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BACKGROUND: method is applied to data with automatic removal of background fluorescence by the qPCR software. Since the background fluorescence is unknown, subtracting an inaccurate background can lead to distortion of the results. To address these problems, we present an improved method, the individual efficiency corrected calculation. RESULTS: method. CONCLUSIONS: method and is thus a better way to calculate relative gene expression.
Research Article| September 01, 1987 Fan-deltas and braid deltas: Varieties of coarse-grained deltas JOHN G. McPHERSON; JOHN G. McPHERSON 1Mobil Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 Dallas, Texas 75381 Search for other works by this author on: GSW Google Scholar GANAPATHY SHANMUGAM; GANAPATHY SHANMUGAM 1Mobil Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 Dallas, Texas 75381 Search for other works by this author on: GSW Google Scholar RICHARD J. MOIOLA RICHARD J. MOIOLA 1Mobil Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 Dallas, Texas 75381 Search for other works by this author on: GSW Google Scholar Author and Article Information JOHN G. McPHERSON 1Mobil Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 Dallas, Texas 75381 GANAPATHY SHANMUGAM 1Mobil Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 Dallas, Texas 75381 RICHARD J. MOIOLA 1Mobil Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 Dallas, Texas 75381 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1987) 99 (3): 331–340. https://doi.org/10.1130/0016-7606(1987)99<331:FABDVO>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation JOHN G. McPHERSON, GANAPATHY SHANMUGAM, RICHARD J. MOIOLA; Fan-deltas and braid deltas: Varieties of coarse-grained deltas. GSA Bulletin 1987;; 99 (3): 331–340. doi: https://doi.org/10.1130/0016-7606(1987)99<331:FABDVO>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Two types of coarse-grained deltas are recognized: fan-deltas and braid deltas. Fan-deltas are gravel-rich deltas formed where an alluvial fan is deposited directly into a standing body of water from an adjacent highland. They occupy a space between the highland (usually a fault-bounded margin) and the standing body of water. In contrast, braid deltas (here introduced) are gravel-rich deltas that form where a braided fluvial system progrades into a standing body of water. Braid deltas have no necessary relationship with alluvial fans, as exemplified by fluvioglacial braid deltas. Braid deltas have previously been classified as fan-deltas even though the geomorphic and sedimentologic settings of the two systems can be vastly different. Braid deltas are a common present-day geomorphic feature and are abundant in the geological record.Fan-deltas and braid deltas can be distinguished in the rock record by distinctive subaerial components of these depositional systems; the shoreline and subaqueous components of both are similar. Fan-delta sequences have a subaerial component that is an alluvial-fan facies comprising interbedded sheetflood, debris-flow, and braided-channel deposits. Fan-deltas produce small (a few tens of square kilometres), wedge-shaped bodies of sediment, commonly displaying high variability in paleocurrent patterns and abrupt changes in facies. The deposits are generally very coarse grained (with large out-sized clasts), very poorly sorted, matrix-rich, polymictic, heterolithic, partially cemented by penecontemporaneous carbonate, and have low porosity and permeability. Braid-deltas, in contrast, have a subaerial component consisting entirely of braided-river or braidplain facies. Their deposits display better sorting, roundness, and clast orientation than do fan-delta sediments; they lack a muddy matrix; they display size grading and bar migration; they commonly have a sheet geometry with high lateral continuity (tens to hundreds of square kilometres); and they exhibit moderate to high porosity and permeability. Valuable paleogeographic and tectonic information concerning the proximity of highlands and major fault zones may be misinterpreted or lost if these two coarse-grained deltaic systems are not differentiated. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Abstract A delta is a partially subaerial, contiguous mass of sediment deposited around the point where a river enters a standing body of water. A deltaic system is a three-dimensional rock-stratigraphic unit composed of many adjacent delta lobes deposited as a part of a major cycle of terrigenous sediment influx. Delta morphology and internal stratigraphy are primarily the product of an interplay between fluvial sediment input and reworking of sediment by marine or lacustrine processes. Although sources of marine energy include oceanic and wind-generated currents, density currents, gravitational potential, tidal currents, storm surge, and wave surge, deltaic progradation is modified primarily by tidal currents and wave surge. Marine deltas can thus be characterized in terms of three end-member types: (1) fluvial-dominated deltas, (2) wave-dominated deltas, and (3) tide-dominated deltas. Modern fluvial-dominated deltas include the birdfoot lobe of the Holocene Mississippi Delta system and the Po and Danube deltas. The Rhone and Sao Francisco are typical wave-dominated deltas. The Ganges-Brahmaputra, Fly, and Colorado deltas are of the tide-dominated type. Gravity induced sediment transport tends to remove sediment basinward from the delta system into slope, submarine fan, and basin floor environments which are best considered separate depositional systems. Within deltaic depositional systems, longterm evolutionary trends can be recognized and interpreted in terms of response to changing process intensity. Pennsylvanian deltas of north-central Texas changed from fluvial-dominated elongate to wave-influenced or even wave-dominated lobate types as they prograded across a shallow platform into deeper, open marine water. Early Eocene (Wilcox) and Miocene clastic cycles of the Gulf Coast Tertiary basin evolved from fluvial-dominated elongate and lobate deltas of the regressive phase to wave-dominated deltas of the transgressive phase of the cycle.
