Gradient extremals

Gradient extremals on N-dimensional energy hypersurfaces V=V(x ₁ x _n ) are curves defined by the condition that the gradient V is an eigenvector of the hessian matrix V. For variations which are restricted to any (N–1) dimensional hypersurface V(x ₁ x _N ) = V ₀= constant, the absolute value of the gradient V is an extremum at those points where a gradient extremal intersects this surface. In many, though not all, cases gradient extremals go along the bottom of a valley or along the crest of a ridge. The properties of gradient extremals are discussed through a detailed differential analysis and illustrated by an explicit example. Multidimensional generalizations of gradient extremals are defined and discussed.Operated for the U.S. Department of Energy by Iowa State University under Contract No. W-7405-ENG-82. This work was supported by the Office of Basic Energy Sciences     

Approximation properties of the spline fit

Different topics in connection with spline fit are discussed in this paper. In particular, an example is given showing non-convergence of splines, and further some error bounds of cubic spline interpolation are proved.     

Measurement of Upsilon production for p + p and p + d interactions at 800 GeV/c

We report a high statistics measurement of Upsilon production with an 800 GeV/c proton beam on hydrogen and deuterium targets. The dominance of the gluon-gluon fusion process for Upsilon production at this energy implies that the cross section ratio, sigma(p+d-->Upsilon)/2sigma(p+p-->Upsilon), is sensitive to the gluon content in the neutron relative to that in the proton. Over the kinematic region 0相似文献   

Europium complexation by an aquatic fulvic acid - effects of competing ions

Effects of competing ions, Fe (2+)Fe (3+) and Al(3+), on Eu(3+) complexation with an aquatic fulvic acid (FA), have been investigated using an ion exchange technique. The influence of different concentrations (10(-6), 10(-4) M) of the competing ions on the distribution coefficient for Eu was measured, and the overall complex formation function, beta(ov), was resolved for the Eu systems with Fe and Al. All systems showed pH-dependent beta(ov)-functions. The presence of 10(-4) M concentration of competing ion reduced the resolved complex formation function (logbeta(ov)) for Eu complexation with fulvic acid by 0.6 and 0.4 log units at pH 5 for Fe and Al, respectively. this indicates that Fe has a more perturbing effect on Eu-FA complexation than Al. In similar competition studies Sr and Eu were found not to perturb each others complexation with fulvic acid, suggesting therefore that the two metals probably bind to different sites on the fulvic acid molecule.     

Effect of styrene oligomers on syndiospecific polymerization of styrene

Styrene oligomers, preferentially consisting of styrene dimers and trimers, are formed by a free radical mechanism at the thermal polymerization of stabilizer-free styrene during storage and at higher polymerization temperatures. The identity of several dimer and trimer fractions formed in such a free radical polymerization, their influence on a coordinative polymerization reaction, the syndiospecific polymerization of styrene, as well as their effect on the properties of the resulting polymers has been investigated.Styrene dimers and styrene trimers reduce the polymerization activity of the transition metal catalyst significantly, especially at low amounts of oligomers added to the styrene. This behavior is discussed with respect to a proposed mechanism involving complexation of the active transition metal species with the specific oligomer instead of the styrene monomer, resulting in increased steric hindrance towards insertion of a styrene molecule to the active site.Both oligomers reduce the molecular weight of the syndiotactic polystyrene, by acting as chain-transfer agents. The constancy of the polydispersity over the whole concentration range of added dimer or trimer indicates that the uniformity of the active sites of the coordinative polymerization is not significantly influenced by the presence of the oligomers.The thermal properties of the polymers demonstrate that the oligomers do not affect the high syndiospecificity of the active catalytic sites, whereas the increase in crystallization temperature with increasing amounts of styrene dimer or trimer is comparable to effects observed by the addition of crystallization nucleators to semicrystalline polymers.     

The binding of strontium and europium by an aquatic fulvic acid--ion exchange distribution and ultrafiltration studies

The complexation of an aquatic fulvic acid, FA, with Sr(2+) and Eu(3+) was studied at 0.10 and O1.O1M NaClO(4) using trace levels of metal ([Sr(2+)] = 10(-9)M and [Eu(3+)] = 10(-11)M) and a constant FA concentration (0.12 g/l) by an ultrafiltration technique (UF) and an ion exchange distribution method (IEDS). The overall complex formation function, beta(OV) for the two metals was calculated and its dependence on pH, ionic strength and method was investigated. The absolute value of log beta(OV), the pH dependence and the influence of the ionic strength on the complexation differed depending on the metal ion and experimental technique employed. By considering the functional group heterogeneity of the FA molecule, it was possible to predict the most predominantly bound site (keto-enol) and resolve the complex formation function for this site and EU(3+) (IEDS: 9.43 +/- 0.29 l/eq at 0.10M and 10.58 +/- 0.72 l/eq at 0.01M; UF: 7.19 +/- 1.51 l/eq at 0.01M and 6.88 +/- 0.91 l/eq at 0.01M). The results are discussed in the light of possible intrinsic problems of the two experimental methods.     

An automated extraction system for flame atomic absorption spectrometry

A manifold is described which allows continuous liquid/liquid extraction of aqueous solutions of metal ions. A fraction of the organic stream is separated and led into the sample loop of an injector. The injector is situated in an aqueous carrier stream which is pumped into the nebulizer. The organic extract enters as an undispersed plug into the carrier when the valve is actuated. A preconcentration factor of 5.5 resulting in a correspondent sensitivity increase is readily obtained for aqueous samples.     

Orientation and conformation of cell-penetrating peptide penetratin in phospholipid vesicle membranes determined by polarized-light spectroscopy

The orientation and conformation of the cell-penetrating peptide "penetratin" associated with phospholipid vesicle membranes has been determined using polarized-light spectroscopy. The magnitude of orientation of penetratin is unprecedented for a solute in our membrane system, which we believe indicates a strong, specific interaction with the membrane. To validate the spectroscopic technique for studying the orientation of the two tryptophan residues of penetratin, we applied tryptophan octyl ester as a model compound. It is found to be incorporated in the membrane and preferentially oriented with its hydrophobic benzene edge of the indole chromophore pointing into the membrane and its hydrophilic groups oriented toward the water. For penetratin, the results indicate that a central alpha-helical part of the peptide is aligned parallel with the membrane surface, while the ends of the peptide adopt a planar structure. The planes of the two tryptophan side chains show a preferred orientation parallel with the membrane surface, indicating that they are not inserted into the membrane.     

Extraction rate in liquid-liquid segmented flow injection analysis

The extraction mechanism in liquid-liquid segmented flow-injection systems is investigated. A film is formed on the tubing wall by the phase with the highest affinity to the tubing material. This film surrounds the segments of the other phase. To a great extent the extraction takes place at the interface of this film. The extraction rate is influenced by the segment length, the inner diameter of the tubing and the flow velocity. Short segments, small inner diameter and high linear flow velocity lead to a high extraction rate. These findings indicate that miniaturization of the flow system will lead to faster extraction and to decreased sample-zone broadening.     

Detection of n-π* transitions in pyridine and pyrazine in polyethylene solution by linear dichroism

Studies of linear dichroism, using a differential technique, on pyridine and pyrazine, quasi-oriented in stretched polymer matrices, give evidence for the energy positions of the n-π^* transitions. These molecules are mainly oriented in the same way as benzene, i.e., the orientation axes in the molecular plane are almost degenerate, and the out-of-plane polarized transitions appear as negative linear dichroism components.