学科服务 更多>>

关键词： Islamic mutual funds   Seasonal effects   Ramadan effect  

摘要： We examine the influence of financial, economic, and seasonal factors on the performance of international equity, fixed income, cash, and balanced Islamic mutual funds. We analyze monthly mutual fund return observations on 106 funds over 1997-2019 to investigate exposure to global developed Fama and French {1993, 2015) factors for equity and balanced funds, the three factors of Huij and Derwall {2008] for cash and bond funds, and monthly seasonal effects. Seasonal effects are insignificant in balanced, equity, and cash funds. The Fama and French factors significantly affect the performance of equity and balanced funds, whereas the three factors of Huij and Derwall are important in explaining the performance of cash and fixed income funds for almost over the whole year. Our findings suggest that investors should not be concerned about a potential seasonal effect due to the Ramadan period. (C) 2019 Elsevier B.V. All rights reserved.

关键词： News forums   Membership categorisation analysis   Flaming   Political discourse   Epistemic alignment  

摘要： In this article we use Membership Categorisation Analysis to analyse conversations in an online forum in the British newspaper The Guardian. The comments thread followed an Op Ed piece that discussed the exclusion of 'under-performing' children in British secondary schools. Our analysis of these comments contributes to existing studies of online forums as a mode of public discourse and demonstrates the importance of research that focusses on interactional practices rather than on notions such as 'politeness' or 'framing'. We show the ways that participants used endogenous conversational categories to produce epistemic alignment and disalignment with each other, employing various strategies such as expanding category collections, creating relations between 'culpable' categories and 'trouble' categories, and re-describing categories through alternate category predicates. Through this, we see that the conversational actions undertaken in the forum are much more complicated than current concepts allow for, and we reflect on what such complexity might mean for the study and design of news forums. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Constraint satisfaction problem   dichotomy conjecture   polymorphism clone   Mal'cev condition   omega-categoricity   orbit growth   model-complete core  

摘要： There exist two conjectures for constraint satisfaction problems (CSPs) of reducts of finitely bounded homogeneous structures: the first one states that tractability of the CSP of such a structure is, when the structure is a model-complete core, equivalent to its polymorphism clone satisfying a certain nontrivial linear identity modulo outer embeddings. The second conjecture, challenging the approach via model-complete cores by reflections, states that tractability is equivalent to the linear identities (without outer embeddings) satisfied by its polymorphisms clone, together with the natural uniformity on it, being nontrivial. We prove that the identities satisfied in the polymorphism clone of a structure allow for conclusions about the orbit growth of its automorphism group, and apply this to show that the two conjectures are equivalent. We contrast this with a counterexample showing that omega-categoricity alone is insufficient to imply the equivalence of the two conditions above in a model-complete core. Taking another approach, we then show how the Ramsey property of a homogeneous structure can be utilized for obtaining a similar equivalence under different conditions. We then prove that any polymorphism of sufficiently large arity which is totally symmetric modulo outer embeddings of a finitely bounded structure can be turned into a nontrivial system of linear identities, and obtain nontrivial linear identities for all tractable cases of reducts of the rational order, the random graph, and the random poset. Finally, we provide a new and short proof, in the language of monoids, of the theorem stating that every omega-categorical structure is homomorphically equivalent to a model-complete core.

关键词： Radiomics   Breast   Calcification   Predictive value of test   Unnecessary procedures  

摘要： Purpose: We developed and validated a radiomic model based on mammography and assessed its value for predicting the pathological diagnosis of Breast Imaging Reporting and Data System (BI-RADS) category 4 calcifications. Materials and methods: Patients with a total of 212 eligible calcifications were recruited (159 cases in the primary cohort and 53 cases in the validation cohort). In total, 8286 radiomic features were extracted from the craniocaudal (CC) and mediolateral oblique (MLO) images. Machine learning was used to select features and build a radiomic signature. The clinical risk factors were selected from the independent clinical factors through logistic regression analyses. The radiomic nomogram incorporated the radiomic signature and an independent clinical risk factor. The diagnostic performance of the radiomic model and the radiologists' empirical prediction model was evaluated by the area under the receiver operating characteristic curve (AUC). The differences between the various AUCs were compared with DeLong's test. Results: Six radiomic features and the menopausal state were included in the radiomic nomogram, which discriminated benign calcifications from malignant calcifications with an AUC of 0.80 in the validation cohort. The difference between the classification results of the radiomic nomogram and that of radiologists was significant (p < 0.05). Particularly for patients with calcifications that are negative on ultrasounds but can be detected by mammography (MG+/US-calcifications), the identification ability of the radiomic nomogram was very strong. Conclusions: The mammography-based radiomic nomogram is a potential tool to distinguish benign calcifications from malignant calcifications.

