A stable, single-photon emitter in a thin organic crystal for application to quantum-photonic devices

Single organic molecules offer great promise as bright, reliable sources of identical single photons on demand, capable of integration into solid-state devices. It has been proposed that such molecules in a crystalline organic matrix might be placed close to an optical waveguide for this purpose, but so far there have been no demonstrations of sufficiently thin crystals, with a controlled concentration of suitable dopant molecules. Here we present a method for growing very thin anthracene crystals from super-saturated vapour, which produces crystals of extreme flatness and controlled thickness. We show how this crystal can be doped with a widely adjustable concentration of dibenzoterrylene (DBT) molecules and we examine the optical properties of these molecules to demonstrate their suitability as quantum emitters in nanophotonic devices. Our measurements show that the molecules are available in the crystal as single quantum emitters, with a well-defined polarisation relative to the crystal axes, making them amenable to alignment with optical nanostructures. We find that the radiative lifetime and saturation intensity vary little within the crystal and are not in any way compromised by the unusual matrix environment. We show that a large fraction of these emitters are able to deliver more than $10^{12}$ photons without photo-bleaching, making them suitable for real applications.Comment: 12 pages, 10 figures, comments welcom

Primate Primordial Germ Cells Acquire Transplantation Potential by Carnegie Stage 23.

Primordial germ cells (PGCs) are the earliest embryonic progenitors in the germline. Correct formation of PGCs is critical to reproductive health as an adult. Recent work has shown that primate PGCs can be differentiated from pluripotent stem cells; however, a bioassay that supports their identity as transplantable germ cells has not been reported. Here, we adopted a xenotransplantation assay by transplanting single-cell suspensions of human and nonhuman primate embryonic Macaca mulatta (rhesus macaque) testes containing PGCs into the seminiferous tubules of adult busulfan-treated nude mice. We discovered that both human and nonhuman primate embryonic testis are xenotransplantable, generating colonies while not generating tumors. Taken together, this work provides two critical references (molecular and functional) for defining transplantable primate PGCs. These results provide a blueprint for differentiating pluripotent stem cells to transplantable PGC-like cells in a species that is amenable to transplantation and fertility studies

Reversible Actuation via Photoisomerization-Induced Melting of a Semicrystalline Poly(Azobenzene)

Photoisomerization of azobenzene in polymer matrices is a powerful method to convert photon energy into mechanical work. While most previous studies have focused on incorporating azobenzene within amorphous or liquid crystalline materials, the limited extents of molecular ordering and correspondingly modest enthalpy changes upon switching in such systems has limited the achievable energy densities. In this work, we introduce a semicrystalline main-chain poly(azobenzene), where photoisomerization is capable of reversibly triggering melting and recrystallization under essentially isothermal conditions. These materials can be drawn into aligned fibers, yielding optically driven two-way shape memory actuators capable of reversible bending

Single-photon-level sub-Doppler pump-probe spectroscopy of rubidium

We propose and demonstrate pump-probe spectroscopy of rubidium absorption which reveals the sub-Doppler hyperfine structure of the $^{5}$S$_{1/2} \leftrightarrow$ $^{5}$P$_{3/2}$ (D2) transitions. The counter propagating pump and probe lasers are independently tunable in frequency, with the probe operating at the single-photon-level. The two-dimensional spectrum measured as the laser frequencies are scanned shows fluorescence, Doppler-broadened absorption dips and sub-Doppler features. The detuning between the pump and probe lasers allows compensation of the Doppler shift for all atomic velocities in the room temperature vapor, meaning we observe sub-Doppler features for all atoms in the beam. We detail a theoretical model of the system which incorporates fluorescence, saturation effects and optical pumping and compare this with the measured spectrum, finding a mean absolute percentage error of 4.17\%. In the future this technique could assist in frequency stabilization of lasers, and the single-photon-level probe could be replaced by a single photon source.Comment: 5 page paper, 4 page supplemental material. Comments welcom

All plug-in electric vehicles are not the same: Predictors of preference for a plug-in hybrid versus a battery-electric vehicle

This study analyzes data from a survey of drivers (n = 1080) administered in late 2013 to assess factors that influence potential car buyers to consider two different types of plug-in electric vehicles (PEVs) in the United States: plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVs). The results indicate distinct profiles of respondents preferring PHEVs, which have a gasoline backup engine, versus battery BEVs, which rely solely on a battery for power. Respondents interested in selecting a PHEV consider it more for its economic benefits, such as reduced gasoline and maintenance expenditures. Respondents preferring a BEV are drawn to its environmental and technological appeal. The absence of range anxiety for PHEV is a major factor influencing potential PEV buyers

Chromophoric Dissolved Organic Matter and Dissolved Organic Carbon in Lakes Across an Elevational Gradient From the Mountains to the Sea

Dissolved organic matter (DOM) in lakes across elevation gradients is a complex function of topography, climate, vegetation coverage, land use, and lake properties. To examine sources and processing of DOM from sea level to mountain lakes (3–1,574 m), we measured dissolved organic carbon (DOC) concentrations and chromophoric dissolved organic matter (CDOM) optical properties, lake characteristics, and water quality parameters in 62 freshwater lakes in the Pacific Northwest, USA. Higher elevation lakes had lower DOC concentrations and absorbance. These lakes had higher forest cover and minimal wetlands in their watershed, in addition to low nutrients, water temperatures, and chlorophyll a in the lake itself. Two humic-like and one protein-like fluorescent component were identified from excitation-emission matrix spectroscopy. The index of recent autochthonous contribution (BIX), fluorescence index (FIX), and SR optical indices showed that most lakes were dominated by terrestrially derived material. The humification index (HIX) and specific ultra-violet absorbance (SUVA254) were consistent with more aromatic humic CDOM at lower elevations. The lower fluorescence of humic-like components at higher elevation was attributed to lower inputs from vegetation. The relative contribution of the protein-like component increased at higher elevation. This may be due to reduced allochthonous terrestrial inputs relative to in situ production of autochthonous material or increased photochemical/biological degradation of allochthonous material. Differences in optical characteristics associated with the amount and source of CDOM were observed across the elevational gradient. These differences were driven by characteristics at both within-lake and watershed scales

