Impact dynamics of granular debris flows based on a small-scale physical model

The peak pressure of a granular debris flow at low Froude conditions can be calculated with knowledge of the stress anisotropy and the bulk density as well as the run-up height at impact. Based on a small-scale physical model, measurements of stress anisotropy and flow density values at impact are presented and applied to existing run-up prediction models, and further compared with back-calculated run-up coefficients from measured maximum impact pressures. For this purpose, we conducted 17 experiments with impact measurements and six experiments without impact measurements at Froude numbers, ranging from 0.84 to 2.41. Our results indicate that run-up heights are best reproduced by predictive models, either based on energy or mass and moment conservation, when anisotropic stress conditions, found in this study to range from 1.2 to 5.0, and bulk density variations due to impact, ranging in this study from 0.8 to 2.3, are considered. The influence of stress anisotropy and density variation on the run-up prediction differs, depending on the modelling approach. For the calculation of run-up heights based on the energy conservation concept, the influence of stress anisotropy becomes more significant with increasing Froude number, whereas for models based on mass and momentum conservation, bulk density variations have a greater influence on the estimation of the potential run-up

On the effect of surface roughness on velocity profiles and runout lengths of dry granular flows

Gravitative Massenströme wie z.B. Murgänge, werden oft physikalisch als eine Ansammlung von Partikeln modelliert, die in vereinfachten Rinnenkonfigurationen fließen. Es gibt Hinweise, dass das natürliche Fließverhalten eine kombinierte Bewegung aus Gleiten und interner Verformung aufweist.In dieser Masterarbeit wird der Einfluss der Oberflächenrauigkeit auf das Geschwindigkeitsprofil, das basale Gleiten und die Auslauflänge von trockenen, granularen Lawinen anhand von kleinskaligen Laborversuchen untersucht. Vier verschiedene Arten von Oberflächenrauigkeiten und zusätzlich eine Makrorauigkeit wurden getestet. Um auch Informationen über den Einfluss der relativen Rauigkeit zu erhalten, wurden Experimente mit drei verschiedenen Startvolumina durchgeführt. Die Fließhöhen wurden mit Lasersensoren an vier verschiedenen Positionen entlang des Kanals gemessen. Darüber hinaus wurden die Experimente mit einer Hochgeschwindigkeitskamera aufgezeichnet. Die Aufzeichnungen wurden mittels PIV (Particle Image Velocimetry) analysiert, um Geschwindigkeitsprofile abzuleiten. Die Ergebnisse zeigen, dass sich die Geschwindigkeitsprofile vom Kopf bis zum Endbereich der Lawine änderten und dass die Profile der beiden rauesten Oberflächen ähnlicher sind als jene mit der geringsten Rauigkeitskonfiguration. Der Anteil des Gleitens an der Gesamtbewegung variierte zwischen Null und der gesamten Bewegung. Die Auslauflänge verringerte sich je höher die Rauigkeit war und erhöhte sich mit höherem Startvolumen. Die Form der Geschwindigkeitsprofile änderte sich mit der Oberflächenrauigkeit und mit dem Startvolumen. Nur die Geschwindigkeitsprofile für die beiden rauesten Oberflächen zeigen unabhängig vom Startvolumen einen klaren Wendepunkt. Die Experimente unterstreichen die Bedeutung der Oberflächenrauigkeit sowie der relativen Rauigkeit für granulare Massenbewegungen und liefern weitere Daten, um Modelle zu testen.Gravitational mass flows like debris flows are often physically modelled as an assembly of particles flowing in simplified flume configurations. There is indication that natural flows exhibit a combined movement of sliding and internal deformation.In this master’s thesis the effect of surface roughness on velocity profiles, basal sliding, and the runout of small-scale, dry granular avalanches is investigated. Four different types of surface roughness and additionally one macro roughness were tested. To also get information about the influence of the relative roughness experiments with three different starting volumes were undertaken. Flow heights were measured with laser sensors at four different positions along the channel. Furthermore, the experiments were recorded with a high-speed camera. The recordings were analysed using a PIV (Particle Image Velocimetry) software to derive velocity profiles. Results show that the velocity profiles changed from the head to the tail of the flow and that the profiles of the two roughest surfaces are more alike than the smooth roughness configurations. The fraction of sliding on the total movement varied between 0 and close to unity. The runout lengths decreased the higher the roughness was and increased with higher starting volume. The shape of the velocity profiles at the deepest sections of the flows changed with surface roughness and with starting volumes. Only the velocity profiles for the two roughest surfaces show a clear inflection point independent from starting volume. The experiments highlight the importance of surface roughness as well as relative roughness for granular mass flows and provide data for model testing.submitted by: Lukas ReiderMasterarbeit Universität für Bodenkultur Wien 2020Zusammenfassung in deutscher Sprach

