Coincident Pairs Research Articles

Simulation of ionization charge carrier cascade time and density for a new radiation detection method based on modulation of optical properties.

In time-of-flight PET, image quality and accuracy can be enhanced by improving the annihilation photon pair coincidence time resolution, which is the variation in the arrival time difference between the two annihilation photons emitted from each positron decay in the patient. Recent studies suggest direct detection of ionization tracks and their resulting modulation of optical properties, instead of scintillation, can improve the CTR significantly, potentially down to less than 10 ps CTR. However, the arrival times of the 511keV photons are not predictable, leading to challenges in the spatiotemporal localization characterization of the induced charge carriers in the detector crystal. To establish an optimized experimental setup for measuring ionization induced modulation of optical properties, it is critical to develop a versatile simulation algorithm that can handle multiple detector material properties and time-resolved charge carrier dynamics. We expanded our previous algorithm and simulated ionization tracks, cascade time and induced charge carrier density over time in different materials. For designing a proof-of-concept experiment, we simulated ultrafast electrons and free-electron x-ray photons for timing characterization along with alpha and beta particles for higher spatial localization. With 3 MeV ultrafast electrons, by reducing detector crystal thickness, we can effectively reduce the ionization cascade time to 0.79ps and deposited energy to 198.5keV, which is on the order of the desired 511keV energy. Alpha source simulations produced a cascade time of 2.45ps and charge carrier density of 6.39×1020cm-3 . Compared to the previous results obtained from 511keV photon-induced ionization track simulations, the cascade time displayed similar characteristics, while the charge density was found to be higher. These findings suggest that alpha sources have the potential to generate a stronger ionization-induced signal using the modulation of optical properties as the detection mechanism. This work provides a guideline to understand, design and optimize an experimental platform that is highly sensitive and temporally precise enough to detect single 511keV photon interactions with a goal to advance CTR for ToF-PET.

Limits on Fast Radio Burst–like Counterparts to Gamma-Ray Bursts Using CHIME/FRB

Fast radio bursts (FRBs) are a class of highly energetic, mostly extragalactic radio transients lasting for ∼milliseconds. While over 600 FRBs have been published so far, their origins are presently unclear, with some theories for extragalactic FRBs predicting accompanying high-energy emission. In this work, we use the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Fast Radio Burst (CHIME/FRB) Project to explore whether any FRB-like radio emission coincides in space and time with 81 gamma-ray bursts (GRBs) detected between 2018 July 17 and 2019 July 8 by Swift/BAT and Fermi/GBM. We do not find any statistically significant coincident pairs within 3σ of each other’s spatial localization regions and within a time difference of up to one week. In addition to searching for spatial matches between known FRBs and known GRBs, we use CHIME/FRB to constrain FRB-like (∼1–10 ms) radio emission before, at the time of, or after the reported high-energy emission at the position of 39 GRBs. For short gamma-ray bursts (SGRBs), we constrain the radio flux in the 400–800 MHz band to be under a few kJy for ∼5.5–12.5 hr post-high-energy burst. We use these limits to constrain models that predict FRB-like prompt radio emission after SGRBs. For long gamma-ray bursts, we constrain the radio flux to be under a few kJy from ∼6 hr pre-high-energy burst to ∼12 hr post-high-energy burst.

Spatially Resolved Event-Driven 24 × 24 Pixels SPAD Imager With 100% Duty Cycle for Low Optical Power Quantum Entanglement Detection

Quantum microscopy requires efficient detectors able to identify temporal correlations among photons. Photon coincidences are usually detected by postprocessing their timestamps measured by means of time-to-digital converters (TDCs), through a time and power-consuming procedure, which impairs the overall system performance. In this article, we propose an innovative single-photon sensitive imager based on single-photon avalanche diodes (SPADs), able to signal coincident photon pairs along with their position through a TDC-free, event-driven architecture. The result is a highly efficient detector (25.8%) with a 100% duty cycle and minimized data throughput. The modular architecture and the 330 ns readout time, independent of pixel number, pave the way to large format imagers based on the same paradigm. The detector enabled quantum imaging at extremely low, microwatt-level optical pump powers, four orders of magnitude lower than previous experiments with similar optical setups.

