Rubric-Specific Approach to Automated Essay Scoring with Augmentation Training

Neural based approaches to automatic evaluation of subjective responses have shown superior performance and efficiency compared to traditional rule-based and feature engineering oriented solutions. However, it remains unclear whether the suggested neural solutions are sufficient replacements of human raters as we find recent works do not properly account for rubric items that are essential for automated essay scoring during model training and validation. In this paper, we propose a series of data augmentation operations that train and test an automated scoring model to learn features and functions overlooked by previous works while still achieving state-of-the-art performance in the Automated Student Assessment Prize dataset.Comment: 13 page

Blowout and liftoff limits of a hydrogen jet flame in a supersonic, heated, coflowing air stream

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76310/1/AIAA-1993-446-753.pd

Effect of excitation on gas centered swirl coaxial injectors

[EN] Studies on combustion instability in liquid rocket engines are important in improving combustion efficiency and preventing combustion chamber losses. To prevent combustion instability, methods such as baffles and cavities are used. The injector is located in the middle of the perturbation-propagation process in the rocket engine, so it is important to study the suppression of combustion instability using the design of the injector. Much research has been focused on the study of liquid excitation in a single injector; however, the actual injector used in a liquid rocket engine is a coaxial injector. In this study, the dynamic characteristics of a gas-centred swirl coaxial injector were investigated by varying the gap thickness and momentum-flux ratio. Spray photographs were captured by synchronizing a stroboscope and digital camera, and a high-speed camera and Xenon lamp were also used. To measure the liquid film, a measurement system was implemented using the electrical conductance method. For excitation of the gas, an acoustic speaker was used to impart a frequency to the gas. The gGas velocity and effect of excitation were measured by hot-wire anemometry. A mechanical pulsator was used for liquid flow excitation. Liquid fluctuation was measured by a dynamic pressure sensor. In both gas and liquid excitation cases, the gain increased as the gap thickness decreased and the momentum-flux ratio increased. From these results, it can be concluded that gap thickness and momentum-flux ratio are major factors in suppressing combustion instability.This work was supported by the Advanced Research Centre Program (NRF-2013R1A5A1073861) through a National Research Foundation of Korea (NRF) grant, funded by the Korean government (MSIP), and contracted through the Advanced Space Propulsion Research Centre at Seoul National University and was supported by an NRF (National Research Foundation of Korea) Grant funded by the Korean Government (NRF-2016-Fostering Core Leaders of the Future Basic Science Program/Global Ph.D. Fellowship Program).Park, G.; Oh, S.; Bae, J.; Yoon, Y. (2017). Effect of excitation on gas centered swirl coaxial injectors. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 43-49. https://doi.org/10.4995/ILASS2017.2017.4653434

Nitric oxide levels of turbulent jet diffusion flames: Effects of residence time and damkohler number

The global residence time and the deviations from chemical equilibrium (i.e., the Damkohler number) were varied for a number of jet diffusion flames. The resulting effects on the nitric oxide emission index were measured and were compared with existing analysis. The global residence time is defined as Lf/UF, where Lf is the flame length and UF is the fuel jet velocity. Flame length is varied by increasing the jet diameter, by adding either premixed air or inerts to the fuel jet, or by adding a coaxial air stream. In particular, a unique jet flame was studied that is composed of helium---diluted hydrogen fuel; this flame is free of the complicating effects of flame radiation, buoyancy, and prompt NO and provides a useful baseline comparison to theory. It is found that NOx levels for three types of fuels were consistently less than levels predicted by thermal theory, which suggests that one or both of the two mechanisms that suppress NOx, namely strain and radiative cooling, are important. The use of a Damkohler number was found to successfully correlate the NOx data for the hydrogen/helium-air flames that have simple chemistry. As the helium concentration is increased in order to reduce the Damkohler number, the measured NOx emission index exceeds that of the equilibrium theory by as much as a factor of 24, which is further indication that it is important to add the correct nonequilibrium oxygen atom chemistry to current models.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30267/1/0000668.pd

Measured supersonic flame properties - Heat-release patterns, pressure losses, thermal choking limits

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76611/1/AIAA-24093-582.pd

An experimental study of a generic supersonic combustor.

The overall objectives of the present study were to measure the general properties of a hydrogen jet flame in a supersonic air stream, and to compare the supersonic results to subsonic trends and a one-dimensional analysis. The general properties measured were blowout stability limits, heat release distributions, thermal choking limits, stagnation pressure loss, static pressure profiles, and \rm NO\sb{x} emission index. While supersonic flame properties were of primary interest, subsonic flame blowout limits and \rm NO\sb{x} levels also were measured for comparison. A supersonic (Mach 2.2) combustor was designed which provided a wide range of conditions, including stagnation temperature from 294 K to the autoignition temperature of 900 K. It was found that the flame blowout curves display two distinct stable regions which are bounded by the far-field blowout limit and near-field blowout limit. Supersonic flame stability requires fuel tube lip thickness and sufficient stagnation temperature to extend the near-field blowout limit curve into the supersonic regime. It was determined from the data and a one-dimensional analysis that a supersonic flame has a heat release distribution with a log-normal shape. Using this log-normal shape, the one-dimensional supersonic analysis does adequately predict the measured loss of stagnation pressure and the amount of heat addition that causes the onset of thermal choking. Measurements quantify the wall divergence half angle that is required to avoid thermal choking. The \rm NO\sb{x} emission index was measured for numerous subsonic and supersonic cases. In the subsonic cases, the global residence time and the deviations from chemical equilibrium (i.e. the Damkohler number) were varied and the resulting effects were compared with the thermal \rm NO\sb{x} theory. In particular, a unique jet flame was studied that is composed of helium-diluted hydrogen fuel, and the \rm NO\sb{x} data of this helium-diluted hydrogen flame was found to be correlated successfully by the use of a Damkohler number. In the supersonic cases, the global residence time was varied for a hydrogen jet diffusion flame and it was found that the measured \rm NO\sb{x} emission index data increased with the global residence time, which is the same trend as that observed in the subsonic cases.Ph.D.Aerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104229/1/9501073.pdfDescription of 9501073.pdf : Restricted to UM users only

