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Search Results: 1 - 10 of 27598 matches for " Robert Main "
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Hepatic steatosis in patients with HIV-Hepatitis C Virus coinfection: is it associated with antiretroviral therapy and more advanced hepatic fibrosis?
Sumita Verma, Robert D Goldin, Janice Main
BMC Research Notes , 2008, DOI: 10.1186/1756-0500-1-46
Abstract: HIV-HCV coinfected patients were retrospectively identified from the HIV clinic. ART was classified as none, nucleoside reverse transcriptase inhibitors (NRTIs) only, highly active antiretroviral therapy (HAART) only, and sequential therapy (initial NRTIs followed by HAART). Fibrosis stage and necroinflammation grade were assessed by the modified HAI (Ishak) scoring method. Steatosis was graded as 0–3.Sixty patients were identified. The overall prevalence of hepatic steatosis was 58%. Those that received HAART only had a lower prevalence of steatosis (41%) compared to those on NRTIs only (70%) or sequential therapy (82%). Independent predictors of hepatic steatosis were absence of HAART only therapy, OR 2.9, p = 0.09, and presence of cirrhosis, OR 4.6, p = 0.044. Forty five percent of the patients had advanced fibrosis (fibrosis stage ≥ 3). NI grade (OR 1.9, p = 0.030), and steatosis grade (OR 3.6, p = 0.045), were independent predictors of advanced fibrosis.Hepatic steatosis is associated with more advanced hepatic fibrosis in the HIV-HCV coinfected population. HAART only therapy (rather than NRTIs only or sequential therapy) appears to be associated with a lower prevalence of hepatic steatosis. This may be one of the mechanisms by which HAART could attenuate hepatic fibrosis in such a cohort.Highly active antiretroviral therapy (HAART) has significantly improved survival in patients with human immunodeficiency virus (HIV) infection [1]. Increasing attention is now being focused on co infection with other viruses like hepatitis C (HCV). Because of similar routes of transmission, approximately 25–30% of patients with HIV are also coinfected with HCV [2]. Factors associated with more advanced hepatic fibrosis in HCV infection include HIV coinfection [3] and hepatic steatosis, (prevalence of 47%–79%) [4-6].Patients with HIV are also at increased risk of developing hepatic steatosis due to multiple factors including antiretroviral therapy (ART), obesity, hyperglycemia,
AGN Feedback, Host Halo Mass and Central Cooling Time: Implications for Galaxy Formation Efficiency and $M_{BH} - σ$
Robert Main,Brian McNamara,Paul Nulsen,Helen Russell,Adrian Vantyghem
Physics , 2015,
Abstract: We derive X-ray mass, luminosity, and temperature profiles for 45 galaxy clusters to explore relationships between halo mass, AGN feedback, and central cooling time. We find that radio--mechanical feedback power (referred to here as "AGN power") in central cluster galaxies correlates with halo mass, but only in halos with central atmospheric cooling times shorter than 1 Gyr. This timescale corresponds approximately to the cooling time (entropy) threshold for the onset of cooling instabilities and star formation in central galaxies (Rafferty et al. 2008). No correlation is found in systems with central cooling times greater than 1 Gyr. The trend with halo mass is consistent with self-similar scaling relations assuming cooling is regulated by feedback. The trend is also consistent with galaxy and central black hole co-evolution along the $M_{BH} - \sigma $ relation. AGN power further correlates with X-ray gas mass and the host galaxy's K-band luminosity. AGN power in clusters with central atmospheric cooling times longer than ~1 Gyr typically lies two orders of magnitude below those with shorter central cooling times. Galaxies centred in clusters with long central cooling times nevertheless experience ongoing and occasionally powerful AGN outbursts. We further investigate the impact of feedback on cluster scaling relations. We find L-T, and M-T relations, excluding regions directly affected by AGN, that are consistent with the cluster population as a whole. While the gas mass rises, the stellar mass remains nearly constant with rising total mass, consistent with earlier studies. This trend is found regardless of central cooling time, implying tight regulation of star formation in central galaxies as their halos grew, and long-term balance between AGN heating and atmospheric cooling. Our scaling relations are presented in forms that can be incorporated easily into galaxy evolution models.
