Showing papers by "Vaughn College of Aeronautics and Technology published in 2016"

The frequency of snowline-region planets from four-years of OGLE-MOA-Wise second-generation microlensing.

Abstract: We present a statistical analysis of the first four seasons from a second-generation microlensing survey for extrasolar planets, consisting of near-continuous time coverage of 8 deg to the 2nd power of the Galactic bulge by the Optical Gravitational Lens Experiment (OGLE), Microlensing Observations in Astrophysics (MOA), and Wise microlensing surveys. During this period, 224 microlensing events were observed by all three groups. Over 12% of the events showed a deviation from single-lens microlensing, and for approx. 1/3 of those the anomaly is likely caused by a planetary companion. For each of the 224 events, we have performed numerical ray-tracing simulations to calculate the detection efficiency of possible companions as a function of companion-to-host mass ratio and separation. Accounting for the detection efficiency, we find that 55 +34 -22%of microlensed stars host a snowline planet. Moreover, we find that Neptune-mass planets are approx.10 times more common than Jupiter-mass planets. The companion-to-host mass-ratio distribution shows a deficit at q approx. 10 (exp -2), separating the distribution into two companion populations, analogous to the stellar-companion and planet populations, seen in radial-velocity surveys around solar-like stars. Our survey, however, which probes mainly lower mass stars, suggests a minimum in the distribution in the super-Jupiter mass range, and a relatively high occurrence of brown-dwarf companions.

Spitzer parallax of OGLE-2015-BLG-0966 : a cold Neptune in the Galactic disk

Abstract: We report the detection of a cold Neptune mplanet = 21 ± 2 M⊕ orbiting a 0.38 M⊙ M dwarf lying 2.5–3.3 kpc toward the Galactic center as part of a campaign combining ground-based and Spitzer observations to measure the Galactic distribution of planets. This is the first time that the complex real-time protocols described by Yee et al., which aim to maximize planet sensitivity while maintaining sample integrity, have been carried out in practice. Multiple survey and follow up teams successfully combined their efforts within the framework of these protocols to detect this planet. This is the second planet in the Spitzer Galactic distribution sample. Both are in the near to mid-disk and are clearly not in the Galactic bulge.

Adaptive Neural Control for a Class of Pure-Feedback Nonlinear Systems via Dynamic Surface Technique

Abstract: This brief addresses the adaptive control problem for a class of pure-feedback systems with nonaffine functions possibly being nondifferentiable. Without using the mean value theorem, the difficulty of the control design for pure-feedback systems is overcome by modeling the nonaffine functions appropriately. With the help of neural network approximators, an adaptive neural controller is developed by combining the dynamic surface control (DSC) and minimal learning parameter (MLP) techniques. The key features of our approach are that, first, the restrictive assumptions on the partial derivative of nonaffine functions are removed, second, the DSC technique is used to avoid “the explosion of complexity” in the backstepping design, and the number of adaptive parameters is reduced significantly using the MLP technique, third, smooth robust compensators are employed to circumvent the influences of approximation errors and disturbances. Furthermore, it is proved that all the signals in the closed-loop system are semiglobal uniformly ultimately bounded. Finally, the simulation results are provided to demonstrate the effectiveness of the designed method.

The First Circumbinary Planet Found by Microlensing: OGLE-2007-BLG-349L(AB)c

Abstract: © 2016. The American Astronomical Society. All rights reserved.We present the analysis of the first circumbinary planet microlensing event, OGLE-2007-BLG-349. This event has a strong planetary signal that is best fit with a mass ratio of q ≈ 3.4 × 10-4, but there is an additional signal due to an additional lens mass, either another planet or another star. We find acceptable light-curve fits with two classes of models: two-planet models (with a single host star) and circumbinary planet models. The light curve also reveals a significant microlensing parallax effect, which constrains the mass of the lens system to be M L ≈ 0.7 M⊙. Hubble Space Telescope (HST) images resolve the lens and source stars from their neighbors and indicate excess flux due to the star(s) in the lens system. This is consistent with the predicted flux from the circumbinary models, where the lens mass is shared between two stars, but there is not enough flux to be consistent with the two-planet, one-star models. So, only the circumbinary models are consistent with the HST data. They indicate a planet of mass m c = 80 ± 13 M⊙, orbiting a pair of M dwarfs with masses of M A = 0.41 ± 0.07 and M B = 0.30 ± 0.07, which makes this the lowest-mass circumbinary planet system known. The ratio of the separation between the planet and the center of mass to the separation of the two stars is ∼40, so unlike most of the circumbinary planets found by Kepler, the planet does not orbit near the stability limit.

