With cigarette users as the referent category, the analysis suggests that exclusive e-cigarette users are less likely to have their respiratory symptoms worsen, along with consistent findings , than they are more likely to have their symptoms improve. In sum, with respect to short-term changes in functionally-important respiratory symptoms, the results suggest risk for exclusive e-cigarette users are intermediate–increased harm compared to never tobacco users, but reduced harm compared to cigarette users. Cigar smokers had consistently lower risk for functionally-important respiratory symptoms compared to exclusive cigarette smokers, as was previously reported for some of the single respiratory symptom items in another PATH Study report.Cigar smoking has been associated with higher mortality from respiratory disease and lung cancer,increased risk for diagnosis of lung cancer and COPD,decreased lung function and airflow obstruction,and respiratory symptoms. In all studies including cigarette smokers, risks associated with cigars were lower than for cigarettes; former cigarette smokers switching to cigars had higher risk vs. those who had smoked only cigars.Respiratory symptom risk among hookah smokers has not been studied extensively but was intermediate between never smokers and cigarette smokers in one study.Lower symptom risk with exclusive cigar use may be explained by reduced smoke inhalation.In contrast to cigarettes, cigar tobacco is fermented, and many cigars are smoked with lower frequency. Cigar smokers also tend to inhale less deeply because of smoke alkalinity which also enhances oral nicotine absorption. Only 15% of exclusive cigar smokers report actively inhaling the smoke, compared to two-thirds for users of both cigars and cigarettes .Marijuana was associated with functionally-important respiratory symptoms, consistent with 8 of 10 previous studies.The findings are backed by research involving dual users of marijuana and cigarettes showing higher puff volumes, deeper inhalation,movable vertical grow rack system and greater tar retention from marijuana vs. cigarettes,animal research documenting pulmonary cell changes with chronic marijuana smoking, and prospective research showing changes in lung function among marijuana smokers.
Marijuana use was also a confounder of the e-cigarette—respiratory symptoms association. One study showing an association between e-cigarette use and cough among young never cigarette smokers, failed to adjust for marijuana use in the multi-variable model . Another study of adult PATH Study W4 data found vaping with marijuana to be associated with wheezing , consistent with our findings.Two other studies of youth, one using PATH Study data, have shown that the e-cigarette—respiratory outcome is confounded by marijuana use and marijuana vaping.Clinicians need to be aware of the association between marijuana use and respiratory symptoms as use increases.The study strengths include a nationally representative sample, a validated respiratory outcome related to functional impairment, and adjustment for multiple confounding influences. Limitations include small numbers in some product groups, increasing the probability of a chance finding. Because switching from cigarette smoking to exclusive e-cigarette use is an uncommon event, randomized e-cigarette switching trials may be required to better assess how e-cigarette substitution affects wheezing symptoms among adult cigarette smokers. Risk of marijuana smoking on respiratory symptoms may be underestimated because marijuana use may have included non-combustible products. Relying on self-report of COPD may have resulted in some who were unaware of their diagnosis being retained in the study. The findings relate only to short-term changes in wheezing and nighttime cough, not other bothersome symptoms , longer-term symptom effects, relation to respiratory disease onset, or vaping-related acute lung injury—medical issues that underline concern about any inhaled product use. The analysis included many comparisons and nevertheless employed a p-value of 0.05; the associations reported should be confirmed in other samples. Finally, future analyses with the latest available data from the PATH Study may provide a more refined look at the questions addressed in the present study. In summary, this study of a nationally representative sample of US adults without severe respiratory disease found an association between cigarette smoking and functionally-important respiratory symptoms – and substantially less evidence of associations between respiratory symptoms and exclusive non-cigarette tobacco product use. Microporous materials, which are defined by a pore size of less than 2 nm, are used in both research and industrial applications in chemical separations, catalysis, and energy storage.
They comprise a diverse group of materials, including zeolites, metal-organic frameworks, covalent organic frameworks, and porous carbons. These classes of materials are distinct in their synthesis methods and compositions, but are united by their small pore sizes, which are on the scale of many chemically and industrially important molecules, as well as their potential for large accessible surface areas. Zeolites are naturally occuring aluminosilicate materials that were discovered in 1756.Today, they are produced on an industrial scale, and are ubiquitous in catalysis and other industrial applications due to their chemical and thermal stability.234 distinct zeolite framework types have been classified as of 2019,and the potential for chemical modifications such as ion exchange further increases the design space of such materials. Metal-organic frameworks are a newer class of materials, first synthesized a few decades ago, and comprise a three-dimensional network of metal centers connected to organic linkers by coordination bonds. They are synthesized using reticular chemistry, in which molecular building blocks are assembled to form extended crystalline structures. Like other microporous materials, MOFs also have very high surface areas, with record Brunauer-Emmett-Teller surface areas of about 7000 m g−2 reported to date and hypothetical maximum surface areas predicted to be up to two times larger.The design and synthesis of new MOFs has been a flourishing research area in the past few decades, and the development of more chemically stable MOFs has led to their increasingly widespread use in organic catalysis, gas separations, imaging, sensing, and proton, electron, and ion conduction.Zeolites and MOFs are both crystalline materials, which is a desirable characteristic as it means that composition and pore geometry are well-defined on a large scale. Other microporous materials which have short-range order but can be disordered on longer scales include covalent organic frameworks ,which are also synthesized using reticular chemistry but are composed of organic nodes and linkers and are therefore fully covalently bonded, as well as zeolite-templated carbons .