关键词： Track category   Comonad cohomology   Simplicial category  

摘要： We define a comonad cohomology of track categories, and show that it is related via a long exact sequence to the corresponding (S,O)-cohomology. Under mild hypotheses, the comonad cohomology coincides, up to reindexing, with the (S,O)-cohomology, yielding an algebraic description of the latter. We also specialize to the case where the track category is a 2-groupoid.

关键词： residuality   metric space   Hilbert space   first passage percolation  

摘要： In this paper we continue our earlier work about topological first passage percolation and answer certain questions asked in our previous paper. Notably, we prove that apart from trivialities, in the generic configuration there exists exactly one geodesic ray, in the sense that we consider two geodesic rays distinct if they only share a finite number of edges. Moreover, we show that in the generic configuration any not too small and not too large convex set arises as the limit of a sequence B(t(n))/t(n) for some t(n) -> infinity. Finally, we define topological Hilbert first passage percolation, and amongst others we prove that certain geometric properties of the percolation in the generic configuration guarantee that we consider a setting linearly isomorphic to the ordinary topological first passage percolation.

摘要： This is the second part in a two-part series of papers constructing a unitary structure for the modular tensor category associated to a unitary rational vertex operator algebra (VOA). We define, for a unitary rational vertex operator algebra V, a nondegenerate sesquilinear form Delta on each vector space of intertwining operators. We give two sets of criteria for the positivity of Delta, both concerning the energy bounds condition of vertex operators and intertwining operators. These criteria can be applied to many familiar examples, including unitary Virasoro VOAs, unitary affine VOAs of type A, D, and more. Having shown that Delta is an inner product, we prove that Delta induces a unitary structure on the modular tensor category of V.

关键词： Biomass pellet   Laser-induced breakdown spectroscopy   Chemometrics methods   Discrimination  

摘要： As a renewable energy alternative to fossil fuels, biomass pellets have attracted much attention due to its promising advantages of convenient use and easy combustion. Rapid discrimination of different biomass pellets and selecting the one with better combustion performance are of great significance to improve the energy utilization. In this study, laser -induced breakdown spectroscopy (LIBS) coupled with chemometrics methods were used to discriminate biomass pellets. Lignocellulose components were firstly determined and further analyzed according to LIBS spectra. Principal component analysis (PCA), partial least squares discrimination analysis (PLS-DA), support vector machines (SVM), radial basis function neural network (RBFNN) and extreme learning machine (ELM) were applied to quantitatively distinguish biomass pellets. The RBFNN model showed a reliable discrimination power, with 100% and 96.88% average recognition accuracy in calibration and prediction sets respectively. Visualization analysis based on the RBFNN model was applied to intuitively discriminate the biomass pellets with different colors. In addition, rice husk with relatively poor combustion performance could be accurately distinguished from wood biomass pellets by all discrimination models. The results indicated that LIBS combined with chemometrics methods could be a novel and reliable approach to discriminate biomass pellets and select the category with better combustion performance. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Hypersurface   Countable representation type   Singularity category   Cohen-Macaulay module   Level   Rouquier dimension   13D09   13C14   16G60  

摘要： The Orlov spectrum and Rouquier dimension are invariants of a triangulated category to measure how big the category is, and they have been studied actively. In this paper, we investigate the singularity category Dsg(R) of a hypersurface R of countable representation type. For a thick subcategory T of Dsg(R) and a full subcategory X of T, we calculate the Rouquier dimension of T with respect to X. Furthermore, we prove that the level in Dsg(R) of the residue field of R with respect to each nonzero object is at most one.