O segundo vídeo é uma palestra do nobelista em Física Murray Gell-Mann, onde o mesmo fala sobre a evolução da linguagem:

Vale muito a pena assisti-los. Um ótimo ano novo para todos!

The future of cosmology and the role of non-linear perturbations. (arXiv:1111.6853v1 [astro-ph.CO]):

Cosmological perturbation theory is a key tool to study the universe. The
linear or first order theory is well understood, however, developing and
applying the theory beyond linear order is at the cutting edge of current
research in theoretical cosmology. In this article, I will describe some
signatures of non-linear perturbation theory that do not exist at linear order,
focusing on vorticity generation at second order. In doing so, we discuss why
this, among other features such as induced gravitational waves and
non-Gaussianities, shows that cosmological perturbation theory is crucial for
testing models of the universe.

Cosmological Perturbations from a Group Theoretical Point of View. (arXiv:1111.7027v1 [gr-qc]):

We present a new approach to cosmological perturbations based on the theory
of Lie groups and their representations. After re-deriving the standard
covariant formalism from SO(3) considerations, we provide a new expansion of
the perturbed Friedmann-Lemaitre-Robertson-Walker (FLRW) metric in terms of
irreducible representations of the Lorentz group. The resulting decomposition
splits into (scalar, scalar), (scalar, vector) and (vector, vector) terms.
These equations directly correspond to the standard Lifshitz classification of
cosmological perturbations using scalar, vector and tensor modes which arise
from the irreducible SO(3) representation of the spatial part of the metric.
While the Lorentz group basis matches the underlying local symmetries of the
FLRW spacetime better than the SO(3), the new equations do not provide further
simplification compared to the standard cosmological perturbation theory. We
conjecture that this is due to the fact that the so(3,1) ~ su(2) x su(2)
Lorentz algebra has no pair of commuting generators commuting with any of the
translation group generators.

Cosmological models and misunderstandings about them. (arXiv:1110.1828v2 [gr-qc] CROSS LISTED):

Advantages of inhomogeneous cosmological models that are exact solutions of
Einstein’s equations over linearised perturbations of homogeneous models are
presented. Examples of effects that can be described in the inhomogeneous ones
are given: the non-repeatable light paths, the observed anisotropies in the
cosmic microwave background, the redshift drift and the maximum diameter
distance. Criticisms of inhomogeneous models that are based on
misunderstandings or fallacious reasonings are pointed out and corrected; these
include the “weak singularity”, the positivity of deceleration “theorem”, the
“pathology” of redshift behaviour at the “critical point” and the alleged
necessity of the bang time to be constant.

Quantifying the behaviour of curvature perturbations during inflation. (arXiv:1111.6940v1 [astro-ph.CO]):

How much does the curvature perturbation change after it leaves the horizon,
and when should one evaluate the power spectrum? To answer these questions we
study single field inflation models numerically, and compare the evolution of
different curvature perturbations from horizon crossing to the end of
inflation. In particular we calculate the number of efolds it takes for the
curvature perturbation at a given wavenumber to settle down to within a given
fraction of their value at the end of inflation.

We find that e.g. in chaotic inflation, the amplitude of the comoving and the
curvature perturbation on uniform density hypersurfaces differ by up to 180 %
at horizon crossing assuming the same amplitude at the end of inflation, and
that it takes approximately 3 efolds for the curvature perturbation to be
within 1 % of its value at the end of inflation.

Zero-point quantum fluctuations in cosmology. (arXiv:1111.5575v1 [astro-ph.CO]):

We re-examine the classic problem of the renormalization of zero-point
quantum fluctuations in a Friedmann-Robertson-Walker background. We discuss a
number of issues that arise when regularizing the theory with a momentum-space
cutoff, and show explicitly how introducing non-covariant counter-terms allows
to obtain covariant results for the renormalized vacuum energy-momentum tensor.
We clarify some confusion in the literature concerning the equation of state of
vacuum fluctuations. Further, we point out that the general structure of the
effective action becomes richer if the theory contains a scalar field phi with
mass m smaller than the Hubble parameter H(t). Such an ultra-light particle
cannot be integrated out completely to get the effective action. Apart from the
volume term and the Einstein-Hilbert term, that are reabsorbed into
renormalizations of the cosmological constant and Newton’s constant, the
effective action in general also has a term proportional to F(phi)R, for some
function F(phi). As a result, vacuum fluctuations of ultra-light scalar fields
naturally lead to models where the dark energy density has the form
rho_{DE}(t)=rho_X(t)+rho_Z(t), where rho_X is the component that accelerates
the Hubble expansion at late times and rho_Z(t) is an extra contribution
proportional to H^2(t). We perform a detailed comparison of such models with
CMB, SNIa and BAO data.

