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Review of Scientific Instruments

Issue 9 • Date Sep 2004

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Displaying Results 1 - 25 of 50
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Optical trapping

    Page(s): 2787 - 2809
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    Since their invention just over 20 years ago, optical traps have emerged as a powerful tool with broad-reaching applications in biology and physics. Capabilities have evolved from simple manipulation to the application of calibrated forces on—and the measurement of nanometer-level displacements of—optically trapped objects. We review progress in the development of optical trapping apparatus, including instrument design considerations, position detection schemes and calibration techniques, with an emphasis on recent advances. We conclude with a brief summary of innovative optical trapping configurations and applications. View full abstract»

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  • Transient torque method: A fast and nonintrusive technique to simultaneously determine viscosity and electrical conductivity of semiconducting and metallic melts

    Page(s): 2810 - 2816
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    A transient torque method was developed to rapidly and simultaneously determine the viscosity and electrical conductivity of liquid metals and molten semiconductors. The experimental setup of the transient torque method is similar to that of the oscillation cup method. The melt sample is sealed inside a fused silica ampoule, and the ampoule is suspended by a long quartz fiber to form a torsional oscillation system. A rotating magnetic field is used to induce a rotating flow in the conductive melt, which causes the ampoule to rotate around its vertical axis. A sensitive angular detector is used to measure the deflection angle of the ampoule. Based on the transient behavior of the deflection angle as the rotating magnetic field is applied, the electrical conductivity and viscosity of the melt can be obtained simultaneously by numberically fitting the data to a set of governing equations. The transient torque viscometer was applied successfully to measure the viscosity and electrical conductivity of high purity mercury at 53.4°C. The results were in excellent agreement with published data. The method is nonintrusive; capable of rapid measurement of the viscosity of toxic, high vapor pressure melts at elevated temperatures. In addition, the transient torque viscometer can also be operated as an oscillation cup viscometer to measure just the viscosity of the melt or as a rotating magnetic field method to determine the electrical conductivity of a melt or a solid if desired. View full abstract»

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  • Inductive measurements of magnetic properties of ribbon materials

    Page(s): 2817 - 2821
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    Inductive measurements of thin ribbon materials are usually done with wrapped toroidal cores. To avoid this time consuming procedure, measurements can also be performed on short straight pieces in a solenoidal setup. We show that demagnetizing effects should be unimportant for the latter case in determining coercive field, saturation field, and core loss. These two types of measurement were performed on samples of amorphous ribbon material. It was found that there is reasonable agreement for these magnetic parameters as long as care was taken to ensure that the samples were strain-free. Strain is particularly important when the material has significant magnetostriction. Based on demagnetization estimates we would expect agreement on permeability determinations in all but the most extreme cases; in fact results can be quite different for the two measurements. Similarly, we can get rather different answers for coercive field when it is very small. This may be due to uniaxial anisotropy which is different for the two sample geometries. It is concluded that the rapid turnaround in solenoid measurements is particularly useful when optimization of saturation field or core loss is of primary importance. View full abstract»

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  • Digital imaging processing for biophysical applications

    Page(s): 2822 - 2827
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    Many biological and biophysical experimental setups rely on digital imaging processing. The introduction of a new generation of digital cameras enables new experiments where time dependent processes can be detected with a high time resolution and high signal-to-noise ratio. However, there are no software tools available with which the full potential of the digital cameras can be explored. Although the data streams of up to 24 MB/s are readily processed by the available hardware, they present an immense challenge to the current software packages. We present a software concept based on the object oriented paradigm, with which digital cameras can be controlled and full images at full rate are captured, processed, and displayed simultaneously over extended time periods, just limited by the capacity of the hard disk space. By implementing wavelet based compression algorithms the obstacle of archiving the immense amount of data is overcome. We present examples in which original data files are compressed to 10% of its original size without loss of information. The modular character of the object based program enables the implementation of a wide range of different applications into the program. View full abstract»

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  • Measuring methods of cell performance of dye-sensitized solar cells

