scholarly journals CRACKING OF MONOLITHIC POLYCARBONATE SHEETS IN A STRESSED STATE

2018 ◽  
Vol 13 (3) ◽  
pp. 72-78 ◽  
Author(s):  
A. V. Markov ◽  
P. A. Semenyak
Keyword(s):  
Activation Energy ◽  
Main Role ◽  
Start Time ◽  
Stress Cracking ◽  
Organic Glasses ◽  
Thermal Oxidative Destruction ◽  
Active Liquid ◽  
Cracking Process ◽  
Adsorption Active Medium ◽  
Structural Coefficient

The accelerated stress cracking of monolithic polycarbonate sheets was investigated. Cracking of polycarbonate organic glasses during operation leading to a drop in impact strength and transparency is their main disadvantage. The main role in the acceleration of the process of cracking is played by the stresses that arise when they are formed and mounted. The aim of this work was to investigate the dependence of the cracking start time on the stress applied to the sheet monolithic polycarbonate. This makes it possible to predict the lifetime of polycarbonate products. The experiments were carried out in air and in contact with an adsorption-active medium (a mixture of toluene and n-propanol). The stresses applied to the samples varied in the range from 25 to 55 MPa. It is shown that the dependence of the cracking start time of a polycarbonate on the applied stress can be described by Zhurkov exponential equation. The coefficients of this equation for the processes of cracking in air and in contact with the adsorption-active liquid are calculated. It is established that the activation energy of the polycarbonate cracking process (129.5 kJ/mol) is close in magnitude to the activation energy of the thermal-oxidative destruction (about 145-155 kJ/mol). In contact with the adsorption-active mixture of toluene (25% mass.) and n-propanol, the activation energy of the cracking is reduced to 98.5 kJ/mol. At the same time, the structural coefficient in the Zhurkov equation ("activation volume") increases from 1.45 to 2.45 nm3. The analysis of the obtained results made it possible to predict the lifetime of monolithic polycarbonate sheets and products made of them at various operating stresses

Effects of Nb on Strain-Induced Precipitation of NbC and Static Recrystallization for High Nb Pipeline Steels

2010 ◽  
Vol 146-147 ◽  
pp. 1315-1321 ◽  
Author(s):  
Gui Ying Qiao ◽  
Fu Ren Xiao ◽  
Xiao Bing Zhang ◽  
Shao Hui Chen ◽  
Bo Liao
Keyword(s):  
Activation Energy ◽  
Stress Relaxation ◽  
Compression Test ◽  
Static Recrystallization ◽  
Pipeline Steel ◽  
Relaxation Technique ◽  
Start Time ◽  
Pipeline Steels ◽  
Kinetics Of Precipitation ◽  
Kinetics Of

Strain-induced precipitation of complex carbonitrides and recrystallization for three high-Nb pipeline steels with different Nb and C content have been studied by using a stress relaxation technique and two-passes interrupted compression test. Sequentially, the PTT diagrams were obtained, and static recrystallization activation energy was calculated. Furthermore, the effects of Nb and C content on strain-induced NbC precipitation and static recrystallization were discussed. The results confirm the faster kinetics of precipitation and its retarded recrystallization in the case of higher Nb pipeline steel, and that the recrystallization is easier in low Nb pipeline steel in comparison to the case of high Nb steel. However, the effects of Nb on strain-induced precipitation and static recrystallization were associated with the Nb/C ratio. The precipitation start time (Ps) of strain-induced NbC is delayed in lower Nb/C ratio pipeline steel. It is suggested that the reduced supersaturation of Nb can result in the delay of precipitation of strain-induced NbC carbides forming in the low Nb/C ratio steel.

scholarly journals Obtaining and Investigation of the β-Cyclodextrin Inclusion Complex with Vitamin D3 Oil Solution

Scientifica ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Ryszhan Bakirova ◽  
Altynbek Nukhuly ◽  
Ainara Iskineyeva ◽  
Serik Fazylov ◽  
Meiram Burkeyev ◽  
...  
Keyword(s):  
Activation Energy ◽  
Inclusion Complex ◽  
Spectral Properties ◽  
Thermal Destruction ◽  
Cyclodextrin Inclusion ◽  
Measurement Results ◽  
Thermal Oxidative Destruction ◽  
Cyclodextrin Inclusion Complex ◽  
Thermographic Measurement ◽  
C Nmr

