CO Molar Ratio Research Articles

Evenly dispersed microspherical amorphous alloy CoxB1-x: Robust and magnetically recyclable catalyst for alcoholyzing ammonia borane to release H2

By properly adjusting mole ratio of Co2+/BH4-, a series of CoxB1-x (x = 0.25, 0.50, 0.75) amorphous alloys were synthesized via an one-step mild liquid reduction route with assistance of suitable shape modifier and dispersant The characterization results of morphology, phase composition and magnetism by virtue of various analytical techniques demonstrate that under the given conditions the as-fabricated CoxB1-x products all belong to the typical amorphous alloys with a level of ferromagnetism, mostly taking the shape of nearly monodispersed microspheres with size distribution of 200–300 nm; the grain size gets smaller with rise of Co content. The catalytic ability evaluations of the CoxB1-x samples via alcoholyzing ammonia borane for liberating H2 gas confirm that the Co0.75B0.25 sample holds the highest catalytic activity, enabling to fully release H2 in 40 min at 298 K with the apparent activation energy of 38.93 kJ/mol, which can still remain 71% initial catalytic activity after 5 recycles. In theory, the special microsphere constructing strategy could be also extended to other metal-nonmetal systems for fabricating highly active amorphous alloy catalysts.

Rational design of hollow N/Co-doped carbon spheres from bimetal-ZIFs for high-efficiency electrocatalysis

To explore efficient non-noble metal-based electrocatalysts for oxygen reduction reaction (ORR), herein we developed a facile bottom-up approach for the fabrication of a hollow porous carbon sphere codoped with ultra-small Co nanoparticles and uniform nitrogen distribution (Co-HNCS) via one-step pyrolysis of a core-shell type precursor composing of polystyrene (PS) core and bimetallic ZIF (zeolite imidazolate framework) shell. The bimetallic Co-Zn-ZIFs (BMZIFs) was selected as the sacrifice template due to not only its high nitrogen content and regular porosity but also the superiority that Zn species in BMZIFs can both spatially separate Co species to suppress the aggregation of ultra-small Co NPs and be evaporated to afford extra pores during high-temperature pyrolysis. As expected, by adjusting the starting molar ratio of Zn to Co, we were able to prepare Co-HNCS-x (x represent the molar ratio of Co to total starting metal feeding) that exhibited unique hollow structure with large surface areas, enhanced mass transport, high porosities, tunable particle sizes and graphitization degrees, abundant highly active CoNx sites, and thus significantly improved ORR performance. Particularly, the optimal Co-HNCS-0.2 exhibited the remarkable ORR activity (the onset and half-wave potentials were 0.94 and 0.82Vvs. RHE, respectively) via an efficient four-electron-dominant ORR process in alkaline medium, which outperformed that of commercial Pt/C (20wt%, the onset and half-wave potentials were 0.93 and 0.80Vvs. RHE, respectively) and most of previously reported Co-based catalysts. Moreover, it also displayed much superior stability and tolerance to methanol as compared to Pt/C, further highlighting the merit of this facile synthesis approach. Our findings might inspire new thoughts on the development of precious-metal-free, highly-efficient and cost-effective ORR electrocatalysts derived from MOF.

Hierarchical CoMn-layered double hydroxide nanowires on nickel foam as electrode material for high-capacitance supercapacitor

CoMn-layered double hydroxide (LDH) nanowires are successfully embedded on the surface of nickel foam (NF) through a simple one-step hydrothermal method. The morphology and electrochemical properties of the samples can be controlled using different molar ratios of Co and Mn salts. CoMn LDH nanowires on NF with Co2+/Mn2+ molar ratio of 3:1 exhibit excellent electrochemical properties, high specific capacitance (1409 F g−1 at current density of 1 A g−1), good cycling stability (93.2% retention after 3000 charge-discharge cycles), and excellent performance rate (71.1% retention at 10 A g−1) when used as an electrode material for supercapacitors.

