Search

Background and Objective: The intrinsic electrical material properties of the laminar components of the mammalian peripheral nerve bundle are important parameters necessary for the accurate simulation of the electrical interaction between nerve fibers and neural interfaces. Improvements in the accuracy of these parameters improve the realism of the simulation and enables realistic screening of novel devices used for extracellular recording and stimulation of mammalian peripheral nerves. This work aims to characterize these properties for mammalian peripheral nerves to build upon the resistive parameter set established by Weerasuriya et al. in 1984 for amphibian somatic peripheral nerves (frog sciatic nerve) that is currently used ubiquitously in the in‐silico peripheral nerve modeling community. Methods: A custom designed characterization chamber was implemented and used to measure the radial and longitudinal impedance between 10 mHz and 50 kHz of freshly excised canine vagus nerves using four‐point impedance spectroscopy. The impedance spectra were parametrically fitted to an equivalent circuit model to decompose and estimate the components of the various laminae. Histological sections of the electrically characterized nerves were then made to quantify the geometry and laminae thicknesses of the perineurium and epineurium. These measured values were then used to calculate the estimated intrinsic electrical properties, resistivity and permittivity, from the decomposed resistances and reactances. Finally, the estimated intrinsic electrical properties were used in a finite element method (FEM) model of the nerve characterization setup to evaluate the realism of the model. Results: The geometric measurements were as follows: nerve bundle (1.6 ± 0.6 mm), major nerve fascicle diameter (1.3 ± 0.23 mm), and perineurium thickness (13.8 ± 2.1 μm). The longitudinal resistivity of the endoneurium was estimated to be 0.97 ± 0.05 Ωm. The relative permittivity and resistivity of the perineurium were estimated to be 2018 ± 391 and 3.75 kΩm ± 981 Ωm, respectively. The relative permittivity and resistivity of the epineurium were found to be 9.4 × 106 ± 8.2 × 106 and 55.0 ± 24.4 Ωm, respectively. The root mean squared (RMS) error of the experimentally obtained values when used in the equivalent circuit model to determine goodness of fit against the measured impedance spectra was found to be 13.0 ± 10.7 Ω, 2.4° ± 1.3°. The corner frequency of the perineurium and epineurium were found to be 2.6 ± 1.0 kHz and 368.5 ± 761.9 Hz, respectively. A comparison between the FEM model in‐silico impedance experiment against the ex‐vivo methods had a RMS error of 159.0 ± 95.4 Ω, 20.7° ± 9.8°. Conclusion: Although the resistive values measured in the mammalian nerve are similar to those of the amphibian model, the relative permittivity of the laminae bring new information about the reactance and the corner frequency (frequency at peak reactance) of the peripheral nerve. The measured and estimated corner frequency are well within the range of most bioelectric signals, and are important to take into account when modeling the nerve and neural interfaces. [ABSTRACT FROM AUTHOR]

Background: The stimulation and recording performance of implanted neural interfaces are functions of the physical and electrical characteristics of the neural interface, its electrode material and structure. Therefore, rapid optimization of such characteristics is becoming critical in most clinical and research studies. This paper describes the development of an upgraded 3D printed cuff electrode shell design containing a novel intrinsically conductive polymer (ICP) for stimulation and recording of peripheral nerve fibers. Methods: A 3D stereolithography (SLA) printer was used to print a scalable, custom designed, C‐cuff electrode and I‐beam closure for accurate, rapid implementation. A novel contact consisting of a percolated carbon graphite base electrodeposited with an intrinsically conductive polymer (ICP), poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) produced a PEDOT:PSS + carbon black (CB) matrix that was used to form the electrochemical interface on the structure. Prototype device performance was tested both in‐vitro and in‐vivo for electrical chemical capacity, electrochemical interfacial impedance, surgical handling, and implantability. The in‐vivo work was performed on the sciatic nerve of 25 anesthetized Sprague Dawley rats to demonstrate recording and stimulating ability. Results: Prototypes of different spatial geometries and number of contacts (bipolar, tripolar, and tetrapolar) were designed. The design was successfully printed with inner diameters down to 500 μm. Standard bipolar and tripolar cuffs, with a 1.3 mm inner diameter (ID), 0.5 mm contact width, 1.0 mm pitch, and a 1.5 mm end distance were used for the functional tests. This geometry was appropriate for placement on the rat sciatic nerve and enabled in‐vivo testing in anesthetized rats. The contacts on the standard bipolar electrode had an area of 2.1 × 10−2 cm2. Cyclic voltammetry on ICP coated and uncoated graphite contacts showed that the ICP increased the average charge storage capacity (CSC) by a factor of 30. The corresponding impedance at 1 Hz was slightly above 1 kΩ, a 99.99% decrease from 100 kΩ in the uncoated state. The statistical comparison of the pre‐ versus post‐stimulation impedance measurements were not significantly different (p‐value > 0.05). Conclusions: The new cuff electrode enables rapid development of cost‐effective functional stimulation devices targeting nerve bundles less than 1.0 mm in diameter. This allows for recording and modulation of a low‐frequency current targeted within the peripheral nervous system. [ABSTRACT FROM AUTHOR]

