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In this paper, a radio-frequency magnetron sputtering system without any assisting ion source was employed to fabricate biaxially textured MgO films on the substrates of amorphous Y 2 O 3 /Al 2 O 3 /Hastelloy stacks. During the deposition process, the growing MgO film was bombarded by an off-normal energetic particle flux mainly composed of oxygen atoms and negative oxygen ions, which originated from the target surface. MgO obtained a biaxial texture due to such bombardment; thus, this method is named energetic particle self-assist deposition (EPSAD). The texture of EPSAD-MgO films was evaluated via the X-ray diffraction measurement of the postdeposited homoepitaxial MgO layers. An out-of-plane orientation of MgO(111) and a three-fold symmetric in-plane alignment were observed. The MgO texture was optimal when the EPSAD-MgO thickness was about 10 nm. The formation of biaxial texture during the EPSAD process was verified by a control study, and the influences of targetinclined angle and target-substrate distance were also investigated. Furthermore, the mechanism of the EPSAD-MgO method was compared with those of the inclined substrate deposition and ion beam assisted deposition. This study proposed a new method to fabricate a biaxially textured MgO buffer layer for high temperature superconducting (HTS) coated conductors. More optimization research will be conducted in our future study.

During the fabrication of $\text{YBa}_{2}\text{Cu}_{3}\text{O}_{7-\delta}$ (YBCO) superconducting films via metal organic deposition (MOD) method, the crystallization temperature $(T)$ is an important parameter for YBCO nucleation and growth. In this paper, in situ resistance measurements were performed to investigate the influence of $T$ on the growth rate $(R)$ and saturation nuclei density $(N)$ of the YBCO film. Based on the reaction–diffusion model, the specific equation of $R$ as a function of $T$ was established, and the thermodynamics variables, including standard entropy change, standard enthalpy change, and standard Gibbs free energy change of YBCO formation reaction, were estimated. The influence of $T$ on $N$ was analyzed, according to the “capture zone” kinetics mechanism, and the average activation energy for surface diffusion during YBCO nucleation was estimated. The thermodynamics and kinetics analysis in this paper could help to obtain more understanding on the heat treatment process of MOD-YBCO film fabrication.

Cellulose and xylan are two major components of lignocellulosic biomass, which represents a potentially important energy source, as it is abundant and can be converted to methane by microbial action. However, it is recalcitrant to hydrolysis, and the establishment of a complete anaerobic digestion system requires a specific repertoire of microbial functions. In this study, we maintained 2-year enrichment cultures of anaerobic digestion sludge amended with cellulose or xylan to investigate whether a cellulose- or xylan-digesting microbial system could be assembled from sludge previously used to treat neither of them. While efficient methane-producing communities developed under mesophilic (35°C) incubation, they did not under thermophilic (55°C) conditions. Illumina amplicon sequencing results of the archaeal and bacterial 16S rRNA genes revealed that the mature cultures were much lower in richness than the inocula and were dominated by single archaeal (genus Methanobacterium ) and bacterial (order Clostridiales ) groups, although at finer taxonomic levels the bacteria were differentiated by substrates. Methanogenesis was primarily via the hydrogenotrophic pathway under all conditions, although the identity and growth requirements of syntrophic acetate-oxidizing bacteria were unclear. Incubation conditions (substrate and temperature) had a much greater effect than inoculum source in shaping the mature microbial community, although analysis based on unweighted UniFrac distance found that the inoculum still determined the pool from which microbes could be enriched. Overall, this study confirmed that anaerobic digestion sludge treating nonlignocellulosic material is a potential source of microbial cellulose- and xylan-digesting functions given appropriate enrichment conditions.

We prove a functional central limit theorem for Markov additive arrival processes where the modulating Markov process has the transition rate matrix scaled up by $$n^{\alpha }$$nź ($$\alpha >0$$ź>0) and the mean and variance of the arrival process are scaled up by n. It is applied to an infinite-server queue and a fork---join network with a non-exchangeable synchronization constraint, where in both systems both the arrival and service processes are modulated by a Markov process. We prove functional central limit theorems for the queue length processes in these systems joint with the arrival and departure processes, and characterize the transient and stationary distributions of the limit processes. We also observe that the limit processes possess a stochastic decomposition property.

