Neurophysiological validation of simultaneous intrinsic and reflexive joint impedance estimates

Background People with brain or neural injuries, such as cerebral palsy or spinal cord injury, commonly have joint hyper-resistance. Diagnosis and treatment of joint hyper-resistance is challenging due to a mix of tonic and phasic contributions. The parallel-cascade (PC) system identification technique offers a potential solution to disentangle the intrinsic (tonic) and reflexive (phasic) contributions to joint impedance, i.e. resistance. However, a simultaneous neurophysiological validation of both intrinsic and reflexive joint impedances is lacking. This simultaneous validation is important given the mix of tonic and phasic contributions to joint hyper-resistance. Therefore, the main goal of this paper is to perform a group-level neurophysiological validation of the PC system identification technique using electromyography (EMG) measurements. Methods Ten healthy people participated in the study. Perturbations were applied to the ankle joint to elicit reflexes and allow for system identification. Participants completed 20 hold periods of 60 seconds, assumed to have constant joint impedance, with varying magnitudes of intrinsic and reflexive joint impedances across periods. Each hold period provided a paired data point between the PC-based estimates and neurophysiological measures, i.e. between intrinsic stiffness and background EMG, and between reflexive gain and reflex EMG. Results The intrinsic paired data points, with all subjects combined, were strongly correlated, with a range of $$r = [0.87\ 0.91]$$ r = [ 0.87 0.91 ] in both ankle plantarflexors and dorsiflexors. The reflexive paired data points were moderately correlated, with $$r = [0.64\ 0.69]$$ r = [ 0.64 0.69 ] in the ankle plantarflexors only. Conclusion An agreement with the neurophysiological basis on which PC algorithms are built is necessary to support its clinical application in people with joint hyper-resistance. Our results show this agreement for the PC system identification technique on group-level. Consequently, these results show the validity of the use of the technique for the integrated assessment and training of people with joint hyper-resistance in clinical practice.

Full-Scale Step-Load-Hold Tests on X65 and X70 Line Pipe Steels

A time-delayed failure due to stress-activated creep (cold-creep) will occur if the applied load is held constant at a level above the threshold. The results of small and full-scale tests on line pipe steels conducted by the Battelle Memorial Institute and the British Gas Corporation in the 1960s and 70s indicated that the (empirical) threshold for a time-delayed failure was approximately 85–95% SAPF (straight-away-pressure-to-failure). The line pipe steels were Grades X52 or X60, and the full-size equivalent Charpy V-notch impact energy (where reported) did not exceed 35 J. The strength and toughness of line pipe steels has significantly increased over the decades due to developments in steel-making and processing. The question then is whether an empirical threshold based on tests on lower strength and lower toughness steels is applicable to higher strength and higher toughness steels. A Tripartite Project was established to answer this question. The Australian Pipelines and Gas Association (APGA), the European Pipeline Research Group (EPRG) and the Pipeline Research Council International (PRCI) collaborated in conducting six full-scale step-load-hold tests on higher strength and higher toughness steels. Companion papers present the other aspects of this multi-year project. The line pipe supplied for testing is summarised below. • Identifier — Dimensions and Grade — f.s.e. Charpy V-notch impact energy at 0 C • APGA [A] — 457.0 × 9.1 mm, Grade X70M, ERW — 263 J • EPRG [E] — 1016.0 × 13.6 mm, Grade X70M, SAWL — 165 J • PRCI [P] — 609.6 × 6.4 mm, Grade X65, SAWL — 160 J Six step-load-hold tests, each with four part-through-wall defects, were conducted. Test Nos. APGA 1 and 2, and Nos. EPRG 1 and 2 were conducted at Engie, France. Test Nos. PRCI 1 and 2 were conducted at EWI, USA. The full-scale tests, and associated small-scale testing, are described and discussed. A time-delayed failure due to stress-activated creep occurred in each of the step-load-hold tests. The failures occurred during a hold-period at 93.7–104.4% SAPF, after a hold of approximately 1.0–13.9 hours. The results of the six step-load-hold tests are consistent with a threshold for a time-delayed failure of approximately 90% SAPF.

