A polynomial-time algorithm to solve the large scale of airplane refueling problem

Airplane refueling problem is a nonlinear combinatorial optimization problem with $n!$ feasible feasible solutions. Given a fleet of $n$ airplanes with mid-air refueling technique, each airplane has a specific fuel capacity and fuel consumption rate. The fleet starts to fly together to a same target and during the trip each airplane could instantaneously refuel to other airplanes and then be dropped out. The question is how to find the best refueling policy to make the last remaining airplane travels the farthest. To solve the large scale of the airplane refueling problem in polynomial-time, we propose the definition of the sequential feasible solution by employing the data structural properties of the airplane refueling problem. We prove that if an airplane refueling problem has feasible solutions, it must have sequential feasible solutions, and its optimal feasible solution must be the optimal sequential feasible solution. Then we present the sequential search algorithm which has a computational complexity that depends on the number of sequential feasible solutions referred to $Q_n$, which is proved to be upper bounded by $2^{n-2}$ as an exponential bound that lacks of applicability on larger input for worst case. Therefore we investigate the complexity behavior of the sequential search algorithm from dynamic perspective, and find out that $Q_n$ is bounded by $\frac{m^2}{n}C_n^m$ when the input $n$ is greater than $2m$. Here $m$ is a constant and $2m$ is regarded as the "inflection point" of the complexity of the sequential search algorithm from exponential-time to polynomial-time. Moreover, we build an efficient computability scheme according to which we shall predict the specific complexity of the sequential search algorithm to choose a proper algorithm considering the available running time for decision makers or users.Comment: 18 pages, 2 figure

The nn-vehicle exploration problem is NP-complete

The $n$-vehicle exploration problem (NVEP) is a combinatorial optimization problem, which tries to find an optimal permutation of a fleet to maximize the length traveled by the last vehicle. NVEP has a fractional form of objective function, and its computational complexity of general case remains open. We show that Hamiltonian Path $\leq_P$ NVEP, and prove that NVEP is NP-complete.Comment: 5 pages, 6 figure

Effect of bioaugmentation on gas production and microbial community during anaerobic digestion in a low-temperature fixed-bed reactor

Low temperature is one of the limiting factors for anaerobic digestion in cold regions. To improve the efficiency of anaerobic digestion for methane production in stationary reactors under low-temperature conditions, and to improve the structure of the microbial community for anaerobic digestion at low temperatures. We investigated the effects of different concentrations of exogenous Methanomicrobium (10, 20, 30%) and different volumes of carbon fiber carriers (0, 10, 20%) on gas production and microbial communities to improve the performance of low-temperature anaerobic digestion systems. The results show that the addition of 30% exogenous microorganisms and a 10% volume of carbon fiber carrier led to the highest daily (128.15 mL/g VS) and cumulative (576.62 mL/g VS) methane production. This treatment effectively reduced the concentrations of COD and organic acid, in addition to stabilizing the pH of the system. High-throughput sequencing analysis revealed that the dominant bacteria under these conditions were Acidobacteria and Firmicutes and the dominant archaea were Candidatus_Udaeobacter and Methanobacterium. While the abundance of microorganisms that metabolize organic acids was reduced, the functional abundance of hydrogenophilic methanogenic microorganisms was increased. Therefore, the synergistic effect of Methanomicrobium bioaugmentation with carbon fiber carriers can significantly improve the performance and efficiency of low-temperature anaerobic fermentation systems

Phase engineering of multimetallic nanostructures for electrocatalytic applications

Noble metallic nanomaterials have abundant potential applications in the field of energy conversion. Synthesizing novel crystal-structured nanomaterials such as multicomponent nanostructures provides a facile way to reach novel functionalities owing to the modification of atomic arrangements, electronic structures, and exceptional functionalities originating from their synergistic components, which is also a promising strategy for novel nanocatalyst development. To date, various effective approaches have been fostered to discover the novel nanocatalysts with fine-tuned size, morphology, structure and composition, which can indeed optimize the electrocatalytic performance. Nonetheless, it is indeed fully challengeable to prepare multimetallic hybrid nanostructures with desired chemical composition, surface structure, and crystal phase for specific applications, which are critical in fundamental studies, as well as practical applications. In this thesis, I will present my research works on structure engineering (i.e., phase engineering and defects engineering) of multimetallic nanostructures via wet chemical synthesis and electron beam irradiation under high-resolution TEM for electrocatalytic applications. Structure engineering of noble metal nanomaterials are effective strategy to obtain novel nanostructures with desired morphology, composition, defects, and crystal phase. A series of Au nanostructures with unconventional phases such as fcc, hcp (i.e., 2H), 4H, 4H/fcc, and 2H/fcc heterophase have been synthesized via wet chemical synthesis. In the first project, the effects on the synthesis of multimetallic nanostructures of various Au templates such as fcc Au nanowires, 4H/fcc Au nanorods and 4H Au nanoribbons are investigated systematically. In addition, the crystal structure effects on the as-synthesized structures and properties are studied. In this project, the noble metallic hybrid heterostructures with various morphologies and crystalline structures were well characterized. Moreover, the crystal phase selective growth and etching strategies will be further studied. As known, defects such as twins, stacking faults, atomic steps and lattice strain in metallic nanostructures can modulate their atomic arrangement in atomic scale, electronic structures and surface activities, and thus improve their electrocatalytic performance. However, defect engineering in multimetallic nanostructures with desired composition, morphology and surface structure, which can further optimize their stability and activity, still remains a great challenge. Therefore, the rational design and synthesis of multimetallic nanostructures with rich defects are highly desirable, which is important not only in fundamental studies but also in practical applications. Phase transformation of the aforementioned Au based nanostructures with unconventional phases can generate various novel nanostructures with new phase, which can be induced by ligand exchange, metal coating, high pressure and high temperature. Nevertheless, direct observation of phase transformation pathway is still of great challenge. In the second project, the size-dependent phase transformation between various Au based nanostructures with novel phases are investigated under electron beam irradiation via in-situ TEM observation. Particularly, the phase transformation is dependent on the ratio of the size of the monocrystalline nanoparticle (NP) to the diameter of 4H nanodomains in 4H/fcc Au nanorod (4H AuND). Furthermore, molecular dynamics simulation and theoretical modeling are used to explain the experimental results, giving a size-dependent phase transformation diagram which provides a general guidance to predict the phase transformation pathway between fcc and 4H Au nanomaterials.Doctor of Philosoph

