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We present an L q ( L p ) -theory for the equation ∂ t α u = ϕ ( Δ ) u + f , t > 0 , x ∈ R d ; u ( 0 , ⋅ ) = u 0 . Here p , q > 1 , α ∈ ( 0 , 1 ) , ∂ t α is the Caputo fractional derivative of order α, and ϕ is a Bernstein function satisfying the following: ∃ δ 0 ∈ ( 0 , 1 ] and c > 0 such that (0.1) c ( R r ) δ 0 ≤ ϕ ( R ) ϕ ( r ) , 0 r R ∞ . We prove uniqueness and existence results in Sobolev spaces, and obtain maximal regularity results of the solution. In particular, we prove ‖ | ∂ t α u | + | u | + | ϕ ( Δ ) u | ‖ L q ( [ 0 , T ] ; L p ) ≤ N ( ‖ f ‖ L q ( [ 0 , T ] ; L p ) + ‖ u 0 ‖ B p , q ϕ , 2 − 2 / α q ) , where B p , q ϕ , 2 − 2 / α q is a modified Besov space on R d related to ϕ. Our approach is based on BMO estimate for p = q and vector-valued Calderon-Zygmund theorem for p ≠ q . The Littlewood-Paley theory is also used to treat the non-zero initial data problem. Our proofs rely on the derivative estimates of the fundamental solution, which are obtained in this article based on the probability theory.

NAND flash storage has become a standard choice in consumer electronics and is gaining popularity in enterprise systems due to its superior performance and low-power consumption. While its cost disadvantage is rapidly fading thanks to multibit cell technologies and 3-D stacking architectures, the challenge of limited endurance is still lingering and is expected to become more daunting as bits-per-cell continues to increase. In this article, we propose a novel flash translation layer (FTL) design named AxFTL (Approximate FTL) that extends the lifetime of NAND flash storage for error-tolerant applications. For error-tolerant data, AxFTL adopts shallow erase that lowers erase voltage to reduce the erase-induced wearing at the cost of an increased error rate. AxFTL manages multiple groups of blocks by error rates and allocates them according to the error tolerance of write requests. The key components of AxFTL include error tolerance-aware garbage collection and wear leveling schemes that manage the blocks with different error rates with minimal overhead. We implement AxFTL in an SSD simulator for the evaluation of the lifetime improvement and the actual allocation of the blocks. For application-level evaluation, we apply AxFTL to compressed video storage and evaluate the quality of video playback. Our experimental results show that AxFTL greatly improves the lifetime of NAND flash storage by 61% while maintaining a high structural similarity (SSIM) of 0.86 as compared to the conventional FTL.

A monitoring method of biofouling in reverse osmosis (RO) system was proposed based on the fluorescent signal of resorufin, which is reduced by nicotinamide adenine dinucleotide released from viable cells during aerobic respiration. The fluorescent signal of resorufin reduced by planktonic cells and microorganisms of biofilm showed linearity, indicating its feasibility to monitor biofouling in a RO system. For the application of the method to the lab-scale RO system, the injection concentration of resazurin and the injection flow rate were optimized. Biofilm on RO membranes continuously operated in a lab-scale RO system was estimated by resorufin fluorescence under optimized detection condition. As a result, resorufin fluorescence on RO membrane showed a significant increase in which the permeability of RO system decreased by 30.48%. Moreover, it represented the development of biofilm as much as conventional biofilm parameters such as adenosine triphosphate, extracellular polymeric substances, and biofilm thickness. The proposed method could be used as a sensitive and low-cost technology to monitor biofouling without autopsy of membranes.

Membrane autopsies were performed to understand causes of irreversible fouling on fouled membranes that were used for five years to treat surface water. The results of the autopsies of the membranes taken from the 1st and 2nd stages, i.e., a dual stage configuration to obtain 99% water recovery, showed that fouling layers occurred in both stages and severe fouling of the 2nd stage membrane was obvious. The severe flux decline in the 2nd stage illustrated the importance of the feed water quality. Compositional analyses by scanning electron microscopy with energy dispersive X-ray spectroscopy noted a great increase in the amount of Al on the 2nd stage membrane. Infrared spectra revealed that carboxylic acids, polysaccharide, and aromatic compounds originating from the feed water remained in the membrane. This study suggests that coagulation pretreatment should be implemented with great care because large amounts of Al remain on the membrane surface. In addition, cleaning should be performed in response to both organic and inorganic foulants. The fouling layer on the membrane captured the substantial amounts of inorganics such as Al in addition to organic foulants such as polysaccharide/protein-like compounds.

