State Transitions in the Green Alga Scenedesmus Obliquus Probed by Time-Resolved Chlorophyll Fluorescence Spectroscopy and Global Data Analysis

Decay-associated fluorescence spectra of the green alga Scenedesmus obliquus have been measured by single-photon timing with picosecond resolution in various states of light adaptation. The data have been analyzed by applying a global data analysis procedure. The amplitudes of the decay-associated spectra allow a determination of the relative antenna sizes of the photosystems. We arrive at the following conclusions: (a) The fluorescence kinetics of algal cells with open PS II centers (F₀ level) have to be described by a sum of three exponential components. These decay components are attributed to photosystem (PS) I (τ ≈ 85 ps, λ_max^em ≈ 695-700 nm), open PS II α-centers (τ ≈ 300 ps, λ_max^em = 685 nm), and open PS II β-centers (τ ≈ 600 ps, λ_max^em = 685 nm). A fourth component of very low amplitude (τ ≈ 2.2-2.3 ns, λ_max^em = 685 nm) derives from dead chlorophyll. (b) At the F_max level of fluorescence there are also three decay components. They originate from PS I with properties identical to those at the F₀ level, from closed PS II α-centers (τ ≈ 2.2 ns, λ_max^em = 685 nm) and from closed PS β-centers (τ ≈ 1.2 ns, λ_max^em = 685 nm). (c) The major effect of light-induced state transitions on the fluorescence kinetics involves a change in the relative antenna size of α- and β-units brought about by the reversible migration of light-harvesting complexes between α-centers and β-centers. (d) A transition to state II does not measurably increase the direct absorption cross-section (antenna size) of PS I. Our data can be rationalized in terms of a model of the antenna organization that relates the effects of state transitions and light-harvesting complex phosphorylation with the concepts of PS II α,β-heterogeneity. We discuss why our results are in disagreement with those of a recent lifetime study of Chlorella by M. Hodges and I. Moya (1986, Biochim. Biophys. Acta., 849:193-202).     

Simple Uniaxial and Uniform Biaxial Deformation of Nearly Isotropic Incompressible Tissues

A method is developed for analyzing in a unified manner both uniaxial and uniform biaxial strain data obtained from nearly isotropic tissues. The formulation is a direct application of nonlinear elasticity theory pertaining to large deformations. The general relation between Eulerian stress (σ) and extension ratio (λ) in soft isotropic elastic bodies undergoing uniform deformation takes the simple form: σ = ((λ³ - 1)/λ) f(λ), where f(λ) must be determined for each material. The extension ratio may be either greater than 1.0 (uniaxial elongation), or lie between zero and 1.0 (uniform biaxial extension). Simple analytical functions for f(λ) are most readily found for each tissue by plotting all data as (λ³ - 1)/λσ vs. λ. Of those tissues investigated in this way (dog pericardium and pleura, and cat mesentery and dura), all but pleura could be adequately described by a parabola: 1/f(λ) = 1/k{[(λ_M - λ)(λ - λ_m)]/[λ_M - λ_m}. In these instances, three material constants per tissue (K, λ_M, λ_m) served to predict approximately the stresses attained during both small and large deformations, in strips and sheets alike. It was further found that the uniaxial strain asymptote (λ_M) was linearly related to the biaxial strain asymptote (Λ_M), thus effectively reducing the number of constants by one.     

Life‐history responses of a freshwater rotifer to copper pollution

In organisms with dormant stages, life‐history responses to past pollution can be studied retrospectively. Here, we study such responses in a rotifer (Brachionus calyciflorus) from the once heavily copper‐polluted Lake Orta (Italy). We extracted resting eggs from sediments, established clonal lineages from hatchlings, and exposed newborns of these lineages to one of three copper concentrations that each mimicked a specific period in the lake''s pollution history. For each rotifer, we daily collected life‐table data. We then estimated treatment‐specific vital rates and used a stage‐structured population model to project population growth rate λ. We also estimated elasticities of λ to vital rates and contributions of vital rates to observed Δλ between copper treatments. As expected, λ decreased with increasing copper concentration. This decrease resulted mostly from a decline in juvenile survival rate (S_J ) and partly from a decline in the survival rate of asexually reproducing females (S_A ). Maturation rate, and with one exception fecundity, also declined but did not contribute consistently to Δλ. λ was most elastic to S_J and S_A , indicating that survival rates were under stronger selection than maturation rate and fecundity. Together, our results indicate that variation in juvenile survival is a key component in the rotifers’ copper response. The consistent decrease in S_J with increasing copper stress and the sensitivity of λ to that decrease also suggest that juvenile survival is a useful indicator of population performance under environmental pollution.     

