2,116 research outputs found
Microlensing towards M31 with MDM data
We report the final analysis of a search for microlensing events in the
direction of the Andromeda galaxy, which aimed to probe the MACHO composition
of the M31 halo using data collected during the 1998-99 observational campaign
at the MDM observatory. In a previous paper, we discussed the results from a
first set of observations. Here, we deal with the complete data set, and we
take advantage of some INT observations in the 1999-2000 seasons. This merging
of data sets taken by different instruments turns out to be very useful, the
study of the longer baseline available allowing us to test the uniqueness
characteristic of microlensing events. As a result, all the candidate
microlensing events previously reported turn out to be variable stars. We
further discuss a selection based on different criteria, aimed at the detection
of short--duration events. We find three candidates whose positions are
consistent with self--lensing events, although the available data do not allow
us to conclude unambiguously that they are due to microlensing.Comment: Accepted for publication in Astronomy and Astrophysic
Multiple Loop Self-Triggered Model Predictive Control for Network Scheduling and Control
We present an algorithm for controlling and scheduling multiple linear
time-invariant processes on a shared bandwidth limited communication network
using adaptive sampling intervals. The controller is centralized and computes
at every sampling instant not only the new control command for a process, but
also decides the time interval to wait until taking the next sample. The
approach relies on model predictive control ideas, where the cost function
penalizes the state and control effort as well as the time interval until the
next sample is taken. The latter is introduced in order to generate an adaptive
sampling scheme for the overall system such that the sampling time increases as
the norm of the system state goes to zero. The paper presents a method for
synthesizing such a predictive controller and gives explicit sufficient
conditions for when it is stabilizing. Further explicit conditions are given
which guarantee conflict free transmissions on the network. It is shown that
the optimization problem may be solved off-line and that the controller can be
implemented as a lookup table of state feedback gains. Simulation studies which
compare the proposed algorithm to periodic sampling illustrate potential
performance gains.Comment: Accepted for publication in IEEE Transactions on Control Systems
Technolog
Threshold concentration for H blistering in defect free W
Lattice distortion induced by high concentration of H is believed to be
precursor of H blistering in single crystalline W (SCW) during H isotope
irradiation. However, the critical H concentration needed to trigger
bond-breaking of metal atoms presents a challenge to measure. Using density
functional theory, we have calculated the formation energy of a vacancy and a
self-interstitial atom (SIA) in supersaturated defect-free SCW with various H
concentrations. When the ratio of H:W exceeds 1:2, the formation of both
vacancies and self-interstitials becomes exothermic, meaning that spontaneous
formation of micro-voids which can accommodate molecular H2 will occur.
Molecular H2 is not allowed to form, and it is not needed either at the very
initial stage of H blistering in SCW. With supersaturated H, the free volume at
the vacancy or SIA is greatly smeared out with severe lattice distortion and
more H can be trapped than in the dilute H case.Comment: 13 pages, 4 figure
Sputtering yields exceeding 1000 by 80keV Xe irradiation of Au nanorods
Using experiments and computer simulations, we find that 80 keV Xe ion irradiation of Au nanorods can produce sputtering yields exceeding 1000, which to our knowledge are the highest yields reported for sputtering by single ions in the nuclear collision regime. This value is enhanced by more than an order of magnitude compared to the same irradiation of flat Au surfaces. Using MD simulations, we show that the very high yield can be understood as a combination of enhanced yields due to low incoming angles at the sides of the nanowire, as well as the high surface-to-volume ratio causing enhanced explosive sputtering from heat spikes. We also find, both in experiments and simulations, that channeling has a strong effect on the sputtering yield: if the incoming beam happens to be aligned with a crystal axis of the nanorod, the yield can decrease to about 100
Cognitive ability in young adulthood predicts risk of early-onset dementia in Finnish men
