Summary
The dynamic performance of base‐isolated buildings can be improved by introducing a tuned mass damper (TMD) at basement, below the isolation floor where most of the earthquake‐induced ...displacement demand is concentrated. In order to enhance the effectiveness of the TMD without simultaneously amplifying the relevant mass ratio, the use of supplemental inertial mass dampers has been envisaged by the authors and other authors in earlier studies. These schemes exploit the mass‐amplification effect of the inerter, a two‐terminal device whose generated force is ideally proportional to the relative acceleration between its terminals. In this paper, we present a review along with a systematic comparative study of six different strategies proposed in the literature, each one featuring a specific combination of mass‐spring‐dashpot elements arranged in series or in parallel with an inerter for the displacement mitigation of base‐isolated structures. Frequency‐response functions of each model are derived in closed form. Optimal design is based on a common strategy, considering a white‐noise random process as seismic input, by minimization of the displacement variance but with an eye also for the superstructure acceleration (associated with forces arising in the superstructure) and for the TMD stroke. Then, the seismic performance of the six systems is assessed considering an ensemble of 52 natural earthquake ground motions, by comparing several response indicators including TMD stroke, deformation of the base‐isolation floor, superstructure acceleration, interstory drifts, base shear, and reactions associated with spring, oil damper, and inertial damper supporting the TMD, which are significant for outlining preliminary economic assessments.
•More than 150 tests for mechanical characterization of extrudable foamed concrete.•Different reinforcement strategies to enhance the flexural strength through fibers.•Short polymer fibers embedded ...in the lightweight cementitious paste and GFRP mesh.•Different curing conditions and fiber contents were investigated.•Optimum reinforcement arrangement with and without GFRP mesh was identified.
An extensive experimental campaign was carried out to investigate the mechanical strength of fiber-reinforced lightweight foamed concrete. The considered foamed concrete was prepared with a viscosity enhancing agent that increases the cohesion and consistency of the cement paste at the fresh state (extrudable foamed concrete). The flexural strength was evaluated on almost 60 small-scale prismatic beam specimens, and the compressive strength on 100 cubic specimens in accordance with two different testing standards for comparative purposes. The effects of three different curing conditions (air, cellophane and water), three target dry densities (400, 600, 800 kg/m3), three fiber contents (0.7%, 2.0%, 5.0%), and the presence of an additional glass-fiber-reinforced-polymer (GFRP) mesh in the tensile zone of the beams (besides the short fibers) were analyzed. The polymer fibers increased the flexural capacity of the beams, especially for the low-density specimens and for the higher contents of fibers (2.0% and, above all, 5.0%), but had a negligible influence on the compressive strength. The additional GFRP mesh combined with the short fibers improved the flexural capacity considerably in all the examined conditions, turning out to be the best strategy for obtaining high mechanical strengths associated with low densities typical of ultra-lightweight concrete elements.
Digital Image Correlation (DIC) provides measurements without disturbing the specimen, which is a major advantage over contact methods. Additionally, DIC techniques provide full-field maps of ...response quantities like strains and displacements, unlike traditional methods that are limited to a local investigation. In this work, an experimental application of DIC is presented to investigate a problem of relevant interest in the civil engineering field, namely the interface behavior between externally bonded fabric reinforced cementitious mortar (FRCM) sheets and concrete substrate. This represents a widespread strengthening technique of existing reinforced concrete structures, but its effectiveness is strongly related to the bond behavior between composite fabric and underlying concrete. To investigate this phenomenon, a set of notched concrete beams are realized, reinforced with FRCM sheets on the bottom face, subsequently cured in different environmental conditions (humidity and temperature) and finally tested up to failure under three-point bending. Mechanical tests are carried out vis-à-vis DIC measurements using two distinct cameras simultaneously, one focused on the concrete front face and another focused on the FRCM-concrete interface. This experimental setup makes it possible to interpret the mechanical behavior and failure mode of the specimens not only from a traditional macroscopic viewpoint but also under a local perspective concerning the evolution of the strain distribution at the FRCM-concrete interface obtained by DIC in the pre- and postcracking phase.