On the visibility of radiation at the human fovea

1. Seeing-frequency functions (ψ[S]) determined uniocularly for small (1.6'), brief images at the thoroughly dark-adapted human central fovea take the form of log-Gaussian integrals, for intensity or for exposure-time as the independent variable. They cannot be of Poisson type, since mean (τ') and standard deviation (σ) are quite independently modifiable. 2. The properties of τ', the abscissa of inflection in the log-Gaussian integrals, and of σ, are discussed in relation to customary determinations of spectral visibilities; agreements and certain necessary divergences are considered. 3. The values of σ_{logΔIlogΔI0}, are distributed periodically, with 5 maxima in the range λ383 to λ712. Outside the fovea this is not the case. These maxima, and the intervening minima, are definitely correlated with "irregularities" in the values of τ' as function of λ, with data on color threshold intensities, with data on "saturation," and quite specifically with minima and maxima in the data of λ discrimination. They are unmistakably of analytical significance. 4. The interpretation of these properties is taken to require (consistent with the indications of other evidence) that under specified conditions the magnitude of σ is a measure of the "size" of the population of excitable elements of neural effect, in the range of 0 to 100 per cent response-frequency as a function of wave number. This means that under the procedure used there is detectable the spectral distribution of local, specific, photosensitization. The σ's refer to a property of the excitation process which is not affected by the action of irrelevant absorbers. 5. A preliminary test of this has been made by the use of mixed "monochromatic" lights. The total energy is empirically the significant quantity, although the separate effects of λ's are sharply exhibited. 6. The λ distribution of photosensitization indices, σ_{logΔIlogΔI0}, is necessarily taken to have the nature of "action spectra." Careful search discloses, surprisingly enough, precise and apparently unique correspondence with the maxima and minima (and details of shape) required for the participation of: cytochrome-c reductase; the reduced forms of cytochromes-a and -c; and the often overlooked ferric-prophyrin bands of oxidized cytochrome-c. 7. For the central fovea, in which blood vessels are absent, and in which resistance to anoxia is at a maximum, the presence of an enzyme system of the sort here indicated is entirely reasonable. It is pointed out that a number of specific experiments can be based upon the general finding, whatever the causal mechanism for the sensitized λ regions may in the end prove to be. The data cannot be reconciled to the demands of existing color primary theories, although apparently quite accurately consistent with varied observational data.     

A Comprehensive Analysis of the Phylogeny,Genomic Organization and Expression of Immunoglobulin Light Chain Genes in Alligator sinensis,an Endangered Reptile Species

Crocodilians are evolutionarily distinct reptiles that are distantly related to lizards and are thought to be the closest relatives of birds. Compared with birds and mammals, few studies have investigated the Ig light chain of crocodilians. Here, employing an Alligator sinensis genomic bacterial artificial chromosome (BAC) library and available genome data, we characterized the genomic organization of the Alligator sinensis IgL gene loci. The Alligator sinensis has two IgL isotypes, λ and κ, the same as Anolis carolinensis. The Igλ locus contains 6 C_λ genes, each preceded by a J_λ gene, and 86 potentially functional V_λ genes upstream of (J_λ-C_λ)_n. The Igκ locus contains a single C_κ gene, 6 J_κs and 62 functional V_κs. All V_L genes are classified into a total of 31 families: 19 V_λ families and 12 V_κ families. Based on an analysis of the chromosomal location of the light chain genes among mammals, birds, lizards and frogs, the data further confirm that there are two IgL isotypes in the Alligator sinensis: Igλ and Igκ. By analyzing the cloned Igλ/κ cDNA, we identified a biased usage pattern of V families in the expressed V_λ and V_κ. An analysis of the junctions of the recombined VJ revealed the presence of N and P nucleotides in both expressed λ and κ sequences. Phylogenetic analysis of the V genes revealed V families shared by mammals, birds, reptiles and Xenopus, suggesting that these conserved V families are orthologous and have been retained during the evolution of IgL. Our data suggest that the Alligator sinensis IgL gene repertoire is highly diverse and complex and provide insight into immunoglobulin gene evolution in vertebrates.     

