Precise Time Interval Research Articles

Focus on Data Acquisition

Focus on Data Acquisition

Advanced system on a chip microelectronics for spacecraft and science instruments

The explosive growth of the modern microelectronics field opens new horizons for the development of new lightweight, low power, and smart spacecraft and science instrumentation systems in the new millennium explorations. Although this growth is mostly driven by the commercial need for low power, portable and computationally intensive products, the applicability is obvious in the space sector. The additional difficulties needed to be overcome for applicability in space include radiation hardness for total ionizing dose and single event effects (SEE), and reliability. Additionally, this new capability introduces a whole new philosophy of design and R&D, with strong implications in organizational and inter-agency program management. One key component specifically developed towards low power, small size, highly autonomous spacecraft systems, is the smart sensor remote input/output (TRIO) chip. TRIO can interface to 32 transducers with current sources/sinks and voltage sensing. It includes front-end analog signal processing, a 10-bit ADC, memory, and standard serial and parallel I/Os. These functions are very useful for spacecraft and subsystems health and status monitoring, and control actions. The key contributions of the TRIO are feasibility of modular architectures, elimination of several miles of wire harnessing, and power savings by orders of magnitude. TRIO freely operates from a single power supply 2.5– 5.5 V with power dissipation <10 mW . This system on a chip device rapidly becomes a NASA and Commercial Space standard as it is already selected by thousands in several new millennium missions, including Europa Orbiter, Mars Surveyor Program, Solar Probe, Pluto Express, Stereo, Contour, Messenger, etc. In the Science Instrumentation field common instruments that can greatly take advantage of the new technologies are: energetic-particle/plasma and wave instruments, imagers, mass spectrometers, X-ray and UV spectrographs, magnetometers, laser rangefinding instruments, etc. Common measurements that apply to many of these instruments are precise time interval measurement and high resolution read-out of solid state detectors. A precise time interval measurement chip was specially developed that achieves ∼100 ps (×10 improvement) time resolution at a power dissipation ∼20 mW (×50 improvement), dead time ∼1.5 μs (×20 improvement), and chip die size 5 mm×5 mm versus two 20 cm×20 cm doubled sided boards. This device is selected as a key enabling technology for several NASA particle, delay line imaging, and laser range finding instruments onboard (NASA Image, Messenger, etc. missions). Another device with universal application is radiation energy read-out from solid state detectors. Multi-channel low-power and end-to-end sensor input—digital output is key for the new generation instruments. The readout channel comprises of a Charge Sensitive Preamplifier with a target sensitivity of ∼1 KeV FWHM at 20 pf detector capacitance, a Shaper Amplifier with programmable time constant/gain, and an ADC. The read-out chip together with the precise time interval chip comprises the essential elements of a common particle spectroscopy instrument. To mention some more applications fast-signal acquisition—and digitization is a very useful function for a category of instrument such as mass spectroscopy and profile laser rangefinding. The single chip approach includes a high bandwidth preamplifier, fast sampling ∼5 ns , analog memory ∼10K locations, 12-bit ADC and serial/parallel I/Os. The wealth of the applications proves the advanced microelectronics field as a key enabling technology for the new millennium space exploration.

Late Paleozoic faunal, climatic, and geographic changes in the Baoshan block as a Gondwana-derived continental fragment in southwest China

The Carboniferous and Permian of the Baoshan block consist of three major depositional sequences: a Lower Carboniferous carbonate sequence, a Lower Permian siliciclastic sequence, and a Middle Permian carbonate sequence. These three sequences were interrupted by two major regressive events: first, the Namurian Uplift ranging in age from Serpukovian to Gzhelian, and second, the Post-Sakmarian Regression occurring probably at Artinskian time in the Baoshan block, although the precise time interval of the latter event is still unclear. The Baoshan block is characterized by warm-water, highly diverse and abundant faunas during the Early Carboniferous, by cold-water and low diversity faunas during the Early Permian, and by possibly warm-water but low diversity faunas during the Middle Permian. The Sweetognathus bucaramangus conodont fauna constrains the upper boundary of the diamictite-bearing siliciclastic deposits (Dingjiazhai Formation) to the Sakmarian to early Artinskian, as well as the eruption of the rifting basalts (Woniusi Formation) to, at least, the post-early Artinskian. Paleozoogeographically, affiliation of the faunas in the Baoshan block changed from Eurasian in the Early Carboniferous, to Peri-Gondwanan in the Early Permian, and to Marginal Cathaysian/Cimmerian in the Middle Permian. Cimmerian blocks have more or less comparable geohistory to one another in the Carboniferous and Permian. During the Middle Permian, the eastern Cimmerian blocks such as Sibumasu (s.s), Baoshan, and Tengchong are not far from the palaeoequator, but apparently more distant than the western Cimmerian blocks based on the presence or absence of some index taxa such as the fusulinaceans Eopolydiexodina and Neoschwagerina, and the corals Thomasiphyllum and Wentzellophyllum persicum.

