A variable resistance element whose resistance changes with application of a voltage pulse is brought to a low resistance state by applying an erase pulse to a path shown by the broken line through selection of selection transistors. Also described are a ball trap for collecting cleaning balls, blocking elements for a ball trap screen and a method of enhancing the movement of the cleaning ball through the ball trap of a closed fluid flow system by blocking portions of a ball trap screen deployed within a ball trap housing so as to modify the fluid flow through the ball trap. A corresponding sorting unit and a system as well as a corresponding computer program and a computer program product are also disclosed. When the tubing has been fully inserted, a device is activated to generate a local electromagnetic field surrounding the fitting component. This causes the battery, the electric motor and the power transmission mechanism to be located below a view line of an operator when he looks at the snow removing plate, avoiding the view line from being disturbed to allow the operator to look at the upper end of the snow removing plate in his working attitude for thereby providing ease of operation of the snow removing machine. Moreover, selective fluorescence in the tumor tissue can provide further improvement in accuracy of diagnosing a tumor using the complex.