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At least 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Stochastic differential equation in a random environment

Solutions of the Itô stochastic differential equation in a random environment are considered. The random environment is formed by the generalized telegraph process. It is proved that the initial problem is equivalent to a system of two stochastic differential equations with nonrandom coefficients. The first equation is the Itô equation, and the initial process is its solution. The second equation is an equation with Poisson process, and its solution is a generalized telegraph process. The theorems of existence and uniqueness of strong and weak solutions are proved.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Coherence and entropy squeezing in the spin-boson model under non-Markovian environment

We study the dynamical behavior of the coherence and squeezing for a two-level system immersed in an environment modeled by a spin degree of freedom in a magnetic field coupled linearly to an oscillator bath with non-Markovian environment. The dependence of the coherence and squeezing on the system and reservoir parameters shows that these quantities could be greatly controlled and manipulated with the assistance of the reservoir cutoff frequency, system oscillator frequency, and reservoir temperature. Moreover, we show that the proper choice of the external control field can make further control on the coherence and squeezing of the atomic system under the effect of environmental noises. The results show new interest features that are usefully utilized in controlling the physical quantities and show how the enhancement and preservation of coherence and squeezing can greatly benefit from the combination of the all physical parameters.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Corrosion Performance of Fe-Based Alloys in Simulated Oxy-Fuel Environment

The long-term corrosion of Fe-based alloys in simulated oxy-fuel environment at 1023 K (750 A degrees C) was studied. Detailed results are presented on weight change, scale thickness, internal penetration, microstructural characteristics of the corrosion products, and the cracking of scales for the alloys after exposure at 1023 K (750 A degrees C) for up to 3600 hours. An incubation period during which the corrosion rate was low was observed for the alloys. After the incubation period, the corrosion accelerated, and the corrosion process followed linear kinetics. Effects of alloy, CaO-containing ash, and gas composition on the corrosion rate were also studied. In addition, synchrotron nanobeam X-ray analysis was employed to determine the phase and chemical composition of the oxide layers on the alloy surface. Results from these studies are being used to address the long-term corrosion performance of Fe-based alloys in various coal-ash combustion environments and to develop methods to mitigate high-temperature ash corrosion.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Oxidation Behavior of Carbon Steel: Effect of Formation Temperature and pH of the Environment

The nature of surface oxide formed on carbon steel piping used in nuclear power plants affects flow-accelerated corrosion. In this investigation, carbon steel specimens were oxidized in an autoclave using demineralized water at various temperatures (150-300 °C) and at pH levels (neutral, 9.5). At low temperatures (< 240 °C), weight loss of specimens due to dissolution of iron in water occurred to a greater extent than weight gain due to oxide formation. With the increase in temperature, the extent of iron dissolution reduced and weight gain due to oxide formation increased. A similar trend was observed with the increase in pH as was observed with the increase in temperature. XRD and Raman spectroscopy confirmed the formation of magnetite. The oxide film formed by precipitation process was negligible at temperatures from 150 to 240 °C compared to that at higher temperatures (> 240 °C) as confirmed by scanning electron microscopy. Electrochemical impedance measurement followed by Mott–Schottky analysis indicated an increase in defect density with exposure duration at 150 °C at neutral pH but a low and stable defect density in alkaline environment. The defect density of the oxide formed at neutral pH at 150-300 °C was always higher than that formed in alkaline environment as reported in the literature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Antifouling Properties and Release of Dissolved Copper of Cold Spray Cu/Cu{sub 2}O Coatings for Ships and Steel Structures in Marine Environment

At the submarine screen doors of ships, the flow of water was fast and organic coatings were easy to peel off. To solve the problems of biofouling, the Cu/Cu{sub 2}O coatings were prepared by cold spray technology. In this paper, the release mechanism of effective antifouling components of the coatings was studied by micro-domain electrochemical potential scanning technique. Cuprous oxide in the coatings and the surrounding copper constituted micro-cells which accelerated the local electrochemical dissolution of copper. Cuprous oxide acted as the cathode, and the surrounding copper acted as the anode. Meanwhile, under the action of current, chloride ions were transferred from cathode to the anode and promoted local electrochemical dissolution of copper. Experiments show that the higher the Cu{sub 2}O content in the coatings, the greater the release rate of dissolved copper and inhibitory effect on diatoms. In the environments varied in dissolved oxygen, salinity, temperature and flow rate, the coatings maintained sufficient release rate of dissolved copper, unless the salinity was very low. Most of the dissolved copper was provided by the electrochemical dissolution process of copper. Whether in the indoor test or marine environment experiments, 30% Cu{sub 2}O coatings show the best performance. After insulating layer was sprayed, the effect of antifouling was improved evidently and the coatings were applied to the submarine screen doors of ships.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Tempered Martensite and Ferrite/Bainite on Corrosion Behavior of Low Alloy Steel Used for Flexible Pipe Exposed to High-Temperature Brine Environment