Abstract Using modern and ancient examples we show that river-dominated deltas formed in shallow basins have multiple coeval terminal distributary channels at different scales. Sediment dispersion through multiple terminal distributary channels results in an overall lobate shape of the river-dominated delta that is opposite to the digitate Mississippi type, but similar with deltas described as wave-dominated. The examples of deltas that we present show typical coarsening-upward delta-front facies successions but do not contain deep distributary channels, as have been routinely interpreted in many ancient deltas. We show that shallow-water river-dominated delta-front deposits are typically capped by small terminal distributary channels, the cross-sectional area of which represents a small fraction of the main fluvial "trunk" channel. Recognizing terminal distributary channels is critical in interpretation of river-dominated deltas. Terminal distributary channels are the most distal channelized features and can be both subaerial and subaqueous. Their dimensions vary between tens of meters to kilometers in width, with common values of 100–400 m and depths of 1–3 m, and are rarely incised. The orientation of the terminal distributary channels for the same system has a large variation, with values between 123° (Volga Delta) and 248° (Lena Delta). Terminal distributary channels are intimately associated with mouth-bar deposits and are infilled by aggradation and lateral or upstream migration of the mouth bars. Deposits of terminal distributary channels have characteristic sedimentary structures of unidirectional effluent flow but also show evidence of reworking by waves and tides.
Chapter 1: Introduction.Chapter 2: The first-order delta-sigma modulator.Chapter 3: The second-order delta-sigma modulator.Chapter 4: Higher-order delta-sigma modulation.Chapter 5: Bandpass and quadrature delta-sigma modulation.Chapter 6: Implementation considerations for [Delta][Sigma] ADCs.Chapter 7: Delta-sigma DACs.Chapter 8: High-level design and simulation.Chapter 9: Example modulator systems.Appendix A: Spectral estimation.Appendix B: The delta-sigma toolbox.Appendix C: Noise in switched-capacitor delta-sigma data converters.
Before TCR rearrangements, T cell progenitors are committed not only to the alpha beta and gamma delta T cell lineage but also to various subsets of both lineages. In the mouse, distinct gamma delta T cell subsets can develop in the fetal thymus, the adult thymus, or independently of a thymus, probably in intestinal epithelia. The two subsets that develop in the fetal thymus home to and are maintained throughout adult life in the skin and the mucosa of the uterus, vagina, and tongue. They are monospecific. This unusual restriction in receptor repertoires is the result of severe limitations in the generation of diversity in the fetal progenitors of these subsets and the thymic selection. After birth, one gamma delta T cell subset appears in the blood, spleen, and lymph nodes and one in the intestinal epithelia. The receptor repertoires of these subsets are characterized by the preferential usage of particular V gamma gene segments and extensive junctional diversity. Several murine and human gamma delta T cell clones have been shown to recognize classical MHC class I and class II proteins or MHC class I-like proteins, and in very few cases the presented peptides are known. We suspect that the various murine gamma delta T cell subsets interact with different antigen presenting cells which utilize different antigen presenting proteins and reside in different tissues. The function of gamma delta T cells remains unknown. Preliminary results of experiments with gene knock out mice which lack either alpha beta T cells or gamma delta T cells or both suggest that gamma delta T cells do not function as helper cells in humoral immune responses but may complement alpha beta T cells in the defense against various microorganisms.