Photon pair generation in lithium niobate waveguide periodically poled by femtosecond laser

Reliable generation of single photons is of key importance for fundamental physical experiments and quantum protocols. The periodically poled lithium niobate (LN) waveguide has shown promise for an integrated quantum source due to its large spectral tunability and high efficiency, benefiting from the quasi-phase-matching. Here we demonstrate photon-pair sources based on an LN waveguide periodically poled by a tightly focused femtosecond laser beam. The pair coincidence rate reaches ∼8000 counts per second for average pump power of 3.2 mW (peak power is 2.9 kW). Our results prove the possibility of application of the nonlinear photonics structure fabricated by femtosecond laser to the integrated quantum source. This method can be extended to three-dimensional domain structures, which provide a potential platform for steering the spatial degree of freedom of the entangled two-photon states.

Tomographic detection of photon pairs produced from high-energy X-rays for the monitoring of radiotherapy dosing

Measuring the radiation dose reaching a patient’s body is difficult. Here we report a technique for the tomographic reconstruction of the location of photon pairs originating from the annihilation of positron–electron pairs produced by high-energy X-rays travelling through tissue. We used Monte Carlo simulations on pre-recorded data from tissue-mimicking phantoms and from a patient with a brain tumour to show the feasibility of this imaging modality, which we named ‘pair-production tomography’, for the monitoring of radiotherapy dosing. We simulated three image-reconstruction methods, one applicable to a pencil X-ray beam scanning through a region of interest, and two applicable to the excitation of tissue volumes via broad beams (with temporal resolution sufficient to identify coincident photon pairs via filtered back projection, or with higher temporal resolution sufficient for the estimation of a photon’s time-of-flight). In addition to the monitoring of radiotherapy dosing, we show that image contrast resulting from pair-production tomography is highly proportional to the material’s atomic number. The technique may thus also allow for element mapping and for soft-tissue differentiation.

Landsat 9 Geometric Characteristics Using Underfly Data

The Landsat program has a long history of providing remotely sensed data to the user community. This history is being extended with the addition of the Landsat 9 satellite, which closely mimics the Landsat 8 satellite and its instruments. These satellites contain two instruments, the Operational Land Imager (OLI) and the Thermal Infrared Sensor (TIRS). OLI is a push-broom sensor that collects visible and near-infrared (VNIR) and short-wave infrared (SWIR) wavelengths at 30 m ground sample distance, along with a panchromatic 15 m band. The TIRS sensor contains two long-wave thermal spectral channels centered at 10.9 and 12 µm. The data from these two instruments, on both satellites, are combined into a single Landsat product. The Landsat 5–9 satellites follow a 16 day repeat cycle designated as the Worldwide Reference System (WRS-2), which provides a global notional gridded mapping for identifying individual Landsat scenes. The Landsat 8 and 9 satellites are flown such that their orbital tracks are separated by 8 days in this 16 day cycle. During the commissioning period of Landsat 9, and during its ascent to its operational WRS-2 orbit, the Landsat 9 satellite’s orbital track went under and crossed over the orbital track of the Landsat 8 satellite. This produced a unique situation where nearly time-coincident imagery could be obtained from the instruments of the two spacecrafts. From a radiometric standpoint, this allowed for near-time cross-calibration between the instruments to be performed. From a geometry perspective, calibration is achieved through high-resolution reference imagery over specific ground locations, thus ensuring calibration of the instruments and for the instruments to be well cross-calibrated geometrically. Although these underfly data do not provide calibration of the instruments between the platforms from a geometric perspective, they allow for the verification of the calibration steps involving the instruments and spacecraft. This paper discusses the co-registration of this unique set of data while also discussing other geometric aspects of these data by looking at and comparing the differences in sensor viewing and sun angles associated with the collections from the two platforms for imagery obtained over common geographic locations. The image-to-image comparisons between Landsat 8 and 9 coincident pairs, where both datasets are precision terrain products, are registered to within 2.2 m with respect to their root-mean-squared radial error (RMSEr). The 2.2 m represents less than 0.1 of a 30 m multispectral pixel in misregistration between the L9 and L8 underfly products that will be available to the user community. This unique dataset will provide well-registered, near-coincident image acquisitions between the two platforms that can be a key to any calibration or application comparisons. The paper also presents that, for images for which one of the image pairs failed precision corrections and became a terrain-corrected only product type, a range of 8–14 m RMSEr could be expected in co-registration, while, in cases where both image pairs failed the precision correction step and both images became a terrain-corrected only product type, a 14 m RMSEr could be expected for co-registration.