Global Positioning System (GPS) Time Dissemination for Real-Time Applications

This paper presents an overview of the Global Positioning System (GPS) for the potential precise time and time interval user with special reference to real-time systems. An overview of GPS operation is presented, and GPS error sources are described as they relate to the timing user. A review of receiver types and receiver tasks provides the basis for understanding GPS time transfer techniques. The accuracies provided by different techniques are reviewed and the special requirements for GPS time and frequency receivers as well as modern timing receiver enhancements are described. The precise time standard provided by GPS is traced through its path from global standards to the user application. GPS time dissemination failure modes that result from control problems, space craft failures, and receiver failures are outlined.

New Possibilities in Time-Frequency Standards

By invitation of Edoardo Proverbio, the President of Commission 31 (Time), this report attempts to summarize “new possibilities in time-frequency standards”. Especially because recent work in this highly specialized field is so diverse and so complex, I appreciate the support of our colleague, Dr. G. Busca, who will survey the extensive progress being made east of the Atlantic. I confine this paper to work that has appeared in the open literature from the United States and Canada.Since much of this work is proprietary, and since it is difficult to assign credit fairly, I will not attempt to give either a comprehensive or selected bibliography of references in this paper. There are three primary symposia where such work is published: (1) the annual IEEE International Frequency Control Symposia; (2) the more recently organized annual European Frequency and Time Forums; and (3) the (United States) Annual Precise Time and Time Interval (PTTI) Applications and Planning Meetings, organized jointly by the Department of Defense and NASA. The best general review of recent work on frequency standards, which appeared just before our last IAU General Assembly and is not yet outdated, is the special issue of the Proceedings of the IEEE, volume 79, no 7 (July 1991), and especially the papers “An Introduction to Frequency Standards” by Lindon L. Lewis, “Atomic Ion Frequency Standards” by Wayne M. Itano, and “Laser- Cooled Neutral Atom Frequency Standards” by Steven L. Rolston and William D. Phillips.

Effects of gonadotropins upon the incidence and kinetics of meiotic maturation of macaque oocytes in vitro

The specific aim of this study was to determine the effects of gonadotropins in vitro upon the incidence of and precise time interval to germinal vesicle breakdown (GVB) and extrusion of the first polar body (PB1) in oocytes from nonstimulated rhesus monkeys. Cumulus-enclod germinal vesicle (GV) stage oocytes from 10 normal, cycling rhesus monkeys in the follicular phase of the menstrual cycle were cultured with either: (1) 1.0 micrograms/ml human follicle-stimulating hormone (hFSH), (2) 10 micrograms/ml human luteinizing hormone (hLH), (3) 1.0 microgram/ml hFSH and 10 micrograms/ml hLH, or (4) no gonadotropins (controls). Oocytes (n = 234) were examined at 3-hr intervals from 0 to 21 hr and at 4-hr intervals from 24 to 52 hr for GVB and PB1. Neither the incidence of GVB (hFSH: 63.5%; hLH: 56.1%; both gonadotropins: 63.1%; no gonadotropins: 53.6%) nor extrusion of PB1 (hFSH: 41.3%; hLH: 36.4%; both gonadotropins: 36.9%; no gonadotropins; 31.9%) differed (P > 0.05) among treatments. The time to GVB was accelerated (P < 0.05) by gonadotropins (hFSH: 10.8 +/- 1.7 hr; hLH: 10.1 +/- 1.8 hr; both gonadotropins: 8.8 +/- 1.1 hr) when compared to controls (17.4 +/- 2.0 hr). However, the time interval to extrusion of PB1 did not differ (P > 0.05) among treatments (hFSH: 32.3 +/- 1.2 hr; hLH: 35.1 +/- 1.4 hr; both gonadotropins: 35.2 +/- 1.3 hr; no gonadotropins: 34.1 +/- 1.2 hr). The mean interval to extrusion of PB1 was 34.1 +/- 0.6 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

