Spillover Efficiency Research Articles

Efficient hydrogen storage using Pt-incorporated nitrogen/oxygen-containing activated carbon with an ultra-large pore volume

Developing efficient hydrogen storage technologies is essential for meeting the rapidly increasing energy demand and promoting the hydrogen economy. In this study, hierarchical porous activated carbon (HPAC) with nitrogen and oxygen surface atoms, and an ultra-large total pore volume (3.00 cc/g) was prepared via a single-step synthesis using melamine, terephthalaldehyde, and KOH. Subsequently, a series of Ptx@HPAC materials was prepared by introducing Pt nanoparticles at varied concentrations (x = 5, 10, and 15 wt%). As the Pt concentration increased, the H2 storage performance at room temperature showed steady improvement, with Pt10@HPAC achieving a 31 % higher H2 uptake compared to pristine HPAC and demonstrating an impressive spillover efficiency of 4.7. This can be explained by the even dispersion of Pt by nitrogen and oxygen surface atoms. Moreover, due to considerably large total pore volume, Pt10@HPAC showed a large total H2 uptake (1.34 wt%) at 298 K and 40 bar, which is superior to that of other metal-doped adsorbents with similar excess H2 uptakes. The incorporation of Pt into nitrogen/oxygen-containing activated carbon with an ultra-large pore volume is an effective strategy for developing efficient materials for H2 storage at room temperature.

Agarose derived carbon based nanocomposite for hydrogen storage at near-ambient conditions

Nanocomposites of high surface area adsorption materials and nanosized transition metals have emerged as a promising strategy for hydrogen storage applications. However, their potential use in both transport and stationary applications depends on reaching the ultimate storage capacity at near-ambient conditions along with scalable synthesis protocols. Herein, a direct and simple thermal decomposition technique is reported to synthesize carbon-based nanocomposite, where nickel nanoparticles are dispersed in a porous carbon matrix. It is also demonstrated that the storage capacity can be enhanced at near-ambient conditions by effectively engineering the microstructure and synergistically combining the ‘physisorption’ and ‘spillover’ mechanism. The structure, composition and morphology of the samples were investigated using X-ray diffraction, energy dispersive spectroscopy, transmission and scanning electron microscopy. Sorption-desorption isotherms were obtained to study the hydrogen storage capacity at a moderate H2 pressure of 20 bar. The nanocomposite showed a promising storage capacity of 0.73 wt% at 298 K with reversible cyclability. It is shown that the uniform dispersion of catalytic nanoparticles leads to an increase in the spillover efficiency, which further helps in the enhancement of hydrogen storage capacity by a factor of 6.5 over pure carbon.

A 77 GHz Transmit Array for In-Package Automotive Radar Applications

A packaged transmit array (TA) antenna is designed for automotive radar applications operating at 77 GHz. The compact dimensions of the proposed configuration make it compatible with standard quad flat no-lead package (QFN) technology. The TA placed inside the package cover is used to focus the field radiated by a feed placed in the same package. The unit cell of the array is composed of two pairs of stacked patches separated by a central ground plane. A planar patch antenna surrounded by a mushroom-type EBG (Electromagnetic Band Gap) structure is used as the primary feed. An analytical approach is employed to evaluate the primary parameters of the suggested TA, including its directivity, gain and spillover efficiency. The final design has been refined using comprehensive full-wave simulations. The simulated gain is 14.2 dBi at 77 GHz, with a half-power beamwidth of 22°. This proposed setup is a strong contender for highly integrated mid-gain applications in the automotive sector.

Hydrogen Spillover Mechanisms on Copper on Zinc Oxide-Based Catalysts for Carbon Dioxide Hydrogenation to Methanol

This literature review examines the hydrogen spillover mechanisms on copper on zinc oxide (Cu/ZnO)-based catalysts for CO2 hydrogenation to methanol. The production of methanol from CO2 is an attractive process for mitigating greenhouse gas emissions and producing a valuable chemical feedstock. Cu/ZnO-based catalysts are known to exhibit high activity and selectivity towards methanol production and the hydrogen spillover effect is believed to play a crucial role in their performance. The review discusses the current understanding of the hydrogen spillover mechanism, including the nature of the active sites and the factors that affect spillover efficiency. It also summarises recent advances in catalyst design, such as the use of promoters and dopants, to enhance the hydrogen spillover effect and improve catalytic performance. This article provides a comprehensive overview of the hydrogen spillover mechanism on Cu/ZnO-based catalysts for CO2 hydrogenation to methanol, highlighting the potential of this technology for sustainable methanol production.

