Counting Array Research Articles

A new mathematical model for determining full-energy peak efficiency of an array of two gamma detectors counting rectangular parallelepiped sources

This work deals with full-energy peak efficiency for a counting array of two NaI(Tl) scintillation detectors (2"x 2" and 3" x 3" with 7.5% and 8.5% resolutions, respectively) and radioactive sources in the form of rectangular parallelepipeds of various dimensions. Aqueous solutions containing the 152Eu radionuclide were used; the latter exhibits a favourable multiline gamma spectrum covering a wide energy range from121.78 keV up to 1408.03 keV. A new mathematical and analytical approach to the problem is developed. The well known, accurate and widely used efficiency transfer principle is applied, together with detector efficiency calculations based on the effective solid angle concept. The self-attenuation of the source matrix, attenuation by the source container and detector housing materials, as well as a number of other relevant details of the experimental set-up were duly accounted for. A remarkable agreement between the measured and calculated efficiencies was observed for a variety of source-to-detectors distances, confirming the reliability of the method developed.

Photon location in spacetime

The Newton–Wigner basis of orthonormal localized states is generalized to orthonormal and relativistic biorthonormal bases on an arbitrary hyperplane in spacetime. This covariant formalism is applied to the measurement of photon location using a hypothetical three-dimensional (3D) array with pixels throughout space turned on at a fixed time and a timelike 2D photon counting array detector with good time resolution. A moving observer will see these detector arrays as rotated in spacetime but the spacelike and timelike experiments remain distinct.

Alpinetin suppresses proliferation of human hepatoma cells by the activation of MKK7 and elevates sensitization to cis-diammined dichloridoplatium.

Alpinetin is a type of novel plant flavonoid derived from Alpinia katsumadai Hayata, found to possess strong anti-hepatoma effects. However, the detailed antitumor mechanism of Alpinetin remains unclear. Mitogen-activated protein kinase kinase-7 (MKK7) can regulate cellular growth, differentiation and apoptosis. The aim of this study was to investigate the role of MKK7 in the anti-hepatoma effect mediated by Alpinetin. HepG2 cells were treated with Alpinetin at various doses and for different times, and the levels of phosphorylated MKK7 (p-MKK7) and total MKK7 were tested by RT-PCR and Western blotting. Following transient transfection with RNA interference, cell viability and cell cycle stage were determined using methyl thiazolyl tetrazolium assay and flow cytometry, in order to assess the antitumor action of Alpinetin. In addition, chemosensitization to cis-diammined dichloridoplatium (CDDP) by Alpinetin was assessed by cell counting array and the cell growth inhibitory rate was calculated. The results showed that Alpinetin suppressed HepG2 cell proliferation and arrested cells in the G0/G1 phase by up-regulating the expression levels of p-MKK7. On the contrary, inhibiting the expression of MKK7 reversed the antitumor effect of Alpinetin. Moreover, Alpinetin enhanced the sensitivity of HepG2 hepatoma cells to the chemotherapeutic agent CDDP. Taken together, our studies indicate that activation of MKK7 mediates the anti-hepatoma effect of Alpinetin. MKK7 may be a putative target for molecular therapy against hepatoma and Alpinetin could serve as a potential agent for the development of hepatoma therapy.

β-elemene inhibits proliferation of human glioblastoma cells through the activation of glia maturation factor β and induces sensitization to cisplatin

β-elemene, a natural drug extracted from Curcuma wenyujin, strongly inhibits glioblastoma growth. However, the mechanism of β-elemene antitumor action remains unclear. Glia maturation factor β (GMFβ) regulates cellular growth, fission, differentiation and apoptosis. It has been reported that overexpression of GMFβ inhibits the growth of glioblastoma cells and decreases tumor volume. To illustrate the role of GMFβ in the anti-proliferative effect of β-elemene in glioblastoma, U87 cells were treated with β-elemene at various doses and for different periods of time, and levels of phospho-GMFβ (p-GMFβ) and total GMFβ were determined by immunoprecipitation and western blot analysis. Upon GMFβ silencing using RNA interference, the antitumor action of β-elemene was evaluated in a methyl thiazolyl tetrazolium assay and by semi-quantitative western blot analysis of MKK3/6 and p-MKK3/6 expression. Finally, chemosensitization to cisplatin by β-elemene was examined using a cell counting array, and the cell growth inhibitory rate was calculated. The results showed that β-elemene inhibits U87 cell viability through the activation of the GMFβ signaling pathway. Conversely, silencing the expression of GMFβ reversed the antitumor effect of β-elemene and impaired the phosphorylation of MKK3/6. Furthermore, β-elemene increased the sensitivity of U87 glioblastoma cells to the chemotherapeutic agent cisplatin. Taken together, these results suggest that activation of the GMFβ pathway mediates the antitumor effect of β-elemene in glioblastoma. GMFβ is a putative molecular target for glioblastoma therapy.

