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Direct-to-indirect mapping for optimal low-thrust trajectories

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Astrodynamics 2024年第1期8卷 27-46页

作者： David Ottesen Ryan P.Russell Department of Aerospace Engineering and Engineering Mechanics The University of Texas at AustinAustinTexas78712USA

Optimal,many-revolution spacecraft trajectories are challenging to solve.A connection is made for a class of models between optimal direct and indirect *** transfers that minimize thrust-acceleration-squared,primer vector theory maps direct,many-impulsive-maneuver trajectories to the indirect,continuous-thrust-acceleration *** mapping algorithm is independent of how the direct solution is obtained and requires only a solver for a boundary value problem and its partial derivatives.A Lambert solver is used for the two-body problem in this *** mapping is simple because the impulsive maneuvers and co-states share the same linear space around an optimal *** numerical results,the direct coast-impulse solutions are demonstrated to converge to the indirect continuous solutions as the number of impulses and segments *** two-body design space is explored with a set of three many-revolution,many-segment examples changing semimajor axis,eccentricity,and *** first two examples involve a small change to either semimajor axis or eccentricity,and the third example is a transfer to geosynchronous *** a single processor,the optimization runtime is seconds to minutes for revolution counts of 10 to 100,and on the order of one hour for examples with up to 500 *** of these thrust-acceleration-squared solutions are good candidates to start a homotopy to a higher-fidelity minimization problem with practical constraints.

关键词： direct optimization indirect optimization impulsive maneuvers Lambert's problem two-body dynamics primer vectortheory

Opto-thermoelectric pulling of light-absorbing particles

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Light(Science & Applications) 2020年第1期9卷 1686-1696页

作者： Linhan Lin Pavana Siddhartha Kollipara Abhay Kotnala Taizhi Jiang Yaoran Liu Xiaolei Peng Brian A.Korgel Yuebing Zheng Walker Department of Mechanical Engineering The University of Texas at AustinAustinTX 78712USA Materials Science&Engineering Program and texas Materials Institute The University of Texas at AustinAustinTX 78712USA State Key Laboratory of Precision Measurement Technology and Instruments Department of Precision InstrumentTsinghua UniversityBeijing 100084People’s Republic of China McKetta Department of Chemical Engineering The University of Texas at AustinAustinTX 78712USA Department of Electrical and Computer Engineering The University of Texas at AustinAustinTX 78712USA

Optomechanics arises from the photon momentum and its exchange with low-dimensional *** is well known that optical radiation exerts pressure on objects,pushing them along the light ***,optical pulling of an object against the light path is still a counter-intuitive ***,we present a general concept of optical pulling-opto-thermoelectric pulling(OTEP)—where the optical heating of a light-absorbing particle using a simple plane wave can pull the particle itself against the light *** irradiation orientation-directed pulling force imparts self-restoring behaviour to the particles,and three-dimensional(3D)trapping of single particles is achieved at an extremely low optical intensity of 10^(−2)mWμm^(−2).Moreover,the OTEP force can overcome the short trapping range of conventional optical tweezers and optically drive the particle flow up to a macroscopic *** concept of selfinduced opto-thermomechanical coupling is paving the way towards freeform optofluidic technology and lab-on-achip devices.

关键词： absorbing light trapping

Optical Patterning of Two-Dimensional Materials

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Research 2020年第1期2020卷 1064-1078页

作者： Pavana Siddhartha Kollipara Jingang Li Yuebing Zheng Walker Department of Mechanical Engineering The University of Texas at AustinAustinTX 78712USA Materials Science&Engineering Program and texas Materials Institute The University of Texas at AustinAustinTX 78712USA

Recent advances in the field of two-dimensional(2D)materials have led to new electronic and photonic devices enabled by their unique properties at atomic *** 2D materials into desired patterns on substrates is often an essential and foremost step for the optimum performance of the functional *** this regard,optical patterning of 2D materials has received enormous interest due to its advantages of high-throughput,site-specific,and on-demand *** years have witnessed scientific reports of a variety of optical techniques applicable to patterning 2D *** this minireview,we present the state-of-the-art optical patterning of 2D materials,including laser thinning,doping,phase transition,oxidation,and *** applications based on optically patterned 2D materials will be discussed as *** further developments,optical patterning is expected to hold the key in pushing the frontiers of manufacturing and applications of 2D materials.

关键词： frontier doping optimum

Design rules for strong electro-optic materials

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npj Computational Materials 2020年第1期6卷 579-587页

作者： Ali K.Hamze Marc Reynaud Jacqueline Geler-Kremer Alexander A.Demkov Department of Physics The University of Texas at AustinAustinTX 78712USA

The explosive rise of silicon photonics has led to renewed interest in the electro-optic(EO)or Pockels effect due to its potential uses in many next generation device *** find materials with a strong EO response in thin film form,which are essential for low power and small footprint devices,one needs to find a general design rule for strong Pockels materials.

