New and Improved - The Broadcast Interfrequency Biases
One of the latest GPS enhancements is an improvement of the interfrequency bias values conatined in the navigation message broadcast by GPS satellites.
GPS↗
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Results for “biasing”
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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Performance Evaluation of the GPS Yaw Bias Implementation
Yaw bias was implemented on most GPS satellites in 1994, and on all Block II satellites by 1995. It was introduced as a way to model the yaw attitude of the GPS satellites during shadow crossings. A yaw attitude model was written to simulate the new satellite attitude during eclipse seasons. Proper use of this model improves the accuracy of precise positioning with the GPS.
Yaw↗
Estimation of of the Electromagnetic Bias from Retracked TOPEX Data
We examine the EM bias by using retracked TOPEX altimeter data.
TOPEX↗
Digital-Threat Bias and Psychological Distance: Barriers to Foundational Digital-Security Improvement
Modern life is held together by a web of digital dependencies that enable and provide delivery of critical services and functions—think the provision of utilities such as electricity and water, as well as our dependency on digital services for social and economic services (internet, communication, etc.). As this dependency grows, the complexity related to the delivery of these critical services increases as well. As complexity increases, the understanding of the risk and impact associated with potential disruption, degradation, or destruction—due to either malicious or non-malicious events of those digitally enabled functions—decreases. One potential explanation for the difficulty to 1) understand the risks faced and 2) address them appropriately and effectively is the abstractness and psychological distance assigned to “digital threat.” The complexity of these digitally enabled services creates a perceived complicatedness; as a result, digital threats are treated differently than similarly devasting (but more easily understood) kinetic or physical threats. How we categorize these threats also matters. Acts of cyber-enabled sabotage to critical infrastructure need to be defined as irregular warfare. By inadequately defining the threat, we compound the problem. Acknowledging this digital-threat bias is foundational to improving the ability to protect critical infrastructure. Using construal-level theory and psychological-distance concepts provides an intriguing starting point to address these issues, to reframe the challenges faced, and pursue more effective critical infrastructure security and defense policy.
29 - ENERGY PLANNING, POLICY AND ECONOMY↗
Select strengths and biases of models in representing the Arctic winter boundary layer over sea ice: the Larcform 1 single column model intercomparison
We struggle to represent lower tropospheric temperature and moisture profiles and surface fluxes in Artic winter using weather and climate models, partly because they lack or misrepresent physical processes that are specific to high latitudes. Observations have revealed two preferred states of the Arctic winter boundary layer. In the cloudy state, cloud liquid water limits surface radiative cooling, and temperature inversions are weak and elevated. In the radiatively clear state, strong surface radiative cooling leads to the build-up of surface-based temperature inversions. Many large-scale models lack the cloudy state, and some substantially underestimate inversion strength in the clear state. The transformation from a moist to a cold dry air mass is modeled using an idealized Lagrangian perspective. The trajectory includes both boundary layer states, and the single-column experiment is the first Lagrangian Arctic air formation experiment (Larcform 1) organized within GEWEX GASS (Global atmospheric system studies). The intercomparison reproduces the typical biases of large-scale models: some models lack the cloudy state of the boundary layer due to the representation of mixed-phase microphysics or to the interaction between micro- and macrophysics. In some models, high emissivities of ice clouds or the lack of an insulating snow layer prevent the build-up of surface-based inversions in the radiatively clear state. Models substantially disagree on the amount of cloud liquid water in the cloudy state and on turbulent heat fluxes under clear skies. Finally, observations of air mass transformations including both boundary layer states would allow for a tighter constraint of model behavior.
54 ENVIRONMENTAL SCIENCES↗
Continuously amplified warming in the Alaskan Arctic: Implications for estimating global warming hiatus: SPATIAL COVERAGE AND BIAS IN TREND
Historically, in-situ measurements have been notoriously sparse over the Arctic. As a consequence, the existing gridded data of Surface Air Temperature (SAT) may have large biases in estimating the warming trend in this region. Using data from an expanded monitoring network with 31 stations in the Alaskan Arctic, we demonstrate that the SAT has increased by 2.19 °C in this region, or at a rate of 0.23 °C/decade during 1921-2015. Mean- while, we found that the SAT warmed at 0.71 °C/decade over 1998-2015, which is two to three times faster than the rate established from the gridded datasets. Focusing on the "hiatus" period 1998-2012 as identied by the Intergovernmental Panel on Climate Change (IPCC) report, the SAT has increased at 0.45 °C/decade, which captures more than 90% of the regional trend for 1951- 2012. We suggest that sparse in-situ measurements are responsible for underestimation of the SAT change in the gridded datasets. It is likely that enhanced climate warming may also have happened in the other regions of the Arctic since the late 1990s but left undetected because of incomplete observational coverage.
