Trial and error

A pac-learning algorithm isd-space bounded, if it stores at mostd examples from the sample at any time. We characterize thed-space learnable concept classes. For this purpose we introduce the compression parameter of a concept classb and design our Trial and Error Learning Algorithm. We show: b isd-space learnable if and only if the compression parameter ofb is at mostd. This learning algorithm does not produce a hypothesis consistent with the whole sample as previous approaches e.g. by Floyd, who presents consistent space bounded learning algorithms, but has to restrict herself to very special concept classes. On the other hand our algorithm needs large samples; the compression parameter appears as exponent in the sample size. We present several examples of polynomial time space bounded learnable concept classes:

- all intersection closed concept classes with finite VC-dimension.

- convexn-gons in ?².

- halfspaces in ?ⁿ.

- unions of triangles in ?².

We further relate the compression parameter to the VC-dimension, and discuss variants of this parameter.     

Title characteristics and citations in economics

We provide a view of the literature aging features in the sciences and social sciences, at different aggregation levels, of major fields, subfields, journals and individual papers and from different perspectives. Against to the wide belief that scientific literature may become more rapidly obsolete, we found that, in general, the share of more recent references were distinctly lower in 2014 than that in 1992, which holds for all aggregation levels. As exceptions, the subfields related to Chemistry and the subfield energy and fuels, have shown a clear trend to cite more recent literature than older articles. Particle and nuclear physics and astronomy and astrophysics, the two subfields which strongly rely on e-print archives, have shown a ‘polarization’ tendency of reference distribution. Furthermore, we stress that it is very important to measure the Price Index at the paper level to account for differences between the documents published in the same journals and (sub-)fields.     

Synthesis,characterization and in situ monitoring of the mechanochemical reaction process of two manganese(II)-phosphonates with N-containing ligands

Two divalent manganese aminophosphonates, manganese mono(nitrilotrimethylphosphonate) (MnNP₃) and manganese bis(N-(carboxymethyl)iminodi(methylphosphonate)) (Mn(NP₂AH)₂), have been prepared by mechanochemical synthesis and characterized by powder X-ray diffraction (PXRD). The structure of the novel compound Mn(NP₂AH)₂ was determined from PXRD data. MnNP₃ as well as Mn(NP₂AH)₂ exhibits a chain-like structure. In both cases, the manganese atom is coordinated by six oxygen atoms in a distorted octahedron. The local coordination around Mn was further characterized by extended X-ray absorption fine structure. The synthesis process was followed in situ by synchrotron X-ray diffraction revealing a three-step reaction mechanism. The as-prepared manganese(II) phosphonates were calcined on air. All samples were successfully tested for their suitability as catalyst material in the oxygen evolution reaction.     

Modelling the dynamics of landscape transformations and population growth in the highlands of Ethiopia using remote-sensing data

This study models landscape transformations and settlement dynamics in a highland area of Ethiopia over a 56 year period (1957–2013). The analyses were performed using aerial photographs, satellite images, and field data. The remotely sensed images were geometrically and radiometrically corrected. Visual interpretation of aerial photographs and supervised classification of multispectral satellite images using the maximum likelihood algorithm were chosen for land-cover mapping. The population size was estimated by counting the houses on the aerial photographs and on the high-resolution images, and by direct census. The overall trend showed an increase of cropland and a decrease of other types of land cover. Landscape transformation rates recently slowed down due to ownership and policy restrictions. The average cropland holding size per family has decreased from 2.6 to 1.1 ha due to the exponential growth of the population. The relationship between settlement and cropland expansion is statistically significant. Models of logistic growth were fitted to the cropland area, and models of exponential and logistic growth to the population development to estimate the carrying capacity. The concomitant increase of population and the decrease of cropland per head resulted in a shortage of food and energy, highlighting the importance of policy decisions on land management.     

