A Householder-based algorithm for Hessenberg-triangular reduction

The QZ algorithm for computing eigenvalues and eigenvectors of a matrix pencil $A - \lambda B$ requires that the matrices first be reduced to Hessenberg-triangular (HT) form. The current method of choice for HT reduction relies entirely on Givens rotations regrouped and accumulated into small dense matrices which are subsequently applied using matrix multiplication routines. A non-vanishing fraction of the total flop count must nevertheless still be performed as sequences of overlapping Givens rotations alternately applied from the left and from the right. The many data dependencies associated with this computational pattern leads to inefficient use of the processor and poor scalability. In this paper, we therefore introduce a fundamentally different approach that relies entirely on (large) Householder reflectors partially accumulated into block reflectors, by using (compact) WY representations. Even though the new algorithm requires more floating point operations than the state of the art algorithm, extensive experiments on both real and synthetic data indicate that it is still competitive, even in a sequential setting. The new algorithm is conjectured to have better parallel scalability, an idea which is partially supported by early small-scale experiments using multi-threaded BLAS. The design and evaluation of a parallel formulation is future work

Regional Growth and Access to Knowledge and Dense Markets -An Empirical Study of the Performance in Sweden.

Access to knowledge and local service markets can be assumed to explain regional growth performance. The supply of services and knowledge with respect to regional development are stressed in the seminal papers by for example Rivera-Batiz (1988) and Knowledge referens. In this paper we make an empirical analyse using panel data for Swedish regions. The purpose is to analyse the relationship between regional growth and access to knowledge. We also acknowledge the size of the regional economy and access to the local labour market. We estimate first a cross-section model by using OLS. Second we employ a panel data model, using time distance access to population and the share local labour force with high education as explanatory variables. In the analysis we compare the results from the different models and our own results from the Swedish economy with other studies in this field. We find that local externalities for increasing returns are very important in the Swedish economy. Our estimated models yields a high level of goodness of fit, and the results indicates significant elasticity for high education and population density in the Swedish economy with respect to performance of regional gross domestic product.

GPS measurement of Swedish car movements for assessment of possible electrification

To enhance the transition to electrified vehicles, such as PHEVs, the use patterns of cars need to be well understood and thus information about individual vehicle’s movements over longer time periods is needed. This is of major importance for instance for optimal powertrain and battery design, estimation of consumer viability and potential for PHEVs and for assessment of policies for shifting energy use in transport sector from fuel to electricity. Good and publicly available data of this kind is today unfortunately lacking. The aim of this project has been to gather a larger amount of data on the characteristics and distribution of individual movements for privately driven cars in Sweden by measurement with GPS equipment. The logging was performed with commercial equipment containing a GPS unit, including a roof-mounted antenna, and a gprs communication unit. Data logged (2.5 Hz) were: time, position, velocity, and number and id of used satellites. The measurements started in June 2010 and ended in September 2012. The target has been to accomplish good quality measurements of at least 30 days for about 500 representative vehicles. The paper includes a description of the project, an analysis of its representativeness and some car movement statistics for the full results

The possibility for energy regeneration by electrification in Swedish car driving

The ability to regenerate energy when braking is a valuable advantage of hybrid and fully electric vehicles. How much energy that can be regenerated depends mainly on the car driving and the capacity of the driveline. Detailed studies of possibilities for brake energy regeneration in real world driving are needed to better understand the potential gains of car-electrification since test cycles do not take individual driving or elevation into account. This study has analysed the potential for regeneration in Swedish car driving by applying a model for a normalized vehicle to a highly detailed and representative data set of individual car movements for privately driven cars in Sweden. The share of energy at the wheels used for braking was found to range from 12% to 63%, with an average of 30%. Engine braking could however reduce the amount of recoverable energy to about 16%. On average 42% and 89% of the potentially regenerable energy is available below 10 and 40 kW, respectively. Drivers with lower average speed have in general a higher share of the energy at the wheels potentially available for regeneration. This is however not an important factor to determine the total yearly energy/cost savings. Instead the yearly mileage is shown to be a more relevant indicator on total energy savings from regeneration. The results are compared to the NEDC and WLTP test cycles

