Significant Experimental Effort Research Articles

Reconstruction of air shower muon densities using segmented counters with time resolution

Despite the significant experimental effort made in the last decades, the origin of the ultra-high energy cosmic rays is still largely unknown. Key astrophysical information to identify where these energetic particles come from is provided by their chemical composition. It is well known that a very sensitive tracer of the primary particle type is the muon content of the showers generated by the interaction of the cosmic rays with air molecules. We introduce a likelihood function to reconstruct particle densities using segmented detectors with time resolution. As an example of this general method, we fit the muon distribution at ground level using an array of counters like AMIGA, one of the Pierre Auger Observatory detectors. For this particular case we compare the reconstruction performance against a previous method. With the new technique, more events can be reconstructed than before. In addition the statistical uncertainty of the measured number of muons is reduced, allowing for a better discrimination of the cosmic ray primary mass.

Quantification of chloride in concrete samples using LA-ICP-MS

Inspection of the chloride content in concrete samples is an important factor for determination and planning of maintenance measures. The standard method given by European legislative for chloride determination is the titrimetric Volhard method. However, it requires significant experimental effort, and knowledge about the cement content in the concrete is required. In this work, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is proposed as an alternative method to the commonly used wet-chemical approach. LA-ICP-MS allows analysis of drilled core concrete samples with increased depth resolution, minimal workload for sample preparation, and fast analysis time. Furthermore, exploiting the multi-elemental capabilities of ICP-MS, an in-depth analysis of the sample composition, allowing a differentiation between cement phase and aggregates is feasible. Using this information, selective determination of chloride in the cement phase becomes possible, which helps to increase the reliability of the determined chloride concentrations.

Ocular lubrication

SummaryLubricants are the mainstay of dry eye treatment. Whereas they do not target the disease itself they relief from the symptoms associated with both tear‐deficient and hyper‐evaporative dry eye. The duration of action of lubricants critically depends on the residence time at the ocular surface. This is influenced by the viscosity of the eyedrops, their charge, but also by their ability to bind to mucins. Residence time of drugs at the ocular surface has traditionally been investigated using radio‐active labelling of the drugs. This does, however, have several drawbacks. Labelling changes the molecule thereby potentially changing the residence time. In addition, experiments are costly and require significant experimental effort. We have developed a technique that is capable of measuring tear film thickness using a custom‐built OCT. With this device it is possible to get insight into the residence time of topically administered lubricants. Data for hyaluronic acid, osmoprotective substances and chitosan thiomer are presented.

Insights into the oxygen-based ligand of the low pH component of the Cu(2+)-amyloid-β complex.

In spite of significant experimental effort dedicated to the study of Cu(2+) binding to the amyloid beta (Aβ) peptide, involved in Alzheimer's disease, the nature of the oxygen-based ligand in the low pH component of the Cu(2+)-Aβ(1-16) complex is still under debate. This study reports density-functional-theory-based calculations that explore the potential energy surface of Cu(2+) complexes including N and O ligands at the N-terminus of the Aβ peptide, with a focus on evaluating the role of Asp1 carboxylate in copper coordination. Model conformers including 3, 6, and 17 amino acids have been used to systematically study several aspects of the Cu(2+)-coordination such as the Asp1 side chain conformation, local peptide backbone geometry, electrostatic and/or hydrogen bond interactions, and number and availability of Cu(2+) ligands. Our results show that the Asp1 peptide carbonyl binds to Cu(2+) only if the coordination number is less than four. In contrast, if four ligands are available, the most stable structures include the Asp1 carboxylate in equatorial position instead of the Asp1 carbonyl group. The two lowest energy Cu(2+)-Aβ(1-17) models involve Asp1 COO(-), the N-terminus, and His6 and His14 as equatorial ligands, with either a carbonyl or a water molecule in the axial position. These models are in good agreement with experimental data reported for component I of the Cu(2+)-Aβ(1-16) complex, including EXAFS- and X-ray-derived Cu(2+)-ligand distances, Cu(2+) EPR parameters, and (14)N and (13)C superhyperfine couplings. Our results suggest that at low pH, Cu(2+)-Aβ species with Asp1 carboxylate equatorial coordination coexist with species coordinating the Asp1 carbonyl. Understanding the bonding mechanism in these species is relevant to gain a deeper insight on the molecular processes involving copper-amyloid-β complexes, such as aggregation and redox activity.

Plasmon-induced hot carriers in metallic nanoparticles.

