375 research outputs found
Latitudinal differences in the amplitude of the OAE-2 carbon isotopic excursion: pCO2 and paleoproductivity [Discussion paper]
A complete, well-preserved record of the Cenomanian/Turonian (C/T) Oceanic Anoxic Event 2 (OAE-2) was recovered from Demerara Rise in the southern North Atlantic Ocean (ODP site 1260). Across this interval, we determined changes in the stable carbon isotopic composition of sulfur-bound phytane (δ13Cphytane, a biomarker for photosynthetic algae. The δ13Cphytane record shows a positive excursion at the onset of the OAE-2 interval, with an unusually large amplitude (~7 ‰) compared to existing C/T proto-North Atlantic δ13Cphytane records (3–6 ‰). Overall, the amplitude of the excursion of δ13Cphytane decreases with latitude. Using reconstructed sea surface temperature (SST) gradients for the proto-North Atlantic, we investigated environmental factors influencing the latitudinal δ13Cphytane gradient. The observed gradient is best explained by high productivity at DSDP Site 367 and Tarfaya basin before OAE-2, which changed in overall high productivity throughout the proto-North Atlantic during OAE-2. During OAE-2, productivity at site 1260 and 603B was thus more comparable to the mid-latitude sites. Using these constraints as well as the SST and δ13Cphytane-records from Site 1260, we subsequently reconstructed pCO2 levels across the OAE-2 interval. Accordingly, pCO2 decreased from ca. 1750 to 900 ppm during OAE-2, consistent with enhanced organic matter burial resulting in lowering pCO2. Whereas the onset of OAE-2 coincided with increased pCO2, in line with a volcanic trigger for this event, the observed cooling within OAE-2 probably resulted from CO2 sequestration in black shales outcompeting CO2 input into the atmosphere. Together these results show that the ice-free Cretaceous world was sensitive to changes in pCO2 related to perturbations of the global carbon cycle
Latitudinal differences in the amplitude of the OAE-2 carbon isotopic excursion : pCO2 and paleo productivity
A complete, well-preserved record of the Cenomanian/Turonian (C/T) Oceanic Anoxic Event 2 (OAE-2) was recovered from Demerara Rise in the southern North Atlantic Ocean (ODP site 1260). Across this interval, we determined changes in the stable carbon isotopic composition of sulfur-bound phytane (δ13Cphytane), a biomarker for photosynthetic algae. The δ13Cphytane record shows a positive excursion at the onset of the OAE-2 interval, with an unusually large amplitude (~7‰) compared to existing C/T proto-North Atlantic δ13Cphytane records (3–6‰). Overall, the amplitude of the excursion of δ13Cphytane decreases with latitude. Using reconstructed sea surface temperature (SST) gradients for the proto-North Atlantic, we investigated environmental factors influencing the latitudinal δ13Cphytane gradient. The observed gradient is best explained by high productivity at DSDP Site 367 and Tarfaya basin before OAE-2, which changed in overall high productivity throughout the proto-North Atlantic during OAE-2. During OAE-2, productivity at site 1260 and 603B was thus more comparable to the mid-latitude sites. Using these constraints as well as the SST and δ13Cphytane-records from Site 1260, we subsequently reconstructed pCO2 levels across the OAE-2 interval. Accordingly, pCO2 decreased from ca. 1750 to 900 ppm during OAE-2, consistent with enhanced organic matter burial resulting in lowering pCO2. Whereas the onset of OAE-2 coincided with increased pCO2, in line with a volcanic trigger for this event, the observed cooling within OAE-2 probably resulted from CO2 sequestration in black shales outcompeting CO2 input into the atmosphere. Together these results show that the ice-free Cretaceous world was sensitive to changes in pCO2 related to perturbations of the global carbon cycle
Fast Deterministic Fully Dynamic Distance Approximation
In this paper, we develop deterministic fully dynamic algorithms for
computing approximate distances in a graph with worst-case update time
guarantees. In particular, we obtain improved dynamic algorithms that, given an
unweighted and undirected graph undergoing edge insertions and
deletions, and a parameter , maintain
-approximations of the -distance between a given pair of
nodes and , the distances from a single source to all nodes
("SSSP"), the distances from multiple sources to all nodes ("MSSP"), or the
distances between all nodes ("APSP").
Our main result is a deterministic algorithm for maintaining
-approximate -distance with worst-case update time
(for the current best known bound on the matrix multiplication
exponent ). This even improves upon the fastest known randomized
algorithm for this problem. Similar to several other well-studied dynamic
problems whose state-of-the-art worst-case update time is , this
matches a conditional lower bound [BNS, FOCS 2019]. We further give a
deterministic algorithm for maintaining -approximate
single-source distances with worst-case update time , which also
matches a conditional lower bound.
