Gate-tunable photoemission from graphene transistors

In this Letter, we report gate-tunable X-ray photoelectron emission from back-gated graphene transistors. The back-gated transistor geometry allows us to study photoemission from graphene layer and the dielectric substrate at various gate voltages. Application of gate voltage electrostatically dopes graphene and shifts the binding energy of photoelectrons in various ways depending on the origin and the generation mechanism(s) of the emitted electrons. The gate-induced shift of the Fermi energy of graphene alters the binding energy of the C 1s electrons, whereas the electric field of the gate electrodes shift the binding energy of core electrons emitted from the gate dielectric underneath the graphene layer. The gradual change of the local potential through depths of the gate dielectric provides quantitative electrical information about buried interfaces. Our results suggest that gate-tunable photoemission spectra with chemically specific information linked with local electrical properties opens new routes to elucidating operation of devices based especially on layered materials. © 2014 American Chemical Society

Hydatid Disease of the Femur with an Extraosseous Extent due to a Former Biopsy Complicated by a Pathological Fracture

Hydatid disease of the bone represents about 1–2.5% of all human hydatid disease. Spine is the most affected part of the skeleton with 50% incidence of all bone hydatidosis. Extraspinal bone hydatidosis is much rare. Diagnosis is difficult in the bone hydatid disease. Bone tumors, tumor-like lesions, and specific and nonspecific infections should be considered in the differential diagnosis. Radiological, laboratory, and clinical findings combined with strong element of suspicion are the key for diagnosis. Bone biopsies should be avoided because of the danger of anaphylaxis, sensitization, and spread. This paper describes the management of a patient with primary hydatidosis of the femur, which had been complicated by an extraosseous involvement, cortical erosion, and a pathological fracture due to a former needle biopsy

Influence of the alkali-silica reaction on the mechanical degradation of concrete

The alkali-silica reaction (ASR) is an important problem that has yet to be completely understood. Owing to the complexity of thisphenomenon, a number of studies have been conducted to characterize its kinetics, its impact on the material, and its structural consequences.This paper focuses on the deteriorating impact of ASR on concrete material, not only in terms of concrete swelling but also in considerationof the induced mechanical degradation. The relationships between concrete expansion and various engineering properties, which are keyparameters in structural assessments, are investigated. First, new mechanical test results are presented. Second, available literature data on theevolution of engineering properties of ASR-affected concrete under free-expansion conditions are collected and statistically analyzed. Theelastic modulus was found to be the best indicator for identifying the progression of ASR in concrete. Conversely, the evolution of compressivestrength was observed to potentially mask damage resulting from the ASR. The tensile behavior of the affected concrete was betterrepresented by the splitting tensile test.Applied MechanicsMaterials and Environmen

Improved fiber distribution and mechanical properties of engineered cementitious composites by adjusting the mixing sequence

Engineered cementitious composites (ECC) is a class of ultra ductile fiber reinforced cementitious composites, characterized by high ductility and tight crack width control. The polyvinyl alcohol (PVA) fiber with a diameter of 39 lm and a length of 6-12 mm is often used. Unlike plain concrete and normal fiber reinforced concrete, ECC shows a strain-hardening behavior under tensile load. Apart from the mix design, the fiber distribution is another crucial factor for the mechanical properties of ECC, especially the ductility. In order to obtain a good fiber distribution, the plastic viscosity of the ECC mortar before adding fibers needs to be controlled, for example, by adjusting water-to-powder ratio or chemical admixtures. However, such adjustments have some limitations and may result in poor mechanical properties of ECC. This research explores an innovative approach to improve the fiber distribution by adjusting the mixing sequence. With the standard mixing sequence, fibers are added after all solid and liquid materials are mixed. The undesirable plastic viscosity before the fiber addition may cause poor fiber distribution and results in poor hardened properties. With the adjusted mixing sequence, the mix of solid materials with the liquid material is divided into two steps and the addition of fibers is between the two steps. In this paper, the influence of different water mixing sequences is investigated by comparing the experimental results of the uniaxial tensile test and the fiber distribution analysis. Compared with the standard mixing sequence, the adjusted mixing sequence increases the tensile strain capacity and ultimate tensile strength of ECC and improves the fiber distribution. This concept is further applied in the development of ECC with high volume of sand.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94190/1/zhou-improced-fiber-distribution-2012.pd

A tool for concrete performance assessment for ASR affected structures: An outlook

This paper outlines a project (namely PAT-ASR) which entails the development of a multi scale material performance assessment model on simulation of alkali silica reaction deployment and its effects on concrete durability. Performance models require a multi scale approach from micro (namely reaction chemistry) to macro level studies (namely structural mechanics). PAT-ASR aims to combine the tasks of guidelines on ASR prevention and control in a comprehensive integrated tool. This project involves experimental studies, among others including the determination of mechanical properties of ASR gel. A computational model, in conjunction with the already developed Lattice Models, will be used for simulating crack patterns in a concrete matrix. A statistical approach to sample data, harvesting from literature, can be used to increase the reliability of such a prediction model. Final integrated support tool will provide a guideline for engineers on ASR conscious design and a full-scale technical report on the subject.Structural EngineeringCivil Engineering and Geoscience

Assessment of the self-healing capacity of cementitious materials through active thin sections

Since self-healing of cementitious materials can theoretically improve the service-life of concrete structures, it has gathered significant attention from both researchers and industry during the last two decades. Many researchers have proposed different methods to assess and quantify the self-healing capacity (i.e. the ability of cementitious materials to heal cracks) that is generated in concrete autogenously as well as autonomously. Even though many methodologies can be found in the literature, a way to accurately quantify the healing products produced by any self-healing mechanism has not been yet achieved. In this study, a methodology is proposed to observe and to quantify in-time formation of healing products based on active thin sections. Thin sections of Portland cement paste have been prepared with no epoxy impregnation to facilitate reactions between the cement matrix and the surrounding environment. Artificial cracks (260 μm wide) were induced at 28 days of age and the crystal growth was continuously monitored up to 28 days of self-healing. Through image analysis of the micrographs, it was calculated that the autogenous self-healing capacity of paste (triggered by portlandite carbonation in uncontrolled indoor conditions) was around 55% after 28 days of self-healing. Healing products were further characterised through Environmental Scanning Electron Microscope analysis. Based on the results obtained in this study, the proposed methodology seems to be promising to compare the self-healing mechanisms triggered by different healing agents.Materials and Environmen