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San Francisco, CA, United States

URS Corporation was an engineering, design, and construction firm and a U.S. federal government contractor. Headquartered in San Francisco, California, URS was a full-service, global organization with offices located in the Americas, Europe, Africa, and Asia-Pacific. URS was acquired by AECOM on October 17, 2014. Wikipedia.

Zhang Y.,University of Science and Technology Beijing | Zuo T.T.,University of Science and Technology Beijing | Tang Z.,University of Tennessee at Knoxville | Gao M.C.,U.S. National Energy Technology Laboratory | And 4 more authors.
Progress in Materials Science | Year: 2014

This paper reviews the recent research and development of high-entropy alloys (HEAs). HEAs are loosely defined as solid solution alloys that contain more than five principal elements in equal or near equal atomic percent (at.%). The concept of high entropy introduces a new path of developing advanced materials with unique properties, which cannot be achieved by the conventional micro-alloying approach based on only one dominant element. Up to date, many HEAs with promising properties have been reported, e.g., high wear-resistant HEAs, Co1.5CrFeNi1.5Ti and Al0.2Co 1.5CrFeNi1.5Ti alloys; high-strength body-centered-cubic (BCC) AlCoCrFeNi HEAs at room temperature, and NbMoTaV HEA at elevated temperatures. Furthermore, the general corrosion resistance of the Cu 0.5NiAlCoCrFeSi HEA is much better than that of the conventional 304-stainless steel. This paper first reviews HEA formation in relation to thermodynamics, kinetics, and processing. Physical, magnetic, chemical, and mechanical properties are then discussed. Great details are provided on the plastic deformation, fracture, and magnetization from the perspectives of crackling noise and Barkhausen noise measurements, and the analysis of serrations on stress-strain curves at specific strain rates or testing temperatures, as well as the serrations of the magnetization hysteresis loops. The comparison between conventional and high-entropy bulk metallic glasses is analyzed from the viewpoints of eutectic composition, dense atomic packing, and entropy of mixing. Glass forming ability and plastic properties of high-entropy bulk metallic glasses are also discussed. Modeling techniques applicable to HEAs are introduced and discussed, such as ab initio molecular dynamics simulations and CALPHAD modeling. Finally, future developments and potential new research directions for HEAs are proposed.

Batu V.,URS Corporation
Ground Water | Year: 2010

Using a steady-state mass conservative solute transport analytical solution that is based on the third-type (or flux-type or Cauchy) source condition, a method is developed to estimate the degradation parameters of solutes in groundwater. Then, the inadequacy of the methods based on the first-type source-based analytical solute transport solution is presented both theoretically and through an example. It is shown that the third-type source analytical solution exactly satisfies the mass balance constraint at the inlet location. It is also shown that the first-type source (or constant source concentration or Dirichlet) solution fails to satisfy the mass balance constraint at the inlet location and the degree of the failure depends on the value of the degradation as well as the flow and solute transport parameters. The error in the first-type source solution is determined with dimensionless parameters by comparing its results with the third-type source solution. Methods for estimating the degradation parameter values that are based on the first-type steady-state solute transport solution may significantly overestimate the degradation parameter values depending on the values of flow and solute transport parameters. It is recommended that the third-type source solution be used in estimating degradation parameters using measured concentrations instead of the first-type source solution. Copyright © 2010 The Author(s). Journal compilation © 2010 National Ground Water Association.

A mathematical model based on the advection-dispersion equation, modified to account for growth, decay, attachment, and detachment of microorganisms, was developed to describe the transport and growth of bacteria in aquifers. Column experiments on the transport of a species of sulfate-reducing bacteria through saturated-aquifer sediment were conducted to gain a quantitative knowledge of the attachment and detachment processes. Relevant parameter values such as the attachment-site capacity of the sediment and the attachment and detachment coefficients under different conditions, were obtained by fitting the experimental data with the non-growth condition transport model. The transport model was then refined and improved to incorporate the microbial sulfate reduction mechanism. To evaluate the applicability of this model, bacterial transport in aquifers under both nutrient-rich and oligotrophic environments was modeled by employing the parameters gained from experiments and from available literature; the model results were consistent with observations reported in former studies. In addition, the results revealed that the distribution of bacteria in the aqueous phase and in the sediments is directly related to the attachment-site capacity of the sediment. Thus, the attachment-site capacity of the sediment is a key factor to evaluate the transport and growth of bacteria in aquifers. © 2009 Springer-Verlag.

Grigorian M.,MGA Structural Engineers Inc. | Grigorian C.E.,URS Corporation
Journal of Structural Engineering (United States) | Year: 2012

Performance control (PC) is the ability to design a structure in such a way as to expect predetermined modes of response at certain stages of loading, extents of damage, and/or drift ratios. The primary purpose of this paper is to complement the existing literature on performance-based plastic design of moment frames. PC is, in fact, a new analytic performance-based elastic-plastic design method for ductile structures under seismic loading. It empowers the engineer to control the design rather than investigate design-related numerical output. Failure mechanisms and stability conditions are enforced rather than tested. Unlike traditional closed-form procedures, PC enables the designer to control the response of the structure at preselected performance stages such as before and at first yield, any fraction of the failure load, or specified drift ratios up to and including incipient collapse. It offers a simple design solution to a rather complex problem. © 2012 American Society of Civil Engineers.

Rengasamy S.,U.S. National Institute for Occupational Safety and Health | Eimer B.C.,URS Corporation
Annals of Occupational Hygiene | Year: 2011

Nanoparticle (<100 nm size) exposure in workplaces is a major concern because of the potential impact on human health. National Institute for Occupational Safety and Health (NIOSH)-approved particulate respirators are recommended for protection against nanoparticles based on their filtration efficiency at sealed conditions. Concerns have been raised on the lack of information for face seal leakage of nanoparticles, compromising respiratory protection in workplaces. To address this issue, filter penetration and total inward leakage (TIL) through artificial leaks were measured for NIOSH-approved N95 and P100 and European certified Conformit'e Europe'en-marked FFP2 and FFP3 filtering facepiece respirator models sealed to a breathing manikin kept inside a closed chamber. Monodisperse sucrose aerosols (8-80 nm size) generated by electrospray or polydisperse NaCl aerosols (20-1000 nm size) produced by atomization were passed into the chamber. Filter penetration and TIL were measured at 20, 30, and 40 l min -1 breathing flow rates. The most penetrating particle size (MPPS) was ∼50 nm and filter penetrations for 50 and 100 nm size particles were markedly higher than the penetrations for 8 and 400 nm size particles. Filter penetrations increased with increasing flow rates. With artificially introduced leaks, the TIL values for all size particles increased with increasing leak sizes. With relatively smaller size leaks, the TIL measured for 50 nm size particles was ∼2-fold higher than the values for 8 and 400 nm size particles indicating that the TIL for the most penetrating particles was higher than for smaller and larger size particles. The data indicate that higher concentration of nanoparticles could occur inside the breathing zone of respirators in workplaces where nanoparticles in the MPPS range are present, when leakage is minimal compared to filter penetration. The TIL/penetration ratios obtained for 400 nm size particles were larger than the ratios obtained for 50 nm size particles at the three different flow rates and leak sizes indicating that face seal leakage, not filter penetration, contributing to the TIL for larger size particles. Further studies on face seal leakage of nanoparticles for respirator users in workplaces are needed to better understand the respiratory protection against nanoparticle exposure. © The Author 2010. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

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