Polychromatic photonic Floquet-Bloch oscillations.

Photonic Floquet-Bloch oscillations (FBOs), a new type of Bloch-like oscillations in photonic Floquet lattices, have recently been observed as a typical discrete self-imaging effect. Here, we theoretically investigate the spectral range of approximate photonic Floquet-Bloch oscillations in arrays of evanescently coupled optical waveguides and show the adjustability of the spectral range. At an appropriate amplitude of the Floquet modulation, we have demonstrated approximate photonic FBOs over a broad spectral range, termed "polychromatic photonic Floquet-Bloch oscillations," which manifest as approximate self-imaging of polychromatic beams. Furthermore, by designing the functional form of the Floquet modulation, we can cascade two polychromatic photonic FBOs and further enhance the performance of polychromatic self-imaging. Our results provide a simple and novel mechanism for achieving polychromatic self-imaging in waveguide arrays and may find applications in polychromatic beam shaping and broadband optical signal processing.

Observation-based sources evolution of non-methane hydrocarbons (NMHCs) in a megacity of China.

Both concentrations and emissions of many air pollutants have been decreasing due to implement of control measures in China, in contrast to the fact that an increase in emissions of non-methane hydrocarbons (NMHCs) has been reported. This study employed seven years continuous NMHCs measurements and the related activities data of Shanghai, a megacity in China, to explore evolution of emissions and effectiveness of air pollution control measures. The mixing ratio of NMHCs showed no statistical interannual changes, of which their compositions exhibited marked changes. This resulted in a decreasing trend of ozone formation potential by 3.8%/year (p < 0.05, the same below), which should be beneficial to ozone pollution mitigation as its production in Shanghai is in the NMHCs-limited regime. Observed alkanes, aromatics and acetylene changed by +3.7%/year, -5.9%/year and -7.4%/year, respectively, and alkenes showed no apparent trend. NMHCs sources were apportioned by a positive matrix factorization model. Accordingly, vehicular emissions (-5.9%/year) and petrochemical industry emissions (-7.1%/year) decreased significantly, but the decrease slowed down; significant reduction in solvent usage (-9.0%/year) appeared after 2010; however, emissions of natural gas (+12.6%/year) and fuel evaporation (with an increasing fraction) became more important. The inconsistency between observations and inventories was found in interannual trend and speciation as well as source contributions, emphasizing the need for further validation in NMHCs emission inventory. Our study confirms the effectiveness of measures targeting mobile and centralized emissions from industrial sources and reveals a need focusing on fugitive emissions, which provided new insights into future air policies in polluted region.

Polysaccharide-Derived Ice Recrystallization Inhibitors with a Modular Design: The Case of Dextran-Based Graft Polymers.

Ice recrystallization inhibitors inspired from antifreeze proteins (AFPs) are receiving increasing interest for cryobiology and other extreme environment applications. Here, we present a modular strategy to develop polysaccharide-derived biomimetics, and detailed studies were performed in the case of dextran. Poly(vinyl alcohol) (PVA) which has been termed as one of the most potent biomimetics of AFPs was grafted onto dextran via thiol-ene click chemistry (Dex-g-PVA). This demonstrated that Dex-g-PVA is effective in IRI and its activity increases with the degree of polymerization (DP) (sizes of ice crystals were 18.846 ± 1.759 and 9.700 ± 1.920 µm with DPs of 30 and 80, respectively) and fraction of PVA. By means of the dynamic ice shaping (DIS) assay, Dex-g-PVA is found to engage on the ice crystal surfaces, thus the ice affinity accounts for their IRI activity. In addition, Dex- g-PVA displayed enhanced IRI activity compared to that of equivalent PVA alone. We speculate that the hydrophilic nature of dextran would derive PVA in a stretch conformation that favors ice binding. The modular design can not only offer polysaccharides IRI activity but also favor the ice-binding behavior of PVA.

