Abstract
Higher-order topological insulators are a novel topological phase beyond the framework of conventional bulk–boundary correspondence
1,2
. In these peculiar systems, the topologically ...non-trivial boundary modes are characterized by a co-dimension of at least two
3,4
. Despite several promising preliminary considerations regarding the impact of nonlinearity in such systems
5,6
, the flourishing field of experimental higher-order topological insulator research has thus far been confined to the linear evolution of topological states. As such, the observation of the interplay between nonlinearity and the dynamics of higher-order topological phases in conservative systems remains elusive. Here we experimentally demonstrate nonlinear higher-order topological corner states. Our photonic platform enables us to observe nonlinear topological corner states as well as the formation of solitons in such topological structures. Our work paves the way towards the exploration of topological properties of matter in the nonlinear regime, and may herald a new class of compact devices that harnesses the intriguing features of topology in an on-demand fashion.
•Full-field thermomechanical analysis of mesoscopic deformation behaviour of foams.•Synchronisation of digital image correlation and infrared thermography.•Correlation of local strain fields and ...local temperature fields.•Coupling of surface deformation and volumetric deformation.
Display omitted
Open-cell metal/polymer hybrid foams are biomimetic open-porous composites, consisting of a polymeric foam electrochemically coated with a metallic layer. Due to their specific pore structure, they can be used in lightweight applications or as crash absorbers. The nanocrystalline coating leads to a strengthening effect and largely improved energy absorption capacity. Understanding the mesoscopic deformation behaviour of foams is essential for the design of intelligent and safe crash absorbers for the future. The present contribution focuses on the full-field thermomechanical analysis of the mesoscopic deformation of metal/polyurethane hybrid foams and hollow strut foams. Local strain fields from digital image correlation were directly coupled with local temperature fields from infrared thermography. A new software tool allows for the direct correlation of thermal and mechanical fields and for the corresponding experimental stress–strain data. Furthermore, the evolution of the energy absorption capacity as function of the strain rate was determined using infrared thermography.
The water management in proton exchange membrane fuel cells (PEMFC) is strongly influenced by the design of the gas diffusion layers (GDL). Limiting current measurements in small-scale cells ...operating at high stoichiometries are useful to determine the oxygen transport resistance. The oxygen transport resistance increases, once water condenses inside the GDL.
In this study a new electrochemical method for voltage loss estimation of GDL induced oxygen transport losses are presented. This new method, referred to as “transient limiting current” (TLC), is compared with the literature method. TLC allows a direct estimation of oxygen transport resistance at an arbitrarily conditioned state.
This study also presents a case study of liquid water visualization of a PEM fuel cell with varying GDLs types. With the help of quasi in-situ synchrotron X-ray computed tomography and time resolved radiography measurements we investigate appearance and distribution of liquid water inside the GDLs under limiting current conditions.
•In-situ characterization of GDLs.•Transient limiting current measurement for prediction of oxygen transport resistance.•Quasi in-situ synchrotron X-ray computed tomography and radiography measurements on GDLs.•Visualization of liquid water inside GDL microstructure.
Abstract Objective P-selectin is a cellular adhesion molecule that has been shown to be crucial in development of coronary heart disease (CHD). We sought to determine the role of P-selectin on the ...risk of atherosclerosis in a large multi-ethnic population. Methods Data from the Multi-Ethnic Study of Atherosclerosis (MESA), including 1628 African, 702 Chinese, 2393 non-Hispanic white, and 1302 Hispanic Americans, were used to investigate the association of plasma P-selectin with CHD risk factors, coronary artery calcium (CAC), intima-media thickness, and CHD. Regression models were used to investigate the association between P-selectin and risk factors, Tobit model for CAC, and Cox regression for CHD events. Results Mean levels of P-selectin differed by ethnicity and were higher in men ( P < 0.001). For all ethnic groups, P-selectin was positively associated with measures of adiposity, blood pressure, current smoking, LDL, and triglycerides and inversely with HDL. A significant ethnic interaction was observed for the association of P-selectin and prevalent diabetes; however, P-selectin was positively associated with HbA1c in all groups. Higher P-selectin levels were associated with greater prevalence of CAC. Over 10.1 years of follow-up, there were 335 incident CHD events. There was a positive linear association between P-selectin levels and rate of incident CHD after adjustment for traditional risk factors. However, association was only significant in non-Hispanic white Americans (HR: 1.81, 95% CI 1.07 to 3.07, P = 0.027). Conclusion We observed ethnic heterogeneity in the association of P-selectin and risk of CHD.
In-situ diagnostics for single polymer electrolyte membrane fuel cells are well known and established. Comparable stack level techniques are urgently needed to enhance the understanding of ...degradation during real system operation, but have not yet reached a similar level of sophistication. We have therefore developed a new method for the quantification of the hydrogen crossover current in stacks, which in combination with a previously published technique now allows a clear quantitative characterization of the individual cells' membranes and electrodes. The limits of the reported methods are theoretically assessed and application is then demonstrated on automotive short stacks. The results prove to be highly reproducible and are validated for individual cells of the respective stacks by direct comparison with cyclic voltammetry results, showing good quantitative agreement for the hydrogen crossover current, the double layer capacitance and the electrochemically active surface area.
•A method for measuring hydrogen crossover currents in PEMFC stacks is presented.•Quantitative characterization of membrane and electrode in stacks has been achieved.•The method shows good quantitative agreement for all individual cells.
We present a case of a 10-year-old boy with Crouzon syndrome that demonstrates progressive myelinated retinal nerve fibers (MRNF).