Pump–Push–Probe for Ultrafast All‐Optical Switching: The Case of a Nanographene Molecule

In the last two decades, the three‐beam pump–push–probe (PPP) technique has become a well‐established tool for investigating the multidimensional configurational space of a molecule, as it permits disclosure of precious information about the multiple and often complex deactivation pathways of the excited molecule. From the spectroscopic point of view, such a tool has revealed details about the efficiency of charge pair generation and conformational relaxation in π‐conjugated molecules and macromolecules. In addition, PPP is effectively utilized for modulating the gain signal in conjugated materials by taking advantage of the spectral overlap between stimulated emission and charge absorption in those systems. However, the relatively low stability of conjugated polymers under intense photoexcitation is a crucial limitation for their real employment in plastic optical fibers (POFs) and for signal control applications. Herein, the role of PPP for achieving ultrafast all‐optical switching in π‐conjugated systems is highlighted. Furthermore, new experimental data on optical switching of a newly synthesized nanographene molecule, namely dibenzo[hi,st]ovalene (DBOV), is reported. The superior environmental and photostability of DBOV and, in general, of graphene nanostructures can represent a great advantage for their effective applications in POFs and information and communications technology.     

Semantics in space systems architectures

Costs, life cycles, technologies and agreements between stakeholders and organizations make space systems unique with respect to the complexity. A commonly accepted technique to address part of this complexity is to model and to maintain space systems architectures through the life cycle of their space programs. The benefits may range from supporting consistent model definitions and maintenance up to supporting analysis and verification. Space systems architectures have been modeled using UPDM (unified profile for DoDAF And MODAF; a UML profile). In fact, UPDM argues that it provides a clearer understanding of the semantics behind specific views and viewpoints. Nonetheless, while UML defines its semantics imprecisely using plain text and variation points, UPDM does not define any semantics. In this paper, we evaluate an extension of fUML (semantics of a foundational subset for executable UML models) as a semantics for space systems architectures. The extension of fUML as a synchronous language (synchronous fUML) provides a limited, but formally precise and deterministic, form to describe structure and behavior in UML. Through the combination of this semantics with UPDM, a precise language supporting a standardized meta-model emerges for the definition of space systems architectures. At the end, a simplified case study covering the operational view (OV-*) is presented. Our initial results show that synchronous fUML is able to offer a precise and deterministic semantics for UPDM.     

A discontinuous phase field approach to variational growth-based topology optimization

Numerical instabilities cause the well-known problem of checkerboarding during topology optimization: elements that possess material are periodically neighbored to elements that are material-free. Furthermore, such numerical solutions depend on the finite element mesh and no reasonable processing techniques exist for manufacture. Thus, integral- or gradient-based regularization techniques are usually applied during topology optimization. In this paper, a novel approach to regularization is derived for a recently published variational approach to topology optimization that is based on material growth. The presented approach shares some similarities with the discontinuous Galerkin method and completely removes consideration of additional nodal quantities or complex integration schemes. The derivation and numerical treatment of the resulting phase field equation as well as exemplary numerical results are presented.     

AMPK Prevents Palmitic Acid-Induced Apoptosis and Lipid Accumulation in Cardiomyocytes

Palmitic acid, a main fatty acid (FA) in human nutrition, can induce apoptosis of cardiomyocytes. However, a specific combination of palmitic, myristic and palmitoleic acid (CoFA) has been reported to promote beneficial cardiac growth. The aim of this study was to investigate the relevance of CoFA for cardiac growth and to delineate the underlying signaling pathways of CoFA and palmitic acid treatment. CoFA treatment of C57Bl/6 mice increased FA serum concentrations. However, morphologic and echocardiographic analysis did not show myocardial hypertrophy. Cell culture studies using rat ventricular cardiomyocytes revealed an increased phosphorylation of AMP activated protein kinase α (AMPKα) to 155 ± 19% and its target acetyl-CoA-carboxylase to 177 ± 23% by CoFA. Treatment with myristic acid also increased AMPKα phosphorylation to 189 ± 32%. Palmitic acid did not activate AMPKα but increased expression of the FA translocase CD36 (FAT/CD36) to 163 ± 23% and adipose-differentiation-related-protein (ADRP), a sensitive marker of lipid accumulation, to 168 ± 42%. This was associated with an increased phosphorylation of the stress-activated-protein-kinase/Jun-amino-terminal-kinase (SAPK/JNK) to 173 ± 27%. In CoFA-treated cells, phosphorylation of SAPK/JNK was unaltered. FACS analysis revealed increased apoptosis to 159 ± 5% by palmitic acid but not by CoFA. AMPK activator AICAR (5-aminoimidazole-4-carboxamide ribonucleotide) prevented up-regulation of ADRP and increased apoptosis by palmitic acid. Confirming these findings, inhibition of AMPK by compound C in CoFA-treated cardiomyocytes resulted in an increased expression of ADRP to 154 ± 27%, FAT/CD36 to 167 ± 28% and apoptosis to 183 ± 12%. These data reveal that AMPK activation plays an important role in prevention of palmitic acid-induced apoptosis and lipid accumulation in cardiomyocytes.     

