We identify the major public debt overhang episodes in the advanced economies since the early 1800s, characterized by public debt to GDP levels exceeding 90 percent for at least five years. ...Consistent with Reinhart and Rogoff (2010) and most of the more recent research, we find that public debt overhang episodes are associated with lower growth than during other periods. The duration of the average debt overhang episode is perhaps its most striking feature. Among the 26 episodes we identify, 20 lasted more than a decade. The long duration belies the view that the correlation is caused mainly by debt buildups during business cycle recessions. The long duration also implies that the cumulative shortfall in output from debt overhang is potentially massive. These growth-reducing effects of high public debt are apparently not transmitted exclusively through high real interest rates, as in eleven of the episodes, interest rates are not materially higher. PUBLICATION ABSTRACT
On the tear resistance of skin Yang, Wen; Sherman, Vincent R; Gludovatz, Bernd ...
Nature communications,
03/2015, Letnik:
6, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Tear resistance is of vital importance in the various functions of skin, especially protection from predatorial attack. Here, we mechanistically quantify the extreme tear resistance of skin and ...identify the underlying structural features, which lead to its sophisticated failure mechanisms. We explain why it is virtually impossible to propagate a tear in rabbit skin, chosen as a model material for the dermis of vertebrates. We express the deformation in terms of four mechanisms of collagen fibril activity in skin under tensile loading that virtually eliminate the possibility of tearing in pre-notched samples: fibril straightening, fibril reorientation towards the tensile direction, elastic stretching and interfibrillar sliding, all of which contribute to the redistribution of the stresses at the notch tip.
Commentary: Postoperative atrial fibrillation, predictor of late risk? Conti, Vincent R.
Journal of thoracic and cardiovascular surgery/The Journal of thoracic and cardiovascular surgery/The journal of thoracic and cardiovascular surgery,
20/May , Letnik:
161, Številka:
5
Journal Article
Mobility disability is becoming prevalent in the obese older population (≥60 years of age). We included a total of 13 cross-sectional and 15 longitudinal studies based on actual physical assessments ...of mobility in the obese older population in this review. We systematically examined existing evidence of which adiposity estimate best predicted mobility disability. Cross-sectional studies (82-4000 participants) showed poorer lower extremity mobility with increasing obesity severity in both men and women. All longitudinal studies (1-22 years) except for one, reported relationships between adiposity and declining mobility. While different physical tests made interpretation challenging, a consistent finding was that walking, stair climbing and chair rise ability were compromised with obesity, especially if the body mass index (BMI) exceeded 35 kg m⁻². More studies found that obese women were at an increased risk for mobility impairment than men. Existing evidence suggests that BMI and waist circumference are emerging as the more consistent predictors of the onset or worsening of mobility disability. Limited interventional evidence shows that weight loss is related with increased mobility and lower extremity function. Additional longitudinal studies are warranted that address overall body composition fat and muscle mass or change on future disability.
Display omitted
The pangolin has a flexible dermal armor consisting of overlapping keratinous scales. Although they show potential for bioinspired flexible armor, the design principles of pangolin ...armor are barely known. Here we report on the overlapping organization, hierarchical structure (from the nano to the mesolevel), and mechanical response of scales from ground (Chinese) and arboreal (African tree) pangolins. Both scales exhibit the same overlapping organization, with each scale at the center of neighboring scales arranged in a hexagonal pattern. The scales have a cuticle of several layers of loosely attached flattened keratinized cells, while the interior structure exhibits three regions distinguished by the geometry and orientations of the keratinized cells, which form densely packed lamellae; each one corresponds to one layer of cells. Unlike most other keratinous materials, the scales show a crossed-lamellar structure (∼5μm) and crossed fibers (∼50μm). A nano-scale suture structure, observed for the first time, outlines cell membranes and leads to an interlocking interface between lamellae, thus enhancing the bonding and shear resistance. The tensile response of the scales shows an elastic limit followed by a short plateau prior to failure, with Young’s modulus ∼1 GPa and tensile strength 60–100MPa. The mechanical response is transversely isotropic, a result of the cross lamellar structure. The strain rate sensitivity in the range of 10−5–10−1s−1 region is found to be equal to 0.07–0.08, typical of other keratins and polymers. The mechanical response is highly dependent on the degree of hydration, a characteristic of keratins.
Although many fish and reptiles have protective scales and carapaces, mammals are characteristically fast and light. The pangolin is one of the few mammal possessing a flexible dermal armor for protection from predators, such as lions. Here we study the arrangement of the scales as well as their hierarchical structure from the nano to the mesolevel and correlate it to the mechanical properties. The study reveals a unique structure consisting of crossed lamellae and interlocking sutures that provide exceptional performance and in-plane isotropy.
Recent research indicates that monsoon rainfall became less frequent but more intense in India during the latter half of the Twentieth Century, thus increasing the risk of drought and flood damage to ...the country’s wet-season (
kharif
) rice crop. Our statistical analysis of state-level Indian data confirms that drought and extreme rainfall negatively affected rice yield (harvest per hectare) in predominantly rainfed areas during 1966–2002, with drought having a much greater impact than extreme rainfall. Using Monte Carlo simulation, we find that yield would have been 1.7% higher on average if monsoon characteristics, especially drought frequency, had not changed since 1960. Yield would have received an additional boost of nearly 4% if two other meteorological changes (warmer nights and lower rainfall at the end of the growing season) had not occurred. In combination, these changes would have increased cumulative harvest during 1966–2002 by an amount equivalent to about a fifth of the increase caused by improvements in farming technology. Climate change has evidently already negatively affected India’s hundreds of millions of rice producers and consumers.
