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Water and ammonia vapors are known to be the major sources of spectral absorption at pressure levels observed by the microwave radiometer (MWR) on Juno. However, the brightness temperatures and limb darkening observed by the MWR at its longest-wavelength channel of 50 cm (600 MHz) in the first nine perijove passes indicate the existence of an additional source of opacity in the deep atmosphere of Jupiter (pressures beyond 100 bar). The absorption properties of ammonia and water vapor, and their relative abundances in Jupiter’s atmosphere, do not provide sufficient opacity in the deep atmosphere to explain the 600 MHz channel observation. Here we show that free electrons due to the ionization of alkali metals, i.e., sodium and potassium, with subsolar metallicity, [M/H] (log-based 10 relative concentration to solar) in the range of [M/H] = −2 to [M/H] = −5, can provide the missing source of opacity in the deep atmosphere. If the alkali metals are not the source of additional opacity in the MWR data, then their metallicity at 1000 bars can only be even lower. This upper bound of −2 on the metallicity of the alkali metals contrasts with the other heavy elements—C, N, S, Ar, Kr, and Xe—that are all enriched relative to their solar abundances, having a metallicity of approximately +0.5.

The NASA Juno mission includes a six-channel microwave radiometer system (MWR) operating in the 1.3-50 cm wavelength range in order to retrieve abundances of ammonia and water vapor from the microwave signature of Jupiter (see Janssen et al. 2016). In order to plan observations and accurately interpret data from such observations, over 6000 laboratory measurements of the microwave absorption properties of gaseous ammonia, water vapor, and aqueous ammonia solution have been conducted under simulated Jovian conditions using new laboratory systems capable of high-precision measurement under the extreme conditions of the deep atmosphere of Jupiter (up to 100 bars pressure and 505 K temperature). This is one of the most extensive laboratory measurement campaigns ever conducted in support of a microwave remote sensing instrument. New, more precise models for the microwave absorption from these constituents have and are being developed from these measurements. Application of these absorption properties to radiative transfer models for the six wavelengths involved will provide a valuable planning tool for observations, and will also make possible accurate retrievals of the abundance of these constituents during and after observations are conducted. [ABSTRACT FROM AUTHOR]

Ammonia molecules have an important role in the radiation-induced chemistry that occurs on grains in the cold interstellar medium and leads to the formation of nitrogen containing molecules. Such grains and surfaces are primarily covered by water ices; however, these conditions allow the growth of solid ammonia films as well. Yet, solid ammonia know-how lags the vast volume of research that has been invested in the case of films of its "sibling" molecule water, which, in the porous amorphous phase, spontaneously form polar films and can cage coadsorbed molecules within their hydrogen-bonded matrix. Here, we report on the effect of growth temperature on the spontaneous polarization of solid ammonia films (leading to internal electric fields of ∼105 V/m) within the range of 30 K–85 K on top of a Ru(0001) substrate under ultra-high vacuum conditions. The effect of growth temperature on the films' depolarization upon annealing was recorded as well. By demonstrating the ability of ammonia to cage coadsorbed molecules, as water does, we show that temperature-programmed contact potential difference measurements performed by a Kelvin probe and especially their temperature derivative can track film reorganization/reconstruction and crystallization at temperatures significantly lower than the film desorption. [ABSTRACT FROM AUTHOR]

This article discusses the design of the beam-steerable aperiodic linear array antenna with improved sidelobe level (SLL), using the strip-projection method. The strip projection method uses the area of rotated higher-dimensional lattice and projects it to lower dimensions to generate an aperiodic array. This article describes the modeling and analysis of such an array and its optimization for the desired far-field performance. The aperiodic arrays are also generated using various evolutionary optimization algorithms, namely genetic algorithm (GA), particle swarm optimization (PSO), and Jaya algorithms. The far-field performance of the generated aperiodic arrays is compared with the conventional periodic array. The proposed 21-element aperiodic array is also populated with a X-band electromagnetically coupled patch antenna and phase shifter designed using varying width of the high dielectric material. The aperiodic patch array antenna is also developed and characterized for various beam scan angles. A significant improvement of 5.72 dB in peak SLL is achieved at ±30° beam scan angle. [ABSTRACT FROM AUTHOR]

