Tool For Tuning Research Articles

Spin filtering in GaAs/Al0.3Ga0.7As multiple quantum wells

In this study, spin polarization efficiency and spin-dependent transmission of electrons passing through a multiple quantum well structure with constant total effective length (60 nm) made of GaAs/Al0.3Ga0.7As, which was grown along [001] direction, were investigated. The calculations were done with the quantum transmitting boundary method. We presented the number of wells in a constant total length as a tuning tool for spin filtering purposes. In some energy intervals, 100% spin polarization and spin-dependent transmission were observed.

Resonances: tuning into the echoes of the ecological collective

AbstractDrawing on posthumanist and new materialism theorising, we take the concept of resonance for an a/r/tographic ‘walk’ to know, be and do differently, to challenge human-centric separatist ways that have resulted in our current socioecological crises. Beginning with Ingold’s knotty thinking, we identify the notion of resonance as a node for exploring and thinking about interactions in the world. Guided by Barad’s proposition of entangling ethico-onto-epistemic ways, our a/r/tographic thought experiments find resonances that echo through bodies, through connections as nature, through deep-time and modern spaces to notice and attend to intraactions within the ecological collective. Through art-full, thought-full scholartistic enquiry, we explore diffractive encounters to consider resonance as a conceptual tool for tuning into and harmonising with the entanglements of body–mind–space–time–matter. We pose this exploration of resonance as the start of a knotty theory conversation for shifting into a new ‘common world’ knowing, being and doing.

Covalent Post-Assembly Modification: A Synthetic Multipurpose Tool in Supramolecular Chemistry.

The use of covalent post-assembly modification (PAM) in supramolecular chemistry has grown significantly in recent years, to the point where PAM is now a versatile synthesis tool for tuning, modulating, and expanding the functionality of self-assembled complexes and materials. PAM underpins supramolecular template-synthesis strategies, enables modular derivatization of supramolecular assemblies, permits the covalent 'locking' of unstable structures, and can trigger controlled structural transformations between different assembled morphologies. This Review discusses key examples of PAM spanning a range of material classes, including discrete supramolecular complexes, self-assembled soft nanostructures and hierarchically ordered polymeric and framework materials. As such, we hope to highlight how PAM has continued to evolve as a creative and functional addition to the synthetic chemist's toolbox for constructing bespoke self-assembled complexes and materials.

Production and fuel properties of iso-olefins with controlled molecular structure and obtained from butene oligomerization

The ability to control the molecular structure (e.g., degree of branching) of iso-olefins produced from oligomerizing light olefins is a valuable tool for tuning the final compositions of hydrocarbon fuels and targeting specific fuel properties. In this study, we demonstrated that the degree of branching of iso-olefins obtained from butene oligomerization can be controlled by tuning process conditions (i.e., temperature, weight hourly space velocity [WHSV], nature of butene feedstock) and by choosing the proper catalyst (i.e., Amberlyst-36 vs. Y/ZSM-22). We produced three types of iso-olefin mixtures: 1) a methyl-heptenes rich (74 wt%) mixture,2) dimethyl-hexenes rich (80–96 wt%) mixtures, and 3) highly branched (i.e., ≥3 methyl substitutions) iso-olefins rich (>50 wt%) mixtures. While dimethyl-hexenes are preferentially formed at lower temperatures (60–100 °C) and WHSV (i.e., 2 hr−1), methyl-heptenes are favorably produced at higher temperatures (>100 °C) and WHSVs (i.e., 7 hr−1) over Amberlyst-36. The use of either 1-butene or 2-butene as feedstock resulted in liquid products with similar branching because facile intramolecular isomerization occurs prior to oligomerization. The use of isobutylene feedstock forms a more branched olefin product. For each type of iso-olefins mixture, we determined fuel properties including research octane number (RON), motor octane number (MON), and octane sensitivity (S), which is the difference between RON and MON. We found that not only RON and MON but also S values increased with the degree of branching of these complex mixtures of iso-olefins. The highest RON of 99.7 and S value of 9.3 were obtained for a mixture of highly branched iso-olefins.

TuneMPC—A Tool for Economic Tuning of Tracking (N)MPC Problems

Economic nonlinear model predictive control (NMPC) is a variant of NMPC that directly optimizes an economic performance index instead of a tracking error. Although economic NMPC can achieve excellent closed-loop performance, the associated computational effort as well as the difficulty of guaranteeing stability in practice are its main drawbacks. Motivated by these difficulties, a formal procedure was developed that tunes a tracking (non)linear MPC scheme so that it is first-order equivalent to economic NMPC. This letter introduces TuneMPC, a new open-source software framework that closes the gap between the underlying theory and practical application of this tuning procedure. For user-provided system dynamics, constraints and economic objective, TuneMPC enables automated computation of optimal steady states and periodic trajectories, and returns the corresponding tuned stage cost matrices. To demonstrate the potential of the tool, we apply the technique to the challenging example of an autonomous tethered aircraft flying periodic orbits for airborne wind energy harvesting.

