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At least 127 records · Page 7Linked to original sources

PubMed2005

Deoxy-adenosine-monophosphate (dAMP) di-n-butylester induces apoptosis by increasing the dATP level in HL-60 cells.

Deoxy-ATP is a potent inducer of apoptosis. We intended to synthesize a lipophilic dAMP derivative which, according to our working hypothesis penetrates into the cell, is converted to dAMP by intracellular esterases and to dATP by nucleotide kinases. We synthesized dAMP-di-n-butylester (DAB) and tested it. We found that it fulfills the above-described expectations. DAB treatment decreases the viability of HL-60 cells, increases the dATP concentration and induces apoptogenic cytochrome c release from mitochondria with concomitant elevation of caspase-9 activity. Our results indicate that use of dAMP derivatives with masked phosphate may be a feasible approach for pharmacological elevation of intracellular dATP and induction of apoptosis.

Annexin A5↗

PubMed2006

A derivation of the Christoffel equation with damping.

This paper provides a derivation of the Christoffel eigenvalue equation for acoustic wave propagation in an acoustically damped piezoelectric medium. The damping tensor is shown to couple into both the stress and displacement constitutive equations. Application of the quasi-static approximation leads to an additional term in the Christoffel equation that generates a complex k-vector, due both to introduction of a complex term and to breaking of symmetry in the left-hand side of the eigenvalue equation, subsequently resulting in damping and a phase shift for a plane wave solution. Shown are the effects of damping on the eigenvalues of the piezoelectrically stiffened Christoffel equation for plane wave propagation in unconstrained quartz over a 1 MHz to 1 GHz frequency range.

Journal Article↗

PubMed1998

Compliant Keeper system replication of the periodontal ligament protective damping function for implants: Part I.

STATEMENT OF PROBLEM: Numerous reports and studies have been published relative to implant overloading, interfacial integrity, and component failure. A significant amount of literature review supports the concept of progressive loading and damping and that it should be addressed. PURPOSE: This article reviews the literature on load reduction and uses the Periotest instrument to evaluate the viscoelastic materials of the Compliant Keeper implant damping system in vitro. MATERIAL AND METHODS: The test model was a vice-mounted resin mandible replica with a 4-unit fixed-removable implant-supported Compliant Keeper partial denture. Pontics were both cantilevered and bounded. Three 13-gauge measurement extensions were located facially on the gingival, middle, and occlusal thirds of each abutment and pontic for 312 Periotest measurements of O-ring combinations with a titanium O-ring as the null control. Measurements were averaged and recorded. RESULTS: Because the Periotest can measure finite movement below Miller Class I, Periotest values were obtained for O-rings so that they could be used to program a Compliant Keeper system to match the Periotest values of another implant body. CONCLUSIONS: Significant loading differences were found with the O-rings. The O-rings controlled the damping element so they enabled the Compliant Keeper system to provide damping and progressive loading for implant-supported prostheses.

Biomechanical Phenomena↗

PubMed1999

Compliant Keeper system replication of the periodontal ligament protective damping function for implants: part II.

STATEMENT OF PROBLEM: There are numerous articles regarding implant overloading, interfacial integrity and component failure. A significant amount of literature review supports the concept of the progressive loading and damping, and it should be addressed. PURPOSE: This study was designed to correlate durometer measurements of the elastomeric test materials and actual Periotest values (PTV) of the test materials as preloaded sleeve rings in Compliant Keeper abutments to support the Compliant Keeper as a viable implant damping system. MATERIAL AND METHODS: A 4-unit fixed-removable implant-supported partial denture was the test model. Sleeve ring combinations replaced "O" rings and 220 Periotest measurements were graphically recorded, then analyzed by least square of means, 2-way analysis of variance, and a Tukey test. RESULTS: There was a correlation between durometer measurements and PTVs of sleeve rings. Finite movement was measured accurately with the Periotest (P =. 0001) so that Compliant Keeper systems can be programmed to match the movement of another implant abutment, because they might be able to match the PTV of a natural abutment. CONCLUSIONS: Significant differences exist between the "O" rings and sleeve rings. The sleeve ring, as a controllable damping element, enables the Compliant Keeper system to provide progressive loading and damping for implant-supported prostheses.

Analysis of Variance↗

PubMed2001

The responses of single units in the inferior colliculus of the guinea pig to damped and ramped sinusoids.

