Signal Integration Time Research Articles

In vivo detection of dysplastic tissue by Raman spectroscopy.

The detection of dysplasia and early cancer is important because of the improved survival rates associated with early treatment of cancer. Raman spectroscopy is sensitive to the changes in molecular composition and molecular conformation that occur in tissue during carcinogenesis, and recent developments in fiber-optic probe technology enable its application as an in vivo technique. In this study, the potential of Raman spectroscopy for in vivo classification of normal and dysplastic tissue was investigated. A rat model was used for this purpose, in which dysplasia in the epithelium of the palate was induced by topical application of the carcinogen 4-nitroquinoline 1-oxide. High quality in vivo spectra of normal and dysplastic rat palate tissue, obtained using signal integration times of 100 s were used to create tissue classification models based on multivariate statistical analysis methods. These were tested with an independent set of in vivo spectra, obtained using signal collection times of 10 s. The best performing model, in which signal variance due to signal contributions of the palatal bone was eliminated, was able to distinguish between normal tissue, low-grade dysplasia, and high-grade dysplasia/carcinoma in situ with a selectivity of 0.93 and a sensitivity of 0.78 for detecting low-grade dysplasia and a specificity of 1 and a sensitivity of 1 for detecting high-grade dysplasia/ carcinoma in situ.

Designing Lymphocyte Functional Structure for Optimal Signal Detection: Voilà, T cells

One basic task of immune systems is to detect signals from unknown “intruders” amidst a noisy background of harmless signals. To clarify the functional importance of many observed lymphocyte properties, I ask: What properties would a cell have if one designed it according to the theory of optimal detection, with minimal regard for biological constraints? Sparse and reasonable assumptions about the statistics of available signals prove sufficient for deriving many features of the optimal functional structure, in an incremental and modular design. The use of one common formalism guarantees that all parts of the design collaborate to solve the detection task. Detection performance is computed at several stages of the design. Comparison between design variants reveals e.g. the importance of controlling the signal integration time. This predicts that an appropriate control mechanism should exist. Comparing the design to reality, I find a striking similarity with many features of T cells. For example, the formalism dictates clonal specificity, serial receptor triggering, (grades of) anergy, negative and positive selection, co-stimulation, high-zone tolerance, and clonal production of cytokines. Serious mismatches should be found if T cells were hindered by mechanistic constraints or vestiges of their (co-)evolutionary history, but I have not found clear examples. By contrast, fundamental mismatches abound when comparing the design to immune systems of e.g. invertebrates. The wide-ranging differences seem to hinge on the (in)ability to generate a large diversity of receptors.

A model of the high count rate performance of NaI(Tl)-based PET detectors

A detailed model of the response of large area NaI(TI) detectors used in PET and their triggering and data acquisition electronics has been developed, This allows the authors to examine the limitations of the imaging system's performance due to degradation in the detector performance from light pileup and deadtime from triggering and event processing. Comparisons of simulation results to measurements from the HEAD PENN-PET scanner have been performed to validate the Monte Carlo model. The model was then used to predict improvements in the high count rate performance of the HEAD PENN-PET scanner using different signal integration times, light response functions, and detectors.

Low-noise cooled planar Schottky diode receivers for ground-based spectral ozone measurements at 142 GHz

