Mixed Mode Research Articles

Does the Mixing Method of AH Plus Jet Affect its Physicochemical and Mechanical Properties?

IntroductionThe purpose of this study was to evaluate whether the mixing method of AH Plus Jet sealer affects its physicochemical and mechanical properties. MethodsThe properties of AH Plus Jet sealer were analyzed when mixed using either the Auto Mix Tip or manual mixing. The evaluated properties included radiopacity (n = 5), initial and final setting times (n = 5), flow (n = 5), and solubility (n = 3), following specifications outlined in ISO 6876/2012 and ADA Nº 57/2000. pH levels were measured at intervals of 3, 24, 72, and 168 hours (n = 10). The push-out bond strength test was conducted using a universal testing machine and using bovine teeth (n = 30). Failure modes were analyzed with stereomicroscopy. Porosity was evaluated under micro-CT (n = 5), and scanning electron microscopy was also performed (n = 5). One-way analysis of variance and Tukey, unpaired t-tests, or Mann–Whitney tests were used with a significance level of 5%. ResultsThe Auto Mix exhibited a radiopacity value of 12.11 mmAl, whereas manual mixing resulted in 12.55 mmAl (P > .05). For initial and final setting times, Auto Mix showed 901 minutes and 1779 minutes, respectively, while manual mixing recorded values of 631 minutes and 1504 minutes (P < .05). In terms of flow, Auto Mix demonstrated higher values (25.26 mm) than manual mixing (21.71 mm) (P < .05). No statistical differences were observed between the two methods for solubility and pH (P > .05). Manual mixing presented a higher bond strength value (14.52 MPa) than Auto Mix (9.81 MPa) (P < .05). The mixed failure mode was the most frequent outcome for both methods. The highest porosity was observed for Auto Mix (P < .05). Scanning electron microscopy analysis revealed that manual mixing resulted in a smoother surface with fewer pores and smaller, more evenly distributed agglomerates compared to automatic mixing. ConclusionThe mixing method employed for AH Plus Jet sealer influences some physicochemical and mechanical properties of the material.

Phosphatase Alkaline Inhibition and Antithyroid Activity of Acetylacetone Sulfonamide Derived Schiff Base. In Vitro and In Silico Studies

AbstractThe sulfonamide‐derived compounds have demonstrated various pharmaceutical properties. However, the exploration of certain properties, such as phosphatase inhibition and anti‐thyroid activities, has been limited in the existing literature. The present study aimed to investigate these specific activities for the Schiff base (Z)‐4‐(4‐oxopent‐2‐en‐2‐ylamino)benzenesulfonamide. The compound underwent thorough physicochemical characterization, including FTIR, Raman, and UV‐Vis spectroscopy, along with theoretical DFT calculations. It exhibited inhibitory activity against intestinal alkaline phosphatase, showing an IC50 value of 37.0±1.0 μM, with kinetic studies indicating a mixed mode of inhibition. Additional insights into the inhibition process were gained through fluorescence spectroscopy and molecular docking studies. The potential anti‐thyroid activity was explored through charge‐transfer studies with iodine, revealing a strong interaction (Kc=2.16±0.05×104 M−1), suggesting a role in reducing the iodination process of triiodothyronine (T3) and thyroxine (T4). Moreover, the compound showed strong, spontaneous, and reversible binding to albumin, indicating potential pharmaceutical relevance. ADME properties were also calculated, confirming favorable drug‐likeness. This study provides valuable insights into the multifaceted pharmaceutical properties of the investigated sulfonamide‐derived compound, encouraging further exploration of its therapeutic potential.

