A method of extending the dynamic range when transferring the dimensions of the unit of electrostatic field strength

Two equivalent methods of extending the dynamic range when transferring the dimensions of the unit of electrostatic field strength are proposed and analyzed. Both methods are based on the fact that the electrostatic field strength depends on the parameters of the electrostatic field generator and the position of the point of observation. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 49–51, May, 2006.     

Delta-doped electron-multiplied CCD with absolute quantum efficiency over 50% in the near to far ultraviolet range for single photon counting applications

We have used molecular beam epitaxy (MBE) based delta-doping technology to demonstrate nearly 100% internal quantum efficiency (QE) on silicon electron-multiplied charge-coupled devices (EMCCDs) for single photon counting detection applications. We used atomic layer deposition (ALD) for antireflection (AR) coatings and achieved atomic-scale control over the interfaces and thin film materials parameters. By combining the precision control of MBE and ALD, we have demonstrated more than 50% external QE in the far and near ultraviolet in megapixel arrays. We have demonstrated that other important device performance parameters such as dark current are unchanged after these processes. In this paper, we briefly review ultraviolet detection, report on these results, and briefly discuss the techniques and processes employed.     

Monte Carlo simulation of the photon beam characteristics from medical linear accelerators

The MCNPX code has been employed on a personal computer to calculate the dosimetric characteristics of the photon beams from the 6 MV Siemens MX2 and the 10 MV Varian Clinac 2100C linear accelerators. A model of the treatment head includes the major geometric structure within the beam path. The model was used to calculate the energy spectra of the photon beam, percentage depth dose and the dose profiles. The accuracy of the calculated results is examined by comparing them with the measured dose distributions for the two machines. The computed and measured depth dose curves agree to within 2% for all the depths beyond the build-up region for both treatment machines. The calculations agree to within 2% of the measured profiles within the 100-50% dose level. It has been found that the MCNPX code is an effective tool for simulating the clinical photon beam.     

Reply to: Practical voltage/current controlled grounded resistor with dynamic range extension

In response to Prof. Senani comments to our paper entitled 'Practical voltage/current controlled grounded resistor with dynamic range extension', we wish to state that we were not aware of his previous work done in this area as referenced by his supplied list of references. We ourselves had a long list of references as much work has been done in this area. For this, the authors thank him for drawing it to our attention, given his work relies upon the same technique 'Bisection of the drain-to-source voltage of the FET'. As such we would have cited it had we been aware of it. Therefore we welcome his drawing his previous work to our attention.     

Ion mobility separation of variant histone tails extending to the "middle-down" range

Differential ion mobility spectrometry (FAIMS) can baseline-resolve multiple variants of post-translationally modified peptides extending to the 3-4 kDa range, which differ in the localization of a PTM as small as acetylation. Essentially orthogonal separations for different charge states expand the total peak capacity with the number of observed states that increases for longer polypeptides. This potentially enables resolving localization variants for yet larger peptides and even intact proteins.     

Black box linearization for greater linear dynamic range: the effect of power transforms on the representation of data

Power transformations are commonly used in image processing techniques to manipulate image contrast. Many analytical results, including chromatograms, are essentially presented as images, often to convey qualitative information. Power transformations have remarkable effects on the appearance of the image, in chromatography, for example, increasing apparent resolution between peaks by the factor √n and apparent column efficiency (plate counts) by a factor of n for an nth-power transform. The profile of a Gaussian peak is not qualitatively changed, but the peak becomes narrower, whereas for an exponentially tailing peak, asymmetry at the 10% peak height level changes markedly. Using several examples we show that power transforms also increase signal-to-noise ratio and make it easier to discern an event of detection. However, they may not improve the limit of detection. Power responses are intrinsic to some detection schemes, and in others they are imbedded in instrument firmware to increase apparent linear range that the casual user may not be aware of. The consequences are demonstrated and discussed.     

Coupled electron/photon Monte Carlo calculations of X-ray scattering with application to industrial radiography

Monte Carlo transport methods are used to simulate the scattering of X-rays in polystyrene and iron slabs. The calculations are made with monoenergetic X-ray sources in the energy region from 30 keV (100 keV for iron) to 20 MeV. This energy range includes the energy regions for diagnostic radiology (0.03–0.15 MeV), nuclear medicine (0.1–2.0 MeV) and industrial radiography (0.2–20 MeV). slab thicknesses for polystyrene were 53, 100, and 210 mm and for iron 7 and 14 mm. The present calculations include the effects of secondary electron/positron radiation which become quite important at high energies. As a function of the incident photon energy, the ratio of the scattered to the total radiation (scatter fraction) was found to have a characteristic ‘N’ shape. Increasing the atomic number of the scattering media has the effect of ‘squeezing the N’.     

