Mixed Mode Research Articles

Mixed transportation optimization model for oilfield water injection synergizing pipeline network and trucks

The water injection network is a common method in oil extraction processes, generally characterized by high energy consumption. Therefore, the adoption of scientifically sound and rational optimization schemes is crucial. However, due to the limited injection capacity of water injection station (WIS), when their supply is less than the demand of the injection wells, trucks are used for supplementary water injection. This paper introduces an oilfield water injection method under water injection pipeline and trucks coordination transport. An optimization model for oilfield water injection in this mixed transportation mode is established to address the supply-demand imbalance in the water injection network. The study uses a specific oilfield water injection system as a case study to validate the applicability of the mixed transportation water injection model (MTWI-Model) compared to the conventional water injection model (CWI-Model). The findings indicate that when only CWI-Model is used, the water volume from the injection station cannot meet the demands of the injection wells, leading to the cessation of some wells and potential overload of pumps in the station, thus affecting the normal operation of the water injection station and ultimately the oil recovery rate. Furthermore, the paper compares the optimization results of the mixed transportation model under two scenarios: fixed and non-fixed water intake points (namely MTWI-FP-Model and MTWI-NFP-Model). The results show that the mixed transportation mode with non-fixed water intake points is more economical, saving a daily cost of 632.28 Yuan/d compared to the fixed point scenario.

Who uses night trains and why? A mixed-method study profiling night train users in Switzerland

Addressing air travel demand is a key open challenge in transitioning to a low-carbon society. In Switzerland, where most flights are from/to nearby European countries, their substitution with night train services is a promising alternative. However, still little research investigates whether the demand for night trains is well-established and the motivations behind it. We aim to bridge this gap through a mixed-method study involving 389 Swiss residents who travelled by night train in 2022/23. A web survey was first conducted to identify latent classes of participants based on their daily and long-distance travel mode choices and evaluate relevant predictors of class membership. Participants of each class were then randomly selected to be involved in an in-depth interview on personal experiences and motivations underlying their choices. Results identify three classes of travellers distinguished by a predominant use of rail and public transport (greens), mixed long-distance travel mode choices and car-oriented daily mobility (pragmatists), preference for flying combined with public transport and active daily mobility (dissonants). Travel cost reduction is the only motivation significantly differentiating pragmatists and dissonants from the greens. This result suggests that fluctuations in ticket prices are the main driving force in shifting demand from flights to night trains.

Fracture and multiple-cracking modelling of strain-hardening cementitious composites

Strain-hardening cementitious composites (SHCC), composed of short fibres embedded within brittle matrix, exhibit distinctive pre-peak strain-hardening characteristics and remarkable tensile ductility. The fracture and failure process of SHCC, involving both hardening and softening stages as a result of matrix multiple micro-cracking and strain localization, is highly complex and poses a significant challenge for numerical modelling. In the present paper, a novel numerical framework, characterized by the bi-layer superposed cohesive zone strategy, is developed for the numerical modelling of fracture and multiple cracking of SHCC, at both the material scale and structural scale. The developed model is based on diffused cohesive interface model, but with adaptions to consider fibre bridging mechanism. The crack interface is simulated by two cohesive elements sharing the same nodes: one for the matrix-cohesion effect and the other for the fibre-bridging effect. Cohesive constitutive relations of matrix cohesion and fibre bridging are carefully assigned. The proposed model is first validated on the material scale through a uniaxial tension test. With the aid of a random material field, multiple-cracking phenomenon and stress fluctuation are successfully predicted by the model. The model is then applied to the structural fracture modelling, where four case studies, including both pure mode I and mixed mode fracture, are performed. The size effect and boundary effect on the fracture behaviour are well captured by the numerical modelling. The model proposed in the current work has the potential to be extended to the multiple cracking modelling of other materials.