Tailoring microstructure and mechanical properties of U75V steel manufactured by laser direct energy deposition combining cobalt addition with preheating treatment

Laser direct energy deposition (LDED) exhibits great potential for application in rail repairing due to its low cost and high process automation. However, the martensite transformation accompanied by rapid solidification leads to the decrease in the mechanical properties and threatens the service safety. In this study, the reinforcement strategy of combining cobalt (Co) addition with preheating treatment was investigated systematically by combining thermodynamic calculations with experimental characterization to optimize the microstructure and mechanical properties of U75V steel by LDED. The results indicate that cobalt addition can promote the pearlite percentage by facilitating the leftward shift of the continuous cooling transformation (CCT) curve, and refining the interlamellar spacing. But the martensite start (Ms) temperature will also increase from 206.4 °C to 324.1 °C after 7 wt% Co addition. 350 °C preheating treatment on the substrate can also promote the pearlite transformation by elevating the valley temperature of thermal cycling over Ms, as well as the subsequent decrease in cooling rate, but it is not sufficient to prevent martensite formation. A synergistic reinforcement strategy of 7 wt% Co addition and 350 °C preheating was established, which can effectively suppress the occurrence of martensite in the bottom area of deposition layers and expand the pearlite range in the top area. The bonding strength between the substrate and deposition layers has been elevated by ∼20%, accompanied by the increase in elongation and wear resistance. A mixed mode of adhesive and abrasive wear has transformed into a mode dominated by adhesive wear after optimization.

Does VIMC-FMC work well on highly ductile bimetal joints? An investigation on mixed mode I/II fracture of AA1050/Cu bimetal weakened by U-notches

In this study, it is attempted to check if the virtual isotropic material concept (VIMC), originally suggested for fiber-reinforced composite laminates, can be used as an appropriate simplifying tool in fracture estimation of notched bimetals. First, the aluminum alloy AA1050 and the copper are cladded together using the roll-bonding technique. Then, several U-notched bimetal specimens are manufactured to perform fracture tests under mixed mode I/II loading conditions. Due to the highly ductile behavior of the AA1050/Cu bimetal, the fictitious material concept (FMC) is adopted to equate the bimetal with a fictitious material having perfectly linear elastic behavior with the aim to avoid the elastoplastic fracture analysis. Finally, the VIMC and FMC are coupled with three famous brittle fracture models, i.e., the U-notch maximum tangential stress (UMTS), U-notch mean stress (UMS), and U-notch strain energy density (USED) criteria, for predicting the experimentally measured strength of the notched bimetal specimens. The results indicate that the maximum discrepancy between the theoretical predictions and the experimental results in all the combined failure criteria is less than 8%. Therefore, the VIMC-FMC combination is found to be quite effective as a converter to solve the complex problem of highly ductile fracture of notched inhomogeneous anisotropic bimetals under mixed mode I/II loading using only the linear elastic analysis of the fictitious homogeneous isotropic plates. Also, found in this research is that not only VIMC works well on fiber-reinforced composite laminates, but also on bimetal joints.

Microstructure Evolution and Mechanical Properties of AlCoCrFeNi2.1 Eutectic High-Entropy Alloys Processed by High-Pressure Torsion.

High-entropy alloys (HEAs) have garnered significant attention for their exceptional properties, with eutectic high-entropy alloys (EHEAs) emerging as particularly notable due to their incorporation of eutectic structures comprising soft and hard phases. This study investigated the influence of shear strain on the microstructural refinement and mechanical properties of AlCoCrFeNi2.1 EHEAs, which were subjected to high-pressure torsion (HPT) at room temperature under a pressure of 6 GPa across 0.5 to 3 turns, compared to the initial material. After HPT treatment, significant grain refinement occurred due to strong shear strain, evidenced by the absence of B2 phase peaks in X-ray diffraction (XRD) analysis. Microhardness increased substantially post-HPT, reaching a saturation point at approximately 575 HV after three turns, significantly higher than that of the original sample. Moreover, the ultimate tensile strength of HPT-treated specimens reached around 1900 MPa after three revolutions, compared to approximately 1100 MPa for the as-cast alloy, with a mixed fracture mode maintained. This investigation underscores the efficacy of HPT in enhancing the mechanical properties of AlCoCrFeNi2.1 EHEAs through microstructural refinement induced by shear deformation, offering insights into the design and optimization of advanced HEAs for various engineering applications.

