Transport effects selectivity, effect

Typical magnetoconductance data for the individual MWCNT are shown in Fig. 4. At low temperature, reproducible aperiodic fluctuations appear in the magnetoconduclance. The positions of the peaks and the valleys with respect to magnetic field are temperature independent. In Fig. 5, we present the temperature dependence of the peak-to-peak amplitude of the conductance fluctuations for three selected peaks (see Fig. 4) as well as the rms amplitude of the fluctuations, rms[AG]. It may be seen that the fiuctuations have constant amplitudes at low temperature, which decrease slowly with increasing temperature following a weak power law at higher temperature. The turnover in the temperature dependence of the conductance fluctuations occurs at a critical temperature Tc = 0.3 K which, in contrast to the values discussed above, is independent of the magnetic field. This behaviour was found to be consistent with a quantum transport effect of universal character, the universal conductance fluctuations (UCF) [25,26]. UCFs were previously observed in mesoscopic weakly disordered... 

Methylenedioxymethamphetamine (MDMA ecstasy) is a synthetic analog of amphetamine that produces hallucinations, an elevation in mood, and a feeling of emotional closeness . This latter property has led to Ecstasy being referred to as the hug drag . The unique properties of Ecstasy as compared to the parent compound amphetamine are believed to be due to the more selective effects of Ecstasy in promoting transporter-mediated release of serotonin. The use of Ecstasy has become a part of the culture associated with rave style dance parties. 

VMATs are not inhibited by drugs such as cocaine, tricyclic antidqnessants and selective serotonin reuptake inhibitors that affect plasma membrane monoamine transport. Amphetamines have relatively selective effects on monoaminergic cells due to selective uptake by plasma membrane monoamine transporters, but their effect appears to be mediated by their ability as weak bases to reduce ApH, the driving force for vesicular monoamine transport that leads to efflux of the vesicular contents into the cytoplasm. 

In situ perfusion studies assess absorption as lumenal clearance or membrane permeability and provide for isolation of solute transport at the level of the intestinal tissue. Controlled input of drug concentration, perfusion pH, osmolality, composition, and flow rate combined with intestinal region selection allow for separation of aqueous resistance and water transport effects on solute tissue permeation. This system provides for solute sampling from GI lumenal and plasma (mesenteric and systemic) compartments. A sensitive assay can separate metabolic from transport contributions. 

Chan, H. and Butterworth, R. F. Cell-selective effects of ammonia on glutamate transporter and receptor function in the mammalian brain. Neurochem. Int. 43 525-532,2003. 

Daskalakis, K.D. 1995. Silver in oyster soft tissue relations to site selection and sampling size, in A.W. Andren and T.W. Bober (organizers). Transport, Fate and Effects of Silver in the Environment. 3rd International Conference. August 6-9, 1995, Washington, DC. Univ. Wisconsin Sea Grant Inst., Madison, WI. 

Various works has pointed out the role of the nanostructure of the catalysts in their design.18-26 There is a general agreement that the nanostructure of the oxide particles is a key to control the reactivity and selectivity. Several papers have discussed the features and properties of nanostructured catalysts and oxides,27-41 but often the concept of nanostructure is not clearly defined. A heterogeneous catalyst should be optimized on a multiscale level, e.g. from the molecular level to the nano, micro- and meso-scale level.42 Therefore, not only the active site itself (molecular level) is relevant, but also the environment around the active site which orients or assist the coordination of the reactants, may induce sterical constrains on the transition state, and affect the short-range transport effects (nano-scale level).42 The catalytic surface process is in series with the transport of the reactants and the back-diffusion of the products which should be concerted with the catalytic transformation. Heat... 

It must be emphasized that the above considerations were made in the absence of reaction. Interfacial mass transfer followed by reaction requires further consideration. The Hatta regimes classify transfer-reaction situations into infinitely slow transport compared to reaction (Hatta category A) to infinitely fast transport compared to reaction (Hatta category H) [42]. In the first case all reaction occurs at the interface and in the second all reaction occurs in the bulk fluid. Homogenous catalytic hydrogenations, carbonylations etc. require consideration of this issue. An extreme example of the severity of mass transport effects on reactivity and selectivity in hydroformylation has been provided by Chaudari [43]. Further general discussions for homogeneous catalysis can be found elsewhere [39[. 

Fluoxetine Highly selective blockade of serotonin transporter (SERT) little effect on norepinephrine transporter (NET) Acute increase of serotonergic synaptic activity slower changes in several signaling pathways and neurotrophic activity Major depression, anxiety disorders panic disorder obsessive-compulsive disorder post-traumatic stress disorder perimenopausal vasomotor symptoms eating disorder (bulimia) Half-lives from 15-75 h oral activity Toxicity Well tolerated but cause sexual dysfunction Interactions Some CYP inhibition (fluoxetine 2D6, 3A4 fluvoxamine 1A2 paroxetine 2D6)... 

