General Program Synthesis from Examples Using Genetic Programming with Parent Selection Based on Random Lexicographic Orderings of Test Cases

Software developers routinely create tests before writing code, to ensure that their programs fulfill their requirements. Instead of having human programmers write the code to meet these tests, automatic program synthesis systems can create programs to meet specifications without human intervention, only requiring examples of desired behavior. In the long-term, we envision using genetic programming to synthesize large pieces of software. This dissertation takes steps toward this goal by investigating the ability of genetic programming to solve introductory computer science programming problems. We present a suite of 29 benchmark problems intended to test general program synthesis systems, which we systematically selected from sources of introductory computer science programming problems. This suite is suitable for experiments with any program synthesis system driven by input/output examples. Unlike existing benchmarks that concentrate on constrained problem domains such as list manipulation, symbolic regression, or boolean functions, this suite contains general programming problems that require a range of programming constructs, such as multiple data types and data structures, control flow statements, and I/O. The problems encompass a range of difficulties and requirements as necessary to thoroughly assess the capabilities of a program synthesis system. Besides describing the specifications for each problem, we make recommendations for experimental protocols and statistical methods to use with the problems. This dissertation\u27s second contribution is an investigation of behavior-based parent selection in genetic programming, concentrating on a new method called lexicase selection. Most parent selection techniques aggregate errors from test cases to compute a single scalar fitness value; lexicase selection instead treats test cases separately, never comparing error values of different test cases. This property allows it to select parents that specialize on some test cases even if they perform poorly on others. We compare lexicase selection to other parent selection techniques on our benchmark suite, showing better performance for lexicase selection. After observing that lexicase selection increases exploration of the search space while also increasing exploitation of promising programs, we conduct a range of experiments to identify which characteristics of lexicase selection influence its utility

Upwelling in the Humboldt Coastal Current near Valparaiso, Chile

In December, 1975, an upwelling study was conducted at Punta Curaumilla near Valparaiso, Chile. Previous work (Silva, 1973) had indicated a zone of relatively intense upwelling around this point of land. In the present study , a bathythermograph survey confirmed the presence of the intensification, identified as a tongue of cool water extending seaward and equatorward of the point. Following Arthur\u27s (1965) scale analysis it is suggested that the acceleration of relative vorticity past the point of land is responsible for intensification...

ALKOR Scientific Cruise Report The Ocean's Alkalinity - Connecting geological and metabolic processes and time-scales: mechanisms and magnitude of metabolic alkalinity generation in the North Sea Cruise No. AL557

June 04 – June 23, 2021 Cuxhaven (Germany) – Cuxhaven (Germany) North Sea Alkalinit

Pickering emulsions stabilized by stacked catanionic micro-crystals controlled by charge regulation

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.In this paper the mechanism behind the stabilization of Pickering emulsions by stacked catanionic micro-crystals is described. A temperature-quench of mixtures of oppositely charged surfactants (catanionics) and tetradecane from above the chain melting temperature to room temperature produces stable oil-in-water (o/w) Pickering emulsions in the absence of Ostwald ripening. The oil droplets are decorated by stacks of crystalline discs. The stacking of these discs is controlled by charge regulation as derived from conductivity, scattering and zeta potential measurements. Catanionic nanodiscs are ideal solid particles to stabilize Pickering emulsions since they present no density difference and a structural surface charge which is controlled by the molar ratio between anionic and cationic components. The contact angle of catanionic nanodiscs at a water/oil interface is also controlled by the non-stoichiometry of the components. The resulting energy of adhesion and the repulsion between droplets is much larger than kT. As a consequence of these unique properties of nanodiscs, this type of emulsions presents an extremely high resistance towards coalescence and creaming, even in the presence of salt

Looking beyond stratification: a model-based analysis of the biological drivers of oxygen deficiency in the North Sea

Low oxygen conditions, often referred to as oxy- gen deficiency, occur regularly in the North Sea, a temperate European shelf sea. Stratification represents a major process regulating the seasonal dynamics of bottom oxygen, yet, low- est oxygen conditions in the North Sea do not occur in the regions of strongest stratification. This suggests that stratifi- cation is an important prerequisite for oxygen deficiency, but that the complex interaction between hydrodynamics and the biological processes drives its evolution. In this study we use the ecosystem model HAMSOM- ECOHAM to provide a general characterisation of the dif- ferent zones of the North Sea with respect to oxygen, and to quantify the impact of the different physical and biological factors driving the oxygen dynamics inside the entire sub- thermocline volume and directly above the bottom. With respect to oxygen dynamics, the North Sea can be subdivided into three different zones: (1) a highly produc- tive, non-stratified coastal zone, (2) a productive, season- ally stratified zone with a small sub-thermocline volume, and (3) a productive, seasonally stratified zone with a large sub- thermocline volume. Type 2 reveals the highest susceptibility to oxygen deficiency due to sufficiently long stratification pe- riods (textgreater60 days) accompanied by high surface productivity resulting in high biological consumption, and a small sub- thermocline volume implying both a small initial oxygen in- ventory and a strong influence of the biological consumption on the oxygen concentration. Year-to-year variations in the oxygen conditions are caused by variations in primary production, while spatial dif- ferences can be attributed to differences in stratification and water depth. The large sub-thermocline volume dominates the oxygen dynamics in the northern central and northern North Sea and makes this region insusceptible to oxygen de- ficiency. In the southern North Sea the strong tidal mixing inhibits the development of seasonal stratification which pro- tects this area from the evolution of low oxygen conditions. In contrast, the southern central North Sea is highly suscep- tible to low oxygen conditions (type 2). We furthermore show that benthic diagenetic processes represent the main oxygen consumers in the bottom layer, consistently accounting for more than 50% of the overall consumption. Thus, primary production followed by rem- ineralisation of organic matter under stratified conditions constitutes the main driver for the evolution of oxygen defi- ciency in the southern central North Sea. By providing these valuable insights, we show that ecosystem models can be a useful tool for the interpretation of observations and the es- timation of the impact of anthropogenic drivers on the North Sea oxygen conditions

Greenhouse gases in cold water filaments in the Arabian Sea during the Southwest Monsoon

The distribution of partial pressure of carbon dioxide and the concentrations of nitrous oxide and methane were investigated in a cold water filament near the coastal upwelling region off Oman at the beginning of the southwest monsoon in 1997. The results suggest that such filaments are regions of intense biogeochemical activity which may affect the marine cycling of climatically relevant trace gase

Microscopic evidence for strong periodic lattice distortion in 2D charge-density wave systems

In the quasi-2D electron systems of the layered transition metal dichalcogenides (TMD) there is still a controversy about the nature of the transitions to charge-density wave (CDW) phases, i.e. whether they are described by a Peierls-type mechanism or by a lattice-driven model. By performing scanning tunneling microscopy (STM) experiments on the canonical TMD-CDW systems, we have imaged the electronic modulation and the lattice distortion separately in 2H-TaS$_2$, TaSe$_2$, and NbSe$_2$. Across the three materials, we found dominant lattice contributions instead of the electronic modulation expected from Peierls transitions, in contrast to the CDW states that show the hallmark of contrast inversion between filled and empty states. Our results imply that the periodic lattice distortion (PLD) plays a vital role in the formation of CDW phases in the TMDs and illustrate the importance of taking into account the more complicated lattice degree of freedom when studying correlated electron systems