The Momentum Kernel of Gauge and Gravity Theories

We derive an explicit formula for factorizing an $n$-point closed string amplitude into open string amplitudes. Our results are phrased in terms of a momentum kernel which in the limit of infinite string tension reduces to the corresponding field theory kernel. The same momentum kernel encodes the monodromy relations which lead to the minimal basis of color-ordered amplitudes in Yang-Mills theory. There are interesting consequences of the momentum kernel pertaining to soft limits of amplitudes. We also comment on surprising links between gravity and certain combinations of kinematic and color factors in gauge theory.Comment: 19 pages, 1 figur

Monodromy--like Relations for Finite Loop Amplitudes

We investigate the existence of relations for finite one-loop amplitudes in Yang-Mills theory. Using a diagrammatic formalism and a remarkable connection between tree and loop level, we deduce sequences of amplitude relations for any number of external legs.Comment: 24 pages, 6 figures, v2 typos corrected, reference adde

On-shell Recursion in String Theory

We prove that all open string theory disc amplitudes in a flat background obey Britto-Cachazo-Feng-Witten (BCFW) on-shell recursion relations, up to a possible reality condition on a kinematic invariant. Arguments that the same holds for tree level closed string amplitudes are given as well. Non-adjacent BCFW-shifts are related to adjacent shifts through monodromy relations for which we provide a novel CFT based derivation. All possible recursion relations are related by old-fashioned string duality. The field theory limit of the analysis for amplitudes involving gluons is explicitly shown to be smooth for both the bosonic string as well as the superstring. In addition to a proof a less rigorous but more powerful argument based on the underlying CFT is presented which suggests that the technique may extend to a much more general setting in string theory. This is illustrated by a discussion of the open string in a constant B-field background and the closed string on the level of the sphere.Comment: 36 + 9 pages text, one figure, v3: added discussion on relation to old-fashioned factorization, typos corrected, published versio

Quantifying measures to limit wind driven resuspension of sediments for improvement of the ecological quality in some shallow Dutch lakes

Although phosphorus loadings are considered the main pressure for most shallow lakes, wind-driven resuspension can cause additional problems for these aquatic ecosystems. We quantified the potential effectiveness of measures to reduce the contribution of resuspended sediments, resulting from wind action, to the overall light attenuation for three comparable shallow peat lakes with poor ecological status in the Netherlands: Loosdrecht, Nieuwkoop, and Reeuwijk (1.8–2.7 m depth, 1.6–2.5 km fetch). These measures are: 1. wave reducing barriers, 2. water level fluctuations, 3. capping of the sediment with sand, and 4. combinations of above. Critical shear stress of the sediments for resuspension (Vcrit), size distribution, and optical properties of the suspended material were quantified in the field (June 2009) and laboratory. Water quality monitoring data (2002–2009) showed that light attenuation by organic suspended matter in all lakes is high. Spatial modeling of the impact of these measures showed that in Lake Loosdrecht limiting wave action can have significant effects (reductions from 6% exceedance to 2% exceedance of Vcrit), whereas in Lake Nieuwkoop and Lake Reeuwijk this is less effective. The depth distribution and shape of Lake Nieuwkoop and Lake Reeuwijk limit the role of wind-driven resuspension in the total suspended matter concentration. Although the lakes are similar in general appearance (origin, size, and depth range) measures suitable to improve their ecological status differ. This calls for care when defining the programme of measures to improve the ecological status of a specific lake based on experience from other lakes.

Yang-Mills amplitude relations at loop level from non-adjacent BCFW shifts

This article studies methods to obtain relations for scattering amplitudes at the loop level, with concrete examples at one loop. These methods originate in the analysis of large so-called Britto-Cachazo-Feng-Witten shifts of tree level amplitudes and loop level integrands. In particular BCFW shifts for particles which are not color adjacent and some particular generalizations of this situation are analyzed in some detail in four and higher dimensions. For generic non-adjacent shifts our results are independent of loop order for integrands and hold for generic minimally coupled gauge theories with possible scalar potential and Yukawa terms. By a standard argument this result indicates a generalization of the Bern-Carrasco-Johansson relations for tree level amplitudes exists to the integrand at all loop levels. A concrete relation is presented at one loop. Furthermore, inspired by results in QED it is shown that the results on generalized BCFW shifts of tree level amplitudes imply relations for the so-called rational, bubble and triangle terms of one loop amplitudes in pure Yang-Mills theory. Bubble and triangle terms for instance are shown to obey a five photon decoupling identity, while a three photon decoupling identity is demonstrated for the rational terms. Along the same lines recently conjectured relations for helicity equal amplitudes at one loop are shown to generalize to helicity independent relations for the massive box coefficient of the rational terms.Comment: 69 pages, 27 figure

