ALBERT

Description: The NASA Design and Analysis of Rotorcraft (NDARC) software is an aircraft system analysis tool that supports both conceptual design efforts and technology impact assessments. The principal tasks are to design (or size) a rotorcraft to meet specified requirements, including vertical takeoff and landing (VTOL) operation, and then analyze the performance of the aircraft for a set of conditions. For broad and lasting utility, it is important that the code have the capability to model general rotorcraft configurations, and estimate the performance and weights of advanced rotor concepts. The architecture of the NDARC code accommodates configuration flexibility, a hierarchy of models, and ultimately multidisciplinary design, analysis, and optimization. Initially the software is implemented with low-fidelity models, typically appropriate for the conceptual design environment. An NDARC job consists of one or more cases, each case optionally performing design and analysis tasks. The design task involves sizing the rotorcraft to satisfy specified design conditions and missions. The analysis tasks can include off-design mission performance calculation, flight performance calculation for point operating conditions, and generation of subsystem or component performance maps. For analysis tasks, the aircraft description can come from the sizing task, from a previous case or a previous NDARC job, or be independently generated (typically the description of an existing aircraft). The aircraft consists of a set of components, including fuselage, rotors, wings, tails, and propulsion. For each component, attributes such as performance, drag, and weight can be calculated; and the aircraft attributes are obtained from the sum of the component attributes. Description and analysis of conventional rotorcraft configurations is facilitated, while retaining the capability to model novel and advanced concepts. Specific rotorcraft configurations considered are single-main-rotor and tail-rotor helicopter, tandem helicopter, coaxial helicopter, and tiltrotor. The architecture of the code accommodates addition of new or higher-fidelity attribute models for a component, as well as addition of new components.

Description: NASA Ames Research Center (ARC) Aeromechanics Branch hosted more than 60 interns this summer and focused their energies on studying the future of vertical flight. This is the second of two reports from this past years summer interns.

Description: No abstract available

Description: Vacuum airships fueled by renewable energy would reduce reliance on fossil fuel-based modes of transport, lessen the need for limited and non-renewable lifting gases, and can be achieved using novel manufacturing techniques for ultra-light, discrete lattice material systems.The Discrete Lattice Material Vacuum Airships (DLMVA) system combines novel material science and manufacturing technologies for new modes of mass transportation, resulting in a disruptive approach to reduce national resource consumption and emissions. Through the use of high performance building block elements, modular, scalable and extensible aircraft can be rapidly assembled into positive net-buoyancy systems utilizing a vacuum instead of a lifting gas. By using architected lattice material principles, show that lattice materials can overcome stability limitations of previous vacuum balloon designs. Additionally, we show that lattice vacuum balloons are strength limited, rather than stability limited. As a result,airborne infrastructure can be developed to support the proliferation of modern systems such as e-commerce and distributed communications, while simultaneously reducing dependence on finite, non-renewable, emission-heavy resources.

Description: NASA's Unmanned Aircraft Systems Integration into the National Airspace System (UAS in the NAS) project examines the technical barriers associated with the operation of UAS in civil airspace. For UAS, the removal of the pilot from onboard the aircraft has eliminated the ability of the ground-based pilot in command (PIC) to use out-the-window visual information to make judgements about a potential threat of a loss of well clear with another aircraft. NASA's Phase 1 research supported the development of a Detect and Avoid (DAA) system that supports the ground-based pilot's ability to detect potential traffic conflicts and determine a resolution maneuver, but existing display/alerting requirements did not account for multiple UAS control (1:N). Demands for increased scalability of UAS in the NAS operations are expected to create a need for simultaneous control of UAs, and thus, a new DAA HMI design will likely be necessary. Previous research, however, has found performance degradations as the number of vehicles under operator control has increased. The purpose of the current human-in-the-loop (HITL) simulation was to examine the viability of 1:N operations with the Phase 1 DAA alerting and guidance. Sixteen UAS pilots flew three scenarios with varying number of UAs under their control (1:1, 1:3, 1:5). In addition to their supervisory and sensor mission responsibilities, pilots were to utilize the DAA system to remain DAA well clear (DWC) during scripted conflicts of mixed severity. Measured response times, separation performance, mission task data, and subjective feedback were collected to assess how the multi-UAS control configuration impacted pilots' ability to maintain DAA well clear and perform the mission tasks. Overall, the DAA system proved surprisingly adaptive to multi-UAS control for preventing losses of DAA well clear (LoDWC). The findings suggest that, while multi-UAS operators are able to maintain safe separation (DWC) from other traffic, their ability to efficiently perform missions drastically decreases with their number of controlled vehicles. Pilot feedback indicated that, for this context, the use of automation support tools for completing and managing mission tasks would be appropriate and desired, especially for ensuring efficient use of assets. Finally, human-machine interface (HMI) design considerations for multi-UAS operations are discussed.

Description: A computational framework to support the quantification of system uncertainties and sensitivities for rotorcraft applications is presented using the NASA Design and Analysis of Rotorcraft (NDARC) conceptual sizing tool. A 90 passenger conceptual tiltrotor configuration was used for case demonstration in the modeling of uncertainties in NDARCs emission module. A non-intrusive forward propagation uncertainty quantification approach was applied to ensemble simulations using a Monte Carlo methodology with stratified Latin hypercube sampling. An off-the-shelf software, DAKOTA, which supports trade studies and design space exploration, including optimization, surrogate modeling and uncertainty analysis was used to address the research goals. A toolsuite was further developed incorporating DAKOTA with automated design processes and methods using function wrappers to execute program routines including support for data post-processing. Uncertainties in rotorcraft emissions modeling using the Average Temperature Response metric for a set mission profile were studied. It was shown that for the current study, using the base-line best estimate modeling parameters for the Average Temperature Response metric, NDARC under-estimates the effects of emissions when compared with results from Monte Carlo simulations. A global sensitivity analysis was further undertaken to quantify the contribution of the various emission species on output sensitivity, hence uncertainty. The work demonstrates that the developed toolsuite is robust and will support the quantification of system uncertainties and sensitivities in future rotorcraft design efforts.

Description: This presentation is an overview of research being conducted by NASA and the AFRL, including recent successes and failures.

Description: The UAS in the NAS project Flight Test 6 (FT6) campaign scheduled for FY19Q3 will evaluate the proficiency of a Honeywell DAPA-Lite Radar installed on a Tiger Shark unmanned vehicle to detect the presence of air traffic operating in its vicinity. A 3D printed radome will be manufactured for the front of the Tiger Shark to enclose the radar during FT6 operations. The DAPA-Lite radar operates in the 24.5 GHz frequency band. Material properties of 3D printer filaments are widely available for the mechanical and thermal properties, but limited knowledge exists on the electrical properties for radome applications and no data was found to correspond at the 24.5 Ghz frequency band. To minimize project risk associated with the radome performance, transmissivity and reflectivity measurements were conducted on two candidate 3D printed dielectric material filaments (Ultem 1010 Natural and Ultem 9085 Black) and two thicknesses of a solid laminate (Ultem 1000) material. The 3D printed Ultem coupons were tested shortly after being printed and again 8 months later to examine ageing effects of the open cell structure. This paper presents the transmissivity and reflectivity measurement results collected on the Ultem coupons and concludes the 3D printed 1010 Natural coupon is a suitable candidate filament for radome applications at 24.5 GHz. The design of the structures open cell matrix has a significant impact on the materials surface reflectivity.

