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An attempt has been made in this article to critically survey the field of low Reynolds number flows, with particular regard to the hydrodynamic resistance of particles in this regime. A remarkable burgeoning of interest in such problems has occurred wlthin the past decade. Significant advances have been recorded on both the theoretical and experimental sides, with the former gains far outdlstancing the latter m scope. Problems which would have been impossible to solve rigorously before the advent of singular perturbation techniques are now being regularly solved, though hardly in a routine fashion; insight, intuition, inspiration, and ingenuity are still the order of the day. For those interested in direct engineering applications of the material covered by this review, the perspective from which many of the more general results set forth here should be viewed is, perhaps, best illustrated by an example: The resistance of any solid particle to translational and rotational motions in Stokes flow may be completely calculated from knowledge of a set of 21 scalar coefficients (Section II,C,l). While it seems highly improbable to expect that all these coefficients could be experimentally measured in practice, except perhaps in the trivial case of highly symmetrical bodies for which many of the coefficients vanish identically, this does not detract from the conceptual advantages of knowing exactly how much one does not know. Having an ideal goal against which the extent of present knowledge can be gaged permits a rational decision as to how to optimize one's investment of time, effort, and money in the pursuit of additional data. Furthermore, with the development of high-speed digital computers it may soon be possible to calculate all these coefficients for any given body (O 1 b). The general theory provides a rigorous framework into which such knowledge may be embedded. Use of symbolic" drag coefficients" (Section II,C,2) and symbolic heat- and mass-transfer" coefficients" (Section IV,A) furnishes a unique method for describing the intrinsic, interphase transport properties of particles for a wide variety of boundary conditions. Here, the particle resistance is characterized by a partial differential operator that represents its intrinsic resistance to vector or scalar transfer, independently of the physical properties of the fluid, the state of motion of the particle, or of the unperturbed velocity or temperature fields at infinity. Though restricted as yet in applicability, the general ideas underlying the existence of these operators appear capable of extension in a variety of ways. A recurrent theme arising throughout the analysis pertains to the screwlike properties of particles and of their intrinsic right- and left-handedness (Sections II,C, 1; II,C,2; III,C and IV,B). Such properties reflect an inseparable coupling between the translational and rotational motions of the particle. Helicoidally isotropic particles furnish the simplest examples of bodies manifesting screw-like behavior. These particles are isotropic, in that their properties are the same in all directions. Yet they possess a sense, and spin as they settle in a fluid. These id eas are likely to be of interest to microbiologists, biophysicists, geneticists, and others in the life sciences for whom handedness and life are intimately intertwined. The microscopic dimensions of the objects of interest to them insures ipso Jacto that the motion takes place at very small Reynolds numbers. Readers interested in an elementary but broad survey of sense in the physical and biological sciences are referred to Gardner's delightful book "The Ambidextrous Universe" (01). First-order corrections to the Stokes force on a particle, arising from wallor inertial-effects, can be directly expressed in terms of the Stokes force on the body in the absence of such effects. Thus, with regard to wall-effects in the Stokes regime, Eq. (135) expresses the force experienced by a particle falling in, say, a circular cylinder, in terms of the comparable force experienced by the particle when falling with the same velocity and orientation in the unbounded fluid. Equation (139) expresses a similar relationship for the torque on a rotating particle in a circular cylinder, as does Eq. (166) for the first-order interaction between two particles in an unbounded fluid in terms of the properties of the individual particles. Analogously, Eq. (234) expresses the inertial correction to the Stokes drag force in terms of the Stokes force itself. A comparable relationship exists (Section IV, A) between the heat-transfer coefficient at small, nonzero Peelet numbers and the heat-transfer coefficient at zero Peelet number-that is, the coefficient for conduction heat transfer. Finally, Eqs. (78)-(79) (or their symbolic operator counterparts) permit direct calculation of the Stokes force and torque experienced by a particle in an arbitrary field of flow solely from knowledge of the elementary solutions of Stokes equations for translation and rotation of the particle in a fluid at rest at infinity. The utility of already available knowledge is thus greatly extended by the existence of such relations. It permits one whose interests lie entirely in the macroscopic manifestation of the motion, e.g., the force and torque on the body, to bypass the oftentimes difficult problem of obtaining a detailed solution of the equations of motion, and to proceed directly to the computation of the force and torque on the body from the prescribed boundary conditions alone. The calculation is thereby reduced to a quadrature. The contents of this review may be read simultaneously from two different points of view. First and foremost it may be regarded as a compendium of recent advances in low Reynolds number flows. Secondly, from a pedagogic viewpoint it may be profitably used to illustrate the direct application of invariant techniques, that is, vector-polyadic and tensor methods, to a class of physical problems. Because of the relative simplicity and rich variety of physical problems associated with low Reynolds number motions, intuitive arguments may be employed to gain insight into the nature of polyadics and tensors; the role played by the concept of direction as a primitive entity is brought out here to a degree not usually found in standard works on tensor analysis.