Analysing and predicting learning behaviours in computer science: A case study of the blended teaching mode in Digital Signal Processing course

Blended learning is the latest and inevitable trend in the development of education. Although blended learning research is on the rise, fewer studies examine the learning behaviour of college students in blended learning environments. This study aimed to investigate the learning behaviours of students in the field of computer science and examine these behaviours using data mining algorithms, taking the teaching practice of the Digital Signal Processing course as a case study. A total of 18 behavioural indicators were extracted and divided into three categories: basic learning behaviours, self-regulated learning behaviours, and extended learning behaviours. Data analysis of the behavioural indicators yielded the following conclusions: (1) Students did not have the habit of watching course playback and were less receptive to multiple online learning platforms; (2) Students’ midterm performance and duration of livestream watching directly affected their basic learning behaviours, with all indicators of self-regulated and extended learning behaviours showing significant correlations; (3) The clustering of learning behaviours yielded four different learner patterns, which calls for personalised teaching strategies; (4) The random forest algorithm had an accuracy of 95.4% in predicting performance of the four types of learners.

The influence of hydrogen content on the Zr-4 alloy diffusion bonding joint: From experiments to molecular dynamics simulations

Bonding the Zr-4 alloy in the high temperature can lead to many problems, for example grain coarsening and large welding deformation resulting from high residual stresses. Hydrogenation is an effective approach to decrease the bonding temperature. In the present research, the influence of hydrogen contents on the microstructure evolution and shear strength of Zr-4 alloy joints were studied. The number of interface voids markedly decreased with increasing hydrogen content at 650 °C. A sound joint was obtained at the hydrogen content of 0.2 wt% hydrogen. This achieved joint had a shear strength of 244 MPa, and the fracture mode of the joint presented the brittle/ductile mixed mode. With the increase of hydrogen content, the flow stress of the hydrogenated Zr-4 alloy decreased due to the decomposition of zirconium hydrides. The plasticity of the joint enhanced with increasing hydrogen content in the view of electron backscatter diffraction (EBSD) results, and the kernel average misorientation increased from 0.11° to 0.77°. In addition, the diffusion behavior and diffusion coefficient of the Zr atoms were investigated by molecular dynamics simulation. The calculation results showed that hydrogen enhanced the diffusivity of the Zr atoms, and the diffusion coefficient of the Zr atoms accordingly increased by four orders of magnitude. The addition of hydrogen influenced the directly diffusion bonding process through two aspects: improvement of plasticity and enhancement of diffusion ability.

Blind prediction of curved fracture surfaces in gypsum samples under three-point bending using the Discontinuous Galerkin Cohesive Zone method

A computational framework based on a Discontinuous Galerkin (DG)/Cohesive Zone formulation is utilized to simulate the experiments of the Purdue Damage Mechanics Modeling Challenge. The inelastic response of the additively-manufactured gypsum material used in the experimental tests is modeled via a dilatational plasticity model. The constitutive and fracture model parameters are calibrated using the load–displacement curves corresponding to three-point bending tests initially provided by the Challenge organizers. The test samples contained initial notches especially designed to force specific types of mixed fracture modes. The calibrated computational modeling framework is used to blindly simulate the more complex configuration of the Challenge experiments. The numerical predictions of the load–displacement curve and the shape of the curved fracture surface are compared to the experimental data provided a posteriori. It is found that the computational method is able to quantitatively describe the fracture response of the material including crack propagation, plastic wake, and the curved geometry of the fracture surface that results from the evolving fracture mode mixity with significant fidelity.

