Spring structure

Mass and spring structures Solid-state physics... 

Operational characteristics level of spring with nanoscale substructure allows design of new generation coiled spring structures with reduced mass. 

A partial joining of glass components is possible using thermal bonding by applying pressure selectively. The spring structure that is part of the middle sheet shown in Fig. 10.4 can oscillate freely. The structure was created... 

Nesvijski, E.G., Nogin, S.I. Acoustic Emission Technics for Nondestructive Evaluation of Stress of Concrete and Reinforced Concrete Structures and Materials. Third Conference on Nondestructive Evaluation of Civil Structures and Materials, Boulder, CO, 1996. Nesvijski, E. G. Failure Forecast and the Acoustic Emission Silence Effect in Concrete. ASNT s Spring Conference, Houston, TX, 1997. 

A major advance in force measurement was the development by Tabor, Win-terton and Israelachvili of a surface force apparatus (SFA) involving crossed cylinders coated with molecularly smooth cleaved mica sheets [11, 28]. A current version of an apparatus is shown in Fig. VI-4 from Ref. 29. The separation between surfaces is measured interferometrically to a precision of 0.1 nm the surfaces are driven together with piezoelectric transducers. The combination of a stiff double-cantilever spring with one of a number of measuring leaf springs provides force resolution down to 10 dyn (10 N). Since its development, several groups have used the SFA to measure the retarded and unretarded dispersion forces, electrostatic repulsions in a variety of electrolytes, structural and solvation forces (see below), and numerous studies of polymeric and biological systems. 

Berendsen, H.J.C., Postma, J.P.M., Van Gunsteren, W.F. Statistical mechanics and molecular dynamics The calculation of free energy, in Molecular Dynamics and Protein Structure, J. Hermans, ed.. Polycrystal Book Service, PO Box 27, Western Springs, 111., USA, (1985) 43-46. 

To enable an atomic interpretation of the AFM experiments, we have developed a molecular dynamics technique to simulate these experiments [49], Prom such force simulations rupture models at atomic resolution were derived and checked by comparisons of the computed rupture forces with the experimental ones. In order to facilitate such checks, the simulations have been set up to resemble the AFM experiment in as many details as possible (Fig. 4, bottom) the protein-ligand complex was simulated in atomic detail starting from the crystal structure, water solvent was included within the simulation system to account for solvation effects, the protein was held in place by keeping its center of mass fixed (so that internal motions were not hindered), the cantilever was simulated by use of a harmonic spring potential and, finally, the simulated cantilever was connected to the particular atom of the ligand, to which in the AFM experiment the linker molecule was connected. 

Beryllium is used as an alloying agent in producing beryllium copper, which is extensively used for springs, electrical contacts, spot-welding electrodes, and non-sparking tools. It is applied as a structural material for high-speed aircraft, missiles, spacecraft, and communication satellites. Other uses include windshield frame, brake discs, support beams, and other structural components of the space shuttle. 

Imagine, now, a solid held together by such little springs, linking atoms between two planes within the material as shown in Fig. 6.1. For simplicity we shall put atoms at the comers of cubes of side Tq. To be correct, of course, we should draw out the atoms in the positions dictated by the crystal structure of a particular material, but we shall not be too far out in our calculations by making our simplifying assumption - and it makes drawing the physical situation considerably easier ... 

Real polymers require more elaborate systems of springs and dash-pots to describe them. This approach of polymer rheology can be developed to provide criteria for design with structural polymers. At present, this is rarely done instead, graphical data (showing the creep extension after time t at stress a and temperature T) are used to provide an estimate of the likely deformation during the life of the structure. 

Demonstrations (a) Atom spring models (Fig. 4.2) on overhead projector to illustrate effect of structure on modulus, (b) Large models of Na atom and Cl atom, (c) Liquid nitrogen. 

HJC Berendsen. In I Hermans, ed. Molecular Dynamics and Pi otem Structure. Western Springs, IL Polycrystal Book Service, 1985. 

