Action potentials of curved nerves in finite limbs

Previous simulations of volume-conducted nerve-fiber action-potentials have modeled the limb as semi-infinite or circularly cylindrical, and the fibers as straight lines parallel to the limb surface. The geometry of actual nerves and limbs, however, can be considerably more complicated. Here, the authors present a general method for computing the potentials of fibers with arbitrary paths in arbitrary finite limbs. It involves computing the propagating point-source response (PPSR), which is the potential arising from a single point source (dipole or tripole) travelling along the fiber. The PPSR can be applied to fibers of different conduction velocities by simple dilation or compression. The method is illustrated for oblique and spiralling nerve fibers. Potentials from oblique fibers are shown to be different for orthodromic and antidromic propagation. Such results show that the straight-line models are not always adequate for nerves with anatomical amounts of curvature     

Toroidal coil models for transcutaneous magnetic stimulation of nerves

A novel design of coils for transcutaneous magnetic stimulation of nerves is presented. These coils consist of a toroidal winding around a high-permeability material (Supermendur) core embedded in a conducting medium. Theoretical numerical calculations are used to analyze the effect of the design parameters of these coils, such as coil width, toroidal radius, conducting layer thickness and core transversal shape on the induced electric fields in terms of the electric field strength and distribution. Results indicate that stimulation of nerves with these coils has some of the advantages of both electrical and magnetic stimulation. These coils can produce localized and efficient stimulation of nerves with induced electric fields parallel and perpendicular to the skin similar to surface electrical stimulation. However, they retain some of the advantages of magnetic stimulation such as no risk of tissue damage due to electrochemical reactions at the electrode interface and less uncomfortable sensations or pain. The driving current is reduced by over three orders of magnitude compared to traditional magnetic stimulation, eliminating the problem of coil heating and allowing for long duration and high-frequency magnetic stimulation with inexpensive stimulators     

Magnetic stimulation coil and circuit design

A detailed analysis of the membrane voltage rise commensurate with the electrical charging circuit of a typical magnetic stimulator is presented. The analysis shows how the membrane voltage is linked to the energy, reluctance, and resonant frequency of the electrical charging circuit. There is an optimum resonant frequency for any nerve membrane depending on its capacitive time constant. The analysis also shows why a larger membrane voltage will be registered on the second phase of a biphasic pulse excitation [1]. Typical constraints on three key quantities voltage, current, and silicone controlled rectifier (SCR) switching time dictate key components such as capacitance, inductance, and choice of turns.     

Magnetic stimulation of the motor cortex-theoretical considerations

The aim of this paper is to present a first approximation model for the computation of the electric fields produced in the brain tissues by magnetic stimulation. Results are given in terms of induced electric field and current density caused by coils of different radii and locations. Nontraditional coil locations and assemblies are also considered (multicoil arrangements). Model simulations show that a good control of the excitation spread can be achieved by proper positioning of the coil. It is also predicted that one of the major drawbacks of the technique, i.e., the poor ability to concentrate the current spread into a small brain area can be partially overcome by more effective coil positioning and/or assembly. Finally, some comparisons are made among the results obtained from electric and magnetic stimulation. This is thought to be of great help in the design of experiments aimed to understand the relative role of the different brain structures responsible for the motor response.     

Magnetic coil design considerations for functional magnetic stimulation

Our studies have demonstrated effective stimulation of the bladder, bowel, and expiratory muscles in patients with spinal cord injury using functional magnetic stimulation. However, one limitation of the magnetic coils (MC) is related to their inability to specifically stimulate the target tissue without activation of surrounding tissue. The primary goal of this study was to determine the governing parameters in the MC design, such as coil configuration, diameter, and number of turns in one loop of the coil. By varying these parameters, our approach was to design, construct, and evaluate the induced electric field distributions of two sets of novel MC's. Based on the slinky coil design, the first set of coils was constructed to compare their abilities in generating induced electric fields for focal nerve excitation. The second set of coils was built to determine the effect that changes in two parameters, coil diameter and number of turns in one loop, had on field penetration. The results showed that the slinky coil design produced more focalized stimulation when compared to the planar round coils. The primary-to-secondary peak ratios of the induced electric field from slinky 1 to 5 were 1.00, 2.20, 2.85, 2.62, and 3.54. We also determined that coils with larger diameters had better penetration than those with smaller diameters. Coils with less number of turns in one loop had higher initial field strengths; when compared to coils that had more turns per loop, initial field strengths remained higher as distance from the coil increased. In our attempt to customize MC design according to each functional magnetic stimulation application and patients of different sizes, the parameters of MC explored in this study may facilitate designing an optimal MC for a certain clinical application.     

An analytical model to predict the electric field and excitationzones due to magnetic stimulation of peripheral nerves

The main unknown factor in understanding magnetic stimulation of peripheral nerves is the distribution of the induced electric field. The authors have applied the so-called reciprocity theorem and developed an analytical model to compute the electric field and its spatial derivatives inside pseudocylindrical structures. The results can be used to predict the site of excitation in magnetic stimulation of peripheral nerves     

Transmission of X-rays through curved waveguides

The transmission of x-rays through curved cylindrical waveguides is investigated as a function of the guide diameter and the radius of curvature. Measurements were made atlambda = 1.54Å using lead glass capillaries with bore diameters ranging from 150 to 250 μ. It was observed, for example, that for a 150 μm diameter capillary 51.5 cm long, the transmission was reduced by a factor e^-1for a radius of curvature equal to 20 m. A model based on meridian ray analysis is presented and compared with the results of the experiment.     

