5,312 research outputs found
Using Adobe Flash Lite on mobile phones for psychological research: reaction time measurement reliability and inter-device variability
Mobile telephones have significant potential for use in psychological research, possessing unique characteristics—not least their ubiquity—that may make them useful tools for psychologists. We examined whether it is possible to measure reaction times (RTs) accurately using Adobe Flash Lite on mobile phones. We ran simple and choice RT experiments on two widely available mobile phones, a Nokia 6110 Navigator and a Sony Ericsson W810i, using a wireless application protocol (WAP) connection to access the Internet from the devices. RTs were compared within subjects with those obtained using a Linux-based millisecond-accurate measurement system. Results show that measured RTs were significantly longer on mobile devices, and that overall RTs and distribution of RTs varied across device
The steady-state assumption in oscillating and growing systems
The steady-state assumption, which states that the production and consumption of metabolites inside the cell are balanced, is one of the key aspects that makes an efficient analysis of genome-scale metabolic networks possible. It can be motivated from two different perspectives. In the time-scales perspective, we use the fact that metabolism is much faster than other cellular processes such as gene expression. Hence, the steady-state assumption is derived as a quasi-steady-state approximation of the metabolism that adapts to the changing cellular conditions. In this article we focus on the second perspective, stating that on the long run no metabolite can accumulate or deplete. In contrast to the first perspective it is not immediately clear how this perspective can be captured mathematically and what assumptions are required to obtain the steady-state condition. By presenting a mathematical framework based on the second perspective we demonstrate that the assumption of steady-state also applies to oscillating and growing systems without requiring quasi-steady-state at any time point. However, we also show that the average concentrations may not be compatible with the average fluxes. In summary, we establish a mathematical foundation for the steady-state assumption for long time periods that justifies its successful use in many applications. Furthermore, this mathematical foundation also pinpoints unintuitive effects in the integration of metabolite concentrations using nonlinear constraints into steady-state models for long time periods
Star-forming regions of the Aquila rift cloud complex. II. Turbulence in molecular cores probed by NH3 emission
(Abridged) Aims. We intend to derive statistical properties of stochastic gas
motion inside the dense low mass star forming molecular cores traced by
NH3(1,1) and (2,2) emission lines. Methods. We use the spatial two-point
autocorrelation (ACF) and structure functions calculated from maps of the
radial velocity fields. Results. We find oscillating ACFs which eventually
decay to zero with increasing lags on scales of 0.04 <= l <= 0.5 pc. The
current paradigm supposes that the star formation process is controlled by the
interplay between gravitation and turbulence, the latter preventing molecular
cores from a rapid collapse due to their own gravity. Thus, oscillating ACFs
may indicate a damping of the developed turbulent flows surrounding the dense
but less turbulent core - a transition to dominating gravitational forces and,
hence, to gravitational collapse.Comment: 11 pages, 16 figures, 3 tables, to be published in Astronomy and
Astrophysic
An empirical initial-final mass relation from hot, massive white dwarfs in NGC 2168 (M35)
The relation between the zero-age main sequence mass of a star and its
white-dwarf remnant (the initial-final mass relation) is a powerful tool for
exploration of mass loss processes during stellar evolution. We present an
empirical derivation of the initial-final mass relation based on spectroscopic
analysis of seven massive white dwarfs in NGC 2168 (M35). Using an internally
consistent data set, we show that the resultant white dwarf mass increases
monotonically with progenitor mass for masses greater than 4 solar masses, one
of the first open clusters to show this trend. We also find two massive white
dwarfs foreground to the cluster that are otherwise consistent with cluster
membership. These white dwarfs can be explained as former cluster members
moving steadily away from the cluster at speeds of <~0.5 km/s since their
formation and may provide the first direct evidence of the loss of white dwarfs
from open clusters. Based on these data alone, we constrain the upper mass
limit of WD progenitors to be >=5.8 solar masses at the 90% confidence level
for a cluster age of 150 Myr.Comment: 14 pages, 3 figures. Accepted for publication in the Astrophysical
Journal Letters. Contains some acknowledgements not in accepted version (for
space reasons), otherwise identical to accepted versio
Solar-Like Cycle in Asymptotic Giant Branch Stars
I propose that the mechanism behind the formation of concentric semi-periodic
shells found in several planetary nebulae (PNs) and proto-PNs, and around one
asymptotic giant branch (AGB) star, is a solar-like magnetic activity cycle in
the progenitor AGB stars. The time intervals between consecutive ejection
events is about 200-1,000 years, which is assumed to be the cycle period (the
full magnetic cycle can be twice as long, as is the 22-year period in the sun).
