The Structural Performance of Stone-Masonry Bridges

The structural performance of old stone-masonry bridges is examined by studying such structures located at the North-West of Greece, declared cultural heritage structures. A discussion of their structural system is included, which is linked with specific construction details. The dynamic characteristics of four stone bridges, obtained by temporary in situ instrumentation, are presented together with the mechanical properties of their masonry constituents. The basic assumptions of relatively simple three-dimensional (3-D) numerical simulations of the dynamic response of such old stone bridges are discussed based on all selected information. The results of these numerical simulations are presented and compared with the measured response obtained from the in situ experimental campaigns. The seismic response of one such bridge is studied subsequently in some detail as predicted from the linear numerical simulations under combined dead load and seismic action. The performance of the same bridge is also examined applying 3-D non-linear numerical simulations with the results used to discuss the structural performance of stone-masonry bridges that either collapsed or may be vulnerable to future structural failure. Issues that influence the structural integrity of such bridges are discussed combined with the results of the numerical and in situ investigation. Finally, a brief discussion of maintenance issues is also presented

Quantitative identification of functional connectivity disturbances in neuropsychiatric lupus based on resting-state fMRI: a robust machine learning approach

Neuropsychiatric systemic lupus erythematosus (NPSLE) is an autoimmune entity comprised of heterogenous syndromes affecting both the peripheral and central nervous system. Research on the pathophysiological substrate of NPSLE manifestations, including functional neuroimaging studies, is extremely limited. The present study examined person-specific patterns of whole-brain functional connectivity in NPSLE patients (n = 44) and age-matched healthy control participants (n = 39). Static functional connectivity graphs were calculated comprised of connection strengths between 90 brain regions. These connections were subsequently filtered through rigorous surrogate analysis, a technique borrowed from physics, novel to neuroimaging. Next, global as well as nodal network metrics were estimated for each individual functional brain network and were input to a robust machine learning algorithm consisting of a random forest feature selection and nested cross-validation strategy. The proposed pipeline is data-driven in its entirety, and several tests were performed in order to ensure model robustness. The best-fitting model utilizing nodal graph metrics for 11 brain regions was associated with 73.5% accuracy (74.5% sensitivity and 73% specificity) in discriminating NPSLE from healthy individuals with adequate statistical power. Closer inspection of graph metric values suggested an increased role within the functional brain network in NSPLE (indicated by higher nodal degree, local efficiency, betweenness centrality, or eigenvalue efficiency) as compared to healthy controls for seven brain regions and a reduced role for four areas. These findings corroborate earlier work regarding hemodynamic disturbances in these brain regions in NPSLE. The validity of the results is further supported by significant associations of certain selected graph metrics with accumulated organ damage incurred by lupus, with visuomotor performance and mental flexibility scores obtained independently from NPSLE patients. View Full-Text Keywords: neuropsychiatric systemic lupus erythematosus; rs-fMRI; graph theory; functional connectivity; surrogate data; machine learning; visuomotor ability; mental flexibilit

Typical and aberrant functional brain flexibility: lifespan development and aberrant organization in traumatic brain injury and dyslexia

Intrinsic functional connectivity networks derived from different neuroimaging methods and connectivity estimators have revealed robust developmental trends linked to behavioural and cognitive maturation. The present study employed a dynamic functional connectivity approach to determine dominant intrinsic coupling modes in resting-state neuromagnetic data from 178 healthy participants aged 8–60 years. Results revealed significant developmental trends in three types of dominant intra- and inter-hemispheric neuronal population interactions (amplitude envelope, phase coupling, and phase-amplitude synchronization) involving frontal, temporal, and parieto-occipital regions. Multi-class support vector machines achieved 89% correct classification of participants according to their chronological age using dynamic functional connectivity indices. Moreover, systematic temporal variability in functional connectivity profiles, which was used to empirically derive a composite flexibility index, displayed an inverse U-shaped curve among healthy participants. Lower flexibility values were found among age-matched children with reading disability and adults who had suffered mild traumatic brain injury. The importance of these results for normal and abnormal brain development are discussed in light of the recently proposed role of cross-frequency interactions in the fine-grained coordination of neuronal population activity

Modeling of Hydrogen Storage Materials: A Reactive Force Field for NaH

Parameterization of a reactive force field for NaH is done using ab initio derived data. The parameterized force field(ReaxFFNaH) is used to study the dynamics governing hydrogen desorption in NaH. During the abstraction process of surface molecular hydrogen charge transfer is found to be well described by the parameterized force field. To gain more insight into the mechanism governing structural transformation of NaH during thermal decomposition a heating run in a molecular dynamics simulation is done. The result shows that a clear signature of hydrogen desorption is the fall in potential energy surface during heating

Greater repertoire and temporal variability of cross-frequency coupling (CFC) modes in resting-state neuromagnetic recordings among children with reading difficulties

