5,011 research outputs found
Scientific Argumentation as a Foundation for the Design of Inquiry-Based Science Instruction
Despite the attention that inquiry has received in science education research and policy, a coherent means for implementing inquiry in the classroom has been missing [1]. In recent research, scientific argumentation has received increasing attention for its role in science and in science education [2]. In this article, we propose that organizing a unit of instruction around building a scientific argument can bring inquiry practices together in the classroom in a coherent way. We outline a framework for argumentation, focusing on arguments that are central to science—arguments for the best explanation. We then use this framework as the basis for a set of design principles for developing a sequence of inquiry-based learning activities that support students in the construction of a scientific argument. We show that careful analysis of the argument that students are expected to build provides designers with a foundation for selecting resources and designing supports for scientific inquiry. Furthermore, we show that creating multiple opportunities for students to critique and refine their explanations through evidence-based argumentation fosters opportunities for critical thinking, while building science knowledge and knowledge of the nature of science
Charm production in antiproton-nucleus collisions at the and the thresholds
We discuss the production of charmonium states in antiproton-nucleus
collisions at the threshold. It is explained that measurements in collisions will allow to get new information about the strengths of the
inelastic interaction, on the production of and
in charmonium-nucleon interactions and for the first time about
nondiagonal transitions . The inelastic -nucleon
cross section is extracted from the comparison of hadron-nucleus collisions
with hadron-nucleon collisions. We extract the total nucleon cross
section from photon-nucleon collisions by accounting for the color transparency
phenomenon within the frame of the GVDM (Generalized Vector meson Dominance
Model). We evaluate also within the GVDM the inelastic -nucleon cross
section as well as the cross section for the nondiagonal transitions.
Predictions for the ratio of to yields in antiproton-nucleus
scatterings close to the threshold of production for different nuclear
targets are presented.Comment: 13 pages, 10 figures, typos corrected, some discussion adde
Application of the Principle of Maximum Conformality to Top-Pair Production
A major contribution to the uncertainty of finite-order perturbative QCD
predictions is the perceived ambiguity in setting the renormalization scale
. For example, by using the conventional way of setting , one obtains the total production cross-section
with the uncertainty \Delta \sigma_{t \bar{t}}/\sigma_{t
\bar{t}}\sim ({}^{+3%}_{-4%}) at the Tevatron and LHC even for the present
NNLO level. The Principle of Maximum Conformality (PMC) eliminates the
renormalization scale ambiguity in precision tests of Abelian QED and
non-Abelian QCD theories. In this paper we apply PMC scale-setting to predict
the cross-section at the Tevatron and LHC
colliders. It is found that remains almost unchanged by
varying within the region of . The convergence
of the expansion series is greatly improved. For the -channel,
which is dominant at the Tevatron, its NLO PMC scale is much smaller than the
top-quark mass in the small -region, and thus its NLO cross-section is
increased by about a factor of two. In the case of the -channel, which is
dominant at the LHC, its NLO PMC scale slightly increases with the subprocess
collision energy , but it is still smaller than for
TeV, and the resulting NLO cross-section is increased by
. As a result, a larger is obtained in comparison
to the conventional scale-setting method, which agrees well with the present
Tevatron and LHC data. More explicitly, by setting GeV, we
predict pb,
pb and pb. [full abstract can be found in the
paper.]Comment: 15 pages, 11 figures, 5 tables. Fig.(9) is correcte
Anomaly and Condensate in the Light-Cone Schwinger Model
The axial anomaly and fermion condensate in the light cone Schwinger model
are studied following path integral methods. This formalism allows for a simple
and direct calculation for these and other vacuum dependent phenomena.Comment: 10pp, Revte
On the dependence of the wave function of a bound nucleon on its momentum and the EMC effect
It is widely discussed in the literature that the wave function of the
nucleon bound in a nucleus is modified due to the interaction with the
surrounding medium. We argue that the modification should strongly depend on
the momentum of the nucleon. We study such an effect in the case of the
point-like configuration component of the wave function of a nucleon bound in a
