A floquet theory of the linear synchronous machine

The differential equation describing the three-phase linear synchronous machine containing an arbitrary stator MMF distribution is reformulated and solved as a perturbation theory problem. The solution algorithm presented also produces a transformation capable of reducing to constant coefficient form the differential equation describing the machine. The theory is illustrated by applying it to a simple two pole machine.     

An exact formula for the maximum VCO sweep rate of a PLL

In many phase-locked loop (PLL) applications, the natural pull-in mechanism is too slow and unreliable, and it must be accelerated. By adding an externally-generated ramp to its control voltage input, the PLL voltage controlled oscillator (VCO) frequency can be swept towards the input reference frequency in an attempt to speed up the pull-in process. This popular acquisition aid has a significant limitation when it is used in a second-order, Type II PLL. If the applied ramp voltage has a slope magnitude greater than (alternatively, less than) some value R_m, the PLL state can (alternatively, cannot) sweep past the desired lock point, resulting in a phase lock failure (alternatively, success). In general, the maximum sweep rate magnitude R_m can be computed by using a numerical integration-and-search procedure that is described in the PLL literature. A special case exists for a second-order, Type II PLL that incorporates a triangular-characteristic phase detector (with logic-level binary input signals). For this case, it is possible to develop an exact, closed-form expression for R_m, the main result of this paper. For a range of loop parameters most often used in applications, R_m values are computed by using the exact formula, and these are used in two ways. First, they are used to validate the previously-mentioned numerical integration-and-search procedure. Second, they are compared to maximum sweep rate values computed for a PLL that utilizes a sinusoidal phase detector to show that the triangular-phase-detector PLL can be swept significantly faster than the sinusoidal-phase-detector loop.     

An exact formula for the half-plane pull-in range of a PLL

A second-order phase-lock loop (PLL) that is based on a triangular-characteristic phase detector and imperfect-integrator loop filter is found in many applications where simplicity and economics are major considerations. For many of these applications, digital-logic-compatible reference and VCO signals are used, an exclusive-OR gate implements the phase detector, and the loop filter is constructed from passive components. When designing these loops, the half-plane pull-in range Ω₂ is of interest. Until now, this important loop parameter could only be calculated by using a computer-based technique that numerically integrated the nonlinear differential equation that describes the PLL model. This requirement/limitation is removed here by the development of an exact closed-form formula for Ω₂, the main contribution of this paper. More generally, the value of Ω₂ is dependent on the PLL phase detector characteristic that is used, be it triangular, sinusoidal, or something else. With regard to the value of Ω₂ produced, a comparison is given of two PLLs, both described by the same linear model so that the comparison is meaningful. The first PLL is based on a triangular-characteristic phase detector; the second loop is based on a sinusoidal phase detector.     

广枣提取液对小鼠免疫功能和运动耐力的影响

观察了广枣提取液对小鼠免疫功能、运动耐力的影响。结果表明：广枣提取液可明显增加小鼠耐缺氧时间，延长小鼠负重游泳时间，降低运动后小鼠血乳酸水平，显著提高其心肌组织中SOD活力；同时明显增加小鼠脾脏／体重、胸腺／体重比值，增强小鼠对巨噬细胞的吞噬能力．提高小鼠的细胞免疫、体液免疫功能。提示广枣提取液具有显著促进小鼠免疫功能及显著提高小鼠运动耐力的功效。     

VCO sweep-rate limit for a phase-lock loop

Phase-lock loops (PLLs) serve important roles in phase-lock receivers, coherent transponders, and similar applications. For many of these uses, the bandwidth of the loop must be kept small to limit the detrimental influence of noise, and this requirement makes the natural PLL pull-in phenomenon too slow and/or unreliable. For each such case, the phase-lock acquisition process can be aided by the application of an external sweep voltage to the loop voltage controlled oscillators (VCOs). The goal is to have the applied sweep voltage rapidly decrease the closed-loop frequency error to a point where phase lock occurs quickly. For a second-order loop containing a perfect integrator loop filter, there is a maximum VCO sweep-rate magnitude, denoted here as R_m rad/s², for which phase lock is guaranteed. If the applied VCO sweep rate is less than R_m, the loop cannot sweep past a stable phase-lock point, and it will phase lock. On the other hand, for an applied sweep-rate magnitude that is greater than R_m, the PLL may sweep past a lock point and fail to phase lock. In the existing PLL literature, only a trial-and-error approach has been described for estimating R_m, given values of loop damping factor ζ and natural frequency ω_n. Furthermore, no plots exist of computed versus ζ and versus ζ (B_L denotes loop-noise bandwidth). These deficiencies are dealt with in this paper. A new iterative numerical technique is given that converges to the maximum sweep-rate magnitude R_m. It is used to generate data for plots of and versus ζ, the likes of which have never appeared before in the PLL literature.     

An improved lock detector for phase-locked communication receivers

A quadrature lock detector is incorporated in almost all coherent radio communication receivers. This commonly-used receiver subsystem is comprised of a quadrature phase detector that drives a low-pass filter, the output of which is subjected to a user-specified threshold to make a lock/unlock decision. Signal acquisition and phase lock are declared if an above threshold condition is observed. Unfortunately, this method of lock detection may yield a positive lock indication when the receiver is false locked; i.e., a classical quadrature lock detector may generate a false-positive lock indication. This tendency to produce an incorrect lock indication can be reduced significantly by using the new lock detector algorithm that is described here. Compared to the classical quadrature lock detector, the new lock detector is better able to differentiate between true phase lock and anomalous false lock. The classical quadrature lock detector is a simple, first-order approximation of the new lock detector algorithm. That is, the new lock detector algorithm consists of a classical quadrature detector that is augmented by a correction term.