54 ENVIRONMENTAL SCIENCES↗
A Voltage Bias Effect on Catalytic Activity of Electrically Continuous Pt/TiO 2 Nanocomposites
Abstract Recently, efforts to optimize catalytic performance have included the utilization of catalytic nanoparticles with careful control over their shape and size, chemical composition, surface functionalization, and structural architecture. Here, direct measurements are reported detailing the impact of applied external bias on the exothermic catalytic formation of water for a Pt/TiO 2 nanocomposite under exposure to gaseous oxyhydrogen environments. As external voltages of opposite polarity are applied to the system, the surface temperature kinetics, total pressure kinetics within the analytical chamber, and water turnover frequency transition in a reproducible manner between two well‐defined states which result in 1) decreased catalytic activity, 2) decreased initial molecular adsorption onto the Pt catalyst, and 3) lower rates of water production under negative voltage. These findings pave the road toward the realization of a catalytic switch that can be activated by applying a voltage to Schottky barrier systems to enhance or mitigate catalytic surface reactions.
Ray, Nathan J.↗
Revealing the Effects of Trace Oxygen Vacancies on Improper Ferroelectric Manganite with In Situ Biasing
Abstract Multiferroic materials, which exhibit multiple orderings, are promising for next generation data‐storage device applications. YMnO 3 , in particular, because of the coexistence of the ferroelectricity and (anti)ferromagnetism within one single material, has drawn special attentions to application‐based research. However, the role of defect chemistry related to the behaviors of the ferroelectric polarization has been seldomly studied due to its complexity. In this work, a novel switching behavior of multiferroic YMnO 3 single crystal is reported using in situ biasing and Landau based numerical calculation. It is revealed that the domain switching only happens at the topmost surface, which can be well explained by the electric field redistribution due to the trace amount of oxygen vacancies. These in situ observations demonstrate that defect chemistry plays an important role in domain switching and can be utilized as an additional parameter for controlling the distribution of electric field within the multiferroic materials.
Cheng, Shaobo↗
Simulation studies of polypeptoids using replica exchange with dynamical scaling and dihedral biasing
Polypeptoids differ from polypeptides in that the amide bond can more frequently adopt both cis and trans conformations. The transition between the two conformations requires overcoming a large energy barrier, making it difficult for conventional molecular simulations to adequately visit the cis and trans structures. A replica-exchange method is presented that allows for easy rotations of the amide bond and also an efficient linking to a high temperature replica. The method allows for just three replicas (one at the temperature and Hamiltonian of interest, a second high temperature replica with a biased dihedral potential, and a third connecting them) to overcome the amide bond sampling problem and also enhance sampling for other coordinates. Here our results indicate that for short peptoid oligomers, the conformations can range from all cis to all trans with an average cis/trans ratio that depends on side chain and potential model.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
A New Estimator to Correct for Bias from Tag Rate Expansion on Natural-Origin Fish Attributes in Mixed-Stock Analysis Using Parentage-Based Tagging
Abstract In fisheries where hatchery- and natural-origin conspecifics occur as mixed stocks, it is often important to estimate both the natural-origin proportion of the mixture and the composition of attributes within the natural-origin portion (e.g., genetic stock, sex, and age-class). These estimates are facilitated by parentage-based tagging, which allows large numbers of hatchery fish to be efficiently tagged and later identified. When tag rates are less than 100%, the untagged fish in the mixture include both untagged hatchery fish and natural-origin fish. Unbiased estimation of the abundance and attribute composition of the natural-origin portion requires an estimator that accounts for tag rates. Two estimators are described: one “accounting-style” estimator similar to previously described approaches and one maximum likelihood method. These estimators were evaluated and compared using simulations mimicking estimation of the composition of fish migrating past a dam. The two estimators performed similarly at reducing bias when tag rates were high, but the maximum likelihood method had smaller mean square error when tag rates were low. We provide an R package to allow usage of this estimator in a wide variety of fisheries applications.
