Assembly of higher-order SMN oligomers is essential for metazoan viability and requires an exposed structural motif present in the YG zipper dimer
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99 GENERAL AND MISCELLANEOUS↗
SEARCH · Engineering Papers
Results for “SmN”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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A small molecule antagonist of SMN disrupts the interaction between SMN and RNAP II
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Liu, Yanli↗
Tuning of electronic properties in highly lattice-mismatched epitaxial SmN
Here, we establish the relationship between native N vacancies, introduced through varying growth parameters, and the structural and transport properties in SmN thin films grown via molecular beam epitaxy grown on MgO(001). The varying levels of N vacancies introduced by varying the ratio of Sm to N atoms during deposition creates excess carriers that radically transform the electrical behavior of the film, over a range of five orders of magnitude, from highly resistive to highly conductive, and unlocking a phase transition evidenced by the presence of a ferromagnetic feature in resistivity. X-ray photoelectron spectroscopy results show that this effect is much less pronounced when varying the available nitrogen species. These samples retain a highly crystal quality despite being grown on a substrate with a lattice mismatch of 20%, alleviating the strain by forming a highly strained SmO oxide layer. The integration between SmN and several transition metal nitride compounds has the potential to unlock new architectures for Josephson junction devices.
36 - MATERIALS SCIENCE↗
Space Mobile Network (SMN) User Demonstration Satellite (SUDS) for a Practical On-Orbit Demonstration of User Initiated Services (UIS)
This paper will discuss the various aspects of implementation of the Space Mobile Network (SMN) architecture framework within the context of operations of various nodes equipped with the User Initiated Services (UIS) protocol. These aspects include development of a Client-Server architecture in which space based Clients can create links with ground based Servers to negotiate passes with ground stations or contacts with the Tracking and Data Relay Satellite (TDRS) fleet. A key feature of this concept is that Users may require a mix of low data rate continuous contacts with one or more of the TDRS fleet and sporadic contacts with ground stations as passes become available. SUDS (SMN User Demonstration Satellite) will have the availability of TDRS contacts, the U.S. Naval Academy's ground station, NASA Near Earth Network ground sites and others. This mode of operations must be integrated within the traditional mode of scheduling contacts and passes. Thus, SUDS fits into a heterogeneous network operations concept of operations.
CubeSat and Autonomy↗
Materials Data on SmN by Materials Project
SmN is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Sm3+ is bonded to six equivalent N3- atoms to form a mixture of edge and corner-sharing SmN6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Sm–N bond lengths are 2.54 Å. N3- is bonded to six equivalent Sm3+ atoms to form a mixture of edge and corner-sharing NSm6 octahedra. The corner-sharing octahedral tilt angles are 0°.
36 MATERIALS SCIENCE↗
Experimental equation of state of 11 lanthanide nitrides (NdN to LuN) and pressure induced phase transitions in NdN, SmN, EuN, and GdN
Through an extensive data analysis of powder X-ray diffraction data obtained at pressures up to at least 78 GPa, we report the experimental equations of state for all lanthanide nitrides between NdN and LuN, excluding the radioactive Pm. By fitting the obtained unit cell volumes as a function of pressure with the third order Birch–Murnaghan equation of state, we find that the bulk modulus increases with an increasing lanthanide number from K 0 = 146(12) GPa for NdN to 182(7) GPa in EuN. Hereafter, the bulk modulus reaches a plateau for the rest of the series except for TmN which has a lower bulk modulus. We find that the first derivative of the bulk modulus is around 4 for all compounds except TbN, which displays a significantly different compression behavior. In addition, we find a B1 to B10 pressure-induced phase transition in NdN, SmN, EuN, and GdN at increasingly higher pressures. In fact, we observe that the onset pressure of the phase transition increases linearly with Ln atomic number. From TbN and onwards, we do not observe any sign of a B1 to B10 transition indicating that the transition pressure exceeds the studied pressure range. Therefore, we believe that, for the heavier lanthanides, the linear relationship between the onset pressure and the lanthanide number does not hold and even higher pressures are needed to observe the transition. This coherent study of the series of lanthanide nitrides offers a unique opportunity for benchmark studies of computational methods applied to compounds with 4f electrons.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Risk Factors and Trends for HPV-Associated Subsequent Malignant Neoplasms among Adolescent and Young Adult Cancer Survivors
