Extended Wiener-Khinchin theorem for quantum spectral analysis

The classical Wiener-Khinchin theorem (WKT), which can extract spectral information by classical interferometers through Fourier transform, is a fundamental theorem used in many disciplines. However, there is still need for a quantum version of WKT, which could connect correlated biphoton spectral information by quantum interferometers. Here, we extend the classical WKT to its quantum counterpart, i.e., extended WKT (e-WKT), which is based on two-photon quantum interferometry. According to the e-WKT, the difference-frequency distribution of the biphoton wavefunctions can be extracted by applying a Fourier transform on the time-domain Hong-Ou-Mandel interference (HOMI) patterns, while the sum-frequency distribution can be extracted by applying a Fourier transform on the time-domain NOON state interference (NOONI) patterns. We also experimentally verified the WKT and e-WKT in a Mach-Zehnder interference (MZI), a HOMI and a NOONI. This theorem can be directly applied to quantum spectroscopy, where the spectral correlation information of biphotons can be obtained from time-domain quantum interferences by Fourier transform. This may open a new pathway for the study of light-matter interaction at the single photon level.Comment: 13 pages, 5 figure

Optimization of Zn_<i>x</i>Fe_3–<i>x</i>O₄ Hollow Spheres for Enhanced Microwave Attenuation

We report here the composition optimization of Zn_<i>x</i>Fe_3–<i>x</i>O₄ hollow nanospheres for enhancing microwave attenuation. Zn_<i>x</i>Fe_3–<i>x</i>O₄ hollow nanospheres were synthesized through a simple solvothermal process. The maximum magnetization moment of 91.9 emu/g can be obtained at <i>x</i> = 0.6. The composite filled with Zn_0.6Fe_2.4O₄ exhibited the bandwidth of 3.21–8.33 GHz for RL < −10 dB and a maximum relative bandwidth (<i>W</i>_p,max) of 88.6% at optimized thickness <i>t</i>₀ = 0.34 cm. The enhancement should be attributed to the enhanced permeability resonance at high frequency. This optimized hollow material is very promising to be used as a mass efficient and broadband microwave attenuation material

High-Performance Ni–Fe Redox Catalysts for Selective CH₄ to Syngas Conversion via Chemical Looping

In traditional steam reforming of CH₄, the CH₄ conversion and its selectivity to CO and H₂ are thermodynamically limited. In this work, we designed a series of Ni–Fe redox catalysts with varying Ni/Fe ratios. The Ni–Fe redox catalysts could function as oxygen carriers to selectively convert CH₄ to syngas via chemical looping. The selectivity to CO was dramatically enhanced via a selective conversion route of CH₄ to C and H₂ in the reduction, followed by C gasification to syngas with hot steam. Taking the advantages of the highly reactive Ni species for CH₄ activation and Fe species for water splitting, together with the resulting NiFe alloy in the reduced catalyst for catalytic CH₄ decomposition, high CH₄ conversion up to 97.5% and CO selectivity up to 92.9% were achieved at 900 °C with productivity of CO and H₂ of 9.6 and 29.0 mol kg_catalyst^–1, respectively, on equimolar Ni–Fe catalyst

Sub-Surface Boron-Doped Copper for Methane Activation and Coupling: First-Principles Investigation of the Structure, Activity, and Selectivity of the Catalyst

Copper (Cu) is a commercial catalyst for the synthesis of methanol from syngas, low-temperature water gas shift reaction, oleo-chemical processing, and for the fabrication of graphene by chemical vapor deposition. However, high barriers for C–H bond activation and the ease of formation of carbon/graphene on its surface limits its application in the utilization and conversion of methane to bulk chemicals. In the present paper, using first-principles calculations, we predict that Cu catalyst doped with a monolayer of sub-surface boron (B–Cu) can efficiently activate the C–H bond of methane and can selectively facilitate the C–C coupling reaction. Boron binds strongest at the sub-surface octahedral site of Cu and the thermodynamic driving force for the diffusion of B from an on-surface to the sub-surface position in Cu is stronger than that for the experimentally synthesizable B–Ni (sub-surface boron in nickel) catalyst, providing a proof of concept for the experimental synthesis of this novel catalyst. Additionally, the first-principles computed free energy of the reaction to form B–Cu from boron precursor and Cu is also favorable. The presence of the monolayer sub-surface B in Cu creates a corrugated step-like structure on the Cu surface and significantly brings down the methane C–H activation barrier from 174 kJ/mol on Cu(111) to only 75 kJ/mol on B–Cu. The subsequent dehydrogenation of the adsorbed CH₃* to CH₂* is also kinetically and thermodynamically feasible. Our calculations also suggest that, unlike most of the transition metals, complete decomposition of methane to carbon would not be favored on B–Cu. The dissociation of the surface CH₂* moiety on B–Cu is limited due to the high activation barrier of 161 kJ/mol and lower relative stability of the resultant CH* species, under reaction conditions. The coupling of CH₂* fragments however is kinetically and thermodynamically favorable, with an activation barrier of only 92 kJ/mol; suggesting that B–Cu catalyst would have higher selectivity toward C₂ hydrocarbons. Furthermore, the formation of carbon from the adsorbed CH* moiety has a very high activation barrier of 197 kJ/mol and the completely dehydrogenated C* is relatively much less stable than CH*, under reaction conditions; predicting that coking might not be an issue on the B–Cu catalyst. Evaluation of C–H activation on Cu(110) surface, which has a similar step-like surface structure as B–Cu, and Bader charge and density of states analyses of B–Cu reveal that the geometrical/corrugation effect and the charge transfer from B to Cu synergistically promote the C–H activation on B–Cu, making it as active as other expensive transition metals like Rh, Ru, Ir, and Pt