Scintillation induced response in passively-quenched Si-based single photon counting avalanche diode arrays

An optical electrical model which studies the response of Si-based single photon counting arrays, specifically silicon photomultipliers (SiPMs), to scintillation light has been developed and validated with analytically derived and experimental data. The scintillator-photodetector response in terms of relative pulse height, 10%-90% rise/decay times to light stimuli of different rise times (ranging from 0.1 to 5 ns) and decay times (ranging from 1 to 50 ns), as well as for different decay times of the photodetector are compared in theory and simulation. A measured detector response is used as a reference to further validate the model and the results show a mean deviation of simulated over measured values of 1%.

A system for real-time in situ photoelectron spectroscopy

A system is presented which combines photoelectron spectroscopy with complementary characterization techniques in order to provide in situ analysis of surfaces processes. The real-time capability of photoelectron spectroscopy has been enabled by an electron counting array detector that allows core and valence level spectra to be recorded in 1–10 s using a laboratory X-ray source and as low as 25 ms when coupled to synchrotron radiation source.The efficient detection system is combined with a versatile heater stage, temperature and vacuum monitoring, and controllable evaporation sources in order to monitor chemical, structural and electronic changes in situ. The heated stage allows a range of programmed heating and cooling regimes to be applied to samples. Evaporation sources are provided for medium-temperature materials such as small organic molecules and high-temperature metals such as aluminium. The system has a linked vacuum vessel for plasma etching and Ar ion sputtering for surface preparation.

Photon position measure

The positive operator valued measure (POVM) for a photon counting array detector is derived and found to equal photon flux density integrated over pixel area and measurement time. Since photon flux density equals number density multiplied by the speed of light, this justifies theoretically the observation that a photon counting array provides a coarse grained measurement of photon position. The POVM obtained here can be written as a set of projectors onto a basis of localized states, consistent with the description of photon position in a recent quantum imaging proposal [M. Tsang, Phys. Rev. Lett. \textbf{102}, 253601 (2009)]. The wave function that describes a photon counting experiment is the projection of the photon state vector onto this localized basis. Collapse is to the electromagnetic vacuum and not to a localized state, thus violating the text book rules of quantum mechanics but compatible with the theory of generalized observables and the nonlocalizability of an incoming photon.

MRI‐phased array evaluation using a human body model

AbstractWe develop methodology to evaluate MRI‐phased array receivers using an anatomically and electromagnetically accurate human body model. The human body model accurately represents the different permittivity and conductivity values of various tissue types in the human body, at the frequency of interest. The phased array receiver is a posterior array with 16 coils, typically placed on the patient table for imaging. We obtain the electric and magnetic fields associated with each coil using the finite‐difference time‐domain method and estimate a simplified metric to evaluate the receiver array contribution to the signal‐to‐noise ratio (SNR) distribution. The results highlight SNR variation in the left–right direction, an artifact seen in imaging, but not apparent in quasi‐static simulations with uniform phantoms. We use the results to compare two design variations of 16‐coil phased arrays. In addition, we use the results to compare imaging methods that have potential to reduce the computational complexity of high channel count arrays by reducing the number of data streams used in image reconstruction. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 37B: 20–28, 2010

Development and Demonstration of Measurement-Time Efficient Methods for Impedance Spectroscopy of Electrode and Sensor Arrays.

The development of impedance-based array devices is hindered by a lack ofrobust platforms and methods upon which to evaluate and interrogate sensors. One aspectto be addressed is the development of measurement-time efficient techniques forbroadband impedance spectroscopy of large electrode arrays. The objective of this workwas to substantially increase the low frequency impedance measurement throughputcapability of a large channel count array analyzer by developing true parallel measurementmethods. The goal was achieved by Fourier transform-based analysis of simultaneouslyacquiredmulti-channel time-based current and voltage data. Efficacy and quantitativeanalysis of the parallel approach at frequencies less than ca. 10 Hz as well as a combinedsequential parallel approach for efficient broadband impedance spectroscopy over 5-orders of magnitude in frequency is demonstrated through complex impedancemeasurement of arrays consisting of up to 100 elements.

