Model-based Probe State Estimation and Crack Inverse Methods Addressing Eddy Current Probe Variability

Recent work on model-based inverse methods with eddy current inspections of surface breaking discontinuities has shown some sizing error due to variability in probes with the same design specifications [1]. This is an important challenge for model-based inversion crack sizing techniques, to be robust to the varying characteristics of eddy current probes found in the field [1-2]. In this paper, a model-based calibration process is introduced that estimates the state of the probe. First, a carefully designed surrogate model was built using VIC-3D® simulations covering the critical range of probe rotation angles, tilt in two directions, and probe offset (liftoff) for both tangential and longitudinal flaw orientations. Some approximations and numerical compromises in the model were made to represent tilt in two directions and reduce simulation time; however, this surrogate model was found to represent the key trends in the eddy current response for each of the four probe properties in experimental verification studies well. Next, this model was incorporated into an iterative inversion scheme during the calibration process, to estimate the probe state while also addressing the gain/phase fit and centering the calibration notch indication. Results are presented showing several examples of the blind estimation of tilt and rotation angle for known experimental cases with good agreement within +/- 2.5 degrees. The RMS error was found to be significantly reduced by fitting the probe state and, in many instances, probe state estimation addresses the previously un-modelled characteristics (model error) with real probe inversion studies. Additional studies are presented comparing the size of the calibration notch and the quality of the calibration fit, where calibrating with too small or too large a notch can produce poorer inversion results. Once the probe state is estimated, the final step is to transform the base crack inversion surrogate model and apply it for crack characterization. Because of the dimensionality of this problem, simulations were made at a limited set of select flaw sizes with varying length, depth and width, and an interpolation scheme was used to address the effect of the probe state at intermediate solution points. Using this process, results are presented demonstrating improved crack inversion performance for extreme probe states

Model Benchmarking and Reference Signals for Angled-beam Shear Wave Ultrasonic NDE Inspections

NDE modeling and simulation are important tools to support the development and validation of enhanced localization and characterization techniques. Previously, important achievements were made by the USAF to address crack detection in aircraft structures using angled-beam shear wave inspection techniques. However, new work on model benchmarking is needed to move beyond detection and achieve reliable crack characterization. To achieve this goal, simulated studies are needed to verify that models can accurately represent all of the key variables with the inspection of multilayer structures with fastener sites and varying crack conditions. Often with model benchmark studies, the accuracy of the model is evaluated based on the change in response relative to a selected reference signal. During recent simulated and experimental studies, some challenges were discovered concerning the creation and/or selection of a reference signal in a plate with a vertical hole and crack. The focus of this paper is on key findings concerning model benchmarking using CIVA-UT for angled-beam shear wave inspections. The use of a side drilled hole (SDH) in a plate was found to be somewhat problematic as a reference signal for angled beam shear wave inspection. Previously, only a limited number of studies have looked at model benchmarking for angled beam shear wave inspections. Systematic studies were performed with varying SDH depth and size, and varying the ultrasonic probe frequency, focal depth, and probe height. Care must be taken in understanding the precise beam properties with these experiments. One issue is that there is some increased error with the simulation of angled shear wave beams, especially in the near-field. Even more significant, asymmetry in real probes and the inherent sensitivity of signals in the near-field to subtle test conditions were found to provide a greater challenge with achieving model agreement. Through these studies, conditions of good and poor agreement were observed. For some inspection conditions, the skip signal off of the far wall from the side drilled hole can provide a better reference than the direct reflected signal. All in all, these seemingly mundane studies were found to be important with providing guidance on reference signal selection for model benchmarking work on the inspection of fastener sites with cracks

Validating a common tick survey method: cloth-dragging and line transects

Cloth-dragging is the most widely-used method for collecting and counting ticks, but there are few studies of its reliability. By using cloth-dragging, we applied a replicated line transects survey method, in two areas in Sweden with different Ixodes ricinus tick-densities (low at Grimsö and high at Bogesund) to evaluate developmental stage specific repeatability, agreement and precision in estimates of tick abundance. 'Repeatability' was expressed as the Intraclass Correlation Coefficient (ICC), 'agreement' with the Total Deviation Index (TDI) and 'precision' by the coefficient of variation (CV) for a given dragging distance. Repeatability (ICC) and agreement (TDI) were higher for the most abundant instar (nymphs) and in the area of higher abundance. At Bogesund tick counts were higher than at Grimsö and so also repeatability, with fair to substantial ICC estimates between 0.22 and 0.75, and TDI ranged between 1 and 44.5 counts of difference (thus high to moderate agreement). At Grimsö, ICC was poor to moderate and ranged between 0 and 0.59, whereas TDI remained low with estimates lower or equal to 1 count (thus high agreement). Despite a 100-fold lower abundance at Grimsö, the same level of precision for nymphs could be achieved with a 70% increase of dragging effort. We conclude that the cloth-dragging technique is useful for surveying ticks' and primarily to estimate abundance of the nymphal stage, whereas it rarely will be recommended for larvae and adults

Tick-transmitted co-infections among erythema migrans patients in a general practice setting in Norway:a clinical and laboratory follow-up study

