Science

Internship (Ref. SPECT_5) Design study of a time-of-flight spectrometer for extreme-condition experiments with montecarlo methods

Internship (Ref. SPECT_5) design study of a time-of-flight spectrometer for extreme-condition experiments with montecarlo methods

The growing scientific interest in the physical properties of matter in extreme conditions such as very high pressure and temperature calls for dedicated and optimized experimental tools. Time-of-Flight (ToF) spectrometers are in principle the instruments of choice to meet the scientific interests and quality standards required for extreme-condition experiments. However, the ToF instruments currently available have not been optimized for such studies. We are planning to perform a design study of a hybrid ToF spectrometer, i.e. a ToF instrument equipped with a monochromator and chopper system, for optimum performance in extreme conditions and with small samples. This design study will be based on Monte Carlo simulation techniques (McStas) developed and optimized for neutron ray-tracing computation. The necessary software packages are available at the ILL and can be run in a standard operation mode. Expertise in, and hardware components for, running the software packages are present. Preliminary design studies of an instrument called RAMSES (RApid Measurement and Special Environment time-of-flight Spectrometer) have been already performed. For these reasons, we believe it will be possible to complete the optimization work within four months, a period well suited to a student internship.

Activities of the trainee: 
The trainee’s activities will primarily involve computer simulations, together with a few analytical analyses, for the design of the hybrid time-of-flight instrument located at the end position of a dedicated cold-neutron guide:

  • Definition of a dedicated guide (new H15) for the hybrid ToF instrument RAMSES III (McStas calculations)
  • Optimization of guide components for best performance in terms of flux and divergence (McStas calculations)
  • Identification of central components of the primary spectrometer and their geometry for best performance in the time-focusing mode
  • Optimization of the primary spectrometer components for best performance for experiments on mm3-sized samples.

Key words: computer simulation; ray tracing calculation; neutron spectroscopy
Level required: 4th year university studies in physics
Notes: This post is an internship with a maximum duration of 4 months

Please send your application directly to the supervisor: Michael Koza, email: koza(at)ill.fr

Internship (Ref. SPECT_7) Effect of chemical or structural disorder on the lattice dynamics of the brownmillerite ionic conductors sr1-xcaxfeo2.5 and sr2scgao5. An ab-initio study

Internship (Ref. SPECT_7) Effect of chemical or structural disorder on the lattice dynamics of the brownmillerite ionic conductors sr1-xcaxfeo2.5 and sr2scgao5. An ab-initio study

Oxygen ion conductors at low temperatures are materials of major interest for a host of applications, such as fuel cells, battery electrodes and sensors. The discovery of oxygen reversible intercalation into Brownmillerite-type structures down to moderate temperatures is considered of paramount importance. Despite this, SrFeO2.5 has been shown to be a good conductor down to RT, while the iso-structural CaFeO2.5 material only conducts oxygen at high temperatures (over 1000 K). Inelastic neutron scattering (INS) studies on solid solutions of Sr1-xCaxFeO2.5 (chemical disorder) have revealed dramatic differences in the low energy part of vibrational DOS (density of states). At the same time, Raman spectra on end members are also drastically different. Similarly, Sr2ScGaO5 shows good ionic conduction at moderate temperatures, but the Brownmillerite-type structure, with ordered Sc, Ga and vacancy sites, and the cubic-related structure, with random Sc, Ga and vacancy positions, differ in the onset temperature of conduction and conduction mechanism. This is reflected again in the difference observed in the low energy part of vibrational DOS and Raman spectra. 
To understand the microscopic origin of these differences, detailed DFT (density functional theory) calculations on several solid solutions of Sr1-xCaxFeO2.5 and random vacancy supercells of Sr2ScGaO5 are necessary. The experiments will allow us to validate the calculations and the calculations can then be used to gain a better understanding of the material's properties.
The results will shed light on the way that chemical or structural (other than oxygen) disorder affects the ionic conduction properties of this material, helping us to gain a deeper understanding of the factors which promote or hinder ionic conduction.

Activities of the trainee: 
The trainee will run advanced level simulations (solid solutions and random vacancy supercells) with the CRYSTAL code, extract useful electronic and vibrational properties (band structure, vibrational DOS, Raman spectra), compare the data obtained with existing experimental data, and critically interpret the results. He/she will correlate all the experimental and simulated data to establish trends in electronic/vibrational properties. If the results of this work prove to be interesting, the trainee will take an active part in writing articles.

