Vibration analysis of machine tool’s hexapod table

Parallel mechanisms have found new applications in machine tool’s as the end effector carrying the spindle or used as the table of the machine. Investigations on the dynamics and especially the vibration behavior of these mechanisms are in the initial stage. The authors developed a vibration model for the hexapod table of milling machines and machining centers and derived the relevant explicit equations. The eigenvalue problem of the upper platform of hexapod was solved to obtain the natural frequencies of the platform. The results have been verified with FEM simulation. The distinguishing features of the hexapod tables from the view point of dynamic behavior have also been concluded.     

An Improvement Energy Consumption Policy Using Communication Reduction in Wireless Body Sensor Network

Dedicated short-range communications (DSRC) is an important wireless technology for current and future automotive safety and mitigation of traffic jams. In this work, we have designed a Coplanar waveguide microstrip patch antenna with linear, upper and bottom and side slots for application in DSRC. The patch antenna was designed using glass epoxy substrate (FR4). Various parametric analyses such as the current distribution, reflection coefficient, radiation pattern on E- and H-plane as well as the realized gain (dB) were performed. The results were obtained by simulation using high-frequency structure simulator tool. The proposed antenna covers a frequency band of 5.8–5.9 GHz which is highly dedicated to the DSRC wireless communication technology for enhancement of safety of the automotive transport system. The designed antenna shows a good return loss of ??19 dB at 5.9 GHz.The designed antenna shows a promising gain, return loss and radiation pattern for use in DSRC for automotive transport systems.

     

Development of Synthetic Platelet‐Activating Hydrogel Matrices to Induce Local Hemostasis

Several hemostatic strategies rely on the use of blood components such as fibrinogen and thrombin, which suffer from high cost and short shelf‐life. Here, a cost‐effective synthetic biomaterial is developed for rapid local hemostasis. Instead of using thrombin, thrombin‐receptor‐agonist‐peptide‐6 (TRAP6) is covalently engineered in polyvinyl alcohol (PVA) hydrogels. Soluble PVA‐TRAP6 is first prepared by covalent attachment of cysteine‐containing TRAP6 onto the backbone of PVA‐norbornenes (PVA‐NB) through photoconjugation. Cytotoxicity studies using C2C12 myoblasts indicate that PVA‐NB and PVA‐TRAP6 are nontoxic. Thromboelastography reveals that hemostatic activity of TRAP6 is retained in conjugated form, which is comparable to free TRAP6 solutions with equal concentrations. A 0.1% PVA‐TRAP6 solution can shorten the clotting time (CT) to ca. 45% of the physiological CT. High platelet‐activating efficiency is further confirmed by platelet aggregation assay and flow cytometry (FACS). For potential clinical applications, TRAP6‐presenting hydrogel particulates (PVA‐TRAP6‐P) are developed for local platelet activation and hemostasis. PVA‐TRAP6‐P is prepared by biofunctionalization of photopolymerized PVA‐NB hydrogel particulates (PVA‐NB‐P) with TRAP6. It is demonstrated that PVA‐TRAP6‐P can effectively shorten the CT to ca. 50%. FACS shows that PVA‐TRAP6‐P can activate platelets to a comparable extent as soluble TRAP6 control. Altogether, PVA‐TRAP6‐P represents a promising class of biomaterials for safe hemostasis and wound healing.     

Numerical investigation of the mechanism behind the deflagration to detonation transition in homogeneous and inhomogeneous mixtures of H2-air in an obstructed channel

The accidental release of hydrogen into enclosures can result in a flammable mixture with concentration gradients and possible deflagration-to-detonation transition (DDT). This numerical study aims to investigate the effect of obstacle spacing and mixture concentration on the DDT in a homogeneous and inhomogeneous hydrogen-air mixture. The paper focuses on the mechanisms behind the DDT in two mixtures with an average hydrogen concentration of 15% and 30%. Unlike the near-stoichiometric mixture, in the lean mixture, DDT only occurs in the inhomogeneous mixture. Depending on obstacle spacing, three different regimes of DDT were observed in the near-stoichiometric inhomogeneous mixture: i) Detonation was ignited when a strong Mach stem formed and propagated between the obstacles; ii) two explosion centers appeared when incident shock and Mach stem reflected from upper and lower obstacles, respectively; iii) Mach stem did not form but DDT occurred behind the flame front at the top of the obstacle.     

