Impact of oxalate ligand in co-precipitation route on morphological properties and phase constitution of undoped and Rh-Doped BaTiO3 nanoparticles

In order to design and tailor materials for a specific application like gas sensors, the synthesis route is of great importance. Undoped and rhodium-doped barium titanate powders were successfully synthesized by two routes; oxalate route and classic route (a modified conventional route where solid-state reactions and thermal evaporation induced precipitation takes place). Both powders were calcined at different temperatures. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX) and Brunauer-Emmet-Teller (BET) analyses are employed to identify the phases and polymorphs, to determine the morphology, the chemical composition and the specific surface area of the synthesized materials, respectively. The so-called oxalate route yields pure BaTiO3 phase for undoped samples at 700?C and 900?C (containing both cubic and tetragonal structures), while the classic route-synthesized powder contains additional phases such as BaCO3, TiO2 and BaTi2O5. Samples of both synthesis routes prepared by the addition of Rh contain no metallic or oxide phase of rhodium. Instead, it was observed that Ti was substituted by Rh at temperatures 700 °C and 900 °C and there was some change in the composition of BaTiO3 polymorph (increase of tetragonal structure). Heat-treatments above these temperatures show that rhodium saturates out of the perovskite lattice at 1000 °C, yielding other secondary phases such as Ba3RhTi2O9 behind. Well-defined and less agglomerated spherical nanoparticles are obtained by the oxalic route, while the classic route yields particles with an undefined morphology forming very large block-like agglomerates. The surface area of the synthesized materials is higher with the oxalate route than with the classic route (4 times at 900 °C). The presence of the oxalate ligand with its steric hindrance that promotes the uniform distribution and the homogeneity of reactants could be responsible for the great difference observed between the powders prepared by two preparation routes

The Role of Regulated mRNA Stability in Establishing Bicoid Morphogen Gradient in Drosophila Embryonic Development

The Bicoid morphogen is amongst the earliest triggers of differential spatial pattern of gene expression and subsequent cell fate determination in the embryonic development of Drosophila. This maternally deposited morphogen is thought to diffuse in the embryo, establishing a concentration gradient which is sensed by downstream genes. In most model based analyses of this process, the translation of the bicoid mRNA is thought to take place at a fixed rate from the anterior pole of the embryo and a supply of the resulting protein at a constant rate is assumed. Is this process of morphogen generation a passive one as assumed in the modelling literature so far, or would available data support an alternate hypothesis that the stability of the mRNA is regulated by active processes? We introduce a model in which the stability of the maternal mRNA is regulated by being held constant for a length of time, followed by rapid degradation. With this more realistic model of the source, we have analysed three computational models of spatial morphogen propagation along the anterior-posterior axis: (a) passive diffusion modelled as a deterministic differential equation, (b) diffusion enhanced by a cytoplasmic flow term; and (c) diffusion modelled by stochastic simulation of the corresponding chemical reactions. Parameter estimation on these models by matching to publicly available data on spatio-temporal Bicoid profiles suggests strong support for regulated stability over either a constant supply rate or one where the maternal mRNA is permitted to degrade in a passive manner

A Software Tool to Model Genetic Regulatory Networks. Applications to the Modeling of Threshold Phenomena and of Spatial Patterning in Drosophila

We present a general methodology in order to build mathematical models of genetic regulatory networks. This approach is based on the mass action law and on the Jacob and Monod operon model. The mathematical models are built symbolically by the Mathematica software package GeneticNetworks. This package accepts as input the interaction graphs of the transcriptional activators and repressors of a biological process and, as output, gives the mathematical model in the form of a system of ordinary differential equations. All the relevant biological parameters are chosen automatically by the software. Within this framework, we show that concentration dependent threshold effects in biology emerge from the catalytic properties of genes and its associated conservation laws. We apply this methodology to the segment patterning in Drosophila early development and we calibrate the genetic transcriptional network responsible for the patterning of the gap gene proteins Hunchback and Knirps, along the antero-posterior axis of the Drosophila embryo. In this approach, the zygotically produced proteins Hunchback and Knirps do not diffuse along the antero-posterior axis of the embryo of Drosophila, developing a spatial pattern due to concentration dependent thresholds. This shows that patterning at the gap genes stage can be explained by the concentration gradients along the embryo of the transcriptional regulators

Inferring robust gene networks from expression data by a sensitivity-based incremental evolution method

<p>Abstract</p> <p>Background</p> <p>Reconstructing gene regulatory networks (GRNs) from expression data is one of the most important challenges in systems biology research. Many computational models and methods have been proposed to automate the process of network reconstruction. Inferring robust networks with desired behaviours remains challenging, however. This problem is related to network dynamics but has yet to be investigated using network modeling.</p> <p>Results</p> <p>We propose an incremental evolution approach for inferring GRNs that takes network robustness into consideration and can deal with a large number of network parameters. Our approach includes a sensitivity analysis procedure to iteratively select the most influential network parameters, and it uses a swarm intelligence procedure to perform parameter optimization. We have conducted a series of experiments to evaluate the external behaviors and internal robustness of the networks inferred by the proposed approach. The results and analyses have verified the effectiveness of our approach.</p> <p>Conclusions</p> <p>Sensitivity analysis is crucial to identifying the most sensitive parameters that govern the network dynamics. It can further be used to derive constraints for network parameters in the network reconstruction process. The experimental results show that the proposed approach can successfully infer robust GRNs with desired system behaviors.</p

