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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 2 (1985), S. 160-165 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A dual gas flow chromatographic method is proposed. In this method, two different gas streams are introduced separately, one as the carrier gas and the other as the gas for creating the adsorption equilibrium. The thermodesorbed absorbate is eluted by a pure carrier gas. The complete curve of adsorption isotherm can be determined easily; therefore, both the specific area and the pore size distribution can be obtained at ordinary pressure. In addition, this method can be easily changed into the continuous flow method given by Nelsen and Eggertsen [1]. The relationship among R (rate) - V (volume) - A (area) - α (ratio) in elution chromatography are investigated, and the volume of desorbed gas can be obtained from Vd = KRAd directly with K = (αV)/(RA). The standardization for peak area is simplified and more convenient for the treatment by a microcomputer. Some results of specific surface area and pore size distribution by this method, and their comparison with those from other methods are given altogether, and the coincidence is good.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 3 (1986), S. 20-25 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Starting from Wheeler's composite theory, which takes both the multilayer adsorption and the capillary condensation into consideration, and assuming the equivalent cylindrical model, we have deduced a strict and relatively simpler formula for the calculation of pore size distribution by solving the integral equation directly. The formula is more convenient for application because of its recursion form. Following the same line of reasoning and using the mean value theorem of definite integrals under different conditions, we have unified the equations of Barrett-Joyner-Halenda, Dubinin, Cranston-Inkley, Dollimore-Heal and Roberts. A table of parameters which is required in the calculation is given. Besides the adsorption of nitrogen, the adsorption with water vapor as the adsorbate is investigated and the corresponding empirical equation of adsorption thickness is given.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 3 (1986), S. 81-88 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The modelless (ML) and micropore (MP) methods for the pore structure analysis of porous particles have been studied. Concerning the ML method, it has been shown that the Kiselev equation can only be used to describe condensation and evaporation in capillaries, but cannot be used to describe the increase and decrease of the thickness of the adsorption layer. Strictly speaking, therefore, the ML method is not modelless even for the pore core size distribution. A comparison between the ML method and methods using an equivalent pore model is given. The results of using the ML method in conjunction with a certain pore model are little less accurate than those obtained by adopting the equivalent pore model straightaway. The parameters required for the calculation of both the pore core size and the pore size distribution as well as the conversion between these two calculations are given.Concerning the MP method, it has been shown that the three types of v-t curves, the theoretical foundation of the MP method, are not in one to one correspondance to the three kinds of adsorption mechanism. From the viewpoint of accuracy, the MP method has no advantage over the methods which are based on the condensation mechanism, both have their own merits.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0959-8103
    Keywords: hydrolysis ; drug release ; IPN ; gel ; swelling ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper describes a novel hydrogel based on crosslinked chitosan with glutaraldehyde interpenetrating polyether polymer network. The gel can hydrolyse in acid at 37°C due to the cleavage of imine bonds within the network. At pH≥7, there is no hydrolysis. The pH-dependent release of cimetidine from the gel was also investigated.
    Additional Material: 7 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 1221-1228 
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The copolymerization of polypropene (PP) with maleic anhydride (MA) was carried out at 120°C in xylene with benzoyl peroxide (BPO) as initiator. The resulting product was identified as poly(propene-co-maleic anhydride) obtained by reaction of the double bond of maleic anhydride with free radicals created on the PP chain. In the next step this copolymer was reacted with functional poly(ε-caprolactone) (PCL) by a co-melting method to give rise to a graft copolymer. The optimum time for the second step was found to be around 6 h (at 120°C). X-ray diffraction measurements and DSC characterization of PP-g-PCL have shown that the melting point of the PP phase in the graft copolymers is lower than that of homopolypropene and that its glass transition temperature increases with increasing of PCL grafts.
    Additional Material: 6 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 3243-3252 
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Stable monolayers of a novel side-chain liquid crystalline polysiloxane (PI) and its monomer (MI), both having low transition temperatures, are formed at the air/water interface at 20°C. In monolayer films mesogens are packed closely and their long axes are titled slightly to the water surface. Monomer molecules are thought to lie flat on the water surface when they are initially spread, and a possible model is presented to describe the conformational changes after compressing. Multilayer formations have been observed during isothermal compression of both the polymer and the monomer. Monomer monolayers cannot be deposited onto hydrophobic substrates, whereas polymer monolayers can be deposited at various surface pressures with Y-type or Z-type. UV-Vis spectra of PI Langmuir-Blodgett films indicate that H-aggregates are formed during film formation. The absorption of Langmuir-Blodgett films and cast films shows a distinct hypsochromic shift compared with that of PI chloroform solution.
    Additional Material: 7 Ill.
