Numerical models of creep and boundary sliding mechanisms in single-phase, dual-phase, and fully lamellar titanium aluminide

Finite element simulations of the high-temperature behavior of single-phase γ, dual-phase α₂+γ, and fully lamellar (FL) α₂+γTiAl intermetallic alloy microstructures have been performed. Nonlinear viscous primary creep deformation is modeled in each phase based on published creep data. Models were also developed that incorporate grain boundary and lath boundary sliding in addition to the dislocation creep flow within each phase. Overall strain rates are compared to gain an understanding of the relative influence each of these localized deformation mechanisms has on the creep strength of the microstructures considered. Facet stress enhancement factors were also determined for the transverse grain facets in each model to examine the relative susceptibility to creep damage. The results indicate that a mechanism for unrestricted sliding of γ lath boundaries theorized by Hazzledine and co-workers leads to unrealistically high strain rates. However, the results also suggest that the greater creep strength observed experimentally for the lamellar microstructure is primarily due to inhibited former grain boundary sliding (GBS) in this microstructure compared to relatively unimpeded GBS in the equiaxed microstructures. The serrated nature of the former grain boundaries generally observed for lamellar TiAl alloys is consistent with this finding.     

BRCA1 mutations in women attending clinics that evaluate the risk of breast cancer

BACKGROUND: To define the incidence of BRCA1 mutations among patients seen in clinics that evaluate the risk of breast cancer, we analyzed DNA samples from women seen in this setting and constructed probability tables to provide estimates of the likelihood of finding a BRCA1 mutation in individual families. METHODS: Clinical information, family histories, and blood for DNA analysis were obtained from 263 women with breast cancer. Conformation-sensitive gel electrophoresis and DNA sequencing were used to identify BRCA1 mutations. RESULTS: BRCA1 mutations were identified in 16 percent of women with a family history of breast cancer. Only 7 percent of women from families with a history of breast cancer but not ovarian cancer had BRCA1 mutations. The rates were higher among women from families with a history of both breast and ovarian cancer. Among family members, an average age of less than 55 years at the diagnosis of breast cancer, the presence of ovarian cancer, the presence of breast and ovarian cancer in the same woman, and Ashkenazi Jewish ancestry were all associated with an increased risk of detecting a BRCA1 mutation. No association was found between the presence of bilateral breast cancer or the number of breast cancers in a family and the detection of a BRCA1 mutation, or between the position of the mutation in the BRCA1 gene and the presence of ovarian cancer in a family. CONCLUSIONS: Among women with breast cancer and a family history of the disease, the percentage with BRCA1 coding-region mutations is less than the 45 percent predicted by genetic-linkage analysis. These results suggest that even in a referral clinic specializing in screening women from high-risk families, the majority of tests for BRCA1 mutations will be negative and therefore uninformative.     

Performance Optimizations for Deploying VoIP Services in Mesh Networks

In the recent past, there has been a tremendous increase in the popularity of VoIP services as a result of huge growth in broadband access. The same voice-over-Internet protocol (VoIP) service poses new challenges when deployed over a wireless mesh network, while enabling users to make voice calls using WiFi phones. Packet losses and delay due to interference in a multiple-hop mesh network with limited capacity can significantly degrade the end-to-end VoIP call quality. In this work, we discuss the basic requirements for efficient deployment of VoIP services over a mesh network. We present and evaluate practical optimizing techniques that can enhance the network capacity, maintain the VoIP quality and handle user mobility efficiently. Extensive experiments conducted on a real testbed and ns-2 provide insights into the performance issues and demonstrate the level of improvement that can be obtained by the proposed techniques. Specifically, we find that packet aggregation along with header compression can increase the number of supported VoIP calls in a multihop network by 2-3 times. The proposed fast path switching is highly effective in maintaining the VoIP quality. Our fast handoff scheme achieves almost negligible disruption during calls to roaming clients     

Characteristics of microstrip transmission lines withhigh-dielectric-constant substrates

