Publications

Submitted
J. F. Bard, Binici, C., and deSilva, A. H., “Staff Scheduling at the United States Postal Service. ,” Computers & Operations Research, vol. 30, pp. 745–771, Submitted.
In Press
H. Daigle and Dugan, B., “Data report: permeability, consolidation, stress state, and pore system characteristics of sediments from Sites C0011, C0012, and C0018 of the Nankai accretionary complex,” Proceedings of the Integrated Ocean Drilling Program, Scientific Reports, In Press.
In Press, 2018
V. Puzyrev, Calo, V., and Torres-Verdin, C., “Interpretation of deep directional resistivity measurements acquired in high-angle and horizontal wells using 3D inversion,” Geophysical Journal International, In Press, 2018.
J. D. Escobar and Torres-Verdin, C., “Permeability sensitivity functions and rapid simulation of hydraulic testing measurements using perturbation theory,” Water Resources Research, In Press, 2018.
E. Bakolas, “Finite-Horizon Separation-Based Covariance
Control for Discrete-Time Stochastic Linear Systems
,” IEEE CDC. Miami, FL., In Press, 2018.
J. Selvakumar and Bakolas, E., “Robust Time-Optimal Guidance in a Partially Uncertain Time-Varying Flow-Field,” Journal of Optimization Theory and Applications, In Press, 2018.
D. Pylorof and Bakolas, E., “Stabilization of Input Constrained Nonlinear
Systems with Imperfect State Feedback Using Sum-of-Squares
Programming
,” IEEE CDC. Miami, FL., In Press, 2018.
2018
K. Chen, Roy, A., Rai, A., Movva, H. C. P., Meng, X., He, F., Banerjee, S. K., and Wang, Y., “Accelerated carrier recombination by grain boundary/edge defects in MBE grown transition metal dichalcogenides,” APL Materials, vol. 6, pp. 056103, 2018. Publisher's VersionAbstract
Defect-carrier interaction in transition metal dichalcogenides (TMDs) plays important roles in carrier relaxation dynamics and carrier transport, which determines the per- formance of electronic devices. With femtosecond laser time-resolved spectroscopy, we investigated the effect of grain boundary/edge defects on the ultrafast dynamics of photoexcited carrier in molecular beam epitaxy (MBE)-grown MoTe2 and MoSe2. We found that, comparing with exfoliated samples, the carrier recombination rate in MBE- grown samples accelerates by about 50 times. We attribute this striking difference to the existence of abundant grain boundary/edge defects in MBE-grown samples, which can serve as effective recombination centers for the photoexcited carriers. We also observed coherent acoustic phonons in both exfoliated and MBE-grown MoTe2, indi- cating strong electron-phonon coupling in this materials. Our measured sound velocity agrees well with the previously reported result of theoretical calculation. Our findings provide a useful reference for the fundamental parameters: carrier lifetime and sound velocity and reveal the undiscovered carrier recombination effect of grain boundary/edge defects, both of which will facilitate the defect engineering in TMD materials for high speed opto-electronics.
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C. E. Tinney, Panickar, P., and Vogel, P., “Aeroacoustics of a Planar Multistream Supersonic Nozzle with Aft Deck and Sidewalls,” AIAA Journal, pp. 1-12, 2018.Abstract
The exhaust plume produced by a planar, multistream supersonic nozzle is studied with and without the effect of an aft deck and sidewalls. Measurements encompass static wall pressure of the internal flow, shadowgraphy images of the exhaust plume, and far-field acoustics for a range of pressure ratios. An experimentally validated Reynolds averaged Navier–Stokes model of the internal flow is then used to reveal how the aft deck and sidewalls allow the expanding gas to persist longer, thereby extending the location of the separation shock. Where the far-field sound is concerned, the aft deck and sidewall attachments cause a noticeable reduction in overall sound pressure levels by as much as 5 dB at shallow angles and sideline observer positions. Many of the tones associated with screech and broadband shock associated noise are also absent with the addition of the aft deck and sidewalls.
C. Lu, Jing, Z., Wu, C., Piquemal, J. - P., Ponder, J. W., Ren, P., and others,AMOEBA Polarizable Atomic Multipole Force Field for Nucleic Acids,” J Chem Theory Comp, vol. in press, 2018. Publisher's Version
X. Meng, Zhou, Y., Chen, K., Roberts, R. H., Wu, W., Lin, J. ‐F., Chen, R. T., Xu, X., and Wang, Y., “Anisotropic Saturable and Excited-State Absorption in Bulk ReS2,” Advanced Optical Materials, 2018. Publisher's VersionAbstract
The intensity‐scan (I‐scan) technique to study the polarization‐dependent, nonlinear processes in exfoliated bulk ReS2 is utilized. The polarization‐dependent reflection and transmission of ReS2, from which the absorption coefficients are extracted using the transfer matrix method, are measured. Absorption coefficients under high laser peak power show a transition from saturable absorption (SA) to reverse saturable absorption when rotating the laser polarization with respect to the b‐axis. It is found that SA and excited‐state absorption (ESA) contribute to the nonlinear optical processes. Both the SA and ESA show strong dependence on the polarization angle, which is attributed to the anisotropic optical transition probability and electronic band structure in ReS2. The anisotropic nonlinear optical properties of ReS2 may find applications as saturable absorbers in lasers and optical modulators.
