A5047494784- Superconducting and THz Device Technology
- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Spectroscopy and Laser Applications
- Atmospheric Ozone and Climate
- Astrophysical Phenomena and Observations
- Gyrotron and Vacuum Electronics Research
- Microwave Engineering and Waveguides
- Soil Moisture and Remote Sensing
- Radio Frequency Integrated Circuit Design
- Astrophysics and Star Formation Studies
- Physics of Superconductivity and Magnetism
- Cosmology and Gravitation Theories
- Calibration and Measurement Techniques
- Advanced Thermodynamic Systems and Engines
- Astronomy and Astrophysical Research
- Terahertz technology and applications
- Precipitation Measurement and Analysis
- Spacecraft Design and Technology
- Meteorological Phenomena and Simulations
- Pulsars and Gravitational Waves Research
- Electromagnetic Compatibility and Measurements
- Ionosphere and magnetosphere dynamics
- Antenna Design and Optimization
- Atmospheric and Environmental Gas Dynamics
Center for Astrophysics Harvard & Smithsonian
2014-2024
Harvard University
1997-2020
Smithsonian Astrophysical Observatory
2000-2019
Smithsonian Institution
2017
SLAC National Accelerator Laboratory
2016
CFA Institute
2009
Massachusetts Institute of Technology
1997
AT&T (United States)
1984-1985
California Institute of Technology
1984
Abstract The Event Horizon Telescope (EHT) is a very long-baseline interferometer built to image supermassive black holes on event-horizon scales. In this paper, we investigate candidate sites for an expanded EHT array with improved imaging capabilities. We use historical meteorology and radiative transfer analysis evaluate site performance. Most of the existing in have median zenith opacity less than 0.2 at 230 GHz during March/April observing season. Seven 345 0.5 months. Out more 40 new...
Abstract The second Radiative Heating in Underexplored Bands Campaign (RHUBC‐II) was conducted 2009 by the U.S. Department of Energy Atmospheric Radiation Measurement program to improve water vapor spectroscopy far‐infrared spectral region. RHUBC‐II located an extremely dry region Chile ensure very low opacities this Spectrally resolved measurements a spectrometer and submillimeter interferometer from are compared with line‐by‐line radiative transfer model calculations. Water amounts...
Recent years have seen a surge of interest in the community studying effect ultraviolet radiation environment, predominantly set by OB stars, on protoplanetary disc evolution and planet formation. This is important because significant fraction planetary systems, potentially including our own, formed close proximity to stars. rapidly developing field, with broad range observations across many regions recently obtained or scheduled. In this paper, stimulated series workshops topic, we take...
The rapidly changing climate is amplifying both the frequency and severity of extreme weather events in Azores archipelago, Portugal. Understanding underlying dynamics these essential for effective mitigation. Atmospheric water vapor data derived from Global Navigation Satellite System (GNSS) reanalysis outputs an atmospheric general circulation model offer valuable tools studying behavior fronts around Atlantic Ocean environment Azores. This research aims to conduct a detailed comparison...
We develop a model for the recrystallization of Si films that are traversed by molten zone. The simulates branching behavior low-angle grain-boundary defects in these to remarkable degree. simulated subboundary patterns scale approximately as square root scan velocity, excellent agreement with experiment.
A 12 m diameter radio telescope will be deployed to the Summit Station in Greenland provide direct confirmation of a Super Massive Black Hole (SMBH) by observing its shadow image active galaxy M87. The (Greenland Telescope: GLT) is become one Very Long Baseline Interferometry (VLBI) stations at sub-millimeter (submm) regime, providing longest baseline >9000 km achieve an exceptional angular resolution 20 µas 350 GHz, which enable us resolve size ~40 µas. triangle with baselines formed GLT,...
We describe a Fourier transform spectrometer for measurements of atmospheric transmission in the spectral interval 300 GHz to 3.5 THz. This instrument has been developed evaluate prospective sites radio astronomical observations at frequencies above 1 Measurements have made on Mauna Kea, Hawaii, and site future Millimeter Array near Cerro Chajnantor northern Chile. frequently exhibits significant windows Here we outline design characteristics instrument, discuss data processing methods,...
We report on the design and development of a heterodyne receiver, designed to cover frequency range 176-256 GHz. This receiver incorporates niobium superconductor-insulator-superconductor (SIS) tunnel junction mixer, which, chiefly for reasons reliability ease operation, is fixed-tuned waveguide design. On-chip tuning provided resonate out junction's geometric capacitance produce good match circuit. Laboratory measurements first test indicate that required input bandwidth (about 40%)...
A field experiment was conducted in northern Chile at an altitude of 5.3 km to evaluate the accuracy line‐by‐line radiative transfer models regions spectrum that are typically opaque sea level due strong water vapor absorption. suite spectrally resolved radiance instruments collected simultaneous observations that, for first time ever, spanned entire terrestrial thermal (i.e., from 10 3000 cm −1 , or 1000 3.3 μ m). These observations, together with collocated and temperature profiles, used...
