Recent Submissions

  • Exploitation of Field Drilling Data with an Innovative Drilling Simulator: Highly Effective Simulation of Rotating and Sliding Mode

    Koulidis, Alexis; Kelessidis, Vassilios; Ahmed, Shehab (SPE, 2021-05-25) [Conference Paper]
    Drilling challenging wells requires a combination of drilling analytics and comprehensive simulation to prevent poor drilling performance and avoid drilling issues for the upcoming drilling campaign. This work focuses on the capabilities of a drilling simulator that can simulate the directional drilling process with the use of actual field data for the training of students and professionals. This paper presents the results of simulating both rotating and sliding modes and successfully matching the rate of penetration and the trajectory of an S-type well. Monitored drilling data from the well were used to simulate the drilling process. These included weight on bit, revolutions per minute, flow rate, bit type, inclination and drilling fluid properties. The well was an S-type well with maximum inclination of 16 degrees. There were continuous variations from rotating to sliding mode, and the challenge was approached by classifying drilling data into intervals of 20 feet to obtain an appropriate resolution and efficient simulation. The simulator requires formation strength, pore and fracture pressures, and details of well lithology, thus simulating the actual drilling environment. The uniaxial compressive strength of the rock layer is calculated from p–wave velocity data from an offset field. Rock drillability is finally estimated as a function of the rock properties of the drilled layer, bit type and the values of the drilling parameters. It is then converted to rate of penetration and matched to actual data. Changes in the drilling parameters were followed as per the field data. The simulator reproduces the drilling process in real-time and allows the driller to make instantaneous changes to all drilling parameters. The simulator provides the rate of penetration, torque, standpipe pressure, and trajectory as output. This enables the user to have on-the-fly interference with the drilling process and allows him/her to modify any of the important drilling parameters. Thus, the user can determine the effect of such changes on the effectiveness of drilling, which can lead to effective drilling optimization. Certain intervals were investigated independently to give a more detailed analysis of the simulation outcome. Additional drilling data such as hook load and standpipe pressure were analyzed to determine and evaluate the drilling performance of a particular interval and to consider them in the optimization process. The resulting rate of penetration and well trajectory simulation results show an excellent match with field data. The simulation illustrates the continuous change between rotating and sliding mode as well as the accurate synchronous matching of the rate of penetration and trajectory. The results prove that the simulator is an excellent tool for students and professionals to simulate the drilling process prior to actual drilling of the next inclined well.
  • An Adaptive Regularization Approach to Portfolio Optimization

    Ballal, Tarig; Abdelrahman, Abdelrahman S.; Muqaibel, Ali H.; Al-Naffouri, Tareq Y. (IEEE, 2021-05-13) [Conference Paper]
    We address the portfolio optimization problem using the global minimum variance portfolio (GMVP). The GMVP gives the weights as a function of the inverse of the covariance matrix (CM) of the stock net returns in a closed-form. The matrix inversion operation usually intensifies the impact of noise when the matrix is ill-conditioned, which often happens when the sample covariance matrix (SCM) is used. A regularized sample covariance matrix (RSCM) is usually used to alleviate the problem. In this work, we address the regularization issue from a different perspective. We manipulate the expression of the GMVP weights to convert it to an inner product of two vectors; then, we focus on obtaining accurate estimations of these vectors. We show that this approach results in a formula similar to those of the RSCM based methods, yet with a different interpretation of the regularization parameter’s role. In the proposed approach, the regularization parameter is adjusted adaptively based on the current stock returns, which results in improved performance and enhanced robustness to noise. Our results demonstrate that, with proper regularization parameter tuning, the proposed adaptively regularized GMVP outperforms state-of-the-art RSCM methods in different test scenarios.
  • Verification and runtime assurance for dynamical systems with uncertainty

