Radiation pattern of a ground-plane mounted parallel-plate waveguide analyzed by a surface integration technique

Surface integration analysis of radiation pattern of parallel plate waveguid

An Electrically Detonated Downhole Seismic Gun

An electrically detonated downhole seismic gun (EDG) that will fire blank 8-guage shells underwater has been constructed and tested to 80m depth (hydrostatic pressures of 130 psi or 8.9 x 105 Pa). Although other engineering seismic guns which fire blank or projectile sources are available, they are for near-surface shots and are not meant to be used for downhold seismic surveys in water-filled boreholes. The EDG was designed primarily for checkshot surveys (well travel-time surveys) and high-quality reflection/refraction tests, but potential applications include shallow vertical seismic profiling and borehole to borehole or borehole to surface tomography, as well as optimum offset and common midpoint seismic reflection surveys. The EDG consists off four steel subassemblies: (1) chamber; (2) breech; (3) pipe; and (4) hanger. A blank 8-gauge electrical shell is held by the chamber and is detonated by an electrode located inside the breech. O-ring seals prevent water from entering the breech and causing short circuits. The breech is screwed into a pipe which is also fitted with o-ring seals to keep the internal wiring dry. A hanger subassembly provides a convenient attaching point for the hoist cable. Arming of the EDG with an explosives blaster occurs only after lowering to operating depth. The EDG has been tested with various size black powder loads up to 750 grains. Frequency bandwidth and repeatability tests were carried out under saturated conditions in a fluvial and lacustrine sedimentary section. These preliminary tests show significant frequency content in the 25-200 Hz band (peak near 100 Hz) for reflections from depths of 150-300 m, and acceptable waveform repeatability for different shot records obtained with identical geometry and acquisition parameters

Effects of Hydrogen on the Phases and Transition Temperatures of NiTi

Austenitic (B2) NiTi samples were cathodically charged with various amounts of hydrogen. Trends are tracked based on temperature, time and voltage throughout the process to establish consistent and predictive hydrogen charging procedures. The effect of hydrogen on the austenitic structure and the formation of hydrides are studied with x-ray diffraction (XRD). An increase in the austenite lattice parameter with increased hydrogen content is observed up to a hydrogen solubility limit of approximately 85 wppm. At greater hydrogen concentrations, additional XRD peaks appear, suggesting possible hydride formation. Differential scanning calorimetry (DSC) results show a decrease in both the austenitic and martensitic transition temperatures with increased atomic hydrogen content and increased hydride phase. Scanning electron microscopy (SEM) is used to reveal the hydride phase. The effect of atomic hydrogen on NiTi and the structure of the hydride phase are compared with previous hydrogen studies

Practical quantum repeaters with linear optics and double-photon guns

We show how to create practical, efficient, quantum repeaters, employing double-photon guns, for long-distance optical quantum communication. The guns create polarization-entangled photon pairs on demand. One such source might be a semiconducter quantum dot, which has the distinct advantage over parametric down-conversion that the probability of creating a photon pair is close to one, while the probability of creating multiple pairs vanishes. The swapping and purifying components are implemented by polarizing beam splitters and probabilistic optical CNOT gates.Comment: 4 pages, 4 figures ReVTe

Multiple-photon resolving fiber-loop detector

We show first reconstructions of the photon-number distribution obtained with a multi-channel fiber-loop detector. Apart from analyzing the statistics of light pulses this device can serve as a sophisticated postselection device for experiments in quantum optics and quantum information. We quantify its efficiency by means of the Fisher information and compare it to the efficiency of the ideal photodetector.Comment: 5 pages, 6 figure

Transient pluripotent cell populations during primitive ectoderm formation: correlation of in vivo and in vitro pluripotent cell development.

