Morphological instability in rapid directional solidification

Mullins and Sekerka showed for fixed temperature gradient that the planar interface is linearly stable for all pulling speeds V above some critical value, the absolute stability limit. Near this limit, where solidification rates are rapid, the assumption of local equilibrium at the interface may be violated. We incorporate non-equilibrium effects into a linear stability analysis of the planar front by allowing the segregation coefficient and interface temperature to depend on V in a thermodynamically-consistent way. The absolute stability limit of the cellular mode is modified. A new oscillatory state is formed which, in the absence of latent heat, has a critical wavenumber of zero; by itself this instability would lead to the formation of solute bands in the solid. This mode has its own absolute-stability limit determined by solute trapping and kinetics. Under certain conditions there exists a window of stability above the steady absolute-stability boundary and below the oscillatory-stability; here the planar, segregation-free state is restabilized.     

Impingement after total knee arthroplasty caused by cement extrusion and proximal tibiofibular instability

A 57-year-old patient with rheumatoid arthritis showed posterolateral impingement after total knee arthroplasty. The radiographs showed bone cement extrusion posterolateral to the tibial tray. Arthrotomy through a posterolateral approach revealed that the impingement was caused not only by cement extrusion against the fibular head but also by proximal tibiofibular joint instability. It was speculated that rheumatoid arthritis had caused proximal tibiofibular instability, active knee motion had caused fibular head shift by tension of biceps femoris and the fibular head had been impinged on the extruded cement. In cementing the tibial tray, especially in a rheumatoid patient, it is of paramount importance to take caution against posterolateral cement extrusion in order to minimize the risk of fibular head impingement during total knee arthroplasty.     

Morphological transformation caused by a partial sequence of U5 small nuclear RNA

My colleagues and I have reported that a small nuclear RNA, U5, can cause transformation of and chromosomal aberrations in rat fibroblast 3Y1 cells. In the study described here, I found that a partial U5 sequence, the 3' half of the first stem structure (designated RNA3S), transformed the cells morphologically at a high frequency when expressed with a poly(A) tail (RNA3S+). The transformation critically depended upon a polypurine sequence in RNA3S+. The expressed RNA3S+ was associated with polysomes. The transformed cells did not exhibit significant frequencies of chromosome aberrations when compared with control cells, suggesting that the transformation occurs without significant induction of chromosome damage. Heterogeneous subcolonies emerged in monolayers when the morphologically transformed cells were subcultured and maintained at postconfluence. Cells from subcolonies acquired the ability to form small colonies in soft agar and tumors in nude mice, suggesting that RNA3S+ can drive the cells into the neoplastic stage. RNA3S+ also conferred morphological alterations and a growth advantage and decreased levels of fibronectin protein synthesis in human HeLa cells, confirming the transforming potential of the RNA. RNA3S+ transformation may therefore be a useful model system for studying a transformation process.     

Relaxation kinetics and relaxed stresses caused by interface diffusion around spheroidal inclusions

The kinetics of relaxation by interface diffusion around spheroidal inclusions is discussed using the Eshelby method for ellipsodal inclusions and a free energy approach. The relaxation time for the process is derived in the case where the direction of an applied uniaxial stress is parallel to the rotation axis of symmetry of the speroid. The aspect-ratio dependence of the relaxanion time is derived. For prolate inclusions with large aspect ratios, the relaxation time increases proportionally to the aspect ratio. On the other hand, for oblate inclusions with small aspect ratios, the relaxation time becines constant as the aspect ratio approaches zero. The constant value of the relaxation time depends on the elastic moduli of the inclusion but independent of the elastic moduli of the matrix. The hydrostatic stress in the inclusion after the relaxation and its aspect-ratio dependence are also discussed. Although the relaxation time for a rod-like inclusion is longer compared with that for a disk-like inclusion, the relaxed stress in the former is much smaller than that in the latter.     

