An Investigation of the Mechanical and Physical Characteristics of Cement Paste Incorporating Different Air Entraining Agents using X-ray Micro-Computed Tomography

Improving the thermal insulation properties of cement-based materials is the key to reducing energy loss and consumption in buildings. Lightweight cement-based composites can be used efficiently for this purpose, as a structural material with load bearing ability or as a non-structural one for thermal insulation. In this research, lightweight cement pastes containing fly ash and cement were prepared and tested. In these mixes, three different techniques for producing air voids inside the cement paste were used through the incorporation of aluminum powder (AL), air entraining agent (AA), and hollow microspheres (AS). Several experiments were carried out in order to examine the structural and physical characteristics of the cement composites, including dry density, compressive strength, porosity and absorption. A Hot Disk device was used to evaluate the thermal conductivity of different cement composites. In addition, X-ray micro-computed tomography (micro-CT) was adopted to investigate the microstructure of the air-entrained cement pastes and the spatial distribution of the voids inside pastes without destroying the specimens. The experimental results obtained showed that AS specimens with admixture of hollow microspheres can improve the compressive strength of cement composites compared to other air entraining admixtures at the same density level. It was also confirmed that the incorporation of aluminum powder creates large voids, which have a negative effect on specimens’ strength and absorption.EC/H2020/841592/EU/Ultra-Lightweight Concrete for 3D printing technologies/Ultra-LightCon-3

Z3-graded Grassmann Variables, Parafermions and their Coherent States

A relation between the $Z_3$-graded Grassmann variables and parafermions is established. Coherent states are constructed as a direct consequence of such a relationship. We also give the analog of the Bargmann-Fock representation in terms of these Grassmann variables.Comment: 8 page

New method for nonparaxial beam propagation

A new method for solving the wave equation is presented that is nonparaxial and can be applied to wide-angle beam propagation. It shows very good stability characteristics in the sense that relatively larger step sizes can be taken. An implementation by use of the collocation method is presented in which only simple matrix multiplications are involved and no numerical matrix diagonalization or inversion is needed. The method is hence faster and is also highly accurate

Process Variation Analysis for MEMS Design

Process variations, incurred during the fabrication stage of MEMS structures, may lead to substantially different performance than the nominal one. This is mainly due to the small variation of the geometry of the structure with respect to the ideal design. In this paper we propose an approach to estimate performance variations for general planar suspended MEMS structure for low frequency applications. This approach is based on two complementary techniques, one probabilistic and the other deterministic. The former technique, based on the Monte-Carlo method, defines a random distribution on the geometric variables and evaluates the possible outcome performance by sampling that distribution. The latter technique, based on robust optimization and semidefinite programming (SDP) approximations [5], finds bounds on performance parameters given the bounds on the geometric variables, i.e. it considers the worst case scenario. Both techniques have been integrated with SUGAR, a simulation tool for MEMS devices available to the public [4] [2], and tested on different types of folded springs

Determining the structure of Ru(0001) from low-energy electron diffraction of a single terrace

While a perfect hcp (0001) surface has three-fold symmetry, the diffraction patterns commonly obtained are six-fold symmetric. This apparent change in symmetry occurs because on a stepped surface, the atomic layers on adjacent terraces are rotated by 180 degrees. Here we use a Low-Energy Electron Microscope to acquire the three-fold diffraction pattern from a single hcp Ru terrace and measure the intensity-vs-energy curves for several diffracted beams. By means of multiple scattering calculations fitted to the experimental data with a Pendry R-factor of 0.077, we find that the surface is contracted by 3.5(+-0.9) at 456 K.Comment: 10 pages, 4 figures. Corrected some typos, added more details. Accepted for publication in Surface Science (Letters

Using Nyquist or Nyquist-Like Plot to Predict Three Typical Instabilities in DC-DC Converters

By transforming an exact stability condition, a new Nyquist-like plot is proposed to predict occurrences of three typical instabilities in DC-DC converters. The three instabilities are saddle-node bifurcation (coexistence of multiple solutions), period-doubling bifurcation (subharmonic oscillation), and Neimark bifurcation (quasi-periodic oscillation). In a single plot, it accurately predicts whether an instability occurs and what type the instability is. The plot is equivalent to the Nyquist plot, and it is a useful design tool to avoid these instabilities. Nine examples are used to illustrate the accuracy of this new plot to predict instabilities in the buck or boost converter with fixed or variable switching frequency.Comment: Submitted to an IEEE journal in 201

Long‐term followup for rheumatoid arthritis patients in a multicenter outcomes study of silicone metacarpophalangeal joint arthroplasty

Objective Rheumatoid arthritis (RA) often results in deformities at the metacarpophalangeal (MCP) joints. Patients with severe deformities can be treated by silicone metacarpophalangeal joint arthroplasty (SMPA). The objective of the study is to prospectively compare long‐term outcomes for an SMPA surgical and a nonsurgical cohort of RA patients. Methods A total of 67 surgical and 95 nonsurgical patients with severe subluxation and/or ulnar drift of the fingers at the MCP joints were recruited from 2004–2008 in this multicenter prospective cohort study. Patients could elect to undergo SMPA or not. Outcomes included the Michigan Hand Outcomes Questionnaire (MHQ), Arthritis Impact Measurement Scales 2 (AIMS2), grip/pinch strength, Jebsen‐Taylor Test, ulnar deviation, extensor lag, and arc of motion measurements at the MCP joints. Results There was no significant difference in the mean age, race, education, and income at baseline between the 2 groups. Surgical subjects had worse MHQ function and functional measurements at baseline. At 3 years, the mean overall MHQ score and the MHQ function, activities of daily living, aesthetics, and satisfaction scores showed significant improvement in the surgical group compared to the nonsurgical group. Ulnar deviation, extensor lag, and arc of motion in the MCP and proximal interphalangeal joints also improved significantly in the surgical group. No improvement was seen in the mean AIMS2 scores and grip/pinch strength. Complications were minimal with a fracture rate of 9.5%. Conclusion RA patients with poor baseline functioning showed long‐term improvement in hand function and appearance following treatment with SMPA compared to nonsurgical controls.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93508/1/21705_ftp.pd