We describe the creation of circular states hydrogen by adiabatic transfer a Rydberg state in crossed electric and magnetic fields, also passage rotating microwave field. The latter method permits rapid switching between two given $n$ manifold. methods are demonstrated experimentally, results presented an analysis field ionization properties states. An application for is illustrated millimeter-wave resonance $n=29\ensuremath{\rightarrow}n=30$ transition.
Realistic synthetic observations of theoretical source models are essential for our understanding real observational data. In using data, one can verify the extent to which parameters be recovered and evaluate how various data corruption effects calibrated. These studies important when proposing new sources, in characterization capabilities or upgraded instruments, verifying model-based predictions a comparison with We present SYnthetic Measurement creator long Baseline Arrays (SYMBA), novel...
A fixed-tuned superconductor-insulator-superconductor (SIS) receiver has been designed to operate in the 250-350-GHz frequency band. This a double-side-band noise temperature of between 35 and 45 K, or about 3h/spl nu//k/sub B/, over its entire operating Extensive characterization carried out using techniques developed for submillimeter waves. The input noise, side-band ratio, 1 dB compression point, optimum LO drive level, vector near-field beam profile have all measured experimentally....
Abstract Very long baseline interferometry (VLBI) provides the highest-resolution images in astronomy. The sharpest resolution is nominally achieved at highest frequencies, but as observing frequency increases, so too does atmospheric contribution to system noise, degrading sensitivity of array and hampering detection. In this paper, we explore limits high-frequency VLBI observations using ngehtsim , a new tool for generating realistic synthetic data. uses detailed historical models simulate...
In this paper, we describe a superconducting hot-electron-bolometer mixer receiver developed to operate in atmospheric windows between 800-1300 GHz. The uses waveguide element made of 3-4-nm-thick NbN film deposited over crystalline quartz. This yields double-sideband noise temperatures 1000 K at around 1.0 THz, and 1600 1.26 an IF 3.0 was successfully tested the laboratory using gas cell as spectral line test source. It is now use on Smithsonian Astrophysical Observatory terahertz telescope...
We present the 3.5 years monitoring results of 225 GHz opacity at summit Greenland ice sheet (Greenland Summit Camp) an altitude 3200 m using a tipping radiometer. chose this site as our submillimeter telescope Telescope) site, because conditions are expected to have low and its location offers favorable baselines existing telescopes for global-scale Very Long Baseline Interferometry. The shows clear seasonal variation with average lower by factor two during winter. 25%, 50%, 75% quartiles...
We present a novel machinable 90° waveguide twist design suitable for broadband applications from microwave to terahertz frequency. The achieves compactness and ease of fabrication by utilizing series quarter-wave transformer steps machined in split blocks. Three WR3.4 (220-330 GHz) prototypes with standard UG-387 flanges were fabricated measured. outperform two commercial twists both return loss insertion loss. simulation measurement results show that this performance -25 dB full bandwidth....
Isolators are important components of low-noise detector and signal processing systems. Conventional wideband edge-mode isolators offer wide bandwidth, but rarely exceeding two octaves. Using modern computer electromagnetic simulation software, one can optimize the isolator circuit expand bandwidth performance. We report on design, fabrication, measurement an operating over a multioctave frequency range, from 4 to 22 GHz at 4-K cryogenic temperature. This has good input output reflection...
The distribution of 12C16O J = 9 → 8 (1.037 THz) emission has been mapped in OMC-1 at 35 points with 84'' resolution. This is the first map this source transition and only second velocity-resolved ground-based observation a line THz frequency band. There present all map, region roughly 4' × 6' size, peak antenna temperature dropping near edges. Away from Orion KL outflow, velocity structure suggests that most comes photon-dominated region, typical width 3-6 km s-1. Large gradient modeling...
Recent observational evidence that magnetic fields are dynamically important in molecular clouds, compared to self-gravity and turbulence, is reviewed illustrated with data from the NGC 2024 region. One piece of evidence, turbulence anisotropy, was found diffuse envelope a cloud (Av~1; Heyer et al. 2008); our further suggests anisotropy (Av >7) even near core (Av~100). The also shows can channel gravitational contraction for region super-critical N(H2)/2Blos ratio (the between observed...
Very long baseline interferometry (VLBI) provides the highest-resolution images in astronomy. The sharpest resolution is nominally achieved at highest frequencies, but as observing frequency increases so too does atmospheric contribution to system noise, degrading sensitivity of array and hampering detection. In this paper, we explore limits high-frequency VLBI observations using ngehtsim, a new tool for generating realistic synthetic data. ngehtsim uses detailed historical models simulate...
We have performed near-field vector beam measurements at 1.03 THz to characterize and align the receiver optics of a superconducting receiver. The signal source is harmonic generator mounted on an X-Y translation stage. model measured two-dimensional complex pattern by fundamental Gaussian mode, from which we derive position center, radius direction propagation. By performing scans in planes separated 400 mm, confirmed that our are highly reliable.
Millimeter-wave remote sensing technology can significantly improve measurements of volcanic eruptions, yielding new insights into eruption processes and improving forecasts drifting ash for aviation safety. Radiometers measure water vapor density temperature inside clouds, on existing with infrared cameras that are limited to measuring the outer cloud surface. radar 3-D mass distribution plumes their nearby clouds. Millimeter wavelengths better matched typical particle sizes, offering...