Search

This study investigated a forming feasibility for hot forging by using lower strength material as a die. In this paper, the AISI1050 steel was employed not only for heating the billet, but also to forming the billet. In this proposed method, the die can be used as the electrode to raise the temperature of the billet directly by resistance heating. The higher the temperature of the billet; the lower the flow stress of the billet. Then, the billet is easier to press into the cavity of the die. In addition, the die itself could not be heated by electrification and the temperature rise of the die occurred because of the heat transfer from the heated billet. Therefore, the die can be carried out on the hot forging process to achieve the purpose of forming. The result of the experiment shows that the billet could be heated quickly to 1000°C in about 5 seconds, and a spur gear was successfully formed. With the proposed method, it was simple enough to hot forge the high-alloy metals with a poor workability. [ABSTRACT FROM AUTHOR]

Phosphorylcholine (ChoP) is an important virulence factor found on the surface of many mucosal pathogens and its expression enhances bacterial colonization on mucous membranes and reduces susceptibility to antimicrobial peptides. Whole-genome sequencing analyses showed thatAvibacterium paragallinarumcontained an operon with strong sequence similarity to thelic1ABCDoperon fromHaemophilus influenzaeand thepcgDABCoperon fromPasteurella multocida; both operons are involved in metabolism and addition of ChoP on bacterial lipopolysaccharide (LPS). Western immunoblot analysis with ChoP-specific monoclonal antibody showed that ChoP is present on LPS ofAv. paragallinarumand the expression of ChoP is controlled by phase variation mediated by the number of 5′-CAAT-3′ tetranucleotide tandem repeats within the coding region of thelic1Agene. The number of tetranucleotide repeats varied widely among strains, and variation in the number of repeats was observed followingin vivopassage but notin vitropassage. Antimicrobial susceptibility assays showed that ChoP expression decreased susceptibility ofAv. paragallinarumto chicken antimicrobial peptide fowlicidin-1. This is the first report showing that ChoP is present on LPS fromAv. paragallinarumand thatAv. paragallinarumcontains a phase-variable gene. These results could be valuable for understanding the mechanism of pathogenicity ofAv. paragallinarum. [ABSTRACT FROM AUTHOR]

Background: Vietnam is one of the most populous countries in Southeast Asia, yet it displays an unsettling lack of doctors. Aims: Medical education is an important factor contributing to this issue, yet little is known about the system currently in place in Vietnam. Methods: Through an extensive literary search of medical schools' and Ministry of Health's data, we have examined the current medical education system in Vietnam. Results: At present, there are 12 medical universities, and the general curriculum at each university follows a national framework but tends to vary from university to university. Medical training lasts either 4 or 6 years, with competitive graduates attending residency programs following graduation. While examinations are required to graduate, the lack of a national licensing exam makes it difficult to ensure that a nation-wide standard of quality exists, both at the medical universities themselves as well as amongst the doctors graduating from them. Conclusions: The development and institution of a national exam would introduce a standard of training throughout Vietnam's medical education system. Further, a substantial portion of a doctor's education is in subjects that are loosely related to medicine. When looking forward it will be important to evaluate whether or not these non-medical subjects detract from the quality of medical training. [ABSTRACT FROM AUTHOR]

Phase evaluation is extraordinarily important in optical, acoustic and radar techniques where coherent signals are employed as information carriers. In most of the cases, phase information are obtained from an inverse trigonometric function and wrapped into -π to π. A phase unwrapping process is thus required to obtain the final unwrapped phase which represents the ultimate physical quantity to be measured. One-dimensional phase unwrapping is easily achieved by adding or subtracting an integer multiple of 2π to the wrapped phase to establish a smooth phase map. Two-dimensional phase unwrapping, however, is quite troublesome and an elegant unwrapping routing should be chosen in most of the cases to deal with phase residues caused by noise and other error sources. It would be valuable if two-dimensional phase unwrapping can be avoided and the physical quantity obtained directly. In the past, researchers have proposed other methods such as the multiple wavelengths approach which incorporates information from multiple wavelengths to eliminate the need for phase unwrapping. In this study, we extend the multiple wavelengths approach by varying the sensitivity factor, which is more convenient and cost-effective, to achieve the aim of requiring no phase unwrapping. Furthermore, an elegant phase derivative approach is used to solve the phase ambiguity problem in the multiple wavelengths method. Both simulation results and real experiment data of shadow moire and shearography demonstrate the usefulness of this method, especially for discontinuous surface profile measurements such as steps. Advantages and disadvantages for the proposed method are also discussed in this paper. [ABSTRACT FROM AUTHOR]

A series of hexagonal polycrystalline RMnO3 (R = Y, Ho, Er, Tm, Lu and Yb) samples are systematically prepared, and their temperature-dependent magnetic susceptibility, specific heat and dielectric properties are measured, in order to investigate the origin of R-dependent dielectric behavior. The dielectric anomalies are found to be strongly correlated with the antiferromagnetic transitions. Both occur near the same temperatures (70∼100 K) and have a very similar R-dependency. Further analysis suggests that the origin of R-dependent dielectric anomalies in the ferroelectric phases could be the variation of strength of antiferromagnetic interaction via the change of in-plane lattice parameters. [ABSTRACT FROM AUTHOR]

