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At least 271 records · Page 15Linked to original sources

PubMed1989

Effect of M2 muscarinic receptor antagonist 4-DAMP, on prostaglandin synthesis and mechanical function in the isolated rabbit heart.

1. Muscarinic agonist acetylcholine (ACh) (non-selective) and arecaidine propargyl ester (APE) (M2 selective agonist) produced a increase in the output of 6-keto PGF1 alpha and a decrease in the heart rate and myocardial developed tension in a dose-dependent manner. 2. Lower doses of ACh (1.0-5.0 nmol) caused coronary vasodilation, whereas higher doses of ACh (10.0 nmol) and lower as well as higher doses of APE produced a biphasic effect--an initial vasodilation followed by vasoconstriction. 3. The increase in 6-keto PGF1 alpha output elicited by 3 nmol of ACh or APE was inhibited by 10 nM of classical muscarinic receptor antagonist atropine or by the selective M2 beta muscarinic receptor antagonist 4-(diphenylacetoxy-N-methyl piperidine) methiodide (4-DAMP). 4. The decrease in heart rate and myocardial developed tension produced by ACh and APE was attenuated by atropine and 4-DAMP. The coronary vasodilator effect of ACh and APE and the vasoconstrictor effect of APE were also attenuated by both of these muscarinic antagonists.

Animals↗

PubMed1995

The effect of contralateral stimulation on cochlear resonance and damping in the mustached bat: the role of the medial efferent system.

In the unanesthetized mustached bat, stimulation of the ear with an acoustic transient produces damped oscillations which are evident in the cochlear microphonic potential. In this report we demonstrate how the decay time of these oscillations is affected by broadband noise presented to the contralateral ear (CLN). In the absence of CLN, the mean decay time was 1.94 +/- 0.23 ms, but during the presentation of CLN the decay time consistently decreased. The changes were finely graded, the higher the CLN, the greater the change. The effect could be maintained at a constant level for extended periods of time and this was evident when the CLN exceeded 40 dB SPL. The latency of the reflex for 64 dB noise was about 11 ms and near maximum changes occurred within 15 ms of CLN onset. Sectioning medial efferent nerve fibers in the floor of the fourth ventricle or the administration of a single dose of gentamicin eliminated changes produced by CLN. The prominence of CM responses to damped oscillations and the robust changes in response to CLN make the mustached bat an excellent model for studying the influence of the medial efferent system on cochlear mechanics.

Acoustic Stimulation↗

PubMed1995

Characterization of the reactive intermediates in laser flash photolysis of adenine, adenosine and dAMP using acetone as photosensitizer.

Transient absorption spectra of adenine, adenosine and 2'-deoxyadenosine 5'-monophosphate (dAMP) arising from 248 nm laser flash photolysis using acetone as a photosensitizer have been observed. The intermediates recorded are assigned to the excited triplet states and dehydrogenated radicals of adenine and its nucleoside and nucleotide. The excited triplet states of adenine and its derivatives are produced via triplet-triplet excitation transfer and observed for the first time, while the dehydrogenated radicals stemming from the interaction of triplet acetone with adenine and its derivatives via electron transfer through a five-member-ring electron donor-acceptor intermediate. The site of dehydrogenation is suggested to be the hydrogen atom on C(8) of the adenine moiety. Moreover, three sets of kinetic parameters of the triplet decay have been determined. The rate constants of the unimolecular decay (k0), the triplet quenching by the ground state (ksq) and by the triplet quencher Mn2+ (kq) are 1.1 x 10(5), 7.9 x 10(4), 3.7 x 10(4) s-1, 6.9 x 10(8), 8.3 x 10(8), 3.6 x 10(8) dm3 mol-1 s-1 and 4.2 x 10(8), 3.5 x 10(8), 6.0 x 10(8) dm3 mol-1 s-1 respectively for adenine, adenosine and dAMP.

Acetone↗

PubMed2006

Effects of radiation damping on Z-spectra.

