Photon Flux Values Research Articles

Comparison of super-resolution and noise reduction for passive single-photon imaging

Single-photon sensitive image sensors have recently gained popularity in passive imaging applications where the goal is to capture photon flux (brightness) values of different scene points in the presence of challenging lighting conditions and scene motion. Recent work has shown that high-speed bursts of single-photon timestamp information captured using a single-photon avalanche diode camera can be used to estimate and correct for scene motion thereby improving signal-to-noise ratio and reducing motion blur artifacts. We perform a comparison of various design choices in the processing pipeline used for noise reduction, motion compensation, and upsampling of single-photon timestamp frames. We consider various pixelwise noise reduction techniques in combination with state-of-the-art deep neural network upscaling algorithms to super-resolve intensity images formed with single-photon timestamp data. We explore the trade space of motion blur and signal noise in various scenes with different motion content. Using real data captured with a hardware prototype, we achieved super-resolution reconstruction at frame rates up to 65.8 kHz (native sampling rate of the sensor) and captured videos of fast-moving objects. The best reconstruction is obtained with the motion compensation approach, which achieves a structural similarity (SSIM) of about 0.67 for fast-moving rigid objects. We are able to reconstruct subpixel resolution. These results show the relative superiority of our motion compensation compared to other approaches that do not exceed an SSIM of 0.5.

Monte Carlo Study of Several Concrete Shielding Materials Containing Galena and Borated Minerals

Introduction: The heavyweight concretes have been widely used for constructing medical or industrial radiation facilities with photon sources. Materials and Methods: In this study, heavy concretes containing galena (PbS) and several borated minerals are proposed as suitable materials against photons. The shielding properties of 21 galena concretes containing seven borated minerals with three mixing patterns were evaluated using MCNP4C Monte Carlo code. The attenuation of the gamma radiation is computed under the conditions of narrow and beam geometries. The x-ray sources with 40, 60, 90, and 120 kVp and gamma rays of 99mTc, 131I, 137Cs, and 511 keV annihilation photons were considered. The photon flux values and the x-ray spectrum after applying all the concretes were compared to the ordinary ones. Regarding the results, more photon attenuations obtained by using high density concretes simulation in comparison to ordinary concrete. Results: The results revealed that the concretes containing orthopinokiolite as the borated material made by the third mixing pattern, had the most photon attenuation. According to the results, the shielding properties of the concretes containing different borated minerals were alike against high photon energies, whereas in low energy photons the attenuation depended on the type of borated mineral used in the concretes. Conclusion: The high-density heavy-weighted concretes could be effectively used as multi-purpose shield for radiotherapy rooms and nuclear reactors due to the borated minerals.

Factors controlling the photochemical degradation of methylmercury in coastal and oceanic waters.

Many studies have recognized abiotic photochemical degradation as an important sink of methylmercury (CH3Hg) in sunlit surface waters, but the rate-controlling factors remain poorly understood. The overall objective of this study was to improve our understanding of the relative importance of photochemical reactions in the degradation of CH3Hg in surface waters across a variety of marine ecosystems by extending the range of water types studied. Experiments were conducted using surface water collected from coastal sites in Delaware, New Jersey, Connecticut, and Maine, as well as offshore sites on the New England continental shelf break, the equatorial Pacific, and the Arctic Ocean. Filtered water amended with additional CH3Hg at environmentally relevant concentrations was allowed to equilibrate with natural ligands before being exposed to natural sunlight. Water quality parameters - salinity, dissolved organic carbon, and nitrate - were measured, and specific UV absorbance was calculated as a proxy for dissolved aromatic carbon content. Degradation rate constants (0.87-1.67 day-1) varied by a factor of two across all water types tested despite varying characteristics, and did not correlate with initial CH3Hg concentrations or other environmental parameters. The rate constants in terms of cumulative photon flux values were comparable to, but at the high end of, the range of values reported in other studies. Further experiments investigating the controlling parameters of the reaction observed little effect of nitrate and chloride, and potential for bromide involvement. The HydroLight radiative transfer model was used to compute solar irradiance with depth in three representative water bodies - coastal wetland, estuary, and open ocean - allowing for the determination of water column integrated rates. Methylmercury loss per year due to photodegradation was also modeled across a range of latitudes from the Arctic to the Equator in the three model water types, resulting in an estimated global demethylation rate of 25.3 Mmol yr-1. The loss of CH3Hg was greatest in the open ocean due to increased penetration of all wavelengths, especially the UV portion of the spectrum which has a greater ability to degrade CH3Hg. Overall, this study provides additional insights and information to better constrain the importance of photochemical degradation in the cycling of CH3Hg in marine surface waters and its transport from coastal waters to the open ocean.

