1,540 research outputs found
Nonprint Materials: A Definition and Some Practical Considerations on Their Maintenance
published or submitted for publicatio
Prospects for studies of the free fall and gravitational quantum states of antimatter
Different experiments are ongoing to measure the effect of gravity on cold
neutral antimatter atoms such as positronium, muonium and antihydrogen. Among
those, the project GBAR in CERN aims to measure precisely the gravitational
fall of ultracold antihydrogen atoms. In the ultracold regime, the interaction
of antihydrogen atoms with a surface is governed by the phenomenon of quantum
reflection which results in bouncing of antihydrogen atoms on matter surfaces.
This allows the application of a filtering scheme to increase the precision of
the free fall measurement. In the ultimate limit of smallest vertical
velocities, antihydrogen atoms are settled in gravitational quantum states in
close analogy to ultracold neutrons (UCNs). Positronium is another neutral
system involving antimatter for which free fall under gravity is currently
being investigated at UCL. Building on the experimental techniques under
development for the free fall measurement, gravitational quantum states could
also be observed in positronium. In this contribution, we review the status of
the ongoing experiments and discuss the prospects of observing gravitational
quantum states of antimatter and their implications.Comment: This work reviews contributions made at the GRANIT 2014 workshop on
prospects for the observation of the free fall and gravitational quantum
states of antimatte
Hierarchy and Feedback in the Evolution of the E. coli Transcription Network
The E.coli transcription network has an essentially feedforward structure,
with, however, abundant feedback at the level of self-regulations. Here, we
investigate how these properties emerged during evolution. An assessment of the
role of gene duplication based on protein domain architecture shows that (i)
transcriptional autoregulators have mostly arisen through duplication, while
(ii) the expected feedback loops stemming from their initial cross-regulation
are strongly selected against. This requires a divergent coevolution of the
transcription factor DNA-binding sites and their respective DNA cis-regulatory
regions. Moreover, we find that the network tends to grow by expansion of the
existing hierarchical layers of computation, rather than by addition of new
layers. We also argue that rewiring of regulatory links due to
mutation/selection of novel transcription factor/DNA binding interactions
appears not to significantly affect the network global hierarchy, and that
horizontally transferred genes are mainly added at the bottom, as new target
nodes. These findings highlight the important evolutionary roles of both
duplication and selective deletion of crosstalks between autoregulators in the
emergence of the hierarchical transcription network of E.coli.Comment: to appear in PNA
Effects of light and temperature on germination of Pyxidanthera brevifolia Wells (Diapensiaceae)
Pyxidanthera brevifolia is an evergreen semiwoody cushion plant endemic to the Sandhills of North and South Carolina, with the majority of populations occurring on Fort Bragg Military Reservation in North Carolina. Currently the species is listed as Endangered in North Carolina and is designated as a Species at Risk (SAR) by the US Department of Defense. Previous studies have suggested that seeds may not be viable because they failed to germinate under controlled conditions. Our objectives in this study were to attempt germination of Pyxidanthera brevifolia seeds, determine the best temperature conditions for germination, and understand more about germination requirements to aid in future restoration efforts. Using seeds that had been stored at room temperature for six months, we performed a germination experiment at the NCSU Phytotron with six treatments, all combinations of three temperature regimes (low (18 uC day / 14 uC night), medium (22/18 uC), and high (26/ 22 uC)) and two light conditions (light and dark). We monitored the experiment for 13 weeks, recording the number of seeds germinating per dish and the number of days to germination for seeds in each treatment. We found that Pxyidanthera brevifolia produces germinable seeds and that there are significant effects of light and temperature on germination. Highest germination occurred under low temperature and high light conditions (78%); the combination of high temperature and no light produced the lowest germination (6%). Seeds exposed to light germinated significantly earlier at the coolest temperature, compared to medium and high temperatures. These results indicate that it is possible to germinate seeds of this rare plant and suggest that germination of Pyxidanthera brevifolia likely occurs in late fall and is dependent on adequate light availability
Dopaminergic basis for signalling belief updates, but not surprise, and the link to paranoia
Distinguishing between meaningful and meaningless sensory information is fundamental to forming accurate representations of the world. Dopamine is thought to play a central role in processing the meaningful information content of observations, which motivates an agent to update their beliefs about the environment. However, direct evidence for dopamine’s role in human belief updating is lacking. We addressed this question in healthy volunteers who performed a model-based functional magnetic resonance imaging (fMRI) task designed to separate the neural processing of meaningful and meaningless sensory information. We modelled participant behaviour using a normative Bayesian observer model, and used the magnitude of the model-derived belief update following an observation to quantify its meaningful information content. We also acquired positron emission tomography (PET) imaging measures of dopamine function in the same subjects. We show that the magnitude of belief updates about task structure (meaningful information), but not pure sensory surprise (meaningless information), are encoded in midbrain and ventral striatum activity. Using PET we show that the neural encoding of meaningful information is negatively related to dopamine-2/3 receptor availability in the midbrain and dexamphetamine-induced dopamine release capacity in the striatum. Trial-by-trial analysis of task performance indicated that subclinical paranoid ideation is negatively related to behavioural sensitivity to observations carrying meaningful information about the task structure. The findings provide direct evidence implicating dopamine in model-based belief updating in humans, and have implications for understating the pathophysiology of psychotic disorders where dopamine function is disrupted
In situ observation of stress relaxation in epitaxial graphene
Upon cooling, branched line defects develop in epitaxial graphene grown at
high temperature on Pt(111) and Ir(111). Using atomically resolved scanning
tunneling microscopy we demonstrate that these defects are wrinkles in the
graphene layer, i.e. stripes of partially delaminated graphene. With low energy
electron microscopy (LEEM) we investigate the wrinkling phenomenon in situ.