Cross-frequency, phase-to-amplitude coupling (PAC) between neuronal oscillations at rest may serve as the substrate that supports information exchange between functionally specialized neuronal populations both within and between cortical regions. The study utilizes novel algorithms to identify prominent instantaneous modes of cross-frequency coupling and their temporal stability in resting state magnetoencephalography (MEG) data from 25 students experiencing severe reading difficulties (RD) and 27 age-matched non-impaired readers (NI). Phase coherence estimates were computed in order to identify the prominent mode of PAC interaction for each sensor, sensor pair, and pair of frequency bands (from δ to γ) at successive time windows of the continuous MEG record. The degree of variability in the characteristic frequency-pair PACf1−f2 modes over time was also estimated. Results revealed a wider repertoire of prominent PAC interactions in RD as compared to NI students, suggesting an altered functional substrate for information exchange between neuronal assemblies in the former group. Moreover, RD students showed significant variability in PAC modes over time. This temporal instability of PAC values was particularly prominent: (a) within and between right hemisphere temporo-parietal and occipito-temporal sensors and, (b) between left hemisphere frontal, temporal, and occipito-temporal sensors and corresponding right hemisphere sites. Altered modes of neuronal population coupling may help account for extant data revealing reduced, task-related neurophysiological and hemodynamic activation in left hemisphere regions involved in the reading network in RD. Moreover, the spatial distribution of pronounced instability of cross-frequency coupling modes in this group may provide an explanation for previous reports suggesting the presence of inefficient compensatory mechanisms to support reading

Self-aligned photonic defect microcavities with site-controlled quantum dots

Despite the superiority in quantum properties, self-assembled semiconductor quantum dots face challenges in terms of scalable device integration because of their random growth positions, originating from the Stranski-Krastanov growth mode. Even with existing site-controlled growth techniques, for example, nanohole or buried stressor concepts, a further lithography and etching step with high spatial alignment requirements isnecessary to accurately integrate QDs into the nanophotonic devices. Here, we report on the fabrication and characterization of strain-induced site-controlled microcavities where site-controlled quantum dots are positioned at the antinode of the optical mode field in a self-aligned manner without the need of any further nano-processing. We show that the Q-factor, mode volume, height, and the ellipticity of site-controlled microcavities can be tailored by the size of an integrated AlAs/Al2O3 buried stressor, with an opening ranging from 1 to 4 $\mu$m. Lasing signatures, including super-linear input-output response, linewidth narrowing near threshold, and gain competition above threshold, are observed for a 3.6-$\mu$m self-aligned cavity with a Q-factor of 18000. Furthermore, by waiving the rather complex lateral nano-structuring usually performed during the fabrication process of micropillar lasers and vertical-cavity surface emitting lasers, quasi-planar site-controlled cavities exhibit no detrimental effects of excitation power induced heating and thermal rollover. Our straightforward deterministic nanofabrication concept of high-quality quantum dot microcavities integrates seamlessly with the industrial-matured manufacturing process and the buried-stressor techniques, paving the way for exceptional scalability and straightforward manufacturing of high-\b{eta} microlasers and bright quantum light sources

On the liquefaction failure of an earth dam

In an effort to better assess the potential for sliding and liquefaction failure of earthen dams when subjected to earthquake loadings, a dynamic finite element approach focusing on these two failure mechanisms as well as on the vital role of the pore water pressure was undertaken. The constitutive response of the granular soil skeleton and its coupling with the fluid phase is formulated based on the Blot dynamic equations of motion. The constitutive model for the soil material was assumed to be linear with nonlinear terms included in the hysteretic damping terms. Despite the linear character of this theoretical model, one can still draw important conclusions regarding the stability and the liquefaction resistance of the cross-section. As an example, a hypothetical earth dam constructed over a saturated soil layer was considered. The steady state conditions of in-situ stress and pore pressure distributions in both the embankment and the foundation are evaluated and implemented in the stability and liquefaction criteria in conjunction with the dynamic analysis. The latter is carried out in the frequency domain and it reflects the response of the dam-foundation system to a seismic excitation. The computational aspect of the study is performed with finite element analysis. A transmitting boundary formulation for the two phase material was used to treat the infinite space problem. It is anticipated that the intensity of the earthquake input and certain soil properties have a profound effect on the failure susceptibility of the dam section. To address the uncertainties regarding the true values of such parameters, the analysis considered them parametrically

Phase-Fitted Runge–Kutta Pairs of Orders 8(7)

A new phase fitted Runge–Kutta pair of orders 8(7) which is a modification of a well known explicit Runge–Kutta pair for the integration of periodic initial value problems is presented. Numerical experiments show the efficiency of the new pair in a wide range of oscillatory problems. © 2017 Elsevier B.V

Low-threshold lasing of optically pumped micropillar lasers with Al0.2_{0.2}Ga0.8_{0.8}As/Al0.9_{0.9}Ga0.1_{0.1}As distributed Bragg reflectors

We report on the design, realization and characterization of optically pumped micropillar lasers with low-absorbing Al$_{0.2}$Ga$_{0.8}$As/Al$_{0.9}$Ga$_{0.1}$As dielectric Bragg reflectors (DBRs) instead of commonly used GaAs/AlGaAs DBRs. A layer of (In, Ga)As quantum dots (QDs) is embedded in the GaAs $\lambda$-cavity of as an active medium. We experimentally study the lasing characteristics of the fabricated micropillars by means of low-temperature photoluminescence with varying pump laser's wavelength between 532 nm and 899 nm. The incorporation of 20% Al content in the DBRs opens an optical pumping window from 700 nm to 820 nm, where the excitation laser light can effectively reach the GaAs cavity above its bandgap, while remaining transparent to the DBRs. This results in a substantially improved pump efficiency, a low lasing threshold, and a high thermal stability. Pump laser wavelengths outside of the engineered spectral window lead to low pump efficiency due to strong absorption by the top DBR, or inefficient excitation of pump-level excitons, respectively. The superiority of the absorption-free modified DBRs is demonstrated by simply switching the pump laser wavelength from 671 nm to 708 nm, which crosses the DBRs absorption edge and drastically reduces the lasing threshold by more than an order of magnitude from (363.5 $\pm$ 18.5) $\mu$W to (12.8 $\pm$ 0.3) $\mu$W