Quantification of the lateral detachment force for bacterial cells using atomic force microscope and centrifugation

To determine the lateral detachment force for individual bacterial cells, a quantitative method using the contact mode of an atomic force microscope (AFM) was developed in this study. Three key factors for the proposed method, i.e. scan size, scan rate and cantilever choice, were evaluated and optimized. The scan size of 40×40 μm² was optimal for capturing sufficient number of adhered cells in a microscopic field and provide adequate information for cell identification and detachment force measurement. The scan rate affected the measurement results significantly, and was optimized at 40 μm/s considering both force measurement accuracy and experimental efficiency. The hardness of applied cantilevers also influenced force determination. The proposed protocol for cantilever selection is to use those with the lowest spring constant first and then step up to a harder cantilever until all cells are detached. The lateral detachment force of Escherichia coli cells on polished stainless steel and a glass-slide coated with poly-l-lysine were measured as 0.763±0.167 and 0.639±0.136 nN, respectively. The results showed that the established method had good repeatability and sensitivity to various bacteria/substrata combinations. The detachment force quantified by AFM (0.639±0.136 nN) was comparable to that measured by the centrifugation method (1.12 nN).     

Study on carrier mobility measurement using electroluminescence in frequency domain and electrochemical impedance spectroscopy

In this paper, the two methods, electroluminescence in frequency domain and electrochemical impedance spectroscopy, have been applied to investigate the carrier mobility in single layer polymer light-emitting diode employing the polymer MEH-PPV (Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) as the light-emitting layer. The carrier mobility μ is 1.64 × 10⁻⁶ cm²/V s under the electric field 8.3 × 10⁵ V/cm measured by the method of electroluminescence in frequency domain. The electrochemical impedance spectroscopy results indicate that the carrier mobility μ is 1.08 × 10⁻⁶ cm²/V s under the electric field 7.5 × 10⁵ V/cm. A significant advantage of the two methods is that both of them can be applied to measure the carrier mobility in the thin film.     

Metrological characterization of the new 1 MN force standard machine of NPL India

Since November 2010, NPL India’s force scale has been complemented in the range from 10 kN to 1 MN by a further force standard machine. This automatically working 1 MN force standard machine utilizes a lever amplification of a 100 kN mass stack and enables low relative expanded uncertainties of smaller than 9 × 10⁻⁵ on the lever, and 2 × 10⁻⁵ on the deadweight side. In this paper, the constructional design of the machine is described. According to the new EURAMET Calibration Guide, a model for the uncertainties is developed.Supplementary to this, results from comparison measurements of the new NPL India machine with PTB´s force standard machines are presented.     

Design and testing of a 1.5 Tesla double-tuned (H/P) RF surface coil with intrinsic geometric isolation

We analyse the isolation characteristics of axial and transverse field surface radio frequency coils, used to design a double-tuned surface coil composed by two coils, that combine proton (¹H) detection and localized spectra of phosphorous (³¹P). Several geometrical configurations were analysed, including circular loop and figure-of-eight coils, with the aim to optimize the isolation between the two channels. Our analysis shows that by using at least one transverse coil for the design of the double-tuned probe, it is possible to achieve a good intrinsic geometrical decoupling, without the need of additional decoupling circuits. On the basis of the experimental results, we have designed and built a 1.5 T double-tuned probe composed by a circular loop coil and a transverse field coil, with the external coil tuned at the ¹H frequency and the internal coil tuned at the ³¹P frequency, that shows a good intrinsic decoupling and signal-to-noise ratio.     

