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Stress is a risk factor for numerous negative health outcomes, including cognitive impairment in late-life. The negative association between stress and cognition may be mediated by depressive symptoms, which separate studies have identified as both a consequence of perceived stress and a risk factor for cognitive decline. Pathways linking perceived stress, depressive symptoms, and cognition may be moderated by sociodemographics and psychosocial resources. The goal of this cross-sectional study was to identify modifying factors and enhance understanding of the mechanisms underlying the stress–cognition association in a racially and ethnically diverse sample of older adults.
A linear regression estimated the association between perceived stress and episodic memory in 578 older adults (Mage = 74.58) in the Washington Heights-Inwood Columbia Aging Project. Subsequent models tested whether depressive symptoms mediated the stress–memory relationship and whether sociodemographics (gender, race, and ethnicity) or perceived control moderated these pathways.
Independent of sociodemographics and chronic diseases, greater perceived stress was associated with worse episodic memory. This relationship was mediated by more depressive symptoms. Higher perceived control buffered the association between stress and depressive symptoms. There was no significant moderation by gender, race, or ethnicity.
Depressive symptoms may play a role in the negative association between perceived stress and cognition among older adults; however, longitudinal analyses and studies using experimental designs are needed. Perceived control is a modifiable psychological resource that may offset the negative impact of stress.
Previous cross-sectional studies have documented associations between positive psychosocial factors, such as self-efficacy and emotional support, and late-life cognition. Further, the magnitudes of concurrent associations may differ across racial and ethnic groups that differ in Alzheimer’s disease risk. The goals of this longitudinal study were to characterize prospective associations between positive psychosocial factors and cognitive decline and explicitly test for differential impact across race and ethnicity.
578 older adults (42% non-Hispanic Black, 31% non-Hispanic White, and 28% Hispanic) in the Washington Heights-Inwood Columbia Aging Project completed cognitive and psychosocial measures from the NIH Toolbox and standard neuropsychological tests over 2.4 years. Latent difference scores were used to model associations between positive psychosocial factors and cognitive decline controlling for baseline cognition, sociodemographics, depressive symptoms, physical health, and other positive psychosocial factors. Multiple-group modeling was used to test interactions between the positive psychosocial factors and race/ethnicity.
Higher NIH Toolbox Friendship scores predicted less episodic memory decline. One standard deviation increase in friendship corresponded to 6 fewer years of memory aging. This association did not significantly differ across racial/ethnic groups.
This longitudinal study provides support for the potential importance of friendships for subsequent episodic memory trajectories among older adults from three ethnic groups. Further study into culturally informed interventions is needed to investigate whether and how friend networks may be targeted to promote cognitive health in late life.
Social engagement may be an important protective resource for cognitive aging. Some evidence suggests that time spent with friends may be more beneficial for cognition than time spent with family. Because maintaining friendships has been demonstrated to require more active maintenance and engagement in shared activities, activity engagement may be one underlying pathway that explains the distinct associations between contact frequency with friends versus family and cognition.
Using two waves of data from the national survey of Midlife in the United States (n = 3707, Mage = 55.80, 51% female at baseline), we examined longitudinal associations between contact frequency with friends and family, activity engagement (cognitive and physical activities), and cognition (episodic memory and executive functioning) to determine whether activity engagement mediates the relationship between contact frequency and cognition.
The longitudinal mediation model revealed that more frequent contact with friends, but not family, was associated with greater concurrent engagement in physical and cognitive activities, which were both associated with better episodic memory and executive functioning.
These findings suggest that time spent with friends may promote both cognitively and physically stimulating activities that could help to preserve not only these social relationships but also cognitive functioning.
We investigated particle acceleration and shock structure associated with an unmagnetized
relativistic jet propagating into an unmagnetized plasma. Strong magnetic fields generated
in the trailing shock contribute to the electrons transverse deflection and acceleration.
We have calculated, self-consistently, the radiation from electrons accelerated in these
turbulent magnetic fields. We found that the synthetic spectra depend on the bulk Lorentz
factor of the jet, its temperature and strength of the generated magnetic fields. We have
also investigated accelerated electrons in strong magnetic fields generated by kinetic
shear (Kelvin-Helmholtz) instabilities. The calculated properties of the emerging
radiation will guide our understanding of the complex time evolution and/or spectral
structure in gamma-ray bursts, relativistic jets in general, and supernova remnants.
The Franco-Algerian Monitor of Solar Images (MISOLFA) was developped in order to study
the effect of optical turbulence on diameter measurements from ground-based solar
observations. Some first results obtained with MISOLFA are presented.
Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs in the shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and for particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The “jitter” radiation from deflected electrons in turbulent magnetic fields has properties different from synchrotron radiation calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure of gamma-ray bursts, relativistic jets in general, and supernova remnants. In order to calculate radiation from first principles and go beyond the standard synchrotron model, we have used PIC simulations. We present synthetic spectra to compare with the spectra obtained from Fermi observations.
Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs in the shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and for particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The “jitter” radiation from deflected electrons in turbulent magnetic fields has different properties from synchrotron radiation calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure of gamma-ray bursts, relativistic jets in general, and supernova remnants. In order to calculate radiation from first principles and go beyond the standard synchrotron model, we have used PIC simulations. We will present detailed spectra for conditions relevant to various astrophysical sites of collisionless shock formation. In particular we will discuss application to GRBs and SNRs.
We present the analysis of emission line spectra of AGNs and
starbursts with the help of models coupling shocks and photoionization
by AGNs and by massive stars. We show how shocks and photoionization
by the central source have to coexist in AGNs in order to reproduce
the observed emission line ratios. We also show how stellar photoionization
models can be reconciled with the values of the [OI]/Hα and
[SII]/Hα ratios observed in starbursts, without requiring an additional
ionizing source such as shocks.
Using integral field spectroscopy, we detected the broad features
of massive Wolf-Rayet stars in the core of three Seyfert galaxies.
The observed high value of the WR/O number ratio is a clear signature
of a young and powerful starburst. The star-forming regions are distributed
in an arc/ring-like structure around the AGN, at a distance
of about 200 pc. These are the first spatially-resolved detections of
massive starbursts so close of an AGN.
Adaptive Optics Systems are now routinely operated on several
4 meter class telescopes, allowing to achieve angular resolutions
down to 70 msec in the near-infrared. Although these Systems have excellent
performances, their use for exploring the physics and structure
of AGN is still limited for the following reasons: the limiting magnitude
of the wavefront sensor is too high, the sensitivity of infrared
detectors does not give access to medium/high spectral resolution spectroscopy
and the angular resolution achieved does not always fit the
apparent size of the physical components responsible for emission features
close to the central engine. The new generation of 8 — 10 m class
telescopes bring improvements in this matter. However, some interesting
results have been obtained so far with Adonis, the ESO La Silla
adaptive optics System on the 3.60 meter telescope, in the investigation
of AGN structure. In particular, a prominent structure has been
detected in the central arcsec core of NGC 1068, which might feature
the dusty/molecular torus expected on theoretical grounds.
The dynamics of a massive binary System in a galactic nucleus are presented.
These are the first results from simulations applying a hybrid "self consistent field"
(SCF) 1 and direct Aarseth N body integrator (NBODY6) 2, which synthesises
the advantages of the direct force calculation with the efficiency of the field method.
The code is aimed for use on parallel architectures and is therefore applicable
for collisional N-body integrations with extraordinarily large particle numbers
(> 105). It opens the perspective to simulate the dynamics of globular clusters with
realistic collisional relaxation, as well as stellar Systems surrounding a supermassive
black hole in galactic nuclei.
The main characteristics of the average spectrum of radio
quiet AGN in the UV and X-ray range are reviewed, and the emission
mechanisms are discussed in the framework of accretion disk models,
in particular the "irradiated cold relativistic disk". It is shown that
some problems arise in confronting the predictions of the model to the
observations. We propose an alternative model in terms of a hot disk
surrounded by a cold Compton thick medium. Finally we mention
problems with remote regions of the accretion disk.
The modclling of plasma outfiows from central gravitating
objects such as AGN is bricfly discussed via analytic examples in the
context of ideal MHD. The exact solutions are produced via a nonlinear
separation of the variables in the full set of the MHD equations. Attention
is given to the questions of initial acceleration and collimation
of the outflow. A quantitative: criterion is provided for the transition of
the morphologies from highly collimated jets to non collimated winds.
Hydrodynamical simulations have played an important role
in the understanding of extragalactic jets since the late seventies. In
this talk, recent simulations of jets in the relativistic regime are reviewed.
Special attention is payed to simulations of jets at parsec scale
which, for the first time. have allowed to probe the current models of
superluminal radio sources.
The development of a variety of non-electromagnetic detectors
will drastically enlarge our global view on Galactic Nuclei and
AGNs in the future. The possibility of detecting their non-photonic
emission, namely ultra-high energy cosmic rays (UHECRs) and gravitational
waves, may open new Windows on AGN physics in coming
We are interested in the stellar content in the central region
of active galaxies. In this aim, we perform stellar population synthesis
of the integrated starlight in the Optical and NIR using a mathematical
method (Pelat, 1997, MNRAS 284, 365) dedicated to the determination
of the best solution (among the many local solutions) in the stellar
population synthesis problem which is a complex inverse problem. A
new development of the code allows the determination of the error zone
around the solution, expected from the observational uncertainties. In
the next sections, we present this very powerful method and results
obtained from a sample of AGN.