Pancreatic cholesterol esterase (3.1.1.3.) aids in transporting cholesterol to the enterocyte. By utilizing a selective and potent cholesterol esterase inhibitor 6-chloro-3-(l-ethyl-2-cyclohexyl)-2-pyrone, the absorption of cholesterol in hamsters could be reduced [71]. Wadkins et al. [72] synthesized novel sulfonamide derivatives, which demonstrated greater than 200-fold selectivity for human intestinal carboxylesterase compared with the human liver carboxylesterase hCEl, and none of them was an inhibitor of human acetylcholinesterase or butyrylcholinester-ase. Maybe these agents can serve as lead compounds for the development of effective, selective carboxylesterase inhibitors for clinical applications. Also the potent P-gp inhibitor verapamil [73] as well as S,S,S-tributylphosphortrithionate (DEF) [74] may exhibit carboxylesterase inhibitory properties. Various other inhibitors of human esterases are listed in Table 5.6. 

The contents of the present contribution may be outlined as follows. Section 6.2.2 introduces the basic principles of coupled heat and mass transfer and chemical reaction. Section 6.2.3 covers the classical mathematical treatment of the problem by example of simple reactions and some of the analytical solutions which can be derived for different experimental situations. Section 6.2.4 is devoted to the point that heat and mass transfer may alter the characteristic dependence of the overall reaction rate on the operating conditions. Section 6.2.S contains a collection of useful diagnostic criteria available to estimate the influence of transport effects on the apparent kinetics of single reactions. Section 6.2.6 deals with the effects of heat and mass transfer on the selectivity of basic types of multiple reactions. Finally, Section 6.2.7 focuses on a practical example, namely the control of selectivity by utilizing mass transfer effects in zeolite catalyzed reactions. 

The performance indexes, which define an optimal catalyst distribution, include effectiveness, selectivity, yield and deactivation rate. The key parameters, affecting the choice of the optimal catalyst profile, are the reaction kinetics, the transport resistances, and the production cost of the catalyst. An extensive review of the theoretical and experimental developments in this area is available [20]. Two typical examples to demonstrate the importance of an appropriate distribution of the active components are now described. 

Both active and passive fluxes across the cellular membranes can occur simultaneously, but these movements depend on concentrations in different ways (Fig. 3-17). For passive diffusion, the unidirectional component 7jn is proportional to c°, as is indicated by Equation 1.8 for neutral solutes [Jj = Pj(cJ — cj)] and by Equation 3.16 for ions. This proportionality strictly applies only over the range of external concentrations for which the permeability coefficient is essentially independent of concentration, and the membrane potential must not change in the case of charged solutes. Nevertheless, ordinary passive influxes do tend to be proportional to the external concentration, whereas an active influx or the special passive influx known as facilitated diffusion—either of which can be described by a Michaelis-Menten type of formalism—shows saturation effects at higher concentrations. Moreover, facilitated diffusion and active transport exhibit selectivity and competition, whereas ordinary diffusion does not (Fig. 3-17). 

We also examine the structure sensitivity of CO hydrogeneration on Co and Ru crystallites supported on various metal oxide supports at conditions that favor high selectivity (>80%) to C5+ products. We describe procedures for the synthesis of catalytic materials with high active site densities and controlled intrapellet distributions of sites. Finally, we review the extensive literature that has previously described metal dispersion, support, and transport effects on FT synthesis rate and selectivity. 

E. Transport Effects and the Control of Selectivity in Fc-based Fischer-Tropsch Synthesis... 

If solubility alone determined the optimal cleaning conditions, a few selections of T and P would determine the conditions for running the reactor. The transport properties of the fluid interacting with the part to be cleaned may be just as important as solubility in determining the overall success of the cleaning operation. Transport effects and scaleup issues are of crucial concern in cleaning and are discussed in detail in the chapter by M. R. Phelps et al. 

The previous results underline the importance of shape selectivity effects even for the transformation of small olefins such as butene. The results are in agreement with the early, related work by Haag et al. 59). who investigated cracking of olefins and paraffins catalyzed by the zeolite HZSM-5 and distinguished between restricted transition state shape selectivity and mass transport shape selectivity, ft is clear that the effects discussed here are best described in terms of restricted transition state shape selectivity. 

A simulation of trickle-bed hydrogenations was also performed, giving almost the same high selectivity as in the cross-flow case. This shows that the high selectivity is primarily a pore transport effect and not a result of the addition of the arene and hydrogen to opposite sides of the porous plate. 

The manner in which mass transport can affect reaction selectivity depends on the kind of reactions involved.24 Three general types of selectivity have been defined and mass transport effects each in a different way. 

Capillary electrochromatography is a more complicated system than CE and HPLC due to the combination of both electrophoretic and chromatographic transport mechanisms. It is difficult to define an effective selectivity (separation factor) as in the case of general chromatography or general electrophoresis. To better illustrate the interactions that control selectivity, we defined a relative selectivity a,. =. tjt 2), and postulated a model that illustrates the effect of separation parameters on the enantioselectivity [10]. 

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