938 research outputs found
Gaifman Normal Forms for Counting Extensions of First-Order Logic
We consider the extension of first-order logic FO by unary counting quantifiers and generalise the notion of Gaifman normal form from FO to this setting. For formulas that use only ultimately periodic counting quantifiers, we provide an algorithm that computes equivalent formulas in Gaifman normal form. We also show that this is not possible for formulas using at least one quantifier that is not ultimately periodic.
Now let d be a degree bound. We show that for any formula phi with arbitrary counting quantifiers, there is a formula gamma in Gaifman normal form that is equivalent to phi on all finite structures of degree <= d. If the quantifiers of phi are decidable (decidable in elementary time, ultimately periodic), gamma can be constructed effectively (in elementary time, in worst-case optimal 3-fold exponential time).
For the setting with unrestricted degree we show that by using our Gaifman normal form for formulas with only ultimately periodic counting quantifiers, a known fixed-parameter tractability result for FO on classes of structures of bounded local tree-width can be lifted to the extension of FO with ultimately periodic counting quantifiers (a logic equally expressive as FO+MOD, i.e., first-oder logic with modulo-counting quantifiers)
A Cohort Study Followed for 13 Years
Background There is growing evidence of an association between oral health,
specifically dental status, and chronic systemic diseases. However, varying
measures of dental status across different populations and low study sample
has made comparison of studies and conclusion of findings unclear. Our aim is
to examine whether the number of teeth as a measure of dental status is
associated with incident chronic diseases in a cohort setting. Methods We
conducted a cohort study among 24,313 middle-aged Germans followed up for 13
years. Data on number of teeth as a measure of dental status were obtained
through self-reports. Outcomes were clinicallyâverified incident nonâfatal
myocardial infarction, stroke, type 2 diabetes mellitus, and cancer. Hazard
ratio (HR) and 95% confidence intervals (CI) were obtained from Cox regression
models. Results Increasing number of teeth is inversely related to risk of
myocardial infarction (HR: 0.97; 95% CI: 0.96, 0.99). The full multivariate
model of teeth groups showed a strong linear trend for myocardial infarction,
a less strong trend for stroke, and no relation with type 2 diabetes mellitus
and cancer in a competing risk model. Participants with 18â23 teeth and those
without teeth were at 76% (95%CI: 1.04, 3) and 2.93 times (95%CI: 1.61, 5.18)
higher risk of myocardial infarction compared to those with nearly all teeth
(28â32 teeth). Conclusions Number of teeth is specifically associated with
myocardial infarction and not with other chronic disease indicating that
dental status further strengthens the link between oral health and
cardiovascular diseases
Innovative method for cutting edge preparation with flexible diamond tools
The micro geometry of the cutting edge is of central importance for the performance of cutting tools. It influences all essential parameters in the machining process: chip formation, thermal and mechanical load on the tool and the workpiece, tool wear and the resulting workpiece quality. The effect depends on the size and shape of the cutting edge rounding. Depending on the machining process, asymmetrical roundings often show the greatest potential. In addition to increasing tool life, the quality of the surfaces produced can be improved by a specifically designed asymmetrical rounding. For edge preparation, blasting, brushing and drag finishing are used in industrial applications. However, an economic production of asymmetrical cutting edge geometries on cutting tools with complicated cutting edge geometry, such as solid carbide tools with helical cutting edge, cannot be achieved with these methods. Therefore, a novel method for preparation of the cutting edge rounding using flexible bond diamond polishing tools is introduced. Hence, the conducted research in this study analyzes the basic mechanisms and influencing factors using the new preparation method. For this purpose, polishing tests are carried out on carbide indexable inserts. The results show that the polishing tools can be used to create both asymmetrical and symmetrical roundings in an industrially relevant dimension. © 2019 The Authors. Published by Elsevier B.V
Soziale Beziehungen im Luftverkehr
