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Auswahl der wissenschaftlichen Literatur zum Thema „Passive frequency crossover“
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Zeitschriftenartikel zum Thema "Passive frequency crossover"
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Panza, Gino, Justin Stadler, Donal Murray, Nicholas Lerma, Tomas Barrett, Ryan Pettit-Mee und Jeffrey E. Edwards. „Acute Passive Static Stretching and Cramp Threshold Frequency“. Journal of Athletic Training 52, Nr. 10 (01.10.2017): 918–24. http://dx.doi.org/10.4085/1062-6050-52.7.03.
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Context: Exercise-associated muscle cramps are a common clinical problem for athletes. Objective: To determine whether acute passive static stretching altered cramp threshold frequency (CTF) of electrically induced muscle cramps. Design: Crossover study. Setting: Laboratory. Patients or Other Participants: Seventeen healthy college-aged individuals. Intervention(s): Stretching or no stretching. Main Outcome Measure(s): The independent variable was the static stretch versus the no-stretch condition, and the dependent variable was the CTF. Results: The CTF increased in both the control (pretest: 18.12 ± 6.46 Hz, posttest: 19.65 ± 7.25 Hz; P = .033) and stretching (pretest: 18.94 ± 5.96 Hz, posttest: 20.47 ± 7.12 Hz; P = .049) groups. No difference between the groups was found (t15 = 0.035, P = .97). Conclusions: Acute passive static stretching did not seem to increase the CTF.
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McPherson, Trevor, Dorita Berger, Sankaraleengam Alagapan und Flavio Fröhlich. „Active and Passive Rhythmic Music Therapy Interventions Differentially Modulate Sympathetic Autonomic Nervous System Activity“. Journal of Music Therapy 56, Nr. 3 (2019): 240–64. http://dx.doi.org/10.1093/jmt/thz007.
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Abstract Dysregulation of the autonomic nervous system (ANS) and the hypothalamic–pituitary–adrenal (HPA) axis has been implicated in psychiatric disorders. Music therapy (MT) has been shown to modulate heart-rate variability (HRV) and salivary stress markers, physiological markers of the ANS and HPA axes, respectively. Given the prominent role of arousal and stress physiology in many psychiatric disorders, MT has the potential to provide therapeutic benefits in psychiatry. Active MT requires patients to engage rhythmically with music; in contrast, passive MT requires patients to listen to music, eliminating the rhythmic movement seen in active MT. Yet, it remains unknown whether active or passive MT differentially modulates arousal and stress physiology. We contrasted the effects of active and passive MT experiences to examine the differential impact of rhythmic movement on the ANS and HPA axes in healthy participants. Individuals (N = 16) participated in a crossover study of 40 min of an active MT and a passive MT intervention. HRV recordings and saliva samples were collected both before and after each intervention. The high-frequency component (HF) and the ratio of low-frequency to high-frequency components (LF/HF) were calculated as cardiac markers of parasympathetic and sympathetic ANS activation, respectively. Saliva samples were analyzed for alpha-amylase and cortisol, markers of the sympathetic ANS and HPA axes, respectively. Active MT and passive MT interventions differentially modulated LF/HF, where active MT decreased LF/HF and passive MT increased LF/HF. These results indicate that MT affects the ANS and suggests that differences in engagement between active MT and passive MT lead to a differential modulation of the sympathetic ANS.
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Xu, L. M., N. Guo, S. Zeng, R. M. Lin und H. Du. „Dynamics and control performance of hard disk drives with passive dampers“. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 218, Nr. 12 (01.12.2004): 1555–68. http://dx.doi.org/10.1243/0954406042690452.
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The residual vibration is one of the primary mechanical problems that affect the dynamic characteristics of the head actuator assembly in hard disk drives, and the data access speed and positioning resolution. A discrete damping device has been developed to suppress the quasi-rigid-body mode and a reduction of 10 dB in amplitude is shown possible. The servo performance of the head actuator assembly with and without the damping device is presented in this paper, together with the measurement and prediction of the dynamic characteristics. Both closed- and open-loop transfer functions of the plant are measured in the actual operating environment on a servo test stand and compared with the simulation. It is found that the use of passive damping in the structure design allows for a greater margin of error at the crossover frequency since less phase loss results when notch filters are used, thus improving the stability robustness in feedback control.
