Inhibitors of \u3cem\u3eN\u3csup\u3eα\u3c/sup\u3e\u3c/em\u3e-acetyl-l-ornithine Deacetylase: Synthesis, Characterization and Analysis of their Inhibitory Potency

A series of N α-acyl (alkyl)- and N α-alkoxycarbonyl-derivatives of l- and d-ornithine were prepared, characterized, and analyzed for their potency toward the bacterial enzyme N α-acetyl-l-ornithine deacetylase (ArgE). ArgE catalyzes the conversion of N α-acetyl-l-ornithine to l-ornithine in the fifth step of the biosynthetic pathway for arginine, a necessary step for bacterial growth. Most of the compounds tested provided IC50 values in the μM range toward ArgE, indicating that they are moderately strong inhibitors. N α-chloroacetyl-l-ornithine (1g) was the best inhibitor tested toward ArgE providing an IC50 value of 85 μM while N α-trifluoroacetyl-l-ornithine (1f), N α-ethoxycarbonyl-l-ornithine (2b), and N α-acetyl-d-ornithine (1a) weakly inhibited ArgE activity providing IC50 values between 200 and 410 μM. Weak inhibitory potency toward Bacillus subtilis-168 for N α-acetyl-d-ornithine (1a) and N α-fluoro- (1f), N α-chloro- (1g), N α-dichloro- (1h), and N α-trichloroacetyl-ornithine (1i) was also observed. These data correlate well with the IC50 values determined for ArgE, suggesting that these compounds might be capable of getting across the cell membrane and that ArgE is likely the bacterial enzymatic target

Weak Gravitational Lensing Systematics from Image Combination

Extremely accurate shape measurements of galaxy images are needed to probe dark energy properties with weak gravitational lensing surveys. To increase survey area with a fixed observing time and pixel count, images from surveys such as the Wide Field Infrared Survey Telescope (WFIRST) or Euclid will necessarily be undersampled and therefore distorted by aliasing. Oversampled, unaliased images can be obtained by combining multiple, dithered exposures of the same source with a suitable reconstruction algorithm. Any such reconstruction must minimally distort the reconstructed images for weak lensing analyses to be unbiased. In this paper, we use the image combination (IMCOM) algorithm of Rowe, Hirata, and Rhodes to investigate the effect of image combination on shape measurements (size and ellipticity). We simulate dithered images of sources with varying amounts of ellipticity and undersampling, reconstruct oversampled output images from them using IMCOM, and measure shape distortions in the output. Our simulations show that IMCOM creates no significant distortions when the relative offsets between dithered images are precisely known. Distortions increase with the uncertainty in those offsets, but become problematic only with relatively poor astrometric precision; e.g., for images similar to those from the Astrophysics Focused Telescope Asset (AFTA) implementation of WFIRST, combining eight undersampled images (sampling ratio Q = 1) with highly pessimistic uncertainty in astrometric registration (σ_d ∼ 10^(-3) pixels) yields an rms shear error of O(10^(-4)). Our analysis pipeline is adapted from that of the Precision Projector Laboratory—a joint project between NASA Jet Propulsion Laboratory and Caltech that characterizes image sensors using laboratory emulations of astronomical data

Utilizing active single-mode fiber injection for speckle nulling in exoplanet characterization

Despite recent advances in high-contrast imaging techniques, high resolution spectroscopy for characterization of exoplanet atmospheres is still limited by our ability to suppress residual starlight speckles at the planet’s location. We have demonstrated a new concept for speckle nulling by injecting directly imaged planet light into a single-mode fiber, linking a high-contrast adaptively-corrected coronagraph to a high-resolution spectrograph (diffraction-limited or not). The restrictions on the incident electric field that will couple into the single-mode fiber give the adaptive optics system additional degrees of freedom to suppress the speckle noise on top of destructive interference. We are able to achieve a starlight suppression gains that are an order of magnitude better than conventional techniques in broadband light with minimal planet throughput losses

High-contrast spectroscopy testbed for Segmented Telescopes: instrument overview and development progress

