SUMMARY / RELATED TOPICS

POSSLQ

POSSLQ is an abbreviation for "person of opposite sex sharing living quarters", a term coined in the late 1970s by the United States Census Bureau as part of an effort to more gauge the prevalence of cohabitation in American households. After the 1980 Census, the term gained currency in the wider culture for a time. After demographers observed the increasing frequency of cohabitation over the 1980s, the Census Bureau began directly asking respondents to their major surveys whether they were "unmarried partners", thus making obsolete the old method of counting cohabitors, which involved a series of assumptions about "Persons of Opposite Sex Sharing Living Quarters"; the category "unmarried partner" first appeared in the 1990 Census, was incorporated into the monthly Current Population Survey starting in 1995. By the late 1990s, the term had fallen out of general usage, returned to being a specialized term for demographers. CBS commentator Charles Osgood composed a verse which includes Elliot Sperber, the writer of The Hartford Courant's weekly cryptogram, invented a cryptogram that said: In a fifth-season episode of the television show Cheers, Frasier Crane and Lilith Sternin describe themselves as POSSLQs.

Cohabitation in the United States Common-law marriage Significant other Family "How Does POSSLQ Measure Up? Historical Estimates of Cohabitation", a U. S. Census Bureau working paper by Lynne M. Casper, Philip N. Cohen and Tavia Simmons, May 1999

Metastability (electronics)

Metastability in electronics is the ability of a digital electronics system to persist for an unbounded time in an unstable equilibrium or metastable state. In digital logic circuits, a digital signal is required to be within certain voltage or current limits to represent a'0' or'1' logic level for correct circuit operation. In metastable states, the circuit may be unable to settle into a stable'0' or'1' logic level within the time required for proper circuit operation; as a result, the circuit can act in unpredictable ways, may lead to a system failure, sometimes referred to as a "glitch". Metastability is an instance of the Buridan's ass paradox. Metastable states are inherent features of asynchronous digital systems, of systems with more than one independent clock domain. In self-timed asynchronous systems, arbiters are designed to allow the system to proceed only after the metastability has resolved, so the metastability is a normal condition, not an error condition. In synchronous systems with asynchronous inputs, synchronizers are designed to make the probability of a synchronization failure acceptably small.

Metastable states are avoidable in synchronous systems when the input setup and hold time requirements on flip-flops are satisfied. A simple example of metastability can be found in an SR NOR latch, when both Set and Reset inputs are true and both transition to false at about the same time. Both outputs Q and Q are held at 0 by the simultaneous Set and Reset inputs. After both Set and Reset inputs change to false, the flip-flop will end up in one of two stable states, one of Q and Q true and the other false; the final state will depend on which of R or S returns to zero first, but if both transition at about the same time, the resulting metastability, with intermediate or oscillatory output levels, can take arbitrarily long to resolve to a stable state. In electronics, an arbiter is a circuit designed to determine. Arbiters are used in asynchronous circuits to order computational activities for shared resources to prevent concurrent incorrect operations. Arbiters are used on the inputs of synchronous systems, between clock domains, as synchronizers for input signals.

Although they can minimize the occurrence of metastability to low probabilities, all arbiters have metastable states, which are unavoidable at the boundaries of regions of the input state space resulting in different outputs. Synchronous circuit design techniques make digital circuits that are resistant to the failure modes that can be caused by metastability. A clock domain is defined as a group of flip-flops with a common clock; such architectures can form a circuit guaranteed free of metastability, assuming a low-skew common clock. However then, if the system has a dependence on any continuous inputs these are to be vulnerable to metastable states; when synchronous design techniques are used, protection against metastable events causing systems failures need only be provided when transferring data between different clock domains or from an unclocked region into the synchronous system. This protection can take the form of a series of delay flip-flops which delay the data stream long enough for metastability failures to occur at a negligible rate.

Although metastability is well understood and architectural techniques to control it are known, it persists as a failure mode in equipment. Serious computer and digital hardware bugs caused by metastability have a fascinating social history. Many engineers have refused to believe that a bistable device can enter into a state, neither true nor false and has a positive probability that it will remain indefinite for any given period of time, albeit with exponentially decreasing probability over time. However, metastability is an inevitable result of any attempt to map a continuous domain to a discrete one. At the boundaries in the continuous domain between regions which map to different discrete outputs, points arbitrarily close together in the continuous domain map to different outputs, making a decision as to which output to select a difficult and lengthy process. If the inputs to an arbiter or flip-flop arrive simultaneously, the circuit most will traverse a point of metastability. Metastability remains poorly understood in some circles, various engineers have proposed their own circuits said to solve or filter out the metastability.

