A knowledge-based computer tool for casting process design

When designing a manufacturing process, the goal is to cost-effectively produce a high-quality product. In casting, the aim is to generate an optimized process design that can produce a defect-free part as inexpensively as possible. Optimization of process design is an iterative process where an initial design is updated in the light of analysis. A good initial design would reduce the number of cycles in a process optimization. The work described in this article focuses on the development of a computer system that generates an initial design. The main philosophy of this system is based on the observation that a casting process design involves identifying features that are quantified in terms of attributes (e.g., thickness and location). The system operates on these attributes using process design heuristics to arrive at an initial design.     

Wireless data: Systems,standards, services

Wireless data products and services being proposed today include exotic mixes of services and technologies: packet transport over cellular circuits, facsimile service over Cellular Digital Packet Data (CDPD), voice and video over wireless LANs, and everything in between. Data networking terms that seem to have a clear meaning-data-link, network and transport layers; circuit-mode and datagram; connection-less and connection-oriented-in fact have meaning only in context. Thus TCP, a reliable packet transport protocol, is being used in CDMA circuit-mode data to provide a reliable data-link layer for the error-prone wireless link. IP datagrams will be transported over cellular links using dedicated channels with call establishment, possibly per packet. Market demands for timely solutions, competition between alternative technologies and the plethora of alternative fora for standards development are driving wireless data into fragmented directions. The primary constraints come from the limited spectrum, the need for security in the presence of mobility and the size and weight of mobile terminals and devices. Often the optimization for the latter constraints is sacrificed at the altar of the former drivers. Based upon our experience and work with standards and systems we attempt to put wircless data into perspective. We compare and contrast major services and products and identify the choices that were made and why.We acknowledge the contributions of our colleagues at AT&T Bell Laboratories: Ken Budka, Mooi Choo Chuah, Bharat Doshi, Subra Dravida, Richard Ejzak and On-Ching Yue.     

The importance of the Doppler angle

We examined 118 infrainguinal grafts (103 patients) to determine the effect changes in the angle of theta or Doppler angle had on the accuracy of velocity measurements made with a duplex scanner. Four separate measurements of peak velocity were made on each graft. Three measurements were made with the flow toward the probe at 60 degrees, 50 degrees, 120 degrees (60 degrees the other way). The probe was then turned 180 degrees so the flow was away from the probe and measurements were made at 60 degrees. When the primary cursor was aligned with the vessel wall (Technologist A), the mean velocity at 60 degrees was 69.4 cm/sec and 57.3 cm/sec at 50 degrees, a difference of 12 cm/sec. The same measurements done by Technologist B (primary cursor non aligned with the wall), showed a 10 cm/sec difference (60.7 and 50.5). We saw a consistent difference with even this small difference in the angle of theta throughout the study. The mean velocity obtained by Technologist A when the flow was toward the probe was 61.7. When the probe was turned 180 degrees (flow away from the probe), the mean velocity was 60.5. The same measurements by Technologist B were 51.8 and 50.5. This indicates that the direction of the flow of blood towards or away from the probe does not effect the velocity measurements. Using the vessel wall to line up the primary cursor provides a consistent and easily reproducible reference point to compare measurements made on different days but is less important for single measurements.     

Enhanced green emission from La0.4F3:Ce0.45,Tb0.15/TiO2 core/shell structure

Nano sized La0.4F3:Ce0.45,Tb0.15(core), La0.4F3:Ce0.45,Tb0.15(Ti O2)(core) shell, La0.55F:Ce0.45, and La0.85F3:Tb0.15 particles were synthesized by adopting co-precipitation technique in acidic environment and coated with Ti O2 to form a core-shell structure by adopting a mechanical dispersion method at room temperature. The synthesized materials were characterized using X-ray diffraction(XRD), transmission electron microscopy(TEM), Fourier transform infrared spectroscopy(FTIR), ultraviolet-visible spectroscopy(UV-Vis) absorption, photoluminescence and lifetime spectroscopy. The crystal structure of La0.4F3:Ce0.45,Tb0.15 remained the same as La F3 after being doped with Ce and Tb ions but with a slight decrease in the lattice parameter. TEM image confirmed the formation of a core-shell structure. The La0.4F3:Ce0.45,Tb0.15/Ti O2 exhibited Tb3+ fluorescence enhancement by a factor of 1.76. Scintillation from the synthesized materials was also observed under X-ray excitation.     

