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At least 451 records · Page 25Linked to original sources
PubMed2004

Inverse energy transfer by near-resonant interactions with a damped-wave spectrum.

The interaction of long-wavelength anisotropic drift waves with the plasma turbulence of electron density advection is shown to produce the inverse energy transfer that condenses onto zonal modes, despite the expectation of forward transfer on the basis of nonconservation of enstrophy. Wave triads with an unstable wave and two waves of a separate, damped spectrum carry the transfer, provided they satisfy a near-resonance condition dependent on turbulence level and wave number.

Journal Article↗
PubMed2004

Thermoelastic-damping noise from sapphire mirrors in a fundamental-noise-limited interferometer.

We report the first high-precision interferometer using large sapphire mirrors, and we present the first direct, broadband measurements of the fundamental thermal noise in these mirrors. Our results agree well with the thermoelastic-damping noise predictions of Braginsky, et al. and Cerdonio et al., which have been used to predict the astrophysical reach of advanced interferometric gravitational wave detectors.

Journal Article↗
PubMed2005

Experimental evidence of reduced plasma flow damping with quasisymmetry.

Measurements of plasma flow damping have been made in the helically symmetric experiment using a biased electrode to impulsively spin the plasma. There are two time scales in the evolution of the plasma flow, for both the spin-up and relaxation. Compared to a configuration with the quasisymmetry broken, the flow in the quasisymmetric configuration rises more slowly and to a higher value at bias turn-on, and decays more slowly at bias turn-off. The decays of the flows are significantly faster than the neoclassical prediction.

Journal Article↗
PubMed2005

Single-domain wall propagation and damping mechanism during magnetic switching of bistable amorphous microwires.

The mechanism of nucleation and propagation of a single-domain wall is studied as a function of temperature in bistable Fe-based amorphous microwire with a unique simple domain structure. An extended nucleation-propagation model is proposed with a negative nucleation field. From quantitative analysis of the propagating wall characteristics, a new damping is theoretically introduced as arising from structural relaxation which dominates in the low temperature regime.

Journal Article↗
PubMed2005

Femtosecond light transmission and subradiant damping in plasmonic crystals.

We report the first observation of subradiance in plasmonic nanocrystals. Amplitude- and phase-resolved ultrafast transmission experiments directly reveal the coherent coupling between surface plasmon polaritons (SPPs) induced by periodic variations in the dielectric function. This interaction results in the formation of plasmonic band gaps and coupled SPP eigenmodes with different symmetries, as directly shown by near-field imaging. In antisymmetric modes, radiative SPP damping is strongly suppressed, increasing the SPP lifetime from 30 fs to more than 200 fs. The findings are analyzed within a coupled resonance model.

Journal Article↗
PubMed2005

Polarization-reversal-induced damping of left-hand polarized wave on electron cyclotron resonance.

The left-hand polarized wave, which has been believed not to be related to electron cyclotron resonance (ECR), is for the first time demonstrated to be damped near the ECR point in an inhomogeneously magnetized plasma as a result of the polarization reversal to the right-hand polarized wave. The polarization reversal is found to be caused by the existence of the boundary between a plasma and a vacuum region, the local point of which shifts depending on the plasma column radius. This phenomenon is quantitatively explained in terms of the dispersion relation including the effect of the radial boundary condition.

Journal Article↗
PubMed2006

Hydrodynamic damping of membrane thermal fluctuations near surfaces imaged by fluorescence interference microscopy.

Hydrodynamic coupling between closely apposed lipid bilayer membranes can substantially slow the time scale of thermal fluctuations. These effects could dominate the kinetics of macromolecular interactions at membrane interfaces, and may exert important influences over the interactions between living cells. Here, we study a reconstituted membrane system consisting of two planar bilayers with average separation distances of 30-60 nm. This spacing range is comparable to that of natural intercellular junctions. Using real-time fluorescence interference contrast imaging, spatial and temporal characteristics of the thermal fluctuation spectra are monitored simultaneously. Strong hydrodynamic damping of the fluctuation time scale is observed whereas fluctuation spatial dimensions are unaltered by proximity to another surface. These observations provide experimental confirmation of recent theoretical models.

Lipid Bilayers↗
PubMed2006

Caste-specific cytochrome P450 in the damp-wood termite Hodotermopsis sjostedti (Isoptera, Termopsidae).

