56,481 research outputs found
Experiences with Problem-Based Learning: Virginia Initiative for Science Teaching and Achievement
The Virginia Initiative for Science Teaching and Achievement (VISTA) provides high-quality professional development for teachers and administrators to enhance the quality of their science instructional programs. One emphasis of this program is helping teachers learn to implement Problem-Based Learning in the elementary science classroom. Problem-Based Learning (PBL) has the potential to produce significant positive outcomes for students, such as increased student engagement, and opportunities for in-depth critical thinking [1]. Teachers find PBL challenging because it does take additional time for planning and material acquisition, but experience has shown that the benefits outweigh these challenges. Setting clear goals, identifying specific learning objectives, and developing big questions that tie these together help increase the success of the unit. Additionally, administrators can help teachers succeed in implementing a Problem-Based Learning unit by understanding the dynamic nature of the PBL environment, providing flexibility with unit pacing, and setting aside time for refining, reflection, and revision of the unit
Using chiral perturbation theory to extract the neutron-neutron scattering length from pi- d -> n n gamma
The reaction pi- d -> n n gamma is calculated in chiral perturbation theory
so as to facilitate an extraction of the neutron-neutron scattering length
(a_nn). We include all diagrams up to O(Q^3). This includes loop effects in the
elementary pi- p -> gamma n amplitude and two-body diagrams, both of which were
ignored in previous calculations. We find that the chiral expansion for the
ratio of the quasi-free (QF) to final-state-interaction (FSI) peaks in the
final-state neutron spectrum converges well. Our third-order calculation of the
full spectrum is already accurate to better than 5%. Extracting a_nn from the
shape of the entire pi- d -> n n gamma spectrum using our calculation in its
present stage would thus be possible at the +-0.8 fm level. A fit to the FSI
peak only would allow an extraction of a_nn with a theoretical uncertainty of
+-0.2 fm. The effects that contribute to these error bars are investigated. The
uncertainty in the rescattering wave function dominates. This suggests
that the quoted theoretical error of +-0.3 fm for the most recent pi- d -> n n
gamma measurement may be optimistic. The possibility of constraining the nn
rescattering wave function used in our calculation more tightly--and thus
reducing the error--is briefly discussed.Comment: 35 pages, 14 eps figures, references and figure added, discussions of
errors extended and clarified, improved conclusions, typos corrected, to be
published in PR
Computer program for crossed-beam studies of clear air turbulence, Program description /MLTCOR/ Final report, 14 May 1968 - 13 Aug. 1969
Computer program for studies of aerodynamic and clear atmospheric turbulenc
Blue-collar outlook not so blue in Texas
Employment (Economic theory) ; Texas
Using EFT to analyze low-energy Compton scattering from protons and light nuclei
We discuss the application of an effective field theory (EFT) which
incorporates the chiral symmetry of QCD to Compton scattering from the proton
and deuteron. We describe the chiral EFT analysis of the proton Compton
scattering database presented in our recent review (arXiv:1203.6834), which
gives: alpha^{(p)}=10.5 +/- 0.5(stat) +/- 0.8(theory); beta^{(p)}= 2.7 +/-
0.5(stat) +/- 0.8(theory), for the electric and magnetic dipole polarizability
of the proton. We also summarize the chiral EFT analysis of the world data on
coherent Compton scattering from deuterium presented in arXiv:1203.6834. That
yields: alpha^{(s)}=10.5 +/- 2.0(stat) +/- 0.8(theory); beta^{(s)}=3.6 +/-
1.0(stat) +/- 0.8(theory).Comment: 5 pages. Invited talk, presented by Phillips at the 11th Conference
on the Intersections of Nuclear and Particle Physics (CIPANP 2012), St.
