3,090 research outputs found
On the performance of a nonlinear vibration isolator consisting of axially loaded curved beams
No full textA desirable characteristic for nonlinear vibration isolators is a high static stiffness and a low dynamic stiffness. A curved beam is a possible candidate for this role provided that the amplitude of vibration about the static equilibrium position is sufficiently small. However, for large amplitude oscillations, the nonlinear dynamics may have a detrimental effect. This paper considers the force transmissibility of a single degree-of-freedom system where the stiffness element is a curved, axially loaded beam. The transmitted force is calculated by numerical time domain integration of the equations of motion. The exact force-deflection relation for the beam is used for the spring. By comparison, a frequency domain solution is sought using the Harmonic Balance (HB) method in which the system is modelled as a Duffing oscillator. It is shown that the HB and time domain solutions are in close agreement for small amplitudes of excitation and both predict advantageous performance of the nonlinear isolator compared with its equivalent linear counterpart. However, significant discrepancies occur between the two solutions for large excitation since the beam can no longer be approximated by a linear and a cubic stiffness. It is also strongly asymmetric – soft in compression but stiff in extreme extension– which gives rise to an impulse in the transmitted force in each fundamental period. This numerical problem is alleviated by inserting a linear spring in series with the beam isolator with a modest compromise in isolation performance at the excitation frequency
Relationship between biodistribution of a novel thymidine phosphorylase (TP) imaging probe and TP expression levels in normal mice
No full textObjective: Thymidine phosphorylase (TP) is a key enzyme in the pyrimidine nucleoside salvage pathway and its expression is upregulated in a wide variety of solid tumors. In mice, we previously observed high and specific accumulation levels of our TP imaging probe, radioiodinated 5-iodo-6-[(2-iminoimidazolidinyl)methyl]uracil (IIMU) not only in high-TP-expressing tumors, but also in the liver and small intestine. To clarify the reason for the high accumulation levels of radioiodinated IIMU in the liver and small intestine, we investigated the expression levels of TP in mice in comparison with the biodistribution of radioiodinated IIMU (123I-IIMU). Methods: BALB/cCrSlc mice were injected with 123I-IIMU, and the radioactivity levels [%ID/g (normalized to a mouse of 25 g body weight)] in the tissues of interest were determined 0.5, 1, 3 and 24 h after the injection (n = 5, each time point). To determine the expression levels of TP, BALB/cCrSlc and ddy mice (n = 3/each strain) were euthanized, and the heart, liver, lung, spleen, kidney, stomach, small intestine, large intestine and brain were collected. The mRNA and protein expression levels of TP in these organs were examined by quantitative reverse transcription-polymerase chain reaction and western blot analyses, respectively. Results: In BALB/cCrSlc mice administered 123I-IIMU, markedly high radioactivity levels were observed in the liver [1.568 ± 0.237 (%ID/g)] and small intestine [0.506 ± 0.082 (%ID/g)], whereas those in the other tissues were fairly low [<0.010 ± 0.003 (%ID/g)] 30 min after the injection. The highest expression levels of TP mRNA were also observed in the liver and small intestine among the tissues tested. Immunoblotting showed intense immunoreactive bands of the TP protein for the liver and small intestine, whereas no notable bands were detected for other tissues. Similar expression profiles of TP mRNA and protein were observed in ddy mice. Conclusion: We confirmed TP expression in various tissues of mice at the mRNA and protein levels: high TP expression levels were observed in the liver and small intestine. These high TP expression levels are consistent with the high accumulation levels of 123I-IIMU in these tissues. Our results may provide important information about the physiological accumulation of 123I-IIMU, which may be useful for the clinical diagnostic imaging of TP
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The sources of phosphorus in the waters of Great Britain
No full textTotal phosphorus (TP) and soluble reactive phosphorus (SRP) loads to watercourses of the River Basin Districts (RBDs) of Great Britain (GB) were estimated using inventories of industrial P loads and estimates of P loads from sewage treatment works and diffuse P loads calculated using region-specific export coefficients for particular land cover classes combined with census data for agricultural stocking densities and human populations. The TP load to GB waters was estimated to be 60 kt yr(-1), of which households contributed 73%, agriculture contributed 20%, industry contributed 3%, and 4% came from background sources. The SRP load to GB waters was estimated to be 47 kt yr(-1), of which households contributed 78%, agriculture contributed 13%, industry contributed 4%, and 6% came from background Sources. The 'average' area-normalized TP and SRP loads to GB waters approximated 2.4 kg ha(-1) yr(-1) and 1.8 kg ha(-1) yr(-1), respectively. A consideration of uncertainties in the data contributing to these estimates suggested that the TP load to GB waters might lie between 33 and 68 kt yr(-1), with agriculture contributing between 10 and 28% of the TP load. These estimates are consistent with recent appraisals of annual TP and SRP loads to GB coastal waters and area-normalized TP loads from their catchments. Estimates of the contributions of RBDs to these P loads were consistent with the geographical distribution of P concentrations in GB rivers and recent assessments of surface waters at risk from P Pollution
Influence of the hyporheic zone on the phosphorus dynamics of a large gravel-bed river, Garonne River, France
No full textPhosphorus (P) concentrations in sediments and in surface and interstitial water from three gravel bars in a large river (Garonne River, southern France) were measured daily, downstream of a wastewater treatment plant for a city of 740 000 inhabitants (Toulouse). Measurements were made of vertical hydraulic gradient (VHG), total dissolved phosphorus (TDP), soluble reactive phosphorus (SRP) and total phosphorus (TP) in water and of three extractable forms of phosphorus (water extractable, NaOH extractable and H2SO4 extractable) in hyporheic sediments from the gravel bars. Dissolved phosphorus was the major contributor to TP (74–79%) in both interstitial and surface waters on all sampling dates, and in most cases surface water P concentrations were significantly higher than interstitial concentrations. Hyporheic sediment TP concentrations ranged between 269 and 465 μg g -1 and were highest in fine sediment fractions. Acid-extractable P, a non-bioavailable form, represented at least 95% of sediment TP. A positive relationship was observed between VHG and TP in two of the gravel bars, with wells that were strongly downwelling having lower TP concentrations. These results suggest that in downwelling zones, hyporheic sediments can trap surface-derived dissolved P, and that much of this P becomes stored in refractory particulate forms. Bioavailable P is mainly present in dissolved form and only occupies a small fraction of total P, with particulate P comprising the majority of total P
