A hybrid multilevel method for high-order discretization of the Euler equations on unstructured meshes

Higher order discretization has not been widely successful in industrial applications to compressible flow simulation. Among several reasons for this, one may identify the lack of tailor-suited, best-practice relaxation techniques that compare favorably to highly tuned lower order methods, such as finite-volume schemes. In this paper we investigate solution algorithms in conjunction with high-order Spectral Difference discretization for the Euler equations, using such techniques as multigrid and matrix-free implicit relaxation methods. In particular we present a novel hybrid multilevel relaxation method that combines (optionally matrix-free) implicit relaxation techniques with explicit multistage smoothing using geometric multigrid. Furthermore, we discuss efficient implementation of these concepts using such tools as automatic differentiation.     

Molecular reorientation of CD(4) in gas-phase mixtures

Spin-lattice relaxation times were measured for the deuterons in CD(4) in pure gas and in mixtures with the following buffer gases: Ar, Kr, Xe, HCl, N(2), CO, CO(2), CF(4), and SF(6). Effective collision cross sections sigma(theta, 2) for the molecular reorientation of CD(4) in collisions with these ten molecules are obtained as a function of temperature. These cross sections are compared with the corresponding cross sections sigma(J) obtained from (1)H spin-rotation relaxation in mixtures of CH(4) with the same set of buffer gases. Various classical reorientation models typically applied in liquids predict different ratios of the reduced correlation times for the reorientation of spherical tops. The Langevin model comes closest to predicting the magnitude of the sigma(theta, 2)/sigma(J) ratio that we obtain for CD(4).     

突出电极对四杆型RFQ腔体并联阻抗及场平整性的影响

中国科学院近代物理研究所正在进行等离子体直接注入方案的研究,以便为重离子物理研究提供稳定可靠的高流强束流。由于工作频率较低,用于等离子体直接注入方案的RFQ腔体采用了适合于低频的四杆型结构。在完成束流动力学设计的前提下,研究了RFQ腔体支撑臂的各参数对并联阻抗的影响。由于突出电极之间存在着一定大小的电容,会对腔体的性能产生影响,为使腔体达到最优化的设计,进行了突出电极对并联阻抗及场平整性的影响的研究,并给出了突出电极的取值范围。     

Wave equation with porous nonlinear acoustic boundary conditions generates a well-posed dynamical system

We consider a structural acoustic wave equation with nonlinear acoustic boundary conditions. This is a coupled system of second and first order in time partial differential equations, with boundary conditions on the interface. We prove wellposedness in the Hadamard sense for strong and weak solutions. The main tool used in the proof is the theory of nonlinear semigroups. We present the system of partial differential equations as a suitable Cauchy problem . Though the operator A is not maximally dissipative we are able to show that it is a translate of a maximally dissipative operator. The obtained semigroup solution is shown to satisfy a suitable variational equality, thus giving weak solutions to the system of PDEs. The results obtained (i) dispel the notion that the model does not generate semigroup solutions, (ii) provide treatment of nonlinear models, and (iii) provide existence of a correct state space which is invariant under the flow-thus showing that physical model under consideration is a dynamical system. The latter is obtained by eliminating compatibility conditions which have been assumed in previous work (on the linear case).     

Effects of Pressure and pH on the Physical Stability of an I-Motif DNA Structure

The thermodynamic stability of a cytosine(C)-rich i-motif tract of DNA, which features pH-sensitive [C..H..C]⁺ moieties, has been studied as function of both pressure (0.1–200 MPa) and pH (3.7–6.2). Careful attention was paid to correcting citrate buffer pH for known variations that stem from changes in pressure. Once pH-corrected, (i) at pH >4.6 the i-motif becomes less stable as pressure is increased (K_D decreases), giving a small negative volume change for dissociation (Δ_DV°) of the i-motif – a conclusion opposite to that which would be drawn if the buffer pH was not corrected for the effects of pressure; (ii) the i-motif's melting temperature increases by more than 30 K between pH 6.5 and 4.5, the consequence of an enthalpy for dissociation (Δ_DH°) of 77(3) and 90(3) kJ (mol H⁺)⁻¹ at 0.1 and 200 MPa, respectively; (iii) below pH 4.6 at 0.1 MPa (pH 4.3 at 200 MPa) the melting temperature decreases as a result of double protonation of cytosine pairs, and Δ_DH° and Δ_DV° change signs; and (iv) the combination of Δ_DH° and Δ_DV° lead to the melting temperature at pH 4.3 being 3 K higher at 200 MPa than at 0.1 MPa.     