Microwave Assisted Fischer - Tropsch Synthesis at a Atmospheric Pressure

The purpose of this study was to test the efficiency of the microwave activation of a Fischer-Tropsch used catalyst under atmospheric pressure. Experiments were carried out on a cobalt, manganese, calcium catalyst on a 10:1:1 molar ratio that was impregnated on a AlSBA-15 support. The amount of metal impregnated was equivalent to 20% of the supports mass. Experiments were carried out both with conventional as well as microwave heating. In order to compare the efficiency of both types of heating, the product compositions were determined at 110, 140, 170, 190, 200, 225, 250 oC. At each temperature 4:1, 2:1, 1.25:1 H2:CO molar ratios were tested. The microwave assisted Fischer-Tropsch reaction allows the use of lower temperatures, as well as larger CO conversion values with better yields especially in methane.

Thermodynamic Equilibrium Analysis of CO 2 Reforming of Methane: Elimination of Carbon Deposition and Adjustment of H 2 /CO Ratio

Dry (CO2) reforming of methane (DRM) is considered as a promising technique to produce syngas. In this study, to optimise the operating conditions for elimination of carbon deposition, thermodynamic calculations were carried out to understand the effect of various temperatures (550-1200 ̊C), pressures (0.05-5 MPa) and CH4/CO2 mole ratios (0.5-2) on the product of H2/CO ratio as well as the formation of carbon deposition. The suggested DRM operating conditions for carbon free regime are at a temperature greater than 1000 ̊C with CH4/CO2 mole ratio = 1 and pressure P = 0.1 MPa. The operating temperature of carbon free regime could be switched to lower temperature by either lowering the CH4/CO2 mole ratio or decreasing the reaction pressure. The results illustrated that the temperature range for severe carbon formation was between 546 ̊C and 703 ̊C. CH4 decomposition and CO disassociation reaction are considered as the major reactions contributing to carbon formation. The former was promoted at operating conditions of P ≤ 0.1 MPa and 550 ̊C ≤ T ≤ 1000 ̊C, while the latter was enhanced at operating conditions of P ≥ 0.1 MPa and T ≤ 700 ̊C. The syngas produced from optimised carbon free regime operating conditions, could be used to synthesis olefin, heavy hydrocarbons and oxygenated compounds. H2 /CO ratio could be adjusted by the changing CH4 /CO2 mole ratio and/or pressure to satisfy F-T process for different application. Since the latter is only effective when operating temperature is lower than 900 ̊C, the former is proposed as a more efficient method to adjust H2/CO ratio. When the operating temperature of DRM is over 700 ̊C, H2/CO ratio obtained at CH4/CO2 mole ratio of DRM ≤ 1 and P = 0.1 MPa is more preferable to be used for the synthesis of olefin, heavy hydrocarbons and oxygenated compounds. Otherwise the syngas is more suitable for producing alkane (C1 –C5).

Estimation of CO2 Absorption Capacity via Correlating Measured Electrical Conductivity in a Diethanolamine Solvent System Compared to Monoethanolamine Solvent Systems

The objective of this study was to determine the correlation equation between the CO2 absorption capacity and measured electrical conductivity in a CO2 absorption system using diethanolamine (DEA) as a solvent based on various theoretical and experimental results. In addition, the capacity and various results of the system were quantified and compared to those of the monoethanolamine (MEA) system reported in previous papers. DEA solvent at 4 M was confirmed to be the most suitable one for application in a commercial process because its mole ratio of CO2 to amine was approximately 0.5. The ionic conductivities of carbamic acid (R2NH2+) and carbamate (R2NCOO–) were estimated to be 38.46 and 20.01 S·cm2·mol–1·z–1, respectively. They were smaller than those of their corresponding ions of the MEA system. The ionic activity coefficient of the DEA system was also smaller than that of the MEA system. However, the sensitivity of the CO2 absorption capacity to electrical conductivity measured in a constant-concentration solution of the DEA system was higher than that in the MEA system. These results were basically caused by differences in molecular size, the mole ratio of water to all ions present (H2O/ions), and the density of the electron dispersion of molecules between the MEA system and the DEA system.

