Microstructural development and creep deformation in equiaxed γ,γ + α2 and γ + α2 + B2 titanium aluminides

The development of microstructure and its influence on creep properties have been studied for structures including equiaxed γ, duplex, and other structures of varying α₂ morphology in two Ti-48Al-2Cr-2Nb alloys. Heat treatment at 1125°C have been utilized to produce equiaxed γ microstructures in alloys with or without Mo additions. The γ→α transformation produces α₂ plates with several orientation variants with γ grains during subsequent annealing of the equiaxed γ microstructures below the α transus. Formation of this α₂ morphology results from rapid up-quenching (UQ), and this structure persists through annealing, cooling, and creep testing. Differences in minimum creep rates for several microstructures, containing varying amounts of multi-or single variant γ/α₂ grains are shown to be minimal. The presence of Mo has also resulted in improved creep resistance in equiaxed γ and γ + α₂ + B2 structures, as compared to similar microstructures in the Ti-48Al-2Cr-2Nb alloy. Deformation during creep at 760 °C at stresses between 200 and 400 MPa occurs by a combination of twinning and dislocation glide without recrystallization, resulting in power-law stress exponents in the range of 6 to 9. Only minimal strain path dependence of the minimum creep rate is detected in a comparison of creep rates in stress jump, stress drop, and single stress tests. This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides,” presented at the TMS Annual Meeting, February 10–12, 1997, Orlandom, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations Committees.     

Microstructural development and creep deformation in equiaxed γ, γ+α 2, and γ+α 2+B2 titanium aluminides

The development of microstructure and its influence on creep properties have been studied for structures including equiaxed γ, duplex, and other structures of varying α ₂ morphology in two Ti-48Al-2Cr-2Nb alloys. Heat treatments at 1125 °C have been utilized to produce equiaxed γ microstructures in alloys with or without Mo additions. The γ → α transformation produces α ₂ plates with several orientation variants within γ grains during subsequent annealing of the equiaxed γ microstructures below the α transus. Formation of this α ₂ morphology results from rapid up-quenching (UQ), and this structure persists through annealing, cooling, and creep testing. Differences in minimum creep rates for several microstructures containing varying amounts of multi- or single variant γ/α ₂ grains are shown to be minimal. The presence of Mo has also resulted in improved creep resistance in equiaxed γ and γ+α ₂+B2 structures, as compared to similar microstructures in the Ti-48Al-2Cr-2Nb alloy. Deformation during creep at 760 °C at stresses between 200 and 400 MPa occurs by a combination of twinning and dislocation glide without recrystallization, resulting in power-law stress exponents in the range of 6 to 9. Only minimal strain path dependence of the minimum creep rate is detected in a comparison of creep rates in stress jump, stress drop, and single stress tests. This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides,” presented at the TMS Annual Meeting, February 10–12, 1997, Orlando, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations Committees.     

Feline bone marrow transplantation: its use in FIV-infected cats

The use of autologous and allogenic bone marrow transplantations (BMT) in FIV-infected and uninfected cats is a novel therapy for feline hematopoietic diseases and retroviral infections. A total of 13 specific pathogen-free (SPF) cats received either autologous or allogenic BMT and seven of these cats were also infected with FIV before autologous or allogenic BMT. All BMT recipients received total body irradiation of 900 cGy just before BMT. Two FIV-infected and four uninfected cats received autologous uninfected BM cells cryopreserved before BMT. Five infected and two uninfected cats received BM cells from allogenic uninfected donors (RBC-, MHC-, and cross-matched). MHC-matching was based on mixed leucocyte reaction (MLR) and the donor-recipient combination which was compatible by MLR analysis, was used in this study. Recipients were monitored for hematology, immunology, virology, and clinical signs. All FIV-infected and uninfected recipients of autologous BMT had complete engraftment with minimal complications. Uninfected recipients of allogenic BMT had a more severe clinical episode with slower rate of engraftment. None of these BMT groups had mortality. In contrast, only two of the five infected recipients of allogenic BMT survived for a significant period of time (23 and 50 weeks) and rest of the cats succumbed to transfusion reactions. Both infected BMT groups had persistent CD4/CD8 inversion, low CD4+ cell counts, and FIV infection of engrafted peripheral blood mononuclear cells (PBMC). Overall, successful autologous and allogenic BMTs were performed in FIV-free cats. All infected recipients of autologous BMT had compete engraftment and are currently alive, with thelongest survival time being over 1 year. Thus, BMT in combination with antiviral drug therapies may be an alternative therapy against retroviral infection.     

