Characterization and Activity of Cr, Cu and Ga Modified ZSM-5 for Direct Conversion of Methane to Liquid Hydrocarbons

Direct conversion of methane using a metal-loaded ZSM-5 zeolite prepared viaacidic ion exchange was investigated to elucidate the roles of metal and acidity in the formation ofliquid hydrocarbons. ZSM-5 (SiO_2/Al_2O_3=30) was loaded with different metals (Cr, Cu and Ga)according to the acidic ion-exchange method to produce metal-loaded ZSM-5 zeolite catalysts. XRD,NMR, FT-IR and N_2 adsorption analyses indicated that Cr and Ga species managed to occupy thealuminum positions in the ZSM-5 framework. In addition, Cr species were deposited in the pores ofthe structure. However, Cu oxides were deposited on the surface and in the mesopores of the ZSM-5zeolite. An acidity study using TPD-NH_3, FT-IR, and IR-pyridine analyses revealed that the totalnumber of acid sites and the strengths of the Broensted and Lewis acid sites were significantlydifferent after the acidic ion exchange treatment. Cu loaded HZSM-5 is a potential catalyst fordirect conversion of methane to liquid hydrocarbons. The successful production of gasoline via thedirect conversion of methane depends on the amount of aluminum in the zeolite framework and thestrength of the Broensted acid sites.

Preparation and Performance of Ce/Zr Mixed Oxides for Direct Conversion of Methane to Syngas

CexZr1-xO2 mixed oxides with different Ce/Zr ratios were prepared by coprecipitation. The characterizations of mixed oxides were studied by X-ray diffraction (XRD) and H2-TPR. And the performances were tested in a fixed-bed quartz reactor. The results indicated that lattice oxygen of CexZr1-xO2 could oxidate methane to syngas and the incorporation of zirconium into the ceria lattice could improve the O2- mobility. The Ce0.7Zr0.3O2 had the best activity in investigative temperature ranging from 600 to 900 ℃. Effects of reaction time on H2/CO ratio were studied at 850 ℃ when using Ce0.7Zr0.3O2 as catalyst. The results indicated that the ratio was closed to 2 values in the first 10 min, however, it rapidly increased with reaction time after >10 min. The possible reason was that the direct partial oxidation of methane reaction was dominant in the first 10 min. However, the methane pyrogenation was responsible for the rapid increase of H2/CO ratio after 10 min. Thus, if syngas with H2/CO ratio of 2 wanted to be obtained, the reaction time needed to be controlled.

Direct conversion of methane to methanol by electrochemical methods

A convenient method for methane(CH_(4))direct conversion to methanol(CH_(3)OH)is of great significance to use methane-rich resources,especially clathrates and stranded shale gas resources located in remote regions.Theoretically,the activation of CH_(4) and the selectivity to the CH_(3)OH product are challenging due to the extreme stability of CH_(4) and relatively high reactivity of CH_(3)OH.The state-of-the-art‘methane reforming-methanol synthesis’process adopts a two-step strategy to avoid the further reaction of CH_(3)OH under the harsh conditions required for CH_(4) activation.In the electrochemical field,researchers are trying to develop conversion pathways under mild conditions.They have found suitable catalysts to activate the C–H bonds in methane with the help of external charge and have designed the electrode reactions to continuously generate certain active oxygen species.These active oxygen species attack the activated methane and convert it to CH_(3)OH,with the benefit of avoiding over-oxidation of CH_(3)OH,and thus obtain a high conversion efficiency of CH_(4) to CH_(3)OH.This mini-review focuses on the advantages and challenges of electrochemical conversion of CH4 to CH_(3)OH,especially the strategies for supplying electro-generated active oxygen species in-situ to react with the activated methane.

Two-photon live imaging of direct glia-to-neuron conversion in the mouse cortex

Over the past decade,a growing number of studies have reported transcription factor-based in situ reprogramming that can directly conve rt endogenous glial cells into functional neurons as an alternative approach for n euro regeneration in the adult mammalian central ne rvous system.Howeve r,many questions remain regarding how a terminally differentiated glial cell can transform into a delicate neuron that forms part of the intricate brain circuitry.In addition,concerns have recently been raised around the absence of astrocyte-to-neuron conversion in astrocytic lineage-tra cing mice.In this study,we employed repetitive two-photon imaging to continuously capture the in situ astrocyte-to-neuron conversion process following ecto pic expression of the neural transcription factor NeuroD1 in both prolife rating reactive astrocytes and lineage-tra ced astrocytes in the mouse cortex.Time-lapse imaging over several wee ks revealed the ste p-by-step transition from a typical astrocyte with numero us short,tapered branches to a typical neuro n with a few long neurites and dynamic growth cones that actively explored the local environment.In addition,these lineage-converting cells were able to migrate ra dially or to ngentially to relocate to suitable positions.Furthermore,two-photon Ca2+imaging and patch-clamp recordings confirmed that the newly generated neuro ns exhibited synchronous calcium signals,repetitive action potentials,and spontaneous synaptic responses,suggesting that they had made functional synaptic connections within local neural circuits.In conclusion,we directly visualized the step-by-step lineage conversion process from astrocytes to functional neurons in vivo and unambiguously demonstrated that adult mammalian brains are highly plastic with respect to their potential for neuro regeneration and neural circuit reconstruction.