Effects of simulated nitrogen deposition on soil microbial biomass and community function in subtropical evergreen broad-leaved forest

Aim of the study: The aim of this study was to examine the effects of a 5-year simulated nitrogen (N) deposition on soil microbial biomass carbon (MBC), nitrogen (MBN), microbial community activity and diversity in subtropical old-growth forest ecosystems.Area of study: The study was conducted in forest located at subtropical forest in Anhui, east China.Material and methods: Three blocks with three fully randomized plots of 20 m × 20 m with similar forest community and soil conditions were established. The site applied ammonium nitrate (NH4NO3) to simulate N deposition (50 and 100 kg N ha−1 year −1). From three depths (0–10, 10–20 and 20–30 cm), were collected over four seasons (December, March, June and September), and then measured by community-level physiological profiles (CLPPs).Main results: N addition had no significant effect on MBC and MBN. The spatiotemporal variations in MBC and MBN were controlled by seasonality and soil depth. Soil microbial activities and diversity in the growing season (June and September) were apparently higher than the dormant season (March and December), there were significantly lower diversity indices found following N addition in September. However, N addition enhanced microbial activities and increased diversity indices in the dormant season. Redundancy analysis showed that pH, soil moisture, NO3--N and total phosphorus were the most important factors controlling the spatial pattern of microbial metabolic activity.Research highlights: These results suggest that soil microbial community function is more easily influenced than microbial biomass. The site has a trend of P-limited or near-N saturation, and will threaten the whole forest ecosystem with the increasing duration of N addition.Keywords: Nitrogen deposition; Seasonality; Soil microbial biomass; Microbial community; Subtropical old-growth forest

Circulating Endocannabinoids and Insulin Resistance in Patients with Obstructive Sleep Apnea

Objectives. The purpose of this study is to investigate the relationship between plasma endocannabinoids and insulin resistance (IR) in patients with obstructive sleep apnea (OSA). Methods. A population of 64 with OSA and 24 control subjects was recruited. Body mass index (BMI), waist circumference, lipids, blood glucose and insulin, homeostasis model of assessment for insulin resistance index (HOMA-IR), anandamide (AEA), 1/2-arachidonoylglycerol (1/2-AG), and apnea-hypopnea index (AHI) were analyzed. Results. Fasting blood insulin (22.9 ± 7.8 mIU/L versus 18.5 ± 7.2 mIU/L, P<0.05), HOMA-IR (2.9 ± 1.0 versus 2.4 ± 0.9, P<0.01), AEA (3.2 ± 0.7 nmol/L versus 2.5 ± 0.6 nmol/L, P<0.01), and 1/2-AG (40.8 ± 5.7 nmol/L versus 34.3 ± 7.7 nmol/L, P<0.01) were higher in OSA group than those in control group. In OSA group, AEA, 1/2-AG, and HOMA-IR increase with the OSA severity. The correlation analysis showed significant positive correlation between HOMA-IR and AHI (r=0.44, P<0.01), AEA and AHI (r=0.52, P<0.01), AEA and HOMA-IR (r=0.62, P<0.01), and 1/2-AG and HOMA-IR (r=0.33, P<0.01). Further analysis showed that only AEA was significantly correlated with AHI and HOMA-IR after adjusting for confounding factors. Conclusions. The present study indicated that plasma endocannabinoids levels, especially AEA, were associated with IR and AHI in patients with OSA

RNA N6-Methyladenosine Modification in DNA Damage Response and Cancer Radiotherapy

The N6-methyladenosine (M6A) modification is the most common internal chemical modification of RNA molecules in eukaryotes. This modification can affect mRNA metabolism, regulate RNA transcription, nuclear export, splicing, degradation, and translation, and significantly impact various aspects of physiology and pathobiology. Radiotherapy is the most common method of tumor treatment. Different intrinsic cellular mechanisms affect the response of cells to ionizing radiation (IR) and the effectiveness of cancer radiotherapy. In this review, we summarize and discuss recent advances in understanding the roles and mechanisms of RNA M6A methylation in cellular responses to radiation-induced DNA damage and in determining the outcomes of cancer radiotherapy. Insights into RNA M6A methylation in radiation biology may facilitate the improvement of therapeutic strategies for cancer radiotherapy and radioprotection of normal tissues