Signal Integration Time Research Articles

Development and characterization of a High-Temperature Proton-Transfer-Reaction Mass Spectrometer (HT-PTR-MS)

Abstract. We have developed a High-Temperature Proton-Transfer-Reaction Mass Spectrometer (HT-PTR-MS) in which both the ion source and the ion drift tube can be continuously operated at temperatures up to 250 °C. The instrument was characterized in a high E/N-mode (130 Td) and in a low E/N-mode (87 Td) at an operating temperature of 200 °C. Instrumental sensitivities and 2σ-detection limits were on the order of 50–110 cps/ppb and 100 ppt (1 s signal integration time), respectively. The HT-PTR-MS is primarily intended for measuring "sticky" or semi-volatile trace gases. Alternatively, it may be coupled to a particle collection/thermal desorption apparatus to measure particle-bound organics in near real-time. In view of these applications, we have measured instrumental response times for a series of reference compounds. 1/e2-response times for dimethyl sulfoxide, ammonia and monoethanolamine were in the sub-second to second regime. 1/e2-response times for levoglucosan, oxalic acid and cis-pinonic acid ranged from 8 to 370 s.

Spectral measurements of large particles by flow cytometry

Flow cytometers designed to analyze large particles are enabling new applications in biology and chemistry. Similarly, flow spectroscopy approaches are extending the capabilities of the flow cytometry platform. Here, we report on the adaptation of a commercial large particle analyzer to measure fluorescence and Raman spectra of individual particles at high speeds. We modified a Union Biometrica COPAS Plus instrument to allow red excitation and optical fiber-based light collection and spectral analysis using a spectrograph and CCD array detector. These modifications did not compromise the ability of the instrument to resolve different sized particles based on their extinction and time of flight signals. The modified instrument has the sensitivity and spectral resolution to measure the fluorescence and Raman signals from individual particles with signal integration times of 10 usec. The high speed spectral analysis of individual particles in flow will enable new applications in biological and chemical analyses.

384-Channel parallel microfluidic cytometer for rare-cell screening

We have constructed a 384-channel parallel microfluidic cytometer (PMC). The multichannel architecture allows 384 unique samples for a cell-based screen to be read out in approximately 6-10 min, about 30-times the speed of a conventional fluorescence-activated cytometer system (FACS). This architecture also allows the signal integration time to be varied over a larger range than is practical in single-channel FACS and is suitable for detection of rare-cells in a high background of negatives. The signal-to-noise advantages have been confirmed by using the system to count rare clonal osteocytes in the most difficult early stages of an expression-cloning screen for the carboxy-terminal parathyroid hormone receptor (CPTHR). This problem requires finding several dozen positive cells in a background of one million negatives. The system is automated around a scanning laser confocal detector and a 96-tip robotic pipettor and can maintain in vitro cultures on-system in 384-well plates. It is therefore directly practical for biology applications using existing high-throughput culture facilities. The PMC system lends itself to high-sample-number cytometry with an unusual capability for time synchronization and rare-cell sensitivity. A limited ability to handle large sample numbers has restricted applications of single-channel FACS in combinatorial cell assays; therefore the PMC could have a significant application in high-throughput screening.

Surface leakage current control with heterojunction-type passivation in semi-insulating CdZnTe material

Inter-pixel resistance in the planar structure X-ray or gamma-ray detector has severe effects on signal cross-talk and the signal integration time. Generally, Br-MeOH etching in Cd-based compounds leaves a Te-rich or Cd-rich surface resulting from selective etching. The etching then converts the Te-rich or Cd-rich surface in air into TeO 2 or CdO oxides, which exhibit low resistance. To reduce the surface recombination, we adopted (NH 4) 2S for surface passivation in the polycrystalline CdZnTe:Cl grown by thermal evaporation method. The optimization of passivation was confirmed by I–V measurement and X-ray photoemission spectroscopy (XPS) analysis. From the I–V curve, we confirmed that the surface resistance was considerably increased after passivation with (NH 4) 2S. XPS data showed that (NH 4) 2S passivation removed conductive TeO 2 layers and induced formation of insulating CdTeO 3 and CdS layers. A heterojunction by the thin CdS layer and CdZnTe was formed.

