Stochastic Electronic Structure Theory

Accurate electronic structure calculations are difficult in general, and broadly applicable approximationsare at a premium. This thesis describes three stochastic approaches to tackle this problem, focusing on systems where inter-electron interactions are relevant. First, correlated wave functions based on symmetry projection are studied using variational Monte Carlo (VMC). Second, we describe a stochastic multireference perturbation theory that allows calculations with reference spaces larger than possible with conventional deterministic approaches. Finally, we present advances in a projection method called Auxiliary Field Quantum Monte Carlo (AFQMC), achieved using multiconfigurational trial states. Symmetry projection is an effective way to encode electron correlation, and it can be accomplished cheaply in VMC by simply restricting the random walk to the correct symmetry sector. However, VMC is afflicted by the sign problem indirectly through difficulties in sampling and optimization of sophisticated wave functions. With significant improvements in these areas, we can do accurate VMC calculations in challenging systems like the two-dimensional Hubbard model and hydrogen chains. Multireference perturbation theories have been developed to describe intermediate-range electronic interactions, which are difficult to represent with a variational wave function. These calculations are expensive undertakings for large reference spaces due to the requirement to calculate and store up to four-body reduced density matrices. We derive a scheme to sample the perturber energies in a VMC-like fashion that obviates the need to store these eight-index tensors. We demonstrate the utility of this approach by performing perturbation theory calculations in transition metal-containing enzyme active sites that require large reference spaces for even qualitatively accurate energetics. AFQMC is a versatile tool to describe electron correlation in challenging systems. In this projection method, the sign problem is mitigated or eliminated by leveraging information from a trial wave function approximating the state of interest. We describe efficient algorithms for incorporating accurate wave functions from quantum chemistry like coupled-cluster and selected configuration interaction as trial states within AFQMC. Based on these developments, we present unbiased calculations on much larger spaces than hitherto possible and systematic improvements in biased simulations.</p

Outcome analysis of primary cemented bipolar hemiarthroplasty in elderly unstable intertrochanteric fractures during covid phase in Central India

Background: The incidence of inter-trochanteric fractures of the femur is very high in the elderly population. The world-wide incidence of all hip fractures is around 402 per 100000 and the incidence of Intertrochanteric fracture is estimated to be around 171 per 100000 in 2019. All the operative conditions were different during covid phase. We needed early ambulation of our patients for a faster recovery and avoid long stay in hospitals. Methods: 30 patients with unstable intertrochanteric fractures were operated by bipolar hemiarthroplasty during the covid phase. All the patients were followed up at 2, 6, 10 and 16 weeks. Harris hip score and FIM score were assessed. Results: Mean Harris hip score achieved was 87 at 16 weeks and mean FIM score achieved was 78.9 at 16 weeks indicating good functional outcomes. The outcome was excellent in 23.4%, good in 63.3%, fair in 10% and poor in 3.3% as per HHS. Conclusions: This procedure offered pain free mobile hip with early mobilization, easy rehabilitation and early return to functional level, when standard techniques were used

