Precision control of thermal transport in cryogenic single-crystal silicon devices

We report on the diffusive-ballistic thermal conductance of multi-moded single-crystal silicon beams measured below 1 K. It is shown that the phonon mean-free-path $\ell$ is a strong function of the surface roughness characteristics of the beams. This effect is enhanced in diffuse beams with lengths much larger than $\ell$, even when the surface is fairly smooth, 5-10 nm rms, and the peak thermal wavelength is 0.6 $\mu$m. Resonant phonon scattering has been observed in beams with a pitted surface morphology and characteristic pit depth of 30 nm. Hence, if the surface roughness is not adequately controlled, the thermal conductance can vary significantly for diffuse beams fabricated across a wafer. In contrast, when the beam length is of order $\ell$, the conductance is dominated by ballistic transport and is effectively set by the beam area. We have demonstrated a uniformity of $\pm$8% in fractional deviation for ballistic beams, and this deviation is largely set by the thermal conductance of diffuse beams that support the micro-electro-mechanical device and electrical leads. In addition, we have found no evidence for excess specific heat in single-crystal silicon membranes. This allows for the precise control of the device heat capacity with normal metal films. We discuss the results in the context of the design and fabrication of large-format arrays of far-infrared and millimeter wavelength cryogenic detectors

Scalable background-limited polarization-sensitive detectors for mm-wave applications

We report on the status and development of polarization-sensitive detectors for millimeter-wave applications. The detectors are fabricated on single-crystal silicon, which functions as a low-loss dielectric substrate for the microwave circuitry as well as the supporting membrane for the Transition-Edge Sensor (TES) bolometers. The orthomode transducer (OMT) is realized as a symmetric structure and on-chip filters are employed to define the detection bandwidth. A hybridized integrated enclosure reduces the high-frequency THz mode set that can couple to the TES bolometers. An implementation of the detector architecture at Q-band achieves 90% efficiency in each polarization. The design is scalable in both frequency coverage, 30-300 GHz, and in number of detectors with uniform characteristics. Hence, the detectors are desirable for ground-based or space-borne instruments that require large arrays of efficient background-limited cryogenic detectors.Comment: 7 pages, 3 figures, Presented at SPIE Astronomical Telescopes and Instrumentation 2014: Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VII. To be published in Proceedings of SPIE Volume 915

Growth Spectrum Complexity Dictates Aromatic Intensity in Coriander (Coriandrum sativum L.)

© Copyright © 2020 McAusland, Lim, Morris, Smith-Herman, Mohammed, Hayes-Gill, Crowe, Fisk and Murchie. Advancements in availability and specificity of light-emitting diodes (LEDs) have facilitated trait modification of high-value edible herbs and vegetables through the fine manipulation of spectra. Coriander (Coriandrum sativum L.) is a culinary herb, known for its fresh, citrusy aroma, and high economic value. Studies into the impact of light intensity and spectrum on C. sativum physiology, morphology, and aroma are limited. Using a nasal impact frequency panel, a selection of key compounds associated with the characteristic aroma of coriander was identified. Significant differences (P < 0.05) were observed in the concentration of these aromatics between plants grown in a controlled environment chamber under the same photosynthetic photon flux density (PPFD) but custom spectra: red (100%), blue (100%), red + blue (RB, 50% equal contribution), or red + green + blue (RGB, 35.8% red: 26.4% green: 37.8% blue) wavelengths. In general, the concentration of aromatics increased with increasing numbers of wavelengths emitted alongside selective changes, e.g., the greatest increase in coriander-defining E-(2)-decenal occurred under the RGB spectrum. This change in aroma profile was accompanied by significant differences (P < 0.05) in light saturated photosynthetic CO2 assimilation, water-use efficiency (Wi), and morphology. While plants grown under red wavelengths achieved the greatest leaf area, RB spectrum plants were shortest and had the highest leaf:shoot ratio. Therefore, this work evidences a trade-off between sellable commercial morphologies with a weaker, less desirable aroma or a less desirable morphology with more intense coriander-like aromas. When supplemental trichromatic LEDs were used in a commercial glasshouse, the majority of compounds, with the exception of linalool, also increased showing that even as a supplement additional wavelength can modify the aromatic profile increasing its complexity. Lower levels of linalool suggest these plants may be more susceptible to biotic stress such as herbivory. Finally, the concentration of coriander-defining aromatics E-(2)-decenal and E-(2)-hexenal was significantly higher in supermarket pre-packaged coriander leaves implying that concentrations of aromatics increase after excision. In summary, spectra can be used to co-manipulate aroma profile and plant form with increasing spectral complexity leading to greater aromatic complexity and intensity. We suggest that increasing spectral complexity progressively stimulates signaling pathways giving rise to valuable economic traits

Fabrication of Silicon Backshorts with Improved Out-of-Band Rejection for Waveguide-Coupled Superconducting Detectors