    Abate, Matthew; Mote, Mark; Feron, Eric; Coogan, Samuel (ACM, 2021-05-04) [Conference Paper]
    In this work, we show how controlled robustly forward invariant sets for systems with disturbances are efficiently identified via the application of the mixed monotonicity property. A mixed monotone system can be embedded in a related deterministic embedding system with twice as many states but for which the dynamics are monotone; one can then apply the powerful theory of monotone dynamical systems to the embedding system to conclude useful properties of the initial mixed monotone system. Using this technique, we present a method for verifying state-feedback controllers against safety (set invariance) constraints, and our approach involves evaluating a control barrier function type condition that requires the vector field of the embedding system to point into a certain southeast cone. This approach also facilitates the construction of runtime assurance mechanisms for controlled systems with disturbances, and we study system safety in the presence of state uncertainty as well. The results and findings of this work are demonstrated through two numerical examples where we study (i) the verification of a controlled spacecraft system against a safety constraint, and (ii) the formation of a runtime assurance mechanism that functions in the presence of uncertain state measurements.
  • Deep Multi-type Objects Multi-view Multi-instance Multi-label Learning

    Yang, Yuanlin; Yu, Guoxian; Domeniconi, Carlotta; Zhang, Xiangliang (Society for Industrial and Applied Mathematics, 2021-04-26) [Conference Paper]
    Multi-view multi-instance multi-label learning (M3L) can model complex objects (bags) that are composed of multiple instances, represented with heterogeneous feature views and annotated with multiple related semantic labels. Although significant progress has been made toward M3L tasks, the current solutions still focus on a single-type of complex objects, and cannot effectively mine the widely-witnessed interconnected objects of multi-types. To bridge this gap, we propose a Deep Multi-type objects Multi-view Multi-instance Multi-label Learning solution (DeepM4L) based on heterogeneous network embedding. DeepM4L first encodes the inter- and intra-relations among multi-type objects using a heterogeneous network, and performs instance neighbor embedding to learn the representation vectors of instances. Next, it obtains the instance-label score tensor for each view and uses a max pooling operation to induce the bag-label score tensor for each bag. After that, it combines bag-label scores by multi-view learning to guarantee the semantic consistency between bags of different views. Our empirical study on benchmark datasets shows that DeepM4L is significantly superior to the recent advanced baselines.
  • Towards Mitigating Device Heterogeneity in Federated Learning via Adaptive Model Quantization

    Abdelmoniem, Ahmed M.; Canini, Marco (ACM, 2021-04-26) [Conference Paper]
    Federated learning (FL) is increasingly becoming the norm for training models over distributed and private datasets. Major service providers rely on FL to improve services such as text auto-completion, virtual keyboards, and item recommendations. Nonetheless, training models with FL in practice requires significant amount of time (days or even weeks) because FL tasks execute in highly heterogeneous environments where devices only have widespread yet limited computing capabilities and network connectivity conditions. In this paper, we focus on mitigating the extent of device heterogeneity, which is a main contributing factor to training time in FL. We propose AQFL, a simple and practical approach leveraging adaptive model quantization to homogenize the computing resources of the clients. We evaluate AQFL on five common FL benchmarks. The results show that, in heterogeneous settings, AQFL obtains nearly the same quality and fairness of the model trained in homogeneous settings.
  • A Comprehensive Experimental Study to Measure Laminar and Turbulent Burning Velocity of Haltermann Gasoline with Ternary Additives (O3, H2, and CO)

    Khan, Farha; Elbaz, Ayman M.; Katoch, Amit; Badra, Jihad; Costanzo, Vincent; Roberts, William L. (SAE International, 2021-04-06) [Conference Paper]
    In this work, the effects of ozone, hydrogen, carbon monoxide, and exhaust gas recirculation (EGR) addition to Haltermann gasoline combustion were investigated. For these additives, laminar and turbulent flame speeds were experimentally determined using spherically propagating premixed flames in a constant volume combustion vessel. Two initial mixture pressures of Po = 1 and 5 bar, two initial mixture temperatures of 358 and 373 K and a range of equivalence ratios from 0.5 to 1 were investigated. The additives were added as single, binary and ternary mixtures to Haltermann gasoline over a wide range of concentrations. For the stoichiometric mixture, the addition of 10% H;b, 5% CO and 1000 ppm O;b shows remarkable enhancement (80%) in SL0compared to neat Haltermann gasoline. In addition, for this same blend, increasing the mixture initial temperature and pressure results in a significant increase in SL0compared to the neat gasoline. Thus it can be inferred that ternary additives suppress the reduction effect of pressure on SL0 encountered at elevated pressure with neat Haltermann gasoline. With 40% (by mass) addition of synthetic EGR (20% CO;b - 80% N;b to neat Haltermann gasoline, successful propagation of a flame was not attained; however, ternary additives blend improves the kinetics of the combustible mixture and enhances the flame propagation. The presence of a ternary additive limits the reduction of SL0 to 33% compared to base fuel (43% reduction), with a 20% EGR addition. The turbulent burning velocity at two turbulence intensities of 0.4 and 1.2 m/s showed that increasing turbulence intensity enhanced the turbulent burning velocity due to increased flame front wrinkling.
  • Pre-ignition Detection Followed by Immediate Damage Mitigation in a Spark-Ignited Engine

