Solving XCSP problems by using Gecode

Gecode is one of the most efficient libraries that can be used for constraint solving. However, using it requires dealing with C++ programming details. On the other hand several formats for representing constraint networks have been proposed. Among them, XCSP has been proposed as a format based on XML which allows us to represent constraints defined either extensionally or intensionally, permits global constraints and has been the standard format of the international competition of constraint satisfaction problems solvers. In this paper we present a plug-in for solving problems specified in XCSP by exploiting the Gecode solver. This is done by dynamically translating constraints into Gecode library calls, thus avoiding the need to interact with C++.Comment: 5 pages, http://ceur-ws.org/Vol-810 CILC 201

Impacts of agricultural trade and market liberalization of food security in developing countries: comparative study of Kenya and Zambia

The introduction of agricultural reforms has debatable effects on food security in developing countries. This research investigates how such effects influenced maize supply in two developing countries which were among the first to introduce agricultural reforms. Conclusions from the research suggest that agricultural reforms led to mixed results. This may be attributed to the sometimes stop-go nature of reform implementation. The mixed results are reflected in the weak maize output response to price changes. Overall country economic conditions, state of agricultural development can be attributed to the pace of response, hence effect on agricultural supply. Elasticity of maize output to changes in price and acreage are strongly significant in maize output for the case of Kenya. Both restricted models of maize production suggest that prior to the introduction of reforms acreage, prices and alternative crops were more elastic when simulated with Zambian data than with Kenyan data.food security, agricultural reforms, elasticity of supply, International Relations/Trade,

An Enhanced Features Extractor for a Portfolio of Constraint Solvers

Recent research has shown that a single arbitrarily efficient solver can be significantly outperformed by a portfolio of possibly slower on-average solvers. The solver selection is usually done by means of (un)supervised learning techniques which exploit features extracted from the problem specification. In this paper we present an useful and flexible framework that is able to extract an extensive set of features from a Constraint (Satisfaction/Optimization) Problem defined in possibly different modeling languages: MiniZinc, FlatZinc or XCSP. We also report some empirical results showing that the performances that can be obtained using these features are effective and competitive with state of the art CSP portfolio techniques

The Indispensability of Ghost Fields in the Light-Cone Gauge Quantization of Gauge Fields

We continue McCartor and Robertson's recent demonstration of the indispensability of ghost fields in the light-cone gauge quantization of gauge fields. It is shown that the ghost fields are indispensable in deriving well-defined antiderivatives and in regularizing the most singular component of gauge field propagator. To this end it is sufficient to confine ourselves to noninteracting abelian fields. Furthermore to circumvent dealing with constrained systems, we construct the temporal gauge canonical formulation of the free electromagnetic field in auxiliary coordinates $x^{\mu}=(x^-,x^+,x^1,x^2)$ where $x^-=x^0 cos{\theta}-x^3 sin{\theta}, x^+=x^0 sin{\theta}+x^3 cos{\theta}$ and $x^-$ plays the role of time. In so doing we can quantize the fields canonically without any constraints, unambiguously introduce "static ghost fields" as residual gauge degrees of freedom and construct the light-cone gauge solution in the light-cone representation by simply taking the light-cone limit (${\theta}\to \pi/4$). As a by product we find that, with a suitable choice of vacuum the Mandelstam-Leibbrandt form of the propagator can be derived in the ${\theta}=0$ case (the temporal gauge formulation in the equal-time representation).Comment: 21 pages, uses ptptex.st

Vacuum Polarization Effects in the Lorentz and PCT Violating Electrodynamics

In this work we report new results concerning the question of dynamical mass generation in the Lorentz and PCT violating quantum electrodynamics. A one loop calculation for the vacuum polarization tensor is presented. The electron propagator, "dressed" by a Lorentz breaking extra term in the fermion Lagrangian density, is approximated by its first order: this scheme is shown to break gauge invariance. Then we rather consider a full calculation to second order in the Lorentz breaking parameter: we recover gauge invariance and use the Schwinger-Dyson equation to discuss the full photon propagator. This allows a discussion on a possible photon mass shift as well as measurable, observable physical consequences, such as the Lamb-shift.Comment: Latex file, 19 pages, no figures, includes PACS number

