Discovery of the Earth's Van Allen radiation belts by instruments flown on Explorer 1 in 1958 was the first major discovery of the Space Age. The observation of distinct inner and outer zones of ...trapped megaelectron volt (MeV) particles, primarily protons at low altitude and electrons at high altitude, led to early models for source and loss mechanisms including Cosmic Ray Albedo Neutron Decay for inner zone protons, radial diffusion for outer zone electrons and loss to the atmosphere due to pitch angle scattering. This scattering lowers the mirror altitude for particles in their bounce motion parallel to the Earth's magnetic field until they suffer collisional loss. A view of the belts as quasi‐static inner and outer zones of energetic particles with different sources was modified by observations made during the Solar Cycle 22 maximum in solar activity over 1989–1991. The dynamic variability of outer zone electrons was measured by the Combined Radiation Release and Effects Satellite launched in July 1990. This variability is caused by distinct types of heliospheric structure that vary with the solar cycle. The launch of the twin Van Allen Probes in August 2012 has provided much longer and more comprehensive measurements during the declining phase of Solar Cycle 24. Roughly half of moderate geomagnetic storms, determined by intensity of the ring current carried mostly by protons at hundreds of kiloelectron volts, produce an increase in trapped relativistic electron flux in the outer zone. Mechanisms for accelerating electrons of hundreds of electron volts stored in the tail region of the magnetosphere to MeVenergies in the trapping region are described in this review: prompt and diffusive radial transport and local acceleration driven by magnetospheric waves. Such waves also produce pitch angle scattering loss, as does outward radial transport, enhanced when the magnetosphere is compressed. While quasilinear simulations have been used to successfully reproduce many essential features of the radiation belt particle dynamics, nonlinear wave‐particle interactions are found to be potentially important for causing more rapid particle acceleration or precipitation. The findings on the fundamental physics of the Van Allen radiation belts potentially provide insights into understanding energetic particle dynamics at other magnetized planets in the solar system, exoplanets throughout the universe, and in astrophysical and laboratory plasmas. Computational radiation belt models have improved dramatically, particularly in the Van Allen Probes era, and assimilative forecasting of the state of the radiation belts has become more feasible. Moreover, machine learning techniques have been developed to specify and predict the state of the Van Allen radiation belts. Given the potential Space Weather impact of radiation belt variability on technological systems, these new radiation belt models are expected to play a critical role in our technological society in the future as much as meteorological models do today.
Plain Language Summary
Discovery of the Earth's Van Allen radiation belts by instruments flown on Explorer 1 in 1958 was the first major discovery of the Space Age. The dynamic properties of trapped outer zone electrons and the outer boundary of the inner zone proton population, along with source populations, have recently been studied in great detail by instruments on National Aeronautics and Space Administration's Van Allen Probes spacecraft, as well as other data sources like operational spacecraft designed for navigation and terrestrial weather forecasting. The vulnerability of the myriad of spacecraft that is strongly affected by space weather disruptions, as compared to 1958, has motivated the radiation belt community to develop essential improved models for forecasting the space environment we will inhabit in the 21st century and evaluate its impacts on our technological society. In this paper, we provide a review on historical background and recent advances in understanding and modeling acceleration, transport, and loss processes of energetic particles in the Earth's Van Allen radiation belts, followed by outstanding challenges for developing future radiation belt models. The findings on the fundamental physics of the Van Allen radiation belts potentially provide insights into understanding energetic particle dynamics at other magnetized planets in the solar system, exoplanets throughout the universe, as well as in astrophysical and laboratory plasmas. Given the potential Space Weather impact of radiation belt variability on technological systems, these new radiation belt models are expected to play a critical role in our technological society in the future much as meteorological models do today.
Key Points
A brief historical background on the discovery of the Van Allen radiation belts and their response to solar activity is introduced
Recent advances in understanding mechanisms responsible for radiation belt electron acceleration, transport, and loss are reviewed
Outstanding challenges for developing future radiation belt models are summarized
Bioenergy crops are an attractive option for use in energy production. A good plant candidate for bioenergy applications should produce a high amount of biomass and resist harsh environmental ...conditions. Carbon-based nanomaterials (CBNs) have been described as promising seed germination and plant growth regulators. In this paper, we tested the impact of two CBNs: graphene and multi-walled carbon nanotubes (CNTs) on germination and biomass production of two major bioenergy crops (sorghum and switchgrass). The application of graphene and CNTs increased the germination rate of switchgrass seeds and led to an early germination of sorghum seeds. The exposure of switchgrass to graphene (200 mg/l) resulted in a 28% increase of total biomass produced compared to untreated plants. We tested the impact of CBNs on bioenergy crops under salt stress conditions and discovered that CBNs can significantly reduce symptoms of salt stress imposed by the addition of NaCl into the growth medium. Using an ion selective electrode, we demonstrated that the concentration of Na+ ions in NaCl solution can be significantly decreased by the addition of CNTs to the salt solution. Our data confirmed the potential of CBNs as plant growth regulators for non-food crops and demonstrated the role of CBNs in the protection of plants against salt stress by desalination of saline growth medium.