GPU-Based Real-Time Software Coincidence Processing for Digital PET System

In some modern digital positron emission tomography (PET) systems, the coincidence pairs are extracted by software coincidence processing (SCP) for reconstruction. The SCP is typically implemented on central processing units (CPUs) and then it is accelerated by CPU multithreading technology. However, the more detection modules a PET system has, the more CPU threads are used in acquisition and the fewer threads are available in coincidence processing when the number of threads is fixed. This phenomenon results in reduced processing performance of CPU-based SCP, which limits the application of SCP. In this article, we propose low-cost GPU-based real-time SCP (GPU-SCP) methods to solve the limited CPU thread problem. The proposed processing architecture simplifies the management of threads between acquisition and coincidence processing, leading to the decouple of acquisition and coincidence, accelerates the coincidence processing by GPU multiple threads, and finally realizes the online coincidence processing in high-sensitivity digital PET systems with 20 basic detection modules (BDMs). To evaluate the performance of the proposed GPU-based SCP approaches, we adapted them to the home-made PET systems with different architectures. The speedup experimental results show that the proposed sorting-based GPU-SCP achieves up to ~15 times average speedup on GTX1070 compared with serial CPU algorithms, which is comparable to the parallel CPU algorithm with 30 threads. Besides, the proposed combination-based GPU-SCP is superior to the sorting-based GPU-SCP for a specific system architecture. Besides, the image quality experiments indicate the reconstruction images processed by GPU-SCPs are almost the same as the ground truth (differences ~1% in the image domain).

Accessory Genome Dynamics of Local and Global Staphylococcus pseudintermedius Populations.

Staphylococcus pseudintermedius is a major bacterial colonizer and opportunistic pathogen in dogs. Methicillin-resistant S. pseudintermedius (MRSP) continues to emerge as a significant challenge to maintaining canine health. We sought to determine the phylogenetic relationships of S. pseudintermedius across five states in the New England region of the United States and place them in a global context. The New England dataset consisted of 125 previously published S. pseudintermedius genomes supplemented with 45 newly sequenced isolates. The core genome phylogenetic tree revealed many deep branching lineages consisting of 142 multi-locus sequence types (STs). In silico detection of the mecA gene revealed 40 MRSP and 130 methicillin-susceptible S. pseudintermedius (MSSP) isolates. MRSP were derived from five structural types of SCCmec, the mobile genetic element that carries the mecA gene conferring methicillin resistance. Although many genomes were MSSP, they nevertheless harbored genes conferring resistance to many other antibiotic classes, including aminoglycosides, macrolides, tetracyclines and penams. We compared the New England genomes to 297 previously published genomes sampled from five other states in the United States and 13 other countries. Despite the prevalence of the clonally expanding ST71 found worldwide and in other parts of the United States, we did not detect it in New England. We next sought to interrogate the combined New England and global datasets for the presence of coincident gene pairs linked to antibiotic resistance. Analysis revealed a large co-circulating accessory gene cluster, which included mecA as well as eight other resistance genes [aac (6′)-Ie-aph (2″)-Ia, aad (6), aph (3′)-IIIa, sat4, ermB, cat, blaZ, and tetM]. Furthermore, MRSP isolates carried significantly more accessory genes than their MSSP counterparts. Our results provide important insights to the evolution and geographic spread of high-risk clones that can threaten the health of our canine companions.

Study of optical reflectors for a 100ps coincidence time resolution TOF-PET detector design