Insights into the dynamics of market efficiency spillover of financial assets in different equity markets

This paper provides multidisciplinary insights into the dynamics of market efficiency spillover of financial assets, considering Bitcoin, DXY (U.S. Dollar Index), S&P 500, and crude oil in different equity markets. Given this, we employ the multifractal detrended fluctuation analysis (MF-DFA) and the time-varying parameter vector autoregressive models (TVP-VAR) to illuminate these complex interplays between these assets and other equity markets. Our findings display that Bitcoin acts as a net transmitter, whereas DXY functions as a net receiver. Additionally, Bitcoin, DXY, and S&P 500 clearly exhibit dynamics in information transmission, whereas crude oil does not. It means that the low connectedness of the oil market in terms of market efficiency spillover, suggesting that the oil market may play an effective role as a hedging instrument for other assets.

Enhanced room-temperature hydrogen storage by CuNi nanoparticles decorated in metal-organic framework UiO-66(Zr)

This study demonstrates the significant effect of incorporating inexpensive transition metal nanoparticles into metal-organic frameworks (MOFs) to improve their room-temperature hydrogen storage properties. Low-cost nanoparticles (Cu, Ni, and CuNi) were incorporated into UiO-66(Zr) via the double-solvent approach (DSA) plus chemical reduction processes. All composites exhibited higher hydrogen storage capacity compared to pure UiO-66 at both room temperature and 60 bar. Notably, the hydrogen spillover efficiency of CuNi nanoparticles loaded in UiO-66 was comparable to that of MOF adsorbents embedded with noble metals such as Pd and Pt. The hydrogen storage capacity of CuNi@UiO-66 was significantly increased from 0.20 wt% to 0.74 wt%. DFT calculations showed that the CuNi alloys facilitated the adsorption and dissociation of hydrogen molecules in comparison to the single metal nanoparticles, thus favoring the hydrogen spillover effect and improving the hydrogen storage performance. This work demonstrates the potential of designing MOF loaded with inexpensive metal nanoparticles for optimized room-temperature hydrogen storage.

Low-Profile High-Efficiency Transmitarray Antenna for Beamforming Applications

A low-profile high-efficiency transmitarray antenna (TA) for beamforming applications is proposed and investigated in this paper. The partial H-plane waveguide slot array antenna is employed as the compact low-profile feeding structure of the beamforming TA. The designed TA can achieve a high taper efficiency due to the multi-array sources and the compactness of the partial H-plane waveguide. Moreover, the proposed TA can inherently have a high spillover efficiency because the frequency selective surface (FSS) for beamforming is located just above the radiating slot. The FSS with a transmission phase variation of 2π is designed by a square patch array and used to manipulate the wave-front of the transmitted electromagnetic wave instead of a complicated feed network and phase shifters. To verify its beamforming characteristic, three types of FSSs to operate a forming angle of −40°, −20°, 0°, +20°, and +40° are designed at 12 GHz. The distance between the FSS and the slot array antenna is 0.1λ0, and the aperture efficiency is measured to be about 69%. The measured results, such as the reflection coefficient and the far-field radiation pattern, are in good agreement with the simulated results. From the measured results, the proposed TA is confirmed to have good beamforming characteristics and high aperture efficiency.

Direct observation of accelerating hydrogen spillover via surface-lattice-confinement effect

Uncovering how hydrogen transfers and what factors control hydrogen conductivity on solid surface is essential for enhancing catalytic performance of H-involving reactions, which is however hampered due to the structural complexity of powder catalysts, in particular, for oxide catalysts. Here, we construct stripe-like MnO(001) and grid-like Mn3O4(001) monolayers on Pt(111) substrate and investigate hydrogen spillover atop. Atomic-scale visualization demonstrates that hydrogen species from Pt diffuse unidirectionally along the stripes on MnO(001), whereas it exhibits an isotropic pathway on Mn3O4(001). Dynamic surface imaging in H2 atmosphere reveals that hydrogen diffuses 4 times more rapidly on MnO than the case on Mn3O4, which is promoted by one-dimension surface-lattice-confinement effect. Theoretical calculations indicate that a uniform and medium O-O distance favors hydrogen diffusion while low-coordinate surface O atom inhibits it. Our work illustrates the surface-lattice-confinement effect of oxide catalysts on hydrogen spillover and provides a promising route to improve the hydrogen spillover efficiency.