By overlapping disk accesses with computation-intensive operations, prefetching can reduce delays in launching an application and in loading significant amounts of data while the application is running. The key to effective prefetching is making the tradeoff between the mining accuracy of selecting relevant blocks, and the time to decide those blocks. To address this problem, we propose a new prefetcher called ClusterFetch . In its learning mode, ClusterFetch detects periods of intensive disk accesses by monitoring the speed at which read requests are queued; it re-organizes these reads and locates the file opened by the application just before each such period. During subsequent runs of the same application, ClusterFetch prefetches the data associated with the opening of a “trigger” file. Our experimental results show that ClusterFetch implemented in Linux can reduce the application launch time by up to 41.3 percent and the loading time by up to 38.2 percent, while taking up less than 200 KB of main memory.

Applications face additional latency when they launch or access a disk to load data into the memory. In this paper, a user-level disk prefetching framework, called iFetcher, is introduced to hide this delay in Linux-based operating systems. This employs an inode-notification ( inotify ) application programming interface (API), which provides an efficient method of tracing operations in a Linux file system, and reports these events to applications in real time. During an initial training run, iFetcher traces the pattern with which data are read by an application. Subsequently, it searches the areas directly ahead of passages where it is requested that a lot of data are read, and locates events that can be used to trigger preloading. When the application is run again and a trigger event is reported (by the inotify API), the corresponding data are read into the page cache prior to actual demand. iFetcher has a low overhead, because disk reads are only need to be monitored during training. Furthermore, it does not require any modifications to the Linux kernel, because it runs at the user level. Five benchmark applications were run on a PC using a solid-state drive, and results demonstrated that iFetcher reduced the launch times by up to 41% and post-launch data loading times by up to 9%.

A membrane bioreactor with humic acid substrate (MBR-H) was operated to investigate organic removal and membrane performance. Approximately, 60% of chemical oxygen demand removal was observed in MBR-H. The biosorption capacity reached to the maximum value of 29.2 mg g−1 in the experiments with various activated sludge concentrations and the amount adsorbed on the newly produced microbes was limited. To understand key functions of microorganisms in the biodegradation of humic acid, the microbial community was examined. The dominant phylum was changed from Actinobacteria at the raw sludge to Proteobacteria at the MBR-H. Especially, great increases of β-, γ-, and δ-Proteobacteria in the MBR-H indicated that those class of Proteobacteria played a vital role in humic acid removal. Investigation at the genus level showed enrichment of Stenotrophobacter in the MBR-H, which indicated the presence of metabolites in the proposed humic substance degradation pathway. In addition, the bacteria producing extracellular polymeric substances were increased in the MBR-H. Substantial variation of microbial community function was occurred in the MBR to degrade humic acid. Operational parameters in MBRs might be sought to maintain water permeability and to obtain preferable condition to evolution of microbial consortia for degradation of the refractory organic matter.

Numerous studies on forward osmosis (FO) have been conducted to understand fouling mechanisms better, especially compared to the reverse osmosis (RO) process. In this study, characteristics of concentrates from FO and RO filtrations were investigated to evaluate the rejection mechanisms of organic matter and to elucidate the effects of pressure on the active membrane side and hydrophobicity of organic compounds in the feed solution. The fluorescence excitation–emission matrix (FEEM) and a liquid chromatography-online carbon detector were employed to analyze the properties of organic matter. Secondary wastewater effluent was used to compare the concentrates. More humic-like fractions of organic matter remained in the concentrate from the FO than the RO process. In the concentrate from RO, building blocks and low-molecular weight acid were noticeable. The pressurized filtration experiments of the FO membrane revealed that operation with transmembrane pressure produced similar properties of the conce...

Food waste accounts for a substantial portion of the organic waste generated at an increasing rate worldwide. Organic waste, including food waste, is largely subjected to landfill disposal, incineration, and anaerobic digestion; however, more sustainable methods are needed for treating it. Treatment of organic waste using black soldier fly (Hermetia illucens) larvae is an environmentally safe and cost-efficient method that has been attracting increasing attention worldwide. Black soldier fly decomposes various types of organic waste and converts them into high-value biomasses such as oils and proteins. This review introduces the trends in research related to the treatment of organic waste by black soldier fly (Hermetia illucens) larvae (BSFL) and their bioconversion efficiencies in Asian countries. Perspectives on the growth of BSFL during waste treatment operation and optimal rearing conditions are provided. The trends in studies related to the application of BSFL as biofuel and animal feed are also discussed. Such use of BSFL would be beneficial in Asia, especially in countries where the technology for processing organic waste is not readily available. This review may provide further directions of investigations including culture techniques for industrial scale applications of BSFL in food waste treatment and resource production in Asian countries.

