Ultrasonic transducer calibration

When a material is placed under stress, small changes within the specimen release ultrasonic energy in the form of stress waves. The change may, for example, be a dislocation movement or the advancement of a crack tip. These ultrasonic pulses are termed Acoustic Emission and may be detected at the material surface by ultrasonic transducers. The detected pulse shape is related to the generating source, to the material geometry through which the pulse propagates and to the response of the ultrasonic transducer used to detect the waves. Work has been carried out to measure both the effect of wave propagation and to calibrate the response of ultrasonic transducers. Three types of ultrasonic wave may exist in a material with a non-zero shear modulus; these are longitudinal waves, shear waves and surface or Rayleigh waves. In a large number of specimen geometries, the surface wave has the largest amplitude. The response of a transducer to this wave is therefore very important. Most transducers respond to the out of plane motion of a material surface carrying ultrasonic waves. Therefore, to successfully calibrate a transducer, some absolute measurement of the out of plane motion due to surface waves must be made. An interferometer has been designed and constructed for this purpose. The calibration of ultrasonic transducers has enabled some development work to be carried oLt on high-fidelity piezoelectric transducers and on piezomagnetic transducers. It is not always possible to measure an ultrasonic pulse directly with a calibrated interferometric detector and therefore to enable a wider range of propagation problems to be investigated, various methods of ultrasonic pulse generation have been studied. These artificial sources of acoustic emission have included brittle fracture, laser impact and stimulation by piezoelectric transducers. This work has enabled theoretical calculations on pulse propagation to be verified

Recruitment of Veterinarians for Rural Communities through Education: The Veterinary Training Program for Rural Kansas

Veterinarians are important members of rural communities and provide valuable services to both community members and the food production systems in these areas. The population of new veterinary graduates entering rural, mixed animal practice is decreasing and several studies have concluded that a shortage of veterinarians in this area is apparent. The Veterinary Training Program for Rural Kansas (VTPRK) was created to address the educational and financial needs of students entering practice in rural Kansas. The program provides a forgivable loan for a select group of students during veterinary school and specific courses to help prepare these students for success in rural practice

The potential impact of BCG vaccine supply shortages on global paediatric tuberculosis mortality.

BACKGROUND: The Bacillus Calmette-Guérin (BCG) vaccine is provided to over 100 million neonates annually to protect against childhood tuberculosis (TB). Recent BCG manufacturing interruptions highlight global supply risks. We estimated the potential impact of BCG shortfalls on global paediatric (<15 years) TB mortality. METHODS: A static mathematical model was employed to estimate the number of paediatric TB deaths avoided by usual levels of BCG coverage, and potential additional TB deaths in the first 15 years of life due to 1-year BCG supply shortfalls of 6.3 % (as occurred in 2015) to 27.6 % (as anticipated without mitigating action in 2015) assuming no catch-up campaigns. RESULTS: BCG coverage without shortfalls, estimated at 90 % globally, was estimated to avoid 117,132 (95 % uncertainty range (UR): 5049-306,911) TB deaths globally per birth cohort in the first 15 years of life. An estimated 11,713 (UR: 505-30,691) additional TB deaths would occur in the first 15 years of life per 10 % (26 million dose) annual supply shortfall. A 16.5 million dose (6.3 %) shortfall as reported at the close of 2015, reflecting 84 % global coverage, was estimated as associated with 7433 (95 % UR: 320-19,477) excess TB deaths in the affected cohort in the first 15 years. A possible 24,914 (UR: 1074-65,278) additional deaths were avoided due to prompt shortfall reduction measures in 2015. CONCLUSIONS: BCG shortages could greatly increase paediatric TB mortality. Although rapid action in 2015 minimised BCG shortfalls, avoiding a large number of potential additional deaths, the possible public health impact of even relatively small shortfalls highlights the critical importance of ensuring secure future manufacturing capacity and global BCG supply continuity

Authors' reply

Thank you for the complementary comments on the experimental work reported in reference [1]. As you note, when considering the vibration of curved beams, it is important to acknowledge the work of L. S. D. Morley in the early 1960s. In reference [2], Morley developed a unified theory for the vibration of curved rods where the neutral axis forms a curve of constant radius of curvature. Morley's theory included the effects of rotary inertia and radial shear in a manner analogous to that of Timoshenko's theory for straight rods. Morley's theory also included the effect of extension of the neutral axis. It was shown in reference [2] that when the curvature is slight, the equations can be simplified and a Timoshenko-type equation can be obtained for the flexural motion. For this case, it was shown that the extension of the neutral axis has no effect upon the flexural motion. When the rod has pronounced curvature these simplifications are no longer valid and the more general equations must be considered

A review of analytical methods for aircraft structures subjected to high-intensity random acoustic loads

A review of the acoustic fatigue design process for aircraft structures is presented in this paper, together with the current design guides, which are used to predict the stresses that an acousticallly loaded aircraft structure may experience in service. These methods are based on linear theory and use the single-degree-of-freedom approximation method. A recent programme of research which uses this method together with the finite element method to predict the root mean square strains experienced by acoustically excited, doubly curved sandwich panels is briefly discussed. Recent developments in prediction methods based on the non-linear dynamic response of thermoacoustic loaded structures are reviewed, and suggestions are made as to possible future directions in the area of acoustic fatigue researc