Radiation damping induced by the strong water magnetization in Z-spectroscopy experiments can be sufficient to perturb significantly the resultant Z-spectrum. With a probe tuned to exact electrical resonance the effects are relatively straightforward, narrowing the central feature of the Z-spectrum. Where, as is commonly the case, the probe is tuned sufficiently well to give optimum signal-to-noise ratio and radiofrequency field strength but is not at exact resonance, radiation damping introduces an unexpected asymmetry into the Z-spectrum. This has the potential to complicate the use of Z-spectrum asymmetry to study chemical exchange, for example in the estimation of pH in vivo.

Artifacts↗

PubMed1996

Truncated exponential versus damped sinusoidal waveform shocks for transthoracic defibrillation.

Currently available transthoracic defibrillators use either a damped sinusoidal or truncated exponential (TE) waveform. Truncated exponential waveforms deliver a long pulse if the transthoracic impedance is high; it has been suggested that such a long pulse may be less effective for defibrillation. Our objective was to compare the ability of damped sinusoidal (DS) waveform shocks versus TE waveform shocks to terminate ventricular fibrillation (VF) and achieve survival from witnessed cardiac arrest. We retrospectively reviewed field-recorded electrocardiograms from 86 patients with witnessed VF, treated by prehospital personnel equipped with DS or TE waveform defibrillators. Forty-four patients received 130 shocks from TE defibrillators; 42 patients received 108 shocks from DS defibrillators. There were no significant differences in time from arrest to first shock (8.0 vs 8.1 minutes), nor were there any differences in the size of the communities involved. The shocks resulted in the following rhythms: organized rhythm: TE: 15 of 130 (12%), DS: 24 of 108 (22%), p = 0.10 (NS); persistent VF: TE: 85 of 130 (65%), DS: 45 of 108 (42%), p <0.01; asystole: TE: 30 of 130 (23%), DS: 39 of 108 (36%), p = NS; and survival to hospital discharge: TE: 5 of 44 (11%), DS: 8 of 42 (19%), p = NS. We conclude that DS waveforms terminated VF more frequently than TE, but there was no significant difference in resumption of an organized rhythm or survival. A prospective comparison of these 2 waveforms is needed.

Aged↗

PubMed2003

Insulin assembly damps conformational fluctuations: Raman analysis of amide I linewidths in native states and fibrils.

The crystal structure of insulin has been investigated in a variety of dimeric and hexameric assemblies. Interest in dynamics has been stimulated by conformational variability among crystal forms and evidence suggesting that the functional monomer undergoes a conformational change on receptor binding. Here, we employ Raman spectroscopy and Raman microscopy to investigate well-defined oligomeric species: monomeric and dimeric analogs in solution, native T(6) and R(6) hexamers in solution and corresponding polycrystalline samples. Remarkably, linewidths of Raman bands associated with the polypeptide backbone (amide I) exhibit progressive narrowing with successive self-assembly. Whereas dimerization damps fluctuations at an intermolecular beta-sheet, deconvolution of the amide I band indicates that formation of hexamers stabilizes both helical and non-helical elements. Although the structure of a monomer in solution resembles a crystallographic protomer, its encagement in a native assembly damps main-chain fluctuations. Further narrowing of a beta-sheet-specific amide I band is observed on reorganization of insulin in a cross-beta fibril. Enhanced flexibility of the native insulin monomer is in accord with molecular dynamics simulations. Such conformational fluctuations may initiate formation of an amyloidogenic nucleus and enable induced fit on receptor binding.

Animals↗

PubMed1999

Fungal extracellular polysaccharides in house dust as a marker for exposure to fungi: relations with culturable fungi, reported home dampness, and respiratory symptoms.

