Understanding spatial and temporal patterning of astrocyte calcium transients via interactions between network transport and extracellular diffusion

NASA Astrophysics Data System (ADS)

Shtrahman, E.; Maruyama, D.; Olariu, E.; Fink, C. G.; Zochowski, M.

2017-02-01

Astrocytes form interconnected networks in the brain and communicate via calcium signaling. We investigate how modes of coupling between astrocytes influence the spatio-temporal patterns of calcium signaling within astrocyte networks and specifically how these network interactions promote coordination within this group of cells. To investigate these complex phenomena, we study reduced cultured networks of astrocytes and neurons. We image the spatial temporal patterns of astrocyte calcium activity and quantify how perturbing the coupling between astrocytes influences astrocyte activity patterns. To gain insight into the pattern formation observed in these cultured networks, we compare the experimentally observed calcium activity patterns to the patterns produced by a reduced computational model, where we represent astrocytes as simple units that integrate input through two mechanisms: gap junction coupling (network transport) and chemical release (extracellular diffusion). We examine the activity patterns in the simulated astrocyte network and their dependence upon these two coupling mechanisms. We find that gap junctions and extracellular chemical release interact in astrocyte networks to modulate the spatiotemporal patterns of their calcium dynamics. We show agreement between the computational and experimental findings, which suggests that the complex global patterns can be understood as a result of simple local coupling mechanisms.

Guiding, bending, and splitting of coupled defect surface modes in a surface-wave photonic crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Zhen; Gao, Fei; Zhang, Baile, E-mail: blzhang@ntu.edu.sg

2016-01-25

We experimentally demonstrate a type of waveguiding mechanism for coupled surface-wave defect modes in a surface-wave photonic crystal. Unlike conventional spoof surface plasmon waveguides, waveguiding of coupled surface-wave defect modes is achieved through weak coupling between tightly localized defect cavities in an otherwise gapped surface-wave photonic crystal, as a classical wave analogue of tight-binding electronic wavefunctions in solid state lattices. Wave patterns associated with the high transmission of coupled defect surface modes are directly mapped with a near-field microwave scanning probe for various structures including a straight waveguide, a sharp corner, and a T-shaped splitter. These results may find usemore » in the design of integrated surface-wave devices with suppressed crosstalk.« less

Bridging a possible gap of GRACE observations in the Arctic Ocean using existing GRACE data and in situ bottom pressure sensors

NASA Astrophysics Data System (ADS)

Peralta Ferriz, C.; Morison, J.

2014-12-01

Since 2003, the Gravity Recovery and Climate Experiment (GRACE) satellite system has provided the means of investigating month-to-month to inter-annual variability of, among many other things, Arctic Ocean circulation over the entire Arctic Basin. Such a comprehensive picture could not have been achieved with the limited in situ pressure observations available. Results from the first 10 years of ocean bottom pressure measurements from GRACE in the Arctic Ocean reveal distinct patterns of ocean variability that are strongly associated with changes in large-scale atmospheric circulation (Peralta-Ferriz et al., 2014): the leading mode of variability being a wintertime basin-coherent mass change driven by winds in the Nordic Seas; the second mode of variability corresponding to a mass signal coherent along the Siberian shelves, and driven by the Arctic Oscillation; and the third mode being a see-saw between western and eastern Arctic shelves, also driven by the large-scale wind patterns. In order to understand Arctic Ocean changes, it is fundamental to continue to track ocean bottom pressure. Our concern is what to do if the present GRACE system, which is already well beyond its design lifetime, should fail before its follow-on is launched, currently estimated to be in 2017. In this work, we regress time series of pressure from the existing and potential Arctic Ocean bottom pressure recorder locations against the fundamental modes of bottom pressure variation. Our aim is to determine the optimum combination of in situ measurements to represent the broader scale variability now observed by GRACE. With this understanding, we can be better prepared to use in situ observations to at least partially cover a possible gap in GRACE coverage. Reference:Peralta-Ferriz, Cecilia, James H. Morison, John M. Wallace, Jennifer A. Bonin, Jinlun Zhang, 2014: Arctic Ocean Circulation Patterns Revealed by GRACE. J. Climate, 27, 1445-1468. doi: http://dx.doi.org/10.1175/JCLI-D-13-00013.1

Dual mode of embryonic development is highlighted by expression and function of Nasonia pair-rule genes

PubMed Central

Rosenberg, Miriam I; Brent, Ava E; Payre, François; Desplan, Claude

2014-01-01

Embryonic anterior–posterior patterning is well understood in Drosophila, which uses ‘long germ’ embryogenesis, in which all segments are patterned before cellularization. In contrast, most insects use ‘short germ’ embryogenesis, wherein only head and thorax are patterned in a syncytial environment while the remainder of the embryo is generated after cellularization. We use the wasp Nasonia (Nv) to address how the transition from short to long germ embryogenesis occurred. Maternal and gap gene expression in Nasonia suggest long germ embryogenesis. However, the Nasonia pair-rule genes even-skipped, odd-skipped, runt and hairy are all expressed as early blastoderm pair-rule stripes and late-forming posterior stripes. Knockdown of Nv eve, odd or h causes loss of alternate segments at the anterior and complete loss of abdominal segments. We propose that Nasonia uses a mixed mode of segmentation wherein pair-rule genes pattern the embryo in a manner resembling Drosophila at the anterior and ancestral Tribolium at the posterior. DOI: http://dx.doi.org/10.7554/eLife.01440.001 PMID:24599282

Adiabatic Nanofocusing in Hybrid Gap Plasmon Waveguides on the Silicon-on-Insulator Platform.

PubMed

Nielsen, Michael P; Lafone, Lucas; Rakovich, Aliaksandra; Sidiropoulos, Themistoklis P H; Rahmani, Mohsen; Maier, Stefan A; Oulton, Rupert F

2016-02-10

We present an experimental demonstration of a new class of hybrid gap plasmon waveguides on the silicon-on-insulator (SOI) platform. Created by the hybridization of the plasmonic mode of a gap in a thin metal sheet and the transverse-electric (TE) photonic mode of an SOI slab, this waveguide is designed for efficient adiabatic nanofocusing simply by varying the gap width. For gap widths greater than 100 nm, the mode is primarily photonic in character and propagation lengths can be many tens of micrometers. For gap widths below 100 nm, the mode becomes plasmonic in character with field confinement predominantly within the gap region and with propagation lengths of a few microns. We estimate the electric field intensity enhancement in hybrid gap plasmon waveguide tapers at 1550 nm by three-photon absorption of selectively deposited CdSe/ZnS quantum dots within the gap. Here, we show electric field intensity enhancements of up to 167 ± 26 for a 24 nm gap, proving the viability of low loss adiabatic nanofocusing on a commercially relevant photonics platform.

Waveguide-mode polarization gaps in square spiral photonic crystals

NASA Astrophysics Data System (ADS)

Liu, Rong-Juan; John, Sajeev; Li, Zhi-Yuan

2015-09-01

We designed waveguide channels in two types of square spiral photonic crystals. Wide polarization gaps, in which only one circular polarization wave is allowed while the other counter-direction circular polarization wave is forbidden, can be opened up on the waveguide modes within the fundamental photonic band gap according to the calculation of band structures and transmission spectra. This phenomenon is ascribed to the chirality of the waveguide and is independent of the chirality of the background photonic crystal. Moreover, the transmission spectra show a good one-way property of the waveguide channels. The chiral quality factor demonstrates the handedness of the allowed and impeded chiral waveguide modes, and further proved the property of the waveguide-mode polarization gap. Such waveguides with waveguide-mode polarization gap are a good candidate for one-way waveguides with robust backscattering-immune transport.

Low index contrast heterostructure photonic crystal cavities with high quality factors and vertical radiation coupling

NASA Astrophysics Data System (ADS)

Ge, Xiaochen; Minkov, Momchil; Fan, Shanhui; Li, Xiuling; Zhou, Weidong

2018-04-01

We report here design and experimental demonstration of heterostructure photonic crystal cavities resonating near the Γ point with simultaneous strong lateral confinement and highly directional vertical radiation patterns. The lateral confinement is provided by a mode gap originating from a gradual modulation of the hole radii. High quality factor resonance is realized with a low index contrast between silicon nitride and quartz. The near surface-normal directional emission is preserved when the size of the core region is scaled down. The influence of the cavity size parameters on the resonant modes is also investigated theoretically and experimentally.

Features of the Percolation Scheme of Vibrational Spectrum Reconstruction in the Ga1 - x Al x P Alloy

NASA Astrophysics Data System (ADS)

Kozyrev, S. P.

2018-04-01

Specific features of the properties of Ga-P lattice vibrations have been investigated using the percolation model of a mixed Ga1 - x Al x P crystal (alloy) with zero lattice mismatch between binary components of the alloy. In contrast to other two-mode alloy systems, in Ga1 - x Al x P a percolation splitting of δ 13 cm-1 is observed for the low-frequency mode of GaP-like vibrations. An additional GaP mode (one of the percolation doublet components) split from the fundamental mode is observed for the GaP-rich alloy, which coincides in frequency with the gap corresponding to the zero density of one-phonon states of the GaP crystal. The vibrational spectrum of impurity Al in the GaP crystal has been calculated using the theory of crystal lattice dynamics. Upon substitution of lighter Al for the Ga atom, the calculated spectrum includes, along with the local mode, a singularity near the gap with the zero density of phonon states of the GaP crystal, which coincides with the mode observed experimentally at a frequency of 378 cm-1 in the Ga1 - x Al x P ( x < 0.4) alloy.

Photonic crystals: Theory and device applications

NASA Astrophysics Data System (ADS)

Fan, Shanhui

In this thesis, first-principle frequency-domain and time-domain methods are developed and applied to investigate various properties and device applications of photonic crystals. In Chapter 2, I discuss the two numerical methods used to investigate the properties of photonic crystals. The first solves Maxwell's equations in the frequency domain, while the second solves the equations in the time domain. The frequency-domain method yields the frequency, polarization, symmetry, and field distribution of every eigenmode of the system; the time-domain method allows one to determine the temporal behavior of the modes. In Chapter 3, a new class of three-dimensional photonic crystal structures is introduced that is amenable for fabrication at submicron-length scales. The structures give rise to a 3D photonic bandgap. They consist of a layered structure in which a series of cylindrical air holes are etched at normal incidence. The calculation demonstrates the existence of a gap as large as 14% of the mid-gap frequency using Si, SiO2, and air; and 23% using Si and air. In Chapter 4, the bandstructure and transmission properties of three-dimensional metallodielectric photonic crystals are presented. The metallodielectric crystals are modeled as perfect electrical conducting objects embedded in dielectric media. We investigate the face-centered-cubic (fcc) lattice, and the diamond lattice. Partial gaps are predicted in the fcc lattice, in excellent agreement with recent experiments. Complete gaps are found in a diamond lattice of isolated metal spheres. The gaps appear between the second and third bands, and their sizes can be larger than 60% when the radius of the spheres exceeds 21% of the cubic unit cell size. In Chapter 5, I investigate the properties of resonant modes which arise from the introduction of local defects in two-dimensional (2D) and 3D photonic crystals. The properties of these modes can be controlled by changing the nature and the size of the defects. The symmetry associated with these modes translates into an orbital angular momentum for each photon. In Chapter 6, a new type of high-Q microcavity is introduced that consists of a channel waveguide and a one-dimensional photonic crystal. A band gap for the guided modes is opened and a sharp resonant state is created by adding a defect in the periodic system. Strong field confinement of the defect can be achieved with a modal volume less than half of a cubic wavelength. The coupling efficiency to this mode from a channel waveguide exceeds 80%. In Chapter 7, a tunable single-mode waveguide microcavity is proposed that is well suited for frequency modulations and switching. The cavity mode has a volume of less than one cubic half-wavelength, and the resonant frequency is tuned by refractive-index modulation. Picosecond on-off switching times are achievable when two of these cavities are placed in series. In Chapter 8, I show that a thin slab of two-dimensional photonic crystal can alter drastically the radiation pattern of spontaneous emission. By eliminating all guided modes at the transition frequencies, spontaneous emission can be coupled entirely to free space modes. (Copies available exclusively from MIT Libraries, Rm. 14- 0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.) (Abstract shortened by UMI.)

Photonic and phononic surface and edge modes in three-dimensional phoxonic crystals

NASA Astrophysics Data System (ADS)

Ma, Tian-Xue; Wang, Yue-Sheng; Zhang, Chuanzeng

2018-04-01

We investigate the photonic and phononic surface and edge modes in finite-size three-dimensional phoxonic crystals. By appropriately terminating the phoxonic crystals, the photons and phonons can be simultaneously guided at the two-dimensional surface and/or the one-dimensional edge of the terminated crystals. The Bloch surface and edge modes show that the electromagnetic and acoustic waves are highly localized near the surface and edge, respectively. The surface and edge geometries play important roles in tailoring the dispersion relations of the surface and edge modes, and dual band gaps for the surface or edge modes can be simultaneously achieved by changing the geometrical configurations. Furthermore, as the band gaps for the bulk modes are the essential prerequisites for the realization of dual surface and edge modes, the photonic and phononic bulk-mode band gap properties of three different types of phoxonic crystals with six-connected networks are revealed. It is found that the geometrical characteristic of the crystals with six-connected networks leads to dual large bulk-mode band gaps. Compared with the conventional bulk modes, the surface and edge modes provide a new approach for the photon and phonon manipulation and show great potential for phoxonic crystal devices and optomechanics.

Two-dimensional simulation of argon dielectric barrier discharge excited by a Gaussian voltage at atmospheric pressure

NASA Astrophysics Data System (ADS)

Xu, Yonggang; Wang, Jing; Li, Jing; Lei, Bingying; Tang, Jie; Wang, Yishan; Li, Yongfang; Zhao, Wei; Duan, Yixiang

2017-04-01

A two-dimensional self-consistent fluid model was employed to investigate the spatiotemporal characteristics of discharges in atmospheric pressure argon (Ar) dielectric barrier discharge driven by a Gaussian voltage. The simulation results show that a discharge with multiple current pulses occurs each half-cycle in the gas gap. A transition from the Townsend mode to the glow mode is observed with the increasing applied voltage each half-cycle at a lower driving frequency (7.5 kHz). It is also found that the glow mode survives all the discharge phases at a higher driving frequency (12.5 kHz and 40 kHz). The change in the discharge mode with the driving frequency mainly lies in the fact that a lot of charged particles created in the discharge gap have no enough time to drift and diffuse around, and then these particles are assembled in the discharge space at higher frequency. Additionally, the spatial distributions of the electron density indicate that a center-advantage discharge is ignited at the driving frequencies of interest, resulting in the radial non-uniformity of discharge because of the edge effects. However, this overall non-uniformity is weakened with the driving frequency increased to 40 kHz, at which concentric ring patterns are observed. These distinct behaviors are mainly attributed to the fact that many charged particles generated are trapped in the gas gap and then accumulated to make the extension along the radial direction due to the charged particles transport and diffusion, and that the effective overlapping of a large number of avalanches induced by the increased "seed" electron density with the driving frequency. Meanwhile, the surface charged particles accumulated on the dielectric barriers are also shown to play a role in the formation of the discharge structure.

Pseudo-single-bunch mode for a 100 MHz storage ring serving soft X-ray timing experiments

NASA Astrophysics Data System (ADS)

Olsson, T.; Leemann, S. C.; Georgiev, G.; Paraskaki, G.

2018-06-01

At many storage rings for synchrotron light production there is demand for serving both high-flux and timing users simultaneously. Today this is most commonly achieved by operating inhomogeneous fill patterns, but this is not preferable for rings that employ passive harmonic cavities to damp instabilities and increase Touschek lifetime. For these rings, inhomogeneous fill patterns could severely reduce the effect of the harmonic cavities. It is therefore of interest to develop methods to serve high-flux and timing users simultaneously without requiring gaps in the fill pattern. One such method is pseudo-single-bunch (PSB), where one bunch in the bunch train is kicked onto another orbit by a fast stripline kicker. The light emitted from the kicked bunch can then be separated by an aperture in the beamline. Due to recent developments in fast kicker design, PSB operation in multibunch mode is within reach for rings that operate with a 100 MHz RF system, such as the MAX IV and Solaris storage rings. This paper describes machine requirements and resulting performance for such a mode at the MAX IV 1.5 GeV storage ring. A solution for serving all beamlines is discussed as well as the consequences of beamline design and operation in the soft X-ray energy range.

Gap maps and intrinsic diffraction losses in one-dimensional photonic crystal slabs.

PubMed

Gerace, Dario; Andreani, Lucio Claudio

2004-05-01

A theoretical study of photonic bands for one-dimensional (1D) lattices embedded in planar waveguides with strong refractive index contrast is presented. The approach relies on expanding the electromagnetic field on the basis of guided modes of an effective waveguide, and on treating the coupling to radiative modes by perturbation theory. Photonic mode dispersion, gap maps, and intrinsic diffraction losses of quasi guided modes are calculated for the case of self-standing membranes as well as for silicon-on-insulator structures. Photonic band gaps in a waveguide are found to depend strongly on the core thickness and on polarization, so that the gaps for transverse electric and transverse magnetic modes most often do not overlap. Radiative losses of quasiguided modes above the light line depend in a nontrivial way on structure parameters, mode index, and wave vector. The results of this study may be useful for the design of integrated 1D photonic structures with low radiative losses.

Gap discrete breathers in strained boron nitride

NASA Astrophysics Data System (ADS)

Barani, Elham; Korznikova, Elena A.; Chetverikov, Alexander P.; Zhou, Kun; Dmitriev, Sergey V.

2017-11-01

Linear and nonlinear dynamics of hexagonal boron nitride (h-BN) lattice is studied by means of molecular dynamics simulations with the use of the Tersoff interatomic potentials. It is found that sufficiently large homogeneous elastic strain along zigzag direction opens a wide gap in the phonon spectrum. Extended vibrational mode with boron and nitrogen sublattices vibrating in-plane as a whole in strained h-BN has frequency within the phonon gap. This fact suggests that a nonlinear spatially localized vibrational mode with frequencies in the phonon gap, called discrete breather (also often termed as intrinsic localized mode), can be excited. Properties of the gap discrete breathers in strained h-BN are contrasted with that for analogous vibrational mode found earlier in strained graphene. It is found that h-BN modeled with the Tersoff potentials does not support transverse discrete breathers.

Permissive and instructive anterior patterning rely on mRNA localization in the wasp embryo.

PubMed

Brent, Ava E; Yucel, Gozde; Small, Stephen; Desplan, Claude

2007-03-30

The long-germ mode of embryogenesis, in which segments arise simultaneously along the anteriorposterior axis, has evolved several times in different lineages of the holometabolous, or fully metamorphosing, insects. Drosophila's long-germ fate map is established largely by the activity of the dipteran-specific Bicoid (Bcd) morphogen gradient, which operates both instructively and permissively to accomplish anterior patterning. By contrast, all nondipteran long-germ insects must achieve anterior patterning independently of bcd. We show that bcd's permissive function is mimicked in the wasp by a maternal repression system in which anterior localization of the wasp ortholog of giant represses anterior expression of the trunk gap genes so that head and thorax can properly form.

Special purpose modes in photonic band gap fibers

DOEpatents

Spencer, James; Noble, Robert; Campbell, Sara

2013-04-02

Photonic band gap fibers are described having one or more defects suitable for the acceleration of electrons or other charged particles. Methods and devices are described for exciting special purpose modes in the defects including laser coupling schemes as well as various fiber designs and components for facilitating excitation of desired modes. Results are also presented showing effects on modes due to modes in other defects within the fiber and due to the proximity of defects to the fiber edge. Techniques and devices are described for controlling electrons within the defect(s). Various applications for electrons or other energetic charged particles produced by such photonic band gap fibers are also described.

Mode jumping of split-ring resonator metamaterials controlled by high-permittivity BST and incident electric fields

PubMed Central

Fu, Xiaojian; Zeng, Xinxi; Cui, Tie Jun; Lan, Chuwen; Guo, Yunsheng; Zhang, Hao Chi; Zhang, Qian

2016-01-01

We investigate the resonant modes of split-ring resonator (SRR) metamaterials that contain high-permittivity BST block numerically and experimentally. We observe interesting mode-jumping phenomena from the BST-included SRR absorber structure as the excitation wave is incident perpendicularly to the SRR plane. Specifically, when the electric field is parallel to the SRR gap, the BST block in the gap will induce a mode jumping from the LC resonance to plasmonic resonance (horizontal electric-dipole mode), because the displacement current excited by the Mie resonance in the dielectric block acts as a current channel in the gap. When the electric field is perpendicular to the gap side, the plasmonic resonance mode (vertical electric-dipole mode) in SRR changes to two joint modes contributed simultaneously by the back layer, SRR and BST block, as a result of connected back layer and SRR layer by the displacement current in the BST dielectric block. Based on the mode jumping effect as well as temperature and electric-field dependent dielectric constant, the BST-included SRR metamaterials may have great potentials for the applications in electromagnetic switches and widely tunable metamaterial devices. PMID:27502844

[Ecological agriculture: future of Good Agriculture Practice of Chinese materia medica].

PubMed

Guo, Lan-ping; Zhou, Liang-yun; Mo, Ge; Wang, Sheng; Huang, Lu-qi

2015-09-01

Based on the ecological and economic problems in Good Agriculture Practice (GAP) of Chinese material medica, we introduced the origin, concept, features and operative technology of eco-agriculture worldwide, emphasizing its modes on different biological levels of landscape, ecosystem, community, population, individual and gene in China. And on this basis, we analyzed the background and current situation of eco-agriculture of Chinese materia medica, and proposed its development ideas and key tasks, including: (1) Analysis and planning of the production pattern of Chinese material medica national wide. (2) Typical features extraction of regional agriculture of Chinese materia medica. (3) Investigation of the interaction and its mechanism between typical Chinese materia medica in each region and the micro-ecology of rhizosphere soil. (4) Study on technology of eco-agriculture of Chinese materia medica. (5) Extraction and solidification of eco-agriculture modes of Chinese materia medica. (6) Study on the theory of eco-agriculture of Chinese materia medica. Also we pointed out that GAP and eco-agriculture of Chinese material medica are both different and relative, but they are not contradictory with their own features. It is an irresistible trend to promote eco-agriculture in the GAP of Chinese material medica and coordinate ecological and economic development.

Visualization of multipolar longitudinal and transversal surface plasmon modes in nanowire dimers.

PubMed

Alber, Ina; Sigle, Wilfried; Müller, Sven; Neumann, Reinhard; Picht, Oliver; Rauber, Markus; van Aken, Peter A; Toimil-Molares, Maria Eugenia

2011-12-27

We study the transversal and longitudinal localized surface plasmon resonances in single nanowires and nanowire dimers excited by the fast traveling electron beam in a transmission electron microscope equipped with high-resolution electron energy-loss spectroscopy. Bright and dark longitudinal modes up to the fifth order are resolved on individual metallic nanowires. On nanowire dimers, mode splitting into bonding and antibonding is measured up to the third order for several dimers with various aspect ratio and controlled gap size. We observe that the electric field maxima of the bonding modes are shifted toward the gap, while the electric field maxima of the antibonding modes are shifted toward the dimer ends. Finally, we observe that the transversal mode is not detected in the region of the dimer gap and decays away from the rod more rapidly than the longitudinal modes.

Magnetic field effects on charge structure factors of gapped graphene structure

NASA Astrophysics Data System (ADS)

Rezania, Hamed; Tawoose, Nasrin

2018-02-01

We present the behaviors of dynamical and static charge susceptibilities of undoped gapped graphene using the Green's function approach in the context of tight binding model Hamiltonian. Specially, the effects of magnetic field on the plasmon modes of gapped graphene structure are investigated via calculating correlation function of charge density operators. Our results show the increase of magnetic field leads to disappear high frequency plasmon mode for gapped case. We also show that low frequency plasmon mode has not affected by increase of magnetic field and chemical potential. Finally the temperature dependence of static charge structure factor of gapp graphene structure is studied. The effects of both magnetic field and gap parameter on the static structure factor are discusses in details.

Axisymmetric Density Waves in Saturn's Rings

NASA Astrophysics Data System (ADS)

Hedman, Matthew; Nicholson, Philip

2018-04-01

Density waves in Saturn's rings are typically tightly wrapped spiral patterns generated by resonances with either Saturn's moons or structures inside the planet. However, between the Barnard and Bessel Gaps in the Cassini Division (i.e. between 120,240 and 120,300 km), there are density variations that appear to form an axisymmetric density wave, which consists of concentric regions of varying density that propagate radially through the rings. Such a wave requires some process that forces ring particles at all longitudes to pass through pericenter at the same time, and so cannot be generated by satellite resonances. Instead this particular wave appears to be excited by interference between a nearby satellite resonance and normal mode oscillations on the inner edge of the Barnard Gap. Similar axisymmetric waves may exist within the Dawes ringlet and the outermost part of the B ring, which are also just interior to resonantly confined edges that exhibit a large number of normal modes. These waves may therefore provide new insights into how resonant perturbations near an edge can propagate through a disk of material.

Direct observation of mode-specific phonon-band gap coupling in methylammonium lead halide perovskites.

PubMed

Kim, Heejae; Hunger, Johannes; Cánovas, Enrique; Karakus, Melike; Mics, Zoltán; Grechko, Maksim; Turchinovich, Dmitry; Parekh, Sapun H; Bonn, Mischa

2017-09-25

Methylammonium lead iodide perovskite is an outstanding semiconductor for photovoltaics. One of its intriguing peculiarities is that the band gap of this perovskite increases with increasing lattice temperature. Despite the presence of various thermally accessible phonon modes in this soft material, the understanding of how precisely these phonons affect macroscopic material properties and lead to the peculiar temperature dependence of the band gap has remained elusive. Here, we report a strong coupling of a single phonon mode at the frequency of ~ 1 THz to the optical band gap by monitoring the transient band edge absorption after ultrafast resonant THz phonon excitation. Excitation of the 1 THz phonon causes a blue shift of the band gap over the temperature range of 185 ~ 300 K. Our results uncover the mode-specific coupling between one phonon and the optical properties, which contributes to the temperature dependence of the gap in the tetragonal phase.Methylammonium lead iodide perovskite, a promising material for efficient photovoltaics, shows a unique temperature dependence of its optical properties. Kim et al. quantify the coupling between the optical gap and a lattice phonon at 1 THz, which favorably contributes to the thermal variation of the gap.

Hybrid photonic-plasmonic crystal nanocavity sensors

NASA Astrophysics Data System (ADS)

Cheng, Pi-Ju; Chiang, Chih-Kai; Chou, Bo-Tsun; Huang, Zhen-Ting; Ku, Yun-Cheng; Kuo, Mao-Kuen; Hsu, Jin-Chen; Lin, Tzy-Rong

2018-02-01

We have investigated a hybrid photonic-plasmonic crystal nanocavity consisting of a silicon grating nanowire adjacent to a metal surface with a gain gap between them. The hybrid plasmonic cavity modes are highly confined in the gap due to the strong coupling of the photonic crystal cavity modes and the surface plasmonic gap modes. Using finite-element method (FEM), guided modes of the hybrid plasmonic waveguide (WG) were numerically determined at a wavelength of 1550 nm. The modal characteristics such as WG confinement factors and modal losses of the fundamental hybrid plasmonic modes were obtained as a function of groove depth at various gap heights. Furthermore, the band structure of the hybrid crystal modes corresponding to a wide band gap of 17.8 THz is revealed. To enclose the optical energy effectively, a single defect was introduced into the hybrid crystal. At a deep subwavelength defect length as small as 270 nm, the resonant mode exhibits a high quality factor of 567 and an ultrasmall mode volume of 1.9 × 10- 3 ( λ/ n eff)3 at the resonance wavelength of 1550 nm. Compared to conventional photonic crystal nanowire cavities in the absence of a metal surface, the factor Q/ V m is significantly enhanced by about 15 times. The designed hybrid photonic-plasmonic cavity sensors exhibit distinguished characteristics such as sensitivity of 443 nm/RIU and figure of merit of 129. The proposed nanocavities open new possibilities for various applications with strong light-matter interaction, such as biosensors and nanolasers.

Improvement in the statistical operation of a Blumlein pulse forming line in bipolar pulse mode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pushkarev, A. I., E-mail: aipush@mail.ru; Isakova, Y. I.; Khaylov, I. P.

The paper presents the results of studies on shot-to-shot performance of a water Blumlein pulse forming line of 1–1.2 kJ of stored energy. The experiments were carried using the TEMP-4M pulsed ion beam accelerator during its operation in both unipolar pulse mode (150 ns, 250–300 kV) and bipolar-pulse mode with the first negative (300–600 ns, 100–150 kV) followed by a second positive (120 ns, 250–300 kV) pulse. The analysis was carried out for two cases when the Blumlein was terminated with a resistive load and with a self-magnetically insulated ion diode. It was found that in bipolar pulse mode themore » shot-to-shot variation in breakdown voltage of a preliminary spark gap is small, the standard deviation (1σ) does not exceed 2%. At the same time, the shot-to-shot variation in the breakdown voltage of the main spark gap in both bipolar-pulse and unipolar pulse mode is 3–4 times higher than that for the preliminary spark gap. To improve the statistical performance of the main spark gap we changed the regime of its operation from a self-triggered mode to an externally triggered mode. In the new arrangement the first voltage pulse at the output of Blumlein was used to trigger the main spark gap. The new trigatron-type regime of the main spark gap operation showed a good stability of breakdown voltage and thus allowed to stabilize the duration of the first pulse. The standard deviation of the breakdown voltage and duration of the first pulse did not exceed 2% for a set of 50 pulses. The externally triggered mode of the main gap operation also allowed for a decrease in the charging voltage of the Blumlein to a 0.9–0.95 of self-breakdown voltage of the main spark gap while the energy stored in Marx generator was decreased from 4 kJ to 2.5 kJ. At the same time the energy stored in Blumlein remained the same.« less

Effect of interstitial palladium on plasmon-driven charge transfer in nanoparticle dimers.

PubMed

Lerch, Sarah; Reinhard, Björn M

2018-04-23

Capacitive plasmon coupling between noble metal nanoparticles (NPs) is characterized by an increasing red-shift of the bonding dipolar plasmon mode (BDP) in the classical electromagnetic coupling regime. This model breaks down at short separations where plasmon-driven charge transfer induces a gap current between the NPs with a magnitude and separation dependence that can be modulated if molecules are present in the gap. Here, we use gap contained DNA as a scaffold for the growth of palladium (Pd) NPs in the gap between two gold NPs and investigate the effect of increasing Pd NP concentration on the BDP mode. Consistent with enhanced plasmon-driven charge transfer, the integration of discrete Pd NPs depolarizes the capacitive BDP mode over longer interparticle separations than is possible in only DNA-linked Au NPs. High Pd NP densities in the gap increases the gap conductance and induces the transition from capacitive to conductive coupling.

Effect of ripple taper on band-gap overlap in a coaxial Bragg structure operating at terahertz frequency

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ding Xueyong; Li Hongfan; Lv Zhensu

Based on the mode-coupling method, numerical analysis is presented to demonstrate the influence of ripple taper on band-gap overlap in a coaxial Bragg structure operating at terahertz frequency. Results show that the interval between the band-gaps of the competing mode and the desired working mode is narrowed by use of positive-taper ripples, but is expanded if negative-taper ripples are employed, and the influence of the negative-taper ripples is obviously more advantageous than the positive-taper ripples; the band-gap overlap of modes can be efficiently separated by use of negative-taper ripples. The residual side-lobes of the frequency response in a coaxial Braggmore » structure with ripple taper also can be effectively suppressed by employing the windowing-function technique. These peculiarities provide potential advantage in constructing a coaxial Bragg cavity with high quality factor for single higher-order-mode operation of a high-power free-electron maser in the terahertz frequency range.« less

Hollow-Core Photonic Band Gap Fibers for Particle Acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Noble, Robert J.; Spencer, James E.; /SLAC

Photonic band gap (PBG) dielectric fibers with hollow cores are being studied both theoretically and experimentally for use as laser driven accelerator structures. The hollow core functions as both a longitudinal waveguide for the transverse-magnetic (TM) accelerating fields and a channel for the charged particles. The dielectric surrounding the core is permeated by a periodic array of smaller holes to confine the mode, forming a photonic crystal fiber in which modes exist in frequency pass-bands, separated by band gaps. The hollow core acts as a defect which breaks the crystal symmetry, and so-called defect, or trapped modes having frequencies inmore » the band gap will only propagate near the defect. We describe the design of 2-D hollow-core PBG fibers to support TM defect modes with high longitudinal fields and high characteristic impedance. Using as-built dimensions of industrially-made fibers, we perform a simulation analysis of the first prototype PBG fibers specifically designed to support speed-of-light TM modes.« less

The properties of optimal two-dimensional phononic crystals with different material contrasts

NASA Astrophysics Data System (ADS)

Liu, Zong-Fa; Wu, Bin; He, Cun-Fu

2016-09-01

By modifying the spatial distribution of constituent material phases, phononic crystals (PnCs) can be designed to exhibit band gaps within which sound and vibration cannot propagate. In this paper, the developed topology optimization method (TOM), based on genetic algorithms (GAs) and the finite element method (FEM), is proposed to design two-dimensional (2D) solid PnC structures composed of two contrasting elastic materials. The PnCs have the lowest order band gap that is the third band gap for the coupled mode, the first band gap for the shear mode or the XY 34 Z band gap for the mixed mode. Moreover, the effects of the ratios of contrasting material properties on the optimal layout of unit cells and the corresponding phononic band gaps (PBGs) are investigated. The results indicate that the topology of the optimal PnCs and corresponding band gaps varies with the change of material contrasts. The law can be used for the rapid design of desired PnC structures.

Band gap in tubular pillar phononic crystal plate.

PubMed

Shu, Fengfeng; Liu, Yongshun; Wu, Junfeng; Wu, Yihui

2016-09-01

In this paper, a phononic crystal (PC) plate with tubular pillars is presented and investigated. The band structures and mode displacement profiles are calculated by using finite element method. The result shows that a complete band gap opens when the ratio of the pillar height to the plate thickness is about 1.6. However, for classic cylinder pillar structures, a band gap opens when the ratio is equal or greater than 3. A tubular pillar design with a void room in it enhances acoustic multiple scattering and gives rise to the opening of the band gap. In order to verify it, a PC structure with double tubular pillars different in size (one within the other) is introduced and a more than 2times band gap enlargement is observed. Furthermore, the coupling between the resonant mode and the plate mode around the band gap is characterized, as well as the effect of the geometrical parameters on the band gap. The behavior of such structure could be utilized to design a pillar PC with stronger structural stability and to enlarge band gaps. Copyright © 2016 Elsevier B.V. All rights reserved.

Experimental study on microsphere assisted nanoscope in non-contact mode

NASA Astrophysics Data System (ADS)

Ling, Jinzhong; Li, Dancui; Liu, Xin; Wang, Xiaorui

2018-07-01

Microsphere assisted nanoscope was proposed in existing literatures to capture super-resolution images of the nano-structures beneath the microsphere attached on sample surface. In this paper, a microsphere assisted nanoscope working in non-contact mode is designed and demonstrated, in which the microsphere is controlled with a gap separated to sample surface. With a gap, the microsphere is moved in parallel to sample surface non-invasively, so as to observe all the areas of interest. Furthermore, the influence of gap size on image resolution is studied experimentally. Only when the microsphere is close enough to the sample surface, super-resolution image could be obtained. Generally, the resolution decreases when the gap increases as the contribution of evanescent wave disappears. To keep an appropriate gap size, a quantitative method is implemented to estimate the gap variation by observing Newton's rings around the microsphere, serving as a real-time feedback for tuning the gap size. With a constant gap, large-area image with high resolution can be obtained during microsphere scanning. Our study of non-contact mode makes the microsphere assisted nanoscope more practicable and easier to implement.

Numerical simulation of operation modes in atmospheric pressure uniform barrier discharge excited by a saw-tooth voltage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Xuechen; Niu Dongying; Yin Zengqian

2012-08-15

The characteristics of dielectric barrier discharge excited by a saw-tooth voltage are simulated in atmospheric pressure helium based on a one-dimensional fluid model. A stepped discharge is obtained per half voltage cycle with gas gap width less than 2 mm by the simulation, which is different to the pulsed discharge excited by a sinusoidal voltage. For the stepped discharge, the plateau duration increases with increasing the voltage amplitude and decreasing the gas gap. Therefore, uniform discharge with high temporal duty ratio can be realized with small gap through increasing the voltage amplitude. The maximal densities of both electron and ionmore » appear near the anode and the electric field is almost uniformly distributed along the gap, which indicates that the stepped discharge belongs to a Townsend mode. In contrast to the stepped discharge with small gas gap, a pulsed discharge can be obtained with large gas gap. Through analyzing the spatial density distributions of electron and ion and the electric field, the pulsed discharge is in a glow mode. The voltage-current (V-I) characteristics are analyzed for the above mentioned discharges under different gas gaps, from which the different discharge modes are verified.« less

Study of optical reflectance properties in 1D annular photonic crystal containing double negative (DNG) metamaterials

NASA Astrophysics Data System (ADS)

Srivastava, Sanjeev K.; Aghajamali, Alireza

2016-05-01

Theoretical investigation of photonic band gaps or reflection bands in one-dimensional annular photonic crystal (APC) containing double negative (DNG) metamaterials and air has been presented. The proposed structure consists of the alternate layers of dispersive DNG material and air immersed in free space. In order to study photonic band gaps we obtain the reflectance spectrum of the annular PC by employing the transfer matrix method (TMM) in the cylindrical waves for both TE and TM polarizations. In this work we study the effect of azimuthal mode number (m) and starting radius (ρ0) on the three band gaps viz. zero averaged refractive index (zero-nbar) gap, zero permittivity (zero- ε) and zero permeability (zero- μ) gaps. It is found that for m ≥ 1 , zero- μ gap appears in TE mode and zero- ε gap appears in TM mode. The width of both zero- μ and zero- ε gap increases by increasing m values, but the enhancement of zero- μ gap is more appreciable. Also, the effect of ρ0 on the three band gaps (reflection bands) of annular PC structure at the given m-number has been studied, for both TE and TM polarizations. The result shows that in both polarizations zero- ε and zero- μ gaps decreases when ρ0 increases, whereas zero-nbar gap remains invariant.

The Medial Stitch in Transosseous-Equivalent Rotator Cuff Repair: Vertical or Horizontal Mattress?

PubMed

Montanez, Anthony; Makarewich, Christopher A; Burks, Robert T; Henninger, Heath B

2016-09-01

Despite advances in surgical technique, rotator cuff repair retears continue to occur at rates of 10%, 22%, and 57% for small, medium, and large tears, respectively. A common mode of failure in transosseous-equivalent rotator cuff repairs is tissue pullout of the medial mattress stitch. While the medial mattress stitch has been studied extensively, no studies have evaluated a vertical mattress pattern placed near the musculotendinous junction in comparison with a horizontal mattress pattern. Vertical mattress stitches will have higher load to failure and lower gapping compared with horizontal mattress stitches in a transosseous-equivalent rotator cuff repair. Controlled laboratory study. Double-row transosseous-equivalent rotator cuff repairs were performed in 9 pairs of human male cadaveric shoulders (mean age ± SD, 58 ± 10 years). One shoulder in each pair received a medial-row suture pattern using a vertical mattress stitch, and the contralateral shoulder received a horizontal mattress. Specimens were mounted in a materials testing machine and tested in uniaxial tensile deformation for cyclic loading (500 cycles at 1 Hz to 1.0 MPa of effective stress), followed by failure testing carried out at a rate of 1 mm/s. Construct gapping and applied loads were monitored continuously throughout the testing. Vertical mattress sutures were placed in 5 right and 4 left shoulders. Peak cyclic gapping did not differ between vertical (mean ± SD, 2.8 ± 1.1 mm) and horizontal mattress specimens (3.0 ± 1.2 mm) (P = .684). Vertical mattress sutures failed at higher loads compared with horizontal mattress sutures (568.9 ± 140.3 vs 451.1 ± 174.3 N; P = .025); however, there was no significant difference in failure displacement (8.0 ± 1.6 vs 6.0 ± 2.1 mm; P = .092). Failure stiffness did not differ between the suture patterns (P = .204). In transosseous-equivalent rotator cuff repairs near the musculotendinous junction, a vertical mattress suture used as the medial stitch has a higher load to failure but no difference in gapping compared with a horizontal mattress pattern. A vertical mattress suture may offer enhanced strength of repair for transosseous-equivalent repairs. © 2016 The Author(s).

Gap-Mode Surface-Plasmon-Enhanced Photoluminescence and Photoresponse of MoS2.

PubMed

Wu, Zhi-Qian; Yang, Jing-Liang; Manjunath, Nallappagar K; Zhang, Yue-Jiao; Feng, Si-Rui; Lu, Yang-Hua; Wu, Jiang-Hong; Zhao, Wei-Wei; Qiu, Cai-Yu; Li, Jian-Feng; Lin, Shi-Sheng

2018-05-22

2D materials hold great potential for designing novel electronic and optoelectronic devices. However, 2D material can only absorb limited incident light. As a representative 2D semiconductor, monolayer MoS 2 can only absorb up to 10% of the incident light in the visible, which is not sufficient to achieve a high optical-to-electrical conversion efficiency. To overcome this shortcoming, a "gap-mode" plasmon-enhanced monolayer MoS 2 fluorescent emitter and photodetector is designed by squeezing the light-field into Ag shell-isolated nanoparticles-Au film gap, where the confined electromagnetic field can interact with monolayer MoS 2 . With this gap-mode plasmon-enhanced configuration, a 110-fold enhancement of photoluminescence intensity is achieved, exceeding values reached by other plasmon-enhanced MoS 2 fluorescent emitters. In addition, a gap-mode plasmon-enhanced monolayer MoS 2 photodetector with an 880% enhancement in photocurrent and a responsivity of 287.5 A W -1 is demonstrated, exceeding previously reported plasmon-enhanced monolayer MoS 2 photodetectors. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Radiation of the high-order plasmonic modes of large gold nanospheres excited by surface plasmon polaritons.

PubMed

Chen, Jing-Dong; Xiang, Jin; Jiang, Shuai; Dai, Qiao-Feng; Tie, Shao-Long; Lan, Sheng

2018-05-17

Large metallic nanoparticles with sizes comparable to the wavelength of light are expected to support high-order plasmon modes exhibiting resonances in the visible to near infrared spectral range. However, the radiation behavior of high-order plasmon modes, including scattering spectra and radiation patterns, remains unexplored. Here, we report on the first observation and characterization of the high-order plasmon modes excited in large gold nanospheres by using the surface plasmon polaritons generated on the surface of a thin gold film. The polarization-dependent scattering spectra were measured by inserting a polarization analyzer in the collection channel and the physical origins of the scattering peaks observed in the scattering spectra were clearly identified. More interestingly, the radiation of electric quadrupoles and octupoles was resolved in both frequency and spatial domains. In addition, the angular dependences of the radiation intensity for all plasmon modes were extracted by fitting the polarization-dependent scattering spectra with multiple Lorentz line shapes. A significant enhancement of the electric field was found in the gap plasmon modes and it was employed to generate hot-electron intraband luminescence. Our findings pave the way for exploiting the high-order plasmon modes of large metallic nanoparticles in the manipulation of light radiation and light-matter interaction.

The Nature of Accelerating Modes in PBG Fibers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Noble, TRobert J.; /SLAC

Transverse magnetic (TM) modes with phase velocities at or just below the speed of light, c, are intended to accelerate relativistic particles in hollow-core, photonic band gap (PBG) fibers. These are so-called 'surface defect modes', being lattice modes perturbed by the defect to have their frequencies shifted into the band gap, and they can have any phase velocity. PBG fibers also support so-called 'core defect modes' which are characterized as having phase velocities always greater than c and never cross the light line. In this paper we explore the nature of these two classes of accelerating modes and compare theirmore » properties.« less

Effects of gap width on droplet transfer behavior in ultra-narrow gap laser welding of high strength aluminum alloys

NASA Astrophysics Data System (ADS)

Song, Chaoqun; Dong, Shiyun; Yan, Shixing; He, Jiawu; Xu, Binshi; He, Peng

2017-10-01

Ultra-narrow gap laser welding is a novel method for thick high strength aluminum alloy plate for its lower heat input, less deformation and higher efficiency. To obtain a perfect welding quality, it is vital to control the more complex droplet transfer behavior under the influence of ultra-narrow gap groove. This paper reports the effects of gap width of groove on droplet transfer behavior in ultra-narrow gap laser welding of 7A52 aluminum alloy plates by a high speed camera, using an ER 5356 filler wire. The results showed that the gap width had directly effects on droplet transfer mode and droplet shape. The droplet transfer modes were, in order, both-sidewall transfer, single-sidewall transfer, globular droplet transfer and bridging transfer, with different droplet shape and transition period, as the gap width increased from 2 mm to 3.5mm. The effect of gap width on lack of fusion was also studied to analyze the cause for lack of fusion at the bottom and on the sidewall of groove. Finally, with a 2.5 mm U-type parallel groove, a single-pass joint with no lack of fusion and other macro welding defects was successfully obtained in a single-sidewall transfer mode.

High sensitivity waveguide micro-displacement sensor based on intermodal interference

NASA Astrophysics Data System (ADS)

Ji, Lanting; He, Guobing; Gao, Yang; Xu, Yan; Liang, Honglei; Sun, Xiaoqiang; Wang, Xibin; Yi, Yunji; Chen, Changming; Wang, Fei; Zhang, Daming

2017-11-01

An optical waveguide displacement sensor according to core-cladding modes interference is theoretically proposed and experimentally demonstrated. Ultraviolet sensitive SU-8 polymer on silica is used as the guiding layer. It is covered by a 12 nm thick planar gold grating. The air gap sensing head which consists of the waveguide end and the single-mode fiber facet can realize the displacement detection by monitoring the wavelength dip shifting in transmission spectra. Cladding modes propagating in the exposed SU-8 can be effectively excited by the end-fire coupling because of the mode field mismatch between the SU-8 waveguide and lead-in fiber. A sinusoidal pattern transmission spectrum in C-band with the depth of over 14 dB can be observed due to the interference between the core and cladding modes. Peaks in the transmission spectrum vary continuously with the position offset of input fiber facet from the center of waveguide end. Both the sensitivity and the stability of sensing are enhanced by the introduction of nanometric gold gratings. The fabricated displacement sensor exhibits a high sensitivity of 2.3 nm μm-1, promising potentials for micromechanical processing and integrated optics application.

Reconfigurable antenna options for 2.45/5 GHz wireless body area networks in healthcare applications.

PubMed

Abbas, Syed Muzahir; Ranga, Yogesh; Esselle, Karu P

2015-01-01

This paper presents electronically reconfigurable antenna options in healthcare applications. They are suitable for wireless body area network devices operating in the industrial, scientific, and medical (ISM) band at 2.45 GHz and IEEE 802.11 Wireless Local Area Network (WLAN) band at 5 GHz (5.15-5.35 GHz, 5.25-5.35 GHz). Two types of antennas are investigated: Antenna-I has a full ground plane and Antenna-II has a partial ground plane. The proposed antennas provide ISM operation in one mode while in another mode they support 5 GHz WLAN band. Their performance is assessed for body centric wireless communication using a simplified human body model. Antenna sensitivity to the gap between the antenna and the human body is investigated for both modes of each antenna. The proposed antennas exhibit a wide radiation pattern along the body surface to provide wide coverage and their small width (14 mm) makes them suitable for on-body communication in healthcare applications.

Collective Beam Instabilities in the Taiwan Light Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chao, Alex W.

2002-08-12

The storage ring at Taiwan Light Source has experienced a strong collective instability since 1994. Various cures have been attempted to suppress this instability, including the use of damping antenna, tunable rf plungers, different filling patterns, and rf gap voltage modulation. So far these cures have improved the beam intensity, but the operation remains to be limited by the instability. The dominant phenomenon is the longitudinal coupled bunch instability. The major source of longitudinal impedance is from rf cavities of Doris type. The high-order modes of the cavity were numerically analyzed using a 3-D code GdfidL. The correlation of themore » observed phenomenon in user operation with high-order modes of rf cavities will be presented. Results of various attempts to suppress beam instabilities will be summarized. Proposed cures for beam instabilities will be discussed.« less

Topological Valley Currents in Gapped Dirac Materials

NASA Astrophysics Data System (ADS)

Lensky, Yuri D.; Song, Justin C. W.; Samutpraphoot, Polnop; Levitov, Leonid S.

2015-06-01

Gapped 2D Dirac materials, in which inversion symmetry is broken by a gap-opening perturbation, feature a unique valley transport regime. Topological valley currents in such materials are dominated by bulk currents produced by electronic states just beneath the gap rather than by edge modes. The system ground state hosts dissipationless persistent valley currents existing even when topologically protected edge modes are absent. Valley currents induced by an external bias are characterized by a quantized half-integer valley Hall conductivity. The undergap currents dominate magnetization and the charge Hall effect in a light-induced valley-polarized state.

Short germ insects utilize both the ancestral and derived mode of Polycomb group-mediated epigenetic silencing of Hox genes

PubMed Central

Matsuoka, Yuji; Bando, Tetsuya; Watanabe, Takahito; Ishimaru, Yoshiyasu; Noji, Sumihare; Popadić, Aleksandar; Mito, Taro

2015-01-01

In insect species that undergo long germ segmentation, such as Drosophila, all segments are specified simultaneously at the early blastoderm stage. As embryogenesis progresses, the expression boundaries of Hox genes are established by repression of gap genes, which is subsequently replaced by Polycomb group (PcG) silencing. At present, however, it is not known whether patterning occurs this way in a more ancestral (short germ) mode of embryogenesis, where segments are added gradually during posterior elongation. In this study, two members of the PcG family, Enhancer of zeste (E(z)) and Suppressor of zeste 12 (Su(z)12), were analyzed in the short germ cricket, Gryllus bimaculatus. Results suggest that although stepwise negative regulation by gap and PcG genes is present in anterior members of the Hox cluster, it does not account for regulation of two posterior Hox genes, abdominal-A (abd-A) and Abdominal-B (Abd-B). Instead, abd-A and Abd-B are predominantly regulated by PcG genes, which is the mode present in vertebrates. These findings suggest that an intriguing transition of the PcG-mediated silencing of Hox genes may have occurred during animal evolution. The ancestral bilaterian state may have resembled the current vertebrate mode of regulation, where PcG-mediated silencing of Hox genes occurs before their expression is initiated and is responsible for the establishment of individual expression domains. Then, during insect evolution, the repression by transcription factors may have been acquired in anterior Hox genes of short germ insects, while PcG silencing was maintained in posterior Hox genes. PMID:25948756

Designing broad phononic band gaps for in-plane modes

NASA Astrophysics Data System (ADS)

Li, Yang Fan; Meng, Fei; Li, Shuo; Jia, Baohua; Zhou, Shiwei; Huang, Xiaodong

2018-03-01

Phononic crystals are known as artificial materials that can manipulate the propagation of elastic waves, and one essential feature of phononic crystals is the existence of forbidden frequency range of traveling waves called band gaps. In this paper, we have proposed an easy way to design phononic crystals with large in-plane band gaps. We demonstrated that the gap between two arbitrarily appointed bands of in-plane mode can be formed by employing a certain number of solid or hollow circular rods embedded in a matrix material. Topology optimization has been applied to find the best material distributions within the primitive unit cell with maximal band gap width. Our results reveal that the centroids of optimized rods coincide with the point positions generated by Lloyd's algorithm, which deepens our understandings on the formation mechanism of phononic in-plane band gaps.

A taxonomy for mechanical ventilation: 10 fundamental maxims.

PubMed

Chatburn, Robert L; El-Khatib, Mohamad; Mireles-Cabodevila, Eduardo

2014-11-01

The American Association for Respiratory Care has declared a benchmark for competency in mechanical ventilation that includes the ability to "apply to practice all ventilation modes currently available on all invasive and noninvasive mechanical ventilators." This level of competency presupposes the ability to identify, classify, compare, and contrast all modes of ventilation. Unfortunately, current educational paradigms do not supply the tools to achieve such goals. To fill this gap, we expand and refine a previously described taxonomy for classifying modes of ventilation and explain how it can be understood in terms of 10 fundamental constructs of ventilator technology: (1) defining a breath, (2) defining an assisted breath, (3) specifying the means of assisting breaths based on control variables specified by the equation of motion, (4) classifying breaths in terms of how inspiration is started and stopped, (5) identifying ventilator-initiated versus patient-initiated start and stop events, (6) defining spontaneous and mandatory breaths, (7) defining breath sequences (8), combining control variables and breath sequences into ventilatory patterns, (9) describing targeting schemes, and (10) constructing a formal taxonomy for modes of ventilation composed of control variable, breath sequence, and targeting schemes. Having established the theoretical basis of the taxonomy, we demonstrate a step-by-step procedure to classify any mode on any mechanical ventilator. Copyright © 2014 by Daedalus Enterprises.

Effect of a crystal-melt interface on Taylor-vortex flow

NASA Technical Reports Server (NTRS)

Mcfadden, G. B.; Coriell, S. R.; Murray, B. T.; Glicksman, M. E.; Selleck, M. E.

1990-01-01

The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case that the stationary outer cylinder is a crystal-melt interface rather than a rigid surface. A radial temperature difference is maintained across the liquid gap, and equations for heat transport in the crystal and melt phases are included to extend the ordinary formulation of this problem. The stability of this two-phase system depends on the Prandtl number. For small Prandtl number the linear stability of the two-phase system is given by the classical results for a rigid-walled system. For increasing values of the Prandtl number, convective heat transport becomes significant and the system becomes increasingly less stable. Previous results in a narrow-gap approximation are extended to the case of a finite gap, and both axisymmetric and nonaxisymmetric disturbance modes are considered. The two-phase system becomes less stable as the finite gap tends to the narrow-gap limit. The two-phase system is more stable to nonaxisymmetric modes with azimuthal wavenumber n = 1; the stability of these n = 1 modes is sensitive to the latent heat of fusion.

Hybrid photonic crystal cavity and waveguide for coupling to diamond NV-centers.

PubMed

Barclay, Paul E; Fu, Kai-Mei; Santori, Charles; Beausoleil, Raymond G

2009-06-08

A design for an ultra-high Q photonic crystal nanocavity engineered to interact with nitrogen-vacancy (NV) centers located near the surface of a single crystal diamond sample is presented. The structure is based upon a nanowire photonic crystal geometry, and consists of a patterned high refractive index thin film, such as gallium phosphide (GaP), supported by a diamond substrate. The nanocavity supports a mode with quality factor Q > 1.5 x 10(6) and mode volume V < 0.52(lambda/nGaP)(3), and promises to allow Purcell enhanced collection of spontaneous emission from an NV located more than 50 nm below the diamond surface. The nanowire photonic crystal waveguide can be used to efficiently couple light into and out of the cavity, or as an efficient broadband collector of NV phonon sideband emission. The proposed structures can be fabricated using existing materials and processing techniques.

Stabilization of Fermi level via electronic excitation in Sn doped CdO thin films

NASA Astrophysics Data System (ADS)

Das, Arkaprava; Singh, Fouran

2018-04-01

Pure and Sn doped CdO sol-gel derived thin films were deposited on corning glass substrate and further irradiated by swift heavy ion (SHI) (Ag and O) with fluence upto 3×1013 ions/cm2. The observed tensile stress from X-ray diffraction pattern at higher fluence for Ag ions can be corroborated to the imbrications of cylindrical tracks due to multiple impacts. The anomalous band gap enhancement after irradiation may be attributed to the consolidated effect of Burstein-Moss shift (BMS) and impurity induced virtual gap states (ViGs). At higher excitation density as Fermi stabilization level (EFS) tends to coincide with charge neutrality level (CNL), band gap enhancement saturates as further creation of additional defects inside the lattice becomes unsustainable. Raman spectroscopy divulges an intensity enhancement of 478 cm-1 LO phonon mode with Sn doping and irradiation induces further asymmetric peak broadening due to damage and disordering inside the lattice. However for 3% Sn doped thin film irradiated with Ag ions having 3×1013 fluence shows a drastic change in structural properties and reduction in band gap which might be attributed to the generation of localized energy levels between conduction and valance band due to high density of defects.

Gaps in the Rock and Fossil Records and Implications for the Rate and Mode of Evolution.

ERIC Educational Resources Information Center

Smith, Grant Sackett

1988-01-01

Examines three types of gaps in the fossil record: real gaps, imaginary gaps, and temporary gaps. Reviews some recent evidence concerning evolution from the paleontological record of microfossils, invertebrates, and vertebrates in order to make some general conclusions regarding the manner in which life evolved on earth. (CW)

Dynamic patterning by the Drosophila pair-rule network reconciles long-germ and short-germ segmentation

PubMed Central

2017-01-01

Drosophila segmentation is a well-established paradigm for developmental pattern formation. However, the later stages of segment patterning, regulated by the “pair-rule” genes, are still not well understood at the system level. Building on established genetic interactions, I construct a logical model of the Drosophila pair-rule system that takes into account the demonstrated stage-specific architecture of the pair-rule gene network. Simulation of this model can accurately recapitulate the observed spatiotemporal expression of the pair-rule genes, but only when the system is provided with dynamic “gap” inputs. This result suggests that dynamic shifts of pair-rule stripes are essential for segment patterning in the trunk and provides a functional role for observed posterior-to-anterior gap domain shifts that occur during cellularisation. The model also suggests revised patterning mechanisms for the parasegment boundaries and explains the aetiology of the even-skipped null mutant phenotype. Strikingly, a slightly modified version of the model is able to pattern segments in either simultaneous or sequential modes, depending only on initial conditions. This suggests that fundamentally similar mechanisms may underlie segmentation in short-germ and long-germ arthropods. PMID:28953896

Localized transversal-rotational modes in linear chains of equal masses.

PubMed

Pichard, H; Duclos, A; Groby, J-P; Tournat, V; Gusev, V E

2014-01-01

The propagation and localization of transversal-rotational waves in a two-dimensional granular chain of equal masses are analyzed in this study. The masses are infinitely long cylinders possessing one translational and one rotational degree of freedom. Two dispersive propagating modes are predicted in this granular crystal. By considering the semi-infinite chain with a boundary condition applied at its beginning, the analytical study demonstrates the existence of localized modes, each mode composed of two evanescent modes. Their existence, position (either in the gap between the propagating modes or in the gap above the upper propagating mode), and structure of spatial localization are analyzed as a function of the relative strength of the shear and bending interparticle interactions and for different boundary conditions. This demonstrates the existence of a localized mode in a semi-infinite monatomic chain when transversal-rotational waves are considered, while it is well known that these types of modes do not exist when longitudinal waves are considered.

Robustness of Thirty Meter Telescope primary mirror control

NASA Astrophysics Data System (ADS)

Macmynowski, Douglas G.; Thompson, Peter M.; Shelton, Chris; Roberts, Lewis C., Jr.

2010-07-01

The primary mirror control system for the Thirty Meter Telescope (TMT) maintains the alignment of the 492 segments in the presence of both quasi-static (gravity and thermal) and dynamic disturbances due to unsteady wind loads. The latter results in a desired control bandwidth of 1Hz at high spatial frequencies. The achievable bandwidth is limited by robustness to (i) uncertain telescope structural dynamics (control-structure interaction) and (ii) small perturbations in the ill-conditioned influence matrix that relates segment edge sensor response to actuator commands. Both of these effects are considered herein using models of TMT. The former is explored through multivariable sensitivity analysis on a reduced-order Zernike-basis representation of the structural dynamics. The interaction matrix ("A-matrix") uncertainty has been analyzed theoretically elsewhere, and is examined here for realistic amplitude perturbations due to segment and sensor installation errors, and gravity and thermal induced segment motion. The primary influence of A-matrix uncertainty is on the control of "focusmode"; this is the least observable mode, measurable only through the edge-sensor (gap-dependent) sensitivity to the dihedral angle between segments. Accurately estimating focus-mode will require updating the A-matrix as a function of the measured gap. A-matrix uncertainty also results in a higher gain-margin requirement for focus-mode, and hence the A-matrix and CSI robustness need to be understood simultaneously. Based on the robustness analysis, the desired 1 Hz bandwidth is achievable in the presence of uncertainty for all except the lowest spatial-frequency response patterns of the primary mirror.

Topological protection of photonic mid-gap cavity modes

NASA Astrophysics Data System (ADS)

Benalcazar, Wladimir A.; Noh, Jiho; Huang, Sheng; Collins, Matthew J.; Chen, Kevin; Hughes, Taylor L.; Rechtsman, Mikael

Defect modes in two-dimensional periodic photonic structures have found use in a highly diverse set of optical devices. Here, we show in theory and experiment that a photonic topological crystalline insulator structure can be used to generate topological defect-localized modes. These defect modes are protected by chiral and crystalline symmetries, and have resonance frequencies in the middle of the photonic band gap (which minimize the mode volume). This protection of zero-dimensional states (defect modes) embedded in a two-dimensional environment constitutes a novel form of topological protection that has not been previously demonstrated. WAB and TLH are supported by the ONR YIP Award N00014-15-1-2383. M.C.R. and J.N. are supported by NSF, Grant ECCS-1509546; M.C.R. is supported by the Alfred P. Sloan foundation fellowship FG-2016-6418.

Transition from Townsend to radio-frequency homogeneous dielectric barrier discharge in a roll-to-roll configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bazinette, R.; SIAME, Université de Pau et des Pays de l'Adour, Pau; Paillol, J.

The aim of this paper is to better understand the transition from Townsend to radio-frequency homogeneous dielectric barrier discharge (DBD) at atmospheric pressure. The study is done in an Ar/NH{sub 3} Penning mixture for an electrode configuration adapted to roll-to-roll plasma surface treatment. The study was led in a frequency range running from 50 kHz up to 8.3 MHz leading to different DBD modes with a 1 mm gas gap: Glow (GDBD), Townsend (TDBD), and Radio-frequency (RF-DBD). In the frequency range between TDBD and RF-DBD, from 250 kHz to 2.3 MHz, additional discharges are observed outside the inter-electrode gas gap. Because each high voltagemore » electrode are inside a dielectric barrel, these additional discharges occur on the side of the barrel where the gap is larger. They disappear when the RF-DBD mode is attained in the 1 mm inter-electrode gas gap, i.e., for frequencies equal or higher than 3 MHz. Fast imaging and optical emission spectroscopy show that the additional discharges are radio-frequency DBDs while the inter-electrode discharge is a TDBD. The RF-DBD discharge mode is attained when electrons drift becomes low enough compared to the voltage oscillation frequency to limit electron loss at the anode. To check that the additional discharges are due to a larger gas gap and a lower voltage amplitude, the TDBD/RF-DBD transition is investigated as a function of the gas gap and the applied voltage frequency and amplitude. Results show that the increase in the frequency at constant gas gap or in the gas gap at constant frequency allows to obtain RF-DBD instead of TDBD. At low frequency and large gap, the increase in the applied voltage allows RF-DBD/TDBD transition. As a consequence, an electrode configuration allowing different gap values is a solution to successively have different discharge modes with the same applied voltage.« less

Tunable liquid-crystal microshell-laser based on whispering-gallery modes and photonic band-gap mode lasing.

PubMed

Lu, Yuelan; Yang, Yue; Wang, Yan; Wang, Lei; Ma, Ji; Zhang, Lingli; Sun, Weimin; Liu, Yongjun

2018-02-05

The lasing behaviors of dye-doped cholesteric liquid crystal (DDCLC) microshells fabricated with silica-glass-microsphere coated DDCLCs were examined. Lasing characteristics were studied in a carrier medium with different refractive indices. The lasing in spherical cholesteric liquid crystals (CLCs) was attributed to two mechanisms, photonic band-gap (PBG) lasing and whispering-gallery modes (WGMs), which can independently exist by varying the chiral agent concentration and pumping energy. It was also found that DDCLC microshells can function as highly sensitive thermal sensors, with a temperature sensitivity of 0.982 nm °C -1 in PBG modes and 0.156 nm °C -1 in WGMs.

Fano-like resonance phenomena by flexural shell modes in sound transmission through two-dimensional periodic arrays of thin-walled hollow cylinders

NASA Astrophysics Data System (ADS)

Kosevich, Yuriy A.; Goffaux, Cecile; Sánchez-Dehesa, Jose

2006-07-01

It is shown that the n=2 and 3 flexural shell vibration modes of thin-walled hollow cylinders result in Fano-like resonant enhancement of sound wave transmission through or reflection from two-dimensional periodic arrays of these cylinders in air. The frequencies of the resonant modes are well described by the analytical theory of flexural (circumferential) modes of thin-walled hollow cylinders and are confirmed by finite-difference time-domain simulations. When the modes are located in the band gaps of the phononic crystal, an enhancement of the band-gap widths is produced by the additional restoring forces caused by the flexural shell deformations. Our conclusions provide an alternative method for the vibration control of airborne phononic crystals.

Damping-free collective oscillations of a driven two-component Bose gas in optical lattices

NASA Astrophysics Data System (ADS)

Shchedrin, Gavriil; Jaschke, Daniel; Carr, Lincoln D.

2018-04-01

We explore the quantum many-body physics of a driven Bose-Einstein condensate in optical lattices. The laser field induces a gap in the generalized Bogoliubov spectrum proportional to the effective Rabi frequency. The lowest-lying modes in a driven condensate are characterized by zero group velocity and nonzero current. Thus, the laser field induces roton modes, which carry interaction in a driven condensate. We show that collective excitations below the energy of the laser-induced gap remain undamped, while above the gap they are characterized by a significantly suppressed Landau damping rate.

Intra-band gap in Lamb modes propagating in a periodic solid structure

NASA Astrophysics Data System (ADS)

Pierre, J.; Rénier, M.; Bonello, B.; Hladky-Hennion, A.-C.

2012-05-01

A laser ultrasonic technique is used to measure the dispersion of Lamb waves at a few MHz, propagating in phononic crystals made of dissymmetric air inclusions drilled throughout silicon plates. It is shown that the specific shape of the inclusions is at the origin of the intra-band gap that opens within the second Brillouin zone, at the crossing of both flexural and dilatational zero-order modes. The magnitude of the intra-band gap is measured as a function of the dissymmetry rate of the inclusions. Experimental data and the computed dispersion curves are in very good agreement.

Integrator or Coincidence Detector: A Novel Measure Based on the Discrete Reverse Correlation to Determine a Neuron's Operational Mode.

PubMed

Kanev, Jacob; Koutsou, Achilleas; Christodoulou, Chris; Obermayer, Klaus

2016-10-01

In this letter, we propose a definition of the operational mode of a neuron, that is, whether a neuron integrates over its input or detects coincidences. We complete the range of possible operational modes by a new mode we call gap detection, which means that a neuron responds to gaps in its stimulus. We propose a measure consisting of two scalar values, both ranging from -1 to +1: the neural drive, which indicates whether its stimulus excites the neuron, serves as background noise, or inhibits it; the neural mode, which indicates whether the neuron's response is the result of integration over its input, of coincidence detection, or of gap detection; with all three modes possible for all neural drive values. This is a pure spike-based measure and can be applied to measure the influence of either all or subset of a neuron's stimulus. We derive the measure by decomposing the reverse correlation, test it in several artificial and biological settings, and compare it to other measures, finding little or no correlation between them. We relate the results of the measure to neural parameters and investigate the effect of time delay during spike generation. Our results suggest that a neuron can use several different modes simultaneously on different subsets of its stimulus to enable it to respond to its stimulus in a complex manner.

Electromagnetically induced transparency control in terahertz metasurfaces based on bright-bright mode coupling

NASA Astrophysics Data System (ADS)

Yahiaoui, R.; Burrow, J. A.; Mekonen, S. M.; Sarangan, A.; Mathews, J.; Agha, I.; Searles, T. A.

2018-04-01

We demonstrate a classical analog of electromagnetically induced transparency (EIT) in a highly flexible planar terahertz metamaterial (MM) comprised of three-gap split-ring resonators. The keys to achieve EIT in this system are the frequency detuning and hybridization processes between two bright modes coexisting in the same unit cell as opposed to bright-dark modes. We present experimental verification of two bright modes coupling for a terahertz EIT-MM in the context of numerical results and theoretical analysis based on a coupled Lorentz oscillator model. In addition, a hybrid variation of the EIT-MM is proposed and implemented numerically to dynamically tune the EIT window by incorporating photosensitive silicon pads in the split gap region of the resonators. As a result, this hybrid MM enables the active optical control of a transition from the on state (EIT mode) to the off state (dipole mode).

