An urn model study of variability within a compartment

Formulas are derived for the mean and variance of the number of radioactive atoms present in a compartment (or urn). Initally,n ₁ radioactive atoms andb stable atoms are placed in the urn; and subsequently,r stable atoms are added and an equal number,r, of a random mixture of stable and radioactive atoms is removed per unit time. The expected number of radioactive atoms,E(t), present at timet is, as expected,n ₁ e^−λt where λ=(r/Δt)/(b+r+n ₁). The relative variance, σ²(t)/n ₁ ² , vanishes to zero forr=1, atoms per unit time and for a large number ofn ₁ radioactive atoms; but for a large number of bothr andn ₁ atoms the relative variance is ∼e ^−λt , equal to the fractional retention, fort>1/λ. Thus in studies where radionuclides are injected into animals and a single compartment represents the data, if a large variance is observed it might be due to the fact that large numbers of atoms are transferred out in unit time. When a small variance is observed, this is probably due to the fact that few atoms are transferred in smaller units of time (such that λ is the same in both cases). Research sponsored by the Energy Research and Development Administration under contract with Union Carbide Corporation.     

Dose dependence of sister chromatid exchanges in human lymphocytes induced by in vitro α-particle irradiation

Exposure of human G₀ lymphocytes to high-LET particles under different conditions has been seen, unlike low-LET radiations, to be substantially effective in the induction of sister chromatid exchanges (SCE). However, whereas for fast neutrons a linear dose response of SCE has been determined, there is no sign of a dose-response relationship for α-particles. A likely reason for this lack of dose dependence may be the irradiation procedure. Therefore, a technique developed in our laboratory to ensure uniformity of irradiation with α-particles was used in the present study. Monolayers of 3 h-stimulated lymphocytes were exposed with α-particles from ²⁴¹Am. Underdispersion was found for the cell-to-cell variance of the number of SCE. The dose response of SCE was linear, with a yield of 3.4 SCE per cell and per Gray. Received: 26 April 1996 / Accepted in revised form: 24 July 1996     

A charge transfer process in the visual pigments

A physical model that incorporates all the experimental information on the formation of the visual pigment rhodopsin is presented. The visual pigments consist of a chromophore bound to an appropriate protein. Thus rhodopsin (λ_m 505 mμ) is formed by a Schiff’s base linkage C₁₉H₂₇CH=NH⁺-opsin (λ_m 440 mμ) between 11-cis retinal (λ_m 380 mμ) and the protein opsin (λ_m 280 mμ). It is found that there exists a red shift in the spectrum of rhodopsin from the Schiff’s base. The model brings an explanation for this red shift. It is shown that such a shift may be due to a charge transfer process (R. S. Mulliken,J. Am. Chem. Soc.,74, 811–824, 1952) between an electron at the double bond of carbons C₁₁−C₁₂ and an atomic orbital of the sulphur present in cysteine. This provides an explanation of the presence of SH-groups in the protein after the absorption of light. A one-electron approximation is used and the dipole momentμ _NV ; hence, the oscillator strengthf of the transitionNV is estimated and compared with the experimentally determined extinction coefficient ∈_m by mixing 3.5×10⁻³ M of 11-cis retinal with 8.3×10⁻⁵ M of cysteine at pH ranges 6 through 8. Reasonable agreement is found. Solvent, concentration and temperature dependence are shown also.     

Molecular dynamics simulations of nafion and sulfonated poly ether sulfone membranes II. Dynamic properties of water and hydronium

We measured the self-diffusion coefficients of water in a Nafion membrane and two sulfonated polyethersulfone (SPES) membranes with varying ion-exchange capacities (IEC) in terms of relative humidity using the pulse field gradient NMR (PFG-NMR) technique. The self-diffusion coefficients were plotted against the number of water molecules per sulfonic acid group, λ, and compare these values with the results of molecular dynamics (MD) simulations. Classical MD simulations for all membranes were carried out using a consistent force field at λ = 3, 6, 9, 12, and 15. The dynamic properties of water (H₂O) and hydronium (H₃O⁺) on a molecular level were estimated as self-diffusion coefficients and residence times around a sulfonate group ( \textSO₃^- {\text{SO}}_3^{-} ). The diffusion coefficients of H₂O and H₃O⁺ followed the order, Nafion > SPES with IEC = 1.4 > SPES with IEC = 1.0 > SPES with IEC = 0.75, which agreed with the experimental data. The residence time distribution of H₂O around \textSO₃^- {\text{SO}}_3^{-} in Nafion was in the range of 1–6 ps, whereas H₂O in the SPES exhibited a residence time of greater than 20 ps.     