Positron Emission Tomography (PET) reconstructed image signal-to-noise ratio (SNR) can be improved by including the 511 keV photon pair coincidence time-of-flight (TOF) information. The degree of SNR improvement from this TOF capability depends on the coincidence time resolution (CTR) of the PET system, which is essentially the variation in photon arrival time differences over all coincident photon pairs detected for a point positron source placed at the system center. The CTR is determined by several factors including the intrinsic properties of the scintillation crystals and photodetectors, crystal-to-photodetector coupling configurations, reflective materials, and the electronic readout configuration scheme. The goal of the present work is to build a novel TOF-PET system with 100 picoseconds (ps) CTR, which provides an additional factor of 1.5–2.0 improvement in reconstructed image SNR compared to state-of-the-art TOF-PET systems which achieve 225–400 ps CTR. A critical parameter to understand is the optical reflector’s influence on scintillation light collection and transit time variations to the photodetector. To study the effects of the reflector covering the scintillation crystal element on CTR, we have tested the performance of four different reflector materials: Enhanced Specular Reflector (ESR) –coupled with air or optical grease to the scintillator; Teflon tape; BaSO4 paint alone or mixed with epoxy; and TiO2 paint. For the experimental set-up, we made use of 3 × 3 × 10 mm3 fast-LGSO:Ce scintillation crystal elements coupled to an array of silicon photomultipliers (SiPMs) using a novel ‘side-readout’ configuration that has proven to have lower variations in scintillation light collection efficiency and transit time to the photodetector. Results: show CTR values of 102.0 ± 0.8, 100.2 ± 1.2, 97.3 ± 1.8 and 95.0 ± 1.0 ps full-width-half-maximum (FWHM) with non-calibrated energy resolutions of 10.2 ± 1.8, 9.9 ± 1.2, 7.9 ± 1.2, and 8.6 ± 1.7% FWHM for the Teflon, ESR (without grease), BaSO4 (without epoxy) and TiO2 paint treatments, respectively.

Self-adaptive macroslip array for friction force prediction in contact interfaces with non-conforming meshes

The steady-state nonlinear forced response (NFR) of finite element (FE) models with friction joints is usually computed in the frequency domain through the combination of node-to-node contact elements and the Harmonic Balance Method (HBM). In the current state of the art, rare are the cases where the friction forces are estimated for contact interfaces with non-conforming mesh grids. This need is nowadays taking place due to the improving capability of commercial FE software to manage any kind of boundary condition (i.e., either coupling or contact), without requiring coincident pairs of nodes at the joint interfaces. Such an advantage becomes a drawback when the analysts are requested to investigate the NFR of the assembly by using build-in codes, where the contact forces prediction usually requires node-to-node contact elements whose parameters (i.e., the contact stiffnesses and friction coefficients) can be easily identified by means of experiments. This paper addresses the mentioned limitation, and proposes a novel self-adaptive macroslip array (SAMA) model for the estimation of the nonlinear friction forces on FE contact interfaces with non-conforming meshes. The SAMA model consists on a set of node-to-node contact elements ordered in parallel, whose contact parameters and normal preloads are identified through a step-by-step self-adaptive weighting algorithm that depends on the topology of the meshes in contact. The goodness of the proposed model is assessed on the calculation of the NFR of a bladed disk with shroud contacts, under the hypotheses of cyclic symmetry and HBM. The nonlinear dynamic behavior of the bladed disk is evaluated in two different cases. First, in the case of lack of node-to-node congruence at the contact interface for the structure being in its undeformed configuration, and second, in the case of a relevant static misalignment of the contact interfaces due to the application of large static loads.

Extended Pseudo Invariant Calibration Site-Based Trend-to-Trend Cross-Calibration of Optical Satellite Sensors

Satellite sensors have been extremely useful and are in massive demand in the understanding of the Earth’s surface and monitoring of changes. For quantitative analysis and acquiring consistent measurements, absolute radiometric calibration is necessary. The most common vicarious approach of radiometric calibration is cross-calibration, which helps to tie all the sensors to a common radiometric scale for consistent measurement. One of the traditional methods of cross-calibration is performed using temporally and spectrally stable pseudo-invariant calibration sites (PICS). This technique is limited by adequate cloud-free acquisitions for cross-calibration which would require a longer time to study the differences in sensor measurements. To address the limitation of traditional PICS-based approaches and to increase the cross-calibration opportunity for quickly achieving high-quality results, the approach presented here is based on using extended pseudo invariant calibration sites (EPICS) over North Africa. With the EPICS-based approach, the area of extent of the cross-calibration site covers a large portion of the North African continent. With targets this large, many sensors should image some portion of EPICS nearlydaily, allowing for evaluation of performance with much greater frequency. By using these near-daily measurements, trends of the sensor’s performance are then used to evaluate sensor-to-sensor daily cross-calibration. With the use of the proposed methodology, the dataset for cross-calibration is increased by an order of magnitude compared to traditional approaches, resulting in the differences between any two sensors being detected within a much shorter time. Using this new trend in trend cross-calibration approaches, gains were evaluated for Landsat 7/8 and Sentinel 2A/B, with the results showing that the sensors are calibrated within 2.5% (within less than 8% uncertainty) or better for all sensor pairs, which is consistent with what the traditional PICS-based approach detects. The proposed cross-calibration technique is useful to cross-calibrate any two sensors without the requirement of any coincident or near-coincident scene pairs, while still achieving results similar to traditional approaches in a short time.