    Page(s): 2828 - 2831
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    Cell performance measuring methods for dye-sensitized solar cells (DSCs) were investigated in comparison with those of crystalline silicon solar cells. It was found that cell performances of DSCs varied according to voltage sweep direction and sampling delay time. On the other hand, this dependence was not observed in silicon solar cells. Measurement of the transient photocurrent revealed that the dependence on sweep direction and sampling delay time may be explained by the longer time constant of DSCs. To improve accuracy, measurement should be carried out with a sampling delay time exceeding several seconds. However, it is also found that the average value of the efficiency measured by two sweeping directions is constant when the sampling delay time is longer than 40 ms. These measurement conditions will be useful to measuring cell performance more accurately and rapidly. Additionally, determining cell area using a shading mask with an area smaller than that of TiO2 electrodes will improve accuracy when evaluating solar cell performance. View full abstract»

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  • Resistive wall mode identification by contrast enhancing technique of soft x-ray measurements on DIII-D

    Page(s): 2832 - 2842
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    A contrast enhancing technique (CET) for soft x-ray (SXR) measurements has been developed and tested for the early identification of the low amplitude resistive wall mode (RWM) on the DIII-D tokamak. The technique is simple and fast. It utilizes the chord-by-chord difference of low-pass digitally filtered time derivatives of the signals from the twelve-chord fan-shape soft x-ray arrays located at toroidal angles of 195° and 45°. The two arrays allow a demonstration of the CET method principle, although they cannot completely resolve the RWM structure. The time derivative of the x-ray signal amplifies the effect of the temperature perturbation convected by the RWM, while naturally incorporating the equilibrium evolution effect. The correlation with the parameters measured by other diagnostics, such as the radial magnetic field δBr from the magnetic probes, the radial profiles of plasma current density j, pressure p, and safety factor q from the motional Stark effect, the radial profile of the temperature perturbation ΔTe from electron cyclotron emission, the normalized beta parameter βNT(I/aB)-1, and the Dα light emission, confirm the early detection of the low-amplitude RWMs by the soft x-ray CET. Upon validation the SXR CET could be implemented into a multisensor scheme using other diagnostics for the real-time identification of RWM. View full abstract»

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  • Design and fabrication of physical vapor transport system for the growth of SiC crystals

    Page(s): 2843 - 2847
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    A physical vapor transport (PVT) system has been designed and fabricated for growing SiC single crystals. Novel multisegmented graphite insulation has been used for improved heat containment in the hotzone. Numerical modeling was applied to obtain the temperature field inside the hotzone, which also helped in predicting various growth parameters. Single crystals of 6H SiC were grown by the modified Lely method using the PVT system developed in the laboratory. The grown crystals were subjected to preliminary characterization. View full abstract»

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  • Design and operational characteristics of a cast steel mass spectrometer

    Page(s): 2848 - 2853
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    A cast steel magnetic sector mass analyzer is developed for studies of hydrogen and helium ion beams generated by a gas discharge compact ion source. The optimum induced magnetic flux density of 3500 G made it possible to scan the whole spectrum of hydrogen and helium ion species. Analysis of beam characteristics shows that the mass spectrometer sensitivity, and resolving power are approximately inversely proportional. The resolution is enhanced at higher pressures and lower current discharges. In contrast, the instrument sensitivity increased at higher current discharges and decreased at higher pressures. Calculations of the ultimate resolving power with reference to analyzer dimensions yield a numerical value of 30. System anomaly in the form of spherical aberrations was also analyzed using the paraxial beam envelope equation. Beam divergence is most significant at high discharge conditions where angular spread reaches an upper limit of 8.6°. View full abstract»

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  • Enhanced microchannel plate performance at high particle fluxes by pulsed exposure mode of operation

    Page(s): 2854 - 2859
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    Operating a microchannel plate (MCP) in saturated mode provides a simple photon and particle counting detector. However, there is a finite recovery time after individual events during which individual microchannels no longer respond, reducing the overall sensitivity. At continuous high flux levels, the corrections from measured to true flux become increasingly large as the fraction of live microchannels rapidly decays to low values. Gating the flux arriving at the MCP greatly increases the proportion of live microchannels allowing periodic measurements to be made that accommodate high fluxes and associated low errors. Such improvements have been observed in a neutral particle analyzer on the Mega Ampere Spherical Tokamak. A simple analytical treatment accounts for the measured improvements. View full abstract»

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  • Characteristics of a miniature parallel-plate free-air ionization chamber for measuring the intensity of synchrotron radiation from an undulator

