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PubMed1989

A theoretical treatment of damped oscillations in the transient state kinetics of single-enzyme reactions.

An extension of the available kinetic theory for reactions in the transient state is presented which establishes that single-enzyme reactions may exhibit damped oscillations under the conditions of standard kinetic experiments performed by stopped-flow techniques. Such oscillations may occur for reasonable magnitudes of rate constants in the enzymic reaction mechanism and at physiological concentrations of enzyme and substrate. In the simplest reaction systems, the oscillations will be strongly damped and lead to progress curves resembling those of a reaction governed by standard exponential transients; statistical regression methods may then have to be applied for their detection and characterization. The observation that single-enzyme reactions may exhibit oscillatory behaviour points to a previously unrecognized possible source of the damped oscillations observed in metabolic systems such as the pathways of glycolysis or photosynthesis.

Catalysis↗

PubMed1993

Children with deficits in attention, motor control and perception (DAMP) almost grown up: general health at 16 years.

One hundred and one children (56 with and 45 without deficits in attention, motor control and perception (DAMP)), originally diagnosed at six or seven years of age and belonging to a representative cohort of children from the general population were followed up at 16 and 17 years of age. There was a significant excess of substance abuse, fractures and other accidents in the DAMP group than among controls, in addition to more motor co-ordination problems, clumsiness, and height and weight problems. Mean complex visual reaction time was significantly longer in the DAMP group, accounted for by the number of boys in the group. It appears that 10-year outcome for children who had attention problems and clumsiness during the preschool period is considerably poorer than for those who did not have such problems.

Adolescent↗

PubMed1988

The affinity of some acetylenic analogues of 4-DAMP methobromide for muscarinic receptors in guinea-pig ileum and atria.

1. The replacement of 4-hydroxy-N-methyl piperidine (HO NMe) in 4-diphenylacetoxy-N-methyl piperidine (4-DAMP) metho-bromide by 4-hydroxy-but-2-ynylamines (HOCH2C=CCH2NR2) reduces the affinity for muscarine-sensitive acetylcholine receptors in guinea-pig ileum and atria. It does not abolish selectivity. The tertiary amines are more active and more selective than the corresponding quaternary salts. 2. Analogous derivatives of 4-hydroxy-but-2-ynylamines which lack the ester group (i.e. substituted 4-hydroxymethyl-propynyl amines) are less active and less selective. The quaternary compounds are more active than the tertiary bases. 3. The diphenylcarbamyl ester of 4-hydroxy-N-methylpiperidine methobromide has less than one-thousandth of the activity of the diphenylacetyl ester (4-DAMP methobromide) and is not selective. 4. Although 4-diphenylacetoxy-butynyl dimethylamine is only about one-hundredth as active as 4-DAMP methobromide it appears to have comparable selectivity. It is an interesting compound because it is a tertiary amine and should cross membranes.

Animals↗

PubMed2004

Dampness in buildings and health (DBH): Report from an ongoing epidemiological investigation on the association between indoor environmental factors and health effects among children in Sweden.

UNLABELLED: With the aim of identifying health-relevant exposures in buildings, an epidemiological study "Dampness in Buildings and Health" (DBH) started in the year 2000 in Sweden. The health focus of the study is on asthma and allergic symptoms among small children and their parents. The first step in the study was an epidemiological cross-sectional questionnaire on housing and health involving 14,077 preschool children in the county of Värmland in Sweden (March-April 2000). Self-reported moisture-related problems in the building were strongly associated with asthma, allergic symptoms, and airway infections among children and adults. Other factors associated with symptoms among the children were allergic heredity, smoking in the family, male sex, urban living, short breast feeding, pet keeping, daycare attendance, non-farming life and some food habits. The second step in the study was a nested case-control study including 198 children with symptoms and 202 healthy controls. A detailed clinical examination by physicians in parallel with extensive inspections and measurements in the subjects' homes were conducted from October 2001 to April 2002. The influence of selection bias in case-control studies has been studied, and questionnaires on self-reported symptoms and building characteristics have been validated. Identified risk factors for allergic symptoms are, e.g., inspector-observed dampness, a low ventilation rate, endotoxin, Penicillium and phthalates in dust. In the third phase, a 5-year follow-up study will be carried out during 2005. The same questionnaire as used in DBH-phase 1 will be distributed to the 10,852 children/parents who responded to the first questionnaire in 2000. Finally, in a fourth phase, controlled experimental studies in climate chambers and in vitro tests regarding findings from DBH-Phase 2 are planned to be conducted during 2004-08. PRACTICAL IMPLICATIONS: Asthma and allergies among small children are associated with a number of risk factors in the indoor environment. In investigations of building-related health problems many factors have to be considered, including "dampness" emissions from building materials, and ventilation rates.

