scholarly journals High-frequency Magnetic Fluctuations in Space Plasmas and the Role of Electron Landau Damping

2022 ◽  
Vol 924 (2) ◽  
pp. L26
Author(s):  
Vincenzo Carbone ◽  
Daniele Telloni ◽  
Fabio Lepreti ◽  
Antonio Vecchio
Keyword(s):  
High Frequency ◽  
Interplanetary Space ◽  
Magnetic Energy ◽  
Low Frequency ◽  
Theoretical Models ◽  
Landau Damping ◽  
Magnetic Fluctuations ◽  
Frequency Plasma ◽  
New Framework

Abstract While low-frequency plasma fluctuations in the interplanetary space have been successfully described in the framework of classical turbulence, high-frequency fluctuations still represent a challenge for theoretical models. At these scales, kinetic plasma processes are at work, but although some of them have been identified in spacecraft measurements, their global effects on observable quantities are sometimes not fully understood. In this paper we present a new framework to the aim of describing the observed magnetic energy spectrum and directly identify in the data the presence of Landau damping as the main collisionless dissipative process in the solar wind.

scholarly journals On the Origin of High–Frequency Magnetic Fluctuations in the Interplanetary Medium: A Brownian–like Approach

2021 ◽  
Vol 9 ◽  
Author(s):  
Vincenzo Carbone ◽  
Fabio Lepreti ◽  
Antonio Vecchio ◽  
Tommaso Alberti ◽  
Federica Chiappetta
Keyword(s):  
High Frequency ◽  
Interplanetary Medium ◽  
Interplanetary Space ◽  
Plasma Heating ◽  
Low Frequency ◽  
Solar Wind Plasma ◽  
Magnetic Fluctuations ◽  
Fluctuation Dissipation ◽  
Frequency Fluctuations ◽  
Collisionless Dissipation

Low–frequency fluctuations in the interplanetary medium have been extensively investigated and described in the framework of turbulence, and the observed universal scaling behavior represents a clear signature of the underlying energy cascade. On the contrary, the interpretation of observations of plasma fluctuations at high frequencies, where wave–wave coupling, collisionless dissipation, and anomalous plasma heating play a key role, still represents a challenge for theoretical modeling. In this paper the high frequency fluctuations occurring in the interplanetary space are described through a Brownian–like approach, where the plasma dynamics at small scales is described through a stochastic process. It is shown that a simple model based on this framework is able to successfully reproduce the main features of the spectrum of the observed magnetic fluctuations. Moreover, the Fluctuation-Dissipation Relation, derived by our model, leads to a power law between dissipation rate and temperature, which is compatible with the occurrence of Landau damping, interpreted thus as the main mechanism of dissipation in the solar wind plasma.

Calculation-and-experimental estimation of the role of the frequency ratio in changing the endurance at two-frequency deformation modes

2019 ◽  
Vol 85 (1(I)) ◽  
pp. 64-71 ◽  
Author(s):  
M. M. Gadenin
Keyword(s):  
High Frequency ◽  
Experimental Studies ◽  
Low Frequency ◽  
Reduction Factor ◽  
Single Frequency ◽  
Cyclic Loads ◽  
Small Ratio ◽  
Harmonic Components ◽  
Deformation Modes

The cycle configuration at two-frequency loading regimes depends on the number of parameters including the absolute values of the frequencies and amplitudes of the low-frequency and high-frequency loads added during this mode, the ratio of their frequencies and amplitudes, as well as the phase shift between these harmonic components, the latter having a significant effect only with a small ratio of frequencies. Presence of such two-frequency regimes or service loading conditions for parts of machines and structures schematized by them can significantly reduce their endurance. Using the results of experimental studies of changes in the endurance of a two-frequency loading of specimens of cyclically stable, cyclically softened and cyclically hardened steels under rigid conditions we have shown that decrease in the endurance under the aforementioned conditions depends on the ratio of frequencies and amplitudes of operation low-frequency low-cycle and high-frequency vibration stresses, and, moreover, the higher the level of the ratios of amplitudes and frequencies of those stacked harmonic processes of loading the greater the effect. It is shown that estimation of such a decrease in the endurance compared to a single frequency loading equal in the total stress (strains) amplitudes can be carried out using an exponential expression coupling those endurances through a parameter (reduction factor) containing the ratio of frequencies and amplitudes of operation cyclic loads and characteristic of the material. The reduction is illustrated by a set of calculation-experimental curves on the corresponding diagrams for each of the considered types of materials and compared with the experimental data.

