Search results for "arcs"
showing 10 items of 32 documents
Continuous images of arcs: Extensions of Cornette's Theorem
2015
In [J.L. Cornette “Image of a Hausdorff arc” is cyclically extensible and reducible Trans. Am. Math. Soc., 199 (1974), pp. 253–267], Cornette proved that a locally connected Hausdorff continuum X is the continuous image of an arc if and only if each of its cyclic elements is the continuous image of an arc. Cyclic elements form a closed null cover of X by retracts of X. We generalize Cornette's result to closed null covers of X with a dendritic structure. We give examples to show that some of our conditions are necessary and we pose some open questions.
Lifting paths on quotient spaces
2009
Abstract Let X be a compactum and G an upper semi-continuous decomposition of X such that each element of G is the continuous image of an ordered compactum. If the quotient space X / G is the continuous image of an ordered compactum, under what conditions is X also the continuous image of an ordered compactum? Examples around the (non-metric) Hahn–Mazurkiewicz Theorem show that one must place severe conditions on G if one wishes to obtain positive results. We prove that the compactum X is the image of an ordered compactum when each g ∈ G has 0-dimensional boundary. We also consider the case when G has only countably many non-degenerate elements. These results extend earlier work of the firs…
Characterization of DC series arc faults in PV systems based on current low frequency spectral analysis
2021
Abstract This work presents an experimental study focused on the characterization of series arc faults in direct current (DC) photovoltaic (PV) systems. The aim of the study is to identify some relevant characteristics of arcing current, which can be obtained by means of low frequency spectral analysis of current signal. On field tests have been carried out on a real PV system, in accordance with some tests requirements of UL 1699B Standard for protection devices against PV DC arc faults. Arcing and non-arcing current signals are acquired and compared and the behavior of a set of indicators proposed by authors is analyzed. Different measurement equipment have been used, in order to study th…
Heritage and knowledge: apparatus, logic and strategies in the formation of heritage
2016
Heritage as a category reflects diverse political positions. All heritagisation processes imply the creation of hierarchies, selection, ranking, and categorization of what is worthy or unworthy of being heritage, and all heritage creation involves certain disciplinary processes that confer legitimacy. As a modern invention, heritage was built on two closely-related cornerstones: the distinction between nature and culture and the difference between normalized knowledge and marginal knowledge. As a result, refining processes were applied which became strategies to legitimise political domination. In this paper the constituent process of heritage creation and its links to normative knowledge a…
Countable connected spaces and bunches of arcs in R3
2006
Abstract We investigate the images (also called quotients) of countable connected bunches of arcs in R 3 , obtained by shrinking the arcs to points (see Section 2 for definitions of new terms). First, we give an intrinsic description of such images among T 1 -spaces: they are precisely countable and weakly first countable spaces. Moreover, an image is first countable if and only if it can be represented as a quotient of another bunch with its projection hereditarily quotient (Theorem 2.7). Applying this result we see, for instance, that two classical countable connected T 2 -spaces—the Bing space [R.H. Bing, A connected countable Hausdorff space, Proc. Amer. Math. Soc. 4 (1953) 474], and th…
A set of indicators for arc faults detection based on low frequency harmonic analysis
2016
In this paper a novel set of indicators is presented for arc faults detection in electrical circuits. The indicators are defined starting from an experimental characterization of the arc fault phenomenon and the study of the arcing current in several test conditions, which were chosen in accordance with the UL 1699 Standard requirements. The proposed parameters are measured by means of a high resolution low frequency spectral analysis of the arcing current, which allows to achieve a good spectral resolution even with short observation windows.
Arc Fault Detection Method Based on CZT Low-Frequency Harmonic Current Analysis
2017
This paper presents a method for the detection of series arc faults in electrical circuits, which has been developed starting from an experimental characterization of the arc fault phenomenon and an arcing current study in several test conditions. Starting from this, the authors have found that is it possible to suitably detect arc faults by means of a high-resolution low-frequency harmonic analysis of current signal, based on chirp zeta transform, and a proper set of indicators. The proposed method effectiveness is shown by means of experimental tests, which were carried in both arcing and nonarcing conditions and in the presence of different loads, chosen according to the UL 1699 standard…
Experimental characterization of series arc faults in AC and DC electrical circuits
2014
This paper presents an experimental characterization of the arc fault phenomenon, for both AC and DC systems, focusing the attention on series arcs. The aim of the study is to find some current characteristics, which can be significant for the purpose of arc detection. The arcing current signal is analyzed in both time and frequency domain. For the AC analysis, the test conditions are chosen in accordance with the “unwanted tripping tests” and the “operation inhibition tests” reported in the Standard UL 1699. The DC study is carried out on the currents waveforms acquired during some on-field tests on a PV plant. Starting from the study herein presented, the authors have found that is it pos…
Creating stable Floquet–Weyl semimetals by laser-driving of 3D Dirac materials
2017
Nature Communications 8, 13940 (2017). doi:10.1038/ncomms13940
The Role of Immunosenescence in Cerebral Small Vessel Disease: A Review.
2022
Cerebral small vessel disease (CSVD) is one of the most important causes of vascular dementia. Immunosenescence and inflammatory response, with the involvement of the cerebrovascular system, constitute the basis of this disease. Immunosenescence identifies a condition of deterioration of the immune organs and consequent dysregulation of the immune response caused by cellular senescence, which exposes older adults to a greater vulnerability. A low-grade chronic inflammation status also accompanies it without overt infections, an “inflammaging” condition. The correlation between immunosenescence and inflammaging is fundamental in understanding the pathogenesis of age-related CSVD (ArCSVD). Th…