A DEM investigation of water-bridged granular materials at the critical state

The critical state is an important concept for saturated and partially saturated granular materials as the strength and volume become constant and unique under continuous shear. By incorporating the water bridge effect, the mechanical behaviours of wet granular matters can be studied by the discrete element method (DEM). A series of DEM simulations are performed following the conventional triaxial loading path for dry and wet granular materials, and different suction values are applied at various confining stress levels. Unique critical state behaviours have been observed in both macroscopic and microscopic scales. It shows that the confining stress level plays an important role in the critical state behaviour of wet granular materials. The critical stress ratio for a wet material is not a constant value at different stress levels, and it is found that both the critical stress ratio and void ratio in wet granular matters are also much higher with a low confining stress. A framework is proposed by considering both the contact stress and the capillary stress effects to model the critical state lines. At large strain, the coordination number, the mean inter-particle force and fabric anisotropies evolve to constant critical state values for both dry and wet materials. The macro-parameters formulating the critical state stress ratio are found to be associated with the critical state anisotropies in solid skeleton and water phase fabrics, respectively

Uniaxial tensile behavior of aligned steel fibre reinforced cementitious composites

By applying an external uniform magnetic field to a fresh cement mixture during casting, an aligned steel fibre reinforced cementitious composites (ASFRC) was prepared. This investigation compares the performance of ASFRC with its counterpart—ordinary steel fibre reinforced cementitious composite (SFRC) containing randomly distributed steel fibres. First, the orientation of the steel fibres in ASFRC and SFRC specimens was examined using X-ray computed tomography analysis; this confirmed that the steel fibres were effectively aligned in the ASFRC. Then, uniaxial tensile tests were performed to allow a comparison of the uniaxial tensile stress–strain curves of the ASFRC and SFRC; and to determine the advantages, if any of ASFRC over SFRC in terms of uniaxial tensile strength (fUtu), ultimate strain (εUtu) and energy dissipation (Gf-A). The uniaxial tensile test results were also used to show that, if the tensile strength of ASFRC is equal to that of SFRC (actually slightly exceeding) using the aligned steel fibre technology, the dosage of steel fibres can be reduced at least 40%. It was also found that the alignment of the steel fibres affects the strain-hardening and multiple cracking behavior of the composites during uniaxial tension testing. Finally, the multiple cracking behavior of the composites was analyzed using a digital image correlation method. These results show that ASFRC exhibits a multiple cracking pattern at a much lower fibre content compared to SFRC

Rigidity of SU(2,2|2)-symmetric solutions in Type IIB

We investigate the existence of half-BPS solutions in Type IIB supergravity which are invariant under the superalgebra SU(2,2|2) realized on either AdS_5 x S^2 x S^1 or AdS_5 x S^3 warped over a Riemann surface \Sigma with boundary. We prove that, in both cases, the only solution is AdS_5 x S^5 itself. We argue that this result provides evidence for the non-existence of fully back-reacted intersecting D3/D7 branes with either AdS_5 x S^2 x S^1 x \Sigma or AdS_5 x S^3 x \Sigma near-horizon limits.Comment: 55 page

Web-based multimodal graphs for visually impaired people

This paper describes the development and evaluation of Web-based multimodal graphs designed for visually impaired and blind people. The information in the graphs is conveyed to visually impaired people through haptic and audio channels. The motivation of this work is to address problems faced by visually impaired people in accessing graphical information on the Internet, particularly the common types of graphs for data visualization. In our work, line graphs, bar charts and pie charts are accessible through a force feedback device, the Logitech WingMan Force Feedback Mouse. Pre-recorded sound files are used to represent graph contents to users. In order to test the usability of the developed Web graphs, an evaluation was conducted with bar charts as the experimental platform. The results showed that the participants could successfully use the haptic and audio features to extract information from the Web graphs

Mesoscopic structure and social aspects of human mobility

The individual movements of large numbers of people are important in many contexts, from urban planning to disease spreading. Datasets that capture human mobility are now available and many interesting features have been discovered, including the ultra-slow spatial growth of individual mobility. However, the detailed substructures and spatiotemporal flows of mobility - the sets and sequences of visited locations - have not been well studied. We show that individual mobility is dominated by small groups of frequently visited, dynamically close locations, forming primary "habitats" capturing typical daily activity, along with subsidiary habitats representing additional travel. These habitats do not correspond to typical contexts such as home or work. The temporal evolution of mobility within habitats, which constitutes most motion, is universal across habitats and exhibits scaling patterns both distinct from all previous observations and unpredicted by current models. The delay to enter subsidiary habitats is a primary factor in the spatiotemporal growth of human travel. Interestingly, habitats correlate with non-mobility dynamics such as communication activity, implying that habitats may influence processes such as information spreading and revealing new connections between human mobility and social networks.Comment: 7 pages, 5 figures (main text); 11 pages, 9 figures, 1 table (supporting information

Induced Pluripotent Stem Cells for Inherited Optic Neuropathies—Disease Modeling and Therapeutic Development

