30,098 research outputs found
Base-controlled mechanical systems and geometric phases
In this paper, we carry a detailed study of mechanical systems with
configuration space for which the base variables
are being controlled. The overall system's motion is considered to be induced
from the base one due to the presence of general non-holonomic constraints. It
is shown that the solution can be factorized into dynamical and geometrical
parts. Moreover, under favorable kinematical circumstances, the dynamical part
admits a further factorization since it can be reconstructed from an
intermediate (body) momentum solution, yielding a reconstruction phase formula.
Finally, we apply this results to the study of concrete mechanical systems.Comment: 44 pages, 1 figur
The Hopf bifurcation for nonlinear semigroups
Several authors, have shown by perturbation techniques that the Hopf theorem on the development of periodic stable solutions is valid for the Navier-Stokes equations; in particular, solutions near the stable periodic ones remain defined and smooth for all t ≥ 0 . The principal difficulty is that the Hopf theorem deals with flows of smooth vector fields on finite-dimensional spaces, whereas the Navier-Stokes equations define a flow (or evolution operator) for a nonlinear partial differential operator (actually it is a nonlocal operator).
The aim of this note is to outline a method for overcoming this difficulty which is entirely different in appearance from the perturbation approach. The method depends on invariant manifold theory plus certain smoothness properties of the flow which actually hold for the Navier-Stokes flow
The multi modal study of transport investment plans.
In 1998 the UK Department for Transport
commissioned a programme of 22 studies to examine
the most acute congestion problems on the English road
network. The studies promised a new approach to
reducing road congestion by examining the contribution
that all modes of transport could make to solve these
problems. The studies have provided the most
convincing evidence to date that road building alone will
not be able to solve congestion and pollution problems.
Extra road infrastructure will, in most cases, buy a few
years’ respite from congestion on the inter-urban road
network. The studies have proposed substantial packages
of road and public transport improvements, combined
with demand management and traffic restraint
measures, to tackle the problems. The evidence suggests
that some form of road-user charging will be required in
many areas to ensure that the efficiency benefits gained
from the extra road capacity will not simply be eroded
by traffic growth as has been seen to date on routes such
as the M25. The outcomes of the studies have prompted
the Government to undertake a review of the potential
for a national road-user charging system. The multimodal
studies have undoubtedly brought about a more
balanced and integrated approach to transport planning.
There have been quite significant changes to the roads
schemes that were initially remitted to the studies and
evidence to suggest that significant environmental
concerns are now playing a much stronger role in
decisions taken by the Department for Transport. The
challenge now is to ensure that all of the major parts of
the integrated strategies proposed are delivered. A
failure to do so will not only reduce the benefits the
proposals offer but will also devalue the multi-modal
approach taken to the studies
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Brexit and the mythologies of nationalism: a warning for Wales
Richard Marsden explores the historical distinctions between nationalist movements in Scotland, Ireland and Wales - and what this means for the UK after Brexit
The real reason Yes Scotland avoids Braveheart nostalgia
In 1998 Alex Salmond dismissed doubts over Scotland’s Celtic lineage as “ignorance bordering on silliness”. In 2007 he expounded a vision of the country as a “Celtic lion” economy. In 2005 a Scottish National Party press release on the anniversary of William Wallace’s execution stated that he “saved the nation from surrender and annihilation”. More recently, Salmond’s impassioned speeches have channelled Mel Gibson’s Wallace from the 1995 Hollywood blockbuster Braveheart
A formula for the solution of the Navier-Stokes equation based on a method of Chorin
Recently, A. Chorin has found a numerical scheme for solving the Navier-Stokes equations which has the pleasing feature of not breaking down at high Reynolds numbers R . The purpose of this announcement is to present a formula which is designed to establish the convergence of Chorin's time step iteration procedure, assuming that the relevant equations (heat equation and Euler's equations) are solved exactly at each step
Bush, Obama and a faith-based US foreign policy
In a calculated move to appeal to his core constituency during his first term, President George W. Bush launched domestic and international faith-based initiatives designed to leverage public finance for religious groupings to carry out social and welfare functions formerly performed by government or secular organizations. In December 2002 the Center for Faith-Based and Community Initiatives (CFBCI) was extended to the United States Agency for International Development (USAID). The Center's intention was to 'create a level playing field' for faith-based and community groups to compete for foreign assistance funding. These presidential initiatives are problematic, however, calling into question the first amendment-the separation of church and state. Upon taking office Barack Obama set up the Office of Faith-based and Neighborhood Partnerships, promising a greater emphasis on community/neighbourhood programs. The CFBCI remains a fixture in USAID and Obama shows as much enthusiasm for the initiative as his predecessor. Faith-based international relations and political science scholars have sought to build on these initiatives and call for a greater role for faith in US foreign policy. On the eve of the 2012 presidential election, this article considers the claims for a faith-based foreign policy by examining the construction of a faith-based discourse by academics and successive presidents. Using faith-based initiatives and USAID as a case-study, the article discusses criticisms of the policy and focuses on the role of a conservative evangelical organization, Samaritan's Purse, to illustrate the advantages and disadvantages of faith-based approaches. © 2012 The Author(s). International Affairs © 2012 The Royal Institute of International Affairs
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Hyper-power and private monopoly: the unholy marriage of (neo) corporatism and the imperial surveillance state
American hyper-power world dominance by public and private agencies has replaced British Empire hyper-power world domination in the period 1815-1914. Snowden’s revelations have given rise to several important papers examining the geographical and territorial limits on the Internet, comparing it to the imperial telegraph (Kurbalija 2013) and even to the Roman imperial road (Moglen 2013). This paper recalls earlier telegraphy research (Standage 1999, Hills 2007) and explains how the previous hyperpower
(Marsden 2004, describing a global super-power without effective opposition, from the French hyperpuissance)
was able to control communications in order to extend its extraterritorial application of domestic law. I
explain that the telegraph ‘cables that girdled the Earth’ (Clarke 1958) were sunk into the sea in Cornwall,
southwest England, and that today’s Internet fibre cables are in the same places – with the result that the greatest
National Security Agency espionage-gathering operation is a joint US/UK operation from the small town of Bude,
Cornwall. Add to that espionage the invention of encryption/decryption computing, devices from Babbage’s
Difference Engine to Turing and Tommy Flower’s Colossus Marks I and II that broke both Enigma and Lorenz1.
The recipe now exists for what the National Security Agency calls ‘Total Information Awareness’ and the
Orwellian nightmare of totally efficient surveillance and ‘war is peace’ according to the Ministry of Truth2. But it
existed before, and we should learn from the past
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