3,517 research outputs found
Non-Equilibrium Dynamics and Superfluid Ring Excitations in Binary Bose-Einstein Condensates
We revisit a classic study [D. S. Hall {\it et al.}, Phys. Rev. Lett. {\bf
81}, 1539 (1998)] of interpenetrating Bose-Einstein condensates in the
hyperfine states and of Rb and observe striking new non-equilibrium
component separation dynamics in the form of oscillating ring-like structures.
The process of component separation is not significantly damped, a finding that
also contrasts sharply with earlier experimental work, allowing a clean first
look at a collective excitation of a binary superfluid. We further demonstrate
extraordinary quantitative agreement between theoretical and experimental
results using a multi-component mean-field model with key additional features:
the inclusion of atomic losses and the careful characterization of trap
potentials (at the level of a fraction of a percent).Comment: 4 pages, 3 figures (low res.), to appear in PR
An inquiry-based learning approach to teaching information retrieval
The study of information retrieval (IR) has increased in interest and importance with the explosive growth of online information in recent years. Learning about IR within formal courses of study enables users of search engines to use
them more knowledgeably and effectively, while providing the starting point for the explorations of new researchers into novel search technologies. Although IR can be taught in a traditional manner of formal classroom instruction with students being led through the details of the subject and expected to reproduce this in assessment, the nature of IR as a topic makes it an ideal subject for inquiry-based learning approaches to teaching. In an inquiry-based learning approach students are introduced to the principles of a subject and then encouraged to develop their understanding by solving structured or open problems. Working through solutions in subsequent class discussions enables students to appreciate the availability of alternative solutions as proposed by their classmates. Following this approach students not only learn the details of IR techniques, but significantly, naturally learn to apply them in solution of problems. In doing this they not only gain an appreciation of alternative solutions to a problem, but also how to assess their relative strengths and weaknesses. Developing confidence and skills in problem solving enables student assessment to be structured around solution of problems. Thus students can be assessed on the basis of their understanding and ability to apply techniques, rather simply their skill at reciting facts. This has the additional benefit of encouraging general problem solving skills which can be of benefit in other subjects. This approach to teaching IR was successfully implemented in an undergraduate module where students were
assessed in a written examination exploring their knowledge and understanding of the principles of IR and their ability to apply them to solving problems, and a written assignment based on developing an individual research proposal
Deriving a Provisional Tolerable Intake for Intravenous Exposure to Silver Nanoparticles Released from Medical Devices
Silver nanoparticles (AgNP) are incorporated into medical devices for their anti-microbial characteristics. The potential exposure and toxicity of AgNPs is unknown due to varying physicochemical particle properties and lack of toxicological data. The aim of this safety assessment is to derive a provisional tolerable intake (pTI) value for AgNPs released from blood-contacting medical devices. A literature review of in vivo studies investigating critical health effects induced from intravenous (i. v.) exposure to AgNPs was evaluated by the Annapolis Accords principles and Toxicological Data Reliability Assessment Tool (ToxRTool). The point of departure (POD) was based on an i. v. 28-day repeated AgNP (20 nm) dose toxicity study reporting an increase in relative spleen weight in rats with a 5% lower confidence bound of the benchmark dose (BMDL05) of 0.14 mg/kg bw/day. The POD was extrapolated to humans by a modifying factor of 1,000 to account for intraspecies variability, interspecies differences and lack of long-term toxicity data. The pTI for long-term i. v. exposure to 20 nm AgNPs released from blood-contacting medical devices was 0.14 μg/kg bw/day. This pTI may not be appropriate for nanoparticles of other physicochemical properties or routes of administration. The methodology is appropriate for deriving pTIs for nanoparticles in general
Studying the Pulsation of Mira Variables in the Ultraviolet
We present results from an empirical study of the Mg II h & k emission lines
of selected Mira variable stars, using spectra from the International
Ultraviolet Explorer (IUE). The stars all exhibit similar Mg II behavior during
the course of their pulsation cycles. The Mg II flux always peaks after optical
maximum near pulsation phase 0.2-0.5, although the Mg II flux can vary greatly