Комплексирование измерителей при некратности частот следования показаний и выходных оценок

The problem of measurement fusion from two sensors with no coincident pairs of measurement at any time is considered. Besides, the required moments of returning the result also lie between indication times. Several association algorithms based on Kalman filtering both with use of the centralized filter, and on the basis of two parallel local filters as a part of decentralized filtration approach are proposed. Filter parameter adjustment to operation at non-equidistant times is described. The options for combining the assessments of the process state inside the filtration loop and outside it are considered. Comparison of methods is carried out in terms of the relative mean square error value of result estimate. The case of uniformly precise measurements and a case when the noise level into indications of sensors considerably differs are separately analyzed. The operability of methods is investigated at various values of bandwidth determined by a ratio of process noise intensity and the measurement noise one.

Fourier domain quantum optical coherence tomography.

Quantum optical coherence tomography (Q-OCT) is the non-classical counterpart of optical coherence tomography (OCT), a high-resolution 3D imaging technique based on white-light interferometry. Because Q-OCT uses a source of frequency-entangled photon pairs, not only is the axial resolution not affected by dispersion mismatch in the interferometer but is also inherently improved by a factor of two. Unfortunately, practical applications of Q-OCT are hindered by image-scrambling artefacts and slow acquisition times. Here, we present a theoretical analysis of a novel approach that is free of these problems: Fourier domain Q-OCT (Fd-Q-OCT). Based on a photon pair coincidence detection as in the standard Q-OCT configuration, it also discerns each photon pair by their wavelength. We show that all the information about the internal structures of the object is encoded in the joint spectrum and can be easily retrieved through Fourier transformation. No depth scanning is required, making our technique potentially faster than standard Q-OCT. Finally, we show that the data available in the joint spectrum enables artefact removal and discuss prospective algorithms for doing so.

Behavioural and functional changes in neglect after multisensory stimulation

ABSTRACT The present cohort study investigated whether systematic multisensory audio-visual stimulation might improve clinical signs of neglect. To this aim, patients with neglect (n = 7) and patients with neglect associated with hemianopia (n = 12) were exposed to a course of audio-visual stimulation with spatially and temporally coincident audio-visual pairs of stimuli for 10 daily training sessions (4 h of training per day), over two weeks. Performance on neuropsychological tests assessing neglect was measured before training, immediately after the training and months after the training at a follow-up session. The results showed significant post-training improvements in clinical signs of neglect, which were stable at the follow-up. These findings suggest that intensive and prolonged multisensory audio-visual stimulation affects orientation towards the neglected hemifield, therefore inducing long-term improvements in visual exploration and neglect symptoms in both patients with neglect and patients with neglect associated with hemianopia. Previous evidence from hemianopic patients suggests that these post-training effects might be mediated by activity in spared subcortical structures, such as the superior colliculus, which are relevant to multisensory integrative processing and spatial orientation.

KINSHIP IN POETIC DISCOURSE (ON THE MATERIAL OF MYKOLAIV AUTHORS’ WORKS)