Effect of an aerosol deposition pattern in the lung on the counting efficiency of a large area germanium detector array

The Human Monitoring Laboratory has extended the use of sliced lungs containing planar sources to simulate heterogeneous radionuclide deposition patterns. This work examined two deposition patterns and their effect on the counting efficiency of low-energy photons. The results have shown that heterogenous distributions can be difficult to detect in some cases and can still lead to large uncertainties (up to a factor of 2.5) in the activity estimate, especially at low photon energies. At higher energies ( approximately 60 keV), the effect of the heterogeneous distribution is greatly reduced and errors in the activity estimate reduced to approximately 25%. The presence of a heterogenous distribution can be detected by comparing the ratio of the individual detector counts with the expected values obtained from measuring multiple lungs sets that contained a homogeneous distribution. The distributions tested in this paper were detectable (at 2sigma) as heterogeneous by two of the four detectors in the counting array.

Photon counting arrays for astrophysics

A compact system for counting and time-tagging single photons is presented, based on a monolithic array sensor of 60 pixels able to detect single photons, namely the single-photon avalanche diode array (SPADA). First, the working principle and performance of the single-photon detector pixel is detailed, with particular attention paid to monolithic array integration. Then the electronics needed to quench each pixel after avalanche ignition, namely the active-quenching circuit (AQC) is discussed, since the features of this quenching electronics dramatically affect the operating conditions of the detector, hence its actual performance. The discussion then focuses on integration of the SPADA system into Astrophysics applications such as adaptive optics, fast-transient imaging and atmospheric layer sensing. The whole electronics necessary to control SPADA operating conditions and temperature is also described, together with the complete opto-mechanics used to focus the telescope pupil onto the detector. Finally, experimental results are reported.

What do the hands externalize in simple arithmetic?

In 4 experiments, the authors examined the use of the hands in simple arithmetic tasks. Experiments 1 and 2 demonstrated that pointing increases both accuracy and speed in counting arrays of items, whether those items are identical or distinctive. Experiment 3 demonstrated that individuals tend to nod their heads when not allowed to point and that nodding is associated with greater accuracy, suggesting that pointing is functional for reasons other than simply providing additional visual information. Experiment 4 examined changes in speech when adding arrays of digits, depending on whether participants were allowed to use their hands to manipulate the tokens on which the digits were presented. Taken together, the results of these experiments are consistent with recent research suggesting that gesture can serve cognitive functions and that the hands can support the binding of representational elements to their functional roles by providing phase markers for cyclic cognitive processes.

Pyroelectric IR sensor arrays for fall detection in the older population

Uncooled pyroelectric sensor arrays have been studied over many years for their uses in thermal imaging applications. These arrays will only detect changes in IR flux and so systems based upon them are very good at detecting movements of people in the scene without sensing the background, if they are used in staring mode. Relatively-low element count arrays (16x 16) can be used for a variety of people sensing applications, including people counting (for safety applications), queue monitoring etc. With appropriate signal processing such systems can be also be used for the detection of particular events such as a person falling over. There is a considerable need for automatic fall detection amongst older people, but there are important limitations to some of the current and emerging technologies available for this. Simple sensors, such as I or 2 element pyroelectric infra-red sensors provide crude data that is difficult to interpret; the use of devices worn on the person, such as wrist communicator and motion detectors have potential, but are reliant on the person being able and willing to wear the device; video cameras may be seen as intrusive and require considerable human resources to monitor activity while machine-interpretation of camera images is complex and may be difficult in this application area. The use of a pyroelectric thermal array sensor was seen to have a number of potential benefits. The sensor is wall-mounted and does not require the user to wear a device. It enables detailed analysis of a subject's motion to be achieved locally, within the detector, using only a modest processor. This is possible due to the relative ease with which data from the sensor can be interpreted relative to the data generated by alternative sensors such as video devices. In addition to the cost-effectiveness of this solution, it was felt that the lack of detail in the low-level data, together with the elimination of the need to transmit data outside the detector, would help to avert feelings intrusiveness on the part of the end-user. The main benefits of this type of technology would be for older people who spend time alone in unsupervised environments. This would include people living alone in ordinary housing or in sheltered accommodation (apartment complexes for older people with local warden) and non-communal areas in residential/nursing home environments (e.g. bedrooms and ensuite bathrooms and toilets). This paper will review the development of the array, the pyroelectric ceramic material upon which it is based and the system capabilities. It will present results from the Framework 5 SIMBAD project, which used the system to monitor the movements of elderly people over a considerable period of time.

An evaluation of germanium detectors employed for the measurement of radionuclides deposited in lungs using an experimental and Monte Carlo approach.

