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Cell-structure and mechanical properties of closed-cell aluminum foam

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中国有色金属学会会刊：英文版 2004年第2期14卷 340-344页

作者：周芸左孝青孙加林 S.R.nutt Department of Materials Engineering Materials Science Department

The density, cell size and structure of closed-cell aluminum foam were measured by optical microscopy and image analysis. The properties and the mechanism of compressive deformation that occur in closed-cell aluminum foam were measured and discussed. The results show that the cell size of foam with density of 0.37 mg/m^3 is distributed in the range of 0.5 4.0 mm. The cell size of foam with density of 0.33 mg/m^3 is distributed in the range of 0.55.0 mm. The cell wall thickness of both types is 0.10.3 mm. The closed-cell aluminum foam almost belongs to isotropic one, with a variation of ±15% in elastic modulus and yield strength in longitudinal and transverse direction. Under compressive loading, foam materials show inhomogeneous macroscopic deformation. The site of the onset of local plastic deformation depends on the cell structure. The shape of cell is more important than size in determining the yielding susceptibility of the cells. At early stage of deformation,the deformation is localized in narrow bands having width of one cells diameter, and outside the bands the cell still remains the original shape. The cells within bands experience large permanent deformation. The band normals are usually within 20° of the loading axis.

关键词：泡沫铝单元结构机械性能泡沫金属

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Parametric Analysis of Tensile Properties of Bimodal Al Alloys by Finite Element Method

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Journal of Materials Science & Technology 2009年第2期25卷 281-288页

作者： W.L. Zhang S. Li S.R. nutt State Key Lab of MMCs Shanghai Jiao Tong University Shanghai 200030 China Department of Materials Science University of Southern California Los Angeles CA 90089 USA

An axisymmetrical unit cell model was used to represent a bimodal Al alloy that was composed of both nano-grained （NG） and coarse-grained （CG） aluminum. Effects of microstructural and materials parameters on tensile properties of bimodal AI alloy were investigated by finite element method （FEM）. The parameters analyzed included aspect ratios of CG Al and the unit cell, volume fraction of CG Al （VFCG）, and yield strength and strain hardening exponent of CG Al. Aspect ratios of CG Al and the unit cell have no significant influence on tensile stress-strain response of the bimodal Al alloy. This phenomenon derives from the similarity in elastic modulus and coefficient of thermal expansion between CG AI and NG Al. Conversely, tensile properties of bimodal Al alloy are extremely sensitive to VFCG, yield strength and strain hardening exponent of CG Al. Specifically, as VFCG increases, both yield strength and ultimate tensile strength （UTS） of the bimodal Al alloy decreases, while uniform strain of bimodal AI alloy increases. In addition, an increase in yield strength of CG Al results in an increase in both yield stress and UTS of bimodal AI alloy and a decrease in uniform strain of bimodal Al alloy. The lower capability in lowering the increase of stress concentration in NG Al due to a higher yield strength of CG Al causes the lower uniform strain of the bimodal AI alloy. When strain hardening exponent of CG Al increases, 0.2% yield stress, UTS, and uniform strain of the bimodal Al alloy increases. This can be attributed to the increased work-hardening ability of CG Al with a higher strain hardening exponent.

关键词： Nanomaterials Bimodal alloys Finite element method Tensile properties Parametric analysis

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Stepping up to meet the challenge of freezing of gait in Parkinson’s disease

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Translational Neurodegeneration 2022年第1期11卷 589-600页

作者： Simon Lewis Stewart Factor Nir Giladi Alice Nieuwboer John nutt Mark Hallett ForeFront Parkinson’s Disease Research Clinic Brain and Mind CentreSchool of Medical SciencesUniversity of SydneySydneyNSWAustralia Jean and Paul Amos Parkinson’s Disease and Movement Disorders Program Emory University School of MedicineAtlantaGAUSA Movement Disorders Unit Department of NeurologyTel-Aviv Sourasky Medical CenterSackler School of Medicine and Sagol School of NeuroscienceTel Aviv UniversityTel AvivIsrael Department of Rehabilitation Sciences KU LeuvenLeuvenBelgium Movement Disorder Section Department of NeurologyOregon Health&Science UniversityPortlandORUSA Human Motor Control Section National Institute of Neurological Disorders and StrokeNational Institutes of HealthBethesdaMDUSA.

There has been a growing appreciation for freezing of gait as a disabling symptom that causes a significant burden in Parkinson’s disease. Previous research has highlighted some of the key components that underlie the phenomenon, but these reductionist approaches have yet to lead to a paradigm shift resulting in the development of novel treatment strategies. Addressing this issue will require greater integration of multi-modal data with complex computational modeling, but there are a number of critical aspects that need to be considered before embarking on such an approach. This paper highlights where the field needs to address current gaps and shortcomings including the standardization of definitions and measurement, phenomenology and pathophysiology, as well as considering what available data exist and how future studies should be constructed to achieve the greatest potential to better understand and treat this devastating symptom.