Signatures of neutral evolution in exponentially growing tumors: A theoretical perspective

Recent work of Sottoriva, Graham, and collaborators have led to the controversial claim that exponentially growing tumors have a site frequency spectrum that follows the 1/f law consistent with neutral evolution. This conclusion has been criticized based on data quality issues, statistical considerations, and simulation results. Here, we use rigorous mathematical arguments to investigate the site frequency spectrum in the two-type model of clonal evolution. If the fitnesses of the two types are λ₀ < λ₁, then the site frequency spectrum is c/f^α where α = λ₀/λ₁. This is due to the advantageous mutations that produce the founders of the type 1 population. Mutations within the growing type 0 and type 1 populations follow the 1/f law. Our results show that, in contrast to published criticisms, neutral evolution in an exponentially growing tumor can be distinguished from the two-type model using the site frequency spectrum.     

Passive Cutaneous Anaphylaxis with Antigens from Coxiella burneti

Passive cutaneous anaphylaxis (PCA) was produced in guinea pigs sensitized with guinea pig Coxiella burneti phase I–II antiserum and challenged with dimethylsulfoxide- or trichloroacetic acid-soluble extracts from phase I cells. The PCA reaction could not be induced by whole or mechanically disrupted phase I or phase II C. burneti cells or by extracted cells or extracts of phase II cells. The antibody responsible for PCA was in the 7Sγ₁ (fast γ) globulin. Sensitization of the skin by 7Sγ₁ antibody could be blocked nonspecifically by 7Sγ₁ globulin from normal serum or from phase II antiserum. The 7Sγ₂ (slow γ) globulin antibody inhibited the reaction specifically. Some antiserum pools containing high agglutinin and complement-fixing titers to phase I C. burneti cells failed to initiate the PCA reaction, perhaps due to an imbalanced ratio of γ₁ to γ₂ specific globulins or to an imbalance in the ratio of specific to nonspecific γ₁ globulins. Agglutinins to phase I cells were found in both γ₁ and γ₂ antibody globulins. Complement-fixing antibodies were found in the γ₂ globulin fraction.     

Interpreting scratch assays using pair density dynamics and approximate Bayesian computation

Quantifying the impact of biochemical compounds on collective cell spreading is an essential element of drug design, with various applications including developing treatments for chronic wounds and cancer. Scratch assays are a technically simple and inexpensive method used to study collective cell spreading; however, most previous interpretations of scratch assays are qualitative and do not provide estimates of the cell diffusivity, D, or the cell proliferation rate, λ. Estimating D and λ is important for investigating the efficacy of a potential treatment and provides insight into the mechanism through which the potential treatment acts. While a few methods for estimating D and λ have been proposed, these previous methods lead to point estimates of D and λ, and provide no insight into the uncertainty in these estimates. Here, we compare various types of information that can be extracted from images of a scratch assay, and quantify D and λ using discrete computational simulations and approximate Bayesian computation. We show that it is possible to robustly recover estimates of D and λ from synthetic data, as well as a new set of experimental data. For the first time, our approach also provides a method to estimate the uncertainty in our estimates of D and λ. We anticipate that our approach can be generalized to deal with more realistic experimental scenarios in which we are interested in estimating D and λ, as well as additional relevant parameters such as the strength of cell-to-cell adhesion or the strength of cell-to-substrate adhesion.     

Spectral Sensitivity Measured with Electroretinogram Using a Constant Response Method

A new method is presented to determine the retinal spectral sensitivity function S(λ) using the electroretinogram (ERG). S(λ)s were assessed in three different species of myomorph rodents, Gerbils (Meriones unguiculatus), Wistar rats (Ratus norvegicus), and mice (Mus musculus). The method, called AC Constant Method, is based on a computerized automatic feedback system that adjusts light intensity to maintain a constant-response amplitude to a flickering stimulus throughout the spectrum, as it is scanned from 300 to 700 nm, and back. The results are presented as the reciprocal of the intensity at each wavelength required to maintain a constant peak to peak response amplitude. The resulting S(λ) had two peaks in all three rodent species, corresponding to ultraviolet and M cones, respectively: 359 nm and 511 nm for mice, 362 nm and 493 nm for gerbils, and 362 nm and 502 nm for rats. Results for mouse and gerbil were similar to literature reports of S(λ) functions obtained with other methods, confirming that the ERG associated to the AC Constant-Response Method was effective to obtain reliable S(λ) functions. In addition, due to its fast data collection time, the AC Constant Response Method has the advantage of keeping the eye in a constant light adapted state.     

