607 research outputs found
A Kind of Imagination that has Nothing to Do with Fiction: Art in Public Life
Davidts, W. [Promotor]Oostdijk, D.M. [Copromotor]Slager, H. [Copromotor
Extended Superscaling of Electron Scattering from Nuclei
An extended study of scaling of the first and second kinds for inclusive
electron scattering from nuclei is presented. Emphasis is placed on the
transverse response in the kinematic region lying above the quasielastic peak.
In particular, for the region in which electroproduction of resonances is
expected to be important, approximate scaling of the second kind is observed
and the modest breaking of it is shown probably to be due to the role played by
an inelastic version of the usual scaling variable.Comment: LaTeX, 36 pages including 5 color postscript figures and 4 postscript
figure
Superscaling of Inclusive Electron Scattering from Nuclei
We investigate the degree to which the concept of superscaling, initially
developed within the framework of the relativistic Fermi gas model, applies to
inclusive electron scattering from nuclei. We find that data obtained from the
low energy loss side of the quasielastic peak exhibit the superscaling
property, i.e., the scaling functions f(\psi') are not only independent of
momentum transfer (the usual type of scaling: scaling of the first kind), but
coincide for A \geq 4 when plotted versus a dimensionless scaling variable
\psi' (scaling of the second kind). We use this behavior to study as yet poorly
understood properties of the inclusive response at large electron energy loss.Comment: 33 pages, 12 color EPS figures, LaTeX2e using BoxedEPSF macros; email
to [email protected]
Realistic Model of the Nucleon Spectral Function in Few- and Many- Nucleon Systems
By analysing the high momentum features of the nucleon momentum distribution
in light and complex nuclei, it is argued that the basic two-nucleon
configurations generating the structure of the nucleon Spectral Function at
high values of the nucleon momentum and removal energy, can be properly
described by a factorised ansatz for the nuclear wave function, which leads to
a nucleon Spectral Function in the form of a convolution integral involving the
momentum distributions describing the relative and center-of-mass motion of a
correlated nucleon-nucleon pair embedded in the medium. The Spectral Functions
of and infinite nuclear matter resulting from the convolution formula
and from many-body calculations are compared, and a very good agreement in a
wide range of values of nucleon momentum and removal energy is found.
Applications of the model to the analysis of inclusive and exclusive processes
are presented, illustrating those features of the cross section which are
sensitive to that part of the Spectral Function which is governed by
short-range and tensor nucleon-nucleon correlations.Comment: 40 pages Latex , 16 ps figures available from the above e-mail
address or from [email protected]
Rigidity percolation in a field
Rigidity Percolation with g degrees of freedom per site is analyzed on
randomly diluted Erdos-Renyi graphs with average connectivity gamma, in the
presence of a field h. In the (gamma,h) plane, the rigid and flexible phases
are separated by a line of first-order transitions whose location is determined
exactly. This line ends at a critical point with classical critical exponents.
Analytic expressions are given for the densities n_f of uncanceled degrees of
freedom and gamma_r of redundant bonds. Upon crossing the coexistence line, n_f
and gamma_r are continuous, although their first derivatives are discontinuous.