Effect of the spatial distribution of macroinvertebrates in the benthic and hyporheic zones on the vertical hydraulic conductivity of the streambed

Water quality, aquatic habitat, and groundwater recharge, which have a critical impact on the river ecosystem health, are associated with the vertical hydraulic conductivity of streambed (Kv). Macroinvertebrates bioturbation can generate heterogeneity in the benthic and hyporheic zones to influence Kv by particle reworking and burrow construction, which are directly and indirectly related to the physicochemical conditions of sediments. However, understanding how these factors and processes influence Kv and its role is deficient. Here the spatial distribution of benthic macroinvertebrates and its effects on Kv in the Weihe River were investigated. Macroinvertebrate bioturbation had a significant effect on Kv when the biomass was greater than 1 mg/m2, and yet when the biomass exceeded 102 mg/m2, bioturbation had a significant inhibitory effect on Kv as the result of clogging due to the fine sediment particles and secrete mucus produced by benthic Macroinvertebrates. Macroinvertebrate distribution and biomass are often influenced by temperature which could also decrease the fluid viscosity, thus improving Kv. Moreover, the mixed bioturbation mode with the predominated Tubificidae was better than the bioturbation mode of single-type benthic macroinvertebrates in improving sediment permeability. These findings have important implications for revealing the disturbance mechanism of benthic macroinvertebrates on Kv and provide a reliable theoretical basis for the protection and planning of river ecosystems.

Investigation on failure characteristics of mode II crack in heat-treated granite specimen subjected to dynamic loading

In order to solve the energy crisis, geothermal energy development has been increasingly valued in recent years. In many geothermal engineering projects, hydraulic fracturing can cause many cracks to appear inside the rock mass during the extraction process of dry hot rock. At present, there have been many studies on mode I cracks and mixed mode I/II cracks. In order to ensure the smooth progress of the project, it is necessary to supplement the research on mode II crack rocks in high-temperature geothermal environments. A series of experiments were conducted using the Split Hopkinson Pressure Bar (SHPB) device and cracked granite specimens treated at different temperatures, the failure modes could be tracked by using a high-speed camera. The dynamic experiment was simulated using software coupling. The Grain Boundary Model (GBM) can well describe the force-thermal coupling damage behavior among various crystal particles. Some analyses were conducted on dynamic fracture toughness, failure mode, strain distribution, thermal damage, and changes in the number of cracks. The research results illustrated that high temperatures lead to a decrease in the mode II fracture toughness of granite, an increase in fracture time, and greater susceptibility to damage. High temperature will increase the maximum strain at the moment of failure. It was also found that the proportion of intra-grain cracks increased with the temperature. After 500 °C, the number of cracks generated during the fracture process is inversely proportional to the temperature.

Rickettsia symbionts spread via mixed mode transmission, increasing female fecundity and sex ratio shift by host hormone modulating

Heritable symbionts are common among animals in nature, but the molecular mechanisms underpinning symbiont invasions of host populations have been elusive. In this study, we demonstrate the spread of Rickettsia in an invasive agricultural pest, the whitefly Bemisia tabaci Mediterranean (MED), across northeastern China from 2018 to 2023. Here, we show that the beneficial symbiont Rickettsia spreads by manipulating host hormone signals. Our analyses suggest that Rickettsia have been horizontally acquired by B. tabaci MED from another invasive whitefly B. tabaci Middle East-Asia Minor 1 during periods of coexistence. Rickettsia is transmitted maternally and horizontally from female B. tabaci MED individuals. Rickettsia infection enhances fecundity and results in female bias among whiteflies. Our findings reveal that Rickettsia infection stimulates juvenile hormone (JH) synthesis, in turn enhancing fecundity, copulation events, and the female ratio of the offspring. Consequently, Rickettsia infection results in increased whitefly fecundity and female bias by modulating the JH pathway. More female progeny facilitates the transmission of Rickettsia. This study illustrates that the spread of Rickettsia among invasive whiteflies in northeastern China is propelled by host hormone regulation. Such symbiont invasions lead to rapid physiological and molecular evolution in the host, influencing the biology and ecology of an invasive species.

