9,095 research outputs found
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
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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
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