Intrinsic artefacts in optical oxygen sensors--how reliable are our measurements?

Optical oxygen sensing is of broad interest in many areas of research, such as medicine, food processing, and micro- and marine biology. The operation principle of optical oxygen sensors is well established and these sensors are routinely employed in lab and field experiments. Ultratrace oxygen sensors, which enable measurements in the sub-nanomolar region (dissolved oxygen), are becoming increasingly important. Such sensors prominently exhibit phenomena that complicate calibration and measurements. However, these phenomena are not constrained to ultratrace sensors; rather, these effects are inherent to the way optical oxygen sensors work and may influence any optical oxygen measurement when certain conditions are met. This scenario is especially true for applications that deal with high-excitation light intensities, such as microscopy and microfluidic applications. Herein, we present various effects that we could observe in our studies with ultratrace oxygen sensors and discuss the reasons for their appearance, the mechanism by which they influence measurements, and how to best reduce their impact. The phenomena discussed are oxygen photoconsumption in the sensor material; depletion of the dye ground state by high-excitation photon-flux values, which can compromise both intensity and ratiometric-based measurements; triplet-triplet annihilation; and singlet-oxygen accumulation, which affects measurements at very low oxygen concentrations.

SIMULATING THREE-DIMENSIONAL NONTHERMAL HIGH-ENERGY PHOTON EMISSION IN COLLIDING-WIND BINARIES

Massive stars in binary systems have long been regarded as potential sources of high-energy gamma rays.The emission is principally thought to arise in the region where the stellar winds collide and accelerate relativistic particles which ubsequently emit gamma rays. On the basis of a three-dimensional distribution function of high-energy particles in the wind collision region - as obtained by a numerical hydrodynamics and particle transport model - we present the computation of the three-dimensional nonthermal photon emission for a given line of sight. Anisotropic inverse Compton emission is modelled using the target radiation field of both stars. Photons from relativistic bremsstrahlung and neutral pion decay are computed on the basis of local wind plasma densities. We also consider photon photon opacity effects due to the dense radiation fields of the stars. Results are shown for different stellar separations of a given binary system comprising of a B star and a Wolf-Rayet star. The influence of orbital orientation with respect to the line of sight is also studied by using different orbital viewing angles. For the chosen electron-proton injection ratio of 0.01, we present the ensuing photon emission in terms of two-dimensional projections maps, spectral energy distributions and integrated photon flux values in various energy bands. Here, we find a transition from hadron-dominated to lepton-dominated high-energy emission with increasing stellar separations. In addition, we confirm findings from previous analytic modeling that the spectral energy distribution varies significantly with orbital orientation.

Responses to light intensity in a genome-scale model of rice metabolism.

We describe the construction and analysis of a genome-scale metabolic model representing a developing leaf cell of rice (Oryza sativa) primarily derived from the annotations in the RiceCyc database. We used flux balance analysis to determine that the model represents a network capable of producing biomass precursors (amino acids, nucleotides, lipid, starch, cellulose, and lignin) in experimentally reported proportions, using carbon dioxide as the sole carbon source. We then repeated the analysis over a range of photon flux values to examine responses in the solutions. The resulting flux distributions show that (1) redox shuttles between the chloroplast, cytosol, and mitochondrion may play a significant role at low light levels, (2) photorespiration can act to dissipate excess energy at high light levels, and (3) the role of mitochondrial metabolism is likely to vary considerably according to the balance between energy demand and availability. It is notable that these organelle interactions, consistent with many experimental observations, arise solely as a result of the need for mass and energy balancing without any explicit assumptions concerning kinetic or other regulatory mechanisms.

The direct–indirect kinetic model in photocatalysis: A reanalysis of phenol and formic acid degradation rate dependence on photon flow and concentration in TiO2 aqueous dispersions