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Quenzer-Hohmuth, Samuel, Thoralf Rosahl, Steffen Ritzmann und Bernhard Wicht. „Challenges and implementation aspects of switched-mode power supplies with digital control for automotive applications“. Advances in Radio Science 14 (28.09.2016): 85–90. http://dx.doi.org/10.5194/ars-14-85-2016.
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Abstract. Switched-mode power supplies (SMPS) convert an input DC-voltage into a higher or lower output voltage. In automotive, analog control is mostly used in order to keep the required output voltages constant and resistant to disturbances. The design of robust analog control for SMPS faces parameter variations of integrated and external passive components. Using digital control, parameter variations can be eliminated and the required area for the integrated circuit can be reduced at the same time. Digital control design bears challenges like the prevention of limit cycle oscillations and controller-wind-up. This paper reviews how to prevent these effects. Digital control loops introduce new sources for dead times in the control loop, for example the latency of the analog-to-digital-converter (ADC). Dead times have negative influence on the stability of the control loop, because they lead to phase delays. Consequently, low latency is one of the key requirements for analog-to-digital-converters in digitally controlled SMPS. Exploiting the example of a 500 kHz-buck converter with a crossover frequency of 70 kHz, this paper shows that the 5 µs-latency of a ΔΣ-analog-to-digital-converter leads to a reduction in phase margin of 126°. The latency is less critical for boost converters because of their inherent lower crossover frequencies. Finally, the paper shows a comparison between analog and digital control of SMPS with regard to chip area and test costs.
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Li, Li, Barbara T. Sweet und Leland S. Stone. „Effect of Contrast on the Active Control of a Moving Line“. Journal of Neurophysiology 93, Nr. 5 (Mai 2005): 2873–86. http://dx.doi.org/10.1152/jn.00200.2004.
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In many passive visual tasks, human perceptual judgments are contrast dependent. To explore whether these contrast dependencies of visual perception also affect closed-loop manual control tasks, we examined visuomotor performance as humans actively controlled a moving luminance-defined line over a range of contrasts. Four subjects were asked to use a joystick to keep a horizontal line centered on a display as its vertical position was perturbed by a sum of sinusoids under two control regimes. The total root mean square (RMS) position error decreased quasi-linearly with increasing log contrast across the tested range (mean slope across subjects: −8.0 and −7.7% per log2 contrast, for the two control regimes, respectively). Frequency–response (Bode) plots showed a systematic increase in open-loop gain (mean slope: 1.44 and 1.30 dB per log2 contrast, respectively), and decrease in phase lag with increasing contrast, which can be accounted for by a decrease in response time delay (mean slope: 32 and 40 ms per log2 contrast, respectively). The performance data are well fit by a Crossover Model proposed by McRuer and Krendel, which allowed us to identify both visual position and motion cues driving performance. This analysis revealed that the position and motion cues used to support manual control under both control regimes appear equally sensitive to changes in stimulus contrast. In conclusion, our data show that active control of a moving visual stimulus is as dependent on contrast as passive perception and suggest that this effect is attributed to a shared contrast sensitivity early in the visual pathway, before any specialization for motion processing.
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Mohdami Norashid, Muhammad Adib Akram, und M. Kamil Abd-Rahman. „Non-Resonance Acousto-Optics Signal Analysis from Photonics Microphone Using 1 mW Laser“. Materials Science Forum 846 (März 2016): 740–47. http://dx.doi.org/10.4028/www.scientific.net/msf.846.740.
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This paper presents an acousto-optics analysis on free space optical signals modulated by two distinguishable non-resonant acoustic waves. The acoustic waves were directed at two different directions and locations along a laser beam and created non-interference modulated optical signals. The photonics microphone deploys low-powered eye-safe continuous-wave 633-nm laser; high-speed photodiode and a series of Fourier lenses. Two transducers generating 20 Hz to 20 kHz acoustic waves were directed across the laser beam. The receiving modulated signal was filtered and amplified electronically by two sets of passive bandpass filter separated by a transimpedance amplifier and connected to a computer for analysis. The signal was further digitally filtered and amplified to enhance the signal-to-noise ratio via MATLAB software. These signals were analyzed in time and frequency domains using Fast Fourier Transform (FFT) and Spectrogram. It was found that the recorded signals demonstrated higher signal intensities for lower acoustic frequencies with digital signal-to-noise ratio (SNR) ranging from 10.77 to 71.92 for frequency of 1 kHz to 20 kHz and 20 Hz to 1 kHz respectively. The frequencies of both transducers were simultaneously swept through from 20 Hz and 20 kHz respectively. These scanning frequencies approached one another and crossover with no resonant frequency was observed. This illustrates that it is able to detect multiple acoustic signals for any given frequencies along the laser beam and found its applications in stealth sound detection and long range sound sensor. Though low-powered 1-mW laser was used, a relatively high signal-to-noise ratio with clear-recorded playback was achieved.
