21,547 research outputs found
Delay differential equations in a nonlinear cochlear model.
No full textThe human auditory system performs its primary function in the cochlea, the main organ of the inner ear, where the spectral analysis of a sound signal and its transduction into a neural signal occur. It is filled with liquid and divided in two cavities by the basilar membrane (BM). A sound stimulus propagates in air as an acoustic pressure wave through the outer and the middle ear. The pressure of the stapes on the oval window (boundary between the middle and the inner ear) causes the cochlear fluid to flow between the two cavities through a hole at the end of the BM. A spatial partial differential equation of fluid-dynamics describes this physical process. As a consequence of the differential pressure between the two cavities, each micro-element of the BM oscillates as a forced damped harmonic oscillator. The BM displacement is amplified by the overlying outer hair cells (OHCs) through a nonlinear nonlocal active feedback mechanism. The latter can be modeled by means of various representations. Among them, the delayed stiffness model of Talmadge et al. (J. Acoust. Soc. Am. 104, 1998) has been considered in this thesis. Specifically, the cochlear nonlinearity is introduced as a quadratic function of the BM displacement in the passive linear damping function. Moreover, the active mechanism is described by two additional forces, each one proportional to the BM displacement delayed by a slow and a fast feedback constant time, respectively. According to this model, a time delay differential equation (DDE) of the second order describes the oscillating dynamics of the BM. A different formulation of the nonlinear active mechanism, driven by the OHCs, is expressed as a nonlinear function of the BM velocity by the anti-damping model of Moleti et al. (J. Acoust. Soc. Am. 133, 2013). In this case the model equations do not contain time delays.
The numerical integration of the above mentioned models has been obtained by finite differencing with respect to the space variable in the state space, as introduced by Elliott et al. (J. Acoust. Soc. Am. 122, 2007), and then integrating in time with the adaptive package introduced by Bertaccini and Sisto as a modification of the popular Matlab ode15s package (J. Comput. Phys. 230, 2011). The semidiscrete formulation of the delayed stiffness model and the anti-damping model has a non trivial mass matrix, and eigenvalues of the system matrix with large negative real part and imaginary part. That is why an implicit solver with an infinite region of absolute stability should be used. Therefore, the customized Matlab ode15s package by Bertaccini and Sisto seems to be the convenient choice to integrate the problem at hand numerically. In particular, for the delayed stiffness model, an integrator for constant DDEs (the method of steps; Bellen and Zennaro, Oxford University Press 2003) has been formulated and based on the customized ode15s.
All these topics have been discussed in this doctoral thesis, which is subdivided in the following chapters.
Chapter 1 describes the anatomy of the human ear, with special regard to the cochlea. Some experimental evidences about the cochlear mechanisms are discussed, in order to support the cochlear modeling. Two physical models with one degree of freedom are shown: the anti-damping model of Sisto et al. (J. Acoust. Soc. Am. 128, 2010) and Moleti et al. (J. Acoust. Soc. Am. 133, 2013), and the delayed stiffness model of Talmadge et al. (J. Acoust. Soc. Am. 104, 1998).
Chapter 2 discusses the general theory of DDEs, with greater reference to constant and time dependent DDEs from Bellen and Zennaro (Oxford University Press 2003). Existence and uniqueness of time dependent DDEs are briefly analyzed, while the method of steps is shown as a basic approach to find a numerical approximation of the DDEs solution. According to this method, IVPs of constant DDEs (as for the semidiscrete delayed stiffness model) are turned into IVPs of ODEs in a subinterval (of length less than or equal to the time delay) of the whole integration interval. Each IVP of ODEs can be integrated by means of any ODEs numerical method, and its convergence is then discussed.
Chapter 3 describes the main tools used to find an approximate solution of the considered models. In particular, the discretization for spatial partial derivatives by means of finite differences is shown. Such a representation turns a model, which is continuous in the space-time domain, into a semidiscrete model to be integrated in time. The models considered in this thesis are stiff, so the phenomenon of stiffness is discussed and the ode15s package of Matlab for integrating stiff ODEs is described. Nevertheless, greater benefits can be obtained by using the ode15s package customized by Bertaccini and Sisto as a hybrid direct-iterative solver which exploits Krylov subspace methods.
