Imaging propagative exciton polaritons in atomically thin WSe2 waveguides

The exciton polariton (EP) is a half-light and half-matter quasiparticle that is promising for exploring both fundamental quantum phenomena as well as photonic applications. Van der Waals materials, such as transition-metal dichalcogenide (TMD), emerge as a promising nanophotonics platform due to its support of long propagative EPs even at room temperature. However, real-space studies have been limited to bulk crystal waveguides with a thickness no less than 60 nm. Here we report the nano-optical imaging of the transverse-electric EPs in WSe2 nanoflakes down to a few atomic layers, which can be turned on and off by tuning the polarization state of the excitation laser. Unlike previously studied transverse-magnetic modes that exist only in bulk TMD waveguides, we found that the transverse-electric EPs could reside in ultrathin WSe2 samples, owing to the alignment of the electric field with the in-plane dipole orientation of two-dimensional excitons. Furthermore, we show that the EP wavelength and propagation length can be largely controlled by varying laser energy and sample thickness. These findings open opportunities to realize near-infrared polaritonic devices and circuits truly at the atomically thin limit

Characterization of high-resolution aerosol mass spectra of primary organic aerosol emissions from Chinese cooking and biomass burning

Aerosol mass spectrometry has proved to be a powerful tool to measure submicron particulate composition with high time resolution. Factor analysis of mass spectra (MS) collected worldwide by aerosol mass spectrometer (AMS) demonstrates that submicron organic aerosol (OA) is usually composed of several major components, such as oxygenated (OOA), hydrocarbon-like (HOA), biomass burning (BBOA), and other primary OA. In order to help interpretation of component MS from factor analysis of ambient OA datasets, AMS measurements of different primary sources is required for comparison. Such work, however, has been very scarce in the literature, especially for high resolution MS (HR-MS) measurements, which performs improved characterization by separating the ions of different elemental composition at each <i>m</i>/<i>z</i> in comparison with unit mass resolution MS (UMR-MS) measurements. In this study, primary emissions from four types of Chinese cooking (CC) and six types of biomass burning (BB) were simulated systematically and measured using an Aerodyne High-Resolution Time-of-Flight AMS (HR-ToF-AMS). The MS of the CC emissions show high similarity, with <i>m</i>/<i>z</i> 41 and <i>m</i>/<i>z</i> 55 being the highest signals; the MS of the BB emissions also show high similarity, with <i>m</i>/<i>z</i> 29 and <i>m</i>/<i>z</i> 43 being the highest signals. The MS difference between the CC and BB emissions is much bigger than that between different CC (or BB) types, especially for the HR-MS. The O/C ratio of OA ranges from 0.08 to 0.13 for the CC emissions and from 0.18 to 0.26 for the BB emissions. The UMR ions of <i>m</i>/<i>z</i> 43, <i>m</i>/<i>z</i> 44, <i>m</i>/<i>z</i> 57, and <i>m</i>/<i>z</i> 60, usually used as tracers in AMS measurements, were examined for their HR-MS characteristics in the CC and BB emissions. In addition, the MS of the CC and BB emissions are also compared with component MS from factor analysis of ambient OA datasets observed in China, as well as with other AMS measurements of primary sources in the literature. The MS signatures of cooking and biomass burning emissions revealed in this study can be used as important reference for factor analysis of ambient OA datasets, especially for the relevant studies in East Asia

Determinants of childhood overweight and obesity in China

In order to investigate the determinants of childhood overweight and obesity in China, the prevalence of overweight (including obesity) was compared according to different dietary and physical activity patterns and parental body weight status. A total of 6826 children aged 7-17 years from the 2002 China National Nutrition and Health Survey were included in the study. Information for dietary intake was collected using three consecutive 24-h recalls by trained interviewers. The amounts of cooking oil and condiments consumed were weighed. An interview-administered 1-year physical activity questionnaire was used to collect physical activity information. The results showed that the heavier the parental body weight, the higher the overweight prevalence in children. The prevalence ratio increased if parent(s) were overweight and/or obese, up to 12.2 if both parents were obese. Overweight children consumed significantly more dietary energy, protein and fat, but less carbohydrate than their normal weight counterparts. On average, overweight children spent 0.5h less on moderate/vigorous activities and 2.3h more on low intensity activities per week. The following prevalence ratios were statistically significant: walking to and from school (0.6); moderate/vigorous activities >= 45 min/d (0.8); low intensity physical activities > 2 h/d (1.3); the consumption of >= 25 g/d cooking oil (1.4); >= 200g/d meat and meat products consumption (1.5); >= 100 g/d dairy products (1.8). After adjustment for parental body weight status and socioeconomic status, only cooking oil consumption and walking to and from school remained significantly related to child overweight. In conclusion, parental weight status is an important determinant. Fat intake, low intensity activities and active transport to/from school may be suitable entry points for overweight prevention among Chinese school children

