<p> Two-pion production reactions in proton-proton collisions have been studied using the PROMICE/WASA detector and an internal cluster gas-jet target at the CELSIUS storage ring in Uppsala. Three out of the four isospin-independent reaction channels have been measured at several energies in the intermediate and near threshold energy region. Important parts of the analysis include the identification of neutral pions from the invariant mass of the decay gammas, the identification of positive pions with the delayed pulse technique and the use of Monte Carlo simulations to understand the detector response. The total cross sections for the pp®ppπ⁺π^-, the pp®ppπ⁰π⁰ and the pp®pnπ⁺π⁰ reactions are presented at beam energies ranging from 650 to 775 MeV. </p><p>The production mechanism for two-pion production near threshold seems to be dominated by resonance production. The contribution from the non-resonant terms alone can not reproduce the total cross sections. In most models, two-pion production is governed by the δ and the <i>N</i>^* resonances in either one or both of the participating nucleons. </p><p>The <i>N</i>^*(1440)®N(πp)^T=0_S−<i>wave</i> transition has been suggested as the dominating production mechanism for two-pion production in proton-proton collisions. However, the total cross sections presented in this thesis show that other production mechanisms also must give large contributions. </p>

In an effort to develop an optical-acoustical understanding of ultrasound contrast agent microbubble dynamics in a micro-environment that resembles blood vessels, this thesis presents experimental work on optical trapping and acoustical probing of ultrasound contrast agent microbubbles confined in regenerated cellulose capillaries. First, we showed by acoustical means that the pressure threshold of an individual microbubble shell rupture increases significantly when confined in regenerated cellulose capillaries. We report that the shell rupture threshold in regenerated cellulose capillaries increased by at least 0.3 MPa from 0.8 MPa for unconfined microbubbles. Second, we achieved optical trapping and manipulation of ultrasound contrast agent microbubbles confined in capillaries using Hermite-Gaussian laser beams. / Graduation date: 2012

This paper involves the calculation for composition of different layer used in laser structure and the simulation of cavity, formed by creating air columns in the InGaAsP medium, for square lattice. The aim of this project is to fabricate approximately zero threshold current lasers. This project involves FDTD simulation for optimizing dimension of the device, fabrication of laser structure and finally characterization of the device structure. / Singapore-MIT Alliance (SMA)

The history of management practice is filled with innovations that failed to live up to the promise suggested by their early success. A paradox facing organization theory is that the failure of these innovations often cannot be attributed to an intrinsic lack of efficacy. To resolve this paradox, in this paper I study the process of innovation implementation. Working from existing theoretical frameworks, I synthesize a model that describes the process through which participants in an organization develop commitment to using a newly adopted innovation. I then translate that framework into a formal model and analyze it using computer simulation. The analysis suggests three new constructs—reversion, regeneration and the motivation threshold—characterizing the dynamics of implementation. Taken together, these constructs offer an alternative explanation for the paradox of innovations that produce early results but fail to find a permanent home in the organizations that adopt them.

Issued also as a Ph.D. Thesis in the Dept. of Electrical Engineering, 1966. / Bibliography: p.56.

With growing trend in "cloud computing" and increase in the data moving into the Internet, the need to store large amounts of data by service providers such as Google, Yahoo and Microsoft has increased over time. Now, more than ever, there is a need to efficiently and securely store large amounts of data. This thesis presents an implementation of a Ramp Scheme that confidentially splits a data file into a configurable number of parts or shares of equal size such that a subset of those shares can recover the data entirely. Furthermore, the implementation supports a threshold for data compromise and data verification to verify that the data parts have not been tampered with. This thesis addresses two key problems faced in large-scale data storage, namely, data availability and confidentiality.

