Unfavorable Modes Research Articles

Impact of Access Cavity Design on Fracture Resistance of Endodontically Treated Maxillary First Premolar: In Vitro.

This study was designed to investigate the impact of access cavity designs on fracture resistance of endodontically treated maxillary first premolars. The study sample consisted of 72 intact maxillary first premolars, randomly divided into six groups (n = 12). A standardized proximal cavity preparation was prepared for all samples using standard bur. Groups I: control group with only standard proximal cavity and no endodontic access, group II: Truss access cavity, group III: Separated access to buccal and palatal canals without removal of dentine in between, group IV: Access to buccal and palatal canals with removal of dentine in between, group V: Traditional access cavity, group VI: Mesio-occlusal-distal cavity (MOD). For groups I and VI, only composite restoration was used to restore the proximal cavity, while for groups II- V, the access was prepared and endodontic treatment was performed on all teeth, then composite restoration was placed. The root canals were instrumented using nickel-titanium files, irrigated with sodium hypochlorite, and filled with AH plus sealer and gutta-percha using warm vertical condensation. All samples were then placed in an acrylic mold and underwent thermal aging for 10,000 cycles between 5 and 55°C. The samples were fixed in a universal testing machine with the long axis of the roots positioned at 20° to a load applied at a crosshead speed of 1 mm/min using a stainless steel semi-spherical indenter (Ø = 3 mm) until fracture occurred to determine the fracture resistance force in Newton. The normality test (Shapiro-Wilk) showed that data are normally distributed. Group II exhibited the highest mean fracture resistance, and group VI was the least likely to resist the fracture. No statistically significant differences between tested groups (p-value = 0.237). The MOD group showed a more unfavorable mode of fracture compared to other groups. No significant difference in fracture resistance between conservative and traditional access cavities. The missing marginal ridges, such as in MOD cavities played an important role in decreasing the fracture resistance of endodontically treated teeth.

Mode restrictions in the power supply system of industrial induction equipment

The article investigates the frequency features of the power supply of induction heaters designed for aluminum extrusion. Mode regulation is performed by local connection of capacitor banks with the creation of parallel resonance. The scheme of the power supply system is built on the basis of an adjustable frequency converter. To study the induction complex, a mathematical model was created in the frequency and time domains. The calculation showed the possibility of a resonant mode with a deterioration in the frequency regulation of currents with an unsuccessful choice of design. In the course of modeling using a modified nodal analysis, a set of parameters that create a resonance is considered. The frequency characteristics and vector diagrams of the induction device are obtained, which reveal the unfavorable mode. Based on the results of the study, recommendations are proposed for correcting the algorithms for controlling the inverter of the power supply system and overcoming the limitations.

NEW PIDHID UP TO THE MOVEMENT OF FIRE SAFETY WATER SYSTEMS

When obtaining estimates that characterize the level of fire safety of the hydrogen storage and supply system, there is an error due to the subjective nature of its occurrence. It is noted that it is possible to weaken the influence of the subjective nature on these estimates by using the probabilistic characteristics of failure of the main elements of the hydrogen storage and supply system. Such basic elements include a gas generator. It is shown that the diffusion processes between the hydroreactive sample and the liquid - water are accompanied by the appearance of gas bubbles located on the reacting surface. This process - chemical boiling is characterized by internal characteristics. Internal characteristics were obtained experimentally for hydroreactive samples based on sodium aluminum hydride, which are approximated by polynomials of the fourth order and represent the dependence of the diameter of gas bubbles and the generation frequency on the diameter of the reacting surface. It is noted that the characteristics of the gas generator depend on the orientation of the reacting surfaces of the hydroreactive sample. The growth rate of basic bubbles practically does not depend on the diameter of the reacting surface, and the size of this surface for the vertical arrangement of the reacting surface is several percent larger than for its horizontal arrangement. The most unfavorable mode of gas generation is the case when the reactive surface of the hydro-reactive sample is oriented downwards. It is shown that increasing the reliability of the gas generator of the hydrogen storage and supply system is possible due to the implementation of a hydroreactive sample with a polylike one - a passive method and due to the formation of hydrodynamic forces acting on gas bubbles - an active method. These recommendations are embodied on the example of a hydrogen storage and supply system with vibrational movement of a hydroreactive sample, which is made in the form of a set of identical long cylinders assembled in a mesh cassette. Keywords: water saving and supply system, gas generator, fire safety, reliability.

