Dissimilar Substrates Research Articles

Characterization of tetA-like gene encoding for a major facilitator superfamily efflux pump in Streptococcus thermophilus.

Efflux pumps are membrane proteins involved in the active extrusion of a wide range of structurally dissimilar substrates from cells. A multidrug efflux pump named TetA belonging to the major facilitator superfamily (MFS) of transporters was identified in the Streptococcus thermophilus DSM 20617(T) genome. The tetA-like gene was found in the genomes of a number of S.thermophilus strains sequenced to date and in Streptococcus macedonicus ACA-DC 198, suggesting a possible horizontal gene transfer event between these two Streptococcus species, which are both adapted to the milk environment. Flow cytometry (single-cell) analysis revealed bistable TetA activity in the S.thermophilus population, and tetA-like gene over-expression resulted in a reduced susceptibility to ethidium bromide, tetracycline, and other toxic compounds even when the efflux pump was over-expressed in a strain naturally lacking tetA-like gene.

Bonding PDMS Microfluidic Devices to PMMA and Glass Substrate Using Pulsed UV Laser Technology

This study presents a new method for surface modification of polymeric materials by using pulsed UV laser welding technology. The bonding procedures including ablation treatment, Oxygen plasma treatment, adhesive layer bonding and cured by pulsed UV laser writing system was exhibited. The investigation of various parameters for UV laser writing system was performed and discussed by using water contact angle measurement. This technique has been successfully applied to bond dissimilar polymer substrates (polydimethylsiloxane (PDMS) to polymethylmethacrylate (PMMA)). The scanning electron microscopy (SEM) image reveals clearly that there was no clogging in the microchannel or deformation observed between PDMS and PMMA. The method was straightforward and the integrity of microfluidic features was successfully preserved after bonding.

Effect of base steels on mechanical behavior of adhesive joints with dissimilar steel substrates

The hybrid steel materials (e.g., advanced high strength steels combined with mild steels) have been increasingly applied in vehicle components to achieve the compromise among mechanical performance, lightweight and material cost. A significant issue related to the bonding of dissimilar steel materials is that the differences in substrate physical properties often lead to bond separation at strength levels far less than the bond strength established by the adhesive manufacturer for the joint with similar substrates. This research studied several important factors influencing the strengths of adhesive-bonded lap shear (LS) and coach-peel (CP) joints. Four types of steel substrates were used to fabricate the unbalanced adhesive joints (dissimilar steels or same steels with different thicknesses). The quasi-static tensile tests of the unbalanced joints were performed. A finite-element model was proposed to characterize the fracture behavior of joints. The effects of substrate properties such as bending stiffness and load-carrying capability of substrates on the joint strength (peak force) and fracture modes were investigated. It was observed that the interfacial fracture is prone to occur on the substrate with the relatively weak yield strength. A cohesive fracture can be produced when the load-carrying capabilities of the two substrates are similar. In order to optimize the load-carrying capability of the unbalanced joint, a design guideline was put forward.

Experimental analysis of bonded single lap joint with flexible adhesive

Flexible adhesives play an important role in various applications. The possibility of bonding dissimilar substrates has generated wide interest in flexible adhesives. However, most of the theoretical and experimental investigations have focused on rigid epoxy adhesives. The purpose of this work is to investigate the mechanical behavior of a flexible adhesive joint in the overlap region. Aluminum adherends were used for single lap joint made with an adhesive characterized by high flexibility and large strains. The specimen was tested in tension. Full-field displacements of the overlap region were measured by the Digital Image Correlation method. A large shear strain of the order of 48% was observed. Small transverse deflections of the adherends were estimated. Also, it was observed that the shear strain distribution in the adhesive layer decreases at the overlap ends, which is different from previously reported results in the literature.

