This study investigates the design of robust nonlinear controller for control of voltage and frequency of variable‐speed standalone Wind Energy Conversion System (WECS). The variation in wind‐speed ...and load raise the oscillation in terminal‐voltage and frequency. These oscillation need to be minimized for enhancing the power management. To overcome this issue, an Intelligent Proportional Integral Terminal Sliding Mode Controller (iPI‐TSMC) is proposed. Proposed iPI‐TSMC establishes a fast‐finite‐time convergence with minimum steady‐state error. Also this controller is robust against the wind velocity perturbation, load variations, and external disturbances. Closed‐loop stability of the proposed controller is validated using Lyapunov‐stability‐theorem. The cogency of the proposed iPI‐TSMC has been validated through MATLAB/simulink environment for different operating conditions. Also performance of iPI‐TSMC is compared with fractional‐order‐proportional‐integral (FOPI) and conventional integer‐order‐proportional‐integral (IOPI) controllers. The simulation results, signifies the efficacy of iPI‐TSMC as compared to other controllers. Feasibility of proposed iPI‐TSMC controller is verified in real‐time HIL simulator using op4510 platform.
Statement of Industrial Relevance
Simulation analysis and the comparative study of iPI‐TSMC with FOPI, and IOPI shows better performance to keep constant terminal‐voltage during different wind‐profiles, load variation, and external disturbance. Also, performance assessment of iPI‐TSMC for different matrices during varying wind‐profiles is found superior than FOPI and IOPI controllers. Performance validation of proposed iPI‐TSMC for varying wind‐velocity and load in real‐time HIL simulator op4510 platform shows the feasibility of the proposed controller, which makes it suitable for real‐time application.
This paper reviews the potential of polymer and ceramic matrix composites for aerospace/space vehicle applications. Special, unique and multifunctional properties arising due to the dispersion of ...nanoparticles in ceramic and metal matrix are briefly discussed followed by a classification of resulting aerospace applications. The paper presents polymer matrix composites comprising majority of aerospace applications in structures, coating, tribology, structural health monitoring, electromagnetic shielding and shape memory applications. The capabilities of the ceramic matrix nanocomposites to providing the electromagnetic shielding for aircrafts and better tribological properties to suit space environments are discussed. Structural health monitoring capability of ceramic matrix nanocomposite is also discussed. The properties of resulting nanocomposite material with its disadvantages like cost and processing difficulties are discussed. The paper concludes after the discussion of the possible future perspectives and challenges in implementation and further development of polymer and ceramic nanocomposite materials.
Glioblastoma multiforme (GBM) is an aggressive, Grade IV astrocytoma with a poor survival rate, primarily due to the GBM tumor cells migrating away from the primary tumor site along the ...nanotopography of white matter tracts and blood vessels. It is unclear whether this nanotopography influences the biomechanical properties (i.e. cytoskeletal stiffness) of GBM tumor cells. Although GBM tumor cells have an innate propensity to migrate, we believe this capability is enhanced due to the influence of nanotopography on the tumor cells' biomechanical properties. In this study, we used an aligned nanofiber film that mimics the nanotopography in the tumor microenvironment to investigate the mechanical properties of GBM tumor cells in vitro. The data demonstrate that the cytoskeletal stiffness, cell traction stress, and focal adhesion area were significantly lower in the GBM tumor cells compared to healthy astrocytes. Moreover, the cytoskeletal stiffness was significantly reduced when cultured on aligned nanofiber films compared to smooth and randomly aligned nanofiber films. Gene expression analysis showed that tumor cells cultured on the aligned nanotopography upregulated key migratory genes and downregulated key proliferative genes. Therefore, our data suggest that the migratory potential is elevated when GBM tumor cells are migrating along aligned nanotopographical substrates.
Large-area PVDF thin films have been prepared and characterized for quasi-static and high frequency dynamic strain sensing applications. These films are prepared using hot press method and the ...piezoelectric phase (β-phase) has been achieved by thermo-mechanical treatment and poling under DC field. The fabricated films have been characterized for quasi-static strain sensing and the linear strain–voltage relationship obtained is promising. In order to evaluate the ultrasonic sensing properties, a PZT wafer has been used to launch Lamb waves in a metal beam on which the PVDF film sensor is bonded at a distance. The voltage signals obtained from the PVDF films have been compared with another PZT wafer sensor placed on the opposite surface of the beam as a reference signal. Due to higher stiffness and higher thickness of the PZT wafer sensors, certain resonance patterns significantly degrade the sensor sensitivity curves. Whereas, the present results show that the large-area PVDF sensors can be superior with the signal amplitude comparable to that of PZT sensors and with no resonance-induced effect, which is due to low mechanical impedance, smaller thickness and larger area of the PVDF film. Moreover, the developed PVDF sensors are able to capture both A
0 and S
0 modes of Lamb wave, whereas the PZT sensors captures only A
0 mode in the same scale of voltage output. This shows promises in using large-area PVDF films with various surface patterns on structures for distributed sensing and structural health monitoring under quasi-static, vibration and ultrasonic situations.