Photodynamic biologic tissue glue to enhance corneal wound healing after radial keratotomy

BACKGROUND: In this study, we describe the development of a novel experimental system in which rejection of porcine skin grafts by human peripheral blood cells can be studied directly in vivo in immunodeficient mice. METHODS: To construct a small animal model of discordant xenograft rejection, recombinase-activating gene-deficient mice (R-) lacking both mature B and T cells were grafted with porcine skin grafts and administered, by adoptive cell transfer, human cells stimulated in vitro with irradiated porcine peripheral blood cells to create Hu-R- mice. RESULTS: R- mice accepted porcine skin grafts indefinitely without the need for immunosuppression. In contrast, Hu-R- mice were able to reject porcine skin grafts. Immunohistochemical analysis of rejecting skin grafts revealed the accumulation of human T cells around dermal porcine vessels and focally in the epidermis. Graft rejection was manifested by vascular endothelial cell proliferation, edema at the dermal-epidermal border, and perivascular hemorrhage. The tissue damage observed in the rejecting grafts was similar to that observed in delayed primate anti-porcine cell-mediated rejection of vascularized organ xenografts. CONCLUSIONS: The development and characterization of a small animal model, to study cellular immune responses of human cells to discordant xenografts in vivo, should provide a convenient means for asking mechanistic questions related to discordant xenotransplantation, and may also provide a practical system for testing new approaches designed to prevent xenograft rejection.     

Axisymmetric Stress Analysis of a Thick Conical Shell with Varying Thickness under Nonuniform Internal Pressure

A mathematical approach based on the perturbation theory has been used for axisymmetric stress analysis of a thick conical shell with varying thickness under nonuniform internal pressure. The equilibrium equations have been derived using the energy principle and considering the second-order shear deformation theory (SSDT), which includes shear deformation effects. This system of ordinary differential equations with variable coefficients has been solved analytically using the matched asymptotic expansion method of the perturbation theory. A comparison of the results with the finite-element method and the first-order shear deformation theory shows that the SSDT can predict the displacements and stresses of the shell for a wide range of thicknesses as well with less calculations than other analytical methods such as the Frobenius series method.     

Non-linear free vibrations of Kelvin–Voigt visco-elastic beams

A full visco-elastic non-linear beam with cubic non-linearities is considered, and the governing equations of motion of the system for large amplitude vibrations are derived. By using the method of multiple scales, the non-linear mode shapes and natural frequencies of the beam are then analytically formulated. The resulting formulations for amplitude, non-linear natural frequencies and mode shapes can be used for any type of boundary conditions. Next, method of Galerkin is used to separate the time and space variables. The equations of motion show the presence of a non-linear damping term in addition to the ones with non-linear inertia and geometry. As it is known, the presence of non-linear inertia and the geometric terms make the non-linear natural frequencies to be dependent on constant amplitude of vibration. But, when damping non-linearities are present, it is seen that the amplitude is exponentially time-dependent, and so, the non-linear natural frequencies will be logarithmically time-dependent. Additionally, it is shown that the mode shapes will be dependent on the third power of time-dependent amplitude. The analytical results are applied to hinged–hinged and hinged–clamped boundary conditions and the results are compared with numerical simulations. The results match very closely for both cases specially for the case of hinged–hinged beam.     

Improved harmonic suppression efficiency of single-phase APFs in distorted distribution systems

In this study, a control method is proposed to improve the harmonic suppression efficiency of the single-phase active power filter in a distorted power system to suppress current harmonics and reactive power. The proposed method uses the self-tuning filter (STF) algorithm to process single-phase grid voltage in order to provide a uniform reference grid current, which increases the efficiency of the system. The results of the simulation study are presented to verify the effectiveness of the proposed control technique in this study.     

Characterization and the hydrogen storage capacity of titania-coated electrospun boron nitride nanofibers

In the present work, titania-coated (TiO₂) boron nitride nanofibers were produced by the electrospinning method, and the effect of heat treatment on the nanofibers was studied. Electrospinning method is often adopted for the synthesis of one-dimensional nanofibers due to high productivity, simplicity, and cost-effectiveness. In this study, boric oxide was deposited on co-electrospun polyacrylonitrile and TiO₂. TiO₂-coated boron nitride nanofibers, with a diameter of 100 nm, were obtained after heat treatment and nitridation. The effects of heat treatment on the morphology, surface area and hydrogen storage capacity were studied extensively. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) showed long, bead-free nanofibers and the presence of TiO₂ nanoparticles on the nanofibers. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy depicted hexagonal structures of boron nitride. The hydrogen uptake capacities of the nanofibers were investigated by pressure composition isotherm (PCI) in the pressure range of 1–70 bar at room temperature.     

The role of Al and Mg in the hydrogen storage of electrospun ZnO nanofibers

Pure and doped ZnO nanofibers with Al and Mg were successfully synthesized via an electrospinning method using a sol–gel containing Polyvinylpyrrolidone as a spinning aid and a zinc nitrate precursor. Calcination of the doped and undoped electrospun nanofibers was conducted at 500 °C in air, and the resultant structures were analyzed by X-ray diffraction (XRD) and Raman spectroscopy. The diameter of the doped nanofibers decreased with increasing viscosity and conductivity, as measured by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive spectroscopy (EDS) showed that Mg and Al are present in ZnO nanofibers. The pressure composition isotherm (PCI) demonstrated that the capacity of hydrogen storage in pure zinc oxide nanofibers is a factor of two greater than that of zinc oxide nanoparticles. However, Al-doped ZnO nanofibers have the highest capacity of hydrogen storage (2.81 wt%) at room temperature.