Radially self-accelerating beams are rotating shape-invariant solutions of the Helmholtz equation. As such, they exhibit continuous indefinitely spiraling trajectories. Here we present the possibility to tailor those beams to achieve almost any desired beam cross section, without sacrificing the unique propagation characteristics. We discuss analytical tailoring opportunities and highlight their inherent limitations. Following that, by way of example, a genetic optimization algorithm is applied to demonstrate the feasibility of heuristic computer optimization methods in general. The convergence towards several test-targets is demonstrated and the influence of the chosen fitness function is discussed. [ABSTRACT FROM AUTHOR]

We report on the properties of radially self-accelerating intensity distributions consisting of two components in the angular frequency domain. We show how this subset of solutions, in literature also known as helicon beams, possesses peculiar characteristics that enable a better control over its properties. In this work, we present a step-by-step optimization procedure to achieve the best possible intensity contrast, a distinct rotation rate and long propagation lengths. All points are discussed on a theoretical basis and are experimentally verified. [ABSTRACT FROM AUTHOR]

We report, in theory and experiment, on a new class of optical beams that are radially self-accelerating and nondiffracting. These beams continuously evolve on spiraling trajectories while maintaining their amplitude and phase distribution in their rotating rest frame. We provide a detailed insight into the theoretical origin and characteristics of radial self-acceleration and prove our findings experimentally. As radially self-accelerating beams are nonparaxial and a solution to the full scalar Helmholtz equation, they can be implemented in many linear wave systems beyond optics, from acoustic and elastic waves to surface waves in fluids and soft matter. Our work generalized the study of classical helicon beams to a complete set of solutions for rotating complex fields. [ABSTRACT FROM AUTHOR]

Abstract: The calibration of parallel mechanisms with hexapod design is very complex due to the kinematic transformation. In this paper a calibration algorithm is developed which allows the re-calibration of hexapod mechanisms with relatively little effort, and the applicability of the calibration in an industrial environment is discussed. All parameters associated with the replacement of a leg and corresponding joints are determined only by performing six tool center point (TCP) measurements in each six degrees of freedom (DOF) after the new leg has been separately measured. The choice of measurement poses is based on the condition of the identification Jacobian matrix, so that increased robustness can be shown compared to the evaluation of a much bigger number of measurement poses using the Householder transformation. [Copyright &y& Elsevier]

Postpartum hemorrhage (PPH) is a leading cause of maternal morbidity and mortality. Routine treatment of PPH includes uterotonics, tranexamic acid, curettage, uterine (balloon) tamponade, compression sutures, uterine artery ligation, and, if available, transcatheter arterial embolization (TAE). In cases of severe PPH refractory to standard medical and surgical management, hysterectomy is usually the ultima ratio, and is equally associated with a higher rate of complications. In addition, this sudden loss of fertility, especially in young women, can be devastating. Here, we report a case of a 29-year-old woman who suffered from severe PPH with a blood loss > 1500 mL and hemodynamic instability after delivery of her first baby at a smaller hospital. She was consequently successfully treated with resuscitative endovascular balloon occlusion of the aorta (REBOA) by first placing a balloon catheter into the infra-renal aorta and subsequent TAE after failure of all other available treatment options prior to hysterectomy. TAE has been suggested in PPH treatment to avoid hysterectomies and thus to preserve patients' reproductive function. If hemodynamic stabilization cannot be achieved with mass transfusion, REBOA seems to be an effective rescue strategy with which to achieve hemodynamic stabilization and gain additional time for embolization. Although REBOA is already recommended in several PPH guidelines, this approach seems relatively unknown in German-speaking countries. [ABSTRACT FROM AUTHOR]

A new approach for generating long‐distance self‐healing Bessel beams, which is based on a ring‐shaped (annular) lens and a spherical lens in 4f‐configuration, is reported. With this, diffraction‐free light evolution of a zeroth order Bessel beam over several meters is shown and available scaling opportunities that surpass current technologies by far are discussed. Furthermore, it is demonstrated how this setup can be adapted to create Bessel beam superpositions, realizing the longest ever reported optical conveyor beam and helicon beam, respectively. Last, the self‐healing capabilities of the beams are tested against strong opaque and non‐opaque scatterers, which again emphasizes the great potential of this new method. [ABSTRACT FROM AUTHOR]