Direct conversion of human fibroblasts into retinal pigment epithelium-like cells by defined factors

The generation of functional retinal pigment epithelium （RPE） is of great therapeutic interest to the field of regenerative medicine and may provide possible cures for retinal degenerative diseases, including age-related macular degeneration （AMD）. Although RPE cells can be produced from either embryonic stem cells or induced pluripotent stem cells, direct cell reprogramming driven by lineage-determining transcription factors provides an immediate route to their generation. By monitoring a human RPE specific Bestl：：GFP reporter, we report the conversion of human fibroblasts into RPE lineage using defined sets of transcription factors. We found that Bestl：：GFP positive cells formed colonies and exhibited morphological and molecular features of early stage RPE cells. Moreover, they were able to obtain pigmen- tation upon activation of Retinoic acid （RA） and Sonic Hedgehog （SHH） signaling pathways. Our study not only established an ideal platform to investigate the tran- scriptional network regulating the RPE cell fate deter- mination, but also provided an alternative strategy to generate functional RPE cells that complement the useof pluripotent stem cells for disease modeling, drug screening, and cell therapy of retinal degeneration.

Acquisition of functional neurons by direct conversion:Switching the developmental clock directly

Identifying approaches for treating neurodegeneration is a thorny task but is important for a growing number of patients.Researchers have focused on discovering the underlying molecular mechanisms of reprogramming and optimizing the technologies for acquiring neurons.Direct conversion is one of the most important processes for treating neurological disorders.Induced neurons derived from direct conversion,which bypass the pluripotency stage,are more effective,more quickly obtained,and are safer than those produced via induced pluripotent stem cells(iPSCs).Based on iPSC strategies,scientists have derived methods to obtain functional neurons by direct conversion,such as neuron-related transcriptional factors,small molecules.microRNAs,and epigenetic modifiers.In this review,we discuss the present strategies for direct conversion of somatic cells into functional neurons and the potentials of direct conversion for producing functional neurons and treating neurodeeeneration.

Tumor cells undergoing direct lineage conversion to neurons: unnatural but useful?

Dear Editor, In 2011, Son et al. （2011） reported that the forced expression of selected transcription factors is sufficient to convert mouse and human fibroblasts into induced motor neurons （iMNs）. The authors used three factors （Ascll, Brn2, and Mytll） to convert fibroblasts into neuronal-like ceils. After confirming that the cells had neuronal morphology, but with absence of motor neuron markers, eight candidate transcription factors were added, which participate in various stages of motor neuron specification. As expected, a significant number of motor cells emerged with known characteristics of cultured embryonic motor neurons.

Direct transformation of fossil carbon into chemicals: A review

Despite the long tradition of fossil carbon(coal,char,and related carbon-based materials)for fueling mankind,the science of transforming them into chemicals is still demandingly progressing in the current energy scenario,especially when considering its responsibilities to the global climate change.Traditionally,there are four routes of preparing chemicals directly from fossil carbon,including hydrogasification,gasification,direct liquefaction,and oxidation,in the macroscope of gas-solid reaction(hydrogasification and gasification)and liquid-solid reaction(direct liquefaction and oxidation).When the study goes to microscale,the gas-solid reaction can be considered as the reaction between the severe condensed radicals and gas,while the liquid-solid reaction is the direct reaction between the radical and the activated-molecule.To have a full overview of the area,this review systematically summarizes the main factors in these processes and shows our own perspectives as follows,(ⅰ)stabilizing the free radicals generated from coal and then directly converting them has the highest efficiency in coal utilization;(ⅱ)the research on the self-catalytic process of coal structure will have a profound impact on the direct preparation of chemicals from fossil carbon.Further discussions are also proposed to guide the future study of the area into a more sustainable direction.

BEST DIRECT AND CONVERSE RESULTS FOR LAGRANGE-TYPE OPERATORS

The aim of this paper is to give direct and converse theorems for the approximation by using a discretely defined method Ln (see D. H. Mache [10], which is a modification of the Lagrange operator. Furthermore we obtain with a matrix construction technique (see M. D. Ye and D. X. Zhou [11]) a Lagrange-type operator n, for which we get a characterization for Lipschitz functions by the approximation rate of these methods.