BACKGROUND: Epidemiologic studies have demonstrated an association between indoor fungal growth and respiratory symptoms. However, in only a few studies was fungal exposure actually measured. OBJECTIVE: The purpose of this study was to evaluate the measurement by enzyme immunoassay of extracellular polysaccharides of Aspergillus and Penicillium species (EPS-Asp/Pen ) in house dust as a marker for fungal exposure and to study the relations between EPS-Asp/Pen levels and home dampness and respiratory symptoms in children. METHODS: Extracts of house dust samples from bedroom and living room floors and mattresses from homes of 31 children with chronic respiratory symptoms and 29 children with no chronic respiratory symptoms were analyzed for EPS-Asp/Pen. RESULTS: EPS-Asp/Pen were readily detectable (40 to 46,513 nanogram equivalent/g dust) in 161 house dust extracts, with highest concentrations in living room floor dust. EPS-Asp/Pen levels were 2 to 3 times higher on carpeted floors than on smooth floors. EPS-Asp/Pen were significantly correlated with total culturable fungi (r = 0.3 to 0.5) and with house dust mite allergens (r = 0.3 to 0.5). EPS-Asp/Pen levels in living room floor dust were positively associated with occupant-reported home dampness. This was not observed for EPS-Asp/Pen in bedroom floor and mattress dust. EPS-Asp/Pen levels in living room floor dust were positively associated with respiratory symptoms. EPS-Asp/Pen in bedroom floor and mattress dust showed a reversed association with respiratory symptoms, possibly because of allergen-avoidance measures taken in the bedroom. CONCLUSION: The enzyme immunoassay for fungal EPS-Asp/Pen may be a useful method for exposure assessment of indoor fungi.

Antigens, Fungal↗

PubMed2003

Damping of Crank-Nicolson error oscillations.

The Crank-Nicolson (CN) simulation method has an oscillatory response to sharp initial transients. The technique is convenient but the oscillations make it less popular. Several ways of damping the oscillations in two types of electrochemical computations are investigated. For a simple one-dimensional system with an initial singularity, subdivision of the first time interval into a number of equal subintervals (the Pearson method) works rather well, and so does division with exponentially increasing subintervals, where however an optimum expansion parameter must be found. This method can be computationally more expensive with some systems. The simple device of starting with one backward implicit (BI, or Laasonen) step does damp the oscillations, but not always sufficiently. For electrochemical microdisk simulations which are two-dimensional in space and using CN, the use of a first BI step is much more effective and is recommended. Division into subintervals is also effective, and again, both the Pearson method and exponentially increasing subintervals methods are effective here. Exponentially increasing subintervals are often considerably more expensive computationally. Expanding intervals over the whole simulation period, although capable of satisfactory results, for most systems will require more cpu time compared with subdivision of the first interval only.

Journal Article↗

PubMed1999

Low-frequency damped electroretinographic wavelets in young asymptomatic patients with dominant retinitis pigmentosa: a new electroretinographic finding.

OBJECTIVE: To describe a previously unreported electroretinographic (ERG) pattern in early retinitis pigmentosa (RP). DESIGN: Two case reports. PARTICIPANTS: Two unrelated young asymptomatic patients with autosomal-dominant retinitis pigmentosa were studied. MAIN OUTCOME MEASURES: Clinical findings and ERG responses were assessed. RESULTS: No ERG responses were detected scotopically with low-luminance stimuli. With increasingly brighter stimuli, a series of three to five low-frequency damped wavelets developed under both scotopic and photopic conditions. The period of the wavelets was 25 to 37 msec. CONCLUSIONS: Low-frequency damped ERG wavelets occur in some young asymptomatic patients with autosomal-dominant RP. The ERG pattern suggests that these wavelets are predominantly cone-generated.

Adult↗

PubMed2003

Dynamic stiffness and damping of porcine muscle specimens.

The aim of this study was to quantify the mechanical properties of the muscles of the buttock, using dynamic compression (5-->30 Hz). Tests were conducted in vitro on porcine muscles, using a lever arm device, which applied a dynamic load onto cylindrical samples. A two-parameter viscoelastic model allowed the calculation of stiffness and damping of the samples with respect to frequency. The average stiffness curve showed a monotonous increase (5 Hz: 8.5 kN/m-->30 Hz: 347 kN/m). Concerning damping, between 5 and 20 Hz, values were typically inferior to 300 Ns/m, which then increased till 30 Hz (556 Ns/m). The lever arm device may be used to evaluate dynamic properties of other biological tissues also.