Tracer-based characterization of source variations of PM2.5 and organic carbon in Shanghai influenced by the COVID-19 lockdown.

Air quality in megacities is significantly impacted by emissions from vehicles and other urban-scale human activities. Amid the outbreak of Coronavirus (COVID-19) in January 2020, strict policies were in place to restrict people's movement, bringing about steep reductions in pollution activities and notably lower ambient concentrations of primary pollutants. In this study, we report hourly measurements of fine particulate matter (i.e., PM2.5) and its comprehensive chemical speciation, including elemental and molecular source tracers, at an urban site in Shanghai spanning a period before the lockdown restriction (BR) (1 to 23 Jan. 2020) and during the restriction (DR) (24 Jan. to 9 Feb. 2020). The overall PM2.5 was reduced by 27% from 56.2 ± 40.9 (BR) to 41.1 ± 25.3 µg m-3 (DR) and the organic carbon (OC) in PM2.5 was similar, averaged at 5.45 ± 2.37 (BR) and 5.42 ± 1.75 µgC m-3 (DR). Reduction in nitrate was prominent, from 18.1 (BR) to 9.2 µg m-3 (DR), accounting for most of the PM2.5 decrease. Source analysis of PM2.5 using positive matrix factorization modeling of comprehensive chemical composition, resolved nine primary source factors and five secondary source factors. The quantitative source analysis confirms reduced contributions from primary sources affected by COVID-19, with vehicular emissions showing the largest drop, from 4.6 (BR) to 0.61 µg m-3 (DR) and the percentage change (-87%) in par with vehicle traffic volume and fuel sale statistics (-60% to -90%). In the same time period, secondary sources are revealed to vary in response to precursor reductions from the lockdown, with two sources showing consistent enhancement while the other three showing reductions, highlighting the complexity in secondary organic aerosol formation and the nonlinear response to broad primary precursor pollutants. The combined contribution from the two secondary sources to PM2.5 increased from 7.3 ± 6.6 (BR) to 14.8 ± 9.3 µg m-3 (DR), partially offsetting the reductions from primary sources and nitrate while their increased contribution to OC, from 1.6 ± 1.4 (BR) to 3.2 ± 2.0 µgC m-3 (DR), almost offset the decrease coming from the primary sources. Results from this work underscore challenges in predicting the benefits to PM2.5 improvement from emission reductions of common urban primary sources.

Bifunctional Carbenium Dications as Metal-Free Catalysts for the Reduction of Oxygen.

The development of catalysts for the oxygen reduction reaction is a coveted objective of relevance to energy research. This study describes a metal-free approach to catalyzing the reduction of O2 into H2O2, based on the use of redox-active carbenium species. The most active catalysts uncovered by these studies are the bifunctional dications 1,8-bis(xanthylium)-biphenylene ([3]2+) and 4,5-bis(xanthylium)-9,9-dimethylxanthene ([4]2+) which promote the reaction when in the presence of decamethylferrocene and methanesulfonic acid. Electrochemical studies carried out with [4]2+ suggest the intermediacy of an organic peroxide that, upon protonation, converts back into the starting dication while also releasing H2O2. Kinetic studies point to the second protonation event as being rate-determining.

Small-sized long wavelength infrared absorber with perfect ultra-broadband absorptivity.

Two types of ultra-broadband long wavelength infrared (LWIR) absorbers with small period and super thin thickness are designed. The absorption with high absorptivity and large bandwidth is achieved through combined propagating and localized surfaced plasmon resonances. We first design a three-layer absorber with a Ti-Ge-Ti configuration, the period of the structure is only 1.4 µm (nearly 1/8 of the center wavelength), the thickness of its dielectric is only 0.5 µm (1/22 of the center wavelength), and the average absorption is 87.9% under normal incident from 8µm to 14µm. Furthermore, the four-layer absorber with a Ti-Ge-Si3N4-Ti configuration is designed to obtain more average absorption increasing to 94.5% from 8 µm to 14µm under normal incident, the period of the structure increases to 1.6 µm and the total thickness of dielectric increases to 0.6µm. The proposed absorber is polarization-independent and possesses a good tolerance of incident angle. We calculate that the average absorption of the four-layer absorber for both TE- and TM-modes still exceeds 90% up to an incident angle of θ = 40° (90.7% for TE-mode, 91.9% for TM-mode), and exceed 80% up to an incident angle of θ = 60° (80.2% for TE-mode, 82.1% for TM-mode).

