797 research outputs found
UV Spectroscopy of Metal-Poor Massive Stars in the Small Magellanic Cloud
The Hubble Space Telescope has provided the first clear evidence for weaker
winds of metal-poor massive stars in the Small Magellanic Cloud, confirming
theoretical predictions of the metallicity dependence of mass-loss rates and
wind terminal velocities. For lower luminosity O-type stars however, derived
mass-loss rates are orders of magnitude lower than predicted, and are at
present unexplained.Comment: 4 pages, 3 figures. To appear in 'The Impact of HST on European
Astronomy', Eds., G. De Marchi & F.D. Macchetto, Astrophysics & Space
Science, Springe
Nietzsche and classical greek philosophy: Essays on Socrates, Plato, Aristotle, and Heraclitus
In my dissertation I attempt to answer one question: What is the precise nature of Nietzsche’s view of Socrates, Plato, and Aristotle? I answer this question over four chapters. Each chapter is a self-contained essay that explores the contours of Nietzsche’s ambivalence toward these figures. In Chapter I I show how Nietzsche’s ambivalence toward Socrates is a manifestation of Nietzsche’s ambivalence toward reason. In Chapter II I argue that Nietzsche’s ambivalence toward Plato culminates in four features of Plato’s philosophy: (1) his political philosophy, (2) his metaphysics and epistemology, and (3) his dramatic style. In Chapter III I argue that there are four areas of inquiry that help clarify Nietzsche’s ambivalence toward Aristotle: (1) philosophical methods, (2) ethics, (3) free will, and (4) Greek tragedy. Despite Nietzsche’s attack on Aristotle for misunderstanding the nature of Greek tragedy, I show that Nietzsche owes multiple debts of gratitude for what he seemingly gleaned from the Macedonian philosopher. Finally, in Chapter IV, despite Nietzsche’s objections, I show that the classical Greek philosophers are just as responsible, if not more responsible, than their archaic predecessors for Nietzsche’s intellectual development through a comparative analysis of Nietzsche’s engagement with Plato and Heraclitus
Hydrogeological and geotechnical rock property characterization from geophysics
Boreholes drilled at Sellafield penetrated a variety of rock units. Core samples and wireline logs indicate that rock mass properties and in situ fluid properties vary from one unit to another, but that properties are relatively uniform for each unit within a particular borehole. Variability is superimposed upon the bulk rock mass properties, however, where faults or zones of fractured rock intersect a borehole. Furthermore, lateral variability within a particular unit may be expected between boreholes and throughout the rock volume.
The primary objectives of the work were: to establish a means of determining the spatial heterogeneity and distribution of rock mass and fluid properties using measurements made on core samples and derived from wireline logs; to determine the spatial heterogeneity and distribution of rock mass properties away from boreholes and in three-dimensions, by extrapolating the detailed understanding gained from boreholes into the seismic survey volume; and to develop a visualization model of rock mass properties in three-dimensions.
It has been demonstrated that acoustic impedance is the principal property in common between surface seismic and borehole measurements, and that it provides a link between the various scales of measurement. Dynamic rock quality and hydrogeological indices have been developed which allow qualitative comparisons to be made between the boreholes. Empirical relationships have also been established between acoustic impedance and rock quality, and between acoustic impedance and hydrogeological properties. These relationships enable continuous profile quantitative estimations of Rock Mass Rating and hydraulic conductivity to be made from wireline logs, and have allowed these properties to be extrapolated into the seismic acoustic impedance volume, thereby providing three-dimensional visualizations of the spatial heterogeneity of rock mass properties
The comparison of core and geophysical log measurements obtained in the Nirex investigation of the Sellafield region
The Sellafield region, west Cumbria, is the focus of one of the most thorough geological investigations in the United Kingdom. The Sellafield Site is defined as an area immediately around the potential repository, extending 6.5 km north-south by 8 km eastwest. Twenty six deep boreholes were drilled within the area up to the end of 1995, with a total depth of approximately 28 km. Most of these boreholes have been continuously cored, a total of over 17 kilometres of core, with average core recovery well in excess of 90%. All boreholes were logged with a comprehensive suite of geophysical logs, including many state of the art tools. Laboratory physical property analysis of hundreds of sample cores has been carried out.
Pilot studies were carried out to compare and contrast datasets and to investigate the relationships between the different data scales. Various techniques, including fractal analysis and Artificial Neural Networks, were tried in order to explore the relationships of these data at a variety of measurement scales.