Reforming of methane to syngas in a microwave plasma torch at atmospheric pressure

Abstract 1 Carbon dioxide was converted to synthesis gas (syngas) in a microwave plasma torch by methane reforming at atmospheric pressure. The microwave plasma torch converts CO 2 + CH 4 into synthesis gas. This study examined conversion rates as a function of gas temperature for dry methane reforming. The temperature of the torch flame is measured 6760 K by making use of optical spectroscopy. The CO 2 /CH 4 reforming can be completely converted into synthesis gas (conversions: 68.4%, CO 2 ; 96.8%, CH 4 ) through their reforming reactions at a microwave power of 6 kW. When the reforming gas (CO 2 :CH 4 ) mole ratio was 1:1, the resulting synthesis gas (H 2 :CO) mole ratio was 0.9:1.1. The H 2 and CO mass yield rates increased to 0.24 kg/h and 1.86 kg/h, respectively. Also, the energy yield are 240 g/h and 41.4 g/kWh. The CO 2 microwave plasma torch not only exhibited noteworthy results for CO 2 reduction and syngas production, but the H 2 :CO mole ratio of the gas produced is easily controlled by adjusting the CO 2 :CH 4 ratio during the feeding process.

Synthesis of Co3O4 nanoclusters via an EDTANa4-assisted route for enhanced electrochemical application

Three-dimensional (3D) Co3O4 nanoclusters were fabricated with the assistance of tetrasodium ethylene diamine tetraacetic acid (EDTANa4) through a one-pot wet-chemical reaction, featuring self-limiting assembly of building blocks and controlled regrowth process. The molar ratio of Co2+ and EDTANa4 plays a key role in building initial clusters as blocks, and the amount of NaOH effects the regrowth process. A possible formation mechanism for the Co3O4 nanoclusters was proposed based on the characterization results of X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The designed hierarchical Co3O4 nanoclusters exhibit a high specific capacitance of 221Fg−1 at a current density of 2Ag−1 in 2molL−1 KOH electrolyte.

Investigation of structural, optical and magnetic properties of thermal plasma synthesized Ni-Co spinel ferrite nanoparticles

Magnetic nanoparticles of nickel substituted cobalt ferrites, NixCo1−xFe2O4, (x=0 to 1 in the step of 0.2) were successfully synthesized by gas phase nucleation and growth process. For the first time, we report feasibility of synthesizing such mixed ferrite system using thermal plasma route. Further, effect of change in molar ratio of Co:Ni on the structural, optical and magnetic properties has been investigated in detail. The structural and phase formation analysis of the samples under investigation have been carried out using powder X-ray diffraction and Raman spectroscopy. The surface morphology of these particles has been studied using scanning electron microscopy and the micrographs so obtained were used to find out average gain size and size distribution. The optical and magnetic properties of the as synthesized samples were finally correlated with the magnetic moment of substituted species such as Ni for Co and cation distribution, analyzed using Mössbauer spectroscopy. Special modification in Thermo Gravimetric Analyzer was used to determine magnetic transition temperature.

Hydrogen-rich syngas production and tar removal from biomass gasification using sacrificial tyre pyrolysis char

Carbonaceous materials have been proven to have a high catalytic activity for tar removal from the syngas produced from biomass gasification. The simultaneous reforming and gasification of pyrolysis gases and char could have a significant role in increasing the gas yield and decreasing the tar in the product syngas. This study investigates the use of tyre char as a catalyst for H2-rich syngas production and tar reduction during the pyrolysis-reforming of biomass using a two stage fixed bed reactor. The biomass sample was pyrolysed under nitrogen at a pyrolysis temperature of 500°C, the evolved pyrolysis volatiles were passed to a second stage with steam and the gases were reformed in the presence of tyre char as catalyst. The influence of catalyst bed temperature, steam to biomass ratio, reaction time and tyre ash metals were investigated. The influence of the catalytic activity of tyre ash minerals on composition of syngas and tar decomposition during the steam reforming of biomass was significant as the removal of minerals led to a decrease in the H2 yield. Raising the steam injection rate and reforming temperature resulted in an increase in H2 production as steam reforming and char gasification reactions were enhanced. The maximum H2 content in the product syngas of 56vol.% was obtained at a reforming temperature of 900°C and with a steam to biomass mass ratio of 6 (g/g). Further investigation of the influence of the biomass:steam ratio on syngas quality showed that the H2:CO molar ratio was increased from 1.8 (steam: biomass ratio; 1.82gg−1) to 3 (steam: biomass ratio; 6gg−1).