Efficient excitation of dye molecules for single photon generation

A reliable photon source is required for many aspects of quantum technology. Organic molecules are attractive for this application because they can have high quantum yield and can be photostable, even at room temperature. To generate a photon with high probability, a laser must excite the molecule efficiently. We develop a simple model for that efficiency and discuss how to optimise it. We demonstrate the validity of our model through experiments on a single dibenzoterrylene (DBT) molecule in an anthracene crystal. We show that the excitation probability cannot exceed 75\% at room temperature, but can increase to over 99\% if the sample is cooled to liquid nitrogen temperature. The possibility of high photon generation efficiency with only modest cooling is a significant step towards a reliable photon source that is simple and practical.Comment: Main article (8 pages), Supplementary material (4 pages). Comments welcom

Production of crystallizable human chymase from a Bacillus subtilis system

AbstractA Bacillus subtilis strain deficient in seven extracellular proteases was used to produce human mast cell chymase and is a viable expression system for serine proteases and other classes of proteins. Chymase is produced at 0.3–0.5 mg/l and is purified by three chromatography steps. Two crystal forms of PMSF-treated chymase were optimized. The first is C2 with a=47.94 Å, b=85.23 Å, c=174.18 Å, β=96.74°, and diffracts to at least 2.1 Å, while the second is P212121, with cell dimensions a=43.93 Å, b=58.16 Å, and c=86.09 Å, and a diffraction limit of approximately 1.9 Å. The first crystal form has either three or four molecules/asymmetric unit, while the second has one molecule/asymmetric unit

Differentiation of primate primordial germ cell-like cells following transplantation into the adult gonadal niche.

A major challenge in stem cell differentiation is the availability of bioassays to prove cell types generated in vitro are equivalent to cells in vivo. In the mouse, differentiation of primordial germ cell-like cells (PGCLCs) from pluripotent cells was validated by transplantation, leading to the generation of spermatogenesis and to the birth of offspring. Here we report the use of xenotransplantation (monkey to mouse) and homologous transplantation (monkey to monkey) to validate our in vitro protocol for differentiating male rhesus (r) macaque PGCLCs (rPGCLCs) from induced pluripotent stem cells (riPSCs). Specifically, transplantation of aggregates containing rPGCLCs into mouse and nonhuman primate testicles overcomes a major bottleneck in rPGCLC differentiation. These findings suggest that immature rPGCLCs once transplanted into an adult gonadal niche commit to differentiate towards late rPGCs that initiate epigenetic reprogramming but do not complete the conversion into ENO2-positive spermatogonia

Impact of the Macrophyte Nymphaea odorata (Lily Pads) on Dissolved Organic Matter (DOM) in a Lake

(Files are available for download below.) Macrophytes are a potential source of dissolved organic matter (DOM) in lakes. To probe the contribution of Nymphaea odorata (lily pads), dissolved organic carbon concentrations (DOC) and optical properties of chromophoric DOM were measured in a lake in the Pacific Northwest, United States over a year. Lily pads are prevalent around the shoreline during summer, dying back in fall. Indices of recent autochthonous contribution (BIX), fluorescence (FIX) and SR showed the lake was dominated by terrestrially-derived material. DOC concentrations were not correlated with rainfall, but were positively correlated with absorption coefficients. Values were highest in the summer dry season and decreased in the winter wet season, suggesting a source in the lake being diluted by precipitation rather than a dominant source from watershed runoff. Humic-like and protein-like fluorescent components were identified from excitation-emission matrix spectroscopy in lake waters and lily pad leachates. The protein-like component was highest during the summer, indicative of an in situ autochthonous source. Lily pad leachates had BIX, FIX, and SR values characteristic of terrestrial material and lake samples. However, leachates had lower humification index (HIX), specific ultraviolet absorbance (SUVA), flu/abs ratios and spectral slope (S) values. Higher absorption coefficients and DOC concentrations in the lake in summer were correlated with lower HIX, SUVA, flu/abs and S values, consistent with material leaching from lily pads. Seasonal trends in optical indices, absorption coefficients and DOC concentrations are consistent with lily pads being a significant DOM source in the lake, particularly in the summer dry season with low watershed runoff. This is for the supporting data for the paper in Limnology and Oceanography, specifically the absorbance and fluorescence spectra of the Lake Louise water samples (taken weekly over the course of a year). These files include large spreadsheets with raw and corrected absorbance and fluorescence intensity data as a function of wavelength, as well as the raw and corrected absorbance and fluorescence 3D excitation-emission matrix spectra (EEMs). These files are in .opj format, which is readable with commercially available Origin graphing software. Data includes tables with optical parameters and indices for absorbance and fluorescence for the weekly lake water samples, and spreadsheets with raw and corrected absorbance and fluorescence intensity data as a function of wavelength, as well as raw and corrected absorbance and fluorescence 3D excitation-emission matrix spectra (EEMs)