Overflow Phenomenon Research Articles

On the anisotropic coalescence of elliptic cylindrical voids considering the geometric and distributive properties

The geometric and distributive properties of voids significantly influence anisotropic coalescence behaviour. However, this problem has received little attention owing to the complexity of considering all the properties in the current analytical framework of limit analysis. To address this issue, this study proposes an analytical framework based on an elliptic coordinate system, including the determination of the ligament zone, characterization of plastic flow, and derivation of the void coalescence criterion, for porous materials with various geometric and distributive properties, including size, shape, spacing, and orientation. This framework is motivated by our observations that the evolution of the void geometry and surrounding plastic flow can be well characterized by the grid of the elliptic coordinate system. Subsequently, an analytical function is proposed to determine the ligament zone and coalescence direction with various void properties. A hollow nonaxisymmetric cylindrical unit cell is proposed to describe this ligament zone, and the corresponding trial velocity field is derived by extending the previous Gurson-like velocity field into the elliptic cylindrical coordinate system. The rationality of the field is validated by comparing its equivalent strain rate field with numerical simulations. Finally, a coalescence criterion is derived via the limit analysis of the proposed unit cell undergoing internal necking. Two heuristic adjustments are formulated for the overflow phenomenon in the rigid zone and outer ligament zones. Numerical assessments with various void properties confirm the accuracy of the analytical model. The coalescence criterion can predict the independent and coupling effects of geometric and distributive properties on anisotropic void coalescence. This study provides possible solutions to future plasticity problems of ellipsoidal inclusions.

QZRAM: A Transparent Kernel Memory Compression System Design for Memory-Intensive Applications with QAT Accelerator Integration

In recent decades, memory-intensive applications have experienced a boom, e.g., machine learning, natural language processing (NLP), and big data analytics. Such applications often experience out-of-memory (OOM) errors, which cause unexpected processes to exit without warning, resulting in negative effects on a system’s performance and stability. To mitigate OOM errors, many operating systems implement memory compression (e.g., Linux’s ZRAM) to provide flexible and larger memory space. However, these schemes incur two problems: (1) high-compression algorithms consume significant CPU resources, which inevitably degrades application performance; and (2) compromised compression algorithms with low latency and low compression ratios result in insignificant increases in memory space. In this paper, we propose QZRAM, which achieves a high-compression-ratio algorithm without high computing consumption through the integration of QAT (an ASIC accelerator) into ZRAM. To enhance hardware and software collaboration, a page-based parallel write module is introduced to serve as a more efficient request processing flow. More importantly, a QAT offloading module is introduced to asynchronously offload compression to the QAT accelerator, reducing CPU computing resource consumption and addressing two challenges: long CPU idle time and low usage of the QAT unit. The comprehensive evaluation validates that QZRAM can reduce CPU resources by up to 49.2% for the FIO micro-benchmark, increase memory space (1.66×) compared to ZRAM, and alleviate the memory overflow phenomenon of the Redis benchmark.

Generation mechanism of lack of fusion in X70 steel welded joint by fully automatic welding under steep slope conditions based on numerical simulation of flow field

X70 pipeline steel is butt welded by fully automatic welding at 25° slope, and the characteristic information of welding process is collected. A 3D transient heat and mass transfer model of weld pool is established. This model was verified by means of the shape of the weld pool and the two-dimensional shape of the weld, and then, the flow field of the fully automatic welding process under steep slope conditions was simulated to clarify the mechanism of the lack of fusion defect. The results show that the welding arc is deflected when it stays on both side walls of the groove. The slope makes the liquid metal tend to gather at the lower groove. When gravity plays a leading role in the flow of the molten pool, some liquid metal begins to flow out from the lower groove to the front end, resulting in an overflow phenomenon. The generation of overflow phenomenon and arc deflection cause the formation of a “void zone” at the structure mutation position in front of the groove. In the welding process, the liquid metal tends to flow to the side walls for heat transfer under various thermal effects, and forms a large range of eddy current at the side walls. This has a positive effect on sidewall melting. In addition, the effect of surface tension at the lower groove is more obvious than that at the upper groove, and the trend of upward flow along the side wall is stronger, so it is difficult for the high-temperature liquid metal in the arc center to flow to the “void area” located at the bottom of the side wall of the lower groove. Therefore, the bottom of the lower groove is more likely to cause lack of fusion defect.