A magnetically tunable non-Bragg defect mode in a corrugated waveguide filled with liquid crystals

NASA Astrophysics Data System (ADS)

Zhang, Lu; Fan, Ya-Xian; Liu, Huan; Han, Xu; Lu, Wen-Qiang; Tao, Zhi-Yong

2018-04-01

A magnetically tunable, non-Bragg defect mode (NBDM) was created in the terahertz frequency range by inserting a defect in the middle of a periodically corrugated waveguide filled with liquid crystals (LCs). In the periodic waveguide, non-Bragg gaps beyond the Bragg ones, which appear in the transmission spectra, are created by different transverse mode resonances. The transmission spectra of the waveguide containing a defect showed that a defect mode was present inside the non-Bragg gap. The NBDM has quite different features compared to the Bragg defect mode, which includes more complex, high-order guided wave modes. In our study, we filled the corrugated waveguide with LCs to realize the tunability of the NBDM. The simulated results showed that the NBDM in a corrugated waveguide filled with LCs can be used in filters, sensors, switches, and other terahertz integrated devices.

Energy band gap and spectroscopic studies in Mn{sub 1-x}Cu{sub x}WO{sub 4} (0 ≤ x ≤ 0.125)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mal, Priyanath; Rambabu, P.; Turpu, G. R.

2016-05-06

A study on the effect of nonmagnetic Cu{sup 2+} substitution at Mn{sup 2+} site on the structural and energy band gap of the MnWO{sub 4} is reported. Convenient solid state reaction route has been adopted for the synthesis of Mn{sub 1-x}Cu{sub x}WO{sub 4}. X-ray diffraction (XRD) pattern showed high crystalline quality of the prepared samples. Raman spectroscopic studies were carried out to understand the structural aspects of the doping. 15 Raman active modes were identified out of 18, predicted for wolframite type monoclinic structure of MnWO{sub 4}. UV-visible diffuse reflectance spectra were recorded and analyzed to get energy band gapmore » of the studied system and are found in the range of 2.5 eV to 2.04 eV with a systematic decrease with the increase in Cu{sup 2+} concentration. Energy band gap values are verified by Density Functional Theory calculations based on projector augmented wave (PAW) method. The calculated values are in good agreement with the experimental data.« less

Improvement in delivery of type 2 diabetes services differs by mode of care: a retrospective longitudinal analysis in the Aboriginal and Torres Strait Islander Primary Health Care setting.

PubMed

Schierhout, Gill; Matthews, Veronica; Connors, Christine; Thompson, Sandra; Kwedza, Ru; Kennedy, Catherine; Bailie, Ross

2016-10-07

Addressing evidence-practice gaps in primary care remains a significant public health challenge and is likely to require action at different levels of the health system. Whilst Continuous Quality Improvement (CQI) is associated with improvements in overall delivery, little is known about delivery of different types of care processes, and their relative improvement during CQI. We used data from over 15,000 clinical audit records of clients with Type 2 diabetes collected as part of a wide-scale CQI program implemented between 2005 and 2014 in 162 Aboriginal and Torres Strait Islander health centres. We abstracted data from clinical records on 15 service items recommended in clinical guidelines and categorised these items into five modes of care on the basis of the mechanism through which care is delivered: laboratory tests; generalist-delivered physical checks; specialist-delivered checks; education/counselling for nutrition and physical activity and education/counselling for high risk substance use. We calculated delivery for each patient for each of mode of care by determining the proportion of recommended services delivered for that mode. We used multilevel regression models to quantify variation attributable to health centre or client level factors and to identify factors associated with greater adherence to clinical guidelines for each mode of care. Clients on average received 43 to 60 % of recommended care in 2005/6. Different modes of care showed different patterns of improvement. Generalist-delivered physical checks (delivered by a non-specialist) showed a steady year on year increase, delivery of laboratory tests showed improvement only in the later years of the study, and delivery of counselling/education interventions showed early improvement which then plateaued. Health centres participating in CQI had increased odds of top quartile service delivery for all modes compared to baseline, but effects differed by mode. Health centre factors explained 20-52 % of the variation across jurisdictions and health centres for different modes of care. Levels of adherence to clinical guidelines and patterns of improvement during participation in a CQI program differed for different modes of care. Policy and funding decisions may have had important effects on the level and nature of improvements achieved.

Toking, Vaping, and Eating for Health or Fun: Marijuana Use Patterns in Adults, U.S., 2014.

PubMed

Schauer, Gillian L; King, Brian A; Bunnell, Rebecca E; Promoff, Gabbi; McAfee, Timothy A

2016-01-01

Policies legalizing marijuana for medical and recreational use have been increasing in the U.S. Considering the potential impact of these policies, important knowledge gaps exist, including information about the prevalence of various modes of marijuana use (e.g., smoked in joints, bowls, bongs; consumed in edibles or drinks) and about medical versus recreational use. Accordingly, this study assessed (1) prevalence and correlates of modes of current and ever marijuana use and (2) prevalence of medicinal and recreational marijuana use in U.S. adults. Data came from Summer Styles (n=4,269), a nationally representative consumer panel survey of adults aged ≥18 years, collected in 2014. The survey asked about past 30-day (current) and ever mode of marijuana use and current reason for use (medicinal, recreational, both). Weighted prevalence estimates were computed and correlates were assessed in 2014 using logistic regression. Overall, 7.2% of respondents reported current marijuana use; 34.5% reported ever use. Among current users, 10.5% reported medicinal-only use, 53.4% reported recreational-only use, and 36.1% reported both. Use of bowl or pipe (49.5%) and joint (49.2%) predominated among current marijuana users, with lesser use of bong, water pipe, or hookah (21.7%); blunts (20.3%); edibles/drinks (16.1%); and vaporizers (7.6%); 92.1% of the sample reported combusted-only marijuana use. Combusted modes of marijuana use are most prevalent among U.S. adults, with a majority using marijuana for recreation. In light of changing policies and patterns of use, improved marijuana surveillance is critical for public health planning. Copyright © 2016 American Journal of Preventive Medicine. All rights reserved.

Band structures in two-dimensional phononic crystals with periodic Jerusalem cross slot

NASA Astrophysics Data System (ADS)

Li, Yinggang; Chen, Tianning; Wang, Xiaopeng; Yu, Kunpeng; Song, Ruifang

2015-01-01

In this paper, a novel two-dimensional phononic crystal composed of periodic Jerusalem cross slot in air matrix with a square lattice is presented. The dispersion relations and the transmission coefficient spectra are calculated by using the finite element method based on the Bloch theorem. The formation mechanisms of the band gaps are analyzed based on the acoustic mode analysis. Numerical results show that the proposed phononic crystal structure can yield large band gaps in the low-frequency range. The formation mechanism of opening the acoustic band gaps is mainly attributed to the resonance modes of the cavities inside the Jerusalem cross slot structure. Furthermore, the effects of the geometrical parameters on the band gaps are further explored numerically. Results show that the band gaps can be modulated in an extremely large frequency range by the geometry parameters such as the slot length and width. These properties of acoustic waves in the proposed phononic crystals can potentially be applied to optimize band gaps and generate low-frequency filters and waveguides.

RX and Z Mode Growth Rates and Propagation at Cavity Boundaries

NASA Astrophysics Data System (ADS)

Mutel, R. L.; Christopher, I. W.; Menietti, J. D.; Gurnett, D. A.; Pickett, J. S.; Masson, A.; Fazakerley, A.; Lucek, E.

Recent Cluster WBD observations in the Earth's auroral acceleration region have detected trapped Z mode auroral kilometric radiation while the spacecraft were entering a deep density cavity. The Z mode has a clear cutoff at the local upper hybrid resonance frequency, while RX mode radiation is detected above the RX mode cutoff frequency. The small gap between the upper hybrid resonance and the RX mode cutoff frequencies is proportional to the local electron density as expected from cold plasma theory. The width of the observed gap provides a new sensitive measure of the ambient electron density. In addition, the relative intensities of RX and Z mode radiation provide a sensitive probe of the plasma β = Ω_pe /Ω_ce at the source since the growth rates, although identical in form, have different ranges of allowed resonant radii which depend on β. In particular, the RX mode growth is favored for low β, while the Z mode is favored at higher β. The observed mode intensities and β's appear to be consistent with this model, and favor generation of Z mode at the source over models in which Z mode is generated by mode-conversion at cavity boundaries. These are the first multi-point direct measurements of mode-specific AKR propagation in the auroral acceleration region of any planet.

Majorana splitting from critical currents in Josephson junctions

NASA Astrophysics Data System (ADS)

Cayao, Jorge; San-Jose, Pablo; Black-Schaffer, Annica M.; Aguado, Ramón; Prada, Elsa

2017-11-01

A semiconducting nanowire with strong Rashba spin-orbit coupling and coupled to a superconductor can be tuned by an external Zeeman field into a topological phase with Majorana zero modes. Here we theoretically investigate how this exotic topological superconductor phase manifests in Josephson junctions based on such proximitized nanowires. In particular, we focus on critical currents in the short junction limit (LN≪ξ , where LN is the junction length and ξ is the superconducting coherence length) and show that they contain important information about nontrivial topology and Majoranas. This includes signatures of the gap inversion at the topological transition and a unique oscillatory pattern that originates from Majorana interference. Interestingly, this pattern can be modified by tuning the transmission across the junction, thus providing complementary evidence of Majoranas and their energy splittings beyond standard tunnel spectroscopy experiments, while offering further tunability by virtue of the Josephson effect.

Modeling of Electronic Transport in Scanning Tunneling Microscope Tip-Carbon Nanotube Systems

NASA Technical Reports Server (NTRS)

Yamada, Toshishige; Kwak, Dochan (Technical Monitor)

2000-01-01

A model is proposed for two observed current-voltage (I-V) patterns in a recent experiment with a scanning tunneling microscope tip and a carbon nanotube. We claim that there are two mechanical contact modes for a tip (metal) -nanotube (semiconductor) junction (1) with or (2) without a tiny vacuum gap (0.1 - 0.2 nm). With the tip grounded, the tunneling case in (1) would produce large dI/dV with V > 0, small dI/dV with V < 0, and I = 0 near V = 0 for an either n- or p-nanotube; the Schottky mechanism in (2) would result in I does not equal 0 only with V < 0 for an n-nanotube, and the bias polarities would be reversed for a p-nanotube. The two observed I-V patterns are thus entirely explained by a tip-nanotube contact of the two types, where the nanotube must be n-type.

IGOS improvements for Seasat

NASA Technical Reports Server (NTRS)

Warmke, J. M.

1979-01-01

Modifications to Battelle's Interactive Graphics Orbit Selection (IGOS) computer program to assist in the planning and evaluation of the Seasat-A Scatterometer System (SASS) flight program were studied. To meet the planning needs of the LaRC Seasat-A Scatterometer team, the following features/modifications were implemented in IGOS: (1) display and specification of time increments in orbital passes represented by the cross-hatching of ground swaths; (2) addition of pass number annotations on the horizontal axis of the STPLNG and STPTOD plots; (3) modification of the sensor model to include more than two swaths associated with a single sensor to approximate the SASS cell pattern; (4) inclusion of down range and cross-track swath geometry to display the characteristic skewed SASS pattern; (5) addition of a swath schedule to allow the display of the SASS mode changes and to calibrate gaps; and (6) development of a set of commands to generate the detailed swath data from sensor characteristics and orbit/earth motion.

Effects of beam configurations on wire melting and transfer behaviors in dual beam laser welding with filler wire

NASA Astrophysics Data System (ADS)

Ma, Guolong; Li, Liqun; Chen, Yanbin

2017-06-01

Butt joints of 2 mm thick stainless steel with 0.5 mm gap were fabricated by dual beam laser welding with filler wire technique. The wire melting and transfer behaviors with different beam configurations were investigated detailedly in a stable liquid bridge mode and an unstable droplet mode. A high speed video system assisted by a high pulse diode laser as an illumination source was utilized to record the process in real time. The difference of welding stability between single and dual beam laser welding with filler wire was also compartively studied. In liquid bridge transfer mode, the results indicated that the transfer process and welding stability were disturbed in the form of "broken-reformed" liquid bridge in tandem configuration, while improved by stabilizing the molten pool dynamics with a proper fluid pattern in side-by-side configuration, compared to sigle beam laser welding with filler wire. The droplet transfer period and critical radius were studied in droplet transfer mode. The transfer stability of side-by-side configuration with the minium transfer period and critical droplet size was better than the other two configurations. This was attributed to that the action direction and good stability of the resultant force which were beneficial to transfer process in this case. The side-by-side configuration showed obvious superiority on improving welding stability in both transfer modes. An acceptable weld bead was successfully generated even in undesirable droplet transfer mode under the present conditions.

Optimization Of Shear Modes To Produce Enhanced Bandwidth In Ghz GaP Bragg Cells

NASA Astrophysics Data System (ADS)

Soos, J., I.; Rosemeier, R. G.; Rosenbaum, J.

1988-02-01

Applications of Gallium Phosphide (GaP) acousto-optic devices, at wavelengths from 570nm - 1.06um seem to be ideal for fiber optic modulators, scanners, deflectors, frequency shifters, Q-switches and mode lockers. One of the major applications are for RF spectrometers in early warning radar receivers and auto-correlators. Longitudinal GaP acousto-optic Bragg cells which have respectively operational frequencies in the range of 200 MHz - 3 GHz and diffraction efficiencies in the range of 120%/RF watt to 1%/RF watt have recently been fabricated. Comparatively, shear GaP devices which have operational frequencies in the range of 200 MHz to 2 GHz and diffraction efficiencies from 80%/RF watt to 7%/RF watt have also been constructed.

Gap-mode enhancement on MoS2 probed by functionalized tip-enhanced Raman spectroscopy

NASA Astrophysics Data System (ADS)

Alajlan, Abdulrahman M.; Voronine, Dmitri V.; Sinyukov, Alexander M.; Zhang, Zhenrong; Sokolov, Alexei V.; Scully, Marlan O.

2016-09-01

Surface enhancement of molecular spectroscopic signals has been widely used for sensing and nanoscale imaging. Because of the weak electromagnetic enhancement of Raman signals on semiconductors, it is motivating but challenging to study the electromagnetic effect separately from the chemical effects. We report tip-enhanced Raman scattering measurements on Au and bulk MoS2 substrates using a metallic tip functionalized with copper phthalocyanine molecules and demonstrate similar gap-mode enhancement on both substrates. We compare the experimental results with theoretical calculations to confirm the gap-mode enhancement on MoS2 using a well-established electrostatic model. The functionalized tip approach allows for suppressing the background and is ideal for separating electromagnetic and chemical enhancement mechanisms on various substrates. Our results may find a wide range of applications in MoS2-based devices, sensors, and metal-free nanoscale bio-imaging.

Waveguides having patterned, flattened modes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Messerly, Michael J.; Pax, Paul H.; Dawson, Jay W.

Field-flattening strands may be added to and arbitrarily positioned within a field-flattening shell to create a waveguide that supports a patterned, flattened mode. Patterning does not alter the effective index or flattened nature of the mode, but does alter the characteristics of other modes. Compared to a telecom fiber, a hexagonal pattern of strands allows for a three-fold increase in the flattened mode's area without reducing the separation between its effective index and that of its bend-coupled mode. Hexagonal strand and shell elements prove to be a reasonable approximation, and, thus, to be of practical benefit vis-a-vis fabrication, to thosemore » of circular cross section. Patterned flattened modes offer a new and valuable path to power scaling.« less

Lamb wave band gaps in a double-sided phononic plate

NASA Astrophysics Data System (ADS)

Wang, Peng; Chen, Tian-Ning; Yu, Kun-Peng; Wang, Xiao-Peng

2013-02-01

In this paper, we report on the theoretical investigation of the propagation characteristics of Lamb wave in a phononic crystal structure constituted by a square array of cylindrical stubs deposited on both sides of a thin homogeneous plate. The dispersion relations, the power transmission spectra, and the displacement fields of the eigenmodes are studied by using the finite-element method. We investigate the evolution of band gaps in the double-sided phononic plate with stub height on both sides arranged from an asymmetrical distribution to a symmetrical distribution gradually. Numerical results show that as the double stubs in a unit cell arranged more symmetrically on both sides, band width shifts, new band gaps appear, and the bands become flat due to localized resonant modes which couple with plate modes. Specially, more band gaps and flat bands can be found in the symmetrical system as a result of local resonances of the stubs which interact in a stronger way with the plate modes. Moreover, the symmetrical double-sided plate exhibits lower and smaller band gap than that of the asymmetrical plate. These propagation properties of elastic or acoustic waves in the double-sided plate can potentially be utilized to generate filters, slow the group velocity, low-frequency sound insulation, and design acoustic sensors.

Higgs amplitude mode in the BCS superconductors Nb1-xTi(x)N induced by terahertz pulse excitation.

PubMed

Matsunaga, Ryusuke; Hamada, Yuki I; Makise, Kazumasa; Uzawa, Yoshinori; Terai, Hirotaka; Wang, Zhen; Shimano, Ryo

2013-08-02

Ultrafast responses of BCS superconductor Nb(1-x)Ti(x)N films in a nonadiabatic excitation regime were investigated by using terahertz (THz) pump-THz probe spectroscopy. After an instantaneous excitation with the monocycle THz pump pulse, a transient oscillation emerges in the electromagnetic response in the BCS gap energy region. The oscillation frequency coincides with the asymptotic value of the BCS gap energy, indicating the appearance of the theoretically anticipated collective amplitude mode of the order parameter, namely the Higgs amplitude mode. Our result opens a new pathway to the ultrafast manipulation of the superconducting order parameter by optical means.

Anisotropic quantum quench in the presence of frustration or background gauge fields: A probe of bulk currents and topological chiral edge modes

NASA Astrophysics Data System (ADS)

Killi, Matthew; Trotzky, Stefan; Paramekanti, Arun

2012-12-01

Bosons and fermions, in the presence of frustration or background gauge fields, can form many-body ground states that support equilibrium charge or spin currents. Motivated by the experimental creation of frustration or synthetic gauge fields in ultracold atomic systems, we propose a general scheme by which making a sudden anisotropic quench of the atom tunneling across the lattice and tracking the ensuing density modulations provides a powerful and gauge-invariant route to probing diverse equilibrium current patterns. Using illustrative examples of trapped superfluid Bose and normal Fermi systems in the presence of artificial magnetic fluxes on square lattices, and frustrated bosons in a triangular lattice, we show that this scheme to probe equilibrium bulk current order works independent of particle statistics. We also show that such quenches can detect chiral edge modes in gapped topological states, such as quantum Hall or quantum spin Hall insulators.

Characterizing the ``Higgs'' amplitude mode in a Spin-1 Bose Einstein Condensate

NASA Astrophysics Data System (ADS)

Hebbe Madhusudhana, Bharath; Boguslawski, Matthew; Anquez, Martin; Robbins, Bryce; Barrios, Maryrose; Hoang, Thai; Chapman, Michael

2016-05-01

Spontaneous symmetry breaking in a physical system is often characterized by massless Nambu-Goldstone modes and massive Anderson-Higgs modes. It occurs when a system crosses a quantum critical point (QCP) reaching a state does not share the symmetry of the underlying Hamiltonian. In a spin-1 Bose Einstein condensate, the transverse spin component can be considered as an order parameter. A quantum phase transition (QPT) of this system results in breaking of the symmetry group U(1) × SO(2) shared by the Hamiltonian. As a result, two massless coupled phonon-magnon modes are produced along with a single massive mode or a Higgs-like mode, in the form of amplitude excitations of the order parameter. Here we characterize the amplitude excitations experimentally by inducing coherent oscillation in the spin population. We further use the amplitude oscillations to measure the energy gap for different phases of the QPT. At the QCP, finite size effects lead to a non-zero gap, and our measurements are consistent with this prediction.

Electromagnetic resonance in the asymmetric terahertz metamaterials with triangle microstructure

NASA Astrophysics Data System (ADS)

Xing, Yuanyuan; Zhang, Xiaoyu; Zhang, Qiang; Gu, Yanping; Qian, Yunan; Lin, Xingyue; Tang, Yunhai; Cheng, Xinli; Qin, Changfa; Shen, Jiaoyan; Zang, Taocheng; Ma, Chunlan

2018-05-01

We investigate terahertz transmission properties and electromagnetic resonance modes in the asymmetric triangle structures with the change of asymmetric distance and the direction of electric field. When the THz electric field is perpendicular to the split gap of triangle, the electric field can better excite the THz absorption in the triangle structures. Importantly, electromagnetically induced transparency (EIT) characteristics are observed in the triangle structures due to the destructive interference of the different excited modes. The distributions of electric field and surface current density simulated by finite difference time domain indicate that the bright mode is excited by the side of triangle structures and dark mode is excited by the gap-side of triangle. The present study is helpful to understand the electromagnetic resonance in the asymmetric triangular metamaterials.

Superconductivity induced by flexural modes in non-σh-symmetric Dirac-like two-dimensional materials: A theoretical study for silicene and germanene

NASA Astrophysics Data System (ADS)

Fischetti, Massimo V.; Polley, Arup

2018-04-01

In two-dimensional crystals that lack symmetry under reflections on the horizontal plane of the lattice (non-σh-symmetric), electrons can couple to flexural modes (ZA phonons) at first order. We show that in materials of this type that also exhibit a Dirac-like electron dispersion, the strong coupling can result in electron pairing mediated by these phonons, as long as the flexural modes are not damped or suppressed by additional interactions with a supporting substrate or gate insulator. We consider several models: The weak-coupling limit, which is applicable only in the case of gapped and parabolic materials, like stanene and HfSe2, thanks to the weak coupling; the full gap-equation, solved using the constant-gap approximation and considering statically screened interactions; its extensions to energy-dependent gap and to dynamic screening. We argue that in the case of silicene and germanene superconductivity mediated by this process can exhibit a critical temperature of a few degrees K, or even a few tens of degrees K when accounting for the effect of a high-dielectric-constant environment. We conclude that the electron/flexural-modes coupling should be included in studies of possible superconductivity in non-σh-symmetric two-dimensional crystals, even if alternative forms of coupling are considered.

Multi-mode ultra-strong coupling (I): spectroscopic experiments using a vacuum-gap transmon circuit architecture

NASA Astrophysics Data System (ADS)

Bosman, Sal J.; Gely, Mario F.; Singh, Vibhor; Bruno, Alessandro; Bothner, Daniel; Steele, Gary A.

In circuit QED, multi-mode extensions of the quantum Rabi model suffer from divergence problems. Here, we spectroscopically study multi-mode ultra-strong coupling using a transmon circuit architecture, which provides no clear guidelines on how many modes play a role in the dynamics of the system. As our transmon qubit, we employ a suspended island above the voltage anti-node of a λ / 4 coplanar microwave resonator, thereby realising a circuit where 88% of the qubit capacitance is formed by a vacuum-gap capacitor with the center conductor of the resonator. We measure vacuum Rabi splitting over multiple modes up to 2 GHz, reaching coupling ratios of g / ω = 0 . 18 , well within the ultra-strong coupling regime. We observe a qubit-mediated mode coupling, measurable up to the fifth mode at 38 GHz. Using a novel analytical quantum circuit model of this architecture, which includes all modes without introducing divergencies, we are able to fit the full spectrum and extract a vacuum fluctuations induced Bloch-Siegert shift of up to 62 MHz. This circuit architecture expands the versatility of the transmon technology platform and opens many possibilities in multi-mode physics in the ultra-strong coupling regime.

Quantum origins of molecular recognition and olfaction in Drosophila.

PubMed

Bittner, Eric R; Madalan, Adrian; Czader, Arkadiusz; Roman, Gregg

2012-12-14

The standard model for molecular recognition of an odorant is that receptor sites discriminate by molecular geometry as evidenced that two chiral molecules may smell very differently. However, recent studies of isotopically labeled olfactants indicate that there may be a molecular vibration-sensing component to olfactory reception, specifically in the spectral region around 2300 cm(-1). Here, we present a donor-bridge-acceptor model for olfaction which attempts to explain this effect. Our model, based upon accurate quantum chemical calculations of the olfactant (bridge) in its neutral and ionized states, posits that internal modes of the olfactant are excited impulsively during hole transfer from a donor to acceptor site on the receptor, specifically those modes that are resonant with the tunneling gap. By projecting the impulsive force onto the internal modes, we can determine which modes are excited at a given value of the donor-acceptor tunneling gap. Only those modes resonant with the tunneling gap and are impulsively excited will give a significant contribution to the inelastic transfer rate. Using acetophenone as a test case, our model and experiments on D. melanogaster suggest that isotopomers of a given olfactant give rise to different odorant qualities. These results support the notion that inelastic scattering effects may play a role in discriminating between isotopomers but that this is not a general spectroscopic effect.

The Bragg gap vanishing phenomena in one-dimensional photonic crystals.

PubMed

Zhang, Hui; Chen, Xi; Li, Youquan; Fu, Yunqi; Yuan, Naichang

2009-05-11

We theoretically deduce the Bragg gap vanishing conditions in one-dimensional photonic crystals and experimentally demonstrate the m=0 band-gap vanishing phenomena at microwave frequencies. In the case of mismatched impedance, the Bragg gap will vanish as long as the discrete modes appear in photonic crystals containing dispersive materials, while for the matched impedance cases, Bragg gaps will always disappear. The experimental results and the simulations agree extremely well with the theoretical expectation.

Evaluation of Landsat-7 SLC-off image products for forest change detection

USGS Publications Warehouse

Wulder, Michael A.; Ortlepp, Stephanie M.; White, Joanne C.; Maxwell, Susan

2008-01-01

Since July 2003, Landsat-7 ETM+ has been operating without the scan line corrector (SLC), which compensates for the forward motion of the satellite in the imagery acquired. Data collected in SLC-off mode have gaps in a systematic wedge-shaped pattern outside of the central 22 km swath of the imagery; however, the spatial and spectral quality of the remaining portions of the imagery are not diminished. To explore the continued use of Landsat-7 ETM+ SLC-off imagery to characterize change in forested environments, we compare the change detection results generated from a reference image pair (a 1999 Landsat-7 ETM+ image and a 2003 Landsat-5 TM image) with change detection results generated from the same 1999 Landsat-7 ETM+ image coupled with three different 2003 Landsat-7 SLC-off products: unremediated SLC-off (i.e., with gaps); histogram-based gap-filled; and segment-based gap-filled. The results are compared on both a pixel and polygon basis; on a pixel basis, the unremediated SLC-off product missed 35% of the change identified by the reference data, and the histogram- and segment-based gap-filled products missed 23% and 21% of the change, respectively. When using forest inventory polygons as a context for change (to reduce commission error), the amount of change missed was 31%, 14%, and 12% for the each of the unremediated, histogram-based gap-filled, and segment-based gap-filled products, respectively. Our results indicate that over the time period considered, and given the types and spatial distribution of change events within our study area, the gap-filled products can provide a useful data source for change detection in forested environments. The selection of which product to use is, however, very dependent on the nature of the application and the spatial configuration of change events. ?? 2008 Government of Canada.

Structural dynamics of tropical moist forest gaps

Treesearch

Maria O. Hunter; Michael Keller; Douglas Morton; Bruce Cook; Michael Lefsky; Mark Ducey; Scott Saleska; Raimundo Cosme de Oliveira; Juliana Schietti

2015-01-01

Gap phase dynamics are the dominant mode of forest turnover in tropical forests. However, gap processes are infrequently studied at the landscape scale. Airborne lidar data offer detailed information on three-dimensional forest structure, providing a means to characterize fine-scale (1 m) processes in tropical forests over large areas. Lidar-based estimates of forest...

Bismuth-induced Raman modes in GaP 1– xBi x

DOE PAGES

Christian, Theresa M.; Fluegel, Brian; Beaton, Daniel A.; ...

2016-09-02

Here, dilute bismide semiconductor alloys are a promising material platform for optoelectronic devices due to drastic impacts of bismuth on the electronic structure of the alloy. At the same time, the details of bismuth incorporation in the lattice are not fully understood. In this work, we conduct Raman scattering spectroscopy on GaP 1- xBi x epilayers grown by molecular beam epitaxy (MBE) and identify several bismuth-related Raman features including gap vibration modes at 296, 303, and 314 cm -1. This study paves the way for more detailed analysis of the local symmetry at bismuth incorporation sites in the dilute bismidemore » alloy regime.« less

Design of ultra compact polarization splitter based on complete photonic band gap

NASA Astrophysics Data System (ADS)

Sinha, R. K.; Nagpal, Yogita

2005-11-01

Certain select structures in photonic crystals (PhCs) exhibit complete photonic band gap i.e. a frequency region where the photonic band gaps for both polarizations (i.e. transverse electric and transverse magnetic modes) exist and overlap. One of the most fundamental applications of the photonic band gap structures is the design of photonic crystal waveguides, which can be made by inserting linear defects in the photonic crystal structures. By setting closely two parallel 2D PhC waveguides, a directional waveguide coupler can be designed, which can be used to design a polarization splitter. In this paper we design a polarization splitter in a photonic crystal structure composed of two dimensional honeycomb pattern of dielectric rods in air. This photonic crystal structure exhibits a complete photonic band gap that extends from λ = 1.49 μm to λ = 1.61 μm, where lambda is the wavelength in free space, providing a large bandwidth of 120 nm. A polarization splitter can be made by designing a polarization selective coupler. The coupling lengths at various wavelengths for both polarizations have been calculated using the Finite Difference Time Domain method. It has been shown that the coupling length, for TE polarization is much smaller as compared to that for the TM polarization. This principle is used to design a polarization splitter of length 32 μm at λ = 1.55 μm. Further, the spectral response of the extinction ratios for both polarizations in the two waveguides at propagation distance of 32 μm has been studied.

Radiative heat transfer exceeding the blackbody limit between macroscale planar surfaces separated by a nanosize vacuum gap

NASA Astrophysics Data System (ADS)

Bernardi, Michael P.; Milovich, Daniel; Francoeur, Mathieu

2016-09-01

Using Rytov's fluctuational electrodynamics framework, Polder and Van Hove predicted that radiative heat transfer between planar surfaces separated by a vacuum gap smaller than the thermal wavelength exceeds the blackbody limit due to tunnelling of evanescent modes. This finding has led to the conceptualization of systems capitalizing on evanescent modes such as thermophotovoltaic converters and thermal rectifiers. Their development is, however, limited by the lack of devices enabling radiative transfer between macroscale planar surfaces separated by a nanosize vacuum gap. Here we measure radiative heat transfer for large temperature differences (~120 K) using a custom-fabricated device in which the gap separating two 5 × 5 mm2 intrinsic silicon planar surfaces is modulated from 3,500 to 150 nm. A substantial enhancement over the blackbody limit by a factor of 8.4 is reported for a 150-nm-thick gap. Our device paves the way for the establishment of novel evanescent wave-based systems.

Field coupling-induced pattern formation in two-layer neuronal network

NASA Astrophysics Data System (ADS)

Qin, Huixin; Wang, Chunni; Cai, Ning; An, Xinlei; Alzahrani, Faris

2018-07-01

The exchange of charged ions across membrane can generate fluctuation of membrane potential and also complex effect of electromagnetic induction. Diversity in excitability of neurons induces different modes selection and dynamical responses to external stimuli. Based on a neuron model with electromagnetic induction, which is described by magnetic flux and memristor, a two-layer network is proposed to discuss the pattern control and wave propagation in the network. In each layer, gap junction coupling is applied to connect the neurons, while field coupling is considered between two layers of the network. The field coupling is approached by using coupling of magnetic flux, which is associated with distribution of electromagnetic field. It is found that appropriate intensity of field coupling can enhance wave propagation from one layer to another one, and beautiful spatial patterns are formed. The developed target wave in the second layer shows some difference from target wave triggered in the first layer of the network when two layers are considered by different excitabilities. The potential mechanism could be pacemaker-like driving from the first layer will be encoded by the second layer.

Research on low-frequency band gap property of a hybrid phononic crystal

NASA Astrophysics Data System (ADS)

Dong, Yake; Yao, Hong; Du, Jun; Zhao, Jingbo; Chao, Ding; Wang, Benchi

2018-05-01

A hybrid phononic crystal has been investigated. The characteristic frequency of XY mode, transmission loss and displacement vector have been calculated by the finite element method. There are Bragg scattering band gap and local resonance band gap in the band structures. We studied the influence factors of band gap. There are many flat bands in the eigenfrequencies curve. There are many flat bands in the curve. The band gap covers a large range in low frequency. The band gaps cover more than 95% below 3000 Hz.

Oscillatory modes of extended Nile River records (A.D. 622-1922)

NASA Astrophysics Data System (ADS)

Kondrashov, D.; Feliks, Y.; Ghil, M.

2005-05-01

The historical records of the low- and high-water levels of the Nile River are among the longest climatic records that have near-annual resolution. There are few gaps in the first part of the records (A.D. 622-1470) and larger gaps later (A.D. 1471-1922). We apply advanced spectral methods, Singular-Spectrum Analysis (SSA) and the Multi-Taper Method (MTM), to fill the gaps and to locate interannual and interdecadal periodicities. The gap filling uses a novel, iterative version of SSA. Our analysis reveals several statistically significant features of the records: a nonlinear, data-adaptive trend that includes a 256-year cycle, a quasi-quadriennial (4.2-year) and a quasi-biennial (2.2-year) mode, as well as additional periodicities of 64, 19, 12, and, most strikingly, 7 years. The quasi-quadriennial and quasi-biennial modes support the long-established connection between the Nile River discharge and the El-Niño/Southern Oscillation (ENSO) phenomenon in the Indo-Pacific Ocean. The longest periods might be of astronomical origin. The 7-year periodicity, possibly related to the biblical cycle of lean and fat years, seems to be due to North Atlantic influences.

Gene expression in spider appendages reveals reversal of exd/hth spatial specificity, altered leg gap gene dynamics, and suggests divergent distal morphogen signaling.

PubMed

Prpic, Nikola-Michael; Janssen, Ralf; Wigand, Barbara; Klingler, Martin; Damen, Wim G M

2003-12-01

Leg development in Drosophila has been studied in much detail. However, Drosophila limbs form in the larva as imaginal discs and not during embryogenesis as in most other arthropods. Here, we analyze appendage genes in the spider Cupiennius salei and the beetle Tribolium castaneum. Differences in decapentaplegic (dpp) expression suggest a different mode of distal morphogen signaling suitable for the specific geometry of growing limb buds. Also, expression of the proximal genes homothorax (hth) and extradenticle (exd) is significantly altered: in the spider, exd is restricted to the proximal leg and hth expression extends distally, while in insects, exd is expressed in the entire leg and hth is restricted to proximal parts. This reversal of spatial specificity demonstrates an evolutionary shift, which is nevertheless compatible with a conserved role of this gene pair as instructor of proximal fate. Different expression dynamics of dachshund and Distal-less point to modifications in the regulation of the leg gap gene system. We comment on the significance of this finding for attempts to homologize leg segments in different arthropod classes. Comparison of the expression profiles of H15 and optomotor-blind to the Drosophila patterns suggests modifications also in the dorsal-ventral patterning system of the legs. Together, our results suggest alterations in many components of the leg developmental system, namely proximal-distal and dorsal-ventral patterning, and leg segmentation. Thus, the leg developmental system exhibits a propensity to evolutionary change, which probably forms the basis for the impressive diversity of arthropod leg morphologies.

Saturn's Misbegotten Moonlets

NASA Astrophysics Data System (ADS)

Spitale, Joseph N.

2017-06-01

Saturn's rings are interspersed with numerous narrow (tens of km wide) gaps. Two of the largest of these gaps -- Encke and Keeler -- contain satellites -- Pan and Daphnis -- that maintain their respective gaps via the classical Goldreich/Tremaine-style shepherding mechanism wherein angular momentum is transferred across the essentially empty gap via torques acting between the satellites and the ring. Other prominent gaps are shepherded by resonances with external satellites or planetary modes: Mimas shepherds the outer edge of the B ring, clearing the inner part of the Cassini Division, Titan shepherds the Columbo ringlet / gap, and the Maxwell ringlet / gap is likely maintained by a resonance with a planetary mode. Prior to Cassini, it was expected that all of the gaps would be shepherded in a similar manner.However, many small gaps do not correspond with known resonances, and no satellites were spotted within those gaps during Cassini's prime and extended mission. To address this issue, a series of Cassini imaging observations were planned to examine 11 gaps in the C ring and Cassini division at a resolution and longitudinal coverage sufficient to either discover the shepherds or rule out their presence. The survey discovered no embedded satellites. Longitudinal coverage was incomplete, but within longitudes covered by the survey, satellites are ruled out to sizes in the 100-m range, far too small keep the observed gaps open. It is possible (about even odds) that there could be a larger satellite residing at a longitude not covered in the survey, but the probability that the survey was unfortunate enough to miss significant satellites in all 11 gaps is exceedingly small (~0.002%). Moreover, these gaps appear in earlier imaging sequences, with some high-resolution coverage, so the true probability is smaller yet. Therefore, a new theory is likely needed to explain the presence of the gaps.

The effects of in-vehicle tasks and time-gap selection while reclaiming control from adaptive cruise control (ACC) with bus simulator.

PubMed

Lin, Tsang-Wei; Hwang, Sheue-Ling; Su, Jau-Ming; Chen, Wan-Hui

2008-05-01

This research aimed to find out the effects of in-vehicle distractions and time-gap settings with a fix-based bus driving simulator in a following scenario. Professional bus drivers were recruited to perform in-vehicle tasks while driving with adaptive cruise control (ACC) of changeable time-gap settings in freeway traffic. Thirty subjects were divided equally into three groups for different in-vehicle task modes (between subjects), including no task distraction, hands-free, and manual modes. Further, time-gap settings for the experimental ACC were: shorter than 1.0 s, 1.0-1.5 s, 1.5-2.0 s, and longer than 2.0 s (within subjects). Longitudinal (mean headway, forward collision rate, and response time) and lateral control (mean lateral lane position and its standard deviation) performance was assessed. In the results, longitudinal control performance was worsened by both shorter time-gaps and heavier in-vehicle tasks. But the interaction indicated that the harm by heavier in-vehicle distraction could be improved by longer time-gaps. As for the lateral control, it would only be negatively affected by shorter time-gap settings. This research indicates the effects of time-gaps and in-vehicle distraction, as well as the interaction. Proper time-gap selection under different in-vehicle distractions can help avoid accidents and keep safe.

Photon-phonon-enhanced infrared rectification in a two-dimensional nanoantenna-coupled tunnel diode

DOE PAGES

Kadlec, Emil A.; Jarecki, Robert L.; Starbuck, Andrew; ...

2016-12-28

The interplay of strong infrared photon-phonon coupling with electromagnetic confinement in nanoscale devices is demonstrated to have a large impact on ultrafast photon-assisted tunneling in metal-oxide-semiconductor (MOS) structures. Infrared active optical phonon modes in polar oxides lead to strong dispersion and enhanced electric fields at material interfaces. We find that the infrared dispersion of SiO 2 near a longitudinal optical phonon mode can effectively impedance match a photonic surface mode into a nanoscale tunnel gap that results in large transverse-field confinement. An integrated 2D nanoantenna structure on a distributed large-area MOS tunnel-diode rectifier is designed and built to resonantly excitemore » infrared surface modes and is shown to efficiently channel infrared radiation into nanometer-scale gaps in these MOS devices. This enhanced-gap transverse-electric field is converted to a rectified tunneling displacement current resulting in a dc photocurrent. We examine the angular and polarization-dependent spectral photocurrent response of these 2D nanoantenna-coupled tunnel diodes in the photon-enhanced tunneling spectral region. Lastly, our 2D nanoantenna-coupled infrared tunnel-diode rectifier promises to impact large-area thermal energy harvesting and infrared direct detectors.« less

Photon-phonon-enhanced infrared rectification in a two-dimensional nanoantenna-coupled tunnel diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kadlec, Emil A.; Jarecki, Robert L.; Starbuck, Andrew

The interplay of strong infrared photon-phonon coupling with electromagnetic confinement in nanoscale devices is demonstrated to have a large impact on ultrafast photon-assisted tunneling in metal-oxide-semiconductor (MOS) structures. Infrared active optical phonon modes in polar oxides lead to strong dispersion and enhanced electric fields at material interfaces. We find that the infrared dispersion of SiO 2 near a longitudinal optical phonon mode can effectively impedance match a photonic surface mode into a nanoscale tunnel gap that results in large transverse-field confinement. An integrated 2D nanoantenna structure on a distributed large-area MOS tunnel-diode rectifier is designed and built to resonantly excitemore » infrared surface modes and is shown to efficiently channel infrared radiation into nanometer-scale gaps in these MOS devices. This enhanced-gap transverse-electric field is converted to a rectified tunneling displacement current resulting in a dc photocurrent. We examine the angular and polarization-dependent spectral photocurrent response of these 2D nanoantenna-coupled tunnel diodes in the photon-enhanced tunneling spectral region. Lastly, our 2D nanoantenna-coupled infrared tunnel-diode rectifier promises to impact large-area thermal energy harvesting and infrared direct detectors.« less

Slab photonic crystals with dimer colloid bases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riley, Erin K.; Liddell Watson, Chekesha M., E-mail: cliddell@ccmr.cornell.edu

2014-06-14

The photonic band gap properties for centered rectangular monolayers of asymmetric dimers are reported. Colloids in suspension have been organized into the phase under confinement. The theoretical model is inspired by the range of asymmetric dimers synthesized via seeded emulsion polymerization and explores, in particular, the band structures as a function of degree of lobe symmetry and degree of lobe fusion. These parameters are varied incrementally from spheres to lobe-tangent dimers over morphologies yielding physically realizable particles. The work addresses the relative scarcity of theoretical studies on photonic crystal slabs with vertical variation that is consistent with colloidal self-assembly. Odd,more » even and polarization independent gaps in the guided modes are determined for direct slab structures. A wide range of lobe symmetry and degree of lobe fusion combinations having Brillouin zones with moderate to high isotropy support gaps between odd mode band indices 3-4 and even mode band indices 1-2 and 2-3.« less

Performance and Flowfield Measurements on a 10-inch Ducted Rotor VTOL UAV

NASA Technical Reports Server (NTRS)

Martin, Preston; Tung, Chee

2004-01-01

A ducted fan VTOL UAV with a 10-inch diameter rotor was tested in the US Army 7-by 10-Foot Wind Tunnel. The test conditions covered a range of angle of attack from 0 to 110 degrees to the freestream. The tunnel velocity was varied from 0 (simulating a hover condition) to 128 ft/sec in propeller mode. A six-component internal balance measured the aerodynamic loads for a range of model configurations. including the isolated rotor, the isolated duct, and the full configuration of the duct and rotor. For some conditions, hotwire velocity surveys were conducted along the inner and outer surface of the duct and across the downstream wake. In addition, fluorescent oil flow visualization allowed the flow separation patterns inside and outside of the duct to be mapped for a few test conditions. Two different duct shapes were tested to determine the performance effects of leading edge radius. For each duct, a range of rotor tip gap from 1%R to 4.5%R was tested to determine the performance penalty in hover and axial flight. Measured results are presented in terms of hover performance, hover performance in a crosswind, and high angle of attack performance in propeller mode. In each case, the effects of both tip gap and duct leading edge radius are illustrated using measurements. Some of the hover performance issues were also studied using a simple analytical method, and the results agreed with the measurements.

Multifrequency Gap Solitons in Nonlinear Photonic Crystals

NASA Astrophysics Data System (ADS)

Xie, Ping; Zhang, Zhao-Qing

2003-11-01

We predict the existence of multifrequency gap solitons (MFGSs) in both one- and two-dimensional nonlinear photonic crystals. A MFGS is a single intrinsic mode possessing multiple frequencies inside the gap. Its existence is a result of synergic nonlinear coupling among solitons or soliton trains at different frequencies. Its formation can either lower the threshold fields of the respective frequency components or stabilize their excitations. These MFGSs form a new class of stable gap solitons.

Elastic dependence of defect modes in one-dimensional photonic crystals with a cholesteric elastomer slab

NASA Astrophysics Data System (ADS)

Avendanño, Carlos G.; Martínez, Daniel

2018-07-01

We studied the transmission spectra in a one-dimensional dielectric multilayer photonic structure containing a cholesteric liquid crystal elastomer layer as a defect. For circularly polarized incident electromagnetic waves, we analyzed the optical defect modes induced in the band gap spectrum as a function of the incident angle and the axial strain applied along the same axis as the periodic medium. The physical parameters of the structure were chosen in such a way the photonic band gap of the cholesteric elastomer lies inside that of the multilayer. We found that, in addition to the defect modes associated with the thickness of the defect layer and the anisotropy of the elastic polymer, two new defect modes appear at both band edges of the cholesteric structure, whose amplitudes and spectral positions can be elastically tuned. Particularly, we showed that, at normal incidence, the defect modes shift toward the long-wavelength region with the strain; whereas, for constant elongation, such defects move toward larger frequencies with the incidence angle.

Marginal and Internal Gap of Handmade, Milled and 3D Printed Additive Manufactured Patterns for Pressed Lithium Disilicate Onlay Restorations.

PubMed

Revilla-León, M; Olea-Vielba, M; Esteso-Saiz, A; Martínez-Klemm, I; Özcan, M

2018-03-01

On a pressed lithium disilicate restoration, the building up of a wax pattern of the future restoration is a necessary step on the fabrication process. Conventionally, a wax pattern can be produced by handmade or milled procedures; however, the development of additive manufacturing technologies allows a new fabrication method. The present study measured the marginal and internal gap of handmade, milled and additive manufactured patterns for an onlay restoration. A preparation of an onlay restoration was made on an extracted mandibular tooth. A definitive cast was fabricated from a conventional silicone impression of the prepared tooth. Three groups were established: handmade (HM), milled (ML) and additive manufactured (AM); 4 specimens per group were obtained. The marginal and internal gap of each pattern was measured on the extracted molar through a computed tomography test. Sixty measurements were done to measure the marginal gap and another 60 measurements were calculated to analyze the internal gap on each pattern on the prepared tooth. A total of 1.440 measurements were completed. Mann-Whitney and Turkey statistical tests were used for pairwise comparison. The mean of the marginal and internal gap was of 67.56 ± 6.08 μm and 80.62 ± 3.26 μm for the HM group, 85.28 ± 2.17 μm and 96 ± 1.97 μm for the ML group and 86.49 ± 1.74 μm and 91.86 ± 2.88 μm for the AM group, respectively. The HM group presented significantly lower marginal (p=0.029) and internal (p=0.029) gap compared to the ML and AM groups. There was no statistical significant difference (p=0.486) on the marginal gap between the ML and the AM groups, but the AM group, showed significantly (p=0.029) smaller internal gap than the ML group. All the groups presented less than 100 μm marginal and internal gap, which is a considered clinically acceptable. The three fabrication processes are viable option for manufacturing patterns for lithium disilicate onlay restorations, but the best marginal and internal fit was still obtained by the conventional handmade procedures. Copyright© 2018 Dennis Barber Ltd.

TOPICAL REVIEW: Experimental study of organic zero-gap conductor α-(BEDT-TTF)2I3

NASA Astrophysics Data System (ADS)

Tajima, Naoya; Kajita, Koji

2009-04-01

A zero-gap state with a Dirac cone type energy dispersion was discovered in the organic conductor α-(BEDT-TTF)2I3 under high hydrostatic pressures. This is the first two-dimensional (2D) zero-gap state discovered in bulk crystals with a layered structure. In contrast to the case of graphene, the Dirac cone in this system is highly anisotropic. The present system, therefore, provides a new type of massless Dirac fermion system with anisotropic Fermi velocity. This system exhibits remarkable transport phenomena characteristic to electrons on the Dirac cone type energy structure. The carrier density, written as n~T2, is a characteristic feature of the 2D zero-gap structure. On the other hand, the resistivity per layer (sheet resistance RS) is given as RS=h/e2 and is independent of temperature. The effect of a magnetic field on samples in the zero-gap system was examined. The difference between zero-gap conductors and conventional conductors is the appearance of a Landau level called the zero mode at the contact points when a magnetic field is applied normal to the conductive layer. Zero-mode Landau carriers give rise to strong negative out-of-plane magnetoresistance.

Surface electromagnetic waves in Fibonacci superlattices: Theoretical and experimental results

NASA Astrophysics Data System (ADS)

El Hassouani, Y.; Aynaou, H.; El Boudouti, E. H.; Djafari-Rouhani, B.; Akjouj, A.; Velasco, V. R.

2006-07-01

We study theoretically and experimentally the existence and behavior of the localized surface modes in one-dimensional (1D) quasiperiodic photonic band gap structures. These structures are made of segments and loops arranged according to a Fibonacci sequence. The experiments are carried out by using coaxial cables in the frequency region of a few tens of MHz. We consider 1D periodic structures (superlattice) where each cell is a well-defined Fibonacci generation. In these structures, we generalize a theoretical rule on the surface modes, namely when one considers two semi-infinite superlattices obtained by the cleavage of an infinite superlattice, it exists exactly one surface mode in each gap. This mode is localized on the surface either of one or the other semi-infinite superlattice. We discuss the existence of various types of surface modes and their spatial localization. The experimental observation of these modes is carried out by measuring the transmission through a guide along which a finite superlattice (i.e., constituted of a finite number of quasiperiodic cells) is grafted vertically. The surface modes appear as maxima of the transmission spectrum. These experiments are in good agreement with the theoretical model based on the formalism of the Green function.

Soliton microdynamics and thermal conductivity of uranium nitride at high temperatures

NASA Astrophysics Data System (ADS)

Dubovsky, O. A.; Orlov, A. V.; Semenov, V. A.

2011-09-01

The microdynamics of soliton waves and localized modes of nonlinear vibrations of the acoustic and optical types in uranium nitride has been investigated. It has been shown that, with an increase in the excitation energy in the spectral gap between the bands of optical and acoustic phonons, the energies of solitons increase, whereas the energies of local modes decrease. The previously experimentally observed unidentified quasi-resonant features, which shift in the gap with variations in the temperature, can represent the revealed soliton waves and local modes. The microdynamics of heat conduction of uranium nitride has been studied for the stochastic generation of soliton waves and local modes in the case of spatially distant energy absorption. The thermal conductivity coefficient determined from the temperature gradient and the absorbed energy flux insignificantly exceeds the experimentally observed values, which are decreased because of the presence of structural defects of different types in the material.

Identification of strained black phosphorous by Raman spectroscopy

NASA Astrophysics Data System (ADS)

Wan, Jiawei; Guo, Junhong; Hu, Fangren

2017-04-01

Phosphorene has a very high hole mobility and can be a tuned band structure, and has become an ideal material for electronic devices. For this new type of two-dimensional material, in the applied strain, black phosphorus (BP) can be changed into an indirect band gap and metallic materials from the direct band gap semiconductor material, which greatly affect its inherent physical characteristics. How to identify strained microstructure changes becomes an important problem. The calculated Raman spectra disclose that the A{}{{g}}2 mode and B{}2{{g}} mode will split and the Raman spectra appear, while the A{}{{g}}1 mode is shifted to low-frequency region. The deformation induced by strain will effectively change the Raman mode position and intensity, this can be used to identify phosphorus changes. Project supported by the National Science Foundation of China (Nos. 61505085, 61574080, 61274127) and the Innovation Project of Jiangsu Graduate Student, China (No. SJLX15_0379).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Dongbo; Zhao, Jinfeng, E-mail: jinfeng.zhao@tongji.edu.cn; Li, Libing

In this work, we applied a robust and fully air-coupled method to investigate the propagation of the lowest-order antisymmetric Lamb (A{sub 0}) mode in both a stubbed and an air-drilled phononic-crystal (PC) plate. By measuring simply the radiative acoustic waves of A{sub 0} mode close to the plate surface, we observed the band gaps for the stubbed PC plate caused by either the local resonance or the Bragg scattering, in frequency ranges in good agreement with theoretical predictions. We measured then the complete band gap of A{sub 0} mode for the air-drilled PC plate, in good agreement with the bandmore » structures. Finally, we compared the measurements made using the air-coupled method with those obtained by the laser ultrasonic technique.« less

Electronic and thermal properties of germanene and stanene by first-principles calculations

NASA Astrophysics Data System (ADS)

Jomehpour Zaveh, S.; Roknabadi, M. R.; Morshedloo, T.; Modarresi, M.

2016-03-01

The electronic, vibrational and thermal properties of germanene and stanene have been investigated based on density functional theory (DFT) and density functional perturbation theory (DFPT). The electronic band structure, total and partial density of states and phonon dispersion spectrum and states are analyzed. The phonon spectrum is positive for all modes in the first Brillouin zone and there is a phonon energy band gap between acoustic and optical modes which is around 50 cm-1 for both structure. The constant-volume specific heats of two structures are calculated by using phonon spectrum and density of states. The spin-orbit coupling (SOC) opens a direct energy band gap at the Dirac point, softens phonon spectrum and decreases phonon group velocity of ZA mode.

Surface acoustic waves in one-dimensional piezoelectric-metallic phononic crystal: Effect of a cap layer.

PubMed

Alami, M; El Boudouti, E H; Djafari-Rouhani, B; El Hassouani, Y; Talbi, A

2018-06-18

We study the propagation of transverse acoustic waves associated with the surface of a semi-infinite superlattice (SL) composed of piezoelectric-metallic layers and capped with a piezoelectric layer. We present closed-form expressions for localized surface waves, the so-called Bleustein-Gulyaev (BG) waves depending on whether the cap layer is open-circuited or short-circuited. These expressions are obtained by means of the Green's function method which enables to deduce also the densities of states. These theoretical results are illustrated by a few numerical applications to SLs made of piezoelectric layers of hexagonal symmetry belonging to the 6 mm class such as PZT4 and ZnO in contact with metallic layers such as Fe, Al, Au, Cu and boron-doped-diamond. We demonstrate a rule about the existence of surface modes when considering two complementary semi-infinite SLs obtained by the cleavage of an infinite SL along a plane parallel to the piezoelectric layers. Indeed, when the surface layers are open-circuited, one obtains one surface mode per gap, this mode is associated with one of the two complementary SLs. However, when the surface layers are short-circuited, this rule is not fulfilled and one can obtain zero, one or two modes inside each gap of the two complementary SLs depending on the position of the plane where the cleavage is produced. We show that in addition to the BG surface waves localized at the surface of the cap layer, there may exist true guided waves and pseudo-guided waves (i.e. leaky waves) induced by the cap layer either inside the gaps or inside the bands of the SL respectively. Also, we highlight the possibility of existence of interface modes between the SL and a cap layer as well as an interaction between these modes and the BG surface mode when both modes fall in the same band gaps of the SL. The strength of the interaction depends on the width of the cap layer. Finally, we show that the electromechanical coupling coefficient (ECC) is very sensitive to the cap layer thickness, in particular we calculate and discuss the behavior of the ECC as a function of the adlayer thickness for the low velocity surface modes of the SL which exhibit the highest ECC values. The effect of the nature of the metallic layers inside the SL on the ECC is also investigated. The different surface modes discussed in this work should have applications in sensing applications. Copyright © 2018. Published by Elsevier B.V.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Far-field pattern of transverse modes in LOC structures

NASA Astrophysics Data System (ADS)

Petrescu-Prahova, I. B.; Lazanu, S.; Lepşa, M.; Mihailovici, P.

1988-11-01

An investigation was made of the emission from GaAlAs large-optical-cavity (LOC) laser heterostructures with an active layer more than 2 μm thick. The far-field radiation pattern, representing a superposition of the fundamental and several higher-order transverse modes, had a central maximum. The gain, mirror losses, near- and far-field patterns of each propagation mode, as well as mode competition were analyzed on the basis of a simple model. The far-field pattern of single modes was determined by selecting separate spectral intervals from the total emission spectrum of the laser.

Multimodal far-field acoustic radiation pattern: An approximate equation

NASA Technical Reports Server (NTRS)

Rice, E. J.

1977-01-01

The far-field sound radiation theory for a circular duct was studied for both single mode and multimodal inputs. The investigation was intended to develop a method to determine the acoustic power produced by turbofans as a function of mode cut-off ratio. With reasonable simplifying assumptions the single mode radiation pattern was shown to be reducible to a function of mode cut-off ratio only. With modal cut-off ratio as the dominant variable, multimodal radiation patterns can be reduced to a simple explicit expression. This approximate expression provides excellent agreement with an exact calculation of the sound radiation pattern using equal acoustic power per mode.

Factors Influencing Students' Choice of Study Mode: An Australian Case Study

ERIC Educational Resources Information Center

Ifenthaler, Dirk; Gosper, Maree; Bailey, Matthew; Kretzschmar, Mandy

2014-01-01

Despite the expansion of online and blended learning, as well as open education, little research has been undertaken on what motivates students to enrol in particular study modes at university level. This project addresses this gap in higher education research by exploring the reasons why humanities students choose to study through specific modes.…

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Superlattice Patterns in Coupled Turing Systems

NASA Astrophysics Data System (ADS)

Liu, Fu-Cheng; He, Ya-Feng; Pan, Yu-Yang

2010-05-01

In this paper, superlattice patterns have been investigated by using a two linearly coupled Brusselator model. It is found that superlattice patterns can only be induced in the sub-system with the short wavelength. Three different coupling methods have been used in order to investigate the mode interaction between the two Turing modes. It is proved in the simulations that interaction between activators in the two sub-systems leads to spontaneous formation of black eye pattern and/or white eye patterns while interaction between inhibitors leads to spontaneous formation of super-hexagonal pattern. It is also demonstrated that the same symmetries of the two modes and suitable wavelength ratio of the two modes should also be satisfied to form superlattice patterns.

"A manager in the minds of doctors:" a comparison of new modes of control in European hospitals.

PubMed

Kuhlmann, Ellen; Burau, Viola; Correia, Tiago; Lewandowski, Roman; Lionis, Christos; Noordegraaf, Mirko; Repullo, Jose

2013-07-02

Hospital governance increasingly combines management and professional self-governance. This article maps the new emergent modes of control in a comparative perspective and aims to better understand the relationship between medicine and management as hybrid and context-dependent. Theoretically, we critically review approaches into the managerialism-professionalism relationship; methodologically, we expand cross-country comparison towards the meso-level of organisations; and empirically, the focus is on processes and actors in a range of European hospitals. The research is explorative and was carried out as part of the FP7 COST action IS0903 Medicine and Management, Working Group 2. Comprising seven European countries, the focus is on doctors and public hospitals. We use a comparative case study design that primarily draws on expert information and document analysis as well as other secondary sources. The findings reveal that managerial control is not simply an external force but increasingly integrated in medical professionalism. These processes of change are relevant in all countries but shaped by organisational settings, and therefore create different patterns of control: (1) 'integrated' control with high levels of coordination and coherent patterns for cost and quality controls; (2) 'partly integrated' control with diversity of coordination on hospital and department level and between cost and quality controls; and (3) 'fragmented' control with limited coordination and gaps between quality control more strongly dominated by medicine, and cost control by management. Our comparison highlights how organisations matter and brings the crucial relevance of 'coordination' of medicine and management across the levels (hospital/department) and the substance (cost/quality-safety) of control into perspective. Consequently, coordination may serve as a taxonomy of emergent modes of control, thus bringing new directions for cost-efficient and quality-effective hospital governance into perspective.

Giant Linear Nonreciprocity, Zero Reflection, and Zero Band Gap in Equilibrated Space-Time-Varying Media

NASA Astrophysics Data System (ADS)

Taravati, Sajjad

2018-06-01

This article presents a class of space-time-varying media with giant linear nonreciprocity, zero space-time local reflections, and zero photonic band gap. This is achieved via equilibrium in the electric and magnetic properties of unidirectionally space-time-modulated media. The enhanced nonreciprocity is accompanied by a larger sonic regime interval which provides extra design freedom for achieving strong nonreciprocity by a weak pumping strength. We show that the width of photonic band gaps in general periodic space-time permittivity- and permeability-modulated media is proportional to the absolute difference between the electric and magnetic pumping strengths. We derive a rigorous analytical solution for investigation of wave propagation and scattering from general periodic space-time permittivity- and permeability-modulated media. In contrast with weak photonic transitions, from the excited mode to its two adjacent modes, in conventional space-time permittivity-modulated media, in an equilibrated space-time-varying medium, strong photonic transitions occur from the excited mode to its four adjacent modes. We study the enhanced nonreciprocity and zero band gap in equilibrated space-time-modulated media by analysis of their dispersion diagrams. In contrast to conventional space-time permittivity-modulated media, equilibrated space-time media exhibit different phase and group velocities for forward and backward harmonics. Furthermore, the numerical simulation scheme of general space-time permittivity- and permeability-modulated media is presented, which is based on the finite-difference time-domain technique. Our analytical and numerical results provide insights into general space-time refractive-index-modulated media, paving the way toward optimal isolators, nonreciprocal integrated systems, and subharmonic frequency generators.

Gas-enabled resonance and rectified motion of a piston in a vibrated housing filled with a viscous liquid

DOE PAGES

Romero, Louis A.; Torczynski, John R.; Clausen, Jonathan R.; ...

2015-11-16

Herein, we show how introducing a small amount of gas can completely change the motion of a solid object in a viscous liquid during vibration. We analyze an idealized system exhibiting this behavior: a piston moving in a liquid-filled housing, where the gaps between the piston and the housing are narrow and depend on the piston position. Recent experiments have shown that vibration causes some gas to move below the piston and the piston to subsequently move downward and compress its supporting spring. Herein, we analyze the analogous but simpler situation in which the gas regions are replaced by bellowsmore » with similar pressure-volume relationships. We show that these bellows form a spring (analogous to the pneumatic spring formed by the gas regions) which enables the piston and the liquid to oscillate in a mode that does not exist without this spring. This mode is referred to here as the Couette mode because the liquid in the gaps moves essentially in Couette flow (i.e., with almost no component of Poiseuille flow). Since Couette flow by itself produces extremely low damping, the Couette mode has a strong resonance. We show that, near this resonance, the dependence of the gap geometry on the piston position produces a large rectified (net) force on the piston during vibration. As a result, this force can be much larger than the piston weight and the strength of its supporting spring and is in the direction that decreases the flow resistance of the gap geometry.« less

High power experimental studies of hybrid photonic band gap accelerator structures

DOE PAGES

Zhang, JieXi; Munroe, Brian J.; Xu, Haoran; ...

2016-08-31

This paper reports the first high power tests of hybrid photonic band gap (PBG) accelerator structures. Three hybrid PBG (HPBG) structures were designed, built and tested at 17.14 GHz. Each structure had a triangular lattice array with 60 inner sapphire rods and 24 outer copper rods sandwiched between copper disks. The dielectric PBG band gap map allows the unique feature of overmoded operation in a TM 02 mode, with suppression of both lower order modes, such as the TM 11 mode, as well as higher order modes. The use of sapphire rods, which have negligible dielectric loss, required inclusion ofmore » the dielectric birefringence in the design. The three structures were designed to sequentially reduce the peak surface electric field. Simulations showed relatively high surface fields at the triple point as well as in any gaps between components in the clamped assembly. The third structure used sapphire rods with small pin extensions at each end and obtained the highest gradient of 19 MV/m, corresponding to a surface electric field of 78 MV/m, with a breakdown probability of 5×10 –1 per pulse per meter for a 100-ns input power pulse. Operation at a gradient above 20 MV/m led to runaway breakdowns with extensive light emission and eventual damage. For all three structures, multipactor light emission was observed at gradients well below the breakdown threshold. As a result, this research indicated that multipactor triggered at the triple point limited the operational gradient of the hybrid structure.« less

Demonstration of suppressed phonon tunneling losses in phononic bandgap shielded membrane resonators for high-Q optomechanics.

PubMed

Tsaturyan, Yeghishe; Barg, Andreas; Simonsen, Anders; Villanueva, Luis Guillermo; Schmid, Silvan; Schliesser, Albert; Polzik, Eugene S

2014-03-24

Dielectric membranes with exceptional mechanical and optical properties present one of the most promising platforms in quantum opto-mechanics. The performance of stressed silicon nitride nanomembranes as mechanical resonators notoriously depends on how their frame is clamped to the sample mount, which in practice usually necessitates delicate, and difficult-to-reproduce mounting solutions. Here, we demonstrate that a phononic bandgap shield integrated in the membrane's silicon frame eliminates this dependence, by suppressing dissipation through phonon tunneling. We dry-etch the membrane's frame so that it assumes the form of a cm-sized bridge featuring a 1-dimensional periodic pattern, whose phononic density of states is tailored to exhibit one, or several, full band gaps around the membrane's high-Q modes in the MHz-range. We quantify the effectiveness of this phononic bandgap shield by optical interferometry measuring both the suppressed transmission of vibrations, as well as the influence of frame clamping conditions on the membrane modes. We find suppressions up to 40 dB and, for three different realized phononic structures, consistently observe significant suppression of the dependence of the membrane's modes on sample clamping-if the mode's frequency lies in the bandgap. As a result, we achieve membrane mode quality factors of 5 × 10(6) with samples that are tightly bolted to the 8 K-cold finger of a cryostat. Q × f -products of 6 × 10(12) Hz at 300 K and 14 × 10(12) Hz at 8 K are observed, satisfying one of the main requirements for optical cooling of mechanical vibrations to their quantum ground-state.

Tendon–bone contact pressure and biomechanical evaluation of a modified suture-bridge technique for rotator cuff repair

PubMed Central

Geyer, Michael; Büschken, Meike; Buchhorn, Gottfried H.; Spahn, Gunter; Klinger, Hans-Michael

2009-01-01

The aim of the study was to evaluate the time-zero mechanical and footprint properties of a suture-bridge technique for rotator cuff repair in an animal model. Thirty fresh-frozen sheep shoulders were randomly assigned among three investigation groups: (1) cyclic loading, (2) load-to-failure testing, and (3) tendon–bone interface contact pressure measurement. Shoulders were cyclically loaded from 10 to 180 N and displacement to gap formation of 5- and 10-mm at the repair site. Cycles to failure were determined. Additionally, the ultimate tensile strength and stiffness were verified along with the mode of failure. The average contact pressure and pressure pattern were investigated using a pressure-sensitive film system. All of the specimens resisted against 3,000 cycles and none of them reached a gap formation of 10 mm. The number of cycles to 5-mm gap formation was 2,884.5 ± 96.8 cycles. The ultimate tensile strength was 565.8 ± 17.8 N and stiffness was 173.7 ± 9.9 N/mm. The entire specimen presented a unique mode of failure as it is well known in using high strength sutures by pulling them through the tendon. We observed a mean contact pressure of 1.19 ± 0.03 MPa, applied on the footprint area. The fundamental results of our study support the use of a suture-bridge technique for optimising the conditions of the healing biology of a reconstructed rotator cuff tendon. Nevertheless, an individual estimation has to be done if using the suture-bridge technique clinically. Further investigation is necessary to evaluate the cell biological healing process in order to achieve further sufficient advancements in rotator cuff repair. PMID:19826786

Formation of Degenerate Band Gaps in Layered Systems

PubMed Central

Ignatov, Anton I.; Merzlikin, Alexander M.; Levy, Miguel; Vinogradov, Alexey P.

2012-01-01

In the review, peculiarities of spectra of one-dimensional photonic crystals made of anisotropic and/or magnetooptic materials are considered. The attention is focused on band gaps of a special type—the so called degenerate band gaps which are degenerate with respect to polarization. Mechanisms of formation and properties of these band gaps are analyzed. Peculiarities of spectra of photonic crystals that arise due to the linkage between band gaps are discussed. Particularly, it is shown that formation of a frozen mode is caused by linkage between Brillouin and degenerate band gaps. Also, existence of the optical Borrmann effect at the boundaries of degenerate band gaps and optical Tamm states at the frequencies of degenerate band gaps are analyzed. PMID:28817024

Long-term treatment patterns of testosterone replacement medications.