Surgical management for instability and paraplegia caused by spinal sarcoidosis. A case report

STUDY DESIGN: Report of a patient with paraplegia caused by vertebral sarcoidosis. OBJECTIVES: To report a rare case of vertebral sarcoidosis accompanied by progressive neurologic symptoms from the lower extremities, and to discuss the diagnostic and therapeutic approach to its management. SUMMARY OF BACKGROUND DATA: Vertebral sarcoidosis is a rare condition, and only a few case reports exist in the literature. A needle or open biopsy is required to establish the diagnosis. In most cases, treatment with steroids improves associated neurologic symptoms. Operative intervention is necessary in cases with progressive vertebral destruction, spinal instability, and impending or progressive neurologic deterioration. METHODS: Operative treatment by a two-stage anterior vertebrectomy and fusion followed by posterior stabilization was given to a patient with vertebral sarcoidosis and progressive neurologic deterioration of the lower extremities. RESULTS: After surgery, the patient had a complete neurologic recovery and satisfactory spinal fusion. CONCLUSIONS: In the absence of any spinal instability, neurologic symptoms associated with vertebral sarcoidosis respond satisfactorily to nonoperative treatment with steroids. Progressive neurologic deterioration or spinal instability caused by bone destruction requires operative intervention. Anterior vertebrectomy and fusion combined with posterior stabilization provided a satisfactory result for the patient in this report.     

Bovine mastitis caused by Listeria monocytogenes: kinetics of antibody responses in serum and milk after experimental infection

The kinetics of antibodies in serum and milk directed against proteins from Listeria monocytogenes were studied using 4 lactating cows after infection was experimentally induced in the udder with four strains of serotypes 4b or 1/2a. Antibodies (IgG and IgA) in samples of composite quarter milk and serum of the cow were measured by indirect ELISA. Microtiter plates were coated with proteins obtained from the culture supernatant of L. monocytogenes 4b. After challenge, an IgG response in serum and milk to listerial infections in the udder occurred for all cows, although the response varied among cows. In sera, the IgG titers reached a peak at 9 to 13 wk after challenge and remained elevated until 21 to 33 wk after challenge. In milk, the IgG titer increased significantly 3 wk after the challenge for all cows. A weak and nonpersistent increase in IgA antibodies also occurred. These results indicate that IMI by L. monocytogenes induced an increase of antibodies in milk, which could be detected with an ELISA test using our antigenic preparation. Therefore, this antigenic preparation could be used for the evaluation of a new method of diagnosis for bovine mastitis caused by L. monocytogenes.     

Morphological transformation of liposomes caused by assembly of encapsulated tubulin and determination of shape by microtubule-associated proteins (MAPs)

To examine the role of cytoskeletons in cellular morphogenesis, we generated liposomes encapsulating tubulin, with or without microtubule-associated proteins (MAPs), and observed their transformation using dark-field microscopy. When tubulin was polymerized with MAPs in liposomes, liposomes were transformed into a "bipolar" shape with a central sphere and two tubular membrane protrusions that aligned in a straight line. On the other hand, when pure tubulin was polymerized in liposomes without MAPs, they initially transformed into a bipolar shape but subsequently re-transformed into a "monopolar" shape, i.e. a sphere with only one straight tubular portion. This re-transformation occurred in two ways: first, by shortening of one of the tubular portions due to microtubule disassembly; or second, by fluctuation of the central sphere toward one of the ends without shortening of the tube portion. MAPs prevented this re-transformation, and their role in stabilizing the shape of transformed liposomes was studied by the co-sedimentation method. The results show that MAPs, particularly MAP1 and MAP2, mediate binding between microtubules and the liposomal membrane. However, MAP2 by itself did not bind to liposomes, but was able to stabilize bipolar liposomes. This stabilization is caused not only by direct links between microtubules and liposomes, but also by prevention of Brownian motion of microtubules through an increase in friction.     

Ti-6Al-4V在步进轧制中的显微组织变化

对步进轧制在940℃α β区轧制Ti 6Al 4V合金棒材的锥形体取变形量不同的部位,利用光学显微镜、透射电镜观察其组织形貌及位错组态,分析了其变形机制,探讨了材料显微组织随变形量变化的规律及其形变硬化、回复、再结晶的演变过程.实验表明利用步进轧机加工,所得Ti 6Al 4V合金棒材芯部和边部的组织较均匀.     

Disturbances caused by noise in offices

Noise measurements were carried out in 57 offices. At the same time 228 employees were asked about their opinion on the noise situation. Relations between objective and subjective criteria, noise values and complaints about disturbance caused by different types of noise were analyzed. Noise parameters comprising noise peaks are more adequate to assess disturbing noise than parameters based on a mean noise level. Statements on extent and frequency of disturbance in general and of communication depend on noise. Statements on disturbances of concentration and on impairment of performance do not depend on noise. Outdoor noise and "subjectively worst noise" are measurable in dB values; indoor noise, however, is independent from the measured values.