Critical concentrations of cumulative scattered damage

1995 ◽  
Vol 27 (4) ◽  
pp. 219-224
Author(s):  
S. R. Ignatovich
Keyword(s):  
Critical Concentrations ◽  
Scattered Damage

Mesoscopic gelation of chitosan and genipin at below critical concentrations

2017 ◽  
Author(s):  
Christoph Engwer ◽  
Ronja Loy ◽  
Ioannis S. Chronakis ◽  
Ana C. Mendes ◽  
Francisco M. Goycoolea
Keyword(s):  
Sol Gel ◽  
Crosslinking Agent ◽  
Small Deformation ◽  
Macroscopic Appearance ◽  
Critical Concentrations ◽  
Gelation Kinetics ◽  
Gardenia Jasminoides ◽  
Sol Gel Transition ◽  
Low Cytotoxicity ◽  
High Concentrations

Genipin is increasingly used as a crosslinking agent for chitosans due to its low cytotoxicity as a naturally occurring extract of the plant <i>Gardenia jasminoides</i>. Genipin reacts with the primary amino groups of chitosan to form blue hydrogels. We studied the gelation kinetics of different chitosans varying in their properties (molar mass 34 000-213 000 g mol<sup>-1</sup>, degree of acetylation 9-20%) and genipin in detail. We found that critical sol-gel transition times obtained from dynamic light scattering were in good agreement with the results obtained by small deformation oscillatory rheometry and microviscosimetry at high concentrations of chitosan. However, at below critical concentrations, we found a second regime of gelation that followed the same Ross-Murphy's gelation kinetics. The macroscopic appearance of these samples was a suspension of weak gel-like particles that were sensitive to mechanical forces. We believe that the material is a mesoscopic gel, as described for other polymers. To the best of our knowledge, this is the first time that this phenomenon has been described for the gelling system of chitosan and genipin.

scholarly journals Initiation and propagation kinetics of inhibited lipid peroxidation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Reza Farhoosh
Keyword(s):  
Lipid Peroxidation ◽  
Reverse Micelles ◽  
Fish Oils ◽  
Lipid Hydroperoxides ◽  
Critical Concentrations ◽  
Initial Values ◽  
Initiation And Propagation ◽  
Kinetics Of

AbstractEffect of hydroxytyrosol (HT) and tert-butylhydroquinone (TBHQ) on the kinetics of lipid hydroperoxides (LOOH) accumulation during the initiation and propagation peroxidations of canola and fish oils at 60 °C was studied. The initiation kinetics of the inhibited peroxidation indicated considerable relative activities, A, for HT and TBHQ in the canola (> 3200 and > 27,000, respectively) and fish (> 120 and > 5000, respectively) oils. The critical concentrations of LOOH reverse micelles (CMCL = 33 mM and 57 mM in the canola and fish, respectively, oils) significantly decreased, on average, to about one-third and 8% of the initial values for HT and TBHQ, respectively. Interestingly, the propagation kinetics of the inhibited peroxidation demonstrated that the antioxidants were still able to inhibit peroxidation, so that the relative propagation oxidizability parameter Rn′ was significantly improved to < 0.5 for HT and to < 0.2 for TBHQ in the canola and fish, respectively, oils.

A Systematic Study on Iron Carbides from First-Principles

2010 ◽  
Vol 654-656 ◽  
pp. 47-50 ◽  
Author(s):  
In Gee Kim ◽  
Gul Rahman ◽  
Jae Hoon Jang ◽  
You Young Song ◽  
Seung Woo Seo ◽  
...  
Keyword(s):  
Crystal Structures ◽  
Systematic Study ◽  
First Principles ◽  
Formation Enthalpy ◽  
The Other ◽  
Iron Carbides ◽  
Ratio Dependence ◽  
Critical Concentrations

The formation enthalpy of a series of Fe-C carbides has been estimated using a first-principles approach. The Fe to C ratio dependence of the formation enthalpy is reasonable, but it is revealed that - and -carbides require an extraordinary environment to be able to form. Furthermore, an addition of substitutional solutes other than Fe and C should promote other carbides with different crystal structures. The analysis suggests further studies to discover the critical concentrations of alloying which stimulate the other carbides to become more stable.

