Determination of a unique configuration of free-form tensegrity structures

2011 ◽  
Vol 220 (1-4) ◽  
pp. 331-348 ◽  
Author(s):  
Hoang Chi Tran ◽  
Jaehong Lee
2016 ◽  
Vol 20 (5) ◽  
pp. 784-796 ◽  
Author(s):  
Fatih Uzun

Free-form tensegrities are composed of randomly connected cable and strut elements. The complexity of these structures causes determination of their self-equilibrium form to be a formidable task. There can be an infinite number of solutions with different forms, but it is difficult to identify the best form in terms of stability. Based on the fact that stability of structures is inversely proportional to potential energy, a genetic algorithm minimization process is developed to determine the self-equilibrium form of free-form regular tensegrity structures. The capability of the form-finding process on determination of the most stable form with minimum potential energy is investigated using two main parameters of free-form regular tensegrities which are cable–strut length ratio at rest and number of strut elements. The computational performance of the proposed method is also tested using free-form tensegrities with different number of structural elements.


2020 ◽  
Vol 501 (1) ◽  
pp. 784-801 ◽  
Author(s):  
Philipp Denzel ◽  
Jonathan P Coles ◽  
Prasenjit Saha ◽  
Liliya L R Williams

ABSTRACT We present a determination of the Hubble constant from the joint, free-form analysis of eight strongly, quadruply lensing systems. In the concordance cosmology, we find $H_0{} = 71.8^{+3.9}_{-3.3}\, \mathrm{km}\, \mathrm{s}^{-1}\, \mathrm{Mpc}^{-1}{}{}$ with a precision of $4.97{{\ \rm per\ cent}}$. This is in agreement with the latest measurements from supernovae Type Ia and Planck observations of the cosmic microwave background. Our precision is lower compared to these and other recent time-delay cosmography determinations, because our modelling strategies reflect the systematic uncertainties of lensing degeneracies. We furthermore are able to find reasonable lensed image reconstructions by constraining to either value of H0 from local and early Universe measurements. This leads us to conclude that current lensing constraints on H0 are not strong enough to break the ‘Hubble tension’ problem of cosmology.


Author(s):  
Andrew P. Schmalz ◽  
Sunil K. Agrawal

This paper addresses the issues of control and workspace determination of planar active tensegrity or tensegrity-like structures. The motion of such structures is generally produced by actuated cables, which cannot tolerate compressive forces. Hence, a controller which not only satisfies the system dynamic equations, but also maintains positive tension in cables is necessary. A null-space controller based on feedback linearization theory is developed for this purpose. This controller utilizes redundant active cables to overactuate the system. The concept of a ‘dynamic workspace’ for these structures is then introduced. This workspace consists of all configurations that are achievable from a given initial configuration while maintaining positive tensions throughout the entire system motion and is a powerful tool in analyzing the performance of a variety of tensegrity structures. This idea extends the concept of the static workspace, which consists of statically maintainable configurations, by incorporating system motion and dynamics to guarantee positive tensions during transition between the states. A critical benefit of this procedure is that it may be used to find the dynamic workspace of a system regardless of whether actuator redundancy is utilized, and thus can be used to objectively illustrate the degree to which overactuation improves mobility of a tensegrity structure. The effectiveness of the developed concepts is demonstrated through computer simulation and actual physical experimentation.


Author(s):  
Yao Chen ◽  
Jian Feng ◽  
Yongfen Wu

Tensegrity structures are drawing the attention of architects and engineers due to their remarkable configurations. They have inextensional mechanisms, yet they are stable. The determination of connectivity patterns of the compression bars and tension cables is a key to design tensegrity structures. In this paper, a discrete optimization model for the form-finding of tensegrity structures was developed, and converted into a modified travelling salesman problem (TSP). The ant colony system (ACS) was used to search for feasible solutions, where all the given nodes were taken as different cities in the network. To obtain optimized shapes of tensegrity structures with stable equilibriums and adequate stiffness, an objective function was introduced. Examples based on the geometries of some polyhedra were carried out using the proposed technique. Many different configurations of the assemblies which consist of cables and bars are transformed into interesting tensegrity structures. It concludes that this novel algorithm could be applicable to the form-finding of both regular and nonregular tensegrity structures.