Recent progress in methane dehydroaromatization: From laboratory curiosities to promising technology

Direct conversion of methane to benzene or other valuable chemicals is a very promising process for the efficient application of natural gas. Compared with conversion processes that require oxidants, non-oxidative direct conversion is more attractive due to high selectivity to the target product. In this paper, an alternative route for methane dehydrogenation and selective conversion to benzene and hydrogen without the participation of oxygen is discussed. A brief review of the catalysts used in methane dehydroaromatization （MDA） is first given, followed by our current understanding of the location and the active phase of Mo species, the reaction mechanism, the mechanism of carbonaceous deposit and the deactivation of Mo/zeolite catalysts are systematically discussed. Ways to improve the catalytic activity and stability are described in detail based on catalyst and reaction as well as reactor design. Future prospects for methane dehydroaromatization process are also presented.

A programmable gain amplifier with digitally assisted DC offset calibration for a direct-conversion WLAN receiver

This paper presents a programmable gain amplifier（PGA） circuit with a digitally assisted DC offset cancellation（DCOC） scheme for a direct conversion WLAN receiver.Implemented in a standard 0.13-μm CMOS process,the PGA occupies 0.39 mm2 die area and dissipates 6.5 mW power from a 1.2 V power supply.By using a single loop single digital-to-analog converter（DAC） mixed signal DC offset cancellation topology,the minimum DCOC settling time achieved is as short as 1.6μs with the PGA gain ranging from -8 to 54 dB in a 2 dB step.The DCOC loop utilizes a segmented DAC structure to lower the design complexity without sacrificing accuracy and a digital control algorithm to dynamically set the DCOC loop to fast or normal response mode,making the PGA circuit in compliance with the targeted WLAN specifications.

CMOS highly linear direct-conversion transmitter for WCDMA with fine gain accuracy

A highly linear,high output power,0.13μm CMOS direct conversion transmitter for wideband code division multiple access（WCDMA） is described.The transmitter delivers 6.8 dBm output power with 38 mA current consumption.With careful design on the resistor bank in the IQ-modulator,the gain step accuracy is within 0.1 dB,hence the image rejection ratio can be kept below—47 dBc for the entire output range.The adjacent channel leakage ratio and the LO leakage at 6.8 dBm output power are -44 dBc @ 5 MHz and -37 dBc,respectively,and the corresponding EVM is 3.6%.The overall gain can be programmed in 6 dB steps in a 66-dB range.

Exosome-guided direct reprogramming of tumor-associated macrophages from protumorigenic to antitumorigenic to fight cancer

Highly immunosuppressive tumor microenvironment containing various protumoral immune cells accelerates malignant transformation and treatment resistance.In particular,tumor-associated macrophages(TAMs),as the predominant infiltrated immune cells in a tumor,play a pivotal role in regulating the immunosuppressive tumor microenvironment.As a potential therapeutic strategy to counteract TAMs,here we explore an exosome-guided in situ direct reprogramming of tumor-supportive M2-polarized TAMs into tumor-attacking M1-type macrophages.Exosomes derived from M1-type macrophages(M1-Exo)promote a phenotypic switch from anti-inflammatory M2-like TAMs toward pro-inflammatory M1-type macrophages with high conversion efficiency.Reprogrammed M1 macrophages possessing protein-expression profiles similar to those of classically activated M1 macrophages display significantly increased phagocytic function and robust cross-presentation ability,potentiating antitumor immunity surrounding the tumor.Strikingly,these M1-Exo also lead to the conversion of human patient-derived TAMs into M1-like macrophages that highly express MHC class II,offering the clinical potential of autologous and allogeneic exosome-guided direct TAM reprogramming for arming macrophages to join the fight against cancer.

A novel method for extracting vanadium by low temperature sodium roasting from converter vanadium slag

Long-term high temperature in conventional vanadium extraction process would cause particles to be sintered and wrapped, thus reducing extraction efficiency of vanadium. Based on the purpose of directional conversion and process intensification, this work proposed a combination of low temperature sodium roasting and high efficiency selective oxidation leaching in vanadium extraction. The investigation of the reaction mechanism suggested that the structure of vanadium slag was changed by roasting, which also caused the fracture of spinel.The addition of MnO2 promoted the directional oxidation of low-valent vanadium into high valence. It also found that Na2S2O8 could oxidize low-valent vanadium effectively in leaching. The leaching efficiency of vanadium reached 87.74% under the optimum conditions, including a roasting temperature of 650 ℃, a roasting time of 2.0 h, a molar ratio of sodium-to-vanadium of 0.6, a MnO2(roasting additive) dosage of 5 wt% and a Na2S2O8(leaching oxidant) dosage of 5 wt%. This percentage is 7.18% higher than that of direct roasting-andleaching under the same conditions.