Equilibrium binding studies and viscosity experiments are described that characterize the interaction of delta- and lambda-[Ru(o-phen)3]2+ with calf thymus DNA. The mode of binding of these compounds to DNA is a matter of controversy. Both isomers of [Ru(o-phen)3]2+ were found to bind but weakly to DNA, with binding constants of 4.9 (+/- 0.3) x 10(4) M-1 and 2.8 (+/- 0.2) x 10(4) M-1 determined for the delta and lambda isomers, respectively, at 20 degrees C in a solution containing 5 mM Tris-HCl (pH 7.1) and 10 mM NaCl. We determined that the quantity delta log K/delta log [Na+] equals 1.37 and 1.24 for the delta and lambda isomers, respectively. Application of polyelectrolyte theory allows us to use these values to show quantitatively that both the delta and lambda isomers are essentially electrostatically bound to DNA. Viscosity experiments show that binding the lambda isomer does not alter the relative viscosity of DNA to any appreciable extent, while binding of the delta isomer decreases the relative viscosity of DNA. From these viscosity results, we conclude that neither isomer of [Ru(o-phen)3]2+ binds to DNA by classical intercalation.
BACKGROUND: The B.1.617.2 (delta) variant of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (Covid-19), has contributed to a surge in cases in India and has now been detected across the globe, including a notable increase in cases in the United Kingdom. The effectiveness of the BNT162b2 and ChAdOx1 nCoV-19 vaccines against this variant has been unclear. METHODS: ) gene status. Data on all symptomatic sequenced cases of Covid-19 in England were used to estimate the proportion of cases with either variant according to the patients' vaccination status. RESULTS: Effectiveness after one dose of vaccine (BNT162b2 or ChAdOx1 nCoV-19) was notably lower among persons with the delta variant (30.7%; 95% confidence interval [CI], 25.2 to 35.7) than among those with the alpha variant (48.7%; 95% CI, 45.5 to 51.7); the results were similar for both vaccines. With the BNT162b2 vaccine, the effectiveness of two doses was 93.7% (95% CI, 91.6 to 95.3) among persons with the alpha variant and 88.0% (95% CI, 85.3 to 90.1) among those with the delta variant. With the ChAdOx1 nCoV-19 vaccine, the effectiveness of two doses was 74.5% (95% CI, 68.4 to 79.4) among persons with the alpha variant and 67.0% (95% CI, 61.3 to 71.8) among those with the delta variant. CONCLUSIONS: Only modest differences in vaccine effectiveness were noted with the delta variant as compared with the alpha variant after the receipt of two vaccine doses. Absolute differences in vaccine effectiveness were more marked after the receipt of the first dose. This finding would support efforts to maximize vaccine uptake with two doses among vulnerable populations. (Funded by Public Health England.).
ABSTRACT From the approach of the geological oceanographer, this paper attempts to develop rational lines of reasoning for hindcasting how nature disposed of sediments brought into a lake or ocean at a particular place and time. By assuming the ocean to be a currentless, tideless, wave-free basin, jet theory as developed by Tollmien and subsequent workers is utilized in determining the magnitude and interrelations of limnological and oceanographic phenomena observed off mouths of sediment-laden rivers. To do this, the basic theory of jets is modified by introducing a rotating fluid system and postulating a hydraulic head at the orifice. If a delta is defined as a sedimentary deposit built by jet flow into or within a permanent body of water, these modifications allow for the existence of three basic types of deltaic deposits, depending on the density contrast between entraining and entrained fluids. Examples of these different types of inflow are cited from the Mississippi Delta region. In the case of hyperpycnal inflow (inflow more dense), it is suggested that turbidity currents carrying coarse-grained material during glacial stages eroded the Mississippi Submarine Canyon and supplied the material for the submarine delta off the canyon’s mouth. Homopycnal inflow (inflow equally dense), which gives rise to the deltaic deposit characterized by classical top-, fore-, and bottom-set beds, is described for the Lake Ponchartrain, Louisiana, area when the Bonnet Carre Floodway is in operation and for crevasses in the Lower Mississippi River. Hypopycnal inflow (inflow less dense) is discussed in some detail, including such aspects as flocculation effects, lunate bar development at river mouths, development of distributaries and flank depressions, the seaward movement of river water upon leaving the river’s mouths, and effects of the earth’s rotation. Modifying effects of wind, waves, and tides on deltaic deposits are discussed briefly.
