High C2 Research Articles

Root traits of perennial C4 grasses contribute to cultivar variations in soil chemistry and species patterns in particulate and mineral‐associated carbon pool formation

AbstractRecent studies have indicated that the C4 perennial bioenergy crops switchgrass (Panicum virgatum) and big bluestem (Andropogon gerardii) accumulate significant amounts of soil carbon (C) owing to their extensive root systems. Soil C accumulation is likely driven by inter‐ and intraspecific variability in plant traits, but the mechanisms that underpin this variability remain unresolved. In this study we evaluated how inter‐ and intraspecific variation in root traits of cultivars from switchgrass (Cave‐in‐Rock, Kanlow, Southlow) and big bluestem (Bonanza, Southlow, Suther) affected the associations of soil C accumulation across soil fractions using stable isotope techniques. Our experimental field site was established in June 2008 at Fermilab in Batavia, IL. In 2018, soil cores were collected (30 cm depth) from all cultivars. We measured root biomass, root diameter, specific root length, bulk soil C, C associated with coarse particulate organic matter (CPOM) and fine particulate organic matter plus silt‐ and clay‐sized fractions, and characterized organic matter chemical class composition in soil using high‐resolution Fourier‐transform ion cyclotron resonance mass spectrometry. C4 species were established on soils that supported C3 grassland for 36 years before planting, which allowed us to use differences in the natural abundance of stable C isotopes to quantify C4 plant‐derived C. We found that big bluestem had 36.9% higher C4 plant‐derived C compared to switchgrass in the CPOM fraction in the 0–10 cm depth, while switchgrass had 60.7% higher C4 plant‐derived C compared to big bluestem in the clay fraction in the 10–20 cm depth. Our findings suggest that the large root system in big bluestem helps increase POM‐C formation quickly, while switchgrass root structure and chemistry build a mineral‐bound clay C pool through time. Thus, both species and cultivar selection can help improve bioenergy management to maximize soil carbon gains and lower CO2 emissions.

Designing Heteroatom-Codoped Iron Metal-Organic Framework for Promotional Photoreduction of Carbon Dioxide to Ethylene.

Rational engineering active sites and vantage defects of catalysts are promising but grand challenging task to enhance photoreduction CO2 to high value-added C2 products. In this study, we designed an N,S-codoped Fe-based MIL-88B catalyst with well-defined bipyramidal hexagonal prism morphology via a facile and effective process, which was synthesized by addition of appropriate 1,2-benzisothiazolin-3-one (BIT) and acetic acid to the reaction solution. Under simulated solar irradiation, the designed catalyst exhibits high C2 H4 evolution yield of 17.7 μmol g-1 ⋅h, which has been rarely achieved in photocatalytic CO2 reduction process. The synergistic effect of Fe-N coordinated sites and reasonable defects in the N,S-codoped photocatalyst can accelerate the migration of photogenerated carriers, resulting in high electron density, and this in turn helps to facilitate the formation and dimerization of C-C coupling intermediates for C2 H4 effectively.

P-d Orbital Hybridization Induced by p-Block Metal-Doped Cu Promotes the Formation of C2+ Products in Ampere-Level CO2 Electroreduction.

Large-current electrolysis of CO2 to multi-carbon (C2+) products is critical to realize the industrial application of CO2 conversion. However, the poor binding strength of *CO intermediates on the catalyst surface induces multiple competing pathways, which hinder the C2+ production. Herein, we report that p-d orbital hybridization induced by Ga-doped Cu (CuGa) could promote efficient CO2 electrocatalysis to C2+ products at ampere-level current density. It was found that CuGa exhibited the highest C2+ productivity with a remarkable Faradaic efficiency (FE) of 81.5% at a current density of 0.9 A/cm2, and the potential at such a high current density was -1.07 V versus reversible hydrogen electrode. At 1.1 A/cm2, the catalyst still maintained a high C2+ productivity with an FE of 76.9%. Experimental and theoretical studies indicated that the excellent performance of CuGa results from the p-d hybridization of Cu and Ga, which not only enriches reactive sites but also enhances the binding strength of the *CO intermediate and facilitates C-C coupling. The p-d hybridization strategy can be extended to other p-block metal-doped Cu catalysts, such as CuAl and CuGe, to boost CO2 electroreduction for C2+ production. As far as we know, this is the first work to promote electrochemical CO2 reduction reaction to generate the C2+ product by p-d orbital hybridization interaction using a p-block metal-doped Cu catalyst.

