Testing for a $$delta $$ -neighborhood of a generalized Pareto copula

Annals of the Institute of Statistical Mathematics - A multivariate distribution function F is in the max-domain of attraction of an extreme value distribution if and only if this is true for the...     

Further studies on the application of vinylogous amides and β-halovinylaldehydes to the regiospecific synthesis of unsymmetrical,polyfunctionalized 2,3,4- and 1,2,3,4- substituted pyrroles

Highly functionalized pyrroles with appropriate regiochemical functionality represent an important class of marine natural products and potential drug candidates. We describe herein a detailed study of the reaction of α-aminoacid esters with vinylogous amides and also β-halovinylaldehydes for the regiospecific synthesis of 2,3,4-trisubstituted and 1,2,3,4-tetrasubstituted pyrroles. Since the vinylogous amides and β-halovinylaldehydes are readily available precursors, rapid access to a wide variety of unsymmetrically substituted pyrroles is accomplished via this methodology.     

A Variational Finite Element Discretization of Compressible Flow

Foundations of Computational Mathematics - We present a finite element variational integrator for compressible flows. The numerical scheme is derived by discretizing, in a structure-preserving way,...     

1‐Hydroxy‐1H‐benzo[d][1,2,6]oxazaborinin‐4(3H)‐one

The structure of the title compound, C₇H₆BNO₃, a new boron heterocycle, prepared by the condensation of (2‐ethoxycarbonylphenyl)boronic acid and hydroxylamine, reveals the specific mode of intramolecular condensation between a phenylboronic acid and an ortho hydroxamic acid substituent. The crystal structure shows that dehydration occurs to form a planar oxazaborinine ring possessing both phenol‐like B—O—H and lactam functional groups. In the extended structure, intermolecular hydrogen bonding generates a 14‐membered ring. To our knowledge, this is the first crystal structure determination involving a six‐membered ring that exhibits consecutive B—OH, O, NH, and C=O functional groups.     

Symmetric Functions and Generating Functions for Descents and Major Indices in Compositions

In [18], Mendes and Remmel showed how Gessel’s generating function for the distributions of the number of descents, the major index, and the number of inversions of permutations in the symmetric group could be derived by applying a ring homomorphism defined on the ring of symmetric functions to a simple symmetric function identity. We show how similar methods may be used to prove analogues of that generating function for compositions.     

The effect of slip in the flow of a branched PP melt: experiments and simulations

In this paper visualisation and direct velocity profile measurement experiments for a branched polypropylene melt in a 10:1 axisymmetric contraction demonstrate the onset of wall slip. Video processing of the flow shows the formation of vortices and their diminution with increasing flow rate. Numerical simulations using a multimode K-BKZ viscoelastic and a purely viscous (Cross) model—both of them incorporating a nonlinear slip law—were used to predict the flow kinematics and dynamics as well as to deduce the slip velocity function by performing fitting to the velocity profiles. It was found that the numerical predictions agree well with the experimental results for the velocity profiles, and vortex formation, growth and reduction. It is suggested that such experiments (visualisation of entrance flow and direct velocity profile measurement) can be useful in evaluating the validity of constitutive equations and slip laws in the flow of polymer melts through processing equipment.     

Fountain flow of pseudoplastic and viscoplastic fluids

Numerical simulations have been undertaken for the benchmark problem of fountain flow present in injection-mold filling. The Finite Element Method (FEM) is used to provide numerical results for both cases of planar and axisymmetric domains under steady-state conditions. The Herschel–Bulkley model of viscoplasticity is used, which reduces with appropriate modifications to the Bingham, power-law and Newtonian models. The present results extend previous ones regarding the shape of the front, which is essential in correctly capturing the flow field. In particular the centreline front position is found as a function of the dimensionless power-law index (in the case of pseudoplasticity) and the dimensionless yield stress (in the case of viscoplasticity). The pressures from the simulations have been used to compute the excess pressure losses in the system (front pressure correction or exit correction). Both shear-thinning and shear-thickening lead to more extended front positions relative to the Newtonian values, which are 0.895 for the planar case and 0.835 for the axisymmetric one. Viscoplasticity leads also to more extended front positions as the dimensionless yield stress goes from zero (Newtonian behaviour) to higher values of the yield stress. In both cases of non-Newtonian behaviour, the front tends to follow the development of the fully developed Poiseuille velocity profile, which tends towards a plug-like profile at the extreme cases of non-Newtonianness. The front pressure (exit) correction increases monotonically with the decrease in the power-law index and the increase in the dimensionless yield stress.     

Ionization mechanism of the ambient pressure pyroelectric ion source (APPIS) and its applications to chemical nerve agent detection

We present studies of the ionization mechanism operative in the ambient pressure pyroelectric ionization source (APPIS), along with applications that include detection of simulants for chemical nerve agents. It is found that ionization by APPIS occurs in the gas-phase. As the crystal is thermally cycled over a narrow temperature range, electrical discharges near the surface of the crystal produce energetic species which, through reactions with atmospheric molecules, result in reactant ions such as protonated water clusters or clusters of hydroxide and water. Reactant ions can be observed directly in the mass spectrometer. These go on to react with trace neutrals via proton transfer reactions to produce the ions observed in mass spectra, which are usually singly protonated or deprotonated species. Further implicating gas-phase ionization, observed product distributions are highly dependent on the composition of ambient gases, especially the concentration of water vapor and oxygen surrounding the source. For example, basic species such as triethylamine are observed as singly protonated cations at a water partial pressure of 10 torr. At a water pressure of 4 torr, reactive oxygen species are formed and lead to observation of protonated amine oxides. The ability of the APPIS source to detect basic molecules with high proton affinities makes it highly suited for the detection of chemical nerve agents. We demonstrate this application using simulants corresponding to VX and GA (Tabun). With the present source configuration pyridine is detected readily at a concentration of 4 ppm, indicating ultimate sensitivity in the high ppb range.