Author Correction: MiR-31 promotes mammary stem cell expansion and breast tumorigenesis by suppressing Wnt signaling antagonists.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

MiR-31 promotes mammary stem cell expansion and breast tumorigenesis by suppressing Wnt signaling antagonists

MicroRNA-mediated post-transcriptional regulation plays key roles in stem cell self-renewal and tumorigenesis. However, the in vivo functions of specific microRNAs in controlling mammary stem cell (MaSC) activity and breast cancer formation remain poorly understood. Here we show that miR-31 is highly expressed in MaSC-enriched mammary basal cell population and in mammary tumors, and is regulated by NF-κB signaling. We demonstrate that miR-31 promotes mammary epithelial proliferation and MaSC expansion at the expense of differentiation in vivo. Loss of miR-31 compromises mammary tumor growth, reduces the number of cancer stem cells, as well as decreases tumor-initiating ability and metastasis to the lung, supporting its pro-oncogenic function. MiR-31 modulates multiple signaling pathways, including Prlr/Stat5, TGFβ and Wnt/β-catenin. Particularly, it activates Wnt/β-catenin signaling by directly targeting Wnt antagonists, including Dkk1. Importantly, Dkk1 overexpression partially rescues miR31-induced mammary defects. Together, these findings identify miR-31 as the key regulator of MaSC activity and breast tumorigenesis

220 fs Er-Yb:glass laser mode-locked by a broadband low-loss Si/Ge saturable absorber

We demonstrate femtosecond performance of an ultra-broadband high-index-contrast saturable Bragg reflector consisting of a silicon/silicon-dioxide/germanium structure that is fully compatible with CMOS processing. This device offers a reflectivity bandwidth of over 700 nm and sub-picosecond recovery time of the saturable loss. It is used to achieve mode-locking of an Er-Yb:glass laser centered at 1540 nm, generating 220 fs pulses, with the broadest output spectrum to date

Laser propagation in dense magnetized plasma

A right-hand circularly polarized electromagnetic wave can propagate in a sufficiently magnetized plasma of any density without cutoff in the so-called whistler mode. With the recent realization of tens-kilotesla magnetic fields, laser propagation in highly magnetized high-density plasmas has become of practical interest, especially for heating plasmas to high energy density and igniting fusion targets. In this paper, the whistler regime of laser-plasma interaction is discussed. It is shown that moderately intense right-hand circularly polarized laser light can enter and propagate in high-density plasma and heat it efficiently because of the significantly reduced wave length and speed

Tailored Plasmons in Pentacene/Graphene Heterostructures with Interlayer Electron Transfer

van der Waals (vdW) heterostructures, which are produced by the precise assemblies of varieties of two-dimensional (2D) materials, have demonstrated many novel properties and functionalities. Here we report a nanoplasmonic study of vdW heterostructures that were produced by depositing ordered molecular layers of pentacene on top of graphene. We find through nanoinfrared (IR) imaging that surface plasmons formed due to the collective oscillations of Dirac Fermions in graphene are highly sensitive to the adjacent pentacene layers. In particular, the plasmon wavelength declines systematically but nonlinearly with increasing pentacene thickness. Further analysis and density functional theory (DFT) calculations indicate that the observed peculiar thickness dependence is mainly due to the tunneling-type electron transfer from pentacene to graphene. Our work unveils a new method for tailoring graphene plasmons and deepens our understanding of the intriguing nano-optical phenomena due to interlayer couplings in novel vdW heterostructures

Neutron reflection study of the adsorption of the phosphate surfactant NaDEHP onto alumina from water.

The adsorption of a phosphorus analogue of the surfactant AOT, sodium bis(2-ethylhexyl) phosphate (NaDEHP), at the water/alumina interface is described. The material is found to adsorb as an essentially water-free bilayer from neutron reflection measurements. This is similar to the behavior of AOT under comparable conditions, although AOT forms a thicker, more hydrated layer. The NaDEHP shows rather little variation with added salt, but a small thickening of the layer on increasing the pH, in contrast to the behavior of AOT.We thank BP plc and EPSRC for financial support for this work as well as the ISIS and ILL staff and scientists for the allocation of beam time and technical assistance with NR measurements. We also appreciate Chris Sporikou at Department of Chemistry, University of Cambridge, for help with the surfactant synthesis.This is the final version of the article. It first appeared at http://dx.doi.org/10.1021/la504837