Chapter 4 shows the semidiscrete formulation of the continuous models (anti-damping model and delayed stiffness model) in the state space with respect to the spatial variable, as introduced by Elliott et al. (J. Acoust. Soc. Am. 122, 2007). The algebraic properties of the semidiscrete models are discussed in order to show why the customized ode15s package may perform a faster numerical integration of the semidiscrete models and how this solver can be used in an integration numerical technique for constant DDEs (the method of steps).
Chapter 5 shows the results produced by the numerical experiments of the delayed stiffness model by supplying a sinusoidal tone, and compares them with the numerical results produced by the anti-damping model. Some considerations about the numerical approach of the time integration are also discussed, and a part of the simplified code used for integrating the semidiscrete delayed stiffness model, is reported. The results are comparable with those obtained by the anti-damping model, and then the numerical experimental evidences seem to justify the proposed integration technique for constant DDEs. Delayed model properties of tonotopicity, anti-damping and nonlinearity are verified, as well as the dependence of the approximate solution on some free parameters of the model. The cochlear response described by the delayed stiffness model shows a typical tall and broad BM activity pattern. This behavior is also found in the numerical results of a model with two degree of freedom produced by Neely and Kim (J. Acoust. Soc. Am. 79, 1986) and Elliott et al. (J. Acoust. Soc. Am. 122, 2007)
Protecting Animals 36: Author Witi Ihimaera
No full textIn this very special episode of Knowing Animals I am joined by beloved New Zealand author Witi Ihimaera. Witi has written many books featuring nonhuman animals. He offers us a non-colonial lens through which to think about the human/nonhuman relationship
I Think I Am Philip K. Dick
No full textFor years, noted writer Laurence A. Rickels often found himself compared to novelist Philip K. Dickthough in fact Rickels had never read any of the science fiction writers work. When he finally read his first Philip K. Dick novel, while researching for his recent book The Devil Notebooks , it prompted a prolonged immersion in Dicks writing as well as a recognition of Rickelss own long-documented intellectual pursuits. The result of this engagement is I Think I Am: Philip K. Dick , a profound thought experiment that charts the wide relevance of the pulp sci-fi author and paranoid visionary. I Think I Am: Philip K. Dick explores the science fiction authors meditations on psychic reality and psychosis, Christian mysticism, Eastern religion, and modern spiritualism. Covering all of Dicks science fiction, Rickels corrects the lack of scholarly interest in the legendary Californian author and, ultimately, makes a compelling case for the philosophical and psychoanalytic significance of Philip K. Dicks popular and influential science fiction.Intro -- Contents -- Introjection -- Part I -- Endopsychic Allegories -- Schreber Guardian -- Belief System Surveillance -- Part II -- Deeper Problems -- Veil of Tears -- Go West -- Dick Manfred -- Timing -- Glimmung -- Part III -- Spiritualism Analogy -- Imitating the Dead -- Indexical Layer -- Ilse -- Hammers and Things -- Crucifictions -- Over There -- Martyrology -- Can't Live, Can't Live -- Lola -- Umwelt, Mitwelt, and Eigenwelt -- Outer Race -- The German Introject -- Part IV -- Materialism, Idealism, and Cybernetics -- Startling Stories -- A Couple of Years -- Android Empathy -- Homunculus and Robot -- ALL OF YOU ARE DEAD. I AM ALIVE. -- Go with the Flow -- Part V -- Room for Thought -- Caduceus -- Jump -- Still -- A Wake -- Spätwerk -- Let the Dead Be -- Play Bally -- Das Hund -- Notes -- BibliographyFor years, noted writer Laurence A. Rickels often found himself compared to novelist Philip K. Dickthough in fact Rickels had never read any of the science fiction writers work. When he finally read his first Philip K. Dick novel, while researching for his recent book The Devil Notebooks , it prompted a prolonged immersion in Dicks writing as well as a recognition