ABSTRACT The coastal sedimentary basin of Nigeria has been the scene of three depositional cycles. The first began with a marine incursion in the middle Cretaceous and was terminated by a mild folding phase in Santonian time. The second included the growth of a proto-Niger delta during the Late Cretaceous and ended in a major Paleocene marine transgression. The third cycle, from Eocene to Recent, marked the continuous growth of the main Niger delta. A new threefold lithostratigraphic subdivision is introduced for the Niger delta subsurface, comprising an upper sandy Benin Formation, an intervening unit of alternating sandstone and shale named the Agbada Formation, and a lower shaly Akata Formation. These three units extend across the whole delta and each ranges in age from early Tertiary to Recent. They are related to the present outcrops and environments of deposition. A separate member of the Benin Formation is recognized in the Port Harcourt area. This is the Afam Clay Member, which is interpreted to be an ancient valley fill formed in Miocene sediments. Subsurface structures are described as resulting from movement under the influence of gravity and their distribution is related to growth stages of the delta. Rollover anticlines in front of growth faults form the main objectives of oil exploration, the hydrocarbons being found in sandstone reservoirs of the Agbada Formation.
This paper presents a rapid yet accurate method, the “delta-Eddington” approximation, for calculating monochromatic radiative fluxes in an absorbing-scattering atmosphere. By combining a Dirac delta function and a two-term approximation, it overcomes the poor accuracy of the Eddington approximation for highly asymmetric phase functions. The fraction of scattering into the truncated forward peak is taken proportional to the square of the phase function asymmetry factor, which distinguishes the delta-Eddington approximation from others of similar nature. Comparisons of delta-Eddington albedos, transnmissivities and absorptivities with more exact calculations reveal typical differences of 0–0.022 and maximum differences of 0.15 over wide ranges of optical depth, sun angle, surface albedo, single-scattering albedo and phase function asymmetry. Delta-Eddington fluxes are in error, on the average, by no more than 0.5%0, and at the maximum by no more than 2% of the incident flux. This computationally fast and accurate approximation is potentially of utility in applications such as general circulation and climate modelling.
A new antigen-antibody system associated with the hepatitis B virus and immunologically distinct from the HB surface, core, and e systems is reported. The new antigen, termed delta, was detected by direct immunofluorescence only in the liver cell nuclei of patients with HBsAg positive chronic liver disease. At present, the intrahepatic expression of HBcAg and delta antigen appears to be mutually exclusive. No ultrastructural aspect corresponding to the delta antigen could be identified under the electron microscope. delta antibody was found in the serum of chronic HBsAg carriers, with a higher prevalence in patients with liver damage. The nuclear fluorescence patterns of HBcAg and delta antigen were similar; it is only possible to discriminate between the two antigens by using the respective specific antisera.
While there is an abundance of pharmacological and biochemical evidence to suggest the existence of multiple opioid receptors, their precise localization within the brain is unclear. To help clarify this issue, the present study examined the distributions of the mu, delta, and kappa opioid receptor subtypes in the rat forebrain and midbrain using in vitro autoradiography. Mu and delta receptors were labeled with the selective ligands 3H-DAGO (Tyr- D-Ala-Gly-MePhe-Gly-ol), and 3H-DPDPE (D-Pen2, D-Pen5-enkephalin), respectively, while the kappa receptors were labeled with 3H-(-)bremazocine in the presence of unlabeled DAGO and DPDPE. Based on previous findings in our laboratory, the labeling conditions were such that each ligand selectively occupied approximately 75% of each of the opioid sites. The results demonstrated that all 3 opioid receptor subtypes were differentially distributed in the rat brain. Mu binding was dense in anterior cingulate cortex, neocortex, amygdala, hippocampus, ventral dentate gyrus, presubiculum, nucleus accumbens, caudate putamen, thalamus, habenula, interpeduncular nucleus, pars compacta of the substantia nigra, superior and inferior colliculi, and raphe nuclei. In contrast, delta binding was restricted to only a few brain areas, including anterior cingulate cortex, neocortex, amygdala, olfactory tubercle, nucleus accumbens, and caudate putamen. Kappa binding, while not as widespread as observed with mu binding, was densely distributed in the amygdala, olfactory tubercle, nucleus accumbens, caudate putamen, medial preoptic area, hypothalamus, median eminence, periventricular thalamus, and interpeduncular nucleus. While all 3 opioid receptor subtypes could sometimes be localized within the same brain area, their precise distribution within the region often varied widely. For example, in the caudate putamen, mu binding had a patchy distribution, while delta and kappa sites were diffusely distributed, with delta sites being particularly dense ventrolaterally and kappa sites being concentrated ventromedially. These results support the existence of at least 3 distinct opioid receptors with possibly separate functional roles.
