Measurement of adhesion energies and Young's modulus in thin polymer films using a novel axi-symmetric peel test geometry

We present a novel method of probing adhesion energies of solids, particularly polymers. This method uses the axi-symmetric deformation of a thin spincast polymer membrane brought into contact with a flat substrate to probe the work of adhesion. The use of a thin membrane minimizes uncertainty in the radius of contact, while the use of spincast films provides very smooth surfaces by means of a very simple method. The experimental profile of the deformed membrane shows good agreement with the expected logarithmic profile. The experimental setup enables the measurement of Young's modulus and the solid-solid work of adhesion for thin films. The value obtained for Young's modulus of polystyrene (PS) was found to be in agreement with other conventional measurement techniques. In addition, measurement of the work of adhesion at the PS/silicon oxide interface was possible. The apparatus is well suited to studying the dependence of Young's modulus, work of adhesion and fracture energy on membrane thickness, temperature, pulling rate, and ageing of the interface, and can readily be modified to study biologically relevant samples.     

Molecular Dynamics Study of Effects of Si-Doping Upon Structure and Mechanical Properties of Carbon Nanotube

In this paper, a Si-doped single-walled carbon nanotube (SWCNT) (7,7) and several perfect armchair SWCNTs are investigated using the classical molecular dynamics simulations method. The inter-atomic short-range interaction is represented by empirical Tersoff bond order potential. The computational results show that the axial Young's modulus of the perfect SWCNTs are in the range of 1.099 ± 0.005 TPa, which is in good agreement with the existing experimental results. From our simulation, the Si-doping decreases the Young's modulus of SWCNT, and with the increased strain levels, the effect of Si-doped layer in enhancing the local stress level increases. The Young's modulus of armchair SWCNTs are weakly affected by tube radius.     

Search for CP violation in the decays D(0)→K(S)(0)P(0)

We have searched for CP violation in the decays D(0)→K(S)(0)P(0) where P(0) denotes a neutral pseudoscalar meson that is either a π(0), η, or η' using KEKB asymmetric-energy e(+)e(-) collision data corresponding to an integrated luminosity of 791 fb(-1) collected with the Belle detector. No evidence of significant CP violation is observed. We report the most precise CP asymmetry measurement in the decay D(0)→K(S)(0)π(0) to date: A(CP)(D(0)→K(S)(0)π(0))=(-0.28±0.19±0.10)%. We also report the first measurements of CP asymmetries in the decays D(0)→K(S)(0)η and D(0)→K(S)(0)η': A(CP)(D(0)→K(S)(0)η)=(+0.54±0.51±0.16)% and A(CP)(D(0)→K(S)(0)η')=(+0.98±0.67±0.14)%, respectively.     

Observation of D+ → K(+)η(') and search for CP violation in D+ → π(+)η(') decays

We report the first observation of the doubly Cabibbo-suppressed decays D(+)→K(+)η((')) using a 791 fb(-1) data sample collected with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. The ratio of the branching fractions of doubly Cabibbo-suppressed relative to singly Cabibbo-suppressed D(+)→π(+)η((')) decays are B(D(+)→K(+)η)/B(D(+)→π(+)η)=(3.06±0.43±0.14)% and B(D(+)→K(+)η')/B(D(+)→π(+)η')=(3.77±0.39±0.10)%. From these, we find that the relative final-state phase difference between the tree and annihilation amplitudes in D(+) decays, δ(TA), is (72±9)° or (288±9)°. We also report the most precise measurements of CP asymmetries to date: A(CP)(D(+)→π(+)η)=(+1.74±1.13±0.19)% and A(CP)(D(+)→π(+)η')=(-0.12±1.12±0.17)%.     

Effect of a rippling mode on resonances of carbon nanotubes

A recent study determined the Young's modulus of carbon nanotubes by measuring resonance frequency and using the modulus-frequency relation resulting from the linear vibration theory. It leads to the report that the Young's modulus decreases sharply, from about 1 to 0.1 TPa with the diameter D increasing from 8 to 40 nanometers, and the investigators attributed this decrease to the emergence of an unusual bending mode during the measurement that corresponds to rippling on the inner arc of the bent nanotubes. The nonlinear analysis presented in this paper that captures the rippling mode suggests that the effective Young's modulus can indeed decrease substantially with increasing diameter, and that the results from the classical linear theory may be invalid in such measurements.     