Non-local stress approach in conjunction with reinforcement isotropic solid model (NLS-RIS): an efficient orthotropic mixed mode I/II fracture criterion

Non-local stress approach in conjunction with reinforcement isotropic solid model (NLS-RIS): an efficient orthotropic mixed mode I/II fracture criterion

Research on the hybrid teaching model of "race track + basic accounting practice"

To enter the information age, we must adapt to the requirements of the times, and we must have the ability to learn by using information technology in order not to be abandoned by the times. Only by adapting to the development of the times can students have their own stage in society in the future, so as to assume historical responsibilities for society and the people and bloom their own life value. The mixed teaching mode is the product of the information age and the only way for the teaching mode to develop forward. Therefore, the implementation of mixed teaching mode is the need of social development and the development of modern teaching. Autonomous learning ability is a comprehensive ability that students show in their learning activities. Students with this ability have a strong thirst for knowledge, are good at using scientific learning methods, reasonably arranging their own learning activities, are good at positive thinking, dare to question questions, and show a strong spirit of exploration and enterprising in the learning process. Cultivating students' autonomous learning ability is the requirement of quality education and the need of cultivating students' all-round development. Promoting the formation of students' autonomous learning consciousness, autonomous learning ability, autonomous learning habits and autonomous learning quality is an important purpose of classroom teaching reform. Can promote students to achieve excellent results in various competitions.

Study of Ridostin Pro and Poly(I:C) as adjuvants that enhance the immunogenicity of an antitumor vaccine

Aim of the study: to compare the antitumor efficacy and immunogenicity of vaccines with the same antigens but different adjuvants: Ridostin Pro or Poly(I:C); to evaluate the effect of Ridostin Pro and Poly(I:C) on the cytokine profile of serum and the immunophenotype of mouse spleen cells. Material and Methods. To evaluate the antitumor efficacy of vaccines with different adjuvants, two transplantable tumor lines were used: melanoma B16-F10 and EG 7-OVA lymphoma (expressing ovalbumin) for C57BL/6 mice. Against melanoma B16-F10, vaccination with the peptide TRP2 180–188 with the studied adjuvants was performed in a mixed (preventive/therapeutic) and therapeutic regimens. Ovalbumin with adjuvants was vaccinated against EG 7 lymphoma in a therapeutic mode. The immunogenicity of vaccines with different adjuvants in mice without tumors was evaluated by the ELISPOT method. In this case, the peptide TRP2 180–188 and the protein ovalbumin also served as antigens. The cytokine profile of blood serum and changes in the immunophenotype of mouse spleen cells after administration of Ridostin Pro or Poly(I:C) were studied using flow cytometry. Results. In the B16-F10 model, vaccination in a mixed mode protected mice from tumor formation, and the mice lived for more than 100 days. For B16-F10 and EG 7, vaccination in the therapeutic mode led only to inhibition of tumor growth. Ridostin Pro and Poly(I:C) showed a similar ability to develop specific immunity to the peptide TRP2 and ovalbumin. Ridostin Pro increased cytokine levels in the blood serum of mice more strongly than Poly(I:C). Both drugs caused similar changes in the immunophenotype of spleen cells, but Ridostin Pro increased the number of CD 69+ T cells more strongly than Poly(I:C). Conclusion. The comparison of two drugs as adjuvants for antitumor vaccines showed that the domestic drug Ridostin Pro did not inferior in effectiveness to Poly(I:C) on mouse models. In this regard, Ridostin Pro can be considered as a promising adjuvant for antitumor vaccines and deserves further study.

Investigation of mild steel corrosion inhibition in acidic media by Viola extract based on bulk and nanometer size

In the present work, the inhibition performance of Viola extract based on bulk and nano size as a green corrosion inhibitor on mild steel in 0.5 M phosphoric acid and 1M hydrochloric acid solutions is investigated using different techniques (potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and Optical microscopy). The gained results demonstrated that various concentrations of Viola Extract (bulk and nano) inhibited the corrosion of the alloy in both of the acid solutions. The temperature impact on corrosion rate without/with this extract was examined. Certain thermodynamic parameters were determined based on the temperature impact on inhibition and corrosion processes. The adsorption mechanism of the extract on the alloy was explored using the Langmuir adsorption isotherm. A mixed mode of adsorption was observed, wherein the nano-sized extract in 1.0 M HCl predominantly underwent chemisorption, while the bulk-sized extract in 1.0 M HCl and both bulk and nano-sized extracts in 0.5 M H3PO4 were primarily subjected to physisorption. Scanning electron microscopy (SEM) and Optical microscopy analyses were employed to scrutinize alloys’ surface morphology.