On the effect of surface roughness on velocity profiles and runout lengths of dry granular flows

&amp;lt;p&amp;gt;Gravitational mass flows like debris flows are often physically modelled as an assembly of particles flowing in simplified flume configurations. There is indication that natural flows exhibit a combined movement of sliding and internal deformation, which is not well understood and underrepresented in scaled laboratory experiments. In this study we investigate the effect of the surface roughness on the velocity profile and the runout of small-scale, dry granular avalanches. The experimental set-up is a 0.17 m wide flume with an inclination of 34&amp;amp;#176; for the first 1.5 m, following an 0.8 m curved transition zone with a radius of 1.7 m, and ending in a runout zone with an angle of 4&amp;amp;#176;. The tested material consisted of non-perfect spherical ceramic beads with a diameter of 2.8 to 4.3 mm. We tested four different types of surface roughness ranging from 0 to 6 mm height and additionally one macro roughness, which was higher than the maximum flow height. To also get information about the influence of the relative roughness experiments with three different starting volumes were undertaken. All fourteen experimental variations were repeated three times. Flow heights were measured with laser sensors at four different positions along the channel. Three of them were used to calculate the mean front velocity of the flowing mass in two cross sections. Furthermore, the experiments were recorded with a high-speed camera through one sidewall out of acrylic glass. The recordings were analysed using a PIV (Particle Image Velocimetry) software to derive velocity profiles in 1/1500 second time steps. Results show that the velocity profiles changed from the head to the tail of the flow and that the profiles of the two roughest surfaces are more alike than the smooth roughness configurations. The fraction of sliding on the total movement varied between 0 and close to unity. The runout length decreased the higher the roughness was and increased with higher starting volume. The shape of the velocity profiles at the deepest sections of the flows changed with surface roughness and with starting volumes. Only the velocity profiles for the two roughest surfaces show an inflection point. Our experiments highlight the importance of surface roughness as well as relative roughness for granular mass flows and provide data for model testing.&amp;lt;/p&amp;gt; </jats:p

Hematopoietic Stem Cell Transplantation in Refractory Crohn&rsquo;s Disease: Should It Be Considered?

Hematopoietic stem cell transplantation (HSCT) is widely used in benign and malignant hematological diseases. During the last decade, HSCT, mainly autologous, also gained increasing attention in the treatment of refractory autoimmune diseases. Crohn&rsquo;s disease (CD) is an inflammatory bowel disease leading to transmural inflammation potentially affecting all parts of the luminal gastrointestinal tract. Despite improving therapeutic options, including various biologics, some patients are refractory to all lines of available conservative therapy, leading to increased morbidity and reduced quality of life. Apart from surgery, HSCT might be a reasonable treatment alternative for refractory CD patients. This review aims to describe the current role of HSCT in CD and discusses the procedure, the correct patient selection, the clinical efficacy from initial remission to following relapse rates, and complications of this treatment

