Electron beam damage of behenic acid films

The rate of fading of electron diffraction patterns of behenic acid monolayer crystals as well as multilayer crystals was measured at 100 kV at room temperature to investigate the dependence of beam damage on specimen thickness. The diffracted intensities for monolayers and double layers decreased nearly exponentially with electron exposure; however, the intensities for multilayers were unchanged during initial electron exposures, often increased temporarily and then decreased with electron exposure. The critical dose, D_e, defined as the dose at which the diffracted intensity falls to 1/e of its initial value, was 1.0 electrons/Ų for the monolayers, 1.8 electrons/Ų for the double layers and more for multilayers. These results lead to the conclusion that D_e for behenic acid increases nearly linearly with specimen thickness in the range of about 25–100 Å for dose rate of 0.1–2 electrons/Ų min.     

A plasma generator based on nonself-sustained low-pressure glow discharge with a large-volume hollow cathode

The results of studying nonself-sustained glow discharges in an electrode system with a hollow cathode with a volume of 0.25 m³ are presented. A high-current (up to 35 A) nonself-sustained glow discharge at low pressures (0.3–1.0 Pa) is initiated and sustained with the help of an auxiliary cold-hollow-cathode arc discharge. When the current of a nonself-sustained glow discharge increases from 2 to 35 A, its burning voltage changes from 40 to 300 V. These values are much lower than the voltage for a self-sustained glow discharge in the same electrode system. At a discharge current of 30 A, the electron concentration at the center of the hollow cathode is n _e ∼ 10¹⁰–10¹¹ cm⁻³ and the electron temperature is T _e ≈ 2 eV. The discharge considered can be used in the system for modification of materials and products.     

Beam induced mass loss in high resolution biological microanalysis

Electron beam induced loss of mass from the organic matrix and from higher Z constituents of biological samples was measured by monitoring bremsstrahlung and peak changes in EDS spectra. When any effects of contamination, extraneous X-rays, beam current drift, specimen drift, and specimen shrinkage were monitored and corrected for, the three types of samples gave consistent and similar results at 296 K. Bremsstrahlung losses averaged 45%, 46% and 50% respectively for muscle homogenate, salivary gland sections and albumin. Sulphur losses average 74%, 72% and 86% for the same three sample types. No other elements suffered significant losses. D_l/e for bremsstrahlung averaged 0·14 C/cm². Bremsstrahlung loss at 93 K began approximately one order of magnitude higher in dose, and the extent of loss varied. Sulphur losses, however, were greatly reduced at low temperatures.     

Limitations of beam damage in electron spectroscopic tomography of embedded cells

Elemental mapping in the energy filtering transmission electron microscope (EFTEM) can be extended into three dimensions (3D) by acquiring a series of two‐dimensional (2D) core‐edge images from a specimen oriented over a range of tilt angles, and then reconstructing the volume using tomographic methods. EFTEM has been applied to imaging the distribution of biological molecules in 2D, e.g. nucleic acid and protein, in sections of plastic‐embedded cells, but no systematic study has been undertaken to assess the extent to which beam damage limits the available information in 3D. To address this question, 2D elemental maps of phosphorus and nitrogen were acquired from unstained sections of plastic‐embedded isolated mouse thymocytes. The variation in elemental composition, residual specimen mass and changes in the specimen morphology were measured as a function of electron dose. Whereas 40% of the total specimen mass was lost at doses above 10⁶ e^?/nm², no significant loss of phosphorus or nitrogen was observed for doses as high as 10⁸ e^?/nm². The oxygen content decreased from 25 ± 2 to 9 ± 2 atomic percent at an electron dose of 10⁴ e^?/nm², which accounted for a major component of the total mass loss. The specimen thickness decreased by 50% after a dose of 10⁸ e^?/nm², and a lateral shrinkage of 9.5 ± 2.0% occurred from 2 × 10⁴ to 10⁸ e^?/nm². At doses above 10⁷ e^?/nm², damage could be observed in the bright field as well in the core edge images, which is attributed to further loss of oxygen and carbon atoms. Despite these artefacts, electron tomograms obtained from high‐pressure frozen and freeze‐substituted sections of C. elegans showed that it is feasible to obtain useful 3D phosphorus and nitrogen maps, and thus to reveal quantitative information about the subcellular distributions of nucleic acids and proteins.     

