two intrinsic noise sources on the flux noise spectral density of (Double) Relaxation Oscillation SQUIDs ((D)ROSs) based on hysteretic Josephson tunnel junctions. An important noise source is the spread in the critical current of the SQUID due to thermal fluctuations. Critical current noise mainly determines the noise on the average output voltage of DROSs with high flux to voltage transfer. A second noise source is the spread in the relaxation frequency due to the random interaction between the Josephson oscillations and the relaxation oscillations during switching to the zero-voltage state. This effect can dominate the voltage noise of a ROS
Mathematical models for sleep-wake dynamics: comparison of the two-process model and a mutual inhibition neuronal model
Sleep is essential for the maintenance of the brain and the body, yet many
features of sleep are poorly understood and mathematical models are an
important tool for probing proposed biological mechanisms. The most well-known
mathematical model of sleep regulation, the two-process model, models the
sleep-wake cycle by two oscillators: a circadian oscillator and a homeostatic
oscillator. An alternative, more recent, model considers the mutual inhibition
of sleep promoting neurons and the ascending arousal system regulated by
homeostatic and circadian processes. Here we show there are fundamental
similarities between these two models. The implications are illustrated with
two important sleep-wake phenomena. Firstly, we show that in the two-process
model, transitions between different numbers of daily sleep episodes occur at
grazing bifurcations.This provides the theoretical underpinning for numerical
results showing that the sleep patterns of many mammals can be explained by the
mutual inhibition model. Secondly, we show that when sleep deprivation disrupts
the sleep-wake cycle, ostensibly different measures of sleepiness in the two
models are closely related. The demonstration of the mathematical similarities
of the two models is valuable because not only does it allow some features of
the two-process model to be interpreted physiologically but it also means that
knowledge gained from study of the two-process model can be used to inform
understanding of the mutual inhibition model. This is important because the
mutual inhibition model and its extensions are increasingly being used as a
tool to understand a diverse range of sleep-wake phenomena such as the design
of optimal shift-patterns, yet the values it uses for parameters associated
with the circadian and homeostatic processes are very different from those that
have been experimentally measured in the context of the two-process model
Watching the Watchers Behind the Camera; Current Trends in Casino Surveillance and Loss Prevention
Casino surveillance expert Derk Boss gives the September 2009 Gaming Research Colloquium lecture and tackles many topics, including the latest developments in casino surveillance, how much it costs to corrupt a dealer, and how someone embarks on a career in surveillance
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