The article is devoted to the functional-semantic analysis of the group of terms of in poetic discourse. A broad approach to understanding the terms of as an open, formally and functionally open lexical-semantic system has been presented. The purpose of the article is to determine the system of family relations in the poetic discourse on the material of the modern Mykolaiv author A. Surov’s works. Achieving this goal necessitates the solution of a number of tasks: 1) to objectify lexical means of expressing in poetic discourse; 2) to make a semantic interpretation of the terms of in A. Surov’s poetic speech; 3) to identify syntagmatic and paradigmatic connections of words that explain the in the texts; 4) to analyse the ways of poetic images formation with the help of terms of kinship. The object of the research is fragments of poetic discourse that contain explicators of kinship; the subject of the research is the semantic features of the terms of in A. Surov’s poetic speech. All published works of the author, having about three hundred uses of words containing kinship seme, have been analysed. The study of words with the semantics of is carried out according to the method of complex semantic description, which involves the use of systematic contextual analysis, which takes into account the syntagmatic and paradigmatic relationships of words in the text. Descriptive and statistical methods have also been used during the material collection and processing. The discourse analysis showed that the terms of blood are used in A. Surov’s poetic speech much more often than the terms of formed as a result of marriage. The author uses mainly the terms of blood relationship in neighbouring generations (father – mother, son – daughter), in one generation (brother – sister) and across generations (grandmother – grandfather, grandchildren) and the terms of formed as a result of marriage (husband – wife, groom – bride). The coincidence of convertible pairs in one poetic text is natural for A. Surov's poetic language. Terms of acquire connotative semes due to the combination with words expressing evaluation, when using forms with reduced-loving suffixes synochek (sonny), dochka, dochenka (daughter), dedushka (grandfather), babulia (granny) and spatial forms of mam (mom), mamka (mummy), batka (dad), bratan (brother), bratukha ( brother). The leading ways of figurative meaning formation are the use of terms of in comparisons (And the wind smelled like a bride's skirt), set expressions (I am a northern snow lost son) and in addresses (All your emerald deposits, father of the Urals!). Peculiar is the use of terms of as a conversion pair, which do not have a correlation in the language system (grandmother – children, mother – grandfather, etc.): And my grandmother in the Warsaw ghetto / Under a black skirt hid children. The system of family relations is the most significant fragment of A. Surov's poetic picture of the world. With these terms, the poet builds a single and holistic picture of the world, in the centre of which there is a person connected with the surrounding reality primarily by blood. The analysis of this group of terms of in A. Surov’s poetry has shown the productivity of this approach and opens up prospects for the poetic discourse study

Simulation of Human Limb Movement

Simulation of any processes is based on some laws that take place inside the simulated object and outside it (changing the environment in which the object is located). In the study of complex biosystems, the identification of patterns is complicated by the fact that such systems have a chaotic structure. In such systems, it is impossible to arbitrarily repeat the initial state xi, any intermediate xn and final xk. Simulation of complex biosystems should be based on random patterns. The created simulation model works based on the random number generation. There are no static values in the model. The inclusion of regulatory mechanisms of the model is based on the search of F-solutions. Chaotic dynamics of changes in the trajectory of a person's limb is established based on experimental data. In accordance with this, in the simulation model, the level of limb retention in space changes its direction by random images in real time. In the framework of the above patterns, a mathematical model of the interaction of muscle bundles was developed to solve the problem of holding the limb in space. When analyzing the performance of the simulation model, the basis of the evaluation measure was taken. The results were obtained on the basis of mathematical statistics and the calculation of the quasiattractor parameters in the framework of the theory of chaos and self-organization. As a result, the correspondence of experimental and model data was established. In the framework of mathematical statistics, when constructing matrices of paired comparisons for experimental data, the number of pairs of matches (the word "matches" refers to the possibility of assigning the compared pairs of samples to one general set) is k = 11 %. The same number of coincidence pairs in percentage terms was established when comparing model data and model with experimental data. In the framework of the theory of chaos and self-organization, the quasiattractor parameters coincide in their area and visual assessment of phase planes. As a result of the research, high accuracy of the model is established, which is ensured by some chaotic dynamics of the model with chaotic selfregulation mechanisms. There are no constants in the mathematical form of the simulation model, which ensures the reproduction of N.A. Bernstein "repetition without repetition" hypothesis, which has been proven for experimental data. For theoretical biophysics, the constructed simulation model is able to provide understanding of the neuromuscular system functioning, as well as, with some complication and expansion of the algorithm, the central nervous system.

Coinfinder: detecting significant associations and dissociations in pangenomes.

