One-dimensional Position Research Articles

Demonstration of imaging via backscattering of annihilation gamma rays

Imaging via backscattering of annihilation gamma rays (IBAG) is a technique for three-dimensional gamma ray imaging of objects when only one side is accessible, such as for objects behind a wall or other barrier. This technique utilizes a positron source to produce nearly collinear, 511-keV gamma rays in opposite directions. One of these provides timing and directionality tagging, while the other backscatters off the object to be imaged. The scattering location can be reconstructed using the relative timing of the two gamma ray signals and the positions at which they are detected. Excellent timing resolution is required, since the time-of-flight information is essential for reconstruction. Three-dimensional imaging requires two arrays of detectors, one for the 511-keV tagging gamma ray and one for the backscattered gamma ray. We are studying the feasibility of an IBAG system using LaBr 3 to give good timing resolution and energy-based event selection. This paper presents one-dimensional position reconstruction measurements from our laboratory system for a variety of objects and barriers.

Complexity and uniqueness in nursing practice: Commentary on Richards and Hamers (2009)

Richards and Hamers (2009) aim in their paper to ‘consider the place of randomised controlled trials in nursing’. In doing so, they make a number of largely unsubstantiated observations about ‘those that reject the positivist approach to science’, assuming that ‘readers will be familiar with the case made by objectors’. In fact, the only source cited by Richards and Hamers for the arguments against RCTs is a paper I wrote seven years ago for a somewhat different purpose (Rolfe, 2002). As the sole named ‘objector’ to the RCT, I will attempt here to correct some of the unreferenced and unsubstantiated misconceptions that Richards and Hamers put forward in their paper, and then expand on the somewhat simplistic and one-dimensional position attributed to myself and other unnamed and unreferenced authors who have questioned the place of the RCT in nursing. First, I do not ‘reject the positivist approach to science’, and nowhere in my paper which they cite as evidence of this view do I even mention positivism. What I have claimed elsewhere, however, is that whilst the positivist approach to science produces useful evidence for certain types of nursing interventions, the value of the ‘hard science’ paradigm for nursing is somewhat over-

Novel neutron spectroscopy and neutron monitoring using position sensitive detector

Neutron spectrometry is carried out using various methods, whereas the Bonner sphere method is widely used. The wide range of neutron energy measurements need to use multiple moderator spheres enclosing a neutron counting detector. We introduce the development of a novel type of neutron energy spectrometer using a high efficiency, one-dimensional position sensitive detector (PSD) and a cone shaped single moderator structure. This device is portable and useful to record data simultaneously. Such operations for rarely occurring events are not possible with multisphere device. Two different moderator structures with symmetrical and non-symmetrical shapes of variable thicknesses over the sensitive length of the PSD are designed and will be optimized for the best energy resolution. The neutron response along the PSD position is recorded using the compact module for pulse processing and digital division with an FPGA. The PSD response as a function of moderator thickness and neutron energy is observed for various neutron sources. We present the design concept of the spectrometer and results of the measurements carried out at DT neutron generator and using an AmF source. Neutron transmission and moderation data is simulated using the GEANT4 code. The measured data and energy response function is proposed to be used for the measurement of the neutron energy spectrum.

Cost-effective and high-resolution wavelength interrogation unit using an incomplete asymmetric arrayed waveguide grating

This paper presents a wavelength interrogation unit using an incomplete asymmetric arrayed waveguide grating (AWG) without output waveguides. The incomplete asymmetric AWG converts the wavelengths of the incident light into a spatial intensity distribution. The center of the spatial distribution is determined by a one-dimensional position sensitive detector (PSD). The simulation results show that wavelength shifts can be precisely interrogated by the device with a wavelength resolution of 3.5 pm. The device can be applied to the interrogation of fiber Bragg grating (FBG) temperature sensors with the temperature resolution of 0.3°C.

A method for measuring and calibrating resistive microtorque of a mechanical microcounter

This paper reports a technique for measuring the calibrating resistive input torque of a micro counter and gearbox assembly. The technique presented uses a hairspring (with a quantifiable output torque) to drive the input shaft to a mechanical counter and gearbox assembly in order to determine its resistive torque. The angular displacement of this spring, a parameter needed to compute the torque, is measured using a combination of a laser diode and a monolithic one-dimensional position sensitive device (PSD). This study includes the steps undertaken to develop it from a concept to functional prototype and interpretation of the results it yields. Tests show that in principle the use of a hairspring and PSD is a viable method of measuring micro-torque.