Determining the Effective Space Debris Attitude Motion Modes for Ion-Beam-Assisted Transportation

Contactless space debris transportation systems based on the use of an ion beam are a promising direction among active space debris removal systems. The magnitude of the force generated by the ion beam depends on the orientation of the space debris object in the ion beam created by an active spacecraft. During the ion transport process, the space debris object can oscillate or rotate, which leads to a change in the generated force. The aim of this study is to develop an algorithm for determining the attitude motion mode of space debris, which is most favorable for its contactless transportation. The time-averaged generated ion force is used as the performance index. A simplified system of equations describing the spatial motion of a cylindrical axisymmetric object in a circular orbit is obtained. A generalized energy integral is found. An algorithm for determining the most favorable angular motion mode of a space debris object is developed. A numerical study of a cylindrical space debris object attitude motion under the action of an ion torque is carried out. The favorable attitude motion mode is determined, and the average forces in the most favorable and unfavorable modes are compared.

Prediction of energy and cavitation characteristics of high specific speed Francis hydraulic turbines

BACKGROUND: Cavitation is a phenomenon that occurs in vane hydraulic machines: pumps, hydraulic turbines, when the pressure in a certain area of the flow reaches the level of saturated steam pressure. Its occurrence depends on the design and mode of operation of the hydraulic turbine. In order to design a hydraulic turbine with high cavitation qualities, it is necessary to be able to reliably predict this phenomenon.
 AIMS: The article describes approaches to modeling the operation of Francis hydraulic turbines based on the ANSYS software package.
 METHODS: Using quasi-3D methods was modeled turbine blade system with 75 meters head. Hydrodynamic computation carried out in single-phase and two-phase formulations using the ANSYS CFX package.
 RESULTS: The design of a flow path Francis turbine 3D solid model with a specific speed coefficient ns =283 has been completed. The flow part of the hydraulic turbine includes a spiral case, a stator, a guide vane, an impeller and a draft tube. Computational modeling of the flow of a single-phase viscous fluid in a hydraulic turbine in different modes was carried out to construct a universal characteristic. The optimal efficiency is found and the flow characteristics are calculated. The losses in the elements of the flow part of the hydroturbine under various operating modes are determined, the zone of optimal operation is found. The cavitation flow is calculated using a two-phase flow model (water-steam). For both sides of the impeller blade, a pressure distribution was obtained, which can be used to judge the possibility of cavitation in areas where the pressure of the water column is less than the vaporization pressure. The value of the critical cavitation coefficient for the three most unfavorable modes was determined, and the dependence of the efficiency on the cavitation coefficient was constructed. The area occupied by steam on the blade during cavitation flow is visualized, its area is determined relative to the surface area of the blade.
 CONCLUSIONS: The designed hydraulic turbine has good energy and cavitation qualities, confirmed by the calculation. This version of the hydroturbine can be used as the initial one with further optimization of the blade system and elements of the flow path, to improve the energy and cavitation qualities.