    Page(s): 2860 - 2862
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    In order to develop an absolute intensity monitor for synchrotron radiation from an undulator, the characteristics of a parallel-plate free-air ionization chamber with a plate separation of 4.2 mm, which was considered to be as narrow as possible, were investigated using 8–30 keV monoenergetic photons at SPring-8. Using a Si-PIN photodiode as the reference monitor, saturation was confirmed at 8–30 keV at a photon intensity of an order of 1013 photons/s. The collection efficiency became almost unity at 8 and 10 keV within 3.8% and 1.1%, respectively, which gradually decreased with increasing energy and attained 0.52 at 30 keV because some of the high-energy electrons escaped from the sensitive volume. When the pair of electrodes was transferred from the upper and lower sides to the left and right sides of the beam axis in order to investigate the influence of linear polarization of synchrotron radiation, a decrease in the collection efficiency was observed. Monte Carlo simulations considering linear polarization showed that the plate separation required for no electron loss was 26, 14, and 8 mm for 30, 20, and 15 keV photons, respectively. For 20 keV photons, saturation characteristics were investigated using an ionization chamber with 14 mm plate separation. View full abstract»

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  • Optical microphone: New results

    Page(s): 2863 - 2864
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    Despite the fact that the optical microphone increased the sensitivity of the photoacoustic technique by 4 orders of magnitude, it was not used for a period of more than 10 yrs after it was published. This is because the manufacture of this microphone demands a great ability and some of its details are not fully described. Due to the importance of the optical microphone for photoacoustics we report some improved results and try to describe the details more adequately. View full abstract»

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  • Characterizations of symmetry and asymmetry high-density gas jets without Abel inversion

    Page(s): 2865 - 2868
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    Characterizations of the high-density gas jets are performed for the laser–gas interaction. It is shown that the gas density profile can be obtained without the Abel inversion, when a Gaussian distribution is assumed. In addition, a rectangular nozzle is characterized for the long plasma generation. In this case, the Boltzmann distribution is introduced for the density profile and its result shows a good agreement with the experimental result. View full abstract»

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  • Determination of thermal diffusivity in a disk shaped sample using edge heating applications to Stainless Steel

    Page(s): 2869 - 2875
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    We describe a methodology for determining thermal diffusivities in real time by using temperature measurements at only two locations in a cylindrical sample. The technique is based on an analytical solution of heat transfer in a circular cylinder. This methodology does not require knowing the initial temperature increase or any timing between the applied and measured response. Starting with a cylinder heated on the outer surface and unique temperature measurement locations, the analytical solution for temperature at two specific radii can be approximated, after an initial transient, by a constant plus a single term that decreases exponentially with time. There are two special radii that fulfill the required condition. The data are analyzed by taking logarithms of the differences of the temperature versus time at these two radii, resulting in lines having slopes that are proportional to the thermal diffusivity. Surprisingly, other choices of the measurement locations lead to similar results, except with longer transients. Experimental results for type 304 stainless steel from room temperature to 450 °C agree with our numerical simulations and published data. This technique is applicable to solids and to liquids if heat transport due to convection is negligible. View full abstract»

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  • Chromatic characterization of a three-channel colorimeter using back-propagation neural networks

    Page(s): 2876 - 2879
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    This work describes a method for the chromatic characterization of a three-channel colorimeter of recent design and construction dedicated to color vision research. The colorimeter consists of two fixed monochromators and a third monochromator interchangeable with a cathode ray tube or any other external light source. Back-propagation neural networks were used for the chromatic characterization to establish the relationship between each monochromator’s input parameters and the tristimulus values of each chromatic stimulus generated. The results showed the effectiveness of this type of neural-network-based system for the chromatic characterization of the stimuli produced by any monochromator. View full abstract»

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  • A power-efficient thermocycler based on induction heating for DNA amplification by polymerase chain reaction

    Page(s): 2880 - 2883
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    We have built a thermocycler based on the principles of induction heating for polymerase chain reaction (PCR) of target sequences in DNA samples of interest. The cycler has an average heating rate of ∼0.8 °C/s and a cooling rate of ∼0.5 °C/s, and typically takes ∼4 h to complete a 40-cycle PCR protocol. It is power-efficient (∼6 W per reaction tube), micro-processor controlled, and can be adapted for battery operation. Using this instrument, we have successfully amplified a 350 bp segment from a plasmid and SRY, the human sex determining gene, which occurs as a single-copy sequence in genomic DNA of human males. The PCR products from this thermocycler are comparable to those obtained by the use of commercially available machines. Its easy front-end operation, low-power design, portability and low cost makes it suitable for diagnostic field applications of PCR. View full abstract»

