We present a search for the e+e− decay of a hypothetical dark photon, also named U vector boson, in inclusive dielectron spectra measured by HADES in the p(3.5 GeV) + p, Nb reactions, as well as the ...Ar (1.756 GeV/u) + KCl reaction. An upper limit on the kinetic mixing parameter squared ϵ2 at 90% CL has been obtained for the mass range MU=0.02–0.55 GeV/c2 and is compared with the present world data set. For masses 0.03–0.1 GeV/c2, the limit has been lowered with respect to previous results, allowing now to exclude a large part of the parameter region favored by the muon g−2 anomaly. Furthermore, an improved upper limit on the branching ratio of 2.3×10−6 has been set on the helicity-suppressed direct decay of the eta meson, η→e+e−, at 90% CL.
Exposures to nanosecond pulsed electric fields (nsPEFs) are known to induce intracellular responses, such as the induction of apoptosis, offering a promising new method to treat cancer. This and ...other secondary biological responses are believed to be promoted by an initial formation of nanopores in cellular membranes. The primarily responsible charging mechanisms depend on pulse duration and amplitude, as well as the conductivity of the extracellular medium. In comparison, the postexposure development of membrane integrity and secondary-cell responses depend on complex interaction of biophysical and biochemical processes. To assess the effect of exposure media beyond their electrical characteristics, we studied different exposure media with similar conductivities and osmolalities. Experiments were performed using a typical nsPEF regimen, as is used in apoptosis studies (eight pulses of 60-ns duration and 60 kV/cm). We investigated the development of membrane permeability with propidium iodide and cell survival with calcein-AM on biologically relevant times out to 20 or 90 min, respectively. We found a tenfold increase in permeabilization of the plasma membrane depending on the exposure medium and a similar effect on the cell viability. The results suggest that progression of membrane permeability and cell survival strongly depend on the composition of the extracellular medium, rather than its electrical characteristic alone.
Better understanding of variation in soil carbon dioxide (CO₂) efflux caused by measurement techniques is needed, especially over gradients of site disturbance, to accurately estimate the global ...carbon cycle. We present soil CO₂ efflux data from a gradient of disturbance to ponderosa pine (Pinus ponderosa C. Lawson var. scopulorum Engelm.) forests in northern Arizona, USA that were obtained using four different techniques: vented static chambers, a Licor 6400-09, and soil CO₂ diffusion profiles using two different models (Moldrup, Millington-Quirk) to estimate soil gas diffusivity. We also compared soil CO₂ efflux measured by the Moldrup and Millington-Quirk diffusion profile methods to nighttime total ecosystem respiration (TER) data from an eddy covariance tower. We addressed four questions: (1) Does the use of a given method to measure soil CO₂ efflux bias results across a disturbance gradient? (2) Does the magnitude of difference between observed and modeled estimates of soil CO₂ differ between methods and across sites? (3) What is the spatial variability of each method at each site? (4) Which method is closest to the estimate of TER measured by the eddy covariance tower? Although soil CO₂ efflux varied significantly among methods the differences were consistent among sites. Measured and modeled total growing season fluxes were generally higher for the Licor 6400-09 and Millington-Quirk diffusion gradient methods compared with static chamber and the Moldrup diffusion gradient methods. A power analysis showed that the larger static chamber was the most efficient method at sampling spatial variation in soil CO₂ efflux. Nighttime measurements of soil CO₂ efflux from the Moldrup diffusion gradient method were most strongly related to nighttime TER assessed with eddy covariance. The use of a single, well-implemented method to measure soil CO₂ efflux is unlikely to create bias in comparisons across a gradient of forest disturbance.
Methane emissions were measured at nine U.S. landfill sites using chamber and/or tracer flux techniques. These flux measurement methodologies were compared at two sites, and excellent agreement (<10% ...difference) was observed. Total methane emissions ranged from 540 to 30 100 L min-1. Expressed on an area basis, methane fluxes ranged from a low of 9.1 g of CH4 m-2 d-1 at a closed 20-ha site with active gas recovery to 130 g of CH4 m-2 d-1 at a 23-ha active site with no gas recovery. Methane emission factors in units of m3 of CH4 min-1 (106 m3 waste-in-place)-1 were calculated for seven of the nine sites. The two sites with no active gas recovery exhibited the highest emission factors of 4.8 and 5.1. Values were significantly lower at three sites with partial gas recovery, ranging from 1.6 to 3.7. At the two closed sites with active gas recovery, emission factors were much lower still (0.4 and 1.1). It is evident that even partial gas recovery at active landfill sites can significantly reduce methane emissions, and gas recovery at closed, covered sites reduces methane emissions to the atmosphere by as much as a factor of 10.
Flow coefficients vn of the orders n = 1 – 6 are measured with the High-Acceptance Spectrometer (HADES) at GSI for protons, deuterons, and tritons as a function of centrality, transverse momentum, ...and rapidity in Au + Au collisions at √sNN = 2.4 GeV. Combining the information from the flow coefficients of all orders allows us to construct for the first time, at collision energies of a few GeV, a multidifferential picture of the angular emission pattern of these particles. It reflects the complicated interplay between the effect of the central fireball pressure on the emission of particles and their subsequent interaction with spectator matter. The high precision information on higher order flow coefficients is a major step forward in constraining the equation of state of dense baryonic matter.
Diesel-powered vehicles are intensively used in urban areas for transporting goods and people but can substantially contribute to high emissions of black carbon (BC), organic carbon (OC), and other ...gaseous pollutants. Strategies aimed at controlling mobile emissions sources thus have the potential to improve air quality and help mitigate the impacts of air pollutants on climate, ecosystems, and human health. However, in developing countries there are limited data on the BC and OC emission characteristics of diesel-powered vehicles, and thus there are large uncertainties in the estimation of the emission contributions from these sources. We measured BC, OC, and other inorganic components of fine particulate matter (PM), as well as carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), ethane, acetylene, benzene, toluene, and C2-benzenes under real-world driving conditions for 20 diesel-powered vehicles encompassing multiple emission level technologies in Mexico City with the chasing technique using the Aerodyne mobile laboratory. Average BC emission factors ranged from 0.41–2.48 g kg−1 of fuel depending on vehicle type. The vehicles were also simultaneously measured using the cross-road remote sensing technique to obtain the emission factors of nitrogen oxide (NO), CO, total hydrocarbons, and fine PM, thus allowing for the intercomparison of the results from the two techniques. There is overall good agreement between the two techniques and both can identify high and low emitters, but substantial differences were found in some of the vehicles, probably due to the ability of the chasing technique to capture a larger diversity of driving conditions in comparison to the remote sensing technique. A comparison of the results with the US EPA MOVES2014b model showed that the model underestimates CO, OC, and selected VOC species, whereas there is better agreement for NOx and BC. Larger OC / BC ratios were found in comparison to ratios measured in California using the same technique, further demonstrating the need for using locally obtained diesel-powered vehicle emission factor database in developing countries in order to reduce the uncertainty in the emissions estimates and to improve the evaluation of the effectiveness of emissions reduction measures.
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