We study $$G/GI/N(+GI)$$ queues with alternating renewal service interruptions in the Halfin–Whitt regime. The systems experience up and down alternating periods. In the up periods, the systems operate normally as the usual $$G/GI/N(+GI)$$ queues with non-idling first-come–first-served service discipline. In the down periods, arrivals continue entering the systems, but all servers stop functioning while the amount of service that each customer has received will be conserved and services will resume when the next up period starts. For models with abandonment, interruptions do not affect customers’ patience times. We assume that the up periods are of the same order as the service times but the down periods are asymptotically negligible compared with the service times. We establish the functional central limit theorems for the queue-length processes and the virtual-waiting time processes in these models, where the limit processes are represented as stochastic integral convolution equations driven by jump processes. The convergence in these limit theorems is proved in the space $${\mathbb D}$$ endowed with the Skorohod $$M_1$$ topology.

While CaO has exhibited promising prospects and been identified as one of the best candidates for high-temperature CO2 capture, it suffers a well-known problem of loss-in-capacity; that is, its sorption capacity decays quickly with the increase of cycle numbers. In the last decade, extensive work has been conducted on the incorporation of CaO into inert solid support particles to preventing sintering and, thus, to enhance its cyclic CO2 sorption performance. With the rapid progress in this aspect, a timely review is highly required. This work summarized the state-of-the-art researches in the literature, mainly including the synthesis methods to finely disperse inert supports among CaO particles and various inert supports to prevent sintering. In addition, the effectiveness of various supports via different incorporating methods and test conditions are discussed and quantitatively compared in the current work. The highly required future development trends of synthetic CaO sorbents are also recommended in the last part of this work. We expect that this work will inspire and guide researchers from both academic and industrial communities and help pave the way for major breakthroughs in both fundamental research and industrial applications in this field.

Microorganisms can manufacture a wide range of biobased chemicals that are useful for diverse industrial applications. However, the overexpression of heterologous enzymes in recombinant strains often leads to metabolic imbalance, resulting in growth retardation and suboptimal production of the target compounds. Here we discuss the recent development of modular metabolic engineering approaches that enable the global fine-tuning of engineered pathways by modularizing the synthetic pathway in single or multiple hosts. In particular, we highlight applications with microbial consortia. To build a vibrant biobased economy, multivariate modular metabolic engineering (MMME), modular coculture engineering (MCE), and spatiotemporal and integrative genome-scale metabolic modeling can be exploited to expedite strain optimization and improve the production of a broad variety of high-value biobased chemicals.

Background Although anaerobic digestion for biogas production is used worldwide in treatment processes to recover energy from carbon-rich waste such as cellulosic biomass, the activities and interactions among the microbial populations that perform anaerobic digestion deserve further investigations, especially at the population genome level. To understand the cellulosic biomass-degrading potentials in two full-scale digesters, this study examined five methanogenic enrichment cultures derived from the digesters that anaerobically digested cellulose or xylan for more than 2 years under 35 or 55 °C conditions. Results Metagenomics and metatranscriptomics were used to capture the active microbial populations in each enrichment culture and reconstruct their meta-metabolic network and ecological roles. 107 population genomes were reconstructed from the five enrichment cultures using a differential coverage binning approach, of which only a subset was highly transcribed in the metatranscriptomes. Phylogenetic and functional convergence of communities by enrichment condition and phase of fermentation was observed for the highly transcribed populations in the metatranscriptomes. In the 35 °C cultures grown on cellulose, Clostridium cellulolyticum-related and Ruminococcus-related bacteria were identified as major hydrolyzers and primary fermenters in the early growth phase, while Clostridium leptum-related bacteria were major secondary fermenters and potential fatty acid scavengers in the late growth phase. While the meta-metabolism and trophic roles of the cultures were similar, the bacterial populations performing each function were distinct between the enrichment conditions. Conclusions Overall, a population genome-centric view of the meta-metabolism and functional roles of key active players in anaerobic digestion of cellulosic biomass was obtained. This study represents a major step forward towards understanding the microbial functions and interactions at population genome level during the microbial conversion of lignocellulosic biomass to methane. The knowledge of this study can facilitate development of potential biomarkers and rational design of the microbiome in anaerobic digesters. Electronic supplementary material The online version of this article (10.1186/s13068-018-1121-0) contains supplementary material, which is available to authorized users.

Additional file 6. Heatmap showing the transcriptional profiles of major CAZymes for the highly transcribed PGs based on log-transformed TPM values. The top 10 glycoside hydrolase families and top 5 families of other functional categories were plotted with other lower transcribed families grouped into the â Otherâ category. The grey color represents no detected transcription.

