Qualitative models of seat discomfort including static and dynamic factors

Judgements of overall seating comfort in dynamic conditions sometimes correlate better with the static characteristics of a seat than with measures of the dynamic environment. This study developed qualitative models of overall seat discomfort to include both static and dynamic seat characteristics. A dynamic factor that reflected how vibration discomfort increased as vibration magnitude increased was combined with a static seat factor which reflected seating comfort without vibration. The ability of the model to predict the relative and overall importance of dynamic and static seat characteristics on comfort was tested in two experiments. A paired comparison experiment, using four polyurethane foam cushions (50, 70, 100, 120 mm thick), provided different static and dynamic comfort when 12 subjects were exposed to one-third octave band random vertical vibration with centre frequencies of 2.5 and 5.5 Hz, at magnitudes of 0.00, 0.25 and 0.50 m x s(-2) rms measured beneath the foam samples. Subject judgements of the relative discomfort of the different conditions depended on both static and dynamic characteristics in a manner consistent with the model. The effect of static and dynamic seat factors on overall seat discomfort was investigated by magnitude estimation using three foam cushions (of different hardness) and a rigid wooden seat at six vibration magnitudes with 20 subjects. Static seat factors (i.e. cushion stiffness) affected the manner in which vibration influenced the overall discomfort: cushions with lower stiffness were more comfortable and more sensitive to changes in vibration magnitude than those with higher stiffness. The experiments confirm that judgements of overall seat discomfort can be affected by both the static and dynamic characteristics of a seat, with the effect depending on vibration magnitude: when vibration magnitude was low, discomfort was dominated by static seat factors; as the vibration magnitude increased, discomfort became dominated by dynamic factors.     

Quantitative prediction of overall seat discomfort

Static seat characteristics (seat stiffness) and dynamic seat characteristics (vibration magnitude) can both influence judgements of seat comfort. It is proposed that seat comfort can be predicted on the basis of Steven's psychophysical law: psi = kphi(n), where psi is a sensation magnitude, phi is the stimulus magnitude and k is a constant. The law is modified to: psi = a + bphis[n(s)] + cphiv[n(v)], where phis and phiv represent seat stiffness and vibration magnitude, n(s) and n(v) are exponents determined by the rate of increase in discomfort associated with the stiffness and vibration magnitude, and a, b and c are constants. The stiffness of foam loaded to 490 N may indicate static seat comfort, while the vibration dose value (VDV) on the seat surface may indicate vibration discomfort. Two experiments with 20 subjects investigated this approach. The first experiment with five magnitudes of vibration, three foams and a rigid wooden flat seat yielded 0.929 for the exponent, n(v), for VDV. In the second experiment subjects judged the overall seat discomfort while exposed six vibration magnitudes with the same four seating conditions. This experiment yielded 1.18 for the exponent, n(s), for seat stiffness. The overall prediction of seat discomfort was given by: psi = -50.3 + 2.68phis1.18 + 101phiv0.929. The prediction equation provided more accurate estimates of subject discomfort than models using either the VDV alone or the stiffness alone, especially when the vibration magnitude was low or the seats were similar. An interaction variable between the VDV and the stiffness slightly improved the prediction. The equivalence of the two stimuli was given by log10 (stiffness) = 0.787 log10 (VDV) + 1.34, or log10 (VDV) = 1.27 log10 (stiffness) - 1.70.     