Barrier fluctuations and stochastic resonance in membrane transport

The role of barrier fluctuations in membrane enzymatic processes, in particular in the active transport of ions through cell membranes, is examined. For enzymes embedded in the cell membrane the role of the barrier height (activation energy) is played by the membrane electric potential. This barrier height can be modulated either by internal fluctuations or by external electrical fields, either random or periodic. Existing experimental data on active transport of Na(+) and Rb(+) in human erythrocytes (catalyzed by Na(+)-K(+)-ATPase) can be interpreted as evidence of stochastic resonance between the external ac field and the fluctuations of the membrane potential. The obtained results suggest that the significant part of these fluctuations is supplied by the stimulated action of neighbor voltage-gated ionic channels. This supports the idea that intrinsic noise plays a constructive role in one of most important and most frequent biophysical processs, viz. ion transmission through cell membranes. Means of further experimental verification of this conjecture are proposed. (c) 1998 American Institute of Physics.     

Search for CP violation in D± meson decays to ϕπ±

We search for CP violation in Cabibbo-suppressed charged D meson decays by measuring the difference between the CP-violating asymmetries for the Cabibbo-suppressed decays D(±)→K(+)K(-)π(±) and the Cabibbo-favored decays D(s)(±)→K(+)K(-)π(±) in the K(+)K(-) mass region of the ? resonance. Using 955 fb(-1) of data collected with the Belle detector, we obtain A(CP)(D+→?π+)=(+0.51±0.28±0.05)%. The measurement improves the sensitivity of previous searches by more than a factor of 5. We find no evidence for direct CP violation.     

First observation of the decays B(0) → D(+)K(-)π(+)π(-) and B(-) → D(0)K(-)π(+)π(-)

First observations of the Cabibbo-suppressed decays B(0) → D(+)K(-)π(+)π(-) and B(-) → D(0)K(-)π(+)π(-) are reported using 35 pb(-1) of data collected with the LHCb detector. Their branching fractions are measured with respect to the corresponding Cabibbo-favored decays, from which we obtain B(B(0) → D(+)K(-)π(+)π(-))/B(B(0) → D(+)π(-)π(+)π(-))=(5.9±1.1±0.5)×10(-2) and B(B(-) → D(0)K(-)π(+)π(-))/B(B(-) → D(0)π(-)π(+)π(-))=(9.4±1.3±0.9)×10(-2), where the uncertainties are statistical and systematic, respectively. The B(-) → D(0)K(-)π(+)π(-) decay is particularly interesting, as it can be used in a similar way to B(-) → D(0)K(-) to measure the Cabibbo-Kobayashi-Maskawa phase γ.     

Determination of f(s)/f(d) for 7 TeV pp collisions and measurement of the B0→D-K+ branching fraction

The relative abundance of the three decay modes B(0)→D(-)K(+), B(0)→D(-)π(+), and B(s)(0)→D(s)(-)π(+) produced in 7 TeV pp collisions at the LHC is determined from data corresponding to an integrated luminosity of 35 pb(-1). The branching fraction of B(0)→D(-)K(+) is found to be B(B(0)→D(-)K(+)) = (2.01 ± 0.18(stat) ± 0.14(syst)) × 10(-4). The ratio of fragmentation fractions f(s)/f(d) is determined through the relative abundance of B(s)(0)→D(s)(-)π(+) to B(0)→D(-)K(+) and B(0)→D(-)π(+), leading to f(s)/f(d) = 0.253 ± 0.017 ± 0.017 ± 0.020, where the uncertainties are statistical, systematic, and theoretical, respectively.     

氢对纯镍弹性模量的影响

用静电激发调频检测法对比测量了纯镍试样电解充氢和人为部分应力松弛后在室温时效过程中杨氏模量随时间的变化。结果表明:在人为部分应力松弛后的时效过程中,杨氏模量逐渐升高,其稳态值比初始值升高0.87％;而在充氢后的时效过程中,氢不断地从试样中逸出,同时杨氏模量也不断地降低,其稳态值比充氢后的瞬时值低2.87％;即,氢原子能明显地增高纯镍的弹性模量。 关键词：     

Passive or active fluctuations in membranes containing proteins

We have experimentally investigated the effect of a transmembrane protein, the Ca2+-ATPase, on shape fluctuations of giant vesicles. By using the micropipette method, we have measured a substantial renormalization of the bending modulus due to the presence of proteins in the membrane. Moreover, we have produced the first quantitative measurement of the active force dipole associated with the amplification of the fluctuations when the proteins are activated by adenosine 5'-triphosphate (ATP).     

