Nominal Conversion Research Articles

Overcoming limitations in propane dehydrogenation by codesigning catalyst-membrane systems.

Propylene production through propane dehydrogenation (PDH) is endothermic, and high temperatures required to achieve acceptable propane conversions lead to low selectivity and severe carbon-induced deactivation of conventional catalysts. We developed a catalyst-membrane system that removes the hydrogen by-product and can thus achieve propane conversions that exceed equilibrium limits. In this codesigned system, a silica/alumina (SiO2/Al2O3) hollow-fiber hydrogen membrane was packed with a selective platinum-tin (Pt1Sn1/SiO2) PDH catalyst on the tube side with hydrogen diffusing from the tube to the shell side. We demonstrate that the catalyst-membrane system can achieve propane conversions >140% of the nominal equilibrium conversion with a propylene selectivity >98% without deactivation of the system components. We also show that by introducing oxygen on the shell side of the catalyst-membrane system, we can couple the endothermic PDH reaction on the tube side with exothermic hydrogen oxidation on the shell side. This coupling results in higher rates of hydrogen transport, leading to further enhancements in the propane conversion as well as desired thermoneutral system operation.

Analysis and Research on Load Behavior of H-shaped Steel Concrete

Steel-reinforced concrete (SRC) possesses excellent strength and numerous advantages over traditional concrete, making it extensively used in high-rise buildings and large-span bridge structures. This paper commences with the constitutive relationship of steel reinforcement in SRC, the nominal stress-strain conversion, and real stress-strain transformation. It employs Abaqus for nonlinear finite element analysis to study the stress variations in compressed SRC columns subjected to reciprocating loads and examines load-displacement curves. The paper analyzes the hysteresis loops of SRC columns under reciprocating loads, the trends in skeleton curves, energy dissipation, and stiffness degradation. Consequently, it concludes that the variation of compressive stress along the axis of SRC columns is consistent with the change in bearing capacity. Under reciprocating loads, the stress at the lower end of the SRC column is greater than that at the upper end, suggesting the need for reinforcement in the lower portion. The hysteresis loop of SRC columns exhibits a rich characteristic, with increasing energy absorption as displacement increases.

Linear-to-circular polarization conversion with full-silica meta-optics to reduce nonlinear effects in high-energy lasers

High-energy lasers have benefited from intense efforts to bring light-matter interactions to new standards and to achieve laser fusion ignition. One of the main issues to further increasing laser energy is the resistance of optical materials to high laser fluences, in particular at the final stage of the laser beamline where nonlinear Kerr effects can occur in optical materials and provoke laser filamentation. One promising way to mitigate this process is to reduce the nonlinear susceptibility of the material by switching the polarization from a linear to a circular state. Here, we report a significant reduction in the laser filamentation effect on glass by using a full-silica metamaterial waveplateable to switch the linear-to-circular polarization of high fluence laser beams. This result is achieved through the use of a large size full-silica meta-optics exhibiting nominal polarization conversion associated with an excellent transmission efficiency and wavefront quality, as well as a high laser damage resistance.

400–48-V Stacked Active Bridge Converter

This article presents a transformerless high step-down dc–dc converter based on a stacked active bridge (SAB) configuration. The SAB converter consists of series-stacked capacitively coupled inverter modules and parallel-connected rectifier modules. The nominal step-down conversion ratio is determined by the number of the inverter modules, while the output current capability scales with the number of the paralleled rectifier modules. SAB operating principles, including phase-shift control and soft switching, achieved through series inductors, are similar to transformer-isolated dual active bridge converters. It is found that the best size versus loss tradeoff is achieved by integration of the series inductors on a custom core. Furthermore, it is shown that how soft switching contributes to natural voltage sharing among the series-stacked inverter modules. The approach is verified by experimental results on a 400–48 V, 3-kW SAB prototype using GaN devices and featuring 400- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathrm{W/}}{\text{in}}^{3}$</tex-math></inline-formula> power density. A flat efficiency curve is obtained with 99% peak efficiency, 97.5% full-load efficiency, and 98% efficiency at 20% load.

