A fixed terrestrial wireless system such as the Microwave Multi-channel Distribution Service (MMDS) can be used as the ``last mile' to provide a high speed Internet connection from a base station to a home in a rural or suburban residential area. Such a broadband wireless system works very well under line-of-sight transmission. It works quite well even if the line-of-sight is obstructed with a large number of trees. However, when trees obstruct the line-of-sight, under conditions of wind, the user may experience loss of the RF signal from time to time. This is especially true under gusty conditions. As part of this research a high precision DSP-based measuring system is devised to accurately measure and characterize the distortions caused by tree foliage on the RF line-of-sight signal. The approach is to digitally generate a signal composed of several tones, up-convert the signal to 2.5 GHz and send it through tree foliage to a receiver where the signal is down-converted and sampled for a duration of five seconds. The samples collected are processed using Matlab to compute the temporal amplitude and phase variations of the tones. The measurement system provides estimates of the amplitude and phase of the receive tones with a time resolution of 3.2 ms. The standard deviation of the amplitude estimates is 0.3\% of the actual amplitude of the tones and the standard deviation of the phase estimates is 0.23 degree. This accuracy is obtained when the signal-to-noise ratio of the receive signal is greater than 20 dB. Measurement in the field with tree foliage in the line-of-sight shows that the swaying of the branches in the wind can cause rapid signal fading. This research determines the type of fade, the depth and duration of the fade, as well as the fading rate.

Recently, the transmission of vector quantization (VQ) over a code-division multiple access (CDMA) channel has received a considerable attention in research community. The complexity of the optimal decoding for VQ in CDMA communications is prohibitive for implementation, especially for systems with a medium or large number of users. A suboptimal approach to VQ decoding over a CDMA channel, disturbed by additive white Gaussian noise (AWGN), was recently developed. Such a suboptimal decoder is built from a soft-output multiuser detector (MUD), a soft bit estimator and the optimal soft VQ decoders of individual users. <p>Due to its lower complexity and good performance, such a decoding scheme is an attractive alternative to the complicated optimal decoder. It is necessary to extend this decoding scheme for a frequency-selective Rayleigh fading CDMA channel, a channel model typically seen in mobile wireless communications. This is precisely the objective of this thesis. <p>Furthermore, the suboptimal decoders are obtained not only for binary phase shift keying (BPSK), but also for M-ary pulse amplitude modulation (M-PAM). This extension offers a flexible trade-off between spectrum efficiency and performance of the systems. In addition, two algorithms based on distance measure and reliability processing are introduced as other alternatives to the suboptimal decoder. <p>Simulation results indicate that the suboptimal decoders studied in this thesis also performs very well over a frequency-selective Rayleigh fading CDMA channel.

No description available.

A fixed terrestrial wireless system such as the Microwave Multi-channel Distribution Service (MMDS) can be used as the ``last mile' to provide a high speed Internet connection from a base station to a home in a rural or suburban residential area. Such a broadband wireless system works very well under line-of-sight transmission. It works quite well even if the line-of-sight is obstructed with a large number of trees. However, when trees obstruct the line-of-sight, under conditions of wind, the user may experience loss of the RF signal from time to time. This is especially true under gusty conditions. As part of this research a high precision DSP-based measuring system is devised to accurately measure and characterize the distortions caused by tree foliage on the RF line-of-sight signal. The approach is to digitally generate a signal composed of several tones, up-convert the signal to 2.5 GHz and send it through tree foliage to a receiver where the signal is down-converted and sampled for a duration of five seconds. The samples collected are processed using Matlab to compute the temporal amplitude and phase variations of the tones. The measurement system provides estimates of the amplitude and phase of the receive tones with a time resolution of 3.2 ms. The standard deviation of the amplitude estimates is 0.3\% of the actual amplitude of the tones and the standard deviation of the phase estimates is 0.23 degree. This accuracy is obtained when the signal-to-noise ratio of the receive signal is greater than 20 dB. Measurement in the field with tree foliage in the line-of-sight shows that the swaying of the branches in the wind can cause rapid signal fading. This research determines the type of fade, the depth and duration of the fade, as well as the fading rate.

Several challenges are still holding back the technological transfer of printed electronics to industry in spite of recent progresses. In this thesis work, the printing method of inks based on silver nanoparticles (<Ø>=25 nm) was optimized according to its rheology and to the fluid/substrate interactions for the fabrication of electrical interconnections with a thickness of 500 nm. These lines were printed on silicon or flexible substrates and annealed either by conventional (oven or infrared) or selective methods (microwave) at temperatures comprised between 100 and 300 °C.A better understanding of the relationship between process and microstructure of these printed thin films, based on several crystallographic equipments (XRD, EBSD and EDX), led to the optimization of nanocrystallites growth with an activation energy of about 3 to 5 kJ*mol-1. In addition to the low residual stress (70 MPa), this optimization is used to achieve low electrical resistivity (3.4 μOhm*cm) associated with a greater coherence of the crystal lattices at grain boundaries. The probability of electron scattering at such interfaces can be further reduced using an innovative approach of oriented crystallite growth by atomic interdiffusion from the substrate.The low mechanical stiffness (E<50 GPa) of these porous lines requires a reinforcement step either by crystalline texturation or by electroless growth to withstand the assembly and wire-bonding steps. The fabrication of a functional demonstrator thus validated the printing technology for the manufacture of electronic components.

