Highly Nonlinear Solitary Waves for Rail Buckling Prevention

One of the major structural problems in the railroads made of continuous welded rails is buckling in hot weather and breakage or pulling apart in cold weather. Buckling is usually caused by the high compressive stress due to thermal load or weak track conditions, and sometimes vehicle loads. The prevention of track buckling is related to the determination of the temperature, called rail neutral temperature, at which the net longitudinal force in the rail is zero. In the project presented in this thesis we investigated the capability of a novel sensing system to indirectly measure applied stress in rails and predict incipient buckling. This system consists of a simple and cost-effective transducer, recently developed at the University of Pittsburgh, which enables the generation and detection of highly nonlinear solitary waves (HNSWs), which are compact non-dispersive mechanical waves that can form and travel in highly nonlinear systems such as granular, layered, or porous materials, where they are conventionally generated by the mechanical impact of a striker. To prove the feasibility of this novel system to predict buckling temperature or measure applied stress, we investigated numerically and experimentally the interaction between solitary waves propagating along a chain of granular particles and slender beams of different shapes, lengths, and boundary conditions. We found that the geometric and mechanical properties of the beam or thermal stress applied to the beam alter certain features of the solitary waves. Overall, the work presented in this thesis was articulated in four main tasks: 1) literature review; 2) create a semi-analytical model; 3) design and test new transducers; and 4) conduct a series of experiments including a field test at the University of California, San Diego. This HNSWs approach does not require many electronic accessories and shows a good sensitivity to the properties of the material that is at the interface with the chain of particles. Moreover, it only observes the propagation of solitary waves within the transducer without the waves in the rail

Magnetic Resonance Imaging for the Functional Analysis of Tissues and Biomaterials

Articular cartilage provides mechanical load dissipation and lubrication between joints, and additionally provides protects from abrasion. At present, there are no treatments to cure or attenuate the degradation of cartilage. Early detection and the ability to monitor the progression of osteoarthritis is important for developing effective therapies. However, few reliable imaging biomarkers exist to detect cartilage disease before advanced degeneration in the tissue. One specialized MRI technique, termed displacements under applied loading by MRI (dualMRI), was developed to measure displacements and strain in musculoskeletal tissues, hydrogels and engineered constructs. However, deformation information does not directly describe spatial distributions of tissue properties (e.g. stiffness), which is critical to the understanding of disease progression. To achieve the stiffness measurement, we developed and validated an inverse modeling workflow that combined dualMRI, to directly measure intratissue deformation, with topology optimization in the application of heterogeneous (layered) materials representative of the complex gradient architecture of articular cartilage. We successfully reconstructed bi-layer stiffness from ideal displacements calculated from forward simulation as well as from experimental data measured from dualMRI. To monitor the progression of osteoarthritis, we measured and analyzed biomechanical changes of sheep stifle cartilage after meniscectomy. We found that 2nd principal strain and max shear strain in the femur contact region are sensitive to cartilage degeneration at different stages and compared to more conventional methods like quantitative MRI. To investigate the biomechanical changes in articular cartilage with defect and repair, we implanted decellularized cartilage implant into sheep cartilage defect and evaluate the repair results using quantitative MRI and dualMRI. We found that implants placed in joints demonstrated lower strains compared to joints with untreated defects

Influence of a biofilm bioreactor on water quality and microbial communities in a hypereutrophic urban river.

Biofilms play an important role in degradation, transformation and assimilation of anthropogenic pollutants in aquatic ecosystems. In this study, we assembled a tubular bioreactor containing a biofilm substrate and aeration device, which was introduced into mesocosms to explore the effects of bioreactor on physicochemical and microbial characteristics of a hypereutrophic urban river. The biofilm bioreactor greatly improved water quality, especially by decreasing dissolved inorganic nitrogen (DIN) concentrations, suggesting that biofilms were the major sites of nitrification and denitrification with an oxygen concentration gradient. The biofilm bioreactor increased the abundance of planktonic bacteria, whereas diversity of the planktonic microbial community decreased. Sequencing revealed that Proteobacteria, Bacteroidetes, Planctomycetes, and Actinobacteria were the four predominant phyla in the planktonic microbial community, and the presence of the biofilm bioreactor increased the relative abundance of Proteobacteria. Variations in microbial communities were most strongly affected by the presence of the biofilm bioreactor, as indicated by principal component analysis (PCA) and redundancy analysis (RDA). This study provides valuable insights into changes in ecological characteristics associated with self-purification processes in hypereutrophic urban rivers, and may be of important for the application of biofilm bioreactor in natural urban river

