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Regions of cell division and cell elongation were established during stem growth of Xanthium pensylvanicum (cocklebur). From percent mitosis it was determined that the region of cell division in a Xanthium stem of Plastochron Index (PI) 13.89 was 20 mm long, starting from the stem apex and proceeding in a basipetal direction. Measurements of cortical cell lengths demonstrated that mature cell length in the stem of the same plant was reached at about 55 mm distance from the stem apex. Between 20 and 55 mm distance from the apex, shoot growth occurred by cell elongation alone. The maximum rate of change in cell length (dC/dX) was at about 15 mm distance from the stem apex. The length of the apical growth region was a function of the age of the plants. The older the plant, the longer its apical region of elongation. Growth of Xanthium stems was due primarily to elongation of internodes; the nodal regions did not seem to elongate.

Background: Propolis is a honeybee product that has been used in traditional medicine for antioxidant, immune-stimulating, anti-inflammatory and anti-cancer effects. Here, the potential of the topical application of a crude ethanolic extract of Sydney propolis to protect against UV-radiation-induced impairments associated with an increased risk of photocarcinogenesis has been tested in the hairless mouse. Methods: Solutions providing between 10 and 200 mg/kg propolis were applied to the skin following UV irradiation. The inflammation from exposure to UV (290–400 nm) was quantitated by measurement of increased skinfold thickness; lipid peroxidation was assayed by the induction of thiobarbituric acid reactive species in the skin; immune function was measured by the contact hypersensitivity (CHS) reaction and supported by the changes in epidermal cytokine expression. Results: Propolis protected significantly and dose-dependently against both sunburn oedema and the suppression of CHS, and (at 100 mg/kg) against lipid peroxidation. The overexpression of IL-10 and the depletion of IL-12 characteristic of photoimmune suppression were markedly reduced by propolis. Further, the upregulation of IL-6 was decreased, and the associated induction of haem oxygenase was shown to play a role in propolis skin protection. Conclusions: Sydney propolis was able to effectively reduce cutaneous inflammation, immunosuppression and lipid peroxidation induced by UV exposure. It is concluded that Sydney propolis might have strong beneficial protective effects against photodamage and skin cancer development in humans. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

A robust, time-dependent methodology is used to investigate impact-ionization-induced mixed-mode reliability stress (the simultaneous application of high JE and high VCB) in advanced SiGe HBTs. We present comprehensive stress data on second-generation 120-GHz SiGe HBTs, and use specially designed test structures with variable emitter-to-shallow trench spacing to shed light on the resultant damage mechanisms. We also explore the impact of mixed-mode stress on low frequency noise, ac performance, high-temperature device characteristics, and employ two-dimensional calibrated MEDICI simulations using the hot carrier injection current technique to better understand the physical damage locations. [ABSTRACT FROM PUBLISHER]

As device scaling for higher performance bipolar transistors continues, the operation current density increases as well. To investigate the reliability impact of the increased operation current density on Si-based bipolar transistors, an accelerated-current wafer-level stress was conducted on 120-GHz SiGe heterojunction bipolar transistors (HBTs), with stress current density up to as high as JC=34 mA/μm2. With a novel projection technique based on accelerated-current stress, a current gain shift of less than ∼15% after 106 h of operation is predicted at T=140°C. Degradation mechanisms for the observed dc parameter shifts are discussed for various VBE regions, and the separation of the current stress effect from the self-heating effect is made based on thermal resistance of the devices. Module-level stress results are shown to be consistent with wafer-level stress results. The results obtained in this work indicate that the high-speed SiGe HBTs employed for the stress are highly reliable for long-term operation at high operation current density. [ABSTRACT FROM PUBLISHER]

Examines the timing of leaf type determination in maize to test models for the regulation of phase change. Division of the vegetative development of the maize shoot into juvenile and adult phases based on the type of leaves produced at different times in shoot development; Occurrence of rejuvenation simultaneously in all leaf primordia.