Abstract: It is an object of the invention to reduce mixing of an impurity from a friction stir welding tool, reduce abrasion of the tool, and prevent the tool from being easily broken even though an object to be worked formed by a metal or an alloy having a high melting point of 1350° C. or more is friction-stir-welded. The friction stir welding tool according to the invention can friction-stir-weld a metal or alloy having a high melting point of 1350° C. or more as an object to be worked. At least a portion brought into contact with the object to be worked has a composition containing iridium, containing rhenium, ruthenium, molybdenum, tungsten, niobium, tantalum, rhodium, or two or more of them, and containing zirconium, hafnium, lanthanum, cerium, samarium, gadolinium, scandium, yttrium, or two or more of them, and has a Micro Vickers Hardness of 300 Hv or more.

Abstract: A carrier has an impedance Z having a frequency dependence, obtained by alternating current impedance measurement. When the frequency dependence is fitted by a fitting function, parameter ? lies in a range of 0.70 to 0.90 in an electric field of 103 V/cm.

Abstract: An image forming apparatus includes a photosensitive drum to which an electrostatic image is formed and a developing sleeve carrying a developer including toner carrier. An alternating voltage is applied to the sleeve to form an alternating electric field between the sleeve and the drum to develop the electrostatic image with the developer. A relation |K1|<|K2| is satisfied, where K1: a slope at an electric field intensity Ed=|(Vp2?VL)/D|, K2: a slope at an electric field intensity Eb=|(Vp1?VL)/D|, VL: a potential [V] of the electrostatic image at which a maximum density is obtained, Vp1: a peak potential [V] that provides a potential difference to move the toner toward the drum, Vp2: a peak potential [V] that provides a potential difference to move the toner toward the sleeve, and D: a closest distance [m] between the drum and the sleeve.

Abstract: An image forming apparatus includes a developer carrying member to which a developing bias is applied. A frequency f of a developing bias waveform, a developing area S1 which is a time-integrated value of a difference between a voltage value of the developing bias and a solid electrostatic image potential VL in a developing period of the developing bias, a collecting area S2 which is a time-integrated value of a difference between the voltage value of the developing bias and VL in a collecting period of the developing bias, and a developing contrast value Vcon are used for defining a range of a value of the developing bias frequency f, a range of a value of a voltage change rate ? at VL during transition of the developing bias voltage value from a developing-side voltage to a collecting-side voltage, and a range of a value represented by the formula: {(S1?1.28×S2)×f/Vcon}×exp(?2.0×10?5×f/Hz).

Abstract: It is an object of the invention to reduce mixing of an impurity from a friction stir welding tool, reduce abrasion of the tool, and prevent the tool from being easily broken even though an object to be worked formed by a metal or an alloy having a high melting point of 1350° C. or more is friction-stir-welded. The friction stir welding tool according to the invention can friction-stir-weld a metal or alloy having a high melting point of 1350° C. or more as an object to be worked. At least a portion brought into contact with the object to be worked has a composition containing iridium, containing rhenium, ruthenium, molybdenum, tungsten, niobium, tantalum, rhodium, or two or more of them, and containing zirconium, hafnium, lanthanum, cerium, samarium, gadolinium, scandium, yttrium, or two or more of them, and has a Micro Vickers Hardness of 300 Hv or more.

Abstract: An image forming apparatus includes a photosensitive drum to which an electrostatic image is formed and a developing sleeve carrying a developer including toner carrier. An alternating voltage is applied to the sleeve to form an alternating electric field between the sleeve and the drum to develop the electrostatic image with the developer. A relation |K1|<|K2| is satisfied, where K1: a slope at an electric field intensity Ed=|(Vp2?VL)/D|, K2: a slope at an electric field intensity Eb=|(Vp1?VL)/D|, VL: a potential [V] of the electrostatic image at which a maximum density is obtained, Vp1: a peak potential [V] that provides a potential difference to move the toner toward the drum, Vp2: a peak potential [V] that provides a potential difference to move the toner toward the sleeve, and D: a closest distance [m] between the drum and the sleeve.