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Given that cloud servers are usually remotely located from the devices of mobile apps, the end-users of the apps can face delays. The Fog has been introduced to augment the apps with machines located at the network edge close to the end-users. However, edge machines are usually resource constrained. Thus, the execution of online data-analytics on edge machines may not be feasible if the time complexity of the data-analytics algorithm is high. To overcome this, multiple instances of the back-end should be deployed on edge and remote machines. In this case, the research question is how the switching of the app among the instances of the back-end can be dynamically decided based on the response time of the service instances. To answer this, we contribute an AI approach that trains machine-learning models of the response time of service instances. Our approach extends a back-end as a service into an AI self-back-end as a service that self-decides at runtime the right edge/remote instance that achieves the lowest response-time. We evaluate the accuracy and the efficiency of our approach by using real-word machine-learning datasets on an existing auction app., Comment: 12 pages; accepted to IEEE Transactions on Services Computing on 1 October 2021

In this paper, the effects of hot isostatic pressing (HIP) temperature on the crystal structure, optical, dielectric and magnetic properties of GdMnO3 ceramics were studied. All samples form a single-phase structure without structural transformation, while HIP temperature induces the changes in lattice parameters. HIP causes the change in Mn ions valence state, oxygen vacancy concentration, Raman vibration modes and microscopic morphology of GdMnO3. Vacancy concentration of the samples prepared by HIP at 800 °C increases compared with that of the samples without HIP, then remains unchanged when the HIP temperature is from 800 to 900 °C, and finally decreases with the further increase of HIP temperature. Appropriate HIP temperature can increase the dielectric constant and decrease the dielectric loss. The transition temperature of paramagnetism to antiferromagnetism and magnetization can be significantly affected by HIP temperature. Magnetic transition temperature and magnetization are closely related to Mn2+ ions concentration and cation vacancy concentration, respectively.

The influences of Lu3+ doping on the structure and electrical properties of CaCu3Ti4O12 (CCTO) ceramics are systematically studied. We find that Lu3+ doping inhibits the grain growth of CCTO while the dielectric constant decreases firstly and then increases with the increase of Lu3+ content. The positron annihilation results indicate defect concentrations increase with the increment of Lu3+ content. At low Lu3+ doped level, the huge dielectric response of the samples mainly derives from the internal barrier layer capacitor (IBLC) effect while intrinsic polarization as defect dipoles makes more contribution at higher doped level. The dielectric loss is depressed due to the increase of cation vacancies and grain boundary resistivity. Good performances (high e′ of ∼ 1.1 × 104 and low tanδ of ∼ 0.025) at 1 kHz are obtained in Ca0.85Lu0.15Cu3Ti4O12 sample. Moreover, the enhanced nonlinear electrical properties are associated with cation vacancy defects generated by Lu3+ doping in the GB region. These findings are helpful in exploring the physical nature of the dielectric properties of CCTO.

To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration.

In this paper, M (Sc3+ and Zr4+)-doped CuFeO2 ceramics were prepared by using a solid-state reaction method. The effects of isovalent Sc3+ and nonisovalent Zr4+ substitution on the structure, defects, optical, and magnetic properties of CuFeO2 ceramics are comparatively investigated. The results demonstrated that all of the obtained samples are well crystallized, and M substitution leads to lattice structure distortion. The average grain sizes reduce with the addition of M. Positron annihilation lifetime results indicate that the vacancy clusters are present in all samples, and the Zr-substituted CFO sample has the maximum open volume and concentration of the defect among those three samples. Furthermore, the bandgap of the M-substituted samples becomes wider due to the broad bandgap of Sc2O3 and ZrO2. M substitution enhances the Urbach energy (EU) values in CFO system, which is in good consistent with the dependences of the defect concentration on the substitution elements. The magnetic measurements reveal that Sc and Zr substitution decrease the magnetic temperatures TN1 and TN2, which may be attributed to the consequence of the magnetic dilution effect and the change in the strength of exchange interaction. In addition, the defects are of major importance for regulating the magnetic properties of CFO ceramics.