Mode II fracture energy in the adhesive bonding of dissimilar substrates: carbon fibre composite to aluminium joints

The end-notched flexure (ENF) test calculates the value of mode II fracture energy in adhesive bonding between the substrates of same nature. Traditional methods of calculating fracture energy in the ENF test are not suitable in cases where the thickness of the adhesive is non-negligible compared with adherent thicknesses. To address this issue, a specific methodology for calculating mode II fracture energy has been proposed in this paper. To illustrate the applicability of the proposed method, the fracture energy was calculated by the ENF test for adhesive bonds between aluminium and a composite material, which considered two different types of adhesive (epoxy and polyurethane) and various surface treatments. The proposed calculation model provides higher values of fracture energy than those obtained from the simplified models that consider the adhesive thickness to be zero, supporting the conclusion that the calculation of mode II fracture energy for adhesives with non-negligible thickness relative to their adherents should be based on mathematical models, such as the method proposed in this paper, that incorporate the influence of this thickness.

Brain Structural Alterations in Obsessive-Compulsive Disorder Patients with Autogenous and Reactive Obsessions

Obsessive-compulsive disorder (OCD) is a clinically heterogeneous condition. Although structural brain alterations have been consistently reported in OCD, their interaction with particular clinical subtypes deserves further examination. Among other approaches, a two-group classification in patients with autogenous and reactive obsessions has been proposed. The purpose of the present study was to assess, by means of a voxel-based morphometry analysis, the putative brain structural correlates of this classification scheme in OCD patients. Ninety-five OCD patients and 95 healthy controls were recruited. Patients were divided into autogenous (n = 30) and reactive (n = 65) sub-groups. A structural magnetic resonance image was acquired for each participant and pre-processed with SPM8 software to obtain a volume-modulated gray matter map. Whole-brain and voxel-wise comparisons between the study groups were then performed. In comparison to the autogenous group, reactive patients showed larger gray matter volumes in the right Rolandic operculum. When compared to healthy controls, reactive patients showed larger volumes in the putamen (bilaterally), while autogenous patients showed a smaller left anterior temporal lobe. Also in comparison to healthy controls, the right middle temporal gyrus was smaller in both patient subgroups. Our results suggest that autogenous and reactive obsessions depend on partially dissimilar neural substrates. Our findings provide some neurobiological support for this classification scheme and contribute to unraveling the neurobiological basis of clinical heterogeneity in OCD.

Toughening mechanisms in multiphase nanocomposites

Our research is concerned with nanoreinforced structural adhesive bonds (SAB) for aerospace applications that contain dissimilar substrates and a theromoset epoxy adhesive with dispersed nanofillers. The interactions between these different phases results in unique fracture properties and mechanisms that dictate the toughness of the nanocomposite. In view of the varied length-scale, one cannot implement mere traditional approaches to evaluate the possible toughening mechanisms needed to ensure the integrity of the multiphase nanocomposite. Our current research is devoted to establishing the appropriate toughening mechanisms in multiphase nanocomposites by adopting traditional mechanisms such as crack-bridging, crack deflection, crack pinning and void nucleation, as well as investigating new nano-mechanisms such as fracture ridge creation. In this paper, the toughening mechanisms of carbon nanotube (CNT) reinforced polymer SABs are identified and their effects quantified in order to effectively estimate the fracture toughness of nanocomposite. Specific attention is devoted to examining the effect of dispersion of the nanofillers upon the strengthening mechanisms and interfacial debonding in nanocomposites, and the propensity of agglomerations-assisted crack initiation sites using atomistic based continuum modeling techniques.

Durability of adhesively-bonded single lap–shear joints in accelerated hygrothermal exposure for automotive applications

Structural adhesives offer unique advantages in joining mixed lightweight materials in vehicle applications. One of the concerns is the potential aging during the service life, especially under exposure of hygrothermal conditions. In this study, adhesively-bonded single lap–shear (SLS) joints with thin panel sheets were exposed under various designed accelerated constant and cyclic hygrothermal environments. The residual strengths of SLS joints with different adherends were compared to assess their durability. It has been observed that the electro-galvanized steel (EGS) joints have a significant loss of the bonding strength at 80°C constant exposure, and the aluminum alloy (AL) joints exhibit a relatively stable durability in the same scenario. Moreover, the aging of SLS joints with dissimilar substrates is determined by the weaker adhesive–substrate interface, which is the adhesive–zinc interface of the EGS/AL joint under hot-wet condition. The history effect of temperature-path on residual strengths of SLS joints was also investigated. It is deduced that the durability of SLS joints under long-term exposure may be estimated by some short-term hygrothermal aging with appropriate scenarios.

