Explosive Joining for Nuclear-Reactor Repair

NASA Technical Reports Server (NTRS)

Bement, L. J.; Bailey, J. W.

1983-01-01

In explosive joining technique, adapter flange from fuel channel machined to incorporate a V-notch interface. Ribbon explosive, 1/2 inch (1.3 cm) in width, drives V-notched wall of adapter into bellows assembly, producing atomic-level metallurgical bond. Ribbon charge yields joint with double parent metal strength.

Electron Transport in Multi-Terminal Graphene Nanodevice with Inclined Cross Structures

NASA Astrophysics Data System (ADS)

Ye, En-Jia; Shi, Yi-Jian; Zhao, Xuean

2014-12-01

The DC and AC transport properties are investigated in multi-terminal graphene nanoribbon (GNR) devices. The devices are composed of three or four graphene ribbons connected with different angles. It is found that DC and AC conductances depend on the structural configurations and ribbon properties. In the vicinity of Dirac point, the intersection of graphene ribbons forms band mixing and results in resonant or anti-resonant states. The edge and width, as well as, the angles of the graphene ribbons influence the DC and AC transport properties drastically. These properties can be used to build future graphene-based nanoelectronics.

Low Angle Silicon Sheet Growth. Large Area Silicon Sheet Task Low Cost Solar Array Project

NASA Technical Reports Server (NTRS)

1982-01-01

The results of a program to demonstrate the feasibility of a low angle silicon ribbon growth process are described. Twenty-six experimental runs were performed. Ribbons were grown at pull rates from 5 to 68 cm/min. Ribbon lengths up to 74 cm were grown while widths varied from 5 to 25 mm. Thicknesses varied from 0.6 to 2.5 mm, with typical values of about 1 mm.

Width-Tuned Magnetic Order Oscillation on Zigzag Edges of Honeycomb Nanoribbons.

PubMed

Chen, Wen-Chao; Zhou, Yuan; Yu, Shun-Li; Yin, Wei-Guo; Gong, Chang-De

2017-07-12

Quantum confinement and interference often generate exotic properties in nanostructures. One recent highlight is the experimental indication of a magnetic phase transition in zigzag-edged graphene nanoribbons at the critical ribbon width of about 7 nm [ Magda , G. Z. et al. Nature 2014 , 514 , 608 ]. Here we show theoretically that with further increase in the ribbon width, the magnetic correlation of the two edges can exhibit an intriguing oscillatory behavior between antiferromagnetic and ferromagnetic, driven by acquiring the positive coherence between the two edges to lower the free energy. The oscillation effect is readily tunable in applied magnetic fields. These novel properties suggest new experimental manifestation of the edge magnetic orders in graphene nanoribbons and enhance the hopes of graphene-like spintronic nanodevices functioning at room temperature.

Large area silicon sheet by EFG

NASA Technical Reports Server (NTRS)

1981-01-01

A multiple growth run with three 10 cm cartridges was carried out with the best throughput rates and time percentage of simultaneous three ribbon growth achieved to date in this system. Growth speeds were between 3.2 and 3.6 cm/minute on all three cartridges and simultaneous full width growth of three ribbons was achieved 47 percent of the time over the eight hour duration of the experiment. Improvements in instrumentation and in the main zone temperature uniformity were two factors that have led to more reproducible growth conditions in the multiple ribbon furnace.

Width-Tuned Magnetic Order Oscillation on Zigzag Edges of Honeycomb Nanoribbons

DOE PAGES

Chen, Wen-Chao; Zhou, Yuan; Yu, Shun-Li; ...

2017-06-24

Quantum confinement and interference often generate exotic properties in nanostructures. One recent highlight is the experimental indication of a magnetic phase transition in zigzag-edged graphene nanoribbons at the critical ribbon width of about 7 nm [Magda, G. Z. et al. Nature 2014, 514, 608]. Here in this work, we show theoretically that with further increase in the ribbon width, the magnetic correlation of the two edges can exhibit an intriguing oscillatory behavior between antiferromagnetic and ferromagnetic, driven by acquiring the positive coherence between the two edges to lower the free energy. The oscillation effect is readily tunable in applied magneticmore » fields. In conclusion, these novel properties suggest new experimental manifestation of the edge magnetic orders in graphene nanoribbons and enhance the hopes of graphene-like spintronic nanodevices functioning at room temperature.« less

Helical tape forming device

NASA Technical Reports Server (NTRS)

Bush, J. E.; Cole, P. T.

1969-01-01

Using a device that is not limited to a minimum thickness or width-to-thickness ratio, a very thin metal tape or ribbon is formed into a continuous flat wound helical coil. The device imparts the desired circular shape by squeeze rolling it with an unequal force across its width.

Tuning conductivity in boron nanowire by edge geometry

NASA Astrophysics Data System (ADS)

Bhuyan, Prabal Dev; Gupta, Sanjeev K.; Sonvane, Yogesh; Gajjar, P. N.

2018-04-01

In present study, we have investigated electronic and temperature dependent transport properties of carbyne like linear chain and ribbon like zigzag structures of Boron (B) nanowire. The linear chain structure showed higher electric and thermal conductivity, as it is sp-hybridized, than its counterpart ribbon (R) structure. However the conductivity of ribbon structure increases with increases in width due to edge geometry effect. The ribbon (3R) structure showed high electric and thermal conductivity of 8.0×1019 1/Ω m s and 0.59×1015 W/ m K respectively. Interestingly we have observed that B linear chain showed higher thermal conductivity of 0.23×1015 W/ m K than its ribbon R and 2R structure above 600K. Because of high Seebeck co-efficient of boron chain and ribbon (R) structures at low temperature, they could find applications in thermoelectric sensors. Our results show that tuning conductivity property of boron nanowire could be of great interest in research for future electric connector in nanodevices.

Investigation of structural and magnetic properties of rapidly-solidified iron-silicon alloys at ambient and elevated temperatures

DOE PAGES

Jayaraman, T. V.; Meka, V. M.; Jiang, X.; ...

2018-01-09

Here we investigated the ambient temperature structural properties (thickness, width, microstructure, and lattice parameter), and the ambient and high temperature (up to 900 K) direct current (DC) magnetic properties—saturation magnetization (M S) and intrinsic coercivity (H CI)—of rapidly-solidified (melt-spun) Fe-x wt.% Si (x = 3, 5, & 8) alloys. The wheel surface speeds selected for the study were 30 m/s and 40 m/s. The ribbons produced at the lower wheel surface speed (30 m/s) were continuous having relatively uniform edges compared to the ribbons produced at the higher wheel surface speed. The thickness and the width of the melt-spun ribbonsmore » ranged between ~15 and 60 μm and 500–800 μm, respectively. The x-ray diffraction spectra of the melt-spun ribbons indicated the presence of disordered α-phase, irrespective of the composition, and the wheel surface speed. The lattice parameter decreased gradually as a function of increasing silicon content from ~0.2862 nm (Fe-3 wt.% Si) to ~0.2847 nm (Fe-8 wt.% Si). The wheel surface speed showed an insignificant effect on M S while increased silicon content resulted in a decreasing trend in M S. Elevated temperature evaluation of the magnetization (M-T curves at ~7.96 kA/m) in the case of Fe-3 & 5 wt.% Si alloy ribbons was distinctly different from that of the Fe-8 wt.% Si alloy ribbons. The curves of the as-prepared Fe-3 wt.% Si and Fe-5 wt.% Si alloy ribbons were irreversible while that of Fe-8 wt.% Si was reversible. The M S for any of the combinations of wheel surface speed and composition decreased monotonically with the increase in temperature (from 300 to 900 K). While H CI increased with the increase in temperature for all the wheel surface speed and composition combination, its nature of increase is distinct for Fe-8 wt.% Si alloy ribbons compared to Fe-3 & 5 wt.% Si alloys ribbons. Finally, it appears that rapidly-solidified Fe-3 wt.% Si and Fe-5 wt.% Si alloys ribbons are primarily comprised of the α phase (disordered phase) while the Fe-8 wt.% Si alloy ribbons are comprised primarily of disordered phase along with minor constituents of an ordered phase.« less

Investigation of structural and magnetic properties of rapidly-solidified iron-silicon alloys at ambient and elevated temperatures

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

Jayaraman, T. V.; Meka, V. M.; Jiang, X.

Here we investigated the ambient temperature structural properties (thickness, width, microstructure, and lattice parameter), and the ambient and high temperature (up to 900 K) direct current (DC) magnetic properties—saturation magnetization (M S) and intrinsic coercivity (H CI)—of rapidly-solidified (melt-spun) Fe-x wt.% Si (x = 3, 5, & 8) alloys. The wheel surface speeds selected for the study were 30 m/s and 40 m/s. The ribbons produced at the lower wheel surface speed (30 m/s) were continuous having relatively uniform edges compared to the ribbons produced at the higher wheel surface speed. The thickness and the width of the melt-spun ribbonsmore » ranged between ~15 and 60 μm and 500–800 μm, respectively. The x-ray diffraction spectra of the melt-spun ribbons indicated the presence of disordered α-phase, irrespective of the composition, and the wheel surface speed. The lattice parameter decreased gradually as a function of increasing silicon content from ~0.2862 nm (Fe-3 wt.% Si) to ~0.2847 nm (Fe-8 wt.% Si). The wheel surface speed showed an insignificant effect on M S while increased silicon content resulted in a decreasing trend in M S. Elevated temperature evaluation of the magnetization (M-T curves at ~7.96 kA/m) in the case of Fe-3 & 5 wt.% Si alloy ribbons was distinctly different from that of the Fe-8 wt.% Si alloy ribbons. The curves of the as-prepared Fe-3 wt.% Si and Fe-5 wt.% Si alloy ribbons were irreversible while that of Fe-8 wt.% Si was reversible. The M S for any of the combinations of wheel surface speed and composition decreased monotonically with the increase in temperature (from 300 to 900 K). While H CI increased with the increase in temperature for all the wheel surface speed and composition combination, its nature of increase is distinct for Fe-8 wt.% Si alloy ribbons compared to Fe-3 & 5 wt.% Si alloys ribbons. Finally, it appears that rapidly-solidified Fe-3 wt.% Si and Fe-5 wt.% Si alloys ribbons are primarily comprised of the α phase (disordered phase) while the Fe-8 wt.% Si alloy ribbons are comprised primarily of disordered phase along with minor constituents of an ordered phase.« less

Cabling design for phased arrays

NASA Technical Reports Server (NTRS)

Kruger, I. D.; Turkiewicz, L.

1972-01-01

The ribbon-cabling system used for the AEGIS phased array which provides minimum cable bulk, complete EMI shielding, rugged mechanical design, repeatable electrical characteristics, and ease of assembly and maintenance is described. The ribbon cables are 0.040-inch thick, and in widths up to 2 1/2 inches. Their terminations are molded connectors that can be grouped in a three-tier arrangement, with cable branching accomplished by a matrix-welding technique.

Synthesis and Evaluation of Polymeric Materials

DTIC Science & Technology

1993-07-01

Twin Screw Extruder Using a Blown Film Die ..................... 5 I 3. Twin Screw Extruder Using a Vertical...be done.6 They are then fed into a Twin Screw Mixer (T’SM) Extrusion Unit with either a blown film or ribbon die attached. The use of the ribbon die...width with a 0.020 inch gap)(See Figure 1). The extrusion system contained three (3) heated zones located on the twin screw barrel area

Large area silicon sheet by EFG

NASA Technical Reports Server (NTRS)

Kalejs, J. P.

1982-01-01

Work carried out on the JPL Flat Plate Solar Array Project, for the purpose of developing a method for silicon ribbon production by Edge-defined Film-fed Growth (EEG) for use as low-cost substrate material in terrestrial solar cell manufacture, is described. A multiple ribbon furnace unit that is designed to operate on a continuous basis for periods of at least one week, with melt replenishment and automatic ribbon width control, and to produce silicon sheet at a rate of one square meter per hour, was constructed. Program milestones set for single ribbon furnace operation to demonstrate basic EEG system capabilities with respect to growth speed, thickness and cell performance were achieved for 10 cm wide ribbon: steady-state growth at 4 cm/min and 200 micron thickness over periods of an hour and longer was made routine, and a small area cell efficiency of 13+% demonstrated. Large area cells of average efficiency of 10 to 11%, with peak values of 11 to 12% were also achieved. The integration of these individual performance levels into multiple ribbon furnace operation was not accomplished.

Non-Hookean statistical mechanics of clamped graphene ribbons

NASA Astrophysics Data System (ADS)

Bowick, Mark J.; Košmrlj, Andrej; Nelson, David R.; Sknepnek, Rastko

2017-03-01

Thermally fluctuating sheets and ribbons provide an intriguing forum in which to investigate strong violations of Hooke's Law: Large distance elastic parameters are in fact not constant but instead depend on the macroscopic dimensions. Inspired by recent experiments on free-standing graphene cantilevers, we combine the statistical mechanics of thin elastic plates and large-scale numerical simulations to investigate the thermal renormalization of the bending rigidity of graphene ribbons clamped at one end. For ribbons of dimensions W ×L (with L ≥W ), the macroscopic bending rigidity κR determined from cantilever deformations is independent of the width when W <ℓth , where ℓth is a thermal length scale, as expected. When W >ℓth , however, this thermally renormalized bending rigidity begins to systematically increase, in agreement with the scaling theory, although in our simulations we were not quite able to reach the system sizes necessary to determine the fully developed power law dependence on W . When the ribbon length L >ℓp , where ℓp is the W -dependent thermally renormalized ribbon persistence length, we observe a scaling collapse and the beginnings of large scale random walk behavior.

Top-down fabrication of sub-nanometre semiconducting nanoribbons derived from molybdenum disulfide sheets.

PubMed

Liu, Xiaofei; Xu, Tao; Wu, Xing; Zhang, Zhuhua; Yu, Jin; Qiu, Hao; Hong, Jin-Hua; Jin, Chuan-Hong; Li, Ji-Xue; Wang, Xin-Ran; Sun, Li-Tao; Guo, Wanlin

2013-01-01

Developments in semiconductor technology are propelling the dimensions of devices down to 10 nm, but facing great challenges in manufacture at the sub-10 nm scale. Nanotechnology can fabricate nanoribbons from two-dimensional atomic crystals, such as graphene, with widths below the 10 nm threshold, but their geometries and properties have been hard to control at this scale. Here we find that robust ultrafine molybdenum-sulfide ribbons with a uniform width of 0.35 nm can be widely formed between holes created in a MoS2 sheet under electron irradiation. In situ high-resolution transmission electron microscope characterization, combined with first-principles calculations, identifies the sub-1 nm ribbon as a Mo5S4 crystal derived from MoS2, through a spontaneous phase transition. Further first-principles investigations show that the Mo5S4 ribbon has a band gap of 0.77 eV, a Young's modulus of 300GPa and can demonstrate 9% tensile strain before fracture. The results show a novel top-down route for controllable fabrication of functional building blocks for sub-nanometre electronics.

Melt Spinning of Intermetallic Alloys: Heat Transfer and Microstructure

DTIC Science & Technology

1992-04-21

newly emerging mdLerials such as titanium aluminides and other intermetallic alloys[4,5]. These materials must possess good mechanical and corrosion...alloys such as titanium aluminides with the surrounding atmosphere, it utilizes a tilting water-cooled copper hearth and the apparatus is in a 5 psi Argon... titanium aluminide in the form of filament or ribbon break olf into short segments. The solidified ribbons have lengths of 5 - 15 mm, widths of 0.5

Investigation of structural and magnetic properties of rapidly-solidified iron-silicon alloys at ambient and elevated temperatures

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

Jayaraman, T. V.; Meka, V. M.; Jiang, X.

In this work, we investigated the ambient temperature structural properties (~300 K) and the ambient and high temperature (up to 900 K) direct current (DC) magnetic properties of melt-spun Fe-x wt.% Si (x = 3, 5, & 8) alloys. The wheel surface speeds selected for the study were 30 m/s and 40 m/s. The thickness, width, lattice parameter, saturation magnetization (MS), and intrinsic coercivity (HCI) of the melt spun ribbons are presented and compared with data in the literature. The ribbons produced at the lower wheel surface speed (30 m/s) were continuous having relatively uniform edges compared to the ribbonsmore » produced at the higher wheel surface speed. The thickness and the width of the melt-spun ribbons ranged between ~15-60 μm and 500-800 μm, respectively. The x-ray diffraction spectra of the melt-spun ribbons indicated the presence of disordered α-phase, irrespective of the composition, and the wheel-surface speed. The lattice parameter decreased gradually as a function of increasing silicon content from ~0.2862 nm (Fe-3 wt.% Si) to ~0.2847 nm (Fe-8 wt.% Si). Wheel surface speed was not shown to have a significant effect on the magnetization, but primarily impacted the ribbon structure. A decreasing trend in the saturation magnetization was observed as a function of increased silicon content. The intrinsic coercivity of the melt-spun alloys ranged between ~50 to 200 A/m. Elevated temperature evaluation of the magnetization in the case of Fe-3 & 5 wt.% Si alloy ribbons was distinctly different from the Fe-8 wt.% Si alloy ribbons. The curves of the as-prepared Fe-3 wt.% Si and Fe-5 wt.% Si alloy ribbons were irreversible while that of Fe-8 wt.% Si was reversible. The MS for any of the combinations of wheel surface speed and composition decreased monotonically with the increase in temperature (from 300 – 900 K). The percentage decrease in MS from 300 K to 900 K for the Fe-3 wt.% Si and Fe-5 wt.% Si alloys was ~19-22 %, while the percentage decrease in the same temperature range for Fe-8 wt.% Si alloy was ~26-30 %. It appears that Fe-3 wt.% Si and Fe-5 wt.% Si alloys ribbons are primarily comprised of the α phase (disordered phase) with any minor constituents being beyond the detection limits of the studies performed, while the Fe-8 wt.% Si alloy ribbons are comprised of disordered and regions of short-range ordering.« less

Instrumented roll technology for the design space development of roller compaction process.

PubMed

Nesarikar, Vishwas V; Vatsaraj, Nipa; Patel, Chandrakant; Early, William; Pandey, Preetanshu; Sprockel, Omar; Gao, Zhihui; Jerzewski, Robert; Miller, Ronald; Levin, Michael

2012-04-15

Instrumented roll technology on Alexanderwerk WP120 roller compactor was developed and utilized successfully for the measurement of normal stress on ribbon during the process. The effects of process parameters such as roll speed (4-12 rpm), feed screw speed (19-53 rpm), and hydraulic roll pressure (40-70 bar) on normal stress and ribbon density were studied using placebo and active pre-blends. The placebo blend consisted of 1:1 ratio of microcrystalline cellulose PH102 and anhydrous lactose with sodium croscarmellose, colloidal silicon dioxide, and magnesium stearate. The active pre-blends were prepared using various combinations of one active ingredient (3-17%, w/w) and lubricant (0.1-0.9%, w/w) levels with remaining excipients same as placebo. Three force transducers (load cells) were installed linearly along the width of the roll, equidistant from each other with one transducer located in the center. Normal stress values recorded by side sensors and were lower than normal stress values recorded by middle sensor and showed greater variability than middle sensor. Normal stress was found to be directly proportional to hydraulic pressure and inversely to screw to roll speed ratio. For active pre-blends, normal stress was also a function of compressibility. For placebo pre-blends, ribbon density increased as normal stress increased. For active pre-blends, in addition to normal stress, ribbon density was also a function of gap. Models developed using placebo were found to predict ribbon densities of active blends with good accuracy and the prediction error decreased as the drug concentration of active blend decreased. Effective angle of internal friction and compressibility properties of active pre blend may be used as key indicators for predicting ribbon densities of active blend using placebo ribbon density model. Feasibility of on-line prediction of ribbon density during roller compaction was demonstrated using porosity-pressure data of pre-blend and normal stress measurements. Effect of vacuum to de-aerate pre blend prior to entering the nip zone was studied. Varying levels of vacuum for de-aeration of placebo pre blend did not affect the normal stress values. However, turning off vacuum completely caused an increase in normal stress with subsequent decrease in gap. Use of instrumented roll demonstrated potential to reduce the number of DOE runs by enhancing fundamental understanding of relationship between normal stress on ribbon and process parameters. Copyright © 2012 Elsevier B.V. All rights reserved.

Nanostructural reorganization of bacterial cellulose by ultrasonic treatment.

PubMed

Tischer, Paula C S Faria; Sierakowski, Maria Rita; Westfahl, Harry; Tischer, Cesar Augusto

2010-05-10

In this work, bacterial cellulose was subjected to a high-power ultrasonic treatment for different time intervals. The morphological analysis, scanning electron microscopy, and atomic force microscopy revealed that this treatment changed the width and height of the microfibrillar ribbons and roughness of their surface, originating films with new nanostructures. Differential thermal analysis showed a higher thermal stability for ultrasonicated samples with a pyrolysis onset temperature of 208 degrees C for native bacterial cellulose and 250 and 268 degrees C for the modified samples. The small-angle X-ray scattering experiments demonstrated that the treatment with ultrasound increased the thickness of the ribbons, while wide-angle X-ray scattering experiments demonstrated that the average crystallite dimension and the degree of crystallinity also increased. A model is proposed where the thicker ribbons and crystallites result from the fusion of neighboring ribbons due to cavitation effects.

Gigatron microwave amplifier

DOEpatents

McIntyre, P.M.

1993-07-13

An electron tube for achieving high power at high frequency with high efficiency is described, including an input coupler, a ribbon-shaped electron beam and a traveling wave output coupler. The input coupler is a lumped constant resonant circuit that modulates a field emitter array cathode at microwave frequency. A bunched ribbon electron beam is emitted from the cathode in periodic bursts at the desired frequency. The beam has a ribbon configuration to eliminate limitations inherent in round beam devices. The traveling wave coupler efficiently extracts energy from the electron beam, and includes a waveguide with a slot there through for receiving the electron beam. The ribbon beam is tilted at an angle with respect to the traveling wave coupler so that the electron beam couples in-phase with the traveling wave in the waveguide. The traveling wave coupler thus extracts energy from the electron beam over the entire width of the beam.

Gigatron microwave amplifier

DOEpatents

McIntyre, Peter M.

1993-01-01

An electron tube for achieving high power at high frequency with high efficiency, including an input coupler, a ribbon-shaped electron beam and a traveling wave output coupler. The input coupler is a lumped constant resonant circuit that modulates a field emitter array cathode at microwave frequency. A bunched ribbon electron beam is emitted from the cathode in periodic bursts at the desired frequency. The beam has a ribbon configuration to eliminate limitations inherent in round beam devices. The traveling wave coupler efficiently extracts energy from the electron beam, and includes a waveguide with a slot therethrough for receiving the electron beam. The ribbon beam is tilted at an angle with respect to the traveling wave coupler so that the electron beam couples in-phase with the traveling wave in the waveguide. The traveling wave coupler thus extracts energy from the electron beam over the entire width of the beam.

SEPARATION OF THE RIBBON FROM GLOBALLY DISTRIBUTED ENERGETIC NEUTRAL ATOM FLUX USING THE FIRST FIVE YEARS OF IBEX OBSERVATIONS

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

Schwadron, N. A.; Moebius, E.; Kucharek, H.

2014-11-01

The Interstellar Boundary Explorer (IBEX) observes the IBEX ribbon, which stretches across much of the sky observed in energetic neutral atoms (ENAs). The ribbon covers a narrow (∼20°-50°) region that is believed to be roughly perpendicular to the interstellar magnetic field. Superimposed on the IBEX ribbon is the globally distributed flux that is controlled by the processes and properties of the heliosheath. This is a second study that utilizes a previously developed technique to separate ENA emissions in the ribbon from the globally distributed flux. A transparency mask is applied over the ribbon and regions of high emissions. We thenmore » solve for the globally distributed flux using an interpolation scheme. Previously, ribbon separation techniques were applied to the first year of IBEX-Hi data at and above 0.71 keV. Here we extend the separation analysis down to 0.2 keV and to five years of IBEX data enabling first maps of the ribbon and the globally distributed flux across the full sky of ENA emissions. Our analysis shows the broadening of the ribbon peak at energies below 0.71 keV and demonstrates the apparent deformation of the ribbon in the nose and heliotail. We show global asymmetries of the heliosheath, including both deflection of the heliotail and differing widths of the lobes, in context of the direction, draping, and compression of the heliospheric magnetic field. We discuss implications of the ribbon maps for the wide array of concepts that attempt to explain the ribbon's origin. Thus, we present the five-year separation of the IBEX ribbon from the globally distributed flux in preparation for a formal IBEX data release of ribbon and globally distributed flux maps to the heliophysics community.« less

Top–down fabrication of sub-nanometre semiconducting nanoribbons derived from molybdenum disulfide sheets

PubMed Central

Liu, Xiaofei; Xu, Tao; Wu, Xing; Zhang, Zhuhua; Yu, Jin; Qiu, Hao; Hong, Jin-Hua; Jin, Chuan-Hong; Li, Ji-Xue; Wang, Xin-Ran; Sun, Li-Tao; Guo, Wanlin

2013-01-01

Developments in semiconductor technology are propelling the dimensions of devices down to 10 nm, but facing great challenges in manufacture at the sub-10 nm scale. Nanotechnology can fabricate nanoribbons from two-dimensional atomic crystals, such as graphene, with widths below the 10 nm threshold, but their geometries and properties have been hard to control at this scale. Here we find that robust ultrafine molybdenum-sulfide ribbons with a uniform width of 0.35 nm can be widely formed between holes created in a MoS2 sheet under electron irradiation. In situ high-resolution transmission electron microscope characterization, combined with first-principles calculations, identifies the sub-1 nm ribbon as a Mo5S4 crystal derived from MoS2, through a spontaneous phase transition. Further first-principles investigations show that the Mo5S4 ribbon has a band gap of 0.77 eV, a Young’s modulus of 300GPa and can demonstrate 9% tensile strain before fracture. The results show a novel top–down route for controllable fabrication of functional building blocks for sub-nanometre electronics. PMID:23653188

Large Area Silicon Sheet by EFG

NASA Technical Reports Server (NTRS)

Wald, F. V.

1979-01-01

Displaced die concepts were explored along with some initial work on buckle characterization. Convective impurity redistribution was further studied. Growth from single cartridges was continued to create a quality baseline to allow comparison of the results with those in the upcoming multiple run and to choose the most appropriate die design. Fabrication and assembly work on the actual five ribbon furnace continued. Progress was made toward the development of the video optical system for edge position and meniscus height control. In preparation for a detailed program, designed to explore the buckling problem, ribbon guidance in the machine was improved. Buckle free, full width ribbon was grown under stable conditions without a cold shoe, an achievement essential to finally arrive at quantitative correlations between growth conditions and buckle formation.

Synaptic Ribbon Active Zones in Cone Photoreceptors Operate Independently from One Another

PubMed Central

Grassmeyer, Justin J.; Thoreson, Wallace B.

2017-01-01

Cone photoreceptors depolarize in darkness to release glutamate-laden synaptic vesicles. Essential to release is the synaptic ribbon, a structure that helps organize active zones by clustering vesicles near proteins that mediate exocytosis, including voltage-gated Ca2+ channels. Cone terminals have many ribbon-style active zones at which second-order neurons receive input. We asked whether there are functionally significant differences in local Ca2+ influx among ribbons in individual cones. We combined confocal Ca2+ imaging to measure Ca2+ influx at individual ribbons and patch clamp recordings to record whole-cell ICa in salamander cones. We found that the voltage for half-maximal activation (V50) of whole cell ICa in cones averaged −38.1 mV ± 3.05 mV (standard deviation [SD]), close to the cone membrane potential in darkness of ca. −40 mV. Ca2+ signals at individual ribbons varied in amplitude from one another and showed greater variability in V50 values than whole-cell ICa, suggesting that Ca2+ signals can differ significantly among ribbons within cones. After accounting for potential sources of technical variability in measurements of Ca2+ signals and for contributions from cone-to-cone differences in ICa, we found that the variability in V50 values for ribbon Ca2+ signals within individual cones showed a SD of 2.5 mV. Simulating local differences in Ca2+ channel activity at two ribbons by shifting the V50 value of ICa by ±2.5 mV (1 SD) about the mean suggests that when the membrane depolarizes to −40 mV, two ribbons could experience differences in Ca2+ influx of >45%. Further evidence that local Ca2+ changes at ribbons can be regulated independently was obtained in experiments showing that activation of inhibitory feedback from horizontal cells (HCs) to cones in paired recordings changed both amplitude and V50 of Ca2+ signals at individual ribbons. By varying the strength of synaptic output, differences in voltage dependence and amplitude of Ca2+ signals at individual ribbons shape the information transmitted from cones to downstream neurons in vision. PMID:28744203

49 CFR 587.15 - Verification of aluminum honeycomb crush strength.

Code of Federal Regulations, 2010 CFR

2010-10-01

..., the fringes (“e”) are at least half the length of one bonded cell wall (“d”) (in the ribbon direction... width is 150 mm (5.9 in) ±6 mm (0.24 in), and the thickness is 25 mm (1 in) ±2 mm (0.08 in). The walls of incomplete cells around the edge of the sample are trimmed as follows (See Figure 3). In the width...

Direct growth of aligned graphitic nanoribbons from a DNA template by chemical vapour deposition.

PubMed

Sokolov, Anatoliy N; Yap, Fung Ling; Liu, Nan; Kim, Kwanpyo; Ci, Lijie; Johnson, Olasupo B; Wang, Huiliang; Vosgueritchian, Michael; Koh, Ai Leen; Chen, Jihua; Park, Jinseong; Bao, Zhenan

2013-01-01

Graphene, laterally confined within narrow ribbons, exhibits a bandgap and is envisioned as a next-generation material for high-performance electronics. To take advantage of this phenomenon, there is a critical need to develop methodologies that result in graphene ribbons <10 nm in width. Here we report the use of metal salts infused within stretched DNA as catalysts to grow nanoscopic graphitic nanoribbons. The nanoribbons are termed graphitic as they have been determined to consist of regions of sp(2) and sp(3) character. The nanoscopic graphitic nanoribbons are micrometres in length, <10 nm in width, and take on the shape of the DNA template. The DNA strand is converted to a graphitic nanoribbon by utilizing chemical vapour deposition conditions. Depending on the growth conditions, metallic or semiconducting graphitic nanoribbons are formed. Improvements in the growth method have potential to lead to bottom-up synthesis of pristine single-layer graphene nanoribbons.

Graphene Statistical Mechanics

NASA Astrophysics Data System (ADS)

Bowick, Mark; Kosmrlj, Andrej; Nelson, David; Sknepnek, Rastko

2015-03-01

Graphene provides an ideal system to test the statistical mechanics of thermally fluctuating elastic membranes. The high Young's modulus of graphene means that thermal fluctuations over even small length scales significantly stiffen the renormalized bending rigidity. We study the effect of thermal fluctuations on graphene ribbons of width W and length L, pinned at one end, via coarse-grained Molecular Dynamics simulations and compare with analytic predictions of the scaling of width-averaged root-mean-squared height fluctuations as a function of distance along the ribbon. Scaling collapse as a function of W and L also allows us to extract the scaling exponent eta governing the long-wavelength stiffening of the bending rigidity. A full understanding of the geometry-dependent mechanical properties of graphene, including arrays of cuts, may allow the design of a variety of modular elements with desired mechanical properties starting from pure graphene alone. Supported by NSF grant DMR-1435794

Web-dendritic growth. [single crystal silicon ribbons for solar cells

NASA Technical Reports Server (NTRS)

Hilborn, R. B.; Faust, J. W., Jr.; Rhodes, C.

1977-01-01

The effects of various machine design parameters on the growth of web dendritic silicon ribbon were investigated. Ribbons were grown up to lengths of one meter, with widths increasing linearly up to one cm at the point of termination of growth. Thermal data were collected and evaluated for actual seeding and growth with variations in parameters affecting heat loss. It was found that for suitable growth, the mechanical system should be very rigid and stable, and the tolerances and specifications of the quartz crucibles must be far tighter than normal quartz tolerances. The widening rates of the ribbons were found to be a function of the temperature gradient rather than the temperature differences alone. A twin spacing in the seed of 3 microns to 2 microns was found to be unfavorable for growth; whereas spacing of 0.9 microns to 2 microns and 8 microns to 2 microns were favorable. Thermal modeling studies of the effects of furnace design parameters on the temperature distributions in melt and the growth of the dendritic web ribbon showed that the pull rate of the ribbon is strongly dependent on the temperature of the top thermal shield, the spacing between this shield and the melt, and the thickness of the growing web.

Quantum correlations in chiral graphene nanoribbons.

PubMed

Tan, Xiao-Dong; Koop, Cornelie; Liao, Xiao-Ping; Sun, Litao

2016-11-02

We compute the entanglement and the quantum discord (QD) between two edge spins in chiral graphene nanoribbons (CGNRs) thermalized with a reservoir at temperature T (canonical ensemble). We show that the entanglement only exists in inter-edge coupled spin pairs, and there is no entanglement between any two spins at the same ribbon edge. By contrast, almost all edge spin pairs can hold non-zero QD, which strongly depends on the ribbon width and the Coulomb repulsion among electrons. More intriguingly, the dominant entanglement always occurs in the pair of nearest abreast spins across the ribbon, and even at room temperature this type of entanglement is still very robust, especially for narrow CGNRs with the weak Coulomb repulsion. These remarkable properties make CGNRs very promising for possible applications in spin-quantum devices.

The application of terahertz pulsed imaging in characterising density distribution of roll-compacted ribbons.

PubMed

Zhang, Jianyi; Pei, Chunlei; Schiano, Serena; Heaps, David; Wu, Chuan-Yu

2016-09-01

Roll compaction is a commonly used dry granulation process in pharmaceutical, fine chemical and agrochemical industries for materials sensitive to heat or moisture. The ribbon density distribution plays an important role in controlling properties of granules (e.g. granule size distribution, porosity and strength). Accurate characterisation of ribbon density distribution is critical in process control and quality assurance. The terahertz imaging system has a great application potential in achieving this as the terahertz radiation has the ability to penetrate most of the pharmaceutical excipients and the refractive index reflects variations in density and chemical compositions. The aim of this study is to explore whether terahertz pulse imaging is a feasible technique for quantifying ribbon density distribution. Ribbons were made of two grades of microcrystalline cellulose (MCC), Avicel PH102 and DG, using a roll compactor at various process conditions and the ribbon density variation was investigated using terahertz imaging and section methods. The density variations obtained from both methods were compared to explore the reliability and accuracy of the terahertz imaging system. An average refractive index is calculated from the refractive index values in the frequency range between 0.5 and 1.5THz. It is shown that the refractive index gradually decreases from the middle of the ribbon towards to the edges. Variations of density distribution across the width of the ribbons are also obtained using both the section method and the terahertz imaging system. It is found that the terahertz imaging results are in excellent agreement with that obtained using the section method, demonstrating that terahertz imaging is a feasible and rapid tool to characterise ribbon density distributions. Copyright © 2016 Elsevier B.V. All rights reserved.

Edge-Dependent Electronic and Magnetic Characteristics of Freestanding β 12-Borophene Nanoribbons

NASA Astrophysics Data System (ADS)

Izadi Vishkayi, Sahar; Bagheri Tagani, Meysam

2018-03-01

This work presents an investigation of nanoribbons cut from β 12-borophene sheets by applying the density functional theory. In particular, the electronic and magnetic properties of borophene nanoribbons (BNR) are studied. It is found that all the ribbons considered in this work behave as metals, which is in good agreement with the recent experimental results. β 12-BNR has significant diversity due to the existence of five boron atoms in a unit cell of the sheet. The magnetic properties of the ribbons are strongly dependent on the cutting direction and edge profile. It is interesting that a ribbon with a specific width can behave as a normal or a ferromagnetic metal with magnetization at just one edge or two edges. Spin anisotropy is observed in some ribbons, and the magnetic moment is not found to be the same in both edges in an antiferromagnetic configuration. This effect stems from the edge asymmetry of the ribbons and results in the breaking of spin degeneracy in the band structure. Our findings show that β 12 BNRs are potential candidates for next-generation spintronic devices. [Figure not available: see fulltext.

Electro-statically controllable graphene local heater

NASA Astrophysics Data System (ADS)

Wang, Hui-Shan; Deng, Lian-Wen; Li, Lei; Sun, Qiu-Juan; Xie, Hong; Wang, Hao-Min

2018-03-01

We report on current-induced thermal power investigation of graphene nanostructure for potential local-heating applications. It is found that the efficiency of heating can be greatly improved if graphene is patterned into structures with narrow width and long channel. In a narrow graphene-ribbon, the Joule heating power exhibits an obvious dependence on the back-gate voltage. By monitoring Raman spectra, the temperature of graphene-ribbon can be determined. The temperature of graphene-ribbon is modulated by the electric field effect when the sample is sourced with a relatively high current. Project supported by the National Key R&D Program of China (Grant No. 2017YFF0206106), the Chinese Academy of Sciences (Grant No. XDB04040300), the National Natural Science Foundation of China (Grant No. 51772317), and the Science and Technology Commission of Shanghai Municipality, China (Grant No. 16ZR1442700).

Strain-Induced Pseudomagnetic Fields in Twisted Graphene Nanoribbons

NASA Astrophysics Data System (ADS)

Zhang, Dong-Bo; Seifert, Gotthard; Chang, Kai

2014-03-01

We present, for the first time, an atomic-level and quantitative study of a strain-induced pseudomagnetic field in graphene nanoribbons with widths of hundreds of nanometers. We show that twisting strongly affects the band structures of graphene nanoribbons with arbitrary chirality and generates well-defined pseudo-Landau levels, which mimics the quantization of massive Dirac fermions in a magnetic field up to 160 T. Electrons are localized either at ribbon edges forming the edge current or at the ribbon center forming the snake orbit current, both being valley polarized. Our result paves the way for the design of new graphene-based nanoelectronics.

Spontaneous Periodic Delamination of Thin Films To Form Crack-Free Metal and Silicon Ribbons with High Stretchability.

PubMed

Zhang, Qiuting; Tang, Yichao; Hajfathalian, Maryam; Chen, Chunxu; Turner, Kevin T; Dikin, Dmitriy A; Lin, Gaojian; Yin, Jie

2017-12-27

Design of electronic materials with high stretchability is of great importance for realizing soft and conformal electronics. One strategy of realizing stretchable metals and semiconductors is to exploit the buckling of materials bonded to elastomers. However, the level of stretchability is often limited by the cracking and fragmentation of the materials that occurs when constrained buckling occurs while bonded to the substrate. Here, we exploit a failure mechanism, spontaneous buckling-driven periodic delamination, to achieve high stretchability in metal and silicon films that are deposited on prestrained elastomer substrates. We find that both globally periodic buckle-delaminated pattern and ordered cracking patterns over large areas are observed in the spontaneously buckle-delaminated thin films. The geometry of periodic delaminated buckles and cracking periodicity can be predicted by theoretical models. By patterning the films into ribbons with widths smaller than the predicted cracking periodicity, we demonstrate the design of crack-free and spontaneous delaminated ribbons on highly prestrained elastomer substrates, which provides a high stretchability of about 120% and 400% in Si and Au ribbons, respectively. We find that the high stretchability is mainly attributed to the largely relaxed strain in the ribbons via spontaneous buckling-driven delamination, as made evident by the small maximum tensile strain in both ribbons, which is measured to be over 100 times smaller than that of the substrate prestrain.

Impact of strain on electronic and transport properties of 6 nm hydrogenated germanane nano-ribbon channel double gate field effect transistor

NASA Astrophysics Data System (ADS)

Meher Abhinav, E.; Sundararaj, Anuraj; Gopalakrishnan, Chandrasekaran; Kasmir Raja, S. V.; Chokhra, Saurabh

2017-11-01

In this work, chair like fully hydrogenated germanane (CGeH) nano-ribbon 6 nm short channel double gate field effect transistor (DG-FET) has been modeled and the impact of strain on the I-V characteristics of CGeH channel has been examined. The bond lengths, binding and formation energies of various hydrogenated geometries of buckled germanane channel were calculated using local density approximation (LDA) with Perdew-Zunger (PZ) and generalized gradient approximation (GGA) with Perdew Burke Ernzerhof (PBE) parameterization. From four various geometries, chair like structure is found to be more stable compared to boat like obtuse, stiruup structure and table like structure. The bandgap versus width, bandgap versus strain characteristics and I-V characteristics had been analyzed at room temperature using density functional theory (DFT). Using self consistent calculation it was observed that the electronic properties of nano-ribbon is independent of length and band structure, but dependent on edge type, strain [Uni-axial (ɛ xx ), bi-axial (ɛ xx   =  ɛ yy )] and width of the ribbon. The strain engineered hydrogenated germanane (GeH) showed wide direct bandgap (2.3 eV) which could help to build low noise electronic devices that operates at high frequencies. The observed bi-axial compression has high impact on the device transport characteristics with peak to valley ratio (PVR) of 2.14 and 380% increase in peak current compared to pristine CGeH device. The observed strain in CGeH DG-FET could facilitate in designing novel multiple-logic memory devices due to multiple negative differential resistance (NDR) regions.

Occurrence of flow parallel and flow transverse bedforms in Fehmarn Belt (SW Baltic Sea) related to the local palaeomorphology

NASA Astrophysics Data System (ADS)

Feldens, P.; Diesing, M.; Schwarzer, K.; Heinrich, C.; Schlenz, B.

2015-02-01

This study describes the spatial distribution of flow-parallel sand ribbons and flow-transverse large and very large subaqueous dunes in the south-western Baltic Sea offshore Fehmarn Island between 13 m and 20 m water depth, based on hydroacoustic and grain size data. The system of sand ribbons and dunes is intermittently active due to currents induced during major inflows of the North Sea water into the Baltic Sea. The sand ribbons are located on a lag deposit on top of glacial till, while the dunes rest on top of drowned Holocene nearshore deposits. The sand ribbons reach heights between 0.4 m and 0.6 m, with widths varying between 60 m and several hundreds of metres. The observed dunes have heights between 0.09 m and 2.35 m, while their wavelengths range from 17 m to 120 m. Offshore Fehmarn Island, the transition from sand ribbons to dunes is most likely linked to a contrast in sediment supply, as reworked drowned nearshore deposits provide sediment available for transport in significantly larger amounts than glacial till. Similar to an earlier approach for river bed states, the dimensionless thickness of sediment available for transport is able to differentiate between the bed states.

Graphene Nanoribbons Fabricated by Helium Ion microscope

NASA Astrophysics Data System (ADS)

Pickard, D.; Oezyilmaz, B.; Thong, J.; Loh, K. P.; Viswanathan, V.; Zhongkai, A.; Mathew, S.; Kundu, T.; Park, C.; Yi, Z.; Xu, X.; Zhang, K.; Tat, T. C.; Wang, H.; Venkatesan, T.; Botton, G.; Couillard, M.

2010-03-01

Graphene, a monolayer graphitic lattice of carbon atoms has tremendous promise for a variety of applications on account of the zero mass of electrons, high mobility and the sensitivity of transport to perturbations at the interface. Patterning graphene is an obvious challenge and mesoscopic devices based on graphene require high spatial resolution patterning that will induce as little damage as possible. We use a helium ion microscope with its 0.4nm spot size beam to directly write patterns on free standing graphene films. TEM images of the patterns reveal holes as small as 4 nm and ribbons with line widths as narrow as 3 nm. The images show recovery of the graphene lattice at a distance of about a nm from the patterned edge. The linewidths of the ribbon can be varied considerably in a controllable fashion over ribbon lengths of the order of microns. . .

Tunable manipulation of terahertz wavefront based on graphene metasurfaces

NASA Astrophysics Data System (ADS)

Luo, Linbao; Wang, Kuiyuan; Guo, Kai; Shen, Fei; Zhang, Xudong; Yin, Zhiping; Guo, Zhongyi

2017-11-01

We have systematically investigated the performances of a tunable graphene metasurface that can dynamically manipulate the terahertz wavefronts. The metasurface consists of a silver substrate, SiO2 interlayer and the top graphene ribbons that can exhibit plasmon resonances to realize a phase shift by changing the Fermi levels of graphene ribbons. The plasmon resonances in graphene ribbons and Fabry-Perot resonances in the SiO2 interlayer work together for making the designed metasurface cover 2π phase range nearly. In the simulations, we can realize anomalous reflection at any angle by using the continuous phase modulation. On this basis, a reflective focusing lens based on the graphene metasurface has also been designed, which is designed in the frequency of 5.0 THz with a reasonable operation bandwidth from 4.5 THz to 6.5 THz. The corresponding focal lengths are designed as 300 μm and 100 μm, and the depths of focus (full width at half maximum along the Z direction) are 114 μm and 104 μm, respectively. Especially, the diameters of focal points (full width at half maximum along the X direction) are 29.5 μm and 24.1 μm, which are smaller than a half-wavelength (30 μm) in the focusing plane. It indicates that our designed focusing lenses have superior performance and can provide an opportunity to develop a tunable wavefront-controlling device.

Simultaneous measurements of Cotton fiber maturity, fineness, ribbon width, and micronaire

USDA-ARS?s Scientific Manuscript database

Maturity (degree of secondary wall development) and fineness (linear density) are important cotton quality and processing properties, but their direct measurement is often difficult and/or expensive to perform. An indirect but critical measurement of maturity and fineness is micronaire, which is on...

The Role of Pickup Ion Dynamics Outside of the Heliopause in the Limit of Weak Pitch Angle Scattering: Implications for the Source of the IBEX Ribbon.

PubMed

Zirnstein, E J; Heerikhuisen, J; Dayeh, M A

2018-01-01

We present a new model of the Interstellar Boundary Explorer ( IBEX ) ribbon based on the secondary energetic neutral atom (ENA) mechanism, under the assumption that there is negligible pitch angle scattering of pickup ions (PUIs) outside the heliopause. Using the results of an MHD-plasma/kinetic-neutral simulation of the heliosphere, we generate PUIs in the outer heliosheath, solve their transport using guiding center theory, and compute ribbon ENA fluxes at 1 AU. We implement several aspects of the PUI dynamics, including (1) parallel motion along the local interstellar magnetic field (ISMF), (2) advective transport with the interstellar plasma, (3) the mirror force acting on PUIs propagating along the ISMF, and (4) betatron acceleration of PUIs as they are advected within an increasing magnetic field towards the heliopause. We find that ENA fluxes at 1 AU are reduced when PUIs are allowed to move along the ISMF, and ENA fluxes are reduced even more by the inclusion of the mirror force, which pushes particles away from IBEX lines-of-sight. Inclusion of advection and betatron acceleration do not result in any significant change in the ribbon. Interestingly, the mirror force reduces the ENA fluxes from the inner edge of the ribbon more than its outer edge, effectively reducing the ribbon's width by ∼6° and increasing its radius projected on the sky. This is caused by the asymmetric draping of the ISMF around the heliopause, such that ENAs from the ribbon's inner edge originate closer to the heliopause, where the mirror force is strongest.

When confrontational images may be counter productive: reinforcing the case for pre-testing communications in sensitive areas.

PubMed

Donovan, Robert J; Jalleh, Geoffrey; Fielder, Lynda; Ouschan, Robyn

2008-08-01

White Ribbon Day is an international campaign that encourages men to speak out about and demonstrate their opposition to violence against women by wearing a white ribbon on 25 November. This study assesses the effectiveness of a graphic confrontational image in the Australian 2006 campaign versus an alternative non-violent image to motivate men to wear a white ribbon on White Ribbon Day. An intercept survey was conducted with a sample of 45 males aged 30-49 years recruited in an inner city suburban shopping strip. Respondents were presented with two alternatives: a graphic 'amputated arm' image and a non-violent 'father-daughter' image. The primary dependent variable was the relative ability of the two alternatives in motivating respondents to wear a white ribbon on White Ribbon Day. The vast majority of respondents nominated the 'father-daughter' as image being more motivating than the 'amputated arm' image to wear a white ribbon on White Ribbon Day: 84% vs 9%. The bland 'father-daughter' image was far more motivating than the macabre/violent 'amputated arm' image in motivating men to wear a white ribbon on White Ribbon Day. This is contrary to the UNIFEM Australia and White Ribbon Day assertion that 'confrontational/provocative' images are necessary to achieve this behaviour.

MoS2 edges and heterophase interfaces: energy, structure and phase engineering

NASA Astrophysics Data System (ADS)

Zhou, Songsong; Han, Jian; Sun, Jianwei; Srolovitz, David J.

2017-06-01

The transition metal dichalcogenides exhibit polymorphism; i.e. both 2H and 1T‧ crystal structures, each with unique electronic properties. These two phases can coexist within the same monolayer microstructure, producing 2H/1T‧ interfaces. Here we report a systematic investigation of the energetics of the experimentally most important MoS2 heterophase interfaces and edges. The stable interface and edge structures change with chemical potential (these edges/interfaces are usually non-stoichiometric). Stable edges tend to be those of highest atomic density and the stable interfaces correspond to those with local atomic structure very similar to the 2H crystal. The interfacial energies are lower than those of the edges, and the 1T‧ edges have lower energy than the 2H edges. Because the 1T‧ edges have much lower energy than the 2H edges, a sufficiently narrow 1T‧ ribbon will be more stable than the corresponding 2H ribbon (this critical width is much larger in MoTe2 than in MoS2). Similarly, a large 2H flake have an equilibrium strip of 1T‧ along its edge (again this effect is much larger in MoTe2 than in MoS2). Application of tensile strains can increase the width of the stable 1T‧ strip or the critical thickness below which a ribbon favors the 1T‧ structure. These effects provide a means to phase engineer transition metal dichalcogenide microstructures.

Enlargement of Ribbons in Zebrafish Hair Cells Increases Calcium Currents But Disrupts Afferent Spontaneous Activity and Timing of Stimulus Onset

PubMed Central

Schreck, Mary; Petralia, Ronald S.; Wang, Ya-Xian; Zhang, Qiuxiang

2017-01-01

In sensory hair cells of auditory and vestibular organs, the ribbon synapse is required for the precise encoding of a wide range of complex stimuli. Hair cells have a unique presynaptic structure, the synaptic ribbon, which organizes both synaptic vesicles and calcium channels at the active zone. Previous work has shown that hair-cell ribbon size is correlated with differences in postsynaptic activity. However, additional variability in postsynapse size presents a challenge to determining the specific role of ribbon size in sensory encoding. To selectively assess the impact of ribbon size on synapse function, we examined hair cells in transgenic zebrafish that have enlarged ribbons, without postsynaptic alterations. Morphologically, we found that enlarged ribbons had more associated vesicles and reduced presynaptic calcium-channel clustering. Functionally, hair cells with enlarged ribbons had larger global and ribbon-localized calcium currents. Afferent neuron recordings revealed that hair cells with enlarged ribbons resulted in reduced spontaneous spike rates. Additionally, despite larger presynaptic calcium signals, we observed fewer evoked spikes with longer latencies from stimulus onset. Together, our work indicates that hair-cell ribbon size influences the spontaneous spiking and the precise encoding of stimulus onset in afferent neurons. SIGNIFICANCE STATEMENT Numerous studies support that hair-cell ribbon size corresponds with functional sensitivity differences in afferent neurons and, in the case of inner hair cells of the cochlea, vulnerability to damage from noise trauma. Yet it is unclear whether ribbon size directly influences sensory encoding. Our study reveals that ribbon enlargement results in increased ribbon-localized calcium signals, yet reduces afferent spontaneous activity and disrupts the timing of stimulus onset, a distinct aspect of auditory and vestibular encoding. These observations suggest that varying ribbon size alone can influence sensory encoding, and give further insight into how hair cells transduce signals that cover a wide dynamic range of stimuli. PMID:28546313

QUASI-PERIODIC SLIPPING MAGNETIC RECONNECTION DURING AN X-CLASS SOLAR FLARE OBSERVED BY THE SOLAR DYNAMICS OBSERVATORY AND INTERFACE REGION IMAGING SPECTROGRAPH

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

Li, Ting; Zhang, Jun, E-mail: liting@nao.cas.cn, E-mail: zjun@nao.cas.cn

2015-05-01

We first report the quasi-periodic slipping motion of flare loops during an eruptive X-class flare on 2014 September 10. The slipping motion was investigated at a specific location along one of the two ribbons and can be observed throughout the impulsive phase of the flare. The apparent slipping velocity was 20–110 km s{sup −1}, and the associated period was 3–6 minutes. The footpoints of flare loops appeared as small-scale bright knots observed in 1400 Å, corresponding to fine structures of the flare ribbon. These bright knots were observed to move along the southern part of the longer ribbon and alsomore » exhibited a quasi-periodic pattern. The Si iv 1402.77 Å line was redshifted by 30–50 km s{sup −1} at the locations of moving knots with a ∼40–60 km s{sup −1} line width, larger than other sites of the flare ribbon. We suggest that the quasi-periodic slipping reconnection is involved in this process and the redshift at the bright knots is probably indicative of reconnection downflow. The emission line of Si iv at the northern part of the longer ribbon also exhibited obvious redshifts of about 10–70 km s{sup −1} in the impulsive phase of the flare, with the redshifts at the outer edges of the ribbon larger than those in the middle. The redshift velocities at post-flare loops reached about 80–100 km s{sup −1} in the transition region.« less

Silicon Web Process Development. [for solar cell fabrication

NASA Technical Reports Server (NTRS)

Duncan, C. S.; Seidensticker, R. G.; Hopkins, R. H.; Mchugh, J. P.; Hill, F. E.; Heimlich, M. E.; Driggers, J. M.

1979-01-01

Silicon dendritic web, ribbon form of silicon and capable of fabrication into solar cells with greater than 15% AMl conversion efficiency, was produced from the melt without die shaping. Improvements were made both in the width of the web ribbons grown and in the techniques to replenish the liquid silicon as it is transformed to web. Through means of improved thermal shielding stress was reduced sufficiently so that web crystals nearly 4.5 cm wide were grown. The development of two subsystems, a silicon feeder and a melt level sensor, necessary to achieve an operational melt replenishment system, is described. A gas flow management technique is discussed and a laser reflection method to sense and control the melt level as silicon is replenished is examined.

Optimizing the thermoelectric performance of graphene nano-ribbons without degrading the electronic properties.

PubMed

Tran, Van-Truong; Saint-Martin, Jérôme; Dollfus, Philippe; Volz, Sebastian

2017-05-24

The enhancement of thermoelectric figure of merit ZT requires to either increase the power factor or reduce the phonon conductance, or even both. In graphene, the high phonon thermal conductivity is the main factor limiting the thermoelectric conversion. The common strategy to enhance ZT is therefore to introduce phonon scatterers to suppress the phonon conductance while retaining high electrical conductance and Seebeck coefficient. Although thermoelectric performance is eventually enhanced, all studies based on this strategy show a significant reduction of the electrical conductance. In this study we demonstrate that appropriate sources of disorder, including isotopes and vacancies at lowest electron density positions, can be used as phonon scatterers to reduce the phonon conductance in graphene ribbons without degrading the electrical conductance, particularly in the low-energy region which is the most important range for device operation. By means of atomistic calculations we show that the natural electronic properties of graphene ribbons can be fully preserved while their thermoelectric efficiency is strongly enhanced. For ribbons of width M = 5 dimer lines, room-temperature ZT is enhanced from less than 0.26 to more than 2.5. This study is likely to set the milestones of a new generation of nano-devices with dual electronic/thermoelectric functionalities.

Rapid amyloid fiber formation from the fast-folding WW domain FBP28.

PubMed

Ferguson, Neil; Berriman, John; Petrovich, Miriana; Sharpe, Timothy D; Finch, John T; Fersht, Alan R

2003-08-19

The WW domains are small proteins that contain a three-stranded, antiparallel beta-sheet. The 40-residue murine FBP28 WW domain rapidly formed twirling ribbon-like fibrils at physiological temperature and pH, with morphology typical of amyloid fibrils. These ribbons were unusually wide and well ordered, making them highly suitable for structural studies. Their x-ray and electron-diffraction patterns displayed the characteristic amyloid fiber 0.47-nm reflection of the cross-beta diffraction signature. Both conventional and electron cryomicroscopy showed clearly that the ribbons were composed of many 2.5-nm-wide subfilaments that ran parallel to the long axis of the fiber. There was a region of lower density along the center of each filament. Lateral association of these filaments generated twisted, often interlinked, sheets up to 40 nm wide and many microns in length. The pitch of the helix varied from 60 to 320 nm, depending on the width of the ribbon. The wild-type FBP28 fibers were formed under conditions in which multiexponential folding kinetics is observed in other studies and which was attributed to a change in the mechanism of folding. It is more likely that those phases result from initial events in the off-pathway aggregation observed here.

Thermoplastic Ribbon-Ply Bonding Model

NASA Technical Reports Server (NTRS)

Hinkley, Jeffrey A.; Marchello, Joseph M.; Messier, Bernadette C.

1996-01-01

The aim of the present work was to identify key variables in rapid weldbonding of thermoplastic tow (ribbon) and their relationship to matrix polymer properties and to ribbon microstructure. Theoretical models for viscosity, establishment of ply-ply contact, instantaneous (Velcro) bonding, molecular interdiffusion (healing), void growth suppression, and gap filling were reviewed and synthesized. Consideration of the theoretical bonding mechanisms and length scales and of the experimental weld/peel data allow the prediction of such quantities as the time and pressure required to achieve good contact between a ribbon and a flat substrate, the time dependence of bond strength, pressures needed to prevent void growth from dissolved moisture and conditions for filling gaps and smoothing overlaps.

Anomalously Soft Non-Euclidean Springs

NASA Astrophysics Data System (ADS)

Levin, Ido; Sharon, Eran

2016-01-01

In this work we study the mechanical properties of a frustrated elastic ribbon spring—the non-Euclidean minimal spring. This spring belongs to the family of non-Euclidean plates: it has no spontaneous curvature, but its lateral intrinsic geometry is described by a non-Euclidean reference metric. The reference metric of the minimal spring is hyperbolic, and can be embedded as a minimal surface. We argue that the existence of a continuous set of such isometric minimal surfaces with different extensions leads to a complete degeneracy of the bulk elastic energy of the minimal spring under elongation. This degeneracy is removed only by boundary layer effects. As a result, the mechanical properties of the minimal spring are unusual: the spring is ultrasoft with a rigidity that depends on the thickness t as t7 /2 and does not explicitly depend on the ribbon's width. Moreover, we show that as the ribbon is widened, the rigidity may even decrease. These predictions are confirmed by a numerical study of a constrained spring. This work is the first to address the unusual mechanical properties of constrained non-Euclidean elastic objects.

Tunable multi-band absorption in metasurface of graphene ribbons based on composite structure

NASA Astrophysics Data System (ADS)

Ning, Renxia; Jiao, Zheng; Bao, Jie

2017-05-01

A tunable multiband absorption based on a graphene metasurface of composite structure at mid-infrared frequency was investigated by the finite difference time domain method. The composite structure were composed of graphene ribbons and a gold-MgF2 layer which was sandwiched in between two dielectric slabs. The permittivity of graphene is discussed with different chemical potential to obtain tunable absorption. And the absorption of the composite structure can be tuned by the chemical potential of graphene at certain frequencies. The impedance matching was used to study the perfect absorption of the structure in our paper. The results show that multi-band absorption can be obtained and some absorption peaks of the composite structure can be tuned through the changing not only of the width of graphene ribbons and gaps, but also the dielectric and the chemical potential of graphene. However, another peak was hardly changed by parameters due to a different resonant mechanism in proposed structure. This flexibily tunable multiband absorption may be applied to optical communications such as optical absorbers, mid infrared stealth devices and filters.

Length divergence of the lattice thermal conductivity in suspended graphene nanoribbons

NASA Astrophysics Data System (ADS)

Majee, Arnab K.; Aksamija, Zlatan

2016-06-01

Thermal properties of graphene have attracted much attention, culminating in a recent measurement of its length dependence in ribbons up to 9 μ m long. In this paper, we use the improved Callaway model to solve the phonon Boltzmann transport equation while capturing both the resistive (umklapp, isotope, and edge roughness) and nonresistive (normal) contributions. We show that for lengths smaller than 100 μ m , scaling the ribbon length while keeping the width constant leads to a logarithmic divergence of thermal conductivity. The length dependence is driven primarily by a ballistic-to-diffusive transition in the in-plane (LA and TA) branches, while in the hydrodynamic regime when 10 μ m 100 μ m due to the coupling between in-plane and flexural modes. This coupling leads to renormalization of ZA phonon dispersion in the long-wavelength range, preventing further divergence of thermal conductivity. We also uncover a strong dependence on sample width, which we attribute to the interplay between nonresistive normal and diffusive edge scattering in the Poisseuille flow regime. We conclude that normal processes play a crucial role in the length and width dependence of thermal transport in graphene in the hydrodynamic regime and dictate the relative in-plane (LA+TA) to out-of-plane (ZA) contribution to transport.

Observations and Numerical Modeling of the Jovian Ribbon

NASA Technical Reports Server (NTRS)

Cosentino, R. G.; Simon, A.; Morales-Juberias, R.; Sayanagi, K. M.

2015-01-01

Multiple wavelength observations made by the Hubble Space Telescope in early 2007 show the presence of a wavy, high-contrast feature in Jupiter's atmosphere near 30 degrees North. The "Jovian Ribbon," best seen at 410 nanometers, irregularly undulates in latitude and is time-variable in appearance. A meridional intensity gradient algorithm was applied to the observations to track the Ribbon's contour. Spectral analysis of the contour revealed that the Ribbon's structure is a combination of several wavenumbers ranging from k equals 8-40. The Ribbon is a dynamic structure that has been observed to have spectral power for dominant wavenumbers which vary over a time period of one month. The presence of the Ribbon correlates with periods when the velocity of the westward jet at the same location is highest. We conducted numerical simulations to investigate the stability of westward jets of varying speed, vertical shear, and background static stability to different perturbations. A Ribbon-like morphology was best reproduced with a 35 per millisecond westward jet that decreases in amplitude for pressures greater than 700 hectopascals and a background static stability of N equals 0.005 per second perturbed by heat pulses constrained to latitudes south of 30 degrees North. Additionally, the simulated feature had wavenumbers that qualitatively matched observations and evolved throughout the simulation reproducing the Jovian Ribbon's dynamic structure.

Magnetocaloric properties of rapidly solidified Dy{sub 3}Co alloy ribbons

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

Sánchez Llamazares, J. L., E-mail: jose.sanchez@ipicyt.edu.mx; Flores-Zúñiga, H.; Sánchez-Valdés, C. F.

2015-05-07

The magnetic and magnetocaloric (MC) properties of melt-spun ribbons of the Dy{sub 3}Co intermetallic compound were investigated. Samples were fabricated in an Ar environment using a homemade melt spinner system at a linear speed of the rotating copper wheel of 40 ms{sup −1}. X-ray diffraction analysis shows that ribbons crystallize into a single-phase with the Fe{sub 3}C-type orthorhombic crystal structure. The M(T) curve measured at 5 mT reveals the occurrence of a transition at 32 K from a first to a second antiferromagnetic (AFM) state and an AFM-to-paramagnetic transition at T{sub N} = 43 K. Furthermore, a metamagnetic transition is observed below T{sub N}, but themore » magnetization change ΔM is well below the one reported for bulk alloys. Below 12 K, large inverse MC effect and hysteresis losses are observed. This behavior is related to the metamagnetic transition. For a magnetic field change of 5 T (2 T) applied along the ribbon length, the produced ribbons show a peak value of the magnetic entropy change ΔS{sub M}{sup peak} of −6.5 (− 2.1) Jkg{sup −1}K{sup −1} occurring close to T{sub N} with a full-width at half-maximum δT{sub FWHM} of 53 (37) K, and refrigerant capacity RC = 364 (83) Jkg{sup −1} (estimated from the product |ΔS{sub M}{sup peak}| × δT{sub FWHM})« less

Functionalization and migration of bromine adatoms on zigzag graphene nanoribbons: A first-principles study

NASA Astrophysics Data System (ADS)

Jaiswal, Neeraj K.; Kumar, Amit; Patel, Chandrabhan

2018-05-01

Tailoring the electronic band gap of graphene nanoribbons (GNR) through edge functionalization and understanding the adsorption of guest adatoms on GNR is crucial for realization of upcoming organic devices. In the present work, we have investigated the structural stability and electronic property of bromine (Br) termination at the edges of zigzag GNR (ZGNR). The migration pathways of Br adatom on ZGNR have also been discussed along four different diffusion paths. It is revealed that Br termination induces metallicity in ZGNR and caused upward shifting of Fermi level. Further, the migration is predicted to take place preferable along the ribbon edges whereas across the ribbon width, migration is least probable to take place due to sufficiently higher migration barrier of ˜160 meV.

Water ring-bouncing on repellent singularities.

PubMed

Chantelot, Pierre; Mazloomi Moqaddam, Ali; Gauthier, Anaïs; Chikatamarla, Shyam S; Clanet, Christophe; Karlin, Ilya V; Quéré, David

2018-03-28

Texturing a flat superhydrophobic substrate with point-like superhydrophobic macrotextures of the same repellency makes impacting water droplets take off as rings, which leads to shorter bouncing times than on a flat substrate. We investigate the contact time reduction on such elementary macrotextures through experiment and simulations. We understand the observations by decomposing the impacting drop reshaped by the defect into sub-units (or blobs) whose size is fixed by the liquid ring width. We test the blob picture by looking at the reduction of contact time for off-centered impacts and for impacts in grooves that produce liquid ribbons where the blob size is fixed by the width of the channel.

49 CFR 587.14 - Deformable face component dimensions and material specifications.

Code of Federal Regulations, 2010 CFR

2010-10-01

... tolerance of ±2.5 mm (0.1 in) unless otherwise specified. (a) Main honeycomb block. (1) Dimensions. The main honeycomb block has a height of 650 mm (25.6 in) (in the direction of honeycomb ribbon axis), a width of 1,000 mm (39.4 in), and a depth of 450 mm (17.7 in)(in the direction of honeycomb cell axis). (2...

49 CFR 587.14 - Deformable face component dimensions and material specifications.

Code of Federal Regulations, 2012 CFR

2012-10-01

... tolerance of ±2.5 mm (0.1 in) unless otherwise specified. (a) Main honeycomb block. (1) Dimensions. The main honeycomb block has a height of 650 mm (25.6 in) (in the direction of honeycomb ribbon axis), a width of 1,000 mm (39.4 in), and a depth of 450 mm (17.7 in)(in the direction of honeycomb cell axis). (2...

49 CFR 587.14 - Deformable face component dimensions and material specifications.

Code of Federal Regulations, 2014 CFR

2014-10-01

... tolerance of ±2.5 mm (0.1 in) unless otherwise specified. (a) Main honeycomb block. (1) Dimensions. The main honeycomb block has a height of 650 mm (25.6 in) (in the direction of honeycomb ribbon axis), a width of 1,000 mm (39.4 in), and a depth of 450 mm (17.7 in)(in the direction of honeycomb cell axis). (2...

49 CFR 587.14 - Deformable face component dimensions and material specifications.

Code of Federal Regulations, 2013 CFR

2013-10-01

... tolerance of ±2.5 mm (0.1 in) unless otherwise specified. (a) Main honeycomb block. (1) Dimensions. The main honeycomb block has a height of 650 mm (25.6 in) (in the direction of honeycomb ribbon axis), a width of 1,000 mm (39.4 in), and a depth of 450 mm (17.7 in)(in the direction of honeycomb cell axis). (2...

49 CFR 587.14 - Deformable face component dimensions and material specifications.

Code of Federal Regulations, 2011 CFR

2011-10-01

... tolerance of ±2.5 mm (0.1 in) unless otherwise specified. (a) Main honeycomb block. (1) Dimensions. The main honeycomb block has a height of 650 mm (25.6 in) (in the direction of honeycomb ribbon axis), a width of 1,000 mm (39.4 in), and a depth of 450 mm (17.7 in)(in the direction of honeycomb cell axis). (2...

Hierarchical self-assembly of chiral rod-like molecules as a model for peptide β-sheet tapes, ribbons, fibrils, and fibers

PubMed Central

Aggeli, A.; Nyrkova, I. A.; Bell, M.; Harding, R.; Carrick, L.; McLeish, T. C. B.; Semenov, A. N.; Boden, N.

2001-01-01

A generic statistical mechanical model is presented for the self-assembly of chiral rod-like units, such as β-sheet-forming peptides, into helical tapes, which with increasing concentration associate into twisted ribbons (double tapes), fibrils (twisted stacks of ribbons), and fibers (entwined fibrils). The finite fibril width and helicity is shown to stem from a competition between the free energy gain from attraction between ribbons and the penalty because of elastic distortion of the intrinsically twisted ribbons on incorporation into a growing fibril. Fibers are stabilized similarly. The behavior of two rationally designed 11-aa residue peptides, P11-I and P11-II, is illustrative of the proposed scheme. P11-I and P11-II are designed to adopt the β-strand conformation and to self-assemble in one dimension to form antiparallel β-sheet tapes, ribbons, fibrils, and fibers in well-defined solution conditions. The energetic parameters governing self-assembly have been estimated from the experimental data using the model. The 8-nm-wide fibrils consist of eight tapes, are extremely robust (scission energy ≈200 kBT), and sufficiently rigid (persistence length l̃fibril ≈ 20–70 μm) to form nematic solutions at peptide concentration c ≈ 0.9 mM (volume fraction ≈0.0009 vol/vol), which convert to self-supporting nematic gels at c > 4 mM. More generally, these observations provide a new insight into the generic self-assembling properties of β-sheet-forming peptides and shed new light on the factors governing the structures and stability of pathological amyloid fibrils in vivo. The model also provides a prescription of routes to novel macromolecules based on a variety of self-assembling chiral units, and protocols for extraction of the associated energy changes. PMID:11592996

Enantiopure distorted ribbon-shaped nanographene combining two-photon absorption-based upconversion and circularly polarized luminescence.

PubMed

Cruz, Carlos M; Márquez, Irene R; Mariz, Inês F A; Blanco, Victor; Sánchez-Sánchez, Carlos; Sobrado, Jesús M; Martín-Gago, José A; Cuerva, Juan M; Maçôas, Ermelinda; Campaña, Araceli G

2018-04-28

Herein we describe a distorted ribbon-shaped nanographene exhibiting unprecedented combination of optical properties in graphene-related materials, namely upconversion based on two-photon absorption (TPA-UC) together with circularly polarized luminescence (CPL). The compound is a graphene molecule of ca. 2 nm length and 1 nm width with edge defects that promote the distortion of the otherwise planar lattice. The edge defects are an aromatic saddle-shaped ketone unit and a [5]carbohelicene moiety. This system is shown to combine two-photon absorption and circularly polarized luminescence and a remarkably long emission lifetime of 21.5 ns. The [5]helicene is responsible for the chiroptical activity while the push-pull geometry and the extended network of sp 2 carbons are factors favoring the nonlinear absorption. Electronic structure theoretical calculations support the interpretation of the results.

Roller compaction of moist pharmaceutical powders.

PubMed

Wu, C-Y; Hung, W-L; Miguélez-Morán, A M; Gururajan, B; Seville, J P K

2010-05-31

The compression behaviour of powders during roller compaction is dominated by a number of factors, such as process conditions (roll speed, roll gap, feeding mechanisms and feeding speed) and powder properties (particle size, shape, moisture content). The moisture content affects the powder properties, such as the flowability and cohesion, but it is not clear how the moisture content will influence the powder compression behaviour during roller compaction. In this study, the effect of moisture contents on roller compaction behaviour of microcrystalline cellulose (MCC, Avicel PH102) was investigated experimentally. MCC samples of different moisture contents were prepared by mixing as-received MCC powder with different amount of water that was sprayed onto the powder bed being agitated in a rotary mixer. The flowability of these samples were evaluated in terms of the poured angle of repose and flow functions. The moist powders were then compacted using the instrumented roller compactor developed at the University of Birmingham. The flow and compression behaviour during roller compaction and the properties of produced ribbons were examined. It has been found that, as the moisture content increases, the flowability of moist MCC powders decreases and the powder becomes more cohesive. As a consequence of non-uniform flow of powder into the compaction zone induced by the friction between powder and side cheek plates, all produced ribbons have a higher density in the middle and lower densities at the edges. For the ribbons made of powders with high moisture contents, different hydration states across the ribbon width were also identified from SEM images. Moreover, it was interesting to find that these ribbons were split into two halves. This is attributed to the reduction in the mechanical strength of moist powder compacts with high moisture contents produced at high compression pressures. Copyright (c) 2010 Elsevier B.V. All rights reserved.

The Role of Pickup Ion Dynamics Outside of the Heliopause in the Limit of Weak Pitch Angle Scattering: Implications for the Source of the IBEX Ribbon

NASA Astrophysics Data System (ADS)

Zirnstein, E. J.; Heerikhuisen, J.; Dayeh, M. A.

2018-03-01

We present a new model of the Interstellar Boundary Explorer (IBEX) ribbon based on the secondary energetic neutral atom (ENA) mechanism, under the assumption that there is negligible pitch angle scattering of pickup ions (PUIs) outside the heliopause. Using the results of an MHD-plasma/kinetic-neutral simulation of the heliosphere, we generate PUIs in the outer heliosheath, solve their transport using guiding center theory, and compute ribbon ENA fluxes at 1 au. We implement several aspects of the PUI dynamics, including (1) parallel motion along the local interstellar magnetic field (ISMF), (2) advective transport with the interstellar plasma, (3) the mirror force acting on PUIs propagating along the ISMF, and (4) betatron acceleration of PUIs as they are advected within an increasing magnetic field toward the heliopause. We find that ENA fluxes at 1 au are reduced when PUIs are allowed to move along the ISMF, and ENA fluxes are reduced even more by the inclusion of the mirror force, which pushes particles away from IBEX lines of sight. Inclusion of advection and betatron acceleration do not result in any significant change in the ribbon. Interestingly, the mirror force reduces the ENA fluxes from the inner edge of the ribbon more than those from its outer edge, effectively reducing the ribbon’s width by ∼6° and increasing its radius projected on the sky. This is caused by the asymmetric draping of the ISMF around the heliopause, such that ENAs from the ribbon’s inner edge originate closer to the heliopause, where the mirror force is strongest.

First principles study on the electronic structures and transport properties of armchair/zigzag edge hybridized graphene nanoribbons

NASA Astrophysics Data System (ADS)

Yi, Xiuying; Long, Mengqiu; Liu, Anhua; Li, Mingjun; Xu, Hui

2018-05-01

Graphene nanoribbons (GNRs) can be mainly classified into armchair graphene nanoribbons (aGNRs) and zigzag graphene nanoribbons (zGNRs) by different edge chiral directions. In this work, by introducing Stone-Wales defects on the edges of the V-shaped aGNRs, we propose a kind of armchair/zigzag edge hybridized GNRs (a/zHGNRs) and using the density functional theory and the nonequilibrium Green's function method, the band structures and electronic transport properties of the a/zHGNRs have been calculated. Our results show that an indirect bandgap appears in the band structures of the a/zHGNRs, which is very different from the direct bandgap of aGNRs and gapless of zGNRs. We also find that the valance band is mainly derived from the armchair partial atoms on the hybridized edge, while the conduction band comes mainly from the zigzag partial atoms of the hybridized edge. Meanwhile, the bandgap also oscillates with a period of three when the ribbon width increases. In addition, our quantum transport calculations show that there is a remarkable transition between the semiconductor and the metal with different ribbon widths in the a/zHGNRs devices, and the corresponding physical analysis is given.

Anomalously soft non-Euclidean spring

NASA Astrophysics Data System (ADS)

Levin, Ido; Sharon, Eran

In this work we study the mechanical properties of a frustrated elastic ribbon spring - the non-Euclidean minimal spring. This spring belongs to the family of non-Euclidean plates: it has no spontaneous curvature, but its lateral intrinsic geometry is described by a non-Euclidean reference metric. The reference metric of the minimal spring is hyperbolic, and can be embedded as a minimal surface. We argue that the existence of a continuous set of such isometric minimal surfaces with different extensions leads to a complete degeneracy of the bulk elastic energy of the minimal spring under elongation. This degeneracy is removed only by boundary layer effects. As a result, the mechanical properties of the minimal spring are unusual: the spring is ultra-soft with rigidity that depends on the thickness, t , as t raise 0 . 7 ex 7 7 2 lower 0 . 7 ex 2, and does not explicitly depend on the ribbon's width. These predictions are confirmed by a numerical study of a constrained spring. This work is the first to address the unusual mechanical properties of constrained non-Euclidean elastic objects. We also present a novel experimental system that is capable of constructing such objects, along with many other non-Euclidean plates.

On-Surface Synthesis and Characterization of 9-Atom Wide Armchair Graphene Nanoribbons

DOE PAGES

Talirz, Leopold; Söde, Hajo; Dumslaff, Tim; ...

2017-01-27

The bottom-up approach to synthesize graphene nanoribbons strives not only to introduce a band gap into the electronic structure of graphene but also to accurately tune its value by designing both the width and edge structure of the ribbons with atomic precision. Within this paper, we report the synthesis of an armchair graphene nanoribbon with a width of nine carbon atoms on Au(111) through surface-assisted aryl–aryl coupling and subsequent cyclodehydrogenation of a properly chosen molecular precursor. By combining high-resolution atomic force microscopy, scanning tunneling microscopy, and Raman spectroscopy, we demonstrate that the atomic structure of the fabricated ribbons is exactlymore » as designed. Angle-resolved photoemission spectroscopy and Fourier-transformed scanning tunneling spectroscopy reveal an electronic band gap of 1.4 eV and effective masses of ≈0.1 m e for both electrons and holes, constituting a substantial improvement over previous efforts toward the development of transistor applications. We use ab initio calculations to gain insight into the dependence of the Raman spectra on excitation wavelength as well as to rationalize the symmetry-dependent contribution of the ribbons’ electronic states to the tunneling current. Lastly, we propose a simple rule for the visibility of frontier electronic bands of armchair graphene nanoribbons in scanning tunneling spectroscopy.« less

A New Model for the Heliosphere’s “IBEX Ribbon”

NASA Astrophysics Data System (ADS)

Giacalone, J.; Jokipii, J. R.

2015-10-01

We present a model for the narrow, ribbon-like enhancement in the emission of ∼keV energetic neutral atoms (ENA) coming from the outer heliosphere, coinciding roughly with the plane of the very local interstellar magnetic field (LISMF). We show that the pre-existing turbulent LISMF has sufficient amplitude in magnitude fluctuations to efficiently trap ions with initial pitch-angles near 90°, primarily by magnetic mirroring, leading to a narrow region of enhanced pickup-proton intensity. The pickup protons interact with cold interstellar hydrogen to produce ENAs seen at 1 AU. The computed width of the resulting ribbon of emission is consistent with observations. We also present results from a numerical model that are also generally consistent with the observations. Our interpretation relies only on the pre-existing turbulent interstellar magnetic field to trap the pickup protons. This leads to a broader local pitch-angle distribution compared to that of a ring. Our numerical model also predicts that the ribbon is double-peaked with a central depression. This is a further consequence of the (primarily) magnetic mirroring of pickup ions with pitch-angles close to 90° in the pre-existing, turbulent interstellar magnetic field.

A NEW MODEL FOR THE HELIOSPHERE’S “IBEX RIBBON”

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

Giacalone, J.; Jokipii, J. R.

We present a model for the narrow, ribbon-like enhancement in the emission of ∼keV energetic neutral atoms (ENA) coming from the outer heliosphere, coinciding roughly with the plane of the very local interstellar magnetic field (LISMF). We show that the pre-existing turbulent LISMF has sufficient amplitude in magnitude fluctuations to efficiently trap ions with initial pitch-angles near 90°, primarily by magnetic mirroring, leading to a narrow region of enhanced pickup-proton intensity. The pickup protons interact with cold interstellar hydrogen to produce ENAs seen at 1 AU. The computed width of the resulting ribbon of emission is consistent with observations. Wemore » also present results from a numerical model that are also generally consistent with the observations. Our interpretation relies only on the pre-existing turbulent interstellar magnetic field to trap the pickup protons. This leads to a broader local pitch-angle distribution compared to that of a ring. Our numerical model also predicts that the ribbon is double-peaked with a central depression. This is a further consequence of the (primarily) magnetic mirroring of pickup ions with pitch-angles close to 90° in the pre-existing, turbulent interstellar magnetic field.« less

The influence of API concentration on the roller compaction process: modeling and prediction of the post compacted ribbon, granule and tablet properties using multivariate data analysis.

PubMed

Boersen, Nathan; Carvajal, M Teresa; Morris, Kenneth R; Peck, Garnet E; Pinal, Rodolfo

2015-01-01

While previous research has demonstrated roller compaction operating parameters strongly influence the properties of the final product, a greater emphasis might be placed on the raw material attributes of the formulation. There were two main objectives to this study. First, to assess the effects of different process variables on the properties of the obtained ribbons and downstream granules produced from the rolled compacted ribbons. Second, was to establish if models obtained with formulations of one active pharmaceutical ingredient (API) could predict the properties of similar formulations in terms of the excipients used, but with a different API. Tolmetin and acetaminophen, chosen for their different compaction properties, were roller compacted on Fitzpatrick roller compactor using the same formulation. Models created using tolmetin and tested using acetaminophen. The physical properties of the blends, ribbon, granule and tablet were characterized. Multivariate analysis using partial least squares was used to analyze all data. Multivariate models showed that the operating parameters and raw material attributes were essential in the prediction of ribbon porosity and post-milled particle size. The post compacted ribbon and granule attributes also significantly contributed to the prediction of the tablet tensile strength. Models derived using tolmetin could reasonably predict the ribbon porosity of a second API. After further processing, the post-milled ribbon and granules properties, rather than the physical attributes of the formulation were needed to predict downstream tablet properties. An understanding of the percolation threshold of the formulation significantly improved the predictive ability of the models.

Roller compaction: Effect of relative humidity of lactose powder.

PubMed

Omar, Chalak S; Dhenge, Ranjit M; Palzer, Stefan; Hounslow, Michael J; Salman, Agba D

2016-09-01

The effect of storage at different relative humidity conditions, for various types of lactose, on roller compaction behaviour was investigated. Three types of lactose were used in this study: anhydrous lactose (SuperTab21AN), spray dried lactose (SuperTab11SD) and α-lactose monohydrate 200M. These powders differ in their amorphous contents, due to different manufacturing processes. The powders were stored in a climatic chamber at different relative humidity values ranging from 10% to 80% RH. It was found that the roller compaction behaviour and ribbon properties were different for powders conditioned to different relative humidities. The amount of fines produced, which is undesirable in roller compaction, was found to be different at different relative humidity. The minimum amount of fines produced was found to be for powders conditioned at 20-40% RH. The maximum amount of fines was produced for powders conditioned at 80% RH. This was attributed to the decrease in powder flowability, as indicated by the flow function coefficient ffc and the angle of repose. Particle Image Velocimetry (PIV) was also applied to determine the velocity of primary particles during ribbon production, and it was found that the velocity of the powder during the roller compaction decreased with powders stored at high RH. This resulted in less powder being present in the compaction zone at the edges of the rollers, which resulted in ribbons with a smaller overall width. The relative humidity for the storage of powders has shown to have minimal effect on the ribbon tensile strength at low RH conditions (10-20%). The lowest tensile strength of ribbons produced from lactose 200M and SD was for powders conditioned at 80% RH, whereas, ribbons produced from lactose 21AN at the same condition of 80% RH showed the highest tensile strength. The storage RH range 20-40% was found to be an optimum condition for roll compacting three lactose powders, as it resulted in a minimum amount of fines in the product. Copyright © 2016 Elsevier B.V. All rights reserved.

High-resolution laser-projection display system using a grating electromechanical system (GEMS)

NASA Astrophysics Data System (ADS)

Brazas, John C.; Kowarz, Marek W.

2004-01-01

Eastman Kodak Company has developed a diffractive-MEMS spatial-light modulator for use in printing and display applications, the grating electromechanical system (GEMS). This modulator contains a linear array of pixels capable of high-speed digital operation, high optical contrast, and good efficiency. The device operation is based on deflection of electromechanical ribbons suspended above a silicon substrate by a series of intermediate supports. When electrostatically actuated, the ribbons conform to the supporting substructure to produce a surface-relief phase grating over a wide active region. The device is designed to be binary, switching between a reflective mirror state having suspended ribbons and a diffractive grating state having ribbons in contact with substrate features. Switching times of less than 50 nanoseconds with sub-nanosecond jitter are made possible by reliable contact-mode operation. The GEMS device can be used as a high-speed digital-optical modulator for a laser-projection display system by collecting the diffracted orders and taking advantage of the low jitter. A color channel is created using a linear array of individually addressable GEMS pixels. A two-dimensional image is produced by sweeping the line image of the array, created by the projection optics, across the display screen. Gray levels in the image are formed using pulse-width modulation (PWM). A high-resolution projection display was developed using three 1080-pixel devices illuminated by red, green, and blue laser-color primaries. The result is an HDTV-format display capable of producing stunning still and motion images with very wide color gamut.

High throughput analysis of samples in flowing liquid

DOEpatents

Ambrose, W. Patrick; Grace, W. Kevin; Goodwin, Peter M.; Jett, James H.; Orden, Alan Van; Keller, Richard A.

2001-01-01

Apparatus and method enable imaging multiple fluorescent sample particles in a single flow channel. A flow channel defines a flow direction for samples in a flow stream and has a viewing plane perpendicular to the flow direction. A laser beam is formed as a ribbon having a width effective to cover the viewing plane. Imaging optics are arranged to view the viewing plane to form an image of the fluorescent sample particles in the flow stream, and a camera records the image formed by the imaging optics.

Geometrical structure of Neural Networks: Geodesics, Jeffrey's Prior and Hyper-ribbons

NASA Astrophysics Data System (ADS)

Hayden, Lorien; Alemi, Alex; Sethna, James

2014-03-01

Neural networks are learning algorithms which are employed in a host of Machine Learning problems including speech recognition, object classification and data mining. In practice, neural networks learn a low dimensional representation of high dimensional data and define a model manifold which is an embedding of this low dimensional structure in the higher dimensional space. In this work, we explore the geometrical structure of a neural network model manifold. A Stacked Denoising Autoencoder and a Deep Belief Network are trained on handwritten digits from the MNIST database. Construction of geodesics along the surface and of slices taken from the high dimensional manifolds reveal a hierarchy of widths corresponding to a hyper-ribbon structure. This property indicates that neural networks fall into the class of sloppy models, in which certain parameter combinations dominate the behavior. Employing this information could prove valuable in designing both neural network architectures and training algorithms. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No . DGE-1144153.

Insulator-semimetallic transition in quasi-1D charged impurity-infected armchair boron-nitride nanoribbons

NASA Astrophysics Data System (ADS)

Dinh Hoi, Bui; Yarmohammadi, Mohsen

2018-04-01

We address control of electronic phase transition in charged impurity-infected armchair-edged boron-nitride nanoribbons (ABNNRs) with the local variation of Fermi energy. In particular, the density of states of disordered ribbons produces the main features in the context of pretty simple tight-binding model and Green's functions approach. To this end, the Born approximation has been implemented to find the effect of π-band electron-impurity interactions. A modulation of the π-band depending on the impurity concentrations and scattering potentials leads to the phase transition from insulator to semimetallic. We present here a detailed physical meaning of this transition by studying the treatment of massive Dirac fermions. From our findings, it is found that the ribbon width plays a crucial role in determining the electronic phase of disordered ABNNRs. The obtained results in controllable gap engineering are useful for future experiments. Also, the observations in this study have also fueled interest in the electronic properties of other 2D materials.

WSe2 nanoribbons: new high-performance thermoelectric materials.

PubMed

Chen, Kai-Xuan; Luo, Zhi-Yong; Mo, Dong-Chuan; Lyu, Shu-Shen

2016-06-28

In this work, for the first time, we systematically investigate the ballistic transport properties of WSe2 nanoribbons using first-principles methods. Armchair nanoribbons with narrow ribbon width are mostly semiconductive but the zigzag nanoribbons are metallic. Surprisingly, an enhancement in thermoelectric performance is discovered moving from monolayers to nanoribbons, especially armchair ones. The maximum room-temperature thermoelectric figure of merit of 2.2 for an armchair nanoribbon is discovered. This may be contributed to by the effects of the disordered edges, owing to the existence of dangling bonds at the ribbon edge. H-passivation has turned out to be an effective way to stabilize the edge atoms, which enhances the thermodynamic stability of the nanoribbons. In addition, after H-passivation, all of the armchair nanoribbons exhibit semiconductive properties with similar band gaps (∼1.3 eV). Our work provides instructional theoretical evidence for the application of armchair WSe2 nanoribbons as promising thermoelectric materials. The enhancement mechanism of the disordered edge effect can also encourage further exploration to achieve outstanding thermoelectric materials.

Are Complex Magnetic Field Structures Responsible for the Confined X-class Flares in Super Active Region 12192?

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

Zhang, Jun; Li, Ting; Chen, Huadong, E-mail: zjun@nao.cas.cn, E-mail: hdchen@nao.cas.cn

From 2014 October 19 to 27, six X-class flares occurred in super active region (AR) 12192. They were all confined flares and were not followed by coronal mass ejections. To examine the structures of the four flares close to the solar disk center from October 22 to 26, we firstly employ composite triple-time images in each flare process to display the stratified structure of these flare loops. The loop structures of each flare in both the lower (171 Å) and higher (131 Å) temperature channels are complex, e.g., the flare loops rooting at flare ribbons are sheared or twisted (enwound)more » together, and the complex structures were not destroyed during the flares. For the first flare, although the flare loop system appears as a spindle shape, we can estimate its structures from observations, with lengths ranging from 130 to 300 Mm, heights from 65 to 150 Mm, widths at the middle part of the spindle from 40 to 100 Mm, and shear angles from 16° to 90°. Moreover, the flare ribbons display irregular movements, such as the left ribbon fragments of the flare on October 22 sweeping a small region repeatedly, and both ribbons of the flare on October 26 moved along the same direction instead of separating from each other. These irregular movements also imply that the corresponding flare loops are complex, e.g., several sets of flare loops are twisted together. Although previous studies have suggested that the background magnetic fields prevent confined flares from erupting,based on these observations, we suggest that complex flare loop structures may be responsible for these confined flares.« less

The electrical and thermal transport properties of hybrid zigzag graphene-BN nanoribbons

NASA Astrophysics Data System (ADS)

Gao, Song; Lu, Wei; Zheng, Guo-Hui; Jia, Yalei; Ke, San-Huang

2017-06-01

The electron and phonon transport in hybrid graphene-BN zigzag nanoribbons are investigated by the nonequilibrium Green’s function method combined with density functional theory calculations. A 100% spin-polarized electron transport in a large energy window around the Fermi level is found and this behavior is independent of the ribbon width as long as there contain 3 zigzag carbon chains. The phonon transport calculations show that the ratio of C-chain number to BN-chain number will modify the thermal conductance of the hybrid nanoribbon in a complicated manner.

On the stability of pick-up ion ring distributions in the outer heliosheath

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

Summerlin, Errol J.; Viñas, Adolfo F.; Moore, Thomas E.

The 'secondary energetic neutral atom (ENA)' hypothesis for the ribbon feature observed by the Interstellar Boundary Explorer (IBEX) posits that the neutral component of the solar wind continues beyond the heliopause and charge exchanges with interstellar ions in the Outer Heliosheath (OHS). This creates pick-up ions that gyrate about the draped interstellar magnetic field (ISMF) lines at pitch angles near 90° on the locus where the ISMF lies tangential to the heliopause and perpendicular to the heliocentric radial direction. This location closely coincides with the location of the ribbon feature according to the prevailing inferences of the ISMF orientation andmore » draping. The locally gyrating ions undergo additional charge exchange and escape as free-flying neutral atoms, many of which travel back toward the inner solar system and are imaged by IBEX as a ribbon tracing out the locus described above. For this mechanism to succeed, the pick-up ions must diffuse in pitch angle slowly enough to permit secondary charge exchange before their pitch angle distribution substantially broadens away from 90°. Previous work using linear Vlasov dispersion analysis of parallel propagating waves has suggested that the ring distribution in the OHS is highly unstable, which, if true, would make the secondary ENA hypothesis incapable of rendering the observed ribbon. In this paper, we extend this earlier work to more realistic ring distribution functions. We find that, at the low densities necessary to produce the observed IBEX ribbon via the secondary ENA hypothesis, growth rates are highly sensitive to the temperature of the beam and that even very modest temperatures of the ring beam corresponding to beam widths of <1° are sufficient to damp the self-generated waves associated with the ring beam. Thus, at least from the perspective of linear Vlasov dispersion analysis of parallel propagating waves, there is no reason to expect that the ring distributions necessary to produce the observed IBEX ENA flux via the secondary ENA hypothesis will be unstable to their own self-generated turbulence.« less

On the Stability of Pick-up Ion Ring Distributions in the Outer Heliosheath

NASA Astrophysics Data System (ADS)

Summerlin, Errol J.; Viñas, Adolfo F.; Moore, Thomas E.; Christian, Eric R.; Cooper, John F.

2014-10-01

The "secondary energetic neutral atom (ENA)" hypothesis for the ribbon feature observed by the Interstellar Boundary Explorer (IBEX) posits that the neutral component of the solar wind continues beyond the heliopause and charge exchanges with interstellar ions in the Outer Heliosheath (OHS). This creates pick-up ions that gyrate about the draped interstellar magnetic field (ISMF) lines at pitch angles near 90° on the locus where the ISMF lies tangential to the heliopause and perpendicular to the heliocentric radial direction. This location closely coincides with the location of the ribbon feature according to the prevailing inferences of the ISMF orientation and draping. The locally gyrating ions undergo additional charge exchange and escape as free-flying neutral atoms, many of which travel back toward the inner solar system and are imaged by IBEX as a ribbon tracing out the locus described above. For this mechanism to succeed, the pick-up ions must diffuse in pitch angle slowly enough to permit secondary charge exchange before their pitch angle distribution substantially broadens away from 90°. Previous work using linear Vlasov dispersion analysis of parallel propagating waves has suggested that the ring distribution in the OHS is highly unstable, which, if true, would make the secondary ENA hypothesis incapable of rendering the observed ribbon. In this paper, we extend this earlier work to more realistic ring distribution functions. We find that, at the low densities necessary to produce the observed IBEX ribbon via the secondary ENA hypothesis, growth rates are highly sensitive to the temperature of the beam and that even very modest temperatures of the ring beam corresponding to beam widths of <1° are sufficient to damp the self-generated waves associated with the ring beam. Thus, at least from the perspective of linear Vlasov dispersion analysis of parallel propagating waves, there is no reason to expect that the ring distributions necessary to produce the observed IBEX ENA flux via the secondary ENA hypothesis will be unstable to their own self-generated turbulence.

Characterization of Atrophic Changes in the Cerebral Cortex Using Fractal Dimensional Analysis

PubMed Central

George, Anuh T.; Jeon, Tina; Hynan, Linda S.; Youn, Teddy S.; Kennedy, David N.; Dickerson, Bradford

2010-01-01

The purpose of this project is to apply a modified fractal analysis technique to high-resolution T1 weighted magnetic resonance images in order to quantify the alterations in the shape of the cerebral cortex that occur in patients with Alzheimer’s disease. Images were selected from the Alzheimer’s Disease Neuroimaging Initiative database (Control N=15, Mild-Moderate AD N=15). The images were segmented using a semi-automated analysis program. Four coronal and three axial profiles of the cerebral cortical ribbon were created. The fractal dimensions (Df) of the cortical ribbons were then computed using a box-counting algorithm. The mean Df of the cortical ribbons from AD patients were lower than age-matched controls on six of seven profiles. The fractal measure has regional variability which reflects local differences in brain structure. Fractal dimension is complementary to volumetric measures and may assist in identifying disease state or disease progression. PMID:20740072

Formation of structural steady states in lamellar/sponge phase-separating fluids under shear flow

NASA Astrophysics Data System (ADS)

Panizza, P.; Courbin, L.; Cristobal, G.; Rouch, J.; Narayanan, T.

2003-05-01

We investigate the effect of shear flow on a lamellar-sponge phase-separating fluid when subjected to shear flow. We show the existence of two different steady states (droplets and ribbons structures) whose nature does not depend on the way to reach the two-phase unstable region of the phase diagram (temperature quench or stirring). The transition between ribbons and droplets is shear thickening and its nature strongly depends on what dynamical variable is imposed. If the stress is fixed, flow visualization shows the existence of shear bands at the transition, characteristic of coexistence in the cell between ribbons and droplets. In this shear-banding region, the viscosity oscillates. When the shear rate is fixed, no shear bands are observed. Instead, the transition exhibits a hysteretic behavior leading to a structural bi-stability of the phase-separating fluid under flow.

High Performance Graphene Nano-ribbon Thermoelectric Devices by Incorporation and Dimensional Tuning of Nanopores

PubMed Central

Sharafat Hossain, Md; Al-Dirini, Feras; Hossain, Faruque M.; Skafidas, Efstratios

2015-01-01

Thermoelectric properties of Graphene nano-ribbons (GNRs) with nanopores (NPs) are explored for a range of pore dimensions in order to achieve a high performance two-dimensional nano-scale thermoelectric device. We reduce thermal conductivity of GNRs by introducing pores in them in order to enhance their thermoelectric performance. The electrical properties (Seebeck coefficient and conductivity) of the device usually degrade with pore inclusion; however, we tune the pore to its optimal dimension in order to minimize this degradation, enhancing the overall thermoelectric performance (high ZT value) of our device. We observe that the side channel width plays an important role to achieve optimal performance while the effect of pore length is less pronounced. This result is consistent with the fact that electronic conduction in GNRs is dominated along its edges. Ballistic transport regime is assumed and a semi-empirical method using Huckel basis set is used to obtain the electrical properties, while the phononic system is characterized by Tersoff empirical potential model. The proposed device structure has potential applications as a nanoscale local cooler and as a thermoelectric power generator. PMID:26083450

High Performance Graphene Nano-ribbon Thermoelectric Devices by Incorporation and Dimensional Tuning of Nanopores.

PubMed

Hossain, Md Sharafat; Al-Dirini, Feras; Hossain, Faruque M; Skafidas, Efstratios

2015-06-17

Thermoelectric properties of Graphene nano-ribbons (GNRs) with nanopores (NPs) are explored for a range of pore dimensions in order to achieve a high performance two-dimensional nano-scale thermoelectric device. We reduce thermal conductivity of GNRs by introducing pores in them in order to enhance their thermoelectric performance. The electrical properties (Seebeck coefficient and conductivity) of the device usually degrade with pore inclusion; however, we tune the pore to its optimal dimension in order to minimize this degradation, enhancing the overall thermoelectric performance (high ZT value) of our device. We observe that the side channel width plays an important role to achieve optimal performance while the effect of pore length is less pronounced. This result is consistent with the fact that electronic conduction in GNRs is dominated along its edges. Ballistic transport regime is assumed and a semi-empirical method using Huckel basis set is used to obtain the electrical properties, while the phononic system is characterized by Tersoff empirical potential model. The proposed device structure has potential applications as a nanoscale local cooler and as a thermoelectric power generator.

Spin-polarized electron transport in hybrid graphene-BN nanoribbons

NASA Astrophysics Data System (ADS)

Gao, Song; Lu, Wei; Zheng, Guo-Hui; Jia, Yalei; Ke, San-Huang

2017-05-01

The experimental realization of hybrid graphene and h-BN provides a new way to modify the electronic and transport properties of graphene-based materials. In this work, we investigate the spin-polarized electron transport in hybrid graphene-BN zigzag nanoribbons by performing first-principles nonequilibrium Green’s function method calculations. A 100% spin-polarized electron transport in a large energy window around the Fermi level is found and this behavior is independent of the ribbon width as long as there contain 3 zigzag carbon chains. This behavior may be useful in making perfect spin filters.

Method and apparatus for conducting variable thickness vapor deposition

DOEpatents

Nesslage, G.V.

1984-08-03

A method of vapor depositing metal on a substrate in variable thickness comprises conducting the deposition continuously without interruption to avoid formation of grain boundaries. To achieve reduced deposition in specific regions a thin wire or ribbon blocking body is placed between source and substrate to partially block vapors from depositing in the region immediately below.

Statistical and observational research of solar flare for total spectra and geometrical features

NASA Astrophysics Data System (ADS)

Nishimoto, S.; Watanabe, K.; Imada, S.; Kawate, T.; Lee, K. S.

2017-12-01

Impulsive energy release phenomena such as solar flares, sometimes affect to the solar-terrestrial environment. Usually, we use soft X-ray flux (GOES class) as the index of flare scale. However, the magnitude of effect to the solar-terrestrial environment is not proportional to that scale. To identify the relationship between solar flare phenomena and influence to the solar-terrestrial environment, we need to understand the full spectrum of solar flares. There is the solar flare irradiance model named the Flare Irradiance Spectral Model (FISM) (Chamberlin et al., 2006, 2007, 2008). The FISM can estimate solar flare spectra with high wavelength resolution. However, this model can not express the time evolution of emitted plasma during the solar flare, and has low accuracy on short wavelength that strongly effects and/or controls the total flare spectra. For the purpose of obtaining the time evolution of total solar flare spectra, we are performing statistical analysis of the electromagnetic data of solar flares. In this study, we select solar flare events larger than M-class from the Hinode flare catalogue (Watanabe et al., 2012). First, we focus on the EUV emission observed by the SDO/EVE. We examined the intensities and time evolutions of five EUV lines of 55 flare events. As a result, we found positive correlation between the "soft X-ray flux" and the "EUV peak flux" for all EVU lines. Moreover, we found that hot lines peaked earlier than cool lines of the EUV light curves. We also examined the hard X-ray data obtained by RHESSI. When we analyzed 163 events, we found good correlation between the "hard X-ray intensity" and the "soft X-ray flux". Because it seems that the geometrical features of solar flares effect to those time evolutions, we also looked into flare ribbons observed by SDO/AIA. We examined 21 flare events, and found positive correlation between the "GOES duration" and the "ribbon length". We also found positive correlation between the "ribbon length" and the "ribbon distance", however, there was no remarkable correlation of the "ribbon width". To understand physical process of flare emission, we performed numerical simulation (Imada et al., 2015), and compared with the observational flare model. We also discuss the flare numerical model which can be fitted to the observational flare model.

Partial pseudospin polarization, latticetronics and Fano resonances in quantum dots based in graphene ribbons: a conductance spectroscopy

NASA Astrophysics Data System (ADS)

López, Luis I. A.; Champi, Ana; Ujevic, Sebastian; Mendoza, Michel

2015-11-01

In this work we study, as a function of the height V and width L b of the potential barriers, the transport of Dirac quasi-particles through quantum dots in graphene ribbons. We observed, as we increase V, a partial polarization ( PP) of the pseudospin due to the participation of the hyperbolic bands. This generates polarizations in the sub-lattices A or B outside the dot regions for single, coupled, and open dots. Thus for energies around the Dirac point, the conductance G at both sides of the dot shows a latticetronics of conductances G A and G B as a function of V and L b . This fact can be used as a PP spectroscopy which associates hole-type waves with the latticetronics. A periodic enhancement of PP is obtained with the increase of V in dots formed by barriers that completely occupy the nanoribbon width. For this case, a direct correspondence between G( V) and PP( V) exists. On the other hand, for the open dots, the PP( V) and the G( V) show a complex behavior that exhibit higher intensities when compared to the previous case. In the Dirac limit we have no backscattering signs, however when we move slightly away from this limit the first signs of confinement appear in the PP( V) (it freezes in a given sub-lattice). In the last case the backscattering fingerprints are obtained directly from the conductance (splittings). The open quantum dots are very sensible to their opening w d and this generates Fano line-shapes of difficult interpretation around the Dirac point. The PP spectroscopy used here allows us to understand the influence of w d in the relativistic analogues and to associate electron-type waves with the observed Fano line-shapes.

Graphene FETs Based on High Resolution Nanoribbons for HF Low Power Applications

NASA Astrophysics Data System (ADS)

Mele, David; Mehdhbi, Sarah; Fadil, Dalal; Wei, Wei; Ouerghi, Abdelkarim; Lepilliet, Sylvie; Happy, Henri; Pallecchi, Emiliano

2018-03-01

In this paper we present high frequency field effect transistors based on graphene nanoribbons arrays (GNRFETs). The nanoribbons serve as a channel for the transistors and are fabricated with a process based on e-beam lithography and dry etching of high mobility hydrogen intercalated epitaxial graphene. The widths of the nanoribbons vary from 50 to 20 nm, less than half those measured in previous reports for GNRFETs. Hall measurements reveal that the devices are p-doped, with mobility on the order of 2300 cm2/Vs. From DC characteristics, we find that the maximum ratio IMAX/IMIN is 5 obtained at 50 nm ribbons width. The IV characteristics of the GNRFETs are slightly non-linear at high bias without a full saturation. Therefore, despite the aggressive scaling of the graphene nanoribbon width, a bandgap is still not observed in our measurements. The high frequency performances of our GNRFETs are already significant at low bias. At 300 mV drain source voltage, the highest intrinsic (extrinsic) cut-off frequency ft reaches 82 (18) GHz and the extrinsic maximum oscillation frequency fmax is 20 GHz, which is promising for low power applications.

A study of the microstructure of a rapidly solidified nickel-base superalloy modified with boron. M.S. Thesis. Final Contractor Report

NASA Technical Reports Server (NTRS)

Speck, J. S.

1986-01-01

The microstructures of melt-spun superalloy ribbons with variable boron levels have been studied by transmission electron microscopy. The base alloy was of approximate composition Ni-11% Cr-5%Mo-5%Al-4%Ti with boron levels of 0.06, 0.12, and 0.60 percent (all by weight). Thirty micron thick ribbons display an equiaxed chill zone near the wheel contact side which develops into primary dendrite arms in the ribbon center. Secondary dendrite arms are observed near the ribbon free surface. In the higher boron bearing alloys, boride precipitates are observed along grain boundaries. A concerted effort has been made to elucidate true grain shapes by the use of bright field/dark field microscopy. In the low boron alloy, grain shapes are often convex, and grain faces are flat. Boundary faces frequently have large curvature, and grain shapes form concave polygons in the higher boron level alloys. It is proposed that just after solidification, in all of the alloys studied, grain shapes were initially concave and boundaries were wavy. Boundary straightening is presumed to occur on cooling in the low boron alloy. Boundary migration is precluded in the higher boron alloys by fast precipitation of borides at internal interfaces.

Physical determinants of vesicle mobility and supply at a central synapse

PubMed Central

Rothman, Jason Seth; Kocsis, Laszlo; Herzog, Etienne; Nusser, Zoltan; Silver, Robin Angus

2016-01-01

Encoding continuous sensory variables requires sustained synaptic signalling. At several sensory synapses, rapid vesicle supply is achieved via highly mobile vesicles and specialized ribbon structures, but how this is achieved at central synapses without ribbons is unclear. Here we examine vesicle mobility at excitatory cerebellar mossy fibre synapses which sustain transmission over a broad frequency bandwidth. Fluorescent recovery after photobleaching in slices from VGLUT1Venus knock-in mice reveal 75% of VGLUT1-containing vesicles have a high mobility, comparable to that at ribbon synapses. Experimentally constrained models establish hydrodynamic interactions and vesicle collisions are major determinants of vesicle mobility in crowded presynaptic terminals. Moreover, models incorporating 3D reconstructions of vesicle clouds near active zones (AZs) predict the measured releasable pool size and replenishment rate from the reserve pool. They also show that while vesicle reloading at AZs is not diffusion-limited at the onset of release, diffusion limits vesicle reloading during sustained high-frequency signalling. DOI: http://dx.doi.org/10.7554/eLife.15133.001 PMID:27542193

A tunable electronic beam splitter realized with crossed graphene nanoribbons

NASA Astrophysics Data System (ADS)

Brandimarte, Pedro; Engelund, Mads; Papior, Nick; Garcia-Lekue, Aran; Frederiksen, Thomas; Sánchez-Portal, Daniel

2017-03-01

Graphene nanoribbons (GNRs) are promising components in future nanoelectronics due to the large mobility of graphene electrons and their tunable electronic band gap in combination with recent experimental developments of on-surface chemistry strategies for their growth. Here, we explore a prototype 4-terminal semiconducting device formed by two crossed armchair GNRs (AGNRs) using state-of-the-art first-principles transport methods. We analyze in detail the roles of intersection angle, stacking order, inter-GNR separation, GNR width, and finite voltages on the transport characteristics. Interestingly, when the AGNRs intersect at θ =60° , electrons injected from one terminal can be split into two outgoing waves with a tunable ratio around 50% and with almost negligible back-reflection. The split electron wave is found to propagate partly straight across the intersection region in one ribbon and partly in one direction of the other ribbon, i.e., in analogy with an optical beam splitter. Our simulations further identify realistic conditions for which this semiconducting device can act as a mechanically controllable electronic beam splitter with possible applications in carbon-based quantum electronic circuits and electron optics. We rationalize our findings with a simple model suggesting that electronic beam splitters can generally be realized with crossed GNRs.

The Si ribbon crystal for the solar battery using the horizontal pull method

NASA Technical Reports Server (NTRS)

Norifuji, H.; Matsuo, M.; Maki, T.

1979-01-01

A method utilizing a device to spray noble gases to cool the site of silicon crystal growth is described. The salient points are: (1) soft and uniform cooling was possible, (2) the length of the boundary surface of growth along the growth direction was made long over a wide width compared to the thickness, and (3) this made it possible to effectively remove the heat produced from solification. By using forced gas spraying on the solution surface in contact with the points of crystal growth, growth at the points of growth is enhanced and the rate of growth is speeded up.

On the intra- and interband plasmon modes in doped armchair graphene nanoribbons

NASA Astrophysics Data System (ADS)

Hoi, Bui Dinh; Davoudiniya, Masoumeh; Yarmohammadi, Mohsen

2018-01-01

With the help of the simple tight-binding Hamiltonian and Green's function technique, we study how intraband and interband plasmon modes of both semiconducting and metallic armchair graphene nanoribbons are influenced by the width, chemical doping, and incident momentum direction. In particular, we investigate the behavior of the frequency-dependent susceptibility when the system is exposed to photons or electrons. Injecting electrons by doping creates a new collective mode due to new states between the valence and conduction bands corresponding to intraband transition for which the effect of ribbon width on these transitions in the semiconducting case is much more sensitive than metallic ones. Furthermore, some critical chemical potential and momentum values for both intraband and interband modes lead to different behaviors for resonant peaks. Another remarkable point is the high sensitivity of intraband plasmons to the direction of incident momentum. In particular, the susceptibility of doped nanoribbons vanishes at perpendicular directions, i.e., the intraband plasmons disappear.

Homochiral polymerization-driven selective growth of graphene nanoribbons

NASA Astrophysics Data System (ADS)

Sakaguchi, Hiroshi; Song, Shaotang; Kojima, Takahiro; Nakae, Takahiro

2017-01-01

The surface-assisted bottom-up fabrication of graphene nanoribbons (GNRs), which consists of the radical polymerization of precursors followed by dehydrogenation, has attracted attention because of the method's ability to control the edges and widths of the resulting ribbon. Although these reactions on a metal surface are believed to be catalytic, the mechanism has remained unknown. Here, we demonstrate 'conformation-controlled surface catalysis': the two-zone chemical vapour deposition of a 'Z-bar-linkage' precursor, which represents two terphenyl units linked in a 'Z' shape, results in the efficient formation of acene-type GNRs with a width of 1.45 nm through optimized cascade reactions. These precursors exhibit flexibility that allows them to adopt chiral conformations with height asymmetry on a Au(111) surface, which enables the production of self-assembled homochiral polymers in a chain with a planar conformation, followed by dehydrogenation via a conformation-controlled mechanism. This is conceptually analogous to enzymatic catalysis and will be useful for the fabrication of new nanocarbon materials.

Direct oriented growth of armchair graphene nanoribbons on germanium

PubMed Central

Jacobberger, Robert M.; Kiraly, Brian; Fortin-Deschenes, Matthieu; Levesque, Pierre L.; McElhinny, Kyle M.; Brady, Gerald J.; Rojas Delgado, Richard; Singha Roy, Susmit; Mannix, Andrew; Lagally, Max G.; Evans, Paul G.; Desjardins, Patrick; Martel, Richard; Hersam, Mark C.; Guisinger, Nathan P.; Arnold, Michael S.

2015-01-01

Graphene can be transformed from a semimetal into a semiconductor if it is confined into nanoribbons narrower than 10 nm with controlled crystallographic orientation and well-defined armchair edges. However, the scalable synthesis of nanoribbons with this precision directly on insulating or semiconducting substrates has not been possible. Here we demonstrate the synthesis of graphene nanoribbons on Ge(001) via chemical vapour deposition. The nanoribbons are self-aligning 3° from the Ge〈110〉 directions, are self-defining with predominantly smooth armchair edges, and have tunable width to <10 nm and aspect ratio to >70. In order to realize highly anisotropic ribbons, it is critical to operate in a regime in which the growth rate in the width direction is especially slow, <5 nm h−1. This directional and anisotropic growth enables nanoribbon fabrication directly on conventional semiconductor wafer platforms and, therefore, promises to allow the integration of nanoribbons into future hybrid integrated circuits. PMID:26258594

Baffles Promote Wider, Thinner Silicon Ribbons

NASA Technical Reports Server (NTRS)

Seidensticker, Raymond G.; Mchugh, James P.; Hundal, Rolv; Sprecace, Richard P.

1989-01-01

Set of baffles just below exit duct of silicon-ribbon-growing furnace reduces thermal stresses in ribbons so wider ribbons grown. Productivity of furnace increased. Diverts plume of hot gas from ribbon and allows cooler gas from top of furnace to flow around. Also shields ribbon from thermal radiation from hot growth assembly. Ribbon cooled to lower temperature before reaching cooler exit duct, avoiding abrupt drop in temperature as entering duct.

Flare Ribbons Approach Observed by the Interface Region Imaging Spectrograph and the Solar Dynamics Observatory

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

Li, Ting; Zhang, Jun; Hou, Yijun, E-mail: liting@nao.cas.cn

We report flare ribbons approach (FRA) during a multiple-ribbon M-class flare on 2015 November 4 in NOAA AR 12443, obtained by the Interface Region Imaging Spectrograph and the Solar Dynamics Observatory. The flare consisted of a pair of main ribbons and two pairs of secondary ribbons. The two pairs of secondary ribbons were formed later than the appearance of the main ribbons, with respective time delays of 15 and 19 minutes. The negative-polarity main ribbon spread outward faster than the first secondary ribbon with the same polarity in front of it, and thus the FRA was generated. Just before theirmore » encounter, the main ribbon was darkening drastically and its intensity decreased by about 70% in 2 minutes, implying the suppression of main-phase reconnection that produced two main ribbons. The FRA caused the deflection of the main ribbon to the direction of secondary ribbon with a deflection angle of about 60°. A post-approach arcade was formed about 2 minutes later and the downflows were detected along the new arcade with velocities of 35–40 km s{sup −1}, indicative of the magnetic restructuring during the process of FRA. We suggest that there are three topological domains with footpoints outlined by the three pairs of ribbons. Close proximity of these domains leads to deflection of the ribbons, which is in agreement with the magnetic field topology.« less

Lightweight, variable solidity knitted parachute fabric. [for aerodynamic decelerators

NASA Technical Reports Server (NTRS)

Matthews, F. R., Jr.; White, E. C. (Inventor)

1973-01-01

A parachute fabric for aerodynamic decelerator applications is described. The fabric will permit deployment of the decelerator at high altitudes and low density conditions. The fabric consists of lightweight, highly open, circular knitted parachute fabric with ribbon-like yarns to assist in air deflection.

Ribbon Crystals

PubMed Central

Bohr, Jakob; Markvorsen, Steen

2013-01-01

A repetitive crystal-like pattern is spontaneously formed upon the twisting of straight ribbons. The pattern is akin to a tessellation with isosceles triangles, and it can easily be demonstrated with ribbons cut from an overhead transparency. We give a general description of developable ribbons using a ruled procedure where ribbons are uniquely described by two generating functions. This construction defines a differentiable frame, the ribbon frame, which does not have singular points, whereby we avoid the shortcomings of the Frenet–Serret frame. The observed spontaneous pattern is modeled using planar triangles and cylindrical arcs, and the ribbon structure is shown to arise from a maximization of the end-to-end length of the ribbon, i.e. from an optimal use of ribbon length. The phenomenon is discussed in the perspectives of incompatible intrinsic geometries and of the emergence of long-range order. PMID:24098360

Influence of an irregular surface and low light on the step variability of patients with peripheral neuropathy during level gait.

PubMed

Thies, Sibylle B; Richardson, James K; Demott, Trina; Ashton-Miller, James A

2005-08-01

Patients with peripheral neuropathy (PN) report greater difficulty walking on irregular surfaces with low light (IL) than on flat surfaces with regular lighting (FR). We tested the primary hypothesis that older PN patients would demonstrate greater step width and step width variability under IL conditions than under FR conditions. Forty-two subjects (22 male, 20 female: mean +/- S.D.: 64.7 +/- 9.8 years) with PN underwent history, physical examination, and electrodiagnostic testing. Subjects were asked to walk 10 m at a comfortable speed while kinematic and force data were measured at 100 Hz using optoelectronic markers and foot switches. Ten trials were conducted under both IL and FR conditions. Step width, time, length, and speed were calculated with a MATLAB algorithm, with the standard deviation serving as the measure of variability. The results showed that under IL, as compared to FR, conditions subjects demonstrated greater step width (197.1 +/- 40.8 mm versus 180.5 +/- 32.4 mm; P < 0.001) and step width variability (40.4 +/- 9.0 mm versus 34.5 +/- 8.4 mm; P < 0.001), step time and its variability (P < 0.001 and P = 0.003, respectively), and step length variability (P < 0.001). Average step length and gait speed decreased under IL conditions (P < 0.001 for both). Step width variability and step time variability correlated best under IL conditions with a clinical measure of PN severity and fall history, respectively. We conclude that IL conditions cause PN patients to increase the variability of their step width and other gait parameters.

38 CFR 21.9700 - Yellow Ribbon Program.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 38 Pensions, Bonuses, and Veterans' Relief 2 2011-07-01 2011-07-01 false Yellow Ribbon Program. 21... Ribbon Program. (a) Establishment. The “Yellow Ribbon G.I. Education Enhancement Program”, known as the “Yellow Ribbon Program,” permits an institution of higher learning (IHL), at the IHL's option, to enter...

38 CFR 21.9700 - Yellow Ribbon Program.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 38 Pensions, Bonuses, and Veterans' Relief 2 2013-07-01 2013-07-01 false Yellow Ribbon Program. 21... Ribbon Program. (a) Establishment. The “Yellow Ribbon G.I. Education Enhancement Program”, known as the “Yellow Ribbon Program,” permits an institution of higher learning (IHL), at the IHL's option, to enter...

38 CFR 21.9700 - Yellow Ribbon Program.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 38 Pensions, Bonuses, and Veterans' Relief 2 2010-07-01 2010-07-01 false Yellow Ribbon Program. 21... Ribbon Program. (a) Establishment. The “Yellow Ribbon G.I. Education Enhancement Program”, known as the “Yellow Ribbon Program,” permits an institution of higher learning (IHL), at the IHL's option, to enter...

38 CFR 21.9700 - Yellow Ribbon Program.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 38 Pensions, Bonuses, and Veterans' Relief 2 2014-07-01 2014-07-01 false Yellow Ribbon Program. 21... Ribbon Program. (a) Establishment. The “Yellow Ribbon G.I. Education Enhancement Program”, known as the “Yellow Ribbon Program,” permits an institution of higher learning (IHL), at the IHL's option, to enter...

38 CFR 21.9700 - Yellow Ribbon Program.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 38 Pensions, Bonuses, and Veterans' Relief 2 2012-07-01 2012-07-01 false Yellow Ribbon Program. 21... Ribbon Program. (a) Establishment. The “Yellow Ribbon G.I. Education Enhancement Program”, known as the “Yellow Ribbon Program,” permits an institution of higher learning (IHL), at the IHL's option, to enter...

Ribbon curling

NASA Astrophysics Data System (ADS)

Juel, Anne; Prior, Chris; Moussou, Julien; Chakrabarti, Buddhapriya; Jensen, Oliver

The procedure of curling a ribbon by running it over a sharp blade is commonly used when wrapping presents. Despite its ubiquity, a quantitative explanation of this everyday phenomenon is still lacking. We address this using experiment and theory, examining the dependence of ribbon curvature on blade curvature, the longitudinal load imposed on the ribbon and the speed of pulling. Experiments in which a ribbon is drawn steadily over a blade under a fixed load show that the ribbon curvature is generated over a restricted range of loads, the curvature/load relationship can be non-monotonic, and faster pulling (under a constant imposed load) results in less tightly curled ribbons. We develop a theoretical model that captures these features, building on the concept that the ribbon under the imposed deformation undergoes differential plastic stretching across its thickness, resulting in a permanently curved shape. The model identifies factors that optimize curling and clarifies the physical mechanisms underlying the ribbon's nonlinear response to an apparently simple deformation.

Controlling the microstructure and associated magnetic properties of Ni 0.2Mn 3.2Ga 0.6 melt-spun ribbons by annealing

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

Khan, Mahmud; Alshammari, Ohud; Balasubramanian, Balamurugan

2017-03-01

Here we report on the structural and magnetic properties of Ni 0.2Mn 3.2Ga 0.6 melt-spun ribbons. The as-spun ribbons were found to exhibit mixed cubic phases that transform to non-cubic structure upon annealing. Additionally, an amorphous phase was found to co-exist in all ribbons. The SEM images show that minor grain formation occurs on the as-spun ribbons. However, the formation of extensive nano-grains was observed on the surfaces of the annealed ribbons. While the as-spun ribbons exhibit predominantly paramagnetic behavior, the ribbons annealed under various thermal conditions were found to be ferromagnetic with a Curie temperature of about 380 K.more » The ribbons annealed at 450 °C for 30 minutes exhibit a large coercive field of about 2500 Oe. The experimental results show that the microstructure and associated magnetic properties of the ribbons can be controlled by annealing techniques. The coercive fields and the shape of the magnetic hysteresis loops vary significantly with annealing conditions. As a result, exchange bias effects have also been observed in the annealed ribbons.« less

Generation Mechanisms of Quasi-parallel and Quasi-circular Flare Ribbons in a Confined Flare

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

Hernandez-Perez, Aaron; Thalmann, Julia K.; Veronig, Astrid M.

We analyze a confined multiple-ribbon M2.1 flare (SOL2015-01-29T11:42) that originated from a fan-spine coronal magnetic field configuration, within active region NOAA 12268. The observed ribbons form in two steps. First, two primary ribbons form at the main flare site, followed by the formation of secondary ribbons at remote locations. We observe a number of plasma flows at extreme-ultraviolet temperatures during the early phase of the flare (as early as 15 minutes before the onset) propagating toward the formation site of the secondary ribbons. The secondary ribbon formation is co-temporal with the arrival of the pre-flare generated plasma flows. The primarymore » ribbons are co-spatial with Ramaty High Energy Spectroscopic Imager ( RHESSI ) hard X-ray sources, whereas no enhanced X-ray emission is detected at the secondary ribbon sites. The (E)UV emission, associated with the secondary ribbons, peaks ∼1 minute after the last RHESSI hard X-ray enhancement. A nonlinear force-free model of the coronal magnetic field reveals that the secondary flare ribbons are not directly connected to the primary ribbons, but to regions nearby. Detailed analysis suggests that the secondary brightenings are produced due to dissipation of kinetic energy of the plasma flows (heating due to compression), and not due to non-thermal particles accelerated by magnetic reconnection, as is the case for the primary ribbons.« less

Phonon stiffen and soften at zigzag- and armchair-dominated edges of exfoliated bilayer graphene ribbon presented by Raman spectra

NASA Astrophysics Data System (ADS)

Xia, Minggang; Zhou, Xiaohua; Xin, Duqiang; Xu, Qiang

2018-01-01

The Raman spectra at the edge of the exfoliated bilayer graphene ribbon (GR) were investigated in detail. Results show that both G and 2D phonons stiffen (wave number increases) at zigzag-dominated edge, while they soften at armchair-dominated edge compared with those at the middle position in the GR. Furthermore, the full widths at half maximum intensity of both G and 2D Raman peaks narrow at the zigzag-dominated edge, while they broaden at the armchair-dominated edge. The stiffness and softness are attributed to the C-C bonds at the edge. For zigzag-dominated edge, the stiffness may originate in the increase of the force constant induced by the shrinking of C-C bond. For armchair-dominated edge, the softness may be due to the decrease of the force constant induced by the unsaturated hanging bonds at edge, which is different from Kohn anomaly and charge doping. The analysis is in agreement well with others calculation results about C-C bonds and the edge energy. These results may be useful to understand physical properties at the bilayer graphene edge and for applications in the device by taking advantage of the edge states in bilayer graphene.

Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6 m New Solar Telescope

PubMed Central

Jing, Ju; Xu, Yan; Cao, Wenda; Liu, Chang; Gary, Dale; Wang, Haimin

2016-01-01

Solar flares signify the sudden release of magnetic energy and are sources of so called space weather. The fine structures (below 500 km) of flares are rarely observed and are accessible to only a few instruments world-wide. Here we present observation of a solar flare using exceptionally high resolution images from the 1.6 m New Solar Telescope (NST) equipped with high order adaptive optics at Big Bear Solar Observatory (BBSO). The observation reveals the process of the flare in unprecedented detail, including the flare ribbon propagating across the sunspots, coronal rain (made of condensing plasma) streaming down along the post-flare loops, and the chromosphere’s response to the impact of coronal rain, showing fine-scale brightenings at the footpoints of the falling plasma. Taking advantage of the resolving power of the NST, we measure the cross-sectional widths of flare ribbons, post-flare loops and footpoint brighenings, which generally lie in the range of 80–200 km, well below the resolution of most current instruments used for flare studies. Confining the scale of such fine structure provides an essential piece of information in modeling the energy transport mechanism of flares, which is an important issue in solar and plasma physics. PMID:27071459

Modeling the Charge Transport in Graphene Nano Ribbon Interfaces for Nano Scale Electronic Devices

NASA Astrophysics Data System (ADS)

Kumar, Ravinder; Engles, Derick

2015-05-01

In this research work we have modeled, simulated and compared the electronic charge transport for Metal-Semiconductor-Metal interfaces of Graphene Nano Ribbons (GNR) with different geometries using First-Principle calculations and Non-Equilibrium Green's Function (NEGF) method. We modeled junctions of Armchair GNR strip sandwiched between two Zigzag strips with (Z-A-Z) and Zigzag GNR strip sandwiched between two Armchair strips with (A-Z-A) using semi-empirical Extended Huckle Theory (EHT) within the framework of Non-Equilibrium Green Function (NEGF). I-V characteristics of the interfaces were visualized for various transport parameters. The distinct changes in conductance and I-V curves reported as the Width across layers, Channel length (Central part) was varied at different bias voltages from -1V to 1 V with steps of 0.25 V. From the simulated results we observed that the conductance through A-Z-A graphene junction is in the range of 10-13 Siemens whereas the conductance through Z-A-Z graphene junction is in the range of 10-5 Siemens. These suggested conductance controlled mechanisms for the charge transport in the graphene interfaces with different geometries is important for the design of graphene based nano scale electronic devices like Graphene FETs, Sensors.

Kinematics of ribbon-fin locomotion in the bowfin, Amia calva.

PubMed

Jagnandan, Kevin; Sanford, Christopher P

2013-12-01

An elongated dorsal and/or anal ribbon-fin to produce forward and backward propulsion has independently evolved in several groups of fishes. In these fishes, fin ray movements along the fin generate a series of waves that drive propulsion. There are no published data on the use of the dorsal ribbon-fin in the basal freshwater bowfin, Amia calva. In this study, frequency, amplitude, wavelength, and wave speed along the fin were measured in Amia swimming at different speeds (up to 1.0 body length/sec) to understand how the ribbon-fin generates propulsion. These wave properties were analyzed to (1) determine whether regional specialization occurs along the ribbon-fin, and (2) to reveal how the undulatory waves are used to control swimming speed. Wave properties were also compared between swimming with sole use of the ribbon-fin, and swimming with simultaneous use of the ribbon and pectoral fins. Statistical analysis of ribbon-fin kinematics revealed no differences in kinematic patterns along the ribbon-fin, and that forward propulsive speed in Amia is controlled by the frequency of the wave in the ribbon-fin, irrespective of the contribution of the pectoral fin. This study is the first kinematic analysis of the ribbon-fin in a basal fish and the model species for Amiiform locomotion, providing a basis for understanding ribbon-fin locomotion among a broad range of teleosts. © 2013 Wiley Periodicals, Inc.

27 CFR 9.182 - Ribbon Ridge.

Code of Federal Regulations, 2011 CFR

2011-04-01

... Ribbon Ridge. (a) Name. The name of the viticultural area described in this section is “Ribbon Ridge.” (b) Approved Maps. The appropriate maps used to determine the boundaries of the Ribbon Ridge viticultural area... 27 Alcohol, Tobacco Products and Firearms 1 2011-04-01 2011-04-01 false Ribbon Ridge. 9.182...

27 CFR 9.182 - Ribbon Ridge.

Code of Federal Regulations, 2010 CFR

2010-04-01

... Ribbon Ridge. (a) Name. The name of the viticultural area described in this section is “Ribbon Ridge.” (b) Approved Maps. The appropriate maps used to determine the boundaries of the Ribbon Ridge viticultural area... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Ribbon Ridge. 9.182...

77 FR 9624 - Narrow Woven Ribbons With Woven Selvedge From Taiwan: Rescission, in Part, of Antidumping Duty...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-17

...) Multicolor Inc.; (7) Novelty Handicrafts Co., Ltd.; (8) Pacific Imports; (9) Papillon Ribbon & Bow (Canada... Lion Ribbon Company, Inc., for the following companies: (1) Apex Ribbon; (2) Apex Trimmings; (3) FinerRibbon.com ; (4) Hsien Chan Enterprise Co., Ltd.; (5) Hubschercorp; (6) Intercontinental Skyline; (7...

Patterned helical metallic ribbon for continuous edge winding applications

DOEpatents

Liebermann, Howard H.; Frischmann, Peter G.; Rosenberry, Jr., George M.

1983-04-19

Metallic ribbon having cutout patterns therein is provided in continuous helical form. The cutout patterns may be situated to intersect either or both of the ribbon edges or may be situated entirely within the ribbon. The helical ribbon with the cutout patterns may additionally have a nesting, or self-stacking, feature.

TWISTED RIBBON FUEL ELEMENT

DOEpatents

Breden, C.R.; Schultz, A.B.

1961-06-01

A reactor core formed of bundles of parallel fuel elements in the form of ribbons is patented. The fuel ribbons are twisted about their axes so as to have contact with one another at regions spaced lengthwise of the ribbons and to be out of contact with one another at locations between these spaced regions. The contact between the ribbons is sufficient to allow them to be held together in a stable bundle in a containing tube without intermediate support, while permitting enough space between the ribbon for coolant flowing.

Hard X-Ray Flare Source Sizes Measured with the Ramaty High Energy Solar Spectroscopic Imager

NASA Technical Reports Server (NTRS)

Dennis, Brian R.; Pernak, Rick L.

2009-01-01

Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations of 18 double hard X-ray sources seen at energies above 25 keV are analyzed to determine the spatial extent of the most compact structures evident in each case. The following four image reconstruction algorithms were used: Clean, Pixon, and two routines using visibilities maximum entropy and forward fit (VFF). All have been adapted for this study to optimize their ability to provide reliable estimates of the sizes of the more compact sources. The source fluxes, sizes, and morphologies obtained with each method are cross-correlated and the similarities and disagreements are discussed. The full width at half-maximum (FWHM) of the major axes of the sources with assumed elliptical Gaussian shapes are generally well correlated between the four image reconstruction routines and vary between the RHESSI resolution limit of approximately 2" up to approximately 20" with most below 10". The FWHM of the minor axes are generally at or just above the RHESSI limit and hence should be considered as unresolved in most cases. The orientation angles of the elliptical sources are also well correlated. These results suggest that the elongated sources are generally aligned along a flare ribbon with the minor axis perpendicular to the ribbon. This is verified for the one flare in our list with coincident Transition Region and Coronal Explorer (TRACE) images. There is evidence for significant extra flux in many of the flares in addition to the two identified compact sources, thus rendering the VFF assumption of just two Gaussians inadequate. A more realistic approximation in many cases would be of two line sources with unresolved widths. Recommendations are given for optimizing the RHESSI imaging reconstruction process to ensure that the finest possible details of the source morphology become evident and that reliable estimates can be made of the source dimensions.

A study to improve the mechanical properties of silicon carbide ribbon fibers

NASA Technical Reports Server (NTRS)

Debolt, H. E.; Robey, R. J.

1976-01-01

Preliminary deposition studies of SiC ribbon on a carbon ribbon substrate showed that the dominant strength limiting flaws were at the substrate surface. Procedures for making the carbon ribbon substrate from polyimide film were improved, providing lengths up to 450 meters (1,500 ft.) of flat carbon ribbon substrate 1,900 microns (75 mils) wide by 25 microns (1 mil) thick. The flaws on the carbon ribbon were smaller and less frequent than on carbon ribbon used earlier. SiC ribbon made using the improved substrate, including a layer of pyrolytic graphite to reduce further the severity of substrate surface flaws, showed strength levels up to the 2,068 MPa (300 Ksi) target of the program, with average strength levels over 1,700 MPa (250 Ksi) with coefficient of variation as low as 10% for some runs.

Invalidity of the Fermi liquid theory and magnetic phase transition in quasi-1D dopant-induced armchair-edged graphene nanoribbons

NASA Astrophysics Data System (ADS)

Hoi, Bui Dinh; Davoudiniya, Masoumeh; Yarmohammadi, Mohsen

2018-04-01

Based on theoretically tight-binding calculations considering nearest neighbors and Green's function technique, we show that the magnetic phase transition in both semiconducting and metallic armchair graphene nanoribbons with width ranging from 9.83 Å to 69.3 Å would be observed in the presence of injecting electrons by doping. This transition is explained by the temperature-dependent static charge susceptibility through calculation of the correlation function of charge density operators. This work showed that charge concentration of dopants in such system plays a crucial role in determining the magnetic phase. A variety of multicritical points such as transition temperatures and maximum susceptibility are compared in undoped and doped cases. Our findings show that there exist two different transition temperatures and maximum susceptibility depending on the ribbon width in doped structures. Another remarkable point refers to the invalidity (validity) of the Fermi liquid theory in nanoribbons-based systems at weak (strong) concentration of dopants. The obtained interesting results of magnetic phase transition in such system create a new potential for magnetic graphene nanoribbon-based devices.

Analytical Modeling of Acoustic Phonon-Limited Mobility in Strained Graphene Nanoribbons

NASA Astrophysics Data System (ADS)

Yousefvand, Ali; Ahmadi, Mohammad T.; Meshginqalam, Bahar

2017-11-01

Recent advances in graphene nanoribbon-based electronic devices encourage researchers to develop modeling and simulation methods to explore device physics. On the other hand, increasing the operating speed of nanoelectronic devices has recently attracted significant attention, and the modification of acoustic phonon interactions because of their important effect on carrier mobility can be considered as a method for carrier mobility optimization which subsequently enhances the device speed. Moreover, strain has an important influence on the electronic properties of the nanoelectronic devices. In this paper, the acoustic phonons mobility of armchair graphene nanoribbons ( n-AGNRs) under uniaxial strain is modeled analytically. In addition, strain, width and temperature effects on the acoustic phonon mobility of strained n-AGNRs are investigated. An increment in the strained AGNR acoustic phonon mobility by increasing the ribbon width is reported. Additionally, two different behaviors for the acoustic phonon mobility are verified by increasing the applied strain in 3 m, 3 m + 2 and 3 m + 1 AGNRs. Finally, the temperature effect on the modeled AGNR phonon mobility is explored, and mobility reduction by raising the temperature is reported.

Biased Target Ion Beam Deposition and Nanoskiving for Fabricating NiTi Alloy Nanowires

NASA Astrophysics Data System (ADS)

Hou, Huilong; Horn, Mark W.; Hamilton, Reginald F.

2016-12-01

Nanoskiving is a novel nanofabrication technique to produce shape memory alloy nanowires. Our previous work was the first to successfully fabricate NiTi alloy nanowires using the top-down approach, which leverages thin film technology and ultramicrotomy for ultra-thin sectioning. For this work, we utilized biased target ion beam deposition technology to fabricate nanoscale (i.e., sub-micrometer) NiTi alloy thin films. In contrast to our previous work, rapid thermal annealing was employed for heat treatment, and the B2 austenite to R-phase martensitic transformation was confirmed using stress-temperature and diffraction measurements. The ultramicrotome was programmable and facilitated sectioning the films to produce nanowires with thickness-to-width ratios ranging from 4:1 to 16:1. Energy dispersive X-ray spectroscopy analysis confirmed the elemental Ni and Ti make-up of the wires. The findings exposed the nanowires exhibited a natural ribbon-like curvature, which depended on the thickness-to-width ratio. The results demonstrate nanoskiving is a potential nanofabrication technique for producing NiTi alloy nanowires that are continuous with an unprecedented length on the order of hundreds of micrometers.

Blue Ribbon Commissions and Higher Education: Changing Academe from the Outside. ASHE-ERIC Higher Education Report No. 2, 1986.

ERIC Educational Resources Information Center

Johnson, Janet Rogers-Clarke; Marcus, Laurence R.

Blue ribbon commissions in the United States from 1965-1983 are reviewed, and two commissions are covered in-depth. Attention is directed to: nationally-oriented blue-ribbon commissions, state-level commissions, blue ribbon commissions on campus, and factors that make commissions effective. For purposes of the study, a blue ribbon commission was…

Development of a process for producing ribbon shaped filaments. [production of silicon carbide filaments

NASA Technical Reports Server (NTRS)

Debolt, H. E.; Krukonis, V. J.

1973-01-01

Silicon carbide (SiC) ribbon filaments were produced on a carbon ribbon substrate, about 1500 microns (60 mils) wide and 100 microns (4 mils) thick in lengths up to 2 meters (6 ft), and with tensile strengths up to 142 KN/cm sq (206 Ksi). During the course of the study, ribbon filaments of boron were also produced on the carbon ribbon substrate; the boron ribbon produced was extremely fragile. The tensile strength of the SiC ribbon was limited by large growths or flaws caused by anomalies at the substrate surface; these anomalies were either foreign dirt or substrate imperfections or both. Related work carried out on round 100 micron (4 mils) diameter SiC filaments on a 33 micron (1.3 mil) diameter, very smooth carbon monofilament substrate has shown that tensile strengths as high as 551 KN/cm sq (800 Ksi) are obtainable with the SiC-carbon round substrate combination, and indicates that if the ribbon substrate surface and ribbon deposition process can be improved similar strengths can be realizable. Cost analysis shows that 100 micron x 5-10 micron SiC ribbon can be very low cost reinforcement material.

Quantifying inter- and intra-population niche variability using hierarchical bayesian stable isotope mixing models.

PubMed

Semmens, Brice X; Ward, Eric J; Moore, Jonathan W; Darimont, Chris T

2009-07-09

Variability in resource use defines the width of a trophic niche occupied by a population. Intra-population variability in resource use may occur across hierarchical levels of population structure from individuals to subpopulations. Understanding how levels of population organization contribute to population niche width is critical to ecology and evolution. Here we describe a hierarchical stable isotope mixing model that can simultaneously estimate both the prey composition of a consumer diet and the diet variability among individuals and across levels of population organization. By explicitly estimating variance components for multiple scales, the model can deconstruct the niche width of a consumer population into relevant levels of population structure. We apply this new approach to stable isotope data from a population of gray wolves from coastal British Columbia, and show support for extensive intra-population niche variability among individuals, social groups, and geographically isolated subpopulations. The analytic method we describe improves mixing models by accounting for diet variability, and improves isotope niche width analysis by quantitatively assessing the contribution of levels of organization to the niche width of a population.

Low cost silicon solar arrays

NASA Technical Reports Server (NTRS)

Ravi, K. V.; Serreze, H. B.; Bates, H. E.; Morrison, A. D.; Jewett, D. N.; Ho, J. C. T.; Schwuttke, G. H.; Ciszek, T. F.; Kran, A.

1975-01-01

Continuous growth methodology for silicon solar cell ribbons deals with capillary effects, die effects, thermal effects and crystal shape effects. Emphasis centers on the shape of the meniscus at the ribbon edge as a factor contributing to ribbon quality with respect to defect densities. Structural and electrical characteristics of edge defined, film-fed grown silicon ribbons are elaborated. Ribbon crystal solar cells produce AMO efficiencies of 6 to 10%.

Laser-zone growth in a Ribbon-To-Ribbon, RTR, process silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

NASA Technical Reports Server (NTRS)

Gurtler, R. W.; Baghdadi, A.

1977-01-01

A ribbon-to-ribbon process was used for routine growth of samples for analysis and fabrication into solar cells. One lot of solar cells was completely evaluated: ribbon solar cell efficiencies averaged 9.23% with a highest efficiency of 11.7%. Spherical reflectors have demonstrated significant improvements in laser silicon coupling efficiencies. Material analyses were performed including silicon photovoltage and open circuit photovoltage diffusion length measurements, crystal morphology studies, modulus of rupture measurements, and annealing/gettering studies. An initial economic analysis was performed indicating that ribbon-to-ribbon add-on costs of $.10/watt might be expected in the early 1980's.

Twisted, multifilament Nb3Sn superconductive ribbon

NASA Technical Reports Server (NTRS)

Coles, W. D.

1972-01-01

An experimental study of superconductor stabilization has resulted in the successful application of the concepts of filamentary structure and conductor twist to Nb3Sn ribbon. The Nb3Sn is formed in parallel, helical paths, which are continuous around the ribbon. Short lengths (12-18cm) of 1.27 cm wide superconductive ribbon were produced. The filamentary and twist characteristics are incorporated in the ribbon by means of an inert mask formed on the ribbon surface early in the fabrication process. Diffusion reaction of the niobium and tin is prevented at the filament boundaries. Described are the conductor methods of fabrication, and test results obtained. The technology required to adapt the processes for the production of long lengths of ribbon is available.

Silicon ribbon growth by a capillary action shaping technique

NASA Technical Reports Server (NTRS)

Schwuttke, G. H.; Schwuttke, G. H.; Ciszek, T. F.; Kran, A.

1977-01-01

Substantial improvements in ribbon surface quality are achieved with a higher melt meniscus than that attainable with the film-fed (EFG) growth technique. A capillary action shaping method is described in which meniscus shaping for the desired ribbon geometry occurs at the vertex of a wettable die. As ribbon growth depletes the melt meniscus, capillary action supplies replacement material. Topics discussed cover experimental apparatus and growth procedures; die materials investigations, fabrication and evaluation; process development for 25 mm, 38 mm, 50 mm and 100 mm silicon ribbons; and long grain direct solidification of silicon. Methods for the structural and electrical characterization of cast silicon ribbons are assessed as well as silicon ribbon technology for the 1978 to 1986 period.

Variable-Period Undulators For Synchrotron Radiation

DOEpatents

Shenoy, Gopal; Lewellen, John; Shu, Deming; Vinokurov, Nikolai

2005-02-22

A new and improved undulator design is provided that enables a variable period length for the production of synchrotron radiation from both medium-energy and high-energy storage rings. The variable period length is achieved using a staggered array of pole pieces made up of high permeability material, permanent magnet material, or an electromagnetic structure. The pole pieces are separated by a variable width space. The sum of the variable width space and the pole width would therefore define the period of the undulator. Features and advantages of the invention include broad photon energy tunability, constant power operation and constant brilliance operation.

Ca(2+) influx and neurotransmitter release at ribbon synapses.

PubMed

Cho, Soyoun; von Gersdorff, Henrique

2012-01-01

Ca(2+) influx through voltage-gated Ca(2+) channels triggers the release of neurotransmitters at presynaptic terminals. Some sensory receptor cells in the peripheral auditory and visual systems have specialized synapses that express an electron-dense organelle called a synaptic ribbon. Like conventional synapses, ribbon synapses exhibit SNARE-mediated exocytosis, clathrin-mediated endocytosis, and short-term plasticity. However, unlike non-ribbon synapses, voltage-gated L-type Ca(2+) channel opening at ribbon synapses triggers a form of multiquantal release that can be highly synchronous. Furthermore, ribbon synapses appear to be specialized for fast and high throughput exocytosis controlled by graded membrane potential changes. Here we will discuss some of the basic aspects of synaptic transmission at different types of ribbon synapses, and we will emphasize recent evidence that auditory and retinal ribbon synapses have marked differences. This will lead us to suggest that ribbon synapses are specialized for particular operating ranges and frequencies of stimulation. We propose that different types of ribbon synapses transfer diverse rates of sensory information by expressing a particular repertoire of critical components, and by placing them at precise and strategic locations, so that a continuous supply of primed vesicles and Ca(2+) influx leads to fast, accurate, and ongoing exocytosis. Copyright © 2012 Elsevier Ltd. All rights reserved.

Quasiparticle Energies and Band Gaps in Graphene Nanoribbons

NASA Astrophysics Data System (ADS)

Yang, Li; Park, Cheol-Hwan; Son, Young-Woo; Cohen, Marvin L.; Louie, Steven G.

2007-11-01

We present calculations of the quasiparticle energies and band gaps of graphene nanoribbons (GNRs) carried out using a first-principles many-electron Green’s function approach within the GW approximation. Because of the quasi-one-dimensional nature of a GNR, electron-electron interaction effects due to the enhanced screened Coulomb interaction and confinement geometry greatly influence the quasiparticle band gap. Compared with previous tight-binding and density functional theory studies, our calculated quasiparticle band gaps show significant self-energy corrections for both armchair and zigzag GNRs, in the range of 0.5 3.0 eV for ribbons of width 2.4 0.4 nm. The quasiparticle band gaps found here suggest that use of GNRs for electronic device components in ambient conditions may be viable.

Electronic and Optical properties of Graphene Nanoribbons

NASA Astrophysics Data System (ADS)

Molinari, Elisa; Ferretti, Andrea; Cardoso, Claudia; Prezzi, Deborah; Ruini, Alice

Narrow graphene nanoribbons (GNRs) exhibit substantial electronic band gaps, and optical properties expected to be fundamentally different from the ones of their parent material graphene. Unlike graphene the optical response of GNRs may be tuned by the ribbon width and the directly related electronic band gap. We have addressed the optical properties of chevron-like and finite-size armchair nanoribbons by computing the fundamental and optical gap from ab initio methods. Our results are in very good agreement with the experimental values obtained by STS, ARPES, and differential reflectance spectroscopy, indicating that this computational scheme can be quantitatively predictive for electronic and optical spectroscopies of nanostructures. These study has been partly supported by the EU Centre of Excellence ''MaX - MAterials design at the eXascale''.

Geometry in the mechanics of origami

NASA Astrophysics Data System (ADS)

Dias, Marcelo A.; Santangelo, Christian D.

2012-02-01

We present a mechanical model for curved fold origami in which the bending energies of developable regions are balanced with a phenomenological energy for the crease. The latter energy comes into play as a source of geometric frustration, allowing us to study shape formation by prescribing crease patterns. For a single fold annular configuration, we show how geometry forces a symmetry breaking of the ground state by increasing the width of the ribbon. We extend our model to study multiple fold structures, where we derive geometrical constraints that can be written as recursive relations to build the surface from valley to mountain, and so on. We also suggest a mechanical model for single vertex folds, mapping this problem to an elastica on the sphere.

Electronic and magnetic properties of bare armchair BC2N nanoribbons

NASA Astrophysics Data System (ADS)

Li, Hong; Xiao, Xiang; Tie, Jun; Lu, Jing

2017-03-01

We present the electronic and magnetic properties of bare armchair BC2N nanoribbons (ABC2NNRs) in the view of density functional calculations. We consider three types of edge terminations with a width of 0.75 2.10 nm. All the investigated ribbons exhibit magnetic ground states with the magnetic moments mainly located on the edge C atoms. Room temperature accessible magnetic stabilities are obtained for ABC2NNRs with NC-NC and NC-BC edge alignments. We find the ABC2NNRs have various electronic structures, where half-metal, metal, and semiconductor are all acquired depend on the edge alignment and magnetic coupling state. The results show the ABC2NNRs can be a promising candidate material in nanoelectronics and nanospintronics.

Effects of edge magnetism on the Kohn anomalies of zigzag graphene nanoribbons.

PubMed

Culchac, F J; Capaz, Rodrigo B

2016-02-12

The effects of edge magnetism on the Kohn anomaly (KA) of the G-band phonons of zigzag graphene nanoribbons (ZGNRs) are studied using a combination of the tight-binding and mean-field Hubbard models. We show that the opening of an energy gap, induced by magnetic ordering, significantly changes the KA effects, particularly for narrow ribbons in which the gap is larger than the phonon energy. Therefore, the G-band phonon frequency and lifetime are altered for a magnetically-ordered edge state with respect to an unpolarized edge state. The effects of temperature, ZGNR width, doping and transverse electric fields are systematically investigated. We propose using this effect to probe the magnetic order of edge states in graphene nanoribbons using Raman spectroscopy.

On the location of the Io plasma torus: Voyager 1 observations

NASA Astrophysics Data System (ADS)

Volwerk, Martin

2018-06-01

The Voyager 1 outbound ultraviolet observations of the Io plasma torus are used to determine the location of the ansae, to obtain a third viewing angle of this structure in the Jovian magnetosphere. At an angle of -114° with respect to the Sun-Jupiter line, or a Jovian local time of 04:30 LT, the Voyager 1 data deliver a distance of 5.74±0.10 RJ for the approaching and 5.83±0.15 RJ for the receding ansa. Various periodicities in the radial distance, brightness and width of the ansae are seen with respect to system III longitude and Io phase angle. The torus ribbon feature does not appear in all ansa scans.

Effect of wheel speed and annealing temperature on microstructure and texture evolution of Ni{sub 45}Mn{sub 36.6}In{sub 13.4}Co{sub 5} ribbon

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

Feng, Yan, E-mail: yanfeng@nwpu.edu.cn

Ni{sub 45}Mn{sub 36.6}In{sub 13.4}Co{sub 5} magnetic shape memory alloy was successfully produced as preferentially textured ribbon by melting spinning with different wheel speed. X-ray diffraction (XRD) and electron back scatter diffraction (EBSD) were used to study structure and texture evolution of these melt-spun ribbons. The thickness of melt-spun ribbon is 42 μm, 65 μm and 30 μm depending on wheel speed of 1 0 m/s, 15 m/s and 20 m/s, respectively. Density of α fiber texture (〈100〉//ND) vary with wheel speed changes, and is most intensive in the ribbon with wheel speed of 15 m/s. Grains of the ribbons growmore » after being annealed at 873 K, 973 K, 1073 K and 1173 K, recrystallization was not observed in ribbons after being annealed at 873 K but occurred in ribbons after being annealed at higher temperatures. The α fiber texture becomes weaker to some extent after annealing at different temperatures, due to new recrystallization texture formed at the process of annealing. - Highlights: •Sectional part of shape memory ribbon is firstly investigated by EBSD method. •Thickness and texture of ribbons vary with wheel speed. •Annealing temperature affect texture and microstructure evolution greatly. •Recrystallization textures were observed in ribbons after being annealed.« less

Thick silicon growth techniques

NASA Technical Reports Server (NTRS)

Bates, H. E.; Mlavsky, A. I.; Jewett, D. N.

1973-01-01

Hall mobility measurements on a number of single crystal silicon ribbons grown from graphite dies have shown some ribbons to have mobilities consistent with their resistivities. The behavior of other ribbons appears to be explained by the introduction of impurities of the opposite sign. Growth of a small single crystal silicon ribbon has been achieved from a beryllia dia. Residual internal stresses of the order of 7 to 18,000 psi have been determined to exist in some silicon ribbon, particularly those grown at rates in excess of 1 in./min. Growth experiments have continued toward definition of a configuration and parameters to provide a reasonable yield of single crystal ribbons. High vacuum outgassing of graphite dies and evacuation and backfilling of growth chambers have provided significant improvements in surface quality of ribbons grown from graphite dies.

Are All Flare Ribbons Simply Connected to the Corona?

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

Judge, Philip G.; Paraschiv, Alin; Lacatus, Daniela

We consider the observational basis for the belief that flare ribbons in the chromosphere result from energy transport from the overlying corona. We study ribbons of small flares using magnetic and intensity data from the Hinode , Solar Dynamics Observatory , and IRIS missions. While most ribbons appear connected to the corona and overlie regions of significant vertical magnetic field, we examine one ribbon with no clear evidence for such connections. Evolving horizontal magnetic fields seen with Hinode suggest that reconnection with preexisting fields below the corona can explain the data. The identification of just one, albeit small, ribbon, withmore » no apparent connection to the corona, leads us to conclude that at least two mechanisms are responsible for the heating that leads to flare ribbon emission.« less

Dry Ribbon for Heated Head Automated Fiber Placement

NASA Technical Reports Server (NTRS)

Hulcher, A. Bruce; Marchello, Joseph M.; Hinkley, Jeffrey A.; Johnston, Norman J.; Lamontia, Mark A.

2000-01-01

Ply-by-ply in situ processes involving automated heated head deposition are being developed for fabrication of high performance, high temperature composite structures from low volatile content polymer matrices. This technology requires (1) dry carbon fiber towpreg, (2) consolidation of towpreg to quality, placement-grade unidirectional ribbon or tape, and (3) rapid, in situ, accurate, ply-by-ply robotic placement and consolidation of this material to fabricate a composite structure. In this study, the physical properties of a candidate thermoplastic ribbon, PIXA/IM7, were evaluated and screened for suitability in robotic placement. Specifically, towpreg was prepared from PIXA powder. Various conditions (temperatures) were used to convert the powder-coated towpreg to ribbons with varying degrees of processability. Ribbon within preset specifications was fabricated at 3 temperatures: 390, 400 and 410 C. Ribbon was also produced out-of-spec by purposely overheating the material to a processing temperature of 450 C. Automated placement equipment at Cincinnati Milacron and NASA Langley was used to fabricate laminates from these experimental ribbons. Ribbons were placed at 405 and 450 C by both sets of equipment. Double cantilever beam and wedge peel tests were used to determine the quality of the laminates and, especially, the interlaminar bond formed during the placement process. Ribbon made under conditions expected to be non-optimal (overheated) resulted in poor placeability and composites with weak interlaminar bond strengths, regardless of placement conditions. Ribbon made under conditions expected to be ideal showed good processability and produced well-consolidated laminates. Results were consistent from machine to machine and demonstrated the importance of ribbon quality in heated-head placement of dry material forms. Preliminary screening criteria for the development and evaluation of ribbon from new matrix materials were validated.

Process for fabricating continuous lengths of superconductor

DOEpatents

Kroeger, Donald M.; List, III, Frederick A.

1998-01-01

A process for manufacturing a superconductor. The process is accomplished by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon, overlaying a continuous length of a second substrate ribbon on said first substrate ribbon, and applying sufficient pressure to form a bound layered superconductor precursor between said first substrate ribbon and said second substrates ribbon. The layered superconductor precursor is then heat treated to form a super conductor layer.

Large area silicon sheet by EFG

NASA Technical Reports Server (NTRS)

Morrison, A. D.; Ravi, K. V.; Rao, C. V. H.; Surek, T.; Bliss, D. F.; Garone, L. C.; Hogencamp, R. W.

1976-01-01

Progress in a program to produce high speed, thin, wide silicon sheets for fabricating 10% efficient solar cells is reported. An EFG ribbon growth system was used to perform growth rate and ribbon thickness experiments. A new, wide ribbon growth system was developed. A theoretical study of stresses in ribbons was also conducted. The EFG ribbons were observed to exhibit a characteristic defect structure which is orientation dependent in the early stages of growth.

75 FR 81592 - Blue Ribbon Commission on America's Nuclear Future

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-28

... DEPARTMENT OF ENERGY Blue Ribbon Commission on America's Nuclear Future AGENCY: Department of... meeting of the Blue Ribbon Commission on America's Nuclear Future (the Commission). The Commission was...: The President directed that the Blue Ribbon Commission on America's Nuclear Future (the Commission) be...

76 FR 1607 - Blue Ribbon Commission on America's Nuclear Future

Federal Register 2010, 2011, 2012, 2013, 2014

2011-01-11

... DEPARTMENT OF ENERGY Blue Ribbon Commission on America's Nuclear Future AGENCY: Department of... meeting of the Blue Ribbon Commission on America's Nuclear Future (the Commission). The Commission was...: Background: The President directed that the Blue Ribbon Commission on America's Nuclear Future (the...

Acute destruction of the synaptic ribbon reveals a role for the ribbon in vesicle priming.

PubMed

Snellman, Josefin; Mehta, Bhupesh; Babai, Norbert; Bartoletti, Theodore M; Akmentin, Wendy; Francis, Adam; Matthews, Gary; Thoreson, Wallace; Zenisek, David

2011-07-24

In vision, balance and hearing, sensory receptor cells translate sensory stimuli into electrical signals whose amplitude is graded with stimulus intensity. The output synapses of these sensory neurons must provide fast signaling to follow rapidly changing stimuli while also transmitting graded information covering a wide range of stimulus intensity and must be able to sustain this signaling for long time periods. To meet these demands, specialized machinery for transmitter release, the synaptic ribbon, has evolved at the synaptic outputs of these neurons. We found that acute disruption of synaptic ribbons by photodamage to the ribbon markedly reduced both sustained and transient components of neurotransmitter release in mouse bipolar cells and salamander cones without affecting the ultrastructure of the ribbon or its ability to localize synaptic vesicles to the active zone. Our results indicate that ribbons mediate both slow and fast signaling at sensory synapses and support an additional role for the synaptic ribbon in priming vesicles for exocytosis at active zones.

Ribbon curling via stress relaxation in thin polymer films

PubMed Central

Prior, Chris; Moussou, Julien; Chakrabarti, Buddhapriya

2016-01-01

The procedure of curling a ribbon by running it over a sharp blade is commonly used when wrapping presents. Despite its ubiquity, a quantitative explanation of this everyday phenomenon is still lacking. We address this using experiment and theory, examining the dependence of ribbon curvature on blade curvature, the longitudinal load imposed on the ribbon, and the speed of pulling. Experiments in which a ribbon is drawn steadily over a blade under a fixed load show that the ribbon curvature is generated over a restricted range of loads, the curvature/load relationship can be nonmonotonic, and faster pulling (under a constant imposed load) results in less tightly curled ribbons. We develop a theoretical model that captures these features, building on the concept that the ribbon under the imposed deformation undergoes differential plastic stretching across its thickness, resulting in a permanently curved shape. The model identifies factors that optimize curling and clarifies the physical mechanisms underlying the ribbon’s nonlinear response to an apparently simple deformation. PMID:26831118

Innervation regulates synaptic ribbons in lateral line mechanosensory hair cells

PubMed Central

Pujol, Remy; Cunningham, Dale E.; Hailey, Dale W.; Prendergast, Andrew; Rubel, Edwin W.; Raible, David W.

2016-01-01

ABSTRACT Failure to form proper synapses in mechanosensory hair cells, the sensory cells responsible for hearing and balance, leads to deafness and balance disorders. Ribbons are electron-dense structures that tether synaptic vesicles to the presynaptic zone of mechanosensory hair cells where they are juxtaposed with the post-synaptic endings of afferent fibers. They are initially formed throughout the cytoplasm, and, as cells mature, ribbons translocate to the basolateral membrane of hair cells to form functional synapses. We have examined the effect of post-synaptic elements on ribbon formation and maintenance in the zebrafish lateral line system by observing mutants that lack hair cell innervation, wild-type larvae whose nerves have been transected and ribbons in regenerating hair cells. Our results demonstrate that innervation is not required for initial ribbon formation but suggest that it is crucial for regulating the number, size and localization of ribbons in maturing hair cells, and for ribbon maintenance at the mature synapse. PMID:27103160

Innervation regulates synaptic ribbons in lateral line mechanosensory hair cells.

PubMed

Suli, Arminda; Pujol, Remy; Cunningham, Dale E; Hailey, Dale W; Prendergast, Andrew; Rubel, Edwin W; Raible, David W

2016-06-01

Failure to form proper synapses in mechanosensory hair cells, the sensory cells responsible for hearing and balance, leads to deafness and balance disorders. Ribbons are electron-dense structures that tether synaptic vesicles to the presynaptic zone of mechanosensory hair cells where they are juxtaposed with the post-synaptic endings of afferent fibers. They are initially formed throughout the cytoplasm, and, as cells mature, ribbons translocate to the basolateral membrane of hair cells to form functional synapses. We have examined the effect of post-synaptic elements on ribbon formation and maintenance in the zebrafish lateral line system by observing mutants that lack hair cell innervation, wild-type larvae whose nerves have been transected and ribbons in regenerating hair cells. Our results demonstrate that innervation is not required for initial ribbon formation but suggest that it is crucial for regulating the number, size and localization of ribbons in maturing hair cells, and for ribbon maintenance at the mature synapse. © 2016. Published by The Company of Biologists Ltd.

Texture inheritance from austenite to 7 M martensite in Ni-Mn-Ga melt-spun ribbons

NASA Astrophysics Data System (ADS)

Li, Zongbin; Jiang, Yiwen; Li, Zhenzhuang; Yang, Yiqiao; Yang, Bo; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang

In this work, Ni53Mn22Ga25 and Ni51Mn27Ga22 ribbons with austenite and 7 M martensite at room temperature respectively, were prepared by melt-spinning. Through the detailed crystallographic analyses, the preferred orientation in ribbons was confirmed. It is shown that the austenite in Ni53Mn22Ga25 ribbons forms a preferred orientation with {4 0 0}A in parallel to ribbon plane, whereas the 7 M martensite in Ni51Mn27Ga22 ribbons develops the preferred orientation with {2 0 -20}7M, {2 0 20}7M, and {0 4 0}7M crystallographic planes parallel to the ribbon plane. Since {2 0 -20}7M, {2 0 20}7M, and {0 4 0}7M are originated from {4 0 0}A, the preferred orientation in ribbons thus can be inherited after the martensitic transformation. Such texture inheritance is attributed to the intrinsic orientation relationship between austenite and 7 M martensite.

The status of silicon ribbon growth technology for high-efficiency silicon solar cells

NASA Technical Reports Server (NTRS)

Ciszek, T. F.

1985-01-01

More than a dozen methods have been applied to the growth of silicon ribbons, beginning as early as 1963. The ribbon geometry has been particularly intriguing for photovoltaic applications, because it might provide large area, damage free, nearly continuous substrates without the material loss or cost of ingot wafering. In general, the efficiency of silicon ribbon solar cells has been lower than that of ingot cells. The status of some ribbon growth techniques that have achieved laboratory efficiencies greater than 13.5% are reviewed, i.e., edge-defined, film-fed growth (EFG), edge-supported pulling (ESP), ribbon against a drop (RAD), and dendritic web growth (web).

OBSERVATIONS OF AN X-SHAPED RIBBON FLARE IN THE SUN AND ITS THREE-DIMENSIONAL MAGNETIC RECONNECTION

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

Li, Y.; Ding, M. D.; Yang, K.

2016-05-20

We report evolution of an atypical X-shaped flare ribbon that provides novel observational evidence of three-dimensional (3D) magnetic reconnection at a separator. The flare occurred on 2014 November 9. High-resolution slit-jaw 1330 Å images from the Interface Region Imaging Spectrograph reveal four chromospheric flare ribbons that converge and form an X-shape. Flare brightening in the upper chromosphere spreads along the ribbons toward the center of the “X” (the X-point), and then spreads outward in a direction more perpendicular to the ribbons. These four ribbons are located in a quadrupolar magnetic field. Reconstruction of magnetic topology in the active region suggestsmore » the presence of a separator connecting to the X-point outlined by the ribbons. The inward motion of flare ribbons in the early stage therefore indicates 3D magnetic reconnection between two sets of non-coplanar loops that approach laterally, and reconnection proceeds downward along a section of vertical current sheet. Coronal loops are also observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory confirming the reconnection morphology illustrated by ribbon evolution.« less

75 FR 57898 - NIST Blue Ribbon Commission on Management and Safety-II

Federal Register 2010, 2011, 2012, 2013, 2014

2010-09-23

... DEPARTMENT OF COMMERCE National Institute of Standards and Technology NIST Blue Ribbon Commission... Commerce. ACTION: Notice of establishment of the NIST Blue Ribbon Commission on Management and Safety--II... NIST Blue Ribbon Commission on Management and Safety--II ``Commission''. The Commission will assess...

CIRCULARITY OF THE INTERSTELLAR BOUNDARY EXPLORER RIBBON OF ENHANCED ENERGETIC NEUTRAL ATOM (ENA) FLUX

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

Funsten, H. O.; Higdon, D. M.; Larsen, B. A.

2013-10-10

As a sharp feature in the sky, the ribbon of enhanced energetic neutral atom (ENA) flux observed by the Interstellar Boundary Explorer (IBEX) mission is a key signature for understanding the interaction of the heliosphere and the interstellar medium through which we are moving. Over five nominal IBEX energy passbands (0.7, 1.1, 1.7, 2.7, and 4.3 keV), the ribbon is extraordinarily circular, with a peak location centered at ecliptic (λ{sub RC}, β{sub RC}) = (219.°2 ± 1.°3, 39.°9 ± 2.°3) and a half cone angle of φ{sub C} = 74.°5 ± 2.°0. A slight elongation of the ribbon, generally perpendicularmore » to the ribbon center-heliospheric nose vector and with eccentricity ∼0.3, is observed over all energies. At 4.3 keV, the ribbon is slightly larger and displaced relative to lower energies. For all ENA energies, a slice of the ribbon flux peak perpendicular to the circular arc is asymmetric and systematically skewed toward the ribbon center. We derive a spatial coherence parameter δ{sub C} ≤ 0.014 that characterizes the spatial uniformity of the ribbon over its extent in the sky and is a key constraint for understanding the underlying processes and structure governing the ribbon ENA emission.« less

Statistical Properties of Ribbon Evolution and Reconnection Electric Fields in Eruptive and Confined Flares

NASA Astrophysics Data System (ADS)

Hinterreiter, J.; Veronig, A. M.; Thalmann, J. K.; Tschernitz, J.; Pötzi, W.

2018-03-01

A statistical study of the chromospheric ribbon evolution in Hα two-ribbon flares was performed. The data set consists of 50 confined (62%) and eruptive (38%) flares that occurred from June 2000 to June 2015. The flares were selected homogeneously over the Hα and Geostationary Operational Environmental Satellite (GOES) classes, with an emphasis on including powerful confined flares and weak eruptive flares. Hα filtergrams from the Kanzelhöhe Observatory in combination with Michelson Doppler Imager (MDI) and Helioseismic and Magnetic Imager (HMI) magnetograms were used to derive the ribbon separation, the ribbon-separation velocity, the magnetic-field strength, and the reconnection electric field. We find that eruptive flares reveal statistically larger ribbon separation and higher ribbon-separation velocities than confined flares. In addition, the ribbon separation of eruptive flares correlates with the GOES SXR flux, whereas no clear dependence was found for confined flares. The maximum ribbon-separation velocity is not correlated with the GOES flux, but eruptive flares reveal on average a higher ribbon-separation velocity (by ≈ 10 km s-1). The local reconnection electric field of confined (cc=0.50 ±0.02) and eruptive (cc=0.77 ±0.03) flares correlates with the GOES flux, indicating that more powerful flares involve stronger reconnection electric fields. In addition, eruptive flares with higher electric-field strengths tend to be accompanied by faster coronal mass ejections.

Centrifugally decoupling touchdown bearings

DOEpatents

Post, Richard F

2014-06-24

Centrifugally decoupling mechanical bearing systems provide thin tensioned metallic ribbons contained in a support structure. This assembly rotates around a stationary shaft being centered at low speeds by the action of the metal ribbons. Tension springs are connected on one end to the ribbons and on the other end to the support structure. The ribbons pass through slots in the inner ring of the support structure. The spring preloading thus insures contact (or near-contact) between the ribbons and the shaft at rotation speeds below the transition speed. Above this speed, however, the centrifugal force on the ribbons produces a tensile force on them that exceeds the spring tensile force so that the ribbons curve outward, effectively decoupling them from mechanical contact with the shaft. They still remain, however, in position to act as a touchdown bearing in case of abnormally high transverse accelerations.

Are All Flare Ribbons Simply Connected to the Corona?

NASA Astrophysics Data System (ADS)

Judge, Philip G.; Paraschiv, Alin; Lacatus, Daniela; Donea, Alina; Lindsey, Charlie

2017-04-01

We consider the observational basis for the belief that flare ribbons in the chromosphere result from energy transport from the overlying corona. We study ribbons of small flares using magnetic and intensity data from the Hinode, Solar Dynamics Observatory, and IRIS missions. While most ribbons appear connected to the corona and overlie regions of significant vertical magnetic field, we examine one ribbon with no clear evidence for such connections. Evolving horizontal magnetic fields seen with Hinode suggest that reconnection with preexisting fields below the corona can explain the data. The identification of just one, albeit small, ribbon, with no apparent connection to the corona, leads us to conclude that at least two mechanisms are responsible for the heating that leads to flare ribbon emission. The National Center for Atmospheric Research is sponsored by the National Science Foundation.

7 CFR 1217.2 - Blue Ribbon Commission or BRC.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 7 Agriculture 10 2014-01-01 2014-01-01 false Blue Ribbon Commission or BRC. 1217.2 Section 1217.2 Agriculture Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (MARKETING... Education, and Industry Information Order Definitions § 1217.2 Blue Ribbon Commission or BRC. Blue Ribbon...

7 CFR 1217.2 - Blue Ribbon Commission or BRC.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 7 Agriculture 10 2012-01-01 2012-01-01 false Blue Ribbon Commission or BRC. 1217.2 Section 1217.2 Agriculture Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (MARKETING... Education, and Industry Information Order Definitions § 1217.2 Blue Ribbon Commission or BRC. Blue Ribbon...

7 CFR 1217.2 - Blue Ribbon Commission or BRC.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 7 Agriculture 10 2013-01-01 2013-01-01 false Blue Ribbon Commission or BRC. 1217.2 Section 1217.2 Agriculture Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (MARKETING... Education, and Industry Information Order Definitions § 1217.2 Blue Ribbon Commission or BRC. Blue Ribbon...

78 FR 14963 - Narrow Woven Ribbons With Woven Selvedge From Taiwan: Rescission, in Part, of Antidumping Duty...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-03-08

... companies: (1) Apex Ribbon; (2) Apex Trimmings Inc. (d.b.a. Papillon Ribbon & Bow (Canada)) (Apex Trimmings... an administrative review for the following companies: (1) Apex Ribbon; (2) Apex Trimmings; (3...; (2) Apex Trimmings; (3) Hubschercorp; (4) [[Page 14964

Crystallographic control and texture inheritance during mylonitization of coarse grained quartz veins

NASA Astrophysics Data System (ADS)

Ceccato, Alberto; Pennacchioni, Giorgio; Menegon, Luca; Bestmann, Michel

2017-10-01

Quartz veins within Rieserferner pluton underwent deformation during post-magmatic cooling at temperature around 450 °C. Different crystallographic orientations of cm-sized quartz vein crystals conditioned the evolution of microstructures and crystallographic preferred orientations (CPO) during vein-parallel simple shear up to high shear strains (γ ≈ 10). For γ < 2, crystals stretched to ribbons of variable aspect ratios. The highest aspect ratios resulted from {m} glide in ribbons with c-axis sub-parallel to the shear zone vorticity Y-axis. Ribbons with c-axis orthogonal to Y (XZ-type ribbons) were stronger and hardened more quickly: they show lower aspect ratios and fine (grain size 10-20 μm) recrystallization along sets of microshear zones (μSZs) exploiting crystallographic planes. Distortion of XZ-type ribbons and recrystallization preferentially exploited the slip systems with misorientation axis close to Y. New grains of μSZs initiated by subgrain rotation recrystallization (SGR) and thereupon achieved high angle misorientations by a concurrent process of heterogeneous rigid grain rotation around Y associated with the confined shear within the μSZ. Dauphiné twinning occurred pervasively, but did not play a dominant role on μSZ nucleation. Recrystallization became widespread at γ > 2 and pervasive at γ ≈ 10. Ultramylonitic quartz veins are fine grained ( 10 μm, similar to new grains of μSZ) and show a CPO banding resulting in a bulk c-axis CPO with a Y-maximum, as part of a single girdle about orthogonal to the foliation, and orientations at the pole figure periphery at moderate to high angle to the foliation. This bulk CPO derives from steady-state SGR associated with preferential activity, in the different CPO bands, of slip systems generating subgrain boundaries with misorientation axes close to Y. The CPO of individual recrystallized bands is largely inherited from the original crystallographic orientation of the ribbons (and therefore vein crystals) from which they derived. High strain and pervasive recrystallization were not enough to reset the initial crystallographic heterogeneity and this CPO memory is explained by the dominance of SGR. This contrast with experimental observation of a rapid erasure of a pristine CPO by cannibalism from grains with the most favourably oriented slip system under dominant grain boundary migration recrystallization.

Silicon ribbon growth by a capillary action shaping technique

NASA Technical Reports Server (NTRS)

Schwuttke, G. H.; Ciszek, T. F.; Kran, A.; Yang, K.

1977-01-01

The crystal-growth method under investigation is a capillary action shaping technique. Meniscus shaping for the desired ribbon geometry occurs at the vertex of a wettable dye. As ribbon growth depletes the melt meniscus, capillary action supplies replacement material. The configuration of the technique used in our initial studies is shown. The crystal-growth method has been applied to silicon ribbons it was found that substantial improvements in ribbon surface quality could be achieved with a higher melt meniscus than that attainable with the EFG technique.

Statistical mechanics of ribbons under bending and twisting torques.

PubMed

Sinha, Supurna; Samuel, Joseph

2013-11-20

We present an analytical study of ribbons subjected to an external torque. We first describe the elastic response of a ribbon within a purely mechanical framework. We then study the role of thermal fluctuations in modifying its elastic response. We predict the moment-angle relation of bent and twisted ribbons. Such a study is expected to shed light on the role of twist in DNA looping and on bending elasticity of twisted graphene ribbons. Our quantitative predictions can be tested against future single molecule experiments.

Apparatus for fabricating continuous lengths of superconductor

DOEpatents

Kroeger, Donald M.; List, III, Frederick A.

2002-01-01

A process and apparatus for manufacturing a superconductor. The process is accomplished by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon, overlaying a continuous length of a second substrate ribbon on said first substrate ribbon, and applying sufficient pressure to form a bound layered superconductor comprising a layer of said superconducting precursor powder between said first substrate ribbon and said second substrates ribbon. The layered superconductor is then heat treated to establish the superconducting phase of said superconductor precursor powder.

Apparatus for fabricating continuous lengths of superconductor

DOEpatents

Kroeger, Donald M.; List, III, Frederick A.

2001-01-01

A process and apparatus for manufacturing a superconductor. The process is accomplished by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon, overlaying a continuous length of a second substrate ribbon on said first substrate ribbon, and applying sufficient pressure to form a bound layered superconductor comprising a layer of said superconducting precursor powder between said first substrate ribbon and said second substrates ribbon. The layered superconductor is then heat treated to establish the superconducting phase of said superconductor precursor powder.

Continuous lengths of oxide superconductors

DOEpatents

Kroeger, Donald M.; List, III, Frederick A.

2000-01-01

A layered oxide superconductor prepared by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon. A continuous length of a second substrate ribbon is overlaid on the first substrate ribbon. Sufficient pressure is applied to form a bound layered superconductor precursor powder between the first substrate ribbon and the second substrate ribbon. The layered superconductor precursor is then heat treated to establish the oxide superconducting phase. The layered oxide superconductor has a smooth interface between the substrate and the oxide superconductor.

Guidance system for low angle silicon ribbon growth

DOEpatents

Jewett, David N.; Bates, Herbert E.; Milstein, Joseph B.

1986-07-08

In a low angle silicon sheet growth process, a puller mechanism advances a seed crystal and solidified ribbon from a cooled growth zone in a melt at a low angle with respect to the horizontal. The ribbon is supported on a ramp adjacent the puller mechanism. Variations in the vertical position of the ribbon with respect to the ramp are isolated from the growth end of the ribbon by (1) growing the ribbon so that it is extremely thin, preferably less than 0.7 mm, (2) maintaining a large growth zone, preferably one whose length is at least 5.0 cm, and (3) spacing the ramp from the growth zone by at least 15 cm.

Enantiopure distorted ribbon-shaped nanographene combining two-photon absorption-based upconversion and circularly polarized luminescence† †Electronic supplementary information (ESI) available: General details, synthesis and spectroscopy data of new compounds. Experimental details on optical, chiroptical, electrochemical and on-surface measurements. Crystal data and structure refinement of compounds 1, and 6. Further details on theoretical calculations and Cartesian coordinates of computed structures. VT-H1NMR, 2D-NMR and HRMS spectra of 1. CCDC 1561552 and 1561553. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8sc00427g

PubMed Central

Cruz, Carlos M.; Márquez, Irene R.; Mariz, Inês F. A.; Blanco, Victor; Sánchez-Sánchez, Carlos; Sobrado, Jesús M.; Martín-Gago, José A.; Cuerva, Juan M.

2018-01-01

Herein we describe a distorted ribbon-shaped nanographene exhibiting unprecedented combination of optical properties in graphene-related materials, namely upconversion based on two-photon absorption (TPA-UC) together with circularly polarized luminescence (CPL). The compound is a graphene molecule of ca. 2 nm length and 1 nm width with edge defects that promote the distortion of the otherwise planar lattice. The edge defects are an aromatic saddle-shaped ketone unit and a [5]carbohelicene moiety. This system is shown to combine two-photon absorption and circularly polarized luminescence and a remarkably long emission lifetime of 21.5 ns. The [5]helicene is responsible for the chiroptical activity while the push–pull geometry and the extended network of sp2 carbons are factors favoring the nonlinear absorption. Electronic structure theoretical calculations support the interpretation of the results. PMID:29780523

Solid-liquid interfacial free energy of ice Ih, ice Ic, and ice 0 within a mono-atomic model of water via the capillary wave method.

PubMed

Ambler, Michael; Vorselaars, Bart; Allen, Michael P; Quigley, David

2017-02-21

We apply the capillary wave method, based on measurements of fluctuations in a ribbon-like interfacial geometry, to determine the solid-liquid interfacial free energy for both polytypes of ice I and the recently proposed ice 0 within a mono-atomic model of water. We discuss various choices for the molecular order parameter, which distinguishes solid from liquid, and demonstrate the influence of this choice on the interfacial stiffness. We quantify the influence of discretisation error when sampling the interfacial profile and the limits on accuracy imposed by the assumption of quasi one-dimensional geometry. The interfacial free energies of the two ice I polytypes are indistinguishable to within achievable statistical error and the small ambiguity which arises from the choice of order parameter. In the case of ice 0, we find that the large surface unit cell for low index interfaces constrains the width of the interfacial ribbon such that the accuracy of results is reduced. Nevertheless, we establish that the interfacial free energy of ice 0 at its melting temperature is similar to that of ice I under the same conditions. The rationality of a core-shell model for the nucleation of ice I within ice 0 is questioned within the context of our results.

Edge effects on the electronic properties of phosphorene nanoribbons

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

Peng, Xihong, E-mail: xihong.peng@asu.edu; Copple, Andrew; Wei, Qun

2014-10-14

Two dimensional few-layer black phosphorus crystal structures have recently been fabricated and have demonstrated great potential in electronic applications. In this work, we employed first principles density functional theory calculations to study the edge and quantum confinement effects on the electronic properties of the phosphorene nanoribbons (PNR). Different edge functionalization groups, such as H, F, Cl, OH, O, S, and Se, in addition to a pristine case were studied for a series of ribbon widths up to 3.5 nm. It was found that the armchair-PNRs (APNRs) are semiconductors for all edge groups considered in this work. However, the zigzag-PNRs (ZPNRs)more » show either semiconductor or metallic behavior in dependence on their edge chemical species. Family 1 edges (i.e., H, F, Cl, OH) form saturated bonds with P atoms in the APNRs and ZPNRs, and the edge states keep far away from the band gap. However, Family 2 edges (pristine, O, S, Se) form weak unsaturated bonds with the p{sub z} orbital of the phosphorus atoms and bring edge states within the band gap of the ribbons. For the ZPNRs, the edge states of Family 2 are present around the Fermi level within the band gap, which close up the band gap of the ZPNRs. For the APNRs, these edge states are located at the bottom of the conduction band and result in a reduced band gap.« less

Chirality effect in disordered graphene ribbon junctions

NASA Astrophysics Data System (ADS)

Long, Wen

2012-05-01

We investigate the influence of edge chirality on the electronic transport in clean or disordered graphene ribbon junctions. By using the tight-binding model and the Landauer-Büttiker formalism, the junction conductance is obtained. In the clean sample, the zero-magnetic-field junction conductance is strongly chirality-dependent in both unipolar and bipolar ribbons, whereas the high-magnetic-field conductance is either chirality-independent in the unipolar or chirality-dependent in the bipolar ribbon. Furthermore, we study the disordered sample in the presence of magnetic field and find that the junction conductance is always chirality-insensitive for both unipolar and bipolar ribbons with adequate disorders. In addition, the disorder-induced conductance plateaus can exist in all chiral bipolar ribbons provided the disorder strength is moderate. These results suggest that we can neglect the effect of edge chirality in fabricating electronic devices based on the magnetotransport in a disordered graphene ribbon.

Sm5(Fe,Ti)17 melt-spun ribbons with high coercivity

NASA Astrophysics Data System (ADS)

Saito, Tetsuji; Horita, Toru

2018-05-01

It has previously been reported that annealing of amorphous Sm5Fe17 melt-spun ribbon resulted in the formation of the Sm5Fe17 phase and the resultant Sm5Fe17 melt-spun ribbon exhibited a high coercivity. However, the annealing condition of the amorphous Sm5Fe17 melt-spun ribbon was somewhat critical and it was not easy to obtain Sm5Fe17 grains with high coercivity. In the present study, it was found that the small substitution of Ti for Fe in the Sm5Fe17 melt-spun ribbon stabilized the Sm5Fe17 phase. Annealed Sm5Fe16.7Ti0.3 melt-spun ribbon consisted of small and homogeneous Sm5(Fe,Ti)17 grains and exhibited a higher coercivity than the annealed Sm5Fe17 melt-spun ribbon.

Asymmetric Die Grows Purer Silicon Ribbon

NASA Technical Reports Server (NTRS)

Kalejs, J. P.; Chalmers, B.; Surek, T.

1983-01-01

Concentration of carbide impurities in silicon ribbon is reduced by growing crystalline ribbon with die one wall higher than other. Height difference controls shape of meniscus at liquid/crystal interface and concentrates silicon carbide impurity near one of broad faces. Opposite face is left with above-average purity. Significantly improves efficiency of solar cells made from ribbon.

Blue Ribbon Commissions and Higher Education. ERIC Digest.

ERIC Educational Resources Information Center

Johnson, Janet R.; Marcus, Laurence R.

Blue ribbon commissions in the United States from 1965-1983 are discussed with attention to what makes a commission effective, the history of blue ribbon commissions, features of a commission, whether these commissions are useful on campus, and criticisms of blue ribbon commissions. Factors that contribute to the effectiveness of a blue ribbon…

Investigation of ablation of thin foil aluminum ribbon array at 1.5 MA

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

Ye, Fan, E-mail: yefan1931@126.com; Li, Zhenghong; Chen, Faxin

We present experimental studies of initiation and ablation of a thin foil aluminum ribbon array at the 1.5 MA current level. In contrast to the previous work, we employ ribbon arrays with different ribbon gap parameters to investigate how this affects plasma initiation and foil ablation. Gated narrowband ultraviolet imaging indicated that the current was disorderly distributed at early period of discharge. But later on, it became axially stable and azimuthally symmetrical even for load with a gap as small as 0.1 mm. Using magnetic field probes installed inside and outside the array, we also observed that precursor current at positionsmore » with a distance of less than 2.7 mm to the central axis for 4-mm-radius arrays decreased when ribbon gap became small. Results of 0.2 mm gap ribbon array showed an evidence that ribbons can be merged. These observations imply that thin foil ribbon arrays may have potential applications in z-pinch experiments on large scale pulsed power facilities.« less

Large area silicon sheet by EFG

NASA Technical Reports Server (NTRS)

1981-01-01

Progress was made in improving ribbon flatness and reducing stress, and in raising cell performance for 10 cm wide ribbon grown in single cartridge EFG furnaces. Optimization of growth conditions resulted in improved ribbon thickness uniformity at a thickness of 200 micron, grown at 4 cm/minute, and growth at this target speed is routinely achieved over periods of the order of one hour or more. With the improved ribbon flatness, fabrication of large area (50 cm2) cells is now possible, and 10 to 11% efficiencies were demonstrated on ribbon grown at 3.5 to 4 cm/minute. Factors limiting performance of the existing multiple ribbon furnace were identified, and growth system improvements implemented to help raise throughput rates and the time percentage of simultaneous three-ribbon growth. However, it is evident that major redesign of this furnace would be needed to overcome shortfalls in its ability to achieve the Technical Features Demonstration goals of 1980. It was decided to start construction of a new multiple ribbon furnace and to incorporate the desired improvements into its design. The construction of this furnace is completed.

Roller compaction: Effect of morphology and amorphous content of lactose powder on product quality.

PubMed

Omar, Chalak S; Dhenge, Ranjit M; Osborne, James D; Althaus, Tim O; Palzer, Stefan; Hounslow, Michael J; Salman, Agba D

2015-12-30

The effect of morphology and amorphous content, of three types of lactose, on the properties of ribbon produced using roller compaction was investigated. The three types of lactose powders were; anhydrous SuperTab21AN, α-lactose monohydrate 200 M, and spray dried lactose SuperTab11SD. The morphology of the primary particles was identified using scanning electron microscopy (SEM) and the powder amorphous content was quantified using NIR technique. SEM images showed that 21AN and SD are agglomerated type of lactose whereas the 200 M is a non-agglomerated type. During ribbon production, an online thermal imaging technique was used to monitor the surface temperature of the ribbon. It was found that the morphology and the amorphous content of lactose powders have significant effects on the roller compaction behaviour and on ribbon properties. The agglomerated types of lactose produced ribbon with higher surface temperature and tensile strength, larger fragment size, lower porosity and lesser fines percentages than the non-agglomerated type of lactose. The lactose powder with the highest amorphous content showed to result in a better binding ability between the primary particles. This type of lactose produced ribbons with the highest temperature and tensile strength, and the lowest porosity and amount of fines in the product. It also produced ribbon with more smooth surfaces in comparison to the other two types of lactose. It was noticed that there is a relationship between the surface temperature of the ribbon during production and the tensile strength of the ribbon; the higher the temperature of the ribbon during production the higher the tensile strength of the ribbon. Copyright © 2015 Elsevier B.V. All rights reserved.

Variation of Hardness and Modulus across thickness of Zr-Cu-Al Metallic Glass Ribbons

Treesearch

Z. Humberto Melgarejo; J.E. Jakes; J. Hwang; Y.E. Kalay; M.J. Kramer; P.M. Voyles; D.S. Stone

2012-01-01

We investigate through-thickness hardness and modulus of Zr50Cu45Al5 metallic glass melt-spun ribbon. Because of their thinness, the ribbons are challenging to measure, so we employ a novel nanoindentation based-method to remove artifacts caused by ribbon flexing and edge effects. Hardness and modulus...

Numerical Simulations of a Jovian Ribbon-like Feature

NASA Astrophysics Data System (ADS)

Morales-Juberias, R.; Simon-Miller, A. A.; Dowling, T. E.; Sayanagi, K. M.; Choi, D. S.

2013-12-01

HST observations show the presence of a Ribbon like feature in Jupiter's atmosphere at ≈ 30 degrees North. The presence of this feature seems to correlate with periods when the jet amplitude velocities are highest. Studies of motions can help to determine the nature of the feature. Its detailed structure will be studied using Hubble data at multiple wavelengths and it may be possible to reprocess the long global movies of the Voyager era to study motions at this latitude. Preliminary model results without forcing show that the morphology of the produced instabilities is dependent on the conditions of the background flow and static stability of the atmosphere. Different forcing terms will be used to study the variable nature of this feature. We use numerical simulations to investigate the instabilities produced by different kinds of forcing on the westward jet centered at ≈ 30 degrees North in Jupiter's atmosphere as well as in its two flanking eastward jets to the north and south. Our goal is to understand how the background flow and static stability of the atmosphere affect the ability of the model to reproduce the Ribbon-like cloud pattern observed in Hubble Space Telescope (HST) images of that latitude taken in support of the 2007 New Horizons Jupiter flyby.

Tree Wave Migration Across an Elevation Gradient in the Altai Mountains, Siberia

NASA Technical Reports Server (NTRS)

Kharuk, Viacheslav I.; Im, Sergei T.; Dvinskaya, Maria L.; Ranson, Kenneth J.; Petrov, Il'ya

2017-01-01

The phenomenon of tree waves (hedges and ribbons) formation within the alpine ecotone in Altai Mountains and its response to observed air temperature increase was considered. At the upper limit of tree growth Siberian pine (Pinus sibirica) forms hedges on windward slopes and ribbons on the leeward ones. Hedges were formed by prevailing winds and oriented along winds direction. Ribbons were formed by snow blowing and accumulating on the leeward slope and perpendicular to the prevailing winds, as well as to the elevation gradient. Hedges were always linked with microtopography features, whereas ribbons were not. Trees are migrating upward by waves and new ribbons and hedges are forming at or near tree line, whereas at lower elevations ribbons and hedges are being transformed into closed forests. 19 Time series of high-resolution satellite scenes (from 1968 to 2010) indicated an upslope shift in the position ribbons averaged 15526 m (or 3.7 m yr -1) and crown closure increased (about 3590). The hedges advance was limited by poor regeneration establishment and was negligible. Regeneration within the ribbon zone was approximately 2.5 times (5060 vs 2120 ha -1) higher then within the hedges zone. During the last four decades, Siberian pine in both hedges and ribbons strongly increased its growth increment and recent tree growth rate for 50 year old trees was about twice higher than recorded for similarly aged trees at the beginning of the 20th century. Hedges and ribbons are phenomena that are widespread within the southern and northern Siberian Mountains

Two Episodes of Magnetic Reconnections during a Confined Circular-ribbon Flare

NASA Astrophysics Data System (ADS)

Li, Ting; Yang, Shuhong; Zhang, Qingmin; Hou, Yijun; Zhang, Jun

2018-06-01

We analyze a unique event with an M1.8 confined circular-ribbon flare on 2016 February 13, with successive formations of two circular ribbons at the same location. The flare had two distinct phases of UV and extreme ultraviolet emissions with an interval of about 270 s, of which the second peak was energetically more important. The first episode was accompanied by the eruption of a mini-filament and the fast elongation motion of a thin circular ribbon (CR1) along the counterclockwise direction at a speed of about 220 km s‑1. Two elongated spine-related ribbons were also observed, with the inner ribbon co-temporal with CR1 and the remote brightenings forming ∼20 s later. In the second episode, another mini-filament erupted and formed a blowout jet. The second circular ribbon and two spine-related ribbons showed similar elongation motions with that during the first episode. The extrapolated three-dimensional coronal magnetic fields reveal the existence of a fan-spine topology, together with a quasi-separatrix layer (QSL) halo surrounding the fan plane and another QSL structure outlining the inner spine. We suggest that continuous null-point reconnection between the filament and ambient open field occurs in each episode, leading to the sequential opening of the filament and significant shifts of the fan plane footprint. For the first time, we propose a compound eruption model of circular-ribbon flares consisting of two sets of successively formed ribbons and eruptions of multiple filaments in a fan-spine-type magnetic configuration.

Statistical Properties of Ribbon Evolution and Reconnection Electric Fields in Eruptive and Confined Flares.

PubMed

Hinterreiter, J; Veronig, A M; Thalmann, J K; Tschernitz, J; Pötzi, W

2018-01-01

A statistical study of the chromospheric ribbon evolution in H[Formula: see text] two-ribbon flares was performed. The data set consists of 50 confined (62%) and eruptive (38%) flares that occurred from June 2000 to June 2015. The flares were selected homogeneously over the H[Formula: see text] and Geostationary Operational Environmental Satellite (GOES) classes, with an emphasis on including powerful confined flares and weak eruptive flares. H[Formula: see text] filtergrams from the Kanzelhöhe Observatory in combination with Michelson Doppler Imager (MDI) and Helioseismic and Magnetic Imager (HMI) magnetograms were used to derive the ribbon separation, the ribbon-separation velocity, the magnetic-field strength, and the reconnection electric field. We find that eruptive flares reveal statistically larger ribbon separation and higher ribbon-separation velocities than confined flares. In addition, the ribbon separation of eruptive flares correlates with the GOES SXR flux, whereas no clear dependence was found for confined flares. The maximum ribbon-separation velocity is not correlated with the GOES flux, but eruptive flares reveal on average a higher ribbon-separation velocity (by ≈ 10 km s -1 ). The local reconnection electric field of confined ([Formula: see text]) and eruptive ([Formula: see text]) flares correlates with the GOES flux, indicating that more powerful flares involve stronger reconnection electric fields. In addition, eruptive flares with higher electric-field strengths tend to be accompanied by faster coronal mass ejections. The online version of this article (10.1007/s11207-018-1253-1) contains supplementary material, which is available to authorized users.

Passive diffusion as a mechanism underlying ribbon synapse vesicle release and resupply.

PubMed

Graydon, Cole W; Zhang, Jun; Oesch, Nicholas W; Sousa, Alioscka A; Leapman, Richard D; Diamond, Jeffrey S

2014-07-02

Synaptic ribbons are presynaptic protein structures found at many synapses that convey graded, "analog" sensory signals in the visual, auditory, and vestibular pathways. Ribbons, typically anchored to the presynaptic membrane and surrounded by tethered synaptic vesicles, are thought to regulate or facilitate vesicle delivery to the presynaptic membrane. No direct evidence exists, however, to indicate how vesicles interact with the ribbon or, once attached, move along the ribbon's surface to reach the presynaptic release sites at its base. To address these questions, we have created, validated, and tested a passive vesicle diffusion model of retinal rod bipolar cell ribbon synapses. We used axial (bright-field) electron tomography in the scanning transmission electron microscopy to obtain 3D structures of rat rod bipolar cell terminals in 1-μm-thick sections of retinal tissue at an isotropic spatial resolution of ∼3 nm. The resulting structures were then incorporated with previously published estimates of vesicle diffusion dynamics into numerical simulations that accurately reproduced electrophysiologically measured vesicle release/replenishment rates and vesicle pool sizes. The simulations suggest that, under physiologically realistic conditions, diffusion of vesicles crowded on the ribbon surface gives rise to a flow field that enhances delivery of vesicles to the presynaptic membrane without requiring an active transport mechanism. Numerical simulations of ribbon-vesicle interactions predict that transient binding and unbinding of multiple tethers to each synaptic vesicle may achieve sufficiently tight association of vesicles to the ribbon while permitting the fast diffusion along the ribbon that is required to sustain high release rates. Copyright © 2014 the authors 0270-6474/14/348948-15$15.00/0.

Fluid-Structure Interaction Study on a Pre-Buckled Deformable Flat Ribbon

NASA Astrophysics Data System (ADS)

Fovargue, Lauren; Shams, Ehsan; Watterson, Amy; Corson, Dave; Filardo, Benjamin; Zimmerman, Daniel; Shan, Bob; Oberai, Assad

2015-11-01

A Fluid-Structure Interaction study is conducted for the flow over a deformable flat ribbon. This mechanism, which is called ribbon frond, maybe used as a device for pumping water and/or harvesting energy in rivers. We use a lower dimensional mathematical model, which represents the ribbon as a pre-buckled structure. The surface forces from the fluid flow, dictate the deformation of the ribbon, and the ribbon in turn imposes boundary conditions for the incompressible Navier-Stokes equations. The mesh motion is handled using an Arbitrary Lagrangian-Eulerian (ALE) scheme and the fluid-structure coupling is handled by iterating over the staggered governing equations for the structure, the fluid and the mesh. Simulations are conducted at three different free stream velocities. The results, including the frequency of oscillations, show agreement with experimental data. The vortical structures near the surface of the ribbon and its deformation are highly correlated. It is observed that the ribbon motion exhibits deviation from a harmonic motion, especially at lower free stream velocities. The behavior of the ribbon is compared to swimming animals, such as eels, in order to better understand its performance. The authors acknowledge support from ONR SBIR Phase II, contract No. N0001412C0604 and USDA, NIFA SBIR Phase I, contract No. 2013-33610-20836 and NYSERDA PON 2569, contract No. 30364.

Melt dumping in string stabilized ribbon growth

DOEpatents

Sachs, Emanuel M.

1986-12-09

A method and apparatus for stabilizing the edge positions of a ribbon drawn from a melt includes the use of wettable strings drawn in parallel up through the melt surface, the ribbon being grown between the strings. A furnace and various features of the crucible used therein permit continuous automatic growth of flat ribbons without close temperature control or the need for visual inspection.

Edge modulation of electronics and transport properties of cliff-edge phosphorene nanoribbons

NASA Astrophysics Data System (ADS)

Guo, Caixia; Wang, Tianxing; Xia, Congxin; Liu, Yufang

2017-12-01

Based on the first-principles calculations, we study the electronic structures and transport properties of cliff-like edge phosphorene nanoribbons (CPNRs), considering different types of edge passivation. The band structures of bare CPNRs possess the metallic features; while hydrogen (H), fluorine (F), chlorine (Cl) and oxygen (O) atoms-passivated CPNRs are semiconductor materials, and the band gap values monotonically decrease when the ribbon width increases. Moreover, the H and F-passivated CPNRs exhibit the direct band gap characteristics, while the Cl and O-passivated cases show the features of indirect band gap. In addition, the edge passivated CPNRs are more energetically stable than bare edge case. Meanwhile, our results also show that the transport properties of the CPNRs can be obviously influenced by the different edge passivation.

Density functional theory calculations for armchair stanene nanoribbons with fluorine and sulfur functionalization

NASA Astrophysics Data System (ADS)

Zhang, J.; Lang, X. Y.; Jiang, Q.

2018-07-01

A systematic density functional theory calculation has been carried out to study the effect of edge terminating of F and S elements with different edge natures on the structure and electronic properties of armchair stanene nanoribbons (ASnNRs). Moreover, the corresponding size (ribbon width Na) dependence on these properties is also considered. The energy gap was found to be oscillated as a function of Na and could be classified into three distinct groups of 3m, 3m + 1 and 3m + 2. In addition, the energy gaps of ASnNRs saturated by S atoms differ from that did by F and H atoms in vibration trends as well VBM and CBM changes, where the energy gap is a direct energy gap with a moderate size.

Speculations on processes responsible for mesoscale current lineations on the continental shelf, southern California

USGS Publications Warehouse

Karl, Herman A.

1980-01-01

A side-scan sonar survey of San Pedro shelf, California, reveals areas of mesoscale current lineations oriented approximately north-northeast in water depths of 20-25 m. Widths of sand ribbons range from 40 to 120 m and intervening erosional furrows, from 15 to 50 m. A conceptual model shows that the scale and orientation of current lineations agree with the dimensions and axial directions of Langmuir circulations theoretically generated by a combination either of southerly and southwesterly winds with regular trains of swell from the southern hemisphere or of two sets of wave trains crossing from the south and west. These longitudinal bedforms indicate shore-normal sediment transport at the times and on the areas of the shelf when and where they have been observed.

Processing and characterization of α-elastin electrospun membranes

NASA Astrophysics Data System (ADS)

Araujo, J.; Padrão, J.; Silva, J. P.; Dourado, F.; Correia, D. M.; Botelho, G.; Gomez Ribelles, J. L.; Lanceros-Méndez, S.; Sencadas, V.

2014-06-01

Elastin isolated from fresh bovine ligaments was dissolved in a mixture of 1,1,1,3,3,3-Hexafluoro-2-propanol and water were electrospun into fiber membranes under different processing conditions. Fiber mats of randomly and aligned fibers were obtained with fixed and rotating ground collectors and fibrils were composed by thin ribbons whose width depends on electrospinning conditions; fibrils with 721 nm up to 2.12 μm width were achieved. After cross-linking with glutaraldehyde, α-elastin can uptake as much as 1700 % of PBS solution and a slight increase on fiber thickness was observed. The glass transition temperature of electrospun fiber mats was found to occur at ˜80 °C. Moreover, α-Elastin showed to be a perfect elastomeric material, and no mechanical hysteresis was found in cycle mechanical measurements. The elastic modulus obtained for random and aligned fibers mats in a PBS solution was 330±10 kPa and 732±165 kPa, respectively. Finally, the electrospinning and cross-linking process does not inhibit MC-3T3-E1 cell adhesion. Cell culture results showed good cell adhesion and proliferation in the cross-linked elastin fiber mats.

Wearable energy-smart ribbons for synchronous energy harvest and storage

PubMed Central

Li, Chao; Islam, Md. Monirul; Moore, Julian; Sleppy, Joseph; Morrison, Caleb; Konstantinov, Konstantin; Dou, Shi Xue; Renduchintala, Chait; Thomas, Jayan

2016-01-01

A promising energy source for many current and future applications is a ribbon-like device that could simultaneously harvest and store energy. Due to the high flexibility and weavable property, a fabric/matrix made using these ribbons could be highly beneficial for powering wearable electronics. Unlike the approach of using two separate devices, here we report a ribbon that integrates a solar cell and a supercapacitor. The electrons generated by the solar cell are directly transferred and stored on the reverse side of its electrode which in turn also functions as an electrode for the supercapacitor. When the flexible solar ribbon is illuminated with simulated solar light, the supercapacitor holds an energy density of 1.15 mWh cm−3 and a power density of 243 mW cm−3. Moreover, these ribbons are successfully woven into a fabric form. Our all-solid-state ribbon unveils a highly flexible and portable self-sufficient energy system with potential applications in wearables, drones and electric vehicles. PMID:27834367

Laser-zone growth in a Ribbon-To-Ribbon (RTR) process silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

NASA Technical Reports Server (NTRS)

Gurtler, R. W.; Baghdadi, A.; Wise, J.; Ellis, R. J.

1977-01-01

The Ribbon-to-Ribbon (RTR) approach to silicon ribbon growth was investigated. An existing RTR apparatus, RTR#1, was upgraded to allow for 5 cm wide ribbon growth with a finite stroke length of at least 15 cm. A second RTR apparatus, RTR#2, was designed, built, and operated which utilizes continuous feed mechanisms and allows continuous growth of 7.5 cm wide ribbons. RTR#2 includes development and utilization of advanced beam scanning (or shaping), high power lasers, and thermal profile modification elements to attain maximum growth velocities (with a design goal of 18 cm/min). Materials studies, process development, and thermal analyses are also described. Residual stresses and dislocation densities were minimized through theoretical and experimental efforts towards optimization of thermal profiles. Growth runs were performed on RTR#2 and solar cells were fabricated which demonstrated efficiencies greater than 10%.

Wearable energy-smart ribbons for synchronous energy harvest and storage

NASA Astrophysics Data System (ADS)

Li, Chao; Islam, Md. Monirul; Moore, Julian; Sleppy, Joseph; Morrison, Caleb; Konstantinov, Konstantin; Dou, Shi Xue; Renduchintala, Chait; Thomas, Jayan

2016-11-01

A promising energy source for many current and future applications is a ribbon-like device that could simultaneously harvest and store energy. Due to the high flexibility and weavable property, a fabric/matrix made using these ribbons could be highly beneficial for powering wearable electronics. Unlike the approach of using two separate devices, here we report a ribbon that integrates a solar cell and a supercapacitor. The electrons generated by the solar cell are directly transferred and stored on the reverse side of its electrode which in turn also functions as an electrode for the supercapacitor. When the flexible solar ribbon is illuminated with simulated solar light, the supercapacitor holds an energy density of 1.15 mWh cm-3 and a power density of 243 mW cm-3. Moreover, these ribbons are successfully woven into a fabric form. Our all-solid-state ribbon unveils a highly flexible and portable self-sufficient energy system with potential applications in wearables, drones and electric vehicles.

Wearable energy-smart ribbons for synchronous energy harvest and storage.

PubMed

Li, Chao; Islam, Md Monirul; Moore, Julian; Sleppy, Joseph; Morrison, Caleb; Konstantinov, Konstantin; Dou, Shi Xue; Renduchintala, Chait; Thomas, Jayan

2016-11-11

A promising energy source for many current and future applications is a ribbon-like device that could simultaneously harvest and store energy. Due to the high flexibility and weavable property, a fabric/matrix made using these ribbons could be highly beneficial for powering wearable electronics. Unlike the approach of using two separate devices, here we report a ribbon that integrates a solar cell and a supercapacitor. The electrons generated by the solar cell are directly transferred and stored on the reverse side of its electrode which in turn also functions as an electrode for the supercapacitor. When the flexible solar ribbon is illuminated with simulated solar light, the supercapacitor holds an energy density of 1.15 mWh cm -3 and a power density of 243 mW cm -3 . Moreover, these ribbons are successfully woven into a fabric form. Our all-solid-state ribbon unveils a highly flexible and portable self-sufficient energy system with potential applications in wearables, drones and electric vehicles.

The Role of Ribbons at Sensory Synapses

PubMed Central

LoGiudice, Lisamarie; Matthews, Gary

2009-01-01

Synaptic ribbons are organelles that tether vesicles at the presynaptic active zones of sensory neurons in the visual, auditory and vestibular systems. These neurons generate sustained, graded electrical signals in response to sensory stimuli, and fidelity of transmission therefore requires their synapses to release neurotransmitter continuously at high rates. It has long been thought that the ribbons at the active zones of sensory synapses accomplish this task by enhancing the size and accessibility of the readily releasable pool of synaptic vesicles, which may represent the vesicles attached to the ribbon. Recent evidence suggests that synaptic ribbons immobilize vesicles in the resting cell and coordinate the transient, synchronous release of vesicles in response to stimulation, but it is not yet clear how the ribbon can efficiently mobilize and coordinate multiple vesicles for release. However, detailed anatomical, electrophysiological and optical studies have begun to reveal the mechanics of release at ribbon synapses, and this multidisciplinary approach promises to reconcile structure, function, and mechanism at these important sensory synapses. PMID:19264728

Analysis of equivalent widths of alluvial channels and application for instream habitat in the Rio Grande

Treesearch

Claudia A. Leon

2003-01-01

Rivers are natural systems that adjust to variable water and sediment discharges. Channels with spatial variability in width that are managed to maintain constant widths over a period of time are able to transport the same water and sediment discharges by adjusting the bed slope. Methods developed to de ne equilibrium hydraulic geometry characteristics of alluvial...

Practical small-scale explosive seam welding

NASA Technical Reports Server (NTRS)

Bement, L. J.

1983-01-01

Joining principles and variables, types of joints, capabilities, and current and potential applications are described for an explosive seam welding process developed at NASA Langley Research Center. Variable small quantities of RDX explosive in a ribbon configuration are used to create narrow (less than 0.5 inch), long length, uniform, hermetrically sealed joints that exhibit parent metal properties in a wide variety of metals, alloys, and combinations. The first major all application of the process is the repair of four nuclear reactors in Canada. Potential applications include pipelines, sealing of vessels, and assembly of large space structures.

Laser-zone growth in a Ribbon-To-Ribbon (RTR) process, silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

NASA Technical Reports Server (NTRS)

Gurtler, R. W.; Baghdadi, A.

1976-01-01

The objective of this research is to fully investigate the Ribbon-To-Ribbon (R-T-R) approach to silicon ribbon growth. Initial work has concentrated on modification and characterization of an existing R-T-R apparatus. In addition, equipment for auxiliary heating of the melt is being evaluated and acquired. Modification of the remote viewing system and mechanical staging are nearly complete. Characterization of the laser and other components is in progress and several auxiliary heating techniques are being investigated.

Stress analysis of ribbon parachutes

NASA Technical Reports Server (NTRS)

Reynolds, D. T.; Mullins, W. M.

1975-01-01

An analytical method has been developed for determining the internal load distribution for ribbon parachutes subjected to known riser and aerodynamic forces. Finite elements with non-linear elastic properties represent the parachute structure. This method is an extension of the analysis previously developed by the authors and implemented in the digital computer program CANO. The present analysis accounts for the effect of vertical ribbons in the solution for canopy shape and stress distribution. Parametric results are presented which relate the canopy stress distribution to such factors as vertical ribbon strength, number of gores, and gore shape in a ribbon parachute.

Amorphous ribbon transducers

NASA Astrophysics Data System (ADS)

Meydan, T.; Overshott, K. J.

1984-02-01

Amorphous ribbon transducers have been investigated which consist of toroidally wound amorphous ribbon with a primary (magnetizing) winding and secondary (search coil) windings. The application of a force to the ribbon gives a linear search coil voltage against applied force characteristic. The positioning of the windings with respect to the applied force has been studied, and it is shown that the effect of the applied force is localized. Domain studies have shown that the applied force produces domain wall motion which can be correlated to the performance. These results have elucidated the operation of ac amorphous ribbon transducers and enabled improved designs to be produced.

Numerical Simulation Of Silicon-Ribbon Growth

NASA Technical Reports Server (NTRS)

Woda, Ben K.; Kuo, Chin-Po; Utku, Senol; Ray, Sujit Kumar

1987-01-01

Mathematical model includes nonlinear effects. In development simulates growth of silicon ribbon from melt. Takes account of entire temperature and stress history of ribbon. Numerical simulations performed with new model helps in search for temperature distribution, pulling speed, and other conditions favoring growth of wide, flat, relatively defect-free silicon ribbons for solar photovoltaic cells at economically attractive, high production rates. Also applicable to materials other than silicon.

76 FR 35379 - Archers Creek, Ribbon Creek, and Broad River; U.S. Marine Corps Recruit Depot, Parris Island, SC...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-06-17

..., Ribbon Creek, and Broad River; U.S. Marine Corps Recruit Depot, Parris Island, SC; Danger Zone AGENCY... use these portions of Archers Creek, Ribbon Creek, and the Broad River when the rifle and pistol.... 334.480 to read as follows: Sec. 334.480 Archers Creek, Ribbon Creek, and Broad River; U.S. Marine...

Modified Withdrawal Slot Increases Silicon Production

NASA Technical Reports Server (NTRS)

Piotrowsky, P. A.; Duncan, C. S.

1988-01-01

New shape reduces ribbon breakage and resulting idle time. Shape for slot through which single-crystal silicon ribbon pulled from melt increases productivity. Reduces tendency of emerging ribbon to grow thin and break.

Tree Waves Upward Migration in the Altai Mountains, Siberia

NASA Astrophysics Data System (ADS)

Kharuk, Viacheslav; Im, Sergei; Dvinskaya, Maria; Petrov, Il'ya

2017-04-01

The phenomenon of "tree waves" (hedges and ribbons) formation within the alpine ecotone in Altai Mountains and its response to observed air temperature increase was considered. At the upper limit of tree growth Siberian pine (Pinus sibirica) forms hedges on windward slopes and ribbons on the leeward ones. Hedges were formed by prevailing winds and oriented along winds direction. Ribbons were formed by snow blowing and accumulating on the leeward slope and perpendicular to the prevailing winds, as well as to the elevation gradient. Hedges were always linked with microtopography features, whereas ribbons were not. Trees are migrating upward by waves and new ribbons and hedges are forming at or near tree line, whereas at lower elevations ribbons and hedges are being transformed into closed forests. Time series of high-resolution satellite scenes (from 1968 to 2010) indicated an upslope shift in the position ribbons averaged 155±26 m (or 3.7 m yr -1) and crown closure increased (about 35-90%). The hedges advance was limited by poor regeneration establishment and was negligible. Regeneration within the "ribbon zone" was approximately 2.5 times (5060 vs 2120 ha -1) higher then within the "hedges zone". During the last four decades, Siberian pine in both hedges and ribbons strongly increased its growth increment and recent tree growth rate for 50 year old trees was about twice higher than recorded for similarly aged trees at the beginning of the 20th century. Growth increment increase was strongly correlated with CO2 concentration in the ambient air (R2 = 0.9), which may indicated CO2- fertilization. Hedges and ribbons are phenomena that are widespread within the southern and northern Siberian Mountains

The preparation and hydrogen brittleness resistance of Pd71.5Cu12Si16.5 metallic glass ribbons

NASA Astrophysics Data System (ADS)

Du, Xiaoqing; Ye, Xiaoqiu; Ren, Qingbo

2017-12-01

Pd71.5Cu12Si16.5 metallic glass ribbons as wide as 10mm were prepared by splat quenching. Structure was identified with X-ray diffraction (XRD) spectrums from the conventional X-ray diffractometer and also short wavelength X-ray stress analyzer. The results confirm fully amorphous structure of the ribbons. Multiple H2 adsorption and desorption cycles under a pressure of 100kPa were carried out in the metallic glass ribbon and also pure palladium membrane for comparison. The former didn’t show any cracks after more than 10 cycles, and thermal desorption spectroscopy (TDS) measurement confirms that hydrogen was adsorbed abundantly in the metallic glass ribbon. Pd71.5Cu12Si16.5 metallic glass ribbons demonstrate excellent hydrogen brittleness resistance.

Laser-zone growth in a Ribbon-To-Ribbon (RTR) process. Silicon sheet growth development for the large area sheet task of the low-cost solar array project

NASA Technical Reports Server (NTRS)

Baghdadi, A.; Gurtler, R. W.; Legge, R.; Sopori, B.; Ellis, R. J.

1978-01-01

A new calculation of the effects of thermal stresses during growth on silicon ribbon quality is reported. Thermal stress distributions are computed for ribbon growth under a variety of temperature profiles. A growth rate of 55 cu cm/min with a single ribbon was achieved. The growth of RTR ribbon with a fairly uniform parallel dendritic structure was demonstrated. Results with two approaches were obtained for reducing the Mo impurity level in polycrystalline feedstock. Coating the Mo substrate with Si3N4 does not effect thermal shear separation of the polyribbon; this process shows promise of improving cell efficiency and also increasing the useful life of the molybdenum substrate. A number of solar cells were fabricated on RTR silicon grown from CVD feedstock.

Electronic properties and mechanical strength of β-phosphorene nano-ribbons

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

Swaroop, Ram; Bhatia, Pradeep; Kumar, Ashok, E-mail: ashok@cup.ac.in

We have performed first principles calculations to find out the effect of mechanical strain on the electronic properties of zig-zag edged nano ribbons of β-phosphorene. It is found that electronic band-gap get opened-up to 2.61 eV by passivation of the edges of ribbons. Similarly, the mechanical strength is found to be increase from 1.75 GPa to 2.65 GPa on going from unpassivated nano ribbons to passivated ones along with the 2% increase in ultimate tensile strain. The band-gap value of passivated ribbon gets decreased to 0.43 eV on applying strain up to which the ribbon does not break. These tunable properties ofmore » β-phospherene with passivation with H-atom and applying mechanical strain offer its use in tunable nano electronics.« less

Elongation of Flare Ribbons

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

Qiu, Jiong; Longcope, Dana W.; Cassak, Paul A.

2017-03-20

We present an analysis of the apparent elongation motion of flare ribbons along the polarity inversion line (PIL), as well as the shear of flare loops in several two-ribbon flares. Flare ribbons and loops spread along the PIL at a speed ranging from a few to a hundred km s{sup −1}. The shear measured from conjugate footpoints is consistent with the measurement from flare loops, and both show the decrease of shear toward a potential field as a flare evolves and ribbons and loops spread along the PIL. Flares exhibiting fast bidirectional elongation appear to have a strong shear, whichmore » may indicate a large magnetic guide field relative to the reconnection field in the coronal current sheet. We discuss how the analysis of ribbon motion could help infer properties in the corona where reconnection takes place.« less

Faceted ceramic fibers, tapes or ribbons and epitaxial devices therefrom

DOEpatents

Goyal, Amit [Knoxville, TN

2012-07-24

A crystalline article includes a single-crystal ceramic fiber, tape or ribbon. The fiber, tape or ribbon has at least one crystallographic facet along its length, which is generally at least one meter long. In the case of sapphire, the facets are R-plane, M-plane, C-plane or A-plane facets. Epitaxial articles, including superconducting articles, can be formed on the fiber, tape or ribbon.

Faceted ceramic fibers, tapes or ribbons and epitaxial devices therefrom

DOEpatents

Goyal, Amit

2013-07-09

A crystalline article includes a single-crystal ceramic fiber, tape or ribbon. The fiber, tape or ribbon has at least one crystallographic facet along its length, which is generally at least one meter long. In the case of sapphire, the facets are R-plane, M-plane, C-plane or A-plane facets. Epitaxial articles, including superconducting articles, can be formed on the fiber, tape or ribbon.

Patients with Chronic Obstructive Pulmonary Disease Walk with Altered Step Time and Step Width Variability as Compared with Healthy Control Subjects.

PubMed

Yentes, Jennifer M; Rennard, Stephen I; Schmid, Kendra K; Blanke, Daniel; Stergiou, Nicholas

2017-06-01

Compared with control subjects, patients with chronic obstructive pulmonary disease (COPD) have an increased incidence of falls and demonstrate balance deficits and alterations in mediolateral trunk acceleration while walking. Measures of gait variability have been implicated as indicators of fall risk, fear of falling, and future falls. To investigate whether alterations in gait variability are found in patients with COPD as compared with healthy control subjects. Twenty patients with COPD (16 males; mean age, 63.6 ± 9.7 yr; FEV 1 /FVC, 0.52 ± 0.12) and 20 control subjects (9 males; mean age, 62.5 ± 8.2 yr) walked for 3 minutes on a treadmill while their gait was recorded. The amount (SD and coefficient of variation) and structure of variability (sample entropy, a measure of regularity) were quantified for step length, time, and width at three walking speeds (self-selected and ±20% of self-selected speed). Generalized linear mixed models were used to compare dependent variables. Patients with COPD demonstrated increased mean and SD step time across all speed conditions as compared with control subjects. They also walked with a narrower step width that increased with increasing speed, whereas the healthy control subjects walked with a wider step width that decreased as speed increased. Further, patients with COPD demonstrated less variability in step width, with decreased SD, compared with control subjects at all three speed conditions. No differences in regularity of gait patterns were found between groups. Patients with COPD walk with increased duration of time between steps, and this timing is more variable than that of control subjects. They also walk with a narrower step width in which the variability of the step widths from step to step is decreased. Changes in these parameters have been related to increased risk of falling in aging research. This provides a mechanism that could explain the increased prevalence of falls in patients with COPD.

Propulsion and hydrodynamic particle transport of magnetically twisted colloidal ribbons

NASA Astrophysics Data System (ADS)

Massana-Cid, Helena; Martinez-Pedrero, Fernando; Navarro-Argemí, Eloy; Pagonabarraga, Ignacio; Tierno, Pietro

2017-10-01

We describe a method to trap, transport and release microscopic particles in a viscous fluid using the hydrodynamic flow field generated by a magnetically propelled colloidal ribbon. The ribbon is composed of ferromagnetic microellipsoids that arrange with their long axis parallel to each other, a configuration that is energetically favorable due to their permanent magnetic moments. We use an external precessing magnetic field to torque the anisotropic particles forming the ribbon, and to induce propulsion of the entire structure due to the hydrodynamic coupling with the close substrate. The propulsion speed of the ribbon can be controlled by varying the driving frequency, or the amplitude of the precessing field. The latter parameter is also used to reduce the average inter particle distance and to induce the twisting of the ribbon due to the increase in the attraction between the rotating ellipsoids. Furthermore, non magnetic particles are attracted or repelled with the hydrodynamic flow field generated by the propelling ribbon. The proposed method may be used in channel free microfluidic applications, where the precise trapping and transport of functionalized particles via non invasive magnetic fields is required.

Fabrication of an ideal nanoring from a black phosphorus nanoribbon upon movable bundling carbon nanotubes

NASA Astrophysics Data System (ADS)

Cai, Kun; Shi, Jiao; Liu, Lingnan; Qin, Qing H.

2017-09-01

As a low dimensional material, black phosphorus (BP) continues to attract much attention from researchers due to its excellent electric properties. In particular, the one-dimensional material, in the form of a ring or tube formed from BP, has been extensively studied and found to be a perfect semiconductor. But the BP ring has never been reported in laboratories. To form an ideal ring from a rectangular BP ribbon, we choose a carbon nanotube (CNT) bundle to attract the ribbon and move one or more CNTs in the bundle to induce the unsaturated ends of the BP ribbon to become covalently bonded. Numerical experiments are applied to BP ribbons with lengths either equal to, shorter, or longer than the perimeter of the CNT bundle, to investigate the formation of a BP ring. Experiments show that if one end of the BP ribbon is attracted by a CNT, moving the other CNTs away endows the ribbon with high probability of forming an ideal ring. The conclusions drawn from these results will benefit future in situ experiments involving forming a ring from a BP ribbon.

Polymorphism complexity and handedness inversion in serum albumin amyloid fibrils.

PubMed

Usov, Ivan; Adamcik, Jozef; Mezzenga, Raffaele

2013-12-23

Protein-based amyloid fibrils can show a great variety of polymorphic structures within the same protein precursor, although the origins of these structural homologues remain poorly understood. In this work we investigate the fibrillation of bovine serum albumin--a model globular protein--and we follow the polymorphic evolution by a statistical analysis of high-resolution atomic force microscopy images, complemented, at larger length scales, by concepts based on polymer physics formalism. We identify six distinct classes of coexisting amyloid fibrils, including flexible left-handed twisted ribbons, rigid right-handed helical ribbons and nanotubes. We show that the rigid fibrils originate from flexible fibrils through two diverse polymorphic transitions, first, via a single-fibril transformation when the flexible left-handed twisted ribbons turn into the helical left-handed ribbons, to finally evolve into nanotube-like structures, and second, via a double-fibril transformation when two flexible left-handed twisted ribbons wind together resulting in a right-handed twisted ribbon, followed by a rigid right-handed helical ribbon polymorphic conformation. Hence, the change in handedness occurs with an increase in the level of the fibril's structural organization.

Position of the IBEX ribbon as a key to understand its origin

NASA Astrophysics Data System (ADS)

Swaczyna, Pawel; Bzowski, Maciej; Sokół, Justyna M.; Christian, Eric R.; Funsten, Herbert O.; McComas, David J.; Schwadron, Nathan A.

2017-04-01

Observations of the energetic neutral atom (ENA) emission by the Interstellar Boundary Explorer (IBEX) allow for remote sensing of the plasma properties in heliosheath. The first IBEX results revealed an unexpected arc-like enhancement of the ENA flux in the sky, dubbed the IBEX ribbon. This discovery led to formulation of more than a dozen hypotheses on its origin. The emission source region proposed in these hypotheses span the heliospheric termination shock up to a hypothetical nearby interface between the Local Interstellar Cloud and a local bay in the Local Bubble. Among these hypotheses is the concept that the ribbon is produced by the secondary ENA mechanism, operating in the outer heliosheath. The observational strategy of IBEX allows observation of the same part of the sky from the opposite sides of the Sun every six months and thus provides parallax viewing with a baseline of 2 AU. After correcting the observations for the Compton-Getting effect and for gravitational deflection and radiation pressure, we use this parallax viewing to precisely determine the apparent position of the maximum flux associated with the ribbon. We find that the ribbon peak position differs semi-annually by an angle of 0.41±0.15 deg, which we interpret as the parallax effect. This angle corresponds to a distance of 140-38+84 AU, and thus suggests that most likely the ribbon's source is located just beyond the heliopause. Comparison of the IBEX ribbon position in five energy steps of IBEX-Hi shows a systematic shift, which changes the position of the ribbon center by ˜10 deg. We find that it can be explained using an analytic model of the secondary ENA mechanism with the neutralized supersonic solar wind as the source of the primary ENAs, which are ionized in the outer heliosheath, picked up by the ambient magnetic field, and eventually re-neutralized (as originally conceived, McComas et al. 2009). We use a realistic model of the solar wind evolution dependent on heliographic latitude, calculated the neutral solar wind flux and averaged it over the solar cycle, which was then used as the input in the analytic model of the secondary ENAs. The modeled ENA emission signal as observed at IBEX reproduces the observed features of the IBEX ribbon: the relative signal intensity along the ribbon in each energy channel and the shift of the ribbon center. The combination of the distance to the ribbon source obtained from parallax and the energy progression of the ribbon center location suggest that the secondary ENA mechanism is a plausible explanation for the ribbon origin. A better resolution of the ENA detectors expected on the IMAP mission will enable a more accurate determination of the ribbon's position and will extend observations to higher energies. In consequence, a better determination of its parallax should be possible, and time-dependent effects resulting from the evolution of the supersonic solar wind structure with time will provide additional, critical signatures of the ribbon origin.

75 FR 45608 - Blue Ribbon Commission on America's Nuclear Future, Transportation and Storage Subcommittee

Federal Register 2010, 2011, 2012, 2013, 2014

2010-08-03

... DEPARTMENT OF ENERGY Blue Ribbon Commission on America's Nuclear Future, Transportation and...) Subcommittee. The T&S Subcommittee is a subcommittee of the Blue Ribbon Commission on America's Nuclear Future... 45609

Effects of Thermomechanical History on the Tensile Behavior of Nitinol Ribbon

NASA Technical Reports Server (NTRS)

Lach, Cynthia L.; Turner, Travis L.; Taminger, Karen M.; Shenoy, Ravi N.

2002-01-01

Shape memory alloys (SMAs) have enormous potential for a wide variety of applications. A large body of work exists on the characterization of the microstructure and stress-strain behavior of these alloys, Nitinol (NiTi) in particular. However, many attributes of these materials are yet to be fully understood. Previous work at NASA Langley Research Center (LaRC) has included fabrication of hybrid composite specimens with embedded Nitinol actuators and modeling of their thermomechanical behavior. An intensive characterization effort has been undertaken to facilitate fundamental understanding of this alloy and to promote implementation of Nitinol in aerospace applications. Previous work revealed attributes of the Nitinol ribbon that were not easily rationalized with existing data in the literature. In particular, tensile behavior at ambient temperature showed significant dependence on the thermomechanical history prior to testing. The present work is focused on characterizing differences in the microstructure of Nitinol ribbons exposed to four different thermomechanical histories and correlation of the microstructure with tensile properties. Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) analysis were employed to rationalize the microstructures present after exposure to various thermomechanical histories. Three of the Nitinol ribbon conditions were reversible upon heating (in the DSC) through the reverse transformation temperature (A(sub f) to transform the microstructure to austenite. However, the prior thermomechanical conditioning for the Nitinol ribbon that reflected the entire fabrication procedure (4% thermal cycle condition) was found to have an irreversible effect on the microstructure, as it remained unchanged after repeated complete thermal cycles. Tensile tests were conducted to determine the effect of prior thermomechancal conditioning on both the tensile behavior of the Nitinol ribbons and the stress state of the microstructure. The stress-strain behavior of the Nitinol actuators appears to be governed by the interplay between two major variables: namely, microstructural constituents such as the R-phase and the martensite; and the stress state of these constituents (whether twinned with low residual stresses, or detwinned with high residual stresses). The most significant difference in the stress-strain behavior of the four conditions, the critical stress required to achieve an initial stress plateau, was found to depend on both the amount and stress state (twinned or detwinned) of R-phase present in the initial microstructure. Thus, the effect of prior thermomechanical processing is critical to the resulting tensile behavior of the Nitinol actuator. For numerical modeling inputs one must take into account the entire fabrication process on the Nitinol actuator.

Plastic deformation of silicon dendritic web ribbons during the growth

NASA Technical Reports Server (NTRS)

Cheng, L. J.; Dumas, K. A.; Su, B. M.; Leipold, M. H.

1984-01-01

The distribution of slip dislocations in silicon dendritic web ribbons due to plastic deformation during the cooling phase of the growth was studied. The results show the existence of two distinguishable stress regions across the ribbon formed during the plastic deformation stage, namely, shear stress at the ribbon edges and tensile stress at the middle. In addition, slip dislocations caused by shear stress near the edges appear to originate at the twin plane.

Electrostatics-Driven Hierarchical Buckling of Charged Flexible Ribbons.

PubMed

Yao, Zhenwei; Olvera de la Cruz, Monica

2016-04-08

We investigate the rich morphologies of an electrically charged flexible ribbon, which is a prototype for many beltlike structures in biology and nanomaterials. Long-range electrostatic repulsion is found to govern the hierarchical buckling of the ribbon from its initially flat shape to its undulated and out-of-plane twisted conformations. In this process, the screening length is the key controlling parameter, suggesting that a convenient way to manipulate the ribbon morphology is simply to change the salt concentration. We find that these shapes originate from the geometric effect of the electrostatic interaction, which fundamentally changes the metric over the ribbon surface. We also identify the basic modes by which the ribbon reshapes itself in order to lower the energy. The geometric effect of the physical interaction revealed in this Letter has implications for the shape design of extensive ribbonlike materials in nano- and biomaterials.

Thermally induced spin rate ripple on spacecraft with long radial appendages

NASA Technical Reports Server (NTRS)

Fedor, J. V.

1983-01-01

A thermally induced spin rate ripple hypothesis is proposed to explain the spin rate anomaly observed on ISEE-B. It involves the two radial 14.5 meter beryllium copper tape ribbons going in and out of the spacecraft hub shadow. A thermal lag time constant is applied to the thermally induced ribbon displacements which perturb the spin rate. It is inferred that the averaged thermally induced ribbon displacements are coupled to the ribbon angular motion. A possible exponential build up of the inplane motion of the ribbon which in turn causes the spin rate ripple, ultimately limited by damping in the ribbon and spacecraft is shown. It is indicated that qualitative increase in the oscillation period and the thermal lag is fundamental for the period increase. found that numerical parameter values required to agree with in orbit initial exponential build up are reasonable; those required for the ripple period are somewhat extreme.

Metallurgical characterization of melt-spun ribbons of U-5.4 wt%Nb alloy

NASA Astrophysics Data System (ADS)

Ma, Rong; Ren, Zhiyong; Tang, Qingfu; Chen, Dong; Liu, Tingyi; Su, Bin; Wang, Zhenhong; Luo, Chao

2018-06-01

The microstructures and micro-mechanical properties of the melt-spun ribbons of U-5.4 wt%Nb alloy were characterized using optical microscopy, scanning electron microscopy, X-ray diffraction and nanoindentation. Observed variations in microstructures and properties are related to the changes in ribbon thicknesses and cooling rates. The microstructures of the melt-spun ribbon consist of fine-scale columnar grains (∼1 μm) adjacent to the chill surface and coarse cellular grains in the remainder of the ribbon. In addition, the formation of inclusions in the ribbon is suppressed kinetically due to the high cooling rate during melt spinning. Compared with the water-quenched specimen prepared by traditional gravity casting and solution heat treatment, the elastic modulus values of the U-5.4 wt%Nb alloy were examined to vary with grain size and exhibited diverse energy dissipation capacities.

Data mining the Kansas traffic-crash database : final report.

DOT National Transportation Integrated Search

2009-08-01

Traffic crashes results from the interaction of different parameters which includes highway geometrics, traffic characteristics and human factors. Geometric variables include number of lanes, lane width, median width, shoulder width, roadway section ...

Data mining the Kansas traffic-crash database : summary.

DOT National Transportation Integrated Search

2009-08-01

Traffic crashes results from the interaction of different parameters which includes highway geometrics, traffic : characteristics and human factors. Geometric variables include number of lanes, lane width, median width, shoulder : width, roadway sect...

Passive Diffusion as a Mechanism Underlying Ribbon Synapse Vesicle Release and Resupply

PubMed Central

Graydon, Cole W.; Zhang, Jun; Oesch, Nicholas W.; Sousa, Alioscka A.; Leapman, Richard D.

2014-01-01

Synaptic ribbons are presynaptic protein structures found at many synapses that convey graded, “analog” sensory signals in the visual, auditory, and vestibular pathways. Ribbons, typically anchored to the presynaptic membrane and surrounded by tethered synaptic vesicles, are thought to regulate or facilitate vesicle delivery to the presynaptic membrane. No direct evidence exists, however, to indicate how vesicles interact with the ribbon or, once attached, move along the ribbon's surface to reach the presynaptic release sites at its base. To address these questions, we have created, validated, and tested a passive vesicle diffusion model of retinal rod bipolar cell ribbon synapses. We used axial (bright-field) electron tomography in the scanning transmission electron microscopy to obtain 3D structures of rat rod bipolar cell terminals in 1-μm-thick sections of retinal tissue at an isotropic spatial resolution of ∼3 nm. The resulting structures were then incorporated with previously published estimates of vesicle diffusion dynamics into numerical simulations that accurately reproduced electrophysiologically measured vesicle release/replenishment rates and vesicle pool sizes. The simulations suggest that, under physiologically realistic conditions, diffusion of vesicles crowded on the ribbon surface gives rise to a flow field that enhances delivery of vesicles to the presynaptic membrane without requiring an active transport mechanism. Numerical simulations of ribbon–vesicle interactions predict that transient binding and unbinding of multiple tethers to each synaptic vesicle may achieve sufficiently tight association of vesicles to the ribbon while permitting the fast diffusion along the ribbon that is required to sustain high release rates. PMID:24990916

Vesicle Pool Size at the Salamander Cone Ribbon Synapse

PubMed Central

Bartoletti, Theodore M.; Babai, Norbert

2010-01-01

Cone light responses are transmitted to postsynaptic neurons by changes in the rate of synaptic vesicle release. Vesicle pool size at the cone synapse constrains the amount of release and can thus shape contrast detection. We measured the number of vesicles in the rapidly releasable and reserve pools at cone ribbon synapses by performing simultaneous whole cell recording from cones and horizontal or off bipolar cells in the salamander retinal slice preparation. We found that properties of spontaneously occurring miniature excitatory postsynaptic currents (mEPSCs) are representative of mEPSCs evoked by depolarizing presynaptic stimulation. Strong, brief depolarization of the cone stimulated release of the entire rapidly releasable pool (RRP) of vesicles. Comparing charge transfer of the EPSC with mEPSC charge transfer, we determined that the fast component of the EPSC reflects release of ∼40 vesicles. Comparing EPSCs with simultaneous presynaptic capacitance measurements, we found that horizontal cell EPSCs constitute 14% of the total number of vesicles released from a cone terminal. Using a fluorescent ribeye-binding peptide, we counted ∼13 ribbons per cone. Together, these results suggest each cone contacts a single horizontal cell at ∼2 ribbons. The size of discrete components in the EPSC amplitude histogram also suggested ∼2 ribbon contacts per cell pair. We therefore conclude there are ∼20 vesicles per ribbon in the RRP, similar to the number of vesicles contacting the plasma membrane at the ribbon base. EPSCs evoked by lengthy depolarization suggest a reserve pool of ∼90 vesicles per ribbon, similar to the number of additional docking sites further up the ribbon. PMID:19923246

Preparing Solar Cells for Soldering

NASA Technical Reports Server (NTRS)

Hagerty, J. J.

1983-01-01

Solder paste and contact ribbon dispensed in synchronism. Solder-paste dispenser operates on one cell at a time. Ribbon fed up ramps and into positioned while solder paste is applied. When ramps are moved out of way, ribbon lies down onto cell.

Reconnection Mediated by Magnetic Fractures and the Solar Flare

NASA Astrophysics Data System (ADS)

Haerendel, Gerhard

2018-03-01

Reconnection of sheared magnetic fields is commonly treated by regarding the component perpendicular to the antiparallel components as a largely inert guide field. In this paper an alternative is proposed in which the free energy residing in the shear field is being converted prior to reconnection. This happens in high-density, dissipative current sheets bordering the reconnection site. A global scenario is presented in which low-intensity currents out of the photosphere are converging into the narrow, high-intensity currents at high altitude. This is enabled by the obliqueness of the latter. The very short timescale of the energy conversion causes a lateral propagation of the current sheets. In a quasi-stationary situation, it balances the reconnection rate, which turns out to be much lower than in guide-field approaches. Another important consequence of the obliqueness is the field-parallel emission of runaway electrons. Accelerated up to tens of keV, they are possibly important contributors to the production of hard X-rays during the impulsive phase of a flare, but only in areas of upward-directed currents. Quantitative evaluation of the model predicts various potentially observable properties, such as width and propagation speed of the generated flare ribbons, spatial dependences of the electron spectrum, size of the area of energy deposition, and successive decrease of the shear angle between conjugate footpoints. The presented theoretical model can account for the observed brightness asymmetry of flare ribbons with respect to the direction of the vertical currents.

Failure Predictions of Out-of-Autoclave Sandwich Joints with Delaminations under Flexure Loads

NASA Technical Reports Server (NTRS)

Nordendale, Nikolas; Goyal, Vinay; Lundgren, Eric; Patel, Dhruv; Farrokh, Babak; Jones, Justin; Fischetti, Grace; Segal, Kenneth

2015-01-01

An analysis and a test program was conducted to investigate the damage tolerance of composite sandwich joints. The joints contained a single circular delamination between the face-sheet and the doubler. The coupons were fabricated through out-of-autoclave (OOA) processes, a technology NASA is investigating for joining large composite sections. The four-point bend flexure test was used to induce compression loading into the side of the joint where the delamination was placed. The compression side was chosen since it tends to be one of the most critical loads in launch vehicles. Autoclave cure was used to manufacture the composite sandwich sections, while the doubler was co-bonded onto the sandwich face-sheet using an OOA process after sandwich panels were cured. A building block approach was adopted to characterize the mechanical properties of the joint material, including the fracture toughness between the doubler and facesheet. Twelve four-point-bend samples were tested, six in the sandwich core ribbon orientation and six in sandwich core cross-ribbon direction. Analysis predicted failure initiation and propagation at the pre-delaminated location, consistent with experimental observations. A building block approach using fracture analyses methods predicted failure loads in close agreement with tests. This investigation demonstrated a small strength reduction due to a flaw of significant size compared to the width of the sample. Therefore, concerns of bonding an OOA material to an in-autoclave material was mitigated for the geometries, materials, and load configurations considered.

Failure Predictions of Out-of-Autoclave Sandwich Joints with Delaminations Under Flexure Loads

NASA Technical Reports Server (NTRS)

Nordendale, Nikolas A.; Goyal, Vinay K.; Lundgren, Eric C.; Patel, Dhruv N.; Farrokh, Babak; Jones, Justin; Fischetti, Grace; Segal, Kenneth N.

2015-01-01

An analysis and a test program was conducted to investigate the damage tolerance of composite sandwich joints. The joints contained a single circular delamination between the face-sheet and the doubler. The coupons were fabricated through out-of-autoclave (OOA) processes, a technology NASA is investigating for joining large composite sections. The four-point bend flexure test was used to induce compression loading into the side of the joint where the delamination was placed. The compression side was chosen since it tends to be one of the most critical loads in launch vehicles. Autoclave cure was used to manufacture the composite sandwich sections, while the doubler was co-bonded onto the sandwich face-sheet using an OOA process after sandwich panels were cured. A building block approach was adopted to characterize the mechanical properties of the joint material, including the fracture toughness between the doubler and face-sheet. Twelve four-point-bend samples were tested, six in the sandwich core ribbon orientation and six in sandwich core cross-ribbon direction. Analysis predicted failure initiation and propagation at the pre-delaminated location, consistent with experimental observations. A building block approach using fracture analyses methods predicted failure loads in close agreement with tests. This investigation demonstrated a small strength reduction due to a flaw of significant size compared to the width of the sample. Therefore, concerns of bonding an OOA material to an in-autoclave material was mitigated for the geometries, materials, and load configurations considered.

Failure Predictions of Out-of-Autoclave Sandwich Joints with Delaminations Under Flexure Loads

NASA Technical Reports Server (NTRS)

Nordendale, Nikolas; Goyal, Vinay; Lundgren, Eric; Patel, Dhruv; Farrokh, Babak; Jones, Justin; Fischetti, Grace; Segal, Kenneth

2015-01-01

An analysis and a test program was conducted to investigate the damage tolerance of composite sandwich joints. The joints contained a single circular delamination between the face-sheet and the doubler. The coupons were fabricated through out-of-autoclave (OOA) processes, a technology NASA is investigating for joining large composite sections. The four-point bend flexure test was used to induce compression loading into the side of the joint where the delamination was placed. The compression side was chosen since it tends to be one of the most critical loads in launch vehicles. Autoclave cure was used to manufacture the composite sandwich sections, while the doubler was co-bonded onto the sandwich face-sheet using an OOA process after sandwich panels were cured. A building block approach was adopted to characterize the mechanical properties of the joint material, including the fracture toughness between the doubler and face-sheet. Twelve four-point-bend samples were tested, six in the sandwich core ribbon orientation and six in sandwich core cross-ribbon direction. Analysis predicted failure initiation and propagation at the pre-delaminated location, consistent with experimental observations. Fracture analyses methods predicted failure loads in close agreement with tests. This investigation demonstrated a strength reduction of 10 percent due to a flaw of significant size compared to the width of the sample. Therefore, concerns of bonding an OOA material to an in-autoclave material was mitigated for the geometries, materials, and load configurations considered.

Magnetic properties enhancement of melt spun CoZrB ribbons by elemental substitutions

NASA Astrophysics Data System (ADS)

Chang, H. W.; Tsai, C. F.; Hsieh, C. C.; Shih, C. W.; Chang, W. C.; Shaw, C. C.

2013-11-01

Effect of elemental substitution of M (M=C, Cu, Ga, Al and Si) for Zr on the magnetic properties, phase evolution, and microstructure of melt spun Co80Zr18-xMxB2 (x=0-2) ribbons have been investigated. The x-ray diffraction (XRD) and thermal magnetic analysis (TMA) results showed that two magnetically soft phases, namely fcc-Co and Co23Zr6, coexisted with hard phase Co5Zr in Co80Zr17M1B2 ribbons with M=Cu, Ga, Al and Si, while an extra unknown magnetic phase was present in ribbons with M=C. The ribbons with M=C and Si were found to improve the remanence (σr) of the Co80Zr17M1B2 ribbons. However, only M=Si could improve the whole magnetic properties, including Br, intrinsic coercivity (iHc) and energy product ((BH)max) of the above ribbons. The optimal magnetic properties of Br=5.2 kG, iHc=4.5 kOe, and (BH)max=5.3 MGOe were obtained in Co80Zr17Si1B2 ribbons, which possessed Co5Zr and minor fcc-Co phases with much finer grain size (10-30 nm) in comparison with its counterpart Co80Zr18B2 (20-60 nm).

Continuous-annealing method for producing a flexible, curved, soft magnetic amorphous alloy ribbon

NASA Astrophysics Data System (ADS)

Francoeur, Bruno; Couture, Pierre

2012-04-01

A method has been developed for continuous annealing of an amorphous alloy ribbon moving forward at several meters per second, giving a curved shape to the ribbon that remains flexible afterward and can be easily wound into a toroidal core with excellent soft magnetic properties. A heat pulse was applied by a compact system on a Metglas 2605HB1 ribbon moving forward at 5 m/s to initiate a thermal treatment at 460 °C, near crystallization onset. The treatment duration was less than 0.1 s, and the heating and cooling rates were above 10 000 °C/s, which helped preserve most of the alloy as-cast ductility state. Such high temperature rates were achieved by forcing a static contact between the moving ribbon and a temperature-controlled roller. A tensile stress and a series of bending configurations were applied on the moving ribbon during the treatment to induce the development of magnetic anisotropy and to obtain the desired natural curvature radius. The core losses at 60 Hz of a toroidal test core wound with the resulting ribbon are lower than the specific values reported by the alloy manufacturer. This method can be implemented at the casting plant for supplying a low-cost, ready-to-use ribbon, easy to handle and cut, for mass production of toroidal cores for distribution transformer kernels (core and coil only), pulse power cores, etc.

The Disease Protein Tulp1 Is Essential for Periactive Zone Endocytosis in Photoreceptor Ribbon Synapses

PubMed Central

Wahl, Silke; Magupalli, Venkat Giri; Dembla, Mayur; Katiyar, Rashmi; Schwarz, Karin; Köblitz, Louise; Alpadi, Kannan; Krause, Elmar; Rettig, Jens; Sung, Ching-Hwa; Goldberg, Andrew F. X.

2016-01-01

Mutations in the Tulp1 gene cause severe, early-onset retinitis pigmentosa (RP14) in humans. In the retina, Tulp1 is mainly expressed in photoreceptors that use ribbon synapses to communicate with the inner retina. In the present study, we demonstrate that Tulp1 is highly enriched in the periactive zone of photoreceptor presynaptic terminals where Tulp1 colocalizes with major endocytic proteins close to the synaptic ribbon. Analyses of Tulp1 knock-out mice demonstrate that Tulp1 is essential to keep endocytic proteins enriched at the periactive zone and to maintain high levels of endocytic activity close to the synaptic ribbon. Moreover, we have discovered a novel interaction between Tulp1 and the synaptic ribbon protein RIBEYE, which is important to maintain synaptic ribbon integrity. The current findings suggest a new model for Tulp1-mediated localization of the endocytic machinery at the periactive zone of ribbon synapses and offer a new rationale and mechanism for vision loss associated with genetic defects in Tulp1. SIGNIFICANCE STATEMENT Mutations in the Tulp1 gene cause severe, early-onset retinitis pigmentosa (RP14) and Leber congenital amaurosis (LCA15) in human patients. In this study, we discovered that the phosphoinositol-4,5-bisphosphate-binding protein Tulp1 is essential for the structural and functional organization of the periactive zone in photoreceptor synapses. Using Tulp1 knock-out mice, we found that Tulp1 is required to enrich major endocytic proteins at the periactive zone next to the synaptic ribbon. We demonstrate that Tulp1 is needed to promote endocytic vesicle retrieval at the periactive zone. Moreover, we discovered a novel interaction between Tulp1 and the synaptic ribbon protein RIBEYE. This newly discovered disease-sensitive interaction provides a molecular model for the control of endocytosis close to the synaptic ribbon. PMID:26911694

Evolutionary analysis of a novel zinc ribbon in the N-terminal region of threonine synthase.

PubMed

Kaur, Gurmeet; Subramanian, Srikrishna

2017-10-18

Threonine synthase (TS) catalyzes the terminal reaction in the biosynthetic pathway of threonine and requires pyridoxal phosphate as a cofactor. TSs share a common catalytic domain with other fold type II PALP dependent enzymes. TSs are broadly grouped into two classes based on their sequence, quaternary structure, and enzyme regulation. We report the presence of a novel zinc ribbon domain in the N-terminal region preceding the catalytic core in TS. The zinc ribbon domain is present in TSs belonging to both classes. Our sequence analysis reveals that archaeal TSs possess all zinc chelating residues to bind a metal ion that are lacking in the structurally characterized homologs. Phylogenetic analysis suggests that TSs with an N-terminal zinc ribbon likely represents the ancestral state of the enzyme while TSs without a zinc ribbon must have diverged later in specific lineages. The zinc ribbon and its N- and C-terminal extensions are important for enzyme stability, activity and regulation. It is likely that the zinc ribbon domain is involved in higher order oligomerization or mediating interactions with other biomolecules leading to formation of larger metabolic complexes.

Preventing Freezeup in Silicon Ribbon Growth

NASA Technical Reports Server (NTRS)

Mackintosh, B.

1983-01-01

Carefully-shaped heat conductor helps control thermal gradients crucial to growth of single-crystal silicon sheets for solar cells. Ends of die through which silicon sheet is drawn as ribbon from molten silicon. Profiled heat extractor prevents ribbon ends from solidifying prematurely and breaking.

Carbon nanotube fiber spun from wetted ribbon

DOEpatents

Zhu, Yuntian T; Arendt, Paul; Zhang, Xiefei; Li, Qingwen; Fu, Lei; Zheng, Lianxi

2014-04-29

A fiber of carbon nanotubes was prepared by a wet-spinning method involving drawing carbon nanotubes away from a substantially aligned, supported array of carbon nanotubes to form a ribbon, wetting the ribbon with a liquid, and spinning a fiber from the wetted ribbon. The liquid can be a polymer solution and after forming the fiber, the polymer can be cured. The resulting fiber has a higher tensile strength and higher conductivity compared to dry-spun fibers and to wet-spun fibers prepared by other methods.

Decomposition of the linking number of a closed ribbon: A problem from molecular biology

PubMed Central

Fuller, F. Brock

1978-01-01

A closed duplex DNA molecule relaxed and containing nucleosomes has a different linking number from the same molecule relaxed and without nucleosomes. What does this say about the structure of the nucleosome? A mathematical study of this question is made, representing the DNA molecule by a ribbon. It is shown that the linking number of a closed ribbon can be decomposed into the linking number of a reference ribbon plus a sum of locally determined “linking differences.” PMID:16592550

Silicon ribbon growth by a capillary action shaping technique

NASA Technical Reports Server (NTRS)

Schwuttke, G. H.; Ciszek, T. F.; Kran, A.

1976-01-01

The crystal growth method described is a capillary action shaping technique. Meniscus shaping for the desired ribbon geometry occurs at the vertex of a wettable die. As ribbon growth depletes the melt meniscus, capillary action supplies replacement material. A capillary die is so designed that the bounding edges of the die top are not parallel or concentric with the growing ribbon. The new dies allow a higher melt meniscus with concomitant improvements in surface smoothness and freedom from SiC surface particles, which can degrade perfection.

Onset of a Large Ejective Solar Eruption from a Typical Coronal-jet-base Field Configuration

NASA Astrophysics Data System (ADS)

Joshi, Navin Chandra; Sterling, Alphonse C.; Moore, Ronald L.; Magara, Tetsuya; Moon, Yong-Jae

2017-08-01

Utilizing multiwavelength observations and magnetic field data from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), SDO/Helioseismic and Magnetic Imager (HMI), the Geostationary Operational Environmental Satellite (GOES), and RHESSI, we investigate a large-scale ejective solar eruption of 2014 December 18 from active region NOAA 12241. This event produced a distinctive “three-ribbon” flare, having two parallel ribbons corresponding to the ribbons of a standard two-ribbon flare, and a larger-scale third quasi-circular ribbon offset from the other two. There are two components to this eruptive event. First, a flux rope forms above a strong-field polarity inversion line and erupts and grows as the parallel ribbons turn on, grow, and spread apart from that polarity inversion line; this evolution is consistent with the mechanism of tether-cutting reconnection for eruptions. Second, the eruption of the arcade that has the erupting flux rope in its core undergoes magnetic reconnection at the null point of a fan dome that envelops the erupting arcade, resulting in formation of the quasi-circular ribbon; this is consistent with the breakout reconnection mechanism for eruptions. We find that the parallel ribbons begin well before (˜12 minutes) the onset of the circular ribbon, indicating that tether-cutting reconnection (or a non-ideal MHD instability) initiated this event, rather than breakout reconnection. The overall setup for this large-scale eruption (diameter of the circular ribbon ˜105 km) is analogous to that of coronal jets (base size ˜104 km), many of which, according to recent findings, result from eruptions of small-scale “minifilaments.” Thus these findings confirm that eruptions of sheared-core magnetic arcades seated in fan-spine null-point magnetic topology happen on a wide range of size scales on the Sun.

Flexible cryogenic conduit

DOEpatents

Brindza, Paul Daniel; Wines, Robin Renee; Takacs, James Joseph

1999-01-01

A flexible and relatively low cost cryogenic conduit is described. The flexible cryogenic conduit of the present invention comprises a first inner corrugated tube with single braided serving, a second outer corrugated tube with single braided serving concentric with the inner corrugated tube, and arranged outwardly about the periphery of the inner corrugated tube and between the inner and outer corrugated tubes: a superinsulation layer; a one half lap layer of polyester ribbon; a one half lap layer of copper ribbon; a spirally wound refrigeration tube; a second one half lap layer of copper ribbon; a second one half lap layer of polyester ribbon; a second superinsulation layer; a third one half lap layer of polyester ribbon; and a spirally wound stretchable and compressible filament.

Microstructure, magnetic and magnetocaloric properties in Ni42.9Co6.9Mn38.3Sn11.9 alloy ribbons

NASA Astrophysics Data System (ADS)

Ma, S. C.; Ge, Q.; Yang, S.; Liu, K.; Han, X. Q.; Yu, K.; Song, Y.; Zhang, Z. S.; Jiang, Q. Z.; Chen, C. C.; Liu, R. H.; Zhong, Z. C.

2018-05-01

The microstructure, magnetic and magnetocaloric properties are investigated in the melt-spun and annealed Ni42.9Co6.9Mn38.3Sn11.9 ribbons. The columnar grains grow perpendicular to ribbon surfaces. After annealing, the grain size increases greatly. Meanwhile, the parent phase is suppressed and therefore L10 martensite predominates, indicating obvious shift of martensitic transformation to high temperature. More interestingly, the martensite variants are distinctly observed on the fractured cross-section of annealed ribbons, not just on the free surface in general. The significant enhancement of magnetic entropy change and effective refrigerant capacities with relatively smaller thermal hysteresis make annealed ribbons potential candidate in magnetic refrigeration around room temperature.

High speed shutter. [electrically actuated ribbon loop for shuttering optical or fluid passageways

NASA Technical Reports Server (NTRS)

Mcclenahan, J. O. (Inventor)

1974-01-01

A shutter element is described which is formed by a loop of an electrically conductive ribbon disposed adjacent to the end of a passageway to be shuttered. The shuttered end of the passageway is cut at an acute angle. The two leg portions of the ribbon loop are closely spaced to each other and disposed in a plane parallel to the axis of the passageway. A pulse of high current is switched through the loop to cause the current flowing in opposite directions through adjacent leg portions of the ribbon. This produces a magnetically induced pressure on one of the legs of the ribbon forcing the leg over the end of the passageway in gas tight sealing engagement, and thereby blocking passageway.

77 FR 15188 - Proposed Information Collection Activity Comment Request: Yellow Ribbon Agreement

Federal Register 2010, 2011, 2012, 2013, 2014

2012-03-14

... Activity Comment Request: Yellow Ribbon Agreement AGENCY: Veterans Benefits Administration, Department of Veterans Affairs. ACTION: Notice. SUMMARY: The Veterans Benefits Administration (VBA), Department of... institutions of higher learning (IHLs) will be participating in the Yellow Ribbon G. I. Education Enhancement...

Effect of heat treatment procedure on magnetic and magnetocaloric properties of Ni43Mn46In11 melt spun ribbons

NASA Astrophysics Data System (ADS)

Kaya, M.; Elerman, Y.; Dincer, I.

2018-07-01

The effect of heat treatment on the structural, magnetic and magnetocaloric properties of Ni43Mn46In11 melt-spun ribbons was systematically investigated using X-ray powder diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), magnetic force microscope (MFM) and magnetic measurements. From the XRD studies, tetragonal and cubic phases were detected at room temperature for as-spun, quenched and slow-cooled ribbons. Furthermore, it was observed, upon annealing martensite transition temperatures increased when compared to the as-spun ribbon. To avoid magnetic hysteresis losses in the vicinity of the structural transition region, the magnetic entropy changes-ΔS m of the investigated ribbons were evaluated from temperature-dependent magnetisation-M(T) curves on cooling for different applied magnetic fields. The maximum ΔS m value was found to be 6.79 J kg-1 K-1 for the quenched ribbon in the vicinity of structural transition region for a magnetic field change of 50 kOe.

Large Area Silicon Sheet by EFG. [quality control and productivity of edge-defined film-fed growth of ribbons

NASA Technical Reports Server (NTRS)

1979-01-01

Influences on ribbon quality which might be caused by various materials of construction which are used in the growth furnace were assessed. At the present level of ribbon quality, which has produced 8.5% to 9.5% efficient solar cells, no particular influence of any furnace part was detected. The experiments led to the suspicion that the general environment and the somewhat unoptimized materials handling procedures might be responsible for the current variations in ribbon quality and that, therefore, continuous work with this furnace under rather more stringent environmental conditions and operating procedures could perhaps improve materials quality to some extent. The work on the multiple furnace was continued with two multiple growth runs being performed. In these runs, the melt replenishment system performed poorly and extensive modifications to it were designed to make reliable melt feeding for five ribbon growth possible. Additional characterization techniques for wide ribbons, stress measurements, and growth dynamics experiments are reported.

Multiple EFG silicon ribbon technology as the basis for manufacturing low-cost terrestrial solar cells. [Epitaxial Film Growth

NASA Technical Reports Server (NTRS)

Mackintosh, B.; Kalejs, J. P.; Ho, C. T.; Wald, F. V.

1981-01-01

Mackintosh et al. (1978) have reported on the development of a multiple ribbon furnace based on the 'edge defined film fed growth' (EFG) process for the fabrication of silicon ribbon. It has been demonstrated that this technology can meet the requirements for a silicon substrate material to be used in the manufacture of solar panels which can meet requirements regarding a selling price of $0.70/Wp when certain goals in terms of throughput and quality are achieved. These goals for the multiple ribbon technology using 10 cm wide ribbon require simultaneous growth of 12 ribbons by one operator at average speeds of 4 to 4.5 cm/min, and 13% efficient solar cells. A description is presented of the progress made toward achieving these goals. It is concluded that the required performance levels have now been achieved. The separate aspects of technology must now be integrated into a single prototype furnace.

Mena–GRASP65 interaction couples actin polymerization to Golgi ribbon linking

PubMed Central

Tang, Danming; Zhang, Xiaoyan; Huang, Shijiao; Yuan, Hebao; Li, Jie; Wang, Yanzhuang

2016-01-01

In mammalian cells, the Golgi reassembly stacking protein 65 (GRASP65) has been implicated in both Golgi stacking and ribbon linking by forming trans-oligomers through the N-terminal GRASP domain. Because the GRASP domain is globular and relatively small, but the gaps between stacks are large and heterogeneous, it remains puzzling how GRASP65 physically links Golgi stacks into a ribbon. To explore the possibility that other proteins may help GRASP65 in ribbon linking, we used biochemical methods and identified the actin elongation factor Mena as a novel GRASP65-binding protein. Mena is recruited onto the Golgi membranes through interaction with GRASP65. Depleting Mena or disrupting actin polymerization resulted in Golgi fragmentation. In cells, Mena and actin were required for Golgi ribbon formation after nocodazole washout; in vitro, Mena and microfilaments enhanced GRASP65 oligomerization and Golgi membrane fusion. Thus Mena interacts with GRASP65 to promote local actin polymerization, which facilitates Golgi ribbon linking. PMID:26538023

Performance of an attention-demanding task during treadmill walking shifts the noise qualities of step-to-step variation in step width.

PubMed

Grabiner, Mark D; Marone, Jane R; Wyatt, Marilynn; Sessoms, Pinata; Kaufman, Kenton R

2018-06-01

The fractal scaling evident in the step-to-step fluctuations of stepping-related time series reflects, to some degree, neuromotor noise. The primary purpose of this study was to determine the extent to which the fractal scaling of step width, step width and step width variability are affected by performance of an attention-demanding task. We hypothesized that the attention-demanding task would shift the structure of the step width time series toward white, uncorrelated noise. Subjects performed two 10-min treadmill walking trials, a control trial of undisturbed walking and a trial during which they performed a mental arithmetic/texting task. Motion capture data was converted to step width time series, the fractal scaling of which were determined from their power spectra. Fractal scaling decreased by 22% during the texting condition (p < 0.001) supporting the hypothesized shift toward white uncorrelated noise. Step width and step width variability increased 19% and five percent, respectively (p < 0.001). However, a stepwise discriminant analysis to which all three variables were input revealed that the control and dual task conditions were discriminated only by step width fractal scaling. The change of the fractal scaling of step width is consistent with increased cognitive demand and suggests a transition in the characteristics of the signal noise. This may reflect an important advance toward the understanding of the manner in which neuromotor noise contributes to some types of falls. However, further investigation of the repeatability of the results, the sensitivity of the results to progressive increases in cognitive load imposed by attention-demanding tasks, and the extent to which the results can be generalized to the gait of older adults seems warranted. Copyright © 2018 Elsevier B.V. All rights reserved.

SYMMETRY OF THE IBEX RIBBON OF ENHANCED ENERGETIC NEUTRAL ATOM (ENA) FLUX

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

Funsten, H. O.; Cai, D. M.; Higdon, D. M.

2015-01-20

The circular ribbon of enhanced energetic neutral atom (ENA) emission observed by the Interstellar Boundary Explorer (IBEX) mission remains a critical signature for understanding the interaction between the heliosphere and the interstellar medium. We study the symmetry of the ribbon flux and find strong, spectrally dependent reflection symmetry throughout the energy range 0.7-4.3 keV. The distribution of ENA flux around the ribbon is predominantly unimodal at 0.7 and 1.1 keV, distinctly bimodal at 2.7 and 4.3 keV, and a mixture of both at 1.7 keV. The bimodal flux distribution consists of partially opposing bilateral flux lobes, located at highest and lowest heliographic latitude extentsmore » of the ribbon. The vector between the ribbon center and heliospheric nose (which defines the so-called BV plane) appears to play an organizing role in the spectral dependence of the symmetry axis locations as well as asymmetric contributions to the ribbon flux. The symmetry planes at 2.7 and 4.3 keV, derived by projecting the symmetry axes to a great circle in the sky, are equivalent to tilting the heliographic equatorial plane to the ribbon center, suggesting a global heliospheric ordering. The presence and energy dependence of symmetric unilateral and bilateral flux distributions suggest strong spectral filtration from processes encountered by an ion along its journey from the source plasma to its eventual detection at IBEX.« less

Method of forming a variable width channel

NASA Technical Reports Server (NTRS)

Andrews, James T. (Inventor)

1989-01-01

A method of forming a channel of varying width in a body comprises the steps of forming a plurality of masking elements having an opening therethrough intersecting a plurality of the elements on a surface of the body, partially flowing the elements into the opening to form a masking pattern having a variable width opening therethrough, and removing portions of the exposed body to form the channel with a sidewall having a surface contour corresponding to an edge of the masking pattern.

75 FR 53685 - Blue Ribbon Commission on America's Nuclear Future

Federal Register 2010, 2011, 2012, 2013, 2014

2010-09-01

... DEPARTMENT OF ENERGY Blue Ribbon Commission on America's Nuclear Future AGENCY: Office of Nuclear Energy, Department of Energy. ACTION: Notice of open meeting. SUMMARY: This notice announces an open meeting of the Blue Ribbon Commission on America's Nuclear Future (the Commission). The Commission was...

76 FR 71334 - Blue Ribbon Commission on America's Nuclear Future

Federal Register 2010, 2011, 2012, 2013, 2014

2011-11-17

... DEPARTMENT OF ENERGY Blue Ribbon Commission on America's Nuclear Future AGENCY: Office of Nuclear Energy, Department of Energy. ACTION: Notice of open meeting. SUMMARY: This notice announces an open meeting of the Blue Ribbon Commission on America's Nuclear Future (the Commission). The Commission was...

75 FR 65465 - Blue Ribbon Commission on America's Nuclear Future, Disposal Subcommittee

Federal Register 2010, 2011, 2012, 2013, 2014

2010-10-25

... DEPARTMENT OF ENERGY Blue Ribbon Commission on America's Nuclear Future, Disposal Subcommittee AGENCY: Department of Energy, Office of Nuclear Energy. ACTION: Notice of open meeting. SUMMARY: This... subcommittee of the Blue Ribbon Commission on America's Nuclear Future (the Commission). The establishment of...

Process Makes Thermoplastic Prepreg Ribbon

NASA Technical Reports Server (NTRS)

Wilson, Maywood L.; Johnson, Gary S.

1995-01-01

Manufacturing process produces ribbon of composite material (prepreg) consisting of continuous lengthwise fibers impregnated with thermoplastic resin. Ribbon can later be cut into sheets of required sizes and shapes, stacked, then heated under pressure to form composite-material structural components. Process accommodates variety of thermoplastic resins and variety of fibers.

77 FR 1743 - U.S. Antarctic Program Blue Ribbon Panel; Notice of Meeting

Federal Register 2010, 2011, 2012, 2013, 2014

2012-01-11

... NATIONAL SCIENCE FOUNDATION U.S. Antarctic Program Blue Ribbon Panel; Notice of Meeting In accordance with Federal Advisory Committee Act (Pub. L. 92-463, as amended), the National Science Foundation announces the following meeting: Name: U.S. Antarctic Program Blue Ribbon Panel Review, 76826. Date/Time...

75 FR 36647 - Blue Ribbon Commission on America's Nuclear Future

Federal Register 2010, 2011, 2012, 2013, 2014

2010-06-28

... DEPARTMENT OF ENERGY Blue Ribbon Commission on America's Nuclear Future AGENCY: Office of Nuclear Energy, DOE. ACTION: Notice of open meeting. SUMMARY: This notice announces an open meeting of the Blue... directed that the Blue Ribbon Commission on America's Nuclear Future (the Commission) be established to...

75 FR 64720 - Blue Ribbon Commission on America's Nuclear Future, Transportation and Storage Subcommittee

Federal Register 2010, 2011, 2012, 2013, 2014

2010-10-20

... DEPARTMENT OF ENERGY Blue Ribbon Commission on America's Nuclear Future, Transportation and Storage Subcommittee AGENCY: Office of Nuclear Energy, Department of Energy. ACTION: Notice of Open...) Subcommittee. The T&S Subcommittee is a subcommittee of the Blue Ribbon Commission on America's Nuclear Future...

75 FR 53686 - Blue Ribbon Commission on America's Nuclear Future, Transportation and Storage Subcommittee

Federal Register 2010, 2011, 2012, 2013, 2014

2010-09-01

... DEPARTMENT OF ENERGY Blue Ribbon Commission on America's Nuclear Future, Transportation and Storage Subcommittee AGENCY: Department of Energy, Office of Nuclear Energy. ACTION: Notice of open...) Subcommittee. The T&S Subcommittee is a subcommittee of the Blue Ribbon Commission on America's Nuclear Future...

Silicon ribbon stress/strain workshop

NASA Technical Reports Server (NTRS)

Leipold, M. H.

1985-01-01

Highlights of the Flat Plate Solar Array Project sponsored Silicon Ribbon Stress/Strain Workshop that was held 23 to 24 January 1985 are reported. The presentations and discussions were aimed at acquiring a generic understanding of the sources of stress, deformation, and structural characteristics occurring during the growth of silicon ribbon.

Ribbon networks for modeling navigable paths of autonomous agents in virtual environments.

PubMed

Willemsen, Peter; Kearney, Joseph K; Wang, Hongling

2006-01-01

This paper presents the Environment Description Framework (EDF) for modeling complex networks of intersecting roads and pathways in virtual environments. EDF represents information about the layout of streets and sidewalks, the rules that govern behavior on roads and walkways, and the locations of agents with respect to navigable structures. The framework serves as the substrate on which behavior programs for autonomous vehicles and pedestrians are built. Pathways are modeled as ribbons in space. The ribbon structure provides a natural coordinate frame for defining the local geometry of navigable surfaces. EDF includes a powerful runtime interface supported by robust and efficient code for locating objects on the ribbon network, for mapping between Cartesian and ribbon coordinates, and for determining behavioral constraints imposed by the environment.

ON THE GEOMETRY OF THE IBEX RIBBON

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

Sylla, Adama; Fichtner, Horst

2015-10-01

The Energetic Neutral Atom (ENA) full-sky maps obtained with the Interstellar Boundary Explorer (IBEX) show an unexpected bright narrow band of increased intensity. This so-called ENA ribbon results from charge exchange of interstellar neutral atoms with protons in the outer heliosphere or beyond. Among other hypotheses it has been argued that this ribbon may be related to a neutral density enhancement, or H-wave, in the local interstellar medium. Here we quantitatively demonstrate, on the basis of an analytical model of the principal large-scale heliospheric structure, that this scenario for the ribbon formation leads to results that are fully consistent withmore » the observed location of the ribbon in the full-sky maps at all energies detected with high-energy sensor IBEX-Hi.« less

Effects of substitution of Mo for Nb on less-common properties of Finemet alloys

NASA Astrophysics Data System (ADS)

Butvin, P.; Butvinová, B.; Silveyra, J. M.; Chromčíková, M.; Janičkovič, D.; Sitek, J.; Švec, P.; Vlasák, G.

2010-10-01

Particular properties of Fe-Nb/Mo-Cu-B-Si rapidly quenched ribbons were examined. Apart from minor variation, no significant difference due to the Mo for Nb substitution was observed in alloy density and its annealing-induced changes. The same holds for the anisotropic thermal expansion of as-cast ribbon when annealed and for induced anisotropy when annealed under stress. The Mo-substituted ribbons show only slightly higher crystallinity and lower coercivity if annealed in inert gas ambience than in vacuum. Some diversity in surface to interior heterogeneity of the differently annealed ribbons can still be distinguished. Preserving a minor percentage of Nb together with Mo does not seem substantiated to obtain favorable soft magnetic properties of ribbons annealed in inert gas.

Variation of magnetic properties with mischmetal content in the resource saving magnets of MM-Fe-B ribbons

NASA Astrophysics Data System (ADS)

Li, Zhu-bai; Wang, Li-chen; Geng, Xiao-peng; Hu, Feng-xia; Sun, Ji-rong; Shen, Bao-gen

2017-03-01

Magnetic materials of MM-Fe-B (MM=mischmetal) ribbons were prepared using melt spinning method by varying the content of MM. The ribbons contain minor phases besides the main phase of Re2Fe14B. X-ray techniques show that the diffraction peak intensities of the minor phase Fe3B vary with the content of constituent elements, indicating that the amount of minor phase could be tunable. The squareness of hysteresis loop is the best in MM13Fe80.5B6.5 ribbons, which should mainly ascribe to the less amount of minor phase. Henkel plots verify the more uniform magnetization reversals in MM13Fe80.5B6.5 ribbons, and the energy product achieves to the maximum of 12.74 MGOe with the coercivity of 6.50 kOe. With the increase of MM content the coercivity increases monotonically, and reaches to 9.13 kOe in MM15Fe77.5B7.5 ribbons, which should be related with the nature of the defects in the main phase. These investigations show that optimizing the content of constituent elements and phase constitution could improve magnetic properties in the resource-saving magnets of MM-Fe-B ribbons.

Supramolecular ribbons from amphiphilic trisamides self-assembly.

PubMed

García, Fátima; Buendía, Julia; Sánchez, Luis

2011-08-05

Two amphiphilic C(3)-symmetric OPE-based trisamides have been synthesized and their self-assembling features investigated in solution and on surface. Variable-temperature UV-vis experiments demonstrate the cooperative supramolecular polymerization of these trisamides that self-assemble by the operation of triple C═O···H-N H-bonding arrays between the amide functional groups and π-π stacking between the aromatic units. The helical organization of the aggregates has been demonstrated by circular dichroism at a concentration as low as 1 × 10(-4) M in acetonitrile. In the reported trisamides, the large hydrophobic aromatic core acts as a solvophobic module impeding the interaction between the polar TEG chains and the amide H-bonds. This strategy makes unnecessary the separation of the amide functional groups to the polar tri(ethylene glycol) chains by paraffinic fragments. Achiral trisamide 1 self-assembles into flat ribbon-like structures that experience an amplification of chirality by the addition of a small amount of chiral 2 that generates twisted stripes.

Design of a variable width pulse generator feasible for manual or automatic control

NASA Astrophysics Data System (ADS)

Vegas, I.; Antoranz, P.; Miranda, J. M.; Franco, F. J.

2017-01-01

A variable width pulse generator featuring more than 4-V peak amplitude and less than 10-ns FWHM is described. In this design the width of the pulses is controlled by means of the control signal slope. Thus, a variable transition time control circuit (TTCC) is also developed, based on the charge and discharge of a capacitor by means of two tunable current sources. Additionally, it is possible to activate/deactivate the pulses when required, therefore allowing the creation of any desired pulse pattern. Furthermore, the implementation presented here can be electronically controlled. In conclusion, due to its versatility, compactness and low cost it can be used in a wide variety of applications.

Relationship between microstructure, cytotoxicity and corrosion properties of a Cu-Al-Ni shape memory alloy.

PubMed

Colić, Miodrag; Rudolf, Rebeka; Stamenković, Dragoslav; Anzel, Ivan; Vucević, Dragana; Jenko, Monika; Lazić, Vojkan; Lojen, Gorazd

2010-01-01

Cu-Al-Ni shape memory alloys (SMAs) have been investigated as materials for medical devices, but their biomedical application is still limited. The aim of this work was to compare the microstructure, corrosion and cytotoxicity in vitro of a Cu-Al-Ni SMA. Rapidly solidified (RS) thin ribbons, manufactured via melt spinning, were used for the tests. The control alloy was a permanent mould casting of the same composition, but without shape memory effect. The results show that RS ribbons are significantly more resistant to corrosion compared with the control alloy, as judged by the lesser release of Cu and Ni into the conditioning medium. These results correlate with the finding that RS ribbons were not cytotoxic to L929 mouse fibroblasts and rat thymocytes. In addition, the RS ribbon conditioning medium inhibited cellular proliferation and IL-2 production by activated rat splenocytes to a much lesser extent. The inhibitory effects were almost completely abolished by conditioning the RS ribbons in culture medium for 4 weeks. Microstructural analysis showed that RS ribbons are martensitic, with boron particles as a minor phase. In contrast, the control Cu-Al-Ni alloy had a complex multiphase microstructure. Examination of the alloy surfaces after conditioning by energy dispersive X-ray and Auger electron spectroscopy showed the formation of Cu and Al oxide layers and confirmed that the metals in RS ribbons are less susceptible to oxidation and corrosion compared with the control alloy. In conclusion, these results suggest that rapid solidification significantly improves the corrosion stability and biocompatibility in vitro of Cu-Al-Ni SMA ribbons.

76 FR 23798 - Blue Ribbon Commission on America's Nuclear Future

Federal Register 2010, 2011, 2012, 2013, 2014

2011-04-28

... DEPARTMENT OF ENERGY Blue Ribbon Commission on America's Nuclear Future AGENCY: Office of Nuclear... meeting of the Blue Ribbon Commission on America's Nuclear Future (the Commission). The Commission was... high-level wastes--in light of the events in Japan. The second purpose is to allow the Co-chairs of the...

77 FR 9707 - U.S. Antarctic Program Blue Ribbon Panel Review; Notice of Meeting

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-17

... NATIONAL SCIENCE FOUNDATION U.S. Antarctic Program Blue Ribbon Panel Review; Notice of Meeting In accordance with Federal Advisory Committee Act (Pub. L. 92-463, as amended), the National Science Foundation announces the following meeting: Name: U.S. Antarctic Program Blue Ribbon Panel Review, 76826. Date/Time...

76 FR 63329 - U.S. Antarctic Program Blue Ribbon Panel Review; Notice of Meeting

Federal Register 2010, 2011, 2012, 2013, 2014

2011-10-12

... NATIONAL SCIENCE FOUNDATION U.S. Antarctic Program Blue Ribbon Panel Review; Notice of Meeting In accordance with Federal Advisory Committee Act (Pub. L. 92-463, as amended), the National Science Foundation announces the following meeting: Name: U.S. Antarctic Program Blue Ribbon Panel Review (76826). Date/Time...

77 FR 20852 - U.S. Antarctic Program Blue Ribbon Panel Review; Notice of Meeting

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-06

... NATIONAL SCIENCE FOUNDATION U.S. Antarctic Program Blue Ribbon Panel Review; Notice of Meeting In accordance with Federal Advisory Committee Act (Pub. L. 92-463, as amended), the National Science Foundation announces the following meeting: Name: U.S. Antarctic Program Blue Ribbon Panel Review, 76826. Date/Time...

75 FR 7244 - Narrow Woven Ribbons with Woven Selvedge from the People's Republic of China: Preliminary...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-02-18

.... (``Guangzhou Complacent''); Ningbo Huarui Import & Export Co., Ltd.; Ningbo Jinfeng Thread & Ribbon Co. Ltd... limited to nylon, polyester, rayon, polypropylene, and polyethylene teraphthalate), metal threads and/or... 13) or rubber thread; (4) narrow woven ribbons of a kind used for the manufacture of typewriter or...

76 FR 38648 - Availability of the Geothermal Technologies Program Blue Ribbon Panel Report and Request for...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-07-01

... Renewable Energy (EERE) Geothermal Technologies Program (the Program) assembled a geothermal Blue Ribbon... of geothermal energy in the United States and the role of the DOE Program. The Geothermal Blue Ribbon...://geothermal.energy.gov/brp . DATES: Submit electronic or written comments on or before July 29, 2011...

The Impact of Leadership Behaviors of Blue Ribbon Catholic School Principals on School Culture

ERIC Educational Resources Information Center

Cardarelli, Rosaline

2014-01-01

The purpose of this study was to conduct an analysis of six successful Blue Ribbon Catholic schools to determine the relationship between principal's leadership behaviors, teacher's perceptions of principals and resulting school culture within six successful Blue Ribbon schools. A mixed methods approach for analysis was used through both…

Adolescent Help-Seeking and the Yellow Ribbon Suicide Prevention Program: An Evaluation

ERIC Educational Resources Information Center

Freedenthal, Stacey

2010-01-01

The Yellow Ribbon Suicide Prevention Program has gained national and international recognition for its school- and community-based activities. After the introduction of Yellow Ribbon to a Denver-area high school, staff and adolescents were surveyed to determine if help-seeking behavior had increased. Using a prepost intervention design, staff at…

78 FR 10130 - Narrow Woven Ribbons With Woven Selvedge From the People's Republic of China: Final Results of...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-13

... Department selected two respondents for review, Precious Planet Ribbons & Bows Co., Ltd. (``Precious Planet'') and Hubschercorp. On January 24, 2012, Precious Planet timely withdrew its request for an...\\ See Letter from Precious Planet to the Secretary of Commerce, ``Narrow Woven Ribbons With Woven...

The silicon on dust substrate path to make solar cells directly from a gaseous feedstock

NASA Astrophysics Data System (ADS)

Serra, J M; Pinto, C R; Silva, J A; Brito, M C; Maia Alves, J; Vallêra, A M

2009-04-01

In this paper, we present a silicon on dust substrate (SDS) process, a new method for the growth of silicon ribbons. As a demonstration of the concept, we also present results on solar cells made of these new silicon ribbons. SDS ribbons were obtained directly from a gaseous feedstock by a fast CVD step using silane. The resulting self-supported intrinsic ribbons were microcrystalline and porous. To make these ribbon films suitable for photovoltaic applications, a novel recrystallization with an in situ doping step was developed. To this purpose, the ribbons were sprayed with boric acid and then recrystallized by float zone melting. Simple solar cells were prepared by employing: aluminium back contacts, Ti/Pd/Ag front grid contacts, with no anti-reflective coating, doping optimization, passivation or gettering. The 1-sun I-V characteristics of the cells were: Voc ~ 530 mV and Jsc ~ 24 mA cm-2. The minority carrier diffusion length obtained from a spectral response at long wavelengths gave values of Ln ~ 70 µm.

Highly conductive ribbons prepared by stick-slip assembly of organosoluble gold nanoparticles.

PubMed

Lawrence, Jimmy; Pham, Jonathan T; Lee, Dong Yun; Liu, Yujie; Crosby, Alfred J; Emrick, Todd

2014-02-25

Precisely positioning and assembling nanoparticles (NPs) into hierarchical nanostructures is opening opportunities in a wide variety of applications. Many techniques employed to produce hierarchical micrometer and nanoscale structures are limited by complex fabrication of templates and difficulties with scalability. Here we describe the fabrication and characterization of conductive nanoparticle ribbons prepared from surfactant-free organosoluble gold nanoparticles (Au NPs). We used a flow-coating technique in a controlled, stick-slip assembly to regulate the deposition of Au NPs into densely packed, multilayered structures. This affords centimeter-scale long, high-resolution Au NP ribbons with precise periodic spacing in a rapid manner, up to 2 orders-of-magnitude finer and faster than previously reported methods. These Au NP ribbons exhibit linear ohmic response, with conductivity that varies by changing the binding headgroup of the ligands. Controlling NP percolation during sintering (e.g., by adding polymer to retard rapid NP coalescence) enables the formation of highly conductive ribbons, similar to thermally sintered conductive adhesives. Hierarchical, conductive Au NP ribbons represent a promising platform to enable opportunities in sensing, optoelectronics, and electromechanical devices.

Wrinkles, loops, and topological defects in twisted ribbons

NASA Astrophysics Data System (ADS)

Chopin, Julien

Nature abounds with elastic ribbon like shapes including double-stranded semiflexible polymers, graphene and metal oxide nanoribbons which are examples of elongated elastic structures with a strongly anisotropic cross-section. Due to this specific geometry, it is far from trivial to anticipate if a ribbon should be considered as a flat flexible filament or a narrow thin plate. We thus perform an experiment in which a thin elastic ribbon is loaded using a twisting and traction device coupled with a micro X-ray computed tomography machine allowing a full 3D shape reconstruction. A wealth of morphological behaviors can be observed including wrinkled helicoids, curled and looped configurations, and faceted ribbons. In this talk, I will show that most morphologies can be understood using a far-from-threshold approach and simple scaling arguments. Further, we find that the various shapes can be organized in a phase diagram using the twist, the tension, and the geometry of the ribbon as control parameters. Finally, I will discuss the spontaneous formation of topological defects with negatively-signed Gaussian charge at large twist and small but finite stretch.

String stabilized ribbon growth a method for seeding same

DOEpatents

Sachs, Emanuel M.

1987-08-25

This invention is a method of initiating or seeding the growth of a crystalline or polycrystalline ribbon by the String Stabilized Ribbon Growth Method. The method for seeding the crystal growth comprises contacting a melt surface with a seed and two strings used in edge stabilization. The wetted strings attach to the wetted seed as a result of the freezing of the liquid melt. Upon drawing the seed, which is attached to the strings, away from the melt surface a melt liquid meniscus, a seed junction, and a growth interface forms. Further pulling of the attached seed causes a crystal ribbon to grow at the growth interface. The boundaries of the growing ribbon are: at the top the seed junction, at the bottom the freezing boundary of the melt liquid meniscus, and at the edges frozen-in strings.

Laser-zone Growth in a Ribbon-to-ribbon (RTR) Process Silicon Sheet Growth Development for the Large Area Silicon Sheet Task of the Low Cost Solar Array Project

NASA Technical Reports Server (NTRS)

Baghdadi, A.; Gurtler, R. W.; Legge, R.; Sopori, B.; Rice, M. J.; Ellis, R. J.

1979-01-01

A technique for growing limited-length ribbons continually was demonstrated. This Rigid Edge technique can be used to recrystallize about 95% of the polyribbon feedstock. A major advantage of this method is that only a single, constant length silicon ribbon is handled throughout the entire process sequence; this may be accomplished using cassettes similar to those presently in use for processing Czochralski waters. Thus a transition from Cz to ribbon technology can be smoothly affected. The maximum size being considered, 3 inches x 24 inches, is half a square foot, and will generate 6 watts for 12% efficiency at 1 sun. Silicon dioxide has been demonstrated as an effective, practical diffusion barrier for use during the polyribbon formation.

Surface effects on the magnetic properties of nearly zero-magnetostriction amorphous ribbons subjected to nonuniform stresses

NASA Astrophysics Data System (ADS)

Buttino, G.; Cecchetti, A.; Poppi, M.; Zini, G.

1992-11-01

A remarkable initial permeability associated with a decrease of the disaccomodation has been obtained in nearly zero-magnetostrictive Metglas by applying weak elastic bending stresses. The stresses are produced by winding the ribbons to form toroids of different radii. The above effects depend on the way of winding the ribbon i.e whether the shiny surface of the ribbon is at the inside or the outside of the core. The discussion emphasizes a different role of the two surface layers of the ribbon on the behaviour of the samples. The results are explained on the basis of the hypothesis advanced by Hernando et al. who assume the λ s ≃ 0 condition in the above materials as due to the coexistence of different magnetostrictive phases on a macroscopic scale.

Effect of Mechanical Stresses in Rapidly Heated Fe73Cu1Nb3Si16B7 Ribbon Arising During the Ring Core Formation on Their Magnetic Properties

NASA Astrophysics Data System (ADS)

Nosenko, Anton; Mika, Taras; Semyrga, Olexandr; Nosenko, Viktor

2017-04-01

The influence of winding-induced mechanical stresses on the magnetic anisotropy and core loss in toroidal cores made of Fe73Cu1Nb3Si16B7 ribbon is studied. The ribbon for the cores was rapidly pre-heated under tensile stress up to 120 MPa. It was found that magnetic characteristics of the material (magnetic anisotropy energy and the core loss) can be controlled by varying the tensile stress during the preliminary rapid heating of the ribbon. It was shown that with reducing core diameter, the magnetic anisotropy energy and core loss significantly increase. However, relatively high winding-induced core loss in small cores can be significantly reduced by increasing tensile stresses applied to the ribbon during pre-heating.

Effect of Mechanical Stresses in Rapidly Heated Fe73Cu1Nb3Si16B7 Ribbon Arising During the Ring Core Formation on Their Magnetic Properties.

PubMed

Nosenko, Anton; Mika, Taras; Semyrga, Olexandr; Nosenko, Viktor

2017-12-01

The influence of winding-induced mechanical stresses on the magnetic anisotropy and core loss in toroidal cores made of Fe 73 Cu 1 Nb 3 Si 16 B 7 ribbon is studied. The ribbon for the cores was rapidly pre-heated under tensile stress up to 120 MPa. It was found that magnetic characteristics of the material (magnetic anisotropy energy and the core loss) can be controlled by varying the tensile stress during the preliminary rapid heating of the ribbon. It was shown that with reducing core diameter, the magnetic anisotropy energy and core loss significantly increase. However, relatively high winding-induced core loss in small cores can be significantly reduced by increasing tensile stresses applied to the ribbon during pre-heating.

Estimating tree crown widths for the primary Acadian species in Maine

Treesearch

Matthew B. Russell; Aaron R. Weiskittel

2012-01-01

In this analysis, data for seven conifer and eight hardwood species were gathered from across the state of Maine for estimating tree crown widths. Maximum and largest crown width equations were developed using tree diameter at breast height as the primary predicting variable. Quantile regression techniques were used to estimate the maximum crown width and a constrained...

Onset of a Large Ejective Solar Eruption from a Typical Coronal-jet-base Field Configuration

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

Joshi, Navin Chandra; Magara, Tetsuya; Moon, Yong-Jae

Utilizing multiwavelength observations and magnetic field data from the Solar Dynamics Observatory ( SDO )/Atmospheric Imaging Assembly (AIA), SDO /Helioseismic and Magnetic Imager (HMI), the Geostationary Operational Environmental Satellite ( GOES ), and RHESSI , we investigate a large-scale ejective solar eruption of 2014 December 18 from active region NOAA 12241. This event produced a distinctive “three-ribbon” flare, having two parallel ribbons corresponding to the ribbons of a standard two-ribbon flare, and a larger-scale third quasi-circular ribbon offset from the other two. There are two components to this eruptive event. First, a flux rope forms above a strong-field polarity inversionmore » line and erupts and grows as the parallel ribbons turn on, grow, and spread apart from that polarity inversion line; this evolution is consistent with the mechanism of tether-cutting reconnection for eruptions. Second, the eruption of the arcade that has the erupting flux rope in its core undergoes magnetic reconnection at the null point of a fan dome that envelops the erupting arcade, resulting in formation of the quasi-circular ribbon; this is consistent with the breakout reconnection mechanism for eruptions. We find that the parallel ribbons begin well before (∼12 minutes) the onset of the circular ribbon, indicating that tether-cutting reconnection (or a non-ideal MHD instability) initiated this event, rather than breakout reconnection. The overall setup for this large-scale eruption (diameter of the circular ribbon ∼10{sup 5} km) is analogous to that of coronal jets (base size ∼10{sup 4} km), many of which, according to recent findings, result from eruptions of small-scale “minifilaments.” Thus these findings confirm that eruptions of sheared-core magnetic arcades seated in fan–spine null-point magnetic topology happen on a wide range of size scales on the Sun.« less

Large area silicon sheet by EFG. [Edge-defined Film-fed Growth

NASA Technical Reports Server (NTRS)

Rao, C. V. H.; Surek, T.; Mackintosh, B.; Ravi, K. V.; Wald, F. V.

1978-01-01

The edge-defined, film-fed growth (EFG) technique has been employed to grow silicon ribbons for photovoltaic applications. Considerable progress has been made in recent years in developing the technique to the point that long lengths of silicon ribbon can be routinely grown. In order to attain the full low-cost potential of the EFG technique, several further developments such as the growth of thinner and wider ribbons, increase in ribbon growth rate, and improvements in material quality are needed. The technological problems to be solved and the approaches employed to achieve these goals are discussed.

THE ENERGY-DEPENDENT POSITION OF THE IBEX RIBBON DUE TO THE SOLAR WIND STRUCTURE

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

Swaczyna, Paweł; Bzowski, Maciej; Sokół, Justyna M., E-mail: pswaczyna@cbk.waw.pl

2016-08-10

Observations of energetic neutral atoms (ENAs) allow for remote studies of the condition of plasma in the heliosphere and the neighboring local interstellar medium. The first results from the Interstellar Boundary Explorer ( IBEX ) revealed an arc-like enhancement of the ENA intensity in the sky, known as the ribbon. The ribbon was not expected from the heliospheric models prior to the launch of IBEX . One proposed explanation for the ribbon is the mechanism of secondary ENA emission. The ribbon reveals energy-dependent structure in the relative intensity along its circumference and in its position. That is, the geometric centermore » of the ribbon varies systematically by about 10° in the energy range 0.7–4.3 keV. Here, we show by analytical modeling that this effect is a consequence of the helio-latitudinal structure of the solar wind reflected in the secondary ENAs. Along with a recently measured distance to the ribbon’s source just beyond the heliopause, our findings support the connection of the ribbon with the local interstellar magnetic field by the mechanism of secondary ENA emission. However, the magnitude of the center shift in the highest IBEX energy channel is much larger in the observations than expected from the modeling. This may be due to another, not currently recognized, process of ENA generation.« less

Insights into the Structure and Function of Ciliary and Flagellar Doublet Microtubules

PubMed Central

Linck, Richard; Fu, Xiaofeng; Lin, Jianfeng; Ouch, Christna; Schefter, Alexandra; Steffen, Walter; Warren, Peter; Nicastro, Daniela

2014-01-01

Cilia and flagella are conserved, motile, and sensory cell organelles involved in signal transduction and human disease. Their scaffold consists of a 9-fold array of remarkably stable doublet microtubules (DMTs), along which motor proteins transmit force for ciliary motility and intraflagellar transport. DMTs possess Ribbons of three to four hyper-stable protofilaments whose location, organization, and specialized functions have been elusive. We performed a comprehensive analysis of the distribution and structural arrangements of Ribbon proteins from sea urchin sperm flagella, using quantitative immunobiochemistry, proteomics, immuno-cryo-electron microscopy, and tomography. Isolated Ribbons contain acetylated α-tubulin, β-tubulin, conserved protein Rib45, >95% of the axonemal tektins, and >95% of the calcium-binding proteins, Rib74 and Rib85.5, whose human homologues are related to the cause of juvenile myoclonic epilepsy. DMTs contain only one type of Ribbon, corresponding to protofilaments A11-12-13-1 of the A-tubule. Rib74 and Rib85.5 are associated with the Ribbon in the lumen of the A-tubule. Ribbons contain a single ∼5-nm wide filament, composed of equimolar tektins A, B, and C, which interact with the nexin-dynein regulatory complex. A summary of findings is presented, and the functions of Ribbon proteins are discussed in terms of the assembly and stability of DMTs, ciliary motility, and other microtubule systems. PMID:24794867

Exploring the charge localization and band gap opening of borophene: a first-principles study.

PubMed

Kistanov, Andrey A; Cai, Yongqing; Zhou, Kun; Srikanth, Narasimalu; Dmitriev, Sergey V; Zhang, Yong-Wei

2018-01-18

Recently synthesized two-dimensional (2D) boron, borophene, exhibits a novel metallic behavior rooted in the s-p orbital hybridization, distinctively different from other 2D materials such as sulfides/selenides and semi-metallic graphene. This unique feature of borophene implies new routes for charge delocalization and band gap opening. Herein, using first-principles calculations, we explore the routes to localize the carriers and open the band gap of borophene via chemical functionalization, ribbon construction, and defect engineering. The metallicity of borophene is found to be remarkably robust against H- and F-functionalization and the presence of vacancies. Interestingly, a strong odd-even oscillation of the electronic structure with width is revealed for H-functionalized borophene nanoribbons, while an ultra-high work function (∼7.83 eV) is found for the F-functionalized borophene due to its strong charge transfer to the atomic adsorbates.

Imaging the Localized Plasmon Resonance Modes in Graphene Nanoribbons

DOE PAGES

Hu, F.; Luan, Y.; Fei, Z.; ...

2017-08-14

Here, we report a nanoinfrared (IR) imaging study of the localized plasmon resonance modes of graphene nanoribbons (GNRs) using a scattering-type scanning near-field optical microscope (s-SNOM). By comparing the imaging data of GNRs that are aligned parallel and perpendicular to the in-plane component of the excitation laser field, we observed symmetric and asymmetric plasmonic interference fringes, respectively. Theoretical analysis indicates that the asymmetric fringes are formed due to the interplay between the localized surface plasmon resonance (SPR) mode excited by the GNRs and the propagative surface plasmon polariton (SPP) mode launched by the s-SNOM tip. And with rigorous simulations, wemore » reproduce the observed fringe patterns and address quantitatively the role of the s-SNOM tip on both the SPR and SPP modes. Moreover, we have seen real-space signatures of both the dipole and higher-order SPR modes by varying the ribbon width.« less

Sensory Organ Like Response of Zigzag Edge Graphene Nanoribbons

NASA Astrophysics Data System (ADS)

Shenoy, Vijay; Bhowmick, Somnath

2011-03-01

Using a continuum Dirac theory, we study the density and spin response of zigzag edge terminated graphene ribbons subjected to edge potentials and Zeeman fields. Our analytical calculations of the density and spin responses of the closed system (fixed particle number) to the static edge fields, show a highly nonlinear Weber-Fechner type behavior where the response depends logarithmically on the edge potential. The dependence of the response on the size of the system (e.g.~width of a nanoribbon) is also uncovered. Zigzag edge graphene nanoribbons, therefore, provide a realization of response of organs such as the eye and ear that obey Weber-Fechner law. We validate our analytical results with tight binding calculations. These results are crucial in understanding important effects of electron-electron interactions in graphene nanoribbons such as edge magnetism etc., and also suggest possibilities for device applications of graphene nanoribbons. Work supported by DST, India through MONAMI and Ramanujan grants.

Flow Caster Produces Custom Alloy Magnetic Ribbon

NASA Image and Video Library

2016-12-21

NASA Glenn’s large-scale, 5 kg planar flow caster cools a vat of molten metallic alloy, producing a magnetic ribbon that spouts into a collection bin. The caster has the ability to produce a magnetized ribbon that measures up to one mile long and 50 mm wide to support NASA’s hybrid electric aircraft propulsion and power management work.

Perceptions of Factors Affecting the Relative Effectiveness of Temporary Blue Ribbon State Commissions.

ERIC Educational Resources Information Center

Johnson, Janet Rogers-Clarke

Elements in the composition and process of higher education blue ribbon commissions that influence their effectiveness were studied. Blue ribbon commissions, which have been used as one type of statewide planning strategy, are defined here as commissions with (1) a predetermined life span; (2) authority established by the legislature and/or the…

Ultrasonic Measurement Of Silicon-Growth Interface

NASA Technical Reports Server (NTRS)

Heyser, Richard C.

1988-01-01

Position of interface between silicon melt and growing ribbon of silicon measured with aid of reflected ultrasound, according to proposal. Reflections reveal characteristics of ribbon and melt. Ultrasound pulses travel through rods to silicon ribbon growing by dendritic-web process. Rods return reflections of pulses to sonic transducers. Isolate transducers thermally, but not acoustically, from hot silicon melt.

Thin-Ribbon Tapered Couplers For Dielectric Waveguides

NASA Technical Reports Server (NTRS)

Otoshi, Tom Y.; Shimabukuro, Fred I.; Yeh, Cavour

1996-01-01

Thin-ribbon tapered couplers proposed for launching electro-magnetic waves into dielectric waveguides, which include optical fibers. Intended for use with ribbon dielectric waveguides designed for operation at millimeter or submillimeter wavelengths, made of high-relative-permittivity, low-loss materials and thicknesses comparable to or less than free-space design wavelengths. Coupling efficiencies exceeds those of older tapered couplers.

Size effects on magnetic actuation in Ni-Mn-Ga shape-memory alloys.

PubMed

Dunand, David C; Müllner, Peter

2011-01-11

The off-stoichiometric Ni(2)MnGa Heusler alloy is a magnetic shape-memory alloy capable of reversible magnetic-field-induced strains (MFIS). These are generated by twin boundaries moving under the influence of an internal stress produced by a magnetic field through the magnetocrystalline anisotropy. While MFIS are very large (up to 10%) for monocrystalline Ni-Mn-Ga, they are near zero (<0.01%) in fine-grained polycrystals due to incompatibilities during twinning of neighboring grains and the resulting internal geometrical constraints. By growing the grains and/or shrinking the sample, the grain size becomes comparable to one or more characteristic sample sizes (film thickness, wire or strut diameter, ribbon width, particle diameter, etc), and the grains become surrounded by free space. This reduces the incompatibilities between neighboring grains and can favor twinning and thus increase the MFIS. This approach was validated recently with very large MFIS (0.2-8%) measured in Ni-Mn-Ga fibers and foams with bamboo grains with dimensions similar to the fiber or strut diameters and in thin plates where grain diameters are comparable to plate thickness. Here, we review processing, micro- and macrostructure, and magneto-mechanical properties of (i) Ni-Mn-Ga powders, fibers, ribbons and films with one or more small dimension, which are amenable to the growth of bamboo grains leading to large MFIS, and (ii) "constructs" from these structural elements (e.g., mats, laminates, textiles, foams and composites). Various strategies are proposed to accentuate this geometric effect which enables large MFIS in polycrystalline Ni-Mn-Ga by matching grain and sample sizes.

Simulations of a dynamic solar cycle and its effects on the interstellar boundary explorer ribbon and globally distributed energetic neutral atom flux

DOE PAGES

Zirnstein, E. J.; Heerikhuisen, J.; Pogorelov, N. V.; ...

2015-04-23

Observations by the Interstellar Boundary Explorer (IBEX) have vastly improved our understanding of the interaction between the solar wind (SW) and local interstellar medium through direct measurements of energetic neutral atoms (ENAs); this informs us about the heliospheric conditions that produced them. An enhanced feature of flux in the sky, the so-called IBEX ribbon, was not predicted by any global models before the first IBEX observations. A dominating theory of the origin of the ribbon, although still under debate, is a secondary charge-exchange process involving secondary ENAs originating from outside the heliopause. According to this mechanism, the evolution of themore » solar cycle should be visible in the ribbon flux. Therefore, in this paper we simulate a fully time-dependent ribbon flux, as well as globally distributed flux from the inner heliosheath (IHS), using time-dependent SW parameters from Sokol et al. as boundary conditions for our time-dependent heliosphere simulation. After post-processing the results to compute H ENA fluxes, these results show that the secondary ENA ribbon indeed should be time dependent, evolving with a period of approximately 11 yr, with differences depending on the energy and direction. Our results for the IHS flux show little periodic change with the 11 yr solar cycle, but rather with short-term fluctuations in the background plasma. And, while the secondary ENA mechanism appears to emulate several key characteristics of the observed IBEX ribbon, it appears that our simulation does not yet include all of the relevant physics that produces the observed ribbon.« less

SIMULATIONS OF A DYNAMIC SOLAR CYCLE AND ITS EFFECTS ON THE INTERSTELLAR BOUNDARY EXPLORER RIBBON AND GLOBALLY DISTRIBUTED ENERGETIC NEUTRAL ATOM FLUX

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

Zirnstein, E. J.; Heerikhuisen, J.; Pogorelov, N. V.

2015-05-01

Since 2009, observations by the Interstellar Boundary Explorer (IBEX) have vastly improved our understanding of the interaction between the solar wind (SW) and local interstellar medium through direct measurements of energetic neutral atoms (ENAs), which inform us about the heliospheric conditions that produced them. An enhanced feature of flux in the sky, the so-called IBEX ribbon, was not predicted by any global models before the first IBEX observations. A dominating theory of the origin of the ribbon, although still under debate, is a secondary charge-exchange process involving secondary ENAs originating from outside the heliopause. According to this mechanism, the evolutionmore » of the solar cycle should be visible in the ribbon flux. Therefore, in this paper we simulate a fully time-dependent ribbon flux, as well as globally distributed flux from the inner heliosheath (IHS), using time-dependent SW parameters from Sokół et al. as boundary conditions for our time-dependent heliosphere simulation. After post-processing the results to compute H ENA fluxes, our results show that the secondary ENA ribbon indeed should be time dependent, evolving with a period of approximately 11 yr, with differences depending on the energy and direction. Our results for the IHS flux show little periodic change with the 11 yr solar cycle, but rather with short-term fluctuations in the background plasma. While the secondary ENA mechanism appears to emulate several key characteristics of the observed IBEX ribbon, it appears that our simulation does not yet include all of the relevant physics that produces the observed ribbon.« less

THE 2-3 kHz HELIOSPHERIC RADIATION, THE IBEX RIBBON, AND THE THREE-DIMENSIONAL SHAPE OF THE HELIOPAUSE

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

Fuselier, Stephen A.; Cairns, Iver H.

2013-07-10

Recent Interstellar Boundary Explorer (IBEX) observations indicate that the total dynamic pressure in the interstellar medium is closely partitioned between the plasma and the magnetic field, with an Alfven Mach number M{sub A} {approx} 1 and a sonic Mach number {approx}2. Observations of the IBEX Ribbon provide a unique determination of the orientation of the undraped interstellar magnetic field along the heliopause. There is also a striking correspondence between the Ribbon location and the source locations of 2-3 kHz radiation determined from Voyager observations: the radiation sources north of the ecliptic form a line parallel to but offset by aboutmore » 30 Degree-Sign from the Ribbon. A general Rankine-Hugoniot analysis is used to argue that the heliopause should not be symmetric about the velocity vector V{sub ISM} of the interstellar medium relative to the Sun (the nominal nose direction). Furthermore, the closest point on the heliopause to the Sun should be on the Ribbon for M{sub A} = 0 and at least 9 Degree-Sign from the nominal nose direction toward the Ribbon for M{sub A} = 1. These new results are combined into a conceptual model of the heliopause that includes (1) a plasma depletion layer formed as the interstellar magnetic field drapes against the heliopause, (2) a minimum inner heliosheath thickness and closest point between the Sun and heliopause along (or close to) the Ribbon rather than in the nominal nose direction (along V{sub ISM}), and (3) inference of an asymmetric heliopause shape from the angular offset of the radio sources and Ribbon and from the Rankine-Hugoniot analysis.« less

Herbaceous versus forested riparian vegetation: narrow and simple versus wide, woody and diverse stream habitat

Treesearch

C.R. Jackson; D.S. Leigh; S.L. Scarbrough; J.F. Chamblee

2014-01-01

We investigated interactions of riparian vegetative conditions upon a suite of channel morphological variables: active channel width, variability of width within a reach, large wood frequency, mesoscale habitat distributions, mesoscale habitat diversity, median particle size and per cent fines. We surveyed 49 wadeable streams, 45 with low levels of development,...

Random walk in nonhomogeneous environments: A possible approach to human and animal mobility

NASA Astrophysics Data System (ADS)

Srokowski, Tomasz

2017-03-01

The random walk process in a nonhomogeneous medium, characterized by a Lévy stable distribution of jump length, is discussed. The width depends on a position: either before the jump or after that. In the latter case, the density slope is affected by the variable width and the variance may be finite; then all kinds of the anomalous diffusion are predicted. In the former case, only the time characteristics are sensitive to the variable width. The corresponding Langevin equation with different interpretations of the multiplicative noise is discussed. The dependence of the distribution width on position after jump is interpreted in terms of cognitive abilities and related to such problems as migration in a human population and foraging habits of animals.

Customized ATP towpreg. [Automated Tow Placement

NASA Technical Reports Server (NTRS)

Sandusky, Donald A.; Marchello, Joseph M.; Baucom, Robert M.; Johnston, Norman J.

1992-01-01

Automated tow placement (ATP) utilizes robotic technology to lay down adjacent polymer-matrix-impregnated carbon fiber tows on a tool surface. Consolidation and cure during ATP requires that void elimination and polymer matrix adhesion be accomplished in the short period of heating and pressure rolling that follows towpreg ribbon placement from the robot head to the tool. This study examined the key towpreg ribbon properties and dimensions which play a significant role in ATP. Analysis of the heat transfer process window indicates that adequate heating can be achieved at lay down rates as high as 1 m/sec. While heat transfer did not appear to be the limiting factor, resin flow and fiber movement into tow lap gaps could be. Accordingly, consideration was given to towpreg ribbon having uniform yet non-rectangular cross sections. Dimensional integrity of the towpreg ribbon combined with customized ribbon architecture offer great promise for processing advances in ATP of high performance composites.

High temperature (900-1300 C) mechanical behaviour of dendritic web grown silicon ribbons - Strain rate and temperature dependence of the yield stress

NASA Technical Reports Server (NTRS)

Mathews, V. K.; Gross, T. S.

1987-01-01

The mechanical behavior of dendritic web Si ribbons close the melting point was studied experimentally. The goal of the study was to generate data for modeling the generation of stresses and dislocation structures during growth of dendritic web Si ribbons, thereby permitting modifications to the production process, i.e., the temperature profile, to lower production costs for the photovoltaic ribbons. A laser was used to cut specimens in the direction of growth of sample ribbons, which were then subjected to tensile tests at temperatures up to 1300 C in an Ar atmosphere. The tensile strengths of the samples increased when the temperature rose above 1200 C, a phenomena which was attributed to the diffusion of oxygen atoms to the quasi-dislocation sites. The migration to the potential dislocations sites effectively locked the dislocations.

Self-Assembly of Helical Ribbons

NASA Astrophysics Data System (ADS)

Zastavker, Yevgeniya V.; Asherie, Neer; Lomakin, Aleksey; Pande, Jayanti; Donovan, Joanne M.; Schnur, Joel M.; Benedek, George B.

1999-07-01

The self-assembly of helical ribbons is examined in a variety of multicomponent enantiomerically pure systems that contain a bile salt or a nonionic detergent, a phosphatidylcholine or a fatty acid, and a steroid analog of cholesterol. In almost all systems, two different pitch types of helical ribbons are observed: high pitch, with a pitch angle of 54± 2 degrees, and low pitch, with a pitch angle of 11± 2 degrees. Although the majority of these helices are right-handed, a small proportion of left-handed helices is observed. Additionally, a third type of helical ribbon, with a pitch angle in the range 30-47 degrees, is occasionally found. These experimental findings suggest that the helical ribbons are crystalline rather than liquid crystal in nature and also suggest that molecular chirality may not be the determining factor in helix formation. The large yields of helices produced will permit a systematic investigation of their individual kinetic evolution and their elastic moduli.

Metal — Insulator Transition-like in Nano-Crystallized Ni-Fe-Zr Metallic Glasses

NASA Astrophysics Data System (ADS)

Hamed, F.; Obaidat, I. M.; Benkraouda, M.

2007-08-01

Ni-Fe-Zr based Metallic glassy ribbons were prepared by melt spinning technique. The compositional and structural integrity of the melt spun ribbons were verified by means of X-ray diffraction, SEM, EDX and DSC. 5 to 7 cm long ribbons of Ni-Fe-Zr based metallic glasses with different compositions were sealed inside quartz ampoules under vacuum. The sealed metallic glassy ribbons were nano-crystallized at 973 K for varying periods of time. The temperature dependence of the electrical resistivity of the nano-crystallized samples had been investigated over the temperature range 25-280 K. The crystallized ribbons at 973 K for periods for less than 4 hours displayed insulating electrical behavior like at low temperatures, while those annealed for more than 4 hours showed metallic behavior like. Nonlinear I-V characteristics were also observed at low temperatures for samples annealed for less than four hours.

Effect of Heat Treatment on Microstructure and Magnetostrictive Property of Melt-Spun Fe85Ga15 Ribbons

NASA Astrophysics Data System (ADS)

Liu, Hao; Wang, Haiou; Cao, Mengxiong; Tan, Weishi; Shi, Yangguang; Chen, Yu; Huang, Yuying

2013-09-01

In order to study the microstructure of Fe-Ga alloy, Fe85Ga15 ribbons prepared with different wheel velocity were studied by high resolution X-ray diffraction (HRXRD) and extend X-ray absorption fine structure (EXAFS). HRXRD patterns showed that only disordered A2 phase was observed in as-cast Fe85Ga15 alloy. A modified-DO3 phase was detected in all of the melt spun samples. The HRXRD associated with EXAFS results indicated that Ga atoms were located as second-nearest neighbor along [100] orientation. A little DO3 phase was found in ribbons annealed at 1000°C under 0.06 MPa Ar atmosphere. The result of magnetostriction measurement revealed that in the ribbon prepared with higher wheel velocity, more modified-DO3 phase will enhance the magnetostriction. DO3 phase in the annealed sample will deteriorate the magnetostrictive properties of Fe-Ga ribbons.

Magnetostructural transitions and magnetocaloric effects in Ni50Mn35In14.25B0.75 ribbons

NASA Astrophysics Data System (ADS)

Pandey, Sudip; Quetz, Abdiel; Ibarra-Gaytan, P. J.; Sánchez-Valdés, C. F.; Aryal, Anil; Dubenko, Igor; Sanchez Llamazares, Jose Luis; Stadler, Shane; Ali, Naushad

2018-05-01

The structural, thermal, and magnetic behaviors, as well as the martensitic phase transformation and related magnetocaloric response of Ni50Mn35In14.25B0.75 annealed ribbons have been investigated using room-temperature X-ray diffraction (XRD), differential scanning calorimetry (DSC), and magnetization measurements. Ni50Mn35In14.25B0.75 annealed ribbons show a sharper change in magnetization at the martensitic transition, resulting in larger magnetic entropy changes in comparison to bulk Ni50Mn35In14.25B0.75. A drastic shift in the martensitic transformation temperature (TM) of 70 K to higher temperature was observed for the annealed ribbons relative to that of the bulk (TM = 240 K). The results obtained for magnetic, thermal, structural, and magnetocaloric properties of annealed ribbons have been compared to those of the corresponding bulk alloys.

Powder-Coated Towpreg: Avenues to Near Net Shape Fabrication of High Performance Composites

NASA Technical Reports Server (NTRS)

Johnston, N. J.; Cano, R. J.; Marchello, J. M.; Sandusky, D. A.

1995-01-01

Near net shape parts were fabricated from powder-coated preforms. Key issues including powder loss during weaving and tow/tow friction during braiding were addressed, respectively, by fusing the powder to the fiber prior to weaving and applying a water-based gel to the towpreg prior to braiding. A 4:1 debulking of a complex 3-D woven powder-coated preform was achieved in a single step utilizing expansion rubber molding. Also, a process was developed for using powder-coated towpreg to fabricate consolidated ribbon having good dimensional integrity and low voids. Such ribbon will be required for in situ fabrication of structural components via heated head advanced tow placement. To implement process control and ensure high quality ribbon, the ribbonizer heat transfer and pulling force were modeled from fundamental principles. Most of the new ribbons were fabricated from dry polyarylene ether and polymide powders.

Revised techniques for estimating peak discharges from channel width in Montana

USGS Publications Warehouse

Parrett, Charles; Hull, J.A.; Omang, R.J.

1987-01-01

This study was conducted to develop new estimating equations based on channel width and the updated flood frequency curves of previous investigations. Simple regression equations for estimating peak discharges with recurrence intervals of 2, 5, 10 , 25, 50, and 100 years were developed for seven regions in Montana. The standard errors of estimates for the equations that use active channel width as the independent variables ranged from 30% to 87%. The standard errors of estimate for the equations that use bankfull width as the independent variable ranged from 34% to 92%. The smallest standard errors generally occurred in the prediction equations for the 2-yr flood, 5-yr flood, and 10-yr flood, and the largest standard errors occurred in the prediction equations for the 100-yr flood. The equations that use active channel width and the equations that use bankfull width were determined to be about equally reliable in five regions. In the West Region, the equations that use bankfull width were slightly more reliable than those based on active channel width, whereas in the East-Central Region the equations that use active channel width were slightly more reliable than those based on bankfull width. Compared with similar equations previously developed, the standard errors of estimate for the new equations are substantially smaller in three regions and substantially larger in two regions. Limitations on the use of the estimating equations include: (1) The equations are based on stable conditions of channel geometry and prevailing water and sediment discharge; (2) The measurement of channel width requires a site visit, preferably by a person with experience in the method, and involves appreciable measurement errors; (3) Reliability of results from the equations for channel widths beyond the range of definition is unknown. In spite of the limitations, the estimating equations derived in this study are considered to be as reliable as estimating equations based on basin and climatic variables. Because the two types of estimating equations are independent, results from each can be weighted inversely proportional to their variances, and averaged. The weighted average estimate has a variance less than either individual estimate. (Author 's abstract)

The discovery of 9/8-ribbons, β/γ-peptides with curved shapes governed by a combined configuration-conformation code.

PubMed

Grison, Claire M; Robin, Sylvie; Aitken, David J

2015-11-21

The de novo design of a β/γ-peptidic foldamer motif has led to the discovery of an unprecedented 9/8-ribbon featuring an uninterrupted alternating C9/C8 hydrogen-bonding network. The ribbons adopt partially curved topologies determined synchronistically by the β-residue configuration and the γ-residue conformation sets.

Polymer film composite transducer

DOEpatents

Owen, Thomas E.

2005-09-20

A composite piezoelectric transducer, whose piezoeletric element is a "ribbon wound" film of piezolectric material. As the film is excited, it expands and contracts, which results in expansion and contraction of the diameter of the entire ribbon winding. This is accompanied by expansion and contraction of the thickness of the ribbon winding, such that the sound radiating plate may be placed on the side of the winding.

33 CFR 334.480 - Archers Creek, Ribbon Creek, and Broad River; U.S. Marine Corps Recruit Depot, Parris Island...

Code of Federal Regulations, 2013 CFR

2013-07-01

... Broad River; U.S. Marine Corps Recruit Depot, Parris Island, South Carolina; danger zones. 334.480... DEFENSE DANGER ZONE AND RESTRICTED AREA REGULATIONS § 334.480 Archers Creek, Ribbon Creek, and Broad River... danger zone on Archers Creek (between the Broad River and Beaufort River), Ribbon Creek, and the Broad...

33 CFR 334.480 - Archers Creek, Ribbon Creek, and Broad River; U.S. Marine Corps Recruit Depot, Parris Island...

Code of Federal Regulations, 2012 CFR

2012-07-01

... Broad River; U.S. Marine Corps Recruit Depot, Parris Island, South Carolina; danger zones. 334.480... DEFENSE DANGER ZONE AND RESTRICTED AREA REGULATIONS § 334.480 Archers Creek, Ribbon Creek, and Broad River... danger zone on Archers Creek (between the Broad River and Beaufort River), Ribbon Creek, and the Broad...

33 CFR 334.480 - Archers Creek, Ribbon Creek, and Broad River; U.S. Marine Corps Recruit Depot, Parris Island...

Code of Federal Regulations, 2014 CFR

2014-07-01

... Broad River; U.S. Marine Corps Recruit Depot, Parris Island, South Carolina; danger zones. 334.480... DEFENSE DANGER ZONE AND RESTRICTED AREA REGULATIONS § 334.480 Archers Creek, Ribbon Creek, and Broad River... danger zone on Archers Creek (between the Broad River and Beaufort River), Ribbon Creek, and the Broad...

Synaptic ribbon. Conveyor belt or safety belt?

PubMed

Parsons, T D; Sterling, P

2003-02-06

The synaptic ribbon in neurons that release transmitter via graded potentials has been considered as a conveyor belt that actively moves vesicles toward their release sites. But evidence has accumulated to the contrary, and it now seems plausible that the ribbon serves instead as a safety belt to tether vesicles stably in mutual contact and thus facilitate multivesicular release by compound exocytosis.

Utilization of multiwalled boron nitride nanotubes for the reinforcement of lightweight aluminum ribbons

PubMed Central

2013-01-01

Multiwalled boron nitride nanotubes (BNNTs) have very attractive mechanical and thermal properties, e.g., elasticity, tensile strength, and high resistance to oxidation, and may be considered as ideal reinforcing agents in lightweight metal matrix composites. Herein, for the first time, Al-BNNT ribbons with various BNNT contents (up to 3 wt.%) were fabricated via melt spinning in an argon atmosphere. BNNTs were randomly dispersed within a microcrystalline Al matrix under ribbon casting and led to more than doubling of room-temperature ultimate tensile strength of the composites compared to pure Al ribbons produced at the similar conditions. PMID:23279813

Solar harvesting by a heterostructured cell with built-in variable width quantum wells

NASA Astrophysics Data System (ADS)

Brooks, W.; Wang, H.; Mil'shtein, S.

2018-02-01

We propose cascaded heterostructured p-i-n solar cells, where inside of the i-region is a set of Quantum Wells (QWs) with variable thicknesses to enhance absorption of different photonic energies and provide quick relaxation for high energy carriers. Our p-i-n heterostructure carries top p-type and bottom n-type 11.3 Å thick AlAs layers, which are doped by acceptors and donor densities up to 1019/cm3. The intrinsic region is divided into 10 segments where each segment carries ten QWs of the same width and the width of the QWs in each subsequent segment gradually increases. The top segment consists of 10 QWs with widths of 56.5Å, followed by a segment with 10 wider QWs with widths of 84.75Å, followed by increasing QW widths until the last segment has 10 QWs with widths of 565Å, bringing the total number of QWs to 100. The QW wall height is controlled by alternating AlAs and GaAs layers, where the AlAs layers are all 11.3Å thick, throughout the entire intrinsic region. Configuration of variable width QWs prescribes sets of energy levels which are suitable for absorption of a wide range of photon energies and will dissipate high electron-hole energies rapidly, reducing the heat load on the solar cell. We expect that the heating of the solar cell will be reduced by 8-11%, enhancing efficiency. The efficiency of the designed solar cell is 43.71%, the Fill Factor is 0.86, the density of short circuit current (ISC) will not exceed 338 A/m2 and the open circuit voltage (VOC) is 1.51V.

[Vertical variability of Pinus sylvestris var. mongolica tree ring delta13C and its relationship with tree ring width in northern Daxing' an Mountains of Northeast China].

PubMed

Shang, Zhi-Yuan; Wang, Jian; Zhang, Wen; Li, Yan-Yan; Cui, Ming-Xing; Chen, Zhen-Ju; Zhao, Xing-Yun

2013-01-01

A measurement was made on the vertical direction tree ring stable carbon isotope ratio (delta13C) and tree ring width of Pinus sylvestris var. mongolica in northern Daxing' an Mountains of Northeast China, with the relationship between the vertical direction variations of the tree ring delta13C and tree ring width analyzed. In the whole ring of xylem, earlywood (EW) and bark endodermis, the delta13C all exhibited an increasing trend from the top to the base at first, with the maximum at the bottom of tree crown, and then, decreased rapidly to the minimum downward. The EW and late-wood (LW) had an increasing ratio of average tree ring width from the base to the top. The average annual sequence of the delta13C in vertical direction had an obvious reverse correspondence with the average annual sequence of tree ring width, and had a trend comparatively in line with the average annual sequence of the tree ring width ratio of EW to LW above tree crown. The variance analysis showed that there existed significant differences in the sequences of tree ring delta13C and ring width in vertical direction, and the magnitude of vertical delta13C variability was basically the same as that of the inter-annual delta13C variability. The year-to-year variation trend of the vertical delta13C sequence was approximately identical. For each sample, the delta13C sequence at the same heights was negatively correlated with the ring width sequence, but the statistical significance differed with tree height.

Genetic variability and phenotypic plasticity of metric thoracic traits in an invasive drosophilid in America.

PubMed

Bitner-Mathé, Blanche Christine; David, Jean Robert

2015-08-01

Thermal phenotypic plasticity of 5 metric thoracic traits (3 related to size and 2 to pigmentation) was investigated in Zaprionus indianus with an isofemale line design. Three of these traits are investigated for the first time in a drosophilid, i.e. thorax width and width of pigmented longitudinal white and black stripes. The reaction norms of white and black stripes were completely different: white stripes were insensitive to growth temperature while the black stripes exhibited a strong linear decrease with increasing temperatures. Thorax width exhibited a concave reaction norm, analogous but not identical to those of wing length and thorax length: the temperatures of maximum value were different, the highest being for thorax width. All traits exhibited a significant heritable variability and a low evolvability. Sexual dimorphism was very variable among traits, being nil for white stripes and thorax width, and around 1.13 for black stripes. The ratio thorax length to thorax width (an elongation index) was always >1, showing that males have a more rounded thorax at all temperatures. Black stripes revealed a significant increase of sexual dimorphism with increasing temperature. Shape indices, i.e. ratios between size traits all exhibited a linear decrease with temperature, the least sensitive being the elongation index. All these results illustrate the complexity of developmental processes but also the analytical strength of biometrical plasticity studies in an eco-devo perspective.

Gender differences in foot shape: a study of Chinese young adults.

PubMed

Hong, Youlian; Wang, Lin; Xu, Dong Qing; Li, Jing Xian

2011-06-01

One important extrinsic factor that causes foot deformity and pain in women is footwear. Women's sports shoes are designed as smaller versions of men's shoes. Based on this, the current study aims to identify foot shape in 1,236 Chinese young adult men and 1,085 Chinese young adult women. Three-dimensional foot shape data were collected through video filming. Nineteen foot shape variables were measured, including girth (4 variables), length (4 variables), width (3 variables), height (7 variables), and angle (1 variable). A comparison of foot measures within the range of the common foot length (FL) categories indicates that women showed significantly smaller values of foot measures in width, height, and girth than men. Three foot types were classified, and distributions of different foot shapes within the same FL were found between women and men. Foot width, medial ball length, ball angle, and instep height showed significant differences among foot types in the same FL for both genders. There were differences in the foot shape between Chinese young women and men, which should be considered in the design of Chinese young adults' sports shoes.

Development of a relationship between external measurements and reinforcement stress

NASA Astrophysics Data System (ADS)

Brault, Andre; Hoult, Neil A.; Lees, Janet M.

2015-03-01

As many countries around the world face an aging infrastructure crisis, there is an increasing need to develop more accurate monitoring and assessment techniques for reinforced concrete structures. One of the challenges associated with assessing existing infrastructure is correlating externally measured parameters such as crack widths and surface strains with reinforcement stresses as this is dependent on a number of variables. The current research investigates how the use of distributed fiber optic sensors to measure reinforcement strain can be correlated with digital image correlation measurements of crack widths to relate external crack width measurements to reinforcement stresses. An initial set of experiments was undertaken involving a series of small-scale beam specimens tested in three-point bending with variable reinforcement properties. Relationships between crack widths and internal reinforcement strains were observed including that both the diameter and number of bars affected the measured maximum strain and crack width. A model that uses measured crack width to estimate reinforcement strain was presented and compared to the experimental results. The model was found to provide accurate estimates of load carrying capacity for a given crack width, however, the model was potentially less accurate when crack widths were used to estimate the experimental reinforcement strains. The need for more experimental data to validate the conclusions of this research was also highlighted.

Echo characteristics of two salmon species

NASA Astrophysics Data System (ADS)

Nealson, Patrick A.; Horne, John K.; Burwen, Debby L.

2005-04-01

The Alaska Department of Fish and Game relies on split-beam hydroacoustic techniques to estimate Chinook salmon (Oncorhynchus tshawytscha) returns to the Kenai River. Chinook counts are periodically confounded by large numbers of smaller sockeye salmon (O. nerka). Echo target-strength has been used to distinguish fish length classes, but was too variable to separate Kenai River chinook and sockeye distributions. To evaluate the efficacy of alternate echo metrics, controlled acoustic measurements of tethered chinook and sockeye salmon were collected at 200 kHz. Echo returns were digitally sampled at 48 kHz. A suite of descriptive metrics were collected from a series of 1,000 echoes per fish. Measurements of echo width were least variable at the -3 dB power point. Initial results show echo elongation and ping-to-ping variability in echo envelope width were significantly greater for chinook than for sockeye salmon. Chinook were also observed to return multiple discrete peaks from a single broadcast echo. These characteristics were attributed to the physical width of chinook exceeding half of the broadcast echo pulse width at certain orientations. Echo phase variability, correlation coefficient and fractal dimension distributions did not demonstrate significant discriminatory power between the two species. [Work supported by ADF&G, ONR.

Relationship between innervation zone width and mean muscle fiber conduction velocity during a sustained isometric contraction.

PubMed

Ye, X; Beck, T W; Wages, N P

2015-03-01

To examine the relationship between the biceps brachii muscle innervation zone (IZ) width and the mean muscle fiber conduction velocity (MFCV) during a sustained isometric contraction. Fifteen healthy men performed a sustained isometric elbow flexion exercise at their 60% maximal voluntary contraction (MVC) until they could not maintain the target force. Mean MFCV was estimated through multichannel surface electromyographic recordings from a linear electrode array. Before exercise, IZ width was quantified. Separate non-parametric one-way analyses of variance (ANOVAs) were used to examine whether there was a difference in each mean MFCV variable among groups with different IZ width. In addition, separate bivariate correlations were also performed to examine the relationships between the IZ width and the mean MFCV variables during the fatiguing exercise. There was a significant difference in the percent decline of mean MFCV (%ΔMFCV) among groups with different IZ width (χ(2) (3)=11.571, p=0.009). In addition, there was also a significant positive relationship between the IZ width and the %ΔMFCV (Kendall's tau= 0.807; p<0.001). We believe that such relationship is likely influenced by both muscle fiber size and the muscle fiber type composition.

U.S. Department of Education 2008 No Child Left Behind -- Blue Ribbon Schools Program: Statistical Summary of National Participation

ERIC Educational Resources Information Center

US Department of Education, 2008

2008-01-01

The No Child Left Behind Blue Ribbon Schools Program honors public and private K-12 schools that are either academically superior in their state or that demonstrate dramatic gains in student achievement. This document includes 2008 statistical information for public and private blue ribbon schools for 45 states. In addition to summarized totals,…

A Comparison of Teachers' Perceptions of Principal Effectiveness in National Blue Ribbon Schools and Matched Sets of Selected Non-Blue Ribbon Schools in Pennsylvania

ERIC Educational Resources Information Center

Giffing, Ryan Robert

2010-01-01

With a focus on leadership, this study examines the leadership characteristics of principals in schools that are recognized as National Blue Ribbon Schools by the United States Department of Education. This mixed methodology study utilizes the causal comparative method to compare what teachers consider to be effective leadership characteristics of…

What Professional and Personal Strategies Do Successful Principals Possess to Cultivate a School Culture That Promotes Academic Success in a Blue Ribbon School

ERIC Educational Resources Information Center

McKinney, Carlos LaTeetha

2012-01-01

Principals who are presiding over schools that have received a blue ribbon certification have evidently used specific professional and personal strategies, as well as behaviors, to enhance the academic and social culture of their schools. The current study examined Mississippi Gulf Coast Schools that received blue ribbon status in the last six…

33 CFR 334.480 - Archers Creek, Ribbon Creek and Broad River, S.C.; U.S. Marine Corps Recruit Depot rifle and...

Code of Federal Regulations, 2011 CFR

2011-07-01

... Broad River, S.C.; U.S. Marine Corps Recruit Depot rifle and pistol ranges, Parris Island. 334.480... DEFENSE DANGER ZONE AND RESTRICTED AREA REGULATIONS § 334.480 Archers Creek, Ribbon Creek and Broad River... navigation: (1) At the rifle range. Archers Creek between Broad River and Beaufort River and Ribbon Creek...

33 CFR 334.480 - Archers Creek, Ribbon Creek and Broad River, S.C.; U.S. Marine Corps Recruit Depot rifle and...

Code of Federal Regulations, 2010 CFR

2010-07-01

... Broad River, S.C.; U.S. Marine Corps Recruit Depot rifle and pistol ranges, Parris Island. 334.480... DEFENSE DANGER ZONE AND RESTRICTED AREA REGULATIONS § 334.480 Archers Creek, Ribbon Creek and Broad River... navigation: (1) At the rifle range. Archers Creek between Broad River and Beaufort River and Ribbon Creek...

Sensor assembly

DOEpatents

Bennett, Thomas E.; Nelson, Drew V.

2004-04-13

A ribbon-like sensor assembly is described wherein a length of an optical fiber embedded within a similar lengths of a prepreg tow. The fiber is ""sandwiched"" by two layers of the prepreg tow which are merged to form a single consolidated ribbon. The consolidated ribbon achieving a generally uniform distribution of composite filaments near the embedded fiber such that excess resin does not ""pool"" around the periphery of the embedded fiber.

Degree of target utilization influences the location of movement endpoint distributions.

PubMed

Slifkin, Andrew B; Eder, Jeffrey R

2017-03-01

According to dominant theories of motor control, speed and accuracy are optimized when, on the average, movement endpoints are located at the target center and when the variability of the movement endpoint distributions is matched to the width of the target (viz., Meyer, Abrams, Kornblum, Wright, & Smith, 1988). The current study tested those predictions. According to the speed-accuracy trade-off, expanding the range of variability to the amount permitted by the limits of the target boundaries allows for maximization of movement speed while centering the distribution on the target center prevents movement errors that would have occurred had the distribution been off center. Here, participants (N=20) were required to generate 100 consecutive targeted hand movements under each of 15 unique conditions: There were three movement amplitude requirements (80, 160, 320mm) and within each there were five target widths (5, 10, 20, 40, 80mm). According to the results, it was only at the smaller target widths (5, 10mm) that movement endpoint distributions were centered on the target center and the range of movement endpoint variability matched the range specified by the target boundaries. As target width increased (20, 40, 80mm), participants increasingly undershot the target center and the range of movement endpoint variability increasingly underestimated the variability permitted by the target region. The degree of target center undershooting was strongly predicted by the difference between the size of the target and the amount of movement endpoint variability, i.e., the amount of unused space in the target. The results suggest that participants have precise knowledge of their variability relative to that permitted by the target, and they use that knowledge to systematically reduce the travel distance to targets. The reduction in travel distance across the larger target widths might have resulted in greater cost savings than those associated with increases in speed. Copyright © 2017. Published by Elsevier B.V.

Effects of surface crystallization and oxidation in nanocrystalline FeNbCuSiB(P) ribbons

NASA Astrophysics Data System (ADS)

Butvinová, B.; Butvin, P.; Brzózka, K.; Kuzminski, M.; Maťko, I.; Švec, P., Sr.; Chromčíková, M.

2017-02-01

Si-poor Fe74Nb3Cu1Si8B14-xPx, (x=0, 3) nanocrystalline ribbon-form alloys often form surfaces, which exert in-plane force on underlying ribbon interior when nanocrystallized in even modest presence of oxygen. Mostly unwanted hard-ribbon-axis magnetic anisotropy is standard result. Essential sources of the surface-caused stress have been sought and influence of P instead of B substitution on this effect was studied too. Preferred surface crystallization (PSC) was found to be the major reason. However P substitution suppresses PSC and promotes Fe-oxide formation, which eases the stress, softens the surfaces and provides different annealing evolution of surface properties.

Apparatus for assembling space structure

NASA Technical Reports Server (NTRS)

Johnston, J. D.; Tuggle, R. H., Jr.; Burch, J. L.; Clark, K. H. (Inventor)

1978-01-01

An apparatus for producing a structure in outer space from rolls of prepunched ribbon or sheet material that are transported from the earth to the apparatus located in outer space is described. The apparatus spins the space structure similar to a spider spinning a web utilizing the prepunched ribbon material. The prepunched ribbon material is fed through the apparatus and is shaped into a predetermined channel-shaped configuration. Trusses are punched out of the ribbon and are bent downwardly and attached to a track which normally is a previously laid sheet of material. The size of the overall space structure may be increased by merely attaching an additional roll of sheet material to the apparatus.

Interaction of Graphene ribbon with atmospheric chemical species

DTIC Science & Technology

2017-04-14

graphene ribbons is an important process in interaction of atmospheric radical with graphene. This study examines how the size of the graphene ribbon...an important process in interaction of atmospheric  radical  with  graphene.   This  study  examines how  the  size of  the  graphene  ribbon affects  the... journals   [a1]  Journal  name:CARBON              Title: Size dependence of graphene chemistry: A computational  study  on CO desorption reaction    Date

Defects in High Speed Growth of EFG Silicon Ribbon

NASA Technical Reports Server (NTRS)

Rao, C. V. H. N.; Cretella, M. C.

1984-01-01

Silicon ribbons grown by the Edge-defined Film-fed Growth (EFG) technique exhibit a characteristic defect structure typified by twins, dislocations, grain boundaries and silicon carbide inclusions. As growth speed is increased from less than 2.5 cm per minute, the structural details change. The major difference between the ribbons grown at speeds below and above 2.5 cm per minute is in the generation of a cellular structure at the higher growth speeds, observable in the ribbon cross section. The presence of the cross sectional structure leads, in general, to a reduction in cell performance. Models to explain the formation of such a cross sectional structure are presented and discussed.

Large area silicon sheet by EFG

NASA Technical Reports Server (NTRS)

1981-01-01

The influence of parameters such as CO2 concentration, gas flow patterns, quartz in the bulk melt, melt doping level and growth speed on ribbon properties was examined for 10 cm wide ribbon. Ribbon quality is optimized for ambient CO2 in argon concentrations in the range from 1000 to 5000 ppm. Cell performance degrades at CO2 concentrations above 5000 ppm and IR interstitial oxygen levels decrease. These experiments were done primarily at a growth speed of 3.5 cm/minute. Cartridge parameters influencing the ribbon thickness were studied and thickness uniformity at 200 micrometers (8 mils) has been improved. Growth stability at the target speed of 4.0 cm/minute was improved significantly.

Variation of alluvial-channel width with discharge and character of sediment

USGS Publications Warehouse

Osterkamp, W.R.

1979-01-01

Use of channel measurements to estimate discharge characteristics of alluvial streams has shown that little agreement exists for the exponent of the width-discharge relation. For the equation Q = aWAb, where Q is mean discharge and WA is active-channel width, it is proposed that the exponent, b, should be of fixed value for most natural, perennial, alluvial stream channels and that the coefficient, a, varies with the characteristics of the bed and bank material.Three groups of perennial stream channels with differing characteristics were selected for study using consistent procedures of data collection. A common feature of the groups was general channel stability, that is, absence of excessive widening by erosive discharges. Group 1 consisted of 32 channels of gradient exceeding 0.0080, low suspended-sediment discharge, high channel roughness, and low discharge variability. Group 2 consisted of 13 streams in Kansas having at least 70 percent silt and clay in the bed material and having similar discharge variability, climate, gradient, and riparian vegetation. Group 3, in southern Missouri, consisted of discharge channels of 18 springs having similar conditions of very low discharge variability, climate and vegetation, but variable bed and bank material. Values for the exponent for the three groups of data are 1.98, 1.97, and 1.97, respectively, whereas values of the coefficients are 0.017, 0.042, and 0.011 when discharge is expressed in cubic meters per second and width is in meters. The relation for high-gradient channels (group 1) is supported by published data from laboratory flumes.The similarity of the three values of the exponent demonstrates that a standard exponent of 2.0, significant to two figures, is reasonable for the width-mean discharge relation of perennial, alluvial stream channels, and that the exponent is independent of other variables. Using a fixed exponent of 2.0, a family of simple power-function equations was developed expressing the manner in which channel sediment affects the width-discharge relation.

How Do Rab Proteins Determine Golgi Structure?

PubMed Central

Liu, Shijie; Storrie, Brian

2015-01-01

Rab proteins, small GTPases, are key regulators of mammalian Golgi apparatus organization. Based on the effect of Rab activation state, Rab proteins fall into two functional classes. In Class1, inactivation induces Golgi ribbon fragmentation and/or redistribution of Golgi enzymes to the ER, while overexpression of wild type or activation has little, if any, effect on Golgi ribbon organization. In Class 2, the reverse is true. We give emphasis to Rab6, the most abundant Golgi-associated Rab protein. Rab6 depletion in HeLa cells causes an increase in Golgi cisternal number, longer, more continuous cisternae, and a pronounced accumulation of vesicles; the effect of Rab6 on Golgi ribbon organization is probably through regulation of vesicle transport. In effector studies, motor proteins and their regulators are found to be key Rab6 effectors. A related Rab, Rab41, affects Golgi ribbon organization in a contrasting manner. The balance between minus- and plus-end directed motor recruitment may well be the major Rab-dependent factor in Golgi ribbon organization. PMID:25708460

Geometry and surface controlled formation of nanoparticle helical ribbons

NASA Astrophysics Data System (ADS)

Pham, Jonathan; Lawrence, Jimmy; Lee, Dong; Grason, Gregory; Emrick, Todd; Crosby, Alfred

2013-03-01

Helical structures are interesting because of their space efficiency, mechanical tunability and everyday uses in both the synthetic and natural world. In general, the mechanisms governing helix formation are limited to bilayer material systems and chiral molecular structures. However, in a special range of dimensions where surface energy dominates (i.e. high surface to volume ratio), geometry rather than specific materials can drive helical formation of thin asymmetric ribbons. In an evaporative assembly technique called flow coating, based from the commonly observed coffee ring effect, we create nanoparticle ribbons possessing non-rectangular nanoscale cross-sections. When released into a liquid medium of water, interfacial tension between the asymmetric ribbon and water balances with the elastic cost of bending to form helices with a preferred radius of curvature and a minimum pitch. We demonstrate that this is a universal mechanism that can be used with a wide range of materials, such as quantum dots, metallic nanoparticles, or polymers. Nanoparticle helical ribbons display excellent structural integrity with spring-like characteristics and can be extended high strains.

First-principles investigation of armchair boron nitride nanoribbons for sensing PH3 gas molecules

NASA Astrophysics Data System (ADS)

Srivastava, Pankaj; Jaiswal, Neeraj K.; Sharma, Varun

2014-09-01

The present work exhibits density functional theory (DFT) based first-principles calculations to explore the sensing properties of bare armchair boron nitride nanoribbons (ABNNR) for PH3 gas molecules. Edges of the ribbon were considered as the sites of possible adsorption with two different configurations i.e. adsorption at one edge and adsorption at both edges of the ribbon. It is revealed that B atoms of the ribbons are more energetically favorable sites for the adsorption of PH3 molecules as compared with N atoms. The adsorption of PH3 affects the electronic properties of nanoribbons. One edge PH3 adsorbed ribbons are metallic whereas in both edges PH3 adsorption, the band gap is decreased than that of bare ribbon. The changes in electronic properties caused by PH3 adsorption are further supported by the current-voltage (I-V) characteristics of the considered configurations. The results show that ABNNR can serve as a potential candidate for PH3 sensing applications.

Alteration of in vivo cellulose ribbon assembly by carboxymethylcellulose and other cellulose derivatives.

PubMed

Haigler, C H; White, A R; Brown, R M; Cooper, K M

1982-07-01

In vivo cellulose ribbon assembly by the Gram-negative bacterium Acetobacter xylinum can be altered by incubation in carboxymethylcellulose (CMC), a negatively charged water-soluble cellulose derivative, and also by incubation in a variety of neutral, water-soluble cellulose derivatives. In the presence of all of these substituted celluloses, normal fasciation of microfibril bundles to form the typical twisting ribbon is prevented. Alteration of ribbon assembly is most extensive in the presence of CMC, which often induces synthesis of separate, intertwining bundles of microfibrils. Freeze-etch preparations of the bacterial outer membrane suggest that particles that are thought to be associated with cellulose synthesis or extrusion may be specifically organized to mediate synthesis of microfibril bundles. These data support the previous hypothesis that the cellulose ribbon of A. xylinum is formed by a hierarchical, cell-directed, self-assembly process. The relationship of these results to the regulation of cellulose microfibril size and wall extensibility in plant cell walls is discussed.

Elevated temperature strengthening of a melt spun austenitic steel by TiB2

NASA Technical Reports Server (NTRS)

Michal, G. M.; Glasgow, T. K.; Moore, T. J.

1986-01-01

Mechanical properties of an iron-based alloy containing (by wt pct) 33Ni, 2Al, 6Ti, and 2B (resulting in an alloy containing 10 vol pct TiB2) were evaluated by hardness and tensile testing. The alloy was cast as a ribbon using a dual 'free-jet' variation of Jech et al. (1984) method of chill-block melt-spinning against a copper wheel; to simulate thermal cycles the alloy ribbon would experience during compaction into shapes, various segments of the ribbon were annealed under a vacuum at temperatures ranging from 500 to 1150 C. The results show that maximum strengths at 650 and 760 C were developed in ribbons annealed at 1100 C; in these ribbons an optimal combination of grain coarsening with minimum TiB2 particle growth was observed. However, the elevated-temperature strength of the TiB2-strengthened alloy under optimal annealing conditions was poorer than that of conventional iron-based superalloys strengthened by gamma-prime precipitates.

Symmetries and band gaps in nanoribbons

NASA Astrophysics Data System (ADS)

Zhang, Zhiwei; Tian, Yiteng; Fernando, Gayanath; Kocharian, Armen

In ideal graphene-like systems, time reversal and sublattice symmetries preserve the degeneracies at the Dirac point(s). We have examined such degeneracies in the band structure as well as the transport properties in various arm-twisted (graphene-related) nanoribbons. A twist angle is defined such that at 0 degrees the ribbon is a rectangular ribbon and at 60 degrees the ribbon is cut from a honeycomb lattice. Using model Hamiltonians and first principles calculations in these nanoribbons with Z2 topology, we have monitored the band structure as a function of the twist angle θ. In twisted ribbons, it turns out that the introduction of an extra hopping term leads to a gap opening. We have also calculated the size and temperature broadening effects in similar ribbons in addition to Rashba-induced transport properties. The authors acknowledge the computing facilities provided by the Center for Functional Nanomaterials, Brookhaven National Laboratory supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No.DE-AC02- 98CH10886.

Nanoporous Ag prepared from the melt-spun Cu-Ag alloys

NASA Astrophysics Data System (ADS)

Li, Guijing; Song, Xiaoping; Sun, Zhanbo; Yang, Shengchun; Ding, Bingjun; Yang, Sen; Yang, Zhimao; Wang, Fei

2011-07-01

Nanoporous Ag ribbons with different morphology and porosity were achieved by the electrochemical corrosion of the melt-spun Cu-Ag alloys. The Cu-rich phase in the alloys was removed, resulting in the formation of the nanopores distributed across the whole ribbon. It is found that the structures, morphology and porosity of the nanoporous Ag ribbons were dependent on the microstructures of the parent alloys. The most of ligaments presented a rod-like shape due to the formation of pseudoeutectic microstructure in the melt-spun Cu 55Ag 45 and Cu 70Ag 30 alloys. For nanoporous Ag prepared from Cu 85Ag 15 alloys, the ligaments were camber-like because of the appearance of the divorced microstructures. Especially, a novel bamboo-grove-like structure could be observed at the cross-section of the nanoporous Ag ribbons. The experiment reveals that nanoporous Ag ribbons exhibited excellent enhancement of surface-enhanced Raman scattering (SERS) effect, but a slight difference existed due to the discrepancy of their morphology.

Ribbon electron beam formation by a forevacuum plasma electron source

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

Klimov, A. S., E-mail: klimov@main.tusur.ru; Burdovitsin, V. A.; Grishkov, A. A.

2016-01-15

Results of the numerical analysis and experimental research on ribbon electron beam generation based on hollow cathode discharge at forevacuum gas pressure are presented. Geometry of the accelerating gap has modified. It lets us focus the ribbon electron beam and to transport it on a distance of several tens of centimeters in the absence of an axial magnetic field. The results of numerical simulations are confirmed by the experiment.

The Disturbing Effect of the Stray Magnetic Fields on Magnetoimpedance Sensors

PubMed Central

Wang, Tao; Zhou, Yong; Lei, Chong; Zhi, Shaotao; Guo, Lei; Li, Hengyu; Wu, Zhizheng; Xie, Shaorong; Luo, Jun; Pu, Huayan

2016-01-01

The disturbing effect of the stray magnetic fields of Fe-based amorphous ribbons on the giant magnetoimpedance (GMI) sensor has been investigated systematically in this paper. Two simple methods were used for examining the disturbing effect of the stray magnetic fields of ribbons on the GMI sensor. In order to study the influence of the stray magnetic fields on the GMI effect, the square-shaped amorphous ribbons were tested in front, at the back, on the left and on the top of a meander-line GMI sensor made up of soft ferromagnetic films, respectively. Experimental results show that the presence of ribbons in front or at the back of GMI sensor shifts the GMI curve to a lower external magnetic field. On the contrary, the presence of ribbons on the left or on the top of the GMI sensor shifts the GMI curve to a higher external magnetic field, which is related to the coupling effect of the external magnetic field and the stray magnetic fields. The influence of the area and angle of ribbons on GMI was also studied in this work. The GMI sensor exhibits high linearity for detection of the stray magnetic fields, which has made it feasible to construct a sensitive magnetometer for detecting the typical stray magnetic fields of general soft ferromagnetic materials. PMID:27763498

The response of macrophages to a Cu-Al-Ni shape memory alloy.

PubMed

Colić, Miodrag; Tomić, Sergej; Rudolf, Rebeka; Anzel, Ivan; Lojen, Gorazd

2010-09-01

Cu-Al-Ni shape memory alloys (SMAs) have been investigated as materials for medical devices, but little is known about their biocompatibility. The aim of this work was to study the response of rat peritoneal macrophages (PMØ) to a Cu-Al-Ni SMA in vitro, by measuring the functional activity of mitochondria, necrosis, apoptosis, and production of proinflammatory cytokines. Rapidly solidified (RS) thin ribbons were used for the tests. The control alloy was a permanent mold casting of the same composition, but without the shape memory effect. Our results showed that the control alloy was severely cytotoxic, whereas RS ribbons induced neither necrosis nor apoptosis of PMØ. These findings correlated with the data that RS ribbons are significantly more resistant to corrosion compared to the control alloy, as judged by the lesser release of Cu and Ni in the conditioning medium. However, the ribbons generated intracellular reactive oxygen species and upregulated the production of IL-6 by PMØ. These effects were almost completely abolished by conditioning the RS ribbons for 5 weeks. In conclusion, RS significantly improves the corrosion stability and biocompatibility of Cu-Al-Ni SMA. The biocompatibility of this functional material could be additionally enhanced by conditioning the ribbons in cell culture medium.

Impacts of amorphous and crystalline cobalt ferrite layers on the giant magneto-impedance response of a soft ferromagnetic amorphous ribbon

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

Mukherjee, D.; Devkota, J.; Ruiz, A.

2014-09-28

A systematic study of the effect of depositing CoFe₂O₄ (CFO) films of various thicknesses (d = 0–600 nm) on the giant magneto-impedance (GMI) response of a soft ferromagnetic amorphous ribbon Co₆₅Fe₄Ni₂Si₁₅B₁₄ has been performed. The CFO films were grown on the amorphous ribbons by the pulsed laser deposition technique. X-ray diffraction and transmission electron microscopy revealed a structural variation of the CFO film from amorphous to polycrystalline as the thickness of the CFO film exceeded a critical value of 300 nm. Atomic force microscopy evidenced the increase in surface roughness of the CFO film as the thickness of the CFOmore » film was increased. These changes in the crystallinity and morphology of the CFO film were found to have a distinct impact on the GMI response of the ribbon. Relative to the bare ribbon, coating of amorphous CFO films significantly enhanced the GMI response of the ribbon, while polycrystalline CFO films decreased it considerably. The maximum GMI response was achieved near the onset of the structural transition of the CFO film. These findings are of practical importance in developing high-sensitivity magnetic sensors.« less

Mena-GRASP65 interaction couples actin polymerization to Golgi ribbon linking.

PubMed

Tang, Danming; Zhang, Xiaoyan; Huang, Shijiao; Yuan, Hebao; Li, Jie; Wang, Yanzhuang

2016-01-01

In mammalian cells, the Golgi reassembly stacking protein 65 (GRASP65) has been implicated in both Golgi stacking and ribbon linking by forming trans-oligomers through the N-terminal GRASP domain. Because the GRASP domain is globular and relatively small, but the gaps between stacks are large and heterogeneous, it remains puzzling how GRASP65 physically links Golgi stacks into a ribbon. To explore the possibility that other proteins may help GRASP65 in ribbon linking, we used biochemical methods and identified the actin elongation factor Mena as a novel GRASP65-binding protein. Mena is recruited onto the Golgi membranes through interaction with GRASP65. Depleting Mena or disrupting actin polymerization resulted in Golgi fragmentation. In cells, Mena and actin were required for Golgi ribbon formation after nocodazole washout; in vitro, Mena and microfilaments enhanced GRASP65 oligomerization and Golgi membrane fusion. Thus Mena interacts with GRASP65 to promote local actin polymerization, which facilitates Golgi ribbon linking. © 2016 Tang et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).

Concurrent gradients of ribbon volume and AMPA-receptor patch volume in cochlear afferent synapses on gerbil inner hair cells.

PubMed

Zhang, Lichun; Engler, Sina; Koepcke, Lena; Steenken, Friederike; Köppl, Christine

2018-07-01

The Mongolian gerbil is a classic animal model for age-related hearing loss. As a prerequisite for studying age-related changes, we characterized cochlear afferent synaptic morphology in young adult gerbils, using immunolabeling and quantitative analysis of confocal microscopic images. Cochlear wholemounts were triple-labeled with a hair-cell marker, a marker of presynaptic ribbons, and a marker of postsynaptic AMPA-type glutamate receptors. Seven cochlear positions covering an equivalent frequency range from 0.5 - 32 kHz were evaluated. The spatial positions of synapses were determined in a coordinate system with reference to their individual inner hair cell. Synapse numbers confirmed previous reports for gerbils (on average, 20-22 afferents per inner hair cell). The volumes of presynaptic ribbons and postsynaptic glutamate receptor patches were positively correlated: larger ribbons associated with larger receptor patches and smaller ribbons with smaller patches. Furthermore, the volumes of both presynaptic ribbons and postsynaptic receptor patches co-varied along the modiolar-pillar and the longitudinal axes of their hair cell. The gradients in ribbon volume are consistent with previous findings in cat, guinea pig, mouse and rat and further support a role in differentiating the physiological properties of type I afferents. However, the positive correlation between the volumes of pre- and postsynaptic elements in the gerbil is different to the opposing gradients found in the mouse, suggesting species-specific differences in the postsynaptic AMPA receptors that are unrelated to the fundamental classes of type I afferents. Copyright © 2018 Elsevier B.V. All rights reserved.

Inter-ribbon tunneling in graphene: An atomistic Bardeen approach

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

Van de Put, Maarten L., E-mail: maarten.vandeput@uantwerpen.be; Magnus, Wim; imec, B-3001 Heverlee

A weakly coupled system of two crossed graphene nanoribbons exhibits direct tunneling due to the overlap of the wavefunctions of both ribbons. We apply the Bardeen transfer Hamiltonian formalism, using atomistic band structure calculations to account for the effect of the atomic structure on the tunneling process. The strong quantum-size confinement of the nanoribbons is mirrored by the one-dimensional character of the electronic structure, resulting in properties that differ significantly from the case of inter-layer tunneling, where tunneling occurs between bulk two-dimensional graphene sheets. The current-voltage characteristics of the inter-ribbon tunneling structures exhibit resonance, as well as stepwise increases inmore » current. Both features are caused by the energetic alignment of one-dimensional peaks in the density-of-states of the ribbons. Resonant tunneling occurs if the sign of the curvature of the coupled energy bands is equal, whereas a step-like increase in the current occurs if the signs are opposite. Changing the doping modulates the onset-voltage of the effects as well as their magnitude. Doping through electrostatic gating makes these structures promising for application towards steep slope switching devices. Using the atomistic empirical pseudopotentials based Bardeen transfer Hamiltonian method, inter-ribbon tunneling can be studied for the whole range of two-dimensional materials, such as transition metal dichalcogenides. The effects of resonance and of step-like increases in the current we observe in graphene ribbons are also expected in ribbons made from these alternative two-dimensional materials, because these effects are manifestations of the one-dimensional character of the density-of-states.« less

Hard magnetic property enhancement of Co{sub 7}Hf-based ribbons by boron doping

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

Chang, H. W.; Liao, M. C.; Shih, C. W.

2014-11-10

Hard magnetic property enhancement of melt spun Co{sub 88}Hf{sub 12} ribbons by boron doping is demonstrated. B-doping could not only remarkably enhance the magnetic properties from energy product ((BH){sub max}) of 2.6 MGOe and intrinsic coercivity ({sub i}H{sub c}) of 1.5 kOe for B-free Co{sub 88}Hf{sub 12} ribbons to (BH){sub max} = 7.7 MGOe and {sub i}H{sub c} = 3.1 kOe for Co{sub 85}Hf{sub 12}B{sub 3} ribbons but also improve the Curie temperature (T{sub C}) of 7:1 phase. The (BH){sub max} value achieved in Co{sub 85}Hf{sub 12}B{sub 3} ribbons is the highest in Co-Hf alloy ribbons ever reported, which is about 15% higher thanmore » that of Co{sub 11}Hf{sub 2}B ribbons spun at 16 m/s [M. A. McGuire, O. Rios, N. J. Ghimire, and M. Koehler, Appl. Phys. Lett. 101, 202401 (2012)]. The structural analysis confirms that B enters the orthorhombic Co{sub 7}Hf (7:1) crystal structure as interstitial atoms, forming Co{sub 7}HfB{sub x}, in the as-spun state. Yet B may diffuse out from the 7:1 phase after post-annealing, leading to the reduction of Curie temperature and the magnetic properties. The uniformly refined microstructure with B-doping results in high remanence (B{sub r}) and improves the squareness of demagnetization curve. The formation of interstitial-atom-modified Co{sub 7}HfB{sub x} phase and the microstructure refinement are the main reasons to give rise to the enhancement of hard magnetic properties in the B-containing Co{sub 7}Hf-based ribbons.« less

The Lord Howe Rise continental ribbon: a fragment of eastern Gondwana that reveals the drivers of continental rifting and plate tectonics

NASA Astrophysics Data System (ADS)

Saito, S.; Hackney, R. I.; Bryan, S. E.; Kimura, J. I.; Müller, D.; Arculus, R. J.; Mortimer, N. N.; Collot, J.; Tamura, Y.; Yamada, Y.

2016-12-01

Plate tectonics and resulting changes in crustal architecture profoundly influence global climate, oceanic circulation, and the origin, distribution and sustainability of life. Ribbons of continental crust rifted from continental margins are one product of plate tectonics that can influence the Earth system. Yet we have been unable to fully resolve the tectonic setting and evolution of huge, thinned, submerged, and relatively inaccessible continental ribbons like the Lord Howe Rise (LHR), which formed during Cretaceous fragmentation of eastern Gondwana. Thinned continental ribbons like the LHR are not easily explained or predicted by plate-tectonic theory. However, because Cretaceous rift basins on the LHR preserve the stratigraphy of an un-accreted and intact continental ribbon, they can help to determine whether plate motion is self-organised—passively driven by the pull of negatively-buoyant subducting slabs—or actively driven by convective flow in the mantle. In a self-organising scenario, the LHR formed in response to ocean-ward retreat of the long-lived eastern Gondwana subduction zone and linked upper-plate extension. In the mantle-driven scenario, the LHR resulted from rifting near the eastern edge of Gondwana that was triggered by processes linked to emplacement of a silicic Large Igneous Province. These scenarios can be distinguished using the ribbon's extensional history and the composition and tectonic affinity of igneous rocks within rift basins. However, current knowledge of LHR rift basins is based on widely-distributed marine and satellite geophysical data, limited dredge samples, and sparse shallow drilling (<600 m below-seafloor). This limits our ability to understand the evolution of extended continental ribbons, but a recent deep crustal seismic survey across the LHR and a proposed IODP deep stratigraphic well through a LHR rift basin provide new opportunities to explore the drivers behind rifting, continental ribboning and plate tectonics.

Tunable electronic properties of partially edge-hydrogenated armchair boron-nitrogen-carbon nanoribbons.

PubMed

Alaal, Naresh; Medhekar, Nikhil; Shukla, Alok

2018-04-18

We employ a first-principles calculations based density-functional-theory (DFT) approach to study the electronic properties of partially and fully edge-hydrogenated armchair boron-nitrogen-carbon (BNC) nanoribbons (ABNCNRs), with widths between 0.85 nm to 2.3 nm. Due to the partial passivation of edges, the electrons, which do not participate in the bonding, form new energy states located near the Fermi-level. Because of these additional bands, some ABNCNRs exhibit metallic behavior, which is quite uncommon in armchair nanoribbons. Our calculations reveal that metallic behavior is observed for the following passivation patterns: (i) when the B atom from one edge and the N atom from another edge are unpassivated. (ii) when the N atoms from both the edges are unpassivated. (iii) when the C atom from one edge and the N atom from another edge are unpassivated. Furthermore, spin-polarization is also observed for certain passivation schemes, which is also quite uncommon for armchair nanoribbons. Thus, our results suggest that the ABNCNRs exhibit a wide range of electronic and magnetic properties in that the fully edge-hydrogenated ABNCNRs are direct band gap semiconductors, while the partially edge-hydrogenated ones are either semiconducting, or metallic, while simultaneously exhibiting spin polarization, based on the nature of passivation. We also find that the ribbons with larger widths are more stable as compared to the narrower ones.

Surface ablation of aluminum and silicon by ultrashort laser pulses of variable width

NASA Astrophysics Data System (ADS)

Zayarny, D. A.; Ionin, A. A.; Kudryashov, S. I.; Makarov, S. V.; Kuchmizhak, A. A.; Vitrik, O. B.; Kulchin, Yu. N.

2016-06-01

Single-shot thresholds of surface ablation of aluminum and silicon via spallative ablation by infrared (IR) and visible ultrashort laser pulses of variable width τlas (0.2-12 ps) have been measured by optical microscopy. For increasing laser pulse width τlas < 3 ps, a drastic (threefold) drop of the ablation threshold of aluminum has been observed for visible pulses compared to an almost negligible threshold variation for IR pulses. In contrast, the ablation threshold in silicon increases threefold with increasing τlas for IR pulses, while the corresponding thresholds for visible pulses remained almost constant. In aluminum, such a width-dependent decrease in ablation thresholds has been related to strongly diminished temperature gradients for pulse widths exceeding the characteristic electron-phonon thermalization time. In silicon, the observed increase in ablation thresholds has been ascribed to two-photon IR excitation, while in the visible range linear absorption of the material results in almost constant thresholds.

Characterization of the spatial variability of channel morphology

USGS Publications Warehouse

Moody, J.A.; Troutman, B.M.

2002-01-01

The spatial variability of two fundamental morphological variables is investigated for rivers having a wide range of discharge (five orders of magnitude). The variables, water-surface width and average depth, were measured at 58 to 888 equally spaced cross-sections in channel links (river reaches between major tributaries). These measurements provide data to characterize the two-dimensional structure of a channel link which is the fundamental unit of a channel network. The morphological variables have nearly log-normal probability distributions. A general relation was determined which relates the means of the log-transformed variables to the logarithm of discharge similar to previously published downstream hydraulic geometry relations. The spatial variability of the variables is described by two properties: (1) the coefficient of variation which was nearly constant (0.13-0.42) over a wide range of discharge; and (2) the integral length scale in the downstream direction which was approximately equal to one to two mean channel widths. The joint probability distribution of the morphological variables in the downstream direction was modelled as a first-order, bivariate autoregressive process. This model accounted for up to 76 per cent of the total variance. The two-dimensional morphological variables can be scaled such that the channel width-depth process is independent of discharge. The scaling properties will be valuable to modellers of both basin and channel dynamics. Published in 2002 John Wiley and Sons, Ltd.

Two Independent Contributions to Step Variability during Over-Ground Human Walking

PubMed Central

Collins, Steven H.; Kuo, Arthur D.

2013-01-01

Human walking exhibits small variations in both step length and step width, some of which may be related to active balance control. Lateral balance is thought to require integrative sensorimotor control through adjustment of step width rather than length, contributing to greater variability in step width. Here we propose that step length variations are largely explained by the typical human preference for step length to increase with walking speed, which itself normally exhibits some slow and spontaneous fluctuation. In contrast, step width variations should have little relation to speed if they are produced more for lateral balance. As a test, we examined hundreds of overground walking steps by healthy young adults (N = 14, age < 40 yrs.). We found that slow fluctuations in self-selected walking speed (2.3% coefficient of variation) could explain most of the variance in step length (59%, P < 0.01). The residual variability not explained by speed was small (1.5% coefficient of variation), suggesting that step length is actually quite precise if not for the slow speed fluctuations. Step width varied over faster time scales and was independent of speed fluctuations, with variance 4.3 times greater than that for step length (P < 0.01) after accounting for the speed effect. That difference was further magnified by walking with eyes closed, which appears detrimental to control of lateral balance. Humans appear to modulate fore-aft foot placement in precise accordance with slow fluctuations in walking speed, whereas the variability of lateral foot placement appears more closely related to balance. Step variability is separable in both direction and time scale into balance- and speed-related components. The separation of factors not related to balance may reveal which aspects of walking are most critical for the nervous system to control. PMID:24015308

A Versatile Applet to Explore the Wave Behaviour of Particles

ERIC Educational Resources Information Center

Fernandez Palop, J. I.

2009-01-01

A pedagogical tool that consists of a Java applet has been developed so that undergraduate students in physics can explore the wave behaviour of particles. The applet executes a simulation in which a two-dimensional wave packet moves towards a slit and an obstacle with variable widths. By changing three parameters, slit width, obstacle width and…

Robotic Telesurgery Research

DTIC Science & Technology

2009-03-01

closed (right) positions. The upper jaw is constructed out of a super-elastic shape- memory nickel titanium alloy ( Nitinol ) ribbon (Memry Corporation...tissue. The Nitinol ribbon is glued to a fixed nylon rod insert that fits inside the bottom jaw. The nylon rod is also glued to the bottom jaw, and...configurations (bottom). The two collar pieces are connected to one another by two 0.12 mm thick Nitinol ribbons that are anchored to the collar walls. A

Effect of short wavelength illumination on the characteristic bulk diffusion length in ribbon silicon solar cells

NASA Technical Reports Server (NTRS)

Ho, C. T.; Mathias, J. D.

1981-01-01

The influence of short wavelength light on the characteristic bulk minority carrier diffusion length of the ribbon silicon photovoltaic cell has been investigated. We have measured the intensity and wavelength dependence of the diffusion length in an EFG ribbon cell, and compared it with a standard Czochralski grown silicon cell. While the various short wavelength illuminations have shown no influence on the diffusion length in the CZ cell, the diffusion lengths in the ribbon cell exhibit a strong dependence on the volume generation rate as well as on the wavelength of the superimposed lights. We have concluded that the trap-filling phenomenon at various depths in the bulk neutral region of the cell is consistent with the experimental observation.

Bending effects on magnetic properties of nearly zeromagnetostrictive Co-rich amorphous ribbons

NASA Astrophysics Data System (ADS)

Buttino, G.; Cecchetti, A.; Poppi, M.; Zini, G.

1991-06-01

In as received nearly zeromagnetostriction Co-based Metglas, magnetic properties in low magnetic field are anomalously affected by bending stresses. The behavior of Co-based alloys, in particular 2714A Metglas, is here compared with that of Fe-rich Metglas for which λ s ranges between 10 × 10 -6 and 35 × 10 -6. The specimens here analyzed are in the form of flat ribbons and tape-wound toroids with different radii. In 2714A Metglas, the bending effects on the ac initial permeability are unexpectedly large and depend on the way of winding the ribbons. These results emphasize a significant and different role of the two ribbon sides in determining the magnetomechanical properties of Co-based alloys.

Deformation of fluctuating chiral ribbons

NASA Astrophysics Data System (ADS)

Panyukov, Sergey

2003-03-01

We find analytical solution of the model of a fluctuating filament with a spontaneously twisted noncircular cross section in the presence of external force and torque. We show that when such ribbon is subjected to a sufficiently strong extensional force, it exhibits an asymmetric response to large degrees of overwinding and unwinding. We construct the stability diagram that describes the buckling transition of such ribbons under the opposing action of force and torque and show that all the observed behaviors can be understood in terms of continuous transformations between straight and spiral states of the ribbon. The relation between our results and experimental observations on DNA is discussed and a new reentrant spiral to rod transition is predicted at intermediate values of twist rigidity and applied force.

A prototype scintillating fibre beam profile monitor for Ion Therapy beams

NASA Astrophysics Data System (ADS)

Leverington, B. D.; Dziewiecki, M.; Renner, L.; Runze, R.

2018-05-01

A prototype plastic scintillating fibre based beam profile monitor was tested at the Heidelberg Ion Therapy Centre/Heidelberg Ionenstrahl Therapiezentrum (HIT) in 2016 to determine its beam property reconstruction performance and the feasibility of further developing an expanded system. At HIT protons, helium, carbon, and oxygen ions are available for therapy and experiments. The beam can be scanned in two dimensions using fast deflection magnets. A tracking system is used to monitor beam position and to adjust scanning magnet currents online. A new detector system with a finer granularity and without the drift time delay of the current MWPC system with a similar amount of material along the beamline would prove valuable in patient treatment. The sensitive detector components in the tested prototype detector are double-clad Kuraray SCSF-78MJ scintillating fibres with a diameter of 0.250 mm wound as a thin multi-layer ribbon. The scintillation light is detected at the end of the ribbon with Hamamatsu S11865-64 photodiode arrays with a pitch of 0.8 mm. Commercial or readily available readout electronics have been used to evaluate the system feasibility. The results shown in this paper include the linearity with respect to beam intensity, the RMS of the beam intensity as measured by two planes, along with the RMS of the mean position, and the measured beam width RMS. The Signal-to-Noise ratio of the current system is also measured as an indicator of potential performance. Additionally, the non-linear light yield of the scintillating fibres as measured by the photodiode arrays is compared to two models which describe the light yield as a function of the ion stopping power and Lorentz β.

One-step internal-tin Nb/sub 3/Sn superconductor fabrication. Final report, June 1983-August 1984

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

Marancik, W.

1985-03-01

The object of this research is to demonstrate the feasibility of producing a Nb/sub 3/Sn superconductor in a single extrusion process with a large number of filaments with internal tin. The technique chosen uses .010'-diameter Nb and tin-plated Cu wires formed into a solenoid. The solenoid is covered with tin-plated copper foil and isostatically compacted to a pressure of 17,000 psi. The solenoid is slit along its length. This results in a ribbon about 40 inches long by about 5-inches wide, with the Nb wires running across the 5-inch-width. The ribbon is then rolled up (Jelly Roll) around a 0.5more » inch diameter Ta covered copper rod to produce a composite of about 1.5 inches in diameter by 5 inches long. The composite geometry is now a cylindrical bundle of 0.010-inch-diameter Nb wire separated from each other by tin-plated copper. Each Nb wire is aligned with the axis of cylinder. The cylinder is slid into a Ta-lined copper extrusion can which is evacuated and sealed. The can is extruded at a low temperature and drawn to final wire size without intermediate annealing. The advantage of the process is that it is an internal tin process with the tin uniformly distributed through the matrix. The Nb is in a relatively soft state having been fully annealed at 0.020-inch diameter. Only one extrusion is required since the bundling technique allows a large number of wires to be precisely aligned and spaced in the matrix.« less

Calmodulin enhances ribbon replenishment and shapes filtering of synaptic transmission by cone photoreceptors

PubMed Central

Parmelee, Caitlyn M.; Chen, Minghui; Cork, Karlene M.; Curto, Carina; Thoreson, Wallace B.

2014-01-01

At the first synapse in the vertebrate visual pathway, light-evoked changes in photoreceptor membrane potential alter the rate of glutamate release onto second-order retinal neurons. This process depends on the synaptic ribbon, a specialized structure found at various sensory synapses, to provide a supply of primed vesicles for release. Calcium (Ca2+) accelerates the replenishment of vesicles at cone ribbon synapses, but the mechanisms underlying this acceleration and its functional implications for vision are unknown. We studied vesicle replenishment using paired whole-cell recordings of cones and postsynaptic neurons in tiger salamander retinas and found that it involves two kinetic mechanisms, the faster of which was diminished by calmodulin (CaM) inhibitors. We developed an analytical model that can be applied to both conventional and ribbon synapses and showed that vesicle resupply is limited by a simple time constant, τ = 1/(Dρδs), where D is the vesicle diffusion coefficient, δ is the vesicle diameter, ρ is the vesicle density, and s is the probability of vesicle attachment. The combination of electrophysiological measurements, modeling, and total internal reflection fluorescence microscopy of single synaptic vesicles suggested that CaM speeds replenishment by enhancing vesicle attachment to the ribbon. Using electroretinogram and whole-cell recordings of light responses, we found that enhanced replenishment improves the ability of cone synapses to signal darkness after brief flashes of light and enhances the amplitude of responses to higher-frequency stimuli. By accelerating the resupply of vesicles to the ribbon, CaM extends the temporal range of synaptic transmission, allowing cones to transmit higher-frequency visual information to downstream neurons. Thus, the ability of the visual system to encode time-varying stimuli is shaped by the dynamics of vesicle replenishment at photoreceptor synaptic ribbons. PMID:25311636

Low-loss terahertz ribbon waveguides.

PubMed

Yeh, Cavour; Shimabukuro, Fred; Siegel, Peter H

2005-10-01

The submillimeter wave or terahertz (THz) band (1 mm-100 microm) is one of the last unexplored frontiers in the electromagnetic spectrum. A major stumbling block hampering instrument deployment in this frequency regime is the lack of a low-loss guiding structure equivalent to the optical fiber that is so prevalent at the visible wavelengths. The presence of strong inherent vibrational absorption bands in solids and the high skin-depth losses of conductors make the traditional microstripline circuits, conventional dielectric lines, or metallic waveguides, which are common at microwave frequencies, much too lossy to be used in the THz bands. Even the modern surface plasmon polariton waveguides are much too lossy for long-distance transmission in the THz bands. We describe a concept for overcoming this drawback and describe a new family of ultra-low-loss ribbon-based guide structures and matching components for propagating single-mode THz signals. For straight runs this ribbon-based waveguide can provide an attenuation constant that is more than 100 times less than that of a conventional dielectric or metallic waveguide. Problems dealing with efficient coupling of power into and out of the ribbon guide, achieving low-loss bends and branches, and forming THz circuit elements are discussed in detail. One notes that active circuit elements can be integrated directly onto the ribbon structure (when it is made with semiconductor material) and that the absence of metallic structures in the ribbon guide provides the possibility of high-power carrying capability. It thus appears that this ribbon-based dielectric waveguide and associated components can be used as fundamental building blocks for a new generation of ultra-high-speed electronic integrated circuits or THz interconnects.

Antiguided fiber ribbon laser

DOEpatents

Wilcox, Russel B [El Cerrito, CA; Page, Ralph H [Castro Valley, CA; Beach, Raymond J [Livermore, CA; Feit, Michael D [Livermore, CA; Payne, Stephen A [Castro Valley, CA

2003-05-27

The invention is a ribbon of an optical material with a plurality of cores that run along its length. The plurality of cores includes lasing impurity doped cores in an alternating spaced arrangement with index-modifying impurity doped cores. The ribbon comprises an index of refraction that is substantially equal to or greater than the indices of refraction of said array of lasing impurity doped cores. Index-increasing impurity doped cores promote antiguiding and leaky modes which provide more robust single "supermode" operation.

Evaluation of ULV Applications Against Old World Sand Fly (Diptera: Psychodidae) Species in Equatorial Kenya

DTIC Science & Technology

2011-01-01

patterns of UV-labeled droplets captured on cotton ribbons adjacent to sand ßy cages in spray plots did not match patterns ofmortality.Wediscuss the...untreated areas. Surprisingly, ULV active ingredient deposition inferred from patterns of UV-labeled droplets captured on cotton ribbons adjacent to...the west plot on the second spray day; looking south. Cotton droplet capture ribbons have already been attached in position between the posts at each

Shape Memory Characteristics of Rapidly Solidified Ti-37.8Cu-18.7Ni Alloy Ribbons

NASA Astrophysics Data System (ADS)

Ramos, Alana Pereira; de Castro, Walman Benicio

Amorphization and martensitic transformation (Ms) characteristics of Ti-Ni-Cu alloy ribbons prepared by melt spinning were investigated by means of differential scanning calorimetry and X-ray diffraction. In these experiments particular attention has been paid to change the wheel linear velocity from 21 to 63 m/s. Then the cooling rates of ribbons were controlled. The effect of this cooling rate and alloy composition on martensitic transformation behavior is discussed.

RIBEYE(B)-domain binds to lipid components of synaptic vesicles in an NAD(H)-dependent, redox-sensitive manner.

PubMed

Schwarz, Karin; Schmitz, Frank

2017-03-20

Synaptic ribbons are needed for fast and continuous exocytosis in ribbon synapses. RIBEYE is a main protein component of synaptic ribbons and is necessary to build the synaptic ribbon. RIBEYE consists of a unique A-domain and a carboxyterminal B-domain, which binds NAD(H). Within the presynaptic terminal, the synaptic ribbons are in physical contact with large numbers of synaptic vesicle (SV)s. How this physical contact between ribbons and synaptic vesicles is established at a molecular level is not well understood. In the present study, we demonstrate that the RIBEYE(B)-domain can directly interact with lipid components of SVs using two different sedimentation assays with liposomes of defined chemical composition. Similar binding results were obtained with a SV-containing membrane fraction. The binding of liposomes to RIBEYE(B) depends upon the presence of a small amount of lysophospholipids present in the liposomes. Interestingly, binding of liposomes to RIBEYE(B) depends on NAD(H) in a redox-sensitive manner. The binding is enhanced by NADH, the reduced form, and is inhibited by NAD + , the oxidized form. Lipid-mediated attachment of vesicles is probably part of a multi-step process that also involves additional, protein-dependent processes. © 2017 The Author(s); published by Portland Press Limited on behalf of the Biochemical Society.

Ribbons of semithin sections: an advanced method with a new type of diamond knife.

PubMed

Blumer, Michael J F; Gahleitner, P; Narzt, T; Handl, C; Ruthensteiner, B

2002-10-15

Complete series of semithin sections are imperative for 3-D reconstruction, but with traditional microtomy techniques it is difficult and time-consuming to trace stained and labeled structures. In the present study we introduce a method for making and collecting ribbons of semithin sections with a new, commercial available diamond knife (histo-jumbo-diamond knife, Diatome AG, Biel, Switzerland). The special feature of the diamond knife is the large water bath (boat) into which a glass slide can be dipped. The method has distinct advantages and the handling is simple. The resin block is trimmed into a truncated pyramid. Contact glue is applied to the leading face of the pyramid, which makes sections stick together to form a ribbon. Following sectioning, the ribbons are mounted onto glass slides and aligned in parallel. Stretching out and drying the ribbons on a hot plate is the final step of the method. Major advantages of this method are the perfect alignment of sections with identical orientation of structures, the completeness of series, and the significant saving of time. This facilitates tracing of stained and labeled structures, yielding quick 3-D reconstruction. Semithin sections can be cut from 0.5 to 2 micro m and several ribbons can be mounted side by side onto the slide. Two examples are presented to illustrate the advantages of the method.

Structure and magnetic properties of Alnico ribbons

NASA Astrophysics Data System (ADS)

Zhang, Ce; Li, Ying; Han, Xu-Hao; Du, Shuai-long; Sun, Ji-bing; Zhang, Ying

2018-04-01

Al-Ni-Co alloy has been widely applied in various industrial fields due to its excellent thermal and magnetic stability. In this paper, new Al-Ni-Co ribbons are prepared by simple processes combining melt-spinning with annealing, and their phase transition, microstructure and magnetic properties are studied. The results show that after as-spun ribbons are annealed, the grain size of ribbons increases from 1.1 ± 0.3 μm to 4.8 ± 0.8 μm, but still much smaller than that of the bulk Al-Ni-Co alloy manufactured by traditional technologies. In addition, some rod-like Al70Co20Ni10-type, Al9Co2-type and Fe2Nb-type phases are precipitated at grain boundaries; simultaneously, the distinct spinodal decomposition microstructure with periodic ingredient variation is thoroughly formed in all grains by the reaction of α → α1 + α2. Furthermore, the α1 and α2 distribute alternately like a maze, the Fe-Co-rich α1 phase holds 35.9-47.3 vol%, while the Al-Ni-rich α2 phase occupies the rest. Finally, the coercivity of annealed ribbons can reach to 485.3 ± 76.6 Oe. If the annealed ribbons are further aged at 560 °C, their Hc even increases to 738.1 ± 81.0 Oe. The coercivity mechanism is discussed by the combination of microstructure and domain structure.

Adiabatic magnetocaloric effect in Ni50Mn35In15 ribbons

NASA Astrophysics Data System (ADS)

Álvarez-Alonso, P.; Aguilar-Ortiz, C. O.; Camarillo, J. P.; Salazar, D.; Flores-Zúñiga, H.; Chernenko, V. A.

2016-11-01

Heusler-type Ni-Mn-based metamagnetic shape memory alloys (MetaMSMAs) are promising candidates for magnetic refrigeration. To increase heat exchange rate and efficiency of cooling, the material should have a high surface/volume ratio. In this work, the typical Ni50Mn35In15 MetaMSMA was selected to fabricate thin ribbons by melt-spinning. The characteristic transformations of the ribbons were determined by calorimetry, X-ray diffraction, scanning electron microscopy and thermomagnetization measurements. The inverse and conventional magnetocaloric effects (MCEs) associated with the martensitic transformation (MT) and the ferromagnetic transition of the austenite (TCA), respectively, were measured directly by the adiabatic method (ΔTad) and indirectly by estimating the magnetic entropy change from magnetization measurements. It is found that the ribbons exhibit large values of ΔTad = -1.1 K at μ0ΔH = 1.9 T, in the vicinity of the MT temperature of 300 K for inverse MCE, and ΔTad = 2.3 K for conventional MCE at TCA = 309 K. This result strongly motivates further development of different MetaMSMA refrigerants shaped as ribbons.

Electromigration process for the purification of molten silicon during crystal growth

DOEpatents

Lovelace, Alan M. Administrator of the National Aeronautics and Space; Shlichta, Paul J.

1982-01-01

A process for the purification of molten materials during crystal growth by electromigration of impurities to localized dirty zones. The process has particular applications for silicon crystal growth according to Czochralski techniques and edge-defined film-fed growth (EFG) conditions. In the Czochralski crystal growing process, the impurities are electromigrated away from the crystallization interface by applying a direct electrical current to the molten silicon for electromigrating the charged impurities away from the crystal growth interface. In the EFG crystal growth process, a direct electrical current is applied between the two faces which are used in forming the molten silicon into a ribbon. The impurities are thereby migrated to one side only of the crystal ribbon. The impurities may be removed or left in place. If left in place, they will not adversely affect the ribbon when used in solar collectors. The migration of the impurity to one side only of the silicon ribbon is especially suitable for use with asymmetric dies which preferentially crystallize uncharged impurities along one side or face of the ribbon.

Low field magnetocaloric effect in bulk and ribbon alloy La(Fe0.88Si0.12)13

NASA Astrophysics Data System (ADS)

Vuong, Van-Hiep; Do-Thi, Kim-Anh; Nguyen, Duy-Thien; Nguyen, Quang-Hoa; Hoang, Nam-Nhat

2018-03-01

Low-field magnetocaloric effect occurred in itinerant metamagnetic materials is at core for magnetic cooling application. This works reports the magnetocaloric responses obtained at 1.35 T for the silicon-doped iron-based binary alloy La(Fe0.88Si0.12)13 in the bulk and ribbon form. Both samples possess a same symmetry but with different crystallite sizes and lattice parameters. The ribbon sample shows a larger maximum entropy change (nearly 8.5 times larger) and a higher Curie temperature (5 K higher) in comparison with that of the bulk sample. The obtained relative cooling power for the ribbon is also larger and very promising for application (RCP = 153 J/kg versus 25.2 J/kg for the bulk). The origin of the effect observed is assigned to the occurrence of negative magnetovolume effect in the ribbon structure with limit crystallization, caused by rapid cooling process at the preparation, which induced smaller crystallite size and large lattice constant at the overall weaker local crystal field.

Mass distribution and spatial organization of the linear bacterial motor of Spiroplasma citri R8A2.

PubMed

Trachtenberg, Shlomo; Andrews, S Brian; Leapman, Richard D

2003-03-01

In the simple, helical, wall-less bacterial genus Spiroplasma, chemotaxis and motility are effected by a linear, contractile motor arranged as a flat cytoskeletal ribbon attached to the inner side of the membrane along the shortest helical line. With scanning transmission electron microscopy and diffraction analysis, we determined the hierarchical and spatial organization of the cytoskeleton of Spiroplasma citri R8A2. The structural unit appears to be a fibril, approximately 5 nm wide, composed of dimers of a 59-kDa protein; each ribbon is assembled from seven fibril pairs. The functional unit of the intact ribbon is a pair of aligned fibrils, along which pairs of dimers form tetrameric ring-like repeats. On average, isolated and purified ribbons contain 14 fibrils or seven well-aligned fibril pairs, which are the same structures observed in the intact cell. Scanning transmission electron microscopy mass analysis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified cytoskeletons indicate that the 59-kDa protein is the only constituent of the ribbons.

Laser-zone growth in a Ribbon-To-Ribbon (RTR) process. Silicon sheet growth development for the large area silicon sheet task of the low cost silicon solar array project

NASA Technical Reports Server (NTRS)

Gurtler, R. W.; Baghdadi, A.; Legge, R.; Sopori, B.; Ellis, R. J.

1977-01-01

The Ribbon-to-Ribbon (RTR) approach to silicon ribbon growth is investigated. An existing RTR apparatus is to be upgraded to its full capabilities and operated routinely to investigate and optimize the effects of various growth parameters on growth results. A new RTR apparatus was constructed to incorporate increased capabilities and improvements over the first apparatus and to be capable of continuous growth. New high power lasers were implemented and this led to major improvements in growth velocity -- 4 inch/min. growth has been demonstrated. A major step in demonstration of the full feasibility of the RTR process is reported in the demonstration of RTR growth from CVD polyribbon rather than sliced polyribbon ingots. Average solar cell efficiencies of greater than 9% and a best cell efficiency of 11.7% are reported. Processing was shown to provide a substantial improvement in material minority carrier diffusion length. An economic analysis is reported which treats both the polyribbon fabrication and RTR processes.

Effect of Sm content on energy product of rapidly quenched and oriented SmCo5 ribbons

NASA Astrophysics Data System (ADS)

Zhang, Wenyong; Li, Xingzhong; Valloppilly, Shah

2015-03-01

The Sm-content dependence of phase composition, anisotropy, and other magnetic properties of Sm1+ δ Co5 ( δ ≤ 0.12) ribbons melt spun at 10 m/s has been studied. The samples consist of hexagonal SmCo5 grains whose c axes are preferentially aligned along the long direction of the ribbon. The lattice parameter a and the cell volume ( V) increase with increasing Sm content δ, whereas c decreases. Sm addition appears to improve the degree of the preferred orientation of the c-axis and to increase the mean grain size, which weakens the effective intergranular exchange coupling. Therefore, the remanence ratio, coercivity, and squareness of the hysteresis loops are significantly enhanced. The remanence ratio of 0.91 and the maximum energy product of 21.2 MGOe, which is the highest value reported so far for Sm-Co ribbons, are achieved for δ = 0.06. High performance in combination with simple processing may facilitate high-temperature applications for anisotropic Sm1+ δ Co5 ribbons.

Extrusion of metal oxide superconducting wire, tube or ribbon

DOEpatents

Dusek, Joseph T.

1993-10-05

A process for extruding a superconducting metal oxide composition YBa.sub.2 Cu.sub.3 O.sub.7-x provides a wire (tube or ribbon) having a cohesive mass and a degree of flexibility together with enhanced electrical properties. Wire diameters in the range of 6-85 mils have been produced with smaller wires on the order of 10 mils in diameter exhibiting enhanced flexibility for forming braided, or multistrand, configurations for greater current carrying capacity. The composition for extrusion contains a polymeric binder to provide a cohesive mass to bind the particles together during the extrusion process with the binder subsequently removed at lower temperatures during sintering. The composition for extrusion further includes a deflocculent, an organic plasticizer and a solvent which also are subsequently removed during sintering. Electrically conductive tubing with an inner diameter of 52 mil and an outer diameter of 87-355 mil has also been produced. Flat ribbons have been produced in the range of 10-125 mil thick by 100-500 mil wide. The superconducting wire, tube or ribbon may include an outer ceramic insulating sheath co-extruded with the wire, tubing or ribbon.

Extrusion of metal oxide superconducting wire, tube or ribbon

DOEpatents

Dusek, Joseph T.

1993-01-01

A process for extruding a superconducting metal oxide composition YBa.sub.2 Cu.sub.3 O.sub.7-x provides a wire (tube or ribbon) having a cohesive mass and a degree of flexibility together with enhanced electrical properties. Wire diameters in the range of 6-85 mils have been produced with smaller wires on the order of 10 mils in diameter exhibiting enhanced flexibility for forming braided, or multistrand, configurations for greater current carrying capacity. The composition for extrusion contains a polymeric binder to provide a cohesive mass to bind the particles together during the extrusion process with the binder subsequently removed at lower temperatures during sintering. The composition for extrusion further includes a deflocculent, an organic plasticizer and a solvent which also are subsequently removed during sintering. Electrically conductive tubing with an inner diameter of 52 mil and an outer diameter of 87-355 mil has also been produced. Flat ribbons have been produced in the range of 10-125 mil thick by 100-500 mil wide. The superconducting wire, tube or ribbon may include an outer ceramic insulating sheath co-extruded with the wire, tubing or ribbon.

Interannual Variability of Fisheries Economic Returns and Energy Ratios Is Mostly Explained by Gear Type

PubMed Central

Trenkel, Verena M.; Daurès, Fabienne; Rochet, Marie-Joëlle; Lorance, Pascal

2013-01-01

According to portfolio theory applied to fisheries management, economic returns are stabilised by harvesting in a portfolio stocks of species whose returns are negatively correlated and for which the portfolio economic return variance is smaller than the sum of stock specific return variances. Also, variability is expected to decrease with portfolio width. Using a range of indicators, these predictions were tested for the French fishing fleets in the Bay of Biscay (Northeast Atlantic) during the period 2001–2009. For this, vessels were grouped into eight fishing fleets based on the gears used and exploited species were grouped into five functional groups. The portfolio width of fleets ranged from 1–3 functional groups, or 4–19 species. Economic fleet returns (sale revenues minus fishing costs) varied strongly between years; the interannual variability was independent of portfolio width (species or functional groups). Energy ratio expressed by the ratio between fuel energy used for fishing and energy contained in landings varied from 0.3 for purse seines to 9.7 for trawlers using bottom trawls alone or in combination with pelagic trawls independent of portfolio width. Interannual variability in total sale revenues was larger than the sum of species specific sales revenue variability, except for fleets using hooks and pelagic trawlers; it increased with the number of species exploited. In conclusion, the interannual variability of economic returns or energy ratios of French fisheries in the Bay of Biscay did not decrease with the number of species or functional groups exploited, though it varied between fleets. PMID:23922951

Effects of Zr on microstructure and mechanical properties of Al-Cu base ribbons spun by planar flow casting

NASA Astrophysics Data System (ADS)

Lee, S. M.; Hong, C. P.

1998-04-01

The effects of the Zr addition on the solidification behavior and mechanical properties of the AI-Cu alloy ribbon have been investigated. Zr addition reduced the average grain size of the ribbon at the wheel-side surface, and promoted the microstructural transition into cellular/dendritic structure. Another noteworthy effect of Zr was the homogenization of the microstructure. The addition of Zr up to 0.5 wt.% in the /U-4.3 wt.% Cu ribbon resulted in a considerable increase in hardness at both the wheel-side and the air-side surfaces. The yield strength increased with the addition of Zr due to the grain refincment and more homogeneous distribution of ZrAI, particles. despite no noticeable improvement of the ductility.

Shape selection of twist-nematic-elastomer ribbons

PubMed Central

Sawa, Yoshiki; Ye, Fangfu; Urayama, Kenji; Takigawa, Toshikazu; Gimenez-Pinto, Vianney; Selinger, Robin L. B.; Selinger, Jonathan V.

2011-01-01

How microscopic chirality is reflected in macroscopic scale to form various chiral shapes, such as straight helicoids and spiral ribbons, and how the degree of macroscopic chirality can be controlled are a focus of studies on the shape formation of many biomaterials and supramolecular systems. This article investigates both experimentally and theoretically how the chiral arrangement of liquid crystal mesogens in twist-nematic-elastomer films induces the formation of helicoids and spiral ribbons because of the coupling between the liquid crystalline order and the elasticity. It is also shown that the pitch of the formed ribbons can be tuned by temperature variation. The results of this study will facilitate the understanding of physics for the shape formation of chiral materials and the designing of new structures on basis of microscopic chirality. PMID:21464276

A new analysis of the unwinding ribbon as a delayed arming device

NASA Astrophysics Data System (ADS)

Dunn, W. P.

1982-06-01

The objective of this work was to formulate theoretical methods to enable engineers to design unwinding ribbons for use as delay arming mechanisms with reasonable accuracy and a minimum development effort. The unwinding ribbon considered here is a "wrapped' spring, which is a spiral spring made from flat metal stock closely wound. In the unstressed condition all the coils of the spring are touching. The results of the analysis are given and compared with the experimental results obtained by T. B. Alfriend. This is a more complete study than that of Alfriend since no assumptions are made concerning the moment of inertia of the coil and hub or the tension force in the ribbon bridge. Hence, two empirical constants in Alfriend's analysis were dropped in favor of exact expressions.

On the deformation of fluctuating chiral ribbons

NASA Astrophysics Data System (ADS)

Panyukov, S.; Rabin, Y.

2002-02-01

A theoretical analysis of the effect of force and torque on fluctuating chiral ribbons is presented. We find that when a filament with a straight centerline and a spontaneously twisted noncircular cross-section is subjected to a sufficiently strong extensional force, it exhibits an asymmetric response to large degrees of overwinding and unwinding. We construct the stability diagram that describes the buckling transition of such ribbons under the opposing action of force and torque and show that all the observed behaviors can be understood in terms of continuous transformations between straight and spiral states of the ribbon. The relation between our results and experimental observations on DNA is discussed and a new re-entrant spiral-to-rod transition is predicted at intermediate values of twist rigidity and applied force.

HRTEM and neutron diffraction study of Li{sub x}Mo{sub 5}O{sub 17}: From the ribbon (x=5) structure to the rock salt (x=12) structure

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

Lebedev, O.I.; Caignaert, V.; Raveau, B.

2011-04-15

Structure determination of the fully intercalated phase Li{sub 12}Mo{sub 5}O{sub 17} and of the deintercalated oxide Li{sub 5}Mo{sub 5}O{sub 17} has been carried out by electron microscopy and neutron powder diffraction. The reversible topotactic transformation between the ordered rock salt structure of the former and the ribbon structure of the latter (closely related to that of Li{sub 4}Mo{sub 5}O{sub 17}) is explained on the following basis: both structures can be described as strips built up as an assembly of infinite ribbons of MoO{sub 6} octahedra that are five octahedra thick, and that differ by slight displacements of the octahedral ribbons.more » We show that the electrochemical behavior of the Li{sub x}Mo{sub 5}O{sub 17} system is based on two sorts of Li{sup +} sites; those that are located within the strips between the ribbons, and those that are located at the border of the strips. The high rate of Li intercalation in this oxide and its reversibility are discussed in terms of its peculiar structure. -- Graphical abstract: Structure determination of the fully intercalated phase Li{sub 12}Mo{sub 5}O{sub 17} and of the deintercalated oxide Li{sub 5}Mo{sub 5}O{sub 17} has been carried out by electron microscopy and neutron powder diffraction. The reversible topotactic transformation between the ordered rock salt structure of the former and the ribbon structure of the latter is explained on the following basis: both structures can be described as strips built up as an assembly of infinite ribbons of MoO{sub 6} octahedra that are five octahedra thick, and that differ by slight displacements of the octahedral ribbons. We show that the electrochemical behavior of the Li{sub x}Mo{sub 5}O{sub 17} system is based on two sorts of Li{sup +} sites; those that are located within the strips between the ribbons, and those that are located at the border of the strips. The high rate of Li intercalation in this oxide and its reversibility are discussed in terms of its peculiar structure. Research highlights: {yields} Electron microscopy and neutron powder diffraction structure determination {yields} We have explained the reversible topotactic transformation between an ordered rock salt structure and a ribbon structure {yields} We show that the electrochemical behavior of the Li{sub x}Mo{sub 5}O{sub 17} system is based on two sorts of Li{sup +} sites {yields} The high rate of Li intercalation in this oxide and its reversibility are discussed in terms of its peculiar structure.« less

Magnetoimpedance studies on urine treated Co66Ni7Si7B20 ribbons

NASA Astrophysics Data System (ADS)

Kotagiri, Ganesh; Markandeyulu, G.; Doble, Mukesh; Nandakumar, V.

2015-11-01

Magnetoimpedance (MI) response of Co66Ni7Si7B20 ribbons treated with artificial urine with protein bovine serum albumin (BSA), artificial urine without protein BSA and healthy male urine was studied as a function of time of incubation. The maximum MI [(MI)m] values of the ribbons treated with artificial urine without protein (RTAU) after 3 h, 6 h, 12 h and 24 h of incubation are 30% (at 4 MHz), 15% (at 5 MHz), 14% (at 10 MHz) and 8% (at 13 MHz) respectively. On the other hand, the respective (MI)m values of the ribbons treated with artificial urine with protein (RTAUP) are 33% (at 4 MHz), 25% (at 5 MHz), 20% (at 8 MHz) and 15% (12 MHz). However (MI)m values of the ribbons treated with healthy male urine (RTHMU) after 4 h, 5 h, 10 h and 15 h of incubation are 71% (at 3 MHz), 57% (at 3 MHz), 25% (at 6 MHz) and 25% (at 5 MHz), respectively. The saturation magnetization (Ms) values of RTAU after 3 h, 6 h, 12 h and 24 h of incubation are 71 emu/g, 65 emu/g, 63 emu/g and 60 emu/g respectively whereas, the respective Ms values of RTAUP are 73 emu/g, 69 emu/g, 67 emu/g and 64 emu/g. The Ms values of RTHMU after 4 h, 5 h, 10 h and 15 h of incubation are 96 emu/g, 90 emu/g, 75 emu/g and 75 emu/g respectively. The decrease in Ms and (MI)m values in RTAU and RTAUP compared to as-quenched ribbon is related to the amounts of various elements etched out from the ribbons and increased surface roughness. The Ms and (MI)m values of RTHMU are seen to have increased after 4 h and 5 h of incubation, due to strain relaxation through removal of strain developed during rapid quenching of the ribbons. On the other hand, the Ms and (MI)m values of RTHMU after 10 h and 15 h have decreased due to deterioration of the surface of the ribbons and thus, increase in magnetic (surface) anisotropy. The decrease in (MI)m and MS of RTAU with the time of incubation are more rapid compared to that of RTAUP, probably due to the larger surface anisotropy due to rapid deterioration of the surface of the RTAU than in RTAUP. Asymmetry in MI profiles of RTAU, RTAUP and RTHMU was observed and is attributed to the non-uniform etching of the surface of the ribbons leading to pinning of the domain wall motion.

Blue Ribbon Panel Report-BRP-Cancer Moonshot

Cancer.gov

The Blue Ribbon Panel Report outlines 10 recommendations to accelerate progress against cancer. The panel was established to ensure that the Cancer Moonshot's approaches are grounded in the best science.

Center Director Bridges addresses guests at ribbon cutting for the new Checkout & Launch Control

NASA Technical Reports Server (NTRS)

2000-01-01

KSC Director Roy Bridges addresses attendees at a ribbon cutting for the new Checkout and Launch Control System (CLCS) at the Hypergolic Maintenance Facility (HMF). The CLCS was declared operational in a ribbon cutting ceremony earlier. The new control room will be used to process the Orbital Maneuvering System pods and Forward Reaction Control System modules at the HMF. This hardware is removed from Space Shuttle orbiters and routinely taken to the HMF for checkout and servicing.

NASA Associate Administrator for Space Flight Rothenberg addresses guests at ribbon cutting for the

NASA Technical Reports Server (NTRS)

2000-01-01

NASA Associate Administrator for Space Flight Joseph Rothenberg addresses attendees at a ribbon cutting for the new Checkout and Launch Control System (CLCS) at the Hypergolic Maintenance Facility (HMF). The CLCS was declared operational in a ribbon cutting ceremony earlier. The new control room will be used to process the Orbital Maneuvering System pods and Forward Reaction Control System modules at the HMF. This hardware is removed from Space Shuttle orbiters and routinely taken to the HMF for checkout and servicing.

Stennis cuts ribbon on records retention facility

NASA Image and Video Library

2010-08-24

NASA's John C. Stennis Space Center cut the ribbon Aug. 24 on a new, storm-resistant Records Retention Facility that consolidates and protects records storage at the nation's premier rocket engine test facility. This facility will also house history office operations. Participants in the ribbon-cutting included: (l to r) Gay Irby, Center Operations deputy director at Stennis; Linda Cureton, NASA chief information officer; Patrick Scheuermann, Stennis director; Jane Odom, NASA chief archivist; Dinna Cottrell, Stennis chief information officer; and James Cluff, Stennis records manager.

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

Benedek, George; Casparay, Alfred H.

In this project, we are developing a new system for measuring forces within and between nanoscale biological molecules based on mesoscopic springs made of cholesterol helical ribbons. These ribbons self-assemble in a wide variety of complex fluids containing sterol, a mixture of surfactants and water [1] and have spring constants in the range from 0.5 to 500 pN/nm [2-4]. By the end of this project, we have demonstrated that the cholesterol helical ribbons can be used for measuring forces between biological objects and for mapping the strain fields in hydrogels.

Woven ribbon cable for cryogenic instruments

NASA Astrophysics Data System (ADS)

Cunningham, C. R.; Hastings, P. R.; Strachan, J. M. D.

Robust woven ribbon cables are described for connecting sensors at low temperatures to higher temperature systems. Woven cables have several advantages over conventional wiring or flat ribbon cables in cryostats: heat sinking is easier; twisted pairs may be used; and miniature multi-way connectors are easily incorporated. Their use is demonstrated in making connections from 131 bolometers in two arrays mounted in a dilution refrigerator at 100 mK. Thermal and electrical properties are discussed, as are other possible applications in cryogenic instruments.

Silicon web process development

NASA Technical Reports Server (NTRS)

Duncan, C. S.; Seidensticker, R. G.; Mchugh, J. P.; Skutch, M. E.; Driggers, J. M.; Hopkins, R. H.

1981-01-01

The silicon web process takes advantage of natural crystallographic stabilizing forces to grow long, thin single crystal ribbons directly from liquid silicon. The ribbon, or web, is formed by the solidification of a liquid film supported by surface tension between two silicon filaments, called dendrites, which border the edges of the growing strip. The ribbon can be propagated indefinitely by replenishing the liquid silicon as it is transformed to crystal. The dendritic web process has several advantages for achieving low cost, high efficiency solar cells. These advantages are discussed.

Optimization of permanent magnetic properties in melt spun Co{sub 82−x}Hf{sub 12+x}B{sub 6} (x = 0–4) nanocomposites

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

Chang, H. W.; Liao, M. C.; Shih, C. W.

2015-05-07

Magnetic properties of melt spun Co{sub 82−x}Hf{sub 12+x}B{sub 6} ribbons made with various wheel speeds have been studied. The ribbons with x = 0–1 are not easy to crystallize and thus display soft magnetic behavior even at wheel speed of 10 m/s. In contrast, the ribbons with x = 1.5–4 at optimized wheel speed exhibit good permanent magnetic properties of B{sub r} = 0.41–0.59 T, {sub i}H{sub c} = 120–400 kA/m, and (BH){sub max} = 10.6–48.1 kJ/m{sup 3}. The optimal magnetic properties of B{sub r} = 0.59 T, {sub i}H{sub c} = 384 kA/m, and (BH){sub max} = 48.1 kJ/m{sup 3} are achieved for Co{sub 80}Hf{sub 14}B{sub 6} ribbons at wheel speed of 30 m/s. X-ray diffraction, thermo-magnetic analysis, and transmission electron microscopy resultsmore » show that good hard magnetic properties of Co{sub 82−x}Hf{sub 12+x}B{sub 6} ribbons (x = 2–4) are originated from the Co{sub 11}Hf{sub 2} phase well coupled with the Co phase. The change of magnetic properties for Co{sub 82−x}Hf{sub 12+x}B{sub 6} ribbons spun at various wheel speeds is correlated to microstructure and phase constitution. The strong exchange-coupling effect between magnetic grains for the ribbons with x = 2–3 at wheel speed = 30 m/s leads to remarkable permanent magnetic properties. The presented results suggest that the optimized Co{sub 82−x}Hf{sub 12+x}B{sub 6} (x = 2–3) ribbons are much suitable than others (x = 0–1.5 and 4) for making rare earth and Pt-free magnets.« less

The Relationship between Dental Follicle Width and Maxillary Impacted Canines' Descriptive and Resorptive Features Using Cone-Beam Computed Tomography.

PubMed

Dağsuyu, İlhan Metin; Okşayan, Rıdvan; Kahraman, Fatih; Aydın, Mehmet; Bayrakdar, İbrahim Şevki; Uğurlu, Mehmet

2017-01-01

To assess the relationship between dental follicle width and maxillary impacted canines' descriptive and resorptive features with three-dimensional (3D) cone-beam computed tomography (CBCT). The study comprised 102 patients with cone-beam computed tomography 3D images and a total of 140 impacted canines. The association between maxillary impacted canine dental follicle width and the variables of gender, impaction side (right and left), localization of impacted canine (buccal, central, and palatal), and resorption of the adjacent laterals was compared. Measurements were analyzed with Student's t -test, Kruskal-Wallis test, and Mann-Whitney U statistical test. According to gender, no statistically significant differences were found in the follicle size of the maxillary impacted canine between males and females ( p > 0.05). Widths of the follicles were determined for the right and left impaction sides, and no statistically significant relation was found ( p > 0.05). There were statistically significant differences between root resorption degrees of lateral incisors and maxillary impacted canine follicle width ( p < 0.05). Statistically significant higher follicle width values were present in degree 2 (mild) resorption than in degree 1 (no) and degree 3 (moderate) resorption samples ( p < 0.05). No significant correlation was found between follicle width and the variables of gender, impaction side, and localization of maxillary impacted canines. Our study could not confirm that increased dental follicle width of the maxillary impacted canines exhibited more resorption risk for the adjacent lateral incisors.

INFINITY ribbon-cutting

NASA Image and Video Library

2012-04-11

Stennis Space Center welcomes participants during ribbon-cutting activities for the INFINITY at NASA Stennis Space Center facility April 11, 2012. The visitor center and museum is located on Interstate 10, Exit 2, in south Mississippi.

Self-deploying boom

NASA Technical Reports Server (NTRS)

Tumulty, W. T.; Sours, W. P.

1972-01-01

Development and operation of metal ribbon which acts like self deploying boom are described. Metal ribbon is retained on two rollers for storage and extends into nonretractable tubular structure upon release. Illustration of equipment is provided.

Blue Ribbon Panel Report

Cancer.gov

An NCI Cancer Currents blog by the NCI acting director thanking the cancer community for contributing to the Cancer Moonshot Blue Ribbon Panel report, which was presented to the National Cancer Advisory Board on September 7.

Large Area Silicon Sheet by EFG

NASA Technical Reports Server (NTRS)

Wald, F. V.

1979-01-01

Progress made in the development of EFG ribbon growth is discussed. Specific areas covered include: (1) demonstration of multiple growth for ribbons 5 cm wide in runs of 12 and 20 hours duration; (2) a single cartridge crystal growth station was built expanding observational capacity by virtue of an anamorphic optical-video system which allows close observation of the meniscus over 7.5 cm wide, as well as video taping of the ribbon growth process; (3) growth station no.1 achieved reproducible and reliable growth of 7.5 cm wide ribbon at speeds up to 4 cm/min; (4) introduction of the 'mini cold shoe'; (5) increases in cell efficiency due to interface shaping using the 'displaced die' concept; and (6) clarification of the role of gaseous impurities in cartridge furnaces and stabilization of their destabilizing influence on growth.

From Cylindrical to Stretching Ridges and Wrinkles in Twisted Ribbons

NASA Astrophysics Data System (ADS)

Pham Dinh, Huy; Démery, Vincent; Davidovitch, Benny; Brau, Fabian; Damman, Pascal

2016-09-01

Twisted ribbons under tension exhibit a remarkably rich morphology, from smooth and wrinkled helicoids, to cylindrical or faceted patterns. This complexity emanates from the instability of the natural, helicoidal symmetry of the system, which generates both longitudinal and transverse stresses, thereby leading to buckling of the ribbon. Here, we focus on the tessellation patterns made of triangular facets. Our experimental observations are described within an "asymptotic isometry" approach that brings together geometry and elasticity. The geometry consists of parametrized families of surfaces, isometric to the undeformed ribbon in the singular limit of vanishing thickness and tensile load. The energy, whose minimization selects the favored structure among those families, is governed by the tensile work and bending cost of the pattern. This framework describes the coexistence lines in a morphological phase diagram, and determines the domain of existence of faceted structures.

EBIC/TEM investigations of defects in solar silicon ribbon materials

NASA Technical Reports Server (NTRS)

Ast, D. G.

1981-01-01

Transmission electron microscopy was used to investigate the defect structure of edge defined film growth (EFG) material, web dentritic ribbons (WEB), and ribbon to ribbon recrystallized material (RTR). The most common defects in all these materials are coherent first order twin boundaries. These coherent twins can be very thin, a few atomic layers. Bundles of the twins which contain odd numbers of twins will in optical images appear as a seemingly single first twin boundary. First-order coherent twin boundaries are not electrically active, except at locations where they contain intrinsic (grain boundary) dislocations. These dislocations take up small deviations from the ideal twin relation and play the same role in twin boundaries as conventional and play the some role in twin boundaries as conventional edge and screw dislocations in small angle tilt and twist boundaries.

Large area silicon sheet by EFG. [furnace growth techniques

NASA Technical Reports Server (NTRS)

1981-01-01

The development of a technique for the production of silicon ribbon is discussed. Extensive characterization of the multiple ribbon Furnace 3A main zone temperature profile was performed and the information used to improve uniformity of heating. Irregularities in the main zone heater were associated with growth difficulties at specific cartridge locations, and growth conditions subsequently improved by profiling the main zone heater. Good growth conditions were established in all three cartridge positions. These improvements allowed multiple growth of three 10 cm wide ribbons to be demonstrated for periods of an hour on several occasions. A gas distribution system for the 10 cm cartridge was introduced and demonstrated to lead to improved ambient control during growth. Growth without and with CO2 showed that quality improvement in 10 cm ribbon grown with cold shoes results from ambient manipulation.

Homogeneity and structure of CuZrAlY metallic glass ribbons

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

Fetić, A. Salčinović, E-mail: amra.s@pmf.unsa.ba; Selimović, A.; Hrvat, K.

2016-03-25

Metallic glasses are metastable amorphous structures produced by quenching-rapid cooling technique. Due to very high cooling rates during the production process, it is very difficult to produce homogeneous samples with identical chemical composition. In this paper we will present preliminary results of homogeneity and structure examinations of a CuZrAlY metallic glass ribbon. The ribbon, approximately 1.5 m long and 1 mm wide, was produced using melt spinning technique. Samples from the middle and the end of the ribbon were chosen for further examination. Surface was checked by metallographic and electron scanning microscopy. Chemical composition in different areas of each sample was checkedmore » by energy-dispersive X-ray spectroscopy. Electrical resistivity measurements in the temperature range from 80 K to 280 K were also conducted.« less

Design of a LiNbO(3) ribbon waveguide for efficient difference-frequency generation of terahertz wave in the collinear configuration.

PubMed

Takushima, Y; Shin, S Y; Chung, Y C

2007-10-29

We propose and investigate a ribbon waveguide for difference-frequency generation of terahertz (THz) wave from infrared light sources. The proposed ribbon waveguide is composed of a nonlinear optic crystal and has a thickness less than the wavelength of the THz wave to support the surface-wave mode in the THz region. By utilizing the waveguide dispersion of the surface-wave mode, the phase matching condition between infrared pump, idler and THz waves can be realized in the collinear configuration. Owing to the weak mode confinement of the THz wave, the absorption coefficient can also be reduced. We design the ribbon waveguide which uses LiNbO(3) crystal and discuss the phase-matching condition for DFG of THz wave. Highly efficient THz-wave generation is confirmed by numerical simulations.

Microstructure and mechanical properties of the NiNbZrTiAl amorphous alloys with 10 and 25 at.% Nb content.

PubMed

Czeppe, T; Ochin, P; Sypień, A; Major, L

2010-03-01

The results of investigation of two different Ni-based glasses with compositions Ni(58)Nb(10)Zr(13)Ti(12)Al(7) and Ni(58)Nb(25)Zr(8)Ti(6)Al(3) are presented. The structure of the melt spun ribbons was amorphous. The supercooled liquid range decreased and primary crystallization temperature increased with increasing Nb content while the parameter T(g)/T(m) slightly increased. The crystallization process proceeded in a different way. The ribbon containing 10 at.% Nb showed typical primary crystallization of the 50 nm grains of the NiTi(Nb) cubic phase; the ribbon containing 25 at.% of Nb revealed high thermal stability of the amorphous phase, which crystallized only in a small amount in the range of primary crystallization, preserving large fraction of the amorphous phase even high above the end of the crystallization. The tensile load-displacement curves were also different. In both cases, the ribbons revealed quite a large range of the plastic elongation. The ribbon containing 10% Nb showed stress relaxation and was maximally elongated up to 0.6. The ribbon with 25 at.% Nb revealed a hardening effect and the slightly smaller maximal elongation following it. The microstructure of the deformed specimens showed deformation bands parallel to the tensile axis, microcracks formation along shear bands and river-like pattern at the fracture surfaces. In both cases, high resolution electron microscope did not reveal any crystallization after deformation.

Microstructure, biocorrosion and cytotoxicity evaluations of rapid solidified Mg-3Ca alloy ribbons as a biodegradable material.

PubMed

Gu, X N; Li, X L; Zhou, W R; Cheng, Y; Zheng, Y F

2010-06-01

Rapidly solidified (RS) Mg–3Ca alloy ribbons were prepared by the melt-spinning technique at different wheel rotating speeds (15 m s(-1), 30 m s(-1) and 45 m s(-1) with the as-cast Mg–3Ca alloy ingot as a raw material. The RS45 Mg–3Ca alloy ribbon showed a much more fine grain size feature (approximately 200–500 nm) in comparison to the coarse grain size (50–100 μm)of the original as-cast Mg–3Ca alloy ingot. The corrosion electrochemical tests in simulated body fluid indicated that the corrosion rate of the as-cast Mg–3Ca alloy was strongly reduced by the RS procedure and tended to be further decreased with increasing wheel rotating speeds(1.43 mm yr(-1) for RS15, 0.94 mm yr(-1) for RS30 and 0.36 mm yr(-1) for RS45). The RS Mg–3Ca alloy ribbons showed more uniform corrosion morphology compared with the as-cast Mg–3Ca alloy after polarization. The cytotoxicity evaluation revealed that the three experimental as-spun Mg–3Ca alloy ribbon extracts did not induce toxicity to the L-929 cells,whereas the as-cast Mg–3Ca alloy ingot extract did. The L-929 cells showed more improved adhesion on the surfaces of the three as-spun Mg–3Ca alloy ribbons than that of the as-cast Mg–3Ca alloy ingot.

The role of electronic dopant on full band in-plane RKKY coupling in armchair graphene nanoribbons-magnetic impurity system

NASA Astrophysics Data System (ADS)

Hoi, Bui Dinh; Yarmohammadi, Mohsen

2018-05-01

Motivated by the growing interest in solving the obstacles of spintronics applications, we study the Ruderman-Kittel-Kasuya-Yosida (RKKY) effective pairwise interaction between magnetic impurities interacting through the π -electrons embedded in both electronically doped-semiconducting and metallic armchair graphene nanoribbons. In terms of the Green's function formalism, treated in a tight-binding approximation with hopping beyond Dirac cone approximation, the RKKY coupling is an attraction or a repulsion depending on the magnetic impurities distances. Our results show that the RKKY coupling in semiconducting nanoribbons is much more affected by doping than metallic ones. Furthermore, we found that the RKKY coupling increases with ribbon width, while there exist some critical electronic concentrations in RKKY interaction oscillations. On the other hand, we find an unusual incoming wave-vector direction for electrons which describes more clearly the ferro- and antiferromagnetic spin configurations in such system. Also, the RKKY coupling at low and high-temperature regions has been addressed for both ferro- and antiferromagnetic spin arrangements.

Large-area sheet task: Advanced dendritic-web-growth development

NASA Technical Reports Server (NTRS)

Duncan, C. S.; Seidensticker, R. G.; Mchugh, J. P.; Schruben, J.

1983-01-01

Thermally generated stresses in the growing web crystal were reduced. These stresses, which if too high cause the ribbon to degenerate, were reduced by a factor of three, resulting in the demonstrated growth of high-quality web crystals to widths of 5.4 cm. This progress was brought about chiefly by the application of thermal models to the development of low-stress growth configurations. A new temperature model was developed which can analyze the thermal effects of much more complex lid and top shield configurations than was possible with the old lumped shield model. Growth experiments which supplied input data such as actual shield temperature and melt levels were used to verify the modeling results. Desirable modifications in the melt level-sensing circuitry were made in the new experimental web growth furnace, and this furnace has been used to carry out growth experiments under steady-state conditions. New growth configurations were tested in long growth runs at Westinghouse AESD which produced wider, lower stress and higher quality web crystals than designs previously used.

Surface-based atlases of cerebellar cortex in the human, macaque, and mouse.

PubMed

Van Essen, David C

2002-12-01

This study describes surface reconstructions and associated flat maps that represent the highly convoluted shape of cerebellar cortex in three species: human, macaque, and mouse. The reconstructions were based on high-resolution structural MRI data obtained from other laboratories. The surface areas determined for the fiducial reconstructions are about 600 cm(2) for the human, 60 cm(2) for the macaque, and 0.8 cm(2) for the mouse. As expected from the ribbon-like pattern of cerebellar folding, the cerebellar flat maps are elongated along the axis parallel to the midline. However, the degree of elongation varies markedly across species. The macaque flat map is many times longer than its mean width, whereas the mouse flat map is only slightly elongated and the human map is intermediate in its aspect ratio. These cerebellar atlases, along with associated software for visualization and for mapping experimental data onto the atlas, are freely available to the neuroscience community (see http:/brainmap.wustl.edu).

Front-Side Microstrip Line Feeding a Raised Antenna Patch

NASA Technical Reports Server (NTRS)

Hodges, Richard; Hoppe, Daniel

2005-01-01

An improved design concept for a printed-circuit patch antenna and the transmission line that feeds the patch calls for (1) a microstrip transmission line on the front (radiative) side of a printed-circuit board based on a thin, high-permittivity dielectric substrate; (2) using the conductor covering the back side of the circuit board as a common ground plane for both the microstrip line and the antenna patch; (3) supporting the antenna patch in front of the circuit board on a much thicker, lower-permittivity dielectric spacer layer; and (4) connecting the microstrip transmission line to the patch by use of a thin wire or narrow ribbon that extends through the thickness of the spacer and is oriented perpendicularly to the circuit-board plane. The thickness of the substrate is typically chosen so that a microstrip transmission line of practical width has an impedance between 50 and 100 ohms. The advantages of this design concept are best understood in the context of the disadvantages of prior design concepts, as explained

Electron transport in gated InGaAs and InAsP quantum well wires in selectively grown InP ridge structures

NASA Astrophysics Data System (ADS)

Granger, G.; Kam, A.; Studenikin, S. A.; Sachrajda, A. S.; Aers, G. C.; Williams, R. L.; Poole, P. J.

2010-09-01

The purpose of this work is to fabricate ribbon-like InGaAs and InAsP wires embedded in InP ridge structures and investigate their transport properties. The InP ridge structures that contain the wires are selectively grown by chemical beam epitaxy (CBE) on pre-patterned InP substrates. To optimize the growth and micro-fabrication processes for electronic transport, we explore the Ohmic contact resistance, the electron density, and the mobility as a function of the wire width using standard transport and Shubnikov-de Haas measurements. At low temperatures the ridge structures reveal reproducible mesoscopic conductance fluctuations. We also fabricate ridge structures with submicron gate electrodes that exhibit non-leaky gating and good pinch-off characteristics acceptable for device operation. Using such wrap gate electrodes, we demonstrate that the wires can be split to form quantum dots evidenced by Coulomb blockade oscillations in transport measurements.

One-dimensional nanowires of pseudoboehmite (aluminum oxyhydroxide γ-AlOOH)

PubMed Central

Iijima, Sumio; Yumura, Takashi; Liu, Zheng

2016-01-01

We report the discovery of a 1D crystalline structure of aluminum oxyhydroxide. It was found in a commercial product of fibrous pseudoboehmite (PB), γ-AlOOH, synthesized easily with low cost. The thinnest fiber found was a ribbon-like structure of only two layers of an Al–O octahedral double sheet having a submicrometer length along its c axis and 0.68-nm thickness along its b axis. This thickness is only slightly larger than half of the lattice parameter of the b-axis unit cell of the boehmite crystal (b/2 = 0.61 nm). Moreover, interlayer splittings having an average width of 1 nm inside the fibrous PB are found. These wider interlayer spaces may have intercalation of water, which is suggested by density functional theory (DFT) calculation. The fibers appear to grow as almost isolated individual filaments in aqueous Al-hydroxide sols and the growth direction of fibrous PB is always along its c axis. PMID:27708158

Surface-based atlases of cerebellar cortex in the human, macaque, and mouse

NASA Technical Reports Server (NTRS)

Van Essen, David C.

2002-01-01

This study describes surface reconstructions and associated flat maps that represent the highly convoluted shape of cerebellar cortex in three species: human, macaque, and mouse. The reconstructions were based on high-resolution structural MRI data obtained from other laboratories. The surface areas determined for the fiducial reconstructions are about 600 cm(2) for the human, 60 cm(2) for the macaque, and 0.8 cm(2) for the mouse. As expected from the ribbon-like pattern of cerebellar folding, the cerebellar flat maps are elongated along the axis parallel to the midline. However, the degree of elongation varies markedly across species. The macaque flat map is many times longer than its mean width, whereas the mouse flat map is only slightly elongated and the human map is intermediate in its aspect ratio. These cerebellar atlases, along with associated software for visualization and for mapping experimental data onto the atlas, are freely available to the neuroscience community (see http:/brainmap.wustl.edu).

A two-ply polymer-based flexible tactile sensor sheet using electric capacitance.

PubMed

Guo, Shijie; Shiraoka, Takahisa; Inada, Seisho; Mukai, Toshiharu

2014-01-29

Traditional capacitive tactile sensor sheets usually have a three-layered structure, with a dielectric layer sandwiched by two electrode layers. Each electrode layer has a number of parallel ribbon-like electrodes. The electrodes on the two electrode layers are oriented orthogonally and each crossing point of the two perpendicular electrode arrays makes up a capacitive sensor cell on the sheet. It is well known that compatibility between measuring precision and resolution is difficult, since decreasing the width of the electrodes is required to obtain a high resolution, however, this may lead to reduction of the area of the sensor cells, and as a result, lead to a low Signal/Noise (S/N) ratio. To overcome this problem, a new multilayered structure and related calculation procedure are proposed. This new structure stacks two or more sensor sheets with shifts in position. Both a high precision and a high resolution can be obtained by combining the signals of the stacked sensor sheets. Trial production was made and the effect was confirmed.

Tuning Nanocrystal Surface Depletion by Controlling Dopant Distribution as a Route Toward Enhanced Film Conductivity

NASA Astrophysics Data System (ADS)

Staller, Corey M.; Robinson, Zachary L.; Agrawal, Ankit; Gibbs, Stephen L.; Greenberg, Benjamin L.; Lounis, Sebastien D.; Kortshagen, Uwe R.; Milliron, Delia J.

2018-05-01

Electron conduction through bare metal oxide nanocrystal (NC) films is hindered by surface depletion regions resulting from the presence of surface states. We control the radial dopant distribution in tin-doped indium oxide (ITO) NCs as a means to manipulate the NC depletion width. We find in films of ITO NCs of equal overall dopant concentration that those with dopant-enriched surfaces show decreased depletion width and increased conductivity. Variable temperature conductivity data shows electron localization length increases and associated depletion width decreases monotonically with increased density of dopants near the NC surface. We calculate band profiles for NCs of differing radial dopant distributions and, in agreement with variable temperature conductivity fits, find NCs with dopant-enriched surfaces have narrower depletion widths and longer localization lengths than those with dopant-enriched cores. Following amelioration of NC surface depletion by atomic layer deposition of alumina, all films of equal overall dopant concentration have similar conductivity. Variable temperature conductivity measurements on alumina-capped films indicate all films behave as granular metals. Herein, we conclude that dopant-enriched surfaces decrease the near-surface depletion region, which directly increases the electron localization length and conductivity of NC films.

Tuning Nanocrystal Surface Depletion by Controlling Dopant Distribution as a Route Toward Enhanced Film Conductivity.

PubMed

Staller, Corey M; Robinson, Zachary L; Agrawal, Ankit; Gibbs, Stephen L; Greenberg, Benjamin L; Lounis, Sebastien D; Kortshagen, Uwe R; Milliron, Delia J

2018-05-09

Electron conduction through bare metal oxide nanocrystal (NC) films is hindered by surface depletion regions resulting from the presence of surface states. We control the radial dopant distribution in tin-doped indium oxide (ITO) NCs as a means to manipulate the NC depletion width. We find in films of ITO NCs of equal overall dopant concentration that those with dopant-enriched surfaces show decreased depletion width and increased conductivity. Variable temperature conductivity data show electron localization length increases and associated depletion width decreases monotonically with increased density of dopants near the NC surface. We calculate band profiles for NCs of differing radial dopant distributions and in agreement with variable temperature conductivity fits find NCs with dopant-enriched surfaces have narrower depletion widths and longer localization lengths than those with dopant-enriched cores. Following amelioration of NC surface depletion by atomic layer deposition of alumina, all films of equal overall dopant concentration have similar conductivity. Variable temperature conductivity measurements on alumina-capped films indicate all films behave as granular metals. Herein, we conclude that dopant-enriched surfaces decrease the near-surface depletion region, which directly increases the electron localization length and conductivity of NC films.

The Sloan Digital Sky Survey Reverberation Mapping Project: The C IV Blueshift, Its Variability, and Its Dependence Upon Quasar Properties

NASA Astrophysics Data System (ADS)

Sun, Mouyuan; Xue, Yongquan; Richards, Gordon T.; Trump, Jonathan R.; Shen, Yue; Brandt, W. N.; Schneider, D. P.

2018-02-01

We use the multi-epoch spectra of 362 quasars from the Sloan Digital Sky Survey Reverberation Mapping project to investigate the dependence of the blueshift of C IV relative to Mg II on quasar properties. We confirm that high-blueshift sources tend to have low C IV equivalent widths (EWs), and that the low-EW sources span a range of blueshift. Other high-ionization lines, such as He II, also show similar blueshift properties. The ratio of the line width (measured as both the full width at half maximum and the velocity dispersion) of C IV to that of Mg II increases with blueshift. Quasar variability enhances the connection between the C IV blueshift and quasar properties (e.g., EW). The variability of the Mg II line center (i.e., the wavelength that bisects the cumulative line flux) increases with blueshift. In contrast, the C IV line center shows weaker variability at the extreme blueshifts. Quasars with the high-blueshift C IV lines tend to have less variable continuum emission, when controlling for EW, luminosity, and redshift. Our results support the scenario that high-blueshift sources tend to have large Eddington ratios.

Evolution of flare ribbons, electric currents, and quasi-separatrix layers during an X-class flare

NASA Astrophysics Data System (ADS)

Janvier, M.; Savcheva, A.; Pariat, E.; Tassev, S.; Millholland, S.; Bommier, V.; McCauley, P.; McKillop, S.; Dougan, F.

2016-07-01

Context. The standard model for eruptive flares has been extended to three dimensions (3D) in the past few years. This model predicts typical J-shaped photospheric footprints of the coronal current layer, forming at similar locations as the quasi-separatrix layers (QSLs). Such a morphology is also found for flare ribbons observed in the extreme ultraviolet (EUV) band, and in nonlinear force-free field (NLFFF) magnetic field extrapolations and models. Aims: We study the evolution of the photospheric traces of the current density and flare ribbons, both obtained with the Solar Dynamics Observatory instruments. We aim to compare their morphology and their time evolution, before and during the flare, with the topological features found in a NLFFF model. Methods: We investigated the photospheric current evolution during the 06 September 2011 X-class flare (SOL2011-09-06T22:20) occurring in NOAA AR 11283 from observational data of the magnetic field obtained with the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory. We compared this evolution with that of the flare ribbons observed in the EUV filters of the Atmospheric Imager Assembly. We also compared the observed electric current density and the flare ribbon morphology with that of the QSLs computed from the flux rope insertion method-NLFFF model. Results: The NLFFF model shows the presence of a fan-spine configuration of overlying field lines, due to the presence of a parasitic polarity, embedding an elongated flux rope that appears in the observations as two parts of a filament. The QSL signatures of the fan configuration appear as a circular flare ribbon that encircles the J-shaped ribbons related to the filament ejection. The QSLs, evolved via a magnetofrictional method, also show similar morphology and evolution as both the current ribbons and the EUV flare ribbons obtained several times during the flare. Conclusions: For the first time, we propose a combined analysis of the photospheric traces of an eruptive flare, in a complex topology, with direct measurements of electric currents and QSLs from observational data and a magnetic field model. The results, obtained by two different and independent approaches 1) confirm previous results of current increase during the impulsive phase of the flare and 2) show how NLFFF models can capture the essential physical signatures of flares even in a complex magnetic field topology. A movie associated to Fig. 1 is available in electronic form at http://www.aanda.org

The identification of a sensitizing component used in the manufacturing of an ink ribbon.

PubMed

Anderson, Stacey E; Tapp, Loren; Durgam, Srinivas; Meade, B Jean; Jackson, Laurel G; Cohen, David E

2012-01-01

Skin diseases including dermatitis constitute ≈ 30% of all occupational illnesses, with a high incidence in the printing industry. An outbreak of contact dermatitis among employees at an ink ribbon manufacturing plant was investigated by scientists from the National Institute for Occupational Safety and Health (NIOSH). Employees in the process areas of the plant were exposed to numerous chemicals and many had experienced skin rashes, especially after the introduction of a new ink ribbon product. To identify the causative agent(s) of the occupational dermatitis, the murine local lymph node assay (LLNA) was used to identify the potential of the chemicals used in the manufacture of the ink ribbon to induce allergic contact dermatitis. Follow-up patch testing with the suspected allergens was conducted on exposed employees. Polyvinyl butyral, a chemical component used in the manufacture of the ink ribbon in question and other products, tested positive in the LLNA, with an EC3 of 3.6%, which identifies it as a potential sensitizer; however, no employees tested positive to this chemical during skin patch testing. This finding has implications beyond those described in this report because of occupational exposure to polyvinyl butyral outside of the printing industry.

Ultra-broad polypyrrole (PPy) nano-ribbons seeded by racemic surfactants aggregates and their high-performance electromagnetic radiation elimination.

PubMed

Jiao, Yingzhi; Wu, Fan; Zhang, Kun; Sun, Mengxiao; Xie, Aming; Dong, Wei

2017-08-04

Ribbon-like nano-structures possess high aspect ratios, and thus have great potential in the development of high-performance microwave absorption (MA) materials that can effectively eliminate adverse electromagnetic radiation. However, these nano-structures have been scarcely constructed in the field of MA, because of the lack of efficient synthetic routes. Herein, we developed an efficient method to successfully construct polypyrrole (PPy) nano-ribbons using the self-assembly aggregates of a racemic surfactant as the seeds. The frequency range with a reflection loss value of lower than -10 dB reached 7.68 GHz in the frequency range of 10.32-18.00 GHz, and surpassed all the currently reported PPy nano-structures, as well as most other MA nano-materials. Through changing the amount of surfactant, both the nano-structures and MA performance can be effectively regulated. Furthermore, the reason behind the high-performance MA of PPy nano-ribbons has been deeply explored. It opens up the opportunity for the application of conducting polymer nano-ribbons as a lightweight and tunable high-performance MA material, especially in applications of special aircraft and flexible electronics.

The identification of a sensitizing component used in the manufacturing of an ink ribbon

PubMed Central

Anderson, Stacey E.; Tapp, Loren; Durgam, Srinivas; Meade, B. Jean; Jackson, Laurel G.; Cohen, David E.

2015-01-01

Skin diseases including dermatitis constitute ≈ 30% of all occupational illnesses, with a high incidence in the printing industry. An outbreak of contact dermatitis among employees at an ink ribbon manufacturing plant was investigated by scientists from the National Institute for Occupational Safety and Health (NIOSH). Employees in the process areas of the plant were exposed to numerous chemicals and many had experienced skin rashes, especially after the introduction of a new ink ribbon product. To identify the causative agent(s) of the occupational dermatitis, the murine local lymph node assay (LLNA) was used to identify the potential of the chemicals used in the manufacture of the ink ribbon to induce allergic contact dermatitis. Follow-up patch testing with the suspected allergens was conducted on exposed employees. Polyvinyl butyral, a chemical component used in the manufacture of the ink ribbon in question and other products, tested positive in the LLNA, with an EC3 of 3.6%, which identifies it as a potential sensitizer; however, no employees tested positive to this chemical during skin patch testing. This finding has implications beyond those described in this report because of occupational exposure to polyvinyl butyral outside of the printing industry. PMID:22375946

Fish Marketing of Ribbon Fish (Trichiurus sp.) in Nusantara Fishing Port (NFP)at Palabuhanratu, West Java

NASA Astrophysics Data System (ADS)

Bambang, Azis Nur

2018-02-01

The objective of this research is to study the marketing process of ribbon fish (Trichiurus sp.), including the marketing margin, marketing agencies, traders and marketing channels The research was carried out for 3 mo in Nusantara Fishing Port (NFP), Palabuhanratu, Sukabumi, West Java. A case study was used in this research. A purposive sampling method was used to collect data from 55 respondents of fish marketing, consisting of fishermen, agents, traders, and retailers, who were involved in the marketing of ribbon fish in NFP Palabuhanratu. The result of the research showed that ribbon fish production in Palabuhanratu fluctuated from year to year. There are two types of ribbon fish marketing, i.e. type one is from fishermen to retailers, and type two is indirect marketing from fisherman to consumers through intermediate traders (exporters). The greatest marketing margin was obtained from the first type, while the smallest marketing margin was obtained from type two. The form of the market was considered to be oligopsony market. Fisherman's share is greatest in the collectors and the smallest share is on retailers. Marketing process in traders is efficient due to its lowest margin and highest fisherman's share.

Stretchable interconnections for flexible electronic systems.

PubMed

Jianhui, Lin; Bing, Yan; Xiaoming, Wu; Tianling, Ren; Litian, Liu

2009-01-01

Sensors, actuators and integrated circuits (IC) can be encapsulated together on an elastic substrate, which makes a flexible electronic system. In this system, electrical interconnections that can sustain large and reversible stretching are in great need. This paper is devoted to the fabrication of highly stretchable metal interconnections. Transfer printing technology is utilized, which mainly involves the transfer of 100-nm-thick gold ribbons from silicon wafers to pre-stretched elastic substrates. After the elastic substrates relax from the pre-strain, the gold ribbons buckle and form wavy geometries. These wavy geometries change in shapes to accommodate the applied strain and can be reversely stretched without cracks or fractures occurring, which will greatly raise the stretchability of the gold ribbons. As an application example, some of these wavy ribbons can accommodate high levels of stretching (up to 100%) and bending (with curvature radius down to 1.20 mm). Moreover, the efficiency and reliability of the transfer, especially for slender ribbons, have been increased due to the improvement of the technology. All the characteristics above will permit making stretchable gold conductors as interconnections for flexible electronic systems such as implantable medical systems and smart clothes.

Ultra-broad polypyrrole (PPy) nano-ribbons seeded by racemic surfactants aggregates and their high-performance electromagnetic radiation elimination

NASA Astrophysics Data System (ADS)

Jiao, Yingzhi; Wu, Fan; Zhang, Kun; Sun, Mengxiao; Xie, Aming; Dong, Wei

2017-08-01

Ribbon-like nano-structures possess high aspect ratios, and thus have great potential in the development of high-performance microwave absorption (MA) materials that can effectively eliminate adverse electromagnetic radiation. However, these nano-structures have been scarcely constructed in the field of MA, because of the lack of efficient synthetic routes. Herein, we developed an efficient method to successfully construct polypyrrole (PPy) nano-ribbons using the self-assembly aggregates of a racemic surfactant as the seeds. The frequency range with a reflection loss value of lower than -10 dB reached 7.68 GHz in the frequency range of 10.32-18.00 GHz, and surpassed all the currently reported PPy nano-structures, as well as most other MA nano-materials. Through changing the amount of surfactant, both the nano-structures and MA performance can be effectively regulated. Furthermore, the reason behind the high-performance MA of PPy nano-ribbons has been deeply explored. It opens up the opportunity for the application of conducting polymer nano-ribbons as a lightweight and tunable high-performance MA material, especially in applications of special aircraft and flexible electronics.

Magnetic properties and macroscopic heterogeneity of FeCoNbB Hitperms

NASA Astrophysics Data System (ADS)

Butvin, Pavol; Butvinová, Beata; Sitek, Jozef; Degmová, Jarmila; Vlasák, Gabriel; Švec, Peter; Janičkovič, Dušan

Nanocrystalline ribbons of Fe 81-xCo xNb 7B 12 (where x ranges from 0 to 40.5 at%) Hitperm alloys have been investigated as to their basic magnetic properties and the influence of the macroscopic heterogeneity. Different crystalline share at surfaces compared with the volume average is observed by conversion electron Mössbauer spectroscopy (CEMS) and Mössbauer spectroscopy (MS), respectively. This marks the presence of macroscopic heterogeneity in these Hitperms. The heterogeneity is generally more significant in Ar-annealed samples than in the vacuum-annealed ones. The characteristic slant hysteresis loops (hard-ribbon-axis) are seen as a rule with few exceptions. An inspection of hysteresis loop response of resin potted samples shows that the surfaces bi-axially squeeze the ribbon interior in heterogeneous Hitperms when the ribbons cool down after annealing. Certain compositions show macroscopic viscous flow prior to crystallization so the heterogeneity gets another chance to induce anisotropy during annealing. The induction attains 1.5 T but saturates poorly due to the heterogeneity and the ensuing anisotropy. Moreover the heterogeneity appears to hamper the crystallization within the ribbon interior. Unlike Finemets, the density of these Hitperms show no pronounced trend with annealing.

Displaced capillary dies

DOEpatents

Kalejs, Juris P.; Chalmers, Bruce; Surek, Thomas

1982-01-01

An asymmetrical shaped capillary die made exclusively of graphite is used to grow silicon ribbon which is capable of being made into solar cells that are more efficient than cells produced from ribbon made using a symmetrically shaped die.

Displaced capillary dies

DOEpatents

Kalejs, Juris P.; Chalmers, Bruce; Surek, Thomas

1984-01-01

An asymmetrical shaped capillary die made exclusively of graphite is used to grow silicon ribbon which is capable of being made into solar cells that are more efficient than cells produced from ribbon made using a symmetrically shaped die.

Report of the Governor's Blue Ribbon Transportation Task Force

DOT National Transportation Integrated Search

1982-12-01

Governor Ray appointed the Blue Ribbon Transportation Task Force to provide guidance concerning specific steps that can be taken to: achieve maximum efficiency in the utilization of transportation resources; preserve essential transportation services...

Blue Ribbon Commission Tour of Hanford Site

ScienceCinema

Paul Saueressig

2017-12-09

The Blue Ribbon Commission on America's Nuclear Future toured the Department of Energy's Hanford Site on July 14, 2010. Commission members, invited guests, and members of the public visited facilities that store high-level, radioactive waste.

Systems and Methods for Fabricating Structures Including Metallic Glass-Based Materials Using Ultrasonic Welding

NASA Technical Reports Server (NTRS)

Hofmann, Douglas C. (Inventor); Roberts, Scott N. (Inventor)

2017-01-01

Systems and methods in accordance with embodiments of the invention fabricate objects including metallic glass-based materials using ultrasonic welding. In one embodiment, a method of fabricating an object that includes a metallic glass-based material includes: ultrasonically welding at least one ribbon to a surface; where at least one ribbon that is ultrasonically welded to a surface has a thickness of less than approximately 150.mu.m; and where at least one ribbon that is ultrasonically welded to a surface includes a metallic glass-based material.

Cryogenic ribbon-cutting

NASA Image and Video Library

2011-03-30

NASA cut the ribbon on a new cryogenics control center at John C. Stennis Space Center on March 30. The new facility is part of a project to strengthen Stennis facilities to withstand the impacts of future storms like hurricane Katrina in 2005. Participants in the ribbon-cutting included (l to r): Jason Zuckerman, director of project management for The McDonnel Group; Keith Brock, director of the NASA Project Directorate at Stennis; Stennis Deputy Director Rick Gilbrech; Steve Jackson of Jacobs Technology; and Troy Frisbie, Cryo Control Center Construction project manager for NASA Center Operations at Stennis.

Study of Defect Behaviour in Ga2O3 Nanowires and Nano-Ribbons under Reducing Gas Annealing Conditions: Applications to Sensing

DTIC Science & Technology

2007-01-01

Study of defect behaviour in Ga2O3 nanowires and nano-ribbons under reducing gas annealing conditions: applications to...estd.nrl.navy.mil E-mail: Carlos@bloch.nrl.navy.mil E-mail: Glaser@ bloch.nrl.navy.mil *Corresponding author Abstract: The growth of monoclinic Ga2O3 ...an Au catalyst, while single crystal nano-ribbons and nano-sheets require no metal catalyst for growth. Since bulk Ga2O3 is a promising material

Low-loss silicide/silicon plasmonic ribbon waveguides for mid- and far-infrared applications.

PubMed

Cho, Sang-Yeon; Soref, Richard A

2009-06-15

We report low-loss silicide/silicon plasmonic ribbon waveguides for mid- and far-IR applications. The composite modes in silicide ribbon waveguides offer a low-loss and highly confined mode profile, giving excellent plasmon waveguiding for long-wavelength applications. The calculated propagation loss of the composite long-range surface-plasmon polariton mode at a wavelength of 100 microm is 2.18 dB/cm with a mode height of less than 30 microm. The results presented provide important design guidelines for silicide/Si plasmon waveguides.

Sub-arcsecond observations of the solar X-ray corona

NASA Technical Reports Server (NTRS)

Golub, L.; Nystrom, G.; Herant, M.; Kalata, K.; Lovas, I.

1990-01-01

Results from a high-resolution multi-layer-coated X-ray imaging telescope, part of the Normal Incidence X-ray Telescope sounding rocket payload are presented. Images of the peak of a two-ribbon flare showed detailed structure within each ribbon, as well as the expected bright arches of emission connecting the ribbons. The number of X-ray bright points is small, consistent with predictions based on the previous solar cycle. Topology of the magnetic structure is complex and highly tangled, implying that the magnetic complexity of the photosphere is paralleled in the corona.

A method for estimating mean and low flows of streams in national forests of Montana

USGS Publications Warehouse

Parrett, Charles; Hull, J.A.

1985-01-01

Equations were developed for estimating mean annual discharge, 80-percent exceedance discharge, and 95-percent exceedance discharge for streams on national forest lands in Montana. The equations for mean annual discharge used active-channel width, drainage area and mean annual precipitation as independent variables, with active-channel width being most significant. The equations for 80-percent exceedance discharge and 95-percent exceedance discharge used only active-channel width as an independent variable. The standard error or estimate for the best equation for estimating mean annual discharge was 27 percent. The standard errors of estimate for the equations were 67 percent for estimating 80-percent exceedance discharge and 75 percent for estimating 95-percent exceedance discharge. (USGS)

Gas Atmospheres Improve Silicon-Ribbon Quality

NASA Technical Reports Server (NTRS)

Wald, F. V.; Kalejs, J. P.

1985-01-01

Growing crystal surrounded by gas containing carbon or oxygen. Ribbon of solid silicon, edgewise, grows from pool of molten silicon in die. Gases flowing through orifice ensure longer diffusion length and less contaminiation by carbide particles in product.

Achieving Clean Air and Clean Water: The Report of the Blue Ribbon Panel on Oxygenates in Gasoline

EPA Pesticide Factsheets

The Blue Ribbon Panel's report consists of five issue summaries: water contamination; air quality benefits; prevention; treatment and remediation; fuel supply and cost; and comparing the fuel additives.

Analysis of stress-strain relationships in silicon ribbon

NASA Technical Reports Server (NTRS)

Dillon, O. W., Jr.

1984-01-01

An analysis of stress-strain relationships in silicon ribbon is presented. A model to present entire process, dynamical Transit Analysis is developed. It is found that knowledge of past-strain history is significant in modeling activities.

Ribbon cutting opens new ELV offices

NASA Technical Reports Server (NTRS)

2000-01-01

Center Director Roy Bridges welcomes the audience to a ribbon- cutting ceremony at the E&O Building at KSC. Home for NASA's unmanned missions since 1964, the building has been renovated to house the Expendable Launch Vehicle Program.

25 CFR 309.15 - What are examples of apparel that are Indian products?

Code of Federal Regulations, 2013 CFR

2013-04-01

... products. (b) Specific examples include, but are not limited to: seal skin parkas, ribbon appliqué dance shawls, smoked moose hide slippers, deer skin boots, patchwork jackets, calico ribbon shirts, wing...

25 CFR 309.15 - What are examples of apparel that are Indian products?

Code of Federal Regulations, 2012 CFR

2012-04-01

... products. (b) Specific examples include, but are not limited to: seal skin parkas, ribbon appliqué dance shawls, smoked moose hide slippers, deer skin boots, patchwork jackets, calico ribbon shirts, wing...

25 CFR 309.15 - What are examples of apparel that are Indian products?

Code of Federal Regulations, 2014 CFR

2014-04-01

... products. (b) Specific examples include, but are not limited to: seal skin parkas, ribbon appliqué dance shawls, smoked moose hide slippers, deer skin boots, patchwork jackets, calico ribbon shirts, wing...

Sublid Speeds Growth Of Silicon Ribbon

NASA Technical Reports Server (NTRS)

Seidensticker, R. G.; Mchugh, J. P.

1988-01-01

Heat shield permits enhancement of exit cooling without formation of unwanted crystals. Thermal barrier between molten silicon and lid of susceptor and crucible allows solidifying ribbon of silicon to be withdrawn faster. Barrier, or sublid, increases production rate.

Buildup of a highly twisted magnetic flux rope during a solar eruption.

PubMed

Wang, Wensi; Liu, Rui; Wang, Yuming; Hu, Qiang; Shen, Chenglong; Jiang, Chaowei; Zhu, Chunming

2017-11-06

The magnetic flux rope is among the most fundamental magnetic configurations in plasma. Although its presence after solar eruptions has been verified by spacecraft measurements near Earth, its formation on the Sun remains elusive, yet is critical to understanding a broad spectrum of phenomena. Here we study the dynamic formation of a magnetic flux rope during a classic two-ribbon flare. Its feet are identified unambiguously with conjugate coronal dimmings completely enclosed by irregular bright rings, which originate and expand outward from the far ends of flare ribbons. The expansion is associated with the rapid ribbon separation during the flare main phase. Counting magnetic flux through the feet and the ribbon-swept area reveals that the rope's core is more twisted than its average of four turns. It propagates to the Earth as a typical magnetic cloud possessing a similar twist profile obtained by the Grad-Shafranov reconstruction of its three dimensional structure.

Table-like magnetocaloric effect and enhanced refrigerant capacity in crystalline Gd55Co35Mn10 alloy melt spun ribbons

NASA Astrophysics Data System (ADS)

Mo, H. Y.; Zhong, X. C.; Jiao, D. L.; Liu, Z. W.; Zhang, H.; Qiu, W. Q.; Ramanujan, R. V.

2018-06-01

Gd55Co35Mn10 ribbons were prepared by melt-spinning and subsequent crystallization treatment. Crystallization resulted in the precipitation of the Gd3Co-type and Gd12Co7-type phases in the amorphous matrix. Under a magnetic field change of 0-5 T, a table-like magnetocaloric effect, with a maximum magnetic entropy change (- ΔSM) max of 5.46Jkg-1K-1 in the temperature range of 137-180 K and enhanced refrigerant capacity (RC) of 536.4Jkg-1, was achieved in Gd55Co35Mn10 ribbons crystallized at 600 K for 30 min. The table-like (- ΔSM) max feature and enhanced RC values make Gd55Co35Mn10 crystallized ribbons promising for Ericsson-cycle magnetic refrigeration in the temperature range from 137 to 180 K.

Glassy formation ability, magnetic properties and magnetocaloric effect in Al27Cu18Er55 amorphous ribbon

NASA Astrophysics Data System (ADS)

Li, Lingwei; Xu, Chi; Yuan, Ye; Zhou, Shengqiang

2018-05-01

In this work, we have fabricated the Al27Cu18Er55 amorphous ribbon with good glassy formation ability by melt-spinning technology. A broad paramagnetic (PM) to ferromagnetic (FM) transition (second ordered) together with a large reversible magnetocaloric effect (MCE) in Al27Cu18Er55 amorphous ribbon was observed around the Curie temperature TC ∼ 11 K. Under the magnetic field change (ΔH of 0-7 T, the values of MCE parameter of the maximum magnetic entropy change (-ΔSMmax) and refrigerant capacity (RC) for Al27Cu18Er55 amorphous ribbon reach 21.4 J/kg K and 599 J/kg, respectively. The outstanding glass forming ability as well as the excellent magneto-caloric properties indicate that Al27Cu18Er55 amorphous could be a good candidate for low temperature magnetic refrigeration.

Theoretical analysis of heat flow in horizontal ribbon growth from a melt. [silicon metal

NASA Technical Reports Server (NTRS)

Zoutendyk, J. A.

1978-01-01

A theoretical heat flow analysis for horizontalribbon growth is presented. Equations are derived relating pull speed, ribbon thickness, thermal gradient in the melt, and melt temperature for limiting cases of heat removal by radiation only and isothermal heat removal from the solid surface over the melt. Geometrical cross sections of the growth zone are shown to be triangular and nearly parabolic for the two respective cases. Theoretical pull speed for silicon ribbon 0.01 cm thick, where the loss of latent heat of fusion is by radiation to ambient temperature (300 K) only, is shown to be 1 cm/sec for horizontal growth extending 2 cm over the melt and with no heat conduction either to or from the melt. Further enhancement of ribbon growth rate by placing cooling blocks adjacent to the top surface is shown to be theoretically possible.

Piezoelectric ribbons printed onto rubber for flexible energy conversion.

PubMed

Qi, Yi; Jafferis, Noah T; Lyons, Kenneth; Lee, Christine M; Ahmad, Habib; McAlpine, Michael C

2010-02-10

The development of a method for integrating highly efficient energy conversion materials onto stretchable, biocompatible rubbers could yield breakthroughs in implantable or wearable energy harvesting systems. Being electromechanically coupled, piezoelectric crystals represent a particularly interesting subset of smart materials that function as sensors/actuators, bioMEMS devices, and energy converters. Yet, the crystallization of these materials generally requires high temperatures for maximally efficient performance, rendering them incompatible with temperature-sensitive plastics and rubbers. Here, we overcome these limitations by presenting a scalable and parallel process for transferring crystalline piezoelectric nanothick ribbons of lead zirconate titanate from host substrates onto flexible rubbers over macroscopic areas. Fundamental characterization of the ribbons by piezo-force microscopy indicates that their electromechanical energy conversion metrics are among the highest reported on a flexible medium. The excellent performance of the piezo-ribbon assemblies coupled with stretchable, biocompatible rubber may enable a host of exciting avenues in fundamental research and novel applications.

Stress and efficiency studies

NASA Technical Reports Server (NTRS)

1985-01-01

Optical and electrical characterization of defects has been started in EFG ribbon grown in a system that will be used to test the stress model. Temperature and stress field modeling aimed at defining low stress growth configuration is also in progress, and results will be used to guide development of the experimental system. The baseline defect configuration for ribbon grown at speeds of approx. 1 cm/min consists of dislocation densities of the order of 10 to the 5th power to 10 to the 6th power/sq cm, as well as saucer type etch pits and line defects. All these defects are inhomogeneously distributed. EBIC measurements indicate that diffusion lengths are in the range 20 to 60 microns, and significant spatial inhomogeneities occur through the ribbon thickness. Growth speed changes in the range 0.7-1.0 cm/min do not produce significant variations in ribbon defect configurations.

Buildup of a highly twisted magnetic flux rope during a solar eruption

NASA Astrophysics Data System (ADS)

Wang, Wensi; Liu, Rui; Wang, Yuming; Hu, Qiang; Shen, Chenglong; Jiang, Chaowei; Zhu, Chunming

2017-11-01

The magnetic flux rope is among the most fundamental magnetic configurations in plasma. Although its presence after solar eruptions has been verified by spacecraft measurements near Earth, its formation on the Sun remains elusive, yet is critical to understanding a broad spectrum of phenomena. Here we study the dynamic formation of a magnetic flux rope during a classic two-ribbon flare. Its feet are identified unambiguously with conjugate coronal dimmings completely enclosed by irregular bright rings, which originate and expand outward from the far ends of flare ribbons. The expansion is associated with the rapid ribbon separation during the flare main phase. Counting magnetic flux through the feet and the ribbon-swept area reveals that the rope's core is more twisted than its average of four turns. It propagates to the Earth as a typical magnetic cloud possessing a similar twist profile obtained by the Grad-Shafranov reconstruction of its three dimensional structure.

Formation and stability of twisted ribbons in mixtures of rod-like fd-virus and non-adsorbing polymer

NASA Astrophysics Data System (ADS)

Dogic, Z.; Didonna, B.; Bryning, M.; Lubensky, T. C.; Yodh, A. G.; Janmey, P. A.

2003-03-01

We are investigating the behavior of mixtures of monodisperse fd-virus rods and non-adsorbing polymer. We observe the formation of isolated smectic disks. The single smectic disk is of a monolayer of aligned rods while its thickness equal to the length of a single rod. As disks coalesce they undergo shape transformations from flat structures to elongated twisted ribbons. A theoretical model is formulated wherein the chirality of the molecule favors the formation of the elongated ribbon structure while the line tension favors formation of untwisted disks. To check the validity of the theoretical model line tension and twist constants are experimentally measured. The line tension is deduced from thermal fluctuations of the interface. The twist constant is determined by unwinding the twisted ribbons using optical tweezers. This work is partially supported by NSF grants DMR-0203378, the PENN MRSEC, DMR-0079909, and NASA grant NAG8-2172.

Exploring the Role of Overlying Fields and Flare Ribbons in CME Speeds

NASA Astrophysics Data System (ADS)

Deng, M.; Welsch, B. T.

2013-12-01

The standard model of eruptive, two-ribbon flares involves reconnection of overlying magnetic fields beneath a rising ejection. Numerous observers have reported evidence linking this reconnection, indicated by photospheric flux swept out by flare ribbons, to coronal mass ejection (CME) acceleration. This acceleration might be caused by reconnected fields that wrap around the ejection producing an increased outward "hoop force." Other observations have linked stronger overlying fields, measured by the power-law index of the fitted decay rate of field strengths overlying eruption sites, to slower CME speeds. This might be caused by greater downward magnetic tension in stronger overlying fields. So overlying fields might both help and hinder the acceleration of CMEs: reconnection that converts overlying fields into flux winding about the ejection might help, but unreconnected overlying fields might hurt. Here, we investigate the roles of both ribbon fluxes and the decay rates of overlying fields in a set of eruptive events.

Sensitive bistable magnetic sensors using twisted amorphous magnetostrictive ribbons due to Matteucci effect

NASA Astrophysics Data System (ADS)

Mohri, K.; Takeuchi, S.

1982-11-01

New sensitive magnetic-field sensors are presented using twisted amorphous magnetostrictive ribbons such as Fe80B20 and Fe81-xCrxB17Si2. Sharp voltage pulses are induced between ends of the ribbon of as short as 25 mm or at the terminals of the detecting coil against external fields of as low as 1 Oe and 0.01 Hz-6 kHz. The domain nucleation field at the bistable flux reversal is very constant for 130 °C, 600 h using Fe79Cr2B17Si2, and a possible maximum operating temperature is about 180 °C. Small sized magnetic sensors without any windings for detecting rotational speed, distance, and other mechanical quantities are realized using the twisted ribbons by combining with small magnets. These sensitive and reliable magnetic sensors with digital outputs are suitable for applications in industrial robots and automobiles controlled with microcomputers.

Influence of a Polymer Coating and the Compacting Pressure on the Magnetic Properties of Cobalt-Based Amorphous Alloys

NASA Astrophysics Data System (ADS)

Skulkina, N. A.; Ivanov, O. A.; Mazeeva, A. K.; Kuznetsov, P. A.; Stepanova, E. A.; Blinova, O. V.; Mikhalitsyna, E. A.; Denisov, N. D.; Chekis, V. I.

2017-12-01

The influence of a polymer coating applied in the manufacture of magnetic shields on magnetic properties has been studied based on the example of ribbons of a cobalt-based soft magnetic alloy (Co-Fe-Ni-Cr-Mn-Si-B) with the saturation magnetostriction close to zero. The influence of polymer coating has been separated from the effect of the compacting pressure applied upon its formation. The polymer coating was formed on the ribbon in the states with different signs of the saturation magnetostriction. It has been shown that the compacting pressure and the polymer coating have opposite effects on the properties of the ribbon and that these impacts partly level off upon the formation of the coating. The degree of the influence of the polymer coating on the magnetic properties depends on the state of the ribbon and on the sign of the saturation magnetostriction in this state.

The presynaptic ribbon maintains vesicle populations at the hair cell afferent fiber synapse

PubMed Central

Becker, Lars; Schnee, Michael E; Niwa, Mamiko; Sun, Willy; Maxeiner, Stephan; Talaei, Sara; Kachar, Bechara; Rutherford, Mark A

2018-01-01

The ribbon is the structural hallmark of cochlear inner hair cell (IHC) afferent synapses, yet its role in information transfer to spiral ganglion neurons (SGNs) remains unclear. We investigated the ribbon’s contribution to IHC synapse formation and function using KO mice lacking RIBEYE. Despite loss of the entire ribbon structure, synapses retained their spatiotemporal development and KO mice had a mild hearing deficit. IHCs of KO had fewer synaptic vesicles and reduced exocytosis in response to brief depolarization; a high stimulus level rescued exocytosis in KO. SGNs exhibited a lack of sustained excitatory postsynaptic currents (EPSCs). We observed larger postsynaptic glutamate receptor plaques, potentially compensating for the reduced EPSC rate in KO. Surprisingly, large-amplitude EPSCs were maintained in KO, while a small population of low-amplitude slower EPSCs was increased in number. The ribbon facilitates signal transduction at physiological stimulus levels by retaining a larger residency pool of synaptic vesicles. PMID:29328021

Fish Swimming and Bird/Insect Flight

NASA Astrophysics Data System (ADS)

Wu, Theodore Yaotsu

2011-01-01

This expository review is devoted to fish swimming and bird/insect flight. (a) The simple waving motion of an elongated flexible ribbon plate of constant width propagating a wave distally down the plate to swim forward in a fluid, initially at rest, is first considered to provide a fundamental concept on energy conservation. It is generalized to include variations in body width and thickness, with appended dorsal, ventral and caudal fins shedding vortices to closely simulate fish swimming, for which a nonlinear theory is presented for large-amplitude propulsion. (b) For bird flight, the pioneering studies on oscillatory rigid wings are discussed with delineating a fully nonlinear unsteady theory for a two-dimensional flexible wing with arbitrary variations in shape and trajectory to provide a comparative study with experiments. (c) For insect flight, recent advances are reviewed by items on aerodynamic theory and modeling, computational methods, and experiments, for forward and hovering flights with producing leading-edge vortex to yield unsteady high lift. (d) Prospects are explored on extracting prevailing intrinsic flow energy by fish and bird to enhance thrust for propulsion. (e) The mechanical and biological principles are drawn together for unified studies on the energetics in deriving metabolic power for animal locomotion, leading to the surprising discovery that the hydrodynamic viscous drag on swimming fish is largely associated with laminar boundary layers, thus drawing valid and sound evidences for a resounding resolution to the long-standing fish-swim paradox proclaimed by Gray (1936, 1968 ).

Laser direct writing of combinatorial libraries of idealized cellular constructs: Biomedical applications

NASA Astrophysics Data System (ADS)

Schiele, Nathan R.; Koppes, Ryan A.; Corr, David T.; Ellison, Karen S.; Thompson, Deanna M.; Ligon, Lee A.; Lippert, Thomas K. M.; Chrisey, Douglas B.

2009-03-01

The ability to control cell placement and to produce idealized cellular constructs is essential for understanding and controlling intercellular processes and ultimately for producing engineered tissue replacements. We have utilized a novel intra-cavity variable aperture excimer laser operated at 193 nm to reproducibly direct write mammalian cells with micrometer resolution to form a combinatorial array of idealized cellular constructs. We deposited patterns of human dermal fibroblasts, mouse myoblasts, rat neural stem cells, human breast cancer cells, and bovine pulmonary artery endothelial cells to study aspects of collagen network formation, breast cancer progression, and neural stem cell proliferation, respectively. Mammalian cells were deposited by matrix assisted pulsed laser evaporation direct write from ribbons comprised of a UV transparent quartz coated with either a thin layer of extracellular matrix or triazene as a dynamic release layer using CAD/CAM control. We demonstrate that through optical imaging and incorporation of a machine vision algorithm, specific cells on the ribbon can be laser deposited in spatial coherence with respect to geometrical arrays and existing cells on the receiving substrate. Having the ability to direct write cells into idealized cellular constructs can help to answer many biomedical questions and advance tissue engineering and cancer research.

Difference between manual and digital measurements of dental arches of orthodontic patients.

PubMed

Jiménez-Gayosso, Sandra Isabel; Lara-Carrillo, Edith; López-González, Saraí; Medina-Solís, Carlo Eduardo; Scougall-Vilchis, Rogelio José; Hernández-Martínez, César Tadeo; Colomé-Ruiz, Gabriel Eduardo; Escoffié-Ramirez, Mauricio

2018-06-01

The objective of this study was to compare the differences between the measurements performed manually to those obtained using a digital model scanner of patients with orthodontic treatment.A cross-sectional study was performed in a sample of 30 study models from patients with permanent dentition who attended a university clinic between January 2010 and December 2015. For the digital measurement, a Maestro 3D Ortho Studio scanner (Italy) was used and Mitutoyo electronic Vernier calipers (Kawasaki, Japan) were used for manual measurement. The outcome variables were the measurements for maxillary intercanine width, mandibular intercanine width, maxillary intermolar width, mandibular intermolar width, overjet, overbite, maxillary arch perimeter, mandibular arch perimeter, and palate height. The independent variables, besides age and sex, were a series of arc characteristics. The Student t test, paired Student t test, and Pearson correlation in SPSS version 19 were used for the analysis.Of the models, 60% were from women. Two of nine measurements for pre-treatment and 6 of 9 measurements for post-treatment showed a difference. The variables that were different between the manual and digital measurements in the pre-treatment were maxillary intermolar width and palate height (P < .05). Post-treatment, differences were found in mandibular intercanine width, palate height, overjet, overbite, and maxillary and mandibular arch perimeter (P < .05).The models measured manually and digitally showed certain similarities for both vertical and transverse measurements. There are many advantages offered to the orthodontist, such as easy storage; savings in time and space; facilitating the reproducibility of information; and conferring the security of not deteriorating over time. Its main disadvantage is the cost.

Ultrastructural Analysis of the Cristae Ampullares in the Squirrel Monkey (Saimiri sciureus)*

PubMed Central

Lysakowski, Anna; Goldberg, Jay M.

2008-01-01

Type I hair cells outnumber type II hair cells (HCs) in squirrel monkey (Saimiri sciureus) cristae by a nearly 3:1 ratio. Associated with this type I HC preponderance, calyx fibers make up a much larger fraction of the afferent innervation than in rodents (Fernández et al., 1995). To study how this affected synaptic architecture, we used disector methods to estimate various features associated with type I and type II HCs in central (CZ) and peripheral (PZ) zones of monkey cristae. Each type I HC makes, on average, 5–10 ribbon synapses with the inner face of a calyx ending. Inner-face synapses outnumber those on calyx outer faces by a 40:1 ratio. Expressed per afferent, there are, on average, 15 inner-face ribbon synapses, 0.38 outer-face ribbons and 2.6 efferent boutons on calyx-bearing endings. Calyceal invaginations per type I HC range from 19 in CZ to 3 in PZ. For type II HCs, there are many more ribbons and afferent boutons in PZ than in CZ, whereas efferent innervation is relatively uniform throughout the neuroepithelium. Despite outer-face ribbons being more numerous in chinchilla than in squirrel monkey, afferent discharge properties are similar (Lysakowski et al., 1995), reinforcing the importance of inner-face ribbons in synaptic transmission. Comparisons across mammalian species suggest the prevalence of type I HCs is a primate characteristic, rather than an arboreal lifestyle adaptation. Unlike cristae, type II HCs predominate in monkey maculae. Differences in hair-cell counts may reflect the stimulus magnitudes handled by semicircular canals and otolith organs. PMID:18729176

Body sway at sea for two visual tasks and three stance widths.

PubMed

Stoffregen, Thomas A; Villard, Sebastien; Yu, Yawen

2009-12-01

On land, body sway is influenced by stance width (the distance between the feet) and by visual tasks engaged in during stance. While wider stance can be used to stabilize the body against ship motion and crewmembers are obliged to carry out many visual tasks while standing, the influence of these factors on the kinematics of body sway has not been studied at sea. Crewmembers of the RN Atlantis stood on a force plate from which we obtained data on the positional variability of the center of pressure (COP). The sea state was 2 on the Beaufort scale. We varied stance width (5 cm, 17 cm, and 30 cm) and the nature of the visual tasks. In the Inspection task, participants viewed a plain piece of white paper, while in the Search task they counted the number of target letters that appeared in a block of text. Search task performance was similar to reports from terrestrial studies. Variability of the COP position was reduced during the Search task relative to the Inspection task. Variability was also reduced during wide stance relative to narrow stance. The influence of stance width was greater than has been observed in terrestrial studies. These results suggest that two factors that influence postural sway on land (variations in stance width and in the nature of visual tasks) also influence sway at sea. We conclude that--in mild sea states--the influence of these factors is not suppressed by ship motion.

Ribbon cutting opens new ELV offices

NASA Technical Reports Server (NTRS)

2000-01-01

Bobby Bruckner, manager, ELV and Payload Carrier Programs, speaks at the ribbon-cutting ceremony of the E&O Building at KSC. Home for NASA's unmanned missions since 1964, the building has been renovated to house the Expendable Launch Vehicle Program.

INFINITY ribbon-cutting

NASA Image and Video Library

2012-04-11

Clare Johnston, 10, and Eden Landis, 3, stare in wonder at the moon rock on display at the INFINITY at NASA Stennis Space Center visitor center and museum. The children toured INFINITY exhibits during ribbon-cutting activities for the facility April 11, 2012.

Maxillary and mandibular anterior crown width/height ratio and its relation to various arch perimeters, arch length, and arch width groups

PubMed Central

Shahid, Fazal; Alam, Mohammad Khursheed; Khamis, Mohd Fadhli

2015-01-01

Objective: To investigate the maxillary and mandibular anterior crown width/height ratio and its relation to various arch perimeters, arch length, and arch width (intercanine, interpremolar, and intermolar) groups. Materials and Methods: The calculated sample size was 128 subjects. The crown width/height, arch length, arch perimeter, and arch width of the maxilla and mandible were obtained via digital calliper (Mitutoyo, Japan). A total of 4325 variables were measured. The sex differences in the crown width and height were evaluated. Analysis of variance was applied to evaluate the differences between arch length, arch perimeter, and arch width groups. Results: Males had significantly larger mean values for crown width and height than females (P ≤ 0.05) for maxillary and mandibular arches, both. There were no significant differences observed for the crown width/height ratio in various arch length, arch perimeter, and arch width (intercanine, interpremolar, and intermolar) groups (P ≤ 0.05) in maxilla and mandible, both. Conclusions: Our results indicate sexual disparities in the crown width and height. Crown width and height has no significant relation to various arch length, arch perimeter, and arch width groups of maxilla and mandible. Thus, it may be helpful for orthodontic and prosthodontic case investigations and comprehensive management. PMID:26929686

On the granular fingering instability: controlled triggering in laboratory experiments and numerical simulations

NASA Astrophysics Data System (ADS)

Vriend, Nathalie; Tsang, Jonny; Arran, Matthew; Jin, Binbin; Johnsen, Alexander

2017-11-01

When a mixture of small, smooth particles and larger, coarse particles is released on a rough inclined plane, the initial uniform front may break up in distinct fingers which elongate over time. This fingering instability is sensitive to the unique arrangement of individual particles and is driven by granular segregation (Pouliquen et al., 1997). Variability in initial conditions create significant limitations for consistent experimental and numerical validation of newly developed theoretical models (Baker et al., 2016) for finger formation. We present an experimental study using a novel tool that sets the initial fingering width of the instability. By changing this trigger width between experiments, we explore the response of the avalanche breakup to perturbations of different widths. Discrete particle simulations (using MercuryDPM, Thornton et al., 2012) are conducted under a similar setting, reproducing the variable finger width, allowing validation between experiments and numerical simulations. A good agreement between simulations and experiments is obtained, and ongoing theoretical work is briefly introduced. NMV acknowledges the Royal Society Dorothy Hodgkin Research Fellowship.

Fabrication of metallic glass structures

DOEpatents

Cline, Carl F.

1986-01-01

Amorphous metal powders or ribbons are fabricated into solid shapes of appreciable thickness by the application of compaction energy. The temperature regime wherein the amorphous metal deforms by viscous flow is measured. The metal powders or ribbons are compacted within the temperature range.

Fabrication of metallic glass structures

DOEpatents

Cline, C.F.

1983-10-20

Amorphous metal powders or ribbons are fabricated into solid shapes of appreciable thickness by the application of compaction energy. The temperature regime wherein the amorphous metal deforms by viscous flow is measured. The metal powders or ribbons are compacted within the temperature regime.

Saturn -- Ribbon-like Wave Structure in Atmosphere

NASA Image and Video Library

1999-08-30

A view of Saturn clouds extending from 40 N latitude shows a ribbon-like wave structure in the south with small convective features marking a westward jet in the north. This image was obtained on November 10, 1980 by NASA Voyager 1.

Defect characterization of silicon dendritic web ribbons

NASA Technical Reports Server (NTRS)

Cheng, L. J.

1985-01-01

Progress made in the study of defect characterization of silicon dendritic web ribbon is presented. Chemical etching is used combined with optical microscopy, as well as the electron beam induced current (EBIC) technique. Thermal annealing effect on carrier lifetime is examined.

The Blue Ribbon Panel on Oxygenates in Gasoline : executive summary and recommendations.

DOT National Transportation Integrated Search

1999-07-27

In November, 1998, U.S. EPA Administrator Carol M. Browner appointed a Blue Ribbon : Panel to investigate the air quality benefits and water quality concerns associated with : oxygenates in gasoline, and to provide independent advice and recommendati...

Defect-mediated turbulence in ribbons of viscoelastic Taylor-Couette flow.

PubMed

Latrache, Noureddine; Abcha, Nizar; Crumeyrolle, Olivier; Mutabazi, Innocent

2016-04-01

Transition to defect-mediated turbulence in the ribbon patterns observed in a viscoelastic Taylor-Couette flow is investigated when the rotation rate of the inner cylinder is increased while the outer cylinder is fixed. In four polymer solutions with different values of the elasticity number, the defects appear just above the onset of the ribbon pattern and trigger the appearance of disordered oscillations when the rotation rate is increased. The flow structure around the defects is determined and the statistical properties of these defects are analyzed in the framework of the complex Ginzburg-Landau equation.

Cryogenic ribbon-cutting

NASA Image and Video Library

2011-03-30

NASA cut the ribbon on a new cryogenics control center at John C. Stennis Space Center on March 30. The new facility is part of a project to strengthen Stennis facilities to withstand the impacts of future storms like hurricane Katrina in 2005. Participants in the ribbon-cutting included (l to r): Jason Zuckerman, director of project management for The McDonnel Group; Keith Brock, director of the NASA Project Directorate at Stennis; Stennis Deputy Director Rick Gilbrech; Steve Jackson, outgoing program manager of the Jacobs Technology NASA Test Operations Group; and Troy Frisbie, Cryo Control Center Construction project manager for NASA Center Operations at Stennis.

Large area silicon sheet by EFG

NASA Technical Reports Server (NTRS)

1977-01-01

Some hypotheses to explain both of these features are advanced and the possible implications for solar cell performance are touched upon. The multiple ribbon growth system has shown a number of flaws with respect to the reliability of the basic furnace design. These definitely need to be rectified before any significant demonstration of multiple ribbon growth can proceed. The cartridges, however, have performed quite well. The work on 3" cartridge design and automatic controls has proceeded nearly on schedule and the report contains a detailed description of the approach and the equipment to be used for automatic control of ribbon growth.

Winding trajectories of noncircular composite shells

NASA Astrophysics Data System (ADS)

Nikityuk, V. A.; Fedorov, V. V.

1995-07-01

An approach has been proposed for determination of the trajectory parameters of a layer formed by winding of continuous ribbons on a complicated surface. An algorithm has been developed for determining the geodesic trajectories of the reinforcement fiber arrangement, reinforcement angles, and geodesic deviation angles. Conditions have been formulated for positional stability of the ribbons on the surface and avoidance of gaps and overlapping between the ribbons along with restrictions to the surface form. Results are given for a calculation of the geodesic turn parameters on a fuselage surface, which is not a surface of revolution, of a light airplane.

Electrophoretic deposition of graphene oxide on magnetic ribbon: Toward high sensitive and selectable magnetoimpedance response

NASA Astrophysics Data System (ADS)

Jamilpanah, L.; Azadian, S.; Shoa e Gharehbagh, J.; Haghniaz Jahromi, S.; Sheykhifard, Z.; Hosseinizadeh, S.; Erfanifam, S.; Hajiali, M. R.; Tehranchi, M. M.; Mohseni, S. M.

2018-07-01

Graphene oxide (GO) layers have shown to be fascinating elements for application in high performance sensors. They can be applied in multi-disciplinary designs based on surface selective sensing mechanisms. One immediate application of such surface sensitive elements is implementing of GO layer in magnetoimpedance (MI) sensors to improve their multi-functionality. In this paper, deposition of GO on the surface of Co-based amorphous ribbons (Co68.15Fe4.35Si12.5B15) is performed using electrophoretic deposition (EPD) method to evaluate the MI response. MI ratio increased from 271% (bare ribbon) up to 281% and 301% EPD GO deposited within 4 and 8 min, respectively. Similar experiment for the ribbon drop coated with GO was carried out while no enhancement in MI response was seen. Vertical growth of GO on the surface of the ribbon in EPD and drop coated layers observed by topographical measurements. We explained the difference between the MI responses based on layers verticality and surface coverage. UV-Visible absorption and Raman spectroscopy were used to study the nature of GO. Gaining a high surface area of GO along with their biocompatible and anticorrosive properties atop the MI sensors can open pathways towards increasing applications of surface selective and high sensitive MI sensors.

Temperature dependent evolution of wrinkled single-crystal silicon ribbons on shape memory polymers.

PubMed

Wang, Yu; Yu, Kai; Qi, H Jerry; Xiao, Jianliang

2017-10-25

Shape memory polymers (SMPs) can remember two or more distinct shapes, and thus can have a lot of potential applications. This paper presents combined experimental and theoretical studies on the wrinkling of single-crystal Si ribbons on SMPs and the temperature dependent evolution. Using the shape memory effect of heat responsive SMPs, this study provides a method to build wavy forms of single-crystal silicon thin films on top of SMP substrates. Silicon ribbons obtained from a Si-on-insulator (SOI) wafer are released and transferred onto the surface of programmed SMPs. Then such bilayer systems are recovered at different temperatures, yielding well-defined, wavy profiles of Si ribbons. The wavy profiles are shown to evolve with time, and the evolution behavior strongly depends on the recovery temperature. At relatively low recovery temperatures, both wrinkle wavelength and amplitude increase with time as evolution progresses. Finite element analysis (FEA) accounting for the thermomechanical behavior of SMPs is conducted to study the wrinkling of Si ribbons on SMPs, which shows good agreement with experiment. Merging of wrinkles is observed in FEA, which could explain the increase of wrinkle wavelength observed in the experiment. This study can have important implications for smart stretchable electronics, wrinkling mechanics, stimuli-responsive surface engineering, and advanced manufacturing.

Laser based thermo-conductometry as an approach to determine ribbon solid fraction off-line and in-line.

PubMed

Wiedey, Raphael; Šibanc, Rok; Kleinebudde, Peter

2018-06-06

Ribbon solid fraction is one of the most important quality attributes during roll compaction/dry granulation. Accurate and precise determination is challenging and no in-line measurement tool has been generally accepted, yet. In this study, a new analytical tool with potential off-line as well as in-line applicability is described. It is based on the thermo-conductivity of the compacted material, which is known to depend on the solid fraction. A laser diode was used to punctually heat the ribbon and the heat propagation monitored by infrared thermography. After performing a Gaussian fit of the transverse ribbon profile, the scale parameter σ showed correlation to ribbon solid fraction in off-line as well as in-line studies. Accurate predictions of the solid fraction were possible for a relevant range of process settings. Drug stability was not affected, as could be demonstrated for the model drug nifedipine. The application of this technique was limited when using certain fillers and working at higher roll speeds. This study showed the potentials of this new technique and is a starting point for additional work that has to be done to overcome these challenges. Copyright © 2018 Elsevier B.V. All rights reserved.

Longitudinal Changes of Angle Configuration in Primary Angle-Closure Suspects

PubMed Central

Jiang, Yuzhen; Chang, Dolly S.; Zhu, Haogang; Khawaja, Anthony P.; Aung, Tin; Huang, Shengsong; Chen, Qianyun; Munoz, Beatriz; Grossi, Carlota M.

2015-01-01

Objective To determine longitudinal changes in angle configuration in the eyes of primary angle-closure suspects (PACS) treated by laser peripheral iridotomy (LPI) and in untreated fellow eyes. Design Longitudinal cohort study. Participants Primary angle-closure suspects aged 50 to 70 years were enrolled in a randomized, controlled clinical trial. Methods Each participant was treated by LPI in 1 randomly selected eye, with the fellow eye serving as a control. Angle width was assessed in a masked fashion using gonioscopy and anterior segment optical coherence tomography (AS-OCT) before and at 2 weeks, 6 months, and 18 months after LPI. Main Outcome Measures Angle width in degrees was calculated from Shaffer grades assessed under static gonioscopy. Angle configuration was also evaluated using angle opening distance (AOD250, AOD500, AOD750), trabecular-iris space area (TISA500, TISA750), and angle recess area (ARA) measured in AS-OCT images. Results No significant difference was found in baseline measures of angle configuration between treated and untreated eyes. At 2 weeks after LPI, the drainage angle on gonioscopy widened from a mean of 13.5° at baseline to a mean of 25.7° in treated eyes, which was also confirmed by significant increases in all AS-OCT angle width measures (P<0.001 for all variables). Between 2 weeks and 18 months after LPI, a significant decrease in angle width was observed over time in treated eyes (P<0.001 for all variables), although the change over the first 5.5 months was not statistically significant for angle width measured under gonioscopy (P = 0.18), AOD250 (P = 0.167) and ARA (P = 0.83). In untreated eyes, angle width consistently decreased across all follow-up visits after LPI, with a more rapid longitudinal decrease compared with treated eyes (P values for all variables ≤0.003). The annual rate of change in angle width was equivalent to 1.2°/year (95% confidence interval [CI], 0.8–1.6) in treated eyes and 1.6°/year (95% CI, 1.3–2.0) in untreated eyes (P<0.001). Conclusions Angle width of treated eyes increased markedly after LPI, remained stable for 6 months, and then decreased significantly by 18 months after LPI. Untreated eyes experienced a more consistent and rapid decrease in angle width over the same time period. PMID:24835757

Using a Bayesian network to predict barrier island geomorphologic characteristics

USGS Publications Warehouse

Gutierrez, Ben; Plant, Nathaniel G.; Thieler, E. Robert; Turecek, Aaron

2015-01-01

Quantifying geomorphic variability of coastal environments is important for understanding and describing the vulnerability of coastal topography, infrastructure, and ecosystems to future storms and sea level rise. Here we use a Bayesian network (BN) to test the importance of multiple interactions between barrier island geomorphic variables. This approach models complex interactions and handles uncertainty, which is intrinsic to future sea level rise, storminess, or anthropogenic processes (e.g., beach nourishment and other forms of coastal management). The BN was developed and tested at Assateague Island, Maryland/Virginia, USA, a barrier island with sufficient geomorphic and temporal variability to evaluate our approach. We tested the ability to predict dune height, beach width, and beach height variables using inputs that included longer-term, larger-scale, or external variables (historical shoreline change rates, distances to inlets, barrier width, mean barrier elevation, and anthropogenic modification). Data sets from three different years spanning nearly a decade sampled substantial temporal variability and serve as a proxy for analysis of future conditions. We show that distinct geomorphic conditions are associated with different long-term shoreline change rates and that the most skillful predictions of dune height, beach width, and beach height depend on including multiple input variables simultaneously. The predictive relationships are robust to variations in the amount of input data and to variations in model complexity. The resulting model can be used to evaluate scenarios related to coastal management plans and/or future scenarios where shoreline change rates may differ from those observed historically.