Abstract: A polling is executed periodically among each of nodes connected by a transmission path mutually. The node recognizes that a defect occurred in a connection state of the transmission path, when it detects a lack of a periodic polling from an adjacent node three times. Then, the node registers that all of permanent connections which are set up so as to pass through the transmission path are invalid in its Permanent Virtual Circuit (PVC) management table, and notifies the invalidity of the permanent connection to the node of the next step in the permanent connection. The node of the next step which received the notification registers that the notified permanent connection is invalid in its PVC table and notifies the invalidity of the notified permanent connection to the node of the further next step.

Abstract: An optical recording medium comprising a transparent substrate; a recording layer on the transparent substrate; a metal reflective layer; and one or more protective layers. These layers are laminated successively on the transparent substrate. The outermost protective layer is formed of an ultraviolet curable resin containing an organic filler and/or an inorganic filler having water absorbency and/or oil absorbency. The protective layer has a printable surface permitting writing characters with writing instruments or ink jet printers.

Abstract: An optical recording medium comprises a transparent substrate, a recording layer containing at least one organic dye overlying the substrate, a metallic layer directly contacting and overlying the recording layer, a protective layer comprising at least one layer directly contacting and overlying the metal layer, a layered print portion comprising at least one layer directly contacting and overlying the protective layer, and said protective layer and said print portion satisfying the following relationship:.SIGMA.AiBi+.SIGMA.CjDj<3 (.mu.m) (1)where Ai (.mu.m) is a thickness and Bi is a curing shrinkage rate of the i-th protective layer, respectively, where i is an integer of 1 or more, Cj (.mu.m) is a thickness and Dj is a curing shrinkage rate of the j-th print portion layer, respectively, where J is an integer of 1 or more.

Abstract: An optical recording medium of a single plate type capable of recording comprises a transparent resin substrate having a groove of 900-1800 .ANG. in depth and 0.3-0.6 .mu.m in width, a recording layer containing a dye overlying the substrate, a reflective layer overlying the recording layer and a protective layer overlying the reflective layer, the thickness of the recording layer being 800-1250 .ANG. at the groove portion and 500-1100 .ANG. at the land portion.

Abstract: A direct current resistance welding machine and a method of controlling the direct current resistance welding machine wherein primary current of a welding transformer is detected when a plurality of switching devices of an inverter are controlled based on corresponding pulses having a predetermined frequency and each having a time width corresponding to the value of a required secondary current. Rise and fall times of the detected primary current are detected. An upper limit frequency Of the primary current is computed based on the time width of each pulse and on the rise and fall times. Thus, the primary current of the welding transformer is controlled by controlling the switching devices based on pulses having a frequency falling within the computed upper limit frequency.