A General Solution to Determine Strain Profile in the Core of Distributed Fiber Optic Sensors under Any Arbitrary Strain Fields

Despite recent publications, the strain transfer in distributed optical fiber sensors is still often overlooked and poorly understood. In the first part of this paper, strain transfer is shown to be driven by a second-order differential equation, whether the optical fiber is embedded into the host material or surface-mounted. In this governing equation, only the value of a key parameter, called strain lag parameter, varies according to the attachment configuration and the type of optical fiber used as a sensor. Then, a general solution of the governing equation is proposed. It is an analytical expression established from new boundary conditions that are more adequate than those used previously in the literature and allows the determination of the strain profile in the core of a distributed optical fiber sensor under any arbitrary strain fields. This general solution has been validated by two experiments presented in the third part of the paper. A very good agreement between the analytical solutions and measured strain profiles using a high spatial resolution optical interrogator for both uniform and non-uniform strain fields has been obtained. These results highlight the importance of the strain lag parameter which must be taken into account for a correct interpretation of measurements, especially in the case of important strain gradients.

Emergence of distinct and heterogeneous strains of amyloid beta as Alzheimer′s disease progresses in Down syndrome

Amyloid beta (A&#946) is thought to play a critical role in the pathogenesis of Alzheimer&#8242s disease (AD). Prion-like Aβ polymorphs, or strains, can have varying pathogenicity and may underlie the phenotypic heterogeneity of the disease. In order to develop effective AD therapies, it is critical to identify the strains of A&#946 that might arise prior to the onset of clinical symptoms and understand how they may change with progressing disease. Down syndrome (DS), as the most common genetic cause of AD, presents promising opportunities to compare such features between early and advanced AD. In this work, we evaluate the neuropathology and A&#946 strain profile in the post-mortem brain tissues of 210 DS, AD, and control individuals. We assayed the levels of various A&#946 and tau species and used conformation-sensitive fluorescent probes to detect differences in A&#946 strains among individuals and populations. We found that these cohorts have some common but also some distinct strains from one another, with the most heterogeneous populations of A&#946 emerging in subjects with high levels of AD pathology. The emergence of distinct strains in DS at these later stages of disease suggests that the confluence of aging, pathology, and other DS-linked factors may favor conditions that generate strains that are unique from sAD.

Post-gel polymerisation shrinkage profiling of polymer biomaterials using a chirped fibre Bragg grating

A strain profile measurement technique using a chirped fibre Bragg grating (CFBG) sensor by implementing an integration of differences (IOD) method is reported in this paper. Using the IOD method the spatial distribution of strain along the length of the CFBG is extracted from its power reflectance spectra. As a proof of concept demonstration, the developed technique is applied to measure the polymerisation shrinkage strain profile of a photo-cured polymer dental composite which exhibits a non-uniform strain distribution attributed to the curing lamp characteristics. The result from the CFBG technique is compared with that of an FBG array embedded in the dental composite and is correlated with the degree of conversion of the material which also depends on the curing lamp intensity distribution. This technology will have significant impact and applications in a range of medical, materials and engineering areas where strain or temperature gradient profile measurement is required in smaller scales.

Field-Plate Geometry Dependent Electrostatics and Strain Mapping in AlGaAs/GaAs HEMTs

GaAs based power transistors provides higher switching speed compared to conventional Si transistors. The high electron mobility transistors (HEMTs) with AlGaAs/GaAs have got recent attentions for alternative suitable candidate for high frequency operation. The primary focus of the work is to study the electrostatics and stress/strain profile mapping due to the presence of field plate in AlGaAs/GaAs high electron mobility transistors. Using TCAD simulations, we examine the stress strain profile mapping as a function of field plate geometry and also study the electrostatics as function of field plate geometry and applied electric field.