Pure Even Harmonic Generation from Oriented CO in Linearly Polarized Laser Fields

The first high harmonic spectrum, containing only the odd orders, was observed in experiments 30 years ago (1987). However, a spectrum containing pure even harmonics has never been observed. We investigate the generation of pure even harmonics from oriented CO molecules in linearly polarized laser fields employing the time-dependent density-functional theory. We find that the even harmonics, with no odd orders, are generated with the polarization perpendicular to the laser polarization, when the molecular axis of CO is perpendicular to the laser polarization. Generation of pure even harmonics reveals a type of dipole acceleration originating from the permanent dipole moment. This phenomenon exists in all system with permanent dipole moments, including bulk crystal and polyatomic molecules

Angle-selective perfect absorption with two-dimensional materials

Two-dimensional (2D) materials have great potential in photonic and optoelectronic devices. However, the relatively weak light absorption in 2D materials hinders their application in practical devices. Here, we propose a general approach to achieve angle-selective perfect light absorption in 2D materials. As a demonstration of the concept, we experimentally show giant light absorption by placing large-area single-layer graphene on a structure consisting of a chalcogenide layer atop a mirror and achieving a total absorption of 77.6% in the mid-infrared wavelength range (~13 μm), where the graphene contributes a record-high 47.2% absorptivity of mid-infrared light. Construction of such an angle-selective thin optical element is important for solar and thermal energy harvesting, photo-detection and sensing applications. Our study points to a new opportunity to combine 2D materials with photonic structures to enable novel device applications

New Broad-Spectrum Viral Fusion Inhibitors Act by Deleterious Effect on the Viral Membrane through the Production Singlet Oxygen Molecules

Chitosan oligosaccharides (COS), the degraded products of chitosan, have been demonstrated to have versatile biological functions. In primary studies, it has displayed significant adjuvant effects when mixed with other vaccines. In this study, chitosan oligosaccharides with different deacetylation degrees were prepared and conjugated to porcine circovirus type 2 (PCV2) subunit vaccine to enhance its immunogenicity. The vaccine conjugates were designed by the covalent linkage of COSs to PCV2 molecules and administered to BALB/c mice three times at two-week intervals. The results indicate that, as compared to the PCV2 group, COS-PCV2 conjugates remarkably enhanced both humoral and cellular immunity against PCV2 by promoting lymphocyte proliferation and initiating a mixed T-helper 1 (Th1)/T-helper 2 (Th2) response, including raised levels of PCV2-specific antibodies and an increased production of inflammatory cytokines. Noticeably, with the increasing deacetylation degree, the stronger immune responses to PCV2 were observed in the groups with COS-PCV2 vaccination. In comparison with NACOS (chitin oligosaccharides)-PCV2 and LCOS (chitosan oligosaccharides with low deacetylation degree)-PCV2, HCOS (chitosan oligosaccharides with high deacetylation degree)-PCV2 showed the highest adjuvant effect, even comparable to that of PCV2/ISA206 (a commercialized adjuvant) group. In summary, COS conjugation might be a viable strategy to enhance the immune response to PCV2 subunit vaccine, and the adjuvant effect was positively correlated with the deacetylation degree of COS.</p

