STANDARDS TO CONTROL FRACTURE IN STEEL BRIDGES THROUGH THE USE OF HIGH-TOUGHNESS STEEL AND RATIONAL INSPECTION INTERVALS

Non-redundant steel bridge systems have been used for major bridges in the United States since the late 1800’s. Designers recognized the inherent structural efficiency and economy associated with two-girder and truss systems. Unfortunately, early knowledge was limited regarding fatigue, fracture, and overall system behavior; subsequently, a small number of these structures experienced fatigue and fracture issues leading to the creation of the Fracture Control Plan (FCP). The FCP resulted in more stringent design, material, fabrication, and inspection requirements for non-redundant steel bridges; specifically, a 24 month hands-on inspection criteria for all fracture critical members was established. Significant advances have been made over the past 40 years since the original FCP was introduced. Developments in fracture mechanics, material and structural behavior, fatigue crack initiation and growth, and fabrication and inspection technologies now allow fracture to be addressed in a more integrated manner. Through these advances, it is now possible to create an integrated FCP, combining the intent of the original FCP with modern materials, design, fabrication, and inspection methodologies. The current study is focused on the development of new design standards which founded an integrated approach to prevent fracture in steel bridges through the use of high-toughness steel. The project is comprised of small-scale material testing, full-scale fracture testing of steel bridge axial and bending members, three-dimensional finite element modeling, and an analytical parametric study. Results from this research demonstrate large defects are well-tolerated by high-toughness steel. Further, rational inspection intervals were calculated to demonstrate how an integrated FCP will allow for a better allocation of owner resources while also leading to increased steel bridge safety

Fostering Student Engagement: Four Strategies

In response to studies demonstrating that poor teaching was the cause of many students leaving math, science, and engineering programs, the American Society of Civil Engineers (ASCE) developed the ExCEEd(Excellence in Civil Engineering Education) Teaching Workshop. Several faculty from the UNLV Department of Civil & Environmental Engineering and Construction have attended the highly intensive five-day workshop. To evaluate the impact on student engagement, four basic instructional strategies from the ExCEEdworkshop, applicable to all fields, were tested and assessed during the Fall 2018 semester: Questioning techniques, physical models, instructor involvement, and group work.https://digitalscholarship.unlv.edu/btp_expo/1066/thumbnail.jp

Attitude Design for the LADEE Mission

The Lunar Atmosphere and Dust Environment Explorer (LADEE) satellite successfully completed its 148-day science investigation in a low-altitude, near-equatorial lunar orbit on April 18, 2014. The LADEE spacecraft was built, managed and operated by NASA's Ames Research Center (ARC). The Mission Operations Center (MOC) was located at Ames and was responsible for activity planning, command sequencing, trajectory and attitude design, orbit determination, and spacecraft operations. The Science Operations Center (SOC) was located at Goddard Space Flight Center and was responsible for science planning, data archiving and distribution. This paper details attitude design and operations support for the LADEE mission. LADEE's attitude design was shaped by a wide range of instrument pointing requirements that necessitated regular excursions from the baseline one revolution per orbit "Ram" attitude. Such attitude excursions were constrained by a number of flight rules levied to protect instruments from the Sun, avoid geometries that would result in simultaneous occlusion of LADEE's two star tracker heads, and maintain the spacecraft within its thermal and power operating limits. To satisfy LADEE's many attitude requirements and constraints, a set of rules and conventions was adopted to manage the complexity of this design challenge and facilitate the automation of ground software that generated pointing commands spanning multiple days of operations at a time. The resulting LADEE Flight Dynamics System (FDS) that was developed used Visual Basic scripts that generated instructions to AGI's Satellite Tool Kit (STK) in order to derive quaternion commands at regular intervals that satisfied LADEE's pointing requirements. These scripts relied heavily on the powerful "align and constrain" capability of STK's attitude module to construct LADEE's attitude profiles and the slews to get there. A description of the scripts and the attitude modeling they embodied is provided. One particular challenge analysts faced was in the design of LADEE maneuver attitudes. A flight rule requiring pre-maneuver verification of in-flight maneuver conditions by ground operators prior to burn execution resulted in the need to accommodate long periods in the maneuver attitude. This in turn complicated efforts to satisfy star tracker interference and communication constraints in lunar orbit. In response to this challenge, a graphical method was developed and used to survey candidate rotation angles about the thrust vector. This survey method is described and an example of its use on a particular LADEE maneuver is discussed. Finally, the software and methodology used to satisfy LADEE's attitude requirements are also discussed in the context of LADEE's overall activity planning effort. In particular, the way in which strategic schedules of instrument and engineering activities were translated into actual attitude profiles at the tactical level, then converted into precise quaternion commands to achieve those pointing goals is explained. In order to reduce the risk of time-consuming re-planning efforts, this process included the generation of long-term projections of constraint violation predictions for individual attitude profiles that could be used to establish keep-out time-frames for particular attitude profiles. The challenges experienced and overall efficacy of both the overall LADEE ground system and the attitude components of the Flight Dynamics System in meeting LADEE's varied pointing requirements are discussed