The potential for brake energy regeneration under Swedish conditions

The ability to regenerate energy when braking is a valuable advantage of hybrid and fully electric vehicles. The regeneration potential mainly depends on how a car is driven and on the capacity of the drivetrain. Detailed studies of the regeneration potential based on brake energy in real-world driving are needed to better understand the potential gains of car-electrification, since test cycles do not take individual driving characteristics or route elevation into account. This study uses a model of a normalized vehicle and a highly detailed and representative data set of individual car movements including elevation to analyze the potential for energy regeneration in cars when driven under current real-world Swedish conditions.The ultimate energy regeneration potential (defined as the braking energy at the wheels) varies by about a factor of six among individual movement patterns, with an average of 0.033 kW h/km, corresponding to 27% of the total average energy supplied at the wheels. Earlier studies have shown a higher energy regeneration potential per km for cars driving under urban conditions with low average velocity and many starts and stops. Our results confirm this but also point out that a low average velocity and a high share of city driving are not very well correlated with the yearly energy savings; for this the yearly mileage is a more important indicator. This suggests that drivers who rack up the miles should be targeted as potential early adopters of regenerative technologies rather than city drivers per se. The results from real-world driving are compared to the NEDC and WLTP test cycles

Predator faunas past and present: quantifying the influence of waterborne cues in divergent ecotypes of the isopod Asellus aquaticus

Waterborne chemical cues are an important source of information for many aquatic organisms, in particular when assessing the current risk of predation. The ability to use chemical cues to detect and respond to potential predators before an actual encounter can improve prey chances of survival. We investigated predator recognition and the impact of chemical cues on predator avoidance in the freshwater isopod Asellus aquaticus. This isopod has recently colonised a novel habitat and diverged into two distinct ecotypes, which encounter different predator communities. Using laboratory-based choice experiments, we have quantified behavioural responses to chemical cues from predators typical of the two predator communities (larval dragonflies in the ancestral habitat, perch in the newly colonised habitat) in wild-caught and lab-reared Asellus of the two ecotypes. Individuals with prior experience of predators showed strong predator avoidance to cues from both predator types. Both ecotypes showed similar antipredator responses, but sexes differed in terms of threat-sensitive responses with males avoiding areas containing predator cues to a larger extent than females. Overall, chemical cues from fish elicited stronger predator avoidance than cues from larval dragonflies. Our results indicate that in these isopods, prior exposure to predators is needed to develop antipredator behaviour based on waterborne cues. Furthermore, the results emphasise the need to analyse predator avoidance in relation to waterborne cues in a sex-specific context, because of potential differences between males and females in terms of vulnerability and life history strategies

Recent Research Concerning the Walls at Asea

Papers from the third international seminar on Ancient Arcadia, held at the Norwegian Institute at Athens, 7-10 May 2002The fortification walls of Asea Paleokastro in Arcadia have recently been studied in several different aspects. Thus, the parts of the walls which are still visible above the ground have been documented in detail. Furthermore, an attempt has been made to trace the course of the lower city walls which are covered by modem alluvium with the help of various geophysical methods. As a result we suggest that the acropolis walls should be dated to the classical period, whereas the lower city walls probably were constructed during the Kleomenic war (229/28-222 B.C.) Cleaning work done around the main gateway of the acropolis indicates that the road leading up to the acropolis originallly was constructed for carts. During the Late Byzantine period the acropolis was refortified, and some walls belonging to this phase are still to be seen at the main gateway and the summit of the acropolis. Preliminary results of the geophysical prospection finally indicate that the lower circuit wall may have had a total length of ca. 1 km, enclosing an area of about 11 ha