Methods for calculating stress intensity factors in anisotropic materials: Part II—Arbitrary geometry

The problem of a crack in a general anisotropic material under conditions of linear elastic fracture mechanics (LEFM) is examined. In Part I, three methods were presented for calculating stress intensity factors for various anisotropic materials in which z = 0 is a symmetry plane and the crack front is along the z-axis. These included displacement extrapolation, the M-integral and the separated J-integrals.In this study, general material anisotropy is considered in which the material and crack coordinates may be at arbitrary angles. A three-dimensional treatment is required for this situation in which there may be two or three modes present. A three-dimensional M-integral is extended to obtain stress intensity factors. It is applied to several test problems, in which excellent results are obtained. Results are obtained for a Brazilian disk specimen made of isotropic and cubic material. Two examples for the latter are examined with material coordinates rotated with respect to the crack axes.     

Adaptive low-latency peer-to-peer streaming and its application

Peer-to-peer (P2P) streaming is emerging as a viable communications paradigm. Recent research has focused on building efficient and optimal overlay multicast trees at the application level. A few commercial products are being implemented to provide voice services through P2P streaming platforms. However, even though many P2P protocols from the research community claim to be able to support large scale low-latency streaming, none of them have been adopted by a commercial voice system so far. This gap between advanced research prototypes and commercial implementations shows that there is a lack of a practical and scalable P2P system design that can provide low-latency service in a real implementation. After analyzing existing P2P system designs, we found two important issues that could lead to improvements. First, many existing designs that aim to build a low-latency streaming platform often make the unreasonable assumption that the processing time involved at each node is zero. However in a real implementation, these delays can add up to a significant amount of time after just a few overlay hops and make interactive applications difficult. Second, scant attention has been paid to the fact that even in a conversation involving a large number of users, only a few of the users are actually actively speaking at a given time. We term these users, who have more critical demands for low-latency, active users. In this paper, we detail the design of a novel peer-to-peer streaming architecture called ACTIVE. We then present a complete commercial scale voice chat system called AudioPeer that is powered by the ACTIVE protocol. The ACTIVE system significantly reduces the end-to-end delay experienced among active users while at the same time being capable of providing streaming services to very large multicast groups. ACTIVE uses realistic processing assumptions at each node and dynamically optimizes the streaming structure while the group of active users changes over time. Consequently, it provides virtually all users with the low-latency service that before was only possible with a centralized approach. We present results from both simulations and our real implementation, which clearly show that our ACTIVE system is a feasible approach to scalable, low-latency P2P streaming.     

Fast Paxos

As used in practice, traditional consensus algorithms require three message delays before any process can learn the chosen value. Fast Paxos is an extension of the classic Paxos algorithm that allows the value to be learned in two message delays. How and why the algorithm works are explained informally, and a TLA⁺ specification of the algorithm appears as an appendix.     

Synchronization of estrus and pregnancy risk in anestrous dairy cows after treatment with a progesterone-releasing intravaginal device

Lactating Holstein cows (located in 4 dairy herds) that had failed to display estrus as defined by increased pedometer activity by 63 ± 3 d in milk, were enrolled to investigate the effect of a progesterone-releasing intravaginal device (PRID, n = 268) relative to a placebo intravaginal device (PID, control, n = 266) on days from device removal to artificial insemination (AI), the probability of pregnancy at first AI, and days from device removal to pregnancy. Cows were assigned randomly to receive a PRID or PID for 7 d and an injection of PGF_2α at device removal. Upon device removal, a vaginitis score was assigned and AI occurred at observed estrus. Cows failing to display estrus within 14 d of device removal were subjected to a subsequent reproductive exam and were treated with PGF_2α. Two percent of PRID-treated cows and 11% of control cows displayed estrus during the 7-d exposure period. Among the remaining cows, 93% of the devices were present at the scheduled removal. Cows treated with the PRID were 60% less likely to have purulent debris on the device than control cows. Vaginal reaction, however, was not associated with any of the reproductive outcomes. Investigation of the reproductive outcomes revealed a treatment × parity interaction. Progesterone-treated primiparous cows were inseminated 17 d earlier, with no significant change in the probability of pregnancy at first AI (30.3 vs. 42.0%), and no difference in median time from device removal to pregnancy (52 vs. 53 d) relative to control primiparous cows. Conversely, PRID-treated multiparous cows were inseminated 8 d earlier, with no change in probability of pregnancy at first AI (24.6 vs. 18.8%); however, median time from device removal to pregnancy was reduced by 20 d (67 vs. 87 d). These results support the efficacy of a PRID to induce estrus in previously anestrous cows. The reason, however, for the variable response between primiparous and multiparous cows was not clear.     