Biogeography of Wood-Boring Crustaceans (Isopoda: Limnoriidae) Established in European Coastal Waters
No full textMarine wood-borers of the Limnoriidae cause great destruction to wooden structures exposed in the marine environment. In this study we collated occurrence data obtained from field surveys, spanning over a period of 10 years, and from an extensive literature review. We aimed to determine which wood-boring limnoriid species are established in European coastal waters; to map their past and recent distribution in Europe in order to infer species range extension or contraction; to determine species environmental requirements using climatic envelopes. Of the six species of wood-boring Limnoria previously reported occurring in Europe, only Limnoria lignorum, L. quadripunctata and L. tripunctata are established in European coastal waters. L. carinata and L. tuberculata have uncertain established status, whereas L. borealis is not established in European waters. The species with the widest distribution in Europe is Limnoria lignorum, which is also the most tolerant species to a range of salinities. L. quadripunctata and L. tripunctata appear to be stenohaline. However, the present study shows that both L. quadripunctata and L. tripunctata are more widespread in Europe than previous reports suggested. Both species have been found occurring in Europe since they were described, and their increased distribution is probably the results of a range expansion. On the other hand L. lignorum appears to be retreating poleward with ocean warming. In certain areas (e.g. southern England, and southern Portugal), limnoriids appear to be very abundant and their activity is rivalling that of teredinids. Therefore, it is important to monitor the distribution and destructive activity of these organisms in Europe
Modelling of phosphorus inputs to rivers from diffuse and point sources.
No full textThe difference in timing of point and diffuse phosphorus (P) delivery to a river produces clear differences in the P concentration – flow relationship. Point inputs decrease in concentration with increasing river flow, due to dilution of a relatively constant input, whereas diffuse load usually increases with river flow. This study developed a simple model, based on this fundamental difference, which allowed point and diffuse inputs to be quantified by modelling their contribution to river P concentration as a power law function of flow.
The relationships between total phosphorus (TP) concentration and river flow were investigated for three contrasting UK river catchments; the Swale (Yorkshire), the Frome (Dorset) and the Avon (Warwickshire). The model was fitted to this empirical data to give estimates of point and diffuse load inputs at each monitoring site, at high temporal resolution. The model produced TP source apportionments that were similar to those derived from an export coefficient approach. For many diffuse-dominated sites within this study (with up to 75% of the annual TP load derived from diffuse sources), the model showed that reductions of point inputs would be most effective in order to reduce eutrophication risk, due to point source dominance during the plant and algae growing period. This modelling approach should provide simple, robust and rapid TP source apportionment from most concentration – flow datasets. It does not require GIS, information on land use, catchment size, population or livestock density, and could provide a valuable and versatile tool to catchment managers for determining suitable river mitigation options
Free vibration characteristics of an isolation system with a spring relaxed damper
No full textVibration isolators are frequently represented by the classical Voigt model of a spring and viscous damper in parallel. In cases where this model is appropriate, isolation at high frequencies is compromised by transmission of forces through the damper. This drawback can be mitigated against to some extent by including a ‘relaxation’ spring in series with the damper. The forced response of this ‘Zener’ model is discussed in the literature.
This paper is concerned with the free vibration characteristics of the Zener model. Analytical expressions are given for the roots of the characteristic equation and the root loci are presented. As the damping coefficient increases, the effective damping in the system is seen to rise, peak and then tend to zero as the damping coefficient tends to infinity. It is further shown that when the relaxation spring stiffness is less than precisely eight times the primary spring stiffness then critical damping cannot be achieved. Conversely, when this ratio of stiffnesses is greater than eight then two critical damping values exist and the damping ratio can no longer be defined in the conventional way. Alternative ways of quantifying damping for such a model are discussed
Analysis of an isolation system consisting of a parallel combination of a spring and an elastically supported damper
No full textDelamination of surface accretions with structural waves: piezo-actuation and power requirements
No full textUnwanted accretions on structures, such as aircraft and wind turbine icing or deposits in pipes, are a common problem, which can pose a serious safety threat if not treated effectively and punctually. In this paper we investigate the capability of piezo-excited structural waves for delaminating accreted material. The core of the concept is to utilise the stress distribution associated with waves propagating through the structure to detach unwanted build-up. We apply a wave-based technique for modelling piezoelectric excitation based on semi-analytical finite elements to calculate the shear stress at the interface between the host structure and the accretion generated by piezoactuated waves. Our analyses include the effects of the actuator’s dynamics and allow for comparing different types of actuators, identifying the most effective frequency of excitation and formulating realistic power requirements. For the dual purpose of proof of concept and validation of the model, we present a demonstration experiment in which patches of accreted material are removed from a beam-like waveguide with emulated anechoic terminations using ultrasonic excitation
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