Nine orders of magnitude dynamic range: picomolar to millimolar concentration measurement in capillary electrophoresis with laser induced fluorescence detection employing cascaded avalanche photodiode photon counters

The dynamic range of capillary electrophoresis analysis is ultimately limited by molecular shot noise at low concentrations and by concentration-induced band broadening at high concentrations. We report a system that approaches these fundamental limits. A laser-induced fluorescence detector is reported that employs a cascade of four fiber-optic beam splitters connected in series to generate a primary signal and four attenuated signals, each monitored by a single-photon counting avalanche photodiode. Appropriate scaling of the signals from the five photodiodes produces a linear optical calibration curve for 5-carboxyl-tetramethylrhodamine from the concentration detection limit of 1 pM to the upper limit of 1 mM. Mass detection limits are 120 yoctomoles (70 molecules) injected into the instrument. The very-wide dynamic range instrument was used to study the metabolic products of the fluorescently labeled glycosphingolipid tetramethylrhodamine labeled GM1 (GM1-TMR) produced by single cells isolated from the rat cerebellum.     

Sorting method to extend the dynamic range of the Shack-Hartmann wave-front sensor

We propose a simple and powerful algorithm to extend the dynamic range of a Shack-Hartmann wave-front sensor. In a conventional Shack-Hartmann wave-front sensor the dynamic range is limited by the f-number of a lenslet, because the focal spot is required to remain in the area confined by the single lenslet. The sorting method proposed here eliminates such a limitation and extends the dynamic range by tagging each spot in a special sequence. Since the sorting method is a simple algorithm that does not change the measurement configuration, there is no requirement for extra hardware, multiple measurements, or complicated algorithms. We not only present the theory and a calculation example of the sorting method but also actually implement measurement of a highly aberrated wave front from nonrotational symmetric optics.     

The response of lif thermoluminescence dosemeters to photon beams in the energy range from 30 kV x rays to 60Co gamma rays

The energy response of standard (TLD-100) and high-sensitivity (TLD-100H) LiF thermoluminescence dosemeters (TLDs) has been studied for photon beams with mean energies from about 25 keV to 1100 keV. Canadian primary standards for air kerma were used to establish the air kerma rates for each of the photon beams. TLDs were mounted in a PMMA holder and the air kerma response was measured as a function of energy. The EGSnrc Monte Carlo code was used to model the TLD holder and calculate the absorbed dose to the TLD chip per unit air kerma for each beam. The measured and calculated results were combined to obtain the intrinsic dose response of the TLD chip. Broadly, our results are consistent with existing data, which show a marked difference in the energy dependence of the two materials. However, the precision of our measurements (standard uncertainty of about 0.6%) has permitted the identification of features that have not been noted before. In particular, the energy dependence of the two materials is quite different in the important energy region delimited by 137Cs and 60Co gamma rays.     

Operation of ion-selective electrode detectors in the sub-Nernstian/linear response range: application to flow-injection/enzymatic determination of L-glutamine in bioreactor media.

A novel approach for eliminating positive errors from endogenous ionic interferences when using ion-selective electrodes as detectors in flow-injection enzyme-based blosensing configurations is described. The method involves using a high background level of interfering ions in the sample diluent/carrier stream to convert the normally logarithmic potentiometric sensor into a linear detector over a given concentration range of primary ions. A split-stream single-detector arrangement provides a convenient means to compensate for varying levels of background interferent ions in the injected samples. One portion of the split stream passes directly to the ion-electrode detector, yielding a signal linearly related to the concentration of endogenous primary ions in the sample. The second portion of the split sample is delayed while passing through an immobilized enzyme that generates electrode detectable primary ions in proportion to the concentration of the substrate analyte in the sample. Two linear equations with two unknowns describe the twin potentiometric responses observed. The concept is demonstrated by the accurate determination of L-glutamine in hybridoma bioreactor media via the use of an ammonium-ion-selective membrane electrode detector and immobilized glutaminase enzyme.     

Towards the enhancement of the photon/neutron discrimination of C6D6 detectors in the range from 1 to 10 MeV using liquid scintillator materials doped with high-Z elements

The study on the behaviour of deuterated benzene detectors in the energy range from 1 to 10 MeV has been carried out. It is shown that the photon-to-neutron discrimination, attained with standard detectors, can be improved by doping the C6D6 liquid scintillator with high-Z elements. The motivation for doping the organic scintillator stems from the fact that they should increase the gamma detection efficiencies with no significant changes in the abilities to detect neutrons. The results obtained using the MCNP and EGS4 codes show that increasing the fraction of high-Z elements: (a) the energy deposited in the medium by photons increases, (b) the energy deposited by neutrons decreases and (c) the rate of detection of photon/neutron is enhanced. Owing to their low sensitivity to neutrons and the enhanced gamma detection efficiency, these detectors could be ideally used to carry out studies in mixed neutron-photon fields in the energy range considered and to assess the gamma backgrounds in noisy neutron environments.     

Response of linear dynamic systems to non-Erlang renewal impulses: Stochastic equations approach

Linear dynamical systems under random trains of impulses driven by a class of non-Erlang renewal processes are considered. The class considered is the one where the renewal events are selected from an Erlang renewal process. The original train of impulses is recast, with the aid of an auxiliary stochastic variable, in terms of two independent Poisson processes. Thus, by augmenting the state vector of the dynamic system with the auxiliary stochastic variables, the original non-Markov problem is converted to a Markov one.

The differential equations for the response statistical moments can then be derived from the generalised Ito's differential rule.

Numerical results obtained for a few different models and various sets of parameters, show that the present approach allows to account for a variety of inter arrival time's probability distributions. Transient mean value and variance of the response of a linear oscillator have been obtained from the equations for moments.