Petersburg, FL, May 201
Dynamical fluctuations in biochemical reactions and cycles
We develop theory for the dynamics and fluctuations in some cyclic and linear biochemical reactions. We use the approach of maximum caliber, which computes the ensemble of paths taken by the system, given a few experimental observables. This approach may be useful for interpreting single-molecule or few-particle experiments on molecular motors, enzyme reactions, ion-channels, and phosphorylation-driven biological clocks. We consider cycles where all biochemical states are observable. Our method shows how: (1) the noise in cycles increases with cycle size and decreases with the driving force that spins the cycle and (2) provides a recipe for estimating small-number features, such as probability of backward spin in small cycles, from experimental data. The back-spin probability diminishes exponentially with the deviation from equilibrium. We believe this method may also be useful for other few-particle nonequilibrium biochemical reaction systems
Nucleon Polarisabilities at and Beyond Physical Pion Masses
We examine the results of Chiral Effective Field Theory (EFT) for the
scalar- and spin-dipole polarisabilities of the proton and neutron, both for
the physical pion mass and as a function of . This provides chiral
extrapolations for lattice-QCD polarisability computations. We include both the
leading and sub-leading effects of the nucleon's pion cloud, as well as the
leading ones of the resonance and its pion cloud. The analytic
results are complete at NLO in the -counting for pion masses close
to the physical value, and at leading order for pion masses similar to the
Delta-nucleon mass splitting. In order to quantify the truncation error of our
predictions and fits as \% degree-of-belief intervals, we use a Bayesian
procedure recently adapted to EFT expansions. At the physical point, our
predictions for the spin polarisabilities are, within respective errors, in
good agreement with alternative extractions using experiments and
dispersion-relation theory. At larger pion masses we find that the chiral
expansion of all polarisabilities becomes intrinsically unreliable as
approaches about MeV---as has already been seen in other observables.
EFT also predicts a substantial isospin splitting above the physical
point for both the electric and magnetic scalar polarisabilities; and we
speculate on the impact this has on the stability of nucleons. Our results
agree very well with emerging lattice computations in the realm where EFT
converges. Curiously, for the central values of some of our predictions, this
agreement persists to much higher pion masses. We speculate on whether this
might be more than a fortuitous coincidence.Comment: 39 pages LaTeX2e (pdflatex) including 12 figures as 16 .pdf files
using includegraphics. Version approved for publication in EPJA includes
modifications, clarifications and removal of typographical errors in
refereeing and publication proces
Resonance tube igniter
Reasonance induced in stoichiometric mixtures of gaseous hydrogen-oxygen produces temperatures /over 1100 deg F/ high enough to cause ignition. Resonance tube phenomenon occurs when high pressure gas is forced through sonic or supersonic nozzle into short cavity. Various applications for the phenomenon are discussed
Compton scattering from the proton in an effective field theory with explicit Delta degrees of freedom
We analyse the proton Compton-scattering differential cross section for
photon energies up to 325 MeV using Chiral Effective Field Theory and extract
new values for the electric and magnetic polarisabilities of the proton. Our
EFT treatment builds in the key physics in two different regimes: photon
energies around the pion mass ("low energy") and the higher energies where the
Delta(1232) resonance plays a key role. The Compton amplitude is complete at
N4L0, O(e^2 delta^4), in the low-energy region, and at NLO, O(e^2 delta^0), in
the resonance region. Throughout, the Delta-pole graphs are dressed with pi-N
loops and gamma-N-Delta vertex corrections. A statistically consistent database
of proton Compton experiments is used to constrain the free parameters in our
amplitude: the M1 gamma-N-Delta transition strength b_1 (which is fixed in the
resonance region) and the polarisabilities alpha and beta (which are fixed from
data below 170 MeV). In order to obtain a reasonable fit we find it necessary
to add the spin polarisability gammaM1 as a free parameter, even though it is,
strictly speaking, predicted in chiral EFT at the order to which we work. We
show that the fit is consistent with the Baldin sum rule, and then use that sum
rule to constrain alpha+beta. In this way we obtain
alpha=[10.65+/-0.35(stat})+/-0.2(Baldin)+/-0.3(theory)]10^{-4} fm^3, and beta
=[3.15-/+0.35(stat)-/+0.2(Baldin)-/+0.3(theory)]10^{-4} fm^3, with chi^2 =
113.2 for 135 degrees of freedom. A detailed rationale for the theoretical
uncertainties assigned to this result is provided.Comment: 36 pages, 15 figures Version 2 is shortened for publication; version
1 is more self-contained. Results section unchange
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