339 research outputs found
Computing the endomorphism ring of an elliptic curve over a number field
We describe deterministic and probabilistic algorithms to determine whether
or not a given monic irreducible polynomial H in Z[X] is a Hilbert class
polynomial, and if so, which one. These algorithms can be used to determine
whether a given algebraic integer is the j-invariant of an elliptic curve with
complex multiplication (CM), and if so, the associated CM discriminant. More
generally, given an elliptic curve E over a number field, one can use them to
compute the endomorphism ring of E. Our algorithms admit simple implementations
that are asymptotically and practically faster than existing approaches.Comment: updated and extended Table 1; 20 page
Selmer Groups in Twist Families of Elliptic Curves
The aim of this article is to give some numerical data related to the order
of the Selmer groups in twist families of elliptic curves. To do this we assume
the Birch and Swinnerton-Dyer conjecture is true and we use a celebrated
theorem of Waldspurger to get a fast algorithm to compute . Having
an extensive amount of data we compare the distribution of the order of the
Selmer groups by functions of type with small. We discuss how the
"best choice" of is depending on the conductor of the chosen elliptic
curves and the congruence classes of twist factors.Comment: to appear in Quaestiones Mathematicae. 16 page
Probabilistic and predictive performance-based approach for assessing reinforced concrete structures lifetime: The applet project
International audienceConcrete deterioration results in different damage extents, from cracking to concrete spalling, from losses of reinforcement cross-sections to bond losses. A relevant prediction of this performance is the basis for a successful management of the concrete structures. Conversely, the large amount of uncertainties related to parameters and models require a specific analysis in order to provide relevant results. The APPLET project intends to develop a probabilistic and predictive performance-based approach by quantifying the various sources of variability (material and structure), studying the interaction between environmental aggressive agents and the concrete material, ensuring a transfer of the physical-chemical models at the material scale towards models at the structure level, including and understanding in a better manner the corrosion process, integrating interface models between reinforcement and concrete, proposing relevant numerical models, integrating know-how from monitoring or inspection. To provide answers, a consortium of 19 partners has been established and has promoted a research project funded by the French Research Science Agency (ANR). Started in May 2007, the project has ended in November 2010. This paper will resume the most significant advances targeted by this research project
K-Rational D-Brane Crystals
In this paper the problem of constructing spacetime from string theory is
addressed in the context of D-brane physics. It is suggested that the knowledge
of discrete configurations of D-branes is sufficient to reconstruct the motivic
building blocks of certain Calabi-Yau varieties. The collections of D-branes
involved have algebraic base points, leading to the notion of K-arithmetic
D-crystals for algebraic number fields K. This idea can be tested for D0-branes
in the framework of toroidal compactifications via the conjectures of Birch and
Swinnerton-Dyer. For the special class of D0-crystals of Heegner type these
conjectures can be interpreted as formulae that relate the canonical Neron-Tate
height of the base points of the D-crystals to special values of the motivic
L-function at the central point. In simple cases the knowledge of the
D-crystals of Heegner type suffices to uniquely determine the geometry.Comment: 36 page
Milied it-tajjeb
Ä abra taâ poeĆŒiji u proĆŒa li tinkludi: Imħabba taħt siÄĄra taâ V. Caruana â L-isptar tal-GwardamanÄĄa taâ P. Mattew â Lourdes â il-Belt tal-Madonna taâ Ä uĆŒĂš Chetcuti â Ja iblah, ma temminx? taâ John C. Friggieri â ÄŠolma taâ A. Cremona â Il-Milied it-tajjeb taâ Ä uĆŒĂš Borg Pantalleresco.peer-reviewe
The variability of birth weight
The material for this study was obtained from the maternity records relating to single births occurring in Malta throughout 1965. In this year there were 5,719 total births; of these the sample studied covers 2,517 births (44.11 percent). The records were personally examined by one of the authors (Cremona, 1967) from St. Luke's Hospital Malta, from Maltese private Hospitals, and from the District Nursing Association. In Malta the mean birth weight for male babies is 3446g, and for female babies 3358g. The mean birth weight tends to increase with the mother's parity, and this trend continues even with the higher parities. The association between birth weight and rising maternal age remains uncertain. It is also probable that birth weight has a geographical determinant. Birth weight is a multifactorial product and cannot be very reliable as a clinical parameter. A new terminology is necessary to distinguish between three different groups of babies with low birth weights.peer-reviewe
Deo Altissimo
Ä abra taâ poeĆŒiji u proĆŒa li tinkludi: Presepju taâ Tfuliti taâ Dun Karm â Lil Mikiel Anton Vassalli taâ A. Cremona â Lil Rosario Briffa taâ Giorgio Pisani â Rmied taâ Dun Karm â L-Ewwel Tqarbina â L-Ewwel Quddiesa taâ Dun Karm â Deo Altissimo taâ C. V.N/
