Crystallisation and Diffusion in Oriented Sapphire Amorphised by Zinc Ion Implantation

1990 ◽  
Vol 201 ◽  
Author(s):  
L. A. Bunn ◽  
D. K. Sood
Keyword(s):  
Epitaxial Growth ◽  
Zinc Ion ◽  
High Dose ◽  
Low Doses ◽  
Surface Layers ◽  
Rapid Diffusion ◽  
High Doses ◽  
Amorphous Surface ◽  
And Diffusion ◽  
Post Implantation

AbstractHigh dose zinc implantation (1×1016 to 6×1016 ions/cm2) into c-axis sapphire at 770K produces amorphous surface layers. Post-implantation annealing at temperatures at and above 800°C show that the modes of recrystallisation are strongly dependant on ion dose. At low doses formation of crystallites of α and γ phase Al2O3 is seen, with no evidence of any planar epitaxial growth at the original crystalline-amorphous interface. The zinc is seen to diffuse isotropically within the crystallised layer and becomes partially substitutional within the crystallites. At high doses, however, the formation of crystallites is inhibited, with the layer remaining amorphous. A more rapid diffusion of zinc is seen in the amorphous Al2O3, with some of the zinc being lost at the surface.

Recrystallization of ion-implanted α-SiC

1987 ◽  
Vol 2 (1) ◽  
pp. 107-116 ◽  
Author(s):  
H. G. Bohn ◽  
J. M. Williams ◽  
C. J. McHargue ◽  
G. M. Begun
Keyword(s):  
Raman Scattering ◽  
Single Crystal ◽  
Temperature Interval ◽  
High Dose ◽  
Low Doses ◽  
Surface Layers ◽  
Annealing Behavior ◽  
Narrow Temperature Interval ◽  
Amorphous Surface ◽  
Ion Implanted

The annealing behavior of ion-implanted α-SiC single crystal was determined for samples implanted with 62 keV 14N to doses of 5.5X1014/cm2 and 8.0X1016/cm2 and with 260 keV 52Cr to doses of 1.5X1014/cm2 and 1.0X1016/cm2. The high-dose samples formed amorphous surface layers to depths of 0.17 μm (N) and 0.28 μm (Cr), while for the low doses only highly damaged but not randomized regions were formed. The samples were isochronically annealed up to 1600°C, holding each temperature for 10 min. The remaining damage was analyzed by Rutherford backscattering of 2 MeV He+, Raman scattering, and electron channeling. About 15% of the width of the amorphous layers regrew cpitaxially from the underlying undamaged material up to 1500°C, above which the damage annealed rapidly in a narrow temperature interval. The damage in the crystalline samples annealed linearly with temperature and was unmeasurable above 1000°C.

scholarly journals Low-DoseAronia melanocarpaConcentrate Attenuates Paraquat-Induced Neurotoxicity

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
A. J. Case ◽  
D. Agraz ◽  
I. M. Ahmad ◽  
M. C. Zimmerman
Keyword(s):  
Reactive Oxygen Species ◽  
Hydrogen Peroxide ◽  
Cell Death ◽  
Neuronal Cell Death ◽  
Neuronal Cell ◽  
Reactive Oxygen ◽  
High Dose ◽  
Low Doses ◽  
Oxygen Species ◽  
High Doses

Herbicides containing paraquat may contribute to the pathogenesis of neurodegenerative disorders such as Parkinson’s disease. Paraquat induces reactive oxygen species-mediated apoptosis in neurons, which is a primary mechanism behind its toxicity. We sought to test the effectiveness of a commercially available polyphenol-richAronia melanocarpa(aronia berry) concentrate in the amelioration of paraquat-induced neurotoxicity. Considering the abundance of antioxidants in aronia berries, we hypothesized that aronia berry concentrate attenuates the paraquat-induced increase in reactive oxygen species and protects against paraquat-mediated neuronal cell death. Using a neuronal cell culture model, we observed that low doses of aronia berry concentrate protected against paraquat-mediated neurotoxicity. Additionally, low doses of the concentrate attenuated the paraquat-induced increase in superoxide, hydrogen peroxide, and oxidized glutathione levels. Interestingly, high doses of aronia berry concentrate increased neuronal superoxide levels independent of paraquat, while at the same time decreasing hydrogen peroxide. Moreover, high-dose aronia berry concentrate potentiated paraquat-induced superoxide production and neuronal cell death. In summary, aronia berry concentrate at low doses restores the homeostatic redox environment of neurons treated with paraquat, while high doses exacerbate the imbalance leading to further cell death. Our findings support that moderate levels of aronia berry concentrate may prevent reactive oxygen species-mediated neurotoxicity.