Adolescent↗

PubMed2004

Modal damping for monitoring bone integrity and osteoporosis.

We applied a noninvasive method to assess bone structural integrity. The method is based on the measurement of the dynamic characteristics of the bone (quality factor and modal damping factor) by applying vibration excitation in the range of acoustic frequencies, in the form of an acoustic sweep signal. Excised sheep femora were tested to detect changes in modal damping, density (kg/m3), bone mineral density (kg/m2) and bone mineral (hydroxyapatite) percentage. The changes were recorded after each time of chemical treatment of the bones performed to gradually cause mineral removal, thus simulating osteoporosis. It was shown that the change in quality factor and damping was in all cases on average equal or greater to the change in all other measured characteristics, thus strengthening the potential of the proposed method to become a valuable assessment tool for monitoring bone integrity and osteoporosis.

Acoustics↗

PubMed2001

Time-domain simulation of damped impacted plates. II. Numerical model and results.

A time-domain model for the flexural vibrations of damped plates was presented in a companion paper [Part I, J. Acoust. Soc. Am. 109, 1422-1432 (2001)]. In this paper (Part II), the damped-plate model is extended to impact excitation, using Hertz's law of contact, and is solved numerically in order to synthesize sounds. The numerical method is based on the use of a finite-difference scheme of second order in time and fourth order in space. As a consequence of the damping terms, the stability and dispersion properties of this scheme are modified, compared to the undamped case. The numerical model is used for the time-domain simulation of vibrations and sounds produced by impact on isotropic and orthotropic plates made of various materials (aluminum, glass, carbon fiber and wood). The efficiency of the method is validated by comparisons with analytical and experimental data. The sounds produced show a high degree of similarity with real sounds and allow a clear recognition of each constitutive material of the plate without ambiguity.

Journal Article↗

PubMed2004

Transient energy exchange between a primary structure and a set of oscillators: return time and apparent damping.

In this paper we examine the conditions that influence the return time, the time it takes before energy returns from a set of satellite oscillators attached to a primary structure. Two methods are presented to estimate the return time. One estimate is based on an analysis of the reaction force on a rigid base by a finite number of oscillators as compared with an infinite number of continuously distributed oscillators. The result gives a lower-bound estimate for the return time. A more accurate estimation results from considering the dynamic behavior of a set of oscillators as waves in a waveguide. Such an analogy explains energy flow between a primary structure and the oscillators in terms of pseudowaves and shows that a nonlinear frequency distribution of the oscillators leads to pseudodispersive waves. The resulting approximate expressions show the influence of the natural frequency distribution within the set of oscillators, and of their number, on the return time as compared with the asymptotic case of a continuous set with infinite oscillators. In the paper we also introduce a new method based on a Hilbert envelope to estimate the apparent damping loss factor of the primary structure during the return time considering transient energy flow from the primary structure before any energy reflects back from the attached oscillators. The expressions developed for return time and damping factor show close agreement with direct numerical simulations. The paper concludes with a discussion of the return time and its relation to apparent damping and optimum frequency distribution within a set of oscillators that maximize these quantities.

Journal Article↗

PubMed1990

Biological Control of Damping-Off of Alfalfa Seedlings with Bacillus cereus UW85.

