Abstract
One aspect of earthquake physics not adequately addressed is why some earthquakes generate thousands of aftershocks while other earthquakes generate few, if any, aftershocks. It also remains ...unknown why aftershock rates decay as ~1/time. Here, I show that these two are linked, with a dearth of aftershocks reflecting the absence of high-pressure fluid sources at depth, while rich and long-lasting aftershock sequences reflect tapping high-pressure fluid reservoirs that drive aftershock sequences. Using a physical model that captures the dominant aspects of permeability dynamics in the crust, I show that the model generates superior fits to observations than widely used empirical fits such as the Omori-Utsu Law, and find a functional relationship between aftershock decay rates and the tectonic ability to heal the co- and post-seismically generated fracture networks. These results have far-reaching implications, and can help interpret other observations such as seismic velocity recovery, attenuation, and migration.
With advances in neonatal care, preterm neonates are surviving with an evolving constellation of motor and cognitive disabilities that appear to be related to widespread cellular maturational ...disturbances that target cerebral gray and white matter. Whereas preterm infants were previously at high risk for destructive brain lesions that resulted in cystic white matter injury and secondary cortical and subcortical gray matter degeneration, contemporary cohorts of preterm survivors commonly display less severe injury that does not appear to involve pronounced glial or neuronal loss. Nevertheless, these milder forms of injury are also associated with reduced cerebral growth. Recent human and experimental studies support that impaired cerebral growth is related to disparate responses in gray and white matter. Myelination disturbances in cerebral white matter are related to aberrant regeneration and repair responses to acute death of premyelinating late oligodendrocyte progenitors (preOLs). In response to preOL death, early oligodendrocyte progenitors rapidly proliferate and differentiate, but the regenerated preOLs fail to normally mature to myelinating cells required for white matter growth. Although immature neurons appear to be more resistant to cell death from hypoxia–ischemia than glia, they display widespread disturbances in maturation of their dendritic arbors, which further contribute to impaired cerebral growth. These complex and disparate responses of neurons and preOLs thus result in large numbers of cells that fail to fully mature during a critical window in development of neural circuitry. These recently recognized forms of cerebral gray and white matter dysmaturation raise new diagnostic challenges and suggest new therapeutic directions centered on reversal of the processes that promote dysmaturation. Ann Neurol 2014;75:469–486
Camphoric acid, an inexpensive and biorenewable diacid derived from the terpene (+)-camphor, was copolymerized with a variety of diols to afford polyesters with glass transition temperatures ( T g ) ...ranging from −16 °C to 125 °C. Polyethylene camphorate (PEC, 51 °C), polyerythritan camphorate (100 °C), and polyisosorbide camphorate (125 °C) exhibited T g values matching or excelling those of important commercial polymers. Agitation of PEC in deionized water for 14 days dramatically degraded the polymer from M n = 20 200 to M n < 600. Incremental replacement of terephthalic acid with camphoric acid led to a series of polyethylene (camphorate/terephthalate) analogues with increased biobased content and T g values (71 to 41 °C) that were diminished, but still competitive with that of polylactic acid (PLA).
The field of biorenewable polymers is ever-expanding, aided by the interest of the general public to adopt more sustainable practices for natural resource utilization as well as waste generation. ...This review summarizes recent efforts to synthesize biobased thermoplastics with glass transition temperature (
T
g
) values exceeding that of polylactic acid (PLA), near 55 °C. A high
T
g
is essential for materials that aspire to replace any incumbent commodity plastics employed in the amorphous state. The first section focuses on commercial bioplastics and describes: approaches toward biorenewable polyethylene terephthalate (PET); efforts to improve the
T
g
of PLA; and advances toward polyethylene furanoate (PEF). The remaining sections catalogue a wide variety of novel, high
T
g
bioplastics categorized as: aromatic biopolymers, carbocyclic and heterocyclic biopolymers, and vinyl-type biopolymers synthesized
via
radical polymerization.
This review describes recent strategies for synthesizing polymers that are mostly or fully biobased and exhibit a high glass transition temperature.
