1,246 research outputs found
Second order perturbation theory for embedded eigenvalues
We study second order perturbation theory for embedded eigenvalues of an
abstract class of self-adjoint operators. Using an extension of the Mourre
theory, under assumptions on the regularity of bound states with respect to a
conjugate operator, we prove upper semicontinuity of the point spectrum and
establish the Fermi Golden Rule criterion. Our results apply to massless
Pauli-Fierz Hamiltonians for arbitrary coupling.Comment: 30 pages, 2 figure
Does enhanced nitrogen deposition represent a threat to Sphagnum and thus the sustainability of Scottish peatlands?
Nutrient limited ombrotrophic bogs and peatlands support high conservation valued ecosystems, potentially susceptible to current elevated levels of reactive nitrogen (N) deposition. Here, we present the effects and consequences of different N forms, wet, dry, reduced and oxidised N on the functioning of a bog moss, Sphagnum capillifolium. Sphagnum mosses maintain the acid, low nutrient conditions, crucial for the sustainability of peat lands, where productivity must exceed decomposition. Dry deposited ammonia substantially elevated shoot N status, which led to tissue breakdown loss of function and death in S. capillifolium. Wet deposited nitrate and ammonium also negatively affected S. capillifolium, significantly reducing shoot extension and cover and significantly elevating N status. These effects occurred over 5 years and were significant even at the lowest reduced N dose, 8 kg N ha-1 y1 (background = 8-10 kg N ha-1 y-1), highlighting the threat N poses for the effective functioning of bog ecosystems
Climatic and palaeoceanographic changes during the Pliensbachian (Early Jurassic) 2 inferred from clay mineralogy and stable isotope (C-O) geochemistry (NW Europe)
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Available online 17 January 2017The Early Jurassic was broadly a greenhouse climate period that was punctuated by short
warm and cold climatic events, positive and negative excursions of carbon isotopes, and
episodes of enhanced organic matter burial. Clay minerals from Pliensbachian sediments
recovered from two boreholes in the Paris Basin, are used here as proxies of detrital supplies,
runoff conditions, and palaeoceanographic changes. The combined use of these minerals with
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stable isotope data (C-O) from bulk carbonates and organic matter allows palaeoclimatic
reconstructions to be refined for the Pliensbachian. Kaolinite/illite ratio is discussed as a
reliable proxy of the hydrological cycle and runoff from landmasses. Three periods of
enhanced runoff are recognised within the Pliensbachian. The first one at the SinemurianPliensbachian
transition shows a significant increase of kaolinite concomitant with the
negative carbon isotope excursion at the so-called Sinemurian Pliensbachian Boundary Event
(SPBE). The Early/Late Pliensbachian transition was also characterised by more humid
conditions. This warm interval is associated with a major change in oceanic circulation during
the Davoei Zone, likely triggered by sea-level rise; the newly created palaeogeography,
notably the flooding of the London-Brabant Massif, allowed boreal detrital supplies, including
kaolinite and chlorite, to be exported to the Paris Basin. The last event of enhanced runoff
occurred during the late Pliensbachian (Subdonosus Subzone of the Margaritatus Zone),
which occurred also during a warm period, favouring organic matter production and
preservation. Our study highlights the major role of the London Brabant Massif in influencing
oceanic circulation of the NW European area, as a topographic barrier (emerged lands) during
periods of lowstand sea-level and its flooding during period of high sea-level. This massif was
the unique source of smectite in the Paris Basin. Two episodes of smectite-rich sedimentation
(‘smectite events’), coincide with regressive intervals, indicating emersion of the London
Brabant Massif and thus suggesting that an amplitude of sea-level change high enough to be
linked to glacio-eustasy. This mechanism is consistent with sedimentological and
geochemical evidences of continental ice growth notably during the Latest Pliensbachian
(Spinatum Zone), and possibly during the Early Pliensbachian (late Jamesoni/early Ibex
Zones).The study was supported by the “Agence Nationale pour la Gestion des Déchets Radioactifs” (Andra––French National Radioactive Waste Management Agency)
Scattering Theory Approach to Random Schroedinger Operators in One Dimension
Methods from scattering theory are introduced to analyze random Schroedinger
operators in one dimension by applying a volume cutoff to the potential. The
key ingredient is the Lifshitz-Krein spectral shift function, which is related
to the scattering phase by the theorem of Birman and Krein. The spectral shift
density is defined as the "thermodynamic limit" of the spectral shift function
per unit length of the interaction region. This density is shown to be equal to
the difference of the densities of states for the free and the interacting
Hamiltonians. Based on this construction, we give a new proof of the Thouless
formula. We provide a prescription how to obtain the Lyapunov exponent from the
scattering matrix, which suggest a way how to extend this notion to the higher
dimensional case. This prescription also allows a characterization of those
energies which have vanishing Lyapunov exponent.Comment: 1 figur
Random repeated quantum interactions and random invariant states
We consider a generalized model of repeated quantum interactions, where a
system is interacting in a random way with a sequence of
independent quantum systems . Two types of randomness
are studied in detail. One is provided by considering Haar-distributed
unitaries to describe each interaction between and
. The other involves random quantum states describing each copy
. In the limit of a large number of interactions, we present
convergence results for the asymptotic state of . This is achieved
by studying spectral properties of (random) quantum channels which guarantee
the existence of unique invariant states. Finally this allows to introduce a
new physically motivated ensemble of random density matrices called the
\emph{asymptotic induced ensemble}
Scattering induced current in a tight-binding band
International audienceIn the single band tight-binding approximation, we consider the transport properties of an electron in a homogeneous static electric field. We show that repeated interactions of the electron with two-level systems in thermal equilibrium suppress the Bloch oscillations and induce a steady current, the statistical properties of which we study
Loss of 5-hydroxymethylcytosine is a frequent event in peripheral T-cell lymphomas.
International audienc
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