Assessing myocardial architecture:the challenges and controversies

In recent decades, investigators have strived to describe and quantify the orientation of the cardiac myocytes in an attempt to classify their arrangement in healthy and diseased hearts. There are, however, striking differences between the investigations from both a technical and methodological standpoint, thus limiting their comparability and impeding the drawing of appropriate physiological conclusions from the structural assessments. This review aims to elucidate these differences, and to propose guidance to establish methodological consensus in the field. The review outlines the theory behind myocyte orientation analysis, and importantly has identified pronounced differences in the definitions of otherwise widely accepted concepts of myocytic orientation. Based on the findings, recommendations are made for the future design of studies in the field of myocardial morphology. It is emphasised that projection of myocyte orientations, before quantification of their angulation, introduces considerable bias, and that angles should be assessed relative to the epicardial curvature. The transmural orientation of the cardiomyocytes should also not be neglected, as it is an important determinant of cardiac function. Finally, there is considerable disagreement in the literature as to how the orientation of myocardial aggregates should be assessed, but to do so in a mathematically meaningful way, the normal vector of the aggregate plane should be utilised

Effects of Cardiac Structural Remodelling During Heart Failure on Cardiac Excitation – Insights from a Heterogeneous 3D Model of the Rabbit Atria

Heart failure is a leading cause of morbidity and mortality in the western world. One of the effects of heart failure is the structural remodelling of cardiac tissue, including tissue dilation and development of fibrosis. It is therefore important to study these changes and their effect on cardiac activity, in order to gain a better understanding of the underlying mechanisms in arrhythmogenesis, which will hopefully enable us to develop better treatments for heart failure. In this study we developed biophysically detailed models of the rabbit atria for normal and heart failure conditions. These models were used to study the effects of structural remodelling of heart failure on cardiac excitation wave conduction. Anatomical reconstructions of the control and heart failure hearts were based on contrast enhanced micro-CT imaging. Fibre orientation was extracted from the control and heart failure datasets. Effects of heart failure geometry on the activation pattern of atrial excitation waves were analyzed. It was found that atrial activation time increased from the control to the heart failure case in both isotropic and anisotropic conditions, which is attributed primarily to the dilation of tissue caused by heart failure

Forecasting the impact of virtual environment technology on maintenance training

To assist NASA and the Air Force in determining how and when to invest in virtual environment (VE) technology for maintenance training, we identified possible roles for VE technology in such training, assessed its cost-effectiveness relative to existing technologies, and formulated recommendations for a research agenda that would address instructional and system development issues involved in fielding a VE training system. In the first phase of the study, we surveyed VE developers to forecast capabilities, maturity, and estimated costs for VE component technologies. We then identified maintenance tasks and their training costs through interviews with maintenance technicians, instructors, and training developers. Ten candidate tasks were selected from two classes of maintenance tasks (seven aircraft maintenance and three space maintenance) using five criteria developed to identify types of tasks most likely to benefit from VE training. Three tasks were used as specific cases for cost-benefit analysis. In formulating research recommendations, we considered three aspects of feasibility: technological considerations, cost-effectiveness, and anticipated R&D efforts. In this paper, we describe the major findings in each of these areas and suggest research efforts that we believe will help achieve the goal of a cost-effective VE maintenance training system by the next decade

Quantification of the Electrophilicities of Diazoalkanes: Kinetics and Mechanism of Azo Couplings with Enamines and Sulfonium Ylides

Kinetics and mechanism of the reactions of methyl diazoacetate, dimethyl diazomalonate, 4-nitrophenyldiazomethane, and diphenyldiazomethane with sulfonium ylides and enamines were investigated by UV-Vis and NMR spectroscopy. Ordinary alkenes undergo 1,3-dipolar cycloadditions with these diazo compounds. In contrast, sulfonium ylides and enamines attack at the terminal nitrogen of the diazo alkanes to give zwitterions, which undergo various subsequent reactions. As only one new bond is formed in the rate-determining step of these reactions, the correlation lg k(2)(20 degrees C)=s(N)(N+E) could be used to determine the one-bond electrophilicities E of the diazo compounds from the measured second-order rate constants and the known reactivity indices N and s(N) of the sulfonium ylides and enamines. The resulting electrophilicity parameters (-21<E<-18), which are 11-14 orders of magnitude smaller than that of the benzenediazonium ion, are used to define the scope of one-bond nucleophiles which may react with these diazoalkanes

An Overlooked Pathway in 1,3-Dipolar Cycloadditions of Diazoalkanes with Enamines

Methyl diazoacetate reacts with 1-(N-pyrrolidino)cycloalkenes to give products of 1,3-dipolar cycloadditions and azo couplings. The kinetics and mechanisms of these reactions were investigated by NMR spectroscopy and DFT calculations. Orthogonal pi-systems in the 1,3-dipoles of the propargyl-allenyl type allow for two separate reaction pathways for the (3+2)-cycloadditions. The commonly considered concerted pathway is rationalized by the interaction of the enamine HOMO with LUMO+1, the lowest unoccupied orbital of the heteropropargyl anion fragment of methyl diazoacetate. We show that HOMO/LUMO(pi*(N=N)) interactions between enamines and methyl diazoacetate open a previously unrecognized reaction path for stepwise cycloadditions through zwitterionic intermediates with barriers approximately 40 kJ mol(-1) lower in energy in CHCl3 (DFT calculations) than for the concerted path

