Improved selectivity from a wavelength addressable device for wireless stimulation of neural tissue

Electrical neural stimulation with micro electrodes is a promising technique for restoring lost functions in the central nervous system as a result of injury or disease. One of the problems related to current neural stimulators is the tissue response due to the connecting wires and the presence of a rigid electrode inside soft neural tissue. We have developed a novel, optically activated, microscale photovoltaic neurostimulator based on a custom layered compound semiconductor heterostructure that is both wireless and has a comparatively small volume (<0.01 mm3). Optical activation provides a wireless means of energy transfer to the neurostimulator, eliminating wires and the associated complications. This neurostimulator was shown to evoke action potentials and a functional motor response in the rat spinal cord. In this work, we extend our design to include wavelength selectivity and thus allowing independent activation of devices. As a proof of concept, we fabricated two different microscale devices with different spectral responsivities in the near-infrared region. We assessed the improved addressability of individual devices via wavelength selectivity as compared to spatial selectivity alone through on-bench optical measurements of the devices in combination with an in vivo light intensity profile in the rat cortex obtained in a previous study. We show that wavelength selectivity improves the individual addressability of the floating stimulators, thus increasing the number of devices that can be implanted in close proximity to each other. © 2014 Seymour, Freedman, Gökkavas, Özbay, Sahinand Ünlü

Distribution of mast cells in lung tissues of rats exposed to biomass smoke

This study was designed to evaluate the distribution of mast cells in the lung tissues of rats exposed to biomass  smoke. Fifty six female Wistar albino adult rats were used. They were divided into two experimental groups  (control and biomass smoke-treated), each containing 28 animals. Control rats were not exposed to the  biomass smoke at any time during the experiment. Rats in the treatment group were exposed daily (one hour)  to biomass smoke for 3, 6 or 9 months. Lung tissues samples were obtained under deep anesthesia from the  randomly selected 7 animals in both groups. Lung tissues were fixed in Mota’s fixative (BLA) for 24 h and  embedded in paraffin. Sections of 6 μm thickness were cut and stained with 0.5% toluidine blue in 0.5 N  hydrochloric acid at pH 0.5 for 30 min. The numbers of mast cell in lung tissues of the animals exposed to  the biomass for 6 or 9 months were significantly (P<0.05) higher than controls. This study showed that long  term exposure to biomass smoke was associated with the increased number of mast cells in the lung.

A Mathematical Model for Cholesterol Biosynthesis under Nicotine Exposure

In this paper, a mathematical model is considered for analyzing the impact of nicotine exposure to cholesterol biosynthesis. The dynamical model is nonlinear. Its equilibrium points are computed and conditions are provided under which a unique locally stable positive equilibrium exists. Moreover, effect of internal time delays on local stability is also investigated. © 201

Defect structures in metallic photonic crystals

Cataloged from PDF version of article.We have investigated metallic photonic crystals built around a layer‐by‐layer geometry. Two different crystal structures (face‐centered‐tetragonal and tetragonal) were built and their properties were compared. We obtained rejection rates of 7–8 dB per layer from both metallic crystals. Defect modes created by removing rods resulted in high peak transmission (80%), and high quality factors (1740). Our measurements were in good agreement with theoretical simulations. © 1996 American Institute of Physic

Sensitivity reduction by stable controllers for MIMO infinite dimensional systems via the tangential nevanlinna-pick interpolation

We study the problem of finding a stable stabilizing controller that satisfies a desired sensitivity level for an MIMO infinite dimensional system. The systems we consider have finitely many simple transmission zeros in C +, but they are allowed to possess infinitely many poles in C +. We compute both upper and lower bounds of the minimum sensitivity achievable by a stable controller via the tangential Nevanlinna-Pick interpolation. We also obtain stable controllers attaining such an upper bound. To illustrate the results, we discuss a repetitive control system as an application of the proposed method. © 1963-2012 IEEE

Infinite dimensional and reduced order observers for Burgers equation

Obtaining a representative model in feedback control system design problems is a key step and is generally a challenge. For spatially continuous systems, it becomes more difficult as the dynamics is infinite dimensional and the well known techniques of systems and control engineering are difficult to apply directly. In this paper, observer design is reported for one-dimensional Burgers equation, which is a non-linear partial differential equation. An infinite dimensional form of the observer is demonstrated to converge asymptotically to the target dynamics, and proper orthogonal decomposition is used to obtain the reduced order observer. When this is done, the corresponding observer is shown to be successful under certain circumstances. The paper unfolds the connections between target dynamics, observer and their finite dimensional counterparts. A set of simulation results has been presented to justify the theoretical claims of the paper. © 2005 Taylor & Francis Group Ltd

Stability analysis of switched systems with time-varying discontinuous delays

A new technique is proposed to ensure global asymptotic stability for nonlinear switched time-varying systems with time-varying discontinuous delays. It uses an adaptation of Halanay's inequality to switched systems and a recent trajectory based technique. The result is applied to a family of linear time-varying systems with time-varying delays. © 2017 American Automatic Control Council (AACC)

Stable controllers for robust stabilization of systems with infinitely many unstable poles

This paper studies the problem of robust stabilization by a stable controller for a linear time-invariant single-input single-output infinite dimensional system. We consider a class of plants having finitely many simple unstable zeros but possibly infinitely many unstable poles. First we show that the problem can be reduced to an interpolation-minimization by a unit element. Next, by the modified Nevanlinna-Pick interpolation, we obtain both lower and upper bounds on the multiplicative perturbation under which the plant can be stabilized by a stable controller. In addition, we find stable controllers to provide robust stability. We also present a numerical example to illustrate the results and apply the proposed method to a repetitive control system. © 2013 Elsevier B.V. All rights reserved

Sensitivity reduction by strongly stabilizing controllers for MIMO distributed parameter systems

This note investigates a sensitivity reduction problem by stable stabilizing controllers for a linear time-invariant multi-input multioutput distributed parameter system. The plant we consider has finitely many unstable zeros, which are simple and blocking, but can possess infinitely many unstable poles. We obtain a necessary condition and a sufficient condition for the solvability of the problem, using the matrix Nevanlinna-Pick interpolation with boundary conditions. We also develop a necessary and sufficient condition for the solvability of the interpolation problem, and show an algorithm to obtain the solutions. Our method to solve the interpolation problem is based on the Schur-Nevanlinna algorithm. © 2012 IEEE

A switching control approach to stabilization of parameter varying time delay systems

Robust stabilization problem is considered for time varying time delay systems, where the system parameters are scheduled along a measurable signal trajectory. A switching control approach is proposed for a class of parameter varying systems, where candidate controllers are designed for robust stabilization at certain operating regions. A dwell time based hysteresis switching logic is proposed to guarantee the stability of the switched parameter varying time delay system in the whole operating range. It is shown that if the parameter variation is slow enough (upper bound of the time derivative is determined in terms the dwell time for the switched delay system), then the system is stable with the proposed switched controllers. ©2009 IEEE