Connection between biomechanics and cytoskeleton structure of lymphocyte and Jurkat cells: An AFM study

The mechanical properties of cells are important for many cellular processes. Here, atomic force microscopy (AFM) and laser scanning confocal microscopy (LSCM) were carried out to characterize lymphocyte and Jurkat cells. The average elastic modulus of lymphocyte is 1.24 ± 0.09 kPa, which is almost twofold higher than that of Jurkat cell (0.51 ± 0.06 kPa). LSCM images of sub-membrane cytoskeleton showed a significant difference in the organization of their F-actin structures. Lymphocyte cells had more and thicker actin bundles than that of Jurkat cells. Lymphocyte and Jurkat cells after adding the F-actin destabilizing agent Cytochalasin-B (Cyt-B) were also investigated by AFM. A decrease in the elastic modulus of lymphocyte from a value of 1.24 ± 0.09 kPa down to 0.34 ± 0.04 kPa for 24 h was observed, and that of Jurkat cell decreased from 0.51 ± 0.06 kPa to 0.23 ± 0.04 kPa. We really believe that this technology will be used for cancer detection and opens a door to study the biophysical properties of signaling domains extending from the cell surface to deeper parts of the cell.     

Effect of spraying power on the microstructure and mechanical properties of supersonic plasma-sprayed Ni-based alloy coatings

The aim of this paper was to investigate the microstructure and mechanical properties of the supersonic plasma-sprayed Ni-Cr-B-Si-C coatings prepared at different spraying powers. The microstructure, phase composition, porosity, Young's modulus, micro-hardness, and residual stresses of the coatings were investigated and determined. The variations of the porosity, Young's modulus and micro-hardness of the coatings were evaluated by using statistical method. Results showed that the variations of porosity, Young's modulus and micro-hardness of the coatings followed the Weibull distributions. With increasing the porosity, the micro-hardness and Young's modulus of the coating decreased. The mean value of the Young's modulus of the coating calculated from Weibull plot was almost proportional to the square root of the micro-hardness of the coating. With increasing the power, Young's modulus of the coating increased, which, in turn, resulted in the increment of the residual stress at the coating surface.     

Cancer cell recognition--mechanical phenotype

The major characteristics of cancer metastasis is the ability of the primary tumor cells to migrate by way of the blood or lymph vessels and to form tumors at multiple, distant sites. There are evidences that cancer progression is characterized by disruption and/or reorganization of cytoskeleton (i.e. cellular scaffold). This is accompanied by various molecular alterations influencing the overall mechanical resistance of cells. Current approach in diagnosis focuses mainly on microbiological, immunological, and pathological aspects rather than on the biomechanics of diseases. The determination of mechanical properties of an individual living cell has became possible with the development of local measurement techniques, such as atomic force microscopy, magnetic or optical tweezers. The advantage of them lies in the capability to measure living cells at a single cell level and in liquid conditions, close to natural environment. Here, we present the studies on mechanical properties of single cells originating from various cancers. The results show that, independently of the cancer type (bladder, melanoma, prostate, breast and colon), single cells are characterized by the lower Young's modulus, denoting higher deformability of cancerous cells. However, the obtained Young's modulus values were dependent on various factors, like the properties of substrates used for cell growth, force loading rate, or indentation depth. Their influence on elastic properties of cells was considered. Based on these findings, the identification of cancerous cells based on their elastic properties was performed. These results proved the AFM capability in recognition of a single, mechanically altered cell, also in cases when morphological changes are not visible. The quantitative analysis of cell deformability carried out using normal (reference) and cancerous cells and, more precisely, their characterization (qualitative and quantitative) can have a significant impact on the development of methodological approaches toward precise identification of pathological cells and would allow for more effective detection of cancer-related changes.     