Campaign 9 of the K2 Mission: Observational Parameters, Scientific Drivers, and Community Involvement for a Simultaneous Space- and Ground-based Microlensing Survey

Abstract: K2's Campaign 9 (K2C9) will conduct a ~3.7 deg^2 survey toward the Galactic bulge from 2016 April 22 through July 2 that will leverage the spatial separation between K2 and the Earth to facilitate measurement of the microlens parallax πE for ≳170 microlensing events. These will include several that are planetary in nature as well as many short-timescale microlensing events, which are potentially indicative of free-floating planets (FFPs). These satellite parallax measurements will in turn allow for the direct measurement of the masses of and distances to the lensing systems. In this article we provide an overview of the K2C9 space- and ground-based microlensing survey. Specifically, we detail the demographic questions that can be addressed by this program, including the frequency of FFPs and the Galactic distribution of exoplanets, the observational parameters of K2C9, and the array of resources dedicated to concurrent observations. Finally, we outline the avenues through which the larger community can become involved, and generally encourage participation in K2C9, which constitutes an important pathfinding mission and community exercise in anticipation of WFIRST.

The first Neptune analog or super-earth with a Neptune-like orbit : MOA-2013-BLG-605LB

Abstract: We present the discovery of the first Neptune analog exoplanet or super-Earth with a Neptune-like orbit, MOA-2013-BLG-605Lb. This planet has a mass similar to that of Neptune or a super-Earth and it orbits at 9 ∼ 14 times the expected position of the snow line, a snow, which is similar to Neptune's separation of 11 a snow from the Sun. The planet/host-star mass ratio is q = (3.6 ± 0.7) × 10-4 and the projected separation normalized by the Einstein radius is s = 2.39 ± 0.05. There are three degenerate physical solutions and two of these are due to a new type of degeneracy in the microlensing parallax parameters, which we designate "the wide degeneracy." The three models have (i) a Neptune-mass planet with a mass of Mp = 21-7 +6M⊕ orbiting a low-mass M-dwarf with a mass of Mh = 0.19-0.06 +0.05M⊙, (ii) a mini-Neptune with Mp = 7.9-1.2 +1.8M⊕ orbiting a brown dwarf host with Mh = 0.068-0.011 +0.019M⊙, and (iii) a super-Earth with Mp = 3.2-0.3 +0.5MM⊕ orbiting a low-mass brown dwarf host with Mh = 0.025-0.0004 +0.005M⊙, which is slightly favored. The 3D planet-host separations are 4.6-1.2 +4.7au, 2.1-0.2 +1.0au, and 0.94-0.02 +0.67au, which are 8.9-1.4 +10.5, 12-1 +7, or 14-1 +11 times larger than a snow for these models, respectively. Keck adaptive optics observations confirm that the lens is faint. This discovery suggests that low-mass planets with Neptune-like orbits are common. Therefore processes similar to the one that formed Neptune in our own solar system or cold super-Earths may be common in other solar systems.

Spitzer Observations of OGLE-2015-BLG-1212 Reveal a New Path toward Breaking Strong Microlens Degeneracies

Abstract: Spitzer microlensing parallax observations of OGLE-2015-BLG-1212 decisively break a degeneracy between planetary and binary solutions that is somewhat ambiguous when only ground-based data are considered. Only eight viable models survive out of an initial set of 32 local minima in the parameter space. These models clearly indicate that the lens is a stellar binary system possibly located within the bulge of our Galaxy, ruling out the planetary alternative. We argue that several types of discrete degeneracies can be broken via such space-based parallax observations.