Adjustable Resolution for Localized FSS-Based Sensing by Synthetic Beamforming

Recently, frequency-selective surface (FSS)-based sensors have shown potential for structural health monitoring due to their sensitivity to changes in element geometry, interelement spacing, substrate properties, and local environment. In addition, these sensors are remotely interrogated and are planar in design, thereby providing a wireless sensing solution that can cover large areas. Traditionally, FSS sensors are analyzed assuming a uniform (plane wave) illumination. However, practically speaking, the sensor will be illuminated with a nonuniform excitation. In this way, the resolution of the sensor is limited to the illumination pattern (footprint) on the sensor. As such, an adjustable illumination pattern is advantageous as it relates to the ability to interrogate the sensor on a localized or comprehensive basis. To this end, this article considers a synthetic beamforming approach to adjust the beamwidth of the focused illumination beam on the sensor as a solution for localized sensing applications. This approach is proposed to generate an arbitrary beam shape with a desired footprint. Moreover, the illumination and spillover efficiencies of the synthetic beam (SB) are defined, simulated, and discussed. The results show that a minimum focal area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\lambda _{0} \times 1\lambda _{0}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times3$ </tex-math></inline-formula> unit cells for the FSS sensors considered here) is essential to achieve a spillover efficiency of greater than 80%, thereby reducing the contribution of other neighboring unit cells on the sensor response. In addition, the illumination efficiency when an SB is utilized for illumination is greater than 80% due to the uniformity of the SB. Representative measurements were also performed on a sensor with a simulated strain profile.

An Optimal 18 m Shaped Offset Gregorian Reflector for the ngVLA Radio Telescope

This article describes the design of the 18 m shaped offset Gregorian reflector system for the Next Generation Very Large Array (ngVLA) radio interferometer and the associated 1.66:1 axially corrugated conical horn antennas. A parametric sweep determined feed horns with the goal of pattern symmetry and low spillover efficiency. Given these feeds, a mapping function for the shaped offset Gregorian reflector system was then determined, by a full-factorial design, to achieve maximum receiving sensitivity with secondary parameters such as plate scale, scan loss, sidelobe, and cross-polarization at acceptable levels. A subreflector extension is included in a feed-down tipping configuration with improved performance over the feed-up case. The resultant optics and feeds achieve very symmetrical patterns with an aperture efficiency of around 95%, a plate scale of 15 arcsec/mm, and first and second sidelobe levels of −18 and −24 dB, respectively. The receiving sensitivity at 30 GHz is 8.7 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /K and it increases to above 12 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /K at 12.3 GHz and reduces to 1.5 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /K at 116 GHz (ignoring the efficiency loss due to nonideal reflector surfaces). These sensitivities are close to the theoretical optimum.

Oxygen Vacancy Engineering Synergistic with Surface Hydrophilicity Modification of Hollow Ru Doped CoNi-LDH Nanotube Arrays for Boosting Hydrogen Evolution.

With the development of clean hydrogen energy, the cost effective and high-performance hydrogen evolution reaction (HER) electrocatalysts are urgently required. Herein, a green, facile, and time-efficient Ru doping synergistic with air-plasma treatment strategy is reported to boost the HER performance of CoNi-layered double hydroxide (LDH) nanotube arrays (NTAs) derived from zeolitic imidazolate framework nanorods. The Ru doping and air-plasma treatment not only regulate the oxygen vacancy to optimize the electron structure but also increase the surface roughness to improve the hydrophilicity and hydrogen spillover efficiency. Therefore, the air plasma treated Ru doped CoNi-LDH (P-Ru-CoNi-LDH) nanotube arrays display superior HER performance with an overpotential of 29mV at a current density of 10mAcm-2 . Furthermore, by assembling P-Ru-CoNi-LDH as both cathode and anode for two-electrode urea-assisted water electrolysis, a small cell voltage of 1.36V is needed at 10mAcm-2 and can last for 100h without any obvious activity attenuation that showing outstanding durability. In general, the P-Ru-CoNi-LDH can improve the HER performance from intrinsic electronic structure regulation cooperated with extrinsic surface wettability modification. These findings provide an effective intrinsic and extrinsic synergistic effect avenue to develop high performance HER electrocatalysts, which is potential to be applied to other research fields.