Temporal asymmetry can have a pronounced effect on the perception of a sinusoid. For instance, if a sinusoid is amplitude modulated by a decaying exponential that restarts every 50 ms, (a damped sinusoid) listeners report a two-component percept: a tonal component corresponding to the carrier and a drumming component corresponding to the envelope modulation period. When the amplitude modulation is reversed in time (a ramped sinusoid) the perception changes markedly; the tonal component increases while the drumming component decreases. The long-term Fourier energy spectra are identical for damped and ramped sinusoids with the same exponential half-life. Modelling studies suggest that this perceptual asymmetry must occur central to the peripheral stages of auditory processing (Patterson and Irino, 1998). To test this hypothesis, we have recorded the responses of single units in the inferior colliculus of the anaesthetised guinea pig. We divided single units into three groups: onset, on-sustained and sustained, based on their temporal adaptation properties to suprathreshold tone bursts at the unit's best frequency. The asymmetry observed in the neural responses of single units was quantified in two ways: a simple total spike count measure and a ratio of the tallest bin of the modulation period histogram to the total number of spikes. Responses were more diverse than those observed with similar stimuli in a previous study in the ventral cochlear nucleus (Pressnitzer et al., 2000). The main results were: (1) The shape of the responses of on-sustained units to ramped sinusoids resembled the shape of the responses to damped sinusoids. This is in contrast to the response shapes in the VCN, which were always similar to the stimulating sinusoid. (2) Units classified as onsets often responded only to the damped stimuli. (3) All units display significant asymmetry in discharge rate for at least one of the half-lives tested and 20% showed significant response asymmetry over all of the half-lives tested. (4) A summary population measure of temporal asymmetry based on total spike count reveals the same pattern of results as that obtained psychophysically using the same stimuli (Patterson, 1994a).

Acoustic Stimulation↗

PubMed2006

Excitation of magnetization using a modulated radiation damping field.

In this work, pulsed-field gradients are used to modulate the radiation damping field generated by the detection coil in an NMR experiment in order that spins with significantly different chemical shifts can affect one another via the radiation damping field. Experiments performed on solutions of acetone/water and acetone/DMSO/water demonstrate that spins with chemical shift differences much greater than the effective radiation damping field strength can still be coupled by modulating the radiation damping field. Implications for applications in high-field NMR and for developing sensitive magnetization detectors are discussed.

Journal Article↗

PubMed2004

Characterization of distance-dependent damping in tapping-mode atomic force microscopy force measurements in liquid.

We have used a spectral analysis method to characterize changes in the local damping coefficient for an acoustically driven cantilever as it approaches a hard surface in liquid. We show a significant distance dependence of the damping coefficient (and associated quality factor) that must be accounted for to achieve successful theoretical reproduction of experimental tapping-mode force curves. We model the cantilever dynamics using a forced damped harmonic oscillator model and solve the equation of motion using the method of finite differences. Experiments in solutions of differing viscosities show that bulk viscous damping is not the source of the system dissipation, while simulations of the cantilever dynamics including adhesion hysteresis also eliminate this as the origin of the dissipation. We conclude that frictional dissipation that occurs with the intermittent contact is the likely source of dissipation in the system. Our results identify a semiquantitative means of interpreting tapping-mode force curves on nondeformable surfaces in liquid.

Journal Article↗

PubMed1986

Damping the hearing aid frequency response: effects on speech clarity and preferred listening level.

Damped hearing aid frequency responses were compared with undamped responses to determine the effect of response smoothing on speech clarity and on gain received when the hearing aid was adjusted to the preferred listening level (PLL). Damping elements were located in the hearing aid's earhook. Three commercially available hearing aids, two bandwidths, and two speech input levels were evaluated in a completely crossed experimental design. Data were collected using a paired comparison method and 10 hearing-impaired subjects. Results indicated that the undamped frequency responses were judged to produce more clear, pleasant, natural sounding speech than the damped responses (p = .09). Although significant midfrequency peak reduction was achieved through earhook damping, the effects on gain at PLL were negligible.

Acoustics↗

PubMed1998

Home dampness and respiratory health status in european children.