scholarly journals Hormetic effect of amyloid-beta peptide in hippocampal synaptic plasticity and memory

2021 ◽  
Vol 11 (40) ◽  
pp. 156-156
Author(s):  
Daniela Puzzo ◽  
Agostino Palmeri
Keyword(s):  
Synaptic Plasticity ◽  
Amyloid Beta ◽  
Hippocampal Slices ◽  
Reference Memory ◽  
High Dose ◽  
Low Doses ◽  
Hormetic Effect ◽  
Physiologic Function ◽  
High Doses

Background: The term hormesis refers to a biphasic dose-response phenomenon characterized by low-dose stimulation and high-dose inhibition represented by a J-shaped or U-shaped curve, depending on the parameter measured (Calabrese and Baldwin, Hum Exp Toxicol, 2002). Indeed, several, if not all, physiological molecules (i.e. glutamate, glucocorticoids, nitric oxide) are likely to present a hormetic effect, exhibiting opposite effects at high or low concentrations. In the last few years, we have focused on amyloid-beta (A), a peptide widely known because it is produced in high amounts during Alzheimer’s disease (AD). A is considered a toxic fragment causing synaptic dysfunction and memory impairment (Selkoe, Science, 2002). However, the peptide is normally produced in the healthy brain and growing evidences indicate that it might have a physiologic function. Aim: Based on previous results showing that picomolar concentrations of A42 enhance synaptic plasticity and memory (Puzzo et al, J Neurosci, 2008) and that endogenous A is necessary for synaptic plasticity and memory (Puzzo et al, Ann Neurol, 2011), the aim of our study was to demonstrate the hormetic role of A in synaptic plasticity and memory. Methods: We used 3-month old wild type mice to analyze how synaptic plasticity, measured on hippocampal slices in vitro, and spatial reference memory were modified by treatment with different doses of A (from 2 pM to 20 μM). Results: We demonstrated that A has a hormetic effect (Puzzo et al, Neurobiol Aging, 2012) with low-doses (200 pM) stimulating synaptic plasticity and memory and high-doses (≥ 200 nM) inhibiting these processes. Conclusions: Our results suggest that, paradoxically, very low doses of A might serve to enhance memory at appropriate concentrations and conditions. These findings raise several issues when designing effective and safe approaches to AD therapy.

ANDROGENIZATION OF THE NEONATAL FEMALE RAT WITH VERY LOW DOSES OF ANDROGEN

1973 ◽  
Vol 57 (1) ◽  
pp. 33-45 ◽  
Author(s):  
P. J. SHERIDAN ◽  
M. X. ZARROW ◽  
V. H. DENENBERG
Keyword(s):  
Low Dose ◽  
Physiological Effect ◽  
Neonatal Rat ◽  
Female Rats ◽  
High Dose ◽  
Female Rat ◽  
Low Doses ◽  
Minimal Effective Dose ◽  
High Doses ◽  
Long Acting

SUMMARY The administration of a high dose of androgen on a single day to a neonatal female rat has been shown repeatedly to induce persistent vaginal cornification (PVC). However, this type of treatment does not parallel the continuous androgen secretion present in the male, and the high doses that have been used could represent a pharmacological and not a physiological effect. Experiments were carried out to determine the minimal effective dose of testosterone propionate (TP) needed to cause PVC when the androgen is administered to the neonatal rat for the first 10 days of life or as a long-acting ester. Injection of 1, 3 or 9 μg TP on days 1–10 of life in female rats induced PVC in adulthood. All three doses were found to be more effective than a testicular transplant on day 1. In female rats injected with low doses of TP twice daily for the first 10 days of life, PVC was shown between 90 and 100 days of life in 21 out of 22 animals given 0·5 μg TP/injection, and in eight out of 22 animals given 0·05 μg TP/injection. In an experiment where female rats were given a single injection of 0·1, 1·0 or 10·0 μg TP, or 0·1 or 1·0 μg testosterone cyclopentylpropionate (TC, a long-acting androgen) on the first day after birth, PVC occurred at 90–100 days of age in 15 of the 18 animals which were injected with 10 μg TP, in none of the 17 animals which were injected with 1 μg TP, and in 10 of 11 animals which were injected with 1 μg TC. The effects of all treatments on vaginal opening, first oestrus, ovarian weight, body weight and sexual behaviour are reported. The use and implications of low dose regimens are discussed in relation to the construction of an experimental model for the study of sexual differentiation.