The Bitter Touch: Acquired Tactile-Gustatory Synesthesia

AbstractIntroductionGustatory sensation in response to tactile stimulation has been reported to occur in only 0.6% of synesthetes and has rarely been formally described.MethodsCase Study: A 29-year-old female with schizoaffective disorder – depressed subtype, two months prior to presentation, began noticing that when she touched objects, she would experience an abnormal taste in her mouth. When she would touch specific items with her fingertips, for instance wood, bedsheets, tables, cups, plates, silverware, metal, trash cans, and toothpaste would induce a bitter taste. Touching wood caused the most intense bitter taste. Touching glass did not precipitate a taste.ResultsMental Status Examination: Disheveled and guarded with minimal eye contact. Anxious and agitated. She believes people are stalking her and that cell phones, radios, and computers emit radiation which makes her head burn as if it is on fire. She perceived that inanimate objects, such as furniture, were staring at her. Other: CT scan of brain with and without contrast: normal.DiscussionThis could be due to neural overactivation between brain regions due to a neighborhood effect, with cross-firing of connecting fibers. The cortical taste area of the brain lies within the Brodmann area 43 of the parietal lobe which includes the pre- as well as post-central gyri extending into the parietal operculum. Brodmann areas 3, 1, and 2 in the postcentral gyrus is where the primary sensation for touch is mediated. The stimulation in adjacent and overlapping anatomical structures may be explained by ephaptic transmission with firing of one causing discharge of the second, yclept the adjacency principle.This co-localization hypothesis is further supported by the occurrence of pathological state of seizures which manifest both tactile and gustatory sensation. Such a hypothesis would be supported by Anderson’s 1886 observation discussing a peculiar sensation in the right arm and hand elicited concurrently with a bitter sensation in the mouth. Through an overflow phenomenon, touch may induce a diffuse serotonergic discharge to more remote regions of the brain that may mediate their functions through serotonin, such as taste. Possibly, other pathology may be invoked to explain this synesthesia. A deprived sensory system may be hyper-receptive to stray or overflow of sensations which are then interpreted within the sensorily deprived sensory system, as in Charles Bonnet syndrome. In the chemosensory sphere, sensory deprivation is associated with chemosensory hallucinations. If the patient manifests gustatory deficit, it may have predisposed her to sensitivity to such stray or overflowing sensory stimulus from touch manifesting as gustation. In those who present with synesthesia, investigation of pathology in the sensory system of the receiving concurrent sensation is warranted.FundingNo Funding

Investigation of Tip Leakage Vortex Structure and Trajectory in a Centrifugal Pump with a New Omega Vortex Identification Method

Semi-open centrifugal pumps are widely used in various fields. However, the tip leakage vortex (TLV) has a malign effect on the impeller flow field. The structure and trajectory of a TLV under different discharge conditions were simulated and are discussed herein. Then, the characteristics of the TLV were analyzed using a new omega vortex identification method. The external characteristic and pressure fluctuation of the simulation and experiment were consistent. A secondary leakage vortex near the blade outlet was formed under the high-discharge condition. A leading-edge overflow phenomenon under the low-discharge condition and led to the formation of a reverse-flow vortex. The interface between the main flow and tip leakage flow moved toward the impeller upstream with decreased discharge. As a result, the peak of the entropy production curve moved upstream, and leading-edge overflow and reverse flow occurred. The tip leakage flow changed the blade pressure distribution, resulting in a decrease in the blade load.

