Indentation vs. Uniaxial Power-law Creep of Sn-based Solder Material: A Numerical Assessment

It is crucial to understand the creep behavior of Pb-free solder alloys in electronic packaging. Typical service environments are between 298 and 373K. The thermal mismatch induced stresses acting on solder joints result in extensive rate-dependent plastic deformation. The solder alloy is potentially the weakest component in the electronic package because normal operating temperatures are already above 0.5 of the melting temperate (in K). Characterization of small-volume materials has been primarily relying on the method of indentation. The topic of concern in this study is the relationship between indentation creep and uniaxial power-law creep. Two stages of numerical simulation were involved, the first a uniaxial creep test and the other an indentation test. Both were based on rate-dependent viscoplastic behavior as the input material model for the pure Sn and Sn alloys. The objective is to establish a connection between uniaxial creep and indentation creep. For conical and pyramidal indenters, the indentation strain rate is usually expressed as (ε_I ) \u0307=1/h dh/dt , where h is the instantaneous indentation depth and t is time. By using this definition of indentation strain rate, the four materials studied here were found to have stress exponents similar to the uniaxial creep response. This similar stress exponent gives rise to a near parallel strain rate-flow stress curves (on the logarithmic scale) between uniaxial creep and indentation creep. The separation between the curves thus provides the strain rate relationship between the two forms of creep. Relatively consistent ratios between uniaxial and indentation strain rates, between 0.20 to 0.28 was obtained, and can serve as guidance for obtaining uniaxial creep behavior using the indentation technique

NUWC Universal Undersea Gripper

The main objective of the Let it Grip 2017-2018 NUWC Universal Undersea Gripper project was to design an effective and efficient individual gripper capable of securing a pay- load of various sizes, shapes, and orientations. This an important and relevant project being that the current way of securing payloads throughout the duration of a mission involves pre-installed molds that can only hold a payload of a specific size and shape. Though there were many ways to improve upon the current payload-carrying apparatus, the team decided to focus on finding the optimal shape and material of a potential universal gripper. After conducting rigorous patent and literature searches, a more thorough understanding of how to accomplish this specific, yet challenging goal was established. In addition to increased comprehension, this research aided in further understanding of competition in terms of current devices already used in practice. Upon discovering current products, an in-depth analysis of each was conducted in order to find ways to improve and capitalize on mistakes of these current products. Through a means of preliminary concept generation, 120 possible designs were produced varying from gripper material, gripper layout, as well as the individual gripper itself. These designs varied in practicality, however, led to a plethora of truly useful and feasible ideas. With these possible concepts in mind, comprehensive QFD and engineering analyses were conducted. This process was used to aid in logical analysis in terms of specific needs required by NUWC to efficiently accomplish the goal of designing the universal gripper. Using these analyses, the 120 possible concepts were narrowed down to a select two. The first of which was an extending, pyramid-shaped, hybrid design with a metallic base for increased strength, with an elastomer tip for increased shock absorption and coefficient of friction against the payload. The second design incorporated a hydraulically powered, conical telescopic device with a convex metallic head coated with an elastomer layer to increase shock absorption and coefficient of friction against the payload. Stress, shock, displacement, and factor of safety analyses were conducted on these two concepts using SolidWorks simulations to determine how each possible gripper design would perform under the acute stresses that will inevitably be subjected to it. After careful consideration, the conclusion was made that the hydraulically powered, conical telescopic convex-tipped gripper would be able to accomplish the goal of securing a payload of varying size, shape, and orientation in the most effective and efficient way possible. Throughout the year, the team conducted further research and FEA analysis including internal pressure and deformation due to load testing in order to optimize the gripper design. This resulted in redesign additions such as guiding track lines to prevent unwanted gripper rotation and chamfered edges to prevent payload damage. As a result of this work, the team was able to produce a realistically modeled 3D high quality prototype and be a considerable improvement on the current apparatus in place

