High Extension Rates Research Articles

From yield stress to elastic instabilities: Tuning the extensional behavior of elastoviscoplastic fluids.

In this study, we delve into the intricacies of elastoviscoplastic (EVP) fluids, particularly focusing on how polymer additives influence their extensional behavior. Our findings reveal that polymer additives significantly alter the extensional properties of the EVP fluids, such as relaxation time and extensional stresses while having negligible impact on the shear rheology. Interestingly, the modified fluids exhibit a transition from yield stress-like behavior to viscoelastic-like behavior under high extensional rates, ultimately leading to destabilization under extreme deformation. This research enhances the fundamental understanding of EVP fluids and highlights potential advancements in applications, especially in precision-demanding fields like 3D printing.

Stretchable, flexible fabric heater based on carbon nanotubes and water polyurethane nanocomposites by wet spinning process

Wearable heaters are essential for people living in cold regions, but creating heaters that are low-cost, lightweight, and high air permeability poses challenges. In this study, we developed a wearable heater using carbon nanotube/water polyurethane (CNT/WPU) nanocomposite fibers that achieve high extension rate and conductivity. We produced low-cost and mass-produced fibers using the wet spinning. With heat treatment, we increased the elongation rate of the fibers to 1893.8% and decreased the resistivity to 0.07 Ω*m. then wove the fibers into a heating fabric using warp knitting, that resistance is 493 Ω. Achieved a uniform temperature of 58 °C at voltage of 36 V, with a thermal stability fluctuation of −5.0 °C to +6.3 °C when bent from 0° to 360°. Our results show that wearable heaters have excellent flexibility and stretchability, due to nanocomposite fibers and special braided structure, which offer a novel idea for wearable heaters.

Holocene paleoearthquakes activity in the Nieru graben, southern Tibet

The Yadong-Gulu Rift (YGR) is the longest and most prominent rift in southern Tibet. While 14 large historical earthquakes have occurred on the northern-central segment of the YGR, historical or paleoearthquake records along the southern segment remain poorly understood. The spatial discrepancy of large earthquakes has significant implications for assessing seismic hazards along the entire YGR. To address this knowledge gap, this study presents the paleoseismic events for the first time in the Nieru graben located along the southern segment of the YGR. The excavation of a paleoseismic trench reveals two Holocene earthquakes with calibrated radiocarbon dates constraining the timing of the two events to be after 4084-3954 cal yr BP. The paleoearthquake had a magnitude of M 7. The study shows that the southern segment of the YGR experienced strong paleoseismic events, except for the Relong graben. Considering the high present extension rate of the southern rifts and the magnitude of the paleoseismic events along the Nieru graben, the southern segment of the YGR holds the potential for producing large earthquakes. Furthermore, the ongoing tectonic deformation in the area, coupled with stress changes from large earthquakes on Himalayan thrust faults, may increase the likelihood of future rupture along the active faults in the Nieru graben.

Clinical and prognostic significance of granulation patterns in somatotroph adenomas/tumors of the pituitary: a meta-analysis.

Sparsely granulated somatotroph adenoma/tumor (SGST) is thought to be more clinically aggressive than densely granulated somatotroph adenoma/tumor (DGST). However, the literature is not entirely consistent as to the disparate demographic and behavioral features of these subtypes. In this study, we conducted a meta-analysis to further clarify the demographic, clinicopathological, prognostic, and molecular characteristics of SGST versus DGST. We accessed two electronic databases to search for potential data. Pooled estimates of odds ratio (OR), mean difference (MD), and corresponding 95% confidence interval (CI) were calculated using the random-effect model. SGST was associated with younger patient age and lower male-to-female ratio (p < 0.001) compared to DGST. Clinically, SGST had larger tumor size and high rate of cavernous sinus and suprasellar extension (p < 0.001) than DGST. During postoperative follow-up, SGST was associated with a lower endocrinological remission rate (OR 0.60; 95% CI 0.40 to 0.90; p = 0.01) and a poorer response rate to SRL (OR 0.16; 95% CI 0.08-0.35; p < 0.001) in comparison to DGST. The prevalence of GSP mutations was significantly lower in SGST (OR 0.36; 95% CI 0.17 to 0.79; p = 0.01). SGST and DGST were demographically, clinicopathologically, and molecularly different from each other with the former associated with adverse treatment outcomes and poor response to medical therapy. There are still gaps in translational studies that could help us better understand the behavior of these tumors and identify potential targets in the treatment of sparsely granulated tumors.