Chips using multiple clock sources are tested with tester clocks that have fixed phase relationships, not the independent clocks drifting past each other that will be experienced during operation. This explicitly prevents the metastable failure mode that will occur in the field from being seen or reported. Proper testing for metastability employs clocks of different frequencies and ensuring correct circuit operation. Analog-to-digital converter Buridan's ass Asynchronous CPU Ground bounce Metastability Performance of Clocked FIFOs The'Asynchronous' Bibliography Asynchronous Logic Efficient Self-Timed Interfaces for Crossing Clock Domains Dr. Howard Johnson: Deliberately inducing the metastable state Detailed explanations and Synchronizer designs Metastability Bibliography Clock Domain Crossing: Closing the Loop on Clock Domain Functional Implementation Problems, Cadence Design Systems Stephenson, Jennifer. Understanding Metastability in FPGAs. Altera Corpor

Gas flow computer

The gas flow computer was a mechanical or a pneumatic or hydraulic computing module, subsequently superseded in most applications by an electronic module, as the primary elements switched from transmitting the measured variables from pneumatic or hydraulic pressure signals to electric current as explosion-proof ) and intrinsically safe transmitters became available, that provided a dedicated gas flow computer function. Today "gas flow computers" as such have become uncommon, since gas flow computing is a subfunction of a data acquisition and control program implemented with programmable logic controller and remote terminal unit; the "gas flow computer" senses a mixed "dry" gas stream flow rate plus gas pressure. The most common method of measuring gas flow is via differential pressure across an orifice plate inserted into a flow metering pipe; as the differential pressure is not directly proportional to the gas flow rate, a flow computer algorithm is required to convert the differential pressure reading into a flow rate.

Since gas is compressible and affected by temperature, the gas temperature and pressure must be monitored and compared to a specified standard temperature and pressure within the algorithm. This is referred to as volumetric flow measurement. Next we need to calculate mass flow AGA3 based upon the specific gravity of the gas. Since a natural gas stream contains a mix of various hydrocarbon gases of different specific gravities, mole percentages must be determined via a gas sample analysis; the mixed gas stream will contain some inert gases such as nitrogen and carbon dioxide. Therefore the gas flow computer requires the entry of mole percentages for each gas component. Based on accurate mass flow calculations it becomes possible, based upon the energy content of each gas component, to calculate energy flow, i.e. API 14.5 since each gas component contains different energy content. These values in joules are built into the gas flow computer algorithm; therefore energy flow metering is our ultimate goal since this is where the true value is for the client.

These mineral reserves are taxed based upon energy content. The inert gases such as nitrogen have no value. Other input parameters include contract hour as well as location latitude and altitude above sea level, isentropic exponent and type of materials used in the metering device to optimize the accuracy of calculations. In summary the gas flow computer requires 30 initial input parameters in conjunction with "near realtime" gas flow and temperature sensing. In addition to providing volumetric and energy flow data, the gas flow computer provides date and time, instantaneous and daily data; the gas flow computer stores date/time stamped volume records in RAM for up to 35 days in order to provide sufficient time for a host system to retrieve the records as well as to allow time for human intervention if this retrieval fails to occur. The flow computer tracks modifications to flow parameters in an "Audit Trail" that identifies the modified parameter, the time and date of the value change, the old and new values, may identify the person making the change.

The data log format and contents vary by flow computer manufacturer, with all manufacturers designing to a specification outlined by the American Petroleum Institute. Flow metering accuracy is compromised if there are liquids in the gas stream; therefore methods are implemented to remove liquids from the gas stream before measurement. However a newer V-Cone technology is being used to more meter gas that contains some liquids. AGA-8 AGA-3 American Gas Association Landfill gas monitoring NX-19 http://www.sgc-valid8.com -- Free online Flow Measurement Calculation and Verification Engine https://web.archive.org/web/20080828212148/http://www.squinch.org/gas.html -- Provides working hands-on examples of AGA 3, AGA 7 and AGA 8 gas flow calculations. Http://www.aga.org/ -- website for American Gas Association, publisher of AGA report no. 3, report no. 7 and report no. 8 http://www.api.org/ -- website for American Petroleum Institute website, publisher of the Manual of Petroleum Measurement Standards, a compendium of petroleum gas and liquid measurement specifications.

Chapter 21 of the MPMS specifies an industry standard for electronic flow measurement