The atmosphere of Venus remains mysterious, with many outstanding chemical connundra. These include the unexpected presence of ~10 ppm O2 in the cloud layers, an unknown composition of large particles in the lower cloud layers, and hard to explain measured vertical abundance profiles of SO2 and H2O. We propose a hypothesis for the chemistry in the clouds that largely addresses all of the above anomalies. We include ammonia (NH3), a key component that has been tentatively detected both by the Venera 8 and Pioneer Venus probes. NH3 dissolves in some of the sulfuric acid cloud droplets, effectively neutralizing the acid and trapping dissolved SO2 as ammonium sulfite salts. This trapping of SO2 in the clouds, together with the release of SO2 below the clouds as the droplets settle out to higher temperatures, explains the vertical SO2 abundance anomaly. A consequence of the presence of NH3 is that some Venus cloud droplets must be semisolid ammonium salt slurries, with a pH of ~1, which matches Earth acidophile environments, rather than concentrated sulfuric acid. The source of NH3 is unknown but could involve biological production; if so, then the most energy-efficient NH3-producing reaction also creates O2, explaining the detection of O2 in the cloud layers. Our model therefore predicts that the clouds are more habitable than previously thought, and may be inhabited. Unlike prior atmospheric models, ours does not require forced chemical constraints to match the data. Our hypothesis, guided by existing observations, can be tested by new Venus in situ measurements. [ABSTRACT FROM AUTHOR]

After decades of research on non-invasive glucose monitoring, invasive devices based on finger blood sampling are still the predominant reference for diabetic patients for accurately measuring blood glucose levels. Meanwhile, research continues improving point-of-care technology toward the development of painless and more accurate devices. Raman spectroscopy is well-known as a potentially valuable and painless approach for measuring glucose levels. However, previous Raman studies deal with glucose concentrations that are still order of magnitudes away with respect to human tissues' physiological concentrations, or they propose enhancement methodologies either invasive or much complex to assure sufficient sensitivity in the physiological range. Instead, this study proposes an alternative non-enhanced Raman spectroscopy approach sensitive to glucose concentrations from 1 to 5 mmol/l, which correspond to the lowest physiopathological glucose level in human blood. Our findings suggest a very selective detection of glucose with respect to other typical metabolites, usually interfering with Raman spectroscopy's glucose detection. We validate the proposed univariate sensing methodology on glucose solutions mixed with lactate and urea, the two most common molecules found in human serum with concentrations similar to glucose and similar features in the Raman spectra. Our findings clearly illustrate that reliable detection of glucose by Raman spectroscopy is feasible by exploiting the shifted peak at 1125 ± 10 cm–1 within physiopathological ranges. [ABSTRACT FROM AUTHOR]

In electronic beam scanning, the number of phase shifters is an obvious challenge. So, there are several methods to reduce the number of phase shifters. The aim of this paper is to investigate the use of the meta-heuristic algorithm to lower the grating lobe level in the subarray antenna. Improve the result obtained by group subarray optimization techniques to determine topology and space between elements, and complex optimization of weight, simultaneously. Uniform subarray and random subarray are analyzed in Matlab to determine the coefficient of excitation by the evolutionary algorithm, as well as swarm and hybrid. The results of the simulation are shown; this method leads to radiation pattern without grating lobe in wide scanning angle. It indicates that there is a possibility of obtaining wide electronic scanning with minimum number of phase shifters and improving result. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate that the uncertainty of the dual-satellite ephemeris must be included in order for the geolocation covariance to be accurate. Without the inclusion of this additional error source, the covariance is no longer consistent with the true uncertainty and can convey misleading results. The larger the uncertainty associated with the dual-satellite ephemeris the larger the geolocation covariance becomes. Therefore, we first demonstrate a technique for improving the dual-satellite ephemeris knowledge by using calibrator transmitters for orbit determination. Second, we derive a consider batch filter, which computes the best estimate of position of the unknown radio frequency source while taking into account the dual-satellite ephemeris uncertainty. An algorithm is also proposed for adding a probabilistic altitude constraint, which significantly reduces the solution error. Finally, we briefly touch upon a technique that allows for the dual-satellite ephemeris and source position to be estimated simultaneously thereby maintaining the correlations and optimality. All algorithms introduced have since been applied to real-world data and conveys actual capabilities rather than a theoretical approach alone. [ABSTRACT FROM AUTHOR]

Investigates the induction and imaging molecule dissociation on a semiconductor surface. Use of variable-temperature, ultrahigh vacuum scanning tunneling microscope; Effect of sulfidation on the materials properties of alloys; Calculation of the activation barrier from the atomistic analysis of the dissociation rates.

