This invention relates to highly purified biogenic silica product obtained from diatomite and methods for preparing same. When the catalyst is determined to have deteriorated on the basis of the excess air ratio difference, the air-fuel ratio of the engine is feedback-controlled to a stoichiometric air-fuel ratio, and deterioration of the catalyst is determined again on the basis of a value expressing a difference in the air-fuel ratio variation on the upstream side and downstream side of the catalyst at that time. In order to avoid undesired temperature peaks provisions are made that the head supporting the HF electrode or the HF electrodes, respectively, comprises highly heat conductive portions in order to dissipate heat generating at the HF electrode or the HF electrodes, respectively, in particular in the proximal direction. A surgeon may aim the steerable laser probe by varying a rotational position of the handle and an amount of compression of the actuation structure. The truck of the present invention has a payload capacity up to three times greater than that of similar trucks of the prior art.