BACKGROUND: Living in a damp home has been associated with impaired respiratory health in previous studies, but objective data on lung function variability and atopy have been lacking from most studies. OBJECTIVES: Data collected in the winter of 1993-1994 in the framework of the PEACE study (Pollution Effects on Asthmatic Children in Europe) were used to study the association between home dampness and Peak Flow (PEF) variability, frequency of respiratory symptoms and relief medication use during the period of observation. METHODS: Children were selected with a screening questionnaire on the basis of positive answers to questions on symptoms of asthma and chronic cough. Children were instructed to perform PEF measurements with Miniwright PEF meters twice daily over a period of 2 months. Parents kept diaries on respiratory symptoms and medication use of their children. Data on demographic and housing characteristics were derived from a parent-administered questionnaire. As indicators for home dampness reported moisture stains and moulds were used. Children were tested for atopy with skin-prick tests. Data from 1614 children from 13 centres in 10 different countries were available for analysis. Linear regression models and prevalence rate ratios were used to investigate the association between home dampness and PEF variability and the period prevalence of cough, phlegm, lower and upper respiratory symptoms and bronchodilator use. RESULTS: In atopic children, PEF variability was positively related to self-reported moulds but not to moisture stains. The period prevalence of cough and upper respiratory symptoms was significantly higher in children living in houses with reported moulds, compared with 'dry' homes. CONCLUSIONS: These results show that self-reported moulds in homes are associated with objective as well as subjective markers of airway lability in European children with chronic respiratory symptoms.

Adolescent↗

PubMed2005

Effects of counterion valency on the damping of phonons propagating along the axial direction of liquid-crystalline DNA.

The phonon propagation and damping along the axial direction of films of aligned 40 wt % calf-thymus DNA rods are studied by inelastic x-ray scattering (IXS). The IXS spectra are analyzed with the generalized three effective eigenmode theory, from which we extract the dynamic structure factor S(Q,E) as a function of transferred energy E=variant Planck's over 2piomega, and the magnitude of the transferred wave vector Q. S(Q,E) of a DNA sample typically consists of three peaks, one central Rayleigh scattering peak, and two symmetric Stokes and anti-Stokes Brillouin side peaks. By analyzing the Brillouin peaks, the phonon excitation energy and damping can be extracted at different Q values from about 4 to 30 nm(-1). A high-frequency sound speed is obtained from the initial slope of the linear portion of the dispersion relation below Q=4 nm(-1). The high-frequency sound speed obtained in this Q range is 3100 ms, which is about twice faster than the ultrasound speed of 1800 ms, measured by Brillouin light scattering at Q approximately 0.01 nm(-1) at the similar hydration level. Our observations provide further evidence of the strong coupling between the internal dynamics of a DNA molecule and the dynamics of the solvent. The effect on damping and propagation of phonons along the axial direction of DNA rods due to divalent and trivalent counterions has been studied. It is found that the added multivalent counterions introduce stronger phonon damping. The phonons at the range between approximately 12.5 and approximately 22.5 nm(-1) are overdamped by the added counterions according to our model analyses. The intermediate scattering function is extracted and it shows a clear two-step relaxation with the fast relaxation time ranging from 0.1 to 4 ps.

DNA↗

PubMedDate not supplied

Ocular, airway, and dermal symptoms related to building dampness and odors in dwellings.

The authors examined the relationship between symptoms of Sick Building Syndrome and reports of building dampness and odors. Two hundred thirty-one multifamily buildings built prior to 1961 in Stockholm, Sweden, contained a total of 4,815 dwellings. The authors selected these buildings for study by stratified random sampling. Occupants answered a postal questionnaire that assessed weekly symptoms, personal factors, population density in each apartment, water leakage in the preceding 5 yr, different types of odors, and signs of high indoor air humidity. The response rate was 77%. Independent information on building characteristics was gathered from the building owners and the central building register in Stockholm. Multiple logistic-regression analysis was applied and odds ratios were calculated, with adjustments for age, gender, current smoking, hay fever, population density, type of ventilation, and ownership of the building. In total, 22% reported at least 1 sign of dampness, and 32% reported odor in the dwelling. Condensation on windows, high air humidity in the bathroom, moldy odor, and water leakage were reported from 6.8%, 8.8%, 5.7%, and 13% of the dwellings, respectively. A combination of odor and signs of high humidity was related to an increased occurrence of all symptoms (odds ratios = 2.2-3.6). Similar findings were observed for a combination of odors and a history of water leakage in the past 5 yr (odds ratios = 1.2-4.4). Symptoms increased with the number of signs of dampness. The study indicated that dampness in dwellings, with emissions of odorous compounds, are associated with an increase in symptoms consistent with Sick Building Syndrome.