Subsequent malignant neoplasms (SMN; new cancers that arise after an original diagnosis) contribute to premature mortality among adolescent and young adult (AYA) cancer survivors. Because of the high population prevalence of human papillomavirus (HPV) infection, we identify demographic and clinical risk factors for HPV-associated SMNs (HPV-SMN) among AYA cancer survivors in the SEER-9 registries diagnosed from 1976 to 2015. Outcomes included any HPV-SMN, oropharyngeal-SMN, and cervical-SMN. Follow-up started 2 months after their original diagnosis. Standardized incidence ratios (SIR) compared risk between AYA survivors and general population. Age-period-cohort (APC) models examined trends over time. Fine and Gray's models identified therapy effects controlling for cancer and demographic confounders. Of 374,408 survivors, 1,369 had an HPV-SMN, occurring on average 5 years after first cancer. Compared with the general population, AYA survivors had 70% increased risk for any HPV-SMN [95% confidence interval (CI), 1.61–1.79] and 117% for oropharyngeal-SMN (95% CI, 2.00–2.35); cervical-SMN risk was generally lower in survivors (SIR, 0.85; 95% CI, 0.76–0.95), but Hispanic AYA survivors had a 8.4 significant increase in cervical-SMN (SIR, 1.46; 95% CI, 1.01–2.06). AYAs first diagnosed with Kaposi sarcoma, leukemia, Hodgkin, and non-Hodgkin lymphoma had increased HPV-SMN risks compared with the general population. Oropharyngeal-SMN incidence declined over time in APC models. Chemotherapy and radiation were associated with any HPV-SMN among survivors with first HPV-related cancers, but not associated among survivors whose first cancers were not HPV-related. HPV-SMN in AYA survivors are driven by oropharyngeal cancers despite temporal declines in oropharyngeal-SMN. Hispanic survivors are at risk for cervical-SMN relative to the general population. Encouraging HPV vaccination and cervical and oral cancer screenings may reduce HPV-SMN burden among AYA survivors.
60 APPLIED LIFE SCIENCES↗
Structure–activity relationship-based chemical classification of highly imbalanced Tox21 datasets
Abstract The specificity of toxicant-target biomolecule interactions lends to the very imbalanced nature of many toxicity datasets, causing poor performance in Structure–Activity Relationship (SAR)-based chemical classification. Undersampling and oversampling are representative techniques for handling such an imbalance challenge. However, removing inactive chemical compound instances from the majority class using an undersampling technique can result in information loss, whereas increasing active toxicant instances in the minority class by interpolation tends to introduce artificial minority instances that often cross into the majority class space, giving rise to class overlapping and a higher false prediction rate. In this study, in order to improve the prediction accuracy of imbalanced learning, we employed SMOTEENN, a combination of Synthetic Minority Over-sampling Technique (SMOTE) and Edited Nearest Neighbor (ENN) algorithms, to oversample the minority class by creating synthetic samples, followed by cleaning the mislabeled instances. We chose the highly imbalanced Tox21 dataset, which consisted of 12 in vitro bioassays for > 10,000 chemicals that were distributed unevenly between binary classes. With Random Forest (RF) as the base classifier and bagging as the ensemble strategy, we applied four hybrid learning methods, i.e., RF without imbalance handling (RF), RF with Random Undersampling (RUS), RF with SMOTE (SMO), and RF with SMOTEENN (SMN). The performance of the four learning methods was compared using nine evaluation metrics, among which F 1 score, Matthews correlation coefficient and Brier score provided a more consistent assessment of the overall performance across the 12 datasets. The Friedman’s aligned ranks test and the subsequent Bergmann-Hommel post hoc test showed that SMN significantly outperformed the other three methods. We also found that a strong negative correlation existed between the prediction accuracy and the imbalance ratio (IR), which is defined as the number of inactive compounds divided by the number of active compounds. SMN became less effective when IR exceeded a certain threshold (e.g., > 28). The ability to separate the few active compounds from the vast amounts of inactive ones is of great importance in computational toxicology. This work demonstrates that the performance of SAR-based, imbalanced chemical toxicity classification can be significantly improved through the use of data rebalancing.