Dynamics of relativistic heavy-ion collisions is investigated on the basis of a simple (1+1)-dimensional hydrodynamical model in light-cone coordinates. The main emphasis is put on studying sensitivity of the dynamics and observables to the equation of state and initial conditions. Low sensitivity of pion rapidity spectra to the presence of the phase transition is demonstrated, and some inconsistencies of the equilibrium scenario are pointed out. Possible non-equilibrium effects are discussed, in particular, a possibility of an explosive disintegration of the deconfined phase into quark-gluon droplets. Simple estimates show that the characteristic droplet size should decrease with increasing the collective expansion rate. These droplets will hadronize individually by emitting hadrons from the surface. This scenario should reveal itself by strong non-statistical fluctuations of observables. Critical Point and Onset of Deconfinement 4th International Workshop July 9-13 2007 GSI Darmstadt,Germany
We introduce a model for the real-time evolution of a relativistic fluid of quarks coupled to non-equilibrium dynamics of the long wavelength (classical) modes of the chiral condensate. We solve the equations of motion numerically in 3+1 spacetime dimensions. Starting the evolution at high temperature in the symmetric phase, we study dynamical trajectories that either cross the line of first-order phase transitions or evolve through its critical endpoint. For those cases, we predict the behavior of the azimuthal momentum asymmetry for highenergy heavy-ion collisions at nonzero impact parameter.
Introduction: We report on successful endovascular treatment of a hydrofluoric acid burn to the hand.
Report: A worker complained of severe pain in the fingers D II to D V after injury with 60% hydrofluoric acid. A digital subtraction angiography showed vasospasm of the common palmar digital artery. We selectively applied 20% calcium gluconate intra-arterially.
After treatment all arteries were perfused. Alprostadil, acetylsalicylic acid and clopidogrel were administered in conjunction. Pain symptoms improved and sensory and motor functions were restored.
Discussion: Immediate angiography and intra-arterial application of calcium gluconate are recommended to treat hydrofluoric acid burn to a limb.
The E-pathway of transmembrane proton transfer has been demonstrated previously to be essential for catalysis by the diheme-containing quinol:fumarate reductase (QFR) of Wolinella succinogenes. Two constituents of this pathway, Glu-C180 and heme b(D) ring C (b(D)-C-) propionate, have been validated experimentally. Here, we identify further constituents of the E-pathway by analysis of molecular dynamics simulations. The redox state of heme groups has a crucial effect on the connectivity patterns of mobile internal water molecules that can transiently support proton transfer from the b(D)-C-propionate to Glu-C180. The short H-bonding paths formed in the reduced states can lead to high proton conduction rates and thus provide a plausible explanation for the required opening of the E-pathway in reduced QFR. We found evidence that the b(D)-C-propionate group is the previously postulated branching point connecting proton transfer to the E-pathway from the quinol-oxidation site via interactions with the heme b(D) ligand His-C44. An essential functional role of His-C44 is supported experimentally by site-directed mutagenesis resulting in its replacement with Glu. Although the H44E variant enzyme retains both heme groups, it is unable to catalyze quinol oxidation. All results obtained are relevant to the QFR enzymes from the human pathogens Campylobacter jejuni and Helicobacter pylori.