Characterization of the interface fracture energy dependency on mixed mode fracture between rigid fiber and soft matrix

An enhanced version of the Rubber Cord Adhesion Inflation Test (RCAIT) has been designed to experimentally assess the internal pressure and cable tension applied to the specimen needed to propagate a crack along the matrix/reinforcement interface. To calculate the critical strain energy release rate, we develop a semi-analytical model describing the deformation of a hyperelastic tube under loading conditions that reflect the ones applied experimentally. A more comprehensive numerical model of the test is also proposed to investigate the influence of loading conditions on rubber deformation near the crack tip. Comparison of different experimental data sets with the theoretical/numerical data demonstrates that the new experimental setup allows for a reliable determination of the rubber/cord interface failure envelope under combined loading conditions.

Acoustic emission and fracture morphology characteristics of thermal-damage granite under mixed mode I/III loading

To explore the fracture morphology and acoustic emission characteristics of thermally damaged granite under mixed mode I/III loading, a series of heat treatment and mixed mode I/III loading tests were conducted on edge-notched disc bend (ENDB) granite samples. First, the thermal damage samples’ strength and crack opening displacement were analyzed. Subsequently, based on 3D laser scanning technology, the fracture morphology of the sample was studied, and the fractal dimension was calculated. Then, the samples’ acoustic emission characteristics were discussed, including the ringing count, b value, spectrum signature, and AF-RA. Finally, an acoustic early warning index was proposed based on the critical slowing down theory, and the influence of temperature on the early warning effect was analyzed. The results show that under mixed mode I/III loading, the samples formed an antisymmetric curved surface with out-of-plane torsion. As the thermal damage effect is enhanced, the peak strength decreases linearly, and the fractal dimension increases linearly. The failure mode changes from sudden instability to progressive instability. Shear cracks gradually dominate the sample failure. The peak frequency signal of the sample is mainly distributed between 80 kHz and 400 kHz. The appearance of the sudden drop in the b value and a zero-frequency signal has an early warning effect. The quadratic function can describe the relationship between warning time and temperature. As the temperature increases, the deterioration effect of historical loading on the sample is enhanced, the development time of sample failure is prolonged, and the early warning effect is better.

Revealing the failure mechanism of industrial Fe-25Cr-20Ni stainless steel plate: Fine-grained segregation band and brittle phase induced delamination cracking

The use of heat-resistant stainless steel thick plates in industrial production often presents challenges due to the presence of uneven microstructure and segregation, which can pose a persistent challenge for the prolonged safe operation of critical components made from such materials. This study aimed to investigate the fracture mechanism of an industrial Fe-25Cr-20Ni stainless steel plate at room temperature through uniaxial tensile experiments and fully reversed strain-controlled tension-compression fatigue experiments. Delamination cracks were observed on the fracture surfaces of both experiments. The specimens with fracture delamination were systematically studied by detailed microstructural evolution, and the failure mechanism and main reasons of fracture delamination were analyzed. The results show that the fracture delamination is related to the fine-grained segregation band (FGSB) consisted of fine grains and sigma phase located at the center of the thickness of the stainless-steel plate. The FGSB demonstrates low transgranular and intergranular fracture modes and exhibits bamboo knobs crack during plastic deformation, leading to a mixed fracture mode of ductile and brittle fracture. Furthermore, FGSB, as an anisotropic microstructure, which has a high stress concentration with nearby grains during plastic deformation. The sigma phase fracture and the weakening of the interface strength of the microstructure in FGSB provide a potential initiation site for fatigue crack initiation, thereby contributing to the possibility of aggravating fatigue damage and deteriorating fatigue performance. It is concluded that FGSB, as a metallurgical defect in stainless steel plates, is responsible for delamination failure.