Tuning a general purpose software cache library for TaihuLight’s SW26010 processor

The Sunway TaihuLight supercomputer has been installed for several years and many applications have been ported or built for TaihuLight. Initially most applications running on TaihuLight are with regular memory access patterns, such as dense linear algebra, structured grids and dynamic programming. At the year of 2018, developers have published a general purpose graph processing framework, a ported version of LAMMPS and a sparse triangular solver. These applications are with irregular memory access patterns which need a lot of special processings to make use of the computing processing elements (CPEs) of TaihuLight. While those strategies are efficient, doing such processing may be difficult for wider range of applications, especially for the constantly changing molecular dynamics applications or dynamic unstructured grids. In this paper, we present our work of designing a general purpose software cache library, SWCache, for simplifying the work of applying software cache in kernels, as well as a series of tools for tuning and modelling the performance of our software cache. After a series of optimizations including reordering branches for better branch prediction, hand-tuning register allocation, we evaluate our implementation in two mini-apps: miniFE and miniMD. Experiments show that our tuned software cache library can be applied in these applications, and can provide 20% speedup in miniMD compared to the strategies in a previous port of LAMMPS. Also, the workload of writing code can be reduced by using our library. Besides, the experience of efficient macro-based programming should be valuable for further application development on CPEs which are lack of C++ support.

Hybrid Gain Data Assimilation Using Variational Corrections in the Subspace Orthogonal to the Ensemble

AbstractThe viability of a parameterless hybrid data assimilation algorithm is investigated. As an alternative to the traditional hybrid covariance scheme, hybrid gain data assimilation (HGDA) was proposed to blend the gain matrix derived from the variational method and the ensemble-based Kalman filter (EnKF). A previously proposed HGDA algorithm uses a two-step process applying the EnKF with a variational update. The algorithm is modified here to limit the variational correction to the subspace orthogonal to the ensemble perturbation subspace without the use of a hybrid weighting parameter, as the optimization of such a parameter is nontrivial. The modified HGDA algorithm is investigated with a quasigeostrophic (QG) model. Results indicate that when the climatological background error covariance matrix B and the observation error covariance R are well estimated, state estimates from the parameterless HGDA are more accurate than the parameter-dependent HGDA. The parameterless HGDA not only has potential advantages over the standard HGDA as an online data assimilation algorithm but can also serve as a valuable diagnostic tool for tuning the B and R matrices. It is also found that in this QG model, the empirically best static B matrix for the stand-alone 3DVAR has high variance at larger spatial scales, which degrades the accuracy of the HGDA systems and may not be the best choice for hybrid methods in general. A comparison of defining the orthogonal subspace globally or locally demonstrates that global orthogonality is more advantageous for stabilizing the hybrid system and maintains large-scale balances.

Fragment-based Design of Zwitterionic, Strong Cation- and Weak Anion-Exchange Type Mixed-mode Liquid Chromatography Ligands and their Chromatographic Exploration

The role of individual functional groups has been assessed with regard to surface charge and chromatographic retention. Coatings were prepared from various fragments of the chiral zwitterionic materials Chiralpak ZWIX(+) and ZWIX(-). The different chromatographic ligands allowed fine tuning of the surface charge. Chiralpak ZWIX phases showed strongly negative ζ-potentials over the entire pH-range. Zwitterionic congeners with quinuclidine and sulfonic acid moieties but lacking the quinolone ring in the ligand structure exhibited shifted ζ-potentials of around + 5 to 20 mV depending on the surrounding residues. Capillary electrophoretic mobilitiy measurements with the chromatographic ligands and molecular dynamics simulations were carried out to offer some explanation of these surface charge differences of the distinct zwitterionic stationary phases. The new mixed-mode phases were also chromatographically characterized by simple RP and HILIC tests. The results allowed their positioning within a large variety of different commercially available RP, HILIC and mixed-mode phases, which were evaluated as well, by multivariate data processing using principal component analysis. The new mixed-mode phases overall exhibit reasonable hydrophilicity-lipophilicity balance and enable retention of ionic compounds by additional ionic interactions through weak anion-exchange (WAX-type), strong cation-exchange (SCX-type) or both (RP/ZWIX-type). Hence, the new RP/ZWIX phases can be flexible tools for selectivity tuning in RP and HILIC separations.

