Long-Term Studies of Rubber Materials by Dynamic Mechanical Stress Relaxation

1989 ◽  
Vol 62 (3) ◽  
pp. 387-425 ◽  
Author(s):  
Folke Björk ◽  
Ola Dickman ◽  
Bengt Stenberg
Keyword(s):  
Stress Relaxation ◽  
Crosslink Density ◽  
Dynamic Stress ◽  
Life Time ◽  
Reasonable Estimate ◽  
Undesirable Characteristic ◽  
Dynamic Seal ◽  
Proper Values ◽  
Long Term Studies

Abstract The measurement of dynamic stress relaxation can reveal otherwise hidden weaknesses in rubber materials. The stress relaxation of the minimum of the restoring foce has the undesirable characteristic of being greater than the continuous stress relaxation. An increase in the amplitude of the deformation increases the decay in the minimum values of the varying retractive stress, and an increase in the prestrain makes it smaller. The normalized curve for continuous stress relaxation is found to lie somewhere between the normalized curves for the maximum and minimum of the retractive stress. The measurement of network density on specimens aged under continuous and dynamic stress relaxation indicate that the mechanism behind the degradation of the rubber network is the same in both cases. The relations between intermittent, continuous, and dynamic stress relaxation give a reasonable estimate of the dynamic stress relaxation from the other two when proper values of the coefficients are used. This relation says that results both of continuous and intermittent stress relaxation are important for predicting the life time of a dynamic seal. The relations offers an explanation of the differences between maximum and minimum values obtained during the measurement of dynamic stress relaxation and their relation to continuous stress relaxation. From these relations it can be concluded that a rubber intended for dynamic seals should contain neither reversion nor secondary crosslinking. Crosslink density should be high in order to overpower effects on crosslinking of factors in the surroundings.

Implications of Long-Term Studies of Three Model Preschool Programs for Head Start

2008 ◽  
Author(s):  
Lawrence J. Schweinhart ◽  
Elena V. Malofeeva ◽  
Lawrence J. Schweinhart ◽  
Michelle M. Englund ◽  
Arthur J. Reynolds ◽  
...  
Keyword(s):  
Head Start ◽  
Preschool Programs ◽  
Long Term Studies

Primary varicose veins

Phlebologie ◽  
2010 ◽  
Vol 39 (03) ◽  
pp. 133-137
Author(s):  
H. Partsch
Keyword(s):  
Varicose Veins ◽  
Compression Therapy ◽  
Daily Practice ◽  
Clinical Severity ◽  
Compression Stockings ◽  
Primary Varicose Veins ◽  
The Cost ◽  
Convincing Data ◽  
Long Term Studies

SummaryBackground: Compression stockings are widely used in patients with varicose veins. Methods: Based on published literature three main points are discussed: 1. the rationale of compression therapy in primary varicose veins, 2. the prescription of compression stockings in daily practice, 3. studies required in the future. Results: The main objective of prescribing compression stockings for patients with varicose veins is to improve subjective leg complaints and to prevent swelling after sitting and standing. No convincing data are available concerning prevention of progression or of complications. In daily practice varicose veins are the most common indication to prescribe compression stockings. The compliance depends on the severity of the disorder and is rather poor in less severe stages. Long-term studies are needed to proof the cost-effectiveness of compression stockings concerning subjective symptoms and objective signs of varicose veins adjusted to their clinical severity. Conclusion: Compression stockings in primary varicose veins are able to improve leg complaints and to prevent swelling.

Diatoms and aquatic palynomorphs in the sediments of the Eurasian Arctic seas and their significance for paleooceanological investigations in the Arctic

2019 ◽  
pp. 246-251
Author(s):  
Yelena I. Polyakova ◽  
Yekaterina I. Novichkova ◽  
Tatiana S. Klyuvitkina ◽  
Elizaveta A. Agafonova ◽  
Irina M. Kryukova
Keyword(s):  
Bering Sea ◽  
Surface Sediments ◽  
Sea Water ◽  
The Arctic ◽  
Marginal Filter ◽  
Arctic Seas ◽  
Hydrological Parameters ◽  
The Arctic Ocean ◽  
Long Term Studies

Presented the results of long-term studies of diatoms and aquatic palynomorphs in surface sediments of the Arctic seas and the possibility of their use for the reconstructions of paleocirculation water masses, advection of Atlantic and Bering sea water into the Arctic ocean, changes in the river runoff to the seas, sedimentary processes in the marginal filter of the largest rivers, seasonal sea ice cover and other hydrological parameters.

