Determination of elastic moduli of thin layers of soft material using the atomic force microscope

We address three problems that limit the use of the atomic force microscope when measuring elastic moduli of soft materials at microscopic scales. The first concerns the use of sharp cantilever tips, which typically induce local strains that far exceed the linear material regime. We show that this problem can be alleviated by using microspheres as probes, and we establish the criteria for their use. The second relates to the common use of the Hertz contact mechanics model, which leads to significant errors when applied to thin samples. We develop novel, simple to use corrections to apply for such cases. Samples that are either bonded or not bonded to a rigid substrate are considered. The third problem concerns the difficulty in establishing when contact occurs on a soft material. We obtain error estimates for the elastic modulus resulting from such uncertainty and discuss the sensitivity of the estimation methods to error in contact point. The theoretical and experimental results are compared to macroscopic measurements on poly(vinyl-alcohol) gels.     

Effect of knee position on hip and knee torques during the barbell squat

Some recommendations suggest keeping the shank as vertical as possible during the barbell squat, thus keeping the knees from moving past the toes. This study examined joint kinetics occurring when forward displacement of the knees is restricted vs. when such movement is not restricted. Seven weight-trained men (mean +/- SD; age = 27.9 +/- 5.2 years) were videotaped while performing 2 variations of parallel barbell squats (barbell load = body weight). Either the knees were permitted to move anteriorly past the toes (unrestricted) or a wooden barrier prevented the knees from moving anteriorly past the toes (restricted). Differences resulted between static knee and hip torques for both types of squat as well as when both squat variations were compared with each other (p < 0.05). For the unrestricted squat, knee torque (N.m; mean +/- SD) = 150.1 +/- 50.8 and hip torque = 28.2 +/- 65.0. For the restricted squat, knee torque = 117.3 +/- 34.2 and hip torque = 302.7 +/- 71.2. Restricted squats also produced more anterior lean of the trunk and shank and a greater internal angle at the knees and ankles. The squat technique used can affect the distribution of forces between the knees and hips and on the kinematic properties of the exercise. PRACTICAL APPLICATIONS: Although restricting forward movement of the knees may minimize stress on the knees, it is likely that forces are inappropriately transferred to the hips and low-back region. Thus, appropriate joint loading during this exercise may require the knees to move slightly past the toes.     

RESPONSE OF PACIFIC WALRUSES TO DISTURBANCES FROM CAPTURE AND HANDLING ACTIVITIES AT A HAUL-OUT IN BRISTOL BAY, ALASKA

Observations were made on herds of the Pacific walrus ( Odobenus rosmarus divergens ) to study their response during the capturing and handling of adult males in summer 1995 at a haul-out at Cape Peirce in southwestern Alaska. Three behaviors (alertness, displacement, and dispersal) were quantified from 16 capture sessions. Herd sizes ranged from 622 to 5,289 walruses. Handling of an immobilized walrus consisted of attempts to attach telemetry devices to the tusks and collect various biological samples. Handling activities resulted in an average of about 10-fold or greater levels of behavior in alertness, displacement, and dispersal than during precapture and darting periods. High levels of behavior usually occurred within the first 45 min of handling. In 8 of 10 capture sessions, walruses returned to predisturbance levels of behavior within 40 min of cessation of the handling disturbance. Alertness and displacement were moderately and negatively correlated with herd size during the handling period, which may reflect an effect of a threshold distance from the point of disturbance to responding individuals. Observations of walruses tagged with VHF radio transmitters indicated that the activities from a given capture session did not preclude tagged walruses from using the haul-out over a subsequent 11 -wk monitoring period. Moreover, non-tagged walruses continued to extensively use the haul-out during and after the period in which capture sessions were conducted.     

Strains of protoplasts of Entomophthora egressa in spruce budworm larvae

Protoplasts of strain 458 (S458) and strain 521 (S521) of Entomophthora egressa had LD₅₀s of 620 and 8.8 cells/insect, respectively, for sixth-instar spruce budworm larvae. Both protoplast strains exhibited biphasic growth profiles with comparable growth rates in the larval hemocoel. The growth rates of the fungal strains increased as the total hemocyte counts declined. Hemocytopenia was greatest and most rapid in larvae containing S521 protoplasts. Protoplasts of S521 exposed to α-mannosidase and β-N-acetylglucosaminidase were as virulent as the control cells. β-Galactosidase reduced protoplast virulence.     

The evaluation of novel chromogenic substrates for the detection of lipolytic activity in clinical isolates of Staphylococcus aureus and MRSA from two European study groups

Pinellia ternata , a traditional Chinese herb that has been used in China for over 1000 years, is susceptible to a soft rot disease, which may cause major loss of yield. The use of bacteria as potential antagonists against Pectobacterium carotovorum SXR1, the causal agent of the disease on P. ternata , was evaluated. Altogether, 1107 candidate bacteria were isolated from the rhizosphere and surface-sterilized plants of P. ternata . In Petri dish tests, 55 isolates inhibited the growth of strain SXR1, and 21 of these reduced the disease development on P. ternata slices by over 50%. Four selected antagonists significantly reduced the disease incidence on tissue culture seedlings, and also prevented the disease on the transplants. Agonist P-Y2-2 yielded a good prevention level of 81.9%. The four antagonists rapidly colonized the tissue culture seedlings and transplants, whereas greater populations of the antagonists (10⁷–10⁹ CFU g⁻¹ fresh tissues) were observed in the seedlings and in the preinoculated transplants than in those inoculated during transplanting. The use of pathogen-free tissue culture seedlings pre-inoculated with antagonist may provide a strategy for production of P. ternata plantlets resistant to soft rot disease. This is the first report on the efficacy of biocontrol agents against pathogens on P. ternata .     

Cattle feed or bioenergy? Consequential life cycle assessment of biogas feedstock options on dairy farms

On‐farm anaerobic digestion (AD) of wastes and crops can potentially avoid greenhouse gas (GHG) emissions, but incurs extensive environmental effects via carbon and nitrogen cycles and substitution of multiple processes within and outside farm system boundaries. Farm models were combined with consequential life cycle assessment (CLCA) to assess plausible biogas and miscanthus heating pellet scenarios on dairy farms. On the large dairy farm, the introduction of slurry‐only AD led to reductions in global warming potential (GWP) and resource depletion burdens of 14% and 67%, respectively, but eutrophication and acidification burden increases of 9% and 10%, respectively, assuming open tank digestate storage. Marginal GWP burdens per Mg dry matter (DM) feedstock codigested with slurry ranged from –637 kg CO₂e for food waste to +509 kg CO₂e for maize. Codigestion of grass and maize led to increased imports of concentrate feed to the farm, negating the GWP benefits of grid electricity substitution. Attributing grass‐to‐arable land use change (LUC) to marginal wheat feed production led to net GWP burdens exceeding 900 kg CO₂e Mg^?1 maize DM codigested. Converting the medium‐sized dairy farm to a beef‐plus‐AD farm led to a minor reduction in GWP when grass‐to‐arable LUC was excluded, but a 38% GWP increase when such LUC was attributed to marginal maize and wheat feed required for intensive compensatory milk production. If marginal animal feed is derived from soybeans cultivated on recently converted cropland in South America, the net GWP burden increases to 4099 kg CO₂e Mg^?1 maize DM codigested – equivalent to 55 Mg CO₂e yr^?1 per hectare used for AD‐maize cultivation. We conclude that AD of slurry and food waste on dairy farms is an effective GHG mitigation option, but that the quantity of codigested crops should be strictly limited to avoid potentially large international carbon leakage via animal feed displacement.