nucleus A, considering the case of arbitrary final state of the spectator A-1
system. We show that for non relativistic values of the nucleon momentum, the
momentum dependence of the nucleon deformation appears to follow from rather
general considerations and discuss the implications of our theoretical
observation for two different phenomena: i) the search for medium induced
modifications of the nucleon radius of a bound nucleon through the measurement
of the electromagnetic nucleon form factors via the A(e,e'p)X process, and ii)
the A-dependence of the EMC effect; in this latter case we also present a new
method of estimating the fraction of the nucleus light-cone momentum carried by
the photons and find that in a heavy nuclei protons loose about 2% of their
momentum.Comment: 38 pages, 1 figure; changed references and text in Section I
(Introduction
Tetramixing of vector and pseudoscalar mesons: A source of intrinsic quarks
The tetramixing of pseudoscalar mesons --- and
vector mesons --- are studied in the light-cone
constituent quark model, and such mixing of four mesons provides a natural
source for the intrinsic charm components of light mesons. By mixing
with the light mesons, the charmonium states and could decay
into light mesons more naturally, without introducing gluons or a virtual
photon as intermediate states. Thus, the introduction of light quark components
into is helpful to reproduce the new experimental data of
decays. The mixing matrices and the behaviors of the transition form
factors are also calculated and compared with experimental data.Comment: 20 pages, 10 figures. Version for publication in PR
Vector meson - mixing and their form factors in light-cone quark model
The vector meson - mixing is studied in two alternative
scenarios with different numbers of mixing angles, i.e., the one-mixing-angle
scenario and the two-mixing-angle scenario, in both the octect-singlet mixing
scheme and the quark flavor mixing scheme. Concerning the reproduction of
experimental data and the behavior of transition form factors,
one-mixing-angle scenario in the quark flavor scheme performs better than that
in the octet-singlet scheme, while the two-mixing-angle scenario works well for
both mixing schemes. The difference between the two mixing angles in the
octet-singlet scheme is bigger than that in the quark flavor scheme.Comment: 16 pages, 7 figures, final version to appear in PR
High Energy Photon-Photon and Electron-Photon Collisions
The advent of a next linear collider and back-scatterd laser
beams will allow the study of a vast array of high energy processes of the
Standard Model through the fusion of real and virtual photons and other gauge
bosons. As examples, I discuss virtual photon scattering in the region dominated by BFKL hard Pomeron exchange and report the
predicted cross sections at present and future colliders. I also
discuss exclusive reactions in QCD as a measure of hadron
distribution amplitudes and a new method for measuring the anomalous magnetic
and quadrupole moments of the and gauge bosons to high precision in
polarized electron-photon collisions.Comment: LaTex, 12 page
The running coupling method with next-to-leading order accuracy and pion, kaon elm form factors
The pion and kaon electromagnetic form factors are calculated at
the leading order of pQCD using the running coupling constant method. In
calculations the leading and next-to-leading order terms in
expansion in terms of are taken into
account. The resummed expression for is found. Results of numerical
calculations for the pion (asymptotic distribution amplitude) are presented.Comment: 9 pages, 1 figur
Structure Functions are not Parton Probabilities
The common view that structure functions measured in deep inelastic lepton
scattering are determined by the probability of finding quarks and gluons in
the target is not correct in gauge theory. We show that gluon exchange between
the fast, outgoing partons and target spectators, which is usually assumed to
be an irrelevant gauge artifact, affects the leading twist structure functions
in a profound way. This observation removes the apparent contradiction between
the projectile (eikonal) and target (parton model) views of diffractive and
small x_{Bjorken} phenomena. The diffractive scattering of the fast outgoing
quarks on spectators in the target causes shadowing in the DIS cross section.
Thus the depletion of the nuclear structure functions is not intrinsic to the
wave function of the nucleus, but is a coherent effect arising from the
destructive interference of diffractive channels induced by final state
interactions. This is consistent with the Glauber-Gribov interpretation of
shadowing as a rescattering effect.Comment: 35 pages, 8 figures. Discussion of physical consequences of final
state interactions amplified. Material on light-cone gauge choices adde
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