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  • 1
    Online Resource
    Online Resource
    Cham :Springer International Publishing AG,
    Keywords: Stochastic control theory. ; Electronic books.
    Type of Medium: Online Resource
    Pages: 1 online resource (598 pages)
    Edition: 1st ed.
    ISBN: 9783030823313
    Series Statement: Probability Theory and Stochastic Modelling Series ; v.101
    DDC: 519.2
    Language: English
    Note: Intro -- Preface -- Contents -- 1 Introduction -- 1.1 Why Stochastic Distributed Parameter Control Systems? -- 1.2 Two Fundamental Issues in Control Theory -- 1.3 Range Inclusion and the Duality Argument -- 1.4 Two Basic Methods in This Book -- 2 Some Preliminaries in Stochastic Calculus -- 2.1 Measures and Probability, Measurable Functions and Random Variables -- 2.2 Integrals and Expectation -- 2.3 Signed/Vector Measures, Conditional Expectation -- 2.3.1 Signed Measures -- 2.3.2 Distribution, Density and Characteristic Functions -- 2.3.3 Vector Measures -- 2.3.4 Conditional Expectation -- 2.4 A Riesz-Type Representation Theorem -- 2.4.1 Proof of the Necessity for a Special Case -- 2.4.2 Proof of the Necessity for the General Case -- 2.4.3 Proof of the Sufficiency -- 2.5 A Sequential Banach-Alaoglu-Type Theorem in the Operator Version -- 2.6 Stochastic Processes -- 2.7 Stopping Times -- 2.8 Martingales -- 2.8.1 Real Valued Martingales -- 2.8.2 Vector-Valued Martingales -- 2.9 Brownian Motions -- 2.9.1 Brownian Motions in Finite Dimensions -- 2.9.2 Construction of Brownian Motions in one Dimension -- 2.9.3 Vector-Valued Brownian Motions -- 2.10 Stochastic Integrals -- 2.10.1 Itô's Integrals w.r.t. Brownian Motions in Finite Dimensions -- 2.10.2 Itô's Integrals w.r.t. Vector-Valued Brownian Motions -- 2.11 Properties of Stochastic Integrals -- 2.11.1 Itô's Formula for Itô's Processes (in a Strong Form) -- 2.11.2 Burkholder-Davis-Gundy Inequality -- 2.11.3 Stochastic Fubini Theorem -- 2.11.4 Itô's Formula for Itô's processes in a Weak Form -- 2.11.5 Martingale Representation Theorem -- 2.12 Notes and Comments -- 3 Stochastic Evolution Equations -- 3.1 Stochastic Evolution Equations in Finite Dimensions -- 3.2 Well-Posedness of Stochastic Evolution Equations -- 3.2.1 Notions of Solutions -- 3.2.2 Well-Posedness in the Sense of Mild Solution. , 3.3 Regularity of Mild Solutions to Stochastic Evolution Equations -- 3.3.1 Burkholder-Davis-Gundy Type Inequality and Time Regularity -- 3.3.2 Space Regularity -- 3.4 Notes and Comments -- 4 Backward Stochastic Evolution Equations -- 4.1 The Case of Finite Dimensions and Natural filtration -- 4.2 The Case of Infinite Dimensions -- 4.2.1 Notions of Solutions -- 4.2.2 Well-Posedness in the Sense of Mild Solution for the Case of Natural Filtration -- 4.3 The Case of General Filtration -- 4.4 The Case of Natural Filtration Revisited -- 4.5 Notes and Comments -- 5 Control Problems for Stochastic Distributed Parameter Systems -- 5.1 An Example of Controlled Stochastic Differential Equations -- 5.2 Control Systems Governed by Stochastic Partial Differential Equations -- 5.3 Some Control Problems for Stochastic Distributed Parameter Systems -- 5.4 Notes and Comments -- 6 Controllability for Stochastic Differential Equations in Finite Dimensions -- 6.1 The Control Systems With Controls in Both Drift and Diffusion Terms -- 6.2 Control System With a Control in the Drift Term -- 6.3 Lack of Robustness for Null/Approximate Controllability -- 6.4 Notes and Comments -- 7 Controllability for Stochastic Linear Evolution Equations -- 7.1 Formulation of the Problems -- 7.2 Well-Posedness of Stochastic Systems With Unbounded Control Operators -- 7.3 Reduction to the Observability of Dual Problems -- 7.4 Explicit Forms of Controls for the Controllability Problems -- 7.5 Relationship Between the Forward and the Backward Controllability -- 7.5.1 The Case of Bounded Control Operators -- 7.5.2 The Case of Unbounded Control Operators -- 7.6 