High voltage gain bi‐directional Z‐source inverters with dual‐loop feed‐forward peak DC‐link voltage compensation for fuel cell vehicles

High boost inverter is an essential part to interface the fuel cell stack and traction motor for fuel cell vehicles (FCVs). This paper proposes two novel high voltage gain bi-directional Quasi-ZSIs (QZSI) with new active switched inductor cells for FCVs application. The disadvantages of low voltage boost ratio, large start up current, unfavourable mode operations and unidirectional power flow in conventional Z-source inverter (ZSI) are eliminated. The proposed Z-source inverters are combined with active switched inductor cells to achieve a higher voltage gain and lower voltage stress over capacitors, which can be widely applied in energy storage systems. A small signal model is derived by dynamic analysis. In order to achieve a constant peak dc-link voltage, a dual-loop feed-forward peak dc-link voltage control strategy for the proposed QZSI is introduced in this paper. Simulation and experiment waveforms are presented to verify the theoretic analysis of the designed QZSIs and the proposed control strategy.

Bond performance of sand-coated and ribbed-surface glass fiber reinforced polymer bars in high-performance concrete

This paper presents an experimental study on the bond characteristics of both sand-coated and ribbed-surface glass fiber reinforced polymer (GFRP) bars embedded in high-performance concrete (HPC). A total of 145 pullout tests were conducted in order to examine the effect of varying parameters on the bond characteristics, namely: embedment length, bar diameter, surface treatment, concrete cover and bond stress-slip relationships. The experimental results showed that the sand-coated bars exhibited better bond strength than that developed by the ribbed-surface GFRP bars, which entails lower development lengths. Besides, it was found that the increase in bar diameter was accompanied by a decrease in the bond strength. Furthermore, experimental results displayed a slight increase in the bond strength as the concrete cover increased from 40 to 60 mm. Finally, based on the material properties of the used GFRP bars and concrete patch, using HPC surrounding both sand-coated and ribbed surface GFRP bars resulted in unfavorable modes of failure. That is because in most cases GFRP bars failed by either shearing of the ribs of the ribbed-surface bars or peeling of the sand-coating layer out of the core diameter for the sand-coated bars.

Impact of Concrete Mix Ingredients and Surface Treatments on Epoxy Overlay Performance

Epoxy overlays are applied on bridge decks after curing concrete in patches and repairs for 28 days. A tensile bond pull-off strength of at least 250 pounds per square inch (psi) is expected from a properly applied overlay. Even though the overlay performance at room temperature is mostly satisfactory, the performance at elevated temperatures is not convincing. The degradation of mechanical and adhesion properties of epoxy, shear stress at the concrete/overlay interface caused by thermal incompatibility, and the interface moisture vapor pressure are the commonly cited parameters for poor bond strength at elevated temperatures. A combined effect of these parameters results in the most unfavorable failure mode (which is bond failure at the concrete/overlay interface) at a strength lower than the specified limit of 250 psi. The moisture migration through concrete depends on many factors including moisture content along the depth of concrete, pore microstructure, exposure condition, and drying period. This study investigated the impact of concrete mix ingredients and surface treatments on the thin epoxy overlay bond strength. The results show that the use of concrete mixes with slag and penetrating sealant pretreatment improves the bond strength.

FEATURES OF NOISE REDUCTION IN GAS PATHS OF BOILERS DURING CONDENSATION OF WATER VAPOR FROM FLUE GASES

An important characteristic of noise silencers, which determines the effectiveness of their use, in addition to reducing the noise level and the pressure losses they create, is the operational resource. Short-term unfavorable operating modes of boilers are possible, in which condensation of water vapor on the walls of flues through which flue gases are evacuated to the environment is possible. Condensation in the gas path leads to corrosion of the metal of the flues, as well as noise silencers. The article lists recommendations for the design of noise silencers installed in the gas paths of boilers operating under conditions of possible condensation of water vapor from flue gases. The introduced silencers of noise of gas paths of boilers which not only reduce noise highly effectively, but also allow to work in difficult operational conditions are given.

