A stability analysis of turning a tailstock supported flexible work-piece

This paper proposes a new approach to analyze the stability of a cutting process. Previously, most studies have generally assumed the work-piece to be rigid and have, therefore, ignored work-piece deformation. In analyzing, the stability of the cutting process, these studies simply considered the dynamic equation of the tool. However, in practice, the work-piece undergoes deformation as a result of the application of an external force by the cutting tool. This deformation changes the chip thickness and has an effect on the critical chip thickness. Consequently, this study proposes a novel stability analysis method for the turning process in which deformation of the work-piece is considered. The cutting, which takes place in the turning process, is described using partial differential equations, and a set of dynamic equations is developed by considering the interaction between the tool and the work-piece. Having performed Laplace transformation, the stability of the cutting system can be analyzed in terms of the work-piece length, radius, natural frequency, deflection, slenderness ratio, cutting point, and material. The relationship between the critical chip width and the cutter spindle speed is investigated under a range of cutting and work-piece conditions. The analytical results for the current flexible work-piece are compared with those for a rigid work-piece. It is found that the critical chip width of the flexible work-piece is always greater than that of the rigid body.     

Ambient‐Stable,Annealing‐Free,and Ambipolar Organic Field‐Effect Transistors Based on Solution‐Processable Poly(2,2′‐bis(trifluoromethyl)biphenyl‐alt‐2,5‐divinylthiophene) without Long Alkyl Side Chains

An ambipolar conjugated polymer CF₃‐PBTV, poly(2,2′‐bis(trifluoromethyl)biphenyl‐alt‐2,5‐divinylthiophene), consisting of thienylenevinylene as the donor and trifluoromethyl‐substituted biphenyl as the acceptor has been successfully synthesized. CF₃‐PBTV shows solution‐processability without electrically insulating long alkyl side chains. Grazing incidence X‐ray diffraction results suggest a nearly equal population of flat‐on and end‐on domains in CF₃‐PBTV thin film. The excellent ambipolarity of CF₃‐PBTV is demonstrated by well‐equivalent charge mobilities of 0.065 and 0.078 cm² V^?1 s^?1 for p‐ and n‐channel, respectively. The organic field‐effect transistors (OFET) also shows very high on/off ratio (≈10⁷) which is attributed to the relatively large bandgap and low‐lying highest occupied molecular orbital (HOMO) of CF₃‐PBTV. The OFET performance barely changes after the device is stored in ambient conditions for 90 days. The ambient‐stability is attributed to the enhanced oxidative stability from its low‐lying HOMO and the better moisture resistance from its fluorine contents. The performance of CF₃‐PBTV based OFET is annealing independent. It is noteworthy that the solution‐processable, ambipolar, and thienylenevinylene‐containing conjugated polymer without any long alkyl side chains is reported for the first time. And to the best of our knowledge, it is the first ambient‐stable, annealing‐free OFET with well‐equivalent ambipolarity.     

Role of mass transfer in overall substrate removal rate in a sequential aerobic sludge blanket reactor treating a non-inhibitory substrate

A laboratory study was undertaken to explore the role of mass transfer in overall substrate removal rate and the subsequent kinetic behavior in a glucose-fed sequential aerobic sludge blanket (SASB) reactor. At the organic loading rates (OLRs) of 2-8 kg chemical oxygen demand (COD)/m³-d, the SASB reactor removed over 98% of COD from wastewater. With an increase in OLR, the average granule diameter (d_p = 1.1-1.9 mm) and the specific oxygen utilization rate increased; whereas biomass density of granules and solids retention time decreased (13-32 d). The intrinsic and apparent kinetic parameters were evaluated using break-up and intact granules, respectively. The calculated COD removal efficiencies using the kinetic model (incorporating intrinsic kinetics) and empirical model (incorporating apparent kinetics) agreed well with the experimental results, implying that both models can properly describe the overall substrate removal rate in the SASB reactor. By applying the validated kinetic model, the calculated mass transfer parameter values and the simulated substrate concentration profiles in the granule showed that the overall substrate removal rate is intra-granular diffusion controlled. By varying different d_p within a range of 0.1-3.5 mm, the simulated COD removal efficiencies disclosed that the optimal granular size could be no greater than 2.5 mm.     

Wirebond profiles characterized by a modified linkage-spring model which includes a looping speed factor

The linkage-spring model based on a quasi-static looping has been used to determine the design rules to reduce the loop heights and the sagging altitude of gold wire in the package. In order to further simulating the capillary trajectory which includes a looping speed factor from the first bond to the second bond stages, a linkage-spring model is modified in this study. The factors of the inertia mass and variations in material properties with different strain-rates need to be considered due to a high speed looping.It is found that the looping speed effects on the wirebond profiles due to the inertia mass can be neglected at a regular looping process of 3–5g acceleration even up to around 10g acceleration. However, variations in the material properties during deformation at different strain-rates could be an important factor on the wirebond profiles. Fortunately, a pure annealed state like pure gold wire would be little strain-rate sensitivity. The effects of the strain-rate in pure gold wire, therefore, can be excluded in analysis. Accordingly, a linkage-spring model based on the quasi-static looping is still applicable in analyzing the wirebond profiles.     

