2,243 publications from this institution
The applicability of nonlinear static procedures for estimating the seismic demands of typical regular RC moment-resisting frames is evaluated. This work, conducted within the framework of the ATC-76-6 project, shows the degree to which nonlinear static methods can characterize global and local response demands vis-à–vis those determined by nonlinear dynamic analysis for three RC moment-frame buildings. The response quantities (engineering demand parameters) considered are peak story displacements, story drifts, story shears, and floor overturning moments. The single-mode pushover methods evaluated include the N2 and the ASCE-41 coefficient methods. Multi-modal pushover methods, such as modal pushover analysis and the consecutive modal pushover method, were also evaluated. The results indicate that the relatively good performance of the single-mode methods observed for low-rise buildings rapidly deteriorates as the number of stories increases. The multi-modal techniques generally extend the range of applicability of pushover methods, but at the cost of additional computation and without ensuring the reliability of the results.
The mechanisms underlying the initiation of puberty, one of the cornerstones of human evolution, have not been fully elucidated as yet. However, recently, an accumulating body of evidence has helped unravel several critical aspects of the process. It is clear that a change in the pattern of pituitary gonadotropin secretion serves as a hormonal trigger for puberty induction. This change is directly guided by the hypothalamic GnRH pulse generation, a phenomenon regulated by the Kisspeptin-Neurokinin-Dynorphin (KNDy) system also in the hypothalamus. This represents the kisspeptin molecule, which is crucial in augmenting GnRH secretion at puberty, whose secretion is fine-tuned by the opposing signals neurokinin B and dynorphin. Recently, the novel kisspeptin inhibitory signal MKRN3 was described, whose role in puberty initiation provided further insight into the mechanistic aspects of pubertal onset. Furthermore, the description of higher inhibitory and stimulatory signals acting upstream of the KNDy neurons suggested that the trigger point of puberty is located upstream of the KNDy system and the GnRH pulse generator. However, the mechanism of pubertal onset should not be considered as an isolated closed loop system. On the contrary, it is influenced by such factors as adipose tissue, gastrointestinal function, adrenal androgen production, energy sensing, and physical and psychosocial stress. Also, fetal and early life stressful events, as well as exposure to endocrine disruptors, may play important roles in pubertal initiation, the latter primarily through epigenetic modifications. Here we present the available data in the field and attempt to provide an integrated view of this unique and crucial phenomenon.
Abstract Pallet racking is a long-established material handling solution that optimizes warehouse space through multi-level pallet storage and ensures time efficiency through the absence of any mechanical fasteners between the goods and the supporting steel structure. This however could lead to potentially vulnerable situations since heavy pallets are stored at high load-levels, with only the force of gravity and friction keeping them in place. Recent earthquakes have highlighted these risks, with pallet sliding and fall-offs causing operational disruptions and structural collapses; such failure modes are not adequately addressed by current seismic design codes for racks. The ERIES project RACKSLIDE addresses this knowledge gap through an extensive experimental campaign that investigates pallet sliding on two rack configurations with diverse structural characteristics. Test specimens, that depict small portions of the actual frames, are designed and constructed by industry experts and then installed on an innovative 9 degrees-of-freedom shake table system. By using as input motion, the load-level accelerations, evaluated by numerical modelling of the entire system, the proposed setup allows to assess sliding phenomena on the uppermost levels of high-rise racks. Afterwards, the experimental results are compared with blind predictions from numerical analyses, leveling the ground for future model calibrations and code applications.
Design spectra are commonly defined for a constant value of hazard associated to an “ultimate” limit state (LS) of reference, typically 10% in 50 years. Given a specific structure, this approach results in different limit‐state exceedance risk levels even for sites characterized by the same design peak ground acceleration (PGA), mainly because of differences in hazard curve shape/slope. Instead, Risk Targeted design maps (first applied in ASCE7‐10) suggest the application of suitable spectra adjustment factors, the so‐called risk coefficients, in order to ensure a uniform collapse risk across different sites and buildings. Making use of simplified single‐degree‐of‐freedom (SDoF) structures for several configurations of vibration period and ductility, we test the effectiveness of the adjustment factors computed under different assumptions in matching a specific target risk or, at least, in harmonizing the risk of multiple buildings at different sites with respect to different LSs. Although risk matching is shown to be only theoretically possible and unachievable in practice, we claim that harmonization remains a viable target, and we offer insights for possible future adoption of Risk Targeted Spectra in the European code provisions.
