Effective Atomic N Doping on CeO2 Nanoparticles by Environmentally Benign Urea Thermolysis and Its Significant Effects on the Scavenging of Reactive Oxygen Radicals.

Atomic nitrogen doping on CeO2 nanoparticles (NPs) by an efficient and environmentally benign urea thermolysis approach is first studied, and its effects on the intrinsic scavenging activity of the CeO2 NPs for reactive oxygen radicals are investigated. The N-doped CeO2 (N-CeO2) NPs, characterized by X-ray photoelectron and Raman spectroscopy analyses, showed considerably high levels of N atomic doping (2.3-11.6%), accompanying with an order of magnitude increase of the lattice oxygen vacancies on the CeO2 crystal surface. The radical scavenging properties of the N-CeO2 NPs are characterized by applying Fenton's reaction with collective and quantitative kinetic analysis. The results revealed that the significant increase of surface oxygen vacancies is the leading cause for the enhancements of radical scavenging properties by the N doping of CeO2 NPs. Enriched with abundant surface oxygen vacancies, the N-CeO2 NPs prepared by urea thermolysis provided about 1.4-2.5 times greater radical scavenging properties than the pristine CeO2. The collective kinetic analysis revealed that the surface-area-normalized intrinsic radical scavenging activity of the N-CeO2 NPs is about 6- to 8-fold greater than that of the pristine CeO2 NPs. The results suggest the high effectiveness of the N doping of CeO2 by the environmentally benign urea thermolysis approach to enhance the radical scavenging activity of CeO2 NPs for extensive applications such as that in polymer electrolyte membrane fuel cells.

Utilizing multiplexing of structured THz beams carrying orbital-angular-momentum for high-capacity communications.

Structured electromagnetic (EM) waves have been explored in various frequency regimes to enhance the capacity of communication systems by multiplexing multiple co-propagating beams with mutually orthogonal spatial modal structures (i.e., mode-division multiplexing). Such structured EM waves include beams carrying orbital angular momentum (OAM). An area of increased recent interest is the use of terahertz (THz) beams for free-space communications, which tends to have: (a) larger bandwidth and lower beam divergence than millimeter-waves, and (b) lower interaction with matter conditions than optical waves. Here, we explore the multiplexing of THz OAM beams for high-capacity communications. Specifically, we experimentally demonstrate communication systems with two multiplexed THz OAM beams at a carrier frequency of 0.3 THz. We achieve a 60-Gbit/s quadrature-phase-shift-keying (QPSK) and a 24-Gbit/s 16 quadrature amplitude modulation (16-QAM) data transmission with bit-error rates below 3.8 × 10-3. In addition, to show the compatibility of different multiplexing approaches (e.g., polarization-, frequency-, and mode-division multiplexing), we demonstrate an 80-Gbit/s QPSK THz communication link by multiplexing 8 data channels at 2 polarizations, 2 frequencies, and 2 OAM modes.

Receiver aperture and multipath effects on power loss and modal crosstalk in a THz wireless link using orbital-angular-momentum multiplexing.

The channel capacity of terahertz (THz) wireless communications can be increased by multiplexing multiple orthogonal data-carrying orbital-angular-momentum (OAM) beams. In THz links using OAM multiplexing (e.g., Laguerre-Gaussian [Formula: see text] beams with p = 0), the system performance might degrade due to limited receiver aperture size and multipath effects. A limited-size aperture can truncate the received beam profile along the radial direction. In addition, due to beam divergence, part of the beam might interact with reflectors in the environment, causing the signal to reflect and interfere at the receiver with the directly propagating part of the beam; this is known as the multipath effect. In this paper, we simulate and analyze the impact of both effects on the equality of the THz OAM link by considering a full two-dimensional (2-D) LG modal set. The simulation results show (i) a limited-size receiver aperture can induce power loss and modal power coupling mainly to LG modes with the same ℓ but p > 0 for directly propagated OAM beams; (ii) the multipath effect can induce modal power coupling across multiple 2-D LG modes, which leads to inter-channel coupling among the different channels in an OAM multiplexed link; (iii) the interference between the reflected and direct beams can induce intra-channel coupling between the received signals from the reflected and direct beams; and (iv) beams with a higher OAM order (e.g., from ± 1 to ± 5) or a lower carrier frequency (e.g., from 0.1 to 1 THz) experience larger intra- and inter-channel coupling. The intra- and inter-channel coupling in an OAM-multiplexed THz link can degrade the signal-to-noise ratio (SNR) and induce SNR penalty when compared to a single-channel system.

Morphology Controlled Synthesis of γ-Al2O3 Nano-Crystallites in Al@Al2O3 Core-Shell Micro-Architectures by Interfacial Hydrothermal Reactions of Al Metal Substrates.

