3,335 research outputs found
Access to undergraduate research experiences at a large research university
The American Physical Society recently released a statement calling on all
university physics departments to provide or facilitate access to research
experiences for all undergraduate students. In response, we investigated the
current status of access to undergraduate research at University of Colorado
Boulder (CU), a large research institution where the number of undergraduate
physics majors outnumber faculty by roughly ten to one. We created and
administered two surveys within CU's Physics Department: one probed
undergraduate students' familiarity with, and participation in, research; the
other probed faculty members' experiences as research mentors to
undergraduates. We describe the development of these instruments, our results,
and our corresponding evidence-based recommendations for improving local access
to undergraduate research experiences. Reflecting on our work, we make several
connections to an institutional change framework and note how other
universities and colleges might adapt our process.Comment: 4 pages, 3 figures, 1 table; Submitted to 2015 PERC Proceeding
Observation of a Large Atomic Parity Violation Effect in Ytterbium
Atomic parity violation has been observed in the 6s^2 1S0 - 5d6s 3D1 408-nm
forbidden transition of ytterbium. The parity-violating amplitude is found to
be two orders of magnitude larger than in cesium, where the most precise
experiments to date have been performed. This is in accordance with theoretical
predictions and constitutes the largest atomic parity-violating amplitude yet
observed. This also opens the way to future measurements of neutron skins and
anapole moments by comparing parity-violating amplitudes for various isotopes
and hyperfine components of the transition
The Metallicity of Pre-Galactic Globular Clusters: Observational consequences of the first stars
We explore a scenario where metal-poor globular clusters (GCs) are enriched
by the first supernovae in the Universe. If the first stars in a 10^7 Msun dark
halo were very massive (>180 Msun), then a pair instability supernova from a
single massive star can produce sufficient iron to enrich 10^6 Msun of
pristine, primordial gas to [Fe/H] ~ -2. In such a scenario, where a single
massive star acts as a seed for halo GCs, the accurate abundance analysis of GC
stars would allow a direct measurement of the Population III initial mass.
Using the latest theoretical yields for zero metallicity stars in the mass
range 140-260 Msun, we find that the metals expelled from a ~230 Msun star are
consistent with [Si/Fe] and [Ca/Fe] observed in GC stars. However, no single
star in this mass range can simultaneously explain all halo GC heavy-element
abundance ratios, such as [V/Fe], [Ti/Fe] and [Ni/Fe]. These require a
combination masses for the Population III stellar progenitors. The various
observational consequences of this scenario are discussed.Comment: 5 pages, 2 figures, accepted for publication in ApJ Lette
Shoot growth of woody trees and shrubs is predicted by maximum plant height and associated traits
1. The rate of elongation and thickening of individual branches (shoots) varies across plant species. This variation is important for the outcome of competition and other plant-plant interactions. Here we compared rates of shoot growth across 44 species from tropical, warm temperate, and cool temperate forests of eastern Australia.2. Shoot growth rate was found to correlate with a suite of traits including the potential height of the species, xylem-specific conductivity, leaf size, leaf area per xylem cross-section, twig diameter (at 40 cm length), wood density and modulus of elasticity.3. Within this suite of traits, maximum plant height was the clearest correlate of growth rates, explaining 50 to 67% of the variation in growth overall (p p 4. Growth rates were not strongly correlated with leaf nitrogen or leaf mass per unit leaf area.5. Correlations between growth and maximum height arose both across latitude (47%, p p p p < 0.0001), reflecting intrinsic differences across species and sites
Constraints on UV Absorption in the Intracluster Medium of Abell 1030
We present results from an extensive HST spectroscopic search for UV
absorption lines in the spectrum of the quasar B2~1028+313, which is associated
with the central dominant galaxy in the cluster Abell~1030 (). This is
one of the brightest known UV continuum sources located in a cluster, and
therefore provides an ideal opportunity to obtain stringent constraints on the
column densities of any cool absorbing gas that may be associated with the
intracluster medium (ICM). Our HST spectra were obtained with the FOS and GHRS,
and provide continuous coverage at rest-frame wavelengths from to
4060~\AA, thereby allowing the investigation of many different elements and
ionization levels. We utilize a new technique that involves simultaneous
fitting of large numbers of different transitions for each species, thereby
yielding more robust constraints on column densities than can be obtained from
a single transition. This method yields upper limits of cm on the column densities of a wide range of molecular, atomic
