Relativistic transport theory for simple fluids at first order in the gradients: a stable picture

In this paper we show how using a relativistic kinetic equation the ensuing expression for the heat flux can be casted in the form required by Classical Irreversible Thermodynamics. Indeed, it is linearly related to the temperature and number density gradients and not to the acceleration as the so called \textit{first order in the gradients} theories propose. Since the specific expressions for the transport coefficients are irrelevant for our purposes, the BGK form of the kinetic equation is used. Moreover, from the resulting hydrodynamic equations it is readily seen that the equilibrium state is stable in the presence of the spontaneous fluctuations in the transverse hydrodynamic velocity mode of the simple relativistic fluid. The implications of this result are thoroughly discussed.Comment: 9 pages. Accepted in Physica

The Rayleigh-Brillouin Spectrum in Special Relativistic Hydrodynamics

In this paper we calculate the Rayleigh-Brillouin spectrum for a relativistic simple fluid according to three different versions available for a relativistic approach to non-equilibrium thermodynamics. An outcome of these calculations is that Eckart's version predicts that such spectrum does not exist. This provides an argument to question its validity. The remaining two results, which differ one from another, do provide a finite form for such spectrum. This raises the rather intriguing question as to which of the two theories is a better candidate to be taken as a possible version of relativistic non-equilibrium thermodynamics. The answer will clearly require deeper examination of this problem.Comment: 13 pages, no figures. Accepted for publication in Phys. Rev.

Immigrant overeducation : evidence from recent arrivals to Australia.

Australian immigration policy, in common with the US and Canada, has increased the emphasis on skill-based selection criteria. A key premise of this policy is that skilled immigrants are more employable and can add to the productive capacity of the economy. However, this effect will be diminished if immigrants are working in occupations that fail to utilise their skills. We examine the extent of overeducation for recently arrived immigrants to Australia. We find that they are more likely to be overeducated than the native population, even if they enter on skill assessed visas. Overeducation is greater for immigrants from non-English speaking backgrounds (NESB) and generates lower returns to education. Tighter restrictions to welfare support on entry raised employment levels but increased overeducation. This will serve to reduce the potential productivity gains from skill biased immigration policies

A first--order irreversible thermodynamic approach to a simple energy converter

Several authors have shown that dissipative thermal cycle models based on Finite-Time Thermodynamics exhibit loop-shaped curves of power output versus efficiency, such as it occurs with actual dissipative thermal engines. Within the context of First-Order Irreversible Thermodynamics (FOIT), in this work we show that for an energy converter consisting of two coupled fluxes it is also possible to find loop-shaped curves of both power output and the so-called ecological function against efficiency. In a previous work Stucki [J.W. Stucki, Eur. J. Biochem. vol. 109, 269 (1980)] used a FOIT-approach to describe the modes of thermodynamic performance of oxidative phosphorylation involved in ATP-synthesis within mithochondrias. In that work the author did not use the mentioned loop-shaped curves and he proposed that oxidative phosphorylation operates in a steady state simultaneously at minimum entropy production and maximum efficiency, by means of a conductance matching condition between extreme states of zero and infinite conductances respectively. In the present work we show that all Stucki's results about the oxidative phosphorylation energetics can be obtained without the so-called conductance matching condition. On the other hand, we also show that the minimum entropy production state implies both null power output and efficiency and therefore this state is not fulfilled by the oxidative phosphorylation performance. Our results suggest that actual efficiency values of oxidative phosphorylation performance are better described by a mode of operation consisting in the simultaneous maximization of the so-called ecological function and the efficiency.Comment: 20 pages, 7 figures, submitted to Phys. Rev.

Violations of local equilibrium and linear response in classical lattice theories

We study the dynamics of $\phi^4$ theory and the FPU $\beta$ model under thermal gradients, from first principles. We analyze quantitatively how local equilibrium and linear response are violated, paying special care to how we find observables that unambiguously display these violations. Relations between these quantities to equations of state are also examined. Further, we discuss how we can approach similar dynamical problems in continuum quantum field theory. We analyze how close we are to obtaining the continuum results.Comment: 7pp, 4figs, talk given by KA at "Thermal field theory and applications" workshop 200

Structure formation in the presence of relativistic heat conduction: corrections to the Jeans wave number with a stable first order in the gradients formalism