Plasmon-induced hot carrier formation is attracting an increasing research interest due to its potential for applications in photocatalysis, photodetection and solar energy harvesting. However, despite very significant experimental effort, a comprehensive theoretical description of the hot carrier generation process is still missing. In this work we develop a theoretical model for the plasmon-induced hot carrier process and apply it to spherical silver nanoparticles and nanoshells. In this model, the conduction electrons of the metal are described as free particles in a finite spherical potential well, and the plasmon-induced hot carrier production is calculated using Fermi’s golden rule. We show that the inclusion of many-body interactions has only a minor influence on the results. Using the model we calculate the rate of hot carrier generation, finding that it closely follows the spectral profile of the plasmon. Our analysis reveals that particle size and hot carrier lifetime play a central role in determining both the production rate and the energy distribution of the hot carriers. Specifically, larger nanoparticle sizes and shorter lifetimes result in higher carrier production rates but smaller energies, and vice versa. We characterize the efficiency of the hot carrier generation process by introducing a figure of merit that measures the number of high energy carriers generated per plasmon. Furthermore, we analyze the spatial distribution and directionality of these excitations. The results presented here contribute to the basic understanding of plasmon-induced hot carrier generation and provide insight for optimization of the process.

Hydrodynamic analogy approach for modelling reactive absorption

Abstract Design of separation units for reactive gas–liquid systems is usually based on conventional modelling methods employing the stage concept, either equilibrium or rate-based. The parameters of such models (e.g., mass transfer coefficients) are determined experimentally, and, most often, significant experimental effort is necessary when new processes are explored or new types of column internals are developed. In the context of a novel approach based on hydrodynamic analogies, rigorous partial differential transport equations are applied for modelling of non-reactive and reactive separation processes in columns filled with structured packings. The approach has already been verified for distillation and reactive desorption processes. In this work, its application to reactive absorption – also known as chemical absorption – is examined. Different types of reactions appearing in a wide range of absorption systems are considered. To account for absorption processes operated at high gas and liquid loads, an adjustment of the turbulent gas flow description is performed. Therefore, different test systems are used, namely physical absorption of ammonia into water, chemical absorption of sulphur dioxide and chemical absorption of carbon dioxide into sodium hydroxide solutions. The absorption of ammonia and sulphur dioxide took place under turbulent gas flow conditions, while in the absorption of carbon dioxide, the gas flow was laminar. Based on the carbon dioxide system, different types of corrugated sheet packings were compared. The hydrodynamic analogy model was successfully validated using available experimental data.

Searching for high-k RE2O3 nanoparticles embedded in SiO2 glass matrix

Significant experimental effort has been explored to search and characterize high-k materials with magnetodielectric effect (MDE) of series of rare earth (RE) oxide (RE2O3) nanoparticles (NPs) embedded in SiO2 glass matrix by a sol-gel route. Properly annealed sol-gel glass (in which RE = Sm, Gd, and Er) shows colossal response of dielectric constant along with diffuse phase transition and MDE around room temperature. The radial distribution functions, reconstructed from extended x-ray absorption fine structure, show the shortening of RE3 + -O depending on the RE2O3 NP size, which is consistent with oxygen vacancy induced dielectric anomaly. The magnetoresistive MDE is very much conditioned by magnetic property of RE2O3 NP grain, the degree of deformation of the lattice and constituent host.

Development of a local three-dimensional numerical simulation model for the laser forming process of aluminium components

The laser beam forming (LBF) process uses the energy of relatively high-powered lasers to cause permanent deformations of components, through the local introduction of thermal stresses. LBF of aluminium material is a process, complex and sensitive, due to the complicated physical phenomena taking place during laser processing. Therefore, definition of optimal process parameters, such as laser power and processing velocity, which will result to desired bending patterns, as well as investigation of forming limits of various components require significant experimental effort. Herein, numerical simulation of LBF process is used to provide partial solution to the problem, by developing a local Finite Element simulation model, capable to predict temperature fields and deformation shapes of laser beam-treated aluminium specimens. The numerical algorithm is based on a non-linear three-dimensional transient thermal–structural analysis, temperature-dependent thermal and mechanical material properties and a laser beam heat flux model. The developed model is validated through the comparison of numerically predicted distribution of temperatures and bending angles to corresponding experimental data of single and multiple laser beam passes. The validated model is then used to define optimal process parameters for the laser forming process of aluminium panels.

