Broadband IF Circuits for Superconductor Isolator Superconductor (SIS) Mixers for the Heterodyne Instrument for the Far Infrared on the Herschel Space Observatory and for Sideband Separating Mixers

This thesis describes the development and manufacturing of the IF circuits for two different heterodyne receivers used for sub-mm radio astronomy. The first project is the broadband 4-8 GHz IF circuitry for the mixer units for band 2 of the Heterodyne Instrument for the Far Infrared (HIFI). This instrument will be operating onboard of ESA's Herschel space observatory. The band 2 mixer units for HIFI, built by KOSMA, implement low noise SIS mixers in a very compact, modular design. The complete IF path in the mixer units consist of the mixer block (with the SIS mixer chip) and the bias-T, which is needed to apply a bias voltage to the SIS-junction and to extract the IF signal. The detailed investigation of the IF performance of the mixer block must consider the geometric capacitances of the SIS-junction and the tuning structure as well as the inductance of the bond wires used to establish the contact between the mixer chip and the SMA output connector. The calculations presented in this thesis show that the design can be used for IF frequencies up to 12 GHz. The bias-T, which is implemented in the mixer unit, is a dedicated, new development with high performance and high reliability complying with the special requirements for a spaceborne instrument. These include the survival under high mechanical stress such as vibration during the launch and extensive thermal cycling to cryogenic temperatures during the tests of the mixer unit and the instrument. An excellent (S21 > -0.25 dB) IF signal transmission of the bias-T is achieved by special high reliability connections in the signal path. Different coefficients of thermal expansion are compensated by the mechanical flexibility of the connections. These special parts have been developed, manufactured, integrated and tested within this work in a three phase design cycle (Demonstration Model(DM) - Qualification Model (QM) - Flight Model (FM)). In addition to the high transmission, the bias-T provides filter circuits, which effectively protect the signal path from electromagnetic interference (EMI) entering the mixer unit via the unshielded bias lines. The mixer units have passed all performance and environmental tests and are presently integrated into the HIFI instrument. The second project is the development and fabrication of very broadband nonuniform couplers, which can be used as -3 dB 90°-hybrids on the IF side of sideband separating mixers with large IF bandwidth. By the smooth (e.g., nonuniform, not stepped-uniform) change of the even- and odd-mode impedances along the wave propagation direction, uncontrolled reflections are avoided, which is indispensable to achieve a large bandwidth. Strong power coupling (-3 dB, e.g., 50%) is achieved with broadside coupled lines in a homogeneous stripline configuration, which ensures TEM mode propagation. This TEM mode propagation and the smooth distribution of the electrical parameters allow to achieve a large bandwidth. The impedances can be calculated by Fourier transformation of the power coupling bandshape. In order to determine the actual geometry (e.g., stripline width and spacing) from even mode line impedances, a design procedure has been developed, which is presented in this thesis. It includes an appropriate mix of analytic calculations and an interpolation scheme which uses results from a commercial 2D EM-field solver. This procedure has been successfully applied in order to design various couplers, which have been manufactured and tested. By introducing mode launchers in the vicinity of the coupler ports, the TEM mode purity could be improved, which led to an increased coupler bandwidth of 1.9-9.3 GHz

A 490 GHz planar circuit balanced Nb-Al2_\mathbf{2}O3_{\mathbf{3}}-Nb quasiparticle mixer for radio astronomy: Application to quantitative local oscillator noise determination