The Cosmology Large Angular Scale Surveyor (CLASS) is a ground-based instrument that will measure the polarization of the cosmic microqave background to search for gravitational waves form a posited epoch of inflation early in the universe's history. This measurement will require integration of superconducting transition-edge sensors with microwave waveguide inputs with good conrol of systematic errors, such as unwanted coupling to stray signals at frequencies outside of a precisely defined microwave band. To address these needs we will present work on the fabrication of silicon quarter-wave backshorts for the CLASS 40GHz focal plane. The 40GHz backshort consists of three degeneratively doped silicon wafers. Two spacer wafers are micromachined with through wafer vins to provide a 2.0mm long square waveguide. The third wafer acts as the backshort cap. The three wafers are bonded at the wafer level by Au-Au thermal compression bonding then aligned and flip chip bonded to the CLASS detector at the chip level. The micromachining techniques used have been optimized to create high aspect ratio waveguides, silicon pillars, and relief trenches with the goal of providing improved out of band signal rejection. We will discuss the fabrication of integrated CLASS superconducting detectors with silicon quarter wave backshorts and present current measurement results

Fabrication of a Silicon Backshort Assembly for Waveguide-Coupled Superconducting Detectors

The Cosmology Large Angular Scale Surveyor (CLASS) is a ground-based instrument that will measure the polarization of the cosmic microwave background to search for evidence for gravitational waves from a posited epoch of inflation early in the Universe s history. This measurement will require integration of superconducting transition-edge sensors with microwave waveguide inputs with excellent control of systematic errors, such as unwanted coupling to stray signals at frequencies outside of a precisely defined microwave band. To address these needs we present work on the fabrication of micromachined silicon, producing conductive quarter-wave backshort assemblies for the CLASS 40 GHz focal plane. Each 40 GHz backshort assembly consists of three degeneratively doped silicon wafers. Two spacer wafers are micromachined with through-wafer vias to provide a 2.04 mm long square waveguide delay section. The third wafer terminates the waveguide delay in a short. The three wafers are bonded at the wafer level by Au-Au thermal compression bonding then aligned and flip chip bonded to the CLASS detector at the chip level. The micromachining techniques used have been optimized to create high aspect ratio waveguides, silicon pillars, and relief trenches with the goal of providing improved out of band signal rejection. We will discuss the fabrication of integrated CLASS superconducting detector chips with the quarter-wave backshort assemblies

CLASS: The Cosmology Large Angular Scale Surveyor

The Cosmology Large Angular Scale Surveyor (CLASS) is an experiment to measure the signature of a gravitational wave background from inflation in the polarization of the cosmic microwave background (CMB). CLASS is a multi-frequency array of four telescopes operating from a high-altitude site in the Atacama Desert in Chile. CLASS will survey 70% of the sky in four frequency bands centered at 38, 93, 148, and 217 GHz, which are chosen to straddle the Galactic-foreground minimum while avoiding strong atmospheric emission lines. This broad frequency coverage ensures that CLASS can distinguish Galactic emission from the CMB. The sky fraction of the CLASS survey will allow the full shape of the primordial B-mode power spectrum to be characterized, including the signal from reionization at low-length. Its unique combination of large sky coverage, control of systematic errors, and high sensitivity will allow CLASS to measure or place upper limits on the tensor-to-scalar ratio at a level of r = 0:01 and make a cosmic-variance-limited measurement of the optical depth to the surface of last scattering, tau. (c) (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

The Cosmology Large Angular Scale Surveyor (CLASS) Telescope Architecture

We describe the instrument architecture of the Johns Hopkins University-led CLASS instrument, a groundbased cosmic microwave background (CMB) polarimeter that will measure the large-scale polarization of the CMB in several frequency bands to search for evidence of inflation

Socioeconomic Inequalities in Newborn Care During Facility and Home Deliveries: A Cross Sectional Analysis of Data from Demographic Surveillance Sites in Rural Bangladesh, India and Nepal

Background: In Bangladesh, India and Nepal, neonatal outcomes of poor infants are considerably worse than those of better-off infants. Understanding how these inequalities vary by country and place of delivery (home or facility) will allow targeting of interventions to those who need them most. We describe socio-economic inequalities in newborn care in rural areas of Bangladesh, Nepal and India for all deliveries and by place of delivery. Methods: We used data from surveillance sites in Bangladesh, India and from Makwanpur and Dhanusha districts in Nepal, covering periods from 2001 to 2011. We used literacy (ability to read a short text) as indicator of socioeconomic status. We developed a composite score of nine newborn care practices (score range 0–9 indicating infants received no newborn care to all nine newborn care practices). We modeled the effect of literacy and place of delivery on the newborn care score and on individual practices. Results: In all study sites (60,078 deliveries in total), use of facility delivery was higher among literate mothers. In all sites, inequalities in newborn care were observed: the difference in new born care between literate and illiterate ranged 0.35–0.80. The effect of literacy on the newborn care score reduced after adjusting for place of delivery (range score difference literate-illiterate: 0.21–0.43). Conclusion: Socioeconomic inequalities in facility care greatly contribute to inequalities in newborn care. Improving newborn care during home deliveries and improving access to facility care are a priority for addressing inequalities in newborn care and newborn mortality