Atomic structure and Mott nature of the insulating charge density wave phase of 1T-TaS2.

Using x-ray pair distribution function (PDF) analysis and computer modeling, we explore structure models for the complex charge density wave (CDW) phases of layered 1T-TaS2that both well capture their atomic-level features and are amenable to electronic structure calculations. The models give the most probable position of constituent atoms in terms of 3D repetitive unit cells comprising a minimum number of Ta-S layers. Structure modeling results confirm the emergence of star-of-David (SD) like clusters of Ta atoms in the high-temperature incommensurate (IC) CDW phase and show that, contrary to the suggestions of recent studies, the low-temperature commensurate (C) CDW phase expands upon cooling thus reducing lattice strain. The C-CDW phase is also found to preserve the stacking sequence of Ta-S layers found in the room temperature, nearly commensurate (NC) CDW phase to a large extent. DFT based on the PDF refined model shows that bulk C-CDW 1T-TaS2also preserves the insulating state of individual layers of SD clusters, favoring the Mott physics description of the metal-to-insulator (NC-CDW to C-CDW) phase transition in 1T-TaS2. Our work highlights the importance of using precise crystal structure models in determining the nature of electronic phases in complex materials.

MDANSE: An Interactive Analysis Environment for Molecular Dynamics Simulations.

The MDANSE software-Molecular Dynamics Analysis of Neutron Scattering Experiments-is presented. It is an interactive application for postprocessing molecular dynamics (MD) simulations. Given the widespread use of MD simulations in material and biomolecular sciences to get a better insight for experimental techniques such as thermal neutron scattering (TNS), the development of MDANSE has focused on providing a user-friendly, interactive, graphical user interface for analyzing many trajectories in the same session and running several analyses simultaneously independently of the interface. This first version of MDANSE already proposes a broad range of analyses, and the application has been designed to facilitate the introduction of new analyses in the framework. All this makes MDANSE a valuable tool for extracting useful information from trajectories resulting from a wide range of MD codes.

Structure and dynamics of ionic micelles: MD simulation and neutron scattering study.

Fully atomistic molecular dynamics (MD) simulations have been carried out on sodium dodecyl sulfate (SDS), an anionic micelle, and three cationic (CnTAB; n = 12, 14, 16) micelles, investigating the effects of size, the form of the headgroup, and chain length. They have been used to analyze neutron scattering data. MD simulations confirm the dynamical model of global motion of the whole micelle, segmental motion (headgroup and alkyl chain), and fast torsional motion associated with the surfactants that is used to analyze the experimental data. It is found that the solvent surrounding the headgroups results in their significant mobility, which exceeds that of the tails on the nanosecond time scale. The middle of the chain is found to be least mobile, consolidating the micellar configuration. This dynamical feature is similar for all the ionic micelles investigated and therefore independent of headgroup form and charge and chain length. Diffusion constants for global and segmental motion of the different micelles are consistent with experimentally obtained values as well as known structural features. This work provides a more realistic model of micelle dynamics and offers new insight into the strongly fluctuating surface of micelles which is important in understanding micelle dispersion and related functionality, like drug delivery.

New treatment strategies in idiopathic nephrotic syndrome.

Idiopathic nephrotic syndrome (INS) is probably due to a plasma factor of immunologic origin. This circulating factor probably interacts with the glomerular filtration barrier and is responsible for massive proteinuria. Most patients respond to steroids. However, a considerable proportion of children run a steroid dependent course. Cyclosporine A (CyA) and cyclophosphamide (CyP) have been classical treatment strategies for such cases, but specific toxicity limits the use of these drugs. Mycophenolate mofetil (MMF), an inhibitor of inosine monophosphate dehydrogenase and thus de novo purine synthesis. Clinical trials have demonstrated the efficacy of MMF in steroid dependent NS and in children with nephrotoxicity due to prolonged CyA treatment. While MMF is a well established strategy against steroid dependency, rituximab (RTX) has emerged as a new treatment option in case of calcineurin inhibitor dependency. Non-compliance to steroid therapy can be responsible for multiple relapses and may be misinterpreted as steroid dependency and may therefore lead to unjustified increase of the immunosuppressive treatment. Triamcinolone acetonide, a long acting steroid for intramuscular injection, can replace the usual oral prednisone treatment if non-compliance is suspected. Whereas the treatment of the primary course of INS is well established, steroid dependent and steroid resistant forms are still a challenge for pediatric nephrologists. Both under-treatment with multiple relapses with disease or steroid associated morbidity on the one hand and over-treatment with specific side effects of immunosuppressive drugs may have severe consequences for the patients. The narrow path between steroid side effects and potential nephrotoxicity emphasizes the need for individualized management in severe form of INS.

Pediatric idiopathic nephrotic syndrome: treatment strategies in steroid dependent and steroid resistant forms.

Idiopathic nephrotic syndrome (INS) is defined as massive proteinuria and hypoalbuminemia associated with dyslipidemia and generalized oedema in most cases. It is thought to be due to a plasma factor of immunologic origin. Most cases are steroid responsive. However, a considerable proportion of children run a steroid dependent course. Calcineurin inhibitors and alkylating agents have been classical treatment strategies for such cases, but specific toxicity limits the use of these drugs. Mycophenolate mofetil (MMF) is an inhibitor of inosine monophosphate dehydrogenase and thus de novo purine synthesis. Several uncontrolled clinical trials have demonstrated the efficacy of MMF in steroid dependent NS with or without prior use of CyP and in children with nephrotoxicity due to prolonged CyA treatment. Non-compliance to steroid therapy can be responsible for multiple relapses and may be misinterpreted as steroid dependency and may therefore lead to unjustified increase of immunosuppressive treatment. Triamcinolone acetonide, a long acting steroid for intramuscular injection, can replace the usual oral prednisone treatment if non-compliance is suspected. Whereas the treatment of the primary course of INS is well established, steroid dependent and steroid resistant forms are still a challenge for pediatric nephrologists. Both under-treatment with multiple relapses with disease or steroid associated morbidity on the one hand and over-treatment with specific side effects of immunosuppressive drugs may have severe consequences for the patients.