127 research outputs found
Constraints on leptogenesis from a symmetry viewpoint
It is shown that type I seesaw models based on the standard model Lagrangian
extended with three heavy Majorana right-handed fields do not have leptogenesis
in leading order, if the symmetries of mass matrices are also the residual
symmetry of the Lagrangian. In particular, flavor models that lead to a
mass-independent leptonic mixing have a vanishing leptogenesis CP asymmetry.
Based on symmetry arguments, we prove that in these models the Dirac-neutrino
Yukawa coupling combinations relevant for leptogenesis are diagonal in the
physical basis where the charged leptons and heavy Majorana neutrinos are
diagonal.Comment: 5 pages; a few comments added; final version to appear in Phys. Rev.
Computing the zeros of quaternion polynomials
A method is developed to compute the zeros of a quaternion polynomial with all terms of the form qkXk. This method is based essentially in Niven's algorithm [1], which consists of dividing the polynomial by a characteristic polynomial associated to a zero. The information about the trace and the norm of the zero is obtained by an original idea which requires the companion matrix associated to the polynomial. The companion matrix is represented by a matrix with complex entries. Three numerical examples using Mathematica 2.2 version are given.http://www.sciencedirect.com/science/article/B6TYJ-444G6J6-N/1/2ab1f648c1929ffc5374c2a8b11c2a7
Modulating intermolecular interactions and rheological properties in silk fibroin using ultrasound frequencies
info:eu-repo/semantics/draf
Differential equations over octonions
Differential equations with constant and variable coefficients over octonions
are investigated. It is found that different types of differential equations
over octonions can be resolved. For this purpose non-commutative line
integration is used. Such technique is applied to linear and non-linear partial
differential equations in real variables. Possible areas of applications of
these results are outlined.Comment: 50 page
Intrahepatic Colangiocarcinoma
Introdução: o colangiocarcinoma intra-hepático (CCIhp) é um tumor maligno raro, normalmente diagnosticado num estadio avançado.
São objectivos deste estudo avaliar os resultados da terapêutica do CCIhp e os factores prognósticos com significado estatístico na sobrevida de doentes com esta entidade nosológica tratados no nosso Serviço. Material e métodos: Vinte e um doentes submetidos
a tratamento por CCIhp nos últimos anos, dos quais onze foram operados com intuitos curativos: quatro hepatectomias esquerdas, duas hepatectomias esquerdas alargadas aos segmentos V e VIII, duas hepatectomias direitas, duas bissegmentectomias e uma trissegmentectomia.
Resultados: a mortalidade per-operatória foi de 0% e a pós-operatória (três meses) de 6%. As sobrevidas cumulativas aos 5 anos foram de 14% no total da população, 26% nos doentes submetidos a cirurgia com intuitos curativos e 26% para a sobrevida cumulativa livre de doença. Observou-se recidiva tumoral hepática em cinco doentes, a qual ocorreu aos 1,09 ± 0,82 anos (limites:
0,24-2,08). Os factores que influenciaram a sobrevida da globalidade dos doentes foram o tratamento cirúrgico com intuitos curativos (p=0,028), a presença de invasão vascular (p=0,002) e o valor da fosfatase alcalina no momento do diagnóstico (p=0,044). Entre os doentes operados com intuitos curativos, a presença de invasão vascular influenciou a sobrevida global (p=0,025) e a sobrevida livre
de doença (p=0,002). Conclusões: A ressecção cirúrgica com intuitos curativos aumentou, de forma estatisticamente significativa, a sobrevida dos doentes com CCIhp. No entanto, sendo o diagnóstico geralmente tardio, apenas uma pequena percentagem destes doentes pode beneficiar deste tratamento.info:eu-repo/semantics/publishedVersio
Resonant leptogenesis and tribimaximal leptonic mixing with A4 symmetry
We investigate the viability of thermal leptogenesis in type-I seesaw models
with leptonic flavour symmetries that lead to tribimaximal neutrino mixing. We
consider an effective theory with an A4 x Z3 x Z4 symmetry, which is
spontaneously broken at a scale much higher than the electroweak scale. At the
high scale, leptonic Yukawa interactions lead to exact tribimaximal mixing and
the heavy Majorana neutrino mass spectrum is exactly degenerate. In this
framework, leptogenesis becomes viable once this degeneracy is lifted either by
renormalization group effects or by a soft breaking of the A4 symmetry. The
implications for low-energy neutrino physics are discussed.Comment: 14 pages, 15 figures; final version to appear in Phys. Rev.
