Abstract: A transparent simulation disk for measuring flying height of a magnetic head (i.e., distance between a magnetic head and a magnetic disk such as a hard disk of a computer) in place of a magnetic disk is made of a SiO.sub.2 --R.sub.2 O (where R is Li, Na or K) glass or glass-ceramic having electric resistivity of 10.sup.8 -10.sup.14 .OMEGA.cm and abrasion of 90 or below.

Abstract: A glass-ceramic substrate for a magnetic information storage medium such as a magnetic disk having a super flatness suited for a contact recording system includes a SiO.sub.2 --Al.sub.2 O.sub.3 --Li.sub.2 O system glass-ceramic and has either .beta.-quartz solid solution (.beta.-SiO.sub.2 solid solution) or a mixture of .beta.-quartz solid solution (.beta.-SiO.sub.2 solid solution) and .beta.-spodumene solid solution (.beta.-Li.sub.2 O.Al.sub.2 O.sub.3.4SiO.sub.2 solid solution) as its main crystal phase. The surface roughness (Ra) of the glass-ceramic substrate after polishing is within a range from 1 .ANG. to 5 .ANG..

Abstract: A crystallized glass and a manufacturing method therefor are disclosed. The crystallized glass comprises .beta.-spodumene solid solution as the predominant crystal phase, and is produced by forming a melted raw glass, cooling and thereafter heat-treating it. The raw glass has a composition comprising, expressed in terms of weight percent: 52-65% SiO.sub.2 ; 8-15% Al.sub.2 O.sub.3 ; 0-4% P.sub.2 O.sub.5, 3-8% TiO.sub.2, and 0-4% ZrO.sub.2, wherein the following inequality is satisfied,0.1<(% of P.sub.2 O.sub.5 +% of ZrO.sub.2)/(% of TiO.sub.2)<0.8; 0-10% ZnO, 0-10% MgO, and 0-5% BaO, wherein the following inequality is satisfied,<(% of ZnO+% of MgO+% of BaO)<15; 3-12% Li.sub.2 O; 0-4% K.sub.2 O; and As.sub.2 O.sub.3 and Sb.sub.2 O.sub.3, wherein the following inequality is satisfied,0<% of As.sub.2 O.sub.3 +% of Sb.sub.2 O.sub.3 <2.

Abstract: A magnetic disk substrate is made of a glass-ceramic having crystal phases of lithium disilicate (Li.sub.2 O.2SiO.sub.2) and alpha-quartz (SiO.sub.2). The crystal phase of alpha-quartz is formed of grown crystal grains each having a globular grain structure made of aggregated particles. Each globular grain has a size within a range from 0.3 .mu.m to 3 .mu.m. Surface roughness (Ra) of a polished surface of the magnetic disk substrate is within a range from 15 .ANG. to 50 .ANG. which is an optimum range of surface roughness for the magnetic disk.

Abstract: A precure tread for a tire has surface grooves facing a tread face, rear grooves facing a crown portion of a base tire, and a passage for communication between the rear grooves to atmosphere. The groove bottom of the rear grooves is located at a higher level than a groove bottom of the surface groove in the radial direction. The tire durability can be considerably improved when this precure tread is applied to a new tire or a retreaded tire.

Abstract: A low expansion glass-ceramic which has a coefficient of thermal expansion (.alpha..times.10.sup.-7 /.degree.C.) within the range of from -5 to +5 within a temperature range of from -60.degree. C. to +160.degree. C., has a remarkably reduced variation of 10 ppm or below in relative length of .DELTA.1/1, has an excellent optical homogeneity owing to reduced melting temperature in the base glass, and has an improved transparency is obtained by restricting the ratio in weight of P.sub.2 O.sub.5 to SiO.sub.2 within the range of from 0.08 to 0.20, and adding Li.sub.2 O, MgO, ZnO, CaO and BaO of specific content ranges as essential ingredients in a base glass of a SiO.sub.2 -P.sub.2 O.sub.5 -Al.sub.2 O.sub.3 -Li.sub.2 O system containing TiO.sub.2 and ZrO.sub.2 as nucleating agents, and As.sub.2 O.sub.3 as an optional ingredient.

Abstract: A method for detecting a defect in a glass-ceramic for magnetic disks includes steps of forming a colored glass-ceramic having Munsell value within the range of 0 to 7 in the CIE color system by subjecting to heat treatment a base glass comprising in weight percent:______________________________________ SiO.sub.2 65-83% Li.sub.2 O 8-13% K.sub.2 O 0-7% MgO + ZnO + PbO 0.5-5.5% in which MgO 0.5-5.5% ZnO 0-5% PbO 0-5% P.sub.2 O.sub.5 1-4% Al.sub.2 O.sub.3 0-7% As.sub.2 O.sub.3 + Sb.sub.2 O.sub.3 0-2% a coloring agent of at least one ingredient 0.5-5% selected from the group consisting of metal oxides of V, Cu, Mn, Cr, Co, Mo, Ni, Fe, Te, Ce, Pr, Nd and Er ______________________________________and checking the glass-ceramic visually or by means of an automatic checking device for detecting a defect in the glass-ceramic.

