Morphology and Mechanics of the Actin Cytoskeleton

Contained in this thesis is the quest to model the growth, form and mechanics of part of the cellular cytoskeleton known as the lamellipodium. The cellular cytoskeleton is made of filamentous proteins, such as F-actin, and provides for structural support for the cell. Lamellipodia are extensions of the cellular cytoskeleton at the leading edge of a crawling cell generated so that the cell can extend, and thereby move in a particular direction. In the first two chapters, we focus on morphological characteristics of lamellipodia formation, which is, in part, shaped by branched filament nucleation via the branching protein Arp2/3. For example, we find that the orientation of filaments with respect to the leading edge of a crawling cell is optimized for filament growth. In addition, orientational and spatial degrees of freedom of the filaments are married to derive the overall shape of the filament density profile along the leading edge, another morphological characteristic. In the next two chapters, we explore the mechanics of model lamellipodia, where both freely-rotating and angle-constraining cross-linkers of actin filaments are present, in addition to the angle-constraining effect that the branching protein Arp2/3 has between mother and daughter filaments. We compare the mechanical properties of the compositely cross-linked filament networks to that of purely freely-rotating cross-linked filament networks, which has been studied by others previously. Using both theory and numerical simulations, we find that the addition of angle-constraining cross-linkers allows the lamellipodium to become rigid and transmit forces with a minimal amount of material---yet another optimization principle. Therefore, in our quest to model lamellipodia formation, we have uncovered along the way several optimization principles, which may ultimately guide, in part, our understanding of how cells crawl to heal wounds or create organs

Half-open Penning trap with efficient light collection for precision laser spectroscopy of highly charged ions

We have conceived, built and operated a 'half-open' cylindrical Penning trap for the confinement and laser spectroscopy of highly charged ions. This trap allows fluorescence detection employing a solid angle which is about one order of magnitude larger than in conventional cylindrical Penning traps. At the same time, the desired electrostatic and magnetostatic properties of a closed-endcap cylindrical Penning trap are preserved in this congfiuration. We give a detailed account on the design and confinement properties, a characterization of the trap and show first results of light collection with in-trap produced highly charged ions

Switchable Magnetic Bottles and Field Gradients for Particle Traps

Versatile methods for the manipulation of individual quantum systems, such as confined particles, have become central elements in current developments in precision spectroscopy, frequency standards, quantum information processing, quantum simulation, and alike. For atomic and some subatomic particles, both neutral and charged, a precise control of magnetic fields is essen- tial. In this paper, we discuss possibilities for the creation of specific magnetic field configurations which find appli- cation in these areas. In particular, we pursue the idea of a magnetic bottle which can be switched on and off by transition between the normal and the superconducting phase of a suitable material in cryogenic environments, for example in trap experiments in moderate magnetic fields. Methods for a fine-tuning of the magnetic field and its linear and quadratic components in a trap are presented together with possible applications

An integrative model of the personal growth process in a T-group

Thesis (S.M.)--Massachusetts Institute of Technology, Sloan School of Management, 1970.Includes bibliographical references (leaves 72-74).by Stanley David Quint and Aaron Kleiner.S.M

Self-reported symptoms of chronic cough and breathlessness in working-age men in the city of Izhevsk, Russia: associations with cardiovascular disease risk factors and comorbidities.

INTRODUCTION: Very little is known about the prevalence of respiratory symptoms or their associations with other health conditions in Russia. METHODS: Between 2008 and 2010, a sample of 983 men resident in Izhevsk, Russia, took part in a cross-sectional survey. Presence of respiratory symptoms was determined from self-report of chronic productive cough and breathlessness assessed using the British Medical Research Council (MRC) breathlessness scale. Self-reported physical and mental health were measured using the 12-Item Short-Form Health Survey (SF-12). Hypertension was assessed from mean blood pressure measured at the health check and/or self-reported use of antihypertensive medication. Other comorbidities were assessed from self-report. Logistic regression models were fitted assessing the association between respiratory symptoms and comorbidities. Linear regression models were fitted to investigate the association between respiratory symptoms and self-reported health scores. All models were adjusted for age, education and smoking status. RESULTS: The age-standardised prevalence of cough and breathlessness was 20.9% (prevalence with breathlessness MRC grade 3 or above 3.7%). The majority of men with respiratory symptoms (87.3%) were current smokers. Cough and breathlessness were associated with substantially worse self-reported physical and mental health (test for trend with severity of breathlessness p<0.001). Those with chronic cough and grade 3 or above breathlessness had higher odds of having hypertension (OR 3.03; 95% CI 1.36 to 6.74), diabetes (OR 10.55; 95% CI 2.69 to 41.37), angina pectoris (OR 7.54; 95% CI 3.61 to 15.73), previous myocardial infarction (OR 7.61; 95% CI 2.10 to 27.4) and previous stroke (OR 6.61; 95% CI 1.75 to 23.34) compared with those without respiratory symptoms. CONCLUSIONS: The prevalence of respiratory symptoms was high. Strong associations were found between respiratory symptoms and cardiovascular comorbidities. These are of particular importance given the extremely high level of cardiovascular disease mortality in Russia