A study was undertaken to evaluate the performance of an advanced design broad energy germanium detector for the in vivo measurement of radionuclides in lungs. Relative counting efficiency, background, and sensitivity for lung counting arrays consisting of four, three, and two 80-mm-diameter by 20-mm-thick (80 x 20 mm) broad energy germanium detectors were simulated by collecting spectra with the single 80 x 20 mm broad energy germanium at each of four locations over a humanoid torso phantom. Regions of interest were evaluated for photon energies ranging from 17 to 1,500 keV. The 80 x 20 mm detector arrays were then benchmarked against a standard array of four 70-mm-diameter by 20-mm-thick (70 x 20 mm) broad energy germanium detectors. Since testing new equipment can be an expensive and time consuming process, an alternative approach, using Monte Carlo simulations instead of physical measurements, was also evaluated and compared to experimental data. With this approach, counting efficiency and minimum detectable amount were simulated for two sizes of germanium detectors (70 mm and 80 mm diameter) at four different crystal thicknesses (15, 20, 25, and 30 mm). For the experimental measurements, arrays consisting of three and four 80 x 20 mm broad energy germanium detectors resulted in an increase in counting efficiencies, relative to the standard array, at all photon energies. The greatest relative increase was observed for the four-detector array (24-35%). In contrast, counting efficiency decreased, relative to the standard array, by 24-28% with a two-detector array. Arrays consisting of two and three 80 x 20 mm broad energy germanium detectors resulted in decreased relative background at all photon energies, with the exception of the 946 keV photon for the three-detector array. The most significant decrease in background occurred with the two-detector array (28 to 40%), while background was increased by 18-43% for the four-detector array. Arrays consisting of three and four 80 x 20 mm broad energy germanium detectors resulted in increased relative sensitivity at all photon energies. The three-detector array provided the greatest sensitivity at photon energies below 344 keV. The four-detector array provided slightly better measurement sensitivity at photon energies greater than 344 keV. The two 80 x 20 mm detector array provided sensitivity unexpectedly comparable to the standard array. Monte Carlo predictions on how size affects counting efficiency and minimum detectable amount agreed well with the experimental results. From the Monte Carlo predictions, the effect of detector thickness on counting efficiency was unimportant at photon energies up to 60 keV and independent of detector diameter. At higher photon energies for both detector diameters, the counting efficiency decreased as the thickness decreased. The values of minimum detectable amount for the 70-mm and 80-mm diameter detectors did not differ by more than 15% at 17 keV or 20% at 60 keV when compared to detectors of equivalent thickness. Minimum detectable amount increased slightly at 17 keV and rose by approximately 52% at 660 keV, with decreases in thickness from 30 mm to 15 mm.

A neural interface for a cortical vision prosthesis

The development of a cortically based vision prosthesis has been hampered by a lack of basic experiments on phosphene psychophysics. This basic research has been hampered by the lack of a means to safely stimulate large numbers of cortical neurons. Recently, a number of laboratories have developed arrays of silicon microelectrodes that could enable such basic studies on phosphene psychophysics. This paper describes one such array, the Utah electrode array, and summarizes neurosurgical, physiological and histological experiments that suggest that such an array could be implanted safely in visual cortex. We also summarize a series of chronic behavioral experiments that show that modest levels of electrical currents passed into cortex via this array can evoke sensory percepts. Pending the successful outcome of biocompatibility studies using such arrays, high count arrays of penetrating microelectrodes similar to this design could provide a useful tool for studies of the psychophysics of phosphene perception in human volunteers. Such studies could provide a proof-of-concept for cortically based artificial vision.

CAN DEFICITS IN SPATIAL INDEXING CONTRIBUTE TO SIMULTANAGNOSIA?

Patient AMA suffered a head trauma that left her with several visual complaints, including a reading disability. AMA appears to suffer from simultanagnosia, as established with tasks such as naming briefly presented multiple stimuli or overlapping figures, describing the theme of complex scenes, and counting arrays of stimuli. Specifically, AMA has difficulty perceiving immediately successive stimuli and, in particular, multiple stimuli that appear at novel or unexpected locations. Her ability to encode spatial relations rapidly (of either the categorical and coordinate type) is markedly reduced. However, when a familiar target appears among multiple stimuli at expected (previously encoded) locations, AMA's performance can be within normal limits. These results suggest that this patient's simultanagnosia cannot be reduced to an inability to process multiple stimuli per se. Rather it is better characterised as (1) an inability to index new locations of multiple stimuli, and (2) a reduced efficiency in pattern analysis. The former deficit, in turn, may lead to difficulty in focusing on objects efficiently and using objects as landmarks or reference points. Damage to one or both of the above mechanisms could produce simultanagnosia and reading difficulty.