Abstract: A magnetic disk substrate is made of a glass-ceramic having crystal phases of lithium disilicate (Li.sub.2 O.2SiO.sub.2) and alpha-quartz (SiO.sub.2). The crystal phase of alpha-quartz is formed of grown crystal grains each having a globular grain structure made of aggregated particles. Each globular grain has a size within a range from 0.3 .mu.m to 3 .mu.m. Surface roughness (Ra) of a polished surface of the magnetic disk substrate is within a range from 15 .ANG. to 50 .ANG. which is an optimum range of surface roughness for the magnetic disk.

Abstract: Glass-ceramic for information recording disks have a crystalline structure suitably used for substrate materials and the like for magnetic disks and magneto-optic disks as well as have improved surface characteristics obtained by polishing the glass, and besides the base glass thereof is excellent in melting properties and moldability thereof. The base glass composition consists essentially of ingredients of SiO.sub.2 -Al.sub.2 O.sub.3 -ZnO-MgO-CaO-SrO-BaO-TiO.sub.2 system. The main crystalline phase of the glass-ceramic produced by heat-treating the base glass having a viscosity of log .eta.=3.0 poise or less at 1250.degree. C. is gahnite, a size of the crystal grain is within a range of from 50 to 1000 Angstrom, and a degree of surface roughness (Ra) of the polished glass-ceramic is within a range of from 0.5 to 9.0 Angstrom.

Abstract: A cordierite glass-ceramic having a cordierite crystal phase as a predominant crystal phase is obtained by melting a base glass consisting in weight percent of:______________________________________ SiO.sub.2 38-50% Al.sub.2 O.sub.3 18-30% MgO 10-20% ______________________________________the ratio in weight of Al.sub.2 O.sub.3 to MgO being 1.2 to 2.3 ______________________________________ B.sub.2 O.sub.3 0-5% CaO 0-5% BaO 0-5% SrO 0-5% ZnO 0.5-7.5% TiO.sub.2 4-15% ZrO.sub.2 0-5% As.sub.2 O.sub.3 + Sb.sub.2 O.sub.3 0-2% ______________________________________and forming the glass and subjecting the glass to heat treatment. This glass-ceramic is suitable for use as a high strength material reqiring high resistivity to heat and impact and as materials requiring a fine processing or a precision processing such as electronic parts, magnetic disk substrates and machine parts.

Abstract: A precure tread for a tire has surface grooves facing a tread face, rear grooves facing a crown portion of a base tire, and a passage for communication between the grooves to atmosphere. The groove bottom of the rear grooves is located at a high level than a groove bottom of the surface groove in the radial direction. The tire durability can be considerably improved when this precure tread is applied to a new tire or a retreated tire.

Abstract: A glass-ceramic for a magnetic disk substrate in which the grain size can be controlled and the surface roughness after polishing is within the range from 15 .ANG. to 50 .ANG. is provided by heat treating a base glass including in weight percent:______________________________________ SiO.sub.2 65-83% Li.sub.2 O 8-13% K.sub.2 O 0-7% Mgo + ZnO + PbO 0.5-5.5% in which MgO 0.5-5.5% ZnO 0-5% PbO 0-5% P.sub.2 O.sub.5 1-4% Al.sub.2 O.sub.3 0-7% As.sub.2 O.sub.3 + Sb.sub.2 O.sub.3 0-2% ______________________________________The glass-ceramic contains lithium disilicate (Li.sub.2 O. 2SiO.sub.2) and alpha-quartz (SiO.sub.2) as the main crystal phases.

Abstract: A low expansion crystallized glass-ceramic which has a coefficient of thermal expansion (.alpha..times.10.sup.-7 /.degree. C.) within the range of from -10 to +10, has a remarkably reduced variation in the coefficient of thermal expansion accompanied by variation in heat treatment conditions, has an excellent optical homogeniety owing to reduced melting temperature in the base glass and has an improved transparency is obtained by restricting the ratio in weight of Al.sub.2 O.sub.3 to (SiO.sub.2 +P.sub.2 O.sub.5) within the range of 0.38 and 0.50 and adding MgO, BaO and ZnO of specific content ranges as essential ingredients in a base glass of a SiO.sub.2 -Al.sub.2 O.sub.3 -Li.sub.2 O system containing P.sub.2 O.sub.5 as an optional ingredient and TiO.sub.2 and ZrO.sub.2 as nucleating agents.

Abstract: An optical glass which is a SiO.sub.2 -Nb.sub.2 O.sub.5 -R'.sub.2 O (where R' is an alkali metal element)-F system of a specific composition range exhibits optical constants of a refractive index (Nd) of about 1.52-1.67 and an Abbe number (.upsilon. d) of about 32-50, is free of PbO and has an improved light transmissivity.

Abstract: A precure tread for a tire has surface grooves facing a tread face, rear grooves facing a crown portion of a base tire, and a passage for communication between the rear grooves to atmosphere. The groove bottom of the rear grooves is located at a higher level than a groove bottom of the surface groove in the radial direction. The tire durability can be considerably improved when this precure tread is applied to a new tire or a retread tire.

Abstract: A heavy duty pneumatic tire comprises a tread portion having a pitch pattern and provided with at least two circumferential main grooves extending circumferentially of the tire, wherein at least one dimple is arranged in a region of an island part ranging from a side end of the tread to a position corresponding to not more than 20% of a tread width per one pitch, and a pair of sipes are disposed at opposed positions of each dimple to a widthwise direction of the tire so as to extend in the widthwise direction of the tire. This dimple has a particular ratio of opening size in widthwise direction to opening size in circumferential direction, a size of not more than 8 mm, a particular depth, and a particular total opening area ratio per one pitch.