This article presents a heterodyne experiment which uses a 380-520 GHz planar circuit balanced Nb-$\mathrm{Al_2O_3}$-Nb superconductor-insulator-superconductor (SIS) quasiparticle mixer with 4-8 GHz instantaneous intermediate frequency (IF) bandwidth to quantitatively determine local oscillator (LO) noise. A balanced mixer is a unique tool to separate noise at the mixer's LO port from other noise sources. This is not possible in single-ended mixers. The antisymmetric IV characteristic of a SIS mixer further helps to simplify the measurements. The double-sideband receiver sensitivity of the balanced mixer is 2-4 times the quantum noise limit $h\nu/k_B$ over the measured frequencies with a maximum LO noise rejection of 15 dB. This work presents independent measurements with three different LO sources that produce the reference frequency but also an amount of near-carrier noise power which is quantified in the experiment as a function of the LO and IF frequency in terms of an equivalent noise temperature $T_{LO}$. In a second experiment we use only one of two SIS mixers of the balanced mixer chip, in order to verify the influence of near-carrier LO noise power on a single-ended heterodyne mixer measurement. We find an IF frequency dependence of near-carrier LO noise power. The frequency-resolved IF noise temperature slope is flat or slightly negative for the single-ended mixer. This is in contrast to the IF slope of the balanced mixer itself which is positive due to the expected IF roll-off of the mixer. This indicates a higher noise level closer to the LO's carrier frequency. Our findings imply that near-carrier LO noise has the largest impact on the sensitivity of a receiver system which uses mixers with a low IF band, for example superconducting hot-electron bolometer (HEB) mixers.Comment: 13 pages, 8 figures, 2 tables, see manuscript for complete abstrac

Structure of the W3A Low Density Foreground Region

We present analysis of OI 63 micron and CO $J$ = 5-4 and 8-7 multi-position data in the W3A region and use it to develop a model for the extended low-density foreground gas that produces absorption features in the OI and $J$ = 5-4 CO lines. We employ the extinction to the exciting stars of the background HII region to constrain the total column density of the foreground gas. We have used the Meudon PDR code to model the physical conditions and chemistry in the region employing a two-component model with high density layer near the HII region responsible for the fine structure line emission, and an extended low density foreground layer. The best-fitting total proton density, constrained largely by the CO lines, is $n$(H) = 250 cm$^{-3}$ in the foreground gas, and 5$\times$10$^5$ cm$^{-3}$ in the material near the HII region. The absorption is distributed over the region mapped in W3A, and is not restricted to the foreground of either the embedded exciting stars of the HII region or the protostar W3 IRS5. The low-density material associated with regions of massive star formation, based on an earlier study by Goldsmith et al. (2021), is quite common, and we now see that it is extended over a significant portion of W3A. It thus should be included in modeling of fine structure line emission, including interpreting low-velocity resolution observations made with incoherent spectrometer systems, in order to use these lines as accurate tracers of massive star formation

First detection of the atomic O18 isotope in the mesosphere and lower thermosphere of Earth

In the lower atmosphere of Earth, oxygen contains a higher fraction of the heavy O18 isotope than ocean water does (Dole effect). This isotopic enrichment is a signature of biological activity, set by the equilibrium between oxygenic photosynthesis and respiratory metabolisms in terrestrial and oceanic ecosystems. While the mixing between stratospheric and tropospheric oxygen leads to a slow isotopic homogenization, little is known about the isotopic oxygen enrichment in the mesosphere and thermosphere of Earth. In situ measurements from rocket-borne air samplers are limited to altitudes below the mesopause, while higher layers have only been accessible through the analysis of the oxidation of ancient cosmic spherules. Here we report the detection of the far-infrared fine-structure lines (3P1<-3P2 and 3P0<-3P1) of O18 in absorption against the Moon, and determine the O16/O18 ratio in atomic oxygen from the mesosphere and lower thermosphere in absorption. After correcting for isotopic exchange between atomic and molecular oxygen, our values for the bulk O16/O18 ratio of 468 and 382 in February and November 2021, respectively, fall significantly below that found in solar wind samples (530±2), and encompass, within uncertainties, the corresponding ratios pertaining to the Dole effect in the troposphere (487), and those found in stratospheric ozone (429 to 466). We show that with existing technology, future, more sensitive measurements will allow us to monitor deviations from isotopic homogeneity in the mesosphere and lower thermosphere of Earth by remote sensing. We demonstrate that the collisional excitation of the fine-structure levels of the P3 ground-state triplet of O18 may compete with isotopic exchange reactions, implying a deviation from the Boltzmann distribution that would be established under local thermodynamic equilibrium

Body weight and blood pressure changes on dolutegravir-, efavirenz- or atazanavir-based antiretroviral therapy in Zimbabwe: a longitudinal study.