A W-Band Low-Profile Dual-Polarized Reflectarray With Integrated Feed for In-Band Full-Duplex Application

A W-band low-profile dual-polarized Cassegrain reflectarray with an integrated feed is designed in this work. High isolation, which is necessary for the in-band full-duplex (IBFD) applications, is realized between two feeding ports corresponding to the orthogonal polarizations. The antenna is composed of two parts, i.e., the dual-polarized planar-array feed and the Cassegrain reflectarray with a small focal-length to diameter ratio ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$F/D)$ </tex-math></inline-formula> . The dual-polarized planar array feed is appressed behind the main-reflectarray, and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$F/D$ </tex-math></inline-formula> is reduced to 0.2 to realize the integration and the low-profile property. For the array feed, high isolation is achieved through the orthogonal-mode isolation and the differential signal cancellation. Its radiation pattern is also manipulated to fit the reflectarray considering the taper and spillover efficiency. For the reflectarray, the rotational symmetry configuration and the dual-layer-patch cell are applied to suit the dual-polarization operation and the large incident angle, respectively. The measured operation band, where the gain variation is within 1 dB, is 93.4–95.6 GHz. At the center frequency, the gains of the Cassegrain reflectarray for the two ports are 31.86 and 30.88 dBi, and the corresponding aperture efficiencies are 31.4% and 25.1%, respectively. The isolation between the two ports is higher than 55 dB within the operation band. This work is a low-profile candidate for W-band point-to-point IBFD communication.

Independent Research and Development or Technology Mergers and Acquisitions? Decision Mechanisms of Research and Development Strategies in a Two-Stage Game

This research introduces the three variables of spillover effect, research and development efficiency, and cost of mergers and acquisitions as the chief factors affecting independent research and development and technology mergers and acquisitions based on a two-stage game theory model of research and development strategies. Using these three variables, this research explains the selection of independent research and development or technology mergers and acquisitions according to profit maximization. Based on the theory model, this research finds that costs of mergers and acquisitions and spillover effects play a significant role in research and development decisions. In addition, excessive costs of mergers and acquisitions can increase research and development expenditures, therefore reducing profit and affecting the organizational operation and development. Therefore, when the costs of mergers and acquisitions exceed a certain level, companies will abandon technology mergers and acquisitions and choose independent research and development; and a higher knowledge spillover effect reduces the costs of independent research and development, therefore increasing profit. In conclusion, given certain costs of mergers and acquisitions, a higher spillover effect helps business organizations to choose independent research and development strategies.

Low-profile high efficiency transmitarray antenna using optimized phase compensation surface (PCS) and PEC sidewalls

A low-profile high efficiency transmitarray antenna (TA) using an optimized phase compensation surface (PCS) and PEC sidewalls is proposed in this paper. Generally, TAs are composed of a source antenna and a planar PCS, and the PCS makes the phase of transmitted wave through the PCS be in-phase, resulting in a highly directive beam. The unit cells of a PCS cannot have a 100% transmittance at all transmission phases. Since there may be combinations of PCS that make various in-phases, the transmit efficiency of the TA can be improved. Also, the four PEC sidewalls are employed to maximize the amount of power reaching the PCS from the source antenna. As a result, the 100% spillover efficiency is achieved without diminishing taper efficiency. To verify its feasibility, the square TA was designed and measured at 5.8 GHz and a high aperture efficiency of 54% was obtained through the above design methodology.

Low‐costlens antenna for5Gmulti‐beam communication

AbstractA planar dielectric lens has been designed for low‐cost multi‐beam antennas in the 26‐GHz band of 5G communications. The lens feeder is a stacked‐patch microstrip antenna with four input ports, thus permitting four independent high‐directivity radiation beams. Maximum steering of 25° can be attained, which a simulated gain over 18 dB for all scanning angles. The antenna has been implemented with low‐cost manufacturing techniques. The feeder is fabricated as a printed circuit board, while the lens is realized as a perforated 3D‐printed dielectric piece. Experimental results confirm the multi‐beam capability of the lens system, suggesting that the spillover efficiency can be improved in further works.

Research on the Structural Features and Influential Factors of the Spatial Network of China’s Regional Ecological Efficiency Spillover

A regional coordinated development strategy is an important measure that is often used to implement sustainable development in China. However, many obstacles greatly limit the realization of regional ecological coordinated sustainable development. In this paper, ecological efficiency is utilized as an important indicator of sustainable development, and the network analysis method is used to explore the spatial correlation relationship of regional ecological coordinated sustainable development. This paper calculates the ecological efficiency of each region using the Window slacks-based measure (Window-SBM) model, formulates the spatial network of regional ecological efficiency spillover through the vector auto-regressive (VAR) Granger causality model, and analyzes the spatial spillover relationship and influencing factors of regional ecological efficiency by using the social network analysis method. It is found that the spillover network of ecological efficiency in each region presents a typical core-edge structure. In addition, there is an obvious hierarchical structure among blocks with different directions and functions. Industrial structure, economic development, and geographical proximity have a positive impact on the spatial spillover of regional ecological efficiency, while environmental regulation has a negative impact. Finally, relevant policy suggestions are put forward.