In vivo articular cartilage deformation: noninvasive quantification of intratissue strain during joint contact in the human knee

The in vivo measurement of articular cartilage deformation is essential to understand how mechanical forces distribute throughout the healthy tissue and change over time in the pathologic joint. Displacements or strain may serve as a functional imaging biomarker for healthy, diseased, and repaired tissues, but unfortunately intratissue cartilage deformation in vivo is largely unknown. Here, we directly quantified for the first time deformation patterns through the thickness of tibiofemoral articular cartilage in healthy human volunteers. Magnetic resonance imaging acquisitions were synchronized with physiologically relevant compressive loading and used to visualize and measure regional displacement and strain of tibiofemoral articular cartilage in a sagittal plane. We found that compression (of 1/2 body weight) applied at the foot produced a sliding, rigid-body displacement at the tibiofemoral cartilage interface, that loading generated subject- and gender-specific and regionally complex patterns of intratissue strains, and that dominant cartilage strains (approaching 12%) were in shear. Maximum principle and shear strain measures in the tibia were correlated with body mass index. Our MRI-based approach may accelerate the development of regenerative therapies for diseased or damaged cartilage, which is currently limited by the lack of reliable in vivo methods for noninvasive assessment of functional changes following treatment

The treatment of a Morel-Lavallée lesion of the thigh with incision and drainage along with tissue debridement and a surgically placed drain: A case report and literature review

BackgroundA Morel-Lavallée lesion (MLL) is a rare closed degloving injury that usually occurs around the hips and is associated with pelvic fractures after high-energy trauma, which is commonly overshadowed by other severe post-traumatic manifestations. An isolated MLL, mostly caused by low-energy violence, is even rarer. Thus, the rates of misdiagnosis and missed diagnosis are often high. In this case report and literature review, we review the pathophysiology, clinical manifestations, imaging data, and treatment of this lesion to increase awareness of this rare disease.Case reportWe report the case of an isolated MLL in the right thigh caused by trauma, which happened to be one of missed diagnosis both at the initial visit and at the return visit of the patient, with a significant sign of a mass on MRI. Given the size of the lesion, open debridement and irrigation were adopted to treat the lesion, and the patient recovered well post-operatively.ConclusionYoung surgeons should pay attention to the MLL with sufficient recognization to avoid missed diagnosis and misdiagnosis. Comprehensive physical examination and imaging data play important roles in the diagnosis of MLL. In the early stages of this injury, a detailed history review combined with physical examination and MRI, can reduce the rates of missed diagnosis and misdiagnosis. The choice of the therapeutic scheme depends on the size and severity of the lesion. For an isolated MLL, compared with conservative treatments, we suggest that incision and drainage, along with tissue debridement and a surgically placed drain, will reduce the rates of infection and recurrence

Finite deformation elastography of articular cartilage and biomaterials based on imaging and topology optimization

Tissues and engineered biomaterials exhibit exquisite local variation in stiffness that defines their function. Conventional elastography quantifies stiffness in soft (e.g. brain, liver) tissue, but robust quantification in stiff (e.g. musculoskeletal) tissues is challenging due to dissipation of high frequency shear waves. We describe new development of finite deformation elastography that utilizes magnetic resonance imaging of low frequency, physiological-level (large magnitude) displacements, coupled to an iterative topology optimization routine to investigate stiffness heterogeneity, including spatial gradients and inclusions. We reconstruct 2D and 3D stiffness distributions in bilayer agarose hydrogels and silicon materials that exhibit heterogeneous displacement/strain responses. We map stiffness in porcine and sheep articular cartilage deep within the bony articular joint space in situ for the first time. Elevated cartilage stiffness localized to the superficial zone is further related to collagen fiber compaction and loss of water content during cyclic loading, as assessed by independent T2 measurements. We additionally describe technical challenges needed to achieve in vivo elastography measurements. Our results introduce new functional imaging biomarkers, which can be assessed nondestructively, with clinical potential to diagnose and track progression of disease in early stages, including osteoarthritis or tissue degeneration. </div

