139 research outputs found
A Dem Study of the Reduction of Volumetric Flow in Bubbling Fluidized Bed Methanation Reactors
Direct structural identification of carbenium ions and investigation of host-guest interaction in the methanol to olefins reaction obtained by multinuclear NMR correlations
Probing and determining the intermediates formed during catalytic reactions in heterogeneous catalysis are strong challenges. Using C-13 labelling and two dimensional C-13-C-13 through-bond NMR correlations, we directly reveal the structures of a range of carbenium ion species formed during the conversion of methanol to olefins on acidic H-ZSM-5 zeolite by mapping the carbon-carbon bond connectivities. Additionally, we use C-13-Al-27 and Si-29-C-13 through-space NMR experiments to probe the interactions between the confined carbon species (including carbenium ions) and the framework of the zeolite, which quantitatively provide an estimate for the carbon-aluminium and carbon-silicon distances, respectively
Anchor-Free Localization Method for Mobile Targets in Coal Mine Wireless Sensor Networks
Severe natural conditions and complex terrain make it difficult to apply precise localization in underground mines. In this paper, an anchor-free localization method for mobile targets is proposed based on non-metric multi-dimensional scaling (Multi-dimensional Scaling: MDS) and rank sequence. Firstly, a coal mine wireless sensor network is constructed in underground mines based on the ZigBee technology. Then a non-metric MDS algorithm is imported to estimate the reference nodes’ location. Finally, an improved sequence-based localization algorithm is presented to complete precise localization for mobile targets. The proposed method is tested through simulations with 100 nodes, outdoor experiments with 15 ZigBee physical nodes, and the experiments in the mine gas explosion laboratory with 12 ZigBee nodes. Experimental results show that our method has better localization accuracy and is more robust in underground mines
TINGKAT KEMAMPUAN SISWA TERHADAP MATERIRNMENGHARGAI PENINGGALAN SEJARAHRNKELAS IV SDN GUGUS MONTASIK
Banda Ace
Fast detection and structural identification of carbocations on zeolites by dynamic nuclear polarization enhanced solid-state NMR
Acidic zeolites are porous aluminosilicates used in a wide range of industrial processes such as adsorption and catalysis. The formation of carbocation intermediates plays a key role in reactivity, selectivity and deactivation in heterogeneous catalytic processes. However, the observation and determination of carbocations remain a significant challenge in heterogeneous catalysis due to the lack of selective techniques of sufficient sensitivity to detect their low concentrations. Here, we combine 13C isotopic enrichment and efficient dynamic nuclear polarization magic angle spinning nuclear magnetic resonance spectroscopy to detect carbocations in zeolites. We use two dimensional 13C–13C through-bond correlations to establish their structures and 29Si–13C through-space experiments to quantitatively probe the interaction between multiple surface sites of the zeolites and the confined hydrocarbon pool species. We show that a range of various membered ring carbocations are intermediates in the methanol to hydrocarbons reaction catalysed by different microstructural β-zeolites and highlight that different reaction routes for the formation of both targeted hydrocarbon products and coke exist. These species have strong van der Waals interaction with the zeolite framework demonstrating that their accumulation in the channels of the zeolites leads to deactivation. These results enable understanding of deactivation pathways and open up opportunities for the design of catalysts with improved performances
Energy loss enhancement of very intense proton beams in dense matter due to the beam-density effect
Thoroughly understanding the transport and energy loss of intense ion beams
in dense matter is essential for high-energy-density physics and inertial
confinement fusion. Here, we report a stopping power experiment with a
high-intensity laser-driven proton beam in cold, dense matter. The measured
energy loss is one order of magnitude higher than the expectation of individual
particle stopping models. We attribute this finding to the proximity of beam
ions to each other, which is usually insignificant for relatively-low-current
beams from classical accelerators. The ionization of the cold target by the
intense ion beam is important for the stopping power calculation and has been
considered using proper ionization cross section data. Final theoretical values
agree well with the experimental results. Additionally, we extend the stopping
power calculation for intense ion beams to plasma scenario based on Ohm's law.
Both the proximity- and the Ohmic effect can enhance the energy loss of intense
beams in dense matter, which are also summarized as the beam-density effect.