Direct lineage conversion of astrocytes to induced neural stem cells or neurons

Since the generation of induced pluripotent stem cells in 2006, cellular reprogramming has attracted increasing attention as a revolutionary strategy for cell replacement therapy. Recent advances have revealed that somatic cells can be directly converted into other mature cell types, which eliminates the risk of neoplasia and the generation of undesired cell types. Astrocytes become reactive and undergo proliferation, which hampers axon regeneration following injury, stroke, and neurodegenerative diseases. An emerging technique to directly reprogram astrocytes into induced neural stem cells （iNSCs） and induced neurons （iNs） by neural fate determinants brings potential hope to cell replacement therapy for the above neurological problems. Here, we discuss the development of direct reprogramming of various cell types into iNs and iNSCs, then detail astrocyte-derived iNSCs and iNs in vivo and in vitro. Finally, we highlight the unsolved challenges and opportunities for improvement.

WEIGHTED L^p-APPROXIMATION BY THE MODIFIED NEVAI OPERATORS

The present paper gives a Jackson type estimate for Nevai operators under weighted L^p norm, and establishes the direct and converse theorems in some proper Besov spaces

Approximation of Generalized Bernstein Operators

This paper is devoted to study direct and converse approximation theorems of the generalized Bemstein operators Cn （f, sn,x） via so-called unified modulus ωφλ^2 （f,t）, 0 ≤ λ ≤1. We obtain main results as followsωφλ^2 （f,t）=O（t^α）←→｜Cn（f,sn,x）-f（x）｜=O（（n^-1/2δn^1-λ（x））^α）,where δn^2（x）=max{φ^2（x）,1/n} and 0〈α〈2.

IMPACT OF WIDE-BAND I/Q MODULATION ERRORS IN SAR IMAGING ANALYSIS AND COMPENSATION METHOD RESAERCH

Direct quadrature modulation technology is suitable for wide-band radar signal generation. However, this method has rigorous requirements on amplitude and phase balance of the orthogonal input signals. If the requirements are not satisfied, there would be modulation errors such as image frequency and oscillator leakage that cannot be filtered. The modulation errors will therefore raise the noise floor of the range profile and reduce the dynamic range of the Synthetic Aperture Radar (SAR) image as a whole. In this paper, the wide-band In-phase/Quadrature-phase (I/Q) modulation errors are modeling analyzed, and the influence of wide-band I/Q modulation errors on SAR imaging is discussed. Furthermore, a compensation method of modulation errors is proposed, and the circuit implementation of the radar signal generation and pre-distortion is presented. The experimental results illustrate that the curves of the I/Q amplitude and phase imbalance errors are successfully extracted and the rejection of image frequency improved significantly, thus meets the requirements of the SAR imaging.

Folded down-conversion mixer for a 60 GHz receiver architecture in 65-nm CMOS technology

We present the design of a folded down-conversion mixer which is incorporated at the final down-conversion stage of a 60 GHz receiver. The mixer employs an ac-coupled current reuse transconductance stage. It performs well under low supply voltages, and is less sensitive to temperature variations and process spread. The mixer operates at an input radio frequency(RF) band ranging from 10.25 to 13.75 GHz, with a fixed local oscillator(LO) frequency of 12 GHz, which down-converts the RF band to an intermediate frequency(IF) band ranging from dc to 1.75 GHz. The mixer is designed in a 65 nm low power(LP) CMOS process with an active chip area of only 0.0179 mm2. At a nominal supply voltage of 1.2 V and an IF of 10 MHz, a maximum voltage conversion gain(VCG) of 9.8 d B, a double sideband noise figure(DSB-NF) of 11.6 d B, and a linearity in terms of input 1 d B compression point(Pin,1d B) of-13 d Bm are measured. The mixer draws a current of 5 m A from a 1.2 V supply dissipating a power of only 6 m W.

Transition metal-catalyzed conversion of aldehydes to ketones

Ketones are one of the most important classes of organic compounds, and widely present in various pharmacological compounds, biologically active molecules and functional materials. Over the past few decades, transition metal-catalyzed conversion of aldehydes has been found to be a powerful method.With the continuous development in recent years, it has become an efficient and uncomplicated strategy for constructing ketones. There are four major mechanisms for transition metal-catalyzed ketone synthesis from aldehyde:(1) carbonyl-Heck reaction, that is 1,2-insertion of organometal species to aldehydic C=O double bond,(2) direct insertion of transition metal catalysts to aldehydic C-H bond,(3) aldehyde as acyl radical,(4) aldehyde as carbon radical acceptor. This article summarizes related reports on the transformations of aldehydes to generate corresponding ketones under different reaction conditions.