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  • Resistive substrate heater for film processing by spray pyrolysis

    Page(s): 2884 - 2886
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    We describe a simple and inexpensive resistive heater usable in the spray pyrolysis process. It is based on a resistively heated ceramic plate. By using such a heater substrate temperatures exceeding 900 °C are easily achieved on the substrate. The heater consists of a ceramic plate enclosed in a stainless steel box. A refractory wire woven in a regular frame inside the ceramic provides an excellent heating uniformity over the entire surface. Performances and parameters of the system are given. We apply this device to the preparation of thick films of HTc oxides such as (Hg,Re)Ba2Ca2Cu3O8+δ. View full abstract»

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  • Signal processing in photoacoustic detection of phase transitions by means of the autospectra correlation-based method: Evaluation with ceramic BaTiO3

    Page(s): 2887 - 2891
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    This work describes a simple numerical procedure which, when applied to digitally recorded photoacoustic (PA) signals, allows the construction of thermal profiles (rS,drS/dT) to determine: the transition order, the phase transition temperature (Tc), and the phase transformation temperature range (ΔT), on samples, which undergo low–high transitions. During continuous heating of the sample, the ultrasonic signal was generated using a pulsed laser beam incident on a surface and detected on the opposite surface of the sample using a long quartz bar attached to a piezoelectric sensor. The thermal profile, rS, is built from a sequence of the ordinary correlation coefficients ri associated with an interval of temperature. The ri coefficients are calculated from amplitude spectra pairs. The amplitude spectra are obtained via fast Fourier transforms from original PA records. This procedure is applied on samples of bulk ceramic BaTiO3 to obtain their thermal behavior. The PA signal and temperature sample were registered every 0.2°. The samples were heated from room temperature to 137 °C at a rate of 0.1 °C min-1. The thermal profile rS shows the entire thermal history including the structural phase transition from tetragonal to cubic (T-C), which appears as a jump on the graph within an uncertainty of 2%. The drS/dT profile shows that the T-C phase transformation occurs over a range of temperatures. The results are in agreement with those reported in the literature. View full abstract»

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  • Design of a confocal microfluidic particle sorter using fluorescent photon burst detection

    Page(s): 2892 - 2898
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    An instrumental system is described for detecting and sorting single fluorescent particles such as microspheres, bacteria, viruses, or even smaller macromolecules in a flowing liquid. The system consists of microfluidic chips (biochips), computer controlled high voltage power supplies, and a fluorescence microscope with confocal optics. The confocal observation volume and detection electro-optics allow measurements of single flowing fluorescent particles. The output of the avalanche photodiode (single photon detector) is coupled to a real-time photon-burst detection device, which output can address the control of high voltage power supplies for sorting purposes. Liquid propulsion systems like electro-osmotic flow and plain electric fields to direct the particles through the observation volume have been tested and evaluated. The detection and real-time sorting of fluorescent microspheres are demonstrated. Applications of these biochips for screening of bacteriophages-type biolibraries are briefly discussed. View full abstract»

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  • Automated system for the study of volume holographic recording

    Page(s): 2899 - 2902
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    An instrument, the “Holometer,” for the automatic recording, reading, and evaluation of multiplexed volume holograms, has been designed and constructed. This apparatus is a valuable tool for the characterization of holographic recording materials, in the context of volume holographic technologies, as well as for general studies of holographic recording physics. View full abstract»

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  • Reduction of spurious resonance peaks in microcantilever tuning through substrate contact surface reduction

    Page(s): 2903 - 2905
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    The tuning capabilities of otherwise similar tapping mode atomic force microscope (AFM) cantilever probes, for use in air, can be improved by patterning the backside of the respective probe substrate. Three designs were tested and rated against a standard unpatterned substrate. It was shown that lowering the probe substrate contact surface area decreased the occurrence of spurious resonance peaks and resulted in cleaner tuning curves as compared to probes with higher contact surface areas. View full abstract»