Photochemical Apparatus Organization in the Chloroplasts of Two Beta vulgaris Genotypes

The composition and structural organization of thylakoid membranes of a low chlorophyll mutant of Beta vulgaris was investigated using spectroscopic, kinetic and electrophoretic techniques. The data obtained were compared with those of a standard F1 hybrid of the same species. The mutant was depleted in chlorophyll b relative to the hybrid and it had a higher photosystem II/photosystem I reaction center (Q/P₇₀₀) ratio and a smaller functional chlorophyll antenna size. Analysis of thylakoid membranes by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the mutant lacked a portion of the chlorophyll a/b light-harvesting complex but was enriched in the photosystem II reaction center chlorophyll protein complex. Comparison of functional antenna sizes and of photosystem stoichiometries determined electrophoretically were in good agreement with those determined spectroscopically. Both approaches indicated that about 30% of the total chlorophyll was associated with photosystem I and about 70% with photosystem II. A greater proportion of photosystem II_β was detected in the mutant. The results suggest that a higher photosystem II to photosystem I ratio in the sugar beet mutant has apparently compensated for the smaller photosystem II chlorophyll light-harvesting antenna in its chloroplasts. Moreover, a lack of chlorophyll a/b light-harvesting complex correlates with the abundance of photosystem II_β. It is proposed that a developmental relationship exists between the two types of photosystem II where photosystem II_β is a precursor form of photosystem II_α occurring prior to the addition of the chlorophyll a/b light-harvesting complex and grana formation.     

Y chromosome lineage- and village-specific genes on chromosomes 1p22 and 6q27 control visceral leishmaniasis in Sudan

Familial clustering and ethnic differences suggest that visceral leishmaniasis caused by Leishmania donovani is under genetic control. A recent genome scan provided evidence for a major susceptibility gene on Chromosome 22q12 in the Aringa ethnic group in Sudan. We now report a genome-wide scan using 69 families with 173 affected relatives from two villages occupied by the related Masalit ethnic group. A primary ten-centimorgan scan followed by refined mapping provided evidence for major loci at 1p22 (LOD score 5.65; nominal p = 1.72 × 10⁻⁷; empirical p < 1 × 10⁻⁵; λ_S = 5.1) and 6q27 (LOD score 3.74; nominal p = 1.68 × 10⁻⁵; empirical p < 1 × 10⁻⁴; λ_S = 2.3) that were Y chromosome–lineage and village-specific. Neither village supported a visceral leishmaniasis susceptibility gene on 22q12. The results suggest strong lineage-specific genes due to founder effect and consanguinity in these recently immigrant populations. These chance events in ethnically uniform African populations provide a powerful resource in the search for genes and mechanisms that regulate this complex disease.     

Renal Water Molecular Diffusion Characteristics in Healthy Native Kidneys: Assessment with Diffusion Tensor MR Imaging

Background

To explore the characteristics of diffusion tensor imaging (DTI) and magnetic resonance (MR) imaging in healthy native kidneys.

Methods

Seventy-three patients without chronic kidney disease underwent DTI-MRI with spin echo-echo planar (SE-EPI) sequences accompanied by an array spatial sensitivity encoding technique (ASSET). Cortical and medullary mean, axial and radial diffusivity (MD, AD and RD), fractional anisotropy (FA) and primary, secondary and tertiary eigenvalues (λ₁, λ₂, λ₃) were analysed in both kidneys and in different genders.

Results

Cortical MD, λ₂, λ₃, and RD values were higher than corresponding medullary values. The cortical FA value was lower than the medullary FA value. Medullary λ₁ and RD values in the left kidney were lower than in the right kidney. Medullary λ₂, and λ₃ values in women were higher than those in men. Medullary FA values in women were lower than those in men. Medullary FA (r = 0.351, P = 0.002) and λ₁ (r = 0.277, P = 0.018) positively correlated with eGFR. Medullary FA (r = −0.25, P = 0.033) negatively correlated with age.

Conclusions

Renal water molecular diffusion differences exist in human kidneys and genders. Age and eGFR correlate with medullary FA and primary eigenvalue.     

