20,608 research outputs found
Accretion Disk Temperatures of QSOs: Constraints from the Emission Lines
QSO emission-line spectra are compared to predictions based on theoretical
ionizing continua of accretion disks. Observed line intensities do not show the
expected trend of higher ionization with higher accretion disk temperature as
derived from the black hole mass and accretion rate. This suggests that, at
least for accretion rates close to the Eddington limit, the inner disk does not
reach temperatures as high as expected from standard disk theory. Modified
radial temperature profiles, taking account of winds or advection in the inner
disk, achieve better agreement with observation. This conclusion agrees with an
earlier study of QSO continuum colors as a function of disk temperature. The
emission lines of radio-detected and radio-undetected sources show different
trends as a function of disk temperature.Comment: 9 pages, 8 figures, submitted to Ap
A theoretical study of the aerodynamic characteristics of lifting-body entry vehicles Summary report, Mar. 1965 - Mar. 1966
Aerodynamic characteristics of lifting-body entry vehicle
Asteroseismology of red giants: photometric observations of Arcturus by SMEI
We present new results on oscillations of the K1.5 III giant Arcturus (alpha
Boo), from analysis of just over 2.5 yr of precise photometric observations
made by the Solar Mass Ejection Imager (SMEI) on board the Coriolis satellite.
A strong mode of oscillation is uncovered by the analysis, having frequency
3.51+/-0.03 micro-Hertz. By fitting its mode peak, we are able offer a highly
constrained direct estimate of the damping time (tau = 24+/-1 days). The data
also hint at the possible presence of several radial-mode overtones, and maybe
some non-radial modes. We are also able to measure the properties of the
granulation on the star, with the characteristic timescale for the granulation
estimated to be 0.50+/-0.05 days.Comment: 6 pages, 5 figures; accepted for publication in MNRAS Letter
Achieving change in the NHS: a feasibility study to introduce a home-based cancer chemotherapy service
A major focus of current health policyin the United Kingdom is the development of services that meet the public’s expectations. To achieve this there is a need to evaluate current provision to ensure that the best use is made of finite resources. The studyreported here adopted an interview approach to examine an existing outpatient chemotherapy service, and to consider the feasibilityof introducing a home based model. Following a review of literature on this topic data were obtained from in-depth interviews with patients and professionals regarding the present service. These were then combined with an analysis of service contracts and financial estimates. The poor quality of much of the costrelated information limited the conclusions which could be drawn, and emphasised the need for access to more accessible and robust financial information upon which to base change. The studyalso illustrated the benefits of feasibility studies; especially when cost-effectiveness and patient satisfaction are the driving forces behind proposed
changes to clinical services
Human subjective response to steering wheel vibration caused by diesel engine idle
This study investigated the human subjective response to steering wheel vibration of the type caused by a four-cylinder diesel engine idle in passenger cars. Vibrotactile perception was assessed using sinusoidal amplitude-modulated vibratory stimuli of constant energy level (r.m.s. acceleration, 0.41 m/s(2)) having a carrier frequency of 26 Hz (i.e. engine firing frequency) and modulation frequency of 6.5 Hz (half-order engine harmonic). Evaluations of seven levels of modulation depth parameter m (0.0, 0.1, 0.2, 0.4, 0.6, 0.8, and 1.0) were performed in order to define the growth function of human perceived disturbance as a function of amplitude modulation depth. Two semantic descriptors were used (unpleasantness and roughness) and two test methods (the Thurstone paired-comparison method and the Borg CR-10 direct evaluation scale) for a total of four tests. Each test was performed using an independent group of 25 individuals. The results suggest that there is a critical value of modulation depth m = 0.2 below which human subjects do not perceive differences in amplitude modulation and above which the stimulus-response relationship increases monotonically with a power function. The Stevens power exponents suggest that the perceived unpleasantness is non-linearly dependent on modulation depth m with an exponent greater than 1 and that the perceived roughness is dependent with an exponent close to unity
Non-abelian dynamics in first-order cosmological phase transitions
Bubble collisions in cosmological phase transitions are explored, taking the
non-abelian character of the gauge fields into account. Both the QCD and
electroweak phase transitions are considered. Numerical solutions of the field
equations in several limits are presented.Comment: 8 pages, 2 figures. Contribution to the CosPA 2003 Cosmology and
Particle Astrophysics Symposium. Typos correcte
Role of Charged Gauge Fields in Generating Magnetic Seed Fields in Bubble Collisions during the Cosmological Electroweak Phase Transition
We calculate the magnetic field generated during bubble collisions in a
first-order electroweak phase transition that may occur for some choices of
parameters in the minimal supersymmetric Standard Model. We show that for
sufficiently gentle collisions, where the Higgs field is relatively unperturbed
in the bubble overlap region, the equations of motion can be linearized so that
in the absence of fermions the charged W fields are the source of the
electromagnetic current for generating the seed fields. Solutions of the
equations of motion for the charged gauge fields and Maxwell's equations for
the magnetic field in O(1,2) space-time symmetry are expressed in closed form
by applying boundary conditions at the time of collision. Our results indicate
that the magnetic fields generated by charged fields in the collision
are comparable to those found in previous work. The magnetic fields so produced
could seed galactic and extra-galactic magnetic fields observed today.Comment: 15 Pages, 7 Figure
Response of selected microorganisms to experimental planetary environments
The anaerobic utilization of phosphite or phosphine and the significance of this conversion to potential contamination of Jupiter were investigated. A sporeforming organism was isolated from Cape Canaveral soil which anaerobically converts hypophosphite to phosphate. This conversion coincides with an increase in turbidity of the culture and with phosphate accumulation in the medium. Investigations of omnitherms (organisms which grow over a broad temperature range, i.e. 3 -55 C were also conducted. The cellular morphology of 28 of these isolates was investigated, and all were demonstrated to be sporeformers. Biochemical characterizations are also presented. Procedures for replicate plating were evaluated, and those results are also presented. The procedures for different replicate-plating techniques are presented, and these are evaluated on the basis of reproducibility, percentage of viable transfer, and ease of use. Standardized procedures for the enumeration of microbial populations from ocean-dredge samples from Cape Canaveral are also presented
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