6,174 research outputs found
Ultra-Light Scalar Fields and the Growth of Structure in the Universe
Ultra-light scalar fields, with masses of between m=10^{-33} eV and
m=10^{-22} eV, can affect the growth of structure in the Universe. We identify
the different regimes in the evolution of ultra-light scalar fields, how they
affect the expansion rate of the universe and how they affect the growth rate
of cosmological perturbations. We find a number of interesting effects, discuss
how they might arise in realistic scenarios of the early universe and comment
on how they might be observed.Comment: 12 pages, 11 figure
Domestic Impact of Internationalisation: The case of JM
The influence of internationalisation processes in the domestic activities of firms’ has not been considered as an important issue in existing models, because they tend to focus on a partial and restricted view of the firm. The purpose of this paper is to challenge that view by attempting a dynamic view of the firm is which primal importance is given to the relationship between international and domestic activities. The main research question is whether domestic activities can be significantly affected by international activities, namely knowledge transfer. Results confirm the dynamic approach adopted by firms however there are no definitive answers in terms of the domestic impact of internationalisation. Despite clear hints of evidence for the internationaldomestic relationship, there was no confirmation of this relationship at the financial level.
Exploring the consistency of the SF-6D
Objective: The six dimensional health state short form (SF-6D) was designed to be derived from the short-form 36 health survey (SF-36). The purpose of this research was to compare the SF-6D index values generated from the SF 36 (SF-6D(SF-36)) with those obtained from the SF-6D administered as an independent instrument (SF-6D(Ind)). The goal was to assess the consistency of respondents answers to these two methods of deriving the SF-6D. Methods: Data were obtained from a sample of the Portuguese population (n = 414). Agreement between the instruments was assessed on the basis of a descriptive system and their indexes. The analysis of the descriptive system was performed by using a global consistency index and an identically classified index. Agreement was also explored by using correlation coefficients. Parametric tests were used to identify differences between the indexes. Regression models were estimated to understand the relationship between them. Results: The SF-6D(Ind) generates higher values than does the SF-6D(SF-36), There were significant differences between the indexes across sociodemographic groups. There was a significant ceiling effect in the SF-6D(Ind) a but not in the SF-6D(SF-36). The correlation between the indexes was high but less than what was anticipated. The global consistency index identified the dimensions with larger differences. Considerable differences were found in two dimensions, possibly as a result of different item contexts. Further research is needed to fully understand the role of the different layouts and the length of the questionnaires in the respondents' answers. Conclusions: The results show that as the SF-6D was designed to derive utilities from the SF-36 it should be used in this way and not as an independent instrument.Fundacao para a Ciencia e a Tecnologia (FCT
Quintessence in a quandary: prior dependence in dark energy models
The archetypal theory of dark energy is quintessence: a minimally coupled
scalar field with a canonical kinetic energy and potential. By studying random
potentials we show that quintessence imposes a restricted set of priors on the
equation of state of dark energy. Focusing on the commonly-used
parametrisation, , we show that there is a natural
scale and direction in the plane that distinguishes quintessence
as a general framework. We calculate the expected information gain for a given
survey and show that, because of the non-trivial prior information, it is a
function of more than just the figure of merit. This allows us to make a
quantitative case for novel survey strategies. We show that the scale of the
prior sets target observational requirements for gaining significant
information. This corresponds to a figure of merit FOM, a
requirement that future galaxy redshift surveys will meet.Comment: 5 pages, 3 figures. For the busy reader, Fig. 1 is the money plot.
v2: Minor changes, matches published version. Code open source at
gitorious.org/random-quintessenc
Tensor Detection Severely Constrains Axion Dark Matter
The recent detection of B-modes by BICEP2 has non-trivial implications for
axion dark matter implied by combining the tensor interpretation with
isocurvature constraints from Planck. In this paper the measurement is taken as
fact, and its implications considered, though further experimental verification
is required. In the simplest inflation models implies . If the axion decay constant constraints on
the dark matter (DM) abundance alone rule out the QCD axion as DM for (where accounts for theoretical
uncertainty). If then vacuum fluctuations of the axion field
place conflicting demands on axion DM: isocurvature constraints require a DM
abundance which is too small to be reached when the back reaction of
fluctuations is included. High QCD axions are thus ruled out. Constraints
on axion-like particles, as a function of their mass and DM fraction, are also
considered. For heavy axions with we find
, with stronger constraints on heavier
axions. Lighter axions, however, are allowed and (inflationary)
model-independent constraints from the CMB temperature power spectrum and large
scale structure are stronger than those implied by tensor modes.Comment: 6 pages, 1 figure. v2: Some discussion and references added. v3
Update on QCD discussion. Version accepted for publication in Physical Review
Letter
A medição de preferências em saúde na população portuguesa
Introdução: um tema estudado pelos investigadores da
economia da saúde é a medição da qualidade de vida relacionada
com a saúde, em especial captando as preferências
dos indivíduos em relação a determinados resultados em
saúde. Este tipo de medição permite a sua incorporação em
modelos de decisão clínica, de planeamento e de políticas de
saúde. Nos últimos anos, têm sido desenvolvidos instrumentos
genéricos de avaliação dos estados de saúde baseados na
teoria multi-atributo de utilidade, fáceis de aplicar e que
permitem o cálculo dos valores de utilidade que os indivíduos
atribuem aos estados de saúde, como os questionários
EuroQol (EQ-5D), Health Utilities Index (HUI) e o SF-6D.