Formation and differentiation of a pluripotent cell population is central to mammalian development, and the isolation, identification and manipulation of human pluripotent cells is predicted to be of therapeutic use. Within the early mammalian embryo, two distinct populations of pluripotent cells have been described: the inner cell mass (ICM), which differentiates to form a second pluripotent cell populations, the primitive ectoderm. Indirect evidence suggests the existence of temporally distinct intermediate pluripotent cell populations as primitive ectoderm is formed. We coupled an in vitro model of primitive ectoderm formation (the transition of embryonic stem cells to early primitive ectoderm-like (EPL) cells) with ddPCR-based techniques to identify three novel genes, Psc1, CRTR-1 and PRCE, that were expressed differently during pluripotent cell progression. Detailed mapping of these genes with Oct4, Rex1 and Fgf5 on pregastrulation embryos provided the first molecular evidence for the existence of successive, temporally distinct pluripotent cell populations in the embryo between the ICM and primitive ectoderm. No evidence was found for spatial heterogeneity within the Oct4+ pool. The transition between populations correlated with morphological or developmental alterations in pluripotent cells in vivo. Genes that are temporally expressed during pluripotent cell progression may provide an opportunity for molecular discrimination of pluripotent cells at different stages of maturation in vivo and an understanding of the cellular origins and properties of pluripotent cell lines isolated from diverse sources. Furthermore, the strong correlation of gene expression demonstrated between EPL cell formation in vitro and primitive ectoderm formation in vivo validates EPL cells as a model for primitive ectoderm, thereby providing a model system for the investigation of pluripotent differentiation and an opportunity for directed differentiation of pluripotent cells to therapeutically useful cell populations.T. A. Pelton, S. Sharma, T. C. Schulz, J. Rathjen and P. D. Rathje

A calcium ion in a cavity as a controlled single-photon source

We present a single calcium ion, coupled to a high-finesse cavity, as an almost ideal system for the controlled generation of single photons. Photons from a pump beam are Raman-scattered by the ion into the cavity mode, which subsequently emits the photon into a well-defined output channel. In contrast with comparable atomic systems, the ion is localized at a fixed position in the cavity mode for indefinite times, enabling truly continuous operation of the device. We have performed numeric calculations to assess the performance of the system and present the first experimental indication of single-photon emission in our set-up

Response patterns in the developing social brain are organized by social and emotion features and disrupted in children diagnosed with autism spectrum disorder

© 2019 Elsevier Ltd Adults and children recruit a specific network of brain regions when engaged in “Theory of Mind” (ToM) reasoning. Recently, fMRI studies of adults have used multivariate analyses to provide a deeper characterization of responses in these regions. These analyses characterize representational distinctions within the social domain, rather than comparing responses across preferred (social) and non-preferred stimuli. Here, we conducted opportunistic multivariate analyses in two previously collected datasets (Experiment 1: n = 20 5–11 year old children and n = 37 adults; Experiment 2: n = 76 neurotypical and n = 29 5–12 year old children diagnosed with Autism Spectrum Disorder (ASD)) in order to characterize the structure of representations in the developing social brain, and in order to discover if this structure is disrupted in ASD. Children listened to stories that described characters' mental states (Mental), non-mentalistic social information (Social), and causal events in the environment (Physical), while undergoing fMRI. We measured the extent to which neural responses in ToM brain regions were organized according to two ToM-relevant models: 1) a condition model, which reflected the experimenter-generated condition labels, and 2) a data-driven emotion model, which organized stimuli according to their emotion content. We additionally constructed two control models based on linguistic and narrative features of the stories. In both experiments, the two ToM-relevant models outperformed the control models. The fit of the condition model increased with age in neurotypical children. Moreover, the fit of the condition model to neural response patterns was reduced in the RTPJ in children diagnosed with ASD. These results provide a first glimpse into the conceptual structure of information in ToM brain regions in childhood, and suggest that there are real, stable features that predict responses in these regions in children. Multivariate analyses are a promising approach for sensitively measuring conceptual and neural developmental change and individual differences in ToM.NSF (Award 1122374

Time-resolved spectroscopy of multi-excitonic decay in an InAs quantum dot

The multi-excitonic decay process in a single InAs quantum dot is studied through high-resolution time-resolved spectroscopy. A cascaded emission sequence involving three spectral lines is seen that is described well over a wide range of pump powers by a simple model. The measured biexcitonic decay rate is about 1.5 times the single-exciton decay rate. This ratio suggests the presence of selection rules, as well as a significant effect of the Coulomb interaction on the biexcitonic wavefunction.Comment: one typo fixe

Improving the performance of bright quantum dot single photon sources using amplitude modulation

Single epitaxially-grown semiconductor quantum dots have great potential as single photon sources for photonic quantum technologies, though in practice devices often exhibit non-ideal behavior. Here, we demonstrate that amplitude modulation can improve the performance of quantum-dot-based sources. Starting with a bright source consisting of a single quantum dot in a fiber-coupled microdisk cavity, we use synchronized amplitude modulation to temporally filter the emitted light. We observe that the single photon purity, temporal overlap between successive emission events, and indistinguishability can be greatly improved with this technique. As this method can be applied to any triggered single photon source, independent of geometry and after device fabrication, it is a flexible approach to improve the performance of solid-state systems, which often suffer from excess dephasing and multi-photon background emission