The Juno Microwave Radiometer (MWR) is a six-frequency scientific instrument designed and built to investigate the deep atmosphere of Jupiter. It is one of a suite of instruments on NASA's New Frontiers Mission Juno launched to Jupiter on August 5, 2011. The focus of this paper is the description of the scientific objectives of the MWR investigation along with the experimental design, observational approach, and calibration that will achieve these objectives, based on the Juno mission plan up to Jupiter orbit insertion on July 4, 2016. With frequencies distributed approximately by octave from 600 MHz to 22 GHz, the MWR will sample the atmospheric thermal radiation from depths extending from the ammonia cloud region at around 1 bar to pressure levels as deep as 1000 bars. The primary scientific objectives of the MWR investigation are to determine the presently unknown dynamical properties of Jupiter's subcloud atmosphere and to determine the global abundance of oxygen and nitrogen, present in the atmosphere as water and ammonia deep below their respective cloud decks. The MWR experiment is designed to measure both the thermal radiation from Jupiter and its emission-angle dependence at each frequency relative to the atmospheric local normal with high accuracy. The antennas at the four highest frequencies (21.9, 10.0, 5.2, and 2.6 GHz) have ∼12° beamwidths and will achieve a spatial resolution approaching 600 km near perijove. The antennas at the lowest frequencies (0.6 and 1.25 GHz) are constrained by physical size limitations and have 20° beamwidths, enabling a spatial resolution of as high as 1000 km to be obtained. The MWR will obtain Jupiter's brightness temperature and its emission-angle dependence at each point along the subspacecraft track, over angles up to 60° from the normal over most latitudes, during at least six perijove passes after orbit insertion. The emission-angle dependence will be obtained for all frequencies to an accuracy of better than one part in $10^{3}$ , sufficient to detect small variations in atmospheric temperature and absorber concentration profiles that distinguish dynamical and compositional properties of the deep Jovian atmosphere. [ABSTRACT FROM AUTHOR]

The Juno mission's primary science objectives include the investigation of Jupiter interior structure via the determination of its gravitational field. Juno will provide more accurate determination of Jupiter's gravity harmonics that will provide new constraints on interior structure models. Juno will also measure the gravitational response from tides raised on Jupiter by Galilean satellites. This is accomplished by utilizing Gravity Science instrumentation to support measurements of the Doppler shift of the Juno radio signal by NASA's Deep Space Network at two radio frequencies. The Doppler data measure the changes in the spacecraft velocity in the direction to Earth caused by the Jupiter gravity field. Doppler measurements at X-band ( $\sim 8$ GHz) are supported by the spacecraft telecommunications subsystem for command and telemetry and are used for spacecraft navigation as well as Gravity Science. The spacecraft also includes a Ka-band ( $\sim 32$ GHz) translator and amplifier specifically for the Gravity Science investigation contributed by the Italian Space Agency. The use of two radio frequencies allows for improved accuracy by removal of noise due to charged particles along the radio signal path. [ABSTRACT FROM AUTHOR]

Juno is a PI-led mission to Jupiter, the second mission in NASA's New Frontiers Program. The 3625-kg spacecraft spins at 2 rpm and is powered by three 9-meter-long solar arrays that provide ∼500 watts in orbit about Jupiter. Juno carries eight science instruments that perform nine science investigations (radio science utilizes the communications antenna). Juno's science objectives target Jupiter's origin, interior, and atmosphere, and include an investigation of Jupiter's polar magnetosphere and luminous aurora. [ABSTRACT FROM AUTHOR]