Experimental and virtual testing of mode II and mixed mode crack propagation under dynamic loading

Under static loading, measuring experimentally the mode II and mixed mode fracture toughness of composite materials and adhesive joints is well standardised. However, under dynamic loading, no standard procedure has been defined yet. Therefore, this paper proposes an experimental methodology to measure the mode II and mixed mode interlaminar fracture toughness of composite materials and adhesive joints. The methodology is based on a modified split Hopkinson compression bar. Two different data reduction schemes are explored and compared, one based on measuring the crack length, and another based on measuring the force from the strains in the transmitted bar. The two data reduction methods provided considerably different results. By using the method based on measuring the force, the mode II and mixed mode fracture toughness for both interlaminar and adhesive joints decreased for higher strain rates, while the opposite was found with the other approach. The method based on the crack length measurement was deemed to be unreliable due to the difficulties in measuring it.

Development of large-size dissimilar stainless steel/α-Ti alloy joints by diffusion bonding using vacuum hot press: Interface microstructure and tensile response in the temperature range of 77–773 K

In the present study, dissimilar metal joints of SS321 and Ti–5Al-2.5Sn (α-Ti alloy) are produced by diffusion bonding at temperatures of 850, 900, and 950 °C under 10 MPa pressure for 30 min duration using a vacuum hot press (VHP). The interface of the joints was characterized through scanning electron microscopy coupled with energy dispersive spectroscopy and electron backscattered diffraction analysis for examining microstructure, morphology, and microchemistry across the interface. The effect of change in the heating process during diffusion bonding on the growth kinetics of interface layers was investigated. The interface of the joints comprised of intermetallic phases of σ phase, χ phase, (Fe,Cr)2Ti, FeTi and β-Ti. The joint produced at 900 °C has exhibited a maximum tensile strength of 315 MPa, 253 MPa, and 208 MPa at the test temperatures of −196 °C (77 K), room temperature (300 K), and 500 °C (773 K), respectively. Reduction in joint strength was noticed at test temperatures of RT and −196 °C for the samples bonded at a higher temperature of 950 °C due to the increased widths of the intermetallic phases at the interface. The effect of the bonding temperature on the tensile strength of the joints at an elevated test temperature of 500 °C was found to be negligible; however, the joints displayed good retention of strength along with substantial strain hardening followed by ductility at 500 °C. Fracture surfaces of RT and −196 °C tested samples showed the mixed mode of featureless smooth and cleavage fracture, whereas the 500 °C tested sample displayed planar interface failure. The zone of failure of the joints was noted to be around the interphase layer made of (Fe,Cr)2Ti + FeTi intermetallics.

Impact of surface preparation method on the fracture toughness of adhesive joints subjected to diverse loading modes

While research has explored surface treatment effects on fracture energies in pure modes (I or II), there is a lack of research under mixed-mode loading. The aim of this paper is to investigate the influence of surface treatment approaches on the fracture behaviour and fracture energy of adhesive joints at different loading modes. To achieve this, double cantilever beam (DCB) adhesive joints were manufactured considering two different surface treatment methods namely grit blasting and mechanical bristle blasting. The joints were subjected to five different mode mixities. Fracture energy for each tested condition was calculated based on a compliance-based approach. The fracture energies in mode I reached an increase of 55 % when grit blasting surface treatment was applied, while for mode II the fracture energy reached a value three times higher for mechanical bristle blasting surface treatment, both energies from the mixed mode tests. The failure mechanisms were also evaluated for joints with different surface treatments as a function of loading mode. In all tested conditions, a cohesive failure mode was observed; however, the results underscore the substantial influence of the surface treatment method on the fracture energy of adhesive joints. This is attributed to the distinct failure mechanisms observed under varying surface treatment conditions.

