Results 1 - 10 of 142
Results 1 - 10 of 142. Search took: 0.02 seconds
|Sort by: date | relevance|
[en] The neutralization of H- beam with a gas like Xe is an important part of low energy beam transport (LEBT). It is well known that choppers which use an electric field when placed in the LEBT strongly affects the neutralization of H-. The question then naturally arises as to whether a magnetic chopper has a better neutralization time than an electric chopper. To answer this question, a simple 1-space, 1 time drift-diffusion model of H- beam in Xe gas has been used to calculate the neutralization times for the following scenarios: (a) a region initially cleared of Xe+ ions with an electric field but partially neutralized outside, (b) a region within and outside the chopper which is initially partially neutralized.
[en] A finite-difference pseudopotential density-functional theory in real space and Langevin molecular dynamics annealing technique are applied to determine the ground state structure of sulfur cluster S7 and the corresponding optical absorption spectra from a linear response method within the adiabatic time-dependent local density approximation. It is found that the ground state structure of sulfur cluster S7 belongs to a chair structure with Cs symmetry and the calculated spectra exhibit a variety of features that can be used for comparison against future experimental investigations
[en] Although the interactions of soft x-rays and hard x-rays with polymers are fundamentally the same and are characterized by absorption and phase shifts, the relative and absolute strength of these interactions as a function of photon energy has profound practical implications. We delineate the basic physics of x-ray interactions with polymers as expressed in the optical constants of polymeric materials and exemplify the resulting advantages of soft x-rays over hard x-rays for real space and reciprocal space characterization methods in the context of a number of recent and ongoing applications. A perspective on future capabilities and applications will be provided.
[en] Highlights: • The sensing strategy is based on cleavage reaction of target-assistant Zn"2"+-dependent DNAzyme. • A dual quenching mechanism of ECL is identified. • A sensitive and selective ECL sensor is constructed for detection of ATP. • The biosensor can detect ATP in serum samples with good accuracy. - Abstract: A signal-on electrochemiluminescent (ECL) approach for ultrasensitive ATP detection was developed using target-assistant Zn"2"+-dependent DNAzyme via a dual quenching pathway between quantum dots (QDs) and Au nanoclusters (Au NCs). The facile ECL biosensor was constructed by covalent assembly of Au NCs-labeled hairpin DNA on QDs modified glassy carbon electrode. A dual quenching ECL mechanism was identified to be via resonance energy transfer between QDs and Au NCs and electrocatalytic reduction of coreactant oxygen by Au NCs. With the assistance of two help DNAs, the G-quadruplex structure of ATP aptamer was formed, and thus narrowed the two fragments of Zn"2"+-dependent DNAzyme. In the presence of Zn"2"+, Zn"2"+-dependent DNAzyme can be generated in situ on the biosensor's surface. The as-prepared DNAzyme can cleave the substrate strand, and release the Au NCs from the electrode, resulting in the signal-on ECL state. This biosensor showed good analytical performance with 4 orders magnitude linear range, excellent specificity, and acceptable stability. The biosensor had been applied in detection of ATP in real serum sample and provided significant potential application in clinical analysis
[en] A detailed chemical kinetic mechanism based on the Appel-Bockhorn-Frenklach (ABF) model was established to describe acetylene decomposition, ethylene formation, and soot formation during quenching in coal pyrolysis to acetylene process. The predictions agreed well with the reported acetylene pyrolysis experimental data. Numerical simulations were then performed to deeply understand the reaction behaviors during quenching of coal pyrolysis in thermal plasma, and to optimize the quenching design for better heat recovery. Two key operating parameters of quenching, i.e., the temperature after quenching and the quenching rate, were studied in detail and optimized after the kinetics were validated. The simulation results also proved that hydrogen can promote the formation of ethylene and inhibit the condensation of acetylene during quenching. In particular, in-depth discussion of acetylene decomposition and ethylene formation using this detailed kinetic mechanism combined with thermodynamic method provided a comprehensive understanding of the thermodynamics and kinetics interpreting pilot plant experimental data. - Highlights: • A detailed kinetic model for C_2H_2 decomposition and soot formation is established. • Two key operating parameters of quenching are studied in detail and optimized. • Effects of H_2 on C_2H_4 formation and C_2H_2 condensation during quenching are discussed. • A comprehensive understanding of the pilot plant experimental data is achieved.
