Cosmological Evolution of a Purely Conical Codimension-2 Brane World

We study the cosmological evolution of isotropic matter on an infinitely thin conical codimension-two brane-world. Our analysis is based on the boundary dynamics of a six-dimensional model in the presence of an induced gravity term on the brane and a Gauss-Bonnet term in the bulk. With the assumption that the bulk contains only a cosmological constant Lambda_B, we find that the isotropic evolution of the brane-universe imposes a tuned relation between the energy density and the brane equation of state. The evolution of the system has fixed points (attractors), which correspond to a final state of radiation for Lambda_B=0 and to de Sitter state for Lambda_B>0. Furthermore, considering anisotropic matter on the brane, the tuning of the parameters is lifted, and new regions of the parametric space are available for the cosmological evolution of the brane-universe. The analysis of the dynamics of the system shows that, the isotropic fixed points remain attractors of the system, and for values of Lambda_B which give acceptable cosmological evolution of the equation of state, the line of isotropic tuning is a very weak attractor. The initial conditions, in this case, need to be fine tuned to have an evolution with acceptably small anisotropy.Comment: 20 pages, 4 figures, typo correcte

Operator normalized quantum arrival times in the presence of interactions

We model ideal arrival-time measurements for free quantum particles and for particles subject to an external interaction by means of a narrow and weak absorbing potential. This approach is related to the operational approach of measuring the first photon emitted from a two-level atom illuminated by a laser. By operator-normalizing the resulting time-of-arrival distribution, a distribution is obtained which for freely moving particles not only recovers the axiomatically derived distribution of Kijowski for states with purely positive momenta but is also applicable to general momentum components. For particles interacting with a square barrier the mean arrival time and corresponding ``tunneling time'' obtained at the transmission side of the barrier becomes independent of the barrier width (Hartman effect) for arbitrarily wide barriers, i.e., without the transition to the ultra-opaque, classical-like regime dominated by wave packet components above the barrier.Comment: 10 pages, 5 figures, RevTe

Reference point hyperplane trees

Our context of interest is tree-structured exact search in metric spaces. We make the simple observation that, the deeper a data item is within the tree, the higher the probability of that item being excluded from a search. Assuming a fixed and independent probability p of any subtree being excluded at query time, the probability of an individual data item being accessed is (1−p)d for a node at depth d. In a balanced binary tree half of the data will be at the maximum depth of the tree so this effect should be significant and observable. We test this hypothesis with two experiments on partition trees. First, we force a balance by adjusting the partition/exclusion criteria, and compare this with unbalanced trees where the mean data depth is greater. Second, we compare a generic hyperplane tree with a monotone hyperplane tree, where also the mean depth is greater. In both cases the tree with the greater mean data depth performs better in high-dimensional spaces. We then experiment with increasing the mean depth of nodes by using a small, fixed set of reference points to make exclusion decisions over the whole tree, so that almost all of the data resides at the maximum depth. Again this can be seen to reduce the overall cost of indexing. Furthermore, we observe that having already calculated reference point distances for all data, a final filtering can be applied if the distance table is retained. This reduces further the number of distance calculations required, whilst retaining scalability. The final structure can in fact be viewed as a hybrid between a generic hyperplane tree and a LAESA search structure

New prospects for Ethyl formate as a fumigant for the date industry

Date infestation of nitidulid beetles poses a serious contamination problem for which methyl bromide (MB) provided a solution. However, because of the phase out of MB, alternatives were investigated. Thermal disinfestation method has been successfully applied to some dry date varieties except to Deglet-Noor, Zahidi, and Ameri which are handled in crates of 200 kg to 400 kg. Therefore, thermal disinfestation was not successful because of delayed heating due to the resistance of the dates to hot airflow. The fumigant formulation VapormateTM was tested as alternative to MB for the disinfestation (proportion of insects found outside the feeding sites) and control of nitidulid beetles from artificial feeding sites at laboratory and for  dates in crates at semi-commercial conditions. VapormateTM contains 16.7% ethyl formate mixed with carbon dioxide. At laboratory conditions the effect of various dosages of VapormateTM was tested at 30oC and at fixed exposure time of 12 h. Exposure of infested artificial feeding sies by larvae of Carpophilus spp. to the concentration of 280 g m-3 of VapormateTM caused 69.3% disinfestation and 79.9% mortality, 350 g m-3 resulted in 72.7% disinfestation and 98.8% of mortality and the optimal results were obtained at 420 g m-3 that caused 69.6% disinfestations and 100% mortality. Commercial pilot-plant tests were carried out by applying 420 g m-3 VapormateTM for 12 h in a 9 m3 flexible liner made of laminate composed of polypropylene/aluminum/polyethylene to cover crates containing infested dates. Disinfestation was tested on naturally infested dates that resulted in an average 100% disinfestation and 95% mortality, while with the artificially infested dates, disinfestation was 97% and mortality 96%. In a second series of tests, a commercial rigid fumigation chamber of 95.6 m3 was used. After 12 h exposure, 100% mortality was recorded in all date samples. Following the promising results, VapormateTM was registered in Israel for use by the date industry as an alternative to MB. Keywords: Date, Nitidulid beetles, Ethyl formate, VapormateTM, Fumigation