Background: Inherited optic neuropathies (IONs) cause progressive irreversible visual loss in children and young adults. There are limited disease-modifying treatments, and most patients progress to become severely visually impaired, fulfilling the legal criteria for blind registration. The seminal discovery of the technique for reprogramming somatic nondividing cells into induced pluripotent stem cells (iPSCs) has opened several exciting opportunities in the field of ION research and treatment. / Evidence Acquisition: A systematic review of the literature was conducted with PubMed using the following search terms: autosomal dominant optic atrophy, ADOA, dominant optic atrophy, DOA, Leber hereditary optic neuropathy, LHON, optic atrophy, induced pluripotent stem cell, iPSC, iPSC derived, iPS, stem cell, retinal ganglion cell, and RGC. Clinical trials were identified on the ClinicalTrials.gov website. / Results: This review article is focused on disease modeling and the therapeutic strategies being explored with iPSC technologies for the 2 most common IONs, namely, dominant optic atrophy and Leber hereditary optic neuropathy. The rationale and translational advances for cell-based and gene-based therapies are explored, as well as opportunities for neuroprotection and drug screening. / Conclusions: iPSCs offer an elegant, patient-focused solution to the investigation of the genetic defects and disease mechanisms underpinning IONs. Furthermore, this group of disorders is uniquely amenable to both the disease modeling capability and the therapeutic potential that iPSCs offer. This fast-moving area will remain at the forefront of both basic and translational ION research in the coming years, with the potential to accelerate the development of effective therapies for patients affected with these blinding diseases

Mitochondria and the eye—manifestations of mitochondrial diseases and their management

Historically, distinct mitochondrial syndromes were recognised clinically by their ocular features. Due to their predilection for metabolically active tissue, mitochondrial diseases frequently involve the eye, resulting in a range of ophthalmic manifestations including progressive external ophthalmoplegia, retinopathy and optic neuropathy, as well as deficiencies of the retrochiasmal visual pathway. With the wider availability of genetic testing in clinical practice, it is now recognised that genotype-phenotype correlations in mitochondrial diseases can be imprecise: many classic syndromes can be associated with multiple genes and genetic variants, and the same genetic variant can have multiple clinical presentations, including subclinical ophthalmic manifestations in individuals who are otherwise asymptomatic. Previously considered rare diseases with no effective treatments, considerable progress has been made in our understanding of mitochondrial diseases with new therapies emerging, in particular, gene therapy for inherited optic neuropathies

Quantum fluctuations in high field magnetization of 2D square lattice J1-J2 antiferromagnets

The J1-J2 square lattice Heisenberg model with spin S=1/2 has three phases with long-range magnetic order and two unconventionally ordered phases depending on the ratio of exchange constants. It describes a number of recently found layered vanadium oxide compounds. A simple means of investigating the ground state is the study of the magnetization curve and high-field susceptibility. We discuss these quantities by using the spin-wave theory and the exact diagonalization in the whole J1-J2 plane. We compare both results and find good overall agreement in the sectors of the phase diagram with magnetic order. Close to the disordered regions the magnetization curve shows strong deviations from the classical linear behaviour caused by large quantum fluctuations and spin-wave approximation breaks down. On the FM side (J1<0) where one approaches the quantum gapless spin nematic ground state this region is surprisingly large. We find that inclusion of second order spin-wave corrections does not lead to fundamental improvement. Quantum corrections to the tilting angle of the ordered moments are also calculated. They may have both signs, contrary to the always negative first order quantum corrections to the magnetization. Finally we investigate the effect of the interlayer coupling and find that the quasi-2D picture remains valid up to |J_\perp/J1| ~ 0.3.Comment: 13 pages, 6figure

Implication of the overlap representation for modelling generalized parton distributions

Based on a field theoretically inspired model of light-cone wave functions, we derive valence-like generalized parton distributions and their double distributions from the wave function overlap in the parton number conserved s-channel. The parton number changing contributions in the t-channel are restored from duality. In our construction constraints of positivity and polynomiality are simultaneously satisfied and it also implies a model dependent relation between generalized parton distributions and transverse momentum dependent parton distribution functions. The model predicts that the t-behavior of resulting hadronic amplitudes depends on the Bjorken variable x_Bj. We also propose an improved ansatz for double distributions that embeds this property.Comment: 15 pages, 8 eps figure

Combined modelling and experimental studies of failure in thick laminates under out-of-plane shear

A multi-scale model validated with out-of-plane shear testing is presented to analyse thick composite structural failure. Key features of this multi-scale analysis approach are inclusion of shear non linearity and modelling the response at a sub-laminate level whilst the structural failure is predicted at a ply level. Based on this multi-scale approach, a user-defined FORTRAN subroutine (VUMAT) has been written for ABAQUS/EXPLICIT solver and is used to model the shear nonlinearity and intra-laminar failure. In addition, a cohesive zone model is used to predict the inter-laminar delamination. The modelling has been employed to predict the failure processes for Iosipescu shear test specimens with different fibre orientations. The results show that both the failure mode and the load-displacement trace for finite element simulations agree closely with the experimental findings. This demonstrates the validity of this multi-scale, nonlinear, three-dimensional model for thick laminates. In particular, for the Iosepescu shear test, the effect of the fibres being aligned along the length of the specimen or out-of-plane is investigated as well as different dimensions of the specimen. These simulations are validated by experiments using Digital Image Correlation (DIC)