Longterm Influence of Inertia on the Diffusion of a Brownian Particle

We demonstrate experimentally that a Brownian particle is subject to inertial effects at long time scales. By using a blinking optical tweezers, we extend the range of previous experiments by several orders of magnitude up to a few seconds. The measured mean square displacement of a freely diffusing Brownian particle in a liquid shows a deviation from the Einstein-Smoluchowsky theory that diverges with time. These results are consistent with a generalized theory that takes into account not only the particle inertia but also the inertia of the fluid surrounding the particle. This can lead to a bias in the estimation of the diffusion coefficient from finite-time measurements. We show that the decay of the relative error is polynomial and not exponential and, therefore, can have significant effects at time scales relevant for experiments.Comment: 5 pages, 4 figure

A Step-by-step Guide to the Realisation of Advanced Optical Tweezers

Since the pioneering work of Arthur Ashkin, optical tweezers have become an indispensable tool for contactless manipulation of micro- and nanoparticles. Nowadays optical tweezers are employed in a myriad of applications demonstrating the importance of these tools. While the basic principle of optical tweezers is the use of a strongly focused laser beam to trap and manipulate particles, ever more complex experimental set-ups are required in order to perform novel and challenging experiments. With this article, we provide a detailed step- by-step guide for the construction of advanced optical manipulation systems. First, we explain how to build a single-beam optical tweezers on a home-made microscope and how to calibrate it. Improving on this design, we realize a holographic optical tweezers, which can manipulate independently multiple particles and generate more sophisticated wavefronts such as Laguerre-Gaussian beams. Finally, we explain how to implement a speckle optical tweezers, which permit one to employ random speckle light fields for deterministic optical manipulation.Comment: 29 pages, 7 figure

Angiotensin II receptor blockers and myocardial infarction: deeds and misdeeds

BACKGROUND: A recent editorial published by Verma and Strauss, entitled 'Angiotensin receptor blockers and myocardial infarction', examined, through a partial analysis of individual trials, the use of angiotensin receptor blockers (ARBs) in a variety of clinical settings. This editorial was reported widely in the lay press and media, and generated disappointment and concern among physicians in many countries, probably because of its provocative subtitle in the British Medical Journal: 'These drugs may increase myocardial infarction and patients may need to be told'. OBJECTIVE AND METHODS: In order to explore the influence of ARBs on myocardial infarction, we performed a more comprehensive and updated meta-analysis, taking into account all major international, randomized trials using ARBs compared with another active drug or conventional therapy (placebo), and reporting information on rates of myocardial infarction. RESULTS: We found no significant differences in fatal and non-fatal myocardial infarction between treatment with ARBs, placebo or active treatment, and the same result was obtained when considering only trials in which ARBs were compared with angiotensin-converting enzyme inhibitors (ACEIs), or when pooling all trials together. The pooled analysis of these trials shows that the relative risk of myocardial infarction lies substantially on the indifference line. CONCLUSION: Our analysis demonstrates that, at this time, there is no evidence of increased risk of myocardial infarction in patients treated with ARBs

Industrial districts and elective affinities

Industrial districts palyed a very important role in the Italian economic development. This paper provides fresh evidence based on microdata (Veneto Worker Histories) and discusses the ambiguities in the district definition, its uncertain boundaries and the development into territorial affinities as economic development progresses.Industrial districts; Italy, Regional policy, Geography

SHEAR-INDUCED NUCLEATION AND GROWTH IN ISOTACTIC POLYPROPYLENE

The possibility of controlling the final morphology, and thus the resulting mechanical and functional properties, of semicrystalline polymers based on the study of polymer crystallization stimulated by flow is highly intriguing. Recent advances in experimental techniques that allow in situ measurements of material morphology under deformation have escalated research in this subject area. However, despite of the huge efforts spent, the description of the evolution of morphology under shear conditions is still challenging and even the basic principles of the phenomenon are not well understood yet. In this work, experiments of nucleation density and growth rate of spherulites were carried out under continuous shear in a range of temperature (138-144 degrees C) and shear rate (0-0.30 s(-1)) which, although narrow in absolute, can be considered quite wide taking into account the experimental difficulties presented by this kind of tests. Collected data were analyzed with the aim of determining scaling rules which can describe the effect of flow on crystallization kinetics. It was found that a proportionality exists between nucleation rate and spherulitic growth rate under flow, suggesting that whatever the controlling mechanism for the enhancement of nucleation rate is, it has a similar effect also on growth rate. The effect of flow on nucleation and growth rates was attributed to the increase of the melting temperature due to flow. In turn, the melting temperature estimated for the tests conducted in the whole range of temperatures and shear rates was found to be dependent on the Weissenberg number

Why leave wage work and become self-employed ? Independence, earnings or unemployment.

The paper addresses the problem of the relation between self-employment and employee status. The issue is whether self-employment is a form of disguised unemployment or a suitable long term form of employment towards which gravitate the most successful wage-workers: wage-workers attracted by an activity that is more independent and more apt to bring their personality to the foreground. The paper focuses on a detailed study of previous experience as an employee (entrance, duration, mobility, status, firm’s size) to evaluate this point. Individuals enter self-employment for the first time at a very young age, and the choice is the result of a period of high mobility, unemployment and inactivity after the first entrance into the labour market as an employee. Self-employment does not seem to be bound by a liquidity constraint or by the need to accumulate assets in order to start a viable businesses, the usual reasons brought about to explain deferred entry, or by the time necessary to discover a viable business opportunity: it is directly linked to movements in wage employment and represents a temporary solution to face an unattended negative shock

Quantitative assessment of non-conservative radiation forces in an optical trap

The forces acting on an optically trapped particle are usually assumed to be conservative. However, the presence of a non-conservative component has recently been demonstrated. Here we propose a technique that permits one to quantify the contribution of such non-conservative component. This is an extension of a standard optical tweezers calibration technique and, therefore, can easily become a standard test to verify the conservative optical force assumption. Using this technique we have analyzed different-sized optically trapped particles under different trapping conditions. We conclude that the non-conservative effects are effectively negligible and do not affect the standard calibration procedure, unless for extremely low-power trapping, far away from the trapping regimes usually used in experiments.Comment: 8 pages, 4 figures; Europhys. Lett. (EPL) (2009), accepte

PINK1 homozygous W437X mutation in a patient with apparent dominant transmission of parkinsonism.

We analyzed the PINK1 gene in 58 patients with early-onset Parkinsonism and detected the homozygous mutation W437X in 1 patient. The clinical phenotype was characterized by early onset (22 years of age), good re- sponse to levodopa, early fluctuations and dyskinesias, and psychiatric symptoms. The mother, heterozygote for W437X mutation, was affected by Parkinson’s disease and 3 further relatives were reported affected, according to an autosomal dominant transmission