3,796 research outputs found
The effects of repetitive electric cardiac stimulation in dogs with normal hearts, complete heart block and experimental cardiac arrest
Direct cardiac stimulation was conducted in the open chest. In normal animals, auricular stimulation at frequencies faster than the spontaneous rate caused little change in vascular pressures or cardiac output. Comparable ventricular stimulation in the same animals caused falls in cardiac output and blood pressure, with elevations in venous pressure. In contrast, ventricular stimulation in animals with complete heart block caused elevations in cardiac output and blood pressure, and declines in venous pressure. A study was also made of repetitive stimulation in experimental cardiac arrest. Occasionally pacemaking was of value in the resuscitation, but in most cases effective contractions could not be induced with stimulation
Compressibility of titanosilicate melts
The effect of composition on the relaxed adiabatic bulk modulus (K0) of a range of alkali- and alkaline earth-titanosilicate [X 2 n/n+ TiSiO5 (X=Li, Na, K, Rb, Cs, Ca, Sr, Ba)] melts has been investigated. The relaxed bulk moduli of these melts have been measured using ultrasonic interferometric methods at frequencies of 3, 5 and 7 MHz in the temperature range of 950 to 1600°C (0.02 Pa s < s < 5 Pa s). The bulk moduli of these melts decrease with increasing cation size from Li to Cs and Ca to Ba, and with increasing temperature. The bulk moduli of the Li-, Na-, Ca- and Ba-bearing metasilicate melts decrease with the addition of both TiO2 and SiO2 whereas those of the K-, Rb- and Cs-bearing melts increase. Linear fits to the bulk modulus versus volume fraction of TiO2 do not converge to a common compressibility of the TiO2 component, indicating that the structural role of TiO2 in these melts is dependent on the identity of the cation. This proposition is supported by a number of other property data for these and related melt compositions including heat capacity and density, as well as structural inferences from X-ray absorption spectroscopy (XANES). The compositional dependence of the compressibility of the TiO2 component in these melts explains the difficulty incurred in previous attempts to incorporate TiO2 in calculation schemes for melt compressibility. The empirical relationship KV-4/3 for isostructural materials has been used to evaluate the compressibility-related structural changes occurring in these melts. The alkali metasilicate and disilicate melts are isostructural, independent of the cation. The addition of Ti to the metasilicate composition (i.e. X2TiSiO5), however, results in a series of melts which are not isostructural. The alkaline-earth metasilicate and disilicate compositions are not isostructural, but the addition of Ti to the metasilicate compositions (i.e. XTiSiO5) would appear, on the basis of modulus-volume systematics, to result in the melts becoming isostructural with respect to compressibility
Energy in the home: Everyday life and the effect on time of use
The application of building simulation and modelling is becoming more widespread, particularly in the analysis of residential buildings. The energy consumption and control of systems in residential buildings are tightly linked to the behaviour of people, arguably more so than in commercial buildings which have traditionally been the preserve of building simulation analysis. The input profiles used in simulation pay little attention to the link between numerical characterisations of observed ‘behaviour’ and the way people actually live in the home. Understanding this is important if we are to improve the modelling of buildings, gain greater insight into energy consumption and make better decisions about future energy production and generation. This paper explores this link by combining conventional numerical analysis of appliance data with insights from the ethnographic study of families in 20 UK homes. Ethnographic insights provide a context to the analysis and understanding of monitoring data that would not otherwise be possible. Importantly, this paper highlights the need to rethink previously static notions of simulation input, such as occupancy and individual appliance use
Plasma Pro-Endothelin-1 Peptide Concentrations Rise in Chronic Kidney Disease and Following Selective Endothelin A Receptor Antagonism
The new analyses described in this article were funded by the
Medical Research Council (Grant G0801509). Additional
funding was from the British Heart Foundation (Project Grant
PG/05/91), Encysive Pharmaceuticals, and Pfizer. Dr Dhaun
is supported by a British Heart Foundation Intermediate
Clinical Research Fellowship (FS/13/30/29994)
Predicting Risky Drinking Outcomes Longitudinally: What Kind of Advance Notice Can We Get?