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Krug, Annemarie, Corinne Cannavale, Naiman Khan und Hannah Holscher. „Prebiotics Affect the Fecal Microbiota and Gastrointestinal Health of Adults Participating in a Randomized, Double-Blind, Placebo-Controlled, Crossover Trial“. Current Developments in Nutrition 4, Supplement_2 (29.05.2020): 1570. http://dx.doi.org/10.1093/cdn/nzaa062_027.
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Abstract Objectives Prebiotics are defined as substrates that are selectively utilized by host microorganisms conferring a health benefit. We aimed to determine the effects of the prebiotics fructooligosaccharides (FOS) and galactooligosaccharides (GOS) on the fecal microbiota and gastrointestinal health in adults. Methods We conducted a randomized, double-blind, placebo-controlled, crossover trial in healthy adults (n = 26) 25–45 years of age. Participants consumed two 4-week treatments in a randomized, counterbalanced order. The prebiotic beverage (PRE) was 8 oz low-fat lactose-free milk with 5 g FOS and 5 g GOS. The control beverage (CON) was 8 oz low-fat lactose-free milk without the added prebiotics. Each condition was separated by a 4-week washout. Fecal samples were collected at baseline and end of each condition. Fecal short-chain fatty acid (SCFA) concentrations were quantified using gas chromatography-mass spectrometry (GC-MS). Fecal pH was measured using a pH meter. Gastrointestinal health was assessed using the Bristol stool scale and a stool frequency and ease of passage log before the first and during the last week of each condition. SAS 9.4 was used to conduct general linear mixed modeling with treatment as a fixed effect and participant and period as random effects. Normality was assessed using the Shapiro-Wilk test and log and arcsine transformations were applied as needed. Results There was a 153% increase in fecal bifidobacteria relative abundances in the prebiotic group compared to control (CON: 2.8 ± 0.6, PRE: 6.9 ± 1.7; P = 0.002). No differences were detected between the groups in fecal acetate (CON: 278 ± 30.1, PRE: 231 ± 24.4; P = 0.2), butyrate (CON: 68.4 ± 10.1, PRE: 62.9 ± 12.2; P = 0.4), or propionate (CON: 76.5 ± 7.5, PRE: 76.7 ± 12.5; P = 0.4) concentrations, or fecal pH (CON: 6.86 ± 0.10, PRE: 6.91 ± 0.14; P = 0.5). Stool frequency (stool/day) increased by 26% in PRE compared to CON (CON: 1.0 ± 0.1, PRE: 1.3 ± 0.1; P = 0.01). Ease of stool passage tended to improve in PRE compared to CON (CON: 2.2 ± 0.1, PRE: 2.0 ± 0.1; P = 0.1). There was no difference in stool consistency (CON: 3.7 ± 0.3, PRE: 3.7 ± 0.2; P = 0.8). Conclusions These findings are suggestive of the beneficial health effects of consumption of the prebiotics FOS and GOS on gastrointestinal health in adults. Funding Sources USDA National Institute of Food and Agriculture, Hatch Project 1009249.
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Bundy, Emily L., und David J. Zajac. „Estimation of Transpalatal Nasalance during Production of Voiced Stop Consonants by Noncleft Speakers Using an Oral-Nasal Mask“. Cleft Palate-Craniofacial Journal 43, Nr. 6 (November 2006): 691–701. http://dx.doi.org/10.1597/04-103.