Background: The sinusoidal low‐frequency alternating current (LFAC) waveform was explored recently as a novel means to evoke nerve conduction block. In the present work, we explored whether increasing the amplitude of the LFAC waveform results in nerve fiber activation in autonomic nerves. In‐silico methods and preliminary work in somatic nerves indicated a potential frequency dependency on the threshold of activation. The Hering‐Breuer (HB) reflex was used as a biomarker to detect cervical vagus nerve activation. Methods: Experiments were conducted in isoflurane‐anesthetized swine (n = 5). Two stimulating bipolar cuff electrodes and a tripolar recording cuff electrode were implanted on the left vagus nerve. To ensure the electrical stimulation affects only the afferent pathways, the nerve was crushed caudal to the electrodes to eliminate cardiac effects. (1) Standard pulse stimulation (Vstim) using a monophasic train of pulses was applied through the caudal electrode to elicit HB reflex and to identify the activated nerve fiber type. (2) Continuous sinusoidal LFAC waveform with a frequency ranging from 5 through 20 Hz was applied to the rostral electrode without Vstim to explore the activation thresholds at each LFAC frequency. In both cases, the activation of nerve fibers was detected by a HB reflex‐induced reduction in the breathing rate. Results: LFAC was found to be capable of eliciting an HB response. The LFAC activation thresholds were found to be frequency‐dependent. The HB threshold was 1.02 ± 0.3 mAp at 5 Hz, 0.66 ± 0.3 mAp at 10 Hz, and 0.44 ± 0.2 mAp at 20 Hz. In comparison, it was 0.7 ± 0.47 mA for a 100 μs pulse. The LFAC amplitude was within the linear limits of the electrode interface. Damage to the cuff electrodes or the nerve tissues was not observed. Analysis of Vstim‐based compound nerve action potentials (CNAP) indicated that the decrease in breathing rate was found to be correlated with the activation of slower components of the CNAP suggesting that LFAC reached and elicited responses from these slower fibers associated with afferents projecting to the HB response. Conclusions: These results suggest the feasibility of the LFAC waveform at 5, 10, and 20 Hz to activate autonomic nerve fibers and potentially provide a new modality to the neurorehabilitation field. [ABSTRACT FROM AUTHOR]

Background Context: Despite the growing senior population within the United States, there is a lack of consensus regarding the safety and efficacy of performing lumbar spinal fusion for this population.Purpose: To evaluate the clinical and radiographic outcomes in different age cohorts following lumbar spinal fusion.Study Design: Retrospective cohort analysis.Patient Sample: Analysis of 1,184 patients who underwent posterolateral lumbar fusion from 2011 to 2018. Surgery was indicated after failure of conservative treatment to address radiculopathy and/or neurogenic claudication. Patients were excluded if they were under 18 years of age at the time of surgery, had a lumbar fracture, tumor, or infection, or had fusions involving the thoracic spine, high-grade spondylolisthesis, or concomitant deformity. Of the 1,184 patients, 850 patients were included. Patients were divided into three roughly equal groups for analysis: young (18-54 years), middle-aged (55-69 years), and senior (≥70 years).Outcome Measures: Visual Analog Scale Back/Leg pain, and Oswestry Disability Index (ODI) were collected, and achievement of minimal clinically important difference was evaluated. Lumbar lordosis (LL), pelvic tilt (PT), pelvic incidence (PI), and PI-LL difference were measured on radiographs. Rates of postoperative complications were analyzed.Methods: Several radiographic parameters were measured using plain radiographs obtained at preoperative, immediately postoperative (standing radiographs performed on postoperative day 1), and most recent follow-up visits. Preoperative and final patient-reported outcomes, along with demographic information, were obtained all patients. Binary outcome variables were compared between groups with multivariate logistic regression, and continuous outcome variables were compared using multivariate linear regression, with age 18 to 54 years used as the reference. Multivariate regressions were used to compare outcomes between cohorts while controlling baseline characteristics.Results: A total of 850 patients were included; 330 young (38.80%), 317 middle-aged (37.30%), and 203 senior (23.90%). Seniors had higher postoperative length of stay compared to younger patients (p<.001). Younger patients had worse final ODI scores compared to middle-aged patients (p=.002). Seniors had higher rates of proximal ASD (p=.002) compared to young patients. There was no difference in achievement of minimal clinically important differences (MCID) between all three groups.Conclusions: Senior patients have significant improvement in patient-reported clinical outcomes, despite having greater comorbidities, and longer length of stay. However, given a general lack of achievement of MCID across all cohorts, these findings suggest the need for a critical re-evaluation of the role of lumbar spinal fusion in the management of patients with refractory radiculopathic and/or neurogenic claudication symptoms. [ABSTRACT FROM AUTHOR]

