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排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Zhicheng Wang Yaw D. Yeboah Tiejun Bai Kofi B. Bota 《Plasma Chemistry and Plasma Processing》2004,24(3):405-420
Given the operational constraints of aerospace ground equipments (AGE), the nonthermal plasma discharge (NTPD) has been identified as a promising technology for their NOx removal. As part of a program to optimize an NTPD system for this particular application, an investigation of the effect of discharge gap spacing on the electrical and chemical processes that occur in NTPDs was initiated. A number of experiments were performed to examine how the gap spacing affects the NO removal efficiency, discharge characteristics, and chemical reactions in a NTPD device. Gap spacings ranging from 0.8 to 4.0 mm were investigated in this study. An optimum gap spacing for NO removal was observed at approximately 2 mm and, based on the experimental data, a physical explanation for the optimum was developed. The experiments, results and conclusions are discusssed in detail in this paper. 相似文献
982.
In the present study, the acid-base equilibria of N,O-carboxymethy chitosan abbreviated as (NOCC), is investigated. The complex
formation equilibria with the metal ions Cu(II), Ni(II), Co(II), Mn(II), and Zn(II) are investigated potentiometrically. The stability constant values of the binary and ternary complexes formed in solution
were determined and the binding centers of the ligands were assigned. The relationships between the properties of the studied
central metal ions as ionic radius, electronegativity, atomic number, and ionization potential, and the stability constants
of the formed complexes were investigated in an effort to give information about the nature of chemical bonding in complexes
and make possible the calculation of unknown stability constants. Cu(II), Ni(II), and U(VI) complexes with NOCC are isolated as solid complexes and characterized by conventional chemical and physical methods. The
structures of the isolated solid complexes are proposed on the basis of the spectral and magnetic studies. The ternary copper(II)
complexes involving NOCC and various biologically relevant ligands containing different functional groups, as amino acids
and DNA constituents are investigated. The stability constants of the complexes are determined and the concentration distribution
diagrams of the complexes are evaluated. 相似文献
983.
Sun YX Huang YX Li FL Wang HY Fan C Bao YL Sun LG Ma ZQ Kong J Li YX 《Chemistry Central journal》2012,6(1):2
Background
The virtual screening (VS) of lead compounds using molecular docking and pharmacophore detection is now an important tool in drug discovery. VS tasks typically require a combination of several software tools and a molecular graphics system. Thus, the integration of all the requisite tools in a single operating environment could reduce the complexity of running VS experiments. However, only a few freely available integrated software platforms have been developed. 相似文献984.
Kamal YT Mohammed Musthaba S Singh M Parveen R Ahmad S Baboota S Ali I Siddiqui KM Arif Zaidi SM 《Biomedical chromatography : BMC》2012,26(10):1183-1190
An attempt has been made to develop and validate a simultaneous HPLC method for novel approach of drug release via oil‐in‐water (o/w) nanoemulsion formulation and Habb‐e‐Khardal Unani tablet containing piperine and guggul sterones E and Z as main ingredients. Nanoemulsion was prepared by titration method using sefsol‐218 as an oily phase, cremophor‐EL as a surfactant, transcutol as a co‐surfactant and distilled water as an aqueous phase. The formulation was optimized on the basis of thermodynamic stability and dispersibilty test. The nanoformulation was evaluated for particle size, surface morphology, electrical conductivity and viscosity determination. The in vitro dissolution was carried out by dialysis bag method. Drugs were quantified using an HPLC method developed in‐house with a C18 column as stationary phase and acetonitrile and water as mobile phase at λmax of 240 nm. The optimized formulation showed higher drug release, lower droplet size and less viscosity as compared with the conventional Habb‐e‐Khardal Unani tablet. The present study illustrated the potential of nanoemulsion dosage form in improving biopharmaceutic performance of piperine and guggul sterone. The HPLC method was also found to be quite sufficient for the routine quality control of formulations containing piperine and guggul sterone E and Z as ingredients and also for in vitro drug release studies. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
985.
Structural characterization of intact proteins is enhanced by prevalent fragmentation pathways rarely observed for peptides 总被引:2,自引:0,他引:2
Jennifer S. Cobb Michael L. Easterling Jeffrey N. Agar 《Journal of the American Society for Mass Spectrometry》2010,21(6):949-959
While collisionally activated dissociation (CAD) pathways for peptides are well characterized, those of intact proteins are
not. We systematically assigned CAD product ions of ubiquitin, myoglobin, and bovine serum albumin generated using high-yield,
in-source fragmentation. Assignment of >98% of hundreds of product ions implies that the fragmentation pathways described
are representative of the major pathways. Protein dissociation mechanisms were found to be modulated by both source declustering
potential and precursor ion charge state. Like peptides, higher charge states of proteins fragmented at lower energies next
to Pro, via mobile protons, while lower charge states fragmented at higher energies after Asp and Glu, via localized protons.
Unlike peptides, however, predominant fragmentation channels of proteins occurred at intermediate charge states via non-canonical
mechanisms and produced extensive internal fragmentation. The non-canonical mechanisms include prominent cleavages C-terminal
to Pro and Asn, and N-terminal to Ile, Leu, and Ser; these cleavages, along with internal fragments, led to a 45% increase
in sequence coverage, improving the specificity of top-down protein identification. Three applications take advantage of the
different mechanisms of protein fragmentation. First, modulation of declustering potential selectively fragments different
charge states, allowing the source region to be used as the first stage of a low-resolution tandem mass spectrometer, facilitating
pseudo-MS3 of product ions with known parent charge states. Second, development and integration of automated modulation of
ion funnel declustering potential allows users access to a particular fragmentation mechanism, yielding facile cleavage on
a liquid chromatography timescale. Third, augmentation of a top-down search engine improved protein characterization. 相似文献
986.