A combined model approach for debris-flow impact forces

&amp;lt;p&amp;gt;For the design of mitigation measures knowledge of debris-flow impact forces, usually estimated based on hydrostatic, hydrodynamic, or combined approaches, is essential. As these approaches are based on Newtonian fluids, they must be adjusted by empirical correction factors to account for the solid-fluid nature of debris flows. The values for the correction factors shown in the literature vary over a wide range and several studies showed a clear dependence with the Froude regime of debris flows.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;To better understand the correction factors and to be able to calculate them using parameters that describe the flow behaviour a total of 32 experiments were conducted in the course of the project &amp;amp;#8220;Debris flow impact forces on bridge super structures (DEFSUP)&amp;amp;#8221;, funded by the Austrian Science Fund (FWF). Two different material compositions, different water contents as well as a total impact and a bypassing of the measuring block were tested.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The experimental setup designed within the project consists of a 4 m long semi-circular channel with a diameter of 300 mm and an inclination of 20&amp;amp;#176;. The material is released from a rectangular reservoir in a dam-break scenario and accelerated with zero roughness on a length of 1.2 m and transferred to the semi-circle profile. The subsequently introduced roughness with a grain diameter of 1-2 mm generates a stationary phenomenological debris flow until it hits the measuring setup. With a starting volume of 50 kg, flow heights between 8 and 12 cm and velocities from 0.8 to 2.2 m/s were achieved according to the material composition and different water content. With these different mixtures a Froude-range from 0.6 to 3.6 was covered. In addition, normal stresses and pore water pressures were measured at the exact same point.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;A detailed analysis of the measured impact forces together with the above mentioned measured parameters showed that the hydrodynamic correction factor is a constant mainly corresponding to the liquification ratio of the debris-flow mixture. Hence, the hydrodynamic correction factor can be regarded as a drag coefficient and seems to depend mainly on the internal friction of the flowing medium. At low Froude numbers measured impact forces exceed even a full momentum transfer if the mean bulk density is used for the calculation. This indicates that the impact forces can no longer be described by the hydrodynamic approach alone. For this reason, an additional pressure term based on a hydrostatic approach is considered in the combined concept. This additional pressure term depends on the dynamics of flow (Froude number) and can be modelled via a dynamic earth pressure coefficient.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The findings from these experiments contribute to a better prediction of debris-flows impact forces in terms of their material composition and flow behaviour.&amp;lt;/p&amp;gt;</jats:p

Impaired gp100-Specific CD8+ T-Cell Responses in the Presence of Myeloid-Derived Suppressor Cells in a Spontaneous Mouse Melanoma Model

Murine tumor models that closely reflect human diseases are important tools to investigate carcinogenesis and tumor immunity. The transgenic (tg) mouse strain tg(Grm1)EPv develops spontaneous melanoma due to ectopic overexpression of the metabotropic glutamate receptor 1 (Grm1) in melanocytes. In the present study, we characterized the immune status and functional properties of immune cells in tumor-bearing mice. Melanoma development was accompanied by a reduction in the percentages of CD4+ T cells including regulatory T cells (Tregs) in CD45+ leukocytes present in tumor tissue and draining lymph nodes (LNs). In contrast, the percentages of CD8+ T cells were unchanged, and these cells showed an activated phenotype in tumor mice. Endogenous melanoma-associated antigen glycoprotein 100 (gp100)-specific CD8+ T cells were not deleted during tumor development, as revealed by pentamer staining in the skin and draining LNs. They, however, were unresponsive to ex vivo gp100-peptide stimulation in late-stage tumor mice. Interestingly, immunosuppressive myeloid-derived suppressor cells (MDSCs) were recruited to tumor tissue with a preferential accumulation of granulocytic MDSC (grMDSCs) over monocytic MDSC (moMDSCs). Both subsets produced Arginase-1, inducible nitric oxide synthase (iNOS), and transforming growth factor-β and suppressed T-cell proliferation in vitro. In this work, we describe the immune status of a spontaneous melanoma mouse model that provides an interesting tool to develop future immunotherapeutical strategies

Minimal residual ascites 3 months after TIPS implantation implicates worse clinical outcomes in patients with cirrhosis

