Novel generic models for differentiating stem cells reveal oscillatory mechanisms

Understanding cell fate selection remains a central challenge in developmental biology. We present a class of simple yet biologically motivated mathematical models for cell differentiation that generically generate oscillations and hence suggest alternatives to the standard framework based on Waddington’s epigenetic landscape. The models allow us to suggest two generic dynamical scenarios that describe the differentiation process. In the first scenario, gradual variation of a single control parameter is responsible for both entering and exiting the oscillatory regime. In the second scenario, two control parameters vary: one responsible for entering, and the other for exiting the oscillatory regime. We analyse the standard repressilator and four variants of it and show the dynamical behaviours associated with each scenario. We present a thorough analysis of the associated bifurcations and argue that gene regulatory networks with these repressilator-like characteristics are promising candidates to describe cell fate selection through an oscillatory process.

Novel Generic Models for Differentiating Stem Cells Reveal Oscillatory Mechanisms

Understanding cell fate selection remains a central challenge in developmental biology. We present a class of simple yet biologically-motivated mathematical models for cell differentiation that generically generate oscillations and hence suggest alternatives to the standard framework based on Waddington's epigenetic landscape. The models allow us to suggest two generic dynamical scenarios that describe the differentiation process. In the first scenario gradual variation of a single control parameter is responsible for both entering and exiting the oscillatory regime. In the second scenario two control parameters vary: one responsible for entering, and the other for exiting the oscillatory regime. We analyse the standard repressilator and four variants of it and show the dynamical behaviours associated with each scenario. We present a thorough analysis of the associated bifurcations and argue that gene regulatory networks with these repressilator-like characteristics are promising candidates to describe cell fate selection through an oscillatory process.

Variations to Spin Crossover in [FexZn(1−x)(Me1,3bpp)2(ClO4)2] molecular alloys examined by Magnetometry and Single Crystal X-Ray Diffraction

Spin crossover (SCO) active solid solutions with formula [FexZn1-x(Me1,3bpp)2](ClO4)2 (x = 0.10, 0.15, 0.22, 0.33, 0.41, 0.48, 0.56 and 0.64, Me1,3bpp is a bis-pyrazolylpyridine) and the complex [Zn(Me1,3bpp)2](ClO4)2 have been prepared and characterized by single crystal X-ray diffraction. The structural data and the powder diffraction patterns of all the compounds have been compared with the reported isostructural molecular crystal [Fe(Me1,3bpp)2](ClO4)2. Increasing amounts of Zn diminishes monotonically the cooperativity of the SCO of the parent Fe(II) complex (T1/2=183 K) and cause a decrease of T1/2 in line with the negative chemical pressure exerted by the Zn(II) complexes on the Fe(II) lattice. The gradual variation of the magnetic properties as the composition changes are paralleled by the evolution of the structural parameters at the molecular, intermolecular and crystal lattice scales. Thermal trapping of a portion of the Fe(II) centers of these alloys by quenching the crystals to 2 K unveils that, upon warming, the temperature of relaxation of the metastable states is almost constant for all compositions.

The California Bearing Ratio and Pore Structure Characteristics of Weakly Expansive Soil in Frozen Areas

The California Bearing Ratio (CBR) of weakly expansive soil is specially relevant to its expansibility. The mechanisms affecting the bearing strength, in terms of the CBR, of weakly expansive soil that could be used as embankments filler are worth studying. In the present study, the effects of compaction energy on the compaction characteristics and CBR value were investigated. Additionally, the pore size distributions of soils with different compaction degrees were studied with nuclear magnetic resonance (NMR), and the effect of freeze–thaw cycles on the pore size distribution of soils with different compaction degrees was considered. Subsequently, the mechanisms influencing the CBR were analyzed at both the macroscale and microscale. A linear relationship between the CBR value and compaction degree was determined, characterizing the gradual variation of expansive soils with different moisture contents. With increasing freeze–thaw cycles, the volume of micropores decreased and mesopores increased, causing the CBR value to decrease. The expansion was a dominant factor for the CBR values. The CBR values rose with an increase in micropores and decreased with an increase in pore volume. It was considered that the tested weakly expansive soil could be used as an embankment filler in frozen areas.