Wire-on-flake heterostructured ternary Co0.5Ni0.5P/CC: an efficient hydrogen evolution electrocatalyst

Illustration of the formation of ternary composites with different morphologies when changing the relative molar ratios of non-noble-metal precursors. The wire-on-flake morphology exists when the molar ratio of Co(NO3)2·6H2O and Ni(NO3)2·6H2O is 1 : 1. When adding more Co(NO3)2·6H2O, the morphology becomes a nanowire morphology, and when adding more Ni(NO3)2·6H2O, the morphology becomes a nanoflake morphology.

The impact of divergent breed types and diets on methane emissions, rumen characteristics and performance of finishing beef cattle

This study was undertaken to further develop our understanding of the links between breed, diet and the rumen microbial community and determine their effect on production characteristics and methane (CH4) emissions from beef cattle. The experiment was of a 2×2 factorial design, comprising two breeds (crossbred Charolais (CHX); purebred Luing (LU)) and two diets (concentrate-straw or silage-based). In total, 80 steers were used and balanced for sire within each breed, farm of origin and BW across diets. The diets (fed as total mixed rations) consisted of (g/kg dry matter (DM)) forage to concentrate ratios of either 500 : 500 (Mixed) or 79 : 921 (Concentrate). Steers were adapted to the diets over a 4-week period and performance and feed efficiency were then measured over a 56-day test period. Directly after the 56-day test, CH4 and carbon dioxide (CO2) emissions were measured (six steers/week) over a 13-week period. Compared with LU steers, CHX steers had greater average daily gain (ADG; P<0.05) and significantly (P<0.001) lower residual feed intake. Crossbred Charolais steers had superior conformation and fatness scores (P<0.001) than LU steers. Although steers consumed, on a DM basis, more Concentrate than Mixed diet (P<0.01), there were no differences between diets in either ADG or feed efficiency during the 56-day test. At slaughter, however, Concentrate-fed steers were heavier (P<0.05) and had greater carcass weights than Mixed-fed steers (P<0.001). Breed of steer did not influence CH4 production, but it was substantially lower when the Concentrate rather than Mixed diet was fed (P<0.001). Rumen fluid from Concentrate-fed steers contained greater proportions of propionic acid (P<0.001) and lower proportions of acetic acid (P<0.001), fewer archaea (P<0.01) and protozoa (P=0.09), but more Clostridium Cluster XIVa (P<0.01) and Bacteroides plus Prevotella (P<0.001) than Mixed-fed steers. When the CH4 to CO2 molar ratio was considered as a proxy method for CH4 production (g/kg DM intake), only weak relationships were found within diets. In conclusion, although feeding Concentrate and Mixed diets produced substantial differences in CH4 emissions and rumen characteristics, differences in performance were influenced more markedly by breed.

Co2SiO4 nanostructures: New simple synthesis, characterization and investigation of optical property

Herein, a new and simple method for synthesis of Co2SiO4 nanostructures at low temperature is reported. The nanostructures are obtained by solvothermal reaction of Co(CH3COO)2·4H2O with tetraethyl orthosilicate (TEOS) in methanol solvent at 120–150°C for 8–12h, followed by calcination at 700°C for 5h. Effects of using polymer, molar ratio of Co:Si, reaction time and temperature are optimized to achieve the best products on morphology and purity. It is the first time that optical property and also the effects of using the polymer on properties of the cobalt orthosilicates are investigated. At the temperature of 150°C for a 12h period of time, when the molar ratio of Co:Si is 1:1, the product is rod-shape Co2SiO4 with diameters of 20–40nm. A mixture of the rod-shape and spherical structures of the Co2SiO4, with diameters of 20–40nm, is obtained by using of ratio of 2:1 of Co:Si at 150°C for 12h. With decreasing reaction time to 10h, the spherical clusters of the Co2SiO4 are prepared. The Co2SiO4 nanostructures are characterized by XRD, SEM and TEM to analyze their structure and morphology. The optical and magnetic properties of the nanostructures are investigated.