Status in clinical and molecular characteristics of differentiated thyroid carcinoma in children and adolescents

The epidemiological, clinical, and molecular characteristics of differentiated thyroid carcinoma (DTC) in children and adolescents are different from those in adults. The incidence of DTC in children and adolescents is very low, with high rates of lymph node metastasis, extra-thyroidal extension and recurrence, but mortality is lower than that in adults. Younger children with DTC tend to show a higher rate of recurrence, more lymph node metastases, and more extra-thyroidal extension. Furthermore, studies on molecular characteristics suggest that the diversity of gene mutations causes the clinical manifestations of DTC in children and adolescents that are different from those in adults. The incidence of gene fusion is significantly higher than in adults, while the incidence of point mutations is lower than in adults, which may be closely related to clinicopathological characteristics such as high tumor aggressiveness and poor prognosis.

Ultra-slow transverse waves during continental breakup

Continental rifting is one of the four fundamental geological processes of the Wilson cycle. Rifting results from the continuous stretching of continental lithosphere and involves mechanical, thermodynamic, and rheological processes. It may be followed by a catastrophic breakup stage, which determines cessation of extensional deformation and the final separation of a continent into two distinct tectonic plates that grow by accretion of oceanic lithosphere. To date, the transition to sea−floor spreading and the conditions for the development of a new ocean have not been fully understood. We propose that a consistent description of this process must consider the existence of long−term retarded elasticity in the mantle lithosphere, the superadiabatic conditions of this layer, and the combined action of such elastic forces with the localized buoyancy arising from thermal anomalies. We present a solution of the rheological equation for a nonlinear viscoelastic model of the lithosphere mantle and numerical experiments showing that transient thermal anomalies are generated during the extension, which lead to the formation of transverse waves having wavelengths of the order of hundreds to thousands km and periods of several tens kyrs. These waves induce oscillating topography and influence the relief. Therefore, they could be responsible for eustatic cycles both in the axial rift lacustrine system and in off−axis (dendritic) lakes placed in areas of reversed drainage. At sufficiently high extension rates, deformation localizes and these ultra-slow waves determine cyclic shear failure, with formation of X−shaped cross structures through the lithosphere that prelude to the final rupture.

High-strength and flexible mechanism for body weight support

Wearable body weight support systems can assist individuals with mobility impairments in performing daily living activities with greater ease and independence. However, existing systems have limitations in terms of balancing their strength, compact size, interaction with the ground, and driving. In this paper, we present the High-Strength and Flexible Mechanism (HSFM) designed for body weight support. The HSFM utilizes a coiling truss mechanism to perform flexible transformation between a straight and spiral shape. Its complex linkages create the mechanical constraints of the structure and enhance its stiffness. Additionally, the HSFM achieved a high extension rate, effective wire-driven mechanism, and smooth shift of the grounding point. We provide a detailed description of the HSFM, including the simplest 4-linkage mechanism, its mechanical constraints, and the wire-driven mechanism. Moreover, we conducted parametric analysis and geometric calculation on the link structure. The results justified the mechanical constraints of the HSFM and ensured the high extension rate. Further, its functionality for body weight support was evaluated with the hardware and showed sufficient results in terms of strength, smooth grounding, and wire-driven. This novel mechanism has the potential to develop a wearable body weight support robot enhancing daily living activities such as sit-to-stand transfer and walking.