Aspects of the Evolution of the Romanian Tourists’ Preferences Concerning the Domestic Tourist Destinations

2019 ◽  
Vol 10 (1) ◽  
pp. 21-28
Author(s):  
Aniela Bălăcescu ◽  
Radu Șerban Zaharia
Keyword(s):  
Logistic Model ◽  
Local Level ◽  
Medium Term ◽  
Tourist Destinations ◽  
Tourism Management ◽  
Production And Consumption ◽  
On Line ◽  
The One ◽  
Long Term Studies

Abstract Tourist services represent a category of services in which the inseparability of production and consumption, the inability to be storable, the immateriality, and last but not least non-durability, induces in tourism management a number of peculiarities and difficulties. Under these circumstances the development of medium-term strategies involves long-term studies regarding on the one hand the developments and characteristics of the demand, and on the other hand the tourist potential analysis at regional and local level. Although in the past 20 years there has been tremendous growth of on-line booking made by household users, the tour operators agencies as well as those with sales activity continue to offer the specific services for a large number of tourists, that number, in the case of domestic tourism, increased by 1.6 times in case of the tour operators and by 4.44 times in case of the agencies with sales activity. At the same time, there have been changes in the preferences of tourists regarding their holiday destinations in Romania. Started on these considerations, paper based on a logistic model, examines the evolution of the probabilities and scores corresponding to the way the Romanian tourists spend their holidays on the types of tourism agencies, actions and tourist areas in Romania.

The generalized regularities of damageability and integrity in estimations of the endurance in conditions of variability of loading regimes

2019 ◽  
Vol 85 (9) ◽  
pp. 61-65
Author(s):  
N. A. Makhutov
Keyword(s):  
Life Time ◽  
Cyclic Strength ◽  
Laboratory Diagnostics ◽  
Methodological Issues ◽  
Break Points ◽  
Number Of Cycles ◽  
Cyclic Damage ◽  
Damage Summation ◽  
Temperature Factors

We consider and analyze general methodological issues regarding the strength and endurance (life-time) of the materials and structure elements under a combined effect of various force, deformation and temperature factors. The Journal "Zavodskaya laboratoriya. Diagnostika materialov" (Industrial laboratory. Diagnostics of materials) has launched systematic publications on this problematic since 2018. For many decades, domestic and foreign laboratory studies have gleaned to a traditional methodology for obtaining initial curves of the long-term and cyclic strength that related the breaking stresses with time or number of cycles. These curves, with the characteristic sections and break points, separating the areas of elastic and inelastic (plastic strain or creep strain) strain, are used in analysis of long-term and cyclic damage. Using the elementary linear law of damage summation, it is possible to calculate at a first approximation the strength and endurance under varying conditions of loading. Stepping up the requirements to the accuracy of calculations necessitates a transition from force fracture criteria (at stresses a) to deformation criteria (in elastic and inelastic deformations e). Thus, it becomes possible to construct and use a unified expression for the curve of the long-term cyclic fracture (taking into account the temporal x and cyclic N factors) and a long-term cyclic damage. With such approach it is possible to remain the linear law of damage summation though those damages are obviously nonlinear. The goal of the study is to continue and support the discussion of the most complex problems of a comprehensive assessment of the strength, resource, survivability and safety of high-risk engineering equipment within the journal pages.

