13,657 research outputs found
Moduli Corrections to Gauge and Gravitational Couplings in four dimensional Superstrings
We study one-loop, moduli-dependent corrections to gauge and gravitational
couplings in supersymmetric vacua of the heterotic string. By exploiting their
relation to the integrability condition for the associated CP-odd couplings, we
derive general expressions for them, both for and models, in
terms of tree level four-point functions in the internal superconformal
theory. The case, in particular symmetric orbifolds, is discussed in
detail.Comment: 19 page
Modelling the local and global cloud formation on HD 189733b
Context. Observations suggest that exoplanets such as HD 189733b form clouds
in their atmospheres which have a strong feedback onto their thermodynamical
and chemical structure, and overall appearance. Aims. Inspired by mineral cloud
modelling efforts for Brown Dwarf atmospheres, we present the first spatially
varying kinetic cloud model structures for HD 189733b. Methods. We apply a
2-model approach using results from a 3D global radiation-hydrodynamic
simulation of the atmosphere as input for a detailed, kinetic cloud formation
model. Sampling the 3D global atmosphere structure with 1D trajectories allows
us to model the spatially varying cloud structure on HD 189733b. The resulting
cloud properties enable the calculation of the scattering and absorption
properties of the clouds. Results. We present local and global cloud structure
and property maps for HD 189733b. The calculated cloud properties show
variations in composition, size and number density of cloud particles which are
strongest between the dayside and nightside. Cloud particles are mainly
composed of a mix of materials with silicates being the main component. Cloud
properties, and hence the local gas composition, change dramatically where
temperature inversions occur locally. The cloud opacity is dominated by
absorption in the upper atmosphere and scattering at higher pressures in the
model. The calculated 8{\mu}m single scattering Albedo of the cloud particles
are consistent with Spitzer bright regions. The cloud particles scattering
properties suggest that they would sparkle/reflect a midnight blue colour at
optical wavelengths.Comment: Accepted for publication (A&A) - 21/05/2015 (Low Resolution Maps
Limits on extra dimensions in orbifold compactifications of superstrings
Perturbative breaking of supersymmetry in four-dimensional string theories
predict in general the existence of new large dimensions at the TeV scale. Such
dimensions can be consistent with perturbative unification up to the Planck
scale in a class of string models and open the exciting possibility of lowering
a part of the massive string spectrum at energies accessible to future
accelerators. The main signature is the production of Kaluza-Klein excitations
which have a very particular structure, strongly correlated with the
supersymmetry breaking mechanism. We present a model independent analysis of
the physics of these states in the context of orbifold compactifications of the
heterotic superstring. In particular, we compute the limits on the size of
large dimensions used to break supersymmetry.Comment: 16 pages, CPTH-A257.079
Rapid Prototyping Using 3-D Welding
Rapid prototyping systems are based, almost exclusively on polymer, or paper materials.
The dimensions of the parts produced are limited by the volume of the processing area within
the machine, and parts tend to warp or distort due to shrinkage and lack of support. Also the
mechanical properties of the part are restricted to those of the processable materials and thus,
in many cases, required 'engineering properties' cannot be obtainedMechanical Engineerin
What is the Value of Home? NOT FOR SALE - West End Interventions
Many Australians today are image consumers. We fail to question the importance of lifestyle imagery created and promoted by Real Estate Agencies whom have no actual part in the physical creation of house, or indeed the intimate making of "home" through our experiences of place. Real Estate Markets dictate how, where, when and what we buy. Re-sale values, profit-making, and value-adding interfere with the crafting of a home over time as a tangible, individual, collaborative, and rich lived experience of dwelling. The "NOT FOR SALE" project is a response and critique of the dominance of real estate forces in West End within the context and unshakable presence of a booming inner-city property market. This proposal originated from an experimental dwelling in Avebury St., West End. This project has been fashioned over a period of several years primarily from recycled local materials, interconnected with the changing needs and spatial requirements of the occupants and project participants. The influence of property markets is of little concern in this home "making". The "NOT FOR SALE" project attempts to question and critique the purely financial value that we as a society place upon our homes. By appropriating and re-coding the Real Estate Signage typologies, we aim to provoke social commentary on the dominance of real estate forces in the West End suburb. There is a strong and rich tradition of anti-consumerist activist graffiti in West End. Activists re-code signs and property with political commentary and critique. The "NOT FOR SALE" project draws upon this tradition through our RRESign (Recodified Real Estate Signs): we aim to redress the dominant commercial forces associated with the single house/property. Collectively, at the scale of the street, these RRESigns will reflect a critique of street scale, amenity, and character. Finally, at the