Effect of hypertension on the delamination and tensile strength of ascending thoracic aortic aneurysm with a focus on right lateral region

Hypertension is a major predisposing factor to initiate thoracic aortopathy. The objective of this study is to investigate effect of hypertension on delamination and tensile strength of ascending thoracic aortic aneurysms (ATAAs). A total of 35 fresh ATAA samples were harvested from 19 hypertensive and 16 non-hypertensive patients during elective aortic surgery. Peeling tests with two extension rates were performed to determine delamination strength, while uniaxial tensile (UT) tests were employed to measure failure stresses. The delamination strength and failure stresses of the ATAAs were further correlated with patient ages for hypertensive and non-hypertensive groups. The delamination strength to peel apart the ATAA tissue along the longitudinal direction was statistically significantly lower for the hypertensive patients than that of the non-hypertensive patients (35 ± 11 vs. 49 ± 9 mN/mm, p = 0.02). A higher delamination strength was measured if peeling was performed with a higher extension rate. The circumferential failure stresses were significantly lower for the hypertensive ATAAs than those of the non-hypertensive ATAAs (1.03 ± 0.27 vs. 1.43 ± 0.38 MPa, p = 0.02). Histology showed that laminar structures of elastic fibers were mainly disrupted in the hypertensive ATAAs. The longitudinal delamination strength of the ATAAs was significantly decreased and strongly correlated with ages for the hypertensive patients. Strong inverse correlations were also identified between the circumferential and longitudinal failure stresses of the ATAAs and ages for the hypertensive patients. Results suggest that the ATAAs of the elderly hypertensive patients may have a higher propensity for dissection or rupture. The dissection properties of the ATAA tissue are rate dependent.

Extensional Rheology of Poly(vinylidene fluoride)/N,N-dimethylformamide Solutions

Typical extension flow occurs in electrospinning process of Poly(vinylidene fluoride) (PVDF) solutions such that researchers focus on extensional rheological behaviors of PVDF solutions. The extensional viscosity of PVDF solutions is measured to know the fluidic deformation in extension flows. The solutions are prepared by dissolving PVDF powder into N,N-dimethylformamide (DMF) solvent. A homemade extensional viscometric device is used to produce uniaxial extension flows and the feasibility of the viscometric device is verified by applying the glycerol as a test fluid. Experimental results show that PVDF/DMF solutions are extension shinning as well as shear shinning. The Trouton ratio of thinning PVDF/DMF solution is close to three at very low strain rate and then reaches a peak value until it drops to a small value at high strain rate. Furthermore, an exponential model may be used to fit the measured values of uniaxial extensional viscosity at various extension rates, while traditional power-law model is applicable to steady shear viscosity. For 10~14% PVDF/DMF solution, the zero-extension viscosity by fitting reaches 31.88~157.53 Pa·s and the peak Trouton ratio is 4.17~5.16 at applied extension rate of less than 34 s-1. Characteristic relaxation time is λ~100 ms and corresponding critical extension rate is ε˙c~5 s-1. The extensional viscosity of very dilute PVDF/DMF solution at very high extension rate is beyond the limit of our homemade extensional viscometric device. This case needs a higher sensitive tensile gauge and a higher-accelerated motion mechanism for test.

P150 Identification of features associated with poor outcomes in pediatric patients with ulcerative proctitis: A Multicentre Study From the Paediatric IBD Porto Group of ESPGHAN

