Big bang bifurcations in von Bertalanffy’s dynamics with strong and weak Allee effects

The main purpose of this work was to study population dynamic discrete models in which the growth of the population is described by generalized von Bertalanffy's functions, with an adjustment or correction factor of polynomial type. The consideration of this correction factor is made with the aim to introduce the Allee effect. To the class of generalized von Bertalanffy's functions is identified and characterized subclasses of strong and weak Allee's functions and functions with no Allee effect. This classification is founded on the concepts of strong and weak Allee's effects to population growth rates associated. A complete description of the dynamic behavior is given, where we provide necessary conditions for the occurrence of unconditional and essential extinction types. The bifurcation structures of the parameter plane are analyzed regarding the evolution of the Allee limit with the aim to understand how the transition from strong Allee effect to no Allee effect, passing through the weak Allee effect, is realized. To generalized von Bertalanffy's functions with strong and weak Allee effects is identified an Allee's effect region, to which is associated the concepts of chaotic semistability curve and Allee's bifurcation point. We verified that under some sufficient conditions, generalized von Bertalanffy's functions have a particular bifurcation structure: the big bang bifurcations of the so-called box-within-a-box type. To this family of maps, the Allee bifurcation points and the big bang bifurcation points are characterized by the symmetric of Allee's limit and by a null intrinsic growth rate. The present paper is also a significant contribution in the framework of the big bang bifurcation analysis for continuous 1D maps and unveil their relationship with the explosion birth and the extinction phenomena.

The 100th anniversary of the four-point probe technique: the role of probe geometries in isotropic and anisotropic systems

The electrical conductivity of solid-state matter is a fundamental physical property and can be precisely derived from the resistance measured via the four-point probe technique excluding contributions from parasitic contact resistances. Over time, this method has become an interdisciplinary characterization tool in materials science, semiconductor industries, geology, physics, etc, and is employed for both fundamental and application-driven research. However, the correct derivation of the conductivity is a demanding task which faces several difficulties, e.g. the homogeneity of the sample or the isotropy of the phases. In addition, these sample-specific characteristics are intimately related to technical constraints such as the probe geometry and size of the sample. In particular, the latter is of importance for nanostructures which can now be probed technically on very small length scales. On the occasion of the 100th anniversary of the four-point probe technique, introduced by Frank Wenner, in this review we revisit and discuss various correction factors which are mandatory for an accurate derivation of the resistivity from the measured resistance. Among others, sample thickness, dimensionality, anisotropy, and the relative size and geometry of the sample with respect to the contact assembly are considered. We are also able to derive the correction factors for 2D anisotropic systems on circular finite areas with variable probe spacings. All these aspects are illustrated by state-of-the-art experiments carried out using a four-tip STM/SEM system. We are aware that this review article can only cover some of the most important topics. Regarding further aspects, e.g. technical realizations, the influence of inhomogeneities or different transport regimes, etc, we refer to other review articles in this field.

Desenvolvimento de um método para correção de curvas de desempenho em bombas centrífugas submersas operando com fluidos viscosos

Electrical Submersible Pump (ESP) is used as an artificial lift technique. However, pumping viscous oil is generally associated with low Reynolds number flows. This condition leads to a performance degradation respect to the performance expected from the regular operation with water that most of the centrifugal pumps are originally designed for. These issues are considered in this investigation through a numerical study of the flow in two different multistage, semi-axial type ESPs. This investigation is carried out numerically using a Computational Fluid Dynamics (CFD) package, where the transient RANS equations are solved numerically. The turbulence is modeled using the SST model. Head curves for several operating conditions are compared with manufacturer’s curves and experimental data for a three-stage ESP, showing good agreement for a wide range of fluid viscosities and rotational speeds. Dimensionless numbers (n, n, n e Re) are used to investigate performance degradation of the ESPs. In addition, flow phenomena through the impellers of the ESPs are investigated using flow field from numerical results. Results show that performance degradation is directly related to rotational Reynolds number, Re. In addition, it was verified that performance degradation occurs for constant normalized specific speedn, which shows that performance degradation occurs similarly for different centrifugal pumps. Moreover, experimental data and numerical results agreed with a correlation from literature between head and flow correction factors proposed by Stepanoff (1967). A definition of modified Reynolds number was proposed and relates the head correction factor to viscosity. A correlation between head correction factor and the modified Reynolds number was proposed, which agreed well with numerical and experimental data. Then, a method to predict performance degradation based on the previous correlations was proposed. This method was compared with others from literature. In general, results and conclusions from this work can also be useful to bring more information about the flow of highly viscous fluids in pumps, especially in semi-axial, multistage ESPs.

