Bandgap is a key property that determines electrical and optical properties in materials. Modulating the bandgap thus is critical in developing novel materials particularly semiconductors with ...improved features. This study examines the bandgap, highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) energy level trends in a metal organic framework, metal–organic framework 5 (MOF‐5), as a function of Hammett substituent effect (with the constant σm in the meta‐position of the benzene ring) and solvent dielectric effect (with the constant ε). Specifically, experimental design and response surface methodologies helped to assess the significance of trends and correlations between these molecular properties with σm and ε. While the HOMO and LUMO decrease with increasing σm, the LUMO exhibits greater sensitivity to the substituent's electron withdrawing capability. The relative difference in these trends helps to explain why the bandgap tends to decrease with increasing σm.
This study examines the bandgap, highest occupied molecular orbital, and lowest unoccupied molecular orbital energy level trends in a metal organic framework, metal–organic framework 5, as a function of Hammett substituent effect (with the constant σm in the meta‐position of the benzene ring) and solvent dielectric effect (with the constant ε).
The reaction kinetics and the oriented attachment (OA) crystal growth mechanism of anisotropic metal oxide/hydroxide nanowire formation in a sol–gel colloidal system have not been well understood. ...Herein, the kinetics of a base-catalyzed sol–gel synthesis of anisotropic copper hydroxide nanowires was studied to gain an in-depth understanding of the OA-directed crystal growth mechanism and its chemical kinetic reaction pathways in a quasi-homogeneous colloidal system. The OA-directed sol–gel synthesis process developed in this work followed the initial stage of salt metathesis and nucleation by base-catalyzed hydrolysis, then sol formation by hydrolysis and condensation stages, and finally nanowire formation by the polycondensation process. A novel chemical kinetic model that governs the crystal growth at each stage of this sol–gel process was elucidated from the nanoscopic insight provided by high-resolution transmission electron microscopy (HR-TEM) and UV–vis absorbance kinetic plots. The time-dependent HR-TEM analysis revealed the initiation step of the OA-directed crystal growth mechanism that began from the sol formation. The nanocrystals’ volume growth analysis showed sigmoidal growth behavior, confirming a second-order sigmoidal Boltzmann kinetic growth model with a growth rate constant of 0.243 ± 0.867 min–1 for the hydrolysis and condensation stage. The time-dependent HR-TEM images, collected during the polycondensation process at ambient temperature, exhibited longitudinal crystal growth of nanoarrays by facet-specific alignment and fusion of nanocrystals to form single-crystal nanowires. In the subsequent low-temperature polycondensation step, these nanowires showed further growth via directional elongation along the 020 crystal facet to form fully grown nanowires. The respective kinetic growth models for these two subsequent polycondensation steps supported the propagation step of the OA-directed crystal growth and followed a sigmoidal Boltzmann zeroth-order growth model, with mean growth rates of 0.197 ± 0.064 nm/min and 2.448 ± 0.633 nm/h, respectively. These experimentally derived multistep kinetic models using a simple but versatile analytical approach could be used to understand the OA mechanism of metal hydroxides’/oxides’ nanowire growth in a sol–gel colloidal system. Furthermore, this study tests and verifies a robust anisotropic single-crystal growth process to make size- and shape-controlled nanowires with a spatial lattice orientation.
The US National Science Foundation defines convergence as the deep integration of knowledge, techniques, and expertise from multiple fields to form new and expanded frameworks for addressing ...scientific and societal challenges and opportunities. Because convergence research is progressing at a rapid clip, the quick evolution of non-traditional perspectives that it engenders will present a number of challenges/opportunities to education. NSF, the Organization for Economic Cooperation and Development; the US National Academies of Sciences, Engineering and Medicine; and the University of Southern California sponsored a workshop, with global participation, to explore actions that would facilitate convergence in education. A descriptive of the workshop and the key action items it identified are presented.
