917 research outputs found
Physical Constraints to Aquatic Plant Growth in New Zealand Lakes
The nature of aquatic plant communities often defines
benthic habitat within oligotrophic and mesotrophic lakes
and lake management increasingly recognizes the importance
of maintaining plant diversity in order to sustain biological
diversity and capacity within lakes. We have developed
simple statistical relationships between key physical and vegetation
variables that define the habitat requirements, or
âhabitat-templatesâ, of key vegetation types to facilitate management
of plant communities in New Zealand lakes. Statistical
relationships were derived from two datasets. The first
was a multi-lake dataset to determine the effects of water level
fluctuation and water clarity. The second dataset was from
a comprehensive shoreline survey of Lake Wanaka, which allowed
us to examine within-lake variables such as beach
slope and wave action. Sufficient statistical relationships were
established to develop a habitat template for each of the major
species or assemblages. The relationships suggested that
the extent and diversity of shallow-growing species was related
to a combination of the extent of water level fluctuation
and wave exposure. (PDF contains 9 pages.
A slow and dark atomic beam
We demonstrate a method to produce a very slow atomic beam from a vapour cell
magneto-optical trap. Atoms are extracted from the trap using the radiation
pressure imbalance caused by a push beam. An additional transfer beam placed
near the center of the trap transfers the atomic beam into an off-resonant
state. The velocity of the atomic beam has been varied by changing the
intensity of the push beam or the position of the transfer beam. The method can
be used to generate a continuous, magnetically guided atomic beam in a dark
state.Comment: 14 page
Short-term mortality after perforated or bleeding peptic ulcer among elderly patients: a population-based cohort study
<p>Abstract</p> <p>Background</p> <p>Mortality after perforated and bleeding peptic ulcer increases with age. Limited data exist on how the higher burden of comorbidity among elderly patients affects this association. We aimed to examine the association of age with short-term mortality after perforated and bleeding peptic ulcer and to determine the impact of comorbidity on this association.</p> <p>Methods</p> <p>In this population-based cohort study in three Danish counties between 1991 and 2003 we identified two cohorts of patients: those hospitalized with a first-time discharge diagnosis of perforated peptic ulcer and those with bleeding peptic ulcer. The diagnoses were ascertained from hospital discharge registries and mortality through the Danish Civil Registration System. Information on comorbidity and use of ulcer-related drugs was obtained through administrative medical databases. We computed age-, gender- and comorbidity-standardized 30-day mortality rates and used Cox's regression to estimate adjusted 30-day mortality rate ratios (MRR) for elderly compared with younger patients.</p> <p>Results</p> <p>Among 2,061 patients with perforated peptic ulcer, 743 (36%) were 65â79 years old and 513 patients (25%) were aged 80+ years. Standardized 30-day mortality was 8.9% among patients younger than 65 years rising to 44.6% among patients aged 80+ years, corresponding to an adjusted MRR of 5.3 (95% CI: 4.0â7.0). Among 7,232 patients with bleeding peptic ulcer 2,372 (33%) were aged 80+ years. Standardized 30-day mortality among patients younger than 65 was 4.3% compared with 16.9% among patients aged 80+ years, corresponding to an adjusted MRR of 3.7 (95% CI: 2.9â4.7). Analyses stratified by comorbidity consistently showed high MRRs among elderly patients, regardless of comorbidity level.</p> <p>Conclusion</p> <p>Ageing is a strong predictor for a poor outcome after perforated and bleeding peptic ulcer independently of comorbidity.</p
Explainable Metamodels for ATM Performance Assessment
Fast-time simulation constitutes a well-known and
long-established technique within the Air Traffic Management
(ATM) community. However, it is often the case that simulation input and output spaces are underutilized, limiting the full understandability, transparency, and interpretability of the obtained results.
In this paper, we propose a methodology that combines simulation metamodeling and SHapley Additive exPlanations (SHAP) values, aimed at uncovering the intricate hidden relationships among the input and output variables of a simulated ATM system in a rather practical way. Whereas metamodeling provides explicit functional approximations mimicking the behavior of the simulators, the SHAP-based analysis delivers a systematic framework for improving their explainability. We illustrate our approach using a state-of-the-art ATM simulator across two case studies in which two delay-centered performance metrics are analyzed. The results show that the proposed methodology can effectively make simulation and its results more explainable, facilitating the interpretation of the obtained emergent behavior, and additionally opening new opportunities towards novel performance assessment processes within the ATM research field
NOSTROMO - D5.2 - ATM Performance Metamodels - Final Release
This deliverable presents the third iteration of the development of the two micromodels Flitan and Mercury and the results obtained with them with the active learning process, as described in the deliverables D3.X. In this iteration, Flitan implemented concepts from PJ08.01 and PJ02.08, and Mercury implemented a module related to PJ07.02. Mercury also developed an additional module related to PJ01.01, which description is presented in Annex only, since no results could be produced in time with it for this deliverable.
The development is presented in two different chapters for each simulator, with general descriptions referred to from D5.1. The modules related to each SESAR solution are described separately.
The latest version of the meta-modelling process is described briefly, followed by the results obtained with the two simulators, in distinct sections. This chapter shows the performance of the meta-model with respect to approximating micro simulators
Scalable Group Level Probabilistic Sparse Factor Analysis
Many data-driven approaches exist to extract neural representations of
functional magnetic resonance imaging (fMRI) data, but most of them lack a
proper probabilistic formulation. We propose a group level scalable
probabilistic sparse factor analysis (psFA) allowing spatially sparse maps,
component pruning using automatic relevance determination (ARD) and subject
specific heteroscedastic spatial noise modeling. For task-based and resting
state fMRI, we show that the sparsity constraint gives rise to components
similar to those obtained by group independent component analysis. The noise
modeling shows that noise is reduced in areas typically associated with
activation by the experimental design. The psFA model identifies sparse
components and the probabilistic setting provides a natural way to handle
parameter uncertainties. The variational Bayesian framework easily extends to
more complex noise models than the presently considered.Comment: 10 pages plus 5 pages appendix, Submitted to ICASSP 1
Free-induction-decay magnetometer based on a microfabricated Cs vapor cell
We describe an optically pumped Cs magnetometer containing a 1.5 mm thick microfabricated vapor cell with nitrogen buffer gas operating in a free-induction-decay (FID) configuration. This allows us to monitor the free Larmor precession of the spin coherent Cs atoms by separating the pump and probe phases in the time domain. A single light pulse can sufficiently polarize the atomic sample however, synchronous modulation of the light field actively drives the precession and maximizes the induced spin coherence. Both amplitude and frequency modulation have been implemented with noise floors of 3 pT / â Hz and 16 pT / â Hz respectively within the Nyquist limited bandwidth of 500 Hz
Single-board low-noise fluxgate magnetometer
Low-noise fluxgate magnetometers are normally comprised of three separate devices: a power supply, the sensor head/electronics and an analog-to-digital converter (ADC). This paper presents a parallel rod fluxgate magnetometer in a single printed circuit board of size = 5x12âcm, weight = 45âg, and sensor head average power dissipationâ=â40âmW. The open-loop noise spectral densityâ = 5pTrms/âHz@1 Hzâ , competitive with state-of-the-art devices. This is realized using a new amorphous wire core material and programmable mixed-signal electronics with low amplifier and ADC noise. We have compared the sensor performance to a low-noise observatory magnetometer and found sub-nT correlation when tracking the Y (East-West) component of the Earthâs geomagnetic field
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