| 1. |
- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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| 2. |
- Lindh, Magnus, 1973-
(författare)
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Evolution of Plants : a mathematical perspective
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Earth harbors around 300 000 plant species. The rich and complex environment provided by plants is considered a key factor for the extraordinary diversity of the terrestrial fauna by, for example, providing food and shelter. This thesis contributes to the understanding of these questions by investigating how the interplay of physiology, demography, and evolution gives rise to variation and diversity in fundamental plant traits. This will help us answer questions such as: How has this amazing diversity of plant species emerged? Which mechanisms maintain diversity? How are plant strategies and plant diversity influenced by variations in the environment?A plant faces multiple problems to survive and reproduce successfully. These problems can be modeled by considering traits, trade-offs and a fitness measure. For example: How to maximize growth rate, while maximizing structural stability? I will investigate four plant models in order to understand the function of plants, and mechanisms promoting diversity. Paper I: We study how annual plants with and without growth constraints should optimize their flowering time when productivity or season length changes. With a dynamic ontogenetic growth model and optimal control theory we prove that a bang-bang reproductive control is optimal under constrained growth and constant mortality rate. We find that growth constraints can flip the direction of optimal phenological response for increasing productivity. The reason is that the growth rate of vegetative mass saturates at high productivity and therefore it is better to flower earlier and take advantage of a longer reproductive period. If season length extends equally both in the beginning and the end of the season, growth constraints control the direction of the optimal response as well. Our theory can help explaining phenological patterns along productivity gradients, and can be linked to empirical observations made on a calendar scale.Paper II: We introduce a new measure of tree crown-rise efficiency based on the loss of biomass of the tree during growth. The more mass the tree looses during growth, the less crown-rise efficient it is. Top-heavy shapes loose more biomass than bottom-heavy shapes. Light-use efficiency is defined as the mean light assimilation of the leaves in the crown times the ratio of leaf mass and total mass. We then study the trade-off between light-use efficiency to crown-rise efficiency for tree crown shapes. We assume that the total tree mass is constant, and a constant vertical light gradient represent the shading from a surrounding forest. We find large differences in crown shapes at intermediate vertical light gradient, when both self-shading and mean-field shading are important, suggesting light-use vs crown-rise efficiency as a new trade-off that can explain tree diversity. Our crown-rise efficiency measure could easily be integrated into existing forest models.Paper III: We extend an evolutionary tree crown model, where trees with different heights compete for light, with drought-induced mortality rates depending on ground-water availability and the depth of an optional taproot. The model does not include competition for ground water. Our model explains how ground-water availability can shape plant communities, when taproot and non-taproot strategies can coexist, and when only one of these strategies can persist. We investigate how emerging plant diversity varies with water table depth, soil water gradient and drought-induced mortality rate. The taproot enables plants to reach deep water, thus reducing mortality, but also carries a construction cost, thus inducing a trade-off. We find that taproots maintain plant diversity under increasing drought mortality, and that taproots evolve when groundwater is accessible at low depths. There are no viable strategies at high drought mortality and deep water table. Red Queen evolutionary dynamics appear at intermediate drought mortality in mixed communities with and without taproots, as the community never reaches a final evolutionarily stable composition.Paper IV: We extend a size-structured plant model, with self-shading and two evolving traits, crown top-heaviness and crown width-to-height ratio. The model allows us to identify salient trade-offs for the crown shape. The most important trade-off for top-heaviness is light-use efficiency vs crownrise efficiency, and the most important trade-off for width-to-height ratio is self-shading vs branch costs. We find that when the two traits coevolve; the outcome is a single common evolutionarily stable strategy (ESS), far away from the highest net primary production (NPP). When only sun angle is decreasing with increasing latitude both the crown width-to-height ratio and crown top-heaviness decrease. However, when light response in addition to the sun angle decreases with increasing latitude, the crown width-to-height ratio is nearly invariant of latitude except at low site productivity when the ratio decreases with latitude. Top-heaviness is always decreasing with increasing latitude. Finally, we find that crown top-heaviness increases with the NPP or leaf-area index (LAI) at ESS, but crown width-to-height ratio is maximal at an intermediate NPP or LAI.
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| 3. |
- Jencson, Jacob E., et al.