Termites are eusocial insects with a well-defined caste system, which is an example of polyphenism. This polyphenism is based on hormonally controlled differential gene expression. In the damp-wood termite Hodotermopsis sjostedti, we induced differentiation into the soldier caste by using juvenile hormone analogue treatment. We then investigated specific gene expression, which appeared during the hormonal response and triggered caste differentiation, using fluorescent differential display. A candidate cDNA sequence with similarity to cytochromes P450, CYP6AM1, was characterized and its transcript shown to be repressed between 1 and 3 days after hormone treatment. CYP6AM1 was specifically expressed in the fat body of pseudergates and soldiers. The putative function of this P450 is discussed with respect to the caste differentiation system.

Amino Acid Sequence↗
PubMed1992

Cytotoxic fungal spores in the indoor atmosphere of the damp domestic environment.

Eight-three fungal isolates collected and cultured from the air spora of damp public sector Scottish housing have been screened for cytotoxic properties. A bioassay procedure has been utilised for this purpose involving cytotoxic effects on human embryonic diploid fibroblast lung cells grown as monolayer cultures within the wells of microtitre plates. The MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] biochemical assay system employed has revealed that 39 (47%) of the moulds investigated possessed spore-associated cytotoxic properties; a value which emphasises the potential health hazards of the continual inhalation of toxigenic fungal propagules by occupants of mouldy houses. Penicillia, the most prevalent fungi found in the internal atmosphere of the domestic environment, accounted for the great majority of cytotoxic strains identified.

Air Microbiology↗
PubMed2006

Resonance frequency analysis and damping capacity assessment. Part 2: peri-implant bone loss follow-up. An in vitro study with the Periotest and Osstell instruments.

OBJECTIVE: We compared the performance of damping capacity assessment (Periotest device) to resonance frequency analysis (Osstell device) in the assessment of peri-implant bone loss in an in vitro experiment. MATERIAL AND METHODS: Screw-type oral implants were polymerized into acrylic blocks. Peri-implant bone loss was simulated by successively removing defined portions of material surrounding the implants in millimeter increments. Measurement values of both devices were compared by assessing the associated measurement errors, by calculating correlation analyses and drawing scatterplots, and by means of regression analysis referring to increasing bone loss. RESULTS: Both devices produced comparable results suggesting agreement of the measured implant stability values to the actual loss of peri-implant resin. There was a noticeable correlation of the Periotest and Osstell implant stability values. CONCLUSION: The results of this experiment suggest agreement in predicting the actual implant stability with both the instruments with the Osstell instrument being the more precise device.

Acrylic Resins↗
PubMed1995

The influence of splinting procedures on the periodontal and peri-implant tissue damping characteristics. A longitudinal study with the Periotest device.

The aim of the present study was to evaluate the capability of the Periotest device in detecting and monitoring functional changes in the periodontal as well as in the pari-implant damping characteristics. In the first part of this study, 107 teeth were splinted by means of 40 full acrylic fixed prostheses (AFP) and another 37 teeth were splinted by means of 14 ceramometallic fixed prostheses (C-MFP). The Periotest measurements of individual teeth were done the day the fixed prostheses were cemented temporary (PTV 1), and again after a mean observation period of 27.4 days (PTV 2). In the 2nd part, 78 osseointegrated two-stage implants were splinted by means of 23 full acrylic fixed prosthesis (AFP) and other 18 implants were left without it. Using the same abutment length, Periotest measurements were performed, at abutment connections and before installation of the final prosthesis. In a 3rd part, using both implants and teeth as abutments, 29 osseointegrated implants were connected with 25 abutment teeth by means of 7 AFP. The measurements were performed at the beginning of the prosthetic treatment and 2, 4 and 6 weeks later. After splinting teeth by means of AFP for the observation period, no statistically significant reduction in PTVs was found. When on the other hand, a C-MFP was used, PTV 2 showed a significant reduction. The PTVs at abutment connection went down after a period of time, during which some implants were interconnected by means of an AFP and others were not.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylic Resins↗
PubMed2005

Viruses as the causative agent related to 'dampness' and the missing link between allergen exposure and onset of allergic disease.