Ample evidence suggests that electroencephalographic (EEG) oscillatory activity is linked to a broad variety of perceptual, sensorimotor, and cognitive operations. However, few studies have investigated the delta band (0.5-3.5 Hz) during different cognitive processes. The aim of this review is to present data and propose the hypothesis that sustained delta oscillations inhibit interferences that may affect the performance of mental tasks, possibly by modulating the activity of those networks that should be inactive to accomplish the task. It is clear that two functionally distinct and potentially competing brain networks can be broadly distinguished by their contrasting roles in attention to the external world vs. the internally directed mentation or concentration. During concentration, EEG delta (1-3.5 Hz) activity increases mainly in frontal leads in different tasks: mental calculation, semantic tasks, and the Sternberg paradigm. This last task is considered a working memory task, but in neural, as well as phenomenological, terms, working memory can be best understood as attention focused on an internal representation. In the Sternberg task, increases in power in the frequencies from 1 to 3.90 Hz in frontal regions are reported. In a Go/No-Go task, power increases at 1 Hz in both conditions were observed during 100-300 ms in central, parietal and temporal regions. However, in the No-Go condition, power increases were also observed in frontal regions, suggesting its participation in the inhibition of the motor response. Increases in delta power were also reported during semantic tasks in children. In conclusion, the results suggest that power increases of delta frequencies during mental tasks are associated with functional cortical deafferentation, or inhibition of the sensory afferences that interfere with internal concentration. These inhibitory oscillations would modulate the activity of those networks that should be inactive to accomplish the task.
Abstract The Tertiary Niger delta covers an area of about 75,000 sq km and is composed of an overall regressive clastic sequence which reaches a maximum thickness of 30,000 to 40,000 ft (9,000 to 12,000 m). The development of the delta has been dependent on the balance between the rate of sedimentation and the rate of subsidence. This balance and the resulting sedimentary patterns appear to have been influenced by the structural configuration and tectonics of the basement. Structural analysis of the Tertiary overburden shows that individual fault blocks can be grouped into macrostructural and eventually megastructural units. Such megaunits are separate provinces with regard to time-stratigraphy, sedimentation, deformation, generation and migration of hydrocarbons, and hydrocarbon distribution. A recurrent pattern emerges in the distribution both of absolute volumes of hydrocarbons and the ratio of volume of gas-bearing reservoir rocks to the volume of oil-bearing reservoir rocks within megaunits and macrounits. The maturity of potential source rock in a given fault trend was achieved when sedimentation had almost reached the present surface, and when the active depocenter had been advanced seaward by several trends. Thus, migration started when deposition, together with the intrinsically synsedimentary structural deformation, had almost come to a halt in that particular trend. The source rocks of the Niger delta yield a light waxy paraffinic oil, which is transformed bacterially to a heavier nonwaxy crude at temperatures below 150 to 180°F (65 to 80°C). The coincidence of the boundary between transformed and unaltered oils, within a rather narrow temperature range on a delta-wide basis, implies that little or no subsidence with concomitant increase in geotemperature of the oil-bearing reservoirs has occurred after migration. The conclusion that migration took place after the structural geometry of a given trend had been determined originates from several independent lines of evidence. The observed uneven distribution of oil and gas in the delta therefore cannot be explained in terms of the passage of the source rocks through the oil-generating zone into the gas-generating zone (oil and gas “kitchens,” respectively), with early structures receiving mainly oil and late traps receiving mainly gas. Rather, the hydrocarbon distribution probably is the result of original heterogeneity of the source rock and of segregation during migration and remigration.