MOA-2011-BLG-028Lb: A NEPTUNE-MASS MICROLENSING PLANET IN THE GALACTIC BULGE*

Abstract: We present the discovery of a Neptune-mass planet orbiting a $0.8\pm 0.3M_{\odot}$ star in the Galactic bulge. The planet manifested itself during the microlensing event MOA-2011-BLG-028/OGLE-2011-BLG-0203 as a low-mass companion to the lens star. The analysis of the light curve provides the measurement of the mass ratio $(1.2 \pm 0.2) \times 10^{-4}$, which indicates that the mass of the planet is 12–60 Earth masses. The lensing system is located at 7.3 ± 0.7 kpc away from the Earth near the direction of Baade's Window. The projected separation of the planet at the time of the microlensing event was 3.1–5.2 au. Although the microlens parallax effect is not detected in the light curve of this event, preventing the actual mass measurement, the uncertainties of mass and distance estimation are narrowed by the measurement of the source star proper motion on the OGLE-III images spanning eight years, and by the low amount of blended light seen, proving that the host star cannot be too bright and massive. We also discuss the inclusion of undetected parallax and orbital motion effects into the models and their influence onto the final physical parameters estimates.

Ogle-2012-blg-0724lb: A Saturn Mass Planet Around an M-dwarf

Abstract: We report the discovery of a planet by the microlensing method, OGLE-2012-BLG-0724Lb. Although the duration of the planetary signal for this event was one of the shortest seen for a planetary event, the anomaly was well covered thanks to high-cadence observations taken by the survey groups OGLE and MOA. By analyzing the light curve, this planetary system is found to have a mass ratio q = (1.58 +/- 0.15) x 10(exp -3). By conducting a Bayesian analysis, we estimate that the host star is an M dwarf with a mass of M(sub L) = 0.29(+0.33/-0.16) solar mass located at D(sub L) = 6.7(+1.1/-1.2) kpc away from the Earth and the companion's mass is m(sub P) = 0.47(+0.54/-0.26) M(Jup). The projected planet- host separation is a falsum = 1.6(+0.4/-0.3) AU. Because the lens-source relative proper motion is relatively high, future highresolution images would detect the lens host star and determine the lens properties uniquely. This system is likely a Saturn-mass exoplanet around an M dwarf, and such systems are commonly detected by gravitational microlensing. This adds another example of a possible pileup of sub-Jupiters (0.2 less than m(sub P)/M(sub Jup) less than 1) in contrast to a lack of Jupiters (approximately 1-2 M(sub Jup)) around M dwarfs, supporting the prediction by core accretion models that Jupiter-mass or more massive planets are unlikely to form around M dwarfs.

Research on unmanned combat aerial vehicle robust maneuvering decision under incomplete target information

Abstract: This article investigates the problem of designing a novel maneuvering decision-making method for the unmanned combat aerial vehicle. The design objective is to promote the real-time ability of dec...

Review of board-level solder joint reliability under environmental stress

Abstract: The reliability of board-level solder joint that provides the mechanical and electrical connections between the chip and print circuit board is such an import issue that they can result in the failure of the whole equipment under real service condition. The multiple stresses in service environment such as temperature and vibration loadings can cause the fatigue failure of solder joints easily. In this paper, a review was presented on the research situation and prospect of the reliability of solder joints with an emphasis on accelerated tests, numerical simulation and life prediction models. The failure behaviors of solder joints under coupling loadings of temperature and vibration were also introduced which represent the research trend in the future.

$L_{1}$ -Norm Low-Rank Matrix Decomposition by Neural Networks and Mollifiers

Abstract: The $L_{1}$ -norm cost function of the low-rank approximation of the matrix with missing entries is not smooth, and also cannot be transformed into a standard linear or quadratic programming problem, and thus, the optimization of this cost function is still not well solved. To tackle this problem, first, a mollifier is used to smooth the cost function. High closeness of the smoothed function to the original one can be obtained by tuning the parameters contained in the mollifier. Next, a recurrent neural network is proposed to optimize the mollified function, which will converge to a local minimum. In addition, to boost the speed of the system, the mollifying process is implemented by a filtering procedure. The influence of two mollifier parameters is theoretically analyzed and experimentally confirmed, showing that one of the parameters is critical to computational efficiency and accuracy, while the other not. A large number of experiments on synthetic data show that the proposed method is competitive to the state-of-the-art methods. In particular, the experiments on large matrices and a real application in the structure from motion indicate that the memory requirement of the proposed algorithm is mild, making it suitable for real applications that often involve large-scale matrix decomposition.

