Semi-active vibration isolation using a near-zero-spring-rate device:steady state analysis of a single-degree-of-freedom model

A vibration isolator is described which incorporates a near-zero-spring-rate device within its operating range. The device is an assembly of a vertical spring in parallel with two inclined springs. A low spring rate is achieved by combining the equivalent stiffness in the vertical direction of the inclined springs with the stiffness of the vertical central spring. It is shown that there is a relation between the geometry and the stiffness of the individual springs that results in a low spring rate. Computer simulation studies of a single-degree-of-freedom model for harmonic base input show that the performance of the proposed scheme is superior to that of the passive schemes with linear springs and skyhook damping configuration. The response curves show that, for small to large amplitudes of base disturbance, the system goes into resonance at low frequencies of excitation. Thus, it is possible to achieve very good isolation over a wide low-frequency band. Also, the damper force requirements for the proposed scheme are much lower than for the damper force of a skyhook configuration or a conventional linear spring with a semi-active damper.

Passive vibration isolation of reaction wheel disturbances using a low frequency flexible space platform

Reaction wheel assemblies (RWAs) are momentum exchange devices used in fine pointing control of spacecrafts. Even though the spinning rotor of the reaction wheel is precisely balanced to minimize emitted vibration due to static and dynamic imbalances, precision instrument payloads placed in the neighborhood can always be severely impacted by residual vibration forces emitted by reaction wheel assemblies. The reduction of the vibration level at sensitive payloads can be achieved by placing the RWA on appropriate mountings. A low frequency flexible space platform consisting of folded continuous beams has been designed to serve as a mount for isolating a disturbance source in precision payloads equipped spacecrafts. Analytical and experimental investigations have been carried out to test the usefulness of the low frequency flexible platform as a vibration isolator for RWAs. Measurements and tests have been conducted at varying wheel speeds, to quantify and characterize the amount of isolation obtained from the reaction wheel generated vibration. These tests are further extended to other variants of similar design in order to bring out the best isolation for given disturbance loads. Both time and frequency domain analysis of test data show that the flexible beam platform as a mount for reaction wheels is quite effective and can be used in spacecrafts for passive vibration control. (C) 2011 Elsevier Ltd. All rights reserved.

A rational synthesis of vibration isolators

The paper deals with a rational approach to the development of general design criteria for non-dissipative vibration isolation systems. The study covers straight-through springmass systems as well as branched ones with dynamic absorbers. Various design options, such as the addition of another spring-mass pair, replacement of an existing system by one with more spring-mass pairs for the same space and material requirements, provision of one or more dynamic absorbers for the desired frequency range, etc., are investigated quantitatively by means of an algebraic algorithm which enables one to write down straightaway the velocity ratio and hence transmissibility of a linear dynamical system in terms of the constituent parameters.

Hybrid stiff-string-polynomial basis functions for vibration analysis of high speed rotating beams

A new finite element is developed for free vibration analysis of high speed rotating beams using basis functions which use a linear combination of the solution of the governing static differential equation of a stiff-string and a cubic polynomial. These new shape functions depend on rotation speed and element position along the beam and account for the centrifugal stiffening effect. The natural frequencies predicted by the proposed element are compared with an element with stiff-string, cubic polynomial and quintic polynomial shape functions. It is found that the new element exhibits superior convergence compared to the other basis functions.

Free vibration of a kinked cantilever with attached masses

In this paper free vibration characteristics of a centrally kinked cantilever beam of unit mass carrying masses at the kink (m(k)) and at the tip (m(t)) are analyzed. Frequency factors are presented for the first two modes for different combinations of m(k),m(t) and the kink angle delta. A relationship of the form f(m(k),m(t), delta) = m(k) + m(t)(4 + 10/3 cos delta+ 2/3 cos(2) delta)=const appears to give the same fundamental frequency for a given delta and different combinations of [m(k), m(t)]. Mode shapes as well as bending moments at the support and at the kink are also discussed. The utility of a discrete beam model in understanding the free vibration characteristics is also highlighted.

