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At least 55 records · Page 3

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NASA NTRS2011

Vacuum Nuller Testbed (VNT) Performance, Characterization and Null Control: Progress Report

Herein we report on the development. sensing and control and our first results with the Vacuum Nuller Testbed to realize a Visible Nulling Coronagraph (VNC) for exoplanet coronagraphy. The VNC is one of the few approaches that works with filled. segmented and sparse or diluted-aperture telescope systems. It thus spans a range of potential future NASA telescopes and could be Hown as a separate instrument on such a future mission. NASA/Goddard Space Flight Center (GSFC) has a well-established effort to develop VNC technologies. and has developed an incremental sequence of VNC testbeds to advance this approach and the enabling technologies associated with it. We discuss the continued development of the vacuum Visible Nulling Coronagraph testbed (VNT). Tbe VNT is an ultra-stable vibration isolated testbed that operates under closed-loop control within a vacuum chamber. It will be used to achieve an incremental sequence of three visible-light nulling milestones with sequentially higher contrasts of 10(sup 8), 10(sup 9) and ideally 10(sup 10) at an inner working angle of 2*lambda/D. The VNT is based on a modified Mach-Zehnder nulling interferometer, with a "W" configuration to accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters. We discuss the initial laboratory results, the optical configuration, critical technologies and the null sensing and control approach.

Lyon, Richard G.↗

NASA NTRS2012

High Contrast Vacuum Nuller Testbed (VNT) Contrast, Performance and Null Control

Herein we report on our contrast assessment and the development, sensing and control of the Vacuum Nuller Testbed to realize a Visible Nulling Coronagraphy (VNC) for exoplanet detection and characterization. Tbe VNC is one of the few approaches that works with filled, segmented and sparse or diluted-aperture telescope systems. It thus spans a range of potential future NASA telescopes and could be flown as a separate instrument on such a future mission. NASA/Goddard Space Flight Center has an established effort to develop VNC technologies, and an incremental sequence of testbeds to advance this approach and its critical technologies. We discuss the development of the vacuum Visible Nulling Coronagraph testbed (VNT). The VNT is an ultra-stable vibration isolated testbed that operates under closed-loop control within a vacuum chamber. It will be used to achieve an incremental sequence of three visible-light nulling milestones with sequentially higher contrasts of 10(exp 8), 10(exp 9) and ideally 10(exp 10) at an inner working angle of 2*lambda/D. The VNT is based on a modified Mach-Zehnder nulling interferometer, with a "W" configuration to accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters. We discuss the laboratory results, optical configuration, critical technologies and the null sensing and control approach.

Lyon, Richard G.↗

NASA NTRS2013

Current Structure and Nonideal Behavior at Magnetic Null Points in the Turbulent Magnetosheath

The Poincaré index indicates that the Cluster spacecraft tetrahedron entraps a number of 3-D magnetic nulls during an encounter with the turbulent magnetosheath. Previous researchers have found evidence for reconnection at one of the many filamentary current layers observed by Cluster in this region. We find that many of the entrained nulls are also associated with strong currents. We dissect the current structure of a pair of spiral nulls that may be topologically connected. At both nulls, we find a strong current along the spine, accompanied by a somewhat more modest current perpendicular to the spine that tilts the fan toward the axis of the spine. The current along the fan is comparable to the that along the spine. At least one of the nulls manifests a rotational flow pattern in the fan plane that is consistent with torsional spine reconnection as predicted by theory. These results emphasize the importance of examining the magnetic topology in interpreting the nature of currents and reconnection in 3-D turbulence.

cluster↗

NASA NTRS2024

Direct Imaging of Magnetohydrodynamic Wave Mode Conversion Near A 3D Null Point on the Sun

Mutual conversion of various kinds of magnetohydrodynamic (MHD) waves can have profound impacts on wave propagation, energy transfer, and heating of the solar chromosphere and corona. Mode conversion occurs when an MHD wave travels through a region where the Alfvén and sound speeds are equal (e.g., a 3D magnetic null point). Here we report the direct extreme ultraviolet (EUV) imaging of mode conversion from a fast-mode to a slow-mode MHD wave near a 3D null point using Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) observations. An incident fast EUV wavefront associated with an adjacent eruptive flare propagates laterally through a neighboring pseudostreamer. Shortly after the passage of the fast EUV wave through the null point, a slow-mode wave appears near the null that propagates upward along the open structures and simultaneously downward along the separatrix encompassing the fan loops of the pseudostreamer base. These observations suggest the existence of mode conversion near 3D nulls in the solar corona, as predicted by theory and MHD simulations. Moreover, we observe decaying transverse oscillations in both the open and closed structures of the pseudostreamer, along with quasiperiodic type III radio bursts indicative of repetitive episodes of electron acceleration.