Photoluminescence, photoabsorption and photoemission studies of hydrazone thin film used as hole transporting material in OLEDs
A fotoluminescĂȘncia de filmes finos de 1-(3-metilfenil)-1,2,3,4-tetrahidroquinolina-6-carboxialdeĂdo-1,1â-difenilhidrazona foi monitorada em função da irradiação com luz UV. A intensidade da emissĂŁo decresce exponencialmente com o tempo de exposição, sugerindo degradação das amostras. Com o objetivo de investigar os mecanismos de degradação e determinar a estrutura eletrĂŽnica desse material orgĂąnico usado com sucesso como camada transportadora de buracos na fabricação de diodos orgĂąnicos emissores de luz (OLEDs), foram empregadas as tĂ©cnicas de fotoabsorção e de fotoemissĂŁo nas bordas 1s do carbono e do nitrogĂȘnio bem como na banda de valĂȘncia. A influĂȘncia da luz solar foi simulada usando radiação sĂncrotron nĂŁo-monocromĂĄtica. ApĂłs exposição, todos os espectros apresentam um decrĂ©scimo nos sinais de fotoabsorção e de fotoemissĂŁo, que Ă© menos acentuado na borda do carbono, apresentando, entretanto, um decrĂ©scimo drĂĄstico na borda do nitrogĂȘnio e na regiĂŁo de valĂȘncia. O estudo sugere que a perda de nitrogĂȘnio Ă© a principal causa para a quebra do sistema Ï, levando, dessa forma, Ă falha do dispositivo fabricado com esse composto.Photoluminescence (PL) emission of 1-(3-methylphenyl)-1,2,3,4-tetrahydroquinoline-6-carboxyaldehyde-1,1â-diphenylhydrazone (MTCD) thin films was monitored as a function of UV irradiation, and it was found to decrease exponentially with the exposure time. In order to gain insight into the degradation mechanisms and evaluate the electronic structure of this organic material used with good results as hole transporting layer (HTL) in the fabrication of organic light emitting diodes (OLEDs), synchrotron radiation-based photoabsorption and photoemission techniques at the carbon and nitrogen 1s edges as well as at the valence band were employed. The influence of sunlight was simulated using non-monochromatized synchrotron radiation. After exposure all the spectra show a decrease of the photoabsorption and photoemission signals, however, while it is less accentuated at the carbon edge, at the nitrogen edge and at the valence region it decreases drastically. The loss of nitrogen is suggested to be the main step in the disruption of the Ï system, leading to the failure of the devices fabricated with this compound as hole transporting layer
Word reading strategies: A replication and follow up intervention
The first stage of this study involved a replication of the cluster analysts procedures used by Freebody and Byrne (1988) to classify Year 2 readers according to their word reading strategies based on lists of irregular and pseudowords. A four-cluster-solution produced three groups similar to those reported by Freebody and Byrne (1988), and a fourth group which could not be classified using their criteria. A three-cluster-solution produced a more parsimonious interpretation, with these groups meeting the criteria for LB (low on both Irregular and pseudowords), HB (high on both), and Phoenician readers (average or above on pseudoword, low on irregular words). There was no evidence of a discrete group of Chinese readers (low on pseudowords, average or above average on irregular words). These results were interpreted in the context of stage models of reading development. A replication was carried out of Freebody and Byrnes (1988) examination of differences in the phonemic awareness abilities of the subjects grouped on the basis of the four-cluster-solution. Subjects were tested using the initial-consonant-elision and the final-consonant-matching tasks. Three additional phonemic awareness tasks were also used: telescoping, segmenting and rhyming. Results showed unacceptable reliability of the telescoping, segmenting and final consonant-matching tasks, coupled with ceiling effects for telescoping and segmenting. Consequently, only the results from the combined initial-consonant-elision and final-consonant matching tasks, and the rhyming tasks were used. Consistent with the findings of Freebody and Byrne (1988), the LB group showed significantly lower phonemic awareness than the other groups combined, the HB group showed the reverse outcome. This finding is consistent with previous research that has shown a relationship between phonemic awareness and reading achievement. There was a significant difference for the remaining two groups, but only on the rhyming task in favour of the Phoenician readers, reflecting their ability to recognise sound patterns within words. The second stage of the study consisted of a single subject design investigation in which baseline data was collected for six (LB) subjects. As the requirement of stable and level baselines was not met for five of the six subjects, the decision was made to implement a changing criterion design with the other subject. He was given explicit Instruction In which he was taught to discriminate between the letters he previously confused, and the strategy of sounding out regular word types without stopping between sounds. His daily data showed that by the end of the Intervention phase, consisting of 16 half-hour teaching sessions, he had reached criteria in reading mixed regular word types. In addition, his post-test score on the pseudoword list indicated that he would now qualify as a Phoenician reader. Further research is required to investigate the extent to which changes In word reading strategy can be brought about by Instruction
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