Constant Background Level Research Articles

Revised GLE database: Fluences of solar energetic particles as measured by the neutron-monitor network since 1956

Aims.Continuous measurements of ground-based neutron monitors (NMs) form the main data source for studying high-energy high-intensity solar energetic particle (SEP) events that are called ground-level enhancements (GLEs). All available data are collected in the International GLE Database (IGLED), which provides formal NM count-rate increases above the constant pre-increase level which is due to galactic cosmic rays (GCR). This data set is used to reconstruct the energy spectra of GLE events. However, the assumption of a constant GCR background level throughout GLE events is often invalid. Here we thoroughly revise the IGLED and provide a data set of detrended NM count-rate increases that accounts for the variable GCR background.Methods.The formal GLE count-rate increases were corrected for the variable GCR background, which may vary significantly during GLE events. The corresponding integral omnidirectional fluences of SEPs were reconstructed for all GLEs with sufficient strength from the detrended data using the effective rigidity method.Results.The database of the detrended NM count rate is revised for GLE events since 1956. Integral omnidirectional fluences were estimated for 58 GLE events and parametrised for 52 sufficiently strong events using the modified Ellison-Ramaty spectral shape.Conclusions.The IGLED was revised to account for the variable GCR background. Integral omnidirectional fluences reconstructed for most of GLE events were added to IGLED. This forms the basis for more precise studies of parameters of SEP events and thus for solar and space physics.

Robust Bayesian target detection algorithm for depth imaging from sparse single-photon data

This paper presents a new Bayesian model and associated algorithm for depth and intensity profiling using full waveforms from time-correlated single-photon counting measurements in the limit of very low photon counts (i.e., typically less than 20 photons per pixel). The model represents each Lidar waveform as an unknown constant background level, which is combined in the presence of a target, to a known impulse response weighted by the target intensity and finally corrupted by Poisson noise. The joint target detection and depth imaging problem is expressed as a pixelwise model selection and estimation problem, which is solved using Bayesian inference. Prior knowledge about the problem is embedded in a hierarchical model that describes the dependence structure between the model parameters while accounting for their constraints. In particular, Markov random fields (MRFs) are used to model the joint distribution of the background levels and of the target presence labels, which are both expected to exhibit significant spatial correlations. An adaptive Markov chain Monte Carlo algorithm including reversible-jump updates is then proposed to compute the Bayesian estimates of interest. This algorithm is equipped with a stochastic optimization adaptation mechanism that automatically adjusts the parameters of the MRFs by maximum marginal likelihood estimation. Finally, the benefits of the proposed methodology are demonstrated through a series of experiments using real data.

HARD X-RAY MORPHOLOGICAL AND SPECTRAL STUDIES OF THE GALACTIC CENTER MOLECULAR CLOUD SGR B2: CONSTRAINING PAST SGR A⋆ FLARING ACTIVITY

Galactic Center (GC) molecular cloud Sgr B2 is the best manifestation of an X-ray reflection nebula (XRN) reprocessing a past giant outburst from the supermassive black hole Sgr A*. Alternatively, Sgr B2 could be illuminated by low-energy cosmic ray electrons (LECRe) or protons (LECRp). In 2013, NuSTAR for the first time resolved Sgr B2 hard X-ray emission on sub-arcminute scales. Two prominent features are detected above 10 keV - a newly emerging cloud G0.66-0.13 and the central 90" radius region containing two compact cores Sgr B2(M) and Sgr B2(N) surrounded by diffuse emission. It is inconclusive whether the remaining level of Sgr B2 emission is still decreasing or has reached a constant background level. A decreasing Fe K$\alpha$ emission can be best explained by XRN while a constant background emission can be best explained by LECRp. In the XRN scenario, the 3-79 keV Sgr B2 spectrum can well constrain the past Sgr A* outburst, resulting in an outburst spectrum with a peak luminosity of $L_{3-79\rm~keV} \sim 5\times10^{38} \rm~erg~s^{-1}$ derived from the maximum Compton-scattered continuum and the Fe K$\alpha$ emission consistently. The XRN scenario is preferred by the fast variability of G0.66-0.13, which could be a molecular clump located in the Sgr B2 envelope reflecting the same Sgr A* outburst. In the LECRp scenario, we derived the required CR ion power $dW/dt=(1-4)\times10^{39}\rm~erg~s^{-1}$ and the CR ionization rate $\zeta_{H}=(6-10)\times 10^{-15}\rm~H^{-1}~s^{-1}$. The Sgr B2 background level X-ray emission will be a powerful tool to constrain GC CR population.