[en] Pressurizer is one of key components in nuclear power system. It's important to control the dimension in the design of pressurizer through optimization techniques. In this work, a mathematic model of a vertical electric heating pressurizer was established. A new Genetic-Simplex Algorithm (GSA) that combines genetic algorithm and simplex algorithm was developed to enhance the searching ability, and the comparison among modified and original algorithms is conducted by calculating the benchmark function. Furthermore, the optimization design of pressurizer, taking minimization of volume and net weight as objectives, was carried out considering thermal-hydraulic and geometric constraints through GSA. The results indicate that the mathematical model is agreeable for the pressurizer and the new algorithm is more effective than the traditional genetic algorithm. The optimization design shows obvious validity and can provide guidance for real engineering design
[en] Highlights: • Tricin is a valuable pharmaceutical compound. • The solubility of tricin increases with an increase in temperature. • The solubility of tricin increases with an enrichment in ethanol content. • Two models were well correlated the solubility data. - Abstract: The solubility of tricin in water and ethanol mixtures was measured over the temperature range of (288.15 to 328.15) K. The concentrations of tricin in the aqueous mixtures were assayed by the ultraviolet spectrophotometric method. The experimental solubility data indicated that the solubility of tricin increases with an increase in temperature and an enrichment in ethanol content. The two models, including the modified Apelblat equation and λh equation were used to correlate the experimental solubility data. The calculated solubility of tricin shows good agreement with the experimental results. Additionally, the estimation of thermodynamic properties including the activity coefficients, dissolution enthalpy, and entropy were obtained from the experimental data. Within the studied temperature range the dissolution process of tricin is endothermic, and the driving force is the entropy
[en] Highlights: • Aloe-emodin is a bioactive anthraquinone compound. • The solubility of aloe-emodin increases with an increase in temperature. • 1-Pentanol is a suitable solvent for industrial preparation of aloe-emodin. • Two models were well correlated the solubility data. - Abstract: The solubility of aloe-emodin in seven pure solvents namely water, methanol, ethanol, 1-propanol, 1-butanol, 2-butanol, and 1-pentanol was measured by a static analytic method. The measurements were carried out over the temperature range from (278.15 to 318.15) K at 5 K intervals under atmospheric pressure using a UV/vis spectrophotometer analysis. The effects of experimental temperature and solvent type on the solubility are discussed. The relative solubility of aloe-emodin in seven solvents was determined in elevated order to be x_w_a_t_e_r < x_m_e_t_h_a_n_o_l < x_e_t_h_a_n_o_l < x_2_-_b_u_t_a_n_o_l < x_1_-_p_r_o_p_a_n_o_l < x_1_-_b_u_t_a_n_o_l < x_1_-_p_e_n_t_a_n_o_l. The experimental result shows that 1-pentanol could be a suitable solvent for industrial preparation of aloe-emodin. The experimental solubility values were correlated with the modified Apelblat and λh models. It was found that the two empirical thermodynamic models can satisfactorily correlate the solubility of aloe-emodin in the seven solvents over the range of temperature studied.
[en] The X-rays generated and transported in target bombarded by electron beams in CT have been simulated with Monte Carlo code MCNP4. Photon efficiencies and forward directional characteristics of X-rays for several kinds of often-used targets were calculated and analyzed. Calculations show that as the thickness of the target increases, the photon efficiency increases and reaches a maximum, and then drops sharply for gold and tungsten target, while drops gently for cooper target. Also, the photon efficiency for cooper target is relatively small, but the angular distribution shows good forward directional characteristics, with the dose rate in the forward direction equivalent to those of tungsten or gold target. Experiment results show that the dose rate in the forward direction of a copper target is higher than that of a tungsten target for 20 MeV electrons, while the angular distribution presents better forward directional characteristics compared with a tungsten target. (authors)
[en] Nitrobenzene (NB), a widely used industrial chemical, is a likely human carcinogen. Many dietary constituents can suppress the DNA-adduction, acting as the inhibitors of cancer. In this study, we investigated the inhibitory effects of vitamin C (VC), vitamin E (VE), tea polyphenols (TP), garlic squeeze, curcumin, and grapestone extract on NB-DNA and NB-hemoglobin (Hb) adductions in mice using an ultrasensitive method of accelerator mass spectrometry (AMS) with 14C-labelled nitrobenzene. All of these dietary constituents showed their inhibitory effects on DNA or Hb adduction. VC, VE, TP and grapestone extract could efficaciously inhibit the adductions by 33-50%, and all of these six agents could inhibit Hb adduction by 30-64%. We also investigated resveratrol, curcumin, VC and VE as inhibitors of NB-DNA adduction in vitro using liquid scintillation counting technique. These agents in the presence of NADPH and S9 components also pronouncedly blocked DNA adduction in a dose-dependent profile. Our study suggests that these seven constituents may interrupt the process of NB-induced chemical carcinogenesis