Investigation of the BOLD-Based MRI Signal Time Course During Short Breath-Hold Periods for Estimation of the Cerebrovascular Reactivity

For the prognosis of stroke, patients with moyamoya disease (MMD) require the estimation of remaining cerebrovascular reactivity. For this purpose, CO2-triggered BOLD fMRI by use of short breath-hold periods seems to be a highly available alternative to nuclear medicine methods. Too long breath-hold periods are difficult to perform, too short breath-hold periods do not lead to sufficient BOLD signal changes. We aimed to investigate the required minimum breath-hold duration to detect distinct BOLD signals in the tissue of healthy subjects to find out how long the minimum breath-hold duration in clinical diagnostics of MMD should be. A prospective study was performed. Fourteen healthy subjects underwent fMRI during end-expiration breath-hold periods of different duration (3, 6, 9, and 12 s). Additionally, we compared the influence of paced and self-paced breathing altering the breath-hold periods. Data of a patient with MMD was evaluated to investigate whether the tested procedure is suitable for clinical use. Significant global BOLD signal increases were detected after breath-hold periods of 6, 9, and 12 s. The signals were significantly higher after breath-hold periods of 9 s than after 6 s, while not when the duration was extended from 9 to 12 s. Furthermore, we found additional BOLD signal changes before the expected signal increases, which could be avoided by paced respiratory instructions. This investigation indicates that end-expiration breath-hold period of at least 9 s might be used to measure the cerebrovascular reactivity. This time period resulted in distinct BOLD signal changes and could be performed easily.

Postural control of arm and fingers through integration of movement commands

Every movement ends in a period of stillness. Current models assume that commands that hold the limb at a target location do not depend on the commands that moved the limb to that location. Here, we report a surprising relationship between movement and posture in primates: on a within-trial basis, the commands that hold the arm and finger at a target location depend on the mathematical integration of the commands that moved the limb to that location. Following damage to the corticospinal tract, both the move and hold period commands become more variable. However, the hold period commands retain their dependence on the integral of the move period commands. Thus, our data suggest that the postural controller possesses a feedforward module that uses move commands to calculate a component of hold commands. This computation may arise within an unknown subcortical system that integrates cortical commands to stabilize limb posture.

Effect of Ambient and Elevated Temperature on the Residual Splitting and Flexural Tensile Strength of Normal and High Strength Concrete

Experimental test have carried out to investigate the behavior of residual tensile strength of concrete prepared using normal and high strength concrete. For the same purpose, cylindrical and prism-shaped specimens of concrete were caste and consecutively subjected to heating and cooling condition in the laboratory-controlled environment. A hold period of three hours was provided to impart the heating-cooling phenomenon inside the electrical furnace at four different sets of temperatures. The elevated temperatures chosen for the present tensile behavior study are 200oC, 400oC, 600oC, and 800oC. Strength was also determined at the ambient environment for the purpose of comparing the effects of thermal loads on the behavior of strength. A significant loss in tensile strength has been observed in concrete mixes at various temperatures. The outcomes of the current experimental work are termed useful for understanding key mechanical characteristics of concrete under the effect of thermal loads.

