Determination of Compton profiles at solid surfaces from first-principles calculations

Projected momentum distributions of electrons, i.e. Compton profiles above the topmost atomic layer have recently become experimentally accessible by kinetic electron emission in grazing-incidence scattering of atoms at atomically flat single crystal metal surfaces. Sub-threshold emission by slow projectiles was shown to be sensitive to high-momentum components of the local Compton profile near the surface. We present a method to extract momentum distribution, Compton profiles, and Wigner and Husimi phase space distributions from ab-initio density-functional calculations of electronic structure. An application for such distributions to scattering experiments is discussed.Comment: 13 pages, 5 figures, submitted to PR

Ethernet - a survey on its fields of application

During the last decades, Ethernet progressively became the most widely used local area networking (LAN) technology. Apart from LAN installations, Ethernet became also attractive for many other fields of application, ranging from industry to avionics, telecommunication, and multimedia. The expanded application of this technology is mainly due to its significant assets like reduced cost, backward-compatibility, flexibility, and expandability. However, this new trend raises some problems concerning the services of the protocol and the requirements for each application. Therefore, specific adaptations prove essential to integrate this communication technology in each field of application. Our primary objective is to show how Ethernet has been enhanced to comply with the specific requirements of several application fields, particularly in transport, embedded and multimedia contexts. The paper first describes the common Ethernet LAN technology and highlights its main features. It reviews the most important specific Ethernet versions with respect to each application field’s requirements. Finally, we compare these different fields of application and we particularly focus on the fundamental concepts and the quality of service capabilities of each proposal

Many-Electron Systems with Constrained Current

A formulation for transport in an inhomogeneous, interacting electron gas is described. Electronic current is induced by a constraint condition imposed as a vector Lagrange multiplier. Constrained minimization of the total energy functional on the manifold of an arbitrary constant current leads to a many-electron Schroedinger equation with a complex, momentum-dependent potential. Constant current Hartree-Fock and Kohn-Sham approximations are formulated within the method and application to transport for quantum wires is developed. No appeal is made to near equilibrium conditions or other approximations allowing development of a general ab initio electronic transport formulation

Enzymatic Surface Erosion of High Tensile Strength Polycarbonates Based on Natural Phenols

Surface erosion has been recognized as a valuable design tool for resorbable biomaterials within the context of drug delivery devices, surface coatings, and when precise control of strength retention is critical. Here we report on high tensile strength, aromatic−aliphatic polycarbonates based on natural phenols, tyrosol (Ty) and homovanillyl alcohol (Hva), that exhibit enzymatic surface erosion by lipase. The Young’s moduli of the polymers for dry and fully hydrated samples are 1.0 to 1.2 GPa and 0.8 to 1.2 GPa, respectively. Typical characteristics of enzymatic surface erosion were confirmed for poly(tyrosol carbonate) films with concomitant mass-loss and thickness-loss at linear rates of 0.14 ± 0.01 mg cm−2 d−1 and 3.0 ± 0.8 μm d−1, respectively. The molecular weight and the mechanical properties of the residual films remained constant. Changing the ratio of Ty and Hva provided control over the glass transition temperature (Tg) and the enzymatic surface erosion: increasing the Hva content in the polymers resulted in higher Tg and lower enzymatic erosion rate. Polymers with more than 50 mol % Hva were stable at 37 °C in enzyme solution. Analysis on thin films using quartz crystal microbalance with dissipation (QCM-D) demonstrated that the onset temperature of the enzymatic erosion was approximately 20 °C lower than the wet Tg for all tested polymers. This new finding demonstrates that relatively high tensile strength polycarbonates can undergo enzymatic surface erosion. Moreover, it also sheds light on the connection between Tg and enzymatic degradation and explains why few of the high strength polymers follow an enzyme-meditated degradation pathway

Association of hydrophobically-modified poly(ethylene glycol) with fusogenic liposomes

