Linear and non-linear behaviour of steel plates with circular and rectangular holes under shear loading

In this work, linear buckling and the non-linear behaviour of steel plates with one perforation subjected to shear loading was studied. The influence of the dimension, position with respect to the two main axes, shape (circular or rectangular) and orientation of a hole with respect to the panel slenderness and aspect ratio were all investigated.In both circular and rectangular holes, the strong influence of hole dimensions on the shear buckling coefficient was observed, and the values of the shear buckling coefficient fell with the plate aspect ratio. Small differences in buckling coefficients were noted in rectangular plates with various hole diameters, and buckling coefficients were practically not influenced by the orientation of the rectangular hole. In both rectangular and circular holes, the coefficient remained constant, regardless of hole position for a given distance from the edge.Linear buckling and non-linear behaviour were compared by observing different shear failure modes for slender and thick perforated plates. Elastic and plastic regions were found, on the basis of critical slenderness, for some common geometries.     

Rotating waves in rings of coupled oscillators

In this paper we discuss the types of stable oscillation created via Hopf bifurcations for a ring of identical nonlinear oscillators, each of which is diffusively and symmetrically coupled to both its neighbours, and which, when uncoupled, undergo a supercritical Hopf bifurcation creating a stable periodic orbit as a parameter, λ is increased. We show that for small enough coupling, the only stable rotating waves produced are either one or a conjugate pair, depending on the parity of the number of oscillators in the ring and the sign of the coupling constant, and that the magnitude of the phase difference between neighbouring oscillators for these rotating waves is either zero (i.e. the oscillators are synchronized) or the maximum possible, depending on the sign of the coupling constant. These brances of rotating waves are produced supercritically.     

Cervical spine abnormalities in professional singers

BACKGROUND AND OBJECTIVE: The purpose of this study was to determine irradiation parameters of a 780 nm low power CW diode laser (6.5 mW) leading to enhanced proliferation of cultured normal human keratinocytes (NHK). The possible role of reactive oxygen species (ROS) in this response was evaluated. STUDY DESIGN/MATERIALS AND METHODS: NHK were exposed to a single dose of 0 to 3.6 J/cm2 (0-180 sec) of irradiation. Proliferation parameters studied were: incorporation of 3H-thymidine during 6-24 hr following irradiation; percentage of dividing cells and number of cells, 24 hr and 48 hr following irradiation, respectively. RESULTS: Proliferation of NHK exposed to 0.45-0.95 J/cm2 was significantly enhanced by 1.3-1.9-folds relative to sham-irradiated controls, as inferred from parameters studied. Exposure to other energy densities was considerably less effective in enhancing proliferation parameters. Added enzymatic antioxidants, superoxide dismutase or catalase, scavenging superoxide anions and H2O2, suppressed this enhanced proliferation. Added scavengers (alpha-tocopherol acetate, scavenging lipid peroxidation, or sodium azide, histidine, mannitol, scavenging singlet oxygen, superoxide anions, and hydroxyl radicals, respectively), or N-acetyl cysteine, the thiol-reducing agent, suppressed the response, but to different extents. CONCLUSIONS: The results indicate that 780 nm low power diode laser irradiation enhanced keratinocytes proliferation in vitro, with an apparent involvement of ROS in this response, and comparably, might be used to promote their proliferation in vivo to enhance wound healing.     

A new 6‐DOF parallel robotic structure actuated by wires: The WiRo‐6.3

This paper describes a novel parallel robotic structure with six degrees of freedom, whose end effector is driven by nine wires operated by motors: the WiRo‐6.3. The ideas that led to the conception of the robot are thoroughly discussed and analyzed. The workspace of WiRo‐6.3 has been numerically analyzed, and it is significantly larger than the one of other analogous seven‐wire structures. The forward and inverse kinematics are both solved in closed form. © 2004 Wiley Periodicals, Inc.     

Heat dissipation and non-equilibrium phonon distributions in molecular devices

Using a density functional approach we compute vibrations of a styrene molecule adsorbed on a Si(100) substrate and the electron-phonon coupling of these modes. A non-equilibrium Green’s function approach is used to compute the partially coherent transmission in molecular junctions due to electron-vibration scattering. The electronic power dissipated into molecular vibrations allows to set a rate equation for the phonon population in the vibrational degrees of freedom of the molecule. The rate of phonon decay is computed using a microscopic approach which includes a first-principle calculation of the coupling of the molecular modes with the vibrations of the contacts. In turn, the calculated phonon lifetime is used to correct the phonon propagator. A self consistent loop allows to compute the steady state non-equilibrium phonon population of the molecular junction under bias condition.     

Theoretical and experimental sensitivity analysis of extra insensitive input shapers applied to open loop control of flexible arm

In this paper, the motion input pre-shaping, applied to flexible manipulators for space applications, is analyzed in terms of sensitivity and robustness to parameters uncertainties. The special environment of space operations and the project specifications lead to the design of manipulators with light and flexible structures. In order to highlight the performances of these methods an open loop control technique is implemented. The control technique is verified by both numerical simulations and experiments. This paper presents the experimental set-up and the results of a series of experimental tests carried out on the space robot simulator assembly, called test-bed for microgravity simulation in robotic arm dynamics (TeMSRAD). The innovative task of the research is to determine experimentally the sensitivity curve for one-hump and two-hump extra-insensitive input shapers, for different vibration limits, by purposely introducing errors in the system model, in order to simulate typical operating conditions. Paper was presented at M2D’2006, 5th International Conference on Mechanics and Materials in Design, Porto, Portugal, 24–26 July 2006.     

Volume Contents

Multibody System Dynamics -     

A novel supply and process independent ECL-to-CMOS level converter for VLSI systems

This paper presents novel circuit schemes for the ECL-to-CMOS level conversion in BiCMOS digital ICs. The proposed topologies show electrical characteristics (delay time, duty cycle, output currents) independent from the supply voltage and process variations. Thus, they are suitable to be used with both 3.3 V and 5 V supplies and over a huge temperature range. Moreover, their average current consumption is lower than 320 μA while operating with a signal frequency higher than 120 MHz. The propagation delay time in the presence of the load of a minimum-sized inverter ranges from 1 ns to 1.2 ns for the two different proposed solutions at room temperature, and varies less than 2% over the temperature range 0° to 70°. A prototype of the proposed cell has been integrated in a conventional 0.8 μm BiCMOS technology and the measurements confirm the. expected performance.     

Education and the risk of physical disability and mortality among men and women aged 65 to 84: the Italian Longitudinal Study on Aging

BACKGROUND: Most studies report that people with higher education enjoy better health and longer life. Although it is well known that most risk factors are more common among individuals with a lower level of education, the underlying mechanism of this association is not fully understood. The objective of this study was to assess the association between education, disability, and mortality. METHODS: We analyzed data on 1,817 men and 1,643 women, aged 65-84 years, to assess the association of educational level with physical disability and mortality adjusting for age, sex, smoking habit, occupation, and major chronic conditions. RESULTS: The association between educational level and disability was characterized by a dose-response effect, with the relative odds significantly decreased by about 30%, 60%, and 79% in those with 4 or 5, 6 to 8, and more than 8 years of education, compared to those with 3 or less years of education. Death rates were lower among persons with 4 or more years of education compared to those with less education. However, after adjusting for disability status, education was no longer associated with mortality (RR=0.97, CI=0.65-1.43). CONCLUSIONS: The strong association of low education with disability found in this study may explain the inverse association with mortality reported in previous studies. Disability, indeed, seems to be the mediator between education and mortality and might be due to the higher severity level of diseases, leading to death, in the lower educated group.