Hormesis and risk assessment

2005 ◽  
Vol 24 (5) ◽  
pp. 255-257 ◽  
Author(s):  
Karl K Rozman
Keyword(s):  
Mathematical Method ◽  
Risk Assessment ◽  
Point Estimate ◽  
High Dose ◽  
Low Doses ◽  
Beneficial Effects ◽  
Dose Effects ◽  
High Doses ◽  
Living Organisms

It is postulated in this paper that at low doses all chemicals have hormetic/hormoligotic (beneficial) effects in living organisms. It has been known since Paracelsus that at high doses all chemicals are toxic. The combination of low and high dose effects can be empirically described by a β-curve or an inverted β-curve. A mathematical method is suggested to determine the maximum of the β-curve or the minimum of the inverted β-curve, yielding a point estimate for risk assessment.

scholarly journals Anti-Inflammatory Properties of Low and High Doxycycline Doses: AnIn VitroStudy

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Roberta Di Caprio ◽  
Serena Lembo ◽  
Luisa Di Costanzo ◽  
Anna Balato ◽  
Giuseppe Monfrecola
Keyword(s):  
Gene Expression ◽  
Skin Diseases ◽  
High Dose ◽  
Low Doses ◽  
Dose Administration ◽  
Doxycycline Treatment ◽  
Anti Inflammatory ◽  
High Doses ◽  
Bacterial Resistances

Doxycycline is used to treat infective diseases because of its broadspectrum efficacy. High dose administration (100 or 200 mg/day) is often responsible for development of bacterial resistances and endogenous flora alterations, whereas low doses (20–40 mg/day) do not alter bacteria susceptibility to antibiotics and exert anti-inflammatory activities. In this study, we wanted to assess the efficacy of both low and high doxycycline doses in modulating IL-8, TNF-α, and IL-6 gene expression in HaCaT cells stimulated with LPS. Three experimental settings were used, differing in the timing of doxycycline treatment in respect to the insult induced by LPS: pretreatment, concomitant, and posttreatment. Low doses were more effective than high doses in modulating gene expression of LPS-induced proinflammatory cytokines (IL-8, TNF-α, and IL-6), when added before (pretreatment) or after (posttreatment) LPS stimulation. This effect was not appreciated when LPS and doxycycline were simultaneously added to cell cultures: in this case high doses were more effective. In conclusion, ourin vitrostudy suggests that low doxycycline doses could be safely used in chronic or acute skin diseases in which the inflammatory process, either constantly in progress or periodically recurring, has to be prevented or controlled.

Response of rat jejunum to angiotensin II: role of norepinephrine and prostaglandins

1981 ◽  
Vol 240 (1) ◽  
pp. G17-G24 ◽  
Author(s):  
N. R. Levens ◽  
M. J. Peach ◽  
R. M. Carey ◽  
J. A. Poat ◽  
K. A. Munday
Keyword(s):  
Angiotensin Ii ◽  
Water Absorption ◽  
Rapid Onset ◽  
Inhibitory Response ◽  
High Dose ◽  
Low Doses ◽  
Slow Decay ◽  
High Doses ◽  
Stimulation Of

At low doses, angiotensin II (AII) stimulates jejunal sodium and water absorption in the pentobarbital sodium-anesthetized rat. This response to the hormone can be blocked by cycloheximide and has a rapid onset and decay, indicating that any protein involved must have a short half-life and/or fast turnover. At high doses, AII inhibits jejunal absorption by a process that does not involve protein synthesis and has a rapid onset but slow decay. The AII-induced inhibition of water absorption can be abolished, and a net stimulation ensues after pretreatment of the animals with meclofenamate or indomethacin, suggesting that at high doses AII stimulates intestinal prostaglandin biosynthesis. The AII analogue, [Sar1,Leu8]AII, significantly stimulated jejunal water absorption and was devoid of any inhibitory response at any dose administered. Simultaneous infusion of low doses of [Sar1,Leu8]AII and AII resulted in a stimulation of water transport, while simultaneous infusion of high dose [Sar1,Leu8]AII and AII also stimulated water absorption. It is suggested that the AII analogue is a full agonist with regard to stimulation of jejunal transfer but antagonizes the inhibitory response to high doses of AII. A model consistent with these data is discussed.

scholarly journals The Effects of Increasing Doses of Ranitidine on Gastric pH in Children

2004 ◽  
Vol 9 (4) ◽  
pp. 259-264 ◽  
Author(s):  
Seema Khan ◽  
Theresa M. Shalaby ◽  
Susan R. Orenstein
Keyword(s):  
Low Dose ◽  
Ph Monitoring ◽  
Phase 1 ◽  
Randomized Study ◽  
Gastric Ph ◽  
Fixed Dose ◽  
High Dose ◽  
Low Doses ◽  
The Mean ◽  
High Doses

