Novel Method For Tuning Research Articles

Utilization of cage germoxanes as templates for tuning pore characteristics of siloxane-based materials

Abstract We demonstrate the utilization of cage germoxanes as templates for tuning the pore characteristics of siloxane-based materials. Molecular-scale composites of cage germoxanes and cage siloxanes were prepared by hydrosilylation reactions between SiH- and vinyl-modified cage siloxanes in the presence of vinyl-modified cage germoxanes. Subsequent acid treatments selectively removed the germoxane moiety, resulting in variation in the pore structures. These results contribute to developing a novel method for tuning the pore characteristics of siloxane-based nanoporous materials.

Optimized PIDD2 controller for AVR systems regarding robustness

The novel method for tuning proportional-integral-derivative controller with second order derivative term (PIDD2) for the automatic voltage regulator (AVR) of synchronous generator is presented. The design method minimizes load disturbance response regarding constraints on sensitivity functions: maximum sensitivity Ms, maximum complementary sensitivity Mp and measurement noise sensitivity Mn. Simple solution is obtained by shifting PIDD2 controller in a new parameter space and by employing an iterative procedure. In each iteration the five controller parameters are obtained by solving the constrained optimization problem concerning sensitivities Ms and Mn for the fixed value of controller zeros damping factor ξ. The robustness index Mp is calculated subsequently. In that manner, maximum of complementary sensitivity Mp is met by means of auxiliary parameter ξ. The performance improvements are achieved in comparison with traditional PID controller, while robustness is retained. Further, the comparison is made with an optimization method using amplitude optimum principle that also minimizes load disturbance response with different optimality criterion. Experiments are carried out on a small lab synchronous generator setup in order to demonstrate practical potential in real noisy environment of the proposed method and to justify the increased order of AVR controller.

A cooperative particle swarm optimization approach for tuning an MPC-based quadrotor trajectory tracking scheme

This paper presents a novel method for tuning a quadrotor trajectory-tracking model predictive control (MPC) framework, based on cooperative particle swarm optimization (PSO). The overall control strategy is decomposed into two different schemes; the first scheme, which is responsible for position control, is based on MPC, whereas the second one, which regulates the attitude of the quadrotor, makes use of three standard PID controllers. To optimize the trajectory tracking ability of the quadrotor, a cooperative PSO framework is introduced for tuning the large number of parameters of diverse nature, which are employed by the different controllers. The method makes use of two distinct swarms, with the first one containing the position controller parameters and the second one the attitude controller parameters. By exchanging information, the two swarms work together in a cooperative way in order to explore more efficiently the search space and discover tuning parameters that improve the trajectory tracking performance. Simulation results on a detailed quadcopter model over trajectories with different geometric characteristics, and comparisons to other tuning approaches verified by statistical testing, illustrate the efficiency of the proposed scheme in optimizing the control parameters. The scheme's robustness is also verified by testing the performance of the resulting controller on trajectories different than the ones used for tuning it.

Mechanical strain and electric-field modulation of graphene transistors integrated on MEMS cantilevers

This work proposes a structure which allows characterization of graphene monolayers under combined electric field and mechanical strain modulation. Our approach is based on a cantilever integrated into a two-dimensional graphene-based Field effect transistor (FET). This allows us to change graphene properties either separately or together via two methods. The first way involves electric field induced by the gate. The second is induction of mechanical strain caused by external force pushing the cantilever up or down. We fabricated devices using silicon-on-insulator wafer with practically zero value of residual stress and a high-quality dielectric layer which allowed us to precisely characterize structures using both mentioned stimuli. We used the electric field/strain interplay to control resistivity and position of the charge neutrality point often described as the Dirac point of graphene. Furthermore, values of mechanical stress can be obtained during the preparation of thin films, which enables the cantilever to bend after the structure is released. Our device demonstrates a novel method of tuning the physical properties of graphene in silicon and/or complementary metal-oxide-semiconductor technology and is thus promising for tunable physical or chemical sensors.

Predicting the distribution of a rare chipmunk (Neotamias quadrivittatus oscuraensis): comparing MaxEnt and occupancy models.