Determination of As in tree-rings of poplar (Populus alba L.) by U-shaped DC arc

An argon-stabilized U-shaped DC arc with a system for aerosol introduction was used for determination of As in poplar (Populus alba L.) tree-rings. After optimization of the operating parameters and selection of the most appropriate signal integration time (30 s), the limit of detection for As was reduced to 15.0 ng/mL. This detection limit obtained with the optimal integration time was compared with those for other methods: inductively coupled plasma-atomic emission spectrometry (ICP-AES), direct coupled plasma-atomic emission spectrometry (DCP-AES), microwave induced plasma-atomic emission spectrometry (MIP-AES) and improved thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS). Arsenic is toxic trace element which can adversely affect plant, animal and human health. As an indicator of environment pollution we collected poplar tree-rings from two locations. The first area was close to the "Nikola Tesla" (TENT-A) power plant, Obrenovac, while the other was in the urban area of Novi Sad. In all cases elevated average concentrations of As were registered in poplar tree-rings from the Obrenovac location.

Invited article: The fast readout low noise camera as a versatile x-ray detector for time resolved dispersive extended x-ray absorption fine structure and diffraction studies of dynamic problems in materials science, chemistry, and catalysis

Originally conceived and developed at the European Synchrotron Radiation Facility (ESRF) as an "area" detector for rapid x-ray imaging studies, the fast readout low noise (FReLoN) detector of the ESRF [J.-C. Labiche, ESRF Newsletter 25, 41 (1996)] has been demonstrated to be a highly versatile and unique detector. Charge coupled device (CCD) cameras at present available on the public market offer either a high dynamic range or a high readout speed. A compromise between signal dynamic range and readout speed is always sought. The parameters of the commercial cameras can sometimes be tuned, in order to better fulfill the needs of specific experiments, but in general these cameras have a poor duty cycle (i.e., the signal integration time is much smaller than the readout time). In order to address scientific problems such as time resolved experiments at the ESRF, a FReLoN camera has been developed by the Instrument Support Group at ESRF. This camera is a low noise CCD camera that combines high dynamic range, high readout speed, accuracy, and improved duty cycle in a single image. In this paper, we show its application in a quasi-one-dimensional sense to dynamic problems in materials science, catalysis, and chemistry that require data acquisition on a time scale of milliseconds or a few tens of milliseconds. It is demonstrated that in this mode the FReLoN can be applied equally to the investigation of rapid changes in long range order (via diffraction) and local order (via energy dispersive extended x-ray absorption fine structure) and in situations of x-ray hardness and flux beyond the capacity of other detectors.

Determination of Fe, Hg, Mn, and Pb in three-rings of poplar (Populus alba L.) by U-shaped DC arc

The U-shaped DC arc with aerosol supply was applied for the determination of Fe, Hg, Mn, and Pb in poplar (Populus alba L.) tree-rings. By optimization of the operating parameters and by selection of the most appropriate signal integration time (20 s for Fe, Mn, and Pb and 30 s for Hg), the obtained limits of detection for Fe, Hg, Mn, and Pb are 5.8, 2.6, 1.6, and 2.0 ng/ml, respectively. The detection limits achieved by this method for Fe, Hg, Mn, and Pb are comparable with the detection limits obtained for these elements by such methods as inductively coupled plasma-atomic emission spectrometry (ICP-AES), direct coupled plasmatomic emission spectrometry (DCP-AES), and microwave-induced plasma-atomic emission spectrometry (MIP-AES). We used the tree-rings of poplar from two different locations. The first one is in the area close to the power plant “Nikola Tesla” TENT A, Obrenovac, while the other one is in the urban area of Novi Sad. In almost all cases, samples from the location at Obrenovac registered elevated average concentrations of Fe, Hg, Mn, and Pb in the tree-rings of poplar.

