Realization of the purely spatial Einstein-Podolsky-Rosen paradox in full-field images of spontaneous parametric down conversion

We demonstrate Einstein-Podolsky-Rosen (EPR) entanglement by detecting purely spatial quantum correlations in the near and far fields of spontaneous parametric down-conversion generated in a type-2 beta barium borate crystal. Full-field imaging is performed in the photon-counting regime with an electron-multiplying CCD camera. The data are used without any postselection, and we obtain a violation of Heisenberg inequalities with inferred quantities taking into account all the biphoton pairs in both the near and far fields by integration on the entire two-dimensional transverse planes. This ensures a rigorous demonstration of the EPR paradox in its original position momentum form

The plasma-wall transition layers in the presence of collisions with a magnetic field parallel to the wall

International audienceThe plasma-wall transition is studied by mean of a particle-in-cell (PIC) simulations in the configuration of a parallel to the wall magnetic field (B), with collisions between charged particles vs. neutral atoms taken into account. The investigated system consists in a plasma bounded by two absorbing walls separated by 200 electron Debye lengths (λ d). The strength of the magnetic field is chosen such as the ratio λ d /r l , with r l the electron Larmor radius, is smaller or larger than the unity. Collisions are modelled with a simple operator that reorients randomly ion or electron velocity, keeping constant the total kinetic energy of both the neutral atom (target) and the incident charged particle. The PIC simulations show that the plasma-wall transition consists in a quasi-neutral region (pre-sheath), from the center of the plasma towards the walls, where the electric potential or electric field profiles are well described by an ambipolar diffusion model, and in a second region at the vicinity of the walls, called the sheath, where the quasi-neutrality breaks down. In this peculiar geometry of B and for a certain range of the mean-free-path, the sheath is found to be composed by two charged layers, a first, positive, close to the walls, and a second one, negative, towards the plasma and before the neutral pre-sheath. Depending on the amplitude of B, the spatial variation of the electric potential can be non-monotonic and presents a maximum within the sheath region. More generally, the sheath extent as well as the potential drop within the sheath and the pre-sheath are studied with respect to B, the mean-free-path and the ion and electron temperature

Plasma sheath properties in a magnetic field parallel to the wall

International audienceParticle in cell simulations were carried out with a plasma bounded by two absorbing walls and a magnetic field applied parallel to them. Both the sheath extent and the potential drop in it were derived from simulations for different plasma parameters such as the electron and ion temperature T i , particle density and ion mass. Both of them exhibit a power law dependent on the Larmor to plasma ion pulsation ratio Ω i. For increasing values of the magnetic field, the potential drop within the sheath decreases from a few T i /e down to zero, where e stands for the electron charge. The space charge extent increases with Ω i and saturates to 2.15 ion Larmor radius. A simple model of sheath formation in such a magnetic field configuration is presented. Assuming strongly magnetized electrons, and neglecting collisions and ionizations, a new typical length is evidenced, which depends on the ratio Ω i. The charge separation sheath width is theoretically found to increase from a combination of the electron gyroradius and the ion Debye length for low Ω i ratios up to several ion gyroradii for strongly magnetized ions. Both the calculated sheath extent and plasma potential show a fair agreement with the numerical simulations

Étude préliminaire sur les échanges de phosphore à l'interface eau- sédiment au sein de la retenue d'Al Massira (Maroc)