The integration of dark and photo fermentation is a promising strategy to enhance biohydrogen productivity and substrate utilization, and therefore can be adopted to advance the development of industrial biohydrogen production. However, the mutualistic interactions between dark fermentative and purple non-sulfur photosynthetic microorganisms remain poorly understood due to the challenges of incorporating two physiologically different bacteria in one integrated fermentation system. In this work, an experimentally and genetically tractable model combining the cellulose-degrading bacterium Clostridium cellulovorans 743B and photosynthetic bacterium Rhodopseudomonas palustris CGA009 was successfully established. The responses of this coculture system to different cellulose concentrations were characterized. At all four levels of initial cellulose concentrations (2, 3, 4 or 5 g/L), the hydrogen productivity and cellulose degradation of cocultures were all significantly enhanced to varying extents in comparison to monocultures. The mechanism of the beneficial interaction was due to consumption of volatile fatty acids by R. palustris , which in turn balanced the pH to increase cellulose consumption by C. cellulovorans . Overall, the results demonstrated that the mutualism between C. cellulovorans and R. palustris could lead to a more efficient biohydrogen production process, thus making the pairing of these two strains a suitable model for further study on syntrophic interactions.

Additional file 1:Table S1. Primer sequences for selected genes in RT-qPCR. Table S2. Primer sequences for internal control genes in RT-qPCR. Figure S1. Acetate concentration and CH4 production profiles of (a) monocultures of M. barkeri and (b) monocultures of M. mazei. Figure S2. (a) Acetate and formate concentrations and (b) H2 consumption and CH4 production of monocultures of M. barkeri grown with 10 mM of formate, 3 mM of acetate, and 0.95 mmol of H2. Figure S3. (a) Acetate concentration and (b) H2 consumption and CH4 production of monocultures of M. barkeri grown with 3 mM of acetate and 0.95 mmol of H2. Table S3. Products of cellulose fermentation by C. cellulovorans monocultures. Table S4. Gene expression of the selected C. cellulovorans (CC) genes in response to cocultivation with M. barkeri (MB) or M. mazei (MM) at mid-exponential growth phase. Table S5. Gene expression of the selected M. barkeri (MB) genes in response to cocultivation with C. cellulovorans (CC) at mid-exponential growth phase. Table S6. Gene expression of the selected M. mazei (MM) genes in response to cocultivation with C. cellulovorans (CC) at mid-exponential growth phase Figure S4. Comparison of the increase in cell density over the course of the experiment. Cell density at time zero was about 3.0 Ă 107 cells/mL for the experiments.

Anaerobic digestion (AD) is a microbial process widely used to treat organic wastes. While the microbes involved in digestion of municipal sludge are increasingly well characterized, the taxonomic and functional compositions of AD digesters treating industrial wastewater have been understudied. This study examined metagenomes from a biogas-producing digester treating municipal sludge in Shek Wu Hui (SWH), Hong Kong and an industrial wastewater digester in Guangzhou (GZ), China, and compared their taxonomic composition and reconstructed biochemical pathways. Genes encoding carbohydrate metabolism and protein metabolism functions were overrepresented in GZ, while genes encoding functions related to fatty acids, lipids and isoprenoids were overrepresented in SWH, reflecting the plants’ feedstocks. Mapping of genera to functions in each community indicated that both digesters had a high level of functional redundancy, and a more even distribution of genera in GZ suggested that it was more functionally stable. While fermentation in both samples was dominated by Clostridia, SWH had an overrepresentation of Proteobacteria, including syntrophic acetogens, reflecting its more complex substrate. Considering the growing importance of biogas as an alternative fuel source, a detailed mechanistic understanding of anaerobic digestion is important and this report will be a basis for further study of industrial wastewater AD.

Coculturing dark- and photofermentative bacteria is a promising strategy for enhanced hydrogen (H 2 ) production. In this study, next-generation sequencing was used to query the global transcriptomic responses of an artificial coculture of Clostridium cellulovorans 743B and Rhodopseudomonas palustris CGA009. By analyzing differentially regulated gene expression, we showed that, consistent with the physiological observations of enhanced H 2 production and cellulose degradation, the nitrogen fixation genes in R. palustris and the cellulosomal genes in C. cellulovorans were upregulated in cocultures. Unexpectedly, genes related to H 2 production in C. cellulovorans were downregulated, suggesting that the enhanced H 2 yield was contributed mainly by R. palustris . A number of genes related to biosynthesis of volatile fatty acids (VFAs) in C. cellulovorans were upregulated, and correspondingly, a gene that mediates organic compound catabolism in R. palustris was also upregulated. Interestingly, a number of genes responsible for chemotaxis in R. palustris were upregulated, which might be elicited by the VFA concentration gradient created by C. cellulovorans . In addition, genes responsible for sulfur and thiamine metabolism in C. cellulovorans were downregulated in cocultures, and this could be due to a response to pH changes. A conceptual model illustrating the interactions between the two organisms was constructed based on the transcriptomic results. IMPORTANCE The findings of this study have important biotechnology applications for biohydrogen production using renewable cellulose, which is an industrially and economically important bioenergy process. Since the molecular characteristics of the interactions of a coculture when cellulose is the substrate are still unclear, this work will be of interest to microbiologists seeking to better understand and optimize hydrogen-producing coculture systems.