Notes and Comments -- 8 Exact Controllability for Stochastic Transport Equations -- 8.1 Formulation of the Problem and the Main Result -- 8.2 Hidden Regularity and a Weighted Identity. , 8.3 Observability Estimate for Backward Stochastic Transport Equations -- 8.4 Notes and Comments -- 9 Controllability and Observability of Stochastic Parabolic Systems -- 9.1 Formulation of the Problems -- 9.2 Controllability of a Class of Stochastic Parabolic Systems -- 9.2.1 Preliminaries -- 9.2.2 Proof of the Null Controllability -- 9.2.3 Proof of the Approximate Controllability -- 9.3 Controllability of a Class of Stochastic Parabolic Systems by one Control -- 9.3.1 Proof of the Null Controllability Result -- 9.3.2 Proof of the Negative Null Controllability Result -- 9.4 Carleman Estimate for a Stochastic Parabolic-Like Operator -- 9.5 Observability Estimate for Stochastic Parabolic Equations -- 9.5.1 Global Carleman Estimate for Stochastic Parabolic Equations, I -- 9.5.2 Global Carleman Estimate for Stochastic Parabolic Equations, II -- 9.5.3 Proof of the Observability Result -- 9.6 Null and Approximate Controllability of Stochastic Parabolic Equations -- 9.6.1 Global Carleman Estimate for Backward Stochastic Parabolic Equations -- 9.6.2 Proof of the Observability Estimate for Backward Stochastic Parabolic Equations -- 9.7 Notes and Comments -- 10 Exact Controllability for a Refined Stochastic Wave Equation -- 10.1 Formulation of the Problem -- 10.2 Well-Posedness of Stochastic Wave Equations With Boundary Controls -- 10.3 Main Controllability Results -- 10.4 A Reduction of the Exact Controllability Problem -- 10.5 A Fundamental Identity for Stochastic Hyperbolic-Like Operators -- 10.6 Observability Estimate for the Stochastic Wave Equation -- 10.7 Notes and Comments -- 11 Exact Controllability for Stochastic Schrödinger Equations -- 11.1 Formulation of the Problem and the Main Result -- 11.2 Well-Posedness of the Control System -- 11.3 A Fundamental Identity for Stochastic Schrödinger-Like Operators. , 11.4 Observability Estimate for Backward Stochastic Schrödinger Equations -- 11.5 Notes and Comments -- 12 Pontryagin-Type Stochastic Maximum Principle and Beyond -- 12.1 Formulation of the Optimal Control Problem -- 12.2 The Case of Finite Dimensions -- 12.3 Necessary Condition for Optimal Controls for Convex Control Regions -- 12.4 Operator-Valued Backward Stochastic Evolution Equations -- 12.4.1 Notions of Solutions -- 12.4.2 Preliminaries -- 12.4.3 Proof of the Uniqueness Results -- 12.4.4 Well-Posedness Result for a Special Case -- 12.4.5 Proof of the Existence and Stability for the General Case -- 12.4.6 A Regularity Result -- 12.5 Pontryagin-Type Maximum Principle -- 12.6 Sufficient Condition for Optimal Controls -- 12.6.1 Clarke's Generalized Gradient -- 12.6.2 A Sufficient Condition for Optimal Controls -- 12.7 Second Order Necessary Condition for Optimal Controls -- 12.8 Notes and Comments -- 13 Linear Quadratic Optimal Control Problems -- 13.1 Formulation of the Problem -- 13.2 Optimal Feedback for Deterministic LQ Problem in Finite Dimensions -- 13.3 Optimal Feedback for Stochastic LQ Problem in Finite Dimensions -- 13.3.1 Differences Between Deterministic and Stochastic LQ Problems in Finite Dimensions -- 13.3.2 Characterization of Optimal Feedbacks for Stochastic LQ Problems in Finite Dimensions -- 13.4 Finiteness and Solvability of Problem (SLQ) -- 13.5 Pontryagin-Type Maximum Principle for Problem (SLQ) -- 13.6 Transposition Solutions to Operator-Valued Backward Stochastic Riccati Equations -- 13.7 Existence of Optimal Feedback Operator for Problem (SLQ) -- 13.8 Global Solvability of Operator-Valued Backward Stochastic Riccati Equations -- 13.8.1 Some Preliminary Results -- 13.8.2 Proof of the Main Solvability Result -- 13.9 Some Examples -- 13.9.1 LQ Problems for Stochastic Wave Equations. , 13.9.2 LQ problems for Stochastic Schrödinger Equations -- 13.10 Notes and Comments -- References -- Index.