We studied cycle time (0.01–10 s with triangular input waves) and poling history (continuous versus fresh poling) dependent electric energy storage and discharge behaviors in poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] films using the electric displacement ― the electric field (D-E) hysteresis loop measurements. Since the permanent dipoles in PVDF are orientational in nature, it is generally considered that both charging and discharging processes should be time and poling history dependent. Intriguingly, our experimental results showed that the charging process depended heavily on the cycle time and the prior poling history, and thus the D-E hysteresis loops had different shapes accordingly. However, the discharged energy density did not change no matter how the D-E loop shape varied due to different measurements. This experimental result could be explained in terms of reversible and irreversible polarizations. The reversible polarization could be charged and discharged fairly quickly (< 5 ms for each process), while the irreversible polarization depended heavily on the poling time and the prior poling history. This study suggests that it is only meaningful to compare the discharged energy density for PVDF and its copolymer films when different cycle times and poling histories are used. 相似文献
987.
Distribution of Heavy Metal Contents and Chemical Fractions in Anaerobically Digested Manure Slurry 总被引:9,自引:0,他引:9
Digested slurry samples from twenty-one large-scale anaerobic digestion plants together with intensive pig and dairy farms
in Jiangsu Province of China were collected and analyzed for total and dissolved concentrations of Zn, Cu and As, as well
as chemical characteristics. The results showed that total concentrations of Zn, Cu and As in digested pig slurries were concentrated
to <10, <5 and 0.02–0.1 mg/l, respectively; while <2 and 10–30, <1, and 0.02–0.1 mg/l, respectively, in digested dairy slurries.
Lowering the dietary supply of these elements to pig and dairy would be the most effective way to control heavy metal contents
in digested manure slurries. Dissolved fractions of Zn, Cu and As accounted for 1–74%, 1–33% and 2–53% of the total concentrations,
respectively, in digested pig slurries; and 18–65%, 12–58% and 3–68% in digested dairy slurries. The chemical fractions of
heavy metals in digested slurries were not only dependent on the total concentrations of heavy metals in raw manures but also
on conditions of digestion and storage. Oxidation pond systems could significantly cripple the total contents of heavy metals
in digested slurries, and the removal effect was better in multi-oxidation-pond systems than that in primary-oxidation-pond
systems. However, the chemical fractions of heavy metals in digested slurries changed in a complicated manner when stored
in oxidation ponds, due to the suspended solid deposition, elements reduction, as well as variations of pH values and oxidation-reduction
potential. 相似文献
988.
989.
One-step reaction compatibilized microfibrillar reinforced iPP/PET blends(CMRB) were successfully prepared through a "slit extrusion-hot stretching-quenching" process.Crystallization behavior and morphology of CMRB were systematically investigated.Scanning electronic microscopy(SEM) observations showed blurry interface of compatibilized common blend(CCB).The crystallization behavior of neat iPP,CCB,microfibrillar reinforced iPP/PET blend(MRB) and CMRB was investigated by differential scanning calorimetry(DSC) and polarized optical microscopy(POM).The increase of crystallization temperature and crystallization rate during nonisothermal crystallization process indicated both PET particles and microfibrils could serve as nucleating agents and PET microfibrils exhibited higher heterogeneous nucleation ability,which were also vividly revealed by results of POM.Compared with MRB sample,CMRB sample has lower crystallization temperature due to existence of PET microfibrils with smaller aspect ratio and wider distribution.In addition, since in situ compatibilizer tends to stay in the interphase,it could also hinder the diffusion of iPP molecules to the surface of PET phase,leading to decrease of crystallization rate.Two-dimensional wide-angle X-ray diffraction(2D-WAXD) was preformed to characterize the crystalline structure of the samples by injection molding,and it was found that well-developed PET microfibrils contained in MRB sample promoted formation ofβ-phase of iPP. 相似文献
990.
Garrido Frenich A Romero-González R Martínez Vidal JL Martínez Ocaña R Baquero Feria P 《Analytical and bioanalytical chemistry》2011,399(6):2043-2059
This work compares two miniaturised sample preparation methods, solid phase microextraction (SPME) and hollow fiber liquid
phase microextraction (HF-LPME), in combination with gas chromatography coupled to tandem mass spectrometry with a triple
quadrupole analyzer for the determination of 77 pesticides in drinking water. In the case of SPME, extraction temperature
and time were optimized by experimental design, although other parameters, as desorption time, pH, and ionic strength, were
also evaluated. The extraction and desorption solvents [octanol/dihexyl ether (75:25, v/v) and cyclohexane, respectively],
as well as the extraction and desorption time, ionic strength, and pH, were studied for the HF-LPME procedure. Under the optimal
conditions, recoveries (70.2–113.5% for SPME and 70.0–119.5% for HF-LPME), intra-day precision (2.1–19.4% for SPME and 4.3–22.5%
for HF-LPME), inter-day precision (5.2–21.5% for SPME and 8.4–27.3% for HF-LPME), and limits of detection, between 0.1 and
28.8 ng/L for SPME and 0.2 and 47.1 ng/L for HF-LPME and overall uncertainty (9.6–25.2% for SPME and 13.3–27.5% for HF-LPME)
were established for both extraction procedures. Finally, the proposed methods were successfully applied to the analysis of
41 drinking water samples, and similar results were obtained with both extraction approaches. 相似文献