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1.
Direct RF sampling receiver – a fully digital receiver architecture – undoubtedly becomes a favored choice for HF/VHF as this approach inherently bypasses the legacy nonlinearities caused by analog components. In DRF-RF and wideband multichannel in general, LNA is still an indispensable component to ensure the receiver’s sensitivity. However, with the presence of multiple channels, the total RF power often surpasses the linear threshold that LNA and the amplified signal become severely distorted. This paper proposed a method for mitigating the LNA distortion using the look-up table (LUT) approach. Specifically, our receiver is designed with two modes of operation. In training mode, a built-in signal circuit generates a training signal for extracting the LNA characteristic and eventually reconstructs the inverse LNA nonlinear model in the form of a LUT memory. During the receiving mode, a linearization circuit reverses the distortion impact by matching the RF power level with the inverse nonlinear model pre-stored in the LUT. The effectiveness of the proposed distortion compensation method first is evaluated by a MATLAB simulation with a multi-channel DRF-RF model. The simulation results show that the proposed approach significantly improved the SNDR for the channel of interest. Furthermore, the model has been practically verified, where the actual distorted signals are sampled from a commercial LNA (ZFL-500LN+) by a customized FPGA board. Results from measurements show an improvement of 7 dB for SNDR and 27% for EVM in a strong distortion scenario of QPSK modulation signal.  相似文献   
2.
Proppants transport is an advanced technique to improve the hydraulic fracture phenomenon, in order to promote the versatility of gas/oil reservoirs. A numerical simulation of proppants transport at both hydraulic fracture (HF) and natural fracture (NF) intersection is performed to provide a better understanding of key factors which cause, or contribute to proppants transport in HF–NF intersection. Computational fluid dynamics (CFD) in association with discrete element method (DEM) is used to model the complex interactions between proppant particles, host fluid medium and fractured walls. The effect of non-spherical geometry of particles is considered in this model, using the multi-sphere method. All interaction forces between fluid flow and particles are considered in the computational model. Moreover, the interactions of particle–particle and particle–wall are taken into account via Hertz–Mindlin model. The results of the CFD-DEM simulations are compared to the experimental data. It is found that the CFD-DEM simulation is capable of predicting proppant transport and deposition quality at intersections which are in agreement with experimental data. The results indicate that the HF–NF intersection type, fluid velocity and NF aperture affect the quality of blockage occurrence, presenting a new index, called the blockage coefficient which indicates the severity of the blockage.  相似文献   
3.
Molecular structure and vibrational spectroscopic studies of higher homologous series nematogenic p-n-alkylbenzoic acids (nBAC) that have 6 (6BAC) and 7 (7BAC) carbon atoms in the alkyl chain have been investigated using the Density Functional Becke3-Lee-Yang-Parr (B3LYP) level with the basis set 6-31++G (d.p) and Hartree Fock (HF) with the same basis set. The observed vibrational spectra has been resolved and assigned in detail for comparision with both the molecules. These results indicate that DFT and HF values are slightly different at both the levels. A comparision of chemical reactivity such as HOMO (EH), LUMO (EL) energies, energy gap (Eg), ionization energy (I), electron affinity (A), electro negativity (χ), chemical hardness (η), electronic chemical potential (μ), electrophilicity index (ω), and softness (S) has been made. It has been observed that the decrement has occurred in the energy band gap value of isolated molecule with increment in alkyl chain length. This provides valuable information regarding enhancing the stability of liquid crystal materials by maintaining the conductivity.  相似文献   
4.
Flunitrazepam (FNZ) is a potent hypnotic, sedative, and amnestic drug used to treat severe insomnia. In our recent study, FNZ metabolic profiles were investigated carefully. Six authentic human urine samples were purified using solid phase extraction (SPE) without enzymatic hydrolysis, and urine extracts were then analyzed by liquid chromatography‐Q exactive‐HF hybrid quadrupole‐Orbitrap‐mass spectrometry (LC‐QE‐HF‐MS), using the full scan positive ion mode and targeted MS/MS (ddms2) technique to make accurate mass measurements. There were 25 metabolites, including 13 phase I and 12 phase II metabolites, which were detected and tentatively identified by LC‐QE‐HF‐MS. In addition, nine previously unreported phase II glucuronide conjugates and four phase I metabolites are reported here for the first time. Eight metabolic pathways, including N‐reduction and O‐reduction, N‐glucuronidation, O‐glucuronidation, mono‐hydroxylation and di‐hydroxylation, demethylation, acetylation, and combinations, were implicated in this work, and 2‐O‐reduction together with dihydroxylation were two novel metabolic pathways for FNZ that were identified tentatively. Although 7‐amino FNZ is widely considered to be the primary metabolite, a previously unreported metabolites (M12) can also serve as a potential biomarker for FNZ misuse.  相似文献   
5.
