Characterization of circulation patterns in the Gulf of Cadiz based on satellite altimetry

Os dados de altimetria de satélite (1993-2020) são utilizados para analisar as correntes geostróficas e a Topografia Dinâmica Absoluta (ADT) do Golfo de Cádis (GoC). O estudo do ADT anual mostrou que a subida do nível do mar do GoC está bem dentro da tendência global. A análise sazonal do ADT e dos fluxos geostróficos mostrou um padrão bilateral. Nos meses de Verão, ocorrem fortes correntes equatoriais sobre a área da plataforma, enquanto que as correntes no interior do GoC são mais fracas. No Inverno, contudo, as correntes do Equador sobre a área da prateleira são mais fracas e mais fortes no interior do GoC. Dois mecanismos em particular poderiam ser identificados para estes padrões opostos: (1) a ocorrência de ventos fortes a norte, que formam frentes de afloramento sobre a plataforma no Verão, e (2) a Corrente dos Açores que atinge e influencia os fluxos no interior do GoC no Inverno. Além disso, são explorados os efeitos das variações do nível da água nos padrões de circulação na plataforma norte do GoC. O ADT e as circulações são comparados com medições in situ utilizando medidores de marés e Perfis Acústicos de Corrente Doppler (ADCP), respectivamente. Foi demonstrado que o ADT tem correlações moderadas a boas com as medições de marés. Não foi possível encontrar correspondência clara entre a direcção do fluxo alongshore e o declive alongshore. Isto pode ser devido ao erro do ADT perto da costa. Além disso, os dados do Radar de Alta Frequência (HFR) são utilizados para examinar a relação entre o ADT e a Corrente Contadora Costeira (CCC) estabelecida durante cinco exemplos com as mais fortes variações do ADT. Demonstra-se que o ADT era adequado para identificar gradientes de pressão alongshore desequilibrados, que são condutores plausíveis do CCC para os exemplos analisados. As medições do HFR revelaram que os fluxos de fluxo em direcção aos pólos atingem a sua velocidade máxima dois dias após a inclinação alongshore se tornar desequilibrada.Satellite altimetry data (1993-2020) is used to analyze the geostrophic currents and Absolute Dynamic Topography (ADT) of the Gulf of Cadiz (GoC). The study of the annual ADT showed that the sea level rise of the GoC is well within the global trend. The seasonal analysis of ADT and geostrophic flows showed a bilateral pattern. In the summer months, strong equatorward currents occur over the shelf area, whereas the currents in the interior of the GoC are weaker. In winter, however the equatorward currents over the shelf area are weaker and stronger at the interior of the GoC. Two mechanisms in particular could be identified for these countervailing patterns: (1) the occurrence of strong northerly winds, which form upwelling fronts over the shelf in summer, and (2) the Azores Current which reaches and influences the flows in the interior of the GoC in winter. Further, the effects of water level variations on circulation patterns at the northern shelf of the GoC are explored. The ADT and circulations are compared with in situ measurements using tidal gauges and Acoustic Doppler Current Profiles (ADCP), respectively. It was shown that the ADT has moderate to good correlations to tidal gauge measurements. No clear correspondence between the alongshore flow direction and alongshore slope could be found. This might be due to the ADT error near the coast. Moreover, High Frequency Radar (HFR) data is used to examine the relation between ADT and Coastal Counter Current (CCC) set up during five examples with strongest ADT variations. It is shown that the ADT was suitable to identify unbalanced alongshore pressure gradients, which are plausible drivers of the CCC for the analyzed examples. The HFR measurements revealed that poleward flows reach their maximum velocity two days after the alongshore slope becomes unbalanced

Long-term bank lending and the transfer of aggregate risk

Long-term debt contracts transfer aggregate risk from borrowing firms to lending banks. When aggregate shocks increase the future default probability of firms, banks are not compensated for the default risk of existing contracts. If banks are highly leveraged, this can lead to financial instability with severe repercussions in the real economy. To study this mechanism quantitatively, we build a macroeconomic model of financial intermediation with long-term defaultable loan contracts and calibrate it to match aggregate firm and bank exposure to business cycle risks. Our model exhibits banking crises that closely resemble observed crisis episodes. We find that such crises do not arise in an economy with short-term debt. Our results on the role of long-term debt completely reverse if financial regulation is implemented to increase banks' risk bearing capacity. The financial sector is then well equipped to take on the aggregate risk, such that long-term lending stabilizes the business cycle by providing insurance to the corporate sector

Brill–Noether general K3 surfaces with the maximal number of elliptic pencils of minimal degree