Normative reference values for the 20-meter shuttlerun test in a population-based sample of schoolchildren in Bogota, Colombia: The FUPRECOL Study

Our aim was to determine the normative reference values of cardiorespiratory fitness (CRF) and to establish the proportion of subjects with low CRF suggestive of future cardio-metabolic risk.

Transfer factor for carbon monoxide: a glance behind the scene.

The transfer factor for carbon monoxide (TLCO) is widely used in pulmonary function laboratories because it represents a unique non-invasive window on pulmonary microcirculation. The TLCO is the product of two primary measurements, the alveolar volume (VA) and the CO transfer coefficient (KCO). This test is most informative when VA and KCO are examined, together with their product TLCO. In a normal lung, a low VA due to incomplete expansion is associated with an elevated KCO, resulting in a mildly reduced TLCO. Thus, in case of low VA, a seemingly "normal KCO" must be interpreted as an abnormal gas transfer. The most common clinical conditions associated with an abnormal TLCO are characterised by a limited number of patterns for VA and KCO: incomplete lung expansion, discrete loss of alveolar units, diffuse loss of alveolar units, emphysema, pulmonary vascular disorders, high pulmonary blood volume, alveolar haemorrhage.

New 12kW three-phase 18-pulse high power factor AC-DC converter with regulated output voltage for rectifier units

This work presents a new high power factor three-phase rectifier based on a Y-connected differential autotransformer with reduced kVA and 18-pulse input current followed by three DC-DC boost converters. The topology provides a regulated output voltage and natural three-phase input power factor correction. The lowest input current harmonic components are the 17th and the 19th. Three boost converters, with constant input currents and regulated parallel connected output voltages are used to process 4kW each one. Analytical results from Fourier analyses of winding currents and the vector diagram of winding voltages are presented. Simulation results to verify the proposed concept and experimental results are shown in the paper.

Short-term correction of factor VIII deficiency in a murine model of hemophilia A after delivery of adenovirus murine factor VIII in utero

Development of in utero gene transfer approaches may provide therapies for genetic disorders with perinatal morbidity. In hemophilia A, prenatal and postnatal bleeding may be catastrophic, and modest increments in factor VIII (FVIII) activity are therapeutic. We performed transuterine i.p. gene transfer at day 15 of gestation in a murine model of hemophilia A. Normal, carrier (XHX), and FVIII-deficient (XHY and XHXH) fetuses injected with adenoviral vectors carrying luciferase or β-galactosidase reporter genes showed high-level gene expression with 91% fetal survival. The live-born rates of normal and FVIII-deficient animals injected in utero with adenovirus murine FVIII (3.3 × 105 plaque-forming units) was 87%. FVIII activity in plasma was 50.7 ± 10.5% of normal levels at day 2 of life, 7.2 ± 2.2% by day 15 of life, and no longer detectable at day 21 of life in hemophilic animals. Injection of higher doses of murine FVIII adenovirus at embryonic day 15 produced supranormal levels of FVIII activity in the neonatal period. PCR analysis identified viral genomes primarily in the liver, intestine, and spleen, although adenoviral DNA was detected in distal tissues when higher doses of adenovirus were administered. These studies show that transuterine i.p. injection of adenoviral vectors produces therapeutic levels of circulating FVIII throughout the neonatal period. The future development of efficient and persisting vectors that produce long-term gene expression may allow for in utero correction of genetic diseases originating in the fetal liver, hematopoietic stem cells, as well as other tissues.