Author(s):  
Н. P. Ryvak ◽  
T. R. Levytskyy ◽  
R. O. Ryvak ◽  
S. V. Chorniy

The article presents a literature review on the need to balance feed on L-arginine content, its characteristics, ways to supplement the diet of animals and poultry, as well as modern methods for quantitative determination of L-arginine in food, pharmaceuticals, etc. In the section «Materials and methods» the characteristic of the developed test technique, parameters of carrying out research, calibration characteristics with application of a standard sample of L-arginine and carrying out tests of amino acid content in a feed additive by means of system of capillary electrophoresis «Kapel-105M» are given. A description of the validation characteristics performed in the process of validation of the method is given. As a result of the conducted researches the technique of definition of the content of L-arginine in feed additives by means of a method of capillary electrophoresis is developed. The test procedure is based on the dissolution of the feed additive sample, further separation and quantification of the free form of L-arginine, its identification by individual absorption at a wavelength of 200 nm, temperature in the working capillary 30 ºC, voltage 25 kV and conductive electrolyte. The results of validation of this technique by the following characteristics are presented: repeatability, reproducibility, trueness, linearity, limit of quantification, budget uncertainty. The values of trueness, repeatability, reproducibility and uncertainty of the method (with a confidence level of (P) 0.95) does not exceed 5.0 %, the hypothesis of Linearity is acceptable, calculated on the basis of standard deviation (SD) limit of quantification for determining the content of arginine are satisfactory. The results allow us to conclude that the method of capillary electrophoresis using the device «Kapel-105M» is quite accurate and reliable in the case of studies of feed additives L-arginine with a content of the main substance of at least 98,0 %.


2000 ◽  
Vol 46 (3) ◽  
pp. 379-384 ◽  
Author(s):  
Michael Landt

Abstract Background: Leptin, a hormone produced primarily by adipose tissue, is known to be present in serum as both monomeric (free) and higher molecular mass (bound) forms, but little is known about the nature of the bound forms or physiological variation in binding capacity. Methods: A new method to quantify the free and bound forms was developed, based on HPLC separation and RIA quantification in chromatography fractions. Reanalysis of specimens after addition of exogenous leptin allowed direct determination of leptin-binding capacity and the degree of saturation of leptin-binding capacity. Results: HPLC chromatography fractionated serum leptin into both the free form and as a broad peak of 59–130 kDa. Several experiments were conducted to validate the new method. The concentrations of bound leptin in serum were 0.45–3.94 μg/L, and they increased as total leptin (reflecting adiposity) increased in 24 lean and obese volunteers. Leptin was readily dissociated from the bound fraction by competition from exogenous leptin. Rechromatography of the bound fraction led to dissociation of leptin, which was promoted by warming the sera before chromatography. Leptin-binding capacity was 1.8–5.3 μg/L; binding capacity was nearly constant over a range of total leptin concentrations of 2–10 μg/L, and slowly increased at higher total leptin concentrations. Saturation of binding capacity was low (15%) at very low total leptin concentrations (<5 μg/L), but rose quickly to a plateau near 80% at higher total leptin concentrations. Conclusions: The new method facilitates measurement of free and bound fractions of serum leptin, and is the first method measuring leptin-binding capacity. These experiments demonstrate that the concentration of bound leptin and leptin-binding capacity vary physiologically, with binding/binding capacity increasing with adiposity. Except in very lean individuals, binding capacity is nearly completely saturated.


1963 ◽  
Vol 46 (2) ◽  
pp. 276-284 ◽  
Author(s):  
J F Guymon ◽  
E A Crowell

Abstract Methods for the determination of aldehydes in wines and spirits, based on the reaction of aldehydes with bisulfite ion, must allow for the normal presence of sulfites in wines and in some spirits and for the fraction of acetaldehyde combined with ethyl alcohol as acetal. The direct procedure avoids errors due to sulfites already present. An acid hydrolysis step differentiates between the free form and acetal form of the aldehyde; addition of 120 ppm of EDTA eliminates the interference of copper. Detailed procedures are given for distinguishing between free and combined aldehydes in distilled spirits, with and without extract content. The percentages of free and combined aldehyde at equilibrium are graphically shown for varying strengths of alcohol. A method is proposed for wines in which only the free aldehydes are determined, since the percentage combined with alcohol at equilibrium is small.


1981 ◽  
Vol 27 (12) ◽  
pp. 2035-2037 ◽  
Author(s):  
G Avigad ◽  
B Robertson

Abstract We describe a modified enzymic reagent for determination of cholesterol and cholesterol ester in serum and in high-density lipoprotein. In this new procedure, the hydrogen peroxide produced by the action of cholesterol oxidase is used as a substrate for NAD+ peroxidase. Spectrophotometric determination of the NADH consumed in this coupled reaction provides a direct and absolute measure of the cholesterol originally present in free form and that liberated by the action of cholesterol ester hydrolase.


Sign in / Sign up

Export Citation Format

Share Document