Diffuse gliomas are defined on the isocitrate dehydrogenase (IDH) gene (IDH) mutational mutational status. The most frequent IDH mutation is IDH1 R132H, which is detectable by immunohistochemistry; ...other IDH mutations are rare (10%). IDH mutant gliomas have better prognosis. Further, IDH wild‐type low‐grade (II/III) gliomas have clinical behaviors similar to those of glioblastoma (GBM) and it was suggested that they are submitted to similar post‐surgical treatment. The incidence of IDH mutant gliomas (2%) and that of GBMs with non‐canonical IDH mutations (< 1%) are very low in patients ≥ 55 years. For this reason, it was suggested that immunohistochemistry against IDH1 R132H is sufficient to classify GBM as IDH wild‐type in this age group. However, no indication was provided for IDH mutational testing in low‐grade diffuse gliomas. To address this issue, 273 diffuse gliomas were tested for IDH1 R132H immunohistochemistry. 2/4 diffuse astrocytomas (DAs), 4/9 anaplastic astrocytomas (AAs), 2/256 GBMs, and 4/4 oligodendrogliomas had positive staining. No other IDH mutations were found in immuno‐negative low‐grade cases by DNA sequencing. To validate our findings, we considered 311 diffuse gliomas in patients ≥ 55 years in The Cancer Genome Atlas database. Fifty‐five out of 311 gliomas had IDH R132H mutations (9/16 DAs; 8/48 AAs; 3/211 GBMs; 35/36 oligodendrogliomas), one DA, and one oligodendroglioma had other IDH mutations. IDH mutant gliomas had significantly higher frequency of O‐6‐methylguanine‐DNA methyltransferase promoter methylation (P = 0.0008) and longer overall survival (P < 0.0001). In conclusion, low‐grade gliomas are a minor part of gliomas (117/584) in patients ≥ 55 years, albeit they represent most IDH mutant gliomas in this age group (64/69 cases). IDH non‐canonical mutations can be found in immunonegative low‐grade gliomas (2/54). In view of its significance for prognosis and therapeutic management, our results suggest that IDH mutational status is assessed in all diffuse gliomas in patients ≥ 55 years by immunohistochemistry, followed by IDH sequencing in low‐grade immunonegative cases.
This paper is the second in a series of two that deal with a generalized theory of nonlocal elasticity of
n
-Helmholtz type. This terminology is motivated by the fact that the attenuation function ...(kernel) of the integral type nonlocal constitutive equation is the Green function associated with a generalized Helmholtz differential operator of order
n
. In the first paper, the governing equations have been derived and supported by suitable thermodynamic arguments. In this second paper, the proposed nonlocal model is specialized for the one-dimensional case to solve boundary-value problems. First, the relevant higher-order nonstandard boundary conditions in the differential (or, more precisely, integro-differential) version of the theory are derived. These boundary conditions are consistent with the particular family of attenuation functions adopted in the integral formulation. Then, some simple applications to statics and dynamics problems are presented. In particular, the theory is used to capture the static response and to perform free vibration analysis of a discrete lattice model with periodic microstructure (mass-and-spring chain) featured by nearest neighbor and next nearest neighbor particle interactions. In the latter case, boundary effects arise at the two lattice ends that are well captured by the proposed nonlocal continuum formulation. The nonlocal material parameters are identified a priori by matching the dispersion curve of the discrete lattice model, and a comparison in terms of attenuation function is also presented.
A generalized theory of nonlocal elasticity is elaborated. The proposed integral type nonlocal formulation is based on attenuation functions being assumed as the convolution product of
n
first order ...(Eringen type) kernels. The theory stems from a generalized higher-order constitutive relation between the nonlocal stress and the local strain. Inspired by the Eringen two-phase local/nonlocal integral model, this theory can also be thought of as the constitutive relation for an (
n
+ 1)-phase material, in which one phase has local elastic behavior, and the remaining
n
phases comply with nonlocal elasticity of higher order. The theory is supported by a suitable thermodynamic framework. In the spirit of Eringen’s 1983 paper, the particular family of attenuation functions adopted are the Green functions associated with generalized Helmholtz type differential operators of order
n
—which suggests denoting this model as a generalized nonlocal elasticity theory of
n
-Helmholtz type. Besides the integral type nonlocal formulation, elegant and compact expressions for the differential and integro-differential counterpart are derived. For
n
= 1 this formulation straightforwardly leads to the Aifantis 2003 implicit gradient elasticity theory with simultaneous stress gradients and strain gradients, which was postulated to eliminate stress and strain singularities from crack tips and dislocation lines. For
n
= 2 an implicit gradient elasticity formulation with bi-Helmholtz type stress and strain gradients is obtained. The paper is complemented by a companion Part II on the particularization of the generalized theory of nonlocal elasticity for the one-dimensional case, along with some applications in statics and dynamics.