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J. Dueñas, Sulzer, J., Stämpfli, P., Hepp-Reymond, M. - C., Kollias, S., Seifritz, E., and Gassert, R., “BOLD signal in sensorimotor regions reveals differential encoding of passive forefinger velocity and displacement amplitude,” NeuroImage, vol. 173, pp. 332-340, 2018.
K. Chen, Roy, A., Rai, A., Valsaraj, A., Meng, X., He, F., Xu, X., Register, L. F., Banerjee, S., and Wang, Y., “Carrier Trapping by Oxygen Impurities in Molybdenum Diselenide,” ACS Applied Materials & Interfaces, vol. 10, no. 1, pp. 1125–1131, 2018. Publisher's VersionAbstract
Understanding defect effect on carrier dynamics is essential for both fundamental physics and potential applications of transition metal dichalcogenides (TMDs). Here, the phenomenon of oxygen impurities trapping photoexcited carriers has been studied with ultrafast pump-probe spectroscopy. Oxygen impurities are intentionally created in exfoliated multilayer MoSe2 with Ar+plasma irradiation and air exposure. After plasma treatment, the signal of transient absorption first increases and then decreases, which is a signature of defect-capturing carriers. With larger density of oxygen defects, the trapping effect becomes more prominent. The trapping defect densities are estimated from the transient absorption signal, and its increasing trend in the longer-irradiated sample agrees with the results from X-ray photoelectron spectroscopy. First-principle calculations with density functional theory reveal that oxygen atoms occupying Mo vacancies create mid-gap defect states, which are responsible for carrier trapping. Our findings shed light on the important role of oxygen defects as carrier trappers in TMDs, and facilitate defect engineering in relevant materials and device applications.
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N. D. Espinoza, Jung, H., Major, J. R., Sun, Z., Ramos, M. J., Eichhubl, P., Balhoff, M. T., Choens, C. R., and Dewers, T. A., “CO2 charged brines changed rock strength and stiffness at Crystal Geyser, Utah: Implications for leaking subsurface CO2 storage reservoirs,” International Journal of Greenhouse Gas Control, vol. 73, pp. 16–28, 2018. Publisher's Version
M. Aman, Espinoza, N. D., Ilgen, A. G., Major, J. R., Eichhubl, P., and Dewers, T. A., “CO2-induced chemo-mechanical alteration in reservoir rocks assessed via batch reaction experiments and scratch testing,” Greenhouse Gases: Science and Technology, vol. 8, pp. 133–149, 2018. Publisher's Version
K. Chen, Meng, X., He, F., Zhou, Y., Jeong, J., Sheehan, N., Bank, S. R., and Wang, Y., “Comparison between grating imaging and transient grating techniques on measuring carrier diffusion in semiconductor,” arXiv:1805.01561, 2018. Publisher's VersionAbstract
Optical grating technique, where optical gratings are generated via light inference, has been widely used to measure charge carrier and phonon transport in semiconductors. In this paper, compared are three types of transient optical grating techniques: transient grating diffraction, transient grating heterodyne, and grating imaging, by utilizing them to measure carrier diffusion coefficient in a GaAs/AlAs superlattice. Theoretical models are constructed for each technique to extract the carrier diffusion coefficient, and the results from all three techniques are consistent. Our main findings are: (1) the transient transmission change obtained from transient grating heterodyne and grating imaging techniques are identical, even these two techniques originate from different detection principles; and (2) By adopting detection of transmission change (heterodyne amplification) instead of pure diffraction, the grating imaging technique (transient grating heterodyne) has overwhelming advantage in signal intensity than the transient grating diffraction, with a signal intensity ratio of 315:1 (157:1).
J. Kim, Fleming, E., Zhou, Y., and Shi, L., “Comparison of four-probe thermal and thermoelectric transport measurements of thin films and nanostructures with microfabricated electro-thermal transducers,” Journal of Physics D: Applied Physics, vol. 51, pp. 103002, 2018. Publisher's Version
N. K. Roy, Dibua, O. G., Jou, W., He, F., Jeong, J., Wang, Y., and Cullinan, M., “A comprehensive study of the sintering of copper nanoparticles using femtosecond, nanosecond and continuous wave lasers,” Journal of Micro and Nano-Manufacturing, vol. 6, no. 1, pp. 010903, 2018. Publisher's VersionAbstract
A high electrical and thermal conductivity coupled with low costs make copper (Cu) an enticing alternative to aluminum for fabrication of interconnects in packaging applications. To tap into the benefits of the ever-reducing size of transistors, it is required to increase the input/output (I/O) pin count on electronic chips and thus minimize the size of chip to board interconnects. Laser sintering of Cu nanoparticle (NP) inks can serve as a promising process for developing these micron sized, 3D interconnect structures. However, the exact processing windows for Cu NP sintering are not well known. Therefore, this paper presents an extensive experimental investigation of the sintering processing window with different lasers including femtosecond (fs), nanosecond (ns) and continuous-wave (CW) lasers. The dependence of the processing window on Cu layer thicknesses and laser exposure durations has also been investigated. A simplified model to estimate optimum laser sintering windows for Cu NPs using pulsed lasers is presented and the predicted estimates are compared against the experimental results. Given the simplicity of the model, it is shown to provide good estimates for fluence required for the onset of sintering and the processing window for good sintering of Cu NPs.
S. Y. Shin, Deshpande, A., and Sulzer, J., “Design of an Underactuated, Adaptable Electromechanical Gait Trainer for People with Neurological Injury,” Journal of Mechanisms and Robotics, 2018.

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