Network cross-validation by edge sampling

Summary While many statistical models and methods are now available for network analysis, resampling of network data remains a challenging problem. Cross-validation is a useful general tool for model selection and parameter tuning, but it is not directly applicable to networks since splitting network nodes into groups requires deleting edges and destroys some of the network structure. In this paper we propose a new network resampling strategy, based on splitting node pairs rather than nodes, that is applicable to cross-validation for a wide range of network model selection tasks. We provide theoretical justification for our method in a general setting and examples of how the method can be used in specific network model selection and parameter tuning tasks. Numerical results on simulated networks and on a statisticians’ citation network show that the proposed cross-validation approach works well for model selection.

Role of Polar Protic Solvents in the Dissociation and Reactivity of Photogenerated Radical Ion Pairs.

The UV photolysis of bimolecular charge transfer complexes is employed to yield reactive radical ions in their solvent-equilibrated electronic ground state. In polar protic media, noncovalent complexes of 1,2,4,5-tetracyanobenzene and toluene undergo efficient, ultrafast dissociation to ion pairs and equilibrate with their solvent environment before the resulting radical ions engage in electron transfer and proton abstraction on subnanosecond time scales. Solvent molecules play a critical role in these reactive pathways and in the dissociation and relaxation processes that precede them. We report a clear separation of time scales for these relaxation and reactive processes, which implies that solvent-solute interactions can be used as a tool for tuning the reaction pathways of equilibrated radical ions in solution.

Theoretical investigation on the surface and morphological properties of lead nickelate multiferroics: vacancy dependency

In the context of the development of materials, morphology control represents an important tool for tuning their properties, thus enabling their application on photocatalysis, energy conversion and other areas. In this work, DFT/B3LYP methodology was carried out to investigate the surface structure and the electronic, ferroelectric and magnetic properties of low index surfaces of the multiferroic PbNiO3 material at the R3c crystalline phase. The results indicate that the surface energy increases in the following the order (110) < (012) < (111) < (001) < (101) < (100). These results allow us to predict the available morphologies, finding that six theoretical morphologies correspond to those reported experimentally, while nine morphologies have not yet been reported experimentally. The properties of the exposed surfaces for each morphology can be associated with the number of oxygen vacancies (V0), and the presence of uncoordinated [NiO6] and [PbO6] clusters.

Co-development of a decision support system for integrated weed management: Contribution from future users

Abstract Farmers and farm advisors need a decision support system (DSS) to develop multiperformant weed management strategies adapted to economic, social and environmental stakes and farmers' constraints. We worked with future users, farmers, and crop advisors to define the uses and type of DSS they needed, via an online survey, group meetings and workshops. The feedback from future users helped to define the structure of the DSS with two complementary DSS needed: (1) a synthetic tool working with meta-decision rules to help with a complete overhaul of a cropping system, and (2) a precise and detailed tool for fine tuning cropping systems. Here, we present how we interacted with future users to transform an existing research model into a DSS by (1) defining its goal, application field and structure, (2) entering into the DSS knowledge on biophysical processes comprised in the mechanistic weed dynamics model FlorSys . We selected a more appropriate vocabulary for describing agricultural practices and formats with future users. Based on their feedback, a large range of weed impact indicators was included in the DSS so that farmers can choose the most pertinent for their objectives. Based on workshops with farmers, a decision tree format with numerical values of weed impact indicators was chosen to demonstrate the impacts of multiple cultural practices combinations. The DSS also includes an online calculator predicting weed (dis)services from meta-decision rules which was tested by crop advisors. Responses of the DSS were sometimes not expected by users, but were still considered interesting highlighting the need of agronomical support while using the tool.

Progress of refactoring first principle package of Beijing Simulation Tool for Atom TEchnology