O 2+ as reagent ion in the PTR-MS instrument: Detection of gas-phase ammonia

Oxygen was used as a source gas in a conventional Innsbruck PTR-MS instrument to produce O 2 + ions as chemical ionization (CI) reagents instead of H 3O + ions. The use of O 2 + ions as CI reagents allows for fast, highly sensitive and specific measurements of gas-phase ammonia (NH 3) via the electron transfer reaction O 2 + + NH 3 → NH 3 + + O 2. The instrument was tested to be linear in the 2–2000 ppbv range. Instrument sensitivity was observed to be humidity-independent and amounted to ∼40 cps/ppbv. The instrumental background was determined by sampling NH 3-free air from a heated platinum/palladium catalyst. A humidity-dependent increase of the instrumental background from 70 pptv at dry conditions to 470 pptv at humid conditions was observed. The corresponding 2 σ-detection limits at 1 s signal integration time were 90 pptv for dry conditions and 230 pptv for humid conditions, respectively. The observed background may be intrinsically formed in the instrument's ion source but it may also be the result of incomplete NH 3 oxidation in the catalyst used for zeroing. The reported background levels and detection limits are thus to be considered as upper limits. The 1/ e response time of the instrument was in the range of 3–5 s. The PTR-MS instrument was successfully deployed in the field to monitor changes in gas-phase NH 3 concentrations in the few seconds to tens of seconds time range. Laboratory intercomparison measurements between the PTR-MS instrument and a commercial NH 3 analyzer (AiRRmonia) were in good agreement. The use of O 2 + ions as CI reagents will significantly improve the analytical capabilities of the Innsbruck PTR-MS instrument.

Single-shot method for bias-free LER/LWR evaluation with little damage

A new method of evaluating line-edge or linewidth roughness (LER/LWR) is proposed. Conventional, directly measured LER/LWR values always contain a random noise contribution called LER/LWR bias. Our method can separate this bias artifact from the true LER/LWR using a single image of the pattern. The idea is based on the dependence of calculated LER/LWR value on the image-processing parameter for noise reduction. Both the conventional and the new bias-free LER/LWR were calculated using a series of images with different signal integration times (numbers of frames) but a fixed field of view. The LER/LWR obtained by our method was independent of the number of frames, and agreed with the conventional LER/LWR as measured using an image with a sufficiently large number of frames. It is concluded that the proposed bias-free LER/LWR measurement method will be a powerful tool in lithography metrology, especially for achieving practical and accurate LER/LWR measurement with little sample damage.

Calibration of a Soft X-Ray Digital Imaging System for Biological Materials

Soft X-ray imaging of agricultural products for quality determination is gaining worldwide interest. Recent advances in technology have made it possible to capture, store, and instantaneously process digital X-ray images at higher resolution for lower cost. An X-ray imaging system was developed and calibrated to capture images with a resolution of 1024 × 1024 pixels over a 50 × 50 mm area. Maximum X-ray tube voltage was 50 kVp, maximum current was 1 mA, and signal integration time ranged from 460 to 6700 ms. The system consists of an X-ray source tube, a camera composed of a CMOS photodiode array, a frame grabber, and a data acquisition and control card. Because the X-ray beam is polychromatic, and the detector responses are variable, calibration is necessary to relate image intensity to X-ray attenuation. Imprecision of the system was 0.64% of the response range (1.63 gray level for an 8-bit pixel depth). Response, measured as mean pixel intensity, varied linearly with X-ray tube current and integration time and had a quadratic relationship with peak tube voltage. A regression model was developed to estimate blank image intensity at higher voltages and currents. Prediction and validation errors for the model were 0.46% and 1.06% (1.18 and 2.72 gray level), respectively. Beam hardening effect was demonstrated using a polystyrene target. The procedure explained in this article can be used to calibrate a soft X-ray imaging system for radiometric measurements.

46.4: Distinguished Student Paper: A 2-Inch a-Si:H TFT-LCD with an Embedded Sensor

We developed a 2 inch, QCIF (160×128, black and white), amorphous silicon thin-film transistor liquid-crystal display with an embedded sensor on glass. A pixel is divided into LCD and sensor, in which the size of sensor is optimized to have the linear relationship between the output signal voltage and signal integration time. A very thin top glass was used to make a TFT-LCD. A metal mask is put on the LCD with a top glass of 0.1 mm to improve the contrast of the image.

Scanning the Membrane-bound Conformation of Helix 1 in the Colicin E1 Channel Domain by Site-directed Fluorescence Labeling

Helix 1 of the membrane-associated closed state of the colicin E1 channel domain was studied by site-directed fluorescence labeling where bimane was covalently attached to a single cysteine residue in each mutant protein. A number of fluorescence properties of the tethered bimane fluorophore were measured in the membrane-bound state of the channel domain, including fluorescence emission maximum, fluorescence quantum yield, fluorescence anisotropy, membrane bilayer penetration depth, surface accessibility, and apparent polarity. The data show that helix 1 is an amphipathic alpha-helix that is situated parallel to the membrane surface. A least squares fit of the various data sets to a harmonic function indicated that the periodicity and angular frequency for helix 1 are typical for an amphipathic alpha-helix (3.7 +/- 0.1 residues per turn and 97 +/- 3.0 degrees, respectively) that is partially bathing into the membrane bilayer. Dual fluorescence quencher analysis also revealed that helix 1 is peripherally membrane-associated, with one face of the helix dipping into the lipid bilayer and the other face projecting toward the solvent. Finally, our data suggest that the helical boundaries of helix 1, at least at the C-terminal region, remain unaffected upon binding to the surface of the membrane in support of a toroidal pore model for this colicin.