Study of seizure of coated and treated titanium alloy under fretting conditions

Titanium alloys are well known to present poor sliding behaviour and high wear values. Various coatings (soft thick coatings and thin hard coatings) and treatments have been tested to prevent such an occurrence under fretting conditions at high frequency of displacement (100 Hz). An original test apparatus, using an open-loop system, has been performed to directly display the phenomenon of seizure. No seizure was recorded at low load (6 N), while, at higher load (10 N), all samples undergo a more or less early seizure. The total sliding distance D₀ proved to be a pertinent parameter to study the seizure resistance. Furthermore, the results highlight that D₀ is linked to the total energy dissipated in the contact, E_dt, and reveal two distinct behaviours at low load, which suggest two distinct dissipating mechanisms of energy. The first trend can be connected with the plastic deformation and the trapping process of debris within the contact zone occurring on soft coatings. The second trend can be related to the higher debris ejection observed on hard samples. So, soft thick coating satisfies most of the chosen criteria except those of wear. In contrast, thin and hard coatings are not sufficient to totally protect the substrate but they are already able to efficiently reduce wear.     

Effect of divergence ratio on heat transfer and friction factor in the ribbed rectangular channel

The local heat transfer and pressure drop of turbulent flows developed in stationary ribbed rectangular divergent channels are experimentally investigated. The rectangular divergent channels with a one sided ribbed surface only have inclination angles of 0.72° and 1.43°. The ribbed wall is manufactured with a fixed rib height (e) of 10 mm and rib spacing (p) to height (e) ratio of 10. The measurement was conducted within a Reynolds number range of 15,000 to 89,000. The local heat transfer characteristics of the rectangular divergent channels are quite different from those of the square straight channels because of the streamwise flow deceleration. The thermal performances of the ribbed rectangular divergent channels are compared with those of the ribbed square straight channels under three constraints: identical mass flow rate, identical pumping power, and identical pressure drop. The comparison shows that between the two channels D1 (D _ho /D _hi = 1.16) and D2 (D _ho /D _hi = 1.49), the divergent channel D2 (D _ho /D _hi = 1.49) has the higher thermal performance at identical mass flow rate, and the divergent channel D1 (D _ho /D _hi = 1.16) has the higher thermal performance under the constraints of identical pumping power and static pressure drop.     

Quantitative assessment of radiation damage in a thin protein crystal

Radiation damage is a limiting factor for high resolution structural determination of protein crystals. We have used the median and quartile values of N_e exposures and the structural disordering factor (ΔB) to describe the crystalline disordering due to radiation damage in thin crystals of crotoxin complex embedded in glucose at room and low temperatures and in ice embedded crystals. By approximating the radiation damage to follow first order kinetics, we applied a correction to the diffraction intensities from patterns with high accumulated exposures. We used the structural similarity factor (R) to show that, for some data, the effectiveness of the correction can be as good as those in protein X-ray crystallography.     

Simultaneous measurement of quantum yield ratio and absorption ratio between acceptor and donor by linearly unmixing excitation–emission spectra

Quantum yield ratio (Q_A/Q_D) and absorption ratio (K_A/K_D) in all excitation wavelengths used between acceptor and donor are indispensable to quantitative fluorescence resonance energy transfer (FRET) measurement based on linearly unmixing excitation–emission spectra (ExEm‐spFRET). We here describe an approach to simultaneously measure Q_A/Q_D and K_A/K_D values by linearly unmixing the excitation–emission spectra of at least two different donor–acceptor tandem constructs with unknown FRET efficiency. To measure the Q_A/Q_D and K_A/K_D values of Venus (V) to Cerulean (C), we used a wide‐field fluorescence microscope to image living HepG2 cells separately expressing each of four different C–V tandem constructs at different emission wavelengths with 435 nm and 470 nm excitation respectively to obtain the corresponding excitation–emission spectrum (S_DA). Every S_DA was linearly unmixed into the contributions (weights) of three excitation–emission spectra of donor (W_D) and acceptor (W_A) as well as donor–acceptor sensitisation (W_S). Plot of W_S/W_D versus W_A/W_D for the four C–V plasmids from at least 40 cells indicated a linear relationship with 1.865 of absolute intercept (Q_A/Q_D) and 0.273 of the reciprocal of slope (K_A/K_D), which was validated by quantitative FRET measurements adopting 1.865 of Q_A/Q_D and 0.273 of K_A/K_D for C32V, C5V, CVC and VCV constructs respectively in living HepG2 cells.     