scholarly journals The Influence ofNrf2on Cardiac Responses to Environmental Stressors

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Reuben Howden ◽  
Eva Gougian ◽  
Marcus Lawrence ◽  
Samantha Cividanes ◽  
Wesley Gladwell ◽  
...  
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
High Frequency ◽  
Low Frequency ◽  
Therapeutic Strategies ◽  
Environmental Stressors ◽  
Total Power ◽  
Airborne Pollutants ◽  
Cardiac Responses

Nrf2protects the lung from adverse responses to oxidants, including 100% oxygen (hyperoxia) and airborne pollutants like particulate matter (PM) exposure, but the role ofNrf2on heart rate (HR) and heart rate variability (HRV) responses is not known. We hypothesized that genetic disruption ofNrf2would exacerbate murine HR and HRV responses to severe hyperoxia or moderate PM exposures.Nrf2-/-andNrf2+/+mice were instrumented for continuous ECG recording to calculate HR and HRV (low frequency (LF), high frequency (HF), and total power (TP)). Mice were then either exposed to hyperoxia for up to 72 hrs or aspirated with ultrafine PM (UF-PM). Compared to respective controls, UF-PM induced significantly greater effects on HR (P<0.001) and HF HRV (P<0.001) inNrf2-/-mice compared toNrf2+/+mice.Nrf2-/-mice tolerated hyperoxia significantly less thanNrf2+/+mice (~22 hrs;P<0.001). Reductions in HR, LF, HF, and TP HRV were also significantly greater inNrf2-/-compared toNrf2+/+mice (P<0.01). Results demonstrate thatNrf2deletion increases susceptibility to change in HR and HRV responses to environmental stressors and suggest potential therapeutic strategies to prevent cardiovascular alterations.

scholarly journals Peranan Lingkungan Sosial terhadap Pembentukan Karakter Peduli Lingkungan Mahasiswa Pendidikan Geografi di Universitas Samudra Langsa

2018 ◽  
Vol 10 (2) ◽  
pp. 235
Author(s):  
Fitria Mustika ◽  
Tengku Muhammad Sahudra
Keyword(s):  
Family Environment ◽  
High Frequency ◽  
Low Frequency ◽  
Measurement Scale ◽  
Education Student ◽  
Achievement Level ◽  
Very High Frequency ◽  
Environmental Care ◽  
The Family

This study aims to determine the role of the family, community, and tertiary environment towards the formation of caring character in the geography education student environment. The output of this study was a four-indexed indexed education journal and a UNIMED google scolar. Samples from the study population were 20 respondents with 30 items about questionnaires. The time of the study starts from May 2018 to October 2018. The measurement scale in this study is the scale of the briquette. Data collection by means of library studies, interviews, questionnaires, and documentation. This research was conducted by distributing questionnaire questionnaires and interviews. Based on the results of questionnaire data processing, the family environment has a very high frequency in the formation of character of the student's environmental care with an achievement level of a total score of 91%. Furthermore, the role of the campus environment also has a high frequency in the formation of the character of the student's environmental care with a total score of 89%. Whereas the family environment has a low frequency in the formation of character of student environmental care with a total score of 57%. It can be concluded that the family environment has the most role in forming the character of the student's environmental care.

Role of fascia in maintenance of muscle tension and pressure

1981 ◽  
Vol 51 (2) ◽  
pp. 317-320 ◽  
Author(s):  
S. R. Garfin ◽  
C. M. Tipton ◽  
S. J. Mubarak ◽  
S. L. Woo ◽  
A. R. Hargens ◽  
...  
Keyword(s):  
High Frequency ◽  
Muscle Tension ◽  
Fluid Pressure ◽  
Low Frequency ◽  
Testing Procedure ◽  
Force Transducer ◽  
High Frequency Stimulation ◽  
Low Frequency Stimulation ◽  
Frequency Stimulation

The effect of fasciotomy on muscle tension (measured by a force transducer attached to the tendon) and interstitial fluid pressure (measured by Wick catheters in the muscle belly) was studied in the anterolateral compartments of 13 dog hindlimbs. Muscle tension and pressure were monitored in the tibialis cranialis muscle after low- and high-frequency stimulation of the peroneal nerve to produce twitch- and tetanic-type contractions. Fasciotomy decreased muscle force during the low-frequency stimulation by 16% (35.3 +/- 4.9 to 28.4 +/- 3.9 N) and during the high-frequency stimulation by 10% (60.8 %/- 4.9 to 54.8 +/- 3.9 N). Muscle pressure decreased 50% after fasciotomy under both conditions, 15 +/- 2 to 6 +/- 1 mmHg and 84 +/- 17 to 41 +/- 8 mmHg), respectively. Repeated functional evaluations during the testing procedure indicated that muscle fatigue was not a major factor in these results. It was concluded that fascia is important in the development of muscle tension and changes in interstitial pressure. Furthermore, the results raised questions concerning the merits of performing a fasciotomy for athletes with a compartment syndrome.

