443 research outputs found
Direct and mediated effects of a social-emotional and character development program on adolescent substance use
Mitigating and preventing substance use among adolescents requires approaches that
address the multitude of factors that influence this behavior. Such approaches must be
tested, not only for evidence of empirical effectiveness, but also to determine the
mechanisms by which they are successful. The aims of the present study were twofold:
1) To determine the effectiveness of a school-based social-emotional and character
development (SECD) program, Positive Action (PA), in reducing substance use (SU)
among a sample of U.S. youth living in a low-income, urban environment, and 2) to test
one mechanism by which the program achieves its success. We used longitudinal
mediation analysis to test the hypotheses that: 1) students attending PA intervention
schools engage in significantly less SU than students attending control schools, 2)
students attending PA intervention schools show significantly better change in SECD
than students attending control schools, and 3) the effect of the PA intervention on SU is
mediated by the change in SECD. Analyses revealed program effects on both SECD and
SU, a relationship between SECD and SU, and the effects of PA on SU were completely
mediated by changes in SECD. Future research directions and implications for schoolbased social-emotional and character development efforts and substance use prevention are addressed.peer-reviewe
Measurements of d(2)(n) and A(1)(n) : Probing the neutron spin structure
We report on the results of the E06-014 experiment performed at Jefferson Lab in Hall A, where a precision measurement of the twist-3 matrix element d(2) of the neutron (d(2)(n)) was conducted. The quantity d(2)(n) represents the average color Lorentz force a struck quark experiences in a deep inelastic electron scattering event off a neutron due to its interaction with the hadronizing remnants. This color force was determined from a linear combination of the third moments of the He-3 spin structure functions, g(1) and g(2), after nuclear corrections had been applied to these moments. The structure functions were obtained from a measurement of the unpolarized cross section and of double-spin asymmetries in the scattering of a longitudinally polarized electron beam from a transversely and a longitudinally polarized He-3 target. The measurement kinematics included two average Q(2) bins of 3.2 GeV2 and 4.3 GeV2, and Bjorken-x 0.25 = 3.2 GeV2, and even smaller for \u3c Q(2)\u3e = 4.3 GeV2, consistent with the results of a lattice QCD calculation. The twist-4 matrix element f(2)(n) was extracted by combining our measured d(2)(n) with the world data on the first moment in x of g(1)(n), Gamma(n)(1). We found f(2)(n) to be roughly an order of magnitude larger than d(2)(n). Utilizing the extracted d(2)(n) and f(2)(n) data, we separated the Lorentz color force into its electric and magnetic components, F-E(y,n) and F-B(y,n), and found them to be equal and opposite in magnitude, in agreement with the predictions from an instanton model but not with those from QCD sum rules. Furthermore, using the measured double-spin asymmetries, we have extracted the virtual photon-nucleon asymmetry on the neutron A(1)(n), the structure function ratio g(1)(n)/F-1(n), and the quark ratios (Delta u + Delta(u) over bar)/(u + (u) over bar) and (Delta d + Delta(d) over bar)/(d + (d) over bar). These results were found to be consistent with deep-inelastic scattering world data and with the prediction of the constituent quark model but at odds with the perturbative quantum chromodynamics predictions at large x
Measurement of the Target-Normal Single-Spin Asymmetry in Quasi-Elastic Scattering from the Reaction He
We report the first measurement of the target single-spin asymmetry, ,
in quasi-elastic scattering from the inclusive reaction
He on a He gas target polarized normal to the
lepton scattering plane. Assuming time-reversal invariance, this asymmetry is
strictly zero for one-photon exchange. A non-zero can arise from the
interference between the one- and two-photon exchange processes which is
sensitive to the details of the sub-structure of the nucleon. An experiment
recently completed at Jefferson Lab yielded asymmetries with high statistical
precision at 0.13, 0.46 and 0.97 GeV. These measurements
demonstrate, for the first time, that the He asymmetry is clearly non-zero
and negative with a statistical significance of (8-10). Using measured
proton-to-He cross-section ratios and the effective polarization
approximation, neutron asymmetries of (1-3)% were obtained. The neutron
asymmetry at high is related to moments of the Generalized Parton
Distributions (GPDs). Our measured neutron asymmetry at GeV
agrees well with a prediction based on two-photon exchange using a GPD model
and thus provides a new, independent constraint on these distributions
The European Union in the World — A Community of Values
These are momentous times in Europe. The Euro has been successfully introduced, the enlargement negotiations are approaching their climax, and the European Convention (“Convention”) is moving towards the drafting of a constitution for a new, continent-wide political entity. At the same time, unrest is manifest, particularly in two areas. On the one hand, many of our citizens, and not just the political elites, are dissatisfied with Europe\u27s performance on the world stage and are concerned about the maintenance of peace and security within the Union. In these areas they would like to see a strengthened, more effective entity-- “more Europe.” On the other hand, their disenchantment with the long reach of European Union (“EU” or “Union”) regulation in the first pillar area of economic policy is growing. The feeling of loss of local control over their destiny and a vague feeling of potential loss of identity within an ever more centralized polity is palpable. Here, they want “less Europe.” In the outside world, change is also the order of the day. The ice-sheet of bipolarity, which overlaid and hid the complexity of international relations during the Cold War, is breaking up at an ever-increasing speed