Analysis techniques for multivariate root loci

Analysis and techniques are developed for the multivariable root locus and the multivariable optimal root locus. The generalized eigenvalue problem is used to compute angles and sensitivities for both types of loci, and an algorithm is presented that determines the asymptotic properties of the optimal root locus

An experimental investigation of the parallel blade-vortex interaction

A scheme for investigating the parallel blade vortex interaction (BVI) has been designed and tested. The scheme involves setting a vortex generator upstream of a nonlifting rotor so that the vortex interacts with the blade at the forward azimuth. The method has revealed two propagation mechanisms: a type C shock propagation from the leading edge induced by the vortex at high tip speeds, and a rapid but continuous pressure pulse associated with the proximity of the vortex to the leading edge. The latter is thought to be the more important source. The effects of Mach number and vortex proximity are discussed

Low Speed Wind Tunnel Tests on a One-Seventh Scale Model of the H.126 Jet Flap Aircraft

Low speed wind tunnel tests were performed on a one-seventh scale model of the British H.126 jet flap research aircraft over a range of jet momentum coefficients. The primary objective was to compare model aerodynamic characteristics with those of the aircraft, with the intent to provide preliminary data needed towards establishing small-to-full scale correlating techniques on jet flap V/STOL aircraft configurations. Lift and drag coefficients from the model and aircraft tests were found to be in reasonable agreement. The pitching moment coefficient and trim condition correlation was poor. A secondary objective was to evaluate a modified thrust nozzle having thrust reversal capability. The results showed there was a considerable loss of lift in the reverse thrust operational mode because of increased nozzle-wing flow interference. A comparison between the model simulated H.126 wing jet efflux and the model uniform pressure distribution wing jet efflux indicated no more than 5% loss in weight flow rate

Photonic band-gap properties for two-component slow light

We consider two-component "spinor" slow light in an ensemble of atoms coherently driven by two pairs of counterpropagating control laser fields in a double tripod-type linkage scheme. We derive an equation of motion for the spinor slow light (SSL) representing an effective Dirac equation for a massive particle with the mass determined by the two-photon detuning. By changing the detuning the atomic medium acts as a photonic crystal with a controllable band gap. If the frequency of the incident probe light lies within the band gap, the light tunnels through the sample. For frequencies outside the band gap, the transmission probability oscillates with increasing length of the sample. In both cases the reflection takes place into the complementary mode of the probe field. We investigate the influence of the finite excited state lifetime on the transmission and reflection coefficients of the probe light. We discuss possible experimental implementations of the SSL using alkali atoms such as Rubidium or Sodium.Comment: 7 figure

Airloads on bluff bodies, with application to the rotor-induced downloads on tilt-rotor aircraft

The aerodynamic characteristics of airfoils with several flap configurations were studied theoretically and experimentally in environments that simulate a wing immersed in the downwash of a hovering rotor. Special techniques were developed for correcting and validating the wind tunnel data for large blockage effects, and the test results were used to evaluate two modern blockage effects, and the test results were used to evaluate two modern computational aerodynamics codes. The combined computed and measured results show that improved flap and leading-edge configurations can be designed which will achieve large reductions in the downloads of tilt-rotor aircraft, and thereby improve their hover efficiency

On the efficiency of estimating penetrating rank on large graphs

P-Rank (Penetrating Rank) has been suggested as a useful measure of structural similarity that takes account of both incoming and outgoing edges in ubiquitous networks. Existing work often utilizes memoization to compute P-Rank similarity in an iterative fashion, which requires cubic time in the worst case. Besides, previous methods mainly focus on the deterministic computation of P-Rank, but lack the probabilistic framework that scales well for large graphs. In this paper, we propose two efficient algorithms for computing P-Rank on large graphs. The first observation is that a large body of objects in a real graph usually share similar neighborhood structures. By merging such objects with an explicit low-rank factorization, we devise a deterministic algorithm to compute P-Rank in quadratic time. The second observation is that by converting the iterative form of P-Rank into a matrix power series form, we can leverage the random sampling approach to probabilistically compute P-Rank in linear time with provable accuracy guarantees. The empirical results on both real and synthetic datasets show that our approaches achieve high time efficiency with controlled error and outperform the baseline algorithms by at least one order of magnitude

Onset of collective and cohesive motion

We study the onset of collective motion, with and without cohesion, of groups of noisy self-propelled particles interacting locally. We find that this phase transition, in two space dimensions, is always discontinuous, including for the minimal model of Vicsek et al. [Phys. Rev. Lett. {\bf 75},1226 (1995)] for which a non-trivial critical point was previously advocated. We also show that cohesion is always lost near onset, as a result of the interplay of density, velocity, and shape fluctuations.Comment: accepted for publication in Phys. Rev. Let

Dynamics of two phosphorelays controlling cell cycle progression in 1 Caulobacter crescentus