We explicitly construct Brill–Noether general K3 surfaces of genus 4, 6 and 8 having the maximal number of elliptic pencils of degrees 3, 4 and 5, respectively, and study their moduli spaces and moduli maps to the moduli space of curves. As an application we prove the existence of Brill–Noether general K3 surfaces of genus 4 and 6 without stable Lazarsfeld–Mukai bundles of minimal c2

CONODONTS OF THE LOWERMOST TRIASSIC OF SPITI, AND NEW ZONATION BASED ON NEOGONDOLELLA SUCCESSIONS

Conodonts from the lowermost Triassic Otoceras woodwardi beds and adjacent strata of Spiti are described and compared with Permian-Triassic (P-T) boundary bed faunas from elsewhere. A new pelagic zonation based on Neogondolella is introduced: the interval characterized by N. carinata-N. taylorae is subdivided into three parts based on successive first appearances of N. meishanensis, N. krystyni Orchard n. sp. and N. discreta Orchard and Krystyn n. sp., the nominal species of three successive zones. The development of these Griesbachian species involves a progressive morphological change in the configuration of the axial part (blade-carina-cusp) of the pectiniform elements. The pelagic conodont zonation is intercalibrated with the parallel zonation based on species of Hindeodus and Isarcicella, and with ammonoid faunas from Spiti, other Himalayan localities, and the Arctic. The meishanensis Zone embraces the parvus Zone and part of the overlying staeschei Zone. Strata containing O. woodwardi in Spiti carry the indices to the staeschei and krystyni zones. The Neogondolella conodont fauna associated with Otoceras differs from that of the latest Permian Changshing Limestone of China, but resembles that from the P-T boundary transition beds at Meishan, where a meishanensis Zone of restricted scope occurs beneath the parvus datum. The faunal change which introduces the characteristic Neogondolella species of the N. carinata-N. taylorae fauna occurs at the base of the P-T boundary transition beds at Meishan, the proposed boundary stratotype. Slightly above this level, the disappearance of most Neogondolella species and the introduction of new Hindeodus species coincides with a change in conodont biofacies rather than an extinction event. In the Spiti sections, the N. carinata-N. taylorae fauna, associated at first with H. parvus (as in Selong, Tibet), persists through the entire Griesbachian. Indices of the three Neogondolella zones are also recognized in the Salt Range and the Canadian Arctic. Four new conodont species are described: Neogondolella discreta, N. kazi, N. krystyni, and N. nassichuki.&nbsp

Enhanced Electrochemistry of Nanoparticle-Embedded Polyelectrolyte Films: Interfacial Electronic Coupling and Distance Dependence

Factors affecting the electronic communication believed to be responsible for the enhanced solution electrochemistry observed at electrodes modified with hybrid polyelectrolyte–nanoparticle (PE–NP) film assemblies were systematically investigated. Specifically, the faradaic current and voltammetric peak splitting recorded for cyclic voltammetry of ferricyanide redox species (Fe(CN)63−/4−) at films constructed with various architectures of citrate-stabilized gold NPs embedded in polyelectrolyte films composed of poly-l-lysine and poly-S-styrene were used to establish the relative importance of both distance and electronic coupling. Layer-by-layer construction of PE–NP films allowed for the position and density of NPs to be varied within the film to assess electronic coupling between particles (interparticle coupling) as well as at the electrode–film interface. The cumulative results observed at these films suggest that, while distance dependence prevails in nearly every case and interparticle coupling can contribute to facilitating the Fe(CN)63−/4− electrochemistry, interfacial electronic coupling of the PE–NP films is of critical importance and decoupling is easily achieved by disengaging NP–electrode interactions

Safety Aware Reinforcement Learning by Identifying Comprehensible Constraints in Expert Demonstrations

When used in real-world environments, agents must meet high safety requirements as errors have direct consequences. Besides the safety aspect, the explainability of the systems is of particular importance. Therefore, not only should errors be avoided during the learning process, but also the decision process should be made transparent. Existing approaches are limited to solving a single problem. For real-world use, however, several criteria must be fulfilled at the same time. In this paper we derive comprehensible rules from expert demonstrations which can be used to monitor the agent. The developed approach uses state of the art classification and regression trees for deriving safety rules combined with concepts in the field of association rule mining. The result is a compact and comprehensible rule set that explains the expert’s behavior and ensures safety. We evaluate our framework in common OpenAI environments. Results show that the elaborated approach is able to identify safety-relevant rules and imitate expert behavior especially in edge cases. Evaluations on higher dimensional observation spaces and continuous action spaces highlight the transferability of the approach to new tasks while maintaining compactness and comprehensibility of the rule set