Knowledge spillover efficiency of carbon capture, utilization, and storage technology: A comparison among countries

Abstract This study examines the carbon capture, utilization, and storage research performance of 31 countries from the knowledge spillover perspective. Knowledge spillover efficiency—operationally defined as the level of academic and practical influence of research and development outputs—is measured using the output-oriented constant return to scale, variable returns to scale, and super efficiency models using data envelopment analysis. We consider the number of patents and research articles from 2000 to 2016 as input variables, while the number of research article citations, patent citations, and registration of triadic patent families as of 2017 are the three output variables. The samples for measuring efficiency were obtained by collecting patents and research articles using Wintelips and Scopus database, respectively. The results of the super-efficiency data envelopment analysis were used to examine each country’s position in terms of knowledge spillover. More specifically, the US, European countries, Japan, Australia, and New Zealand showed relatively high efficiency, which might be characteristic of their R&D policies and environmental factors. Moreover, the returns to scale analysis provide implications for R&D resource allocation as to whether to encourage the quantitative or qualitative expansion of R&D outputs to improve efficiency. This study can provide meaningful information to policymakers to identify ex post R&D activities and planning.

Media Coverage, Tourism Growth, and Spatial Spillover: Evidence from China

This study investigates the direct and spillover effects of media coverage on tourism growth in China. The theoretical foundation for how media affects development of regional tourism economy is deduced. An empirical analysis based on panel data from 31 Chinese provinces for the years 2003–2014 is presented through ordinary and spatial regression model. The main conclusions of the econometric analysis are that media coverage can significantly promote the development of local tourism growth by acting as an information intermediary, enhancing the image of the tourism destination, and forming public opinion pressure. Local media coverage can yield a positive impact on the economic development of neighboring tourism areas, as a result of accelerating the exchange and spillover efficiency of regional tourism information. Comparing to the geographical distance between provinces, the correlations degree of interregional tourism economy is more conducive to promote the spillover effect of media coverage on tourism growth.

The Impact of Government Competition on Regional R&amp;D Efficiency: Does Legal Environment Matter in China’s Innovation System?

Local governments are encouraged to compete in R&amp;D investments and activities in China’s innovation system. We aim to understand the influence of government competition on regional R&amp;D efficiency. We are also interested in examining how the attributes of legal environment act as a moderating variable for the relationship between government competition and R&amp;D efficiency. We developed Tobit spatial models with spatial panel data of 30 provinces of China in 2008–2016. The results show that: (1) There exists spatial dependence of R&amp;D efficiency, and the regions with high efficiency have “spillover effect” on the surrounding areas. (2) Government competition has a significant promoting effect on R&amp;D efficiency and/or R&amp;D efficiency spillover. Specifically, government competition has both R&amp;D efficiency promotion and R&amp;D efficiency “spillover” promotion in Eastern China, only R&amp;D efficiency positive spillover promotion in Middle-area and R&amp;D efficiency promotion but negative spillover in Western China. (3) The impact of government competition on efficiency is affected by the legal environment, and the promotion effect of government competition only exists in good legal environment. The results of this study reveal an important way to improve R&amp;D efficiency by establishing a new R&amp;D competition mechanism for local government which is oriented by efficiency and ruled by the legal environment.

A spatial productivity index in the presence of efficiency spillovers: Evidence for U.S. banks, 1992–2015

We present the methodology for a new spatial decomposition of total factor productivity (TFP) growth. The relevant literature is underdeveloped as there is just one short study which proposes a partial spatial TFP growth decomposition. We develop this literature in four respects. The first two developments are methodological to go from a partial decomposition to a complete one. First, we augment the partial decomposition with a cost efficiency spillover growth component. Second, we introduce own and spillover allocative efficiency growth components. Third, we provide a more detailed coverage of the spatial decomposition of TFP growth. Fourth, in contrast to the traditional application to geographical areas (e.g., countries) in the relevant literature, we apply our decomposition using firm level data, which suggests that there can be an important role for spatial productivity analysis in OR. Our application is to large U.S. banks over the period 1992–2015. Among other things, we find for the average large U.S. bank that TFP growth since the financial crisis has become much more dependent on the bank itself and less so on spatial spillovers.