By a novel freeze-gelcasting technique, ceramic bodies with unidirectional ordered and gradient porous structures were fabricated, using tert-butyl alcohol (TBA)/acrylamide (AM)/ alumina (Al 2 O 3 ) slurries. TBA, which can freeze below 251C and volatilize rapidly above 301C, was used as a template for forming pores. The porous structures could be controlled by the temperature conditions, resulting in special unidirectional and gradient porous structures over a long range of several millimeters. At the same time, gelation of AM was successfully introduced in this process, and played an important role in strengthening the green bodies (with compression strength over 10 MPa). Sintered Al 2 O 3 with a high porosity showed high compression mechanical properties, which contributed to the high density of ceramic walls. This technique combines the two processes of cold freezing and thermal gelation in one procedure, and is considered to be potentially useful in many applications.

Articles you may be interested inModel for the voltage and temperature dependence of the soft breakdown current in ultrathin gate oxides A physical model has been developed which complies with the experimental observation on the failure mechanism of ultrathin gate oxide breakdown during constant voltage stress. Dynamic equilibrium needs to be established between the percolation conductive path and the dielectric breakdown induced epitaxy ͑DBIE͒ formation during gate dielectric breakdown transient. The model is capable of linking the percolation model, soft breakdown, and hard breakdown to the DBIE growth for a variety of stress conditions and gate oxide thickness without involving new empirical parameters.

Objectives The purpose of this study was to determine the impact of contraception, menopause and vaginal flora on the physical and biochemical properties of cervicovaginal fluid. Study Design Vaginal swabs, cervicovaginal fluid (CVF) and cervicovaginal lavage (CVL) were collected from a total of 165 healthy asymptomatic women including: post-menopausal women (n=29), women in the proliferative (n=26) or follicular (n=27) phase, and women using the levonogestrel intrauterine device (LNG-IUD) (n=28), depomedroxyprogesterone acetate (DMPA) (n=28) or combined oral contraceptives (OCPs) (n=27). Vaginal smears were evaluated using the Nugent score. The osmolality, viscosity, density and pH of CVL samples were measured. Results CVL from postmenopausal women and women with abnormal vaginal flora was less viscous and had higher pH than premenopausal women and women with normal flora, respectively. Women using hormonal contraceptives had more viscous CVL as compared to premenopausal women not using hormonal contraceptives, but this increase in viscosity was mitigated in the presence of bacterial vaginosis. Women using DMPA had less total protein in the CVL as compared to women using the LNG-IUD, and had similar protein content when compared to postmenopausal women. Conclusion The differences in CVL protein content between DMPA and LNG-IUD suggest that type of progesterone and route of delivery impact the vaginal environment. Contraceptive hormone users had more viscous CVL than women not using contraceptives. However, the presence of bacterial vaginosis impacted both the pH and viscosity (regardless of hormonal contraceptive use), demonstrating that vaginal flora has a greater impact on the physical properties of cervicovaginal fluid than reproductive hormones.

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Breakdowns in ultrathin gate oxide (Gox) ranging from 16 -33 A were physically analyzed with transmission electron microscope after constant voltage stress. In the Gox of 25 and 33A, a dielectric breakdown induced epitaxy (DBIE) at the gate oxide region is detected for compliance current of 100 nA and above, regardless of breakdown hardness (1).The compliance cunent for the transition of soft breakdown (SBD) to hard breakdown (HBD) is found to be in the range of 10-100 el, whereas for the thinner Gox of 16 A, the upper compliance current limit of SBD to HBD is greatly reduced to around 1 -10 pA and SBD DBIE is hardly detected. The results clearly indicate that DBIE is always present in the HBD oxides regardless of its thickness. Its presence in the SBD oxides is an indication of the early stage of catastrophic failure process that poses a Cox reliability concern.

This paper deals with analytic studies and numerical results of the scattering of plane sound waves from an elastic circular cylinder and from an elastic sphere in a viscous fluid. The elastic properties of the cylinder and the sphere and the viscosity of the surrounding fluid are taken into account in the solution of the acoustic-scattering problems. The associated acoustic quantities, such as the acoustic-scattering patterns, the acoustic-radiation forces, and the acoustic attenuation, are first derived in closed forms and then evaluated numerically for a given set of material properties. Numerical results show that increasing fluid viscosity tends to increase the directionality of the angular distribution of the scattering patterns, especially in the forward direction. The acoustic-radiation force on the cylinder or on the sphere is in the direction of the incident wave and increases as the viscosity of the fluid increases. The plots of the acoustic-attenuation coefficients versus the dimensionless wavenumber of the incident sound wave reveal oscillatory phenomena, which are caused by the resonant vibrations of the cylinder or the sphere.