A fault diagnosis approach for airborne fuel pump based on EMD and probabilistic neural networks

Abstract: Airborne fuel pump is an important part of aircraft fuel system, for the lack of fault samples, low diagnostic efficiency and high maintenance cost, in order to achieve more accurate and reliable fault diagnosis of airborne fuel pump, an experimental platform of fuel transfusion system is developed and a fault diagnosis method based on empirical mode decomposition (EMD) and probabilistic neural networks (PNN) is proposed. Firstly, the vibration signals and pressure signals of normal state and six types of representative fuel pump faults are collected on the experimental platform. Then the EMD method is applied to decompose the original vibration signals into a finite Intrinsic Mode Functions (IMFs) and a residual. Secondly, the energy of first four IMFs is extracted as a vibration signals failure feature, combined with the mean outlet pressure to structure the fault feature vector and then divided into training samples and testing samples. Training samples are used to train the PNN fault diagnosis model and testing samples are used to verify the model. Experimental results show that compared with SVM and GA-BP, the PNN fault diagnosis model has fast convergence, high efficiency and a higher performance and recognition for the typical faults of airborne fuel pump.

Research on the water-entry attitude of a submersible aircraft

Abstract: The water entry of a submersible aircraft, which is transient, highly coupled, and nonlinear, is complicated. After analyzing the mechanics of this process, the change rate of every variable is considered. A dynamic model is build and employed to study vehicle attitude and overturn phenomenon during water entry. Experiments are carried out and a method to organize experiment data is proposed. The accuracy of the method is confirmed by comparing the results of simulation of dynamic model and experiment under the same condition. Based on the analysis of the experiment and simulation, the initial attack angle and angular velocity largely influence the water entry of vehicle. Simulations of water entry with different initial and angular velocities are completed, followed by an analysis, and the motion law of vehicle is obtained. To solve the problem of vehicle stability and control during water entry, an approach is proposed by which the vehicle sails with a zero attack angle after entering water by controlling the initial angular velocity. With the dynamic model and optimization research algorithm, calculation is performed, and the optimal initial angular velocity of water-entry is obtained. The outcome of simulations confirms that the effectiveness of the propose approach by which the initial water-entry angular velocity is controlled.

Minimum Thrust of a Morphing Unmanned Submersible Aerial Vehicle in the Water-to-Air Motion

Abstract: This study proposes a new water-to-air motion pattern that combines morphing with power switch. Under the conditions of this pattern, the vehicle needs a certain thrust to avoid falling back after jumping out of the water. The minimum thrust is among the most important design parameters of a vehicle. The water-exit and take-off dynamic models of the vehicle are constructed through the force and motion analysis before and after morphing. The control model of the vehicle is created by analysing the control problem in the take-off motion. The minimum thrust at different initial water-exit angles is computed using the optimum searching algorithm. The following law is then established: the greater the initial water-exit angle, the smaller the minimum thrust required in the air. Such a relationship becomes insignificant when the initial water-exit angle exceeds 40°.

The grid-based identity signcryption algorithm and application in Ad Hoc network

Abstract: Identity-based signcryption which guarantees the confidentiality and authentication of message is suitable for the key management of Ad Hoc network due to its low computation cost. Aiming at the deficiencies of the existing identity-based signcryption algorithms, this paper proposes an efficient grid-based identity signcryption algorithm which adopts a low overhand, high expandability and high connectivity grid as the logical structure. By using this signcryption algorithm in the key management scheme of Ad Hoc network, the communication and computation cost of key management is reduced and the safety and efficiency of the key management scheme is enhanced. The analyses show that the Ad Hoc network has a good ability of resistance to the attack when the new signcryption algorithm is used in key management.