The problem of structure formation in relativistic dissipative fluids was analyzed in a previous work within Eckart's framework, in which the heat flux is coupled to the hydrodynamic acceleration, additional to the usual temperature gradient term. It was shown that in such case, the pathological behavior of fluctuations leads to the disapperance of the gravitational instability responsible for structure formation. In the present work the problem is revisited now using a constitutive equation derived from relativistic kinetic theory. The new relation, in which the heat flux is not coupled to the hydrodynamic acceleration, leads to a consistent first order in the gradients formalism. In this case the gravitational instability remains, and only relativistic corrections to the Jeans wave number are obtained. In the calculation here shown the non-relativistc limit is recovered, opposite to what happens in Eckart's case.Comment: 10 pages, no figure

Association of Education and Intracranial Volume With Cognitive Trajectories and Mortality Rates Across the Alzheimer Disease Continuum

OBJECTIVE: To investigate relationships of education and intracranial volume (factors related to cognitive versus brain reserve, respectively) with cognitive trajectories and mortality in individuals with biomarker-defined Alzheimer's disease (AD). METHODS: We selected 1,298 amyloid-β-positive memory clinic patients with subjective cognitive decline (SCD, n=142), mild cognitive impairment (MCI, n=274) and AD dementia (n=882) from the Amsterdam Dementia Cohort. All participants underwent baseline MRI and neuropsychological assessment, and 68% received cognitive follow-up (median=2.3 years, interquartile range=2.4). Mortality data were collected from the Central Public Administration. In the total sample and stratified by disease stage (i.e., SCD/MCI versus dementia), we examined education and intracranial volume as predictors of baseline and longitudinal cognitive performance on five cognitive domains [memory, attention, executive, language and visuospatial functions] (linear mixed models) and time-to-death (Cox proportional hazard models). Analyses were adjusted for age, sex, whole-brain gray matter atrophy and MRI field strength. RESULTS: Education and intracranial volume showed consistent positive associations with baseline cognition across disease stages. Longitudinally, we observed a relationship between higher education and faster cognitive decline among dementia patients on global cognition, memory, executive function and language (range β=-0.06-[-0.13], all p<0.05). Furthermore, in the total sample, both higher education and intracranial volume related to lower mortality risk (hazard ratio=0.84 and 0.82, respectively, p<0.05). CONCLUSIONS: In this amyloid-β-positive memory clinic sample, both reserve factors were positively associated with baseline cognition, whereas only education related to longitudinal cognition (i.e., accelerated decline among higher-educated patients with dementia). Moreover, higher education and intracranial volume both moderately attenuated overall mortality risk in AD

On the nature of the so-called generic instabilities in dissipative relativistic hydrodynamics

It is shown that the so-called generic instabilities that appear in the framework of relativistic linear irreversible thermodynamics, describing the fluctuations of a simple fluid close to equilibrium, arise due to the coupling of heat with hydrodynamic acceleration which appears in Eckart's formalism of relativistic irreversible thermodynamics. Further, we emphasize that such behavior should be interpreted as a contradiction to the postulates of linear irreversible thermodynamics (LIT), namely a violation of Onsager's hypothesis on the regression of fluctuations, and not as fluid instabilities. Such contradictions can be avoided within a relativistic linear framework if a Meixner-like approach to the phenomenological equations is employed.Comment: 13 pages, no figures. Accepted for publication in GR

Impact of sharing Alzheimer's disease biomarkers with individuals without dementia:A systematic review and meta-analysis of empirical data

Introduction: We conducted a systematic literature review and meta-analysis of empirical evidence on expected and experienced implications of sharing Alzheimer's disease (AD) biomarker results with individuals without dementia. Methods: PubMed, Embase, APA PsycInfo, and Web of Science Core Collection were searched according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Results from included studies were synthesized, and quantitative data on psychosocial impact were meta-analyzed using a random-effects model. Results: We included 35 publications. Most personal stakeholders expressed interest in biomarker assessment. Learning negative biomarker results led to relief and sometimes frustration, while positive biomarkers induced anxiety but also clarity. Meta-analysis of five studies including 2012 participants (elevated amyloid = 1324 [66%], asymptomatic = 1855 [92%]) showed short-term psychological impact was not significant (random-effect estimate = 0.10, standard error = 0.23, P = 0.65). Most professional stakeholders valued biomarker testing, although attitudes and practices varied considerably. Discussion: Interest in AD biomarker testing was high and sharing their results did not cause psychological harm. Highlights: Most personal stakeholders expressed interest in Alzheimer's disease biomarker assessment. Personal motivations included gaining insight, improving lifestyle, or preparing for the future. There was no short-term psychological impact of sharing biomarker status, implying it can be safe. Most professional stakeholders valued biomarker testing, believing the benefits outweigh the risk. Harmonized guidelines on biomarker testing and sharing results are required.</p