Microcontinuum approach to the pulsatile flow in tubes with and without longitudinal vibration

A fully developed pulsatile flow in a circular rigid tube is analysed by a microcontinuum approach. Solutions for radial variation of axial velocity and cell rotational velocity across the tube are obtained using the momentum integral method. Simplified forms of the solutions are presented for the relevant physiological data. Marked deviations in the results are observed when compared to a Newtonian fluid model. It is interesting to see that there is sufficient reduction in the mass flow rate, phase lag and friction due to the micropolar character of the fluid.

On vibration of eccentrically stiffened plates with varying stiffener length

Results of a study of the variation of natural frequencies with respect to the length of the stiffener of a square panel clamped all along its boundary and stiffened in the middle by a concentric stiffener were recently reported [ 11. Significant increases in certain frequencies, namely those with modes symmetric about both the medians of the plate, were observed when small gaps were not left between the plate boundary and the stiffener end. As an extension to that work, results of a study of the effect of the eccentricity of the stiffener on the frequency variation with the length of the stiffener are reported here.

Isolation and characterization of binding proteins for retinol from the cytosol, nucleosol and chromatin of the oviduct magnum of laying hens

Protein fractions that bind retinol were isolated from the cytosol, nucleosol and chromatin of the oviduct magnum of laying hens. The proteins isolated from the three sources showed similar elution profiles on chromatography through Sephadex G-75 and G-50 columns, and comparable mobility during electrophoresis on sodium dodecyl sulphate/polyacrylamide gels. Their molecular weights were calculated to be around 14500. When oviducts from vitamin A-depleted and vitamin A-repleted immature chicks given oestrogen injections for 6 consecutive days were incubated with [3H]retinyl acetate, uptake of the radioactivity in the nuclei of the vitamin A-depleted tissue was severalfold higher than that in the nuclei from the vitamin A-repleted tissue.

A rapid procedure for the isolation of spheroplasts from Mycobacterium smegmatis

Abstract is not available.

Isolation and characterization of a methionine adduct of DOPA o-quinone

The o-quinone of DOPA, an important intermediate implicated in many biological processes, has been found to react with methionine. The product has been isolated and studied, and tentative structure has been assigned.

Isolation, characterization and mapping of temperature-sensitive mutants of mycobacteriophage I3

Eighteen temperature-sensitive mutants of mycobacteriophage I3 have been isolated and partially characterized. All the mutants were defective in vegetative replication. Based on temperature shift experiments with the temperature sensitive mutants, the thermosensitive phase of the phage development period has been characterized for each mutant. The genes have been mapped by recombination analysis. The early, continuous and middle genes seem to cluster on the genetic map

Isolation and Estimation of Cytokinins and Cytokinin-Containing Transfer RNAs from Cucumis

N6-({Delta}2-Isopentenyl) adenosine antibodies were used for the isolation of free cytokinins and cytokinin-containing tRNAs from parts of Cucumis sativus L. var. Guntur seedlings and for the estimation of cytokinins in them. Immobilized N6-({Delta}2-isopentenyl) adenosine antibodies retained tRNAs containing N6-({Delta}2-isopentenyl) adenosine and N6-(4-hydroxy-3-methylbut-2-enyl) adenosine with equal efficiencies. There were at least five cytokinins in the free form in cucumber seedlings. N6-(4-Hydroxy-3-methylbut-2-enyl) adenosine, N6-({Delta}2-isopentenyl) adenosine, and N6-({Delta}2-isopentenyl) adenine were present at least to the extent of 80, 23, and 9 nanograms, respectively, in the cotyledons and 40, 6, and 3 nanograms, respectively, in the decotyledonated seedlings per gram of tissue. Only two cytokinins were found in the tRNAs of cucumber cotyledons, namely N6-({Delta}2-isopentenyl) adenosine and N6-(4-hydroxy-3-methylbut-2-enyl) adenosine in amounts of 12 and 318 nanograms, respectively, per gram of tissue. Immunoaffinity chromatographic analysis of radiolabeled aminoacyl tRNAs from cucumber cotyledons showed that tRNAPhe and tRNATyr contained cytokinins whereas tRNAAla did not.