We consider many-server queues with delayed feedback where the service (patience) times of new customers and feedback customers are differentiated, and new and feedback customers are served under the first-come-first-serve (FCFS) discipline in the service station. The arrival process, service, patience and delay times are all general and mutually independent. A two-parameter fluid model for the system dynamics in the many-server regime is investigated, where we use four two-parameter processes to describe the service and queueing processes of the new and feedback customers, two for the service dynamics and two for the queueing dynamics. When the arrival rate is constant, we derive the steady state performance measures and study the impact of impatience differentiation and service differentiation upon them. When the arrival rate is time-varying, we provide an algorithm to compute the fluid processes. Numerical experiments are conducted, and show that the algorithm is very effective, compared with simulations.

Carbon nitride thin films were synthesized by the reactive ionized cluster beam (RICB) deposition. Raman scattering analysis shows the existence of a characteristic peak due to covalent CN single bonds. This is consistent with the results of Fourier transform infrared (FTIR) transmission measurements. Rutherford backscattering (RBS) measurements show that the composition ratio, N/C, as high as 0.67, can be obtained. The films deposited under the optimized experimental conditions exhibit an extremely high hardness of 61 GPa. The friction and wear behavior of these films without any lubrication were measured by a reciprocating-motion ball-on-disk tribometer. It is noted that the deposited films have low initial and a steady-state friction coefficients less than 0.08. The wear factor of carbon nitride films is significantly lower than that of carbon thin films prepared by the same deposition system and evaluated under similar test conditions. These results are very encouraging for the tribological applications of carbon nitride films.

In this study, MgO thin films were deposited by radio-frequency magnetron sputtering. The film thickness in the deposition area directly facing the target center obviously decreased compared with that in other areas. This reduction in thickness could be attributed to the resputtering effect resulting from bombardment by energetic particles mainly comprising oxygen atoms and negative oxygen ions. The influences of deposition position and sputtering pressure on the deposition rate were investigated. Resputtering altered the orientation of the MgO film from (111) to (001) when the film was deposited on a single crystal yttria-stabilized zirconia substrate. The density distribution of energetic particles was calculated on the basis of the measured thicknesses of the MgO films deposited at different positions. The divergence angle of the energetic particle flux was estimated to be approximately 15°. The energetic particle flux might be similar to the assisting ion flux in the ion beam assisted deposition process and could affect the orientation of the MgO film growth.

Background The interspecies interactions in a biomethanation community play a vital role in substrate degradation and methane (CH4) formation. However, the physiological and molecular mechanisms of interaction among the microbial members of this community remain poorly understood due to the lack of an experimentally tractable model system. In this study, we successfully established two coculture models combining the cellulose-degrading bacterium Clostridium cellulovorans 743B with Methanosarcina barkeri Fusaro or Methanosarcina mazei Gö1 for the direct conversion of cellulose to CH4. Results Physiological characterizations of these models revealed that the methanogens in both cocultures were able to efficiently utilize the products produced by C. cellulovorans during cellulose degradation. In particular, the simultaneous utilization of hydrogen, formate, and acetate for methanogenesis was observed in the C. cellulovorans–M. barkeri cocultures, whereas monocultures of M. barkeri were unable to grow with formate alone. Enhanced cellulose degradation was observed in both cocultures, and the CH4 yield of the C. cellulovorans–M. barkeri cocultures (0.87 ± 0.02 mol CH4/mol glucose equivalent) was among the highest compared to other coculture studies. A metabolic shift in the fermentation pattern of C. cellulovorans was observed in both cocultures. The expression levels of genes in key pathways that are important to the regulation and metabolism of the interactions in cocultures were examined by reverse transcription-quantitative PCR, and the expression profiles largely matched the physiological observations. Conclusions The physiological and molecular characteristics of the interactions of two CH4-producing cocultures are reported. Coculturing C. cellulovorans with M. barkeri or M. mazei not only enabled direct conversion of cellulose to CH4, but also stabilized pH for C. cellulovorans, resulting in a metabolic shift and enhanced cellulose degradation. This study deepens our understanding of interspecies interactions for CH4 production from cellulose, providing useful insights for assembling consortia as inocula for industrial biomethanation processes. Electronic supplementary material The online version of this article (doi:10.1186/s13068-017-0719-y) contains supplementary material, which is available to authorized users.