PubMed

Donatucci, Craig; Cui, Zhanglin; Fang, Yun; Muram, David

2014-08-01

Testosterone replacement therapy (TRT) is prescribed to men diagnosed with hypogonadism to alleviate symptoms, improve quality of life, and improve overall health. However, most men use TRT for only a short duration. To evaluate the long-term treatment patterns in hypogonadal men using topical TRT or short-lasting TRT injections. Using the Truven MarketScan(®) Database, 15,435 men who received their first (index) topical TRT prescription and 517 men who received their short-lasting TRT injection index prescription in 2009 were followed from 12 to 30 months after treatment initiation. Treatment interruption was defined as a medication gap of >30 days. Patients who remained off treatment were classified as having discontinued treatment. Patients who restarted therapy after 30 days were classified as cyclic users. Patients were required to have continuous insurance coverage during 1 year prior to treatment initiation and at least 1 year afterward. Main outcome measures were length of therapy, discontinuation, and restarts of topical TRT or short-lasting TRT injections. The patient characteristics were similar for patients who received topical TRT or short-lasting TRT injections. Of the patients who discontinued therapy during the follow-up period, the percentages of patients who were still on therapy after 3 months were 52% and 31% for topical TRT and short-lasting TRT users, respectively. For cyclic users, there was an attrition rate of approximately 40% to 50% of patients in each cycle. For both topical TRT and short-lasting TRT injections, the gap between stopping and restarting therapy tended to decrease over time. In this analysis, high discontinuation rates were observed. The treatment pattern of TRT may be related to the disease state rather than dosing, daily use, or mode of administration. © 2014 International Society for Sexual Medicine.

StreamMap: Smooth Dynamic Visualization of High-Density Streaming Points.

PubMed

Li, Chenhui; Baciu, George; Han, Yu

2018-03-01

Interactive visualization of streaming points for real-time scatterplots and linear blending of correlation patterns is increasingly becoming the dominant mode of visual analytics for both big data and streaming data from active sensors and broadcasting media. To better visualize and interact with inter-stream patterns, it is generally necessary to smooth out gaps or distortions in the streaming data. Previous approaches either animate the points directly or present a sampled static heat-map. We propose a new approach, called StreamMap, to smoothly blend high-density streaming points and create a visual flow that emphasizes the density pattern distributions. In essence, we present three new contributions for the visualization of high-density streaming points. The first contribution is a density-based method called super kernel density estimation that aggregates streaming points using an adaptive kernel to solve the overlapping problem. The second contribution is a robust density morphing algorithm that generates several smooth intermediate frames for a given pair of frames. The third contribution is a trend representation design that can help convey the flow directions of the streaming points. The experimental results on three datasets demonstrate the effectiveness of StreamMap when dynamic visualization and visual analysis of trend patterns on streaming points are required.

Self-organized pattern on the surface of a metal anode in low-pressure DC discharge

NASA Astrophysics Data System (ADS)

Yaqi, YANG; Weiguo, LI

2018-03-01

Self-organization phenomena on the surface of a metal electrode in low-pressure DC discharge is studied. In this paper, we carry out laboratory investigations of self-organization in a low-pressure test platform for 100-200 mm rod-plane gaps with a needle tip, conical tip and hemispherical tip within 1-10 kPa. The factors influencing the pattern profile are the pressure value, gap length and shape of the electrode, and a variety of pattern structures are observed by changing these factors. With increasing pressure, first the pattern diameter increases and then decreases. With the needle tip, layer structure, single-ring structure and double-ring structure are displayed successively with increasing pressure. With the conical tip, the ring-like structure gradually forms separate spots with increasing pressure. With the hemispherical tip, there are anode spots inside the ring structure. With the increase of gap length, the diameter of the self-organized pattern increases and the profile of the pattern changes. The development process of the pattern contains three key stages: pattern enlargement, pattern stabilization and pattern shrink.

Air-Gapped Structures as Magnetic Elements for Use in Power Processing Systems. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Ohri, A. K.

1977-01-01

Methodical approaches to the design of inductors for use in LC filters and dc-to-dc converters using air gapped magnetic structures are presented. Methods for the analysis and design of full wave rectifier LC filter circuits operating with the inductor current in both the continuous conduction and the discontinuous conduction modes are also described. In the continuous conduction mode, linear circuit analysis techniques are employed, while in the case of the discontinuous mode, the method of analysis requires computer solutions of the piecewise linear differential equations which describe the filter in the time domain. Procedures for designing filter inductors using air gapped cores are presented. The first procedure requires digital computation to yield a design which is optimized in the sense of minimum core volume and minimum number of turns. The second procedure does not yield an optimized design as defined above, but the design can be obtained by hand calculations or with a small calculator. The third procedure is based on the use of specially prepared magnetic core data and provides an easy way to quickly reach a workable design.

Dynamics of a localized spin excitation close to the spin-helix regime

NASA Astrophysics Data System (ADS)

Salis, Gian; Walser, Matthias; Altmann, Patrick; Reichl, Christian; Wegscheider, Werner

2014-03-01

The time evolution of a local spin excitation in a (001)-confined two-dimensional electron gas subjected to Rashba and Dresselhaus spin-orbit interactions of similar strength is investigated theoretically and compared with experimental data. Specifically, the consequences of a finite spatial extension of the initial spin polarization are studied for non-balanced Rashba and Dresselhaus terms and for finite cubic Dresselhaus spin-orbit interaction. We show that the initial out-of-plane spin polarization evolves into a helical spin pattern with a wave number that gradually approaches the value q0 of the persistent spin helix mode. In addition to an exponential decay of the spin polarization that is proportional to both the spin-orbit imbalance and the cubic Dresselhaus term, the finite width w of the spin excitation reduces the spin polarization by a factor that approaches exp(-q02w2 / 2) at longer times. This result bridges the gap between the formation of a long-lived helical spin mode and a spatially homogeneous spin decay described by the Dyakonov-Perel mechanism. This work is financially supported by NCCR QSIT.

Emergent central pattern generator behavior in gap-junction-coupled Hodgkin-Huxley style neuron model.

PubMed

Horn, Kyle G; Memelli, Heraldo; Solomon, Irene C

2012-01-01

Most models of central pattern generators (CPGs) involve two distinct nuclei mutually inhibiting one another via synapses. Here, we present a single-nucleus model of biologically realistic Hodgkin-Huxley neurons with random gap junction coupling. Despite no explicit division of neurons into two groups, we observe a spontaneous division of neurons into two distinct firing groups. In addition, we also demonstrate this phenomenon in a simplified version of the model, highlighting the importance of afterhyperpolarization currents (I(AHP)) to CPGs utilizing gap junction coupling. The properties of these CPGs also appear sensitive to gap junction conductance, probability of gap junction coupling between cells, topology of gap junction coupling, and, to a lesser extent, input current into our simulated nucleus.

Propagational characteristics in a warm hybrid plasmonic waveguide

NASA Astrophysics Data System (ADS)

Mahmodi Moghadam, M.; Shahmansouri, M.; Farokhi, B.

2017-12-01

We theoretically analyze the properties of guided modes in a warm planar conductor-gap-dielectric (CGD) system. The latter consists of a high index dielectric, separated from a warm metallic plasma with a low index nano-sized dielectric layer (gap) by using the hydrodynamic model coupled to Maxwell's equations. The effects of thermal pressure on the confinement and the propagation losses of Hybrid Plasmon Polariton (HPP) modes are studied. We found that the thermal effect leads to a reduction in the effective refractive index as well as in the propagation losses of the HPP mode. Furthermore, the cutoff thickness in the warm CGD waveguide is found to be smaller than that in a cold CGD waveguide. The results may be useful in understanding the essential physics of active/passive Plasmonic devices and chip-scale systems.

Impurity-generated non-Abelions

NASA Astrophysics Data System (ADS)

Simion, G.; Kazakov, A.; Rokhinson, L. P.; Wojtowicz, T.; Lyanda-Geller, Y. B.

2018-06-01

Two classes of topological superconductors and Majorana modes in condensed matter systems are known to date: one in which disorder induced by impurities strongly suppresses topological superconducting gap and is detrimental to Majorana modes, and another where Majorana fermions are protected by a disorder-robust topological superconductor gap. Observation and control of Majorana fermions and other non-Abelions often requires a symmetry of an underlying system leading to a gap in the single-particle or quasiparticle spectra. In semiconductor structures, impurities that provide charge carriers introduce states into the gap and enable conductance and proximity-induced superconductivity via the in-gap states. Thus a third class of topological superconductivity and Majorana modes emerges, in which topological superconductivity and Majorana fermions appear exclusively when impurities generate in-gap states. We show that impurity-enabled topological superconductivity is realized in a quantum Hall ferromagnet, when a helical domain wall is coupled to an s -wave superconductor. As an example of emergence of topological superconductivity in quantum Hall ferromagnets, we consider the integer quantum Hall effect in Mn-doped CdTe quantum wells. Recent experiments on transport through the quantum Hall ferromagnet domain wall in this system indicated a vital role of impurities in the conductance, but left unresolved the question whether impurities preclude generation of Majorana fermions and other non-Abelions in such systems in general. Here, solving a general quantum-mechanical problem of impurity bound states in a system of spin-orbit coupled Landau levels, we demonstrate that impurity-induced Majorana modes emerge at boundaries between topological and conventional superconducting states generated in a domain wall due to proximity to an s superconductor. We consider both short-range disorder and a smooth random potential. The phase diagram of the system is defined by characteristic disorder, gate voltage induced angular momentum splitting of impurity levels, and by a proximity superconducting gap. The phase diagram exhibits two ranges of gate voltage with conventional superconducting order separated by a gate voltage range with topological superconductivity. We show that electrostatic control of domain walls in an integer quantum Hall ferromagnet allows manipulation of Majorana fermions. Ferromagnetic transitions in the fractional quantum Hall regime may lead to the formation and electrostatic control of higher order non-Abelian excitations.

Pulse-periodic generation of supershort avalanche electron beams and X-ray emission

NASA Astrophysics Data System (ADS)

Baksht, E. Kh.; Burachenko, A. G.; Erofeev, M. V.; Tarasenko, V. F.

2014-05-01

Pulse-periodic generation of supershort avalanche electron beams (SAEBs) and X-ray emission in nitrogen, as well as the transition from a single-pulse mode to a pulse-periodic mode with a high repetition frequency, was studied experimentally. It is shown that, in the pulse-periodic mode, the full width at halfmaximum of the SAEB is larger and the decrease rate of the gap voltage is lower than those in the single-pulse mode. It is found that, when the front duration of the voltage pulse at a nitrogen pressure of 90 Torr decreases from 2.5 to 0.3 ns, the X-ray exposure dose in the pulse-periodic mode increases by more than one order of magnitude and the number of SAEB electrons also increases. It is shown that, in the pulse-periodic mode of a diffuse discharge, gas heating in the discharge gap results in a severalfold increase in the SAEB amplitude (the number of electrons in the beam). At a generator voltage of 25 kV, nitrogen pressure of 90 Torr, and pulse repetition frequency of 3.5 kHz, a runaway electron beam was detected behind the anode foil.

Passive harmonic mode locking by mode selection in Fabry-Perot diode lasers with patterned effective index.

PubMed

Bitauld, David; Osborne, Simon; O'Brien, Stephen

2010-07-01

We demonstrate passive harmonic mode locking of a quantum-well laser diode designed to support a discrete comb of Fabry-Perot modes. Spectral filtering of the mode spectrum was achieved using a nonperiodic patterning of the cavity effective index. By selecting six modes spaced at twice the fundamental mode spacing, near-transform-limited pulsed output with 2 ps pulse duration was obtained at a repetition rate of 100 GHz.

Spatio-temporal analysis of irregular vocal fold oscillations: Biphonation due to desynchronization of spatial modes

NASA Astrophysics Data System (ADS)

Neubauer, Jürgen; Mergell, Patrick; Eysholdt, Ulrich; Herzel, Hanspeter

2001-12-01

This report is on direct observation and modal analysis of irregular spatio-temporal vibration patterns of vocal fold pathologies in vivo. The observed oscillation patterns are described quantitatively with multiline kymograms, spectral analysis, and spatio-temporal plots. The complex spatio-temporal vibration patterns are decomposed by empirical orthogonal functions into independent vibratory modes. It is shown quantitatively that biphonation can be induced either by left-right asymmetry or by desynchronized anterior-posterior vibratory modes, and the term ``AP (anterior-posterior) biphonation'' is introduced. The presented phonation examples show that for normal phonation the first two modes sufficiently explain the glottal dynamics. The spatio-temporal oscillation pattern associated with biphonation due to left-right asymmetry can be explained by the first three modes. Higher-order modes are required to describe the pattern for biphonation induced by anterior-posterior vibrations. Spatial irregularity is quantified by an entropy measure, which is significantly higher for irregular phonation than for normal phonation. Two asymmetry measures are introduced: the left-right asymmetry and the anterior-posterior asymmetry, as the ratios of the fundamental frequencies of left and right vocal fold and of anterior-posterior modes, respectively. These quantities clearly differentiate between left-right biphonation and anterior-posterior biphonation. This paper proposes methods to analyze quantitatively irregular vocal fold contour patterns in vivo and complements previous findings of desynchronization of vibration modes in computer modes and in in vitro experiments.

Quantum memories with zero-energy Majorana modes and experimental constraints

NASA Astrophysics Data System (ADS)

Ippoliti, Matteo; Rizzi, Matteo; Giovannetti, Vittorio; Mazza, Leonardo

2016-06-01

In this work we address the problem of realizing a reliable quantum memory based on zero-energy Majorana modes in the presence of experimental constraints on the operations aimed at recovering the information. In particular, we characterize the best recovery operation acting only on the zero-energy Majorana modes and the memory fidelity that can be therewith achieved. In order to understand the effect of such restriction, we discuss two examples of noise models acting on the topological system and compare the amount of information that can be recovered by accessing either the whole system, or the zero modes only, with particular attention to the scaling with the size of the system and the energy gap. We explicitly discuss the case of a thermal bosonic environment inducing a parity-preserving Markovian dynamics in which the memory fidelity achievable via a read-out of the zero modes decays exponentially in time, independent from system size. We argue, however, that even in the presence of said experimental limitations, the Hamiltonian gap is still beneficial to the storage of information.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bahrdt, J.; Baecker, H.-J.; Frentrup, W.

Helmholtzzentrum Berlin has built an APPLE II undulator for the storage ring PETRA III. The device has a total length of 5m and a minimum gap of 11mm. The high magnetic forces in particular in the inclined mode have been analyzed by means of finite element methods (FEM). Specific mechanic components such as flexible joints have been optimized to cope with the gap- and shift-dependent 3D-forces and a sophisticated control and drive system has been implemented. After completion of the device, detailed laser interferometer measurements for all operation modes have been performed. The data are compared to the FEM simulations.

Opportunities and barriers in service delivery through mobile phones (mHealth) for Severe Mental Illnesses in Rajasthan, India: A multi-site study.

PubMed

Jain, Nikhil; Singh, Harful; Koolwal, Ghanshyam Das; Kumar, Sunil; Gupta, Aditya

2015-04-01

Widespread use of mobile technology holds a lot of promise for mental health service delivery in regions where mental health resources are scarce and the treatment gap is large. The felt needs of the clients, and the patterns and barriers of mobile usage must be understood before some intervention can be planned. The study presented in this paper was designed to fill this gap in the region of Rajasthan, India. The study was conducted in three tertiary care hospitals. Clients utilizing services for Severe Mental Illnesses (SMIs) were the participants of the study. Information about ownership, usage patterns and barriers to accessing mobile technology and felt needs in terms of mental health services that could be delivered through mobile phones were sought from the participants. The typical respondents in all three centres were middle-aged, married, Hindu males belonging to lower socio-economic strata from rural background. Seventy two to 92% of participants had access to mobile phone. The most preferred mode of service delivery was through calls. Helpline for crisis resolution and telephonic follow-up of stable patients emerged as the most felt need of the participants. Barriers to mobile phones usage included affordability, lack of necessity, poor signal. In conclusion, the study shows that the access to mobile phones amongst clients receiving services for SMI is widespread and offers new opportunities in service delivery in the region. Copyright © 2015 Elsevier B.V. All rights reserved.

Molecular-dynamics simulation of a model with incommensurate phases

NASA Astrophysics Data System (ADS)

Parlinski, Krzysztof

1987-06-01

Two-dimensional models of displacive and order-disorder behavior, in the form of crystallites with free boundary conditions and with one-dimensional incommensurate and/or commensurate phases, have been studied using the molecular-dynamics method. The incommensurate phase can be characterized with any wave vector by the appropriate choice of potential-energy parameters. The ground-state devil's staircases of the models are complete. By a series of cooling runs the phase diagram is established. The map of the particle configuration, a result of the cooling run, formed a nonideal incommensurate phase. In the diffraction pattern of that configuration the intensities of the satellites, especially those of higher order, are considerably lower. The displacive system shows a soft, underdamped phonon mode, which with lowering temperature condenses at the critical wave vector, producing the incommensurate phase, in which the phase and amplitude modes are observed. The phase-mode dispersion curve does not show a gap. Adding 2% point defects to the system does not influence the phase and amplitude modes. The kinetics of the variation of the wave-vector modulation of the incommensurate phase has also been studied. The relevant non- equilibrium devil's staircase exhibits quasisteps at irrational numbers which are attributed to the nucleation and growth of new incommensurate periods observed as a stripple. Examples of nucleation inside and at the edges of the crystallite are given. Point defects hinder the propagation of the deperiodization line which borders the stripple.

Gap Gene Regulatory Dynamics Evolve along a Genotype Network

PubMed Central

Crombach, Anton; Wotton, Karl R.; Jiménez-Guri, Eva; Jaeger, Johannes

2016-01-01

Developmental gene networks implement the dynamic regulatory mechanisms that pattern and shape the organism. Over evolutionary time, the wiring of these networks changes, yet the patterning outcome is often preserved, a phenomenon known as “system drift.” System drift is illustrated by the gap gene network—involved in segmental patterning—in dipteran insects. In the classic model organism Drosophila melanogaster and the nonmodel scuttle fly Megaselia abdita, early activation and placement of gap gene expression domains show significant quantitative differences, yet the final patterning output of the system is essentially identical in both species. In this detailed modeling analysis of system drift, we use gene circuits which are fit to quantitative gap gene expression data in M. abdita and compare them with an equivalent set of models from D. melanogaster. The results of this comparative analysis show precisely how compensatory regulatory mechanisms achieve equivalent final patterns in both species. We discuss the larger implications of the work in terms of “genotype networks” and the ways in which the structure of regulatory networks can influence patterns of evolutionary change (evolvability). PMID:26796549

Gap junctions composed of connexins 41.8 and 39.4 are essential for colour pattern formation in zebrafish

PubMed Central

Irion, Uwe; Frohnhöfer, Hans Georg; Krauss, Jana; Çolak Champollion, Tuǧba; Maischein, Hans-Martin; Geiger-Rudolph, Silke; Weiler, Christian; Nüsslein-Volhard, Christiane

2014-01-01

Interactions between all three pigment cell types are required to form the stripe pattern of adult zebrafish (Danio rerio), but their molecular nature is poorly understood. Mutations in leopard (leo), encoding Connexin 41.8 (Cx41.8), a gap junction subunit, cause a phenotypic series of spotted patterns. A new dominant allele, leotK3, leads to a complete loss of the pattern, suggesting a dominant negative impact on another component of gap junctions. In a genetic screen, we identified this component as Cx39.4 (luchs). Loss-of-function alleles demonstrate that luchs is required for stripe formation in zebrafish; however, the fins are almost not affected. Double mutants and chimeras, which show that leo and luchs are only required in xanthophores and melanophores, but not in iridophores, suggest that both connexins form heteromeric gap junctions. The phenotypes indicate that these promote homotypic interactions between melanophores and xanthophores, respectively, and those cells instruct the patterning of the iridophores. DOI: http://dx.doi.org/10.7554/eLife.05125.001 PMID:25535837

Comparative Evaluation of Marginal and Internal Gap of Co-Cr Copings Fabricated from Conventional Wax Pattern, 3D Printed Resin Pattern and DMLS Tech: An In Vitro Study.

PubMed

Bhaskaran, Eswaran; Azhagarasan, N S; Miglani, Saket; Ilango, T; Krishna, G Phani; Gajapathi, B

2013-09-01

Accuracy of the fit of the restoration has always remained as one of the primary factors in determining success of the restoration. A well fitting restoration needs to be accurate both along its margins and internal surface. This study was conducted to comparatively evaluate the marginal gap and internal gap of cobalt-chromium (Co-Cr) copings fabricated by conventional casting procedures and with direct metal laser sintering (DMLS) technique. Among the total of 30 test samples 10 cast copings were made from inlay casting wax and 10 from 3D printed resin pattern. 10 copings were obtained from DMLS technique. All the 30 test samples were then cemented sequentially on stainless steel model using pressure indicating paste and evaluated for vertical marginal gap in 8 predetermined reference areas. All copings were then removed and partially sectioned and cemented sequentially on same master model for evaluation of internal gap at 4 predetermined reference areas. Both marginal gap and internal gap were measured in microns using video measuring system (VMS2010F). The results obtained for both marginal and internal gap were statistically analyzed and the values fall within the clinically acceptable range. The DMLS technique had an edge over the other two techniques used, as it exhibited minimal gap in the marginal region which is an area of chief concern.

Mass hierarchy, mass gap and corrections to Newton's law on thick branes with Poincaré symmetry

NASA Astrophysics Data System (ADS)

Barbosa-Cendejas, Nandinii; Herrera-Aguilar, Alfredo; Kanakoglou, Konstantinos; Nucamendi, Ulises; Quiros, Israel

2014-01-01

We consider a scalar thick brane configuration arising in a 5D theory of gravity coupled to a self-interacting scalar field in a Riemannian manifold. We start from known classical solutions of the corresponding field equations and elaborate on the physics of the transverse traceless modes of linear fluctuations of the classical background, which obey a Schrödinger-like equation. We further consider two special cases in which this equation can be solved analytically for any massive mode with , in contrast with numerical approaches, allowing us to study in closed form the massive spectrum of Kaluza-Klein (KK) excitations and to analytically compute the corrections to Newton's law in the thin brane limit. In the first case we consider a novel solution with a mass gap in the spectrum of KK fluctuations with two bound states—the massless 4D graviton free of tachyonic instabilities and a massive KK excitation—as well as a tower of continuous massive KK modes which obey a Legendre equation. The mass gap is defined by the inverse of the brane thickness, allowing us to get rid of the potentially dangerous multiplicity of arbitrarily light KK modes. It is shown that due to this lucky circumstance, the solution of the mass hierarchy problem is much simpler and transparent than in the thin Randall-Sundrum (RS) two-brane configuration. In the second case we present a smooth version of the RS model with a single massless bound state, which accounts for the 4D graviton, and a sector of continuous fluctuation modes with no mass gap, which obey a confluent Heun equation in the Ince limit. (The latter seems to have physical applications for the first time within braneworld models). For this solution the mass hierarchy problem is solved with positive branes as in the Lykken-Randall (LR) model and the model is completely free of naked singularities. We also show that the scalar-tensor system is stable under scalar perturbations with no scalar modes localized on the braneworld configuration.

Time-resolved X-ray excited optical luminescence using an optical streak camera

NASA Astrophysics Data System (ADS)

Ward, M. J.; Regier, T. Z.; Vogt, J. M.; Gordon, R. A.; Han, W.-Q.; Sham, T. K.

2013-03-01

We report the development of a time-resolved XEOL (TR-XEOL) system that employs an optical streak camera. We have conducted TR-XEOL experiments at the Canadian Light Source (CLS) operating in single bunch mode with a 570 ns dark gap and 35 ps electron bunch pulse, and at the Advanced Photon Source (APS) operating in top-up mode with a 153 ns dark gap and 33.5 ps electron bunch pulse. To illustrate the power of this technique we measured the TR-XEOL of solid-solution nanopowders of gallium nitride - zinc oxide, and for the first time have been able to resolve near-band-gap (NBG) optical luminescence emission from these materials. Herein we will discuss the development of the streak camera TR-XEOL technique and its application to the study of these novel materials.

Simultaneous large band gaps and localization of electromagnetic and elastic waves in defect-free quasicrystals.

PubMed

Yu, Tianbao; Wang, Zhong; Liu, Wenxing; Wang, Tongbiao; Liu, Nianhua; Liao, Qinghua

2016-04-18

We report numerically large and complete photonic and phononic band gaps that simultaneously exist in eight-fold phoxonic quasicrystals (PhXQCs). PhXQCs can possess simultaneous photonic and phononic band gaps over a wide range of geometric parameters. Abundant localized modes can be achieved in defect-free PhXQCs for all photonic and phononic polarizations. These defect-free localized modes exhibit multiform spatial distributions and can confine simultaneously electromagnetic and elastic waves in a large area, thereby providing rich selectivity and enlarging the interaction space of optical and elastic waves. The simulated results based on finite element method show that quasiperiodic structures formed of both solid rods in air and holes in solid materials can simultaneously confine and tailor electromagnetic and elastic waves; these structures showed advantages over the periodic counterparts.

Vortex-induced vibrations of two cylinders in tandem arrangement in the proximity–wake interference region

PubMed Central

BORAZJANI, IMAN; SOTIROPOULOS, FOTIS

2009-01-01

We investigate numerically vortex-induced vibrations (VIV) of two identical two-dimensional elastically mounted cylinders in tandem in the proximity–wake interference regime at Reynolds number Re = 200 for systems having both one (transverse vibrations) and two (transverse and in-line) degrees of freedom (1-DOF and 2-DOF, respectively). For the 1-DOF system the computed results are in good qualitative agreement with available experiments at higher Reynolds numbers. Similar to these experiments our simulations reveal: (1) larger amplitudes of motion and a wider lock-in region for the tandem arrangement when compared with an isolated cylinder; (2) that at low reduced velocities the vibration amplitude of the front cylinder exceeds that of the rear cylinder; and (3) that above a threshold reduced velocity, large-amplitude VIV are excited for the rear cylinder with amplitudes significantly larger than those of the front cylinder. By analysing the simulated flow patterns we identify the VIV excitation mechanisms that lead to such complex responses and elucidate the near-wake vorticity dynamics and vortex-shedding modes excited in each case. We show that at low reduced velocities vortex shedding provides the initial excitation mechanism, which gives rise to a vertical separation between the two cylinders. When this vertical separation exceeds one cylinder diameter, however, a significant portion of the incoming flow is able to pass through the gap between the two cylinders and the gap-flow mechanism starts to dominate the VIV dynamics. The gap flow is able to periodically force either the top or the bottom shear layer of the front cylinder into the gap region, setting off a series of very complex vortex-to-vortex and vortex-to-cylinder interactions, which induces pressure gradients that result in a large oscillatory force in phase with the vortex shedding and lead to the experimentally observed larger vibration amplitudes. When the vortex shedding is the dominant mechanism the front cylinder vibration amplitude is larger than that of the rear cylinder. The reversing of this trend above a threshold reduced velocity is associated with the onset of the gap flow. The important role of the gap flow is further illustrated via a series of simulations for the 2-DOF system. We show that when the gap-flow mechanism is triggered, the 2-DOF system can develop and sustain large VIV amplitudes comparable to those observed in the corresponding (same reduced velocity) 1-DOF system. For sufficiently high reduced velocities, however, the two cylinders in the 2-DOF system approach each other, thus significantly reducing the size of the gap region. In such cases the gap flow is entirely eliminated, and the two cylinders vibrate together as a single body with vibration amplitudes up to 50% lower than the amplitudes of the corresponding 1-DOF in which the gap flow is active. Three-dimensional simulations are also carried out to examine the adequacy of two-dimensional simulations for describing the dynamic response of the tandem system at Re = 200. It is shown that even though the wake transitions to a weakly three-dimensional state when the gap flow is active, the three-dimensional modes are too weak to affect the dynamic response of the system, which is found to be identical to that obtained from the two-dimensional computations. PMID:19693281

Entangled singularity patterns of photons in Ince-Gauss modes

NASA Astrophysics Data System (ADS)

Krenn, Mario; Fickler, Robert; Huber, Marcus; Lapkiewicz, Radek; Plick, William; Ramelow, Sven; Zeilinger, Anton

2013-01-01

Photons with complex spatial mode structures open up possibilities for new fundamental high-dimensional quantum experiments and for novel quantum information tasks. Here we show entanglement of photons with complex vortex and singularity patterns called Ince-Gauss modes. In these modes, the position and number of singularities vary depending on the mode parameters. We verify two-dimensional and three-dimensional entanglement of Ince-Gauss modes. By measuring one photon and thereby defining its singularity pattern, we nonlocally steer the singularity structure of its entangled partner, while the initial singularity structure of the photons is undefined. In addition we measure an Ince-Gauss specific quantum-correlation function with possible use in future quantum communication protocols.

Discrete monotron oscillator having one-half wavelength coaxial resonator with one-quarter wavelength gap spacing

DOEpatents

Carlsten, B.E.; Haynes, W.B.

1998-02-03

A discrete monotron oscillator for use in a high power microwave device is formed with a microwave oscillator having a half-wavelength resonant coaxial microwave cavity operating in fundamental TEM mode for microwave oscillation with an inner conductor defining a drift tube for propagating an electron beam and an outer conductor coaxial with the inner conductor. The inner conductor defines a modulating gap and an extraction gap downstream of the modulating gap. The modulating gap and the extraction gap connect the coaxial microwave cavity with the drift tube so that energy for the microwave oscillation is extracted from the electron beam at the extraction gap and modulates the electron beam at the modulating gap. For high power operation, an annular electron beam is used. 8 figs.

Discrete monotron oscillator having one-half wavelength coaxial resonator with one-quarter wavelength gap spacing

DOEpatents

Carlsten, Bruce E.; Haynes, William B.

1998-01-01

A discrete monotron oscillator for use in a high power microwave device is formed with a microwave oscillator having a half-wavelength resonant coaxial microwave cavity operating in fundamental TEM mode for microwave oscillation with an inner conductor defining a drift tube for propagating an electron beam and an outer conductor coaxial with the inner conductor. The inner conductor defines a modulating gap and an extraction gap downstream of the modulating gap. The modulating gap and the extraction gap connect the coaxial microwave cavity with the drift tube so that energy for the microwave oscillation is extracted from the electron beam at the extraction gap and modulates the electron beam at the modulating gap. For high power operation, an annular electron beam is used.

A model of the transverse modes of stable and unstable porro-prism resonators using symmetry considerations

NASA Astrophysics Data System (ADS)

Burger, Liesl; Forbes, Andrew

2007-09-01

A simple model of a Porro prism laser resonator has been found to correctly predict the formation of the "petal" mode patterns typical of these resonators. A geometrical analysis of the petals suggests that these petals are the lowest-order modes of this type of resonator. Further use of the model reveals the formation of more complex beam patterns, and the nature of these patterns is investigated. Also, the output of stable and unstable resonator modes is presented.

Study on tip leakage vortex cavitating flows using a visualization method

NASA Astrophysics Data System (ADS)

Zhao, Yu; Jiang, Yutong; Cao, Xiaolong; Wang, Guoyu

2018-01-01

Experimental investigations of unsteady cavitating flows in a hydrofoil tip leakage region with different gap sizes are conducted to highlight the development of gap cavitation. The experiments were taken in a closed cavitation tunnel, during which high-speed camera had been used to capture the cavitation patterns. A new visualization method based on image processing was developed to capture time-dependent cavitation patterns. The results show that the visualization method can effectively capture the cavitation patterns in the tip region, including both the attached cavity in the gap and the tip leakage vortex (TLV) cavity near the trailing edge. Moreover, with the decrease of cavitation number, the TLV cavity develops from a rapid onset-growth-collapse process to a continuous process, and extends both upstream and downstream. The attached cavity in the gap develops gradually stretching beyond the gap and combines with the vortex cavity to form the triangle cavitating region. Furthermore, the influences of gap size on the cavitation are also discussed. The gap size has a great influence on the loss across the gap, and hence the locations of the inception attached cavity. Besides, inception locations and extending direction of the TLV cavity with different gap sizes also differ. The TLV in the case with τ = 0.061 is more likely to be jet-like compared with that in the case with τ = 0.024, and the gap size has a great influence on the TLV strength.

How does the plasmonic enhancement of molecular absorption depend on the energy gap between molecular excitation and plasmon modes: a mixed TDDFT/FDTD investigation.

PubMed

Sun, Jin; Li, Guang; Liang, WanZhen

2015-07-14

A real-time time-dependent density functional theory coupled with the classical electrodynamics finite difference time domain technique is employed to systematically investigate the optical properties of hybrid systems composed of silver nanoparticles (NPs) and organic adsorbates. The results demonstrate that the molecular absorption spectra throughout the whole energy range can be enhanced by the surface plasmon resonance of Ag NPs; however, the absorption enhancement ratio (AER) for each absorption band differs significantly from the others, leading to the quite different spectral profiles of the hybrid complexes in contrast to those of isolated molecules or sole NPs. Detailed investigations reveal that the AER is sensitive to the energy gap between the molecular excitation and plasmon modes. As anticipated, two separate absorption bands, corresponding to the isolated molecules and sole NPs, have been observed at a large energy gap. When the energy gap approaches zero, the molecular excitation strongly couples with the plasmon mode to form the hybrid exciton band, which possesses the significantly enhanced absorption intensity, a red-shifted peak position, a surprising strongly asymmetric shape of the absorption band, and the nonlinear Fano effect. Furthermore, the dependence of surface localized fields and the scattering response functions (SRFs) on the geometrical parameters of NPs, the NP-molecule separation distance, and the external-field polarizations has also been depicted.

Optical Potential Field Mapping System

NASA Technical Reports Server (NTRS)

Reid, Max B. (Inventor)

1996-01-01

The present invention relates to an optical system for creating a potential field map of a bounded two dimensional region containing a goal location and an arbitrary number of obstacles. The potential field mapping system has an imaging device and a processor. Two image writing modes are used by the imaging device, electron deposition and electron depletion. Patterns written in electron deposition mode appear black and expand. Patterns written in electron depletion mode are sharp and appear white. The generated image represents a robot's workspace. The imaging device under processor control then writes a goal location in the work-space using the electron deposition mode. The black image of the goal expands in the workspace. The processor stores the generated images, and uses them to generate a feedback pattern. The feedback pattern is written in the workspace by the imaging device in the electron deposition mode to enhance the expansion of the original goal pattern. After the feedback pattern is written, an obstacle pattern is written by the imaging device in the electron depletion mode to represent the obstacles in the robot's workspace. The processor compares a stored image to a previously stored image to determine a change therebetween. When no change occurs, the processor averages the stored images to produce the potential field map.

Continuum absorption in the vicinity of the toroidicity-induced Alfvén gap

DOE PAGES

Li, M.; Breizman, B. N.; Zheng, L. J.; ...

2015-12-04

Excitation of Alfvén modes is commonly viewed as a concern for energetic particle confinement in burning plasmas. The 3.5 MeValpha particles produced by fusion may be affected as well as other fast ions in both present and future devices. Continuum damping of such modes is one of the key factors that determine their excitation thresholds and saturation levels. This work examines the resonant dissipative response of the Alfvén continuum to an oscillating driving current when the driving frequency is slightly outside the edges of the toroidicity-induced spectral gap. The problem is largely motivated by the need to describe the continuummore » absorption in the frequency sweeping events. Akey element of this problem is the negative interference of the two closely spaced continuum crossing points.Weexplain why the lower and upper edges of the gap can have very different continuum absorption features. Lastly, the difference is associated with an eigenmode whose frequency can be arbitrarily close to the upper edge of the gap whereas the lower edge of the gap is always a finite distance away from the closest eigenmode.« less

Larval adaptations and patterns of brachiopod diversity in space and time

NASA Technical Reports Server (NTRS)

Valentine, J. W.; Jablonski, D.

1983-01-01

Modern biodistributional patterns suggest that modes of larval development are a factor in determining the patterns of diversity in benthic invertebrates. Paleozoic brachiopods had diversity patterns suggesting that they possessed both planktotrophic and nonplanktotrophic modes. It is presently hypothesized that the planktotrophic lineages were lost to extinction, largely or entirely during the Permian-Triassic event, and that the failure of the articulate brachiopods to regain their former importance is substantially due to their nonplanktotrophic developmental mode.

Quantum fluctuations and gapped Goldstone modes in spinor Bose-Einstein condensates

NASA Astrophysics Data System (ADS)

Beekman, Aron

2015-03-01

The classical Heisenberg ferromagnet is an exact eigenstate of the quantum Hamiltonian and therefore has no quantum fluctuations. Furthermore it has a reduced number of Goldstone modes, an order parameter that is itself a symmetry generator, is a highest-weight state for the spin algebra, and has no tower of states of vanishing energy. We derive the connection between all these properties and provide general criteria for their presence in other spontaneously-broken symmetry states. The phletora of groundstates in spinor Bose-Einstein condensates is an ideal testing ground for these predictions. In particular the phases with non-maximal polarization (e.g. the F-phase in spin-3 condensates) have an additional gapped mode that is a partner to the quadratically dispersing Goldstone mode, as compared to the maximally polarized, ferromagnetic phase. Furthermore there is a fundamental limit to the coherence time of superpositions in the non-maximally polarized state, which should manifest itself for small-size systems.

Ultra-high-Q three-dimensional photonic crystal nano-resonators.

PubMed

Tang, Lingling; Yoshie, Tomoyuki

2007-12-10

Two nano-resonator modes are designed in a woodpile three-dimensional photonic crystal by the modulation of unit cell size along a low-loss optical waveguide. One is a dipole mode with 2.88 cubic half-wavelengths mode volume. The other is a quadrupole mode with 8.3 cubic half-wavelengths mode volume. Light is three-dimensionally confined by a complete photonic band gap so that, in the analyzed range, the quality factor exponentially increases as the increase in the number of unit cells used for confinement of light.

Optical phonon modes of III-V nanoparticles and indium phosphide/II-VI core-shell nanoparticles: A Raman and infrared study

NASA Astrophysics Data System (ADS)

Manciu, Felicia Speranta

The prospects for realizing efficient nanoparticle light emitters in the visible/near IR for communications and bio-medical applications have benefited from progress in chemical fabrication of nanoparticles. III-V semiconductor nanopaticles such as GaP and InP are promising materials for the development of "blue" and "green" emitters, respectively, due to their large effective bandgaps. Enhanced emission efficiency has been achieved for core-shell nanoparticles, since inorganic shell materials increase electronic tunability and may decrease surface defects that often occur for nanoparticles capped with organic molecules. Also, the emission wavelength of InP nanoparticle cores can be tuned from green to red by changing the shell material in InP/II-VI core-shell nanoparticles. Investigations of phonon modes in nanocrystals are of both fundamental and applied interest. In the former case the optical phonon modes, such as surface/interface modes, are dependent on the nanoparticle dimensions, and also can provide information about dynamical properties of the nanoparticles and test the validity of various theoretical approaches. In the latter case the vibronic properties of nanoparticle emitters are controlled by confined phonons and modifications of the electron-phonon interaction by the confinement. Thus, the objective of the present thesis is the detailed study of the phonon modes of III-V nanoparticles (GaP and InP) and InP/II-VI core-shell nanoparticles by IR absorption and Raman scattering spectroscopies, and an elucidation of their complex vibrational properties. With the exception of three samples (two GaP and one InP), all samples were synthesized by a novel colloidal chemistry method, which does not requires added surfactant, but rather treatment of the corresponding precursors in octadecene noncoordinative solvent. Sample quality was characterized by ED, TEM and X-ray diffraction. Based on a comparison with a dielectric continuum model, the observed features in the IR and Raman results are assigned to the surface optical (SO) modes of the corresponding nanoparticles (InP and GaP), and to SO/interface modes for InP/II-VI core-shell nanoparticles. For the latter systems, an evaluation of the ratio of the shell material thickness to the core radius is achieved. Reasonable agreement is obtained between the Raman and FIR results, as well as with the calculations. (Abstract shortened by UMI.)

High efficient OLED displays prepared with the air-gapped bridges on quantum dot patterns for optical recycling

PubMed Central

Kim, Hyo-Jun; Shin, Min-Ho; Kim, Joo-Suc; Kim, Se-Eun; Kim, Young-Joo

2017-01-01

An optically efficient structure was proposed and fabricated to realize high brightness organic light emitting diode (OLED) displays based on a white OLED prepared with the air-gapped bridges on the quantum dot (QD) patterns. Compared with a conventional white OLED display, in our experiments, the optical intensity of the proposed OLED display shows the enhancement of 58.2% in the red color and 16.8% in the green color after applying the air-gapped bridge structure on QD patterns of 20 wt% concentration. This enhancement comes from the two facts that the QD patterns downconvert unnecessary blue or blue/green light to the required green or red light and the air-gapped bridges increase the color conversion efficiency of QDs by optical recycling using total internal reflection (TIR) at the interface. In addition, the color gamut of the proposed OLED display increases from 65.5 to 75.9% (NTSC x, y ratio) due to the narrow emission spectra of QDs. PMID:28211516

High efficient OLED displays prepared with the air-gapped bridges on quantum dot patterns for optical recycling

NASA Astrophysics Data System (ADS)

Kim, Hyo-Jun; Shin, Min-Ho; Kim, Joo-Suc; Kim, Se-Eun; Kim, Young-Joo

2017-02-01

An optically efficient structure was proposed and fabricated to realize high brightness organic light emitting diode (OLED) displays based on a white OLED prepared with the air-gapped bridges on the quantum dot (QD) patterns. Compared with a conventional white OLED display, in our experiments, the optical intensity of the proposed OLED display shows the enhancement of 58.2% in the red color and 16.8% in the green color after applying the air-gapped bridge structure on QD patterns of 20 wt% concentration. This enhancement comes from the two facts that the QD patterns downconvert unnecessary blue or blue/green light to the required green or red light and the air-gapped bridges increase the color conversion efficiency of QDs by optical recycling using total internal reflection (TIR) at the interface. In addition, the color gamut of the proposed OLED display increases from 65.5 to 75.9% (NTSC x, y ratio) due to the narrow emission spectra of QDs.

High efficient OLED displays prepared with the air-gapped bridges on quantum dot patterns for optical recycling.

PubMed

Kim, Hyo-Jun; Shin, Min-Ho; Kim, Joo-Suc; Kim, Se-Eun; Kim, Young-Joo

2017-02-17

An optically efficient structure was proposed and fabricated to realize high brightness organic light emitting diode (OLED) displays based on a white OLED prepared with the air-gapped bridges on the quantum dot (QD) patterns. Compared with a conventional white OLED display, in our experiments, the optical intensity of the proposed OLED display shows the enhancement of 58.2% in the red color and 16.8% in the green color after applying the air-gapped bridge structure on QD patterns of 20 wt% concentration. This enhancement comes from the two facts that the QD patterns downconvert unnecessary blue or blue/green light to the required green or red light and the air-gapped bridges increase the color conversion efficiency of QDs by optical recycling using total internal reflection (TIR) at the interface. In addition, the color gamut of the proposed OLED display increases from 65.5 to 75.9% (NTSC x, y ratio) due to the narrow emission spectra of QDs.

Effects of tip-substrate gap, deposition temperature, holding time, and pull-off velocity on dip-pen lithography investigated using molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Wu, Cheng-Da; Fang, Te-Hua; Lin, Jen-Fin

2012-05-01

The process parameters in the dip-pen nanolithography process, including tip-substrate gap, deposition temperature, holding time, and pull-off velocity are evaluated in terms of the mechanism of molecular transference, alkanethiol meniscus characteristic, surface adsorbed energy, and pattern formation using molecular dynamics simulations. The simulation results clearly show that the optimum deposition occurs at a smaller tip-substrate gap, a slower pull-off velocity, a higher temperature, and a longer holding time. The pattern area increases with decreasing tip-substrate gap and increasing deposition temperature and holding time. With an increase in deposition temperature, the molecular transfer ability significantly increases. Pattern height is a function of meniscus length. When the pull-off velocity is decreased, the pattern height increases. The height of the neck in meniscus decreases and the neck width increases with holding time. Meniscus size increases with increasing deposition temperature and holding time.

Two modes of the silk road pattern and their interannual variability simulated by LASG/IAP AGCM SAMIL2.0

NASA Astrophysics Data System (ADS)

Song, Fengfei; Zhou, Tianjun; Wang, Lu

2013-05-01

In this study, two modes of the Silk Road pattern were investigated using NCEP2 reanalysis data and the simulation produced by Spectral Atmospheric Circulation Model of IAP LASG, Version 2 (SAMIL2.0) that was forced by SST observation data. The horizontal distribution of both modes were reasonably reproduced by the simulation, with a pattern correlation coefficient of 0.63 for the first mode and 0.62 for the second mode. The wave train was maintained by barotropic energy conversion (denoted as CK) and baroclinic energy conversion (denoted as CP) from the mean flow. The distribution of CK was dominated by its meridional component (CK y ) in both modes. When integrated spatially, CK y was more efficient than its zonal component (CK x ) in the first mode but less in the second mode. The distribution and efficiency of CK were not captured well by SAMIL2.0. However, the model performed reasonably well at reproducing the distribution and efficiency of CP in both modes. Because CP is more efficient than CK, the spatial patterns of the Silk Road pattern were well reproduced. Interestingly, the temporal phase of the second mode was well captured by a single-member simulation. However, further analysis of other ensemble runs demonstrated that the successful reproduction of the temporal phase was a result of internal variability rather than a signal of SST forcing. The analysis shows that the observed temporal variations of both CP and CK were poorly reproduced, leading to the low accuracy of the temporal phase of the Silk Road pattern in the simulation.

Observation and discrimination of the mode patterns in a micron-sized hollow optical fiber and its synthetic measurements: far-field micro-imaging technique

NASA Astrophysics Data System (ADS)

Yin, Jianping; Kim, Kihwan; Shim, Wooshik; Zhu, Yifu; Jhe, Wonho

1998-08-01

We report a far-field micro-imaging technique that is used for the observation and discrimination of the mode patterns in a micron-sized hollow optical fiber as well as for the synthetic measurement of the fiber. By using an M-20X microscope objective lens, we obtained images, magnified by a factor of about 460, from the mode patterns at an output end facet of the hollow fiber with relative measurement accuracy better than 3%. This method can be used for clear identification of the mode patterns in the hollow fiber and detailed study of the relationship between the excitation conditions and the excited modes in the hollow fiber. Moreover, it is useful for the measurement of the geometrical sizes of the hollow fiber end and for testing the coupling efficiencies of the core and cladding modes in their mixed mode pattern. In addition, this method can be also used in the generation of a dark hollow laser beam with 10-micrometers dark-spot size and the measurement of the focused- spot size of a Gaussian laser beam with about 1-micrometers diameter.

The locking and unlocking thresholds for tearing modes in a cylindrical tokamak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Wenlong; Zhu, Ping, E-mail: pzhu@ustc.edu.cn; Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706

2016-03-15

The locking and unlocking thresholds for tearing modes are in general different. In this work, the physics origin for this difference is illustrated from theory analysis, and a numerical procedure is developed to find both locking and unlocking thresholds. In particular, a new scaling law for the unlocking threshold that is valid in both weak and strong rotation regimes has been derived from the lowest amplitude of the RMP (resonant magnetic perturbation) allowed for the locked-mode solution. Above the unlocking threshold, the criterion for the phase-flip instability is extended to identify the entire locked-mode states. Two different regimes of themore » RMP amplitude in terms of the accessibility of the locked-mode states have been found. In the first regime, the locked-mode state may or may not be accessible depending on the initial conditions of an evolving island. In the second regime, the locked-mode state can always be reached regardless of the initial conditions of the tearing mode. The lowest RMP amplitude for the second regime is determined to be the mode-locking threshold. The different characteristics of the two regimes above the unlocking threshold reveal the underlying physics for the gap between the locking and unlocking thresholds and provide an explanation for the closely related and widely observed hysteresis phenomena in island evolution during the sweeping process of the RMP amplitude up and down across that threshold gap.« less

Deterministic multidimensional nonuniform gap sampling.

PubMed

Worley, Bradley; Powers, Robert

2015-12-01

Born from empirical observations in nonuniformly sampled multidimensional NMR data relating to gaps between sampled points, the Poisson-gap sampling method has enjoyed widespread use in biomolecular NMR. While the majority of nonuniform sampling schemes are fully randomly drawn from probability densities that vary over a Nyquist grid, the Poisson-gap scheme employs constrained random deviates to minimize the gaps between sampled grid points. We describe a deterministic gap sampling method, based on the average behavior of Poisson-gap sampling, which performs comparably to its random counterpart with the additional benefit of completely deterministic behavior. We also introduce a general algorithm for multidimensional nonuniform sampling based on a gap equation, and apply it to yield a deterministic sampling scheme that combines burst-mode sampling features with those of Poisson-gap schemes. Finally, we derive a relationship between stochastic gap equations and the expectation value of their sampling probability densities. Copyright © 2015 Elsevier Inc. All rights reserved.

Plexciton Dirac points and topological modes

DOE PAGES

Yuen-Zhou, Joel; Saikin, Semion K.; Zhu, Tony; ...

2016-06-09

Plexcitons are polaritonic modes that result from the strong coupling between excitons and plasmons. Here, we consider plexcitons emerging from the interaction of excitons in an organic molecular layer with surface plasmons in a metallic film. We predict the emergence of Dirac cones in the two-dimensional band-structure of plexcitons due to the inherent alignment of the excitonic transitions in the organic layer. An external magnetic field opens a gap between the Dirac cones if the plexciton system is interfaced with a magneto-optical layer. The resulting energy gap becomes populated with topologically protected one-way modes, which travel at the interface ofmore » this plexcitonic system. Furthermore, our theoretical proposal suggests that plexcitons are a convenient and simple platform for the exploration of exotic phases of matter and for the control of energy flow at the nanoscale.« less

Coherent perfect absorption mediated enhancement of transverse spin in a gap plasmon guide

NASA Astrophysics Data System (ADS)

Mukherjee, Samyobrata; Dutta Gupta, Subhasish

2017-01-01

We consider a symmetric gap plasmon guide (a folded Kretschmann configuration) supporting both symmetric and antisymmetric coupled surface plasmons. We calculate the transverse spin under illumination from both the sides like in coherent perfect absorption (CPA), whereby all the incident light can be absorbed to excite one of the modes of the structure. Significant enhancement in the transverse spin is shown to be possible when the CPA dip and the mode excitation are at the same frequency. The enhancement results from CPA-mediated total transfer of the incident light to either of the coupled modes and the associated large local fields. The effect is shown to be robust against small deviations from the symmetric structure. The transverse spin is localized in the structure since in the ambient dielectric there are only incident plane waves lacking any structure.

The gap-startle paradigm to assess auditory temporal processing: Bridging animal and human research.

PubMed

Fournier, Philippe; Hébert, Sylvie

2016-05-01

The gap-prepulse inhibition of the acoustic startle (GPIAS) paradigm is the primary test used in animal research to identify gap detection thresholds and impairment. When a silent gap is presented shortly before a loud startling stimulus, the startle reflex is inhibited and the extent of inhibition is assumed to reflect detection. Here, we applied the same paradigm in humans. One hundred and fifty-seven normal-hearing participants were tested using one of five gap durations (5, 25, 50, 100, 200 ms) in one of the following two paradigms-gap-embedded in or gap-following-the continuous background noise. The duration-inhibition relationship was observable for both conditions but followed different patterns. In the gap-embedded paradigm, GPIAS increased significantly with gap duration up to 50 ms and then more slowly up to 200 ms (trend only). In contrast, in the gap-following paradigm, significant inhibition-different from 0--was observable only at gap durations from 50 to 200 ms. The finding that different patterns are found depending on gap position within the background noise is compatible with distinct mechanisms underlying each of the two paradigms. © 2016 Society for Psychophysiological Research.

Cleaved-coupled nanowire lasers

PubMed Central

Gao, Hanwei; Fu, Anthony; Andrews, Sean C.; Yang, Peidong

2013-01-01

The miniaturization of optoelectronic devices is essential for the continued success of photonic technologies. Nanowires have been identified as potential building blocks that mimic conventional photonic components such as interconnects, waveguides, and optical cavities at the nanoscale. Semiconductor nanowires with high optical gain offer promising solutions for lasers with small footprints and low power consumption. Although much effort has been directed toward controlling their size, shape, and composition, most nanowire lasers currently suffer from emitting at multiple frequencies simultaneously, arising from the longitudinal modes native to simple Fabry–Pérot cavities. Cleaved-coupled cavities, two Fabry–Pérot cavities that are axially coupled through an air gap, are a promising architecture to produce single-frequency emission. The miniaturization of this concept, however, imposes a restriction on the dimensions of the intercavity gaps because severe optical losses are incurred when the cross-sectional dimensions of cavities become comparable to the lasing wavelength. Here we theoretically investigate and experimentally demonstrate spectral manipulation of lasing modes by creating cleaved-coupled cavities in gallium nitride (GaN) nanowires. Lasing operation at a single UV wavelength at room temperature was achieved using nanoscale gaps to create the smallest cleaved-coupled cavities to date. Besides the reduced number of lasing modes, the cleaved-coupled nanowires also operate with a lower threshold gain than that of the individual component nanowires. Good agreement was found between the measured lasing spectra and the predicted spectral modes obtained by simulating optical coupling properties. This agreement between theory and experiment presents design principles to rationally control the lasing modes in cleaved-coupled nanowire lasers. PMID:23284173

Discovery of fairy circles in Australia supports self-organization theory

PubMed Central

Getzin, Stephan; Yizhaq, Hezi; Bell, Bronwyn; Erickson, Todd E.; Postle, Anthony C.; Katra, Itzhak; Tzuk, Omer; Zelnik, Yuval R.; Wiegand, Kerstin; Wiegand, Thorsten; Meron, Ehud

2016-01-01

Vegetation gap patterns in arid grasslands, such as the “fairy circles” of Namibia, are one of nature’s greatest mysteries and subject to a lively debate on their origin. They are characterized by small-scale hexagonal ordering of circular bare-soil gaps that persists uniformly in the landscape scale to form a homogeneous distribution. Pattern-formation theory predicts that such highly ordered gap patterns should be found also in other water-limited systems across the globe, even if the mechanisms of their formation are different. Here we report that so far unknown fairy circles with the same spatial structure exist 10,000 km away from Namibia in the remote outback of Australia. Combining fieldwork, remote sensing, spatial pattern analysis, and process-based mathematical modeling, we demonstrate that these patterns emerge by self-organization, with no correlation with termite activity; the driving mechanism is a positive biomass–water feedback associated with water runoff and biomass-dependent infiltration rates. The remarkable match between the patterns of Australian and Namibian fairy circles and model results indicate that both patterns emerge from a nonuniform stationary instability, supporting a central universality principle of pattern-formation theory. Applied to the context of dryland vegetation, this principle predicts that different systems that go through the same instability type will show similar vegetation patterns even if the feedback mechanisms and resulting soil–water distributions are different, as we indeed found by comparing the Australian and the Namibian fairy-circle ecosystems. These results suggest that biomass–water feedbacks and resultant vegetation gap patterns are likely more common in remote drylands than is currently known. PMID:26976567

Photoionization of Trapped Carriers in Avalanche Photodiodes to Reduce Afterpulsing During Geiger-Mode Photon Counting

NASA Technical Reports Server (NTRS)

Krainak, Michael A.

2005-01-01

We reduced the afterpulsing probability by a factor of five in a Geiger-mode photon-counting InGaAs avalanche photodiode by using sub-band-gap (lambda = 1.95 micron) laser diode illumination, which we believe photoionizes the trapped carriers.

Square Turing patterns in reaction-diffusion systems with coupled layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jing; Wang, Hongli, E-mail: hlwang@pku.edu.cn, E-mail: qi@pku.edu.cn; Center for Quantitative Biology, Peking University, Beijing 100871

Square Turing patterns are usually unstable in reaction-diffusion systems and are rarely observed in corresponding experiments and simulations. We report here an example of spontaneous formation of square Turing patterns with the Lengyel-Epstein model of two coupled layers. The squares are found to be a result of the resonance between two supercritical Turing modes with an appropriate ratio. Besides, the spatiotemporal resonance of Turing modes resembles to the mode-locking phenomenon. Analysis of the general amplitude equations for square patterns reveals that the fixed point corresponding to square Turing patterns is stationary when the parameters adopt appropriate values.

Understanding Adherence and Prescription Patterns Using Large-Scale Claims Data.

PubMed

Bjarnadóttir, Margrét V; Malik, Sana; Onukwugha, Eberechukwu; Gooden, Tanisha; Plaisant, Catherine

2016-02-01

Advanced computing capabilities and novel visual analytics tools now allow us to move beyond the traditional cross-sectional summaries to analyze longitudinal prescription patterns and the impact of study design decisions. For example, design decisions regarding gaps and overlaps in prescription fill data are necessary for measuring adherence using prescription claims data. However, little is known regarding the impact of these decisions on measures of medication possession (e.g., medication possession ratio). The goal of the study was to demonstrate the use of visualization tools for pattern discovery, hypothesis generation, and study design. We utilized EventFlow, a novel discrete event sequence visualization software, to investigate patterns of prescription fills, including gaps and overlaps, utilizing large-scale healthcare claims data. The study analyzes data of individuals who had at least two prescriptions for one of five hypertension medication classes: ACE inhibitors, angiotensin II receptor blockers, beta blockers, calcium channel blockers, and diuretics. We focused on those members initiating therapy with diuretics (19.2%) who may have concurrently or subsequently take drugs in other classes as well. We identified longitudinal patterns in prescription fills for antihypertensive medications, investigated the implications of decisions regarding gap length and overlaps, and examined the impact on the average cost and adherence of the initial treatment episode. A total of 790,609 individuals are included in the study sample, 19.2% (N = 151,566) of whom started on diuretics first during the study period. The average age was 52.4 years and 53.1% of the population was female. When the allowable gap was zero, 34% of the population had continuous coverage and the average length of continuous coverage was 2 months. In contrast, when the allowable gap was 30 days, 69% of the population showed a single continuous prescription period with an average length of 5 months. The average prescription cost of the period of continuous coverage ranged from US$3.44 (when the maximum gap was 0 day) to US$9.08 (when the maximum gap was 30 days). Results were less impactful when considering overlaps. This proof-of-concept study illustrates the use of visual analytics tools in characterizing longitudinal medication possession. We find that prescription patterns and associated prescription costs are more influenced by allowable gap lengths than by definitions and treatment of overlap. Research using medication gaps and overlaps to define medication possession in prescription claims data should pay particular attention to the definition and use of gap lengths.

Intercellular ice propagation: experimental evidence for ice growth through membrane pores.

PubMed Central

Acker, J P; Elliott, J A; McGann, L E

2001-01-01

Propagation of intracellular ice between cells significantly increases the prevalence of intracellular ice in confluent monolayers and tissues. It has been proposed that gap junctions facilitate ice propagation between cells. This study develops an equation for capillary freezing-point depression to determine the effect of temperature on the equilibrium radius of an ice crystal sufficiently small to grow through gap junctions. Convection cryomicroscopy and video image analysis were used to examine the incidence and pattern of intracellular ice formation (IIF) in the confluent monolayers of cell lines that do (MDCK) and do not (V-79W) form gap junctions. The effect of gap junctions on intracellular ice propagation was strongly temperature-dependent. For cells with gap junctions, IIF occurred in a directed wave-like pattern in 100% of the cells below -3 degrees C. At temperatures above -3 degrees C, there was a marked drop in the incidence of IIF, with isolated individual cells initially freezing randomly throughout the sample. This random pattern of IIF was also observed in the V-79W monolayers and in MDCK monolayers treated to prevent gap junction formation. The significant change in the low temperature behavior of confluent MDCK monolayers at -3 degrees C is likely the result of the inhibition of gap junction-facilitated ice propagation, and supports the theory that gap junctions facilitate ice nucleation between cells. PMID:11509353

THE ARCHITECTURE OF THE CASSINI DIVISION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hedman, M. M.; Nicholson, P. D.; Baines, K. H.

2010-01-15

The Cassini Division in Saturn's rings contains a series of eight named gaps, three of which contain dense ringlets. Observations of stellar occultations by the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft have yielded {approx}40 accurate and precise measurements of the radial position of the edges of all of these gaps and ringlets. These data reveal suggestive patterns in the shapes of many of the gap edges: the outer edges of the five gaps without ringlets are circular to within 1 km, while the inner edges of six of the gaps are eccentric, with apsidal precession rates consistentmore » with those expected for eccentric orbits near each edge. Intriguingly, the pattern speeds of these eccentric inner gap edges, together with that of the eccentric Huygens Ringlet, form a series with a characteristic spacing of 0.{sup 0}06 day{sup -1}. The two gaps with non-eccentric inner edges lie near first-order inner Lindblad resonances (ILRs) with moons. One such edge is close to the 5:4 ILR with Prometheus, and the radial excursions of this edge do appear to have an m = 5 component aligned with that moon. The other resonantly confined edge is the outer edge of the B ring, which lies near the 2:1 Mimas ILR. Detailed investigation of the B-ring-edge data confirm the presence of an m = 2 perturbation on the B-ring edge, but also show that during the course of the Cassini Mission, this pattern has drifted backward relative to Mimas. Comparisons with earlier occultation measurements going back to Voyager suggest the possibility that the m = 2 pattern is actually librating relative to Mimas with a libration frequency L {approx} 0.{sup 0}06 day{sup -1} (or possibly 0.{sup 0}12 day{sup -1}). In addition to the m = 2 pattern, the B-ring edge also has an m = 1 component that rotates around the planet at a rate close to the expected apsidal precession rate. Thus, the pattern speeds of the eccentric edges in the Cassini Division can be generated from various combinations of the pattern speeds of structures observed on the edge of the B ring. We therefore suggest that most of the gaps in the Cassini Division are produced by resonances involving perturbations from the massive edge of the B ring. We find that a combination of gravitational perturbations generated by the radial excursions in the B-ring edge and the gravitational perturbations from the Mimas 2:1 ILR yields terms in the equations of motion that should act to constrain the pericenter location of particle orbits in the vicinity of each of the eccentric inner gap edges in the Cassini Division. This alignment of pericenters could be responsible for forming the Cassini-Division Gaps and thus explain why these gaps are located where they are.« less

The architecture of the Cassini division

USGS Publications Warehouse

Hedman, M.M.; Nicholson, P.D.; Baines, K.H.; Buratti, B.J.; Sotin, Christophe; Clark, R.N.; Brown, R.H.; French, R.G.; Marouf, E.A.

2010-01-01

The Cassini Division in Saturn's rings contains a series of eight named gaps, three of which contain dense ringlets. Observations of stellar occultations by the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft have yielded 40 accurate and precise measurements of the radial position of the edges of all of these gaps and ringlets. These data reveal suggestive patterns in the shapes of many of the gap edges: the outer edges of the five gaps without ringlets are circular to within 1 km, while the inner edges of six of the gaps are eccentric, with apsidal precession rates consistent with those expected for eccentric orbits near each edge. Intriguingly, the pattern speeds of these eccentric inner gap edges, together with that of the eccentric Huygens Ringlet, form a series with a characteristic spacing of 006 day-1. The two gaps with non-eccentric inner edges lie near first-order inner Lindblad resonances (ILRs) with moons. One such edge is close to the 5:4 ILR with Prometheus, and the radial excursions of this edge do appear to have an m = 5 component aligned with that moon. The other resonantly confined edge is the outer edge of the B ring, which lies near the 2:1 Mimas ILR. Detailed investigation of the B-ring-edge data confirm the presence of an m = 2 perturbation on the B-ring edge, but also show that during the course of the Cassini Mission, this pattern has drifted backward relative to Mimas. Comparisons with earlier occultation measurements going back to Voyager suggest the possibility that the m = 2 pattern is actually librating relative to Mimas with a libration frequency L 006 day-1 (or possibly 012 day -1). In addition to the m = 2 pattern, the B-ring edge also has an m = 1 component that rotates around the planet at a rate close to the expected apsidal precession rate (?? ?? ?? B ??? 5.??06 day -1). Thus, the pattern speeds of the eccentric edges in the Cassini Division can be generated from various combinations of the pattern speeds of structures observed on the edge of the B ring: ??p = ?? ?? ??B -jL for j = 1, 2, 3, ???, 7. We therefore suggest that most of the gaps in the Cassini Division are produced by resonances involving perturbations from the massive edge of the B ring. We find that a combination of gravitational perturbations generated by the radial excursions in the B-ring edge and the gravitational perturbations from the Mimas 2:1 ILR yields terms in the equations of motion that should act to constrain the pericenter location of particle orbits in the vicinity of each of the eccentric inner gap edges in the Cassini Division. This alignment of pericenters could be responsible for forming the Cassini-Division Gaps and thus explain why these gaps are located where they are. ?? 2010. The American Astronomical Society. All rights reserved.

Chiral zero energy modes in two-dimensional disordered Dirac semimetals

NASA Astrophysics Data System (ADS)

Liu, Lei; Yu, Yan; Wu, Hai-Bin; Zhang, Yan-Yang; Liu, Jian-Jun; Li, Shu-Shen

2018-04-01

The vacancy-induced chiral zero energy modes (CZEMs) of chiral-unitary-class (AIII) and chiral-symplectic-class (CII) two-dimensional (2 D ) disordered Dirac semimetals realized on a square bipartite lattice are investigated numerically by using the Kubo-Greenwood formula with the kernel polynomial method. The results show that, for both systems, the CZEMs exhibit the critical delocalization. The CZEM conductivity remains a robust constant (i.e., σ CZEM≈1.05 e2/h ), which is insensitive to the sample sizes, the vacancy concentrations, and the numbers of moments of Chebyshev polynomials, i.e., the dephasing strength. For both kinds of chiral systems, the CZEM conductivities are almost identical. However, they are not equal to that of graphene (i.e., 4 e2/π h ), which belongs to the chiral orthogonal class (BDI) semimetal on a 2 D hexagonal bipartite lattice. In addition, for the case that the vacancy concentrations are different in the two sublattices, the CZEM conductivity vanishes, and thus both systems exhibit localization at the Dirac point. Moreover, a band gap and a mobility gap open around zero energy. The widths of the energy gaps and mobility gaps are increasing with larger vacancy concentration difference. The width of the mobility gap is greater than that of the band gap, and a δ -function-like peak of density of states emerges at the Dirac point within the band gap, implying the existence of numerous localized states.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, T.; Zimoch, D.

The operation of an APPLE II based undulator beamline with all its polarization states (linear horizontal and vertical, circular and elliptical, and continous variation of the linear vector) requires an effective description allowing an automated calculation of gap and shift parameter as function of energy and operation mode. The extension of the linear polarization range from 0 to 180 deg. requires 4 shiftable magnet arrrays, permitting use of the APU (adjustable phase undulator) concept. Studies for a pure fixed gap APPLE II for the SLS revealed surprising symmetries between circular and linear polarization modes allowing for simplified operation. A semi-analyticalmore » model covering all types of APPLE II and its implementation will be presented.« less

About APPLE II Operation

NASA Astrophysics Data System (ADS)

Schmidt, T.; Zimoch, D.

2007-01-01

The operation of an APPLE II based undulator beamline with all its polarization states (linear horizontal and vertical, circular and elliptical, and continous variation of the linear vector) requires an effective description allowing an automated calculation of gap and shift parameter as function of energy and operation mode. The extension of the linear polarization range from 0 to 180° requires 4 shiftable magnet arrrays, permitting use of the APU (adjustable phase undulator) concept. Studies for a pure fixed gap APPLE II for the SLS revealed surprising symmetries between circular and linear polarization modes allowing for simplified operation. A semi-analytical model covering all types of APPLE II and its implementation will be presented.

Stückelberg formulation of holography

NASA Astrophysics Data System (ADS)

Dvali, Gia; Gomez, Cesar; Wintergerst, Nico

2016-10-01

We suggest that holography can be formulated in terms of the information capacity of the Stückelberg degrees of freedom that maintain gauge invariance of the theory in the presence of an information boundary. These Stückelbergs act as qubits that account for a certain fraction of quantum information. Their information capacity is measured by the ratio of the inverse Stückelberg energy gap to the size of the system. Systems with the smallest gap are maximally holographic. For massless gauge systems this information measure is universally equal to the inverse coupling evaluated at the systems' length scale. In this language it becomes very transparent why the Stückelberg information capacity of black holes saturates the Bekenstein bound and accounts for the entire information of the system. The physical reason is that the strength of quantum interaction is bounded from below by the gravitational coupling, which scales as area. Observing the striking similarity between the scalings of the energy gap of the boundary Stückelberg modes and the Bogoliubov modes of critical many-body systems, we establish a connection between holography and quantum criticality through the correspondence between these modes.

