Long-time dynamics of de Gennes' model for reptation

Diffusion of a polymer in a gel is studied within the framework of de Gennes' model for reptation. Our results for the scaling of the diffusion coefficient D and the longest relaxation time tau are markedly different from the most recently reported results, and are in agreement with de Gennes' reptation arguments: D ~ 1/N^2 and tau ~ N^3. The leading exponent of the finite-size corrections to the diffusion coefficient is consistent with the value of -2/3 that was reported for the Rubinstein model. This agreement suggests that its origin might be physical rather than an artifact of these models.Comment: 5 pages, 5 figures, submitted to J. Chem. Phy

Novel Biodegradable Composite of Calcium Phosphate Cement and the Collagen I Mimetic P-15 for Pedicle Screw Augmentation in Osteoporotic Bone

Osteoporotic vertebral fractures often necessitate fusion surgery, with high rates of implant failure. We present a novel bioactive composite of calcium phosphate cement (CPC) and the collagen I mimetic P-15 for pedicle screw augmentation in osteoporotic bone. Methods involved expression analysis of osteogenesis-related genes during osteoblastic differentiation by RT-PCR and immunostaining of osteopontin and Ca2+ deposits. Untreated and decalcified sheep vertebrae were utilized for linear pullout testing of pedicle screws. Bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry (DEXA). Expression of ALPI II (p p p p p p p p p = 0.04) with PMMA, and 1252 ± 131 N (p < 0.0078) with CPC-P-15. CPC-P-15 induces osteoblastic differentiation of human MES and improves pullout resistance of pedicle screws in osteoporotic and non-osteoporotic bone

A computationally inspired in-vivo approach identifies a link between amygdalar transcriptional heterogeneity, socialization and anxiety

Pharmaceutical breakthroughs for anxiety have been lackluster in the last half-century. Converging behavior and limbic molecular heterogeneity has the potential to revolutionize biomarker-driven interventions. However, current in vivo models too often deploy artificial systems including directed evolution, mutations and fear induction, which poorly mirror clinical manifestations. Here, we explore transcriptional heterogeneity of the amygdala in isogenic mice using an unbiased multidimensional computational approach that segregates intra-cohort reactions to moderate situational adversity and intersects it with high content molecular profiling. We show that while the computational approach stratifies known features of clinical anxiety including nitric oxide, opioid and corticotropin signaling, previously unrecognized druggable biomarkers emerge, such as calpain11 and scand1. Through ingenuity pathway analyses, we further describe a role for neurosteroid estradiol signaling, heat shock proteins, ubiquitin ligases and lipid metabolism. In addition, we report a remarkable behavioral pattern that maps to molecular features of anxiety in mice through counterphobic social attitudes, which manifest as increased, yet spatially distant socialization. These findings provide an unbiased approach for interrogating anxiolytics, and hint toward biomarkers underpinning behavioral and social patterns that merit further exploration

Explicit solution for a Gaussian wave packet impinging on a square barrier

The collision of a quantum Gaussian wave packet with a square barrier is solved explicitly in terms of known functions. The obtained formula is suitable for performing fast calculations or asymptotic analysis. It also provides physical insight since the description of different regimes and collision phenomena typically requires only some of the terms.Comment: To be published in J. Phys.

Dynamics of complex molecules and multidimensional nuclear magnetic resonance

The relation between multidimensional Nuclear Magnetic Resonance (NMR) techniques and the dynamical behaviour of complex molecules is considered in this work. Two important NMR-interactions, the chemical shift and anisotropic contributions in the case of restricted motions of molecules, are introduced and discussed in two well-established models for polymer dynamics. Complex molecules exhibit non-trivial time-dependent interactions between relaxing or diffusing units. Dense polymer melts are considered, where the crossing of chains is prohibited and excluded-volume interactions affect the dynamics. Multidimensional NMR-techniques allow for the characterization and correlation of molecular conformations at successive points in time. The notion of "dimensionality" refers to the number of correlated points in time; here the two-dimensional case is considered. In the first part of the thesis, analytical investigations for a simplified model of polymer dynamics are presented. A two-point correlation-function or, equivalently, a joint probability - with which the outcome of a 2D NMR experiment can be compared - is calculated for the Rubinstein-model. The results are displayed in histograms, which have been designed according to 2D NMR spectra. In the second part of the thesis, computer-simulations of a three-dimensional coarse grained model for polymer dynamics were carried out. Monte-Carlo simulations of the bondfluctuation-model for chains of different length were performed with particular emphasis on neighbourhood-conditions of monomers and bond-orientations. The correlation-functions obtained were visualized in two-dimensional spectra. From both models, information on local dynamical properties of polymer chain segments was extracted and related to the effects on simulated 2D NMR spectra