One‐Pot Facile Fabrication of Multiple Nickel Nanoparticles Confined in Microporous Silica Giving a Multiple‐Cores@Shell Structure as a Highly Efficient Catalyst for Methane Dry Reforming

AbstractMethane dry reforming (MDR) is a very important reaction, which can efficiently use two kinds of greenhouse gases (CO2 and CH4) to prepare synthesis gas or produce green hydrogen energy. What inhibits the industrialization of MDR is the sintering of active Ni nanoparticles and severe carbon deposition for Ni‐based catalysts. To resolve these problems, a novel structured catalyst with multiple ultra‐small Ni nanoparticles (4.3 nm) as the core and microporous silica as the shell was rationally fabricated by a facial one‐pot reverse micelle method and applied for MDR. The multiple‐cores@shell (M‐Ni@SiO2) catalyst displays superior carbon resistance and long‐term durability with the methane and carbon dioxide conversion close to thermodynamic equilibrium and a H2 to CO molar ratio near 1, whereas the commercial catalyst, Ni/Al2O3, and Ni directly supported on silica spheres (Ni/SiO2) show low stability and notable carbon deposition. The ultra‐small Ni particle size and confinement effect of the porous silica shell are believed to be the determining factors for the outstanding performance of the multiple‐cores@shell catalyst. The novel multiple‐cores@shell structure catalyst could be potentially used for industrial applications of MDR.

Synthesis of high-surface-area rod-like alumina materials with enhanced Cr(VI) removal efficiency

A facile synthesis of rod-like alumina materials was developed through systematical investigation, which enables the control of the specific surface area of ammonium aluminium carbonate hydroxide (AACH) using aluminum nitrate as a precursor and urea as a precipitant. Our studies indicated that the molar ratio of CO(NH2)2/Al influences crystallinity, morphology and the surface area of alumina materials. Amorphous alumina materials with nanorod morphology and high surface area (1029 m2 g-1) was obtained with 15:1 M ratio of CO(NH2)2 to Al. In addition, the results demonstrated that thermal behaviors of the as-prepared AACH affect their crystallinities. Furthermore, the amorphous Al2O3 prepared from AACH by calcination at 773 K was used as an adsorbent for Cr(VI) removal from water solution, and external factors were investigated, including contact time, adsorbent dosage, initial concentration of adsorbate and the pH of solution. It was found that the maximum adsorption capacity of prepared amorphous Al2O3 for Cr(VI) was 52.1 mg g−1, which was higher than those of other reported Al2O3 samples.

Experimental and modeling investigation on CO2 sorption kinetics over K2CO3-modified silica aerogels

K2CO3-modified silica aerogels (K2CO3/SG) were synthesized by the two-step sol-gel and wet impregnation method using K2CO3 and tetraethoxysilane (TEOS) as starting materials and ethanol as solvent. CO2 sorption behaviors of the sorbent were tested under ultra-dilute flue gas conditions of 20–60°C, 1%CO2, 2%H2O and balanced N2 with gas hourly space velocity (GHSV) of 4000h−1 using a modified fixed-bed reactor. Experimental CO2 uptakes of the sorbent under different temperatures were correlated to several kinetics models to study the kinetics performances. The effects of temperature, K2CO3 loading, GHSV, H2O:CO2 molar ratio and H2O pretreatment time on CO2 sorption capacity and kinetics performances of the sorbent were further demonstrated. It is found that the two-step sol-gel and wet impregnation method could benefit the sorbent improved physical properties, superior surface characteristics and enhanced CO2 sorption performances. Amongst various kinetics equations, the modified Avrami fractional kinetics model could well describe the CO2 sorption process over K2CO3/SG. CO2 sorption capacity decreases with the increase of temperature. With the increasing K2CO3 loading, GHSV, H2O:CO2 molar ratio and H2O pretreatment time, CO2 sorption capacity increases first and then decreases. CO2 sorption kinetics increases with the increasing temperature and H2O pretreatment time, while it decreases with the increasing K2CO3 loading. CO2 sorption kinetics keeps rather stable and then increases significantly with the increasing GHSV and H2O:CO2 molar ratio.