    Singh, Eshan; Dibble, Robert W. (SAE International, 2021-04-06) [Conference Paper]
    Pre-ignition remains a significant bottleneck to further downsizing and downspeeding technologies employed for reducing CO2 emissions in modern turbocharged spark-ignited engines. Pre-ignition, which occurs rarely, may lead to high peak pressures that auto-ignite the entire charge before TDC. The resulting high-pressure oscillations are known as super-knock, leading to sudden and permanent hardware damage to the engine. Over the years, numerous researchers have investigated the stochastic phenomenon's source and concluded that there is a role of lubricant additives, deposits, gasoline properties, and hot surfaces in triggering pre-ignition. No single source has been identified; the research continues. Here, we take a different approach; rather than continue the search for the source(s) of super-knock, we explore mitigating super-knock by detecting pre-ignition early enough to take immediate evasive action. Such evasive action is expected to suppress knock intensity, thereby saving the engine from any permanent damage. In this regard, the current work offers ways to detect pre-ignition (using ion sensors) and then mitigate engine damage by using immediate fuel enrichment. We present three related explorations. In exploration #1, we explore if the occurrence of ions products from the exhaust can warn that the next cycle has a high probability of pre-ignition. For this next cycle, the intake fuel injection can be suspended or increased to operate engine fuel-rich. We find strong ion activity on every cycle. However, there is a weak correlation between the ion signal and pre-ignition occurrence. In exploration #2, an in-cylinder ion-current sensor is used to discover pre-ignition event unfolding during the compression stroke. When such a rare event is detected, more fuel is immediately injected, making the end gas far less reactive and avoiding autoignition and knock. These explorations #1 and #2 were conducted with a DC-based ion sensor. These explorations showed exciting and promising findings. However, our DC-based ion sensors are prone to low signal-to-noise ratio SNR, leading to false positives (unacceptably high number of false positives.) In Exploration #3, the signal-to-noise ratio improvement is explored by replacing the DC-based system with a novel AC-based system. We find the bandpass filtering of the ion signal is key to improved SNR.
  • A Simulation Study to Understand the Efficiency Analysis of Multiple Injectors for the Double Compression Expansion Engine (DCEE) Concept

    Goyal, Harsh; Nyrenstedt, Gustav; Moreno Cabezas, Kevin; Panthi, Niraj; Im, Hong G.; Andersson, Arne; Johansson, Bengt (SAE International, 2021-04-06) [Conference Paper]
    Heavy-duty vehicles face increasing demands of emission regulations. Reduced carbon-dioxide (CO2) emission targets motivate decreased fuel consumption for fossil fuel engines. Increased engine efficiency contributes to lower fuel consumption and can be achieved by lower heat transfer, friction and exhaust losses. The double compression expansion engine (DCEE) concept achieves higher efficiency, as it utilizes a split-cycle approach to increase the in-cylinder pressure and recover the normally wasted exhaust energy. However, the DCEE concept suffers heat losses from the high-pressure approach. This study utilizes up to three injectors to reduce the wall-gas temperature gradient rendering lower convective heat losses. The injector configuration consists of a standard central injector and two side-injectors placed at the rim of the bowl. An increased distance from side-injector to the wall delivered lower heat losses by centralizing hot gases in the combustion chamber. Computational fluid dynamics (CFD) simulations investigated two different piston bowls, in a heavy-duty diesel engine, to obtain in-cylinder conditions for one, two and three-injector concepts. One-dimensional (1D) simulations then used the CFD data to obtain the complete efficiency analysis of the DCEE concept. The results showed that the three-injector case improved the brake thermal efficiency and reduced the heat transfer losses, compared to the two-injector and single-injector cases. In particular, the three-injector case resulted in a high indicated and brake thermal efficiency of 58.5 % and 54.2 %, respectively.
  • Effects of Multiple Injectors on Spray Characteristics and Efficiency in Internal Combustion Engines

