A Modeling Study on How Cell Division Affects Properties of Epithelial Tissues Under Isotropic Growth

Cell proliferation affects both cellular geometry and topology in a growing tissue, and hence rules for cell division are key to understanding multicellular development. Epithelial cell layers have for long times been used to investigate how cell proliferation leads to tissue-scale properties, including organism-independent distributions of cell areas and number of neighbors. We use a cell-based two-dimensional tissue growth model including mechanics to investigate how different cell division rules result in different statistical properties of the cells at the tissue level. We focus on isotropic growth and division rules suggested for plant cells, and compare the models with data from the Arabidopsis shoot. We find that several division rules can lead to the correct distribution of number of neighbors, as seen in recent studies. In addition we find that when also geometrical properties are taken into account other constraints on the cell division rules result. We find that division rules acting in favor of equally sized and symmetrically shaped daughter cells can best describe the statistical tissue properties

Navigation Devices for Mobile Phones

A mobile phone has several buttons/keys e.g. numerical keys, side keys, camera buttons and navigation keys. SEMC, Sony Ericsson Mobile Communications AB, has mainly used the joystick and the rocker key as their navigation devices since they released their first phone in 2002. These technologies are used in all their phones except smart phones, e.g. W950 and P990. During the years SEMC has experienced some quality problems with their navigation devices, mainly with the joystick, because of the lack of ability to keep dust out. As the development of mobile phones progress, with more functions and larger quantity of data to go through, the need of a navigation device with more possibilities arise. The purpose of this master thesis was to perform a pre-study on the next generation navigation devices for mobile phones and based on that give recommendations to SEMC of which navigation devices suitable to be used in the future

Models of sequestration and receptor cross-talk for explaining multiple mutants in plant stem cell regulation

<p>Abstract</p> <p>Background</p> <p>Stem cells reside in a plant's shoot meristem throughout its life and are main regulators of above-ground plant development. The stem cell maintenance depends on a feedback network between the <it>CLAVATA </it>and <it>WUSCHEL </it>genes. The CLAVATA3 peptide binds to the CLAVATA1 receptor leading to WUSCHEL inhibition. WUSCHEL, on the other hand, activates CLAVATA3 expression. Recent experiments suggest a second pathway where CLAVATA3 inhibits WUSCHEL via the CORYNE receptor pathway. An interesting question, central for understanding the receptor signaling, is why the <it>clavata1-11 </it>null mutant has a weaker phenotype compared with the <it>clavata1-1 </it>non-null mutant. It has been suggested that this relies on interference from the mutated CLAVATA1 acting on the CORYNE pathway.</p> <p>Results</p> <p>We present two models for the CLAVATA-WUSCHEL feedback network including two receptor pathways for WUSCHEL repression and differing only by the hypothesized mechanisms for the <it>clavata1-1 </it>non-null mutant. The first model is an implementation of the previously suggested interference mechanism. The other model assumes an unaltered binding between CLAVATA3 and the mutated CLAVATA1 but with a loss of propagated signal into the cell. We optimize the models using data from wild type and four single receptor mutant experiments and use data from two receptor double mutant experiments in a validation step. Both models are able to explain all seven phenotypes and in addition qualitatively predict CLAVATA3 perturbations. The two models for the <it>clavata1-1 </it>mutant differ in the direct mechanism of the mutant, but they also predict other differences in the dynamics of the stem cell regulating network. We show that the interference hypothesis leads to an abundance of receptors, while the loss-of-signal hypothesis leads to sequestration of CLAVATA3 and relies on degradation or internalization of the bound CLAVATA1 receptor.</p> <p>Conclusions</p> <p>Using computational modeling, we show that an interference hypothesis and a more parsimonious loss-of-signal hypothesis for a <it>clavata1 </it>non-null mutant both lead to behaviors predicting wild type and six receptor mutant experiments. Although the two models have identical implementations of the unperturbed feedback network for stem cell regulation, we can point out model-predicted differences that may be resolved in future experiments.</p