Immersion experiments and electrochemical measurements were carried out to study the effect of tempered martensite and ferrite/bainite on corrosion behavior of low alloy steel used for flexible pipe exposed to high-temperature brine environment in terms of microstructure morphology, corrosion rate, corrosion products characteristics, potentiodynamic polarization curves and electrochemical impedance spectroscopy. The experimental results indicated that the proportion of high-angle grain boundaries of tempered martensite steel was greater than ferrite/bainite steel. The corrosion rate of ferrite/bainite steel was lower than tempered martensite steel. With increasing immersion time, the structure of corrosion products formed on the surface of ferrite/bainite steel was more compact and denser than tempered martensite steel. In addition, the current density of ferrite/bainite steel was lower than tempered martensite steel. The charge transfer resistance and total impedance of ferrite/bainite steel were larger than tempered martensite steel. Thus, the corrosion resistance of ferrite/bainite steel exposed to high-temperature brine environment was excellent compared to the tempered martensite steel.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Sulfide Stress Corrosion Cracking Behavior of G105 and S135 High-Strength Drill Pipe Steels in H{sub 2}S Environment

Slow strain rate testing was employed to investigate the sulfide stress corrosion cracking (SSCC) behavior of low-carbon high-strength drill pipe steels (G105 and S135) in the simulated drilling environment containing H{sub 2}S. Results reveal that both G105 and S135 steels have a high SSCC susceptibility in the simulated drilling environment containing H{sub 2}S. In the range of experimental slow strain rate, the SSCC sensitivity of drill pipe steel increases with the decrease in slow strain rate, and the ductility and fracture properties of drill pipe steels also decrease obviously. With the increase in the steel strength, the SSCC sensitivity of the drill pipe steel increases, and the S135 drill pipe steel has higher SSCC sensitivity than G105. There is no obvious plastic deformation on the fracture surface of G105 and S135 steels in H{sub 2}S solution. The cracks of fracture sprout on the surface of the specimen, the instantaneous fracture zone is in the middle, and the fracture can be divided into the cracking and the final fracture zone. The SSCC mechanisms of two drill pipe steels are hydrogen embrittlement. The hydrogen enters the steel and reduces the binding force of the iron atom, resulting in cleavage fracture.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Corrosion Behavior of Fe-7Cr-1Mo-12Zr Metal Waste Form Alloy in Simulated Repository Environment

Metal waste forms (MWF) are solid metallic waste categorized as high-level radioactive waste generated during pyro-reprocessing of spent metallic fuels and geologically disposed off. This waste form generated requires an excellent corrosion resistance in a geological repository environment. In the present work, Fe-7Cr-1Mo-12Zr MWF alloy was developed by casting in an arc melting furnace. The x-ray diffraction analysis revealed the formation of stable phases of α-Fe solid solution and the intermetallic phases of Fe{sub 2}Zr and Fe{sub 23}Zr{sub 6}. The corrosion behavior of Fe-7Cr-1Mo-12Zr alloy was investigated using electrochemical techniques in aggressive (highly acidic with Cl{sup −}) and nominal repository pH environment. Cyclic potentiodynamic polarization studies indicated the shift in corrosion potential toward cathodic potential in highly acidic solution with Cl{sup −}. The corrosion mechanism of pitting is associated with acidified pH medium with more Cl{sup −}, whereas uniform corrosion or transpassive dissolution is resultant of mild acidity or mild alkaline medium. The passive region is wider in pH 5 and 8 when compared to pH 1 and 3. Electrochemical impedance spectroscopic (EIS) analysis revealed the lowering of passive film stability in the highly acidic medium in the presence of Cl{sup −}. The role of passive oxide layers on the corrosion resistance of the Fe-7Cr-1Mo-12Zr MWF alloy is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2021

High-Temperature Oxidation of Steels in Direct-Fired CO 2 Power Cycle Environments

We report future direct-fired supercritical CO 2 power cycles require steels resistant to oxidation/corrosion in high-temperature CO 2 environments containing various impurities. Herein we studied the oxidation behavior of 14 candidate steels in a simulated direct-fired CO 2 power cycle environment consisting of 95% CO 2 , 4% H 2 O, 1% O 2 with/without 0.1% SO 2 at 1 atm and 550 °C, 600 °C, 650 °C for up to 2500 hours. Steels with ≥11.5 wt% Cr exhibited at least partial coverage by Cr-rich oxide scales leading to a significant decrease in the oxidation rates in both gases. While SO 2 had little effect on low-Cr steels that formed Fe-rich oxides, it generally worsened performance of high-Cr (> 11.5 wt%) steels by hindering the establishment of a protective Cr-rich oxide. This effect was most pronounced at the lowest temperature of 550 °C, which was attributed to strong preferential adsorption of sulfur-containing species within the oxide at relatively low temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Mechanistic modeling of copper corrosions in data center environments