Recent progress in high-performance anion-exchange chromatography/ionspray mass spectrometry for molecular mass determination and characterization of carbohydrates using static and scanning array detection

Position- and time-resolved ion counting (PATRIC) array detection with a magnetic sector mass spectrometer equipped with an ionspray interface in the on-line coupling of high-performance anion-exchange chromatography (HPAEC) with mass spectrometry (MS) is described. PATRIC array detection is used in both the static and scanning mode for molecular mass determination and structure characterization caused by nozzle/skimmer-induced fragmentation in the ionspray interface. The virtual mass range is extended to over 7000 Da by the presence of triply and quadruply sodiated molecules in an enzyme digest of an exocellular polysaccharide (EPS) of Lactococcus lactis and quadruply sodiated molecules of β-1,4-xylose oligomers. After optimization of the HPAEC/MS system, molecular mass information could be obtained down to ∽700 pg per injection for each α-1,4-glucose oligomer up to a degree of polymerization of 7 using PATRIC array detection in the static mode. Structure information was obtained for α-1,4 glucose oligomers, galacturonic acid oligomers and an EPS digest using PATRIC array detection in the scanning mode. © 1998 John Wiley & Sons, Ltd.

Indicating acts during counting by a chimpanzee (Pan troglodytes).

A chimpanzee (Pan troglodytes) experienced in counting arrays of 0-7 items and trained for comprehension of number symbols, spontaneously displayed a variety of indicating acts (e.g., pointing, touching, and rearranging items) during counting. Twenty-five sessions were videotaped, and all trials were evaluated for the relations among number of items presented, number of indicating acts displayed, and the Arabic number selected to represent the array. Significant correlations included the relations between number of items and the cardinal number selected by the animal, between the number of items and indicating acts displayed by the chimpanzee, and between the number of indicating acts and the numeral selected. These data suggest that the use of indicating acts by this animal may have functional significance and serves as an organizing schema, comparable to similar behaviors observed in children in the early stages of learning to count.

GROUP DELAY TRACKING WITH THE SYDNEY UNIVERSITY STELLAR INTERFEROMETER

ABSTRACT The Sydney University Stellar Interferometer (SUSI) is a long baseline optical interferometer, located at the Paul Wild Observatory near Narrabri, in northern New South Wales, Australia. It is designed to measure stellar angular diameters using light collected from a pair of siderostats, with 11 fixed siderostats giving separations between 5 and 640 m. Apertures smaller than Fried's coherence length, r0, are used and active tilt-compensation is employed. This ensures that when the beams are combined in the pupil plane the wavefronts are parallel. Fringes are detected when the optical path-difference between the arriving wavefronts is less than tne coherence length of light used for the observation. While observing a star it is necessary to compensate for the changes in pathlength due to the earth's rotation. It is also highly desirable to compensate for path changes due to the effects of atmospheric turbulence. Tracking the path-difference permits an accurate calibration of the fringe visibility, allows larger bandwidths to be used, and therefore improves the sensitivity of the instrument. I describe a fringe tracking system which I developed for SUSI, based on group delay tracking with a PAPA (Precision Analog Photon Address) detector. The method uses short exposure images of fringes, 1-10 ms, detected in the dispersed spectra of the combined starlight. The number of fringes across a fixed bandwidth of channeled spectrum is directly proportional to the path-difference between the arriving wavefronts. A Fast Fourier Transform, implemented in hardware, is used to calculate the spatial power spectrum of the fringes, thereby locating the delay. The visibility loss due to a non-constant fringe spacing on the detector is investigated, and the improvements obtained from rebinning the photon data are shown. The low light level limitations of group delay tracking are determined theoretically with emphasis on the probability of tracking error, rather than the signal-to-noise ratio. Experimental results from both laboratory studies and stellar observations are presented. These show the first closed-loop operation of a fringe tracking system based on observations of group delay with a stellar interferometer. The Sydney University PAPA camera, a photon counting array detector developed for use in this work, is also described. The design principles of the PAPA camera are outlined and the potential sources of image artifacts are identified. The artifacts arise from the use of optical encoding with Gray coded masks, and teh new camera is distinguished by its mask-plate, which was designed to overcome artifacts due to vignetting. Nw lens mounts are also presented which permit a simplified optical alignment without the need for tilt-plates. The performance of the camera is described.

MILLISECOND TIME RESOLUTION WITH THE KITT PEAK PHOTON COUNTING ARRAY

ABSTRACT The Kitt Peak Photon-Counting Array (KPCA) has been modified to provide access to individual frames, with the accompanying short frame time per exposure of between two and five milliseconds. These changes are described and the instrument's performance is illustrated. Imaging of the Crab pulsar with millisecond time resolution is presented as an astronomical example. Poor observing conditions precluded the photometric quality which would normally be achieved with a photon counter.