4,278 research outputs found
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Can we rehabilitate the guilds? A sceptical re-appraisal
This paper examines recent attempts to rehabilitate pre-modern craft guilds as efficient economic institutions. Contrary to rehabilitation views, craft guilds adversely
affected quality, skills, and innovation. Guild rent-seeking imposed deadweight losses on the economy and generated no demonstrable positive externalities. Industry flourished where
guilds decayed. Despite impairing efficiency, guilds persisted because they redistributed resources to powerful groups. The ‘rehabilitation’ view of guilds, it concludes, is theoretically
contradictory and empirically untenable
Social capital and collusion: the case of merchant guilds
Merchant guilds have been portrayed as ‘social networks’ that generated beneficial ‘social capital’ by sustaining
shared norms, effectively transmitting information, and successfully undertaking collective action. This social capital, it is claimed,
benefited society as a whole by enabling rulers to commit to providing a secure trading environment for alien merchants. But
was this really the case? We develop a new model of the emergence, rise and eventual decline of European merchant guilds
which explores the collusive relationship between rulers and guilds, and calls into question the prevailing positive view of merchant guilds.
We then confront the model’s predictions with the available historical data. The empirical evidence strongly support our model and
refutes existing theories. Our findings show that merchant guilds used their social capital for socially harmful as well as beneficial ends
The effect of planetary migration on the corotation resonance
The migration of a planet through a gaseous disc causes the locations of
their resonant interactions to drift and can alter the torques exerted between
the planet and the disc. We analyse the time-dependent dynamics of a
non-coorbital corotation resonance under these circumstances. The ratio of the
resonant torque in a steady state to the value given by Goldreich & Tremaine
(1979) depends essentially on two dimensionless quantities: a dimensionless
turbulent diffusion time-scale and a dimensionless radial drift speed. When the
drift speed is comparable to the libration speed and the viscosity is small,
the torque can become much larger than the unsaturated value in the absence of
migration, but is still proportional to the large-scale vortensity gradient in
the disc. Fluid that is trapped in the resonance and drifts with it acquires a
vortensity anomaly relative to its surroundings. If the anomaly is limited by
viscous diffusion in a steady state, the resulting torque is inversely
proportional to the viscosity, although a long time may be required to achieve
this state. A further, viscosity-independent, contribution to the torque comes
from fluid that streams through the resonant region. In other cases, torque
oscillations occur before the steady value is achieved. We discuss the
significance of these results for the evolution of eccentricity in
protoplanetary systems. We also describe the possible application of these
findings to the coorbital region and the concept of runaway (or type III)
migration. [Abridged]Comment: 15 pages, 6 figures, to be published in MNRA
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The economics of guilds
Occupational guilds in medieval and early modern Europe offered an effective institutional mechanism whereby two powerful groups, guild members and political elites, could collaborate in capturing a larger slice of the economic pie and redistributing it to themselves at the expense of the rest of the economy. Guilds provided an organizational mechanism for groups of businessmen to negotiate with political elites for exclusive legal privileges that allowed them to reap monopoly rents. Guild members then used their guilds to redirect a share of these rents to political elites in return for support and enforcement. In short, guilds enabled their members and political elites to negotiate a way of extracting rents in the manufacturing and commercial sectors, rents that neither party could have extracted on its own. First, I provide an overview of where and when European guilds arose, what occupations they encompassed, how large they were, and how they varied across time and space. I then examine how guild activities affected market competition, commercial security, contract enforcement, product quality, human capital, and technological innovation. The historical findings on guilds provide strong support for the view that institutions arise and survive for centuries not because they are efficient but because they serve the distributional interests of powerful groups. </jats:p
The evolution of a warped disc around a Kerr black hole
We consider the evolution of a warped disc around a Kerr black hole, under
conditions such that the warp propagates in a wavelike manner. This occurs when
the dimensionless effective viscosity, alpha, that damps the warp is less than
the characteristic angular semi-thickness, H/R, of the disc. We adopt
linearized equations that are valid for warps of sufficiently small amplitude
in a Newtonian disc, but also account for the apsidal and nodal precession that
occur in the Kerr metric. Through analytical and time-dependent studies, we
confirm the results of Demianski & Ivanov, and of Ivanov & Illarionov, that
such a disc takes on a characteristic warped shape. The inner part of the disc
is not necessarily aligned with the equator of the hole, even in the presence
of dissipation. We draw attention to the fact that this might have important
implications for the directionality of jets emanating from discs around
rotating black holes.Comment: 8 pages, 6 figures, to be published in MNRA
Perceived characteristics of the environment associated with active travel: development and testing of a new scale
Background
Environmental characteristics may be associated with patterns of physical activity. However, the development of instruments to measure perceived characteristics of the local environment is still at a comparatively early stage, and published instruments are not necessarily suitable for application in all settings. We therefore developed and established the test-retest reliability of a new scale for use in a study of the correlates of active travel and overall physical activity in deprived urban neighbourhoods in Glasgow, Scotland.
