Design and simulation of a descent controller for strategic four-dimensional aircraft navigation

A time-controlled navigation system applicable to the descent phase of flight for airline transport aircraft was developed and simulated. The design incorporates the linear discrete-time sampled-data version of the linearized continuous-time system describing the aircraft's aerodynamics. Using optimal linear quadratic control techniques, an optimal deterministic control regulator which is implementable on an airborne computer is designed. The navigation controller assists the pilot in complying with assigned times of arrival along a four-dimensional flight path in the presence of wind disturbances. The strategic air traffic control concept is also described, followed by the design of a strategic control descent path. A strategy for determining possible times of arrival at specified waypoints along the descent path and for generating the corresponding route-time profiles that are within the performance capabilities of the aircraft is presented. Using a mathematical model of the Boeing 707-320B aircraft along with a Boeing 707 cockpit simulator interfaced with an Adage AGT-30 digital computer, a real-time simulation of the complete aircraft aerodynamics was achieved. The strategic four-dimensional navigation controller for longitudinal dynamics was tested on the nonlinear aircraft model in the presence of 15, 30, and 45 knot head-winds. The results indicate that the controller preserved the desired accuracy and precision of a time-controlled aircraft navigation system

Functional approach to the catalytic site of the sarcoplasmic reticulum Ca(2+)-ATPase: binding and hydrolysis of ATP in the absence of Ca(2+)

Isolated sarcoplasmic reticulum vesicles in the presence of Mg(2+) and absence of Ca(2+) retain significant ATP hydrolytic activity that can be attributed to the Ca(2+)-ATPase protein. At neutral pH and the presence of 5 mM Mg(2+), the dependence of the hydrolysis rate on a linear ATP concentration scale can be fitted by a single hyperbolic function. MgATP hydrolysis is inhibited by either free Mg(2+) or free ATP. The rate of ATP hydrolysis is not perturbed by vanadate, whereas the rate of p-nitrophenyl phosphate hydrolysis is not altered by a nonhydrolyzable ATP analog. ATP binding affinity at neutral pH and in a Ca(2+)-free medium is increased by Mg(2+) but decreased by vanadate when Mg(2+) is present. It is suggested that MgATP hydrolysis in the absence of Ca(2+) requires some optimal adjustment of the enzyme cytoplasmic domains. The Ca(2+)-independent activity is operative at basal levels of cytoplasmic Ca(2+) or when the Ca(2+) binding transition is impeded

How to detect level crossings without looking at the spectrum

We remind the reader that it is possible to tell if two or more eigenvalues of a matrix are equal, without calculating the eigenvalues. We then use this property to detect (avoided) crossings in the spectra of quantum Hamiltonians representable by matrices. This approach provides a pedagogical introduction to (avoided) crossings, is capable of handling realistic Hamiltonians analytically, and offers a way to visualize crossings which is sometimes superior to that provided by the spectrum. We illustrate the method using the Breit-Rabi Hamiltonian to describe the hyperfine-Zeeman structure of the ground state hydrogen atom in a uniform magnetic field.Comment: Accepted for publication in the American Journal of Physic

Dissecting the Hydrolytic Activities of Sarcoplasmic Reticulum ATPase in the Presence of Acetyl Phosphate

Sarcoplasmic reticulum vesicles and purified Ca$^{2+}$-ATPase hydrolyze acetyl phosphate both in the presence and absence of Ca$^{2+}$. The Ca$^{2+}$-independent activity was fully sensitive to vanadate, insensitive to thapsigargin, and proceeded without accumulation of phosphorylated enzyme. Acetyl phosphate hydrolysis in the absence of Ca$^{2+}$ was activated by dimethyl sulfoxide. The Ca$^{2+}$-dependent activity was partially sensitive to vanadate, fully sensitive to thapsigargin, and associated with steady phosphoenzyme accumulation. The Ca$^{2+}$/P(i) coupling ratio at neutral pH sustained by 10 mm acetyl phosphate was 0.57. Addition of 30% dimethyl sulfoxide completely blocked Ca$^{2+}$ transport and partially inhibited the hydrolysis rate. Uncoupling induced by dimethyl sulfoxide included the accumulation of vanadate-insensitive phosphorylated enzyme. When acetyl phosphate was the substrate, the hydrolytic pathway was dependent on experimental conditions that might or might not allow net Ca$^{2+}$ transport. The interdependence of both Ca$^{2+}$-dependent and Ca$^{2+}$-independent hydrolytic activities was demonstrated

Optical injection and terahertz detection of the macroscopic Berry curvature

We propose an experimental scheme to probe the Berry curvature of solids. Our method is sensitive to arbitrary regions of the Brillouin zone, and employs only basic optical and terahertz techniques to yield a background free signal. Using semiconductor quantum wells as a prototypical system, we discuss how to inject Berry curvature macroscopically, and probe it in a way that provides information about the underlying microscopic Berry curvature.Comment: 4 pages, accepted in Physical Review Letter

Coexistence of thermal noise and squeezing in the intensity fluctuations of small laser diodes

The intensity fluctuations of laser light are derived from photon number rate equations. In the limit of short times, the photon statistics for small laser devices such as typical semiconductor laser diodes show thermal characteristics even above threshold. In the limit of long time averages represented by the low frequency component of the noise, the same devices exhibit squeezing. It is shown that squeezing and thermal noise can coexist in the multi-mode output field of laser diodes. This result implies that the squeezed light generated by regularly pumped semiconductor laser diodes is qualitatively different from single mode squeezed light. In particular, no entanglement between photons can be generated using this type of collective multi-mode squeezing.Comment: 9 pages, 8 figures, submitted to J. Opt. Soc. Am. B, added references and clarifications of the contex