2,808 research outputs found
Leibnizian, Galilean and Newtonian structures of spacetime
The following three geometrical structures on a manifold are studied in
detail: (1) Leibnizian: a non-vanishing 1-form plus a Riemannian
metric \h on its annhilator vector bundle. In particular, the possible
dimensions of the automorphism group of a Leibnizian G-structure are
characterized. (2) Galilean: Leibnizian structure endowed with an affine
connection (gauge field) which parallelizes and \h. Fixed
any vector field of observers Z (), an explicit Koszul--type
formula which reconstruct bijectively all the possible 's from the
gravitational and vorticity fields
(plus eventually the torsion) is provided. (3) Newtonian: Galilean structure
with \h flat and a field of observers Z which is inertial (its flow preserves
the Leibnizian structure and ). Classical concepts in Newtonian
theory are revisited and discussed.Comment: Minor errata corrected, to appear in J. Math. Phys.; 22 pages
including a table, Late
Nanostructuring lithium niobate substrates by focused ion beam milling
We report on two novel ways for patterning Lithium Niobate (LN) at
submicronic scale by means of focused ion beam (FIB) bombardment. The first
method consists of direct FIB milling on LiNbO3 and the second one is a
combination of FIB milling on a deposited metallic layer and subsequent RIE
(Reactive Ion Etching) etching. FIB images show in both cases homogeneous
structures with well reproduced periodicity. These methods open the way to the
fabrication of photonic crystals on LiNbO3 substrates
Signals of CP Violation Beyond the MSSM in Higgs and Flavor Physics
We study an extension of the Higgs sector of the Minimal Supersymmetric
Standard Model (MSSM), considering the effects of new degrees of freedom at the
TeV scale, and allowing for sources of CP violation beyond the MSSM (BMSSM). We
analyze the impact of the BMSSM sources of CP violation on the Higgs collider
phenomenology and on low energy flavor and CP violating observables. We
identify distinct Higgs collider signatures that cannot be realized, either in
the case without CP violating phases or in the CP violating MSSM, and
investigate the prospects to probe them at the Tevatron and the LHC. The most
striking benchmark scenario has three neutral Higgs bosons that all decay
dominantly into W boson pairs and that are well within the reach of the 7 TeV
LHC run. On the other hand, we also present scenarios with three Higgs bosons
that have masses M_Hi > 150 GeV and decay dominantly into b bbar. Such
scenarios are much more challenging to probe and can even lie completely
outside the reach of the 7 TeV LHC run. We explore complementary scenarios with
standard MSSM Higgs signals that allow to accommodate a sizable B_s mixing
phase as indicated by D0, as well as the excess in B_s --> mu+ mu- candidates
recently reported by CDF. We find that, in contrast to the MSSM, a minimal
flavor violating soft sector is sufficient to generate significant corrections
to CP violating observables in meson mixing, compatible with EDM constraints.
In particular, a sizable B_s mixing phase, S_psiphi < 0.4, can be achieved for
specific regions of parameter space. Such a large B_s mixing phase would
unambiguously imply a sizable suppression of S_psiKs with respect to the SM
prediction and a BR(B_s --> mu+ mu-) close to the 95% C.L. upper bound reported
by CDF.Comment: 58 pages, 15 figures, 2 tables, v2 matches published versio
J D Bernal: philosophy, politics and the science of science
This paper is an examination of the philosophical and political legacy of John Desmond Bernal. It addresses the evidence of an emerging consensus on Bernal based on the recent biography of Bernal by Andrew Brown and the reviews it has received. It takes issue with this view of Bernal, which tends to be admiring of his scientific contribution, bemused by his sexuality, condescending to his philosophy and hostile to his politics. This article is a critical defence of his philosophical and political position
J D Bernal: philosophy, politics and the science of science
This paper is an examination of the philosophical and political legacy of John Desmond Bernal. It addresses the evidence of an emerging consensus on Bernal based on the recent biography of Bernal by Andrew Brown and the reviews it has received. It takes issue with this view of Bernal, which tends to be admiring of his scientific contribution, bemused by his sexuality, condescending to his philosophy and hostile to his politics. This article is a critical defence of his philosophical and political position
Columnar and lamellar phases in attractive colloidal systems
In colloidal suspensions, the competition between attractive and repulsive
interactions gives rise to a rich and complex phenomenology. Here, we study the
equilibrium phase diagram of a model system using a DLVO interaction potential
by means of molecular dynamics simulations and a thermodynamical approach. As a
result, we find tubular and lamellar phases at low volume fraction. Such
phases, extremely relevant for designing new materials, may be not easily
observed in the experiments because of the long relaxation times and the
presence of defects.Comment: 5 pages, 5 figure
Fertilizer value and greenhouse gas emissions from solid fraction pig slurry compost pellets
Conversion of pig slurry to pellets is a desirable fertilizer option for farmers who want to mitigate environmental pollution from slurry accumulation. The goals of the current investigation were to determine the fertilizer properties of pig slurry solid fraction (SF) pellets and to assess its potential to enhance soil properties in order to reduce ammonia (NH3) volatilization and greenhouse gas (GHG) emissions. Various parameters influence SF-based pellet fertilizer effectiveness: bulking agent use during composting, pellet diameter sizing and soil application type (superficially or incorporated into the soil). Two composts from the same pig slurry SF obtained from a screw press separator were prepared: pig SF compost without a bulking agent (SSFC) and pig SF compost with wood chips as the bulking agent (wood chip compost (WCC)). For each compost type, pellets of two different diameters (6 and 8 mm) were produced. A mesocosm experiment, conducted with maize plants, was used to test the fertilizer value of the considered pellets. In total, three compost fertilizers â SSFC, WCC and nitrogen: phosphorus: potassium mineral fertilizer 15 : 15 : 15, plus one unfertilized control treatment â were applied at the same N rate (equivalent to 200 kg/ha) using two different methods (surface and soil incorporation). After 65 days, above-ground biomass, roots and soil samples were collected and analysed. Subsequently, a second mesocosm study was undertaken to measure NH3 and GHG emissions released from pellet fertilization. Ammonia volatilization was determined immediately after pellet application, while carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions were monitored for 57 days. Study results indicated that both pellet types were effective slow-release fertilizers for maize. Additionally, three actions seemed to make the nutrients contained in pig SF compost pellets more available to plants: addition of a bulking agent before composting, use of small diameter pellets and soil incorporation of the fertilizer.This work was carried out within the framework of the âFITRAREFâ project, funded by the Italian Ministry of Agriculture and Forestry (GRANT NUMBER, DM29638/7818/10). The authors thank CEBAS-CSIC for the infrastructure and materials made available for the mesocosm experiments run during the stay of Dr Pampuro at the Department of Soil and Water Conservation and Organic Wastes Management of CEBAS-CSIC (financed by the Spanish Ministry of Economy and
Competitiveness and the European Union through FEDER funds; CTM2013-48697-C2-1-R).Peer reviewe
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