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Objective: Our objective was to estimate nasalance due to transpalatal transfer of acoustic energy during production of voiced stop consonants by noncleft speakers. We also determined the relationship between the transpalatal nasalance and fundamental frequency (F0) of the speakers. Method: Participants were 8 men and 10 women (mean age = 21.9 years, SD = 4.0) without cleft palate who produced voiced stop (/b d g/) and nasal (/m n η/) consonants in syllables embedded in a carrier phrase. Participants also read the Zoo Passage. A divided OroNasal Nasality System mask was used to simultaneously obtain acoustic nasalance and airflow during production of the consonants. Both F0-derived and first formant (F1)–derived nasalance were computed. Results: F0-derived and F1-derived peak nasalance across all speakers ranged from a low of 20% to a high of 80% during production of stop consonants. An estimate of error from the combined sources of transoral transfer of energy (5%) and acoustic crossover between microphones (15%) was no greater than 20%. Analysis of variance revealed no significant effects of the sex of the speakers for either F0-derived or F1-derived nasalance of stops. There was a significant effect of the place of stop production for F0-derived nasalance (p;th< .05). Nonsignificant but positive correlations were found between the F0 of the speakers and F0-derived (r = .25) and F1-derived (r = .45) nasalance. Conclusions: Transpalatal transfer of oral acoustic energy accounts for most nasalance obtained during production of voiced stop consonants by noncleft speakers. F1-derived nasalance appears to better reflect transpalatal effects. Clinical implications are discussed.
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Taucher, Christian, Angelika Berger und Christian W. Mandl. „A trans-Complementing Recombination Trap Demonstrates a Low Propensity of Flaviviruses for Intermolecular Recombination“. Journal of Virology 84, Nr. 1 (28.10.2009): 599–611. http://dx.doi.org/10.1128/jvi.01063-09.
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ABSTRACT Intermolecular recombination between the genomes of closely related RNA viruses can result in the emergence of novel strains with altered pathogenic potential and antigenicity. Although recombination between flavivirus genomes has never been demonstrated experimentally, the potential risk of generating undesirable recombinants has nevertheless been a matter of concern and controversy with respect to the development of live flavivirus vaccines. As an experimental system for investigating the ability of flavivirus genomes to recombine, we developed a “recombination trap,” which was designed to allow the products of rare recombination events to be selected and amplified. To do this, we established reciprocal packaging systems consisting of pairs of self-replicating subgenomic RNAs (replicons) derived from tick-borne encephalitis virus (TBEV), West Nile virus (WNV), and Japanese encephalitis virus (JEV) that could complement each other in trans and thus be propagated together in cell culture over multiple passages. Any infectious viruses with intact, full-length genomes that were generated by recombination of the two replicons would be selected and enriched by end point dilution passage, as was demonstrated in a spiking experiment in which a small amount of wild-type virus was mixed with the packaged replicons. Using the recombination trap and the JEV system, we detected two aberrant recombination events, both of which yielded unnatural genomes containing duplications. Infectious clones of both of these genomes yielded viruses with impaired growth properties. Despite the fact that the replicon pairs shared approximately 600 nucleotides of identical sequence where a precise homologous crossover event would have yielded a wild-type genome, this was not observed in any of these systems, and the TBEV and WNV systems did not yield any viable recombinant genomes at all. Our results show that intergenomic recombination can occur in the structural region of flaviviruses but that its frequency appears to be very low and that therefore it probably does not represent a major risk in the use of live, attenuated flavivirus vaccines.
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Porter, Jessica L., Nicholas J. Tobias, Hui Hong, Kellie L. Tuck, Grant A. Jenkin und Timothy P. Stinear. „Transfer, stable maintenance and expression of the mycolactone polyketide megasynthase mls genes in a recombination-impaired Mycobacterium marinum“. Microbiology 155, Nr. 6 (01.06.2009): 1923–33. http://dx.doi.org/10.1099/mic.0.027029-0.