Description: The first years effort identified sampling and interviewing as the principal risks to assessment of prompt reactions to overflights producing low-amplitude sonic booms. It also 1) established the utility of geo-information system-based route planning for LBFD flight missions, 2) developed and demonstrated a prototype of a geographically-distributed, Internet-enabled instrumentation system capable of wide-area tracking of LBFD aircraft in near-real time. The latter system permits synchronizing the conduct of interviews in multiple overflown communities with arrival times of shock waves at interviewing sites; and of measuring, archiving, and processing their acoustic signatures. Means were also recommended for constructing representative, telephone-based samples of eligible respondents living in households within carpet boom corridors adjacent to LBFD flight tracks, and for conducting interviews with cross-sectional (independent) samples of such respondents about their prompt reactions to exposure to low-amplitude sonic booms. A detailed study design was prepared and accepted by NASA for a set of single-contact attempt telephone interviews with a nationally representative sample of households. The study design focused on testing automated and live agent interview completion rates obtainable without callbacks. A minimal (two monitoring station) version of the aircraft tracking system was built and installed near a civil airport in a successful demonstration of the systems ability to detect and track aircraft movements. The field exercise also demonstrated the ability of the system to capture the acoustic emissions of departing aircraft, and to serve aircraft position and sound level information to remote, geographically-distributed analysts in near-real time. Upon approval of OMB and IRB of the detailed study plan, a stratified, nationally representative sample of landline and wireless telephone-subscribing households was constructed. A total of 12,734 telephone interview contact attempts of the sort required by a straightforward cross-sectional study design were then made. These contact attempts demonstrated the impracticality of conducting a time-critical, cross-sectional study of prompt community response to low-amplitude sonic booms by means of independent (single contact attempt per respondent for each LBFD flight mission) telephone samples of respondents. The observed interview completion rates for these single telephone contact attempts were so low (~ 1% to 3% for automated and live agent interviews, respectively) that: 1) the representativeness of collected opinions would be susceptible to intuitive challenge as inadequate, even absent conclusive evidence of non-representativeness. Refuting challenges to representativeness would have to demonstrate that the composition of the actual sample did not differ from that of the target population, a task that is tantamount to proving a negative; 2) the information required to refute allegations of non-representativeness would require a questionnaire considerably lengthier than that required simply to determine the prevalence of boom-induced startle and annoyance. Such a questionnaire would have to inquire about potentially sensitive and intrusive matters, including respondents age, gender, education, employment, home ownership, income, ethnicity, family size, and other demographic factors; and 3) unreasonable numbers of attempts would be required to re-contact households with unsuccessful initial contact attempts, given the limited time available for doing so. For example, if about 500 completed interviews were desired in a supersonically overflown community, approximately 50,000 automated interview attempts would have to be made within ten to fifteen minutes of each LBFD overflight. Such large numbers of contact attempts could well exceed the numbers of households available for interview in areas of similar boom exposure levels in some communities near LBFD flight tracks. Such large numbers of interviews could be cost-effectively undertaken only by means of automated (i.e., outgoing interactive voice response) interviewing, a data collection method ill-suited for complex and sensitive questionnaire items. The infeasibility of independent sampling for evaluating prompt responses to LBFD overflights in a cross-sectional study is due in large part to simple non-response: that is, potential respondents particularly those contacted on wireless telephones refusing to answer calls with unfamiliar caller IDs. It is also due in part, however, to 1) the lack of time to attempt to contact the same respondent more than once within a few minutes after the arrival of a shock wave at the respondents location; and 2) the need to place calls during weekday/daytime hours, when response rates are notably lower than during evenings and weekends. Despite the poor interview completion rates achieved under the above constraints, cross sectional assessments of delayed reactions to LBFD overflights could still be feasible, if multiple attempts could be made to contact respondents during evening and weekend time periods, over extended time periods. Detailed plans for a longitudinal (panel) sample were developed as an alternative to a cross sectional sample design.

Description: A full-scale isolated proprotor test was recently conducted in the USAF National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel at NASA Ames. The test article was a 3-bladed research rotor derived from the right-hand rotor of the AW609. For this test, the NASA Tiltrotor Test Rig (TTR) and rotor were installed in the 40- by 80-Foot Wind Tunnel. This paper covers the analyses and testing done to prepare for a safe entry. Included are brief descriptions of the following: NASTRAN models of the TTR, ground vibration tests of the TTR (and resulting modal data), loads analyses, and stability predictions using the comprehensive analysis CAMRAD II. The evolution of these analyses from early in the TTR program until the initiation of actual testing is also discussed. The intent is to show how all of these efforts were integrated to ensure a successful test. This paper includes stability predictions based on NASTRAN modal data and worst-case damping test data. The stability predictions covered all test conditions: hover, cruise (airplane mode), conversion, and helicopter mode. The predictions showed that the TTR and rotor are stable within the test envelope.

Description: After testing grooved over-the-rotor acoustic casing treatments on a turbofan rotor, a follow-on study was performed to investigate the effect of flow on grooved acoustic liners. The experiment was performed to understand the scaling of acoustic liner absorption with grazing flow and investigate a potential noise source from grooved acoustic liners. Acoustic liner absorption and reflection characteristics were quantified by examining the reduction in amplitude of a plane wave traveling over 2 inch liners with grazing flow. For all liners tested, as the grazing flow Mach number is increased, the absorption curves broadened and the frequency of peak absorption decreased. Grazing flow over a series of grooves was found to generate resonances up to 152 dB sound pressure level. Adding acoustic treatment to the bottom of these grooves was found to reduce the magnitude of this resonance by up to 10 dB sound pressure level and increase its frequency by up to 10%. The quantification of the grazing flow effect and identification of a mechanism behind the noise penalty from the prior turbofan rotor experiment will aid in the design of future over-the-rotor treatments.

Description: This presentation covers recent process improvements regarding environmental parameters, w.r.t convection, and future plans for thermal models.

Description: Presentation will cover new high level requirement changes for gondolas launched by Columbia Scientific Balloon Facility (CSBF), and discuss recommendations for the design and design process.

Description: This paper describes an aero-structural modeling method for the Transonic Truss-Braced Wing (TTBW) aircraft using VSPAERO. A vortex-lattice model of the TTBW aircraft is developed, and a transonic and viscous flow correction method is implemented in the VSPAERO models to account for transonic and viscous flow effects. A correction method for the wing-strut interference aerodynamics is developed and applied to the VSPAERO solver. Also, a structural dynamic finite-element model of the TTBW aircraft is developed. This finite-element model includes the geometric nonlinear effect due to the tension in the struts which cause a deflection dependent nonlinear stiffness. The VSPAERO models are coupled to the finite-element model to provide a rapid capability for aero-structural modeling and flutter analysis. A flight-optimized jig twist model is being developed and will be applied for the purpose of generating a full flight dynamic model of the TTBW aircraft.

Description: This student poster describes their experiences during the current intern period.

Description: NASA's all-electric X-57 airplane will utilize 14 electric motors, of which 12 are exclusively for lift augmentation during takeoff and landing. This report covers the design and development process taken to create an open reference model representative of the 12 lift augmenting motors. A combined worst case scenario was used as the design point, which represents the simultaneously occurring worst case aspects of thermal, static stress, electromagnetic, and rotor dynamic conditions. This work also highlights the tightly coupled nature of aerospace electric motor design, requiring constant iteration between all disciplines involved. Further adding to the uniqueness is the cooling method, which is limited to nacelle skin forced convection cooling only, no internal air flow is permitted. The stator outer diameter limit of 156.45 mm greatly impacts the degree of coupling between the electromagnetic design with the thermal analysis. The permanent magnet synchronous motor developed here operates between 385 V and 538 V, at a peak current of 50 A. Detailed electromagnetic, thermal, static load, and rotordynamic analysis was completed for this electric motor; all of which are required for a full design. The rotordynamic analysis took into consideration the motor housing which is designed specifically for this motor. The final electric motor has a mass of 2.34 kg, produces 24.1 Nm of torque with a specific power of 5.56 kW/kg, and has an efficiency of 96.61% at the combined worst case design point.

Description: Adding an ACTE II (Adaptive Compliant Trailing Edge II) closeout summary to the ACTE II TechPort page.