In Caulobacter crescentus, progression through the cell cycle is governed by the periodic activation and inactivation of the master regulator CtrA. Two phosphorelays, each initiating with the histidine kinase CckA, promote CtrA activation by driving its phosphorylation and by inactivating its proteolysis. Here, we examined whether the CckA phosphorelays also influence the downregulation of CtrA. We demonstrate that CckA is bifunctional, capable of acting as either a kinase or phosphatase to drive the activation or inactivation, respectively, of CtrA. By identifying mutations that uncouple these two activities, we show that CckA's phosphatase activity is important for downregulating CtrA prior to DNA replication initiation in vivo but that other phosphatases may exist. Our results demonstrate that cell cycle transitions in Caulobacter require and are likely driven by the toggling of CckA between its kinase and phosphatase states. More generally, our results emphasize how the bifunctional nature of histidine kinases can help switch cells between mutually exclusive states

Investigation of Glacier Dynamics During the Last Glacial Maximum at Tioga Pass, Yosemite National Park

Previous investigations of glacier dynamics at Tioga Pass during the Last Glacial Maximum (LGM) have produced different conclusions. A map of the LGM ice extent and flow direction (Alpha et al., 1987) illustrates a south-to-north direction of ice flow across the pass with little evidence to support this inference. Since the production of this map, unexpected glacial erratics of Cathedral Peak Granodiorite (CPG) have been noted in the vicinity of Tioga Pass, which are not consistent with the inferred flow direction. A comprehensive spatial data set of CPG erratics was collected. This data was collected between Tioga Lake and the southeastern boundary of the CPG bedrock, south of Tioga Pass. The erratics display trends of decreasing abundance from north to south, characteristic of boulder trains used to infer glacier flow patterns. Based on these trends, the erratics indicate a north-to-south flow across the pass, opposite to what Alpha et al. (1987) had inferred. This flow is determined to have originated from the eastern cirque of Mt. Conness, the northeastern boundary of the CPG bedrock. The Excel spreadsheet, “Profiler V. 2” (Benn and Hulton, 2009) was used to model the flows from Mt. Conness down the Lee Vining Canyon and the Grand Canyon of the Tuolumne River; these flows branched at Tioga Lake. The model provided insight into the ice dynamics in this region but was unable to provide insight into small flow reversals. Based on the distribution of CPG erratics, the “Profiler V. 2” analysis, past field research yielding evidence of other erratic boulder trains, a comprehensive set of striations and glacial landforms, and a plan-view map of ice coverage and flow direction at the peak of the LGM (Wahrhaftig et al., 2019), there is evidence to support the standing hypothesis that ice flowed south across Tioga Pass at the peak of the LGM, then became stagnant, with ice from Mt. Conness and Tioga pass eventually flowing into Lee Vining Canyon after peak LGM conditions receded

Selection and Certification of TPS: Constraints and Considerations of Venus Missions

This presentation was part of the session : Probe Missions to the Giant Planets, Titan and VenusSixth International Planetary Probe WorkshopThe science community currently has interest in planetary entry probe missions to improve our understanding of the atmosphere of Saturn [1], missions to Venus and also sample return missions from comets and asteroids. In addition, the In-Space Propulsion Program has completed aerocapture mission design studies that have defined the requirements for the Thermal protection System (TPS) to Venus, Mars, Titan and Neptune. There have been investments in new TPS materials and to revive flight qualified materials such as PICA (used on Stardust and currently baselined for MSL and Orion) and Carbon-Phenolic, the TPS material of choice for Venus and Outer Planet missions. Mission studies have shown the heating rates for the "shallow" Saturn probes are in the range of (2 - 5) KW/cm2 in its H(2)/He atmosphere. Venus entry probes will experience heat fluxes in the similar range of (3 - 7) kW/cm(2) in CO2. High-speed Earth reentry missions from comets and asteroids will experience heating of the range of (1 - 5) kW/cm(2) and at pressures equal to or higher than Stardust. Aerocapture during Venus missions will experience heat fluxes in the range of (2 - 4) kW/cm(2) in CO2. Titan aero-capture missions will experience far smaller heating fluxes in the N2/methane atmosphere. Since the flight times are longer during aerocapture missions, TPS design requirements involve much larger heatloads at relatively lower heat-fluxes compared to those for direct entry probe missions. It is clear that qualification and certification of the heritage ablative materials or the development of new, ablative Thermal Protection System (TPS) materials for entry or aerocapture probe missions is needed [2] and the challenges are in testing, especially in the appropriate atmospheric gases. NASA Ames has nearly completed the construction of a small, low cost, 5 MW arc jet facility, called the Development Arcjet Facility (DAF) that will permit testing of small models at high heat fluxes and in different gases. This paper will review the entry conditions from a collection of mission studies to various solar system destinations, the testing needs of both newer as well as heritage TPS for each destination and provide the approach, we at NASA Ames plan to adopt, in testing and analysis by making use of both existing arc jet facilities as well as an affordable, small 5 MW arc jet that can be used for TPS development in test gases appropriate for the Neptune, Titan, Saturn, Venus or Earth applications. [1] Atreya, S. K., et. al. "Formation of Giant Planets and Their Atmospheres: Entry Probes for Saturn and Beyond; 5 th International Planetary Probe Workshop, June 25-29, Bordeaux, France. [2] Venkatapathy, E. and Laub, B. "Requirements for Development of Thermal Protection Systems for Multiple Missions: 5th International Planetary Probe Workshop, June 25-29, Bordeaux, France.NASA In-Space Propulsion Progra