Evaluation of an integrated Fourier-transform spectrometer utilizing a lateral effect position sensitive detector with a multi-channel Fabry–Perot interferometer

The basis of this paper is the evaluation of an integrated multi-channel Fourier-transform (FT) spectrometer based on a multi-channel wedge Fabry–Perot interferometer and a one-dimensional lateral effect position sensitive detector (PSD). The use of a PSD for an interferogram readout allows for a simple scanning mechanism with no requirement for any position reference. The use of a wedge-shaped interferometer makes it possible to integrate it directly onto the PSD surface, thus producing a very compact spectrometer. The capabilities of the spectrometer are demonstrated by absorption spectral measurements using a reference sample. In addition, spectral measurements on 532 nm DPSS and 632.8 nm He–Ne lasers are presented. The resolution of the spectrometer is approximately 5 nm. The evaluated spectrometer set-up can be used in applications where compact and low cost spectrometers are required, such as in process control and in education. Further, it is shown that there are deteriorations in very high accuracy position measurements, which are caused by changes in incident light intensity. A model describing the above-mentioned nonlinearities was developed based on analysing the equivalent circuit for PSDs and parameters such as leakage current and serial resistance. Additionally, a method is proposed to assist in the reduction of the nonlinearity caused by this effect.

Characterization of one-dimensional position sensitive detectors with improved efficiency and position resolution for neutron spectrometers

Development and characterization of one-dimentional (1D) position sensitive detectors (PSDs) with improved efficiency and position resolution for neutron scattering applications are reported. The PSDs are characterized for energy resolution, count rate capability, sensitivity, efficiency, position resolution, and uniformity of response over the sensitive length. The studies are carried out to verify the dependence of position resolution on detector geometry, electronic noise, and stopping power of the fill gas. One of the PSDs is mounted on the small angle neutron scattering spectrometer and spectra from CTAB micelle sample are recorded using 5.4 A neutrons. A gain of factors 1.1 and 1.2 is obtained compared to earlier in house made 1D PSD and LND-made 1D PSD, respectively. The diffraction patterns from standard vanadium, nickel, and silicon samples are recorded on a powder diffractometer using newly designed PSDs. Gain in efficiency obtained at shorter wavelength of 0.783 A is by a factor of 1.6. All high pressure PSDs show improvement in the position resolution by 2-3 mm. It is observed that 1D PSD filled with isobutane as stopping gas improves the gamma tolerance and position resolution at lower partial pressures as compared to Kr. It is advantageous to use two or more 36C-type PSDs stacked together. It is economic and gives better efficiency due to scanning more beam height.

Developments of a New 1-Dimensional$gamma$-Ray Position Sensor Using Scintillators Coupled to a Si Strip Detector

In order to operate an improved Fourier synthesis imager at higher photon energies than are accessible with solid-state detectors, we developed a new one-dimensional gamma-ray position sensor consisting of inorganic scintillators whose light is read out by a silicon strip detector (SSD). The SSD is read out through stripped p-electrodes (DC-coupled, 32 channels at 400 mum pitch). The n-side of the SSD does not have a metallic surface, and has a relatively good optical transparency. A stack of optically isolated thin CsI(Tl) scintillator plates (10 mmtimes10 mm in area and 0.3 mm thick) is attached, edge-on, to the n-side of the SSD. When a gamma-ray photon hits the stacked scintillator, the generated scintillation light is detected by the SSD, with the signal pulse-height largest in the p-electrode which is just beneath the CsI plate hit by the gamma-ray. The 32-channel outputs from the SSD are acquired simultaneously for each event with a low-noise analog ASIC. The gamma-ray position can be calculated as a weighted mean of pulse heights. Using this system, we have obtained a position resolution significantly finer than 1 mm for gamma-rays with energies greater than ~500 keV up to ~ 1300 keV

Simultaneous position and state measurement of Rydberg atoms

We present a technique for state-selective position detection of cold Rydberg atoms. Ground state Rb atoms in a magneto-optical trap are excited to a Rydberg state and are subsequently ionized with a tailored electric field pulse. This pulse selectively ionizes only atoms in e.g. the 54d state and not in the 53d state. The released electrons are detected after a slow flight towards a micro channel plate. From the time of flight of the electrons the position of the atoms is deduced. The state selectivity is about 20:1 when comparing 54d with 53d and the one-dimensional position resolution ranges from 6 to 40 μm over a range of 300 μm. This state selectivity and position resolution are sufficient to allow for the observation of coherent quantum excitation transport.

