Description of isolated macroscopic systems inside quantum mechanics

For an isolated macrosystem classical state parameters $\zeta(t)$ are introduced inside a quantum mechanical treatment. By a suitable mathematical representation of the actual preparation procedure in the time interval $[T,t_0]$ a statistical operator is constructed as a solution of the Liouville von Neumann equation, exhibiting at time $t$ the state parameters $\zeta(t')$, $t_0\leq t' \leq t$, and {\it preparation parameters} related to times $T \leq t'\leq t_0$. Relation with Zubarev's non-equilibrium statistical operator is discussed. A mechanism for memory loss is investigated and time evolution by a semigroup is obtained for a restricted set of relevant observables, slowly varying on a suitable time scale.Comment: 13 pages, latex, romp31 style, no figures, to appear in the Proceedings of the XXXI Symposium on Mathematical Physics (Torun, Poland), to be published in Rep. Math. Phy

Effective calculation of LEED intensities using symmetry-adapted functions

The calculation of LEED intensities in a spherical-wave representation can be substantially simplified by symmetry relations. The wave field around each atom is expanded in symmetry-adapted functions where the local point symmetry of the atomic site applies. For overlayer systems with more than one atom per unit cell symmetry-adapted functions can be used when the division of the crystal into monoatomic subplanes is replaced by division into subplanes containing all symmetrically equivalent atomic positions

Identifying predictors for energy poverty in Europe using machine learning

In this paper we identify drivers for energy poverty in Europe using machine learning. The establishment of predictors for energy poverty valid across countries is a call made by many experts, since it could provide a basis to effectively target energy-poor households with adequate policy measures. We apply a “low income, high expenditure” framework that classifies households as being at risk of energy poverty to a dataset from a survey conducted at the household-level in 11 European countries with vastly different economies, cultures, and climates. A gradient boosting classifier is successfully trained on a set of socio-economic features hypothesized as predictors for energy poverty in this diverse set of countries. The classifier's internal model is analyzed, providing novel insights into the intricacies that underlie energy poverty. We find that besides the main driver - income - floor area and household size can be confirmed as predictors. Our results suggest the presence of universal predictors that are valid across Europe, and contextual ones that are governed by local characteristics. To facilitate advanced research into energy poverty in Europe, we recommend to increase and streamline household data collection efforts, both at the country- and EU-level

Modelsimulaties van het stadsklimaat van Rotterdam

Modelsimulaties zijn uitgevoerd ter inschatting van het Urban Heat Island effect van Rotterdam. Hiervoor is de meest recente versie van het Weather Research & Forecasting (WRF) model gebruikt dat is uitgerust met een Urban Canopy Model. Bovendien is gebruik gemaakt van specifieke stadeigenschappen die zeer recent beschikbaar zijn gekome

Self-induced decoherence approach: Strong limitations on its validity in a simple spin bath model and on its general physical relevance

The "self-induced decoherence" (SID) approach suggests that (1) the expectation value of any observable becomes diagonal in the eigenstates of the total Hamiltonian for systems endowed with a continuous energy spectrum, and (2), that this process can be interpreted as decoherence. We evaluate the first claim in the context of a simple spin bath model. We find that even for large environments, corresponding to an approximately continuous energy spectrum, diagonalization of the expectation value of random observables does in general not occur. We explain this result and conjecture that SID is likely to fail also in other systems composed of discrete subsystems. Regarding the second claim, we emphasize that SID does not describe a physically meaningful decoherence process for individual measurements, but only involves destructive interference that occurs collectively within an ensemble of presupposed "values" of measurements. This leads us to question the relevance of SID for treating observed decoherence effects.Comment: 11 pages, 4 figures. Final published versio

From Bloch model to the rate equations II: the case of almost degenerate energy levels