Objective To test if the Finnish Defence Forces Basic Intellectual Ability Test scores at 20.1 years predicted risk of organic dementia or Alzheimer disease (AD). Methods Dementia was defined as inpatient or outpatient diagnosis of organic dementia or AD risk derived from Hospital Discharge or Causes of Death Registers in 2,785 men from the Helsinki Birth Cohort Study, divided based on age at first diagnosis into early onset (= 65 years). The Finnish Defence Forces Basic Intellectual Ability Test comprises verbal, arithmetic, and visuospatial subtests and a total score (scores transformed into a mean of 100 and SD of 15). We used Cox proportional hazard models and adjusted for age at testing, childhood socioeconomic status, mother's age at delivery, parity, participant's birthweight, education, and stroke or coronary heart disease diagnosis. Results Lower cognitive ability total and verbal ability (hazard ratio [HR] per 1 SD disadvantage > 1.69, 95% confidence interval [CI] 1.01-2.63) scores predicted higher early-onset any dementia risk across the statistical models; arithmetic and visuospatial ability scores were similarly associated with early-onset any dementia risk, but these associations weakened after covariate adjustments (HR per 1 SD disadvantage > 1.57, 95% CI 0.96-2.57). All associations were rendered non-significant when we adjusted for participant's education. Cognitive ability did not predict late-onset dementia risk. Conclusion These findings reinforce previous suggestions that lower cognitive ability in early life is a risk factor for early-onset dementia.Peer reviewe
Association between breastfeeding and better preserved cognitive ability in an elderly cohort of Finnish men
Background. Being breastfed in infancy has been shown to benefit neurodevelopment. However, whether the benefits persist to old age remains unclear. Methods. We examined the associations between breastfeeding and its duration on cognitive ability in young adulthood and old age, and on aging-related cognitive change over five decades. In total, 931 men from the Helsinki Birth Cohort Study born in 1934-1944 in Finland took the Finnish Defence Forces Basic Intellectual Ability Test (total and verbal, arithmetic and visuospatial subtest scores) twice, at ages 20.2 and 67.9 years, and had data on breastfeeding (yes v. no) and its duration ('never breastfed', 'up to 3', '3 to 6' and 6 or more months'). Linear and mixed model regressions tested the associations. Results. At 20.2 years, breastfed men had higher cognitive ability total and visuospatial subtest scores [mean differences (MDs) ranged between 3.0-3.9, p values <0.013], and its longer duration predicted higher cognitive ability total and arithmetic and visuospatial subtest scores (MDs ranged between 3.0 and 4.8, p values <0.039). At 67.9 years, breastfed men had higher total cognitive ability and all subtest scores (MDs ranged between 2.6 and 3.4, p values <0.044) and its longer duration predicted all cognitive ability scores (MDs ranged between 3.1 and 4.7, p values <0.050). Verbal subtest scores decreased over five decades in men who were never breastfed or were breastfed for 3 months or less, and increased in those breastfed for longer than 3 months. Conclusions. Neurodevelopmental advantages of breastfeeding and its longer duration persist into old age, and longer duration of breastfeeding may benefit aging-related change, particularly in verbal reasoning ability.Peer reviewe
On the structure and oxygen transmission rate of biodegradable cellulose nanobarriers
Cellulose nanofibrils have been proposed for novel barrier concepts, based on their capability to form smooth, strong and transparent films, with high oxygen barrier properties. A series of cellulose-based films were manufactured and tested with respect to their oxygen transmission rate (OTR) capabilities. The obtained OTR levels were considerably better than the levels recommended for packaging applications. Part of the nanofibrillated material applied in this study was produced with 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) mediated oxidation as pretreatment. Films made of TEMPO-pretreated samples yielded lower OTR values. The minimum obtained OTR value was 3.0 mL m-2 day-1 atm-1 with a corresponding oxygen permeability of 0.04 mL mm m-2 day-1 atm-1, tested at 50% relative humidity. The good barrier properties are due to the compact and dense structure of the films, as revealed by field-emission scanning electron microscopy. A relationship between OTR and the structure of the corresponding nanofibril-based films was confirmed
Spatial distributions and seasonal cycles of aerosols in India and China seen in global climate-aerosol model
Peer reviewe
Search for exoplanets in M31 with pixel-lensing and the PA-99-N2 event revisited
Several exoplanets have been detected towards the Galactic bulge with the
microlensing technique. We show that exoplanets in M31 may also be detected
with the pixel-lensing method, if telescopes making high cadence observations
of an ongoing microlensing event are used. Using a Monte Carlo approach we find
that the mean mass for detectable planetary systems is about .
However, even small mass exoplanets () can cause
significant deviations, which are observable with large telescopes. We
reanalysed the POINT-AGAPE microlensing event PA-99-N2. First, we test the
robustness of the binary lens conclusion for this light curve. Second, we show
that for such long duration and bright microlensing events, the efficiency for
finding planetary-like deviations is strongly enhanced with respect to that
evaluated for all planetary detectable events.Comment: 14 pages, 8 figures. Paper presented at the "II Italian-Pakistani
Workshop on Relativistic Astrophysics, Pescara, July 8-10, 2009. To be
published in a special issue of General Relativity and Gravitation (eds. F.
De Paolis, G.F.R. Ellis, A. Qadir and R. Ruffini
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