1,180 research outputs found
Saturation of a spin 1/2 particle by generalized Local control
We show how to apply a generalization of Local control design to the problem
of saturation of a spin 1/2 particle by magnetic fields in Nuclear Magnetic
Resonance. The generalization of local or Lyapunov control arises from the fact
that the derivative of the Lyapunov function does not depend explicitly on the
control field. The second derivative is used to determine the local control
field. We compare the efficiency of this approach with respect to the
time-optimal solution which has been recently derived using geometric methods.Comment: 12 pages, 4 figures, submitted to new journal of physics (2011
Amyloid fibril length distribution quantified by atomic force microscopy single-particle image analysis
Amyloid fibrils are proteinaceous nano-scale linear aggregates. They are of key interest not only because of their association with numerous disorders, such as type II diabetes mellitus, Alzheimer's and Parkinson's diseases, but also because of their potential to become engineered high-performance nano-materials. Methods to characterise the length distribution of nano-scale linear aggregates such as amyloid fibrils are of paramount importance both in understanding the biological impact of these aggregates and in controlling their mechanical properties as potential nano-materials. Here, we present a new quantitative approach to the determination of the length distribution of amyloid fibrils using tapping-mode atomic force microscopy. The method described employs single-particle image analysis corrected for the length-dependent bias that is a common problem associated with surface-based imaging techniques. Applying this method, we provide a detailed characterisation of the length distribution of samples containing long-straight fibrils formed in vitro from β2-microglobulin. The results suggest that the Weibull distribution is a suitable model in describing fibril length distributions, and reveal that fibril fragmentation is an important process even under unagitated conditions. These results demonstrate the significance of quantitative length distribution measurements in providing important new information regarding amyloid assembly
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Home-ownership as a social norm and positional good: subjective well-being evidence from panel data
Much attention has been devoted to examining the absolute benefits
of home-ownership (e.g. security and autonomy). This paper by contrast is
concerned with conceptualising and testing the relative benefits of homeownership;
those benefits that depend on an individual’s status in society.
Home-ownership has previously been analysed as a social norm, implying that
the relative benefits (costs) associated with being an owner (renter) are
positively related to relevant others’ home-ownership values. The theoretical
contribution of this paper is to additionally conceptualise home-ownership as a
positional good, implying that the status of both home-owners and renters is
negatively related to relevant others’ home-ownership consumption.
The empirical contribution of this paper is to quantitatively test for these relative
benefits in terms of subjective well-being. We run fixed effects regressions on
three waves of the British Household Panel Study. We find that i) a strengthening
of relevant others’ home-ownership values is associated with increases
(decreases) in the subjective well-being of home-owners (renters), and ii) an
increase in relevant others’ home-ownership consumption decreases the life
satisfaction of owners but has no effect for renters.
Overall our findings suggest that i) the relative benefit of home-ownership are
both statistically significant and of a meaningful magnitude, and ii) homeownership
is likely to be both a social norm and a positional good. Without
explicitly recognising these relative benefits, policymakers risk overestimating
the contribution of home-ownership to societal well-being
Longitudinal Peer Network Data in Higher Education
This chapter employs a longitudinal social network approach to research small group teaching in higher education. Longitudinal social network analyses can provide in-depth understanding of the social dynamics in small groups. Specifically, it is possible to investigate and disentangle the processes by which students make or break social connections with peers and are influenced by them, as well as how those processes relate to group compositions and personal attributes, such as achievement level. With advanced methods for modelling longitudinal social networks, researchers can identify social processes affecting small group teaching and learning
Attitudes Toward Organizational Change among Public Middle Managers
Positive attitudes toward change (PATC) are an important current issue in public
organizations facing profound financial and managerial reforms. This study aims to
identify social and organizational antecedents of PATC. The investigated population
is composed of middle managers working in Swiss public hospitals (N = 720), which
are currently being confronted by major reforms. Partial mediation effects of
organizational commitment (OC) in the relationships between independent variables
and PATC are also controlled. The findings show that perceived social support (work
relationships with colleagues and supervisors) as well as perceived organizational
support (employee voice and participation, information and communication, work-life
balance) are positively and significantly related to PATC. Stress perception is shown
to have a negative impact on PATC. This article provides valuable contributions with
respect to antecedents of attitudes toward change in a population of public middle
managers
Cooperation, Norms, and Revolutions: A Unified Game-Theoretical Approach
Cooperation is of utmost importance to society as a whole, but is often
challenged by individual self-interests. While game theory has studied this
problem extensively, there is little work on interactions within and across
groups with different preferences or beliefs. Yet, people from different social
or cultural backgrounds often meet and interact. This can yield conflict, since
behavior that is considered cooperative by one population might be perceived as
non-cooperative from the viewpoint of another.