Highly Sensitive Paper-Disc Assays for Detecting Penicillin in Milk

1985 ◽  
Vol 48 (1) ◽  
pp. 16-20 ◽  
Author(s):  
GINA M. BALBI ◽  
PAUL A. HARTMAN
Keyword(s):  
Detection Limit ◽  
Starter Cultures ◽  
Biologically Active ◽  
Penicillin G ◽  
Lower Detection Limit ◽  
Critical Concentrations ◽  
Plate Assay ◽  
Lower Detection ◽  
Standard Assay ◽  
Dairy Starter Cultures

A modified Bacillus subtilis disc-plate assay could detect 0.015 I.U. of penicillin G per ml of milk, whereas the lower detection limit of the standard assay was 0.050 I.U. per ml. Likewise, a modified Bacillus stearothermophilus disc-plate assay could detect 0.003 I.U. of penicillin G per ml of milk, whereas the lower detection limit of the standard assay was 0.005 I.U. per ml. Increased sensitivities were accomplished by preloading assay discs with “critical” concentrations so that minute quantities of antibiotic above the “critical” concentrations would produce zones of inhibition. Only a few alterations in routine laboratory procedure were required to perform the assays. Use of these assays should assure a milk supply that would not cause allergic reactions in humans or significantly inhibit dairy starter cultures. The general principal of “critical” concentration might have applications other than those that we have described, to increase the sensitivity of radial-diffusion analyses for biologically active compounds.

Electrical and Rheological Properties of Double Percolated Poly(methyl methacrylate)/Multiwalled Carbon Nanotube Nanocomposites

2007 ◽  
Vol 7 (11) ◽  
pp. 3847-3851 ◽  
Author(s):  
Sung-Hun Jin ◽  
Dai-Soo Lee
Keyword(s):  
Carbon Nanotube ◽  
Methyl Methacrylate ◽  
Rheological Properties ◽  
Critical Concentration ◽  
Threshold Concentration ◽  
Multiwalled Carbon Nanotube ◽  
Multiwalled Carbon ◽  
Poly Methyl Methacrylate ◽  
Critical Concentrations ◽  
Double Percolation

Electrical and rheological properties of nanocomposites based on poly(methyl methacrylate) (PMMA) and multiwalled carbon nanotube (MWCNT) were studied from view points of double percolation by adding crosslinked methyl methacrylate-butadiene-styrene (MBS) copolymer particles to lower percolation threshold concentration of MWCNTs. It was found that the critical concentrations of MWCNTs for the percolation in the nanocomposites decrease and then increase with increasing the MBS contents of the nanocomposites. It is postulated that the addition of MBS at low concentrations results in double percolation of MWCNT and the significant decrease of critical concentration for the percolations. However, adding MBS particles in large amounts results in limited space for the distribution of MWCNTs and less efficient dispersion of the MWCNTs and the increase of the critical concentrations of MWCNTs for the percolations. Rheological properties and change of Tgs reflect large interfacial areas in the well dispersed nanocomposite and were also interpreted to support the speculations for the effects of MBS contents and MWCNT concentrations of PMMA/MWCNT nanocomposites.

Critical concentrations for site percolation in the dense-random-packed hard-sphere Bernal model

1982 ◽  
Vol 25 (7) ◽  
pp. 4633-4638 ◽  
Author(s):  
M. Ahmadzadeh ◽  
A. W. Simpson
Keyword(s):  
Hard Sphere ◽  
Site Percolation ◽  
Critical Concentrations

The growth of Yellow Bells (Geleznowia verrucosa) seedlings in response to additions of nitrogen, potassium and phosphorus fertiliser

1998 ◽  
Vol 38 (4) ◽  
pp. 385
Author(s):  
R. F. Brennan ◽  
A. M. Crowhurst ◽  
M. G. Webb
Keyword(s):  
Plant Growth ◽  
Western Australia ◽  
Growth Response ◽  
Shoot Growth ◽  
Native Plants ◽  
Dry Weight ◽  
Critical Concentrations ◽  
Phosphorus Fertiliser ◽  
N Fertilisers ◽  
Optimum Production

Summary. Native plants are increasingly grown in Western Australia to produce flowers for export. The nitrogen (N), phosphorus (P) and potassium (K) requirements for optimum production of one of these species, Geleznowia verrucosa (Yellow Bells), was measured for 17-week-old seedlings in a glasshouse experiment reported here. There was a significant (P<0.05) growth response to all levels of N fertilisers. At all levels of P and K, except for the nil K treatments, the lowest level of applied N (20 mg N/kg soil) gave the maximum dry weight of shoots. The dry weight of shoots increased with the addition of P fertiliser to the highest level (160 mg P/kg soil), particularly for the lower levels of applied K (0 and 30 mg/kg soil) and the lowest level of applied N (20 mg/kg soil). Combinations of high levels of P (P160) and N (N80) fertiliser severely depressed shoot growth. When applied at greater than 30 mg K/kg soil, K fertiliser depressed plant growth at all levels of N and P when compared with the lower levels of applied K. At the seedling stage of growth, critical concentrations for deficiency of both N and K were 1.3% in shoots. The critical concentrations for toxicity in whole shoots of Yellow Bells appeared to be about 1.7% for N and about 2.2% for K. Adequate concentrations of N were 1.4–1.5%, while 1.7% K appeared adequate for growth of Yellow Bell shoots.