Polychlorierte Biphenyle (PCB) in Fischen aus Teichwirtschaften und Nachkl?rteichen

Zusammenfassung Das Muskelgewebe von 58 Fischen aus Teichwirtschaften und 17 Fischen aus Nachklärteichen wurde auf seinen Gehalt an den sechs in der Schadstoff-Höchstmengenverordnung aufgeführten polychlorierten Biphenyl-(PCB)-Kongeneren sowie 2,2,4,5-Tetrachlorbiphenyl (PCB Nr. 49) untersucht. Die Tiere wurden in den Jahren 1986 und 1987 den Gewässern entnommen. Sie waren mit hoch und auch mit niedrig chlorierten Biphenylen belastet. Die Konzentrationen derniedrig chlorierten Kongeneren Nr. 28, 49 und 52 lagen deutlich unter denen der hoch chlorierten. Dennoch belegen die Ergebnisse den Eintrag von Komponenten des niedrig chlorierten technischen Gemisches Clophen C in Umwelt und Nahrungsketten. Verglichen mit den 1980/81 durchgeführten Untersuchungen an Fischen aus Teichwirtschaften war—bezogen auf das hoch chlorierte technische Gemisch Clophen A 60—ein Rückgang der PCB-Belastung des Muskelgewebes erkennbar. Dies steht mit den kürzlich von der hiesigen Arbeitsgruppe an Füchsen und Lebensmitteln erhaltenen Befunden in Übereinstimmung. Die Konzentrationen aller untersuchten PCB-Kongenere waren im Muskelgewebe von Fischen aus Nachklärteichen statistisch signifikant höher als bei den Tieren aus Teichwirtschaften. Die PCB-Gehalte sind somit vom Kontaminationsgrad der verschiedenen Lebensräume abhängig. Demnach können Fische als Bioindikator für den Eintrag hoch und niedrig chlorierter PCB-Kongenere in aquatische Ökosysteme dienen.

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Polychlorinated biphenyls in fish from fish hatcheries and settle ponds

Summary The concentrations of six selected single polychlorinated biphenyl (PCB) congeners, for which legal tolerance levels became valid in 1988, and the congener no. 49 (2,2,4,5-tetrachlorobiphenyl) were determined in the muscle tissue of 58 fishes from fish hatcheries and in 17 fishes from settle ponds. The fish were taken from flowing waters in the years 1986 and 1987. High and low chlorinated biphenyls were present in each sample, but the concentration of the low chlorinated biphenyls was distinctly lower than that of the higher chlorinated ones. Nevertheless these results demonstrate the intake of components of low chlorinated technical PCB mixtures in the environment and food chains. Compared with the investigations carried out in 1980/81 in fishes from fish hatcheries, a decrease of PCB contamination in the muscle tissues with regard to the technical mixture Clophen A 60 was observed. This is in accordance with the results our team obtained a short time previously in muscle tissue from foxes and in food-stuffs. The concentration of all PCB congeners determined in the muscle tissue from fish of settle ponds was significantly higher than in the tissue from fish taken from hatcheries. Thus, the PCB content depends on the PCB load in different environments. Therefore, fishes can be useful as bioindicators for the intake of low and high chlorinated PCB congeners in aquatic ecosystems.