UNLABELLED: Asthma and asthma-like symptoms occur more often among people living in humid indoor climates. It has been postulated that the higher concentration of allergens in these environments is the cause for the increase in the number of affected people. However, poor correlations between allergen concentration and symptoms indicate a missing link between allergen exposure and onset of asthma. Respiratory viruses have been identified in up to 85% cases of asthma or exacerbations of asthma. The missing link between respiratory diseases and humid indoor climates could therefore be attributed to viruses. The infectious effectiveness of respiratory viruses depends strongly on the environment where the viruses are spread. For respiratory viruses, survival and infectivity are dependent on temperature and relative humidity. A direct link between virus-induced inflammation and the asthmatogenic process has been proposed. Therefore, a more effective spreading of viral infections in damp indoor climates is likely to represent the main cause for the increased prevalence of asthma in these environments. Moreover, the incidence of viral infections is higher in patients with asthma compared with that in control subjects. Therefore, a humid indoor climate could also represent a higher risk for persons already sensitized to one or more allergens. PRACTICAL IMPLICATIONS: In epidemiological studies where the relationship between moisture in the indoor climate, respiratory symptoms and exposure to allergens is investigated it will be necessary to analyze the role of respiratory viruses in relation to respiratory symptoms. Today, the necessary techniques to address the presence of viruses [e.g. polymerase chain reaction (PCR), antibodies] are highly sensitive. In order to further our understanding of why the frequency of asthma and atopic diseases is still increasing, it is mandatory to implement these methods.

Air Pollution, Indoor↗
PubMed1994

Optimization of the contact damping and stiffness coefficients to minimize human body vibration.

In this paper, a lumped mass human model is used to minimize the energy absorption at the feet/hip level when the body is subjected to vertical vibration. The contact forces are assumed unknown. By coupling the dynamic response of the body with certain objective criteria, the optimum damping and stiffness coefficients of shoes/chairs are sought. The optimization technique is based on the quasi-Newton and finite-difference gradient method and is used to seek optimum coefficients of the contact forces in the solution of the body's response in the frequency domain. The criteria of acceleration, displacement and internal forces response area swept for a range of 0-15 Hz form the basis of our simulation study. In the seated/standing postures it is found that for each criteria the frequency response shifts the peak of resonance of each body segment response from 4.5/3.67 Hz to 2.5/2.255 Hz. In addition, the total energy reduces drastically when the contact conditions are optimum. The method presented in this paper is useful in modeling the medium of contacts and especially in controlling the effects of human body vibration.

Compliance↗
PubMed2004

Virtual sensing for broadband noise control in a lightly damped enclosure.

Available virtual sensing schemes either depend on assumptions that are valid for isolated frequencies, or require heavy online adaptations. A simple method is proposed here to predict the virtual signal exactly for broadband noise control in a lightly damped enclosure. The proposed method requires two physical sensors installed judiciously in a sound field to predict a virtual signal. The method is based on an exact mathematical relation between the virtual and physical sensors, which is valid for the entire frequency of interest. It is possible to use multiple sensor-pairs to reduce the sensitivity of the proposed method with respect to acoustic parameters, such as speed of sound or sensor mismatching. Experimental results are presented to verify the analytical results.

Acoustics↗
PubMed2005

Acoustic power measurements of a damped aeroacoustically driven resonator.

Strong self-sustained acoustic oscillations may occur in a gas pipe network under certain gas flow velocities within the network. The pipe network under consideration consists of a main pipe, with a variable mean airflow, with two closed coaxial side branches of variable but equal length joined to the main pipe. Coupling between resonant acoustic standing waves and instabilities of the shear layers separating the flow in the main pipe from the stagnant gas in the closed side branches leads to strong acoustic oscillations at a frequency corresponding to the half-wavelength acoustic mode defined by the total side-branch length. An acoustic damper consisting of a variable acoustic resistance and compliance is used to dissipate power from the resonating mode. The response of the aeroacoustically driven resonator to variable damping will be examined for different fluid flow regimes as well as side-branch geometries.

Journal Article↗
PubMed1988

Sharp mechanical tuning in a cochlear model without negative damping.

It is possible for a cochlear model without active negative damping to exhibit a mechanical response peak that is arbitrarily high and arbitrarily wide. Conventional active models rely on external energy inputs to the cochlea to produce the required peak shape. The new model proposed here produces very similar response profiles by assuming that outer hair cell stereocilia stiffness suppresses the mechanical motion in all regions basal of the response peak. Therefore, the model is not active in the usual sense of adding energy to the cochlea. The model suggests a reason for the differing basilar membrane structure in the arcuate and pectinate zones and simulates in vivo and postmortem responses similar to those measured in the real cochlea.

Animals↗
PubMed1968

Rete mirabile of dolphin: its pressure-damping effect on cerebral circulation.

In the bottlenose dolphin Tursiops truncatus, a massive retial complex is interposed between the systemic and cerebral circulations at the cervicothoracic level. Pressure measurements in the retial efferent arteries supplying the brain revealed relatively nonpulsatile pressure profiles. These measurements in the anesthetized dolphin demonstrate the pressure-damping effect of the retia mirabile.

Animals↗