Transient experiments on a full-scale DOC—Methodology and techniques to support modelling

A methodology was developed, which enables transient experiments to be performed on a DOC connected to a live diesel engine, while the temperature of the DOC substrate is monitored at various locations. This was demonstrated on a full-scale Pt/γ-alumina DOC (o.d.=106mm; length=114mm), connected to a Ford 2.0L diesel engine. The engine was operated at a constant speed of 2000rpm, and by varying the engine torque, experiments were performed at fixed gas inlet temperatures to the DOC, e.g. 150, 320°C, and at each setting a constant background level of exhaust emissions was obtained. Then, a known quantity of pollutant (e.g. CO, propane) was injected into the exhaust, so as to create an approximated pulse input into the DOC (e.g. with peak CO concentration=3000ppm). The transient response of the system was monitored. So as to examine more closely local changes in response to a change in inlet conditions, experiments were also performed with a short 5mm thin-slice of DOC (o.d.=106mm).These techniques enable better control to be achieved over such experiments, and provide valuable data to support mathematical modelling. It was interesting to note, that in the examples studied, there was no evidence of any significant competition between CO and THCs for the active sites.The DOC was also characterised, and it was shown that key properties can have different values depending on the location from which the sample was taken – and this would also have important implications on modelling work.

HEARING COMPENSATION SYSTEM INCORPORATING SIGNAL PROCESSING TECHNIQUES

A hearing compensation system comprises a plurality of bandpass filters having an input connected to an input transducer and each bandpass filter having an output connected to the input of one of a plurality of multiplicative automatic gain control (MAGC) circuits whose outputs are summed together and connected to the input of an output transducer. The MAGC circuits attenuate acoustic signals having a constant background level without the loss of speech intelligibility. The identification of the background noise portion of the acoustic signal is made by the constancy of the envelope of the input signal in each of the several frequency bands. The background noise that will be suppressed includes multi-talker speech babble, fan noise, feedback whistle, florescent light hum, and white noise. For use in the consumer electronics field background acoustic noise may be sensed and used to adjust gain in the various MAGC circuits so as to improve a user's listening experience, whether the user is hearing impaired or not.

3′-Deoxy-3′-[F-18]Fluorothymidine Positron Emission Tomography in Patients with Recurrent Glioblastoma Multiforme: Comparison with Gd-DTPA Enhanced Magnetic Resonance Imaging

The accumulation of 3'-deoxy-3'-[F-18]fluorothymidine (FLT) on positron emission tomography (PET) images in patients with glioblastoma multiforme was evaluated and correlated with gadopentetate dimeglumine (Gd-DTPA) enhancement in magnetic resonance images (MRIs). FLT studies in 10 patients with recurrent glioblastoma multiforme were retrospectively investigated. Dynamic emission data were acquired for 60 minutes immediately after injection of FLT. The standardized uptake value (SUV) for tumor and reference tissue (contralateral hemisphere and ipsilateral cerebellum) was calculated. The volumes of the metabolically active part of the tumor (V (PET)) and that of the Gd-DTPA enhancing part of the tumor (V (MR)) were calculated. FLT uptake in tumors peaked before 5 minutes and sometimes as early as 0.5 minutes, and reached a constant level at approximately 10 minutes after injection. The reference tissue time-activity curves had an early peak and reached a constant low background level. All tumors had increased FLT uptake and showed Gd-DTPA enhancement. The SUV in tumor was significantly higher than that in the reference tissue (P<0.0001). A significant correlation between V (PET) and V (MR) was found (P<0.0001) although there was a difference in the areas of Gd-DTPA enhancement and FLT uptake. These preliminary results indicate that FLT-PET may be useful for the detection of recurrent glioblastoma multiforme. Our data in a relatively small patient population do not support a clear-cut relationship between FLT accumulation and Gd-DTPA enhancement. Further pathologic correlation will determine if it can be used for detecting recurrent tumoral disease.