FORMULATION AND CHARACTERIZATION OF HPMC AND HPMCAS BASED SOLID DISPERSIONS OF FENOFIBRATE: A COMPARATIVE STUDY

Objective: The aim of the present study was to investigate the effect of novel polymeric carriers and to develop solid dispersion formulation that could improve in vitro profile of Fenofibrate (FB). Methods: Spray drying technique was used to fabricate solid dispersions with hydrophilic carriers, mainly hydroxypropyl methylcellulose (HPMC) and hydroxypropyl methylcellulose acetate succinate (HPMCAS). Solid dispersions in the form of spray-dried powder were characterized with respect to the pure drug and the corresponding physical mixtures by optical microscopy, x-ray diffraction (XRD), fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). Size and morphology of optimized solid dispersion were performed by scanning electron microscopy (SEM). Furthermore, in vitro dissolution comparisons were carried out between the optimized solid dispersion against the pure drug and the physical mixtures. Results: Solubility studies demonstrated that the solubility of FB was not affected by pH change. The transformation of crystalline FB into an amorphous solid dispersion powder has been clearly demonstrated by optical microscopy. The molecular dispersion of drug in the dispersion matrix prepared by spray drying was confirmed in XRD and DSC studies. IR spectroscopy was observed with negligible incompatibility of the drug with polymers. Spherical morphology was observed in SEM with no evidence of FB crystals. The prepared solid dispersions exhibited dissolution improvement as compared to the pure drug and spray dried FB in 0.05 M SLS, with HPMCAS as the superior carrier over HPMC. Conclusion: The present study vouches better in vitro profile of FB from spray-dried HPMCAS based solid dispersions

Use of capillary flow to create flexible and embedded electronics

Continuous printing processes are attractive for manufacturing electronic devices on flexible substrates and embedding electronically functional materials into polymers. In this presentation, a new method to create flexible electronics based on embedded conductive networks is presented. The route involves creating the electronic architecture in a curable polymer layer on a flexible substrate and then using capillary flow to create the conductive network. In this presentation, the method will be discussed with an emphasis on the role of processing. A key process step is liquid ink flow in channels. Liquid flow in open capillary channels depends on the channel geometry and ink properties, including the drying behavior. The length of travel of a reactive silver ink down an open capillary was measured for a variety of rectangular capillary geometries with widths of ~1 – 100 µm and depths from ~3 – 20 µm1. For a capillary channel of fixed depth, the length of travel of the ink initially increased with the channel width due to a lessening of the flow resistance and then decreased due to a decrease in the capillary pressure driving force and the increased importance of drying, which raises the viscosity and eventually halts flow. To gain a better understanding of these phenomena, scaled up channels with dimensions in the 50 – 250 µm range were created and a long working distance microscope was used to track the velocity of the liquid flowing in the capillary. For non-evaporating liquids (e.g., glycerol), channels with height-to-width ratios close to 1 gave the highest rates of liquid flow. Using polyvinyl alcohol – water solution as a model system2, experiments are underway to determine the influence of concurrent drying on liquid front velocity and extent of travel. The goal of this study is to not only explore the relative importance of drying compared to capillarity, but also to uncover key parameters for ink and capillary design so that the extent of ink travel can be engineered

Use of capillary flow to create flexible and embedded electronics

Continuous printing processes are attractive for manufacturing electronic devices on flexible substrates and embedding electronically functional materials into polymers. In this presentation, a new method to create flexible electronics based on embedded conductive networks is presented. The route involves creating the electronic architecture in a curable polymer layer on a flexible substrate and then using capillary flow to create the conductive network. In this presentation, the method will be discussed with an emphasis on the role of processing. A key process step is liquid ink flow in channels. Liquid flow in open capillary channels depends on the channel geometry and ink properties, including the drying behavior. The length of travel of a reactive silver ink down an open capillary was measured for a variety of rectangular capillary geometries with widths of ~1 – 100 µm and depths from ~3 – 20 µm1. For a capillary channel of fixed depth, the length of travel of the ink initially increased with the channel width due to a lessening of the flow resistance and then decreased due to a decrease in the capillary pressure driving force and the increased importance of drying, which raises the viscosity and eventually halts flow. To gain a better understanding of these phenomena, scaled up channels with dimensions in the 50 – 250 µm range were created and a long working distance microscope was used to track the velocity of the liquid flowing in the capillary. For non-evaporating liquids (e.g., glycerol), channels with height-to-width ratios close to 1 gave the highest rates of liquid flow. Using polyvinyl alcohol – water solution as a model system2, experiments are underway to determine the influence of concurrent drying on liquid front velocity and extent of travel. The goal of this study is to not only explore the relative importance of drying compared to capillarity, but also to uncover key parameters for ink and capillary design so that the extent of ink travel can be engineered