An efficient numerical code is developed from a full-wave analysis in the Fourier transform domain to determine the characteristics of a single-strip or multistrip coplanar transmission line. Modes of both even and odd symmetries are included. The impedance of the transmission line is calculated using the power-current equivalent model. Coupling constants between the even and the odd modes are also calculated. Results are provided for a shielded two-strip coupled microstrip transmission line on high-dielectric-constant substrate such as lanthanum aluminate with applications to superconducting transmission lines     

Evaluation of hot hardness and creep of a 350 grade commercial maraging steel

The hardening response and the indentation creep of a 350 grade commercial maraging steel were evaluated using a hot hardness tester. The hardness versus temperature plot exhibited three distinct regions. Hardness response was noted between 500–800 K. The unusually high values of activation energy and stress exponent obtained during the creep experiment could be rationalized by a novel concept of introducing a back stress term in the indentation creep relation. The corrected value of the activation energy was found to be reasonably in agreement with the activation energy for diffusion of Ni in iron. Results are supplemented with microstructural observation.     

An automated, parallel processing approach to biomolecular sample preparation

Sample preparation for DNA and RNA assays is a prime candidate for laboratory automation. A novel, parallel processing device that performs the three separate liquid-handling functions necessary for such sample preparation-dispensing, pipetting, and pressurizing-is presented. The device comprises an array of fine nozzles connected by fluidic channels to automatically and precisely distribute flow between one source and an array of points. The design principles, as well as the experimental and computational methods used to develop the device, are described. Test results, including accuracy, uniformity, volume range, and timing, are presented. The functionality of the device is demonstrated by performing a solid-phase extraction of DNA with two types of microcolumns.     

Aggregation dynamics of particles in a microchannel due to an applied magnetic field

Functionalized magnetic microspheres have promising applications in different microfluidic devices including MEMS-scale biosensors. These particles exhibit magnetic field-induced aggregation, which can be harnessed to achieve several practical tasks in microfluidic devices. For this, the particle aggregation needs to be well characterized. Herein, a numerical simulation and experimental validation of particle-chaining is presented. Simulations show that the particle aggregation time scales linearly with a group parameter. The predicted growth of one- two- and three-particle chains with time shows a similar trend as that found in the experiments. The results of the study could help predicting the performance of magnetic aggregate-based lab-on-a-chip devices.     

An Experimental Study to Evaluate the Effect of Ambient Temperature during Manual Lifting and Design of Optimal Task Parameters

In the present study, the effect of lifting task parameters on the heart rate and oxygen uptake of workers during manual lifting tasks in different ambient conditions was evaluated. The experiments conducted in two different temperature conditions showed a significantly higher oxygen uptake and heart rate in colder conditions as compared to warmer conditions. Three other factors, namely, load, lifting frequency, and vertical distance were found to significant affect the responses. Various combinations of significant factors were used to calculate oxygen uptake and heart rate. These were then compared with the safe limits as per the maximum aerobic capacity of workers. Based on these comparisons, the safe combinations were identified that can be used to design lifting tasks in varied ambient conditions. The study further concluded that lifting tasks performed in winter should have different relaxation or fatigue allowances built into the cycle time of the task to compensate for higher exertion. © 2011 Wiley Periodicals, Inc.     

Structure-property relations for a phase-pure,nanograined tetragonal zirconia ceramic stabilized with minimum CaO doping

Dense (~97%) CaO-stabilized ZrO₂ ceramic was stabilized with minimum (3 mol%) doping (reported to date) and processed via conventional sintering at a low temperature (~1200°C); compositional analysis via X-ray florescence confirmed the CaO doping accuracy. Phase-pure tetragonal structure (characterized via both X-ray diffraction and Raman spectroscopy) along with uniform nanograins (90 nm) of the ceramic ensured the evolution of no monoclinic phase even after vigorous low-temperature degradation experiments (both thermal and hydrothermal aging for 80-100 h). The sintered ceramic recorded a high hardness (~15 GPa); the indentation toughness value was also comparable to a 3 mol% yttria-stabilized zirconia system. The remarkable structure–property correlations in the 3 mol% CaO-stabilized ZrO₂ ceramic suggests that the same may be worth examining for suitable future applications (e.g., in dental ceramics).