Bloch equations give a quantum description of the coupling between an atom and a driving electric force. In this article, we address the asymptotics of these equations for high frequency electric fields, in a weakly coupled regime. We prove the convergence towards rate equations (i.e. linear Boltzmann equations, describing the transitions between energy levels of the atom). We give an explicit form for the transition rates. This has already been performed in [BFCD03] in the case when the energy levels are fixed, and for different classes of electric fields: quasi or almost periodic, KBM, or with continuous spectrum. Here, we extend the study to the case when energy levels are possibly almost degenerate. However, we need to restrict to quasiperiodic forcings. The techniques used stem from manipulations on the density matrix and the averaging theory for ordinary differential equations. Possibly perturbed small divisor estimates play a key role in the analysis. In the case of a finite number of energy levels, we also precisely analyze the initial time-layer in the rate aquation, as well as the long-time convergence towards equilibrium. We give hints and counterexamples in the infinite dimensional case

Decoherence time in self-induced decoherence

A general method for obtaining the decoherence time in self-induced decoherence is presented. In particular, it is shown that such a time can be computed from the poles of the resolvent or of the initial conditions in the complex extension of the Hamiltonian's spectrum. Several decoherence times are estimated: $10^{-13}-$ $10^{-15}s$ for microscopic systems, and $10^{-37}-10^{-39}s$ for macroscopic bodies. For the particular case of a thermal bath, our results agree with those obtained by the einselection (environment-induced decoherence) approach.Comment: 11 page

Modelling and observing urban climate in the Netherlands

Volgens de klimaatscenario’s van het KNMI uit 2006 zal de gemiddelde temperatuur in Nederland in de komende decennia verder stijgen. Hittegolven zullen naar verwachting vaker voorkomen en de intensiteit van met name zomerse buien kan toenemen. In steden zijn de gevolgen van de opwarming extra voelbaar, omdat de temperaturen er door het zogenoemde Urban Heat Island (UHI) effect veel hoger kunnen zijn dan in het omliggende gebied. Zulke periodes met hoge temperaturen gaan veelal gepaard met verslechterde luchtkwaliteit en droogte. Dit alles kan grote gevolgen hebben voor de leefbaarheid en de gezondheid van de bevolking in stedelijke gebieden. Veranderingen in de buienintensiteit beïnvloeden de waterhuishouding van de stad

Surface and Bulk Structural Properties of Single Crystalline Sr3Ru2O7

We report temperature and thermal-cycling dependence of surface and bulk structures of double-layered perovskite Sr3Ru2O7 single crystals. The surface and bulk structures were investigated using low-energy electron diffraction (LEED) and single-crystal X-ray diffraction (XRD) techniques, respectively. Single-crystal XRD data is in good agreement with previous reports for the bulk structure with RuO6 octahedral rotation, which increases with decreasing temperature (~ 6.7(6)degrees at 300 K and ~ 8.1(2) degrees at 90 K). LEED results reveal that the octahedra at the surface are much more distorted with a higher rotation angle (~ 12 degrees between 300 and 80 K) and a slight tilt ((4.5\pm2.5) degrees at 300 K and (2.5\pm1.7) degrees at 80 K). While XRD data confirms temperature dependence of the unit cell height/width ratio (i.e. lattice parameter c divided by the average of parameters a and b) found in a prior neutron powder diffraction investigation, both bulk and surface structures display little change with thermal cycles between 300 and 80 K.Comment: 25 pages, 5 figures, 5 tables, to appear in Physical Review

Self-limited oxide formation in Ni(111) oxidation

The oxidation of the Ni(111) surface is studied experimentally with low energy electron microscopy and theoretically by calculating the electron reflectivity for realistic models of the NiO/Ni(111) surface with an ab-initio scattering theory. Oxygen exposure at 300 K under ultrahigh-vacuum conditions leads to the formation of a continuous NiO(111)-like film consisting of nanosized domains. At 750 K, we observe the formation of a nano-heterogeneous film composed primarily of NiO(111)-like surface oxide nuclei, which exhibit virtually the same energy-dependent reflectivity as in the case of 300 K and which are separated by oxygen-free Ni(111) terraces. The scattering theory explains the observed normal incidence reflectivity R(E) of both the clean and the oxidized Ni(111) surface. At low energies R(E) of the oxidized surface is determined by a forbidden gap in the k_parallel=0 projected energy spectrum of the bulk NiO crystal. However, for both low and high temperature oxidation a rapid decrease of the reflectivity in approaching zero kinetic energy is experimentally observed. This feature is shown to characterize the thickness of the oxide layer, suggesting an average oxide thickness of two NiO layers.Comment: 10 pages (in journal format), 9 figure