Study on droplet transition behavior, bead geometric characteristics and formability of wire + arc additively manufactured Inconel 718 alloy by using CMT MIX+ Synchropulse process

In this paper, the droplet transfer behavior, geometric characteristics of weld bead and formability of CMT MIX + Synchropulse (CSP) wire + arc additively manufactured Inconel 718 alloy under high wire feeding speed are studied. The results show that a CSP cycle is composed of a CSP high-frequency pulse stage (CSP–HFP) and CSP-CMT stage, and the periods ratio is about 1.7:1. The high frequency and large average welding current of CSP-HFP increase the arc force, which further increases the droplet impact force on the molten pool. The molten pool is significantly deformed, resulting in the penetration depth of the CSP weld bead (1.8 mm) apparently higher than that of CMT (0.5 mm). The surface of the CMT-WAAM sample is more rough and irregular. The large penetration depth provides sufficient support for the molten pool, which promotes the overall stability of the molten pool. The increase of the droplet impact and arc forces enhance the convections in the molten pool, which finally suppresses the overflow phenomenon.

Overflow phenomenon in serum lutein after supplementation: a systematic review supported with SNPs analyses.

Lutein, a type of carotenoids, is found to delay the onset and progression of age-related macular degeneration (AMD). Several lutein supplementation studies showed that after an initial increase, lutein serum levels demonstrated a subsequent decrease despite continuous supplementation. In this systematic literature review, this obscure phenomenon was tried to be explained. The subsequent drop in lutein levels was postulated due to down-regulation of lutein receptors scavenger receptor class B type I (SR-BI) in the gastrointestinal tract, upregulation of lutein degrading enzyme β-carotene dioxygenase (BCDO2), or perhaps a combination of both. Some single nucleotides polymorphisms (SNPs) that could have influence on the occurrence of this phenomenon. To date, an exact scientific explanation for this phenomenon has not been established. Further research is needed to investigate this phenomenon in depth to reach an irrefutable explanation, giving that lutein is proven to be effective in delaying the onset and progression of AMD and its metabolism in the human body becomes of equal importance.

Experimental investigation on ceiling flame extension subject to relative large area of liquid fuel in a channel-like structure with confined portals

This paper provides a quantitative model study for ceiling impinging flame extension behaviors subject to the relatively large area of liquid fuel in channel-like structure with confined portals (eg. tunnel), based on experimental results. The fire tests were conducted in a model tunnel [8 m (Length) × 0.8 m (Height) × 0.6 m (Width)]. Different portal-confined areas and liquid fuel areas were considered. Results show that the ceiling flame extension is non-monotonously varied with the portal-confined area, which can be mainly attributed to the combined influence of two action mechanisms of restricting external air inflow and reducing internal heat loss. And there is a critical confined area determined by fuel area, at which the ceiling flame extension length is maximized. Especially, when fuel area is relatively large, a fuel-rich area appears inside tunnel and the high-temperature combustion region moves towards the portals. This provides a prior condition for the flame overflow phenomenon. Based on the analysis of ceiling impinging flame extension behaviors and experimental observations, a global dimensionless factor is introduced to characterize flame extension. A new empirical correlation for ceiling impinging flame extension is proposed accordingly by considering the portal-confined boundary. This empirical correlation performs well in the prediction of ceiling impinging flame extension in channel-like structure fires.

Boarding of Mentally Ill Patients in Emergency Departments: American Psychiatric Association Resource Document.

