Implementation of an Associative Flow Rule Including Hydrostatic Stress Effects into the High Strain Rate Deformation Analysis of Polymer Matrix Composites

A previously developed analytical formulation has been modified in order to more accurately account for the effects of hydrostatic stresses on the nonlinear, strain rate dependent deformation of polymer matrix composites. State variable constitutive equations originally developed for metals have been modified in order to model the nonlinear, strain rate dependent deformation of polymeric materials. To account for the effects of hydrostatic stresses, which are significant in polymers, the classical J2 plasticity theory definitions of effective stress and effective inelastic strain, along with the equations used to compute the components of the inelastic strain rate tensor, are appropriately modified. To verify the revised formulation, the shear and tensile deformation of a representative polymer are computed across a wide range of strain rates. Results computed using the developed constitutive equations correlate well with experimental data. The polymer constitutive equations are implemented within a strength of materials based micromechanics method to predict the nonlinear, strain rate dependent deformation of polymer matrix composites. The composite mechanics are verified by analyzing the deformation of a representative polymer matrix composite for several fiber orientation angles across a variety of strain rates. The computed values compare well to experimentally obtained results.     

Becoming an Engineer: Toward a Three Dimensional View of Engineering Learning

In this paper we develop an analytical framework we refer to as “Becoming an Engineer” that focuses upon changes occurring over time as students traverse their undergraduate educations in engineering. This analytical framework involves three related dimensions that we track over time: disciplinary knowledge, identification, and navigation. Our analysis illustrates how these three dimensions enable us to understand how students become, or do not become, engineers by examining how these three interrelated dimensions unfold over time. This study is based on longitudinal ethnographic data from which we have developed “person‐centered ethnographies” focused on individual students' pathways through engineering. We present comparative analysis, spanning four schools and four years. We also present person‐centered ethnographic case studies that illustrate how our conceptual dimensions interrelate. Our discussion draws some educational implications from our analysis and proposes further lines of research.     

Bounds on the sample complexity for private learning and private data release

Learning is a task that generalizes many of the analyses that are applied to collections of data, in particular, to collections of sensitive individual information. Hence, it is natural to ask what can be learned while preserving individual privacy. Kasiviswanathan et al. (in SIAM J. Comput., 40(3):793–826, 2011) initiated such a discussion. They formalized the notion of private learning, as a combination of PAC learning and differential privacy, and investigated what concept classes can be learned privately. Somewhat surprisingly, they showed that for finite, discrete domains (ignoring time complexity), every PAC learning task could be performed privately with polynomially many labeled examples; in many natural cases this could even be done in polynomial time. While these results seem to equate non-private and private learning, there is still a significant gap: the sample complexity of (non-private) PAC learning is crisply characterized in terms of the VC-dimension of the concept class, whereas this relationship is lost in the constructions of private learners, which exhibit, generally, a higher sample complexity. Looking into this gap, we examine several private learning tasks and give tight bounds on their sample complexity. In particular, we show strong separations between sample complexities of proper and improper private learners (such separation does not exist for non-private learners), and between sample complexities of efficient and inefficient proper private learners. Our results show that VC-dimension is not the right measure for characterizing the sample complexity of proper private learning. We also examine the task of private data release (as initiated by Blum et al. in STOC, pp. 609–618, 2008), and give new lower bounds on the sample complexity. Our results show that the logarithmic dependence on size of the instance space is essential for private data release.     

Opioid-mediated responses of dietary protein on reticular motility and plasma insulin

This study explores the effects of infusion of nerve growth factor (NGF) on behavioral outcome and cell death in the septal region using the clinically relevant model of fluid-percussion brain injury in the rat. Animals were subjected to fluid-percussion brain injury and 24 hours later a miniosmotic pump was implanted to infuse NGF (12 animals) or vehicle (12 animals) directly into the region of maximum injury for 2 weeks. Four weeks postinjury the animals were tested for cognitive function using a Morris Water Maze paradigm. Neurological motor function was evaluated over a 4-week postinjury period. The rats receiving NGF infusions had significantly higher memory scores than vehicle-treated animals. Examination of the cholinergic neurons in the medial septal region using choline acetyltransferase immunohistochemistry demonstrated significant cell loss after injury. Infusion of NGF significantly attenuated loss of these cholinergic neurons. A second group of animals was subjected to fluid-percussion brain injury alone (23 rats) or injury followed by NGF infusion (18 rats). These animals were killed between 24 hours and 2 weeks postinjury and the septal region was examined for the presence of apoptotic cells using the terminal deoxynucleotidyl transferase-mediated biotinylated-deoxyuridinetriphosphate nick-end labeling technique. Apoptotic cells were identified as early as 24 hours postinjury; their numbers peaked at 4 and 7 days, and then declined by 14 days. The NGF-treated animals had some apoptotic cells; however, even at 7 days there were significantly fewer of these cells. No significant motor differences were observed between the NGF- and vehicle-treated groups. These data indicate that NGF administration beginning 24 hours after fluid-percussion brain injury has a beneficial effect on cognition and results in sparing of cholinergic septal neurons. These improvements persist after cessation of NGF administration. The beneficial effects of NGF may be related to its ability to attenuate traumatically induced apoptotic cell death.     