Survival rates for most paediatric cancers have improved at a remarkable pace over the past four decades. In developed countries, cure is now the probable outcome for most children and adolescents ...who are diagnosed with cancer: their 5-year survival rate approaches 80%. However, the vast majority of these cancer survivors will have at least one chronic health condition by 40 years of age. The burden of responsibility to understand the long-term morbidity and mortality that is associated with currently successful treatments must be borne by many, including the research and health care communities, survivor advocacy groups, and governmental and policy-making entities.
African Americans who moved to California in hopes of finding
freedom and full citizenship instead faced all-too-familiar racial
segregation. As one transplant put it, "The only difference between
...Pasadena and Mississippi is the way they are spelled." From the
beaches to streetcars to schools, the Golden State-in contrast to
its reputation for tolerance-perfected many methods of controlling
people of color.
Lynn M. Hudson deepens our understanding of the practices that
African Americans in the West deployed to dismantle Jim Crow in the
quest for civil rights prior to the 1960s. Faced with
institutionalized racism, black Californians used both established
and improvised tactics to resist and survive the state's color
line. Hudson rediscovers forgotten stories like the experimental
all-black community of Allensworth, the California Ku Klux Klan's
campaign of terror against African Americans, the bitter struggle
to integrate public swimming pools in Pasadena and elsewhere, and
segregationists' preoccupation with gender and sexuality.
Self-assembly of molecular and block copolymer amphiphiles represents a well-established route to micelles with a wide variety of shapes and gel-like phases. We demonstrate an analogous process, but ...on a longer length scale, in which amphiphilic P-H-P and H-P-H cylindrical triblock comicelles with hydrophobic (H) or polar (P) segments that are monodisperse in length are able to self-assemble side by side or end to end in nonsolvents for the central or terminal segments, respectively. This allows the formation of cylindrical supermicelles and one-dimensional (1D) or 3D superstructures that persist in both solution and the solid state. These assemblies possess multiple levels of structural hierarchy in combination with existence on a multimicrometer-length scale, features that are generally only found in natural materials.
Three-coordinate organoboron compounds have recently found a wide range of applications in materials chemistry as nonlinear optical materials, chemical sensors, and emitters for organic ...light-emitting diodes (OLEDs). These compounds are excellent electron acceptors due to the empty pπ orbital on the boron center. When accompanied by electron donors such as amines, these molecules possess large electronic dipoles, which promote donor−acceptor charge-transfer upon excitation with light. Because of this, donor−acceptor triarylboranes are often highly luminescent both in the solid state and in solution. In this Account, we describe our research to develop donor−acceptor triarylboranes as efficient blue emitters for OLEDs. Through the use of hole-transporting donor groups such as 1-napthylphenylamines, we have prepared multifunctional triarylboranes that can act as the emissive, electron transport, or hole transport layers in OLEDs. We have also examined donor−acceptor compounds based on 2,2′-dipyridylamine or 7-azaindolyl donors, several of which have fluorescent quantum efficiencies approaching 100%. We are also investigating the chemistry of metal-containing triarylboranes. Our studies show that the electron-deficient boryl group can greatly facilitate metal-to-ligand charge-transfer transitions and phosphorescence. In addition, electronegative linker groups such as 2,2′-bipyridine can act in synergy with metal chelation to greatly improve the electron-accepting ability and Lewis acidity of triarylboranes. Donor−acceptor triarylboranes developed in our laboratory can also serve as a series of “switch-on” sensors for fluoride ions. When the donor and acceptor are linked by rigid naphthyl or nonrigid silane linkers, donor−acceptor conjugation is disrupted and charge transfer occurs primarily through space. The binding of fluoride ions to the boron center disrupts this charge transfer, activating alternative π → π* transitions in the molecule and changing the emission color of the sample. More recently, we have used these nonconjugated linkers to prepare organometallic donor−acceptor triarylboranes in which fluorescence and phosphorescence can simultaneously be observed from two different chromophores in the same molecule at ambient temperature. These dual emissive molecules remain sensitive to fluoride ions, and give synergistic singlet−triplet emission responses when titrated with F−. Fluoride ions can also act as valuable chemical probes, providing insight into the electronic structure of this new class of optoelectronic materials. We have demonstrated that donor−acceptor triarylboranes are promising materials in anion sensing and electroluminescent device applications. Nonetheless, despite our work and that of other research groups, there is still much to be learned about organometallic and multiply emissive triarylboron systems.
