Effect of Ambient Temperature and Humidity on Aging of Nanocarbons

We researched effect of ambient temperature and humidity on aging of nanocarbons, including carbon nanotubes and fullerenes. We studied physicochemical properties of these nanocarbons stored in ambient conditions (20oC, 35-55%RH) for 24 months, in 90% relative humidity (RH) environment for 8 months and in 37oC environment for 13 months. We measured surface area and pore volume of samples by using N2 adsorption (77K) technique and characterized surface chemistry by using X-Ray photospectroscopy and FT-IR spectroscopy. We also analyzed structural defects with Raman spectroscopy. All tests were conducted periodically. In ambient condition, we found that nanocarbons exhibited a trend of decreasing surface area and pore volume up to 7 to 15 months but then stabilized. We also observed a trend of decreasing surface oxygen from the beginning with much lower % oxygen observed after 12 to 15 months of aging. There was also evidence that structural-defect concentration was lowered. We conclude that nanocarbons are metastable materials, and that their aging in ambient conditions has an unexpected effect whereby oxygen leaves their surface, the structure repairs itself and they become more thermodynamically stable. Aged nanocarbons (16 months in ambient conditions) were moved to 90% RH environment and 37oC environment. We observed that in 90% RH condition, chemisorption of oxygen and/or water to nanocarbons was enhanced and % oxygen was increased; surface area, pore volume and structural defects were reduced with a trend of approaching to equilibrium. We conclude that humidity could promote chemisorption of oxygen/water in the air to nanocarbons. We found that in 37oC condition, chemical properties of nanocarbons were only slightly decreased, but their surface area and pore volume were deceased in 1 to 3 months, and then increased in 3 to 13 months. Their physical changes may be related to the temperature dependent thermal expansion which softened intertubular interaction and enlarged spaces between tubes. This study demonstrated that ambient temperature and humidity play important roles in aging of nanocarbons and also showed that nanocarbons possess differences from bulk carbons in aging. This study could benefit potential applications of nanocarbons and improve understanding long-term environmental impacts of nanocarbons

Ultra-wideband THz/IR Metamaterial Absorber based on Doped Silicon

Metamaterial-based absorbers have been extensively investigated in the terahertz (THz) range with ever increasing performances. In this paper, we propose an all-dielectric THz absorber based on doped silicon. The unit cell consists of a silicon cross resonator with an internal cross-shaped air cavity. Numerical results suggest that the proposed absorber can operate from THz to mid-infrared, having an average power absorption of >95% between 0.6 and 10 THz. Experimental results using THz time-domain spectroscopy show a good agreement with simulations. The underlying mechanisms for broadband absorptions are attributed to the combined effects of multiple cavities modes formed by silicon resonators and bulk absorption in the substrate, as confirmed by simulated field patterns. This ultra-wideband absorption is polarization insensitive and can operate across a wide range of the incident angle. The proposed absorber can be readily integrated into silicon-based platforms and is expected to be used in sensing, imaging, energy harvesting and wireless communications systems.Comment: 6 pages, 5 figure

Superdirectivity-enhanced wireless communications: A multi-user perspective

Superdirective array may achieve an array gain proportional to the square of the number of antennas $M^2$. In the early studies of superdirectivity, little research has been done from wireless communication point of view. To leverage superdirectivity for enhancing the spectral efficiency, this paper investigates multi-user communication systems with superdirective arrays. We first propose a field-coupling-aware (FCA) multi-user channel estimation method, which takes into account the antenna coupling effects. Aiming to maximize the power gain of the target user, we propose multi-user multipath superdirective precoding (SP) as an extension of our prior work on coupling-based superdirective beamforming. Furthermore, to reduce the inter-user interference, we propose interference-nulling superdirective precoding (INSP) as the optimal solution to maximize user power gains while eliminating interference. Then, by taking the ohmic loss into consideration, we further propose a regularized interference-nulling superdirective precoding (RINSP) method. Finally, we discuss the well-known narrow directivity bandwidth issue, and find that it is not a fundamental problem of superdirective arrays in multi-carrier communication systems. Simulation results show our proposed methods outperform the state-of-the-art methods significantly. Interestingly, in the multi-user scenario, an 18-antenna superdirective array can achieve up to a 9-fold increase of spectral efficiency compared to traditional multiple-input multiple-output (MIMO), while simultaneously reducing the array aperture by half.Comment: 11 pages, 8 figure

