Search

Even after centuries-old experience in carbonizing materials we can still learn new lessons and find new applications for carbonized materials. In the past decades, laser-assisted syntheses of materials have emerged as versatile tools for the fabrication of micro- and nanostructured functional devices. In this regard, laser-carbonization is of particular interest, as it provides a method for patterning eco-friendly and potentially biodegradable electronic materials for future applications in comparison to the state-of-the-art in flexible electronics. However, using molecular precursors for laser-carbonization has been a challenge for many years. We identified a set of three different precursors and conducted an in-depth morphological and compositional study to understand how molecular precursors must be prepared for the high-speed carbonization reactions used in laser-patterning. The resulting laser-patterned carbons (LP-C) or N-doped carbons (LP-NC) are different from their conventionally pyrolyzed reference products mostly in terms of morphology. A generally porous structure and a carbonization gradient induced by the top-to-bottom energy input are the most remarkable features. Additionally, the microstructure, the elemental composition and the resulting electronic properties are different as demonstrated by X-ray photoelectron spectroscopy (XPS) and wide-angle X-ray scattering (WAXS) analysis.

Unlike growth on tissue, microbes can grow freely on implantable devices with minimal immune system intervention and often form resilient biofilms that continuously pump out pathogenic cells. The efficacy of antibiotics used to treat infection is declining due to increased rates of pathogenic resistance. A simple, one-step zwitterionic surface modification is developed to significantly reduce protein and microbial adhesion to synthetic materials and demonstrate the successful modification of several clinically relevant materials, including recalcitrant materials such as elastomeric polydimethylsiloxane. The treated surfaces exhibit robust adhesion resistance against proteins and microorganisms in both static and flow conditions. Furthermore, the surface treatment prevents the adhesion of mammalian fibroblast cells while displaying no cytotoxicity. To demonstrate the clinical efficacy of the novel technology in the real-world, a surface-treated, commercial silicone foley catheter is developed that is cleared for use by the U.S. Food and Drug Administration (K192034). 16long-term catheterized patients received surface-treated catheters and completed a Patient Global Impression of Improvement (PGI-I) questionnaire. 10out of 16patients described their urinary tract condition post implantation as "much better" or "very much better" and 72% (n=13) of patients desire to continue using the surface-treated catheter over conventional latex or silicone catheters.

Graphene oxide (GO) membranes have great potential for separation applications due to their low-friction water permeation combined with unique molecular sieving ability. However, the practical use of deposited GO membranes is limited by the inferior mechanical robustness of the membrane composite structure derived from conventional deposition methods. Here, we report a nanostructured GO membrane that possesses great permeability and mechanical robustness. This composite membrane consists of an ultrathin selective GO nanofilm (as low as 32 nm thick) and a postsynthesized macroporous support layer that exhibits excellent stability in water and under practical permeability testing. By utilizing thin-film lift off (T-FLO) to fabricate membranes with precise optimizations in both selective and support layers, unprecedented water permeability (47 L·m-2·hr-1·bar-1) and high retention (>98% of solutes with hydrated radii larger than 4.9 A) were obtained.

For the past 30 years, thin-film membrane composites have been the state-of-the-art technology for reverse osmosis, nanofiltration, ultrafiltration, and gas separation. However, traditional membrane casting techniques, such as phase inversion and interfacial polymerization, limit the types of material that are used for the membrane separation layer. Here, we describe a novel thin-film liftoff (T-FLO) technique that enables the fabrication of thin-film composite membranes with new materials for desalination, organic solvent nanofiltration, and gas separation. The active layer is cast separately from the porous support layer, allowing for the tuning of the thickness and chemistry of the active layer. A fiber-reinforced, epoxy-based resin is then cured on top of the active layer to form a covalently bound support layer. Upon submersion in water, the cured membrane lifts off from the substrate to produce a robust, freestanding, asymmetric membrane composite. We demonstrate the fabrication of three novel T-FLO membranes for chlorine-tolerant reverse osmosis, organic solvent nanofiltration, and gas separation. The isolable nature of support and active-layer formation paves the way for the discovery of the transport and selectivity properties of new polymeric materials. This work introduces the foundation for T-FLO membranes and enables exciting new materials to be implemented as the active layers of thin-film membranes, including high-performance polymers, two-dimensional materials, and metal-organic frameworks.