The treatment of severe mental illness has undergone a paradigm shift over the last 50 years, away from a primary emphasis on hospital-based care and toward community-based care. Some of the forces driving this deinstitutionalization have been scientific and patient-centered, such as better differentiation between acute and subacute risk, innovations in outpatient and crisis care (assertive community treatment programs, dialectical behavioral therapy, treatment-oriented psychiatric emergency services), gradually improving psychopharmacology, and an increased appreciation of the negative effect of coercive hospitalization, except when risk is very high. On the other hand, some of the forces have been less focused on patient needs: budget-driven cuts in public hospital beds divorced from population-based need; managed care’s profit-driven impact on private psychiatric hospitals and outpatient services; and purported patient-centered approaches promoting non-hospital care that may under-recognize that some extremely ill patients need years of painstaking effort to make a community transition.The result has been a reconfiguration of the country’s mental health system that, at times, leaves large numbers of people without adequate mental health and substance abuse services. Often their only option is to seek care in medical emergency departments (ED) that have not been designed for the needs of mentally ill patients. Increasingly, many of those individuals end up waiting in EDs for appropriate care and disposition for hours or days. This overflow phenomenon has become so prevalent that it has been given a name: “boarding.” This practice is almost certainly detrimental to patients and staff, and it has spawned efforts on multiple fronts to understand and resolve it. When considering solutions, both ED-focused and systemwide considerations must be explored. This resource document provides an overview and recommendations regarding this complex topic.

A differential game approach to dynamic optimal control strategies for watershed pollution across regional boundaries under eco-compensation criterion

In recent years, transboundary pollution reflected by watershed pollution has emerged in an endless stream, manifesting as the overflow phenomenon of one-way or crossing between river basins. Such pollution significantly seriously affects the inherent requirements for achieving regional sustainable and coordinated development in China. By introducing the eco-compensation criterion, a cross-regional boundaries pollution abatement differential game model covering upstream and downstream regions in a continuous time is established. Subsequently, the optimal control theory is adopted by maximizing the net present value of river basin welfare to explore relevant optimal feedback equilibriums on the overall watershed environmental quality under the Stackelberg and cooperative game contracts. Eventually, a case study of Xiang Jiang River Basin (XJRB) in Hunan Province of China serves to verify the practicable effectiveness of the foregoing model combined with numerical simulation and support key insights as below: (i) the watershed environmental degradation cost factor as well as the payoff factor possess significant impact on emission capacities of upstream and downstream; (ii) the optimal trajectory of pollutant stock in the downstream affected by the upstream pollutant stock and pollution transfer coefficient is higher than that in the upstream; (iii) the setting of eco-compensation criterion can effectively stimulate upstream governments to invest more in environmentally friendly technologies; and (iv) the joint decisions of the two game parties improve the total welfare level of both river basin regions. Findings present an efficient approach for the design of environmental policies addressing conflicts over water pollution across regional boundaries.

DURABILITAS CAMPURAN HOT ROLLED SHEET-WEARING COURSE (HRS-WC) AKIBAT RENDAMAN MENERUS DAN BERKALA AIR ROB

Tide phenomenon that often occurs in the coastal areas of Indonesia resulted in flooding, which is called the tidal flood. A tidal flood overflow phenomenon of sea water inland. Often some of the roads located in coastal areas are flooded by tidal flood and often causing some damages to the road. Therefore it is necessary to investigate the effect caused by tidal inundation or water bath for asphalt pavement.This research aims to know the durability performance of asphalt concrete mixtures with marinade modification Marshall. The study was conducted with two standard methods of soaking in tidal water and laboratory. Water Immersion method is made by soaking continuous (continuous) and periodic (intermittent). Soaking the specimen in water tidal variation within 6 hours; 12 hours; 24 hours; 48 hours; and 72 hours. While the periodic immersion done by soaking the specimen for 12 hours, then removed during the next 12 hours during 3-days. To view the durability performance of asphalt concrete mixtures used indicator Index of Retained Stability (IRS), Stability Deformation Index, namely First Durability Index (IDP), and the Second Durability Index (IDK).The results showed that continuous immersion damage effects mix quicker on asphalt mixtures than regular immersion. Tidal water used to soak the asphalt mixture Hot Rolled Sheet-Wearing Course (HRS-WC) either continuous or periodic method, has a greater influence than the use of laboratory water. It is shown by the value of the durability of asphalt mixture soaked-tidal water smaller than water-soaked asphalt mixture laboratory standards.