Photothermal switch of sub-microsecond response: a monolithic-integrated ring resonator and a metasurface absorber in silicon photonic crystals.

Here, we demonstrate an all-silicon photonic switch, working at an infrared communication wavelength and pumped by spatial light, where a ring resonator and a metasurface absorber are both designed in photonic crystals and monolithically integrated on a silicon-on-insulator wafer. Through selective doping, the absorber gets a pump absorption completely different from near zero of the resonator. Based on the thermo-optical effect, the device is capable of tuning the wavelength of the guided mode by $\sim{341}\;{\rm pm/mW}$∼341pm/mW and switching in time $ {\lt} {1.0}\;\unicode{x00B5} {\rm s}$<1.0µs to the pump response. The high responsivity and switching speed as well as all-silicon processing techniques make the design potentially for free-space optical communication and detection.

Mid-wave and long-wave infrared dual-band stacked metamaterial absorber for broadband with high refractive index sensitivity.

A dual-band metamaterial absorber based on local surface plasmon resonance is designed, which is composed of a periodic arrangement of stacked nanodisk structures. The structure unit consists of two dielectric layers and three metal layers. Based on the finite difference time domain method, under the condition of vertically incident plane light, two absorption peaks in the mid-wave infrared and long-wave infrared (MWIR/LWIR) are obtained, and the absorption is greater than 98%. The absorber has good incident state tolerance characteristics. We can modulate the MWIR/LWIR absorption peaks by changing the radius of the stacked disk structure, and MWIR and LWIR dual-band broadband absorption can be achieved by integrating different size elements in the plane. The average absorption is 71% for MWIR with 1.1 µm bandwidth from 3.2 to 4.3 µm and 88% for LWIR with 3 µm bandwidth from 8.5 to 11.5 µm. At the same time, the structure also has effective refractive index (RI) sensitivity characteristics. In the RI range of 1.8-2, the maximum RI sensitivity of the LWIR and the MWIR is 1085 nm/refractive index unit (RIU) and 1472 nm/RIU, respectively.

Progranulin deficiency exacerbates spinal cord injury by promoting neuroinflammation and cell apoptosis in mice.

PURPOSE: Spinal cord injury (SCI) often results in significant and catastrophic dysfunction and disability and imposes a huge economic burden on society. This study aimed to determine whether progranulin (PGRN) plays a role in the progressive damage following SCI and evaluate the potential for development of a PGRN derivative as a new therapeutic target in SCI. METHODS: PGRN-deficient (Gr-/-) and wild-type (WT) littermate mice were subjected to SCI using a weight-drop technique. Local PGRN expression following injury was evaluated by Western blotting and immunofluorescence. Basso Mouse Scale (BMS), inclined grid walking test, and inclined plane test were conducted at indicated time points to assess neurological recovery. Inflammation and apoptosis were examined by histology (Hematoxylin and Eosin (H&E) staining and Nissl staining, TUNEL assays, and immunofluorescence), Western blotting (from whole tissue protein for iNOS/p-p65/Bax/Bcl-2), and ex vivo ELISA (for TNFα/IL-1ß/IL-6/IL-10). To identify the prophylactic and therapeutic potential of targeting PGRN, a PGRN derived small protein, Atsttrin, was conjugated to PLGA-PEG-PLGA thermosensitive hydrogel and injected into intrathecal space prior to SCI. BMS was recorded for neurological recovery and Western blotting was applied to detect the inflammatory and apoptotic proteins. RESULTS: After SCI, PGRN was highly expressed in activated macrophage/microglia and peaked at day 7 post-injury. Grn-/- mice showed a delayed neurological recovery after SCI at day 21, 28, 35, and 42 post-injury relative to WT controls. Histology, TUNEL assay, immunofluorescence, Western blotting, and ELISA all indicated that Grn-/- mice manifested uncontrolled and expanded inflammation and apoptosis. Administration of control-released Atsttrin could improve the neurological recovery and the pro-inflammatory/pro-apoptotic effect of PGRN deficiency. CONCLUSION: PGRN deficiency exacerbates SCI by promoting neuroinflammation and cellular apoptosis, which can be alleviated by Atsttrin. Collectively, our data provide novel evidence of using PGRN derivatives as a promising therapeutic approach to improve the functional recovery for patients with spinal cord injury.

