Differential phase technique with the Keck Interferometer

We present the motivation and development of the novel `differential phase' technique being developed for the Keck Interferometer with the goal of detecting faint companions near a bright source. The differential phase technique uses simultaneous phase measurements at several infrared wavelengths to detect the astrophysical signature produced by a chromatic, asymmetric brightness distribution. We discuss the origin of the differential phase signature and present results of test observations taken at the Palomar Testbed Interferometer. One important test result is the larger than expected effect of water vapor turbulence on these multi-wavelength observations due to the infrared dispersion of water. In order to reach the design goal of 0.1 milliradians, the phase noise caused by both temperature and water vapor fluctuations in the atmosphere must be corrected, and we discuss several ways to achieve this

Longitudinal dispersion control for the Keck interferometer nuller

The control of longitudinal dispersion, which determines the position of the null fringe as a function of wavelength, is central to the problem of producing deep broadband interferometric nulls. The dispersion is the sum of terms due to environmental factors such as the dry-air and water-vapor atmospheric seeing, the unbalanced air column due to the unequal delay-line paths between the telescopes the combiner, and to the distance from the central fringe. The difference between an achromatic nuller and a normal constructive combiner operating at its first (chromatic) null can be thought of as an added longitudinal dispersion, which for the case of the Keck Interferometer is smaller than the environmental terms. We demonstrate that the sum of these effects can be adequately compensated by an appropriate thickness of ZnSe combined with an additional achromatic pathlength. The Keck Interferometer nulling combiners take advantage of this result. They are intrinsically constructive combiners made to produce achromatic nulls by inserting a ZnSe dispersion corrector into each of the four input beams. We describe the null fringe stabilization control algorithm and present calculations of the required loop bandwidth and precision. A potentially important advantage of the present approach is that the system will be able to function as either a destructive or constructive combiner, depending on the value of a single control-loop parameter (the target fringe phase)

Keck Interferometer status and plans

Keck Interferometer is a NASA-funded project to combine the two 10 m Keck telescopes for high sensitivity near-infrared fringe visibility measurements, nulling interferometry at 10 μm to measure the quantity of exozodiacal emission around nearby stars, and differential-phase measurements to detect "hot-Jupiters" by their direct emission. It is being developed by the Jet Propulsion Laboratory, the W. M. Keck Observatory, and the Michelson Science Center. Recent activity has included formal visibility mode commissioning, as well as science observations, and we briefly review some of the significant technical aspects and updates to the system. We have also completed laboratory development of the nuller. The nuller uses two modified Mach-Zehnder input nullers, a Michelson cross combiner, and a 10 μm array camera to produce background-limited null measurements. To provide required temporal stability for the nuller, the system incorporates end-to-end laser metrology with phase referencing from two 2.2 μm fringe trackers. The nuller recently completed its pre-ship review and is being installed on the summit. After nuller integration and test, the differential phase mode will be deployed, which will use a 2-5 μm fringe detector in combination with a precision path length modulator and a vacuum delay line for dispersion control

Differential phase technique with the Keck Interferometer

We present the motivation and development of the novel `differential phase' technique being developed for the Keck Interferometer with the goal of detecting faint companions near a bright source. The differential phase technique uses simultaneous phase measurements at several infrared wavelengths to detect the astrophysical signature produced by a chromatic, asymmetric brightness distribution. We discuss the origin of the differential phase signature and present results of test observations taken at the Palomar Testbed Interferometer. One important test result is the larger than expected effect of water vapor turbulence on these multi-wavelength observations due to the infrared dispersion of water. In order to reach the design goal of 0.1 milliradians, the phase noise caused by both temperature and water vapor fluctuations in the atmosphere must be corrected, and we discuss several ways to achieve this

The Value of the Keck Observatory to NASA and Its Scientific Community

Over the last 13 years, NASA and its astrophysics and planetary science communities have greatly benefited from access to the Keck Observatory, the world’s largest optical/infrared telescopes. Studies using NASA Keck time have ranged from observations of the closest solar system bodies to discoveries of many of the known extrasolar planets. Observations at Keck have supported spaceflight missions to Mercury and the technology development of the James Webb Space Telescope. Access to Keck for the NASA community is an extremely cost effective method for NASA to meet its strategic goals and we encourage NASA to continue its long-term partnership with the Keck Observatory