General theories for the electrical transport properties of carbon nanotubes

We have shown that the general theories of metals and semiconductors can be employed to understand the diameter and voltage dependency of current through metallic and semiconducting carbon nanotubes, respectively. The current through a semiconducting multiwalled carbon nanotube (MWCNT) is associated with the energy gap that is different for different shells. The contribution of the outermost shell is larger as compared to the inner shells. The general theories can also explain the diameter dependency of maximum current through nanotubes. We have also compared the current carrying ability of a MWCNT and an array of the same diameter of single wall carbon nanotubes (SWCNTs) and found that MWCNTs are better suited and deserve further investigation for possible applications as interconnects.     

Synergistic Effect of PVDF-Coated PCL-TCP Scaffolds and Pulsed Electromagnetic Field on Osteogenesis

Bone exhibits piezoelectric properties. Thus, electrical stimulations such as pulsed electromagnetic fields (PEMFs) and stimuli-responsive piezoelectric properties of scaffolds have been investigated separately to evaluate their efficacy in supporting osteogenesis. However, current understanding of cells responding under the combined influence of PEMF and piezoelectric properties in scaffolds is still lacking. Therefore, in this study, we fabricated piezoelectric scaffolds by functionalization of polycaprolactone-tricalcium phosphate (PCL-TCP) films with a polyvinylidene fluoride (PVDF) coating that is self-polarized by a modified breath-figure technique. The osteoinductive properties of these PVDF-coated PCL-TCP films on MC3T3-E1 cells were studied under the stimulation of PEMF. Piezoelectric and ferroelectric characterization demonstrated that scaffolds with piezoelectric coefficient d₃₃ = −1.2 pC/N were obtained at a powder dissolution temperature of 100 °C and coating relative humidity (RH) of 56%. DNA quantification showed that cell proliferation was significantly enhanced by PEMF as low as 0.6 mT and 50 Hz. Hydroxyapatite staining showed that cell mineralization was significantly enhanced by incorporation of PVDF coating. Gene expression study showed that the combination of PEMF and PVDF coating promoted late osteogenic gene expression marker most significantly. Collectively, our results suggest that the synergistic effects of PEMF and piezoelectric scaffolds on osteogenesis provide a promising alternative strategy for electrically augmented osteoinduction. The piezoelectric response of PVDF by PEMF, which could provide mechanical strain, is particularly interesting as it could deliver local mechanical stimulation to osteogenic cells using PEMF.     

Multiple promoters direct stimulus and temporal specific expression of brain-derived neurotrophic factor in the somatosensory cortex

Patients operated on for infective endocarditis (n = 69) at two regional hospitals between 1988 and 1994 are reviewed. 70% had a known valvular heart disease and 16% had prosthetic valve endocarditis. In 28% the offending microorganism was Staphylococcus aureus; in 26% Streptococcus viridans. Therapy was intended to be a six-week antibiotic course before operating, but 55% of the patients had to be operated on earlier. The postoperative course was uncomplicated in 59%, mortality was 16% and one-year survival 81%. Increased risk of death was associated with operating before the six-week course of antibiotics was completed (p = 0.005), with preoperative renal failure (p = 0.006) or lung failure (p = 0.008), with the growth of microorganisms from tissue samples extirpated during the operation (p = 0.01), with additional surgical procedures concomitant to valvular replacement (p = 0.02), S. aureus endocarditis (p = 0.03), and with the presence of paravalvular abscesses or intracardial fistulas (p = 0.03). The study shows that infective endocarditis is a serious disease. Wherever clinically feasible, all patients should be given antibiotics for six weeks before evaluating surgery. However, close surveillance of infection and haemodynamics is necessary to allow for the possibility of acute surgery before the development of organ failure. Special attention must be paid to cases of S. aureus endocarditis.     

A study on osmotic resistance of RBC and ESR in stored blood

The present work was undertaken to study the changes in osmotic resistance of stored blood, used for blood transfusion. Blood samples of 50 cases from Orissa Red Cross Blood Bank, Cuttack, were studied. The blood was collected in acid citrate dextrose solution and stored at 4 degrees C. Storage was done under usual condition followed in blood banks. Osmotic fragility was determined at 3 days interval up to 15 days. In each case ESR was determined and in 20 cases plasma fibrinogen level was determined. In this study there was gradual increase in fragility which was maximum on 9th day and then slowly declined, which was statistically significant. ESR decreased markedly after 6th day, which was also statistically significant.