Morphology of fluvial networks on Titan: Evidence for structural control

Although Titan’s surface shows clear evidence of erosional modification, such as fluvial incision, evidence for tectonism has been less apparent. On Earth, fluvial networks with strongly preferred orientations are often associated with structural features, such as faults or joints, that influence flow or erodibility. We delineated and classified the morphologies of fluvial drainages on Titan and discovered evidence of structural control. Fluvial networks were delineated both on synthetic aperture radar (SAR) images covering ∼40% of Titan from the Cassini Titan Radar Mapper up through T71 and on visible light images of the Huygens landing site collected by the Descent Imager/Spectral Radiometer (DISR). The delineated networks were assigned to one of three morphologic classes—dendritic, parallel or rectangular—using a quantitative terrestrial drainage pattern classification algorithm modified for use with Titan data. We validated our modified algorithm by applying it to synthetic fluvial networks produced by a landscape evolution model with no structural control of drainage orientations, and confirmed that only a small fraction of the networks are falsely identified as structurally controlled. As a second validation, we confirmed that our modified algorithm correctly classifies terrestrial networks that are classified in multiple previous works as rectangular. Application of this modified algorithm to our Titan networks results in a classification of rectangular for one-half of the SAR and DISR networks. A review of the geological context of the four terrestrial rectangular networks indicates that tensional stresses formed the structures controlling those terrestrial drainages. Based on the similar brittle response of rock and cryogenic ice to stress, we infer that structures formed under tension are the most likely cause of the rectangular Titan networks delineated here. The distribution of these rectangular networks suggests that tensional stresses on Titan may have been widespread.United States. National Aeronautics and Space Administration (NASA Cassini Data Analysis Program Grant NNX08BA81G

Rock physics in four dimensions

The measurement of the seismic velocity of a medium is fundamental to many applications in geoscience and engineering. Examples include the monitoring of: ice sheet melting, the health of concrete structures, temperature in volcanic regions, and sub-surface fluid pressure due to hydrocarbon extraction or the injection of CO2 to mitigate climate change. Velocities are also used to infer elastic properties, such as bulk and shear moduli and density, which can then be used to develop a wide range of rock physics models. This thesis addresses two key areas of research related to the seismic velocity: first, the improvement in the methodology of measuring changes in velocity in the time-lapse or four dimensional mode; and second, the interpretation of changing velocity measurements in terms of underlying processes, using various rock physics models. First, I investigate the use of coda wave interferometry (CWI) for measuring temporal changes in bulk velocity, particularly in an experimental rock physics setting. CWI uses the diffuse, multiply-scattered waves that arrive in the tail of the seismogram, sampling the entire medium and sampling the same sub-volumes many times, thus coda waves are far more sensitive to changes in a medium compared to the first arriving ballistic waves. Compared to conventional methods of phase picking of first arriving waves, CWI provides significant improvements in the accuracy and precision of estimates of velocity changes and is far more robust in the presence of background noise. CWI is also capable of jointly estimating changing source locations, allowing the estimation of the relative locations of a cluster of acoustic emissions with simultaneous velocity perturbations, all with a single receiver. Previously, the estimate of velocity change made by CWI has been an average of changes in compressional (P) and shear (S) wave velocities, which has previously been a major limitation to the application of the CWI method. I present a new method to use CWI for estimating changes in both P and S wave velocities individually. I then validate this method using numerical simulations on a range of media and the results of triaxial rock deformation experiments. The second part of this thesis is based on understanding the relationship between seismic velocity and time-dependent variables, including the evolving differential stress during deformation and changes in porosity during cementation. I investigate the seismic velocity-differential stress relationship during the experimental deformation of two finely laminated carbonate samples, using CWI to measure the temporal changes in both P and S wave velocity, allowing the inversion of crack density to interpret the mechanical behaviour of these carbonate samples. I then investigate the velocity-porosity relationship with an entirely digital method, using digital rocks where deposition and cementation are computationally simulated. I then simulate wavefield propagation through the digital rocks using a 3D finite-difference method to estimate the velocity of the medium. I statistically test two competing inclusion models for modelling elastic moduli-porosity data and find one that allows variable inclusion aspect ratio to be the most appropriate for fitting the data. I find CWI to be an effective method characterising changes in a medium in a rock physics environment. By providing a method for estimating separate changes in P and S wave velocity, I greatly improve the relevance and applicability of CWI for experimental rock physics. The method can be extended for the characterisation of media for a variety of applications in geoscience and engineering

Dynamics of a small neutrally buoyant sphere in a fluid and targeting in Hamiltonian systems

We show that, even in the most favorable case, the motion of a small spherical tracer suspended in a fluid of the same density may differ from the corresponding motion of an ideal passive particle. We demonstrate furthermore how its dynamics may be applied to target trajectories in Hamiltonian systems.Comment: See home page http://lec.ugr.es/~julya

Risk factors for Hodgkin's disease by Epstein-Barr virus (EBV) status: prior infection by EBV and other agents