Semiconductor materials are crucial components in current and upcoming green industrial sectors, such as electric vehicles. As supply chain issues loom with sources of semiconductor materials, there ...is an emerging need for alternative and environmentally friendly semiconducting materials. One of the potential candidates is iron metal-organic frameworks (Fe-MOFs) which have been used as photocatalysts. Studying the bandgap modulation trends in Fe-MOFs thus will be beneficial for future applications in semiconductor technologies. With a response surface method, here we examine the bandgap, HOMO, and LUMO energy level trends in MOF-5 fully transmetalated with iron (i.e., Fe-MOF-5), as a function of the substituent effect (in the term of Hammett constant σ m ) and solvent effect (in the term of dielectric constant ε). The bandgap, HOMO, and LUMO energy levels all decrease with decreasing ε and increasing σ m . However, the dominating influence for the bandgap switches from σm and ε to just ε as the value of ε increases. This result along with the polynomial equations of fit from statistical analysis suggest that the bandgap in these transmetalated models is significantly influenced by the dipole-induced dipole interactions. These results provide insight into the impact of shifting interactions of σ m and ε on the bandgap of Fe-MOF-5.
In the quest for new semiconductor materials and processes, researchers focus on self-assembly, a concept that draws from diverse disciplines like chemistry, biology, material science, and electrical ...engineering. The following areas are examined: information theory; thermodynamics, synergetics and self-assembly; ribosome based lithography; nanofabrication by self-assembly; molecular electronics; and smart matter.
Recent attention has focused on the high rates of annual carbon sequestration in vegetated coastal ecosystems--marshes, mangroves, and seagrasses--that may be lost with habitat destruction ...('conversion'). Relatively unappreciated, however, is that conversion of these coastal ecosystems also impacts very large pools of previously-sequestered carbon. Residing mostly in sediments, this 'blue carbon' can be released to the atmosphere when these ecosystems are converted or degraded. Here we provide the first global estimates of this impact and evaluate its economic implications. Combining the best available data on global area, land-use conversion rates, and near-surface carbon stocks in each of the three ecosystems, using an uncertainty-propagation approach, we estimate that 0.15-1.02 Pg (billion tons) of carbon dioxide are being released annually, several times higher than previous estimates that account only for lost sequestration. These emissions are equivalent to 3-19% of those from deforestation globally, and result in economic damages of $US 6-42 billion annually. The largest sources of uncertainty in these estimates stems from limited certitude in global area and rates of land-use conversion, but research is also needed on the fates of ecosystem carbon upon conversion. Currently, carbon emissions from the conversion of vegetated coastal ecosystems are not included in emissions accounting or carbon market protocols, but this analysis suggests they may be disproportionally important to both. Although the relevant science supporting these initial estimates will need to be refined in coming years, it is clear that policies encouraging the sustainable management of coastal ecosystems could significantly reduce carbon emissions from the land-use sector, in addition to sustaining the well-recognized ecosystem services of coastal habitats.
To revise the "Clinical Practice Guidelines for the Sustained Use of Sedatives and Analgesics in the Critically Ill Adult" published in Critical Care Medicine in 2002.
The American College of ...Critical Care Medicine assembled a 20-person, multidisciplinary, multi-institutional task force with expertise in guideline development, pain, agitation and sedation, delirium management, and associated outcomes in adult critically ill patients. The task force, divided into four subcommittees, collaborated over 6 yr in person, via teleconferences, and via electronic communication. Subcommittees were responsible for developing relevant clinical questions, using the Grading of Recommendations Assessment, Development and Evaluation method (http://www.gradeworkinggroup.org) to review, evaluate, and summarize the literature, and to develop clinical statements (descriptive) and recommendations (actionable). With the help of a professional librarian and Refworks database software, they developed a Web-based electronic database of over 19,000 references extracted from eight clinical search engines, related to pain and analgesia, agitation and sedation, delirium, and related clinical outcomes in adult ICU patients. The group also used psychometric analyses to evaluate and compare pain, agitation/sedation, and delirium assessment tools. All task force members were allowed to review the literature supporting each statement and recommendation and provided feedback to the subcommittees. Group consensus was achieved for all statements and recommendations using the nominal group technique and the modified Delphi method, with anonymous voting by all task force members using E-Survey (http://www.esurvey.com). All voting was completed in December 2010. Relevant studies published after this date and prior to publication of these guidelines were referenced in the text. The quality of evidence for each statement and recommendation was ranked as high (A), moderate (B), or low/very low (C). The strength of recommendations was ranked as strong (1) or weak (2), and either in favor of (+) or against (-) an intervention. A strong recommendation (either for or against) indicated that the intervention's desirable effects either clearly outweighed its undesirable effects (risks, burdens, and costs) or it did not. For all strong recommendations, the phrase "We recommend …" is used throughout. A weak recommendation, either for or against an intervention, indicated that the trade-off between desirable and undesirable effects was less clear. For all weak recommendations, the phrase "We suggest …" is used throughout. In the absence of sufficient evidence, or when group consensus could not be achieved, no recommendation (0) was made. Consensus based on expert opinion was not used as a substitute for a lack of evidence. A consistent method for addressing potential conflict of interest was followed if task force members were coauthors of related research. The development of this guideline was independent of any industry funding.