Nanohybrid hydrogels with micro or mesoporores were designed and synthesised in the case of polyacrylamide and multiwalled carbon nanotube (MWCNT) or hydroxyl functionalised MWCNT (MWCNT-OH). Investigations indicated that the addition of carbon nanotubes can induce an improved swelling with the temperature increased from 25 to 42°C. The nanohybrid hydrogel samples displayed relatively sensitive response to an acidic environment of pH ≤3, although the equilibrium swelling ratios declined as the MWCNT proportions and pH values were elevated. Mechanical analysis affirmed that the hydrogels exhibited high compression strength and low retention rate of elastic deformation. Fourier transform infrared, SEM and TEM findings implied that MWCNT or MWCNT-OH chains may be wrapped or inserted in the polyacrylamide networks by a non-covalent interaction like intermolecular hydrogen bonding. Hence, a supramolecular assembly was created, which was adopted to shed light on the compression mechanical properties and swelling behaviour. [ABSTRACT FROM AUTHOR]

Experimentally incorporated Zr or Ti into the framework of MCM-41 could enhance the photocatalytic decomposition of H[sub 2]O to H[sub 2]. The hydrogen yield, for instance, on Zr-MCM-41 was about 7 mmol H[sub 2]/hr-gZrO[sub 2]. The enhancement of Zr-MCM-41 was over 80 times if compared to the bulk ZrO[sub 2]. The Ti-MCM-41 also possessed an enhancement of about 17 times for the H[sub 2] yield (over TiO[sub 2]). [ABSTRACT FROM AUTHOR]

Surface radiation heat transfer may become a dominant mode of heat transfer in many engineering applications, and its accurate and efficient modeling is the key to the efficient design of the involved systems. In the study, an improved discrete transfer method (DTM) is developed to meet practical needs for surface radiation modeling. A direct application of the DTM to modeling surface radiative heat transfer usually leads to a large error, due to the strong ray effects. In order to eliminate the ray effects, a total of nine discrete directions over a control angle instead of a single discrete direction as used in the traditional DTM is selected, and the incident radiative intensity over this control angle is then replaced by a weighted-averaged intensity from these nine discrete directions. This approach provides a more accurate value on the mean radiative intensity over a control angle, while it does not increase the total number of radiative intensity to be solved at a surface element. Compared to the modified DTM we developed previously, the present approach is much simpler in terms of numerical treatment. In order to examine the accuracy of the present method, two 3-D benchmark problems are selected and investigated. With a reasonably fine angular discretization, the present solutions are found to match the exact solutions and they are much more accurate than the results from the traditional DTM. [ABSTRACT FROM AUTHOR]

Precise modeling of the optical fiber drawing process is extremely important for identifying optimum drawing conditions in a furnace that would produce high-quality fibers at a low cost. In this study, a numerical approach for detailed simulation of thermal transport in an optical fiber drawing furnace is developed by implementing a primitive variable computational fluid dynamics algorithm. To accurately simulate the underlying fluid dynamics, the complete Navier–Stokes equations are solved for both glass and external gas, which are coupled by the conjugate boundary conditions at the interface. The governing equations are discretized by a finite volume approach and the solution algorithm for the discretized equations is based on the semi-implicit method for the pressure linked equations revised (SIMPLER) method instead of the traditional streamfunction approach. Radiative heat transfer is the most dominant mode of heat transfer during optical fiber drawing and it is modeled by the finite volume method. The gas-preform interface is treated as a Fresnel surface instead of a diffuse surface. To validate the present numerical approach and to examine the effects of the Fresnel interface condition on the preform temperature, a benchmark optical fiber drawing problem containing a prescribed neck-down profile is investigated with various fiber drawing speeds, furnace wall temperatures, and preform diameters. For the diffuse interface, the present prediction in temperature is found to match the available other solution very well. For the Fresnel interface, the present prediction is usually higher in comparison with that of the same approach with the diffuse interface. However, the temperature difference between two interfaces is found to be small, implying that the error caused by the diffuse assumption may be not significant. [ABSTRACT FROM AUTHOR]

Radiative heat transfer is the most dominant mode of heat transfer in an optical fiber drawing process, and its accurate prediction is the key to a realistic simulation of flow and heat transfer in the system. In this study, the finite-volume method (FVM ) is developed to model radiative heat transfer in a gas enclosure as well as inside a glass preform with a Fresnel boundary at the gas–glass interface. Unlike diffuse boundaries, the reflections and transmissions at Fresnel boundaries are governed by Fresnel’s relation and Snell’s law, and they are strongly dependent on the angular direction. During the implementation of the FVM in semitransparent media, control-angle overlap may occur, and it is treated by assuming that the flux of radiant energy across a control angle is determined only by the discrete direction over this control angle and the corresponding radiative intensity. At the Fresnel boundary, a reflective or refractive intensity may not coincide with any discrete direction, and it is approximated by an intensity whose discrete direction makes the smallest angle with the corresponding reflective or refractive intensity. To validate the present FVM in semitransparent media with Fresnel boundaries, two benchmark problems are examined and the present solutions are found to be very accurate with a fine angular discretization. After that, the present model is applied to investigate an optical fiber drawing process with different boundary conditions and temperature distributions. For the diffuse boundary at the gas–preform interface, the results from the FVM are very close to those from the zonal method in each case. For the Fresnel boundary, the FVM provides a solution that tends to be higher in the upper neck-down region and lower in the low neck-down region than that from the same method with the diffuse boundary. The maximum difference betweentwo solutions varies and may reach 10–15% at some cases. [ABSTRACT FROM AUTHOR]

