78 research outputs found
Scale-Free Crystallization of two-dimensional Complex Plasmas: Domain Analysis using Minkowski Tensors
Experiments of the recrystallization processes in two-dimensional complex
plasmas are analyzed in order to rigorously test a recently developed
scale-free phase transition theory. The "Fractal-Domain-Structure" (FDS) theory
is based on the kinetic theory of Frenkel. It assumes the formation of
homogeneous domains, separated by defect lines, during crystallization and a
fractal relationship between domain area and boundary length. For the defect
number fraction and system energy a scale free power-law relation is predicted.
The long range scaling behavior of the bond order correlation function shows
clearly that the complex plasma phase transitions are not of KTHNY type.
Previous preliminary results obtained by counting the number of dislocations
and applying a bond order metric for structural analysis are reproduced. These
findings are supplemented by extending the use of the bond order metric to
measure the defect number fraction and furthermore applying state-of-the-art
analysis methods, allowing a systematic testing of the FDS theory with
unprecedented scrutiny: A morphological analysis of lattice structure is
performed via Minkowski tensor methods. Minkowski tensors form a complete
family of additive, motion covariant and continuous morphological measures that
are sensitive to non-linear properties. The FDS theory is rigorously confirmed
and predictions of the theory are reproduced extremely well. The predicted
scale-free power law relation between defect fraction number and system energy
is verified for one more order of magnitude at high energies compared to the
inherently discontinuous bond order metric. Minkowski Tensor analysis turns out
to be a powerful tool for investigations of crystallization processes. It is
capable to reveal non-linear local topological properties, however, still
provides easily interpretable results founded on a solid mathematical
framework.Comment: 17 pages, 13 figures, 4 tables accepted for publication in PR
Direct experimental observation of binary agglomerates in complex plasmas
A defocusing imaging technique has been used as a diagnostic to identify
binary agglomerates (dimers) in complex plasmas. Quasi-two-dimensional plasma
crystal consisting of monodisperse spheres and binary agglomerates has been
created where the agglomerated particles levitate just below the spherical
particles without forming vertical pairs. Unlike spherical particles, the
defocused images of binary agglomerates show distinct, stationary/periodically
rotating interference fringe patterns. The results can be of fundamental
importance for future experiments on complex plasmas
Interaction of a supersonic particle with a three-dimensional complex plasma
The influence of a supersonic projectile on a three-dimensional complex
plasma is studied. Micron sized particles in a low-temperature plasma formed a
large undisturbed system in the new 'Zyflex' chamber during microgravity
conditions. A supersonic probe particle excited a Mach cone with Mach number M
1.5 - 2 and double Mach cone structure in the large weakly damped
particle cloud. The speed of sound is measured with different methods and
particle charge estimations are compared to calculations from standard
theories. The high image resolution enables the study of Mach cones in
microgravity on the single particle level of a three-dimensional complex plasma
and gives insight to the dynamics. A heating of the microparticles is
discovered behind the supersonic projectile but not in the flanks of the Mach
cone
Direct neural pathways convey distinct visual information to Drosophila mushroom bodies
Previously, we demonstrated that visual and olfactory associative memories of Drosophila share mushroom body (MB) circuits (Vogt et al., 2014). Unlike for odor representation, the MB circuit for visual information has not been characterized. Here, we show that a small subset of MB Kenyon cells (KCs) selectively responds to visual but not olfactory stimulation. The dendrites of these atypical KCs form a ventral accessory calyx (vAC), distinct from the main calyx that receives olfactory input. We identified two types of visual projection neurons (VPNs) directly connecting the optic lobes and the vAC. Strikingly, these VPNs are differentially required for visual memories of color and brightness. The segregation of visual and olfactory domains in the MB allows independent processing of distinct sensory memories and may be a conserved form of sensory representations among insects
Yukawa potentials in systems with partial periodic boundary conditions I : Ewald sums for quasi-two dimensional systems
Yukawa potentials are often used as effective potentials for systems as
colloids, plasmas, etc. When the Debye screening length is large, the Yukawa
potential tends to the non-screened Coulomb potential ; in this small screening
limit, or Coulomb limit, the potential is long ranged. As it is well known in
computer simulation, a simple truncation of the long ranged potential and the
minimum image convention are insufficient to obtain accurate numerical data on
systems. The Ewald method for bulk systems, i.e. with periodic boundary
conditions in all three directions of the space, has already been derived for
Yukawa potential [cf. Y., Rosenfeld, {\it Mol. Phys.}, \bm{88}, 1357, (1996)
and G., Salin and J.-M., Caillol, {\it J. Chem. Phys.}, \bm{113}, 10459,
(2000)], but for systems with partial periodic boundary conditions, the Ewald
sums have only recently been obtained [M., Mazars, {\it J. Chem. Phys.}, {\bf
126}, 056101 (2007)]. In this paper, we provide a closed derivation of the
Ewald sums for Yukawa potentials in systems with periodic boundary conditions
in only two directions and for any value of the Debye length. A special
attention is paid to the Coulomb limit and its relation with the
electroneutrality of systems.Comment: 40 pages, 5 figures and 4 table
Scale-free vortex cascade emerging from random forcing in a strongly coupled system
The notions of self-organised criticality (SOC) and turbulence are
traditionally considered to be applicable to disjoint classes of phenomena.
