The relationship between electropermeabilization and cell cycle and cell size of Saccharomyces cerevisiae

Yeast cells (Sacchromyces cerevisiae) in 0.9% NaCl solution containing phloxine B (dye) were treated by an application of a rectangular electric pulse. We input microscopic images of the yeast suspensions after the application into a computer, and measured whether each cell dyes or not, the phase in the cell cycle, and each cell size, using the software we had developed. After those measurements, we discussed the relationship between the yield of electropermeabilization (the ratio of dyed cells to the total cell number) and the phase in the cell cycle, and cell size. From the results, it was found that the yeast cells from S-phase to M-phase (S-M phase) in the cell cycle tend to be more permeated than G1-phase yeast cells, and in both phases the yield decreases with the increase in cell size.     

SERS microscopic imaging as novel tool for assessing viability and enumerating yeast cells at various stages of cell cycle in lag,log, exponential and stationary phases of growth in culture

Surface enhanced Raman scattering (SERS) microscopic imaging was employed to enumerate the yeast cells in culture. We found this imaging method as an efficient tool for easily differentiating and quantitatively enumerating yeast cell at different stages of cell-division cycle (G1, S, G2 and M phase) at various stages of growth phases namely lag, log, exponential and stationary phases in culture. Apart from enumerating the cells at different stages of cell cycle under lag, log, exponential and stationary phases, it was possible using SERS microscopy to differentiate the live cells from dead ones. The dead cells were SERS inactive and gave enhanced autofluorescence compared with the live cells, which were SERS active. The results from the present investigation suggest that SERS microscopic imaging, using silver nanoparticles (AgNPs) as a sensitive tool to enumerate the yeast cells in culture.     

Hygroscopic swelling and shrinkage of latewood cell wall micropillars reveal ultrastructural anisotropy

We document the hygroscopic swelling and shrinkage of the central and the thickest secondary cell wall layer of wood (named S2) in response to changes in environmental humidity using synchrotron radiation-based phase contrast X-ray tomographic nanoscopy. The S2 layer is a natural fibre-reinforced nano-composite polymer and is strongly reactive to water. Using focused ion beam, micropillars with a cross section of few micrometres are fabricated from the S2 layer of the latewood cell walls of Norway spruce softwood. The thin neighbouring cell wall layers are removed to prevent hindering or restraining of moisture-induced deformation during swelling or shrinkage. The proposed experiment intended to get further insights into the microscopic origin of the anisotropic hygro-expansion of wood. It is found that the swelling/shrinkage strains are highly anisotropic in the transverse plane of the cell wall, larger in the normal than in the direction parallel to the cell wall''s thickness. This ultrastructural anisotropy may be due to the concentric lamellation of the cellulose microfibrils as the role of the cellulose microfibril angle in the transverse swelling anisotropy is negligible. The volumetric swelling of the cell wall material is found to be substantially larger than the one of wood tissues within the growth ring and wood samples made of several growth rings. The hierarchical configuration in wood optimally increases its dimensional stability in response to a humid environment with higher scales of complexity.     

用核糖体工程技术开拓海洋微生物药用资源的研究

利用核糖体工程技术对海洋中无活性的放线菌B3054进行诱导,获得了突变菌株B3054／M,其形态、菌丝体颜色都与母体菌株有显著的差异,发酵液经HPLC分析发现,代谢产物有明显的变化,特别是突变株产生了能抑制小鼠乳腺癌tsFT210细胞周期活性的活性代谢产物。这是首次利用核糖体工程技术诱变得到的具有细胞周期抑制活性的海洋放线菌菌株,这一研究结果表明,利用该技术对自然界的无活性微生物进行诱导来拓展微生物药用资源是可行的。     

Tuning Susceptibility via Misfit Strain in Relaxed Morphotropic Phase Boundary PbZr1‐xTixO3 Epitaxial Thin Films