"Der Beitrag stellt erste empirische Ergebnisse aus einem DFG-Forschungsprojekt an der TU Chemnitz vor, das zu Formen multipler Entgrenzung bei Flugpersonal forscht. Der Fokus ist auf den Arbeitsalltag von Piloten und Flugbegleitern gerichtet. Hierzu werden verschiedene Themenbereiche untersucht: Arbeitsorganisation und Technologie, die alltĂ€gliche Arbeitspraxis des Flugpersonals, betriebliche Bedingungen, das Berufsfeld von Piloten und Flugbegleitern und die VerĂ€nderungen, mit denen sich diese Berufsfelder auseinandersetzen mĂŒssen, Qualifikationsmöglichkeiten innerhalb der Unternehmen sowie die Wechselwirkungen zwischen Arbeit und Leben. WĂ€hrend die meisten Themenfelder nur angerissen werden, befasst sich der Vortrag zentral mit sozialen Beziehungen der Arbeitenden auf drei Ebenen: das VerhĂ€ltnis zwischen Cockpit und Kabine, Flugpersonal und Passagieren sowie Luft- und Bodenpersonal. Exemplarisch fĂŒr das VerhĂ€ltnis zwischen Cockpit und Kabine stehen Ungleichheitsaspekte, z.B. in Form der Wahrnehmung eines unterschiedlichen sozialen Status auf der individuellen und betrieblichen Ebene oder der unterschiedlichen ZugĂ€nge zu Informationen wĂ€hrend des Fluges. Bei der Konstellation Flugpersonal - Passagiere kann beispielhaft der Trend zur Billigfliegerei und die damit verbundene Servicereduktion genannt werden, was das DienstleistungsverhĂ€ltnis gegenĂŒber dem Kunden neu bewertet. Die dritte Ebene, welche die Wechselwirkungen zwischen dem fliegenden Personal und dem Bodenpersonal umfasst, beleuchtet u.a. die Diskrepanz der gegenseitigen Wahrnehmung, aber auch die Kooperation beider Arbeitsbereiche. Im Ergebnis resĂŒmiert der Beitrag ein multidimensionales Beziehungsgeflecht als Grundlage der Arbeit des Flugpersonals und beleuchtet dies als Voraussetzung verschiedener Formen der Dienstleistungsarbeit." (Autorenreferat
Murine Toll-Like Receptor 2 Activation Induces Type I Interferon Responses from Endolysosomal Compartments
Background: Toll-like receptors (TLRs) are among the first-line sentinels for immune detection and responsiveness to pathogens. The TLR2 subfamily of TLRs (TLR1, TLR2, TLR6) form heterodimers with each other and are thus able to recognize a broad range of components from several microbes such as yeast, Gram-positive bacteria and protozoa. Until now, TLR2 activation by bacterial ligands has long been associated with pro-inflammatory cytokines but not type I interferon responses. Methodology/Principal Findings: Using a variety of transgenic mice, here we provide in vivo and in vitro data showing that TLR2 activation does in fact induce interferon-beta and that this occurs via MyD88-IRF1 and-IRF7 pathways. Interestingly, by microscopy we demonstrate that although a cell surface receptor, TLR2 dependent induction of type I interferons occurs in endolysosomal compartments where it is translocated to upon ligand engagement. Furthermore, we could show that blocking receptor internalization or endolysosomal acidification inhibits the ability of TLR2 to trigger the induction type I interferon but not pro-inflammatory responses. Conclusion/Significance: The results indicate that TLR2 activation induces pro-inflammatory and type I interferon responses from distinct subcellular sites: the plasma membrane and endolysosomal compartments respectively. Apart from identifying and characterizing a novel pathway for induction of type I interferons, the present study offers new insights into how TLR signaling discriminates and regulates the nature of responses to be elicited against extracellular and endocytosed microbes
An Empirical Examination of an Agile Contingent Project/Method Fit Model
While research has demonstrated positive productivity and quality gains from using agile software development methods (SDMs), some experts argue that no single SDM suits every project context. We lack empirical evidence about the project contextual factors that influence when one should use these methods. Research suggests several factors to explain agile method appropriateness; however, generalizable empirical evidence supporting these suggestions is weak. To address this need, we used contingency theory and the information processing model to develop the agile contingent project/method fit model. Subsequently, we used the model to analyze the influence of project contextual factors and agile practices on software development professionalsâ perceptions regarding agile SDM appropriateness. We tested the model using survey data collected from 122 systems development professionals who provided information regarding: 1) contextual factors surrounding a recent agile development project, 2) agile practices applied during the course of that project, and 3) perceptions regarding the relative fit (appropriateness) of the agile method used. Linear regression identified several significant relationships between project contextual factors, agile practices, and respondentsâ relative fit perceptions
MicronâSized Pored Membranes Based on Polyvinylidene Difluoride Hexafluoropropylene Prepared by Phase Inversion Techniques
In this study, micronâsized pored membranes, based on the coâpolymer polyvinylidene difluoride hexafluoropropylene (PVdFâHFP) were prepared via phase inversion techniques. The aim of the approach was to find less harmful and less toxic solvents to fabricate such films.
