88 research outputs found
A Pilot Double-Blind Randomized Controlled Trial of Cognitive Training Combined with Transcranial Direct Current Stimulation for Amnestic Mild Cognitive Impairment
Background: There is currently no effective intervention for improving memory in people at increased risk for dementia. Cognitive training (CT) has been promising, though effects are modest, particularly at follow-up. Objective: To investigate whether adjunctive non-invasive brain stimulation (transcranial direct current stimulation, tDCS) could enhance the memory benefits of CT in amnestic mild cognitive impairment (aMCI). Methods: Participants with aMCI were randomized to receive CT with either Active tDCS (2mA for 30min and 0.016mA for 30min) or Sham tDCS (0.016mA for 60min) for 15 sessions over a period of 5 weeks in a double-blind, sham-controlled, parallel group clinical trial. The primary outcome measure was the California Verbal Learning Task 2nd Edition. Results: 68 participants commenced the intervention. Intention-to-treat (ITT) analysis showed that the CT+Active tDCS group significantly improved at post treatment (p=0.033), and the CT+Sham tDCS group did not (p=0.050), but there was no difference between groups. At the 3-month follow-up, both groups showed large-sized memory improvements compared to pre-treatment (CT+Active tDCS: p<0.01, d=0.99; CT+Sham tDCS: p<0.01, d=0.74), although there was no significant difference between groups. Conclusion: This study found that CT+Active tDCS did not produce greater memory improvement compared to CT+Sham tDCS. Large-sized memory improvements occurred in both conditions at follow-up. One possible interpretation, based on recent novel findings, is that low intensity tDCS (used as 'sham') may have contributed biological effects. Further work should use a completely inert tDCS sham condition
The Hypermultiplet with Heisenberg Isometry in N=2 Global and Local Supersymmetry
The string coupling of N=2 supersymmetric compactifications of type II string
theory on a Calabi-Yau manifold belongs to the so-called universal dilaton
hypermultiplet, that has four real scalars living on a quaternion-Kaehler
manifold. Requiring Heisenberg symmetry, which is a maximal subgroup of
perturbative isometries, reduces the possible manifolds to a one-parameter
family that describes the tree-level effective action deformed by the only
possible perturbative correction arising at one-loop level. A similar argument
can be made at the level of global supersymmetry where the scalar manifold is
hyper-Kaehler. In this work, the connection between global and local
supersymmetry is explicitly constructed, providing a non-trivial gravity
decoupled limit of type II strings already in perturbation theory.Comment: 24 page
The Lick AGN Monitoring Project: Reverberation Mapping of Optical Hydrogen and Helium Recombination Lines
We have recently completed a 64-night spectroscopic monitoring campaign at
the Lick Observatory 3-m Shane telescope with the aim of measuring the masses
of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected
masses in the range ~10^6-10^7M_sun and also the well-studied nearby active
galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including
NGC 5548) showed optical variability of sufficient strength during the
monitoring campaign to allow for a time lag to be measured between the
continuum fluctuations and the response to these fluctuations in the broad
Hbeta emission, which we have previously reported. We present here the light
curves for the Halpha, Hgamma, HeII 4686, and HeI 5876 emission lines and the
time lags for the emission-line responses relative to changes in the continuum
flux. Combining each emission-line time lag with the measured width of the line
in the variable part of the spectrum, we determine a virial mass of the central
supermassive black hole from several independent emission lines. We find that
the masses are generally consistent within the uncertainties. The time-lag
response as a function of velocity across the Balmer line profiles is examined
for six of the AGNs. Finally we compare several trends seen in the dataset
against the predictions from photoionization calculations as presented by
Korista & Goad. We confirm several of their predictions, including an increase
in responsivity and a decrease in the mean time lag as the excitation and
ionization level for the species increases. Further confirmation of
photoionization predictions for broad-line gas behavior will require additional
monitoring programs for these AGNs while they are in different luminosity
states. [abridged]Comment: 37 pages, 18 figures and 15 tables, accepted for publication in the
Astrophysical Journa
The Lick AGN Monitoring Project: Photometric Light Curves and Optical Variability Characteristics
The Lick AGN Monitoring Project targeted 13 nearby Seyfert 1 galaxies with
the intent of measuring the masses of their central black holes using
reverberation mapping. The sample includes 12 galaxies selected to have black
holes with masses roughly in the range 10^6-10^7 solar masses, as well as the
well-studied AGN NGC 5548. In conjunction with a spectroscopic monitoring
campaign, we obtained broad-band B and V images on most nights from 2008
February through 2008 May. The imaging observations were carried out by four
telescopes: the 0.76-m Katzman Automatic Imaging Telescope (KAIT), the 2-m
Multicolor Active Galactic Nuclei Monitoring (MAGNUM) telescope, the Palomar
60-in (1.5-m) telescope, and the 0.80-m Tenagra II telescope. Having
well-sampled light curves over the course of a few months is useful for
obtaining the broad-line reverberation lag and black hole mass, and also allows
us to examine the characteristics of the continuum variability. In this paper,
we discuss the observational methods and the photometric measurements, and
present the AGN continuum light curves. We measure various variability
characteristics of each of the light curves. We do not detect any evidence for
a time lag between the B- and V-band variations, and we do not find significant
color variations for the AGNs in our sample.Comment: 16 pages, 20 figures, 8 tables, accepted for publication in ApJ
The Lick AGN Monitoring Project: Broad-Line Region Radii and Black Hole Masses from Reverberation Mapping of Hbeta
We have recently completed a 64-night spectroscopic monitoring campaign at
the Lick Observatory 3-m Shane telescope with the aim of measuring the masses
of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected
masses in the range ~10^6-10^7 M_sun and also the well-studied nearby active
galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including
