Apparatus for using a time interval counter to measure frequency stability

An apparatus for measuring the relative stability of two signals is disclosed comprising a means for mixing the two signals down to a beat note sine wave and for producing a beat note square wave whose upcrossings are the same as the sine wave. A source of reference frequency is supplied to a clock divider and interval counter to synchronize them and to generate a picket fence for providing a time reference grid of period shorter than the beat period. An interval counter is employed to make a preliminary measurement between successive upcrossings of the beat note square wave for providing an approximate time interval therebetween as a reference. The beat note square wave and the picket fence are then provided to the interval counter to provide an output consisting of the time difference between the upcrossing of each beat note square wave cycle and the next picket fence pulse such that the counter is ready for each upcrossing and dead time is avoided. A computer containing an algorithm for calculating the exact times of the beat note upcrossings then computes the upcrossing times

Frequency stability review

Certain aspects of the description and measurement of oscillator stability are treated. Topics covered are time and frequency deviations, Allan variance, the zero-crossing counter measurement technique, frequency drift removal, and the three-cornered hat

The fundamental structure function of oscillator noise models

Continuous-time models of oscillator phase noise x(t) usually have stationary nth differences, for some n. The covariance structure of such a model can be characterized in the time domain by the structure function: D sub n (t;gamma sub 1, gamma sub 2) = E delta (n) sub gamma sub 1 x(s+t) delta(n) sub gamma sub 2 x (s). Although formulas for the special case D sub 2 (0;gamma,gamma) (the Allan variance times 2 gamma(2)) exist for power-law spectral models, certain estimation problems require a more complete knowledge of (0). Exhibited is a much simpler function of one time variable, D(t), from which (0) can easily be obtained from the spectral density by uncomplicated integrations. Believing that D(t) is the simplest function of time that holds the same information as (0), D(t) is called the fundamental structure function. D(t) is computed for several power-law spectral models. Two examples are D(t) = K/t/(3) for random walk FM, D(t) = Kt(2) 1n/t/ for flicker FM. Then, to demonstrate its use, a BASIC program is given that computes means and variances of two Allan variance estimators, one of which incorporates a method of frequency drift estimation and removal

What is new in the management of rapidly progressive glomerulonephritis?

Rapidly progressive glomerulonephritis (RPGN) results from severe crescentic damage to glomeruli and leads to irreversible kidney failure if not diagnosed and managed in a timely fashion. Traditional treatment has relied on glucocorticoids and cyclophosphamide, with additional plasmapheresis for certain conditions. Here we describe updates in the management of RPGN, according to the underlying renal pathology. However, there remains a paucity of trials that have enrolled patients with more advanced renal disease, dialysis dependence or with RPGN, and we are therefore still reliant on extrapolation of data from studies of patients with a less severe form of disease. In addition, reporting bias results in publication of cases or cohorts showing benefit for newer agents in advanced disease or RPGN, but it remains unclear how many unsuccessful outcomes in these circumstances take place. Since clinical trials specifically in RPGN are unlikely, use of biologic registries or combination of sufficient sized cohort series may provide indications of benefit outside of a clinical trial setting and should be encouraged, in order to provide some evidence for the efficacy of therapeutic regimens in RPGN and advanced renal disease

Orthogonal sets of data windows constructed from trigonometric polynomials

Suboptimal, easily computable substitutes for the discrete prolate-spheroidal windows used by Thomson for spectral estimation are given. Trigonometric coefficients and energy leakages of the window polynomials are tabulated

A structure function representation theorem with applications to frequency stability estimation

Random processes with stationary nth differences serve as models for oscillator phase noise. A theorem which obtains the structure function (covariance of the nth differences) of such a process in terms of the differences of a single function of one time variable is proven. In turn, this function can easily be obtained from the spectral density of the process. The theorem is used for computing the variance of two estimators of frequency stability

Open-loop radio science with a suppressed-carrier signal

When a suppressed-carrier signal is squared, the carrier reappears in doubled form. An open-loop receiver can be used to deliver a recording of a band-limited waveform containing this carrier, whose amplitude and phase can be tracked by the radio science experimenter

A compact presentation of DSN array telemetry performance

The telemetry performance of an arrayed receiver system, including radio losses, is often given by a family of curves giving bit error rate vs bit SNR, with tracking loop SNR at one receiver held constant along each curve. This study shows how to process this information into a more compact, useful format in which the minimal total signal power and optimal carrier suppression, for a given fixed bit error rate, are plotted vs data rate. Examples for baseband-only combining are given. When appropriate dimensionless variables are used for plotting, receiver arrays with different numbers of antennas and different threshold tracking loop bandwidths look much alike, and a universal curve for optimal carrier suppression emerges

Doctor of Philosophy

dissertationEngineered materials consisting of nano- or microparticles embedded in a matrix material may exhibit unique physical properties that are attributed to the specific type, geometry, and spatial pattern of the particles. However, existing techniques for fabricating such engineered materials are limited to laboratory scale, specific materials, and/or 2D implementations. We employ ultrasound directed self-assembly (DSA), which relies on the acoustic radiation force associated with an ultrasound wave field of wavelength significantly larger than the particle size, to organize particles of any material type dispersed in a fluid medium, into a user-specified pattern over a macroscale area or volume. We first derive the dynamics of a single particle in a fluid medium subject to a one-dimensional standing ultrasound wave field. We analyze the trajectory of the particle, driven to either a node or antinode of the ultrasound wave field by the acoustic radiation force, and we show that the particle oscillates around the node of the standing wave with an amplitude that depends on the ratio of the time-dependent drag forces and the particle inertia. We then theoretically derive and experimentally implement a method for single and multidimensional ultrasound DSA, which enables manipulating the position of a single particle and organizing user-specified patterns of nano- and microparticles dispersed in a fluid medium contained within a reservoir lined with ultrasound transducers, respectively. In contrast with existing ultrasound DSA techniques, this method works for any user-specified pattern of particles within a reservoir of arbitrary geometry and ultrasound transducer arrangement. Additionally, the method accounts for all ultrasound wave reflections in the reservoir, which allows for straightforward experimental implementation of the method. Finally, we integrate ultrasound DSA with stereolithography to fabricate engineered materials layer-by-layer via stereolithography, where in each layer we organize a user-specified pattern of particles using ultrasound DSA. This process enables manufacturing macroscale 3D materials with a user-specified microstructure consisting of particles of any material. We demonstrate 3D printing macroscale multilayer engineered materials containing a Bouligand microstructure of nickel-coated carbon fibers. Additionally, we fabricate engineered materials containing a pattern of electrically conductive nickel-coated carbon fibers, which illustrates the feasibility of 3D printing structures with embedded insulated electrical wiring. This process has implications for applications including manufacturing of metamaterials, and multifunctional composite materials

Spectroscopic studies of model biological membranes

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