Epitaxial strain is a powerful tool to manipulate the properties of ferroelectric materials. But despite extensive work in this regard, few studies have explored the effect of epitaxial strain on PbZr_0.52Ti_0.48O₃. Here we explore how epitaxial strain impacts the structure and properties of 75 nm thick films of the morphotropic phase boundary composition. Single‐phase, fully epitaxial films are found to possess “relaxed” or nearly “relaxed” structures despite growth on a range of substrates. Subsequent studies of the dielectric and ferroelectric properties reveal films with low leakage currents facilitating the measurement of low‐loss hysteresis loops down to measurement frequencies of 30 mHz and dielectric response at background dc bias fields as large as 850 kV/cm. Despite a seeming insensitivity of the crystal structure to the epitaxial strain, the polarization and switching characteristics are found to vary with substrate. The elastic constraint from the substrate produces residual strains that dramatically alter the electric‐field response including quenching domain wall contributions to the dielectric permittivity and suppressing field‐induced structural reorientation. These results demonstrate that substrate mediated epitaxial strain of PbZr_0.52Ti_0.48O₃ is more complex than in conventional ferroelectrics with discretely defined phases, yet can have a marked effect on the material and its responses.     

A low-cycle fatigue life prediction model of ultrafine-grained metals

A (high strain) low‐cycle fatigue (LCF) life prediction model of ultrafine‐grained (UFG) metals has been proposed. The microstructure of a UFG metal is treated as a two‐phase ‘composite’ consisting of the ‘soft’ matrix (all the grain interiors) and the ‘hard’ reinforcement (all the grain boundaries). The dislocation strengthening of the grain interiors is considered as the major strengthening mechanism in the case of UFG metals. The proposed model is based upon the assumption that there is a fatigue‐damaged zone ahead of the crack tip within which the actual degradation of the UFG metal takes place. In high‐strain LCF conditions, the fatigue‐damaged zone is described as the region in which the local cyclic stress level approaches the ultimate tensile strength of the UFG metal, with the plastic strain localization caused by a dislocation sliding‐off process within it. The fatigue crack growth rate is directly correlated to the range of the crack‐tip opening displacement. The empirical Coffin–Manson and Basquin relationships are derived theoretically and compared with experimental fatigue data obtained on UFG copper (99.99%) at room temperature under both strain and stress control. Good agreement is found between the model and the experimental data. It is remarkable that, although the model is essentially formulated for high strains (LCF), it is also found to be applicable at low strains in the high‐cycle fatigue (HCF) regime.     

Anisotropic Aerogels for Studying Superfluid 3He

It may be possible to stabilize new superfluid phases of ³He with anisotropic silica aerogels. We discuss two methods that introduce anisotropy in the aerogel on length scales relevant to superfluid ³He. First, anisotropy can be induced with uniaxial strain. A second method generates anisotropy during the growth and drying stages. We have grown cylindrical ∼98% aerogels with anisotropy indicated by preferential radial shrinkage after supercritical drying and find that this shrinkage correlates with small angle x-ray scattering (SAXS). The growth-induced anisotropy was found to be ∼90° out of phase relative to that induced by strain. This has implications for the possible stabilization of superfluid phases with specific symmetry.     

On the fracture toughness and stable crack growth in shape memory alloy actuators in the presence of transformation-induced plasticity

The effect of transformation-induced plasticity (TRIP) on the fracture response of polycrystalline shape memory alloys is analyzed in the prototype infinite center-cracked plate subjected to thermal cycling under constant mechanical loading in plain strain. Finite element calculations are carried out to determine the mechanical fields and the crack-tip energy release rate using the virtual crack closure technique. Similar to phase transformation, TRIP is found to affect both the driving force for crack growth and the crack growth kinetics by promoting crack advance when occurring in a fan in front of the crack tip and providing a “shielding” effect when occurring behind that fan. Accumulation of TRIP strains over the cycles results in higher energy release rates from one cycle to another and may result in crack growth if the crack-tip energy release rate reaches a material “specific” critical value after a sufficient number of cycles. During crack advance, the shielding effect of the TRIP strains left in the wake of the growing crack dominates and therefore TRIP is found to both promote the initiation of crack growth and extend the stable crack growth regime.     