Key words: ionic conductors; chemical or structural disorder; ab-initio simulations; comparison with INS and Raman spectra
Level required: 5th year university studies in physics or theoretical chemistry
Notes: This post is an internship with a maximum duration of 5 months 

Please send your application directly to the supervisor: Andrea Piovano, email: piovano(at)ill.fr
 

Internship (Ref. SPECT_8) Adsorption energy and geometry of dihydrogen on a pt-substituted uio-67 mof

Internship (Ref. SPECT_8) Adsorption energy and geometry of dihydrogen on a pt-substituted uio-67 mof

Microporous materials have proven to be highly valuable materials for industrial applications such as petrochemistry, catalysis, selective separation and gas storage. In this regard, metal-organic frameworks (MOFs) open up new possibilities for the design of both the geometrical shape and chemical properties of the internal surface, enabling very high pore volumes and surface areas. Moreover, they are in principle able to display novel functionalities, potentially exploitable for a number of applications in catalysis, as sensors, in gas separation, and/or storage.
The synthesis of a Pt-functionalised UiO-67 MOF creates exposed metal species from the PtCl2 functionalisation that are considered to induce enhanced adsorption properties during gas dosing. For this reason, the evolution of the rotational transition of H2 molecules (15 meV) during hydrogen uptake has been investigated by inelastic neutron scattering up to 25 bar pressure. 
Simulations of the bare UiO-67 have been performed and the matching with experimental vibrational DOS (density of states) is remarkable, opening the way for a reliable and detailed study of the adsorption of H2 on the different adsorption sites. The calculation of the adsorption energies and geometries will make it possible to assign with consistency the features detected during the INS experiment.

Activities of the trainee: 
The trainee will run advanced level simulations (adsorption of molecules on surfaces) with the CRYSTAL code, extract useful electronic and vibrational properties (band structure, vibrational DOS, Raman spectra, adsorption energies), compare the data obtained with existing experimental data, and critically interpret the results. If the results of this work prove to be interesting, the trainee will take an active part in writing articles.

Key words: metal-organic framework; UiO-67; H2 adsorption; ab-initio simulations; comparison with INS spectra
Level required: 5th year university studies in physics or theoretical chemistry
Notes: This post is an internship with a maximum duration of 3 months

Please send your application directly to the supervisor: Andrea Piovano, email: piovano(at)ill.fr

Internship (Ref. LSS_4) An efficient and versatile microfluid system for electrophysiology measurements

Internship (Ref. LSS_4) An efficient and versatile microfluid system for electrophysiology measurements

Electrophysiology is a technique involving the measurement of the flow of ions across a lipid membrane, with the aim of assessing the membrane's permeability or of studying the proteins specifically devoted to the transport of the ions, including at the single molecule scale. This method is particularly challenging and requires special equipment capable of measuring electric current in pico amps. We use the technique on artificial membranes, created at the interface between two droplets surrounded by a lipid monolayer. 
Through the use of microfabrication techniques, we would like to improve our experimental setup in order to reduce the volume of reagents required and increase its sensitivity and the quality of the signal recorded. 

Activities of the trainee:
After familiarising yourself with the equipment in the laboratory, you will design and produce milli/micro-fluidic devices by 3D printing and PDMS moulding, and then evaluate their efficiency:

  • formation and characterisation of the artificial membrane, 
  • comparison with the current device, in terms of sample quantity, signal quality and ease of use
  • estimation of the limits of the new device: membrane size, possibility of multiplexing, etc. 

Key words: microfluids; 3D printing; electrophysiology
Level required: Equivalent of 1st year university studies in a general technical field (covering instrumentation and measurement techniques)
Notes: This post is an internship with a maximum duration of 2 months 

Please send your application directly to the supervisor: Anne Martel, email: martela(at)ill.fr
 

Internship (Ref. LSS_7) Bio-inspired emulsions and microemulsions with cholesteryl esters as model systems for ldl/hdl particles

Internship (Ref. LSS_7) bio-inspired emulsions and microemulsions with cholesteryl esters as model systems for ldl/hdl particles

