Covariant Approach Research Articles

Crowd events recognition in a video without threshold value setting

Behavioural recognition and prediction of people's activities since video present major concerns in the field of computer vision. The main objective of the proposed work is the introduction of a new algorithm which allows analysing objects in motion from the video to extract human behaviours in a complex environment. This analysis is carried out for the indoor or the outdoor environments filmed by simple means of detection (surveillance camera). The analysed scene presents in a group of people, one distinguishes the crowd scenes for an important number of people. In this type of scene, we are interested in the problems of crowd event detection by an automatic technique without setting the threshold value by neural networks to detect several anomalies in a crowd scene. To achieve these objectives, we propose a calculation of covariance and automatic artificial neural networks-based approach in order to detect several anomalies. Experiment validation has been done based on known data, where in a satisfactory results has been obtained comparing to some previous works mentioned in the state-of-the-art.

Electromagnetic transition form factors of baryons in a relativistic Faddeev approach

The covariant Faddeev approach which describes baryons as relativistic three-quark bound states and is based on the Dyson-Schwinger and Bethe-Salpeter equations of QCD is briefly reviewed. All elements, including especially the baryons’ three-body-wave-functions, the quark propagators and the dressed quark-photon vertex, are calculated from a well-established approximation for the quark-gluon interaction. Selected previous results of this approach for the spectrum and elastic electromagnetic form factors of ground-state baryons and resonances are reported. The main focus of this talk is a presentation and discussion of results from a recent investigation of the electromagnetic transition form factors between ground-state octet and decuplet baryons as well as the octet-only Σ0 to Λ transition.

Crowd events recognition in a video without threshold value setting

Behavioural recognition and prediction of people's activities since video present major concerns in the field of computer vision. The main objective of the proposed work is the introduction of a new algorithm which allows analysing objects in motion from the video to extract human behaviours in a complex environment. This analysis is carried out for the indoor or the outdoor environments filmed by simple means of detection (surveillance camera). The analysed scene presents in a group of people, one distinguishes the crowd scenes for an important number of people. In this type of scene, we are interested in the problems of crowd event detection by an automatic technique without setting the threshold value by neural networks to detect several anomalies in a crowd scene. To achieve these objectives, we propose a calculation of covariance and automatic artificial neural networks-based approach in order to detect several anomalies. Experiment validation has been done based on known data, where in a satisfactory results has been obtained comparing to some previous works mentioned in the state-of-the-art.

Mass Spectrum of Mesons and Their Leptonic Decay Widths within the Relativistic Quasipotential Approach

New relativistic semiclassical conditions and leptonic decay widths are obtained within quantum chromodynamics for nonsingular confining quasipotentials and funnel-type potentials (instantoninteraction approximation). The respective analysis is performed within a fully covariant quasipotential approach in quantum field theory. This approach is formulated in the relativistic configuration representation for the case of interaction between two relativistic spinless particles of arbitrary mass.

Carbon balance assessment by eddy covariance method for agroecosystems with potato plants and oats & vetch mixture on sod-podzolic soils of Russia

The carbon balance for the agroecosystems with potato plants and oats & vetch mixture on sod-podzolics soils was evaluated using the eddy covariance approach. Absorption of carbon was recorded only during the growing season; maximum values were detected for all crops in July. The number of days during the vegetation period, when the carbon stocked in the fields with potatoes and oats & vetch mixture was about the same and accounted for 53-55 days. During this period, the increase in gross primary production (GPP) is well correlated with the crop yields. The curve of the gross primary productivity is closely linked to the phases of development of plants; for potatoes, this graph differs significantly for all phases. Form of oats & vetch mixture biomass curve shown linear increases. Carbon losses were observed for all the studied agroecosystems: for fields with an oats & vetch mixture they were 254 g C m-2 y-1, while for fields with potato plants they were 307 g C m-2 y-1. Values about 250-300 g C m-2 per year may be considered as estimated values for the total carbon uptake for agroecosystems with potato plants and oats & vetch mixture on sod-podzolic soils.

