In this paper, the following robust control problems are shown to be NP-hard: given a purely complex uncertainty structure Δ, determine if: 1) μΔ(M)<1, for a given rational matrix M; 2) ∥M(·)∥μ<1, for a given rational transfer matrix M(s); and 3) inf(Q∈H∞)∥F(T,Q)∥μ<1, for a given linear fractional transformation F(T,Q) with rational coefficients. In other words, purely complex μ computation, analysis, and synthesis problems are NP-hard. It is also shown that checking stability and computing the H∞ norm of a multidimensional system, are NP-hard problems. Therefore, it is rather unlikely to find nonconservative polynomial time algorithms for solving the problems in complete generality 相似文献
Flank wear of an alumina-based ceramic cutting tool was determined in hard turning two workpieces (AISI 4340 and 52100 hardened steels) at three cutting speeds (142, 181, and 264?m/min) to devise a real-time monitoring system. Results of the six turning tests were assessed using Kruskal?CWallis test, regression models, and linear trend analysis. Multiple non-linear regression models that explained variation in flank wear as a function of time (second) had a range of $ R_{\rm{adj}}^2 $ values of 27.7% for the test 4340-142 to 95% for the test 52100-181. Linear trend models revealed that the highest flank wear rate of the ceramic cutting tool belonged to the test 52100-181. Interaction effect of the three cutting speeds and the two workpiece types was determined to account for 82.2% of variation in flank wear (P?<?0.001). The real-time monitoring system designed in this study appeared to be promising in terms of determining and quantifying flank wear behavior of the ceramic cutting tool and optimal hard turning conditions. 相似文献
This study evaluated the current crushed rock aggregate resources and defined the suitability of potential crushed rock aggregate resource areas in the north of Kocaeli Province by using the geographical information system (GIS). Evaluation of the current aggregate market showed that almost 80 % of the total annual production (14.35 million tonnes) is supplied by the quarries located in Gebze and 20 % of the total annual production (3.65 million tonnes) is supplied by the quarries located in Hereke. The commercial crushed rock aggregate is totally supplied from the limestone and dolomite type carbonate rocks in the northern Kocaeli region. Defining the suitability of potential crushed rock aggregate resource areas was achieved by using GIS methods. First, an aggregate bedrock potential map was developed by using the geological map of the area and categorized as high, moderate and low bedrock potential areas. The high potential areas, which comprised almost 25 % of the northern Kocaeli region, contain carbonate rocks with varying physical, chemical and engineering properties. Secondly, the suitability of the bedrock potential areas was checked by considering the land-use, distance to the county centres and distance to major roads and highways layers in the weighted overlay function of the GIS. The resulting final map contained not suitable, low suitability and suitable areas for crushed rock aggregate. The suitable areas were grouped into three zones according to their geographic distributions. Further, the most promising crushed rock aggregate areas were defined based on the previous field work and surveys in the suitable areas. 相似文献
A straightforward, one-step route has been established to fabricate reduced- (rGO) and nitrogen-doped reduced graphene oxide (NrGO) with remarkable lithium-ion storage properties. The graphene oxide (GO) was synthesized as starting material by improved Hummers’ method. Thereafter, thermally annealing GO with NH3 at elevated temperature to synthesize NrGO was yielded a more open structure with nitrogen sites suitable for enhanced Li intercalation. NrGO exhibited a reversible capacity of 240 mAhg?1 at 10 Ag-1 after 500 cycles with 90% capacity retention, which is the best result achieved among graphene oxide-based anodes at this current density. In contrast to rGO, NrGO cells exhibited a gradually increasing capacity profile, reaching up to 114% of the initial capacity at 0.1, 2, and 10 Ag-1 current densities. Results showed that high occupancy of pyridinic N within NrGO enhanced battery performance and cell kinetics upon cycling which offers long-time operability at high current density. 相似文献
Metalloporphyrazines with a 2-methyl-2-pentenyl group fused to each pyrrole unit were synthesized starting with the corresponding unsaturated dicarbonitrile derivative. The new compounds were characterized by elemental analysis together with FTIR, 1H-NMR, and UV-Vis spectroscopy and via voltammetric and spectrochemical methods. Electrochemical and spectroelectrochemical measurements demonstrate that while metal-free and magnesium porphyrazines gave common porphyrazine (Pz) ring-based electron-transfer reactions, incorporating redox active metal center, CoII, into the porphyrazine core extended the redox activity of the ring system with reversible metal-based reduction and oxidation couples of the metal center in addition to the common Pz ring-based electron transfer processes. The unsaturated functional groups of the porphyrazines did not alter the common electrochemical behavior of the complexes. An in situ electrocolorimetric method, based on the 1931 CIE (Commission Internationale de l’Eclairage) system of colorimetry, was applied to investigate the color of the electro-generated anionic and cationic forms of the complexes for possible electrochromatic applications. 相似文献
Lefke stone is a sandstone that has been widely used in mosques, madrasas, churches, and houses as building stone. The geological features and engineering properties of Lefke stone outcropped in the southern part of Osmaneli/Bilecik were investigated in field and laboratory studies. Samples acquired during the fieldwork were tested to determine the physical, mechanical, durability, and hygrothermal properties in the laboratory. The mean physico-mechanical properties of Lefke stone yielded apparent density of 2.38 g/cm3, specific gravity of 2.68 g/cm3, total porosity of 11.26%, 2.93% water absorption by weight, uniaxial compressive strength of 94 MPa, flexure strength of 11.45 MPa, a 3.90 MPa point load strength, 4.5–5 Mohs hardness, and field Schmidt hammer rebound value of 36. According to durability tests, Lefke stone is resistant to CaCl2 salt mist but has low resistance to SO2 aging. Salt crystals placed in the discontinuities of the rock caused slight crack growth. The stone’s resistance to crystallization of sodium sulphate salt is low, and an increase in the volume of salts crystallized in the rock results in low corner strengths. A capillary water-absorption value of 0.0016 kg/m2.h places Lefke stone into the category of very low water absorption capacity and permeability. The water vapor diffusion resistance factor (μ) less than 1 indicates that the sandstone has high breathability. Its performance in historical buildings, field observations, and values obtained through laboratory tests confirm that Lefke sandstone can be used as a building stone.