The facile fabrication of functionally graded all-graphene films using a single-step casting process is reported. The films consist of a self-assembled graphene oxide (GO) precursor that can be reduced to different levels on an active metal substrate. Control of processing conditions such as the underlying substrate metal and the film-drying environment results in an ability to tailor the internal architecture of the films as well as to functionally grade the reduction of GO. A gradient arrangement within each film, where one side is electrically conductive reduced GO (rGO) and the other side is insulating GO, was confirmed by scanning electron microscopy, Raman, X-ray diffraction, Fourier transform infrared, and X-ray photoelectron spectroscopy characterization studies. All-graphene-based freestanding films with selectively reduced GO were used in transient electronic applications such as flexible circuitry and RFID tag antennas, where their decommissioning is easily achieved by capitalizing on GO's ability to readily dissociate and create a stable suspension in water. Furthermore, the functionally graded structure was found to exhibit differential swelling behavior, and its potential applications in graphene-based actuators are outlined.

Carbon-based supercapacitors exhibit great rate capability, power density and cycle life, but suffer from relatively low energy density. Polyaniline provides high specific capacitance, but lacks cycling stability. By combining carbon-based materials with tetraaniline, an oligomer of polyaniline, a hybrid composite is formed that demonstrates improved supercapacitor performance relative to either material alone. In this study, the reduced graphene oxide-oligoaniline composites have been synthesized by a one-step hydrothermal process without the need for adding any oxidizing or reducing agents. FTIR, Raman spectroscopy, XPS, and MALDI-TOF mass spectroscopy indicate the successful reduction of GO to rGO and the formation of aniline oligomers. Unlike most polyaniline nanostructures for which charge storage kinetics are limited by slow diffusion-controlled reactions, the majority of oligoaniline in this composite is exposed to the electrolyte and stores charge through fast surface-controlled reactions. The unique microstructure of the rGO-oligoaniline composites facilitates transport of ions and electrons, leading to greater utilization of the active materials, high specific capacitance of 640 F/g at 0.2 mA/cm2 (corresponding to 707 C/g specific capacity), great rate capability and good cycle stability (91% retention after 2000 cycles).

The conversion of small bio-based molecules into electro-active functional carbon nanomaterials such as carbon nanodots or graphene is attracting increasing interest. In this communication we demonstrate the use of laser-reduced carbon nanodots (lrCND) as electrodes for electrochemical capacitors. A CO2-laser-assisted process is utilized to convert CNDs into highly conductive 3D-carbon monoliths. Exclusion of molecular oxygen from the reaction environment has a positive effect on device parameters and particularly on the frequency response. Using this simple and inexpensive method, an extremely fast RC time constant of 0.29 ms and a capacitance of 0.259 mF cm−2 at 120 Hz were obtained. This can be attributed to an effective conversion of CNDs into graphitic carbon in an oxygen-free environment and the presence of unconverted CNDs in the 3D-carbon network acting as doping agents.

We estimate change in total water and its components each month from January 2006 to the Present using geodetic observations from space and complementary hydrologic measurements. Estimates of changes in total water inferred from GPS elastic displacements are used to strengthen the spatial resolution of GRACE observations of mass change, resulting in sharper images of water change. We furthermore distinguish between different components of water change. Change in surface water in man's artificial reservoirs and natural lakes are known from gauging measurements of water levels. The distribution and magnitude of snow accumulation is inferred from sticks and scales on the ground. We remove the effect of surface water and snow to infer change in water in the ground, consisting of soil moisture and groundwater. This determination is bringing powerful insights into understanding the water cycle. We are finding more water to be lost during drought and gained during heavy precipitation than in the hydrology models, suggesting that the hydrology models must be revised to have a greater capacity to store water in the ground. Not all rain and melting snow that falls on the mountains of California, Oregon, and Washington is found to runoff into rivers taking water to the ocean. Rain and melting snow is instead found to infiltrate the ground in the wet fall and winter and and to be parched from the ground in the dry spring and summer.

The COVID‐19 outbreak has posed significant threats to international health and the economy. In the absence of treatment for this virus, public health officials asked the public to practice social distancing to reduce the number of physical contacts. However, quantifying social distancing is a challenging task and current methods are based on human movements. We propose a time and cost‐effective approach to measure how people practice social distancing. This study proposes a new method based on utilizing the frequency of hashtags supporting and encouraging social distancing for measuring social distancing. We have identified 18 related hashtags and tracked their trends between Jan and May 2020. Our evaluation results show that there is a strong correlation (p

Social media has become a mainstream channel of communication during the COVID‐19 pandemic. While some studies have been developed on investigating public opinion on social media data regarding COVID‐19 pandemic, there is no study analyzing anti‐quarantine comments on social media. This study has collected and analyzed near 80,000 tweets to understand anti‐quarantine social comments. Using text mining, we found 11 topics representing different issues such as comparing COVID‐19 and flu and health side effects of quarantine. We believe that this study shines a light on public opinion of people who are against quarantine.