Two new low-noise cooled receivers based on planar Schottky diode mixers were designed and built for the Lebedev Physics Institute (LPI) spectrometer for ground-based measurements of the atmospheric ozone spectral line of 142.175 GHz central frequency. The receivers differ in the intermediate frequency (IF) bands, of around 3.7 and 1.5 GHz. Review description of the spectrometer equipped with the 3.7–GHz IF receiver is given, and its performance is compared with other millimeter-wave ground-based ozone spectrometers. Special attention was paid to design of the input Gaussian optics and the mixers. Techniques of laboratory tests of the receivers and results of the tests through all 2–mm wavelength range are considered and discussed. SSB mixer noise temperature of 460±60 K was obtained at 151 GHz for room temperature mixer, and the value of 180±30 K was measured at 134 GHz under cooling to 85 K in liquid nitrogen cryostat. SSB mixer conversion losses were less than 5.5 dB in both the cases. SSB noise temperature of the spectrometer is less than 1500 K without cooling and less than 700 K at cryogenic operation at 142 GHz. This provides sensitivity of about 0.2 and 0.1 K for the narrowest spectral channel width of 0.1 MHz and signal integration time of 1 hour. Using the optimized spectrum analyzers delivers data on high-accuracy retrieval of the ozone vertical profile in the atmosphere at altitudes about from 15 to 75 km. Examples of the ozone observation data are given.

Ultra-Low Temperature Thermometry Using Zeeman Perturbed NQR

We report the results of measurements of the magnetic field perturbed nuclear quadrupole resonance (NQR) lines of powdered Sb immersed in liquid 3He at low temperatures. The magnetic field was used to separate the frequencies of the allowed transitions between the $$I_Z = \pm \frac{1}{2}$$ and $$\frac{3}{2}$$ levels that correspond to the zero field NQR absorption at 11.5289 MHz for121 Sb. The spectrum for the powder sample consists of two sharp lines with known separation. The ratios of the intensities of these two lines depends only on the difference in thermal population of the nuclear spin levels and can be used for thermometry at very low temperatures. Pulsed NQR measurements of this intensity ratio from 0.25 to 1.45 mK were in good agreement with the expected Boltzmann distributions. Temperature resolutions of 20% could be achieved for signal integration times of ∼ 1 hour.

Implementation and initial deployment of a field instrument for measurement of OH and HO2 in the troposphere by laser-induced fluorescence

An instrument to detect atmospheric concentrations of the hydroxyl (OH) and hydroperoxyl (HO 2 ) radicals has been developed using the FAGE (fluorescence assay by gas expansion) technique. The instrument is housed in a mobile laboratory and monitors the OH radical via on-resonance laser-induced fluorescence (LIF) spectroscopy of the A 2 Σ + (v′=0)–X 2 Π i (v ″ =0) transition at ca. 308 nm. Ambient air is expanded through a 1 mm nozzle to low pressure where it is irradiated by the laser pulse at a repetition rate of 7 kHz, with the resultant fluorescence being detected by gated photon counting. HO 2 is monitored by chemical conversion to OH by the addition of NO, with subsequent detection using LIF. Following laboratory and field calibrations to characterise the instrument sensitivity, detection limits of 1.8×10 6 and 2.1×10 7 molecule cm -3 were determined for OH and HO 2 respectively, for a signal-to-noise ratio, S/N, of 1 with 150 s signal integration time. The instrument was deployed for the first time during the ACSOE field campaign at Mace Head, Eire, for which illustrative results are given.

Laser-induced incandescence: detection issues

Theoretical predictions suggest that soot particle size and local gas temperature affect both the spectral intensity and the temporal evolution of laser-induced incandescence. A discussion of both the physical structure and the theoretical absorption models of soot aggregates is presented, suggesting that the soot particle size relevant to laser-induced incandescence (LII) is the primary particle size regardless of whether the primary particle exists individually or is assembled into an aggregate. Experimental results of LII measurements in a laminar gas-jet flame with different signal collection strategies for the LII are presented. These results suggest that (a) signal integration during the laser pulse is essential for minimizing particle size and local temperature bias in the LII signal, (b) signal integration times subsequent to the laser pulse produce a size and local gas-temperature-dependent bias in the LII signal with long integration times more sensitive to these effects, and (c) long wavelength detection produces less of a size and local gas-temperature-dependent bias than short wavelength detection.

