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Influence of Inter-Particle Friction and Damping on the Dynamics of Spherical Projectile Impacting Onto a Soil Bed
This study investigates the dynamics of a spherical projectile impact onto a granular bed via numerical simulations by discrete element method (DEM). The granular bed is modeled as an assembly of polydisperse spherical particles and the projectile is represented by a rigid sphere. The DEM model is used to investigate the cratering process, including the dynamics of the projectile and energy transformation and dissipation. The cratering process is illustrated by tracking the motion of the projectile and granular particles in the bed. The numerical results show that the dynamics of the projectile follows the generalized Poncelet law that the final penetration depth is a power-law function of the falling height. The numerical results can match well the experimental data reported in the literature, demonstrating the reliability of the DEM model in analyzing the impact of a spherical projectile on a granular bed. Further analyses illustrate that the impact process consists of three main stages, namely the impact, penetration and collapse, as characterized by the evolution of projective velocity, strong force chains and crater shape. The initial kinetic and potential energy of the projectile is dissipated mainly by inter-particle friction which governs the projectile dynamics. The stopping time of projectile decreases as the initial impact velocity increases. The final penetration depth scales as one-third the power of total falling height and is inversely proportional to the macroscopic granular friction coefficient.National Natural Science Foundation of China (No.
42107155), the Royal Society, Sino-British Fellowship Trust
International Exchanges Award (No. IES\R2\202023), the
Fundamental Research Funds for the Central Universities
(No. 2682021CX061), the National Key R&D Program of
China (No. 2017YFC1502500
Dynamic Fragmentation of Jointed Rock Blocks During Rockslide-Avalanches: Insights From Discrete Element Analyses
The dynamic fragmentation of jointed rock blocks during rockslide avalanches has been
investigated by discrete element method simulations for a multiple arrangement of a rock block sliding
over a simple slope geometry. The rock blocks are released along an inclined sliding plane and subsequently
collide onto a flat horizontal plane at a sharp kink point. The contact force chains generated by the impact
appear initially at the bottom frontal corner of the rock block and then propagate radially upward to the top
rear part of the block. The jointed rock blocks exhibit evident contact force concentration and discontinuity of
force wave propagation near the joint, associating with high energy dissipation of granular dynamics. The
corresponding force wave propagation velocity can be less than 200 m/s, which is much smaller than that of
an intact rock (1,316 m/s). The concentration of contact forces at the bottom leads to high rock fragmentation
intensity and momentum boosts, facilitating the spreading of many fine fragments to the distal ends.
However, the upper rock block exhibits very low rock fragmentation intensity but high energy dissipation
due to intensive friction and damping, resulting in the deposition of large fragments near the slope toe. The
size and shape of large fragments are closely related to the orientation and distribution of the block joints.
The cumulative fragment size distribution can be well fitted by the Weibull’s distribution function, with very
gentle and steep curvatures at the fine and coarse size ranges, respectively. The numerical results of fragment
size distribution can match well some experimental and field observations
A Macroelement Approach for the Stability Assessment of Trees
Interaction diagrams in the generalized 3D loading space of vertical (V), horizontal (H) and moment (M) actions constitute the basis of the design of foundation structures in case of complex loads combinations. The mechanical response of such systems is frequently interpreted in terms of the ‘macroelement’ theory, where a generalized incremental constitutive relationship is introduced, linking the displacements and rotations of the foundation (playing the role of generalized strains) to the histories of applied loading components (i.e. the generalized stresses). In this paper an attempt to extend a classical macroelement framework, to the case of root-soil interaction presented. The model is calibrated on small scale experimental data on 3D printed plastic root systems, subject to combined V-H-M loads, and a parametric analysis on the main governing parameters is discussed. The comparison between numerical and experimental data suggests that the macroelement approach could be an efficient and simple analytical tool for describing the whole moment-rotation curve, overcoming the main simplifying hypotheses currently employed in arboriculture practice
Cognitive processess and cognitive reserve in multiple sclerosis
Multiple Sclerosis (MS) is characterized by motor, cognitive, and neuropsychiatric symptoms, which can occur
independently.
While MS is traditionally considered an inflammatory disease of the white matter, degeneration of gray matter is increasingly
recognized as an important contributor to the progressive cognitive decline. A protective factor against the progression
of cognitive dysfunction in MS could be the cognitive reserve, defined as resistance to brain dysfunction.
Aim of the present study is to evaluate the role of cognitive reserve for different aspects of cognitive dysfunction
of patients with MS.
We found that patients with MS and lower cognitive reserve have poorer neuropsychological performance and
slower information speed processing.
