Micro and Macro Fluidic Effects in Cochlear Mechanics.

The cochlea is a fluid-filled organ with multiple structures. The scales of the structures in the cochlea range from millimeter (macro) to sub-micrometer (micro). In this work, both the micro and macro fluidic effects in cochlear mechanics are studied to understand the working mechanism of the cochlea. Topics include wave generation and propagation, fluid viscosity, complex boundary conditions for fluid-structure interactions, power flow, and inverse problems. In addition, a method is developed to bridge the gap for the modeling effort among different scales. This method is applicable to other fluid-structure coupling problems with multiple scales. The entire work is based on a physiologically-based finite element cochlear model that couples mechanical, electric, and acoustic fields. On the macro scale, the direction of wave propagation is studied under various stimulation methods, including acoustic, bone conduction, internal force, and internal pressure sources excitations. In a passive cochlea, the reciprocity relation holds. The effect of structural (active component) perturbations on the wave propagation is also analyzed. Multiple sources are identified to the contribution of the extended ringings of the basilar membrane under an impulse response. The power dissipation and amplification are analyzed in the cochlear channels as well. On the micro scale, the viscous flow in the sub-tectorial membrane region is modeled. The flow is coupled to the motion of surrounding micro structures. The micro fluid is also coupled to the macro fluid. The model combines both analytical solutions for the micro fluid-structure interaction and numerical solutions for the intermediate and macro scale fluid behaviors. The interactive usage of analytic and numerical solutions makes the multiscale model computationally efficient and physically interpretable. This model provides a tool to determine the spatial dependence of flow modality in the sub-tectorial membrane region; determine the relative importance of motility (either outer hair cell somatic or hair bundle motility) on inner hair cell hair bundle stimulation; and analyze the role of the Hessen's stripe and the noise to signal ratio in the hearing.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/98059/1/yizengli_1.pd

Successor Liability in Bankruptcy: Some Unifying Themes of Intertemporal Creditor Priorities Created by Running Covenants, Products Liability, and Toxic-Waste Cleanup

The exceptional sensitivity of mammalian hearing organs is attributed to an active process, where force produced by sensory cells boost sound-induced vibrations, making soft sounds audible. This process is thought to be local, with each section of the hearing organ capable of amplifying sound-evoked movement, and nearly instantaneous, since amplification can work for sounds at frequencies up to 100 kHz in some species. To test these fundamental precepts, we developed a method for focally stimulating the living hearing organ with light. Light pulses caused intense and highly damped mechanical responses followed by traveling waves that developed with considerable delay. The delayed response was identical to movements evoked by click-like sounds. This shows that the active process is neither local nor instantaneous, but requires mechanical waves traveling from the cochlear base toward its apex. A physiologically-based mathematical model shows that such waves engage the active process, enhancing hearing sensitivity.Funding Agencies|NIH [DC-004554, DC-004084]; Swedish Research Council [K2011-63X-14061-11-39]; Research Council for Health, Working Life and Welfare [2006-1526]; Horselskadades Riksforbund; Tysta skolan foundation</p

Factors in the occurrence and restoration of hypoparathyroidism after total thyroidectomy for thyroid cancer patients with intraoperative parathyroid autotransplantation

