Use of fine aggregate matrix for computational modeling of low temperature fracture of asphalt concrete

In this study, a discrete element computational model is applied to simulate the fracture behavior of asphalt mixtures at low temperatures. In this model, coarse aggregates are explicitly represented by rigid spherical particles. The bonds that connect these particles represent the fine aggregate matrix (FAM), which is defined as the combination of asphalt binder and fine aggregates. The bending beam rheometer (BBR) tests are performed to determine the strength and Young’s modulus of FAM at low temperatures. The model is then used to simulate the semi-circular bend (SCB) tests on the mixtures. The model is verified by a series of BBR and SCB tests on both conventional and graphite nano-platelet modified asphalt materials. The comparison between the experimental and simulated results indicates that the peak load capacity of the SCB specimens is primarily governed by the tensile strength of the FAM. However, in order to capture the entire load–displacement curve of the SCB specimens, one needs to employ a softening constitutive model of the FAM, which requires the information on its fracture energy. Several experimental methods for measuring the fracture energy of FAM are discussed for future prediction of the complete load–displacement response of asphalt mixtures at low temperatures.     

Order Statistics in the Farey Sequences in Sublinear Time and Counting Primitive Lattice Points in Polygons

We present the first sublinear-time algorithms for computing order statistics in the Farey sequence and for the related problem of ranking. Our algorithms achieve a running times of nearly O(n ^2/3), which is a significant improvement over the previous algorithms taking time O(n). We also initiate the study of a more general problem: counting primitive lattice points inside planar shapes. For rational polygons containing the origin, we obtain a running time proportional to D ^6/7, where D is the diameter of the polygon. This work represents a merging of 19 and 21, with additional extensions.     

Anticipation and the artificial: aesthetics, ethics, and synthetic life

If complexity is a necessary but not sufficient premise for the existence and expression of the living, anticipation is the distinguishing characteristic of what is alive. Anticipation is at work even at levels of existence where we cannot refer to intelligence. The prospect of artificially generating aesthetic artifacts and ethical constructs of relevance to a world in which the natural and the artificial are coexistent cannot be subsumed as yet another product of scientific and technological advancement. Beyond the artificial, the synthetic conjures the understanding of aesthetics and ethics no longer from the perspective of the How? type of question, but rather the Why? Given the current infatuation with synthetic biology (i.e., making life from non-life), there is a practical consequence to such considerations. Synthetic life, as any other form of life, implies the possibility of evolution. Anticipation, which is the underlying factor of evolution, is thus expected. At the level of human existence, anticipation is expressed, for instance (but not exclusively), in aesthetic forms and ethical values. This translates, in turn, into an argument for the role aesthetics and ethics play in the process. Consequently, to qualify as life, the synthesis of the physical and the living will have to efficiently handle ambiguity. Current computational facilities, regardless of their nature or performance, operate exclusively in the semiotic domain of the well defined non-ambiguous.     

Properties of X-, C- and L-band repeat-pass interferometric SAR coherence in Mediterranean pine forests affected by fires

Synthetic Aperture Radar (SAR) data has been investigated to determine the relationship between burn severity and interferometric coherence at three sites affected by forest fires in a hilly Mediterranean environment. Repeat-pass SAR images were available from the TerraSAR-X, ERS-1/2, Envisat ASAR and ALOS PALSAR sensors. Coherence was related to measurements of burn severity (Composite Burn Index) and remote sensing estimates expressed by the differenced normalized burn ratio (dNBR) index. In addition, the effects of topography and weather on coherence estimates were assessed. The analysis for a given range of local incidence angle showed that the co-polarized coherence increases with the increase of burn severity at X- and C-band whereas cross-polarized coherence was practically insensitive to burn severity. Higher sensitivity to burn severity was found at L-band for both co- and cross-polarized channels. The association strength between coherence and burn severity was strongest for images acquired under stable, dry environmental conditions. When the local incidence angle is accounted for the determination coefficients increased from 0.6 to 0.9 for X- and C-band. At L-band the local incidence angle had less influence on the association strength to burn severity.     

