Block copolymers of poly(L-lactide) and poly(ε-caprolactone) or poly(ethylene glycol) prepared by reactive extrusion

Blends of poly(L-lactide) (PLLA) and poly(-caprolactone) (PCL) were prepared in a co-rotating twin screw miniextruder (40 rpm, 200°). It was attempted to prepare multiblock copolymers by allowing a controlled number of transesterification reactions. Various cat-alysts (n-Bu3SnOMe, Sn(Oct)2, Ti(OBu)4, Y(Oct)3, para-toluene sulphonic acid) were introduced to promote these transesterification reactions. However, PLLA degradation by ring-closing depolymerization was the dominant reaction in every case. Alternatively, after showing that L-lactide can be conveniently polymerized in the extruder, L-lactide and hy-droxyl functionalized prepolymers of PCL or poly(ethylene glycol) (PEG) were fed to the extruder in the presence of stannous octoate. Monomer conversions of over 90% and effective transformation of all hydroxyl end groups present were generally reached. Di-and triblock copolymers could be prepared in this way with characteristics very similar to polymers prepared in a batch-type process, but with considerably reduced reaction times in a fashion, which is, in principle, scaleable to a continuous process for the production of such block copolymers

The Calogero-Sutherland Model and Polynomials with Prescribed Symmetry

The Schr\"odinger operators with exchange terms for certain Calogero-Sutherland quantum many body systems have eigenfunctions which factor into the symmetric ground state and a multivariable polynomial. The polynomial can be chosen to have a prescribed symmetry (i.e. be symmetric or antisymmetric) with respect to the interchange of some specified variables. For four particular Calogero-Sutherland systems we construct an eigenoperator for these polynomials which separates the eigenvalues and establishes orthogonality. In two of the cases this involves identifying new operators which commute with the corresponding Schr\"odinger operators. In each case we express a particular class of the polynomials with prescribed symmetry in a factored form involving the corresponding symmetric polynomials.Comment: LaTeX 2.09, 31 page

Spin structure of the nucleon at low energies

The spin structure of the nucleon is analyzed in the framework of a Lorentz-invariant formulation of baryon chiral perturbation theory. The structure functions of doubly virtual Compton scattering are calculated to one-loop accuracy (fourth order in the chiral expansion). We discuss the generalization of the Gerasimov-Drell-Hearn sum rule, the Burkhardt-Cottingham sum rule and moments of these. We give predictions for the forward and the longitudinal-transverse spin polarizabilities of the proton and the neutron at zero and finite photon virtuality. A detailed comparison to results obtained in heavy baryon chiral perturbation theory is also given.Comment: 29 pp, 14 fig

Baryon Masses in Chiral Perturbation Theory with Infrared Regularization

The baryon masses are examined in SU(3) chiral perturbation theory to third order using the recently proposed infrared regularization scheme. Fourth order is estimated by evaluating the dominant diagram. With this regularization the magnitude of the loop integrals is reduced so that the convergence of the series appears to be better than in the heavy baryon approach.Comment: The original third order calculation is supplemented by an estimate of fourth order using just the dominant diagram. The convergence still appears to be better than in the heavy baryon approach. To be published in Phys. Rev. C. 15 pages latex, 2 postscript figure

An Effective Lagrangian with Broken Scale and Chiral Symmetry IV: Nucleons and Mesons at Finite Temperature

We study the finite temperature properties of an effective chiral Lagrangian which describes nuclear matter. Thermal fluctuations in both the nucleon and the meson fields are considered. The logarithmic and square root terms in the effective potential are evaluated by expansion and resummation with the result written in terms of the exponential integral and the error function, respectively. In the absence of explicit chiral symmetry breaking a phase transition restores the symmetry, but when the pion has a mass the transition is smooth. The nucleon and meson masses as a functions of density and temperature are discussed.Comment: 21 pages LaTeX + 11 postscript figures, uses epsf.st

Exact operator solution of the Calogero-Sutherland model

The wave functions of the Calogero-Sutherland model are known to be expressible in terms of Jack polynomials. A formula which allows to obtain the wave functions of the excited states by acting with a string of creation operators on the wave function of the ground state is presented and derived. The creation operators that enter in this formula of Rodrigues-type for the Jack polynomials involve Dunkl operators.Comment: 35 pages, LaTeX2e with amslate

Integral Representations of the Macdonald Symmetric Functions

Multiple-integral representations of the (skew-)Macdonald symmetric functions are obtained. Some bosonization schemes for the integral representations are also constructed.Comment: LaTex 21page

The impacts of artificial light at night in Africa: Prospects for a research agenda

Artificial light at night (ALAN) has increasingly been recognised as one of the world’s most pernicious global change drivers that can negatively impact both human and environmental health. However, when compared to work elsewhere, the dearth of research into the mapping, expansion trajectories and consequences of ALAN in Africa is a surprising oversight by its research community. Here, we outline the scope of ALAN research and elucidate key areas in which the African research community could usefully accelerate work in this field. These areas particularly relate to how African conditions present underappreciated caveats to the quantification of ALAN, that the continent experiences unique challenges associated with ALAN, and that these also pose scientific opportunities to understanding its health and environmental impacts. As Africa is still relatively free from the high levels of ALAN found elsewhere, exciting possibilities exist to shape the continent’s developmental trajectories to mitigate ALAN impacts and help ensure the prosperity of its people and environment. Significance: We show that the African research community can usefully accelerate work into understudied aspects of ALAN, which demonstrably impacts human and environmental health. Africa presents a unique, and in places challenging, research environment to advance understanding of this global change driver

Stochastic processes and conformal invariance

We discuss a one-dimensional model of a fluctuating interface with a dynamic exponent $z=1$. The events that occur are adsorption, which is local, and desorption which is non-local and may take place over regions of the order of the system size. In the thermodynamic limit, the time dependence of the system is given by characters of the $c=0$ conformal field theory of percolation. This implies in a rigorous way a connection between CFT and stochastic processes. The finite-size scaling behavior of the average height, interface width and other observables are obtained. The avalanches produced during desorption are analyzed and we show that the probability distribution of the avalanche sizes obeys finite-size scaling with new critical exponents.Comment: 4 pages, 6 figures, revtex4. v2: change of title and minor correction

Transition Form Factors between Pseudoscalar and Vector Mesons in Light-Front Dynamics

We study the transition form factors between pseudoscalar and vector mesons using a covariant fermion field theory model in $(3+1)$ dimensions. Performing the light-front calculation in the $q^+ =0$ frame in parallel with the manifestly covariant calculation, we note that the suspected nonvanishing zero-mode contribution to the light-front current $J^+$ does not exist in our analysis of transition form factors. We also perform the light-front calculation in a purely longitudinal $q^+ > 0$ frame and confirm that the form factors obtained directly from the timelike region are identical to the ones obtained by the analytic continuation from the spacelike region. Our results for the $B \to D^* l \nu_l$ decay process satisfy the constraints on the heavy-to-heavy semileptonic decays imposed by the flavor independence in the heavy quark limit.Comment: 20 pages, 14 figure