Increased water storage in the Missouri River basin as inferred from GRACE gravity [Reager et al. 2014] preceded the May–June 2011 catastrophic floods. In this study, we analyze the evolution and lateral distribution of water components in the four years before and two years after the 2011 floods (believed to occur once every 500 years). We integrate GPS measurements of solid Earth's elastic response to water change and GRACE gravity data to infer change in total water storage as a function of time in the Missouri River basin. We furthermore evaluate relative water storage and discharge in 6 major sub-basins as measured by gauging stations along the Kansas, Platte, Yellowstone, and Missouri Rivers. We aim to understand how water changes between different components (snow, soil moisture, groundwater, surface water) and how the spatial distribution of water changes in the Missouri River basin.

Thin-film composite (TFC) membranes are favored for precise molecular sieving in liquid-phase separations; they possess high permeability due to the minimal thickness of the active layer and the high porosity of the support layer. However, current TFC membrane fabrication techniques are limited by the available materials for the selective layer and do not demonstrate the level of structural control needed to substantially advance organic solvent nanofiltration (OSN) membrane technology. In this work, we employ the newly developed thin-film lift-off (T-FLO) technique to fabricate polybenzimidazole (PBI) TFC membranes with porous support layers uniquely tailored to OSN. The drop-cast dense PBI selective layers endow the membranes with an almost complete rejection of common small dye molecules. The polymeric support layer is optimized by a combinatorial approach using four different monomers that alter the cross-linking density and polymer chain flexibility of the final composite. These two properties substantially affect the porogen holding capacity of the reticular polymer network, leading to the formation of different macropore structures. With a 150 nm thick PBI selective layer and fine-tuning of the support layer, the resulting membrane achieves stable and superior permeance of 14.0, 11.7, 16.4, 11.4, 17.1, and 19.7 L m-2 h-1 bar-1 for water, ethanol, methanol, isopropanol, tetrahydrofuran (THF), and acetonitrile, respectively.

Modified polyolefin separators fabricated via a roll-to-roll system exhibit markedly improved compatibility with lithium ion battery electrolytes. Zwitterionic molecules containing a perfluorophenyl azide functional group were synthesized and covalently bound to the surface of commercial polyolefin separators via UV-activated photochemistry. A roll-to-roll prototype system was constructed allowing for the functionalization of large areas of separator under ambient conditions at low cost. Lithium-ion battery cells containing the modified separators exhibit superior electrochemical performance using a common commercial electrolyte. The modified separators, both monolayer PE and trilayer PP/PE/PP, are wetted instantly upon contact with liquid electrolytes lacking linear carbonates. These electrolytes have been designed for use in batteries with advanced thermal stability properties and/or higher voltage windows, which have previously been hindered by incompatibility with commercial trilayer polyolefin separa...

Supercapacitors are energy storage and conversion devices that display high power. In order to increase energy density, redox-active materials can be incorporated into the carbonaceous electrode(s). Although in recent years many studies have offered different redox-active candidates and composite methods, there is a constant search for an effective, easily producible and stable composite material. Here, we present a graphene/ferrocene composition as a redox active 3-D supercapacitor electrode material. The combination of highly reversible, conductive and strongly attached ferrocene with the high surface area and open porous structure of graphene results in high-power, high-energy density supercapacitors. The graphene scaffold is converted from graphene-oxide (GO) by laser irradiation, a facile, fast and eco-friendly method. The ferrocene is chemically bonded to the graphene by two different approaches that take advantage of the strong and stable pi–pi interactions between the carbon and the aromatic ligands. The excellent bonding between the components results in low internal resistance and high reversibility of the redox reaction. The composite demonstrated a 205% increase in specific capacitance from 87 F g−1 for pure laser reduced graphene oxide to 178 F g−1 for the composite with ferrocene. This is equivalent to an energy density of 6.19 W h kg−1 while maintaining a power density of 26.0 kW kg−1.