A theoretical and experimental study on transverse field radio frequency surface coils

We have analysed, theoretically and experimentally, transverse field RF surface coils comprising two parallel linear current elements (figure-of-eight, FO8). A quasi-static numerical integration of the Biot–Savart law was used to simulate the B₁ field distribution of FO8 coils comprising a range of coil diameters and linear element separations. RF coil prototypes, suitable for ¹H and ³¹P magnetic resonance imaging/spectroscopy at 1.5 T, that closely match the simulated models, were built and tested using workbench and MRI methods. A comparison with standard loop RF coils was made. Testing with phantoms showed a good agreement between the theoretical and experimental RF field distributions. Our findings should be useful to optimize the sensitivity and spatial selectivity of FO8 coils by a careful choice of the geometrical parameters. A number of applications where the use of FO8 RF coils could be of benefit are discussed, these include in vivo nuclear magnetic resonance imaging/spectroscopy.     

A three-axes-compensated inductive magnetometer for measurements in high pulsed magnetic fields

A high-sensititity magnetometer intended for studying the magnetic properties of materials in pulsed magnetic fields of up to 43 T is described. A distinctive feature of the magnetometer is its method for compensating pickups generated in the magnetometer sensing element by a pulsed field. The commonly used uniaxial high-order compensation is replaced by a triaxial compensation of the lowest (quadrupole) order, combined with a transverse arrangement of the main probe coils. This method has allowed us to achieve a compensation level of the signal in the working coil (with an inner diameter of 1.4 or 1.75 mm) of the magnetometer without a sample of up to 10⁻⁶ for the longitudinal and 10⁻⁴ for the transverse field components. The magnetic moment sensitivity of the magnetometer is 10⁻⁴ mA·m² in fields below 10 T and 10⁻³ mA·m² at a field pulse amplitude of 35 T. A deviation of the compensation is below 2×10⁻⁴ for a temperature increase from 77 to 300 K and below 5×10⁻⁵ after sample replacement. The sample temperature is controlled by a fast-acting temperature control system in a range of 6–300 K to an accuracy of 0.3–0.05 K.     

Analysis of damping resistor’s effects on pulse response of self-integrating Rogowski coil with magnetic core

A self-integrating Rogowski coil with magnetic core is investigated for accurate measurement of high-impulse current in this paper. Usually, the distributed parameters of Rogowski coil generate deleterious high-frequency resonant signal parasitizing in the useful signal of the coil circuit. Damping resistors can be used to eliminate the parasitic resonant component of the signal. In this paper, damping effects of the damping resistors on the output signal of Rogowski coil are studied in detail. According to circuit theory, approximate circuit equations of Rogowski coil with lumped parameters in simplification are put forward. Response signal of coil is analyzed and a reasonable method for choosing damping resistance is also presented. When the 50 Ω damping resistance is used, the amplitude of parasitic resonant signal has been damped by 5.7 times in contrast to the situation without any damping resistance. Result of Pspice circuit simulation corresponds to the theoretical calculation result. A standard 10 ns square pulse has been used to calibrate the coil signal before and after the damping resistors soldering on the coil, respectively. Experimental results show that the response time of the coil with magnetic core is 1.1 ns and the parasitic resonance in the coil signal is almost eliminated. The coil can accurately detect high-pulse current at kA range.     

Scanning probe lithography for fabrication of Ti metal nanodot arrays

We report fabrication of Ti metal nanodot arrays by scanning probe microscopic indentation. A thin poly-methylmethacrylate (PMMA) layer was spin-coated on Si substrates with thickness of 70 nm. Nanometer-size pore arrays were formed by indenting the PMMA layer using a cantilever of a scanning probe microscope. Protuberances with irregular boundaries appeared during the indentation process. Control of approach and pulling-out speed during indentation was able to dispose of the protrusions. Ti metal films were deposited on the patterned PMMA layers by a radio-frequency sputtering method and subsequently lifted off to obtain metal nanodot arrays. The fabricated metal nanodot arrays have 200 nm of diameter and 500 nm of interdistance, which corresponds to a density of 4×10⁸/cm². Scanning probe-based measurement of current–voltage (I–V) behaviors for a single Ti metal nanodot showed asymmetric characteristics. Applying external bias is likely to induce oxidation of Ti metal, since the conductance decreased and volume change of the dots was observed. I–V behaviors of Ti metal nanodots by conventional e-beam lithography were also characterized for comparison.     