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  • 2
    Publication Date: 2024-04-20
    Description: We present basal melt rates for the ice shelves in equilibrium simulations of the Antarctic ice sheet (AIS), using the 3D thermodynamical Parallel Ice Sheet Model (PISM) version 1.1 with PICO as ocean component. The applied climate forcing consists of yearly mean present-day temperature and precipitation fields from RACMO2.3 (RACMO2 ANT27), and 400-800 m depth average ocean temperature and salinity, obtained from simulations using the atmosphere-ocean general circulation model COSMOS (ocean model MPIOM). COSMOS was run using pre-industrial settings (PID; 278 ppm CO2), settings from 40 kyr ago (40ka; 195 ppm CO2), and Last Glacial Maximum settings (LGM; 185 ppm CO2). All simulations are started with present-day bedrock conditions, and a present-day AIS size (Bedmap2). The steady state simulations are conducted by applying the same climate forcing over 200 kyr, after a thermodynamical spin-up (no mass changes) of 200,100 yr.
    Keywords: 40ka; Antarctica; Antarctic Ice Sheet; Basal melt rates; Glacial climate; Last Glacial Maximum; pre-industrial
    Type: Dataset
    Format: application/zip, 164.5 kBytes
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  • 3
    Publication Date: 2024-04-20
    Description: Herein, we publish the simulated global annual mean sea surface temperature (THO), surface air temperature (SAT) over a time period of 100 years retrieved from equilibrium climate simulations for the Last Glacial Maximum (~21 ka BP). We investigate the range of temperature variability that occurs in response to uncertainties in the boundary conditions of Laurentide ice sheet (LIS). We performed LGM simulations, applying six different LIS reconstructions (ICE-6g, GLAC-1a, ANU, Gowan, Licciardi and PMIP3) in a fully coupled atmosphere-ocean-sea-ice model. The model data has been used in the publication by Hossain et al., 2021. The climate data has been produced with Consortium for Small-scale Modeling (COSMOS; ECHAM5/JSBACH/MPIOM/OASIS3), utilized at a resolution of T31 in the atmosphere with 19 vertical layers and a resolution of GR30 (~3.0°x1.8°) in the ocean with 40 vertical layers. The model setup refers to boundary conditions (terrestrial topography, ocean bathymetry), greenhouse gas concentrations (CO2 = 185 ppm; CH4 = 350 ppb; N2O = 200 ppb) and orbital forcing representative for the LGM and are imposed in accordance with the PMIP3 protocol. We also run COSMOS using PI boundary conditions (ice-sheet topography, orbital forcing, greenhouse gas concentrations and ocean bathymetry). Details on setup and identifiers of LGM model simulations can be found in Table S1 of Hossain et al., 2021.
    Keywords: AWI_PaleoClimate; Last Glacial Maximum; Laurentide ice sheet reconstructions; Paleo-climate Dynamics @ AWI; Paleoclimate Modelling Intercomparison Project Phase III (PMIP3); Sea surface temperature; Surface air temperature
    Type: Dataset
    Format: application/zip, 22.8 MBytes
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  • 4
    Publication Date: 2024-04-20
    Description: In this study, we used MITgcm-REcoM2 to simulate the stepwise glacial-interglacial atmospheric pCO2 change. A general description of the model can be found in the supporting material for Hauck et al. 2013. There are seven simulations included in this dataset: two control runs for interglacial and glacial conditions (IG_ctl, G_ctl); three region-specific sensitivity runs(IG_Gso, IG_Gna, IG_Gns); and two simulations regarding the glacial iron fertilization in the Southern Ocean. Dissolved Inorganic Carbon (DIC) and Export Production in all runs are included in this study, and the potential temperature (THETA), salinity (SALT), meridional velocity (VVEL), sea ice concentration(SIarea), air-sea surface pCO2 (dpCO2surface) difference are available in IG_ctl, IG_Gso, IG_Gna, IG_Gns, and G_ctl.