Tetranuclear CuII Cluster as the Ten Node Building Unit for the Construction of a Metal-Organic Framework for Efficient C2 H2 /CO2 Separation.

Rational design of high nuclear copper cluster-based metal-organic frameworks has not been established yet. Herein, we report a novel MOF (FJU-112) with the ten-connected tetranuclear copper cluster [Cu4 (PO3 )2 (μ2 -H2 O)2 (CO2 )4 ] as the node which was capped by the deprotonated organic ligand of H4 L (3,5-Dicarboxyphenylphosphonic acid). With BPE (1,2-Bis(4-pyridyl)ethane) as the pore partitioner, the pore spaces in the structure of FJU-112 were divided into several smaller cages and smaller windows for efficient gas adsorption and separation. FJU-112 exhibits a high separation performance for the C2 H2 /CO2 separation, which were established by the temperature-dependent sorption isotherms and further confirmed by the lab-scale dynamic breakthrough experiments. The grand canonical Monte Carlo simulations (GCMC) studies show that its high C2 H2 /CO2 separation performance is contributed to the strong π-complexation interactions between the C2 H2 molecules and framework pore surfaces, leading to its more C2 H2 uptakes over CO2 molecules.

Highly Selective CO2 Electroreduction to C2+ Products over Cu2O-Decorated 2D Metal-Organic Frameworks with Rich Heterogeneous Interfaces.

The electroreduction of carbon dioxide into high-value-added products is an effective approach to alleviating the energy crisis and pollution issues. However, there are still significant challenges for multicarbon (C2+) product production due to the lack of efficient catalysts with high selectivity. Herein, a Cu-rich electrocatalyst, where Cu2O nanoparticles are decorated on two-dimensional (2D) Cu-BDC metal-organic frameworks (MOFs) with abundant heterogeneous interfaces, is synthesized for highly selective CO2 electroreduction into C2+ products. A high C2+ Faradaic efficiency of 72.1% in an H-type cell and 58.2% in a flow cell are obtained, respectively. The heterogeneous interfaces of Cu2O/Cu-BDC can optimize the adsorption energy of reaction intermediates during CO2 electroreduction. An in situ infrared spectroscopy study indicates that the constructed interfaces can maintain the particular distribution of Cu valence states, where the C-C coupling is promoted to efficiently produce C2+ products owing to the stabilization of *CHO and *COH intermediates.

Co-Generation of Electricity and Chemicals via Solid Oxide Fuel Cells Using Li-Doped LSGM and LSF Composite Anodes

In this work, co-generation of C2+ hydrocarbons and electricity in solid oxide fuel cells (SOFCs) was realized using methane as fuel. The SOFCs were prepared with Li-La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM)/Lr0.7Sr0.3FeO3 (LSF) as the composite anode and LSGM and (La0.6Sr0.4)0.95Co0.2Fe0.8O3−δ (LSCF)/Sm0.2Ce0.8O2−δ (SDC) as the electrolyte and cathode, respectively. Among the anode materials, Li-LSGM has higher C2+ product selectivity. It can be seen from the XPS data that the doping of Li introduces a strong alkaline active center Li+O–, changes the lattice and electronic structure, and increases the surface absorption of oxygen species, which is more conducive to the improvement of the selectivity of C2+ products. LSF has strong electron-conducting ability and high catalytic activity for methane. After mixing with Li-LSGM, XPS data show that more oxygen vacancies are generated, which is beneficial to the electrochemical reaction of the anode and effectively reduces carbon deposition. The maximum power density of the composite anode can reach 188.15 mW/cm–2 with H2 as the fuel at 850 °C, and a C2+ product selectivity of 57.48% is achieved with CH4 as the fuel at 800 °C and the current density is 40 mA/cm–2. In addition, the change of C2+ product selectivity with current density and temperature during cell operation was further investigated, providing enlightenment on how to adjust the output ratio of chemicals and electricity.