These guidelines provide a roadmap for developing integrated, evidence-based, and patient-centered protocols for preventing and treating pain, agitation, and delirium in critically ill patients.
Background.Catheter-related bloodstream infection (CRBSI) causes substantial morbidity and mortality, but few randomized, controlled studies have been conducted to guide therapeutic interventions. ...Methods.To determine whether linezolid would be noninferior to vancomycin in patients with CRBSI, we conducted an open-label, multicenter, comparative study. Patients with suspected CRBSI were randomized to receive linezolid or vancomycin (control group). The primary end point was microbiologic outcome at test of cure 1 2 weeks after treatment, as assessed by step-down procedure. The first analysis population was complicated skin and skin structure infection (cSSSI) in patients with suspected CRBSI; patients with CRBSI were analyzed if noninferiority criteria (lower bound of the 95% confidence interval CI not outside −15%) were met. Results.Noninferiority criteria were met for cSSSI (microbiologic success rate for linezolid recipients, 89.6% 146 for 163 patients; for the control group, 89.9% 134 of 149; 95% CI, −7.1 to 6.4) and CRBSI (for linezolid recipients, 86.3% 82 of 95; for the control group, 90.5% 67 of 74; 95% CI, −13.8 to 5.4). The frequency and severity of adverse events were similar between groups. Mortality rates were 10.4% for linezolid recipients (28 of 269 patients) and 10.1% for control subjects (26 of 257) in the modified intent-to-treat population (i.e., all patients with gram-positive baseline culture) through test of cure, and they were 21.5% for linezolid recipients (78 of 363) and 16.0% for the control group (58 of 363; 95% CI, −0.2 to 11.2) for all treated patients through poststudy treatment day 84. Conclusions.Linezolid demonstrated microbiologic success rates noninferior to those for vancomycin in patients with cSSSIs and CRBSIs caused by gram-positive organisms. Patients with catheter-related infections must be carefully investigated for the heterogeneous underlying causes of high morbidity and mortality, particularly for infections with gram-negative organisms.
The airways of patients afflicted with cystic fibrosis (CF) are colonized by many pathogens, the most predominant of which is the Gram-negative bacterium Pseudomonas aeruginosa . In the thick CF ...airway mucus, P. aeruginosa forms antibiotic- and phagocyte-resistant structures known as biofilms, which enable the survival and growth of the organism. P. aeruginosa can undergo dramatic genetic, physiological and morphological changes in this milieu. Chronic infection leads to a considerably reduced oxygen tension, and it is believed that some bacteria grow anaerobically, especially during late-stage disease. In this article, factors that enable long-term survival of P. aeruginosa and two novel drug targets (the rhl quorum-sensing circuit and the anti-sigma factor, MucA) are discussed. Mutants lacking these factors might be uniquely susceptible to nitrogen oxide, specifically the nitrite anion (NO2− ), in the treatment of P. aeruginosa airway infections in CF.
A 26-year-old otherwise healthy man died of fulminant myocarditis. Nasopharyngeal specimens collected premortem tested negative for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). ...Histopathological evaluation of the heart showed myocardial necrosis surrounded by cytotoxic T-cells and tissue-repair macrophages. Myocardial T-cell receptor (TCR) sequencing revealed hyper-dominant clones with highly similar sequences to TCRs that are specific for SARS-CoV-2 epitopes. SARS-CoV-2 RNA was detected in the gut, supporting a diagnosis of multisystem inflammatory syndrome in adults (MIS-A). Molecular targets of MIS-associated inflammation are not known. Our data indicate that SARS-CoV-2 antigens selected high-frequency T-cell clones that mediated fatal myocarditis.
PDF
