Northrop Grumman (United Kingdom)

Photopatterning of graphene oxide films can be achieved by exposing a thin film of graphene oxide to a photographic flash. Absorption of light causes rapid heating of the graphene oxide resulting in deoxygenation to graphitic carbon. Using a transmission electron microscope grid as a mask, the grid pattern can be transferred to a graphene oxide film. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Twenty-three coronary bypass graft patients were evaluated by a contrast-enhanced computed tomography (CT) technique to determine graft patency. Four to six 4.8-second sequenced scans with a 1-second interscan interval were obtained in each patient during the hand injection of 25-30 ml of contrast medium in a peripheral vein. Patency of grafts was determined by a characteristic contrast enhancement. The CT technique correlated with angiographic assessment of graft patency in 59 of 62 grafts (95%). We conclude that this relatively noninvasive technique shows promise as a method for determining coronary bypass graft patency.

Abstract Capillary‐fed boiling of water from microporous metal surfaces is promising for low thermal resistance vapor chamber heat spreaders for hot spot management. Vapor transport through the void spaces in porous metals enables high heat fluxes at low evaporator superheat. In this work, the critical heat fluxes of capillary‐fed boiling in copper inverse opal (IO) wicks that consist of uniform pores with 3D periodicity is investigated. Template sintering is used to enlarge the “necks”, or hydraulic vias, that bridge adjacent IO pores of diameters from 0.6 to 2.1 µm. The enhanced neck size increases the hydraulic permeability for vapor extraction by an order of magnitude, and subsequently the CHF from 100 to 1100 W cm −2 . Modeling of the boiling limit accounts for the vapor pressure drop through an IO wick using Darcy's law at a given bubble departure rate. This work links the effect of wick structure design on the boiling crises phenomenon in microporous surfaces and demonstrates material capabilities for ultrathin and low superheat thermal management solutions for high‐power‐density electronic devices.

Systems requiring very high levels of reliability, such as aircraft controls or spacecraft, often use redundancy to achieve their requirements. Reliability models for such redundant systems have been widely treated in the literature. These models describe k-out-of-n:G systems, where n is the number of components in the system, and k is the minimum number of components that must work if the overall system is to work. Most of this literature treats the perfect fault coverage case, meaning that the system is perfectly capable of detecting, isolating, and accommodating failures of the redundant elements. However, the probability of accomplishing these tasks, termed fault coverage, is frequently less than unity. Correct modeling of imperfect coverage is critical to the design of highly reliable systems. Even very high values of coverage, only slightly less than unity, will have a major impact on the overall system reliability when compared to the ideal system with perfect coverage. The appropriate coverage modeling approach depends on the system design architecture, particularly the technique(s) used to select among the redundant elements. This paper demonstrates how coverage effects can be computed, using both combinatorial, and recursive techniques, for four different coverage models: perfect fault coverage (PFC), element level coverage (ELC), fault level coverage (FLC), and one-on-one level coverage (OLC). The designation of PFC, ELC, FLC, and OLC to distinguish types of coverage modeling is suggested in this paper.

In vivo studies were performed on 28 dogs to evaluate the usefulness of transmission computed tomography (CT) in the detection and quantitation of experimentally induced myocardial infarction. Intravenously administered contrast material was required to define the internal structure of the heart and to differentiate normal from infarcted tissue. Transmural infarcts with homogeneous central regions were visualized as areas of diminished contrast enhancement compared with the normal myocardium. All transmural infarcts of at least 24 hours' duration showed a surrounding border zone of patchy necrosis that was variable in size and had high CT numbers due to slow washout of the contrast material from this region. Infarct area determined from the images for individual slices correlated well (r = 0.976) with that calculated using pathology. The technique is very sensitive and can detect infarction within a papillary muscle. Nontransmural or patchy infarcts show up as areas of diffuse contrast enhancement without a central core of diminished enhancement. The distribution of the contrast material is similar to that of technetium-99m pyrophosphate in the border zone of the infarct in infusion studies, but in bolus studies it behaves more like thallium-201.

