Concentration profiles retention—flux curves for composite membranes in reverse osmosis

The influence of a transition layer between the skin porous sublayer in asymmetric membranes was investigated, using a numerical integration of the Spiegler—Kedem equation. It is shown that the transition layer will only interfere if the resistance to solute diffusion within this layer is of the same order of magnitude as in the skin layer.Experiments with multi-layer membranes were performed by placing a highly selective asymmetric membrane on top of a membrane of lower selectivity, and vice versa. The resulting retention-flux curves can be simulated by a three-layer model: σ $\text{P}$/Δx for the two skin layers were determined from reverse osmosis data on the individual membranes whereas the values for the interjacent porous layer were correlated with the porosity and thickness of that layer.     

A cascade-evaporation model for photonuclear reactions

Detailed and systematic Monte Carlo calculations have been performed for different characteristics of inelastic photonuclear reactions for an energy range of T_γ ≈ 50 MeV–1 GeV in the framework of the intranuclear cascade model taking into account the competition between particle evaporation and fission of excited residual nuclei. The calculated results agree well with experimental data. On the basis of the data listed it is possible to extrapolate the corresponding characteristics for intermediate energies and nuclei.     

Experimental and theoretical studies of positive pion production on 10B and 40Ca by 163–186 MeV protons

The reactions ${}^{10}\text{B(p}\text{,π}{}^{\mathrm{+}}\text{)}{}^{11}\text{B}$ and ${}^{40}\text{Ca(p}\text{,π}{}^{\mathrm{+}}\text{)}{}^{41}\text{Ca}$ have been studied for proton energies between 163 and 186 MeV. Angular distributions for the ground states and the excited state at 2.13 MeV in ¹¹B are presented. Cross sections calculated in the one-nucleon model, under different assumptions about the interaction Hamiltonian as well as the pion and proton optical potentials, are compared with the experimental distribution from the $\text{1}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ state in ⁴¹Ca.     

(γ, γ′) reactions in 89Y, 115In and 197Au at intermediate energies

The yields of isomeric states in ⁸⁹Y, ¹¹⁵In and ¹⁹⁷Au produced by the (γ, γ') reaction have been measured in the energy range 100–800 MeV by the activation method. From the yields the cross sections have been deduced. Large cross sections around the first pion resonance are found. The experimental results are compared to calculations based on the impulse approximation.     

Comparative yields of alkali elements and thallium from uranium irradiated with GeV protons,3He and12C

Mass-separated ion beams of the alkali elements Na, K, and Fr, and of the element Tl, were produced by bombarding a uranium target with 600 MeV protons, 890 MeV³He^{2 +}, and 936 MeV¹²C^{4 +}. Isotopic production yields are reported. In the case of the¹²C beam, these are thick target yields. Absolute cross-sections for the proton beam data were deduced by normalizing the delay-time corrected yield curves to measured cross-sections. For products farthest away from stability, the³He^{2 +} beam generally gives the highest yields.     

Solvent effects on the redox properties of Cu complexes used as mediators in atom transfer radical polymerization

Solvent effects on the redox properties of six Cu(I) complexes used as mediators in atom transfer radical polymerization (ATRP) have been studied using cyclic voltammetry. The six ligands used were tris[2-(dimethylamino)ethyl]amine, N-(n-propyl)-2-pyridylmethanimine, N,N,N',N',N'-pentamethyldiethylenetriamine, 1,1,4,7,10,10-hexamethyl-triethylenetetramine, 2,2'-bipyridine, and 1,4,8,11-tetraaza-1,4,8,11-tetramethylcyclotetradecan. The solvents used were DMSO, DMF, MeCN, MeOH, IP, and BuOH. Significant solvent effects were observed and quantitatively analyzed in terms of Kamlet-Taft relationships. The resulting Kamlet-Taft equations were found to successfully describe the solvent effects and could thus be used as tools for the design of ATRP in new solvents. The solvent sensitivity of the different ligands and the nature of the solvent effects are also discussed to some extent.     

On the Spectral Dimension of Causal Triangulations

We introduce an ensemble of infinite causal triangulations, called the uniform infinite causal triangulation, and show that it is equivalent to an ensemble of infinite trees, the uniform infinite planar tree. It is proved that in both cases the Hausdorff dimension almost surely equals 2. The infinite causal triangulations are shown to be almost surely recurrent or, equivalently, their spectral dimension is almost surely less than or equal to 2. We also establish that for certain reduced versions of the infinite causal triangulations the spectral dimension equals 2 both for the ensemble average and almost surely. The triangulation ensemble we consider is equivalent to the causal dynamical triangulation model of two-dimensional quantum gravity and therefore our results apply to that model.     

Predicting catalysis: understanding ammonia synthesis from first-principles calculations

Here, we give a full account of a large collaborative effort toward an atomic-scale understanding of modern industrial ammonia production over ruthenium catalysts. We show that overall rates of ammonia production can be determined by applying various levels of theory (including transition state theory with or without tunneling corrections, and quantum dynamics) to a range of relevant elementary reaction steps, such as N(2) dissociation, H(2) dissociation, and hydrogenation of the intermediate reactants. A complete kinetic model based on the most relevant elementary steps can be established for any given point along an industrial reactor, and the kinetic results can be integrated over the catalyst bed to determine the industrial reactor yield. We find that, given the present uncertainties, the rate of ammonia production is well-determined directly from our atomic-scale calculations. Furthermore, our studies provide new insight into several related fields, for instance, gas-phase and electrochemical ammonia synthesis. The success of predicting the outcome of a catalytic reaction from first-principles calculations supports our point of view that, in the future, theory will be a fully integrated tool in the search for the next generation of catalysts.     

Certain Homology Cycles of the Independence Complex of Grids

Let G be an infinite graph such that the automorphism group of G contains a subgroup K ?? ^d with the property that G/K is finite. We examine the homology of the independence complex Σ(G/I) of G/I for subgroups I of K of full rank, focusing on the case that G is the square, triangular, or hexagonal grid. Specifically, we look for a certain kind of homology cycles that we refer to as “cross-cycles,” the rationale for the terminology being that they are fundamental cycles of the boundary complex of some cross-polytope. For the special cases just mentioned, we determine the set Q(G,K) of rational numbers r such that there is a group I with the property that Σ(G/I) contains cross-cycles of degree exactly r?|G/I|?1; |G/I| denotes the size of the vertex set of G/I. In each of the three cases, Q(G,K) turns out to be an interval of the form [a,b]∩?={r∈?:a≤r≤b}. For example, for the square grid, we obtain the interval $[\frac{1}{5},\frac{1}{4}]\cap \mathbb{Q}Let G be an infinite graph such that the automorphism group of G contains a subgroup K ≅ℤ ^d with the property that G/K is finite. We examine the homology of the independence complex Σ(G/I) of G/I for subgroups I of K of full rank, focusing on the case that G is the square, triangular, or hexagonal grid. Specifically, we look for a certain kind of homology cycles that we refer to as “cross-cycles,” the rationale for the terminology being that they are fundamental cycles of the boundary complex of some cross-polytope. For the special cases just mentioned, we determine the set Q(G,K) of rational numbers r such that there is a group I with the property that Σ(G/I) contains cross-cycles of degree exactly r⋅|G/I|−1; |G/I| denotes the size of the vertex set of G/I. In each of the three cases, Q(G,K) turns out to be an interval of the form [a,b]∩ℚ={r∈ℚ:a≤r≤b}. For example, for the square grid, we obtain the interval [\frac15,\frac14]?\mathbbQ[\frac{1}{5},\frac{1}{4}]\cap \mathbb{Q}.