Low, intermediate and high strain rate tensile experiments are carried Out on flat smooth, notched and central-hole tensile specimens extracted from advanced high strength steel sheets. A split ...Hopkinson pressure bar testing system is used in conjunction with a load inversion device to perform the high strain rate tension experiments. Selected surface strains, as well as local displacements, are measured using high speed photography in conjunction with planar digital image correlation (video extensometer). Through thickness necking precedes fracture in all experiments. A hybrid experimental-numerical approach is therefore employed to determine the strain to fracture inside the neck. To obtain an accurate description of the local strain fields at very large deformations, a plasticity model with a Johnson-Cook type of rate and temperature-dependency and a combined Swift-Voce strain hardening law is used in conjunction with a non-associated anisotropic flow rule. The incremental change in temperature is computed using a strain rate dependent weighting function instead of solving the thermal field equations. The comparison of the computed and measured force-displacement curves and surface strain histories shows good agreement before and after the onset of necking. From each experiment, the loading path to fracture is determined describing the evolution of the equivalent plastic strain in terms of the stress triaxiality, Lode angle parameter, strain rate and temperature. An empirical extension of the stress-state dependent Hosford-Coulomb fracture initiation model is proposed to account for the effect of strain rate on the onset of ductile fracture. The model is subsequently calibrated and successfully validated using the results from fracture experiments on DP590 and TRIP780 steels.
During high-frequency network activities, fast-spiking, parvalbumin-expressing basket cells (PV
-BCs) generate barrages of fast synaptic inhibition to control the probability and precise timing of ...action potential (AP) initiation in principal neurons. Here we describe a subcellular specialization that contributes to the high speed of synaptic inhibition mediated by PV
-BCs. Mapping of hyperpolarization-activated cyclic nucleotide-gated (HCN) channel distribution in rat hippocampal PV
-BCs with subcellular patch-clamp methods revealed that functional HCN channels are exclusively expressed in axons and completely absent from somata and dendrites. HCN channels not only enhance AP initiation during sustained high-frequency firing but also speed up the propagation of AP trains in PV
-BC axons by dynamically opposing the hyperpolarization produced by Na
-K
ATPases. Since axonal AP signaling determines the timing of synaptic communication, the axon-specific expression of HCN channels represents a specialization for PV
-BCs to operate at high speed.
Post-COVID-19 Cholangiopathy: A Novel Entity Roth, Nitzan C; Kim, Angela; Vitkovski, Taisia ...
The American journal of gastroenterology,
05/2021, Volume:
116, Issue:
5
Journal Article
Peer reviewed
Open access
Liver chemistry abnormalities are a frequent manifestation of coronavirus disease 2019 (COVID-19) but are usually transient and resolve with disease resolution.
We describe the clinical course and ...histologic features of 3 adults who developed prolonged and severe cholestasis during recovery from critical cardiopulmonary COVID-19.
These patients had clinical and histologic features similar to secondary sclerosing cholangitis of the critically ill patient, but with unique histologic features including severe cholangiocyte injury and intrahepatic microangiopathy suggestive of direct hepatic injury from COVID-19.
We believe that these cases constitute a novel severe post-COVID-19 cholangiopathy with potential for long-term hepatic morbidity.
The extension of in vivo optical imaging for disease screening and image-guided surgical interventions requires brightly emitting, tissue-specific materials that optically transmit through living ...tissue and can be imaged with portable systems that display data in real-time. Recent work suggests that a new window across the short-wavelength infrared region can improve in vivo imaging sensitivity over near infrared light. Here we report on the first evidence of multispectral, real-time short-wavelength infrared imaging offering anatomical resolution using brightly emitting rare-earth nanomaterials and demonstrate their applicability toward disease-targeted imaging. Inorganic-protein nanocomposites of rare-earth nanomaterials with human serum albumin facilitated systemic biodistribution of the rare-earth nanomaterials resulting in the increased accumulation and retention in tumour tissue that was visualized by the localized enhancement of infrared signal intensity. Our findings lay the groundwork for a new generation of versatile, biomedical nanomaterials that can advance disease monitoring based on a pioneering infrared imaging technique.
Background: The skeleton is regarded recently as an endocrine organ that affects energy metabolism. However, there are very limited data available concerning the relationships between the ...osteoblast-derived hormone osteocalcin, weight status, adiponectin and leptin in obese humans, especially in children. Methods: We analyzed osteocalcin, adiponectin, leptin and insulin resistance (IR) index homeostasis model assessment (HOMA) in 60 obese and 19 age- and gender-matched normal weight children. Furthermore, these parameters were determined in 60 obese children after participating in an outpatient 1-year lifestyle intervention based on exercise, behavior and nutrition therapy. Results: Sixty obese children had significantly lower osteocalcin levels (26.8±0.8 ng ml−1) than 19 normal weight controls (32.2±2.3 ng ml−1). Boys (29.9±1.1 ng ml−1) showed significantly (P=0.046) higher osteocalcin levels compared with girls (26.4±1.2 ng ml−1). In stepwise multiple linear regression analysis adjusted for age, gender and pubertal stage, osteocalcin was significantly negatively related to leptin and HOMA, but not to adiponectin. Changes of osteocalcin in the course of 1 year correlated significantly negatively with changes of IR index HOMA (r=−0.25), standard deviation score–body mass index (SDS–BMI) (r=−0.33) and leptin (r=−0.50). Substantial weight loss in 29 obese children led to a significant increase in osteocalcin and a significant decrease in leptin and HOMA. In 31 obese children without substantial weight loss, osteocalcin levels did not change significantly in the course of 1 year. Conclusion: Osteocalcin levels were lower in obese children and were related to IR and leptin both in cross-sectional and longitudinal analyses. Therefore, osteocalcin might be a new promising link between obesity and IR.