Species distribution models (SDMs) use presence records to determine the relationship between species occurrence and various environmental variables to create predictive maps describing the species’ distribution. The Oscura Mountains Colorado chipmunk (Neotamias quadrivittatus oscuraensis) occurs in central New Mexico and is of conservation concern due to its relict distribution and threats to habitat. We previously created an occupancy model for this taxon, but were concerned that the model may not have adequately captured the ecological factors influencing the chipmunk’s distribution because of the data hungry nature of occupancy modeling. MaxEnt is another SDM method that is particularly effective at testing large numbers of variables and handling small sample sizes. Our goal was to create a MaxEnt model for the Oscura Mountains Colorado chipmunk and to compare it with our previous occupancy model for this taxon, either to strengthen our original assessment of the relevant ecological factors or identify additional factors that were not captured by our occupancy model. We created MaxEnt models using occurrence records from baited camera traps and opportunistic surveys. We adjusted model complexity using a novel method for tuning both the regularization multiplier and feature class parameters while also performing variable selection. We compared the distribution maps and variables selected by MaxEnt to the results of our occupancy model for this taxon. The MaxEnt and occupancy models selected similar environmental variables and the overall spatial pattern of occurrence was similar for each model. Likelihood of occurrence was positively related to elevation, piñon woodland vegetation type, and topographic variables associated with escarpments. The overall similarities between the MaxEnt and occupancy models increased our confidence of the ecological factors influencing the distribution of the chipmunk. We conclude that MaxEnt offers advantages for predicting the distribution of rare species, which can help inform conservation actions.

Using Contrast Motion to Generate Patient-Specific Blood Flow Simulations During Invasive Coronary Angiography.

Virtual fractional flow reserve (vFFR) is an emerging technology employing patient-specific computational fluid dynamics (CFD) simulations to infer the hemodynamic significance of a coronary stenosis. Patient-specific boundary conditions are an important aspect of this approach and while most efforts make use of lumped parameter models to capture key phenomena, they lack the ability to specify the associated parameters on a patient-specific basis. When applying vFFR in a catheter laboratory setting using X-ray angiograms as the basis for creating the simulations, there is some indirect functional information available through the observation of the radio-opaque contrast agent motion. In this work, we present a novel method for tuning the lumped parameter arterial resistances (commonly incorporated in such simulations), based on simulating the physics of the contrast motion and comparing the observed and simulated arrival times of the contrast front at key points within a coronary tree. We present proof of principle results on a synthetically generated coronary tree comprised of multiple segments, demonstrating that the method can successfully optimize the arterial resistances to reconstruct the underlying velocity and pressure fields, providing a potential new means to improve the patient specificity of simulation-based technologies in this area.

Tuning MEMS cantilever devices using photoresponsive polymers

Microelectromechanical systems (MEMS) energy harvesting devices have had limited commercial success partly due to the frequency mismatch between the device and the vibration source. Tuning the cantilever device is one possible solution but developing a tunable MEMS device is difficult. This paper demonstrates a novel method of tuning a MEMS cantilever device post-fabrication by using light-responsive azobenzene liquid crystal polymers (LCP). Light exposure causes the photoresponsive polymers to change their elastic modulus, thus affecting the resonant frequency of the device. The photoresponsive polymer was integrated with three different MEMS cantilever substrates including LCP, parylene, and silicon. The three cantilever beams all demonstrated changes in resonant frequency when exposed to UV light of 10.4%, 8.13%, and 4.86%, respectively. The change in resonant frequency is dependent on the stiffness of the substrate, the thickness of the azo-LCP, the intensity and duration of the light exposure, and the wavelength of the light. The results in this paper validate that light responsive polymers can be used to reduce the frequency of MEMS cantilevers post-fabrication, which could lead to developing devices that can be precisely tuned for specific applications.

Novel method of tuning the size of Y2BaCuO5 particles and their influence on the physical properties of bulk YBa2Cu3O7-δ superconductor

A novel technique for modifying RE2BaCuO5 (211, RE = rare earth elements such as Nd, Sm, Gd, Y etc) particles and tuning their size, distribution and content in REBa2Cu3O7-δ bulk superconductors was demonstrated. Varied ultrasonic power was employed to produce fine-sized, individual, sharp-edged 211 phase particles along with mechanically damaged surfaces. The size and content of the 211 phase of infiltration growth-processed YBa2Cu3O7-δ bulk samples were gradually decreased. The effective grain refinement enhanced the critical current density by a factor of two. A maximum trapped field of 0.48 T at 77 K was obtained for a sample with 20 mm diameter by treating the 211 phase particles for 60 min with 300 W energy.

