33 research outputs found
Dark energy as a mirage
Motivated by the observed cosmic matter distribution, we present the
following conjecture: due to the formation of voids and opaque structures, the
average matter density on the path of the light from the well-observed objects
changes from Omega_M ~ 1 in the homogeneous early universe to Omega_M ~ 0 in
the clumpy late universe, so that the average expansion rate increases along
our line of sight from EdS expansion Ht ~ 2/3 at high redshifts to free
expansion Ht ~ 1 at low redshifts. To calculate the modified observable
distance-redshift relations, we introduce a generalized Dyer-Roeder method that
allows for two crucial physical properties of the universe: inhomogeneities in
the expansion rate and the growth of the nonlinear structures. By treating the
transition redshift to the void-dominated era as a free parameter, we find a
phenomenological fit to the observations from the CMB anisotropy, the position
of the baryon oscillation peak, the magnitude-redshift relations of type Ia
supernovae, the local Hubble flow and the nucleosynthesis, resulting in a
concordant model of the universe with 90% dark matter, 10% baryons, no dark
energy, 15 Gyr as the age of the universe and a natural value for the
transition redshift z_0=0.35. Unlike a large local void, the model respects the
cosmological principle, further offering an explanation for the late onset of
the perceived acceleration as a consequence of the forming nonlinear
structures. Additional tests, such as quantitative predictions for angular
deviations due to an anisotropic void distribution and a theoretical derivation
of the model, can vindicate or falsify the interpretation that light
propagation in voids is responsible for the perceived acceleration.Comment: 33 pages, 2 figs; v2: minor clarifications, results unchanged; v3:
matches the version published in General Relativity and Gravitatio
Association between the CHRM2 gene and intelligence in a sample of 304 Dutch families.
The CHRM2 gene is thought to be involved in neuronal excitability, synaptic plasticity and feedback regulation of acetylcholine release and has previously been implicated in higher cognitive processing. In a sample of 667 individuals from 304 families, we genotyped three singlenucleotide polymorphisms (SNPs) in the CHRM2 gene on 7q31â35. From all individuals, standardized intelligence measures were available. Using a test of within-family association, which controls for the possible effects of population stratification, a highly significant association was found between the CHRM2 gene and intelligence. The strongest association was between rs324650 and performance IQ (PIQ), where the T allele was associated with an increase of 4.6 PIQ points. In parallel with a large familybased association, we observed an attenuated â although still significant â population-based association, illustrating that population stratification may decrease our chances of detecting alleleâtrait associations. Such a mechanism has been predicted earlier, and this article is one of the first to empirically show that family-based association methods are not only needed to guard against false positives, but are also invaluable in guarding against false negatives
Fungos conidiais em Euterpe oleracea Mart. (açaizeiro) na Ilha do Combu, Parå-Brasil
Influences de la sylviculture sur le risque de dégùts biotiques et abiotiques dans les peuplements forestiers
The Cinderella story of metabolic profiling: does metabolomics get to go to the functional genomics ball?
To date most global approaches to functional genomics have centred on genomics, transcriptomics and proteomics. However, since a number of high-profile publications, interest in metabolomics, the global profiling of metabolites in a cell, tissue or organism, has been rapidly increasing. A range of analytical techniques, including (1)H NMR spectroscopy, gas chromatographyâmass spectrometry (GCâMS), liquid chromatographyâmass spectrometry (LCâMS), Fourier Transform mass spectrometry (FTâMS), high performance liquid chromatography (HPLC) and electrochemical array (EC-array), are required in order to maximize the number of metabolites that can be identified in a matrix. Applications have included phenotyping of yeast, mice and plants, understanding drug toxicity in pharmaceutical drug safety assessment, monitoring tumour treatment regimes and disease diagnosis in human populations. These successes are likely to be built on as other analytical and bioinformatic approaches are developed to fully exploit the information obtained in metabolic profiles. To assist in this process, databases of metabolomic data will be necessary to allow the passage of information between laboratories. In this prospective review, the capabilities of metabolomics in the field of medicine will be assessed in an attempt to predict the impact this âCinderella approachâ will have at the âfunctional genomic ballâ
Regulating biomedicine in Europe and North America: A qualitative comparative analysis
This article explains the variation in policy design processes and the resulting policy-outputs of âbiopolicies' implemented within the domain of Assisted Reproductive Technology (ART) for eleven European and North-American countries. By applying the method of Qualitative Comparative Analysis, the comparison describes and defines the âmultiple conjunctural causation' to explain the divergences or similarities of ART policies in Europe and North America. The policy preferences of the actors involved in the relevant ART policy network and the institutional rules characterizing the respective polity need to be considered together in order to explain why different countries adopted similar or different ART policies. In particular, the analysis stresses the influence of party politics, the self-regulation of ART by the physicians, the mobilization of interest groups, the number of institutional arenas involved in the designing process and the nature of decision-making rules (power-sharing versus majority) on the designing processes and the resulting policies. Thus, different policy designs are linked to different designing processes, encompassing four ideal-typical decision-making modes: âdesigning by non-decisions', âdesigning by elites', âdesigning by accommodation' and âdesigning by mobilization and consultation'. These results shed new light on the challenges for developing a policy design theory that could provide a robust framework for describing and explaining policy formulation
Photoinduced quantum magnetotransport properties of silicene and germanene
Silicene and germanene have remarkable electronic properties due to strong spin orbit
coupling and buckled single layer structures. We derive and analyze the band structures of
these materials in the presence of perpendicular electric and magnetic fields taking into
account the effects of off-resonant light. Using linear response theory,
analytical expressions are derived and evaluated for the Hall and longitudinal
conductivities. Contrary to graphene, we show that the light leads to a single Dirac cone
state and thus to unusual plateaus and magnetotransport properties, which are desirable
for electronic applications