Elevated platelet factor 4 and beta-thromboglobulin plasma levels in depressed patients with ischemic heart disease

Clinical depression has recently been recognized as an independent risk factor for cardiac mortality in patients after myocardial infarction. The underlying mechanisms of this increased mortality remain unclear. This study investigated the hypothesis that patients suffering from ischemic heart disease (IHD) and depression concurrently may have abnormal platelet activation resulting in an increased risk of thrombosis. Platelet factor 4 (PF4) and beta-thromboglobulin (beta-TG) were measured in young healthy control subjects, in nondepressed patients with IHD, and in depressed patients with IHD. Mean PF4 and beta-TG plasma levels in the IHD group with depression were found to be significantly higher than those of the control and IHD groups. This increase was not related to age, gender, racial difference, aspirin use, or severity of cardiac disease. This finding suggests that in depressed patients with IHD there is greater platelet activation, and may indicate an increased risk of thrombotic complications.     

Testosterone concentrations and oligomenorrhea in women with acne

BACKGROUND: Androgen excess is frequently associated with oligomenorrhea as well as acne. Oligomenorrhea in hirsute women has been demonstrated to be associated with higher active testosterone levels than found in eumenorrheic hirsute women. This study was designed to evaluate whether similar findings are present in women with acne. Forty-four consecutive women with acne were evaluated by measuring their levels of total testosterone, biologically active testosterone, and free testosterone. The women with oligomenorrhea and acne had significantly higher levels of biologically active testosterone than those with eumenorrhea and acne. This implies that biological active testosterone should be measured in oligomenorrheic women with acne and, if elevated, consideration should be given to antiandrogen therapy. METHODS: Data were collected from 44 consecutive Caucasian women aged 14 to 38 years. The patients were separated into two groups based on menstrual history. Group 1 had regular menses, and group 2 had oligomenorrhea, defined as menstrual intervals of greater than 36 days. All patients had blood samples drawn on their initial office visit, regardless of the phase of the menstrual cycle, and the levels of total testosterone (TT), biologically active testosterone (BT), and free testosterone (FT) were obtained. RESULTS: The serum TT level was 87 +/- 41.3 ng/dL (range, 31-150 ng/dL) in oligomenorrheic women and 56 +/- 27.5 ng/dL (range 8-107 ng/dL) in eumenorrheic women. There was no statistically significant difference. The serum BT level in oligomenorrheic women was 33 +/- 16.9 ng/dL (range, 11-51 ng/dL) and in eumenorrheic women 19 +/- 13.6 ng/dL (range, 11-51 ng/dL). This difference was statistically significant (p < 0.05). The serum FT level in oligomenorrheic women was 18 +/- 9.4 pg/mL (range, 1-29 pg/mL) and in eumenorrheic women 10 +/- 7.1 pg/mL (range, 1-32 pg/mL). This difference was not statistically significant (Table 1). CONCLUSIONS: Women with acne and oligomenorrhea, similar to women with hirsutism and oligomenorrhea, have higher levels of biologically active testosterone than those with normal menses.     

Substitutional and defect doping effects on the photoelectrochemical properties of Fe2O3

Fe₂O₃ samples have been prepared using both substitutional and defect doping techniques. Defect doped samples were sintered in air at 1350° C for 20 hours, reduced in a H₂ atmosphere for various times at 300° C, and finally reoxidized at 700–900° C for short periods. Resulting resistivities ranged from .01 to 5000 ohm-cm. Such electrodes were found to have good photoelectrochemical properties, and to be quite sensitive to chemical etching. Substitutional doping of Fe₂O₃ with Si, Ca, Nb, Cu, Ru, Mg, and Zr was performed, with Si and Cu providing the best results. The effects of quenching time and temperature on the properties of these electrodes are discussed.