How to Create Trusted Tribological Characterization Data of Soft Polymers as Input for FEM Simulations?

Soft polymers such as the investigated polyurethane, characterized by low Young's moduli and prone to high shear deflection, are frequently applied in pneumatic cylinders. Their performance and lifetime without external lubrication are highly determined by the friction between seal and shaft and the wear rate. FEM simulation has established itself as a tool in seal design processes but requires input values for friction and wear depending on material, load, and velocity. This paper presents a tribological test configuration for long stroke, reciprocating movement, allowing the generation of data which meet the requirements of input parameters for FEM simulations without the geometrical influences of specific seal profiles. A numerical parameter study, performed with an FEM model, revealed the most eligible sample geometry as a flat, disc-shaped sample of the polymer glued on a stiff sample holder. At the same time, the study illustrates that the sensitivity of the contact pressure distribution to Poisson's ratio and CoF can be minimized by the developed and verified setup. It ensures robust, reliable, and repeatable experimental results with uniform contact pressures and constant contact areas to be used in databases and FEM simulations of seals, enabling upscaling from generically shaped samples to complex seal profiles.

Hyponatraemia in acute brain disease

Hyponatraemia (HN) can result from a wide range of mechanisms, and therapy must be individualized. Two theories of the origin of HN in acute brain disease have prevailed. The first is the cerebral salt wasting syndrome (CSWS), where excessive natriuresis caused by some unknown cerebral natriuretic factor lowers the total sodium pool of the body and hence the plasma concentration. The second theory is the syndrome of inappropriate secretion of antidiuretic hormone (SIADH), where an increase in total body water is caused by unphysiological secretion of ADH, lowering the concentration of sodium in the plasma. A third possibility is 'sodium shift', i.e. a displacement of sodium from the extracellular to the intracellular space with a simultaneous movement of potassium in the opposite direction. The morbidity and mortality associated with HN only arise in cases where the rate of development of HN was 0.5 mmol h-1 or more. Symptoms respond promptly when the HN is quickly corrected with furosemide and 3% sodium chloride.

Chromogranin A and B in adenomas of the pituitary. An immunohistochemical study of 42 cases

Forty-two pituitary adenomas (10 prolactinomas; three ACTH-, nine GH-, two FSH- and two TSH-secreting adenomas; and 16 clinically nonfunctioning null cell adenomas) were investigated immunohistochemically with antibodies against chromogranin A and B as well as ACTH, GH, prolactin (PRL), FSH, LH, TSH, and alpha-HCG antibodies. For the demonstration of chromogranin B, two different antibodies were used--e.g., a polyclonal antihuman antibody and an antiserum against a synthetic peptide (DK-21, chromogranin B 306-326) present in the chromogranin B amino acid sequence. All tumors were positive for both chromogranin B antibodies. Chromogranin A was found in FSH- (two of two) and TSH- (two of two) secreting adenomas; it was also found in a focal distribution in ACTH- (one of three) and GH- (four of nine) secreting adenomas. Thirteen of 16 null cell adenomas contained chromogranin A, whereas no chromogranin A was found in prolactinomas. We conclude that null cell adenomas may arise either from FSH/LH or TSH cells (null cell adenomas with both chromogranin A and B positivity) or from ACTH, GH, or PRL cells (the respective tumors are only positive for chromogranin B). Chromogranin B may be used as a universal marker for pituitary adenomas.

Small cell carcinoma of the thyroid. A reclassification of cases originally diagnosed as small cell carcinomas of the thyroid

99 cases of undifferentiated carcinomas of the thyroid and nine cases of primary malignant Non-Hodgkin lymphomas of the thyroid were examined from 1967 to 1983 in our institute. Among the undifferentiated carcinomas nine cases were classified as small cell subtype. Over the years, the histopathological handling in regard to small cell subtype of undifferentiated carcinoma and primary malignant Non-Hodgkin lymphoma has changed. The frequency of primary malignant Non-Hodgkin lymphoma has increased conspicuously in the last few years, whereas the number of small cell carcinomas decreased. A reclassification, based on immunohistochemical investigation for tumor markers of the nine cases originally diagnosed as small cell carcinomas from 1967 to 1983 revealed that five cases were poorly differentiated carcinomas or undifferentiated carcinomas of the spindle cell type. In three cases the primary diagnosis had to be revised into malignant Non-Hodgkin lymphoma of the diffuse "histiocytic" type. The postmortem examination of the patient with the remaining small cell carcinoma "of the thyroid" revealed a clinically undetected small cell carcinoma of the lung with metastases to the cervical lymph nodes and the thyroid gland. These findings are in agreement with the results of several recently published papers indicating that true small cell carcinoma of the thyroid must be a very rare tumor.