Force and energy analysis of single-piston free-piston expander—linear generator

The movement of piston in free-piston expander-linear generator (FPE-LG) mainly depends on the dynamic force balance among four kinds of forces (air impetus, air resistance, electromagnetic resistance and frictional resistance). In this paper, the Newton's Second Law and the first law of thermodynamics are used to analyze the single-piston FPE-LG, the change of four kinds of forces and work produced by the four kinds of forces are analyzed. Nominal work-electricity conversion loss coefficient is proposed for the firs time to represent the energy loss. The experiment results show that the work produced by four forces from top dead center (TDC) to bottom dead center (BDC) are higher than those from BDC to TDC. The minimum proportion of air resistance energy consumption is also more than 50%, the proportion of electromagnetic resistance energy consumption is less than 20%, and the proportion of frictional resistance energy consumption is more than 20%. Therefore, the total nominal work-electricity conversion loss can be effectively reduced by increasing intake time or intake pressure.

Development and Accuracy Assessment of a High-Precision Dual-Axis Pre-Commercial Solar Tracker for Concentrating Photovoltaic Modules

In recent decades, advances in the development of solar tracking systems (STSs) have led to concentrating solar technologies to increase their energy conversion efficiency. These systems, however, still have areas of opportunity or improving their performance and reducing their manufacturing costs. This paper presents the design, construction and evaluation of a high-precision dual-axis solar tracking system with a technology readiness level of 7–8. The system is controlled by a low-cost Arduino board in a closed-loop control using a micro-electromechanical solar sensor. Real-time tracking experiments were performed under a clear sky as well as during partly and mostly cloudy days. Solar tracking accuracy was evaluated in an operational environment using test procedures adapted from the International Electrotechnical Commission (IEC) 62817 standard. The total mean instantaneous solar tracking error on a clear day measured with a calibrated digital solar sensor was 0.37° and 0.52° with a developed pinhole projection system. Similarly, the total mean reported solar tracking accuracy achieved was 0.390° on a sunny day and 0.536° on a partially cloudy day. An annual power generation analysis considering a conventional photovoltaic (PV) panel system and a typical concentrator photovoltaic (CPV) module as payloads was also presented. Simulations showed an increase in the generation of up to 37.5% for a flat panel with dual-axis tracking versus a fixed panel. In the case of the CPV system, first, a ray tracing study was implemented to determine the misalignment coefficient, then the annual power generation was estimated. The developed STS allowed the CPV modules to reach at least 90% of their nominal energy conversion efficiency.

Control-Bounded Analog-to-Digital Conversion

A control-bounded analog-to-digital converter consists of a linear analog system that is subject to digital control, and a digital filter that estimates the analog input signal from the digital control signals. Such converters have many commonalities with delta–sigma converters, but they can use more general analog filters. The paper describes the operating principle, gives a transfer function analysis, and describes the digital filtering. In addition, the paper discusses two examples of such architectures. The first example is a cascade structure reminiscent of, but simpler than, a high-order MASH converter. The second example combines two attractive properties that have so far been considered incompatible. Its nominal conversion noise (assuming ideal components) essentially equals that of the first example. However, its analog filter is a fully connected network to which the input signal is fed in parallel, which potentially makes it more robust against nonidealities.

An Asymmetric Control Method for Switched-Capacitor-Based Resonant Converters

This article proposes an asymmetric control method for switched-capacitor-based resonant converters (SCRCs). The proposed method simultaneously controls the switching frequency, phase-shift angle, and the duty ratio of each half-bridge circuit. By controlling the duty ratios, the asymmetric control method is capable to regulate the switched-capacitor average voltage, allowing the asymmetric resonant current to flow. Either positive or negative portion of the asymmetric resonant current always resembles the resonant current with the frequency and phase-shift control method at the nominal voltage conversion ratio even though the actual voltage conversion ratio is not equal to the nominal value. As a result, the asymmetric control method is capable to reduce the operating frequency, and thus, improves the power conversion efficiency by reducing the frequency-dependent losses. A 350-kHz, 3-kW prototype was constructed and tested to verify the loss reduction and the improvement in the conversion efficiency. The SCRC with the proposed asymmetric control method reduces the power loss by 40% compared with the frequency and phase-shift control method and exhibits the maximum power conversion efficiency of 98.6% at the input and output voltages of 300 and 200 V.