Abstract Background Ulcerative proctitis (UP) is an uncommon presentation in paediatric patients with ulcerative colitis, accounting for &amp;lt;10% of cases. Here we aimed to characterize the clinical features and natural history of paediatric patients with UP, and to identify predictors of poor outcomes. Methods A retrospective cohort study involving 37 sites affiliated with the IBD Interest group of ESPGHAN. Data were collected at different timepoints from patients diagnosed with UP aged &amp;lt;18 years between 01/01/2016-31/12/2020. Outcomes included time to initiation of systemic steroids, thiopurines or biologics, time to acute severe colitis (ASC), IBD-related admission and colectomy. Univariate cox regression was used to study the association between potential predictors and study outcomes. Results Two hundred and fifty patients with UP were included, with a median age at diagnosis of 14.5 (IQR 12.3-15.9) years, and a median follow-up of 2.7 (IQR 1.7-3.9) years. The most common presenting symptoms were bloody stools (94%), abdominal pain (59%) and diarrhea (53%). At diagnosis, the median pediatric ulcerative colitis activity index (PUCAI) score was 25 (IQR 20-35), and only 3 patients (1.3%) presented with ASC. Most children had normal inflammatory markers and albumin levels. the median fecal calprotectin level was 720 mcg/g (IQR 310-1800), while 16 patients (9.9%) had a calprotectin level &amp;lt;100mcg/g at diagnosis. Administration of oral or topical 5-ASA resulted in clinical remission rates of 52% and 48%, respectively, by the end of induction, while the combination of both led to remission in 73% of patients. The rates of treatment escalation to thiopurines and biologics at 1, 3 and 5 years were 11%, 27% and 45%, and 11%, 23% and 45%, respectively (Figure 1). Within 5 years from diagnosis, 20% of patients had presented with ASC. The PUCAI score at diagnosis of UP was highly associated with initiation of systemic steroids, thiopurines or biologics, as well as later ASC event and IBD admission, while a Mayo endoscopic score of 3 was associated with the initiation of biologics and subsequent ASC event and IBD admission (Table 1). Seven patients (4%) underwent colectomy by the end of follow-up. Among the 151/250 patients who had a repeat endoscopy, only 16% achieved mucosal healing and in 48% inflammation extended proximally. Cecal patch (P=0.009) and higher PUCAI score (P=0.009) at diagnosis, as well as higher PUCAI score (P=0.009) and lack of steroid-free clinical remission (P=0.005) by the end of induction were associated with proximal disease extension. Conclusion Disease burden is significant in paediatric patients that present with UP, with high rates of proximal disease extension and requirement for treatment escalation.

Three-dimensional simulation of capillary rheometry for an estimation of extensional viscosity

Abstract It is difficult to directly measure the steady extensional viscosity of thermoplastic composite materials, especially at high extension rates. The famous Cogswell method was derived analytically from the pressure drop of entrance flow in commercial capillary rheometers for estimating the extensional viscosity. However, using Cogswell´s extensional viscosity has always resulted in over-predictions of pressure drop. Recently, the GNF-X (eXtended Generalized Newtonian Fluid) model with a weighted shear/extensional viscosity was proposed to show the typical extension-induced vortex growth in entrance flow simulations. Under given various values of Trouton’s ratio for extensional viscosity, the GNF-X model is introduced to perform three-dimensional flow simulations of capillary rheometry over a range of apparent shear rates. The difference between the predicted pressure drops and the relevant experimental data is minimized such that the estimation of extensional viscosity is optimized herein.

Mode of continental breakup of marginal seas

AbstractWe investigated the continent-ocean transition (COT) structure of three main marginal seas in the western Pacific Ocean (South China Sea, Coral Sea, and Woodlark Basin) to determine the tectono-magmatic processes acting during continental breakup. The COT formed from the activity of a low-angle normal fault system localizing deformation during final rifting. Extension was contemporaneous with magmatic activity, including volcanic edifices, dikes, and sills in the distalmost parts of these basins. The COT shows a sharp juxtaposition in space and time of continental crust against igneous oceanic crust, and its overall structure differs from that of magma-poor or magma-rich passive-margin archetypes. We propose that this mode of breakup is characteristic of marginal seas due to the high extension rates imposed by kinematic forces of nearby subduction zones. Revealed in the context of marginal seas, this mode of breakup and the resulting COT structures highlight the underestimated diversity of continental breakup mechanisms.

Assessment of Cavitation Intensity in Accelerating Syringes of Spring-Driven Autoinjectors.