In-depth profile analysis of thin films deposited on non-conducting glasses by radiofrequency glow-discharge–optical emission spectrometry

The potential of radiofrequency glow-discharge-optical emission spectrometry (rf-GD-OES) for quantification of thin films on non-conducting materials has been investigated. A commercial rf-GD chamber from Jobin Yvon operated at 13.56 MHz with Ar as discharge gas was used. The signal integration time was 0.1 s. The effect on emission yields of thin conducting layers on glasses of different thickness was studied in detail, using the rf-GD in the common operating mode "constant pressure-constant forward power". Calibration curves were obtained for two types of material-conducting reference materials and a set of non-conductors comprising homogeneous glass of known composition and three different thicknesses coated (or not) with thin layers of gold. Qualitative and quantitative in-depth profile analyses of different coated non-conducting samples were investigated. A variety of samples, including different thick glass substrates (from 1.8 to 5.8 mm), different thin films deposited on homogeneous glasses (from 6 nm to 35 nm), and different kinds of coating (conductors such as Fe, Ni, Cr, Al, and Nb and non-conductors such as Si3N4) were studied at 450 Pa pressure and 20 W forward power. The quantitative in-depth profiles proved satisfactory and results for depths and concentrations were similar to nominal values.

Heterotrimeric G-protein α-Subunit Adopts a “Preactivated” Conformation When Associated with βγ-Subunits

Heterotrimeric G-protein α-Subunit Adopts a “Preactivated” Conformation When Associated with βγ-Subunits

TU‐FF‐A4‐06: Dynamic Accuracy of An Implanted Wireless AC Electromagnetic Sensor for Guided Radiation Therapy; Implications for Real‐Time Tumor Position Tracking

Purpose: A wireless tumor localization and tracking system using three implanted AC electromagnetic transponders is in clinical trials for use in prostate cancer (Calypso® Medical). Phantom‐based studies have shown sub‐millimeter spatial localization accuracy in static tests. Accuracy has not been evaluated for dynamic motion found in lung tumors. This study was designed to determine the feasibility of using this patient positioning system for real‐time tumor‐tracking. Materials and Methods: A 4‐dimensional (4D) stage capable of arbitrary multidimensional motion with speeds up to 10 cm/sec was constructed. Two elliptical trajectory paths were created with peak‐to‐peak motion of 1cm × 2cm × 1cm and 2cm × 4cm × 2cm in the x, y and z directions. Each trajectory was operated with periods of 15 – 20 cycles per minute. The Calypso System was operated using one and two transponders with radiofrequency signal integration times of 33 ms 100 ms. The transponders were mounted on the 4D‐stage, with the ellipse centroids positioned 14 cm from the array. The effects of ellipse size, speed, number of transponders and signal integration time on transponder localization accuracy were evaluated by comparing the intended and measured trajectories. Results: The root mean square (RMS) position difference was less than 1 mm for all tested combinations. While small, the RMS error was largest for the large ellipse at 20 cycles per minute compared with the small ellipse at 15 cycles per minute. The single‐transponder system with 67 ms integration time had the smallest overall error, with a maximum single‐point error of 1.3mm. Conclusions Use of a wireless electromagnetic implanted transponder system for real‐time tumor‐tracking is feasible, with RMS errors less than 1mm for high‐speed multidimensional ellipses. This compares favorably with continuous fluoroscopic tracking methods without an ionizing radiation burden. This work is currently being expanded to patient‐derived tumor trajectories.

A Method of Suppressing Self-Heating Signal of Bolometers

A scheme of full self-heating compensation for the bolometer-based infrared (IR) sensors was proposed. Infrared-sensitive and infrared-insensitive bolometers with nearly identical self-heating characteristics were connected in parallel in a Wheatstone bridge to suppress the common mode. The time-dependent component of the output signal due to the self-heating effect was substantially limited. The effectiveness of the scheme was demonstrated by testing of micromachined bolometers. The output signals from the bridge were fed into a differential amplifier and the self-heating component of the output signal dropped from 34 to 1.5 mV. The signal was then dominated by the IR radiation response. The proposed scheme enabled signal integration time to increase for the purpose of signal-to-noise ratio improvement.

