Coaxial temperature controlled cryoprinting: A biomimetic technology inspired by the freezing survival mechanisms of the frog Ranasylvatica.

There are conflicting reports as to whether ageing causes a decreased thermoregulatory response, or if observed differences in previous studies are related to maximal aerobic capacity or training status. This study hypothesized that thermoregulatory response to severe exercise-heat stress is maintained with ageing when both young and older subjects are well trained. Seven older highly trained (OHT = 51-63 years) cyclists were matched with two groups of young cyclists (19-35 years); one group matched for training status [young highly trained (YHT) participants, n = 7] and another for V ˙ O 2 max [young moderately trained (YMT), n = 7]. Each participant exercised at 70% V ˙ O 2 max in hot (35°C, 40% relative humidity) and thermoneutral (20°C, 40% relative humidity) conditions for 60 min. Final rectal temperature in the thermoneutral and heat (YHT = 39.13 ± 0.33°C, YMT = 39.11 ± 0.38°C, OHT = 39.11 ± 0.51°C) tests were similar between all three groups. %HR(max) (heat test: YHT = 92.5 ± 6.0%, YMT = 91.6 ± 4.4%, OHT = 88.6 ± 5.1%), skin temperature, and cutaneous vascular conductance during cycling in both environments were similar between groups. Lower sweat loss and evaporative heat loss in the heat test in the OHT and YMT groups when compared with the YHT group reflected lower metabolic heat production. The findings of the present study suggest that thermoregulatory response is maintained with age among highly trained subjects.

Mechanical properties are one of the most important characteristics of biomaterials for many different applications, including biomedicine. Soft biomaterials, such as hydrogels, are difficult to characterize by conventional mechanical testing, because their mechanical properties are much lower than required by conventional testing machines. In this work, we aimed to systematically study the mechanical behavior of a model soft material, polyacrylamide hydrogels, under different loading modes: tension, torsion, compression, and indentation. This allowed us to develop a comprehensive approach to the mechanical testing of soft materials. To overcome excessive compression and slippage of the hydrogel samples when fixed in the grips during tension, additional 3D-printed grips were designed. Digital image correlation was used to determine the Poisson's ratio of the hydrogels. The Young's modulus values obtained from all types of mechanical tests analyzed were highly correlated. However, for hydrogels with a low crosslinker concentration, 1-2%, tension-compression asymmetry was observed. Moreover, the results of the mechanical tests were verified in indentation tests, including analytical estimation, and full-scale and numerical experiments. We also discuss the limits of using a two-parameter Mooney-Rivlin model for fitting hydrogel uniaxial tension deformation curves, which was unstable for the hydrogels with 4 and 9% crosslinker concentration. The implemented approach provided a comprehensive analysis of the mechanical behavior of biomaterials. The elastic moduli for all hydrogels studied were in the range from 20 to 160 kPa, which corresponds well to human soft tissues, making them a promising material for application as tissue-mimicking phantoms.

A mathematical model was developed to account for the evolution of polymer product attributes in the emulsion polymerization of styrene. The effects of transfer agent, surfactant, initiator and temperature were investigated. Polymerization rate, $\overline M _{\rm n}$ and particle size decreased with increasing concentration of the transfer agent. The polymerization rate increased with increasing surfactant and initiator concentrations, while an increase in temperature led to a decrease of molecular weight but an increase of polymerization rate and particle size. Chain extension was successfully achieved in the presence of our RAFT agent. The model predictions compared well with our experimental results.magnified image

Reaction kinetics and producer gas compositions of steam gasification of coal and biomass blend chars, part 2: Mathematical modelling and model validation

The structural integrity of sapphire optical windows was numerically and experimentally evaluated under the wall heat flux of the scramjet intake. The considered heating profile was during 60 s, and the heating profile for the numerical and experimental approaches was the same. A numerical study was performed using the finite element method; the numerical results predicted that the maximum temperature of the optical window under the heating condition was about 600 K, the maximum principal stress was less than the strength of the sapphire, and the failure of the optical window would not occur based on the brittle Coulomb–Mohr material failure theory. The heating test was performed using an electrical heater under the heating condition, and the morphology was investigated using scanning electron and atomic force microscopies. The experimental results indicated that no cracks or fractures occurred on the surface of the optical window after the heating test, except for a slight change in the shape and roughness of the microstructure.