Research on crack discontinuous interface simulation method based on the meshfree diffraction criterion

Meshfree method is a new numerical method whose solution domain only discredited into independent nodes. To model crack discontinuous interface in practical, the equivalent distance for the weight function arguments is adapted. Firstly, the paper analysis the feature of the function, which point out that the methods have their own disadvantages. And then the paper put forward new binary linear equation, which is used to the weight function arguments to dispose of the crack’s noncontiguous interface. The function can simulate the displacement field around crack tip or crack closure line and also avoid the value overflow phenomenon which the node and a computation superposition occurs in the present processing method. The method has provided new mentality and idea for the present meshfree method in crack analysis. Finally three typical crack theoretical models are established as example. The comparison with the analytical solution shows that the displacement value the crack and the stress intensity factors has a better precise based on the new method, and also verified the method is valid.DOI: http://dx.doi.org/10.5755/j01.mech.24.3.19009

Theoretical prediction for thermal expansion coefficients of unidirectional fiber‐reinforced composites with variable elliptical cross‐sections

A three‐dimensional theoretical model is established to predict the coefficients of thermal expansion for unidirectional fiber‐reinforced composites. Based on ellipse cross‐sections to approach to the actual state of transversely isotropic fibers, this thermo‐elastic mechanics analysis reveals the influence of fiber azimuth angular variation, which is superior to other known theoretical solutions. Taking different material systems and some other theoretical solutions into consideration, we could find the theoretical predictions are consistent with the results of the finite element method and existing experiments and the proposed model offers better agreements. Particularly, we focus on the overflow phenomenon of the transverse coefficient at low fiber volume fractions, contributing to developing fiber‐reinforced composite designability. For adapting to irregular fiber shape, this article is innovative with the fiber shape factor concept as the main point of cross‐section shape effect. POLYM. COMPOS., 40:187–201, 2019. © 2017 Society of Plastics Engineers

Dystonia as a patterned motor malflow

The definition of dystonia has been renewed repeatedly but always within the context of overactive muscle contractions. In dystonia the muscles unnecessary for a motion fail to be adequately suppressed because of the loss of central motor control, resulting in inappropriate movements or abnormal postures (“overflow phenomenon”). This represents, however, only one side of the disrupted motor control. Some patients complain of the inability to activate muscles necessary for the intended task despite the lack of motor paresis, as best exemplified by the apraxia of eyelid opening. The author has ever coined the term “negative dystonia” for this phenomenon, which occurs hypothetically as a result of failed central motor flow and is often co-existent with overflow. Negative dystonia has a fixed pattern and sensory trick may be effective to ameliorate the symptom just as in the case of conventional dystonia. Hence we can speculate that the overflow and flow failure are the two sides of the same coin, both being caused by the loss of motor control. The current hypothesis is that dystonia is a representation of the patterned motor malflow (malicious flow) due to the loss of motor control.

Improved Road-Network-Flow Control Strategy Based on Macroscopic Fundamental Diagrams and Queuing Length in Connected-Vehicle Network

Connected-vehicles network provides opportunities and conditions for improving traffic signal control, and macroscopic fundamental diagrams (MFD) can control the road network at the macrolevel effectively. This paper integrated proposed real-time access to the number of mobile vehicles and the maximum road queuing length in the Connected-vehicles network. Moreover, when implementing a simple control strategy to limit the boundary flow of a road network based on MFD, we determined whether the maximum queuing length of each boundary section exceeds the road-safety queuing length in real-time calculations and timely adjusted the road-network influx rate to avoid the overflow phenomenon in the boundary section. We established a road-network microtraffic simulation model in VISSIM software taking a district as the experimental area, determined MFD of the region based on the number of mobile vehicles, and weighted traffic volume of the road network. When the road network was tending to saturate, we implemented a simple control strategy and our algorithm limits the boundary flow. Finally, we compared the traffic signal control indicators with three strategies: (1) no control strategy, (2) boundary control, and (3) boundary control with limiting queue strategy. The results show that our proposed algorithm is better than the other two.