Laser-Induced Fluorescence Instrument for the Detection of Tropospheric OH Radicals

Abstract An instrument for the measurement of troposphric OH radical concentrations using a laser-induced fluorescence technique has been developed. Ambient air is expanded through a pinhole into a low-pressure fluorescence cell and irradiated by the second harmonic of a dye laser at a high repetition rate of 1 kHz. The OH radicals are electronically excited using A2Σ+(ν′ = 0) ← X2Π (ν′′ = 0) transitions around 308 nm. The fluorescence from OH radicals is collected by a lens system and detected by a photomultiplier. The photoelectron pulses from the photomultiplier are processed by a photon-counting system. The dynode gate of the photomultiplier and counting gate systems are made to minimize the detection of the chamber and Rayleigh scattering signal. The sensitivity of the developed instrument is calibrated with two methods: one is a long-path absorption technique and the other is a titration technique with simultaneous photolysis of water vapor and oxygen. It is found that the background signal is mainly produced by after-pulse effects in the photomultiplier for the fluorescence detection with a dynode gate system. The minimum detection limit is determined to be 7.0×105 molecules cm-3 for OH radicals with a signal-to-noise ratio of 2 and a signal integration time of 60 s.

Multichannel mixed-mode IC for digital readout of silicon strip detectors

The design of a mixed mode 64-channel ASIC for digital readout of silicon strip detectors used in X-ray imaging applications is presented. The design is implemented in a 0.8 μm CMOS n-well epi-type substrate technology. The single channel consists of a charge sensitive preamplifier, a shaping amplifier, a discriminator and a pseudo-random 20-bit counter. In addition to the 64-channel core which is responsible for signal processing and data storage, the IC comprises additional blocks like an internal calibration circuit, internal DACs and a command decoder which governs communication of the IC with the external world. Those blocks have been designed keeping in mind testability features and using the chips for building multi-chip modules. The equivalent input noise charge measured at room temperature for a detector capacitance of 2.5 pF and signal integration time of 0.7 μs is 167 e − rms. The average power dissipation is 2.5 mW/channel. The channel-to-channel offset spread referred to the input is only 28 e − rms, while the standard deviation of gain spread is 0.5% of the mean value. The chip occupies area of 2.8×6.5 mm 2.

Marine snow, organic solute plumes, and optimal chemosensory behavior of bacteria

Leaking organic solutes form an elongated plume in the wake of a sinking aggregate. These solutes may both be assimilated by suspended bacteria and guide bacteria with chemokinetic swimming behavior toward the aggregate. We used modifications of previously published models of the flow and concentration fields around sinking aggregates and of chemokinetic behavior of bacteria to identify the behavior that optimizes aggregate colonization and plume utilization. The optimal solution is governed by physical constraints and is a trade off between a high sensitivity to chemical signals and a long signal integration time. For a runߚandߚtumble swimming behavior, the predicted tumbling frequency is between 1 and 10 s21, similar to that reported for marine bacteria. The predicted optimal sensitivity to chemical signals is similar to or greater than that known for Escherichia coli. The optimal behavior was used to examine the potential contribution of aggregateߚgenerated solute plumes for water column bacterial production. Despite occupying only a small volume fraction, the plumes may provide important growth habitats for free bacteria and account for a significant proportion of water column bacterial production at typical concentrations of marine snow aggregates.

The improvement of the detection power of a U-shaped DC plasma

Optimization of the operating parameters of U-shpaed DC arc plasma and spectrometer parameters has been undertaken to explore the possibilities of improving its detection power. It is demonstrated, with a U-shaped arc as an example, that the limits of detection, in addition to well-defined parameters as described by Boumans1,2 and Winge,3 depend on the signal integration time. It is shown that with increasing integration time, the limits of detection are decreased within some limits and that the precision and concentration sensitivity are improved as well. A mathematical expression for the dependence of the detection limit on the integration time is presented. To increase the reliability of the measurement of the mentioned parameters, the working conditions were optimized for the following analytes: Ag, Al, Au, Cr, Fe, Mn, Ni, Pb, Pd, Pt, and V. The obtained limits of detection are comparable or better than those obtained by ICP for the elements studied. It was estimed that the possibility exists for their further improvement up to 10 times.