Photovoltage Management Based on Enhanced Excitation Levels in Surface Arrays of Subwavelength Silicon Formations

Surface arrangements of subwavelength formations are extensively discussed in the context of photocurrent enhancement for photovoltaic (PV) applications. Recently, the potential contribution of such arrangements toward photovoltage augmentation is suggested. This study numerically demonstrates the potential for photovoltage management based on arrays composed of inverted silicon cones, referred to as light funnel (LF) arrays. The transition from an optimized nanopillar (NP) array into an LF array is examined. It is shown that a decrease in NP bottom diameter (Db) is accompanied by an increase in open‐circuit voltage (Voc). The highest photovoltage enhancement is recorded for the smallest considered Db = 50 nm with a Voc increase of 75 mV and reflects a 22% Voc enhancement compared with the NP Voc. It is shown that this Voc increase is due to 250% increase in the excitation level, and that the spatially resolved excitation level of the array‐nested LFs is more than two orders of magnitude higher than the highest spatially resolved excitation level in the array‐nested NPs. Finally, it is shown that the suggested photovoltage management entails almost a factor of 2 increase in the nominal power conversion efficiency upon the transition from an NP PV cell into LF PV cell.

Flight Safety Detection Using Modified Zeror Approach with Nominal Data Conversion

Flight Safety Detection Using Modified Zeror Approach with Nominal Data Conversion

Solar radius determined from PICARD/SODISM observations and extremely weak wavelength dependence in the visible and the near-infrared

Context. In 2015, the International Astronomical Union (IAU) passed Resolution B3, which defined a set of nominal conversion constants for stellar and planetary astronomy. Resolution B3 defined a new value of the nominal solar radius (R⊙N = 695 700 km km) that is different from the canonical value used until now (695 990 km). The nominal solar radius is consistent with helioseismic estimates. Recent results obtained from ground-based instruments, balloon flights, or space-based instruments highlight solar radius values that are significantly different. These results are related to the direct measurements of the photospheric solar radius, which are mainly based on the inflection point position methods. The discrepancy between the seismic radius and the photospheric solar radius can be explained by the difference between the height at disk center and the inflection point of the intensity profile on the solar limb. At 535.7 nm (photosphere), there may be a difference of ∼330 km between the two definitions of the solar radius. Aims. The main objective of this work is to present new results of the solar radius in the near-ultraviolet, the visible, and the near-infrared from PICARD space-based and ground-based observations. Simulations show the strong influence of atmosphere effects (refraction and turbulence) on ground-based solar radius determinations and highlight the interest of space-based solar radius determinations, particularly during planet transits (Venus or Mercury), in order to obtain more realistic and accurate measurements. Methods. Solar radius observations during the 2012 Venus transit have been made with the SOlar Diameter Imager and Surface Mapper (SODISM) telescope on board the PICARD spacecraft. We used the transit of Venus as an absolute calibration to determine the solar radius accurately at several wavelengths. Our results are based on the determination of the inflection point position of the solar limb-darkening function (the most common solar radius definition). A realistic uncertainty budget is provided for each solar radius obtained with the PICARD space-based telescope during the 2012 Venus transit. The uncertainty budget considers several sources of error (detection of the centers of Venus and Sun in PICARD images, positions of Sun and Venus from ephemeris (planetary theory), PICARD on-board timing, PICARD spacecraft position, and optical distortion correction from PICARD images). Results. We obtain new values of the solar radius from the PICARD mission at several wavelengths and in different solar atmosphere regions. The PICARD spacecraft with its SODISM telescope was used to measure the radius of the Sun during the Venus transit in 2012. At 535.7 nm, the solar radius is equal to 696 134 ± 261 km (combined standard uncertainty based (ξ) on the uncertainty budget). At 607.1 nm, the solar radius is equal to 696 156 ± 145 km (ξ), and the standard deviation of the solar radius mean value is ±22 km. At 782.2 nm, the solar radius is equal to 696 192 ± 247 km (ξ). The PICARD space-based results as well as PICARD ground-based results show that the solar radius wavelength dependence in the visible and the near-infrared is extremely weak. The differences in inflection point position of the solar radius at 607.1 nm, 782.2 nm, and 1025.0 nm from a reference at 535.7 nm are less than 60 km for the different PICARD measurements.