High lubricity meets load capacity: cartilage mimicking bilayer structure by brushing up stiff hydrogels from subsurface

Natural articular cartilage has ultralow friction even at high squeezing pressure. Biomimicking cartilage with soft materials has been and remains a grand challenge in the fields of materials science and engineering. Inspired by the unique structural features of the articular cartilage, as well as by its remarkable lubrication mechanisms dictated by the properties of the superficial layers, a novel archetype of cartilage‐mimicking bilayer material by robustly entangling thick hydrophilic polyelectrolyte brushes into the subsurface of a stiff hydrogel substrate is developed. The topmost soft polymer layer provides effective aqueous lubrication, whereas the stiffer hydrogel layer used as a substrate delivers the load‐bearing capacity. Their synergy is capable of attaining low friction coefficients (order 0.010) under heavily loaded conditions (order 10 MPa contact pressure) in water environment, a performance incredibly close to that of natural articular cartilage. The bioinspired material can maintain low friction even when subjected to 50k reciprocating cycles under high contact pressure, with almost no wear observed on the sliding track. These findings are theoretically explained and compounded by multiscale simulations used to shed light on the mechanisms responsible for this remarkable performance. This work opens innovative technology routes for developing cartilage‐mimicking ultralow friction soft materials

Challenges in QCD matter physics - The Compressed Baryonic Matter experiment at FAIR

Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (sqrt(s_NN) = 2.7 - 4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (mu_B > 500 MeV), effects of chiral symmetry, and the equation-of-state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2022, in the context of the worldwide efforts to explore high-density QCD matter.Comment: 15 pages, 11 figures. Published in European Physical Journal

The Ets Transcription Factor GABP Is a Component of the Hippo Pathway Essential for Growth and Antioxidant Defense

这是周大旺教授继2009年首次发现了Hippo信号通路在哺乳动物中控制器官大小及肿瘤发生具有重要作用后的又一重大研究成果，该研究系统阐述了 YAP基因在转录调控水平上的的调控机理，进一步完善了人们对Hippo信号通路的认识，也为由YAP调控异常所引发的癌症提供了一个潜在的治疗靶点。 该论文的第一作者为博士生吴黉坦和硕士生肖玉波和张世浩, 通讯作者是周大旺教授和陈兰芬副教授，该工作是与厦门市中医院、中山医院和医学高等专科学校等单位合作完成的。周大旺教授是中央首批“青年千人计划”入选者并获得国家首批“优秀青年科学基金”资助。The transcriptional coactivator Yes-associated protein (YAP) plays an important role in organ-size control and tumorigenesis. However, how Yap gene expression is regulated remains unknown. This study shows that the Ets family member GABP binds to the Yap promoter and activates YAP transcription. The depletion of GABP downregulates YAP, resulting in a G1/S cell-cycle block and increased cell death, both of which are substantially rescued by reconstituting YAP. GABP can be inactivated by oxidative mechanisms, and acetaminophen-induced glutathione depletion inhibits GABP transcriptional activity and depletes YAP. In contrast, activating YAP by deleting Mst1/Mst2 strongly protects against acetaminophen-induced liver injury. Similar to its effects on YAP, Hippo signaling inhibits GABP transcriptional activity through several mechanisms. In human liver cancers, enhanced YAP expression is correlated with increased nuclear expression of GABP. Therefore, we conclude that GABP is an activator of Yap gene expression and a potential therapeutic target for cancers driven by YAP