Ecology and Evolution of Phosphorus Use in Daphnia

Understanding how populations respond to environmental change is an important challenge in contemporary biology. Ecological stoichiometry uses elemental composition of species to make predictions about success in defined conditions of elemental supply. Understanding the success of genotypes within a species as a function of their elemental composition is a first step in understanding the mechanisms generating and maintaining such variation in elemental content. I tested the extent to which P content, a pivotal element in biology, predicted growth and competition in several Daphnia genotypes. Further, I measured the use of 33P to understand the extent to which such parameters improved predictions. Genotypes showed significant variation in P content, 33P use, and growth rate. P content alone was a poor predictor of growth and competition. These results suggest that decomposing P content of an individual into physiological components of P use will improve stoichiometric models predicting growth. Further, I examined the link between phosphoglucose isomerase (PGI) and P-use efficiency (PUE). PGI genotype was shown to underlie differences in PUE in an F2 recombinant D. pulicaria population. Additionally, to better understand how multiple elements that comprise biomass covary with PUE, I quantified several elements that comprise biological tissues (i.e. ionomes) within the F2 population. Substantial variation in the ionomes of these genotypes were found, with several correlations among element concentrations. Finally, we know little about how the content and demand for these elements change across ontogeny. I tested how Daphnia ionomes vary across species and ontogeny. I found significant effects of age, species, and ontogeny on the ionome content of three species of Daphnia. Understanding the genetic basis of these patterns and the ecological implications should contribute to the integration of elements and traits, and the extent to which shifts in elemental contents impact eco-evolutionary dynamics. Ionomic datasets should be a useful diagnostic tool to decipher multi-element constraints on biomass production

Retrieval cues fail to influence contextualized evaluations.

Initial evaluations generalise to new contexts, whereas counter-attitudinal evaluations are context-specific. Counter-attitudinal information may not change evaluations in new contexts because perceivers fail to retrieve counter-attitudinal cue-evaluation associations from memory outside the counter-attitudinal learning context. The current work examines whether an additional, counter-attitudinal retrieval cue can enhance the generalizability of counter-attitudinal evaluations. In four experiments, participants learned positive information about a target person, Bob, in one context, and then learned negative information about Bob in a different context. While learning the negative information, participants wore a wristband as a retrieval cue for counter-attitudinal Bob-negative associations. Participants then made speeded as well as deliberate evaluations of Bob while wearing or not wearing the wristband. Internal meta-analysis failed to find a reliable effect of the counter-attitudinal retrieval cue on speeded or deliberate evaluations, whereas the context cues influenced speeded and deliberate evaluations. Counter to predictions, counter-attitudinal retrieval cues did not disrupt the generalisation of first-learned evaluations or the context-specificity of second-learned evaluations (Experiments 2-4), but the counter-attitudinal retrieval cue did influence evaluations in the absence of context cues (Experiment 1). The current work provides initial evidence that additional counter-attitudinal retrieval cues fail to disrupt the renewal and generalizability of first-learned evaluations

Role of disulphide bond formation in folding, secretion, and assembly of human chorionic gonadotropin subunits.

Ability of a glycoprotein hormone to fold and assemble correctly is an essential requirement for the attainment of its biological activity . Cells have a quality control system to assure that when proteins of the endoplasmic reticulum mi sfold or fail to assemble correctly they do not exit the cell. But human chorionic gonadotropin (hCG) is an exception to this rule as is illustrated by the following observations. First, both hCG subunits are secreted efficiently as unassembled monomers. Second, some mis(un)folded forms of hCG-β can be efficiently secreted from cells that do not facilitate the secretion of other misfolded proteins. Third, the efficient secretion of an assembly incompetent α-subunit occurs in spite of lacking both of its non-cystine knot disulphide bonds. And fourth, hCG heterodimers that contain misfolded α-subunits as a result of lack ing cystine knot disulphides are also secreted. In this report, we review direct ex perimental evidence demonstrating that the structural requirements necessary for the secretion of hCG subunits differ from the structural requirements necessary for hCG assembly by using disulphide bond formation as an index with which to monitor the folding, assembly, and secretion of hCG and its α - and β-subunits

Toward improved transit station access in pedestrian-unfriendly environments

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2001.Includes bibliographical references (p. 235-241).The resurgence of rail transit in the United States has introduced transit stations into environments of dispersed development oriented primarily to automobile travel. In addition, alignments for new transit lines have frequently been chosen in highway and railroad corridors where walking conditions are poor. Park-and-ride lots and feeder bus routes have facilitated access to stations in these compromised locations, while pedestrian access has often been neglected. This research examines the untapped potential of increased ridership and expanded ridership markets that can be realized through improved pedestrian access to transit stations. It finds that wider benefits to society, including reduced air pollution, increased development potential, enhanced equity, individual health benefits, and an improved quality of life can be realized through more walkable station area environments. Case studies of stations representing urban, inner suburban "greyfield", and outer suburban "greenfield" environments are undertaken to evaluate both the various impediments to pedestrian access found at different station areas, as well as to identify strategies for facilitating pedestrian access to stations in a range of contexts. The examination of specific stations is augmented by a review of previous research on pedestrian behavior and travel to arrive at specific guidelines for improving pedestrian access. Walking to stations is encouraged by: a dense network of direct and continuous routes to stations; convenient and safe opportunities for crossing streets; a perception of safety and security prevailing along pedestrian routes; the provision of information and station identification; and a level of urban vitality marked by pedestrian activity, pedestrian-oriented uses, and pedestrian-scaled design. The guidelines are applied to both an existing rapid transit system currently undergoing renovations as well as to an entirely new one now under construction: the elevated and subway lines of Chicago, Illinois, and Tren Urbano in metropolitan San Juan, Puerto Rico. Recommendations for specific interventions to improve pedestrian access to four Chicago Transit Authority rapid transit stations and two future Tren Urbano station sites, along with suggested implementation frameworks, are advanced.by Ryan Sherman Park.S.M