Cold-electron bolometers for future mm and sub-mm sky surveys

Future sky surveys in the mm/sub-mm range, like the forthcoming balloon-borne missions LSPE, OLIMPO, SPIDER etc., will need detectors insensitive to cosmic rays (CRs) and with a NEP of the order of $10^{-17} \div 10^{-18}\,$W/sqrt(Hz). The Cold-Electron Bolometers (CEBs) technology is promising, having the required properties, since the absorber volume is extremely small and the electron system of the absorber is thermally insulated from the phonon system. We have developed an experimental setup to test the optical performance and the CRs insensitivity of CEBs, with the target of integrating them in the OLIMPO and LSPE focal planes.Comment: 6 figure

Fast tunable high Q-factor superconducting microwave resonators

We present fast tunable superconducting microwave resonators fabricated from planar NbN on a sapphire substrate. The $3\lambda/4$ wavelength resonators are tuning fork shaped and tuned by passing a dc current which controls the kinetic inductance of the tuning fork prongs. The $\lambda/4$ section from the open end operates as an integrated impedance converter which creates a nearly perfect short for microwave currents at the dc terminal coupling points, thus preventing microwave energy leakage through the dc lines. We measure an internal quality factor $Q_{\rm int}>10{^{5}}$ over the entire tuning range. We demonstrate a tuning range of $> 3\%$ and tuning response times as short as 20 ns for the maximum achievable detuning. Due to the quasi-fractal design, the resonators are resilient to magnetic fields of up to 0.5 T

Anomalous geomagnetic variations and possible causative structures along foothills of Himachal Pradesh-Kumaun-Himalaya

This paper presents the results of a magnetometer array study covering Kangra region to supplement information already available on the nature of geoelectrical structure at the foothills of Himachal Pradesh-Kumaun-Himalaya. The observed induction pattern across the Himalayan frontal fault is found to be the expression of a psuedo-geomagnetic coast effect associated with the edge of sheet current flowing in the sediments of the Indo Gangetic Plains. An additional conductive sheet that is required beneath the frontal folded belt may represent increased hydration of certain sedimentary layers

Two-level systems in superconducting quantum devices due to trapped quasiparticles

A major issue for the implementation of large scale superconducting quantum circuits is the interaction with interfacial two-level system defects (TLS) that leads to qubit relaxation and impedes qubit operation in certain frequency ranges that also drift in time. Another major challenge comes from non-equilibrium quasiparticles (QPs) that result in qubit dephasing and relaxation. In this work we show that such QPs can also serve as a source of TLS. Using spectral and temporal mapping of TLS-induced fluctuations in frequency tunable resonators, we identify a subset of the general TLS population that are highly coherent TLS with a low reconfiguration temperature $\sim$ 300 mK, and a non-uniform density of states. These properties can be understood if these TLS are formed by QPs trapped in shallow subgap states formed by spatial fluctutations of the superconducting order parameter $\Delta$. Magnetic field measurements of one such TLS reveals a link to superconductivity. Our results imply that trapped QPs can induce qubit relaxation.Comment: 7 pages, 4 figures, plus 18 pages, 13 figures supplementa

Experimental study of a SINIS detector response time at 350 GHz signal frequency

Response time constant of a SINIS bolometer integrated in an annular ring antenna was measured at a bath temperature of 100 mK. Samples comprising superconducting aluminium electrodes and normal-metal Al/Fe strip connected to electrodes via tunnel junctions were fabricated on oxidized Si substrate using shadow evaporation. The bolometer was illuminated by a fast black-body radiation source through a band-pass filter centered at 350 GHz with a passband of 7 GHz. Radiation source is a thin NiCr film on sapphire substrate. For rectangular 10\uf7100 μs current pulse the radiation front edge was rather sharp due to low thermal capacitance of NiCr film and low thermal conductivity of substrate at temperatures in the range 1-4 K. The rise time of the response was ∼1-10 μs. This time presumably is limited by technical reasons: high dynamic resistance of series array of bolometers and capacitance of a long twisted pair wiring from SINIS bolometer to a room-Temperature amplifier