AbstractWe present results on using cooperative interactions to shield liposomes by incorporating multiple hydrophobic anchoring sites on polyethylene glycol (PEG) polymers. The hydrophobically-modified PEGs (HMPEGs) are comb-graft polymers with strictly alternating monodisperse PEG blocks (Mw=6, 12, or 35 kDa) bonded to C18 stearylamide hydrophobes. Cooperativity is varied by changing the degree of oligomerization at a constant ratio of PEG to stearylamide. Fusogenic liposomes prepared from N-C12-DOPE:DOPC 7:3 (mol:mol) were equilibrated with HMPEGs. Affinity for polymer association to liposomes increases with the degree of oligomerization; equilibrium constants (given as surface coverage per equilibrium concentration of free polymer) for 6 kDa PEG increased from 6.1±0.8 (mg/m2)/(mg/ml) for 2.5 loops to 78.1±12.2 (mg/m2)/(mg/ml) for 13 loops. In contrast, the equilibrium constant for distearoylphosphatidylethanolamine-poly(ethylene glycol) (DSPE-PEG5k) was 0.4±0.1 (mg/m2)/(mg/ml).The multi-loop HMPEGs demonstrate higher levels of protection from complement binding than DSPE-PEG5k. Greater protection does not correlate with binding strength alone. The best shielding was by HMPEG6k-DP3 (with three 6 kDa PEG loops), suggesting that PEG chains with adequate surface mobility provide optimal protection from complement opsonization. Complement binding at 30 min and 12 h demonstrates that protection by multi-looped PEGs is constant whereas DSPE-PEG5k initially protects but presumably partitions off of the surface at longer times

Complex-band structure: a method to determine the off-resonant electron transport in oligomers

We validate that off-resonant electron transport across {\it ultra-short} oligomer molecular junctions is characterised by a conductance which decays exponentially with length, and we discuss a method to determine the damping factor via the energy spectrum of a periodic structure as a function of complex wavevector. An exact mapping to the complex wavevector is demonstrated by first-principle-based calculations of: a) the conductance of molecular junctions of phenyl-ethynylene wires covalently bonded to graphitic ribbons as a function of the bridge length, and b) the complex-band structure of poly-phenyl-ethynylene.Comment: version to appear in Chem Phys Lett; 8 pages, 4 figures; minor changes to the 06/08/03 submission (nomenclature and added concluding remark

Enhancement of plasma protein adsorption and osteogenesis of hMSCs by functionalized siloxane coatings for titanium implants

A series of sol–gel derived silicon based coatings were developed to improve the osseointegration of commer- cial titanium dental implants. The osseointegration starts with a positive interaction between the implant surface and surrounding tissues, which is facilitated by the adsorption of plasma proteins onto the biomaterial surface immediately after implantation. It is likely that the enhancement of protein adsorption to titanium implants leads to a better implant/tis- sue integration. In addition, silica based biomaterials have been shown to promote osteoblast differentiation. To improve the protein adsorption and the osteogenesis, meth- yltrimethoxysilane (MTMOS), tetraethoxysilane (TEOS), 3- glycidoxypropyltrimethoxysilane (GPTMS), and gelatin were selected to coat titanium surfaces. Compared with non- coated titanium, the functionalized coatings enhanced the adsorption of adhesive proteins such as fibronectin and colla- gen. The Si release was successfully modulated by the con- trol of the chemical composition of the coating, showing a higher dissolution rate with the gelatin and GPTMS incorpo- ration. While the roughness of commercial implants seemed to promote the adhesion of mesenchymal stem cells (MSC), the osteogenic differentiation was greater on surfaces with Si-coatings. In this study, an improved osteogenic surface has been achieved by using the siloxane-gelatin coatings and such coatings can be used in dental implants to promote osseointegration

Developing a Suitable Model for Water Uptake for Biodegradable Polymers Using Small Training Sets

Prediction of the dynamic properties of water uptake across polymer libraries can accelerate polymer selection for a specific application. We first built semiempirical models using Artificial Neural Networks and all water uptake data, as individual input. These models give very good correlations (R2>0.78 for test set) but very low accuracy on cross-validation sets (less than 19% of experimental points within experimental error). Instead, using consolidated parameters like equilibrium water uptake a good model is obtained (R2=0.78 for test set), with accurate predictions for 50% of tested polymers. The semiempirical model was applied to the 56-polymer library of L-tyrosine-derived polyarylates, identifying groups of polymers that are likely to satisfy design criteria for water uptake. This research demonstrates that a surrogate modeling effort can reduce the number of polymers that must be synthesized and characterized to identify an appropriate polymer that meets certain performance criteria