A Wiener-Laguerre Model of VIV Forces Given Recent Cylinder Velocities
Philippe Main on
Mathematical Problems in Engineering , 2011, DOI: 10.1155/2011/414702
Abstract: Slender structures immersed in a cross flow can experience vibrations induced by vortex shedding (VIV), which cause fatigue damage and other problems. VIV models that are used in structural design today tend to assume harmonic oscillations in some way or other. A time domain model would allow to capture the chaotic nature of VIV and to model interactions with other loads and nonlinearities. Such a model was developed in the present work: for each cross section, recent velocity history is compressed using Laguerre polynomials. The compressed information is used to enter an interpolation function to predict the instantaneous force, allowing to step the dynamic analysis. An offshore riser was modeled in this way: some analyses provided an unusually fine level of realism, while in other analyses, the riser fell into an unphysical pattern of vibration. It is concluded that the concept is promising, yet that more work is needed to understand orbit stability and related issues, in order to produce an engineering tool.
Student Disengagement in Higher Education : Two Trends in Technology
Eric Main
Journal of Educational Media & Library Sciences , 2004,
Abstract: As internet-based technologies increasingly colonize learning environments in higher education, they allow purposes contrary to learning to have direct access to students. The internet as a governing metaphor for transparent connectivity and equal access is a red herring because the power relations across the connections are unequal. The internet also functions as a mechanism for the operant conditioning of students by commercial interests and for surveillance and control by political authorities, purposes which can, if not restrained, undermine the intentions of teachers using technology.Teachers should resist fully automating their course management, especially grading and assessment because too much mechanization can only produce reductive thinking.A related trend is the gradual replacement of liberal studies by vocational courses that feature technology as the subject. This cooperates with the aforementioned trend to effectively censor the creative and critical thinking that instructors strive to teach.
Use of Harmonic Inversion Techniques in Semiclassical Quantization and Analysis of Quantum Spectra
J. Main
Physics , 1999, DOI: 10.1016/S0370-1573(98)00131-8
Abstract: Harmonic inversion is introduced as a powerful tool for both the analysis of quantum spectra and semiclassical periodic orbit quantization. The method allows to circumvent the uncertainty principle of the conventional Fourier transform and to extract dynamical information from quantum spectra which has been unattainable before, such as bifurcations of orbits, the uncovering of hidden ghost orbits in complex phase space, and the direct observation of symmetry breaking effects. The method also solves the fundamental convergence problems in semiclassical periodic orbit theories - for both the Berry-Tabor formula and Gutzwiller's trace formula - and can therefore be applied as a novel technique for periodic orbit quantization, i.e., to calculate semiclassical eigenenergies from a finite set of classical periodic orbits. The advantage of periodic orbit quantization by harmonic inversion is the universality and wide applicability of the method, which will be demonstrated in this work for various open and bound systems with underlying regular, chaotic, and even mixed classical dynamics. The efficiency of the method is increased, i.e., the number of orbits required for periodic orbit quantization is reduced, when the harmonic inversion technique is generalized to the analysis of cross-correlated periodic orbit sums. The method provides not only the eigenenergies and resonances of systems but also allows the semiclassical calculation of diagonal matrix elements and, e.g., for atoms in external fields, individual non-diagonal transition strengths. Furthermore, it is possible to include higher order terms of the hbar expanded periodic orbit sum to obtain semiclassical spectra beyond the Gutzwiller and Berry-Tabor approximation.
Comment on "Recurrences without closed orbits"
J. Main
Physics , 1999, DOI: 10.1103/PhysRevA.60.1726
Abstract: In a recent paper Robicheaux and Shaw [Phys. Rev. A 58, 1043 (1998)] calculate the recurrence spectra of atoms in electric fields with non-vanishing angular momentum not equal to 0. Features are observed at scaled actions ``an order of magnitude shorter than for any classical closed orbit of this system.'' We investigate the transition from zero to nonzero angular momentum and demonstrate the existence of short closed orbits with L_z not equal to 0. The real and complex ``ghost'' orbits are created in bifurcations of the ``uphill'' and ``downhill'' orbit along the electric field axis, and can serve to interpret the observed features in the quantum recurrence spectra.