An automated decision‐tree approach to predicting protein interaction hot spots

Protein-protein interactions can be altered by mutating one or more "hot spots," the subset of residues that account for most of the interface's binding free energy. The identification of hot spots requires a significant experimental effort, highlighting the practical value of hot spot predictions. We present two knowledge-based models that improve the ability to predict hot spots: K-FADE uses shape specificity features calculated by the Fast Atomic Density Evaluation (FADE) program, and K-CON uses biochemical contact features. The combined K-FADE/CON (KFC) model displays better overall predictive accuracy than computational alanine scanning (Robetta-Ala). In addition, because these methods predict different subsets of known hot spots, a large and significant increase in accuracy is achieved by combining KFC and Robetta-Ala. The KFC analysis is applied to the calmodulin (CaM)/smooth muscle myosin light chain kinase (smMLCK) interface, and to the bone morphogenetic protein-2 (BMP-2)/BMP receptor-type I (BMPR-IA) interface. The results indicate a strong correlation between KFC hot spot predictions and mutations that significantly reduce the binding affinity of the interface.

Local 3D perturbation experiments for probing the ELM stability

Empirical estimates indicate that the transient divertor power load induced by type-I ELMs in the standard H-mode ITER scenario might result in intolerably short target life times. Significant experimental effort has been put on the exploration of recipes to avoid or at least mitigate the ELM size by external intervention. Experimental ELM mitigation studies (and related modeling) are of interest from different points of views. First, the active intervention gives access to new, externally controlled ELMy discharge scenarios and ELM diagnostic techniques. Second, the ELM response on the type and amplitude of the applied perturbation provides additional hints on the ELM stability. Third, mitigated ELMs, possibly different from spontaneous ones, and their scaling are of interest ‘per se’, in case that mitigation is to be finally applied in ITER. In this contribution we report on ELM mitigation results in ASDEX Upgrade, where we further restrict the scope to those methods involving 3D, local non-axisymmetric perturbations.

Ultrafast resonant polarization interferometry: Towards the first direct detection of vacuum polarization

Vacuum polarization, an effect predicted nearly 70 years ago, is still yet to be directly detected despite significant experimental effort. Previous attempts have made use of large liquid-helium cooled electromagnets which inadvertently generate spurious signals that mask the desired signal. We present a novel approach for the ultra-sensitive detection of optical birefringence that can be usefully applied to a laboratory detection of vacuum polarization. The new technique has a predicted birefringence measurement sensitivity of $\Delta n \sim 10^{20}$ in a 1 second measurement. When combined with the extreme polarizing fields achievable in this design we predict that a vacuum polarization signal will be seen in a measurement of just a few days in duration.

EVOLUTIONARY DESIGN OF GENETIC CIRCUITS AND CELL-CELL COMMUNICATIONS

Synthetic genetic circuits are artificial networks of transcriptional control elements inserted into living cells in order to 'program' cellular behavior. We can extend this application to programming population behavior by incorporating cell-cell communications capabilities. By designing and building such networks, cellular circuit engineers expect to gain insight into how natural genetic networks function with remarkable robustness, stability, and adaptability to changing environments. Programmed cells also have promising applications in biotechnology and medicine. A major challenge that biological circuit engineers face is the difficulty of predicting circuit performance at the design stage, with the consequence that actual construction requires significant experimental effort, even for very simple circuits. To address this fundamental obstacle we propose the use of laboratory evolution methods to create new circuit components and optimize circuit performance inside living cells.

Energy-Conformational studies of ?-endorphins: Identification of plausible folded conformers

β-Endorphins are 31 amino acid endogenous opioid peptides with high receptor affinity and antinociceptive activity. Because of their importance as neurohormones and the significant experimental effort that has been made to understand their structure activity profiles, we have begun to develop procedures that could be useful first to identify low-energy conformers of β-endorphins and ultimately their bioactive form. In the initial studies reported here, we have identified plausible initial structures of the full peptide by calculating and comparing the conformational preference of all possible extended tetrapeptide fragments of β-endorphin starting from each of the first 28 residues. Comparisons of fragment energies suggested two types of compact folded β-endorphin conformers were plausible: a helix–turn–helix and an antiparallel β-sheet conformer. These structures, as well as an extended α-helical and β-strand conformer, were assembled and total geometry optimization performed using the empirical-energy-based program AMBER. The results yield an α-helical structure as the lowest energy form consistent with recently reported NMR studies of β-endorphin. The two more compact folded structures obtained, however, are reasonable starting conformations for further planned molecular dynamics simulation studies and could yield competing low-energy structures as candidates for the bioactive form of these peptides.