Description: This project details the design and analysis of a structure to replace the interface of the P-3B nadir port with an optimized interface for science installations. A new nadir port plug has been designed to replace the OEM (Original Equipment Manufacturer) plug (Lockheed PN 910169) currently used in Nadir ports 1 and 2 on the NASA P-3B aircraft. The plug consists of a milled frame that can be outfitted with customizable flat plates to meet a broad range of science needs. The frame slides into place using the existing P-3B rail system using a lever and tie-rod assembly. The seal interface will contact the Fuselage skin of the aircraft and consists of a bulb E-seal that is riveted around the perimeter of the frame. The flat plate (20 inches x 31 inches) provides a large profile that can be outfitted based on science mission goals and requirements to attach multiple instruments. This is a significant increase to the aircraft capability. Previously, the OEM plug had to be modified to hold very small plates, windows, or instruments limiting the use of the ports.There were several challenges for this project that included a constrained schedule, lack of historical references, and reverse engineering. The unusually tight schedule for design, manufacture, and install limited potential approaches. In addition, design of a new interface to replace the existing plug, on an aircraft designed in the 1960's by Lockheed for the Navy with little to no documentation, required substantial reverse engineering. In order to accomplish this, a suitable method to determine interface requirements with the aircraft had to be solved. After several iterations, the solution was to implement laser scanning techniques to scan the aircraft and the OEM plug and generate a 3D model to capture the design envelope. The structure is designed to maintain a positive margin of safety when subjected to the inertial, pressure, and aerodynamic load requirements for an external installation on the P-3B, as described in the Wallops' P-3B Design Requirements 548-RQMT-0001 Rev. A . A finite element model is created in FEMAP (Finite Element Modeling And Postprocessing) and is run through NX Nastran solver to analyze the structure. After several iterations of analysis, the structure was enveloped to hold 115 pounds evenly distributed on the plate.

Description: This report characterizes the certification practices for electric propulsion systems by modeling changes to current engine and propeller certification practices (14 CFR 23, 33 and 35 and means of compliance in standards developed by ASTM Committee F39 and F44). Industry technology paths are varied, so this report focuses on insights from the NASA X-57 Maxwell Distributed Electric Propulsion flight demonstrator system technology project. There are 122 sections of the regulation reviewed, where 28 needed tailoring or revision. A second report will examine the regulations to the X-57 system development products. A final report will describe a general regulatory gaps method for new vehicle concepts.

Description: This paper will address NASA activities to monitor and study Earth processes from long-duration unmanned aircraft systems (UAS). NASA is currently supporting both large and small UAS development and demonstration. In a follow-on to previous work, NASA Armstrong Flight Research Center is hosting test flights of a large AeroVironment solar-powered aircraft, while NASA Ames Research Center is supporting the demonstration of a light-weight solar powered aircraft by Swift Engineering. Both are designed for long duration, multi-day flight. NASA Earth Science and Aeronautics researchers have been involved in the development and use of High Altitude Long Endurance (HALE) UAS since the 1990's. The NASA Environmental Research Aircraft Sensor and Technology Program (ERAST) demonstrated the promise of HALE aircraft for providing observations while also proving the importance of triple-redundant avionics to improve system reliability for large unmanned aircraft. Early efforts to develop an operational HALE capability for earth observations languished for nearly two decades owing to insufficient solar panel efficiency, battery power density, and light-weight, yet strong, materials. During this time NASA researchers focused on using the Global Hawk to demonstrate the utility of providing diurnal measurements over severe storms (i.e. HS3) and to track stratospheric water vapor transport (ATTREX). Recent significant commercial investments are now leading to the realization of a long-held goal of week- to month-long sustained observations and measurements from the stratosphere. In addition to a historical review of NASA use and interest in HALE aircraft, this paper will present current concepts for exploiting current and planned HALE aircraft capabilities including in situ characterization of atmospheric composition and dynamics as well as imagery collection and internet connectivity. NASA researchers anticipate HALE will also provide a useful means to test smallsat instruments and components. Observations from HALE-based instruments might also provide useful gap-filler observations to flagship satellite missions where the repeat time doesn't allow for measurements of quickly changing phenomenon. HALE will likely also provide measurements and communications relay to facilitate other aircraft in multi-aircraft campaigns. We will also report on progress towards a NASA-supported flight tests solar electric vehicles planned for 2019. One is the Swift Engineering UAS designed to carry 7kg (15lbs) for 30 days at 20km altitude. The other is the AeroVironment Hawk 30, also designed for multi-day flight.

Description: No abstract available

Description: No abstract available

Description: New manufacturing methods are needed to obtain innovative electric motor designs that have much higher power densities and/or efficiencies compared to the current state-of-the-art. Additive manufacturing offers the potential to radically change motor designs so that they have compact designs, multi-material components, innovative cooling, and optimally designed and manufactured components. New component designs enabled by additive manufacturing technologies have been designed and were fabricated to include the housing, rotors, stator cooling ring, a direct printed stator, and a wire embedded stator. The new components were integrated into the motor and tested evaluate the performance gains in comparison to the baseline electric motor configuration. Partners on the sub-project include NASA GRC, NASA LaRC, NASA AFRC, LaunchPoint Technologies, and the University of Texas El Paso.

Description: NASA Langley and Glenn Research Centers have collaborated on the usage of acoustic liners mounted very near or directly over the rotor of turbofan aircraft engines. This collaboration began over a decade ago with the investigation of a metallic foam liner. Similar to conventional acoustic liner applications, this liner was designed to absorb sound generated by the rotor-alone and rotor-stator interaction sources within the fan duct. Given its proximity to the rotor tips, the expectation was that the liner would also serve as a pressure release and thereby inhibit the amount of noise generated. Initial acoustic results were promising, but there was concern regarding potential aerodynamic penalties. Nevertheless, there were sufficient positive results to warrant further investigation. To that end, the current report presents results obtained in the NASA Langley Normal Incidence Tube for 20 acoustic liner candidates for the OTR application. The majority contain grooves at their surface, designed to minimize aerodynamic penalties caused by placing the liner in close proximity to the fan rotor tips. The intent is to assess the acoustic properties of each liner configuration, and in particular to assess the effects of including the grooves on the overall acoustic performance. An additional intent of this paper is to provide documentation regarding recent enhancements to the NASA Langley Normal Incidence Tube.

Description: A streamlined Multi-Disciplinary Analysis and Optimization (MDAO) process is being developed to provide feedback on conceptual designs and early airspace modeling assessments of unconventional aircraft. This MDAO process has been demonstrated using a Low-Boom Flight Demonstrator (LBFD) like configuration by performing a trade study of various flap sizes. The results of this trade showed that shorter takeoff distances are achieved with increased flap chord and flap deflections. This trend is unlike conventional transport type aircraft which typically show increased required takeoff distances due to the increased drag during its take-off flap configurations. The LBFD like configuration results are attributed to its high engine thrust which overcomes the higher drag associated with these takeoff flap configurations.