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  • Phase mask based interferometer: Operation principle, performance, and application to thermoelastic phenomena

    Page(s): 2906 - 2920
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    A simple, versatile, sensitive optical interferometer based on diffractive optics is presented. The absence of a need for active stabilization, and a compact common-path design requiring two optical elements, make the interferometer ideal for time-resolved measurements in the picosecond through millisecond regimes. Its performance is characterized quantitatively, and its utility for local detection and scanning as well as spatially resolved imaging of thermoelastically induced strain is demonstrated. View full abstract»

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  • Wavelength-specific laser-activated switches for improved contrast ratio in generation of short THz pulses

    Page(s): 2921 - 2925
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    A method for designing and manufacturing wavelength-specific laser-activated reflection switches for use at THz frequencies is described. A key figure of merit for such switches is the contrast ratio, the ratio of power reflected after activation to that reflected before activation. The new switches improve the pulse contrast ratio by utilizing interference to suppress reflections prior to laser activation. Measurements using the University of California, Santa Barbara Free Electron Laser indicate that contrast ratios can be improved from approximately 60 to as large as 4.5×104 using the new switches. The switches improve contrast ratio by an average factor of 400, with peak improvement by a factor as large as 740. Such switches can be used in the generation of short THz pulses from narrow bandwidth sources and may also find applications in the extraction of single pulses from longer pulse trains. View full abstract»

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  • Pulsed Orotron—A new microwave source for submillimeter pulse high-field electron paramagnetic resonance spectroscopy

    Page(s): 2926 - 2936
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    A vacuum-tube device for the generation of pulsed microwave radiation in the submillimeter range (up to 380 GHz) is presented, designed for use as a source in a 360 GHz high-field/high-frequency electron paramagnetic resonance (EPR) spectrometer—the pulsed Orotron. Analogous to the known continuous wave (cw) version, in the pulsed Orotron microwave radiation is generated by the interaction of a nonrelativistic electron beam with a diffraction grating (stimulated Smith–Purcell radiation) in feedback with an open Fabry–Pérot resonator construction. The presented design extends the cw Orotron by a gate electrode and a high-voltage pulsing unit to control the electron beam current. The generated pulses at 360 GHz have pulse lengths from 100 ns–10 μs and a pulse power of (22±5) mW. The output in a broader frequency band between 320 and 380 GHz ranges from 20 up to 60 mW. Within a 10 μs time slot, incoherent pulse trains of arbitrary duration can be generated. The pulsed Orotron has been incorporated in the quasioptical microwave bridge of a heterodyne induction mode EPR spectrometer. The first free induction decay measurements at a microwave frequency of 360 GHz and a magnetic field of 12.8 T on a polycrystalline perylenyl–ion sample are presented and future applications and extensions of Orotron-EPR spectroscopy are discussed. View full abstract»

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  • Combining optical tweezers and patch clamp for studies of cell membrane electromechanics

    Page(s): 2937 - 2942
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    We have designed and implemented a novel experimental setup which combines optical tweezers with patch-clamp apparatus to investigate the electromechanical properties of cellular plasma membranes. In this system, optical tweezers provide measurement of forces at piconewton scale, and the patch-clamp technique allows control of the cell transmembrane potential. A micron-size bead trapped by the optical tweezers is brought in contact with the membrane of a voltage-clamped cell, and subsequently moved away to form a plasma membrane tether. Bead displacement from the trapping center is monitored by a quadrant photodetector for dynamic measurements of tether force. Fluorescent beads and the corresponding fluorescence imaging optics are used to eliminate the shadow of the cell projected on the quadrant photodetector. Salient information associated with the mechanical properties of the membrane tether can thus be obtained. A unique feature of this setup is that the patch-clamp headstage and the manipulator for the recording pipette are mounted on a piezoelectric stage, preventing relative movements between the cell and the patch pipette during the process of tether pulling. Tethers can be pulled from the cell membrane at different holding potentials, and the tether force response can be measured while changing transmembrane potential. Experimental results from mammalian cochlear outer hair cells and human embryonic kidney cells are presented. View full abstract»

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Aims & Scope

Review of Scientific Instruments, published by the American Institute of Physics, is devoted to scientific instruments, apparatus, and techniques.

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Editor
Albert T. Macrander
Argonne National Laboratory