A wide-angle magnetic spectrograph of a novel design

At the 5MV tandem accelerator of the CMAM we install a UHV magnetic spectrograph for the detection of scattered and recoiled ions. Its special feature is that the ions emerging from the sample are passing through a 4nm thick DLC foil before entering the spectrograph. The secondary electrons emerging from this foil upon passage of an ion are focused on a two-dimensional position sensitive multi-channel plate (MCP) detector with delay-line read-out. From their impact position on this detector the direction of the ion is determined with a precision of 0.15° within an elliptical cone of 6°×9°. The spectrograph, consisting of a 115° sector magnet with special shaped pole faces, focuses the ions onto a one-dimensional position sensitive MCP detector, also with delay-line read-out, in the focal plane of the magnet. The time delay of the coincident pulses in the first and second detector is measured so that the velocity v of the ion is known in addition to the magnetic rigidity mv/q, allowing determination of m/q. The energy resolution is determined by the straggling in the foil and amounts to ΔE/E≈10−3 for 2MeV α particles. Blocking patterns of scattered or recoiled ions can be measured in one run. Because of the ion identification implied in the system, recoil spectra can be generated with light ions used as projectile.

Insights on Amorphous Silicon Nip and MIS 3D Position Sensitive Detectors

This work aims to report results of the spatial and frequency optical detection limits of integrated arrays of 32 one-dimensional amorphous silicon thin film position sensitive detectors with nip or MIS structure, under continuous and pulsed laser operation conditions. The arrays occupy a total active area of 45 mm2 and have a plane image resolution better than 15 m with a cut-off frequency of about 6.8 kHz. The non-linearity of the array components varies with the frequency, being about 1.6% for 200 Hz and about 4% for the cut-off frequency (6.8 kHz).

Grant Hill, Postmodern Blackness,and Art: A Cultural Critique

This analysis argues that Grant Hill advances a critique of internal contradictions within Black communities; offers rival epistemologies of how to be Black, male, and an athlete; as well as connects concrete Black experience within an abstract museum setting. This examination grounds Hill's public statements of what he hopes to accomplish with the exhibition "Something All Our Own: The Grant Hill Collection of African American Art" within a rubric featuring theme, function, and quantity. Under examination are Hill's messages to understand the ways in which he seeks to demonstrate his multidimensionality and ability to transcend the one-dimensional identity position of Black male athlete.

Calibration of a Hall effect displacement measurement system for complex motion analysis using a neural network

Biomechanics studies often require the analysis of position and orientation. Although a variety of transducer and camera systems can be utilized, a common inexpensive alternative is the Hall effect sensor. Hall effect sensors have been used extensively for one-dimensional position analysis but their non-linear behavior and cross-talk effects make them difficult to calibrate for effective and accurate two- and three-dimensional position and orientation analysis. The aim of this study was to develop and calibrate a displacement measurement system for a hydraulic-actuation joystick used for repetitive motion analysis of heavy equipment operators. The system utilizes an array of four Hall effect sensors that are all active during any joystick movement. This built-in redundancy allows the calibration to utilize fully connected feed forward neural networks in conjunction with a Microscribe™ 3D digitizer. A fully connected feed forward neural network with one hidden layer containing five neurons was developed. Results indicate that the ability of the neural network to accurately predict the x, y and z coordinates of the joystick handle was good with r 2 values of 0.98 and higher. The calibration technique was found to be equally as accurate when used on data collected 5 days after the initial calibration, indicating the system is robust and stable enough to not require calibration every time the joystick is used. This calibration system allowed an infinite number of joystick orientations and positions to be found within the range of joystick motion.

On the use of one-dimensional position sensitive detector for x-ray diffraction reciprocal space mapping: Data quality and limitations

A homemade x-ray diffractometer using one-dimensional position sensitive detector (PSD) and well suited to the study of thin epitaxial layer systems is presented. It is shown how PSDs can be advantageously used to allow fast reciprocal space mapping, which is especially interesting when analyzing poor crystalline and defective layers as usually observed with oxides and ceramics films. The quality of the data collected with such a setup and the limitations of PSDs in comparison with the use of analyzer crystals are discussed. In particular, the effects of PSD on angular precision, instrument resolution and corrections that must be applied to raw data are presented.

Saturation magnetostriction coefficient measurement of CoCrPt alloy thin films using a highly sensitive optical deflection-detecting system

We report on the saturation magnetostriction coefficient of 500Å(Co82Cr18)100−xPtx and xÅ(Co82Cr18)79Pt21 alloy thin films with perpendicular magnetic anisotropy. The CoCrPt alloy films were prepared by dc magnetron sputtering and the magnetostriction coefficients were measured via a highly sensitive optical deflection-detecting system using a one-dimensional position sensitive detector. The saturation magnetostriction coefficient is increased from −7.23×10−6 to 8.5×10−6 and from −8×10−6 to 14×10−6 with increasing the Pt concentration from 0to35at.% and the film thickness from 400to800Å, respectively. X-ray diffractometry study revealed that crystalline orientation in CoCrPt alloy film, which depends on the Pt concentration and the CoCrPt film thickness, strongly influences the evolution of saturation magnetostriction coefficient.