and revealing a world in which two paradigms are competing to become the underlying ordering principles for the new century. The traditional paradigm of interacting Nation States, each pursuing its own separate interests, with alliances allowing the small to compete with the large, is alive and well, and its proponents like Machiavelli or Churchill continue to be in vogue in the literature of international relations and the rhetoric of world leaders. At the same time, there is a school of thought which points to the growing economic and ecological interdependence of our societies and the necessity for new forms of global governance to complement national action. It is also becoming abundantly clear that the concept of a “Nation State” is often a fiction, positing as it does an identity between the citizens of a State and the members of a culturally homogenous society. For both reasons, the concept of the Nation State as the principal actor on the world stage, is called into question. The experience of the Union with the sharing of State sovereignty is clearly related to the second paradigm and also to the EU\u27s firm support for the development of the United Nations (“U.N.”) as well as other elements of multilateral governance. It would hardly be wise to suggest that any foreign policy, and certainly not that of the EU, should be based only on this paradigm. Given the recurrent threats to security, which seem to be part of the human condition expressed by some as the “inevitability of war”--the defense of territorial integrity; action against threats of aggression; and resistance to crimes against humanity such as genocide--the ability to conduct a security policy based much more on the old paradigm of interacting interests will continue to be required. That the EU needs to develop such a capability will be taken here as a given. Such a crisis-management capability will be essential to the Union, but will be distinguished here from the more long-term elements of foreign policy, which can be thought of as being designed to reduce the need for crisis management in the context of a security policy to a minimum. The crisis-management area of policy will not be treated further here. The thesis of this Essay is that the same set of political concepts can serve as a guide to the future internal development of the EU and as the basis of such a long-term foreign policy. Furthermore, it suggests that neither should be seen in terms of the balancing of interests but rather, as the expression of a small list of fundamental values. The list is as follows: (1) the rule of law as the basis for relations between members of society; (2) the interaction between the democratic process and entrenched human rights in political decision-making; (3) the operation of competition within a market economy as the source of increasing prosperity; (4) the anchoring of the principle of solidarity among all members of society alongside that of the liberty of the individual; (5) the adoption of the principle of sustainability of all economic development; and (6) the preservation of separate identities and the maintenance of cultural diversity within society. These values can be seen as the answer to the question posed both, by citizens of the Union and by our fellow citizens of the world: “What does the EU stand for?” In exploring these values we should, however, remember that in the real world there will be occasions on which Realpolitik will intrude and the interest-based paradigm will prevail
Editors' Introduction: Prevention as Altering the Course of Development and the Complementary Purposes of Developmental and Prevention Sciences
Measurement of the Neutron Radius of 208Pb Through Parity-Violation in Electron Scattering
We report the first measurement of the parity-violating asymmetry A_PV in the
elastic scattering of polarized electrons from 208Pb. A_PV is sensitive to the
radius of the neutron distribution (Rn). The result A_PV = 0.656 \pm 0.060
(stat) \pm 0.014 (syst) ppm corresponds to a difference between the radii of
the neutron and proton distributions Rn - Rp = 0.33 +0.16 -0.18 fm and provides
the first electroweak observation of the neutron skin which is expected in a
heavy, neutron-rich nucleus.Comment: 6 pages, 1 figur
A Precision Measurement of the Neutron Twist-3 Matrix Element : Probing Color Forces
Double-spin asymmetries and absolute cross sections were measured at large
Bjorken (0.25 0.90), in both the deep-inelastic and resonance
regions, by scattering longitudinally polarized electrons at beam energies of
4.7 and 5.9 GeV from a transversely and longitudinally polarized He target.
In this dedicated experiment, the spin structure function on He was
determined with precision at large , and the neutron twist-three matrix
element was measured at \left of 3.21 and 4.32
GeV/, with an absolute precision of about . Our results are
found to be in agreement with lattice QCD calculations and resolve the
disagreement found with previous data at \left = 5 GeV/.
Combining and a newly extracted twist-four matrix element, , the
average neutron color electric and magnetic forces were extracted and found to
be of opposite sign and about 30 MeV/fm in magnitude.Comment: Corrected a typo in the author list and Figure 1 legend. 6 pages, 2
figures, 2 table
Electroexcitation of the at low momentum transfer
We report on new p measurements at the
resonance at the low momentum transfer region. The mesonic
cloud dynamics is predicted to be dominant and rapidly changing in this
kinematic region offering a test bed for chiral effective field theory
calculations. The new data explore the low dependence of the resonant
quadrupole amplitudes while extending the measurements of the Coulomb
quadrupole amplitude to the lowest momentum transfer ever reached. The results
disagree with predictions of constituent quark models and are in reasonable
agreement with dynamical calculations that include pion cloud effects, chiral
effective field theory and lattice calculations. The reported measurements
suggest that improvement is required to the theoretical calculations and
provide valuable input that will allow their refinements
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