Determining the Optimal Dose of Radioactivity for Measuring Glomerular Filtration using Gate’s Method and Obtaining Renogram

Objectives: Measuring Glomerular Filtration (GFR) using Gate’s method gives low radioactivity of approximately 74~111 MBq to a patient. Such low counts on image acquisition degrade image quality. The objective of this study was to limit the amount of radioactivity needed to acquire high-quality dynamic renal images when measuring GFR. Methods/Statistical Analysis: We performed experiments with different radio activities at matrix size of 128 x 128 or other matrix sizes to check overflow phenomenon of gammaray. Findings: Ideal total count was at radioactivity of approximately 37 MBq. However, measured total counts from acquire images showed certain counting loss. The average margin of error was –1.88 ± 1.61%. The mean value of GFR according to the radioactivity at more than 370 MBq was –2.91 ± 1.19 %. We could calculate GFR by substituting these results in GFR formula under the same condition. The mean GFR value was –1.89 ± 1.62% at radioactivity of 37 MBq and –2.93±1.2 % at radioactivity of more than 370 MBq. Conclusion: High-quality functional image could be acquired at the same time by increasing radioactivity to 370 MBq with higher matrix size. Improvements/Applications: With these results, we can improve diagnostic ability and make more accurate evaluation of renal function.

Investigation of the Thermal Drift of MEMS Capacitive Accelerometers Induced by the Overflow of Die Attachment Adhesive

Packaging stress has significant influence on the thermal stability of microelectromechanical system (MEMS) devices, which utilize the die-on-substrate packaging method to connect the chips and the package shell. A certain adhesive, during the packaging process, is deposited on the package shell by hands or machines to shape an intermediate layer for gluing die and substrate. Due to the uncontrollability of deposition amount, the adhesive always flow out to form overflow structure on the side of die chip. The adhesive overflow will change the distribution of thermal stress induced by the changed temperature and further impact the thermal stability of devices, which is characterized by the quantity of thermal drift. This paper investigates the contribution of adhesive overflow to the thermal drift of comb MEMS capacitive accelerometers. The accelerometers with different levels of overflow are modeled by chip-adhesive–substrate models to study the deformation of sensitive component induced by temperature change. The thermal drift is acquired by an analytical method using the structure deformation and the calculation of the differential capacitance. The thermal drift theory for accelerometers with adhesive overflow is verified by a series of experiments. The results indicate that the adhesive overflow can lead to 10% increase of thermal drift compared with accelerometers without adhesive overflow. In addition, this increase can be extended by the asymmetry of supporting beams of accelerometer. Therefore, the overflow phenomenon should be carefully considered in the packaging process for highly accurate MEMS accelerometers.