Övervakning och redovisning av upplysningskraven i IAS 36:134

Syfte: Syftet är dels att analysera hur Nasdaq OMX Stockholm AB:s övervakning av noterade företag står i relation till diskussionen kring överflödiga upplysningar i de finansiella rapporterna. Syftet är även att utifrån empiri analysera hur Nasdaq OMX Stockholm AB, revisorer och företag resonerar kring upplysningskraven i IAS 36:134 och vilka konsekvenser resonemangen kan medföra i redovisningen samt för intressenter. Metod: Vi har valt ett kvalitativt perspektiv på uppsatsen för att undersöka hur de olika parterna resonerar. Utifrån detta genomförde vi intervjuer med en övervakare vid Nasdaq OMX Stockholm AB, revisorer, företag samt en analytiker. En stor del av underlaget i uppsatsen har sin grund i Nasdaq OMX Stockholm AB:s årliga övervakningsrapporter. Teoretiska perspektiv: Uppsatsen utgår från IAS 36:134. Teorin inleds med en definition av goodwill och nedskrivningsprövning. Därefter ges en introduktion till IASB:s kvalitativa egenskaper. Sedan redogörs för redovisningsteorierna positiv redovisningsteori samt institutionell teori. Detta följs av en redogörelse för diskussionen om överflödiga upplysningar. Empiri: Empirin utgörs av data som intervjuerna har resulterat i. Intervjuerna syftar till att utröna respondenternas åsikter kring valt ämne. Resultat: Ett alltför teoretiskt regelverk verkar leda till svårigheter för företagen att uppfylla det som upplysningarna syftar till. Det tycks delvis bero på företags ovilja att upplysa om känslig information i kombination med en låg efterfrågan från intressenter. Revisorer vill att företagen ska lämna mer upplysningar, men incitamentet till att påverka företagen kan vara bristande. Inkonsekvensen mellan teori och praktik tycks vara en anledning till att överflödiga upplysningar riskerar att uppstå. Nasdaq OMX Stockholm AB:s ”påpekanden” kan riskera att påverka företagen att inkludera, enligt företaget, oväsentliga upplysningar.Purpose: The purpose of this essay is to analyze the Issuer Surveillance Nasdaq OMX Stockholm AB’s surveillance of companies, in relation to the discussion on disclosure overload. The purpose is also to analyze how Issuer Surveillance Nasdaq OMX Stockholm AB, auditors and companies reason about the disclosures in IAS 36:134 and what consequences this reasoning may have on accounting and stakeholders. Methodology: Qualitative interviews with the following respondents: Issuer Surveillance Nasdaq OMX Stockholm AB, accountants, companies and a financial analyst. The purpose of the interviews is to analyze the view of the respondents regarding the subject of the thesis. Theoretical perspectives: The first and main theoretical approach is IAS 36:134. This is followed by definitions of goodwill and impairment test. Furthermore, the positive accounting theory and the institutional theory will be accounted for. The qualitative features of IASB and an introduction to information overload are also presented in the essay. Empirical foundation: The empirical data of the analysis was obtained through qualitative interviews. Conclusions: An overly theoretical framework seems to cause difficulties for companies to fulfill the purpose of the disclosures. This seems to depend on the unwillingness of companies to disclose sensitive information, in combination with low demands from stakeholders. Auditors would like companies to disclose more information, but the incitement to affect the companies seem to be insufficient. The inconsistency between theory and practice seems to be one of the reasons why disclosure overload arises. Remarks from Issuer Surveillance Nasdaq OMX Stockholm AB may lead to the fact that companies disclose what they see as irrelevant information

Hydrogen Addition For Improved Lean Burn Capability of Slow and Fast Burning Natural Gas Combustion Chambers

One way to extend the lean-burn limit of a natural gas engine is by addition of hydrogen to the primary fuel. This paper presents measurements made on a one-cylinder, 1.6- liter natural gas engine. Two combustion chambers, one slow and one fast burning, were tested with various amounts of hydrogen (0, 5, 10 and 15%-vol) added to natural gas. Three operating points were investigated for each combustion chamber and each hydrogen content level; idle, part load (5 bar IMEP) and 13 bar IMEP (simulated turbocharging). Air/fuel ratio was varied between stoichiometric and the lean limit. For each operating point, a range of ignition timings were tested to find maximum brake torque (MBT) and/or knock. Heat-release rate calculations were made in order to assess the influence of hydrogen addition on burn rate. Addition of hydrogen showed an increase in burn rate for both combustion chambers, resulting in more stable combustion close to the lean limit. This effect was most pronounced for lean operation with the slow combustion chamber