A spectroscopic binary in the Hercules dwarf spheroidal galaxy

We present the radial velocity curve of a single-lined spectroscopic binary in the faint Hercules dwarf spheroidal (dSph) galaxy, based on 34 individual spectra covering more than two years of observations. This is the first time that orbital elements could be derived for a binary in a dSph. The system consists of a metal-poor red giant and a low-mass companion, possibly a white dwarf, with a 135-days period in a moderately eccentric ($e=0.18$) orbit. Its period and eccentricity are fully consistent with metal-poor binaries in the Galactic halo, while the projected semimajor axis is small, at $a_p$ sin$i$ = 38 R$_{sun}$. In fact, a very close orbit could inhibit the production of heavier elements through $s$-process nucleosynthesis, leading to the very low abundances of neutron-capture elements that are found in this star. We discuss the further implications for the chemical enrichment history of the Hercules dSph, but find no compelling binary scenario that could reasonably explain the full, peculiar abundance pattern of the Hercules dSph galaxy.Comment: 7 pages, 3 figures, accepted for publication in the Astrophysical Journa

Centrifugal Compressors 101

Short CourseThis course is aimed at engineers and technical professionals who need a broad-based introduction to centrifugal compressor design and analysis. This course starts with the basics and builds to provide a full understanding of a centrifugal compressor. The course will include the following topics: reciprocating, axial and centrifugal compressor similarities/differences; centrifugal compressor configurations; design consideration; and balancing aerodynamic, rotordynamic, and mechanical consideration. The course will answer the question "How do they work? factory testing, and future challenges. At the completion of the course, the attendees will hold a strong understanding of basic concepts. This knowledge will act as a springboard to further growth understanding of more complex centrifugal compressor concepts. An emphasis is placed on providing practical information with minimal theory. This is NOT a centrifugal compressor operations and maintenance class. Reciprocating, axial and centrifugal compressor similarities/differences History of compressors Configurations, straight-through, back-to-back, compound, side streams, double flow, overhung, integrally geared

Centrifugal Compressors 101: Part 1

Short CoursesReciprocating and centrifugal compressor similarities/ differences -How do they work? (Potential Energy, Kinetic Energy, PE, KE, …) -History of compressors – Timeline, major advances – Configurations, straight-through, back-to-back, compound, side streams, double-flow -Markets served -Pressure containment – Case – Nozzles and flang -Selection Process – Aerodynamic Selection – Mechanical Design – Rotordynamic Design Impellers – Design Basics -Stationary Aero Components – Inlet, inlet guide – Diffuser, vaned and vaneless, LSD – Volute and collector – Return bend / Return channel -Compressor Performance – Nomenclature – Impact of Operating Conditions – Internal Leakage – Surge Control -Rotordynamics – Critical speed maps – Synchronous unbalance response – Stability, log decrement – Damper seals – Bearings, seals – TP, Sleeve, magnetic – Squeeze film damper – Steady state and transient torsional -Stress analysis – Impeller dynamics -Acoustics -Seals – Gas seals – Oil film seals – Lab

Social polarisation at the local level: why inequality must be re-politicised from within different localities

Mark Fransham and Insa Koch examine how intensifying inequality in the UK plays out at a local level. They distinguish differing dynamics of ‘elite-based’ polarisation (in Oxford and Tunbridge Wells) and ‘poverty-based’ polarisation (in Margate and Oldham). They write that, although across these four towns marginalised communities express a sense of local belonging, tensions between social groups remain strong and all towns are marked by a weak or ‘squeezed middle’

Centrifugal Compressors 101

Short Cours

An inefficient dwarf: Chemical abundances and the evolution of the Ursa Minor dwarf spheroidal galaxy

We present detailed chemical element abundance ratios of 17 elements in three metal poor stars in the Ursa Minor dwarf spheroidal galaxy, which we combine with extant data from the literature to assess the predictions of a novel suite of galaxy chemical evolution models. The spectroscopic data were obtained with the Keck/HIRES instrument and revealed low metallicities of [Fe/H]=-2.12, -2.13 and -2.67 dex. While the most metal poor star in our sample shows an overabundance of [Mn/Fe] and other Fe-peak elements, our overall findings are in agreement with previous studies of this galaxy: elevated values of the [alpha/Fe] ratios that are similar to, or only slightly lower than, the halo values but with SN Ia enrichment at very low metallicity, as well as an enhancement of the ratio of first to second peak neutron capture elements [Y/Ba] with decreasing metallicity. The chemical evolution models which were tailored to reproduce the metallicity distribution function of the dSph, indicate that UMi had an extended star formation which lasted nearly 5 Gyr with low efficiency and are able to explain the [Y/Ba] enhancement at low metallicity for the first time. In particular, we show that the present day lack of gas is probably due to continuous loss of gas from the system, which we model as winds.Comment: 10 pages, 7 figures, table

Office of Career Services and Internships: Community Engaged Employer Partnership Model

Students in all academic areas are prepared to achieve career success in a global society. The Office of Career Services and Internships is a strategic partner with community and employer constituents to enhance the UMass Boston experience

Quantifying uncertainty in pest risk maps and assessments : adopting a risk-averse decision maker’s perspective

Pest risk maps are important decision support tools when devising strategies to minimize introductions of invasive organisms and mitigate their impacts. When possible management responses to an invader include costly or socially sensitive activities, decision-makers tend to follow a more certain (i.e., risk-averse) course of action. We presented a new mapping technique that assesses pest invasion risk from the perspective of a risk-averse decision maker. We demonstrated the method by evaluating the likelihood that an invasive forest pest will be transported to one of the U.S. states or Canadian provinces in infested firewood by visitors to U.S. federal campgrounds. We tested the impact of the risk aversion assumption using distributions of plausible pest arrival scenarios generated with a geographically explicit model developed from data documenting camper travel across the study area. Next, we prioritized regions of high and low pest arrival risk via application of two stochastic ordering techniques that employed, respectively, first- and second-degree stochastic dominance rules, the latter of which incorporated the notion of risk aversion. We then identified regions in the study area where the pest risk value changed considerably after incorporating risk aversion. While both methods identified similar areas of highest and lowest risk, they differed in how they demarcated moderate-risk areas. In general, the second-order stochastic dominance method assigned lower risk rankings to moderate-risk areas. Overall, this new method offers a better strategy to deal with the uncertainty typically associated with risk assessments and provides a tractable way to incorporate decisionmaking preferences into final risk estimates, and thus helps to better align these estimates with particular decision-making scenarios about a pest organism of concern. Incorporation of risk aversion also helps prioritize the set of locations to target for inspections and outreach activities, which can be costly. Our results are especially important and useful given the huge number of camping trips that occur each year in the United States and Canada