Polycyclic aromatic hydrocarbons (PAHs) in sediments of the Baltic Sea and of the German coastal waters

Samples of surface sediments (0–2 cm) and sediment cores (0–45 cm, 1 cm slices) were collected in the Belt Sea and Arkona Sea as well as in the internal and external coastal waters of Mecklenburg-Vorpommern. The concentrations of PAHs were analysed by HPLC and fluorescence detection. The results were verified by GUMS. The sum of PAHs varied between 11 ng/g dry weight for sandy sediments and 1900 ng/g for muddy sediments in the Belt Sea and Arkona Sea. Elevated concentrations up to 17000 ng/g were observed in the surface sediments of the internal coastal waters with highest concentrations in the Warnow estuary and in the Oder Haff. This indicates the significant contribution of river discharge to the contamination of sediments with PAHs. The distribution of the individual PAHs in sediments vary widely depending on their structure and molecular weight. The higher molecular 4 to 6 ring aromatics predominate due to their higher persistence. vertical profiles of PAH-concentrations are characterised by a maximum at depth between 1 cm and 8 cm and by an almost constant background level at depth below 22–24 cm. These patterns may be explained by changes in the anthropogenic release of PAHs. The sedimentological properties also affect the accumulation of PAHs. Strong correlation's between concentrations of PAHs and the content of organic carbon could be established.

Cortical and spinal mechanisms of facilitation to brain stimulation.

Compound muscle action potentials (CMAPs) evoked by magnetic brain stimuli are larger if the subject provides a steady background voluntary contraction of the target muscle. This facilitation could be due either to cortical or spinal mechanisms, or both. Both magnetic and electrical stimuli given immediately after the onset of a ballistic contraction also evoke markedly facilitated CMAPs. By contrast, responses some 200 ms after the onset of such a contraction are facilitated if stimuli are magnetic but not if they are electrical. This second phase of facilitation is largely cortical in origin. By comparing the size of CMAPs evoked by magnetic stimuli at two different delays after electromyogram onset, the total facilitation could be dissected into its spinal and cortical components. The relationship between CMAP area in the first dorsal interosseous and stimulus intensity was different in the two phases of facilitation, suggesting a constant background level of spinal facilitation upon which an increasing descending volley operated. In experiments in which ballistic contractions at increasing force levels were performed it was found that at low force levels, spinal facilitation predominated, but at forces greater than 10% maximum there were roughly equal contributions from increased spinal cord and cortex excitability.

Hearing aid device incorporating signal processing techniques

A hearing compensation system for the hearing impaired comprises a plurality of bandpass filters having an input connected to an input transducer and each bandpass filter having an output connected to the input of one of a plurality of multiplicative AGC circuits whose outputs are summed together and connected to the input of an output transducer. The multiplicative AGC circuits attenuate acoustic signals having a constant background level without the loss of speech intelligibility. The identification of the background noise portion of the acoustic signal is made by the constancy of the envelope of the input signal in each of the several frequency bands. The background noise that will be suppressed includes multi-talker speech babble, fan noise, feedback whistle, fluorescent light hum, and white noise.

Long‐term changes in the acid and salt concentrations of the Greenland Ice Core Project ice core from electrical stratigraphy

Continuous electrical records covering a climatic cycle are presented for the Greenland Ice Core Project deep ice core from Greenland. Electrical conductivity measurement (ECM) measures the acid content of the ice, and the dielectric profile (DEP) responds to acid, ammonium, and chloride. All features seen can be explained by chemical changes in the ice, and there is no evidence so far for any major change in electrical response with depth or age of the ice. Both records are dominated by the acidity of the ice which varies strongly from acidic in warm periods to alkaline in cold periods, controlled by neutralization by alkaline dust (calcareous and other mineral dust). When Ca is low, the acidity (mainly nitric acid) has a fairly constant background level throughout the cycle, with slightly lower values in ice believed to be from the last interglacial. Ca has to rise only slightly to neutralize the available acidity, so that acidity is a highly nonlinear reflection of climate changes. If neutralization occurred in the aerosol (rather than in the ice), then the number of cloud condensation nuclei over parts of the northern hemisphere could have been reduced, leading to reduced cloud albedo. This nonlinear feedback may have some importance for modeling of climate change. When both acid and ammonium levels are low, the DEP signal can be used to give a rapid indication of chloride trends.

