16,410 research outputs found
Do school inspections improve primary school performance?
Inspectors from the Dutch Inspectorate of Education inspect primary schools, write inspection reports on each inspected school, and make recommendations as to how each school can improve. We test whether these inspections result in better school performance. Using a fixed-effects model, we find evidence that school inspections do lead to measurably better school performance. Our assessment of school performance is based on the Cito test scores of pupils in their final year of primary school. Therefore school improvement means increased Cito test scores. The results indicate that the Cito test scores improve by 2% to 3% of a standard deviation of the test score in the two years following an inspection. The arithmetic component shows the largest improvement. Our estimates are the result of an analysis of two types of school inspections performed between 1999 and 2002, where one type was more intensive than the other. In one fixed-effects model, we assume that the effect of the two types of school inspections was the same. We cannot, however, be sure that the estimates from this model are free from the problem of endogeneity bias. Therefore, we also obtain estimates for a less restrictive fixed-effects model. In this less restrictive model, we make use of the fact that a subset of the more intensive school inspections occurs at a representative selection of primary schools. Based on this smaller, essentially randomly drawn sample of schools, we can be confident that these estimates of the effect of school inspections are free from endogeneity bias. Due to the limited number of inspections at randomly selected schools, these estimates are not significantly different from zero. These estimates are, however, consistent with the effects found based on all inspections. The less restrictive model also allows for the effect of the more intensive inspections to differ from that for the less intensive ones. We find evidence that the more intensive inspections are responsible for larger increases in the Cito test scores than the less intensive ones.
A Forensic Speaker Identification Study. An Auditory-Acosutic Analysis of Phonetic Features and an Exploration of the "Telephone Effect"
This study investigates the formant, fundamental frequency, and speech tempo parameters in a forensic speaker identification setting and whether these are adequate features to use in an auditory-acoustic analysis. Furthermore, the 'telephone effect' as described by Künzel (2001) is examined and analysed in terms of whether it applies to the aforementioned phonetic features. The results showed that all three parameters proved to be efficient and appropriate for forensic speaker identification practices, but that the articulation rate of the disputed sample was heavily affected by a task-effect. In terms of the intercept recordings, F1 values, especially those of close vowels, were found to be affected, consistent with Künzel's findings (2001). Mean fundamental frequency values were not altered by the intercept sample, but the standard deviation was, resulting in values twice as high compared to direct recordings.Aquest estudi investiga els paràmetres de formant, freqüència fonamental, i velocitat de l'articulació en un entorn de la identificació forense del parlant i si aquests paràmetres són adequats per utilitzar en una anàlisi auditiva-acústica. D'altra banda, 'l'efecte telefònic' descrit per Künzel (2001) és examinat i analitzat pel que fa a si és aplicable a les característiques fonètiques esmentades anteriorment. Els resultats van mostrar que els tres paràmetres són eficients i adequats per a les pràctiques d'identificació forense del parlant, però que la velocitat de l'articulació estava molt afectada per un efecte de tasca. Pel que fa a les gravacions interceptades, els valors de l'F1, especialment els de les vocals tancades, es van trobar afectats, la qual cosa és consistent amb els resultats de l'experiment de Künzel (2001). Els valors mitjans de la freqüència fonamental no van ser alterats per l'enregistrament telefònic, però la desviació estàndar, sí, mostrant valors el doble d'alts comparats amb les gravacions directes
Fundamental limitations in the purifications of tensor networks
We show a fundamental limitation in the description of quantum many-body
mixed states with tensor networks in purification form. Namely, we show that
there exist mixed states which can be represented as a translationally
invariant (TI) matrix product density operator (MPDO) valid for all system
sizes, but for which there does not exist a TI purification valid for all
system sizes. The proof is based on an undecidable problem and on the
uniqueness of canonical forms of matrix product states. The result also holds
for classical states.Comment: v1: 11 pages, 1 figure. v2: very minor changes. About to appear in
Journal of Mathematical Physic
Heat Kernel Asymptotics on Homogeneous Bundles
We consider Laplacians acting on sections of homogeneous vector bundles over
symmetric spaces. By using an integral representation of the heat semi-group we
find a formal solution for the heat kernel diagonal that gives a generating
function for the whole sequence of heat invariants. We argue that the obtained
formal solution correctly reproduces the exact heat kernel diagonal after a
suitable regularization and analytical continuation.Comment: 29 pages, Proceedings of the 2007 Midwest Geometry Conference in
Honor of Thomas P. Branso
Non-perturbative gluon evolution, squeezing, correlations and chaos in jets
We study evolution of colour gluon states in isolated QCD jet at the
non-perturbative stage. Fluctuations of gluons are less than those for coherent
states under specific conditions. This fact suggests that there gluon squeezed
states can arise. The angular and rapidity dependencies of the normalized
second-order correlation function for present gluon states are studied at this
stage of jet evolution. It is shown that these new gluon states can have both
sub-Poissonian and super-Poissonian statistics corresponding to, respectively,
antibunching and bunching of gluons by analogy with squeezed photon states.