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The human pathogen Mycobacterium ulcerans produces a polyketide metabolite called mycolactone with potent immunomodulatory activity. M. ulcerans strain Agy99 has a 174 kb plasmid called pMUM001 with three large genes (mlsA1, 51 kb; mlsA2, 7.2 kb; mlsB, 43 kb) that encode type I polyketide synthases (PKS) required for the biosynthesis of mycolactone, as demonstrated by transposon mutagenesis. However, there have been no reports of transfer of the mls locus to another mycobacterium to demonstrate that these genes are sufficient for mycolactone production because in addition to their large size, the mls genes contain a high level of internal sequence repetition, such that the entire 102 kb locus is composed of only 9.5 kb of unique DNA. The combination of their large size and lack of stability during laboratory passage makes them a challenging prospect for transfer to a more rapidly growing and genetically tractable host. Here we describe the construction of two bacterial artificial chromosome Escherichia coli/Mycobacterium shuttle vectors, one based on the pMUM001 origin of replication bearing mlsB, and the other based on the mycobacteriophage L5 integrase, bearing mlsA1 and mlsA2. The combination of these two constructs permitted the two-step transfer of the entire 174 kb pMUM001 plasmid to Mycobacterium marinum, a rapidly growing non-mycolactone-producing mycobacterium that is a close genetic relative of M. ulcerans. To improve the stability of the mls locus in M. marinum, recA was inactivated by insertion of a hygromycin-resistance gene using double-crossover allelic exchange. As expected, the ΔrecA mutant displayed increased susceptibility to UV killing and a decreased frequency of homologous recombination. Southern hybridization and RT-PCR confirmed the stable transfer and expression of the mls genes in both wild-type M. marinum and the recA mutant. However, neither mycolactone nor its predicted precursor metabolites were detected in either strain. These experiments show that it is possible to successfully manipulate and stably transfer the large mls genes, but that other bacterial host factors appear to be required to facilitate mycolactone production.
Dissertationen zum Thema "Passive frequency crossover"
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Holínský, Jan. „Měření pasivních kmitočtových výhybek pro reproduktorové soustavy“. Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-442518.
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The content of the master´s thesis is to approach the issue of measuring the characteristics of passive frequency crossover. The work describes individual types of measured characteristics and their possibility of measurement. Then the work describes design of modules for measurement characteristics of passive frequency crossover (shunt, resistive load and amplifier). These modules were made and tested for its functions. For the amplifier is then made a second design for fulfilment requirements. The second version isn’t made in this work. At the end of the work was prepared the theoretical part of the laboratory task: Measurement of characteristics of passive frequency crossover, including protocol.
Konferenzberichte zum Thema "Passive frequency crossover"
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Anil, Chippa, Aparna Satheesh, Babu Santhanagopalakrishnan und Marcin Bielecki. „Bearing Housing Design for Vibration Control, Using Tilting Pad Bearings Instead of Lemon-Bore Type on a Gas Turbine“. In ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-24330.
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Abstract Heavy duty gas turbines are usually equipped with hydrodynamic bearings which are either lemon-bore or tilting pad type. Baker Hughes legacy gas turbines use these two types of bearings, and its selection is based on 1) considering pros & cons from Rotor dynamics, 2) bearing performance, 3) bearing housing stiffness, 4) vibration detection & control. Non-contact probes are used to monitor the vibrations of rotor. Majority of legacy gas turbines are not equipped with these probes. Due to this fact, over the years it resulted in non-detection of dynamics & vibration issue, which caused frequent bearing replacement. As the increase in industry demand to apply and measure vibrations using non-contact probes on bearings, an effort was made by Baker Hughes to implement these on existing fleet units. Also, in order to increase rotor dynamics stability of low-pressure rotor, to improve bearing life and performance, effort was made to replace lemon-bore bearings with tilting pad. This paper demonstrates efforts made to design the titling pad which would fit within envelop of already available bearing housing. Bearing/shaft clearance, bearing performance, modification of bearing retainer clearances are the mandatory tasks which would be dealt in this study. The swap of bearing type, and its effect on whole gas turbine rotor dynamic stability, checking the frequency crossovers with Campbell diagram would also be dealt in this paper. This paper also focuses on assessment on oil passage routing, temperature & proximity probe instrumentation routing design. Re-design is performed by analyzing various configuration, assessing different sensitivity studies & validation of modified bearing housing from structural integrity, ultimate load capability, & split plane oil leakage retention and its comparison with baseline are most important aspects of finalization of this change, which will be showcased in this paper. Instrumentation routing was a critical task when the considering bearing replacement from lemon-bore to tilting pad. As lemon-bore type bearings just have an elliptical inner surface, it’s quite easy to install the thermocouples into a simple hole. But as replacement has tilting pads, the challenge is to instrument the pads without effecting their movement and functionality. Such best practices are also dealt in this paper. Comparison of tilting-pad with lemon-bore, considering the fixed shaft diameter, the retainer outer diameter of tilting pad is higher than lemon-bore. This effect has a change in bearing seat on bearing housing, thereby reducing the effective stiffness of the housing, and the reduced split plane surface. To tackle this situation, several sensitivities were executed, by re-modifying the bolts and bolt holes on the existing housing, without modifying the housing envelop.