DEVELOPMENT OF A MULTI-MODE ACCUMULATIVE MARKOV SYSTEM

Systems are considered that earn a resource, monetary in the economic interpretation, and use it for functioning and accumulation. The conditions for the growth of savings are sought, which simultaneously ensure the non-positivity of the governing Markov chain. The widespread inhomogeneity of the phase space is essential. In the phase space (of a general type) of such a system, a nonnegative function , a function with values 1,2,…, , an irreducible homogeneous Markov chain , n = 0,1,… are given. The values indicate the resource level of the system at time n, the values indicate the mode, which is determined by the number of service locations, devices, service lines, the number of offices, workers, etc., the type of functioning as repair, prevention, downtime work. Let be the average increments of ver the 1-st period for an arbitrary set набора , states, is the probability of transition from the state into mode is the corresponding stochastic matrix, and – is the stationary probability distribution for it. Let be the value of increased by the value of an arbitrary function ψ (x)> 0, monotone and integrable on the interval [0, ∞). In a fairly general case, based on other of the authors' works, it is argued that the condition for large X (w_i) is sufficient for the system to be acceptable in the sense that there is a convergence to 1 of the relative fraction of that time until the moment n, when the level X> C, (as n → ∞ with probability 1, for an arbitrarily large level C). That is, in a time relation that tends to 1, the functioning will take place in an ever better financial condition. Models are also considered that use the asymptotics and the model of deterioration of the system quality in a random way, but gradually, until unfavorable modes and the subsequent transition to the initial favorable mode, after the recovery mode, and further in a similar way. In this case, under the conditions of acceptability, it is not the stationary probabilities that are used, but the probabilities of system deterioration. It examines economic analogies with insurance and profitability.

Analysing the reasons of the inadequate performance for small sewage treatment plants in the Far North

The development of natural resources in the Far North is constrained by the water factor, because intensive use of water resources by the extractive industry enterprises is associated with expenditure, losses, water pollution. As a result, it has a significant impact on the state of the hydrosphere and all other components of the environment. Discharge of untreated and insufficiently treated wastewater into surface water bodies by camp settings constantly worsen their condition. Wastewater is contaminated with phosphorus, nitrogen, all kinds of bacteria, it can also contain viruses and helminth eggs, and it contains large quantities of synthetic surfactants, which are formed after bathing, washing and laundry on the camp settings of the extractive industry enterprises. Wastewater flow rate is 1400 m3/day in the camp settings. However, the degree of toxicity of water-discharge is no less than that of large cities. The characteristic features of wastewater from camp settings and sewerage systems are: remoteness from sources of centralized power supply, water supply and sewerage (isolated location); the interruptions in the supply of wastewater to structures and a low population density (up to 70 people/ha); increased concentrations of contaminants because of the relatively low standards of wastewater disposal (depending on the degree of buildings improvement). Thus, small sewerage treatment facilities are complex, difficult-to-control biological systems operating in an unfavorable mode of a constantly changing composition of wastewater. It should be noted that the published information on the topic of domestic sewage wastewater treatment has a limited scope, due to the specificity of the qualitative and quantitative characteristics of wastewater, natural and climatic conditions, and other factors. The work considers the treatment facilities of the Chukotka Autonomous District of the Far Eastern region of Russia (the Far North region), the microbiological composition of wastewater was studied, which is formed in especially unfavorable conditions (the Far North region), the conditions for the biocenosis formation and the reasons negatively affecting the biocenosis.

EXPERIMENTAL STUDY OF THE INFLUENCE OF THE MODE OF FINAL TREATMENT ON THE QUALITY OF THE FLAT SURFACES OF ALUMINIUM MATERIALS