Ultrathin MoSe2@N-doped carbon composite nanospheres for stable Na-ion storage

Two-dimensional transition metal dichalcogenides are widely studied as anode materials for metal ion batteries. This application requires high electric conductivity which can be achieved by forming composites with conductive carbon. In this work, we demonstrate the creation of nanospheres composed of Mo-based thin nanosheets (MoS2, MoSe2 and Mo2C) uniform embedded within a N-doped carbon matrix. Using MoSe2/N-doped carbon nanospheres as an example, we investigate in detail the electrochemical property in Na ion storage and reveal the advantage over previously reported MoSe2 electrodes (higher capacity and improved capacity retention up to 500 cycles). Furthermore, we provide evidence by ex situ x-ray diffraction to the nominal irreversible conversion reaction during the first discharge.

An optrode for photometric detection of ammonia in air

A scheme of constructing an LED optrode for photometric detection of ammonia in air is considered. The components of the device are (1) a glass plate coated with a film of polydimethylsiloxane with an ion-coupled cation of brilliant-green dye, (2) an LED emitting at a wavelength of 655 nm, and (3) a metal housing. The nominal static conversion function, sensitivity, and relative measurement error of the device are analyzed on the basis of mathematical modeling. The obtained results allow one to design an LED optrode capable of carrying out control for automated technological processes, solving problems in the area of security, etc. The device provides the ability to create photometric gas analyzers of ammonia with small overall dimensions, power consumption, and cost.

Dimensional variation tolerant mode converter/multiplexer fabricated in SOI technology for two-mode transmission at 1550 nm.

The use of an integrated asymmetrical directional coupler for two-mode transmission at 1550 nm is analyzed. The design is based on silicon-on-insulator (SOI) technology and permits mode conversion and mode multiplexing/demultiplexing. In the nominal design, mode conversion and mode (de)multiplexing are achieved with 97% efficiency and a 23.4 dB crosstalk level in the 1540-1560 nm band using a 0.1 μm gap. The dimension tolerance of the SOI process has been taken into account in the selection of the optimum design, and the coupling efficiency would remain above 82.3% (corresponding to 0.8 dB excess loss) with 3σ accuracy. A 90% efficiency has been experimentally obtained.

Metrological characteristics of the torque measurement of electric motors

This paper proposes a method of determination of the basic metrological characteristics of measurement means (MM) in order to measure the torque of electric motors (EM), such as sensitivity, nominal conversion functions, and additive and multiplicative errors. The nature of change of metrological characteristics was researched using the Measurand Model derived, in the conversion measuring range studied in this paper. Summarised values for additive and multiplicative errors were established for the MM of torque, under the conditions of deviation in terms of the impact value from its nominal value. In addition, the methodology was analysed to enable recalculation of additive and multiplicative errors related to the standard uncertainty of type B. This was undertaken to establish the quality of measurement according to international standards. The research was founded on Measurand Model obtained for multiplicative and additive components in the errors inherent in torque MM.

LED optrode for detecting sulfur dioxide in air

Scheme of an LED optrode for detecting sulfur dioxide in the air is considered. The components of the device are (1) a glass plate coated with a copolymer film of n-decylmethacrylate and styrene sulfonate with ion-coupled cation of the brilliant green dye, (2) an LED emitting at a wavelength of 655 nm, and (3) a metal housing. The nominal static conversion function of the device and its sensitivity are analyzed on the basis of mathematical modeling. It is established that the maximum sensitivity in determining the sulfur dioxide concentration in the air is achieved in the case in which the glass plate of the optrode is covered with a polymer film characterized by a specific value of the optical density in pure air containing no sulfur dioxide. For example, for a sulfur dioxide concentration close to zero, the film optical density should be close to one. The presented results allow one to make an optrode suitable for ensuring environmental and sanitaryhygienic safety. The device provides the ability to create analyzers for the measurement of sulfur dioxide in air that have small overall dimensions, power consumption, and cost.