Dipolar interaction induced band gaps and flat modes in surface-modulated magnonic crystals

NASA Astrophysics Data System (ADS)

Gallardo, R. A.; Schneider, T.; Roldán-Molina, A.; Langer, M.; Fassbender, J.; Lenz, K.; Lindner, J.; Landeros, P.

2018-04-01

Theoretical results for the magnetization dynamics of a magnonic crystal formed by grooves on the surface of a ferromagnetic film, called a surface-modulated magnonic crystal, are presented. For such a system, the role of the periodic dipolar field induced by the geometrical modulation is addressed by using the plane-wave method. The results reveal that, under the increasing of the depth of the grooves, zones with magnetizing and demagnetizing fields act on the system in such a way that magnonic band gaps are observed in both Damon-Eshbach and backward volume geometries. Particularly, in the backward volume configuration, high-frequency band gaps and low-frequency flat modes are obtained. By taking into account the properties of the internal field induced by the grooves, the flattening of the modes and their shift towards low frequencies are discussed and explained. To test the validity of the model, the theoretical results of this work are confirmed by micromagnetic simulations, and good agreement between both methods is achieved. The theoretical model allows for a detailed understanding of the physics underlying these kinds of systems, thereby providing an outlook for potential applications on magnonic devices.

Excitation of terahertz modes localized on a layered superconductor: Anomalous dispersion and resonant transmission

NASA Astrophysics Data System (ADS)

Apostolov, S. S.; Makarov, N. M.; Yampol'skii, V. A.

2018-01-01

We study theoretically the optic transmission through a slab of layered superconductor separated from two dielectric leads by spatial gaps. Based on the transfer matrix formalism along with the Josephson plasma electrodynamic approach, we derive analytic expressions for the transmittance and identify the conditions for the perfect transmission. The special interest of the study is focused on the resonant transmission, which occurs when the wave does not propagate in the spatial gaps. Far from the resonance, the transmittance is exponentially small due to the total internal reflection from the lead-gap interface. However, the excitation of electromagnetic modes localized on the layered superconductor gives rise to a remarkable resonant enhancement of the transmission. Moreover, this phenomenon is significantly modified for the layered superconductors in comparison with usual dielectrics or conductors. The dispersion curves for the modes localized on the layered superconductor are proved to be nonmonotonic, thus resulting in the specific dependence of the transmittance T on the incidence angle θ . In particular, we predict the onset of two resonant peaks in the T (θ ) dependence and their subsequent merge into the broadened single peak with increasing of the wave frequency. Our analytical results are demonstrated by numerical data.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gawai, U. P.; Dole, B. N.; Khawal, H. A.

Ag doped ZnO nanocrystals were synthesized by co-precipitation method with the nominal compositions (x=0.00, 0.02, 0.04, 0.06). The as-synthesized Ag doped ZnO nanocrystals were characterized by X-ray diffraction (XRD), FTIR and UV-Vis. From XRD patterns samples shows hexagonal structure. The average crystallite size is in the range of 41-47 nm. All as synthesized Zn{sub 1−x}Ag{sub x}O nanocrystals are highly textured, with wurtzite structure along the (101) growth direction. The energy band gap of pure and Ag doped ZnO were calculated from UV-Vis spectra. FTIR spectra were confirmed that Ag substituted into ZnO. Chemical species of the samples were detected using FTIRmore » spectra An increase in the hexagonal lattice parameters of ZnO is observed on increasing the Ag concentration. An optical absorption study shows an increment in the band gap with increasing Ag content. From optical study the samples determines blue shift. Atomic packing fraction (APF) and c/a ratio were calculated using XRD data. It confirms the formation of ZnO with the stretching vibrational mode around at 506 to 510 cm{sup −1}.« less

Quantum spill-out in few-nanometer metal gaps: Effect on gap plasmons and reflectance from ultrasharp groove arrays

NASA Astrophysics Data System (ADS)

Skjølstrup, Enok J. H.; Søndergaard, Thomas; Pedersen, Thomas G.

2018-03-01

Plasmons in ultranarrow metal gaps are highly sensitive to the electron density profile at the metal surfaces. Using a quantum mechanical approach and assuming local response, we study the effects of electron spill-out on gap plasmons and reflectance from ultrasharp metal grooves. We demonstrate that the mode index of ultranarrow gap plasmons converges to the bulk refractive index in the limit of vanishing gap and, thereby, rectify the unphysical divergence found in classical models. Surprisingly, spill-out also significantly increases the plasmonic absorption for few-nanometer gaps and lowers the reflectance from arrays of ultrasharp metal grooves. These findings are explained in terms of enhanced gap plasmon absorption taking place inside the gap 1-2 Å from the walls and delocalization near the groove bottom. Reflectance calculations taking spill-out into account are shown to be in much better agreement with measurements compared with classical models.

Simulation of stationary glow patterns in dielectric barrier discharges at atmospheric pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Fucheng, E-mail: hdlfc@hbu.cn; He, Yafeng; Dong, Lifang

2014-12-15

Self-organized stationary patterns in dielectric barrier discharges operating in glow regime at atmospheric pressure are investigated by a self-consistent two-dimensional fluid model. The simulation results show that two different modes, namely, the diffuse mode and the static patterned mode, can be formed in different ranges of the driving frequency. The discharge operates in Townsend regime in the diffuse mode, while it operates in a glow regime inside the filaments and in a Townsend regime outside the filaments in the stable pattered mode. The forming process of the stationary filaments can be divided into three stages, namely, destabilizing stage, self-assembling stage,more » and stable stage. The space charge associated with residual electron density and surface charge is responsible for the formation of these stationary glow patterns.« less

Effect of Pulse and dc Formation on the Performance of One-Transistor and One-Resistor Resistance Random Access Memory Devices

NASA Astrophysics Data System (ADS)

Liu, Hong-Tao; Yang, Bao-He; Lv, Hang-Bing; Xu, Xiao-Xin; Luo, Qing; Wang, Guo-Ming; Zhang, Mei-Yun; Long, Shi-Bing; Liu, Qi; Liu, Ming

2015-02-01

We investigate the effect of the formation process under pulse and dc modes on the performance of one transistor and one resistor (1T1R) resistance random access memory (RRAM) device. All the devices are operated under the same test conditions, except for the initial formation process with different modes. Based on the statistical results, the high resistance state (HRS) under the dc forming mode shows a lower value with better distribution compared with that under the pulse mode. One of the possible reasons for such a phenomenon originates from different properties of conductive filament (CF) formed in the resistive switching layer under two different modes. For the dc forming mode, the formed filament is thought to be continuous, which is hard to be ruptured, resulting in a lower HRS. However, in the case of pulse forming, the filament is discontinuous where the transport mechanism is governed by hopping. The low resistance state (LRS) can be easily changed by removing a few trapping states from the conducting path. Hence, a higher HRS is thus observed. However, the HRS resistance is highly dependent on the length of the gap opened. A slight variation of the gap length will cause wide dispersion of resistance.

The interplay of the gap, the magnetic resonance, and the van Hove singularity

NASA Astrophysics Data System (ADS)

Levy, Giorgio; Berthod, Christophe; Fischer, Oystein

2007-03-01

The characteristic features of the tunneling spectra in the Bi-based HTS are a d-wave like gap structure, strong and often asymmetric coherence peaks, and an asymmetric dip-hump structure at higher energy. Hoogenboom et al. [1] analysed the spectra of the two-layer compound Bi2212 and showed that all of these properties can be understood assuming d-wave superconductivity, a band structure as measured by ARPES, and an interaction of the quasiparticles with the magnetic resonant mode. In particular the asymmetric dip-hump results in this model from the interplay of the gap, the mode and the van Hove singularity present in the band structure. Here we analyse new data for the three-layer compound Bi2223. Unlike in Ref. [1], we perform full unconstrained least-square fits in order to determine the various parameters of the model directly from the experimental data. This allows us to determine the doping dependence of the gap and of the magnetic resonance energy. [1] B. W. Hoogenboom, C. Berthod, M. Peter, ø. Fischer, and A. A. Kordyuk, Phys. Rev. B 67, 224502 (2003).

Edge waves and resonances in two-dimensional phononic crystal plates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsu, Jin-Chen, E-mail: hsujc@yuntech.edu.tw; Hsu, Chih-Hsun

2015-05-07

We present a numerical study on phononic band gaps and resonances occurring at the edge of a semi-infinite two-dimensional (2D) phononic crystal plate. The edge supports localized edge waves coupling to evanescent phononic plate modes that decay exponentially into the semi-infinite phononic crystal plate. The band-gap range and the number of edge-wave eigenmodes can be tailored by tuning the distance between the edge and the semi-infinite 2D phononic lattice. As a result, a phononic band gap for simultaneous edge waves and plate waves is created, and phononic cavities beside the edge can be built to support high-frequency edge resonances. Wemore » design an L3 edge cavity and analyze its resonance characteristics. Based on the band gap, high quality factor and strong confinement of resonant edge modes are achieved. The results enable enhanced control over acoustic energy flow in phononic crystal plates, which can be used in designing micro and nanoscale resonant devices and coupling of edge resonances to other types of phononic or photonic crystal cavities.« less

Topological Valley Transport at Bilayer Graphene Domain Walls

DTIC Science & Technology

2015-04-22

2015. Published online 22 April 2015. 1. McCann, E. Asymmetry gap in the electronic band structure of bilayer graphene . Phys. Rev. B 74, 161403 (2006...6. Yao, W., Yang, S. A. & Niu, Q. Edge states in graphene : from gapped flat- band to gapless chiral modes. Phys. Rev. Lett. 102, 096801 (2009). 7...induced in bilayer graphene by an external electric field1–5, and such gapped bilayer graphene is predicted to be a topo- logical insulating phase

Compact Reconfigurable Antenna with an Omnidirectional Pattern and Four Directional Patterns for Wireless Sensor Systems.

PubMed

Wang, Ren; Wang, Bing-Zhong; Huang, Wei-Ying; Ding, Xiao

2016-04-16

A compact reconfigurable antenna with an omnidirectional mode and four directional modes is proposed. The antenna has a main radiator and four parasitic elements printed on a dielectric substrate. By changing the status of diodes soldered on the parasitic elements, the proposed antenna can generate four directional radiation patterns and one omnidirectional radiation pattern. The main beam directions of the four directional modes are almost orthogonal and the four directional beams can jointly cover a 360° range in the horizontal plane, i.e., the main radiation plane of omnidirectional mode. The whole volume of the antenna and the control network is approximately 0.70 λ × 0.53 λ × 0.02 λ, where λ is the wavelength corresponding to the center frequency. The proposed antenna has a simple structure and small dimensions under the requirement that the directional radiation patterns can jointly cover the main radiation plane of the omnidirectional mode, therefore, it can be used in smart wireless sensor systems for different application scenarios.

Complex Dynamics in Nonequilibrium Economics and Chemistry

NASA Astrophysics Data System (ADS)

Wen, Kehong

Complex dynamics provides a new approach in dealing with economic complexity. We study interactively the empirical and theoretical aspects of business cycles. The way of exploring complexity is similar to that in the study of an oscillatory chemical system (BZ system)--a model for modeling complex behavior. We contribute in simulating qualitatively the complex periodic patterns observed from the controlled BZ experiments to narrow the gap between modeling and experiment. The gap between theory and reality is much wider in economics, which involves studies of human expectations and decisions, the essential difference from natural sciences. Our empirical and theoretical studies make substantial progress in closing this gap. With the help from the new development in nonequilibrium physics, i.e., the complex spectral theory, we advance our technique in detecting characteristic time scales from empirical economic data. We obtain correlation resonances, which give oscillating modes with decays for correlation decomposition, from different time series including S&P 500, M2, crude oil spot prices, and GNP. The time scales found are strikingly compatible with business experiences and other studies in business cycles. They reveal the non-Markovian nature of coherent markets. The resonances enhance the evidence of economic chaos obtained by using other tests. The evolving multi-humped distributions produced by the moving-time -window technique reveal the nonequilibrium nature of economic behavior. They reproduce the American economic history of booms and busts. The studies seem to provide a way out of the debate on chaos versus noise and unify the cyclical and stochastic approaches in explaining business fluctuations. Based on these findings and new expectation formulation, we construct a business cycle model which gives qualitatively compatible patterns to those found empirically. The soft-bouncing oscillator model provides a better alternative than the harmonic oscillator or the random walk model as the building block in business cycle theory. The mathematical structure of the model (delay differential equation) is studied analytically and numerically. The research pave the way toward sensible economic forecasting.

Limited Transfer of Newly Acquired Movement Patterns across Walking and Running in Humans

PubMed Central

Ogawa, Tetsuya; Kawashima, Noritaka; Ogata, Toru; Nakazawa, Kimitaka

2012-01-01

The two major modes of locomotion in humans, walking and running, may be regarded as a function of different speed (walking as slower and running as faster). Recent results using motor learning tasks in humans, as well as more direct evidence from animal models, advocate for independence in the neural control mechanisms underlying different locomotion tasks. In the current study, we investigated the possible independence of the neural mechanisms underlying human walking and running. Subjects were tested on a split-belt treadmill and adapted to walking or running on an asymmetrically driven treadmill surface. Despite the acquisition of asymmetrical movement patterns in the respective modes, the emergence of asymmetrical movement patterns in the subsequent trials was evident only within the same modes (walking after learning to walk and running after learning to run) and only partial in the opposite modes (walking after learning to run and running after learning to walk) (thus transferred only limitedly across the modes). Further, the storage of the acquired movement pattern in each mode was maintained independently of the opposite mode. Combined, these results provide indirect evidence for independence in the neural control mechanisms underlying the two locomotive modes. PMID:23029490

Nonspecific DNA Binding and Bending by HUαβ: Interfaces of the Three Binding Modes Characterized by Salt Dependent Thermodynamics

PubMed Central

Koh, Junseock; Shkel, Irina; Saecker, Ruth M.; Record, M. Thomas

2011-01-01

Previous ITC and FRET studies demonstrated that Escherichia coli HUαβ binds nonspecifically to duplex DNA in three different binding modes: a tighter-binding 34 bp mode which interacts with DNA in large (>34 bp) gaps between bound proteins, reversibly bending it 140° and thereby increasing its flexibility, and two weaker, modestly cooperative small-site-size modes (10 bp, 6 bp) useful for filling gaps between bound proteins shorter than 34 bp. Here we use ITC to determine the thermodynamics of these binding modes as a function of salt concentration, and deduce that DNA in the 34 bp mode is bent around but not wrapped on the body of HU, in contrast to specific binding of IHF. Analyses of binding isotherms (8, 15, 34 bp DNA) and initial binding heats (34, 38, 160 bp DNA) reveal that all three modes have similar log-log salt concentration derivatives of the binding constants (Ski) even though their binding site sizes differ greatly; most probable values of Ski on 34 bp or larger DNA are − 7.5 ± 0.5. From the similarity of Ski values, we conclude that binding interfaces of all three modes involve the same region of the arms and saddle of HU. All modes are entropy-driven, as expected for nonspecific binding driven by the polyelectrolyte effect. The bent-DNA 34 bp mode is most endothermic, presumably because of the cost of HU-induced DNA bending, while the 6 bp mode is modestly exothermic at all salt concentrations examined. Structural models consistent with the observed Ski values are proposed. PMID:21513716

Lattice gauge action suppressing near-zero modes of H{sub W}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukaya, Hidenori; Hashimoto, Shoji; Kaneko, Takashi

2006-11-01

We propose a lattice action including unphysical Wilson fermions with a negative mass m{sub 0} of the order of the inverse lattice spacing. With this action, the exact zero mode of the Hermitian Wilson-Dirac operator H{sub W}(m{sub 0}) cannot appear and near-zero modes are strongly suppressed. By measuring the spectral density {rho}({lambda}{sub W}), we find a gap near {lambda}{sub W}=0 on the configurations generated with the standard and improved gauge actions. This gap provides a necessary condition for the proof of the exponential locality of the overlap-Dirac operator by Hernandez, Jansen, and Luescher. Since the number of near-zero modes ismore » small, the numerical cost to calculate the matrix sign function of H{sub W}(m{sub 0}) is significantly reduced, and the simulation including dynamical overlap fermions becomes feasible. We also introduce a pair of twisted mass pseudofermions to cancel the unwanted higher mode effects of the Wilson fermions. The gauge coupling renormalization due to the additional fields is then minimized. The topological charge measured through the index of the overlap-Dirac operator is conserved during continuous evolutions of gauge field variables.« less

Layered growth with bottom-spray granulation for spray deposition of drug.

PubMed

Er, Dawn Z L; Liew, Celine V; Heng, Paul W S

2009-07-30

The gap in scientific knowledge on bottom-spray fluidized bed granulation has emphasized the need for more studies in this area. This paper comparatively studied the applicability of a modified bottom-spray process and the conventional top-spray process for the spray deposition of a micronized drug during granulation. The differences in circulation pattern, mode of growth and resultant granule properties between the two processes were highlighted. The more ordered and consistent circulation pattern of particles in a bottom-spray fluidized bed was observed to give rise to layered granule growth. This resulted in better drug content uniformity among the granule batches and within a granule batch. The processes' sensitivities to wetting and feed material characteristics were also compared and found to differ markedly. Less robustness to differing process conditions was observed for the top-spray process. The resultant bottom-spray granules formed were observed to be less porous, more spherical and had good flow properties. The bottom-spray technique can thus be potentially applied for the spray deposition of drug during granulation and was observed to be a good alternative to the conventional technique for preparing granules.

Resting State Network Topology of the Ferret Brain

PubMed Central

Zhou, Zhe Charles; Salzwedel, Andrew P.; Radtke-Schuller, Susanne; Li, Yuhui; Sellers, Kristin K.; Gilmore, John H.; Shih, Yen-Yu Ian; Fröhlich, Flavio; Gao, Wei

2016-01-01

Resting state functional magnetic resonance imaging (rsfMRI) has emerged as a versatile tool for non-invasive measurement of functional connectivity patterns in the brain. RsfMRI brain dynamics in rodents, non-human primates, and humans share similar properties; however, little is known about the resting state functional connectivity patterns in the ferret, an animal model with high potential for developmental and cognitive translational study. To address this knowledge-gap, we performed rsfMRI on anesthetized ferrets using a 9.4 tesla MRI scanner, and subsequently performed group-level independent component analysis (gICA) to identify functionally connected brain networks. Group-level ICA analysis revealed distributed sensory, motor, and higher-order networks in the ferret brain. Subsequent connectivity analysis showed interconnected higher-order networks that constituted a putative default mode network (DMN), a network that exhibits altered connectivity in neuropsychiatric disorders. Finally, we assessed ferret brain topological efficiency using graph theory analysis and found that the ferret brain exhibits small-world properties. Overall, these results provide additional evidence for pan-species resting-state networks, further supporting ferret-based studies of sensory and cognitive function. PMID:27596024

Pattern transfer with stabilized nanoparticle etch masks

NASA Astrophysics Data System (ADS)

Hogg, Charles R.; Picard, Yoosuf N.; Narasimhan, Amrit; Bain, James A.; Majetich, Sara A.

2013-03-01

Self-assembled nanoparticle monolayer arrays are used as an etch mask for pattern transfer into Si and SiOx substrates. Crack formation within the array is prevented by electron beam curing to fix the nanoparticles to the substrate, followed by a brief oxygen plasma to remove excess carbon. This leaves a dot array of nanoparticle cores with a minimum gap of 2 nm. Deposition and liftoff can transform the dot array mask into an antidot mask, where the gap is determined by the nanoparticle core diameter. Reactive ion etching is used to transfer the dot and antidot patterns into the substrate. The effect of the gap size on the etching rate is modeled and compared with the experimental results.

Diurnal characteristics of turbulent intermittency in the Taklimakan Desert

NASA Astrophysics Data System (ADS)

Wei, Wei; Wang, Minzhong; Zhang, Hongsheng; He, Qing; Ali, Mamtimin; Wang, Yinjun

2017-12-01

A case study is performed to investigate the behavior of turbulent intermittency in the Taklimakan Desert using an intuitive, direct, and adaptive method, the arbitrary-order Hilbert spectral analysis (arbitrary-order HSA). Decomposed modes from the vertical wind speed series confirm the dyadic filter-bank essence of the empirical mode decomposition processes. Due to the larger eddies in the CBL, higher energy modes occur during the day. The second-order Hilbert spectra L2 (ω ) delineate the spectral gap separating fine-scale turbulence from large-scale motions. Both the values of kurtosis and the Hilbert-based scaling exponent ξ ( q ) reveal that the turbulence intermittency at night is much stronger than that during the day, and the stronger intermittency is associated with more stable stratification under clear-sky conditions. This study fills the gap in the characteristics of turbulence intermittency in the Taklimakan Desert area using a relatively new method.

Homogeneous dielectric barrier discharges in atmospheric air and its influencing factor

NASA Astrophysics Data System (ADS)

Ran, Junxia; Li, Caixia; Ma, Dong; Luo, Haiyun; Li, Xiaowei

2018-03-01

The stable homogeneous dielectric barrier discharge (DBD) is obtained in atmospheric 2-3 mm air gap. It is generated using center frequency 1 kHz high voltage power supply between two plane parallel electrodes with specific alumina ceramic plates as the dielectric barriers. The discharge characteristics are studied by a measurement of its electrical discharge parameters and observation of its light emission phenomena. The results show that a large single current pulse of about 200 μs duration appearing in each voltage pulse, and its light emission is radially homogeneous and covers the entire surface of the two electrodes. The homogeneous discharge generated is a Townsend discharge during discharge. The influences of applied barrier, its thickness, and surface roughness on the transition of discharge modes are studied. The results show that it is difficult to produce a homogeneous discharge using smooth plates or alumina plate surface roughness Ra < 100 nm even at a 1 mm air gap. If the alumina plate is too thin, the discharge also transits to filamentary discharge. If it is too thick, the discharge is too weak to observe. With the increase of air gap distance and applied voltage, the discharge can also transit from a homogeneous mode to a filamentary mode. In order to generate stable and homogeneous DBD at a larger air gap, proper dielectric material, dielectric thickness, and dielectric surface roughness should be used, and proper applied voltage amplitude and frequency should also be used.

Spatial Noise in Coupling Strength and Natural Frequency within a Pacemaker Network; Consequences for Development of Intestinal Motor Patterns According to a Weakly Coupled Phase Oscillator Model

PubMed Central

Parsons, Sean P.; Huizinga, Jan D.

2016-01-01

Pacemaker activities generated by networks of interstitial cells of Cajal (ICC), in conjunction with the enteric nervous system, orchestrate most motor patterns in the gastrointestinal tract. It was our objective to understand the role of network features of ICC associated with the myenteric plexus (ICC-MP) in the shaping of motor patterns of the small intestine. To that end, a model of weakly coupled oscillators (oscillators influence each other's phase but not amplitude) was created with most parameters derived from experimental data. The ICC network is a uniform two dimensional network coupled by gap junctions. All ICC generate pacemaker (slow wave) activity with a frequency gradient in mice from 50/min at the proximal end of the intestine to 40/min at the distal end. Key features of motor patterns, directly related to the underlying pacemaker activity, are frequency steps and dislocations. These were accurately mimicked by reduction of coupling strength at a point in the chain of oscillators. When coupling strength was expressed as a product of gap junction density and conductance, and gap junction density was varied randomly along the chain (i.e., spatial noise) with a long-tailed distribution, plateau steps occurred at pointsof low density. As gap junction conductance was decreased, the number of plateaus increased, mimicking the effect of the gap junction inhibitor carbenoxolone. When spatial noise was added to the natural interval gradient, as gap junction conductance decreased, the number of plateaus increased as before but in addition the phase waves frequently changed direction of apparent propagation, again mimicking the effect of carbenoxolone. In summary, key features of the motor patterns that are governed by pacemaker activity may be a direct consequence of biological noise, specifically spatial noise in gap junction coupling and pacemaker frequency. PMID:26869875

Effect of Ni doping on structural and optical properties of Zn{sub 1−x}Ni{sub x}O nanopowder synthesized via low cost sono-chemical method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Budhendra, E-mail: bksingh@ua.pt; Kaushal, Ajay, E-mail: ajay.kaushal@ua.pt; Bdikin, Igor

2015-10-15

Highlights: • Pure and Ni doped ZnO nanopowders were synthesized by low cost sonochemical method. • The optical properties of Zn{sub 1−x}Ni{sub x}O nanopowders can be tuned by varying Ni content. • The results reveal the solubility limit of Ni into ZnO matrix as below 8%. - Abstract: Zn{sub 1−x}Ni{sub x}O nanopowders with different Ni contents of x = 0.0, 0.04 and 0.08 were synthesized via cost effective sonochemical reaction method. X-ray diffraction (XRD) pattern reveals pure wurtzite phase of prepared nanostructures with no additional impurity peaks. The morphology and dimensions of nanoparticles were investigated using scanning electron microscope (SEM).more » A sharp and strong peak for first order optical mode for wurtzite zinc oxide (ZnO) structure was observed at ∼438 cm{sup −1} in Raman spectra. The calculated optical band gap (E{sub g}) from UV–vis transmission data was found to decrease with increase in Ni content. The observed red shift in E{sub g} with increasing Ni content in ZnO nanopowders were in agreement with band gap behaviours found in their photoluminescence (PL) spectra. The synthesised ZnO nanopowders with controlled band gap on Ni doping reveals their potential for use in various electronic and optical device applications. The results were discussed in detail.« less

Three-Dimensional Analysis of Internal Adaptations of Crowns Cast from Resin Patterns Fabricated Using Computer-Aided Design/Computer-Assisted Manufacturing Technologies.

PubMed

Liu, Yushu; Ye, Hongqiang; Wang, Yong; Zhao, Yijao; Sun, Yuchun; Zhou, Yongsheng

2018-05-17

To evaluate the internal adaptations of cast crowns made from resin patterns produced using three different computer-aided design/computer-assisted manufacturing technologies. A full-crown abutment made of zirconia was digitized using an intraoral scanner, and the design of the crown was finished on the digital model. Resin patterns were fabricated using a fused deposition modeling (FDM) 3D printer (LT group), a digital light projection (DLP) 3D printer (EV group), or a five-axis milling machine (ZT group). All patterns were cast in cobalt-chromium alloy crowns. Crowns made from traditional handmade wax patterns (HM group) were used as controls. Each group contained 10 samples. The internal gaps of the patterns were analyzed using a 3D replica method and optical digitization. The results were compared using Kruskal-Wallis analysis of variance (ANOVA), a one-sample t test, and signed rank test (α = .05). For the LT group, the marginal and axial gaps were significantly larger than in the other three groups (P < .05), but the occlusal adaptation did not reveal a significant difference (P > .05). In the ZT group, the axial gap was slightly smaller than in the HM group (P < .0083). All the means of gaps in all areas in the four groups were less than 150 μm. Casting crowns using casting patterns made from all three CAD/CAM systems could not produce the prescribed parameters, but the crowns showed clinically acceptable internal adaptations.

Triclosan Disrupts Thyroxine: Contribution of Hepatic Transport to the Mode of Action

EPA Science Inventory

Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) (TCS) decreases serum thyroxine (T4) in rats. In previous work, TCS upregulated Phase I and II hepatic metabolism after 4-day exposures in rats. A major data gap in our characterization of the mode of action (MOA) of TCS-induced ...

A miniature extrinsic fiber Fabry-Perot pressure sensor based on fiber etching

NASA Astrophysics Data System (ADS)

Ge, Yixian; Wang, Ming; Yang, Chundi

2009-10-01

This paper presents a miniature fiber optic pressure sensor based on Fabry-Perot interference fabricated on the tip of a single mode (SM) fiber. The sensor measures only 125μm in diameter. A Fabry-Perot cavity and a thin silica diaphragm are fabricated by simple techniques involving only fusion splicing, cleaving, and wet chemical etching. Interference pattern of the sensor is analyzed and issues in sensor design are discussed. The overall chemical reaction of the fiber wet etching is specifically represented. Pressure testing system is carried out. By tracing a peak point in the interference spectrum, the gap length of the sensor can be demodulated. The sensor is made entirely of fused silica, whose structure has good stability, cabinet, simple for fabrication and low cost. It may also find uses in medical applications.

A miniature extrinsic fiber Fabry-Perot pressure sensor based on fiber etching

NASA Astrophysics Data System (ADS)

Ge, Yixian; Zhou, Junping; Wang, Tingting

2011-11-01

A miniature fiber optic pressure sensor based on Fabry-Perot interference fabricated on the tip of a single mode (SM) fiber is presented. The sensor measures only 125μm in diameter. A Fabry-Perot cavity and a thin silica diaphragm are fabricated by simple techniques involving only cleaving, wet chemical etching and fusion splicing. Interference pattern of the sensor is analyzed and issues in sensor design are discussed. The overall chemical reaction of the fiber wet etching is specifically represented. Pressure testing system is carried out. By tracing a peak point in the interference spectrum, the gap length of the sensor can be demodulated. Experimental results show the sensor has a good linearity. The sensor is made entirely of fused silica, whose structure has good stability, cabinet, simple for fabrication and low cost.

A new hysteresis model based on force-displacement characteristics of magnetorheological fluid actuators subjected to squeeze mode operation

NASA Astrophysics Data System (ADS)

Chen, Peng; Bai, Xian-Xu; Qian, Li-Jun; Choi, Seung-Bok

2017-06-01

This paper presents a new hysteresis model based on the force-displacement characteristics of magnetorheological (MR) fluid actuators (or devices) subjected to squeeze mode operation. The idea of the proposed model is originated from experimental observation of the field-dependent hysteretic behavior of MR fluids, which shows that from a view of rate-independence of hysteresis, a gap width-dependent hysteresis is occurred in the force-displacement relationship instead of the typical relationship of the force-velocity. To effectively and accurately portray the hysteresis behavior, the gap width-dependent hysteresis elements, the nonlinear viscous effect and the inertial effect are considered for the formulation of the hysteresis model. Then, a model-based feedforward force tracking control scheme is established through an observer which can estimate the virtual displacement. The effectiveness of the proposed hysteresis model is validated through the identification and prediction of the damping force of MR fluids in the squeeze mode. In addition, it is shown that superior force tracking performance of the feedforward control associated with the proposed hysteresis mode is evaluated by adopting several tracking trajectories.

Entropically Stabilized Colloidal Crystals Hold Entropy in Collective Modes

NASA Astrophysics Data System (ADS)

Antonaglia, James; van Anders, Greg; Glotzer, Sharon

Ordered structures can be stabilized by entropy if the system has more ordered microstates available than disordered ones. However, ``locating'' the entropy in an ordered system is challenging because entropic ordering is necessarily a collective effort emerging from the interactions of large numbers of particles. Yet, we can characterize these crystals using simple traditional tools, because entropically stabilized crystals exhibit collective motion and effective stiffness. For a two-dimensional system of hard hexagons, we calculate the dispersion relations of both vibrational and librational collective modes. We find the librational mode is gapped, and the gap provides an emergent, macroscopic, and density-dependent length scale. We quantify the entropic contribution of each collective mode and find that below this length scale, the dominant entropic contributions are librational, and above this length scale, vibrations dominate. This length scale diverges in the high-density limit, so entropy is found predominantly in libration near dense packing. National Science Foundation Graduate Research Fellowship Program Grant No. DGE 1256260, Advanced Research Computing at the University of Michigan, Ann Arbor, and the Simons Foundation.

Unusual phonon behavior and ultra-low thermal conductance of monolayer InSe.

PubMed

Zhou, Hangbo; Cai, Yongqing; Zhang, Gang; Zhang, Yong-Wei

2017-12-21

Monolayer indium selenide (InSe) possesses numerous fascinating properties, such as high electron mobility, quantum Hall effect and anomalous optical response. However, its phonon properties, thermal transport properties and the origin of its structural stability remain unexplored. Using first-principles calculations, we show that the atoms in InSe are highly polarized and such polarization causes strong long-range dipole-dipole interaction (DDI). For acoustic modes, DDI is essential for maintaining its structural stability. For optical modes, DDI causes a significant frequency shift of its out-of-phase vibrations. Surprisingly, we observed that there were two isolated frequency regimes, which were completely separated from other frequency regimes with large frequency gaps. Within each frequency regime, only a single phonon mode exists. We further reveal that InSe possesses the lowest thermal conductance among the known two-dimensional materials due to the low cut-off frequency, low phonon group velocities and the presence of large frequency gaps. These unique behaviors of monolayer InSe can enable the fabrication of novel devices, such as thermoelectric module, single-mode phonon channel and phononic laser.

Post-Test Analysis of the Deep Space One Spare Flight Thruster Ion Optics

NASA Technical Reports Server (NTRS)

Anderson, John R.; Sengupta, Anita; Brophy, John R.

2004-01-01

The Deep Space 1 (DSl) spare flight thruster (FT2) was operated for 30,352 hours during the extended life test (ELT). The test was performed to validate the service life of the thruster, study known and identify unknown life limiting modes. Several of the known life limiting modes involve the ion optics system. These include loss of structural integrity for either the screen grid or accelerator grid due to sputter erosion from energetic ions striking the grid, sputter erosion enlargement of the accelerator grid apertures to the point where the accelerator grid power supply can no longer prevent electron backstreaming, unclearable shorting between the grids causes by flakes of sputtered material, and rouge hole formation due to flakes of material defocusing the ion beam. Grid gap decrease, which increases the probability of electron backstreaming and of arcing between the grids, was identified as an additional life limiting mechanism after the test. A combination of accelerator grid aperture enlargement and grid gap decrease resulted in the inability to prevent electron backstreaming at full power at 26,000 hours of the ELT. Through pits had eroded through the accelerator grid webbing and grooves had penetrated through 45% of the grid thickness in the center of the grid. The upstream surface of the screen grid eroded in a chamfered pattern around the holes in the central portion of the grid. Sputter deposited material, from the accelerator grid, adhered to the downstream surface of the screen grid and did not spall to form flakes. Although a small amount of sputter deposited material protruded into the screen grid apertures, no rouge holes were found after the ELT.

RNAPattMatch: a web server for RNA sequence/structure motif detection based on pattern matching with flexible gaps

PubMed Central

Drory Retwitzer, Matan; Polishchuk, Maya; Churkin, Elena; Kifer, Ilona; Yakhini, Zohar; Barash, Danny

2015-01-01

Searching for RNA sequence-structure patterns is becoming an essential tool for RNA practitioners. Novel discoveries of regulatory non-coding RNAs in targeted organisms and the motivation to find them across a wide range of organisms have prompted the use of computational RNA pattern matching as an enhancement to sequence similarity. State-of-the-art programs differ by the flexibility of patterns allowed as queries and by their simplicity of use. In particular—no existing method is available as a user-friendly web server. A general program that searches for RNA sequence-structure patterns is RNA Structator. However, it is not available as a web server and does not provide the option to allow flexible gap pattern representation with an upper bound of the gap length being specified at any position in the sequence. Here, we introduce RNAPattMatch, a web-based application that is user friendly and makes sequence/structure RNA queries accessible to practitioners of various background and proficiency. It also extends RNA Structator and allows a more flexible variable gaps representation, in addition to analysis of results using energy minimization methods. RNAPattMatch service is available at http://www.cs.bgu.ac.il/rnapattmatch. A standalone version of the search tool is also available to download at the site. PMID:25940619

Pattern identification in time-course gene expression data with the CoGAPS matrix factorization.

PubMed

Fertig, Elana J; Stein-O'Brien, Genevieve; Jaffe, Andrew; Colantuoni, Carlo

2014-01-01

Patterns in time-course gene expression data can represent the biological processes that are active over the measured time period. However, the orthogonality constraint in standard pattern-finding algorithms, including notably principal components analysis (PCA), confounds expression changes resulting from simultaneous, non-orthogonal biological processes. Previously, we have shown that Markov chain Monte Carlo nonnegative matrix factorization algorithms are particularly adept at distinguishing such concurrent patterns. One such matrix factorization is implemented in the software package CoGAPS. We describe the application of this software and several technical considerations for identification of age-related patterns in a public, prefrontal cortex gene expression dataset.

Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes

NASA Astrophysics Data System (ADS)

Han, Weiqing; Meehl, Gerald A.; Stammer, Detlef; Hu, Aixue; Hamlington, Benjamin; Kenigson, Jessica; Palanisamy, Hindumathi; Thompson, Philip

2017-01-01

Sea level rise (SLR) can exert significant stress on highly populated coastal societies and low-lying island countries around the world. Because of this, there is huge societal demand for improved decadal predictions and future projections of SLR, particularly on a local scale along coastlines. Regionally, sea level variations can deviate considerably from the global mean due to various geophysical processes. These include changes of ocean circulations, which partially can be attributed to natural, internal modes of variability in the complex Earth's climate system. Anthropogenic influence may also contribute to regional sea level variations. Separating the effects of natural climate modes and anthropogenic forcing, however, remains a challenge and requires identification of the imprint of specific climate modes in observed sea level change patterns. In this paper, we review our current state of knowledge about spatial patterns of sea level variability associated with natural climate modes on interannual-to-multidecadal timescales, with particular focus on decadal-to-multidecadal variability. Relevant climate modes and our current state of understanding their associated sea level patterns and driving mechanisms are elaborated separately for the Pacific, the Indian, the Atlantic, and the Arctic and Southern Oceans. We also discuss the issues, challenges and future outlooks for understanding the regional sea level patterns associated with climate modes. Effects of these internal modes have to be taken into account in order to achieve more reliable near-term predictions and future projections of regional SLR.

Closing the gap between research and management

Treesearch

Deborah M. Finch; Marcia Patton-Mallory

1993-01-01

In this paper, we evaluate the reasons for gaps in communication between researchers and natural resource managers and identify methods to close these gaps. Gaps originate from differing patterns of language use, disparities in organizational culture and values, generation of knowledge that is too narrowly-focused to solve complex problems, failure by managers to relay...

A Search for Rapidly Pulsating Hot Subdwarf Stars in the GALEX Survey

NASA Astrophysics Data System (ADS)

Boudreaux, Thomas M.; Barlow, Brad N.; Fleming, Scott W.; Vasquez Soto, Alan; Million, Chase; Reichart, Dan E.; Haislip, Josh B.; Linder, Tyler R.; Moore, Justin P.

2017-08-01

NASA’s Galaxy Evolution Explorer (GALEX) provided near- and far-UV observations for approximately 77% of the sky over a 10-year period; however, the data reduction pipeline initially only released single NUV and FUV images to the community. The recently released Python module gPhoton changes this, allowing calibrated time-series aperture photometry to be extracted easily from the raw GALEX data set. Here we use gPhoton to generate light curves for all hot subdwarf B (sdB) stars that were observed by GALEX, with the intention of identifying short-period, p-mode pulsations. We find that the spacecraft’s short visit durations, uneven gaps between visits, and dither pattern make the detection of hot subdwarf pulsations difficult. Nonetheless, we detect UV variations in four previously known pulsating targets and report their UV pulsation amplitudes and frequencies. Additionally, we find that several other sdB targets not previously known to vary show promising signals in their periodograms. Using optical follow-up photometry with the Skynet Robotic Telescope Network, we confirm p-mode pulsations in one of these targets, LAMOST J082517.99+113106.3, and report it as the most recent addition to the sdBV r class of variable stars.

Black Holes as Brains: Neural Networks with Area Law Entropy

NASA Astrophysics Data System (ADS)

Dvali, Gia

2018-04-01

Motivated by the potential similarities between the underlying mechanisms of the enhanced memory storage capacity in black holes and in brain networks, we construct an artificial quantum neural network based on gravity-like synaptic connections and a symmetry structure that allows to describe the network in terms of geometry of a d-dimensional space. We show that the network possesses a critical state in which the gapless neurons emerge that appear to inhabit a (d-1)-dimensional surface, with their number given by the surface area. In the excitations of these neurons, the network can store and retrieve an exponentially large number of patterns within an arbitrarily narrow energy gap. The corresponding micro-state entropy of the brain network exhibits an area law. The neural network can be described in terms of a quantum field, via identifying the different neurons with the different momentum modes of the field, while identifying the synaptic connections among the neurons with the interactions among the corresponding momentum modes. Such a mapping allows to attribute a well-defined sense of geometry to an intrinsically non-local system, such as the neural network, and vice versa, it allows to represent the quantum field model as a neural network.

Continuous-wave mid-infrared photonic crystal light emitters at room temperature

NASA Astrophysics Data System (ADS)

Weng, Binbin; Qiu, Jijun; Shi, Zhisheng

2017-01-01

Mid-infrared photonic crystal enhanced lead-salt light emitters operating under continuous-wave mode at room temperature were investigated in this work. For the device, an active region consisting of 9 pairs of PbSe/Pb0.96Sr0.04Se quantum wells was grown by molecular beam epitaxy method on top of a Si(111) substrate which was initially dry-etched with a two-dimensional photonic crystal structure in a pattern of hexagonal holes. Because of the photonic crystal structure, an optical band gap between 3.49 and 3.58 µm was formed, which matched with the light emission spectrum of the quantum wells at room temperature. As a result, under optical pumping, using a near-infrared continuous-wave semiconductor laser, the device exhibited strong photonic crystal band-edge mode emissions and delivered over 26.5 times higher emission efficiency compared to the one without photonic crystal structure. The output power obtained was up to 7.68 mW (the corresponding power density was 363 mW/cm2), and a maximum quantum efficiency reached to 1.2%. Such photonic crystal emitters can be used as promising light sources for novel miniaturized gas-sensing systems.

Spatial and polarization entanglement of lasing patterns and related dynamic behaviors in laser-diode-pumped solid-state lasers.

PubMed

Otsuka, K; Chu, S-C; Lin, C-C; Tokunaga, K; Ohtomo, T

2009-11-23

To provide the underlying physical mechanism for formations of spatial- and polarization-entangled lasing patterns (namely, SPEPs), we performed experiments using a c-cut Nd:GdVO(4) microchip laser with off-axis laser-diode pumping. This extends recent work on entangled lasing pattern generation from an isotropic laser, where such a pattern was explained only in terms of generalized coherent states (GCSs) formed by mathematical manipulation. Here, we show that polarization-resolved transverse patterns can be well explained by the transverse mode-locking of distinct orthogonal linearly polarized Ince-Gauss (IG) mode pairs rather than GCSs. Dynamic properties of SPEPs were experimentally examined in both free-running and modulated conditions to identify long-term correlations of IG mode pairs over time. The complete chaos synchronization among IG mode pairs subjected to external perturbation is also demonstrated.

Food Consumption and its impact on Cardiovascular Disease: Importance of Solutions focused on the globalized food system

PubMed Central

Anand, Sonia S.; Hawkes, Corinna; de Souza, Russell J.; Mente, Andrew; Dehghan, Mahshid; Nugent, Rachel; Zulyniak, Michael A.; Weis, Tony; Bernstein, Adam M.; Krauss, Ronald; Kromhout, Daan; Jenkins, David J.A.; Malik, Vasanti; Martinez-Gonzalez, Miguel A.; Mozafarrian, Dariush; Yusuf, Salim; Willett, Walter C.; Popkin, Barry M

2015-01-01

Major scholars in the field, based on a 3-day consensus, created an in-depth review of current knowledge on the role of diet in CVD, the changing global food system and global dietary patterns, and potential policy solutions. Evidence from different countries, age/race/ethnicity/socioeconomic groups suggest the health effects studies of foods, macronutrients, and dietary patterns on CVD appear to be far more consistent though regional knowledge gaps are highlighted. There are large gaps in knowledge about the association of macronutrients to CVD in low- and middle-income countries (LMIC), particularly linked with dietary patterns are reviewed. Our understanding of foods and macronutrients in relationship to CVD is broadly clear; however major gaps exist both in dietary pattern research and ways to change diets and food systems. Based on the current evidence, the traditional Mediterranean-type diet, including plant foods/emphasizing plant protein sources, provides a well-tested healthy dietary pattern to reduce CVD. PMID:26429085

Adhesive micro-line periodicity determines guidance of axonal outgrowth†

PubMed Central

Huang, Yu; Fothergill, Thomas; Lumbard, Derek C.; Dent, Erik W.; Williams, Justin C.

2014-01-01

Adhesive micro-lines of various sub-cellular geometries were created using a non-traditional micro stamping technique. This technique employed the use of commercially available diffraction gratings as the molds for the micro stamps, a method which is quick and inexpensive, and which could easily be adopted as a patterning tool in a variety of research efforts. The atypical saw-tooth profile of the micro stamps enabled a unique degree of control and flexibility over patterned line and gap widths. Cortical neurons cultured on patterned poly-lysine micro-lines on PDMS exhibit a startling transition in axonal guidance: From the expected parallel guidance to an unexpected perpendicular guidance that becomes dominant as patterned lines and gaps become sufficiently narrow. This transition is most obvious when the lines are narrow relative to gaps, while the periodicity of the pattern is reduced. Axons growing perpendicular to micro-lines exhibited ‘vinculated’ growth, a unique morphological phenotype consisting of periodic orthogonal extensions along the axon. PMID:23250489

Semiconductor quantum well irradiated by a two-mode electromagnetic field as a terahertz emitter

NASA Astrophysics Data System (ADS)

Mandal, S.; Liew, T. C. H.; Kibis, O. V.

2018-04-01

We study theoretically the nonlinear optical properties of a semiconductor quantum well (QW) irradiated by a two-mode electromagnetic wave consisting of a strong resonant dressing field and a weak off-resonant driving field. In the considered strongly coupled electron-field system, the dressing field opens dynamic Stark gaps in the electron energy spectrum of the QW, whereas the driving field induces electron oscillations in the QW plane. Since the gapped electron spectrum restricts the amplitude of the oscillations, the emission of a frequency comb from the QW appears. Therefore, the doubly driven QW operates as a nonlinear optical element which can be used, particularly, for optically controlled generation of terahertz radiation.

Quasiperiodic moiré plasmonic crystals.

PubMed

Lubin, Steven M; Hryn, Alexander J; Huntington, Mark D; Engel, Clifford J; Odom, Teri W

2013-12-23

This paper describes the properties of silver plasmonic crystals with quasiperiodic rotational symmetries. Compared to periodic plasmonic crystals, quasiperiodic moiré structures exhibited an increased number of surface plasmon polariton modes, especially at high angles of excitation. In addition, plasmonic band gaps were often formed at the intersections of these new modes. To identify the origin and predict the location of the band gaps, we developed a Bragg-based indexing system using the reciprocal lattice vectors of the moiré plasmonic crystals. We showed that even more complicated quasiperiodic geometries could also be described by this indexing model. We anticipate that these quasiperiodic lattices will be useful for applications that require the concentration and manipulation of light over a broadband spectrum.

Regeneration Patterns in Canopy Gaps of Mixed-oak Forests of the Southern Appalachians: Influences of Topographic Position and Evergreen Understory

Treesearch

Barton D. Clinton; Lindsay R. Boring; Wayne T. Swank

1994-01-01

Canopy gaps in southern Appalachian mixed-oak forests were assessed for the effects of topographic, gap and stand variables on density of wood seedlings. Seedling density was significantly correlated with percent slope and positively with gap age (l-5 yr). Density varied substantially among topographic positions and increased with gap size. Species richness...

Compact Reconfigurable Antenna with an Omnidirectional Pattern and Four Directional Patterns for Wireless Sensor Systems

PubMed Central

Wang, Ren; Wang, Bing-Zhong; Huang, Wei-Ying; Ding, Xiao

2016-01-01

A compact reconfigurable antenna with an omnidirectional mode and four directional modes is proposed. The antenna has a main radiator and four parasitic elements printed on a dielectric substrate. By changing the status of diodes soldered on the parasitic elements, the proposed antenna can generate four directional radiation patterns and one omnidirectional radiation pattern. The main beam directions of the four directional modes are almost orthogonal and the four directional beams can jointly cover a 360° range in the horizontal plane, i.e., the main radiation plane of omnidirectional mode. The whole volume of the antenna and the control network is approximately 0.70 λ × 0.53 λ × 0.02 λ, where λ is the wavelength corresponding to the center frequency. The proposed antenna has a simple structure and small dimensions under the requirement that the directional radiation patterns can jointly cover the main radiation plane of the omnidirectional mode, therefore, it can be used in smart wireless sensor systems for different application scenarios. PMID:27092512

Further development of image processing algorithms to improve detectability of defects in Sonic IR NDE

NASA Astrophysics Data System (ADS)

Obeidat, Omar; Yu, Qiuye; Han, Xiaoyan

2017-02-01

Sonic Infrared imaging (SIR) technology is a relatively new NDE technique that has received significant acceptance in the NDE community. SIR NDE is a super-fast, wide range NDE method. The technology uses short pulses of ultrasonic excitation together with infrared imaging to detect defects in the structures under inspection. Defects become visible to the IR camera when the temperature in the crack vicinity increases due to various heating mechanisms in the specimen. Defect detection is highly affected by noise levels as well as mode patterns in the image. Mode patterns result from the superposition of sonic waves interfering within the specimen during the application of sound pulse. Mode patterns can be a serious concern, especially in composite structures. Mode patterns can either mimic real defects in the specimen, or alternatively, hide defects if they overlap. In last year's QNDE, we have presented algorithms to improve defects detectability in severe noise. In this paper, we will present our development of algorithms on defect extraction targeting specifically to mode patterns in SIR images.

Amplitude mode oscillations in pump-probe photoemission spectra from a d -wave superconductor

NASA Astrophysics Data System (ADS)

Nosarzewski, B.; Moritz, B.; Freericks, J. K.; Kemper, A. F.; Devereaux, T. P.

2017-11-01

Recent developments in the techniques of ultrafast pump-probe photoemission have made possible the search for collective modes in strongly correlated systems out of equilibrium. Including inelastic scattering processes and a retarded interaction, we simulate time- and angle-resolved photoemission spectroscopy (trARPES) to study the amplitude mode of a d -wave superconductor, a collective mode excited through the nonlinear light-matter coupling to the pump pulse. We find that the amplitude mode oscillations of the d -wave order parameter occur in phase at a single frequency that is twice the quasi-steady-state maximum gap size after pumping. We comment on the necessary conditions for detecting the amplitude mode in trARPES experiments.

Practice Patterns of School-Based Occupational Therapists Targeting Handwriting: A Knowledge-to-Practice Gap

ERIC Educational Resources Information Center

Cramm, Heidi; Egan, Mary

2015-01-01

Poor handwriting is a common reason for referral to school-based occupational therapy. A survey was used to explore the extent to which current practice patterns in Ontario, Canada, align with evidence on effective intervention for handwriting. Knowledge-to-practice gaps were identified related to focus on performance components versus…

Multi-mode horn antenna simulation

NASA Technical Reports Server (NTRS)

Dod, L. R.; Wolf, J. D.

1980-01-01

Radiation patterns were computed for a circular multimode horn antenna using waveguide electric field radiation expressions. The circular multimode horn was considered as a possible reflector feed antenna for the Large Antenna Multifrequency Microwave Radiometer (LAMMR). This horn antenna uses a summation of the TE sub 11 deg and TM sub 11 deg modes to generate far field primary radiation patterns with equal E and H plane beamwidths and low sidelobes. A computer program for the radiation field expressions using the summation of waveguide radiation modes is described. The sensitivity of the multimode horn antenna radiation patterns to phase variations between the two modes is given. Sample radiation pattern calculations for a reflector feed horn for LAMMR are shown. The multimode horn antenna provides a low noise feed suitable for radiometric applications.

STEM-EELS analysis of multipole surface plasmon modes in symmetry-broken AuAg nanowire dimers

NASA Astrophysics Data System (ADS)

Schubert, Ina; Sigle, Wilfried; van Aken, Peter A.; Trautmann, Christina; Toimil-Molares, Maria Eugenia

2015-03-01

Surface plasmon coupling in nanowires separated by small gaps generates high field enhancements at the position of the gap and is thus of great interest for sensing applications. It is known that the nanowire dimensions and in particular the symmetry of the structures has strong influence on the plasmonic properties of the dimer structure. Here, we report on multipole surface plasmon coupling in symmetry-broken AuAg nanowire dimers. Our dimers, consisting of two nanowires with different lengths and separated by gaps of only 10 to 30 nm, were synthesized by pulsed electrochemical deposition in ion track-etched polymer templates. Electron energy-loss spectroscopy in scanning transmission electron microscopy allows us to resolve up to nine multipole order surface plasmon modes of these dimers spectrally separated from each other. The spectra evidence plasmon coupling between resonances of different multipole order, resulting in the generation of additional plasmonic modes. Since such complex structures require elaborated synthesis techniques, dimer structures with complex composition, morphology and shape are created. We demonstrate that finite element simulations on pure Au dimers can predict the generated resonances in the fabricated structures. The excellent agreement of our experiment on AuAg dimers with finite integration simulations using CST microwave studio manifests great potential to design complex structures for sensing applications.

Acoustic Resonance and Vortex Shedding from Tube Banks of Boiler Plant

NASA Astrophysics Data System (ADS)

Hamakawa, Hiromitsu; Matsue, Hiroto; Nishida, Eiichi; Fukano, Tohru

This paper focuses on the relationship between acoustic resonance and vortex shedding from the tube banks of a boiler plant. We have built a model similar to the actual boiler plant to clarify the characteristics of acoustic resonance phenomena and vortex shedding. The model used in-line tube banks with a small tube pitch ratio. We examined the relationship between the acoustic resonance of the actual plant and that of the model, and measured the sound pressure level, acoustic pressure mode shape, spectrum of velocity fluctuation, and gap velocity. Gap velocity was defined as the mean velocity in the smallest gaps between two neighboring tubes in the transverse direction. As a result, the resonant frequencies and mode shapes of the acoustic resonances in the actual boiler plant agreed well with those in the similar model. We found many peak frequencies in the sound pressure level spectrum when acoustic resonances occurred. The typical Strouhal numbers at the onset velocity of acoustic resonances were about 0.19, 0.26 and 0.52. Periodic velocity fluctuation caused by vortex shedding was observed inside the tube banks without acoustic resonance. The Strouhal number measured for vortex shedding was 0.15. Acoustic resonances of higher-order modes were generated in this plant.

Impacts of propagating, frustrated and surface modes on radiative, electrical and thermal losses in nanoscale-gap thermophotovoltaic power generators.

PubMed

Bernardi, Michael P; Dupré, Olivier; Blandre, Etienne; Chapuis, Pierre-Olivier; Vaillon, Rodolphe; Francoeur, Mathieu

2015-06-26

The impacts of radiative, electrical and thermal losses on the performances of nanoscale-gap thermophotovoltaic (nano-TPV) power generators consisting of a gallium antimonide cell paired with a broadband tungsten and a radiatively-optimized Drude radiator are analyzed. Results reveal that surface mode mediated nano-TPV power generation with the Drude radiator outperforms the tungsten radiator, dominated by frustrated modes, only for a vacuum gap thickness of 10 nm and if both electrical and thermal losses are neglected. The key limiting factors for the Drude- and tungsten-based devices are respectively the recombination of electron-hole pairs at the cell surface and thermalization of radiation with energy larger than the cell absorption bandgap. A design guideline is also proposed where a high energy cutoff above which radiation has a net negative effect on nano-TPV power output due to thermal losses is determined. It is shown that the power output of a tungsten-based device increases by 6.5% while the cell temperature decreases by 30 K when applying a high energy cutoff at 1.45 eV. This work demonstrates that design and optimization of nano-TPV devices must account for radiative, electrical and thermal losses.

Impacts of propagating, frustrated and surface modes on radiative, electrical and thermal losses in nanoscale-gap thermophotovoltaic power generators

PubMed Central

Bernardi, Michael P.; Dupré, Olivier; Blandre, Etienne; Chapuis, Pierre-Olivier; Vaillon, Rodolphe; Francoeur, Mathieu

2015-01-01

The impacts of radiative, electrical and thermal losses on the performances of nanoscale-gap thermophotovoltaic (nano-TPV) power generators consisting of a gallium antimonide cell paired with a broadband tungsten and a radiatively-optimized Drude radiator are analyzed. Results reveal that surface mode mediated nano-TPV power generation with the Drude radiator outperforms the tungsten radiator, dominated by frustrated modes, only for a vacuum gap thickness of 10 nm and if both electrical and thermal losses are neglected. The key limiting factors for the Drude- and tungsten-based devices are respectively the recombination of electron-hole pairs at the cell surface and thermalization of radiation with energy larger than the cell absorption bandgap. A design guideline is also proposed where a high energy cutoff above which radiation has a net negative effect on nano-TPV power output due to thermal losses is determined. It is shown that the power output of a tungsten-based device increases by 6.5% while the cell temperature decreases by 30 K when applying a high energy cutoff at 1.45 eV. This work demonstrates that design and optimization of nano-TPV devices must account for radiative, electrical and thermal losses. PMID:26112658

Patterns of Change in U.S. Gender Achievement Gaps during Elementary and Middle School

ERIC Educational Resources Information Center

Fahle, Erin

2016-01-01

Research on gender achievement gaps shows they exist, and are largest in the tails of the distribution, starting as early as Kindergarten and persisting through eighth grade. In mathematics, studies find small average gender achievement gaps and larger systematically male-favoring gaps among the highest achieving students. This paper seeks to…

Canopy gaps affect long-term patterns of tree growth and mortality in mature and old-growth forests in the Pacific Northwest

Treesearch

Andrew N. Gray; Thomas A. Spies; Robert J. Pabst

2012-01-01

Canopy gaps created by tree mortality can affect the speed and trajectory of vegetation growth. Species’ population dynamics, and spatial heterogeneity in mature forests. Most studies focus on plant development within gaps, yet gaps also affect the mortality and growth of surrounding trees, which influence shading and root encroachment into gaps and determine whether,...

A new class of tunable hypersonic phononic crystals based on polymer-tethered colloids.

PubMed

Alonso-Redondo, E; Schmitt, M; Urbach, Z; Hui, C M; Sainidou, R; Rembert, P; Matyjaszewski, K; Bockstaller, M R; Fytas, G

2015-09-22

The design and engineering of hybrid materials exhibiting tailored phononic band gaps are fundamentally relevant to innovative material technologies in areas ranging from acoustics to thermo-optic devices. Phononic hybridization gaps, originating from the anti-crossing between local resonant and propagating modes, have attracted particular interest because of their relative robustness to structural disorder and the associated benefit to 'manufacturability'. Although hybridization gap materials are well known, their economic fabrication and efficient control of the gap frequency have remained elusive because of the limited property variability and expensive fabrication methodologies. Here we report a new strategy to realize hybridization gap materials by harnessing the 'anisotropic elasticity' across the particle-polymer interface in densely polymer-tethered colloidal particles. Theoretical and Brillouin scattering analysis confirm both the robustness to disorder and the tunability of the resulting hybridization gap and provide guidelines for the economic synthesis of new materials with deliberately controlled gap position and width frequencies.

Stability considerations for magnetic suspension systems using electromagnets mounted in a planar array

NASA Technical Reports Server (NTRS)

Groom, Nelson J.; Britcher, Colin P.

1991-01-01

Mathematical models of a 5, 6, 7, and 8 coil large gap magnetic suspension system (MSDS) are presented. Some of the topics covered include: force and torque equations, reduction of state-space form, natural modes, origins of modes, effect of rotation in azimuth (yaw), future work, and n-coil ring conclusions.

Study on control of defect mode in hybrid mirror chirped porous silicon photonic crystal

NASA Astrophysics Data System (ADS)

Chen, Ying; Luo, Pei; Han, Yangyang; Cui, Xingning; He, Lei

2018-03-01

Based on the optical resonance principle and the tight-binding theory, a hybrid mirror chirped porous silicon photonic crystal is proposed. The control of the defect mode in hybrid mirror chirped porous silicon photonic crystal is studied. Through the numerical simulation, the control regulations of the defect modes resulted by the number of the periodical layers for the fundamental unit and the cascading number of the chirped structures are analyzed, and the split and the degeneration of the defect modes resulted by the change of the relative location between the mirror structures and the quasi-mirror structures are discussed. The simulation results show that the band gap would be broadened with the increase of the chirp quantity and the layer number of unilateral chirp. Adjusting the structural parameters of the hybrid mirror structure, the multimode characteristics will occur in the band gap. The more the cascading number of the chirped units, the more the number of the filtering channels will be. In addition, with the increase of the relative location between the mirror structures and the quasi-mirror structures, the degeneration of the defect modes will occur and can obtain high Q value. The structure can provide effective theoretical references for the design the multi-channel filters and high Q value sensors.

A high-gain and high-efficiency X-band triaxial klystron amplifier with two-stage cascaded bunching cavities

NASA Astrophysics Data System (ADS)

Zhang, Wei; Ju, Jinchuan; Zhang, Jun; Zhong, Huihuang

2017-12-01

To achieve GW-level amplification output radiation at the X-band, a relativistic triaxial klystron amplifier with two-stage cascaded double-gap bunching cavities is investigated. The input cavity is optimized to obtain a high absorption rate of the external injection microwave. The cascaded bunching cavities are optimized to achieve a high depth of the fundamental harmonic current. A double-gap standing wave extractor is designed to improve the beam wave conversion efficiency. Two reflectors with high reflection coefficients both to the asymmetric mode and the TEM mode are employed to suppress the asymmetric mode competition and TEM mode microwave leakage. Particle-in-cell simulation results show that a high power microwave with a power of 2.53 GW and a frequency of 8.4 GHz is generated with a 690 kV, 9.3 kA electron beam excitation and a 25 kW seed microwave injection. Particularly, the achieved power conversion efficiency is about 40%, and the gain is as high as 50 dB. Meanwhile, there is insignificant self-excitation of the parasitic mode in the proposed structure by adopting the reflectors. The relative phase difference between the injected signals and the output microwaves keeps locked after the amplifier becomes saturated.

“A manager in the minds of doctors:” a comparison of new modes of control in European hospitals

PubMed Central

2013-01-01

Background Hospital governance increasingly combines management and professional self-governance. This article maps the new emergent modes of control in a comparative perspective and aims to better understand the relationship between medicine and management as hybrid and context-dependent. Theoretically, we critically review approaches into the managerialism-professionalism relationship; methodologically, we expand cross-country comparison towards the meso-level of organisations; and empirically, the focus is on processes and actors in a range of European hospitals. Methods The research is explorative and was carried out as part of the FP7 COST action IS0903 Medicine and Management, Working Group 2. Comprising seven European countries, the focus is on doctors and public hospitals. We use a comparative case study design that primarily draws on expert information and document analysis as well as other secondary sources. Results The findings reveal that managerial control is not simply an external force but increasingly integrated in medical professionalism. These processes of change are relevant in all countries but shaped by organisational settings, and therefore create different patterns of control: (1) ‘integrated’ control with high levels of coordination and coherent patterns for cost and quality controls; (2) ‘partly integrated’ control with diversity of coordination on hospital and department level and between cost and quality controls; and (3) ‘fragmented’ control with limited coordination and gaps between quality control more strongly dominated by medicine, and cost control by management. Conclusions Our comparison highlights how organisations matter and brings the crucial relevance of ‘coordination’ of medicine and management across the levels (hospital/department) and the substance (cost/quality-safety) of control into perspective. Consequently, coordination may serve as a taxonomy of emergent modes of control, thus bringing new directions for cost-efficient and quality-effective hospital governance into perspective. PMID:23819578

Thermally Strained Band Gap Engineering of Transition-Metal Dichalcogenide Bilayers with Enhanced Light-Matter Interaction toward Excellent Photodetectors.

PubMed

Wang, Sheng-Wen; Medina, Henry; Hong, Kuo-Bin; Wu, Chun-Chia; Qu, Yindong; Manikandan, Arumugam; Su, Teng-Yu; Lee, Po-Tsung; Huang, Zhi-Quan; Wang, Zhiming; Chuang, Feng-Chuan; Kuo, Hao-Chung; Chueh, Yu-Lun

2017-09-26

Integration of strain engineering of two-dimensional (2D) materials in order to enhance device performance is still a challenge. Here, we successfully demonstrated the thermally strained band gap engineering of transition-metal dichalcogenide bilayers by different thermal expansion coefficients between 2D materials and patterned sapphire structures, where MoS 2 bilayers were chosen as the demonstrated materials. In particular, a blue shift in the band gap of the MoS 2 bilayers can be tunable, displaying an extraordinary capability to drive electrons toward the electrode under the smaller driven bias, and the results were confirmed by simulation. A model to explain the thermal strain in the MoS 2 bilayers during the synthesis was proposed, which enables us to precisely predict the band gap-shifted behaviors on patterned sapphire structures with different angles. Furthermore, photodetectors with enhancement of 286% and 897% based on the strained MoS 2 on cone- and pyramid-patterned sapphire substrates were demonstrated, respectively.

Development of Model for Pedestrian Gap Based on Land Use Pattern at Midblock Location and Estimation of Delay at Intersections

NASA Astrophysics Data System (ADS)

Ramesh, Adepu; Ashritha, Kilari; Kumar, Molugaram

2018-04-01

Walking has always been a prime source of human mobility for short distance travel. Traffic congestion has become a major problem for safe pedestrian crossing in most of the metropolitan cities. This has emphasized for providing a sufficient pedestrian gap for safe crossing on urban road. The present works aims in understanding factors that influence pedestrian crossing behaviour. Four locations were chosen for identification of pedestrian crossing behaviour, gap characteristics, waiting time etc., in Hyderabad city. From the study it was observed that pedestrian behaviour and crossing patterns are different and is influenced by land use pattern. A gap acceptance model was developed from the data for improving pedestrian safety at mid-block location; the model was validated using the existing data. Pedestrian delay was estimated at intersection using Highway Capacity Manual (HCM). It was observed that field delays are less when compared to delay arrived from HCM method.

Direct graphene growth on MgO: origin of the band gap.

PubMed

Gaddam, Sneha; Bjelkevig, Cameron; Ge, Siping; Fukutani, Keisuke; Dowben, Peter A; Kelber, Jeffry A

2011-02-23

A 2.5 monolayer (ML) thick graphene film grown by chemical vapor deposition of thermally dissociated C(2)H(4) on MgO(111), displays a significant band gap. The apparent six-fold low energy electron diffraction (LEED) pattern actually consists of two three-fold patterns with different 'A' and 'B' site diffraction intensities. Similar effects are observed for the LEED patterns of a 1 ML carbon film derived from annealing adventitious carbon on MgO(111), and for a 1.5 ML thick graphene film grown by sputter deposition on the 1 ML film. The LEED data indicate different electron densities at the A and B sites of the graphene lattice, suggesting that the observed band gap results from lifting the graphene HOMO/LUMO degeneracy at the Dirac point. The data also indicate that disparities in A site/B site LEED intensities decrease with increasing carbon overlayer thickness, suggesting that the graphene band gap size decreases with increasing number of graphene layers on MgO(111). © 2011 IOP Publishing Ltd

Asymptotics of surface-plasmon redshift saturation at subnanometric separations

NASA Astrophysics Data System (ADS)

Schnitzer, Ory; Giannini, Vincenzo; Craster, Richard V.; Maier, Stefan A.

2016-01-01

Many promising nanophotonics endeavors hinge upon the unique plasmonic properties of nanometallic structures with narrow nonmetallic gaps, which support superconcentrated bonding modes that singularly redshift with decreasing separations. In this Rapid Communication, we present a descriptive physical picture, complemented by elementary asymptotic formulas, of a nonlocal mechanism for plasmon redshift saturation at subnanometric gap widths. Thus, by considering the electron-charge and field distributions in the close vicinity of the metal-vacuum interface, we show that nonlocality is asymptotically manifested as an effective potential discontinuity. For bonding modes in the near-contact limit, the latter discontinuity is shown to be effectively equivalent to a widening of the gap. As a consequence, the resonance-frequency near-contact asymptotics are a renormalization of the corresponding local ones. Specifically, the renormalization furnishes an asymptotic plasmon-frequency lower bound that scales with the 1 /4 power of the Fermi wavelength. We demonstrate these remarkable features in the prototypical cases of nanowire and nanosphere dimers, showing agreement between our elementary expressions and previously reported numerical computations.

Photonic band gap and defects modes in inorganic/organic photonic crystal based on Si and HMDSO layers deposited by sputtering and PECVD

NASA Astrophysics Data System (ADS)

Amri, R.; Sahel, S.; Gamra, D.; Lejeune, M.; Clin, M.; Zellama, K.; Bouchriha, H.