In the process of multivariate design of machining technology, one of the important tasks is to select the optimal cutting conditions at the final transitions of the forming process, providing a given quality of the surfaces on the workpiece made of the appropriate material. At the same time, to describe most of the design procedures of the machining process, there are problems associated with the algorithm for choosing the solution method, the response function and the range of acceptable solutions at all stages of processing. In this paper, as an algorithm for solving the problem, we propose the use of the known method of extreme planning of the experiment, which allows to obtain a mathematical model of the investigated multifactorial process with incomplete knowledge of its optimization mechanism. In the process of implementation of this algorithm in real production conditions on the basis of a priori information, the research area was chosen and the main levels of factors and intervals of their variation in this area were established. Then a full factorial experiment was carried out and its results were processed on the basis of a linear polynomial taking into account linear effects and interaction effects. As a result of testing the polynomial confidence intervals were determined for all regression coefficients by four parallel experiments at the same values of factors. In the second phase, were evaluated the adequacy of most mathematical models of the Fisher test. In the end, the transition from the coded values of the factors in the mathematical model to their natural values was carried out. Using the final model with natural values of the factors, a numerical experiment was conducted, which determined the optimum region with the most unfavorable treatment mode. Such a study allows to simplify the procedure for assigning the processing mode of the workpiece at the final stage in the conditions of the current production, while ensuring the specified quality of the machined surfaces and maintaining the productivity of the forming process. This technique is the subject of consideration in this work.

Investigation of Machine Tool Developed Settings Influence on Productivity and Quality of Simultaneous Double-Sided Lens Processing

The paper presents methodology for determining rational modes of abrasive processing for high-precision lenses while using a method of free lapping at finishing operations. Analytical expressions have been obtained to determine coordinates of reference points on a spherical surface which are necessary for mathematical modeling of its processing at pivotal machines. The paper contains results of a theoretical qualitative evaluation of high-precision operating lens surfaces formation in case of various combinations of setting parameters for technological equipment. In this case the most rational and unfavorable modes of processing have been identified. In particular, the last case presupposes shaping by changing rotational frequencies of an input link in an executive mechanism of the machine tool w2and the lens wл. An indicative feature is that a poor quality of processing has been obtained over the entire range of variation interval w2 at maximum value wл, and especially in the case when these frequencies are equal. It has been determined that the highest accuracy of processing is achieved with maximum amplitude of an oscillating tool motion, its diameter and frequency of part rotation and minimum rotational speed of the input link in the executive machine-tool mechanism. As such values of these setting parameters lead to an increased removal of an allowance in the marginal zone of a work-piece, then while processing a convex lens surface, its radius of curvature in each previous operation should be larger than a radius of curvature which is to be obtained in the process of subsequent operations. The inverse regularity of curvature radius values must be observed for a concave surface. The most advantageous values of the machine-tool setting parameters with various combinations have been proposed with the purpose to eliminate errors in the form of common as “knoll” and “hole” with due account of processing productivity and accuracy. The paper describes an influence of machine tool spindle wavering value on the processing accuracy of lenses having a wide range of diameters.

Evaluation of effect of oil film of rotor bearing

The high-rpm rotors were subjected to the dynamic analysis. Oscillations of a rotor spinning in gapped bearings were considered. It was stated that the rotor necks motion pattern depends on a lot of factors: a ratio of static and dynamic loads on the bearing, radial clearance size, presence of oil film between a neck and a bearing, elastic and inertial properties of a mounting group. The most unfavourable mode where static and dynamic loads are equal was detected without taking into account the oil film impact. The impact of oil film on the bearing assembly dynamics is significant in high-rpm rotors. The presence of oil film can possibly cause rotor buckling failure and self-starting. Rotor motion stability in small was studied. Herewith, various schemes were considered. Expressions, determining the stability zones of a rigid rotor on the fixed support and the supports with elastic and inertial elements, were given.

Digital simulation of physical processes in vehicles engine power units

This article studies the issues of digital simulation of physical operating processes in vehicles transmission. Simulation of dynamic processes is carried out in power transmissions at the design stage. The procedure for using the digital packages such as MATLab – Simulink and Simscape was considered for the numerical simulation of dynamic processes in mechanical systems based on the example of the theoretical calculation of K-744 tractor transmission dynamics. A digital model of K-744 tractor transmission is constructed, its calculation scheme is given, the initial characteristics are determined. A digital model of the tractor engine was created by means of the Simulink package. A nature of change in tractor engine torqueis determined by it. The calculated analysis of normal transmission frequencies is performed. Forced torsional vibrations are calculated in the tractor change gearbox generated by the vehicle engine operation. The conditions of resonance in the transmission are analyzed. The unfavorable modes of joint operation of the engine and the gearbox are determined for K-744 tractor.