Personality and risk of addiction to Internet in university students Personalidad, hábitos de consumo y riesgo de adicción al Internet en estudiantes universitarios
Lya Mainé Astonitas Villafuerte
Revista de Psicología , 2005,
Abstract: The articles studies the frequency and purpose of Internet use, the indicators of risk for Internet addiction and the persona lit y of 66 university students from a private university in Lima. These variables are analyzed together with the dimensions and facets of the NEOPI-R, based in the big five model. An association was found between the facets values (04) and actions (06), which belong to the Openness dimension (O), and the risk of Internet addiction. A deeper analysis reveals a positive relationship between the number of symptoms of Internet addiction and the Neuroticism (N) dimensiono Additionally, there is a negative relationship between the number of symptoms and the Consciousness (C) dimension, especially on the facets self-discipline (CS), dutifulness (C3), achievement-striving (C4) and deliberation (C6). Se analizan los hábitos de consumo en Internet: frecuencia y finalidad de uso; los indicadores de riesgo de adicción al Internet, y la personalidad de 66 estudiantes de una universidad particular de Lima Metropolitana. Estas variables se analizan junto con las dimensiones y facetas del Inventario de Personalidad NEO-PI-R a partir del modelo de los cinco factores . Se encuentra una asociación entre las facetas valores (04) y acciones (06), pertenecientes a la dimensión Apertura (O), y el riesgo de adicción al Internet. Un análisis más profundo revela una relación positiva entre el número de síntomas de adicción al Internet y la dimensión Neuroticismo (N). Existe también una relación negativa entre el número de síntomas de adicción al Internet y la dimensión Conciencia (C), especialmente con las facetas autodisciplina (CS), sentido del deber (C3), motivación de logro (C4) y reflexión (C6).
Semiclassical form factor of matrix element fluctuations
Bruno Eckhardt,Joerg Main
Physics , 1995, DOI: 10.1103/PhysRevLett.75.2300
Abstract: We analyze within a semiclassical approximation the form factor for the fluctuations of quantum matrix elements around their classical average. We find two contributions: one is proportional to the form factor for the density of states, with an amplitude determined by the squared average of the matrix elements. The other is constant and related to the fluctuations of finite time classical trajectory segments around the phase space average. The results are illustrated for an observable in the quadratic Zeeman effect.
Uniform semiclassical approximations for umbilic bifurcation catastrophes
J. Main,G. Wunner
Physics , 1997, DOI: 10.1103/PhysRevE.57.7325
Abstract: Gutzwiller's trace formula for the semiclassical density of states diverges at the bifurcation points of periodic orbits and has to be replaced with uniform semiclassical approximations. We present a method to derive these expressions from the standard representations of the elementary catastrophes and to directly relate the uniform solutions to classical periodic orbit parameters, thereby circumventing the numerical application of normal form theory. The technique allows an easy handling of ungeneric bifurcations with corank 2 such as the umbilic catastrophes and is demonstrated on a hyperbolic umbilic in the diamagnetic Kepler problem.
Semiclassical Non-Trace Type Formulas for Matrix Element Fluctuations and Weighted Densities of States
J. Main,G. Wunner
Physics , 1999, DOI: 10.1103/PhysRevE.60.1630
Abstract: Densities of states weighted with the diagonal matrix elements of two operators A and B, i.e., rho^(A,B)(E) = sum_n delta(E-E_n) cannot, in general, be written as a trace formula, and therefore no simple extension of semiclassical trace formulas is known for this case. However, from the high resolution analysis of quantum spectra in the semiclassical regime we find strong evidence that weighting the delta-functions in the quantum mechanical density of states with the product of diagonal matrix elements, , is equivalent to weighting the periodic orbit contributions in the semiclassical periodic orbit sum with the product of the periodic orbit means, _p_p, of the classical observables A and B. Results are presented for the hydrogen atom in a magnetic field for both the chaotic and near-integrable regime, and for the circle billiard.
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