Fano effect in an ultracold atom-molecule coupled system

The Fano effect or Fano resonance with a characteristically asymmetric line shape originates from quantum interference between direct and indirect transition pathways in continuum-bound coupled systems, and is a ubiquitous phenomenon in atomic, molecular, nuclear and solid-state physics. In optical nanoscale structures, the Fano effect has wide-ranging applications that include optical filtering, sensing, all-optical switching, quantum interferometry and nonlinear optics, and this opens new avenues for photonic devices. The emergent area of ultracold atomic and molecular gases presents an ideal platform for studying Fano resonances, since the physical parameters of these gases can be extensively tuned with high precision using external fields. However, an experimental demonstration of the Fano effect in hybridized atom-molecular coupled systems has remained elusive. Here, we report on observations of the Fano effect in molecular spectra obtained by photoassociation near a d-wave Feshbach resonance. This effect occurs due to quantum interference in PA transitions involving the continuum of atom-atom scattering states, the underlying Feshbach and photoassociated excited bound molecular states. We measure the variation in atom loss rate with an external magnetic field close to the Feshbach resonance in the presence of PA laser, and thereby clearly demonstrate the Fano effect. Our results further reveal that the Fano effect has significant influence on spectral shifts. Based on Fano's method, we develop a theory that explains the observed experimental results relatively well. Our theoretical formulation takes into account quantum interference between or among multiple transition pathways and between inelastic channels. Our results present a novel method for tuning the collisional interaction strength with laser light using Fano resonance.

Enhanced circular dichroism of tilted zigzag-shaped nanohole arrays.

Circular dichroism (CD) of nanostructures is in great demand for applications in biological molecules, photocurrent devices, and photocatalysis. Planar nanostructures can be prepared in a concise manner, and their CD effects have gained much research interest. In this study, tilted zigzag-shaped nanohole (TZSN) arrays are proposed, and the CD effect is studied by the finite element method. A strong resonance occurs in the gap by tuning the charge distributions between adjacent nanoholes. Meanwhile, the CD effect of TZSN arrays is strongly dependent on the structural parameters of TZSN. Results provide a novel method for tuning the CD effects of nanohole arrays on a film.

Utilization of surface differences to improve dyeing properties of poly(m-phenylene isophthalamide) membranes

Bulk poly(m-phenylene isophthalamide) (PMIA) can achieve flexibility upon dissolution by a LiCl/dimethylacetamide co-solvent, but remains hydrophobic despite the occasional emergence of cis amide groups providing a weak negative charge. In this study, based on the significant surface differences between PMIA membranes processed by nanofiber electrospinning and casting, a series of chemical analyses, in-situ Au nanoparticle depositions, and dye-adsorption experiments revealed that more cis-configuration amide groups appeared on the surface of the electrospun PMIA membrane than on that of the cast membrane. Based on this surface difference, a strategy was proposed to improve the dyeing properties of PMIA by reversibly changing the cis/trans configurations of electrospun and cast membranes. The reversible chain-segment switch mechanism is a novel method for tuning the macroscale properties of polymer materials based on inherent molecular characteristics.

How functional groups change the electronic structure of graphdiyne: Theory and experiment

Graphdiyne's electrons have been verified to display near massless behavior, as was predicted by the Dirac cone-like shape of its band structure, and has thus resulted in an exceptionally promising semiconducting material. We present a study of three graphdiyne samples with different thicknesses grown using a cross coupling reaction. Their electronic structures were examined using synchrotron soft X-ray absorption and emission spectroscopy, together with complementary full-potential, all-electron density functional theory calculations. Excellent agreement between the measured and calculated spectra was achieved, indicating strong evidence that the correct structural model was found. We show the existence of oxygen molecules and hydroxyl functional groups, as well as pyridinic nitrogen sites in each graphdiyne sample studied. Our study shows that the defect type varies with sample thickness, which in turn strongly depends on the synthesis conditions. The band gaps of three graphdiyne samples were measured to be 0.6 eV, 0.8 eV, and 0.9 eV in agreement with our calculated values. We propose that controlling the thickness of graphdiyne films may provide a novel method for tuning their band gaps.