The purpose of this paper is to report on the field test results of the Texaco Canada Petroleum Inc. (TEXCAN) and the Alberta Department of Energy (ADOE, formally AOSTRA), Electrical Horizontal Well Project in the Lloydminster heavy oil area. Two vertical wells (15D-25-56-2W4 and 13C-30-56-1W4) and one horizontal well (16D-25-56-2W4) were connected electrically and heated. This paper presents an overview of electrically heating a horizontal well with vertical wells, the design of the electrical heating system, operational experience, test data, and a discussion on the successes and problems of the project. Three wells were electrically heated; two deviated vertical wells and one horizontal well. The pilot project experienced premature equipment failure and sand production problems. Although a significant production response was achieved at the vertical wells, ongoing operations were not achieved because of sanding problems. The sand problem required daily workovers on the wells to maintain operations. As a result of these problems, and the limited current that can be supplied from just two vertical wells, the thermal response at the horizontal well was 3 - 5 °C and no production response was observed. The project was a technical success in that electrical current from two vertical wells was returned to the power conditioning units via the horizontal well and a thermal response was observed at all the wells. At the vertical wells, there was at times a greater than three times productivity response during electrical heating operations. Introduction Horizontal Wells and Heavy Oil Horizontal wells, typically 500 m in length and longer, are common in the exploitation of heavy oil reservoirs around the world. Horizontal wells offer prospects of improved performance over vertical wells, primarily due to the larger contact area between the formation and the wellbore. Also, the technology for drilling a horizontal well is as advanced as for drilling a vertical well. The cost of drilling a horizontal well is about the same as the cost to drill two to three vertical wells. There are production disadvantages and problems that are unique to a horizontal well application in heavy oil reservoirs. The production rate declines very rapidly during the first several months of production. It is also possible that the entire length of the horizontal well may not be productive. In some production systems, the limiting factor in producing the oil is the mechanical limitation of the pumping equipment, which is exceeded because of the very high viscosity of the oil. Finally, there may be skin effects, such as the visco-skin(1) that may further reduce the productivity of the well. This skin effect and other thermally alterable skin effects (for example, asphaltene precipitation) can block flow into the well, thereby decreasing the effective length and productivity of the well. Increasing the effective length of the well and removing any skin effects can improve the productivity of the well. Electrical Heating Electrical heating of vertical wells has been attempted on several occasions with encouraging results(2-10). Until now, there have been no electrical heating tests that use horizontal wells.

Magnetic resonance elastography (MRE) is a novel experimental technique for estimating the dynamic shear modulus of biological tissue. MRE can be performed non-invasively, in living subjects. Soft biomaterials are notoriously difficult to characterize, since they are typically nonlinear, anisotropic, viscoelastic, and heterogeneous. The ability of MRE to capture the frequency-dependent response of tissue to small amplitude deformation over a range of frequencies was investigated by careful comparison to two different dynamic mechanical tests; direct shear and unconfined compression. The mechanical properties of a standardized gelatin biomaterial were probed over various loading rates. Results confirm direct correlation between estimates of shear modulus obtained by MRE, dynamic shear, and unconfined compression, but quantitative differences between values obtained by MRE compared to direct mechanical test. These results in gelatin are consistent with reports in agar from other groups [1,2]. Differences may be due to non-idealities inherent in loading of soft, wet, material (in mechanical testing), boundary effects (in MRE), or differences in strain amplitude and strain rate.

In vitro assembly of intermediate filaments from tetrameric vimentin consists of a very rapid phase of tetramers laterally associating into unit-length filaments and a slow phase of filament elongation. We focus in this paper on a systematic quantitative investigation of two molecular models for filament assembly, recently proposed in (Kirmse et al. J. Biol. Chem. 282, 52 (2007), 18563-18572), through mathematical modeling, model fitting, and model validation. We analyze the quantitative contribution of each filament elongation strategy: with tetramers, with unit-length filaments, with longer filaments, or combinations thereof. In each case, we discuss the numerical fitting of the model with respect to one set of data, and its separate validation with respect to a second, different set of data. We introduce a high-resolution model for vimentin filament self-assembly, able to capture the detailed dynamics of filaments of arbitrary length. This provides much more predictive power for the model, in comparison to previous models where only the mean length of all filaments in the solution could be analyzed. We show how kinetic observations on low-resolution models can be extrapolated to the high-resolution model and used for lowering its complexity.

In order to investigate the performance of variable thickness scroll compressor, a detail mathematical modeling based on energy and mass balances is established in this two-part. In part II, dynamic modeling and model validation are developed. Temperature, pressure, mass flow of working chambers, friction loss power of moving parts, efficiency, and shaft power are investigated by solving the mathematical modeling. The experimental rig for variable thickness scroll compressor based on involute of circle, high order curve and arc is set up. From the comparison of the simulated and measured data, it can be seen that the compressor model predicts the mass flow, discharge temperature, and shaft power very well. So the proposed mathematical modeling can accurately describe all the suction, compression, and discharge processes for variable thickness scroll compressor.

The paper presents a mathematical modelling of a combined hydraulic clutch consisting of a hydrodynamic clutch and viscous clutches operating with electrorheological fluid and validates the mathematical model via an experimental evaluation. An electric field is generated in some of the clutches consisting in the combined hydraulic clutch, and it influences the electrorheological working fluid to alter characteristics of the clutch. The mathematical model formulated in this work, which is intended for analysis of different design solutions, is verified on the basis of the results achieved from bench testing. Based on the assessment of modelling errors, it is confirmed that the formulated mathematical model can be successfully employed in building clutches of this type applicable to torque transmission system.