Low-density lipoproteins (LDL) and high-density lipoproteins (HDL), commonly referred to as “bad” and “good” cholesterol, are biological assemblies of phospholipids and cholesterol, apolipoproteins and triglycerides. Their main role is to transport fat in the extracellular fluid of organisms. The role of HDL and LDL in common diseases is well known, the main distinction between the two being simply their size, i.e. the number of fatty molecules they transport: HDL particles are small (containing around 100 lipids and as many proteins), LDL particles are large (containing up to 1000s of lipids and far fewer proteins), while even larger particles exist. LDL have a low stability and therefore increase the risk of atherosclerosis (artery wall thickening) by deposition, while HDL take away these deposits as a hydrophobic cargo. The stability of these assemblies and therefore the associated risk of cardiovascular disease is, however, poorly understood.
HDL is in fact a microemulsion in soft matter terms (stable at equilibrium), while LDL is an emulsion (unstable at equilibrium). In between, a miniemulsion domain should be present (presenting long-term stability).
Using simple models based on conventional phospholipids for the stabilizing shell, and various triglycerides and cholesteryl esters for the hydrophobic core, we aim to elucidate, in particular by Small-Angle Neutron Scattering (SANS), the lipoproteins (shape, size, size distribution), including the composition and organisation of their shell and core. Phase diagrams where the composition is varied will help us determine the loading thresholds in triglycerides between microemulsion, miniemulsion and emulsion, based on the choice of triglyceride, for a given composition in phospholipids and amount of cholesteryl esters. Finally, the influence of apolipoproteins (decorating the lipoprotein’s outer surface) on the phase diagram will be evaluated by the trainee.

Activities of the trainee:
Bibliography, sample preparation, phase diagrams from visual observations, Differential Scanning Calorimetry (melting of the triglyceride/cholesteryl ester core), Isothermal Titration Calorimetry (for the addition of apolipoprotein), Dynamic and Static Light Scattering (determination of overall dimensions), Zetametry (determination of surface charge), Small-Angle Neutron and X-ray Scattering (structural characterization).

Key words: small-angle neutron scattering; emulsions and microemulsions; high-density lipoproteins and low-density lipoproteins (HDL and LDL); cholesterol esters; model HDL/LDL particles
Level required: 5th year university studies in physical chemistry
Notes: This post is an internship with a maximum duration of 5 months

Please send your application directly to the supervisor: Sylvain Prévost, email:  prevost(at)ill.eu

Internship (REF. THEO_1) Dynamical transition of proteins, as a function of spatio-temporal scale

Internship (REF. THEO_1) dynamical transition of proteins, as a function of spatio-temporal scale

By dynamical transition we mean the deviation from linear behaviour of the variation in mean-square displacements of atoms, as a function of temperature. Several experiments have shown the existence of a dynamical transition in hydrated protein systems around 180 – 200 K. This transition reveals an activated change in the conformational states of the protein, as a function of temperature. We have a simple view of the dynamical transition as that of at least two conformational states corresponding to potential wells separated by a potential barrier. As, at low temperatures, the (harmonic) motion of the protein atoms is situated around the minimum of the conformational states of lower energies, the mean-square displacements rise linearly with temperature.  At high temperatures the amplitude of the (anharmonic) motion increases, to the point that it crosses the barrier from low-energy conformational states to those of high energies. The result is a non-linear rise in mean-square displacements. A dynamical transition can therefore be summed up as the transition from harmonic motions to anharmonic motions, following the crossing of a potential barrier.

In practice, if we want to study dynamical transition in incoherent neutron scattering experiments, for example, we would classically use the mean-square displacement of the (hydrogen) atoms, obtained from the slope at the origin, as a function of Q2 of the factor or function of the dynamical structure of the incoherent quasi-elastic (? ? 0) scattering of neutrons. The mean-square displacements obtained depend neither on Q nor time, and we therefore consider the protein system as an ensemble in equilibrium averaged over all spatial scales.

The aim of the internship is to study the dynamical transition as a function of Q and of time, to gain a better understanding of how the dynamical transition evolves within a protein. This will require investigating the feasibility of using the multivariate statistical techniques of principal component analysis (PCA) to analyse the dynamical structure function (or mean-square displacements) on the Q and time scales together. These are new techniques in this domain but are certainly promising. They have recently been used at the ILL in a Swedish-ILL collaboration to study the dynamics of an enzyme with and without inhibitor.

Activities of the trainee: 

  1. Use the Bicout-Zaccai dynamical transition model to develop the PCA methodology;
  2. Apply the methodology to analyse the neutron scattering experimental data obtained for proteins by J. Peters (ILL).

Key words: incoherent neutron scattering; dynamical transition; PCA
Level required: 4th year university studies in physics
Notes: This post is an internship with a maximum duration of 5 months. 

Please send your application directly to the supervisor: Dominique Bicout, email: bicout(at)ill.fr