Study of J/ψ and ψ(3686) decays to π+π−η′

Using the data samples of 1.31×109 J/ψ events and 4.48×108 ψ(3686) events collected with the BESIII detector, partial wave analyses on the decays J/ψ and ψ(3686)→π+π−η′ are performed with a relativistic covariant tensor amplitude approach. The dominant contribution is found to be J/ψ and ψ(3686) decays to ρη′. In the J/ψ decay, the branching fraction B(J/ψ→ρη′) is determined to be (7.90±0.19(stat)±0.49(sys))×10−5. Two solutions are found in the ψ(3686) decay, and the corresponding branching fraction B(ψ(3686)→ρη′) is (1.02±0.11(stat)±0.24(sys))×10−5 for the case of destructive interference, and (5.69±1.28(stat)±2.36(sys))×10−6 for constructive interference. As a consequence, the ratios of branching fractions between ψ(3686) and J/ψ decays to ρη′ are calculated to be (12.9±1.4(stat)±3.1(sys))% and (7.2±1.6(stat)±3.0(sys))%, respectively. We also determine the inclusive branching fractions of J/ψ and ψ(3686) decays to π+π−η′ to be (1.36±0.02(stat)±0.08(sys))×10−4 and (1.51±0.14(stat)±0.23(sys))×10−5, respectively.Received 3 September 2017DOI:https://doi.org/10.1103/PhysRevD.96.112012© 2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasParticle decaysParticles & Fields

Effective metrics and a fully covariant description of constitutive tensors in electrodynamics

Using electromagnetism to study analogue space-times is tantamount to considering consistency conditions for when a given (meta-)material would provide an analogue space-time model or --- vice versa --- characterizing which given metric could be modelled with a (meta-)material. While the consistency conditions themselves are by now well known and studied, the form the metric takes once they are satisfied is not. This question is mostly easily answered by keeping the formalisms of the two research fields here in contact as close to each other as possible. While fully covariant formulations of the electrodynamics of media have been around for a long while, they are usually abandoned for (3+1)- or 6-dimensional formalisms. Here we shall use the fully unified and fully covariant approach. This enables us even to generalize the consistency conditions for the existence of an effective metric to arbitrary background metrics beyond flat space-time electrodynamics. We also show how the familiar matrices for permittivity $\epsilon$, permeability $\mu^{-1}$, and magneto-electric effects $\zeta$ can be seen as the three independent pieces of the Bel decomposition for the constitutive tensor $Z^{abcd}$, i.e., the components of an orthogonal decomposition with respect to a given observer with four-velocity $V^a$. Finally, we shall use the Moore--Penrose pseudo-inverse and the closely related pseudo-determinant to then gain the desired reconstruction of the effective metric in terms of the permittivity tensor $\epsilon^{ab}$, the permeability tensor $[\mu^{-1}]^{ab}$, and the magneto-electric tensor $\zeta^{ab}$, as an explicit function $g_{\text{eff}}(\epsilon,\mu^{-1},\zeta)$.

On-shell gauge invariant three-point amplitudes

Assuming locality, Lorentz invariance and parity conservation we obtain a set of differential equations governing the 3-point interactions of massless bosons, which in turn determines the polynomial ring of these amplitudes. We derive all possible 3-point interactions for tensor fields with polarisations that have total symmetry and mixed symmetry under permutations of Lorentz indices. Constraints on the existence of gauge-invariant cubic vertices for totally symmetric fields are obtained in general spacetime dimensions and are compared with existing results obtained in the covariant and light-cone approaches.Expressing our results in spinor helicity formalism we reproduce the perhaps mysterious mismatch between the covariant approach and the light cone approach in 4 dimensions. Our analysis also shows that there exists a mismatch, in the 3-point gauge invariant amplitudes corresponding to cubic self-interactions, between a scalar field ϕ and an antisymmetric rank-2 tensor field Aμν . Despite the well-known fact that in 4 dimensions rank-2 anti-symmetric fields are dual to scalar fields in free theories, such duality does not extend to interacting theories.

Systematic study of octet-baryon electromagnetic form factors in covariant chiral perturbation theory

We perform a complete and systematic calculation of the octet-baryon form factors within the fully covariant approach of SU(3) chiral perturbation theory at O(p^3). We use the extended on-mass shell renormalization scheme, and include explicitly the vector mesons and the spin-3/2 decuplet intermediate states. Comparing these predictions with data including magnetic moments, charges, and magnetic radii, we determine the unknown low-energy constants, and give predictions for yet unmeasured observables, such as the magnetic moment of the Sigma^0, and the charge and magnetic radii of the hyperons.

Quantum field theoretical description of neutrino oscillations and reactor antineutrino anomaly

We suggest a possible explanation of the reactor antineutrino anomaly derived from a covariant quantum field-theoretical approach to neutrino oscillations. Some disadvantages of the currently prevailing interpretation of the anomaly, based upon the sterile neutrino hypothesis are pointed out.