BACKGROUND Ranitidine is widely used for gastroesophageal reflux disease (GERD) in children, but optimal dosing is unclear. We compared effects of weight-based doses of oral ranitidine on gastric pH in children with clinical GERD. METHODS Children ages 4–11 years with clinical GERD were enrolled in a multi-center prospective randomized study comparing a fixed dose of ranitidine (Zantac 75) with placebo after an overnight fast; gastric pH was measured for 6 h after the fixed dose (Phase 1). Of the six enrollees from our center, four received active drug during Phase 1; 12 h after the fixed dose, these four children received ranitidine 5 mg/kg (maximum 150 mg) and gastric pH was measured for another 6–12 hours (Phase 2). This report details the effects of two dose ranges (Low Dose, < 3 mg/kg/dose, and High Dose, ≥ 3 mg/kg/dose) on gastric pH in children. RESULTS The four children were 6.9–11.3 years old and weighed 20.4–49.5 kg. The Low Doses were 1.5–2.7 mg/kg; the High Doses were 3–5 mg/kg. Although the mean percentage of time with gastric pH > 4 during the entire 6 hours following dosing was similar after Low and High Dose (50% vs. 57%, NS), during the last two hours of this interval the mean percentage of time with gastric pH > 4 was only 29% for Low Dose vs. 89% for High Dose (P = 0.006). Moreover, during those two hours, none of the Low Doses kept gastric pH above 4 for > 60% of the time, while all of the High Doses kept pH above 4 for > 60% of the time (P = 0.03). In three of four patients who underwent extended (9–12 h) gastric pH monitoring after High Dose ranitidine, gastric pH was above 4 for more than 40% of total time. CONCLUSIONS Doses of ranitidine ≥ 3 mg/kg/dose may be required for acid suppression lasting beyond 6 hours.

TREATMENT OF SYSTEMIC LUPUS ERYTHEMATOSUS COMPLICATED BY NEPHRITIS IN CHILDREN

PEDIATRICS ◽  
1967 ◽  
Vol 40 (5) ◽  
pp. 822-827
Author(s):  
Wolfgang W. Hagge ◽  
Edmund C. Burke ◽  
Gunnar B. Stickler
Keyword(s):  
Rheumatoid Arthritis ◽  
Systemic Lupus Erythematosus ◽  
Lupus Erythematosus ◽  
Clinical Course ◽  
Discoid Lupus Erythematosus ◽  
High Dose ◽  
Low Doses ◽  
Systemic Lupus ◽  
Drug Induced ◽  
High Doses

The clinical course of 41 patients who had systemic lupus erythematosus complicated by nephritis with symptoms beginning before they were 15 years old was reviewed. The retrospective analysis showed a definite trend toward prolonged survival among the patients receiving high doses of steroids, compared to those receiving no or low doses. We conclude that it is no longer justified to withhold high-dose steroid therapy from children with lupus nephritis, but it should be emphasized equally that this does not apply to children with discoid lupus erythematosus, rheumatoid arthritis with a positive LE clot test, or drug-induced lupus erythematosus. Our present plan of management is outlined.

Furnace Anneal of A–Axis Sapphire Amorphised by Indium Ion Implantation

1988 ◽  
Vol 128 ◽  
Author(s):  
D. K. Sood ◽  
D. X. Cao
Keyword(s):  
Activation Energy ◽  
Ion Implantation ◽  
Amorphous Phase ◽  
Isothermal Annealing ◽  
Amorphous Layer ◽  
Surface Layers ◽  
Epitaxial Regrowth ◽  
Rapid Diffusion ◽  
Amorphous Surface ◽  
Higher Doses

ABSTRACTIndium implantation at 77°K into a–axis sapphire to peak concentrations of 6–45 mol % In produces amorphous surface layers. Isothermal annealing in Ar at temperatures between 600–900°C shows effects strongly dependent on ion dose. At lower doses <2×1016 In/cm2, the amorphous layer undergoes epitaxial regrowth as the amorphous to crystalline interface advances out towards the surface. Regrowth velocity is high in about the first half hour of the anneal. Regrowth obeys Arrhenius behaviour with an activation energy of 0.7eV for initial faster growth and 1.28eV for further anneal times. The amorphous phase transforms directly to ⊥-A12O3 without any evidence of an intermediary γ-phase. At higher doses, epitaxial regrowth is substantially retarded and rapid diffusion of In within the amorphous phase dominates.

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