On close-range air combat based on hidden Markov model

Abstract: Theory of air combat (AC) develops from geometry to energy, the AC process is analyzed more in terms of the fighter performance; nevertheless, a small amount of literature considers how fighter pilot's decision-making process affects AC. According to the variable characteristics of objective data recorded in AC training, analysis method of close-range air combat (CRAC) based on hidden Markov model (HMM) is proposed, Viterbi algorithm is used to predict the changing process of pilot's state sequence in AC, then the decision-making point is acquired. Through simulation, the feasibility of AC based on HMM is verified, it also shows whether the pilot can make decisions effectively and fast will affects the AC result eventually.

Differential Evolution with strategy of improved population diversity

Abstract: Differential Evolution (DE) algorithm is well known as a simple and efficient scheme for global optimization over continuous spaces. In order to ameliorate the population diversity, an improved differential evolution (IDE) algorithm is proposed in this paper. The idea is to vary the assembling positions of the premature individuals by mutation operation. It is proved in theory that the direction pointed to the center individual is the reasonable one to improve the diversity. Then the adaptive disturbance scheme after population premature is designed. The example based on the standard function shows that the IDE with good diversity has much better searching capacity and calculating precision in the whole evolution than that of DE.

Research on Modelling of Aviation Piston Engine for the Hardware-in-the-loop Simulation

Abstract: In order to build the aero piston engine model which is real-time and accurate enough to operating conditions of the real engine for hardware in the loop simulation, the mean value model is studied. Firstly, the air-inlet model, the fuel model and the power-output model are established separately. Then, these sub models are combined and verified in MATLAB/SIMULINK. The results show that the model could reflect the steady-state and dynamic performance of aero engine, the errors between the simulation results and the bench test data are within the acceptable range. The model could be applied to verify the logic performance and control strategy of controller in the hardware-in-the-loop (HIL) simulation.

Process development of a new TGV interposer for wafer level package of inertial MEMS device

Abstract: In this paper, a TGV interposer based wafer level packaging for inertial MEMS devices is presented. For the TGV interposer, there is a redistribution layer of Al wiring on each side, which are electrically connected with Al metalized TGV. Being as a capping wafer, it's bonded to a MEMS accelerometer wafer based on bulk silicon process with a patterned benzocyclobutene(BCB) layer to achieve wafer level package. To verify the process, TGV interposer is fabricated and experiment results prove that Al TGV interconnection is electrically conductive. TGV interposer capped MEMS accelerometer is demonstrated and the tested shear bonding strength is about 69.84N with two concentric rectangular rings made of BCB adhesives, where the inner ring is about 6300µm × 5000µm with a width of 200µm and the outer ring is about 680µm × 5500µm with a width of 150µm.

A Stable Routing Protocol for Mobile Ad Hoc Networks

Abstract: Hierarchical routing is one of the fundamental but challenging topics in mobile ad hoc network, which combine proactive/table-driven with reactive/on-demand routing protocols and take advantages of both. And as an imperative means of hierarchical routing protocol, clustering approach provides an efficient and stable hierarchical structure for mobile ad hoc networks. In this paper, we designed a stable clustering algorithm and a corresponding hierarchical routing protocol for high dynamic mobile ad hoc networks. Each cluster is consisted of a cluster-head, several cluster-gateway nodes, several cluster-guest nodes and other cluster-members. The proposed routing protocol uses proactive protocol in inter-cluster and reactive protocol in intra-cluster communication. Simulation results showed that the clustering algorithm improves its stability by increasing the node number of individual clusters and decreasing node's switch times between clusters. And the proposed routing protocol not only decreases the end-to-end delay to guarantee the validity of data but reduces the communication control expenses to increase the utility of network resource and increases the packet acceptance ratio to verify the validity of the proposed protocol.

Distributed adaptive formation tracking for a class of networked nonlinear systems

Abstract: This paper considers the formation problem of tracking a reference for a class of uncertain nonlinear systems in strict-feedback form under a directed graph. A portion of subsystems have no access to the information of reference. Distributed adaptive controllers are proposed by employing backstepping technique. It is proved that, with the proposed scheme, all the closed-loop signals are bounded and the formation tracking error can converge to zero. Simulation results are given to illustrate the effectiveness of the proposed scheme.