Separation and determination of radioactive caesium in milk

A method is given for the separation and determination of radiocaesium in fluid milk. Caesium is separated from organic material and interfering ions by passage of the milk sample through a cation-exchanger in the lithium form. It is eluted from this column with 6M hydrochloric acid. Two methods are given for the recovery of radiocaesium from the eluate. It may be precipitated with silico-tungstic acid and then converted into caesium perchlorate for counting or weighing. Alternatively, the eluate is passed through a small column of ammonium phosphomolybdate, which quantitatively sorbs the radiocaesium, the activity of which is determined by putting the column in a well-type scintillation counter and measuring the activity. Approximately 90% of the radiocaesium is recovered.     

The expected eigenvalue distribution of a large regular graph

Let K₁, K₂,... be a sequence of regular graphs with degree v?2 such that n(X_i)→∞ and ck(X_i)/n(X_i)→0 as i∞ for each k?3, where n(X_i) is the order of X_i, and c_k(X_i) is the number of k- cycles in X₁. We determine the limiting probability density f(x) for the eigenvalues of X>_i as i→∞. It turns out that

$\text{f(x)=}\text{v}\text{4(v?1)?v}{}^2\text{2π(v}{}^2\text{?x}{}^2\text{)}{}_0$

for ?x??2$\text{v-1}$, otherwise It is further shown that f(x) is the expected eigenvalue distribution for every large randomly chosen labeled regular graph with degree v.     

A Necessary Condition for Transitivity of a Finite Permutation Group

Suppose the group G is generated by permutations g₁, g₂, ...,g₈ acting on a set of size n, such that g₁g₂...g₈ is the identitypermutation. If the generator g_i has exactly c_i cycles (for1 i s), and G is transitive on , then n(s–2)– is a non-negative even integer. Thisis proved using an elementary graph-theoretic argument.     

Unprecedented steric deformation of ortho-carborane

The reduction and subsequent oxidation of meta-carboranes containing bulky groups attached to the cage C atoms affords sterically-crowded ortho-carboranes with unprecedentedly long C-C connectivities.     

Laboratory studies of butane nucleation on organic haze particles: application to Titan's clouds

Titan, Saturn's largest satellite, has a thick nitrogen/methane atmosphere with various hydrocarbons present in minor amounts. Recent observations suggest that CH4 may condense to form clouds near the moon's tropopause. Titan's methane cloud formation is probably triggered by a sequential nucleation of hydrocarbons onto Titan's haze material as tropospheric convection occurs due to differential heating of the surface or as the haze settles through the lower stratosphere. To better constrain Titan's cloud formation mechanism, investigations of the nucleation of several hydrocarbons will be necessary. Butane was chosen for this study because it has a relatively high freezing point and is estimated to be present at 200 part per billion levels. If this amount of butane were to condense on each haze particle, a visible cloud would be observed. Laboratory measurements at T = 125 K were performed to determine the relative ease of solid butane nucleation onto laboratory-produced tholin particles having an elemental composition of C5H5N, and solid films of hexane and acetonitrile. We find that butane nucleation onto the haze particles requires a relatively high saturation ratio of S > 1.30. Because butane nucleation is difficult, it may occur on only a very small subset of the total haze particles available. Such selective nucleation of butane would lead to those particles becoming coated with significant amounts of butane. Requiring a high saturation ratio for butane nucleation will reduce the optical depth of butane clouds by a factor of 100 because the particles will be fewer in number for a given condensed mass.     

More on replicable functions

We examine further properties of the replicable functions defined in [MOM] and characterized in [ACMS].