Literature data concerning TiO2 photocatalytic oxidation of two model organic substrates, phenol and formic acid, are shown to be incompatible with the behavior predicted by the Langmuir–Hinshelwood (L–H) kinetic model. These data are reanalyzed in detail from a kinetic/mechanistic point of view to the light of the direct–indirect (D–I) model (D. Monllor-Satoca, R. Gomez, M. Gonzalez-Hidalgo, P. Salvador, Catal. Today 129 (1–2) (2007) 247), developed as an alternative to the L–H model. Two interfacial charge transfer mechanisms are considered by the (D–I) model: the indirect transfer (IT) mechanism, which is concerned with the adiabatic transfer of holes trapped at TiO2 terminal oxygen ions to dissolved substrate species, and the direct transfer (DT) mechanism dealing with the inelastic transfer of free holes to specifically adsorbed substrate species. While IT is the only mechanism taking place in the absence of specific adsorption, both DT and IT mechanisms actuate simultaneously under specific adsorption, although DT prevails on IT at high enough UV illumination intensity. On the experimental basis that in aqueous solution phenol is not specifically adsorbed on TiO2, it is shown that the experimental photodegradation rate dependence on photon flux (ρ) and phenol concentration (C) is not compatible with a Langmuir type expression, but can be fitted by the photooxidation rate expression (dC/dt)=[(aC)2+2k0aρC]1/2−aC, as predicted by the D–I model for IT, where a is an experimental parameter involving the rate constants for electron–hole recombination and transfer of photogenerated electrons and holes at the semiconductor–electrolyte interface. An apparent dependence of a on ρ and C is observed experimentally. Two possible hypothesis are invoked in order to explain this behaviour:a shift of the TiO2 energy levels, due to an accumullation of electric charge at the semiconductor surface, and/or the partial contribution of inelastic DT of holes to incipiently adsorbed phenol species. Evidence is given that the photooxidation rate of formic acid, which is shown to be specifically adsorbed on TiO2 in the presence of water, depends linearly on ρ, even at high enough photon flux values, as predicted by the D–I model when DT prevails on IT, but in contradiction with the behavior predicted by the L–H model.

TU‐C‐L100J‐06: Pediatric Organ Dose Measurements in Axial and Helical Multi‐Slice CT

Purpose: To determine radiation dose to specific organs in a pediatric phantom from a CT scan, and to determine if there is a significant difference between: axial (step and shoot) and helical acquisitions, when using very similar photon flux values (effective mAs). Method and Materials: An anthropomorphic pediatric phantom (5 year old equivalent) was used to investigate organ dose at the surface and internal to the phantom. The phantom contains four different tissue equivalent materials: soft tissue, bone, brain, and lung, and was imaged on a 64‐channel CT scanner with a head protocol [axial and two helical scans (pitch = 0.516 and 0.984)], and a chest protocol [axial and three helical scans (pitch = 0.516, 0.984, and 1.375)]. Effective mAs was kept constant (within 3%) for head and chest protocols. Dose measurements were acquired using thermoluminescent dosimeter (TLD) powder in capsules placed in the phantom sections in plug holes. The organs of interest for this study were: brain, both eyes, thyroid, sternum, both breasts, and both lungs. Results: All axial organ dose measurements were significantly higher (p<0.05) than all helical organ dose measurements. There was no significant difference (p>0.05) in organ dose values between the pitch values 0.516 and 0.984 for both head and chest scans. The chest organ dose measurements obtained using a pitch of 1.375 were significantly higher (p<0.05) than the other helical pitches used for chest scans (attributed to the automatic selection of the large focal spot). Conclusion: Communications with the vendor indicate that there are likely physical explanations for the difference observed in organ doses due to axial versus helical acquisitions. It is unclear if this difference in organ dose is unique to this scanner design, because dose measurements are not typically performed in helical scan mode and have not been investigated using other scanner models.

The Complete Spectral Catalog of Bright BATSE Gamma‐Ray Bursts

We present a systematic spectral analysis of 350 bright gamma-ray bursts (GRBs) observed with the Burst and Transient Source Experiment (BATSE; ~30 keV-2 MeV) with high temporal and spectral resolution. Our sample was selected from the complete set of 2704 BATSE GRBs based on their energy fluence or peak photon flux values to assure good statistics and included 17 short GRBs. To obtain well-constrained spectral parameters, several photon models were used to fit each spectrum. We compared spectral parameters resulting from the fits using different models, and the spectral parameters that best represent each spectrum were statistically determined, taking into account the parameterization differences among the models. A thorough analysis was performed on 350 time-integrated and 8459 time-resolved burst spectra, and the effects of integration times in determining the spectral parameters were explored. Using the results, we studied correlations among spectral parameters and their evolution pattern within each burst. The resulting spectral catalog is the most comprehensive study of spectral properties of GRB prompt emission to date and is available electronically from the High-Energy Astrophysics Science Archive Research Center (HEASARC). The catalog provides reliable constraints on particle acceleration and emission mechanisms in GRBs.

First results from an aging test of a prototype RPC for the LHCb Muon System

Recent results of an aging test performed at the CERN Gamma Irradiation Facility on a single-gap RPC prototype developed for the LHCb Muon System are presented. The results are based on an accumulated charge of about 0.45 C/cm 2 , corresponding to about 4 years of LHCb running at the highest background rate. The performance of the chamber has been studied, under several photon flux values, exploiting a muon beam. A degradation of the rate capability above 1 kHz/cm 2 is observed, which can be correlated to a sizeable increase of resistivity of the chamber plates. An increase of the chamber dark current is also observed. The chamber performance is found to fulfill the LHCb operation requirements.