Abstract
Intensive cognitive tasks induce inefficient regional and network responses in schizophrenia (SCZ). fMRI-based studies have naturally focused on gray matter, but appropriately titrated ...visuo-motor integration tasks reliably activate inter- and intra-hemispheric
white matter pathways
. Such tasks can assess network inefficiency
without
demanding intensive cognitive effort. Here, we provide the first application of this framework to the study of white matter
functional
responses in SCZ. Event-related fMRI data were acquired from 28 patients (nine females, mean age 43.3, ±11.7) and 28 age- and gender-comparable controls (nine females, mean age 42.1 ± 10.1), using the Poffenberger paradigm, a rapid visual detection task used to induce intra- (ipsi-lateral visual and motor cortex) or inter-hemispheric (contra-lateral visual and motor cortex) transfer. fMRI data were pre- and post-processed to reliably isolate activations in white matter, using probabilistic tractography-based white matter tracts. For intra-
and
inter-hemispheric transfer conditions, SCZ evinced
hyper
-activations in longitudinal and transverse white matter tracts, with hyper-activation in sub-regions of the
corpus callosum
primarily observed during inter-hemispheric transfer. Evidence for the functional inefficiency of white matter was observed in conjunction with small (~50 ms) but significant increases in response times. Functional inefficiencies in SCZ are (1) observable in white matter, with the degree of inefficiency contextually related to task-conditions, and (2) are evoked by simple detection tasks without intense cognitive processing. These cumulative results while expanding our understanding of this dys-connection syndrome, also extend the search of biomarkers beyond the traditional realm of fMRI studies of gray matter.
Background:
Data on the effect of dimethyl fumarate (DMF) on focal and diffuse gray matter (GM) damage, a relevant pathological substrate of multiple sclerosis (MS)-related disability are lacking.
...Objective:
To evaluate the DMF effect on cortical lesions (CLs) accumulation and global and regional GM atrophy in subjects with relapsing–remitting MS.
Methods:
A total of 148 patients (mean age 38.1 ± 9.7 years) treated with DMF ended a 2-year longitudinal study. All underwent regular Expanded Disability Status Scale (EDSS assessment), and at least two 3T-magnetic resonance imaging (MRI) at 3 and 24 months after DMF initiation. CLs and changes in global and regional atrophy of several brain regions were compared with 47 untreated age and sex-matched patients.
Results:
DMF-treated patients showed lower CLs accumulation (median 00–3 vs 20–7, p < 0.001) with respect to controls. Global cortical thickness (p < 0.001) and regional thickness and volume were lower in treated group (cerebellum, hippocampus, caudate, and putamen: p < 0.001; thalamus p = 0.03). Lower relapse rate (14% vs 40%, p < 0.001), EDSS change (0.2 ± 0.4 vs 0.4 ± 0.9, p < 0.001), and new WM lesions (median 00–5 vs 20–6, p < 0.001) were reported. No severe adverse drug reactions occurred.
Conclusions:
Beyond the well-known effect on disease activity, these results provide evidence of the effect of DMF through reduced progression of focal and diffuse GM damage.
Existing civil engineering structures having strategic importance, such as hospitals, fire stations, and power plants, often do not comply with seismic standards in force today, as they were designed ...and built based on past structural guidelines. On the other hand, due to their special importance, structural integrity of such buildings is of vital importance during and after earthquakes, which puts demands on strategies for their seismic protection. In this regard, seismic base isolation has been widely employed; however, the existing limited seismic joint between adjacent buildings may hamper this application because of the large displacements concentrated at the isolation floor. In this paper, we compare two possible remedies: the former is to provide supplemental damping in conventional base isolation systems and the latter consists in a combination of base isolation with supplemental rotational inertia. For the second strategy, a mechanical device, called inerter, is arranged in series with spring and dashpot elements to form the so-called tuned-mass-damper-inerter (TMDI) directly connected to an isolation floor. Several advantages of this second system as compared to the first one are outlined, especially with regard to the limitation of floor accelerations and interstory drifts, which may be an issue for nonstructural elements and equipment, in addition to disturbing occupants. Once the optimal design of the TMDI is established, possible implementation of this system into existing structures is discussed.
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