Experimental study on helium-air exchange flow through small openings with vertical partition

The helium-air exchange flow may occur at the rupture accident of a standpipe in a high temperature engineering test reactor. A test vessel with three types of small opening is used for experiments. An estimation method of mass increment is applied to measure the exchange flow rate. Flow measurements are made with the single opening and partitioned, opening, for opening ratiosH ₁/D ₁ in the range 0.05 to 10, whereH ₁ andD ₁ are height and diameter of the opening, respectively. At lower opening ratios (H ₁/D ₁<0.75), the difference in the exchange flow rates between the opening systems is small. At higher opening ratios (H ₁/D ₁≥0.75), exchange flow rates of the partitioned opening system are higher than those of the single opening system because of separated (unidirectional) flows by partition. An effect of variation of diameters of the partitioned openings on the exchange flow rate is investigated. The exchange flow rate increases with the opening diameter. Finally, an experiment with two-opening is designed to investigate the effect of fluid interaction of the partitioned opening system. It is demonstrated that the exchange flow rate of the two-opening system is higher than that of the partitioned opening system because of the absence of the fluid interaction.     

Twin spray characteristics between two impinging F-O-O-F type injectors

This paper presents twin spray characteristics of two impinging F-O-O-F type injectors in which fuel and oxidizer impinge on each other to atomize under the various conditions. The droplet size and velocity in the impinging spray flow field were measured using PDPA. The droplet size and velocity were investigated at the mixture ratios of 1.5, 2.0, 2.47 and 3.0 for four injectors in which two single F-O-O-F injectors were arranged at the intervals of 20.8, 31.2, 41.6 and 62.4mm respectively. In general, the arithmetic mean diameter, SMD and standard deviation of droplet size in the interaction area (X=0 andY=0mm) were smaller, while the axial velocity in the interaction area was slightly higher. An empirical correlation is obtained for the (D ₁₀) _D /(D ₁₀) _C value under the assumptions of two identical droplets and these with different size and velocity. The droplets with low Weber numbers below 40 have possibility to coalesce, while those over 40 tend to disintegrate after impingement in the interaction area.     

New fine structures resolved at the ELNES Ti-L2,3 edge spectra of anatase and rutile: Comparison between experiment and calculation

Anatase and rutile Ti-L_2,3 edge spectra were measured in electron energy loss spectroscopy (EELS) using a transmission electron microscope (TEM) coupled to a CEOS Cs-probe corrector, an omega-type monochromator and an in-column omega-type energy filter fully corrected for 2nd order aberrations. Thanks to the high energy resolution, high electron probe current and high stability achieved under this instrumental configuration, new fine structures, never reported before, were resolved at the L₃ band of both rutile and anatase. The data suggest that new peaks also exist in the L₂ e_g band. The experimental spectra are compared with multichannel multiple scattering (MMS) calculations. Good agreement is found for number, energy position and intensity of the newly resolved spectral features. Up to now, the L₃ e_g band splitting could not be well described by theory not even through the crystal field multiplet approach. We show that the L₃ e_g band splitting is due to long range band structure effects, contrary to the usual interpretations in terms of local ligand field or near-neighbour hybridization effects.     

Excitation under the scanning electron microscope of DNA-associated fluorescence from chicken erythrocyte nuclei,polytene chromosomes and adenovirus 2 virions

Biological structures not seen by conventional light microscopy, such as longitudinal striations in polytene chromosomes, and, at the limit of sensitivity, virions of adenovirus 2, have been detected via DNA-associated fluorescence excited under the scanning electron microscope. The maximum sensitivity realized, about 1 detected photon per 700 base pairs, falls short by about an order of magnitude of that required to achieve, in unreplicated specimens, the 2 nm intrinsic resolution of the method. A combination of D₂O-H₂O substitution with freeze-drying provides the best unquenching procedure found for in situ DNA. DNA-associated fluorescence for light microscopy can be created by moderate exposure of the specimen in the electron microscope.     