We present aeronomical observations collected using remote sensing instruments on board Venus Express, complemented with ground-based observations and numerical modeling. They are mostly based on VIRTIS and SPICAV measurements of airglow obtained in the nadir mode and at the limb above 90 km. They complement our understanding of the behavior of Venus' upper atmosphere that was largely based on Pioneer Venus observations mostly performed over thirty years earlier. Following a summary of recent spectral data from the EUV to the infrared, we examine how these observations have improved our knowledge of the composition, thermal structure, dynamics and transport of the Venus upper atmosphere. We then synthesize progress in three-dimensional modeling of the upper atmosphere which is largely based on global mapping and observations of time variations of the nitric oxide and O nightglow emissions. Processes controlling the escape flux of atoms to space are described. Results based on the VeRA radio propagation experiment are summarized and compared to ionospheric measurements collected during earlier space missions. Finally, we point out some unsolved and open questions generated by these recent datasets and model comparisons. [ABSTRACT FROM AUTHOR]

A benchmarking procedure for sparse linear array synthesis methods is proposed. Our approach is based on the comparison of the performance of the array synthesis algorithm under test with the performance of a reference solution based on a optimally equispaced array. The benchmark procedure is demonstrated considering some examples regarding sparse synthesis method proposed in literature. Guidelines for the correct comparison of synthesis methods and some "tough problems" for the test of new sparse synthesis algorithms are also provided. [ABSTRACT FROM AUTHOR]

Cognitive radio systems are a promising solution to the spectrum scarcity problem but accurate modeling of both primary and secondary user activity, spectrum utilization, and system throughput are vital to achieve good performance in such systems. In this paper, we consider a set of primary users that are distributed in space based on a Poisson point process and demand for the available spectrum. We assess the effect of these demands on primary user activity, spectrum occupancy, and total system throughput under various subcarrier-request distributions and fading environments. The asymptotic mean number of active primary users and occupied subcarriers are analytically derived and evaluated further considering the primary network traffic and the average probability of miss-detection of an occupied subcarrier by a single sensing secondary user. It is seen that the average probability of miss-detection is a function of system traffic and the subcarrier-request distribution of primary users and that for extreme primary user traffic, the applied subcarrier-request distribution and total number of provided subcarriers cannot improve further the asymptotic sensing accuracy of the secondary user. Finally, the primary network and the secondary user throughputs in the presence of mutual interference due to imperfect detection of secondary users are investigated and their asymptotic values for large primary network traffic, primary user transmit power, and secondary user transmit power are analytically derived. The results are critically investigated, formulated as theorems and compared with simulations. It is observed that analytical and simulation results are in perfect agreement. It is shown that increasing the primary network transmit power benefits both the primary network and the secondary user throughputs. [ABSTRACT FROM PUBLISHER]

The possibility of detecting wave processes in the atmosphere-ionosphere system of the planet from perturbations of radio signals in radio occultation experiments is studied. A method of interpretation of the radio-raying data that does not employ integral transforms and is well-adapted to problems of detecting refractive index oscillations observed during sensing of the stratified gas envelope of the planet is presented. Periodic oscillations of the radio signal power that are linearly related with the rate of variation in the frequency of the signal used for probing of the atmosphere and ionosphere are found, which evidences wave perturbations of the medium near the lower boundary of the daytime ionosphere of Venus. [ABSTRACT FROM AUTHOR]

A physically-based parametric model (PPM) to predict the sky-noise temperature in all weather conditions is proposed. The proposed prediction model is based on the non-linear regression fit of numerical simulations derived from the sky-noise eddington radiative-transfer model (SNEM) in an absorbing and scattering medium such as gaseous, cloudy and rainy atmosphere. The PPM prediction method, dependent on measured path attenuation, beacon frequency, and antenna-pointing elevation angle, describes the statistical behavior of the atmospheric mean radiative temperature, which in its turn relates sky-noise temperature to slant-path attenuation. PPM validity ranges from X- to W- band and from 10^\circ to 90^\circ in terms of elevation angle. A comparison of the estimated PPM radio-propagation variables with corresponding ITALSAT satellite data, collected at the Spino d'Adda receiving station (Italy), is also carried out and discussed. The PPM prediction technique provides a root-mean-square retrieval error generally less than 8 K for all frequencies. Results show an improvement with respect to the current International Telecommunication Union (ITU) recommendations, especially at Q- and V-band and above, where the atmospheric multiple scattering effects cannot be disregarded. [ABSTRACT FROM PUBLISHER]