Hypoxia inducible factor 1α gene (HIF-1α) splice variants: potential prognostic biomarkers in breast cancer

<p>Abstract</p> <p>Background</p> <p>Hypoxia-inducible factor 1 (HIF-1) is a master transcriptional regulator of genes regulating oxygen homeostasis. The HIF-1 protein is composed of two HIF-1α and HIF-1β/aryl hydrocarbon receptor nuclear translocator (ARNT) subunits. The prognostic relevance of HIF-1α protein overexpression has been shown in breast cancer. The impact of HIF-1α alternative splice variant expression on breast cancer prognosis in terms of metastasis risk is not well known.</p> <p>Methods</p> <p>Using real-time quantitative reverse transcription PCR assays, we measured mRNA concentrations of total <it>HIF-1α </it>and 4 variants in breast tissue specimens in a series of 29 normal tissues or benign lesions (normal/benign) and 53 primary carcinomas. In breast cancers <it>HIF-1α </it>splice variant levels were compared to clinicopathological parameters including tumour microvessel density and metastasis-free survival.</p> <p>Results</p> <p><it>HIF-1α </it>isoforms containing a three base pairs TAG insertion between exon 1 and exon 2 (designated <it>HIF-1α</it>^<it>TAG</it>) and <it>HIF-1α</it>^{<it>736 </it>}mRNAs were found expressed at higher levels in oestrogen receptor (OR)-negative carcinomas compared to normal/benign tissues (<it>P </it>= 0.009 and <it>P </it>= 0.004 respectively). In breast carcinoma specimens, lymph node status was significantly associated with <it>HIF-1α</it>^{<it>TAG </it>}mRNA levels (<it>P </it>= 0.037). Significant statistical association was found between tumour grade and <it>HIF-1α</it>^{<it>TAG </it>}(<it>P </it>= 0.048), and total <it>HIF-1α </it>(<it>P </it>= 0.048) mRNA levels. <it>HIF-1α</it>^{<it>TAG </it>}mRNA levels were also inversely correlated with both oestrogen and progesterone receptor status (<it>P </it>= 0.005 and <it>P </it>= 0.033 respectively). Univariate analysis showed that high <it>HIF-1α</it>^{<it>TAG </it>}mRNA levels correlated with shortened metastasis free survival (<it>P </it>= 0.01).</p> <p>Conclusions</p> <p>Our results show for the first time that mRNA expression of a <it>HIF-1α</it>^{<it>TAG </it>}splice variant reflects a stage of breast cancer progression and is associated with a worse prognosis.</p> <p>See commentary: <url>http://www.biomedcentral.com/1741-7015/8/45</url></p

Evaluating the Psychometric Quality of Social Skills Measures: A Systematic Review

Introduction - Impairments in social functioning are associated with an array of adverse outcomes. Social skills measures are commonly used by health professionals to assess and plan the treatment of social skills difficulties. There is a need to comprehensively evaluate the quality of psychometric properties reported across these measures to guide assessment and treatment planning. Objective - To conduct a systematic review of the literature on the psychometric properties of social skills and behaviours measures for both children and adults. Methods - A systematic search was performed using four electronic databases: CINAHL, PsycINFO, Embase and Pubmed; the Health and Psychosocial Instruments database; and grey literature using PsycExtra and Google Scholar. The psychometric properties of the social skills measures were evaluated against the COSMIN taxonomy of measurement properties using pre-set psychometric criteria. Results - Thirty-Six studies and nine manuals were included to assess the psychometric properties of thirteen social skills measures that met the inclusion criteria. Most measures obtained excellent overall methodological quality scores for internal consistency and reliability. However, eight measures did not report measurement error, nine measures did not report cross-cultural validity and eleven measures did not report criterion validity. Conclusions - The overall quality of the psychometric properties of most measures was satisfactory. The SSBS-2, HCSBS and PKBS-2 were the three measures with the most robust evidence of sound psychometric quality in at least seven of the eight psychometric properties that were appraised. A universal working definition of social functioning as an overarching construct is recommended. There is a need for ongoing research in the area of the psychometric properties of social skills and behaviours instruments