Effect of Hydrophilicity of Activated Carbon Electrodes on Desalination Performance in Membrane Capacitive Deionization

Membrane capacitive deionization (MCDI) is a modification of capacitive deionization (CDI) using ion-exchange membranes (IEM) in front of the electrodes. Electrode properties, especially the specific surface area, are known to be strongly related with desalination performance in CDI, but the effects of other properties in MCDI are not fully understood. The objective of this study was to investigate the effect of hydrophilicity in activated carbon electrodes on desalination performance in MCDI. Two types of activated carbon (P60 and YS-2) whose specific surface areas were similar were used as electrode materials, but they had different hydrophilicity (i.e., P60 was originally hydrophobic and YS-2 was relatively hydrophilic due to its nitrogen-containing surface chemistry). These hydrophilic electrodes (either the electrode itself or modified with polydopamine (PDA)) led to an increase in the salt adsorption capacity (SAC) in MCDI because they facilitated the access of both ions and water molecules into the electrode pores. In particular, the SAC of the P60 electrode displayed a large increase to almost reach that of the YS-2 electrode due to the improved hydrophilicity with PDA modification and the insignificant effects of PDA modification on an already hydrophilic YS-2 electrode. Additionally, PDA-modified IEM in MCDI reduced the SAC as a result of the additional insulating PDA layer with little changes in hydrophilicity

Experimental Study of the Combustion Efficiency in Multi-Element Gas-Centered Swirl Coaxial Injectors

The effects of the momentum-flux ratio of propellant upon the combustion efficiency of a gas-centered-swirl-coaxial (GCSC) injector used in the combustion chamber of a full-scale 9-tonf staged-combustion-cycle engine were studied experimentally. In the combustion experiment, liquid oxygen was used as an oxidizer, and kerosene was used as fuel. The liquid oxygen and kerosene burned in the preburner drive the turbine of the turbopump under the oxidizer-rich hot-gas condition before flowing into the GCSC injector of the combustion chamber. The oxidizer-rich hot gas is mixed with liquid kerosene passed through combustion chamber’s cooling channel at the injector outlet. This mixture has a dimensionless momentum-flux ratio that depends upon the dispensing speed of the two fluids. Combustion tests were performed under varying mixture ratios and combustion pressures for different injector shapes and numbers of injectors, and the characteristic velocities and performance efficiencies of the combustion were compared. It was found that, for 61 gas-centered swirl-coaxial injectors, as the moment flux ratio increased from 9 to 23, the combustion-characteristic velocity increased linearly and the performance efficiency increased from 0.904 to 0.938. In addition, excellent combustion efficiency was observed when the combustion chamber had a large number of injectors at the same momentum-flux ratio

Biological UV Photoreceptors‐Inspired Sn‐Doped Polycrystalline β‐Ga2O3 Optoelectronic Synaptic Phototransistor for Neuromorphic Computing

Abstract In this study, the authors fabricate Sn‐doped 100‐nm thick polycrystalline β‐Ga2O3 synaptic field‐effect transistors (FETs) emulating optical and electrical spike stimulation. When stimulated by deep ultraviolet (UV) optical spikes or electric voltage spikes at the gate, the devices exhibit several essential synaptic functions of excitatory‐postsynaptic currents (EPSCs), inhibitory‐postsynaptic currents (IPSCs), paired‐pulse facilitation (PPF), spike‐number‐dependent plasticity (SNDP), and spike‐timing‐dependent plasticity (STDP). Following UV optical stimulation, the devices mimic synaptic plasticity with a photogate effect, and the gate voltage stimulation emulates the synaptic weights according to the state of the gate dielectric interface. The β‐Ga2O3 synaptic FET demonstrates synergistic functions in various optoelectronic stimulation modes and successfully mimics the visual memory formation in bees with UV photoreceptors. Moreover, to verify the translation of optoelectrical‐derived synaptic behaviors of β‐Ga2O3 synaptic FETs into artificial neuromorphic computing, handwritten digit image recognition of the Modified National Institute of Standards and Technology dataset is performed using a convolutional neural network, and a learning accuracy of 96.92% is achieved. The realization of these fundamental functions of biological synapses suggests the utility of Ga2O3‐based optoelectronic devices for next‐generation neuromorphic computing