Satellite-tracked cumulus velocities

The research indicates that extreme caution must be exercised in converting cloud velocities into winds. The motion of fair-weather cumuli obtained by tracking their shadows over Springfield, Missouri revealed that the standard deviation in the individual cloud motion is several times the tracking error. The motion of over-ocean cumuli near Barbados clearly indicated the complicated nature of cumulus velocities. Analysis of whole-sky images obtained near Tampa, Florida failed to show significant continuity and stability of cumulus plumes, less than 0.3 mile in diameter. Cumulus turrets with 0.3 to 2 mile in size appear to be the best target to infer the mean wind within the subcloud layers. Cumulus or stratocumulus cells consisting of x number of turrets do not always move with wind. The addition and deletion of turrets belonging to a specific cell appear to be the cause of the erratic motion of a tracer cell. It may by concluded that the accuracy of wind estimates is unlikely to be better than 2m/sec unless the physical and dynamical characteristics of cumulus motion is futher investigated

Vergrijzing: ramp of uitdaging

De veranderingen in het demografische landschap van ederland zijn snel gegaan.Wetenschappers en politici zijn nog druk bezig met het in kaart brengen van die veranderingen en het doorgronden van hun betekenis. Er is ook veel negativisme en mythevorming. Dit geldt vooral wanneer over onze vergrijzende samenleving wordt gesproken. Rampenscenario’s worden geschetst: de gezondheidszorg en de AOW worden onbetaalbaar, de kosten van de pensioenen zullen exponentieel toenemen, de arbeidsmarkt zal verstarren en de capaciteit van de mantelzorg zal ontoereikend zijn. Het gebrek aan demografische basiskennis in veel van deze toekomstschetsen is opvallend. Daarom hier een beeld dat de demografische realiteit minder geweld aandoet

De aanpak van eenzaamheid

Veel mensen in Nederland zijn eenzaam. Vaak heeft dat te maken met het overlijden van een naaste, scheiding, ziekte, pensionering, verhuizing en een opeenstapeling van problemen. Meestal is eenzaamheid tijdelijk. Langdurige eenzaamheid vermindert de kwaliteit van leven en kan leiden tot ernstige lichamelijke en psychische klachten. Eenzaamheid is ook een maatschappelijk probleem. Denk aan maatschappelijk ongewenst gedrag, verwaarlozing en verslaving. Eenzaam zijn is nog steeds taboe en daardoor ook een verborgen probleem. Mensen willen noch aan zichzelf noch aan anderen toegeven dat ze eenzaam zijn. Via interventies wordt geprobeerd om de eenzaamheid te bestrijden. Er bestaan evenwel hardnekkige misverstanden rond eenzaamheid. Zo zou eenzaamheid zijn toegenomen door de voortschrijdende individualisering, zouden vooral ouderen en alleenstaanden er last van hebben en zou een contactrijke omgeving de eenzaamheid verminderen. Veel zaken kunnen de interventie echter in de weg staan en daardoor de kans op succes verminderen. Eenzaamheid is een complex verschijnsel, van buitenaf niet waarneembaar, en kent vele oorzaken en oplossingsmogelijkheden

Norms of filial obligation in the Netherlands

In this article we examine to what extent norms of filial obligation in the Netherlands are shaped by group value patterns, family constellation, possibilities for helping others, and actual experiences of support exchange. The data are drawn from the first wave of the combined main and migrant sample of the Netherlands Kinship Panel Study, the Dutch participant in the Generations and Gender Programme. The Dutch appear reluctant to prescribe how other people should behave towards their ageing parents. Value patterns are the strongest determinants of filial norms, with migrants, the low-educated, and persons with religious beliefs espousing strong filial norms. Contrary to what traditional gender roles would suggest, women less strongly endorse norms of filial obligation than men, and contrary to the notion that divorce weakens family ties, divorcees and children of divorce do not exhibit less commitment to filial norms. Altruistic tendencies are evident in the weaker filial norms among the older age groups, and among those with non co-resident children. Finally, the results show a high level of consonance between actual support exchanges and filial norms