Canonical Equivalence of a Generic 2D Dilaton Gravity Model and a Bosonic String Theory

We show that a canonical tranformation converts, up to a boundary term, a generic 2d dilaton gravity model into a bosonic string theory with a Minkowskian target space.Comment: LaTeX file, 9 pages, no figure

Dictionary Matching with One Gap

The dictionary matching with gaps problem is to preprocess a dictionary $D$ of $d$ gapped patterns $P_1,\ldots,P_d$ over alphabet $\Sigma$, where each gapped pattern $P_i$ is a sequence of subpatterns separated by bounded sequences of don't cares. Then, given a query text $T$ of length $n$ over alphabet $\Sigma$, the goal is to output all locations in $T$ in which a pattern $P_i\in D$, $1\leq i\leq d$, ends. There is a renewed current interest in the gapped matching problem stemming from cyber security. In this paper we solve the problem where all patterns in the dictionary have one gap with at least $\alpha$ and at most $\beta$ don't cares, where $\alpha$ and $\beta$ are given parameters. Specifically, we show that the dictionary matching with a single gap problem can be solved in either $O(d\log d + |D|)$ time and $O(d\log^{\varepsilon} d + |D|)$ space, and query time $O(n(\beta -\alpha )\log\log d \log ^2 \min \{ d, \log |D| \} + occ)$, where $occ$ is the number of patterns found, or preprocessing time and space: $O(d^2 + |D|)$, and query time $O(n(\beta -\alpha ) + occ)$, where $occ$ is the number of patterns found. As far as we know, this is the best solution for this setting of the problem, where many overlaps may exist in the dictionary.Comment: A preliminary version was published at CPM 201

Continuum coupled cluster expansion

We review the basics of the coupled-cluster expansion formalism for numerical solutions of the many-body problem, and we outline the principles of an approach directed towards an adequate inclusion of continuum effects in the associated single-energy spectrum. We illustrate our findings by considering the simple case of a single-particle quantum mechanics problem.Comment: 16 pages, 1 figur

Lightweight Lempel-Ziv Parsing

We introduce a new approach to LZ77 factorization that uses O(n/d) words of working space and O(dn) time for any d >= 1 (for polylogarithmic alphabet sizes). We also describe carefully engineered implementations of alternative approaches to lightweight LZ77 factorization. Extensive experiments show that the new algorithm is superior in most cases, particularly at the lowest memory levels and for highly repetitive data. As a part of the algorithm, we describe new methods for computing matching statistics which may be of independent interest.Comment: 12 page

Amazônia: diferentes contextos, diferentes interpretações (síntese das entrevistas).

Como parte do estudo "Embrapa na Amazônia", foram realizadas diversas entrevistas com estudiosos de diferentes vínculos institucionais e experiências profissionais. Este documento tem o objetivo de sintetizar os excertos mais salientes das entrevistas, indicativos de temas relevantes e argumentos merecedores de maior atenção. Este relatório apresenta três partes principais. Na primeira delas, são sequenciados temas entendidos como majoritariamente convergentes, ou mais falados, indicando uma presumida concordância entre a maioria dos entrevistados, ainda que diversas nuances específicas possam ocorrer. Na segunda seção, são arroladas diversas manifestações selecionadas que parecem sugerir temas e focos de maior divergência, o principal deles, como seria esperado, a oposição entre "produção e ambiente". Para diversos analistas, esta é ainda uma polaridade, uma antinomia insuperável e um consenso que permita harmonizá-las ainda precisará percorrer caminho mais longo. Finalmente, este texto oferece uma terceira seção, final e mais sucinta, onde são arrolados alguns temas que parecem ser mais "neutros", se afastando de posicionamentos tão explícitos e apenas listando sugestões ou opiniões antes não apresentadas, nas duas seções anteriores.bitstream/item/48147/1/Entrevistas-DA4-V.ISSN.pd

Free Fields for Chiral 2D Dilaton Gravity

We give an explicit canonical transformation which transforms a generic chiral 2D dilaton gravity model into a free field theory.Comment: LaTeX file, 4 pages, to appear in Phys. Rev.