2018-02-01

Hybrid inorganic/organic one dimensional photonic crystal based on alternating layers of Si/HMDSO is elaborated. The inorganic silicon is deposited by radiofrequency magnetron sputtering and the organic HMDSO is deposited by PECVD technique. As the Si refractive index is n = 3.4, and the refractive index of HMDSO layer depend on the deposition conditions, to get a photonic crystal with high and low refractive index presenting a good contrast, we have varied the radiofrequency power of PECVD process to obtain HMDSO layer with low refractive index (n = 1.45). Photonic band gap of this hybrid structure is obtained from the transmission and reflection spectra and appears after 9 alternative layers of Si/HMDSO. The introduction of defects in our photonic crystal leads to the emergence of localized modes within the photonic band gap. Our results are interpreted by using a theoretical model based on transfer matrix.

Tuning of electronic properties and dynamical stability of graphene oxide with different functional groups

NASA Astrophysics Data System (ADS)

Dabhi, Shweta D.; Jha, Prafulla K.

2017-09-01

The structural, electronic and vibrational properties of graphene oxide (GO) with varying proportion of epoxy and hydroxyl functional groups have been studied using density functional theory. The functional groups and oxygen density have an obvious influence on the electronic and vibrational properties. The dependence of band gap on associated functional groups and oxygen density shows a possibility of tuning the band gap of graphene by varying the functional groups as well as oxidation level. The absorption of high oxygen content in graphene leads to the gap opening and resulting in a transition from semimetal to semiconductor. Phonon dispersion curves show no imaginary frequency or no softening of any phonon mode throughout the Brillouin zone which confirms the dynamical stability of all considered GO models. Different groups and different oxygen density result into the varying characteristics of phonon modes. The computed results show good agreement with the experimental observations. Our results present interesting possibilities for engineering the electronic properties of graphene and GO and impact the fabrication of new electronics.

Patterns and Trends in Achievement Gaps in Malaysian Secondary Schools (1999-2011): Gender, Ethnicity, and Socioeconomic Status

ERIC Educational Resources Information Center

Saw, Guan Kung

2016-01-01

Educational inequality is a highly debated yet empirically understudied topic in Malaysia. This paper examines the patterns and trends of academic achievement gaps by student social groups in Malaysia, drawing upon nationally representative data for the most recent four cohorts (1999, 2003, 2007, and 2011) of eighth-grade Malaysian students from…

RIE-based Pattern Transfer Using Nanoparticle Arrays as Etch Masks

NASA Astrophysics Data System (ADS)

Hogg, Chip; Majetich, Sara A.; Bain, James A.

2009-03-01

Nanomasking is used to transfer the pattern of a self-assembled array of nanoparticles into an underlying thin film, for potential use as bit-patterned media. We have used this process to investigate the limits of pattern transfer, as a function of gap size in the pattern. Reactive Ion Etching (RIE) is our chosen process, since the gaseous reaction products and high chemical selectivity are ideal features for etching very small gaps. Interstitial surfactant is removed with an O2 plasma, allowing the etchants to penetrate between the particles. Their pattern is transferred into an intermediate SiO2 mask using a CH4-based RIE. This patterned SiO2 layer is finally used as a mask for the MeOH-based RIE which patterns the magnetic film. We present cross-sectional TEM characterization of the etch profiles, as well as magnetic characterization of the film before and after patterning.

A tripolar pattern as an internal mode of the East Asian summer monsoon

NASA Astrophysics Data System (ADS)

Hirota, Nagio; Takahashi, Masaaki

2012-11-01

A tripolar anomaly pattern with centers located around the Philippines, China/Japan, and East Siberia dominantly appears in climate variations of the East Asian summer monsoon. In this study, we extracted this pattern as the first mode of a singular value decomposition (SVD1) over East Asia. The squared covariance fraction of SVD1 was 59 %, indicating that this pattern can be considered a dominant pattern of climate variations. Moreover, the results of numerical experiments suggested that the structure is also a dominant pattern of linear responses, even if external forcing is distributed homogeneously over the Northern Hemisphere. Thus, the tripolar pattern can be considered an internal mode that is characterized by the internal atmospheric processes. In this pattern, the moist processes strengthen the circulation anomalies, the dynamical energy conversion supplies energy to the anomalies, and the Rossby waves propagate northward in the lower troposphere and southeastward in the upper troposphere. These processes are favorable for the pattern to have large amplitude and to influence a large area.

Eliminating the zero spectrum in Fourier transform profilometry using empirical mode decomposition.

PubMed

Li, Sikun; Su, Xianyu; Chen, Wenjing; Xiang, Liqun

2009-05-01

Empirical mode decomposition is introduced into Fourier transform profilometry to extract the zero spectrum included in the deformed fringe pattern without the need for capturing two fringe patterns with pi phase difference. The fringe pattern is subsequently demodulated using a standard Fourier transform profilometry algorithm. With this method, the deformed fringe pattern is adaptively decomposed into a finite number of intrinsic mode functions that vary from high frequency to low frequency by means of an algorithm referred to as a sifting process. Then the zero spectrum is separated from the high-frequency components effectively. Experiments validate the feasibility of this method.

Resonant tunneling effects on cavity-embedded metal film caused by surface-plasmon excitation.

PubMed

Lan, Yung-Chiang; Chang, Che-Jung; Lee, Peng-Hsiao

2009-01-01

We investigate cavity-modulated resonant tunneling through a silver film with periodic grooves on both surfaces. A strip cavity embedded in the film affects tunneling frequencies via a coupling mode and waveguide mode. In the coupling mode, both the resonant tunneling through the gap between the groove and the cavity and the cavity itself form an entire resonant structure. In the waveguide mode, however, the cavity functions as a surface-plasmon waveguide. Hence, tunneling frequencies are close to resonant absorption frequencies of the groove structure and are irrelevant to cavity properties.

Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Weiqing; Meehl, Gerald A.; Stammer, Detlef

Sea level rise (SLR) can exert significant stress on highly populated coastal societies and low-lying island countries around the world. Because of this, there is huge societal demand for improved decadal predictions and future projections of SLR, particularly on a local scale along coastlines. Regionally, sea level variations can deviate considerably from the global mean due to various geophysical processes. These include changes of ocean circulations, which partially can be attributed to natural, internal modes of variability in the complex Earth’s climate system. Anthropogenic influence may also contribute to regional sea level variations. Separating the effects of natural climate modesmore » and anthropogenic forcing, however, remains a challenge and requires identification of the imprint of specific climate modes in observed sea level change patterns. In this article, we review our current state of knowledge about spatial patterns of sea level variability associated with natural climate modes on interannual-to-multidecadal timescales, with particular focus on decadal-to-multidecadal variability. Relevant climate modes and our current state of understanding their associated sea level patterns and driving mechanisms are elaborated separately for the Pacific, the Indian, the Atlantic, and the Arctic and Southern Oceans. We also discuss the issues, challenges and future outlooks for understanding the regional sea level patterns associated with climate modes. Effects of these internal modes have to be taken into account in order to achieve more reliable near-term predictions and future projections of regional SLR.« less

Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes

DOE PAGES

Han, Weiqing; Meehl, Gerald A.; Stammer, Detlef; ...

2016-10-04

Sea level rise (SLR) can exert significant stress on highly populated coastal societies and low-lying island countries around the world. Because of this, there is huge societal demand for improved decadal predictions and future projections of SLR, particularly on a local scale along coastlines. Regionally, sea level variations can deviate considerably from the global mean due to various geophysical processes. These include changes of ocean circulations, which partially can be attributed to natural, internal modes of variability in the complex Earth’s climate system. Anthropogenic influence may also contribute to regional sea level variations. Separating the effects of natural climate modesmore » and anthropogenic forcing, however, remains a challenge and requires identification of the imprint of specific climate modes in observed sea level change patterns. In this article, we review our current state of knowledge about spatial patterns of sea level variability associated with natural climate modes on interannual-to-multidecadal timescales, with particular focus on decadal-to-multidecadal variability. Relevant climate modes and our current state of understanding their associated sea level patterns and driving mechanisms are elaborated separately for the Pacific, the Indian, the Atlantic, and the Arctic and Southern Oceans. We also discuss the issues, challenges and future outlooks for understanding the regional sea level patterns associated with climate modes. Effects of these internal modes have to be taken into account in order to achieve more reliable near-term predictions and future projections of regional SLR.« less

Kinetic Monte Carlo simulation of self-organized pattern formation induced by ion beam sputtering using crater functions

NASA Astrophysics Data System (ADS)

Yang, Zhangcan; Lively, Michael A.; Allain, Jean Paul

2015-02-01

The production of self-organized nanostructures by ion beam sputtering has been of keen interest to researchers for many decades. Despite numerous experimental and theoretical efforts to understand ion-induced nanostructures, there are still many basic questions open to discussion, such as the role of erosion or curvature-dependent sputtering. In this work, a hybrid MD/kMC (molecular dynamics/kinetic Monte Carlo) multiscale atomistic model is developed to investigate these knowledge gaps, and its predictive ability is validated across the experimental parameter space. This model uses crater functions, which were obtained from MD simulations, to model the prompt mass redistribution due to single-ion impacts. Defect migration, which is missing from previous models that use crater functions, is treated by a kMC Arrhenius method. Using this model, a systematic study was performed for silicon bombarded by Ar+ ions of various energies (100 eV, 250 eV, 500 eV, 700 eV, and 1000 eV) at incidence angles of 0∘ to 80∘. The simulation results were compared with experimental findings, showing good agreement in many aspects of surface evolution, such as the phase diagram. The underestimation of the ripple wavelength by the simulations suggests that surface diffusion is not the main smoothening mechanism for ion-induced pattern formation. Furthermore, the simulated results were compared with moment-description continuum theory and found to give better results, as the simulation did not suffer from the same mathematical inconsistencies as the continuum model. The key finding was that redistributive effects are dominant in the formation of flat surfaces and parallel-mode ripples, but erosive effects are dominant at high angles when perpendicular-mode ripples are formed. Ion irradiation with simultaneous sample rotation was also simulated, resulting in arrays of square-ordered dots. The patterns obtained from sample rotation were strongly correlated to the rotation speed and to the pattern types formed without sample rotation, and a critical value of about 5 rpm was found between disordered ripples and square-ordered dots. Finally, simulations of dual-beam sputtering were performed, with the resulting patterns determined by the flux ratio of the two beams and the pattern types resulting from single-beam sputtering under the same conditions.

Characterizing the canopy gap structure of a disturbed forest using Fourier transform

Treesearch

R. A. Sommerfeld; J. E. Lundquist; J. Smith

2000-01-01

Diseases and other small-scale disturbances alter spatial patterns of heterogeneity in forests by killing trees. Canopy gaps caused by tree death are a common feature of forests. Because gaps are caused by different disturbances acting at different times and places, operationally determining the locations of gap edges is often difficult. In this study, digital image...

Canopy Gap Characteristics and Drought Influences in Oak Forests of the Coweeta Basin

Treesearch

B.D. Clinton; L.R. Boring

1993-01-01

Canopy gaps in southern Appalachian mixed-Quercus forests were characterized to assess the impact of the 1985-l988 record drought on patterns of tree mortality in relation to topographic variables and changes in overstory composition. Using permanent transects, we sampled 68 canopy gaps within the Coweeta Basin. Among l-5 yr old gaps, the most...

Development of optical micro resonance based sensor for detection and identification of microparticles and biological agents

NASA Astrophysics Data System (ADS)

Saetchnikov, Vladimir A.; Tcherniavskaia, Elina A.; Schweiger, Gustav

2009-05-01

A novel emerging technique for the label-free analysis of nanoparticles including biomolecules using optical micro cavity resonance of whispering-gallery-type modes is being developed. Schemes of such a method based on microsphere melted by laser on the tip of a standard single mode fiber optical cable with a laser and free microsphere matrix have been developed. Using a calibration principal of ultra high resolution spectroscopy based on such a scheme the method is being transformed to make further development for microbial application. The sensitivity of developed schemes has been tested to refractive index changes by monitoring the magnitude of the whispering gallery modes spectral shift. Water solutions of ethanol, glucose, vitamin C and biotin have been used. Some other schemes using similar principals: stand-alone, array and matrix microsphere resonators, liquid core optical ring resonators are also being under development. The influences of the gap in whispering-gallery modes on energy coupling, resonance quality and frequency have been investigated. An optimum gap for sensing applications has been defined at the half maximum energy coupling where both the Q factor and coupling efficiency are high and the resonance frequency is little affected by the gap variation. Developed schemes have been demonstrated to be a promising technology platform for sensitive, lab-on-chip type sensor which can be used for development of diagnostic tools for different biological molecules, e.g. proteins, oligonucleotides, oligosaccharides, lipids, small molecules, viral particles, cells as well as in different experimental contexts e.g. proteomics, genomics, drug discovery, and membrane studies.

Amplitude mode oscillations in pump-probe photoemission spectra from a d -wave superconductor

DOE PAGES

Nosarzewski, B.; Moritz, B.; Freericks, J. K.; ...

2017-11-20

Recent developments in the techniques of ultrafast pump-probe photoemission have made possible the search for collective modes in strongly correlated systems out of equilibrium. Including inelastic scattering processes and a retarded interaction, we simulate time- and angle-resolved photoemission spectroscopy (trARPES) to study the amplitude mode of a d-wave superconductor, a collective mode excited through the nonlinear light-matter coupling to the pump pulse. We find that the amplitude mode oscillations of the d-wave order parameter occur in phase at a single frequency that is twice the quasi-steady-state maximum gap size after pumping. As a result, we comment on the necessary conditionsmore » for detecting the amplitude mode in trARPES experiments.« less

Amplitude mode oscillations in pump-probe photoemission spectra from a d -wave superconductor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nosarzewski, B.; Moritz, B.; Freericks, J. K.

Recent developments in the techniques of ultrafast pump-probe photoemission have made possible the search for collective modes in strongly correlated systems out of equilibrium. Including inelastic scattering processes and a retarded interaction, we simulate time- and angle-resolved photoemission spectroscopy (trARPES) to study the amplitude mode of a d-wave superconductor, a collective mode excited through the nonlinear light-matter coupling to the pump pulse. We find that the amplitude mode oscillations of the d-wave order parameter occur in phase at a single frequency that is twice the quasi-steady-state maximum gap size after pumping. As a result, we comment on the necessary conditionsmore » for detecting the amplitude mode in trARPES experiments.« less

Formal Derivation of Lotka-Volterra-Haken Amplitude Equations of Task-Related Brain Activity in Multiple, Consecutively Performed Tasks

NASA Astrophysics Data System (ADS)

Frank, T. D.

The Lotka-Volterra-Haken equations have been frequently used in ecology and pattern formation. Recently, the equations have been proposed by several research groups as amplitude equations for task-related patterns of brain activity. In this theoretical study, the focus is on the circular causality aspect of pattern formation systems as formulated within the framework of synergetics. Accordingly, the stable modes of a pattern formation system inhibit the unstable modes, whereas the unstable modes excite the stable modes. Using this circular causality principle it is shown that under certain conditions the Lotka-Volterra-Haken amplitude equations can be derived from a general model of brain activity akin to the Wilson-Cowan model. The model captures the amplitude dynamics for brain activity patterns in experiments involving several consecutively performed multiple-choice tasks. This is explicitly demonstrated for two-choice tasks involving grasping and walking. A comment on the relevance of the theoretical framework for clinical psychology and schizophrenia is given as well.

Pulsed welding plasma source

NASA Astrophysics Data System (ADS)

Knyaz'kov, A.; Pustovykh, O.; Verevkin, A.; Terekhin, V.; Shachek, A.; Tyasto, A.

2016-04-01

It is shown that in order to form the current pulse of a near rectangular shape, which provides conversion of the welding arc into a dynamic mode, it is rational to connect a forming element made on the basis of an artificial forming line in series to the welding DC circuit. The paper presents a diagram of a pulsed device for welding with a non-consumable electrode in argon which was developed using the forming element. The conversion of the arc into the dynamic mode is illustrated by the current and voltage oscillograms of the arc gap and the dynamic characteristic of the arc within the interval of one pulse generation time in the arc gap. The background current travels in the interpulse interval.

Uniform and non-uniform modes of nanosecond-pulsed dielectric barrier discharge in atmospheric air: fast imaging and spectroscopic measurements of electric field

PubMed Central

Liu, Chong; Dobrynin, Danil; Fridman, Alexander

2014-01-01

In this study, we report experimental results on fast ICCD imaging of development of nanosecond-pulsed dielectric barrier discharge (DBD) in atmospheric air and spectroscopic measurements of electric field in the discharge. Uniformity of the discharge images obtained with nanosecond exposure times were analyzed using chi-square test. The results indicate that DBD uniformity strongly depends on applied (global) electric field in the discharge gap, and is a threshold phenomenon. We show that in the case of strong overvoltage on the discharge gap (provided by fast rise times), there is transition from filamentary to uniform DBD mode which correlates to the corresponding decrease of maximum local electric field in the discharge. PMID:25071294

Uniform and non-uniform modes of nanosecond-pulsed dielectric barrier discharge in atmospheric air: fast imaging and spectroscopic measurements of electric field.

PubMed

Liu, Chong; Dobrynin, Danil; Fridman, Alexander

2014-06-25

In this study, we report experimental results on fast ICCD imaging of development of nanosecond-pulsed dielectric barrier discharge (DBD) in atmospheric air and spectroscopic measurements of electric field in the discharge. Uniformity of the discharge images obtained with nanosecond exposure times were analyzed using chi-square test. The results indicate that DBD uniformity strongly depends on applied (global) electric field in the discharge gap, and is a threshold phenomenon. We show that in the case of strong overvoltage on the discharge gap (provided by fast rise times), there is transition from filamentary to uniform DBD mode which correlates to the corresponding decrease of maximum local electric field in the discharge.

Global-scale modes of surface temperature variability on interannual to century timescales

NASA Technical Reports Server (NTRS)

Mann, Michael E.; Park, Jeffrey

1994-01-01

Using 100 years of global temperature anomaly data, we have performed a singluar value decomposition of temperature variations in narrow frequency bands to isolate coherent spatio-temporal modes of global climate variability. Statistical significance is determined from confidence limits obtained by Monte Carlo simulations. Secular variance is dominated by a globally coherent trend; with nearly all grid points warming in phase at varying amplitude. A smaller, but significant, share of the secular variance corresponds to a pattern dominated by warming and subsequent cooling in the high latitude North Atlantic with a roughly centennial timescale. Spatial patterns associated with significant peaks in variance within a broad period range from 2.8 to 5.7 years exhibit characteristic El Nino-Southern Oscillation (ENSO) patterns. A recent transition to a regime of higher ENSO frequency is suggested by our analysis. An interdecadal mode in the 15-to-18 years period and a mode centered at 7-to-8 years period both exhibit predominantly a North Atlantic Oscillation (NAO) temperature pattern. A potentially significant decadal mode centered on 11-to-12 years period also exhibits an NAO temperature pattern and may be modulated by the century-scale North Atlantic variability.

Adiabatic quenches and characterization of amplitude excitations in a continuous quantum phase transition

PubMed Central

Hoang, Thai M.; Bharath, Hebbe M.; Boguslawski, Matthew J.; Anquez, Martin; Robbins, Bryce A.; Chapman, Michael S.

2016-01-01

Spontaneous symmetry breaking occurs in a physical system whenever the ground state does not share the symmetry of the underlying theory, e.g., the Hamiltonian. This mechanism gives rise to massless Nambu–Goldstone modes and massive Anderson–Higgs modes. These modes provide a fundamental understanding of matter in the Universe and appear as collective phase or amplitude excitations of an order parameter in a many-body system. The amplitude excitation plays a crucial role in determining the critical exponents governing universal nonequilibrium dynamics in the Kibble–Zurek mechanism (KZM). Here, we characterize the amplitude excitations in a spin-1 condensate and measure the energy gap for different phases of the quantum phase transition. At the quantum critical point of the transition, finite-size effects lead to a nonzero gap. Our measurements are consistent with this prediction, and furthermore, we demonstrate an adiabatic quench through the phase transition, which is forbidden at the mean field level. This work paves the way toward generating entanglement through an adiabatic phase transition. PMID:27503886

Spectral statistics and scattering resonances of complex primes arrays

NASA Astrophysics Data System (ADS)

Wang, Ren; Pinheiro, Felipe A.; Dal Negro, Luca

2018-01-01

We introduce a class of aperiodic arrays of electric dipoles generated from the distribution of prime numbers in complex quadratic fields (Eisenstein and Gaussian primes) as well as quaternion primes (Hurwitz and Lifschitz primes), and study the nature of their scattering resonances using the vectorial Green's matrix method. In these systems we demonstrate several distinctive spectral properties, such as the absence of level repulsion in the strongly scattering regime, critical statistics of level spacings, and the existence of critical modes, which are extended fractal modes with long lifetimes not supported by either random or periodic systems. Moreover, we show that one can predict important physical properties, such as the existence spectral gaps, by analyzing the eigenvalue distribution of the Green's matrix of the arrays in the complex plane. Our results unveil the importance of aperiodic correlations in prime number arrays for the engineering of gapped photonic media that support far richer mode localization and spectral properties compared to usual periodic and random media.

Andreev rectifier: A nonlocal conductance signature of topological phase transitions

NASA Astrophysics Data System (ADS)

Rosdahl, T. Ö.; Vuik, A.; Kjaergaard, M.; Akhmerov, A. R.

2018-01-01

The proximity effect in hybrid superconductor-semiconductor structures, crucial for realizing Majorana edge modes, is complicated to control due to its dependence on many unknown microscopic parameters. In addition, defects can spoil the induced superconductivity locally in the proximitized system, which complicates measuring global properties with a local probe. We show how to use the nonlocal conductance between two spatially separated leads to probe three global properties of a proximitized system: the bulk superconducting gap, the induced gap, and the induced coherence length. Unlike local conductance spectroscopy, nonlocal conductance measurements distinguish between nontopological zero-energy modes localized around potential inhomogeneities, and true Majorana edge modes that emerge in the topological phase. In addition, we find that the nonlocal conductance is an odd function of bias at the topological phase transition, acting as a current rectifier in the low-bias limit. More generally, we identify conditions for crossed Andreev reflection to dominate the nonlocal conductance and show how to design a Cooper pair splitter in the open regime.

Exploiting pattern transformation to tune phononic band gaps in a two-dimensional granular crystal.

PubMed

Göncü, F; Luding, S; Bertoldi, K

2012-06-01

The band structure of a two-dimensional granular crystal composed of silicone rubber and polytetrafluoroethylene (PTFE) cylinders is investigated numerically. This system was previously shown to undergo a pattern transformation with uniaxial compression by Göncü et al. [Soft Matter 7, 2321 (2011)]. The dispersion relations of the crystal are computed at different levels of deformation to demonstrate the tunability of the band structure, which is strongly affected by the pattern transformation that induces new band gaps. Replacement of PTFE particles with rubber ones reveals that the change of the band structure is essentially governed by pattern transformation rather than particles' mechanical properties.

Electron Localization States in Asymmetric Shape Carbon Nanotubes Caused by Hydrogen Adsorption

NASA Astrophysics Data System (ADS)

Pan, L. J.; Chen, W. G.

2017-12-01

In this paper, we presented pseudopotential-based density functional theory studies on energy, structure, energy band structure of hydrogenated single-walled carbon nanotube. The stability of the configuration mainly depends on hydrogen coverage. According to the adsorption energies, the stability deteriorates with the increase of the hydrogen adsorption. The cross section of configurations become various shapes such as “beetle” or “lip” appearance without the balanced effects of hydrogen atoms. We also explored the energy band structures of configurations in three typical adsorption patterns, showing that the disparate trends of energy band gap as the hydrogen atoms concentrate. For C32H24, the band gap may reach the large value of 2.79 eV for the adsorption pattern A configuration and reduce to be zero for the adsorption pattern C case, the values of band gap for pattern A configurations decrease, which is opposite of the pattern B configurations as the adsorption hydrogen becomes more disperse. It is deduced that the hydrogen adsorption has significant effect on the electrical properties of the carbon nanotube.

The effects of gap size on some microclimate variables during late summer and autumn in a temperate broadleaved deciduous forest.

PubMed

Abd Latif, Zulkiflee; Blackburn, George Alan

2010-03-01

The creation of gaps can strongly influence forest regeneration and habitat diversity within forest ecosystems. However, the precise characteristics of such effects depend, to a large extent, upon the way in which gaps modify microclimate and soil water content. Hence, the aim of this study was to understand the effects of gap creation and variations in gap size on forest microclimate and soil water content. The study site, in North West England, was a mixed temperate broadleaved deciduous forest dominated by mature sessile oak (Quercus petraea), beech (Fagus sylvatica) and ash (Fraxinus excelsior) with some representatives of sycamore (Acer pseudoplatanus). Solar radiation (I), air temperature (T(A)), soil temperature (T(S)), relative humidity (h), wind speed (v) and soil water content (Psi) were measured at four natural treefall gaps created after a severe storm in 2006 and adjacent sub-canopy sites. I, T(A), T(S), and Psi increased significantly with gap size; h was consistently lower in gaps than the sub-canopy but did not vary with gap size, while the variability of v could not be explained by the presence or size of gaps. There were systematic diurnal patterns in all microclimate variables in response to gaps, but no such patterns existed for Psi. These results further our understanding of the abiotic and consequent biotic responses to gaps in broadleaved deciduous forests created by natural treefalls, and provide a useful basis for evaluating the implications of forest management practices.

Wireless multi-level terahertz amplitude modulator using active metamaterial-based spatial light modulation.

PubMed

Rout, Saroj; Sonkusale, Sameer

2016-06-27

The ever increasing demand for bandwidth in wireless communication systems will inevitably lead to the extension of operating frequencies toward the terahertz (THz) band known as the 'THz gap'. Towards closing this gap, we present a multi-level amplitude shift keying (ASK) terahertz wireless communication system using terahertz spatial light modulators (SLM) instead of traditional voltage mode modulation, achieving higher spectral efficiency for high speed communication. The fundamental principle behind this higher efficiency is the conversion of a noisy voltage domain signal to a noise-free binary spatial pattern for effective amplitude modulation of a free-space THz carrier wave. Spatial modulation is achieved using an an active metamaterial array embedded with pseudomorphic high-electron mobility (pHEMT) designed in a consumer-grade galium-arsenide (GaAs) integrated circuit process which enables electronic control of its THz transmissivity. Each array is assembled as individually controllable tiles for transmissive terahertz spatial modulation. Using the experimental data from our metamaterial based modulator, we show that a four-level ASK digital communication system has two orders of magnitude improvement in symbol error rate (SER) for a degradation of 20 dB in transmit signal-to-noise ratio (SNR) using spatial light modulation compared to voltage controlled modulation.

Evaluation of effect of oil film of rotor bearing

NASA Astrophysics Data System (ADS)

Alekseeva, L. B.; Maksarov, V. V.

2018-03-01

The high-rpm rotors were subjected to the dynamic analysis. Oscillations of a rotor spinning in gapped bearings were considered. It was stated that the rotor necks motion pattern depends on a lot of factors: a ratio of static and dynamic loads on the bearing, radial clearance size, presence of oil film between a neck and a bearing, elastic and inertial properties of a mounting group. The most unfavourable mode where static and dynamic loads are equal was detected without taking into account the oil film impact. The impact of oil film on the bearing assembly dynamics is significant in high-rpm rotors. The presence of oil film can possibly cause rotor buckling failure and self-starting. Rotor motion stability in small was studied. Herewith, various schemes were considered. Expressions, determining the stability zones of a rigid rotor on the fixed support and the supports with elastic and inertial elements, were given.

Combined experimental and computational study of high-pressure behavior of triphenylene

PubMed Central

Zhao, Xiao-Miao; Zhong, Guo-Hua; Zhang, Jiang; Huang, Qiao-Wei; Goncharov, Alexander F.; Lin, Hai-Qing; Chen, Xiao-Jia

2016-01-01

We have performed measurements of Raman scattering, synchrotron x-ray diffraction, and visible transmission spectroscopy combined with density functional theory calculations to study the pressure effect on solid triphenylene. The spectroscopic results demonstrate substantial change of the molecular configuration at 1.4 GPa from the abrupt change of splitting, disappearance, and appearance of some modes. The structure of triphenylene is found be to stable at high pressures without any evidence of structural transition from the x-ray diffraction patterns. The obtained lattice parameters show a good agreement between experiments and calculations. The obtained band gap systematically decreases with increasing pressure. With the application of pressure, the molecular planes become more and more parallel relative to each other. The theoretical calculations indicate that this organic compound becomes metallic at 180 GPa, fueling the hope for the possible realization of superconductivity at high pressure. PMID:27161429

Synthesis of nanocrystalline CdS thin film by SILAR and their characterization

NASA Astrophysics Data System (ADS)

Mukherjee, A.; Satpati, B.; Bhattacharyya, S. R.; Ghosh, R.; Mitra, P.

2015-01-01

Cadmium sulphide (CdS) thin film was prepared by successive ion layer adsorption and reaction (SILAR) technique using ammonium sulphide as anionic precursor. Characterization techniques of XRD, SEM, TEM, FTIR and EDX were utilized to study the microstructure of the films. Structural characterization by x-ray diffraction reveals the polycrystalline nature of the films. Cubic structure is revealed from X-ray diffraction and selected area diffraction (SAD) patterns. The particle size estimated using X-ray line broadening method is approximately 7 nm. Instrumental broadening was taken into account while particle size estimation. TEM shows CdS nanoparticles in the range 5-15 nm. Elemental mapping using EFTEM reveals good stoichiometric composition of CdS. Characteristic stretching vibration mode of CdS was observed in the absorption band of FTIR spectrum. Optical absorption study exhibits a distinct blue shift in band gap energy value of about 2.56 eV which confirms the size quantization.

THE DYNAMICAL RELATIONSHIP BETWEEN THE BAR AND SPIRAL PATTERNS OF NGC 1365

DOE Office of Scientific and Technical Information (OSTI.GOV)

Speights, Jason C.; Rooke, Paul C., E-mail: jcspeights@frostburg.edu

2016-07-20

Theories that attempt to explain the dynamical relationship between bar and spiral patterns in galactic disks make different predictions about the radial profile of the pattern speed. These are tested for the H-alpha bar and spiral patterns of NGC 1365. The radial profile of the pattern speed is measured by fitting mathematical models that are based on the Tremaine–Weinberg method. The results show convincing evidence for the bar rotating at a faster rate than the spiral pattern, inconsistent with a global wave mode or a manifold. There is evidence for mode coupling of the bar and spiral patterns at themore » overlap of corotation and inner Lindblad resonances (ILRs), but the evidence is unreliable and inconsistent. The results are the most consistent with the bar and spiral patterns being dynamically distinct features. The pattern speed of the bar begins near an ILR and ends near the corotation resonance (CR). The radial profile of the pattern speed beyond the bar most closely resembles what is expected for coupled spiral modes and tidal interactions.« less

Band gap narrowing in BaTiO{sub 3} nanoparticles facilitated by multiple mechanisms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramakanth, S.; James Raju, K. C., E-mail: kcjrsp@uohyd.ernet.in; School of Physics, University of Hyderabad, Hyderabad 500046

2014-05-07

In the present work, BaTiO{sub 3} nanoparticles of four different size ranges were prepared by sol-gel method. The optical band gap of these particles at some size ranges has come down to 2.53 eV from 3.2 eV, resulting in substantial increase in optical absorption by these ferroelectric nanoparticles making them potential candidates for light energy harvesting. XRD results show the presence of higher compressive strain in 23 nm and 54 nm size particles, they exhibit a higher band gap narrowing, whereas tensile strain is observed in 31 nm and 34 nm particles, and they do not show the marginal band gap narrowing. The 23 nm and 54 nmmore » particles also show a coupling of free carriers to phonons by increasing the intensity of LO phonon mode at 715 cm{sup −1}. The higher surface charge density is expected in case of enhanced surface optical Raman modes (638 cm{sup −1}) contained in 31 and 34 nm size particles. In addition to this, the red shift in an LO mode Raman spectral line at 305 cm{sup −1} with decrease in particle size depicts the presence of phonon confinement in it. The enhanced optical absorption in 23 nm and 54 nm size particles with a narrowed band gap of 3 eV and 2.53 eV is due to exchange correlation interactions between the carriers present in these particles. In 31 nm and 34 nm range particles, the absorption got bleached exhibiting increased band gaps of 3.08 eV and 3.2 eV, respectively. It is due to filling up of conduction band resulting from weakening of exchange correlation interactions between the charge carriers. Hence, it is concluded that the band gap narrowing in the nanoparticles of average size 23 nm/54 nm is a consequence of multiple effects like strain, electron-phonon interaction, and exchange correlation interactions between the carriers which is subdued in some other size ranges like 31 nm/34 nm.« less

Dynamic Maternal Gradients Control Timing and Shift-Rates for Drosophila Gap Gene Expression

PubMed Central

Verd, Berta; Crombach, Anton

2017-01-01

Pattern formation during development is a highly dynamic process. In spite of this, few experimental and modelling approaches take into account the explicit time-dependence of the rules governing regulatory systems. We address this problem by studying dynamic morphogen interpretation by the gap gene network in Drosophila melanogaster. Gap genes are involved in segment determination during early embryogenesis. They are activated by maternal morphogen gradients encoded by bicoid (bcd) and caudal (cad). These gradients decay at the same time-scale as the establishment of the antero-posterior gap gene pattern. We use a reverse-engineering approach, based on data-driven regulatory models called gene circuits, to isolate and characterise the explicitly time-dependent effects of changing morphogen concentrations on gap gene regulation. To achieve this, we simulate the system in the presence and absence of dynamic gradient decay. Comparison between these simulations reveals that maternal morphogen decay controls the timing and limits the rate of gap gene expression. In the anterior of the embyro, it affects peak expression and leads to the establishment of smooth spatial boundaries between gap domains. In the posterior of the embryo, it causes a progressive slow-down in the rate of gap domain shifts, which is necessary to correctly position domain boundaries and to stabilise the spatial gap gene expression pattern. We use a newly developed method for the analysis of transient dynamics in non-autonomous (time-variable) systems to understand the regulatory causes of these effects. By providing a rigorous mechanistic explanation for the role of maternal gradient decay in gap gene regulation, our study demonstrates that such analyses are feasible and reveal important aspects of dynamic gene regulation which would have been missed by a traditional steady-state approach. More generally, it highlights the importance of transient dynamics for understanding complex regulatory processes in development. PMID:28158178

Dynamic Maternal Gradients Control Timing and Shift-Rates for Drosophila Gap Gene Expression.

PubMed

Verd, Berta; Crombach, Anton; Jaeger, Johannes

2017-02-01

Pattern formation during development is a highly dynamic process. In spite of this, few experimental and modelling approaches take into account the explicit time-dependence of the rules governing regulatory systems. We address this problem by studying dynamic morphogen interpretation by the gap gene network in Drosophila melanogaster. Gap genes are involved in segment determination during early embryogenesis. They are activated by maternal morphogen gradients encoded by bicoid (bcd) and caudal (cad). These gradients decay at the same time-scale as the establishment of the antero-posterior gap gene pattern. We use a reverse-engineering approach, based on data-driven regulatory models called gene circuits, to isolate and characterise the explicitly time-dependent effects of changing morphogen concentrations on gap gene regulation. To achieve this, we simulate the system in the presence and absence of dynamic gradient decay. Comparison between these simulations reveals that maternal morphogen decay controls the timing and limits the rate of gap gene expression. In the anterior of the embyro, it affects peak expression and leads to the establishment of smooth spatial boundaries between gap domains. In the posterior of the embryo, it causes a progressive slow-down in the rate of gap domain shifts, which is necessary to correctly position domain boundaries and to stabilise the spatial gap gene expression pattern. We use a newly developed method for the analysis of transient dynamics in non-autonomous (time-variable) systems to understand the regulatory causes of these effects. By providing a rigorous mechanistic explanation for the role of maternal gradient decay in gap gene regulation, our study demonstrates that such analyses are feasible and reveal important aspects of dynamic gene regulation which would have been missed by a traditional steady-state approach. More generally, it highlights the importance of transient dynamics for understanding complex regulatory processes in development.

Band structures in fractal grading porous phononic crystals

NASA Astrophysics Data System (ADS)

Wang, Kai; Liu, Ying; Liang, Tianshu; Wang, Bin

2018-05-01

In this paper, a new grading porous structure is introduced based on a Sierpinski triangle routine, and wave propagation in this fractal grading porous phononic crystal is investigated. The influences of fractal hierarchy and porosity on the band structures in fractal graidng porous phononic crystals are clarified. Vibration modes of unit cell at absolute band gap edges are given to manifest formation mechanism of absolute band gaps. The results show that absolute band gaps are easy to form in fractal structures comparatively to the normal ones with the same porosity. Structures with higher fractal hierarchies benefit multiple wider absolute band gaps. This work provides useful guidance in design of fractal porous phononic crystals.

Exposing Gaps in/between Discourses of Linguistic Deficits

ERIC Educational Resources Information Center

Johnson, Eric J.; Avineri, Netta; Johnson, David Cassels

2017-01-01

Hart and Risley's (1995) concept of a "word gap" (aka "language gap") is widely used to describe inferior cognitive development and lower academic achievement as by-products of the language patterns of families from economically disadvantaged backgrounds. In recent decades, this line of deficit research has proliferated and…

Influences on Energy Savings of Heavy Trucks Using Cooperative Adaptive Cruise Control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lammert, Michael P; McAuliffe, Brian; Lu, Xiao-Yun

An integrated adaptive cruise control (ACC) and cooperative ACC (CACC) was implemented and tested on three heavy-duty tractor-trailer trucks on a closed test track. The first truck was always in ACC mode, and the followers were in CACC mode using wireless vehicle-vehicle communication to augment their radar sensor data to enable safe and accurate vehicle following at short gaps. The fuel consumption for each truck in the CACC string was measured using the SAE J1321 procedure while travelling at 65 mph and loaded to a gross weight of 65,000 lb, demonstrating the effects of: inter-vehicle gaps (ranging from 3.0 smore » or 87 m to 0.14 s or 4 m, covering a much wider range than previously reported tests), cut-in and cut-out maneuvers by other vehicles, speed variations, the use of mismatched vehicles (standard trailers mixed with aerodynamic trailers with boat tails and side skirts), and the presence of a passenger vehicle ahead of the platoon. The results showed that energy savings generally increased in a non-linear fashion as the gap was reduced. The middle truck saved the most fuel at gaps shorter than 12 m and the trailing truck saved the most at longer gaps, while lead truck saved the least at all gaps. The cut-in and cut-out maneuvers had only a marginal effect on fuel consumption even when repeated every two miles. The presence of passenger-vehicle traffic had a measurable impact. The fuel-consumption savings on the curves was less than on the straight sections.« less

Dependence of Helicon Antenna Loading on the Antenna/Plasma Gap and n|| in DIII-D Experiments

NASA Astrophysics Data System (ADS)

Pinsker, R. I.; Moeller, C. P.

2017-10-01

A comprehensive set of measurements of the plasma loading of a 12-element antenna array, designed to launch helicon waves (i.e., very-high-harmonic fast waves), were performed on DIII-D in 2016. The antenna, operated in the 466 - 486 MHz band, is prototypical of a wider array for a 1-MW-level experiment planned for 2018-9. The dependence of the antenna loading on antenna/plasma gap is of great practical significance, as the gap must be kept greater than a minimum distance to suppress deleterious plasma-material interactions, while the loading must be high enough to retain good efficiency of power transfer to the plasma. While the loading in all examined plasma regimes, including both limited and diverted L-mode discharges and H-mode discharges, decayed exponentially with increasing gap in agreement with simple theory, the characteristic decay length was in all cases larger than expected, motivating the development of a more realistic model. Furthermore, the characteristic decay length did not depend on the launched n||, though the absolute level of loading at a given gap increased as |n||| was decreased from 4 to 2. After the antenna was removed from DIII-D, measurements of the loading produced by a 100 Ω/sq resistive film were carried out on the bench. Both the antenna/film gap and n|| were scanned varied and the results compared with calculations done with the QuickWave FDTD electromagnetics solver. Very good agreement was found in this case. Work supported by the US DOE under DE-FC02-04ER54698.

High-resolution gene expression data from blastoderm embryos of the scuttle fly Megaselia abdita

PubMed Central

Wotton, Karl R; Jiménez-Guri, Eva; Crombach, Anton; Cicin-Sain, Damjan; Jaeger, Johannes

2015-01-01

Gap genes are involved in segment determination during early development in dipteran insects (flies, midges, and mosquitoes). We carried out a systematic quantitative comparative analysis of the gap gene network across different dipteran species. Our work provides mechanistic insights into the evolution of this pattern-forming network. As a central component of our project, we created a high-resolution quantitative spatio-temporal data set of gap and maternal co-ordinate gene expression in the blastoderm embryo of the non-drosophilid scuttle fly, Megaselia abdita. Our data include expression patterns in both wild-type and RNAi-treated embryos. The data—covering 10 genes, 10 time points, and over 1,000 individual embryos—consist of original embryo images, quantified expression profiles, extracted positions of expression boundaries, and integrated expression patterns, plus metadata and intermediate processing steps. These data provide a valuable resource for researchers interested in the comparative study of gene regulatory networks and pattern formation, an essential step towards a more quantitative and mechanistic understanding of developmental evolution. PMID:25977812

Baseline acoustic levels of the NASA Active Noise Control Fan rig

NASA Technical Reports Server (NTRS)

Sutliff, Daniel L.; Heidelberg, Laurence J.; Elliott, David M.; Nallasamy, M.

1996-01-01

Extensive measurements of the spinning acoustic mode structure in the NASA 48 inch Active Noise Control Fan (ANCF) test rig have been taken. A continuously rotating microphone rake system with a least-squares data reduction technique was employed to measure these modes in the inlet and exhaust. Farfield directivity patterns in an anechoic environment were also measured at matched corrected rotor speeds. Several vane counts and spacings were tested over a range of rotor speeds. The Eversman finite element radiation code was run with the measured in-duct modes as input and the computed farfield results were compared to the experimentally measured directivity pattern. The experimental data show that inlet spinning mode measurements can be made very accurately. Exhaust mode measurements may have wake interference, but the least-squares reduction does a good job of rejecting the non-acoustic pressure. The Eversman radiation code accurately extrapolates the farfield levels and directivity pattern when all in-duct modes are included.

Finite element method analysis of band gap and transmission of two-dimensional metallic photonic crystals at terahertz frequencies.

PubMed

Degirmenci, Elif; Landais, Pascal

2013-10-20

Photonic band gap and transmission characteristics of 2D metallic photonic crystals at THz frequencies have been investigated using finite element method (FEM). Photonic crystals composed of metallic rods in air, in square and triangular lattice arrangements, are considered for transverse electric and transverse magnetic polarizations. The modes and band gap characteristics of metallic photonic crystal structure are investigated by solving the eigenvalue problem over a unit cell of the lattice using periodic boundary conditions. A photonic band gap diagram of dielectric photonic crystal in square lattice array is also considered and compared with well-known plane wave expansion results verifying our FEM approach. The photonic band gap designs for both dielectric and metallic photonic crystals are consistent with previous studies obtained by different methods. Perfect match is obtained between photonic band gap diagrams and transmission spectra of corresponding lattice structure.

Periodic dielectric structure for production of photonic band gap and method for fabricating the same

DOEpatents

Ozbay, Ekmel; Tuttle, Gary; Michel, Erick; Ho, Kai-Ming; Biswas, Rana; Chan, Che-Ting; Soukoulis, Costas

1995-01-01

A method for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap.

Variation in motor output and motor performance in a centrally generated motor pattern

PubMed Central

Norris, Brian J.; Doloc-Mihu, Anca; Calabrese, Ronald L.

2014-01-01

Central pattern generators (CPGs) produce motor patterns that ultimately drive motor outputs. We studied how functional motor performance is achieved, specifically, whether the variation seen in motor patterns is reflected in motor performance and whether fictive motor patterns differ from those in vivo. We used the leech heartbeat system in which a bilaterally symmetrical CPG coordinates segmental heart motor neurons and two segmented heart tubes into two mutually exclusive coordination modes: rear-to-front peristaltic on one side and nearly synchronous on the other, with regular side-to-side switches. We assessed individual variability of the motor pattern and the beat pattern in vivo. To quantify the beat pattern we imaged intact adults. To quantify the phase relations between motor neurons and heart constrictions we recorded extracellularly from two heart motor neurons and movement from the corresponding heart segments in minimally dissected leeches. Variation in the motor pattern was reflected in motor performance only in the peristaltic mode, where larger intersegmental phase differences in the motor neurons resulted in larger phase differences between heart constrictions. Fictive motor patterns differed from those in vivo only in the synchronous mode, where intersegmental phase differences in vivo had a larger front-to-rear bias and were more constrained. Additionally, load-influenced constriction timing might explain the amplification of the phase differences between heart segments in the peristaltic mode and the higher variability in motor output due to body shape assumed in this soft-bodied animal. The motor pattern determines the beat pattern, peristaltic or synchronous, but heart mechanics influence the phase relations achieved. PMID:24717348

The sensitivity of tokamak magnetohydrodynamics stability on the edge equilibrium

NASA Astrophysics Data System (ADS)

Zheng, L. J.; Kotschenreuther, M. T.; Valanju, P.

2017-10-01

Due to the X-point singularity, the safety factor tends to infinity as approaching to the last closed flux surface. The numerical treatments of the near X-point behavior become challenging both for equilibrium and stability. The usual solution is to cut off a small fraction of edge region for system stability evaluation or simply use an up-down symmetric equilibrium without X-point as an approximation. In this work, we assess the sensitivity of this type of equilibrium treatments on the stability calculation. It is found that the system stability can depend strongly on the safety factor value (qa) at the edge after the cutting-off. When the edge safety factor value falls in the vicinity of a rational mode number (referred to as the resonant gap), the system becomes quite unstable due to the excitation of the peeling type modes. Instead, when the edge safety factor is outside the resonant gaps, the system is much more stable and the predominant modes become the usual external kink (or ballooning and infernal) type. It is also found that the resonant gaps become smaller and smaller as qa increases. The ideal magnetohydrodynamic peeling ballooning stability diagram is widely used to explain the experimental observations, and the current results indicate that the conventional peeling ballooning stability diagram based on the simplified equilibrium needs to be reexamined.

Weak coupling of pseudoacoustic phonons and magnon dynamics in the incommensurate spin-ladder compound S r 14 C u 24 O 41

DOE PAGES

Chen, Xi; Bansal, Dipanshu; Sullivan, Sean; ...

2016-10-21

Intriguing lattice dynamics have been predicted for aperiodic crystals that contain incommensurate substructures. Here we report inelastic neutron scattering measurements of phonon and magnon dispersions in Sr 14Cu 24O 41, which contains incommensurate one-dimensional (1D) chain and two-dimensional (2D) ladder substructures. Two distinct pseudoacoustic phonon modes, corresponding to the sliding motion of one sublattice against the other, are observed for atomic motions polarized along the incommensurate axis. In the long wavelength limit, it is found that the sliding mode shows a remarkably small energy gap of 1.7–1.9 meV, indicating very weak interactions between the two incommensurate sublattices. The measurements alsomore » reveal a gapped and steep linear magnon dispersion of the ladder sublattice. The high group velocity of this magnon branch and weak coupling with acoustic and pseudoacoustic phonons can explain the large magnon thermal conductivity in Sr 14Cu 24O 41 crystals. In addition, the magnon specific heat is determined from the measured total specific heat and phonon density of states and exhibits a Schottky anomaly due to gapped magnon modes of the spin chains. Furthermore, these findings offer new insights into the phonon and magnon dynamics and thermal transport properties of incommensurate magnetic crystals that contain low-dimensional substructures.« less

Surface Majorana fermions and bulk collective modes in superfluid 3He-B

NASA Astrophysics Data System (ADS)

Park, YeJe; Chung, Suk Bum; Maciejko, Joseph

2015-02-01

The theoretical study of topological superfluids and superconductors has so far been carried out largely as a translation of the theory of noninteracting topological insulators into the superfluid language, whereby one replaces electrons by Bogoliubov quasiparticles and single-particle band Hamiltonians by Bogoliubov-de Gennes Hamiltonians. Band insulators and superfluids are, however, fundamentally different: While the former exist in the absence of interparticle interactions, the latter are broken symmetry states that owe their very existence to such interactions. In particular, unlike the static energy gap of a band insulator, the gap in a superfluid is due to a dynamical order parameter that is subject to both thermal and quantum fluctuations. In this work, we explore the consequences of bulk quantum fluctuations of the order parameter in the B phase of superfluid 3He on the topologically protected Majorana surface states. Neglecting the high-energy amplitude modes, we find that one of the three spin-orbit Goldstone modes in 3He-B couples to the surface Majorana fermions. This coupling in turn induces an effective short-range two-body interaction between the Majorana fermions, with coupling constant inversely proportional to the strength of the nuclear dipole-dipole interaction in bulk 3He. A mean-field theory suggests that the surface Majorana fermions in 3He-B may be in the vicinity of a metastable gapped time-reversal-symmetry-breaking phase.

Metallic Electrode: Semiconducting Nanotube Junction Model

NASA Technical Reports Server (NTRS)

Yamada, Toshishige; Biegel, Bryon (Technical Monitor)

2001-01-01

A model is proposed for two observed current-voltage (I-V) patterns in an experiment with a scanning tunneling microscope tip and a carbon nanotube [Collins et al., Science 278, 100 ('97)]. We claim that there are two contact modes for a tip (metal) -nanotube semi conductor) junction depending whether the alignment of the metal and semiconductor band structure is (1) variable (vacuum-gap) or (2) fixed (touching) with V. With the tip grounded, the tunneling case in (1) would produce large dI/dV with V > 0, small dI/dV with V < 0, and I = 0 near V = 0 for an either n- or p-nanotube. However, the Schottky mechanism in (2) would result in forward current with V < 0 for an n-nanotube, while with V > 0 for an p-nanotube. The two observed I-V patterns are thus entirely explained by a tip-nanotube contact of the two types, where the nanotube must be n-type. We apply this picture to the source-drain I-V characteristics in a long nanotube-channel field-effect-transistor (Zhou et al., Appl. Phys. Lett. 76, 1597 ('00)], and show that two independent metal-semiconductor junctions connected in series are responsible for the observed behavior.

Resting state network topology of the ferret brain.

PubMed

Zhou, Zhe Charles; Salzwedel, Andrew P; Radtke-Schuller, Susanne; Li, Yuhui; Sellers, Kristin K; Gilmore, John H; Shih, Yen-Yu Ian; Fröhlich, Flavio; Gao, Wei

2016-12-01

Resting state functional magnetic resonance imaging (rsfMRI) has emerged as a versatile tool for non-invasive measurement of functional connectivity patterns in the brain. RsfMRI brain dynamics in rodents, non-human primates, and humans share similar properties; however, little is known about the resting state functional connectivity patterns in the ferret, an animal model with high potential for developmental and cognitive translational study. To address this knowledge-gap, we performed rsfMRI on anesthetized ferrets using a 9.4T MRI scanner, and subsequently performed group-level independent component analysis (gICA) to identify functionally connected brain networks. Group-level ICA analysis revealed distributed sensory, motor, and higher-order networks in the ferret brain. Subsequent connectivity analysis showed interconnected higher-order networks that constituted a putative default mode network (DMN), a network that exhibits altered connectivity in neuropsychiatric disorders. Finally, we assessed ferret brain topological efficiency using graph theory analysis and found that the ferret brain exhibits small-world properties. Overall, these results provide additional evidence for pan-species resting-state networks, further supporting ferret-based studies of sensory and cognitive function. Copyright © 2016 Elsevier Inc. All rights reserved.

Trade-off between competition and facilitation defines gap colonization in mountains

PubMed Central

Lembrechts, Jonas J.; Milbau, Ann; Nijs, Ivan

2015-01-01

Recent experimental observations show that gap colonization in small-stature (e.g. grassland and dwarf shrubs) vegetation strongly depends on the abiotic conditions within them. At the same time, within-gap variation in biotic interactions such as competition and facilitation, caused by distance to the gap edge, would affect colonizer performance, but a theoretical framework to explore such patterns is missing. Here, we model how competition, facilitation and environmental conditions together determine the small-scale patterns of gap colonization along a cold gradient in mountains, by simulating colonizer survival in gaps of various sizes. Our model adds another dimension to the known effects of biotic interactions along a stress gradient by focussing on the trade-off between competition and facilitation in the within-gap environment. We show that this trade-off defines a peak in colonizer survival at a specific distance from the gap edge, which progressively shifts closer to the edge as the environment gets colder, ultimately leaving a large fraction of gaps unsuitable for colonization in facilitation-dominated systems. This is reinforced when vegetation size and temperature amelioration are manipulated simultaneously with temperature in order to simulate an elevational gradient more realistically. Interestingly, all other conditions being equal, the magnitude of the realized survival peak was always lower in large than in small gaps, making large gaps harder to colonize. The model is relevant to predict effects of non-native plant invasions and climate warming on colonization processes in mountains. PMID:26558706

Coupling of Higgs and Leggett modes in non-equilibrium superconductors.

PubMed

Krull, H; Bittner, N; Uhrig, G S; Manske, D; Schnyder, A P

2016-06-21

In equilibrium systems amplitude and phase collective modes are decoupled, as they are mutually orthogonal excitations. The direct detection of these Higgs and Leggett collective modes by linear-response measurements is not possible, because they do not couple directly to the electromagnetic field. In this work, using numerical exact simulations we show for the case of two-gap superconductors, that optical pump-probe experiments excite both Higgs and Leggett modes out of equilibrium. We find that this non-adiabatic excitation process introduces a strong interaction between the collective modes, which is absent in equilibrium. Moreover, we propose a type of pump-probe experiment, which allows to probe and coherently control the Higgs and Leggett modes, and thus the order parameter directly. These findings go beyond two-band superconductors and apply to general collective modes in quantum materials.

Single- versus double-row repair for full-thickness rotator cuff tears using suture anchors. A systematic review and meta-analysis of basic biomechanical studies.

PubMed

Hohmann, Erik; König, Anya; Kat, Cor-Jacques; Glatt, Vaida; Tetsworth, Kevin; Keough, Natalie

2018-07-01

The purpose of this study was to perform a systematic review and meta-analysis comparing single- and double-row biomechanical studies to evaluate load to failure, mode of failure and gap formation. A systematic review of MEDLINE, Embase, Scopus and Google Scholar was performed from 1990 through 2016. The inclusion criteria were: documentation of ultimate load to failure, failure modes and documentation of elongation or gap formation. Studies were excluded if the study protocol did not use human specimens. Publication bias was assessed by funnel plot and Egger's test. The risk of bias was established using the Cochrane Collaboration's risk of bias tool. Heterogeneity was assessed using χ 2 and I 2 statistic. Eight studies were included. The funnel plot was asymmetric suggesting publication bias, which was confirmed by Egger's test (p = 0.04). The pooled estimate for load to failure demonstrated significant differences (SMD 1.228, 95% CI: 0.55-5.226, p = 0.006, I 2  = 60.47%), favouring double-row repair. There were no differences for failure modes. The pooled estimate for elongation/gap formation demonstrated significant differences (SMD 0.783, 95% CI: 0.169-1.398, p = 0.012, I 2  = 58.8%), favouring double-row repair. The results of this systematic review and meta-analysis suggest that double-row repair is able to tolerate a significantly greater load to failure. Gap formation was also significantly lower in the double-row repair group, but both of these findings should be interpreted with caution because of the inherent interstudy heterogeneity. Systematic review and meta-analysis.

Monazite-type SrCr O 4 under compression

DOE PAGES

Gleissner, J.; Errandonea, Daniel; Segura, A.; ...

2016-10-20

We report a high-pressure study of monoclinic monazite-type SrCrO 4 up to 26 GPa. Therein we combined x-ray diffraction, Raman, and optical-absorption measurements with ab initio calculations, to find a pressure-induced structural phase transition of SrCrO 4 near 8-9 GPa. Evidence of a second phase transition was observed at 10-13 GPa. The crystal structures of the high-pressure phases were assigned to the tetragonal scheelite-type and monoclinic AgMnO 4-type structures. Both transitions produce drastic changes in the electronic band gap and phonon spectrum of SrCrO 4. We determined the pressure evolution of the band gap for the low- and high-pressure phasesmore » as well as the frequencies and pressure dependencies of the Raman-active modes. In all three phases most Raman modes harden under compression, however the presence of low-frequency modes which gradually soften is also detected. In monazite-type SrCrO 4, the band gap blueshifts under compression, but the transition to the scheelite phase causes an abrupt decrease of the band gap in SrCrO 4. Calculations showed good agreement with experiments and were used to better understand the experimental results. From x-ray-diffraction studies and calculations we determined the pressure dependence of the unit-cell parameters of the different phases and their ambient-temperature equations of state. The results are compared with the high-pressure behavior of other monazites, in particular PbCrO 4. A comparison of the high-pressure behavior of the electronic properties of SrCrO 4 (SrWO 4) and PbCrO 4 (PbWO 4) will also be made. Lastly, the possible occurrence of a third structural phase transition is discussed.« less

Comparative in vitro evaluation of CAD/CAM vs conventional provisional crowns

PubMed Central

ABDULLAH, Adil Othman; TSITROU, Effrosyni A; POLLINGTON, Sarah

2016-01-01

ABSTRACT Objective This study compared the marginal gap, internal fit, fracture strength, and mode of fracture of CAD/CAM provisional crowns with that of direct provisional crowns. Material and Methods An upper right first premolar phantom tooth was prepared for full ceramic crown following tooth preparation guidelines. The materials tested were: VITA CAD-Temp®, Polyetheretherketone “PEEK”, Telio CAD-Temp, and Protemp™4 (control group). The crowns were divided into four groups (n=10), Group1: VITA CAD-Temp®, Group 2: PEEK, Group 3: Telio CAD-Temp, and Group 4: Protemp™4. Each crown was investigated for marginal and internal fit, fracture strength, and mode of fracture. Statistical analysis was performed using GraphPad Prism software version 6.0. Results The average marginal gap was: VITA CAD-Temp® 60.61 (±9.99) µm, PEEK 46.75 (±8.26) µm, Telio CAD-Temp 56.10 (±5.65) µm, and Protemp™4 193.07(±35.96) µm (P<0.001). The average internal fit was: VITA CAD-Temp® 124.94 (±22.96) µm, PEEK 113.14 (±23.55) µm, Telio CAD-Temp 110.95 (±11.64) µm, and Protemp™4 143.48(±26.74) µm. The average fracture strength was: VITA CAD-Temp® 361.01 (±21.61) N, PEEK 802.23 (±111.29) N, Telio CAD-Temp 719.24 (±95.17) N, and Protemp™4 416.40 (±69.14) N. One-way ANOVA test showed a statistically significant difference for marginal gap, internal gap, and fracture strength between all groups (p<0.001). However, the mode of fracture showed no differences between the groups (p>0.05). Conclusions CAD/CAM fabricated provisional crowns demonstrated superior fit and better strength than direct provisional crowns. PMID:27383707

Comparative in vitro evaluation of CAD/CAM vs conventional provisional crowns.

PubMed

Abdullah, Adil Othman; Tsitrou, Effrosyni A; Pollington, Sarah

2016-01-01

This study compared the marginal gap, internal fit, fracture strength, and mode of fracture of CAD/CAM provisional crowns with that of direct provisional crowns. An upper right first premolar phantom tooth was prepared for full ceramic crown following tooth preparation guidelines. The materials tested were: VITA CAD-Temp®, Polyetheretherketone "PEEK", Telio CAD-Temp, and Protemp™4 (control group). The crowns were divided into four groups (n=10), Group1: VITA CAD-Temp®, Group 2: PEEK, Group 3: Telio CAD-Temp, and Group 4: Protemp™4. Each crown was investigated for marginal and internal fit, fracture strength, and mode of fracture. Statistical analysis was performed using GraphPad Prism software version 6.0. The average marginal gap was: VITA CAD-Temp® 60.61 (±9.99) µm, PEEK 46.75 (±8.26) µm, Telio CAD-Temp 56.10 (±5.65) µm, and Protemp™4 193.07(±35.96) µm (P<0.001). The average internal fit was: VITA CAD-Temp® 124.94 (±22.96) µm, PEEK 113.14 (±23.55) µm, Telio CAD-Temp 110.95 (±11.64) µm, and Protemp™4 143.48(±26.74) µm. The average fracture strength was: VITA CAD-Temp® 361.01 (±21.61) N, PEEK 802.23 (±111.29) N, Telio CAD-Temp 719.24 (±95.17) N, and Protemp™4 416.40 (±69.14) N. One-way ANOVA test showed a statistically significant difference for marginal gap, internal gap, and fracture strength between all groups (p<0.001). However, the mode of fracture showed no differences between the groups (p>0.05). CAD/CAM fabricated provisional crowns demonstrated superior fit and better strength than direct provisional crowns.

Leading modes of tropical Pacific subsurface ocean temperature and associations with two types of El Niño.

PubMed

Zhang, Zhiyuan; Ren, Baohua; Zheng, Jianqiu

2017-02-17

Using empirical orthogonal function (EOF) analysis of the monthly tropical Pacific subsurface ocean temperature anomalies (SOTA) from 1979 to 2014, we detected three leading modes in the tropical Pacific subsurface temperature. The first mode has a dipole pattern, with warming in the eastern Pacific and cooling in the western Pacific, and is closely related to traditional El Niño. The second mode has a monopole pattern, with only warming in the central Pacific subsurface. The third mode has a zonal tripole pattern, with warming in the off-equatorial central Pacific and cooling in the far eastern Pacific and western Pacific. The second and third modes are both related to El Niño Modoki. Mode 1 is linked with a Kelvin wave that propagates from the central to the eastern Pacific and is induced by the anomalous westerlies that propagate from the western to the central Pacific. Mode 2 is also linked with a Kelvin wave that propagates from the western to the central Pacific induced by the enhancement of westerlies over the western Pacific. Mode 3 is linked with a Rossby wave that propagates from the central to the western Pacific driven by the anomalous easterlies over the eastern Pacific.

Fabrication of hexagonal star-shaped and ring-shaped patterns arrays by Mie resonance sphere-lens-lithography

NASA Astrophysics Data System (ADS)

Liu, Xianchao; Wang, Jun; Li, Ling; Gou, Jun; Zheng, Jie; Huang, Zehua; Pan, Rui

2018-05-01

Mie resonance sphere-lens-lithography has proved to be a good candidate for fabrication of large-area tunable surface nanopattern arrays. Different patterns on photoresist surface are obtained theoretically by adjusting optical coupling among neighboring spheres with different gap sizes. The effect of light reflection from the substrate on the pattern produced on the photoresist with a thin thickness is also discussed. Sub-micron hexagonal star-shaped and ring-shaped patterns arrays are achieved with close-packed spheres arrays and spheres arrays with big gaps, respectively. Changing of star-shaped vertices is induced by different polarization of illumination. Experimental results agree well with the simulation. By using smaller resonance spheres, sub-400 nm star-shaped and ring-shaped patterns can be realized. These tunable patterns are different from results of previous reports and have enriched pattern morphology fabricated by sphere-lens-lithography, which can find application in biosensor and optic devices.

Two-phase flow patterns in adiabatic and diabatic corrugated plate gaps

NASA Astrophysics Data System (ADS)

Polzin, A.-E.; Kabelac, S.; de Vries, B.

2016-09-01

Correlations for two-phase heat transfer and pressure drop can be improved considerably, when they are adapted to specific flow patterns. As plate heat exchangers find increasing application as evaporators and condensers, there is a need for flow pattern maps for corrugated plate gaps. This contribution presents experimental results on flow pattern investigations for such a plate heat exchanger background, using an adiabatic visualisation setup as well as a diabatic setup. Three characteristic flow patterns were observed in the considered range of two-phase flow: bubbly flow, film flow and slug flow. The occurrence of these flow patterns is a function of mass flux, void fraction, fluid properties and plate geometry. Two different plate geometries having a corrugation angle of 27° and 63°, respectively and two different fluids (water/air and R365mfc liquid/vapor) have been analysed. A flow pattern map using the momentum flux is presented.

Two types of modes in finite size one-dimensional coaxial photonic crystals: General rules and experimental evidence

NASA Astrophysics Data System (ADS)

El Boudouti, E. H.; El Hassouani, Y.; Djafari-Rouhani, B.; Aynaou, H.

2007-08-01

We demonstrate analytically and experimentally the existence and behavior of two types of modes in finite size one-dimensional coaxial photonic crystals made of N cells with vanishing magnetic field on both sides. We highlight the existence of N-1 confined modes in each band and one mode by gap associated to either one or the other of the two surfaces surrounding the structure. The latter modes are independent of N . These results generalize our previous findings on the existence of surface modes in two semi-infinite superlattices obtained from the cleavage of an infinite superlattice between two cells. The analytical results are obtained by means of the Green’s function method, whereas the experiments are carried out using coaxial cables in the radio-frequency regime.

Novel band structures in silicene on monolayer zinc sulfide substrate.

PubMed

Li, Sheng-shi; Zhang, Chang-wen; Yan, Shi-shen; Hu, Shu-jun; Ji, Wei-xiao; Wang, Pei-ji; Li, Ping

2014-10-01

Opening a sizable band gap in the zero-gap silicene without lowering the carrier mobility is a key issue for its application in nanoelectronics. Based on first-principles calculations, we find that the interaction energies are in the range of -0.09‒0.3 eV per Si atom, indicating a weak interaction between silicene and ZnS monolayer and the ABZn stacking is the most stable pattern. The band gap of silicene can be effectively tuned ranging from 0.025 to 1.05 eV in silicene and ZnS heterobilayer (Si/ZnS HBL). An unexpected indirect-direct band gap crossover is also observed in HBLs, dependent on the stacking pattern, interlayer spacing and external strain effects on silicene. Interestingly, the characteristics of Dirac cone with a nearly linear band dispersion relation of silicene can be preserved in the ABS pattern which is a metastable state, accompanied by a small electron effective mass and thus the carrier mobility is expected not to degrade much. These provide a possible way to design effective FETs out of silicene on a ZnS monolayer.

Quasilinear Line Broadened Model for Energetic Particle Transport

NASA Astrophysics Data System (ADS)

Ghantous, Katy; Gorelenkov, Nikolai; Berk, Herbert

2011-10-01

We present a self-consistent quasi-linear model that describes wave-particle interaction in toroidal geometry and computes fast ion transport during TAE mode evolution. The model bridges the gap between single mode resonances, where it predicts the analytically expected saturation levels, and the case of multiple modes overlapping, where particles diffuse across phase space. Results are presented in the large aspect ratio limit where analytic expressions are used for Fourier harmonics of the power exchange between waves and particles, . Implemention of a more realistic mode structure calculated by NOVAK code are also presented. This work is funded by DOE contract DE-AC02-09CH11466.

Experimental study on slow flexural waves around the defect modes in a phononic crystal beam using fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Chuang, Kuo-Chih; Zhang, Zhi-Qiang; Wang, Hua-Xin

2016-12-01

This work experimentally studies influences of the point defect modes on the group velocity of flexural waves in a phononic crystal Timoshenko beam. Using the transfer matrix method with a supercell technique, the band structures and the group velocities around the defect modes are theoretically obtained. Particularly, to demonstrate the existence of the localized defect modes inside the band gaps, a high-sensitivity fiber Bragg grating sensing system is set up and the displacement transmittance is measured. Slow propagation of flexural waves via defect coupling in the phononic crystal beam is then experimentally demonstrated with Hanning windowed tone burst excitations.

Post-Extinction Ecological Recovery of Marine Life Modes

NASA Astrophysics Data System (ADS)

Park, C.; de la Torre, N. G.; Heim, N.; Payne, J.

2016-12-01

A mass extinction is defined by a substantial increase in extinction rates, resulting in a loss of taxonomic and ecological diversity. Bush et al. (2007) defined ecological life modes as the feeding, motility, and tiering habits and organized them in a six-by-six "eco-cube" in which each section represented a life mode. In our research, we analyzed the ecological recovery of each life mode after the five mass extinctions. Using a fossil marine genera database, we compiled five heat maps that depict the recovery of the life modes by plotting the diversity of genera in each life mode two intervals before and five intervals after each mass extinction interval. New life modes seem to appear either immediately following or three or more intervals after a mass extinction, which indicates that ecological recovery is not a gradual process, but rather occurs in a punctuated manner. Furthermore, the "filling order" of new life modes differ in each extinction. However, some seem to have defined patterns, such as the Ordovician, where earlier post-extinction intervals experienced an increase in the diversity of erect (tiering) ecospaces, followed by that of surficial and shallow infaunal life modes. The Devonian mass extinction followed a similar pattern as the end Ordovician where erect organisms came first followed by surficial, deep-infaunal, and pelagic life modes. Conversely, intervals following the end-Permian mass extinction experienced a recovery in pelagic, freely-moving life modes, followed by a recovery in infaunal organisms and an explosion in semi-infaunal, erect, surficial, and pelagic ecospaces in the Ladinian. New life modes in the Triassic and Cretaceous mass extinctions did not seem to generate in a distinct pattern. Overall, we conclude that recovery patterns are unique depending on the cause of each mass extinction, and that any general tendency in post-extinction ecological recovery was most likely overridden by the environmental condition of the recovery intervals.