De-Linker-Enabled Exceptional Volumetric Acetylene Storage Capacity and Benchmark C2H2/C2H4 and C2H2/CO2 Separations in Metal-Organic Frameworks.

An ideal adsorbent for separation requires optimizing both storage capacity and selectivity, but maximizing both or achieving a desired balance remain challenging. Herein, a de-linker strategy is proposed to address this issue for metal-organic frameworks (MOFs). Broadly speaking, the de-linker idea targets a class of materials that may be viewed as being intermediate between zeolites and MOFs. Its feasibility is shown here by a series of ultra-microporous MOFs (SNNU-98-M, M = Mn, Co, Ni, Zn). SNNU-98 exhibit high volumetric C2H2 uptake capacity under low and ambient pressures (175.3 cm3 cm-3 @ 0.1 bar, 222.9 cm3 cm-3 @ 1 bar, 298 K), as well as extraordinary selectivity (2405.7 for C2H2/C2H4, 22.7 for C2H2/CO2). Remarkably, SNNU-98-Mn can efficiently separate C2H2 from C2H2/CO2 and C2H2/C2H4 mixtures with a benchmark C2H2/C2H4 (1/99) breakthrough time of 2325 min g-1, and produce 99.9999% C2H4 with a productivity up to 64.6 mmol g-1, surpassing values of reported MOF adsorbents.

Accelerated Transfer and Spillover of Carbon Monoxide through Tandem Catalysis for Kinetics-boosted Ethylene Electrosynthesis.

Cu-based catalysts have been widely applied in electroreduction of carbon dioxide (CO2ER) to produce multicarbon (C2+) feedstocks (e.g., C2H4). However, the high energy barriers for CO2 activation on the Cu surface is a challenge for a high catalytic efficiency and product selectivity. Herein, we developed an in-situ *CO generation and spillover strategy by engineering single Ni atoms on a pyridinic N-enriched carbon support with a sodalite (SOD) topology (Ni-SOD/NC) that acted as a donor to feed adjacent Cu nanoparticles (NPs) with *CO intermediate. As a result, a high C2H4 selectivity of 62.5% and an industrial-level current density of 160 mA cm-2 at a low potential of -0.72 V were achieved. Our studies revealed that the isolated NiN3 active sites with adjacent pyridinic N species facilitated the *CO desorption and the massive *CO intermediate released from Ni-SOD/NC then overflowed to Cu NPs surface to enrich the *CO coverage for improving the selectivity of CO2ER to C2H4.

Identification and Analysis of Potential Immune-Related Biomarkers in Endometriosis.