These findings support the notion that intellectual reserve may protect some aspects of cognitive function in
patients with MS
Recurrent aphthous stomatitis: Treatment and management
Background: Recurrent aphthous stomatitis consists of the presence of abrasions or ulcerations located on mucosae (oral or genital). Objectives: The aim of this article is to review the current literature providing the main causes related to recurrent aphthous stomatitis and insights into treatment and management of this clinical condition Methods: Articles matching terms that correlated with "recurrent aphthous stomatitis"were searched on PubMed, EMBASE, and Cochrane Library and selected according to their pertinence. Results: Several forms of aphthous stomatitis have been described, based on the extent (minor, major), morphology (herpetiform) and associations to other signs (Beh\ue7et syndrome or more complex inflammatory syndromes). Topical as well as systemic treatments have been described to obtain a faster remission of the aphthosis or to reduce associated symptoms such as pain. Conclusions: Recurrent aphthous stomatitis can have a mild-to-severe clinical appearance, being mainly localized on the oral mucosa or at the level of the genital area. Different strategies have been described so far for its management and treatment
Efficacy and microbiota modulation induced by limpial 2.5%, a new medical device for the inverse psoriasis treatment
(1) Inverse psoriasis (IP), also known as intertriginous, typically affects the groin, armpits, navel, intergluteal fissure, and external genitalia. Skin lesions are erythematous plaques of inflammatory nature, smooth, well-delimited, non-scaly, and non-infiltrated. Lesions may be accompanied by itching, pain, or burning sensation. The aim of this study is both to investigate the modulation of the skin microbiota induced by IP and, on the other hand, to test the effectiveness of the new biotechnological product LimpiAL 2.5%. (2) Patients affected by IP were recruited in a private practice and treated for 4 weeks with LimpiAL 2.5% exclusively. The clinical effects on the lesion skin were evaluated, and the skin microbiotas before and after treatment were compared. (3) The clinical outcomes reveled a significant beneficial effect of the tested product. At the same time, LimpiAL increased the biological diversity of the skin microbiota and exerted a significant decrease of some Corynebacterium species, and the increase of some Staphylococcus species. (4) Together, the clinical outcomes and the microbiota analysis suggest that LimpiAL treatment improves the skin condition of affected patients, basically restoring the eubiosis conditions of the affected sites and modulating the bacterial composition of the resident microbiota
Accounting for the effect of forest and fragmentation in probabilistic rockfall hazard
The presence of trees along the slope and block fragmentation at impact
strongly affect rockfall dynamics and hazard as a consequence. However,
these phenomena are rarely simulated explicitly in rockfall studies. We
performed rockfall simulations by using the 3D rockfall simulator Hy-Stone,
modeling both the presence of trees and fragmentation through specific
algorithms implemented in the code. By comparing these simulations with a
more classical approach that attempts to account implicitly for such
phenomena in the model parameters and by using a new probabilistic rockfall
hazard analysis (PRHA) method, we were able to quantify the impact of these
phenomena on the design of countermeasures and on hazard.
We demonstrated that hazard changes significantly when accounting explicitly
for these phenomena and that a classical implicit approach usually
overestimates both the hazard level and the 95th percentile of kinetic
energy, leading to an oversizing of mitigation measures.</p
Overview of the molecular determinants contributing to the expression of Psoriasis and Psoriatic Arthritis phenotypes
Psoriasis and psoriatic arthritis are multifactorial chronic disorders whose etiopathogenesis essentially derives from the alteration of several signalling pathways and the co-occurrence of genetic, epigenetic and non-genetic susceptibility factors that altogether affect the functional and structural property of the skin. Although shared and differential susceptibility genes and molecular pathways are known to contribute to the onset of pathological phenotypes, further research is needed to dissect the molecular causes of psoriatic disease and its progression towards Psoriatic Arthritis. This review will therefore be addressed to explore differences and similarities in the etiopathogenesis and progression of both disorders, with a particular focus on genes involved in the maintenance of the skin structure and integrity (keratins and collagens), modulation of patterns of recognition (through Toll-like receptors and dectin-1) and immuno-inflammatory response (by NLRP3-dependent inflammasome) to microbial pathogens. In addition, special emphasis will be given to the contribution of epigenetic elements (methylation pattern, non-coding RNAs, chromatin modifiers and 3D genome organization) to the etiopathogenesis and progression of psoriasis and psoriatic arthritis. The evidence discussed in this review highlights how the knowledge of patients' clinical and (epi)genomic make-up could be helpful for improving the available therapeutic strategies for psoriasis and psoriatic arthritis treatment
Spesolimab in patients with flare of generalized pustular psoriasis: A multicentre case-series
Dear Editor,Generalized pustular psoriasis (GPP) is a rare, potentially life-threatening, chronic inf lammatory disease character-ized by acute f lares of pustular eruptions that can be accom-panied by systemic inf lammation. GPP can be associated with chronic plaque psoriasi
Myositis/myasthenia after pembrolizumab in a bladder cancer patient with an autoimmunity-associated HLA: Immune\u2013biological evaluation and case report
Pembrolizumab (mAb to PD-1) has been recently approved for the therapy of pretreated urothelial cancer. Despite the efficacy, it is often accompanied by unpredictable and sometime severe immune-related (ir) adverse events (AEs). Here, we report the clinical and immune\u2013biological characterization of a patient with a metastatic bladder cancer who developed myositis signs (M) and a myasthenia-like syndrome (MLS) during treatment with pembrolizumab. The patient presented an autoimmunity-associated HLA haplotype (HLA-A*02/HLA-B*08/HLA-C*07/HLA-DRB1*03) and experienced an increase in activated CD8 T-cells along the treatment. The symptomatology regressed after pembrolizumab discontinuation and a pyridostigmine and steroids-based therapy. This is the first report of concurrent M and MLS appearance in cancer patients receiving pembrolizumab. More efforts are needed to define early the risk and the clinical meaning of irAEs in this setting
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