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  • 7
    Publication Date: 2019-06-14
    Description: This study discusses an analysis of combined airborne and ground observations of particulate nitrate (NO3(p)) concentrations made during the wintertime DISCOVER-AQ (Deriving Information on Surface Conditions from COlumn and VERtically resolved observations relevant to Air Quality) study at one of the most polluted cities in the United States Fresno, CA in the San Joaquin Valley (SJV) and focuses on developing an understanding of the various processes that impact surface nitrate concentrations during pollution events. The results provide an explicit case-study illustration of how nighttime chemistry can influence daytime surface-level NO3(p) concentrations, complementing previous studies in the SJV. The observations exemplify the critical role that nocturnal chemical production of NO3(p) aloft in the residual layer (RL) can play in determining daytime surface-level NO3(p) concentrations. Further, they indicate that nocturnal production of NO3(p) in the RL, along with daytime photochemical production, can contribute substantially to the buildup and sustaining of severe pollution episodes. The exceptionally shallow nocturnal boundary layer (NBL) heights characteristic of wintertime pollution events in the SJV intensify the importance of nocturnal production aloft in the residual layer to daytime surface concentrations. The observations also demonstrate that dynamics within the RL can influence the early-morning vertical distribution of NO3(p), despite low wintertime wind speeds. This overnight reshaping of the vertical distribution above the city plays an important role in determining the net impact of nocturnal chemical production on local and regional surface-level NO3(p) concentrations. Entrainment of clean free-tropospheric (FT) air into the boundary layer in the afternoon is identified as an important process that reduces surface-level NO3(p) and limits buildup during pollution episodes. The influence of dry deposition of HNO3 gas to the surface on daytime particulate nitrate concentrations is important but limited by an excess of ammonia in the region, which leads to only a small fraction of nitrate existing in the gas phase even during the warmer daytime. However, in the late afternoon, when diminishing solar heating leads to a rapid fall in the mixed boundary layer height (BLH), the impact of surface deposition is temporarily enhanced and can lead to a substantial decline in surface-level particulate nitrate concentrations; this enhanced deposition is quickly arrested by a decrease in surface temperature, which drops the gas-phase fraction to near zero. The overall importance of enhanced late-afternoon gas-phase loss to the multiday buildup of pollution events is limited by the very shallow nocturnal boundary layer. The case study here demonstrates that mixing down of NO3(p) from the RL can contribute a majority of the surface-level NO3(p) in the morning (here, 80%), and a strong influence can persist into the afternoon even when photochemical production is maximum. The particular day-to-day contribution of aloft nocturnal NO3(p) production to surface concentrations will depend on prevailing chemical and meteorological conditions. Although specific to the SJV, the observations and conceptual framework further developed here provide general insights into the evolution of pollution episodes in wintertime environments.
    Keywords: Environment Pollution
    Type: NF1676L-28205 , Atmospheric Chemistry and Physics (ISSN 1680-7316) (e-ISSN 1680-7324); 17; 23; 14747-14770
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  • 8
    Publication Date: 2019-11-23
    Description: The San Joaquin Valley (SJV) of California experiences high concentrations of PM2.5 (particulate matter with aerodynamic diameter 2.5 m) during episodes of meteorological stagnation in winter. Modeling PM2.5 NH4NO3 during these episodes is challenging because it involves simulating meteorology in complex terrain under low wind speed and vertically stratified conditions, representing complex pollutant emissions distributions, and simulating daytime and nighttime chemistry that can be influenced by the mixing of urban and rural air masses. A rich dataset of observations related to NH4NO3 formation was acquired during multiple periods of elevated NH4NO3 during the DISCOVER-AQ (Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality) field campaign in SJV in January and February 2013. Here, NH4NO3 is simulated during the SJV DISCOVER-AQ study period with the Community Multiscale Air Quality (CMAQ) model version 5.1, predictions are evaluated with the DISCOVER-AQ dataset, and process analysis modeling is used to quantify HNO3 production rates. Simulated NO3- generally agrees well with routine monitoring of 24-h average NO3-, but comparisons with hourly average NO3- measurements in Fresno revealed differences at higher time resolution. Predictions of gas-particle partitioning of total nitrate (HNO3 + NO3-) and NHx (NH3 + NH4+) generally agreed well with measurements in Fresno, although partitioning of total nitrate to HNO3 was sometimes overestimated at low relative humidity in afternoon. Gas-particle partitioning results indicate that NH4NO3 formation is limited by HNO3 availability in both the model and ambient. NH3 mixing ratios are underestimated, particularly in areas with large agricultural activity, and the spatial allocation of NH3 emissions could benefit from additional work, especially near Hanford. HNO3 production via daytime and nighttime pathways is reasonably consistent with the conceptual model of NH4NO3 formation in SJV, and production peaked aloft between about 160 and 240 m in the model. During a period of elevated NH4NO3, the model predicted that the OH + NO2 pathway contributed 46% to total HNO3 production in SJV and the N2O5 heterogeneous hydrolysis pathway contributed 54%. The relative importance of the OH + NO2 pathway for HNO3 production is predicted to increase as NOx emissions decrease.
    Keywords: Environment Pollution
    Type: NF1676L-29304 , Journal of Geophysical Research: Atmospheres (ISSN 2169-897X) (e-ISSN 2169-8996); 123; 9; 4727-4745
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