934 research outputs found
Analysis of condensed matter physics records in databases: science and technology indicators in condensed matter physics
Reconnaissance of the HR 8799 Exosolar System. II. Astrometry and Orbital Motion
We present an analysis of the orbital motion of the four substellar objects orbiting HR 8799. Our study relies on the published astrometric history of this system augmented with an epoch obtained with the Project 1640 coronagraph with an integral field spectrograph (IFS) installed at the Palomar Hale telescope. We first focus on the intricacies associated with astrometric estimation using the combination of an extreme adaptive optics system (PALM-3000), a coronagraph, and an IFS. We introduce two new algorithms. The first one retrieves the stellar focal plane position when the star is occulted by a coronagraphic stop. The second one yields precise astrometric and spectrophotometric estimates of faint point sources even when they are initially buried in the speckle noise. The second part of our paper is devoted to studying orbital motion in this system. In order to complement the orbital architectures discussed in the literature, we determine an ensemble of likely Keplerian orbits for HR 8799bcde, using a Bayesian analysis with maximally vague priors regarding the overall configuration of the system. Although the astrometric history is currently too scarce to formally rule out coplanarity, HR 8799d appears to be misaligned with respect to the most likely planes of HR 8799bce orbits. This misalignment is sufficient to question the strictly coplanar assumption made by various authors when identifying a Laplace resonance as a potential architecture. Finally, we establish a high likelihood that HR 8799de have dynamical masses below 13 M_(Jup), using a loose dynamical survival argument based on geometric close encounters. We illustrate how future dynamical analyses will further constrain dynamical masses in the entire system
West Antarctic sites for subglacial drilling to test for past ice-sheet collapse
Mass loss from the West Antarctic Ice Sheet (WAIS) is
increasing, and there is concern that an incipient large-scale deglaciation
of the marine basins may already be underway. Measurements of cosmogenic
nuclides in subglacial bedrock surfaces have the potential to establish
whether and when the marine-based portions of the WAIS deglaciated in the
past. However, because most of the bedrock revealed by ice-sheet collapse
would remain below sea level, shielded from the cosmic-ray flux, drill sites
for subglacial sampling must be located in areas where thinning of the
residual ice sheet would expose presently subglacial bedrock surfaces. In
this paper we discuss the criteria and considerations for choosing drill
sites where subglacial samples will provide maximum information about WAIS
extent during past interglacial periods. We evaluate candidate sites in West
Antarctica and find that sites located adjacent to the large marine basins of
West Antarctica will be most diagnostic of past ice-sheet collapse. There are
important considerations for drill site selection on the kilometer scale that
can only be assessed by field reconnaissance. As a case study of these
considerations, we describe reconnaissance at sites in West Antarctica,
focusing on the Pirrit Hills, where in the summer of 2016â2017 an 8 m
bedrock core was retrieved from below 150 m of ice.</p
High-resolution measurement of the time-modulated orbital electron capture and of the decay of hydrogen-like Pm ions
The periodic time modulations, found recently in the two-body orbital
electron-capture (EC) decay of both, hydrogen-like Pr and
Pm ions, with periods near to 7s and amplitudes of about 20%,
were re-investigated for the case of Pm by using a 245 MHz
resonator cavity with a much improved sensitivity and time resolution. We
observed that the exponential EC decay is modulated with a period s, in accordance with a modulation period s as obtained
from simultaneous observations with a capacitive pick-up, employed also in the
previous experiments. The modulation amplitudes amount to and
for the 245 MHz resonator and the capacitive pick-up,
respectively. These new results corroborate for both detectors {\it exactly}
our previous findings of modulation periods near to 7s, though with {\it
distinctly smaller} amplitudes. Also the three-body decays have been
analyzed. For a supposed modulation period near to 7s we found an amplitude , compatible with and in agreement with the preliminary
result of our previous experiment. These observations could
point at weak interaction as origin of the observed 7s-modulation of the EC
decay. Furthermore, the data suggest that interference terms occur in the
two-body EC decay, although the neutrinos are not directly observed.Comment: In memoriam of Prof. Paul Kienle, 9 pages, 1 table, 5 figures Phys.