Characterization of a modified poly(propylene imine) dendrimer host system

The research in this dissertation focuses on the design of a novel redox-responsive host system that has the ability to encapsulate guest molecules. The host at hand is a tri(ethylene oxide), TEO, pyrrole-terminated PPI dendrimer that possesses water-solubility as a result of the presence of the TEO chains on the pyrrole groups and redox-responsive activity from the pyrrole groups after their oligomerization. The pyrrole moieties at the periphery of the dendrimer exhibit the ability to be oligomerized by oxidation chemistry, and this is shown to aid in the retention and egress of guest molecules located within the dendrimer interior. These studies were followed by Visible spectroscopy, in which various solvents and oxidizing agents were employed for the oligomerization of the pyrrole end groups. The synthesis of this dendrimer system employed many reaction types, including but not limited to, bromination, SN2, deprotection and protection, and coupling reactions. Three substitution of the pyrrole moiety with the TEO chain was necessary to allow the 2- and 5-positions to remain available for oligomerization. Three new three-substituted pyrrole molecules were synthesized in this work, along with 4 new pyrrole-modified PPI dendrimers, referred to as TPDx. Characterization of these TPD host systems consisted of light scattering studies of their aqueous and non-aqueous solutions, encapsulation/release of a hydrophobic guest by TPDx monitored with Vis and fluorescence spectroscopies, and TPDx oligomerization followed with UV-Vis-NIR and FT-IR spectroscopies. The light scattering studies revealed aggregation of the host molecules, which was dependent on many variables, including solvent system, TPDx concentration, and temperature. The ability of the pyrrole moieties on the dendrimer to remain redox-active was clearly demonstrated. The TPDx were treated with different oxidizing agents in various solvent systems, and as a result they were able to form intramolecular oligo(pyrrole) units around the periphery of the dendrimer. The TPDs also have the ability to trap guest molecules, namely Nile Red, in aqueous media within their interior regions through static and dynamic trapping mechanisms. The trapping of guests within the TPDs was determined to be time dependent and largely a function of the steric constraints at the periphery of the TPDs

Co-polymers of Furan with Pyrrole or Thiophene: A Synthetic Study

The use of conductive polymers as a substitute for metallic conductors and semiconductors has attracted much attention in the literature. In particular, aromatic heterocyclic polymers constitute an important class since they possess chemical and electrical stability in both the oxidized (doped) and neutral (undoped) state. Doping a polymer allows one to vary its electrical, mechanical, optical, and thermal properties. The properties of these polymers are promising for their many technological uses such as antistatic coatings, solar cells, and electronic devises. Polyfuran is among the least common heterocyclic polymers. Polyfuran has been reported to be much less stable that either polypyrrole or polythiophene. The preparation of co-polymers of polyfuran with two percent pyrrole or thiophene is reported. The polymers are characterized by *HNMR, IR, and ESR spectroscopy, and the electrical conductivity of the doped and un-doped synthetic polyfuran and co-polymers is provided

Vegetational Change and Land Degradation in the Lake Baringo Area, Kenya, During the Late Holocene: Evidence from the Paleorecord and Remote Sensing

This dissertation investigates the history of vegetational changes and land degradation in the Lake Baringo area, Kenya, East Africa, during the Late Holocene. It uses 14C -and 210Pb-dated fossil pollen, fungal spores, microscopic charcoal, and stratigraphic record from lake-sediment cores to reconstruct the paleoenvironment in the East African region. More recent changes in the Lake Baringo are examined using remote sensing imagery. These data provide one the first high-resolution late Holocene pollen records from the semi-arid region of Kenya (and one of only a handful from East Africa in general). Lake Baringo records a sedimentation rate of 1 cm yr-1, which remained largely unchanged for both the prehistoric period, prior to European settlement in the Baringo ecosystem (AD 1890s), and after, including the present. That raised the possibility that background environmental conditions and not humans are the main drivers of land degradation in the ecosystem. A record from a 363-centimeter core retrieved from Lake Baringo reveals a largely dry environment that is punctuated by a succession of centennial- to decadal-scale wet and dry episodes, separated by rather sharp transitions, including two intense dry episodes at ca. AD 1650 and AD 1750 that led to drying of the lake. The two episodes are reflected by poor pollen preservation environment and by relatively high percentages of dry-indicator species such as Podocarpus, Olea, Euclea, Acacia, Balanitaceae, Gramineae, and Cyperaceae. However, climatic implications of the changes in pollen spectra in the Lake Baringo record are limited by the extremely high sedimentation rate in Lake Baringo that effectively constrains the chronological record of the cores to the last 300 14C yr BP. Satellite imagery analyzed in this dissertation reveals that deforestation and the resultant land degradation have contributed to increased sediment yield in the lake. Consequently, the lake surface area was reduced by over 10% and turbidity increased, which is confirmed by a statistically significant increase (t = -84.699, p \u3c0.001) in the albedo between 1986 and 2000. Although climatic variations account for some of the changes in the lake catchment most of the changes in land cover are inherently linked to mounting human and livestock population in the Lake Baringo catchment