    Ávila Jiménez, Cristian David; Nyrenstedt, Gustav; Goyal, Harsh; Andersson, Arne; Im, Hong G.; Johansson, Bengt (SAE International, 2021-04-06) [Conference Paper]
    High-pressure internal combustion engines promise high efficiency, but a proper injection strategy to minimize heat losses and pollutant emissions remain a challenge. Previous studies have concluded that two injectors, placed at the piston bowl's rim, simultaneously improve the mixing and reduce the heat losses. The two-injector configuration further improves air utilization while keeping hot zones away from the cylinder walls. This study investigates how the two-injector concept delivers even higher efficiency by providing additional control of spray -and injection angles. Three-dimensional Reynolds-averaged Navier-Stokes simulations examined several umbrella angles, spray-to-spray angles, and injection orientations by comparing the two-injector cases with a reference one-injector case. The study focused on heat transfer reduction, where the two-injector approach reduces the heat transfer losses by up to 14.3 % compared to the reference case. Finally, this study connected the two-injector approach to a waste-heat recovery system through GT-Power 1-D simulations, increasing the importance of heat transfer reduction. The final two-injector system then delivered a 54.4% brake thermal efficiency compared to 53% of the one-injector reference case.
  • Analysis of Fuel Properties on Combustion Characteristics in a Narrow-Throat Pre-Chamber Engine

    Hlaing, Ponnya; Echeverri Marquez, Manuel Alejandro; Burgos, Paula; Cenker, Emre; Ben Houidi, Moez; Johansson, Bengt (SAE International, 2021-04-06) [Conference Paper]
    In this study, the authors investigated the effect of fuel properties on the combustion characteristics by employing methane, methanol, ethanol, and primary reference fuels (PRFs) as the main chamber fuel while using methane for the pre-chamber. Global excess air ratios (λ) from 1.6 to lean limit were tested, while 13% of total fuel energy supplied to the engine was delivered via the pre-chamber. The gaseous methane was injected into the pre-chamber at the gas exchange top-dead-center (TDC). Port fuel injection was tested with both open and closed inlet valves. The pre-chamber assembly was designed to fit into the diesel injector pocket of the base engine, which resulted in a narrow throat diameter of 3.3 mm. The combustion stability limit was set at 5% of the coefficient of variation of gross IMEP, and the knock intensity limit was set at 10 bar. GT-Power software was used to estimate the composition of pre-chamber species and was used in heat release analysis of the two chambers. It was found that the rich limit was controlled by engine knock. Hence a higher reactivity fuel (lower octane) had to be operated leaner. However, with the increasing reactivity, the lean limit was also extended, while the peak efficiency was also obtained with a leaner mixture. With PRF 90, the lean limit was at global-λ = 3.0, while the limit was 2.3 with methane. The alcohol fuels exhibited a different behavior from the methane and the PRFs. Ethanol has the same lean limit as PRF100, but methanol could be operated up to global-λ = 3.2. The pre-chamber combustion did not change much with the different fuels in the main chamber, so the combustion stability trends must be related to the transition from burning jets to ignition of the main chamber charge and its subsequent combustion.
  • Attention-Based Multimodal Entity Linking with High-Quality Images

    Zhang, Li; Li, Zhixu; Yang, Qiang (Springer International Publishing, 2021-04-06) [Conference Paper]
    Multimodal entity linking (MEL) is an emerging research field which uses both textual and visual information to map an ambiguous mention to an entity in a knowledge base (KB). However, images do not always help, which may also backfire if they are irrelevant to the textual content at all. Besides, the existing efforts mainly focus on learning a representation of both mentions and entities from their textual and visual contexts, without considering the negative impact brought by noisy irrelevant images, which happens frequently with social media posts. In this paper, we propose a novel MEL model, which not only removes the negative impact of noisy images, but also uses multiple attention mechanism to better capture the connection between mention representation and its corresponding entity representation. Our empirical study on a large real data collection demonstrates the effectiveness of our approach.
  • Reed Valve Evaluation and Selection for the Compressor Cylinder in Double Compression Expansion Engine (DCEE) Concept

