B-Methylated Amine-Boranes:Substituent Redistribution, Catalytic Dehydrogenation, and Facile Metal-Free Hydrogen Transfer Reactions

Although the dehydrogenation chemistry of amine-boranes substituted at nitrogen has attracted considerable attention, much less is known about the reactivity of their B-substituted analogues. When the B-methylated amine-borane adducts, RR′NH·BH₂Me (<b>1a</b>: R = R′ = H; <b>1b</b>: R = Me, R′ = H; <b>1c</b>: R = R′ = Me; <b>1d</b>: R = R′ = <i>i</i>Pr), were heated to 70 °C in solution (THF or toluene), redistribution reactions were observed involving the apparent scrambling of the methyl and hydrogen substituents on boron to afford a mixture of the species RR′NH·BH_3–<i>x</i>Me_<i>x</i> (<i>x</i> = 0–3). These reactions were postulated to arise via amine-borane dissociation followed by the reversible formation of diborane intermediates and adduct reformation. Dehydrocoupling of <b>1a</b>–<b>1d</b> with Rh­(I), Ir­(III), and Ni(0) precatalysts in THF at 20 °C resulted in an array of products, including aminoborane RR′NBHMe, cyclic diborazane [RR′N–BHMe]₂, and borazine [RN–BMe]₃ based on analysis by in situ ¹¹B NMR spectroscopy, with peak assignments further supported by density functional theory (DFT) calculations. Significantly, very rapid, metal-free hydrogen transfer between <b>1a</b> and the monomeric aminoborane, <i>i</i>Pr₂NBH₂, to yield <i>i</i>Pr₂NH·BH₃ (together with dehydrogenation products derived from <b>1a</b>) was complete within only 10 min at 20 °C in THF, substantially faster than for the N-substituted analogue MeNH₂·BH₃. DFT calculations revealed that the hydrogen transfer proceeded via a concerted mechanism through a cyclic six-membered transition state analogous to that previously reported for the reaction of the <i>N</i>-dimethyl species Me₂NH·BH₃ and <i>i</i>Pr₂NBH₂. However, as a result of the presence of an electron donating methyl substituent on boron rather than on nitrogen, the process was more thermodynamically favorable and the activation energy barrier was reduced

Latent Structures based-Multivariate Statistical Process Control: a paradigm shift

The basic fundamentals of statistical process control (SPC) were proposed by Walter Shewhart for data-starved production environments typical in the 1920s and 1930s. In the 21st century, the traditional scarcity of data has given way to a data-rich environment typical of highly automated and computerized modern processes. These data often exhibit high correlation, rank deficiency, low signal-to-noise ratio, multistage and multiway structures, and missing values. Conventional univariate and multivariate SPC techniques are not suitable in these environments. This article discusses the paradigm shift to which those working in the quality improvement field should pay keen attention. We advocate the use of latent structure based multivariate statistical process control methods as efficient quality improvement tools in these massive data contexts. 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The history of degenerate (bipartite) extremal graph problems

This paper is a survey on Extremal Graph Theory, primarily focusing on the case when one of the excluded graphs is bipartite. On one hand we give an introduction to this field and also describe many important results, methods, problems, and constructions.Comment: 97 pages, 11 figures, many problems. This is the preliminary version of our survey presented in Erdos 100. In this version 2 only a citation was complete

Radiation thermo-chemical models of protoplanetary discs. III. Impact of inner rims on Spectral Energy Distributions

We study the hydrostatic density structure of the inner disc rim around HerbigAe stars using the thermo-chemical hydrostatic code ProDiMo. We compare the Spectral Energy Distributions (SEDs) and images from our hydrostatic disc models to that from prescribed density structure discs. The 2D continuum radiative transfer in ProDiMo includes isotropic scattering. The dust temperature is set by the condition of radiative equilibrium. In the thermal-decoupled case the gas temperature is governed by the balance between various heating and cooling processes. The gas and dust interact thermally via photoelectrons, radiatively, and via gas accommodation on grain surfaces. As a result, the gas is much hotter than in the thermo-coupled case, where the gas and dust temperatures are equal, reaching a few thousands K in the upper disc layers and making the inner rim higher. A physically motivated density drop at the inner radius ("soft-edge") results in rounded inner rims, which appear ring-like in near-infrared images. The combination of lower gravity pull and hot gas beyond ~1 AU results in a disc atmosphere that reaches a height over radius ratio z/r of 0.1 while this ratio is 0.2 only in the thermo-coupled case. This puffed-up disc atmosphere intercepts larger amount of stellar radiation, which translates into enhanced continuum emission in the 3- 30 micron wavelength region from hotter grains at ~500 K. We also consider the effect of disc mass and grain size distribution on the SEDs self-consistently feeding those quantities back into the gas temperature, chemistry, and hydrostatic equilibrium computation.Comment: Accepted to MNRA