(författare)
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The SPIRITS Sample of Luminous Infrared Transients : Uncovering Hidden Supernovae and Dusty Stellar Outbursts in Nearby Galaxies
- 2019
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Ingår i: Astrophysical Journal. - : IOP PUBLISHING LTD. - 0004-637X .- 1538-4357. ; 886:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a systematic study of the most luminous (M-IR [Vega magnitudes] brighter than ?14) infrared (IR) transients discovered by the SPitzer InfraRed Intensive Transients Survey (SPIRITS) between 2014 and 2018 in nearby galaxies (D < 35 Mpc). The sample consists of nine events that span peak IR luminosities of M-[4.5],M-peak between ?14 and ?18.2, show IR colors between 0.2;<;([3.6]?[4.5]);<;3.0, and fade on timescales between 55 days;t(fade);<;480 days. The two reddest events (A(V) > 12) show multiple, luminous IR outbursts over several years and have directly detected, massive progenitors in archival imaging. With analyses of extensive, multiwavelength follow-up, we suggest the following possible classifications: five obscured core-collapse supernovae (CCSNe), two erupting massive stars, one luminous red nova, and one intermediate-luminosity red transient. We define a control sample of all optically discovered transients recovered in SPIRITS galaxies and satisfying the same selection criteria. The control sample consists of eight CCSNe and one Type;Iax SN. We find that 7 of the 13 CCSNe in the SPIRITS sample have lower bounds on their extinction of 2;A(V);<;8. We estimate a nominal fraction of CCSNe in nearby galaxies that are missed by optical surveys as high as
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| 4. |
- Johansson, Anders, 1972-
(författare)
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Biopolitics and Reflexivity : A Study of GMO Policymaking in the European Union
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The political discourse that has emerged as a consequence of establishing a European regulatory framework for GMOs has not been without problems. This dissertation addresses the political and regulatory challenges created by the development and use of genetically modified organisms (GMOs) in the EU. The underlying hypothesis in the dissertation is that the emergence of a European policy in the field of GMOs has appeared through new reflexive forms of governance. The aim of this research is to understand how these reflexive forms of regulation have emerged and operate within the EU, with a particular focus on the two GMO directives 90/220/EEC and 2001/18/EC. However, the study scrutinises the regulatory regimes from the 1970s onwards by investigating how the regulatory framework regarding GMOs has been developed and implemented in the EU. This is done through an analysis of the notion of ‘risk’ and the ‘precautionary principle’ since these concepts have been at the forefront of the GMO regulation debate. The empirical approach focuses on how the European Commission, the European Parliament and the European Council as well as other actors and institutions articulate ambivalence, interpretations and uncertainties in the decision-making processes regarding regulative measures for GMOs, with an accent on risk and the precautionary principle. The main empirical material has been documents concerning the inter-institutional process involved in the regulatory process of making the two directives. The analysis indicates that during the process of implementing GMO regulations, new steering strategies have appeared within the EU’s decision-making institutions when the objective of the regulation has taken centre stage in political and scientific controversies.
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| 5. |
- Nordmark, Johanna, 1968-
(författare)
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Aspects of Induced Hypothermia following Cardiopulmonary Resuscitation : Cerebral and Cardiovascular Effects
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hypothermia treatment with cooling to a body temperature of 32-34°C has been shown to be an effective way of improving neurological outcome and survival in unconscious patients successfully resuscitated after cardiac arrest (CA). The method is used clinically but there are still many questions on the biological mechanisms and on how the treatment is best performed. This thesis focuses on cerebral and haemodynamic effects of hypothermia and rewarming. A porcine model of CA was used. To shorten time to reach target temperature, induction of hypothermia, by means of infusion of 4°C cold fluid, was started already during ongoing cardiopulmonary resuscitation. The temperature was satisfactorily reduced without obvious haemodynamic disturbances. Cerebral effects of hypothermia and rewarming were studied. Microdialysis monitoring showed signs of cerebral energy failure (increased lactate/pyruvate-ratio) and excitotoxicity (increased glutamate) immediately after CA. There was a risk of secondary energy failure that was reduced by hypothermia. Intracranial pressure (ICP) increased gradually after CA irrespectively of if hypothermia was used or not. There were no indications of increasing cerebral disturbances during rewarming. Haemodynamic effects of hypothermia treatment and rewarming were examined in a study of patients successfully resuscitated after CA. Hypothermia was induced by means of cold intravenous infusion. No negative effects on the cardiovascular system were revealed. There were indications of decreased intravascular volume in spite of a positive fluid balance. Cerebral microdialysis and ICP recording were performed in four patients. All patients had signs of energy failure and excitotoxicity following CA. ICP was only exceptionally above 20 mmHg. In contrast to the experimental study indications of increasing ischemia were seen during rewarming. Glycerol had a biphasic pattern, perhaps due to an overspill of metabolites from the general circulation. As most patients become extensively anti-coagulated following CA, intracranial monitoring is not suitable to be used in routine care.
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| 6. |
- Touqir Pasha, Muhammad
(författare)
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Circuit Design for All-Digital Frequency Synthesizers
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The market for low cost portable electronics is rapidly growing. Physical activity monitors, portable music players, and smart watches are fast becoming a part of daily life. As the market for wearable devices has grown, a primary concern for IC manufacturers is to provide low cost, low power and lightweight circuit solutions. In a bid to lower the costs and extend battery life there is an increased interest in using low-cost, low-power CMOS processes. As a result fully integrated systems on chips (SOC) have been realized that efficiently perform the required functions. These SOCs house digital, analog and in some cases radio circuits on a single die in a bid to reduce cost and improve productivity.Phase Locked Loops (PLLs) are a key building block for all SOCs where they are used to generate clock signals for synchronous systems. In monolithic implementations the design cost of a circuit is measured in terms of the silicon area and not the number of devices in the circuit. With the advent of all-digital techniques, there is a renewed interest in the design of compact PLLs as the area occupied by the traditional PLLs is very large due to the presence of large passive components in the loop filter and the oscillator. As a result, various digital circuit design techniques are being explored to design compact all-digital PLLs (ADPLLs) while satisfying the performance requirements for the target applications.The focus of this work is to explore new techniques for area, power and time efficient design of ADPLL component blocks. The first part of this works focuses on the feasibility of using automatic place and route (P&R) tools to synthesize a time-to-digital converter (TDC). An area efficient TDC is synthesized in a 65 nm CMOS process using automated P&R which exhibits a time resolution of 6.5 ps with an input sampling rate of 100 MS/s while occupying an area of 0.002 mm2. A modified switching scheme is also presented which reduces the power consumption of the thermometer-to-binary encoder by up to 40%.The second part of this thesis proposes a power supply filter for mitigating the affect of cyclostationary noise on the voltage controlled ring oscillator. The key idea is to raise the impedance in the current supply during the sensitive periods and lower it during insensitive periods of the oscillator operation. To demonstrate the feasibility of the proposed filter, a pseudo differential ring oscillator is designed in a 65 nm CMOS process which exhibits an rms jitter of less than 14 ps at 2.4 GHz in the presence of a 500 mV noise tone in the power supply.
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