Similarity laws of mean velocity profiles and turbulence characteristics of Couette–Poiseuille turbulent flow (C-P flow) have been studied experimentally. The global parameters of C-P flow are the Reynolds number $\hbox{\it Re}^{\ast}$ and the dimensionless shear stress gradient $\mu$ and flow parameter $\beta $. The effects of these parameters on the turbulence structure have also been considered in the wall region and turbulent core region, respectively. In the wall region, the wall law varies greatly with $\mu $ but slightly with $\hbox{\it Re}^{\ast}$. Typically, the additive constant $B$ of the logarithmic law (or Van Driest damping factor $A^{+}$) is shown to depend only on $\mu $. Turbulence characteristics are also strongly influenced by $\mu $, but not much by $\hbox{\it Re}^{\ast}$. Because the relation $\mu \,{=}\, {-}\hbox{\it Re}^{\ast}$ holds in plane Poiseuille flow and $\hbox{\it Re}^{\ast}$ has little effect on the similarity laws for C-P flows, the low-Reynolds-number effect on the additive constant and turbulence quantities for plane Poiseuille flow can be attributed to the $\mu $ effect. In the turbulent core region, however, there is a great difference in the defect law of the velocity profile and the distribution of turbulence intensity between Poiseuille (P)- and Couette (C)-types flows. For P-type flow, an effective friction velocity $u^{\ast}_{e}$ and a new coordinate $\eta \,{=}\,y- h_{s}$ are recommended for the universal profile, where $y\,{=}\,h_{s}\,{=}\,\delta _{p}$ is the position of $\tau \,{=}\,0$ and $\delta _{p}$ is considered to be appropriate as a characteristic length scale of turbulence. For C-type flow, a different effective friction velocity $u^{\ast}_{c,}$ the characteristic length scale 2$h$ and the wall coordinate $y$ are preferred. The turbulence activity away from the wall is extremely high for $\mu \,{>}\,0$ and low for $\mu \,{<}\,0$. A strong sweep event plays a dominant role in the Reynolds shear stress when $0\,{<}\,\mu \,{<}\,50$, whereas strong ejection from the near-wall region prevails in the case of negative $\mu$ with a small absolute value.

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Extraskeletal osteosarcoma is extremely rare in mice. This case report demonstrates a spontaneous murine extraskeletal osteosarcoma that exhibited various histological growth patterns in an ICR mouse. At necropsy, the tumor mass was located in the abdominal wall and was 45 × 30 × 25 mm in size. Histopathologically, the tumor showed the following four growth patterns: a solid pattern of polygonal cells embedded in an osteoid eosinophilic matrix with calcification, an irregular sheet pattern of short spindle cells accompanying some eosinophilic multinucleated cells, a fascicular pattern of spindle cells and a cystic pattern lined by short spindle cells. Immunohistochemically, most of the tumor cells were positive for vimentin, proliferating cell nuclear antigen and osterix. The multinucleated cells mentioned above were desmin positive and were regarded as regenerative striated muscles but not tumor cells. Since no clear continuity with normal bone tissues was observed, the tumor was diagnosed as an “extraskeletal osteosarcoma.”

An extraskeletal osteosarcoma was detected in the auricle of a 110-week-old female Wistar Hannover rat. Grossly, the tumor, measuring 15 mm in size, was observed in the subcutis as a solid and hard mass. Histologically, the majority of the mass comprised mature, compact bone. It was surrounded by neoplastic cells showing a variety of histologies, such as sarcoma, not otherwise specified, and myxosarcoma away from the bone-forming region. However, these different histological regions were considered to be components of a single bone tumor, based on the common expression of osterix and a similar mixture of constituent cells in each region. The tumor was diagnosed as an extraskeletal osteosarcoma because of the presence of infiltrative growth and abnormal mitosis and its development in the auricle without attachment to the skeleton. The present case is a rare histological type of an extraskeletal osteosarcoma with independent and different histological elements in rats.

A whitish mass approximately 30 mm in diameter was noted in the anterior mediastinum of a 67-week-old female Fischer 344 rat. Histopathologically, two types of tumor cells were identified on the basis of morphologic features: epithelial tumor cells with a tubular or cord-like growth pattern and rhabdomyosarcomatous tumor cells characterized by the presence of cross-striations. Immunohistochemically, the epithelial tumor cells reacted positively for cytokeratin AE1/AE3, and some reacted positively for p63, which is expressed in normal thymic epithelial cells. The rhabdomyosarcomatous tumor cells stained positively for desmin, sarcomeric actin, and S-100 protein, which coincides with the stainability of normal thymic myoid cells. Since the tumor was also found to have malignant features such as high proliferative activity, cytologic atypia, and necrotic behavior, it was diagnosed as a malignant myoid thymoma. We believe that this is the first case report of such a tumor in a rodent.