Quorum sensing inhibitors (QSIs) have shown promising results in reducing biofouling in various membrane systems. Vanillin was shown to inhibit QS of gram-negative bacteria during water treatment. Here, four vanillin-analogues with various chemical structures were used to understand the QS mechanisms in biofilm reduction and to compare direct dosing and surface modification of the inhibitors. Biofilm reduction, evaluated based on the content of extracellular polymeric substances (EPS), was the greatest with vanillin (49%) and occurred to some extent with 4-hydroxybenzaldehyde (21%) and m-anisaldehyde (13%), when direct dosing was applied. Experiments using vanillin-analogues revealed crucial roles of the chemical structure and functional groups on the inhibition of biofilm formation. The aldehyde and hydroxyl groups in both vanillin and 4-hydroxybenzaldehyde might be essential for QS inhibition. Further, surface modification with interfacial polymerization and immobilization of QSIs was conducted to evaluate their anti-biofouling capabilities. Surface modification was markedly effective in reducing biofilm formation; the EPS content of biofilms formed on vanillin-incorporated membranes was reduced by 64%. Additionally, the modified membranes showed a water flux comparable to that of pristine membranes, showing little possibility to block membrane pores during modification procedures. These findings will aid the development of QSI-based techniques for biofouling mitigation.

Numerous advantages of forward osmosis (FO) include operation at low or no hydraulic pressure, high rejection of a wide range of contaminants, and low irreversible fouling. The FO has been investigated to reduce effluent discharge in wastewater reclamation. The application of wastewater effluent as a feed stream to FO yields fouling on the active layer of the FO membrane. Fouling was examined using two compounds (i.e., alginate and humic acid) with distinguished hydrophobic properties. The repeated filtration and surface wash were applied and flux decline and reversibility of physical cleaning were evaluated. In addition, the characteristics of fouling cakes and concentrates were also analyzed. The foulants showed different behaviors in flux decline. The thick cake layer of alginate was obvious and the cake enhanced concentration polarization was also observed. The recovery results along with the FTIR spectra and FE-SEM images proved that the surface cleaning was not effective to detach foulants, especially for alginate fouling. The osmotic backwash showed greater flux recovery for alginate fouling than humic acid fouling, which indicated that restoring membrane pores or disturbing cake layers by osmotic backwash might be successful for the foulants for strong interactions between foulants and foulants. The concentrates were mostly composed of humic substances and low-molecular weight neutrals. The differences in the relative portions of the major components were occurred in the concentrates implying that the organic properties of the feed water and also interactions of foulants and membranes should be evaluated prior to determination of disposal options for concentrates.

Application launch time is an important performance metric to user experience in desktop and laptop environment, which mostly depends on the performance of secondary storage. Application launch times can be reduced by utilizing solid-state drive (SSD) instead of hard disk drive (HDD). However, considering a cost-performance trade-off, utilizing SSDs as caches for slow HDDs is a practicable alternative in reducing the application launch times. We propose a new SSD caching scheme which migrates data blocks from HDDs to SSDs. Our scheme operates entirely in the file system level and does not require an extra layer for mapping SSD-cached data that is essential in most other schemes. In particular, our scheme does not incur mapping overheads that cause significant burdens on the main memory, CPU, and SSD space for mapping table. Experimental results conducted with 8 popular applications demonstrate our scheme yields 56% of performance gain in application launch, when data blocks along with metadata are migrated.

Membrane biofouling impedes wide application of membrane bioreactor (MBR) for wastewater treatment. Recently, quorum sensing (QS) mechanisms are accounted for one of major mechanisms in biofouling of MBRs. In this study, vanillin was applied to investigate reduction of biofouling in MBRs. MBR sludge was analyzed to contain QS signal molecules by cross-feeding biosensor assay and HPLC. In addition, the inhibitory activity of vanillin against bacterial quorum sensing was verified using an indicator strain CV026. The vanillin doses greater than 125 mg/L to 100 mL of MBR sludge showed 25% reduction of biofilm formed on the membrane surfaces. Two MBRs, i.e., a typical MBR as a control and an MBR with vanillin, were operated. The TMP increases of the control MBR were more rapid compared to those of the MBR with the vanillin dose of 250 mg/L. The treatment efficiencies of the two MBRs on organic removal and MLSS were maintained relatively constant. Extracellular polymeric substance concentrations measured at the end of the MBR operation were 173 mg/g biocake for the control MBR and 119 mg/g biocake for the MBR with vanillin. Vanillin shows great potential as an anti-biofouling agent for MBRs without any interference on microbial activity for wastewater treatment.