Ionization by bulk heating of electrons in capacitive radio frequency atmospheric pressure microplasmas

Electron heating and ionization dynamics in capacitively coupled radio frequency (RF) atmospheric pressure microplasmas operated in helium are investigated by Particle in Cell simulations and semi-analytical modeling. A strong heating of electrons and ionization in the plasma bulk due to high bulk electric fields are observed at distinct times within the RF period. Based on the model the electric field is identified to be a drift field caused by a low electrical conductivity due to the high electron-neutral collision frequency at atmospheric pressure. Thus, the ionization is mainly caused by ohmic heating in this "Omega-mode". The phase of strongest bulk electric field and ionization is affected by the driving voltage amplitude. At high amplitudes, the plasma density is high, so that the sheath impedance is comparable to the bulk resistance. Thus, voltage and current are about 45{\deg} out of phase and maximum ionization is observed during sheath expansion with local maxima at the sheath edges. At low driving voltages, the plasma density is low and the discharge becomes more resistive resulting in a smaller phase shift of about 4{\deg}. Thus, maximum ionization occurs later within the RF period with a maximum in the discharge center. Significant analogies to electronegative low pressure macroscopic discharges operated in the Drift-Ambipolar mode are found, where similar mechanisms induced by a high electronegativity instead of a high collision frequency have been identified

Simulation for competition of languages with an ageing sexual population

Recently, individual-based models originally used for biological purposes revealed interesting insights into processes of the competition of languages. Within this new field of population dynamics a model considering sexual populations with ageing is presented. The agents are situated on a lattice and each one speaks one of two languages or both. The stability and quantitative structure of an interface between two regions, initially speaking different languages, is studied. We find that individuals speaking both languages do not prefer any of these regions and have a different age structure than individuals speaking only one language.Comment: submitted to International Journal of Modern Physics

Does social sampling differ between online and offline contacts? A computational modeling analysis

Decision makers can infer social statistics (e.g., the relative frequency of health risks or consumer preferences in the population) by drawing on samples from their personal social networks. In light of the growing use of the Internet, much of people’s social interactions occur online (e.g., via social media) rather than offline (e.g., via face-to-face contact). Here, we examine to what extent sampling of social network members from memory (social sampling) is affected by whether one usually has online vs. offline contact to a person. In our study, participants judged the popularity of holiday destinations and recalled people in their own online and offline social networks who had vacationed at each destination. Additionally, participants indicated the respective contact mode (offline, online, or mixed) and social category (self, family member, friend, or acquaintance) of each recalled person. We used a hierarchical Bayesian modeling approach to contrast two variants of a cognitive model that assumes sequential and limited search—the social-circle model. The variants assumed the search process underlying social sampling to be guided by either contact mode (online vs. offline) or social category. The model comparison further included an exhaustive sampling strategy and guessing. The majority of participants was best described by a limited rather than an exhaustive search strategy or guessing. Additionally, more than a third of participants were best described by the variant of the social-circle model assuming search to be guided by contact mode. Interestingly, participants who followed this search strategy also relied more strongly on their own experiences than participants who probed their memory by social category. Overall, these results provide the first evidence that contact mode affects social sampling from memory

Stress-Minimizing Orthogonal Layout of Data Flow Diagrams with Ports

We present a fundamentally different approach to orthogonal layout of data flow diagrams with ports. This is based on extending constrained stress majorization to cater for ports and flow layout. Because we are minimizing stress we are able to better display global structure, as measured by several criteria such as stress, edge-length variance, and aspect ratio. Compared to the layered approach, our layouts tend to exhibit symmetries, and eliminate inter-layer whitespace, making the diagrams more compact

Kinetic simulation of the sheath dynamics in the intermediate radio-frequency regime

The dynamics of temporally modulated plasma boundary sheaths is studied in the intermediate radio frequency regime where the applied radio frequency and the ion plasma frequency are comparable. Two kinetic simulation codes are employed and their results are compared. The first code is a realization of the well-known scheme, Particle-In-Cell with Monte Carlo collisions (PIC/MCC) and simulates the entire discharge, a planar radio frequency capacitively coupled plasma (RF-CCP) with an additional heating source. The second code is based on the recently published scheme Ensemble-in-Spacetime (EST); it resolves only the sheath and requires the time resolved voltage across and the ion flux into the sheath as input. Ion inertia causes a temporal asymmetry (hysteresis) of the sheath charge-voltage relation; also other ion transit time effects are found. The two codes are in good agreement, both with respect to the spatial and temporal dynamics of the sheath and with respect to the ion energy distributions at the electrodes. It is concluded that the EST scheme may serve as an efficient post-processor for fluid or global simulations and for measurements: It can rapidly and accurately calculate ion distribution functions even when no genuine kinetic information is available

A low power clock generator with adaptive inter-phase charge balancing for variability compensation in 40-nm CMOS

Power dissipation besides chip area is still one main optimization issue in high performance CMOS design. Regarding high throughput building blocks for digital signal processing architectures which are optimized down to the physical level a complementary two-phase clocking scheme (CTPC) is often advantageous concerning ATE-efficiency. The clock system dissipates a significant part of overall power up to more than 50% in some applications. <br><br> One efficient power saving strategy for CTPC signal generation is the charge balancing technique. To achieve high efficiency with this approach a careful optimization of timing relations within the control is inevitable. <br><br> However, as in modern CMOS processes device variations increase, timing relations between sensitive control signals can be affected seriously. In order to compensate for the influence of global and local variations in this work, an adaptive control system for charge balancing in a CTPC generator is presented. An adjustment for the degree of charge recycling is performed in each clock cycle. In the case of insufficient recycling the delay elements which define duration and timing position of the recycling pulse are corrected by switchable timing units. <br><br> In a benchmark with the conventional clock generation system, a power reduction gain of up to 24.7% could be achieved. This means saving in power of more than 12% for a complete number-crunching building block

The degradation of MgB2 under ambient environment

The superconductivities of samples prepared by several procedures were found to degrade under ambient environment. The degradation mechanism was studied by measuring the change of surface chemical composition of dense MgB2 pellets (prepared by hot isostatic pressure, HIPed) under atmospheric exposure using X-ray Photoelectron Spectroscopy (XPS). Results showed that samples with poor connectivity between grains and with smaller grain sizes degrade with time when exposed to ambient conditions. In these samples, the Tc did not change with time, but the superconducting transition became broader and the Meissner fraction decreased. In contrast, our well-sintered and the HIPed samples remained stable for several months under ambient condition. The degradation was found to be related to surface decomposition as observed by XPS. We observed the formation of oxidized Mg, primarily in the form of a Mg hydroxide, the increase of C and O contents, and the reduction of B concentration in the surface layer of MgB2 samples.Comment: 15 pages, 3 figure