The materials science of collagen Sherman, Vincent R.; Yang, Wen; Meyers, Marc A.
Journal of the mechanical behavior of biomedical materials,
12/2015, Letnik:
52
Journal Article
Recenzirano
Odprti dostop
Collagen is the principal biopolymer in the extracellular matrix of both vertebrates and invertebrates. It is produced in specialized cells (fibroblasts) and extracted into the body by a series of ...intra and extracellular steps. It is prevalent in connective tissues, and the arrangement of collagen determines the mechanical response. In biomineralized materials, its fraction and spatial distribution provide the necessary toughness and anisotropy. We review the structure of collagen, with emphasis on its hierarchical arrangement, and present constitutive equations that describe its mechanical response, classified into three groups: hyperelastic macroscopic models based on strain energy in which strain energy functions are developed; macroscopic mathematical fits with a nonlinear constitutive response; structurally and physically based models where a constitutive equation of a linear elastic material is modified by geometric characteristics. Viscoelasticity is incorporated into the existing constitutive models and the effect of hydration is discussed. We illustrate the importance of collagen with descriptions of its organization and properties in skin, fish scales, and bone, focusing on the findings of our group.
Display omitted
•Types of collagen and formation of fibril collagen.•Nano-micro-meso description of collagen structure.•Critical assessment of constitutive equations of collagen.•Collagen response in skin and arapaima, alligator gar, and coelacanth, scales.
Formerly known as 'intersex' conditions, disorders of sex development (DSDs) are congenital conditions in which chromosomal, gonadal or anatomical sex is atypical. A complete revision of the ...nomenclature and classification of DSDs has been undertaken, which emphasizes the genetic aetiology of these disorders and discards pejorative terms. Uptake of the new terminology is widespread. DSDs affecting gonadal development are perhaps the least well understood. Unravelling the molecular mechanisms underlying gonadal development has revealed new causes of DSDs, although a specific molecular diagnosis is made in only ∼20% of patients. Conversely, identification of the molecular causes of DSDs has provided insight into the mechanisms of gonadal development. Studies of N-ethyl-N-nitrosourea mutagenesis in the mouse, and multigene diagnostic screening and genome-wide approaches, such as array-comparative genomic hybridization and next-generation sequencing, in patients with DSDs are accelerating the discovery of genes involved in gonadal development and DSDs. Furthermore, long-range gene regulatory mutations and multiple gene mutations are emerging as new causes of DSDs. Patients with DSDs, their parents and medical staff are confronted with challenging decisions regarding gender assignment, genital surgery and lifelong care. These advances are refining prognostic prediction and systematically improving the diagnosis and long-term management of children with DSDs.
Opportunistic premise (i.e., building) plumbing pathogens (OPPPs, e.g., Legionella pneumophila, Mycobacterium avium complex, Pseudomonas aeruginosa, Acanthamoeba, and Naegleria fowleri) are a ...significant and growing source of disease. Because OPPPs establish and grow as part of the native drinking water microbiota, they do not correspond to fecal indicators, presenting a major challenge to standard drinking water monitoring practices. Further, different OPPPs present distinct requirements for sampling, preservation, and analysis, creating an impediment to their parallel detection. The aim of this critical review is to evaluate the state of the science of monitoring OPPPs and identify a path forward for their parallel detection and quantification in a manner commensurate with the need for reliable data that is informative to risk assessment and mitigation. Water and biofilm sampling procedures, as well as factors influencing sample representativeness and detection sensitivity, are critically evaluated with respect to the five representative bacterial and amoebal OPPPs noted above. Available culturing and molecular approaches are discussed in terms of their advantages, limitations, and applicability. Knowledge gaps and research needs towards standardized approaches are identified.
Display omitted
•Opportunistic pathogens in premise plumbing (OPPPs) are a growing source of disease.•Reliable detection and monitoring strategies are urgently needed for OPPPs.•Different OPPPs present distinct requirements for sampling, preservation, and analysis.•The state of the science of monitoring OPPPs is critically reviewed.
The effect of mineral dust aerosols and subsequent deposition in polar regions has historically been underestimated in climate models. Dust aerosols increase melt rates by reducing surface albedo and ...modifying atmospheric radiative properties. In this study 127,413 satellite images covering the Arctic and Antarctic from 2007 to 2019 were assessed for dust content using thermal infrared wavelengths. The results show a strong linear trend in which the relative spatial extent of dust (RSED) increased annually by 0.31% in the Arctic (8.5% to 12.1%) and 0.19% in the Antarctic (5.2% to 7.5%). Seasonally, the maximum aggregated average RSED occurred in the Arctic during boreal winter (11.2%), while the Antarctic peaked in austral spring (9.5%). Maximum RSED rates occurred in boreal winter/austral summer (Dec-Jan-Feb) for both polar regions. The data suggests that finer dust particles are more efficiently distributed by aeolian processes leading to higher RSED values that are not necessarily reflective of polar dust loading models.
PDF