Delomas, Thomas A. (ORCID:000000015154759X)↗
Evaluation of NMME temperature and precipitation bias and forecast skill for South Asia
Systematic error and forecast skill for temperature and precipitation in two regions of Southern Asia are investigated using hindcasts initialized May 1 from the North American Multi-Model Ensemble. We focus on two contiguous but geographically and dynamically diverse regions: the Extended Indian Monsoon Rainfall (70–100E, 10–30 N) and the nearby mountainous area of Pakistan and Afghanistan (60–75E, 23–39 N). Forecast skill is assessed using the Sign test framework, a rigorous statistical method that can be applied to non-Gaussian variables such as precipitation and to different ensemble sizes without introducing bias. We find that models show significant systematic error in both precipitation and temperature for both regions. The multi-model ensemble mean (MMEM) consistently yields the lowest systematic error and the highest forecast skill for both regions and variables. However, we also find that the MMEM consistently provides a statistically significant increase in skill over climatology only in the first month of the forecast. While the MMEM tends to provide higher overall skill than climatology later in the forecast, the differences are not significant at the 95% level. We also find that MMEMs constructed with a relatively small number of ensemble members per model can equal or outperform MMEMs constructed with more members in skill. This suggests some ensemble members either provide no contribution to overall skill or even detract from it.
54 ENVIRONMENTAL SCIENCES↗
Circumventing mesh bias by r- and h-adaptive techniques for variational eigenfracture
This work introduces and compares mesh r- and h-adaptivity for the eigenfracture model originally proposed in Schmidt et al. (Multiscale Model Simul 7:1237–1266, 2009), Pandolfi and Ortiz (J Numer Methods Eng 92:694–714, 2012), with the goal of suppressing potential mesh bias due to the element deletion. In the r-adaptive approach, we compute the configurational force at each incremental step and move nodes near the crack tip parallel to the normalized configurational forces field such that the crack propagation direction can be captured more accurately within each incremental step. In the h-adapative approach, we introduce mesh refinement via a quad-tree algorithm to introduce more degrees of freedom within the nonlocal ϵ-neighborhood such that a more refined crack path can be reproduced with a higher mesh resolution. Our numerical examples indicate that the r-adaptive approach is able to replicate curved cracks and complex geometrical features, whereas the h-adaptive approach is advantageous in simulating sub-scale fracture when the nonlocal regions are smaller than the un-refined coarse mesh.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Giant Exchange Bias of Hysteresis Loops on Cr{sup 3+}-doped Ag Nanoparticles
In this study, we fabricate Cr-doped Ag nanoparticles (AgCrO{sub 2} and Ag{sub 0.5}Cr{sub 2.5}O{sub 4}) by flash autocombustion method. XRD confirmed that the samples have a single-phase spinel structure. The morphology is studied using high-resolution transmission electron microscopy (HRTEM) to confirm that the samples are on nanoscale. The magnetic properties are studied using a vibrating sample magnetometer (VSM) at room temperature (300 K) and at low temperatures (200 and 100 K). Exchange bias has occurred for the investigated samples below room temperatures. The shifts have occurred in the horizontal directions which may be ascribed to the frozen spins in the samples.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Role of A Cation Vacancy in the Exchange-Biased LaFeO{sub 3} Multiferroic Nanocrystals
Multiferroic samples with the chemical formula La{sub 1−x}◻{sub x}FeO{sub 3} (0.0 ≤ x ≤ 0.03) were successfully prepared in nanoscale by citrate nitrate combustion method. XRD data reveals crystallized single-phase orthorhombic symmetry for the prepared nanopowder. All measured magnetic parameters point to the antiferromagnetic character with weak ferromagnetic moment. The value of the molar magnetic susceptibility (χ{sub M}) for La{sub 0.99}◻{sub 0.01}FeO{sub 3} reaches 3.5 times that of the undoped sample. The saturation magnetization of the samples La{sub 0.99}◻{sub 0.01}FeO{sub 3} and La{sub 0.97}◻{sub 0.03}FeO{sub 3} increased two times as compared with that of the parent one. The exchange bias (EB) effect was observed for 1{sup st} time at room temperature and originated from antiferromagnetic–ferromagnetic (AFM-FM) interface effect. Ferroelectric hysteresis loop was observed at room temperature for the samples which highlighted the presence of the ferroelectric ordering. A huge enhancement in the saturation (P{sub s}), the remnant polarization (P{sub r}), and the coercive electric field (E{sub c}) of the sample La{sub 0.98}◻{sub 0.02}FeO{sub 3} by 7.5, 24, and 12 times, respectively, when compared with the parent sample LaFeO{sub 3}. Based on the obtained results, the investigated samples are categorized in type I multiferroics.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Complicated Magnetic Phases and Presence of Exchange Bias in Off-Stoichiometric Mn{sub 50}Ni{sub 25 + x}In{sub 25−x} Heusler Alloys