    Keywords: Binary Object; biogeochemical modeling; Carbon cycle; Glacial – Interglacial; modeling; Paleo Modelling; PalMod
    Type: Dataset
    Format: text/tab-separated-values, 7 data points
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  • 5
    Publication Date: 2021-02-03
    Description: The dominant feature of large-scale mass transfer in the modern ocean is the Atlantic meridional overturning circulation (AMOC). The geometry and vigour of this circulation influences global climate on various timescales. Palaeoceanographic evidence suggests that during glacial periods of the past 1.5 million years the AMOC had markedly different features from today; in the Atlantic basin, deep waters of Southern Ocean origin increased in volume while above them the core of the North Atlantic Deep Water (NADW) shoaled. An absence of evidence on the origin of this phenomenon means that the sequence of events leading to global glacial conditions remains unclear. Here we present multi-proxy evidence showing that northward shifts in Antarctic iceberg melt in the Indian–Atlantic Southern Ocean (0–50°E) systematically preceded deep-water mass reorganizations by one to two thousand years during Pleistocene-era glaciations. With the aid of iceberg-trajectory model experiments, we demonstrate that such a shift in iceberg trajectories during glacial periods can result in a considerable redistribution of freshwater in the Southern Ocean. We suggest that this, in concert with increased sea-ice cover, enabled positive buoyancy anomalies to ‘escape’ into the upper limb of the AMOC, providing a teleconnection between surface Southern Ocean conditions and the formation of NADW. The magnitude and pacing of this mechanism evolved substantially across the mid-Pleistocene transition, and the coeval increase in magnitude of the ‘southern escape’ and deep circulation perturbations implicate this mechanism as a key feedback in the transition to the ‘100-kyr world’, in which glacial–interglacial cycles occur at roughly 100,000-year periods.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
    Publication Date: 2021-07-01
    Description: The evolution of past global ice sheets is highly uncertain. One example is the missing ice problem during the Last Glacial Maximum (LGM, 26 000-19 000 years before present) – an apparent 8-28 m discrepancy between far-field sea level indicators and modelled sea level from ice sheet reconstructions. In the absence of ice sheet reconstructions, researchers often use marine δ 18 O proxy records to infer ice volume prior to the LGM. We present a global ice sheet reconstruction for the past 80 000 years, called PaleoMIST 1.0, constructed inde- pendently of far-field sea level and δ 18 O proxy records. Our reconstruction is compatible with LGM far-field sea-level records without requiring extra ice volume, thus solving the missing ice problem. However, for Marine Isotope Stage 3 (57 000-29 000 years before present) - a pre-LGM period - our reconstruction does not match proxy-based sea level reconstructions, indicating the relationship between marine δ 18 O and sea level may be more complex than assumed.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 7
    Publication Date: 2021-09-20
    Description: Palaeoceanographic evidence suggests that glacial periods of the Mid to Late Pleistocene were characterized by markedly different global ocean circulation patterns to modern; in the Atlantic basin, deep waters of Southern Ocean origin increased in volume while above them the core of the North Atlantic Deep Water (NADW) shoaled. Whilst proxy records and modelling efforts continue to clarify this picture, an evidence alluding to the origin of this phenomenon remains elusive. Because of this, our understanding of the sequence of events leading to global glacial conditions remains incomplete. Here we present multi-proxy evidence showing that northward shifts in Antarctic iceberg melt in the Indian–Atlantic Southern Ocean (0–50°E) systematically preceded deep-water mass reorganizations by 1-2 thousand years during Pleistocene-era glaciations. With the aid of iceberg-trajectory model experiments, we demonstrate that such a shift in iceberg trajectories during glacial periods can result in a considerable redistribution of freshwater in the Southern Ocean. This, in concert with increased sea-ice cover, may have enabled positive buoyancy anomalies to effectively escape into the ‘upper’ Atlantic overturning circulation limb, providing a teleconnection between surface Southern Ocean conditions and the formation of NADW. Furthermore, we observe a distinct obliquity pacing of Antarctic iceberg melt both preceding and following the Mid-Pleistocene Transition, become obscured during this interval. With new and existing data we investigate the evolution of orbital forcing at the Agulhas Plateau, considering the implications for ‘Southern Escape’ of freshwater as a key feedback in the transition to the ‘100-kyr world’.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 8
    Publication Date: 2023-06-21
    Description: The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological timescales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage in vicinity of the modern Polar Front over a complete glacial-interglacial cycle (i.e., the past 140,000 years), based on sediment grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with weakened current strength during glacials and a stronger circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennialscale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We infer that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations modulated Pacific-Atlantic water exchange via the “cold water route” and potentially affected the Atlantic Meridional Overturning Circulation and marine carbon storage.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 9
    Publication Date: 2024-02-07
    Description: The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological time-scales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage in vicinity of the modern Polar Front over a complete glacial-interglacial cycle (i.e., the past 140,000 years), based on sediment grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with weakened current strength during glacials and a stronger circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennial-scale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We infer that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations modulated Pacific-Atlantic water exchange via the “cold water route” and potentially affected the Atlantic Meridional Overturning Circulation and marine carbon storage.
    Type: Article , PeerReviewed
    Format: text
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  • 10
    Publication Date: 2024-02-07
    Description: The evolution of past global ice sheets is highly uncertain. One example is the missing ice problem during the Last Glacial Maximum (LGM, 26 000-19 000 years before present) – an apparent 8-28 m discrepancy between far-field sea level indicators and modelled sea level from ice sheet reconstructions. In the absence of ice sheet reconstructions, researchers often use marine δ18O proxy records to infer ice volume prior to the LGM. We present a global ice sheet reconstruction for the past 80 000 years, called PaleoMIST 1.0, constructed independently of far-field sea level and δ18O proxy records. Our reconstruction is compatible with LGM far-field sea-level records without requiring extra ice volume, thus solving the missing ice problem. However, for Marine Isotope Stage 3 (57 000-29 000 years before present) - a pre-LGM period - our reconstruction does not match proxy-based sea level reconstructions, indicating the relationship between marine δ18O and sea level may be more complex than assumed.
    Type: Article , PeerReviewed
    Format: text
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