Role of Alpha-actinin-3 in Contractile Properties of Human Single Muscle Fibers: A Case Series Study in Paraplegics

A common nonsense polymorphism in the ACTN3 gene results in the absence of α-actinin-3 in XX individuals. The wild type allele has been associated with power athlete status and an increased force output in numeral studies, though the mechanisms by which these effects occur are unclear. Recent findings in the Actn3^−/− (KO) mouse suggest a shift towards ‘slow’ metabolic and contractile characteristics of fast muscle fibers lacking α-actinin-3. Skinned single fibers from the quadriceps muscle of three men with spinal cord injury (SCI) were tested regarding peak force, unloaded shortening velocity, force-velocity relationship, passive tension and calcium sensitivity. The SCI condition induces an ‘equal environment condition’ what makes these subjects ideal to study the role of α-actinin-3 on fiber type expression and single muscle fiber contractile properties. Genotyping for ACTN3 revealed that the three subjects were XX, RX and RR carriers, respectively. The XX carrier’s biopsy was the only one that presented type I fibers with a complete lack of type II_x fibers. Properties of hybrid type II_a/II_x fibers were compared between the three subjects. Absence of α-actinin-3 resulted in less stiff type II_a/II_x fibers. The heterozygote (RX) exhibited the highest fiber diameter (0.121±0.005 mm) and CSA (0.012±0.001 mm²) and, as a consequence, the highest peak force (2.11±0.14 mN). Normalized peak force was similar in all three subjects (P = 0.75). Unloaded shortening velocity was highest in R-allele carriers (P<0.001). No difference was found in calcium sensitivity. The preservation of type I fibers and the absence of type II_x fibers in the XX individual indicate a restricted transformation of the muscle fiber composition to type II fibers in response to long-term muscle disuse. Lack of α-actinin-3 may decrease unloaded shortening velocity and increase fiber elasticity.     

A Neural Network Model for K(λ) Retrieval and Application to Global K par Monitoring

Accurate estimation of diffuse attenuation coefficients in the visible wavelengths K _d(λ) from remotely sensed data is particularly challenging in global oceanic and coastal waters. The objectives of the present study are to evaluate the applicability of a semi-analytical K _d(λ) retrieval model (SAKM) and Jamet’s neural network model (JNNM), and then develop a new neural network K _d(λ) retrieval model (NNKM). Based on the comparison of K _d(λ) predicted by these models with in situ measurements taken from the global oceanic and coastal waters, all of the NNKM, SAKM, and JNNM models work well in K _d(λ) retrievals, but the NNKM model works more stable and accurate than both SAKM and JNNM models. The near-infrared band-based and shortwave infrared band-based combined model is used to remove the atmospheric effects on MODIS data. The K _d(λ) data was determined from the atmospheric corrected MODIS data using the NNKM, JNNM, and SAKM models. The results show that the NNKM model produces <30% uncertainty in deriving K _d(λ) from global oceanic and coastal waters, which is 4.88-17.18% more accurate than SAKM and JNNM models. Furthermore, we employ an empirical approach to calculate K _par from the NNKM model-derived diffuse attenuation coefficient at visible bands (443, 488, 555, and 667 nm). The results show that our model presents a satisfactory performance in deriving K _par from the global oceanic and coastal waters with 20.2% uncertainty. The K _par are quantified from MODIS data atmospheric correction using our model. Comparing with field measurements, our model produces ~31.0% uncertainty in deriving K _par from Bohai Sea. Finally, the applicability of our model for general oceanographic studies is briefly illuminated by applying it to climatological monthly mean remote sensing reflectance for time ranging from July, 2002- July 2014 at the global scale. The results indicate that the high K _d(λ) and K _par values are usually found around the coastal zones in the high latitude regions, while low K _d(λ) and K _par values are usually found in the open oceans around the low-latitude regions. These results could improve our knowledge about the light field under waters at either the global or basin scales, and be potentially used into general circulation models to estimate the heat flux between atmosphere and ocean.     