Somatosensory and auditory startle reaction in patients with movement disorders

Background Startle reflex (SR) is a generalized defense reaction which is elicited by unexpected stimuli. To elicit SR, auditory and electrical stimulations are used in electrophysiological investigations. Somatosensory startle reflex (SS-SR) is recently described in healthy volunteers after median and tibial stimulation. Studies in patients with brainstem lesions showed importance of upper brainstem in development of SS-SR. Here, we aim to investigate SS-SR systematically in various movement disorders to address its characteristics in comparison to ASR. Methods We have examined ASR and SS-SR in patients with dystonia ( n = 12), multiple system atrophy ( n = 8), corticobasal degeneration ( n = 5), restless legs syndrome ( n = 14), progressive supranuclear palsy ( n = 11), essential tremor ( n = 18) and idiopathic PD (n = 16) and healthy volunteers ( n = 35) under the same conditions. ASR and SS-SR were recorded over orbicularis oculi (o.oc), sternocleidomastoid (SCM), and biceps brachii (BB) after bilateral auditory and median nerve electrical stimulations, respectively. Results The pattern and probability rates over each three muscle of ASR were similar in MSA, RLS, ET, PD and healthy individuals. Probability rates of responses over each muscle and total ASR probability were the highest in dystonia group whereas they were the lowest in CBD and PSP ( p o.oc = 0.016, p scm = 0.036, p bb = 0.000, p total = 0.009). Onset latencies of O.oc responses were also longer in CBD and PSP groups ( p = 0.001). Presence of SSR was also the highest in dystonia and lowest in PSP group similar to ASR. Latency of O.oc response was longest in CBD group. Pattern of SS-SR was similar to healthy individuals in all disease groups except dystonia and MSA in which BB responses were more common than SCM responses. Conclusions The findings of ASR parallel the previous findings. Dystonia patients are known to have exaggerated ASRs. The decreased response in PSP was previously suggested as a support to show extent of pathology. Findings regarding SS-SR also parallel ASR. SS-SR is also exaggerated in dystonia. Different pattern of response appears to be a reflection of overflow phenomenon. However, development of withdrawal reaction is a possibility. Shorter onset latencies in dystonia group probably also reflect increased excitability. Absence of SS-SR or longer latencies in PSP reflects impairment of its pathway which supports the opinion that it may share pathway with ASR and its generator is possibly in the upper brainstem.

New Method for Direct Numerical Simulation of Three-Dimensional Ice Accretion

A simple and reasonable mathematical model is developed to simulate ice accretions on three-dimensional bodies directly. Based on the extended heat-transfer model proposed by Myers, this paper brings forward the concept of critical ice thickness as a criterion for the existence of overflow in every icing control volume. Besides, the concept of inner time step is proposed. After each inner time step, the ice-layer thickness and associated icing properties including the ice accretion rate and overflow in all icing control volumes will be updated to make the model more close to the physical reality. Then, the method for deciding the outflow through boundaries of each icing control volume is given based on the contravariant air velocity components just above the icing surface. Ice accretions under typical glaze ice conditions on a GLC-305 swept-wing model are calculated, and the predicted sectional ice shapes are compared with the experimental data as well as LEWICE results. It indicates that the current results reflect some major characteristics of glaze ice and the spanwise overflow phenomenon. Despite some discrepancies between the numerical results and experimental data, the overall growth patterns are reproduced well.

Genome-Scale NAD(H/+) Availability Patterns as a Differentiating Feature between Saccharomyces cerevisiae and Scheffersomyces stipitis in Relation to Fermentative Metabolism

Scheffersomyces stipitis is a yeast able to ferment pentoses to ethanol, unlike Saccharomyces cerevisiae, it does not present the so-called overflow phenomenon. Metabolic features characterizing the presence or not of this phenomenon have not been fully elucidated. This work proposes that genome-scale metabolic response to variations in NAD(H/+) availability characterizes fermentative behavior in both yeasts. Thus, differentiating features in S. stipitis and S. cerevisiae were determined analyzing growth sensitivity response to changes in available reducing capacity in relation to ethanol production capacity and overall metabolic flux span. Using genome-scale constraint-based metabolic models, phenotypic phase planes and shadow price analyses, an excess of available reducing capacity for growth was found in S. cerevisiae at every metabolic phenotype where growth is limited by oxygen uptake, while in S. stipitis this was observed only for a subset of those phenotypes. Moreover, by using flux variability analysis, an increased metabolic flux span was found in S. cerevisiae at growth limited by oxygen uptake, while in S. stipitis flux span was invariant. Therefore, each yeast can be characterized by a significantly different metabolic response and flux span when growth is limited by oxygen uptake, both features suggesting a higher metabolic flexibility in S. cerevisiae. By applying an optimization-based approach on the genome-scale models, three single reaction deletions were found to generate in S. stipitis the reducing capacity availability pattern found in S. cerevisiae, two of them correspond to reactions involved in the overflow phenomenon. These results show a close relationship between the growth sensitivity response given by the metabolic network and fermentative behavior.