One of the major effects of acidic deposition is felt by aquatic ecosystems in mountainous terrain, where considerable precipitation occurs due to orographic lifting. The maximum effect is felt where there is little buffering of the acid by soil or rock structures and where steep lakeshore slopes allow little time for precipitation to remain on the ground surface before entering the lake. Maximum fish kills occur in the early spring due to the "acid shock" of the first meltwater, which releases the pollution accumulated in the winter snowpack. This first melt may be 5-10 times more acidic than rainfall. 

In viw PAI and antithrombin are stabilized in their active forms by binding to vitronectin and heparin, respectively. These two serpins seem to have evolved what Max Perutz has called "a spring-loaded safety catch" mechanism that makes them revert to their latent, stable, inactive form unless the catch is kept in a loaded position by another molecule. Only when the safety catch is in the loaded position is the flexible loop of these serpins exposed and ready for action otherwise it snaps back and is buried inside the protein. This remarkable biological control mechanism is achieved by the flexibility that is inherent in protein structures. 

Throughout this chapter the viscoelastic behaviour of plastics has been described and it has been shown that deformations are dependent on such factors as the time under load and the temperature. Therefore, when structural components are to be designed using plastics, it must be remembered that the classical equations which are available for the design of springs, beams, plates, cylinders, etc., have all been derived under the assumptions that... 

Over the years there have been many attempts to simulate the behaviour of viscoelastic materials. This has been aimed at (i) facilitating analysis of the behaviour of plastic products, (ii) assisting with extrapolation and interpolation of experimental data and (iii) reducing the need for extensive, time-consuming creep tests. The most successful of the mathematical models have been based on spring and dashpot elements to represent, respectively, the elastic and viscous responses of plastic materials. Although there are no discrete molecular structures which behave like the individual elements of the models, nevertheless... 

Table 2. Structural parameters, cohesive energies per atom, and spring constant for helices C4(,0 and C,4(, here / and r, are outer and inner diameter of a helix, respeetively...

Structure / (nm) r, (nm) Pitch length (nm) Cohesive energy (eV/atom) Spring constant (meV/nni)... 

J. C. Ekvall, Structural Behavior ot Monofilament Composites, Proceedings of the AIAA 6th Structures and Materials Conference, Palm Springs, California, 5-7 April... 

The usual structure of off-lattice chain models is reminiscent of the Larson models the water and oil particles are represented by spheres (beads), and the amphiphiles by chains of spheres which are joined together by harmonic springs... 

Watson, J. D., ed., 1983. Structures of DNA. Cold Spring Harbor Symposia on Quantitative Biology, Volume XLVII. New York Cold Spring Harbor Laboratory. 

Fitz, C. W., A Shariat, and L. Spiegel, Performance of Structured Packing at High Pressure, presented at AIChE Spring National Meeting, Houston, Texas, March (1995). 

When all possible vibration reduction has been obtained, the machine must be isolated from the structure. Some form of spring mounting achieves this. Spring mounts have a resonant frequency dependent on the stiffness of the spring and the weight of the object placed on it. It will be apparent that the static deflection of the spring will also be proportional to the resonant frequency. 

While most stationary machine components move during normal operation, they are not always resonant. Some degree of flexing or movement is common in most stationary machine-trains and structural members. The amount of movement depends on the spring constant or stiffness of the member. However, when an energy source coincides and couples with the natural frequency of a structure, excessive and extremely destructive vibration amplitudes result. 

James Dewey Watson (1928- ) was born in Chicago, Illinois, and enrolled in the University of Chicago at age 15. He received his Ph.D. in 1950 at the Unwersity of Indiana and then worked at Cambridge University in England from 1951 to 1953, where he and Francis Crick deduced the structure of DNA. After more than 20 years as professor at Harvard University, he moved in 1976 to the Laboratory of Quantitative Biology at Cold Spring Harbor, Long Island, New York. He shared the 1962 Nobel Prize in medicine for his work on nucleic acids. 

This dement is important mainly because of its use as an additive to iron in the manufacture of steel. A few percent of vanadium stabilizes a high-temperature crystal structure of iron so that it persists at room temperature. This form is tougher, stronger, and more resistant to corrosion than ordinary iron. Automobile springs, for example, are often made of vanadium steel. 

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