Dynamics of Trapped Bose Gases at Finite Temperatures

Starting from an approximate microscopic model of a trapped Bose-condensed gas at finite temperatures, we derive an equation of motion for the condensate wavefunction and a quantum kinetic equation for the distribution function for the excited atoms. The kinetic equation is a generalization of our earlier work in that collisions between the condensate and non-condensate (C ₁₂ ) are now included, in addition to collisions between the excited atoms as described by the Uehling–Uhlenbeck (C ₂₂ ) collision integral. The continuity equation for the local condensate density contains a source term ₁₂ which is related to the C ₁₂ collision term. If we assume that the C ₂₂ collision rate is sufficiently rapid to ensure that the non-condensate distribution function can be approximated by a local equilibrium Bose distribution, the kinetic equation can be used to derive hydrodynamic equations for the non-condensate. The ₁₂ source terms appearing in these equations play a key role in describing the equilibration of the local chemical potentials associated with the condensate and non-condensate components. We give a detailed study of these hydrodynamic equations and show how the Landau two-fluid equations emerge in the frequency domain is a characteristic relaxation time associated with C ₁₂ collisions. More generally, the lack of complete local equilibrium between the condensate and non-condensate is shown to give rise to a new relaxational mode which is associated with the exchange of atoms between the two components. This new mode provides an additional source of damping in the hydrodynamic regime. Our equations are consistent with the generalized Kohn theorem for the center of mass motion of the trapped gas even in the presence of collisions. Finally, we formulate a variational solution of the equations which provides a very convenient and physical way of estimating normal mode frequencies. In particular, we use relatively simple trial functions within this approach to work out some of the monopole, dipole and quadrupole oscillations for an isotropic trap.     

Abel inversion of deflectometric measurements in dynamic flows

We present an Abel-inversion algorithm to reconstruct mean and rms refractive-index profiles from spatially resolved statistical measurements of the beam-deflection angle in time-dependent, axisymmetric flows. An oscillating gas-jet diffusion flame was investigated as a test case for applying the algorithm. Experimental data were obtained across the whole field by a rainbow schlieren apparatus. Results show that simultaneous multipoint measurements are necessary to reconstruct the rms refractive index accurately.     

Plasma corticosterone fluctuations in an infant-learning paradigm.

Plasma corticosterone fluctuations of infant rats were examined in a learning task. A blood sample for analysis of plasma corticosterone was collected from groups of 10- and 15-day-old pups following either no disturbance, standard maternal deprivation only, or deprivation and training in an established approach-mother, avoid-shock conflict task. In the latter condition, pups remained in the goalbox either alone or with an anesthetized dam for either 15 or 60 min before blood sample collection. Plasma corticosterone levels were elevated following deprivation plus training in pups of both ages and following deprivation only in the 15-day-old pups. Further, the presence of the dam in the goalbox reduced plasma corticosterone elevations, particularly among 15-day-old pups and at 60 min. These findings suggest that the mother's capacity to moderate the pup's plasma corticosterone response may contribute to her reinforcement value in infant-learning paradigms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The use of irreversible ligands to inactivate receptor subtypes: 4-DAMP mustard and muscarinic receptors in smooth muscle

Irreversible ligands are useful tools for investigating the function of receptor subtypes in various physiological processes. The mechanism for alkylation involves the formation of a reversible receptor complex followed by a covalent reaction. The extent of receptor alkylation is determined by the dissociation constant of the reversible complex and the rate constant for conversion to the covalent complex. Selectivity can be achieved if the irreversible ligand exhibits a difference in its dissociation constants for receptor subtypes. Selective alkylation can also be achieved using a selective competitive inhibitor to protect the desired receptor subtype. By using the non-M2-selective irreversible antagonist, 4-DAMP mustard, in combination with the competitive M2-selective antagonist, AF-DX 116, it has been possible to achieve a highly selective inactivation of all non-M2 subtypes of the muscarinic receptors in smooth muscle and has enabled the discovery of the functional role of M2 receptors in smooth muscle.     

Mechanism of suppression of cell-mediated immunity by measles virus

The mechanisms underlying the profound suppression of cell-mediated immunity (CMI) accompanying measles are unclear. Interleukin-12 (IL-12), derived principally from monocytes and macrophages, is critical for the generation of CMI. Measles virus (MV) infection of primary human monocytes specifically down-regulated IL-12 production. Cross-linking of CD46, a complement regulatory protein that is the cellular receptor for MV, with antibody or with the complement activation product C3b similarly inhibited monocyte IL-12 production, providing a plausible mechanism for MV-induced immunosuppression. CD46 provides a regulatory link between the complement system and cellular immune responses.     

Design of 3-screw tuners

The screw spacing for a 3-screw waveguide tuner to be usable over an octave frequency band is investigated; an optimum is one-sixth of a guide wavelength at the lowest frequency.