At the core, our approach is to combine algebraic distance maintenance data
structures with near-additive emulator constructions. This also leads to novel
dynamic algorithms for maintaining -emulators that improve
upon the state of the art, which might be of independent interest. Our
techniques also lead to improved randomized algorithms for several problems
such as exact -distances and diameter approximation.Comment: Changes to the previous version: improved bounds for approximate st
distances using new algebraic data structure
Proportionality in Approval-Based Participatory Budgeting
The ability to measure the satisfaction of (groups of) voters is a crucial
prerequisite for formulating proportionality axioms in approval-based
participatory budgeting elections. Two common - but very different - ways to
measure the satisfaction of a voter consider (i) the number of approved
projects and (ii) the total cost of approved projects, respectively. In
general, it is difficult to decide which measure of satisfaction best reflects
the voters' true utilities. In this paper, we study proportionality axioms with
respect to large classes of approval-based satisfaction functions. We establish
logical implications among our axioms and related notions from the literature,
and we ask whether outcomes can be achieved that are proportional with respect
to more than one satisfaction function. We show that this is impossible for the
two commonly used satisfaction functions when considering proportionality
notions based on extended justified representation, but achievable for a notion
based on proportional justified representation. For the latter result, we
introduce a strengthening of priceability and show that it is satisfied by
several polynomial-time computable rules, including the Method of Equal Shares
and Phragm\`en's sequential rule
Cost-Effectiveness of Pharmacotherapy to Reduce Obesity
Aims: Obesity causes a high disease burden in Australia and across the world. We aimed to analyse the cost-effectiveness of weight reduction with pharmacotherapy in Australia, and to assess its potential to reduce the disease burden due to excess body weight
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Investigation of the Processability of Polyether Block Amide in High Speed Sintering
The High Speed Sintering (HSS) process ranks among the processes of Powder Bed
Fusion of polymers (PBF-P) of Additive Manufacturing (AM). Its scalability, constant layer
time and high quality of complex parts compared to other AM processes are some of the
characteristics of the HSS showing its potential for series production for small to medium series.
Most of the investigations for the PBF-P processes were conducted using commercially
available materials like Polyamide 12 (PA12), Polyamide 6 (PA6), Thermoplastic polyurethane
(TPU), Polypropylene (PP) and Polybutylene terephthalate (PBT). This work reports from the
processing of Polyether block amide (PEBA) in HSS. As a block-copolymer on amide basis,
PEBA shows higher performance compared to other block-copolymers like TPU: The high
elastic properties, low density and high service temperature make PEBA an ideal material for
the use in the athletic footwear and outdoor industry. Until now, no research was conducted on
processing PEBA powder in HSS. This work focusses on the material analysis of PEBA powder
and manufacturing of specimens of varying sets of process parameters using methods of Design
of Experiments (DoE) and IFINAM TPA powder from Evonik. Based on a predictive model,
parameter sets for optimum mechanical properties, dimensional accuracy and overall part
properties of HSS PEBA parts were optimised within the framework of this work.Mechanical Engineerin
The rise of policy coherence for development: a multi-causal approach
In recent years policy coherence for development (PCD) has become a key principle in international development debates, and it is likely to become even more relevant in the discussions on the post-2015 sustainable development goals. This article addresses the rise of PCD on the Western donors’ aid agenda. While the concept already appeared in the work of Organisation for Economic Co-operation and Development (OECD) in the early 1990s, it took until 2007 before PCD became one of the Organisation’s key priorities. We adopt a complexity-sensitive perspective, involving a process-tracing analysis and a multi-causal explanatory framework. We argue that the rise of PCD is not as contingent as it looks. While actors such as the EU, the DAC and OECD Secretariat were the ‘active causes’ of the rise of PCD, it is equally important to look at the underlying ‘constitutive causes’ which enabled policy coherence to thrive well
An organic borate salt with superior p‐doping capability for organic semiconductors
Molecular doping allows enhancement and precise control of electrical properties of organic semiconductors, and is thus of central technological relevance for organic (opto‐) electronics. Beyond single‐component molecular electron acceptors and donors, organic salts have recently emerged as a promising class of dopants. However, the pertinent fundamental understanding of doping mechanisms and doping capabilities is limited. Here, the unique capabilities of the salt consisting of a borinium cation (Mes2B+; Mes: mesitylene) and the tetrakis(penta‐fluorophenyl)borate anion [B(C6F5)4]− is demonstrated as p‐type dopant for polymer semiconductors. With a range of experimental methods, the doping mechanism is identified to comprise electron transfer from the polymer to Mes2B+, and the positive charge on the polymer is stabilized by [B(C6F5)4]−. Notably, the former salt cation leaves during processing and is not present in films. The anion [B(C6F5)4]− even enables the stabilization of polarons and bipolarons in poly(3‐hexylthiophene), not yet achieved with other molecular dopants. From doping studies with high ionization energy polymer semiconductors, the effective electron affinity of Mes2B+[B(C6F5)4]− is estimated to be an impressive 5.9 eV. This significantly extends the parameter space for doping of polymer semiconductors
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