Polycrystalline CuFeO2 (CFO) and CuFe0.99R0.01O2 (R–CFO, R = La, Sm, Eu, Gd, Dy, and Ho) were prepared via solid-phase synthesis to investigate the effects of rare-earth (R) ion addition on the microstructures and magnetism. Positron annihilation lifetime spectroscopy (PALS) experimental results demonstrated that the size, concentration, and defect types were altered by R substitution due to the competition between the agglomeration of small-sized defects and the decomposition of vacancy clusters, which resulted in the redistribution of electrons around annihilation sites. The magnetic measurements revealed that the antiferromagnetic stability was influenced by R substitution, which was ascribed to the effect of magnetic moments, variations in exchange interactions, and the partial reduction of spin frustration. The magnetization behaviors of the R–CFO samples were also influenced by doping ions, which was mainly explained by the different magnitudes of the R ions’ magnetic moments. Ferromagnetism and antiferromagnetism were present in all of the samples. The local electron density ne was associated with the maximum magnetization (Mm). The correlative physical mechanisms are discussed in detail. The results demonstrated that the ne plays an important role in regulating the magnetic properties of CFO ceramics.

Three fluorinated polyimide (PI-FP, PI-FO and PI-FH) films with low dielectric constants and excellent comprehensive properties were successfully prepared using a polycondensation reaction method by incorporating p-phenylenediamine (PDA), 4-4′-diaminodiphenyl ether (ODA) and 4,4′-(Hexafluoroisopropylidene) bis (p-phenyleneoxy) dianiline (HFPBDA) into 4,4′-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA), respectively. The effects of the diamine monomer structure on optical, dielectric and mechanical properties were investigated. Compared with PDA and ODA, HFPBDA can effectively improve the optical and dielectric properties of PI due to due to its special chain structure. Among the three PI films, PI-FH film presents the best optic transmission (highest transmittance = 90.2%) and highest energy gap (2.69 eV). The dielectric properties of PI-FH film improve the most. The dielectric constant and loss at 104 Hz are reduced to 2.05 and 0.0034 at 104 Hz, respectively, and remain stable up to 250 °C. The mechanical properties decrease in turn for PI-FP, PI-FO and PI-FH films due to the increase in free volume fraction. Nevertheless, PI-FH film still exhibits good mechanical properties with a tensile strength of 88.4 Mpa, a tensile modulus of 2.11 GPa and an elongation at break of 4.1%. The correlation between the dielectric and mechanical properties of PI films and their free volume characteristics is well explained with the help of positron annihilation spectroscopy.

In this work, a series of VO2(B) samples were synthesized via a hydrothermal process by reducing V2O5 with different concentrations of oxalic acid. The prepared samples were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry, and galvanostatic charge–discharge. Furthermore, the microdefects of VO2 samples were characterized by positron lifetime spectroscopy. The results revealed that VO2(B) was successfully prepared and the concentration of reducing agent had a certain influence on the microstructures and properties. The electrochemical performance measurements showed that all samples had good cycle stability in 2 mol/L KOH solution. The x = 1.50 sample displayed higher discharge capacitance of 149.5 F g−1 at 30 mA g−1 and the discharge capacitance remained about 67% even after 80 charge/discharge cycles. The positron lifetime spectra revealed that the main defects in VO2 samples were microvoids, and the defect concentration and size were affected by the C2H2O4 concentration.

CuFe1−xTixO2 (0 ≤ x ≤ 0.08) ceramics are synthesized by solid state reaction method to investigate the effect of Ti substitution on the microstructure, vacancy-type defects, the local electron density, and magnetic properties. The XRD and Raman spectra results show that all experimental samples possess the characteristic peak of CuFeO2 ceramics. SEM observations indicate that Ti substitution has obvious influence on the morphologies of experimental ceramics, and the microvoids increases significantly with increasing Ti content. Positron annihilation lifetime and Doppler broadening spectra results indicate that the vacancy concentration increases rapidly and then reaches a higher platform (>35%) as x > 0.01, and Ti substitution does not change the defects species in CuFe1-xTixO2 ceramics. The electron density decreases with increasing x and then reaches a low plateau (≈5.7) at x = 0.08. The χ - T curves reveal that the TN1 is independent of Ti content, while, the TN2 decreases with increasing x at x = 0.00–0.02 and even disappears in the magnetization curves as x > 0.02. The M-H curves indicate that the coexistence of weak ferromagnetism and antiferromagnetism for all the samples could be found. The possible reasons for the above observations are discussed in detail.

