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Suitable Replacement (suitable + replacement)
Selected AbstractsA zero ODP replacement for R12 in a centrifugal compressor: an experimental study using R134aINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2002C. Aprea Abstract It is well believed that the hydrofluorocarbons (HFCs) and their mixtures are the most promising candidates to substitute the conventional refrigerants, chlorofluorocarbons (CFCs) and HCFCs which contain chlorine atoms in the molecule. This substitution is necessary for the harmful action of CFCs and of HCFCs toward atmospheric ozone layer damage because the disruption of ozone has been attributed to chlorine. For this reason they must be replaced by more environment-friendly refrigerants, as the new family, designated as HFCs, that are chlorine free. Centrifugal compressors differ from positive displacement compressors in two major respects: high vapour volume flow for a given physical size and lower pressure ratio. They are particularly suited to applications where differences between evaporator and condenser temperatures are low. The preferred properties for fluids used in centrifugal compressors differ in certain important aspects from those preferred for fluids used in positive displacement units. In particular centrifugal compressors typically utilize fluids such as CFC114, CFC113, CFC12 and CFC11 for which many potential candidate replacements exist; however, for CFC12, HFC134a is the most suitable replacement. A comparison of the refrigerants HFC134a and CFC12 has been carried out and the results from the tests, using data from a refrigerating plant operating with a centrifugal compressor are reported. The chilled water cooling plant, with a refrigerating capacity of 6500 kW is made up of a centrifugal two-stage compressor, a condenser linked to a cooling tower, an economizer and a flooded evaporator. Experimental results show that a lower coefficient of performance is found when R134a is used as substitute for R12; the difference between the COP values decreases rising the compression ratio. Copyright © 2002 John Wiley & Sons, Ltd. [source] Influence of stationary phase chemistry and mobile-phase composition on retention, selectivity, and MS response in hydrophilic interaction chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2010Kenneth J. Fountain Abstract A comprehensive retention and selectivity characterization of several hydrophilic interaction chromatography (HILIC) stationary phases was performed with 28 test probes in order to study the influence of particle type, surface chemistry, and mobile-phase pH on chromatographic retention, selectivity, and MS response. Selectivity differences were compared for columns operated at both low and high pH, while ESI-MS was used to study the effects of mobile-phase pH on signal response. Additionally, acetone was explored as a potential alternative to ACN as the weak HILIC solvent. Moderate differences in selectivity were observed on the same column operated at different pH, mostly due to acidic compounds. In addition, the MS response increased when a high pH mobile phase was used, particularly for analytes that were ionized with negative ESI-MS. Even larger selectivity differences were observed for different stationary phases evaluated with the same mobile phase. Acetone was not a suitable replacement for ACN in routine HILIC separations due to differences in selectivity and MS response. Finally, the data from this study were used to establish guidelines for rapid HILIC method development of polar compounds, which is demonstrated with a mixture of histidine dipeptides and organophosphonate nerve agent metabolites. [source] Synthesis and characterization of Li2SO4:P, RE (RE = Dy or Eu), low Z, TLD phosphorsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003S. J. Dhoble Abstract Li2SO4 : P, Dy and Li2SO4 : P, Eu, low Z phosphors (Zeff = 11.19) are reported. These are shown to be more sensitive than the commercially used LiF-TLD 100 phosphor (Zeff = 8.4). The phosphors have a linear response, negligible fading and excellent reusability. These properties make these phosphors a suitable replacement for LiF-TLD 100 which is currently used for the dosimetry of the ionising radiations using thermoluminescence. [source] Resistance and reactance in oscillation lung function reflect basal lung function and bronchial hyperresponsiveness respectivelyRESPIROLOGY, Issue 7 2009Hyeong Yoon KIM ABSTRACT Background and objective: Currently there are few data available regarding the use of impulse oscillometry parameters to assess airflow obstruction during standardized methacholine challenge testing. Methods: Methacholine challenge tests were performed using impulse oscillometry and conventional spirometry in 64 healthy and 39 asthmatic children, in order to determine airway resistance (R) and reactance (X) at frequencies of 5,35 Hz, as well as FEV1. Results: Baseline R and X were significantly different between the healthy and asthmatic children, with the most discriminating parameter being resistance at 5 Hz (R5). In asthmatic children BHR was well demonstrated by FEV1, X5 and X10, but not by R5. However, when the actual R5 values obtained in this study were compared with the predicted values, there appeared to be differences in the lung function measures that corresponded to varying methacholine concentrations. In addition, the PC20_FEV1 and PC70_X5 were significantly more sensitive than other parameters for methacholine challenge testing. Conclusions: Measuring resistance at 5 Hz using impulse oscillometry facilitates significant differentiation of baseline lung function between asthmatic and healthy children. Additionally, X may be a suitable replacement for PC20 in methacholine challenge testing. [source] Formation of highly oriented biodegradable polybutylene succinate adipate nanocomposites: Effects of cation structures on morphology, free volume, and propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009Katherine M. Dean Abstract Many biodegradable polymer materials have not been