Air-side economizers are increasingly used to take advantage of “free-cooling” in data centers with the intent of reducing the carbon footprint of buildings. However, they can introduce outdoor pollutants to indoor environment of data centers and cause corrosion damage to the information technology equipment. Here, to evaluate the reliability of information technology equipment under various thermal and air-pollution conditions, a mechanistic model based on multi-ion transport and chemical reactions was developed. The model was used to predict Cu corrosion caused by Cl2-containing pollutant mixtures. It also accounted for the effects of temperature (25 °C and 28 °C), relative humidity (50%, 75%, and 95%), and synergism. It also identified higher air temperature as a corrosion barrier and higher relative humidity as a corrosion accelerator, which agreed well with the experimental results. The average root mean square error of the prediction was 13.7 Å. The model can be used to evaluate the thermal guideline for data centers design and operation when Cl2 is present based on pre-established acceptable risk of corrosion in data centers’ environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Fisher information due to a phase noisy laser under non-Markovian environment

More recently, K. Berrada [Annals of Physics 340 (2014) 60-69] [1] studied the geometric phase of a two-level atom system driven by a phase noise laser under non-Markovian dynamics in terms of different parameters involved in the whole system, and collapse and revival phenomena were found for large class of states. In this paper, using this noise effect, we study the quantum fisher information (QFI) for a two-level atom system driven by a phase noise laser under non-Markovian dynamics. A new quantity, called QFI flow is used to characterize the damping effect and unveil a fundamental connection between non-Markovian behavior and dynamics of system–environment correlations under phase noise laser. It is shown that QFI flow has disappeared suddenly followed by a sudden birth depending on the kind of the environment damping. QFI flow provides an indicator to characterize the dissipative quantum system’s decoherence by analyzing the behavior of the dynamical non-Markovian coefficients.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Decoherence suppression of tripartite entanglement in non-Markovian environments by using weak measurements

A feasible scheme for protecting the Greenberger–Horne–Zeilinger (GHZ) entanglement state in non-Markovian environments is proposed. It consists of prior weak measurement on each qubit before the interaction with decoherence environments followed by post quantum measurement reversals. It is shown that both the fidelity and concurrence of the GHZ state can be effectively improved. Meanwhile, we also verified that our scenario can enhance tripartite nonlocality remarkably. In addition, the result indicates that the larger the weak measurement strength, the better the effectiveness of the scheme with the lower success probability.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Non-Markovian dynamics of quantum open systems embedded in a hybrid environment

Quantum systems of interest are typically coupled to several quantum channels (more generally environments). In this paper, we develop an exact stochastic Schrödinger equation for an open quantum system coupled to a hybrid environment containing both bosonic and fermionic particles. Such a stochastic differential equation may be obtained directly from a microscopic model through employing a classical complex Gaussian noise and a non-commutative fermionic noise to simulate the hybrid bath. As an immediate application of our developed stochastic approach, we show that the evolution of the reduced density matrix can be derived by taking the average over both the bosonic noise and the fermionic noise. Three specific examples are given in this paper to illustrate that the hybrid quantum trajectory is fully consistent with the standard quantum mechanics. Our examples also shed new light on the special features exhibited by the fermionic bath and bosonic bath. - Highlights: • Exact dynamic equation for quantum open system coupled to a hybrid bath is derived. • The equation is consistent with standard quantum mechanics. • The dynamic equation derived is useful in exploring non-Markovian features.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Environment-induced uncertainties on moving mirrors in quantum critical theories via holography

Environment effects on a n-dimensional mirror from the strongly coupled d-dimensional quantum critical fields with a dynamic exponent z in weakly squeezed states are studied by the holographic approach. The dual description is a n+1-dimensional probe brane moving in the d+1-dimensional asymptotic Lifshitz geometry with gravitational wave perturbations. Using the holographic influence functional method, we find that the large coupling constant of the fields reduces the position uncertainty of the mirror, but enhances the momentum uncertainty. As such, the product of the position and momentum uncertainties is independent of the coupling constant. The proper choices of the phase of the squeezing parameter might reduce the uncertainties, nevertheless large values of its amplitude always lead to the larger uncertainties due to the fact that more quanta are excited as compared with the corresponding normal vacuum and thermal states. In the squeezed vacuum state, the position and momentum of the mirror gain maximum uncertainties from the field at the dynamic exponent z=n+2 when the same squeezed mode is considered. As for the squeezed thermal state, the contributions of thermal fluctuations to the uncertainties decrease as the temperature increases in the case 1 n+2 the contributions increase as the temperature increases. These results are in sharp contrast with those in the environments of the relativistic free field. Some possible observable effects are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Perspectives on novel refractory amorphous high-entropy alloys in extreme environments