Comparative aspects of volatile fatty acid production in the rumen and distal fermentation chamber in Svalbard reindeer

Microbial fermentation end products were investigated in Svalbard reindeer at two different locations, on Nordenskioldland (NL) (n=7) and in a marginal area on Nordaustlandet (NA) (n=11), at different seasons. The pH ranged from 6.51-6.70 in rumen contents and from 6.78-7.17 in the distal fermentation chamber (DFC=caecum and proximal part of the colon) on NL compared to 6.10-6.71 in rumen contents and 6.50-7.35 in DFC contents on NA. The ruminal volatile fatty acid concentration ([VFAJ) was 84.5 &plusmn; 9.5 mmol/l compared to 63-9 &plusmn; 17.6 mmol/kg in the DFC on NL in winter. In autumn, ruminal and DFC [VFA] was high at 113.5 &plusmn; 13.0 mmol/l and 90.4 &plusmn; 10.9 mmol/kg, respectively. On NA ruminal [VFA] was 85.7 &plusmn; 12.4 mmol/l and 59-6 &plusmn; 1.3 mmol/kg in the DFC in winter, compared to 107.3 &plusmn; 18.4 mmol/l and 102.0 &plusmn; 12.7 mmol/kg in rumen and DFC, respectively, in summer. Mean acetate/propionate (A/P) ratios in the rumen indicate fermentation in favour of plant fibre digestion in winter (4.8) but not in autumn (3.0) on NL. On NA, the mean A/P ratio was 5.1 in winter, compared to 4.6 in summer. In all DFC investigated the A/P ratio was higher than 8.9. The initial ruminal [VFA] did not reflect the VFA production measured. On NL, the production rate of VFA was low or not detectable in rumen and DFC in winter, while in autumn the total production rate of VFA was 59.3 kJ/kgW0 75/d, of which 6.5% originated from the DFC. On NA in winter, a total of 121.3 kJ/kgW0 7S/d was estimated of which 17% originated from the DFC, compared to a total of 380.4 kj/kgW0.75/d in summer where the DFC only contributed 2.7%. Plants (grasses and mosses) with low quality in winter do not seem to contribute significantly to the VFA production in rumen and DFC. VFA production in the DFC seems to be of significant importance in reindeer when pastures have low availability but high quality. The concenttation and the rate of VFA production in the DFC contents were not related to the size of the chamber, but to the diet eaten

Modeling energy and reproductive costs in caribou exposed to low flying military jet aircraft

We used simulation modeling to estimate the effect of low-flying military jet aircraft on the productivity of caribou. The base model (CARIBOU, CWS Whitehorse, Yukon Territory) uses daily intake and expenditure of energy to assess the condition of female caribou throughout the annual cycle. The activity budget of the model caribou was adjusted based on field observations of responses to noise disturbance. A subroutine was added that predicted the likelihood of conception based on fall body fat weight. Caribou responses to overflights were evaluated by equipping free-ranging caribou with radio collars and activity sensors that could distinguish between resting and active periods. Collared animals were exposed to 110 overflights by A-10, F-15 and F- 16 jet aircraft during late-winter, post-calving and the insect season. Noise exposure levels for individual animals either were measured directly with collar-mounted dosimeters or were estimated based on the proximity of the caribou to the aircraft during the overflight. A Time-averaged Sound Level (LT) was calculated from the total daily noise exposure for each animal and linear regression was used to evaluate the influence of daily noise exposure on daily hours spent resting. Results of these analyses then were used to modify the time budgets in the CARIBOU model. That is, if time spent resting declined, then time spent in the two rest classes (lying and standing) were proportionately redistributed into the three active classes (foraging, walking and running). Model simulations indicated that caribou increased forage intake in response to increased noise exposure, but it also predicted that increased noise exposure would cause a reduced accumulation of body fat. Because body fat in fall has successfully been used to predict the probability of pregnancy (see Gerhart et al, 1993), this relationship was used in the model. Preliminary model simulations indicate that increased noise exposure decreases the probability of pregnancy and that unfavorable environmental conditions (e.g., deep snow and severe insect harassment) exacerbate the situation. The threshold at which point the caribou fail to conceive has not been determined at this time, but appears to be well beyond the exposure to aircraft that caribou in the Delta herd are currently experiencing

Equivalence of two approaches for the inhomogeneous density in the canonical ensemble

In this article we show that the inhomogeneous density obtained from a density-functional theory of classical fluids in the canonical ensemble (CE), recently presented by White et al [Phys. Rev. Lett. 84 (2000) 1220], is equivalent to first order to the result of the series expansion of the CE inhomogeneous density introduced by Gonzalez et al [Phys. Rev. Lett. 79 (1997) 2466].Comment: 6 pages, RevTe

Unscreened Coulomb repulsion in the one dimensional electron gas

A tight binding model of electrons interacting via bare Coulomb repulsion is numerically investigated by use of the Density Matrix Renormalization Group method which we prove applicable also to very long range potentials. From the analysis of the elementary excitations, of the spin and charge correlation functions and of the momentum distribution, a picture consistent with the formation of a one dimensional "Wigner crystal" emerges, in quantitative agreement with a previous bosonization study. At finite doping, Umklapp scattering is shown to be ineffective in the presence of long range forces.Comment: RevTex, 5 pages with 8 eps figures. To be published on Phys. Rev.