Monitoring gas and heat emissions at Norris Geyser Basin, Yellowstone National Park, USA based on a combined eddy covariance and Multi-GAS approach

We quantified gas and heat emissions in an acid-sulfate, vapor-dominated area (0.04-km2) of Norris Geyser Basin, located just north of the 0.63Ma Yellowstone Caldera and near an area of anomalous uplift. From 14 May to 3 October 2016, an eddy covariance system measured half-hourly CO2, H2O and sensible (H) and latent (LE) heat fluxes and a Multi-GAS instrument measured (1Hz frequency) atmospheric H2O, CO2 and H2S volumetric mixing ratios. We also measured soil CO2 fluxes using the accumulation chamber method and temperature profiles on a grid and collected fumarole gas samples for geochemical analysis. Eddy covariance CO2 fluxes ranged from −56 to 885gm−2d−1. Using wavelet analysis, average daily eddy covariance CO2 fluxes were locally correlated with average daily environmental parameters on several-day to monthly time scales. Estimates of CO2 emission rate from the study area ranged from 8.6td−1 based on eddy covariance measurements to 9.8td−1 based on accumulation chamber measurements. Eddy covariance water vapor fluxes ranged from 1178 to 24,600gm−2d−1. Nighttime H and LE were considered representative of hydrothermal heat fluxes and ranged from 4 to 183 and 38 to 504Wm−2, respectively. The total hydrothermal heat emission rate (H+LE+radiant) estimated for the study area was 11.6MW and LE contributed 69% of the output. The mean±standard deviation of H2O, CO2 and H2S mixing ratios measured by the Multi-GAS system were 9.3±3.1 parts per thousand, 467±61ppmv, and 0.5±0.6ppmv, respectively, and variations in the gas compositions were strongly correlated with diurnal variations in environmental parameters (wind speed and direction, atmospheric temperature). After removing ambient H2O and CO2, the observed variations in the Multi-GAS data could be explained by the mixing of relatively H2O-CO2-H2S-rich fumarole gases with CO2-rich and H2O-H2S-poor soil gases. The fumarole H2O/CO2 and CO2/H2S end member ratios (101.7 and 27.1, respectively, on average) were invariant during the measurement period and fell within the range of values measured in direct fumarole gas samples. The soil gas H2O/CO2 end member ratios (~15–30) were variable and low relative to the fumarole end member, likely resulting from water vapor loss during cooling and condensation in the shallow subsurface, whereas the CO2/H2S end member ratio was high (~160), presumably related to transport of CO2-dominated soil gas emissions mixed with trace fumarolic emissions to the Multi-GAS station. Nighttime eddy covariance ratios of H2O to CO2 flux were typically between the soil gas and fumarole end member H2O/CO2 ratios defined by Multi-GAS measurements. Overall, the combined eddy covariance and Multi-GAS approach provides a powerful tool for quasi-continuous measurements of gas and heat emissions for improved volcano-hydrothermal monitoring.

Carbon Dioxide Fluxes and Their Environmental Controls in a Riparian Forest within the Hyper-Arid Region of Northwest China

Hyper-arid regions are expected to undergo climatic change, but only a few research works have so far been conducted on the dynamics of carbon dioxide (CO2) fluxes and their consequent responses to various bioclimatic factors, which is mainly attributable to a limited set of flux observations. In this study, the CO2 fluxes exchanged between the forest and the atmosphere have been measured continuously by the eddy covariance approach from June 2013 to December 2016 in a riparian forest, which is a primary body of natural oases located within the lower reaches of inland rivers in China. The present results revealed that the climatic conditions characterized by relatively high mean air temperatures (Ta) with fluctuating annual precipitation (P) during the prescribed study periods were comparable to the historical mean value. The annual net ecosystem productivity (NEP) ranged from approximately 278 g C m−2 year−1 to 427 g C m−2 year−1, with a mean value of 334 g C m−2 year−1. The mean annual ecosystem respiration (Re) and the gross primary productivity (GPP) were found to be 558 and 892 g C m−2 year−1, respectively. The results also ascertained that the high inter-annual variations in NEP were attributable to Re rather than to GPP, and this result was driven primarily by Ta and the groundwater depth under similar eco-physiological processes. In addition, the CO2 fluxes were also strongly correlated with the soil temperature and photosynthetically active radiation for the present study site. In conclusion, the desert riparian forest is a considerably significant carbon sink, particularly in the hyper-arid regions.