Background. The research results of fat-soluble vitamin D3 (cholecalciferol) encapsulation with β-cyclodextrin have been presented in this work. The vitamin D3 inclusion complex with β-cyclodextrin was obtained under microwave radiation. The surface morphology of obtained clathrate inclusion complexes was described with the help of a scanning electron microscope. The thermographic measurement results on a differential scanning calorimeter have been presented. The activation energy of the β-cyclodextrin : vitamin D3 clathrate complex thermal oxidative destruction reaction was calculated. The clathrate thermal destruction kinetic parameters were determined. The inclusion complex spectral properties were characterized by IR-Fourier and 1H and 13C NMR spectroscopy. The existence of β-cyclodextrin inclusion complex with vitamin D3 in a 2 : 1 ratio was confirmed by the experimental results. The activation energy of thermal destruction of the inclusion complex of β-cyclodextrin with vitamin D3 was calculated using four different methods.

Stress Crack Resistance of Corrugated High-Density Polyethylene Pipes in Different Test Environments and Temperatures

2005 ◽  
Vol 1928 (1) ◽  
pp. 220-225 ◽  
Author(s):  
Y. Grace Hsuan ◽  
Jingyu Zhang
Keyword(s):  
Crack Resistance ◽  
High Density Polyethylene ◽  
Stress Test ◽  
Standard Test ◽  
High Density ◽  
Cracking Behavior ◽  
Stress Cracking ◽  
Polyethylene Pipes ◽  
Hdpe Pipe ◽  
Cracking Process

Corrugated high-density polyethylene (HDPE) pipe 36 in. (900 mm) in diameter was evaluated for its stress crack resistance with the notched constant ligament stress test (ASTM F 2136). Test specimens were taken directly from the pipe liner to include the processing effects. In addition to the standard test condition of 10% Igepal solution at 50°C, tests were performed in water and air at temperatures of 60°, 70°, and 80°C. The test data were analyzed with the ISO 9080 method to define the transition point and ductile-to-brittle curve. The results indicate that the 10% Igepal solution greatly accelerates the stress cracking process, whereas the stress cracking behavior in water and in air is aggressive and practically the same. Activation energies in both ductile and brittle portions of the curve are in general agreement with the literature for HDPE resins. The results indicate that the rate processing method is an accurate model with which to extrapolate data from elevated test temperatures to lower service temperatures. However, Popelar's shift method tends to overestimate the failure times.

Role of spectrin in membrane fusion and in shape change of human erythrocyte ghost

1978 ◽  
Vol 36 (2) ◽  
pp. 328-329
Author(s):  
Hideo Hayashi ◽  
Yoshikazu Hirai ◽  
John T. Penniston
Keyword(s):  
Conformational Changes ◽  
Human Erythrocyte ◽  
Shape Change ◽  
Membrane Surface ◽  
Slight Modification ◽  
Active Role ◽  
Main Role ◽  
Bank Blood ◽  
Human Erythrocyte Ghost

Spectrin is a membrane associated protein most of which properties have been tentatively elucidated. A main role of the protein has been assumed to give a supporting structure to inside of the membrane. As reported previously, however, the isolated spectrin molecule underwent self assemble to form such as fibrous, meshwork, dispersed or aggregated arrangements depending upon the buffer suspended and was suggested to play an active role in the membrane conformational changes. In this study, the role of spectrin and actin was examined in terms of the molecular arrangements on the erythrocyte membrane surface with correlation to the functional states of the ghosts.Human erythrocyte ghosts were prepared from either freshly drawn or stocked bank blood by the method of Dodge et al with a slight modification as described before. Anti-spectrin antibody was raised against rabbit by injection of purified spectrin and partially purified.