Slow Roll Inflation: A Somehow Different Perspective. (arXiv:1112.1083v1 [astro-ph.CO]):

In this note we point out that, contrary to the standard point of view, slow
roll inflation is due to high gravitational friction. We show that the
requirement of slow roll coincides with the requirement of a flat scalar field
potential in the case of minimally coupled scalar field. In this sense, the
search for a successful inflationary theory may be more fruitful by shifting
the focus on models with high gravitational friction. We review then a
gravitational mechanism, the so called “Gravitationally Enhanced Friction”
mechanism, such that high gravitational friction is dynamically generated
during inflation allowing even steep (i.e. non-flat) scalar potential to
inflate.

Stochastic Quantization and Casimir Forces. (arXiv:1110.2308v1 [quant-ph]):

In this paper we show how the stochastic quantization method developed by
Parisi and Wu can be used to obtain Casimir forces. Both quantum and thermal
fluctuations are taken into account by a Langevin equation for the field. The
method allows the Casimir force to be obtained directly, derived from the
stress tensor instead of the free energy. It only requires the spectral
decomposition of the Laplacian operator in the given geometry. The formalism
provides also an expression for the fluctuations of the force. As an
application we compute the Casimir force on the plates of a finite piston of
arbitrary cross section. Fluctuations of the force are also directly obtained,
and it is shown that, in the piston case, the variance of the force is twice
the force squared.

Cosmological constraints on non-standard inflationary quantum collapse models. (arXiv:1112.1830v1 [astro-ph.CO]):

We briefly review an important shortcoming –unearthed in previous works– of
the standard version of the inflationary model for the emergence of the seeds
of cosmic structure. We consider here some consequences emerging from a
proposal inspired on ideas of Penrose and Di\’osi about a quantum-gravity
induced reduction of the wave function, which has been put forward to address
the shortcomings, arguing that its effect on the inflaton field is what can
lead to the emergence of the seeds of cosmic structure. The proposal leads to a
deviation of the primordial spectrum from the scale-invariant
Harrison-Zel’dovich one, and consequently, to a different CMB power spectrum.
We perform statistical analyses to test two quantum collapse schemes with
recent data from the CMB, including the 7-yr release of WMAP and the matter
power spectrum measured using LRGs by the Sloan Digital Sky Survey. Results
from the statistical analyses indicate that several collapse models are
compatible with CMB and LRG data, and establish constraints on the free
parameters of the models. The data put no restriction on the timescale for the
collapse of the scalar field modes.

Is there a flatness problem in classical cosmology?. (arXiv:1112.1666v1 [astro-ph.CO]):

I briefly review the flatness problem within the context of classical
cosmology and examine some of the debate in the literature with regard to its
definition and even the question whether it exists. I then present some new
calculations for cosmological models which will collapse in the future;
together with previous work by others for models which will expand forever,
this allows one to examine the flatness problem quantitatively for all
cosmological models. This leads to the conclusion that the flatness problem
does not exist, not only for the cosmological models corresponding to the
currently popular values of lambda_0 and Omega_0 but indeed for all
Friedmann-Lema\^itre models.

Black-Scholes model under subordination. (arXiv:1111.3263v1 [q-fin.PR]):

In this paper we consider a new mathematical extension of the Black-Scholes
model in which the stochastic time and stock share price evolution is described
by two independent random processes. The parent process is Brownian, and the
directing process is inverse to the totally skewed, strictly \alpha-stable
process. The subordinated process represents the Brownian motion indexed by an
independent, continuous and increasing process. This allows us to introduce the
long-term memory effects in the classical Black-Scholes model.

The Ig Nobel Prizes honor achievements that first make people laugh, and then make them think. The prizes are intended to celebrate the unusual, honor the imaginative — and spur people’s interest in science, medicine, and technology.

O vídeo-chamada para a cerimônia pode ser conferido aqui embaixo:

Para mais detalhes sobre o prêmio, http://improbable.com/ig/.

Até a próxima!

