With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Nikita is a TV series.
text_B: A parametric oscillator is a driven harmonic oscillator in which the oscillations are driven by varying some parameter of the system at some frequency , typically different from the natural frequency of the oscillator .. harmonic oscillator. harmonic oscillator. A simple example of a parametric oscillator is a child pumping a swing by periodically standing and squatting to increase the size of the swing 's oscillations .. The child 's motions vary the moment of inertia of the swing as a pendulum .. The `` pump '' motions of the child must be at twice the frequency of the swing 's oscillations .. Examples of parameters that may be varied are the oscillator 's resonance frequency and damping .. Parametric oscillators are used in several areas of physics .. The classical varactor parametric oscillator consists of a semiconductor varactor diode connected to a resonant circuit or cavity resonator .. varactor. varactor. varactor diode. varactor diode. resonant circuit. resonant circuit. cavity resonator. cavity resonator. It is driven by varying the diode 's capacitance by applying a varying bias voltage .. The circuit that varies the diode 's capacitance is called the `` pump '' or `` driver '' .. In microwave electronics , waveguide / YAG based parametric oscillators operate in the same fashion .. waveguide. waveguide ( electromagnetism ). YAG. Yttrium aluminum garnet. Another important example is the optical parametric oscillator , which converts an input laser light wave into two output waves of lower frequency. optical parametric oscillator. optical parametric oscillator. laser. laser. When operated at pump levels below oscillation , the parametric oscillator can amplify a signal , becoming a parametric amplifier -LRB- paramp -RRB- .. amplify. amplifier. Varactor parametric amplifiers have been developed as low-noise amplifiers in the radio and microwave frequency range .. Varactor. Varactor. The advantage of a parametric amplifier is that it has much lower noise than an ordinary amplifier based on a gain device like a transistor or vacuum tube .. transistor. transistor. This is because in the parametric amplifier a reactance is varied instead of a -LRB- noise-producing -RRB- resistance .. reactance. Electrical reactance. resistance. electrical resistance. They have been used in very low noise radio receivers in radio telescopes and spacecraft communication antennas .. spacecraft communication. spacecraft communication. Parametric resonance occurs in a mechanical system when a system is parametrically excited and oscillates at one of its resonant frequencies .. Parametric excitation differs from forcing since the action appears as a time varying modification on a system parameter .
not_related.