Description: NASAs Hypersonic Inflatable Aerodynamic Decelerator (HIAD) technology was selected for a Technology Demonstration Mission under the Space Technology Mission Directorate in 2017. HIAD is an enabling technology that can facilitate atmospheric entry of heavy payloads to planets such as Earth and Mars using a deployable aeroshell. The deployable nature of the HIAD technology allows it to avoid the size constraints imposed on current rigid aeroshell entry systems. This enables use of larger aeroshells resulting in increased entry system performance (e.g. higher pay-load mass and/or volume, higher landing altitude at Mars). The Low Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID) is currently scheduled for late-2021. LOFTID will be launched out of Vandenberg Air Force Base as a secondary payload on an Atlas V rocket. The flight test features a 6m diameter, 70-deg sphere-cone aeroshell and will provide invaluable high-energy orbital re-entry flight data. This data will be essential in supporting the HIAD team to mature the technology to diameters of 10m and greater. Aeroshells of this scale are applicable to potential near-term commercial applications and future NASA missions. Currently the LOFTID project has completed fabrication of the engineering design unit (EDU) inflatable structure (IS) and the flexible thermal protection system (F-TPS). These two components along with the rigid nose and center body comprise the HIAD aeroshell system. This EDU aeroshell is the precursor to the LOFTID aeroshell that will be used for flight. The EDU was built to verify the design given the subtle differences between the LOFTID aeroshell and past aeroshell designs that have been fabricated under the NASA HIAD project. To characterize the structural performance of the LOFTID aeroshell design, three structural tests will be performed. The first test to be conducted is static load testing, which will induce a uniform load across the forward surface of the aeroshell to simulate the expected pressure forces during atmospheric entry. The IS integrated with the rigid center body will first be tested alone to provide data for analytical model correlation, and then the F-TPS will be integrated for a second series of static load testing of the full aeroshell system. Instrumentation will be employed during the test series to measure component loads during testing, and a laser scanner will be used to generate a 3D map of the aeroshell surface to verify that the shape of the structure is acceptable at the simulated flight loads. After static load testing, pack and deployment testing will be conducted multiple times on the integrated system to demonstrate the aeroshells ability to fit within the required packed volume for the LOFTID mission without experiencing significant damage. Finally, the aeroshell will undergo modal testing to characterize its structural response. This presentation will discuss the setup and execution of each of the three tests that the EDU aeroshell will undergo. In addition, initial results of the testing will be presented outlining key findings as LOFTID moves for-ward with fabrication of the flight aeroshell.

Description: Heat flux characterization of high-enthalpy boundary layer flows is key to optimize the performance and design of Thermal Protection System of next generation aerospace vehicles [1]. At atmospheric entry hypersonic speeds, ablation as well as surface catalycity impact boundary layer aeroheating. Out-gassing occurring from an ablative surface in planetary entry environment introduces a rich set of problems in thermodynamic, fluid dynamic, and material pyrolysis. Ablation leads to out-gassing and surface roughness, both of which are known to affect surface heating in hypersonic chemically reacting boundary layers via three main routes: gas blowing into the boundary layer from the wall, changing the surface heat transfer due to wall-flow chemical reactions, and modifying surface roughness via ablative processes.

Description: Innovative technology has to prove itself in the context of legacy regulations. The knowledgeable technologist must engage standards process and regulating authorities to understand their roles and to advise the effect of new technology, and with manufacturers to demonstrate technology benefit. A model for Innovative Technology Environment relating NASA to industry, standards and regulation is described. The needs of the standards community of the X-57 are identified, and a NASA standards structure is described. No NASA project works with standards and regulatory organizations like the X-57.

Description: This report describes a generic method for addressing any new technology to its associated set of regulations and certification criteria. The result is a framework under which a detailed assessment can be conducted. Using just such a framework, the report maps the detailed updated regulations and evolving ASTM standards to the particular technology planning and tests. As a result, a roadmap of NASA technology is documented that shows clear transfer of technology data to industry (standards developers, as well as technology developers) and the FAA regulatory policy and certification staff upon whom certification and policy will be data-driven. A clear description of benefits and gaps are identified, as well.

Description: Wing design optimization has been studied extensively and is of continued interest as optimization tools are developed and become more accessible. In each of these studies, certain assumptions and simplifications are made to make the design problem tractable. However, it is difficult to find systematic studies in which several considerations are added or removed one at a time to study how much impact they have. In this work, we examine how certain physical considerations (viscous drag, wave drag, thrust loads, and inertial relief from structural, fuel, and engine masses), impact the aerostructural optimization results for three distinct aircraft wings. The goal is to help develop a rough idea of how important these physical considerations are. We do this using gradient-based optimization and a multidisciplinary design optimization framework, OpenMDAO. We use the open-source tool OpenAeroStruct that couples a vortex lattice method to a finite element method. We establish a baseline aerostructural design optimization problem then perform a series of optimizations, each with one physical consideration removed from the baseline case. We find that depending on the size of the aircraft and flight conditions, the importance of some of these physical considerations varies considerably whereas the importance of others do not. Specifically, the optimal designs change radically without proper viscous and wave drag considerations and smaller aircraft with more distributed propulsion are more affected by the inclusion of engine loads.

Description: The accurate prediction of turbulent mixing in high-pressure turbines that incorporate various airfoil surface-cooling strategies is becoming increasing critical to the design of modern gas turbine engines where the quest for improved efficiency is driving compressor overall pressure ratios and turbine inlet temperatures to much higher levels than ever before. In the present paper, a recently developed computational capability for accurate and efficient scaleresolving simulations of turbomachinery is extended to study the turbulent mixing mechanism of a simplified abstraction of an airfoil trailing-edge cooling slot - a plane wall jet with finite lip thickness discharging into an ambient flow. The computational capability is based on an entropy stable, discontinuousGalerkin approach that extends to arbitrarily high orders of spatial and temporal accuracy. The numerical results show that the present simulations capture the trends observed in the experiments. Discrepancies between the simulations and experiments are believed to be due to differences in the inflow profiles and tunnel sidewall effects. The thick lip configuration leads to a thicker wake and higher unsteadiness in the wall jet compared to the thin lip. A detailed comparison of the turbulent flowfields is presented to highlight differences arising due to lip thickness variations.

Description: The Tiltrotor Test Rig (TTR) was tested in the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel from 2017 to 2018. The rotor system can be configured in airplane mode, with the rotor plane perpendicular to the wind flow, and in helicopter mode, with the rotor plane parallel to the wind flow. Four microphones were placed around the TTR: two on the wind tunnel floor and two on struts. The primary goal of the test was to understand the operational capabilities of the TTR, while also acquiring research data as available. Limited measurements of the blade vortex interaction (BVI) noise of the TTR rotor were taken to not only understand the acoustic testing capabilities of the TTR in the NFAC 40- by 80-Foot Wind Tunnel, but to also compare to previous tests and to be used for future validation studies. In particular, data will be compared to measurements of an XV-15 rotor previously acquired in the NFAC 80- by 120-Foot Wind Tunnel.

Description: Supersonic aircraft are challenging to optimally design due to the widely varying constraints and flight conditions they experience. Additionally, a large number of disciplinary subsystems must be considered due to highly complex design requirements. One subsystem that has a major effect on overall performance is the engine. In this work, we construct a supersonic mixed-flow variable cycle engine and perform multipoint gradient-based optimization using this model. We see that the operational variables allow the optimizer to tailor performance at each individual flight condition, leading to better overall performance. To simulate airframe integration constraints, we run successive optimizations with increasingly restrictive inlet areas and see decreases in engine performance. This work is part of a larger effort to incorporate engine design into aero-thermal-mission optimization of a supersonic aircraft.

Description: Many of the aircraft concepts of the future are exploring the use of hybrid-, turbo- or all-electric propulsion systems to improve performance and decrease environmental impacts. These aircraft concepts range from small rotorcraft for urban air mobility to conventional commercial transports to large blended wing body designs. Developing the conceptual design for these vehicles presents a challenge, however, as traditional aircraft design tools often were not developed to handle these unique propulsion system architectures. Previous studies on these vehicles have therefore relied on relatively simple models of the electrical transmission and distribution system. This paper presents the development of a hybrid AC-DC load flow (or power flow) analysis capability to enhance the conceptual design of these concept vehicles. Specifically, the desire was to create a load flow analysis capability within the OpenMDAO framework that is also being used to develop a set of compatible tools for rapid optimization of conceptual designs. This load flow analysis capability is unique in its flexible object-oriented structure and implementation of analytic derivatives to facilitate the use of solvers and gradient based optimization in the design process. The developed hybrid load flow analysis capability is first verified against a published 13-bus example then used to model the electrical distribution system for a turbo-electric tiltwing aircraft.