Evaluation of an Inexpensive Growth Medium for Direct Detection of Escherichia coli in Temperate and Sub-Tropical Waters

The cost and complexity of traditional methods for the detection of faecal indicator bacteria, including E. coli, hinder widespread monitoring of drinking water quality, especially in lowincome countries and outside controlled laboratory settings. In these settings the problem is exacerbated by the lack of inexpensive media for the detection of E. coli in drinking water. We developed a new low-cost growth medium, aquatest (AT), and validated its use for the direct detection of E. coli in temperate and sub-tropical drinking waters using IDEXX QuantiTray1. AT was compared with IDEXX Colilert-181 and either EC-MUG or MLSB for detecting low levels of E. coli from water samples from temperate (n = 140; Bristol, UK) and subtropical regions (n = 50, Pretoria/Tshwane, South Africa). Confirmatory testing (n = 418 and 588, respectively) and the comparison of quantitative results were used to assess performance. Sensitivity of AT was higher than Colilert-181 for water samples in the UK [98.0% vs. 86.9%; p<0.0001] and South Africa [99.5% vs. 93.2%; p = 0.0030]. There was no significant difference in specificity, which was high for both media (>95% in both settings). Quantitative results were comparable and within expected limits. AT is reliable and accurate for the detection of E. coli in temperate and subtropical drinking water. The composition of the new medium is reported herein and can be used freely

A prospective, multicentre, observational cohort study of analgesia and outcome after pneumonectomy

Background Meta-analysis and systematic reviews of epidural compared with paravertebral blockade analgesia techniques for thoracotomy conclude that although the analgesia is comparable, paravertebral blockade has a better short-term side-effect profile. However, reduction in major complications including mortality has not been proven. Methods The UK pneumonectomy study was a prospective observational cohort study in which all UK thoracic surgical centres were invited to participate. Data presented here relate to the mode of analgesia and outcome. Data were analysed for 312 patients having pneumonectomy at 24 UK thoracic surgical centres in 2005. The primary endpoint was a major complication. Results The most common type of analgesia used was epidural (61.1%) followed by paravertebral infusion (31%). Epidural catheter use was associated with major complications (odds ratio 2.2, 95% confidence interval 1.1–3.8; P=0.02) by stepwise logistic regression analysis. Conclusions An increased incidence of clinically important major post-pneumonectomy complications was associated with thoracic epidural compared with paravertebral blockade analgesia. However, this study is unable to provide robust evidence to change clinical practice for a better clinical outcome. A large multicentre randomized controlled trial is now needed to compare the efficacy, complications, and cost-effectiveness of epidural and paravertebral blockade analgesia after major lung resection with the primary outcome of clinically important major morbidity

Healthier prisons: The role of a prison visitors' centre

Since the inception of the prison as a ‘setting’ for health promotion, there has been a focus on how the health of those men and women who spend ‘time inside’ can at least be maintained and if possible, enhanced, during their prison sentence. This paper presents findings from a mainly qualitative evaluation of a prison visitors' centre in the UK. It reports experiences of prisoners' families, prisoners, prison staff, the local community and the ways in which the visitors' centre has contributed positively to their health and well-being. In addition, key stakeholders were interviewed to ascertain the role this visitors' centre has in policy frameworks related to re-offending. The findings from this evaluation underscore how the visitors' centre improved the quality of visits, and contributed towards the maintenance of family ties through the help and support it provides for families and prisoners. The paper concludes by suggesting that visitors' centres are an essential part of a modern prison service helping to address the government's health inequalities agenda

Transfer Matrices and Partition-Function Zeros for Antiferromagnetic Potts Models. IV. Chromatic polynomial with cyclic boundary conditions

We study the chromatic polynomial P_G(q) for m \times n square- and triangular-lattice strips of widths 2\leq m \leq 8 with cyclic boundary conditions. This polynomial gives the zero-temperature limit of the partition function for the antiferromagnetic q-state Potts model defined on the lattice G. We show how to construct the transfer matrix in the Fortuin--Kasteleyn representation for such lattices and obtain the accumulation sets of chromatic zeros in the complex q-plane in the limit n\to\infty. We find that the different phases that appear in this model can be characterized by a topological parameter. We also compute the bulk and surface free energies and the central charge.Comment: 55 pages (LaTeX2e). Includes tex file, three sty files, and 22 Postscript figures. Also included are Mathematica files transfer4_sq.m and transfer4_tri.m. Journal versio