Expediting the identification of impaired channels in cochlear implants via analysis of speech-based confusion matrices

There is significant variability in the benefit provided by cochlear implants to severely deafened individuals. The reasons why some subjects exhibit low speech recognition scores are unknown; however, underlying physiological or psychophysical factors may be involved. Certain phenomena, such as indiscriminable electrodes and nonmonotonic pitch rankings, might hint at limitations in the ability of individual channels in the cochlear implant and/or sensorineural pathway to convey speech information. In this paper, four approaches for analyzing the results of a simple listening test using speech stimuli are investigated for the purpose of targeting channels of concern in order for follow-on psychophysical experiments to correctly identify channels performing in an "impaired" or anomalous manner. Listening tests were first conducted with normal-hearing subjects and acoustic models simulating channel-specific anomalies. Results indicate that these proposed analyses perform significantly better than chance in providing information about the location of anomalous channels. Vowel and consonant confusion matrices from six cochlear implant subjects were also analyzed to test the robustness of the proposed analyses to variability intrinsic to cochlear implant data. The current study suggests that confusion matrix analyses have the potential to expedite the identification of impaired channels by providing preliminary information prior to exhaustive psychophysical testing.     

Microbial levels in Michigan apple cider and their association with manufacturing practices

In recent decades, apple cider has been implicated in a series of outbreaks of foodborne illness. The objective of this study was to determine the presence and concentrations of pathogenic and indicator microorganisms in apple cider processed in Michigan and to evaluate the impact of thermal pasteurization, UV light radiation, and implementation of hazard analysis critical control point (HACCP) plans on these microbes. Cider samples were obtained from Michigan mills between 1997 and 2004 and analyzed for Escherichia coli O157:H7, Salmonella, generic E. coli, total coliforms, and aerobic bacteria. Neither E. coli O157:H7 nor Salmonella were detected in any tested cider samples, suggesting a very low frequency of pathogens in Michigan apple cider. The persistent and relatively high frequency of generic E. coli observed in samples obtained in all years indicates a continued risk of pathogen contamination in Michigan apple cider, especially when it is untreated. The use of thermal pasteurization or UV light radiation and reported implementation of HACCP plans were associated with lower frequency and counts of generic E. coli, total coliforms, and aerobic microorganisms. However, the relatively high counts of indicator organisms in some cider samples that were claimed to be treated according to these pathogen reduction measures indicates that some processors had inadequate practices, facilities, or equipment for pathogen reduction or did not consistently or adequately apply practices or pathogen-reduction equipment in an effective manner.     

Predictions of psychophysical measurements for sinusoidal amplitude modulated (SAM) pulse-train stimuli from a stochastic model