Description: Urban Air Mobility vehicles are intended to operate near or within large cities, where a significant portion of the public will be exposed to the noise they create. If these vehicles are to become acceptable to the public, designers must be able to manage the amount of noise they generate, and understand the relationship between traditional performance metrics (thrust, efficiency, etc.) and noise. As a first step to addressing this need, this work combines a blade element momentum theory tool (OpenBEMT) with an acoustic prediction tool (ANOPP2) to optimize a propeller subject to both aerodynamic and acoustic constraints. These tools are developed within a optimization framework (OpenMDAO) that allows analytic derivatives to be propagated through the models and passed to a gradient-based optimizer. This tool chain is exercised on the cruise propellers from the X-57 Maxwell, and yields propeller designs that reduced the overall sound pressure level by about 5 dB for a cost of 1% propeller efficiency.

Description: No abstract available

Description: The present paper details the design of the counter rotating fans for a Turboelectric Distributed Propulsion (TeDP) system. Sixteen propulsors installed in mail-slot-shape nacelles are embedded on an aerodynamically optimized hybrid wing-body configuration. The hybrid-wing/body (HWB) configuration which was previously designed to satisfy the conditions of trim, longitudinally static stability and specific cargo space is employed as the baseline configuration in pursuing an optimal distributed propulsion system. A set of distributed propulsors is conceptually designed and the collective performance is evaluated against the target thrust mandated by the mission requirements. The concept of the distributed propulsion allows the fan pressure ratio to be around 1.27~1.32 for the target thrust. In addition, further splitting of the fan pressure ratio by using the counter-rotating fans for each slot realizes the target pressure ratio with low tip speed. In the distributed propulsion system, the nature of the flow conditions and/or the thickness of the ingested boundary layer may differ and result in different propulsive reaction of each individual propulsor. The optimization is, thus, approached from both the propulsion system and individual propulsor perspectives. An optimal distribution of the thrust and power output is determined by how the system utilizes each passage's propulsive characteristics and its interaction with the airframe. These system level analysis and optimization are conducted using an actuator disk model to account for the propulsion-airframe integration numerically. With respect to the propulsor level, aerodynamic shape optimizations of the fan blades are performed in a sequential multi-objective optimization process for various design objectives, such as mass flow rate condition, fan pressure ratio, efficiency and the exit flow angle of the fan stage by using a genetic algorithm, NSGA-II. The radial chord distribution, and meanline distribution of the rotors are designed on the circumferentially averaged axi-symmetric inlet profiles and tested on the six inlet profiles from six divided sectors to reckon flow distortion. The performances of the counter rotating fans are, thus, evaluated accordingly for obtaining distortion tolerant fan. The performance of the distributed propulsion system is evaluated by two CFD tools, i.e., a multi-stage turbo-machinery CFD code and one propulsion-airframe integration flow solver coupled with a body-force model. The optimized boundary layer ingestion propulsion system of 16 distributed slots not only reaches the system target thrust, but also delivers a close to 20% fuel saving benefit against its counterpart 12 distributed clean inlet propulsion system.

Description: Safe Unmanned Aerial Vehicle (UAV) operations near the ground require navigation methods that avoid fixed obstacles such as buildings, power lines and trees. Aerial lidar surveys of ground structures are available with the precision and accuracy to geolocate obstacles, but the high volume of raw survey data can exceed the compute power of onboard processors and the rendering ability of ground-based flight planning maps. Representing ground structures with bounding polyhedra instead of point clouds greatly reduces the data size and can enable effective obstacle avoidance, as long as the bounding geometry envelopes the structures with high spatial fidelity. This report describes in detail four methods to compute bounding geometries of ground obstacles from lidar point clouds. The four methods are: 1) 2.5D Maximum Elevation Box, 2) 2.5D Ground Map Extrusion, 3) 3D Bounding Cylinder, and 4) 3D Bounding Box. The methods are applied to five point cloud datasets from lidar surveys of UAV flight research sites in Georgia and Virginia with an average point spacing that ranges from 0.1m to 0.6m. The methods are assessed using survey areas with geometrically heterogeneous ground structures: buildings, vegetation, power lines, and sub-meter structures such as road signs and guy wires. The 2.5D Maximum Elevation Box method is useful for simple structures. The 2.5D Ground Map Extrusion method efficiently encloses vegetation, but requires handdrawn ground footprints. The 3D Bounding Cylinder method excels at enclosing linear structures such as power lines and fences. The 3D Bounding Box method excels at enclosing planar structures such as buildings. The methods are compared on the basis of data compression and boundary fidelity on selected areas. The 2.5D methods yield the highest data compression but the polyhedra produced by them enclose significant amounts of empty space. Boundary fidelity is superior for the 3D methods, though this fidelity comes at the cost of a roughly thirtyfold lower data compression ratio than the 2.5D Maximum Elevation Box method. A mix of these output geometries is proposed for autonomous UAV navigation with limited on-board computing. Both the accuracy and spatial detail of emerging satellite-based survey technology lower than that of aerial lidar scanning survey technology. Sub-meter structures and thin linear structures are not reliably mapped at present by satellite-based surveys.

Description: The Airborne Spacing for Terminal Arrival Routes (ASTAR) Flight Test was conducted by the NASA Air Traffic Management Technology Demonstration 1 (ATD- 1) project to demonstrate the use of NASAs ASTAR algorithm beyond a simulated environment and assess the operational risks of performing a multi-aircraft flight test of Flight-deck Interval Management (FIM). Utilizing contemporary tools of the Federal Aviation Administrations Next Generation Air Transportation System (NextGen) such as ADS-B, the ASTAR algorithm calculated speeds that the flight crew flew to achieve a precise spacing interval behind another aircraft at the final approach fix. Airspeed commands issued by the algorithm were flown by the flight crew of the FIM-equipped aircraft to achieve or maintain an assigned spacing goal from a target vehicle. The ASTAR algorithm was integrated with the Boeing supplied B-787 ecoDemonstrator aircraft, and five flight trials were conducted as a joint effort between NASA and Boeing on December 12, 2014. Initial results indicated arrival times within several seconds of accuracy of the planned termination point between two aircraft performing FIM in a real world environment. This flight test opened the way for the much more expansive ATD-1 Avionics Phase II flight test which occurred in early 2017. The flight trials under Phase II preceded further testing by the community in preparation for inclusion of the Interval Management concept as a part of the NextGen environment.

Description: These slides are an overview of the FT6 Test and Evaluation program.

Description: A tool to give the public a window into Unmanned Aerial Systems (UAS) Traffic Management (UTM) operations was created from an existing data collection tool. The interface included a map and a table showing details about UAS operations that could be queried in a number of ways. Eleven participants attended the study, successfully completing a 19-item task set in about 30 minutes. They correctly found information for 87% of the non-subjective tasks at a rate of around a minute per task, and rated the usability of the tool at the end of the session above the industry benchmark. Participants gave favorable reviews of the "public portal tool", even reporting that they would be satisfied with less information that it presented. There were one or two elements of the display that users found distracting and some navigation functions that need improvement, but on balance, the public representatives liked the features they saw in, and had few criticisms of, the public portal tool. One important issue for the small Unmanned Aerial System community to resolve will be how much or how little information should be available about UTM operations to members of the public.

Description: A tool to give the public a window into Unmanned Aerial Systems (UAS) Traffic Management (UTM) operations was created from an existing data collection tool. The interface included a map and a table showing details about UAS operations that could be queried in a number of ways. Eleven participants attended the study, successfully completing a 19-item task set in about 30 minutes. They correctly found information for 87% of the non-subjective tasks at a rate of around a minute per task, and rated the usability of the tool at the end of the session above the industry benchmark. Participants gave favorable reviews of the "public portal tool", even reporting that they would be satisfied with less information that it presented. There were one or two elements of the display that users found distracting and some navigation functions that need improvement, but on balance, the public representatives liked the features they saw in, and had few criticisms of, the public portal tool. One important issue for the small Unmanned Aerial System community to resolve will be how much or how little information should be available about UTM operations to members of the public.

Description: Overview of the projects in the Advanced Air Vehicle Program, Aeronautics Research Mission Directorate.