Permanent functional loss usually occurs after injury to the spinal cord. Currently, a clinical strategy to promote regeneration in the injured spinal cord does not exist. It has become evident that ...in order to promote regeneration, a growth permissive substrate at the injury site is critical. In this study, we report the utilization of an agarose scaffold that gels in situ, conformally filling an irregular, dorsal over-hemisection spinal cord defect in adult rats. Besides being growth permissive, the scaffolds also serve as carriers of trophic factors when embedded with BDNF releasing microtubules. We report that our thermo-reversible scaffolds are capable of supporting 3D neurite extension in vivo and are effective carriers of drug delivery vehicles for sustained local delivery of trophic factors. We demonstrate that BDNF encourages neurite growth into the scaffolds, and reduces further the minimal inflammatory response agarose gels generate in vivo as evidenced by quantitative analysis of the extent of NF-160
kDA positive neurons and axons, GFAP positive reactive astrocytes, and CS-56 positive chondroitin sulfate proteoglycan at the interface of the scaffold and host spinal cord. We suggest that these thermo-reversible scaffolds have great potential to serve as growth permissive 3D scaffolds, and to present neurotrophic factors and potentially anti-scar agents to the injury site and enhance regeneration after spinal cord injury.
Spinal cord injury (SCI) often results in permanent functional loss. This physical trauma leads to secondary events, such as the deposition of inhibitory chondroitin sulfate proteoglycan (CSPG) ...within astroglial scar tissue at the lesion.
We examined whether local delivery of constitutively active (CA) Rho GTPases, Cdc42 and Rac1 to the lesion site alleviated CSPG-mediated inhibition of regenerating axons. A dorsal over-hemisection lesion was created in the rat spinal cord and the resulting cavity was conformally filled with an in situ gelling hydrogel combined with lipid microtubes that slowly released constitutively active (CA) Cdc42, Rac1, or Brain-derived neurotrophic factor (BDNF). Treatment with BDNF, CA-Cdc42, or CA-Rac1 reduced the number of GFAP-positive astrocytes, as well as CSPG deposition, at the interface of the implanted hydrogel and host tissue. Neurofilament 160kDa positively stained axons traversed the glial scar extensively, entering the hydrogel-filled cavity in the treatments with BDNF and CA-Rho GTPases. The treated animals had a higher percentage of axons from the corticospinal tract that traversed the CSPG-rich regions located proximal to the lesion site.
Local delivery of CA-Cdc42, CA-Rac1, and BDNF may have a significant therapeutic role in overcoming CSPG-mediated regenerative failure after SCI.
TiAlN films were deposited on silicon (1
1
1) substrates from a TiAl target using a reactive DC magnetron sputtering process in Ar+N
2 plasma. Films were prepared at various nitrogen flow rates and ...TiAl target compositions. Similarly, CrN films were prepared from the reactive sputtering of Cr target. Subsequently, nanolayered TiAlN/CrN multilayer films were deposited at various modulation wavelengths (
Λ). X-ray diffraction (XRD), energy dispersive X-ray analysis, nanoindentation and atomic force microscopy were used to characterize the films. The XRD confirmed the formation of superlattice structure at low modulation wavelengths. The maximum hardness of TiAlN/CrN multilayers was 3900
kg/mm
2, whereas TiAlN and CrN films exhibited maximum hardnesses of 3850 and 1000
kg/mm
2, respectively. Thermal stability of TiAlN and TiAlN/CrN multilayer films was studied by heating the films in air in the temperature range (
T
A) of 500–900
°C for 30
min. The XRD spectra revealed that TiAlN/CrN multilayers were stable up to 800
°C and got oxidized substantially at 900
°C. On the other hand, the TiAlN films were stable up to 700
°C and got completely oxidized at 800
°C. Nanoindentation measurements performed on the films after heat treatment showed that TiAlN retained a hardness of 2200
kg/mm
2 at
T
A=700
°C and TiAlN/CrN multilayers retained hardness as high as 2600
kg/mm
2 upon annealing at 800°
C.
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