Mechanical characterization of adhesive joints with dissimilar substrates for marine applications

The simplicity and efficiency of the adhesive joints have increased more and more their use in many fields. In ship construction the need to join different materials, such as the bonding of the hull/deck, the sea chest, the portholes, the windshields, the panels of cabins, etc. leads to choosing increasingly the adhesive joints. In this work we have evaluated the effects of both SMP (Silyl Modified Polymer) based adhesives and sealants on single lap joints (SLJs) with dissimilar substrates. Three pairs of single lap joints were taken into account among dissimilar adherends: stainless steel (AISI 316) with PMMA (or Altuglas®) and monolithic composite laminates bonded with glass or PMMA. Before tensile testing some SLJ samples were subjected to a three-dimensional computed tomographic analysis to evaluate how the presence of possible defects in the adhesive layer affects the failure mode. A design of experiments was defined in order to quantify the effect of the considered factors and their correlation. The obtained maximum tensile stress values confirm the data provided by the manufacturer, approximately between 2 and 2.5MPa, showing generally cohesive fracture. Finally the considered SMP adhesives and sealants are well suited for the chosen different substrates, although special attention should be placed on the glass–GFRP joint as it is confirmed by statistical analysis.

Adhesion concepts in dentistry: tooth and material aspects

Adhesion concepts require understanding of substrate material properties, surface conditioning methods and chemical interactions, formation of interfaces/interphases between different material combinations, changes at interfaces with time, failure mechanisms and failure modes of the interfaces as a consequence of aging phenomenon. In dentistry, different methods are being used to test adhesion of resin-based materials to various biological and artificial substrates that require individual conditioning protocols. Variations among specimen configurations, material properties and chemical compositions of adhesives, test methods and test conditions all have effect on adhesion of similar or dissimilar substrates. Selection of the test, its proper execution, as well as the interpretation of the data through chemistry of the materials involved is of importance. Although adhesion to enamel is not a major concern today, effective adhesion to dentin requires several steps where failure in any of these consecutive events might result in failure of the whole system after long-term clinical use. Test methodologies used for assessment of mechanical behavior of materials in engineering may not directly apply to tooth–material combinations in dentistry. The objective of this review on adhesion in dentistry is to summarize current materials and methods used in dental materials testing and to summarize the current state-of-the-art in adhesion durability and quality with respect to the material type.

In situ ultra-high vacuum transmission electron microscopy studies of the transient oxidation stage of Cu and Cu alloy thin films

Because environmental stability is an essential property of most engineered materials, many theories exist to explain oxidation mechanisms. Yet, nearly all classical oxidation theories assume a uniform growing film, where structural changes were not considered because of the previous lack of experimental procedure to visualize this non-uniform growth in conditions that allowed for highly controlled surfaces and impurities. With the advent of vacuum technologies and advances in microcopy techniques, especially in situ, one can now see structural changes under controlled surface conditions. Here, we present a review of our systematic studies on the transient oxidation stages of a model metal system, Cu, and its alloys, Cu–Au and Cu–Ni, by in situ ultra-high vacuum transmission electron microscopy (UHV-TEM). The dependence of the oxidation behavior on the crystal orientation, oxygen pressure, temperature and alloying is attributed to the structures of the oxygen-chemisorbed layer, oxygen surface diffusion, surface energy and the interfacial strain energy. Heteroepitaxial concepts, developed to explain thin film formation on a dissimilar substrate material (e.g., Ge on Si), described well these initial oxidation stages.

New Method for Characterizing Interface Fracture between Dissimilar Materials

The interface fracture process of most layered or bonded structures is commonly under the control of mixed mode cracking where the interface shear and normal fracture components exist simultaneously when the hybrid joints are bonded with different adherend materials. In this work, a simple and novel method is proposed to realize and characterize the pure mode I interface fracture for the hybrid joints with dissimilar substrates. The theoretical and experimental results indicate that the present method may be considered as a standard test method for the characterization of hybrid joints with dissimilar materials.