Spiking neural P systems with extended rules: universality and languages

We consider spiking neural P systems with rules allowed to introduce zero, one, or more spikes at the same time. The motivation comes both from constructing small universal systems and from generating strings; previous results from these areas are briefly recalled. Then, the computing power of the obtained systems is investigated, when considering them as number generating and as language generating devices. In the first case, a simpler proof of universality is obtained, while in the latter case we find characterizations of finite and recursively enumerable languages (without using any squeezing mechanism, as it was necessary in the case of standard rules). The relationships with regular languages are also investigated.     

Null controllability of an infinite dimensional SDE with state- and control-dependent noise

We consider a controlled stochastic linear differential equation with state- and control-dependent noise in a Hilbert space H. We investigate the relation between the null controllability of the equation and the existence of the solution of “singular” Riccati operator equations. Moreover, for a fixed interval of time, the null controllability is characterized in terms of the dual state. Examples of stochastic PDEs are also considered.     

Study on highly thermostable low-k polymer films based on fluorene-containing polyetherimides

Highly thermostable low-k polymer films with potential applications as dielectric materials in microelectronic industry were synthesized starting from 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride and various diamines. A polyetherimide/silica nanocomposite film was obtained using methyltriethoxysilane as precursor of inorganic phase. The chemical structure was confirmed by FTIR and ¹H NMR spectroscopy. Water vapor's sorption capacity, thermal stability, glass transition temperature, thermal diffusivity, specific heat, thermal conductivity, and dielectric characteristics of the films were determined. All the films exhibited excellent thermal stability, with an initial decomposition temperature in the range of 500–530°C. They showed low dielectric constant of 1.98–2.86 and low dielectric loss of 0.0037–0.011, at a frequency of 1 Hz and room temperature. The subglass γ- and β-relaxations, primary α-relaxation, and conductivity relaxation processes were discussed according to the chemical structure of the samples. Quantitative structure–property relationship (QSPR) study was conducted, and linear regression models were formulated to describe the causal relationships between different parameters and polyetherimide properties.     

Cohesive Modeling of Fracture in Asphalt Mixtures at Low Temperatures

Low temperature cracking is the major distress observed in asphalt pavements in the northern US and Canada. In the past years fracture mechanics concepts were introduced to investigate the fracture properties of asphalt mixtures at low temperatures. In this paper the cohesive zone model (CZM) is used to describe the fracture behavior of asphalt mixtures at low temperatures and the interface element is used to numerically simulate the material response under monotonic loading. The simulation is calibrated with the experimental results from a newly proposed semi circular bend (SCB) test. A parametric analysis of the input material properties indicates that the tensile strength has a significant effect on the peak load in the SCB configuration, the modulus has a strong effect on the calculated stiffness of the SCB specimen, and the fracture energy influences the post-peak behavior of the asphalt mixtures. The calibrated numerical model was applied to simulate the low temperature cracking in a simplified asphalt pavement and to study the influence of these material parameters on the performance of asphalt pavements.     

New Investigations with Lupane Type A-Ring Azepane Triterpenoids for Antimycobacterial Drug Candidate Design

Twenty lupane type A-ring azepano-triterpenoids were synthesized from betulin and its related derivatives and their antitubercular activity against Mycobacterium tuberculosis, mono-resistant MTB strains, and nontuberculous strains Mycobacterium abscessus and Mycobacterium avium were investigated in the framework of AToMIc (Anti-mycobacterial Target or Mechanism Identification Contract) realized by the Division of Microbiology and Infectious Diseases, NIAID, National Institute of Health. Of all the tested triterpenoids, 17 compounds showed antitubercular activity and 6 compounds were highly active on the H37Rv wild strain (with MIC 0.5 µM for compound 7), out of which 4 derivatives also emerged as highly active compounds on the three mono-resistant MTB strains. Molecular docking corroborated with a machine learning drug-drug similarity algorithm revealed that azepano-triterpenoids have a rifampicin-like antitubercular activity, with compound 7 scoring the highest as a potential M. tuberculosis RNAP potential inhibitor. FIC testing demonstrated an additive effect of compound 7 when combined with rifampin, isoniazid and ethambutol. Most compounds were highly active against M. avium with compound 14 recording the same MIC value as the control rifampicin (0.0625 µM). The antitubercular ex vivo effectiveness of the tested compounds on THP-1 infected macrophages is correlated with their increased cell permeability. The tested triterpenoids also exhibit low cytotoxicity and do not induce antibacterial resistance in MTB strains.