关键词： materials film optic

Designing electrolyte additives for lithium metal batteries through multi-factor principle

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Journal of Energy Chemistry 2021年第10期30卷 147-148,I0004页

作者： Biyi Xu Yutao Li Materials Science and Engineering Program and texas Materials Institute The University of Texas at AustinAustinTexas 78712USA

The rapid development of consumer electronic and electric vehicle markets causes the increasing demand for advanced rechargeable ***(Li)metal batteries(LMBs)have attracted considerable attention in recent years due to their high energy density[1],since the metallic Li anode exhibits the ultra-high theoretical capacity and the lowest electrode potential among various alkali metals[2].

关键词： electrolyte lithium alkali

Porous Medium Flow with Both a Fractional Potential Pressure and Fractional Time Derivative

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Chinese Annals of Mathematics,Series B 2017年第1期38卷 45-82页

作者： Mark ALLEN Luis CAFFARELLI Alexis VASSEUR Department of Mathematics The University of Texas at AustinAustinTX 78712USA

The authors study a porous medium equation with a right-hand side. The operator has nonlocal diffusion effects given by an inverse fractional Laplacian *** derivative in time is also fractional and is of Caputo-type, which takes into account"memory". The precise model isD_t~αu- div(u(-Δ)^(-σ)u) = f, 0 < σ <1/*** paper poses the problem over {t ∈ R^+, x ∈ R^n} with nonnegative initial data u(0, x) ≥0 as well as the right-hand side f ≥ 0. The existence for weak solutions when f, u(0, x)have exponential decay at infinity is proved. The main result is H¨older continuity for such weak solutions.

关键词： Caputo derivative Marchaud derivative Porous medium equation Hlder continuity Nonlocal diffusion

Influence of field emission on microwave microdischarges

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High Voltage 2016年第1期1卷 57-59页

作者： Dmitry Levko Laxminarayan L.Raja Department of Aerospace Engineering and Engineering Mechanics The University of Texas at AustinAustinTexas 78712USA

An instability in the stable operation of microdischarges sustained at microwave frequencies,is investigated by a self-consistent one-dimensional particle-in-cell Monte Carlo collisions *** instability is caused by the field electron emission from electrodes and is triggered by the high electric fields at the sheaths in a dense *** an operating frequency of 9 GHz,and electrode gap of 60μm,the field emission(FE)is not active at the breakdown ***,once a stable dense plasma is produced post-breakdown,a strong sheath results in an electrode electric fields that exceed the threshold for FE causing a runaway in the electron generation in the plasma.

关键词： microwave electrode field

SHOCK AND BOUNDARY STRUCTURE FORMATION BY SPECTRAL-LAGRANGIAN METHODS FOR THE INHOMOGENEOUS BOLTZMANN TRANSPORT EQUATION

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Journal of Computational Mathematics 2010年第4期28卷 430-460页

作者： Irene M.Gamba Sri Harsha Tharkabhushanam Department of Mathematics & Institute of Computational Engineering and Sciences University of Texas Austin Institute of Computational Engineering and Sciences University of Texas Austin

The numerical approximation of the Spectral-Lagrangian scheme developed by the authors in [30] for a wide range of homogeneous non-linear Boltzmann type equations is extended to the space inhomogeneous case and several shock problems are benchmark. Recognizing that the Boltzmann equation is an important tool in the analysis of formation of shock and boundary layer structures, we present the computational algorithm in Section 3.3 and perform a numerical study case in shock tube geometries well modeled in for ID in x times 3D in v in Section 4. The classic Riemann problem is numerically analyzed for Knudsen numbers close to continuum. The shock tube problem of Aoki et al [2], where the wall temperature is suddenly increased or decreased, is also studied. We consider the problem of heat transfer between two parallel plates with diffusive boundary conditions for a range of Knudsen numbers from close to continuum to a highly rarefied state. Finally, the classical infinite shock tube problem that generates a non-moving shock wave is studied. The point worth noting in this example is that the flow in the final case turns from a supersonic flow to a subsonic flow across the shock.

关键词： Spectral Numerical Methods Lagrangian optimization FFT Boltzmann Trans- port Equation Conservative and non-conservative rarefied gas flows.

Nanosecond modulation of thermal emission

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Light(Science & Applications) 2019年第1期8卷 574-576页

作者： Daniel Wasserman Department of Electrical and Computer Engineering University of Texas AustinAustinTX 78758USA

Femtosecond laser pulses are used to modulate the thermal emission from semiconductor materials at the nanosecond timescale.A visible-frequency laser photoexcites energetic free carriers in intrinsic Si and GaAs *** these free carriers return to equilibrium,they not only emit thermal radiation on a picosecond time scale but also modulate the semiconductor thermal emission on a nanosecond to microsecond time scale,offering a novel route towards ultrafast infrared optical pulses.

关键词： thermal laser Femto