Phenotypic plasticity is the ability of a genotype to express different phenotypes in different environments. Despite its common occurrence, few have investigated differences in plasticity between populations, the selection pressures responsible for it, and costs and constraints associated with it. In this thesis, I investigated this by studying local adaptation and phenotypic plasticity in populations of the common frog Rana temporaria, inhibiting islands with different pool types (temporary, permanent or both). The tadpoles develop in these pools, and have to finish metamorphosis before the pool dries out. I found that the tadpoles were locally adapted both in development time and in phenotypic plasticity of development time. Tadpoles from islands with temporary pools had a genetically shorter development time than tadpoles from islands with permanent pools. The population differentiation in development time, estimated as QST, was larger than the population differentiation in neutral molecular markers (FST), which suggest that divergent selection among the populations is responsible for the differentiation. Moreover, tadpoles from islands with more variation in pool drying regimes had higher phenotypic plasticity in development time than tadpoles from islands with only one pool type present. Interestingly, increased migration among populations did not select for increased plasticity, rather it was the local environmental variation that was important. This adaptation has occurred over a short time scale, as the islands are less than 300 generations old. In temporary pools, it is adaptive to finish development before the pool dries out. This could be achieved by entering the metamorphosis at a smaller size, as a smaller size takes shorter time to reach. However, I found that there is a minimum threshold size below which tadpoles’ cannot enter metamorphosis, and that there had been no evolution of this threshold size in populations living in temporary environments. That suggests that this developmental threshold is tightly linked to physiological constraints in the developmental process. Despite their expected importance as constrains on the evolution of plasticity, costs of plasticity are often not found in nature.  However, theories of why they are absent have not been tested empirically. In this thesis, I show that fitness costs of phenotypic plasticity are only found in populations with genotypes expressing high levels of phenotypic plasticity, while in populations with low-plastic genotypes, I find costs of not being plastic. This suggests that costs of plasticity increase with increased level of plasticity in the population, and that might be a reason why costs of plasticity are hard to detect.

Two-pion production reactions in proton-proton collisions have been studied using the PROMICE/WASA detector and an internal cluster gas-jet target at the CELSIUS storage ring in Uppsala. Three out of the four isospin-independent reaction channels have been measured at several energies in the intermediate and near threshold energy region. Important parts of the analysis include the identification of neutral pions from the invariant mass of the decay gammas, the identification of positive pions with the delayed pulse technique and the use of Monte Carlo simulations to understand the detector response. The total cross sections for the pp®ppπ+π-, the pp®ppπ0π0 and the pp®pnπ+π0 reactions are presented at beam energies ranging from 650 to 775 MeV. The production mechanism for two-pion production near threshold seems to be dominated by resonance production. The contribution from the non-resonant terms alone can not reproduce the total cross sections. In most models, two-pion production is governed by the δ and the N* resonances in either one or both of the participating nucleons. The N*(1440)®N(πp)T=0S−wave transition has been suggested as the dominating production mechanism for two-pion production in proton-proton collisions. However, the total cross sections presented in this thesis show that other production mechanisms also must give large contributions.

No description available.

The work presented in this thesis studies the load and loadeffects of traffic loads on railway bridges. The increasedknowledge of the traffic loads, simulated using fieldmeasurements of actual trains, are employed in a reliabilityanalysis in an attempt at upgrading existing railwaybridges. The study utilises data from a weigh-in-motion site whichrecords, for each train, the train speed, the loads from eachaxle and the axle spacings. This data of actual trainconfigurations and axle loads are portrayed as moving forcesand then used in computer simulations of trains crossing twodimensional simply supported bridges at constant speed. Onlysingle track short to medium span bridges are considered in thethesis. The studied load effect is the moment at mid-span. Fromthe computer simulations the moment history at mid-span isobtained. The load effects are analysed by two methods, the first isthe classical extreme value theory where the load effect ismodelled by the family of distributions called the generalisedextreme value distribution (GEV). The other method adopts thepeaks-over-threshold method (POT) where the limiting family ofdistributions for the heights to peaks-over-threshold is theGeneralised Pareto Distribution (GPD). The two models aregenerally found to be a good representation of the data. The load effects modelled by either the GEV or the GPD arethen incorporated into a reliability analysis in order to studythe possibility of raising allowable axle loads on existingSwedish railway bridges. The results of the reliabilityanalysis show that they are sensitive to the estimation of theshape parameter of the GEV or the GPD. While the study is limited to the case of the ultimate limitstate where the effects of fatigue are not accounted for, thefindings show that for the studied cases an increase inallowable axle load to 25 tonnes would be acceptable even forbridges built to the standards of 1940 and designed to LoadModel A of that standard. Even an increase to both 27.5 and 30tonnes appears to be possible for certain cases. It is alsoobserved that the short span bridges ofapproximately fourmetres are the most susceptible to a proposed increase inpermissible axle load. <b>Keywords:</b>bridge, rail, traffic load, load effect,dynamic amplification factor, extreme value theory,peaks-over-threshold, reliability theory, axle loads, fielddata.