We investigate the possibility of coexisting both squeezing and chaos using
Toda criterion and temporal correlator analysis. It is shown that these effects
may coexist under some conditions.Comment: 18 pages, 3 figures, Reported on IPPP Workshop on Multiparticle
Production in QCD Jets (University of Durham, Durham, UK, 12-15 December
2001
Oxygen superstructures throughout the phase diagram of
Short-range lattice superstructures have been studied with high-energy x-ray
diffuse scattering in underdoped, optimally doped, and overdoped . A new four-unit-cell superstructure was observed in
compounds with . Its temperature, doping, and material dependence
was used to attribute its origin to short-range oxygen vacancy ordering, rather
than electronic instabilities in the layers. No significant diffuse
scattering is observed in YBaCuO. The oxygen superstructures must
be taken into account when interpreting spectral anomalies in
Single - particle correlations in events with the total disintegration of nuclei
New experimental data on the behaviour of the single-particle two-dimensional
correlation functions R versus Q (Q is the number of nucleons emitted from nuc-
lei) and Ap (Ap is the mass of projectile nuclei) are presented in this paper.
The interactions of protons, d, 4He and 12C nuclei with carbon nuclei (at a
momentum of 4.2 A GeV/c) are considered.The values of R are obtained separately
for pi minus mesons and protons.In so doing,the values of R are normalized so
that -1=<R=<1.The value of R=0 corresponds to the case of the absence of corre-
lations.It has been found that the Q- and Ap-dependence of R takes place only
for weak correlations (R< 0.3).In the main (90 %),these correlations are con-
nected with the variable pt and have a nonlinear character, that is the regi-
ons with different characters of the Q-dependence of R are separated: there is
a change of regimes in the Q-dependences of R.The correlations weaken with
increasing Ap, and the variable R gets the least values of all the considered
ones in 12CC interactions.Simultaneously with weakening the correlations in the
region of large Q, the character of the Q-dependence of R changes.Comment: 17 pages, submitted to Phys. Rew.
QCD and hybrid NBD on oscillating moments of multiplicity distributions in lepton- and hadron-initiated reactions
QCD predictions for moments of multiplicity distributions are compared with
experimental data on e+e- collisions and their two-NBD fits. Moments of the
multiplicity distribution in a two-NBD model for 1.8 TeV pp collisions are
considered. Three-NBD model predictions and fits for pp at LHC energies are
also discussed. Analytic expressions for moments of hybrid NBD are derived and
used to get insight into jet parameters and multicomponent structure of the
processes. Interpretation of observed correlations is proposed.Comment: 8 pages, no figures, Phys. Lett.
Navigation in Curved Space-Time
A covariant and invariant theory of navigation in curved space-time with
respect to electromagnetic beacons is written in terms of J. L. Synge's
two-point invariant world function. Explicit equations are given for navigation
in space-time in the vicinity of the Earth in Schwarzschild coordinates and in
rotating coordinates. The restricted problem of determining an observer's
coordinate time when their spatial position is known is also considered
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