Summary Survivors of childhood cancer treated with anthracycline chemotherapy or chest radiation are at an increased risk of developing congestive heart failure. In this population, congestive heart ...failure is well recognised as a progressive disorder, with a variable period of asymptomatic cardiomyopathy that precedes signs and symptoms. As a result, several clinical practice guidelines have been developed independently to help with detection and treatment of asymptomatic cardiomyopathy. These guidelines differ with regards to definitions of at-risk populations, surveillance modality and frequency, and recommendations for interventions. Differences between these guidelines could hinder the effective implementation of these recommendations. We report on the results of an international collaboration to harmonise existing cardiomyopathy surveillance recommendations using an evidence-based approach that relied on standardised definitions for outcomes of interest and transparent presentation of the quality of the evidence. The resultant recommendations were graded according to the quality of the evidence and the potential benefit gained from early detection and intervention.
Abstract Background Treatment-related cardiac death is the primary, noncancer cause of mortality in adult survivors of childhood malignancies. Early detection of cardiac dysfunction may identify a ...high-risk subset of survivors for early intervention. Objectives This study sought to determine the prevalence of cardiac dysfunction in adult survivors of childhood malignancies. Methods Echocardiographic assessment included 3-dimensional (3D) left ventricular ejection fraction (LVEF), global longitudinal and circumferential myocardial strain, and diastolic function, graded per American Society of Echocardiography guidelines in 1,820 adult (median age 31 years; range: 18 to 65 years) survivors of childhood cancer (median time from diagnosis 23 years; range: 10 to 48 years) exposed to anthracycline chemotherapy (n = 1,050), chest-directed radiotherapy (n = 306), or both (n = 464). Results Only 5.8% of survivors had abnormal 3D LVEFs (<50%). However, 32.1% of survivors with normal 3D LVEFs had evidence of cardiac dysfunction by global longitudinal strain (28%), American Society of Echocardiography–graded diastolic assessment (8.7%), or both. Abnormal global longitudinal strain was associated with chest-directed radiotherapy at 1 to 19.9 Gy (rate ratio RR: 1.38; 95% confidence interval CI: 1.14 to 1.66), 20 to 29.9 Gy (RR: 1.65; 95% CI: 1.31 to 2.08), and >30 Gy (RR: 2.39; 95% CI: 1.79 to 3.18) and anthracycline dose > 300 mg/m2 (RR: 1.72; 95% CI: 1.31 to 2.26). Survivors with metabolic syndrome were twice as likely to have abnormal global longitudinal strain (RR: 1.94; 95% CI: 1.66 to 2.28) and abnormal diastolic function (RR: 1.68; 95% CI: 1.39 to 2.03) but not abnormal 3D LVEFs (RR: 1.07; 95% CI: 0.74 to 1.53). Conclusions Abnormal global longitudinal strain and diastolic function are more prevalent than reduced 3D LVEF and are associated with treatment exposure. They may identify a subset of survivors at higher risk for poor clinical cardiac outcomes who may benefit from early medical intervention.
Stimuli responsive polymers can provide a variety of applications for the biomedical fields. The interest in these polymers has exponentially increased due to their promising potential. Among them, ...temperature and pH responsive mechanisms have been considerably investigated because they are relatively convenient and effective stimuli in many applications. In this review, our main purposes are focused on temperature and pH responsive polymer systems and additionally the other stimuli-based responsive polymers will be assessed. Dozens of reviews have been recently reported to introduce the field of stimuli responsive polymers. However, most of these reviews have been focused on one specific application such as drug delivery or one specific physical form such as hydrogels. In our point of view, the whole range of applications and physical forms of stimuli responsive polymers will be elucidated, which is more helpful to design new approaches because the basic concepts and mechanisms are systematically connected. This means that any new advanced concepts and mechanisms can be utilized in a variety of other applications as well as other physical forms. Also, we will describe the classification of stimuli responsive polymers by their mechanism of response to stimuli. Moreover, this review focuses on recent approaches of molecular designs which are extremely necessary to develop more desirable and functional stimuli responsive polymers.
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