Significantly enhanced infrared absorption of graphene photodetector under surface-plasmonic coupling and polariton interference.

Here, we present a graphene-based long-wavelength infrared photodetector, for enhancing the infrared absorption of which the design consists of magnetic- and electric-plasmon resonators of metasurface to excite the graphene surface-plasmonic polaritons (SPPs). Through tuning the graphene Fermi energy to achieve the distinct resonances in a matching frequency, peak graphene absorbance exceeding 67.2% is confirmed, even when a lossy dielectric is used, and the field angle of view is up to 90°. If the graphene is of a different carrier mobility, then the absorption frequency is lockable, and the device always can keep the system absorbance close to 100 percent. The significantly enhanced graphene absorbance, up to ~29-fold that of a suspended graphene (general 2.3%), is attributed to the surface-plasmonic coupling between the magnetic and the electric resonances, as well as Fabry-Pérot interference of the coherent SPPs. The plasmonic cavity-mode model and equivalent-circuit method developed in this study will also be useful in guiding other optoelectronic device design.

An Integrated Source Apportionment Methodology and Its Application over the Yangtze River Delta Region, China.

An integrated source apportionment methodology is developed by amalgamating the receptor-oriented model (ROM) and source-oriented numerical simulations (SOM) together to eliminate the weaknesses of individual SA methods. This approach attempts to apportion and dissect the PM2.5 sources in the Yangtze River Delta region during winter. First, three ROM models (CMB, PMF, ME2) are applied and compared for the preliminary SA results, with information from PM2.5 sampling and lab analysis during the winter seasons. The detailed source category contribution of SOM to PM2.5 is further simulated using the WRF-CAMx model. The two pieces of information from both ROM and SOM are then stitched together to give a comprehensive information on the PM2.5 sources over the region. With the integrated approach, the detailed contributing sources of the ambient PM2.5 at different receptors including rural and urban, coastal and in-land, northern and southern receptors are analyzed. The results are compared with previous data and shows good agreement. This integrative approach is more comprehensive and is able to produce a more profound and detailed understanding between the sources and receptors, compared with single models.

Exploiting the Strong Hydrogen Bond Donor Properties of a Borinic Acid Functionality for Fluoride Anion Recognition.

Borinic acids have typically not been considered as hydrogen bond donor groups in molecular recognition. Described herein is a bifunctional borane/borinic acid derivative (2) in which the two functionalities are connected by a 1,8-biphenylenediyl backbone. Anion binding studies reveal that 2 readily binds a fluoride anion by formation of a unique B-F⋅⋅⋅H-O-B hydrogen bond. This hydrogen bond is characterized by a short H-F distance of 1.79(3) Šand a large coupling constant (1 JHF ) of 57.2 Hz. The magnitude of this interaction, which has also been investigated computationally, augments the fluoride anion binding properties of 2, thus making it compatible with aqueous environments.

Digging the Sigma-Hole of Organoantimony Lewis Acids by Oxidation.