Evaporation and CO2 fluxes in a coastal reef: an eddy covariance approach

ABSTRACTIntroduction: We conducted season-long observations of evaporation and carbon flux at the Gulf of Aqaba coast, northern Red Sea. We used the eddy-covariance method with a two-tower setup to measure evaporation rates over land and sea and the advection between them. Using a three-dimensional mass balance approach, we calculated total evaporation as the sum of two main components in our site: horizontal advection and turbulent vertical flux, with half-hourly change of water vapor storage and horizontal flux divergence found to be negligible.Outcomes: Average evaporation rates were 11.4 [mm/day] from April through May (early summer) and 10.5 [mm/day] from June through August (summer). The coastal reef was a CO2 sink over the period of measurements, significantly higher in June through August than in April through May. The main environmental drivers of CO2 flux were humidity, water temperature, sensible heat flux, and wind speed.Discussion: The rates of evaporation near the shore were considerably higher than values reported in other studies typically used to represent the mean for the whole Gulf area. We found that evaporation rates computed by common bulk models approximate the mean values of evaporation but have poor representativeness of the intra-daily temporal variation of evaporation. There was a significant correlation between CO2 flux and evaporation attributed to common environmental drivers of gas diffusion, turbulent fluxes, and horizontal transport.Conclusion: We conclude that observations of fluxes in coastal waters need to use at least a two-tower system to account for the effect of horizontal advection on the total flux.

Covariant variational approach to Yang-Mills theory: Thermodynamics

The thermodynamics of $SU(2)$ Yang-Mills theory in the covariant variational approach is studied by relating the free action density in the background of a non-trivial Polyakov loop to the pressure of the gluon plasma. The correct subtraction of the vacuum contribution in the free action density is argued for. The Poisson resummed expression for the pressure can be evaluated analytically in limiting cases, and shows the correct Stefan-Boltzmann limit at $T \to \infty$, while the limit $T \to 0$ is afflicted by artifacts due to massless modes in the confined phase. Several remedies to remove these artifacts are discussed. Using the numerical $T=0$ solutions for the ghost and gluon propagators in the covariant variational approach as input, the pressure, energy density and interaction strength are calculated and compared to lattice data.

A Time‐varying Covariate Approach for Survival Analysis of Paediatric Outcomes

Conventional survival analysis is commonly applied in the analysis of time-to-event data in paediatric studies, where the exposure variables of interest are often treated as time-fixed. However, the values of these exposure variables can vary over time and time-fixed analysis may introduce time-dependent bias. Time-dependent bias is illustrated graphically considering two scenarios in longitudinal study settings for paediatric time-to-event outcomes. As an illustrative example, the time-varying covariate approach was applied to survival analysis of breast-feeding data (n = 695) collected in China between 2010 and 2011, with an emphasis on the effects of covariates 'solid foods introduction' and 'maternal return to work' on breast-feeding duration up to 12 months postpartum. Time-varying exposures could occur before or after the occurrence of an event of interest so that time-fixed analysis can lead to biased and imprecise parameter estimates. In the illustrative example, the reduced risk of 'solid foods introduction' (hazard ratio (HR) 0.61, 95% confidence interval (CI) 0.50, 0.75) on breast-feeding cessation and an absence of an association with 'maternal return to work' (HR 0.99, 95% CI 0.73, 1.36) from the time-fixed analysis reversed (HR 1.50, 95% CI 1.17, 1.93) and became significant (HR 1.45, 95% CI 1.06, 2.00), respectively, based on the time-varying covariate model. The time-varying covariate approach is preferable for survival analysis of time-to-event data in the presence of time-varying exposures.

Covariant approach to parametrized cosmological perturbations

We present a covariant formulation for constructing general quadratic actions for cosmological perturbations, invariant under a given set of gauge symmetries for a given field content. This approach allows us to analyze scalar, vector, and tensor perturbations at the same time in a straightforward manner. We apply the procedure to diffeomorphism invariant single-tensor, scalar-tensor, and vector-tensor theories and show explicitly the full covariant form of the quadratic actions in such cases, in addition to the actions determining the evolution of vector and tensor perturbations. We also discuss the role of the symmetry of the background in identifying the set of cosmologically relevant free parameters describing these classes of theories, including calculating the relevant free parameters for an axisymmetric Bianchi-I vacuum universe.