Métodos: com base numa amostra aleatória da população
activa portuguesa residente no continente e formada por
2459 indivíduos, obteve-se a preferência dos portugueses
em relação ao seu estado de saúde e qualidade de vida e
calcularam-se os respectivos valores normais para Portugal
continental. Foi utilizada a versão portuguesa do instrumento
de medição SF-6D e o algoritmo econométrico
desenvolvido por Brazier, para a geração de valores de
utilidade, para os diversos estados de saúde.
Resultados: o valor médio da utilidade obtido pelo SF-6D
para toda a população foi 0,697, variando de 0,30 a 1,00 e
associado a um desvio padrão de 0,143. Níveis mais elevados
de défice foram encontrados nas dimensões «desempenho
», «dor», «saúde mental» e «vitalidade». Valores mais
baixos de utilidade foram apresentados pelas mulheres e
pelos idosos. Os indivíduos com níveis mais baixos de instrução,
a viver em áreas rurais, trabalhadores manuais e os
viúvos, divorciados e separados apresentaram, em geral,
também valores mais baixos de utilidade. Em relação às
doenças crónicas, a utilidade média variou de 0,56 para os
enfartes do miocárdio a 0,66 correspondente à hepatite.
Conclusão: deste estudo conclui-se que o instrumento de
medição SF-6D é útil e efectivo na medição da qualidade de
vida relacionada com a saúde na comunidade. As normas
portuguesas são úteis para contextualizar os valores obtidos
pelo SF-6D, sempre que aplicado a doentes ou mesmo
a indivíduos portugueses saudáveis
Dissemination of contextual information for assisted driving
Mestrado em Engenharia Electrónica e TelecomunicaçõesDriver assistance systems can be used to improve road and car safety, reduce
driving fatigue and provide a more e cient driving experience. An
important part of these systems is the communication between vehicles,
and vehicle-to-infrastructure communication. This work presents mechanisms
enabling driving support, exploring the vehicular network to provide
information about the drivers neighborhood.
The network is composed by vehicles, tra c signals and xed stations along
the road. Each car is equipped with a recording camera, a GPS receiver, as
well as communication modules such as WiFi, WAVE and 3G/4G, allowing
the exchange of data between the various nodes. The data exchanged is
composed by positional data of neighboring vehicles, sensor information
from tra c signals and video images incoming from other vehicles. This
data is used to facilitate the driver in decision making, but can also provide
an overview of the tra c density in the neighborhood. The tra c signals
broadcast their position and if they are dynamic (such as tra c lights), their
status is also transmitted. The xed stations are equipped with numerous
sensors and are used to provide environmental data.
The driver can access all the collected data via visual information, on a
display screen that contains a map of the neighborhood along with the
information available of the nearby nodes.
The proposed system is evaluated through real vehicular experiments in two
distinct scenarios: urban and highway. The results show that the communication
delay is higher in the highway scenario, mainly due to the distance
between vehicles and travelling speeds. However, promising results regarding
the maximum delay and the average number of retransmissions foresee
important inputs for future services of assisted-driving, in general, and carovertaking
assistance, in particular.Os sistemas de condução assistida podem ser utilizados para melhorar a
segurança rodoviária e automóvel, reduzir a fadiga da condução e proporcionar
uma experiência de condução mais e ciente. Uma parte importante
desses sistemas e a comunicação entre veículos e comunicação veiculo infraestrutura.
Este trabalho propõe mecanismos que permitem o suporte
a condução, explorando a rede de veicular para fornecer informações sobre
a vizinhança do condutor.
A rede e composta por veículos, sinais de transito e estações fixas ao longo
da estrada. Cada carro esta equipado com uma camera de gravação, um
receptor GPS, bem como módulos de comunicação, como WiFi, WAVE e
3G/4G, permitindo a troca de dados entre os vários nos. Os dados trocados
são compostos por dados posicionais de veículos vizinhos, informações
sensoriais de sinais de trânsito e imagens de vídeo provenientes de outros
veículos. Esses dados s~ao usados para facilitar a tomada de decisões, mas
também podem fornecer uma vis~ao geral da densidade de tráfego na vizinhança. Os sinais de transito transmitem a sua posição e, no caso de serem dinâmicos (como semáforos), o seu estado actual também e transmitido.
As estações fixas estão equipadas com vários sensores e sao usadas para
fornecer dados ambientais.
O condutor pode aceder a todos os dados recolhidos através de informações
visuais, num ecrã que contém um mapa da sua redondeza junto com a
informação disponível dos nos vizinhos.
O sistema proposto e avaliado através de testes reais em dois cenários
distintos: urbano e auto-estrada. Os resultados mostram que o atraso da
comunicação e maior no cenário da auto-estrada, principalmente devido as
maiores distancias entre os veículos e as velocidades mais elevadas. No
entanto, resultados promissores em relação ao atraso máximo e ao numero
médio de retransmissões prevêem contribuições importantes para serviços
futuros de condução assistida em geral, e assistência de ultrapassagem de
veículos, em particular
A tensor instability in the Eddington inspired Born-Infeld Theory of Gravity
In this paper we consider an extension to Eddington's proposal for the
gravitational action. We study tensor perturbations of a homogeneous and
isotropic space-time in the Eddington regime, where modifications to Einstein
gravity are strong. We find that the tensor mode is linearly unstable deep in
the Eddington regime and discuss its cosmological implications.Comment: 5 pages, approved by Phys. Rev. D, additional references and minor
modification
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