Fabrication and characterization of a new MEMS fluxgate sensor with nanocrystalline magnetic core

This paper presents a new MEMS fluxgate sensor with a Fe-based nanocrystalline ribbon magnetic core and 3D micro-solenoid coils. The excitation coils were placed vertically to the sensing coil on the chip plane. Second harmonic operation principle was adopted in this fluxgate sensor. The total size of the fluxgate sensor was 6.25 mm × 4.85 mm × 120 μm. A simple testing system was established to characterize the fabricated devices. A band pass filter was used to pick up the second harmonic signals in the sensing coils. When excitation rms current of 120 mA and the operational frequency of 200 kHz were selected for the testing of the fabricated devices, the sensitivity of the developed fluxgate sensor was 1005 V/T in the linear range of −500 μT to +500 μT. Due to the combination of the 3D structure coils with the nanocrystalline core, relatively low sensor noise was achieved. The noise power density was 544 pT/Hz^0.5@1 Hz and the noise rms level was 9.68 nT in the frequency range of 25 mHz-10 Hz.     

Fretting on the cubic face of a single-crystal Ni-base superalloy at room temperature

Fretting experiments were conducted on the (1 0 0) crystal (cubic) face of a single crystal Ni-base superalloy in two directions, 〈1 0 0〉 and 〈1 1 0〉, to study the effect of crystallographic orientation on the fretting response in both partial slip and gross slip regimes. The study involved point contacts using a tungsten carbide (WC) ball with radius 10 mm tested at room temperature. Ball indentation was used to determine secondary crystallographic orientations. Under sufficiently high normal force, the friction on the cubic face in the 〈1 1 0〉 direction was larger than in the 〈1 0 0〉 direction. This difference can be explained by the extent of plastic deformation in the surface layer and associated microstructure changes, both of which depend on the coupling between the crystallographic orientation and the cyclic deformation field.     

Growth and field emission properties of ZnO nanostructures deposited by a novel pulsed laser ablation source on silicon substrates

Zinc oxide (ZnO) nanostructures were produced using a novel pulsed laser ablation apparatus comprising in-situ analysis of the plume by reflection time-of-flight mass spectrometry. Various morphologies of nano and microstructures were obtained for laser wavelengths of 1064 and 355 nm, and oxygen ambient pressures of 10⁻⁶ and 10⁻² mbar, respectively. None of the produced structures exhibited a particular type of self-organisation whereas all of them showed low aspect ratios and good field emission properties. Optimum values of 5.2 V μm⁻¹ and 2060 were obtained for the turn-on field and Fowler–Nordheim enhancement factor, respectively, for deposited nano-tipped microstructures presenting a high coverage of the substrate. The experimental data showed that for a given laser wavelength, higher field enhancement factors were obtained for the samples grown at the lower pressure of 10⁻⁶ mbar. In these conditions, the deposited materials showed distinct nanostructuring and comparison with existing data showed the corresponding ablation plumes to contain (ZnO)_n clusters, up to n=13. This work also shows that the electronic properties of the nanostructured ZnO produced in our conditions, as determined by the oxygen concentration during deposition, have an influence on the field emission properties in addition to the nanostructure morphology.     

Optimization of multilayer cylindrical coils in a wireless localization system to track a capsule-shaped micro-device