249. Limited Diagnostic Utility of Extended Aerobic Blood Culture Incubation for Fungal Pathogen Detection

Background Blood cultures are an important diagnostic tool for the detection of fungemia. At our institution, fungal blood cultures consist of aerobic blood culture with incubation extended from the standard 5 days to 14 days. Orders for fungal blood cultures exist in multiple electronic order sets for selected populations, including oncology and bone marrow transplant services. Methods To determine the yield of fungal blood cultures at our institution, a 570-bed tertiary-care referral center, we extracted all fungal blood culture results over a 4.5-year period (January 1, 2014–May 15, 2018) from a Laboratory Information System. Results Of the 21,657 fungal blood cultures performed, only 202 (0.9%) demonstrated growth and 189 (0.9%) grew fungal organisms. The majority (90%, n = 182/202) of positive fungal blood cultures grew a Candida or other yeast species. 96% (n = 174/182) of the fungal cultures that grew yeast would have been detected with standard bacterial blood culture. Eight of these cultures became positive during the extended hold period and grew a Candida species. All 8 cultures were collected from patients who had previous positive cultures for the same Candida species detected by standard incubation. Five fungal blood cultures from 4 patients turned positive after 5 days of incubation. Among these, two additional fungal pathogens were identified including 2 cases of Lomentospora prolificans and 2 cases of Fusarium. In both cases of L. prolificans and one case of Fusarium, the patients had previous positive blood cultures that detected the same organism with standard incubation. One patient with Fusarium had no previous positive blood cultures, but had multiple tissue cultures positive for Fusarium. The remaining cultures that turned positive after 5 days of incubation contained bacterial organisms, a number of which were considered clinically insignificant (e.g., Cutibacterium species). Conclusion These data suggest that extended incubation of aerobic blood culture bottles has limited diagnostic utility beyond standard bacterial blood culture for detection of fungemia. Fungal blood cultures represent an opportunity for improved diagnostic test stewardship, and use should be restricted to selected situations in consultation with Infectious Diseases or Laboratory Medicine. Disclosures All authors: No reported disclosures.

Experimental Investigation on the Creep and Low Cycle Fatigue Behaviors of a Serviced Turbine Blade

This paper experimentally investigated the creep and fatigue behaviors of a low-pressure turbine (LPT) blade with 600 hours of service using a novel test system. Pure low cycle fatigue (LCF), pure creep and creep-fatigue interaction (CFI) experiments on the full-scale serviced blades were conducted respectively. Test results showed that the increasing of deformation amplitude was divided into three stages under both pure LCF and creep-fatigue loadings. The deformation of each blade increased rapidly until failure when the test cycle exceeded the 80% of their overall life under the pure LCF and CFI condition. The hold period in creep-fatigue tests shortens the first stage of whole life and has no influence on the proportion of crack initiation life to overall life. The fractures in pure LCF, pure creep and creep-fatigue tests emerged transgranular, intergranular and both transgranular and intergranular behaviors respectively. The crack initiated and propagated in a specific zone of the blade under all the experimental loadings, which limited its creep-fatigue resistance. At last, the remaining life of turbine blade was estimated conservatively by introducing the safety limit into a statistical method.

Effect of Room Temperature Creep on Hydrostatic Leak Test

Because of the stochastic nature of line pipe characteristics a small percentage of the pipe joints in a given pipeline may possess actual yield strengths below the specified minimum yield strength. During a hydrostatic test these segments may experience some plastic deformation as the hoop stress approaches the yield point. It is well known that the effect of room temperature creep near the yield becomes notable and therefore can affect pressure trending during the hold period (leak test). In this work a numerical model is developed for the analysis of creep deformation. A conceptual study is carried out to demonstrate potential effects of creep on hydrostatic test pressure trending during a leak test. This analysis can help operators understand the potential effects of creep and distinguish it from other factors such as temperature changes or leakage and can help identify, or rule out, the occurrence of pipe yielding during hydrostatic tests.

Creep of GLT Beams during Four-Point Bending Test

The present work is concerned with the evaluation of creep deformation developed during the four-point bending test of glued laminated timber beams. In particular, three deflections (at the mid-span of the beam, and below the points of load application) were recorded for each tested beam. The time variation of deflections at 110 loading levels was examined in details for the set of five beams. It can be seen that the effect of creep covers about 10 – 20% of the overall strain. To proceed with numerical simulations requires, however, building first a reliable computational model that agrees well with purely elastic response of the beam. Thus additional measurements were carried out assuming a rather short hold period to eliminate the creep effects. The results were then compared with numerical simulations promoting the computational model to be used in more advanced simulations incorporating a suitable rheological model.