Two approaches have been proposed to reduce the synchrony of the neural response to electrical stimuli in cochlear implants. One approach involves adding noise to the pulse-train stimulus, and the other is based on using a high-rate pulse-train carrier. Hypotheses regarding the efficacy of the two approaches can be tested using computational models of neural responsiveness prior to time-intensive psychophysical studies. In our previous work, we have used such models to examine the effects of noise on several psychophysical measures important to speech recognition. However, to date there has been no parallel analytic solution investigating the neural response to the high-rate pulse-train stimuli and their effect on psychophysical measures. This work investigates the properties of the neural response to high-rate pulse-train stimuli with amplitude modulated envelopes using a stochastic auditory nerve model. The statistics governing the neural response to each pulse are derived using a recursive method. The agreement between the theoretical predictions and model simulations is demonstrated for sinusoidal amplitude modulated (SAM) high rate pulse-train stimuli. With our approach, predicting the neural response in modern implant devices becomes tractable. Psychophysical measurements are also predicted using the stochastic auditory nerve model for SAM high-rate pulse-train stimuli. Changes in dynamic range (DR) and intensity discrimination are compared with that observed for noise-modulated pulse-train stimuli. Modulation frequency discrimination is also studied as a function of stimulus level and pulse rate. Results suggest that high rate carriers may positively impact such psychophysical measures.     

Things in their best order: technical aspects of the Salk Institute and their role in its design

This paper explores the integration of engineering, function and space in the Salk Institute for Biological Studies at La Jolla, California, USA, by Louis Kahn (1959-1967). While traditional interpretation has focused on the Salk's courtyard as a space of uncanny emotional power, this study suggests that the power of this space derives in part from the intensity of Kahn's attention to systems, materials and methods. Using drawings and project correspondence from the Louis I. Kahn archives at the University of Pennsylvania, the paper suggests an alternative understanding of Kahn's work as empirical, evolutionary, and based as much in the prose of engineering as in the claimed poetics of architecture.     

2,3,7,8-TCDD equivalence and mutagenic activity associated with PM10 from three urban locations in New Zealand

Ambient particulate matter (PM(10)) in urban centres varies depending on emission sources, geography, demography, and meteorology. Hence physical (PM(10), wind speed, rainfall, temperature), chemical (polycyclic aromatic hydrocarbons, PAH), and toxicological (Ames Test, H4IIE EROD Assay) analyses were done on daily PM(10) (approximately 1640 m(3)/day) collected from three New Zealand urban sites where winter emissions were predominantly due to domestic home heating. Daily PM(10) levels ranged between 9.7 and 20.8 in summer and between 21.8 and 61.0 microg/m(3) in winter. Daily PAH concentrations were 0.5, 0.45, and 1.5 ng/m(3) in summer and 52.1, 128.9, and 5.8 ng/m(3) in winter at sites Christchurch, Alexandra and Dunedin, respectively. During winter, 74% of PM(10) extracts from all three sites showed significant mutagenicity in the Ames Test (TA 98, -S9), whereas approximately 25% of the daily PM(10) was mutagenic in summer. Benzo[a]pyrene and BaP carcinogenic equivalence concentrations during winter were strongly correlated to both mutagenicity and TCDD-like activity at two sites. Daily levels of TCDD toxicity equivalence concentrations ranged from 0.5 to 3.6 pg TCDD/m(3) air in summer and from 0.3 to 4009 pg TCDD/m(3) air in winter. Chemically and biologically derived TCDD toxicity equivalent concentrations were significantly correlated in all study locations indicating that PAH may represent most of the TCDD-like activity present in the PM(10).     

Fluid migration into lined pipelines

Lining of a pipe with a polymeric liner is a viable trenchless technology for rehabilitating sewer pipelines. Polymeric liners are typically installed within the deteriorated segments of a sewer line, from one access hole to the next, to essentially create a new pipe within the old pipe without the need for excavation and removal. However, some concerns exist regarding the need to grout or seal the joints where the new liner connects with access holes and laterals. The purpose of this study is to provide some insight into the degree of fluid migration into, or from, the system at these connecting points under simulated field conditions. Four groups of three similar vitrified clay pipelines were lined with different types of deformed–reformed or fold-and-form (DR/FF) liners and cured-in-place-pipe (CIPP) liners then tested to assess the conditions of the annular space between the liners and the host pipe. Fluid migration was detected around all liners and flow rates in the annular space increased with the head difference between the upstream and downstream ends of the test pipelines. No significant changes were observed in the flow rates within the annular space in the tested pipelines over the eight-week testing period.