Duplex Laser Doppler Perfusion Imaging

A duplex mode for recording of both spatial and temporal blood perfusion components has been developed and evaluated. This modality, which has been implemented as a software module in the laser Doppler perfusion imager, consists of various local area scan (LAS) configurations. These include single-point recording or multipoint recording after repeated movements of the laser beam in quadratic patterns including 2 × 2 or 4 × 4 measurement sites. For the 2 × 2 and 4 × 4 LAS, the output value constitutes the average perfusion of all values captured within the actual region of interest. The 2 × 2 local area scan is corrected by time shifting the sequentially recorded measurement values at consecutive tissue sites, while the 4 × 4 LAS is presented as a vector of the individual subimages. With the standard setting of 65 msec for the signal integration time at each measurement site, the 1 × 1 and 2 × 2 LAS configurations can capture and reproduce perfusion signals with maximal bandwidths of 7.7 and 1.9 Hz, respectively. System evaluation showed that the signal integration time can be reduced to 45 msec without impaired signal quality, thereby further increasing the system bandwidth with a factor of about 1.5. Skin recordings showed that averaged time traces of adjacent measurement sites improve the signal-to-noise ratio and allow for a more reliable analysis of, for example, the reactive hyperemic response. Individual time-trace extraction, however, showed reperfusion patterns that differed markedly between sites.

Measuring OH and HO2in the Troposphere by Laser-Induced Fluorescence at Low Pressure

Abstract The hydroxyl radical OH oxidizes many lime gases in the atmosphere. It initiates and then participates in chemical reactions that lead to such phenomena as photochemical smog, acid rain, and stratospheric ozone depletion. Because OH is so reactive, its volume mixing ratio is less than 1 part per trillion volume (pptv) throughout the troposphere. Its close chemical cousin, the hydroperoxyl radical HO2, participates in many reactions as well. The authors have developed an instrument capable of measuring OH and HO2 by laser-induced fluorescence in a detection chamber at low pressure. This prototype instrument is able to detect about 1.4 × 105 molecules cm−3 (0.005 pptv) of OH at the ground in a signal integration time of 30 s with negligible interferences. The absolute uncertainty is a factor of 1.5. This instrument is now being adapted to aircraft use for measurements throughout the troposphere.

Response Time For Optical Emission And Mass Spectrometric Signals During Etching Of Heterostructures

AbstractPlasma etching of III-V heterostructures has been monitored using optical emission spectroscopy and mass spectrometry. For the Ga optical emission signal at 417.2 nm, a response time as fast as 0.2 s has been measured. The response time of the mass spectrometer is limited by the transit time of etch products from the wafer surface to the ionizer. A minimum response time of 0.9 s was measured by reducing the signal integration time of the mass spectrometer. Saturation of the optical emission signal has been shown to be related to the residence time of etch gases by varying the flow rate or pressure. Decreasing residence time by reducing the pressure from 6 to 2 mTorr and maintaining a constant flow rate caused the Ga emission signal saturation time to decrease from 7 to 3 min. The 145ASC12+ signal saturated before the Ga emission signal at 417.2 nm. Endpoint detection for etching an AlInAs emitter and stopping on a GaInAs base was studied. By monitoring the changes in the Ga emission intensity, only 2 nm of the GaInAs base layer had been removed when the emitter etch was stopped.

High-precision gas chromatography-combustion isotope ratio mass spectrometry at low signal levels

Precision and accuracy of gas chromatography-combustion isotope ratio mass spectrometry are investigated for sample levels down to about 5 pmol C in fatty acid methyl ester mixtures spanning 1000-fold in concentration. Precision and accuracy of isotope ratios diverge rapidly for conventional summation methods, and become unusable below 30 pmol material on column. At lower levels, mean isotope ratios were statistically different from reference values indicating bias as well as poor precision. In contrast, curve fitting, using the exponentially modified Gaussian line shape, gives improved precision for most peaks and useful results down to 3 pmol. The curve-fitting algorithm was also less sensitive to signal integration time than the summation method. These data indicate that curve fitting may be the method of choice for integration of noisy data when high-precision isotope ratios are desired.