Fusion Peptides Promote Formation of Bilayer Cubic Phases in Lipid Dispersions. An X-Ray Diffraction Study

Small angle x-ray diffraction revealed a strong influence of the N-terminal influenza hemagglutinin fusion peptide on the formation of nonlamellar lipid phases. Comparative measurements were made on a series of three peptides, a 20-residue wild-type X-31 influenza virus fusion peptide, GLFGAIAGFIENGWEGMIDG, and its two point-mutant, fusion-incompetent peptides G1E and G13L, in mixtures with hydrated phospholipids, either dipalmitoleoylphosphatidylethanolamine (DPoPE), or monomethylated dioleoyl phosphatidylethanolamine (DOPE-Me), at lipid/peptide molar ratios of 200:1 and 50:1. All three peptides suppressed the H_II phase and shifted the L_α–H_II transition to higher temperatures, simultaneously promoting formation of inverted bicontinuous cubic phases, Q_II, which becomes inserted between the L_α and H_II phases on the temperature scale. Peptide-induced Q_II had strongly reduced lattice constants in comparison to the Q_II phases that form in pure lipids. Q_II formation was favored at the expense of both L_α and H_II phases. The wild-type fusion peptide, WT-20, was distinguished from G1E and G13L by the markedly greater magnitude of its effect. WT-20 disordered the L_α phase and completely abolished the H_II phase in DOPE-Me/WT-20 50:1 dispersions, converted the Q_II phase type from Im3m to Pn3m and reduced the unit cell size from ∼38 nm for the Im3m phase of DOPE-Me dispersions to ∼15 nm for the Pn3m phase in DOPE-Me/WT-20 peptide mixtures. The strong reduction of the cubic phase lattice parameter suggests that the fusion-promoting WT-20 peptide may function by favoring bilayer states of more negative Gaussian curvature and promoting fusion along pathways involving Pn3m phase-like fusion pore intermediates rather than pathways involving H_II phase-like intermediates.     

Effects of Harvest on the Sustainability and Leaf Productivity of Populations of Two Palm Species in Maya Homegardens

Traditional management practices are usually thought to be sustainable. The Maya manage Sabal (Arecaceae) palms in homegardens, using their leaves for thatching. The sustainability of such production systems depends on the long-term persistence of palm populations, whereas resource availability also depends on the number of leaves on individual palms. We examined how leaf harvest affects Sabal yapa and S. mexicana population growth rates (λ) and leaf production, comparing traditional and alternative harvest regimes in terms of sustainability and productivity. Demographic, harvest and leaf production data were recorded for three years in two homegardens. We used general integral projection models linked to leaf-production models to describe population dynamics and productivity. Harvest had no effect on S. yapa’s vital rates or on λ, but it changed the growth rate of individuals of S. mexicana, with a negligible impact on λ. Homegardens affected λ values, reflecting the species’ ecological affinities. S. mexicana, introduced from mesic forests, required watering and shade; therefore, its population declined rapidly in the homegarden that lacked both water and shade. The λ of the xerophilic S. yapa was slightly larger without watering than with watering. Palms usually compensated for leaf extraction, causing the number of leaves harvested per individual to increase with harvest intensity. Nevertheless, traditional management is relatively mild, allowing standing leaves to accumulate but reducing the homegarden’s yield. Apparently, the Maya do not seek to maximize annual production but to ensure the availability of large numbers of leaves in homegardens. These leaves may then be used when the entire roof of a hut needs to be replaced every few years.     

Minimal Effects of Macromolecular Crowding on an Intrinsically Disordered Protein: A Small-Angle Neutron Scattering Study

Small-angle neutron scattering was used to study the effects of macromolecular crowding by two globular proteins, i.e., bovine pancreatic trypsin inhibitor and equine metmyoglobin, on the conformational ensemble of an intrinsically disordered protein, the N protein of bacteriophage λ. The λ N protein was uniformly labeled with ²H, and the concentrations of D₂O in the samples were adjusted to match the neutron scattering contrast of the unlabeled crowding proteins, thereby masking their contribution to the scattering profiles. Scattering from the deuterated λ N was recorded for samples containing up to 0.12 g/mL bovine pancreatic trypsin inhibitor or 0.2 g/mL metmyoglobin. The radius of gyration of the uncrowded protein was estimated to be 30 Å and was found to be remarkably insensitive to the presence of crowders, varying by <2 Å for the highest crowder concentrations. The scattering profiles were also used to estimate the fractal dimension of λ N, which was found to be ∼1.8 in the absence or presence of crowders, indicative of a well-solvated and expanded random coil under all of the conditions examined. These results are contrary to the predictions of theoretical treatments and previous experimental studies demonstrating compaction of unfolded proteins by crowding with polymers such as dextran and Ficoll. A computational simulation suggests that some previous treatments may have overestimated the effective volumes of disordered proteins and the variation of these volumes within an ensemble. The apparent insensitivity of λ N to crowding may also be due in part to weak attractive interactions with the crowding proteins, which may compensate for the effects of steric exclusion.     

