Cardiovascular instrumentation

A brief introductory treatment is made of the physiology and instrumentation of the cardiovascular system. Two areas are singled out for further investigation. Arterial blood flow is investigated. In particular the effects of atherosclerosis on the pulse wave propagation through the arterial system are considered. A method for assessing arterial condition employing two ultrasonic Doppler flowmeters is proposed. A digital zero-crossing detection system is suggested as a means of producing a relatively simple and inexpensive instrument to provide real-time results. The performance of the heart as a pump and the parameters used to assess this performance are considered. One such parameter is the cardiac ejection fraction, which relates the stroke and end-diastolic volumes of the heart's left ventricle. A new method of estimating left ventricular volume from single-plane cineangiocardiograms is described. Called the Rectangular Rule, this method approximates the volume to a series of circular discs. A special-purpose calculator has been developed to implement the Rectangular Rule and to make cardiac ejection fraction estimations. Results of studies made of patients indicate that the calculator produces results at least as accurate as those of an other popular method, and that the cardiac ejection fraction is a valuable guide to surgical prognosis

Contributions to electrocardiographic science

This thesis reports original theoretical and experimental studies related to the measurement and interpretation of the electrical activity of the heart. The relevant literature and clinical practice are reviewed at length. Part I is a review of the science of electrocardiography. Included in the review are the electrophysiology of the heart, the potential theory which relates the electrocardiogram (E.C.G.) to its source, the various schemes used to measure and interpret the E.C.G. and the use of computer modelling to aid in E.C.G. interpretation. The effects of body shape and internal conductivity inhomogeneities on the E.C.G. are studied by means of a computer model. A simple form of the model has a piecewise homogeneous interior with spherical boundaries and a surface admittance is invoked to model changes in the surface shape. An extended form of the model allows the boundaries to be irregular and it is solved by means of an integral equation and the extended boundary condition. Representative numerical results are presented, illustrating the practical utility of the model. The sensitivity of the E.C.G. to certain types of inhomogeneity and surface shape changes is established. An experimental study, supported by a computer model based on the techniques outlined above, of the non-invasive detection of the signals from the ventricular specialised conduction system is reported. Thirty-five subjects were studied using a measurement system with a frequency response extending from 0.1 Hz to 500 Hz (-3 dB points) and using a pair of chest electrodes (similar to Lead CM1), Signal averaging was performed on groups of approximately 50 beats, using the onset of the QRS wave as a timing reference. The signals were detected with certainty in 85% of the subjects studied. The typical measured signal waveform is remarkably similar to that predicted by the aforementioned computer modelling technique. Two features are identified: an initial positive deflection (which probably represents the initial activation of the bundle branches) and a notch approximately 10 msec later (which may represent the passage of the activation into the bundle branches)

Novel Experimental Simulations of the Atmospheric Injection of Meteoric Metals

A newly developed laboratory, Meteoric Ablation Simulator (MASI), is used to test model predictions of the atmospheric ablation of interplanetary dust particles (IDPs) with experimental Na, Fe, and Ca vaporization profiles. MASI is the first laboratory setup capable of performing time-resolved atmospheric ablation simulations, by means of precision resistive heating and atomic laser-induced fluorescence detection. Experiments using meteoritic IDP analogues show that at least three mineral phases (Na-rich plagioclase, metal sulfide, and Mg-rich silicate) are required to explain the observed appearance temperatures of the vaporized elements. Low melting temperatures of Na-rich plagioclase and metal sulfide, compared to silicate grains, preclude equilibration of all the elemental constituents in a single melt. The phase-change process of distinct mineral components determines the way in which Na and Fe evaporate. Ca evaporation is dependent on particle size and on the initial composition of the molten silicate. Measured vaporized fractions of Na, Fe, and Ca as a function of particle size and speed confirm differential ablation (i.e., the most volatile elements such as Na ablate first, followed by the main constituents Fe, Mg, and Si, and finally the most refractory elements such as Ca). The Chemical Ablation Model (CABMOD) provides a reasonable approximation to this effect based on chemical fractionation of a molten silicate in thermodynamic equilibrium, even though the compositional and geometric description of IDPs is simplistic. Improvements in the model are required in order to better reproduce the specific shape of the elemental ablation profiles

MARS spectral molecular imaging of lamb tissue: data collection and image analysis