We investigate whether the volatility risk premium is negative by examining the statistical properties of delta-hedged option portfolios (buy the option and hedge with stock). Within a stochastic volatility framework, we demonstrate a correspondence between the sign and magnitude of the volatility risk premium and the mean delta-hedged portfolio returns. Using a sample of S&amp;P 500 index options, we provide empirical tests that have the following general results. First, the delta-hedged strategy underperforms zero. Second, the documented underperformance is less for options away from the money. Third, the underperformance is greater at times of higher volatility.Fourth, the volatility risk premium significantly affects delta-hedged gains even after accounting for jump-fears. Our evidence is supportive of a negative market volatility risk premium.
Deltas are highly sensitive to increasing risks arising from local human activities, land subsidence, regional water management, global sea-level rise, and climate extremes. We quantified changing flood risk due to extreme events using an integrated set of global environmental, geophysical, and social indicators. Although risks are distributed across all levels of economic development, wealthy countries effectively limit their present-day threat by gross domestic product-enabled infrastructure and coastal defense investments. In an energy-constrained future, such protections will probably prove to be unsustainable, raising relative risks by four to eight times in the Mississippi and Rhine deltas and by one-and-a-half to four times in the Chao Phraya and Yangtze deltas. The current emphasis on short-term solutions for the world's deltas will greatly constrain options for designing sustainable solutions in the long term.
OBJECTIVES: To determine continuous EEG (cEEG) patterns that may be unique to anti-NMDA receptor (NMDAR) encephalitis in a series of adult patients with this disorder. METHODS: We evaluated the clinical and EEG data of 23 hospitalized adult patients with anti-NMDAR encephalitis who underwent cEEG monitoring between January 2005 and February 2011 at 2 large academic medical centers. RESULTS: Twenty-three patients with anti-NMDAR encephalitis underwent a median of 7 (range 1-123) days of cEEG monitoring. The median length of hospitalization was 44 (range 2-200) days. Personality or behavioral changes (100%), movement disorders (82.6%), and seizures (78.3%) were the most common symptoms. Seven of 23 patients (30.4%) had a unique electrographic pattern, which we named "extreme delta brush" because of its resemblance to waveforms seen in premature infants. The presence of extreme delta brush was associated with a more prolonged hospitalization (mean 128.3 ± 47.5 vs 43.2 ± 39.0 days, p = 0.008) and increased days of cEEG monitoring (mean 27.6 ± 42.3 vs 6.2 ± 5.6 days, p = 0.012). The modified Rankin Scale score showed a trend toward worse scores in patients with the extreme delta brush pattern (mean 4.0 ± 0.8 vs 3.1 ± 1.1, p = 0.089). CONCLUSIONS: Extreme delta brush is a novel EEG finding seen in many patients with anti-NMDAR encephalitis. The presence of this pattern is associated with a more prolonged illness. Although the specificity of this pattern is unclear, its presence should raise consideration of this syndrome.
Using sigma-delta A/D methods, high resolution can be obtained for only low to medium signal bandwidths. This article describes conventional A/D conversion, as well as its performance modeling. We then look at the technique of oversampling, which can be used to improve the resolution of classical A/D methods. We discuss how sigma-delta converters use the technique of noise shaping in addition to oversampling to allow high resolution conversion of relatively low bandwidth signals. We examine the use of sigma-delta converters to convert narrowband bandpass signals with high resolution. Several parallel sigma-delta converters, which offer the potential of extending high resolution conversion to signals with higher bandwidths, are also described.
The hepatitis B virus-associated beta antigen was found in the serum of experimentally infected chimpanzee as an internal component of a discrete subpopulation of hepatitis B surface antigen (HBsAg) particles. The 35- to 37-nm particles banded in CsCl at 1.24-1.25 g/cm3 and sedimented with a mobility intermediate between that of the hepatitis B virion and that of the 22-nm form of HBsAg. The particles contained only indistinct internal structure by electron microscopy and were not unique to delta agent infection, similar particles without delta-antigen activity being observed in the preinfection serum of HBsAg carrier chimpanzees. A small RNA (Mr, 5 X 10(5)) was temporally associated with delta antigen in the serum of infected chimpanzees and copurified with the delta-antigen-associated particles. This RNA is smaller than the genomes of known RNA viruses but larger than the viroids of higher plants.