NOMINAL VALUES FOR SELECTED SOLAR AND PLANETARY QUANTITIES: IAU 2015 RESOLUTION B3* †

ABSTRACT In this brief communication we provide the rationale for and the outcome of the International Astronomical Union (IAU) resolution vote at the XXIXth General Assembly in Honolulu, Hawaii, in 2015, on recommended nominal conversion constants for selected solar and planetary properties. The problem addressed by the resolution is a lack of established conversion constants between solar and planetary values and SI units: a missing standard has caused a proliferation of solar values (e.g., solar radius, solar irradiance, solar luminosity, solar effective temperature, and solar mass parameter) in the literature, with cited solar values typically based on best estimates at the time of paper writing. As precision of observations increases, a set of consistent values becomes increasingly important. To address this, an IAU Working Group on Nominal Units for Stellar and Planetary Astronomy formed in 2011, uniting experts from the solar, stellar, planetary, exoplanetary, and fundamental astronomy, as well as from general standards fields to converge on optimal values for nominal conversion constants. The effort resulted in the IAU 2015 Resolution B3, passed at the IAU General Assembly by a large majority. The resolution recommends the use of nominal solar and planetary values, which are by definition exact and are expressed in SI units. These nominal values should be understood as conversion factors only, not as the true solar/planetary properties or current best estimates. Authors and journal editors are urged to join in using the standard values set forth by this resolution in future work and publications to help minimize further confusion.

Technoeconomic Design of a Micro Gas-turbine for a Solar Dish System

An integrated approach for the design of a custom-tailored hybrid solar MGT with an integrated solar receiver for the use in a small-scale solar dish unit is presented in order to overcome the inherent limitations of adapting a MGT in the desired power range to solar operation. The resulting MGT-dish equipped with the ‘optimal’ MGT shows a nominal conversion efficiency of 29.6%. Then, a thermoeconomic analysis of the entire system is performed to evaluate and compare the economic and environmental performance of the MGT-dish with a Dish-Stirling system. From an economical point of view the MGT-dish outperforms the dish-Stirling with LCoEs as low as 15.3€cts/kWhel compared to 22.4€cts/kWhel.

Outdoor simultaneous testing of four types of photovoltaic tracked modules

Photovoltaic (PV) systems implemented in the built environment must fulfill supplementary design restrictions related to the limited available space and to architectural integration, thus the need for increased output is a must and tracking, whenever possible, represents a feasible solution. Tracking significantly enhances the amount of solar radiation on the module, including infrared radiation which contributes to their heating and influences the conversion efficiency. These efficiency variations are different, mainly depending on the modules' type (materials). The paper analyses the conversion efficiency of four types of commercial photovoltaic modules (amorphous, mono- and polycrystalline silicon, and CuInS2 (CIS)), simultaneously tested in two in-field setups: on a tracked PV platform and fixed tilt at 45°. The input global radiation and the outdoor temperature are correlated with the variation in the conversion efficiencies, outlining significant differences and the advantages of thin film (CIS) modules. A novel criterion is proposed to evaluate the results: the relative efficiency loss based on the actual and the nominal conversion efficiencies.

Crowdsourcing a HIT: Measuring Workers' Pre-Task Interactions on Microtask Markets

The ability to entice and engage crowd workers to participate in human intelligence tasks (HITs) is critical for many human computation systems and large-scale experiments. While various metrics have been devised to measure and improve the quality of worker output via task designs, effective recruitment of crowd workers is often overlooked. To help us gain a better understanding of crowd recruitment strategies we propose three new metrics for measuring crowd workers' willingness to participate in advertised HITs: conversion rate, conversion rate over time, and nominal conversion rate. We discuss how the conversion rate of workers—the number of potential workers aware of a task that choose to accept the task—can affect the quantity, quality, and validity of any data collected via crowdsourcing. We also contribute a tool — turkmill — that enables requesters on Amazon Mechanical Turk to easily measure the conversion rate of HITs. We then present the results of two experiments that demonstrate how conversion rate metrics can be used to evaluate the effect of different HIT designs. We investigate how four HIT design features (value proposition, branding, quality of presentation, and intrinsic motivation) affect conversion rates. Among other things, we find that including a clear value proposition has a strong significant, positive effect on the nominal conversion rate. We also find that crowd workers prefer commercial entities to non-profit or university requesters.