found to be suitable replacements for more traditional non-biodegradable polymers owing to their insufficient gas and vapor barrier properties. The use of a series of novel organically modified synthetic fluorohectorites (FHTs) has been explored to produce biodegradable polybutylene succinate adipate (PBSA)-clay nanocomposites with improved barrier. Highly oriented nanoclay structures (clearly showing a tortuous path required to reduce gas and vapor transmission) were observed using transmission electron microscopy (TEM), resulting in a significant reduction in oxygen permeability (up to a 53% decrease). In particular, these oriented structures were observed in the FHTs modified with di poly(oxyethylene) alkyl methyl ammonium and the longer chain dimethyl dialkyl ammonium. Orientation and dispersion were found to be a result of chemical functionality, chain length, and unique aspect ratios of these FHTs. It was concluded that this reduction in permeability was predominantly due to the tortuous path created by oriented platelets and not from any nucleating effects the platelets may have had. Interestingly, the FHTs were shown to disrupt crystallinity and no change in free volume (as measured using positron annihilation life-time spectroscopy) was observed. The excellent clay dispersion and orientation also led to significant increases in other properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Firm Performance, Governance Structure, and Top Management Turnover in a Transitional Economy*JOURNAL OF MANAGEMENT STUDIES, Issue 6 2006Michael Firth abstract Recent research has argued that political and regulatory environments have a significant impact on corporate governance systems. In particular, countries with poor investor protection laws and weak law enforcement have low levels of corporate governance that manifests itself in substandard financial performance, management entrenchment, and the expropriation of minority shareholders. One implication of this research is that China will have poor corporate governance and entrenched managers as its legal system is relatively underdeveloped and inefficient. However, using data on top management turnover in China's listed firms, our results refute the prediction of entrenched management. We find evidence of very high turnover of company chairmen and there are many cases that we interpret to be forced departures. Our results show that chairman turnover is related to a firm's profitability but not to its stock returns. Turnover-performance sensitivity is higher if legal entities are major shareholders but the proportion of non-executive directors perversely affects it. We find no evidence that profitability improves after a change in chairman and this suggests that a firm's governance structure is ineffective as it is unable to recruit suitable replacements that can turn around its financial performance. [source] Preparation and characterization of PBT nanocomposites compounded with different montmorillonitesPOLYMER ENGINEERING & SCIENCE, Issue 6 2004Domenico Acierno Because of their superior mechanical and thermal properties, light weight, and favorable cost/performance ratio, nanocomposite materials appear to be suitable replacements for metals and alloys in many industrial applications in fields such as automotive, structural plastics, electronics, packaging, and so on (1). The technological relevance of this large-scale market for polymers is evidenced by the numerous patents issued over the last few years, even though only few applications have entered the market. Polymer-clay nanocomposite systems were successfully prepared by melt compounding using several thermoplastic matrices (polyamides, polyolefins, etc.), but few data are reported in the scientific literature on polyester-based nanocomposites (2). Because of the high commercial relevance of polyesters, we have investigated the effect of organoclay inclusion on the structure and properties of these hybrid systems. In particular, we have studied the relationships between processing conditions, hybrid composition (organoclay type and content), nanoscale morphology and properties of poly(butylene terephthalate) (PBT) nanocomposites based upon several commercial organo-modified montmorillonites at different weight percentages. The melt compounding was performed using a twin-screw extruder, at extrusion rates of 90 or 150 rpm. Polym. Eng. Sci. 44:1012,1018, 2004. © 2004 Society of Plastics Engineers. [source] PHA bioplastic: A value-added coproduct for biomass biorefineriesBIOFUELS, BIOPRODUCTS AND BIOREFINING, Issue 4 2009Kristi D. Snell Abstract The petroleum industry has optimized profits by producing value-added coproducts, such as plastics and chemicals, in addition to primary liquid fuels. A similar coproduct strategy applied to biorefineries processing cellulosic biomass to liquid fuels and/or energy would transform a technology that is marginally economic, depending on oil prices, to a sustainable business with enhanced revenue streams from multiple coproducts. The challenge is finding a biobased coproduct that is compatible with a biorefinery scenario and where markets warrant its production on a similar scale as liquid fuels and/or energy. Polyhydroxyalkanoate (PHA) bioplastics represent a coproduct that would be entirely compatible with either production of liquid fuels by hydrolyzing the residual biomass after PHA extraction or by alternative thermochemical processes. PHA bioplastics possess properties making them suitable replacements for many of the applications currently served by petroleum-based plastics, thus providing tremendous market potential. Proof-of-concept technology for production of these plastics in several crops of agronomic interest has been demonstrated. In this review, we show that the potential for developing biomass-based biorefineries producing liquid fuels and a value-added coproduct is both real and realizable. Examples using switchgrass producing PHA bioplastics as a coproduct are described. © 2009 Society of Chemical Industry and John Wiley & Sons, Ltd. [source] | |||||||||||||