Adolescent↗

PubMed2000

Harmonizing dilemmas. Siblings of children with DAMP and Asperger syndrome's experiences of coping with their life situations.

The aim of this qualitative study was to describe, from their own perspective and experiences, how siblings of children with deficits in attention, motor control and perception (DAMP) and Asperger syndrome cope with their life situations in their families. Fifteen adolescent females 12-18 years old, siblings of boys with DAMP (8 subjects) and Asperger syndrome (7 subjects), were interviewed. The method used in sampling and analysis of interview protocols was the constant comparative method for grounded theory. The inductive categorization of data produced two core concepts, one about the siblings' life situations in DAMP and Asperger syndrome ('dilemma of requirements and concerns') and one about the siblings' coping processes ('harmonizing'). Of the six categories identified, four were categories of the processes of coping ('gaining understanding', 'gaining independence', 'following a bonding responsibility' and 'balancing'). The qualitative differences between coping processes were related to the two categories of context to cope within the experienced dilemma 'requirements' and 'concerns'. The findings contribute to a deeper understanding of the siblings' life situations, and may be important for health personnel in encounter families and for identifying siblings with special needs. The findings may also aid in the development of preventive programs for siblings of children with DAMP and Asperger syndrome.

Adaptation, Psychological↗

PubMed1995

Misincorporation of dAMP opposite 2-hydroxyadenine, an oxidative form of adenine.

Nucleotide incorporation opposite an oxidative form of adenine, 2-hydroxyadenine (2-OH-Ade) was investigated. When a primed template with 2-OH-Ade was treated with an exonuclease-deficient Klenow fragment of Escherichia coli DNA polymerase I (KFexo-), recombinant rat DNA polymerase beta (pol beta) or calf thymus DNA polymerase alpha (pol alpha), incorporation of dTMP and dAMP was observed. In addition, KFexo- inserted dGMP as well. A steady-state kinetic study indicated that the insertion of dAMP and dTMP opposite the DNA lesion occurred with similar frequency with KFexo- and pol beta. Insertion of dTMP opposite 2-OH-Ade was favored to that of dAMP by pol alpha. Chain extension from the A.2-OH-Ade pair is less favored than that from the T.2-OH-Ade pair by all three DNA polymerase. Analysis of full-length products of in vitro DNA synthesis showed that dTMP and dAMP were incorporated by DNA polymerases and that exonuclease-proficient and -deficient Klenow fragments also inserted dGMP opposite 2-OH-Ade. These results suggest that formation of 2-OH-Ade from A in DNA will induce A-->T and A-->C transversions in cells.

Animals↗

PubMed1993

The use of a mechanical model to describe the stiffness and damping characteristics of the knee joint in healthy adults.

BACKGROUND AND PURPOSE: Stiffness is a common clinical complaint but is rarely quantified by clinicians. The purpose of this study was to determine the reliability of a relaxed oscillation test that yields stiffness and damping coefficients of the knee. These coefficients describe the knee joint's resistance to bending and the time-dependent nature of that resistance. SUBJECTS AND METHODS: Effects of age, gender, and knee position on these coefficients were assessed in 96 healthy volunteers aged 20 to 79 years. Measures were based on the premise that the knee joint can be modeled as a damped spring. Oscillations of the knee were recorded using an electrogoniometer with the knee oscillating through about 45 and 75 degrees of knee flexion. RESULTS: Intraclass correlation coefficients revealed moderate to high reliability in the measurements taken three times in the same test session and on three separate days. Analysis of variance showed significant increases in stiffness and damping coefficients in the male subjects as compared with the female subjects. Analysis of variance also suggested an age effect on stiffness coefficients at the 75-degree test position, with decreasing stiffness with age. Both stiffness and damping coefficients were significantly smaller when measured at the 75-degree test position compared with the 45-degree position (Student's t test). CONCLUSION AND DISCUSSION: These results demonstrate a reliable method of measuring knee joint stiffness, and they correlate well with known morphological differences related to age and gender. This measure may prove to be more useful in evaluating the function of the knee than more commonly used assessments. It may also lead to a better understanding of how the knee functions in such activities as locomotion.

Adult↗

PubMed2005

Vibration characteristics of the human spine under axial cyclic loads: effect of frequency and damping.