An Extended Gene Protein/Products Boolean Network Model Including Post-Transcriptional Regulation

Background: Networks Biology allows the study of complex interactions between biological systems using formal, well structured, and computationally friendly models. Several different network models can be created, depending on the type of interactions that need to be investigated. Gene Regulatory Networks (GRN) are an effective model commonly used to study the complex regulatory mechanisms of a cell. Unfortunately, given their intrinsic complexity and non discrete nature, the computational study of realistic-sized complex GRNs requires some abstractions. Boolean Networks (BNs), for example, are a reliable model that can be used to represent networks where the possible state of a node is a boolean value (0 or 1). Despite this strong simplification, BNs have been used to study both structural and dynamic properties of real as well as randomly generated GRNs. Results: In this paper we show how it is possible to include the post-transcriptional regulation mechanism (a key process mediated by small non-coding RNA molecules like the miRNAs) into the BN model of a GRN. The enhanced BN model is implemented in a software toolkit (EBNT) that allows to analyze boolean GRNs from both a structural and a dynamic point of view. The open-source toolkit is compatible with available visualization tools like Cytoscape and allows to run detailed analysis of the network topology as well as of its attractors, trajectories, and state-space. In the paper, a small GRN built around the mTOR gene is used to demonstrate the main capabilities of the toolkit. Conclusions: The extended model proposed in this paper opens new opportunities in the study of gene regulation. Several of the successful researches done with the support of BN to understand high-level characteristics of regulatory networks, can now be improved to better understand the role of post-transcriptional regulation for example as a network-wide noise-reduction or stabilization mechanism

Percutaneous pedicle screw implantation for refractory low back pain: from manual 2D to fully robotic intraoperative 2D/3D fluoroscopy.

Many surgical treatments for chronic low back pain that is refractory to medical treatments focus on spine stabilization. One of the main surgical procedures consists of placing an interbody cage with bone grafts associated with pedicle screws [2, 25, 30]. This technique can be performed using different approaches: a large open posterior approach, tubular approaches (minimal open) or percutaneously (minimally invasive percutaneous or MIP) [5, 28]. One of the main difficulties is to precisely locate the screws into the pedicle avoiding especially infero-medial pedicle breaches. This difficulty is even great- er when working percutaneously. This paper focuses on percutaneously placed pedicle screws (PPS), reports the use of a robotic multi-axis 2D/3D fluoros- copy to enhance the accuracy of pedicle screw placement and reviews other strategies and results reported in the literature

Proceedings of papers presented at the RBRS Annual Symposium, Brussels, 19.11.2011

When dealing with chronic low back pain refractory to medical treatments (LBPR), spine stabilization can be a very effective option. This surgical strategy requires most of the time implantation of pedicle screws (1, 5) which can be performed through either a large open posterior approach, or tubular approaches (minimal open) or even percutaneously (minimally invasive percutaneous) (2, 3, 6). A precise placement of these screws is paramount in particular to avoid any additional nerve root lesion. Working percutaneously reduces the aggression on the patient’s muscular system but increases the difficulty of being intrapedicular. Percutaneous surgery requires improved intraoperative imaging quality control. Our use of 'percutaneously placed pedicle screws (PPS), 'led us to test different intraoperative imaging systems reaching a climax of efficiency with the robotic multi-axis 2D/3D fluoroscopy Artis Zeego of Siemens. We report our experience using this system for PPS placement in the treatment of LBPR

Primary intracranial germinoma mimicking meningioma in an elderly patient

International audienc

[Dysembryoplastic neuroepithelial tumors. Analysis of 16 cases.]

Objectives. - We report on 16 cases of dysembryoplastic Neuroepithelial tumor (DNT) treated in the Nancy University Hospital from 1987 to 1997 Patients and methods. - There were 9 males and 7 females. Mean age at onset of symptoms was 9.5 years (range: 3 months to 29 years) and the mean age at surgery was 16 years. Nine patients experienced partial complex seizures, 5 patients generalized seizures, I patient partial seizures with secondary generalization and one patient ataxia. The diagnosis of DNT was made under consideration of clinical, radiological and neuropathological features. All patients underwent surgery. Results. - Removal of the tumor was complete for 10 patients, subtotal or partial for 6 patients. Histological examination revealed that 7 cases were specific forms of DNT due to the presence of the specific glioneuronal element. For the 9 remained cases, the diagnosis of DNT could only be mane with the consideration of clinical and radiological features. Mean post-surgical follow-rip was 3.5 years (range : 1-8 years). Fight patients were seizures-free, 7 had a significative reduction in seizures frequency with minimal anti-convulsivant treatment. The patient with ataxia remained unchanged. Far the patients with partial resection of the tumor, follow-up MRI and CT scan showed no significant growth of the remnant and the remaining patients have had no recurrence to date. Conclusion. - The recognition of this surgically curable entity is mandatory. Knowledge of the good prognosis associated with the DNT is essential to avoid deleterious side effects of overtreatment by radiotherapy and/or chemotherapy