Idakwo, Gabriel↗
Navigation Architecture for a Space Mobile Network
The Tracking and Data Relay Satellite System (TDRSS) Augmentation Service for Satellites (TASS) is a proposed beacon service to provide a global, space based GPS augmentation service based on the NASA Global Differential GPS (GDGPS) System. The TASS signal will be tied to the GPS time system and usable as an additional ranging and Doppler radiometric source. Additionally, it will provide data vital to autonomous navigation in the near Earth regime, including space weather information, TDRS ephemerides, Earth Orientation Parameters (EOP), and forward commanding capability. TASS benefits include enhancing situational awareness, enabling increased autonomy, and providing near real-time command access for user platforms. As NASA Headquarters' Space Communication and Navigation Office (SCaN) begins to move away from a centralized network architecture and towards a Space Mobile Network (SMN) that allows for user initiated services, autonomous navigation will be a key part of such a system. This paper explores how a TASS beacon service enables the Space Mobile Networking paradigm, what a typical user platform would require, and provides an in-depth analysis of several navigation scenarios and operations concepts. This paper provides an overview of the TASS beacon and its role within the SMN and user community. Supporting navigation analysis is presented for two user mission scenarios: an Earth observing spacecraft in low earth orbit (LEO), and a highly elliptical spacecraft in a lunar resonance orbit. These diverse flight scenarios indicate the breadth of applicability of the TASS beacon for upcoming users within the current network architecture and in the SMN.
Data Relay↗
Space Mobile Network: A Near Earth Communications and Navigation Architecture
This paper shares key findings of NASA's Earth Regime Network Evolution Study (ERNESt) team resulting from its 18-month effort to define a wholly new architecture-level paradigm for the exploitation of space by civil space and commercial sector organizations. Since the launch of Sputnik in October 1957 spaceflight missions have remained highly scripted activities from launch through disposal. The utilization of computer technology has enabled dramatic increases in mission complexity; but, the underlying premise that the diverse actions necessary to meet mission goals requires minute-by-minute scripting, defined weeks in advance of execution, for the life of the mission has remained. This archetype was appropriate for a "new frontier" but now risks overtly constraining the potential market-based opportunities for the innovation considered necessary to efficiently address the complexities associated with meeting communications and navigation requirements projected to be characteristics of the next era of space exploration: a growing number of missions in simultaneous execution, increased variance of mission types and growth in location/orbital regime diversity. The resulting ERNESt architectural cornerstone - the Space Mobile Network (SMN) - was envisioned as critical to creating an environment essential to meeting these future challenges in political, programmatic, technological and budgetary terms. The SMN incorporates technologies such as: Disruption Tolerant Networking (DTN) and optical communications, as well as new operations concepts such as User Initiated Services (UIS) to provide user services analogous to today's terrestrial mobile network user. Results developed in collaboration with NASA's Space Communications and Navigation (SCaN) Division and field centers are reported on. Findings have been validated via briefings to external focus groups and initial ground-based demonstrations. The SMN opens new niches for exploitation by the marketplace of mission planners and service providers.
Space Communication Spacecraft↗
Space Mobile Network Concepts for Missions Beyond Low Earth Orbit
The Space Mobile Network (SMN) is an architectural framework that will allow for quicker, more efficient and more easily available space communications services, providing user spacecraft with an experience similar to that of terrestrial mobile network users. While previous papers have described SMN concept using examples of users in low-Earth orbit, the framework can also be applied beyond the near-Earth environment. This paper details how SMN concepts such as user-initiated services, which will enable users to request access to high-performance link resources in response to real-time science or operational events, would be applied in and beyond the near-Earth regime. Specifically, the paper explores the application of user-initiated services to direct-to-Earth (DTE), relay, and DTE/relay hybrid scenarios in near-Earth, lunar, Martian and other space regimes.
CubeSat and Autonomy↗
Space Mobile Network Concepts for Missions Beyond Low Earth Orbit
The Space Mobile Network (SMN) is an architectural framework that will allow for quicker, more efficient and more easily available space communications services, providing user spacecraft with an experience similar to that of terrestrial mobile network users. While previous papers have described SMN concept using examples of users in low-Earth orbit, the framework can also be applied beyond the near-Earth environment. This paper details how SMN concepts such as user-initiated services, which will enable users to request access to high-performance link resources in response to real-time science or operational events, would be applied in and beyond the near-Earth regime. Specifically, the paper explores the application of user-initiated services to direct-to-Earth (DTE), relay, and DTE/relay hybrid scenarios in near-Earth, lunar, martian and other space regimes.