Spectral molecular imaging is a new imaging technique able to discriminate and quantify different components of tissue simultaneously at high spatial and high energy resolution. Our MARS scanner is an x-ray based small animal CT system designed to be used in the diagnostic energy range (20 to 140 keV). In this paper, we demonstrate the use of the MARS scanner, equipped with the Medipix3RX spectroscopic photon-processing detector, to discriminate fat, calcium, and water in tissue. We present data collected from a sample of lamb meat including bone as an illustrative example of human tissue imaging. The data is analyzed using our 3D Algebraic Reconstruction Algorithm (MARS-ART) and by material decomposition based on a constrained linear least squares algorithm. The results presented here clearly show the quantification of lipid-like, water-like and bone-like components of tissue. However, it is also clear to us that better algorithms could extract more information of clinical interest from our data. Because we are one of the first to present data from multi-energy photon-processing small animal CT systems, we make the raw, partial and fully processed data available with the intention that others can analyze it using their familiar routines. The raw, partially processed and fully processed data of lamb tissue along with the phantom calibration data can be found at [http://hdl.handle.net/10092/8531].Comment: 11 pages, 6 fig

Sources of Cosmic Dust in the Earth's Atmosphere

There are four known sources of dust in the inner solar system: Jupiter Family comets, Asteroids, Halley Type comets, and Oort Cloud comets. Here we combine the mass, velocity and radiant distributions of these cosmic dust populations from an astronomical model with a chemical ablation model to estimate the injection rates of Na and Fe into the Earth's upper atmosphere, as well as the flux of cosmic spherules to the surface. Comparing these parameters to lidar observations of the vertical Na and Fe fluxes above 87.5 km, and the measured cosmic spherule accretion rate at South Pole, shows that Jupiter Family Comets contribute (80 ± 17) % of the total input mass (43 ± 14 t d¯¹), in good accord with COBE and Planck observations of the Zodiacal Cloud

Metabolic analysis of the interaction between plants and herbivores

Insect herbivores by necessity have to deal with a large arsenal of plant defence metabolites. The levels of defence compounds may be increased by insect damage. These induced plant responses may also affect the metabolism and performance of successive insect herbivores. As the chemical nature of induced responses is largely unknown, global metabolomic analyses are a valuable tool to gain more insight into the metabolites possibly involved in such interactions. This study analyzed the interaction between feral cabbage (Brassica oleracea) and small cabbage white caterpillars (Pieris rapae) and how previous attacks to the plant affect the caterpillar metabolism. Because plants may be induced by shoot and root herbivory, we compared shoot and root induction by treating the plants on either plant part with jasmonic acid. Extracts of the plants and the caterpillars were chemically analysed using Ultra Performance Liquid Chromatography/Time of Flight Mass Spectrometry (UPLCT/MS). The study revealed that the levels of three structurally related coumaroylquinic acids were elevated in plants treated on the shoot. The levels of these compounds in plants and caterpillars were highly correlated: these compounds were defined as the ‘metabolic interface’. The role of these metabolites could only be discovered using simultaneous analysis of the plant and caterpillar metabolomes. We conclude that a metabolomics approach is useful in discovering unexpected bioactive compounds involved in ecological interactions between plants and their herbivores and higher trophic levels.

Unique, non‐Earthlike, meteoritic ion behavior in upper atmosphere of Mars

Interplanetary dust particles have long been expected to produce permanent ionospheric metal ion layers at Mars, as on Earth, but the two environments are so different that uncertainty existed as to whether terrestrial-established understanding would apply to Mars. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission made the first in situ detection of the continuous presence of Na+, Mg+, and Fe+ at Mars and indeed revealed non-Earthlike features/processes. There is no separation of the light Mg+ and the heavy Fe+ with increasing altitude as expected for gravity control. The metal ions are well-mixed with the neutral atmosphere at altitudes where no mixing process is expected. Isolated metal ion layers mimicking Earth's sporadic E layers occur despite the lack of a strong magnetic field as required at Earth. Further, the metal ion distributions are coherent enough to always show atmospheric gravity wave signatures. All features and processes are unique to Mars

What is the Value of Vagueness?

Classically, vagueness has been considered something bad. It leads to the Sorites paradox, borderline cases, and the (apparent) violation of the logical principle of bivalence. Nevertheless, there have always been scholars claiming that vagueness is also valuable. Many have pointed out that we could not communicate as successfully or efficiently as we do if we would not use vague language. Indeed, we often use vague terms when we could have used more precise ones instead. Many scholars (implicitly or explicitly) assume that we do so because their vagueness has a positive function. But how and in what sense can vagueness be said to have a function or value? This paper is an attempt to give an answer to this question. After clarifying the concepts of vagueness and value, it examines nine arguments for the value of vagueness, which have been discussed in the literature. The (negative) result of this examination is, however, that there is not much reason to believe that vagueness has a value or positive function at all because none of the arguments is conclusive. A tenth argument that has not been discussed so far seems most promising but rests on a solely strategic notion of function