Intermittent activity of radio sources. Accretion instabilities and jet precession

We consider the radiation pressure instability operating on short timescales 10^3 - 10^6 years in the accretion disk around a supermassive black hole as the origin of the intermittent activity of radio sources. We test whether this instability can be responsible for short ages (<10^4 years) of Compact Steep Spectrum sources measured by hot spots propagation velocities in VLBI observations and statistical overabundance of Gigahertz Peaked Spectrum sources.The implied timescales are consistent with the observed ages of the sources. We aslo discuss possible implications of the intermittent activity on the complex morphology of radio sources, such as the quasar 1045+352, dominated by a knotty jet showing several bends. It is possible that we are whitnessing an ongoing jet precession in this source due to internal instabilities within the jet flow.Comment: 2 pages, 1 figure, Proceedings of the 275 IAU Symposium "Jets at all scales", Buenos Aires, 13-17.09.2010; eds. G. Romero, R. Sunyaev, T. Bellon

On the effect of surfactant adsorption and viscosity change on apparent slip in hydrophobic microchannels

Substantial experimental, theoretical, as well as numerical effort has been invested to understand the effect of boundary slippage in microfluidic devices. However, even though such devices are becoming increasingly important in scientific, medical, and industrial applications, a satisfactory understanding of the phenomenon is still lacking. This is due to the extremely precise experiments needed to study the problem and the large number of tunable parameters in such systems. In this paper we apply a recently introduced algorithm to implement hydrophobic fluid-wall interactions in the lattice Boltzmann method. We find a possible explanation for some experiments observing a slip length depending on the flow velocity which is contradictory to many theoretical results and simulations. Our explanation is that a velocity dependent slip can be detected if the flow profile is not fully developed within the channel, but in a transient state. Further, we show a decrease of the measured slip length with increasing viscosity and demonstrate the effect of adding surfactant to a fluid flow in a hydrophobic microchannel. The addition of surfactant can shield the repulsive potential of hydrophobic walls, thus lowering the amount of slip with increasing surfactant concentration.Comment: 9 pages, 6 figure

Speed and accuracy of dyslexic versus typical word recognition: an eye-movement investigation

Developmental dyslexia is often characterized by a dual deficit in both word recognition accuracy and general processing speed. While previous research into dyslexic word recognition may have suffered from speed-accuracy trade-off, the present study employed a novel eye tracking task that is less prone to such confounds. Participants (10 dyslexics and 12 controls) were asked to look at real word stimuli, and to ignore simultaneously presented non-word stimuli, while their eye-movements were recorded. Improvements in word recognition accuracy over time were modeled in terms of a continuous non-linear function. The words’ rhyme consistency and the non-words’ lexicality (unpronounceable, pronounceable, pseudohomophone) were manipulated within-subjects. Speed related measures derived from the model fits confirmed generally slower processing in dyslexics, and showed a rhyme consistency effect in both dyslexics and controls. In terms of overall error rate, dyslexics (but not controls) performed less accurately on rhyme-inconsistent words, suggesting a representational deficit for such words in dyslexics. Interestingly, neither group showed a pseudohomophone effect in speed or accuracy, which might call the task-independent pervasiveness of this effect into question. The present results illustrate the importance of distinguishing between speed- vs. accuracy related effects for our understanding of dyslexic word recognition

On a Heuristic Analysis of Highly Fractionated 2n Factorial Experiments

The paper deals with a method for the analysis of highly fractionated factorial designs proposed by Raghavarao and Altan (2003). We show that the method will find "active" factors with almost any set of random numbers. Once that an alias set is found active, Raghavarao and Altan (2003) claim that their method can resolve the alias structure of the design and identify which of several confounded effects is active. We show that their method cannot do that. The error in Raghavarao and Altan's (2003) arguments lies in the fact that they treat a set of highly dependent (sometimes even identical) F-statistics as if they were independent. --Fractional factorial designs,half-normal plot,heuristic arguments,active effects,alias set

Ageing and Mobility in Germany: Are Women Taking the Fast Lane?

Results from travel demand research in many countries show that - on average - women are less mobile and have different mobility patterns than men. Recent longitudinal studies of gender specific travel demand reveal converging mobility of males and females. Moreover, in some countries results show convergence between cohort and gender specific travel demand: women and men display more and more similar travel behaviour while older individuals today have higher mobility demands than ever before. Do these developments hold also for Germany? Based on socio-economic and demographic analysis of gender specific travel behaviour using the German mobility survey data from 2002, we ask what individual travel patterns can be expected for the future in the year 2025. We place emphasis on the importance of educational attainment and labour force participation for the assessment of future personal mobility.travel demand, cohort effects, gender, households, ageing population

Exact optimal designs for weighted least squares analysis with correlated errors

In the common linear and quadratic regression model with an autoregressive error structure exact D-optimal designs for weighted least squares analysis are determined. It is demonstrated that for highly correlated observations the D-optimal design is close to the equally spaced design. Moreover, the equally spaced design is usually very efficient, even for moderate sizes of the correlation, while the D-optimal design obtained under the assumptions of independent observations yields a substantial loss in efficiency. We also consider the problem of designing experiments for weighted least squares estimation of the slope in a linear regression and compare the exact D-optimal designs for weighted and ordinary least squares analysis. --Autoregressive errors,linear regression,quadratic regression,exact D-optimal designs,estimation of the slope,generalized MANOVA

Mileage of Motor Vehicles in 2004 Higher Than Ever Before

2003 saw a slight decline in the mileage of vehicle kilometers driven annually by all German road passenger and freight vehicles. This development did not continue in 2004; instead the mileage, at 697 billion vehicle kilometers, was higher than ever before, despite the fact that fuel prices continued to rise. Where freight vehicles are concerned, the number of vehicles on the road hardly changed as compared to 2003; the volume of goods to be transported only rose marginally. Since, however, transport distances increased, the mileage of German freight and semitrailer trucks was 1.3% higher in 2004 as compared to the previous year. The mileage of passenger cars registered in Germany even increased by 2.3% to 591 billion vehicle kilometers. The decline in 2003 was clearly not a shift in the trend, but rather one of the short-term adjustment reactions by consumers, as has often occurred in the past. Average consumption of motor vehicles decreased only marginally in the past year; total consumption of fuel in the traffic sector increased by 1.6%. The amount of the climate-relevant CO2 gas emitted even rose by 1.8%, since the increase of consumption was larger for diesel fuel with higher CO2 exhaust per liter than gasoline.