Identifying Antarctic Ice Sheet Tipping Points

<p>Warmer atmospheric and oceanic temperatures have led to a six-fold increase in mass loss from Antarctica in the last four decades. It is difficult to predict how the ice sheet will respond to future warming because it is subject to positive feedback mechanisms, which could lead to destabilisation. Observational and modelling work has shown that ice streams in West Antarctica may be undergoing unstable and possibly irreversible retreat due to increased basal melting beneath their ice shelves. Being able to identify and predict stability thresholds in ice streams draining the Antarctic Ice Sheet could help establish early warning indicators of near-future abrupt changes in sea level. <br> <br>Here, we use the shallow-ice flow model Úa to investigate the stability of an idealised ice stream from the third Marine Ice Sheet Model Intercomparison Project (MISMIP+). Initial results show that a gradual variation in ice viscosity, which corresponds to a change in temperature, causes the ice stream to undergo hysteresis across an overdeepened bed. This hysteresis means there are two tipping points, one for an advance phase and one for a retreat phase, both of which lie off the retrograde sloping bedrock. Beyond these tipping points, changes in ice stream grounding line position are unstable and irreversible. This behaviour is also apparent in wider ice streams although there is a change to the onset of instability and the location of tipping points. Further studies will investigate the additional effects of basal melting on these tipping points.</p>

Synthesis of Hydroxy Sodalite from Coal Fly Ash for Biodiesel Production from Waste-Derived Maggot Oil

Zeolites are aluminosilicate crystalline materials known for their unique characteristics, and have been prominent for nearly half a century due to their wide and important industrial applications. The production of zeolites, however, remains a challenge due to the high cost of commercial reagents conventionally used as feedstocks. In the current study, hydroxy sodalite (HS) zeolite samples were synthesised from coal fly ash feedstock by a direct hydrothermal synthesis method. The effects of hydrothermal crystallisation synthesis time on phase crystallinity, crystal size, and morphology of the formed HS were investigated. The prepared samples were characterised using XRD, SEM, EDS and FT-IR techniques. The XRD results of the samples prepared with varying synthesis times confirmed the formation of HS from low to high phase purity and crystallinity from 11 to over 98%. The SEM results reflected gradual variation in crystal morphology, of which highly crystalline HS samples were associated with hexagonal-cubic and cubic-platelet crystals. The FTIR, depicting zeolite characteristics of T–O and T–O–T stretching vibrations in the molecular framework, further confirmed the formation of HS zeolites for samples obtained above the 24-h synthesis time. These zeolite samples were then evaluated for their catalytic activities in the conversion of maggot oil to biodiesel. The application of the various hydroxy sodalite samples for the transesterification of maggot oil yielded up to 84.10% biodiesel (FAME) with physicochemical properties that were in compliance with the biodiesel specification standards. This study investigated the novel use of a coal fly ash-derived, heterogeneous HS catalyst in biodiesel production from maggot oil, and indicates its potential to enhance biodiesel yield and quality upon process optimisation tests.

Formation and reduction of anodic film on polycrystalline Bi electrode in pure methanol solutions

The processes of film formation and reduction of bismuth in pure methanol are phenomenologically studied by means of cyclic, ac voltammetric and electrochemical impedance spectroscopic methods. Film formation takes place under low electrode potentials within the potential range from -0.1 to about 0.2 V vs. Ag|AgCl resulting in the development of Bi(CH3O)ads layer. The scan rate effect on the anodic current profile is interpreted in terms of a gradual variation of uncompensated resistance, accompanying the processes of film formation and reduction. Phase sensitive ac voltammetry measurements suggest leaky insulating character of a thin anodic film in agreement with the results of electrochemical impedance experiments.

Drying of Sisal Fiber: A Theoretical and Experimental Investigation

This work presents a theoretical and experimental study of drying of sisal fibers. The fibers were submitted to drying in oven with forced air circulation at temperatures ranging from 50°C up to 90°C. Drying and heating lumped models were proposed and fitted to the experimental data. Non-linear regression analyzes were performed to verify the consistency of the models to predict the experimental data. It was verified that the curves of moisture loss and temperature of the sisal fibers were influenced by the drying-air temperature, showing a gradual variation with the drying time, being more accentuated in the higher temperatures of the drying-air. The fitted models presented good agreement with the experimental data.