Teleportation describes the transmission of information without transport of neither matter nor energy. For many years, however, it has been implicitly assumed that this scheme is of inherently nonlocal nature, and therefore exclusive to quantum systems. Here, we experimentally demonstrate that the concept of teleportation can be readily generalized beyond the quantum realm. We present an optical implementation of the teleportation protocol solely based on classical entanglement between spatial and modal degrees of freedom, entirely independent of nonlocality. Our findings could enable novel methods for distributing information between different transmission channels and may provide the means to leverage the advantages of both quantum and classical systems to create a robust hybrid communication infrastructure. [ABSTRACT FROM AUTHOR]

Electrical power from geothermal heat is hardly efficient, if the temperature level of geothermal water is low. This situation is predominant in middle Europe, for example, in Germany, where even in hot-spot areas like Norddeutsches Becken, Oberrheingraben, and Molassebecken the temperature of geothermal water is less than 160°C. For this, efforts have to be made in optimizing the power cycle efficiency. Supercritical fluids provide a higher net energy output per unit mass than subcritical fluids but their physical properties strongly depend on temperature variations, especially close to the supercritical point. Based on the requirements of a new modular and mobile supercritical power cycle MONICA (modular low temperature power cycle Karlsruhe), which will be built within the next few years, different heat exchanger types are investigated within this study in order to determine the most compact design with respect to mobility, mountability, and efficiency. Changes in physical properties of propane, the working fluid of the new cycle, are taken into account by iterative, stepwise calculation of heat exchanger types like double-pipe, shell-and-tube, and plate heat exchangers. For this, common Nusselt number correlations are implemented in the stepwise iteration. Influence of geometry on flow conditions and analysis of part load sensitivity are provided. [ABSTRACT FROM PUBLISHER]

Contraction hierarchies are a simple approach for fast routing in road networks. Our algorithm calculates exact shortest paths and handles road networks of whole continents. During a preprocessing step, we exploit the inherent hierarchical structure of road networks by adding shortcut edges. A subsequent modified bidirectional Dijkstra algorithm can then find a shortest path in a fraction of a millisecond, visiting only a few hundred nodes. This small search space makes it suitable to implement it on a mobile device. We present a mobile implementation that also handles changes in the road network, like traffic jams, and that allows instantaneous routing without noticeable delay for the user. Also, an algorithm to calculate large distance tables is currently the fastest if based on contraction hierarchies. [ABSTRACT FROM AUTHOR]

(1) Background: The aim of this study was to evaluate the impact of endometriosis on postoperative pain following laparoscopic hysterectomy; (2) Methods: A total of 214 women who underwent a laparoscopic hysterectomy between January 2013 and October 2017 were divided into four subgroups as follows: (1) endometriosis with chronic pain before the surgery (n = 57); (2) pain-free endometriosis (n = 50); (3) pain before the surgery without endometriosis (n = 40); (4) absence of both preoperative pain and endometriosis (n = 67). Postoperative pain was compared by using Visual Analog Scale (VAS) scores and by tracking the use of painkillers during the day of surgery and the first two postoperative days; (3) Results: Women with chronic pain before the surgery reported higher VAS scores during the first postoperative days, while the use of analgesics was similar across the groups. There was no difference in the postoperative pain when comparing endometriosis patients to non-endometriosis patients; (4) Conclusions: Women with chronic pelvic pain demonstrated increased postoperative pain after laparoscopic hysterectomy, which was independent of the presence or severity of endometriosis. The increased VAS scores did not, however, translate into equally greater use of painkillers, possibly due to the standardised protocols of analgesia in the immediate postoperative period. These findings support the need for careful postsurgical pain management in patients with pain identified as an indication for hysterectomy, independent of the extent of the surgery or underlying diagnosis. [ABSTRACT FROM AUTHOR]

The origin of waveguiding in the bulk of silicon after sub‐ps laser inscription is investigated. Locally resolved Raman measurements of waveguide cross sections and along the propagation axis reveal highly localized crystal deformations. These modifications consist of highly confined regions of silicon with a disturbed crystal structure accompanied with strain. This transformation is responsible for a local increase of the refractive index allowing localized waveguiding. On the basis of near‐field measurements at an excitation wavelength of 1550 nm, the absolute value of the refractive index change is estimated to be in the range of 10−3. The origin of waveguiding after sub‐picosecond laser inscription in the bulk of crystalline silicon is examined. Micro‐Raman spectroscopy analyses of the waveguide cross sections reveal highly localized disturbed crystal structures. These material transformations result in a local increase of the refractive index responsible for guiding light. [ABSTRACT FROM AUTHOR]