On the Ehrenfest theorem of quantum mechanics

We give a mathematically rigorous derivation of Ehrenfest's equations for the evolution of position and momentum expectation values, under general and natural assumptions which include atomic and molecular Hamiltonians with Coulomb interactions.Comment: To appear in J. Math. Phy

Climbing the water ladder: multiple-use water services for poverty reduction

Multiple use / Models / Water productivity / Research projects / Water supply / Domestic water / Irrigation water / Water governance / Poverty / Gender / Rural areas / Wells / Water harvesting / Runoff / Water storage / Water purification / Appropriate technology / Costs / Local government / Non governmental organizations / Case studies / Ehiopia / Nepal / Zimbabwe / Bolivia / India / Colombia / Thailand / South Africa

Effects of Dust Scattering in Expanding Spherical Nebulae

The mean intensity of planetary nebulae with an expanding atmosphere is modeled by considering dusty and dust-free atmospheres. The bulk matter density is determined from the adopted velocity field through the equation of continuity. The gas is assumed to consist of hydrogen and helium and the gas-to-dust mass ratio is taken to be $3\times10^{-4}$. The Rayleigh phase function is employed for atomic scattering while the full Mie theory of scattering is incorporated for determining the dust scattering and absorption cross-section as well as the phase function for the angular distribution of photons after scattering. It is shown that in a dust free atmosphere, the mean intensity increases with the increase in the expansion velocity that makes the medium diluted. The mean intensity profile changes significantly when dust scattering is incorporated. The increase in forward scattering of photons by the dust particles yields into an increase in the mean intensity as compared to that without dust. The mean intensity increases as the particle size is increased. Thus it is shown that both the expansion of the medium and the presence of dust play important role in determining the mean intensity of a planetary nebulae.Comment: 18 pages, Elseveir style (cls file included), 5 postscript figures, Accepted for publication in New Astronom

Quasar Evolution and the Baldwin Effect in the Large Bright Quasar Survey

From a large homogeneous sample of optical/UV emission line measurements for 993 quasars from the Large Bright Quasar Survey (LBQS), we study correlations between emission line equivalent width and both restframe ultraviolet luminosity (i.e., the Baldwin Effect) and redshift. Our semi-automated spectral fitting accounts for absorption lines, fits blended iron emission, and provides upper limits to weak emission lines. Use of a single large, well-defined sample and consistent emission line measurements allows us to sensitively detect many correlations, most of which have been previously noted. A new finding is a significant Baldwin Effect in UV iron emission. Further analysis reveals that the primary correlation of iron emission strength is probably with redshift, implying an evolutionary rather than a luminosity effect. We show that for most emission lines with a significant Baldwin Effect, and for some without, evolution dominates over luminosity effects. This may reflect evolution in abundances, in cloud covering factors, or overall cloud conditions such as density and ionization. We find that in our sample, a putative correlation between Baldwin Effect slope and the ionization potential is not significant. Uniform measurements of other large quasar samples will extend the luminosity and redshift range of such spectral studies and provide even stronger tests of spectral evolution.Comment: 16 pages, Latex, emulateapj style, including 3 tables and 6 figures. Accepted April 02, 2001 for publication in ApJ Main Journal. See also http://hea-www.harvard.edu/~pgreen/Papers.htm

Initial Ionization of Compressible Turbulence

We study the effects of the initial conditions of turbulent molecular clouds on the ionization structure in newly formed H_{ii} regions, using three-dimensional, photon-conserving radiative transfer in a pre-computed density field from three-dimensional compressible turbulence. Our results show that the initial density structure of the gas cloud can play an important role in the resulting structure of the H_{ii} region. The propagation of the ionization fronts, the shape of the resulting H_{ii} region, and the total mass ionized depend on the properties of the turbulent density field. Cuts through the ionized regions generally show ``butterfly'' shapes rather than spherical ones, while emission measure maps are more spherical if the turbulence is driven on scales small compared to the size of the H_{ii} region. The ionization structure can be described by an effective clumping factor $\zeta=< n > \cdot /^2$, where $n$ is number density of the gas. The larger the value of $\zeta$, the less mass is ionized, and the more irregular the H_{ii} region shapes. Because we do not follow dynamics, our results apply only to the early stage of ionization when the speed of the ionization fronts remains much larger than the sound speed of the ionized gas, or Alfv\'en speed in magnetized clouds if it is larger, so that the dynamical effects can be negligible.Comment: 9 pages, 10 figures, version with high quality color images can be found in http://research.amnh.org/~yuexing/astro-ph/0407249.pd

One Probe - Two Goals: Aspects of agreement in Dutch dialects

In Dutch dialects, verbs and complementizers can bear different morphological affixes depending on which nominal element they agree with in their local syntactic domain. For instance, in a dialect such as tegelen Dutch, the complementizer agrees with the first conjunct of a coordinated subject, while in Lapscheure Dutch, the complementizer agrees with the coordinated subject as a whole. Using a vast array of new data on complementizer agreement, first conjunct agreement, agreement with pronouns, verbal agreement and subject doubling in Dutch dialects, this study argues that the interplay between syntax and morphology is more intricate than has hitherto been assumed. More precisely, it is shown that the syntactic component determines which local nominal elements qualify for agreement with the verb or complementizer, depending on the specificity of the affix. The analysis is extended to similar syntactic contexts in typologically different languages such as Irish, Hebrew, Finnish, Tsez and Arabic.UBL - phd migration 201

Leren in een levensloop : kwalitatief onderzoek naar jeugdervaringen die bijdragen aan betrokkenheid bij natuur en milieu

Dit rapport beschrijft een onderzoek naar de invloed van jeugdervaringen - met name in de basisschoolperiode - op de manier waarop mensen later omgaan met natuur en milieu. Het onderzoek bouwt voort op het onderzoek "Hoe duurzaam is NME?" van Smit et al. (2006). Uit de steekproef van Smit werden 23 respondenten van vier scholen geselecteerd. Daarbij is gezorgd voor een gebalanceerde vertegenwoordiging van leerlingen met meer en minder milieubetrokkenheid en scholen met relatief veel en weinig NME-activiteiten. Uit de resultaten blijkt dat ouders de meeste invloed hebben op de manier waarop mensen met natuur en milieu omgaan. Voor een meerderheid van de respondenten hebben de ouders duidelijk invloed gehad op de huidige omgang met natuur en milieu