A UK population-based case–control study of Hodgkin's disease (HD) in young adults (16–24 years) included 118 cases and 237 controls matched on year of birth, gender and county of residence. The majority (103) of the cases were classified by Epstein–Barr virus (EBV) status (EBV present in Reed–Stenberg cells), with 19 being EBV-positive. Analyses using conditional logistic regression are presented of subject reports of prior infectious disease (infectious mononucleosis (IM), chicken pox, measles, mumps, pertussis and rubella). In these analyses HD cases are compared with matched controls, EBV-positive cases and EBV-negative cases are compared separately with their controls and formal tests of differences of association by EBV status are applied. A prior history of IM was positively associated with HD (odds ratio (OR) = 2.43, 95% confidence interval (CI) = 1.10–5.33) and with EBV-positive HD (OR = 9.16, 95% CI = 1.07–78.31) and the difference between EBV-positive and EBV-negative HD was statistically significant (P = 0.013). The remaining infectious illnesses (combined) were negatively associated with HD, EBV-positive HD and EBV-negative HD (in the total series, for ≥2 episodes compared with ≤1, OR = 0.45, 95% CI = 0.25–0.83). These results support previous evidence that early exposure to infection protects against HD and that IM increases subsequent risk; the comparisons of EBV-positive and EBV-negative HD are new and generate hypotheses for further study. © 2000 Cancer ResearchCampaig

Pion-Muon Asymmetry Revisited

Long ago an unexpected and unexplainable phenomena was observed. The distribution of muons from positive pion decay at rest was anisotropic with an excess in the backward direction relative to the direction of the proton beam from which the pions were created. Although this effect was observed by several different groups with pions produced by different means, the result was not accepted by the physics community, because it is in direct conflict with a large set of other experiments indicating that the pion is a pseudoscalar particle. It is possible to satisfy both sets of experiments if helicity-zero vector particles exist and the pion is such a particle. Helicity-zero vector particles have direction but no net spin. For the neutral pion to be a vector particle requires an additional modification to conventional theory as discussed herein. An experiment is proposed which can prove that the asymmetry in the distribution of muons from pion decay is a genuine physical effect because the asymmetry can be modified in a controllable manner. A positive result will also prove that the pion is NOT a pseudoscalar particle.Comment: 9 pages, 3 figure

Principles and philosophies for speech and language therapists working with people with primary progressive aphasia: An international expert consensus

Purpose: Primary progressive aphasia (PPA) is a language-led dementia associated with Alzheimer’s pathology and fronto-temporal lobar degeneration. Multiple tailored speech and language interventions have been developed for people with PPA. Speech and language therapists/speech-language pathologists (SLT/Ps) report lacking confidence in identifying the most pertinent interventions options relevant to their clients living with PPA during their illness trajectory. Materials and methods: The aim of this study was to establish a consensus amongst 15 clinical-academic SLT/Ps on best practice in selection and delivery of speech and language therapy interventions for people with PPA. An online nominal group technique (NGT) and consequent focus group session were held. NGT rankings were aggregated and focus groups video recorded, transcribed, and reflexive thematic analysis undertaken. Results: The results of the NGT identified 17 items. Two main themes and seven further subthemes were identified in the focus groups. The main themes comprised (1) philosophy of person-centredness and (2) complexity. The seven subthemes were knowing people deeply, preventing disasters, practical issues, professional development, connectedness, barriers and limitations, and peer support and mentoring towards a shared understanding. Conclusions: This study describes the philosophy of expert practice and outlines a set of best practice principles when working with people with PPA.Implications for rehabilitation Primary progressive aphasia (PPA) describes a group of language led dementias which deteriorate inexorably over time. Providing speech and language therapy for people with PPA is complex and must be person centred and bespoke. This study describes the philosophy of expert practice and outlines a set of best practice principles for speech and language therapists/pathologists working with people with people with PPA

Factors associated with self-care activities among adults in the United Kingdom: a systematic review

Background: The Government has promoted self-care. Our aim was to review evidence about who uses self-tests and other self-care activities (over-the-counter medicine, private sector,complementary and alternative medicine (CAM), home blood pressure monitors). Methods: During April 2007, relevant bibliographic databases (Medline, Embase, Cumulative Index to Nursing and Allied Health Literature, Applied Social Sciences Index and Abstracts, PsycINFO,British Nursing Index, Allied and Complementary Medicine Database, Sociological Abstracts, International Bibliography of the Social Sciences, Arthritis and Complementary Medicine Database, Complementary and Alternative Medicine and Pain Database) were searched, and potentially relevant studies were reviewed against eligibility criteria. Studies were included if they were published during the last 15 years and identified factors, reasons or characteristics associated with a relevant activity among UK adults. Two independent reviewers used proformas to assess the quality of eligible studies. Results: 206 potentially relevant papers were identified, 157 were excluded, and 49 papers related to 46 studies were included: 37 studies were, or used data from questionnaire surveys, 36 had quality scores of five or more out of 10, and 27 were about CAM. Available evidence suggests that users of CAM and over-the-counter medicine are female, middle-aged, affluent and/or educated with some measure of poor health, and that people who use the private sector are affluent and/or educated. Conclusion: People who engage in these activities are likely to be affluent. Targeted promotion may, therefore, be needed to ensure that use is equitable. People who use some activities also appear to have poorer measures of health than non-users or people attending conventional services. It is, therefore, also important to ensure that self-care is not used as a second choice for people who have not had their needs met by conventional service