Reduction In Signal Level Research Articles

Enhanced electrochemiluminescence immunoassay: 2. Enabling signal detection at an early stage of incubation for rapid point-of-care testing

Signal detection in a label-based immunoassay is performed normally when the antigen/antibody binding reaction reaches the equilibrium state during the incubation period of an assay process. Shortening the incubation period in an assay helps reduce the turnaround time and is particularly valuable for point-of-care testing, but the cost is the reduction of signal level and, possibly, measurement precision as well. This work demonstrates that the signal loss could be offset by the stronger emission of an electronically neutral ruthenium(II) complex label, Ru(2, 2′-bipyridine) (bathophenanthroline disulfonate)[4-(2, 2′-bipyridin-4-yl)butanoic acid], used in the electrochemiluminescence (ECL) immunoassay. Combined with the uniquely well-established flow-through washing process in the automated ECL analyzers and the precise control over liquid handling, the assays performed with a 5-minute incubation period showed the same signal level and measurement precision as those of conventional ECL assays. Additionally, the absence of biotin and streptavidin components in the reagent formulation avoids the biotin-streptavidin interaction during assay incubation and fundamentally eliminates the interference of biotin, especially when used in some high-dose therapies. The results obtained from the procalcitonin prototype kit and the supporting evidence from other preliminary reagents (for SARS-CoV-2 N protein and troponin T) are general. The nonequilibrium detection, along with the downsized instrument design, makes the enhanced ECL (EECL) technology a fast high-performance POCT platform that provides the same high-quality data as those generated from the widely deployed [Ru(bpy)3]2+based laboratorial ECL systems.The anticipated regulatory approval and follow-up clinical implementation will beasignificant stride in the decade-long pursuit of novel ECL labels.

Frequency-Domain Electromagnetic Characteristics of a 26-Kilowatt Ammonia Arcjet

Abstract : Arcjet thrusters employ an arc discharge to heat propellant, which expands through a nozzle to produce thrust Spacecraft designers who desire to exploit the enhanced specific impulse of arcjets have expressed concern about the electromagnetic environment produced by the thrusters. Laboratory tests were performed to investigate the electromagnetic environment produced by a 26-kW ammonia arcjet in the frequency domain from dc to 10 GHz using antennas intended to characterize electric and magnetic fields. Results obtained with a 30-cm monopole antenna exposed to the arcjet plume correspond to those of similar ground tests at lower power. When the antenna was shielded from electrical contact with the plume by a Pyrex(R) cover, signal levels dropped sharply at all frequencies. With a covered 30-cm monopole antenna near the arcjet plume, arcjet-on signals exceeded ambient levels over the frequency range 10 kHz-5 MHz. The maximum signal level typically exceeded the ambient level of 40 dBumV/MHz by approximately 27 dBumV/MHz near 200 kHz. A likely explanation for The sharp reduction in signal level once the antenna electrode is covered is that electrons and ions from the plume are collected on the exposed antenna but not on the covered antenna. Signals on the shielded antenna may be interpreted as the result of propagating electric fields, but considerable uncertainty remains about the field source and the effects of the facility on the measurements. Although the electromagnetic fields produced by an arcjet operating as part of a satellite are probably lower than previously expected, these results raise new concerns about the character and Spacecraft compatibility of the plasma from an arcjet plume.

Diffraction-limited imaging with partially redundant masks: II Optical imaging of faint sources

In a recent paper [ J. Opt. Soc. Am. A9, 203 ( 1992)] the benefits of pupil apodization were examined for the near-infrared imaging of bright sources. In the current paper we extend these considerations to optical speckle imaging, in which photon noise rather than detector readout noise is important. We demonstrate that a one-dimensional pupil geometry (i.e., a thin slit) has several advantages over an unapodized aperture when faint sources are being observed through atmospheric turbulence. The use of a slit aperture does not decrease the signal-to-noise ratios of the power-spectrum and bispectrum measurements, and in many cases it increases them, despite the large reduction in signal level. The disadvantage of this apodization is a reduction in Fourier-plane coverage, which must be compensated for by observations with the slit aligned at several position angles. The performance of many of the current generation of photon-counting imaging detectors deteriorates at the high counting rates that can be experienced even when one is observing sources that are approaching the limiting magnitude of the speckle imaging technique. Under such conditions, we recommend the use of an apodized pupil, in contrast to the current preference for employing a neutral-density filter to reduce the detector count rate.

Propagation effects on radio range and noise in earth‐space telecommunications

Deep‐space missions and radio navigation satellite operations place high requirements upon the precision of range and Doppler frequency measurements and may be sensitive to even small increases in radio noise. For paths to geostationary satellites and beyond, the excess range delay due to the ionosphere and plasmasphere is proportional to the total electron content along the path and inversely proportional to frequency squared. The delay for a one‐way path is about 8 m for a total electron content of 1018 el/m2 at a frequency of 2.2 GHz. The one‐way excess range delay due to the dry air of the troposphere on earth‐satellite paths is typically of the order of a few meters and is dependent only on surface pressure for a given elevation angle. The delay due to water vapor, a few tens of centimeters, is responsible for most of the temporal variation in the range delay for clear air. In the navigation of Voyager spacecraft, where two‐way range measurements are made, range is determined with a precision of better than 3 m by the National Aeronautics and Space Administration/Jet Propulsion Laboratory Deep Space Network, made up of stations in Goldstone, California, Madrid, Spain, and Canberra, Australia. System noise temperatures for the Deep Space Network are typically 20–30 K. For such low‐noise systems and for attenuation values up to about 10 dB, the increase in sky noise due to rain and clouds degrades the received signal‐to‐noise ratio more than does the reduction in signal level due to attenuation. Clouds as well as rain contribute significantly to attenuation and sky noise, especially for frequencies greater than 10 GHz. Doppler frequency fluctuations due to the interplanetary plasma can be reduced by using higher frequencies (X or K band rather than S band, for example), but scintillation of tropospheric origin may then become the principal factor limiting the ability to detect gravitational waves.

Acoustic link reduction by digital processing

The work described in this paper is concerned with the digital simulation at Bell-Northern Research, Ottawa, of the various acoustic transmission paths between a loudspeaker and a microphone in a room. There are a number of possible applications for this work in the telecommunications industry relating to speaker phones and teleconferencing. A reasonably accurate simulation has been found to produce a reduction in signal level following the microphone of the order of 20 dB for signals which originate from the loudspeaker. Other signals originating in the room pass through the system with no effect. The voice switch has been a necessary but undesirable part of the majority of speaker phones and teleconferencing systems. Its function is to permit adequate audio gains while preventing the oscillations which would normally occur in a two-way conversation using loudspeakers and microphones. The voice switch effectively allows only one-way transmission at any time. It is generally found that the voice switch wfil respond to background noise and other spurious sound souroes as well as to speech and in some applications this action is quite undesirable. The simulation system, on the other hand, can allow in excess of 20 dB of additional gain before oscillations would occur and in a suitably benign acoustic environment, this could be sufficient to dispense with the voice switch altogether. Further applications of this work in telecommunications include the reduction of ambient noise for the benefit of the far-end user in either bandset of hands-free operation. This would be a useful facility for persons wishing to communicate in high ambient noise conditions, such as in or around large pieces of equipment, or aircraft, etc.