We explored the potential of biological control of alfalfa (Medicago sativa L.) seedling damping-off caused by Phytophthora megasperma f. sp. medicaginis by screening root-associated bacteria for disease suppression activity in a laboratory bioassay. A total of 700 bacterial strains were isolated from the roots of field-grown alfalfa plants by using Trypticase soy agar. A simple, rapid assay was developed to screen the bacteria for the ability to reduce the mortality of Iroquois alfalfa seedlings that were inoculated with P. megasperma f. sp. medicaginis zoospores. Two-day-old seedlings were planted in culture tubes containing moist vermiculite, and each tube was inoculated with a different bacterial culture. Sufficient P. megasperma f. sp. medicaginis zoospores were added to each tube to result in 100% mortality of control seedlings. Of the 700 bacterial isolates tested, only 1, which was identified as Bacillus cereus and designated UW85, reduced seedling mortality to 0% in the initial screen and in two secondary screens. Both fully sporulated cultures containing predominantly released spores and sterile filtrates of these cultures of UW85 were effective in protecting seedlings from damping-off; filtrates of cultures containing predominantly vegetative cells or endospores inside the parent cell had low biocontrol activity. Cultures grown in two semidefined media had significantly greater biocontrol activities than cultures grown in the complex tryptic soy medium. In a small-scale trial in a field infested with P. megasperma f. sp. medicaginis, coating seeds with UW85 significantly increased the emergence of alfalfa. The results suggest that UW85 may have potential as a biocontrol agent for alfalfa damping-off, thus providing an alternative to current disease control strategies.

Journal Article↗

PubMed1996

Biocontrol of Rhizoctonia solani Damping-Off of Tomato with Bacillus subtilis RB14.

Bacillus subtilis RB14, which showed antibiotic activities against several phytopathogens in vitro by producing the antibiotics iturin A and surfactin, was subjected to a pot test to investigate its ability to suppress damping-off of tomato seedlings caused by Rhizoctonia solani. To facilitate recovery from soil, B. subtilis RB14-C, a spontaneous streptomycin-resistant mutant of RB14, was used. Damping-off was suppressed when the culture broth, cell suspension, or cell-free culture broth of RB14-C was inoculated into soil. Iturin A and surfactin were recovered from the soils inoculated with the cell suspension of RB14-C, confirming that RB14-C produced them in soil. The gene lpa-14, which was cloned from RB14 and required for the production of both antibiotics, was mutated in RB14-C, and a mutant, R(Delta)1, was constructed. The level of disease suppressibility of R(Delta)1 was low, but R(Delta)1(pC115), a transformant of R(Delta)1 with the plasmid pC115 carrying lpa-14, was restored in suppressibility. These results show that the antibiotics iturin A and surfactin produced by RB14 play a major role in the suppression of damping-off caused by R. solani. RB14-C, R(Delta)1, and R(Delta)1(pC115) persisted in soil during the experimental period and were recovered from the soil, mostly as spores.

Journal Article↗

PubMed1996

Involvement of Pyochelin and Pyoverdin in Suppression of Pythium-Induced Damping-Off of Tomato by Pseudomonas aeruginosa 7NSK2.

The plant growth-promoting rhizobacterium Pseudomonas aeruginosa 7NSK2 produces three siderophores when iron is limited: the yellow-green fluorescent pyoverdin, the salicylate derivative pyochelin, and salicylic acid. This Pseudomonas strain was shown to be an efficient antagonist of Pythium-induced damping-off. The role of pyoverdin and pyochelin in the suppression of Pythium splendens was investigated by using various siderophore-deficient mutants derived from P. aeruginosa 7NSK2 in a bioassay with tomato (Lycopersicon esculentum). To provide more insight into the role of pyochelin in antagonism, mutant KMPCH, deficient in the production of pyoverdin and pyochelin, was complemented for pyochelin production. The complementing clone was further characterized by subcloning and transposon mutagenesis and used to generate a pyochelin-negative, pyoverdin-positive mutant by marker exchange. All mutants were able to reduce Pythium-induced preemergence damping-off to some extent. Production of either pyoverdin or pyochelin proved to be necessary to achieve wild-type levels of protection against Pythium-induced postemergence damping-off. Mutant KMPCH inhibited P. splendens but was less active than the parental strain. This residual protection could be due to the production of salicylic acid. Since pyoverdin and pyochelin are both siderophores, siderophore-mediated iron competition could explain the observed antagonism and the apparent interchangeability of the two compounds. We cannot, however, exclude the possibility that both siderophores act in an indirect way.