Design and Implementation of an Inclusive Ubiquitous Access

The development towards ubiquitous network access requires innovative solutions to get remote areas included, especially rural areas of developing regions. The challenges include robustness of network components, poor or non-existent power supply and sustainable business models. We argue that large scale user-driven community networks are becoming technically viable to deploy in areas that are short of supply of telecommunication services due to little or no commercial interest. To support this claim, we discuss the design of key network elements and careful power management based on alternative energy sources and storage. We also provide a status report from ongoing field-tests regarding provisioning of broadband network services in Serengeti, Tanzania, and outline briefly our strategy to achieve sustainability. On the technical side, we first discuss an affordable, high-performance, low-effect router based on open source software and standard off-the-shelf hardware offering both copper and fibre links. Our design is capable of forwarding more than 700?kpps at 22.3?W. The power consumption is considerably less than all alternatives in our comparison. Then we discuss power management and the use of batteries and super-capacitors as backup and storage solutions.     

Effect of supplemental L-lysine-HCL and corn source on rumen fermentation and amino acid flow to the small intestine

Four lactating Jersey cows fitted with ruminal and duodenal cannulae were used in a 4 x 4 Latin square design trial to determine the effect of supplemental lysine in diets containing dry ground (GC) or steam-flaked (SFC, 360 g/L) corn on ruminal fermentation and amino acid (AA) flow to the duodenum. Supplemental L-lysine-HCL provided 10 g/d of additional Lys to the total mixed rations. There were no interactions between supplemental Lys and corn source. Supplemental Lys increased Lys intake, but did not alter nutrient intake and digestibility or N flow to the duodenum. Intake of dry matter (DM), organic matter (OM), and neutral detergent fiber (NDF) and ruminal digestibility of starch tended to be higher, whereas ruminal digestibility of DM, OM, acid detergent fiber, and NDF was lower for diets supplemented with SFC compared with GC. Whole-tract digestibility was similar for both corn supplements. Ruminal pH and molar proportions of volatile fatty acids were not affected by supplemental Lys or corn source; however, ruminal NH(3) concentrations were lowest when SFC was fed. Intake of N tended to be higher and the flow of total N and individual AA to the duodenum was higher for diets supplemented with SFC. There was a trend for increased flow of microbial N for diets supplemented with SFC. Supplemental L-lysine-HCL did not alter ruminal fermentation, flow of amino acid to the small intestine, or nutrient digestibility, but feeding SFC reduced ruminal fiber digestion and increased microbial protein synthesis and flow of amino acid to the duodenum.     

Influence of dietary protein degradability and energy concentration on growth of heifers and steers and intraruminal protein metabolism

Two studies with 4-mo old Holstein steers and heifers and one abomasal digesta collection study were used to determine the influence of altering the dietary energy content and crude protein escape on growth, intraruminal protein metabolism, and site of digestion of dry matter, starch, cellulose, hemicellulose, and protein. Dietary energy concentration was increased by tallow, and rumen protein escape was increased by dehydrated alfalfa and distillers dried grains with solubles substituted for soybean meal. Tallow appeared to depress intake and gain, but gain was increased by protein escape from the rumen. Total and particulate digesta crude protein reaching the abomasum was increased by protein escape; however, percentage crude protein digested was decreased in these treatments due to increased acid detergent insoluble nitrogen. Decreasing crude protein solubility decreased ruminoreticular digestion of dry matter, cellulose, hemicellulose, and starch; however, lower intestinal starch digestion compensated for decreased ruminoreticular digestion. In a third study, with growing steers and heifers, corn gluten meal provided the escape protein and soybean meal the degradable protein. Total and average daily gain were greater for the corn gluten meal diet, but intake was not influenced by energy concentration or protein escape.     

Performance of lactating dairy cows fed whole cottonseed with elevated concentrations of free fatty acids in the oil

Twenty-four multiparous cows were used in a 10-wk randomized block design trial to evaluate the effects of feeding whole cottonseed (WCS) containing increasing concentrations of free fatty acids (FFA) in the oil on nutrient intake and digestibility, milk yield and composition, and select plasma metabolites. Two lots of WCS containing either 3 or 12% FFA were blended to provide WCS with 3, 6, 9, and 12% FFA. Cottonseeds were included in the wheat silage-based total mixed ration at 12.5% of dry matter (DM). There was no difference in intakes of DM, crude protein (CP), or neutral detergent fiber; yield of milk; or percentages of milk protein, lactose, or SNF. Milk fat percentage was lowest for the diet containing WCS with 6% FFA. Concentrations of individual milk fatty acids C6:0 decreased and C16:1 increased linearly as FFA in WCS increased. A cubic response was observed for concentrations of C8:0, C10:0, and C12:0 because of higher concentrations when diets contained WCS with 6% FFA than 3 and 12% FFA, which were higher than 9% FFA. Intake and apparent total tract digestibility of acid detergent fiber increased linearly as FFA concentration in WCS increased. Apparent NDF digestibility was highest for diets containing WCS with 3 and 6% FFA; CP digestibility was highest with WCS containing 3 and 9% FFA. Differences in milk fatty acid concentration and nutrient digestibility suggest minor changes in rumen fermentation; however, feeding WCS with up to 12% FFA did not negatively impact nutrient intake and digestibility or milk yield or composition.