Israel, David J.↗
Space Mobile Network Concepts for Missions Beyond Low Earth Orbit
The Space Mobile Network (SMN) is an architectural framework that will allow for quicker, more efficient and more easily available space communications services, providing user spacecraft with an experience similar to that of terrestrial mobile network users. While previous papers have described SMN concept using examples of users in low-Earth orbit, the framework can also be applied beyond the near-Earth environment.This paper details how SMN concepts such as user-initiated services, which will enable users to request access to high-performance link resources in response to real-time science or operational events, would be applied in and beyond the near-Earth regime. Specifically, the paper explores the application of user-initiated services to direct-to-Earth (DTE), relay, and DTE/relay hybrid scenarios in near-Earth, lunar, martian and other space regimes.
Israel, David J.↗
Design and Characterization of ALD-Based Overcoats for Supported Metal Nanoparticle Catalysts
Supported metal nanoparticle (SMN) catalysts are enormously crucial for many catalytic applications. However, catalyst deactivation, caused by sintering and coke formation, is a ubiquitous problem that significantly undermines catalytic processing economics. The application of material overcoating onto supported metal nanoparticles by atomic layer deposition (ALD) offers the solution to inhibit catalyst deactivation. Herein, we discuss examples in which ALD has been used to stabilize SMN catalysts in gaseous and aqueous-phase reactions. We highlight the ALD tools and methods in coating high-surface-area catalysts. Besides, various techniques are introduced to understand better how to characterize the overcoating layer and the catalyst itself. Finally, the outlook for new techniques to characterize the ALD overcoated catalytic materials is discussed.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
GdN/SmN superlattices; influence of a Zeeman/exchange conflict
GdN and SmN are two of the lanthanide nitrides, most of which are intrinsic ferromagnetic semiconductors. Superlattices comprising the pair offer a unique opportunity to investigate heterojunctions that feature simultaneous conductivity and magnetic interface influences. In this work, we report an investigation of these influences, using magnetisation and X-ray magnetic circular dichroism for magnetic effects, and magnetoresistance and Hall effect studies of their electrical conductance. Magnetic data show clear signatures of a conflicting Zeeman vs. interfacial exchange and the magnetic disruption that results, while resistivity and Hall measurements show conduction in both GdN and SmN.
36 MATERIALS SCIENCE↗
Synthesis of Samarium Nitride Thin Films on Magnesium Oxide (001) Substrates Using Molecular Beam Epitaxy
Rare-earth nitrides are an exciting family of materials with a wide variety of properties desirable for new physics and applications in spintronics and superconducting devices. Among them, samarium nitride is an interesting compound reported to have ferromagnetic behavior coupled with the potential existence of p-wave superconductivity. Synthesis of high-quality thin films is essential in order to manifest these behaviors and understand the impact that vacancies, structural distortions, and doping can have on these properties. In this study, we report the synthesis of samarium nitride monocrystalline thin films on magnesium oxide (001) substrates with a chromium nitride capping layer using molecular beam epitaxy (MBE). We observed a high-quality monocrystalline SmN film with matching orientation to the substrate, then optimized the growth temperature. Despite the initial 2 nm of growth showing formation of a potential samarium oxide layer, the subsequent layers showed high-quality SmN, with semiconducting behavior revealed by an increase in resistivity with decreasing temperature. These promising results highlight the importance of studying diverse heteroepitaxial schemes and open the door for integration of rare-earth nitrides and transition metal nitrides for future spintronic devices.
36 MATERIALS SCIENCE↗
Space Mobile Network: A Near Earth Communication and Navigation Architecture
This paper describes a Space Mobile Network architecture, the result of a recently completed NASA study exploring architectural concepts to produce a vision for the future Near Earth communications and navigation systems. The Space Mobile Network (SMN) incorporates technologies, such as Disruption Tolerant Networking (DTN) and optical communications, and new operations concepts, such as User Initiated Services, to provide user services analogous to a terrestrial smartphone user. The paper will describe the SMN Architecture, envisioned future operations concepts, opportunities for industry and international collaboration and interoperability, and technology development areas and goals.
Spacecraft Communication↗
The Space Mobile Network
The definition and development of the next generation space communications and navigation architecture is underway. The primary goals are to remove communications and navigations constraints from missions and to enable increased autonomy. The Space Mobile Network (SMN) is an architectural concept that includes new technology and operations that will provide flight systems with an similar user experience to terrestrial wireless mobile networks. This talk will describe the SMN and its proposed new features, such as Disruption Tolerant Networking (DTN), optical communications, and User Initiated Services (UIS).
Spacecraft Communications↗