Endometriosis is an inflammatory gynecological disease leading to deep pelvic pain, dyspareunia, and infertility. The pathophysiology of endometriosis is complex and depends on a variety of biological processes and pathways. Therefore, there is an urgent need to identify reliable biomarkers for early detection and accurate diagnosis to predict clinical outcomes and aid in the early intervention of endometriosis. We screened transcription factor- (TF-) immune-related gene (IRG) regulatory networks as potential biomarkers to reveal new molecular subgroups for the early diagnosis of endometriosis. To explore potential therapeutic targets for endometriosis, the Gene Expression Omnibus (GEO), Immunology Database and Analysis Portal (ImmPort), and TF databases were used to obtain data related to the recognition of differentially expressed genes (DEGs), differentially expressed IRGs (DEIRGs), and differentially expressed TFs (DETFs). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed on the DETFs and DEIRGs. Then, DETFs and DEIRGs were further validated in the external datasets of GSE51981 and GSE1230103. Then, we used quantitative real-time polymerase chain reaction (qRT-PCR) to verify the hub genes. Simultaneously, the Pearson correlation analysis and protein-protein interaction (PPI) analyses were used to indicate the potential mechanisms of TF-IRGs at the molecular level and obtain hub IRGs. Finally, the receiver operating characteristic (ROC) curve analysis was used to assess the diagnostic value of the hub IRGs. We screened a total of 94 DETFs and 121 DEIRGs in endometriosis. Most downregulated DETFs showed decreased expression in the endometria of moderate/severe endometriosis patients. The top-ranked upregulated DEIRGs were upregulated in the endometra of infertile women. Functional analysis showed that DETFs and DEIRGs may be involved in the biological behaviors and pathways of endometriosis. The TF-IRG PPI network was successfully constructed. Compared with the control group, high C3, VCAM1, ITGB2, and C3AR1 expression had statistical significance in endometriosis among the hub DEIRGs. They also showed higher sensitivity and specificity by ROC analysis for the diagnosis of endometriosis. Finally, compared with controls, C3 and VCAM1 were highly expressed in endometriosis tissue samples. In addition, they also showed high specificity and sensitivity for diagnosing endometriosis. Overall, we discovered the TF-IRG regulatory network and analyzed 4 hub IRGs that were closely related to endometriosis, which contributes to the diagnosis of endometriosis. Additionally, we verified that DETFs or DEIRGs were associated with the clinicopathological features of endometriosis, and external datasets also confirmed the hub IRGs. Finally, C3 and VCAM1 were highly expressed in endometriosis tissue samples compared with controls and may be potential biomarkers of endometriosis, which are helpful for the early diagnosis of endometriosis.

TiOx-supported Na-Mn-W oxides for the oxidative coupling of methane

Supported Na-Mn-W oxides are among the most studied catalysts for the oxidative coupling of methane (OCM) because of their superior thermal stability and relatively high C2+ product yields. However, because of the structural complexity, the roles of each component in these catalysts have been controversial. In this work, WOx and MnOx sites were supported on titanate nanowires and employed in OCM studies. Compared to the commonly studied silica support, which is subject to severe restructuring due to the Na-induced crystallization, titanate support not only serves as a reservoir for alkali metals (e.g., Na), but also stabilizes isolated MnOx species. The catalytic performance of the titanate-based catalyst is similar to that of reference catalyst, MnOx/Na2WO4/SiO2, with a synergistic effect between MnOx and WOx sites. Advanced electron microscopy, X-ray diffraction, infrared spectroscopy, and X-ray absorption near edge structure spectroscopy suggest that the basic NaOx and MnOx species have strong interactions with the acidic WOx and TiOx species, which might contribute to the high selectivity toward C2+ products and suppressed COx formation.

P-Mediated Cu-N4 Sites in Carbon Nitride Realizing CO2 Photoreduction to C2 H4 with Selectivity Modulation.

Photocatalytic CO2 reduction to high value-added C2 products (e.g., C2 H4 ) is of considerable interest but challenging. The C2 H4 product selectivity strongly hinges on the intermediate energy levels in the CO2 reduction pathway. Herein, Cu-N4 sites anchored phosphorus-modulated carbon nitride (CuACs/PCN) is designed as a photocatalyst to tailor the intermediate energy levels in the the C2 H4 formation reaction pathway for realizing its high production with tunable selectivity. Theoretical calculations combined with experimental data demonstrate that the formation of the C-C coupling intermediates can be realized on Cu-N4 sites and the surrounding doped P facilitates the production of C2 H4 . Thus, CuACs/PCN exhibits a high C2 H4 selectivity of 53.2% with a yielding rate of 30.51 µmolg-1 . The findings reveal the significant role of the coordination environment and surrounding microenvironment of Cu single atoms in C2 H4 formation and offer an effective approach for highly selective CO2 photoreduction to produce C2 H4 .

