Methanol catalytic oxidation over VO
x
/Al
2O
3, VO
x
/ZrO
2 and VO
x
/MgO catalysts has been studied by solid-state nuclear magnetic resonance (NMR) spectroscopy. It was found that stronger acid ...sites in VO
x
/Al
2O
3 result in almost the same selectivities for dimethoxymethane, paraformaldehyde and formic acid, and weaker acid sites in VO
x
/ZrO
2 favor the formation of paraformaldehyde, while the VO
x
/MgO catalyst with the base support shows high selectivity for formate. Supporting VO
x
species on γ-Al
2O
3 and ZrO
2 leads to the formation of Brønsted acid sites as revealed by the adsorption of probe molecules. The acid strength of Brønsted acid sites on the VO
x
/Al
2O
3 catalyst is found to be stronger than that of the VO
x
/ZrO
2 catalyst which has the acid strength similar to zeolite HZSM-5's. The proposed bridging hydroxyl models accounting for the Brønsted acid sites formation were also confirmed by quantum chemical calculation.
Solid-state NMR spectroscopy results show that stronger acid sites in VO
x
/Al
2O
3 lead to almost the same selectivities for dimethoxymethane (DMM), paraformaldehyde and formic acid, and weaker acid sites in VO
x
/ZrO
2 favor paraformaldehyde synthesis, while the VO
x
/MgO catalyst with base support shows high selectivity for formate.
13C single-pulse MAS NMR spectra (with proton decoupling) of methanol and oxygen reaction on VO
x
/Al
2O
3 at various temperatures.
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The effect of the Martian crustal magnetic field is one of the hot topics of the study of Martian ionosphere. The studies on this topic are summarized in this paper. Main data of the Martian ...ionosphere were resulted from radio occultation experiments. According to the observations, the electron density scale height and the peak electron density of the Martian ionosphere are influenced by its crustal magnetic field. The strong horizontal magnetic field prevents the vertical diffusion of the plasma and makes the electron density scale height in the topside ionosphere close to that in the photo equilibrium region. In the cusp-like regions with strong vertical magnetic field, the enhanced vertical diffusion leads to a larger electron density scale height in the diffusion equilibrium region. The observation of radio occultation experiment onboard Mars Global Surveyor (MGS) showed that the averaged peak electron density observed in the southern hemisphere with strong crustal magnetic field was slightly larger than that in the northern hemisphere with weak crustal magnetic field. The Mars advanced radar for subsurface and ionosphere sounding (MARSIS) onboard Mars Express (MEX) was the first topside sounder to be used to observe Martian ionosphere. The MARSIS results confirmed that the enhancement of the peak electron density occurred in cusp-like regions with open field lines, and the amount of the enhancement was much larger than that observed by the radio occultation experiment. There are two possible mechanisms for the peak electron density enhancement in the cusp-like crustal magnetic field regions: One is the precipitation of the energetic particles and the other is the heating by the waves excited by plasma instabilities. It’s difficult to determine which one is the key mechanism for the peak electron density enhancement. Based on these studies, several interesting problems on the Martian ionosphere and plasma environment are presented.
Three supramolecular architectures based on alpha-Keggin-type polyoxometalates have been synthesized hydrothermally, and their structures have been characterized by elemental analyses, infrared (IR) ...spectroscopy, X-ray photoelectron spectroscopy (XPS) and single crystal X-ray diffraction structure analyses. Ni(enMe)(2)(H(2)O)(2)(2)Ni(enMe)(2)PW(VI)(9)W(V)(3)O(40) x H(2)O (1) (enMe = 1,2'-propanediamine) exhibits a novel 2-D supramolecular sinusoidal layer through the interactions between transition metal complexes and 1-D covalent chains which are constructed from alpha-Keggin units bridged by transition metal complexes. Ni(enMe)(2)(4){Ni(enMe)(2)Ni(enMe)(2)(H(2)O)AsW(VI)(6)W(V)(4)V(IV)(4)O(42)(2)} x 6 H(2)O (2), representing a 3-D supramolecular framework with 1-D channels, contains the first example of a tungstate dimer with inorganic-organic composite surfaces built up from Ni(enMe)(2)(2+) cation bridges and bi-capped alpha-Keggin polyoxometalate building blocks supporting the transition metal complex. Ni(enMe)(2)(4){Ni(enMe)(2)Ni(enMe)(2)(H(2)O)AsMo(VI)(4)Mo(V)(4)V(IV)(8)O(44)(2)} x 8 H(2)O (3), showing a 3-D supramolecular framework with 1-D channels, contains the first example of a molybdoarsenate dimer formed by Ni(enMe)(2)(2+) cations bridging two neighboring tetra-capped alpha-Keggin-based molybdates that support the transition metal complex Ni(enMe)(2)H(2)O. The topological networks of the supramolecular frameworks of 2 and 3 are analogous. Crystal structural analysis reveals that the dimensionality and the organization of polyoxometalate building units in the solid state can be tuned by the steric hindrances of the polyanions. Both 2 and 3 exhibit intensive photoluminescence.