Cavitation is an undesired phenomenon that may occur in certain types of autoinjectors (AIs). Cavitation happens because of rapid changes of pressure in a liquid, leading to the formation of small vapor-filled cavities, which upon collapsing, can generate an intense shock wave that may damage the device container and the protein drug molecules. Cavitation occurs in the AI because of the syringe-drug relative displacement as a result of the syringe's sudden acceleration during needle insertion and the ensuing pressure drop at the bottom of the container. Therefore, it's crucial to analyze the potential effect of cavitation on AI. The goal of the current study is to investigate the effects of syringe and AI design parameters such as air gap size, syringe filling volume, fluid viscosity, and drive spring force (syringe acceleration) on the risk and severity of cavitation. A model autoinjector platform is built to record the syringe and cavitation dynamics which we use to estimate the cavitation intensity in terms of extension rate and to study the effects of design parameters on the severity of cavitation. Our results show the generation of an intense shock wave and a high extension rate upon cavitation collapse. The induced extension rate increases with syringe acceleration and filling volume and decreases with viscosity and air gap size. The most severe cavitation occurred in an AI device with the larger drive spring force and the syringe of a smaller air gap size filled with a less viscous fluid and a larger filling volume.

Spatio-temporal variation of seasonal heat islands mapping of Pakistan during 2000–2019, using day-time and night-time land surface temperatures MODIS and meteorological stations data

Urban heat islands (UHIs) create severe human health risks. Pakistan has about 220 million inhabitants, with 287 people per Km2 on average. Over the last 100 years, the maximum extreme temperature during the previous summer and winter seasons has been recorded. The forecast for the coming 50 years indicates a temperature rise in Pakistan, directly affecting physical and mental health. To address this challenge, this paper analyzes the spatial variability in Heat Islands (HI) in Pakistan from 2000 to 2019, combining MODIS satellite imagery with data from fifty meteorological stations. Different statistical and geostatistical models were applied, including geographically weighted regression (GWR), simple regression, and Geostatistical interpolation models. The results reveal the variations in nocturnal thermal on a fixed temperature of 11 °C, variations in frequency, and the change in day and night temperatures during summer and winter. Data fusion between MODIS and data from fifty metrological stations in Pakistan shows that spatial-temporal variation in the patterns of HI must be considered in planning processes when responding to climate change. The heat island's maximum nocturnal temperatures indicated a high rate of extension and magnitude compared to the daily recorded temperature, which implies that the overall area in the metropolitan category is covered by a temperature value of greater than 20 °C, raising severity to 10 °C in June. During June, intense night-time temperature values spread their concentration, heading towards the urban center over the Islamabad, Gilgit, Peshawar, Lahore, Quetta, and Karachi station sectors. During the day, the extension difference of the heat island was in the range of 8–10 °C, declining steadily from summer 2006 to summer 2015 before finally covering almost the entire metropolitan area. Higher values emerged after 2015–2019, rising in magnitude and expansion until 2019.

Main Factors of Mesozoic Tectonic Deformation in the Erlian Basin, Inner Mongolia, China: Insights from Physical Modelling

Erlian Basin is a Mesozoic oil and gas-bearing basin in northeast of China. The extension rate, extension direction, and stratum thickness of this rift basin have a clear control on its shape and extension. In this study, we design three sandbox models of the Erlian Basin to represent the effects of changing these three factors. The extension rate controls the timing of secondary fault formation inside the rift basin; a high extension rate promotes faster deformation inside the rift. The extension direction controls the strike of the fault inside the rift; a greater angle between the extension direction and the normal direction of the strike of the rift favors rapid evolution of internal secondary faults. The stratum thickness represents the control of sedimentation on the rift basin; the thinner the brittle layer, the wider the rift. The simulation results also show that the extension direction is the major factor controlling tectonic deformation in the basin. Stratum thickness and extension rate are secondary controlling factors. Additionally, according to geometric and kinematic similarities between typical Mesozoic rift basins in eastern and adjacent areas of China, we suggest that southeastward extension is a possible kinematic mechanism for basin formation.

