The inverse problem of determining the filtration function and permeability reduction in flow of water with particles in porous media

Deep bed filtration of particle suspensions in porous media occurs during water injection into oil reservoirs, drilling fluid invasion of reservoir production zones, fines migration in oil fields, industrial filtering, bacteria, viruses or contaminants transport in groundwater etc. The basic features of the process are particle capture by the porous medium and consequent permeability reduction. Models for deep bed filtration contain two quantities that represent rock and fluid properties: the filtration function, which is the fraction of particles captured per unit particle path length, and formation damage function, which is the ratio between reduced and initial permeabilities. These quantities cannot be measured directly in the laboratory or in the field; therefore, they must be calculated indirectly by solving inverse problems. The practical petroleum and environmental engineering purpose is to predict injectivity loss and particle penetration depth around wells. Reliable prediction requires precise knowledge of these two coefficients. In this work we determine these quantities from pressure drop and effluent concentration histories measured in one-dimensional laboratory experiments. The recovery method consists of optimizing deviation functionals in appropriate subdomains; if necessary, a Tikhonov regularization term is added to the functional. The filtration function is recovered by optimizing a non-linear functional with box constraints; this functional involves the effluent concentration history. The permeability reduction is recovered likewise, taking into account the filtration function already found, and the functional involves the pressure drop history. In both cases, the functionals are derived from least square formulations of the deviation between experimental data and quantities predicted by the model.     

Experimental validation of steady shear and dynamic viscosity relation for yield stress fluids

A common problem when studying yield stress fluids under steady shear in rotating rheometry is that of sample fracture. It is therefore preferable to work with oscillating shear, where fracture is limited. Doraiswamy et al. (1991) proposed a model for yield stress fluids that predicts the relation: ^*( _m ) = (y) between the viscosity in steady shear and the complex viscosity in dynamic shear. The present study validates this relation experimentally with both controlled stress and controlled strain, and demonstrates its limitations. Three yield stress fluids were used: a lubricating grease with lithium based soap, a thixotropic dispersion of colloidal silica in a polymer solution and a non-thixotropic aqueous gel.     

Palladium(I) Dimer Enabled Extremely Rapid and Chemoselective Alkylation of Aryl Bromides over Triflates and Chlorides in Air

Disclosed herein is the first general chemo‐ and site‐selective alkylation of C−Br bonds in the presence of COTf, C−Cl and other potentially reactive functional groups, using the air‐, moisture‐, and thermally stable dinuclear Pd^I catalyst, [Pd(μ‐I)PtBu₃]₂. The bromo‐selectivity is independent of the substrate and the relative positioning of the competing reaction sites, and as such fully predictable. Primary and secondary alkyl chains were introduced with extremely high speed (<5 min reaction time) at room temperature and under open‐flask reaction conditions.     

Microfibrillated cellulose with sizing for reinforcing composites with LDPE

Microfibrillated cellulose (MFC) fibers were acylated by the sizing agent, alkenyl succinic anhydride (ASA) reagent in an aqueous medium, by simple impregnation. The chemical modification was confirmed by Fourier transform infrared spectroscopy and solid-state ¹³C NMR. All the samples were combined with low-density polyethylene and the morphology, thermal properties, mechanical properties and water absorption behavior of the ensuing composites were investigated. The chemical modification of the MFC with ASA improved the interfacial adhesion with the matrix and hence the mechanical properties of the composites while decreasing their water uptake capacity. In addition, it was shown that the degree of substitution strongly influenced the performance of the composites.     

Influence of yield stress on the fluid droplet impact control

The impact and the spreading of a drop of the yield stress fluid on a solid surface have been experimentally investigated. A yield stress fluid chosen as a model fluid can shed some light on the manner in which it is possible to control the impacted drop's profile. Several gels based on polymer concentration were prepared to obtain different levels of yield stress. Their shear rheological behaviours were characterized and their flow behaviours were modeled using Herschell–Bulkley equation. Droplets were impacted in a wide range of velocities upon a dry and smooth polymethylmetacrylate substrate. Their dynamics on the impacted surface were captured using a high-speed camera. The spreading and recoil of drops are studied and their behaviour was compared to that of a Newtonian fluid at each impact velocity.Influence of the yield stress level and intensity of inertia on the transient and final stages of drops impact were studied. It was shown how the increasing yield stress dictates the drop formation and also led to an emphasis of the inhibition of spreading and the weakening of retraction in the case of high inertial impacts. It was also noticed that the magnitude of the gravitational subsidence observed for the low impact velocities, is governed by the initial non-spherical shape of droplets. Dimensionless numbers were defined in the case of yield stress fluids, allowing us to compare the effects of forces present in the process and better understand the phenomena observed. Wall slip of gels on the PMMA substrate was characterized. Its influence on the drop spreading has been discussed.     