The High Contrast spectroscopy testbed for Segmented Telescopes (HCST) is being developed at Caltech. It aims at addressing the technology gap for future exoplanet imagers and providing the U.S. community with an academic facility to test components and techniques for high contrast imaging, focusing on segmented apertures proposed for future ground-based (TMT, ELT) and space-based telescopes (HabEx, LUVOIR). We present an overview of the design of the instrument and a detailed look at the testbed build and initial alignment. We offer insights into stumbling blocks encountered along the path and show that the testbed is now operational and open for business. We aim to use the testbed in the future for testing of high contrast imaging techniques and technologies with amongst with thing, a TMT-like pupil

Optimizing optics and opto-mechanical mounting to minimize static aberrations in high-contrast instruments

One of the goals of high-contrast imaging is to reach contrasts of 10^(-10) at small inner working angles to directly image Earth-like exoplanets around solar-type stars. In most imaging systems, a deformable mirror (DM) in the pupil plane can correct for phase errors but surface errors in out-of-pupil optics get coupled into amplitude errors which can only be controlled with a second, out of pupil, DM. Furthermore, correcting static errors introduced by the optics can take up valuable DM stroke. Thus, minimizing the wavefront error within the system is critical to reaching high contrast levels. For example, the High Contrast Spectroscopy for Segmented Telescopes Testbed (HCST) in the Exoplanet Technologoy lab at Caltech aims to develop exoplanet imaging technologies down to small inner working angles (< 3λ/D) which requires an RMS wavefront error of less than 10 nm per optic to achieve a contrast of 10^(−5) with the DM flattened. While aligning HCST, it was determined that despite the excellent surface quality of all the optics, the mounts were introducing significant wavefront errors. Here we assess the effect of mount-induced wavefront errors that can rapidly consume the wavefront budget of a high-contrast system. We also present the method used to mitigate this effect within HCST such that a mean contrast of 6 × 10^(-6) from 3-10λ/D was achieved with a vortex coronagraph and flattened DM

High-contrast spectroscopy testbed for segmented telescopes

The High Contrast Spectroscopy Testbed for Segmented Telescopes (HCST) at Caltech is aimed at filling gaps in technology for future exoplanet imagers and providing the U.S. community with an academic facility to test components and techniques for high contrast imaging with future segmented ground-based telescope (TMT, E-ELT) and space-based telescopes (HabEx, LUVOIR). The HCST will be able to simulate segmented telescope geometries up to 1021 hexagonal segments and time-varying external wavefront disturbances. It also contains a wavefront corrector module based on two deformable mirrors followed by a classical 3-plane single-stage corona- graph (entrance apodizer, focal-plane mask, Lyot stop) and a science instrument. The back-end instrument will consist of an imaging detector and a high-resolution spectrograph, which is a unique feature of the HCST. The spectrograph instrument will utilize spectral information to characterize simulated planets at the photon-noise limit, measure the chromaticity of new optimized coronagraph and wavefront control concepts, and test the overall scientific functions of high-resolution spectrographs on future segmented telescopes

High-contrast spectroscopy testbed for Segmented Telescopes: instrument overview and development progress

The High Contrast spectroscopy testbed for Segmented Telescopes (HCST) is being developed at Caltech. It aims at addressing the technology gap for future exoplanet imagers and providing the U.S. community with an academic facility to test components and techniques for high contrast imaging, focusing on segmented apertures proposed for future ground-based (TMT, ELT) and space-based telescopes (HabEx, LUVOIR). We present an overview of the design of the instrument and a detailed look at the testbed build and initial alignment. We offer insights into stumbling blocks encountered along the path and show that the testbed is now operational and open for business. We aim to use the testbed in the future for testing of high contrast imaging techniques and technologies with amongst with thing, a TMT-like pupil

Utilizing active single-mode fiber injection for speckle nulling in exoplanet characterization

Despite recent advances in high-contrast imaging techniques, high resolution spectroscopy for characterization of exoplanet atmospheres is still limited by our ability to suppress residual starlight speckles at the planet’s location. We have demonstrated a new concept for speckle nulling by injecting directly imaged planet light into a single-mode fiber, linking a high-contrast adaptively-corrected coronagraph to a high-resolution spectrograph (diffraction-limited or not). The restrictions on the incident electric field that will couple into the single-mode fiber give the adaptive optics system additional degrees of freedom to suppress the speckle noise on top of destructive interference. We are able to achieve a starlight suppression gains that are an order of magnitude better than conventional techniques in broadband light with minimal planet throughput losses