Assessment of heterogeneity of residual variances using changepoint techniques

Several studies using test-day models show clear heterogeneity of residual variance along lactation. A changepoint technique to account for this heterogeneity is proposed. The data set included 100 744 test-day records of 10 869 Holstein-Friesian cows from northern Spain. A three-stage hierarchical model using the Wood lactation function was employed. Two unknown changepoints at times T₁ and T₂, (0 <T₁ <T₂ <t_max), with continuity of residual variance at these points, were assumed. Also, a nonlinear relationship between residual variance and the number of days of milking t was postulated. The residual variance at a time t() in the lactation phase i was modeled as: for (i = 1, 2, 3), where λ_ι is a phase-specific parameter. A Bayesian analysis using Gibbs sampling and the Metropolis-Hastings algorithm for marginalization was implemented. After a burn-in of 20 000 iterations, 40 000 samples were drawn to estimate posterior features. The posterior modes of T₁, T₂, λ₁, λ₂, λ₃, , , were 53.2 and 248.2 days; 0.575, -0.406, 0.797 and 0.702, 34.63 and 0.0455 kg², respectively. The residual variance predicted using these point estimates were 2.64, 6.88, 3.59 and 4.35 kg² at days of milking 10, 53, 248 and 305, respectively. This technique requires less restrictive assumptions and the model has fewer parameters than other methods proposed to account for the heterogeneity of residual variance during lactation.     

The Stochastic Theory of Cell Proliferation

A stochastic theory of cell kinetics has been developed based on a realistic model of cell proliferation. A characteristic transit time, _i, has been assigned to each of the four states (G₁, S, G₂, M) of the cell cycle. The actual transit time, t_i, for any cell is represented by a distribution around _i with a variance σ_i². Analytic and computer formulations have been used to describe the time development of such characteristics as age distribution, labeling experiments, and response to perturbations of the system by, for example, irradiation and temperature. The decay of synchrony is analyzed in detail and is shown to proceed as a damped wave. From the first few peaks of the synchrony decay one can obtain the distribution function for the cell cycle time. The later peaks decay exponentially with a characteristic decay constant, λ, which depends only on the average cell-cycle time, , and the associated variance. It is shown that the system, upon any sudden disturbance, approaches new “equilibrium” proliferation characteristics via damped periodic transients, the damping being characterized by λ. Thus, the response time of the system, /λ, is as basic a parameter of the system as the cell-cycle time.     

Thermal Characterization,Crystal Field Analysis and In-Band Pumped Laser Performance of Er Doped NaY(WO4)2 Disordered Laser Crystals

Undoped and Er-doped NaY(WO₄)₂ disordered single crystals have been grown by the Czochralski technique. The specific heat and thermal conductivity (κ) of these crystals have been characterized from T = 4 K to 700 K and 360 K, respectively. It is shown that κ exhibits anisotropy characteristic of single crystals as well as a κ(T) behavior observed in glasses, with a saturation mean free phonon path of 3.6 Å and 4.5 Å for propagation along a and c crystal axes, respectively. The relative energy positions and irreducible representations of Stark Er³⁺ levels up to ⁴G_7/2 multiplet have been determined by the combination of experimental low (<10 K) temperature optical absorption and photoluminescence measurements and simulations with a single-electron Hamiltonian including both free-ion and crystal field interactions. Absorption, emission and gain cross sections of the ⁴I_13/2↔⁴I_15/2 laser related transition have been determined at 77 K. The ⁴I_13/2 Er³⁺ lifetime (τ) was measured in the temperature range of 77–300 K, and was found to change from τ (77K) ≈ 4.5 ms to τ (300K) ≈ 3.5 ms. Laser operation is demonstrated at 77 K and 300 K by resonantly pumping the ⁴I_13/2 multiplet at λ≈1500 nm with a broadband (FWHM≈20 nm) diode laser source perfectly matching the 77 K crystal ⁴I_15/2 → ⁴I_13/2 absorption profile. At 77 K as much as 5.5 W of output power were obtained in π-polarized configuration with a slope efficiency versus absorbed pump power of 57%, the free running laser wavelength in air was λ≈1611 nm with the laser output bandwidth of 3.5 nm. The laser emission was tunable over 30.7 nm, from 1590.7 nm to 1621.4 nm, for the same π-polarized configuration.