Lithostratigraphy determined from downhole logs in the AND-2A borehole

During the 2007-2008 austral spring season, the ANDRILL (Antarctic Drilling project) Southern McMurdo Sound Project recovered an 1138-m-long core, representing the last 20 m.y. of glacial history. An extensive downhole logging program was successfully carried out. Due to drill hole conditions, logs were collected in several passes from the total depth at 1138.54 m below seafloor (mbsf) to 230 mbsf. After data correction, several statistical methods, such as factor analysis, cluster analysis, box-and-whisker diagrams, and cross-plots, were applied. The aim of these analyses was to use detailed interpretation of the downhole logs to obtain a description of the lithologies and their specific physical properties that is independent of the core descriptions. The sediments were grouped into the three main facies, diamictite, mudstone and/or siltstone, and sandstone, and the physical properties of each were determined. Notable findings include the high natural radioactivity values in sandstone and the high and low magnetic susceptibility values in mudstone and/or siltstone and in sandstone. A modified lithology cluster column was produced on the basis of the downhole logs and statistical analyses. It was possible to use the uranium content in the downhole logs to determine hiatuses and thus more accurately place the estimated hiatuses. Using analyses from current literature (geochemistry, clasts, and clay minerals) in combination with the downhole logs (cluster analysis), the depths 225 mbsf, 650 mbsf, 775 mbsf, and 900 mbsf were identified as boundaries of change in sediment composition, provenance, and/or environmental conditions. The main use of log interpretation is the exact definition of lithological boundaries and the modification of the paleoenvironmental interpretation.

S-allylmercaptocysteine reduces carbon tetrachloride-induced hepatic oxidative stress and necroinflammation via nuclear factor kappa B-dependent pathways in mice.

Purpose To study the protective effects and underlying molecular mechanisms of SAMC on carbon tetrachloride (CCl4)-induced acute hepatotoxicity in the mouse model. Methods Mice were intraperitoneally injected with CCl4 (50 μl/kg; single dose) to induce acute hepatotoxicity with or without a 2-h pre-treatment of SAMC intraperitoneal injection (200 mg/kg; single dose). After 8 h, the blood serum and liver samples of mice were collected and subjected to measurements of histological and molecular parameters of hepatotoxicity. Results SAMC reduced CCl4-triggered cellular necrosis and inflammation in the liver under histological analysis. Since co-treatment of SAMC and CCl4 enhanced the expressions of antioxidant enzymes, reduced the nitric oxide (NO)-dependent oxidative stress, and inhibited lipid peroxidation induced by CCl4. SAMC played an essential antioxidative role during CCl4-induced hepatotoxicity. Administration of SAMC also ameliorated hepatic inflammation induced by CCl4 via inhibiting the activity of NF-κB subunits p50 and p65, thus reducing the expressions of pro-inflammatory cytokines, mediators, and chemokines, as well as promoting pro-regenerative factors at both transcriptional and translational levels. Conclusions Our results indicate that SAMC mitigates cellular damage, oxidative stress, and inflammation in CCl4-induced acute hepatotoxicity mouse model through regulation of NF-κB. Garlic or garlic derivatives may therefore be a potential food supplement in the prevention of liver damage.

Thermophoretic control of building units in the plasma-assisted deposition of nanostructured carbon films

The role of the plasma-grown nanoparticles in the plasma-enhanced chemical vapor deposition (PECVD) of the nanostructured carbon-based films was investigated. The samples were grown in the low-pressure rf plasmas of CH 4+H2+Ar gas mixtures. The enhanced deposition of the building units from the gas phase was found to support the formation of polymorphous nanostructured carbon films. The results reveal the crucial role played by the thermophoretic force in controlling the deposition of the plasma-grown fine particles.