なぜプッシュブルーム走査か，その限界は

Pushbroom scan will be used widely in future high resolution imaging spectrometer. What is the reason? Why will not be used the mechanical scan for high resolution? In this paper, comparison of signal integration time was done and it was shown that the pushbroom scan is the ultimate scan scheme from the viewpoint of integration time. Then the parametric estimations of resolution power of each scanning scheme were performed. In each scan scheme, we are reaching to the performance limit.

Microparticle raman spectroscopy of multicomponent aerosols

Inelastic light scattering measurements (Raman and fluorescence spectroscopies) offer the possibility of chemically characterizing micrometer-size particles. Quantitative interpretation of such spectra is complicated by morphological or structural resonances associated with elastic and inelastic scattering. This paper explores the feasibility of using Raman spectroscopy to determine the composition of multicomponent microdroplets by examining the effects of such resonances and microdroplet size on the Raman signal. Raman scattering from electrodynamically suspended droplets of 1-octadecene and 1-bromohexadecane was found to be enhanced by morphology-dependent resonances. By applying Mie theory to the elastic scattering many of the increased Raman intensities were found to coincide with the incident beam resonances, but other peaks can be attributed to “output” resonances. It was also demonstrated that intensity fluctuations associated with resonances can be minimized by increasing the signal integration time, which permits changes in composition to be determined. In this way, the distillative evaporation of binary component droplets of 1,8-dibromooctane and hexadecane was followed by recording the Raman spectrum of the CBr bond. The effects of the system parameters on the interpretation of Raman spectra are elucidated.

Description and performance of a highly sensitive confocal Raman microspectrometer

AbstractA confocal Raman microspectrometer was developed for the study of small biological objects such as single living cells and metaphase and polytene chromosomes. It employs a confocal detection scheme, well known from confocal fluorescence microscopes, in order to avoid signal contributions from the environment of the samples. The resolution is 0.45 ± 0.05 μm in the lateral direction and 1.3 ± 0.1 μm in the axial direction. The laser excitation wavelength is 660 nm. At this wavelength biological samples do not degrade in the laser radiation as was the case when laser radiation of 514.5 nm was used. The signal throughput from the sample position to the detector was optimized to the extent that in the spectral region around a 1000 cm−1 Raman shift 15% of the Raman scattered light collected by the microscope objective is detected. For signal detection a liquid nitrogen‐cooled slow‐scan CCD camera is used. Laser powers of 5–10 mW suffice to obtain high‐quality Raman spectra, with signal integration times of the order of minutes. As an example, spectra obtained from the nucleus and the cytoplasm of an intact human lymphocyte are shown.

Balloon-borne laser spectrometer measurements of NO_2 with gas absorption sensitivities below 10^−5

Infrared spectra of NO2 recorded during a recent flight of the Balloon-borne Laser In-Situ Sensor instrument have been analyzed to determine sensitivity limits for various signal integration times. Implications for direct detection of ClO, HOCl, H2O2, COF2, OH, and HO2 are discussed.

Trace metal assay of thorium oxide by atomic emission spectrometry

An Atomic Emission Spectrometric (AES) method has been developed for the direct determination of twenty-two metallic elements at trace concentrations in thorium oxide. The method is based on the use of a d.c. arc — carrier distillation technique with 12% composition of a mixed carrier, viz. AgCl+SrF2 in 5:1 proportion, and is equally applicable to both volatile and refractory analytes. A direct reading emission spectrometer with computerised data acquisition and processing facility has been used in these studies. The standardisation procedure includes study of volatilisation/excitation characteristics of the analyte elements to optimise choice and proportion of the carrier and signal integration time apart from optimisation of other experimental parameters such as arc current, viewing position of the arc plasma, sample charge etc. The detection limits for the analytes lie in the range 0.1–50 ppm while the precision of determinations is better than 15% for most of the elements as evaluated from the repetitive analyses of spiked samples.