Interlayer damage evolution of CRTS III slab track under passenger and freight train loads

To study the interface damage in CRTS III slab tracks under the concurrent interactions of temperature and mixed passenger and freight train loads, a refined fatigue cohesive zone model (F-CZM) considering the stiffness, strength, and energy fracture degradation factors was presented. Utilizing this model, a finite element model (FEM) of the CRTS III slab track was developed. The interface fatigue damage between the track slab and self-compacting concrete (SCC) under various adhesive strengths and mixed operation modes was calculated. The interface characteristic degradation and stress change of door-type steel bars were revealed. Results show that good performance is ensured within the design service life with intact interface adhesion. The interface damage develops from the slab corner to the edge and then into the inner. The diminished interfacial tangential adhesive strength causes two patterns of interfacial damage procession. Enhanced freight train ratio escalates interface damage. During the development of interface damage, the door-type steel bars act as a safety margin.

Retraction Note: Research on effectiveness of college english blended teaching mode under small private online course based on machine learning

Retraction Note: Research on effectiveness of college english blended teaching mode under small private online course based on machine learning

A survey on the application of online and offline blended teaching in microendodontics

Objective: To evaluate the effect of online and offline blended teaching in microendodontics, attempting to promote the widespread application of blended teaching mode in Operative Dentistry and Endodontics. Methods: A questionnaire survey was carried out among 865 trainees who attended the blended teaching in microendodontics combined the online theory curriculum and offline practice training from April 6 to 28 in 2022, organized by Department of Operative Dentistry and Endodontics, Hospital of Stomatotogy, Sun Yat-sen University. The content of questionnaire included trainees' basic information as well as their perspectives and expectations on the teaching mode. Data was analyzed by SPSS 24.0 and Chi-square test was used for enumeration data. Results: A total of 855 trainees participated in the valid survey with the effective recall rate of 98.8% (855/865), 50.3% (430/855) of which were young people in 18-30 years old. Their working period ranged from 0.5 to 40 years. Physicians and physician assistants occupied 40.9% (350/855) and 32.9% (281/855), respectively. And the intermediate and senior titles accounted for 26.2% (224/855). The proportion of trainees who had used and never used dental operative microscope (DOM) were 70.5% (603/855) and 29.5% (252/855), respectively. The blended teaching in microendodontics was universally approved by the trainees, which showed more superiority in the improvement of learning efficiency and interest, comprehension of knowledge as well as practical ability, etc., compared to the traditional offline teaching. For the current stomatology education, trainees were inclined to choose the blended teaching mode combining online theory curriculum and offline practice training, whereas 41.3% (353/855) and 39.6% (339/855) of trainees agreed that the teaching effectiveness was likely influenced by the condition and frequency of the offline training, respectively. Besides, significant differences were detected in the question about the factors affecting the blended teaching effectiveness of microendodontics between the trainees who had used and not used DOM (χ²=13.37, P=0.004). Conclusions: The application of online and offline blended teaching in microendodontics was affirmed to have some advantages, and it should be considered that the discrepancy in the level of expertise among trainees probably influenced the teaching effectiveness, which may promote the quality and effect of teaching, the spread and sharing of microendodontics, and provide experience and reference for the practice teaching of Operative Dentistry and Endodontics.

Experimental and theoretical investigation of the influence of post-curing on mixed mode fracture properties of 3d-printed polymer samples