A new class of tunable hypersonic phononic crystals based on polymer-tethered colloids

PubMed Central

Alonso-Redondo, E.; Schmitt, M.; Urbach, Z.; Hui, C. M.; Sainidou, R.; Rembert, P.; Matyjaszewski, K.; Bockstaller, M. R.; Fytas, G.

2015-01-01

The design and engineering of hybrid materials exhibiting tailored phononic band gaps are fundamentally relevant to innovative material technologies in areas ranging from acoustics to thermo-optic devices. Phononic hybridization gaps, originating from the anti-crossing between local resonant and propagating modes, have attracted particular interest because of their relative robustness to structural disorder and the associated benefit to ‘manufacturability'. Although hybridization gap materials are well known, their economic fabrication and efficient control of the gap frequency have remained elusive because of the limited property variability and expensive fabrication methodologies. Here we report a new strategy to realize hybridization gap materials by harnessing the ‘anisotropic elasticity' across the particle–polymer interface in densely polymer-tethered colloidal particles. Theoretical and Brillouin scattering analysis confirm both the robustness to disorder and the tunability of the resulting hybridization gap and provide guidelines for the economic synthesis of new materials with deliberately controlled gap position and width frequencies. PMID:26390851

The second-order interference of two independent single-mode He-Ne lasers

NASA Astrophysics Data System (ADS)

Liu, Jianbin; Le, Mingnan; Bai, Bin; Wang, Wentao; Chen, Hui; Zhou, Yu; Li, Fu-li; Xu, Zhuo

2015-09-01

The second-order spatial and temporal interference patterns with two independent single-mode continuous-wave He-Ne lasers are observed when these two lasers are incident to two adjacent input ports of a 1:1 non-polarizing beam splitter, respectively. Two-photon interference based on the superposition principle in Feynman's path integral theory is employed to interpret the experimental results. The conditions to observe the second-order interference pattern with two independent single-mode continuous-wave lasers are discussed. It is concluded that frequency stability is important to observe the second-order interference pattern with two independent light beams.

Editorial: Spatial arrangement of faults and opening-mode fractures

NASA Astrophysics Data System (ADS)

Laubach, Stephen E.; Lamarche, Juliette; Gauthier, Bertand D. M.; Dunne, William M.

2018-03-01

This issue of the Journal of Structural Geology titled Spatial arrangement of faults and opening-mode fractures explores a fundamental characteristic of fault and fracture arrays. The pattern of fault and opening-mode fracture positions in space defines structural heterogeneity and anisotropy in a rock volume, governs how faults and fractures affect fluid flow, and impacts our understanding of the initiation, propagation and interactions during the formation of fracture patterns. This special issue highlights recent progress with respect to characterizing and understanding the spatial arrangements of fault and fracture patterns, providing examples over a wide range of scales and structural settings.

How predictable is the anomaly pattern of the Indian summer rainfall?

NASA Astrophysics Data System (ADS)

Li, Juan; Wang, Bin

2016-05-01

Century-long efforts have been devoted to seasonal forecast of Indian summer monsoon rainfall (ISMR). Most studies of seasonal forecast so far have focused on predicting the total amount of summer rainfall averaged over the entire India (i.e., all Indian rainfall index-AIRI). However, it is practically more useful to forecast anomalous seasonal rainfall distribution (anomaly pattern) across India. The unknown science question is to what extent the anomalous rainfall pattern is predictable. This study attempted to address this question. Assessment of the 46-year (1960-2005) hindcast made by the five state-of-the-art ENSEMBLE coupled dynamic models' multi-model ensemble (MME) prediction reveals that the temporal correlation coefficient (TCC) skill for prediction of AIRI is 0.43, while the area averaged TCC skill for prediction of anomalous rainfall pattern is only 0.16. The present study aims to estimate the predictability of ISMR on regional scales by using Predictable Mode Analysis method and to develop a set of physics-based empirical (P-E) models for prediction of ISMR anomaly pattern. We show that the first three observed empirical orthogonal function (EOF) patterns of the ISMR have their distinct dynamical origins rooted in an eastern Pacific-type La Nina, a central Pacific-type La Nina, and a cooling center near dateline, respectively. These equatorial Pacific sea surface temperature anomalies, while located in different longitudes, can all set up a specific teleconnection pattern that affects Indian monsoon and results in different rainfall EOF patterns. Furthermore, the dynamical models' skill for predicting ISMR distribution primarily comes primarily from these three modes. Therefore, these modes can be regarded as potentially predictable modes. If these modes are perfectly predicted, about 51 % of the total observed variability is potentially predictable. Based on understanding the lead-lag relationships between the lower boundary anomalies and the predictable modes, a set of P-E models is established to predict the principal component of each predictable mode, so that the ISMR anomaly pattern can be predicted by using the sum of the predictable modes. Three validation schemes are used to assess the performance of the P-E models' hindcast and independent forecast. The validated TCC skills of the P-E model here are more than doubled that of dynamical models' MME hindcast, suggesting a large room for improvement of the current dynamical prediction. The methodology proposed here can be applied to a wide range of climate prediction and predictability studies. The limitation and future improvement are also discussed.

The Achievement Gap and the Discipline Gap: Two Sides of the Same Coin?

ERIC Educational Resources Information Center

Gregory, Anne; Skiba, Russell J.; Noguera, Pedro A.

2010-01-01

The gap in achievement across racial and ethnic groups has been a focus of education research for decades, but the disproportionate suspension and expulsion of Black, Latino, and American Indian students has received less attention. This article synthesizes research on racial and ethnic patterns in school sanctions and considers how…

The Timing of a Time Out: The Gap Year in Life Course Context

ERIC Educational Resources Information Center

Vogt, Kristoffer Chelsom

2018-01-01

Based on biographical interviews from a three-generation study in Norway, this article examines the place of the contemporary "gap year" within life course transition trajectories and intergenerational relations embedded in wider patterns of social inequality. Under the heading of taking a gap year, young people on "academic…

Design and development of broadband piezoelectric vibration energy harvester based on compliant orthoplanar spring

NASA Astrophysics Data System (ADS)

Dhote, Sharvari

With advancement in technology, power requirements are reduced drastically for sensor nodes. The piezoelectric vibration energy harvesters generate sufficient power to low-powered sensor nodes. The main requirement of energy harvester is to provide a broad bandwidth. A conventional linear harvester does not satisfy this requirement. Therefore, the research focus is shifted to exploiting nonlinearity to widen the bandwidth of the harvester. Although nonlinear techniques are promising for broadening a bandwidth, reverse sweep shows reduced response as compared to the forward sweep. To overcome this issue, this thesis presents the design and development of a broadband piezoelectric vibration energy harvester based on a nonlinear multi-frequency compliant orthoplanar spring. This thesis is divided into three parts. The first part presents the design and experimental study of a tri-leg compliant orthoplanar spring for a broadband energy harvesting. The harvester performance is enhanced through the use of lightweight masses, which bring nonlinear vibration modes closer. The performance of the harvester is analyzed through development of a mathematical model based on the Duffing oscillator. The experimental and numerical results are in good agreement. The parametric study shows that an optimum performance is achieved by further reducing a gap in between the vibration modes using different weight masses. In the second part of the research, multiple (bi, quad and pent) leg compliant orthoplanar springs are designed to understand their role in expanding the bandwidth and reducing gap between vibration modes. The designed harvesters are compared by calculating the figure of merits. The quad-leg design provides a better performance in terms of power density and bandwidth among all the designs. The reverse sweep response is comparable to the forward sweep in terms of bandwidth. In the final part, a magnetic force is applied to the tri-leg harvester, which enhanced the voltage output and bandwidth. In addition, vibration modes have been brought even closer by reducing the gap between the modes. Overall, the proposed harvester performance is significantly improved using multiple legs attached with piezoelectric plates and masses, bringing the modes closer in the forward and reverse sweeps, making it advantageous to harvest energy from wideband environmental vibrations.

Linear bunchers and half-frequency bunching method

NASA Astrophysics Data System (ADS)

Tang, J. Y.; Jiang, J. Z.; Shi, A. M.; Yin, Z. K.; Wang, Y. F.

2000-12-01

A new buncher system consisting of two bunchers has been designed and constructed for HIRFL injector cyclotron, working at the SFC acceleration modes of H=1 and H=3, respectively. The bunchers use saw-tooth RF waveform, but with double-gap drift tube electrodes and single-gap grid electrodes, respectively. The special merit of the design is introduction of the half-frequency bunching mode, utilizing half of the cyclotron RF frequency. With this method, a perfect longitudinal match between the injector SFC and the main cyclotron SSC has been reached theoretically, compared to the original efficiency of 50% for most cases. Detailed studies have been made concerning space charge effects, longitudinal dispersions through the yoke hole and the spiral inflector, and non-linearity in both the RF waveform and the stray electric field of electrodes.

Endogenous voltage gradients as mediators of cell-cell communication: strategies for investigating bioelectrical signals during pattern formation

PubMed Central

Adams, Dany S.; Levin, Michael

2013-01-01

Alongside the well-known chemical modes of cell-cell communication, we find an important and powerful system of bioelectrical signaling: changes in the resting voltage potential (Vmem) of the plasma membrane driven by ion channels, pumps and gap junctions. Slow Vmem changes in all cells serve as a highly conserved, information-bearing pathway that regulates cell proliferation, migration and differentiation. In embryonic and regenerative pattern formation and in the disorganization of neoplasia, bioelectrical cues serve as mediators of large-scale anatomical polarity, organ identity and positional information. Recent developments have resulted in tools that enable a high-resolution analysis of these biophysical signals and their linkage with upstream and downstream canonical genetic pathways. Here, we provide an overview for the study of bioelectric signaling, focusing on state-of-the-art approaches that use molecular physiology and developmental genetics to probe the roles of bioelectric events functionally. We highlight the logic, strategies and well-developed technologies that any group of researchers can employ to identify and dissect ionic signaling components in their own work and thus to help crack the bioelectric code. The dissection of bioelectric events as instructive signals enabling the orchestration of cell behaviors into large-scale coherent patterning programs will enrich on-going work in diverse areas of biology, as biophysical factors become incorporated into our systems-level understanding of cell interactions. PMID:22350846

Raman intensity and vibrational modes of armchair CNTs

NASA Astrophysics Data System (ADS)

Hur, Jaewoong; Stuart, Steven J.

2017-07-01

Raman intensity changes and frequency patterns have been studied using the various armchair (n, n) to understand the variations of bond polarizability, in regard to changing diameters, lengths, and the number of atoms in the (n, n). The Raman intensity trends of the (n, n) are validated by those of Cn isomers. For frequency trends, similar frequency patterns and frequency inward shifts for the (n, n) are characterized. Also, VDOS trends of the (n, n) expressing Raman modes are interpreted. The decomposition of vibrational modes in the (n, n) into radial, longitudinal, and tangential mode is beneficially used to recognize the distinct characteristics of vibrational modes.

Origin of seasonal predictability for summer climate over the Northwestern Pacific

PubMed Central

Kosaka, Yu; Xie, Shang-Ping; Lau, Ngar-Cheung; Vecchi, Gabriel A.

2013-01-01

Summer climate in the Northwestern Pacific (NWP) displays large year-to-year variability, affecting densely populated Southeast and East Asia by impacting precipitation, temperature, and tropical cyclones. The Pacific–Japan (PJ) teleconnection pattern provides a crucial link of high predictability from the tropics to East Asia. Using coupled climate model experiments, we show that the PJ pattern is the atmospheric manifestation of an air–sea coupled mode spanning the Indo-NWP warm pool. The PJ pattern forces the Indian Ocean (IO) via a westward propagating atmospheric Rossby wave. In response, IO sea surface temperature feeds back and reinforces the PJ pattern via a tropospheric Kelvin wave. Ocean coupling increases both the amplitude and temporal persistence of the PJ pattern. Cross-correlation of ocean–atmospheric anomalies confirms the coupled nature of this PJIO mode. The ocean–atmosphere feedback explains why the last echoes of El Niño–Southern Oscillation are found in the IO-NWP in the form of the PJIO mode. We demonstrate that the PJIO mode is indeed highly predictable; a characteristic that can enable benefits to society. PMID:23610388

Design, analysis and modeling of a novel hybrid powertrain system based on hybridized automated manual transmission

NASA Astrophysics Data System (ADS)

Wu, Guang; Dong, Zuomin

2017-09-01

Hybrid electric vehicles are widely accepted as a promising short to mid-term technical solution due to noticeably improved efficiency and lower emissions at competitive costs. In recent years, various hybrid powertrain systems were proposed and implemented based on different types of conventional transmission. Power-split system, including Toyota Hybrid System and Ford Hybrid System, are well-known examples. However, their relatively low torque capacity, and the drive of alternative and more advanced designs encouraged other innovative hybrid system designs. In this work, a new type of hybrid powertrain system based hybridized automated manual transmission (HAMT) is proposed. By using the concept of torque gap filler (TGF), this new hybrid powertrain type has the potential to overcome issue of torque gap during gearshift. The HAMT design (patent pending) is described in details, from gear layout and design of gear ratios (EV mode and HEV mode) to torque paths at different gears. As an analytical tool, mutli-body model of vehicle equipped with this HAMT was built to analyze powertrain dynamics at various steady and transient modes. A gearshift was decomposed and analyzed based basic modes. Furthermore, a Simulink-SimDriveline hybrid vehicle model was built for the new transmission, driveline and vehicle modular. Control strategy has also been built to harmonically coordinate different powertrain components to realize TGF function. A vehicle launch simulation test has been completed under 30% of accelerator pedal position to reveal details during gearshift. Simulation results showed that this HAMT can eliminate most torque gap that has been persistent issue of traditional AMT, improving both drivability and performance. This work demonstrated a new type of transmission that features high torque capacity, high efficiency and improved drivability.

Organic-inorganic hybrid material SUNCONNECT® for photonic integrated circuit

NASA Astrophysics Data System (ADS)

Nawata, Hideyuki; Oshima, Juro; Kashino, Tsubasa

2018-02-01

In this paper, we report the feature and properties about organic-inorganic hybrid material, "SUNCONNECT®" for photonic integrated circuit. "SUNCONNECT®" materials have low propagation loss at 1310nm (0.29dB/cm) and 1550nm (0.45dB/cm) respectively. In addition, the material has high thermal resistance both high temperature annealing test at 300°C and also 260°C solder heat resistance test. For actual device application, high reliability is required. 85°C /85% test was examined by using multi-mode waveguide. As a result, it indicated that variation of insertion loss property was not changed significantly after high temperature / high humidity test. For the application to photonic integrated circuit, it was demonstrated to fabricate polymer optical waveguide by using three different methods. Single-micron core pattern can be fabricated on cladding layer by using UV lithography with proximity gap exposure. Also, single-mode waveguide can be also fabricated with over cladding. On the other hands, "Mosquito method" and imprint method can be applied to fabricate polymer optical waveguide. Remarkably, these two methods can fabricate gradedindex type optical waveguide without using photo mask. In order to evaluate the optical performance, NFP's observation, measurement of insertion loss and propagation loss by cut-back methods were carried out by using each waveguide sample.

Soil moisture in sessile oak forest gaps

NASA Astrophysics Data System (ADS)

Zagyvainé Kiss, Katalin Anita; Vastag, Viktor; Gribovszki, Zoltán; Kalicz, Péter

2015-04-01

By social demands are being promoted the aspects of the natural forest management. In forestry the concept of continuous forest has been an accepted principle also in Hungary since the last decades. The first step from even-aged stand to continuous forest can be the forest regeneration based on gap cutting, so small openings are formed in a forest due to forestry interventions. This new stand structure modifies the hydrological conditions for the regrowth. Without canopy and due to the decreasing amounts of forest litter the interception is less significant so higher amount of precipitation reaching the soil. This research focuses on soil moisture patterns caused by gaps. The spatio-temporal variability of soil water content is measured in gaps and in surrounding sessile oak (Quercus petraea) forest stand. Soil moisture was determined with manual soil moisture meter which use Time-Domain Reflectometry (TDR) technology. The three different sizes gaps (G1: 10m, G2: 20m, G3: 30m) was opened next to Sopron on the Dalos Hill in Hungary. First, it was determined that there is difference in soil moisture between forest stand and gaps. Second, it was defined that how the gap size influences the soil moisture content. To explore the short term variability of soil moisture, two 24-hour (in growing season) and a 48-hour (in dormant season) field campaign were also performed in case of the medium-sized G2 gap along two/four transects. Subdaily changes of soil moisture were performed. The measured soil moisture pattern was compared with the radiation pattern. It was found that the non-illuminated areas were wetter and in the dormant season the subdaily changes cease. According to our measurements, in the gap there is more available water than under the forest stand due to the less evaporation and interception loss. Acknowledgements: The research was supported by TÁMOP-4.2.2.A-11/1/KONV-2012-0004 and AGRARKLIMA.2 VKSZ_12-1-2013-0034.

Symmetry Enriched Topological Phases and Their Edge Theories

NASA Astrophysics Data System (ADS)

Heinrich, Christopher

In this thesis we investigate topological phases of matter that have a global, unbroken symmetry group--also known as symmetry enriched topological (SET) phases. We address three questions about these phases: (1) how can we build exactly solvable models that realize them? (2) how can we determine if their edge theories can be gapped without breaking the symmetry? and (3) how do we understand the phenomenon of decoupled charge and neutral modes which occurs in certain fractional quantum Hall states? More specifically, we address the first question by constructing exactly solvable models for a wide class of symmetry enriched topological (SET) phases, which we call symmetry-enriched string nets. The construction applies to 2D bosonic SET phases with finite unitary onsite symmetry group G, and we conjecture that our models realize every phase in this class that can be described by a commuting projector Hamiltonian. As an example, we present a model for a phase with the same anyon excitations as the toric code and with a Z2 symmetry which exchanges the e and m type anyons. We further illustrate our construction with a number of additional examples. For the second question, we focus on the edge theories of 2D SET phases with Z2 symmetry. The central problem we seek to solve is to determine which edge theories can be gapped without breaking the symmetry. Previous attempts to answer this question in special cases relied on constructing perturbations of a particular type to gap the edge. This method proves the edge can be gapped when the appropriate perturbations can be found, but is inconclusive if they cannot be found. We build on this previous work by deriving a necessary and sufficient algebraic condition for when the edge can be gapped. Our results apply to Z2 symmetry protected topological phases as well as Abelian Z2 SET phases. Finally, in the fourth chapter, we describe solvable models that capture how impurity scattering in certain fractional quantum Hall edges can give rise to a neutral mode--i.e. an edge mode that does not carry electric charge. These models consist of two counter-propagating chiral Luttinger liquids together with a collection of discrete impurity scatterers. Our main result is an exact solution of these models in the limit of infinitely strong impurity scattering. From this solution, we explicitly derive the existence of a neutral mode and we determine all of its microscopic properties including its velocity. We also study the stability of the neutral mode and show that it survives at finite but sufficiently strong scattering. Our results are applicable to a family of Abelian fractional quantum Hall states of which the nu = 2/3 state is the most prominent example.

Photonic-band-gap gyrotron amplifier with picosecond pulses.

PubMed

Nanni, Emilio A; Jawla, Sudheer; Lewis, Samantha M; Shapiro, Michael A; Temkin, Richard J

2017-12-04

We report the amplification of 250 GHz pulses as short as 260 ps without observation of pulse broadening using a photonic-band-gap circuit gyrotron traveling-wave-amplifier. The gyrotron amplifier operates with a device gain of 38 dB and an instantaneous bandwidth of 8 GHz. The operational bandwidth of the amplifier can be tuned over 16 GHz by adjusting the operating voltage of the electron beam and the magnetic field. The amplifier uses a 30 cm long photonic-band-gap interaction circuit to confine the desired TE 03 -like operating mode while suppressing lower order modes which can result in undesired oscillations. The circuit gain is >55 dB for a beam voltage of 23 kV and a current of 700 mA. These results demonstrate the wide bandwidths and a high gain achievable with gyrotron amplifiers. The amplification of picosecond pulses of variable lengths, 260-800 ps, shows good agreement with the theory using the coupled dispersion relation and the gain-spectrum of the amplifier as measured with quasi-CW input pulses.

Coupling single giant nanocrystal quantum dots to the fundamental mode of patch nanoantennas through fringe field

DOE PAGES

Wang, Feng; Karan, Niladri S.; Minh Nguyen, Hue; ...

2015-09-23

Through single dot spectroscopy and numerical simulation studies, we demonstrate that the fundamental mode of gold patch nanoantennas have fringe-field resonance capable of enhancing the nano-emitters coupled around the edge of the patch antenna. This fringe-field coupling is used to enhance the radiative rates of core/thick-shell nanocrystal quantum dots (g-NQDs) that cannot be embedded into the ultra-thin dielectric gap of patch nanoantennas due to their large sizes. We attain 14 and 3 times enhancements in single exciton radiative decay rate and bi-exciton emission efficiencies of g-NQDs respectively, with no detectable metal quenching. Our numerical studies confirmed our experimental results andmore » further reveal that patch nanoantennas can provide strong emission enhancement for dipoles lying not only in radial direction of the circular patches but also in the direction normal to the antennas surface. Finally, this provides a distinct advantage over the parallel gap-bar antennas that can provide enhancement only for the dipoles oriented across the gap.« less

Photonic-band-gap gyrotron amplifier with picosecond pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nanni, Emilio A.; Jawla, Sudheer; Lewis, Samantha M.

Here, we report the amplification of 250 GHz pulses as short as 260 ps without observation of pulse broadening using a photonic-band-gap circuit gyrotron traveling-wave-amplifier. The gyrotron amplifier operates with a device gain of 38 dB and an instantaneous bandwidth of 8 GHz. The operational bandwidth of the amplifier can be tuned over 16 GHz by adjusting the operating voltage of the electron beam and the magnetic field. The amplifier uses a 30 cm long photonic-band-gap interaction circuit to confine the desired TE 03-like operating mode while suppressing lower order modes which can result in undesired oscillations. The circuit gainmore » is >55 dB for a beam voltage of 23 kV and a current of 700 mA. These results demonstrate the wide bandwidths and a high gain achievable with gyrotron amplifiers. The amplification of picosecond pulses of variable lengths, 260–800 ps, shows good agreement with the theory using the coupled dispersion relation and the gain-spectrum of the amplifier as measured with quasi-CW input pulses.« less

Possible realization of interacting symmetry-protected topological phases in topological crystalline insulators

NASA Astrophysics Data System (ADS)

Isobe, Hiroki; Fu, Liang

2015-03-01

The effects of electron-electron interaction in edge states of mirror-symmetry protected topological crystalline insulators (TCI's) are discussed. The analysis is performed by using bosonized Hamiltonian following the Tomonaga-Luttinger liquid theory. When two pairs of helical edge states exist, electron-electron interaction could gap out one edge mode, which is a possible realization of interacting symmetry-protected topological (SPT) phases. This type of SPT phase is closely related to a Luther-Emery liquid in spinful 1D system. We also propose a method of detecting the SPT phases by STM. The other focus of the study is the classification of SPT phases in mirror-symmetry protected TCI's. By adopting the Chern-Simons theory, we find that electron-electron interaction reduces the classification from Z to Z4. It means that the edge states can be gapped out when four pairs of edge states exist. In other cases, the edge modes cannot be fully gapped. Each of these states corresponds to a different SPT phase depending on the relevant interaction process.

Thermally triggered phononic gaps in liquids at THz scale

DOE PAGES

Bolmatov, Dima; Zhernenkov, Mikhail; Zavyalov, Dmitry; ...

2016-01-14

In this study we present inelastic X-ray scattering experiments in a diamond anvil cell and molecular dynamic simulations to investigate the behavior of phononic excitations in liquid Ar. The spectra calculated using molecular dynamics were found to be in a good agreement with the experimental data. Furthermore, we observe that, upon temperature increases, a low-frequency transverse phononic gap emerges while high-frequency propagating modes become evanescent at the THz scale. The effect of strong localization of a longitudinal phononic mode in the supercritical phase is observed for the first time. The evidence for the high-frequency transverse phononic gap due to themore » transition from an oscillatory to a ballistic dynamic regimes of motion is presented and supported by molecular dynamics simulations. This transition takes place across the Frenkel line thermodynamic limit which demarcates compressed liquid and non-compressed fluid domains on the phase diagram and is supported by calculations within the Green-Kubo phenomenological formalism. These results are crucial to advance the development of novel terahertz thermal devices, phononic lenses, mirrors, and other THz metamaterials.« less

Photonic-band-gap gyrotron amplifier with picosecond pulses

DOE PAGES

Nanni, Emilio A.; Jawla, Sudheer; Lewis, Samantha M.; ...

2017-12-05

Here, we report the amplification of 250 GHz pulses as short as 260 ps without observation of pulse broadening using a photonic-band-gap circuit gyrotron traveling-wave-amplifier. The gyrotron amplifier operates with a device gain of 38 dB and an instantaneous bandwidth of 8 GHz. The operational bandwidth of the amplifier can be tuned over 16 GHz by adjusting the operating voltage of the electron beam and the magnetic field. The amplifier uses a 30 cm long photonic-band-gap interaction circuit to confine the desired TE 03-like operating mode while suppressing lower order modes which can result in undesired oscillations. The circuit gainmore » is >55 dB for a beam voltage of 23 kV and a current of 700 mA. These results demonstrate the wide bandwidths and a high gain achievable with gyrotron amplifiers. The amplification of picosecond pulses of variable lengths, 260–800 ps, shows good agreement with the theory using the coupled dispersion relation and the gain-spectrum of the amplifier as measured with quasi-CW input pulses.« less

Polarization State of Light Scattered from Quantum Plasmonic Dimer Antennas.

PubMed

Yang, Longkun; Wang, Hancong; Fang, Yan; Li, Zhipeng

2016-01-26

Plasmonic antennas are able to concentrate and re-emit light in a controllable manner through strong coupling between metallic nanostructures. Only recently has it found that quantum mechanical effects can drastically change the coupling strength as the feature size approaches atomic scales. Here, we present a comprehensive experimental and theoretical study of the evolution of the resonance peak and its polarization state as the dimer-antenna gap narrows to subnanometer scale. We clearly can identify the classical plasmonic regime, a crossover regime where nonlocal screening plays an important role, and the quantum regime where a charge transfer plasmon appears due to interparticle electron tunneling. Moreover, as the gap decreases from tens of to a few nanometers, the bonding dipole mode tends to emit photons with increasing polarizability. When the gap narrows to quantum regime, a significant depolarization of the mode emission is observed due to the reduction of the charge density of coupled quantum plasmons. These results would be beneficial for the understanding of quantum effects on emitting-polarization of nanoantennas and the development of quantum-based photonic nanodevices.

Periodic dielectric structure for production of photonic band gap and method for fabricating the same

DOEpatents

Ozbay, E.; Tuttle, G.; Michel, E.; Ho, K.M.; Biswas, R.; Chan, C.T.; Soukoulis, C.

1995-04-11

A method is disclosed for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap. 42 figures.

Transverse mode control in proton-implanted and oxide-confined VCSELs via patterned dielectric anti-phase filters

NASA Astrophysics Data System (ADS)

Kesler, Benjamin; O'Brien, Thomas; Dallesasse, John M.

2017-02-01

A novel method for controlling the transverse lasing modes in both proton implanted and oxide-confined vertical- cavity surface-emitting lasers (VCSELs) with a multi-layer, patterned, dielectric anti-phase (DAP) filter is pre- sented. Using a simple photolithographic liftoff process, dielectric layers are deposited and patterned on individual VCSELs to modify (increase or decrease) the mirror reflectivity across the emission aperture via anti-phase reflections, creating spatially-dependent threshold material gain. The shape of the dielectric pattern can be tailored to overlap with specific transverse VCSEL modes or subsets of transverse modes to either facilitate or inhibit lasing by decreasing or increasing, respectively, the threshold modal gain. A silicon dioxide (SiO2) and titanium dioxide (TiO2) anti-phase filter is used to achieve a single-fundamental-mode, continuous-wave output power greater than 4.0 mW in an oxide-confined VCSEL at a lasing wavelength of 850 nm. A filter consisting of SiO2 and TiO2 is used to facilitate injection-current-insensitive fundamental mode and lower order mode lasing in proton implanted VCSELs at a lasing wavelength of 850 nm. Higher refractive index dielectric materials such as amorphous silicon (a-Si) can be used to increase the effectiveness of the anti-phase filter on proton implanted devices by reducing the threshold modal gain of any spatially overlapping modes. This additive, non-destructive method allows for mode selection at any lasing wavelength and for any VCSEL layer structure without the need for semiconductor etching or epitaxial regrowth. It also offers the capability of designing a filter based upon available optical coating materials.

Field patterns without blow up

NASA Astrophysics Data System (ADS)

Mattei, Ornella; Milton, Graeme W.

2017-09-01

Field patterns, first proposed by the authors in Milton and Mattei (2017 Proc. R. Soc. A 473 20160819), are a new type of wave propagating along orderly patterns of characteristic lines which arise in specific space-time microstructures whose geometry in one spatial dimension plus time is somehow commensurate with the slope of the characteristic lines. In particular, in Milton and Mattei (2017 Proc. R. Soc. A 473 20160819) the authors propose two examples of space-time geometries in which field patterns occur: they are two-phase microstructures in which rectangular space-time inclusions of one material are embedded in another material. After a sufficiently long interval of time, field patterns have local periodicity both in time and space. This allows one to focus only on solving the problem on the discrete network on which a field pattern lives and to define a suitable transfer matrix that, given the solution at a certain time, provides the solution after one time period. For the aforementioned microstructures, many of the eigenvalues of this { P }{ T }-symmetric transfer matrix have unit norm and hence the corresponding eigenvectors correspond to propagating modes. However, there are also modes that blow up exponentially with time coupled with modes that decrease exponentially with time. The question arises as to whether there are space-time microstructures such that the transfer matrix only has eigenvalues on the unit circle, so that there are no growing modes (modes that blow-up)? The answer is found here, where we see that certain space-time checkerboards have the property that all the modes are propagating modes, within a certain range of the material parameters. Interestingly, when there is no blow-up, the waves generated by an instantaneous disturbance at a point look like shocks with a wake of oscillatory waves, whose amplitude, very remarkably, does not tend to zero away from the wave front.

Mode-Locked Spike Trains in Responses of Ventral Cochlear Nucleus Chopper and Onset Neurons to Periodic Stimuli

PubMed Central

Laudanski, Jonathan; Coombes, Stephen; Palmer, Alan R.

2010-01-01

We report evidence of mode-locking to the envelope of a periodic stimulus in chopper units of the ventral cochlear nucleus (VCN). Mode-locking is a generalized description of how responses in periodically forced nonlinear systems can be closely linked to the input envelope, while showing temporal patterns of higher order than seen during pure phase-locking. Re-analyzing a previously unpublished dataset in response to amplitude modulated tones, we find that of 55% of cells (6/11) demonstrated stochastic mode-locking in response to sinusoidally amplitude modulated (SAM) pure tones at 50% modulation depth. At 100% modulation depth SAM, most units (3/4) showed mode-locking. We use interspike interval (ISI) scattergrams to unravel the temporal structure present in chopper mode-locked responses. These responses compared well to a leaky integrate-and-fire model (LIF) model of chopper units. Thus the timing of spikes in chopper unit responses to periodic stimuli can be understood in terms of the complex dynamics of periodically forced nonlinear systems. A larger set of onset (33) and chopper units (24) of the VCN also shows mode-locked responses to steady-state vowels and cosine-phase harmonic complexes. However, while 80% of chopper responses to complex stimuli meet our criterion for the presence of mode-locking, only 40% of onset cells show similar complex-modes of spike patterns. We found a correlation between a unit's regularity and its tendency to display mode-locked spike trains as well as a correlation in the number of spikes per cycle and the presence of complex-modes of spike patterns. These spiking patterns are sensitive to the envelope as well as the fundamental frequency of complex sounds, suggesting that complex cell dynamics may play a role in encoding periodic stimuli and envelopes in the VCN. PMID:20042702

Spatial and temporal patterns of beetles associated with coarse woody debris in managed bottomland hardwood forests

Treesearch

Michael D. Ulyshen; James L. Hanula; Scott Horn; John C. Kilgo; Christopher E. Moorman

2004-01-01

Malaise traps were used to sample beetles in artificial canopy gaps of different size (0.13 ha, 0.26 ha, and 0.50 ha) and age in a South Carolina bottomland hardwood forest. Traps were placed at the center, edge, and in the surrounding forest of each gap. Young gaps (~1 year) had large amounts of coarse woody debris compared to the surrounding forest, while older gaps...

Sensitivity of super-efficient data envelopment analysis results to individual decision-making units: an example of surgical workload by specialty.

PubMed

Dexter, Franklin; O'Neill, Liam; Xin, Lei; Ledolter, Johannes

2008-12-01

We use resampling of data to explore the basic statistical properties of super-efficient data envelopment analysis (DEA) when used as a benchmarking tool by the manager of a single decision-making unit. Our focus is the gaps in the outputs (i.e., slacks adjusted for upward bias), as they reveal which outputs can be increased. The numerical experiments show that the estimates of the gaps fail to exhibit asymptotic consistency, a property expected for standard statistical inference. Specifically, increased sample sizes were not always associated with more accurate forecasts of the output gaps. The baseline DEA's gaps equaled the mode of the jackknife and the mode of resampling with/without replacement from any subset of the population; usually, the baseline DEA's gaps also equaled the median. The quartile deviations of gaps were close to zero when few decision-making units were excluded from the sample and the study unit happened to have few other units contributing to its benchmark. The results for the quartile deviations can be explained in terms of the effective combinations of decision-making units that contribute to the DEA solution. The jackknife can provide all the combinations contributing to the quartile deviation and only needs to be performed for those units that are part of the benchmark set. These results show that there is a strong rationale for examining DEA results with a sensitivity analysis that excludes one benchmark hospital at a time. This analysis enhances the quality of decision support using DEA estimates for the potential ofa decision-making unit to grow one or more of its outputs.

Abbreviated epitaxial growth mode (AGM) method for reducing cost and improving quality of LEDs and lasers

DOEpatents

Tansu, Nelson; Chan, Helen M; Vinci, Richard P; Ee, Yik-Khoon; Biser, Jeffrey

2013-09-24

The use of an abbreviated GaN growth mode on nano-patterned AGOG sapphire substrates, which utilizes a process of using 15 nm low temperature GaN buffer and bypassing etch-back and recovery processes during epitaxy, enables the growth of high-quality GaN template on nano-patterned AGOG sapphire. The GaN template grown on nano-patterned AGOG sapphire by employing abbreviated growth mode has two orders of magnitude lower threading dislocation density than that of conventional GaN template grown on planar sapphire. The use of abbreviated growth mode also leads to significant reduction in cost of the epitaxy. The growths and characteristics of InGaN quantum wells (QWs) light emitting diodes (LEDs) on both templates were compared. The InGaN QWs LEDs grown on the nano-patterned AGOG sapphire demonstrated at least a 24% enhancement of output power enhancement over that of LEDs grown on conventional GaN templates.

Trade-off between competition and facilitation defines gap colonization in mountains.

PubMed

Lembrechts, Jonas J; Milbau, Ann; Nijs, Ivan

2015-11-10

Recent experimental observations show that gap colonization in small-stature (e.g. grassland and dwarf shrubs) vegetation strongly depends on the abiotic conditions within them. At the same time, within-gap variation in biotic interactions such as competition and facilitation, caused by distance to the gap edge, would affect colonizer performance, but a theoretical framework to explore such patterns is missing. Here, we model how competition, facilitation and environmental conditions together determine the small-scale patterns of gap colonization along a cold gradient in mountains, by simulating colonizer survival in gaps of various sizes. Our model adds another dimension to the known effects of biotic interactions along a stress gradient by focussing on the trade-off between competition and facilitation in the within-gap environment. We show that this trade-off defines a peak in colonizer survival at a specific distance from the gap edge, which progressively shifts closer to the edge as the environment gets colder, ultimately leaving a large fraction of gaps unsuitable for colonization in facilitation-dominated systems. This is reinforced when vegetation size and temperature amelioration are manipulated simultaneously with temperature in order to simulate an elevational gradient more realistically. Interestingly, all other conditions being equal, the magnitude of the realized survival peak was always lower in large than in small gaps, making large gaps harder to colonize. The model is relevant to predict effects of non-native plant invasions and climate warming on colonization processes in mountains. Published by Oxford University Press on behalf of the Annals of Botany Company.

A high-order mode extended interaction klystron at 0.34 THz

NASA Astrophysics Data System (ADS)

Wang, Dongyang; Wang, Guangqiang; Wang, Jianguo; Li, Shuang; Zeng, Peng; Teng, Yan

2017-02-01

We propose the concept of high-order mode extended interaction klystron (EIK) at the terahertz band. Compared to the conventional fundamental mode EIK, it operates at the TM31-2π mode, and its remarkable advantage is to obtain a large structure and good performance. The proposed EIK consists of five identical cavities with five gaps in each cavity. The method is discussed to suppress the mode competition and self-oscillation in the high-order mode cavity. Particle-in-cell simulation demonstrates that the EIK indeed operates at TM31-2π mode without self-oscillation while other modes are well suppressed. Driven by the electron beam with a voltage of 15 kV and a current of 0.3 A, the saturation gain of 43 dB and the output power of 60 W are achieved at the center frequency of 342.4 GHz. The EIK operating at high-order mode seems a promising approach to generate high power terahertz waves.

Millimeter-Wave Heterojunction Two-Terminal Devices.

DTIC Science & Technology

1986-05-01

saturation velocities and characteristics. In the following, theo basic properties of the IMPATT, MITATT and TUNNETT modes of operation and the properties...in Fig. 5.1 is shown in Fig. 5.2. This mounting structure was inves- tigated by Lewin and Eisenhart . While reasonable results may be obtained in some...significant effect, Eisenhart et al.4 proposed that the coaxial aperture be modeled as a finite gap (which is called "the equivalent gap"). This

Dual-Mode Scramjet Combustor: Numerical Sensitivity and Evaluation of Experiments

DTIC Science & Technology

2012-01-01

effects of the air gap; the second took into account the effects of the air gap by using a backpressure imposed boundary condition. Figure 36 shows an... exhauster housing at the exit of the combustor in RC22’s test apparatus. I. Introduction Previous experimental efforts in...amount of air/fuel mixing, which affects combustion . Other approaches such as Large-Eddy Simulation (LES) and Direct-Numerical Simulation (DNS) are too

Global linkages between teleconnection patterns and the terrestrial biosphere

NASA Astrophysics Data System (ADS)

Dahlin, Kyla M.; Ault, Toby R.

2018-07-01

Interannual variability in the global carbon cycle is largely due to variations in carbon uptake by terrestrial ecosystems, yet linkages between climate variability and variability in the terrestrial carbon cycle are not well understood at the global scale. Using a 30-year satellite record of semi-monthly leaf area index (LAI), we show that four modes of climate variability - El Niño/Southern Oscillation, the North Atlantic Oscillation, the Atlantic Meridional Mode, and the Indian Ocean Dipole Mode - strongly impact interannual vegetation growth patterns, with 68% of the land surface impacted by at least one of these teleconnection patterns, yet the spatial distribution of these impacts is heterogeneous. Considering the patterns' impacts by biome, none has an exclusively positive or negative relationship with LAI. Our findings imply that future changes in the frequency and/or magnitude of teleconnection patterns will lead to diverse changes to the terrestrial biosphere and the global carbon cycle.

Robust manipulation of light using topologically protected plasmonic modes.

PubMed

Liu, Chenxu; Gurudev Dutt, M V; Pekker, David

2018-02-05

We propose using a topological plasmonic crystal structure composed of an array of nearly parallel nanowires with unequal spacing for manipulating light. In the paraxial approximation, the Helmholtz equation that describes the propagation of light along the nanowires maps onto the Schrödinger equation of the Su-Schrieffer-Heeger (SSH) model. Using a full three-dimensional finite difference time domain solution of the Maxwell equations, we verify the existence of topological defect modes, with sub-wavelength localization, bound to domain walls of the plasmonic crystal. We show that by manipulating domain walls we can construct spatial mode filters that couple bulk modes to topological defect modes, and topological beam-splitters that couple two topological defect modes. Finally, we show that the structures are tolerant to fabrication errors with an inverse length-scale smaller than the topological band gap.

A multiple gap plasma cathode electron gun and its electron beam analysis in self and trigger breakdown modes.

PubMed

Kumar, Niraj; Pal, Dharmendra Kumar; Jadon, Arvind Singh; Pal, Udit Narayan; Rahaman, Hasibur; Prakash, Ram

2016-03-01

In the present paper, a pseudospark discharge based multiple gap plasma cathode electron gun is reported which has been operated separately in self and trigger breakdown modes using two different gases, namely, argon and hydrogen. The beam current and beam energy have been analyzed using a concentric ring diagnostic arrangement. Two distinct electron beams are clearly seen with hollow cathode and conductive phases. The hollow cathode phase has been observed for ∼50 ns where the obtained electron beam is having low beam current density and high energy. While in conductive phase it is high current density and low energy electron beam. It is inferred that in the hollow cathode phase the beam energy is more for the self breakdown case whereas the current density is more for the trigger breakdown case. The tailor made operation of the hollow cathode phase electron beam can play an important role in microwave generation. Up to 30% variation in the electron beam energy has been achieved keeping the same gas and by varying the breakdown mode operations. Also, up to 32% variation in the beam current density has been achieved for the trigger breakdown mode at optimized trigger position by varying the gas type.

A multiple gap plasma cathode electron gun and its electron beam analysis in self and trigger breakdown modes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Niraj; Pal, Udit Narayan; Prakash, Ram

In the present paper, a pseudospark discharge based multiple gap plasma cathode electron gun is reported which has been operated separately in self and trigger breakdown modes using two different gases, namely, argon and hydrogen. The beam current and beam energy have been analyzed using a concentric ring diagnostic arrangement. Two distinct electron beams are clearly seen with hollow cathode and conductive phases. The hollow cathode phase has been observed for ∼50 ns where the obtained electron beam is having low beam current density and high energy. While in conductive phase it is high current density and low energy electronmore » beam. It is inferred that in the hollow cathode phase the beam energy is more for the self breakdown case whereas the current density is more for the trigger breakdown case. The tailor made operation of the hollow cathode phase electron beam can play an important role in microwave generation. Up to 30% variation in the electron beam energy has been achieved keeping the same gas and by varying the breakdown mode operations. Also, up to 32% variation in the beam current density has been achieved for the trigger breakdown mode at optimized trigger position by varying the gas type.« less

Effect of boreal spring precipitation anomaly pattern change in the late 1990s over tropical Pacific on the atmospheric teleconnection

NASA Astrophysics Data System (ADS)

Guo, Yuanyuan; Wen, Zhiping; Chen, Ruidan; Li, Xiuzhen; Yang, Xiu-Qun

2018-02-01

Observational evidence showed that the leading mode of precipitation variability over the tropical Pacific during boreal spring experienced a pronounced interdecadal change around the late 1990s, characterized by a precipitation pattern shift from an eastern Pacific (EP) type to a central Pacific (CP) type. The distinct impacts of such a precipitation pattern shift on the extratropical atmospheric teleconnection were examined. An apparent poleward teleconnection extending from the tropics to the North Atlantic region was observed after 1998, while, there was no significant teleconnection before 1998. To understand why only the CP-type precipitation mode is associated with a striking atmospheric teleconnection after 1998, diagnostic analyses with the Eliassen-Palm flux and Rossby wave source (RWS) based on the barotropic vorticity equation were performed. The results show that for the EP-type precipitation mode, no significant RWS anomalies appeared over the subtropical Pacific due to the opposite effect of the vortex stretching and absolute vorticity advection processes. For the CP-type precipitation mode, however, there are both significant vorticity forcing source over the subtropical CP and clear poleward-propagation of Rossby wave. The spatial distribution of the CP-type precipitation pattern tends to excite a conspicuous anomalous southerly and a well-organized negative vorticity center over the subtropical CP where both the mean absolute vorticity gradient and mean divergence flow are large, hence, the interaction between the heating-induced anomalous circulation and the basic state made the generation of Rossby waves conceivable and effective. Such corresponding teleconnection responses to the prescribed heating were also examined by using a Linear Baroclinic Model (LBM). It turned out that significant poleward teleconnection pattern is only caused by the CP-type precipitation mode, rather than by the EP-type precipitation mode. Further sensitive experiments demonstrated that the change in spring basic state before and after 1998 played a relatively minor role in exciting such a teleconnection pattern, when compared with the tropical precipitation anomaly pattern change.

Rogue-wave pattern transition induced by relative frequency.

PubMed

Zhao, Li-Chen; Xin, Guo-Guo; Yang, Zhan-Ying

2014-08-01

We revisit a rogue wave in a two-mode nonlinear fiber whose dynamics is described by two-component coupled nonlinear Schrödinger equations. The relative frequency between two modes can induce different rogue wave patterns transition. In particular, we find a four-petaled flower structure rogue wave can exist in the two-mode coupled system, which possesses an asymmetric spectrum distribution. Furthermore, spectrum analysis is performed on these different type rogue waves, and the spectrum relations between them are discussed. We demonstrate qualitatively that different modulation instability gain distribution can induce different rogue wave excitation patterns. These results would deepen our understanding of rogue wave dynamics in complex systems.

Perturbing Hele-Shaw flow with a small gap gradient

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, H.; Casademunt, J.; Yeung, C.

1992-02-15

A controlled perturbation is introduced into the Saffman-Taylor flow problem by adding a gradient to the gap of a Hele-Shaw cell. The stability of the single-finger steady state was found to be strongly affected by such a perturbation. Compared with patterns in a standard Hele-Shaw cell, the single Saffman-Taylor finger was stabilized or destabilized according to the sign of the gap gradient. While a linear stability analysis shows that this perturbation should have a negligible effect on the early-stage pattern formation, the experimental data indicate that the characteristic length for the initial breakup of a flat interface has been changedmore » by the perturbation.« less

Development and performance evaluation of an MR squeeze-mode damper

NASA Astrophysics Data System (ADS)

Sapiński, Bogdan; Gołdasz, Janusz

2015-11-01

In this paper the authors present results of a magnetorheological (MR) damper prototype development and performance evaluation study. The damper is a device functioning in the so-called squeeze-mode of MR fluid flow regime of operation. By principle, in a squeeze-mode damper the control (working) gap height varies according to the prescribed displacement or force input profile. Such hardware has been claimed to be well suited to small-amplitude vibration damping applications. However, it is still in its infancy. Its potential seems appealing yet unclear. Accordingly, the authors reveal performance figures of the damper complemented by numerical finite-element simulations of the electro-magnetic circuit of the device. The numerical results are presented in the form of maps of averaged magnetic flux density versus coil current and gap height as well as magnetic flux, inductance, and cogging force calculations, respectively. The simulated data are followed by experimental evaluation of the damper performance incorporating plots of force versus piston displacement (velocity) across a prescribed range of excitation inputs. Moreover, some insight into transient (unsteady) characteristics of the device is provided through testing results involving transient currents.

Whispering Gallery Mode Optomechanical Resonator

NASA Technical Reports Server (NTRS)

Aveline, David C.; Strekalov, Dmitry V.; Yu, Nan; Yee, Karl Y.

2012-01-01

Great progress has been made in both micromechanical resonators and micro-optical resonators over the past decade, and a new field has recently emerged combining these mechanical and optical systems. In such optomechanical systems, the two resonators are strongly coupled with one influencing the other, and their interaction can yield detectable optical signals that are highly sensitive to the mechanical motion. A particularly high-Q optical system is the whispering gallery mode (WGM) resonator, which has many applications ranging from stable oscillators to inertial sensor devices. There is, however, limited coupling between the optical mode and the resonator s external environment. In order to overcome this limitation, a novel type of optomechanical sensor has been developed, offering great potential for measurements of displacement, acceleration, and mass sensitivity. The proposed hybrid device combines the advantages of all-solid optical WGM resonators with high-quality micro-machined cantilevers. For direct access to the WGM inside the resonator, the idea is to radially cut precise gaps into the perimeter, fabricating a mechanical resonator within the WGM. Also, a strategy to reduce losses has been developed with optimized design of the cantilever geometry and positions of gap surfaces.

Surface plasmon resonance in electrodynamically coupled Au NPs monolayer/dielectric spacer/Al film nanostructure: tuning by variation of spacer thickness

NASA Astrophysics Data System (ADS)

Yeshchenko, Oleg A.; Kozachenko, Viktor V.; Liakhov, Yuriy F.; Tomchuk, Anastasiya V.; Haftel, Michael; Pinchuk, Anatoliy O.

2017-10-01

Effects of plasmonic coupling between metal nanoparticles and thin metal films separated by thin dielectric film-spacers have been studied by means of light extinction in three-layer planar Au NPs monolayer/dielectric (shellac) film/Al film nanostructure. The influence of coupling on the spectral characteristics of the Au NPs SPR extinction peak has been analyzed with spacer thickness, varied from 3 to 200 nm. The main observed features are a strong red shift (160 nm), and non-monotonical behavior of the magnitude and width of Au NPs SPR, as the spacer thickness decreased. The appearance of an intensive gap mode peak was observed at a spacer thickness smaller than approximately 30 nm, caused by the hybridization of the Au NPs SPR mode and gap mode in the presence of the Al film. Additionally, the appreciable enhancement (5.6 times) of light extinction by the Au NPs monolayer in the presence of Al film has been observed. A certain value of dielectric spacer thickness (70 nm) exists at which such enhancement is maximal.

Analysis of Unsteady Tip and Endwall Heat Transfer in a Highly Loaded Transonic Turbine Stage

NASA Technical Reports Server (NTRS)

Shyam, Vikram; Ameri, Ali; Chen, Jen-Ping

2010-01-01

In a previous study, vane-rotor shock interactions and heat transfer on the rotor blade of a highly loaded transonic turbine stage were simulated. The geometry consists of a high pressure turbine vane and downstream rotor blade. This study focuses on the physics of flow and heat transfer in the rotor tip, casing and hub regions. The simulation was performed using the Unsteady Reynolds-Averaged Navier-Stokes (URANS) code MSU-TURBO. A low Reynolds number k-epsilon model was utilized to model turbulence. The rotor blade in question has a tip gap height of 2.1 percent of the blade height. The Reynolds number of the flow is approximately 3x10(exp 6) per meter. Unsteadiness was observed at the tip surface that results in intermittent "hot spots". It is demonstrated that unsteadiness in the tip gap is governed by inviscid effects due to high speed flow and is not strongly dependent on pressure ratio across the tip gap contrary to published observations that have primarily dealt with subsonic tip flows. The high relative Mach numbers in the tip gap lead to a choking of the leakage flow that translates to a relative attenuation of losses at higher loading. The efficacy of new tip geometry is discussed to minimize heat flux at the tip while maintaining choked conditions. In addition, an explanation is provided that shows the mechanism behind the rise in stagnation temperature on the casing to values above the absolute total temperature at the inlet. It is concluded that even in steady mode, work transfer to the near tip fluid occurs due to relative shearing by the casing. This is believed to be the first such explanation of the work transfer phenomenon in the open literature. The difference in pattern between steady and time-averaged heat flux at the hub is also explained.

Microstrip Antenna Generates Circularly Polarized Beam

NASA Technical Reports Server (NTRS)

Huang, J.

1986-01-01

Circular microstrip antenna excited with higher order transverse magnetic (TM) modes generates circularly polarized, conical radiation patterns. Found both theoretically and experimentally that peak direction of radiation pattern is varied within wide angular range by combination of mode selection and loading substrate with materials of different dielectric constants.

Impact of the Nanoscale Gap Morphology on the Plasmon Coupling in Asymmetric Nanoparticle Dimer Antennas.

PubMed

Popp, Paul S; Herrmann, Janning F; Fritz, Eva-Corinna; Ravoo, Bart Jan; Höppener, Christiane

2016-03-23

Coupling of plasmon resonances in metallic gap antennas is of interest for a wide range of applications due to the highly localized strong electric fields supported by these structures, and their high sensitivity to alterations of their structure, geometry, and environment. Morphological alterations of asymmetric nanoparticle dimer antennas with (sub)-nanometer size gaps are assigned to changes of their optical response in correlative dark-field spectroscopy and high-resolution transmission electron microscopy (HR-TEM) investigations. This multimodal approach to investigate individual dimer structures clearly demonstrates that the coupling of the plasmon modes, in addition to well-known parameters such as the particle geometry and the gap size, is also affected by the relative alignment of both nanoparticles. The investigations corroborate that the alignment of the gap forming facets, and with that the gap area, is crucial for their scattering properties. The impact of a flat versus a rounded gap structure on the optical properties of equivalent dimers becomes stronger with decreasing gap size. These results hint at a higher confinement of the electric field in the gap and possibly a different onset of quantum transport effects for flat and rounded gap antennas in corresponding structures for very narrow gaps. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mixed Mode Fuel Injector And Injection System

DOEpatents

Stewart, Chris Lee; Tian, Ye; Wang, Lifeng; Shafer, Scott F.

2005-12-27

A fuel injector includes a homogenous charge nozzle outlet set and a conventional nozzle outlet set that are controlled respectively by first and second three way needle control valves. Each fuel injector includes first and second concentric needle valve members. One of the needle valve members moves to an open position for a homogenous charge injection event, while the other needle valve member moves to an open position for a conventional injection event. The fuel injector has the ability to operate in a homogenous charge mode with a homogenous charge spray pattern, a conventional mode with a conventional spray pattern or a mixed mode.

Cross-diffusion-induced subharmonic spatial resonances in a predator-prey system

NASA Astrophysics Data System (ADS)

Gambino, G.; Lombardo, M. C.; Sammartino, M.

2018-01-01

In this paper we investigate the complex dynamics originated by a cross-diffusion-induced subharmonic destabilization of the fundamental subcritical Turing mode in a predator-prey reaction-diffusion system. The model we consider consists of a two-species Lotka-Volterra system with linear diffusion and a nonlinear cross-diffusion term in the predator equation. The taxis term in the search strategy of the predator is responsible for the onset of complex dynamics. In fact, our model does not exhibit any Hopf or wave instability, and on the basis of the linear analysis one should only expect stationary patterns; nevertheless, the presence of the nonlinear cross-diffusion term is able to induce a secondary instability: due to a subharmonic spatial resonance, the stationary primary branch bifurcates to an out-of-phase oscillating solution. Noticeably, the strong resonance between the harmonic and the subharmonic is able to generate the oscillating pattern albeit the subharmonic is below criticality. We show that, as the control parameter is varied, the oscillating solution (sub T mode) can undergo a sequence of secondary instabilities, generating a transition toward chaotic dynamics. Finally, we investigate the emergence of sub T -mode solutions on two-dimensional domains: when the fundamental mode describes a square pattern, subharmonic resonance originates oscillating square patterns. In the case of subcritical Turing hexagon solutions, the internal interactions with a subharmonic mode are able to generate the so-called "twinkling-eyes" pattern.

Coupled-cavity drift-tube linac

DOEpatents

Billen, James H.

1996-01-01

A coupled-cavity drift-tube linac (CCDTL) combines features of the Alvarez drift-tube linac (DTL) and the .pi.-mode coupled-cavity linac (CCL). In one embodiment, each accelerating cavity is a two-cell, 0-mode DTL. The center-to-center distance between accelerating gaps is .beta..lambda., where .lambda. is the free-space wavelength of the resonant mode. Adjacent accelerating cavities have oppositely directed electric fields, alternating in phase by 180 degrees. The chain of cavities operates in a .pi./2 structure mode so the coupling cavities are nominally unexcited. The CCDTL configuration provides an rf structure with high shunt impedance for intermediate velocity charged particles, i.e., particles with energies in the 20-200 MeV range.

Coupled-cavity drift-tube linac

DOEpatents

Billen, J.H.

1996-11-26

A coupled-cavity drift-tube linac (CCDTL) combines features of the Alvarez drift-tube linac (DTL) and the {pi}-mode coupled-cavity linac (CCL). In one embodiment, each accelerating cavity is a two-cell, 0-mode DTL. The center-to-center distance between accelerating gaps is {beta}{lambda}, where {lambda} is the free-space wavelength of the resonant mode. Adjacent accelerating cavities have oppositely directed electric fields, alternating in phase by 180 degrees. The chain of cavities operates in a {pi}/2 structure mode so the coupling cavities are nominally unexcited. The CCDTL configuration provides an rf structure with high shunt impedance for intermediate velocity charged particles, i.e., particles with energies in the 20-200 MeV range. 5 figs.

Single mode to dual mode switch through a THz reconfigurable metamaterial

NASA Astrophysics Data System (ADS)

Zhang, Wu; Zhang, Meng; Yan, Zongkai; Zhao, Xin; Cheng, Jianping; Liu, Ai Qun

2017-12-01

Metamaterials interact with incident electromagnetic waves through their consisting subwavelength metamolecules. In this paper, we reported a reconfigurable metamaterial which tunes its THz response experimentally from a single mode resonance at 2.99 THz to a dual mode resonance at 2.94 THz and 2.99 THz. The reconfiguration is realized through a micromachined actuator, and the tunability is achieved by breaking the symmetry of the metamolecule. An abrupt change in the transmission is experimentally observed when the gap between two metallic structures is closed, and a decrease in transmission from 40% to 5% at 2.94 THz is obtained. Such a tunable metamaterial promises widespread applications in optical switches, filters, and THz detectors.

The use of breast ultrasound color Doppler vascular pattern morphology improves diagnostic sensitivity with minimal change in specificity.

PubMed

Svensson, W E; Pandian, A J; Hashimoto, H

2010-10-01

The aim of this study was to evaluate the use of vascular morphology, around and within the B-mode region of abnormality, for improving the diagnostic accuracy of two of the most common solid breast pathologies. The B-mode and Doppler images of 117 breast cancers and 366 fibroadenomas and lesions with a fibroadenoma-like appearance were reviewed retrospectively and the morphology of the vascular pattern was evaluated. The ratio of external to internal color Doppler, the external vascular pattern and the connecting vessels to internal vessels were assessed and differentiated into benign and malignant vascular patterns. These patterns were correlated with the histological diagnosis. Vascularity was demonstrated in 95 % of cancers and in 46 % of benign lesions with a trend to increasing vascularity in cancers. This provided poor specificity for excluding cancer in fibroadenomas. Variations in vascular pattern were recorded. The observed benign vascular patterns were avascularity, vascularity in the periphery and peripheral marginal vessels connecting with internal vascularity. The observed malignant vascular patterns were radially aligned external vessels with internal vessels being more numerous than external vessels which connected to radial vessels. (Fisher exact test p < 0.0001). Analysis of the vascular morphology improved the sensitivity for identifying cancers from 97 % (B-mode) to 99 % (B-mode and color Doppler) with a minimal reduction in specificity (93.7 to 92.6 %) or accuracy (94.6 to 94.2 %). The presence of vascularity within a lesion, by itself, is no longer a good predictor of malignancy because of the increase in Doppler sensitivity associated with improvements in ultrasound technology. The color Doppler ultrasound vascular pattern morphology improves the accuracy and sensitivity of B-mode image diagnosis, breast cancers and fibroadenomas with a minimal loss of specificity. Any breast lesion with radial rather than marginal connecting vessels should be regarded with suspicion. © Georg Thieme Verlag KG Stuttgart · New York.

Multi-mode energy management strategy for fuel cell electric vehicles based on driving pattern identification using learning vector quantization neural network algorithm

NASA Astrophysics Data System (ADS)

Song, Ke; Li, Feiqiang; Hu, Xiao; He, Lin; Niu, Wenxu; Lu, Sihao; Zhang, Tong

2018-06-01

The development of fuel cell electric vehicles can to a certain extent alleviate worldwide energy and environmental issues. While a single energy management strategy cannot meet the complex road conditions of an actual vehicle, this article proposes a multi-mode energy management strategy for electric vehicles with a fuel cell range extender based on driving condition recognition technology, which contains a patterns recognizer and a multi-mode energy management controller. This paper introduces a learning vector quantization (LVQ) neural network to design the driving patterns recognizer according to a vehicle's driving information. This multi-mode strategy can automatically switch to the genetic algorithm optimized thermostat strategy under specific driving conditions in the light of the differences in condition recognition results. Simulation experiments were carried out based on the model's validity verification using a dynamometer test bench. Simulation results show that the proposed strategy can obtain better economic performance than the single-mode thermostat strategy under dynamic driving conditions.

Turing patterns and a stochastic individual-based model for predator-prey systems

NASA Astrophysics Data System (ADS)

Nagano, Seido

2012-02-01

Reaction-diffusion theory has played a very important role in the study of pattern formations in biology. However, a group of individuals is described by a single state variable representing population density in reaction-diffusion models and interaction between individuals can be included only phenomenologically. Recently, we have seamlessly combined individual-based models with elements of reaction-diffusion theory. To include animal migration in the scheme, we have adopted a relationship between the diffusion and the random numbers generated according to a two-dimensional bivariate normal distribution. Thus, we have observed the transition of population patterns from an extinction mode, a stable mode, or an oscillatory mode to the chaotic mode as the population growth rate increases. We show our phase diagram of predator-prey systems and discuss the microscopic mechanism for the stable lattice formation in detail.

Major determinants of the biogeographic pattern of the shallow-sea fauna

NASA Technical Reports Server (NTRS)

Valentine, J. W.; Jablonski, D.

1982-01-01

The benthic shallow-sea is defined as the region of sea floor lying between the supralittoral zone at the shoreline and the impingement of the thermocline separating a warm shallow and variable portion of the water column from rather homogeneous and constant cooler waters beneath. Three types of shallow-sea provinces can be recognized: (1) one-dimensional, linear shelves; (2) two-dimensional shelves; and (3) scattered islands in two-dimensional arrays. Dispersal powers of marine invertebrates vary with developmental mode, and patterns of dispersal, endemism and speciation vary among the different provincial types. Invertebrate developmental modes vary systematically with geography, and presumably are adaptive to environmental conditions. Clades with only a single mode of development tend to be restricted to regions appropriate to that mode, significantly affecting their biogeographic patterns. The consequences of geographic and other environmental changes are reviewed.

Nonstandard convergence to jamming in random sequential adsorption: The case of patterned one-dimensional substrates

NASA Astrophysics Data System (ADS)

Verma, Arjun; Privman, Vladimir

2018-02-01

We study approach to the large-time jammed state of the deposited particles in the model of random sequential adsorption. The convergence laws are usually derived from the argument of Pomeau which includes the assumption of the dominance, at large enough times, of small landing regions into each of which only a single particle can be deposited without overlapping earlier deposited particles and which, after a certain time are no longer created by depositions in larger gaps. The second assumption has been that the size distribution of gaps open for particle-center landing in this large-time small-gaps regime is finite in the limit of zero gap size. We report numerical Monte Carlo studies of a recently introduced model of random sequential adsorption on patterned one-dimensional substrates that suggest that the second assumption must be generalized. We argue that a region exists in the parameter space of the studied model in which the gap-size distribution in the Pomeau large-time regime actually linearly vanishes at zero gap sizes. In another region, the distribution develops a threshold property, i.e., there are no small gaps below a certain gap size. We discuss the implications of these findings for new asymptotic power-law and exponential-modified-by-a-power-law convergences to jamming in irreversible one-dimensional deposition.

Acoustic beam steering by light refraction: illustration with directivity patterns of a tilted volume photoacoustic source.

PubMed

Raetz, Samuel; Dehoux, Thomas; Perton, Mathieu; Audoin, Bertrand

2013-12-01

The symmetry of a thermoelastic source resulting from laser absorption can be broken when the direction of light propagation in an elastic half-space is inclined relatively to the surface. This leads to an asymmetry of the directivity patterns of both compressional and shear acoustic waves. In contrast to classical surface acoustic sources, the tunable volume source allows one to take advantage of the mode conversion at the surface to control the directivity of specific modes. Physical interpretations of the evolution of the directivity patterns with the increasing light angle of incidence and of the relations between the preferential directions of compressional- and shear-wave emission are proposed. In order to compare calculated directivity patterns with measurements of normal displacement amplitudes performed on plates, a procedure is proposed to transform the directivity patterns into pseudo-directivity patterns representative of the experimental conditions. The comparison of the theoretical with measured pseudo-directivity patterns demonstrates the ability to enhance bulk-wave amplitudes and to steer specific bulk acoustic modes by adequately tuning light refraction.

Leakage Account for Radial Face Contact Seal in Aircraft Engine Support

NASA Astrophysics Data System (ADS)

Vinogradov, A. S.; Sergeeva, T. V.

2018-01-01

The article is dedicated to the development of a methodology for the radial face contact seal design taking into consideration the supporting elements deformations in different aircraft engine operating modes. Radial face contact seals are popular in the aircraft engines bearing support. However, there are no published leakage calculation methodologies of these seals. Radial face contact seal leakage is determined by the gap clearance in the carbon seal ring split. In turn, the size gap clearance depends on the deformation of the seal assembly parts and from the engine operation. The article shows the leakage detection sequence in the intershaft radial face contact seal of the compressor support for take-off and cruising modes. Evaluated calculated leakage values (2.4 g/s at takeoff and 0.75 g/s at cruising) go with experience in designing seals.

Topological phase in a two-dimensional metallic heavy-fermion system

NASA Astrophysics Data System (ADS)

Yoshida, Tsuneya; Peters, Robert; Fujimoto, Satoshi; Kawakami, Norio

2013-04-01

We report on a topological insulating state in a heavy-fermion system away from half filling, which is hidden within a ferromagnetic metallic phase. In this phase, the cooperation of the RKKY interaction and the Kondo effect, together with the spin-orbit coupling, induces a spin-selective gap, bringing about topologically nontrivial properties. This topological phase is robust against a change in the chemical potential in a much wider range than the gap size. We analyze these remarkable properties by using dynamical mean field theory and the numerical renormalization group. Its topological properties support a gapless chiral edge mode, which exhibits a non-Tomonaga-Luttinger liquid behavior due to the coupling with bulk ferromagnetic spin fluctuations. We also propose that the effects of the spin fluctuations on the edge mode can be detected via the NMR relaxation time measurement.

Emergence of fully gapped s++-wave and nodal d-wave states mediated by orbital and spin fluctuations in a ten-orbital model of KFe2Se2

NASA Astrophysics Data System (ADS)

Saito, Tetsuro; Onari, Seiichiro; Kontani, Hiroshi

2011-04-01

We study the superconducting state in recently discovered high-Tc superconductor KxFe2Se2 based on the ten-orbital Hubbard-Holstein model without hole pockets. When the Coulomb interaction is large, a spin-fluctuation-mediated d-wave state appears due to the nesting between electron pockets. Interestingly, the symmetry of the body-centered tetragonal structure in KxFe2Se2 requires the existence of nodes in the d-wave gap, although a fully gapped d-wave state is realized in the case of a simple tetragonal structure. In the presence of moderate electron-phonon interaction due to Fe-ion optical modes, however, orbital fluctuations give rise to the fully gapped s++-wave state without sign reversal. Therefore, both superconducting states are distinguishable by careful measurements of the gap structure or the impurity effect on Tc.

Dual-probe near-field fiber head with gap servo control for data storage applications.

PubMed

Fang, Jen-Yu; Tien, Chung-Hao; Shieh, Han-Ping D

2007-10-29

We present a novel fiber-based near-field optical head consisting of a straw-shaped writing probe and a flat gap sensing probe. The straw-shaped probe with a C-aperture on the end face exhibits enhanced transmission by a factor of 3 orders of magnitude over a conventional fiber probe due to a hybrid effect that excites both propagation modes and surface plasmon waves. In the gap sensing probe, the spacing between the probe and the disk surface functions as an external cavity. The high sensitivity of the output power to the change in the gap width is used as a feedback control signal. We characterize and design the straw-shaped writing probe and the flat gap sensing probe. The dual-probe system is installed on a conventional biaxial actuator to demonstrate the capability of flying over a disk surface with nanometer position precision.