The magnetic field has no dynamical effects; it regulates the mass loss rate by
the formation of magnetic cool spots. The enhanced magnetic activity at the
cycle maximum results in more magnetic cool spots, which facilitate the
formation of dust, hence increasing the mass loss rate. The strong magnetic
activity implies that the AGB star is spun up by a companion, via a tidal or
common envelope interaction. The strong interaction with a stellar companion
explains the observations that the concentric semi-periodic shells are found
mainly in bipolar PNs.Comment: 10 pages, submitted to Ap
Pulsation Period Changes as a Tool to Identify Pre-Zero Age Horizontal Branch Stars
One of the most dramatic events in the life of a low-mass star is the He
flash, which takes place at the tip of the red giant branch (RGB) and is
followed by a series of secondary flashes before the star settles into the
zero-age horizontal branch (ZAHB). Yet, no stars have been positively
identified in this key evolutionary phase, mainly for two reasons: first, this
pre-ZAHB phase is very short compared to other major evolutionary phases in the
life of a star; and second, these pre-ZAHB stars are expected to overlap the
loci occupied by asymptotic giant branch (AGB), HB and RGB stars observed in
the color-magnitude diagram (CMD). We investigate the possibility of detecting
these stars through stellar pulsations, since some of them are expected to
rapidly cross the Cepheid/RR Lyrae instability strip in their route from the
RGB tip to the ZAHB, thus becoming pulsating stars along the way. As a
consequence of their very high evolutionary speed, some of these stars may
present anomalously large period change rates. We constructed an extensive grid
of stellar models and produced pre-ZAHB Monte Carlo simulations appropriate for
the case of the Galactic globular cluster M3 (NGC 5272), where a number of RR
Lyrae stars with high period change rates are found. Our results suggest that
some -- but certainly not all -- of the RR Lyrae stars in M3 with large period
change rates are in fact pre-ZAHB pulsators.Comment: Conference Proceedings HELAS Workshop on 'Synergies between solar and
stellar modelling', Rome, June 2009, Astrophys. Space Sci., in the pres
Comment on "Critical properties of highly frustrated pyrochlore antiferromagnets"
We argue that the analysis of Reimers {\it et al.} [ Phys. Rev. B {\bf 45},
7295 (1992)] of their Monte Carlo data on the Heisenberg pyrochlore
antiferromagnet, which suggests a new universality class, is not conclusive. By
re-analysis of their data, we demonstrate asymptotic volume dependence in some
thermodynamic quantities, which suggests the possibility that the transition
may be first order.Comment: 5 pages (RevTex 3.0), 3 figures available upon request, CRPS-93-0
Asymmetry in the Qy Fluorescence and Absorption Spectra of Chlorophyll <i>a</i> Pertaining to Exciton Dynamics.