We extend, for the case of nonzero field, a recently proposed hypothesis,
namely that the density of uncanceled degrees of freedom is a ``free energy''
for Rigidity Percolation. Analytic expressions are obtained for the energy,
entropy, and specific heat. Some analogies with a liquid-vapor transition are
discussed. Particularizing to zero field, we find that the existence of a
(g+1)-core is a necessary condition for rigidity percolation with g degrees of
freedom. At the transition point gamma_c, Maxwell counting of degrees of
freedom is exact on the rigid cluster and on the (g+1)-rigid-core, i.e. the
average coordination of these subgraphs is exactly 2g, although gamma_r, the
average coordination of the whole system, is smaller than 2g. gamma_c is found
to converge to 2g for large g, i.e. in this limit Maxwell counting is exact
globally as well. This paper is dedicated to Dietrich Stauffer, on the occasion
of his 60th birthday.Comment: RevTeX4, psfig, 16 pages. Equation numbering corrected. Minor typos
correcte
Relativistic Structure of the Deuteron: 1.Electro-disintegration and y-scaling
Realistic solutions of the spinor-spinor Bethe-Salpeter equation for the
deuteron with realistic interaction kernel including the exchange of pi, sigma,
omega, rho, eta and delta mesons, are used to systematically investigate
relativistic effects in inclusive quasi-elastic electron-deuteron scattering
within the relativistic impulse approximation. Relativistic y-scaling is
considered by generalising the non relativistic scaling function to the
relativistic case, and it is shown that y-scaling does occur in the usual
relativistic scaling variable resulting from the energy conservation in the
instant form of dynamics. The present approach of y-scaling is fully covariant,
with the deuteron being described by eight components, viz. the 3S_1^{++},
3S_1^{--}, 3D_1^{++}, 3D_1^{--}, 3P_1^{+-}, 3P_1^{-+}, 1P_1^{+-}, 1P_1^{-+}
waves. It is demonstrated that if the negative relative energy states 1P_1,
3P_1 are disregarded, the concept of covariant momentum distributions N(p_0,p),
with p_0=M_D/2-\sqrt{p^2+m^2}, can be introduced, and that calculations of
lectro-disintegration cross section in terms of these distributions agree
within few percents with the exact calculations which include the 1P_1, 3P_1
states, provided the nucleon three momentum |p|\<= 1 GeV/c; in this momentum
range, the asymptotic relativistic scaling function is shown to coincide with
the longitudinal covariant momentum distribution.Comment: 32 LaTeX pages, 18 eps-figures. Final version to appear in Phys. Rev.
Learning L2 collocations incidentally from reading
Previous studies have shown that intentional learning through explicit instruction is effective for the acquisition of collocations in a second language (L2) (e.g. Peters, 2014, 2015), but relatively little is known about the effectiveness of incidental approaches for the acquisition of L2 collocations. The present study examined the incidental acquisition of collocational knowledge when learners encounter adjective-pseudoword collocations while reading. Forty-one L2 learners read a story containing six target collocations in a classroom setting. One week after the reading they were interviewed about their knowledge of the form, meaning and collocation of the target items (at recall and recognition levels). Participants were randomly assigned to one of two experimental groups, i.e. the 4-repetition group and the 8-repetition group. Results showed that collocational knowledge can be learnt incidentally from reading; that it is learnt at a similar rate to other lexical components such as form and meaning of individual words; and that the frequency manipulation in this study did not seem to have a significant effect on the acquisition of any of the aspects examined
Leadership in Improving Schools: A Qualitative Perspective
This article reports early case-study data gathered from 20 schools involved in the ‘Impact of School Leadership on Pupil Outcomes’ project. We present and discuss the perceptions of headteachers and other school leaders regarding leadership factors that directly and indirectly affect pupil outcomes in these improving schools. Included are issues relating to the pivotal role played by the headteacher in setting and communicating a strategic vision for the school; models of distributed leadership; and the building of leadership capacity so as to build a collective responsibility for the improvement of pupil outcomes
Nuclear transparency from quasielastic A(e,e'p) reactions uo to Q^2=8.1 (GeV/c)^2
The quasielastic (e,ep) reaction was studied on targets of
deuterium, carbon, and iron up to a value of momentum transfer of 8.1
(GeV/c). A nuclear transparency was determined by comparing the data to
calculations in the Plane-Wave Impulse Approximation. The dependence of the
nuclear transparency on and the mass number was investigated in a
search for the onset of the Color Transparency phenomenon. We find no evidence
for the onset of Color Transparency within our range of . A fit to the
world's nuclear transparency data reflects the energy dependence of the free
proton-nucleon cross section.Comment: 11 pages, 6 figure
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