This paper addresses the problem of accurately modeling the spectrum occupancy patterns of real radio communication systems, which is an essential aspect in the study of cognitive radio (CR) networks. The main drawbacks and limitations of previous works are identified, and the methodological procedures on which they rely are improved and extended. Two sophisticated measurement platforms, providing low and high time resolutions, are used to obtain extensive real-world data from a multiband spectrum measurement campaign, embracing a wide variety of spectrum bands of practical interest for CR applications. A comprehensive, systematical, and rigorous analysis of the statistical properties observed in the measurement data is then performed to find accurate models capable of capturing and reproducing, within reasonable complexity limits, the statistical properties of temporal patterns, at both short and long timescales, in real wireless systems. Innovative modeling approaches capable of simultaneously describing statistical properties at both timescales are developed as well. In summary, this paper contributes realistic and accurate time-dimension spectrum usage models for their application to the study and development of CR. [ABSTRACT FROM PUBLISHER]

Two new phased array design techniques are introduced that utilize rotational symmetry to avoid grating lobes during scanning and over ultra-wide bandwidths. The first is an optimization method, which employs the covariance matrix adaptation evolutionary strategy to determine the best locations of elements inside a sector of a circle. The second technique uses standard periodic lattices inside the same circular sector. Although the segments themselves are internally periodic, the rotational symmetry of the full array eliminates the occurrence of grating lobes and is capable of generating antenna element layouts with useful ultra-wideband properties. These design techniques yield arrays with not only ultra-wideband characteristics, but properties that lend themselves to relatively straightforward modular construction, especially the semi-periodic variety. [ABSTRACT FROM PUBLISHER]

This paper introduces the self-organizing dynamic spectrum management (SO-DSM) for ad hoc cognitive radio (CR) networks. In this scheme, CR units try to exploit the primary networks' unused bands by establishing links with neighbouring CRs using those bands. Inspired by human brain, the CRs extract and memorize the activity patterns of the primary network and other CRs and create temporal channel assignments on sub-bands with no recent primary user activities using a self-organizing maps (SOM) technique. The proposed scheme is decentralized and employs a simple learning rule with low complexity and minimal memory requirements. The simulation results show that SO-DSM significantly decreases the probability of collision with primary users and also probability of CR link interruption. [ABSTRACT FROM PUBLISHER]

In this paper, a deterministic strategy to generate the aperiodicity, based on three geometric taper distributions is studied and validated. The method is applied to study arrays with average inter-elements spacing larger than a wavelength, exhibiting a reduction of the grating lobe level and requiring lower aperture size against a periodic structure with same directivity. Finally, a microstrip patch aperiodic array has been designed, manufactured and measured for an experimental validation of the concept, obtaining good agreement between simulated and measured radiation patterns. This manufactured antenna demonstrates experimentally the reduction of the grating lobes with a similar level to the side lobe. [ABSTRACT FROM AUTHOR]

The spectrum occupancy models widely used to date in dynamic spectrum access/cognitive radio (DSA/CR) research frequently rely on assumptions and oversimplifications that have not been validated with empirical measurement data. In this context, this paper presents an empirical time-dimension model of spectrum use that is appropriate for DSA/CR studies. Concretely, a two-state discrete-time Markov chain with novel deterministic and stochastic duty cycle models is proposed as an adequate mean to accurately describe spectrum occupancy in the time domain. The validity and accuracy of the proposed modeling approach is evaluated and corroborated with extensive empirical data from a multiband spectrum measurement campaign. The obtained results demonstrate that the proposed approach is able to accurately capture and reproduce the relevant statistical properties of spectrum use observed in real-world channels of various radio technologies. The importance of accurately modeling spectrum use in the design and evaluation of novel DSA/CR techniques is highlighted with a practical case study. [ABSTRACT FROM PUBLISHER]