Two new refractory amorphous high-entropy alloys (RAHEAs) within the W–Ta–Cr–V and W–Ta–Cr–V–Hf systems were herein synthesized using magnetron-sputtering and tested under high-temperature annealing and displacing irradiation using in situ Transmission Electron Microscopy. While the 14W-41Ta-26Cr-19V in at.% RAHEA (defined as WTaCrV RAHEA) was found to be unstable under such tests, additions of Hf in this system composing a new quinary 24W-40Ta-18Cr-5V-13Hf in at.% RAHEA (defined as WTaCrVHf RAHEA) was found to be a route to achieve stability both under annealing and irradiation. A new effect of nanoprecipitate reassembling observed to take place within the WTaCrVHf RAHEA under irradiation indicates that a duplex microstructure composed of an amorphous matrix with crystalline nanometer-sized precipitates enhances the radiation response of the system. Further, it is demonstrated that tunable chemical complexity arises as a new alloy design strategy to foster the use of novel RAHEAs within extreme environments. New perspectives for the alloy design and application of chemically-complex amorphous metallic alloys in extreme environments are presented with focus on their thermodynamic phase stability when subjected to high-temperature annealing and displacing irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Distinct effects of Cr bulk doping and surface deposition on the chemical environment and electronic structure of the topological insulator Bi 2 Se 3

In this report, it is shown that Cr doped into the bulk and Cr deposited on the surface of Bi2Se3 films produced by molecular beam epitaxy (MBE) have strikingly different effects on both the electronic structure and chemical environment. Angle resolved photoemission spectroscopy (ARPES) shows that Cr doped into the bulk opens a surface state energy gap which can be seen at room temperature; much higher than the measured ferromagnetic transition temperature of ≈ 10 K. On the other hand, similar ARPES measurements show that the surface states remain gapless down to 15 K for films with Cr surface deposition. In addition, core-level photoemission spectroscopy of the Bi 5d, Se 3d, and Cr 3p core levels show distinct differences in the chemical environment for the two methods of Cr introduction. Surface deposition of Cr results in the formation of shoulders on the lower binding energy side for the Bi 5d peaks and two distinct Cr 3p peaks indicative of two Cr sites. These striking differences suggests an interesting possibility that better control of doping at only near surface region may offer a path to quantum anomalous Hall states at higher temperatures than reported in the literature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Elucidating the Influence of Residual Polymer and Gas Environment on the Electronic Structure of a Graphene Layer Using in Situ APXPS

We use in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) and ultraviolet photoelectron spectroscopy (UPS) to develop an effective method for studying changes in the graphene (Gr) electronic structure according to certain circumstance. The amount of polymethyl methacrylate (PMMA) residual polymer (RP), inevitably generated during the Gr transfer process, is significantly reduced from Gr surface by thermal annealing. This processed Gr is then sequentially exposed to specific gas environments (Ar, N 2 , O 2 , and CO 2 ), and APXPS or UPS is carried out to investigate the variations in the Gr electronic structure including the work function. When the amount of PMMA RP on Gr is reduced, the position of the main carbon peak shifts by more than 0.4 eV to a higher binding energy (in XPS spectra), and the secondary electron cutoff moves by about 0.2 eV to a lower binding energy (in UPS spectra). These changes are generally caused by a decrease in the Gr work function. On the other hand, exposure to the gas environments at different temperatures that we investigated did not produce significant changes in the work function and chemical states of Gr. These results confirm that the material in contact with Gr should be considered to achieve the desired Gr performance in electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Fine-tuning catalytic selectivity by modulating catalyst-environment interactions: CO 2 hydrogenation over Pd-based catalysts

Capturing catalytic behaviors under operational conditions is pivotal to gaining a mechanistic understanding and promoting the design of robust catalysts. The challenge lies in the difficulty of monitoring real-time surface dynamics driven by catalyst-environment interactions. Here, in this work, we introduce a framework based on density functional calculations and kinetic modeling. This framework significantly improves the accuracy of theoretical models’ descriptions of experimental observations by quantifying environmental impacts on surface phases and active sites. CO 2 hydrogenation over Pd-based catalysts is taken as a showcase. The observed selectivity variations of Pd and Pd-M bimetallic catalysts strongly correlate with hydrogen coverage maintained under typical CO 2 hydrogenation conditions. By reducing the amount of surface hydrogen, the selectivity tuned effectively from formic acid toward CO and methanol. This study not only deepens the comprehension of dynamics of active sites under active chemical conditions but also introduces an alternative opportunity for catalytic tuning by modulating catalyst-environment interactions.

03 NATURAL GAS↗