To study the effects of structural modulation by doping rare earth element on the magnetic and dielectric properties, CuFe1-xGdxO2 (0 ≤ x ≤ 0.2) samples are synthesized using the solid-state reaction method. The XRD and SEM results show that a small amount of Gd3+ ions (x ≤ 0.07) effectively occupies the Fe3+ site and promotes the grain growth of the CuFeO2 system. Judging from the magnetic property measurements, the samples (x = 0, 0.01) undergo two successive magnetic transitions. Further increase of x, the magnetic transition of the samples (x ≥ 0.07) has not been detected in the testing temperature range. The magnetization hysteresis loops show that all of the samples have weak ferromagnetic properties, and the saturation magnetization is obviously enhanced with increasing x. Most interestingly, the dielectric measurements suggests that CuFeO2 samples exhibit a giant dielectric constant (eγ~104), and eγ is obviously improved (~ 4.0 × 104) using the proper Gd content. The dielectric properties are explained using the internal barrier layer capacitance model (IBLC).

Availability issues of industrial microservice systems (e.g., drop of successfully placed orders and processed transactions) directly affect the running of the business. These issues are usually caused by various types of service anomalies which propagate along service dependencies. Accurate and high-efficient root cause localization is thus a critical challenge for large-scale industrial microservice systems. Existing approaches use service dependency graph based analysis techniques to automatically locate root causes. However, these approaches are limited due to their inaccurate detection of service anomalies and inefficient traversing of service dependency graph. In this paper, we propose a high-efficient root cause localization approach for availability issues of microservice systems, called MicroHECL. Based on a dynamically constructed service call graph, MicroHECL analyzes possible anomaly propagation chains, and ranks candidate root causes based on correlation analysis. We combine machine learning and statistical methods and design customized models for the detection of different types of service anomalies (i.e., performance, reliability, traffic). To improve the efficiency, we adopt a pruning strategy to eliminate irrelevant service calls in anomaly propagation chain analysis. Experimental studies show that MicroHECL significantly outperforms two state-of-the-art baseline approaches in terms of both accuracy and efficiency. MicroHECL has been used in Alibaba and achieves a top-3 hit ratio of 68% with root cause localization time reduced from 30 minutes to 5 minutes.

MicroRNAs (miRNAs), considered as therapeutic targets and biomarkers, play important roles in biological processes. Herein, an enzyme-free surface plasmon resonance imaging (SPRi) biosensing method has been developed for miRNA detection based on catalytic hairpin assembly and spherical nucleic acid. The hairpin H1 tethered on the surface of the sensor chip is unfolded by miRNA, and then the hybridized miRNA is released through the displacement of the hairpin H2 for the successive hybridization and assembly process. The emerging DNA fragments on the sensor chip surface after hairpins assembly are further used to hybridize with spherical nucleic acid, inducing a remarkably amplified SPR signal. This biosensing method is highly sensitive to miRNA with a detection limit of 53.7 fM and a linear range of 4 orders of magnitude. Moreover, the biosensor demonstrates good specificity and has the ability to distinguish members of homologous miRNA family even with single base differences. Thus, the SPRi biosensing method may hold a great promise for further application in early clinical diagnosis.

Ho3+-ion doped spin-chain compounds Ca3Co2-xHoxO6 (x = 0, 0.05, 0.1, 0.15) were prepared by a conventional solid-state reaction method. Rietveld refinement of the X-ray diffraction patterns at room temperature confirmed the rhombohedral structure with the R 3 ¯ c space group. The results reveal that the solid solubility of the Ho element in Ca3Co2O6 is in the range of x = 0.1–0.15. Magnetic measurement suggests that with the increased Ho content: (1) the ferromagnetic transition temperature Tc and spin freezing temperature Tƒ decrease obviously; (2) the ferrimagnetic configuration becomes less stable; (3) the dynamic characteristics become slower; and (4) the antiferromagnetic (AFM) interaction enhances gradually. Based on these phenomena, the mechanism was discussed in detail. The magnetic correlation length is broken at a low Ho3+-ion level, and the Ho3+-ion pair formation along the chain with a high level of doping was interpreted.