Search results for "time scale"

Robust regulation with H∞ control of linear two-time-scale systems: A new modelling approach

2010

This paper considers the problem of robust multi-objective

Soil is the best testifier of the diachronous dawn of the Anthropocene

2021

Humans act at worldwide scale as a growing geomorphic agent since mid‐Holocene (8,200–4,200 y BP) through the pervasive impacts of domestication, deforestation, agriculture, urbanization, and mining. The concept of Anthropocene has been introduced exactly to indicate the timespan in which humans have joined with other natural forces in impacting the outermost shell of the planet and the biosphere. Soils, which are the Earth's skin, are sensitive archives of any major human‐induced local to global change. Especially when buried, soils can permanently preserve the primordial traces of a significant impact of man on the environment, which occurred at different times and rates in different area…

An orbital floating time scale of the Hauterivian/Barremian GSSP from a magnetic susceptibility signal (Río Argos, Spain).

2012

10 pages; International audience; An orbital floating time scale of the HauterivianeBarremian transition (Early Cretaceous) is proposed using high-resolution magnetic susceptibility measurements. Orbital tuning was performed on the Río Argos section (southeast Spain), the candidate for a Global boundary Stratotype Section and Point (GSSP) for the HauterivianeBarremian transition. Spectral analyses of MS variations, coupled with the frequency ratio method, allow the recognition of precession, obliquity and eccentricity frequency bands. Orbitallytuned magnetic susceptibility provides minimum durations for ammonite biozones. The durations of well-constrained ammonite zones are assessed at 0.78…

Is the Anthropocene really worthy of a formal geologic definition?

2014

Scientists are actively debating whether the Anthropocene, the geologic time span (GTS) we are now living in, should be considered a period, epoch, or age in the geologic timescale. The solution is not easy, because the beginning of this GTS is undefined and the end unknown. In fact, there is no agreement on when the Anthropocene began, the proposed dates ranging from the Second World War, when radioactive fallout branded soils and sediments all over the world, to little after the end of the last glacial period, i.e. 11.7 thousand years ago, therefore coinciding with the onset of the Holocene. We are in favour of a concurrence of the Anthropocene with the Holocene, although a major impact …

The Burdigalian GSSP: the missing tile to complete the Neogene interval of the Geological Time Scale

2014

Between a rock and a soft place: the role of viruses in lithification of modern microbial mats.

2021

10 pages; International audience; Stromatolites are geobiological systems formed by complex microbial communities, and fossilized stromatolites provide a record of some of the oldest life on Earth. Microbial mats are precursors of extant stromatolites; however, the mechanisms of transition from mat to stromatolite are controversial and are still not well understood. To fully recognize the profound impact that these ecosystems have had on the evolution of the biosphere requires an understanding of modern lithification mechanisms and how they relate to the geological record. We propose here viral mechanisms in carbonate precipitation, leading to stromatolite formation, whereby viruses directl…

Robust regulation with an H<inf>∞</inf> constrain for linear two-time scale systems

2010

In this paper, the problem of robust multi-objective control design with an H ∞ constrain is studied for a class of linear two-time scale systems. The design is based on a new modelling approach under the assumption of norm-boundedness of the fast dynamics. In this method, a portion of the fast dynamics is treated as a norm-bounded perturbation in the design by its maximum possible gain. In this view, the problem of robust multi-objective control design is performed only for the certain dynamics of the two-time scale system, whose order is less than that of the original system. One illustrative example is used to demonstrate the validity of the proposed approach.

1993

The history of life may be compared to a huge cable enclosing as many strands as there are fossil and present species. The biosphere, with its 2 million species, would then correspond to a transverse section through this cable.

ZBL MS 63/6 Satco, Bianca-Renata; Turcu, Corneliu-Octavian Henstock-Kurzweil-Pettis integral and weak topologies in nonlinear integral equations on t…

2013

The authors prove an existence result for a nonlinear integral equation on time scales under weak topology assumption in the target Banach space. In the setting of vector valued functions on time scales they consider the Henstock-Kurzweil-Pettis $\Delta$-integral which is a kind of Henstock integral recently introduced by Cichon, M. [Commun. Math. Anal. 11 (2011), no. 1, 94�110]. In this framework they show the existence of weakly continuous solutions for an integral equation x(t)= f(t, x(t))+ (HKP)\int_0^t g(t,s,x(s)) \Delta s governed by the sum of two operators: a continuous operator and an integral one. The main tool to get the solutions is a generalization of Krasnosel'skii fixed point…

OSL dating of sediments from the Gobi Desert, Southern Mongolia

2010

Abstract The present study focuses on the chronological relationship between alternating dune sand and silty water-lain sediments in the central part of the Khongoryn Els dune field in the Gobi Desert, Southern Mongolia. The 23 m high section evolved from the construction of a natural dam by west–east moving sand dunes and fluvial inundation by a river system from the mountain ranges in the south. To resolve the chronology of events, optically stimulated luminescence (OSL) dating was applied and from sedimentological and geochemical analysis the depositional processes could be characterised. Quartz OSL dating of these sediments is hindered by feldspar contamination. Thus, dating of coarse-g…