6.
Microfabricated silica thin layer chromatography (TLC) plates have previously been prepared on patterned carbon nanotube forests. The high temperatures used in their fabrication reduce the number of hydroxyl groups on their surfaces. Fortunately, silica can be rehydroxylated. In diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), a silanol peak below 3740 cm?1 indicates a well‐hydroxylated silica surface that is fit for chromatography. Hydroxylations of our materials with HF are so effective that it is not possible to discern the position of this peak. In contrast, this signal is discernable when the plates are treated with NH4OH. To find a more convenient method for studying the surfaces of TLC plates, time‐of‐flight secondary ion mass spectroscopy (ToF‐SIMS) was considered. ToF‐SIMS is advantageous because multiple microfabricated TLC plates must be scraped to obtain enough silica for one DRIFT analysis, while static SIMS can be performed on very small regions (500 × 500 µm2 or less) of individual plates. Ratios of the SiOH+ and Si+ ToF‐SIMS signals for microfabricated TLC plates correlated well with ~3740 cm?1 silanol peaks from DRIFT. Thus, SIMS allows direct analysis of all of our treated and untreated plates, including those hydroxylated with HF. The best hydroxylation condition for HF, which was better than any studied for NH4OH, was around 150 ppm at room temperature. The best hydroxylation condition for NH4OH was 50 °C for 72 h. ToF‐SIMS versus DRIFT results of commercial TLC plates were also obtained and evaluated. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
7.
The very strong Lewis acid aluminium chlorofluoride (ACF) was loaded with anhydrous HF. The interaction between the surface of the catalyst and HF was investigated using a variety of characterization methods, which revealed the formation of polyfluorides. Moreover, the reactivity of the HF-loaded ACF towards the hydrofluorination of alkynes was studied.  相似文献   
8.
In the present work, an extended Hulburt–Hirschfelder oscillator model is proposed as a means of simplifying potential energy functions for direct‐potential‐fit analyses. The new potential energy function is joined smoothly to the long‐range inverse‐power dispersion energy expression. The new model is employed in direct‐potential‐fits using spectroscopic line positions that involve the ground electronic states of the principal isotopologues of hydrogen iodide and carbon monoxide, and the ground and first singlet‐sigma excited states of hydrogen fluoride and hydrogen chloride. The present methodology is found to lead to compact, flexible, and robust representations for the potential energy that compare favorably with the results of past work where more complicated models were employed.  相似文献   
9.
As a rising star among porous solid materials, covalent organic frameworks(COFs) with excellent properties including but not limit to facilely controllable structure, high porosity, and multi-chemical functionality represent significant potential for efficient 127Xe/85Kr capture and separation. In this study, through tuning the length of the organic ligands, two-dimensional(2D) COF mate-rials with identical connection group but different pore properties, denoted as ATFG-COF and TpPa-COF with AA-stacking model and TpBD-COF with AB-stacking model were synthesized and tested for Kr and Xe adsorption for the first time. Adsorption measurements indicate that the narrower pore apertures and higher porosity are conducive for COF materials to capture Xe and Kr. Furthermore, the Henry's constant, isosteric heat of adsorption(Qst), and ideal adsorbed solution theory(IAST) selectivity of ATFG-COF, the pore size of which is closest to the kinetic diameter of the Xe atom(0.41 nm) among 2D COF materials, were carried out based on the single component sorption isotherms. The results illustrate that the high isosteric heat values of Xe/Kr adsorption on ATFG-COF are 25 and 16 kJ/mol at room temperature, respectively. Henry's law predicts that the selectivity factor of Xe to Kr is 6.07, consistent with the adsorption selectivity(ca. 6) calculated based on the IAST.  相似文献   
10.
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