The development of first principle methods can represent the summit of the sciences in the material computing and molecular modeling, and the corresponding first principle software packages are closely related with the accumulation of theories and algorithms in this field. In this paper, we reported our recent progress in refactoring the first principle package BSTATE. The key points in the reconstruction are lowering the doorsill, extending the scope of application, as well as adjusting package to the popular computer hardware. And as such, we updated the Makefile system to the new CMake system, in which the GUI can be used and many math libraries can be configured automatically; we added the support for the Libxc library, in which a large quantity of density functionals are included; we updated the interface for supporting GPU, in order to support the heterogeneous computing system. After refactoring, the Makefile system of BSTATE can supply both the Makefile and CMake system, and the Fourier transform libraries such as FFTW2, FFTW3, and Cufftw, the math libraries such as Intel MKL library, Openblas, and the density functional library such as Libxc, can be automatically or manually assigned. The integration of FFTW3 can slightly prompt the calculating efficiency in Intel’s many integrated core (MIC) architecture, and the integration of Cufftw can supply the initial support for the graphics processing unit (GPU) architecture, respectively. The usage of Libxc library makes the BSTATE package has the capacity to use hundreds density functionals, and the usages of various functionals were demonstrated by calculating the density of states of GaAs compound. Beyond the integration of various libraries, the parallel performance of BSTATE was also investigated. It can be found that the Fourier transformation and the solving for the eigenvalue equations are the major contributions. Using the tuning and analysis utilities (TAU) tool, we found that the tasks can be well distributed in modern HPC clusters. It implied that the refactoring didn’t affect the parallel efficiency of original BSTATE package. In a following benchmark test of graphene fragments, one can found that the refactored BSTATE package showed the best performance, its FFTW3 &amp; Libxc version owns about 0–17% acceleration comparing to that of FFTW2 version.

Ligand engineering of immobilized nanoclusters on surfaces: ligand exchange reactions with supported Au11(PPh3)7Br3.

The properties of gold nanoclusters, apart from being size-dependent, are strongly related to the nature of the protecting ligand. Ligand exchange on Au nanoclusters has been proven to be a powerful tool for tuning their properties, but has so far been limited to dissolved clusters in solution. By supporting the clusters previously functionalized in solution, it is uncertain that the functionality is still accessible once the cluster is on the surface. This may be overcome by introducing the desired functionality by ligand exchange after the cluster deposition on the support material. We herein report the first successful ligand exchange on supported (immobilized) Au11 nanoclusters. Dropcast films of Au11(PPh3)7Br3 on planar oxide surfaces were shown to react with thiol ligands, resulting in clusters with a mixed ligand shell, with both phosphines and thiolates being present. Laser ablation inductively coupled plasma mass spectrometry and infrared spectroscopy confirmed that the exchange just takes place on the cluster dropcast. Contrary to systems in solution, the size of the clusters did not increase during ligand exchange. Different structures/compounds were formed depending on the nature of the incoming ligand. The feasibility to extend ligand engineering to supported nanoclusters is proven and it may allow controlled nanocluster functionalization.

Oxidation states of gallium (infrequentiand commoniii) tunableviamedium-sized C60and small-sized C28fullerenes

Differently sized fullerenes are shown to be flexible tools for tuning the oxidation states of gallium, and a fluoridation strategy facilitates the further stabilization of Ga@Ih(1812)-C60.

Computational insights into structural, electronic and optical characteristics of GeC/C2N van der Waals heterostructures: effects of strain engineering and electric field.

Vertical heterostructures from two or more than two two-dimensional materials are recently considered as an effective tool for tuning the electronic properties of materials and for designing future high-performance nanodevices. Here, using first principles calculations, we propose a GeC/C2N van der Waals heterostructure and investigate its electronic and optical properties. We demonstrate that the intrinsic electronic properties of both GeC and C2N monolayers are quite preserved in GeC/C2N HTS owing to the weak forces. At the equilibrium configuration, GeC/C2N HTS forms the type-II band alignment with an indirect band gap of 0.42 eV, which can be considered to improve the effective separation of electrons and holes. Besides, GeC/C2N vdW-HTS exhibits strong absorption in both visible and near ultra-violet regions with an intensity of 105 cm−1. The electronic properties of GeC/C2N HTS can be tuned by applying an electric field and vertical strains. The semiconductor to metal transition can be achieved in GeC/C2N HTS in the case when the positive electric field of +0.3 V Å−1 or the tensile vertical strain of −0.9 Å is applied. These findings demonstrate that GeC/C2N HTS can be used to design future high-performance multifunctional devices.