New instrumentation for time-resolved microanalysis using parallel EELS

The new parallel detection EELS systems have opened up the possibility of performing time-resolved studies of compositional changes and the evolution of near-edge structure caused by radiation damage or positional changes across heterogeneous interfaces. Zaluzec has described a system using a 2-D CCD array in which one axis corresponds to time. Such a system can acquire 100 512-channel spectra in a time limited by the CCD readout and digitization time. Our system is an extension of an existing data acquisition system using modified software and a Gatan 666 parallel EELS equipped with a 1024-element 1-D photodiode array. We have taken advantage of the computer’s memory architecture to stack a time series of multiple spectra (or any portion of these spectra) in the extended memory space above 256 K-bytes. The 4 M-bytes of system memory enables storage of up to 1920 spectra 1024 channels long. For inner-shell edges, a 100-500 msec signal integration time per spectrum is typical. After acquisition the series of spectra are recovered from extended memory and are stored on disk. They can then be retrieved for post processing or can be played back through the display, from which VCR recordings can be directly made.

Molecular fluorescence measurements with a charge-coupled device detector

Abstract : A novel fluorescence spectrometer is described using a two-dimensional charge-coupled device as the detector and a mercury pen lamp as the excitation source. The fluorescence spectra and intensity of anthracene in ethanol standards at concentrations ranging from .0001 to 10 to the -11th power M are shown. The limit of detection measured is 10 to the -12th power M, or 227 parts-per-quadrillion. The linear dynamic range obtained with this instrument is 6 orders of magnitude with excellent linearity using 10 second signal integration time. Keywords: Charge coupled device; Molecular fluorescence; Multichannel detectors; Charge transfer device; Anthracene; Rayleigh spectra; Raman spectra.

Performance of the uranium/plastic scintillator calorimeter for the HELIOS experiment at CERN

We describe the calorimeter system serving the HELIOS experiment at CERN, its calibration, and its performances measured in test experiments. The calorimeter signal for hadrons was found to be proportional to the energy to within 2% over the energy range 8–200 GeV. Over the same energy range the energy resolution σ E scales as 1 E for both electromagnetic and hadronic showers. The values found were (0.215 ± 0.007) E and (0.337 ± 0.012) E , respectively, for the detection of single particles. The signal ratios e/mip and e π are 0.70 ± 0.05 and 0.984 ± 0.006, where the latter ratio was found to be dependent on the signal integration time the quoted number being obtained for a 130 ns gate. The energy resolution for multiparticle detection was found to be about twice as large as for the detection of single particles in the actual calorimeter configuration. The energy flow logic, designed to provide trigger information on physics quantities such as transverse energy and missing energy, was shown to be very accurate and reliable.

On the energy resolution of uranium and other hadron calorimeters

The various components that contribute to the signal from a hadron calorimeter, and the factors that affect the energy resolution with which hadrons can be detected, are examined in detail. The role of the electromagnetic to hadronic signal ratio e h is crucial in this respect. Its value is determined by the Z of the absorber material, the thickness of the passive and active layers, the signal integration time of the detector, and the properties of the readout material, in particular the free proton content and the saturation or recombination properties for few-MeV proton detection. Readout media that contain free protons offer the possibility to tune the e h ratio to the desired value (1.0) through the sampling fraction. Signal equalization ( e h = 1.0) does not seem to be a property unique to 238U, but can also be achieved for lead and even iron calorimeters. The calculations show, on the other hand, that e h values are larger than 1.0 for any calorimeter using liquid-argon readout. The intrinsic energy resolution for hadron detection is largely dominated by fluctuations in the binding energy losses that occur in the nuclear reactions. Efficient neutron detection can considerably reduce these effects provided that energy loss through recoil protons dominates. Calorimeters using 238U, Pb or Fe absorbers, and plastic scintillator, liquid-argon, silicon or TMP readout were investigated. Experimental results on e h values and energy resolution, which are often considered confusing, are nicely reproduced and explained.