Maize and soybean root front velocity and maximum depth in Iowa, USA

Quantitative measurements of root traits can improve our understanding of how crops respond to soil and weather conditions, but such data are rare. Our objective was to quantify maximum root depth and root front velocity (RFV) for maize (Zea mays) and soybean (Glycine max) crops across a range of growing conditions in the Midwest USA. Two sets of root measurements were taken every 10–15 days: in the crop row (in-row) and between two crop rows (center-row) across six Iowa sites having different management practices such as planting dates and drainage systems, totaling 20 replicated experimental treatments. Temporal root data were best described by linear segmental functions. Maize RFV was 0.62 ± 0.2 cm d−1 until the 5th leaf stage when it increased to 3.12 ± 0.03 cm d−1 until maximum depth occurred at the 18th leaf stage (860 °Cd after planting). Similar to maize, soybean RFV was 1.19 ± 0.4 cm d−1 until the 3rd node when it increased to 3.31 ± 0.5 cm d−1 until maximum root depth occurred at the 13th node (813.6 °C d after planting). The maximum root depth was similar between crops (P \u3e 0.05) and ranged from 120 to 157 cm across 18 experimental treatments, and 89–90 cm in two experimental treatments. Root depth did not exceed the average water table (two weeks prior to start grain filling) and there was a significant relationship between maximum root depth and water table depth (R2 = 0.61; P = 0.001). Current models of root dynamics rely on temperature as the main control on root growth; our results provide strong support for this relationship (R2 \u3e 0.76; P \u3c 0.001), but suggest that water table depth should also be considered, particularly in conditions such as the Midwest USA where excess water routinely limits crop production. These results can assist crop model calibration and improvements as well as agronomic assessments and plant breeding efforts in this region

Occupying wide open spaces? Late Pleistocene hunter–gatherer activities in the Eastern Levant

With a specific focus on eastern Jordan, the Epipalaeolithic Foragers in Azraq Project explores changing hunter-gatherer strategies, behaviours and adaptations to this vast area throughout the Late Pleistocene. In particular, we examine how lifeways here (may have) differed from surrounding areas and what circumstances drew human and animal populations to the region. Integrating multiple material cultural and environmental datasets, we explore some of the strategies of these eastern Jordanian groups that resulted in changes in settlement, subsistence and interaction and, in some areas, the occupation of substantial aggregation sites. Five years of excavation at the aggregation site of Kharaneh IV suggest some very intriguing technological and social on-site activities, as well as adaptations to a dynamic landscape unlike that of today. Here we discuss particular aspects of the Kharaneh IV material record within the context of ongoing palaeoenvironmental reconstructions and place these findings in the wider spatial and temporal narratives of the Azraq Basin

The environmental setting of Epipalaeolithic aggregation site Kharaneh IV

The archaeological site of Kharaneh IV in Jordan's Azraq Basin, and its relatively near neighbour Jilat 6 show evidence of sustained occupation of substantial size through the Early to Middle Epipalaeolithic (c. 24,000 - 15,000 cal BP). Here we review the geomorphological evidence for the environmental setting in which Kharaneh IV was established. The on-site stratigraphy is clearly differentiated from surrounding sediments, marked visually as well as by higher magnetic susceptibility values. Dating and analysis of off-site sediments show that a significant wetland existed at the site prior to and during early site occupation (~ 23,000 - 19,000 BP). This may explain why such a substantial site existed at this location. This wetland dating to the Last Glacial Maximum also provides important information on the palaeoenvironments and potential palaeoclimatic scenarios for today's eastern Jordanian desert, from where such evidence is scarce

Argyres-Douglas theories, the Macdonald index, and an RG inequality

We conjecture closed-form expressions for the Macdonald limits of the super-conformal indices of the (A1, A2n − 3) and (A1, D2n) Argyres-Douglas (AD) theories in terms of certain simple deformations of Macdonald polynomials. As checks of our conjectures, we demonstrate compatibility with two S-dualities, we show symmetry enhancement for special values of n, and we argue that our expressions encode a non-trivial set of renormalization group flows. Moreover, we demonstrate that, for certain values of n, our conjectures imply simple operator relations involving composites built out of the SU(2)R currents and flavor symmetry moment maps, and we find a consistent picture in which these relations give rise to certain null states in the corresponding chiral algebras. In addition, we show that the Hall-Littlewood limits of our indices are equivalent to the corresponding Higgs branch Hilbert series. We explain this fact by considering the S1 reductions of our theories and showing that the equivalence follows from an inequality on monopole quantum numbers whose coefficients are fixed by data of the four-dimensional parent theories. Finally, we comment on the implications of our work for more general (Formula presented.) superconformal field theories