    Moreno Cabezas, Kevin; Goyal, Harsh; Andersson, Arne; Johansson, Bengt (SAE International, 2021-04-06) [Conference Paper]
    This paper shows the potential benefits of implementing four configurations of reed valves at the inlet of the two-stroke compressor used in the double compression expansion engine (DCEE) concept or 8-stroke engines over the conventional poppet valves used in 4-stroke internal combustion engines. To model the reed and poppet valve configurations, the discharge coefficient was estimated from RANS computational fluid dynamics simulations using ANSYS Fluent 2020 R1, with a pressure difference up to 0.099 bar. The calculated discharge coefficients for each case were then fed in a zero-one dimension model using GT-Power to understand the valve performance i.e. the volumetric efficiency of the compressor cylinder and the mean indicated pressure during the compression process at 1200 rpm. The results showed that for reed valve configurations, the discharge coefficient and mass flow rate were higher, the pressure drop was lower and the response with negative pressure difference was faster compared to poppet valves. In addition, all the reed valve cases showed improvement in volumetric efficiency and a drop in mean effective pressure than poppet valves. In particular, the optimum reed valve geometry in the present study resulted in a volumetric efficiency improvement of 7.2 percentage points and a mean effective pressure reduction of 3.2 percentage points compared to conventional poppet valves.
  • Optical Diagnostics of Pre-Chamber Combustion with Flat and Bowl-In Piston Combustion Chamber

    Echeverri Marquez, Manuel Alejandro; Hlaing, Ponnya; Ben Houidi, Moez; Magnotti, Gaetano; Johansson, Bengt; Cenker, Emre (SAE International, 2021-04-06) [Conference Paper]
    Pre-chamber Combustion (PCC) extends the lean operation limit operation of spark ignition (SI) engines, thus it has been of interest for researchers as a pathway for increased efficiency and reduced emissions. Optical diagnostic techniques are essential to understand the combustion process, but the engine components such as the piston geometry, are often different from real engines to maximize the optical access. In this study, ignition and subsequent main chamber combustion are compared in an optically accessible PCC engine equipped with a “flat” and a real engine-like “bowl” piston geometry. An active fueled narrow throat pre-chamber was used as the ignition source of the charge in the main-chamber, and both chambers were fueled with methane. Three pre-chamber fuel effective mean pressure (FuelMEP) ratios (PCFR) namely 6%, 9% and 11% of the total amount of fuel were tested at two global excess air ratios (λ) at values of 1.8 and 2.0. The optical engine configuration included a metal liner and a quartz piston, and it was operated for 100 consecutive firing cycles, allowing stable emissions measurements. A high-speed intensified camera was used to record the OH* chemiluminescence of the main-chamber combustion. The camera was operated at 50 kHz, resulting in a resolution smaller than 0.2 Crank Angle Degree (CAD), at the engine speed of 1200 revolutions per minute (RPM). Both pistons exhibited similar pre-chamber pressures and an equal pressure difference between pre- and main-chamber (ΔP) at the peak pressure inside the pre-chamber. The free reacting jet behavior was also comparable between the two piston geometries. However, the flat combustion chamber resulted in a shorter free jet time because of the early reacting jet-piston interaction. The interaction also slowed down the combustion propagation and increased the combustion duration for the flat piston.
  • A Computational Investigation of Fuel Enrichment in the Pre-Chamber on the Ignition of the Main Chamber Charge

    Silva, Mickael; Sanal, Sangeeth; Hlaing, Ponnya; Cenker, Emre; Johansson, Bengt; Im, Hong G. (SAE International, 2021-04-06) [Conference Paper]
    Pre-chamber combustion (PCC) engines allow extending the lean limit of operation compared to common SI engines, thus being a candidate concept for the future clean transportation targets. To understand the fundamental mechanisms of the main chamber charge ignition in PCC engines, the effects of the composition in the pre-chamber were investigated numerically. A well-stirred reactor combustion model coupled with a methane oxidation mechanism reduced from GRI 3.0 was used. An open-cycle simulation was run with initialization at exhaust valve opening (EVO). For posterior simulations, the initial flow field was attained by mapping the field variables obtained from the full cycle simulation. The entire simulation domain (pre-chamber and main chamber) global excess air ratio (λ) was set to 1.3. As parametric variants, additional amounts of fuel were further injected into the pre-chamber to achieve a global pre-chamber λ of 0.7 and 1.0 at spark timing, thus having the pre-chamber and the main chamber with different compositions (emulating an active type pre-chamber). For the same operating conditions, the pre-chamber charge residence time after the spark ignition is mostly governed by the geometry. Therefore, by varying the air/fuel ratio (AFR) in the pre-chamber, it is possible to produce jets with various compositions and ultimately determine the impact of the pre-chamber enrichment on the main chamber response. The results show that the pre-chamber is sensitive to fuel enrichment and the results serve as a baseline guideline for subsequent studies.
  • On the Characterization of Beam Misalignment in Outdoor-to-Indoor 60 GHz mmWave Channel