The tumor volume after radical prostatectomy and its clinical impact on the prognosis of patients with localized prostate cancer

We evaluated the contribution of tumor volume (TV) to localized prostate cancer (PCa) patients’ prognosis. We retrospectively analyzed the data of 2394 patients who underwent radical prostatectomy (RP) for localized PCa. The effect of TV and tumor prostate ratio (TV/PV) on PCa patients' prognosis was analyzed through Kaplan–Meier and Cox-proportional analysis. The mean prostate volume for all patients was 36.5 ± 15.4 cc, and the mean TV was 5.9 ± 8.3 cc. A significant positive relationship was observed between the classification by risk group in D’ Amico risk classification and the National Comprehensive Cancer Network risk group (P < 0.001). The high TV showed significantly worse pathologic outcomes than the low TV in terms of high rates of extra-capsular extension, seminal vesicle invasion, and positive surgical margin (P < 0.05). The patients with high TV and TV/PV had significantly shorter biochemical recurrence-free survivals than those with low TV and TV/PV (P < 0.001). Finally, based on multivariate Cox-proportional analyses, TV and TV/PV was an independent predictor to predict shorter biochemical recurrence-free survival as both a TV (HR: 1.04, 95% CI 1.04–1.05, P < 0.001) and TV/PV (HR: 1.42, 95% CI 1.13–1.78, P = 0.003). TV was revealed to be an independent prognostic factor in the postoperative biochemical recurrence. Patients with a high number of positive core and longer tumor length were significantly related to higher TV.

Clinical-Pathological Features and Treatment Outcome of Patients With Hobnail Variant Papillary Thyroid Carcinoma.

Papillary thyroid carcinoma (PTC) with hobnail areas above 30% is classified as hobnail variant (HVPTC). Although it is widely accepted that HVPTC has a worse outcome than classical PTC, it is unclear whether PTC with hobnail features below 30% is as aggressive as HVPTC. We gathered the largest mono-institutional series of PTC with hobnail areas and HVPTC to evaluate differences in terms of pathological features of aggressiveness, molecular profile, and treatment outcome. A total of 99 PTC with hobnail features above 5% were retrospectively selected; 34 of them met the criteria for HVPTC (0.4% of all PTC diagnosed at our institution). All tumors showed high rates of extra-thyroidal extension (40.4%), lymph node metastasis (68.1% of patients with lymphadenectomy), and vascular emboli (49.5%), with no differences according to the 30% cutoff. On the other hand, distant metastases were present in HVPTC only (9.4%). Also, advanced age, advanced disease stage, and TERT promoter mutation were associated with HVPTC. More than half of the patients with follow-up had structural or biochemical persistence after 1 year from surgery. Structural persistence was significantly more common in patients with HVPTC (37.5% vs. 8.7%), while no differences were observed considering structural and biochemical persistence together. The presence of hobnail features identifies locally aggressive tumors, and, consequently, it should be always acknowledged in the pathological report. However, tumors with more than 30% hobnail areas frequently present TERT promoter mutations, advanced disease stage, and structural persistence after radioiodine ablation.

Characterization of a family B DNA polymerase from Thermococcus eurythermalis A501 and its application in PCR

DNA polymerases are widely used in PCR and play important roles in life science research and related fields. Development of high-performance DNA polymerases is of great commercial interest as the current commercial DNA polymerases could not fully satisfy the requirements of scientific research. In this study, we cloned and expressed a family B DNA polymerase (NCBI accession number TEU_RS04875) from Thermococcus eurythermalis A501, characterized its enzymatic property and evaluated its application in PCR. The recombinant Teu-PolB was expressed in E. coli and purified with affinity chromatography and ion-exchange chromatography. The enzymatic properties of Teu-PolB were characterized using fluorescence-labeled oligonucleotides as substrates. The application potential of Teu-PolB in PCR was evaluated using the phage λ genomic DNA as a template. Teu-PolB has DNA polymerase and 3'→5' exonuclease activities, and is highly thermostable with a half-life of 2 h at 98 ℃. The most suitable PCR buffer is consisted of 50 mmol/L Tris-HCl pH 8.0, 2.5 mmol/L MgCl2, 60 mmol/L KCl, 10 mmol/L (NH4)2SO4, 0.015% Triton X-100 and 0.01% BSA, and the optimal extension temperature is 68 ℃. Under the optimized conditions, a 4 kb target fragment was successfully amplified with an extension rate of 2 kb/min. The yield of the Teu-PolB amplified-DNA was lower than that of Taq DNA polymerase, but its extension rate and fidelity was higher than that of Taq and Pfu DNA polymerases. The biochemical properties of Teu-PolB demonstrate that this enzyme can be used in PCR amplification with high thermostability, good salt tolerance, high extension rate and high fidelity.