Role of cell cycle on the cellular uptake and dilution of nanoparticles in a cell population

Nanoparticles are considered a primary vehicle for targeted therapies because they can pass biological barriers and enter and distribute within cells by energy-dependent pathways. So far, most studies have shown that nanoparticle properties, such as size and surface, can influence how cells internalize nanoparticles. Here, we show that uptake of nanoparticles by cells is also influenced by their cell cycle phase. Although cells in different phases of the cell cycle were found to internalize nanoparticles at similar rates, after 24 h the concentration of nanoparticles in the cells could be ranked according to the different phases: G2/M > S > G0/G1. Nanoparticles that are internalized by cells are not exported from cells but are split between daughter cells when the parent cell divides. Our results suggest that future studies on nanoparticle uptake should consider the cell cycle, because, in a cell population, the dose of internalized nanoparticles in each cell varies as the cell advances through the cell cycle.     

Microstructural evolution of a Ti-4.5Al-3Mo-1V alloy during hot working

The study investigated the variation of microstructure of a Ti-4.5AL-3Mo-1V alloy during hot compressing in α + β phase field. By scanning electron microscopy (SEM) and transmission electron microscopy (TEM), we systematically examined the influences of hot working parameters on the microstructural features including of the morphology of α grain, volume fraction of α phase and dynamic recrystallization (DRX). The experimental evidence showed that both α and β phases underwent DRX under the experimental conditions. Moreover, the recrystallization degree of α phase was more sufficient than that of β phase. The DRX was accelerated with increase of deformation temperature and decrease of strain rate. It was also noted that a certain degree of the (α → β) phase transformation occurred concurrently with the mechanical deformation. In accordance with the microstructural evolution, flow curves of the alloy were characterized by a linear increase until regular oscillations at high strain rates or single peak at low strain rates and softening was followed.     

A method of calculating the mechanical properties of nanoscopic plant cell wall components from tissue properties

Biological tissues are made from nano-composite materials and given the recent interest in manufacturing synthetic nano-composites an analysis of natural nano-composites seems a worthwhile exercise. There is also potential for extracting natural nano-fibres and using them as reinforcements in other materials. In this paper a hierarchical mechanical model is formulated to describe potato tuber tissue and the model is used to back calculate the properties of cell wall nano-fibres. The model contains two structural levels, the cell structure and the cell wall structure. Material properties are assigned at the level of cell wall microfibrils (nano-composite fibres). Force deflection data from the compression of cubes of potato tissue were fed into the model and the properties of the cell wall microfibrils predicted. The modulus was found to vary with strain, but had a maximum value of 130 GPa, which is close to predictions from theoretical chemistry for the stiffness of cellulose microfibrils. At 8% wall strain (the value at which failures were suspected to begin), the stress was predicted to be 7.5 GPa which is also close to theoretical chemistry predictions for the strength of cellulose microfibrils. The large strains and decreasing stiffness indicate the influence of polymers other than cellulose.     

Evaluation of the metal uptake of several algae strains in a multicomponent matrix utilizing inductively coupled plasma emission spectrometry

Three freshwater heat-killed, lyophilized blue-green algae strains have been characterized as to their ability to accumulate heavy metals with a focus on the utilization of these algae as an analytical preconcentration technique. This study examines the metal uptake in several multicomponent mixtures by using inductively coupled plasma optical emission spectrometry (ICP-OES). Six milligrams of a pure strain of algae was added to 20-mL aliquots of buffered (pH 5.5-6.5) multielement solutions containing 0.1, 0.5, 1.0, 2.0, and 4.0 mg/L of K, Mg, Ca, Fe, Sr, Co, Cu, Mn, Ni, V, Zn, As, Cd, Mo, Pb, and Se. All three algae strains exhibit relatively high adsorption affinities for Fe, Pb, and Cu, with uptake between 70 and 98% at the 4 ppm concentration level. Biosorption occurs for essentially every element with the relative affinities decreasing in the order Pb greater than Fe greater than Cu greater than Cd greater than Zn greater than Mn greater than Mo greater than Sr greater than Ni greater than V greater than Se greater than As greater than Co for Chlorella pyrenoidosa at the 4 mg/L concentration level. Although some minor differences were seen, the other algae strains (Stichococcus bacillaris and Chlamydomonas reinharti) displayed similar adsorption behavior over the concentration range studied, indicating similar cell wall binding sites. Langmuirian isotherms exhibited a minimum of two slopes over the concentration range of 0.1-4.0 mg/L, indicating the probable existence of at least two adsorption mechanisms.     