Investigation on the effect of freeze–thaw cycles on damage characteristics of concrete under mixed mode I-II load conditions

In order to investigate the effect of freeze–thaw cycles on the damage characteristics of mixed mode I-II crack propagation in concrete. The three-point bending and three-point shear fracture test were carried out on specimens subjected to different freeze–thaw cycles (0, 50, 100, 150 and 200). The analytical expression of mixed mode I-II damage scale r0(I,II) and ru(I,II) was derived, and the effect of freeze–thaw cycles on damage scale was analyzed. In addition, the critical damage scale of mixed mode I-II fracture was obtained using the numerical simulation method, and the simulation results were compared with the calculation results. Finally, the accumulate energy and tension-shear failure of concrete after freeze–thaw cycles were analyzed based on acoustic emission technology.

Large eddy simulation of a supersonic lifted hydrogen flame: Impacts of Lewis, turbulent Schmidt and Prandtl numbers

Parametric large eddy simulations (LES) of a supersonic lifted hydrogen flame are reported. The emphases are on two aspects: impacts of (1) Lewis number (Lei of the ith species) and (2) turbulent Schmidt and Prandtl numbers (Sct and Prt) on supersonic turbulent flame and flow structures. Five cases are considered: species-specific Lei, Sct=Prt=1.0 (C0); unity Lei, Sct=Prt=1.0 (C1); species-specific Lei, Sct=0.5, Prt=1.0 (C2); species-specific Lei, Sct=1.0, Prt=0.5 (C3); and species-specific Lei, Sct=Prt=0.5 (C4). Numerical results of instantaneous and/or time-averaged species mole fractions, mixture fraction, heat release rate, flame base location, and mixed modes of premixed and diffusion combustion are compared between cases C0 and C1. Differences in auto-ignition locations and strengths and flame structures and stabilization specify the impacts of Lewis number. They are triggered by different predictions of species mass and thermal diffusions at fuel-coflow and/or coflow-ambient air mixing layers. These differences are rationalized by a scale analysis of mass/thermal diffusion and convection for case C0, which suggests the relatively low but non-negligible former against the latter. Cases C0 and C2–C4 barely see differences in terms of instantaneous and/or time-averaged temperature, velocity, and mixed combustion modes except for further downstream areas where combustion occurs. Both Sct and Prt impose less significant influences than Lewis number, as sub-grid scale mass/thermal diffusion is subordinate to its resolved counterpart according to their scale analysis for case C4.

Effect of trialkoxysilane/aminosilane-containing universal adhesive on resin-ceramic microtensile bond strength and ceramic wettability: An in-vitro study

BackgroundThe dual-silane (trialkoxysilane/aminosilane) universal adhesive (UA) is claimed for its enhanced priming capacity of glass-ceramics. ObjectiveThis study evaluated the effect of organofunctional trialkoxysilane- and organofunctional trialkoxysilane/aminosilane-containing UAs on the long-term resin–ceramic microtensile bond strength (μTBS) and wettability of ceramic. MethodsHydrofluoric acid-etched lithium disilicate discs were distributed into four groups as follows: (control), no priming was performed; (MBN), primed using a silane-based primer (Monobond N); (SBU), primed using a trialkoxysilane-containing UA (Single Bond Universal Adhesive) and (SBP), primed using a trialkoxysilane/aminosilane-containing UA (Scotchbond Universal Plus Adhesive). Ceramic discs were cemented into blocks then sectioned into microbeams stored in distilled water at 37° for 1 year. The μTBS was evaluated followed by assessment of the failure modes. The contact angle of the two UAs was measured with a goniometer using the sessile drop technique. ResultsMBN significantly improved the resin-ceramic μTBS (31.71 ± 6.33 MPa) compared to the control group. The resin-ceramic μTBS obtained after priming using SBP (22.83 ± 3.42 MPa) was comparable to those of MBN. SBU showed significantly inferior resin-ceramic μTBS (16.02 ± 6.28 MPa) compared with MBN. Mixed failures mode patterns were the most frequent in the groups. The ceramic wettability of both UAs did not significantly differ. ConclusionCeramic priming using a UA with dual-silane monomers (organofunctional trialkoxysilane/aminosilane) resulted in long-term adhesion comparable to a silane-containing primer. Incorporating aminosilane monomer in UA formulation did not affect the wetting of characteristics of the UA solution and enhanced its glass-ceramic priming capacity. Clinical significanceThe use of UA with optimized silane content as a primer for glass-ceramics simplifies clinical adhesive procedures including resin cementation and repair of ceramic restorations.