STUDY DESIGN: A nonlinear finite element model of lumbar spine segment L3-L5 was developed. The effects of upper body mass, nucleus injury, damping, and different vibration frequency loads were analyzed for the whole body vibration. OBJECTIVES: To analyze the influence of whole body vibration on facets of lumbar spine and to analyze the influence of nucleus injury, upper body mass, and damping on the dynamic characteristics of lumbar spine. SUMMARY OF BACKGROUND DATA: Many studies have investigated whole body vibration for lumbar spine. However, very few investigations analyzed the influence of whole body vibration on facets and vibration characteristics of the injured spine. METHODS: The nonlinear finite element model of the L3-L5 segment was constructed based on the embalmed vertebra geometry and validated. Besides static and modal analyses, transient dynamic analyses were also conducted on the model with an upper body mass under damping and different frequency cyclic loads. RESULTS: In the period of human spine vibration, the vibration effects of different regions of the lumbar spine are not the same. Anterior regions of the L3-L5 segment show small vibration amplitudes, but posterior regions show large amplitudes. The vibration amplitude of facet contact force is more than 2.0-fold as large as that of displacement and stress on vertebrae or discs. To decrease the weight of the upper body will increase the resonant frequency. To remove the nucleus will decrease the resonant frequencies. The vibration displacement, stress, and facet contact force will reduce generally by 50% using damping ratio 0.08. CONCLUSIONS: The posterior regions of intervertebral discs of the lumbar spine are easy to injure during long-term whole body vibration compared to anterior regions. The vibration of human spine is more dangerous to facets, especially during whole body vibration approximating a sympathetic vibration, which may lead to abnormal remodeling and disorder of the lumbar spine.

Cadaver↗

PubMed2003

Human hopping on damped surfaces: strategies for adjusting leg mechanics.

Fast-moving legged animals bounce along the ground with spring-like legs and agilely traverse variable terrain. Previous research has shown that hopping and running humans maintain the same bouncing movement of the body's centre of mass on a range of elastic surfaces by adjusting their spring-like legs to exactly offset changes in surface stiffness. This study investigated human hopping on damped surfaces that dissipated up to 72% of the hopper's mechanical energy. On these surfaces, the legs did not act like pure springs. Leg muscles performed up to 24-fold more net work to replace the energy lost by the damped surface. However, considering the leg and surface together, the combination appeared to behave like a constant stiffness spring on all damped surfaces. By conserving the mechanics of the leg-surface combination regardless of surface damping, hoppers also conserved centre-of-mass motions. Thus, the normal bouncing movements of the centre of mass in hopping are not always a direct result of spring-like leg behaviour. Conserving the trajectory of the centre of mass by maintaining spring-like mechanics of the leg-surface combination may be an important control strategy for fast-legged locomotion on variable terrain.

Biomechanical Phenomena↗

PubMed2002

Collisionless damping of nonlinear dust ion acoustic wave due to dust charge fluctuation.

A dissipation mechanism for the damping of the nonlinear dust ion acoustic wave in a collisionless dusty plasma consisting of nonthermal electrons, ions, and variable charge dust grains has been investigated. It is shown that the collisionless damping due to dust charge fluctuation causes the nonlinear dust ion acoustic wave propagation to be described by the damped Korteweg-de Vries equation. Due to the presence of nonthermal electrons, the dust ion acoustic wave admits both positive and negative potential and it suffers less damping than the dust acoustic wave, which admits only negative potential.

Journal Article↗

PubMed2003

Longitudinal oscillations and linear Landau damping in quark-gluon plasma.

On the basis of the semiclassical kinetic Vlasov equation for quark-gluon plasma and the Yang-Mills equation in covariant gauge, linear Landau damping for electrostatic perturbations such as Langmuir waves is investigated for the extreme-relativistic and strongly relativistic cases. It has been observed that for the extreme-relativistic case, wherein the thermal speed of the particles exceeds the phase velocity of the perturbations, the linear Landau damping is absent as has been reported in the literature. However, a departure from extreme-relativistic case generates an imaginary component of the frequency giving rise to linear Landau damping effect. The relevant integral for the conductivity tensor has been evaluated and the dispersion relation for the longitudinal part of the oscillation was obtained. Further, it is also noted that both the real part of the oscillation frequency and the damping rate are sensitive to the choice of the wave number k and the Debye length lambda(D) associated with quark-gluon plasma.

Journal Article↗