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65954/1/j.1530-0277.2006.00033.x.pd
Imaging and controlling electron transport inside a quantum ring
Traditionally, the understanding of quantum transport, coherent and
ballistic1, relies on the measurement of macroscopic properties such as the
conductance. While powerful when coupled to statistical theories, this approach
cannot provide a detailed image of "how electrons behave down there". Ideally,
understanding transport at the nanoscale would require tracking each electron
inside the nano-device. Significant progress towards this goal was obtained by
combining Scanning Probe Microscopy (SPM) with transport measurements2-7. Some
studies even showed signatures of quantum transport in the surrounding of
nanostructures4-6. Here, SPM is used to probe electron propagation inside an
open quantum ring exhibiting the archetype of electron wave interference
phenomena: the Aharonov-Bohm effect8. Conductance maps recorded while scanning
the biased tip of a cryogenic atomic force microscope above the quantum ring
show that the propagation of electrons, both coherent and ballistic, can be
investigated in situ, and even be controlled by tuning the tip potential.Comment: 11 text pages + 3 figure
Energy spectra of quantum rings
Ring geometries have fascinated experimental and theoretical physicists over
many years. Open rings connected to leads allow the observation of the
Aharonov-Bohm effect, a paradigm of quantum mechanical phase coherence. The
phase coherence of transport through a quantum dot embedded in one arm of an
open ring has been demonstrated. The energy spectrum of closed rings has only
recently been analysed by optical experiments and is the basis for the
prediction of persistent currents and related experiments. Here we report
magnetotransport experiments on a ring-shaped semiconductor quantum dot in the
Coulomb blockade regime. The measurements allow us to extract the discrete
energy levels of a realistic ring, which are found to agree well with
theoretical expectations. Such an agreement, so far only found for few-electron
quantum dots, is here extended to a many-electron system. In a semiclassical
language our results indicate that electron motion is governed by regular
rather than chaotic motion, an unexplored regime in many-electron quantum dots.Comment: 10 pages, 4 figure
Cost-effectiveness of replacing skeletal traction by interlocked intramedullary nailing for femoral shaft fractures in a provincial trauma hospital in Cambodia
In this article the costs and effectiveness of introducing the SIGN nailing system for femoral shaft fractures in a provincial trauma hospital in Cambodia are compared to those of Perkin’s traction treatment. At an average cost per patient of 888 in the nail group (p < 0.01), and with better clinical outcomes in the nail group, internal fixation is more cost-effective than conservative treatment
Modelling the effects of glucagon during glucose tolerance testing
Background
Glucose tolerance testing is a tool used to estimate glucose effectiveness and insulin sensitivity in diabetic patients. The importance of such tests has prompted the development and utilisation of mathematical models that describe glucose kinetics as a function of insulin activity. The hormone glucagon, also plays a fundamental role in systemic plasma glucose regulation and is secreted reciprocally to insulin, stimulating catabolic glucose utilisation. However, regulation of glucagon secretion by α-cells is impaired in type-1 and type-2 diabetes through pancreatic islet dysfunction. Despite this, inclusion of glucagon activity when modelling the glucose kinetics during glucose tolerance testing is often overlooked. This study presents two mathematical models of a glucose tolerance test that incorporate glucose-insulin-glucagon dynamics. The first model describes a non-linear relationship between glucagon and glucose, whereas the second model assumes a linear relationship.
Results
Both models are validated against insulin-modified and glucose infusion intravenous glucose tolerance test (IVGTT) data, as well as insulin infusion data, and are capable of estimating patient glucose effectiveness (sG) and insulin sensitivity (sI). Inclusion of glucagon dynamics proves to provide a more detailed representation of the metabolic portrait, enabling estimation of two new diagnostic parameters: glucagon effectiveness (sE) and glucagon sensitivity (δ).
Conclusions
The models are used to investigate how different degrees of pax‘tient glucagon sensitivity and effectiveness affect the concentration of blood glucose and plasma glucagon during IVGTT and insulin infusion tests, providing a platform from which the role of glucagon dynamics during a glucose tolerance test may be investigated and predicted
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