14,426 research outputs found
Time scheduling of a mix of 4D equipped and unequipped aircraft
In planning for a future automated air traffic system, it is necessary to confront the transition situation in which some percentage of the traffic must be handled by conventional means. A safe, efficient transition system is needed since initially not all aircraft will be able to respond to a more automated system. The specific problem addressed was that of time scheduling a mix of 4D-equipped aircraft (aircraft that can accurately meet a controller specified time schedule at selected way points in the terminal area) when operating in conjunction with unequipped aircraft (aircraft that require air traffic handling by means of standard vectoring techniques). First, a relationship between time separation and system capacity was developed. The time separations were incorporated into a set of scheduling algorithms which contain the required elements of flexibility needed for terminal-area operation, such as delaying aircraft and changing time separations. The problem of reducing the size of time separations allotted for vectored aircraft by means of computer assists to the controller was also addressed
Singular solutions to a semilinear biharmonic equation with a general critical nonlinearity
We consider positive solutions of the semilinear biharmonic equation
in with non-removable singularities at the origin. Under natural
assumptions on the nonlinearity , we show that is a
periodic function of and we classify all such solutions.Comment: To V. Maz'ya on the occasion of his 80th birthday; references adde
A time-based concept for terminal-area traffic management
An automated air-traffic-management concept that has the potential for significantly increasing the efficiency of traffic flows in high-density terminal areas is discussed. The concept's implementation depends on the techniques for controlling the landing time of all aircraft entering the terminal area, both those that are equipped with on-board four dimensional guidance systems as well as those aircraft types that are conventionally equipped. The two major ground-based elements of the system are a scheduler which assigns conflict-free landing times and a profile descent advisor. Landing times provided by the scheduler are uplinked to equipped aircraft and translated into the appropriate four dimensional trajectory by the on-board flight-management system. The controller issues descent advisories to unequipped aircraft to help them achieve the assigned landing times. Air traffic control simulations have established that the concept provides an efficient method for controlling various mixes of four dimensional-equipped and unequipped, as well as low-and high-performance, aircraft
On the stability of randomly sampled systems
Stability of randomly sampled linear systems studied by Liapunov function metho
Real-time manned simulation of advanced terminal area guidance concepts for short-haul operations
A real-time simulation was conducted of three-dimensional area navigation and four-dimensional area navigation equipped (STOL) aircraft operating in a high-density terminal area traffic environment. The objectives were to examine the effects of 3D RNAV and 4D RNAV equipped aircraft on the terminal area traffic efficiency, and to examine the performance of an air traffic control system concept and associated controller display proposed for use with advanced RNAV systems. Three types of STOL aircraft were simulated each with different performance capabilities. System performance was measured in both the 4D mode and in a 3D mode; the 3D mode, used as a baseline, was simply the 4D mode less any time specification. The results show that communications workload in the 4D mode was reduced by about 35 percent compared to the 3D, while 35 percent more traffic was handled with the 4D. Aircraft holding time in the 4D mode was only 30 percent of that required in the 3D mode. In addition, the orderliness of traffic was improved significantly in the 4D mode
Remainder terms in the fractional Sobolev inequality
We show that the fractional Sobolev inequality for the embedding , can be sharpened by
adding a remainder term proportional to the distance to the set of optimizers.
As a corollary, we derive the existence of a remainder term in the weak
-norm for functions supported in a domain of finite measure.
Our results generalize earlier work for the non-fractional case where is an
even integer.Comment: 13 page
Thermocapillary Flow on Superhydrophobic Surfaces
A liquid in Cassie-Baxter state above a structured superhydrophobic surface
is ideally suited for surface driven transport due to its large free surface
fraction in close contact to a solid. We investigate thermal Marangoni flow
over a superhydrophobic array of fins oriented parallel or perpendicular to an
applied temperature gradient. In the Stokes limit we derive an analytical
expression for the bulk flow velocity above the surface and compare it with
numerical solutions of the Navier-Stokes equation. Even for moderate
temperature gradients comparatively large flow velocities are induced,
suggesting to utilize this principle for microfluidic pumping.Comment: 4 pages, 4 figure
Single-Quadrature Continuous-Variable Quantum Key Distribution
Most continuous-variable quantum key distribution schemes are based on the
Gaussian modulation of coherent states followed by continuous quadrature
detection using homodyne detectors. In all previous schemes, the Gaussian
modulation has been carried out in conjugate quadratures thus requiring two
independent modulators for their implementations. Here, we propose and
experimentally test a largely simplified scheme in which the Gaussian
modulation is performed in a single quadrature. The scheme is shown to be
asymptotically secure against collective attacks, and considers asymmetric
preparation and excess noise. A single-quadrature modulation approach renders
the need for a costly amplitude modulator unnecessary, and thus facilitates
commercialization of continuous-variable quantum key distribution.Comment: 13 pages, 7 figure
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