ОСОБЕННОСТИ РАБОТЫ ДИЗЕЛЯ НА РЫЖИКО-МИНЕРАЛЬНОМ ТОПЛИВЕ В РЕЖИМЕ САМОСТОЯТЕЛЬНОГО ХОЛОСТОГО ХОДА

The mode of independent idling, characterized by an impaired process flow, unproductive fuel consumption and increased emissions of harmful substances into the atmosphere, is the most unfavorable mode of the diesel engine operation. Therefore, the aim of the research is to reveal the peculiarities of the tractor diesel engine operation by the camelina-mineral fuel in the mode of independent idling. Camelina-mineral fuel is a mixture of camelina oil and mineral diesel fuel in certain ratio of these components. To assess the possibility of using the camelina oil as biological component of diesel mixed fuel, an experimental study of the D-243 diesel engine in idling mode was carried out, and the degree of influence of the different ratio of the components of the mixed fuel on its parameters was determined. The researches were carried out with the diesel fuel on the L-0.2-62 mineral fuel and the camelina-mineral fuel with a ratio of the biological and mineral components: 25% RyzhM + 75% DT; 50% RyzhM + 50% DT; 75% RyzhM + 25% DT; 90% RyzhM + 10% DT and 90% RyzhM + 10% DT (US). For the parameters of the diesel, the excess air factor, the filling ratio of the diesel cylinder with fresh charge, the maximum cycle pressure, the hourly fuel consumption, smoke and carbon monoxide content in the exhaust gases are taken. It is established that when the diesel engine works on camelina-mineral fuel mode the minimum sustainable speed of the crankshaft idle speed 800 min-1 the values of maximum cycle pressure (6.3 MPa) and the filling ratio of the cylinders of a diesel engine the fresh charge (0,87) remain unchanged. The coefficient of excess air, increasing in mixed fuel shares of camelina oil to 90%, reduced from 7.187 to 4.619, while fuel consumption increases of 1.1 kg/h 2 kg/h. The best environmental indicators are observed when working on red-and-mineral fuel 50% RyzhM + 50% DT. Handling mixed fuel with ultrasound reduces fuel consumption, smoke and content of carbon oxide in the exhaust gas relative to the mixed fuel not treated with ultrasound.

Correlation of intermolecular packing distance and crystallinity of D-A polymers according to π-spacer for polymer solar cells

Abstract Donor–acceptor-type polymers, PBDPBT-T, PBDPBT-TT, and PBDPBT-biT, were polymerized via Stille coupling reactions. In the unfavorable mode of DFT calculations, the distance between BDP in the two different polymer main chains showed different distance of repeating unit (Dn) according to the π-spacers type. Especially, PBDPBT-TT caused larger D2 than PBDPBT-T and PBDPBT-biT. The UV–vis absorption spectra of PBDPBT-T and PBDPBT-biT films were red-shifted compared with the solution absorption, whereas that of a PBDPBT-TT film was blue-shifted. PBDPBT-T and PBDPBT-biT had high crystallinity and a tendency of face-on orientation. In contrast, PBDPBT-TT had low crystallinity. Owing to differences in packing formation, the polymers had different JSC values. When a polymer solar cell device was fabricated through a solution process, PBDPBT-biT (in a 1:1.5 ratio with PC70BM) exhibited a PCE of 4.50%, with a JSC value of 8.6 mA/cm2, a VOC value of 0.88 V, and an FF value of 59.4%.

Inclusion of the periodontal ligament in studies on the biomechanical behavior of fiber post-retained restorations: An in vitro study and three-dimensional finite element analysis.