Terahertz radiation-induced sub-cycle field electron emission across a split-gap dipole antenna

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jingdi; Averitt, Richard D., E-mail: xinz@bu.edu, E-mail: raveritt@ucsd.edu; Department of Physics, Boston University, Boston, Massachusetts 02215

We use intense terahertz pulses to excite the resonant mode (0.6 THz) of a micro-fabricated dipole antenna with a vacuum gap. The dipole antenna structure enhances the peak amplitude of the in-gap THz electric field by a factor of ∼170. Above an in-gap E-field threshold amplitude of ∼10 MV/cm{sup −1}, THz-induced field electron emission is observed as indicated by the field-induced electric current across the dipole antenna gap. Field emission occurs within a fraction of the driving THz period. Our analysis of the current (I) and incident electric field (E) is in agreement with a Millikan-Lauritsen analysis where log (I) exhibits amore » linear dependence on 1/E. Numerical estimates indicate that the electrons are accelerated to a value of approximately one tenth of the speed of light.« less

Mutual regulatory interactions of the trunk gap genes during blastoderm patterning in the hemipteran Oncopeltus fasciatus.

PubMed

Ben-David, Jonathan; Chipman, Ariel D

2010-10-01

The early embryo of the milkweed bug, Oncopeltus fasciatus, appears as a single cell layer - the embryonic blastoderm - covering the entire egg. It is at this blastoderm stage that morphological domains are first determined, long before the appearance of overt segmentation. Central to the process of patterning the blastoderm into distinct domains are a group of transcription factors known as gap genes. In Drosophila melanogaster these genes form a network of interactions, and maintain sharp expression boundaries through strong mutual repression. Their restricted expression domains define specific areas along the entire body. We have studied the expression domains of the four trunk gap gene homologues in O. fasciatus and have determined their interactions through dsRNA gene knockdown experiments, followed by expression analyses. While the blastoderm in O. fasciatus includes only the first six segments of the embryo, the expression domains of the gap genes within these segments are broadly similar to those in Drosophila where the blastoderm includes all 15 segments. However, the interactions between the gap genes are surprisingly different from those in Drosophila, and mutual repression between the genes seems to play a much less significant role. This suggests that the well-studied interaction pattern in Drosophila is evolutionarily derived, and has evolved from a less strongly interacting network. Copyright © 2010 Elsevier Inc. All rights reserved.

Role of the gut endoderm in relaying left-right patterning in mice.

PubMed

Viotti, Manuel; Niu, Lei; Shi, Song-Hai; Hadjantonakis, Anna-Katerina

2012-01-01

Establishment of left-right (LR) asymmetry occurs after gastrulation commences and utilizes a conserved cascade of events. In the mouse, LR symmetry is broken at a midline structure, the node, and involves signal relay to the lateral plate, where it results in asymmetric organ morphogenesis. How information transmits from the node to the distantly situated lateral plate remains unclear. Noting that embryos lacking Sox17 exhibit defects in both gut endoderm formation and LR patterning, we investigated a potential connection between these two processes. We observed an endoderm-specific absence of the critical gap junction component, Connexin43 (Cx43), in Sox17 mutants. Iontophoretic dye injection experiments revealed planar gap junction coupling across the gut endoderm in wild-type but not Sox17 mutant embryos. They also revealed uncoupling of left and right sides of the gut endoderm in an isolated domain of gap junction intercellular communication at the midline, which in principle could function as a barrier to communication between the left and right sides of the embryo. The role for gap junction communication in LR patterning was confirmed by pharmacological inhibition, which molecularly recapitulated the mutant phenotype. Collectively, our data demonstrate that Cx43-mediated communication across gap junctions within the gut endoderm serves as a mechanism for information relay between node and lateral plate in a process that is critical for the establishment of LR asymmetry in mice.

Three-dimensional whispering gallery modes in InGaAs nanoneedle lasers on silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tran, T.-T. D.; Chen, R.; Ng, K. W.

2014-09-15

As-grown InGaAs nanoneedle lasers, synthesized at complementary metal–oxide–semiconductor compatible temperatures on polycrystalline and crystalline silicon substrates, were studied in photoluminescence experiments. Radiation patterns of three-dimensional whispering gallery modes were observed upon optically pumping the needles above the lasing threshold. Using the radiation patterns as well as finite-difference-time-domain simulations and polarization measurements, all modal numbers of the three-dimensional whispering gallery modes could be identified.

Finite-size Scaling of the Density of States in Photonic Band Gap Crystals

NASA Astrophysics Data System (ADS)

Hasan, Shakeeb Bin; Mosk, Allard P.; Vos, Willem L.; Lagendijk, Ad

2018-06-01

The famous vanishing of the density of states (DOS) in a band gap, be it photonic or electronic, pertains to the infinite-crystal limit. In contrast, all experiments and device applications refer to finite crystals, which raises the question: Upon increasing the linear size L of a crystal, how fast does the DOS approach the infinite-crystal limit? We present a theory for finite crystals that includes Bloch-mode broadening due to the presence of crystal boundaries. Our results demonstrate that the DOS for frequencies inside a band gap has a 1 /L scale dependence for crystals in one, two and three dimensions.

Fabrication and characteristics of thin disc piezoelectric transformers based on piezoelectric buzzers with gap circles.

PubMed

Chang, Kuo-Tsai; Lee, Chun-Wei

2008-04-01

This paper investigates design, fabrication and test of thin disc piezoelectric transformers (PTs) based on piezoelectric buzzers with gap circles at different diameters of the gap circles. The performance test is focused on characteristics of voltage gains, including maximum voltage gains and maximum-gain frequencies, for each piezoelectric transformer under different load conditions. Both a piezoelectric buzzer and a gap circle on a silver electrode of the buzzer are needed to build any type of the PTs. Here, the gap circle is used to form a ring-shaped input electrode and a circle-shaped output electrode for each piezoelectric transformer. To do so, both structure and connection of a PT are first expressed. Then, operating principle of a PT and its related vibration mode observed by a carbon-power imaging technique are described. Moreover, an experimental setup for characterizing each piezoelectric transformer is constructed. Finally, effects of diameters of the gap circles on characteristics of voltage gains at different load resistances are discussed.

Aging and the 4-kHz Air-Bone Gap

ERIC Educational Resources Information Center

Nondahl, David M.; Tweed, Ted S.; Cruickshanks, Karen J.; Wiley, Terry L.; Dalton, Dayna S.

2012-01-01

Purpose: In this study, the authors assessed age- and sex-related patterns in the prevalence and 10-year incidence of 4-kHz air-bone gaps and associated factors. Method: Data were obtained as part of the longitudinal, population-based Epidemiology of Hearing Loss Study ( Cruickshanks et al., 1998). An air-bone gap at 4 kHz was defined as an…

Identifying gaps in conservation networks: of indicators and uncertainty in geographic-based analyses

Treesearch

Curtis H. Flather; Kenneth R. Wilson; Denis J. Dean; William C. McComb

1997-01-01

Mapping of biodiversity elements to expose gaps in. conservation networks has become a common strategy in nature-reserve design. We review a set of critical assumptions and issues that influence the interpretation and implementation of gap analysis, including: (1) the assumption that a subset of taxa can be used to indicate overall diversity patterns, and (2) the...

Progressive Seismic Failure, Seismic Gap, and Great Seismic Risk across the Densely Populated North China Basin

NASA Astrophysics Data System (ADS)

Yin, A.; Yu, X.; Shen, Z.

2014-12-01

Although the seismically active North China basin has the most complete written records of pre-instrumentation earthquakes in the world, this information has not been fully utilized for assessing potential earthquake hazards of this densely populated region that hosts ~200 million people. In this study, we use the historical records to document the earthquake migration pattern and the existence of a 180-km seismic gap along the 600-km long right-slip Tangshan-Hejian-Cixian (THC) fault zone that cuts across the North China basin. The newly recognized seismic gap, which is centered at Tianjin with a population of 11 million people and ~120 km from Beijing (22 million people) and Tangshan (7 million people), has not been ruptured in the past 1000 years by M≥6 earthquakes. The seismic migration pattern in the past millennium suggests that the epicenters of major earthquakes have shifted towards this seismic gap along the THC fault, which implies that the 180- km gap could be the site of the next great earthquake with M≈7.6 if it is ruptured by a single event. Alternatively, the seismic gap may be explained by aseismic creeping or seismic strain transfer between active faults.

Experimental verification of the capillary plasma triggered long spark gap under the extremely low working coefficient in air

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, D.; Yang, L. J., E-mail: yanglj@mail.xjtu.edu.cn; Ma, J. B.

The paper has proposed a new triggering method for long spark gap based on capillary plasma ejection and conducted the experimental verification under the extremely low working coefficient, which represents that the ratio of the spark gap charging voltage to the breakdown voltage is particularly low. The quasi-neutral plasma is ejected from the capillary and develops through the axial direction of the spark gap. The electric field in the spark gap is thus changed and its breakdown is incurred. It is proved by the experiments that the capillary plasma ejection is effective in triggering the long spark gap under themore » extremely low working coefficient in air. The study also indicates that the breakdown probabilities, the breakdown delay, and the delay dispersion are all mainly determined by the characteristics of the ejected plasma, including the length of the plasma flow, the speed of the plasma ejection, and the ionization degree of the plasma. Moreover, the breakdown delay and the delay dispersion increase with the length of the long spark gap, and the polarity effect exists in the triggering process. Lastly, compared with the working patterns of the triggering device installed in the single electrode, the working pattern of the devices installed in both the two electrodes, though with the same breakdown process, achieves the ignition under longer gap distance. To be specific, at the gap length of 14 cm and the working coefficient of less than 2%, the spark gap is still ignited accurately.« less

Particle-in-cell modeling of gas-confined barrier discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levko, Dmitry; Raja, Laxminarayan L.

2016-04-15

Gas-confined barrier discharge is studied using the one-dimensional Particle-in-Cell Monte Carlo Collisions model for the conditions reported by Guerra-Garcia and Martinez-Sanchez [Appl. Phys. Lett. 106, 041601 (2015)]. Depending on the applied voltage, two modes of discharge are observed. In the first mode, the discharge develops in the entire interelectrode gap. In the second mode, the discharge is ignited and develops only in the gas layer having smaller breakdown voltage. The one-dimensional model shows that for the conditions considered, there is no streamer stage of breakdown as is typical for a traditional dielectric barrier discharge.

Local symmetry breaking in SnO2 nanocrystals with cobalt doping and its effect on optical properties.

PubMed

Roy, S; Joshi, Amish G; Chatterjee, S; Ghosh, Anup K

2018-06-07

X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to study the structural and morphological characteristics of cobalt doped tin(iv) oxide (Sn1-xCoxO2; 0 ≤ x ≤ 0.04) nanocrystals synthesized by a chemical co-precipitation technique. Electronic structure analysis using X-ray photoemission spectroscopy (XPS) shows the formation of tin interstitials (Sni) and reduction of oxygen vacancies (VO) in the host lattice on Co doping and that the doped Co exists in mixed valence states of +2 and +3. Using XRD, the preferential position of the Sni and doped Co in the unit cell of the nanocrystals have been estimated. Rietveld refinement of XRD data shows that samples are of single phase and variation of lattice constants follows Vegard's law. XRD and TEM measurements show that the crystallite size of the nanocrystals decrease with increase in Co doping concentration. SAED patterns confirm the monocrystalline nature of the samples. The study of the lattice dynamics using Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy shows the existence of many disorder activated forbidden optical phonon modes, along with the corresponding classical modes, signifying Co induced local symmetry breaking in the nanocrystals. UV-Vis spectroscopy shows that the optical band gap has red shifted with increase in doping concentration. The study of Urbach energy confirms the increase in disorder in the nanocrystals with Co doping. Local symmetry breaking induced UV emission along with violet, blue and green luminescence has been observed from the PL study. The spectral contribution of UV emission decreases and green luminescence increases with increase in doping. Using PL, in conjunction with Raman spectroscopy, the type of oxygen vacancy induced in the nanocrystals on Co doping has been confirmed and the position of the defect levels in the forbidden zone (w.r.t. the optical band gap) has been studied.

Tunable graded rod laser assembly

NASA Technical Reports Server (NTRS)

AuYeung, John C. (Inventor)

1985-01-01

A tunable laser assembly including a pair of radially graded indexed optical segments aligned to focus the laser to form an external resonant cavity with an optical axis, the respective optical segments are retativity moveable along the optical axis and provide a variable et aion gap sufficient to permit variable tuning of the laser wavelength without altering the effective length of the resonant cavity. The gap also include a saturable absorbing material providing a passive mode-locking of the laser.

Ab initio study of structural, elastic, and vibrational properties of transition-metal disilicides NbSi2 and TaSi2 in hexagonal C40 structure

NASA Astrophysics Data System (ADS)

Ertürk, Esra; Gürel, Tanju

2018-05-01

We present an ab initio study of structural, elastic and vibrational properties of transition-metal disilicides NbSi2 and TaSi2. The calculations have been carried out within the density-functional theory and linear-response formalism using norm-conserving pseudopotentials and a plane-wave basis. The calculated lattice parameters, bulk moduli, and elastic constants agree well with previous theoretical and experimental results. The calculated phonon frequencies at the Brillouin zone center are in good agreement with the reported Raman spectra and provide reference values for the future infrared and neutron phonon measurements. Phonon dispersion relations, mode Grüneisen parameters, and total and partial phonon density of states are also discussed. Mode Grüneisen parameters of NbSi2 and TaSi2 at Brillouin zone center show similar trends and all values are found to be positive. From phonon dispersion relations and phonon density of states, we have found a gap around 200 cm-1 for TaSi2, where the frequencies below this gap mainly belong to Ta vibrations and frequencies above the gap is mainly related with Si vibrations. In the case of NbSi2, there is no such gap and both Nb and Si atoms contribute to the phonon density of states in an energy range of 150-270 cm-1.

Spatial arrangement of faults and opening-mode fractures

NASA Astrophysics Data System (ADS)

Laubach, S. E.; Lamarche, J.; Gauthier, B. D. M.; Dunne, W. M.; Sanderson, David J.

2018-03-01

Spatial arrangement is a fundamental characteristic of fracture arrays. The pattern of fault and opening-mode fracture positions in space defines structural heterogeneity and anisotropy in a rock volume, governs how faults and fractures affect fluid flow, and impacts our understanding of the initiation, propagation and interactions during the formation of fracture patterns. This special issue highlights recent progress with respect to characterizing and understanding the spatial arrangements of fault and fracture patterns, providing examples over a wide range of scales and structural settings. Five papers describe new methods and improvements of existing techniques to quantify spatial arrangement. One study unravels the time evolution of opening-mode fracture spatial arrangement, which are data needed to compare natural patterns with progressive fracture growth in kinematic and mechanical models. Three papers investigate the role of evolving diagenesis in localizing fractures by mechanical stratigraphy and nine discuss opening-mode fracture spatial arrangement. Two papers show the relevance of complex cluster patterns to unconventional reservoirs through examples of fractures in tight gas sandstone horizontal wells, and a study of fracture arrangement in shale. Four papers demonstrate the roles of folds in fracture localization and the development spatial patterns. One paper models along-fault friction and fluid pressure and their effects on fault-related fracture arrangement. Contributions address deformation band patterns in carbonate rocks and fault size and arrangement above a detachment fault. Three papers describe fault and fracture arrangements in basement terrains, and three document fracture patterns in shale. This collection of papers points toward improvement in field methods, continuing improvements in computer-based data analysis and creation of synthetic fracture patterns, and opportunities for further understanding fault and fracture attributes in the subsurface through coupled spatial, size, and pattern analysis.

Superconductivity and fluctuations in Ba 1–pK pFe 2As 2 and Ba(Fe 1–nCo n) 2As 2

DOE PAGES

Böhm, T.; Hosseinian Ahangharnejhad, R.; Jost, D.; ...

2016-08-11

In this paper, we study the interplay of fluctuations and superconductivity in BaFe 2As 2 (Ba-122) compounds with Ba and Fe substituted by K (p doping) and Co (n doping), respectively. To this end, we measured electronic Raman spectra as a function of polarization and temperature. We observe gap excitations and fluctuations for all doping levels studied. The response from fluctuations is much stronger for Co substitution and, according to the selection rules and the temperature dependence, originates from the exchange of two critical spin fluctuations with characteristic wave vectors (±π,0) and (0,±π). At 22% K doping (p = 0.22),more » we find the same selection rules and spectral shape for the fluctuations but the intensity is smaller by a factor of 5. Since there exists no nematic region above the orthorhombic spin-density-wave (SDW) phase, the identification of the fluctuations via the temperature dependence is not possible. The gap excitations in the superconducting state indicate strongly anisotropic near-nodal gaps for Co substitution which make the observation of collective modes difficult. The variation with doping of the spectral weights of the A 1g and B 1g gap features does not support the influence of fluctuations on Cooper pairing. Thus, the observation of Bardasis–Schrieffer modes inside the nearly clean gaps on the K-doped side remains the only experimental evidence for the relevance of fluctuations for pairing.« less

Spatial mode discriminator based on leaky waveguides

NASA Astrophysics Data System (ADS)

Xu, Jing; Liu, Jialing; Shi, Hongkang; Chen, Yuntian

2018-06-01

We propose a conceptually simple and experimentally compatible configuration to discriminate the spatial mode based on leaky waveguides, which are inserted in-between the transmission link. The essence of such a spatial mode discriminator is to introduce the leakage of the power flux on purpose for detection. Importantly, the leaky angle of each individual spatial mode with respect to the propagation direction are different for non-degenerated modes, while the radiation patterns of the degenerated spatial modes in the plane perpendicular to the propagation direction are also distinguishable. Based on these two facts, we illustrate the operation principle of the spatial mode discriminators via two concrete examples; a w-type slab leaky waveguide without degeneracy, and a cylindrical leaky waveguide with degeneracy. The correlation between the leakage angle and the spatial mode distribution for a slab leaky waveguide, as well as differences between the in-plane radiation patterns of degenerated modes in a cylindrical leaky waveguide, are verified numerically and analytically. Such findings can be readily useful in discriminating the spatial modes for optical communication or optical sensing.

SU-E-T-430: Modeling MLC Leaf End in 2D for Sliding Window IMRT and Arc Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, X; Zhu, T

2014-06-01

Purpose: To develop a 2D geometric model for MLC accounting for leaf end dose leakage for dynamic IMRT and Rapidarc therapy. Methods: Leaf-end dose leakage is one of the problems for MLC dose calculation and modeling. Dosimetric leaf gap used to model the MLC and to count for leakage in dose calculation, but may not be accurate for smaller leaf gaps. We propose another geometric modeling method to compensate for the MLC round-shape leaf ends dose leakage, and improve the accuracy of dose calculation and dose verification. A triangular function is used to geometrically model the MLC leaf end leakagemore » in the leaf motion direction, and a step function is used in the perpendicular direction. Dose measurements with different leaf gap, different window width, and different window height were conducted, and the results were used to fit the analytical model to get the model parameters. Results: Analytical models have been obtained for stop-and-shoot and dynamic modes for MLC motion. Parameters a=0.4, lw'=5.0 mm for 6X and a=0.54, lw'=4.1 mm for 15x were obtained from the fitting process. The proposed MLC leaf end model improves the dose profile at the two ends of the sliding window opening. This improvement is especially significant for smaller sliding window openings, which are commonly used for highly modulated IMRT plans and arc therapy plans. Conclusion: This work models the MLC round leaf end shape and movement pattern for IMRT dose calculation. The theory, as well as the results in this work provides a useful tool for photon beam IMRT dose calculation and verification.« less

Structural analyses of Legionella LepB reveal a new GAP fold that catalytically mimics eukaryotic RasGAP.

PubMed

Yu, Qin; Hu, Liyan; Yao, Qing; Zhu, Yongqun; Dong, Na; Wang, Da-Cheng; Shao, Feng

2013-06-01

Rab GTPases are emerging targets of diverse bacterial pathogens. Here, we perform biochemical and structural analyses of LepB, a Rab GTPase-activating protein (GAP) effector from Legionella pneumophila. We map LepB GAP domain to residues 313-618 and show that the GAP domain is Rab1 specific with a catalytic activity higher than the canonical eukaryotic TBC GAP and the newly identified VirA/EspG family of bacterial RabGAP effectors. Exhaustive mutation analyses identify Arg444 as the arginine finger, but no catalytically essential glutamine residues. Crystal structures of LepB313-618 alone and the GAP domain of Legionella drancourtii LepB in complex with Rab1-GDP-AlF3 support the catalytic role of Arg444, and also further reveal a 3D architecture and a GTPase-binding mode distinct from all known GAPs. Glu449, structurally equivalent to TBC RabGAP glutamine finger in apo-LepB, undergoes a drastic movement upon Rab1 binding, which induces Rab1 Gln70 side-chain flipping towards GDP-AlF3 through a strong ionic interaction. This conformationally rearranged Gln70 acts as the catalytic cis-glutamine, therefore uncovering an unexpected RasGAP-like catalytic mechanism for LepB. Our studies highlight an extraordinary structural and catalytic diversity of RabGAPs, particularly those from bacterial pathogens.

Gene Circuit Analysis of the Terminal Gap Gene huckebein

PubMed Central

Ashyraliyev, Maksat; Siggens, Ken; Janssens, Hilde; Blom, Joke; Akam, Michael; Jaeger, Johannes

2009-01-01

The early embryo of Drosophila melanogaster provides a powerful model system to study the role of genes in pattern formation. The gap gene network constitutes the first zygotic regulatory tier in the hierarchy of the segmentation genes involved in specifying the position of body segments. Here, we use an integrative, systems-level approach to investigate the regulatory effect of the terminal gap gene huckebein (hkb) on gap gene expression. We present quantitative expression data for the Hkb protein, which enable us to include hkb in gap gene circuit models. Gap gene circuits are mathematical models of gene networks used as computational tools to extract regulatory information from spatial expression data. This is achieved by fitting the model to gap gene expression patterns, in order to obtain estimates for regulatory parameters which predict a specific network topology. We show how considering variability in the data combined with analysis of parameter determinability significantly improves the biological relevance and consistency of the approach. Our models are in agreement with earlier results, which they extend in two important respects: First, we show that Hkb is involved in the regulation of the posterior hunchback (hb) domain, but does not have any other essential function. Specifically, Hkb is required for the anterior shift in the posterior border of this domain, which is now reproduced correctly in our models. Second, gap gene circuits presented here are able to reproduce mutants of terminal gap genes, while previously published models were unable to reproduce any null mutants correctly. As a consequence, our models now capture the expression dynamics of all posterior gap genes and some variational properties of the system correctly. This is an important step towards a better, quantitative understanding of the developmental and evolutionary dynamics of the gap gene network. PMID:19876378

Gene circuit analysis of the terminal gap gene huckebein.

PubMed

Ashyraliyev, Maksat; Siggens, Ken; Janssens, Hilde; Blom, Joke; Akam, Michael; Jaeger, Johannes

2009-10-01

The early embryo of Drosophila melanogaster provides a powerful model system to study the role of genes in pattern formation. The gap gene network constitutes the first zygotic regulatory tier in the hierarchy of the segmentation genes involved in specifying the position of body segments. Here, we use an integrative, systems-level approach to investigate the regulatory effect of the terminal gap gene huckebein (hkb) on gap gene expression. We present quantitative expression data for the Hkb protein, which enable us to include hkb in gap gene circuit models. Gap gene circuits are mathematical models of gene networks used as computational tools to extract regulatory information from spatial expression data. This is achieved by fitting the model to gap gene expression patterns, in order to obtain estimates for regulatory parameters which predict a specific network topology. We show how considering variability in the data combined with analysis of parameter determinability significantly improves the biological relevance and consistency of the approach. Our models are in agreement with earlier results, which they extend in two important respects: First, we show that Hkb is involved in the regulation of the posterior hunchback (hb) domain, but does not have any other essential function. Specifically, Hkb is required for the anterior shift in the posterior border of this domain, which is now reproduced correctly in our models. Second, gap gene circuits presented here are able to reproduce mutants of terminal gap genes, while previously published models were unable to reproduce any null mutants correctly. As a consequence, our models now capture the expression dynamics of all posterior gap genes and some variational properties of the system correctly. This is an important step towards a better, quantitative understanding of the developmental and evolutionary dynamics of the gap gene network.

The characteristic analysis of Korean August rainfall using Self-Organizing Maps

NASA Astrophysics Data System (ADS)

Lee, S. H.; Seo, K. H.; Kim, J.

2016-12-01

The characteristics of the low-level pressure pattern during Korean August rainfall have been investigated using a neural network-based cluster analysis called self-organizing map (SOM). On the basis of various SOM mode analyses, five major phases of low-level pressure pattern are dynamically identified. The first mode occurs with a distinct circulation state corresponding to a strengthened subtropical high to the south of Korea and migratory low passing though north of Korea. The cold, dry inflow from the north by the cyclonic anomaly and warm, moist air produced by the WNPSH demonstrate the convective instability that provides reasonably intense precipitation over the Korean Peninsula. The second mode represents that low-level anticyclonic anomaly is located to the south of Korea and low-level anticyclonic anomaly is located over the Sea of Okhotsk. The two high pressure pattern conflict with each other forming front, which is identified as the frontal precipitation. The third mode represents local instability with no specific large-scale environmental condition; weak low-level jets, weak upper-level jets, no front, and no typhoon. The fourth mode is typhoon near Taiwan suppling a lot of water vapor in the Korean peninsula to be unloaded precipitation. This can be represented as an indirect-typhoon mode. The fifth mode can be classified as direct-typhoon mode, which typhoon passes though the Korea.

Secular instabilities of Keplerian stellar discs

NASA Astrophysics Data System (ADS)

Kaur, Karamveer; Kazandjian, Mher V.; Sridhar, S.; Touma, Jihad R.

2018-05-01

We present idealized models of a razor-thin, axisymmetric, Keplerian stellar disc around a massive black hole, and study non-axisymmetric secular instabilities in the absence of either counter-rotation or loss cones. These discs are prograde mono-energetic waterbags, whose phase-space distribution functions are constant for orbits within a range of eccentricities (e) and zero outside this range. The linear normal modes of waterbags are composed of sinusoidal disturbances of the edges of distribution function in phase space. Waterbags that include circular orbits (polarcaps) have one stable linear normal mode for each azimuthal wavenumber m. The m = 1 mode always has positive pattern speed and, for polarcaps consisting of orbits with e < 0.9428, only the m = 1 mode has positive pattern speed. Waterbags excluding circular orbits (bands) have two linear normal modes for each m, which can be stable or unstable. We derive analytical expressions for the instability condition, pattern speeds, growth rates, and normal mode structure. Narrow bands are unstable to modes with a wide range in m. Numerical simulations confirm linear theory and follow the non-linear evolution of instabilities. Long-time integration suggests that instabilities of different m grow, interact non-linearly, and relax collisionlessly to a coarse-grained equilibrium with a wide range of eccentricities.

Space-variant polarization patterns of non-collinear Poincaré superpositions

NASA Astrophysics Data System (ADS)

Galvez, E. J.; Beach, K.; Zeosky, J. J.; Khajavi, B.

2015-03-01

We present analysis and measurements of the polarization patterns produced by non-collinear superpositions of Laguerre-Gauss spatial modes in orthogonal polarization states, which are known as Poincaré modes. Our findings agree with predictions (I. Freund Opt. Lett. 35, 148-150 (2010)), that superpositions containing a C-point lead to a rotation of the polarization ellipse in 3-dimensions. Here we do imaging polarimetry of superpositions of first- and zero-order spatial modes at relative beam angles of 0-4 arcmin. We find Poincaré-type polarization patterns showing fringes in polarization orientation, but which preserve the polarization-singularity index for all three cases of C-points: lemons, stars and monstars.

Evaluation and Analysis of SEASAT-A Scanning Multichannel Microwave Radiometer (SSMR) Antenna Pattern Correction (APC) Algorithm. Sub-task 4: Interim Mode T Sub B Versus Cross and Nominal Mode T Sub B

NASA Technical Reports Server (NTRS)

Kitzis, J. L.; Kitzis, S. N.

1979-01-01

The brightness temperature data produced by the SMMR Antenna Pattern Correction algorithm are evaluated. The evaluation consists of: (1) a direct comparison of the outputs of the interim, cross, and nominal APC modes; (2) a refinement of the previously determined cos beta estimates; and (3) a comparison of the world brightness temperature (T sub B) map with actual SMMR measurements.

Playing in parallel: the effects of multiplayer modes in active video game on motivation and physical exertion.

PubMed

Peng, Wei; Crouse, Julia

2013-06-01

Although multiplayer modes are common among contemporary video games, the bulk of game research focuses on the single-player mode. To fill the gap in the literature, the current study investigated the effects of different multiplayer modes on enjoyment, future play motivation, and the actual physical activity intensity in an active video game. One hundred sixty-two participants participated in a one-factor between-subject laboratory experiment with three conditions: (a) single player: play against self pretest score; (b) cooperation with another player in the same physical space; (c) parallel competition with another player in separated physical spaces. We found that parallel competition in separate physical spaces was the optimal mode, since it resulted in both high enjoyment and future play motivation and high physical intensity. Implications for future research on multiplayer mode and play space as well as active video game-based physical activity interventions are discussed.

Direct observation of the Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point

NASA Astrophysics Data System (ADS)

Hong, Tao; Matsumoto, M.; Qiu, Y.; Chen, W. C.; Gentile, T. R.; Watson, S.; Awwadi, F. F.; Turnbull, M. M.; Dissanayake, S. E.; Agrawal, H.; Toft-Petersen, R.; Klemke, B.; Coester, K.; Schmidt, K. P.; Tennant, D. A.

The emergence of low-energy excitations in the spontaneous symmetry-breaking quantum phase transitions can be characterized by fluctuations of phase and amplitude of the order parameter. The phase oscillations correspond to the massless Nambu-Goldstone (or transverse) modes whereas the massive amplitude (or longitudinal) mode, analogous to the Higgs boson in particle physics, is prone to decay into a pair of low-energy Nambu-Goldstone modes in low dimensions, which makes it experimentally difficult to detect Here, using inelastic neutron scattering and applying the bondoperator theory, we directly and unambiguously identify the Higgs amplitude mode in a two dimensional S = 1/2 quantum antiferromagnet C9H18N2CuBr4 near a quantum critical point in two dimensions. Owing to an anisotropic energy gap of the transverse spin excitation, it kinematically prevents such decay and the Higgs amplitude mode acquires an infinite life time.

Modeling carbachol-induced hippocampal network synchronization using hidden Markov models

NASA Astrophysics Data System (ADS)

Dragomir, Andrei; Akay, Yasemin M.; Akay, Metin

2010-10-01

In this work we studied the neural state transitions undergone by the hippocampal neural network using a hidden Markov model (HMM) framework. We first employed a measure based on the Lempel-Ziv (LZ) estimator to characterize the changes in the hippocampal oscillation patterns in terms of their complexity. These oscillations correspond to different modes of hippocampal network synchronization induced by the cholinergic agonist carbachol in the CA1 region of mice hippocampus. HMMs are then used to model the dynamics of the LZ-derived complexity signals as first-order Markov chains. Consequently, the signals corresponding to our oscillation recordings can be segmented into a sequence of statistically discriminated hidden states. The segmentation is used for detecting transitions in neural synchronization modes in data recorded from wild-type and triple transgenic mice models (3xTG) of Alzheimer's disease (AD). Our data suggest that transition from low-frequency (delta range) continuous oscillation mode into high-frequency (theta range) oscillation, exhibiting repeated burst-type patterns, occurs always through a mode resembling a mixture of the two patterns, continuous with burst. The relatively random patterns of oscillation during this mode may reflect the fact that the neuronal network undergoes re-organization. Further insight into the time durations of these modes (retrieved via the HMM segmentation of the LZ-derived signals) reveals that the mixed mode lasts significantly longer (p < 10-4) in 3xTG AD mice. These findings, coupled with the documented cholinergic neurotransmission deficits in the 3xTG mice model, may be highly relevant for the case of AD.

IMF B(y) and day-night conductivity effects in the expanding polar cap convection model

NASA Technical Reports Server (NTRS)

Moses, J. J.; Gorney, D. J.; Siscoe, G. L.; Crooker, N. U.

1987-01-01

During southward B(z) periods the open field line region in the ionosphere (polar cap) expands due to increased dayside merging. Ionospheric plasma flow patterns result which can be classified by the sign of the interplanetary magnetic field (IMF) B(y) component. In this paper, a time-dependent ionospheric convection model is constructed to simulate these flows. The model consists of a spiral boundary with a gap in it. The sign of the IMF B(y) component determines the geometry of the gap. A potential is applied across the gap and distributed around the boundary. A flow results which enters the polar cap through the gap and uniformly pushes the boundary outward. Results of the model show that B(y) effects are greatest near the gap and virtually unnoticeable on the nightside of the polar cap. Adding a day-night ionospheric conductivity gradient concentrates the polar cap electric field toward dawn. The resulting flow curvature gives a sunward component that is independent of B(y). These patterns are shown to be consistent with published observations.

Low-frequency ultrasonic Bessel-like collimated beam generation from radial modes of piezoelectric transducers

DOE PAGES

Chillara, Vamshi Krishna; Pantea, Cristian; Sinha, Dipen N.

2017-02-06

We present a very simple approach to generate a collimated ultrasonic beam that exploits the natural Bessel-like vibration pattern of the radial modes of a piezoelectric disc with lateral clamping. This eliminates the need for the conventional annular Bessel pattern of the electrodes with individual electrode excitation on the piezo-disc, thus simplifying the transducer design. Numerical and experimental studies are carried out to investigate the Bessel-like vibration patterns of these radial modes showing an excellent agreement between these two studies. Measured ultrasonic beam- pro les in water from the radial modes con rm the profile to be a Bessel beam.more » Collimated beam generation from radial modes is investigated using a coupled electromechanical finite-element model. It is found that clamping the lateral edges of piezoelectric transducers results in a high-degree of collimation with practically no side-lobes similar to a parametric array beam. Ultrasonic beam- profile measurements in water with both free and clamped piezoelectric transducer are presented. The collimated beam generation using the present technique of using the laterally clamped radial modes finds significant applications in low-frequency imaging through highly attenuating materials.« less

Low-frequency ultrasonic Bessel-like collimated beam generation from radial modes of piezoelectric transducers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chillara, Vamshi Krishna; Pantea, Cristian; Sinha, Dipen N.

We present a very simple approach to generate a collimated ultrasonic beam that exploits the natural Bessel-like vibration pattern of the radial modes of a piezoelectric disc with lateral clamping. This eliminates the need for the conventional annular Bessel pattern of the electrodes with individual electrode excitation on the piezo-disc, thus simplifying the transducer design. Numerical and experimental studies are carried out to investigate the Bessel-like vibration patterns of these radial modes showing an excellent agreement between these two studies. Measured ultrasonic beam- pro les in water from the radial modes con rm the profile to be a Bessel beam.more » Collimated beam generation from radial modes is investigated using a coupled electromechanical finite-element model. It is found that clamping the lateral edges of piezoelectric transducers results in a high-degree of collimation with practically no side-lobes similar to a parametric array beam. Ultrasonic beam- profile measurements in water with both free and clamped piezoelectric transducer are presented. The collimated beam generation using the present technique of using the laterally clamped radial modes finds significant applications in low-frequency imaging through highly attenuating materials.« less

Experimental Influence Coefficients and Vibration Modes

NASA Technical Reports Server (NTRS)

Weidman, Deene J.; Kordes, Eldon E.

1959-01-01

Test results are presented for both symmetrical and antisymmetrical static loading of a wing model mounted on a three-point support system. The first six free-free vibration modes were determined experimentally. A comparison is made of the symmetrical nodal patterns and frequencies with the symmetrical nodal patterns and frequencies calculated from the experimental influence coefficients.

Bio rapid prototyping by extruding/aspirating/refilling thermoreversible hydrogel.

PubMed

Iwami, K; Noda, T; Ishida, K; Morishima, K; Nakamura, M; Umeda, N

2010-03-01

This paper reports a method for rapid prototyping of cell tissues, which is based on a system that extrudes, aspirates and refills a mixture of cells and thermoreversible hydrogel as a scaffold. In the extruding mode, a cell-mixed scaffold solution in the sol state is extruded from a cooled micronozzle into a temperature-controlled substrate, which keeps the scaffold in the gel state. In the aspiration mode, the opposite process is performed by Bernoulli suction. In the refilling mode, the solution is extruded into a groove created in the aspiration mode. The minimum width of extruded hydrogel pattern is 114 +/- 15 microm by employing a nozzle of diameter 100 microm, and that of aspirated groove was 355 +/- 10 microm using a 500 microm-diameter nozzle. Gum arabic is mixed with the scaffold solution to avoid peeling-off of the gel pattern from the substrate. Patterning of Sf-9 cell tissue is demonstrated, and the stability of the patterned cell is investigated. This system offers a procedure for rapid prototyping and local modification of cell scaffolds for tissue engineering.

Analysis of strand transfer and template switching mechanisms of DNA gap repair by homologous recombination in Escherichia coli: predominance of strand transfer.

PubMed

Izhar, Lior; Goldsmith, Moshe; Dahan, Ronny; Geacintov, Nicholas; Lloyd, Robert G; Livneh, Zvi

2008-09-12

Daughter strand gaps formed upon interruption of replication at DNA lesions in Escherichia coli can be repaired by either translesion DNA synthesis or homologous recombination (HR) repair. Using a plasmid-based assay system that enables discrimination between strand transfer and template switching (information copying) modes of HR gap repair, we found that approximately 80% of strand gaps were repaired by physical strand transfer from the donor, whereas approximately 20% appear to be repaired by template switching. HR gap repair operated on both small and bulky lesions and largely depended on RecA and RecF but not on the RecBCD nuclease. In addition, we found that HR was mildly reduced in cells lacking the RuvABC and RecG proteins involved in resolution of Holliday junctions. These results, obtained for the first time under conditions that detect the two HR gap repair mechanisms, provide in vivo high-resolution molecular evidence for the predominance of the strand transfer mechanism in HR gap repair. A small but significant portion of HR gap repair appears to occur via a template switching mechanism.

Quantum self-organization and nuclear collectivities

NASA Astrophysics Data System (ADS)

Otsuka, T.; Tsunoda, Y.; Togashi, T.; Shimizu, N.; Abe, T.

2018-02-01

The quantum self-organization is introduced as one of the major underlying mechanisms of the quantum many-body systems. In the case of atomic nuclei as an example, two types of the motion of nucleons, single-particle states and collective modes, dominate the structure of the nucleus. The outcome of the collective mode is determined basically by the balance between the effect of the mode-driving force (e.g., quadrupole force for the ellipsoidal deformation) and the resistance power against it. The single-particle energies are one of the sources to produce such resistance power: a coherent collective motion is more hindered by larger gaps between relevant single particle states. Thus, the single-particle state and the collective mode are “enemies” each other. However, the nuclear forces are demonstrated to be rich enough so as to enhance relevant collective mode by reducing the resistance power by changing singleparticle energies for each eigenstate through monopole interactions. This will be verified with the concrete example taken from Zr isotopes. Thus, when the quantum self-organization occurs, single-particle energies can be self-organized, being enhanced by (i) two quantum liquids, e.g., protons and neutrons, (ii) two major force components, e.g., quadrupole interaction (to drive collective mode) and monopole interaction (to control resistance). In other words, atomic nuclei are not necessarily like simple rigid vases containing almost free nucleons, in contrast to the naïve Fermi liquid picture. Type II shell evolution is considered to be a simple visible case involving excitations across a (sub)magic gap. The quantum self-organization becomes more important in heavier nuclei where the number of active orbits and the number of active nucleons are larger. The quantum self-organization is a general phenomenon, and is expected to be found in other quantum systems.

Effect of survey mode on response patterns: comparison of face-to-face and self-administered modes in health surveys.

PubMed

Christensen, Anne Illemann; Ekholm, Ola; Glümer, Charlotte; Juel, Knud

2014-04-01

While face-to-face interviews are considered the gold standard of survey modes, self-administered questionnaires are often preferred for cost and convenience. This article examines response patterns in two general population health surveys carried out by face-to-face interview and self-administered questionnaire, respectively. Data derives from a health interview survey in the Region of Southern Denmark (face-to-face interview) and The Danish Health and Morbidity Survey 2010 (self-administered questionnaire). Identical questions were used in both surveys. Data on all individuals were obtained from administrative registers and linked to survey data at individual level. Multiple logistic regression analyses were used to examine the effect of survey mode on response patterns. The non-response rate was higher in the self-administered survey (37.9%) than in the face-to-face interview survey (23.7%). Marital status, ethnic background and highest completed education were associated with non-response in both modes. Furthermore, sex and age were associated with non-response in the self-administered mode. No significant mode effects were observed for indicators related to use of health services, but significant mode effects were observed for indicators related to self-reported health-related quality of life, health behaviour, social relations and morbidity (long-standing illness). The same factors were generally associated with non-response in both modes. Indicators based on factual questions with simple answers categories were overall more comparable according to mode than indicators based on questions that involved more subjective assessments. Other measures such as efficiency and cost-effectiveness of the mode should also be considered when determining the most appropriate form of data collection.

Anomalous phonon behavior in superconducting CaKFe 4 As 4 : An optical study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Run; Dai, Yaomin; Xu, Bing

Here, the temperature dependence of ab-plane optical conductivity of CaKFe 4As 4 has been measured below and above its superconducting transition temperature T c≃35.5 K. In the normal state, analysis with the two-Drude model reveals a T-linear scattering rate for the coherent response, which suggests strong spin-fluctuation scattering. Below the superconducting transition, the optical conductivity below 120 cm –1 vanishes, indicating nodeless gap(s). The Mattis-Bardeen fitting in the superconducting state gives two gaps of Δ 1 ≃ 9 meV and Δ 2 ≃ 14 meV, in good agreement with recent angle-resolved photoemission spectroscopy (ARPES) results. In addition, around 255 cmmore » –1, we observe two different infrared-active Fe-As modes with obvious asymmetric lineshape, originating from strong coupling between lattice vibrations and spin or charge excitations. Considering a moderate Hund's rule coupling determined from spectral weight analysis, we propose that the strong fluctuations induced by the coupling between itinerant carriers and local moments may affect the phonon mode, and the electron-phonon coupling through the spin channel is likely to play an important role in the unconventional pairing in iron-based superconductors.« less

Generalized thermoelastic wave band gaps in phononic crystals without energy dissipation

NASA Astrophysics Data System (ADS)

Wu, Ying; Yu, Kaiping; Li, Xiao; Zhou, Haotian

2016-01-01

We present a theoretical investigation of the thermoelastic wave propagation in the phononic crystals in the context of Green-Nagdhi theory by taking thermoelastic coupling into account. The thermal field is assumed to be steady. Thermoelastic wave band structures of 3D and 2D are derived by using the plane wave expansion method. For the 2D problem, the anti-plane shear mode is not affected by the temperature difference. Thermoelastic wave bands of the in-plane x-y mode are calculated for lead/silicone rubber, aluminium/silicone rubber, and aurum/silicone rubber phononic crystals. The new findings in the numerical results indicate that the thermoelastic wave bands are composed of the pure elastic wave bands and the thermal wave bands, and that the thermal wave bands can serve as the low boundary of the first band gap when the filling ratio is low. In addition, for the lead/silicone rubber phononic crystals the effects of lattice type (square, rectangle, regular triangle, and hexagon) and inclusion shape (circle, oval, and square) on the normalized thermoelastic bandwidth and the upper/lower gap boundaries are analysed and discussed. It is concluded that their effects on the thermoelastic wave band structure are remarkable.

Anomalous phonon behavior in superconducting CaKFe 4 As 4 : An optical study

DOE PAGES

Yang, Run; Dai, Yaomin; Xu, Bing; ...

2017-02-08

Here, the temperature dependence of ab-plane optical conductivity of CaKFe 4As 4 has been measured below and above its superconducting transition temperature T c≃35.5 K. In the normal state, analysis with the two-Drude model reveals a T-linear scattering rate for the coherent response, which suggests strong spin-fluctuation scattering. Below the superconducting transition, the optical conductivity below 120 cm –1 vanishes, indicating nodeless gap(s). The Mattis-Bardeen fitting in the superconducting state gives two gaps of Δ 1 ≃ 9 meV and Δ 2 ≃ 14 meV, in good agreement with recent angle-resolved photoemission spectroscopy (ARPES) results. In addition, around 255 cmmore » –1, we observe two different infrared-active Fe-As modes with obvious asymmetric lineshape, originating from strong coupling between lattice vibrations and spin or charge excitations. Considering a moderate Hund's rule coupling determined from spectral weight analysis, we propose that the strong fluctuations induced by the coupling between itinerant carriers and local moments may affect the phonon mode, and the electron-phonon coupling through the spin channel is likely to play an important role in the unconventional pairing in iron-based superconductors.« less

Analysis of polariton dispersion in metal nanocomposite based novel superlattice system

NASA Astrophysics Data System (ADS)

DoniPon, V.; Joseph Wilson, K. S.; Malarkodi, A.

2018-06-01

The influence of metal nanoparticles in tuning the polaritonic gap in a novel piezoelectric superlattice is studied. Dielectric function of the metal nanoparticles is analyzed using Kawabata-Kubo effect and Drude's theory. The effective dielectric function of the nanocomposite system is studied using Maxwell Garnett approximation. Nanocomposite based LiTaO3 novel superlattice is formed by arranging the nanocomposite systems in such a way that their orientations are in the opposite direction. Hence there are two additional modes of propagation. The top most modes reflect the metal behavior of the nanoparticles. It is found that these modes of propagation vary with the filling factor. These additional modes of propagations can be exploited in the field of communication.

Plasmon Mapping in Au@Ag Nanocube Assemblies

PubMed Central

2014-01-01

Surface plasmon modes in metallic nanostructures largely determine their optoelectronic properties. Such plasmon modes can be manipulated by changing the morphology of the nanoparticles or by bringing plasmonic nanoparticle building blocks close to each other within organized assemblies. We report the EELS mapping of such plasmon modes in pure Ag nanocubes, Au@Ag core–shell nanocubes, and arrays of Au@Ag nanocubes. We show that these arrays enable the creation of interesting plasmonic structures starting from elementary building blocks. Special attention will be dedicated to the plasmon modes in a triangular array formed by three nanocubes. Because of hybridization, a combination of such nanotriangles is shown to provide an antenna effect, resulting in strong electrical field enhancement at the narrow gap between the nanotriangles. PMID:25067991

Nonclassical-light generation in a photonic-band-gap nonlinear planar waveguide

NASA Astrophysics Data System (ADS)

Peřina, Jan, Jr.; Sibilia, Concita; Tricca, Daniela; Bertolotti, Mario

2004-10-01

The optical parametric process occurring in a photonic-band-gap planar waveguide is studied from the point of view of nonclassical-light generation. The nonlinearly interacting optical fields are described by the generalized superposition of coherent signals and noise using the method of operator linear corrections to a classical strong solution. Scattered backward-propagating fields are taken into account. Squeezed light as well as light with sub-Poissonian statistics can be obtained in two-mode fields under the specified conditions.

Elastic waves in periodic and non-periodic sets of hollow cylinders

NASA Astrophysics Data System (ADS)

Nikitov, S. A.; Gulyaev, Yu. V.; Lisenkov, I. V.; Popov, R. S.; Grigorievkii, A. V.; Grigorievkii, V. I.

2008-06-01

Two ways of modeling of elastic wave propagation in microstructured acoustic fiber are considered. First one is the calculation of band gap parameters by FEM for phononic crystal forming cross section of fiber. Second one is immediate calculation of dispersion characteristics of elastic fiber containing hole cylindric chanels. For fiber made of fused β quarz numerical results are proposed. For the first type full forbidden gap obtained and for second two different types of modes was found.

Harmonic Brain Modes: A Unifying Framework for Linking Space and Time in Brain Dynamics.

PubMed

Atasoy, Selen; Deco, Gustavo; Kringelbach, Morten L; Pearson, Joel

2018-06-01

A fundamental characteristic of spontaneous brain activity is coherent oscillations covering a wide range of frequencies. Interestingly, these temporal oscillations are highly correlated among spatially distributed cortical areas forming structured correlation patterns known as the resting state networks, although the brain is never truly at "rest." Here, we introduce the concept of harmonic brain modes-fundamental building blocks of complex spatiotemporal patterns of neural activity. We define these elementary harmonic brain modes as harmonic modes of structural connectivity; that is, connectome harmonics, yielding fully synchronous neural activity patterns with different frequency oscillations emerging on and constrained by the particular structure of the brain. Hence, this particular definition implicitly links the hitherto poorly understood dimensions of space and time in brain dynamics and its underlying anatomy. Further we show how harmonic brain modes can explain the relationship between neurophysiological, temporal, and network-level changes in the brain across different mental states ( wakefulness, sleep, anesthesia, psychedelic). Notably, when decoded as activation of connectome harmonics, spatial and temporal characteristics of neural activity naturally emerge from the interplay between excitation and inhibition and this critical relation fits the spatial, temporal, and neurophysiological changes associated with different mental states. Thus, the introduced framework of harmonic brain modes not only establishes a relation between the spatial structure of correlation patterns and temporal oscillations (linking space and time in brain dynamics), but also enables a new dimension of tools for understanding fundamental principles underlying brain dynamics in different states of consciousness.

disorder effect on quantum transport properties of ultra thin Fe film

NASA Astrophysics Data System (ADS)

Zhang, Xiaotian; Nakamura, Kohji; Shindou, Ryuichi

2015-03-01

Ferromagnetic ultrathin films are experimentally known to often exhibit perpendicular magnetic anisotropy, when being placed on certain substrates. Based on reported ab-initio band calculations of free-standing Fe-monolayer and that on MgO substrate, we will introduce an effective tight-binding model, which capture a part of an electronic structure near Fermi level for both cases. We will show that the model supports electronic bands with non-zero Chern number and chiral edge modes which cross a direct band gap on the order of 50meV. Unluckily, however, the direct band gap is also masked by another dispersive bands which have non-zero Berry's curvature in the k-space. To demonstrate how disorder kills conducting characters of the latter bulk bands while leave intact those of the chiral edge modes, we will clarify behaviors of localization length and conductance in the effective model with on-site disorders.

Piezoelectric tunable microwave superconducting cavity

NASA Astrophysics Data System (ADS)

Carvalho, N. C.; Fan, Y.; Tobar, M. E.

2016-09-01

In the context of engineered quantum systems, there is a demand for superconducting tunable devices, able to operate with high-quality factors at power levels equivalent to only a few photons. In this work, we developed a 3D microwave re-entrant cavity with such characteristics ready to provide a very fine-tuning of a high-Q resonant mode over a large dynamic range. This system has an electronic tuning mechanism based on a mechanically amplified piezoelectric actuator, which controls the resonator dominant mode frequency by changing the cavity narrow gap by very small displacements. Experiments were conducted at room and dilution refrigerator temperatures showing a large dynamic range up to 4 GHz and 1 GHz, respectively, and were compared to a finite element method model simulated data. At elevated microwave power input, nonlinear thermal effects were observed to destroy the superconductivity of the cavity due to the large electric fields generated in the small gap of the re-entrant cavity.

Experimental demonstration of a Ku-band radial-line relativistic klystron oscillator based on transition radiation

NASA Astrophysics Data System (ADS)

Dang, Fangchao; Zhang, Xiaoping; Zhang, Jun; Ju, Jinchuan; Zhong, Huihuang

2017-03-01

We report on a radial-line relativistic klystron oscillator (RL-RKO), which is physically designed to generate gigawatt-level high power microwaves (HPMs) at Ku-band. The 3π/4 mode of a four-gap buncher is selected to highly modulate the radially propagating intense relativistic electron beam (IREB). A three-gap extractor operating at the π mode is employed to extract the radio-frequency energy efficiently. The Ku-band RL-RKO is investigated experimentally on an intense-current electron beam accelerator. The radially propagating IREB is well focused with an axial-width of 2 mm by a radial magnetic field of 0.4 T. Microwaves with a frequency of 14.86 GHz and a power of 1.5 GW are generated, corresponding to an efficiency of 24%, which indicates a significant advance for the research of radial-line HPM sources.

Quantum Hall ferromagnets and transport properties of buckled Dirac materials

NASA Astrophysics Data System (ADS)

Luo, Wenchen; Chakraborty, Tapash

2015-10-01

We study the ground states and low-energy excitations of a generic Dirac material with spin-orbit coupling and a buckling structure in the presence of a magnetic field. The ground states can be classified into three types under different conditions: SU(2), easy-plane, and Ising quantum Hall ferromagnets. For the SU(2) and the easy-plane quantum Hall ferromagnets there are goldstone modes in the collective excitations, while all the modes are gapped in an Ising-type ground state. We compare the Ising quantum Hall ferromagnet with that of bilayer graphene and present the domain-wall solution at finite temperatures. We then specify the phase transitions and transport gaps in silicene in Landau levels 0 and 1. The phase diagram depends strongly on the magnetic field and the dielectric constant. We note that there exist triple points in the phase diagrams in Landau level N =1 that could be observed in experiments.

Design and fabrication of hybrid SPP waveguides for ultrahigh-bandwidth low-penalty terabit-scale data transmission.

PubMed

Du, Jing; Wang, Jian

2017-11-27

Here we design and fabricate a hybrid surface plasmon polarities (SPP) waveguide on the silicon-on-insulator (SOI) photonics platform. The designed hybrid SPP waveguide is composed of a metal ridge, an air gap, and a silicon ridge. We simulate the mode characteristics in the structure and design the waveguide with a wide air gap that can simplify the fabrication process and maintain the advantages of the hybrid SPP mode. The performance of ultrahigh-bandwidth data transmission through the proposed waveguide is then investigated using 161 wavelength-division multiplexing (WDM) channels, each carrying a 11.2-Gbit/s orthogonal frequency-division multiplexing (OFDM) 16-ary quadrature amplitude modulation (16-QAM) signal. The bit-error rates (BERs) of all 161 channels are less than 1e-3. The favorable results show the prospect of on-chip optical interconnection using the proposed hybrid SPP waveguide.

Closing the Gaps: competing estimates of Indigenous Australian life expectancy in the scientific literature

PubMed Central

Rosenstock, Amanda; Mukandi, Bryan; Zwi, Anthony B; Hill, Peter S

2013-01-01

Objective: Closing the gap in life expectancy between Indigenous and other Australians within a generation is central to national Indigenous reform policy (Closing the Gap). Over time, various methods of estimating Indigenous life expectancy and with that, the life expectancy gap, have been adopted with differing, albeit non-comparable results. We present data on the extent of the gap and elucidate the pattern of use and interpretations of the different estimates of the gap, between 2007 and 2012. Methods: An extensive search was conducted for all peer-reviewed health publications citing estimates of and/or discussing the life expectancy of Indigenous Australians, for the period 2007–2012. Results: Five predominant patterns of citation of the gap estimates were identified: 20 years, 17 years, 15–20 years, 13 years, and 11.5 years for males and 9.7 years for females. Some authors misinterpret the most recent estimates as reflecting improvement from the 17-year figure, rather than the result of different methods of estimation. Support for the direct methods used to calculate Indigenous life expectancy is indicated. Conclusions and Implications: A specific estimate of the life expectancy gap has not been established among stakeholders in Indigenous health. Agreement on the magnitude of the gap is arguably needed in order to evaluate strategies aimed at improving health outcomes for Indigenous Australians. Moreover, measuring progress towards ‘closing the gap’ depends on the availability of comparable estimates, using the same techniques of measurement to assess changes over time. PMID:23895479

Broken symmetries, zero-energy modes, and quantum transport in disordered graphene: from supermetallic to insulating regimes.

PubMed

Cresti, Alessandro; Ortmann, Frank; Louvet, Thibaud; Van Tuan, Dinh; Roche, Stephan

2013-05-10

The role of defect-induced zero-energy modes on charge transport in graphene is investigated using Kubo and Landauer transport calculations. By tuning the density of random distributions of monovacancies either equally populating the two sublattices or exclusively located on a single sublattice, all conduction regimes are covered from direct tunneling through evanescent modes to mesoscopic transport in bulk disordered graphene. Depending on the transport measurement geometry, defect density, and broken sublattice symmetry, the Dirac-point conductivity is either exceptionally robust against disorder (supermetallic state) or suppressed through a gap opening or by algebraic localization of zero-energy modes, whereas weak localization and the Anderson insulating regime are obtained for higher energies. These findings clarify the contribution of zero-energy modes to transport at the Dirac point, hitherto controversial.

Modeling of Current-Voltage Characteristics in Large Metal-Semiconducting Carbon Nanotube Systems

NASA Technical Reports Server (NTRS)

Yamada, Toshishige; Biegel, Bryon A. (Technical Monitor)

2000-01-01

A model is proposed for two observed current-voltage (I-V) patterns in recent experiment with a scanning tunneling microscope tip and a carbon nanotube [Collins et al., Science 278, 100 (1997)]. We claim that there are two contact modes for a tip (metal)-nanotube (semiconductor) junction depending whether the alignment of the metal and the semiconductor band structures is (1) variable (vacuum-gap) or (2) fixed (touching) with V. With the tip grounded, the tunneling case in (1) would produce large dI/dV with V > 0, small dI/dV with V < 0, and I = 0 near V = 0 for an either n- or p-nanotube. However, the Schottky mechanism in (2) would result in forward current with V < 0 for an n-nanotube, while with V > 0 for an p-nanotube. The two observed I-V patterns are thus entirely explained by a tip-nanotube contact of the two types, where the nanotube must be n-type. We apply this model to the source-drain I-V characteristics in a long nanotube-channel field-effect-transistor with metallic electrodes at low temperature [Zhou et al., Appl. Phys. Lett. 76, 1597 (2000)], and show that two independent metal-semiconductor junctions in series are responsible for the observed behavior.

A scoping review of biomechanical testing for proximal humerus fracture implants.

PubMed

Cruickshank, David; Lefaivre, Kelly A; Johal, Herman; MacIntyre, Norma J; Sprague, Sheila A; Scott, Taryn; Guy, Pierre; Cripton, Peter A; McKee, Michael; Bhandari, Mohit; Slobogean, Gerard P

2015-07-30

Fixation failure is a relatively common sequela of surgical management of proximal humerus fractures (PHF). The purpose of this study is to understand the current state of the literature with regard to the biomechanical testing of proximal humerus fracture implants. A scoping review of the proximal humerus fracture literature was performed, and studies testing the mechanical properties of a PHF treatment were included in this review. Descriptive statistics were used to summarize the characteristics and methods of the included studies. 1,051 proximal humerus fracture studies were reviewed; 67 studies met our inclusion criteria. The most common specimen used was cadaver bone (87%), followed by sawbones (7%) and animal bones (4%). A two-part fracture pattern was tested most frequently (68%), followed by three-part (23%), and four-part (8%). Implants tested included locking plates (52%), intramedullary devices (25%), and non-locking plates (25%). Hemi-arthroplasty was tested in 5 studies (7%), with no studies using reverse total shoulder arthroplasty (RTSA) implants. Torque was the most common mode of force applied (51%), followed by axial loading (45%), and cantilever bending (34%). Substantial testing diversity was observed across all studies. The biomechanical literature was found to be both diverse and heterogeneous. More complex fracture patterns and RTSA implants have not been adequately tested. These gaps in the current literature will need to be addressed to ensure that future biomechanical research is clinically relevant and capable of improving the outcomes of challenging proximal humerus fracture patterns.

Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point

NASA Astrophysics Data System (ADS)

Hong, Tao; Matsumoto, Masashige; Qiu, Yiming; Chen, Wangchun; Gentile, Thomas R.; Watson, Shannon; Awwadi, Firas F.; Turnbull, Mark M.; Dissanayake, Sachith E.; Agrawal, Harish; Toft-Petersen, Rasmus; Klemke, Bastian; Coester, Kris; Schmidt, Kai P.; Tennant, David A.

2017-07-01

Spontaneous symmetry-breaking quantum phase transitions play an essential role in condensed-matter physics. The collective excitations in the broken-symmetry phase near the quantum critical point can be characterized by fluctuations of phase and amplitude of the order parameter. The phase oscillations correspond to the massless Nambu-Goldstone modes whereas the massive amplitude mode, analogous to the Higgs boson in particle physics, is prone to decay into a pair of low-energy Nambu-Goldstone modes in low dimensions. Especially, observation of a Higgs amplitude mode in two dimensions is an outstanding experimental challenge. Here, using inelastic neutron scattering and applying the bond-operator theory, we directly and unambiguously identify the Higgs amplitude mode in a two-dimensional S = 1/2 quantum antiferromagnet C9H18N2CuBr4 near a quantum critical point in two dimensions. Owing to an anisotropic energy gap, it kinematically prevents such decay and the Higgs amplitude mode acquires an infinite lifetime.

Nanomechanical control of optical field and quality factor in photonic crystal structures

NASA Astrophysics Data System (ADS)

Cotrufo, Michele; Midolo, Leonardo; Zobenica, Žarko; Petruzzella, Maurangelo; van Otten, Frank W. M.; Fiore, Andrea

2018-03-01

Actively controlling the properties of localized optical modes is crucial for cavity quantum electrodynamics experiments. While several methods to tune the optical frequency have been demonstrated, the possibility of controlling the shape of the modes has scarcely been investigated. Yet an active manipulation of the mode pattern would allow direct control of the mode volume and the quality factor and therefore of the radiative processes. In this work, we propose and demonstrate a nano-optoelectromechanical device in which a mechanical displacement affects the spatial pattern of the electromagnetic field. The device is based on a double-membrane photonic crystal waveguide which, upon bending, creates a spatial modulation of the effective refractive index, resulting in an effective potential well or antiwell for the optical modes. The change in the field pattern drastically affects the optical losses: large modulations of the quality factors and dissipative coupling rates larger than 1 GHz/nm are predicted by calculations and confirmed by experiments. This concept opens new avenues in solid-state cavity quantum electrodynamics in which the field, instead of the frequency, is coupled to the mechanical motion.

Distal gap junctions and active dendrites can tune network dynamics.

PubMed

Saraga, Fernanda; Ng, Leo; Skinner, Frances K

2006-03-01

Gap junctions allow direct electrical communication between CNS neurons. From theoretical and modeling studies, it is well known that although gap junctions can act to synchronize network output, they can also give rise to many other dynamic patterns including antiphase and other phase-locked states. The particular network pattern that arises depends on cellular, intrinsic properties that affect firing frequencies as well as the strength and location of the gap junctions. Interneurons or GABAergic neurons in hippocampus are diverse in their cellular characteristics and have been shown to have active dendrites. Furthermore, parvalbumin-positive GABAergic neurons, also known as basket cells, can contact one another via gap junctions on their distal dendrites. Using two-cell network models, we explore how distal electrical connections affect network output. We build multi-compartment models of hippocampal basket cells using NEURON and endow them with varying amounts of active dendrites. Two-cell networks of these model cells as well as reduced versions are explored. The relationship between intrinsic frequency and the level of active dendrites allows us to define three regions based on what sort of network dynamics occur with distal gap junction coupling. Weak coupling theory is used to predict the delineation of these regions as well as examination of phase response curves and distal dendritic polarization levels. We find that a nonmonotonic dependence of network dynamic characteristics (phase lags) on gap junction conductance occurs. This suggests that distal electrical coupling and active dendrite levels can control how sensitive network dynamics are to gap junction modulation. With the extended geometry, gap junctions located at more distal locations must have larger conductances for pure synchrony to occur. Furthermore, based on simulations with heterogeneous networks, it may be that one requires active dendrites if phase-locking is to occur in networks formed with distal gap junctions.

How to make stripes: deciphering the transition from non-periodic to periodic patterns in Drosophila segmentation

PubMed Central

Schroeder, Mark D.; Greer, Christina; Gaul, Ulrike

2011-01-01

The generation of metameric body plans is a key process in development. In Drosophila segmentation, periodicity is established rapidly through the complex transcriptional regulation of the pair-rule genes. The ‘primary’ pair-rule genes generate their 7-stripe expression through stripe-specific cis-regulatory elements controlled by the preceding non-periodic maternal and gap gene patterns, whereas ‘secondary’ pair-rule genes are thought to rely on 7-stripe elements that read off the already periodic primary pair-rule patterns. Using a combination of computational and experimental approaches, we have conducted a comprehensive systems-level examination of the regulatory architecture underlying pair-rule stripe formation. We find that runt (run), fushi tarazu (ftz) and odd skipped (odd) establish most of their pattern through stripe-specific elements, arguing for a reclassification of ftz and odd as primary pair-rule genes. In the case of run, we observe long-range cis-regulation across multiple intervening genes. The 7-stripe elements of run, ftz and odd are active concurrently with the stripe-specific elements, indicating that maternal/gap-mediated control and pair-rule gene cross-regulation are closely integrated. Stripe-specific elements fall into three distinct classes based on their principal repressive gap factor input; stripe positions along the gap gradients correlate with the strength of predicted input. The prevalence of cis-elements that generate two stripes and their genomic organization suggest that single-stripe elements arose by splitting and subfunctionalization of ancestral dual-stripe elements. Overall, our study provides a greatly improved understanding of how periodic patterns are established in the Drosophila embryo. PMID:21693522

Clinical application of qualitative assessment for breast masses in shear-wave elastography.

PubMed

Gweon, Hye Mi; Youk, Ji Hyun; Son, Eun Ju; Kim, Jeong-Ah

2013-11-01

To evaluate the interobserver agreement and the diagnostic performance of various qualitative features in shear-wave elastography (SWE) for breast masses. A total of 153 breast lesions in 152 women who underwent B-mode ultrasound and SWE before biopsy were included. Qualitative analysis in SWE was performed using two different classifications: E values (Ecol; 6-point color score, Ehomo; homogeneity score and Esha; shape score) and a four-color pattern classification. Two radiologists reviewed five data sets: B-mode ultrasound, SWE, and combination of both for E values and four-color pattern. The BI-RADS categories were assessed B-mode and combined sets. Interobserver agreement was assessed using weighted κ statistics. Areas under the receiver operating characteristic curve (AUC), sensitivity, and specificity were analyzed. Interobserver agreement was substantial for Ecol (κ=0.79), Ehomo (κ=0.77) and four-color pattern (κ=0.64), and moderate for Esha (κ=0.56). Better-performing qualitative features were Ecol and four-color pattern (AUCs, 0.932 and 0.925) compared with Ehomo and Esha (AUCs, 0.857 and 0.864; P<0.05). The diagnostic performance of B-mode ultrasound (AUC, 0.950) was not significantly different from combined sets with E value and with four color pattern (AUCs, 0.962 and 0.954). When all qualitative values were negative, leading to downgrade the BI-RADS category, the specificity increased significantly from 16.5% to 56.1% (E value) and 57.0% (four-color pattern) (P<0.001) without improvement in sensitivity. The qualitative SWE features were highly reproducible and showed good diagnostic performance in suspicious breast masses. Adding qualitative SWE to B-mode ultrasound increased specificity in decision making for biopsy recommendation. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

TIDAL WAVES: Network mechanisms in the neuroendocrine control of prolactin release.

PubMed

Lyons, David J; Broberger, Christian

2014-10-01

Neuroendocrine tuberoinfundibular dopamine (TIDA) neurons tonically inhibit pituitary release of the hormone, prolactin. Through the powerful actions of prolactin in promoting lactation and maternal behaviour while suppressing sexual drive and fertility, TIDA neurons play a key role in reproduction. We summarize insights from recent in vitro studies into the membrane properties and network behaviour of TIDA neurons including the observations that TIDA neurons exhibit a robust oscillation that is synchronized between cells and depends on intact gap junction communication. Comparisons are made with phasic firing patterns in other neuronal populations. Modulators involved in the control of lactation - including serotonin, thyrotropin-releasing hormone and prolactin itself - have been shown to change the electrical behaviour of TIDA cells. We propose that TIDA discharge mode may play a central role in tuning the amount of dopamine delivered to the pituitary and hence circulating prolactin concentrations in different reproductive states and pathological conditions. Copyright © 2014 Elsevier Inc. All rights reserved.