    Biswal, Monsij; Chandra, Aniruddha; Rahman, Aniq Ur; Prokes, Ales; Mikulasek, Tomas; Blumenstein, Jiri; Kelner, Jan M.; Ziolkowski, Cezary (IEEE, 2021-03-22) [Conference Paper]
    In this paper, the measurement data of an outdoor-to-indoor channel at 60 GHz for various orientations of the receiver is analyzed. We comment on the variation of the received line-of-sight (LOS) component power and delay spread with respect to the misalignment angle and suggest the existence of clusters which map to nearby buildings acting as scatterers. We propose a method to randomly generate the tapped delay line (TDL) filter model of the channel for any orientation of the receiver. We divide the range of misalignment angle into sectors of 5 degrees each and analyzed the similarity between the TDL models of each sector. The analysis enabled us to group the sectors into two categories: (A) [0,10) degrees and (B) [10,25) degrees. The TDL model is used to determine the bit error rate (BER) curve. The BER results are reported for BPSK modulation at 8 Gbps datarate. It is seen that when the misalignment angle exceeds 10 degrees, the BER floor goes up significantly, causing a BER increase of almost two orders. It can also be related to the lack of the LOS component in category (B), as the main-lobe of the receiver is steered further away from LOS.
  • Dual-mode Circular Microstrip Patch Antenna for Airborne Applications

    Akhter, Zubair; Bilal, Rana Muhammad; Shamim, Atif (IEEE, 2021-03-22) [Conference Paper]
    A dual-mode, dual-band 2.4/ 5.2 GHz circular microstrip patch antenna for airborne application is presented. Initially, a reference circular patch antenna is designed on Rogers© 5880 substrate for dual-mode (TM11 and TM01) performance with a single feed location. The bandwidth (BW) of the reference antenna is found to be 33 MHz and 155 MHz at 2.4 GHz and 5.2 GHz bands respectively. Later, the BW of the reference antenna at both the frequency band is enhanced with the help of proximity patches placed around the periphery of the reference/driven patch. It is found that the BW of the antenna at both the bands is enhanced by 2.5% at 2.4 GHz and 3.9 % at the 5.2 GHz band and similar improvements in their gains are also observed. The proposed antenna is fabricated and tested in an anechoic chamber for its impedance bandwidth and radiation pattern performance. A close match in simulated and measured performance of the antenna is achieved and an appropriate comparison of measured quantities is well illustrated in the paper.
  • A Large Frequency Ratio Dual-band Microstrip Antenna with Consistent Radiation Pattern for Internet of Sea Applications

    Liao, Hanguang; Bilal, Rana Muhammad; Shamim, Atif (IEEE, 2021-03-22) [Conference Paper]
    Sensing and retrieving data from ocean to land are challenging tasks, while the Internet of Sea concept provides a realistic solution to that. A large frequency ratio dual-band microstrip antenna design working at GSM, LoRa, and BLE bands with consistent radiation pattern is proposed for Internet of Sea applications. The antenna is based on a modified Split Ring Antenna which provides two radiating modes, where the frequency ratio is close to 3. The proposed microstrip antenna is optimized for a better radiation efficiency and consistent radiation pattern at both bands. The method to control the H-plane HPBW of the proposed antenna is provided. The antenna prototype is fabricated and measured, which shows the radiation pattern at both bands are consistent and the H-plane HPBWs are 94°and 78°, at the lower and higher bands respectively.
  • Full Wavefield Redatuming: Accurate Velocity Modelling for Imaging Beneath Complex Overburden

