Negative-energy perturbations in cylindrical equilibria with a radial electric field

The impact of an equilibrium radial electric field $E$ on negative-energy perturbations (NEPs) (which are potentially dangerous because they can lead to either linear or nonlinear explosive instabilities) in cylindrical equilibria of magnetically confined plasmas is investigated within the framework of Maxwell-drift kinetic theory. It turns out that for wave vectors with a non-vanishing component parallel to the magnetic field the conditions for the existence of NEPs in equilibria with E=0 [G. N. Throumoulopoulos and D. Pfirsch, Phys. Rev. E 53, 2767 (1996)] remain valid, while the condition for the existence of perpendicular NEPs, which are found to be the most important perturbations, is modified. For $|e_i\phi|\approx T_i$ ($\phi$ is the electrostatic potential) and $T_i/T_e > \beta_c\approx P/(B^2/8\pi)$ ($P$ is the total plasma pressure), a case which is of operational interest in magnetic confinement systems, the existence of perpendicular NEPs depends on $e_\nu E$, where $e_\nu$ is the charge of the particle species $\nu$. In this case the electric field can reduce the NEPs activity in the edge region of tokamaklike and stellaratorlike equilibria with identical parabolic pressure profiles, the reduction of electron NEPs being more pronounced than that of ion NEPs.Comment: 30 pages, late

Negative-Energy Perturbations in Circularly Cylindrical Equilibria within the Framework of Maxwell-Drift Kinetic Theory

The conditions for the existence of negative-energy perturbations (which could be nonlinearly unstable and cause anomalous transport) are investigated in the framework of linearized collisionless Maxwell-drift kinetic theory for the case of equilibria of magnetically confined, circularly cylindrical plasmas and vanishing initial field perturbations. For wave vectors with a non-vanishing component parallel to the magnetic field, the plane equilibrium conditions (derived by Throumoulopoulos and Pfirsch [Phys Rev. E {\bf 49}, 3290 (1994)]) are shown to remain valid, while the condition for perpendicular perturbations (which are found to be the most important modes) is modified. Consequently, besides the tokamak equilibrium regime in which the existence of negative-energy perturbations is related to the threshold value of 2/3 of the quantity $\eta_\nu = \frac {\partial \ln T_\nu} {\partial \ln N_\nu}$, a new regime appears, not present in plane equilibria, in which negative-energy perturbations exist for {\em any} value of $\eta_\nu$. For various analytic cold-ion tokamak equilibria a substantial fraction of thermal electrons are associated with negative-energy perturbations (active particles). In particular, for linearly stable equilibria of a paramagnetic plasma with flat electron temperature profile ($\eta_e=0$), the entire velocity space is occupied by active electrons. The part of the velocity space occupied by active particles increases from the center to the plasma edge and is larger in a paramagnetic plasma than in a diamagnetic plasma with the same pressure profile. It is also shown that, unlike in plane equilibria, negative-energy perturbations exist in force-free reversed-field pinch equilibria with a substantial fraction of active particles.Comment: 31 pages, late

Fluorescence activated cell sorting followed by small RNA sequencing reveals stable microRNA expression during cell cycle progression.

BACKGROUND: Previously, drug-based synchronization procedures were used for characterizing the cell cycle dependent transcriptional program. However, these synchronization methods result in growth imbalance and alteration of the cell cycle machinery. DNA content-based fluorescence activated cell sorting (FACS) is able to sort the different cell cycle phases without perturbing the cell cycle. MiRNAs are key transcriptional regulators of the cell cycle, however, their expression dynamics during cell cycle has not been explored. METHODS: Following an optimized FACS, a complex initiative of high throughput platforms (microarray, Taqman Low Density Array, small RNA sequencing) were performed to study gene and miRNA expression profiles of cell cycle sorted human cells originating from different tissues. Validation of high throughput data was performed using quantitative real time PCR. Protein expression was detected by Western blot. Complex statistics and pathway analysis were also applied. RESULTS: Beyond confirming the previously described cell cycle transcriptional program, cell cycle dependently expressed genes showed a higher expression independently from the cell cycle phase and a lower amplitude of dynamic changes in cancer cells as compared to untransformed fibroblasts. Contrary to mRNA changes, miRNA expression was stable throughout the cell cycle. CONCLUSIONS: Cell cycle sorting is a synchronization-free method for the proper analysis of cell cycle dynamics. Altered dynamic expression of universal cell cycle genes in cancer cells reflects the transformed cell cycle machinery. Stable miRNA expression during cell cycle progression may suggest that dynamical miRNA-dependent regulation may be of less importance in short term regulations during the cell cycle

Application of Recursive Adaptive Algorithms for System Identification and Vibration Control.

This paper describes advances in the identification and control of flexible structures by consequent application of recursive adaptive algorithms on controllers with load path-considering design.Control of large structures requires powerful algorithms that are able to influence certain modes of a system with high modal densities. The stability of the adaptation process must be maintained. This paper describes theoretical and experimental investigations within the framework of the DLR program ARES (Actively Reacting Flexible Structures), showing the performance of the modal controllers that are based on recursive digital filters

Application of Recursive Adaptive Algorithms for System Identification and Vibration Control.

This paper describes advances in the identification and control of flexible structures by consequent application of recursive adaptive algorithms on controllers with load path-considering design. Control of large structures requires powerful algorithms that are able to influence certain modes of a system with high modal densities. The stability of the adaptation process must be maintained. This paper describes theoretical and simulational investigations within the framework of the DLR program ARES (:hp2.A:ehp.ctively: hp2.Re:ehp.acting Flexible: hp2.S:ehp.tructures)showing the performance of the modal controllers that are based on recursive digital filters

Modern Adaptive Real-Time Controllers for Actively Reacting Flexible Structures.

This paper describes modern controllers which are based on digital real-time filters, powerful adaptation algorithms and high speed signal processor systems. Such controllers are required for active shape and vibration control on large flexible space structures. Within the framework of the DLR program ARES (Actively Reacting Flexible Structures) - which is an attempt to develop systems capable of changing their characteristics in orbit in order to fulfil essential operational requirements, efforts are specially focused on adaptive signal processing. The hitherto achieved results are presented. The philosophy and capabilities of such controllers are demonstrated, referring to the process of adaptive system identification and inverse modeling. In addition, different types of filtering techniques and adaptation algorithms are theoretically and experimentally discussed concerning structural dynamic requirements

The Challenge of Adaptive Structures.

Future lightweight design in space structure technology has to pay more attention to vibration suppression, to position control, or, more generally, to structure-inherent adaptability. These properties are often called "intelligent" or "smart", ignoring the fact that only creatures can have mental abilities. Having adaptation mechanisms for every dynamic process, living nature indeed teaches us that it is inexpedient if technical structural systems dispense with adaptability. Vibration and stability phenomena are making performance restrictions in space systems more and more evident. The DLR project ARES (Actively Reacting Flexible Structures) intends to overcome these limitations by developing a new class of technical systems. The ARES concept essentially consists of two new technologies: new kinds of integrated sensors and actuators working as components lying in the structural load path, and adaptive controllers consisting of digital filters which are adptive in that they react against changing environmental influences as well as changes within the structure itself