Les échanges de phosphore à l'interface eau-sédiment ont été étudiés dans la retenue Al Massira. La campagne de prélèvements a été menée pendant la faible oxygénation des eaux profondes au mois d'octobre 1991. Les mesures des échanges de phosphore ont été réalisées in situ en chambre benthique.Les valeurs de pH sont élevées et reflètent clairement l'influence de la nature géologique du bassin versant sur la composition chimique des eaux. Ce bassin versant, formé essentiellement de roches sédimentaires calcaires, est vraisemblablement à l'origine des concentrations élevées en calcium mesurées dans les chambres benthiques.En période de faible oxygénation, on note une augmentation des teneurs en phosphore particulaire dans les eaux surnageantes en raison de la présence de complexes calcium-phosphore, fer-phosphore et manganèse-phosphore. En période d'anoxie, la réduction de ces complexes est accompagnée d'une aug- mentation des teneurs en phosphore.La densité bactérienne et la concentration en phosphore total et notamment en orthophosphates suivent une évolution temporelle comparable. Une fraction non négligeable du phosphore particulaire serait liée aux bactéries.Des mesures drastiques de déphosphatation du tributaire Oum Errbia doivent être prises pour éviter la dissociation des complexes Ca, Fe, Mn-Phosphore et le relargage de phosphore biodisponible.Phosphorus exchange at the sediment-water interface was studied in the Al Massira reservoir. This reservoir, located on the Oum Errbia river, is the most important freshwater resource in Morocco. It provides drinking water to the whole population of Casablanca and contributes to farming and to the functioning of several industrial plants. Our investigations were made in October 1991 and coincided with low oxygen concentrations in the deep layers. The measurements of phosphorus exchange have been made in sitn with a benthic chamber device.The results showed that these exchanges were regulated by a combination ofthe physical chemical variability of the environment and the geological composition of the catchment basin.The pH, which permanently exceeded 7 in Massira, suggests that calcium-bound phosphorus was primarily CaHFO4. Moreover, given the high phosphonrs inputs into the reservoir (570 tonnes. year-1), and despite the fact that, as soon as it reached the reservoir, a large fraction of this element was associated with to calcium, it's likely that the Massira reservoir is subject to eutrophication.In low oxygenated deep layers, we observed an increase in particulate phosphorus concentrations of the overlying water, due to the simultaneous presence of calcium-phosphorus, iron-phosphorus and manganese-phosphorus forms. Under anoxic conditions, the reduction ofthese complexes resulted in an increase of phosphorus concentrations.Bacterial cell numbers and total phosphorus concentratioru showed a comparable temporal behaviour. This would suggest that attached bacteria contributed at least partially to the total particulate phosphoms concentrations.We suggest that a drastic control of phosphorus inputs into the waters must be done through a program of dephosphorylation of tributaries to avoid the dissocation of calcium-, iron-, manganese-bound phosphorus with release upwards of bioavailable phosphorus

The plasma-wall transition with collisions and an oblique magnetic field: reversal of potential drops at grazing incidences

International audienceThe plasma-wall transition is studied by using 1d3V particle-in-cell (PIC) simulations in the case of a one dimensional plasma bounded by two absorbing walls separated by 200 Debye lengths (λ d). A constant and oblique magnetic field is applied to the system, with an amplitude such that r < λ d < R, where r and R are the electron and ion Larmor radius respectively. Collisions with neutrals are taken into account and modelled by an energy conservative operator, which randomly reorients ion and electron velocities. The plasma-wall transition (PWT) is shown to depend on both the angle of incidence of the magnetic field with respect to the wall θ, and on the ion mean-free-path to Larmor radius ratio, λ ci /R. In the very low collisionality regime (λ ci R) and for a large angle of incidence, the PWT consists in the classical tri-layer structure (Debye sheath / Chodura sheath / Pre-sheath) from the wall towards the center of the plasma. The drops of potential within the different regions are well consistent with already published models. However, when sin θ ≤ R/λ ci or with the ordering λ ci < R , collisions can not be neglected, leading to the disappearance of the Chodura sheath. In these case, a collisional model yields analytic expressions for the potential drop in the quasi-neutral region, and explains, in qualitative and quantitative agreement with the simulation results, its reversal below a critical angle derived in the paper, a regime possibly met in the SOL of tokamaks. It is further shown that the potential drop in the Debye sheath slightly varies with the collision-ality for λ ci R. However, it tends to decrease with λ ci in the high collisionality regime, until the Debye sheath finally vanishes

Security Analysis of the Silver Bullet Technique for RowHammer Prevention

The purpose of this document is to study the security properties of the Silver Bullet algorithm against worst-case RowHammer attacks. We mathematically demonstrate that Silver Bullet, when properly configured and implemented in a DRAM chip, can securely prevent RowHammer attacks. The demonstration focuses on the most representative implementation of Silver Bullet, the patent claiming many implementation possibilities not covered in this demonstration. Our study concludes that Silver Bullet is a promising RowHammer prevention mechanism that can be configured to operate securely against RowHammer attacks at various efficiency-area tradeoff points, supporting relatively small hammer count values (e.g., 1000) and Silver Bullet table sizes (e.g., 1.06KB).Comment: 40 page