Abstract Understanding how nano‐ or micro‐scale structures and material properties can be optimally configured to attain specific functionalities remains a fundamental challenge. Photonic metasurfaces, for instance, can be spectrally tuned through material choice and structural geometry to achieve unique optical responses. However, existing numerical design methods require prior identification of specific material−structure combinations, or device classes, as the starting point for optimization. As such, a unified solution that simultaneously optimizes across materials and geometries has yet to be realized. To overcome these challenges, a global deep learning‐based inverse design framework is presented, where a conditional deep convolutional generative adversarial network is trained on colored images encoded with a range of material and structural parameters, including refractive index, plasma frequency, and geometric design. It is demonstrated that, in response to target absorption spectra, the network can identify an effective metasurface in terms of its class, materials properties, and overall shape. Furthermore, the model can arrive at multiple design variants with distinct materials and structures that present nearly identical absorption spectra. The proposed framework is thus an important step towards global photonics and materials design strategies that can identify combinations of device categories, material properties, and geometric parameters which algorithmically deliver a sought functionality.

In this paper, we present three MMIC low-noise amplifiers using dual-gate GaAs HEMT devices in a balanced amplifier configuration. The designs target three different frequency bands including 4-9 GHz, 9-20 GHz, and 20-40 GHz. These dual-gate balanced designs demonstrate the excellent qualities of balanced amplifiers in terms of stability and matched characteristics, while demonstrating higher bandwidth than designs with a single-stage common-source device. Additionally, noise performance is excellent, with the 4-9 GHz LNA demonstrating <1.75 dB noise figure (NF), the 9-20 GHz LNA <2.75 dB NF and the 20-40 GHz LNA <2.5 dB NF. Demonstrating high gain and excellent bandwidth, the dual-gate devices seem a logical choice for the balanced amplifier topology.

The effect of oxygen and albumin on the electrochemical behavior of a Ti-6Al-4V alloy immersed in a simulated inorganic plasma (SIP) solution was studied with a rotating-cylindrical electrode configuration to focus on the surface/electrolyte reactions. Potentiokinetic scans and electrochemical impedance spectroscopy have been used to characterize the interface by determining the passive current density and capacitance. For the polarization scans, an albumin addition of 37.7 mg/cm(3) to the SIP solution (oxygenated and unoxygenated) decreased the passive current density, indicating a lowering of the corrosive rate. The surface capacitance for the Ti-6Al-4V alloy immersed in a SIP solution averaged 13 microF/cm(2), which transformed after albumin addition (37.7 mg/cm(3)) from a potential independent behavior to the capacitance ranging from 23 to 6 microF/cm(2) with increasing potentials from -800 to 1500 mV(SCE), respectively, indicative of albumin adsorption. Within the same potential range and albumin addition to oxygenated solutions, the capacitances expanded slightly with a similar decreasing trend from 31 to 6 microF/cm(2), although the capacitance depicts an interaction between the hydrated passive film and the adsorbed albumin from -550 to 500 mV(SCE) in which the capacitance plateaued at 15 microF/cm(2). The hydrated porous oxide film results from the porous rutile layer reacting with H(2)O(2) formed as an intermediary component of oxygen reduction at the Ti-6Al-4V surface. The passive film-albumin interaction would affect the processing of titanium alloys in their surface preparation for biocompatibility, as well as determining the reactivity of titanium alloys to proteins.

Abstract Large scale laser facilities are needed to advance the energy frontier in high energy physics and accelerator physics. Laser plasma accelerators are core to advanced accelerator concepts aimed at reaching TeV electron electron colliders. In these facilities, intense laser pulses drive plasmas and are used to accelerate electrons to high energies in remarkably short distances. A laser plasma accelerator could in principle reach high energies with an accelerating length that is 1000 times shorter than in conventional RF based accelerators. Notionally, laser driven particle beam energies could scale beyond state of the art conventional accelerators. LPAs have produced multi GeV electron beams in about 20 cm with relative energy spread of about 2 percent, supported by highly developed laser technology. This validates key elements of the US DOE strategy for such accelerators to enable future colliders but extending best results to date to a TeV collider will require lasers with higher average power. While the per pulse energies envisioned for laser driven colliders are achievable with current lasers, low laser repetition rates limit potential collider luminosity. Applications will require rates of kHz to tens of kHz at Joules of energy and high efficiency, and a collider would require about 100 such stages, a leap from current Hz class LPAs. This represents a challenging 1000 fold increase in laser repetition rates beyond current state of the art. This whitepaper describes current research and outlook for candidate laser systems as well as the accompanying broadband and high damage threshold optics needed for driving future advanced accelerators.