Pankaj Kumar↗

NASA NTRS2006

Adaptive Nulling for the Terrestrial Planet Finder Interferometer

A description of adaptive nulling for Terrestrial Planet Finder Interferometer (TPFI) is presented. The topics include: 1) Nulling in TPF-I; 2) Why Do Adaptive Nulling; 3) Parallel High-Order Compensator Design; 4) Phase and Amplitude Control; 5) Development Activates; 6) Requirements; 7) Simplified Experimental Setup; 8) Intensity Correction; and 9) Intensity Dispersion Stability. A short summary is also given on adaptive nulling for the TPFI.

adaptive nulling↗

NASA NTRS2003

The Visible Nulling Coronagraph--Progress Toward Mission and Technology Development

This paper describes a space mission for visible direct detection and spectroscopy of Earth like extrasolar planets using a nulling coronagraph instrument behind a moderately sized (approximately 4m) telescope in space. In our design, a 4 beam nulling interferometer is synthesized from the telescope pupil, producing a deep null proportional to theta (sup 4) which is then filtered by a coherent array of single mode fibers to suppress the residual scattered light. With diffraction limited telescope optics and similar quality components in the optical train (lambda/20), suppression of the starlight to 10 (exp -10) is achievable. We describe key features of the basic analysis, show how this effects a space mission design, present latest results of laboratory measurements demonstrating achievable null depth and component development, and discuss future key technical milestones.

coronagraph↗

NASA NTRS2012

High Contrast Vacuum Nuller Testbed (VNT) Contrast, Performance and Null Control

Herein we report on our Visible Nulling Coronagraph high-contrast result of 109 contrast averaged over a focal planeregion extending from 14 D with the Vacuum Nuller Testbed (VNT) in a vibration isolated vacuum chamber. TheVNC is a hybrid interferometriccoronagraphic approach for exoplanet science. It operates with high Lyot stopefficiency for filled, segmented and sparse or diluted-aperture telescopes, thereby spanning the range of potential futureNASA flight telescopes. NASAGoddard Space Flight Center (GSFC) has a well-established effort to develop the VNCand its technologies, and has developed an incremental sequence of VNC testbeds to advance this approach and itsenabling technologies. These testbeds have enabled advancement of high-contrast, visible light, nulling interferometry tounprecedented levels. The VNC is based on a modified Mach-Zehnder nulling interferometer, with a W configurationto accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters.We give an overview of the VNT and discuss the high-contrast laboratory results, the optical configuration, criticaltechnologies and null sensing and control.

visible nulling coronagraph↗

NASA NTRS2020

An Overview of the Null-Field Method. I. Formulation and Basic Results

In this paper we revisit the fundamentals of the null-field method with discrete sources. We prove the unique solvability of the null-field equations for the total field inside the particle and the internal field outside the particle, at all wavenumbers. For this purpose, we use the equivalence between the null-field and surface integral equations methods. Furthermore, we discuss the completeness property of different systems of discrete sources for a surface field approximation, and derive an infinite set of integral equations for the surface fields in a variety of discrete sources. Finally, we formulate the null-field scheme as an approach aiming to construct an approximate solution to the scattering problem. The way in which we introduce the matrix of a particle is different from the standard approach relying on the assumption that the system of regular vector spherical wave functions for the interior problem is a basis.

Null-field method↗

NASA NTRS2002

Nulling interferometry progress

The field of nulling interferometry has seen significant progress over the past several years, in both the conceptual and experimental arenas. Deep, broadband nulling has been demonstrated at optical wavelengths, the techniques have seen initial implementation on telescopes, and the introduction of a symmetric beam-combiner concept has eliminated many of the residual obstacles. Here an overview is provided of promising techniques for effecting the deep cancellation of starlight, and recent results obtained with laboratory and astronomical nulling interferometers are discussed. The next step is the exploitation of nulling techniques at 8-10 m class separated-aperture telescope facilities, and in this vein, a brief overview of the architecture of the Keck Interferometer Nuller is also provided.

