A study of reinforced refractory concretes

Results of a laboratory study of the properties of corundum concrete with metallic fibers of five compositions are presented. It is shown that some of the fibers affect favorably the strength and heat resistance of the concrete. Industrial tests of parts made of the suggested reinforced concrete have proved these conclusions.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp. 22–24, November, 1996.     

Morphology and structure of poly(p-phenylene terephthalamide) crystallized from dilute organic solution

The high-temperature crystallization of poly(p-phenylene terephthalamide) (PPTA) from dilute organic solutions was achieved through the introduction of a non-solvent, or precipitating agent, at the desired crystallization temperature. The morphology and crystal structure were examined for crystals produced from PPTA polymer with two different molecular weights (M_w = 46000 and 3430 g mol⁻¹), using transmission electron microscopy. For the high-molecular-weight polymer, ribbon-like crystals were produced, while the low-molecular-weight polymer yielded small needles or platelets. In both cases, electron diffraction showed that the Northolt allomorph was obtained. For the high-molecular-weight polymer, the molecular axes were parallel to the ribbon axes in a chain-extended type structure. A hypothesis for the orientation of the low-molecular-weight PPTA in the small platelets, is also given.     

Design of an X-band transformer-coupled amplifier withimproved stability and layout

The authors present a push-pull transformer-coupled amplifier for monolithic microwave applications, and discuss how its stability and layout have been improved with respect to conventional approaches by means of opposite-phase feedback and fully symmetrical layout. The circuit provides state-of-the-art performance (10-dB gain and 18-dBm saturated power in the 4-8-GHz band) with only 165-mW DC power consumption     

Study of Desorption and Adsorption During Grain Aeration

One requirement in designing and operating and operating system is to minimize the moisture change in stored grain. Moisture transfer during the aeration process is generally believed to be caused by the partial pressure difference between water in grain and water in air (P₃-P₄). A mathematical model was developed for rough rice, which predicts the partial pressure difference under various grain and ambient conditions. Observations of moisture change over 10 aeration tests confirmed the good correlation between sorption phenomena and partial pressure differences. Studies indicated that air relative humidity, air temperature, grain temperature and grain moisture are significant factors influencing the partial pressure differences and, thus, affecting     

Progress in the study of mechanism of fetal scarless wound healing

From January 1987 to December 1993, 426 patients with lung cancer were operated in our hospital, among which 159 patients were diagnosed postoperatively to be N2 disease by pathology including 81 central type and 78 peripheral type lung cancer. Radical operations were performed on 135 cases, palliative operations on 24 cases. Follow up study: one-year survival rate was 71.7%, three-year survival rate 29.0% and five-year survival rate 21.7%. The main factors affecting operative results are tumor cell type, the number and location of metastatic lymph nodes and the thoroughness of dissection. Tumor staging, except T4 tumor is not a main factor influencing prognosis. The indications of operation performed on N2 lung cancer and the necessity of extensive nodal exenteration are also discussed in this article. We consider extensive hilar and mediastinal nodal exenteration necessary in order to achieve radical resection and good prognosis.     

High speed p-type SiGe modulation-doped field-effect transistors

We report on the fabrication and characterization of high-speed p-type modulation-doped field-effect transistors (MODFETs) with 0.7-μm and 1-μm gate-lengths having unity current-gain cut-off frequencies (f_T) of 9.5 GHz and 5.3 GHz, respectively. The devices were fabricated on a high hole mobility SiGe heterostructure grown by ultra-high-vacuum chemical vapor deposition (UHV-CVD). The dc maximum extrinsic transconductance (g_m) is 105 mS/mm (205 mS/mm) at room temperature (77 K) for the 0.7-μm gate length devices. The fabricated devices show good pinch-off characteristics and have a very low gate leakage current of a few μA/mm at room temperature and a few nA/mm at 77 K     

Criteria of cure and follow-up of central hyperthyroidism due to thyrotropin-secreting pituitary adenomas

The recorded number of patients with central hyperthyroidism due to TSH-secreting pituitary adenoma doubled in the last few years after the introduction of ultrasensitive TSH assays in the assessment of thyroid function; however, information about the results and the criteria for cure after pituitary surgery is scanty. Seventeen patients with a TSH-secreting adenoma, diagnosed on the basis of detectable TSH levels in the face of high free thyroid hormone concentrations and pituitary lesion at neuroimaging, underwent pituitary surgery. Hypersecretion of other pituitary hormones was diagnosed in 5 of 17 patients. Four patients were initially misdiagnosed and treated with thyroid surgery or radioiodine therapy. The majority (86%) of hyperthyroid patients normalized thyroid hormone concentrations and regained euthyroidism, although pituitary imaging, alpha-subunit, and alpha-subunit/TSH molar ratio normalized in only 47%, 54%, and 58% of patients, respectively. Moreover, TSH secretion was normally suppressed by T3 in 40% of the patients. Interestingly, the finding of undetectable TSH levels 7 days after surgery was highly predictive of successful outcome. During long term follow-up, there was one relapse of hyperthyroidism. Early diagnosis of TSH-secreting adenomas permits a high rate of remission of hyperthyroidism after surgery. However, normalization of thyroid function alone does not necessarily reflect complete removal of the tumor, and more comprehensive criteria of cure based on pituitary imaging, hormone measurement, and suppression of TSH during T3 administration should be used. Lastly, all patients need an accurate long term follow-up to monitor the possible recurrence of the adenoma.     

Comparison of different methods of modeling turbulent combustion in a boundary layer

Three methods of modeling a chemical reaction in the combustion of ethanol injected into the boundary layer through a porous plate are compared. In calculations of the average velocity and temperature and also heat-transfer coefficients, simple models of combustion are shown to be close in accuracy to a model that takes into complete account the kinetics of all reactions occurring during combustion. Simple models fail to determine the composition of reaction products, and it is necessary to take into account the formation rate of each substance entrained in combustion.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 4, pp. 37–42, July–August, 1996.     

Composition and thermodynamics of the surface layer of binary melts based on iron,cobalt, and nickel

The composition, thickness, thermodynamic activities of components, Gibbs energy and excess energy of formation of the surface layer on binary melts of iron, cobalt and nickel-based alloys with different interatomic interactions were evaluated with the aid of data from the literature and the authors measurements of the concentration dependence of the surface tension and molar volume.