Influence of live -load deflections on superstructure performance of slab on steel stringer bridges

High performance steel (HPS), specifically HPS 70W, was introduced to the bridge market in the United States in the late 1990s. With its added strength, greater durability, and improved weldability, HPS allows engineers to design longer and shallower spans, which may increase the live-load deflections. The AASHTO Standard Specification limits live-load deflections to L/800 for ordinary bridges and L/1000 for bridges in urban areas subjected to pedestrian use. Bridges designed by the AASHTO LRFD Specification have an optional deflection limit. Previous research focused on evaluating AASHTO live-load deflection limits showed that the justification for existing deflection limits was not clearly defined and the best available information indicated that they were initiated to control undesirable bridge vibrations and assure user comfort. Significant design costs may be saved if more rational live-load serviceability criteria can be adopted. Bridge design specifications from other countries do not commonly employ direct live-load deflection limits. Vibration control is often achieved through a relationship between the first flexural natural frequency of the bridge and live-load deflection. However no direction is provided to how to calculate the flexural natural frequency.;This research establishes the rationale behind existing design provisions and compares AASHTO provisions to design methods used in other countries. The effect of AASHTO and other existing live-load deflection limits on steel bridge design and performance are evaluated through a parametric design study and analysis of existing typical highway bridges. In this work, 3D FEA tools have been developed to investigate the natural frequency of continuous span bridges and have been employed in a comprehensive parametric study. From these results, practical and simplified equations are proposed to predict the natural frequencies of continuous span bridges to be used in conjunction with frequency based serviceability limit states

Embarrassingly Parallel Acceleration of Global Tractography via Dynamic Domain Partitioning

Global tractography estimates brain connectivity by organizing signal-generating fiber segments in an optimal configuration that best describes the measured diffusion-weighted data, promising better stability than local greedy methods with respect to imaging noise. However, global tractography is computationally very demanding and requires computation times that are often prohibitive for clinical applications. We present here a reformulation of the global tractography algorithm for fast parallel implementation amendable to acceleration using multi-core CPUs and general-purpose GPUs. Our method is motivated by the key observation that each fiber segment is affected by a limited spatial neighborhood. In other words, a fiber segment is influenced only by the fiber segments that are (or can potentially be) connected to its two ends and also by the diffusion-weighted signal in its proximity. This observation makes it possible to parallelize the Markov chain Monte Carlo (MCMC) algorithm used in the global tractography algorithm so that concurrent updating of independent fiber segments can be carried out. Experiments show that the proposed algorithm can significantly speed up global tractography, while at the same time maintain or even improve tractography performance

Controlled Synthesis of Organic/Inorganic van der Waals Solid for Tunable Light-matter Interactions

Van der Waals (vdW) solids, as a new type of artificial materials that consist of alternating layers bonded by weak interactions, have shed light on fascinating optoelectronic device concepts. As a result, a large variety of vdW devices have been engineered via layer-by-layer stacking of two-dimensional materials, although shadowed by the difficulties of fabrication. Alternatively, direct growth of vdW solids has proven as a scalable and swift way, highlighted by the successful synthesis of graphene/h-BN and transition metal dichalcogenides (TMDs) vertical heterostructures from controlled vapor deposition. Here, we realize high-quality organic and inorganic vdW solids, using methylammonium lead halide (CH3NH3PbI3) as the organic part (organic perovskite) and 2D inorganic monolayers as counterparts. By stacking on various 2D monolayers, the vdW solids behave dramatically different in light emission. Our studies demonstrate that h-BN monolayer is a great complement to organic perovskite for preserving its original optical properties. As a result, organic/h-BN vdW solid arrays are patterned for red light emitting. This work paves the way for designing unprecedented vdW solids with great potential for a wide spectrum of applications in optoelectronics

Requisite chromatin remodeling for myeloid and erythroid lineage differentiation from erythromyeloid progenitors

The mammalian SWitch/Sucrose Non-Fermentable (SWI/SNF) chromatin-remodeling BAF (BRG1/BRM-associated factor) complex plays an essential role in developmental and pathological processes. We show that the deletion of Baf155, which encodes a subunit of the BAF complex, in the Tie2(+) lineage (Baf155 (CKO) leads to defects in yolk sac myeloid and definitive erythroid (EryD) lineage differentiation from erythromyeloid progenitors (EMPs). The chromatin of myeloid gene loci in Baf155 CKO EMPs is mostly inaccessible and enriched mainly by the ETS binding motif. BAF155 interacts with PU.1 and is recruited to PU.1 target gene loci together with p300 and KDM6a. Treatment of Baf155 CKO embryos with GSK126, an H3K27me2/3 methyltransferase EZH2 inhibitor, rescues myeloid lineage gene expression. This study uncovers indispensable BAF-mediated chromatin remodeling of myeloid gene loci at the EMP stage. Future studies exploiting epigenetics in the generation and application of EMP derivatives for tissue repair, regeneration, and disease are warranted