Effect of different oxygen species on the oxidative coupling of methane over TiO2 catalysts

TiO2 is widely used in oxidative coupling of methane (OCM) reaction because of its low cost, reducibility and nontoxicity, but pure TiO2 has poor activity on methane activation. Density functional theory with an additional Hubbard-like parameter (DFT + U) was used to research OCM reaction on Ir/TiO2(001), Pt/TiO2(001) and Mn/TiO2(001) catalysts to explore catalysts with high activity and C2 hydrocarbon selectivity. The results indicate that Ir, Pt and Mn doping can significantly improve the activity of lattice oxygen and reduce the activation energy of methane dissociation. Additionally, the evolution of oxygen species on Ir/TiO2(001) Pt/TiO2(001) and Mn/TiO2(001) catalysts show that the lattice oxygen species and peroxide species have the strongest activity to activate methane. However, the superoxide species has the worst activity. Furthermore, the formation paths of ethane and ethylene were researched on Ir/TiO2(001), Pt/TiO2(001) and Mn/TiO2(001) surfaces. And we expect that Ir/TiO2(001) is effective for catalyzing OCM reaction.

Identifying an Interfacial Stabilizer for Regeneration-Free 300 h Electrochemical CO2 Reduction to C2 Products.

The electrochemical CO2 reduction reaction (CO2RR) to produce high value-added hydrocarbons and oxygenates presents a sustainable and compelling approach toward a carbon-neutral society. However, uncontrollable migration of active sites during the electrochemical CO2RR limits its catalytic ability to simultaneously achieve high C2 selectivity and ultradurability. Here, we demonstrate that the generated interfacial CuAlO2 species can efficiently stabilize the highly active sites over the Cu-CuAlO2-Al2O3 catalyst under harsh electrochemical conditions without active sites regeneration for a long-term test. We show that this unique Cu-CuAlO2-Al2O3 catalyst exhibits ultradurable electrochemical CO2RR performance with an 85% C2 Faradaic efficiency for a 300 h test. Such a simple interfacial engineering design approach unveiled in this work would be adaptable to develop various ultradurable catalysts for industrial-scale electrochemical CO2RR.

Serum C3 complement levels predict prognosis and monitor disease activity in Guillain-Barré syndrome

ObjectiveBiomarkers are needed to predict prognosis and disease activity in patients with Guillain-Barré syndrome (GBS). The complement system is a key player in the pathogenesis of GBS. This study aimed to assess the potential utility of serum complement proteins as novel biomarkers in GBS. MethodsWe reviewed the medical records of 76 GBS patients with C3 and C4 measurements during hospitalization between 2010 and 2021. Clinical outcomes were correlated with baseline serum C3, C4, and seven additional predictors: four existing biomarkers (GM1, albumin, immunoglobulin G, neutrophil-lymphocyte ratio) and three clinical factors from the modified Erasmus GBS outcome score model. Five complement activation products (C3a, C4a, C5a, soluble C5b-9, factor Bb) were measured in 35 patients and were compared with C3 and C4 levels. Longitudinal changes in C3 and C4 levels were compared with the disease course in 12 patients. ResultsHigher C3, but not C4, was associated with poorer outcomes: lower Medical Research Council sum scores (MRCSS), higher GBS disability score (GBSDS), longer hospitalization, and more frequent treatment-related fluctuations. Age, MRCSS at admission, and baseline serum C3 were significant independent indicators of 1- and 3-month GBSDS. We found that C3 was positively correlated with C3a (r = 0.32) and C5a (r = 0.37), which indicates an activated complement cascade with high C3. Longitudinal change of C3 coincided with clinical severity of the disease course. InterpretationThis study highlights the use of serum C3 as a novel mechanistic biomarker in GBS. Larger prospective studies are needed to validate our findings.