Increased complexity of radiation-induced chromosome aberrations consistent with a mechanism of sequential formation

Complex chromosome aberrations (any exchange involving three or more breaks in two or more chromosomes) are effectively induced in peripheral blood lymphocytes (PBL) after exposure to low doses (mostly single particles) of densely ionising high-linear energy transfer (LET) alpha-particle radiation. The complexity, when observed by multiplex fluorescence in situ hybridisation (m-FISH), shows that commonly four but up to eight different chromosomes can be involved in each rearrangement. Given the territorial organisation of chromosomes in interphase and that only a very small fraction of the nucleus is irradiated by each alpha-particle traversal, the aim of this study is to address how aberrations of such complexity can be formed. To do this, we applied theoretical "cycle" analyses using m-FISH paint detail of PBL in their first cell division after exposure to high-LET alpha-particles. In brief, "cycle" analysis deconstructs the aberration "observed" by m-FISH to make predictions as to how it could have been formed in interphase. We propose from this that individual high-LET alpha-particle-induced complex aberrations may be formed by the misrepair of damaged chromatin in single physical "sites" within the nucleus, where each "site" is consistent with an "area" corresponding to the interface of two to three different chromosome territories. Limited migration of damaged chromatin is "allowed" within this "area". Complex aberrations of increased size, reflecting the path of alpha-particle nuclear intersection, are formed through the sequential linking of these individual sites by the involvement of common chromosomes.     

A proposal for universal formulas for estimating leaf water status of herbaceous and woody plants based on spectral reflectance properties

The present study deals with the relationships between water status parameters of plant leaves and reflectances (R_λ) at characteristic wavelengths, between 522 and 2450 nm, as well as reflectance ratios, R_λ/R₁₄₃₀, R_λ/R₁₆₅₀, R_λ/R₁₈₅₀, R_λ/R₁₉₂₀, and R_λ/R₁₉₅₀, based on the air-drying experimental results of soybean (Glycine max Merr.), maize (Zea mays L.), tuliptree (Liriodendron tulipifera L.) and viburnum (Viburnum awabuki K. Koch.) plants. The water status parameters include leaf water content per unit leaf area (LWC), specific leaf water content (SWC), leaf moisture percentage of fresh weight (LMP), relative leaf water content (RWC) and relative leaf moisture percentage on fresh weight basis (RMP). Effective spectral reflectances and reflectance ratios for estimating the LWC, SWC, LMP, RWC and RMP were identified. With these spectral indices, approaches to estimating LWC, RWC and RMP were discussed. Eventually, an attempt on universal formulas was made for estimating the leaf moisture conditions of both herbaceous and woody plants as mentioned above. Moreover, applicability of these formulas was checked with the field experimental results of soybean and maize grown under water and nutrient stresses. This revised version was published online in June 2006 with corrections to the Cover Date.     

HIV spread in the San Francisco cohort: Scaling of the effective logistic rate for seropositivity

A simple scaling (semigroup) property is manifest in the functional form of the effective logistic rate for the increase in the HIV seropositive fraction in the San Francisco (City Clinic) cohort. Witht _i=4.5 years, this scaling property—r→λ^-2r undert→[λt+(λ−1)t _i] for all parameter values λ≧1—encapsulates the effects of relevant biological and sociological changes in the key epidemiological variables during the 8-year seropositive rise period, 1978–1985 inclusive.     