The martensitic transformation (MT), magnetic phases, and exchange bias (EB) effect in Mn{sub 50}Ni{sub 25 + x}In{sub 25−x} (x = 14.5∼18) Heusler alloys have been investigated. The MT and magnetic state can be tuned significantly by modifying the Ni/In ratio, while the Curie temperature (T{sub C}) remains almost unchanged. With increase of the Ni/In ratio, the ferromagnetic components in the studied samples decrease continuously, while the antiferromagnetic components increase and it therefore enhances the exchange interaction as well. All of the samples exhibit negative horizontally shifted loops after field-cooled procedure. In addition, the samples with the compositional range of 15 ≤ x ≤ 16 also present the EB effect in zero field-cooled condition. To evaluate the causes of this scenario, EB field and coercive field as a function of temperature and cooling field have been investigated. The experimental results imply that the spin reconfiguration of superspin glass (SSG) clusters and the competition between antiferromagnetic and ferromagnetic interactions can account for the behavior of EB effect.
36 MATERIALS SCIENCE↗
The Self-Biased Circulator: Ferrite Materials Design and Process Considerations
A strategic goal of next-generation transmit and receive modules used in radar and communication platforms is the continued miniaturization of semiconductor based electronics in conjunction with their integration with ferrite control elements, chief among them, the circulator. Here, we address the singular goal of efforts to transform the circulator, in its present form a three dimensional construct, to a two-dimensional device. Key to this transformation is the development of self-biased ferrite materials that are necessary for the breaking of time reversal symmetry and nonreciprocal performance of circulators and isolators. A discussion of efforts to integrate this new two-dimensional device with semiconductor-based active components will be addressed.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Tuning the Ground State and Its Relationship to Zero-Field-Cooled Exchange Bias in NiMnSnAl Alloys
The crystal structure, phase transitions, and exchange bias (EB) in Al-doped Ni{sub 50}Mn{sub 36}Sn{sub 14-x}Al{sub x} Heusler alloys were investigated. With the increase of Al content, the cell volume decreases gradually, and the martensitic transformation temperature shifts to a higher temperature. Due to the positive “chemical pressure” by Al substitution, the antiferromagnetic interaction strengthens, leading to the decrease of magnetization and the ground state evolution from “reentrant” spin glass to spin glass. Zero-field-cooled EB is triggered in samples exhibiting spin-glass ground state. These results suggest a viable way to design Ni-Mn-Z-based alloys showing zero-field-cooled EB by tuning the exchange interactions and ground state via lattice modulation.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Convergence and Efficiency of Adaptive Importance Sampling Techniques with Partial Biasing
We propose a new Monte Carlo method to efficiently sample a multimodal distribution (known up to a normalization constant). We consider a generalization of the discrete-time Self Healing Umbrella Sampling method, which can also be seen as a generalization of well-tempered metadynamics. The dynamics is based on an adaptive importance technique. The importance function relies on the weights (namely the relative probabilities) of disjoint sets which form a partition of the space. These weights are unknown but are learnt on the fly yielding an adaptive algorithm. In the context of computational statistical physics, the logarithm of these weights is, up to an additive constant, the free-energy, and the discrete valued function defining the partition is called the collective variable. The algorithm falls into the general class of Wang–Landau type methods, and is a generalization of the original Self Healing Umbrella Sampling method in two ways: (i) the updating strategy leads to a larger penalization strength of already visited sets in order to escape more quickly from metastable states, and (ii) the target distribution is biased using only a fraction of the free-energy, in order to increase the effective sample size and reduce the variance of importance sampling estimators. We prove the convergence of the algorithm and analyze numerically its efficiency on a toy example.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