Phosphorus and nitrogen limitation of primary production in a simulated estuarine gradient

The transition between phosphorus limitation of primary production in freshwater and nitrogen limitation in seawater was examined along an estuarine gradient simulated in 4 large 13 m3 enclosures connected in a series and containing pelagic and benthic subsystems. Nominal salinities of 0, 5, 10 and 25 ppt were maintained by exchanging appropriate volumes of water between enclosures. River water, which served as a freshwater endmember, was naturally high in N relative to P, while the oceanic endmember (water from Narragansett Bay, RI, USA) was low in N relative to P. Production in the water column was supported by external inputs and recycled nutrients. Bioassays, inorganic nutrient concentrations and N:P ratios of the seston and inorganic nutrients indicated that phosphorus was limiting at 0, 5 and 10 ppt, while nitrogen was limiting at 25 ppt. Coincident with this shift in limiting nutrient was a shift in the N:P ratio of nutrient supply from greater than the Redfield ratio of 16 to less than 16. External inputs established relative rates of supply in each enclosure. The relative proportion of N and P in external inputs was largely a function of the hydrodynamic mixing of fresh (high N, low P) and salt water (low N, high P) endmembers. At the scale of the estuarine segment or enclosure, neither recycled inputs from the benthos and water column, nitrogen fixation nor internal losses of N and P to sedimentation and/or denitrification materially altered relative supply rates, despite a hydrodynamic residence time of 27 d

Twisted Classical Poincar\'{e} Algebras

We consider the twisting of Hopf structure for classical enveloping algebra $U(\hat{g})$, where $\hat{g}$ is the inhomogenous rotations algebra, with explicite formulae given for $D=4$ Poincar\'{e} algebra $(\hat{g}={\cal P}_4).$ The comultiplications of twisted $U^F({\cal P}_4)$ are obtained by conjugating primitive classical coproducts by $F\in U(\hat{c})\otimes U(\hat{c}),$ where $\hat{c}$ denotes any Abelian subalgebra of ${\cal P}_4$, and the universal $R-$matrices for $U^F({\cal P}_4)$ are triangular. As an example we show that the quantum deformation of Poincar\'{e} algebra recently proposed by Chaichian and Demiczev is a twisted classical Poincar\'{e} algebra. The interpretation of twisted Poincar\'{e} algebra as describing relativistic symmetries with clustered 2-particle states is proposed.Comment: \Large \bf 19 pages, Bonn University preprint, November 199

The compound Poisson limit ruling periodic extreme behaviour of non-uniformly hyperbolic dynamics

We prove that the distributional limit of the normalised number of returns to small neighbourhoods of periodic points of non-uniformly hyperbolic dynamical systems is compound Poisson. The returns to small balls around a fixed point in the phase space correspond to the occurrence of rare events, or exceedances of high thresholds, so that there is a connection between the laws of Return Times Statistics and Extreme Value Laws. The fact that the fixed point in the phase space is a repelling periodic point implies that there is a tendency for the exceedances to appear in clusters whose average sizes is given by the Extremal Index, which depends on the expansion of the system at the periodic point. We recall that for generic points, the exceedances, in the limit, are singular and occur at Poisson times. However, around periodic points, the picture is different: the respective point processes of exceedances converge to a compound Poisson process, so instead of single exceedances, we have entire clusters of exceedances occurring at Poisson times with a geometric distribution ruling its multiplicity. The systems to which our results apply include: general piecewise expanding maps of the interval (Rychlik maps), maps with indifferent fixed points (Manneville-Pomeau maps) and Benedicks-Carleson quadratic maps.Comment: To appear in Communications in Mathematical Physic

Pretransplant gastroesophageal reflux compromises early outcomes after lung transplantation

ObjectivesGastroesophageal reflux disease (GERD) is implicated as a risk factor for bronchiolitis obliterans syndrome after lung transplantation, but its effects on acute rejection, early allograft function, and survival are unclear. Therefore, we sought to systematically understand the time-related impact of pretransplant GERD on graft function (spirometry), mortality, and acute rejection early after lung transplantation.MethodsFrom January 2005 to July 2008, 215 patients underwent lung transplantation; 114 had preoperative pH testing, and 32 (28%) had objective evidence of GERD. Lung function was assessed by forced 1-second expiratory volume (FEV1; percent of predicted) in 97 patients, mortality by follow-up (median, 2.2 years), and acute rejection by transbronchial biopsy.ResultsPretransplant GERD was associated with decreased FEV1 early after lung transplantation (P = .01) such that by 18 months, FEV1 was 70% of predicted in double lung transplant patients with GERD versus 83% among non-GERD patients (P = .05). A similar decrease was observed in single lung transplantation (50% vs 60%, respectively; P = .09). GERD patients had lower survival early after transplant ( P = .02)—75% versus 90%. Presence of GERD did not affect acute rejection (P = .6).ConclusionsFor lung transplant recipients, pretransplant GERD is associated with worse early allograft function and survival, but not increased acute rejection. The compromise in lung function is substantial, such that FEV1 after double lung transplant in GERD patients approaches that of single lung transplant in non-GERD patients. We advocate thorough testing for GERD before lung transplantation; if identified, aggressive therapy early after transplant, including fundoplication, may prove efficacious