Radial theory of the ion current onto a probe in a low-pressure plasma with allowance for volume ionization and collisions with neutrals

The ion current onto a spherical or cylindrical probe is analyzed in the cold-ion approximation with allowance for ionization and collisions with neutrals. An expression for the ion density that takes into account both ionization and collision in the finite-size perturbed region is derived. The current-voltage characteristics for the dimensionless parameters r _p/λ _D = 0.0001−10, λ _i /λ _D = 0.01 − ∞, and zλ _D/(kT _e /M)^1/2 = 0−5 are determined by numerically solving Poisson’s equation, and the corresponding approximate expressions are obtained.     

Assessment of the exposure pathway in the uptake and distribution of americium and cesium in cuttlefish (Sepia officinalis) at different stages of its life cycle

Laboratory radiotracer experiments were performed to study the uptake, assimilation and retention of americium (²⁴¹Am) and cesium (¹³⁴Cs) by the common cuttlefish Sepia officinalis. Uptake and loss kinetics of the radionuclides were measured following exposure through sediments, seawater and food at different stages of the animal's life cycle. Sediment was found to be a minor uptake pathway for both radionuclides in juveniles. Following a short seawater exposure, cuttlefish accumulated ²⁴¹Am and ¹³⁴Cs, but only to a limited extent (whole-body CF < 2). Among the cuttlefish organs, branchial hearts and their appendages displayed the highest degree of uptake for ²⁴¹Am (CF = 42 and 16, respectively), but these tissues contained low percentage of total ²⁴¹Am due to their relatively small contribution to whole organism weight. The major fraction of incorporated radionuclides was associated with muscular tissues (viz. 65% and 82% of total ²⁴¹Am and ¹³⁴Cs, respectively). Whole-body loss of ²⁴¹Am and ¹³⁴Cs was relatively rapid (T_b½ = 14 and 6 days, respectively). After dietary exposure, around 60% and 30% of ingested ²⁴¹Am was assimilated into the tissues of juvenile and adult cuttlefish, respectively. However, assimilated ²⁴¹Am was more strongly retained in adults than in juveniles (T_b½ = 28 vs. 5 days, respectively), suggesting that different mechanisms govern ²⁴¹Am elimination at both ages. Ingested ¹³⁴Cs was assimilated to a similar extent in juveniles (29%) and adults (23%), but the depuration rate was four times faster in adults. Our results strongly suggest that these two radionuclides follow different excretion pathways and that the mechanisms can vary with age for a given radionuclide.     

Analysis of chromosome aberrations in human peripheral lymphocytes induced by in vitro α-particle irradiation

Irradiation of human lymphocytes by α-particles under different conditions has been seen to be substantially more effective in the induction of dicentric chromosomes than irradiation by ψ-rays. However, the relative biological effectiveness (RBE) determined in these studies RBE are likely to be due in part to differing exposure conditions. Therefore, a technique designed to insure iniformity of irradiation was developed in the present study, and complications due to the cell cycle kinetics were controlled. After stimulation with phytohaemagglutinin (PHA), separated lymphocytes were allowed to attach for 3 h to the thin foil bottom of an irradiation chamber. Cell monolayers were exposed with α-particles from²⁴¹Am. Strong over-dispersion was noted for the cell-to-cell variance of the number of dicentrics. The dose response of dicentrics was linear, with a yield of 0.27 dicentrics per cell and per Gy. This corresponds to a low dose RBE of 15 relative to¹³⁷Cs γ-ray exposure under the same experimental conditions.     

The gas washout determination under a symmetry assumption

In an open circuit gas washout determination the output of test substance is shown to be of the form ∑ _i=0 ^∞ A _i λ _i ^k on thekth expiration whereA _i >0,i=1,2,... and 1 > λ₁ ≥ λ₂...≥ 0 provided the transition from inspiration to expiration has certain symmetry properties with the transition from expiration to inspiration. In general, no direct physical interpretation such as volume for theA _t ’s or fraction of retained gas on expiration for the λ _i is justified.     