An alternative proof of Wigner theorem on quantum transformations based on elementary complex analysis

According to Wigner theorem, transformations of quantum states which preserve the probabilities are either unitary or antiunitary. This Letter presents an elementary proof of this theorem that significantly departs from the numerous ones already existing in the literature. The main line of the argument remains valid even in quantum field theory where Hilbert spaces are non-separable.     

Jump probability and bubble dynamics

The existence of a jump probability is introduced from the interpretation of transport measurements performed on magnetic bubbles. As a consequence the shape of the experimental curve giving the mobility and the extrapolated coercivity is shown to be dependent on the duration of the applied field gradient.     

Simple equilibrium dialysis-high-performance liquid chromatographic method for the in vitro assessment of 5-methoxypsoralen bound to human albumin

Increasingly used in therapeutics, 5-methoxypsoralen (5-MOP), a linear furocoumarin, associated with UVA irradiation (PUVA), is now an established treatment for skin diseases such as vitiligo, mycosis funcoides and particularly psoriasis. Successful PUVA therapy depends on a sufficiently high peak 5-MOP plasma concentration coinciding with the UVA irradiation. However, as with most drugs, only the free plasma fraction is able to enter the target cells and has a pharmacological effect. In this work, the binding of 5-MOP to human albumin was studied in vitro, using a dialysis chamber. Bound and free 5-MOP fractions were quantified by a modification of Stolk's high-performance liquid chromatographic method. Dialysis was performed at 37 degrees C and pH 7.4 for 2 h, against a 4% albumin solution in phosphate buffer. The 5-MOP concentrations used were from 5 x 10(-5) to 5 x 10(-2) g/l in 1 x 10(-1) g/l steps. The 5-MOP bound strongly to human albumin in an unsaturable way. The mean 5-MOP binding to albumin was 95.3%. These results are in accordance with those published by Artuc et al. and not with those of Veronese et al., who found a lower saturable fixation (91%). These two research groups used tritiated 5-MOP. The technique used in this work is simple and inexpensive. It can be employed easily in vivo, e.g., for the assessment of 5-MOP free fractions in different therapeutic conditions.     

Synthesis of 8-(omega-Hydroxyalkyl)-, 8-(omega-hydroxyalk-1-enyl)-, and 8-(omega-hydroxyalk-1-ynyl)adenines using the tert-butyldimethylsilyloxymethyl group, a new and versatile protecting group of adenine

The synthesis of 12 analogues of adenine substituted at C-8 by an omega-hydroxyalkyl, omega-hydroxyalk-1-enyl, or omega-hydroxyalk-1-ynyl chain of various length has been carried out in five or six steps starting from adenine. The analogues were obtained using a new protecting group of adenine, the tert-butyldimethylsilyloxymethyl group. 9-tert-Butyldimethylsilyloxymethyl-adenine is more soluble than adenine in organic solvents. It was prepared regiospecificaly in two steps from adenine and was amenable to C-8 iodination under basic conditions and to subsequent introduction of the various carbon chains at C-8 by palladium-catalyzed cross-coupling reactions (Stille or Sonogashira). The protecting group was removed under acidic conditions, thus demonstrating its versatility.     

Study of the D(+)(s)-->pi(-)pi(+)pi(+) decay and measurement of f(0) masses and widths

From a sample of 848+/-44 D(+)(s)-->pi(-)pi(+)pi(+) decays, we find gamma(D(+)(s)-->pi(-)pi(+)pi(+))/gamma(D(+)(s)-->straight phipi(+)) = 0.245+/-0.028(+0.019)(-0.012). Using a Dalitz plot analysis of this three body decay, we find significant contributions from the channels rho(0)(770)pi(+), rho(0)(1450)pi(+), f(0)(980)pi(+), f(2)(1270)pi(+), and f(0)(1370)pi(+). We also present the values obtained for masses and widths of the resonances f(0)(980) and f(0)(1370).