Upon temperature cycling we observe hysteresis in the appearance and
disappearance of the wrinkles. Simultaneously with wrinkle formation a change
in bright field imaging intensity of adjacent areas and a shift in the moire
spot positions for micro diffraction of such areas takes place. The stress
relieved by wrinkle formation results from the mismatch in thermal expansion
coefficients of graphene and the substrate. A simple one-dimensional model
taking into account the energies related to strain, delamination and bending of
graphene is in qualitative agreement with our observations.Comment: Supplementary information: S1: Photo electron emission microscopy and
LEEM measurements of rotational domains, STM data of a delaminated bulge
around a dislocation. S2: Movie with increasing brightness upon wrinkle
formation as in figure 4. v2: Major revision including new experimental dat
Submillimeter Number Counts From Statistical Analysis of BLAST Maps
We describe the application of a statistical method to estimate submillimeter
galaxy number counts from confusion limited observations by the Balloon-borne
Large Aperture Submillimeter Telescope (BLAST). Our method is based on a
maximum likelihood fit to the pixel histogram, sometimes called 'P(D)', an
approach which has been used before to probe faint counts, the difference being
that here we advocate its use even for sources with relatively high
signal-to-noise ratios. This method has an advantage over standard techniques
of source extraction in providing an unbiased estimate of the counts from the
bright end down to flux densities well below the confusion limit. We
specifically analyse BLAST observations of a roughly 10 sq. deg. map centered
on the Great Observatories Origins Deep Survey South (GOODS-S) field. We
provide estimates of number counts at the three BLAST wavelengths, 250, 350,
and 500 microns; instead of counting sources in flux bins we estimate the
counts at several flux density nodes connected with power-laws. We observe a
generally very steep slope for the counts of about -3.7 at 250 microns and -4.5
at 350 and 500 microns, over the range ~0.02-0.5 Jy, breaking to a shallower
slope below about 0.015 Jy at all three wavelengths. We also describe how to
estimate the uncertainties and correlations in this method so that the results
can be used for model-fitting. This method should be well-suited for analysis
of data from the Herschel satellite.Comment: Accepted for publication in the Astrophysical Journal; see associated
data and other papers at http://blastexperiment.info
Methylphenidate and \u3ci\u3eMemory and Attention Adaptation Training\u3c/i\u3e for persistent cognitive symptoms after traumatic brain injury: a randomized, placebo-controlled trial
The purpose of this multicenter, prospective, randomized, placebo-controlled study was to evaluate and compare the efficacy of two cognitive rehabilitation interventions (Memory and Attention Adaptation Training (MAAT) and Attention Builders Training (ABT)), with and without pharmacologic enhancement (i.e., with methylphenidate (MPH) or placebo), for treating persistent cognitive problems after traumatic brain injury (TBI). Adults with a history of TBI at least four months prior to study enrollment with either objective cognitive deficits or subjective cognitive complaints were randomized to receive MPH or placebo and MAAT or ABT, yielding four treatment combinations: MAAT/MPH (N=17), ABT/MPH (N=19), MAAT/placebo (N=17), and ABT/placebo (N=18). Assessments were conducted pre-treatment (baseline) and after six weeks of treatment (post-treatment). Outcome measures included scores on neuropsychological measures and subjective rating scales. Statistical analyses used linear regression models to predict post-treatment scores for each outcome variable by treatment type, adjusting for relevant covariates. Statistically significant (p\u3c0.05) treatment-related improvements in cognitive functioning were found for word list learning (MAAT/placebo\u3eABT/placebo), nonverbal learning (MAAT/MPH\u3eMAAT/placebo and MAAT/MPH\u3eABT/MPH), and auditory working memory and divided attention (MAAT/MPH\u3eABT/MPH). These results suggest that combined treatment with metacognitive rehabilitation (MAAT) and pharmacotherapy (MPH) can improve aspects of attention, episodic and working memory, and executive functioning after TBI
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