Impact of the growth environment in inductively coupled plasma on the synthesis and morphologies of carbon nanohorns

The fabrication of carbon nanohorns (CNHs) from a methane precursor with argon in an inductively coupled plasma was recently demonstrated with a high production rate of ∼20 g/h by Casteignau et al. [Plasma Chem. Plasma Process. 42, 465 (2022)]. The presence of a promotor gas such as hydrogen was found to be important for the growth of CNHs, but the mechanisms at play remain unclear. Here, we study the impact of different promotor gases by replacing hydrogen with nitrogen and helium at different promotor:precursor (Pm:Pr) ratios, X:CH4 = 0.3–0.7 (X = H2 or N2, Ar, and He), and global flow rates FX+FCH4=1.7 and 3.4 slpm. The nature of the promotor gas is shown to directly influence the morphology and the relative occurrence of CNHs, graphitic nanocapsules (GNCs), and graphene nanoflakes. Using quantitative transmission electron microscopy, we show that CNHs are favored by an X:CH4 = 0.5, preferably with X = He or N2. With a lower total flow rate (1.7 slpm) of N2, even larger production rates and higher selectivity toward CNHs are achieved. Optical emission spectroscopy was used to probe the plasma and to demonstrate that the nature promotor gas strongly modulates the C2 density and temperature profile of the plasma torch. It is shown that CNHs nucleation is favored by high C2 density at temperatures exceeding 3500 K localized at the exit-end of the nozzle, creating a reaction zone with extended isotherms. H2 favors CH4 dissociation and creates a high C2 density but cools the nucleation zone, which leads to structures with a strong graphitic character such as GNCs.

Analysis of Risk Factors and the Establishment of a Predictive Model for Thrombosis in Patients with Antineutrophil Cytoplasmic Antibody-Associated Vasculitis.

To explore the risk factors for thrombi occurring in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) and establish a risk prediction model to better predict the risk of thrombosis in patients with AAV. We retrospectively analyzed 117 AAV patients who had been hospitalized in The Second Affiliated Hospital of Chongqing Medical University between October 2010 and December 2021. For all patients, we recorded demographic characteristics and clinical data, analyzed the risk factors for thrombosis in AAV patients and then developed a risk prediction model. Stepwise logistic regression analysis indicated that a high complement C3 level, a high BVAS score and a high Padua score were independent risk factors for thrombosis in AAV patients. According to multivariate analysis, a predictive model for thrombus risk was successfully established; the area under the ROC curve(AUC) was 0.803 (95% CI: 0.716-0.890) and the maximum Youden index, sensitivity and specificity were 0.487, 59.0% and 89.7%, respectively. A high complement C3 level, high BVAS score, and a high Padua score were shown to be independent risk factors for thrombosis in AAV patients. We developed a risk prediction model based on these three risk factors that could predict the risk of thrombosis in AAV patients to some extent.

Upcycling disposable face masks into fuel range iso-alkanes through hydropyrolysis coupled with vapor-phase hydrocracking

The COVID-19 pandemic has resulted in an alarming accumulation of plastic waste. Herein, an integrated hydropyrolysis and hydrocracking process was performed to upcycle disposable masks into fuel-range iso-alkanes over carbon supported ruthenium (Ru/C). Experimental results indicated that catalyst type significantly affected product distribution during the hydropyrolysis and vapor-phase hydrocracking of disposable masks. Compared with zeolites-induced catalytic cascade process where up to ∼25.9 wt% yield of aromatic hydrocarbons such as toluene and xylenes were generated, a ∼82.7 wt% yield of desirable iso-alkanes with a high C5–C12 gasoline selectivity of 95.5% was obtained over Ru/C under 550 °C hydropyrolysis temperature and 300 °C hydrocracking temperature at 0.2 MPa H2. The cascade hydropyrolysis and hydrocracking process also exhibited high adaptability and flexibility in upcycling single-use syringes, food packaging, and plastic bags, generating 79.1, 81.6, and 80.3 wt% yields of fuel range iso/n-alkanes, respectively. This catalytic cascade hydrotreating process provides an efficient and effective approach to convert pandemic-derived plastic waste into gasoline-range fuel products.