Journal Article↗

PubMed1996

Microbial Properties of Composts That Suppress Damping-Off and Root Rot of Creeping Bentgrass Caused by Pythium graminicola.

Composts prepared from a variety of feedstocks were tested for their ability to suppress seedling and root diseases of creeping bentgrass caused by Pythium graminicola. Among the most suppressive materials in laboratory experiments were different batches of a brewery sludge compost and a biosolids compost from Endicott, N.Y. Batches of these composts that were initially not suppressive to Pythium damping-off became more suppressive with increasing compost age. Leaf, yard waste, food, and spent mushroom composts as well as certain biosolids, cow manure, chicken-cow manure, and leaf-chicken manure composts were not suppressive to Pythium damping-off. In some cases, turkey litter, chicken manure, chicken-leaf, and food waste composts were inhibitory to creeping bentgrass seed germination in laboratory experiments. Microbial populations varied among all of the composts tested. Bacterial populations were high in all composts except the turkey litter compost, in which populations were 1,000- to 10,000-fold lower than in the other composts tested. Among the highest populations of heterotrophic fungi and antibiotic-producing actinomycetes were those found in all batches of the brewery sludge compost, whereas the lowest populations were found in turkey litter, chicken manure, and food waste composts. Heat treatment of suppressive composts reduced populations of bacteria, fungi, and actinomycetes in all composts tested. Disease suppressiveness was also reduced or eliminated in heated composts. Amending heated composts with small amounts of nonheated compost restored suppressive properties and partially restored microbial populations to wild-type levels. A strong negative relationship between compost microbial activity (as measured by the hydrolysis of fluorescein diacetate) and Pythium damping-off severity was observed. When composts were applied to creeping bentgrass in field experiments, a significant level of suppressiveness was evident with some composts when disease pressure was high (i.e., disease ratings high in uninoculated plots). A 1991 batch of turkey litter compost and the 1990 batch of Endicott biosolids were consistently suppressive to foliar symptoms of Pythium root rot on creeping bentgrass. This study indicates that suppression of Pythium diseases of creeping bentgrass in batches of brewery sludge and Endicott biosolids composts, and possibly in other suppressive composts examined in less detail in this study, is related directly to the microbial activities in the composts. On the other hand, the mechanisms of Pythium suppression in turkey litter and perhaps other poultry-based composts is not related directly to the compost microbial activity. Although turkey litter showed a lack of suppressiveness in laboratory bioassays and low microbial populations and activity, it resulted in a significant and consistent level of suppressiveness in field experiments. Therefore, the microbiological properties of Pythium-suppressive composts may differ substantially, and measurements of microbial populations and activity may not be predictive of the level of disease suppression in all composts.

Journal Article↗

PubMed1999

Possible role of xanthobaccins produced by Stenotrophomonas sp. strain SB-K88 in suppression of sugar beet damping-off disease.

Three antifungal compounds, designated xanthobaccins A, B, and C, were isolated from the culture fluid of Stenotrophomonas sp. strain SB-K88, a rhizobacterium of sugar beet that suppresses damping-off disease. Production of xanthobaccin A in culture media was compared with the disease suppression activities of strain SB-K88 and less suppressive strains that were obtained by subculturing. Strain SB-K88 was applied to sugar beet seeds, and production of xanthobaccin A in the rhizosphere of seedlings was confirmed by using a test tube culture system under hydroponic culture conditions; 3 microg of xanthobaccin A was detected in the rhizosphere on a per-plant basis. Direct application of purified xanthobaccin A to seeds suppressed damping-off disease in soil naturally infested by Pythium spp. We suggest that xanthobaccin A produced by strain SB-K88 plays a key role in suppression of sugar beet damping-off disease.

Anti-Bacterial Agents↗

PubMed2002

Occurrence of toxigenic Aspergillus versicolor isolates and sterigmatocystin in carpet dust from damp indoor environments.

