The European Physical Journal D最新文献

Prerequisites for the goal of studying long-lived, magnetically confined, electron–positron pair plasmas in the laboratory include the injection of both species into the trap, long trapping times, and suitable diagnostic methods. Here we report recent progress on these tasks achieved in a simple dipole trap based on a supported permanent magnet. For the injection of electrons, both an (textbf{E}times B) drift technique (of a (sim )2–(upmu )A, 6-eV beam) and “edge injection” (from a filament emitting a few mA and biased to some tens of volts) have been demonstrated; the former is suitable for low-density beams with smaller spatial and velocity spreads, while the latter employs fluctuations arising from collective behavior. To diagnose the edge-injected electrons, image potentials and currents induced on a wall probe, the magnet case, and wall electrodes were measured. Confinement of drift-injected positrons, measured experimentally, exhibited at least two well-separated timescales. Simulations reproduced this qualitatively, using a simple model of elastic collisions with residual background gas, and point to small adjustments for increasing trapping times. In a major upgrade to diagnostic capabilities, 25 bismuth germanate detectors, placed in three reentrant ports, are able to localize annihilation gammas, which will be used in future experiments to distinguish between different loss channels.

The electron capture by heavy charged particles is of interest in a wide range of physical applications. In radiation biophysics, electron capture cross sections (ECCS) is a key information for the implementation of Monte Carlo simulation codes. In this work, the time-dependent density functional theory (TD-DFT) has been used for the determination of ECCS for protons impacting on atoms with presence in organic compounds, in the 1–200 keV energy range. Later, these atomic cross sections were combined through the pixel counting method for determining corresponding cross section of small and large organic molecules and water, which is of primordial importance in radiation biophysics. The large organic molecules include DNA bases and a whole DNA base pair. Excellent results were obtained for the small molecules along the whole energy range. For DNA components, good results were found at high energies (100–200 keV). At lower energies, larger discrepancies were obtained when compared with other theoretical and experimental work. The possible causes for these discrepancies are deeply discussed. This work should support later works for developing a charge equalization method for classical molecular dynamics to describe fast proton collisions with organic materials.

We propose theoretically a non-magnetic optical nonreciprocity (ONR) scheme with high efficiency by employing the four-wave mixing (FWM) effect in an asymmetric semiconductor three-coupled-quantum-well (TCQW) nanostructure. Nonreciprocal transmission and nonreciprocal phase shift in this TCQW, both with high transmission rates, can be achieved using suitable parameters. Considering an orbital-angular-momentum (OAM) probe beam, the perfect nonreciprocity can be obtained based on the highly efficient FWM. Furthermore, the integration of this TCQW nanostructure into a Mach–Zehnder interferometer enables the fabrication of highly efficient optical isolators and optical circulators by selecting appropriate parameters. The optical isolator exhibits an isolation ratio of 97.76 dB and an insertion loss of 0.25 dB, while the optical circulator demonstrates a fidelity of 0.9993 and a photon survival probability of 0.9517. Our approach based on semiconductor media has the advantages of easy fabrication and good integration with adjustable parameters. In conjunction with the distinctive characteristics of the OAM beam, our protocol offers a theoretical framework for the development of highly integrated and multi-dimensional nonreciprocity and nonreciprocal photonic devices.

In a realistic situation, it is very difficult to communicate securely between two distant parties without introducing any disturbances. These disturbances might occur either due to external noise or may be due to the interference of an eavesdropper. In this work, we consider and modify the six-state Quantum Key Distribution (QKD) protocol in which Eve can construct the unitary transformation that make all ancilla states entangled at the output, which is not considered in Bruss’s work [29]. Using the above proposed modification, we would like to study the effect of entangled ancilla states on the mutual information between Alice and Eve. To achieve this task, we calculate the mutual information between Alice and Bob and Alice and Eve and identify the region where the secret key is generated even in the presence of Eve. We find that, in general, the mutual information of Alice and Eve depends not only on the disturbance D but also on the concurrence of the ancilla states. We show that the entanglement of the ancilla states helps in generating the secret key in the region where Bruss’s six-state QKD protocol failed to do so. We have further shown that it is possible to derive the disturbance-free mutual information of Alice and Eve, if Eve manipulates her entangled ancilla state in a particular manner. Thus, in this way, we can show that a secret key can be generated between Alice and Bob even if the disturbance is large enough.

We present a microscopic formalism that accounts for the formation of nano-scale bubbles owing to a burst of water molecules after the passage of high energy charged particles that lead to the formation of “hot” non-ionizing excitations or thermal spikes (TS). We construct amorphous track structures to account for the formation of TS by ionizing radiation in liquid water. Subsequently, we simulate sudden expansion and collective motion of water molecules by employing a molecular dynamics (MD) simulation that allows computation of ({{mathcal {O}}}(10^6)) particle trajectories and breaking/forming of chemical bonds on the fly using a reactive force field, ReaxFF. We calculate the fluctuations of thermodynamic variables before and after TS formation to model the macroscopic abrupt changes in the system, possibly the occurrence of a first-order phase transition, and go beyond the accessible simulation times by engaging fluid dynamic equations with appropriate underlying symmetries and boundary conditions. We demonstrate the coexistence of a rapidly growing condensed state of water and a hot spot that forms a stable state of diluted water at high temperatures and pressures, possibly at a supercritical phase. Depending on the temperature of TS, the thin shell of a highly dense state of water grows by three to five times the speed of sound in water, forming a thin layer of shock wave (SW) buffer, wrapping around the nano-scale cylindrical symmetric bubble. The stability of the bubble, as a result of the incompressibility of water at ambient conditions and the surface tension, allows the transition of supersonic SW to a subsonic contact discontinuity and dissipation to thermo-acoustic sound waves. Thus, TS gradually decays to acoustic waves, a channel of deexcitation that competes with the spontaneous emission of photons, and a direct mechanism for water luminescence. We further study the mergers of nanobubbles that lead to jet-flow structures at the collision interface. We introduce a time delay in the nucleation of nano-bubbles, a novel mechanism, responsible for the growth and stability of much larger or even micro-bubbles, possibly relevant to FLASH ultra-high dose rate (UHDR).

Molecular dynamic simulation of the interaction between two ionizing radiation-induced nano-bubble formed simultaneously.