The pilot study was conducted in two stages:
(1) evaluation of the primary controlling factors of the physical properties;
(2) testing the validity of ‘Up-scaling’.
The rocks of the Borrowdale Volcanic Group provided the most challenging problems due to the physical properties being dominated by fracturing and associated alteration zones.
Relationships between data types at different scales were established suggesting that the extrapolation of properties derived from core and wireline logs across three-dimensional seismic grids would allow an understanding of the properties throughout a three-dimensional volum
Deflection of coronal rays by remote CMEs: shock wave or magnetic pressure?
We analyze five events of the interaction of coronal mass ejections (CMEs)
with the remote coronal rays located up to 90^\circ away from the CME as
observed by the SOHO/LASCO C2 coronagraph. Using sequences of SOHO/LASCO C2
images, we estimate the kink propagation in the coronal rays during their
interaction with the corresponding CMEs ranging from 180 to 920 km/s within the
interval of radial distances form 3 R. to 6 R. . We conclude that all studied
events do not correspond to the expected pattern of shock wave propagation in
the corona. Coronal ray deflection can be interpreted as the influence of the
magnetic field of a moving flux rope related to a CME. The motion of a
large-scale flux rope away from the Sun creates changes in the structure of
surrounding field lines, which are similar to the kink propagation along
coronal rays. The retardation of the potential should be taken into account
since the flux rope moves at high speed comparable with the Alfven speed.Comment: Accepted for Publication in Solar Physic
Existence and Nonlinear Stability of Rotating Star Solutions of the Compressible Euler-Poisson Equations
We prove existence of rotating star solutions which are steady-state
solutions of the compressible isentropic Euler-Poisson (EP) equations in 3
spatial dimensions, with prescribed angular momentum and total mass. This
problem can be formulated as a variational problem of finding a minimizer of an
energy functional in a broader class of functions having less symmetry than
those functions considered in the classical Auchmuty-Beals paper. We prove the
nonlinear dynamical stability of these solutions with perturbations having the
same total mass and symmetry as the rotating star solution. We also prove local
in time stability of W^{1, \infty}(\RR^3) solutions where the perturbations
are entropy-weak solutions of the EP equations. Finally, we give a uniform (in
time) a-priori estimate for entropy-weak solutions of the EP equations
Mesons in gauge/gravity dual with large number of fundamental fields
In view of extending gauge/gravity dualities with flavour beyond the probe
approximation, we establish the gravity dual description of mesons for a
three-dimensional super Yang-Mills theory with fundamental matter. For this
purpose we consider the fully backreacted D2/D6 brane solution of Cherkis and
Hashimoto in an approximation due to Pelc and Siebelink. The low-energy field
theory is the IR fixed point theory of three-dimensional N=4 SU(N_c) super
Yang-Mills with N_f fundamental fields, which we consider in a large N_c and
N_f limit with N_f/N_c finite and fixed. We discuss the dictionary between
meson-like operators and supergravity fluctuations in the corresponding
near-horizon geometry. In particular, we find that the mesons are dual to the
low-energy limit of closed string states. In analogy to computations of
glueball mass spectra, we calculate the mass of the lowest-lying meson and find
that it depends linearly on the quark mass.Comment: 19 pages, LaTeX, 6 figures, v2: fig. 4 added, refs. adde
Problems and possibilities in fine-tuning of the Cepheid P-L relationship
Factors contributing to the scatter around the ridge-line period-luminosity
relationship are listed, followed by a discussion how to eliminate the adverse
effects of these factors (mode of pulsation, crossing number, temperature
range, reddening, binarity, metallicity, non-linearity of the relationship,
blending), in order to reduce the dispersion of the P-L relationship.Comment: 7 pages, 8 figures; accepted for publication in Astrophysics & Space
Scienc
Glueballs of Super Yang-Mills from Wrapped Branes
In this paper we study qualitative features of glueballs in N=1 SYM for
models of wrapped branes in IIA and IIB backgrounds. The scalar mode, 0++ is
found to be a mixture of the dilaton and the internal part of the metric. We
carry out the numerical study of the IIB background. The potential found
exhibits a mass gap and produces a discrete spectrum without any cut-off. We
propose a regularization procedure needed to make these states normalizable.Comment: 22 pages plus a appendixes, 2 figure
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