Background &amp; Aims: Transjugular intrahepatic portosystemic shunt (TIPS) implantation is indicated for recurrent/refractory ascites in patients with cirrhosis. The prognostic impact of residual minimal ascites after TIPS implantation has not yet been investigated. Methods: We included patients with cirrhosis undergoing covered TIPS implantation for refractory ascites in Vienna (2000–2022) and Hannover (2009–2021) with available abdominal ultrasound 3 months after TIPS insertion (3M). The patients were followed up for further decompensation and transplant-free mortality. Two distinct competing risk regression models (Adjusted model I and Adjusted model II) were performed to determine the prognostic impact of no vs. minimal ascites at 3M. Results: Overall, 292 patients with male predominance (71.7%) and mostly alcohol-related liver disease (71.7%) were included. At 3M, n = 105 (36.0%) patients showed no ascites on abdominal ultrasound, whereas n = 82 (28.1%) exhibited minimal and n = 105 (36.0%) moderate/severe ascites. The portal pressure gradient after TIPS implantation was similar in the three groups (median 7 mmHg; p = 0.311). Patients with no or minimal ascites had comparable Model for End-Stage Liver Disease and Freiburg Index of Post-TIPS Survival scores at baseline and 3M. Competing risk regression models showed that minimal ascites (vs. no ascites) was an independent predictor of further decompensation (Adjusted model I: adjusted subdistribution hazard ratio [aSHR], 1.69; 95% CI, 1.03–2.77; p = 0.038; Adjusted model II: aSHR, 1.76; 95% CI, 1.07–2.88; p = 0.026) and transplant-free mortality (Adjusted model I: aSHR, 1.76; 95% CI, 1.08–2.88; p = 0.024; Adjusted model II: aSHR, 1.73; 95% CI, 1.05–2.82; p = 0.030). Conclusions: Patients with residual minimal ascites at 3M remain at higher risk for further decompensation and transplant-free mortality compared with those with no residual ascites. Impact and implications: This study evaluated the prognostic relevance of residual ascites grades in patients with advanced chronic liver disease after TIPS placement. Severe ascites was linked to the worst outcomes, underscoring the need for urgent liver transplantation evaluation. However, even minimal residual ascites significantly increased the risk of further decompensation and transplant-free mortality. These findings suggest that patients with minimal residual ascites will benefit from enhanced post-TIPS clinical monitoring. Further research is warranted to uncover the underlying mechanisms and investigate the potential of targeted interventions to improve outcomes in this vulnerable group

Factors Associated with Response to Systemic Corticosteroids in Active Ulcerative Colitis: Results from a Prospective, Multicenter Trial

Background: Among patients with ulcerative colitis, 30&ndash;50% receive corticosteroids within the first five years after diagnosis. We aimed to reconsider their effectiveness in the context of the biologic era. Methods: In this prospective, multicenter study, patients with active ulcerative colitis (Lichtiger score &ge; 4) were eligible if initiating systemic corticosteroids. The primary endpoint was clinical response (decrease in the Lichtiger score of &ge;50%) at week 4. Secondary endpoints included combined response defined as clinical response and any reduction in elevated biomarkers (CRP and/or calprotectin). Steroid dependence was assessed after three months. Results: A total of 103 patients were included. Clinical response was achieved by 73% of patients, and combined response by 68%. A total of 15% of patients were steroid-dependent. Activity of colitis did not influence short-term response to treatment but increased the risk for steroid dependence. Biologic-na&iuml;ve patients responded better than biologic-experienced patients. Past smoking history (OR 5.38 [1.71, 20.1], p = 0.003), hemoglobin levels (OR 0.76 [0.57, 0.99] for higher levels, p = 0.045), and biologic experience (OR 3.30 [1.08, 10.6], p = 0.036) were independently associated with nonresponse. Conclusion: Disease activity was not associated with short-term response to systemic corticosteroids but was associated with steroid dependence in patients with active ulcerative colitis. Exposure to biologics negatively affects response rates