Endodontically treated teeth are known to have reduced structural strength. Periodontal ligament may influence fracture resistance. The purpose of this study was to assess the influence of including the periodontal ligament in biomechanical studies about endodontically treated and restored teeth. Forty human maxillary central incisors were treated endodontically and randomly divided into four groups: non-crowned (with and without an artificial ligament) and crowned (with and without an artificial ligament) with glass-ceramic crowns. All groups received prefabricated glass-fiber posts and a composite resin core. Specimens were tested, under a flexural-compressive load, until failure occurred. The failure mode was registered for all specimens. The failure loads were recorded and analyzed using an analysis of variance test (p < 0.05). These results were compared with those predicted by a finite element model. The analysis of variance did not show significant differences between the use of crown on the failure load (p = 0.331) and the use of periodontal ligament (p = 0.185). A cohesive mode in crown appeared in crowned teeth and in core in non-crowned groups. For non-crowned teeth, adhesive failure occurred along the cement-enamel junction with a slight tendency in specimens without periodontal ligament. Furthermore, an unfavorable failure mode affects partially the root with no differences regarding non-crown specimens. In crowned teeth, the tendency was an adhesive failure along the cement-enamel junction. The model predicted a distribution of the safety factor consistent with these results. This study showed that inclusion of periodontal ligament is not particularly important on biomechanical behavior of post-retained restorations. However, we recommend its inclusion in fatigue studies.

几何缺陷对索拉穹顶弹塑性承载力的影响分析

利用有限元对索拉穹顶进行了特征值屈曲分析，得到了索拉穹顶的屈曲模态，并确定出最不利的屈曲模态阶数。通过讨论几何缺陷形式、大小的变化对结构弹塑性承载力的影响，进一步分析了预应力和杆件截面变化时几何缺陷对弹塑性承载力的影响。分析结果表明：第二阶特征值屈曲模态的缺陷形式对结构最不利；随着拉索预应力的增加，几何缺陷对弹塑性承载力的影响先不变后减小；钢杆件截面改变时，几何缺陷对弹塑性承载力的影响基本不变。 Eigenvalue buckling analysis of solar dome was done firstly, then the the buckling modes were got and the most unfavorable mode was pointed. The influence factors of bearing capacity, such as the form and bigness of geometric defect, were discussed. The influence of prestress and the section of rod was further studied. The result shows: The second-order buckling mode is the most unfavorable mode; as the prestress of rop grows, the influence of geometric defect to elastoplastic carrying capacity increases firstly and then decreases; as the section of rod changes, the influence of geometric defect to elastoplastic carrying capacity essentially unchanged.

Fsy1, the sole hexose-proton transporter characterized in Saccharomyces yeasts, exhibits a variable fructose:H+ stoichiometry

In the model yeast Saccharomyces cerevisiae, hexose uptake is mediated exclusively by a family of facilitators (Hxt, hexose transporters). Some other Saccharomyces species (e.g. Saccharomyces bayanus and Saccharomyces pastorianus) possess, in addition, a specific fructose transporter (Fsy1, fructose symporter) that has been previously described to function as a proton symporter. In the present work, we compared growth of a yeast strain in which FSY1 occurs naturally in anaerobic, fructose- and glucose-limited chemostat cultures. Especially at low specific growth rates, fructose-proton symport was shown to have a strong impact on the biomass yield on sugar. We subsequently employed energized hybrid plasma membrane vesicles to confirm previous observations concerning the mode of operation and specificity of Fsy1 mediated transport. Surprisingly, these experiments suggested that the carrier exhibits an unusual fructose:H+ stoichiometry of 1:2. This energetically expensive mode of operation was also found consistently in vivo, in shake flask and in chemostat cultures, and both when Fsy1 is the sole transporter and when the Hxt carriers are present. However, it is observed only when Fsy1 is operating at higher glycolytic fluxes, a situation that is normally prevented by downregulation of the gene. Taken together, our results suggest the possibility that fructose symport with more than one proton may constitute an energetically unfavorable mode of operation of the Fsy1 transporter that, in growing cultures, is prevented by transcriptional regulation.