A Narrative Review on Environmental Impacts of Cannabis Cultivation

Interest in growing cannabis for medical and recreational purposes is increasing worldwide. This study reviews the environmental impacts of cannabis cultivation. Results show that both indoor and outdoor cannabis growing is water-intensive. The high water demand leads to water pollution and diversion, which could negatively affect the ecosystem. Studies found out that cannabis plants emit a significant amount of biogenic volatile organic compounds, which could cause indoor air quality issues. Indoor cannabis cultivation is energy-consuming, mainly due to heating, ventilation, air conditioning, and lighting. Energy consumption leads to greenhouse gas emissions. Cannabis cultivation could directly contribute to soil erosion. Meanwhile, cannabis plants have the ability to absorb and store heavy metals. It is envisioned that technologies such as precision irrigation could reduce water use, and application of tools such as life cycle analysis would advance understanding of the environmental impacts of cannabis cultivation

LeTetR Positively Regulates 3-Hydroxylation of the Antifungal HSAF and Its Analogs in \u3ci\u3eLysobacter enzymogenes\u3c/i\u3e OH11

The biocontrol agent Lysobacter enzymogenes OH11 produces several structurally distinct antibiotic compounds, including the antifungal HSAF (Heat Stable Antifungal Factor) and alteramides, along with their 3-dehydroxyl precursors (3-deOH). We previously showed that the 3-hydroxylation is the final step of the biosynthesis and is also a key structural moiety for the antifungal activity. However, the procedure through which OH11 regulates the 3-hydroxylation is still not clear. In OH11, the gene orf3232 was predicted to encode a TetR regulator (LeTetR) with unknown function. Here, we deleted orf3232 and found that the LeTetR mutant produced very little HSAF and alteramides, while the 3-deOH compounds were not significantly affected. The production of HSAF and alteramides was restored in orf3232-complemented mutant. qRT-PCR showed that the deletion of orf3232 impaired the transcription of a putative fatty acid hydroxylase gene, orf2195, but did not directly affect the expression of the HSAF biosynthetic gene cluster (hsaf ). When an enzyme extract from E. coli expressing the fatty acid hydroxylase gene, hsaf -orf7, was added to the LeTetR mutant, the production of HSAF and alteramides increased by 13–14 fold. This study revealed a rare function of the TetR family regulator, which positively controls the final step of the antifungal biosynthesis and thus controls the antifungal activity of the biocontrol agent

Causes and 3-year-incidence of blindness in Jing-An District, Shanghai, China 2001-2009

<p>Abstract</p> <p>Background</p> <p>Registered data can provide valuable information regarding blindness. The purpose of this study was to evaluate the main causes and 3-year incidence of registered blindness in Jing-An district in Shanghai, China.</p> <p>Methods</p> <p>Data from the blindness registry (age, gender and cause of visual disability) were collected and analyzed. The prevalence of blindness for 2003, 2007, 2009 and the 3-year incidence of blindness were calculated.</p> <p>Results</p> <p>The reported blindness increased significantly from 113.7 per 100,000 in 2003 to 145.8 per 100,000 in 2006 to 165.9 per 100,000 in 2009 (P < 0.05, P < 0.05, respectively). Age significantly affects prevalence; the odd ratios (OR) were 2.57 in the 30 y - 49 y range (P < 0.001), 7.27 in the 50 y - 69 y range (P < 0.001) and 21.2 in the ≥ 70 y (P < 0.001). The 3-year incidence increased from 32.3 per 100,000 in 2001-2003 to 34.2 per 100,000 in 2004-2006 to 40.8 per 100,000 in 2007-2009. The causes of new blindness registered in 2001-2009 were myopic macular degeneration (19.4%), followed by glaucoma (17.7%), age-related macular degeneration (11.8%), optical nerve atrophy (9.4%), retinitis pigmentosa (8.6%), diabetic retinopathy (7.8%) and corneal opacity (5.8%).</p> <p>Conclusions</p> <p>The 3-year incidence and prevalence of registered blindness increased in the past 9 years. The leading causes of new blindness were myopic macular degeneration, glaucoma and age-related macular degeneration. The pattern of causes has changed little in the past 9 years and is different from other locations in China. The pattern is similar to that of Taiwan, Hongkong, and Western countries.</p