On group-theoretic eigenvalue vibration analysis of structural systems with C6v symmetry

In considerations of the linear vibration of symmetric systems, group theory allows the space of the eigenvalue problem to be decomposed into independent subspaces that are spanned by symmetry-adapted freedoms. These problems usually feature one or more degenerate subspaces (i.e. subspaces that contain repeating solutions). For such subspaces, the associated idempotents, as calculated from the character table of the symmetry group, are not capable of full decomposition of the subspace. In this paper, and based on group theory, simple algebraic operators that fully decompose the two degenerate subspaces of structural problems belonging to the C6v symmetry group are proposed. The operators are applied to the vibration of a spring-mass system, for which the results for natural frequencies are found to agree exactly with results from the literature. Their application to the vibration of a hexagonal plane grid reveals new insights on the character of the modes of degenerate subspaces. The overall conclusion is that, for problems belonging to the C6v symmetry group, the proposed operators allow the mixed modes of degenerate subspaces to be separated into two distinct symmetry categories, and are very effective in simplifying the actual computation of the repeating eigenvalues of these subspaces.

Bifurcations and mixed mode oscillations in a bi-stable plasma model with slow parametric excitation.

In this study, considering a bi-stable plasma model with slow parametric excitation, the bifurcation of periodic and chaotic responses as well as the resulting fast-slow motions is discussed analytically and numerically. For a nonautonomous fast sub-system, the generalized harmonic balancing method is utilized to obtain an averaged system. Bifurcation analysis about the averaged system shows that the critical manifolds form a S-shape structure. Meanwhile, supercritical and subcritical period doubling (PD) occurs on the upper branch simultaneously. As the frequency of the external excitation changes, bifurcation points on the limit cycle manifolds can present different relative locations. Moreover, an additional bi-stable structure induced by Cusp bifurcation emanates from the upper branch. On the other hand, the existence of a chaotic attractor and the corresponding boundary crisis phenomenon are verified using the Melnikov method and the basin of attraction. The structures of the numerical bifurcation diagram show good agreements with the analytical results. Considering two cases of low-frequency excitation, the corresponding fast-slow dynamics are discussed. It is found that, when the fast-slow flow passing the subcritical PD point, a low frequency with different magnitudes will lead to two patterns of bifurcation delay, i.e., the typical one and the excessive delay, which suppress the PD. As for the boundary crisis point, the slow passage effects show no distinct influence. Thus, three transition mechanisms based on two cases of the bifurcation structure are explained, including "fold of cycle-fold of cycle" type, "fold of cycle-delayed subcritical PD" type, and "fold of cycle-boundary crisis" type.

Detailed simulations on the mixed modes of premixed and diffusion combustion in supersonic hydrogen flames

Detailed simulations on the mixed modes of premixed and diffusion combustion in supersonic hydrogen flames

Covid-19 Pandemic & Post Pandemic-Technology and Education

The COVID-19 pandemic, was occurred in 2019. It is a worldwide pandemic which effect the whole world. The disease is mainly pass through the respiratory track; Infected people transmit the COVID-19 virus when they are Come in contact with other non-infected persons. However, infection can also be occurred in longer distances, particularly indoors. This pandemic has drastically changed the use of digital technologies in the field of education due to the social distancing norms and nationwide lockdowns. People and organizations all over the world have had to adjust to new ways of work and life. Education is field in which there is a dramatic shift to the online mode of transacting. Since the beginning of the lockdown, schools, colleges and universities around the world have shifted their classes to video conferencing platforms like Zoom, goggle classroom, Microsoft and goggle meet Suit. This increases the on-screen community. Some universities are now shifting entirely to the online mode, with the exception where require a physical presence is necessary. Due to Covid-19 pandemic we imagine a largest shift of digital usage on all fields of work and life. These changes are largely depended on our responses to and shaping of the emerging trends (e.g., Some School App). The Covid-19 pandemic has led to online revolution in education fields to shift to work-from-home (WFH). The Covid-19 post pandemic introduce a new mode of education i.e. hybrid or blended mode of learning.