Methods
We developed and piloted a 14-item scale based on seven constructs identified from the literature (aesthetics, green space, access to amenities, convenience of routes, traffic, road safety and personal safety). We administered the scale to all participants in a random postal survey (n = 1322) and readministered the scale to a subset of original respondents (n = 125) six months later. We used principal components analysis and Varimax rotation to identify three principal components (factors) and derived summary scores for subscales based on these factors. We examined the internal consistency of these subscales using Cronbach's alpha and examined the test-retest reliability of the individual items, the subscale summary scores and an overall summary neighbourhood score using a combination of correlation coefficients and Cohen's kappa with and without weighting.
Results
Public transport and proximity to shops were the items most likely to be rated positively, whereas traffic volume, traffic noise and road safety for cyclists were most likely to be rated negatively. Three principal components – 'safe and pleasant surroundings', 'low traffic' and 'convenience for walking' – together explained 45% of the total variance. The test-retest reliability of individual items was comparable with that of items in other published scales (intraclass correlation coefficients (ICCs) 0.34–0.70; weighted Cohen's kappa 0.24–0.59). The overall summary neighbourhood score had acceptable internal consistency (Cronbach's alpha 0.72) and test-retest reliability (ICC 0.73).
Conclusion
This new scale contributes to the development of a growing set of tools for investigating the role of perceived environmental characteristics in explaining or mediating patterns of active travel and physical activity
Evaluating health effects of transport interventions: methodologic case study
Background: There is little evidence about the effects of environmental interventions on population levels of physical activity. Major transport projects may promote or discourage physical activity in the form of walking and cycling, but researching the health effects of such “natural experiments” in transport policy or infrastructure is challenging.
Methods: Case study of attempts in 2004–2005 to evaluate the effects of two major transport projects in Scotland: an urban congestion charging scheme in Edinburgh, and a new urban motorway (freeway) in Glasgow.
Results: These interventions are typical of many major transport projects. They are unique to their context. They cannot easily be separated from the other components of the wider policies within which they occur. When, where, and how they are implemented are political decisions over which researchers have no control. Baseline data collection required for longitudinal studies may need to be planned before the intervention is certain to take place. There is no simple way of defining a population or area exposed to the intervention or of defining control groups. Changes in quantitative measures of health-related behavior may be difficult to detect.
Conclusions: Major transport projects have clear potential to influence population health, but it is difficult to define the interventions, categorize exposure, or measure outcomes in ways that are likely to be seen as credible in the field of public health intervention research. A final study design is proposed in which multiple methods and spatial levels of analysis are combined in a longitudinal quasi-experimental study
Magnetorotational-type instability in Couette-Taylor flow of a viscoelastic polymer liquid
We describe an instability of viscoelastic Couette-Taylor flow that is
directly analogous to the magnetorotational instability (MRI) in astrophysical
magnetohydrodynamics, with polymer molecules playing the role of magnetic field
lines. By determining the conditions required for the onset of instability and
the properties of the preferred modes, we distinguish it from the centrifugal
and elastic instabilities studied previously. Experimental demonstration and
investigation should be much easier for the viscoelastic instability than for
the MRI in a liquid metal. The analogy holds with the case of a predominantly
toroidal magnetic field such as is expected in an accretion disk and it may be
possible to access a turbulent regime in which many modes are unstable.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
Development of a scanning electron mirror microscope
Scanning electron mirrors microscope design and developmen
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