A Self-Forming CO2/O2 Co-Transport Dual-Phase Membrane for Oxidative Coupling of Methane

Direct methane conversion (DMC) has garnered considerable interest from both industries and academia in recent years due to its great economic potential created by significantly increased price differential between low-cost natural gas (NG) and the derived value-added chemicals. Oxidative coupling of methane (OCM), which transforms CH4 into ethylene (C2H4) with molecular O2 as the oxidant in a single step, is one of the most studied DMCs. However, a major technical challenge for the OCM process is the difficulty to achieve high CH4 conversion at high C2 (ethane or ethylene) selectivity. The rudimentary cause for this “tradeoff” behavior is that the products (C2H6 or C2H4) are chemically more reactive than the reactant (CH4). To overcome this thermodynamic hurdle, minimizing the oxidizing power of the oxidant or lowering the local oxygen partial pressure is key. In this presentation, we show a CO2/O2 co-transport membrane reactor for OCM conversion. The results explicitly show that the permeated O2 can react preferably with CH4 as in the conventional OCM to form C2H6; the latter then undergoes thermal cracking into C2H4 and H2. The roles of the permeated CO2 are assumed to be reacting with H2 via reverse water gas shift (RWGS) reaction to shift the C2H6 thermal cracking; another role of CO2 is assumed to be mitigating coke formation via Boudouard (RB) reaction.

Acoustic Effects of the Singing Voice Quality of Untrained Female Singers in Malaysia

Vocal warm-ups are widespread and comprehensive in the singing community. Although it is well recognised and practised by professionals, warm-ups are sometimes bypassed and neglected by singers and voice teachers. The objective of this study is to assess the impact of vocal warm-up on vocal quality through acoustic parameters of jitter (%), shimmer (%), and harmonics-to-noise (HNR [dB]) in two-pitch conditions, A3 (chest register) and C5 (head register), before and after vocal warm-up. Forty untrained female singers were recorded twice while uttering the vowels /a/, /o/, and /i/ in two different pitches: Low—A3 (220.0 Hz) and High—C5 (523.2 Hz) for at least five seconds. A standardised warm-up protocol with a duration of 20-minute was carried out in this study. The subjects were recorded immediately before and after a 20-minute vocal warm-up session. Significant improvements were found in the mean values of measured acoustic parameters. A decrease was observed compared with the mean jitter and shimmer values before and after a vocal warm-up, while the HNR increased. All the acoustic variables, jitter, shimmer, and HNR were found to have significantly larger improvements in the lower pitch, A3 (chest register), compared to the higher pitch, C5 (head register). The findings of this study provided empirical evidence for the beneficial effect of vocal warm-up on the voice quality of untrained female singers. The positive effects of the findings indicated that the vocal warm-up should be encouraged and not bypassed.

Classifying and understanding the role of carbon deposits on cobalt catalyst for Fischer-Tropsch synthesis

There is less agreement on the role of carbon deposits during FT reaction. Identifying and characterizing carbon species of cobalt catalyst is highly challenging for the Fischer-Tropsch Synthesis (FTS). Here, a serial of predeposited composite carbon and single carbon are constructed, and their roles in F-T synthesis are investigated on metal cobalt catalyst excluding the texture influence of the promoter and the support. Different carbon deposits are introduced on cobalt-based catalysts under different carbon-containing reducing atmospheres utilizing the pretreatment method. Atomic carbon, polymeric carbon, graphitic carbon, and combinations of them were distinguished by the characterization techniques of TPH, Raman and XPS. A significant difference occurred in both the catalytic activity and selectivity to methane after predeposited carbon on the Co-based catalysts. The p-Co-5 % syn-3 g-24 h-250-RO catalyst with single atomic carbon shows a remarkably low methane selectivity (4.03 %), high C5+ selectivity (76.38 %), and more importantly, excellent stability (TOS = 144 h) in FTS. Moreover, all of the Co-based catalysts containing the predeposited carbon can be directly used in the FT reaction without reduction procedure.