Quaternionic eigenvalue problem
We discuss the (right) eigenvalue equation for , and
linear quaternionic operators. The possibility to introduce an
isomorphism between these operators and real/complex matrices allows to
translate the quaternionic problem into an {\em equivalent} real or complex
counterpart. Interesting applications are found in solving differential
equations within quaternionic formulations of quantum mechanics.Comment: 13 pages, AMS-Te
Efeitos implícitos da pertença e identificação grupais na discriminação social
Utilizando uma metodologia não-obstrusiva, testámos
a hipótese de que a associação entre estímulos visuais
não salientes e a pertença grupal dos indivíduos
pode interferir na escolha de uma equipa de trabalho
sem que estes se apercebam dessa influência. As participantes
(66 estudantes dos cursos de Psicologia e de
Serviço Social) foram acolhidas por uma Psicóloga vs.
Trabalhadora Social após o que deveriam escolher entre
duas equipas, fisicamente semelhante vs. diferente
da pessoa que as recebeu, para a continuação do mesmo
estudo. Os resultados mostraram que as participantes
que foram acolhidas pelo membro do exogrupo escolheram
mais a equipa diferente do que as participantes
acolhidas pelo membro do endogrupo sendo este
efeito mediado pela identificação ao endogrupo. Os resultados
são discutidos à luz de investigação anterior
utilizando medidas implícitas de discriminação social.ABSTRACT: Using a non-obstrusive measure, we tested the hypothesis
that the association between non-salient visual
stimuli and group membership can affect the
choice of a working team beyond participants’ awareness
of that influence. Participants (66 Psychology and
Social Service students) were received by a Psychologist
vs. Social Worker. They then had to choose between
two teams, physically similar to vs. different
from the person who had just received them, to work
with in the second phase. Results show that most participants
who had been received by an out-group
member chose the different team more than did participants
who had been received by an in-group member.
This effect was mediated by in-group identification.
Results are discussed based on previous research
using implicit measures of social discrimination.info:eu-repo/semantics/publishedVersio
Mathematica tools for quaternionic polynomials
In this paper we revisit the ring of (left) one-sided quaternionic polynomials with special focus on its zero structure. This area of research has attracted the attention of several authors and therefore it is natural to develop computational tools for working in this setting. The main contribution of this paper is a Mathematica collection of functions QPolynomial for solving polynomial problems that we frequently find in applications.(undefined)info:eu-repo/semantics/publishedVersio
Seasonal changes in the biochemical fate of carbon fixed by benthic diatoms in intertidal sediments
Benthic diatoms are important primary producers in intertidal marine sediments and form the basis of the food web in these ecosystems. In order to investigate the carbon flow within diatom mats, we performed in situ 13C pulse-chase labeling experiments and followed in detail the biochemical fate of carbon fixed by the diatoms for five consecutive days. These labeling experiments were done at approximately 2-monthly intervals during 1 yr in order to cover seasonal variations. The fixed carbon was recovered in individual carbohydrates including extracellular polymeric substances (EPS), amino acids, fatty acids, and nucleic acid bases. In addition, we assessed a variety of environmental parameters and photosynthetic characteristics. The fixed carbon was initially mainly stored as carbohydrate (glucose) while nitrogen-rich compounds (e.g., amino acids and RNA/DNA) were produced more slowly. During the year, the diatoms distributed the photosynthetically fixed carbon differently among the various carbon pools that were measured. In summer, the diatoms decreased carbon fixation and accumulated relatively more lipid as a storage compound (27% 6 2% vs. 12% 6 5% in other seasons). The percentage of fixed carbon that was excreted as EPS was lower in summer compared to other seasons, amounting 9% 6 4% and 21% 6 6%, respectively. Hence, it seemed that the physiology of the microphytobenthos was different during summer and caused by higher light intensity and a shift in nitrogen source
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