Asymptotic fractals in the context of grey-scale images

The estimation of the fractal dimension in the case of concave log–log Richardson–Mandelbrot plots can be obtained by using asymptotic fractal equations. We demonstrate here, under asymptotic fractal conditions, that additional derivations making use of the Minkowski dilation in grey-scales lead to two asymptotes, one having a slope of 1 and the other a slope of D_T ? D + 1 (where D_T is the topological dimension and D the fractal dimension). The resulting equation offers important advantages. It allows: (i) evaluation of scaling properties of a grey-scale image; (ii) estimation of D without any iteration and (iii) generation of texture and heterogeneity models. We concentrate here on the first two possibilities. Images from cultured cells in studies of cytoskeleton intermediate filaments and kinetic deformability of endothelial cells were used as examples.     

Retro‐fitting an older (S)TEM with two Cs aberration correctors for 80 kV and 60 kV operation

For the characterization of light materials using transmission electron microscopy, a low electron acceleration voltage of 80 kV or even 60 kV is attractive due to reduced beam damage to the specimen. The concomitant reduction in resolving power of the microscope can be restored when using spherical aberration (C_s) correctors, which for the most part are only available in the latest and most expensive microscopes. Here, we show that upgrading of existing TEMs is an attractive and cost‐effective alternative. We report on the low‐voltage performance on graphitic material of a JEOL JEM‐2010F built in the early 1990s and retro‐fitted with a conventional imaging C_s corrector and a probe C_s corrector. The performance data show C_s retro‐fitted instruments can compete very favourably against more modern state‐of‐the‐art instruments in both conventional imaging (TEM) and scanning (STEM) modes.     

Numerical investigation of surface topography and residual stress after abrasive water jet sequential peening (AWJSP)

Abstract

This article reveals the formation mechanism of surface topography and the formation and coupling mechanism of residual stress field (RSF) after abrasive water jet sequential peening (AWJSP) that can sequential peening on the material surface at a certain distance interval, and proposes a mathematical model of surface dimple characteristic verified by simulation results. In addition, the influences of shot velocity v₀, shot radius R and the distance between the center of adjacent shots D_C on surface topography and RSF were also investigated. Results show the surface dimple forms resulting from the material plastic strain, and the residual stress (RS) is mainly induced by the unrecovered elastic strain resulting from the hindering of plastic strain. Decreasing v₀, R or D_C can decrease the surface roughness R_t, while increasing v₀ and R is beneficial to induce a large and deep compressive RS layer. D_C influences the whole distribution of compressive RS layer directly.     

Spectrometers for recording electromagnetic showers emerging from oriented crystals

The design and main characteristics of combined shower spectrometers (CSSs) are presented: combined Cherenkov and lead-scintillation spectrometers that are intended for investigating shower processes in oriented crystals and that consist of ten independent lightproof counters with thicknesses of 1X₀ and 1.18X₀, respectively. At an electron energy E _e = 26 GeV, the energy resolutions of both CSSs together with a Cherenkov spectrometer with a thickness of 15X₀, which was placed behind them, were 2.4 and 4.3% for the combined Cherenkov and lead-scintillation shower spectrometers, respectively.     

Formation of variable-spatial frequency interference patterns with the use of birefringent crystal prisms for laser Fourier spectroscopy

Splitting of orthogonally polarized radiation components at the exit of birefringent crystal prisms (BCPs) having a special structure and fabricated from uniaxial Iceland spar crystals is studied by the vector analysis method. For these prisms, the angle of splitting between the ordinary (o) and extraordinary (e) beams at the BCP exit depends linearly on the angle of incidence of a collimated laser beam onto the BCP entrance face. This dependence has the maximum slope only for two fixed orientations of the optical axis vectors a ₁ and a ₂ in both crystal wedges (BCP components). As a result of interference of polarized o- and e-waves, a straight-line interference pattern with a controlled and smoothly changed spatial frequency in the range from 0 to 125 periods/mm can be formed directly at the BCP exit. The BCP ability to form a sinusoidal interference pattern with the modulation depth not lower than 30% and with a varied spatial frequency at the aperture up to 30 mm makes it possible to use the BCP as a basis for creating a compact static Fourier spectrometer with the ultimate theoretical resolution λ/Δλ up to ∼2000.     

