An apparatus comprising an analog photocell adapted to capture light energy incident upon it as an analog signal, a sample-and-hold amplifier coupled to the photocell and adapted to store the analog signal and a digital converter coupled to the amplifier, the converter transforming the analog signal into a digital value, the value proportional to the amount of the light energy. The invention further relates to monitoring the severity of brain damage resulting from TBI in a subject and determining the prognosis of a subject that has suffered from mTBI. Thus, the monitoring and differentiation between mixed said low speed and said full speed USB data is allowed which enables a USB keystroke recording apparatus to ensure that keystroke data is not missed. Each feedback loop preferably includes a pair of alternately-toggling switching transistors to minimize unwanted charge injection. 1 MPa, and a3) low boilers having a boiling range below 12\xb0 C. Pipe reactor processes of the present invention have a multitude of advantages over prior art processes including improved heat transfer, volume control, agitation and disengagement functions.