Animals↗

PubMed2005

Equilibrium dynamics of the toy model of dense fluid: the infinite damping limit.

We investigate the equilibrium dynamics of our recently proposed toy model of dense fluid in the infinite damping limit. Contrary to naive expectation, the correlators involving the velocity-like variables do not quickly relax away. Instead, after a very fast transient relaxation, they exhibit rather slow relaxations due to the coupling to the density-like variable. Hence, the so-called "hopping" processes are not suppressed even in the large damping limit. These hopping processes can only be controlled by tuning the parameter delta, which is the ratio of the numbers of the components of the velocity-like and the density-like variables in the model. We analytically prove that there must exist an ergodic-to-nonergodic phase transition for delta such that 0 < delta < 1. The slow dynamics and the dynamic transition in the model are distinct from those in the idealized mode coupling theory.

Journal Article↗

PubMed2005

Emotion as a thermostat: representing emotion regulation using a damped oscillator model.

The authors present in this study a damped oscillator model that provides a direct mathematical basis for testing the notion of emotion as a self-regulatory thermostat. Parameters from this model reflect individual differences in emotional lability and the ability to regulate emotion. The authors discuss concepts such as intensity, rate of change, and acceleration in the context of emotion, and they illustrate the strengths of this approach in comparison with spectral analysis and growth curve models. The utility of this modeling approach is illustrated using daily emotion ratings from 179 college students over 52 consecutive days. Overall, the damped oscillator model provides a meaningful way of representing emotion regulation as a dynamic process and helps identify the dominant periodicities in individuals' emotions.

Adult↗

PubMed2001

Extreme damping in composite materials with negative-stiffness inclusions.

When a force deforms an elastic object, practical experience suggests that the resulting displacement will be in the same direction as the force. This property is known as positive stiffness. Less familiar is the concept of negative stiffness, where the deforming force and the resulting displacement are in opposite directions. (Negative stiffness is distinct from negative Poisson's ratio, which refers to the occurrence of lateral expansion upon stretching an object.) Negative stiffness can occur, for example, when the deforming object has stored (or is supplied with) energy. This property is usually unstable, but it has been shown theoretically that inclusions of negative stiffness can be stabilized within a positive-stiffness matrix. Here we describe the experimental realization of this composite approach by embedding negative-stiffness inclusions of ferroelastic vanadium dioxide in a pure tin matrix. The resulting composites exhibit extreme mechanical damping and large anomalies in stiffness, as a consequence of the high local strains that result from the inclusions deforming more than the composite as a whole. Moreover, for certain temperature ranges, the negative-stiffness inclusions are more effective than diamond inclusions for increasing the overall composite stiffness. We expect that such composites could be useful as high damping materials, as stiff structural elements or for actuator-type applications.

Journal Article↗

PubMed2006

Contributions from radiation damping and surface scattering to the linewidth of the longitudinal plasmon band of gold nanorods: a single particle study.

The scattering spectra of single gold nanorods with aspect ratios between 2 and 4 have been examined by dark field microscopy. The results show that the longitudinal plasmon resonance (electron oscillation along the long axis of the rod) broadens as the width of the rods decreases from 14 to 8 nm. This is attributed to electron surface scattering. Analysis of the data using gamma = gamma(bulk) + Anu(F)/L(eff), where L(eff) is the effective path length of the electrons and nu(F) is the Fermi velocity, allows us to determine a value for the surface scattering parameter of A = 0.3. Larger rods with widths of 19 and 30 nm were also examined. These samples also show spectral broadening, which is attributed to radiation damping. The relative strengths of the surface scattering and radiation damping effects are in excellent agreement with recent work on spherical gold nanoparticles by Sönnichsen et al., Phys. Rev. Lett., 2002, 88, 077402; and by Berciaud et al., Nano Lett., 2005, 5, 515.

Gold↗

PubMed2002

Immunoglobulin G antibodies against indoor dampness-related microbes and adult-onset asthma: a population-based incident case-control study.