Directional Emission from Dielectric Leaky-Wave Nanoantennas

NASA Astrophysics Data System (ADS)

Peter, Manuel; Hildebrandt, Andre; Schlickriede, Christian; Gharib, Kimia; Zentgraf, Thomas; Förstner, Jens; Linden, Stefan

2017-07-01

An important source of innovation in nanophotonics is the idea to scale down known radio wave technologies to the optical regime. One thoroughly investigated example of this approach are metallic nanoantennas which employ plasmonic resonances to couple localized emitters to selected far-field modes. While metals can be treated as perfect conductors in the microwave regime, their response becomes Drude-like at optical frequencies. Thus, plasmonic nanoantennas are inherently lossy. Moreover, their resonant nature requires precise control of the antenna geometry. A promising way to circumvent these problems is the use of broadband nanoantennas made from low-loss dielectric materials. Here, we report on highly directional emission from active dielectric leaky-wave nanoantennas made of Hafnium dioxide. Colloidal semiconductor quantum dots deposited in the nanoantenna feed gap serve as a local light source. The emission patterns of active nanoantennas with different sizes are measured by Fourier imaging. We find for all antenna sizes a highly directional emission, underlining the broadband operation of our design.

Computational prediction of body-centered cubic carbon in an all- s p 3 six-member ring configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhen -Zhen; Lian, Chao -Sheng; Xu, Jing

2015-06-11

Recent shock compression experiments produced clear evidence of a new carbon phase, but a full structural identification has remained elusive. Here we establish by ab initio calculations a body-centered cubic carbon phase in Ia3¯d(O 10 h) symmetry, which contains twelve atoms in its primitive cell, thus termed BC12, and comprises all-sp 3 six-membered rings. This structural configuration places BC12 carbon in the same bonding type as cubic diamond, and its stability is verified by phonon mode analysis. Simulated x-ray diffraction patterns provide an excellent match to the previously unexplained distinct diffraction peak found in shock compression experiments. Electronic band andmore » density of states calculations reveal that BC12 is a semiconductor with a direct band gap of ~2.97eV. Lastly, these results provide a solid foundation for further exploration of this new carbon allotrope.« less

Monolithic integration of InGaAs/InP multiple quantum wells on SOI substrates for photonic devices

NASA Astrophysics Data System (ADS)

Li, Zhibo; Wang, Mengqi; Fang, Xin; Li, Yajie; Zhou, Xuliang; Yu, Hongyan; Wang, Pengfei; Wang, Wei; Pan, Jiaoqing

2018-02-01

A direct epitaxy of III-V nanowires with InGaAs/InP multiple quantum wells on v-shaped trenches patterned silicon on insulator (SOI) substrates was realized by combining the standard semiconductor fabrication process with the aspect ratio trapping growth technique. Silicon thickness as well as the width and gap of each nanowire were carefully designed to accommodate essential optical properties and appropriate growth conditions. The III-V element ingredient, crystalline quality, and surface topography of the grown nanowires were characterized by X-ray diffraction spectroscopy, photoluminescence, and scanning electron microscope. Geometrical details and chemical information of multiple quantum wells were revealed by transmission electron microscopy and energy dispersive spectroscopy. Numerical simulations confirmed that the optical guided mode supported by one single nanowire was able to propagate 50 μm with ˜30% optical loss. This proposed integration scheme opens up an alternative pathway for future photonic integrations of III-V devices on the SOI platform at nanoscale.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Q. G.; Chen, N.; Zhang, M.

Five IDs will be built for the Shanghai Synchrotron Radiation Facility (SSRF). Two identical mini-gap undulators with the period length 25mm and the minimum gap 6mm will use the in-vacuum technology and can operate in tapered mode. Two wigglers with the period lengths 7.9cm and 14cm and the same minimum gap 14mm will produce the peak fields of 1.2T and 1.94T. A variable polarization undulator of the APPLE-II type with 4.2m long and the period length 10cm can provide linearly, circularly and elliptically polarized radiation in a wide spectral range. This paper describes the magnet designs and the mechanical structuremore » designs of these IDs.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, T.; Imhof, A.; Ingold, G.

To vary the polarization vector of an APPLE II undulator continuously from 0 - 180 deg., all four magnet arrays need to be movable. Following the adjustable-phase undulator approach by R. Carr, a 3.4 m long fixed gap undulator for SLS with a gap of 11.6 mm has been constructed. It will be installed in fall 2006. The gap drive is replaced by a pair-wise shift of the magnet arrays to change the energy, while the polarization is changed by shifts of diagonal arrays. The high injection efficiency and standard operation top-up mode at the SLS allows this simplified undulatormore » design. The design as well as the operational aspects will be discussed.« less

Electromagnetic Properties Analysis on Hybrid-driven System of Electromagnetic Motor

NASA Astrophysics Data System (ADS)

Zhao, Jingbo; Han, Bingyuan; Bei, Shaoyi

2018-01-01

The hybrid-driven system made of permanent-and electromagnets applied in the electromagnetic motor was analyzed, equivalent magnetic circuit was used to establish the mathematical models of hybrid-driven system, based on the models of hybrid-driven system, the air gap flux, air-gap magnetic flux density, electromagnetic force was proposed. Taking the air-gap magnetic flux density and electromagnetic force as main research object, the hybrid-driven system was researched. Electromagnetic properties of hybrid-driven system with different working current modes is studied preliminary. The results shown that analysis based on hybrid-driven system can improve the air-gap magnetic flux density and electromagnetic force more effectively and can also guarantee the output stability, the effectiveness and feasibility of the hybrid-driven system are verified, which proved theoretical basis for the design of hybrid-driven system.

Effects of electrode gap and electric current on chlorine generation of electrolyzed deep ocean water.

PubMed

Hsu, Guoo-Shyng Wang; Hsu, Shun-Yao

2018-04-01

Electrolyzed water is a sustainable disinfectant, which can comply with food safety regulations and is environmental friendly. A two-factor central composite design was adopted for studying the effects of electrode gap and electric current on chlorine generation efficiency of electrolyzed deep ocean water. Deep ocean water was electrolyzed in a glass electrolyzing cell equipped with platinum-plated titanium anode and cathode in a constant-current operation mode. Results showed that current density, chlorine concentration, and electrolyte temperature increased with electric current, while electric efficiency decreased with electric current and electrode gap. An electrode gap of less than 11.7 mm, and a low electric current appeared to be a more energy efficient design and operation condition for the electrolysis system. Copyright © 2017. Published by Elsevier B.V.

Sensor apparatus

DOEpatents

Deason, Vance A [Idaho Falls, ID; Telschow, Kenneth L [Idaho Falls, ID

2009-12-22

A sensor apparatus and method for detecting an environmental factor is shown that includes an acoustic device that has a characteristic resonant vibrational frequency and mode pattern when exposed to a source of acoustic energy and, futher, when exposed to an environmental factor, produces a different resonant vibrational frequency and/or mode pattern when exposed to the same source of acoustic energy.

Complexity of possibly gapped histogram and analysis of histogram.

PubMed

Fushing, Hsieh; Roy, Tania

2018-02-01

We demonstrate that gaps and distributional patterns embedded within real-valued measurements are inseparable biological and mechanistic information contents of the system. Such patterns are discovered through data-driven possibly gapped histogram, which further leads to the geometry-based analysis of histogram (ANOHT). Constructing a possibly gapped histogram is a complex problem of statistical mechanics due to the ensemble of candidate histograms being captured by a two-layer Ising model. This construction is also a distinctive problem of Information Theory from the perspective of data compression via uniformity. By defining a Hamiltonian (or energy) as a sum of total coding lengths of boundaries and total decoding errors within bins, this issue of computing the minimum energy macroscopic states is surprisingly resolved by applying the hierarchical clustering algorithm. Thus, a possibly gapped histogram corresponds to a macro-state. And then the first phase of ANOHT is developed for simultaneous comparison of multiple treatments, while the second phase of ANOHT is developed based on classical empirical process theory for a tree-geometry that can check the authenticity of branches of the treatment tree. The well-known Iris data are used to illustrate our technical developments. Also, a large baseball pitching dataset and a heavily right-censored divorce data are analysed to showcase the existential gaps and utilities of ANOHT.

Complexity of possibly gapped histogram and analysis of histogram

PubMed Central

Roy, Tania

2018-01-01

We demonstrate that gaps and distributional patterns embedded within real-valued measurements are inseparable biological and mechanistic information contents of the system. Such patterns are discovered through data-driven possibly gapped histogram, which further leads to the geometry-based analysis of histogram (ANOHT). Constructing a possibly gapped histogram is a complex problem of statistical mechanics due to the ensemble of candidate histograms being captured by a two-layer Ising model. This construction is also a distinctive problem of Information Theory from the perspective of data compression via uniformity. By defining a Hamiltonian (or energy) as a sum of total coding lengths of boundaries and total decoding errors within bins, this issue of computing the minimum energy macroscopic states is surprisingly resolved by applying the hierarchical clustering algorithm. Thus, a possibly gapped histogram corresponds to a macro-state. And then the first phase of ANOHT is developed for simultaneous comparison of multiple treatments, while the second phase of ANOHT is developed based on classical empirical process theory for a tree-geometry that can check the authenticity of branches of the treatment tree. The well-known Iris data are used to illustrate our technical developments. Also, a large baseball pitching dataset and a heavily right-censored divorce data are analysed to showcase the existential gaps and utilities of ANOHT. PMID:29515829

Gap junctions between CA3 pyramidal cells contribute to network synchronization in neonatal hippocampus.

PubMed

Molchanova, Svetlana M; Huupponen, Johanna; Lauri, Sari E; Taira, Tomi

2016-08-01

Direct electrical coupling between neurons through gap junctions is prominent during development, when synaptic connectivity is scarce, providing the additional intercellular connectivity. However, functional studies of gap junctions are hampered by the unspecificity of pharmacological tools available. Here we have investigated gap-junctional coupling between CA3 pyramidal cells in neonatal hippocampus and its contribution to early network activity. Four different gap junction inhibitors, including the general blocker carbenoxolone, decreased the frequency of network activity bursts in CA3 area of hippocampus of P3-6 rats, suggesting the involvement of electrical connections in the generation of spontaneous network activity. In CA3 pyramidal cells, spikelets evoked by local stimulation of stratum oriens, were inhibited by carbenoxolone, but not by inhibitors of glutamatergic and GABAergic synaptic transmission, signifying the presence of electrical connectivity through axo-axonic gap junctions. Carbenoxolone also decreased the success rate of firing antidromic action potentials in response to stimulation, and changed the pattern of spontaneous action potential firing of CA3 pyramidal cells. Altogether, these data suggest that electrical coupling of CA3 pyramidal cells contribute to the generation of the early network events in neonatal hippocampus by modulating their firing pattern and synchronization. Copyright © 2016 Elsevier Ltd. All rights reserved.

Germanene on single-layer ZnSe substrate: novel electronic and optical properties.

PubMed

Ye, H Y; Hu, F F; Tang, H Y; Yang, L W; Chen, X P; Wang, L G; Zhang, G Q

2018-06-01

In this work, the structural, electronic and optical properties of germanene and ZnSe substrate nanocomposites have been investigated using first-principles calculations. We found that the large direct-gap ZnSe semiconductors and zero-gap germanene form a typical orbital hybridization heterostructure with a strong binding energy, which shows a moderate direct band gap of 0.503 eV in the most stable pattern. Furthermore, the heterostructure undergoes semiconductor-to-metal band gap transition when subjected to external out-of-plane electric field. We also found that applying external strain and compressing the interlayer distance are two simple ways of tuning the electronic structure. An unexpected indirect-direct band gap transition is also observed in the AAII pattern via adjusting the interlayer distance. Quite interestingly, the calculated results exhibit that the germanene/ZnSe heterobilayer structure has perfect optical absorption in the solar spectrum as well as the infrared and UV light zones, which is superior to that of the individual ZnSe substrate and germanene. The staggered interfacial gap and tunability of the energy band structure via interlayer distance and external electric field and strain thus make the germanene/ZnSe heterostructure a promising candidate for field effect transistors (FETs) and nanoelectronic applications.

Complexity of possibly gapped histogram and analysis of histogram

NASA Astrophysics Data System (ADS)

Fushing, Hsieh; Roy, Tania

2018-02-01

We demonstrate that gaps and distributional patterns embedded within real-valued measurements are inseparable biological and mechanistic information contents of the system. Such patterns are discovered through data-driven possibly gapped histogram, which further leads to the geometry-based analysis of histogram (ANOHT). Constructing a possibly gapped histogram is a complex problem of statistical mechanics due to the ensemble of candidate histograms being captured by a two-layer Ising model. This construction is also a distinctive problem of Information Theory from the perspective of data compression via uniformity. By defining a Hamiltonian (or energy) as a sum of total coding lengths of boundaries and total decoding errors within bins, this issue of computing the minimum energy macroscopic states is surprisingly resolved by applying the hierarchical clustering algorithm. Thus, a possibly gapped histogram corresponds to a macro-state. And then the first phase of ANOHT is developed for simultaneous comparison of multiple treatments, while the second phase of ANOHT is developed based on classical empirical process theory for a tree-geometry that can check the authenticity of branches of the treatment tree. The well-known Iris data are used to illustrate our technical developments. Also, a large baseball pitching dataset and a heavily right-censored divorce data are analysed to showcase the existential gaps and utilities of ANOHT.

Reproduction, abundance and survivorship of two Alveopora spp. in the mesophotic reefs of Eilat, Red Sea

PubMed Central

Eyal-Shaham, Lee; Eyal, Gal; Tamir, Raz; Loya, Yossi

2016-01-01

Although the study of coral reproduction has advanced tremendously over the last few decades, a particular gap exists in our knowledge of the reproductive modes of corals from ‘mesophotic coral ecosystems’ (MCEs) found at 30–150 m depth. Here, we report for the first time on the reproductive patterns, living cover, and survivorship under different light treatments of two scleractinian species from the MCEs of Eilat, Red-Sea: Alveopora allingi and A. ocellata. Both species are found exclusively within MCEs and are high in both abundance and relative cover. These species display a synchronous gametogenic cycles with consecutive oocyte growth and development. Peak of reproductive activity occurs in late summer (September-October), typified by accelerated oocyte growth, coinciding with the rise in seawater temperature. Estimates of fecundity show mean monthly maxima of 48.5 ± 26.3 and 23.5 ± 11.8 (Mean ± SE) oocytes per cm2 for A. allingi and A. ocellata respectively, prior to spawning. A comparison of light and temperature regimes in the shallow vs. MCE environments is presented, and the response of these species to changes in these parameters is discussed. A call encouraging the much-needed studies on the sexuality and reproductive modes of MCE coral species is expressed. PMID:26860656

Control of 3-D Modes in a Boundary Layer Undergoing Subharmonic Transition.

NASA Astrophysics Data System (ADS)

Corke, T. C.; Peto, J.; Speer, A.; Paroozan, P.; Sciammarella, C.

1997-11-01

The effect of alternating standing patterns of wall displacements in the transition region of a Falkner-Skan boundary layer with an adverse pressure gradient is investigated. Transition is controlled by introducing disturbances to excite a pair of oblique modes along with a plane TS mode. The oblique modes are at the TS subharmonic frequency in order to promote subharmonic resonance. Measurements consist of a spanwise rake of hot-wire sensors placed near the wall below the critical layer, and a 2-D (15 x 15) array of optical pressure sensors. The space-time data series are processed using 2-D Fourier analysis to determine the spanwise wave number content of the flow. Of particular interest is the streamwise vortex mode which results from a difference interaction of the subharmonic oblique modes. We examine the effect of different patterns and amplitudes of upstream wall displacements on the development of the travelling and stationary modes in this case leading to transition. Supported by ARO Grant No. DAAH04-93-G-0212

Amplitude Excitations in a Symmetry-Breaking Quantum Phase Transition

NASA Astrophysics Data System (ADS)

Boguslawski, Matthew; H M, Bharath; Barrios, Maryrose; Chapman, Michael

Quantum phase transitions (QPT) can be characterized using a local order parameter. In a symmetry-breaking phase transition, this order parameter spontaneously breaks one or more of the symmetries of the Hamiltonian while crossing the quantum critical point (QCP). A spin-1 Bose Einstein condensate, in a single spatial mode, undergoes a QPT when the applied magnetic field is quenched through a critical value. The transverse spin component is an order parameter characterizing this QPT. It shares a U(1)Ã'SO(2) symmetry with the Hamiltonian, but one of these two symmetries is broken when the system is quenched through the QCP. As a result, two massless, coupled phonon-magnon modes are present along with a single massive, or Higgs-like mode which has the form of amplitude excitations of the order parameter. Here, we experimentally characterize this phase transition and the resulting amplitude excitations by inducing coherent oscillation in the spin population. We further use the amplitude oscillations to measure the energy gap between the ground state and the first excited state for different phases of the QPT. At the QCP, finite size effects lead to a non-zero gap, and our measurements are consistent with this prediction.

Dynamically tunable graphene/dielectric photonic crystal transmission lines

NASA Astrophysics Data System (ADS)

Williamson, Ian; Mousavi, S. Hossein; Wang, Zheng

2015-03-01

It is well known that graphene supports plasmonic modes with high field confinement and lower losses when compared to conventional metals. Additionally, graphene features a highly tunable conductivity through which the plasmon dispersion can be modulated. Over the years these qualities have inspired a wide range of applications for graphene in the THz and infrared regimes. In this presentation we theoretically demonstrate a graphene parallel plate waveguide (PPWG) that sandwiches a 2D photonic crystal slab. The marriage of these two geometries offers a large two dimensional band gap that can be dynamically tuned over a very broad bandwidth. Our device operates in the low-THz band where the graphene PPWG supports a quasi-TEM mode with a relatively flat attenuation. Unlike conventional photonic crystal slabs, the quasi-TEM nature of the graphene PPWG mode allows the slab thickness to be less than 1/10 of the photonic crystal lattice constant. These features offer up a wealth of opportunities, including tunable metamaterials with a possible platform for large band gaps in 3D structures through tiling and stacking. Additionally, the geometry provides a platform for tunable defect cavities without needing three dimensional periodicity.

Dispersion of doppleron-phonon modes in strong coupling regime.

PubMed

Gudkov, V V; Zhevstovskikh, I V

2004-04-01

The dispersion equation for doppleron-phonon modes was constructed and solved analytically in the strong coupling regime. The Fermi surface model proposed previously for calculating the doppleron spectrum in an indium crystal was used. It was shown that in the vicinity of doppleron-phonon resonance, the dispersion curves of coupled modes form a gap qualitatively different from the one observed under helicon-phonon resonance: there is a frequency interval forbidden for existence of waves of definite circular polarization depending upon direction of the external DC magnetic field. The physical reason for it is interaction of the waves which have oppositely directed group velocities.

Crush testing, characterizing, and modeling the crashworthiness of composite laminates

NASA Astrophysics Data System (ADS)

Garner, David Michael, Jr.

Research in the field of crashworthiness of composite materials is presented. A new crush test method was produced to characterize the crush behavior of composite laminates. In addition, a model of the crush behavior and a method for rank ordering the energy absorption capability of various laminates were developed. The new crush test method was used for evaluating the crush behavior of flat carbon/epoxy composite specimens at quasi-static and dynamic rates. The University of Utah crush test fixture was designed to support the flat specimen against catastrophic buckling. A gap, where the specimen is unsupported, allowed unhindered crushing of the specimen. In addition, the specimen's failure modes could be clearly observed during crush testing. Extensive crush testing was conducted wherein the crush force and displacement data were collected to calculate the energy absorption, and high speed video was captured during dynamic testing. Crush tests were also performed over a range of fixture gap heights. The basic failure modes were buckling, crack growth, and fracture. Gap height variations resulted in poorly, properly, and overly constrained specimens. In addition, guidelines for designing a composite laminate for crashworthiness were developed. Modeling of the crush behavior consisted of the delamination and fracture of a single ply or group of like plies during crushing. Delamination crack extension was modeled using the mode I energy release rate, G lc, where an elastica approach was used to obtain the strain energy. Variations in Glc were briefly explored with double cantilever beam tests wherein crack extension occurred along a multidirectional ply interface. The model correctly predicted the failure modes for most of the test cases, and offered insight into how the input parameters affect the model. The ranking method related coefficients of the laminate and sublaminate stiffness matrices, the ply locations within the laminate, and the laminate thickness. The ranking method correctly ordered the laminates tested in this study with respect to their energy absorption.

Polarization Properties of A Broadband Multi-Moded Concentrator

NASA Technical Reports Server (NTRS)

Kogut, Alan; Fixsen, Dale J.; Hill, Robert S.

2015-01-01

We present the design and performance of a non-imaging concentrator for use in broad-band polarimetry at millimeter through submillimeter wavelengths. A rectangular geometry preserves the input polarization state as the concentrator couples f/2 incident optics to a 2pi sr detector. Measurements of the co-polar and cross-polar beams in both the few-mode and highly over-moded limits agree with a simple model based on mode truncation. The measured co-polar beam pattern is nearly independent of frequency in both linear polarizations. The cross-polar beam pattern is dominated by a uniform term corresponding to polarization efficiency 94%. After correcting for efficiency, the remaining cross-polar response is -18 dB.

Gender and migration on the labour market: Additive or interacting disadvantages in Germany?

PubMed

Fleischmann, Fenella; Höhne, Jutta

2013-09-01

Despite substantial differences in labour market attainment according to gender and migration status, gender and ethnic differences in labour market behaviour are most often studied separately. In contrast, this study describes and analyses interactions between gender, ethnic background and immigrant generation with regard to labour market participation, part-time work, and occupational status. The double comparison aims to reveal whether gender gaps in these labour market outcomes among the majority population generalise to ethnic minorities. Moreover, we ask whether variation in gender gaps in labour market behaviour follows the patterns in migrants' origin countries, and whether gender gaps show signs of intergenerational assimilation. Our heterogeneous choice and OLS regressions of 2009 German Microcensus data reveal considerable variation in gender gaps in labour market behaviour between East and West Germany, across ethnic groups and across generations. Intergenerational comparisons show that most ethnic minorities assimilate towards German patterns of gendered labour market attainment. Copyright © 2013 Elsevier Inc. All rights reserved.

Strain, stabilities and electronic properties of hexagonal BN bilayers

NASA Astrophysics Data System (ADS)

Fujimoto, Yoshitaka; Saito, Susumu

Hexagonal boron nitride (h-BN) atomic layers have been regarded as fascinating materials both scientifically and technologically due to the sizable band gap. This sizable band-gap nature of the h-BN atomic layers would provide not only new physical properties but also novel nano- and/or opto-electronics applications. Here, we study the first-principles density-functional study that clarifies the biaxial strain effects on the energetics and the electronic properties of h-BN bilayers. We show that the band gaps of the h-BN bilayers are tunable by applying strains. Furthermore, we show that the biaxial strains can produce a transition from indirect to direct band gaps of the h-BN bilayer. We also discuss that both AA and AB stacking patterns of h-BN bilayer become feasible structures because h-BN bilayers possess two different directions in the stacking patterns. Supported by MEXT Elements Strategy Initiative to Form Core Research Center through Tokodai Institute for Element Strategy, JSPS KAKENHI Grant Numbers JP26390062 and JP25107005.

Development of guidelines for pedestrian safety treatments at signalized intersections.

DOT National Transportation Integrated Search

2012-01-01

For intersections with a permissive or protected-permissive left-turn mode, pedestrians cross during the : permissive period. This operation requires the left-turn driver to yield to both opposing vehicles and : pedestrians, prior to accepting a gap ...

Dynamic properties of III-V polytypes from density-functional theory

NASA Astrophysics Data System (ADS)

Benyahia, N.; Zaoui, A.; Madouri, D.; Ferhat, M.

2017-03-01

The recently discovered hexagonal wurtzite phase of several III-V nanowires opens up strong opportunity to engineer optoelectronic and transport properties of III-V materials. Herein, we explore the dynamical and dielectric properties of cubic (3C) and wurtzite (2H) III-V compounds (AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, and InSb). For cubic III-V compounds, our calculated phonon frequencies agree well with neutron diffraction and Raman-scattering measurements. In the case of 2H III-V materials, our calculated phonon modes at the zone-center Γ point are in distinguished agreement with available Raman-spectroscopy measurements of wurtzite GaAs, InP, GaP, and InAs nanowires. Particularly, the "fingerprint" of the wurtzite phase, which is our predicted E2(high) phonon mode, at 261 cm-1(GaAs), 308 cm-1(InP), 358 cm-1(GaP), and 214 cm-1(InAs) matches perfectly the respective Raman values of 258 cm-1, 306.4 cm-1, 353 cm-1, and 213.7 cm-1 for GaAs, InP, GaP, and InAs. Moreover, the dynamic charges and high-frequency dielectric constants are predicted for III-V materials in both cubic (3C) and hexagonal (2H) crystal polytypes. It is found that the dielectric properties of InAs and InSb contrast markedly from those of other 2H III-V compounds. Furthermore, InAs and InSb evidence relative strong anisotropy in their dielectric constants and Born effective charges, whereas GaP evinces the higher Born effective charge anisotropy of 2H III-V compounds.

Comparison of response patterns in different survey designs: a longitudinal panel with mixed-mode and online-only design.

PubMed

Rübsamen, Nicole; Akmatov, Manas K; Castell, Stefanie; Karch, André; Mikolajczyk, Rafael T

2017-01-01

Increasing availability of the Internet allows using only online data collection for more epidemiological studies. We compare response patterns in a population-based health survey using two survey designs: mixed-mode (choice between paper-and-pencil and online questionnaires) and online-only design (without choice). We used data from a longitudinal panel, the Hygiene and Behaviour Infectious Diseases Study (HaBIDS), conducted in 2014/2015 in four regions in Lower Saxony, Germany. Individuals were recruited using address-based probability sampling. In two regions, individuals could choose between paper-and-pencil and online questionnaires. In the other two regions, individuals were offered online-only participation. We compared sociodemographic characteristics of respondents who filled in all panel questionnaires between the mixed-mode group (n = 1110) and the online-only group (n = 482). Using 134 items, we performed multinomial logistic regression to compare responses between survey designs in terms of type (missing, "do not know" or valid response) and ordinal regression to compare responses in terms of content. We applied the false discovery rates (FDR) to control for multiple testing and investigated effects of adjusting for sociodemographic characteristic. For validation of the differential response patterns between mixed-mode and online-only, we compared the response patterns between paper and online mode among the respondents in the mixed-mode group in one region (n = 786). Respondents in the online-only group were older than those in the mixed-mode group, but both groups did not differ regarding sex or education. Type of response did not differ between the online-only and the mixed-mode group. Survey design was associated with different content of response in 18 of the 134 investigated items; which decreased to 11 after adjusting for sociodemographic variables. In the validation within the mixed-mode, only two of those were among the 11 significantly different items. The probability of observing by chance the same two or more significant differences in this setting was 22%. We found similar response patterns in both survey designs with only few items being answered differently, likely attributable to chance. Our study supports the equivalence of the compared survey designs and suggests that, in the studied setting, using online-only design does not cause strong distortion of the results.

Ultrawide bandgap pentamode metamaterials with an asymmetric double-cone outside profile

NASA Astrophysics Data System (ADS)

Chu, Yangyang; Li, Yucheng; Cai, Chengxin; Liu, Guangshuan; Wang, Zhaohong; Xu, Zhuo

2018-03-01

The band-gap characteristic is an important feature of acoustic metamaterials, which has important theoretical and practical significance in acoustic devices. Pentamode metamaterials (PMs) with phonon band-gap characteristics based on an asymmetric double-cone outside profile are presented and studied in this paper. The phonon band structures of these PMs are calculated by using the finite element method. In addition to the single-mode band-gaps, the complete 3D band-gaps are also obtained by changing the outside profile of the double-cone. Moreover, by adjusting the outside profile and the diameter of the double-cone to reduce the symmetry of the structure, the complete 3D band-gap can be widened. Further parametric analysis is presented to investigate the effect of geometrical parameters on the phonon band-gap property, the numerical simulations show that the maximum relative bandwidth is expanded by 15.14 times through reducing the symmetry of the structure. This study provides a possible way for PMs to control elastic wave propagation in the field of depressing vibration and noise, acoustic filtering and acoustic cloaking.

Atomistic modeling of the low-frequency mechanical modes and Raman spectra of icosahedral virus capsids

NASA Astrophysics Data System (ADS)

Dykeman, Eric C.; Sankey, Otto F.

2010-02-01

We describe a technique for calculating the low-frequency mechanical modes and frequencies of a large symmetric biological molecule where the eigenvectors of the Hessian matrix are determined with full atomic detail. The method, which follows order N methods used in electronic structure theory, determines the subset of lowest-frequency modes while using group theory to reduce the complexity of the problem. We apply the method to three icosahedral viruses of various T numbers and sizes; the human viruses polio and hepatitis B, and the cowpea chlorotic mottle virus, a plant virus. From the normal-mode eigenvectors, we use a bond polarizability model to predict a low-frequency Raman scattering profile for the viruses. The full atomic detail in the displacement patterns combined with an empirical potential-energy model allows a comparison of the fully atomic normal modes with elastic network models and normal-mode analysis with only dihedral degrees of freedom. We find that coarse-graining normal-mode analysis (particularly the elastic network model) can predict the displacement patterns for the first few (˜10) low-frequency modes that are global and cooperative.

Extremely long nonradiative relaxation of photoexcited graphane is greatly accelerated by oxidation: time-domain ab initio study.

PubMed

Nelson, Tammie R; Prezhdo, Oleg V

2013-03-06

Graphane and its derivatives are stable and extremely thin, wide band gap semiconductors that promise to replace conventional semiconductors in electronics, catalysis, and energy applications, greatly reducing device size and power consumption. In order to be useful, band-gap excitations in these materials should be long lived and nonradiative energy losses to heat should be slow. We use state-of-the-art nonadiabatic molecular dynamics combined with time-dependent density functional theory in order to determine the nonradiative lifetime and radiative line width of the lowest energy singlet excitations in pure and oxidized graphanes. We predict that pure graphane has a very long nonradiative decay time, on the order of 100 ns, while epoxy- and hydroxy-graphanes lose electronic excitation energy to heat 10-20 times faster. The luminescence line width is 1.5 times larger in pristine graphane compared to its oxidized forms, and at room temperature, it is on the order of 50 meV. Hydroxylation lowers graphane's band gap, while epoxidation increases the gap. The nonradiative decay and luminescence line width of pure graphane are governed by electron coupling to the 1200 cm(-1) vibrational mode. In the oxidized forms of graphane, the electronic excitations couple to a broad range of vibrational modes, rationalizing the more rapid nonradiative decay in these systems. The slow electron-phonon energy losses in graphane compared to other graphene derivatives, such as carbon nanotubes and nanoribbons, indicate that graphanes are excellent candidates for semiconductor applications.

Compact nanomechanical plasmonic phase modulators [Ultracompact nano-mechanical plasmonic phase modulators

DOE PAGES

Dennis, B. S.; Haftel, M. I.; Czaplewski, D. A.; ...

2015-03-30

Highly confined optical energy in plasmonic devices is advancing miniaturization in photonics. However, for mode sizes approaching ≈10 nm, the energy increasingly shifts into the metal, raising losses and hindering active phase modulation. Here, we propose a nanoelectromechanical phase-modulation principle exploiting the extraordinarily strong dependence of the phase velocity of metal–insulator–metal gap plasmons on dynamically variable gap size. We experimentally demonstrate a 23-μm-long non-resonant modulator having a 1.5π rad range, with 1.7 dB excess loss at 780 nm. Analysis shows that by simultaneously decreasing the gap, length and width, an ultracompact-footprint π rad phase modulator can be realized. This ismore » achieved without incurring the extra loss expected for plasmons confined in a decreasing gap, because the increasing phase-modulation strength from a narrowing gap offsets rising propagation losses. Here, such small, high-density electrically controllable components may find applications in optical switch fabrics and reconfigurable plasmonic optics.« less

The band gap properties of the three-component semi-infinite plate-like LRPC by using PWE/FE method

NASA Astrophysics Data System (ADS)

Qian, Denghui; Wang, Jianchun

2018-06-01

This paper applies coupled plane wave expansion and finite element (PWE/FE) method to calculate the band structure of the proposed three-component semi-infinite plate-like locally resonant phononic crystal (LRPC). In order to verify the accuracy of the result, the band structure calculated by PWE/FE method is compared to that calculated by the traditional finite element (FE) method, and the frequency range of the band gap in the band structure is compared to that of the attenuation in the transmission power spectrum. Numerical results and further analysis demonstrate that a band gap is opened by the coupling between the dominant vibrations of the rubber layer and the matrix modes. In addition, the influences of the geometry parameters on the band gap are studied and understood with the help of the simple “base-spring-mass” model, the influence of the viscidity of rubber layer on the band gap is also investigated.

H-fractal seismic metamaterial with broadband low-frequency bandgaps

NASA Astrophysics Data System (ADS)

Du, Qiujiao; Zeng, Yi; Xu, Yang; Yang, Hongwu; Zeng, Zuoxun

2018-03-01

The application of metamaterial in civil engineering to achieve isolation of a building by controlling the propagation of seismic waves is a substantial challenge because seismic waves, a superposition of longitudinal and shear waves, are more complex than electromagnetic and acoustic waves. In this paper, we design a broadband seismic metamaterial based on H-shaped fractal pillars and report numerical simulation of band structures for seismic surface waves propagating. Comparative study on the band structures of H-fractal seismic metamaterials with different levels shows that a new level of fractal structure creates new band gap, widens the total band gaps and shifts the same band gap towards lower frequencies. Moreover, the vibration modes for H-fractal seismic metamaterials are computed and analyzed to clarify the mechanism of widening band gaps. A numerical investigation of seismic surface waves propagation on a 2D array of fractal unit cells on the surface of semi-infinite substrate is proposed to show the efficiency of earthquake shielding in multiple complete band gaps.

All-Phononic Digital Transistor on the Basis of Gap-Soliton Dynamics in an Anharmonic Oscillator Ladder.

PubMed

Malishava, Merab; Khomeriki, Ramaz

2015-09-04

A conceptual mechanism of amplification of phonons by phonons on the basis of a nonlinear band-gap transmission (supratransmission) phenomenon is presented. As an example, a system of weakly coupled chains of anharmonic oscillators is considered. One (source) chain is driven harmonically by a boundary with a frequency located in the upper band close to the band edge of the ladder system. Amplification happens when a second (gate) chain is driven by a small signal in the counterphase and with the same frequency as the first chain. If the total driving of both chains overcomes the band-gap transmission threshold, the large amplitude band-gap soliton emerges and the amplification scenario is realized. The mechanism is interpreted as the nonlinear superposition of evanescent and propagating nonlinear modes manifesting in a single or double soliton generation working in band-gap or bandpass regimes, respectively. The results could be straightforwardly generalized for all-optical or all-magnonic contexts and have all the promise of logic gate operations.

Experimental evidence of locally resonant sonic band gap in two-dimensional phononic stubbed plates

NASA Astrophysics Data System (ADS)

Oudich, Mourad; Senesi, Matteo; Assouar, M. Badreddine; Ruzenne, Massimo; Sun, Jia-Hong; Vincent, Brice; Hou, Zhilin; Wu, Tsung-Tsong

2011-10-01

We provide experimental evidence of the existence of a locally resonant sonic band gap in a two-dimensional stubbed plate. Structures consisting of a periodic arrangement of silicone rubber stubs deposited on a thin aluminium plate were fabricated and characterized. Brillouin spectroscopy analysis is carried out to determine the elastic constants of the used rubber. The constants are then implemented in an efficient finite-element model that predicts the band structure and transmission to identify the theoretical band gap. We measure a complete sonic band gap for the out-of-plane Lamb wave modes propagating in various samples fabricated with different stub heights. Frequency domain measurements of full wave field and transmission are performed through a scanning laser Doppler vibrometer. A complete band gap from 1.9 to 2.6 kHz is showed using a sample with 6-mm stub diameter, 5-mm thickness, and 1-cm structure periodicity. Very good agreement between numerical and experimental results is obtained.

All-Phononic Digital Transistor on the Basis of Gap-Soliton Dynamics in an Anharmonic Oscillator Ladder

NASA Astrophysics Data System (ADS)

Malishava, Merab; Khomeriki, Ramaz

2015-09-01

A conceptual mechanism of amplification of phonons by phonons on the basis of a nonlinear band-gap transmission (supratransmission) phenomenon is presented. As an example, a system of weakly coupled chains of anharmonic oscillators is considered. One (source) chain is driven harmonically by a boundary with a frequency located in the upper band close to the band edge of the ladder system. Amplification happens when a second (gate) chain is driven by a small signal in the counterphase and with the same frequency as the first chain. If the total driving of both chains overcomes the band-gap transmission threshold, the large amplitude band-gap soliton emerges and the amplification scenario is realized. The mechanism is interpreted as the nonlinear superposition of evanescent and propagating nonlinear modes manifesting in a single or double soliton generation working in band-gap or bandpass regimes, respectively. The results could be straightforwardly generalized for all-optical or all-magnonic contexts and have all the promise of logic gate operations.

Number Sense Made Simple Using Number Patterns

ERIC Educational Resources Information Center

Su, Hui Fang Huang; Marinas, Carol; Furner, Joseph

2011-01-01

This article highlights investigating intriguing number patterns utilising an emerging technology called the Square Tool. Mathematics teachers of grades K-12 will find the Square Tool useful in making connections and bridging the gap from the concrete to the abstract. Pattern recognition helps students discover various mathematical concepts. With…

SnO2 epitaxial films with varying thickness on c-sapphire: Structure evolution and optical band gap modulation

NASA Astrophysics Data System (ADS)

Zhang, Mi; Xu, Maji; Li, Mingkai; Zhang, Qingfeng; Lu, Yinmei; Chen, Jingwen; Li, Ming; Dai, Jiangnan; Chen, Changqing; He, Yunbin

2017-11-01

A series of a-plane SnO2 films with thickness between 2.5 nm and 1436 nm were grown epitaxially on c-sapphire by pulsed laser deposition (PLD), to allow a detailed probe into the structure evolution and optical band gap modulation of SnO2 with growing thickness. All films exhibit excellent out-of-plane ordering (lowest (200) rocking-curve half width ∼0.01°) with an orientation of SnO2(100) || Al2O3(0001), while three equivalent domains that are rotated by 120° with one another coexist in-plane with SnO2[010] || Al2O3 [11-20]. Initially the SnO2(100) film assumes a two-dimensional (2D) layer-by-layer growth mode with atomically smooth surface (minimum root-mean-square roughness of 0.183 nm), and endures compressive strain along both c and a axes as well as mild tensile strain along the b-axis. With increasing thickness, transition from the 2D to 3D island growth mode takes place, leading to formation of various defects to allow relief of the stress and thus relaxation of the film towards bulk SnO2. More interestingly, with increasing thickness from nm to μm, the SnO2 films present a non-monotonic V-shaped variation in the optical band gap energy. While the band gap of SnO2 films thinner than 6.1 nm increases rapidly with decreasing film thickness due to the quantum size effect, the band gap of thicker SnO2 films broadens almost linearly with increasing film thickness up to 374 nm, as a result of the strain effect. The present work sheds light on future design of SnO2 films with desired band gap for particular applications by thickness control and strain engineering.

Polarization rotation enhancement and scattering mechanisms in waveguide magnetophotonic crystals

NASA Astrophysics Data System (ADS)

Levy, Miguel; Li, Rong

2006-09-01

Intermodal coupling in photonic band gap optical channels in magnetic garnet films is found to leverage the nonreciprocal polarization rotation. Forward fundamental-mode to high-order mode backscattering yields the largest rotations. The underlying mechanism is traced to the dependence of the grating-coupling constant on the modal refractive index and profile of the propagating beam. Large changes in polarization near the band edges are observed in first and second orders. Extreme sensitivity to linear birefringence exists in second order.

Bandwidth Extension of an S-band, Fundamental-Mode Eight-Beam Klystron

DTIC Science & Technology

2006-04-01

Extension of an S - band , Fundamental-Mode Eight-Beam Klystron Khanh T. Nguyen Beam-Wave Research, Inc. Bethesda, MD 20814 Dean E. Pershing ATK Mission...of a five-cavity, approximately 18 cm downstream from the center of the broadband, high - power multiple-beam klystron (MBK) first gap - the logical...the circuit generates >550 kW across the band with a peak power of more than 600 kW at -3.27 Keywords: Multiple-beam klystron ; MBK; bandwidth GHz. The 1

Closing the Achievement Gap on ACT & SAT

ERIC Educational Resources Information Center

Anderson, David

2010-01-01

Research has focused on four groups of factors and the achievement gap: (1) student characteristics (high school GPA, attendance patterns, courses taken in high school, participation in extra-curricular activities, etc.); (2) family characteristics (family structure, in home, parents' level of education, mobility, etc.); (3) school-based…

Modal radiation patterns of baffled circular plates and membranes.

PubMed

Christiansen, Thomas Lehrmann; Hansen, Ole; Thomsen, Erik Vilain; Jensen, Jørgen Arendt

2014-05-01

The far field velocity potential and radiation pattern of baffled circular plates and membranes are found analytically using the full set of modal velocity profiles derived from the corresponding equation of motion. The derivation is valid for a plate or membrane subjected to an external excitation force, which is used as a sound receiver in any medium or as a sound transmitter in a gaseous medium. A general, concise expression is given for the radiation pattern of any mode of the membrane and the plate with arbitrary boundary conditions. Specific solutions are given for the four special cases of a plate with clamped, simply supported, and free edge boundary conditions as well as for the membrane. For all non-axisymmetric modes, the velocity potential along the axis of the radiator is found to be strictly zero. In the long wavelength limit, the radiation pattern of all axisymmetric modes approaches that of a monopole, while the non-axisymmetric modes exhibit multipole behavior. Numerical results are also given, demonstrating the implications of having non-axisymmetric excitation using both a point excitation with varying eccentricity and a homogeneous excitation acting on half of the circular radiator.

Endogenous electromagnetic fields in plant leaves: a new hypothesis for vascular pattern formation.

PubMed

Pietak, Alexis Mari

2011-06-01

Electromagnetic (EM) phenomena have long been implicated in biological development, but few detailed, practical mechanisms have been put forth to connect electromagnetism with morphogenetic processes. This work describes a new hypothesis for plant leaf veination, whereby an endogenous electric field forming as a result of a coherent Frohlich process, and corresponding to an EM resonant mode of the developing leaf structure, is capable of instigating leaf vascularisation. In order to test the feasibility of this hypothesis, a three-dimensional, EM finite-element model (FEM) of a leaf primordium was constructed to determine if suitable resonant modes were physically possible for geometric and physical parameters similar to those of developing leaf tissue. Using the FEM model, resonant EM modes with patterns of relevance to developing leaf vein modalities were detected. On account of the existence of shared geometric signatures in a leaf's vascular pattern and the electric field component of EM resonant modes supported by a developing leaf structure, further theoretical and experimental investigations are warranted. Significantly, this hypothesis is not limited to leaf vascular patterning, but may be applicable to a variety of morphogenetic phenomena in a number of living systems.

Investigation of scanning tunneling spectra on iron-based superconductor FeSe 0.5Te 0.5(in Chinese)

DOE PAGES

Du, Z. -Y.; Fang, D. -L.; Wang, Z. -Y.; ...

2015-05-05

FeSe 0.5Te 0.5 single crystals with superconducting critical temperature of 13.5 K are investigated by scanning tunneling microscopy/spectroscopy (STM/STS) measureflents in detail. STM image on the top surface shows an atomically resolved square lattice consisted by white and dark spots with a constant of about 3.73± 0.03 Å which is consistent with the lattice constant 3.78 Å. The Se and Te atoms with a height difference of about 0.35 Å are successfully identified since the sizes of the two kinds of atoms are different. The tunneling spectra show very large zero-bias conductance value and asymmetric coherent peaks in the superconductingmore » state. According to the positions of coherence peaks, we determine the superconducting gap 2Δ = 5.5 meV, and the reduced gap 2Δ/kBTc = 4.9 is larger than the value predicted by the weak-coupling BCS theory. The zero-bias conductance at 1.7 K only have a decrease of about 40% compared with the normal state conductance, which may originate from some scattering and broadening mechanism in the material. This broadening effect will also make the superconducting gap determined by the distance between the coherence peaks larger than the exact gap value. The asymmetric structure of the tunneling spectra near the superconducting gap is induced by the hump on the background. This hump appears at temperature more than twice the superconducting critical temperature. This kind of hump has also been observed in other iron pnictides and needs further investigation. A possible bosonic mode outside the coherence peak with a mode energy Ω of about 5.5 meV is observed in some tunneling spectra, and the ratio between the mode energy and superconducting transition temperature Ω/kBTc ≈ 4.7 is roughly consistent with the universal ratio 4.3 in iron-based superconductors. The high-energy background of the spectra beyond the superconducting gaps shows a V-shape feature. The slopes of the differential conductance spectra at high energy are very different in the areas of Te-atom cluster and Se-atom cluster, and the difference extends to the energy of more than 300 meV. The differential conductance mapping has very little information about the quasi-particle interference of the superconducting state, which may result from the other strong scattering mechanism in the sample.« less

Investigation of scanning tunneling spectra on iron-based superconductor FeSe 0.5Te 0.5 (in Chinese)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Z. -Y.; Fang, D. -L.; Wang, Z. -Y.

FeSe 0.5Te 0.5 single crystals with superconducting critical temperature of 13.5 K are investigated by scanning tunneling microscopy/spectroscopy (STM/STS) measureflents in detail. STM image on the top surface shows an atomically resolved square lattice consisted by white and dark spots with a constant of about 3.73± 0.03 Å which is consistent with the lattice constant 3.78 Å. The Se and Te atoms with a height difference of about 0.35 Å are successfully identified since the sizes of the two kinds of atoms are different. The tunneling spectra show very large zero-bias conductance value and asymmetric coherent peaks in the superconductingmore » state. According to the positions of coherence peaks, we determine the superconducting gap 2Δ = 5.5 meV, and the reduced gap 2Δ/kBTc = 4.9 is larger than the value predicted by the weak-coupling BCS theory. The zero-bias conductance at 1.7 K only have a decrease of about 40% compared with the normal state conductance, which may originate from some scattering and broadening mechanism in the material. This broadening effect will also make the superconducting gap determined by the distance between the coherence peaks larger than the exact gap value. The asymmetric structure of the tunneling spectra near the superconducting gap is induced by the hump on the background. This hump appears at temperature more than twice the superconducting critical temperature. This kind of hump has also been observed in other iron pnictides and needs further investigation. A possible bosonic mode outside the coherence peak with a mode energy Ω of about 5.5 meV is observed in some tunneling spectra, and the ratio between the mode energy and superconducting transition temperature Ω/kBTc ≈ 4.7 is roughly consistent with the universal ratio 4.3 in iron-based superconductors. The high-energy background of the spectra beyond the superconducting gaps shows a V-shape feature. The slopes of the differential conductance spectra at high energy are very different in the areas of Te-atom cluster and Se-atom cluster, and the difference extends to the energy of more than 300 meV. The differential conductance mapping has very little information about the quasi-particle interference of the superconducting state, which may result from the other strong scattering mechanism in the sample.« less

Sequence-based model of gap gene regulatory network.

PubMed

Kozlov, Konstantin; Gursky, Vitaly; Kulakovskiy, Ivan; Samsonova, Maria

2014-01-01

The detailed analysis of transcriptional regulation is crucially important for understanding biological processes. The gap gene network in Drosophila attracts large interest among researches studying mechanisms of transcriptional regulation. It implements the most upstream regulatory layer of the segmentation gene network. The knowledge of molecular mechanisms involved in gap gene regulation is far less complete than that of genetics of the system. Mathematical modeling goes beyond insights gained by genetics and molecular approaches. It allows us to reconstruct wild-type gene expression patterns in silico, infer underlying regulatory mechanism and prove its sufficiency. We developed a new model that provides a dynamical description of gap gene regulatory systems, using detailed DNA-based information, as well as spatial transcription factor concentration data at varying time points. We showed that this model correctly reproduces gap gene expression patterns in wild type embryos and is able to predict gap expression patterns in Kr mutants and four reporter constructs. We used four-fold cross validation test and fitting to random dataset to validate the model and proof its sufficiency in data description. The identifiability analysis showed that most model parameters are well identifiable. We reconstructed the gap gene network topology and studied the impact of individual transcription factor binding sites on the model output. We measured this impact by calculating the site regulatory weight as a normalized difference between the residual sum of squares error for the set of all annotated sites and for the set with the site of interest excluded. The reconstructed topology of the gap gene network is in agreement with previous modeling results and data from literature. We showed that 1) the regulatory weights of transcription factor binding sites show very weak correlation with their PWM score; 2) sites with low regulatory weight are important for the model output; 3) functional important sites are not exclusively located in cis-regulatory elements, but are rather dispersed through regulatory region. It is of importance that some of the sites with high functional impact in hb, Kr and kni regulatory regions coincide with strong sites annotated and verified in Dnase I footprint assays.

[Response of forest bird communities to forest gap in winter in southwestern China].

PubMed

Zhao, Dong-Dong; Wu, Ying-Huan; Lu, Zhou; Jiang, Guang-Wei; Zhou, Fang

2013-06-01

Although forest gap ecology is an important field of study, research remains limited. By plot setting and point counted observation, the response of birds to forest gaps in winter as well as bird distribution patterns in forest gaps and intact canopies were studied in a north tropical monsoon forest of southwestern China from November 2011 to February 2012 in the Fangcheng Golden Camellia National Nature Reserve, Guangxi. The regression equation of bird species diversity to habitat factor was Y1=0.611+0.002 X13+0.043 X2+0.002 X5-0.003 X8+0.006 X10+0.008 X1 and the regression equation of bird species dominance index to habitat factor was Y3=0.533+0.001 X13+0.019 X2+0.002 X3-0.017 X4+0.002 X1. There were 45 bird species (2 orders and 13 families) recorded in the forest gap, accounting for 84.9% of all birds (n=45), with an average of 9.6 species (range: 2-22). Thirty-nine bird species (5 orders and 14 families) were recorded in non-gap areas, accounting for 73.6% of all birds (n=39), with an average of 5.3 species (range: 1-12). These results suggested that gap size, arbor average height (10 m from gap margin), arbor quantity (10 m from gap margin), shrub quantity (10 m from gap margin), herbal average coverage (1 m from gap margin) and bare land ratio were the key forest gap factors that influenced bird diversities. On the whole, bird diversity in the forest gap was greater than in the intact canopy. Spatial distributions in the forest gaps were also observed in the bird community. Most birds foraged in the "middle" and "canopy" layers in the vertical stratification. In addition, "nearly from" and "close from" contained more birds in relation to horizontal stratification. Feeding niche differentiation was suggested as the main reason for these distribution patterns.

A small mode volume tunable microcavity: Development and characterization

NASA Astrophysics Data System (ADS)

Greuter, Lukas; Starosielec, Sebastian; Najer, Daniel; Ludwig, Arne; Duempelmann, Luc; Rohner, Dominik; Warburton, Richard J.

2014-09-01

We report the realization of a spatially and spectrally tunable air-gap Fabry-Pérot type microcavity of high finesse and cubic-wavelength-scale mode volume. These properties are attractive in the fields of opto-mechanics, quantum sensing, and foremost cavity quantum electrodynamics. The major design feature is a miniaturized concave mirror with atomically smooth surface and radius of curvature as low as 10 μm produced by CO2 laser ablation of fused silica. We demonstrate excellent mode-matching of a focussed laser beam to the microcavity mode and confirm from the frequencies of the resonator modes that the effective optical radius matches the physical radius. With these small radii, we demonstrate wavelength-size beam waists. We also show that the microcavity is sufficiently rigid for practical applications: in a cryostat at 4 K, the root-mean-square microcavity length fluctuations are below 5 pm.

Polarization beam splitter based on a photonic crystal heterostructure.

PubMed

Schonbrun, E; Wu, Q; Park, W; Yamashita, T; Summers, C J

2006-11-01

The design and characterization of a photonic crystal (PC) polarization beam splitter (PBS) that operates with an extinction ratio of greater than 15 dB for both polarizations are presented. The PBS is fabricated on a silicon-on-insulator (SOI) wafer where the input and output ports consist of 5 mum wide ridge waveguides. A large spectral shift is observed in the dispersion plots of the lowest-order even (TE-like) and odd (TM-like) modes due to the SOI confinement. Because of this shift, the TE-like mode is close to a directional gap at the top of the band, and the TM-like mode is in a low-frequency regime where the dispersion surface is almost isotropic. We show that the TE-like mode has very high reflection at the interface between the two PCs, whereas the TM-like mode exhibits a very high transmission.

Nonsymmorphic symmetry-protected topological modes in plasmonic nanoribbon lattices

NASA Astrophysics Data System (ADS)

Zhang, Yong-Liang; Wu, Raymond P. H.; Kumar, Anshuman; Si, Tieyan; Fung, Kin Hung

2018-04-01

Using a dynamic eigenresponse theory, we study the topological edge plasmon modes in dispersive plasmonic lattices constructed by unit cells of multiple nanoribbons. In dipole approximation, the bulk-edge correspondence in the lattices made of dimerized unit cell and one of its square-root daughter with nonsymmorphic symmetry are demonstrated. Calculations with consideration of dynamic long-range effects and retardation are compared to those given by nearest-neighbor approximations. It is shown that nonsymmorphic symmetry opens up two symmetric gaps where versatile topological edge plasmon modes are found. Unprecedented spectral shifts of the edge states with respect to the zero modes due to long-range coupling are found. The proposed ribbon structure is favorable to electrical gating and thus could serve as an on-chip platform for electrically controllable subwavelength edge states at optical wavelengths. Our eigenresponse approach provides a powerful tool for the radiative topological mode analysis in strongly coupled plasmonic lattices.

The role of ion irradiation in activating silent Raman modes via tuning in plasmonic behaviour and surface disorder of Au/ZnO/Pt NFG system

NASA Astrophysics Data System (ADS)

Singh, Udai B.; Gautam, Subodh K.; Kumar, Sunil; Ojha, Sunil; Ghosh, Santanu; Singh, Fouran

2017-09-01

The perceptible progression of Raman modes of zinc oxide (ZnO) is studied in nanostructures film gap (Au (10 nm)/ZnO (70 nm)/Pt (50 nm)) system with 1.2 MeV Xe ion irradiation. Unattainable silent Raman modes of ZnO turn out to be strongly visible after ion irradiation. The creation of ion-beam-induced lattice disorder, defects, and impurities in a ZnO layer leads to breakdown the translational crystal symmetry that results in the origin of silent modes. The formation of hot-spots in the ZnO layer of the NFG system also supports the enhancement of the intensity of Raman modes. Overall results are attributed to combined effects of lattice disorder, defects, and impurities along with plasmonic effect and explained in the framework of elastic-thermal-spike formation.

Magneto-optical microcavity with Au plasmonic layer

NASA Astrophysics Data System (ADS)

Mikhailova, T. V.; Lyashko, S. D.; Tomilin, S. V.; Karavainikov, A. V.; Prokopov, A. R.; Shaposhnikov, A. N.; Berzhansky, V. N.

2017-11-01

Optical and Faraday rotation spectra of magneto-optical microcavity coated with Au plasmonic layer of gradient thickness were investigated theoretically and experimentally. It was shown that the Tamm plasmon-polaritons mode forms near the long-wavelength edge of photonic band gap. The presence of Au coating of thickness of 90.4 nm increase the Faraday rotation at Tamm plasmon-polaritons and cavity resonances in 1.3 and 7 times, respectively. By transfer matrix method it were found that the incorporation of SiO2 buffer layer with a thickness in the range from 155 to 180 nm between microcavity and Au coating leads to the strong coupling between cavity mode and Tamm plasmon-polaritons. In this case, one or two resonances arise in the vicinity of the cavity mode depending on the thickness of plasmonic layer. The Faraday rotation for coupled mode in twice less than the value of rotation for single cavity mode.

Band transition and topological interface modes in 1D elastic phononic crystals.

PubMed

Yin, Jianfei; Ruzzene, Massimo; Wen, Jihong; Yu, Dianlong; Cai, Li; Yue, Linfeng

2018-05-01

In this report, we design a one-dimensional elastic phononic crystal (PC) comprised of an Aluminum beam with periodically arranged cross-sections to study the inversion of bulk bands due to the change of topological phases. As the geometric parameters of the unit cell varies, the second bulk band closes and reopens forming a topological transition point. This phenomenon is confirmed for both longitudinal waves and bending waves. By constructing a structural system formed by two PCs with different topological phases, for the first time, we experimentally demonstrate the existence of interface mode within the bulk band gap as a result of topological transition for both longitudinal and bending modes in elastic systems, although for bending modes, additional conditions have to be met in order to have the interface mode due to the dispersive nature of the bending waves in uniform media compared to the longitudinal waves.

Interannual variability of the frontal activity in the Southern Hemisphere: relationship with atmospheric circulation and precipitation over southern South America

NASA Astrophysics Data System (ADS)

Blázquez, Josefina; Solman, Silvina A.

2017-04-01

The interannual variability of the frontal activity over the western Southern Hemisphere and its linkage with the variability of the atmospheric circulation and precipitation over southern South America is studied. The analysis is focused on the austral winter and spring seasons. The frontal activity is represented by an index defined as the product between the horizontal gradient of temperature and the relative vorticity at 850 hPa (FI) and is computed from the ERA Interim and NCEP2 reanalysis. For the two seasons the main mode of variability of FI, as depicted by the first Empirical Orthogonal Function, presents centres of action located in the southern part of the western Southern Hemisphere. This pattern is present in the two reanalysis datasets. The correlation coefficients between the principal component of the leading mode of FI and the two main modes of the 500 hPa geopotential height indicate that both the ENSO-mode and the SAM modulate the leading pattern of FI in winter while during the spring season the ENSO-mode controls the FI variability. The variability of the FI has a robust influence on the interannual variability of precipitation over southern South America and adjacent oceans. Over the continent, it was found that the pattern of precipitation anomalies associated with the variability of the FI depicts significant signals over southeastern South America (SESA), centre and south of Chile for winter and over SESA and southeastern Brazil for spring and agrees with the pattern of the leading mode of precipitation variability over southern South America.

Growth Patterns and E-Moderating Supports in Asynchronous Online Discussions in an Undergraduate Blended Course

ERIC Educational Resources Information Center

Ghadirian, Hajar; Ayub, Ahmad Fauzi Mohd; Bakar, Kamariah Binti Abu; Hassanzadeh, Maryam

2016-01-01

This study presents a case study of asynchronous online discussions' (AOD) growth patterns in an undergraduate blended course to address the gap in our current understanding of how threads are developed in peer-moderated AODs. Building on a taxonomy of thread pattern proposed by Chan, Hew and Cheung (2009), growth patterns of thirty-six forums…

Opening complete band gaps in two dimensional locally resonant phononic crystals

NASA Astrophysics Data System (ADS)

Zhou, Xiaoling; Wang, Longqi

2018-05-01

Locally resonant phononic crystals (LRPCs) which have low frequency band gaps attract a growing attention in both scientific and engineering field recently. Wide complete locally resonant band gaps are the goal for researchers. In this paper, complete band gaps are achieved by carefully designing the geometrical properties of the inclusions in two dimensional LRPCs. The band structures and mechanisms of different types of models are investigated by the finite element method. The translational vibration patterns in both the in-plane and out-of-plane directions contribute to the full band gaps. The frequency response of the finite periodic structures demonstrate the attenuation effects in the complete band gaps. Moreover, it is found that the complete band gaps can be further widened and lowered by increasing the height of the inclusions. The tunable properties by changing the geometrical parameters provide a good way to open wide locally resonant band gaps.

Photonic band gap in isotropic hyperuniform disordered solids with low dielectric contrast.

PubMed

Man, Weining; Florescu, Marian; Matsuyama, Kazue; Yadak, Polin; Nahal, Geev; Hashemizad, Seyed; Williamson, Eric; Steinhardt, Paul; Torquato, Salvatore; Chaikin, Paul

2013-08-26

We report the first experimental demonstration of a TE-polarization photonic band gap (PBG) in a 2D isotropic hyperuniform disordered solid (HUDS) made of dielectric media with a dielectric index contrast of 1.6:1, very low for PBG formation. The solid is composed of a connected network of dielectric walls enclosing air-filled cells. Direct comparison with photonic crystals and quasicrystals permitted us to investigate band-gap properties as a function of increasing rotational isotropy. We present results from numerical simulations proving that the PBG observed experimentally for HUDS at low index contrast has zero density of states. The PBG is associated with the energy difference between complementary resonant modes above and below the gap, with the field predominantly concentrated in the air or in the dielectric. The intrinsic isotropy of HUDS may offer unprecedented flexibilities and freedom in applications (i. e. defect architecture design) not limited by crystalline symmetries.

Thermal tuning on band gaps of 2D phononic crystals considering adhesive layers

NASA Astrophysics Data System (ADS)

Zhou, Xiaoliang; Chen, Jialin; Li, Yuhang; Sun, Yuxin; Xing, Yufeng

2018-02-01

Phononic crystals are very attractive in many applications, such as noise reduction, filters and vibration isolation, due to their special forbidden band gap structures. In the present paper, the investigation of tunable band gaps of 2D phononic crystals with adhesive layers based on thermal changing is conducted. Based on the lumped-mass method, an analytical model of 2D phononic crystals with relatively thin adhesive layers is established, in which the in-plane and out-of-plane modes are both in consideration. The adhesive material is sensitive to temperature so that the band structure can be tuned and controlled by temperature variation. As temperature increases from 20 °C-80 °C, the first band gap shifts to the frequency zone around 10 kHz, which is included by the audible frequency range. The results propose an important guideline for applications, such as noise suppression using the 2D phononic crystals.

Impact of sodium chloride on the expansion of a liquid-liquid miscibility gap in an API/water system. Case study of Brivaracetam.

PubMed

Couvrat, Nicolas; Mahieux, Julien; Fours, Baptiste; Cartigny, Yohann; Schenkel, Eric; Aerts, Luc; Quéré, Luc; Coquerel, Gérard

2016-12-30

Brivaracetam, or (2S)-2-[(4R)-2-oxo-4-propyl-pyrrolidin-1-yl] butanamide, is an active pharmaceutical ingredient designed for the treatment of epilepsy. During the development of the IV administration mode, a liquid-liquid miscibility gap has been observed with pure water, isotonic and hypertonic solutions (vehicle at 0.9% w/w and 5%w/w NaCl respectively). The study reveals that the NaCl concentration has a direct impact on the extent of the demixing domain; from a sub-micronic demixing in pure water towards a macroscopic miscibility gap in hypertonic aqueous solutions. The thorough exploration of these heterogeneous equilibria led to define experimental parameters for safe IV injections without risk of liquid - liquid miscibility gap at 37°C. Copyright © 2016 Elsevier B.V. All rights reserved.

Reducing support loss in micromechanical ring resonators using phononic band-gap structures

NASA Astrophysics Data System (ADS)

Hsu, Feng-Chia; Hsu, Jin-Chen; Huang, Tsun-Che; Wang, Chin-Hung; Chang, Pin

2011-09-01

In micromechanical resonators, energy loss via supports into the substrates may lead to a low quality factor. To eliminate the support loss, in this paper a phononic band-gap structure is employed. We demonstrate a design of phononic-crystal (PC) strips used to support extensional wine-glass mode ring resonators to increase the quality factor. The PC strips are introduced to stop elastic-wave propagation by the band-gap and deaf-band effects. Analyses of resonant characteristics of the ring resonators and the dispersion relations, eigenmodes, and transmission properties of the PC strips are presented. With the proposed resonator architecture, the finite-element simulations show that the leaky power is effectively reduced and the stored energy inside the resonators is enhanced simultaneously as the operating frequencies of the resonators are within the band gap or deaf bands. Realization of a high quality factor micromechanical ring resonator with minimized support loss is expected.

Simultaneous localization of photons and phonons in defect-free dodecagonal phoxonic quasicrystals

NASA Astrophysics Data System (ADS)

Xu, Bihang; Wang, Zhong; Tan, Yixiang; Yu, Tianbao

2018-03-01

In dodecagonal phoxonic quasicrytals (PhXQCs) with a very high rotational symmetry, we demonstrate numerically large phoxonic band gaps (PhXBGs, the coexistence of photonic and phononic band gaps). By computing the existence and dependence of PhXBGs on the choice of radius of holes, we find that PhXQCs can possess simultaneous photonic and phononic band gaps over a rather wide range of geometric parameters. Furthermore, localized modes of THz photons and tens of MHz phonons may exist inside and outside band gaps in defect-free PhXQCs. The electromagnetic and elastic field can be confined simultaneously around the quasicrytals center and decay in a length scale of several basic cells. As a kind of quasiperiodic structures, 12-fold PhXQCs provide a good candidate for simultaneously tailoring electromagnetic and elastic waves. Moreover, these structures exhibit some interesting characteristics due to the very high symmetry.

Express saccades in distinct populations: east, west, and in-between.

PubMed

Knox, Paul C; Wolohan, Felicity D A; Helmy, Mai S

2017-12-01

Express saccades are low latency (80-130 ms), visually guided saccades. While their occurrence is encouraged by the use of gap tasks (the fixation target is extinguished 200 ms prior to the saccade target appearing) and suppressed by the use of overlap tasks (the fixation target remains present when the saccade target appears), there are some healthy, adult participants, "express saccade makers" (ESMs), who persist in generating high proportions (> 30%) of express saccades in overlap conditions. These participants are encountered much more frequently in Chinese participant groups than amongst the Caucasian participants tested to date. What is not known is whether this high number of ESMs is only a feature of Chinese participant groups. More broadly, there are few comparative studies of saccade behaviour across large participant groups drawn from different populations. We, therefore, tested an independent group of 70 healthy adult Egyptian participants, using the same equipment and procedures as employed in the previous studies. Each participant was exposed to two blocks of 200 gap, and two blocks of 200 overlap trials, with block order counterbalanced. Results from the Schwartz Value Survey were used to confirm that this group of participants was culturally distinct from the Chinese and Caucasian (white British) groups tested previously. Fourteen percent (10/70) of this new group were ESMs, and the pattern of latency distribution in these ESMs was identical to that identified in the other participant groups, with a prominent peak in the express latency range in overlap conditions. Overall, we identified three modes in the distribution of saccade latency in overlap conditions, the timing of which (express peak at 110 ms, subsequent peaks at 160 and 210 ms) were strikingly consistent with our previous observations. That these behavioural patterns of saccade latency are observed consistently in large participant groups, drawn from geographically, ethnically, and culturally distinct populations, suggests that they relate to the underlying architecture of the saccade system.

Age Differences and Dimensions of Religious Behavior

ERIC Educational Resources Information Center

Johnson, Arthur L.; And Others

1974-01-01

This research explores the magnitude, sources, and consequences of differences among age strata in various dimensions of religious orientation and practice. Analysis of a national sample of 4444 Lutheran church members, ages 16-65, revealed patterns of age strata differences that supported a "selective gap" theory rather than a "great gap"…

Pollination Mode and Mating System Explain Patterns in Genetic Differentiation in Neotropical Plants

PubMed Central

Ballesteros-Mejia, Liliana; Lima, Natácia E.; Lima-Ribeiro, Matheus S.

2016-01-01

We studied genetic diversity and differentiation patterns in Neotropical plants to address effects of life history traits (LHT) and ecological attributes based on an exhaustive literature survey. We used generalized linear mixed models (GLMMs) to test the effects as fixed and random factors of growth form, pollination and dispersal modes, mating and breeding systems, geographical range and habitat on patterns of genetic diversity (HS, HeS, π and h), inbreeding coefficient (FIS), allelic richness (AR) and differentiation among populations (FST) for both nuclear and chloroplast genomes. In addition, we used phylogenetic generalized least squares (pGLS) to account for phylogenetic independence on predictor variables and verify the robustness of the results from significant GLMMs. In general, GLMM revealed more significant relationships among LHTs and genetic patterns than pGLS. After accounting for phylogenetic independence (i.e., using pGLS), FST for nuclear microsatellites was significantly related to pollination mode, mating system and habitat. Plants specifically with outcrossing mating system had lower FST. Moreover, AR was significantly related to pollination mode and geographical range and HeS for nuclear dominant markers was significantly related to habitat. Our findings showed that different results might be retrieved when phylogenetic non-independence is taken into account and that LHTs and ecological attributes affect substantially the genetic pattern in Neotropical plants, hence may drive key evolutionary processes in plants. PMID:27472384