The current systematic review and meta-analysis was carried out to compare the diagnostic accuracy of pulp vitality and pulp sensibility tests in assessing pulpal health. PubMed/MEDLINE, Cochrane Central Register of Controlled Trials, Web of Science, Google Scholar and Open Grey databases were searched and after assessing eligibility criteria the data were extracted. True-positive, false-positive, true-negative, false-negative, sensitivity and specificity values were extracted or calculated if not presented. Quality of studies was evaluated based on the QUADAS 2 tool. Meta-analysis was performed in MetaDTA (v2.0; Shinyapps, RStudio PBC, Boston, MA, USA) and Review Manager 5.3 (RevMan web; The Cochrane Collaboration, London, UK). Ten articles were included for qualitative synthesis and five for meta-analysis. The pooled diagnostic odds ratio for pulse oximeter (PO), electric pulp tester (EPT), cold test (CT) and heat test (HT) was 628.5, 10.75, 17.24 and 3.47, respectively. Pairwise comparison demonstrated a higher pooled mean sensitivity and specificity with PO compared with EPT. Comparison between PO and CT and between PO and HT also demonstrated a higher pooled mean sensitivity and specificity for PO. Summary points on receiver operating characteristic curves confirmed the ability of PO to correctly screen negatives in presenting patients as compared to EPT, CT and HT but no study was rated as good on quality assessment. PO can be considered as the most accurate diagnostic method as compared to EPT, CT and HT. This review provides information about the reliability and diagnostic accuracy of using pulp vitality and sensibility tests for assessing pulp status.

Drug Release Properties of Polymer Coated Ion-Exchange Resin Complexes: Experimental and Theoretical Evaluation

The paper deals with the problem of mathematical modeling of thermochemical destruction process. The apparatus of Markov's chains is used to synthesize a mathematical model. The authors of the study suggest to consider the destruction process as a random one, where the system state changes, which is characterized by the proportion of macromolecules in each fraction of the molecular- and weight distribution. The intensities of transitions from one state to another characterize the corresponding rates of destruction processes for each fraction of the molecular- and weight distribution. The processes of crosslinking and polymerization in this work were neglected, and it was accepted that there is a probability of transition from any state with a lower order index (corresponding to fractions with higher molecular weights) to any state with a higher index (corresponding to fractions with lower molecular weights). Markov's chain with discrete states and continuous time was taken as the mathematical model basis. Interactive graphical simulation environment MathWorksSimulink was used as a simulation environment. Experimental studies of polybutadiene destruction in solution were carried out to evaluate the mathematical model parameters. The GPC (gel-penetration chromatography) data of the polybutadiene solution were used as the initial (starting) data for estimating the polymer WMD (molecular weight distribution). Mean-square deviation of the calculated data from the experimental data for each fraction and at specified times was minimized for the numerical search of parameter values. The results of comparison of experimental and calculated on mathematical model data showed an error of calculations on the average about 5%, which indicates an acceptable error in estimating of polymer fractions proportions change during the process of destruction for the process under consideration and conditions.

As part of the vehicle qualification process, the Federal Railroad Administration (FRA) currently requires in its track and passenger equipment safety standards that a validated vehicle model be used to demonstrate safe dynamic vehicle response to allowable track geometry variations. Transportation Technology Center, Inc. (TTCI) was contracted by FRA to characterize, model, and analyze a high speed passenger vehicle in order to provide guidance related to the vehicle qualification process. The overall objective of the project was to evaluate methods required to demonstrate the validity of a vehicle dynamics model project and investigate how different input parameters affect the accuracy of the model. The project consisted of four main tasks: (1) characterize a high speed passenger vehicle; (2) develop a mathematical model of the vehicle using measured parameters; (3) validate the mathematical model using on-track tests; and (4) conduct a sensitivity analysis of the vehicle model to determine the critical parameters. FRA tasked TTCI with applying the testing and modeling methodology to FRA’s DOTX 216 geometry car. Specific parameters were identified that needed to be measured in order to develop a dynamic vehicle model of the car. A characterization test regime was outlined and performed to determine the necessary mass, stiffness, and damping characteristics, and the measured parameter values were used to create a mathematical model of the vehicle using TTCI’s NUCARS®* dynamic modeling software. A series of on-track validation tests were performed on different tracks at the Transportation Technology Center (TTC) using the DOTX 216 car to facilitate model validation efforts. The model was then used to simulate the on-track testing regime conducted at TTC. Model validation was evaluated using displacement, acceleration, and wheel/rail force measurements. Results from the simulations and test data were compared using multiple methods to demonstrate the validation of the DOTX 216 model. TTCI also conducted a parameter sensitivity analysis using the validated model to assess its sensitivity to changes in different parameter values and to identify the most critical parameters for simulating passenger vehicles. The testing, modeling, and model validation methodology described in this work provide a practical example of developing a validated vehicle model for use in the vehicle qualification process.

Use of a computer program for parameter sensitivity studies during thawing of foods