    Dzulkefli, Farah Syazana; Xin, Kefeng; Ghazali, Ahmad Riza; Qiang, Guo; Alkhalifah, Tariq Ali (Society of Petroleum Engineers (SPE), 2021-03-16) [Conference Paper]
    Salt is known for having a generally low density and higher velocity compared with the surrounding rock layers which causes the energy to scatter once the seismic wavefield hits the salt body and relatively less energy is transmitted through the salt to the deeper subsurface. As a result, most of imaging approaches are unable to image the base of the salt and the reservoir below the salt. Even the velocity model building such as FWI often fails to illuminate the deeper parts of salt area. In this paper, we show that Full Wavefield Redatuming (FWR) is used to retrieved and enhance the seismic data below the salt area, leading to a better seismic image quality and allowing us to focus on updating the velocity in target area below the salt. However, this redatuming approach requires a good overburden velocity model to retrieved good redatumed data. Thus, by using synthetic SEAM model, our objective is to study on the accuracy of the overburden velocity model required for imaging beneath complex overburden. The results show that the kinematic components of wave propagation are preserved through redatuming even with heavily smoothed overburden velocity model.
  • Analysis of LO phonon properties in III-nitrides: interaction with carriers and microscopic analysis

    Ishitani, Yoshihiro; Oki, Kensuke; Chizaki, Masaya; Okamoto, Shungo; Nakayama, Tomoya; Lin, Bojin; Ma, Bei; Morita, Ken; Miyake, Hideto; Iida, Daisuke; Ohkawa, Kazuhiro (SPIE-Intl Soc Optical Eng, 2021-03-05) [Conference Paper]
    Longitudinal optical (LO) phonon has strong electric interaction with particles and fields. Particularly, the interaction in III-nitrides is more significant than that in conventional III-V materials. We show phonon-exciton interaction properties in experimental PL spectrum analysis and theoretical calculation of population transfers of excitonic levels. Thermally nonequilibrium occupations of LO phonons and other modes generated by the LO-phonon decomposition are thought to shift the population distribution in principal quantum number states and kinetic energy to the higher energy side. The radiative exciton recombination lifetime is determined by the population distribution in the excitonic states, which is determined by the balance of the electronic and phononic elementary processes. The interaction of excitons and phonons releases the excess energy to the thermal bath of the lattice system, which sometimes yields negligible lattice temperature increase in the excited region or the nonequilibrium state between electron and phonon systems. A Raman scattering imaging measure is introduced to exhibit spatial transport of phonons generated by the energy relaxation and nonradiative recombination of the excited electrons and holes, where pump-probe measurements are enabled by the simultaneous irradiation of two laser beams. It is found that the phonon transport is blocked by the misfit dislocations located on a Ga0.84In0.16N/GaN heterointerface.
  • Time-dependent pulsing of microfluidic pumps to enhance 3D bioprinting of peptide bioinks

    Khan, Zainab; Kahin, Kowther; Hauser, Charlotte (SPIE-Intl Soc Optical Eng, 2021-03-05) [Conference Paper, Presentation]
    Using bioinks for 3D bioprinting of cellular constructs remains a challenge due to factors including viscosity, fluid dynamics and shear stress. The encapsulation of cells within the bioinks directly affects the quality of 3D bioprinting and microfluidic pumping is a commonly used supporting approach. The accuracy of microfluidic pumps can be further improved by introducing various mixing techniques. However, many of these techniques introduce complex geometries or external fields. In this study, we used a simple control technique of time-dependent pulsing for instant gelation of the peptide bioinks and observed its effect during the bioprinting process. Various time-dependent periodic signals are imposed on to a stable flow cycle and the effects are analyzed. The microfluidic pumps are programmed with different flow patterns represented by low frequency sinusoidal pulses, ramp inputs, and duty cycle pulses. Different combinations of these pulses are tested to achieve an optimal pulse for improved quality of printed constructs. Time-varied pulsing of microfluidic pumps, particularly as square waveforms, is found to provide better continuous flow and avoid material buildup within the extruder unit when compared to pumping at a constant flow rate with manual tuning. Clogging is avoided since the gelation rate is periodically reduced which avoids gel clumps in the printed constructs. This study substantially improves the use of suitable peptide bioinks, standardizes the 3D bioprinting process, and reduces clogging and clumping during printing. Our findings allow for printing of more accurate and complex constructs for applications in tissue engineering, such as skin grafting, and other regenerative medical applications.

View more