490 research outputs found
Operational modal analysis with non stationnary inputs
Operational modal analysis (OMA) techniques enable the use of in-situ and uncontrolled vibrations to be used to lead modal analysis of structures. In reality operational vibrations are a combination of numerous excitations sources that are much more complex than a random white noise or a harmonic. Numerous OMA techniques exist like SSI, NExT, FDD and BSS. All these methods are based on the fundamental hypothesis that the input or force applied to the structure to be analyzed is a stationary white noise. For some applications this hypothesis is reasonable. However in numerous situations, the analyzed structure is subject to harmonic and transient forces. Numerous methods and research has enabled to develop methods that are robust to such harmonic contributions. To enable OMA during pressure oscillations in solid rocket boosters, the authors propose to consider transient and harmonic inputs no longer as parasites but as the main force applied to the structure that must be analyzed. This is the case during pressure oscillations in rocket boosters. We propose the use of phase analysis adapted to a transient context to conduct operational modal analysis under a harmonic transient input. This time-based novel OMA method will be exposed. The theoretical developments and algorithmic implementations are exposed. First tests have been conducted on laboratory single degree of freedom setup to validate this new OMA technique and are reported here
Constructing Incremental Sequences in Graphs
Given a weighted graph , we investigate the problem of constructing a sequence of subsets of vertices (called groups) with small diameters, where the diameter of a group is calculated using distances in G. The constraint on these n groups is that they must be incremental: . The cost of a sequence is the maximum ratio between the diameter of each group Mi and the diameter of a group with I vertices and minimum diameter:
.
This quantity captures the impact of the incremental constraint on the diameters of the groups in a sequence. We give general bounds on the value of this ratio and we prove that the problem of constructing an optimal incremental sequence cannot be solved approximately in polynomial time with an approximation ratio less than 2 unless P = NP. Finally, we give a 4-approximation algorithm and we show that the analysis of our algorithm is tight
Membrane models for molecular simulations of peripheral membrane proteins
Peripheral membrane proteins (PMPs) bind temporarily to the surface of biological membranes. They also exist in a soluble form and their tertiary structure is often known. Yet, their membrane-bound form and their interfacial-binding site with membrane lipids remain difficult to observe directly. Their binding and unbinding mechanism, the conformational changes of the PMPs and their influence on the membrane structure are notoriously challenging to study experimentally. Molecular dynamics simulations are particularly useful to fill some knowledge-gaps and provide hypothesis that can be experimentally challenged to further our understanding of PMP-membrane recognition. Because of the time-scales of PMP-membrane binding events and the computational costs associated with molecular dynamics simulations, membrane models at different levels of resolution are used and often combined in multiscale simulation strategies. We here review membrane models belonging to three classes: atomistic, coarse-grained and implicit. Differences between models are rooted in the underlying theories and the reference data they are parameterized against. The choice of membrane model should therefore not only be guided by its computational efficiency. The range of applications of each model is discussed and illustrated using examples from the literature.publishedVersio
Constructing Incremental Sequences in Graphs
Given a weighted graph , we investigate the problem of constructing a sequence of subsets of vertices (called groups) with small diameters, where the diameter of a group is calculated using distances in . The constraint on these groups is that they must be incremental: M_1\subsetM_2 \subset...\subsetM_n=V. The cost of a sequence is the maximum ratio between the diameter of each group and the diameter of a group with vertices and minimum diameter: \max_2 \leqi \leqn \left{ \fracD(M_i)D(N_i^*) \right}. This quantity captures the impact of the incremental constraint on the diameters of the groups in a sequence. We give general bounds on the value of this ratio and we prove that the problem of constructing an optimal incremental sequence cannot be solved approximately in polynomial time with an approximation ratio less than 2 unless . Finally, we give a 4-approximation algorithm and we show that the analysis of our algorithm is tight
The MUSE-Wide survey: A measurement of the Ly emitting fraction among galaxies
We present a measurement of the fraction of Lyman (Ly)
emitters () amongst HST continuum-selected galaxies at
with the Multi-Unit Spectroscopic Explorer (MUSE) on the VLT. Making
use of the first 24 MUSE-Wide pointings in GOODS-South, each having an
integration time of 1 hour, we detect 100 Ly emitters and find
for most of the redshift range covered, with 29
per cent of the Ly sample exhibiting rest equivalent widths (rest-EWs)
15\AA. Adopting a range of rest-EW cuts (0 - 75\AA), we find no evidence
of a dependence of on either redshift or UV luminosity.Comment: 10 pages, 5 figures (MNRAS, updated as per version in press
The MUSE Hubble Ultra Deep Field Survey X. Ly Equivalent Widths at
We present rest-frame Ly equivalent widths (EW) of 417 Ly
emitters (LAEs) detected with Multi Unit Spectroscopic Explorer (MUSE) on the
Very Large Telescope (VLT) at in the Hubble Ultra Deep Field.
Based on the deep MUSE spectroscopy and ancillary Hubble Space Telescope (HST)
photometry data, we carefully measured EW values taking into account extended
Ly emission and UV continuum slopes (). Our LAEs reach
unprecedented depths, both in Ly luminosities and UV absolute
magnitudes, from log(/erg s) 41.0 to 43.0 and
from Muv -16 to -21 (0.01-1.0 ). The EW values span the
range of 5 to 240 \AA\ or larger, and their distribution can be well
fitted by an exponential law exp(EW/). Owing to
the high dynamic range in Muv, we find that the scale factor, ,
depends on Muv in the sense that including fainter Muv objects increases
, i.e., the Ando effect. The results indicate that selection
functions affect the EW scale factor. Taking these effects into account, we
find that our values are consistent with those in the literature
within uncertainties at at a given threshold of Muv
and . Interestingly, we find 12 objects with EW \AA\
above uncertainties. Two of these 12 LAEs show signatures of merger
or AGN activity: the weak CIV emission line. For the remaining
10 very large EW LAEs, we find that the EW values can be reproduced by young
stellar ages ( Myr) and low metallicities ( ). Otherwise, at least part of the Ly emission in these LAEs
needs to arise from anisotropic radiative transfer effects, fluorescence by
hidden AGN or quasi-stellar object activity, or gravitational cooling.Comment: 22 pages, 12 figures, 9 tables, accepted for publication in A&A (MUSE
UDF Series Paper X
Forests in Digital Games - An Ecocritical Framework
Forests are, both culturally and ecologically, one of the most important environments on our planet. As such, there are countless representations of them - with Digital Games being no exception. In this paper we adopt the perspective of ecocriticism, which regards the analysis of the textual portrayal of physical environments of the natural world. In particular, we propose here a framework for the analysis of forest representations in digital games, mindful of the many different layers that coexist together: cultural, discursive, representational and ludic. In order to test our framework and to showcase its potential, in the last section we present a brief analysis of the slicing game Jack Lumber and of the ideological tensions that emerge from the gamepublishedVersionPeer reviewe
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