Water Activity

"Excel spreadsheet “NORRISH-ROSS aW of multi-component solution” can be used to calculate the water activity aW of an aqueous, multi component, solution by  Norrish’  and Ross’ laws. Required input: 1) Total mass of water in the solution;  2) Names and Molecular Masses of each of the dissolved components (molecular masses of common solutes are already included),  3) total mass of each dissolved component in the solutions); 4) k value, needed for Norrish' Law (k values for common soluble food components are already included);  5) water activity of a component which is NOT included in the spreadsheet , and of which a sorption isotherm is available; water activity from isotherm at total mass of water in the solution; 6)  Raoult calculation for a component which is NOT included in the spreadsheet and for which also no isotherm is available.
A worked example calculation is included in the spreadsheet.
For additional information and two worked examples: see "Water Activity aW Calculations of Aqueous Solutions and of Solids Mixtures", by Janwillem Rouweler, at Academia.edu.
"

"Excel spreadsheet  “aW-Raoult-Norrish.xls” can be used to calculate the water activity aW of an aqueous, one component, solution by Raoult’s and Norrish’ laws. Required input: 1) Molecular Mass of dissolved component (table with molecular masses of common solutes included),  2) number of particles an ionic substance dissociates into when dissolved in water (only needed for Raoult's Law on very dilute solutions); 3) k value, needed for Norrish' Law (table with k values for common soluble food components included); 4) solute concentration in mass % (= % w/w).
A worked example calculation is included in the spreadsheet.
For additional information: see "Water Activity aW Calculations of Aqueous Solutions and of Solids Mixtures", by Janwillem Rouweler, at Academia.edu."

"      Reduction of water activity aW can improve the shelf life and the quality of foods. After the optimal water activity is selected, a simple decision scheme helps to choose  the best equation (“Law”) to calculate or adjust  the water activity of an aqueous one component solution (Raoult’s and Norrish’ laws), or of an aqueous multi-component solution (Norrish’ and Ross’ laws). Two spreadsheets, aW-Raoult-Norrish.xls and Norrish-Ross aW of multi-component solution.xls, simplify the tedious exponential calculations.
      The water activity of a mixture of 2 or more solids can be predicted either by constructing the solids mixture sorption isotherm or by using the Salwin equation. When applying the spreadsheet Calculation Water Activity aW Solids Mixture.xls, the separate solids isotherms  are converted into the solids mixture sorption isotherm. As the total water content of the solids mixture is known, the water activity can be found.
The spreadsheet calculation is validated by comparing its predicted solids mixture aW with the water activity, calculated by the Salwin equation. The two calculated solid mixture aW values are in good agreement.
    Annex 1 lists the lowest water activity for growth and/or toxin production of many micro-organisms.
Annex 2 shows the lowest aW for the main food spoiling enzymes.
      Several worked examples illustrate step-by-step the aW calculation of solutions and solid mixtures.
Key words: Water activity calculations; aqueous solutions; solids mixture isotherm; Raoult; Norrish; Ross; Salwin; lowest aW for microbial activity; toxin production; food spoiling enzymes; aW. "

Excel spreadsheet  “Calculation Water Activity aW Solids Mixture.xls” can be used to calculate the water activity aW of a mixture of 2 to 5 solids, by constructing the solids mixture sorption isotherm. Required input: 1) for each solid its name; 2) the total mass of each solid, added to the solids mixture; 3) for each solid the mass % of water on dry matter, prior to the mixing, e.g. the grams of water per 100 grams of dry matter in the original solid; 4) the sorption isotherm for each solid, preferably with on the vertical axis the water content in grams of water per 100 g of dry matter (= "moisture content, % dry matter"). From the sorption isotherm of each solid, for aW = 0.1 to aW = 0.8 (step 0.1), you read the corresponding water content (in g water/100 g dry matter). These water contents have to be typed in the spreadsheet. Then the spreadsheet draws the dry solid mixture isotherm, and calculates the aW of the mixture. A worked example calculation of the aW of a 5 solids mixture is included in the spreadsheet. For additional information, including a worked example on a 2 solids mixture, of which the water activity also has been calculated with the method of Salwin: see "Water Activity aW Calculations of Aqueous Solutions and of Solids Mixtures", by Janwillem Rouweler, at Academia.edu.

"Sulfuric acid based Sn-Ag plating baths were developed to study the individual as well as synergistic effects of thiourea (TU) and gelatin on the characteristics of Sn-Ag deposits. Electrochemical behavior of each bath was investigated by cathodic polarization studies. Results showed that the deposition potential gap of both elements was reduced by both additives, hence allowing co-deposition of Sn-Ag to occur. In this study, TU increases Ag composition and changes deposits microstructure. Low content of gelatin inhibits Ag deposition but high content of gelatin results in enhanced Ag deposition. Microstructure of deposits has been improved by the synergistic effects of these two additives. Near-eutectic composition of Sn-4.0 wt.% Ag is achieved with the aid of 2g/L of TU and 1g/L of gelatin at a current density of 10mA cm -2.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6320518  "

"The effects of an antioxidant, hydroquinone (HQ) and a grain refining additive, gelatin, on the electroplating characteristics of SnBi alloys were investigated. Methane sulfonic acid (MSA) based plating baths with varying contents of additives are prepared and the electrochemical behavior of each bath was investigated. Cathodic polarization studies showed that the presence of HQ possesses insignificant effect on the deposition behavior. The combination of HQ and gelatin successfully reduces the deposition potential gap of both elements hence allows co-deposition of SnBi in this plating bath. The adhesion of deposits and the formation of spongy deposits are respectively improved and eliminated by the synergistic effects of these two additives. The electroplated SnBi deposits showed a decrease in Bi content and with increasing current density. Near eutectic Sn-60.75 wt.%Bi alloy was successfully deposited from the bath with both HQ and gelatin at a current density of 18 mA cm-2.

http://www.sciencedirect.com/science/article/pii/S0013468612019950  "

The anti-carcinogenic activity of dietary fruit and vegetables observed in several epidemiological and experimental animal studies is likely to be an effect of the combined exposure to a large number of substances acting together. This is plausible, as these compounds are present simultaneously in a diet containing vegetables and fruit. Further, some compounds have been experimentally demonstrated to modify several mechanisms involved in carcinogenesis. The effect of combined exposure is demonstrated in the present article, summarizing the effects of a complex mixture of anti-carcinogenic substances (from broccoli) on different antioxidative defense enzymes and on cytochrome P-450 activities in rat liver, kidney and colon. The responses were related to the levels of different specific glucosinolates.

"Based on a pressure-temperature (P-T) phase diagram model of
the Earth, Jones & Lineweaver (2010) described uninhabited terrestrial liquid
water. Our model represents the atmosphere, surface, oceans and interior of the
Earth - allowing the range of P-T conditions in terrestrial environments to be
compared to the phase regime of liquid water. Here we present an overview and
additional results from the Earth model on the location of the deepest liquid
water on Earth and the maximum possible extent of the terrestrial biosphere.
The intersection of liquid water and terrestrial phase space indicates that the
deepest liquid water environments in the lithosphere occur at a depth of ∼ 75 km. 3.5% of the volume of the Earth is above 75 km depth. Considering
the 3.5% of the volume of the Earth where liquid water exists, ∼ 12% of this
volume is inhabited by life while the remaining ∼ 88% is uninhabited. This is
distinct from the fraction of the volume of liquid water occupied by life. We find
that at least 1% of the volume of liquid water on Earth is uninhabited. Better
geothermal gradients in the Earth’s crust and mantle will improve the precision
and accuracy of these preliminary results."