The development of group 15 Lewis acids is an area of active investigation that has led to numerous advances in anion sensing and catalysis. While phosphorus has drawn considerable attention, emerging research shows that organoantimony(III) reagents may also act as potent Lewis acids. Comparison of the properties of SbPh3 , Sb(C6 F5 )3 , and SbArF 3 with those of their tetrachlorocatecholate analogues SbPh3 Cat, Sb(C6 F5 )3 Cat, and SbArF 3 Cat (Cat=o-O2 C6 Cl4 , ArF =3,5-(CF3 )2 C6 H3 ) demonstrates that the Lewis acidity of electron deficient organoantimony(III) reagents can be readily enhanced by oxidation to the +V state-as verified by binding studies, organic reaction catalysis, and computational studies. The results are rationalized by explaining that oxidation of the antimony center leads to a lowering of the accepting σ* orbital and a deeper carving of the associated σ-hole.

Wide-band achromatic flat focusing lens based on all-dielectric subwavelength metasurface.

A new method for realizing achromatic flat focusing based on all-dielectric silicon subwavelength metasurface is presented. The designed subwavelength silicon-air slits waveguide array with varied widths can provide desired phase shift of beam focusing and has the non-dispersive characteristic when the period of each unit cell is far less than the wavelength of incident electromagnetic wave (about λ/10) in mid-infrared and far-infrared spectral range. Numerical simulation of an achromatic flat focusing lens in wide spectral range from 8µm to 12µm is performed by the finite difference time domain method and the results show agreement with theory analysis results. This work indicates an effective solution for wide-band achromatic flat optical elements and potential application in integrated achromatic infrared optical systems.

Fluoride Anion Complexation by a Triptycene-Based Distiborane: Taking Advantage of a Weak but Observable C-H⋠⋠⋠F Interaction.

Fluoride anion complexation impacts a number of areas ranging from sensing to nucleophilic fluorination chemistry. Described here is a new bidentate Lewis acid consisting of two stiborane units connected by a 1,8-triptycenediyl backbone. This neutral derivative captures fluoride with an unprecedented affinity for a neutral, water-compatible Lewis acid. Structural, spectroscopic and computational studies demonstrate that fluoride anion binding is assisted by the formation of a C-H⋅⋅⋅F hydrogen bond which involves a methine group of the 1,8-triptycenediyl backbone.

Study on the synthesis and biological activities of α-substituted arylacetates derivatives.

Anisodamine was isolated from the medicinal herb, it was used in the treatment of gastrointestinal smooth muscle spasm, infective toxic shock and organophosphorus intoxication. But there is no report about anisodamine with α-glucosidase inhibitory activity. In order to find novel α-glucosidase inhibitors, a series of α-substituted arylacetates derivatives have been synthesized based on the active unit of anisodamine. In α-glucosidase assay, compound 9 in Schiff base form and compound 22 in ester form show strong inhibition against α-glucosidase with IC50 value of 46.81µM and 83.76µM, respectively. Compounds 9 and 22 exhibit comparable good antidiabetic activities as commercial drug Glimepiride. In addition, Schiff bases of α-substituted arylacetates show antitumor activities against human cancer cell lines, where compound 9 with thiourea moiety performs the best antitumor activity. We anticipate that our research will provide potential candidate scaffolds for antidiabetic drug design.

Chemical characteristics of fine particles and their impact on visibility impairment in Shanghai based on a 1-year period observation.