Hdconfigor: Automatically Tuning High Dimensional Configuration Parameters for Log Search Engines

Search engines are nowadays widely applied to store and analyze logs generated by large-scale distributed systems. To adapt to various workload scenarios, log search engines such as Elasticsearch usually expose a large number of performance-related configuration parameters. As manual configuring is time consuming and labor intensive, automatically tuning configuration parameters to optimize performance has been an urgent need. However, it is challenging because: 1) Due to the complex implementation, the relationship between performance and configuration parameters is difficult to model and thus the objective function is actually a black box; 2) In addition to application parameters, JVM and kernel parameters are also closely related to the performance and together they construct a high dimensional configuration space; 3) To iteratively search for the best configuration, a tool is necessary to automatically deploy the newly generated configuration and launch tests to measure the corresponding performance. To address these challenges, this paper designs and implements HDConfigor, an automatic holistic configuration parameter tuning tool for log search engines. In order to solve the high dimensional optimization problem, we propose a modified Random EMbedding Bayesian Optimization algorithm (mREMBO) in HDConfigor which is a black-box approach. Instead of directly using a black-box optimization algorithm such as Bayesian optimization (BO), mREMBO first generates a lower dimensional embedded space through introducing a random embedding matrix and then performs BO in this embedded space. Therefore, HDConfigor is able to find a competitive configuration automatically and quickly. We evaluate HDConfigor in an Elasticsearch cluster with different workload scenarios. Experimental results show that compared with the default configuration, the best relative median indexing results achieved by mREMBO can reach $2.07\times $ . In addition, under the same number of trials, mREMBO is able to find a configuration with at least a further 10.31% improvement in throughput compared to Random search, Simulated Annealing and BO.

Effect of Oxygen Interstitial Ordering on Multiple Order Parameters in Rare Earth Ferrite.

Oxygen interstitials and vacancies play a key role in modulating the microstructure and properties of nonstoichiometric oxide systems, such as those used for superconductors and multiferroics. Key to understanding the tuning mechanisms resulting from oxygen doping is a knowledge of the precise positions of these lattice defects, and of the interaction both between these defects and with many order parameters. Here, we report how such information can, for the first time, be obtained from a sample of LuFe_{2}O_{4.22} using a range of techniques including advanced electron microscopy, atomic-resolution spectroscopy, and density functional theory calculations. The results provide quantitative atomic details of the crystal unit cell, together with a description of the ferroelastic, ferroelectric, and ferromagnetic order parameters. We elucidate also the interaction between these order parameters and the positions of the oxygen interstitials in the oxygen-enriched sample. The comprehensive analysis of oxygen interstitial ordering provides insights into understanding the coupling among different degrees of freedom in rare earth ferrites and demonstrates that oxygen content regulation is a powerful tool for tuning the microstructure and properties for this class of quantum material.

Influence of Albumin in the Microfluidic Synthesis of PEG-PLGA Nanoparticles.

A key challenge in the manufacturing of polymeric colloids is producing nanoparticles with good batch-to-batch consistency. Develop a robust microfluidics method for the preparation of PEG-PLGA nanoparticles using dimethyl sulfoxide (DMSO) as the organic phase solvent for the encapsulation of DMSO soluble agents. Microfluidic process parameters, total flow rate (10 mL/min), flow rate ratio (1:1) of the aqueous phase and the organic polymer solution, and polymer concentration (5 mg/ml). Polyvinyl alcohol (PVA) or human serum albumin (HSA) was included in the aqueous phase. Dynamic light scattering and transmission electron microscopy were used to investigate the size and morphology of particles. PLGA nanoparticles made using DMSO with the aqueous solvent containing PVA (2%) had an average size of 60 nm while PLGA-PEG nanoparticles made with and without PVA (2%) had an average size of 70 and 100 nm, respectively. PLGA-PEG nanoparticles generated with or without PVA had a high batch-to-batch coefficient of variation for the particle size of 20% while for PLGA nanoparticles with PVA it was 4%. HSA added to the aqueous phase reduced the size and the zeta potential of PEG-PLGA nanoparticles as well the batch-to-batch coefficient of variation for particle size to < 5%. Nanoparticles were stable in solution and after lyophilized in the presence of sucrose. Albumin was involved in the self-assembly of PEG-PLGA nanoparticles altering the physicochemical properties of nanoparticles. Adding protein to the aqueous phase in the microfluidic fabrication process may be a valuable tool for tuning the properties of nanoparticles and improving batch-to-batch consistency.

“Design of Experiments” as a Method to Optimize Dynamic Disulfide Assemblies: Cages and Functionalizable Macrocycles

AbstractCyclophanes are a venerable class of macrocyclic and cage compounds that often contain unusual conformations, high strain, and unusual properties. However, synthesis of complex, functional derivatives remains difficult due to low functional group tolerance, high dilution, extreme reaction conditions, and sometimes low yields using traditional stepwise synthetic methods. “Design of experiments” (DOE) is a method employed for the optimization of reaction conditions, and we showcase this approach to generate a dramatic increase in the yield of specific targets from two different self‐assembling systems. These examples demonstrate that DOE provides an additional tool in tuning self‐assembling, dynamic covalent systems.