IntroductionPostoperative hypoparathyroidism (POH) is the most common and important complication for thyroid cancer patients who undergo total thyroidectomy. Intraoperative parathyroid autotransplantation has been demonstrated to be essential in maintaining functional parathyroid tissue, and it has clinical significance in identifying essential factors of serum parathyroid hormone (PTH) levels for patients with parathyroid autotransplantation. This retrospective cohort study aimed to comprehensively investigate influential factors in the occurrence and restoration of POH for patients who underwent total thyroidectomy with intraoperative parathyroid autotransplantation (TTIPA).MethodThis study was conducted in a tertiary referral hospital, with a total of 525 patients who underwent TTIPA. The postoperative serum PTH levels were collected after six months, and demographic characteristics, clinical features and associated operative information were analyzed.ResultsA total of 66.48% (349/525) of patients who underwent TTIPA were diagnosed with POH. Multivariate logistic regression indicated that Hashimoto’s thyroiditis (OR=1.93, 95% CI: 1.09-3.42), P=0.024), the number of transplanted parathyroid glands (OR=2.70, 95% CI: 1.91-3.83, P&lt;0.001) and postoperative blood glucose levels (OR=1.36, 95% CI: 1.06-1.74, P=0.016) were risk factors for POH, and endoscopic surgery (OR=0.39, 95% CI: 0.22-0.68, P=0.001) was a protective factor for POH. Multivariate Cox regression indicated that PTG autotransplantation patients with same-side central lymph node dissection (CLND) (HR=0.50; 95% CI: 0.34-0.73, P&lt;0.001) demonstrated a longer time for increases PTH, and female patients (HR=1.35, 95% CI: 1.00-1.81, P=0.047) were more prone to PTH increases. Additionally, PTG autotransplantation with same-side CLND (HR=0.56, 95% CI: 0.38-0.82, P=0.003) patients had a longer time to PTH restoration, and patients with endoscopic surgery (HR=1.54, 95% CI: 1.04-2.28, P=0.029) were more likely to recover within six months.ConclusionHigh postoperative fasting blood glucose levels, a large number of transplanted PTGs, open surgery and Hashimoto’s thyroiditis are risk factors for postoperative POH in TTIPA patients. Elevated PTH levels occur earlier in female patients and patients without CLND on the transplant side. PTH returns to normal earlier in patients without CLND and endoscopic surgery on the transplant side

Comparative study of two approaches to integration over measure spaces

Abstract not availabl

The Coda of the Transient Response in a Sensitive Cochlea: A Computational Modeling Study.

In a sensitive cochlea, the basilar membrane response to transient excitation of any kind-normal acoustic or artificial intracochlear excitation-consists of not only a primary impulse but also a coda of delayed secondary responses with varying amplitudes but similar spectral content around the characteristic frequency of the measurement location. The coda, sometimes referred to as echoes or ringing, has been described as a form of local, short term memory which may influence the ability of the auditory system to detect gaps in an acoustic stimulus such as speech. Depending on the individual cochlea, the temporal gap between the primary impulse and the following coda ranges from once to thrice the group delay of the primary impulse (the group delay of the primary impulse is on the order of a few hundred microseconds). The coda is physiologically vulnerable, disappearing when the cochlea is compromised even slightly. The multicomponent sensitive response is not yet completely understood. We use a physiologically-based, mathematical model to investigate (i) the generation of the primary impulse response and the dependence of the group delay on the various stimulation methods, (ii) the effect of spatial perturbations in the properties of mechanically sensitive ion channels on the generation and separation of delayed secondary responses. The model suggests that the presence of the secondary responses depends on the wavenumber content of a perturbation and the activity level of the cochlea. In addition, the model shows that the varying temporal gaps between adjacent coda seen in experiments depend on the individual profiles of perturbations. Implications for non-invasive cochlear diagnosis are also discussed

Effective Force Generation During Mammalian Cell Migration Under Different Molecular and Physical Mechanisms

We have developed much understanding of actin-driven cell migration and the forces that propel cell motility. However, fewer studies focused on estimating the effective forces generated by migrating cells. Since cells in vivo are exposed to complex physical environments with various barriers, understanding the forces generated by cells will provide insights into how cells manage to navigate challenging environments. In this work, we use theoretical models to discuss actin-driven and water-driven cell migration and the effect of cell shapes on force generation. The results show that the effective force generated by actin-driven cell migration is proportional to the rate of actin polymerization and the strength of focal adhesion; the energy source comes from the actin polymerization against the actin network pressure. The effective force generated by water-driven cell migration is proportional to the rate of active solute flux and the coefficient of external hydraulic resistance; the energy sources come from active solute pumping against the solute concentration gradient. The model further predicts that the actin network distribution is mechanosensitive and the presence of globular actin helps to establish a biphasic cell velocity in the strength of focal adhesion. The cell velocity and effective force generation also depend on the cell shape through the intracellular actin flow field