Hydrogenation of CO₂ at ambient pressure catalyzed by a highly active thermostable biocatalyst
(2018)
Background: Replacing fossil fuels as energy carrier requires alternatives that combine sustainable production, high volumetric energy density, easy and fast refueling for mobile applications, and preferably low risk of hazard. Molecular hydrogen (H2) has been considered as promising alternative; however, practical application is struggling because of the low volumetric energy density and the explosion hazard when stored in large amounts. One way to overcome these limitations is the transient conversion of H2 into other chemicals with increased volumetric energy density and lower risk hazard, for example so-called liquid organic hydrogen carriers such as formic acid/formate that is obtained by hydrogenation of CO2. Many homogenous and heterogenous chemical catalysts have been described in the past years, however, often requiring high pressures and temperatures. Recently, the first biocatalyst for this reaction has been described opening the route to a biotechnological alternative for this conversion.
Results: The hydrogen-dependent CO2 reductase (HDCR) is a highly active biocatalyst for storing H2 in the form of formic acid/formate by reversibly catalyzing the hydrogenation of CO2. We report the identification, isolation, and characterization of the first thermostable HDCR operating at temperatures up to 70 °C. The enzyme was isolated from the thermophilic acetogenic bacterium Thermoanaerobacter kivui and displays exceptionally high activities in both reaction directions, substantially exceeding known chemical catalysts. CO2 hydrogenation is catalyzed at mild conditions with a turnover frequency of 9,556,000 h−1 (specific activity of 900 µmol formate min−1 mg−1) and the reverse reaction, H2 + CO2 release from formate, is catalyzed with a turnover frequency of 9,892,000 h−1 (930 µmol H2 min−1 mg−1). The HDCR of T. kivui consists of a [FeFe] hydrogenase subunit putatively coupled to a tungsten-dependent CO2 reductase/formate dehydrogenase subunit by an array of iron–sulfur clusters.
Conclusions: The discovery of the first thermostable HDCR provides a promising biological alternative for a chemically challenging reaction and might serve as model for the better understanding of catalysts able to efficiently reduce CO2. The catalytic activity for reversible CO2 hydrogenation of this enzyme is the highest activity known for bio- and chemical catalysts and requiring only ambient temperatures and pressures. The thermostability provides more flexibility regarding the process parameters for a biotechnological application.
Mires or peat swamps have a restricted distribution in Australia and are limited to areas where hydrological inputs exceed evapotranspiration. In NSW, mires are restricted to the coast, adjacent ranges or tablelands, and along the Great Dividing Range; most are listed as threatened ecological communities under State or Commonwealth legislation. Due primarily to the relatively high rainfall and suitable geology, the Blue Mountains region includes a number of such threatened mire ecological communities. Most of these mire types are largely included within the Greater Blue Mountains World Heritage Area, although there are notable exceptions, such as the endangered Newnes Plateau Shrub Swamps.
This paper reports on a little-known group of diverse, relatively isolated and largely unprotected mires, in a relatively low rainfall area in the upper Cudgegong River catchment, east of Rylstone in the NSW Central Tablelands, and of their floristic, hydrogeomorphic and typological relationship with other mires of the Blue Mountains. They can be broadly divided into montane bogs, montane fens and hanging swamps. Particular attention is focussed on the largest and most diverse one, Rollen Creek swamp, which contains all three types. It is hoped that highlighting this hitherto unrecognised group of high conservation-value mires will contribute to their improved conservation and encourage further research into mires of eastern NSW.
Die von Herrn Professor Semon bei seinem Besuche der Thursday-Insel und Ambon 1892-1893 gesammelten Hydroidpolypen setzten sich aus 12 Arten zusammen, darunter 5 aus Ambon und 7 von der Thursday-Insel. Eine davon ist neu (Acanthocladium studeri), eine andere Art konnte mangels der Gonotheken nicht näher bestimmt werden. Die Hydroidenfauna Ambons hat PICTET (93) während eines zweimonatlichen Aufentlialtes eingehend studirt und 32 Arten von dort bekannt gemacht, PICTHT hebt die Armuth Ambons an litoralen Hydroiden gegenüber den übrigen dort lebenden Evertebraten hervor. Die wenigen (4) Arten, welche SEMON von hier mitgebracht hat, hat auch PICTET dort beobachtet und beschrieben. Folgende Species sind bei Ambon und der Thursday-lnsel von Herrn Professor SEMON erbeutet worden: ...
Hydroiden von Ternate
(1896)