In this work, a one-year observation focusing on high time resolution characteristics of components in fine particles was conducted at an urban site in Shanghai. Contributions of different components on visibility impairment were also studied. Our research indicates that the major components of PM2.5 in Shanghai are water-soluble inorganic ions and carbonaceous aerosol, accounting for about 60% and 30% respectively. Higher concentrations of sulfate (SO42-) and organic carbon (OC) in PM2.5 occurred in fall and summer, while higher concentrations of nitrate (NO3-) were observed in winter and spring. The mass concentrations of Cl- and K+ were higher in winter. Moreover, NO3- increased significantly during PM2.5 pollution episodes. The high values observed for the sulfate oxidizing rate (SOR), nitrate oxidizing rate (NOR) and secondary organic carbon (SOC) in OC indicate that photochemical reactions were quite active in Shanghai. The IMPROVE (Interagency Monitoring of Protected Visual Environments) formula was used in this study to investigate the contributions of individual PM2.5 chemical components to the light extinction efficient in Shanghai. Both NH4NO3 and (NH4)2SO4 had close relationships with visibility impairment in Shanghai. Our results show that the reduction of anthropogenic SO2, NOx and NH3 would have a significant effect on the improvement of air quality and visibility in Shanghai.

Controllable near-field intensity and spot size of hybrid terahertz metamaterial.

We report controllable near fields around split-ring resonator (SRR) gaps of an active terahertz metamaterial. As extension of parallel-plate capacitors, patterned VO2 is integrated into the metallic SRRs to manipulate the near-field intensity and hot spot size through its metal-insulator transition. This design enhances the device reliability by preventing VO2 dielectric breakdown at a strongly enhanced near field. The near-field intensity and spot size are tunable in broad ranges, and the device is demonstrated to be capable of compensating resonant frequency drift arisen from different interactions due to near-field coupling. It provides an effective method to actively manipulate the light-matter interaction through the strongly enhanced and tunable near fields.

Design and synthesis of aloe-emodin derivatives as potent anti-tyrosinase, antibacterial and anti-inflammatory agents.

Twenty aloe-emodin derivatives were designed, synthesized, and their biological activities were evaluated. Some compounds displayed potent tyrosinase inhibitory activities, especially, compounds with thiosemicarbazide moiety showed more potent inhibitory effects than the other compounds. The structure-activity relationships (SARs) were preliminarily discussed. The inhibition mechanism of selected compounds 1 and 13 were investigated. The results showed compound 1 was reversible inhibitor, however, compound 13 was irreversible. Kinetic analysis indicated that compound 1 was competitive tyrosinase inhibitor. Furthermore, the antibacterial activities and anti-inflammatory activities of some selected compounds were also screened. The results showed that compound 3 exhibited more potent antibacterial activity than the aloe-emodin, compounds 5 and 6 possessed more potent anti-inflammatory activities than the diacerein.

Estimation of aerosol mass scattering efficiencies under high mass loading: case study for the megacity of Shanghai, China.

Aerosol mass scattering efficiency (MSE), used for the scattering coefficient apportionment of aerosol species, is often studied under the condition of low aerosol mass loading in developed countries. Severe pollution episodes with high particle concentration frequently happened in eastern urban China in recent years. Based on synchronous measurement of aerosol physical, chemical, and optical properties at the megacity of Shanghai for two months during autumn 2012, we studied MSE characteristics at high aerosol mass loading. Their relationships with mass concentrations and size distributions were examined. It was found that MSE values from the original US IMPROVE algorithm could not represent the actual aerosol characteristics in eastern China. It results in an underestimation of the measured ambient scattering coefficient by 36%. MSE values in Shanghai were estimated to be 3.5 ± 0.55 m(2)/g for ammonia sulfate, 4.3 ± 0.63 m(2)/g for ammonia nitrate, and 4.5 ± 0.73 m(2)/g for organic matter, respectively. MSEs for three components increased rapidly with increasing mass concentration in low aerosol mass loading, then kept at a stable level after a threshold mass concentration of 12­24 µg/m(3). During severe pollution episodes, particle growth from an initial peak diameter of 200­300 nm to a peak diameter of 500­600 nm accounts for the rapid increase in MSEs at high aerosol mass loading, that is, particle diameter becomes closer to the wavelength of visible lights. This study provides insights of aerosol scattering properties at high aerosol concentrations and implies the necessity of MSE localization for extinction apportionment, especially for the polluted regions.