Role of Dominance Status in Shock-Stimulated Agonistic Behavior

1971 ◽  
Vol 29 (3) ◽  
pp. 768-770 ◽  
Author(s):  
G. McA. Kimbrell ◽  
D. Chesler
Keyword(s):  
High Frequency ◽  
Agonistic Behavior ◽  
Defensive Behavior ◽  
Low Frequency ◽  
Behavior Patterns ◽  
Dominance Status ◽  
Very Low Frequency ◽  
The Relationship ◽  
Shock Situation

To clarify the relationship between dominance status and frequency of specific sub-classes of agonistic behavior in response to foot shock, 30 mice were selected on the basis of high- or low-dominance status and paired in a foot-shock situation. Dominant pairs exhibit a high frequency of defensive behavior patterns whereas submissive pairs exhibit a very low frequency of defensive patterns.

scholarly journals A Facile, Low-Cost Plasma Etching Method for Achieving Size Controlled Non-Close-Packed Monolayer Arrays of Polystyrene Nano-Spheres

Nanomaterials ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 605 ◽  
Author(s):  
Yun Chen ◽  
Dachuang Shi ◽  
Yanhui Chen ◽  
Xun Chen ◽  
Jian Gao ◽  
...  
Keyword(s):  
Plasma Etching ◽  
Silicon Nanowires ◽  
High Frequency ◽  
Low Cost ◽  
Etching Rate ◽  
Low Frequency ◽  
Etching Time ◽  
High Frequency Plasma ◽  
Frequency Plasma ◽  
Etching System

Monolayer nano-sphere arrays attract great research interest as they can be used as templates to fabricate various nano-structures. Plasma etching, and in particular high-frequency plasma etching, is the most commonly used method to obtain non-close-packed monolayer arrays. However, the method is still limited in terms of cost and efficiency. In this study, we demonstrate that a low frequency (40 kHz) plasma etching system can be used to fabricate non-close-packed monolayer arrays of polystyrene (PS) nano-spheres with smooth surfaces and that the etching rate is nearly doubled compared to that of the high-frequency systems. The study reveals that the low-frequency plasma etching process is dominated by a thermal evaporation etching mechanism, which is different from the atom-scale dissociation mechanism that underlines the high-frequency plasma etching. It is found that the polystyrene nano-sphere size can be precisely controlled by either adjusting the etching time or power. Through introducing oxygen as the assisting gas in the low frequency plasma etching system, we achieved a coalesced polystyrene nano-sphere array and used it as a template for metal-assisted chemical etching. We demonstrate that the method can significantly improve the aspect ratio of the silicon nanowires to over 200 due to the improved flexure rigidity.

scholarly journals Timbre and Affect Dimensions: Evidence from Affect and Similarity Ratings and Acoustic Correlates of Isolated Instrument Sounds

2012 ◽  
Vol 30 (1) ◽  
pp. 49-70 ◽  
Author(s):  
Tuomas Eerola ◽  
Rafael Ferrer ◽  
Vinoo Alluri
Keyword(s):  
High Frequency ◽  
Sound Production ◽  
Three Dimensional ◽  
Low Frequency ◽  
Structural Features ◽  
Two Dimensions ◽  
Acoustic Features ◽  
Behavioral Experiments ◽  
Acoustic Correlates