A 10-year-old boy was referred for ophthalmic examination due to ...clusters of opaque white fibers around his optic nerve. Past surgical history includes craniofacial surgery at 3 years of age secondary to the deteriorating vision from increased intracranial pressure and papilledema. Upon examination (now 6.5 years post-craniofacial surgery), the patient denied any ocular complaints. The fundus examination showed progressively enlarged myelination of the retinal nerve fiber layer (right eye > left eye). Although previous cases of MRNF with Crouzon syndrome have been reported, our case is unique given its post-operative status with early onset of MRNF.
This case report documents the photographic progression of bilateral myelinated retinal nerve fibers (MRNF) in a pediatric case of Crouzon syndrome post-craniofacial surgery secondary to increased intracranial pressure and papilledema. Based on our patient, craniofacial decompression surgery may not prevent the development of MRNF. The exact mechanisms of MRNF are still being studied. Further investigations correlating craniofacial surgeries, increased intracranial pressure, and progression of myelinated retinal nerve fibers are needed to understand this process.
There is emerging evidence that lipids play an important role in many neurodegenerative processes, for example in Alzheimer's disease (AD). Although different lipid alterations in the AD brain have ...been reported, there have only been very few investigations of lipid changes in the cerebrospinal fluid (CSF). Recent developments in mass spectrometry (MS) have enabled fast and sensitive detection of lipid species in different biological matrixes. In this study we developed an on-line HPLC-MS method for phospholipid profiling in the CSF based on nano-HPLC separation using an Amide column and detection with electrospray (ESI) quadrupole-time of flight (QTOF) MS. We achieved good separation, reproducibility, and sensitivity in monitoring of the major phospholipid classes, phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylinositol (PI), and sphingomyelin (SM) in CSF. To emphasize the applicability of the method, a pilot study was performed on a group of CSF samples (N = 16) from individuals with probable AD and non-demented controls. We observed a statistically significant increase of SM levels (24.3 ± 2.4%) in CSF from probable AD individuals vs. controls. Our findings indicate that SM levels in the CSF could potentially provide a new lead in AD biomarker research, and show the potential of the method for disease-associated CSF phospholipid screening.
New York City has a heterogeneous population with many undocumented and uninsured immigrants from equatorial areas who have a higher incidence of ocular surface squamous neoplasia. To the best of our ...knowledge, this is the first documented selection of this cost-effective treatment of ocular surface squamous neoplasia (the use of absolute ethanol along the corneal margin, primary excision, double freeze-thaw cryopexy, and primary conjunctival closure) for an undocumented and uninsured New York City patient.
A 35-year-old man from Ecuador presented to a New York City emergency department due to worsening discomfort of a long-standing left eye pterygium. A slit-lamp examination of the left eye demonstrated a nasally located conjunctival mass measuring 6 × 8 mm extending onto the cornea (3 mm superiorly and 6 mm inferiorly on the cornea). Histological diagnosis confirmed squamous cell carcinoma in situ arising from the pterygium. Surgical excision with adjunctive absolute alcohol with additive double freeze-thaw cryopexy was performed. Our patient has remained free of tumor recurrence at year 2 postoperative visit.
Our case highlights the need to choose a cost-effective treatment for ocular surface squamous neoplasia in an at-risk population among undocumented and uninsured patients. Areas in the world with similar types of populations or treatment challenges may need to consider this approach as a primary treatment option.
Electromagnetic tracking systems have found increasing use in medical applications during the last few years. As with most non-trivial spatial measurement systems, the complex determination of ...positions and orientations from their underlying raw sensor measurements results in complicated, non-uniform error distributions over the specified measurement volume. This makes it difficult to unambiguously determine accuracy and performance assessments that allow users to judge the suitability of these systems for their particular needs. Various assessment protocols generally emphasize different measurement aspects that typically arise in clinical use. This can easily lead to inconclusive or even contradictory conclusions. We examine some of the major issues involved and discuss three useful calibration protocols. The measurement accuracy of a system can be described in terms of its 'trueness' and its 'precision'. Often, the two are strongly coupled and cannot be easily determined independently. We present a method that allows the two to be disentangled, so that the resultant trueness properly represents the systematic, non-reducible part of the measurement error, and the resultant precision (or repeatability) represents only the statistical, reducible part. Although the discussion is given largely within the context of electromagnetic tracking systems, many of the results are applicable to measurement systems in general.
We study linear and nonlinear higher-order topological insulators (HOTIs) based on waveguide arrays arranged into Sierpiński gasket and Sierpiński carpet structures, both of which have non-integer ...effective Hausdorff dimensionality. Such fractal structures possess different discrete rotational symmetries, but both lack transverse periodicity. Their characteristic feature is the existence of multiple internal edges and corners in their optical potential landscape, and the formal absence of an insulating bulk. Nevertheless, we show that a systematic geometric shift of the waveguides in the first generation of such fractal arrays, which affects the coupling strengths between sites of this building block as well as in subsequent structure generations, enables the formation of corner states of topological origin at the outer corners of the array. We find that, in contrast to HOTIs based on periodic arrays, Sierpiński gasket arrays always support topological corner states, irrespective of the direction of the shift of the waveguides, while in Sierpiński carpet structures, corner states emerge only for one direction of the waveguide shift. We also find families of corner solitons bifurcating from linear corner states of fractal structures that remain stable practically in the entire gap in which they form. These corner states can be efficiently excited by injecting Gaussian beams into the outer corner sites of the fractal arrays. Our results pave the way toward the investigation of nonlinear effects in topological insulators with non-integer dimensionality and enrich the variety of higher-order topological states.
PDF