Compliance profile of the human cornea as measured by atomic force microscopy

The ability to accurately determine the elastic modulus of each layer of the human cornea is a crucial step in the design of better corneal prosthetics. In addition, knowledge of the elastic modulus will allow design of substrates with relevant mechanical properties for in vitro investigations of cellular behavior. Previously, we have reported elastic modulus values for the anterior basement membrane and Descemet's membrane of the human cornea, the surfaces in contact with the epithelial and endothelial cells, respectively. We have completed the compliance profile of the stromal elements of the human cornea by obtaining elastic modulus values for Bowman's layer and the anterior stroma. Atomic force microscopy (AFM) was used to determine the elastic modulus, which is a measure of the tissue stiffness and is inversely proportional to the compliance. The elastic response of the tissue allows analysis with the Hertz equation, a model that provides a relationship between the indentation force and depth and is a function of the tip radius and the modulus of the substrate. The elastic modulus values for each layer of the cornea are: 7.5±4.2 kPa (anterior basement membrane), 109.8±13.2 kPa (Bowman's layer), 33.1±6.1 kPa (anterior stroma), and 50±17.8 kPa (Descemet's membrane). These results indicate that the biophysical properties, including elastic modulus, of each layer of the human cornea are unique and may play a role in the maintenance of homeostasis as well as in the response to therapeutic agents and disease states. The data will also inform the design and fabrication of improved corneal prosthetics.     

The influence of defects on the effective Young’s modulus of a defective solid

It is difficult to establish structure-property relationships in a defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on the Young’s modulus of a defective solid are studied. Based on the law of the conservation of energy, mathematical formulations are proposed to indicate how the shape, size, and distribution of defects affect the effective Young’s modulus. In this approach, detailed equations are illustrated to represent the shape and size of defects on the effective Young’s modulus. Different from the results obtained from the traditional empirical analyses, mixture law or statistical method, for the first time, our results from the finite element method (FEM) and strict analytical calculation show that the influence of pore radius and crack length on the effective Young’s modulus can be quantified. It is found that the longest crack in a typical microstructure of ceramic coating dominates the contribution of the effective Young’s modulus in the vertical direction of the crack.     

螺旋测微计在测量金属杨氏模量中的应用

本根据拉伸法测量金属杨氏模量的原理,对利用螺旋测微计测量金属杨氏模量的方法做了可行性分析,并在此基础上设计出一套完整的借助螺旋测微计测量金属杨氏模量的方法。     

Processing dependence of Young's modulus of Ti-base nanostructured alloys

The cooling rate and heat treatment dependence of Young's modulus for Ti-base multicomponent nanostructure-dendrite composites exhibits a very different response compared with the monolithic nanostructured or normal grain-sized Ti alloys. With increasing cooling rate, the decrease in the volume fraction of the micrometer-sized β-phase dendrites induces a significant increase in Young's modulus for most of these composites. This increase can cover the decrease in Young's modulus induced by the reduction of grain size of the nanostructured matrix. Heat treatment induces a significant increase in Young's modulus due to the precipitation of intermetallics and/or α-phase in the nanostructured matrix.     

Express Method for Determination of Low Value of Trans-membrane Potential of Living Cells with Fluorescence Probe: Application on Haemocytes at Immune Responses

The method for measurement of trans-membrane potential of cell membrane was evaluated for the case of low potential value using fluorescence probe 4-(4-dimethylaminostyryl)-1-methylpyridinium, DSM. The method is based on comparative titration of cells with probe in buffers containing Na(+) or K(+). The apparent trans-membrane potential obtained with this way is a result of K(+)-Na(+) pump activity. The presented approach allowed measuring the low value of potential with 1-2?mV of accuracy without additional calibration procedures. The method was applied for investigation of potential of cell membrane of haemocytes of Galleria mellonella larvae. The value of potential of intact insect's haemocytes was found in the range from -10 to -20?mV. The change of potential value of haemocytes was investigated under model immune response and natural envenomation and parasitizing. The obtained deviations of cell membrane potential were in good correlation with changes of activity of main immune reactions, described in literature and obtained by us earlier.     

Effect of ending surface on energy and Young's modulus of single-walled carbon nanotubes studied using linear scaling quantum mechanical method

By using a linear scaling self-consistent charge, density functional tight-binding (SCC-DFTB) method and an ab intio Dmol3 calculation, the energy and Young's modulus as a function of tube length for (10, 0) single-walled carbon nanotubes (SWCNTs) are investigated. It was found that with increasing the length of SWCNTs the Young's modulus increases rapidly, then, there is a slow increase, which ultimately approaches a constant value after the length is increased to ~20 nm, whereas a reversed variation tendency was found for the average energy of atoms in SWCNTs with a change of the tube length. We found that the characters of the length-dependent energy and Young's modulus stem from the changed P_y-DOS of atoms in the ending region of the tube. Here one simple formula is proposed for quantitatively explaining the length-dependent energy and modulus.