Complex effects of precipitation and basal resources on the trophic ecology of soil oribatid mites: Implications for stable isotope analysis

Given the relevant role played by soil organisms in fundamental ecosystem processes, current ecological research stresses the importance of understanding the trophic structure of soil communities in order to better predict the effects that global environmental change can have on the soil food web structure and dynamics. Using stable isotope analysis, we examined the trophic ecology of six soil oribatid mite species present in the leaf litter of beech forests which mainly differed in mean annual precipitation. We explored the relationship between animal and leaf litter signatures to determine which of the two approaches, conventional calibration or a novel solution we offer using statistical control (i.e., isotopic signature of the basal resource included as a covariate in the model), is more adequate to evaluate the trophic structure of soil communities across different sites, and investigated if the trophic niches of the species varied under two different precipitation regimes. The trophic position of some species varied with rainfall; the observed enrichment in 15N in dry forests reflects trophic and spatial shifts probably resulting from changes in microbial activity and community composition. In addition, we find interactive effects between precipitation and the basal resource for some species and a lack of correlation between resource and oribatid mite stable isotope values for others. We discuss the pertinence of using conventional data calibration as it appears to mask relevant trends regarding the trophic ecology of oribatid mite species, and suggest using statistical control (a covariate approach) instead.

Dynamics of a particle on an axisymmetric surface under gravitational force: a geometric approach

In this paper the problem of a particle constrained to move on an axisymmetric surface embedded in three-dimensional Euclidean space, under the influence of a gravitational field, is addressed from a geometrical point of view. Using a covariant geometrical approach at undergraduate level, a variational framework is implemented in order to obtain the particle’s motion equation, which is solved in an analytical way for the case where the particle moves on a cylinder and numerically when the particle moves on a catenoid. The trajectories obtained are expressed as functions of conserved quantities such as total energy, E, and the z component of the particle’s angular momentum, L3. Moreover, expressions for normal and geodesic curvatures as well as the speed, tangential acceleration and normal force constraining the particle on the surface along the trajectories are obtained.

An information theoretic framework reveals a tunable allosteric network in group II chaperonins.

The ATP-dependent allosteric regulation of the ring-shaped Group II chaperonins remains ill-defined. Their complex oligomeric topology limited the success of structural techniques in suggesting allosteric determinants. Further, their high sequence conservation has hindered prediction of allosteric networks using mathematical covariation approaches, as they cannot be applied to conserved proteins. Here, we develop an information theoretic strategy robust to residue conservation and apply it to group II chaperonins. We identify a contiguous network of covarying residues that connects all nucleotide binding pockets within each chaperonin ring. An interfacial residue between the networks of neighboring subunits controls positive cooperativity by communicating nucleotide occupancy within each ring. Strikingly, chaperonin allostery is tunable through single mutations at this position. Naturally occurring variants that double the extent of positive cooperativity are less prevalent in nature. We propose that being less cooperative that attainable allows the chaperonins to support robust folding over a wider range of metabolic conditions.

Tundra is a consistent source of CO2 at a site with progressive permafrost thaw during 6 years of chamber and eddy covariance measurements

AbstractCurrent and future warming of high‐latitude ecosystems will play an important role in climate change through feedbacks to the global carbon cycle. This study compares 6 years of CO2 flux measurements in moist acidic tundra using autochambers and eddy covariance (Tower) approaches. We found that the tundra was an annual source of CO2 to the atmosphere as indicated by net ecosystem exchange using both methods with a combined mean of 105 ± 17 g CO2 C m−2 y−1 across methods and years (Tower 87 ± 17 and Autochamber 123 ± 14). The difference between methods was largest early in the observation period, with Autochambers indicated a greater CO2 source to the atmosphere. This discrepancy diminished through time, and in the final year the Autochambers measured a greater sink strength than tower. Active layer thickness was a significant driver of net ecosystem carbon exchange, gross ecosystem primary productivity, and Reco and could account for differences between Autochamber and Tower. The stronger source initially attributed lower summer season gross primary production (GPP) during the first 3 years, coupled with lower ecosystem respiration (Reco) during the first year. The combined suppression of GPP and Reco in the first year of Autochamber measurements could be the result of the experimental setup. Root damage associated with Autochamber soil collar installation may have lowered the plant community's capacity to fix C, but recovered within 3 years. While this ecosystem was a consistent CO2 sink during the summer, CO2 emissions during the nonsummer months offset summer CO2 uptake each year.