The effect of 238Pu alpha-particles on the mouse fibroblast cell line C3H 10T1/2: characterization of source and RBE for cell survival

Considerable interest has been aroused in recent years by reports that the transforming and carcinogenic effectiveness of low doses of high LET radiations can be increased by reducing the dose rate, especially for transformation of 10T1/2 cells in vitro by fission-spectrum neutrons. We report on conditions which have been established for irradiation of 10T1/2 cells with high LET monoenergetic alpha-particles (energy of 3.2 MeV, LET of 124 keV microns-1) from 238Pu. The alpha-particle irradiator allows convenient irradiation of multiple dishes of cells at selectable high or low dose rates and temperatures. The survival curves of irradiated cells showed that the mean lethal dose of alpha-particles was 0.6 Gy and corresponded to an RBE, at high dose rates, of 7.9 at 80 per cent survival and 4.6 at 5 per cent survival, relative to 60Co gamma-rays. The mean areas of the 10T1/2 nuclei, perpendicular to the incident alpha-particles, was measured as 201 microns2, from which it follows that, on average, only one in six of the alpha-particle traversals through a cell nucleus is lethal. Under the well-characterized conditions of these experiments the event frequency of alpha-particle traversals through cell nuclei is 9.8 Gy-1.     

Effects of chemical components and nitrogen sources on zygospore development inPhycomyces blakesleeanus

We examined the effects of chemical components and nitrogen sources on zygospore development, using 62 different ingredients based on Sutter's synthetic medium Sl, which has been widely used for studies of sexual physiology inPhycomyces. An increase of inorganic microelements such as ZnSO₄, NaMoO₄ and CaCl₂ promoted an increase in the number of zygospores per unit area. Glutamate (Glu) contained in Sl as the sole nitrogen source was indispensable for sexual development, and replacement of Glu with NH₄ ⁺ (Am) strongly inhibited it, mainly because of growth inhibition. However, zygospore production was enhanced 1.8-fold by equivalent amounts of both Glu and Am as compared with Glu alone. A newly developed medium, mSl+Am, enriched with Am and the above-mentioned effective microelements doubled the number of zygospores formed per unit area (density), compared with Sutter's original Sl, and increased both the density and the weight (volume) of zygospores, 1.6- and 2-fold, respectively, compared with potato-dextrose-agar medium enriched with yeast extract and casitone (PDAYC). Sexual stimulation by mSl+Am was also observed in the mating of a pair of β-carotene-deficient mutants. Methionine sulfoxime, an inhibitor of glutamine synthetase, strongly inhibited the progress of mating without significant growth inhibition. The first and the second authors contributed equally to this work.     

241Am dating of lake sediments

²⁴¹Am derived from decay of fallout ²⁴¹Pu is now frequently detected in analyses of lake sediments by low-background gamma assay, and offers an alternative to weapons test ¹³⁷Cs in dating recent sediments at those sites where the ¹³⁷Cs record has been degraded by post-depositional mobility or obliterated by Chernobyl fallout. Calculations of the in-growth of ²⁴¹Am from ²⁴¹Pu indicate a nominal distribution broadly similar to that of ¹³⁷Cs, with the maximum ²⁴¹Am activity occuring in fallout dating from 1963. Results from a number of sites suggest that ²⁴¹Am is significantly less mobile in lake sediments than ¹³⁷Cs, and that its distribution in cores reflects more closely the fallout record. Since further decay of existing weapons debris will increase ²⁴¹Am concentrations by about 24% over the next 40 years, ²⁴¹Am is likely to play an increasingly important role in assessing the validity of ²¹⁰Pb dates at sites with varying sediment accumulation rates.     

λ-Glutamylcysteine synthetase in higher plants: catalytic properties and subcellular localization

