University of Vienna

About: University of Vienna is a education organization based out in Vienna, Austria. It is known for research contribution in the topics: Population & Context (language use). The organization has 44686 authors who have published 95840 publications receiving 2907492 citations.

An experimental test of non-local realism

Abstract: Most working scientists hold fast to the concept of ‘realism’—a viewpoint according to which an external reality exists independent of observation. But quantum physics has shattered some of our cornerstone beliefs. According to Bell’s theorem, any theory that is based on the joint assumption of realism and locality (meaning that local events cannot be affected by actions in space-like separated regions) is at variance with certain quantum predictions. Experiments with entangled pairs of particles have amply confirmed these quantum predictions, thus rendering local realistic theories untenable. Maintaining realism as a fundamental concept would therefore necessitate the introduction of ‘spooky’ actions that defy locality. Here we show by both theory and experiment that a broad and rather reasonable class of such non-local realistic theories is incompatible with experimentally observable quantum correlations. In the experiment, we measure previously untested correlations between two entangled photons, and show that these correlations violate an inequality proposed by Leggett for non-local realistic theories. Our result suggests that giving up the concept of locality is not sufficient to be consistent with quantum experiments, unless certain intuitive features of realism are abandoned. Most of us, most of the time, can get along in life and in science with a sturdy concept of what is 'real'. Generally speaking, an external reality exists independent of observation. But in the world of quantum physics, where individual events are predicted only in terms of probabilities, this will not do. According to Bell's theorem, any theory based on the joint assumption of realism and locality (meaning that local events cannot be affected by actions in space-like separated regions) is at variance with certain quantum predictions. Previous work with entangled pairs of particles has confirmed these quantum predictions, rendering local realistic theories untenable. Maintaining physical realism as a fundamental concept would therefore require the introduction of 'spooky' locality-defying actions. A new study combing experiment and theory now shows that a broad and rather reasonable class of such non-local realistic theories is incompatible with observed quantum correlations. This suggests that any future extension of quantum theory, if it is to agree with the experiments, must abandon certain features of realistic descriptions. Giving up the concept of locality is not sufficiently 'unreal'. According to Bell's theorem, any theory that is based on the joint assumption of realism and locality is at variance with certain quantum predictions. Here, theory and experiment agree that a class of such non-local realistic theories is incompatible with experimentally observable quantum correlations, suggesting that giving up the concept of locality is not sufficient to be consistent with quantum experiments, unless certain intuitive features of realism are abandoned.

Communication with spatially modulated light through turbulent air across Vienna

Abstract: Transverse spatial modes of light offer a large state-space with interesting physical properties. For exploiting these special modes in future long-distance experiments, the modes will have to be transmitted over turbulent free-space links. Numerous recent lab-scale experiments have found significant degradation in the mode quality after transmission through simulated turbulence and consecutive coherent detection. Here, we experimentally analyze the transmission of one prominent class of spatial modes?orbital-angular momentum (OAM) modes?through 3 km of strong turbulence over the city of Vienna. Instead of performing a coherent phase-dependent measurement, we employ an incoherent detection scheme, which relies on the unambiguous intensity patterns of the different spatial modes. We use a pattern recognition algorithm (an artificial neural network) to identify the characteristic mode patterns displayed on a screen at the receiver. We were able to distinguish between 16 different OAM mode superpositions with only a ?1.7% error rate and to use them to encode and transmit small grayscale images. Moreover, we found that the relative phase of the superposition modes is not affected by the atmosphere, establishing the feasibility for performing long-distance quantum experiments with the OAM of photons. Our detection method works for other classes of spatial modes with unambiguous intensity patterns as well, and can be further improved by modern techniques of pattern recognition.