Nulling↗

DOE OSTI2021

A Rényi quantum null energy condition: proof for free field theories

The Quantum Null Energy Condition (QNEC) is a lower bound on the stress-energy tensor in quantum field theory that has been proved quite generally. It can equivalently be phrased as a positivity condition on the second null shape derivative of the relative entropy S rel (ρ||σ) of an arbitrary state ρ with respect to the vacuum σ. The relative entropy has a natural one-parameter family generalization, the Sandwiched Rényi divergence S n (ρ||σ), which also measures the distinguishability of two states for arbitrary n ∈ [1/2, ∞). A Rényi QNEC, a positivity condition on the second null shape derivative of S n (ρ||σ), was conjectured in previous work. In this work, we study the Rényi QNEC for free and superrenormalizable field theories in spacetime dimension d > 2 using the technique of null quantization. In the above setting, we prove the Rényi QNEC in the case n > 1 for arbitrary states. We also provide counterexamples to the Rényi QNEC for n < 1.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Defective rapid cell shape and transendothelial migration by calpain-1 null neutrophils

Highlights: • The role of calpain-1 in neutrophil shape change was investigated. • Neutrophils were obtained from knock-out mice and assessed ex vivo. • These cells failed to migrate through endothelial monolayers. • Spontaneous cell spreading was grossly abberant. • Calpain-1 null cells failed to spread in response to IP{sub 3} -induced Ca{sup 2+} signals. It has been proposed that Ca{sup 2+} activation of calpain-1 is an important trigger for rapid cell spreading by neutrophils. In this paper, we have investigated this by assessing the ex vivo functioning of neutrophils from calpain-1 null mice, Calpain-1 null neutrophils failed to migrate through TNF-activated endothelial monolayers. The failure to transmigrate through endothelial monolayers was therefore unlikely to be due to a failure of chemotaxis as chemotaxis by adherent calpain-1 null neutrophils towards fMLP was unpaired. In contrast, the capacity of calpian-1 neutrophils to spontaneously spread was limited to smaller diameters than for wild type cells. Photolytic uncaging of IP{sub 3} with Individual wild type neutrophils resulted in a large Ca{sup 2+} signal and rapid cell spreading. In contrast, calpain-1 neutrophils failed to spread in response to the IP{sub 3}-induced Ca{sup 2+} signal. This work has therefore demonstrated that the presence of calpain-1 was required for effective rapid cell spreading by neutrophils.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2023

EUV debris mitigation using magnetic nulls

Next generation EUV sources for photolithography use light produced by laser-produced plasmas (LPP) from ablated tin droplets. A major challenge for extending the lifetime of these devices is mitigating damage caused by deposition of tin debris on the sensitive collection mirror. Especially difficult to stop are high energy (up to 10 keV) highly charged tin ions created in the plasma. Existing solutions include the use of stopping gas, electric fields, and magnetic fields. One common configuration consists of a magnetic field perpendicular to the EUV emission direction, but such a system can result in ion populations that are trapped rather than removed. Here we investigate a previously unconsidered mitigation geometry consisting of a magnetic null by performing full-orbit integration of the ion trajectories in an EUV system with realistic dimensions and optimize the coil locations for the null configuration. The magnetic null prevents a fraction of ions from hitting the mirror comparable to that of the perpendicular field, but does not trap any ions due to the chaotic nature of ion trajectories that pass close to the null. This technology can potentially improve LPP-based EUV photolithography system efficiency and lifetime and may allow for a different, more efficient formulation of buffer gas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Constraining cosmology with the CMB × line intensity mapping-nulling convergence

Lensing reconstruction maps from the cosmic microwave background (CMB) provide direct observations of the matter distribution of the universe without the use of a biased tracer. Such maps, however, constitute projected observables along the line of sight that are dominated by their low-redshift contributions. To cleanly access high-redshift information, Maniyar et al., [Phys. Rev. D 105, 083509 (2022)] showed that a linear combination of lensing maps from both CMB and line intensity mapping (LIM) observations can exactly null the low-redshift contribution to CMB lensing convergence. In this paper we explore the scientific returns of this nulling technique. Here, we show that LIM-nulling estimators can place constraints on standard Λ⁢CDM plus neutrino mass parameters that are competitive with traditional CMB lensing. Additionally, we demonstrate that as a clean probe of the high-redshift universe, LIM nulling can be used for model-independent tests of cosmology beyond Λ⁢CDM and as a probe of the high-redshift matter power spectrum.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2001