关键词： Freezing of gait Computational modeling Standardized definitions and assessments Novel paradigms Phenomenology Pathophysiology Treatment

CCR2 enhances CD25 expression by FoxP3^(+) regulatory T cells and regulates their abundance independently of chemotaxis and CCR2^(+) myeloid cells

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Cellular & Molecular Immunology 2020年第2期17卷 123-132页

作者： Yifan Zhan Nancy Wang Ajithkumar Vasanthakumar Yuxia Zhang Michael Chopin Stephen L.nutt Axel Kallies Andrew M.Lew The Walter&Eliza Hall Institute of Medical Research ParkvilleVIC 3052Australia Department of Medical Biology University of MelbourneParkvilleVIC 3010Australia Guangzhou Institute of Paediatrics Guangzhou Women and Children’s Medical CentreGuangzhou Medical University510623 GuangzhouGuangdongChina Department of Microbiology and Immunology Peter Doherty Institute for Infection and ImmunityUniversity of MelbourneParkvilleVIC 3010Australia

A wide array of chemokine receptors,including CCR2,are known to control Treg ***,we report that CCR2 regulates Tregs beyond *** found that CCR2 deficiency reduced CD25 expression by FoxP3^(+) Treg *** a change was also consistently present in irradiation chimeras reconstituted with mixed bone marrow from wild-type(WT)and CCR2−/−***,CCR2 deficiency resulted in profound loss of CD25 ^(hi) FoxP3^(+) Tregs in secondary lymphoid organs as well as in peripheral ***2−/−Treg cells were also functionally inferior to WT ***,these changes to Treg cells did not depend on CCR2+monocytes/moDCs(the cells where CCR2 receptors are most abundant).Rather,we demonstrated that CCR2 was required for TLR-stimulated,but not TCR-or IL-2-stimulated,CD25 upregulation on Treg ***,we propose that CCR2 signaling can increase the fitness of FoxP3^(+) Treg cells and provide negative feedback to counter the proinflammatory effects of CCR2 on myeloid cells.

关键词： CCR2 CD25 organs

The flattening of spacetime hierarchy of the N,N-dimethyltryptamine brain state is characterized by harmonic decomposition of spacetime(HADES) framework

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National Science Review 2024年第5期11卷 46-55页

作者： Jakub Vohryzek Joana Cabral Christopher Timmermann Selen Atasoy Leor Roseman David J.nutt Robin L.Carhart-Harris Gustavo Deco Morten L.Kringelbach Centre for Eudaimonia and Human Flourishing Linacre CollegeDepartment of Psychiatry University of Oxford Department of Psychiatry University of Oxford Center for Music in the Brain Aarhus University Center for Brain and Cognition Computational Neuroscience GroupDepartment of Information and Communication TechnologiesUniversitat Pompeu Fabra Life and Health Sciences Research Institute School of MedicineUniversity of Minho ICVS/3B's-PT Government Associate Laboratory Centre for Psychedelic Research Department of Brain Sciences Imperial College London Departments of Neurology and Psychiatry University of California San Francisco Institució Catalana de la Recerca i Estudis Avan?ats (ICREA) Department of Neuropsychology Max Planck Institute for Human Cognitive and Brain Sciences School of Psychological Sciences Monash University

The human brain is a complex system, whose activity exhibits flexible and continuous reorganization across space and time. The decomposition of whole-brain recordings into harmonic modes has revealed a repertoire of gradient-like activity patterns associated with distinct brain functions. However, the way these activity patterns are expressed over time with their changes in various brain states remains unclear. Here, we investigate healthy participants taking the serotonergic psychedelic N,N-dimethyltryptamine(DMT) with the Harmonic Decomposition of Spacetime(HADES) framework that can characterize how different harmonic modes defined in space are expressed over time. HADES demonstrates significant decreases in contributions across most low-frequency harmonic modes in the DMT-induced brain state. When normalizing the contributions by condition(DMT and non-DMT), we detect a decrease specifically in the second functional harmonic, which represents the uni-to transmodal functional hierarchy of the brain,supporting the leading hypothesis that functional hierarchy is changed in psychedelics. Moreover, HADES'dynamic spacetime measures of fractional occupancy, life time and latent space provide a precise description of the significant changes of the spacetime hierarchical organization of brain activity in the psychedelic state.

关键词： spatio-temporal brain dynamics DMT harmonic modes