Hydrogenation of Furfural as Model Reaction of Bio-Oil Stabilization under Mild Conditions Using Multiwalled Carbon Nanotube (MWNT)-Supported Pt Catalysts

Pt nanoparticles supported on multiwalled carbon nanotubes (MWNT) were synthesized and applied in the catalytic hydrogenation of furfural, the model reaction of mild stabilization of reactive bio-oil. The catalytic properties of the catalysts were modified by changing the surface concentration of oxygen-containing groups (OCGs) of MWNT. Various characterization techniques, including fluorescent labeling, nitrogen physisorption, powder X-ray diffraction, transmission electron microscopy, and in situ DRIFTS analysis, were employed to study both the supports and catalysts. Pt nanoparticles supported on MWNT with high OCGs show high activity and selectivity, attributed to the formation of small Pt particles as a result of the high concentration of OCGs

Charge Transfer between Metal Clusters and Growing Carbon Structures in Chirality-Controlled Single-Walled Carbon Nanotube Growth

Synthesis of single-walled carbon nanotubes (SWCNTs) with specific chirality has been a great challenge. The detailed role of catalyst clusters in chirality-selective growth of SWCNTs is still unclear. We studied armchair (5,5), chiral (6,5), and zigzag (9,0) nanotube growths on a relaxed Ni₅₅ cluster. Although adhesion energies and chemical potentials of growing carbon structures only show small differences, charges are evidently transferred (or redistributed) from Ni atoms to the growing end edges of nanotubes, which enhance the reactivity of carbon edges. Different chiral nanotubes exhibit distinct reaction active sites. (5,5) has five identical double-carbon active sites, while (9,0) has nine single-carbon active sites. (6,5) has a kink site with the highest reaction activity. These findings imply that the structures of metal clusters strongly correlate with nanotube growth sites through charge transfer (or redistribution). Potential opportunities exist in enabling (<i>n</i>,<i>m</i>) selective growth by engineering charge transfer between metal clusters and growing carbon structures

Effective Nitrogen Removal and Recovery from Dewatered Sewage Sludge Using a Novel Integrated System of Accelerated Hydrothermal Deamination and Air Stripping

In order to reduce considerable emissions of N-containing pollutants from combustion of sewage sludge derived solid fuel, an integrated system of hydrothermal deamination and air stripping was developed to effectively remove and recover nitrogen from dewatered sewage sludge (DSS). Three characteristic hydrothermal regimes contributing to deamination were identified. Initial hydrolysis of inorganic-N and labile protein-N was responsible for ammonium (NH₄⁺-N) released below 300 °C/9.3 MPa, whereas deamination of pyridine-N dominated when being raised to 340 °C/15.5 MPa. At 380 °C and 22.0 MPa, remarkable deamination of stable protein-N occurred, which was accompanied by formation of more heterocyclic-N compounds and resulted in 76.9% N removal from DSS and 7980 mg/L NH₄⁺-N solution. As a result of catalytic hydrolysis and cracking, calcium oxide additive not only accelerated deamination of stable protein-N, pyrrole-N, and pyridine-N, but also favored transformations of protein-N and quaternary-N to nitrile-N and pyridine-N, respectively, leading to 86.4% total N removal efficiency. The nitrogen transformation reactions and conversion pathways during hydrothermal deamination were proposed and elaborated in detail. Moreover, an efficient air stripping process was coupled to remove and recover ammonia from liquid fraction via ammonium sulfate. Consequently, this system achieved an overall N recovery rate of 62%

White and Grey Matter Changes in the Language Network during Healthy Aging

<div><p>Neural structures change with age but there is no consensus on the exact processes involved. This study tested the hypothesis that white and grey matter in the language network changes during aging according to a “last in, first out” process. The fractional anisotropy (FA) of white matter and cortical thickness of grey matter were measured in 36 participants whose ages ranged from 55 to 79 years. Within the language network, the dorsal pathway connecting the mid-to-posterior superior temporal cortex (STC) and the inferior frontal cortex (IFC) was affected more by aging in both FA and thickness than the other dorsal pathway connecting the STC with the premotor cortex and the ventral pathway connecting the mid-to-anterior STC with the ventral IFC. These results were independently validated in a second group of 20 participants whose ages ranged from 50 to 73 years. The pathway that is most affected during aging matures later than the other two pathways (which are present at birth). The results are interpreted as showing that the neural structures which mature later are affected more than those that mature earlier, supporting the “last in, first out” theory.</p></div

Neural structural changes with age in Group 1.

<p>(A) shows FA changes. Note that the skeletonized results are “thickened” to help visualization. Left SLF-IFC/Prg, left superior longitudinal fasciculus underlying the inferior frontal cortex and precentral gyrus; Left SLF-TP, left superior longitudinal fasciculus underlying the temporal-parietal association cortex; Left and right IFOF-IFC, left and right inferior fronto-occipital fasciculus underlying the inferior frontal cortex; Right FM-MeFC, right forceps minor underlying the medial frontal cortex; Left bCC, left body of corpus callosum. (B) shows cortical thickness changes. The colored blobs (blue for cortical thickness, red for FA) indicate brain areas that correlated negatively with age. Left IFC, left inferior frontal cortex; Left Prg, left precentral gyrus. No positive correlations were found.</p

Linear regression fit results.

<p>(A) shows fitting result when using grand-averaged cortical thickness as the dependent variable in Group 1. (B) shows fitting result when using age as the dependent variable in Group 1. (C) Re-examination of Group 1's ROI in Group 2's data. Age is the dependent variable. Note that the red line is the linear fit result, whereas the green lines are the confidence internal (95%). For all three panels, the x-axis corresponds to the actual age or cortical thickness, whereas the y-axis corresponds to the age or cortical thickness produced by the regression model.</p