λ-Glutamylcysteine synthetase activity (EC 6.3.2.2) was analysed in Sephacryl S-200 eluents of extracts from cell suspension cultures ofNicotiana tabacum L. cv. Samsun by determination of λ-glutamylcysteine as its monobromobimane derivative. The enzyme has a relative molecular mass (M_r) of 60000 and exhibits maximal activity at pH 8 (50% at pH 7.0 and pH9.0) and an absolute requirement for Mg²⁺. With 0.2mM Cd²⁺ or Zn²⁺, enzyme activity was reduced by 35% and 19%, respectively. Treatment with 5 mM dithioerythritol led to a heavy loss of activity and to dissociation into subunits (M_r 34000). Buthionine sulfoximine andl-methionine-sulfoximine, known as potent inhibitors of λ-glutamylcysteine synthetase from mammalian cells, were found to be effective inhibitors of the plant enzyme too. The apparent K_m values forl-glutamate,l-cysteine, and α-aminobutyrate were, respectively, 10.4mM, 0.19 mM, and 6.36 mM. The enzyme was completely inhibited by glutathione (K_i=0.42 mM). The data indicate that the rate of glutathione synthesis in vivo may be influenced substantially by the concentration of cysteine and glutamate and may be further regulated by feedback inhibition of λ-glutamylcysteine synthetase by glutathione itself. λ-Glutamylcysteine synthetase is, like glutathione synthetase, localized in chloroplasts as well as in the cytoplasm. Chloroplasts fromPisum sativum L. isolated on a Percoll gradient contained about 72% of the λ-glutamylcysteine synthetase activity in leaf cells and 48% of the total glutathione synthetase activity. In chloroplasts ofSpinacia oleracea L. about 61% of the total λ-glutamylcysteine synthetase activity of the cells were found and 58% of the total glutathione synthetase activity. These results indicate that glutathione synthesis can take place in at least two compartments of the plant cell. Dedicated to Professor A. Prison on the occasion of his 80th birthday     

Additive and testcross genetic variances in crosses among recombinant inbreds

 Breeders desire populations with a high mean performance and a large genetic variance. Theory and methods are lacking for predicting additive variance (V _A ) and testcross variance (V _T ) in biparental populations. Breeders have unsuccessfully attempted to predict V _A based on the coefficient of coancestry ( f ) or molecular-marker similarity between parents. In this paper, we derive the expected values of V _A and V _T in biparental populations, examine the variability of V _A among biparental crosses, and discuss how V _A and V _T may be predicted in applied breeding programs. Suppose i is a recombinant inbred derived from the cross between inbreds P ₁ and P ₂, and inbred j is not a direct descendant of i. Let V _A(i,j) be the additive variance in the F₂ of the (i×j) biparental cross. Let V _T(i, j) be the variance among testcrosses of F₂ individuals with a specific unrelated inbred or population. Assuming linkage equilibrium and the absence of epistasis, V _A(i, j) =λV _A(P1, j) +(1−λ) V _A(P2, j) , where λ= parental contribution of P ₁ to i. Similarly, V _T(i, j) = λV _T(P1, j) +(1−λ) V _T(P2, j) . Additive variance in crosses between recombinant inbreds cannot be modelled as a function of  f if, as indicated in the literature, V _A differs among crosses of founder inbreds. If molecular-marker similarity between parents is used as an estimate of f, then a strong linear relationship is likewise not expected between V _A and marker similarity. Differences between the actual and expected λ led to variation in V _A . In applied breeding programs, modelling V _A or V _T in biparental crosses may be feasible with estimates of V _A or V _T in prior crosses and information on λ obtained from molecular-marker data. Received: 23 September 1997 / Accepted: 30 December 1997     

Comparison on the genotoxic effects of nuclear vs cytoplasmic irradiation from the alteration ofCD59 gene locus

Using microbeam to irradiate human-hamster hybrid A_L cells with defined number of α particles in a highly localized spatial region, this paper showed that cytoplasmic irradiation induced very little toxicity. For example, the cell killing by 4 α particle traversal through the cytoplasm was about 10%, and about 70% cells survived after their cytoplasm was irradiated with 32 a particles. In contrast, the survival fractions for nuclear irradiation at the same doses were 35% and less than 1% respectively. Mutation induction showed that while nuclear irradiation induced 3—4-fold more CD59^- mutants than cytoplasmic irradiation at equivalent particle traversal, at an equitoxic dose level of 90% survival, the latter exposure mode induced 3.3-fold more mutants than nuclear irradiation. Moreover, using multiplex PCR to analyze five marker genes on chromosome 11 (WT, CAT, PTH, APO-A1 and RAS), the results showed that the majority of mutants induced by cytoplasmic irradiation had retained all of the marker genes analyzed. By comparison, the proportion of mutants suffering loss of additional chromosomal markers increased with increasing number of particle traversal through nuclei.     