Preliminary results of an aging test of RPC chambers for the LHCb Muon System

The preliminary results of an aging test performed at the CERN Gamma Irradiation Facility on a single-gap RPC prototype developed for the LHCb Muon System are presented. The results are based on an accumulated charge density of 0.42C/cm2, corresponding to about 4 years of LHCb running at the highest background rate. We observe a rise in the dark current and noise measured with source off. The current drawn with source on steadily decreased, possibly indicating an increase of resistivity of the chamber plates. The performance of the chamber, studied with a muon beam under several photon flux values, is found to still fulfill the LHCb operation requirements.

An in vitro tuberization bioassay to assess maturity class of new potato clones

SummaryThe maturity of a new potato clone can be determined from physiological measurements in field trials that involve considerable time, space and work. To improve the procedure, an in vitro bioassay based on tuberization behaviour of potato cultivars of different maturity classes was established. Twenty-six sets of temperature, photoperiod and photosynthetic photon flux values were assayed on the eight potato cultivars Jaerla, Zorba, Spunta, Kennebec, Turia, Désirée, Baraka and Fénix. In vitro tuberization was influenced by cultivar, photoperiod and temperature. The environmental condition defined by 12 h photoperiod, 34 μmol m–2 s–1 of photosynthetic photon flux and 25°C temperature produced statistical differences in tuberization among maturity classes. Both the earliness of tuberization and the “degree of tuberization” (based on the type of microtubers developed) permitted assigning a cultivar to a maturity class. Early cultivars showed higher readiness to tuberize and higher values of “degree of tuberization” than late cultivars.

11] Spatially resolved, quantitative determination of luciferase activity by photon-counting microscopy

Luciferase activity offers some distinct advantages as a bioreporter. It can be selected for using relatively simple equipment and signal ceases after the translation of target gene/luciferase gene fusion stops. This chapter describes photon-counting microscopy methodology to spatially resolve and quantitatively determine luciferase activity. Photon-counting microscopy system is designed to operate at photon fluxes of <10 -5 lux and are at least 1 order of magnitude more sensitive than “intensified” or cooled charged-coupled devices (CCD), and ISIT cameras. The methodology presented in this chapter is hardware specific and the principles are those that can be applied to any quantitative, spatially resolved method. For true photon-counting applications, the camera must be isolated from background light. A drawback of this methodology is that the numbers are relative. Data are not absolute photon flux values because the loss of photons occurs from light scattering, from optical transfer, and from conversions within the intensifier. However, if a calibration method based on objects, approximately the size of bacterial cells, were to be developed, then an estimate of the efficiency of the camera/microscope combination could be arrived at and used to calculate absolute photon flux values.

Leaf Attributes as Indices of Fruit Quality in Prune Tree Canopies

Leaf dry weight per leaf area (LDW/LA); weight of leaf N per unit leaf area (LN/LA); leaf dry weight (LDW); and fruit quality, particularly sugar per fruit (SF); fruit fresh weight (FFW); and fruit dry weight (FDW) were measured over a range of daily average incident photosynthetic photon flux values (PPF) (50 to 1000 μmol·s-1·m-2) in 7-year-old prune (Prunus domestics L. syn. `Petite d'Agen') tree canopies. Linear or curvilinear relationships between these leaf attributes and fruit characteristics were significant over the PPF range. Analysis of LDW/LA or LN/LA may be used to indicate tree canopy locations in which fruit size and quality is limited by suboptimal PPF.

Precise determination of gamma-ray peak areas

Experimental pulse height distributions of “gamma lines” taken with a HPGe (high-purity germanium) detector are considered as the sum of exponentials convoluted with a Gaussian. With this model, peak areas have been evaluated from the parameters of the exponentials at gamma-ray energies ranging from 0.1 to 1.8 MeV. In measurements with 137 Cs samples, the ratio of peak areas at 662 keV agreed with the given ratio of photon flux values to within ±0.2%.

Distinctive Light and CO2-Fixation Requirements of Nitrate and Ammonium Utilization by the Cyanobacterium Anacystis nidulans

The effect of light intensity on the rates of ammonium and nitrate uptake and of CO(2) fixation has been determined in intact Anacystis nidulans cells. Ammonium uptake became saturated at photon flux values of about 60 microeinsteins per square meter per second, whereas both nitrate uptake and CO(2) fixation reached saturation at about 250 microeinsteins per square meter per second, the rates of the two latter processes being tightly correlated at any light intensity assayed. Inhibition of ammonium assimilation resulted in the loss of correlation between CO(2) fixation and nitrate uptake, the latter process exhibiting then a reduced light requirement. The results establish a clear distinction between ammonium utilization and nitrate utilization with regard to their light requirement and to the nature of their dependence upon CO(2) fixation.