Immunoglobulin G (IgG) antibodies against microbes related to indoor dampness problems have been used as potential biomarkers of fungal exposure in clinical investigations. There is limited information on their relation to asthma. We conducted a population-based incident case-control study to assess the risk of asthma in relation to specific IgG antibodies to eight dampness-related microbes: Aspergillus fumigatus, A. versicolor, Cladosporium cladosporioides, Fusarium oxysporum, Sporobolomyces salmonicolor, Stachybotrys chartarum, Streptomyces albus and Trichoderma citrinoviride. We recruited systematically all new cases of asthma during a 2.5-year study period and randomly selected controls from a source population of adults 21-63 years of age living in the Pirkanmaa Hospital District, South Finland. The clinically diagnosed case series consisted of 521 adults with newly diagnosed asthma and the control series of 932 controls selected randomly from the source population. IgG antibodies were analysed with ELISA. An increased risk of developing asthma in adulthood was significantly related to IgG antibodies to T. citrinoviride, but not to the other moulds. There was no evidence of a dose-response relation between the IgG antibody level and the risk of asthma. T. citrinoviride may play a role in the aetiology of adult-onset asthma or serve as an indicator of other causal factors.

Adult↗

PubMed2004

Transient response of a Brownian particle with general damping.

We study the transient response of a Brownian particle with general damping in a system of metastable potential well. The escape rate is evaluated as a function of time after an infinite wall is removed from the potential barrier. It takes a relaxation time for the rate to reach its limit value and this rate relaxation time differs from the relaxation time of the majority of the probability around the bottom of the potential well. The rate relaxation time is found to depend on the temperature as well as the damping constant. It involves the diffusion time and the instanton time, in general agreement with recent studies of the overdamped case by Bier et al. [Phys. Rev. E 59, 6422 (1999)].

Journal Article↗

PubMed2005

Theory of damped quantum rotation in NMR spectra. I. Fundamental aspects.

The damped quantum rotation (DQR) theory, formulated originally for methyl-like atomic groupings, is now extended to hindered (N>3)-fold molecular rotors, such as the cyclopentadienyl, benzene, and cycloheptatrienyl rings in solid phase environments. It heightens the significance of the Pauli principle in shaping up the stochastic dynamics of such objects, reflected in NMR line shapes. The corresponding NMR line-shape equation is derived; its stochastic part is shown for the first time to have the double commutator form for any values of the quantum-mechanical (coherence-damping) rate constants entering it. Constraints on the relative magnitudes of such constants are determined under which the DQR line-shape equation is converted into the phenomenological Alexander-Binsch equation describing classical jumps of the rotor. When all the quantum rate constants happen to be equal, the phenomenological model of equal jump rates between any two of the N (equivalent) orientations of the rotor is reproduced. On the other hand, the seemingly most plausible (for N>3) nearest-neighbor hopping model does not have any peculiar grounds in the DQR approach. For the special instances of stochastic molecular motions addressed in this work, the extended DQR formalism affords a quantification of the "degree of classicality" represented by a complete set of the relevant quantum rate constants. In view of our earlier experimental findings for the methyl rotors, the very occurrence of the nonclassical DQR effects seems unquestionable even for the objects of the size of benzene. The question of under what circumstances such effects can be big enough to be detected experimentally will be addressed in Part II of this work.

Journal Article↗

PubMed2006

Diffusion damping during adiabatic z-rotation pulses for NMR spectroscopy in inhomogeneous magnetic fields.

High-resolution nuclear magnetic resonance spectra from samples located in inhomogeneous static and radio frequency magnetic fields can be obtained by applying a train of z-rotation radio frequency pulses to repeatedly refocus the inhomogeneous broadening during signal detection. z-rotation pulses based on an adiabatic double passage are effective over wide bandwidths using a limited amount of radio frequency power at the expense of being time consuming and, consequently, sensitive to motion of the spin bearing molecules. The signal damping resulting from molecular self-diffusion during the pulse was studied experimentally and using Brownian dynamics simulations. The results show that the analytical expression for diffusion damping during a double spin echo is a reasonable approximation for the signal decay during an adiabatic z-rotation pulse. Methods to alleviate the effects of diffusion are discussed.

Journal Article↗