Directional coupler with curved lines

A curved line directional coupler is designed and is found to give very good response. Substantial length reduction is obtained as compared to a quarter wave uniform line directional coupler.     

Radiation from curved single-mode fibres

A study of propagation in curved single-mode fibres shows that the transmission loss increases sharply below a critical bend radius. However the radiation does not leak away uniformly with distance but in a series of discrete well-defined rays.     

Computer analysis of scenes with curved objects

Most research efforts in scene analysis have concentrated on the analysis of block-world scenes. Having developed a good understanding of this limited world of computer vision, researchers are now trying to make computers see curved objects also. This paper presents an overview of the techniques developed for segmentation, representation, and recognition of curved objects in two-dimensional images and in three-dimensional scenes. The possible future directions of research are also discussed.     

Frequency-dependent transmission characteristics of curved microstrip bends

The frequency-dependent transmission characteristics of curved microstrip bends are calculated by utilising a second-order perturbation analysis of the equivalent curved waveguide model and a mode-matching method that includes the higher-order modes. Computational results for the transmission coefficient of typical curved microstrip bends are presented and compared to results obtained for right-angle and chamfered right-angle bends.<>     

Fabrication of curved structures by electron-beam lithography

The suitability of electron-beam lithography for the fabrication of curved structures, of interest for integrated optical devices, can be limited by the available pattern data formats. Extensions to the input format of a Cambridge Instruments electron-beam microfabricator are reported, which have allowed complex patterns to be easily specified for both mask making and direct writing.     

Transient analysis of waveguides with curved boundaries

The transmission-line-matrix method of numerical analysis is modified to allow boundary points to fall anywhere between nodes on the mesh. Results are obtained for circular and elliptical waveguide cross-sections on a cartesian mesh.     

Discrete radiation from curved single-mode fibres

The energy loss and field distribution in a curved single-mode fibre are calculated in terms of the coupling between the fundamental (LP01) mode and the radiation field. In agreement with recent experimental results, it is found that, initially, light travels in a zigzag path around the bend, and radiation is emitted in discrete beams.     

新型手持式智能曲面尺的设计

文中介绍了一款基于TI CC2540的手持式智能曲面尺的设计。该尺通过记录精密滚轮在物体表面滚动的距离,实现长距离不间断测量。设计采用自制的磁电编码组件,利用径向充磁的柱状磁铁作为转轴,将磁电编码器AS5145B和滚轮合二为一,并利用TP4056充电模块实现充电功能,采用OLED屏幕进行显示,结合软件设计,实现了测量数据的读取、存储和显示。     

Modes in curved step-index optical fibres

By using parabolic, instead of circular, cylindrical co-ordinates the field distributions of the natural modes of curved step-index fibres can be described completely, yet simply. The mode caustics corresponding to the geometrical guiding limit of the equivalent rays of curved fibre can be clearly demonstrated. Near-field mode patterns and caustics obtained experimentally are in excellent agreement with the theory.     

Fields in a curved optical fiber

The mutual relation between transverse and longitudinal electromagnetic field components in a curved optical fiber is derived. The wave equations for transverse fields much simpler than those for longitudinal fields are obtained in the first-order perturbation. The wave equations for a radially inhomogeneous fiber derived in a toroidal coordinate system are equivalent to those derived from a straight waveguide approximation with an effective index profile incorporated with the curvature effect. Linearly polarized mode representation holds exactly only for the fundamental mode.     

Edge diffraction at a curved screen

An edge-diffraction formulation is given for an astigmatic electromagnetic wave incident on a screen with a curved surface and a curved edge. The result is used to calculate the near field of a paraboloidal reflector under plane-wave illumination, and this is compared with the physical-optics method. An edge-type term valid along the axial caustic is given.     

Radiation of discrete beams from curved single-mode fibres

A new attempt to explain the phenomenon of discrete radiation from bent single-mode fibres is presented. It is suggested that the set of radiated beams is an interference pattern of the radiation fields of more `whispering-gallery? modes propagating along the fibre coil.     

Perturbation analysis and modeling of curved microstrip bends

The curved microstrip bend consisting of a microstrip ring segment between two microstrip lines is analyzed for its transmission properties. The microstrip lines are modeled by equivalent ideal magnetic wall waveguides for which the electromagnetic field solutions are known. The field solutions in the microstrip ring segment are derived by using a perturbation analysis of a modified (magnetic wall) curved waveguide model. Other techniques have been formulated to evaluate the fields inside curved metallic waveguides. These include the use of an equivalent nonuniformly loaded straight waveguide and rectangular and annular model analysis. The perturbation solution for the fields in the equivalent curved waveguide model presented is readily adaptable to the mode-matching procedure, and is used to calculate the properties of the curved microstrip bend discontinuities. The frequency-dependent reflection and transmission coefficients of curved microstrip bends are determined and compared with those of the right-angle and chamfered right-angle microstrip bends