Fine control of morphology and exposed crystal facets of porous γ-Al2O3 is of significant importance in many application areas such as functional nanomaterials and heterogeneous catalysts. Herein, a morphology controlled in situ synthesis of Al@Al2O3 core-shell architecture consisting of an Al metal core and a porous γ-Al2O3 shell is explored based on interfacial hydrothermal reactions of an Al metal substrate in aqueous solutions of inorganic anions. It was found that the morphology and structure of boehmite (γ-AlOOH) nano-crystallites grown at the Al-metal/solution interface exhibit significant dependence on temperature, type of inorganic anions (Cl-, NO3-, and SO42-), and acid-base environment of the synthesis solution. Different extents of the electrostatic interactions between the protonated hydroxyl groups on (010) and (001) facets of γ-AlOOH and the inorganic anions (Cl-, NO3-, SO42-) appear to result in the preferential growth of γ-AlOOH toward specific crystallographic directions due to the selective capping of the facets by adsorption of the anions. It is hypothesized that the unique Al@Al2O3 core-shell architecture with controlled morphology and exposed crystal-facets of the γ-Al2O3 shell can provide significant intrinsic catalytic properties with enhanced heat and mass transport to heterogeneous catalysts for applications in many thermochemical reaction processes. The direct fabrication of γ-Al2O3 nano-crystallites from Al metal substrate with in-situ modulation of their morphologies and structures into 1D, 2D, and 3D nano-architectures explored in this work is unique and can offer significant opportunities over the conventional methods.

Modal coupling and crosstalk due to turbulence and divergence on free space THz links using multiple orbital angular momentum beams.

Orbital-angular-momentum (OAM) multiplexing has been utilized to increase the channel capacity in both millimeter-wave and optical domains. Terahertz (THz) wireless communication is attracting increasing attention due to its broadband spectral resources. Thus, it might be valuable to explore the system performance of THz OAM links to further increase the channel capacity. In this paper, we study through simulations the fundamental system-degrading effects when using multiple OAM beams in THz communications links under atmospheric turbulence. We simulate and analyze the effects of divergence, turbulence, limited-size aperture, and misalignment on the signal power and crosstalk of THz OAM links. We find through simulations that the system-degrading effects are different in two scenarios with atmosphere turbulence: (a) when we consider the same strength of phasefront distortion, faster divergence (i.e., lower frequency; smaller beam waist) leads to higher power leakage from the transmitted mode to neighbouring modes; and (b) however, when we consider the same atmospheric turbulence, the divergence effect tends to affect the power leakage much less, and the power leakage increases as the frequency, beam waist, or OAM order increases. Simulation results show that: (i) the crosstalk to the neighbouring mode remains < - 15 dB for a 1-km link under calm weather, when we transmit OAM + 4 at 0.5 THz with a beam waist of 1 m; (ii) for the 3-OAM-multiplexed THz links, the signal-to-interference ratio (SIR) increases by ~ 5-7 dB if the mode spacing increases by 1, and SIR decreases with the multiplexed mode number; and (iii) limited aperture size and misalignment lead to power leakage to other modes under calm weather, while it tends to be unobtrusive under bad weather.

Correlations of Through-Plane Cell Voltage Losses, Imbalance of Electrolytes, and Energy Storage Efficiency of a Vanadium Redox Flow Battery.

Correlations of the through-plane voltage losses in the vanadium redox flow battery (VRFB), changes in the posolyte (positive electrolyte) and negolyte (negative electrolyte) conditions, energy storage capacity, and coulomb efficiency were investigated under an operando charge-discharge process. Collective and quantitative in situ studies with Ag/AgCl reference-electrodes inserted into a VRFB single-cell and the state of charge measuring external open-circuit voltage half-cells revealed that the overall performance of a VRFB is predominantly governed by (i) relatively high internal resistance of the anode half-cell and (ii) conditions of the negolyte as the limiting electrolyte. The studies showed that the round-trip coulomb efficiency, which is commonly used for VRFB performance analysis, has limitations in expressing the energy storage efficiency and capacity decay phenomena under a consecutive charge-discharge process. In situ and concurrent analysis of the internal cell overpotential and the electrolytes condition can provide quantitative information on the relative contributions of the coulombic round-trip loss, concentration loss, vanadium crossover, and charge imbalance between the posolyte and negolyte for the overall efficiency and capacity decay phenomena. This operando analysis approach is highly effective for gaining an in-depth and collective understanding of the complex phenomena taking place in the VRFB system.

Interactions between tetrahydrothiophene (THT) and silver species in AgNa-Y.