A wireless electromagnetic localization method has been presented to track capsule-shaped micro-devices in the gastrointestinal tract. And a prototype for the novel localization system has been developed. In the localization method, cylindrical coils placed on the patient’s abdomen generate alternating electromagnetic fields one by one. The system of equations from the localization model has been established and then transformed into a nonlinear optimization problem. The localization method presents excellent anti-interference ability and high stability. In order to solve the magnetic inverse problem in the localization model, an analytical expression between the magnetic flux density and the position & orientation should be derived by superposition of the fields generated by the coil turns, which causes systematic errors. As a result, the geometry of the cylindrical coils is optimized to reduce the errors. A full factorial experiment with two factors has been carried out. The experiment shows that the optimal L/Dout ratio and Din/Dout ratio are 0.4 and 0.8, respectively. In this case, the mean error and the standard deviation are reduced to 0.89% and 0.77%, respectively, where the distance along the axis of the cylindrical coil from the coil’s center to a measured point is 30 mm. Furthermore, the experimental results also show that the imitation error decreases significantly with increased distance from the coil. The accuracy of the localization model can be further improved using the optimized coil.     

Tribological properties of Mn-Zn-Fe magnetic fluids under magnetic field

A controllable and variable magnetic field was got by improving the oil cup of a MS-800 four-ball tester. By this improved four-ball tester, the tribological properties of Mn_0.78Zn_0.22Fe₂O₄ magnetic fluid in the magnetic field were tested. The worn surfaces of the steel balls lubricated with 6 wt% Mn_0.78Zn_0.22Fe₂O₄ magnetic fluid under different magnetic fields were observed by using a scanning electron microscope (SEM), while the elemental compositions of the wear scars were analyzed by means of energy dispersive spectrometry (EDS). It was found that the Mn_0.78Zn_0.22Fe₂O₄ nanoparticles had a diameter about 20 nm. Under magnetic field, the 46^# turbine oil containing 6 wt% Mn_0.78Zn_0.22Fe₂O₄ nanoparticles showed much better friction-reducing and anti-wear abilities compared with lubrication without magnetic field. The worn surface, lubricated by 6 wt% Mn_0.78Zn_0.22Fe₂O₄ magnetic fluid lubricated under the effect of magnetic field, is smooth and the plowing is almost disappeared. Moreover, it is found that 22 mT magnetic induction is the optimum magnetic induction. Form theory study we found that under the effect of magnetic field, the bearing capacity increasing with the increasing of magnetic induction. When the eccentricity is small, the side leakage is highly decreased.     

International comparison of quantum AC voltage standards for frequencies up to 100 kHz

This paper presents results of an international comparison of two quantum AC voltage standards based on pulse-driven Josephson arrays. The two systems differ in several hardware and software characteristics as well as in the level of automation, features which can influence the accuracy of transferring the quantum-standard voltage value to a calibrated instrument. The comparison was performed at 100 mV, 20 mV and 12 mV, at frequencies between 2.5 kHz and 100 kHz. An electronically-aided thermal transfer standard was used as a travelling standard. At the most accurate voltage and frequency point, 100 mV at 2.5 kHz, both laboratories agreed to better than 1 part in 10⁶.     

An Automated High-Sensitivity Vibrating-Coil Magnetometer

A magnetometer allows the measurement of the magnetic moment of samples in a range from 1.3 × 10^–8 to 5.45 × 10^–4 A m². The range of variation of the magnetic field strength is from 0 to 56 kA/m; the temperature range is 20–700°C. Measurements are performed in an air atmosphere. The obtained data are automatically inputted into a PC. In addition, the magnetometer can measure the coercive force H _c and the destructive field H _cr. It can also be used to study the formation of thermoremanent and viscous magnetizations and measure the Curie-temperature spectrum and the blocking-temperature spectrum. Measurements of the field, temperature, and time dependences of the magnetic moment can also be performed by the researcher or by special software using a more complicated algorithm.     

High resolution surface morphology measurements using EBSD cross-correlation techniques and AFM

The surface morphology surrounding wedge indentations in (0 0 1) Si has been measured using electron backscattered diffraction (EBSD) and atomic force microscopy (AFM). EBSD measurement of the lattice displacement field relative to a strain-free reference location allowed the surface uplift to be measured by summation of lattice rotations about the indentation axis. AFM was used in intermittent contact mode to determine surface morphology. The height profiles across the indentations for the two techniques agreed within 1 nm. Elastic uplift theory is used to model the data.     