Kinetic evidence that cysteine reacts with dopaminoquinone via reversible adduct formation to yield 5-cysteinyl-dopamine: an important precursor of neuromelanin

The reaction of cysteine (cys) with dopaminoquinone (DQ) to form (mainly) 5-cysteinyl-dopamine (5-cys-DA) is of interest because it is known to play a role in the production of melanin in the mammalian brain. To gain insight into this important reaction, an in vitro detailed kinetic study was undertaken. It has been established that cys reacts with DQ via the initial reversible formation of an intermediate adduct or complex and that this adduct then decomposes to form 5-cys-DA. A little 2-cys-DA, is almost certainly formed at the same time but its presence could not be kinetically investigated. Clarification of the kinetic data was aided by following the reaction of DQ with a cys analogue, mercaptoacetic acid (maa). Maa was found to react in a similar fashion, but also forms, reversibly, a bis-complex. This bis-complex, 2,5-(maa)(2)-dopaminoquinone, is in equilibrium with the di-protonated compound but neither of these species reacts further over the timescale employed in these kinetic studies. Equilibrium constants and first-order rate constants have been extracted from the data and the cys complex is found to be weaker than its maa analogue by an order of magnitude (K(cys)=(1.09 +/- 0.02 x 10(-3); K(1,maa)=(7.45 +/- 0.11 x 10(-3)). (Note that the possibility that cys also forms a bis-complex at much higher cys concentrations cannot be excluded.) The rates of decomposition differ markedly-the cys complex has the value k(cys)= 1830 +/- 50 s(-1) whereas the rate constant for the decomposition of the maa complex is k(maa)= 69.3 +/- 0.02 s(-1) and we attribute this difference to the effect of the positive charge carried by the amino-group on cys. Finally, the constants obtained are used to compare the reactivity of thiol addition with ring cyclization (U. El-Ayaan, E. Herlinger, R. F. Jameson, and W. Linert, J. Chem. Soc., Dalton Trans., 1997, 2813-2818) and we show how this has important implications concerning the production of neuromelanin.     

The application of power ultrasound to the surface cleaning of silica and heavy mineral sands

Power ultrasound may be used in the processing of minerals to clean their surfaces of oxidation products and fine coatings, mainly through the large, but very localised, forces produced by cavitation. Results of the application of power ultrasound to remove iron-rich coatings from the surfaces of silica sand used in glass making and to improve the electrostatic separation of mineral sand concentrates through lowering the resistivity of the conducting minerals (ilmenite and rutile) are presented. Parameters affecting ultrasonic cleaning, such as input power and levels of reagent addition, are discussed. In particular, we present data showing the relationship between power input and the particle size of surface coatings removed. This can be explained by the Derjaguin approximation for the energy of interaction between a sphere and a flat surface.     

TRYPTOPHAN EMISSION FROM HUMAN HEMOGLOBIN AND ITS ISOLATED SUBUNITS

Abstract— The emission spectra of human adult hemoglobin A₀ and its isolated α and ß subunits were obtained using a highly sensitive photon-counting spectrofluorometer. The quantum yields of the emissions, relative to free tryptophan, were also measured as well as the excitation polarization spectra for hemoglobin A₀ and apohemoglobin. The fluorophore bis-ANS was utilized to probe for the presence of apoproteins in the hemoprotein preparations. The work suggests that tryptophan may be useful as an intrinsic probe to study dynamical processes in hemoglobin.     

Relationship of Pedersen's X-protein to the protein complex in undiluted blood serum

The present investigation is an electrophoretic study of X-protein obtained by separation from blood serum by ultracentrifugation. It has been found that the X-protein of Pedersen, as well as the complexes of undiluted serum are both dissociated by dialysis and dilution. It is suggested that these latter act on the binding material which is responsible for holding the proteins in complex association.