NGC 5548) showed optical variability of sufficient strength during the
monitoring campaign to allow for a time lag to be measured between the
continuum fluctuations and the response to these fluctuations in the broad
Hbeta emission. We present here the light curves for the objects in this sample
and the subsequent Hbeta time lags for the nine objects where these
measurements were possible. The Hbeta lag time is directly related to the size
of the broad-line region, and by combining the lag time with the measured width
of the Hbeta emission line in the variable part of the spectrum, we determine
the virial mass of the central supermassive black hole in these nine AGNs. The
absolute calibration of the black hole masses is based on the normalization
derived by Onken et al. We also examine the time lag response as a function of
velocity across the Hbeta line profile for six of the AGNs. The analysis of
four leads to ambiguous results with relatively flat time lags as a function of
velocity. However, SBS 1116+583A exhibits a symmetric time lag response around
the line center reminiscent of simple models for circularly orbiting broad-line
region (BLR) clouds, and Arp 151 shows an asymmetric profile that is most
easily explained by a simple gravitational infall model. Further investigation
will be necessary to fully understand the constraints placed on physical models
of the BLR by the velocity-resolved response in these objects.Comment: 24 pages, 16 figures and 13 tables, submitted to Ap
The Origin of the Universe as Revealed Through the Polarization of the Cosmic Microwave Background
Modern cosmology has sharpened questions posed for millennia about the origin
of our cosmic habitat. The age-old questions have been transformed into two
pressing issues primed for attack in the coming decade: How did the Universe
begin? and What physical laws govern the Universe at the highest energies? The
clearest window onto these questions is the pattern of polarization in the
Cosmic Microwave Background (CMB), which is uniquely sensitive to primordial
gravity waves. A detection of the special pattern produced by gravity waves
would be not only an unprecedented discovery, but also a direct probe of
physics at the earliest observable instants of our Universe. Experiments which
map CMB polarization over the coming decade will lead us on our first steps
towards answering these age-old questions.Comment: Science White Paper submitted to the US Astro2010 Decadal Survey.
Full list of 212 author available at http://cmbpol.uchicago.ed
Observing the Evolution of the Universe
How did the universe evolve? The fine angular scale (l>1000) temperature and
polarization anisotropies in the CMB are a Rosetta stone for understanding the
evolution of the universe. Through detailed measurements one may address
everything from the physics of the birth of the universe to the history of star
formation and the process by which galaxies formed. One may in addition track
the evolution of the dark energy and discover the net neutrino mass.
We are at the dawn of a new era in which hundreds of square degrees of sky
can be mapped with arcminute resolution and sensitivities measured in
microKelvin. Acquiring these data requires the use of special purpose
telescopes such as the Atacama Cosmology Telescope (ACT), located in Chile, and
the South Pole Telescope (SPT). These new telescopes are outfitted with a new
generation of custom mm-wave kilo-pixel arrays. Additional instruments are in
the planning stages.Comment: Science White Paper submitted to the US Astro2010 Decadal Survey.
Full list of 177 author available at http://cmbpol.uchicago.ed
First Results from the Lick AGN Monitoring Project: The Mass of the Black Hole in Arp 151
We have recently completed a 64-night spectroscopic monitoring campaign at
the Lick Observatory 3-m Shane telescope with the aim of measuring the masses
of the black holes in 13 nearby (z < 0.05) Seyfert 1 galaxies with expected
masses in the range ~10^6-10^7 M_sun. We present here the first results from
this project -- the mass of the central black hole in Arp 151. Strong
variability throughout the campaign led to an exceptionally clean Hbeta lag
measurement in this object of 4.25(+0.68/-0.66) days in the observed frame.
Coupled with the width of the Hbeta emission line in the variable spectrum, we
determine a black hole mass of (7.1 +/- 1.2)x10^6 M_sun, assuming the Onken et
al. normalization for reverberation-based virial masses. We also find
velocity-resolved lag information within the Hbeta emission line which clearly
shows infalling gas in the Hbeta-emitting region. Further detailed analysis may
lead to a full model of the geometry and kinematics of broad line region gas
around the central black hole in Arp 151.Comment: 4 pages, 4 figures and 2 tables, accepted for publication in ApJ
Letter
Cognitive and memory training in adults at risk of dementia: A Systematic Review
<p>Abstract</p> <p>Background</p> <p>Effective non-pharmacological cognitive interventions to prevent Alzheimer's dementia or slow its progression are an urgent international priority. The aim of this review was to evaluate cognitive training trials in individuals with mild cognitive impairment (MCI), and evaluate the efficacy of training in memory strategies or cognitive exercises to determine if cognitive training could benefit individuals at risk of developing dementia.</p> <p>Methods</p> <p>A systematic review of eligible trials was undertaken, followed by effect size analysis. Cognitive training was differentiated from other cognitive interventions not meeting generally accepted definitions, and included both cognitive exercises and memory strategies.</p> <p>Results</p> <p>Ten studies enrolling a total of 305 subjects met criteria for cognitive training in MCI. Only five of the studies were randomized controlled trials. Meta-analysis was not considered appropriate due to the heterogeneity of interventions. Moderate effects on memory outcomes were identified in seven trials. Cognitive exercises (relative effect sizes ranged from .10 to 1.21) may lead to greater benefits than memory strategies (.88 to -1.18) on memory.</p> <p>Conclusions</p> <p>Previous conclusions of a lack of efficacy for cognitive training in MCI may have been influenced by not clearly defining the intervention. Our systematic review found that cognitive exercises can produce moderate-to-large beneficial effects on memory-related outcomes. However, the number of high quality RCTs remains low, and so further trials must be a priority. Several suggestions for the better design of cognitive training trials are provided.</p
- …