Engineering silk fibroin-based nerve conduit with neurotrophic factors for proximal protection after peripheral nerve injury

Artificial nerve conduits capable of adequately releasing neurotrophic factors are extensively studied to bridge nerve defects. However, the lack of neurotrophic factors in the proximal area and their visible effects in axonal retrograde transport following nerve injury is one of the factors causing an incomplete nerve regeneration. Herein, an advanced conduit made of silk fibroin is produced, which can incorporate growth factors and promote an effective regeneration after injury. For that, enzymatically crosslinked silk fibroin-based conduits are developed to be used as a platform for the controlled delivery of neurotrophic factors. Nerve growth factor and glial-cell line derived neurotrophic factor (GDNF) are incorporated using two different methodologies: i) crosslinking and ii) absorption method. The release profile is measured by ELISA technique. The bioactivity of the neurotrophic factors is evaluated in vitro by using primary dorsal root ganglia. When implanted in a 10 mm sciatic nerve defect in rats, GDNF-loaded silk fibroin conduits reveal retrograde neuroprotection as compared to autografts and plain silk fibroin conduit. Therefore, the novel design presents a substantial improvement of retrograde trafficking, neuronsâ protection, and motor nerve reinnervation.This work was supported by C.R.C.’s Ph.D. scholarship (Norte-08-5369-FSE-000037) and awarded FLAD scholarship (Proj. 29/2018). The FCTdistinctions attributed to J.M.O. (IF/00423/2012 and IF/01285/2015) andJ.S.-C. (IF/00115/2015) under the Investigador FCT program are alsogreatly acknowledged. The authors also thank Ijaz Ahmed from the BMEdepartment and Joe Steel from NJCBM, both from Rutgers University, fortheir important contribution in this scientific paper. The New Jersey Centerfor Biomaterials at Rutgers University provided additional support for this study. The authors acknowledge the project: “Nano-accelerated nerve re-generation and optogenetic empowering of neuromuscular functionality”(ref. PTDC/NAN-MAT/29936/2017)

Organizational metrics of interchromatin speckle factor domains: integrative classifier for stem cell adhesion & lineage signaling.

Stem cell fates on biomaterials are influenced by the complex confluence of microenvironmental cues emanating from soluble growth factors, cell-to-cell contacts, and biomaterial properties. Cell-microenvironment interactions influence the cell fate by initiating a series of outside-in signaling events that traverse from the focal adhesions to the nucleus via the cytoskeleton and modulate the sub-nuclear protein organization and gene expression. Here, we report a novel imaging-based framework that highlights the spatial organization of sub-nuclear proteins, specifically the splicing factor SC-35 in the nucleoplasm, as an integrative marker to distinguish between minute differences of stem cell lineage pathways in response to stimulatory soluble factors, surface topologies, and microscale topographies. This framework involves the high resolution image acquisition of SC-35 domains and imaging-based feature extraction to obtain quantitative nuclear metrics in tandem with machine learning approaches to generate a predictive cell state classification model. The acquired SC-35 metrics led to \u3e 90% correct classification of emergent human mesenchymal stem cell (hMSC) phenotypes in populations of hMSCs exposed for merely 3 days to basal, adipogenic, or osteogenic soluble cues, as well as varying levels of dexamethasone-induced alkaline phosphatase (ALP) expression. Early osteogenic cellular responses across a series of surface patterns, fibrous scaffolds, and micropillars were also detected and classified using this imaging-based methodology. Complex cell states resulting from inhibition of RhoGTPase, β-catenin, and FAK could be classified with \u3e 90% sensitivity on the basis of differences in the SC-35 organizational metrics. This indicates that SC-35 organization is sensitively impacted by adhesion-related signaling molecules that regulate osteogenic differentiation. Our results show that diverse microenvironment cues affect different attributes of the SC-35 organizational metrics and lead to distinct emergent organizational patterns. Taken together, these studies demonstrate that the early organization of SC-35 domains could serve as a “fingerprint” of the intracellular mechanotransductive signaling that governs growth factor- and topography-responsive stem cell states