Studying the effect of alginate overproduction on Pseudomonas aeruginosa biofilm by atomic force microscopy

Pseudomonas aeruginosa is the most important pathogen in cystic fibrosis patients and forms biofilms in the lung. P. aeruginosa strains isolated from the lungs of the patients have a mucoid phenotype overproducing alginate. The phenotype forms highly structured biofilms which are more resistant to antibiotics than biofilms formed by its nonmucoid phenotype. Conversion to the alginate-overproducing phenotype occurs through a mutation in rpoN gene in the strains. The biofilms formed by the alginate-overproducing phenotype are highly sticky, but their stickiness has not been measured. Herein, the stickiness of biofilms formed by the rpoN mutant was measured by atomic force microscopy (AFM). Confocal laser scanning microscopy showed that the biofilms formed by the slowly-growing rpoN mutant were more structured than those formed by the wild-type strain. AFM analysis indicated that the biofilms formed by the rpoN mutant were stickier than those formed by the wild type strain during the attachment and establishment stages, but the difference in stickiness was greatly reduced during the maturation stage possibly due to the cytosolic contents released from dead cells in the biofilms formed by the wild type. These results suggest that the alginate overproduction greatly affects the physical properties (topography and stickiness) of P. aeruginosa biofilms as well as the physiological properties (cell death and growth) of the bacterial cells inside the biofilms.     

Determination by neutron diffraction of effect of plasticity on crack tip strains in a metal matrix composite

Abstract

Neutron strain scanning has been used to determine residual and applied stresses along the plane of a fatigue crack in a metal matrix composite. The specimens were studied in two conditions: one was as heat treated, and the other was plastically deformed in tension before fatigue cracking. Neutron diffraction was used to measure the three principal strains as a function of position along the crack growth direction, ahead of and in the wake of the crack, and these measurements were used to calculate the stress variation along the crack line. An Eshelby based model was used to separate the individual components of the stress. It was found that the thermal misfit stress between matrix and reinforcement was changed significantly by the plastic deformation and was effectively reduced to near zero in both phases. This changes the crack tip strains in the material, decreasing the strains in the matrix and increasing those in the reinforcement. Possible implications of this for fatigue crack propagation are discussed.     

Crystal Growth and Melting of Nuclear-Ordered Solid 3He

We measured crystal growth and melting rate of nuclear-ordered solid ³ He in a rectangular sample cell. The melting rate was much faster than the growth rate at all temperatures in the low field phase (U2D2) and strongly depended on temperature. The melting occurred on a rough surface and the dissipation mechanism of the melting was compared with the surface magnon scattering mechanism. The crystal growth rate did not depend on temperature and was compared with the spiral growth model associated with screw-dislocations. We found that a large chemical potential difference started to develop when the crystal grew large enough so that the sample became almost single domain at the upper part of the sample cell. We attributed this saturation to the pinning of the screw dislocation on the sample wall. This chemical potential difference decreased rapidly when the crystal was in the high field phase and the crystal grew as it did before the saturation. The crystal continued to grow even after the crystal returned to the U2D2 phase from the high field phase.     

Influence of naphthalene biodegradation on the adhesion of Pseudomonas putida NCIB 9816-4 to a naphthalene-contaminated soil

In an earlier study, Pseudomonas putida NCIB 9816-4, which was one of the most studied naphthalene-degrading bacteria, showed the preferred adhesion to the naphthalene-contaminated soil when it was in the exponential growth phase. The adhesion was found to take place through a hydrophobic interaction. We postulated that the surface hydrophobicity of P. putida NCIB 9816-4 in the exponential growth phase might be increased during the uptake of naphthalene, which caused the preferred adhesion to the naphthalene-contaminated soil. To verify this postulate, a plasmid-cured strain of P. putida NCIB 9816-4 was obtained in this study and compared with the wild-type for adhesion to the naphthalene-contaminated soil. Only the wild-type in the exponential growth phase showed increased adhesion to naphthalene-contaminated soil. The water contact angles of the two strains were measured in the presence and in the absence of naphthalene as indices of surface hydrophobicity. The water contact angle of the wild-type increased in the presence of naphthalene, whereas that of the cured strain did not change. We conclude that the uptake of naphthalene during naphthalene biodegradation in the exponential growth phase of P. putida NCIB 9816-4 made the cell surface more hydrophobic, resulting in increased adhesion to naphthalene-contaminated soil.     