An averaging mode time-to-amplitude converter with picosecond resolution

A time-to-amplitude converter (TAC) meant to be employed in pulsed time-of-flight (TOF) laser rangefinding and capable of operating at a very high pulse repetition rate (PRR) is described. It is based on a precise time interval between the emitted light pulses and measures the phase difference of the logic-level pulse trains formed by timing pulses derived from the transmitted and received light pulses. The fast part of the TAC is constructed by means of ECL 100 K circuits. Test results indicate that the TAC is well suited for fast, millimeter-level resolution applications, and a full width at half maximum (FWHM) resolution of 1.0 ps is achieved with a 5-MHz pulse repetition rate and 0.1-Hz-10-kHz measurement bandwidth.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Accessible methods for measuring the resonance properties of musical instruments

Increased availability of amplifiers that supply precise time delays for introducing “ambience” effects in music reproduction provides a useful resource for the study of musical instruments. The circuitry provides simultaneous comparison of two parts of a resonance decay separated by a precise time interval. From these data, logarithmic decrement may be measured. For single‐frequency tones, the figure of merit “Q” at that frequency can be ascertained. Examples of the use of these processes will be shown.

An analyzer for autonomic nerve activities in acute and chronic animals.

A real-time analyzer for autonomic nerve activity in acute and chronic animals has been developed. This device, using a finite difference method, can separate individual neural spikes from compound nerve action potentials consisting of base-line drift due to bodily movement, 60 Hz power-line interference, and bioelectrical signals such as electromyogram and electrocardiogram, and with poor signal-to-noise ratio recorded in multifiber preparations or whole nerves. Because there is no phase distortion of neural spikes, the precise time interval between the individual neural spikes can be measured and is converted to analog voltage with a rate meter. This device can perform quantitative analyses of compound nerve action potentials in real time, independent of 60 Hz power-line interference, ECG, and base-line drift.

Automated Timekeeping II

An automated system presently used by the U. S. Naval Observatory (USNO) for determining, maintaining, and disseminating Precise Time and Time Interval (PTTI) to a worldwide community of scientific and military users is described and evaluated on the basis of present capabilities and future requirements. The objective of the system is to provide near-real-time dissemination of PTTI information from a Master Clock time scale with a stability in excess of a few parts in 10-14.

Modern navigation systems and their relation to timekeeping

This paper will discuss the interdependence between navigation and Precise Time and Time Interval (PTTI) systems. The modern role that navigation systems play in the field of timekeeping is shown through examples of how Omega, Loran-C, TRANSIT, and the Global Positioning System (GPS) are utilized by the PTTI community.

Data on Time and Polar Motion: Immediate Accessibility

AbstractUsers of time and polar motion information have requirements for data which are somewhat different from those usually considered for astronomical data files. Because of these requirements, it is necessary to provide immediate access to the latest information on Earth orientation and even predictions of future orientation. For other applications where data of the highest accuracy is required with little concern for the delay between observations and the determination o f the required information, a more traditional approach may be used. To meet all of these needs a versatile automated data retrieval system is demanded. The U. S. Naval observatory is now implementinq such a system in the area of Earth orientation information and for precise time and time interval applications. Data are available through a series of weekly, monthly, and annual reports, as well as through a digital communications link to Time Service machine-readable files.

Applications of Time and Frequency in Geodesy

Many geodetic measurements, especially those using space techniques require very precise time and frequency devices. In this paper, some applications of time and frequency in Satellite-Geodesy are discussed with reference to several observational techniques. Precise laser range measurements to artificial satellites or to the moon using stationary or mobile systems in the centimetre domain need not only a very precise time interval counter or event timer but also the access to a stable and globally available time scale, especially if the data will be used with only short delays or even in real time. New techniques such as interferometry for the determination of short, medium and very long baselines require time and frequency devices with best characteristics in both the short-term and the long-term stability.

Time Dissemination Capabilities via Navigation Satellites

There are currently two navigation satellite systems employing clock-carrying satellites that are useable for the dissemination of Precise Time and Time Interval (PTTI). These are the Navy Navigation Satellite System (NNSS or Transit), which now has five satellites in low altitude (1000 km) polar orbits, and the Global Positioning System (GPS), which currently has six satellites in circular (20,000 km) twelve-hour orbits. The US Naval Observatory (USNO) is engaged in an ongoing program to improve the performance of these systems and to make them operational time dissemination systems as soon as possible.Transit has a demonstrated time-transfer capability in the 25 microsecond region. GPS is capable of time transfers of better than 100 nanoseconds. This paper describes equipment available for recovering time from the satellites, current efforts aimed at improving both satellite system and receiver performance, and the data collection and reporting schemes used at the USNO to provide data for publication. F...