Ultrastructural modification of cellular interactions in cancer tumor

1978 ◽  
Vol 36 (2) ◽  
pp. 318-319
Author(s):  
N. P. Dmitrieva
Keyword(s):  
Cancer Cells ◽  
Human Thyroid ◽  
Adjacent Cell ◽  
Main Role ◽  
Cellular Interactions ◽  
Electron Microscopic ◽  
Cancer Tumor ◽  
Normal Human ◽  
Characteristic Features

One of the most characteristic features of cancer cells is their ability to metastasia. It is suggested that the modifications of the structure and properties of cancer cells surfaces play the main role in this process. The present work was aimed at finding out what ultrastructural features apear in tumor in vivo which removal of individual cancer cells from the cell population can provide. For this purpose the cellular interactions in the normal human thyroid and cancer tumor of this gland electron microscopic were studied. The tissues were fixed in osmium tetroxide and were embedded in Araldite-Epon.In normal human thyroid the most common type of intercellular contacts was represented by simple junction formed by the parallelalignment of adjacent cell membranees leaving in between an intermembranes space 15-20 nm filled with electronlucid material (Fig. 1a). Sometimes in the basal part of cells dilatations of the intercellular space 40-50 nm wide were found (Fig. 1a). Here the cell surfaces may form single short microvilli.

Mesophyll conductance: the leaf corridors for photosynthesis

2020 ◽  
Vol 48 (2) ◽  
pp. 429-439 ◽  
Author(s):  
Jorge Gago ◽  
Danilo M. Daloso ◽  
Marc Carriquí ◽  
Miquel Nadal ◽  
Melanie Morales ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Current Knowledge ◽  
Main Role ◽  
Mesophyll Conductance ◽  
Future Studies ◽  
Cell Structures ◽  
Leaf Tissues ◽  
Change Framework ◽  
Chloroplast Stroma

Besides stomata, the photosynthetic CO2 pathway also involves the transport of CO2 from the sub-stomatal air spaces inside to the carboxylation sites in the chloroplast stroma, where Rubisco is located. This pathway is far to be a simple and direct way, formed by series of consecutive barriers that the CO2 should cross to be finally assimilated in photosynthesis, known as the mesophyll conductance (gm). Therefore, the gm reflects the pathway through different air, water and biophysical barriers within the leaf tissues and cell structures. Currently, it is known that gm can impose the same level of limitation (or even higher depending of the conditions) to photosynthesis than the wider known stomata or biochemistry. In this mini-review, we are focused on each of the gm determinants to summarize the current knowledge on the mechanisms driving gm from anatomical to metabolic and biochemical perspectives. Special attention deserve the latest studies demonstrating the importance of the molecular mechanisms driving anatomical traits as cell wall and the chloroplast surface exposed to the mesophyll airspaces (Sc/S) that significantly constrain gm. However, even considering these recent discoveries, still is poorly understood the mechanisms about signaling pathways linking the environment a/biotic stressors with gm responses. Thus, considering the main role of gm as a major driver of the CO2 availability at the carboxylation sites, future studies into these aspects will help us to understand photosynthesis responses in a global change framework.

Impairment Tutorial: Spinal Cord Stimulation and Intraspinal Opioids:Impairment Rating Issues

2000 ◽  
Vol 5 (5) ◽  
pp. 4-5
Author(s):  
James B. Talmage ◽  
Leon H. Ensalada
Keyword(s):  
Medical Records ◽  
Evaluation Process ◽  
Current Approach ◽  
Satisfaction Survey ◽  
Start Time ◽  
Medical Evaluation ◽  
Independent Medical Evaluation ◽  
Other Information ◽  
Physician Reviews ◽  
Written Informed Consent

Abstract Evaluators must understand the complex overall process that makes up an independent medical evaluation (IME), whether the purpose of the evaluation is to assess impairment or other care issues. Part 1 of this article provides an overview of the process, and Part 2 [in this issue] reviews the pre-evaluation process in detail. The IME process comprises three phases: pre-evaluation, evaluation, and postevaluation. Pre-evaluation begins when a client requests an IME and provides the physician with medical records and other information. The following steps occur at the time of an evaluation: 1) patient is greeted; arrival time is noted; 2) identity of the examinee is verified; 3) the evaluation process is explained and written informed consent is obtained; 4) questions or inventories are completed; 5) physician reviews radiographs or diagnostic studies; 6) physician records start time and interviews examinee; 7) physician may dictate the history in the presence of the examinee; 8) physician examines examinee with staff member in attendance, documenting negative, physical, and nonphysiologic findings; 9) physician concludes evaluation, records end time, and provides a satisfaction survey to examinee; 10) examinee returns satisfaction survey before departure. Postevaluation work includes preparing the IME report, which is best done immediately after the evaluation. To perfect the IME process, examiners can assess their current approach to IMEs, identify strengths and weaknesses, and consider what can be done to improve efficiency and quality.

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