Factor analysis used to peak position optimization and spectral interference correction in inductively coupled plasma atomic emission spectrometry

Target transformation factor analysis was used to correct spectral interference in inductively coupled plasma atomic emission spectrometry (ICP-BES) for the determination of rare earth impurities in high purity thulium oxide. Data matrix was constructed with pure and mixture vectors and background vector. A method based on an error evaluation function was proposed to optimize the peak position, so the influence of the peak position shift in spectral scans on the determination was eliminated or reduced. Satisfactory results were obtained using factor analysis and the proposed peak position optimization method.

APPLICATION OF FACTOR-ANALYSIS TO CORRECTION OF SPECTRAL OVERLAP INTERFERENCE IN INDUCTIVELY COUPLED PLASMA ATOMIC EMISSION-SPECTROMETRY

Correction of spectral overlap interference in inductively coupled plasma atomic emission spectrometry by factor analysis is attempted. For the spectral overlap of two known lines, a data matrix can be composed from one or two pure spectra and a spectrum of the mixture. The data matrix is decomposed into a spectra matrix and a concentration matrix by target transformation factor analysis. The component concentration of interest in a binary mixture is obtained from the concentration matrix and interference from the other component is eliminated. This method is applied to correcting spectral interference of yttrium on the determination of copper and aluminium: satisfactory results are obtained. This method may also be applied to correcting spectral overlap interference for more than two lines. Like other methods of correcting spectral interferences, factor analysis can only be used for additive spectral overlap. Results obtained from measurements on copper/yttrium mixtures with different white noise added show that random errors in measurement data do not significantly affect the results of the correction method.

Action Spectra of P25 TiO2 and a visible light absorbing, carbon-modified titania in the photocatalytic degradation of stearic acid

The photonic efficiencies of films of Evonik (formerly Degussa) P25 TiO2 and carbon-modified TiO2 Kronos VLP 7000 samples are reported as a function of excitation wavelength (300–430 nm; FWHM ∼ 7.5 nm), i.e. the action spectra, for the degradation of stearic acid, a model organic for the photocatalytic destruction of solid surface organic pollutants. For each of these semiconductor photocatalysts, at 365 nm (FWHM = 18 nm), the dependence of the rate of degradation of stearic acid, upon the irradiance, I, is determined and the rate is found to be proportional to I0.65 and I0.82 for P25 and Kronos titania, respectively. Assuming this relationship holds at all wavelengths, the action spectra for two different semiconductor photocatalysts is modified by plotting, (RSA (rate of stearic acid destruction, units: molecules cm−2 s−1)/Iθ) vs. wavelength of excitation (λexcit), and both differ noticeably from those of the original (unmodified) action spectra, which are plots of (RSA/I = photonic efficiency, ξ) vs. λexcit. The shape of the modified action spectrum for P25 TiO2 is consistent with that reported by others for other organic mineralisation reactions and correlates well with diffuse reflectance data for P25 TiO2 (Kubelka–Munk plot), although there is some evidence that the active phase, in the photodegradation of stearic acid, is the anatase form present in P25. The unmodified and modified action spectra of the beige Kronos VLP 7000 TiO2 compound exhibits little or no activity in the visible i.e. (λexcit > 400 nm) and a peak at 350 nm. The Kronos powder contains a yellow/brown conjugated, extractable, organic sensitiser which has been identified by others as the species responsible for its reported photocatalytic visible light activity. But, irradiation of the Kronos powder film, with and without a stearic acid coating, in air, using UVA or visible light, bleaches rapidly (<60 min) most, if not all, of the little colour exhibited by the original Kronos powder. The photobleached form of the Kronos has a similar action spectrum to that of the unbleached form, which, in turn, appears very similar to that of P25 titania, at wavelengths >350 nm. It is proposed that the difference between the Kronos and P25 powder films at wavelengths <350 nm is due to a photodegradation-resistant, previously unidentified (but extractable using MeCN) UV-absorbing organic species in the former which screens the titania particles at these lower wavelengths. The implications of these observations are discussed briefly.