Particle swarm optimization (PSO)-based tuning technique for PI controller for management of a distributed static synchronous compensator (DSTATCOM) for improved dynamic response and power quality

The distributed static synchronous compensator (DSTATCOM) has emerged as an indispensable compensator element in the management of reactive power demand in distributed power management systems as well as grid connected systems. The DSTATCOM maintains the voltage at the point of common coupling (PCC) and at the DC link voltage across the DC link capacitor. For these two purposes, there are two independent controllers and these controllers are predominantly of PI types. Tuning the PI controller is a challenging exercise. In this paper, a novel method for tuning the PI controllers using particle swarm optimization is presented. By MATLAB SIMULINK simulation it is shown that the particle swarm optimization-tuned PI controller performs better than the traditional Ziegler-Nichols technique-tuned PI controller. In order to validate the proposed idea, an experimental setup has also been constructed with a PIC16F877A micro controller as the central control element and as a scale down physical model of the DSTATCOM.

Crystalline Molybdenum Oxide Thin-Films for Application as Interfacial Layers in Optoelectronic Devices.

The ability to control the interfacial properties in metal-oxide thin films through surface defect engineering is vital to fine-tune their optoelectronic properties and thus their integration in novel optoelectronic devices. This is exemplified in photovoltaic devices based on organic, inorganic or hybrid technologies, where precise control of the charge transport properties through the interfacial layer is highly important for improving device performance. In this work, we study the effects of in situ annealing in nearly stoichiometric MoOx (x ∼ 3.0) thin-films deposited by reactive sputtering. We report on a work function increase of almost 2 eV after inducing in situ crystallization of the films at 500 °C, resulting in the formation of a single crystalline α-MoO3 overlaid by substoichiometric and highly disordered nanoaggregates. The surface nanoaggregates possess various electronic properties, such as a work function ranging from 5.5 eV up to 6.2 eV, as determined from low-energy electron microscopy studies. The crystalline underlayer possesses a work function greater than 6.3 eV, up to 6.9 eV, characteristic of a very clean and nearly defect-free MoO3. By combining electronic spectroscopies together with structural characterizations, this work addresses a novel method for tuning, and correlating, the optoelectronic properties and microstructure of device-relevant MoOx layers.

Effect of Nanoemitters on Suppressing the Formation of Metal Adduct Ions in Electrospray Ionization Mass Spectrometry.

In the work, we showed that the use of nanoemitters (tip dimension <1 μm, typically ∼100 nm) could dramatically reduce the nonspecific metal adduction to peptide or protein ions as well as improve the matrix tolerance of electrospray ionization mass spectrometry (ESI-MS). The proton-enriched smaller initial droplets are supposed to have played a significant role in suppressing the formation of metal adduct ions in nanoemitters. The proton-enrichment effect in the nanoemitters is related to both the exclusion-enrichment effect (EEE) and the ion concentration polarization effect (ICP effect), which permit the molecular ions to be regulated to protonated ones. Smaller initial charged droplets generated from nanoemitters need less fission steps to release the gas-phase ions; thus, the enrichment effect of salt was not as significant as that of microemitters (tip dimension >1 μm), resulting in the disappearing of salt cluster peaks in high mass-to-charge (m/z) region. The use of nanoemitters demonstrates a novel method for tuning the distribution of the metal-adducted ions to be in a controlled manner. This method is also characterized by ease of use and high efficiency in eliminating the formation of adduct ions, and no pretreatment such as desalting is needed even in the presence of salt at millimole concentration.

Engineering the strongly correlated properties of bulk Ruddlesden-Popper transition metal oxides via self-doping.

We demonstrate via first-principles calculations a novel method of tuning the electron-electron interactions in bulk oxide materials via controlling the cationic layer arrangement. Using the Ruddlesden-Popper oxides LaSrMnO4 and LaSrTiO4 as examples, our study demonstrates that a self-doping effect can be induced by changing the stacking of the neutral and charged cationic layers. It is believed that such a phenomenon is associated with different movements of apical oxygen atoms, resulting in diverse bandgaps, magnetism and orbital degrees of freedom in the same stoichiometric strongly-correlated material. This finding may open up a new direction to engineer the transition metal oxides for practical applications requiring tunable electronic properties without external doping.