A magnetic MEMS actuator using a permanent magnet and magnetic fluid enclosed in a cavity sandwiched by polymer diaphragms

A magnetic microelectromechanical systems (MEMS) actuator using a small permanent neodymium-magnet surrounded by magnetic fluid (MF) was developed and characterized. The magnet is enclosed in a cavity sandwiched by two identical thin PET-sheet diaphragms and is able to move smoothly due to the MF. The diaphragms deflect when an external magnetic force is applied to the magnet. This structure was adopted to prevent the diaphragms from being stiffened by attaching or fabricating a magnetic layer on the diaphragm surface and to secure the necessary volume of magnetic material. The magnets are 2–4 mm in diameter and the cavity is 5 mm in diameter and 1 mm in depth. The diaphragms are 20 μm in thickness. Experiments showed the displacement amplitude generated at the diaphragm center was in the range of 10–50 μm for attractive and repulsive magnetic force when magnetic flux density of 4–30 mT was applied. The response was within about 1 s. The deflection profile of the diaphragms can also be varied by changing the magnet position.     

Resistance measurement of isolated single-walled carbon nanotubes

Conductive atomic force microscopy (CAFM) and Kelvin force microscopy (KFM) were used to measure the resistance of isolated single-walled carbon nanotubes (SWNTs). By analyzing the current map and surface potential obtained from CAFM and KFM methods respectively, the intrinsic resistance of SWNTs could be calculated. The results calculated by these two methods are the same for the same batch of SWNTs, which is on the order of 10⁷–10⁸ Ω.     

Photo-enhanced field emission study of TiO2 nanotubes array

Aligned TiO₂ nanotubes were synthesized by simple anodization of the Ti foil surface. The as-anodized product is further characterized by SEM, XRD, and PL. The tube inner diameter is found to be ≈60-80 nm with the average wall thickness ≈30 nm and areal density ≈15×10⁶/ cm². FE studies of the aligned TiO₂ nanotubes are carried out at base pressure of ≈1×10⁻⁸ mbar. The turn-on field observed for an emission current density of ≈10 μA/cm² is found to be ≈1.7 V/μm and current density of ≈44 μA/cm² is obtained at an applied field of ≈2.3 V/μm. Photo-enhanced FE study is carried out by shining visible and UV light on the cathode. The aligned TiO₂ nanotubes show sensitivity to both the light sources. The FE current shows fast switching response to the visible light. The increment in the preset current upon UV illumination can be attributed to the band edge excitation of the electrons. The free excitons associated with band gap of the TiO₂ nanotubes array may be responsible for the visible light sensitivity. TiO₂ nanotubes are also grown on the Ti wire and exhibit similar photo-enhanced behavior. The FE and photo-enhanced FE properties demonstrate the applicability of the aligned TiO₂ nanotubes in the FE based micro/nanoelectronic devices.     

Approach to accuracy improvement and uncertainty determination of radius of curvature measurement on standard spheres

In high accuracy radius of curvature (ROC) measurement, significant discrepancy may exist in results on the same optical surface obtained by different techniques. Metrological standard sphere is a potential solution to this problem. Mathematical models are built up to characterize the relationship between the ROC of standard spheres and the roundness error as well as the aperture angle. Equations for calculating the uncertainty of ROC are derived and tested on several ROC measuring methods. The reason for the inconsistency between results of different techniques is analyzed and solutions are proposed. A method is developed which can remarkably reduce the uncertainty of ROC. Experiments are carried out on a set of high quality spheres whose diameters are from 11 mm to 93 mm and roundness below 0.1 μm, measured by instruments with relative accuracy of 10⁻⁵–10⁻⁶, which are a length measuring machine, a profilometer and a homemade differential confocal system. Relative uncertainties of ROC are calculated and analyzed against several factors. Experimental results show good consistency with theoretical analysis. Approaches to trace the ROC to the metrological length standard area discussed.