The role of microstructural morphology on creep properties of a [0 0 1] oriented nickel‐base single crystal superalloy

The experimentally observed microstructure of nickel‐base single crystal alloy consists of a large volume of cuboidal γ′ precipitates coherently embedded in the γ matrix. In calculation, a representative volume element is usually used to represent the whole structures due to the regular γ/γ′ topological structures. Here, three experimentally found microstructures have been extracted to generate the representative volume elements. One is constituted by one cuboidal γ′ phase surrounded by γ phase. The other two consisted of two cuboidal γ′ phases and one rectangle γ′ phase with different arrangement of the two γ′ phases. The misfit stress is taken into consideration by different thermal expansion coefficients of the two phases. The influences of different microstructures on the macro‐creep strain evolution, rafting and stress distributions are discussed.     

Steady ratcheting strains accumulation in varying temperature fatigue tests of PMMA

The evolutions of ratcheting strains of polymethyl methacrylate (PMMA) at different temperatures and stress levels were experimentally investigated. A steady ratcheting strain growth region with a constant rate was observed in all specimens, which occupied significant part of total fatigue failure life. Experimental results also showed that the steady ratcheting growth rate varied with applied temperatures and loading. In this paper, theory of thermally activated process for glassy polymers was used to describe the plastic deformations during the cycle. Based on the correlations between ratcheting strains per cycle and hysteresis loop energy, a new ratcheting strains accumulative model for polymer materials was developed, which quantificationally elucidated the effects of temperature, loading frequency, mean stress and stress amplitude on the accumulative rate of ratcheting strains. Comparing the predications from the proposed model with experimental ratcheting strain data of PMMA, it was found that the model could describe the steady ratcheting strain accumulative behaviors under arbitrary temperatures and loading conditions exactly.     

X-ray high pressure study of polyvinylidene fluoride

An X-ray high pressure study at room temperature of both phase I and phase II crystal structures of polyvinylidene fluoride has been carried out. At room temperature both phases are stable up to pressures greater than 14 kbar. The variation of lattice compressive strains with pressure could be fitted to the Tait equation with little scatter and the variation of the unit cell parameters with pressure computed. The bulk lattice compressibilities of both phase I and phase II was found to be considerably less than that of polyethylene with the lowest compressibility being found for the phase I structure. The linear lattice compressibilities are extremely anisotropic with the lowest compressibility being in the chain direction as expected. However, at the highest pressures, for the case of phase II it was observed that this anisotropy was greatly reduced. Applications of these data to the unique piezo-electric activity of PVF₂ are pointed out.     

Multi-scale study on the heterogeneous deformation behavior in duplex stainless steel

The heterogeneous deformation behavior of austenite and ferrite in the 2205 duplex stainless steel was subjected to multiscale analysis based on the in situ synchrotron-based high energy X-ray diffraction,microscopic digital image correlation,electron backscatter diffraction,and transmission electron microscopy.It is found that the heterogeneous deformation triggers from the yielding of austenite.During this deformation stage,austenite experiences greater strain in the area near the phase boundaries because of the impeded function of the phase boundaries to dislocations.Owing to the relatively small difference in hardness between the constituent phases,the strain in austenite grains extends into the adjacent ferrite grains when entering into the ferrite yielding stage.In addition,the strain distribution of the austenite grains is more homogeneous than that of the ferrite grains because of the lower stacking fault energy of austenite,which results in a planar slip,and higher stacking fault energy in case of ferrite,causing cross slip.The interaction between austenite and ferrite becomes considerably obvious when the strain further increases after both constituent phases yielding because of the back stress and forward stress in austenite and ferrite,respectively,which are generated by the pile-up of the geometrically necessary dislocations.