Adhesive bonded single lap and over-lap joints of C/C, C/C-SiC composites and titanium alloy

Carbon-carbon (C/C), carbon-carbon-silicon carbide (C/C-SiC) composites and titanium alloy substrates were bonded in single lap and overlap joints with phenolic resin to study the differences in joint strength of two similar and dissimilar materials under shear load. The results indicate that the bonding strength of single lap joint of C/C, C/C-SiC is more than the other ceramic and titanium alloy, whereas Ti-Ti bonded over lap joints show remarkable improvement in similar and dissimilar substrates. Scanning electron microscope (SEM) describes the surface morphology and indicates the bonded zone fractured in the form of thin film which shows strong interaction in between two surfaces. Key words: C/C composite, C/C-SiC composite, titanium alloy, adhesive joints, bonding strength.

THEORETICAL ANALYSIS OF COEXISTING TETRAGONAL AND RHOMBOHEDRAL PHASE IN PB(ZR0.35TI0.65)O3 FILMS

Within the framework of Pertsev's thermodynamic theory, the equilibrium polarization states and the physical properties of single-domain Pb ( Zr 0.35 Ti 0.65) O 3 (PZT) thin films epitaxially grown on dissimilar cubic substrates are investigated. The "misfit strain-temperature" phase diagrams are obtained for the films. The presence of stability range of the rhombohedral phase is the characteristic feature of these phase diagrams, which separates the stability ranges of the tetragonal phase and the orthorhombic phase. The coexistence of the rhombohedral phase and the tetragonal phase in PZT film can be explained by Pertsev's theory with the gradient strain case with a suitable stress form.

Role of cleaning methods on bond quality of Ti coated glass/imidex system

Thin film materials are widely used in the fabrication of semiconductor microelectronic devices. In thin film deposition, cleanliness of substrate surface have become critically important as over 50% of yield losses in integrated circuit fabrication are caused by microcontamination [1]. There are many wafer cleaning techniques. The most successful approach for silicon wafer cleaning technique is RCA clean [2]. But for glass substrate it is still not known which procedure of cleaning is the best. This paper provides an understanding of the right way of glass wafer cleaning method, with a focus towards identifying good bond strength. Two wafer cleaning techniques have been used for cleaning glass substrates in the context of laser micro-joining of dissimilar substrates. First cleaning procedure involves two steps, first cleaning in acetone solution and then in DI water solution. After each step dried with N2. Second cleaning procedure involves four steps, first cleaning with 1% Alconox solution, second in DI water, third in acetone solution and finally in a methanol solution and dried with N2 after each step. Deposition of Ti thin film on top of these two types of substrate using DC magnetron sputtering method also showed better adhesion of Ti film on glass for the second type of cleaning method. Scanning electron microscopy (SEM) analyses of the lap shear tested failed surfaces for these two kinds of samples revealed strong bond for samples prepared by second cleaning method compared to first cleaning method. Characterization of these two sets of samples using X-ray photoelectron spectroscopy (XPS) has shown excellent contamination removal for the second cleaning method. This modification is believed to be due to reduction of carbon contamination.

Enhanced Coulombic efficiency in glucose-fed microbial fuel cells by reducing metabolite electron losses using dual-anode electrodes

Glucose-fed microbial fuel cells (MFCs) have displayed low Coulombic efficiency (CE); one reason for a low CE is metabolite generation, causing significant electron loss within MFC systems. In the present study, notable electron loss (15.83%) is observed in glucose-fed MFCs due to residual propionate, a glucose metabolite. In order to enhance the low CE caused by metabolite generation, a dual-anode MFC (DAMFC) is constructed, which are separately enriched by dissimilar substrates (glucose and propionate, respectively) to effectively utilize both glucose and propionate in one-anode chamber. In the DAMFC, propionate ceases to exist as a source of electron loss, and thus the CE increased from 33±6 to 59±4%.

