815 research outputs found
Probing neutrino physics with a self-consistent treatment of the weak decoupling, nucleosynthesis, and photon decoupling epochs
We show that a self-consistent and coupled treatment of the weak decoupling,
big bang nucleosynthesis, and photon decoupling epochs can be used to provide
new insights and constraints on neutrino sector physics from high-precision
measurements of light element abundances and cosmic microwave background
observables. Implications of beyond-standard-model physics in cosmology,
especially within the neutrino sector, are assessed by comparing predictions
against five observables: the baryon energy density, helium abundance,
deuterium abundance, effective number of neutrinos, and sum of the light
neutrino mass eigenstates. We give examples for constraints on dark radiation,
neutrino rest mass, lepton numbers, and scenarios for light and heavy sterile
neutrinos.Comment: 29 pages, 10 figure
Neutrino energy transport in weak decoupling and big bang nucleosynthesis
We calculate the evolution of the early universe through the epochs of weak
decoupling, weak freeze-out and big bang nucleosynthesis (BBN) by
simultaneously coupling a full strong, electromagnetic, and weak nuclear
reaction network with a multi-energy group Boltzmann neutrino energy transport
scheme. The modular structure of our code provides the ability to dissect the
relative contributions of each process responsible for evolving the dynamics of
the early universe in the absence of neutrino flavor oscillations. Such an
approach allows a detailed accounting of the evolution of the ,
, , , , energy
distribution functions alongside and self-consistently with the nuclear
reactions and entropy/heat generation and flow between the neutrino and
photon/electron/positron/baryon plasma components. This calculation reveals
nonlinear feedback in the time evolution of neutrino distribution functions and
plasma thermodynamic conditions (e.g., electron-positron pair densities), with
implications for: the phasing between scale factor and plasma temperature; the
neutron-to-proton ratio; light-element abundance histories; and the
cosmological parameter \neff. We find that our approach of following the time
development of neutrino spectral distortions and concomitant entropy production
and extraction from the plasma results in changes in the computed value of the
BBN deuterium yield. For example, for particular implementations of quantum
corrections in plasma thermodynamics, our calculations show a increase
in deuterium. These changes are potentially significant in the context of
anticipated improvements in observational and nuclear physics uncertainties.Comment: 37 pages, 12 Figures, 6 Table
Monitoring the emergence of antibiotic resistance using the technology ot the DebugIT platform in the HEGP context
International audiencepas de rĂŠsum
Constraints on vacuum energy from structure formation and Nucleosynthesis
This paper derives an upper limit on the density ĎÎ of dark energy based on the requirement that cosmological structure forms before being frozen out by the eventual acceleration of the universe. By allowing for variations in both the cosmological parameters and the strength of gravity, the resulting constraint is a generalization of previous limits. The specific parameters under consideration include the amplitude Q of the primordial density fluctuations, the Planck mass Mpl, the baryon-to-photon ratio Ρ, and the density ratio ΊM/Ίb. In addition to structure formation, we use considerations from stellar structure and Big Bang Nucleosynthesis (BBN) to constrain these quantities. The resulting upper limit on the dimensionless density of dark energy becomes ĎÎ/Mpl4 < 10â90, which is ~30 orders of magnitude larger than the value in our universe ĎÎ/Mpl4 ~ 10â120. This new limit is much less restrictive than previous constraints because additional parameters are allowed to vary. With these generalizations, a much wider range of universes can develop cosmic structure and support observers. To constrain the constituent parameters, new BBN calculations are carried out in the regime where Ρ and G = Mplâ2 are much larger than in our universe. If the BBN epoch were to process all of the protons into heavier elements, no hydrogen would be left behind to make water, and the universe would not be viable. However, our results show that some hydrogen is always left over, even under conditions of extremely large Ρ and G, so that a wide range of alternate universes are potentially habitable
Building Community Capacity for Integrating Engineering in Rural Middle School Science Classrooms
: Broadening participation in engineering is an important national priority and has led to increasing demands
for engineering content to be integrated into traditional K-12 curriculum. However, expecting teachers to incorporate engineering into their classrooms without additional training or resources is unreasonable. Partnering teachers with industry
partners is one promising way to prioritize integrated science and engineering content while also introducing youth to possible career paths. In this programmatic article, we introduce the Partnering with Educators and Engineers in Rural Schools
(PEERS) project that focuses on the collaborative design, implementation, and study of recurrent hands-on engineering
activities with middle school youth in three rural communities in or near Appalachia. We discuss the curricular priorities of
the program as well as preliminary findings on both student-focused and capacity-building metrics across the partnerships.
Key discussion points include (1) a need to distill goals for engineering outreach by wrestling with what success might really
look like for middle-school youth engagement with engineering and (2) cultivating community capacity to better support
education systems and the simultaneous potential for and challenges of collaborating to build such infrastructure
Student Outcomes from the Collective Design and Delivery of Culturally Relevant Engineering Outreach Curricula in Rural and Appalachian Middle Schools
Middle school is a pivotal time for career choice, and research is rich with studies on how students perceive engineering, as well as
corresponding intervention strategies to introduce younger students to engineering and inform their conceptions of engineering.
Unfortunately, such interventions are typically not designed in culturally relevant ways. Consequently, there continues to be a lack
of students entering engineering and a low level of diverse candidates for this profession. The purpose of this study was to explore
how students in rural and Appalachian Virginia conceive of engineering before and after engagement with culturally relevant
hands-on activities in the classroom. We used student responses to the Draw an Engineer Test (DAET), consisting of a drawing
and several open-ended prompts administered before and after the set of engagements, to answer our research questions related to
changes in studentsâ conceptions of engineering. We used this study to develop recommendations for teachers for the use of such
engineering engagement practices and how to best assess their outcomes, including looking at the practicality of the DAET.
Overall, we found evidence that our classroom engagements positively influenced studentsâ conceptions of engineering in these
settings
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