Cytotoxic Polyketides with an Oxygen-Bridged Cyclooctadiene Core Skeleton from the Mangrove Endophytic Fungus \u3ci\u3ePhomosis\u3c/i\u3e sp. A818

Plant endophytic microorganisms represent a largely untapped resource for new bioactive natural products. Eight polyketide natural products were isolated from a mangrove endophytic fungus Phomosis sp. A818. The structural elucidation of these compounds revealed that they share a distinct feature in their chemical structures, an oxygen-bridged cyclooctadiene core skeleton. The study on their structure–activity relationship showed that the α,β-unsaturated δ-lactone moiety, as exemplified in compounds 1 and 2, was critical to the cytotoxic activity of these compounds. In addition, compound 4 might be a potential agonist of AMPK (5\u27-adenosine monophosphate-activated protein kinase)

Orbital-scale nonlinear response of East Asian summer monsoon to its potential driving forces in the late Quaternary

We conducted a statistical study to characterize the nonlinear response of the East Asian summer monsoon (EASM) to its potential forcing factors over the last 260 ka on orbital timescales. We find that both variation in solar insolation and global ice volume were responsible for the nonlinear forcing of orbital-scale monsoonal variations, accounting for similar to 80% of the total variance. Specifically, EASM records with dominated precession variance exhibit a more sensitive response to changes in solar insolation during intervals of enhanced monsoon strength, but are less sensitive during intervals of reduced monsoon strength. In the case of global ice volume with 100-ka variance, this difference is not one of sensitivity but rather a difference in baseline conditions, such as the relative areas of land and sea which affected the land-sea thermal gradient. We therefore suggest that EASM records with dominated precession variance recorded the signal of a shift in the location of the Inter-tropical Convergence Zone, and the associated changes in the incidence of torrential rainfall; while for proxies with dominated 100-ka variance, it recorded changes in the land-sea thermal gradient via its effects on non-torrential precipitation

A Superdirective Beamforming Approach with Impedance Coupling and Field Coupling for Compact Antenna Arrays

In most multiple-input multiple-output (MIMO) communication systems, the antenna spacing is generally no less than half a wavelength. It helps to reduce the mutual coupling and therefore facilitate the system design. The maximum array gain equals the number of antennas in this settings. However, when the antenna spacing is made very small, the array gain of a compact array can be proportional to the square of the number of antennas - a value much larger than the traditional array. To achieve this so-called ``superdirectivity" however, the calculation of the excitation coefficients (beamforming vector) is known to be a challenging problem. In this paper, we address this problem with a novel double coupling-based superdirective beamforming method. In particular, we categorize the antenna coupling effects to impedance coupling and field coupling. By characterizing these two coupling in model, we derive the beamforming vector for superdirective arrays. In order to obtain the field coupling matrix, we propose a spherical wave expansion approach, which is effective in both simulations and realistic scenarios. Moreover, a prototype of the independently controlled superdirective antenna array is developed. Full-wave electromagnetic simulations and real-world experiments validate the effectiveness of our proposed approaches, and superdirectivity is achieved in reality by a compact array with 4 and 5 dipole antennas.Comment: arXiv admin note: text overlap with arXiv:2204.1154

C.E.O. academic experience and firm sustainable growth

Chief executive officers (C.E.O.s) play a dominant role in firm decision- makings and operations, and their characteristics will affect firm sustainable growth. This study investigates whether C.E.O. academic experience affects firm sustainable growth. Using a sample from China, we find that C.E.O. academic experience is positively related to firm sustainable growth, and the effect is pronounced for high-tech firms. Further analyses demonstrate that the results are robust to alternative measures and controlling for endogeneity problems. Finally, the channel analysis shows that the effect is partially driven by firm innovation and internal control