Albumin has a number of important physiologic functions, which include maintaining oncotic pressure, transporting various agents (fatty acids, bile acids, cholesterol, metal ions, and drugs), ...scavenging free oxygen radicals, acting as an antioxidant, and exerting an antiplatelet effect. Hypoalbuminemia in adults, defined by an intravascular albumin level of <3.5 g/dL, is associated with poor postoperative outcomes in patients undergoing surgical intervention. Although the relationship of hypoalbuminemia and poor surgical outcome has been known for many years, the pathophysiology behind the relationship is unclear. Three theoretical constructs might explain this relationship. First, albumin might serve as a nutritional marker, such that hypoalbuminemia represents poor nutritional status in patients who go on to experience poor postoperative outcomes. Second, albumin has its own pharmacologic characteristics as an antioxidant or transporter, and therefore, the lack of albumin might result in a deficiency of those functions, resulting in poor postoperative outcomes. Or third, albumin is known to be a negative acute phase protein, and as such hypoalbuminemia might represent an increased inflammatory status of the patient, potentially leading to poor outcomes. A thorough review of the literature reveals the fallacy of these arguments and fails to show a direct cause and effect between low albumin levels per se and adverse outcomes. Interventions designed solely to correct preoperative hypoalbuminemia, in particular intravenous albumin infusion, do little to change the patient's course of hospitalization. While surgeons may use albumin levels on admission for their prognostic value, they should avoid therapeutic strategies whose main endpoint is correction of this abnormality.
Acrylates and polyacrylates have been produced massively due to their interesting applications like Plexiglas. However, the contemporary issues of fossil depletion associated with climate change have ...raised serious concerns. As a result, utilization of renewable resources such as lignocellulosic materials and the development of greener processes have been investigated intensively. Herein, we review the preparation of competitive (meth)acrylates and the corresponding polymers made from bio-renewable resources with a specific focus on lignocellulose. While covering a few families of biosynthons to produce acrylates through different synthetic pathways, we also analyze the promising properties of the resulting materials.
Acrylates and polyacrylates have been produced massively due to their interesting applications like Plexiglas.
Preparation of porous materials from one‐dimensional polymers is challenging because the packing of polymer chains results in a dense, non‐porous arrangement. Herein, we demonstrate the remarkable ...adaptation of an amorphous, linear, non‐porous, flexible organic polymer into a three‐dimensional, highly porous, crystalline solid, as the organic component of a metal–organic framework (MOF). A polymer with aromatic dicarboxylic acids in the backbone functioned as a polymer ligand upon annealing with ZnII, generating a polymer–metal–organic framework (polyMOF). These materials break the dogma that MOFs must be prepared from small, rigid ligands. Similarly, polyMOFs contradict conventional polymer chemistry by demonstrating that linear and amorphous polymers can be readily coaxed into a highly crystalline, porous, three‐dimensional structure by coordination chemistry.
A bottom‐up strategy is used to generate porosity from non‐porous, one‐dimensional, amorphous polymeric materials by their transformation into crystalline polyMOF materials. These materials harness the advantages of the porosity and crystallinity of MOFs along with certain attributes of the polymers, such as facile film formation and greater chemical stability.
The Montreal Protocol was designed to protect the stratospheric ozone layer by enabling reductions in the abundance of ozone-depleting substances such as chlorofluorocarbons (CFCs) in the atmosphere
.... The reduction in the atmospheric concentration of trichlorofluoromethane (CFC-11) has made the second-largest contribution to the decline in the total atmospheric concentration of ozone-depleting chlorine since the 1990s
. However, CFC-11 still contributes one-quarter of all chlorine reaching the stratosphere, and a timely recovery of the stratospheric ozone layer depends on a sustained decline in CFC-11 concentrations
. Here we show that the rate of decline of atmospheric CFC-11 concentrations observed at remote measurement sites was constant from 2002 to 2012, and then slowed by about 50 per cent after 2012. The observed slowdown in the decline of CFC-11 concentration was concurrent with a 50 per cent increase in the mean concentration difference observed between the Northern and Southern Hemispheres, and also with the emergence of strong correlations at the Mauna Loa Observatory between concentrations of CFC-11 and other chemicals associated with anthropogenic emissions. A simple model analysis of our findings suggests an increase in CFC-11 emissions of 13 ± 5 gigagrams per year (25 ± 13 per cent) since 2012, despite reported production being close to zero
since 2006. Our three-dimensional model simulations confirm the increase in CFC-11 emissions, but indicate that this increase may have been as much as 50 per cent smaller as a result of changes in stratospheric processes or dynamics. The increase in emission of CFC-11 appears unrelated to past production; this suggests unreported new production, which is inconsistent with the Montreal Protocol agreement to phase out global CFC production by 2010.
Recently, polymer–metal–organic frameworks (polyMOFs) were reported as a new class of hybrid porous materials that combine advantages of both organic polymers and crystalline MOFs. Herein, we report ...a bridging coligand strategy to prepare new types of polyMOFs, demonstrating that polyMOFs are compatible with additional MOF architectures besides that of the earlier reported IRMOF-1 type polyMOF. Gas sorption studies revealed that these polyMOF materials exhibited relatively high CO2 sorption but very low N2 sorption, making them promising materials for CO2/N2 separations. Moreover, these polyMOFs demonstrated exceptional water stability attributed to the hydrophobicity of polymer ligands as well as the cross-linking of the polymer chains within the MOF.
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