Significant asymmetry found between the high-resolution Q y emission and absorption spectra of chlorophyll-a is herein explained, providing basic information needed to understand photosynthetic exciton transport and photochemical reactions. The Q y spectral asymmetry in chlorophyll has previously been masked by interference in absorption from the nearby Q x transition, but this effect has recently been removed using extensive quantum spectral simulations or else by analytical inversion of absorption and magnetic circular dichroism data, allowing high-resolution absorption information to be accurately determined from fluorescence-excitation spectra. To compliment this, here, we measure and thoroughly analyze the high-resolution differential fluorescence line narrowing spectra of chlorophyll-a in trimethylamine and in 1-propanol. The results show that vibrational frequencies often change little between absorption and emission, yet large changes in line intensities are found, this effect also being strongly solvent dependent. Among other effects, the analysis in terms of four basic patterns of Duschinsky-rotation matrix elements, obtained using CAM-B3LYP calculations, predicts that a chlorophyll-a molecule excited into a specific vibrational level, may, without phase loss or energy relaxation, reemit the light over a spectral bandwidth exceeding 1,000 cm-1 (0.13 eV) to influence exciton-transport dynamics
Methanol as a tracer of fundamental constants
The methanol molecule CH3OH has a complex microwave spectrum with a large
number of very strong lines. This spectrum includes purely rotational
transitions as well as transitions with contributions of the internal degree of
freedom associated with the hindered rotation of the OH group. The latter takes
place due to the tunneling of hydrogen through the potential barriers between
three equivalent potential minima. Such transitions are highly sensitive to
changes in the electron-to-proton mass ratio, mu = m_e/m_p, and have different
responses to mu-variations. The highest sensitivity is found for the mixed
rotation-tunneling transitions at low frequencies. Observing methanol lines
provides more stringent limits on the hypothetical variation of mu than ammonia
observation with the same velocity resolution. We show that the best quality
radio astronomical data on methanol maser lines constrain the variability of mu
in the Milky Way at the level of |Delta mu/mu| < 28x10^{-9} (1sigma) which is
in line with the previously obtained ammonia result, |Delta mu/mu| < 29x10^{-9}
(1\sigma). This estimate can be further improved if the rest frequencies of the
CH3OH microwave lines will be measured more accurately.Comment: 7 pages, 1 table, 1 figure. Accepted for publication in Ap
Star-forming regions of the Aquila rift cloud complex. I. NH3 tracers of dense molecular cores
(Abridged) Aims. In the present part of our survey we search for ammonia
emitters in the Aquila rift complex which trace the densest regions of
molecular clouds. Methods. From a CO survey carried out with the Delingha 14-m
telescope we selected ~150 targets for observations in other molecular lines.
Here we describe the mapping observations in the NH3(1,1) and (2,2) inversion
lines of the first 49 sources performed with the Effelsberg 100-m telescope.
Results. The NH3(1,1) and (2,2) emission lines are detected in 12 and 7
sources, respectively. Among the newly discovered NH3 sources, our sample
includes the following well-known clouds: the starless core L694-2, the Serpens
cloud Cluster B, the Serpens dark cloud L572, the filamentary dark cloud L673,
the isolated protostellar source B335, and the complex star-forming region
Serpens South. Angular sizes between 40" and 80" (~0.04-0.08 pc) are observed
for compact starless cores but as large as 9' (~0.5 pc) for filamentary dark
clouds. The measured kinetic temperatures of the clouds lie between 9K and 18K.
From NH3 excitation temperatures of 3-8K we determine H2 densities with typical
values of ~(0.4-4) 10^4 cm^-3. The masses of the mapped cores range between
~0.05 and ~0.5M_solar. The relative ammonia abundance, X= [NH3]/[H2], varies
from 10^-7 to 5 10^-7 with the mean = (2.7+/-0.6) 10^-7 (estimated from
spatially resolved cores assuming the filling factor eta = 1). In two clouds,
we observe kinematically split NH3 profiles separated by ~1 km/s. The splitting
is most likely due to bipolar molecular outflows for one of which we determine
an acceleration of <~ 0.03 km/s/yr. A starless core with significant rotational
energy is found to have a higher kinetic temperature than the other ones which
is probably caused by magnetic energy dissipation.Comment: 28 pages, 22 figures, 6 tables, accepted for publication in A&
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