An ideal surface radiation model applied in many manufacturing and materials processing systems must be able to take into account specular, spectral, and shadowing effects with complex geometries, and must be computationally efficient to permit its inclusion in the fluid flow and heat transfer models. In this study, a novel surface radiative heat transfer method is developed to meet all these practical needs. The present model is based on the discrete transfer method (DTM). A direct application of the DTM to modeling surface radiative heat transfer may result in a large error due to strong ray effects. In order to eliminate these ray effects, the DTM is modified by considering radiation contribution from all surface cells intercepted by a control angle. Calculation of these surface cell areas represents one of the most important tasks in the modified DTM (MDTM), and it is described in detail in this study. To investigate the accuracy and efficiency of the MDTM, three benchmark problems covering different geometric and boundary conditions are considered, and the present solution is compared with the solutions from the exact approach, the DTM, and discrete ordinates method (DOM). For each problem, the accuracy of the MDTM, DTM, and DOM appears to be affected by the angular discretization. For a reasonable fine angular discretization, the solutions from the MDTM and DOM match the exact solution very well, while the solution from the DTM usually shows strong ray effects. The CPU times spent on the MDTM and DTM are very similar, but they are usually orders of magnitude less than that for the DOM. The present study indicates that the MDTM is not only accurate but also very efficient for modeling complicated surface radiation problems. Such a model will greatly benefit the simulation of many manufacturing and materials processing systems. [ABSTRACT FROM AUTHOR]

Rapid thermal processing (RTP) has become a key technology in the fabrication of advanced semiconductor devices. As wafers get larger and chip dimensions become smaller, the understanding of the highly coupled physics, such as radiative heat transfer, transient fluid flow, heat transfer, and chemical reactions through numerical modeling using high-performance computing, is the key to the design, optimization, and control of RTP reactors. In this study, an accurate and efficient simulation tool for RTP in a distributed computing environment is developed by implementing various new models and algorithms. Thegoverning equations for highly coupled and transient transport phenomena inRTP are solved by anunstructured finite volume method (FVM). Surface radiative heat transfer is the most dominant mode of heat transfer in RTP and it is modeled by the modified discrete transfer method (MDTM). The radiative properties on the patterned wafer are quite different from those on the bare silicon and they are predicted by the matrix method. To enhance thecomputationefficiency, anefficient parallelalgorithmis implemented in the solution procedure. Data communication among the processors is carried out by the Parallel Virtual Machine (PVM). To evaluate the present simulation tool, an actual commercial RTP reactor is investigated under various conditions. The accuracy of the present model is validated through the comparisons of wafer temperature profile between different models for steady state andtransient flow andheat transfer cases. To demonstrate the importance of the pattern effects in RTP systems, a transient case containing the patterned wafer is investigated. The temperature profile and its uniformity for the patterned wafer are found to be quite different from those for the unpatterned wafer. To examine the performance on parallel computation, the previous transient case is studied with different processor numbers. As the processor number increases, the computationtime is seen to reduce; however, the parallel performance is seen to degrade A larger solution iteration number and higher communication overhead are believed to be the major reasons for the degradation of the parallel performance. The present case studies indicate that the simulation tool developed in this study can be used to systematically investigate various effects in RTP systems because of its high accuracy and efficiency. [ABSTRACT FROM AUTHOR]

A spatial domain-based parallel algorithm is developed for simulating radiative heat transfer in a distributed computing environment. The radiative transfer equation is solved using an unstructured finite-volume method that is applicable for any 2D planar, axisymmetric, and 3D problems with structured, unstructured, or hybrid grids. The domain decomposition is carried out by equally partitioning the spatial domain into many subdomains along the longer geometric dimension. Communication among the subdomains on each processor is performed through a message-passing interface library. In order to examine the parallel performance of the unstructured radiation code, two benchmark problems are investigated for different absorption coefficients, scattering coefficients, and grid sizes in a parallel computer. To help us understand the change of parallel performance, a new parameter, the total inner iteration number, is introduced to analyze the results. For all the cases examined, as expected, the parallel performance is seen to degrade rapidly with an increase of the processor number. However, in contrast with other studies, the parallel performance is found to degrade with an increase of absorption coefficient for a temperature-prescribed problem. Also, the global iteration number is found to be not necessarily independent of the grid size. [ABSTRACT FROM AUTHOR]