Description: No abstract available

Description: The paper describes a feedback controls design approach for a generic regional jet turbofan engine, which can be adapted to aero engines in general. To demonstrate this approach, linear models for control design are generated at different operating conditions from a full envelope nonlinear simulation created with the NASA Glenn Research Center-developed Toolbox for the Modeling and Analysis of Thermodynamic Systems. The primary objective is to design a single feedback controller that achieves good performance, without the need of developing scheduled control designs to cover the engine operating envelope. An additional objective is to progressively design more robust controllers that can perform under large variations in plant dynamics to also cover control for engine limits and potentially for some off nominal or even damaged conditions.

Description: This project intends to update and redesign imperfections in the scanned 3D CAD model of the Viking 400 aircraft. This aircraft, similar to the Sierra-B UAS, will carry payloads of scientific instruments for research purposes. The goals of this project are to modify the current scanned model such that it better represents the physical qualities of the aircraft, as well as creating the features that are missing from the model. As the model was imported from a different software, many of the critical surfaces did not accurately reflect the actual aircraft. Those parts of the model were redesigned entirely so that they can be edited for future use, as well as correctly representing the aircraft as it is now. Additionally, parts of the aircraft that did not appear in the scanned model were designed and added to the new model. In order to prioritize ease of use for future missions, the model has been reorganized in a logical fashion that enables modification of specific parts of the aircraft. The organization of this model imitates the drawing tree of the Sierra-B, with the intention of maintaining a functional system of redesign, analysis, and implementation. Ultimately, this project will be a catalyst for making Viking 400 into a functional aircraft and increasing scientific research in airborne vehicles.

Description: The Parallel Electric-Gas Architecture with Synergistic Utilization Scheme (PE- GASUS) vehicle is a regional aircraft concept that uses electric and hybrid-electric propulsors located strategically to obtain aerodynamic and mission benefits. Traditional aircraft analysis tools are not well suited to analyze the PEGASUS aircraft due to the different propulsor types used. This report summarizes a methodology that addresses some of the mission analysis challenges expected in modeling this vehicle concept. An initial baseline design is selected and sensitivity studies are performed to further understand the potential benefits of the concept.

Description: This work covers the refinement of thermal models from design estimates to actual fabricated performance. Matching the experimental data of the first fully electrified version of the X-57 Maxwell experimental vehicle requires high fidelity thermal analysis to sufficiently capture the electric motor and inverter temperature profiles. Qualification test data of the motors and inverters is used to validate finite element analysis models used to simulate thermal performance over mission transients. An additional thermal-hydraulic models is used to estimate flow characteristics through the propulsor nacelle and component heat sinks. After calibration of the higher order models, overall component sizing and peak temperature constraints can be distilled to reduced order models, to improve modelflexibility and utility.

Description: These slides describe the design and execution of the testing and integration of the X-59 life support system.

Description: 0Genetic polymorphism by means of biochemical genetic markers using polyacrylamide gel electrophoresis system in four barbus fish species has been investigated. Species scientific name were Barbus sharpeyi ; Gunther, 1847 , Barbus grypus ; Heckel, 1843, Barbus xanthopterus ; Heckel, 1843 and Barbus esocinus ; Heckel, 1843.Sampling site and location were mainly in the rivers located in Khoozestan province such as Karoon and Karkheh rivers and the Dez dam. Different organs such as blood, muscle, kidney, eye and heart were sampled and analysed for the presence of tf, es, sod and pgm alleles. High polymorphism and presence of different alleles scored, but populations were not in the H-W equilibrium. Considring results, using current and avaiable genetic markers such as microsattelits is recommended for future works.

Description: Iranian Fisheries Science Research Institute

Description: Published

Description: Cheshmehkileh River and adjacent mountainous streams, play a strategic role as a historical axis for anthropogenic civilization, human welfare also habitat and migration pathway of commercial – biologic valuable fishes e.g. Caspian trout, Caspian kuttum, members of Cyprinidae family in south Caspian Sea drainage. Treats such as overfishing of Caspian trout and Red spotted trout stocks in mountainous headwaters, barriers construction and manipulations those are out of river carrying capacity developed by human activities, affected normal function of river as well. Sand mining big factories establishment next to the river, legal and illegal trade of river sediments, direct entry of Tonekabon landfill leakage into the river, development of Rainbow trout farms since 3 decades and huge effluents into the river containing dead fish and types of solids, escapement of cultured Rainbow trouts into the river, … are major minimum factors which needs basic information for integrating inclusively drainage management system. Cheshmehkileh River contains Headwaters of Dohezar (Daryasar & Nusha), Sehezar and Valamroud rivers during 13 monthly sampling phases between September 2009 and October 2010 based on macrozoobenthoses investigations by EPT, EPT/C EPA protocols, measurements of nominated physic-chemical and microbiologic parameters. Probability of Rainbow trouts escapement and invasion, existence, nutrition in Cheshmehkileh environment indeed investigated. Data analysis explained significant differences (P〈0.05) between groups of measured parameters in different sampling stations. Dendogram of clustered analysis based on consolidation of major biologic/ physic-chemical and microbiologic parameters, separated stations No. 1, 3, 2, 4 in one group and remained classified in different groups. Station 8 and 9 similarly separated which expressed general similarities according to Sehezar river environment which were differs in comparison with other stations. Station 11 separated according to its natural quality of water and environment. Similarities between station 10 to Sehezar river stations 8 and 9 expressed general influence of Sehezar River more than Dohezar River in Cheshmehkileh condition especially in station No. 10. High scores of EPT and EPT/C indices in upstream stations 1, 3 and 8 also low score of indices in stations 7, 13 and 6 expressed levels of environment quality between these groups of stations. Maximum average biomass of macroinvertebrates belongs to Trichoptera order in Cheshmehkileh River. Significant decrease of biomass in stations 11, 12 and 13 in comparison with other stations stated environment degradation in mentioned stations relevant to excessive sand mining as well. Pollution resistant groups of invertebrates significantly increased in downstreams against upstream stations. Also disappearing of Plecoptera order in station No. 7, 9, 10 and 13 stated low quality of environment in comparison with upstream stations. Confirmation of effects quality and quantity for point and non-point sources of imported pollutants require specific management considerations in order to present exploitations, pollutants control and emergencies for river monitoring in forthcoming years.

Description: Iranian Fisheries Science Research Institute

Description: Published

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2018

Description: Many chemical constituents are removed from the ocean by attachment to settling particles, a process referred to as “scavenging.” Radioisotopes of thorium, a highly particle-reactive element, have been used extensively to study scavenging in the ocean. However, this process is complicated by the highly variable chemical composition and concentration of particles in oceanic waters. This thesis focuses on understanding the cycling of thorium as affected by particle concentration and particle composition in the North Atlantic. This objective is addressed using (i) the distributions 228,230,234Th, their radioactive parents, particle composition, and bulk particle concentration, as measured or estimated along the GEOTRACES North Atlantic Transect (GA03) and (ii) a model for the reversible exchange of thorium with particles. Model parameters are either estimated by inversion (chapter 2-4), or prescribed in order to simulate 230Th in a circulation model (chapter 5). The major findings of this thesis follow. In chapters 2 and 3, I find that the rate parameters of the reversible exchange model show systematic variations along GA03. In particular, 𝑘1, the apparent first-order rate "constant" of Th adsorption onto particles, generally presents maxima in the mesopelagic zone and minima below. A positive correlation between 𝑘1 and bulk particle concentration is found, consistent with the notion that the specific rate at which a metal in solution attaches to particles increases with the number of surface sites available for adsorption. In chapter 4, I show that Mn (oxyhydr)oxides and biogenic particles most strongly influence 𝑘1 west of the Mauritanian upwelling, but that biogenic particles dominate 𝑘1 in this region. In chapter 5, I find that dissolved 230Th data are best represented by a model that assumes enhanced values of 𝑘1 near the seafloor. Collectively, my findings suggest that spatial variations in Th radioisotope activities observed in the North Atlantic reflect at least partly variations in the rate at which Th is removed from the water column.