INTRODUCTION Dolutegravir (DTG) is widely used for antiretroviral therapy (ART). We compared weight and blood pressure trends and examined the association between high blood pressure and weight gain among people living with HIV (PLHIV) switching to or starting DTG-based, efavirenz (EFV)-based and ritonavir-boosted atazanavir (ATV/r)-based ART in Zimbabwe. METHODS PLHIV aged 18 years or older who started or switched to DTG, EFV or ATV/r-based ART between January 2004 and June 2022 at Newlands Clinic in Harare, Zimbabwe, were eligible. Weight was measured at all visits (Seca floor scales); blood pressure only at clinician-led visits (Omron M2 sphygmomanometer). We used Bayesian additive models to estimate trends in weight gain and the proportion with high blood pressure (systolic >140 mmHg or diastolic >90 mmHg) in the first 2 years after starting or switching the regimen. Finally, we examined whether trends in the proportion with high blood pressure were related to weight change. RESULTS We analysed 99,969 weight and 35,449 blood pressure records from 9487 adults (DTG: 4593; EFV: 3599; ATV/r: 1295). At 24 months after starting or switching to DTG, estimated median weight gains were 4.54 kg (90% credibility interval 3.88-5.28 kg) in women and 3.71 kg (3.07-4.45 kg) in men, around twice that observed for ATV/r and over four-times the gain observed for EFV. Prevalence of high blood pressure among PLHIV receiving DTG-based ART increased from around 5% at baseline to over 20% at 24 months, with no change in PLHIV receiving EFV- or ATV/r-based ART. High blood pressure in PLHIV switching to DTG was associated with weight gain, with stronger increases in the proportion with high blood pressure for larger weight gains. CONCLUSIONS Among PLHIV starting ART or switching to a new regimen, DTG-based ART was associated with larger weight gains and a substantial increase in the prevalence of high blood pressure. Routine weight and blood pressure measurement and interventions to lower blood pressure could benefit PLHIV on DTG-based ART. Further studies are needed to elucidate the mechanisms and reversibility of these changes after discontinuation of DTG

2D patch antenna array on a double metal quantum cascade laser with >90% coupling to a Gaussian beam and selectable facet transparency at 1.9 THz

2 x 2 parallel fed and 3 x 3 serial fed patch antenna arrays on a benzocyclobutene (BCB) polymer layer are integrated with a 70 mu m wide, dry etched, double metal waveguide quantum cascade laser, operating at about 1.9 THz. The BCB surrounds the quantum cascade laser ridge and is planarized to fit precisely its height. The patch antenna arrays emit a linearly polarized, highly symmetric beam perpendicular to the antenna plane. The beams have a FWHM angle of 49 degrees (2 x 2) and 35 degrees (3 x 3). Both measurements and simulations indicate coupling factors to a Gaussian beam of over 90%. The antenna design is strongly governed by the high thickness (h = 13.6 mu m) and the low dielectric constant (epsilon(r) = 2.45) of the BCB substrate. Because the patch array has a very low input reflectivity of -13 to -20 dB over the 1.7-2.1 THz operation band, the laser needs a partially transmitting reflector to maintain the Q-factor of the active medium resonator to assure lasing in the antennas operation band. By changing the dimensions of the reflector, the facet transparency can be designed in a wide range from fully transmissive to highly reflective. (C) 2016 Optical Society of Americ

Virologic outcomes on dolutegravir-, atazanavir-, or efavirenz-based ART in urban Zimbabwe: A longitudinal study.