from one cycle to the next. The lines are highly blueshifted, with the
magnitude of the blueshift decreasing with phase. The widths of the Mg II lines
are also phase-dependent, decreasing from about 70 km/s to 40 km/s between
phase 0.2 and 0.6. We also study other UV emission lines apparent in the IUE
spectra, most of them Fe II lines. These lines are much narrower and not nearly
as blueshifted as the Mg II lines. They exhibit the same phase-dependent flux
behavior as Mg II, but they do not show similar velocity or width variations.Comment: 26 pages, 12 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty;
to appear in Ap
Asteroid Redirect Mission Concept: A Bold Approach for Utilizing Space Resources
The utilization of natural resources from asteroids is an idea that is older than the Space Age. The technologies are now available to transform this endeavour from an idea into reality. The Asteroid Redirect Mission (ARM) is a mission concept which includes the goal of robotically returning a small Near-Earth Asteroid (NEA) or a multi-ton boulder from a large NEA to cislunar space in the mid 2020's using an advanced Solar Electric Propulsion (SEP) vehicle and currently available technologies. The paradigm shift enabled by the ARM concept would allow in-situ resource utilization (ISRU) to be used at the human mission departure location (i.e., cislunar space) versus exclusively at the deep-space mission destination. This approach drastically reduces the barriers associated with utilizing ISRU for human deep-space missions. The successful testing of ISRU techniques and associated equipment could enable large-scale commercial ISRU operations to become a reality and enable a future space-based economy utilizing processed asteroidal materials. This paper provides an overview of the ARM concept and discusses the mission objectives, key technologies, and capabilities associated with the mission, as well as how the ARM and associated operations would benefit humanity's quest for the exploration and settlement of space
High-resolution spectroscopy of the R Coronae Borealis and Other Hydrogen Deficient Stars
High-resolution spectroscopy is a very important tool for studying stellar
physics, perhaps, particularly so for such enigmatic objects like the R Coronae
Borealis and related Hydrogen deficient stars that produce carbon dust in
addition to their peculiar abundances.
Examples of how high-resolution spectroscopy is used in the study of these
stars to address the two major puzzles are presented: (i) How are such rare
H-deficient stars created? and (ii) How and where are the obscuring soot clouds
produced around the R Coronae Borealis stars?Comment: 16 pages, 9 figures, Astrophysics and Space Science Proceedings,
Springer-Verlag, Berlin, 201
Asymmetric polarity reversals, bimodal field distribution, and coherence resonance in a spherically symmetric mean-field dynamo model
Using a mean-field dynamo model with a spherically symmetric helical
turbulence parameter alpha which is dynamically quenched and disturbed by
additional noise, the basic features of geomagnetic polarity reversals are
shown to be generic consequences of the dynamo action in the vicinity of
exceptional points of the spectrum. This simple paradigmatic model yields long
periods of constant polarity which are interrupted by self-accelerating field
decays leading to asymmetric polarity reversals. It shows the recently
discovered bimodal field distribution, and it gives a natural explanation of
the correlation between polarity persistence time and field strength. In
addition, we find typical features of coherence resonance in the dependence of
the persistence time on the noise.Comment: 5 pages, 7 figure
Using Social Media to Promote STEM Education: Matching College Students with Role Models
STEM (Science, Technology, Engineering, and Mathematics) fields have become
increasingly central to U.S. economic competitiveness and growth. The shortage
in the STEM workforce has brought promoting STEM education upfront. The rapid
growth of social media usage provides a unique opportunity to predict users'
real-life identities and interests from online texts and photos. In this paper,
we propose an innovative approach by leveraging social media to promote STEM
education: matching Twitter college student users with diverse LinkedIn STEM
professionals using a ranking algorithm based on the similarities of their
demographics and interests. We share the belief that increasing STEM presence
in the form of introducing career role models who share similar interests and
demographics will inspire students to develop interests in STEM related fields
and emulate their models. Our evaluation on 2,000 real college students
demonstrated the accuracy of our ranking algorithm. We also design a novel
implementation that recommends matched role models to the students.Comment: 16 pages, 8 figures, accepted by ECML/PKDD 2016, Industrial Trac
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