The purpose of this work is to use a renormalized quantum scalar field to
investigate very early cosmology, in the Planck era immediately following the
big bang. Renomalization effects make the field potential dependent on length
scale, and are important during the big bang era. We use the asymptotically
free Halpern-Huang scalar field, which is derived from renomalization-group
analysis, and solve Einstein’s equation with Robertson-Walker metric as an
initial-value problem. The main prediction is that the Hubble parameter follows
a power law: H\equiva/a\simt^{-p}, and the universe expands at an accelerated
rate: a\simexp t^{1-p}. This gives ‘dark energy’, with an equivalent
cosmological constant that decays in time like t^{-2p}, which avoid the
‘fine-tuning’ problem. The power law predicts a simple relation for the
galactic redshift. Comparison with data leads to the speculation that the
universe experienced a crossover transition, which was completed about 7
billion years ago.

“

Chaotic inflation and supersymmetry breaking. (arXiv:1106.6025v1 [hep-th]): ”

We investigate the recently proposed class of chaotic inflation models in
supergravity with an arbitrary inflaton potential. These models are extended to
include matter fields in the visible sector and we employ a mechanism of SUSY
breaking based on a particular phenomenological version of the KKLT mechanism
(the KL model). We describe specific features of reheating in this class of
models and show how one can solve the cosmological moduli and gravitino
problems in this context.

“

Standard Cosmology Delayed. (arXiv:1106.6231v1 [gr-qc]): ”

The introduction of a delay in the Friedmann equation of cosmological
evolution is shown to result in the very early universe undergoing the
necessary accelerated expansion in the usual radiation (or matter) dominated
phase. Occurring even without a violation of the strong energy condition, this
expansion slows down naturally to go over to the decelerated phase, namely the
standard Hubble expansion. This may obviate the need for a scalar field driven
inflationary epoch.

“

Did Edwin Hubble plagiarize?. (arXiv:1107.0442v1 [physics.hist-ph]): ”

Recently Block published an astro-ph [arXiv:1106.3928 (2011)] insinuating
that Hubble censored a prior publication of his famous and seminal discovery of
the expansion of the universe. This issue was investigated by us in detail as
part of the book: The Quest for Chemical Element Genesis and What the Chemical
Elements Tell about the Universe (Accepted for publication, Springer Pub.
Heidelberg, 2011.) Since the book is due in few months, we extract here the
relevant parts.

Our summary: We exonerate Hubble from the charge that he censored or ignored
or plagiarized Lemaitre’s earlier theoretical discovery.

“

Chern-Simons Inflation and Baryogenesis. (arXiv:1107.0318v1 [hep-th]): ”

We propose a model of inflation where the Chern-Simons interaction and vector
fields play a central role in generating an inflationary epoch. As a result, in
accord with the APS mechanism, the Sakharov conditions for baryogenesis are
self-consistently satisfied, and we calculate the net baryon asymmetry index in
terms of the gauge configuration necessary for inflation, based on the chiral
anomaly. Inflation begins with a large plasma density of interacting gauge
fields and fermions, which interact through gravity and the Chern Simons term.
The Chern-Simons term drives power from an initial white-noise spectrum of
gauge fields into a narrow-band of superhorizon wave vectors. At the same time,
the fermionic current and metric coupling amplifies the gauge field on
superhorizon scales. This phase-correlation and amplification of the gauge
field produces the correct conditions to maintain more than 60 e-folds of
inflation. Eventually the gauge field dissipates by producing the observed
baryon asymmetry $\frac{n_{b}}{s} \sim 10^{-10}$, through the chiral anomaly
and inflation ends.

“

Cosmological Perturbation Theory With Background Anisotropic Curvature. (arXiv:1107.0389v1 [gr-qc]): ”

The theory of cosmological perturbations is extended to spacetimes displaying
isotropic expansion but anisotropic curvature. The perturbed Einstein equation
and Boltzmann equations for massless and massive particles are derived in a
general gauge and a decomposition of perturbations into harmonic modes and
moments is proposed. Generalization to the case where anisotropic expansion is
also present in the background is discussed.

“

Entropic Force Scenarios and Eternal Inflation. (arXiv:1107.1013v1 [hep-th]): ”

We examine various entropic inflation scenarios, under the light of
eternality. After describing the inflation realization and the normal condition
for inflation to last at the background level, we investigate the conditions
for eternal inflation with the effect of thermal fluctuations produced from
standard radiation and from the holographic screen. Furthermore, we incorporate
stochastic quantum fluctuations through a phenomenological, Langevin analysis,
studying whether they can affect the inflation eternality. In
single-holographic-screen scenarios eternality can be easily obtained, while in
double-screen considerations inflation is eternal only in the high-energy
regime. Thus, from the cosmological point of view, one should take these into
account before he can consider entropic gravity as a candidate for the
description of nature. However, form the string theory point of view, inflation
eternality may form the background for the ‘Landscape’ of string/M theory
vacua, leading to new perspectives in entropy gravity.