Abstract This paper describes a forward radiative transfer model and retrieval system (FMRS) for the Tropospheric Water and cloud ICE (TWICE) CubeSat instrument. We use the FMRS to simulate radiances for the TWICE's 14 millimeter‐ and submillimeter‐wavelength channels for a tropical atmospheric state produced by a Weather Research and Forecasting model simulation. We also perform simultaneous retrievals of cloud ice particle size, ice water content (IWC), water vapor content (H 2 O), and temperature from the simulated TWICE radiances using the FMRS. We show that the TWICE instrument is capable of retrieving ice particle size in the range of ~50–1000 μm in mass mean effective diameter with approximately 50% uncertainty. The uncertainties of other retrievals from TWICE are about 1 K for temperature, 50% for IWC, and 20% for H 2 O.

The crux of visible exoplanet detection is overcoming significant star-planet contrast ratios on the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> - at very small angular separations. We are developing a nulling interferometer coronagraph designed to achieve a 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> contrast ratio at a working science bandpass of 20% visible light using a pseudo-achromatic phase flip. Recent results yield contrast ratios at the 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> level with a 15% visible bandpass averaged over three seconds. Further broadening of the bandpass will require hardware modifications, although the argument is made that broadening the bandpass should not adversely affect the null depth until beyond 20% visible light. The current testbed configuration has reached monochromatic null depths of 1.11times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> (lambda = 638 nm) averaged over three seconds. This paper will describe the experimental approach for achieving broadband nulls, as well as error considerations and limitations, and the most recent results of the nulling interferometer testbed.

The paper explains the concept of a cyber range and its use for performing system security assessments. It shows the advantage of evaluating security from a whole-system perspective rather than individual components and undertaking this with no risks of contamination, damage or degradation of the actual system. Moving the architecture of a real system into a cyber range in a meaningful and costeffective way is the key challenge for performing security assessments. A solution is to use representative models and virtualisation however the paper explains that it is necessary to be clear what side effects this might have. (5 pages)

In this paper, we present the framework for developing the first working power amplifiers at sub-millimeter-wave frequencies. The technology is made possible by an advanced InP HEMT transistor. A three-stage power amplifier is presented, which uses a binary combiner to realize a total output periphery of 80 mum and demonstrates 12-dB gain at 335 GHz, making, this the first demonstrated sub-millimeter-wave power amplifier. Measured saturated power of 2 mW at 330 GHz is also presented, which provides a transistor power benchmark of 25 mW/mm at 330 GHz. Finally, single-stage amplifier data with large periphery transistors are presented, which demonstrates 5-dB measured gain at 230 GHz and positive measured S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> gain to ~300 GHz, demonstrating that power amplifiers using larger transistors are feasible at these frequencies as well.

A yellow band electroluminescence (EL) characteristic, which might be attributed to the same origin as the yellow luminescence (YL) defects, was observed in GaN high electron mobility transistors (HEMTs) at room temperature. The YL-like defect origin has been tentatively confirmed by comparing EL and photoluminescence (PL) results. To further explore the properties of YL-like EL centers, EL dependence on the drain-to-source and gate-to-source voltage were investigated. The direct comparison between the EL and temperature distribution images from the same GaN HEMT suggests that two distinct EL emission mechanisms exist at the off-state breakdown. The other type of EL emission at off-state is attributed to carrier intravalley transition due to hot carrier generation by impact ionization at localized breakdown sites. This type of hot carrier induced light emission was observed at on-state and off-state operations. The YL-like emission was shown to have a stronger electric field than the hot carrier induced emission.

