299,329 research outputs found
Looking Inwards for Sustainability: Nigerian Cities and Building Demolition-waste or wealth?
Cities could generally be described as sustainable before the replacement of manual labour with machines known as the industrial revolution of the 18th century in Europe. Nevertheless, the Industrial Revolution has been associated with environmental degradation and other negative impacts. The trend continued for two centuries until it was realised that there is a limit to the capacity of the earth to withstand such impacts. The damage to the earth needs to be halted by choice or forced by natural consequences. The idea of pursuing economic development with minimum negative socio-economic and environmental impacts comes to be known as Sustainability. The built environment becomes at the centre of the sustainability agenda due to the enormous negative impact to the environment. Moreover, it was reported that 90% of all materials resources ever extracted might be used in the built environment. Unfortunately, many of these materials, including 10% unused are discarded as wastes. In the UK example, 90-120 million tonnes of construction and demolition (C&D) waste is generated annually. This makes C&D wastes even more critical to the sustainability agenda; and in search for solution, in the words of Janine Benyus, it may even involve the urban westerners learning from the wisdom of the preindustrial societies that have been living in harmony with the nature. In the preindustrial community of Kano in Nigeria, there is virtually zero C&D waste; rather it is merchandise. The different categories of the stakeholders were interviewed to establish how the system works, the conditions that led to its emergence, and limitations. It was discovered that the end-of-life management of buildings in Kano is a naturally evolved industrial ecology analogous to the natural ecological system, whereby the bye-product of one process becomes the raw material for another with no waste. Furthermore, a conceptual model of the system was developed using the biomorphic adaptation of the shell of an African snail. It was therefore argued that sustainability practices are inherent within the African traditions rather than to be learnt from outside
Quantitative absorption and fluorescence studies of NO between 1060 and 2000 A
Synchrotron radiation in the 1060 to 2000 A region was used to measure the average absorption and fluorescence cross sections of NO and to determine approximate photodissociation quantum yields. Several vibrational levels of the D(2) sigma(+), E(2) sigma(+), and B(2) delta states have high fluorescence quantum yields. The C(2) and B(2) states do not fluoresce when the excitation energies are above the first dissociation limit, in accord with previous experiments. In general, the fluorescence yields decrease with increasing photon energy. The quantitative measurements are compared with spectroscopic observations and are found to be reasonably consistent
Linking Topological Quantum Field Theory and Nonperturbative Quantum Gravity
Quantum gravity is studied nonperturbatively in the case in which space has a
boundary with finite area. A natural set of boundary conditions is studied in
the Euclidean signature theory, in which the pullback of the curvature to the
boundary is self-dual (with a cosmological constant). A Hilbert space which
describes all the information accessible by measuring the metric and connection
induced in the boundary is constructed and is found to be the direct sum of the
state spaces of all Chern-Simon theories defined by all choices of
punctures and representations on the spatial boundary . The integer
level of Chern-Simons theory is found to be given by , where is the cosmological constant and is a
breaking phase. Using these results, expectation values of observables which
are functions of fields on the boundary may be evaluated in closed form. The
Beckenstein bound and 't Hooft-Susskind holographic hypothesis are confirmed,
(in the limit of large area and small cosmological constant) in the sense that
once the two metric of the boundary has been measured, the subspace of the
physical state space that describes the further information that the observer
on the boundary may obtain about the interior has finite dimension equal to the
exponent of the area of the boundary, in Planck units, times a fixed constant.
Finally,the construction of the state space for quantum gravity in a region
from that of all Chern-Simon theories defined on its boundary confirms the
categorical-theoretic ``ladder of dimensions picture" of Crane.Comment: TEX File, Minor Changes Made, 59 page
Defect energy of infinite-component vector spin glasses
We compute numerically the zero temperature defect energy, Delta E, of the
vector spin glass in the limit of an infinite number of spin components m, for
a range of dimensions 2 <= d <= 5. Fitting to Delta E ~ L^theta, where L is the
system size, we obtain: theta = -1.54 (d=2), theta = -1.04 (d=3), theta = -0.67
(d=4) and theta = -0.37 (d=5). These results show that the lower critical
dimension, d_l (the dimension where theta changes sign), is significantly
higher for m=infinity than for finite m (where 2 < d_l < 3).Comment: 4 pages, 5 figure
Spin glasses in the limit of an infinite number of spin components
We consider the spin glass model in which the number of spin components, m,
is infinite. In the formulation of the problem appropriate for numerical
calculations proposed by several authors, we show that the order parameter
defined by the long-distance limit of the correlation functions is actually
zero and there is only "quasi long range order" below the transition
temperature. We also show that the spin glass transition temperature is zero in
three dimensions.Comment: 9 pages, 13 figure
Map of metastable states for thin circular magnetic nano-cylinders
Nano-magnetic systems of artificially shaped ferromagnetic islands, recently
became a popular subject due to their current and potential applications in
spintronics, magneto-photonics and superconductivity. When the island size is
close to the exchange length of magnetic material (around 15 nm), its magnetic
structure becomes markedly different. It determines both static and dynamic
magnetic properties of elements, but strongly depends on their shape and size.
Here we map this dependence for circular cylindrical islands of a few exchange
lengths in size. We outline the region of metastability of "C"-type magnetic
states, proving that they are indeed genuine and not a result of pinning on
particle imperfections. A way to create the smallest particles with guaranteed
magnetic vortex state at zero field becomes evident. It is expected that the
map will help focus the efforts in planning of experiments and devices.Comment: 3 pages, 1 figur
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