Application of refraction contrast tomography

It has been shown in earlier works that smallest beam deviations (μrad) caused by refraction can be used to reconstruct the macroscopic inner structure of samples by the means of tomography. Hence, structures of low contrast materials, i.e. materials with low values or differences of attenuation coefficients, could be imaged by tomographic reconstruction although the conventional attenuation contrast method failed. Such tomographic scans have mainly been performed in a bent crystal-type double crystal diffractometer (DCD) using a one-dimensional position sensitive detector (PSD). This setup provided only q-resolution in the PSD, while the spatial resolution was achieved by scanning the sample through a slit collimated beam. The first practical application of this method shall be introduced here and advantages compared to the conventional method will be discussed. The measurement of two samples, a test with a dummy sample and a measurement of a sample requested by a company, are the examples to be reported.

Fine structure of distributions and central limit theorem in diffusive billiards

We investigate deterministic diffusion in periodic billiard models, in terms of the convergence of rescaled distributions to the limiting normal distribution required by the central limit theorem; this is stronger than the usual requirement that the mean-square displacement grow asymptotically linearly in time. The main model studied is a chaotic Lorentz gas where the central limit theorem has been rigorously proved. We study one-dimensional position and displacement densities describing the time evolution of statistical ensembles in a channel geometry, using a more refined method than histograms. We find a pronounced oscillatory fine structure, and show that this has its origin in the geometry of the billiard domain. This fine structure prevents the rescaled densities from converging pointwise to Gaussian densities; however, demodulating them by the fine structure gives new densities which seem to converge uniformly. We give an analytical estimate of the rate of convergence of the original distributions to the limiting normal distribution, based on the analysis of the fine structure, which agrees well with simulation results. We show that using a Maxwellian (Gaussian) distribution of velocities in place of unit speed velocities does not affect the growth of the mean-square displacement, but changes the limiting shape of the distributions to a non-Gaussian one. Using the same methods, we give numerical evidence that a nonchaotic polygonal channel model also obeys the central limit theorem, but with a slower convergence rate.

The Keller--Segel Model with Logistic Sensitivity Function and Small Diffusivity

The Keller--Segel model is the classical model for chemotaxis of cell populations. It consists of a drift-diffusion equation for the cell density coupled to an equation for the chemoattractant. Here a variant of this model is studied in one-dimensional position space, where the chemotactic drift is turned off for a limiting cell density by a logistic term and where the chemoattractant density solves an elliptic equation modeling a quasi-stationary balance of reaction and diffusion with production of the chemoattractant by the cells. The case of small cell diffusivity is studied by asymptotic and numerical methods. On a time scale characteristic for the convective effects, convergence of solutions to weak entropy solutions of the limiting nonlinear hyperbolic conservation law is proven. Numerical and analytic evidence indicates that solutions of this problem converge to irregular patterns of cell aggregates separated by entropic shocks from vacuum regions as time tends to infinity. Close to each of these p...

Flexible position sensitive photodetectors based on a-Si:H heterostructures

This work describes the fabrication and characterization of an improved version of large area ( 5 mm×80 mm with an active length of 70 mm) flexible position sensitive detectors deposited onto polymeric substrates (polyimide–Kapton ® VN). The new configuration presented by the sensor is based on a heterostructure of a-Si:H/ZnO:Al. The sensors were characterized by spectral response, photocurrent dependence as a function of light intensity and position detection measurements. The set of data obtained on one-dimensional position sensitive detectors based on the heterostructure show excellent performances with a maximum spectral response of 0.12 A/W at 500 nm and a non-linearity of ±10% over 70 mm length. The produced sensors present a non-linearity higher than those ones produced on glass substrates, due to the different thermal coefficients exhibited by the polymer and the amorphous silicon film. In order to prove this behaviour, it was measured the defect density obtained by the constant photocurrent method on amorphous silicon deposited on polymeric substrates bended with different radius of curvature.

Detection Limits of a nip a-Si:H Linear Array Position Sensitive Detector

ABSTRACTThis paper presents results of the spatial and frequency detection limits of an integrated array of 32 one-dimensional amorphous silicon thin film position sensitive detectors with a nip structure, under continuous and pulsed laser operation conditions. The data obtained show that 0.45×0.06 cm arrays, occupying a total active area of about 1 cm2 have a spatial resolution better than 10 m m (modulation transfer function of about 0.2), with a cut-off frequency of about 6.8 KHz. Besides that, under pulsed laser conditions the device non-linearity has its minimum (about 1.6%), for a frequency of about 200Hz. Up to the limits of the cut-off frequency, the device nonlinearity increases to values above 4%.