34,159 research outputs found
A nonlinear filter for compensating for time delays in manual control systems
A nonlinear filter configured to provide phase lead without accompanying gain distortion is analyzed and evaluated. The nonlinear filter is superior to a linear lead/lag compensator in its ability to maintain system stability as open loop crossover frequency is increased. Test subjects subjectively rated the filter as slightly better than a lead/lag compensator in its ability to compensate for delays in a compensatory tracking task. However, the filter does introduce unwanted harmonics. This is particularly noticeable for low frequency pilot inputs. A revised compensation method is proposed which allows such low frequency inputs to bypass the nonlinear filter. A brief analytical and experimental evaluation of the revised filter indicates that further evaluation in more realistic tasks is justified
Managing fisheries in a changing climate
No need to wait for more information: industrialized fishing is already wiping out stocks
An equation of state for oxygen and nitrogen
Recent measurements of thermodynamic properties of oxygen and nitrogen have provided data necessary for development of a single equation of state for both fluids. Data are available in summary report and two-part detailed study on thermodynamic properties of oxygen and nitrogen. Same data are used to develop vapor-pressure equation and heat-capacity equation
Quantum Quenches in Free Field Theory: Universal Scaling at Any Rate
Quantum quenches display universal scaling in several regimes. For quenches
which start from a gapped phase and cross a critical point, with a rate slow
compared to the initial gap, many systems obey Kibble-Zurek scaling. More
recently, a different scaling behaviour has been shown to occur when the quench
rate is fast compared to all other physical scales, but still slow compared to
the UV cutoff. We investigate the passage from fast to slow quenches in scalar
and fermionic free field theories with time dependent masses for which the
dynamics can be solved exactly for all quench rates. We find that renormalized
one point functions smoothly cross over between the regimes.Comment: 40 pages; v2: a bit late, but it includes minor modifications to
match published versio
The thermodynamic properties of oxygen and nitrogen. Part 2: Thermodynamic properties of oxygen from 100 R to 600 R with pressure to 5000 psia
An equation of state is presented for liquid and gaseous oxygen for temperatures from 100 R to 600 R and pressures to 5000 psia. The pressure-density-temperature data available from the published literature have been reviewed, and appropriate corrections have been applied to bring experimental temperatures into accord with the International Practical Temperature Scale of 1968. Representative comparisons of property values calculated from the equation of state to measured values are included to illustrate the accuracy of the equation of state. The coefficients of the equation of state were determined by a weighted least squares fit to selected published data, and simultaneously to isochoric heat capacity data, and to data which define the phase equilibrium for the saturated liquid and saturated vapor. The equation of state is estimated to be accurate for the liquid to within 0.1 percent in density, to within 0.2 percent for the vapor below the critical temperature and for states above the critical temperatures to 250 K, and within 0.1 percent for supercritical states at temperatures from 250 K to 300 K. The vapor pressure equation is accurate to within + or - 0.01 K between the triple point and the critical point
An equation of state for oxygen and nitrogen
Preliminary equations of state are presented for oxygen and nitrogen which provide accurate representations of the available P-density-T data for both fluids. The equation for nitrogen is applicable for temperatures from 70 K to 1300 K at pressures to 10,000 atmospheres, and the equation for oxygen for temperatures from 70 K to 323 K at pressures to 350 atmospheres. Deviations of calculated densities from representative experimental data are included. A volume-explicit equation of state for oxygen to be used in estimating density values in the range of applicability of the equation of state is also presented
The thermodynamic properties of oxygen and nitrogen. Part 1: Thermodynamic properties of nitrogen from 115 R to 3500 R with pressures to 150000 psia
An equation of state is presented for liquid and gaseous nitrogen for temperatures from 115 R to 3500 R and pressures to 150,000 psia. All of the pressure-density-temperature data available from the published literature have been reviewed, and appropriate corrections have been identified and applied to bring experimental temperatures into accord with the International Practical Temperature Scale of 1968. Comparisons of property values calculated from the equation of state to measured values are included to illustrate the accuracy of the equation in representing the data. The coefficients of the equation of state were determined by a weighted least squares fit to selected published data and, simultaneously, to constant volume data determined by corresponding states analysis from oxygen data, and to data which define the phase equilibrium criteria for the saturated liquid and saturated vapor. The methods of weighting the various data for simultaneous fitting are presented and discussed. The equation of state is estimated to be accurate to within 0.5 percent in the liquid region, to within 0.1 percent for supercritical isotherms up to 15,000 psia, and to within 0.3 percent from 15,000 to 150,000 psia
Smooth and fast versus instantaneous quenches in quantum field theory
We examine in detail the relationship between smooth fast quantum quenches,
characterized by a time scale , and {\em instantaneous quenches},
within the framework of exactly solvable mass quenches in free scalar field
theory. Our earlier studies \cite{dgm1,dgm2} highlighted that the two protocols
remain distinct in the limit because of the relation
of the quench rate to the UV cut-off, i.e., always holds
in the fast smooth quenches while for instantaneous
quenches. Here we study UV finite quantities like correlators at finite spatial
distances and the excess energy produced above the final ground state energy.
We show that at late times and large distances (compared to the quench time
scale) the smooth quench correlator approaches that for the instantaneous
quench. At early times, we find that for small spatial separation and small
, the correlator scales universally with , exactly as in
the scaling of renormalized one point functions found in earlier work. At
larger separation, the dependence on drops out. The excess energy
density is finite (for finite ) and scales in a universal fashion
for all . However, the scaling behaviour produces a divergent result in the
limit for , just as in an instantaneous
quench, where it is UV divergent for . We argue that similar results
hold for arbitrary interacting theories: the excess energy density produced is
expected to diverge for scaling dimensions .Comment: 52 pages; v2: minor modifications to match published versio
Improved chlorate candle provides concentrated oxygen source
Improved chlorate candle is used as a solid, portable source of oxygen in emergency situations. It contains sodium chlorate, iron, barium peroxide, and glass mixed in powdered form. The oxygen evolves from the decomposition of the sodium chlorate when an ignition pellet is electrically initiated
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