The Phase Diagram of 1-in-3 Satisfiability Problem

We study the typical case properties of the 1-in-3 satisfiability problem, the boolean satisfaction problem where a clause is satisfied by exactly one literal, in an enlarged random ensemble parametrized by average connectivity and probability of negation of a variable in a clause. Random 1-in-3 Satisfiability and Exact 3-Cover are special cases of this ensemble. We interpolate between these cases from a region where satisfiability can be typically decided for all connectivities in polynomial time to a region where deciding satisfiability is hard, in some interval of connectivities. We derive several rigorous results in the first region, and develop the one-step--replica-symmetry-breaking cavity analysis in the second one. We discuss the prediction for the transition between the almost surely satisfiable and the almost surely unsatisfiable phase, and other structural properties of the phase diagram, in light of cavity method results.Comment: 30 pages, 12 figure

The Bethe approximation for solving the inverse Ising problem: a comparison with other inference methods

The inverse Ising problem consists in inferring the coupling constants of an Ising model given the correlation matrix. The fastest methods for solving this problem are based on mean-field approximations, but which one performs better in the general case is still not completely clear. In the first part of this work, I summarize the formulas for several mean- field approximations and I derive new analytical expressions for the Bethe approximation, which allow to solve the inverse Ising problem without running the Susceptibility Propagation algorithm (thus avoiding the lack of convergence). In the second part, I compare the accuracy of different mean field approximations on several models (diluted ferromagnets and spin glasses) defined on random graphs and regular lattices, showing which one is in general more effective. A simple improvement over these approximations is proposed. Also a fundamental limitation is found in using methods based on TAP and Bethe approximations in presence of an external field.Comment: v3: strongly revised version with new methods and results, 25 pages, 21 figure

Finite-Connectivity Spin-Glass Phase Diagrams and Low Density Parity Check Codes

We obtain phase diagrams of regular and irregular finite connectivity spin-glasses. Contact is firstly established between properties of the phase diagram and the performances of low density parity check codes (LDPC) within the Replica Symmetric (RS) ansatz. We then study the location of the dynamical and critical transition of these systems within the one step Replica Symmetry Breaking theory (RSB), extending similar calculations that have been performed in the past for the Bethe spin-glass problem. We observe that, away from the Nishimori line, in the low temperature region, the location of the dynamical transition line does change within the RSB theory, in comparison with the (RS) case. For LDPC decoding over the binary erasure channel we find, at zero temperature and rate R=1/4 an RS critical transition point located at p_c = 0.67 while the critical RSB transition point is located at p_c = 0.7450, to be compared with the corresponding Shannon bound 1-R. For the binary symmetric channel (BSC) we show that the low temperature reentrant behavior of the dynamical transition line, observed within the RS ansatz, changes within the RSB theory; the location of the dynamical transition point occurring at higher values of the channel noise. Possible practical implications to improve the performances of the state-of-the-art error correcting codes are discussed.Comment: 21 pages, 15 figure

A Novel Document Generation Process for Topic Detection based on Hierarchical Latent Tree Models

We propose a novel document generation process based on hierarchical latent tree models (HLTMs) learned from data. An HLTM has a layer of observed word variables at the bottom and multiple layers of latent variables on top. For each document, we first sample values for the latent variables layer by layer via logic sampling, then draw relative frequencies for the words conditioned on the values of the latent variables, and finally generate words for the document using the relative word frequencies. The motivation for the work is to take word counts into consideration with HLTMs. In comparison with LDA-based hierarchical document generation processes, the new process achieves drastically better model fit with much fewer parameters. It also yields more meaningful topics and topic hierarchies. It is the new state-of-the-art for the hierarchical topic detection

On Cavity Approximations for Graphical Models

We reformulate the Cavity Approximation (CA), a class of algorithms recently introduced for improving the Bethe approximation estimates of marginals in graphical models. In our new formulation, which allows for the treatment of multivalued variables, a further generalization to factor graphs with arbitrary order of interaction factors is explicitly carried out, and a message passing algorithm that implements the first order correction to the Bethe approximation is described. Furthermore we investigate an implementation of the CA for pairwise interactions. In all cases considered we could confirm that CA[k] with increasing $k$ provides a sequence of approximations of markedly increasing precision. Furthermore in some cases we could also confirm the general expectation that the approximation of order $k$, whose computational complexity is $O(N^{k+1})$ has an error that scales as $1/N^{k+1}$ with the size of the system. We discuss the relation between this approach and some recent developments in the field.Comment: Extension to factor graphs and comments on related work adde