Validation of LC-MS/MS method for opioid monitoring in Valencia City wastewater: Assessment of synthetic wastewater as potential aid

In this study, a comprehensive and sensitive method for the simultaneous detection of 17 opioids (OPs) and their human metabolites in wastewater using high-performance liquid chromatography coupled to tandem mass spectrometry was validated. The chromatographic separations of opioids were carried out on a Kinetex® Biphenyl column (1.7 μm, 100 Å, 50 × 2.1 mm). A synthetic wastewater approach was used for recovery studies to mimic a contaminant-free matrix. Two solid-phase extraction (SPE) sorbents (hydrophilic-lipophilic balance and mixed mode with the previous phase and a weak cationic exchange) were studied to optimize sample treatment and obtain higher recoveries. The mixed mode was chosen because the recoveries of 17 target analytes at three spiked concentrations (25, 50, and 100 ng mL−1) were > 80 % for 75 % of the analytes in a simulated wastewater. The intra- and inter-day relative standard deviations (RSDs) were between ±1 % and ±20 %. The method limits of quantification ranged from 5 to 25 ng L−1, the only exceptions being heroin (275 ng L−1) and morphine-3β-glucuronide (250 ng L−1). Suppression/enhancement is comparable between the synthetic and the influent wastewater. The analytical method was applied to the OPs analysis in twenty-one influent samples collected from the treatment plants treating the wastewater of Valencia City (Spain). Twelve OPs were detected with total daily concentrations ranging from 1 ng L−1 to 2135 ng L−1. The widespread presence of these compounds in water suggests potential widespread exposure, highlighting the need for increased environmental awareness. Furthermore, the estimated daily intake results raise concerns about opioid use as a potential future health and social issue.

Under the Blended Teaching Mode based on OBE Concept in Undergraduate Universities in Shandong Province Research on the Development Strategy of Teacher's Teaching Ability

With the advent of the digital age, the deep integration of cutting-edge technology and education continues to innovate, driving the transformation of teaching models. Compared with traditional teaching methods, blended teaching mode reshapes the entire process of education and teaching, and is of great significance in promoting educational fairness, improving educational quality, and building a high-quality education system. In response to the current situation of blended teaching mode with OBE concept among university teachers, how to effectively accelerate the development of teachers' teaching abilities in the digital era has become an important task in the field of higher education. Based on this, this article clarifies the specific connotation of the OBE concept blended teaching model, constructs a professional teaching ability system for university teachers, and proposes strategies to update education and teaching concepts in a timely manner, comprehensively optimize teaching design capabilities, actively improve information literacy of university teachers, and continuously improve training and incentive mechanisms. The aim is to promote university teachers to adapt to the development of the digital era and educational innovation and transformation.

Social Enterprises in Poland in the Face of Recent Crises

Background: The research problem addressed in this study concerns the activities of social enterprises (SEs) within the framework of the social market economy (SME) in Poland during the crises triggered by the COVID-19 pandemic and the war in Ukraine. Research objectives: The article aims to verify the hypothesis that SEs situated within the SME can mitigate the negative effects of crises by undertaking additional actions for recipients during the pandemic and Ukrainian refugees. Research design and methods: An interdisciplinary research model helped examine the stated problem. It synthesizes both the concepts of SME and SE. Moreover, part of the research was a nationwide quantitative study using the CAWI method supported by the CATI method and Dilman’s prompting method (mixed mode). Results: During the pandemic in Poland, 56% of SEs took additional actions for recipients, even though the situation worsened for 41% of them. During the war in Ukraine, 68% of SEs took action for refugees, while the situation worsened for 29% of SEs. Conclusions: Social enterprises experiencing the consequences of crises are also able to minimize their effects. Simultaneously, to an equal extent, they support environmental issues and sustainable development.