Estimación del Cambio de Volumen del Glaciar Champará en la Cordillera Blanca de Ancash a Partir de Datos de Satélite en el Periodo 2000-2010

Estimación del Cambio de Volumen del Glaciar Champará en la Cordillera Blanca de Ancash a Partir de Datos de Satélite en el Periodo 2000-2010 Juvenal Tordocillo Puchuc, Joel Rojas Acuña Universidad Nacional del Callao, Av. Juan Pablo II s/n Callao 2, Perú. Universidad Nacional Mayor de San Marcos, Ap. Postal 14-0149. Lima, Perú. DOI: https://doi.org/10.33017/RevECIPeru2012.0008/ RESUMEN Se ha estimado, el cambio de área y volumen glaciar empleando las herramientas de la teledetección, basado en el procesamiento e interpretación de las imágenes adquiridas de los sensor ASTER a bordo del satélite TERRA, siendo el área de estudio el Glaciar Champará, el periodo de estudio comprende de 2000 -2010. La metodología utilizada para la estimación del área superficial del glaciar se utilizó el Índice de Diferencia Normalizada de la Nieve (NDSI) y el Índice de Diferencia Normalizada del Agua (NDWI), que sirve para eliminar agua pro glaciar que inicialmente se considera como glaciar. En base a ésta metodología se observa, una variación paulatina del área del Glaciar Champará, el cual muestra una reducción del 64% desde 1975 a la actualidad. La tasa de cambio promedio para el periodo 2000-2010 es de 1.03km2 /año. La variación del cambio del volumen del glaciar para el periodo 2000-2010 del Glaciar Champará se determinó a partir de las ecuaciones empíricas propuestos por BARTH y MEIER, (1997) y los modelos de elevación digital generados de las imágenes ASTER de las bandas 3N y 3B. Descriptores: Flujo Glaciar, Teledetección, Sensor ASTER, LANDSAT 5 TM, Glaciar Champará. ABSTRACT It has been estimated, the change in glacier area and volume using remote sensing tools, based on the processing and interpretation of images acquired from the ASTER sensor aboard the Terra satellite, being, the study area the glacier Champará, the studio period covers 2000 to 2010. The methodology used to estimate the glacier's surface area was used Normalized Difference Index of Snow (NDSI) and the Index Normalized Difference Water (NDWI), which serves to remove water that initially pro glacier ice is considered. Based on this methodology can be seen, a gradual variation of the Glacier area Champará, which shows a 64% reduction from 1975 to present. The average exchange rate for the period 2000-2010 is 1.03km2/año. The variation of the volume of the glacier for the period 2000-2010 the glacier Champará was determined from the empirical equations proposed by BARTH and MEIER, (1997) and digital elevation models generated from the ASTER image of the bands 3N and 3B. Keywords: Glacier flow, Remote Sensing, Sensor ASTER, LANDSAT 5 TM, Glacier Champará.

Equivalent Capacitance Approach to Calculate Effective Roughness Dielectric Parameters for Copper Foils on Printed Circuit Boards

Effective roughness dielectric (ERD) is a homogeneous lossy dielectric layer of certain thickness with effective (averaged) dielectric parameters. The ERD layer is used to model copper foil roughness in printed circuit board interconnects by being placed on a smooth conductor surface to substitute an inhomogeneous transition layer between a conductor and laminate substrate dielectric. This work derives the ERD parameters based on the understanding that there is a gradual variation of concentration of metallic inclusions in the transition layer between the dielectric and foil. The gradual variation can be structured as thin layers that are obtained using the equivalent capacitance approach. The concentration profile is extracted from scanning electron microscopy or high-resolution optical microscopy. As the concentration of metallic particles increases along the axis normal to the laminate dielectric and foil boundary, two regions can be discerned: an insulating (prepercolation) region and a conducting (percolation) region. The rates of increase in effective loss (or corresponding conductivity) in these two regions differ significantly. The proposed model of equivalent capacitance with gradient dielectric is applied to a number of different types of copper foils. The frequency-dependent dielectric parameters of the homogenized ERD are calculated from the equivalent capacitance. The results are validated using 3D numerical electromagnetic simulations. There are two types of numerical models: with homogeneous ERD parameters and layered. Both models show excellent agreement with measurements.