Effective supergravity descriptions of superstring cosmology

This text is a review of aspects of supergravity theories that are relevant in superstring cosmology. In particular, it considers the possibilities and restrictions for `uplifting terms', i.e. methods to produce de Sitter vacua. We concentrate on N=1 and N=2 supergravities, and the tools of superconformal methods, which clarify the structure of these theories. Cosmic strings and embeddings of target manifolds of supergravity theories in others are discussed in short at the end.Comment: 12 pages, contribution to the proceedings of the 2nd international conference on Quantum Theories and Renormalization Group in Gravity and Cosmology, Barcelona, July 11-15, 2006, Journal of Physics

Spontaneous preterm labor is associated with an increase in the proinflammatory signal transducer TLR4 receptor on maternal blood monocytes

<p>Abstract</p> <p>Background</p> <p>Localized inflammation and increased expression of TLR4 receptors within the uterus has been implicated in the pathogenesis of preterm labor. It remains unclear whether intrauterine inflammatory responses activate the maternal peripheral circulatory system. Therefore we determined whether increased TLR4 expression is present in the peripheral maternal white blood cells of women with spontaneous preterm labor.</p> <p>Methods</p> <p>This is a cross-sectional study of 41 preterm labor cases and 41 non-preterm controls. For each case and control sample, RNA was purified from white blood cells and TLR4 mRNA pool size was evaluated by quantitative PCR. Protein expression levels were determined by flow cytometry. Statistical evaluation using multiple linear regressions was used to determine any significant differences between the cases and controls. The purpose was to determine association prevalence of TLR4 levels and preterm labor.</p> <p>Results</p> <p>Adjusted mean TLR4 mRNA levels of 0.788 ± 0.037 (standard error) for preterm labor and 0.348 ± 0.038 for the corresponding pregnant control women were statistically significantly different <it>(P </it>= 0.002). Using the lower 95% confidence interval of the mean expression level in PTL subjects (0.7) as a cutoff value for elevated TLR4 mRNA levels, 25/41 (60.9%) of PTL patients expressed elevated TLR4 mRNA as compared to 0/41 (0%) in control subjects. The TLR4 receptor levels in the granulocyte fraction of white blood cells from preterm labor and pregnant controls were similar. However, TLR4⁺/CD14⁺monocytes were 2.3 times more frequent (70% vs. 30%) and TLR4 also had a 2.6-fold higher density (750 vs. 280 molecules per cell) in preterm labor women compared with pregnant controls. There was no difference in the levels of TLR4 in patients at term.</p> <p>Conclusions</p> <p>Patients with preterm labor exhibited elevated levels of CD14⁺maternal blood monocytes each bearing enhanced expression of TLR4, indicating that the peripheral circulatory system is activated in patients with preterm labor. Elevated leukocyte TLR4 levels may be a useful biomarker associated with preterm labor.</p

Polynomial super-gl(n) algebras

We introduce a class of finite dimensional nonlinear superalgebras $L = L_{\bar{0}} + L_{\bar{1}}$ providing gradings of $L_{\bar{0}} = gl(n) \simeq sl(n) + gl(1)$. Odd generators close by anticommutation on polynomials (of degree $>1$) in the $gl(n)$ generators. Specifically, we investigate `type I' super-$gl(n)$ algebras, having odd generators transforming in a single irreducible representation of $gl(n)$ together with its contragredient. Admissible structure constants are discussed in terms of available $gl(n)$ couplings, and various special cases and candidate superalgebras are identified and exemplified via concrete oscillator constructions. For the case of the $n$-dimensional defining representation, with odd generators $Q_{a}, \bar{Q}{}^{b}$, and even generators ${E^{a}}_{b}$, $a,b = 1,...,n$, a three parameter family of quadratic super-$gl(n)$ algebras (deformations of $sl(n/1)$) is defined. In general, additional covariant Serre-type conditions are imposed, in order that the Jacobi identities be fulfilled. For these quadratic super-$gl(n)$ algebras, the construction of Kac modules, and conditions for atypicality, are briefly considered. Applications in quantum field theory, including Hamiltonian lattice QCD and space-time supersymmetry, are discussed.Comment: 31 pages, LaTeX, including minor corrections to equation (3) and reference [60

The interplay of microscopic and mesoscopic structure in complex networks

Not all nodes in a network are created equal. Differences and similarities exist at both individual node and group levels. Disentangling single node from group properties is crucial for network modeling and structural inference. Based on unbiased generative probabilistic exponential random graph models and employing distributive message passing techniques, we present an efficient algorithm that allows one to separate the contributions of individual nodes and groups of nodes to the network structure. This leads to improved detection accuracy of latent class structure in real world data sets compared to models that focus on group structure alone. Furthermore, the inclusion of hitherto neglected group specific effects in models used to assess the statistical significance of small subgraph (motif) distributions in networks may be sufficient to explain most of the observed statistics. We show the predictive power of such generative models in forecasting putative gene-disease associations in the Online Mendelian Inheritance in Man (OMIM) database. The approach is suitable for both directed and undirected uni-partite as well as for bipartite networks