considerable effort has been made towards understanding how acoustic and structural features contribute to emotional expression in music, but relatively little attention has been paid to the role of timbre in this process. Our aim was to investigate the role of timbre in the perception of affect dimensions in isolated musical sounds, by way of three behavioral experiments. In Experiment 1, participants evaluated perceived affects of 110 instrument sounds that were equal in duration, pitch, and dynamics using a three-dimensional affect model (valence, energy arousal, and tension arousal) and preference and emotional intensity. In Experiment 2, an emotional dissimilarity task was applied to a subset of the instrument sounds used in Experiment 1 to better reveal the underlying affect structure. In Experiment 3, the perceived affect dimensions as well as preference and intensity of a new set of 105 instrument sounds were rated by participants. These sounds were also uniform in pitch, duration, and playback dynamics but contained systematic manipulations in the dynamics of sound production, articulation, and ratio of high-frequency to low-frequency energy. The affect dimensions for all the experiments were then explained in terms of the three kinds of acoustic features extracted: spectral (e.g., ratio of high-frequency to low-frequency energy), temporal (e.g., attack slope), and spectro-temporal (e.g., spectral flux). High agreement among the participants' ratings across the experiments suggested that even isolated instrument sounds contain cues that indicate affective expression, and these are recognized as such by the listeners. A dominant portion (50-57%) of the two dimensions of affect (valence and energy arousal) could be predicted by linear combinations of few acoustic features such as ratio of high-frequency to low-frequency energy, attack slope, and spectral regularity. Links between these features and those observed in the vocal expression of affects and other sound phenomena are discussed.

Modeling of Perforated Screens or Membrane Using Rigid Frame Porous Models Combined with Thin Membrane Resonance Sound Absorbing Theory

2013 ◽  
Vol 357-360 ◽  
pp. 1206-1211
Author(s):  
Xiao Ling Gai ◽  
Xian Hui Li ◽  
Bin Zhang ◽  
Peng Xie ◽  
Zhi Hui Ma
Keyword(s):  
High Frequency ◽  
Sound Absorption ◽  
Mass Density ◽  
Low Frequency ◽  
Frequency Region ◽  
Thin Membrane ◽  
High Frequency Region ◽  
Rigid Frame ◽  
Membrane Resonance

The sound absorption ability of screen or perforated membrane is studied based on rigid frame porous models combined with thin membrane resonance sound absorbing theory in this paper. Results show that the sound absorption of screen or perforated membrane is better considering the role of membrane than using the rigid frame porous models when the mass density of screen or perforated membrane is smaller. The rigid frame porous model is very accuracy to model the sound absorption ability of screen or perforated membrane when the mass density of membrane is greater. The parameter studies present that the sound absorption peaks move toward low frequency region with the increasing of the depth of air-back cavity, mass density and thickness of screens or perforated membrane and moves toward high frequency region with the increasing of the perforation and perforated radius of screens or perforated membrane when other parameters keep invariant.

scholarly journals Low-frequency vibrational modes in G-quadruplexes reveal the mechanical properties of nucleic acids

2020 ◽  
Author(s):  
M. González-Jiménez ◽  
G. Ramakrishnan ◽  
K. Wynne
Keyword(s):  
Protein Interactions ◽  
Kerr Effect ◽  
Biological Function ◽  
Low Frequency ◽  
Theoretical Models ◽  
Protein Recognition ◽  
Optical Kerr Effect ◽  
Vibrational Modes ◽  
New Perspective

AbstractLow-frequency vibrations play an essential role in biomolecular processes involving DNA such as gene expression, charge transfer, drug intercalation, and DNA–protein recognition. However, understanding of the vibrational basis of these mechanisms relies on theoretical models due to the lack of experimental evidence. Here we present the low-frequency vibrational spectra of G-quadruplexes (structures formed by four strands of DNA) and B-DNA characterized using femtosecond optical Kerr-effect spectroscopy. Contrary to expectation, we found that G-quadruplexes show several strongly underdamped delocalized phonon-like modes that have the potential to contribute to the biology of the DNA at the atomic level. In addition, G-quadruplexes present modes at a higher frequency than B-DNA demonstrating that changes in the stiffness of the molecule alter its gigahertz to terahertz vibrational profile. These results demonstrate that current theoretical models fail to predict basic properties of the vibrational modes of DNA.Statement of significanceA number of recent studies have identified thermally excited low-frequency vibrational modes as a key deciding factor in the biological function of DNA. However, the nature of these vibrational modes has never been established. Here, vibrational spectroscopy with unrivalled signal-to-noise in the gigahertz to terahertz range is used to determine the low-frequency Raman spectra of nucleotides and oligomeric DNAs carefully chosen to form G-quadruplexes, structures formed by four strands of DNA common in the genome. These G-quadruplexes exhibit an unusual group of highly-underdamped delocalized vibrational modes—not reproduced by any of the theoretical models in use—which are expected to be the thermally excited. This provides a new perspective on the role of low-frequency vibrational modes in protein interactions and allostery.

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