Colonic metabolism of dietary polyphenols: influence of structure on microbial fermentation products

The metabolism of chlorogenic acid., naringin, and rutin, representative members of three common families of dietary polyphenols, the hydroxycinnamates, the flavanones, and the flavonols, respectively, was studied in an in vitro mixed culture model of the human colonic microflora. Time- and concentration-dependent degradation of all three compounds was observed, which was associated with the following metabolic events after cleavage of the ester or glycosidic bond: reduction of the aliphatic double bond of the resulting hydroxycinnamate caffeic acid residue; dehydroxylation and ring fission of the heterocyclic C-ring of the resulting deglycosylated flavanone, naringenin, and of the deglycosylated flavonol, quercetin (which differed depending on the substitution). The metabolic events, their sequences, and major phenolic end products, as identified by GC-MS or LC-MS/MS, were elucidated from the structural characteristics of the investigated compounds. The major phenolic end products identified were 3-D-hydroxyphenyl)propionic acid for chlorogenic acid, 3-(4-hydroxyphenyl)-propionic acid and 3-phenylpropionic acid for naringin, and 3-hydroxyphenylacetic acid and 3-(3-hydroxyphenyl)-propionic acid for rutin. The degree of degradation of the compounds studied was significantly influenced by the substrate concentration as well as individual variations in the composition of the fecal flora. The results support extensive metabolism of dietary polyphenols in the colon, depending on substrate concentration and residence time, with resultant formation of simple phenolics, which can be considered biomarkers of colonic metabolism if subsequently absorbed. It is also apparent that a relatively small number of phenolic degradation products are formed in the colon from the diverse group of natural polyphenols. (C) 2003 Elsevier Inc. All rights reserved.

The effect of environmental change on human migration

The influence of the environment and environmental change is largely unrepresented in standard theories of migration, whilst recent debates on climate change and migration focus almost entirely on displacement and perceive migration to be a problem. Drawing on an increasing evidence base that has assessed elements of the influence of the environment on migration, this paper presents a new framework for understanding the effect of environmental change on migration. The framework identifies five families of drivers which affect migration decisions: economic, political, social, demographic and environmental drivers. The environment drives migration through mechanisms characterised as the availability and reliability of ecosystem services and exposure to hazard. Individual migration decisions and flows are affected by these drivers operating in combination, and the effect of the environment is therefore highly dependent on economic, political, social and demographic context. Environmental change has the potential to affect directly the hazardousness of place. Environmental change also affects migration indirectly, in particular through economic drivers, by changing livelihoods for example, and political drivers, through affecting conflicts over resources, for example. The proposed framework, applicable to both international and internal migration, emphasises the role of human agency in migration decisions, in particular the linked role of family and household characteristics on the one hand, and barriers and facilitators to movement on the other in translating drivers into actions. The framework can be used to guide new research, assist with the evaluation of policy options, and provide a context for the development of scenarios representing a range of plausible migration futures.

Solvability and spectral properties of integral equations on the real line: I. Weighted spaces of continuous functions

We consider in this paper the solvability of linear integral equations on the real line, in operator form (λ−K)φ=ψ, where and K is an integral operator. We impose conditions on the kernel, k, of K which ensure that K is bounded as an operator on . Let Xa denote the weighted space as |s|→∞}. Our first result is that if, additionally, |k(s,t)|⩽κ(s−t), with and κ(s)=O(|s|−b) as |s|→∞, for some b>1, then the spectrum of K is the same on Xa as on X, for 0families of operators, , which ensure that, if λ≠0 and λφ=Kkφ has only the trivial solution in X, for all k∈W, then, for 0⩽a⩽b, (λ−K)φ=ψ has exactly one solution φ∈Xa for every k∈W and ψ∈Xa. These conditions ensure further that is bounded uniformly in k∈W, for 0⩽a⩽b. As a particular application we consider the case when the kernel takes the form k(s,t)=κ(s−t)z(t), with , , and κ(s)=O(|s|−b) as |s|→∞, for some b>1. As an example where kernels of this latter form occur we discuss a boundary integral equation formulation of an impedance boundary value problem for the Helmholtz equation in a half-plane.