Dicarboxylic acids play a key role in atmospheric particle nucleation. Though long assumed to originate from primary sources, little experimental evidence exists directly linking combustion to their emissions. In this work, we sought definitive proof that dicarboxylic acids are produced in diesel engines and that they can slip through a modern aftertreatment system (ATS) at low exhaust temperatures. One difficulty in measuring dicarboxylic acid emissions is that they cannot be identified using conventional mass spectroscopy techniques. In this work, we refined a derivatization gas chromatography-mass spectroscopy technique to measure 11 mono- and dicarboxylic acids from plain and KOH impregnated quartz filters. Filters were loaded with exhaust from a modern passenger car diesel engine on a dynamometer sampled before and after an ATS consisting of an oxidation catalyst and diesel particulate filter. Our findings confirm that dicarboxylic acids are produced in diesel engine combustion, especially during low temperature combustion modes that emit significant concentrations of partially combusted hydrocarbons. Exhaust acids were largely removed by a fully warmed-up ATS, mitigating their environmental impact. Our results also suggest that dicarboxylic acids do not participate in primary particle formation in dilute engine exhaust as low quantities were collected on unimpregnated filters.

Introduction Dizziness is a common complaint presented in the emergency department (ED). A subset of these patients will present with acute vestibular syndrome (AVS). AVS is a clinical syndrome defined by the presence of vertigo, nystagmus, head motion intolerance, ataxia, and nausea/vomiting. These symptoms are most often due to benign vestibular neuritis; however, they can be a sign of a dangerous central cause, i.e., vertebrobasilar stroke. The Head Impulse test, Nystagmus, Test of Skew (HINTS) examination has been proposed as a bedside test for frontline clinicians to rule out stroke in those presenting with AVS. Our objective was to assess the diagnostic accuracy of the HINTS examination to rule out a central cause of vertigo in an adult population presenting to the ED with AVS. Our aim was to assess the diagnostic accuracy when performed by emergency physicians versus neurologists. Methods We searched PubMed, Medline, Embase, the Cochrane database, and relevant conference abstracts from 2009 to September 2019 and performed hand searches. No restrictions for language or study type were imposed. Prospective studies with patients presenting with AVS using criterion standard of computed tomography and/or magnetic resonance imaging were selected for review. Two independent reviewers extracted data from relevant studies. Studies were combined if low clinical and statistical heterogeneity was present. Study quality was assessed using the QUADAS-2 tool. Random effects meta-analysis was performed using RevMan 5 and SAS 9.3. Results A total of five studies with 617 participants met the inclusion criteria. The mean (±SD) study length was 5.3 (±3.3) years. Prevalence of vertebrobasilar stroke ranged 9.3% to 44% (mean ± SD = 39.1% ± 17.1%). The most common diagnoses were vertebrobasilar stroke (mean ± SD = 34.8% ± 17.1%), peripheral cause (mean ± SD = 30.9% ± 16%), and intracerebral hemorrhage (mean ± SD = 2.2% ± 0.5%). The HINTS examination, when performed by neurologists, had a sensitivity of 96.7% (95% CI = 93.1% to 98.5%, I2 = 0%) and specificity of 94.8% (95% CI = 91% to 97.1%, I2 = 0%). When performed by a cohort of physicians including both emergency physicians (board certified) and neurologists (fellowship trained in neurootology or vascular neurology) the sensitivity was 83% (95% CI = 63% to 95%) and specificity was 44% (95% CI = 36% to 51%). Conclusions The HINTS examination, when used in isolation by emergency physicians, has not been shown to be sufficiently accurate to rule out a stroke in those presenting with AVS.

Producing highly oriented graphene is a major challenge that constrains graphene from fulfilling its full potential in technological applications. The exciting properties of graphene are impeded in practical bulk materials due to lattice imperfections that hinder charge mobility. A simple method to improve the structural integrity of graphene by utilizing laser irradiation on a composite of carbon nanodots (CNDs) and 3D graphene is presented. The CNDs attach themselves to defect sites in the graphene sheets and, upon laser-assisted reduction, patch defects in the carbon lattice. Spectroscopic experiments reveal graphitic structural recovery of up to 43% and electrical conductivity four times larger than the original graphene. The composites are tested as electrodes in electrochemical capacitors and demonstrate extremely fast RC time constant as low as 0.57 ms. Due to their low defect concentrations, the reduced graphene oxide-carbon nanodot (rGO-CND) composites frequency response is sufficiently fast to operate as AC line filters, potentially replacing today's electrolytic capacitors. Using this methodology, demonstrated is a novel line filter with one of the fastest capacitive responses ever reported, and an aerial capacitance of 68.8 mF cm-2 . This result emphasizes the decisive role of structural integrity for optimizing graphene in electronic applications.

Solid solutions of tungsten diboride (WB2) with increasing substitution of tungsten (W) by tantalum (Ta) and niobium (Nb)—ranging from 0 to 50 at. % on a metals basis—were synthesized through resis...