Late Holocene ice core records of climate and environment from the tropical Andes, Peru

A 1 500-year history of climatic and environmental variations from the Quelccaya ice cap (13o56'S, 70o50'W, 5 670 m a.s.l.) is compared to a similar 3 000-year ice core record from the col of Huascarán (9o06'S, 77o 36'W, 6 048 m a.s.l.). The parameters which are presented are oxygen isotopic ratios (δ18O), considered to be indicative of temperature, insoluble dust, and (for Huascarán only) nitrate concentrations (NO3) which is indicative of vegetation fluctuations in the Amazon rainforest. The Huascarán δ18O and NO3 profiles for the most recent 3 000 years show that there has been a general decrease in temperature along with a decrease inbiological activity in the Amazon Basin, with the lowest values occurring during the "Little Ice Age" (LIA), 200 to 500 yrs BP. This was followed by an abrupt change in 8180, which increased to the levels of 3 000 years ago. This abrupt warming has dominated the last two centuries in the records from both sites. NO3 levels in Huascarán have also increased during this time, albeit less dramatically. There is evidence for slight isotopic enrichment (warming) between 1 150 and 900 yrs BP, which may be related to the "Medieval Warm Period". The Huascarán dust concentration record shows a fairly constant background level over the last 3 000 years, which was interrupted by a dust event between 2 000 and 1 800 years BP (0-200 A.D.) and centered on 1 900 years BP (100 A.D.). A less intense peaks occurred from 1 400 to 1 600 years BP (400 to 600 A.D.) and 1300 to 1030 years BP (700 to 960 A.D). Examination of the dust associated with this event indicates that it is wind-blown material which is very similar in composition to the granodiorite of which the Cordillera Blanca massif is composed. The more recent peaks are temporally correlative with the much greater 400 to 620 A.D. dust event in the Quelccaya ice core, thus suggesting that it may have been widespread. The more recent dust event in the Quelccaya record from 830 to 960 A.D. is recorded at lower concentrations in the Huascarán ice cores, which gives support to the linkage of the early part of the Quelccaya dust record to prehistoric agriculture activity in the Late Titicaca basin (Thompson et al, 1988).

Pathways of human exposure to arsenic in a community surrounding a copper smelter

Several studies have found elevated levels of urinary arsenic among residents living near a copper smelter in Tacoma, Washington. To assess pathways of exposure to arsenic from the smelter, biological and environmental samples were collected longitudinally from 121 households up to 8 miles from the smelter. The concentration of inorganic and methylated arsenic compounds in spot urine samples was used as the primary measure of exposure to environmental arsenic. Urinary concentration of arsenic dropped off to a constant background level within one-half mile of the smelter in contrast to environmental concentrations, which decreased more steadily with increasing distance. Among all age-sex-specific groups in all areas, only children ages 0-6 living within one-half mile of the smelter had elevated levels of arsenic in urine. A separate analysis of data for these children suggests that hand-to-mouth activity was the primary source of exposure. Inhalation of ambient air and resuspension of contaminated soil were not important sources of exposure for children or adults.

Assessment of lead distribution patterns in urban and rural environments

Abstract The distribution of lead over four (4) square city blocks in a metropolitan area has been determined by analysis of soil, atmospheric particulates, rainwater and vegetation samples taken from four (4) concentric regions. The results revealed that there is a decline in the lead level with increasing distance from the periphery and a sudden increase near the center, suggesting that high levels of lead at the streets are due to vehicular emission while the accumulation near the center of the target area is due to a resulting synergistic buildup. Near the curb the results showed a decrease in lead concentration with distance from traffic lights. However, the profile data revealed some dependency on meteorological conditions, vegetation screening, and traffic light cycling times. Possible consequences of the results with regard to beltways surrounding metropolitan areas are discussed. The lead concentration profile near an isolated highway in a rural area was also determined and results indicated a steady decline in the level of lead with distance from the highway until a constant background level was reached. Lead levels in the urban area were from two to three times higher than lead levels in the rural area. A novel, efficient method for the digestion of used filters for subsequent analysis of trace metals in atmospheric particulates is also presented.

The influence of non-uniformly doped substrates on mos C- V curves

Theoretical C- V curves have been computed for substrate impurity concentrations which drop exponentially to a constant background level on receding from the surface. It is shown that for certain impurity profiles the C- V curves appear similar to those which would be obtained from a uniformly doped substrate with a large surface state density. It is evident therefore that some ambiguity may exist in the interpretation of experimental C- V curves if there is a marked departure from uniformity in the substrate doping level near the surface.