Over the past decade, there has been growing concern regarding the role of toxigenic fungi in damp indoor environments; however, there is still a lack of field investigations on exposure to mycotoxins. The goal of our pilot study was to quantify the proportion of toxigenic Aspergillus versicolor isolates in native carpet dust from damp dwellings with mold problems and to determine whether sterigmatocystin can be detected in this matrix. Carpet dust samples (n = 11) contained from <2.5 x 10(1) to 3.6 x 10(5) (median, 3.1 x 10(4)) A. versicolor CFU/g of dust, and the median proportion of A. versicolor from total culturable fungi was 18%. Based on thin-layer chromatography detection of sterigmatocystin, 49 of 50 A. versicolor isolates (98%) were found to be toxigenic in vitro. By using high-performance liquid chromatography-electrospray ionization tandem mass spectrometry, sterigmatocystin could be detected in low concentrations (2 to 4 ng/g of dust) in 2 of 11 native carpet dust samples. From this preliminary study, we conclude that most strains of A. versicolor isolated from carpet dust are able to produce sterigmatocystin in vitro and that sterigmatocystin may occasionally occur in carpet dust from damp indoor environments. Further research and systematic field investigation are needed to confirm our results and to provide an understanding of the health implications of mycotoxins in indoor environments.

Air Pollution, Indoor↗

PubMed2002

Muscle activity damps the soft tissue resonance that occurs in response to pulsed and continuous vibrations.

This study tested the hypotheses that when the excitation frequency of mechanical stimuli to the foot was close to the natural frequency of the soft tissues of the lower extremity, the muscle activity increases 1) the natural frequency and 2) the damping to minimize resonance. Soft tissue vibrations were measured with triaxial accelerometers, and muscle activity was measured by using surface electromyography from the quadriceps, hamstrings, tibialis anterior, and triceps surae groups from 20 subjects. Subjects were presented vibrations while standing on a vibrating platform. Both continuous vibrations and pulsed bursts of vibrations were presented, across the frequency range of 10-65 Hz. Elevated muscle activity and increased damping of vibration power occurred when the frequency of the input was close to the natural frequency of each soft tissue. However, the natural frequency of the soft tissues did not change in a manner that correlated with the frequency of the input. It is suggested that soft tissue damping may be the mechanism by which resonance is minimized at heel strike during running.

Adult↗

PubMed2000

Transthoracic cardioversion of atrial fibrillation: comparison of rectilinear biphasic versus damped sine wave monophasic shocks.

BACKGROUND: Clinical studies have shown that biphasic shocks are more effective than monophasic shocks for ventricular defibrillation. The purpose of this study was to compare the efficacy of a rectilinear biphasic waveform with a standard damped sine wave monophasic waveform for the transthoracic cardioversion of atrial fibrillation. METHODS AND RESULTS: In this prospective, randomized, multicenter trial, patients undergoing transthoracic cardioversion of atrial fibrillation were randomized to receive either damped sine wave monophasic or rectilinear biphasic shocks. Patients randomized to the monophasic protocol (n=77) received sequential shocks of 100, 200, 300, and 360 J. Patients randomized to the biphasic protocol (n=88) received sequential shocks of 70, 120, 150, and 170 J. First-shock efficacy with the 70-J biphasic waveform (60 of 88 patients, 68%) was significantly greater than that with the 100-J monophasic waveform (16 of 77 patients, 21%, P<0.0001), and it was achieved with 50% less delivered current (11+/-1 versus 22+/-4 A, P<0.0001). Similarly, the cumulative efficacy with the biphasic waveform (83 of 88 patients, 94%) was significantly greater than that with the monophasic waveform (61 of 77 patients, 79%; P=0.005). The following 3 variables were independently associated with successful cardioversion: use of a biphasic waveform (relative risk, 4.2; 95% confidence intervals, 1.3 to 13.9; P=0.02), transthoracic impedance (relative risk, 0.64 per 10-Omega increase in impedance; 95% confidence intervals, 0.46 to 0.90; P=0.005), and duration of atrial fibrillation (relative risk, 0.97 per 30 days of atrial fibrillation; 95% confidence intervals, 0.96 to 0.99; P=0.02). CONCLUSIONS: For transthoracic cardioversion of atrial fibrillation, rectilinear biphasic shocks have greater efficacy (and require less energy) than damped sine wave monophasic shocks.