Description: This work was supported by the US National Science Foundation. Two US NSF grants have supported the research in this thesis (OCE-1232578 and OCE-155644).

Description: The comment and response concerning the report of oxidation of methane to methanol by water (Reports, 5 May 2017, p. 523) do not fully capture the implications of thermodynamic limitations. A nonisothermal process in which each cycle requires a large temperature swing and permits only substoichiometric methane conversion surely could not be carried out on any practical scale.

Description: Labinger argues that stepwise reaction of methane with water to produce methanol and hydrogen will never be commercially feasible because of its substoichiometric basis with respect to the active site and the requirement of a large temperature swing. This comment is not touching any new ground, beyond describing the thermodynamic feasibility, thermal cycling, and the role of water as discussed previously. Most important, it does not have a solid numerical basis.

Description: Vinyl carbocations have been the subject of extensive experimental and theoretical studies over the past five decades. Despite this long history in chemistry, the utility of vinyl cations in chemical synthesis has been limited, with most reactivity studies focusing on solvolysis reactions or intramolecular processes. Here we report synthetic and mechanistic studies of vinyl cations generated through silylium–weakly coordinating anion catalysis. We find that these reactive intermediates undergo mild intermolecular carbon-carbon bond–forming reactions, including carbon-hydrogen (C–H) insertion into unactivated sp 3 C–H bonds and reductive Friedel-Crafts reactions with arenes. Moreover, we conducted computational studies of these alkane C–H functionalization reactions and discovered that they proceed through nonclassical, ambimodal transition structures. This reaction manifold provides a framework for the catalytic functionalization of hydrocarbons using simple ketone derivatives.

Description: It is commonly assumed that recognition and discrimination of chirality, both in nature and in artificial systems, depend solely on spatial effects. However, recent studies have suggested that charge redistribution in chiral molecules manifests an enantiospecific preference in electron spin orientation. We therefore reasoned that the induced spin polarization may affect enantiorecognition through exchange interactions. Here we show experimentally that the interaction of chiral molecules with a perpendicularly magnetized substrate is enantiospecific. Thus, one enantiomer adsorbs preferentially when the magnetic dipole is pointing up, whereas the other adsorbs faster for the opposite alignment of the magnetization. The interaction is not controlled by the magnetic field per se, but rather by the electron spin orientations, and opens prospects for a distinct approach to enantiomeric separations.

Description: Theory has established the importance of geometric phase (GP) effects in the adiabatic dynamics of molecular systems with a conical intersection connecting the ground- and excited-state potential energy surfaces, but direct observation of their manifestation in chemical reactions remains a major challenge. Here, we report a high-resolution crossed molecular beams study of the H + HD -〉 H 2 + D reaction at a collision energy slightly above the conical intersection. Velocity map ion imaging revealed fast angular oscillations in product quantum state–resolved differential cross sections in the forward scattering direction for H 2 products at specific rovibrational levels. The experimental results agree with adiabatic quantum dynamical calculations only when the GP effect is included.

Description: The chemistry of the carbonyl group is essential to modern organic synthesis. The preparation of substituted, enantioenriched 1,3- or 1,5-dicarbonyls is well developed, as their disconnection naturally follows from the intrinsic polarity of the carbonyl group. By contrast, a general enantioselective access to quaternary stereocenters in acyclic 1,4-dicarbonyl systems remains an unresolved problem, despite the tremendous importance of 2,3-substituted 1,4-dicarbonyl motifs in natural products and drug scaffolds. Here we present a broad enantioselective and stereodivergent strategy to access acyclic, polysubstituted 1,4-dicarbonyls via acid-catalyzed [3,3]-sulfonium rearrangement starting from vinyl sulfoxides and ynamides. The stereochemistry at sulfur governs the absolute sense of chiral induction, whereas the double bond geometry dictates the relative configuration of the final products.

Description: With the recent soaring production of natural gas, the use of methane and other light hydrocarbon feedstocks as starting materials in synthetic transformations is becoming increasingly economically attractive, although it remains chemically challenging. We report the development of photocatalytic C–H amination, alkylation, and arylation of methane, ethane, and higher alkanes under visible light irradiation at ambient temperature. High catalytic efficiency (turnover numbers up to 2900 for methane and 9700 for ethane) and selectivity were achieved using abundant, inexpensive cerium salts as photocatalysts. Ligand-to-metal charge transfer excitation generated alkoxy radicals from simple alcohols that in turn acted as hydrogen atom transfer catalysts. The mixed-phase gas/liquid reaction was adapted to continuous flow, enabling the efficient use of gaseous feedstocks in scalable photocatalytic transformations.

Description: Intrigued by the potential of nanoscale machines, scientists have long attempted to control molecular motion. We monitored the individual 0.7-nanometer steps of a single molecular hopper as it moved in an electric field along a track in a nanopore controlled by a chemical ratchet. The hopper demonstrated characteristics desired in a moving molecule: defined start and end points, processivity, no chemical fuel requirement, directional motion, and external control. The hopper was readily functionalized to carry cargos. For example, a DNA molecule could be ratcheted along the track in either direction, a prerequisite for nanopore sequencing.

Description: Phosphorothioate nucleotides have emerged as powerful pharmacological substitutes of their native phosphodiester analogs with important translational applications in antisense oligonucleotide (ASO) therapeutics and cyclic dinucleotide (CDN) synthesis. Stereocontrolled installation of this chiral motif has long been hampered by the systemic use of phosphorus(III) [P(III)]–based reagent systems as the sole practical means of oligonucleotide assembly. A fundamentally different approach is described herein: the invention of a P(V)-based reagent platform for programmable, traceless, diastereoselective phosphorus-sulfur incorporation. The power of this reagent system is demonstrated through the robust and stereocontrolled synthesis of various nucleotidic architectures, including ASOs and CDNs, via an efficient, inexpensive, and operationally simple protocol.

Description: Here we report an anomalous porous molecular crystal built of C–H···N-bonded double-layered roof-floor components and wall components of a segregatively interdigitated architecture. This complicated porous structure consists of only one type of fully aromatic multijoint molecule carrying three identical dipyridylphenyl wedges. Despite its high symmetry, this molecule accomplishes difficult tasks by using two of its three wedges for roof-floor formation and using its other wedge for wall formation. Although a C–H···N bond is extremely labile, the porous crystal maintains its porosity until thermal breakdown of the C–H···N bonds at 202°C occurs, affording a nonporous polymorph. Though this nonporous crystal survives even at 325°C, it can retrieve the parent porosity under acetonitrile vapor. These findings show how one can translate simplicity into ultrahigh complexity.

Description: Some of the simplest and most powerful carbon-carbon bond forming strategies take advantage of readily accessible ubiquitous motifs: carbonyls and olefins. Here we report a fundamentally distinct mode of reactivity between carbonyls and olefins that differs from established acid-catalyzed carbonyl-ene, Prins, and carbonyl-olefin metathesis reaction paths. A range of epsilon, zeta-unsaturated ketones undergo Brønsted acid–catalyzed intramolecular cyclization to provide tetrahydrofluorene products via the formation of two new carbon-carbon bonds. Theoretical calculations and accompanying mechanistic studies suggest that this carbocyclization reaction proceeds through the intermediacy of a transient oxetane formed by oxygen atom transfer. The complex polycyclic frameworks in this product class appear as common substructures in organic materials, bioactive natural products, and recently developed pharmaceuticals.