To understand the dynamics and outcome of the competitive interactions within
and between groups, we study game-dynamical replicator equations for multiple
populations with incompatible interests and different power (be this due to
different population sizes, material resources, social capital, or other
factors). These equations allow us to address various important questions: For
example, can cooperation in the prisoner's dilemma be promoted, when two
interacting groups have different preferences? Under what conditions can costly
punishment, or other mechanisms, foster the evolution of norms? When does
cooperation fail, leading to antagonistic behavior, conflict, or even
revolutions? And what incentives are needed to reach peaceful agreements
between groups with conflicting interests?
Our detailed quantitative analysis reveals a large variety of interesting
results, which are relevant for society, law and economics, and have
implications for the evolution of language and culture as well
Air Travel and Venous Thromboembolism: A Systematic Review
CONTEXT: Despite multiple attempts to document and quantify the danger of venous thromboembolism (VTE) following prolonged travel, there is still uncertainty about the magnitude of risk and what can be done to lower it. OBJECTIVES: To review the methodologic strength of the literature, estimate the risk of travel-related VTE, evaluate the efficacy of preventive treatments, and develop evidence-based recommendations for practice. DATA SOURCES: Studies identified from MEDLINE from 1966 through December 2005, supplemented by a review of the Cochrane Central Registry of Controlled Trials, the Database of Abstracts of Reviews of Effects, and relevant bibliographies. STUDY SELECTION: We included all clinical studies that either reported primary data concerning travel as a risk factor for VTE or tested preventive measures for travel-related VTE. DATA EXTRACTION AND ANALYSIS: Two reviewers reviewed each study independently to assess inclusion criteria, classify research design, and rate methodologic features. The effect of methodologic differences, VTE risk, and travel duration on VTE rate was evaluated using a logistic regression model. DATA SYNTHESIS: Twenty-four published reports, totaling 25 studies, met inclusion criteria (6 case-control studies, 10 cohort studies, and 9 randomized controlled trials). Method of screening for VTE [screening ultrasound compared to usual clinical care, odds ratio (OR) 390], outcome measure [all VTE compared to pulmonary embolism (PE) only, OR 21], duration of travel (<6 hours compared to 6–8 hours, OR 0.011), and clinical risk (“higher” risk travelers compared to “lower,” OR 3.6) were significantly related to VTE rate. Clinical VTE after prolonged travel is rare [27 PE per million flights diagnosed through usual clinical care, 0.05% symptomatic deep venous thrombosis (DVT) diagnosed through screening ultrasounds], but asymptomatic thrombi of uncertain clinical significance are more common. Graduated compression stockings prevented travel-related VTE (P < 0.05 in 4 of 6 studies), aspirin did not, and low-molecular-weight heparin (LMWH) showed a trend toward efficacy in one study. CONCLUSIONS: All travelers, regardless of VTE risk, should avoid dehydration and frequently exercise leg muscles. Travelers on a flight of less than 6 hours and those with no known risk factors for VTE, regardless of the duration of the flight, do not need DVT prophylaxis. Travelers with 1 or more risk factors for VTE should consider graduated compression stockings and/or LMWH for flights longer than 6 hours
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