Retrieval of phytoplankton size from bio-optical measurements: theory and applications

The absorption coefficient of a substance distributed as discrete particles in suspension is less than that of the same material dissolved uniformly in a medium—a phenomenon commonly referred to as the flattening effect. The decrease in the absorption coefficient owing to flattening effect depends on the concentration of the absorbing pigment inside the particle, the specific absorption coefficient of the pigment within the particle, and on the diameter of the particle, if the particles are assumed to be spherical. For phytoplankton cells in the ocean, with diameters ranging from less than 1 µm to more than 100 µm, the flattening effect is variable, and sometimes pronounced, as has been well documented in the literature. Here, we demonstrate how the in vivo absorption coefficient of phytoplankton cells per unit concentration of its major pigment, chlorophyll a, can be used to determine the average cell size of the phytoplankton population. Sensitivity analyses are carried out to evaluate the errors in the estimated diameter owing to potential errors in the model assumptions. Cell sizes computed for field samples using the model are compared qualitatively with indirect estimates of size classes derived from high performance liquid chromatography data. Also, the results are compared quantitatively against measurements of cell size in laboratory cultures. The method developed is easy-to-apply as an operational tool for in situ observations, and has the potential for application to remote sensing of ocean colour data.

Spectral asymmetry of the massless Dirac operator on a 3-torus

Consider the massless Dirac operator on a 3-torus equipped with Euclidean metric and standard spin structure. It is known that the eigenvalues can be calculated explicitly: the spectrum is symmetric about zero and zero itself is a double eigenvalue. The aim of the paper is to develop a perturbation theory for the eigenvalue with smallest modulus with respect to perturbations of the metric. Here the application of perturbation techniques is hindered by the fact that eigenvalues of the massless Dirac operator have even multiplicity, which is a consequence of this operator commuting with the antilinear operator of charge conjugation (a peculiar feature of dimension 3). We derive an asymptotic formula for the eigenvalue with smallest modulus for arbitrary perturbations of the metric and present two particular families of Riemannian metrics for which the eigenvalue with smallest modulus can be evaluated explicitly. We also establish a relation between our asymptotic formula and the eta invariant.

The regulation of seasonal flowering in the Rosaceae

Molecular mechanisms regulating the flowering process have been extensively studied in model annual plants; in perennials, however, understanding of the molecular mechanisms controlling flowering has just started to emerge. Here we review the current state of flowering research in perennial plants of the rose family (Rosaceae), which is one of the most economically important families of horticultural plants. Strawberry (Fragaria spp.), raspberry (Rubus spp.), rose (Rosa spp.), and apple (Malus spp.) are used to illustrate how photoperiod and temperature control seasonal flowering in rosaceous crops. We highlight recent molecular studies which have revealed homologues of TERMINAL FLOWER1 (TFL1) to be major regulators of both the juvenile to adult, and the vegetative to reproductive transitions in various rosaceous species. Additionally, recent advances in understanding of the regulation of TFL1 are discussed.

Reduced relative entropy techniques for a posteriori analysis of multiphase problems in elastodynamics

We give an a posteriori analysis of a semidiscrete discontinuous Galerkin scheme approximating solutions to a model of multiphase elastodynamics, which involves an energy density depending not only on the strain but also the strain gradient. A key component in the analysis is the reduced relative entropy stability framework developed in Giesselmann (2014, SIAM J. Math. Anal., 46, 3518–3539). This framework allows energy-type arguments to be applied to continuous functions. Since we advocate the use of discontinuous Galerkin methods we make use of two families of reconstructions, one set of discrete reconstructions and a set of elliptic reconstructions to apply the reduced relative entropy framework in this setting.

A new calibrated sunspot group series since 1749: statistics of active day fractions

Although the sunspot-number series have existed since the mid-19th century, they are still the subject of intense debate, with the largest uncertainty being related to the "calibration" of the visual acuity of individual observers in the past. Daisy-chain regression methods are applied to inter-calibrate the observers which may lead to significant bias and error accumulation. Here we present a novel method to calibrate the visual acuity of the key observers to the reference data set of Royal Greenwich Observatory sunspot groups for the period 1900-1976, using the statistics of the active-day fraction. For each observer we independently evaluate their observational thresholds [S_S] defined such that the observer is assumed to miss all of the groups with an area smaller than S_S and report all the groups larger than S_S. Next, using a Monte-Carlo method we construct, from the reference data set, a correction matrix for each observer. The correction matrices are significantly non-linear and cannot be approximated by a linear regression or proportionality. We emphasize that corrections based on a linear proportionality between annually averaged data lead to serious biases and distortions of the data. The correction matrices are applied to the original sunspot group records for each day, and finally the composite corrected series is produced for the period since 1748. The corrected series displays secular minima around 1800 (Dalton minimum) and 1900 (Gleissberg minimum), as well as the Modern grand maximum of activity in the second half of the 20th century. The uniqueness of the grand maximum is confirmed for the last 250 years. It is shown that the adoption of a linear relationship between the data of Wolf and Wolfer results in grossly inflated group numbers in the 18th and 19th centuries in some reconstructions.