Detection bandwidth, decreasing

By decreasing the detection bandwidth as much as possible, consistent with maintaining a good signal to noise ratio, a limiting condition can be approximated for which the quenching summation varies in a simple manner from flame to flame. In the limit in which only one transition is monitored from the v J state populated by the laser, almost every vibrational or rotational relaxation from that state is an effective quenching collision. Under these conditions the quench summation term approximates to a gas kinetic quench rate. 

Assuming that the maximum target velocity is equal to 3M (lOOOm/s), the maximum value of the time-bandwidth product is limited to 150,000. The maximum processing gain is then equal to 51.7 dB. The use of a windowing function will decrease this value by a few dB. The maximum detection range for the noise radar is given by the formula... 

The instrument variables Rs, RB, and Rs + 2RB are used in instrument optimization for example, an improved matching of the laser bandwidth to the HO absorption could increase Rs, a reduction in illumination of walls near the detection zone by ambient light or scattered or diffracted laser light could decrease RB, and an increase in photon collection efficiency could increase (Rs + 2RB). The remaining quantities fav, MAT, SNR, and MDC may be traded off during data processing, but the choice of their values is restricted by the instrument variables. 

Strength and the sample concentration, po is the permeability of free space, Q is the quality factor of the coil, coo is the Larmor angular frequency, K is the volume of the coil, F is the noise figure of the preamplifier, k is Boltzmann s constant, is the probe (as opposed to sample) temperature, and A/is the bandwidth (in Hz) of the receiver. It can be seen that the concentration sensitivity 5c (SIN per pM concentration of analyte) is poor for microcoils. This is due to the fact that microcoil probes have very small observation volumes and therefore contain a very small amount of analyte. However, if the sample can be concentrated into a small volume, then the microcoil can more easily detect the signal. This high mass sensitivity 5m (SIN per pmol of analyte) is characteristic of microcoil NMR probes. In essence, the use of microcoil probes enhances the mass sensitivity 5m at the expense of the concentration sensitivity 5c. To better understand the relationship between sensitivity and coil diameter, a detailed analysis was reported by Peck et Their results showed that mass sensitivity increases monotonically with decreasing coil diameter within the 1mm to 50 pm range they studied. However, the concentration sensitivity decreases, and therefore there is a trade-off between Sc and 5m that depends on coil diameter. 

Fortunately, the bandwidth-dictated load resistance, R, can be supplied by the amplifier and the net noise decreased substantially because of the gain in the amplifier first stage. One of the preferred amplifier types is the transimpedance amplifier, which presents an appropriate input resistance using negative feedback, but has an equivalent input noise current smaller than that of a real resistor. Commercial low noise amplifiers for optical detection are usually characterized by an effective input noise current, sometimes called the spot noise current, (/ )usually quoted in pA/VHz, with 1 pA =10 A. Since the amplifier now includes the load resistance, R, of Fig. 2(b), its contribution is included in the effective input noise current. The amplifier limited noise equivalent power, NEPal, is then... 

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