Stress (i.e. the state of threatened homeostasis), is normally associated with adaptive physical and behavioural changes that promote individual survival. Successful maintenance of homeostasis leads to the state of eustasis, which represents health. The prolonged, excessive, or deficient response of the stress system to stress, however, may lead to a state of dyshomeostasis or cacostasis, which may lead to physical and mental health problems. Although research has focused on the detrimental effects of stress, only a few studies have been done on positive stress exposure adaptations. Increased resilience, post-traumatic psychological growth, and increased empathy may benefit chronically stressed individuals, enhancing their abilities to cope with distress. Therapeutic efforts in the treatment of short- or long-term stress aims at reducing its effect on neuroendocrine responses, behaviour changes, and so on. Community investments and interventions should focus on reducing threats and promoting positive adaptation during and after traumatic stress exposures.
Abstract Snoring is the most characteristic symptom of obstructive sleep‐disordered breathing (SDB) and recurrent wheezing is the most common clinical manifestation of asthma. The purpose of the present review is to outline the impact of SDB and recurrent wheezing/asthma on sleep quality and to summarize the epidemiologic and pathophysiologic evidence supporting an association between the two disorders. Enlarged tonsils and adenoid or obesity predispose to obstructive sleep apneas and hypopneas which are accompanied by arousals, restless sleep, and frequently daytime sleepiness, inattention, hyperactivity, and academic difficulties. Subjects with history of wheezing are also at risk for sleep disturbance and daytime cognitive dysfunction. Asthmatic children have more frequent snoring, apneas, and hypopneas during sleep than non‐asthmatic subjects and tonsillar hypertrophy mediates at least in part this epidemiologic association. In addition, preliminary evidence indicates that treatment of sleep apnea with adenotonsillectomy results in improved control of coexisting asthma. Elevated concentrations of leukotrienes and oxidative stress markers have been detected in the exhaled breath condensate of children with asthma and probably contribute to bronchoconstriction. Moreover, sleep apneic children have increased expression of leukotrienes and leukotriene receptors in adenotonsillar tissue. Viral respiratory infections may induce inflammation and oxidative stress in the asthmatic airway enhancing not only bronchospasm, but also biosynthesis of leukotrienes within pharyngeal lymphoid tissues, which promote adenotonsillar enlargement and sleep apnea. In conclusion, taking under consideration the epidemiologic association between obstructive SDB and asthma, when one of the two disorders is diagnosed, the possibility of the other disease being present should be entertained. Pediatr. Pulmonol. 2011; 46:1047–1054. © 2011 Wiley Periodicals, Inc.
To describe the imaging findings in the adrenal glands of 12 patients with adrenocorticotropin (ACTH)-independent macronodular adrenocortical hyperplasia (AIMAH).Computed tomographic (CT) and magnetic resonance (MR) imaging findings in the adrenal glands were reviewed retrospectively in 12 patients (three men, nine women) with ACTH-independent Cushing syndrome and with bilateral nonpigmented multinodular adrenal hyperplasia. The results of pituitary MR imaging, adrenal scintigraphy, and petrosal sampling were available in nine, five, and six patients, respectively. Eleven patients underwent bilateral and one patient underwent unilateral adrenalectomy.Eleven patients had enlarged multinodular adrenal glands: Nodules were 0.1-5.5 cm. The combined weight of both adrenal specimens for the 11 bilateral adrenalectomy specimens was 28-297 g, with a mean weight of 122 g. Glands were hypointense compared with the liver on T1-weighted images and were hyperintense on T2-weighted images. Pituitary MR imaging findings were negative in nine of nine patients. Iodomethylnorcholesterol scintigraphy showed bilateral uptake in four of five patients. Petrosal sinus sampling revealed no petrosal-to-peripheral ACTH gradients before corticotropin-releasing hormone (CRH) stimulation in six of six patients, but three patients had gradients after CRH stimulation. After undergoing bilateral or unilateral adrenalectomy, all patients were cured.AIMAH is a rare cause of ACTH-independent Cushing syndrome, with characteristic CT findings of massively enlarged multinodular adrenal glands. Bilateral adrenalectomy is indicated on the basis of clinical and CT findings.