This study explores the mechanical properties and fracture characteristics of additively manufactured acrylonitrile butadiene styrene specimens, focusing on the impact of raster angle and post-process heat treatment. To this end, a large number of tensile and semi-circular bending samples with three distinct raster angles of 0/90°, 22/ − 68°, and 45/ − 45° were prepared and exposed to four types of heat treatments with different temperature and pressure conditions. Simultaneously, theoretical models of maximum tangential stress (MTS) and generalized MTS (GMTS) were developed to estimate the onset of specimen fracture under mixed-mode in-plane loading conditions. Recognizing the non-linear behavior within the stress–strain curve of tensile test samples, particularly in the annealed samples, an effort was undertaken to transform the original ductile material into a virtual brittle material through the application of the equivalent material concept (EMC). This approach serves the dual purpose of bypassing intricate and tedious elastoplastic analysis, while concurrently enhancing the precision of the GMTS criterion. The experimental findings have revealed that while the annealing process has a minimal effect on the yield strength, it considerably enhances energy absorption capacity, increases fracture toughness, and reduces the anisotropy. Additionally, the combined EMC-GMTS criterion has demonstrated its capability to predict the failure of the additively manufactured parts with an acceptable level of accuracy.

Dissimilar joining of AZ31B and Ti–6Al–4V sheets in lap joint using cold metal transfer welding

Ti–6Al–4V and AZ31B alloy sheets were joined in lap joint configuration using cold metal transfer welding with a synergic power source. The torch angle was kept approximately 45° away from the top plate. Wire feed speeds (WFSs) have been varied from 3.0 m/min to 7.0 m/min. Cold metal transfer welding results in good deposition of weld metal at higher WFSs but at the cost of poor bonding and defects. Joints of the best qualities were fabricated at a WFS of 3.0 m/min and a welding speed of 0.6 m/min. The torch angle assisted in the proper deposition of AZ31B weld metal with a good bond between weld metal and Ti–6Al–4V base metal. Microstructural analysis confirms the joint interface integrity by revealing the absence of defects. Also, there is a significant variation among the grain morphology of weld region, transition zone and base metal. The presence of several oxides (MgO4, Al2O3, etc.) and intermetallics (Mg17Al12, Mg7Zn3, AlMg4Zn11, etc.) is indicated by metallurgical analyses. Tensile-shear tests revealed that the joints could sustain the maximum load of 1871 N. Fractography reveals the mixed mode of fracture containing majority brittle, and a ductile failure at a few locations. The unusual fracture at a few locations indicates the presence of oxides in these regions.

Characterization of reversed-phase liquid chromatographic columns containing positively charged functionality

To date, the most commonly used column characterization databases do not determine the relative positive charge associated with new generation RP columns, or they fail to successfully discriminate between RP columns of purportedly low level positive and neutral characters. This paper rectifies this in that it describes a convenient and robust chromatographic procedure for the assessment of the low levels of positive charge on a range of RP columns. The low degree of positive charge was determined by their electrostatic attraction towards the negatively charged 4-n-octylbenzene sulfonic acid (4-OBSA) relative to their retention of the hydrophobic marker toluene (Tol).The new parameter (α4-OBSA/Tol) was determined for 15 commercially available RP-LC columns. When this was combined with existing Tanaka parameters it was possible to guide the chromatographer towards similar columns as “backup / equivalent phases” or dissimilar columns for exploitation in method development strategies. It should be noted that under certain chromatographic conditions the retention mechanism(s) may be too complex to allow direct location of a “backup / equivalent” column(s).The α4-OBSA/Tol results indicate that even the new generation neutral alkyl phases may exhibit a small degree of positive charge at low buffer concentrations. Mobile phases containing low % MeCN were demonstrated to promote mixed mode (anionic exchange / hydrophobic) retention whereas at high % MeCN anionic exchange retention dominated.The measure of electrostatic repulsion between positively charged columns and positively charged bases was assessed by evaluating the relative retention of a range of bases and neutral analytes. The greatest electrostatic repulsion was observed with hydrophilic bases. While there was no correlation between the positive charge associated with the phases assessed by electrostatic attraction or repulsion, the columns could be broadly divided into three subsets (i.e., significant positive character, medium to low positive character and insignificant positive character).Finally, the results were used to highlight the usefulness of the column characterization database containing the new anionic exchange retention parameter (α4-OBSA/Tol) for the selection of an equivalent column possessing a low level of positive character in the analysis of a real-life biopharmaceutical application.