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Numerical simulations have grown to play a central role in modern sciences over the years. The ever-improving technology of supercomputers has made large and precise models available. However, this accuracy is often limited by the cost of computational resources. Lowering the simulation's spatial resolution in order to conserve resources can lead to key processes being unresolved. We have shown in a previous study how insufficient spatial resolution of the proton cyclotron instability leads to a misrepresentation of ion dynamics in hybrid-Vlasov simulations. This leads to larger than expected temperature anisotropy and loss-cone shaped velocity distribution functions. In this study, we present a sub-grid numerical model to introduce pitch-angle diffusion in a 3D Cartesian velocity space, at a spatial resolution where the relevant wave-particle interactions were previously not correctly resolved. We show that the method is successfully able to isotropize loss-cone shaped velocity distribution functions, and that this method could be applied to simulations in order to save computational resources and still correctly model wave-particle interactions.

Separatrices of magnetic reconnection host intense perpendicular Hall electric fields. The fields are produced by the decoupling of the ion and electron components and are associated with the in-plane electrostatic potential drop between the inflow and outflow regions. The width of these structures is typically less than the ion inertial length, which is small enough to demagnetize ions as they cross the layer. We investigate ion acceleration at separatrices by means of 2D particle-in-cell simulations of magnetic reconnection for two limiting cases: (1) a "GEM-like" setup (here GEM stands for geospace environmental modeling reconnection challenge) with the lobe ion thermal velocity equal to the thermal velocity of the initial current sheet ions, which is comparable to the Alfven velocity and (2) a "cold" ion setup, in which the temperature of the background lobe ions is 1/100 of the initial current sheet temperature. The separatrix Hall electric field is balanced by the ion inertia term in the cold background simulations. The effect is indicative of the quasi-steady local perpendicular acceleration. The electric field introduces a cross field beam of unmagnetized particles, which makes the ion distribution function strongly non-gyrotropic and susceptible to sub-ion scale instabilities. This acceleration mechanism nearly vanishes in the hot ion background simulations. Our particle-in-cell simulations are complemented by one-dimensional test particle calculations. They show that the hot ion particles experience energy-scattering after crossing the accelerating layer, whereas cold ions are uniformly energized up to the energies comparable to the electrostatic potential drop between the inflow and outflow regions.

В статье представлен датчик на основе щелевой моды в акустической линии задержки для экспресс-анализа и оценки жизнеспособности бактериальных клеток непосредственно в жидкой проводящей суспензии. В качестве аналитического сигнала использовали изменение глубины и частоты пиков резонансного поглощения на частотной зависимости полных потерь выходного сигнала датчика до и после биологического взаимодействия бактериальных клеток с бактериофагами. Измерения проводились в суспензиях с начальной проводимостью 5–30 мкСм/см. Для подавления биохимических процессов в бактериальных клетках с целью оценки их жизнеспособности клеточную суспензию подвергали температурному воздействию в температурном интервале 60–100 °С с последующим охлаждением. Конструкция датчика позволяла многократно использовать съемный контейнер, при этом значительно упрощался процесс его очистки от отработанного образца., The article presents a slot-mode sensor in acoustic delay line for rapid analysis and assessment of the viability of bacterial cells directly in a liquid conductive suspension. The main element of the sensor is the delay line made of the Y-X lithium niobate plate. Two interdigital transducers (IDTs) were applied to the surface of the plate to excite and receive the acoustic SH0 wave. A liquid container was placed above the waveguide of the delay line between the IDTs with the given gap of 8 μm. The bottom of the container was made of the Z-X + 30° lithium niobate plate. The sensor was connected to the Sparameter meter E5071C (Agilent, USA), and the frequency dependence of the insertion loss of the sensor output signal was measured. During the measurements the presence of pronounced resonance peaks in the frequency dependence of the insertion loss of the sensor associated with the excitation of the slot mode was observed. The method of the analysis of the microbial cells was based on recording changes in the depth and frequency of resonance absorption peaks on the frequency dependence of the insertion loss of the sensor before and after the biological interaction of the microbial cells with the specific bacteriophages. The sensor recorded the infection of microbial cells with the specific bacteriophages in suspensions with the initial conductivity of 4.5–30 μS/cm. The analysis time was 5–10 minutes, the limit of the determination of the microbial cells was 103 cells/ml. The control experiments were conducted with the nonspecific interactions of the microbial cells with the bacteriophages, in which no change in the sensor parameters was observed. To suppress the biochemical processes in the cells or the further assessment of their viability, the cell suspension was heated to 60, 80, and 100 °C. Then the cell suspension was cooled to the room temperature, placed in the liquid container and the sensor readings were recorded. After that, the specific bacteriophage was ad

We study inflow density dependence of substructures within electron diffusion region (EDR) of collisionless symmetric magnetic reconnection. We perform a set of 2.5D particle-in-cell simulations which start from a Harris current layer with a uniform background density n(b). A scan of n(b) ranging from 0:02 n(0) to 2 n(0) of the peak current layer density (n(0)) is studied keeping other plasma parameters the same. Various quantities measuring reconnection rate, EDR spatial scales, and characteristic velocities are introduced. We analyze EDR properties during quasisteady stage when the EDR length measures saturate. Consistent with past kinetic simulations, electrons are heated parallel to the B field in the inflow region. The presence of the strong parallel anisotropy acts twofold: (1) electron pressure anisotropy drift gets important at the EDR upstream edge in addition to the E x B drift speed and (2) the pressure anisotropy term -del.P-(e)/(ne) modifies the force balance there. We find that the width of the EDR demagnetization region and EDR current are proportional to the electron inertial length similar to d(e) and similar to d(e)n(b)(0.22), respectively. Magnetic reconnection is fast with a rate of similar to 0.1 but depends weakly on density as similar to n(b)(-1/8). Such reconnection rate proxies as EDR geometrical aspect or the inflow-to-outflow electron velocity ratio are shown to have different density trends, making electric field the only reliable measure of the reconnection rate. Published under license by AIP Publishing., QC 20200214