The nucleation, evolution and coalescence of voids is the well-established mechanism leading to ductile fracture under tension-dominated loading conditions. From a theoretical point of view, the same ...mechanism also applies to shear-dominated loading conditions. Here, an attempt is made to provide for the first time tomographic evidence of damage nucleation and evolution under shear-dominated loading in a modern engineering material. Monotonic experiments are performed on a flat double gage section smiley-shear specimen on the laminography stage of a synchrotron X-ray line. Based on fifteen scans of the entire gage section μm3, the mesostructural evolution inside a ferrite-bainite steel (FB600) is imaged in 3D up to the instant of specimen fracture. It is found that the as-received material includes a volume fraction of about 0.015% CaO particles. Upon mechanical loading at stress triaxialities evolving from 0 to 0.3, the ductile matrix detaches from these second phase particles, creating a prolate void space whose principal axis is aligned with the principal direction of the applied macroscopic field of deformation. The void space continues to grow while developing micro-crack like features. A large deformation analysis is performed on a representative volume element of the particle-matrix mesostructure replicating the experimental observations of void growth in an approximate manner. Furthermore, the simulation results suggest that a porosity as low as 0.05% is already sufficient to cause the ductile failure under shear-dominated loading through the formation of a band of localized plastic deformation at the mesoscale.
•Determined stress-state dependent fracture initiation in a ferritic-bainitic steel with CaO particles.•Performed in-situ shear experiment on synchrotron X-ray line.•Observed void nucleation and growth under shear-dominant loading conditions.•Explained observed failure mechanism through computational shear localization analysis.
Minimally invasive experimental methods that can measure local rate dependent mechanical properties are essential in understanding the behaviour of soft and biological materials in a wide range of ...applications. Needle based measurement techniques such as Cavitation Rheology (Zimberlin et al., 2007) and Volume Controlled Cavity Expansion (VCCE, Raayai-Ardakani et al. (2019a)), allow for minimally invasive local mechanical testing, but have been limited to measuring the elastic material properties. Here, we propose several enhancements to the VCCE technique to adapt it for characterisation of viscoelastic response at low to medium stretch rates (10−2 - 1 s−1). Through a carefully designed loading protocol, the proposed technique performs several cycles of expansion–relaxation at controlled stretch rates in a cavity expansion setting and then employs a large deformation viscoelastic model to capture the measured material response. Application of the technique to soft PDMS rubber reveals significant rate dependent material response with high precision and repeatability, while isolating equilibrated states that are used to directly infer the quasistatic elastic modulus. The technique is further established by demonstrating its ability to capture changes in the rate dependent material response of a tuneable PDMS system. The measured viscoelastic properties of soft PDMS samples are used to explain earlier reports of rate insensitive material response by needle based methods: it is demonstrated that the conventional use of constant volumetric rate cavity expansion can induce high stretch rates that lead to viscoelastic stiffening and an illusion of rate insensitive material response. We thus conclude with a cautionary note on possible overestimation of the quasistatic elastic modulus in previous studies and suggest that the stretch rate controlled expansion protocol, proposed in this work, is essential for accurate estimation of both quasistatic and dynamic material parameters.
We present light curves and classification spectra of 17 hydrogen-poor superluminous supernovae (SLSNe) from the Pan-STARRS1 Medium Deep Survey (PS1 MDS). Our sample contains all objects from the PS1 ...MDS sample with spectroscopic classification that are similar to either of the prototypes SN 2005ap or SN 2007bi, without an explicit limit on luminosity. With a redshift range , PS1 MDS is the first SLSN sample primarily probing the high-redshift population; our multifilter PS1 light curves probe the rest-frame UV emission, and hence the peak of the spectral energy distribution. We measure the temperature evolution and construct bolometric light curves, and find peak luminosities of erg s−1 and lower limits on the total radiated energies of erg. The light curve shapes are diverse, with both rise and decline times spanning a factor of ∼5 and several examples of double-peaked light curves. When correcting for the flux-limited nature of our survey, we find a median peak luminosity at 4000 of and a spread of .
The posterior reversible encephalopathy syndrome is an increasingly recognised disorder. Most patients have several symptoms; seizures are the most frequent, often multiple or status epilepticus. A ...combination of seizures, visual disturbance and/or headache, in particular, should lead to an early brain MRI to reveal the typical pattern of bilateral hyperintensities on fluid attenuated inversion recovery imaging, predominantly in the parieto-occipital region. There seem to be many possible triggers, including abrupt arterial hypertension, impaired renal function, pregnancy, immunosuppressive therapies and various inflammatory conditions. The clinical outcome is excellent, with recovery within a few days, while the MRI abnormalities resolve much more slowly. Little is known about the best management. Seizures do not normally progress to chronic epilepsy so antiepileptic drugs should be discontinued after about 3 months.
Pure and simple: Alkylzirconocenes generated in situ from simple alkenes are used in highly enantioselective copper‐catalyzed 1,4‐addition reactions to trisubstituted cyclic enones to generate ...quaternary centers. These reactions operate at room temperature under a range of conditions and tolerate many functional groups. Cp=cyclopentadienyl, Tf=trifluoromethanesulfonyl.
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