Reticular synthesis is modular in nature, yielding a virtually limitless design space for MOFs as different combinations of nodes and linkers can be used, which assemble in different topological nets. Ca. 70 000 MOFs have been synthesized to date, as reported on the Cambridge Crystallographic Structure Database ,and thousands of new structures are reported each year. To add to this abundance of experimental structures, there exist libraries of hypothetical MOFs which bring the total number of experimentally synthesized and hypothetical structures into the hundreds of thousands. In order to make this design space tractable, computational chemistry, and in particular molecular simulations, can be used to predict the properties of structures even before synthesis and identify promising structures for a particular application.In this way, computation and experiment can work in tandem, with simulations “discovering” hypothetical materials in silico to inform and inspire experimental synthesis, and experimental results demonstrating new structures and unexpected properties to direct computational study. Achieving correspondence between experimental and theoretical results is not always straightforward, but has led to breakthroughs in material design and elucidation of mechanisms toward better understanding of material properties. Microporous materials have great potential in technologies to decrease the energy needed for existing industrial processes, to mitigate the effects of increased anthropogenic emissions to the atmosphere through carbon capture and sequestration , and to provide more sustainable energy storage solutions. For example, the amine-appended MOF N,N’-dimethylethylenediamine-Mg2 , was shown to exhibit a step-shaped CO2 adsorption isotherm, which indicates potential for high deliverable capacity in a temperature- or pressure-swing adsorption process,movable vertical growing solutions with lower energy requirements than the currently used amine scrubbing technologies for CCS.This step-shaped adsorption isotherm was shown to be due to a phase-change adsorption mechanism involving the amine functional groups.Another study synthesized a library of COFs in silico and screened them for methane storage applications, finding that one of the materials had better predicted methane deliverable capacity than any other reported structures.Similarly, a screening study of the materials in the Nanoporous Materials Genome identified promising materials for hydrogen storage.Microporous materials are also used extensively in electrochemical energy storage applications as the electrode material for batteries and super capacitors.The field is dominated by carbon-based materials due to their affordability and conductivity,though recently asuper capacitor with electrodes made from a neat MOF was demonstrated.Though the equations that describe force fields are simple, when combined they represent a powerful tool that allows for simulation of large systems with relatively high accuracy. Several features of force fields lend themselves to computational efficiency: the first is that non-bonded interactions are pairwise, meaning that the non-bonded potential of a configuration of atoms can be computed by summing interactions between pairs of atoms. In addition, while the electronic density of atoms is spread over a nonzero volume, in classical force fields the electron density is usually treated as a point charge. These features lead to several computational algorithms that allow for short range cutoffs coupled with long-range corrections . As mentioned throughout this overview of force fields, there are myriad ways to increase the complexity of classical force fields, for example by describing bonding implicitly using “reactive” force field methods that calculate bond order on the fly, or by using functional forms that involve more parameters to fit to a class of systems. With the increase of computational power in the last few decades, it is also possible to compute the potential energy of increasingly large configurations of atoms using electronic structure methods. However, due to the computational efficiency of classical simulations, it is likely that they will always enable simulations of larger and more complex systems compared to quantum mechanical methods, and thus classical force fields will remain relevant for a long time.
The 10.0% enhancement in linear conversion of Ni-MOF-74 relative to FAU is in good agreement with the 11.1% enhancement observed experimentally by Mlinar et al., suggesting that our model and theoretical framework capture quantitatively the influence of the adsorbent material on product distribution. Interestingly, the absolute predicted linear conversions are 13.0% lower than their respective experimental values. This means the experimental materials are consistently more selective towards linear isomers than their simulated counterparts. This could be due to diffusive barriers not accounted for by our simulations, which would favor the less-bulky linear isomers. We also want to emphasize that these calculations rely on equilibrium thermodynamics, and thus presume that Brønsted-Evans-Polanyi conditions are met. From this comparison with the experimental results of Mlinar et al., we can conclude that the contribution of the pores to the free energy of formation is indeed a useful indicator of how the product distribution varies with the catalyst material. It is therefore interesting to explore how this distribution can be further changed by using a different zeolite MOF structure. Expanding the database of structures allows us to better understand how molecular descriptors correlate with product distribution, and further elucidate design principles of materials for propene dimerization.Cannabis has in recent years seen increasing decriminalization for both recreational and medical use under some local and state jurisdictions. Since 2012, 10 U.S. states have legalized recreational use of cannabis and 33 states medical use of the drug, coinciding with a shift in societal attitudes regarding cannabis use.Immoderate cannabis use has been shown to have public health and safety implications, for example a moderate increase in risk of injury or fatality while driving under intoxication.As a result, increasing use of cannabis requires improved methods, similar to alcohol, for portable detection of cannabis intoxication in order to promote more consistent cannabis regulation and safer cannabis use. The pharmacological effects of cannabis result from a variety of chemical compounds, including several hundred types of cannabinoid which can be found in the plant. The principal psychoactive component of cannabis is ∆9 -tetrahydrocannabinol , which affects motor and cognitive function and has been linked to increased risk of motor vehicle crashes.For roadside testing applications, breath-based testing of THC has the greatest potential as it is less invasive than testing of urine or blood. Breath detection has other advantages as well. The window of detection of THC in breath coincides with the period of peak impairment.THC and its metabolites can also be detected in blood and urine, but as cannabinoid compounds persist for several times longer in these bodily fluids they are not a reliable indicator of intoxication.Though the full window of driving impairment may extend longer than 2 h, the short detection window in breath may be able to be extended using methods that have increased sensitivity.