An Annular Plasmonic Lens Under Illumination of Circularly Polarized Light

In this paper, we consider a circular central aperture surrounded with annular depth-tuned grooves and investigate the beaming effect of the structure under illumination of a circularly polarized (CP) plane wave. As a CP plane wave is equivalent to the superposition of two linearly polarized plane waves (TM and TE) with a phase difference of π/2, the superposition of the electric field intensity, ( | E_x |² + | E_y |² ) \left( {{{\left| {E_x} \right|}^2} + {{\left| {E_y} \right|}^2}} \right) , is observed in the transmission field. In addition, two plasmonic modes are found at the resonant wavelengths λ ₁ and λ ₂ with each consisting of multiple wavelengths. At the wavelength λ ₁ = 420 nm, the significant near-field collimation is formed along the direction z, having a long propagation distance up to 1.75 μm (≈4λ) away from the exit plane of the new plasmonic lens.     

Self-renewal capacity of murine hemopoietic stem cells under internal contamination with239Pu and241Am

Summary The self-renewal capacity of murine pluripotent hemopoietic stem cells (CFU-S) of vertebral bone marrow was studied under conditions of short-term and long-term internal contamination with²³⁹Pu or²⁴¹Am in female mice. Measurement of the CFU-S self-renewal capacity was carried out using double transplantation assay. To evaluate the production of differentiated progeny of stem cells average erythroblast numbers/visible spleen colony and⁵⁹Fe-uptake/colony were computed. The marrow cellularity/vertebra and the number of CFU-S/vertebra were decreased and affected more by²³⁹Pu than by²⁴¹Am. The production of erythroblasts per a single CFU-S and the⁵⁹Fe-uptake/colony were reduced, similarly the numbers of secondary spleen colonies and of secondary CFU-S in primary colonies. The above changes resulting from impaired functions of surviving CFU-S were more serious with²⁴¹Am than with²³⁹Pu. The biological effects of plutonium and americium appeared independent of the phase of contamination.     

Long-term development of the radionuclide exposure of murine rodent populations in Belarus after the Chernobyl accident

As a determinant of the associated health risks, the behavior of radionuclides in natural ecosystems needs to be better understood. Therefore, the activity concentration of various long-lived radionuclides released due to the Chernobyl accident, and the corresponding contributions to the whole-body dose rate, was studied as a function of time in mammalian indicator species inhabiting the natural forest ecosystems of Belarus, the bank vole (Clethrionomys glareolus) and the yellow-necked mouse (Apodemus flavicollus). The activity concentrations of ¹³⁷Cs, ¹³⁴Cs, ⁹⁰Sr, ²³⁸Pu, ^239,240Pu, ²⁴¹Pu and ²⁴¹Am in soil and in animals were measured at five monitoring sites with different ground deposition of radionuclides at different distances from the destroyed reactor. The observed temporal pattern of the radionuclide activity concentration in the studied animal populations reflects the changes in biological availability of these isotopes for biota, mostly due to fuel particle destruction and appearance of dissolved and exchangeable forms of radionuclides. The time course of ^134+137Cs activity concentrations in animal populations appeared as a sequence of increase, peak and decrease. Maximal levels of radiocesium occurred 1–2 years after deposition, followed by an exponential decrease. Concentrations of incorporated ⁹⁰Sr increased up to the tenth year after deposition. The activity concentrations of transuranic elements (²³⁸Pu, ^239,240Pu, ²⁴¹Pu and ²⁴¹Am) were much lower than those of the other radionuclides, in the studied animals. A considerable activity of ²⁴¹Am in animals from areas with high levels of contamination was firstly detected 5 years after deposition, it increased up to the tenth year and is expected to increase further in the future. Maximal values of the whole-body absorbed dose rates occurred during the year of deposition, followed by a decrease in the subsequent period. Generally, this decrease was monotonic, mainly determined by the decrease of the external γ-ray dose rate, but there were exceptions due to the delayed maximum of internal exposure. The inter-individual distributions of radionuclide concentrations and lifetime whole-body absorbed doses were asymmetric and close to log-normal, including concentrations and doses considerably higher than the population mean values.