and ionized species that may be associated with the ICM. We also discuss a
possible \Lya and C IV absorption system associated with the quasar. We discuss
the implications of the upper limits on cool intracluster gas in the context of
the physical properties of the ICM and its relationship to the quasar.Comment: Astrophysical Journal, in press, 19 pages, includes 5 PostScript
figures. Latex format, uses aas2pp4.sty and epsfig.sty file
DistiLD Database: diseases and traits in linkage disequilibrium blocks
Genome-wide association studies (GWAS) have identified thousands of single nucleotide polymorphisms (SNPs) associated with the risk of hundreds of diseases. However, there is currently no database that enables non-specialists to answer the following simple questions: which SNPs associated with diseases are in linkage disequilibrium (LD) with a gene of interest? Which chromosomal regions have been associated with a given disease, and which are the potentially causal genes in each region? To answer these questions, we use data from the HapMap Project to partition each chromosome into so-called LD blocks, so that SNPs in LD with each other are preferentially in the same block, whereas SNPs not in LD are in different blocks. By projecting SNPs and genes onto LD blocks, the DistiLD database aims to increase usage of existing GWAS results by making it easy to query and visualize disease-associated SNPs and genes in their chromosomal context. The database is available at http://distild.jensenlab.org/
Spectral functions of isoscalar scalar and isovector electromagnetic form factors of the nucleon at two-loop order
We calculate the imaginary parts of the isoscalar scalar and isovector
electromagnetic form factors of the nucleon up to two-loop order in chiral
perturbation theory. Particular attention is paid on the correct behavior of Im
and Im at the two-pion threshold
in connection with the non-relativistic 1/M-expansion. We recover the
well-known strong enhancement near threshold originating from the nearby
anomalous singularity at . In the
case of the scalar spectral function Im one finds a significant
improvement in comparison to the lowest order one-loop result. Higher order
-rescattering effects are however still necessary to close a remaining
20%-gap to the empirical scalar spectral function. The isovector electric and
magnetic spectral functions Im get additionally enhanced near
threshold by the two-pion-loop contributions. After supplementing their
two-loop results by a phenomenological -meson exchange term one can
reproduce the empirical isovector electric and magnetic spectral functions
fairly well.Comment: 10 pages, 6 figures, submitted to Physical Review
Researching "British [Muslim] Values": Vernacular politics, digital storytelling, and participant researchers
This article reflects on methodological decisions, strategies, and challenges from a recent interdisciplinary project on the relationship between âBritish valuesâ and Islam. The project employed digital storytelling to access âeverydayâ conceptions and constructions of this contentious relationship. The research was undertaken by participant researchers recruited from Muslim communities in the UKâs East Anglia region, working with academics from media studies and political science. In this article we offer a detailed account of key moments relating especially to recruitment, retention, and the production of digital content. It offers two contributions. First, methodological guidance for researchers interested in combining participatory research with digital storytelling. And, second, rationale for so doing given the methodologyâs scope for producing rich visual content with capacity (i) to deepen and disrupt established knowledge, and (ii) to change the views, ideas and aspirations of those involved in the contentâs creation
Student perceptions of laboratory classroom activities and experimental physics practice
We report results from a study designed to identify links between
undergraduate students' views about experimental physics and their engagement
in multiweek projects in lab courses. Using surveys and interviews, we explored
whether students perceived particular classroom activities to be features of
experimental physics practice. We focused on 18 activities, including
maintaining lab notebooks, fabricating parts, and asking others for help.
Interviewees identified activities related to project execution as intrinsic to
experimental physics practice based on high prevalence of those activities in
interviewees' own projects. Fabrication-oriented activities were identified as
conditional features of experimentation based on differences between projects,
which interviewees attributed to variations in project resources. Interpersonal
activities were also viewed as conditional features of experimentation,
dependent upon one's status as novice or expert. Our findings suggest that
students' views about experimental physics are shaped by firsthand experiences
of their own projects and secondhand experiences of those of others.Comment: 6 pages, 1 table, accepted for publication in 2020 Physics Education
Research Conference Proceeding
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