Lett. B (2013) onlin
Regional Differences in the Sensitivity of MEG for Interictal Spikes in Epilepsy
MEG interictal spikes as recorded in epilepsy patients are a reflection of intracranial interictal activity. This study investigates the relationship between the estimated sources of MEG spikes and the location, distribution and size of interictal spikes in the invasive ECoG of a group of 38 epilepsy patients that are monitored for pre-surgical evaluation. An amplitude/surface area measure is defined to quantify and rank ECoG spikes. It is found that all MEG spikes are associated with an ECoG spike that is among the three highest ranked in a patient. Among the different brain regions considered, the fronto-orbital, inter-hemispheric, tempero-lateral and central regions stand out. In an accompanying simulation study it is shown that for hypothesized extended sources of larger sizes, as suggested by the data, source location, orientation and curvature can partly explain the observed sensitivity of MEG for interictal spikes
Wissenschaftliche Monitoringkonzepte fĂŒr die Deutsche Bucht (WIMO) - Abschlussbericht
The state and development of coastal marine systems and an understanding of the interaction of
organisms, sea floor, water column, and biochemical and physical processes can only be obtained by
a combination of long-term monitoring and modelling approaches of different complexity. A need for the development and evaluation of monitoring strategies is driven by a framework of different
European and German regulations. The research project WIMO (Scientific Monitoring Concepts for the German Bight) has developed concepts and methods that aim at a fundamental scientific understanding of marine systems and also meet monitoring requirements of European legislation and regulations like the EU Marine Strategy Framework Directive. In this final report examples of common descriptors of ecosystem state like seabed integrity, eutrophication, and biodiversity are discussed. It has been assessed to what extent established measuring procedures used to survey the characteristics of the sea floor, and newly developed technologies are eligible for governmental monitoring. The significance of integrative modelling for linking and visualising results of measurements and
models is illustrated. It is shown how new concepts have been implemented into governmental monitoring in the form of web based data sheets. These insights enable continuous analyses and developments in the future
Localising the auditory N1m with event-related beamformers:localisation accuracy following bilateral and unilateral stimulation
The auditory evoked N1m-P2m response complex presents a challenging case for MEG source-modelling, because symmetrical, phase-locked activity occurs in the hemispheres both contralateral and ipsilateral to stimulation. Beamformer methods, in particular, can be susceptible to localisation bias and spurious sources under these conditions. This study explored the accuracy and efficiency of event-related beamformer source models for auditory MEG data under typical experimental conditions: monaural and diotic stimulation; and whole-head beamformer analysis compared to a half-head analysis using only sensors from the hemisphere contralateral to stimulation. Event-related beamformer localisations were also compared with more traditional single-dipole models. At the group level, the event-related beamformer performed equally well as the single-dipole models in terms of accuracy for both the N1m and the P2m, and in terms of efficiency (number of successful source models) for the N1m. The results yielded by the half-head analysis did not differ significantly from those produced by the traditional whole-head analysis. Any localisation bias caused by the presence of correlated sources is minimal in the context of the inter-individual variability in source localisations. In conclusion, event-related beamformers provide a useful alternative to equivalent-current dipole models in localisation of auditory evoked responses
Hyperspectral remote sensing of cyanobacterial pigments as indicators for cell populations and toxins in eutrophic lakes
The growth of mass populations of toxin-producing cyanobacteria is a serious concern for the ecological
status of inland waterbodies and for human and animal health. In this study we examined the performance
of four semi-analytical algorithms for the retrieval of chlorophyll a (Chl a) and phycocyanin (C-PC) from data
acquired by the Compact Airborne Spectrographic Imager-2 (CASI-2) and the Airborne Imaging Spectrometer
for Applications (AISA) Eagle sensor. The retrieval accuracies of the semi-analytical models were
compared to those returned by optimally calibrated empirical band-ratio algorithms. The best-performing
algorithm for the retrieval of Chl a was an empirical band-ratio model based on a quadratic function of the
ratio of re!ectance at 710 and 670 nm (R2=0.832; RMSE=29.8%). However, this model only provided a
marginally better retrieval than the best semi-analytical algorithm. The best-performing model for the
retrieval of C-PC was a semi-analytical nested band-ratio model (R2=0.984; RMSE=3.98 mg mâ3). The
concentrations of C-PC retrieved using the semi-analytical model were correlated with cyanobacterial cell
numbers (R2=0.380) and the particulate and total (particulate plus dissolved) pools of microcystins
(R2=0.858 and 0.896 respectively). Importantly, both the empirical and semi-analytical algorithms were
able to retrieve the concentration of C-PC at cyanobacterial cell concentrations below current warning
thresholds for cyanobacteria in waterbodies. This demonstrates the potential of remote sensing to contribute
to early-warning detection and monitoring of cyanobacterial blooms for human health protection at regional
and global scales
Functionally reversible impacts of disturbances on lake food webs linked to spatial and seasonal dependencies
Increasing human impact on the environment is causing drastic changes in disturbance regimes and how they prevail over time. Of increasing relevance is to further our understanding on biological responses to pulse disturbances (short duration) and how they interact with other ongoing press disturbances (constantly present). Because the temporal and spatial contexts of single experiments often limit our ability to generalize results across space and time, we conducted a modularized mesocosm experiment replicated in space (five lakes along a latitudinal gradient in Scandinavia) and time (two seasons, spring and summer) to generate general predictions on how the functioning and composition of multitrophic plankton communities (zoo-, phyto- and bacterioplankton) respond to pulse disturbances acting either in isolation or combined with press disturbances. As pulse disturbance, we used short-term changes in fish presence, and as press disturbance, we addressed the ongoing reduction in light availability caused by increased cloudiness and lake browning in many boreal and subarctic lakes. First, our results show that the top-down pulse disturbance had the strongest effects on both functioning and composition of the three trophic levels across sites and seasons, with signs for interactive impacts with the bottom-up press disturbance on phytoplankton communities. Second, community composition responses to disturbances were highly divergent between lakes and seasons: temporal accumulated community turnover of the same trophic level either increased (destabilization) or decreased (stabilization) in response to the disturbances compared to control conditions. Third, we found functional recovery from the pulse disturbances to be frequent at the end of most experiments. In a broader context, these results demonstrate that top-down, pulse disturbances, either alone or with additional constant stress upon primary producers caused by bottom-up disturbances, can induce profound but often functionally reversible changes across multiple trophic levels, which are strongly linked to spatial and temporal context dependencies. Furthermore, the identified dichotomy of disturbance effects on the turnover in community composition demonstrates the potential of disturbances to either stabilize or destabilize biodiversity patterns over time across a wide range of environmental conditions
Hydrophyte-macroinvertebrate interactions in Zwemlust, a lake undergoing biomanipulation
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