The accessory genes of prokaryote and eukaryote pangenomes accumulate by horizontal gene transfer, differential gene loss, and the effects of selection and drift. We have developed Coinfinder, a software program that assesses whether sets of homologous genes (gene families) in pangenomes associate or dissociate with each other (i.e. are ‘coincident’) more often than would be expected by chance. Coinfinder employs a user-supplied phylogenetic tree in order to assess the lineage-dependence (i.e. the phylogenetic distribution) of each accessory gene, allowing Coinfinder to focus on coincident gene pairs whose joint presence is not simply because they happened to appear in the same clade, but rather that they tend to appear together more often than expected across the phylogeny. Coinfinder is implemented in C++, Python3 and R and is freely available under the GNU license from https://github.com/fwhelan/coinfinder.

Bell-type polarization experiment with pairs of uncorrelated optical photons

We present a Bell-type polarization experiment using two independent sources of polarized optical photons, and detecting the temporal coincidence of pairs of uncorrelated photons which have never been entangled in the apparatus. Very simply, our measurements have tested the quantum-mechanical equivalent of the classical Malus' law on an incoherent beam of polarized photons obtained from two separate and independent laser sources greatly reduced in intensities. The outcome of the experiment gives evidence of violation of the Bell-like inequalities. Drawing the conclusions of the present work, we invoke the distinction between the concepts of state-preparation and measurement to understand this result.

Derivation of Hyperspectral Profile of Extended Pseudo Invariant Calibration Sites (EPICS) for Use in Sensor Calibration

Reference of Earth-observing satellite sensor data to a common, consistent radiometric scale is an increasingly critical issue as more of these sensors are launched; such consistency can be achieved through radiometric cross-calibration of the sensors. A common cross-calibration approach uses a small set of regions of interest (ROIs) in established Pseudo-Invariant Calibration Sites (PICS) mainly located throughout North Africa. The number of available cloud-free coincident scene pairs available for these regions limits the usefulness of this approach; furthermore, the temporal stability of most regions throughout North Africa is not known, and limited hyperspectral information exists for these regions. As a result, it takes more time to construct an appropriate cross-calibration dataset. In a previous work, Shrestha et al. presented an analysis identifying 19 distinct “clusters” of spectrally similar surface cover that are widely distributed across North Africa, with the potential to provide near-daily cloud-free imaging for most sensors. This paper proposes a technique to generate a representative hyperspectral profile for these clusters. The technique was used to generate the profile for the cluster containing the largest number of aggregated pixels. The resulting profile was found to have temporal uncertainties within 5% across all the spectral regions. Overall, this technique shows great potential for generation of representative hyperspectral profiles for any North African cluster, which could allow the use of the entire North Africa Saharan region as an extended PICS (EPICS) dataset for sensor cross-calibration. This should result in the increased temporal resolution of cross-calibration datasets and should help to achieve a cross-calibration quality similar to that of individual PICS in a significantly shorter time interval. It also facilitates the development of an EPICS based absolute calibration model, which can improve the accuracy and consistency in simulating any sensor’s top of atmosphere (TOA) reflectance.

The Inter-Calibration of the DSCOVR EPIC Imager with Aqua-MODIS and NPP-VIIRS

The Deep Space Climate Observatory (DSCOVR) through the earth polychromatic imaging camera (EPIC) continuously observes the illuminated disk from the Lagrange-1 point. The EPIC sensor was designed to monitor the diurnal variation of ozone, clouds, aerosols, and vegetation, especially those features that benefit from observation near-backscatter conditions. The EPIC sensor does not contain any onboard calibration systems. This study describes the inter-calibration of EPIC channels 5 (0.44 µm), 6 (0.55 µm), 7 (0.68 µm), and 10 (0.78 µm) with respect to Aqua-MODIS and NPP-VIIRS. The calibration is transferred using coincident ray-matched reflectance pairs over all-sky tropical ocean (ATO) and deep convective cloud (DCC) targets. A robust and automated image-alignment technique based on feature matching was formulated to improve the navigation quality of the EPIC images. The EPIC V02 dataset exhibits improved navigation over V01. As the visible channels display similar spatial features, a single visible channel can be used to co-register the remaining visible bands. The VIIRS-referenced EPIC ATO and DCC ray-matched calibration coefficients are within 0.3%. The EPIC four-year calibration trends based on VIIRS are within 0.15%/year. The MODIS-based EPIC calibration coefficients were compared against the Geogdzhayev and Marshak 2018 published calibration coefficients and were found to be within 1.6%.