“

Até a próxima!

Bem, com as facilidades e acessibilidade das tecnologias de hoje, fica difícil afirmar se o vídeo é verdadeiro ou não, mas independente disso ele é impressionante. Ele nos faz parar um pouco e pensar em quão longe chegamos no desenvolvimento do conhecimento sobre a natureza. Uma espécie animal dentre tantas outras, num planeta (provavelmente) como tantos outros, numa galáxia banal frente a imensidão do espaço, hoje tece teorias profundas sobre a origem de tudo isso que nos cerca, visível ou invisivel, muito pequeno ou de dimensões do universo. Talvez não tenhamos tomado o melhor caminho nessa linha do tempo do desenvolvimento humano, mas devemos ter a humildade que transparece nesse povo “primitivo” do vídeo para mudar o curso da história enquanto ainda há tempo.

Até a próxima!

Aqui vai uma screenshot da página a lá Twitter/wall do Facebook do ResearchGate (clique para ampliar!):

E aqui vai uma screenshot do equivalente no Mendeley:

Comparação da página do perfil(clique para ampliar!):

(no RG, você deve clicar na aba “Publications” para ter acesso aos artigos publicados pelo usuário, o que é uma desvantagem em relação ao Mendeley)

Embora as informações que julgo mais importante fiquem mais evidentes no perfil do Mendeley, o ResearchGate conta com um perfil bem mais detalhado e rico. Ambas as redes permitem fazer login diretamente de uma conta do Facebook, Twitter, Google (acho que existem outras opções, mas no momento não lembro!). Isso economiza bastante tempo de preenchimento de formulários e upload de foto para o perfil… O RG permite ainda criar um vínculo com sua conta do Facebook. Com esse vínculo ativado, tudo que você postar no “wall” do Facebook automaticamente é postado no RG também. Eu particularmente não gostei dessa opção e a desativei.

Agora vem a grande cereja do bolo que faz com que eu ache o serviço do Mendeley muito melhor do que o do ResearchGate. No RG você pode criar uma biblioteca pessoal importando seu arquivo bibtex, XML ou RIS. E só! No Mendeley, além de poder fazer isso você ainda conta com um software para catalogação e organização dos artigos contidos no seu HD! Isso é uma verdadeira mão na roda! Com o Mendeley Desktop você pode (clique nas figuras para ampliar):

• Atribuir tags aos artigos da sua biblioteca:

• Criar notas referentes ao artigo na coluna lateral
• Buscar por palavras-chave
• Filtrar os artigos por autores, publicações e palavras-chave:
• Usar marcador de texto e criar notas no corpo do pdf:
• Exportar bibliografia em .bib
• Sincronizar tudo isso com o Mendeley online e com qualquer outro PC que tenha o Mendeley Desktop instalado!

O Mendeley desktop está disponível para Linux, Windows e Mac OS e conta com atualizações frequentes. Para mais informações sobre os dois serviços, suas histórias etc, um bom primeiro passo é a Wikipedia:

Mendeley:   http://en.wikipedia.org/wiki/Mendeley
ResearchGate:   http://en.wikipedia.org/wiki/ResearchGate

Até a próxima!

Após a instalação, um pequeno menu irá aparecer abaixo do menu “quick links” (isso vai depender um pouco da disposição espacial dos aplicativos da sua conta do Gmail):

Para digitar suas equações, basta usar o delimitador “$$”. Por exemplo,

$$ \int d^3\vec x e^{-i\vec k \cdot \vec x} f(x) $$

Para ver o resultado, é precido clicar em “TeX Composed” no menu do GmailTeX. Uma janela então se abrirá mostrando sua equação compilada. Veja a screenshot abaixo (clique para ampliar):

Ao receber um email escrito com equações em LaTeX, basta abrí-lo e clicar em “TeX Receiver” no menu do GmailTeX. O resultado é esse:

Bem prático, não? A desvantagem é que tanto quem recebe o email, quanto quem envia deve, necessariamente ter instalado o GmailTeX. Se eu bem me lembro, há algum tempo atrás vi algum aplicativo que transformava o código em LaTeX em imagem, o que facilita bastante para quem recebe o email. Vou pesquisar melhor e depois faço outro post. Quanto mais alternativas, melhor!

Página do desenvolvedor: http://alexeev.org/gmailtex.html

Até a próxima!