Enhanced intestinal adenomatous polyp formation in Pms2-/-;Min mice

Analysis of two human familial cancer syndromes, hereditary nonpolyposis colorectal cancer and familial adenomatous polyposis, indicates that mutations in either one of four DNA mismatch repair gene homologues or the adenomatous polyposis coli (APC) gene, respectively, are important for the development of colorectal cancer. To further investigate the role of DNA mismatch repair in intestinal tumorigenesis, we generated mice with mutations in both Apc and the DNA mismatch repair gene, Pms2. Whereas Pms2-deficient mice do not develop intestinal tumors, mice deficient in Pms2 and heterozygous for Min, an allele of Apc, develop approximately three times the number of small intestinal adenomas and four times the number of colon adenomas relative to Min and Pms2+/-;Min mice. Although Pms2 deficiency clearly increases adenoma formation in the Min background, histological analysis indicated no clear evidence for progression to carcinoma.     

Degradation of annexin I in bronchoalveolar lavage fluid from patients with cystic fibrosis

BACKGROUND/AIMS: The number of perisinusoidal myofibroblasts has been shown to be increased in hepatocellular carcinoma, as compared to cirrhosis. This increase might suggest a cooperative relationship between tumour cells and myofibroblasts. To assess this relationship, we undertook: (a) an immunohistochemical study to confirm the existence of an increased number of perisinusoidal myofibroblasts in human hepatocellular carcinoma, as compared to cirrhosis with or without liver cell dysplasia, (b) an in vitro study testing the role of normal or tumoral human hepatocytes in myofibroblast proliferation. METHODS: Forty explanted cirrhotic livers, including 14 with hepatocellular carcinoma and 24 with liver cell dysplasia, were studied. Myofibroblasts were detected by immunohistochemistry using an antibody directed against alpha-smooth muscle actin. Hepatic myofibroblasts in culture were obtained by outgrowth from human liver explants. RESULTS: There was a progressive increase in the number of perisinusoidal myofibroblasts, from cirrhotic nodules without dysplasia to liver cell dysplasia and hepatocellular carcinoma. Conditioned medium from isolated normal human hepatocytes had only minor mitogenic effects on myofibroblasts, as assessed by measuring DNA synthesis and cell growth. In contrast, conditioned medium from a human hepatoma cell line (HepG2 cells) markedly stimulated the proliferation of human myofibroblasts. This mitogenic activity was stored in HepG2 cells and secreted in the extracellular medium rather than being simply released following cell lysis. CONCLUSIONS: These results suggest that the increased number of myofibroblasts in hepatocellular carcinoma might be due to a paracrine mechanism involving soluble mitogenic factor(s) secreted by tumour cells.     

Control of linear motor machine tool feed drives for end milling: Robust MIMO approach

Linear motors are getting promising for use as high speed, high accuracy machine tool feed drives. The cutting force in the machining process are directly reflected to the linear motor due to no gearing mechanism. To achieve high accuracy machining, the controller for the linear motor system should be designed to compensate for the cutting force.

In this work, a MIMO H_∞ controller for the linear motor machine tool feed drives has been designed to reduce tracking errors induced by cutting forces for end milling. The controller is designed using normalized coprime factorization method for the dynamic model of the linear motor system. The model includes constant in-line and cross coupling force gain, since the feedback cutting force can be considered as the product of the constant gain and the moving velocity of each axis.

Analysis of the structured singular value shows that the designed controller has good robust performance despite wide variations of the cutting force and physical parameters. It is directly implemented on a linear motor X–Y table which is mounted on a milling machine to have cutting experiments via a DSP board. Experimental results verified effectiveness of the proposed scheme to suppress the effects of the cutting force in the high feed rate.     

Rapid diagnosis of tuberculous meningitis by polymerase chain reaction assay of cerebrospinal fluid

A polymerase chain reaction (PCR) method for the rapid diagnosis of tuberculous meningitis (TBM) was used to study prospectively 47 cerebrospinal fluid (CSF) samples from 45 patients. Twenty CSF samples were from patients with clinically suspected TBM and another 27 samples came from patients without clinically suspected TBM. Mycobacterial DNA was detected in 15 CSF samples (14 from patients with clinically suspected TBM and 1 from a patient not suspected of having TBM). Of the PCR-positive samples, 4 were also positive for mycobacterial culture. However, 32 PCR-negative samples were all culture-negative. All samples were negative for the acid-fast bacillus by direct smear. The single PCR-positive patient in the clinically unsuspected TBM group was initially diagnosed as suffering from aseptic meningitis on the basis of his clinical features. The mycobacterial culture of his CSF specimen was also positive and a revised diagnosis of an aseptic type of TBM was made. The estimations of specificity and sensitivity in this study were 100% and 70% respectively. The results showed that using a PCR to detect mycobacterial DNA in CSF for the early diagnosis of TBM is not only a rapid but also an accurate method.