Investigation of the extensional properties of elasto-visco-plastic materials in cross-slot geometries

• Flow of an EVP material is studied in the CSER or the OSCER geometries. • The Saramito/HB model is used to account for elastic and plastic effects. • At higher ε ˙ , flow is destabilized either to time-dependent or steady asymmetric flows. • Values for the HB exponent > 0.5 must be avoided with EVP materials. The generation of a wide region of shear-free, strong extensional flow near a stagnation point has been proven to be a great challenge, especially when considering yield-stress fluids. Capillary break up and filament stretching rheometers cannot approximate such flow field when elasto-visco-plastic (EVP) materials are used, because solidification of the material near the solid disks induces strong shear contributions to the flow. To overcome these limitations, we propose the standard (CSER) and optimized (OSCER) cross-slot devices to investigate the extensional properties of yield-stress fluids. To examine and understand the nonlinear dynamics of elasto-visco-plastic materials in strong extension flows, we model the rheology of a typical Carbopol solution with the popular Saramito/Herschel-Bulkley (SRM/HB) model. Using our stabilized finite element method, PEGAFEM-V, we solve the momentum and mass conservation coupled with the constitutive equation in both cross-slot flow geometries for a wide range of flow parameters. At low extension rates, the flow is steady and symmetric, allowing for plastic effects to be evaluated. At higher extension rates, the interplay of material elasticity and plasticity destabilizes the flow leading either to time-dependent or steady asymmetric flows. Our analysis points out that adopting values for the HB exponent > 0.5 must be avoided when modeling typical EVP materials with the SRM/HB model. Finally, by performing a wide parametric analysis, we conclude that these instruments can produce ideal conditions for the characterization of various EVP materials in a wide spectrum of extension rates.

Clinical Characteristics and Long-term Outcomes of Pediatric Ulcerative Colitis: A Single-Center Experience in Korea.

Background/AimsAlthough pediatric ulcerative colitis (UC) has a different phenotype and clinical course than adult UC, its clinical features and outcomes are poorly defined, especially in Asian populations. This study investigated the clinical features and long-term outcomes of pediatric UC in a Korean population.MethodsWe retrospectively analyzed 208 patients aged <18 years diagnosed with UC between 1987 and 2013. The patient characteristics at diagnosis according to the Paris classification and the clinical course were analyzed.ResultsThe male-to-female ratio was 1.31, and the median patient age was 15.5 years. At diagnosis, 28.8% of patients had proctitis (E1), 27.8%, left-sided colitis (E2); 5.2%, extensive colitis (E3); and 38.2%, pancolitis (E4). The cumulative probabilities of extension after 5, 10, 15, and 20 years were 32.7%, 40.4%, 52.5%, and 65.8%, respectively. Eighteen patients underwent colectomy, and three patients had colorectal cancer. The cumulative probabilities of colectomy after 5, 10, 15, and 20 years were 7.1%, 8.9%, 12.6%, and 15.6%, and those of colorectal cancer after 10, 15, and 20 years were 0%, 2.1%, and 12.0%, respectively. The disease extent, Pediatric Ulcerative Colitis Activity Index severity, and systemic corticosteroid therapy were significant risk factors for colectomy. The development of primary sclerosing cholangitis was significantly associated with colorectal cancer.ConclusionsThis study provides detailed information on the disease phenotype and long-term clinical outcomes in a large cohort of Korean children with UC. They have extensive disease at diagnosis, a high rate of disease extension, and a low rate of cumulative colectomy.