Small RNAs in Gossypium and Their Roles in the Response to Heat Stress

Small regulatory RNAs, which usually are 20 to 24 nt in length, play crucial roles in plant growth, development, and stress response. Based on their origin, biogenesis and function, plant small RNAs can be classified into two major classes, hairpin RNAs (hpRNAs) and short interfering siRNAs (siRNAs). hpRNAs and siRNAs can be subdivided into two and three subfamilies, respectively. hpRNAs, including microRNAs (miRNAs) and other hairpin RNAs (ohpRNAs), are produced from hairpin-shaped precursors. siRNAs are produced from double-stranded precursors and requires RNA dependent Polymerase. siRNAs can be categorized into three subfamilies, repeat-associated siRNAs (ra-siRNAs), pha-siRNAs, and cis natural antisense RNAs (cis-nat siRNAs). In general, miRNAs regulate gene expression at transcription level, while siRNAs can do either postranscriptionally or transcriptionally. In addition, ra-siRNAs are considered to regulate gene expression by DNA methylation. Gossypium plants, such as G. hirsutum and G. barbadense, are economically important plants, and provide natural fiber for textile industry. In addition, they also are important sources for proteins and seed oils. Heat stress caused by elevated high temperature is an important factor that affects diverse physiological processes of plants, resulting serious loss in yield. The mechanism of heat response has been extensively studied in anatomical, biochemical, and gene levels. But till one decade year ago, gene expression regulated by small RNAs is shown to be important for animal and plant stress response. Growing studies have shown that small RNAs, primarily miRNAs and siRNAs, are involved in heat stress response in plants. In Arabidopsis, Oryza, or Medicago, the small RNA loci have been thoroughly annotated, which identified a large number of small RNAs that regulates stress response. However, little is known about Gossypium small RNAs and their regulatory roles in heat stress response. To annotate Gossypium small RNAs and study their roles, we constructed and sequenced forty four small RNAs libraries from eight different tissues from two different Gossypium species, G. raimondii and G. hirsutum. The samples were collected from heat-stressed or non-heat-stressed seedlings grown in growth chamber, or plants grown in fields under high temperature summer. Two deep sequencing methods, ABI Solid and Illumina, were employed to sequence the small RNA libraries. This generated approximately 790 million sequencing reads, which enabled us to annotate a large number of miRNAs, ohpRNAs, ra-siRNAs, pha-siRNAs and cis-nat siRNAs. Expression analysis revealed that a large number of small RNAs were significantly regulated between heat-stressed and non-heat-stressed tissues, or between heat-susceptible and heat-tolerant genotypes. Some small RNAs were differentially expressed among different tissues. This suggested that small RNAs might be involved in the stress response of Gossypium plants to heat stress and might play crucial roles in Gossypium heat stress tolerance. This work in this study developed a systematical method in analyzing the small RNA transcriptomes and in annotating the small RNA loci in the genome. This would facilitate the study in the small RNAs and their regulatory mechanism in plant heat tolerance

On-chip infrared sensors: redefining the benefits of scaling

Infrared (IR) spectroscopy is widely recognized as a gold standard technique for chemical and biological analysis. Traditional IR spectroscopy relies on fragile bench-top instruments located in dedicated laboratory settings, and is thus not suitable for emerging field-deployed applications such as in-line industrial process control, environmental monitoring, and point-of-care diagnosis. Recent strides in photonic integration technologies provide a promising route towards enabling miniaturized, rugged platforms for IR spectroscopic analysis. It is therefore attempting to simply replace the bulky discrete optical elements used in conventional IR spectroscopy with their on-chip counterparts. This size down-scaling approach, however, cripples the system performance as both the sensitivity of spectroscopic sensors and spectral resolution of spectrometers scale with optical path length. In light of this challenge, we will discuss two novel photonic device designs uniquely capable of reaping performance benefits from microphotonic scaling. We leverage strong optical and thermal confinement in judiciously designed micro-cavities to circumvent the thermal diffusion and optical diffraction limits in conventional photothermal sensors and achieve a record 104 photothermal sensitivity enhancement. In the second example, an on-chip spectrometer design with the Fellgett's advantage is analyzed. The design enables sub-nm spectral resolution on a millimeter-sized, fully packaged chip without moving parts.National Science Foundation (U.S.) (Award 1506605)United States. Department of Energy (Grant DE-NA0002509

Substrate-blind photonic integration based on high-index glass materials

Conventional photonic integration technologies are inevitably substrate-dependent, as different substrate platforms stipulate vastly different device fabrication methods and processing compatibility requirements. Here we capitalize on the unique monolithic integration capacity of composition-engineered non-silicate glass materials (amorphous chalcogenides and transition metal oxides) to enable multifunctional, multi-layer photonic integration on virtually any technically important substrate platforms. We show that high-index glass film deposition and device fabrication can be performed at low temperatures ( < 250 °C) without compromising their low loss characteristics, and is thus fully compatible with monolithic integration on a broad range of substrates including semiconductors, plastics, textiles, and metals. Application of the technology is highlighted through three examples: demonstration of high-performance mid-IR photonic sensors on fluoride crystals, direct fabrication of photonic structures on graphene, and 3-D photonic integration on flexible plastic substrates.National Science Foundation (U.S.) (Award 1200406

Chalcogenide Glass-on-Graphene Photonics

Two-dimensional (2-D) materials are of tremendous interest to integrated photonics given their singular optical characteristics spanning light emission, modulation, saturable absorption, and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. In this paper, we present a new route for 2-D material integration with planar photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material which can be directly deposited and patterned on a wide variety of 2-D materials and can simultaneously function as the light guiding medium, a gate dielectric, and a passivation layer for 2-D materials. Besides claiming improved fabrication yield and throughput compared to the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light-matter interactions in the 2-D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as graphene-based mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators