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Results for “switching ratio”

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At least 253 records · Page 14

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NASA NTRS1991

Theory and simulation of a high-frequency magnetic drift wave

The equilibrium of a nonneutral plasma in a toroidal vessel with a toroidal magnetic field is analyzed. In the zero inertia limit it is heuristically shown from force balance considerations that there is an electrostatic hoop force and a force due to diamagnetism along the major radius. The problem of equilibrium is formulated in terms of solutions of a 2D partial difference equation. This equation is solved in the large-aspect-ratio limit and a general expression for the shift of the potential axis is obtained which shows that the shift is approximately epsilon and that it depends solely on the internal capacitance of the cloud. The simulation study is based upon the modified MHD equations and the nonlocal nature of the mode is investigated. Applications to sub-Alfvenic plasma expansions, electromagnetic waves in the earth's magnetosphere, and plasma switches are discussed.

Huba, J. D.↗

NASA NTRS1983

Ozone and water vapor monitoring using a ground-based lidar system

Measurements of atmospheric ozone and water vapor profiles obtained using a differential absorption lidar (DIAL) technique at Haute Provence Observatory are reported. The DIAL technique is based on the comparison of differences in attenuation in backscattered signals at wavelengths centered on strong absorptions or absorption lines of the species in question, and wavelengths corresponding to weaker or no absorption. The system in use is based on three lasers - a Nd:YAG Q-switched laser frequency doubled to emit at 532 nm, and two tunable narrowline dye lasers used to convert this emission into the IR or UV spectral regions. Ozone concentration profiles have been recorded up to a height of 30 km, and reveal large day-to-day variations in number density which were correlated with a decrease in tropopause height. Measurements of water vapor concentrations show a variability of the mixing ratio at heights up to 2.5 km representative of dynamic processes, and a variability above 2.5 km that is within the measurement error. Day-to-day variations in tropospheric mixing ratio were also observed.

Megie, G.↗

DOE OSTI2021

Suppression of the vacuum space-charge effect in fs-photoemission by a retarding electrostatic front lens

The performance of time-resolved photoemission experiments at fs-pulsed photon sources is ultimately limited by the e–e Coulomb interaction, downgrading energy and momentum resolution. Here, we present an approach to effectively suppress space-charge artifacts in momentum microscopes and photoemission microscopes. A retarding electrostatic field generated by a special objective lens repels slow electrons, retaining the k-image of the fast photoelectrons. The suppression of space-charge effects scales with the ratio of the photoelectron velocities of fast and slow electrons. Fields in the range from -20 to 01100 V/mm for E kin = 100 eV to 4 keV direct secondaries and pump-induced slow electrons back to the sample surface. Ray tracing simulations reveal that this happens within the first 40 to 3 μm above the sample surface for E kin = 100 eV to 4 keV. An optimized front-lens design allows switching between the conventional accelerating and the new retarding mode. Time-resolved experiments at E kin = 107 eV using fs extreme ultraviolet probe pulses from the free-electron laser FLASH reveal that the width of the Fermi edge increases by just 30 meV at an incident pump fluence of 22 mJ/cm2 (retarding field -21 V/mm). For an accelerating field of +2 kV/mm and a pump fluence of only 5 mJ/cm 2 , it increases by 0.5 eV (pump wavelength 1030 nm). At the given conditions, the suppression mode permits increasing the slow-electron yield by three to four orders of magnitude. The feasibility of the method at high energies is demonstrated without a pump beam at E kin = 3830 eV using hard x rays from the storage ring PETRA III. The approach opens up a previously inaccessible regime of pump fluences for photoemission experiments.

47 OTHER INSTRUMENTATION↗

DOE OSTI2023

Scalable photonic integrated circuits for high-fidelity light control

Advances in laser technology have driven discoveries in atomic, molecular, and optical (AMO) physics and emerging applications, from quantum computers with cold atoms or ions, to quantum networks with solid-state color centers. This progress is motivating the development of a new generation of optical control systems that can manipulate the light field with high fidelity at wavelengths relevant for AMO applications. These systems are characterized by criteria: (C1) operation at a design wavelength of choice in the visible (VIS) or near-infrared (IR) spectrum, (C2) a scalable platform that can support large channel counts, (C3) high-intensity modulation extinction and (C4) repeatability compatible with low gate errors, and (C5) fast switching times. Here, we provide a pathway to address these challenges by introducing an atom control architecture based on VIS-IR photonic integrated circuit (PIC) technology. Based on a complementary metal–oxide–semiconductor fabrication process, this atom-control PIC (APIC) technology can meet system requirements (C1)–(C5). As a proof of concept, we demonstrate a 16-channel silicon-nitride-based APIC with (5.8±0.4)ns response times and >30dB extinction ratio at a wavelength of 780 nm.

Menssen, Adrian J.↗

NASA NTRS1989

Satellite-matrix-switched, time-division-multiple-access network simulator

A versatile experimental Ka-band network simulator has been implemented at the NASA Lewis Research Center to demonstrate and evaluate a satellite-matrix-switched, time-division-multiple-access (SMS-TDMA) network and to evaluate future digital ground terminals and radiofrequency (RF) components. The simulator was implemented by using proof-of-concept RF components developed under NASA contracts and digital ground terminal and link simulation hardware developed at Lewis. This simulator provides many unique capabilities such as satellite range delay and variation simulation and rain fade simulation. All network parameters (e.g., signal-to-noise ratio, satellite range variation rate, burst density, and rain fade) are controlled and monitored by a central computer. The simulator is presently configured as a three-ground-terminal SMS-TDMA network.

Ivancic, William D.↗

NASA NTRS1990

Satellite-matrix-switched, time-division-multiple-access network simulator

Ivancic, William D.↗

NASA NTRS1972

A proposed magnetic digital temperature transducer, volume 1

A study has been made of the feasibility of using the discontinuous permeability versus temperature characteristics of some magnetic materials for a digital temperature transducer and a thermally controlled ON-OFF switch. Simple logic converts the number of output pulse to a digital word recognizable by the system. Efforts have been concentrated on materials with Curie temperatures between 0 and 100 C. One compound has the composition Mn(5-x)Fe(x)Ge3 where the amount of iron determines the transition temperature. The other compound is Ni-Zn ferrite and has the compositon Ni(1-x)Zn(x)Fe(1.95)O4 where the nickel: zinc ratio determines the transition temperature. A detailed report of materials prepared is presented. Toroidal inductors of the material have been constructed and the change in inductance with temperature measured. In view of these initial measurements, it is felt that a transducer utilizing the permeability versus temperature characteristics of these materials has promise as a reliable and sensitive solid state digital temperature transducer.

Collier, T. E.↗

NASA NTRS2002

Durability of Solar Selective Coatings in a Simulated Space Environment

Solar selective coatings are being considered for heat engine and thermal switching applications on minisatellites. Such coatings must have the combined properties of high solar absorptance and low infrared emittance. High solar absorptance is needed to collect solar energy as efficiently as possible while low infrared emittance is needed to minimize radiant energy loss at operating temperature. These properties are achieved in sputter deposited thin films through the use of molecular mixtures of metal and dielectric. Solar selective coatings having a solar absorptance to infrared emittance ratio of 9 have been successfully deposited using a mixture of nickel and aluminum oxide. The space environment, however, presents some challenges for the use of materials on the exterior of spacecraft, including durability to atomic oxygen and vacuum ultraviolet radiation. To address these concerns, several candidate solar selective coatings were exposed to atomic oxygen in a plasma asher and to ultraviolet radiation in a vacuum facility equipped with calibrated deuterium lamps. The optical properties of the coatings were monitored as a function of time to evaluate their performance over long term exposure to the simulated space environment. Several coatings were found to be durable to both the atomic oxygen and the vacuum ultraviolet environments.

Jaworske, Donald A.↗

DOE OSTI2024

Reversible two-way tuning of thermal conductivity in an end-linked star-shaped thermoset

Polymeric thermal switches that can reversibly tune and significantly enhance their thermal conductivities are desirable for diverse applications in electronics, aerospace, automotives, and medicine; however, they are rarely achieved. Here, we report a polymer-based thermal switch consisting of an end-linked star-shaped thermoset with two independent thermal conductivity tuning mechanisms—strain and temperature modulation—that rapidly, reversibly, and cyclically modulate thermal conductivity. The end-linked star-shaped thermoset exhibits a strain-modulated thermal conductivity enhancement up to 11.5 at a fixed temperature of 60 °C (increasing from 0.15 to 2.1 W m –1 K –1 ). Additionally, it demonstrates a temperature-modulated thermal conductivity tuning ratio up to 2.3 at a fixed stretch of 2.5 (increasing from 0.17 to 0.39 W m –1 K –1 ). When combined, these two effects collectively enable the end-linked star-shaped thermoset to achieve a thermal conductivity tuning ratio up to 14.2. Moreover, the end-linked star-shaped thermoset demonstrates reversible tuning for over 1000 cycles. The reversible two-way tuning of thermal conductivity is attributed to the synergy of aligned amorphous chains, oriented crystalline domains, and increased crystallinity by elastically deforming the end-linked star-shaped thermoset.

42 ENGINEERING↗

DOE OSTI2025

Amorphous Indium Oxide Channel FEFETs With Write Voltage of 0.9 V and Endurance >10 12 for Refresh-Free Embedded Memory

This work presents, for the first time, a back-end-of-the-line (BEOL)-compatible W-doped indium oxide (IWO) ferroelectric field-effect transistor (FEFET) with a record-low operating voltage below 0.9 V and a write speed of 20 ns while achieving a transient read current window (CW) ratio ( I LVT /I HVT ) greater than 10 4 . The device also exhibits exceptional reliability characteristics such as: 1) measured bipolar write endurance up to 10 12 cycles; 2) a fast read speed of 50 ns; 3) read endurance surpassing 10 12 cycles; and 4) retention exceeding 10 4 s at 85 ∘ C. Furthermore, a physics-based numerical model has been developed to investigate the nanoscale characteristics of BEOL FEFET devices, leveraging nucleation-limited switching in HfO 2 ferroelectrics and dc characterization to extract material and channel parameters for accurate device simulation. The simulation uncovers the stochastic switching behavior of BEOL amorphous oxide semiconductor (AOS) FEFETs and demonstrates an intrinsic switching time as low as 1 ps, highlighting the potential of BEOL AOS FEFETs for ultrafast memory applications. These results establish AOS FEFETs as a compelling candidate for high-density embedded memory applications for last-level cache (LLC) (L4) in advanced CMOS technology nodes.

1-V ferroelectric field-effect transistor (FEFET)↗

NASA NTRSDate not supplied

10-kHz PLIF Thermometry for a Turbulent Jet Flame using Single Burst-mode OPO

Two-color Planar laser-induced fluorescence (TC-PLIF) thermometry techniques that employ two laser systems and two cameras face challenges when implemented in practical combustion facilities because of experimental complexity and multiple laser and camera requirements, particularly for high-speed TC-PLIF. To circumvent those problems, we developed a fast, dual-wavelength switching, burst-mode OPO technology to significantly reduce the experimental complexity of high-speed TC-PLIF thermometry and simplify its implementation in harsh combustion and flow test facilities. A fast, dual-wavelength switched seed laser enabled a high-energy, high-repetition-rate burst-mode laser to generate two 10-kHz pulse trains at wavelengths of ~354.8 nm. The injection-seeded OPO efficiently converts the burst-mode laser output to285.62 nm and 285.67 nm to excite the Q2(12) and P1(8) OH transitions. PLIF images were collected from each of the two excitation transitions with a single camera and an UV intensifier, and intensity ratios from the images were used to determine local temperatures. Ten kHz hydroxyl radical (OH) TC-PLIF for premixedCH4/Air/H2 jet flame was demonstrated.

thermometry↗

NASA NTRSDate not supplied

10-kHz PLIF Thermometry for Turbulent Jet Flame using Single Burst-mode OPO

Two-color Planar Laser-Induced Fluorescence (TC-PLIF) thermometry techniques that employ two laser systems and two cameras face challenges when implemented in practical combustion facilities because of experimental complexity and multiple laser and camera requirements, particularly for high-speed TC-PLIF. To circumvent those problems, we developed a fast, dual-wavelength switching, burst-mode OPO technology to significantly reduce the experimental complexity of high-speed TC-PLIF thermometry and simplify its implementation in harsh combustion and flow test facilities. A fast, dual-wavelength switched seed laser enabled a high-energy, high-repetition-rate burst-mode laser to generate two 10-kHz pulse trains at wavelengths of ~354.8 nm. The injection-seeded OPO efficiently converts the burst-mode laser output to 285.62 nm and 285.67 nm to excite the Q2(12) andP1(8) OH transitions. PLIF images were collected from each of the two excitation transitions with a single camera and an UV intensifier, and intensity ratios from the images were used to determine local temperatures. Ten kHz hydroxyl radical (OH) TC-PLIF for premixedCH4/Air/H2 jet flame was demonstrated.

thermometry↗

NASA NTRS1940

Correlation of knocking characteristics of fuels in an engine having a hemispherical combustion chamber

Data are presented to show the effects of inlet-air pressure, inlet-air temperature, and compression ratio on the maximum permissible performance obtained with having a hemispherical-dome combustion chamber. The five aircraft-engine fuels used have octane numbers varying from 90 to 100 plus 2 ml of tetraethyl lead per gallon. The data were obtained on a 5 1/4-inch by 4 3/4-inch liquid-cooled engine operating at 2,500 r.p.m. The compression ratio was varied from 6.0 to 8.9. The inlet-air temperature was varied from 110 to 310 F. For each set of conditions, the inlet-air pressure was increased until audible knock occurred and then reduced 2 inches of mercury before data were recorded. The results for each fuel can be correlated by plotting the calculated end-gas density factor against the calculated end-gas temperature. Measurements of spark-plugs, cutting off the switch to one spark plug lowered the electrode temperature of that plug from a value of 1,365 F to a value of 957 F. The results indicate that the surface temperatures of combustion-chamber areas which become new sources of ignition markedly increase after ignition.

Rothrock, A M↗

DOE OSTI2025

Testing of Novel Semiconductor Opening Switches Using Magnetic Switching

The performance of semiconductor opening switch (SOS) diodes with different doping profiles is assessed with the primary aim of enhancing or substituting hard-to-find devices. SOS devices are capable of providing long lifetime, gigawatt level pulses in generators with risetimes on the nanosecond scale with pulse widths on the order of 20 ns. An experimental testbed is described which allows for rapid testing of diodes with control of the forward pumping time which is a crucial parameter of SOS diodes. A saturable pulse transformer provides both the initial voltage multiplication and reverse current pulse required to drive SOS diodes. Voltage multiplication ratios of 16:1 were achieved with a modest charging voltage of 800 V and simple circuitry. With current densities of up to 1.4 kA ⋅ cm -2 , the testbed produces 10 kV output pulses into a 56 Ω load with a pulsewidth of 16 ns and delivered power of up to 1.9 MW. These novel devices are compared to legacy SOS diodes originating from Russia, with one of the profiles yielding increased performance. Finally, these profiles are studied in hopes of creating manufacturing demand to augment the availability of these useful devices.

drift step recovery diodes↗

DOE OSTI2021

Ferroelectrics everywhere: Ferroelectricity in magnesium substituted zinc oxide thin films

We demonstrate ferroelectricity in Mg-substituted ZnO thin films with the wurtzite structure. Zn 1–x Mg x O films are grown by dual-cathode reactive magnetron sputtering on (111)-Pt // (0001)-Al 2 O 3 substrates at temperatures ranging from 26 to 200 °C for compositions spanning from x = 0 to x = 0.37. X-ray diffraction indicates a decrease in the c-lattice parameter and an increase in the a-lattice parameter with increasing Mg content, resulting in a nearly constant c/a axial ratio of 1.595 over this composition range. Transmission electron microscopy studies show abrupt interfaces between Zn 1–x Mg x O films and the Pt electrode. When prepared at pO 2 = 0.025, film surfaces are populated by abnormally oriented grains as measured by atomic force microscopy for Mg concentrations >29%. Raising pO 2 to 0.25 eliminates the misoriented grains. Optical measurements show increasing bandgap values with increasing Mg content. When prepared on a 200 °C substrate, films display ferroelectric switching with remanent polarizations exceeding 100 μC cm –2 and coercive fields below 3 MVcm –1 when the Mg content is between ~30% and ~7%. Substrate temperature can be lowered to ambient conditions, and when doing so, capacitor stacks show only minor sacrifices to crystal orientation and nearly identical remanent polarization values; however, coercive fields drop below 2 MV/cm. Using ambient temperature deposition, we demonstrate ferroelectric capacitor stacks integrated directly with polymer substrate surfaces.