Reflection-enhanced gain in traveling-wave parametric amplifiers

The operating principle of traveling-wave parametric amplifiers is typically understood in terms of the standard coupled mode theory, which describes the evolution of forward propagating waves without any reflections, i.e., for perfect impedance matching. However, in practice, superconducting microwave amplifiers are unmatched nonlinear finite-length devices, where the reflecting waves undergo complex parametric processes, not described by the standard coupled mode theory. Here, we present an analytical solution for the TWPA gain, which includes the interaction of reflected waves. These reflections result in corrections to the well-known results of the standard coupled mode theory, which are obtained for both three-wave and four-wave mixing processes. Due to these reflections, the gain is enhanced and unwanted nonlinear phase modulations are suppressed. Predictions of the model are experimentally demonstrated on two types of unmatched TWPA, based on coplanar waveguides with a central wire consisting of (i) a high kinetic inductance superconductor, and (ii) an array of 2000 Josephson junctions

Greater fuel efficiency is potentially preferable to reducing NOx emissions for aviation’s climate impacts

Aviation emissions of nitrogen oxides (NOx) alter the composition of the atmosphere, perturbing the greenhouse gases ozone and methane, resulting in positive and negative radiative forcing effects, respectively. In 1981, the International Civil Aviation Organization adopted a first certification standard for the regulation of aircraft engine NOx emissions with subsequent increases in stringency in 1992, 1998, 2004 and 2010 to offset the growth of the environmental impact of air transport, the main motivation being to improve local air quality with the assumed co-benefit of reducing NOx emissions at altitude and therefore their climate impacts. Increased stringency is an ongoing topic of discussion and more stringent standards are usually associated with their beneficial environmental impact. Here we show that this is not necessarily the right direction with respect to reducing the climate impacts of aviation (as opposed to local air quality impacts) because of the tradeoff effects between reducing NOx emissions and increased fuel usage, along with a revised understanding of the radiative forcing effects of methane. Moreover, the predicted lower surface air pollution levels in the future will be beneficial for reducing the climate impact of aviation NOx emissions. Thus, further efforts leading to greater fuel efficiency, and therefore lower CO2 emissions, may be preferable to reducing NOx emissions in terms of aviation’s climate impacts

Antimicrobial Activity and HPLC Fingerprinting of Crude Ocimum Extracts

The antimicrobial activity of crude methanolic and aqueous extracts of Ocimum sanctum and Ocimum kilimandsacharicum against gram positive, gram negative and antifungal activity was evaluated to find the zone of inhibition and to set a HPLC profile or fingerprint of these extracts. The crude methanolic extract of Ocimum sanctum showed strong antimicrobial activity against S.aureus and C. albicans and moderate activity against E. coli and B. subtilis. The crude methanolic extract of Ocimum kilimandsacharicum showed strong antimicrobial activity against S. aureus, E. coli and C. albicans at higher concentration, same as that shown by the standard for C. albicans. It showed moderate activity against B. subtilis. The crude aqueous extracts of Ocimum sanctum showed strong antimicrobial activity against S.aureus and moderate against others. Whereas the crude aqueous extracts of Ocimum kilimandsacharicum showed moderate activity against the gram positive and gram negative organisms and strong activity against C. albicans at higher concentration, same as that shown by the standard for C. albicans

Anisotropic broadening of XRD peaks of α′-Fe: Williamson-Hall and Warren-Averbach analysis using full width at half maximum (FWHM) and integral breadth (IB)

The anisotropic broadening of the X-ray diffraction (XRD) peaks of shear deformed martensite (α′-Fe), using both full-width at half-maximum (FWHM) and integral breadth (IB), has been studied following conventional and modified Williamson-Hall (WH) and Warren-Averbach (WA) analysis. The crystallographic study reveals limited plastic deformation of martensite (α′) within a shallow depth from the shear surface, as indicated by marginal change in the character and density of dislocation, showing the inability of the α′-phase to accommodate the strain energy of shear deformation. More importantly, the study reveals significant perturbation of modified-WH and WA model, when IB is considered for size and strain analysis, especially for higher order peaks, whereas, FWHM shows reasonably good agreement with the above mentioned models for the range of diffraction spectrum considered