The HAPC(Hydraulic Automatic Position Control) requires quick dynamic response and high control accuracy. Based on the research of the HAPC system, I build the HAPC mathematical model, then design ...both the Conventional PID controller and fuzzy PID controllers, simulate the two control methods using the MATLAB software, analyze the main factors which influence the results. The simulation results show that the fuzzy PID controller has the better effect in the dynamic response and the control accuracy than the former.
The photoluminescence properties of CdSe quantum dots with different radii are studied in this paper. The FWHM of photoluminescence of different quantum dots are nearly the same, which reveals that ...the nucleation centers are formed only at the beginning of chemical reaction and the size fluctuation does not increase with the increase of the reaction time. Thermal treatment and light illumination will reduce the photoluminescence efficiency and make a blue shift remarkably, which results from the change of surface states of CdSe quantum dots.
This article investigates the consensus of Multiple Unmanned Ground Vehicles (UGVs) System based on game modeling under external intermittent random Deny of Service (DoS) attacks. Considering the ...increasing complexity of DoS attacks against communication networks of Multiple UGVs System in open environments, the communication topology results multiple switching modes. Under the framework of Game theory, the consensus of Multiple UGVs System under DoS attack is transformed into the Nash equilibrium solution of multiplayer game. Finally, simulation results of a numerical examples are provided to verify the effectiveness of the proposed method.
Three new molybdophosphates, Co(dien)
2·(H
3dien)
6·{CoMo
12O
24(OH)
6(HPO
4)
2(PO
4)
6Co(Hdien)
2CoMo
12O
24(OH)
6(PO
4)
8}·(dien)·4H
3O·5H
2O (
1), (H
3dien)
4
MMo
12O
24(OH)
6(HPO
4)
4(PO
4)
4·10H
...2O
M=Co for (
2), Ni for (
3); dien=diethylenetriamine, have been synthesized by employing hydrothermal method and characterized by single crystal X-ray diffraction. Compound
1 is built up of CoP
4Mo
6
2 units as the structural motif covalently linked by Co(Hdien) complex subunits to yield an unusual 1-D chain. Compounds
2 and
3 are isomorphic and both display covalent discrete
MP
4Mo
6
2 cluster structures which are linked by the hydrogen bonds to form 3-D supramolecular networks. Both
1 and
2 display antiferromagnetic interaction and these three compounds all exhibit intensive photoluminescence.
Three new reduced molybdophoshpates based on P
4MO
6 building blocks have been hydrothermally synthesized.
1 is the first covalent 1-D chain consisting of two kinds of forms of
MP
4MO
6
2 units, standing forms A and lying forms B, while
2 and
3 possess 3-D supramolecular network structures. These three compounds all display photoluminescence.
Abstract
Peony‐like spinel Li
4
Ti
5
O
12
was synthesized via calcination of precursor at the temperature of 400°C, and the precursor was prepared through a hydrothermal process in which the reaction ...of hydrous titanium oxide with lithium hydroxide was conducted at 180°C. The as‐prepared product was investigated by SEM, TEM and XRD, respectively. As anode material for lithium ion battery, the Li
4
Ti
5
O
12
obtained was also characterized by galvanostatic tests and cyclic voltammetry measurements. It is found that the peony‐like Li
4
Ti
5
O
12
exhibited high rate capability of 119.7 mAh·g
−1
at 10 C and good capacity retention of 113.8 mAh·g
−1
after 100 cycles at 5 C, and these results indicate the peony‐like Li
4
Ti
5
O
12
has promising applications for lithium ion batteries with high performance.
The pitch-angle distribution of energetic particles is important for space physics studies on magnetic storm and particle acceleration. A 'pin-hole' imaging structure is built with the 'pin-hole' ...technique and a position sensitive detector, which can be used to measure the pitch angle distribution of energetic particles. To calibrate the angular response of the 'pin-hole' imaging structure, special experiment facilities are needed, such as the particle accelerator with special design. The features of this kind of particle accelerator are: 1) The energy range of the outgoing particles should be mid-energy particles (tens keV to several hundred keV); 2) the particle flux should be consistent in time-scale; 3) the directions of the outgoing particles should be the same and 4) the particle number within the spot should be low enough. In this paper, a method to calibrate the angular response of the 'pin-hole' imaging structure by the super(90)Sr/ super(90)Y beta source with a collimator is introduced and simulated by Geant4 software. The result of the calibration with the collimated beta source is in accord with the Geant4 simulations, which verifies the validity of this method.
