Abstract: An estimation device includes an abnormality score calculation unit that calculates an abnormality score indicating a degree of deviation from a normal time from a metric obtained by quantifying an activity of each of the plurality of services and a trace in which time information and a call order of processing of each of the plurality of services are recorded, a failure occurrence service estimation unit that estimates a service in which a failure has occurred based on the abnormality score, and a root-cause estimation unit that estimates a root-cause based on an abnormality score of a metric of the service in which the failure has occurred.

Abstract: A spark plug having an insulator with a leg portion whose outer circumferential surface has an arithmetic mean roughness Ra of 0.5 ?m or less. The leg portion has a first section, a second section, and a third section. The first section has an outer diameter that decreases toward the forward end of the first section. The second section is located forward of and adjacent to the first section and its outer diameter decreases toward the forward end of the second section. The outer circumferential surface of the second section is located inward of a first straight line passing through the base and forward ends of the outer circumferential surface of the first section. The third section is located forward of and adjacent to the second section. The outer diameter of the third section is equal to or less than a forward end outer diameter Ds of the second section over the entire third section.

Abstract: The spark plug includes an insulator made from an alumina-based sintered body, and the insulator contains 90 to 98 wt % of an Al component in oxide equivalent. The insulator contains 1 to 5 wt % of an Si component, 0.1 to 1 wt % of an Mg component, 2 wt % or less of a Ca component, 0.3 to 6 wt % of a Ba component, and 0.11 to 5 wt % of a rare earth component, in oxide equivalent. In analysis using a scanning transmission electron microscope with a probe diameter of an electron beam set at 1 nm, Si and a rare earth element are detected at a crystal grain boundary having a thickness of 15 nm or less, and an alkaline earth metal at the crystal grain boundary is less than a detection limit.

Abstract: Provided is a spark plug capable of ensuring fouling resistance with a simple configuration. An insulator includes a step portion formed on an outer circumferential surface thereof. A center electrode is arranged in an axial hole of the insulator. A cylindrical metal shell having a shelf portion formed on an inner circumferential surface thereof is arranged radially outside the insulator. The insulator further includes a front end portion located frontward of the step portion. An outer circumferential surface of the front end portion has an arithmetic average roughness of 0.5 ?m or smaller in a circumferential direction. A recess is formed with a depth of 3 to 20 ?m in at least part of an end surface and the outer circumferential surface of the front end portion so as to extend from the front toward the rear.

Abstract: Provided is a spark plug capable of ensuring fouling resistance with a simple configuration. An insulator includes a step portion formed on an outer circumferential surface thereof. A center electrode is arranged in an axial hole of the insulator. A cylindrical metal shell having a shelf portion formed on an inner circumferential surface thereof is arranged radially outside the insulator. The insulator further includes a front end portion located frontward of the step portion. An outer circumferential surface of the front end portion has an arithmetic average roughness of 0.5 ?m or smaller in a circumferential direction. A recess is formed with a depth of 3 to 20 ?m in at least part of an end surface and the outer circumferential surface of the front end portion so as to extend from the front toward the rear.

Abstract: The spark plug includes an insulator made from an alumina-based sintered body, and the insulator contains 90 to 98 wt % of an Al component in oxide equivalent. The insulator contains 1 to 5 wt % of an Si component, 0.1 to 1 wt % of an Mg component, 2 wt % or less of a Ca component, 0.3 to 6 wt % of a Ba component, and 0.11 to 5 wt % of a rare earth component, in oxide equivalent. In analysis using a scanning transmission electron microscope with a probe diameter of an electron beam set at 1 nm, Si and a rare earth element are detected at a crystal grain boundary having a thickness of 15 nm or less, and an alkaline earth metal at the crystal grain boundary is less than a detection limit.

Abstract: A spark plug having an insulator with a leg portion whose outer circumferential surface has an arithmetic mean roughness Ra of 0.5 ?m or less. The leg portion has a first section, a second section, and a third section. The first section has an outer diameter that decreases toward the forward end of the first section. The second section is located forward of and adjacent to the first section and its outer diameter decreases toward the forward end of the second section. The outer circumferential surface of the second section is located inward of a first straight line passing through the base and forward ends of the outer circumferential surface of the first section. The third section is located forward of and adjacent to the second section. The outer diameter of the third section is equal to or less than a forward end outer diameter Ds of the second section over the entire third section.

Abstract: A spark plug including an insulator containing not less than 92 mass % and not greater than 96 mass % of Al component in terms of oxide, wherein the insulator is formed from an alumina sintered body comprising alumina crystal and a grain boundary phase present between crystal grains of the alumina crystal. Assuming that mass contents of an Si component, an Mg component, a Ba component, and a Ca component in terms of oxide are represented by MSiO2, MMgO, MBaO, and MCaO, respectively, and a sum of MSiO2, MMgO, MBaO, and MCaO is represented by Mt, the grain boundary phase contains these components so as to satisfy conditions (1) to (4) as follows: (1) 0.17?MSiO2/Mt?0.47; (2) 0.005?MMgO/Mt?0.07; (3) 0.29?MBaO/Mt?0.77; (4) 0.03?MCaO/Mt?0.19.

Abstract: A spark plug including an insulator containing not less than 92 mass % and not greater than 96 mass % of Al component in terms of oxide, wherein the insulator is formed from an alumina sintered body comprising alumina crystal and a grain boundary phase present between crystal grains of the alumina crystal. Assuming that mass contents of an Si component, an Mg component, a Ba component, and a Ca component in terms of oxide are represented by MSiO2, MMgO, MBaO, and MCaO, respectively, and a sum of MSiO2, MMgO, MBaO, and MCaO is represented by Mt, the grain boundary phase contains these components so as to satisfy conditions (1) to (4) as follows: (1) 0.17?MSiO2/Mt?0.47; (2) 0.005?MMgO/Mt?0.07; (3) 0.29?MBaO/Mt?0.77; (4) 0.03?MCaO/Mt?0.19.