Influence of nozzle exit tip thickness on the performance and flow field of jet pump

The influence of exit tip thickness of nozzle δ _e on the flow field and performance of a jet pump was studied numerically in this paper. It is found that δ _e has influence on the distribution of turbulence kinetic energy k. If δ _e is ignored, k takes the highest value but dissipates rapidly than that of nozzle with a certain tip thickness. δ _e also affect apparently the development of tip vortex, which will occur near the exit tip of nozzle. The bigger the δ _e is, the larger the vortex is. The tip vortex develops with the increase of flow rate ratio q. When q=1 and δ _e =0.6∼0.8mm, a small vortex will be found downstream the tip vortex. And a concomitant vortex happens down the tip vortex in the case of q=1 and δ _e =0.8mm. As q increases to 2, the downstream small vortex disappears and the concomitant vortex becomes bigger. It is also found that the tip vortex might interact with the possible backflow that formed in the throat tube and parts of suction chamber. The center of backflow was affect evidently by δ _e . With the increase of δ _e , the center of backflow under the same q will go downstream. When δ _e =0.4mm, the center of backflow goes farthest. Then, as the further increase of δ _e , the center of backflow will go back some distance. Although, δ _e has relatively great influence on the flow field within the jet pump, it exerts only a little impact on the performance of jet pump. When δ _e =0.2∼0.6mm, the jet pump possess better performance. In most case, it is reasonable to ignore the nozzle exit tip thickness in performance prediction for the purpose of simplicity. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

A method for increasing the photographic contrast of electron micrographs

Emulsion-developer combinations used regularly in conventional electron micrography yield an approximately linear relationship between density (D) and exposure (E) up to quite high densities (> 2.0). This is due to the fact that over the corresponding exposure range the density yield per electron is approximately constant. A practical consequence is that the slope of the D/log₁₀ curve, termed the contrast, is a function of D only, i.e. it is independent of the emulsion-developer combination. To achieve higher than normal contrast requires that the density yield per electron should increase with exposure over some exposure range, at least. This effect may be obtained by using what are known commercially as ‘lith’ films and a system of infectious development. The high contrast of such films results from an acceleration of development rate when the developer oxidation products reach a critical concentration. Sensitometric data are presented for electron exposures which show that for average densities of ～ 1.0 in a micrograph a six-fold increase of contrast can be obtained with a ‘lith’ system. It is also shown that though the special development effect gives higher granularity than that obtained at the same exposure with a conventional system, the signal/noise ratio is not adversely affected. Practical demonstrations of the effectiveness of the ‘lith’ system are presented.     

Tribological Properties of Self-Assembled Monolayers and Their Substrates Under Various Humid Environments

Using friction force microscopy (FFM) under controlled environments, we have systematically investigated the humidity effect on the frictional properties of two important classes of self-assembled monolayers (SAMs), i.e., N-octadecyltrimethoxysilane (OTE, CH₃(CH₂)₁₇Si(OCH₃)₃) on SiO₂(OTE/SiO₂), and N-alkanethiols on Au(111), together with their respective substrates. Experimental results show that both OTE and alkylthiol SAMs can decrease the friction force between a Si₃N₄ atomic force microscope (AFM) tip and substrates. The nearly humidity-independent friction of the two kinds of SAMs indicates that these SAMs are ideal lubricants in applications of micro-electro-mechanical systems (MEMS) under different environments. The humidity dependence—as the humidity increases, the friction first increases and then decreases—of the two substrates, SiO₂ and Au(111), can be explained by the adsorption of water. The decrease in the friction at high humidity is attributed to the low viscosity in the multilayers of water, while the increase in the friction at low humidity can be explained by the high viscosity between the water monolayer and the surfaces (AFM tip and sample), possibly due to the confinement effects. The effect of modification of the AFM tip with alkanethiol molecules on the humidity dependence of Au(111) friction has also been investigated.