Using active fractions of soil organic matter as indicators of the sustainability of Ferrosol farming systems

Soil Research ◽  
1999 ◽  
Vol 37 (2) ◽  
pp. 279 ◽  
Author(s):  
M. J. Bell ◽  
P. W. Moody ◽  
S. A. Yo ◽  
R. D. Connolly
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Management Practices ◽  
Cropping Systems ◽  
Cropping System ◽  
Farming Systems ◽  
Total Carbon ◽  
Critical Concentrations ◽  
Aggregate Breakdown ◽  
Eastern Australia

Chemical and physical degradation of Red Ferrosols in eastern Australia is a major issue necessitating the development of more sustainable cropping systems. This paper derives critical concentrations of the active (permanganate-oxidisable) fraction of soil organic matter (C1) which maximise soil water recharge and minimise the likelihood of surface runoff in these soils. Ferrosol soils were collected from commercial properties in both north and south Queensland, while additional data were made available from a similar collection of Tasmanian Ferrosols. Sites represented a range of management histories, from grazed and ungrazed grass pastures to continuously cropped soil under various tillage systems. The concentration of both total carbon (C) and C1 varied among regions and farming systems. C1 was the primary factor controlling aggregate breakdown, measured by the percentage of aggregates <0·125 mm (P125) in the surface crust after simulated rainfall. The rates of change in P125 per unit change in C1 were not significantly different (P < 0·05) for soils from the different localities. However, soils from the coastal Burnett (south-east Queensland) always produced lower P125 (i.e. less aggregate breakdown) than did soils from the inland Burnett and north Queensland locations given the same concentration of C1. This difference was not associated with a particular land use. The ‘critical’ concentrations of C1 for each region were taken as the C1 concentrations that would allow an infiltration rate greater than or equal to the intensity of a 1 in 1 or 1 in 10 year frequency rainfall event of 30 min duration. This analysis also provided an indication of the risk associated with the concentrations of C1 currently characterising each farming system in each rainfall environment. None of the conventionally tilled Queensland Ferrosols contained sufficient C1 to cope with rainfall events expected to occur with a 1 in 10 frequency, while in many situations the C1 concentration was sufficiently low that runoff events would be expected on an annual basis. Our data suggest that management practices designed both to maximise C inputs and to maintain a high proportion of active C should be seen as essential steps towards developing a more sustainable cropping system.

A simple settling model for batch activated sludge process

2000 ◽  
Vol 42 (3-4) ◽  
pp. 9-16 ◽  
Author(s):  
A.A. Kazmi ◽  
H. Furumai
Keyword(s):  
Activated Sludge ◽  
Mass Balance ◽  
Concentration Profile ◽  
Full Scale ◽  
Initial Mass ◽  
Sediment Surface ◽  
Settling Rate ◽  
Activated Sludge Process ◽  
Time Step ◽  
Critical Concentrations

A simple settling model for the batch activated sludge process was proposed that could predict sludge concentration profile as a function of time. The predicted dynamic biomass profile would be used to quantify biological reactions during settling. The model can be applied by giving easily measurable parameters such as initial MLSS concentration, sludge interface variation which characterizes the settling rate, and SVI as an index of biomass settleability. The model describes the sedimentation process of the sludge by linking three concentrations, namely the MLSS on sludge interface (XH), constant MLSS on sediment surface (XC), and the variable MLSS at the bottom (XB). It was tested for wide ranges of activated sludge concentrations (1750 mg/L-4630 mg/L) and SVI (104-265). The model was applied to express MLSS profile for a full scale SBR as well as for 1 and 2 m column settling tests. The simulated MLSS profile by linking three critical concentrations agrees well with the observed data. Mass balance applied at each time step indicated that the deviation was from −2 to +12% of the total initial mass. The stratified MLSS profile simulated from the model was applied to predict denitrification rate during settling.

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