Aged↗

PubMed2006

Effect of pre-strain on interfacial friction damping in carbon nanotube polymer composites.

This paper investigates the effect of mechanical pre-strain on interfacial friction damping in nanotube polymer composites. Oxidized single-walled carbon nanotubes were dispersed in a polycarbonate matrix using a solution mixing technique. To characterize the damping response, the material storage and loss modulus was measured by application of dynamic (sinusoidal) load to the nanocomposite in the uniaxial direction. A static pre-strain (in 0.35-0.85% range) was then superimposed on the dynamic strain to quantify its effect on the material response. The results indicate that application of pre-strain facilitates the activation of interfacial slip at the nanotube-polymer interfaces at relatively low dynamic strain amplitudes. This is because pre-strain raises the interfacial shear stress for the nanotube inclusions allowing the critical stress for tube-matrix interfacial slip to be reached at lower strain amplitudes. In this way pre-strain significantly improves the effectiveness of the nanotube-matrix sliding energy dissipation mechanism for damping enhancement in composite structures.

Carbon↗

PubMed1991

Light and norepinephrine similarly prevent damping of the melatonin rhythm in cultured chick pineal cells: regulation of coupling between the pacemaker and overt rhythms?

The circadian rhythm of melatonin output displayed by chick pineal cells in static culture damps rapidly in constant red light (RR). This can be seen in the first cycle following a switch from a cycle of 12 hr white light (L) and 12 hr red light (R) to RR. Melatonin output is higher during the "day" in R than it is in L, but higher that next night (in R) after daytime L than after daytime R. This effect might be due entirely to the entraining effect of L. Alternatively, the higher nocturnal output after daytime L could be related to the acute suppression caused by L; it might be a "rebound" phenomenon. These alternative hypotheses differ in their predictions for the effects of norepinephrine (NE) and pertussis toxin (PT). Previous results dissociated the acute and entraining effects of L: PT blocks the acute effect but not the entraining effect of L. NE mimics the acute effect of L (and is blocked by PT), but not the entraining effect. If L prevents damping entirely by entrainment, then NE should not mimic and PT should not block this same-cycle effect of daytime L on nocturnal melatonin output. However, the present research found that NE did mimic and PT did block this effect, indicating that the ability of L to prevent damping is mediated by a same-cycle "rebound" following L's acute inhibition of melatonin production. Furthermore, NE enhanced the "rebound" effect of daytime L, and cycles substituting NE for L were effective in driving the melatonin rhythm. Lowering extracellular potassium did not induce a "rebound," and adding exogenous melatonin did not prevent one. The difference between nocturnal melatonin synthesis after daytime R and that after daytime L or NE implies regulation of coupling between the output of the circadian pacemaker and melatonin production. These results also suggest a role for NE in regulating and maintaining the expression of the melatonin rhythm.

Animals↗

PubMed1996

Home dampness, moulds and their influence on respiratory infections and symptoms in adults in Finland.

The aim of this study was to analyse the prevalence of mouldy homes and their association with respiratory symptoms and diseases in a subarctic climate. A questionnaire was mailed to a random sample of 2,000 males and females, aged 25-64 yrs, living in the county of Kuopio, Finland. A total of 1,521 (76%) responded and 1,460 were selected for the final analysis. The prevalence of homes with visible mould was 4%; with the odour of mould 5%; with damp spots, visible mould or the odour of mould 15%; and with moisture/ water damage, damp spots, visible mould or the odour of mould 23%. The number of reports of bronchitis, common cold, atopy, allergic rhinitis, rhinitis, fever and chills, hoarseness, fatigue, difficulties in concentration, lumbar backache and stomach ache were strongly associated with living in a damp home. Bronchitis, hoarseness and difficulties in concentration had the strongest associations, with adjusted odds ratios (95% confidence limits) of: 2.04 (1.49-2.78), 2.23 (1.37-3.63) and 2.17 (1.35-3.50), respectively. After controlling for a possible reporting bias by excluding those subjects reporting lumbar backache and recurrent stomach pain, eye irritation and tiredness remained significant. In conclusion, living in a home with mould problems may increase the risk of respiratory infections and symptoms in adults.

Adult↗