of Rickelss own long-documented intellectual pursuits. The result of this engagement is I Think I Am: Philip K. Dick , a profound thought experiment that charts the wide relevance of the pulp sci-fi author and paranoid visionary. I Think I Am: Philip K. Dick explores the science fiction authors meditations on psychic reality and psychosis, Christian mysticism, Eastern religion, and modern spiritualism. Covering all of Dicks science fiction, Rickels corrects the lack of scholarly interest in the legendary Californian author and, ultimately, makes a compelling case for the philosophical and psychoanalytic significance of Philip K. Dicks popular and influential science fiction.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
Liftings for noncomplete probability spaces
No full textThe current state of knowledge concerning liftings for noncomplete probability spaces is discussed. This is a somewhat expanded version of the author's talk given at the 1991 Summer Conference on General Topology and Applications in Honor of Mary Ellen Rudin and Her Work.PT: S; CR: BURKE MR, IN PRESS P AM MATH S BURKE MR, 1991, ISRAEL J MATH, V73, P33 BURKE MR, 1992, ISRAEL J MATH, V79, P289 CARLSON T, THEOREM LIFTING CHRISTENSEN JPR, 1974, TOPOLOGY BOREL STRUC FREMLIN DH, 1989, HDB BOOLEAN ALGEBRAS, P877 INOESCUTULCEA A, 1966, 5TH P BERK S MATH ST, V2 IONESCUTULCEA A, 1967, CONTRIBUTIONS PROB 1, P63 IONESCUTULCEA A, 1969, TOPICS THEORY LIFTIN JECH TJ, 1978, SET THEORY JOHNSON RA, 1980, P AM MATH SOC, V80, P234 JUST W, IN PRESS T AM MATH S KUPKA J, 1983, INDIANA U MATH J, V32, P717 LOSERT V, 1983, LNM, V1080, P95 MAHARAM D, 1958, P AM MATH SOC, V9, P987 SHELAH S, 1983, ISRAEL J MATH, V45, P90 TALAGRAND M, 1982, P AM MATH SOC, V84, P379 VONNEUMANN J, 1931, CRELLES J MATH, V165, P109; NR: 18; TC: 0; J9: ANN N Y ACAD SCI; PG: 4; GA: BZ86BSource type: Electronic(1
Synthesis and additive manufacturing of calcium silicate hydrate scaffolds
No full textA Calcium silicate hydrate (CSH) powder containing above 60 wt% xonotlite (remaining being tobermorite, scawtite and calcite) were produced from lime and ordinary recycled soda-lime glass via simple hydrothermal synthesis route. The thermogravimetric analysis demonstrated only ~20%weight loss up to 800 °C (at about the transformation temperature of CSHs to wollastonite), reaching a plateau in the 800-1200 °C temperature range. The synthesized CSH powder was employed for the fabrication of both green and heat-treated scaffolds by additive manufacturing (AM), possessing a high porosity (>80 vol%) and limited strength (~0.9 MPa)
The AM Canum Venaticorum binary SDSS J173047.59+554518.5
No full textThe AM Canum Venaticorum (AM CVn) binaries are a rare group of hydrogen-deficient, ultrashort period, mass-transferring white dwarf binaries and are possible progenitors of Type Ia supernovae. We present time-resolved spectroscopy of the recently discovered AM CVn binary SDSS J173047.59+554518.5. The average spectrum shows strong double-peaked helium emission lines, as well as a variety of metal lines, including neon; this is the second detection of neon in an AM CVn binary, after the much brighter system GP Com. We detect no calcium in the accretion disc, a puzzling feature that has been noted in many of the longer period AM CVn binaries. We measure an orbital period, from the radial velocities of the emission lines, of 35.2 ± 0.2 min, confirming the ultracompact binary nature of the system. The emission lines seen in SDSS J1730 are very narrow, although double-peaked, implying a low-inclination, face-on accretion disc; using the measured velocities of the line peaks, we estimate i ≤ 11°. This low inclination makes SDSS J1730 an excellent system for the identification of emission lines
Research involving dying persons: Time to reconsider?
No full textUsing research to generate evidence to inform clinical practice is a position adopted almost universally in healthcare, with health care organisations, policymakers and clinicians using research evidence to improve the quality of care. Yet, when it comes to palliative and end-of-life care, the situation may be different.No Full Tex
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