Aspects of superconformal multiplets in D > 4

SCOAP

The Changing Epidemiology of Murray Valley Encephalitis in Australia: The 2011 Outbreak and a Review of the Literature

Murray Valley encephalitis virus (MVEV) is the most serious of the endemic arboviruses in Australia. It was responsible for six known large outbreaks of encephalitis in south-eastern Australia in the 1900s, with the last comprising 58 cases in 1974. Since then MVEV clinical cases have been largely confined to the western and central parts of northern Australia. In 2011, high-level MVEV activity occurred in south-eastern Australia for the first time since 1974, accompanied by unusually heavy seasonal MVEV activity in northern Australia. This resulted in 17 confirmed cases of MVEV disease across Australia. Record wet season rainfall was recorded in many areas of Australia in the summer and autumn of 2011. This was associated with significant flooding and increased numbers of the mosquito vector and subsequent MVEV activity. This paper documents the outbreak and adds to our knowledge about disease outcomes, epidemiology of disease and the link between the MVEV activity and environmental factors. Clinical and demographic information from the 17 reported cases was obtained. Cases or family members were interviewed about their activities and location during the incubation period. In contrast to outbreaks prior to 2000, the majority of cases were non-Aboriginal adults, and almost half (40%) of the cases acquired MVEV outside their area of residence. All but two cases occurred in areas of known MVEV activity.This outbreak continues to reflect a change in the demographic pattern of human cases of encephalitic MVEV over the last 20 years. In northern Australia, this is associated with the increasing numbers of non-Aboriginal workers and tourists living and travelling in endemic and epidemic areas, and also identifies an association with activities that lead to high mosquito exposure. This outbreak demonstrates that there is an ongoing risk of MVEV encephalitis to the heavily populated areas of south-eastern Australia

Rationalizing CFTs and Anyonic Imprints on Higgs Branches

We continue our program of mapping data of 4D N=2 superconformal field theories (SCFTs) onto observables of 2D chiral rational conformal field theories (RCFTs) by revisiting an infinite set of strongly coupled Argyres-Douglas (AD) SCFTs and their associated logarithmic 2D chiral algebras. First, we turn on discrete flavor fugacities (for continuous flavor symmetries) in a known correspondence between certain unrefined characters of these logarithmic theories and unrefined characters of a set of unitary 2D chiral RCFTs. Motivated by this discussion, we then study 4D Higgs branch renormalization group flows (i.e., flows activated by vevs for which only su(2)R ⊂ su(2)R × u(1)R is spontaneously broken) emanating from our AD theories from the point of view of the unitary 2D theories and find some surprises. In particular, we argue that certain universal pieces of the topological data underlying the 2D chiral algebra representations associated with the 4D infrared (IR) theory can be computed, via Galois conjugation, in the topological quantum field theory (TQFT) underlying the unitary ultraviolet (UV) chiral RCFT. The mapping of this topological data from UV to IR agrees with the fact that, in our theories, the moduli spaces we study consist of free hypermultiplets at generic points if and only if the UV TQFT is a theory of abelian anyons

Consistent truncations of supergravity and 1/2-BPS RG flows in 4d SCFTs

With the purpose of holographically describing flows from a large family of four dimensional ${\cal N}=1$ and ${\cal N}=2$ conformal field theories, we discuss truncations of seven dimensional supergravity to five dimensions. We write explicitly the reduced gauged supergravity and find BPS equations for simple configurations. Lifting these flows to eleven dimensions or Massive IIA supergravity, we present string duals to RG flows from strongly coupled conformal theories when deformed by marginal and/or relevant operators. We further discuss observables common to infinite families of ${\cal N}=1$ and ${\cal N}=2$ QFTs in this context.Comment: 28 pages plus appendixes. JHEP versio