36 MATERIALS SCIENCE↗

DOE OSTI2020

In-situ resonant band engineering of solution-processed semiconductors generates high performance n-type thermoelectric nano-inks

Thermoelectric devices possess enormous potential to reshape the global energy landscape by converting waste heat into electricity, yet their commercial implementation has been limited by their high cost to output power ratio. No single “champion” thermoelectric material exists due to a broad range of material-dependent thermal and electrical property optimization challenges. While the advent of nanostructuring provided a general design paradigm for reducing material thermal conductivities, there exists no analogous strategy for homogeneous, precise doping of materials. Here, we demonstrate a nanoscale interface-engineering approach that harnesses the large chemically accessible surface areas of nanomaterials to yield massive, finely-controlled, and stable changes in the Seebeck coefficient, switching a poor nonconventional p- type thermoelectric material, tellurium, into a robust n -type material exhibiting stable properties over months of testing. These remodeled, n -type nanowires display extremely high power factors (~500 µW m -1 K -2 ) that are orders of magnitude higher than their bulk p -type counterparts.

42 ENGINEERING↗

NASA NTRS2002

Intermittent Flow Regimes in a Transonic Fan Airfoil Cascade

A study was conducted in the NASA Glenn Research Center linear cascade on the intermittent flow on the suction surface of an airfoil section from the tip region of a modern low aspect ratio fan blade. Experimental results revealed that, at a large incidence angle, a range of transonic inlet Mach numbers exist where the leading-edge shock-wave pattern was unstable. Flush mounted high frequency response pressure transducers indicated large local jumps in the pressure in the leading edge area, which generates large intermittent loading on the blade leading edge. These measurements suggest that for an inlet Mach number between 0.9 and 1.0 the flow is bi-stable, randomly switching between subsonic and supersonic flows. Hence, it appears that the change in overall flow conditions in the transonic region is based on the frequency of switching between two stable flow states rather than on the continuous increase of the flow velocity. To date, this flow behavior has only been observed in a linear transonic cascade. Further research is necessary to confirm this phenomenon occurs in actual transonic fans and is not the byproduct of an endwall restricted linear cascade.

Lepicovsky, J.↗

DOE OSTI2025

Optomechanical Tuning of Second Harmonic Generation Anisotropy in Janus MoSSe/MoS 2 Heterostructures

Symmetry breaking in van der Waals materials enables the realization of quantum states and advanced device functionalities. Janus transition-metal dichalcogenides (TMDs) exhibit distinctive nonlinear optical properties due to their broken out-of-plane mirror symmetry. However, the dynamic control of second harmonic generation (SHG) anisotropy and resonance behavior via optical excitation remains elusive. Here, in this work, we investigate the SHG response of Janus MoSSe/MoS 2 heterostructures with 2H and 3R stackings. We can tune the SHG response by varying the incident photon wavelength from 800 to 1000 nm, which shows a resonance-dependent enhancement in intensity and a deviation from 6-fold symmetry, indicating wavelength-dependent anisotropy. The ratio between maximum and minimum intensity in the armchair directions, associated with the SHG anisotropy, reaches a value of 1.73 at the excitation wavelength of 1000 nm. Group theory analysis and first-principles calculations reveal that the observed anisotropy arises from optically induced strain. Our findings highlight the role of symmetry breaking and optical resonance contributing to the optomechanical tuning of SHG anisotropy, offering opportunities for developing Janus TMD-based photonic devices for frequency conversion, light generation, and optical switching.

Janus transition metal dichalcogenides↗