Planning a system of permanent sample plots for integrated long-term studies of community-based forest management

1970 ◽  
Vol 16 (2) ◽  
pp. 3-11 ◽  
Author(s):  
H Meilby ◽  
L Puri ◽  
M Christensen ◽  
S Rayamajhi
Keyword(s):  
Forest Management ◽  
Key Words ◽  
Research Note ◽  
Managed Forests ◽  
Community Based ◽  
Permanent Sample Plots ◽  
Long Term Studies

To monitor the development of four community-managed forests, networks of permanent sample plots were established in 2005 at sites in Chitwan, Kaski and Mustang Districts, Nepal. This research note documents the procedures used when preparing for establishment of the plot networks, evaluates the applied stratification of the forest on the basis of data gathered in pilot surveys conducted in the early 2005, and provides a discussion on the implications of the choices made. Key words: Community-managed forests; permanent sample plots; stratification; allocation; estimates Banko Janakari Vol.16(2) 2006 pp.3-11

A Novel Potentiometric PVC-membrane Cysteamine-Selective Electrode Based on Cysteamine-Phosphomolybdate Ion-Pair

2020 ◽  
Vol 16 (2) ◽  
pp. 168-175 ◽  
Author(s):  
Merve Tumur ◽  
Gulsah Saydan Kanberoglu ◽  
Fatih Coldur
Keyword(s):  
Analytical Methods ◽  
Pharmaceutical Preparations ◽  
Life Time ◽  
Ion Pair ◽  
Pharmaceutical Formulation ◽  
Pvc Membrane ◽  
Selective Electrode ◽  
Potentiometric Response ◽  
Drug Quality Control

Background: Cysteamine is used as an orphan drug in the treatment of cystinosis to prevent long-term cystine accumulation in lysosomes. Dosing in cysteamine treatment is extremely important and overdose may cause some side effects. Up to now, various analytical methods have been used for cysteamine determination. Many of these methods require sophisticated instruments, expert operators, time-consuming measurement procedures and manipulation steps, expensive supplies and long analysis time. Aims and Objective: The present study deals with the development of a potentiometric PVC-membrane cysteamine-selective electrode based on an ion-pair of cysteamine and its application in a pharmaceutical formulation. Methods: Cysteamine (Cys)-Phosphomolybdate (PM) ion-pair was synthesized by mixing the equal volumes of 10-2 M Cysteamine HCl and sodium phosphomolybdate aqueous solutions. The obtained precipitate was used as ionophore in the structure of PVC-membrane. Results and Discussion: The electrode exhibited a linear response in the concentration range of 1.0×10- 1-1.0×10-5 M cysteamine with a slope of 51,7 mV per decade and detection limit of 1.0×10-5 M. The potentiometric response of the electrode was very rapid (5 s), adequately repeatable, stable and selective. pH working range and life-time of the electrode were also determined as 3.0-7.0 and 25 days, respectively. Conclusion: A PVC-membrane cysteamine selective electrode was easily prepared. Cysteamine determination in a pharmaceutical formulation was performed. Analysis results indicated that it can be successfully used in drug quality control laboratories for routine analysis of cysteamine in pharmaceutical preparations alternative to more sophisticated, expensive and time-consuming analytical methods.

Budapest airport air quality long-term studies by remote sensing with DOAS and FTIR with focus upon runway emissions

2007 ◽  
Author(s):  
Klaus Schäfer ◽  
Gregor Schürmann ◽  
Carsten Jahn ◽  
Candy Matuse ◽  
Herbert Hoffmann ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Air Quality ◽  
Long Term Studies

Modeling of unforced demand response programs

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Hassan Jalili ◽  
Pierluigi Siano
Keyword(s):  
Demand Response ◽  
Load Shifting ◽  
Response Models ◽  
Temperature Changes ◽  
Proposed Model ◽  
Equipment Failures ◽  
Demand Response Programs ◽  
Simultaneous Implementation ◽  
Long Term Studies

Abstract Demand response programs are useful options in reducing electricity price, congestion relief, load shifting, peak clipping, valley filling and resource adequacy from the system operator’s viewpoint. For this purpose, many models of these programs have been developed. However, the availability of these resources has not been properly modeled in demand response models making them not practical for long-term studies such as in the resource adequacy problem where considering the providers’ responding uncertainties is necessary for long-term studies. In this paper, a model considering providers’ unavailability for unforced demand response programs has been developed. Temperature changes, equipment failures, simultaneous implementation of demand side management resources, popular TV programs and family visits are the main reasons that may affect the availability of the demand response providers to fulfill their commitments. The effectiveness of the proposed model has been demonstrated by numerical simulation.

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