This finding is useful for the stopping power estimation of intense beams and
significant to fast ignition fusion driven by intense ion beams
How Foreign Direct Investment Promotes Development: The Case of the People's Republic of China's Inward and Outward FDI
Target density effects on charge tansfer of laser-accelerated carbon ions in dense plasma
We report on charge state measurements of laser-accelerated carbon ions in
the energy range of several MeV penetrating a dense partially ionized plasma.
The plasma was generated by irradiation of a foam target with laser-induced
hohlraum radiation in the soft X-ray regime. We used the tri-cellulose acetate
(CHO) foam of 2 mg/cm density, and -mm interaction
length as target material. This kind of plasma is advantageous for
high-precision measurements, due to good uniformity and long lifetime compared
to the ion pulse length and the interaction duration. The plasma parameters
were diagnosed to be T=17 eV and n=4 10 cm.
The average charge states passing through the plasma were observed to be higher
than those predicted by the commonly-used semiempirical formula. Through
solving the rate equations, we attribute the enhancement to the target density
effects which will increase the ionization rates on one hand and reduce the
electron capture rates on the other hand. In previsous measurement with
partially ionized plasma from gas discharge and z-pinch to laser direct
irradiation, no target density effects were ever demonstrated. For the first
time, we were able to experimentally prove that target density effects start to
play a significant role in plasma near the critical density of Nd-Glass laser
radiation. The finding is important for heavy ion beam driven high energy
density physics and fast ignitions.Comment: 7 pages, 4 figures, 35 conference
The Main Progress of Perovskite Solar Cells in 2020–2021
Perovskite solar cells (PSCs) emerging as a promising photovoltaic technology with high efficiency and low manufacturing cost have attracted the attention from all over the world. Both the efficiency and stability of PSCs have increased steadily in recent years, and the research on reducing lead leakage and developing eco-friendly lead-free perovskites pushes forward the commercialization of PSCs step by step. This review summarizes the main progress of PSCs in 2020 and 2021 from the aspects of efficiency, stability, perovskite-based tandem devices, and lead-free PSCs. Moreover, a brief discussion on the development of PSC modules and its challenges toward practical application is provided
All-Trans Retinoic Acid Promotes TGF-β-Induced Tregs via Histone Modification but Not DNA Demethylation on Foxp3 Gene Locus
It has been documented all-trans retinoic acid (atRA) promotes the development of TGF-β-induced CD4(+)Foxp3(+) regulatory T cells (iTreg) that play a vital role in the prevention of autoimmune responses, however, molecular mechanisms involved remain elusive. Our objective, therefore, was to determine how atRA promotes the differentiation of iTregs.Addition of atRA to naïve CD4(+)CD25(-) cells stimulated with anti-CD3/CD28 antibodies in the presence of TGF-β not only increased Foxp3(+) iTreg differentiation, but maintained Foxp3 expression through apoptosis inhibition. atRA/TGF-β-treated CD4(+) cells developed complete anergy and displayed increased suppressive activity. Infusion of atRA/TGF-β-treated CD4(+) cells resulted in the greater effects on suppressing symptoms and protecting the survival of chronic GVHD mice with typical lupus-like syndromes than did CD4(+) cells treated with TGF-β alone. atRA did not significantly affect the phosphorylation levels of Smad2/3 and still promoted iTreg differentiation in CD4(+) cells isolated from Smad3 KO and Smad2 conditional KO mice. Conversely, atRA markedly increased ERK1/2 activation, and blockade of ERK1/2 signaling completely abolished the enhanced effects of atRA on Foxp3 expression. Moreover, atRA significantly increased histone methylation and acetylation within the promoter and conserved non-coding DNA sequence (CNS) elements at the Foxp3 gene locus and the recruitment of phosphor-RNA polymerase II, while DNA methylation in the CNS3 was not significantly altered.We have identified the cellular and molecular mechanism(s) by which atRA promotes the development and maintenance of iTregs. These results will help to enhance the quantity and quality of development of iTregs and may provide novel insights into clinical cell therapy for patients with autoimmune diseases and those needing organ transplantation
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