There are few data from sub-Saharan Africa on the virological outcomes associated with second-line ART based on protease inhibitors or dolutegravir (DTG). We compared viral load (VL) suppression among people living with HIV (PLWH) on atazanavir (ATV/r)- or DTG-based second-line ART with PLWH on efavirenz (EFV)-based first-line ART. We analyzed data from the electronic medical records system of Newlands Clinic in Harare, Zimbabwe. We included individuals aged ≥12 years when commencing first-line EFV-based ART or switching to second-line DTG- or ATV/r-based ART with ≥24 weeks follow-up after start or switch. We computed suppression rates (HIV VL <50 copies/mL) at weeks 12, 24, 48, 72, and 96 and estimated the probability of VL suppression by treatment regimen, time since start/switch of ART, sex, age, and CD4 cell count (at start/switch) using logistic regression in a Bayesian framework. We included 7013 VL measurements of 1049 PLWH (61% female) initiating first-line ART and 1114 PLWH (58% female) switching to second-line ART. Among those switching, 872 (78.3%) were switched to ATV/r and 242 (21.7%) to DTG. VL suppression was lower in second-line ART than first-line ART, except at week 12, when those on DTG showed higher suppression than those on EFV (aOR 2.10, 95%-credible interval [CrI] 1.48-3.00) and ATV/r-based regimens (aOR 1.87, 95%-CrI 1.32-2.71). For follow-up times exceeding 24 weeks however, first-line participants demonstrated significantly higher VL suppression than second-line, with no evidence for a difference between DTG and ATV/r. Notably, from week 48 onward, VL suppression seemed to stabilize across all regimen groups, with an estimated 89.1% (95% CrI 86.9-90.9%) VL suppression in EFV, 74.5% (95%-CrI 68.0-80.7%) in DTG, and 72.9% (95%-CrI 69.5-76.1%) in ATV/r at week 48, showing little change for longer follow-up times. Virologic monitoring and adherence support remain essential even in the DTG era to prevent second-line treatment failure in settings with limited treatment options

Virologic outcomes on dolutegravir-, atazanavir-, or efavirenz-based ART in urban Zimbabwe: A longitudinal study

There are few data from sub-Saharan Africa on the virological outcomes associated with second-line ART based on protease inhibitors or dolutegravir (DTG). We compared viral load (VL) suppression among people living with HIV (PLWH) on atazanavir (ATV/r)- or DTG-based second-line ART with PLWH on efavirenz (EFV)-based first-line ART. We analyzed data from the electronic medical records system of Newlands Clinic in Harare, Zimbabwe. We included individuals aged ≥12 years when commencing first-line EFV-based ART or switching to second-line DTG- or ATV/r-based ART with ≥24 weeks follow-up after start or switch. We computed suppression rates (HIV VL &lt;50 copies/mL) at weeks 12, 24, 48, 72, and 96 and estimated the probability of VL suppression by treatment regimen, time since start/switch of ART, sex, age, and CD4 cell count (at start/switch) using logistic regression in a Bayesian framework. We included 7013 VL measurements of 1049 PLWH (61% female) initiating first-line ART and 1114 PLWH (58% female) switching to second-line ART. Among those switching, 872 (78.3%) were switched to ATV/r and 242 (21.7%) to DTG. VL suppression was lower in second-line ART than first-line ART, except at week 12, when those on DTG showed higher suppression than those on EFV (aOR 2.10, 95%-credible interval [CrI] 1.48–3.00) and ATV/r-based regimens (aOR 1.87, 95%-CrI 1.32–2.71). For follow-up times exceeding 24 weeks however, first-line participants demonstrated significantly higher VL suppression than second-line, with no evidence for a difference between DTG and ATV/r. Notably, from week 48 onward, VL suppression seemed to stabilize across all regimen groups, with an estimated 89.1% (95% CrI 86.9–90.9%) VL suppression in EFV, 74.5% (95%-CrI 68.0–80.7%) in DTG, and 72.9% (95%-CrI 69.5–76.1%) in ATV/r at week 48, showing little change for longer follow-up times. Virologic monitoring and adherence support remain essential even in the DTG era to prevent second-line treatment failure in settings with limited treatment options

Fig 1 -

Number of PLWH with viral load measurements (panel A) and crude proportions (with 95% credible intervals) of viral load suppression (panel B) by treatment regimen and time post switch (ATV/r, DTG) or start (EFV) of ART. EFV, efavirenz; ATV/r, ritonavir-boosted atazanavir; DTG, dolutegravir; PLWH = people living with HIV.</p