144 research outputs found
Approaching the Heisenberg limit in an atom laser
We present experimental and theoretical results showing the improved beam quality and reduced divergence
of an atom laser produced by an optical Raman transition, compared to one produced by an rf transition. We
show that Raman outcoupling can eliminate the diverging lens effect that the condensate has on the outcoupled
atoms. This substantially improves the beam quality of the atom laser, and the improvement may be greater
than a factor of 10 for experiments with tight trapping potentials. We show that Raman outcoupling can
produce atom lasers whose quality is only limited by the wave function shape of the condensate that produces
them, typically a factor of 1.3 above the Heisenberg limit
A detector for continuous measurement of ultra-cold atoms in real time
We present the first detector capable of recording high-bandwidth real time
atom number density measurements of a Bose Einstein condensate. Based on a
two-color Mach-Zehnder interferometer, our detector has a response time that is
six orders of magnitude faster than current detectors based on CCD cameras
while still operating at the shot-noise limit. With this minimally destructive
system it may be possible to implement feedback to stabilize a Bose-Einstein
condensate or an atom laser.Comment: 3 pages, 3 figures, submitted to optics letter
Visual Attention to Fake News Flags in Social Media News Posts: An Eye Tracking Study
Given the widespread prevalence of fake news on social media, fake news warnings can play a decisive role in combating misinformation. However, research is still debating the extent to which readers of news on social media heed fake news warnings, which is important to evaluate their effectiveness. In this work, we focus on fake news flags with color gradients from green (verification) to red (warning) and investigate conditions under which they receive visual attention. In an eye tracking experiment, we assigned fake news flags to three social media post elements (user, source, news article) and manipulated the number of fake news flags that indicate a warning or verification. Our results reveal that fake news flags for the news article receive more visual attention than those for the user or source. In addition, we provide evidence that confirmation bias moderates the effect of unique flags (warning or verification) on visual attention
Regions of beta 2 and beta 4 responsible for differences between the steady state dose-response relationships of the alpha 3 beta 2 and alpha 3 beta 4 neuronal nicotinic receptors
We constructed chimeras of the rat beta 2 and beta 4 neuronal nicotinic subunits to locate the regions that contribute to differences between the acetylcholine (ACh) dose-response relationships of the alpha 3 beta 2 and alpha 3 beta 4 receptors. Expressed in Xenopus oocytes, the alpha 3 beta 2 receptor displays an EC50 for ACh approximately 20-fold less than the EC50 of the alpha 3 beta 4 receptor. The apparent Hill slope (n(app)) of alpha 3 beta 2 is near one whereas the alpha 3 beta 4 receptor displays an n(app) near two. Substitutions within the first 120 residues convert the EC50 for ACh from one wild-type value to the other. Exchanging just beta 2:104-120 for the corresponding region of beta 4 shifts the EC50 of ACh dose-response relationship in the expected direction but does not completely convert the EC50 of the dose- response relationship from one wild-type value to the other. However, substitutions in the beta 2:104-120 region do account for the relative sensitivity of the alpha 3 beta 2 receptor to cytisine, tetramethylammonium, and ACh. The expression of beta 4-like (strong) cooperativity requires an extensive region of beta 4 (beta 4:1-301). Relatively short beta 2 substitutions (beta 2:104-120) can reduce cooperativity to beta 2-like values. The results suggest that amino acids within the first 120 residues of beta 2 and the corresponding region of beta 4 contribute to an agonist binding site that bridges the alpha and beta subunits in neuronal nicotinic receptors
Investigation and comparison of multi-state and two-state atom laser output-couplers
We investigate the spatial structure and temporal dynamics created in a
Bose-Einstein condensate (BEC) by radio-frequency (RF) atom laser
output-couplers using a one-dimensional mean-field model. We compare the
behavior of a `pure' two-state atom laser to the multi-level systems
demonstrated in laboratories. In particular, we investigate the peak
homogeneous output flux, classical fluctuations in the beam and the onset of a
bound state which shuts down the atom laser output.Comment: 9 pages, 8 figure
Pulsed pumping of a Bose-Einstein condensate
In this work, we examine a system for coherent transfer of atoms into a
Bose-Einstein condensate. We utilize two spatially separate Bose-Einstein
condensates in different hyperfine ground states held in the same dc magnetic
trap. By means of a pulsed transfer of atoms, we are able to show a clear
resonance in the timing of the transfer, both in temperature and number, from
which we draw conclusions about the underlying physical process. The results
are discussed in the context of the recently demonstrated pumped atom laser.Comment: 5 pages, 5 figures, published in Physical Review
ProMoEE - A lightweight web editor supporting study research on process models
Process models are not only used for the sole documentation of the numerous processes in an organization. Among others, they are essential artifacts in the context of service-oriented computing. Hence, high quality process models are the enabler for streamlining, prediction, and automation in many fields (e.g., industrial production). Therefore, a proper and effective comprehension of process models and knowledge about factors influencing the creation of such models constitutes a key criterion for this endeavor. The collection and analysis of data in scientific studies help to understand the objective and subjective factors influencing process model creation and comprehension. This work presents an editor for the definition, execution, and analysis of studies in the context of process model creation and comprehension. The editor features a clean design and allows for a fast implementation for conducting and reporting study research, while ensuring the collection of high-quality data
Achieving peak brightness in an atom laser
In this paper we present experimental results and theory on the first
continuous (long pulse) Raman atom laser. The brightness that can be achieved
with this system is three orders of magnitude greater than has been previously
demonstrated in any other continuously outcoupled atom laser. In addition, the
energy linewidth of a continuous atom laser can be made arbitrarily narrow
compared to the mean field energy of a trapped condensate. We analyze the flux
and brightness of the atom laser with an analytic model that shows excellent
agreement with experiment with no adjustable parameters.Comment: 4 pages, 4 black and white figures, submitted to Physical Revie
A multibeam atom laser: coherent atom beam splitting from a single far detuned laser
We report the experimental realisation of a multibeam atom laser. A single
continuous atom laser is outcoupled from a Bose-Einstein condensate (BEC) via
an optical Raman transition. The atom laser is subsequently split into up to
five atomic beams with slightly different momenta, resulting in multiple,
nearly co-propagating, coherent beams which could be of use in interferometric
experiments. The splitting process itself is a novel realization of Bragg
diffraction, driven by each of the optical Raman laser beams independently.
This presents a significantly simpler implementation of an atomic beam
splitter, one of the main elements of coherent atom optics
PoN-S : a systematic approach for applying the Physics of Notation (PoN)
Visual Modeling Languages (VMLs) are important instruments of communication between modelers and stakeholders. Thus, it is important to provide guidelines for designing VMLs. The most widespread approach for analyzing and designing concrete syntaxes for VMLs is the so-called Physics of Notation (PoN). PoN has been successfully applied in the analysis of several VMLs. However, despite its popularity, the application of PoN principles for designing VMLs has been limited. This paper presents a systematic approach for applying PoN in the design of the concrete syntax of VMLs. We propose here a design process establishing activities to be performed, their connection to PoN principles, as well as criteria for grouping PoN principles that guide this process. Moreover, we present a case study in which a visual notation for representing Ontology Pattern Languages is designed
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