We studied the interaction between tetrahydrothiophene (THT), which is one of sulfur odorants in a pipeline natural gas, and AgNa-Y zeolites, which can be obtained via Ag+ exchange with Na+ of Na-Y and used for the adsorptive removal of THT at ambient temperature and atmospheric pressure, with a temperature-programmed desorption (TPD), a temperature-programmed reduction with H2 (H2-TPR), a transmission electron microscopy (TEM) with an energy dispersive X-ray spectroscopy (EDX) and an X-ray absorption fine structure (XAFS). The presence of the metallic Ag and the Ag+ in the fresh AgNa-Y can be supported with a TEM and an XAFS analysis. The fraction of metallic Ag in silver species increased with increasing the pretreatment temperature. The formation of Ag-S bond with concomitant decreasing the interaction between Ag+ and oxygen in the lattice as well as the interaction of Ag-Ag in the metallic Ag can be observed during the adsorption of THT at ambient temperature. This can explain why there is no noticeable difference in the adsorption capacity in between Ag+ -dominant AgNa-Y and Ag0-rich AgNa-Y. This Ag-S bond was transformed into the Ag-Ag bond during the heat treatment in an inert gas above 673 K. However, the fresh chemical and electronic state of Ag can be recovered after the heat treatment in air above 673 K.

The Effectiveness of Mobile Discharge Instruction Videos (MDIVs) in communicating discharge instructions to patients with lacerations or sprains.

OBJECTIVE: This study evaluates the effectiveness of mobile discharge instruction videos (MDIVs) in communicating discharge instructions to patients with lacerations or sprains. METHOD: A prospective controlled study was performed on patients with lacerations or sprains in a quaternary emergency center from April 1, 2008 to May 31, 2008. Upon discharge, patients were systematically allocated to receive printed discharge instructions (PDIs) or MDIVs. Within 48 hours of the patients' discharge, a standard questionnaire was provided via telephone to evaluate the patients' comprehension of, convenience rating for, and satisfaction with their given discharge instructions. RESULTS: Of the 645 patients with lacerations or sprains during the study period, a convenience sample of 161 patients was enrolled in the study; 77 in the PDIs group (the P group) and 84 in the MDIVs group (the M group). There were no statistically significant differences in the ages, genders, and levels of education of the subjects in the two groups. The mean of the correct answers on wound care in the questionnaire was 2.7 +/- 0.7 in the M group and 2.4 +/- 0.8 in the P group (P < 0.05). The convenience rating was 85.7% in the M group and 63.6% in the P group (P < 0.05). The rate of satisfaction was 90.5% in the M group and 90.9% in the P group (P > 0.05). CONCLUSION: The mobile discharge instruction video (MDIV) improved the communication of discharge instructions. Further studies will be needed to explore the actual compliance of patients to treatment regimens.

Catalytic oxidation of methanol on Pd metal and oxide clusters at near-ambient temperatures.

Supported Pd clusters catalyze methanol oxidation to methyl formate with high turnover rates and >90% selectivity at near ambient temperatures (313 K). Metal clusters are much more reactive than PdO clusters and rates are inhibited by the reactant O(2). These data suggest that ensembles of Pd metal atoms on surfaces nearly saturated with chemisorbed oxygen are required for kinetically-relevant C-H bond activation in chemisorbed methoxide intermediates. Pd metal surfaces become more reactive with increasing metal particle size. The higher coordination of surface atoms on larger clusters leads to more weakly-bound chemisorbed species and to a larger number of Pd metal ensembles available during steady-state catalysis. Chemisorbed oxygen removes H-atoms formed in C-H bond activation steps and inhibits methoxide decomposition and CO(2) formation, two functions essential for the high turnover rates and methyl formate selectivities reported here.

Nanosized Pt-Co catalysts for the preferential CO oxidation.

The preferential CO oxidation in the presence of excess hydrogen was studied over Pt-Co/gamma-Al2O3. CO chemisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDX) and temperature programmed reduction (TPR) were conducted to characterize active catalysts. The catalytic activity for CO oxidation and methanation at low temperatures increased with the amounts of cobalt in Pt-Co/gamma-Al2O3. This accompanied the TPR peak shift to lower temperatures. The optimum molar ratio between Co and Pt was determined to be 10. The co-impregnated Pt-Co/gamma-Al2O3 appeared to be superior to Pt/Co/gamma-Al2O3 and Co/Pt/gamma-Al2O3. The reductive pretreatment at high temperature such as 773 K increased the CO2 selectivity over a wide reaction temperature. The bimetallic phase of Pt-Co seems to give rise to high catalytic activity in selective oxidation of CO in H2-rich stream.