Description: Alkene aminoarylation with a single, bifunctional reagent is a concise synthetic strategy. We report a catalytic protocol for the addition of arylsulfonylacetamides across electron-rich alkenes with complete anti-Markovnikov regioselectivity and excellent diastereoselectivity to provide 2,2-diarylethylamines. In this process, single-electron alkene oxidation enables carbon-nitrogen bond formation to provide a key benzylic radical poised for a Smiles-Truce 1,5-aryl shift. This reaction is redox-neutral, exhibits broad functional group compatibility, and occurs at room temperature with loss of sulfur dioxide. As this process is driven by visible light, uses readily available starting materials, and demonstrates convergent synthesis, it is well suited for use in a variety of synthetic endeavors.

Description: Photocatalysis based on optically active, "plasmonic" metal nanoparticles has emerged as a promising approach to facilitate light-driven chemical conversions under far milder conditions than thermal catalysis. However, an understanding of the relation between thermal and electronic excitations has been lacking. We report the substantial light-induced reduction of the thermal activation barrier for ammonia decomposition on a plasmonic photocatalyst. We introduce the concept of a light-dependent activation barrier to account for the effect of light illumination on electronic and thermal excitations in a single unified picture. This framework provides insight into the specific role of hot carriers in plasmon-mediated photochemistry, which is critically important for designing energy-efficient plasmonic photocatalysts.

Description: Single-electron reduction of a carbonyl to a ketyl enables access to a polarity-reversed platform of reactivity for this cornerstone functional group. However, the synthetic utility of the ketyl radical is hindered by the strong reductants necessary for its generation, which also limit its reactivity to net reductive mechanisms. We report a strategy for net redox-neutral generation and reaction of ketyl radicals. The in situ conversion of aldehydes to α-acetoxy iodides lowers their reduction potential by more than 1 volt, allowing for milder access to the corresponding ketyl radicals and an oxidative termination event. Upon subjecting these iodides to a dimanganese decacarbonyl precatalyst and visible light irradiation, an atom transfer radical addition (ATRA) mechanism affords a broad scope of vinyl iodide products with high Z -selectivity.

Description: Reactions that form a product with the same reactive functionality as that of one of the starting compounds frequently end in oligomerization. As a salient example, selective aldol coupling of the smallest, though arguably most useful, enolizable aldehyde, acetaldehyde, with just one partner substrate has proven to be extremely challenging. Here, we report a highly enantioselective Mukaiyama aldol reaction with the simple triethylsilyl (TES) and tert -butyldimethylsilyl (TBS) enolates of acetaldehyde and various aliphatic and aromatic acceptor aldehydes. The reaction is catalyzed by recently developed, strongly acidic imidodiphosphorimidates (IDPi), which, like enzymes, display a confined active site but, like small-molecule catalysts, have a broad substrate scope. The process is scalable, fast, efficient (0.5 to 1.5 mole % catalyst loading), and greatly simplifies access to highly valuable silylated acetaldehyde aldols.

Description: Single-molecule magnets (SMMs) containing only one metal center may represent the lower size limit for molecule-based magnetic information storage materials. Their current drawback is that all SMMs require liquid-helium cooling to show magnetic memory effects. We now report a chemical strategy to access the dysprosium metallocene cation [(Cp i Pr5 )Dy(Cp*)] + (Cp i Pr5 , penta-iso-propylcyclopentadienyl; Cp *, pentamethylcyclopentadienyl), which displays magnetic hysteresis above liquid-nitrogen temperatures. An effective energy barrier to reversal of the magnetization of U eff = 1541 wave number is also measured. The magnetic blocking temperature of T B = 80 kelvin for this cation overcomes an essential barrier toward the development of nanomagnet devices that function at practical temperatures.

Description: The development of highly reactive and stereoselective catalytic systems is required not only to improve existing synthetic methods but also to invent distinct chemical reactions. Herein, a homogenized combination of nickel-based Lewis acid–surfactant-combined catalysts and single-walled carbon nanotubes is shown to exhibit substantial activity in water. In addition to the enhanced reactivity, stereoselective performance and long-term stability were demonstrated in asymmetric conjugate addition reactions of aldoximes to furnish chiral nitrones in high yields with excellent selectivities. The practical and straightforward application of the designed catalysts in water provides an expedient, environmentally benign, and highly efficient pathway to access optically active compounds.

Description: Exploration of intermediates that enable chemoselective cycloaddition reactions and expeditious construction of fused- or bridged-ring systems is a continuous challenge for organic synthesis. As an intermediate of interest, the oxyallyl cation has been harnessed to synthesize architectures containing seven-membered rings via (4+3) cycloaddition. However, its potential to access five-membered skeletons is underdeveloped, largely due to the thermally forbidden (3+2) pathway. Here, the combination of a tailored precursor and a Pd(0) catalyst generates a Pd-oxyallyl intermediate that cyclizes with conjugated dienes to produce a diverse array of tetrahydrofuran skeletons. The cycloaddition overrides conventional (4+3) selectivity by proceeding through a stepwise pathway involving a Pd-allyl transfer and ring closure sequence. Subsequent treatment of the (3+2) adducts with a palladium catalyst converts the heterocycles to the carbocyclic cyclopentanones.

Description: Understanding the practical limitations of chemical reactions is critically important for efficiently planning the synthesis of compounds in pharmaceutical, agrochemical, and specialty chemical research and development. However, literature reports of the scope of new reactions are often cursory and biased toward successful results, severely limiting the ability to predict reaction outcomes for untested substrates. We herein illustrate strategies for carrying out large-scale surveys of chemical reactivity by using a material-sparing nanomole-scale automated synthesis platform with greatly expanded synthetic scope combined with ultrahigh-throughput matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry (MALDI-TOF MS).

Description: Researchers around the world have observed the formation of molecularly ordered structures of unknown origin on the surface of titanium dioxide (TiO 2 ) photocatalysts exposed to air and solution. Using a combination of atomic-scale microscopy and spectroscopy, we show that TiO 2 selectively adsorbs atmospheric carboxylic acids that are typically present in parts-per-billion concentrations while effectively repelling other adsorbates, such as alcohols, that are present in much higher concentrations. The high affinity of the surface for carboxylic acids is attributed to their bidentate binding. These self-assembled monolayers have the unusual property of being both hydrophobic and highly water-soluble, which may contribute to the self-cleaning properties of TiO 2 . This finding is relevant to TiO 2 photocatalysis, because the self-assembled carboxylate monolayers block the undercoordinated surface cation sites typically implicated in photocatalysis.

Description: The alkaline earth metals calcium (Ca), strontium (Sr), and barium (Ba) typically engage in chemical bonding as classical main-group elements through their n s and n p valence orbitals, where n is the principal quantum number. Here we report the isolation and spectroscopic characterization of eight-coordinate carbonyl complexes M(CO) 8 (where M = Ca, Sr, or Ba) in a low-temperature neon matrix. Analysis of the electronic structure of these cubic O h -symmetric complexes reveals that the metal–carbon monoxide (CO) bonds arise mainly from [M(d )] -〉 (CO) 8 backdonation, which explains the strong observed red shift of the C-O stretching frequencies. The corresponding radical cation complexes were also prepared in gas phase and characterized by mass-selected infrared photodissociation spectroscopy, confirming adherence to the 18-electron rule more conventionally associated with transition metal chemistry.

Description: Mystery surrounds the transition from gas-phase hydrocarbon precursors to terrestrial soot and interstellar dust, which are carbonaceous particles formed under similar conditions. Although polycyclic aromatic hydrocarbons (PAHs) are known precursors to high-temperature carbonaceous-particle formation, the molecular pathways that initiate particle formation are unknown. We present experimental and theoretical evidence for rapid molecular clustering–reaction pathways involving radicals with extended conjugation. These radicals react with other hydrocarbon species to form covalently bound complexes that promote further growth and clustering by regenerating resonance-stabilized radicals through low-barrier hydrogen-abstraction and hydrogen-ejection reactions. Such radical–chain reaction pathways may lead to covalently bound clusters of PAHs and other hydrocarbons that would otherwise be too small to condense at high temperatures, thus providing the key mechanistic steps for rapid particle formation and surface growth by hydrocarbon chemisorption.