Beyond Nanopore Sequencing in Space: Identifying the Unknown

Astronaut Kate Rubins sequenced DNA on the International Space Station (ISS) for the first time in August 2016 (Figure 1A). A 2D sequencing library containing an equal mixture of lambda bacteriophage, Escherichia coli, and Mus musculus was prepared on the ground with a SQK_MAP006 kit and sent to the ISS frozen and loaded into R7.3 flow cells. After a total of 9 on-orbit sequencing runs over 6 months, it was determined that there was no decrease in sequencing performance on-orbit compared to ground controls (1). A total of ~280,000 and ~130,000 reads generated on-orbit and on the ground, respectively, identified 90% of reads that were attributed to 30% lambda bacteriophage, 30% Escherichia coli, and 30% M. musculus (Figure 1B). Extensive bioinformatics analysis determined comparable 2D and 1D read accuracies between flight and ground runs (Figure 1C), and data collected from the ISS were able to construct directed assemblies of E.coli and lambda genomes at 100% and M. musculus mitochondrial genome at 96.7%. These findings validate sequencing as a viable option for potential on-orbit applications such as environmental microbial monitoring and disease diagnosis. Current microbial monitoring of the ISS applies culture-based techniques that provide colony forming unit (CFU) data for air, water, and surface samples. The identity of the cultured microorganisms in unknown until sample return and ground-based analysis, a process that can take up to 60 days. For sequencing to benefit ISS applications, spaceflight-compatible sample preparation techniques are required. Subsequent to the testing of the MinION on-orbit, a sample-to-sequence method was developed using miniPCR and basic pipetting, which was only recently proven to be effective in microgravity. The work presented here details the in- flight sample preparation process and the first application of DNA sequencing on the ISS to identify unknown ISS-derived microorganisms

Keck Interferometer status and plans

Keck Interferometer is a NASA-funded project to combine the two 10 m Keck telescopes for high sensitivity near-infrared fringe visibility measurements, nulling interferometry at 10 μm to measure the quantity of exozodiacal emission around nearby stars, and differential-phase measurements to detect "hot-Jupiters" by their direct emission. It is being developed by the Jet Propulsion Laboratory, the W. M. Keck Observatory, and the Michelson Science Center. Recent activity has included formal visibility mode commissioning, as well as science observations, and we briefly review some of the significant technical aspects and updates to the system. We have also completed laboratory development of the nuller. The nuller uses two modified Mach-Zehnder input nullers, a Michelson cross combiner, and a 10 μm array camera to produce background-limited null measurements. To provide required temporal stability for the nuller, the system incorporates end-to-end laser metrology with phase referencing from two 2.2 μm fringe trackers. The nuller recently completed its pre-ship review and is being installed on the summit. After nuller integration and test, the differential phase mode will be deployed, which will use a 2-5 μm fringe detector in combination with a precision path length modulator and a vacuum delay line for dispersion control

Longitudinal dispersion control for the Keck interferometer nuller

The control of longitudinal dispersion, which determines the position of the null fringe as a function of wavelength, is central to the problem of producing deep broadband interferometric nulls. The dispersion is the sum of terms due to environmental factors such as the dry-air and water-vapor atmospheric seeing, the unbalanced air column due to the unequal delay-line paths between the telescopes the combiner, and to the distance from the central fringe. The difference between an achromatic nuller and a normal constructive combiner operating at its first (chromatic) null can be thought of as an added longitudinal dispersion, which for the case of the Keck Interferometer is smaller than the environmental terms. We demonstrate that the sum of these effects can be adequately compensated by an appropriate thickness of ZnSe combined with an additional achromatic pathlength. The Keck Interferometer nulling combiners take advantage of this result. They are intrinsically constructive combiners made to produce achromatic nulls by inserting a ZnSe dispersion corrector into each of the four input beams. We describe the null fringe stabilization control algorithm and present calculations of the required loop bandwidth and precision. A potentially important advantage of the present approach is that the system will be able to function as either a destructive or constructive combiner, depending on the value of a single control-loop parameter (the target fringe phase)

CRISPRi-based radiation modifier screen identifies long non-coding RNA therapeutic targets in glioma.

BackgroundLong non-coding RNAs (lncRNAs) exhibit highly cell type-specific expression and function, making this class of transcript attractive for targeted cancer therapy. However, the vast majority of lncRNAs have not been tested as potential therapeutic targets, particularly in the context of currently used cancer treatments. Malignant glioma is rapidly fatal, and ionizing radiation is part of the current standard-of-care used to slow tumor growth in both adult and pediatric patients.ResultsWe use CRISPR interference (CRISPRi) to screen 5689 lncRNA loci in human glioblastoma (GBM) cells, identifying 467 hits that modify cell growth in the presence of clinically relevant doses of fractionated radiation. Thirty-three of these lncRNA hits sensitize cells to radiation, and based on their expression in adult and pediatric gliomas, nine of these hits are prioritized as lncRNA Glioma Radiation Sensitizers (lncGRS). Knockdown of lncGRS-1, a primate-conserved, nuclear-enriched lncRNA, inhibits the growth and proliferation of primary adult and pediatric glioma cells, but not the viability of normal brain cells. Using human brain organoids comprised of mature neural cell types as a three-dimensional tissue substrate to model the invasive growth of glioma, we find that antisense oligonucleotides targeting lncGRS-1 selectively decrease tumor growth and sensitize glioma cells to radiation therapy.ConclusionsThese studies identify lncGRS-1 as a glioma-specific therapeutic target and establish a generalizable approach to rapidly identify novel therapeutic targets in the vast non-coding genome to enhance radiation therapy