Proliferation, differentiation and apoptosis in connexin43-null osteoblasts

Osteoblasts are highly coupled by gap junctions formed primarily by connexin43 (Cx43). We have shown that interference with Cx43 expression or function disrupts transcriptional regulation of osteoblast genes, and that deletion of Cx43 in the mouse causes skeletal malformations, delayed mineralization, and osteoblast dysfunction. Here, we studied the mechanisms by which genetic deficiency of Cx43 alters osteoblast development. While cell proliferation rates were similar in osteoblastic cells derived from calvaria of Cx43-null and wild type mice, camptothecin-induced apoptosis was 3-fold higher in mutant compared to wild type osteoblasts. When grown in mineralizing medium, Cx43-null cells were able to produce mineralized matrix but it took one week longer to reach the same mineralization levels as in normal cells. Likewise, expression of alkaline phosphatase activity per cell--a marker of osteoblast differentiation--was maximal only 2 weeks later in Cx43-null relative to wild-type cells. These observations suggest that Cx43 is important for a normal and timely development of the osteoblastic phenotype. Delayed differentiation and increase programmed cell death may explain the skeletal phenotype of Cx43-null mice.

NASA Discipline Cell Biology↗

NASA NTRS2006

The Fourier-Kelvin Stellar Interferometer (FKSI) Nulling Testbed II: Closed-loop Path Length Metrology And Control Subsystem

The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for an imaging and nulling interferometer in the near to mid-infrared spectral region (3-8 microns), and will be a scientific and technological pathfinder for upcoming missions including TPF-I/DARWIN, SPECS, and SPIRIT. At NASA's Goddard Space Flight Center, we have constructed a symmetric Mach-Zehnder nulling testbed to demonstrate techniques and algorithms that can be used to establish and maintain the 10(exp 4) null depth that will be required for such a mission. Among the challenges inherent in such a system is the ability to acquire and track the null fringe to the desired depth for timescales on the order of hours in a laboratory environment. In addition, it is desirable to achieve this stability without using conventional dithering techniques. We describe recent testbed metrology and control system developments necessary to achieve these goals and present our preliminary results.

Frey, B. J.↗

NASA NTRS2010

Self-Nulling Beam Combiner Using No External Phase Inverter

A self-nulling beam combiner is proposed that completely eliminates the phase inversion subsystem from the nulling interferometer, and instead uses the intrinsic phase shifts in the beam splitters. Simplifying the flight instrument in this way will be a valuable enhancement of mission reliability. The tighter tolerances on R = T (R being reflection and T being transmission coefficients) required by the self-nulling configuration actually impose no new constraints on the architecture, as two adaptive nullers must be situated between beam splitters to correct small errors in the coatings. The new feature is exploiting the natural phase shifts in beam combiners to achieve the 180 phase inversion necessary for nulling. The advantage over prior art is that an entire subsystem, the field-flipping optics, can be eliminated. For ultimate simplicity in the flight instrument, one might fabricate coatings to very high tolerances and dispense with the adaptive nullers altogether, with all their moving parts, along with the field flipper subsystem. A single adaptive nuller upstream of the beam combiner may be required to correct beam train errors (systematic noise), but in some circumstances phase chopping reduces these errors substantially, and there may be ways to further reduce the chop residuals. Though such coatings are beyond the current state of the art, the mechanical simplicity and robustness of a flight system without field flipper or adaptive nullers would perhaps justify considerable effort on coating fabrication.

Bloemhof, Eric E.↗

NASA NTRS2010

Alignment of optical system components using an ADM beam through a null assembly

A system for testing an optical surface includes a rangefinder configured to emit a light beam and a null assembly located between the rangefinder and the optical surface. The null assembly is configured to receive and to reflect the emitted light beam toward the optical surface. The light beam reflected from the null assembly is further reflected back from the optical surface toward the null assembly as a return light beam. The rangefinder is configured to measure a distance to the optical surface using the return light beam.

Hayden, Joseph E.↗

NASA NTRS2007

Starlight Nulling Technology at the Jet Propulsion Laboratory

The current interests in extra-solar planet detection and space-based and ground-based interferometry for astronomical observations has led to the development of a number of nulling instrument designs at the Jet Propulsion Laboratory (JPL) and elsewhere. This paper summarizes briefly JPL's efforts in nulling interferometry to date and consists of illustrations of some key nulling activities. Basic layouts of nulling testbeds are described and key applications discussed.

Terrestrial Planet Finder↗