Genome analysis: RNA recognition motif (RRM) and K homology (KH) domain RNA-binding proteins from the flowering plant Arabidopsis thaliana

Abstract: Regulation of gene expression at the post-transcriptional level is mainly achieved by proteins containing well-defined sequence motifs involved in RNA binding. The most widely spread motifs are the RNA recognition motif (RRM) and the K homology (KH) domain. In this article, we survey the complete Arabidopsis thaliana genome for proteins containing RRM and KH RNA-binding domains. The Arabidopsis genome encodes 196 RRM-containing proteins, a more complex set than found in Caenorhabditis elegans and Drosophila melanogaster. In addition, the Arabidopsis genome contains 26 KH domain proteins. Most of the Arabidopsis RRM-containing proteins can be classified into structural and/or functional groups, based on similarity with either known metazoan or Arabidopsis proteins. Approximately 50% of Arabidopsis RRM-containing proteins do not have obvious homologues in metazoa, and for most of those that are predicted to be orthologues of metazoan proteins, no experimental data exist to confirm this. Additionally, the function of most Arabidopsis RRM proteins and of all KH proteins is unknown. Based on the data presented here, it is evident that among all eukaryotes, only those RNA-binding proteins that are involved in the most essential processes of post-transcriptional gene regulation are preserved in structure and, most probably, in function. However, the higher complexity of RNA-binding proteins in Arabidopsis, as evident in groups of SR splicing factors and poly(A)-binding proteins, may account for the observed differences in mRNA maturation between plants and metazoa. This survey provides a first systematic analysis of plant RNA-binding proteins, which may serve as a basis for functional characterisation of this important protein group in plants.

Mild and moderate aortic stenosis. Natural history and risk stratification by echocardiography.

Abstract: AIMS To define the natural history and predictors of outcome in mild and moderate aortic stenosis (AS). METHODS AND RESULTS One hundred and seventy-six consecutive asymptomatic patients (73 women, age 58+/-19 years) with mild to moderate AS (jet velocity 2.5 to 3.9m/s) were followed for 48+/-19 months. Haemodynamic progression and clinical outcome was analysed. Event-free survival with end-points defined as death (n=34) or aortic valve surgery (n=33), was 95+/-2%, 75+/-3% and 60+/-5% at 1, 3 and 5 years, respectively. Both, cardiac and non-cardiac mortality were significantly increased, resulting in a 1.8 times higher mortality than expected (P<0.005). By multivariate analysis, moderate to severe aortic valve calcification, coronary artery disease (CAD) and peak jet velocity were independent predictors of outcome. Event-free survival for patients with moderate or severe valve calcification was 92+/-4%, 61+/-7% and 42+/-7% at 1, 3 and 5 years versus 100%, 90+/-4% and 82+/-5% for patients with no or mild calcification. Patients with calcified aortic valves, CAD or with an event had a significantly faster haemodynamic progression. Of 129 patients with a follow-up echocardiographic exam, 59 (46%) developed severe stenosis during follow-up. CONCLUSION Outcome of mild and moderate AS is worse than commonly assumed. Rapid progression and excess mortality have to be considered. Significant valve calcification, CAD and rapid progression of aortic jet velocity indicate poor outcome. Patients with these characteristics may require closer follow-up than generally assumed.

Mutational meltdowns in sexual populations

Abstract: Although it is widely acknowledged that the gradual accumulation of mildly deleterious mutations is an important source of extinction for asexual populations, it is generally assumed that this process is of little relevance to sexual species. Here we present results, based on computer simulations and supported by analytical approximations, that indicate that mutation accumulation in small, random-mating monoecious populations can lead to mean extinction times less than a few hundred to a few thousand generations. Unlike the situation in obligate asexuals in which the mean time to extinction (te ) increases more slowly than linearly with the population carrying capacity (K), te increases approximately exponentially with K in outcrossing sexual populations. The mean time to extinction for obligately selfing populations is shown to be equivalent to that for asexual populations of the same size, but with half the mutation rate and twice the mutational effect; this suggests that obligate selfing, like obligate asexuality, is inviable as a long-term reproductive strategy. Under all mating systems, the mean time to extinction increases relatively slowly with the logarithm of fecundity, and mutations with intermediate effects (similar to those observed empirically) cause the greatest risk of extinction. Because our analyses ignore sources of demographic and environmental stochasticity, which have synergistic effects that exacerbate the accumulation of deleterious mutations, our results should yield liberal upper bounds to the mean time to extinction caused by mutational degradation. Thus, deleterious mutation accumulation cannot be ruled out generally as a significant source of extinction vulnerability in small sexual populations or as a selective force influencing mating-system evolution.