Background Erythema migrans (EM) is the most common manifestation of Lyme borreliosis. Here, we examined EM patients in Norwegian general practice to find the proportion exposed to tick-transmitted microorganisms other than Borrelia, and the impact of co-infection on the clinical manifestations and disease duration. Methods Skin biopsies from 139/188 EM patients were analyzed using PCR for Neoehrlichia mikurensis, Rickettsia spp., Anaplasma phagocytophilum and Babesia spp. Follow-up sera from 135/188 patients were analyzed for spotted fever group (SFG) Rickettsia, A. phagocytophilum and Babesia microti antibodies, and tested with PCR if positive. Day 0 sera from patients with fever (8/188) or EM duration of ≥ 21 days (69/188) were analyzed, using PCR, for A. phagocytophilum, Rickettsia spp., Babesia spp. and N. mikurensis. Day 14 sera were tested for TBEV IgG. Results We detected no microorganisms in the skin biopsies nor in the sera of patients with fever or prolonged EM duration. Serological signs of exposure against SFG Rickettsia and A. phagocytophilum were detected in 11/135 and 8/135, respectively. Three patients exhibited both SFG Rickettsia and A. phagocytophilum antibodies, albeit negative PCR. No antibodies were detected against B. microti. 2/187 had TBEV antibodies without prior immunization. There was no significant increase in clinical symptoms or disease duration in patients with possible co-infection. Conclusions Co-infection with N. mikurensis, A. phagocytophilum, SFG Rickettsia, Babesia spp. and TBEV is uncommon in Norwegian EM patients. Despite detecting antibodies against SFG Rickettsia and A. phagocytophilum in some patients, no clinical implications could be demonstrated

Microclimatological consequences for plant and microbial composition in Sphagnum-dominated peatlands

In three Scandinavian peatlands we studied to what extent plant and microbial community compositions are governed by local-scale microhabitat, with a special interest in the effect of aspect (i.e. exposition of slopes). Despite differences in solar irradiance between the south- and north-facing slopes, maximum temperature was elevated in the south-facing slopes at the most northern site only. Pore-water nutrient concentrations were not affected by aspect, yet dissolved organic carbon concentrations were higher in the south-facing microhabitats. This was likely caused by higher vascular plant biomass. Plant and microbial community composition clearly differed among sites. In all three sites, microhabitat (i.e. prevailing water-table depth) affected the plant and microbial community compositions. Aspect, however, did not affect community composition, even though microclimate significantly differed between the south- and the north-facing aspects at the northernmost site. Our results highlight the complex link between plant community composition, microbial community and environmental conditions, which deserves much more attention than currently in order to fully understand the effects of climate change on peatland ecosystem function.I

Erratum: Sequence data and association statistics from 12,940 type 2 diabetes cases and controls.

This corrects the article DOI: 10.1038/sdata.2017.179

New genetic loci implicated in fasting glucose homeostasis and their impact on type 2 diabetes risk.

Levels of circulating glucose are tightly regulated. To identify new loci influencing glycemic traits, we performed meta-analyses of 21 genome-wide association studies informative for fasting glucose, fasting insulin and indices of beta-cell function (HOMA-B) and insulin resistance (HOMA-IR) in up to 46,186 nondiabetic participants. Follow-up of 25 loci in up to 76,558 additional subjects identified 16 loci associated with fasting glucose and HOMA-B and two loci associated with fasting insulin and HOMA-IR. These include nine loci newly associated with fasting glucose (in or near ADCY5, MADD, ADRA2A, CRY2, FADS1, GLIS3, SLC2A2, PROX1 and C2CD4B) and one influencing fasting insulin and HOMA-IR (near IGF1). We also demonstrated association of ADCY5, PROX1, GCK, GCKR and DGKB-TMEM195 with type 2 diabetes. Within these loci, likely biological candidate genes influence signal transduction, cell proliferation, development, glucose-sensing and circadian regulation. Our results demonstrate that genetic studies of glycemic traits can identify type 2 diabetes risk loci, as well as loci containing gene variants that are associated with a modest elevation in glucose levels but are not associated with overt diabetes

Hundreds of variants clustered in genomic loci and biological pathways affect human height

Most common human traits and diseases have a polygenic pattern of inheritance: DNA sequence variants at many genetic loci influence the phenotype. Genome-wide association (GWA) studies have identified more than 600 variants associated with human traits, but these typically explain small fractions of phenotypic variation, raising questions about the use of further studies. Here, using 183,727 individuals, we show that hundreds of genetic variants, in at least 180 loci, influence adult height, a highly heritable and classic polygenic trait. The large number of loci reveals patterns with important implications for genetic studies of common human diseases and traits. First, the 180 loci are not random, but instead are enriched for genes that are connected in biological pathways (P = 0.016) and that underlie skeletal growth defects (P < 0.001). Second, the likely causal gene is often located near the most strongly associated variant: in 13 of 21 loci containing a known skeletal growth gene, that gene was closest to the associated variant. Third, at least 19 loci have multiple independently associated variants, suggesting that allelic heterogeneity is a frequent feature of polygenic traits, that comprehensive explorations of already-discovered loci should discover additional variants and that an appreciable fraction of associated loci may have been identified. Fourth, associated variants are enriched for likely functional effects on genes, being over-represented among variants that alter amino-acid structure of proteins and expression levels of nearby genes. Our data explain approximately 10% of the phenotypic variation in height, and we estimate that unidentified common variants of similar effect sizes would increase this figure to approximately 16% of phenotypic variation (approximately 20% of heritable variation). Although additional approaches are needed to dissect the genetic architecture of polygenic human traits fully, our findings indicate that GWA studies can identify large numbers of loci that implicate biologically relevant genes and pathways.