In this paper we present a MMIC amplifier which demonstrates ˜12-dB gain at a center frequency of 245-GHz. The MMIC is intended to demonstrate the potential of power amplification at short-millimeter wave frequencies. Each stage of the three stage amplifier utilizes a 1:2 output split to reach a total output periphery of 80-μm. The combination of high realized gain per stage and output periphery indicate the potential generating output powers on the order of several mW at short mm-wave frequencies using MMIC amplifiers for the first time. The amplifier is implemented in coplanar waveguide and uses an InP HEMT process with a 35-nm gate.

Guidelines issued by the Department of Energy and NASA provide a reference point for an ambitious program.

&lt;div class="htmlview paragraph"&gt;Results of an analytical investigation on the influence of bond thickness upon the stress distribution in single lap adhesive joints are presented. The present work extends the basic approach for bonded joints, originally introduced by Goland and Reissner, through use of a more complete shear-strain/displacement equation for the adhesive layer. This refinement was not found to be included in any of the numerous analytical investigations reviewed.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;As a result of the approach employed, the present work uncovers several interesting phenomena without adding any significant complication to the analysis. Besides modifying some coefficients in the shear stress equations, completely new terms in the differential equation and boundary conditions for bond peel stress are obtained. In addition, a variation of shear stress through the bond thickness - no matter how thin it may be - is analytically predicted only by the present theory. This through-the-bond-thickness variation of shear stress identifies two antisymmetrical adherend-bond interface points at which the shear stresses are highest. The growth of joint failures originating from these points agrees with results obtained from actual experiments.&lt;/div&gt;

Abstract This article introduces the principal methodologies and some technologies that are being applied for nondestructive evaluation of composite materials. These include ultrasonic testing (UT), air-coupled UT, laser UT, ultrasonic spectroscopy, leaky lamb wave method, acousto-ultrasonics, radiography, X-ray computed tomography, thermography, low-frequency vibration methods, acoustic emission, eddy current testing, optical holography, and shearography. The article presents some examples are for fiber-reinforced polymer-matrix composites. Many of the techniques have general applicability to other types of composites such as metal-matrix composites and ceramic-matrix composites.

A high efficiency and high linearity monolithic power amplifier suitable for 20 GHz phased array applications is presented in this paper. The amplifier demonstrates a 17 (IB linear gain, a maximum CW power of 29.4 dBm (870 mW), and a 37.8% power-added-efficiency. Output power of 23.8 dBm with 15% efficiency is measured at 25 dB noise power ratio (NPR) value. For the power amplifier design, we have utilized a novel sinusoid-to-noise transform technique which uses CW simulations to predict NPR. Good agreement is observed between the simulated NPR values and measured data. The power amplifier has been able to achieve high power and efficiency with high linearity, demonstrating the suitability of the InGaAs/InAlAs/InP HBT production process for phased array applications.

A key value proposition for incorporation of Artificial Intelligence (AI) and Machine Learning (ML) methods into aviation is that they offer means of understanding data in ways that allow hitherto unprecedented insights for decision making, whether by a human or a machine. When these techniques are applied to cyber-physical systems, such as unmanned aircraft systems (UAS), they can result in positive societal impacts (e.g., search and rescue). However, the advantages of such techniques must be balanced against appropriate safety and security requirements so that taken together the system can ensure an acceptable level of confidence and assurance in both civilian and military applications. To this end, there is a need for the capability to suitably characterize such techniques and assess how they can be integrated into a viable assurance framework that can maximize safety and security benefits while bounding the inherent risk of non-determinism arising from such these approaches. This paper focuses on assurance and behavior bounds for decision making systems from a) algorithmic functional performance; b) schedulability analysis and candidate scheduling paradigms; and c) processor architectures (including multi-core) to support minimized interference in general. We will place particular emphasis on machine learning approaches for control, navigation and guidance applications for unmanned systems. This paper will review available and emerging approaches (e.g., formal methods, modeling and simulation, real-time monitors/agents among others) to ensuring behavior assurance for unmanned systems engaged in missions of moderate-to-high complexity. The intent is to examine behavior assurance for advanced autonomous operations within a holistic life-cycle process.