No description available.

Populations where three different lethals are segregating as alleles have been analysed for the conditions of equilibrium and for the trends during elimination of one allele. Early and late selection as well as sexdependent and sexindependent selection has been taken into consideration.Cage populations of Drosophila melanogaster with different fourth chromosome lethals have been followed and compared to the theoretical model. When two marker chromosomes (ciDpol and spaCat) and one out of four recessive lethal chromosomes l(4)5, 1(4)8, 1(4)10 or l(4)14 were used, the same marker chromosome (ciDpol) became extinct in all populations. Early and late selective values which were obtained directly from the populations were compared to estimates of fitness components obtained in specially designed experiments of viability, developmental rate, mating ability and fecundity. When two out of the four recessive lethals and the marker chromosome, spaCat , were combined in new populations, all populations attained equilibrium withôut extinction. A correlation was found between the time of death of the lethal homozygotes and the equilibrium genotype frequencies. Overall selective values at equilibrium were estimated. / digitalisering@umu

This study investigates the relocation behaviours of out-movers of deprived areas in the region of Stockholm, Sweden. The research is motivated by the concerns raised by deprived and segregated neighbourhoods in relation to a social fragmentation and an unsuccessful socio-economic inclusion of all citizens. Some researches affirm that the out-movers of deprived neighbourhoods tend to be more integrated than the stayers or the individual moving in such neighbourhoods. And if some studies are concerned about their prospective, they have been restricted to their destinations’ socio-economic features and dismissed any spatial approach.This study aims to analyse flows’ direction and features as well as the areas of destination such as to identify processes of selective migration and how socio-spatial disparities are (re)produced. A specific attention is given to counter-urban movements and their possible correlation to “preservation” objectives: The possible migration of lower classes toward peripheries in order to access a better living environment and avoid a forced economic selective migration toward the urban most deprived neighbourhoods.Descriptive and inferential statistics with binary logistic regressions enabled to put into exergue the selective migration among movers, between the counter-urban and the others but also among counter-urban. If most movers remain in the urban core and in an almost deprived area, a substantial proportion seeks to combine to a move “up” the social ladder (a better suited neighbourhood), a “downward” migration on the urban hierarchy (a move toward the peripheries). And the regression confirms that among this population, a segment is statically significantly disadvantaged and remains in rental after the move.Scholars should consider such evidences by including a spatial dimension to their studies on segregation, neighbourhood sorting processes and selective migration. And most importantly, the results of this study invite them to reassess the traditional life-style and life-cycle explanations of counter-urbanisation in favour of an economic driven migration.

An ad hoc network is a collection of mobile wireless devices that cooperate with each other to route packets amongst themselves. The main difficulty in designing routing algorithms for such a network is the large number of topology changes that the network undergoes due to device movement. Selective flooding is a routing technique that is more resilient to topology changes than traditional algorithms but is more bandwidth efficient than pure flooding. An on-demand selective flooding algorithm has been designed and tested on the ns-2 simulator. In scenarios involving a large number of topology changes, selective flooding outperforms other ad hoc network routing techniques. Unfortunately, selective flooding is much more bandwidth hungry and is unable to scale to handle reasonable traffic loads. Interestingly, the analysis of selective flooding reveals major problems with traditional ad hoc networking techniques. Many current algorithms demonstrate shortcomings when dealing with bursty traffic, and current wireless hardware cannot handle ad hoc networking traffic in an efficient manner. These issues need to be addressed before ad hoc networking technology can become feasible for widespread use.

The present study examined the relation between self-report mindfulness and performance on tasks measuring abilities for three aspects of attention: sustained, selective, and attention switching. Because attention regulation has been described as a core component of mindfulness, and past research suggests that experience with mindfulness meditation is associated with improved attentional skills, the present study predicted that higher self-report mindfulness would be positively related to performance on tasks of attention. Fifty undergraduate students completed self-report mindfulness questionnaires and completed a battery of attention tasks. There was mixed support for the relation between mindfulness scores and sustained attention, such that higher mindfulness scores as measured by the MAAS and CAMS-R were negatively related to target omissions on the CPT-II, but were not related to RT variability on the CPT-II or PASAT performance. Findings are discussed in the context of the measurement of self-report mindfulness, and directions for future research are considered.