High degrees of dispersion are a prerequisite for functional composite materials for applications in electronics such as sensors, charge and data storage, and catalysis. The use of small precursor materials can be a decisive factor in achieving a high degree of dispersion. In this study, carbon nanodots are used to fabricate a homogeneous, finely dispersed Fe2 O3 -graphene composite aerogel in a one-step conversion process from a precursor mixture. The laser-assisted conversion of small size carbon nanodots enables a uniform distribution of 6.5 nm Fe2 O3 nanoparticles during the formation of a highly conductive carbon matrix. Structural and electrochemical characterization shows that the features of both material entities are maintained and successfully integrated. The presence of Fe2 O3 nanoparticles has a positive effect on the active surface area of the carbon aerogel and thus on the capacitance of the material. This is demonstrated by testing the performance of the composite in supercapacitors. Faradaic reactions are exploited in an aqueous electrolyte through the high accessible surface of the incorporated small Fe2 O3 nanoparticles boosting the specific capacitance of the 3D turbostratic graphene network significantly.

We have recently reported a potentially useful application for conjugated polymer films in the field of gas separations (Science, 252, 1412, 1991). Here we report additional findings which show how selective control of gas permeability is facilitated by the doping, undoping and redoping (cycling) process of emeraldine films. Specifically, permeability data for H2, He, CH4, CO2, O2, N2, and CH4 are given for films treated with perchloric acid. There is a large increase in permeability to all gases following the doping and undoping film treatment cycle. Moreover, controlled redoping (of the undoped films) results in large separation factors for industrially important gas pairs. These results are consistent with the model based on dopant occupation of free-volume of the “pin-hole free” film. This cycling phenomenon is also found in other conjugated polymers such as poly-dimethoxy-para-phenylene-vinylene (DMPPV). Another important variable for gas transport properties of polyaniline films is the film curing time. Permeability data for films cured at 125° C for 2, 3, and 6 hours, and then cycled, indicate that a three hour cure time produces the most fully dense films. We also present preliminary gas permeability data for a polyimide thin film by itself and, a polyimide blend containing polyaniline.

Gas permeability values are reported for films of the conducting polymer polyaniline in the emeraldine oxidation state. Substantial improvements in gas selectivity, when compared to literature values, were observed for all gas pairs studied (He/N2, H2/N2, O2/N2, CO2/CH4). The doping procedure which enables conductivity in the film was found to cause significant concurrent changes in the film morphology which resulted in improved gas separations. These morphological changes primarily influence the permeant diffusivity as shown by comparison to the kinetic diameter of the permeant. The potential for development of conducting polymer membranes with precisely controlled morphology is clearly indicated, allowing optimization of films for any gas separation.

We have recently reported a potentially useful application for conducting polymer films in the field of gas separations [1]. Here we report additional findings that show how selective control of gas permeability is facilitated by the doping, undoping and redoping process of emeraldine films. Specifically, permeability data for H2, He, CO2, O2, N2 and CH4 are given for films treated with varying concentrations of acid and base. There is a large decrease in gas permeation after fully doping the as-cast film. The permeability of the gases are increased when fully doped films are immersed in base to remove all dopant ions. Controlled redoping of the undoped films as a function of acid concentration results in large separation factors for the gas pairs H2/N2, He/N2, CO2/CH4 and O2/N2. These results are partially explained by a model based on size selective control of diffusion pathways. Here we include considerations of dopant induced enhancement of oxygen solubility in redoped membranes to further elucidate the mechanism behind large O2/N2 separation factors.

IN the closing chapters of Good Wives, Nasty Wenches, and Anxious Patriarchs, Kathleen M. Brown concludes, from a reading of William Byrd's diaries, that between I739 and I74I-though Byrd was, to all appearances, contentedly married and nearing seventy-he "frequently engaged in sexual activity with enslaved women."1 Byrd was undeniably anxious at many points in his life, and, on at least one occasion, writing to Charles Boyle after his return to Virginia in I726, he famously compared himself to "one of the patriarchs."2 The term "nasty wenches" never appears in Byrd's diaries or other writings, but, in view of the conclusion that Brown draws about his sexual conduct, he would seem to exemplify the exploitative habits and invidious attitudes that her title evokes-habits and attitudes that Brown finds largely confirmed by the major literary works of Byrd's life, The History of the Dividing Line betwixt Virginia and North Carolina and The Secret History of the Line.3 William Byrd has come to share, with Thomas Jefferson, the dubious distinction of being our representative eighteenth-century planter-libertine.4 But such a reading of Byrd imposes a degree of clarity on the textual evidence that, in some respects, resembles the artificial order that a surveyor's