Author&apos;s personal copy Possible temperature limits to range expansion of non-native Asian shore crabs in Maine

a b s t r a c t a r t i c l e i n f o The intertidal Asian shore crab, Hemigrapsus sanguineus (De Haan, 1835), recently (2001) appeared in very low densities along the southern Maine (USA) coast. Indigenous to Russia and Japan, this species arrived in New Jersey around 1988 and rapidly expanded south to the Carolinas and north to southern New England (CT, RI, MA) by the early 1990s. We examined the characteristics of a non-native species invasion by surveying over 30 intertidal sites in Maine from 2002 to 2005. We found relatively low population densities, slow rates of geographic expansion and virtually no colonization northeast of Penobscot Bay on the central coast of Maine. We hypothesized that further geographic expansion of sustaining populations of H. sanguineus in Maine may be limited by coastal temperatures colder than in its native range. To examine this, we deployed recording thermistors at 11 strategic sites and integrated those data with three oceanographic observation buoys and with satellite thermal images of the coastal zone for the period between 2003 and 2005. We found that Maine&apos;s H. sanguineus population densities in the intertidal peaked during the warmest months (July-September) and were lowest during the coldest months (January-March) when the crabs retreated to the subtidal zone. Densities were also greater in warmer localities (southern Maine) than in cooler localities (central and eastern Maine). In fact, populations were absent from areas with mean summer temperatures cooler than 13°C. In southern Maine, seasonal population densities and reproductive periodicity corresponded to periods with mean temperatures warmer than 15°and 12°C, respectively. There are many physical and biological factors that could limit this invasion. However, our temperature and demographic data are consistent with the thesis that the H. sanguineus invasion has stalled at the terminus of the Gulf of Maine&apos;s cold, Eastern Maine Coastal Current. We compared published mean summer and winter SST data for coastal waters in the western North Atlantic and in the native Asian range of H. sanguineus, and we quantified and compared H. sanguineus abundance in Maine with thermal microenvironments at these sites. From this, we speculate that future distribution of this crab may be limited to the warmer areas of the Maine coast (south and west of Penobscot Bay) and up estuaries that warm every summer. Thus, it may be possible for managers to gauge future risks of marine species invasion from vectors such as ships based on the thermal biogeographic match or mismatch between their ports of origin and their destinations. Such information could be useful for focused monitoring and enforcement of existing laws designed to prevent future introductions of non-native marine species. As coastal waters warm, invasion opportunities could increase from cold-limited species

Complex-Temperature Singularities in the d=2d=2 Ising Model. III. Honeycomb Lattice

We study complex-temperature properties of the uniform and staggered susceptibilities $\chi$ and $\chi^{(a)}$ of the Ising model on the honeycomb lattice. From an analysis of low-temperature series expansions, we find evidence that $\chi$ and $\chi^{(a)}$ both have divergent singularities at the point $z=-1 \equiv z_{\ell}$ (where $z=e^{-2K}$), with exponents $\gamma_{\ell}'= \gamma_{\ell,a}'=5/2$. The critical amplitudes at this singularity are calculated. Using exact results, we extract the behaviour of the magnetisation $M$ and specific heat $C$ at complex-temperature singularities. We find that, in addition to its zero at the physical critical point, $M$ diverges at $z=-1$ with exponent $\beta_{\ell}=-1/4$, vanishes continuously at $z=\pm i$ with exponent $\beta_s=3/8$, and vanishes discontinuously elsewhere along the boundary of the complex-temperature ferromagnetic phase. $C$ diverges at $z=-1$ with exponent $\alpha_{\ell}'=2$ and at $v=\pm i/\sqrt{3}$ (where $v = \tanh K$) with exponent $\alpha_e=1$, and diverges logarithmically at $z=\pm i$. We find that the exponent relation $\alpha'+2\beta+\gamma'=2$ is violated at $z=-1$; the right-hand side is 4 rather than 2. The connections of these results with complex-temperature properties of the Ising model on the triangular lattice are discussed.Comment: 22 pages, latex, figures appended after the end of the text as a compressed, uuencoded postscript fil

Preoperative localisation for parathyroid surgery in primary hyperparathyroidism: a study to evaluate the clinical utility of different imaging modalities

Primary hyperparathyroidism (PHPT) is caused by a solitary benign adenoma in 80‐85% of cases, but may also be due to multi‐gland or ectopic disease, hyperplasia, and rarely parathyroid carcinoma. Preoperative localisation studies are important to identify patients suitable for minimally invasive parathyroid surgery. The aim of this study was to evaluate the accuracy of ultrasound (US), parathyroid scintigraphy (MIBI) and computed tomography (CT) utilised in the preoperative setting in a district general hospital, with limited access to single photon‐emission computed tomography (SPECT)