scale of the suburb, the network of RRESigns will reflect a critique of the idea of place making. Collectively, the aim of the "NOT FOR SALE" RRESign interventions is to highlight the idea of making and the material characteristics of dwelling that challenges the cultural value of commodified property, re-defining and prioritising the idea of "home". Conventional Real Estate signs use images and text to sell an idea of home: our proposed interventions sell nothing, and are rather celebrations of the joy of making tactile, handcrafted objects, and by extension, the making and crafting of home. The intimate and experiential understanding of home will be harnessed through the engagement of local residents. Community groups within West End such as Local Push can further disseminate the RRESign interventions. The signs will be constructed West End-specific materials (old signs purchased from inexpensive second-hand material merchant Reverse Garbage in Montague Rd.): turning post-consumer waste into objects of material beauty and social critique. Residents and community groups will be encouraged to place their RRESigns outside their properties and adjacent real estate signs, frustrating and recoding the existing For-Sale signs that currently dominate the West End street scape. The project is dependent on the support of the local residents, extending from a few signs in Avebury St. to a network of RRESigns throughout West End. A commentary on people's responses to the project will be linked to the www.apbv.com.au website. What is the value of home
Spinning test particles and clock effect in Schwarzschild spacetime
We study the behaviour of spinning test particles in the Schwarzschild
spacetime. Using Mathisson-Papapetrou equations of motion we confine our
attention to spatially circular orbits and search for observable effects which
could eventually discriminate among the standard supplementary conditions
namely the Corinaldesi-Papapetrou, Pirani and Tulczyjew. We find that if the
world line chosen for the multipole reduction and whose unit tangent we denote
as is a circular orbit then also the generalized momentum of the
spinning test particle is tangent to a circular orbit even though and
are not parallel four-vectors. These orbits are shown to exist because the spin
induced tidal forces provide the required acceleration no matter what
supplementary condition we select. Of course, in the limit of a small spin the
particle's orbit is close of being a circular geodesic and the (small)
deviation of the angular velocities from the geodesic values can be of an
arbitrary sign, corresponding to the possible spin-up and spin-down alignment
to the z-axis. When two spinning particles orbit around a gravitating source in
opposite directions, they make one loop with respect to a given static observer
with different arrival times. This difference is termed clock effect. We find
that a nonzero gravitomagnetic clock effect appears for oppositely orbiting
both spin-up or spin-down particles even in the Schwarzschild spacetime. This
allows us to establish a formal analogy with the case of (spin-less) geodesics
on the equatorial plane of the Kerr spacetime. This result can be verified
experimentally.Comment: IOP macros, eps figures n. 2, to appear on Classical and Quantum
gravity, 200
Critical velocity ionisation in substellar atmospheres
The observation of radio, X-ray and Hα emission from substellar objects indicates the presence of plasma regions and associated high-energy processes in their surrounding envelopes. This paper numerically simulates and characterises Critical Velocity Ionisation, a potential ionisation process, that can efficiently generate plasma as a result of neutral gas flows interacting with seed magnetized plasmas. By coupling a Gas-MHD interactions code (to simulate the ionisation mechanism) with a substellar global circulation model (to provide the required gas flows) we quantify the spatial extent of the resulting plasma regions, their degree of ionisation and their lifetime for a typical substellar atmosphere. It is found that the typical average ionisation fraction reached at equilibrium (where the ionisation and recombination rates are equal and opposite) ranges from 10-5 to 10-8, at pressures between 10-1 and 10-3 bar, with a trend of increasing ionisation fraction with decreasing atmospheric pressure. The ionisation fractions reached as a result of Critical Velocity Ionisation are sufficient to allow magnetic fields to couple to gas flows in the atmosphere
Bricks for Building the Self Concept of the Disadvantaged Child
Poverty, unemployment, illiteracy, school dropouts, and the necessity for public welfare are not new social problems in our society. At the present time great national effort and much money are being spent to attack many social ills through antipoverty programs. These programs are receiving attention at this time because the increased industrialization and urbanization of today have widened the gap between our American ideals and practices. More people are aware of the resulting inequalities. And people are also aware that society has the power and ability to do something about it. Currently, one of the complex problems facing the United States is putting into practice the ideal of educating all of the children of all of the people.· As a group the children of the poor have not profited from public school education. One effective method of attacking a social problem is through prevention. As a result of this knowledge great emphasis has been placed on improving the schools in the disadvantaged areas
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