Nanostructured biomaterials from electrospun demineralized bone matrix: a survey of processing and crosslinking strategies.

In the design of scaffolds for tissue engineering biochemical function and nanoscale features are of particular interest. Natural polymers provide a wealth of biochemical function, but do not have the processability of synthetic polymers, limiting their ability to mimic the hierarchy of structures in the natural extracellular matrix. Thus, they are often combined with synthetic carrier polymers to enable processing. Demineralized bone matrix (DBM), a natural polymer, is allograft bone with inorganic material removed. DBM contains the protein components of bone, which includes adhesion ligands and osteoinductive signals, such as important growth factors. Herein we describe a novel method for tuning the nanostructure of DBM through electrospinning without the use of a carrier polymer. This work surveys solvents and solvent blends for electrospinning DBM. Blends of hexafluoroisopropanol and trifluoroacetic acid are studied in detail. The effects of DBM concentration and dissolution time on solution viscosity are also reported and correlated to observed differences in electrospun fiber morphology. We also present a survey of techniques to stabilize the resultant fibers with respect to aqueous environments. Glutaraldehyde vapor treatment is successful at maintaining both macroscopic and microscopic structure of the electrospun DBM fibers. Finally, we report results from tensile testing of stabilized DBM nanofiber mats, and preliminary evaluation of their cytocompatibility. The DBM nanofiber mats exhibit good cytocompatibility toward human dermal fibroblasts (HDF) in a 4-day culture; neither the electrospun solvents nor the cross-linking results in any measurable residual cytotoxicity toward HDF.

Modulation of the band gap of graphene oxide: The role of AA-stacking

The unique electronic properties of graphene make it an advantageous material for use in many applications, except those that require a band gap. Much work has been done to introduce an appropriately tuned band gap into graphene, including uniaxial strain and oxidation, with varying levels of success. We report here that the stacking configuration of the sheets in multilayered graphene oxide can have a significant impact on the band gap. Through comparison of X-ray absorption near-edge spectra of multilayered pristine graphene sheets with spectra simulated using density functional theory, we have found that AA-stacking pushes unoccupied states closer to the Fermi level than AB-stacking by widening the π∗ resonance in both graphene oxide and graphene. If the near-Fermi states have been removed such that the nearest unoccupied state to the Fermi level is the π∗ band, then AA-stacked multilayered graphene oxide will have a smaller band gap than AB-stacked graphene oxide. We have confirmed this by measuring the band gap of graphene oxide and reduced graphene oxide indirectly using X-ray absorption near-edge spectroscopy and X-ray emission spectroscopy. Controlling the stacking configuration of multilayered graphene oxide may provide a novel method for tuning its band gap.

Electrochemiluminescence: Alternating-Current-Driven, Color-Tunable Electrochemiluminescent Cells (Advanced Optical Materials 2/2013)

A novel method for tuning the color of electrochemiluminescence (ECL) is investigated by N. Kobayashi and co-workers. The emission color from a single AC-driven ECL cell containing two different luminescent molecules is tuned by modulating the applied frequency. As shown on page 144, yellow emission is observed from an ECL cell to which AC is applied at 900–1800 Hz, whereas the emission becomes white when the frequency is adjusted below 800 Hz.

Analysis of the Distance Between Two Classes for Tuning SVM Hyperparameters

An important step in the construction of a support vector machine (SVM) is to select optimal hyperparameters. This paper proposes a novel method for tuning the hyperparameters by maximizing the distance between two classes (DBTC) in the feature space. With a normalized kernel function, we find that DBTC can be used as a class separability criterion since the between-class separation and the within-class data distribution are implicitly taken into account. Employing DBTC as an objective function, we develop a gradient-based algorithm to search the optimal kernel parameter. On the basis of the geometric analysis and simulation results, we find that the optimal algorithm and the initialization problem become very simple. Experimental results on the synthetic and real-world data show that the proposed method consistently outperforms other existing hyperparameter tuning methods.