Conformational Plasticity and Structure/Function Relationships in Cytochromes P450

The cytochrome P450s are a superfamily of enzymes that are found in all kingdoms of living organisms, and typically catalyze the oxidative addition of atomic oxygen to an unactivated C-C or C-H bond. Over 8000 nonredundant sequences of putative and confirmed P450 enzymes have been identified, but three-dimensional structures have been determined for only a small fraction of these. While all P450 enzymes for which structures have been determined share a common global fold, the flexibility and modularity of structure around the active site account for the ability of P450 enzymes to accommodate a vast number of structurally dissimilar substrates and support a wide range of selective oxidations. In this review, known P450 structures are compared, and some structural criteria for prediction of substrate selectivity and reaction type are suggested. The importance of dynamic processes such as redox-dependent and effector-induced conformational changes in determining catalytic competence and regio- and stereoselectivity is discussed, and noncrystallographic methods for characterizing P450 structures and dynamics, in particular, mass spectrometry and nuclear magnetic resonance spectroscopy are reviewed.

Identification and analysis of residues contained on β → α loops of the dual‐substrate (βα)8 phosphoribosyl isomerase A specific for its phosphoribosyl anthranilate isomerase activity

A good model to experimentally explore evolutionary hypothesis related to enzyme function is the ancient-like dual-substrate (beta alpha)(8) phosphoribosyl isomerase A (PriA), which takes part in both histidine and tryptophan biosynthesis in Streptomyces coelicolor and related organisms. In this study, we determined the Michaelis-Menten enzyme kinetics for both isomerase activities in wild-type PriA from S. coelicolor and in selected single-residue monofunctional mutants, identified after Escherichia coli in vivo complementation experiments. Structural and functional analyses of a hitherto unnoticed residue contained on the functionally important beta --> alpha loop 5, namely, Arg(139), which was postulated on structural grounds to be important for the dual-substrate specificity of PriA, is presented for the first time. Indeed, enzyme kinetics analyses done on the mutant variants PriA_Ser(81)Thr and PriA_Arg(139)Asn showed that these residues, which are contained on beta --> alpha loops and in close proximity to the N-terminal phosphate-binding site, are essential solely for the phosphoribosyl anthranilate isomerase activity of PriA. Moreover, analysis of the X-ray crystallographic structure of PriA_Arg(139)Asn elucidated at 1.95 A herein strongly implicates the occurrence of conformational changes in this beta --> alpha loop as a major structural feature related to the evolution of the dual-substrate specificity of PriA. It is suggested that PriA has evolved by tuning a fine energetic balance that allows the sufficient degree of structural flexibility needed for accommodating two topologically dissimilar substrates--within a bifunctional and thus highly constrained active site--without compromising its structural stability.

Effect of external electric field on phase transitions of ferroelectric thin films

A nonlinear thermodynamic theory is used to investigate the effect of external electric field on the phase transitions of Pb(Zr0.3Ti0.7)O3(PZT) thin films epitaxially grown on dissimilar cubic substrates. The "misfit strain-external electric filed" phase diagram and the relationship between electirc filed and polarization are constructed for PZT thin films. The external electric field can transform the monoclinic r phase into the c phase,when its value reaches 186 kV/cm for PZT thin film grown on the SrTiO3 substrate. On the other hand,the domain switching of PZT thin film is investigated experimentally by scanning probe microscopy(SPM) via varying the applied polarizing electric field. The piezo-phase images reveal that most ferroelectric domains are clearly detectable. In the r phase,the domains can be reversed into the direction of polarization of the c phase,when the applied electric field increases to 200 kV/cm,which is close to the theoretical value (186 kV/cm).

Adhesion to tooth structure: A critical review of “micro” bond strength test methods

The objective of this paper is to critically review the literature regarding the mechanics, geometry, load application and other testing parameters of “micro” shear and tensile adhesion tests, and to outline their advantages and limitations. The testing of multiple specimens from a single tooth conserves teeth and allows research designs not possible using conventional ‘macro’ methods. Specimen fabrication, gripping and load application methods, in addition to material properties of the various components comprising the resin–tooth adhesive bond, will influence the stress distribution and consequently, the nominal bond strength and failure mode. These issues must be understood; as should the limitations inherent to strength-based testing of a complicated adhesive bond joining dissimilar substrates, for proper test selection, conduct and interpretation. Finite element analysis and comprehensive reporting of test conduct and results will further our efforts towards a standardization of test procedures. For the foreseeable future, both “micro” and “macro” bond strength tests will, as well as various morphological and spectroscopic investigative techniques, continue to be important tools for improving resin–tooth adhesion to increase the service life of dental resin-based composite restorations.