Nevertheless, scale-free burst statistics is a feature shared by turbulent as
well as self-organised critical dynamics. It has also been suggested that
another shared feature is universal non-gaussian probability density functions
(PDFs) of global fluctuations. Here, we elucidate the unifying aspects through
analysis of data from a laboratory dusty plasma monolayer. We compare analysis
of experimental data with simulations of a two-dimensional (2D) many-body
system, of 2D fluid turbulence, and a 2D SOC model, all subject to random
forcing at small scales. The scale-free vortex cascade is apparent from
structure functions as well as spatio-temporal avalanche analysis, the latter
giving similar results for the experimental and all model systems studied. The
experiment exhibits global fluctuation statistics consistent with a
non-gaussian universal PDF, but the model systems yield this result only in a
restricted range of forcing conditions
Physics and applications of dusty plasmas: The Perspectives 2023
Dusty plasmas are electrically quasi-neutral media that, along with electrons, ions, neutral gas, radiation, and electric and/or magnetic fields, also contain solid or liquid particles with sizes ranging from a few nanometers to a few micrometers. These media can be found in many natural environments as well as in various laboratory setups and industrial applications. As a separate branch of plasma physics, the field of dusty plasma physics was born in the beginning of 1990s at the intersection of the interests of the communities investigating astrophysical and technological plasmas. An additional boost to the development of the field was given by the discovery of plasma crystals leading to a series of microgravity experiments of which the purpose was to investigate generic phenomena in condensed matter physics using strongly coupled complex (dusty) plasmas as model systems. Finally, the field has gained an increasing amount of attention due to its inevitable connection to the development of novel applications ranging from the synthesis of functional nanoparticles to nuclear fusion and from particle sensing and diagnostics to nano-contamination control. The purpose of the present perspectives paper is to identify promising new developments and research directions for the field. As such, dusty plasmas are considered in their entire variety: from classical low-pressure noble-gas dusty discharges to atmospheric pressure plasmas with aerosols and from rarefied astrophysical plasmas to dense plasmas in nuclear fusion devices. Both fundamental and application aspects are covered
The Radish Gene Reveals a Memory Component with Variable Temporal Properties
Memory phases, dependent on different neural and molecular mechanisms, strongly influence memory performance. Our understanding, however, of how memory phases interact is far from complete. In Drosophila, aversive olfactory learning is thought to progress from short-term through long-term memory phases. Another memory phase termed anesthesia resistant memory, dependent on the radish gene, influences memory hours after aversive olfactory learning. How does the radish-dependent phase influence memory performance in different tasks? It is found that the radish memory component does not scale with the stability of several memory traces, indicating a specific recruitment of this component to influence different memories, even within minutes of learning
dTip60 HAT Activity Controls Synaptic Bouton Expansion at the Drosophila Neuromuscular Junction
Background: Histone acetylation of chromatin plays a key role in promoting the dynamic transcriptional responses in neurons that influence the neuroplasticity linked to cognitive ability, yet the specific histone acetyltransferases (HATs) that create such epigenetic marks remain to be elucidated. Methods and Findings: Here we use the Drosophila neuromuscular junction (NMJ) as a well-characterized synapse model to identify HATs that control synaptic remodeling and structure. We show that the HAT dTip60 is concentrated both pre and post-synaptically within the NMJ. Presynaptic targeted reduction of dTip60 HAT activity causes a significant increase in synaptic bouton number that specifically affects type Is boutons. The excess boutons show a suppression of the active zone synaptic function marker bruchpilot, suggesting defects in neurotransmission function. Analysis of microtubule organization within these excess boutons using immunohistochemical staining to the microtubule associated protein futsch reveals a significant increase in the rearrangement of microtubule loop architecture that is required for bouton division. Moreover, a-tubulin acetylation levels of microtubules specifically extending into the terminal synaptic boutons are reduced in response to dTip60 HAT reduction. Conclusions: Our results are the first to demonstrate a causative role for the HAT dTip60 in the control of synaptic plasticity that is achieved, at least in part, via regulation of the synaptic microtubule cytoskeleton. These findings have implication
Physics and applications of dusty plasmas : The Perspectives 2023
Dusty plasmas are electrically quasi-neutral media that, along with electrons, ions, neutral gas, radiation, and electric and/or magnetic fields, also contain solid or liquid particles with sizes ranging from a few nanometers to a few micrometers. These media can be found in many natural environments as well as in various laboratory setups and industrial applications. As a separate branch of plasma physics, the field of dusty plasma physics was born in the beginning of 1990s at the intersection of the interests of the communities investigating astrophysical and technological plasmas. An additional boost to the development of the field was given by the discovery of plasma crystals leading to a series of microgravity experiments of which the purpose was to investigate generic phenomena in condensed matter physics using strongly coupled complex (dusty) plasmas as model systems. Finally, the field has gained an increasing amount of attention due to its inevitable connection to the development of novel applications ranging from the synthesis of functional nanoparticles to nuclear fusion and from particle sensing and diagnostics to nano-contamination control. The purpose of the present perspectives paper is to identify promising new developments and research directions for the field. As such, dusty plasmas are considered in their entire variety: from classical low-pressure noble-gas dusty discharges to atmospheric pressure plasmas with aerosols and from rarefied astrophysical plasmas to dense plasmas in nuclear fusion devices. Both fundamental and application aspects are covered
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