Size controllable synthesis of cobalt vanadate nanostructures with enhanced photocatalytic activity for the degradation of organic dyes

Different types of cobalt vanadate nanostructures such as Co3V2O8, Co2V2O7 and CoV2O6 have been successfully prepared via a simple solid-state method. For the first time, cobalt vanadate nanostructures were synthesized via Schiff-base ligand and vanadyl sulfate as a capping agent and vanadium source, respectively. The effect of a Schiff-base ligand (N,N-Bis (salicylaldehyde) ethylenediamine=H2salen) as a capping agent, molar ratio of Co: H2salen and Co:V on type of products, morphology and size of cobalt vanadate nanoparticles was investigated to reach optimum condition. The as-prepared nanostructures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmittance electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra, energy dispersive X-ray microanalysis (EDX) and ultraviolet–visible (UV–vis) spectroscopy. This work is the first study on photocatalytic activity of cobalt vanadate nanostructures in different conditions. The influence of different parameters such as type of cobalt vanadate nanostructures, type of dye, size of particles and nanostructures dosage as a catalyst on photocatalytic activity of samples were studied.

Characterization of Ag-promoted Ni/SiO2 Catalysts for Syngas Production via Carbon Dioxide (CO2) Dry Reforming of Glycerol

The carbon dioxide (CO2) dry reforming of glycerol for syngas production is one of the promising ways to benefit the oversupply crisis of glycerol worldwide. It is an attractive process as it converts carbon dioxide, a greenhouse gas into a synthesis gas and simultaneously removed from the carbon biosphere cycle. In this study, the glycerol dry reforming was carried out using Silver (Ag) promoted Nickel (Ni) based catalysts supported on silicon oxide (SiO2) i.e. Ag-Ni/SiO2. The catalysts were prepared through wet impregnation method and characterized by using Brunauer-Emmett-Teller (BET) surface area, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Thermo Gravimetric (TGA) analysis. The experiment was conducted in a tubular reactor which condition fixed at 973 K and CO2:glycerol molar ratio of 1, under atmospheric pressure. It was found that the main gaseous products are H₂, CO and CH4 with H₂:CO molar ratio &lt; 1.0. From the reaction study, Ag(5)-Ni/SiO2 results in highest glycerol conversion and hydrogen yield, accounted for 32.6% and 27.4%, respectively.

Performance of Ni/dolomite pellet catalyst on gas distribution from cassava rhizome gasification with a modular fixed-bed gasifier

ABSTRACTThermal conversion of cassava rhizome was performed using a modular downdraft gasifier with the addition of Ni-based catalysts as promising tar eliminating and produced gas upgrading techniques. The activities of a synthesized 5% Ni/dolomite pellet catalyst prepared by impregnation method were investigated in a secondary reactor downstream of the gasifier. High reforming activity of the Ni/dolomite pellet catalyst on tar reduction was achieved. The conversion to H2 and CO was improved via steam reforming of methane and char reaction with CO2. Moreover, the formation of CH4 and CxHy was diminished through the tar or condensable hydrocarbon reformed on the catalyst surface. The carbon and hydrogen conversions of cassava rhizome with prepared catalyst were 83.79% and 61.78%, respectively, at an air flow rate of 1.98 m3/hr. At this condition, tar formation was low, while the lower heating value was 4.39 MJ/m3 and H2 to CO molar ratio was 1.22. Generally, the addition of a catalyst not only enhanced gas production, but also reduced tar and particulate matter generation; thus, its implementation should help lessen the pollution control requirement and cost of operation, while allowing higher quality fuel gas production.

Synthesis and Characterization of CoMn&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; Nanopowders by a Reverse Micelle Processing

CoMn2O4 nanoparticles were synthesized by reverse micelle processing from the mixed precursor (consisting of Co (NO3)2 ·6H2O and MnCl2·4H2O). The CoMn2O4 was prepared by mixing the aqueous solution at a molar ratio of Co : Mn = 1 : 2. The synthesized powders were calcined at 600°C for 2h. The average size and distribution of synthesized powders were in the range of 10-20nm and narrow, respectively. The average size of the synthesized powders increased with increasing water to surfactant molar ratio. The XRD diffraction patterns show that the phase of CoMn2O4 was spinel (JCPDS no.77-0471). The synthesized and calcined powders were characterized by thermogravimetry-differential scanning calorimeter (TG-DSC), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The magnetic property of the powder was measured by Vibrating Sample Magneto-meter (VSM) at 298K. The effect of synthesis parameter, such as the molar ratio of water to surfactant, is discussed.