Therefore, the Hansen solubility approach was used to identify safer and less toxic organic solvents for the phase inversion process, relative to present solvent mixtures, based on acetone, dimethyl formamide, dimethyl acetamide or methanol. With this approach, it was possible to identify cyclopentanone, ethylene glycol and benzyl alcohol as suitable solvents for the membrane preparation process. Physicochemical and mechanical properties were analyzed and compared, which revealed a uniform membrane structure through the cross section. Differences were observed at the top surface, in dependence of both preparation approaches, which are described in detail
Multilokale Arrangements im Luftverkehr: Voraussetzungen, Bedingungen und Folgen multilokalen Arbeitens und Wohnens
Die Arbeit von Flugbegleiterinnen/-begleitern und Pilotinnen und Piloten ist per se durch MobilitĂ€t gekennzeichnet. Dies begrĂŒndet verschiedenartige MultilokalitĂ€t, der jedoch individuelle AnsprĂŒche des Flugpersonals und konkrete Anforderungen ihrer Lebenssituationen gegenĂŒberstehen. Der dauerhafte Umgang mit MultilokalitĂ€t greift daher auf erprobte Arrangements und individuelle Strategien zurĂŒck, mit den Chancen und Risiken der MultilokalitĂ€t umzugehen, ohne jedoch gĂ€nzlich vor Problemen gefeit zu sein. Er ist gerahmt durch umfassende gesetzliche Regelungen und betriebliche Leistungen einerseits und Anpassungsleistungen der BeschĂ€ftigten andererseits. Auch sind das Nutzen von örtlichen Gegebenheiten und nicht zuletzt Kompensationsleistungen lokaler Personen essenziell. Multilokale sind an verschiedenen Punkten auf LokalitĂ€t, z.B. Dienstleistungen Lokaler angewiesen. Die Kooperation zwischen Multilokalen und Residenten ist jedoch wechselseitig zu strukturieren. Im Ergebnis stehen vermehrt atypische, individualisierte Lebensstile und Belastungen. Der Beitrag fokussiert Möglichkeiten des fliegenden Personals, MultilokalitĂ€t in Arbeit und Leben zu integrieren und als Lebenswirklichkeit tĂ€glich zu gestalten
Mitigating oxygen pick-up during laser powder bed fusion of Ti-6Al-4V by limiting heat accumulation
The dissolution of oxygen in Ti-6Al-4V during laser powder bed fusion (L-PBF) is a limitation for the final ductility of the produced components and a challenge for the end-users. In the present work, the effect of the residual oxygen in the process atmosphere of a laboratory scale L-PBF machine, as well as the role of heat accumulation, are studied. It was shown that oxygen content in the as-built Ti-6Al-4V is determined by the size of the scanned area and build time. The heat accumulation aspect was investigated by adjusting the inter-layer time (ILT), by increasing the recoating time or the number of produced parts. The results showed that oxygen pick-up could be limited by reducing residual oxygen level in the atmosphere or heat accumulation. A 400 ppm O2 reduction measured at the top of a 70 mm column was achieved by increasing the ILT manually by 4.5s, and a 1200 ppm O2 reduction by increasing the scanned area by 7 times. By doing so, the hardness at full height was reduced by approximately 30 HV10. It is shown that design features characterised by high aspect ratio can absorb significant amount of oxygen resulting in increased brittleness
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