First-principles Research Articles

CO adsorption on Pt (1 1 1) and Pd (1 1 1) surfaces: A first-principles based lattice gas Monte-Carlo study

Interaction of carbon monoxide (CO) with transition metal surfaces is an essential part of CO oxidation catalysis. In this report, we investigate and compare CO adsorption behavior on Pt (111) and Pd (111) surfaces combining first-principles (FP) calculations and lattice gas Monte-Carlo (LG-MC) simulations. Our results indicate that despite stronger CO binding on Pd (111) at low coverage, more repulsive lateral interactions on Pd surface lead to a more rapid adsorption energy decrease with respect to coverage. This results in lower saturation coverage and weaker CO desorption energies on Pd (111), which could contribute to its excellent reactivity observed under high pressure reaction conditions.

Research in Pregnancy: Back to First Principles

Research in Pregnancy: Back to First Principles

1404 太陽電池向けSi量子ドットのバンドギャップに関する第一原理解析(OS14.シリコンとシミュレーション(2),OS・一般セッション講演)

1404 太陽電池向けSi量子ドットのバンドギャップに関する第一原理解析(OS14.シリコンとシミュレーション(2),OS・一般セッション講演)

Model Predictive Disturbance Control of a Large Scale Industrial Process

AbstractFor a large scale product stock level control, an automatic Model Predictive Controller (MPC) was implemented. Due to the stable operation of a heavy delayed and disturbed process a significant optimization of operational performance was achieved. The closed loop control system needs to deal with large time delays of actuators (more than 2 hours), semi-parallel batch in between production steps and uncertain and inaccurate predicted (expected) disturbance trajectories. The optimal production rate to keep the product stock close to the optimal desired level for maximum inventory is determined by introducing a so called “Expected Disturbance Value” (EDV) and additional “Unexpected Disturbance Value” (UEDV) as input for the predictive controller. The controller design is based on a validated 1st principle model of the process. The resulting closed loop performance of the Dynamic Matrix Controller showed to be outstanding due to the time optimal production control, compensating expected and unexpected disturbance, retaining the process close to the setpoint in many practical production situations despite unstable process behaviour. Automatic handling of various absolute – and rate constraints on manipulated and controlled variables have been implemented and a robust controller tuning was achieved.

Interpreting diel hysteresis between soil respiration and temperature

Increasing use of automated soil respiration chambers in recent years has demonstrated complex diel relationships between soil respiration and temperature that are not apparent from less frequent measurements. Soil surface flux is often lagged from soil temperature by several hours, which results in semielliptical hysteresis loops when surface flux is plotted as a function of soil temperature. Both biological and physical explanations have been suggested for hysteresis patterns, and there is currently no consensus on their causes or how such data should be analyzed to interpret the sensitivity of respiration to temperature. We used a one-dimensional soil CO2 and heat transport model based on physical first principles to demonstrate a theoretical basis for lags between surface flux and soil temperatures. Using numerical simulations, we demonstrated that diel phase lags between surface flux and soil temperature can result from heat and CO2 transport processes alone. While factors other than temperature that vary on a diel basis, such as carbon substrate supply and atmospheric CO2 concentration, can additionally alter lag times and hysteresis patterns to varying degrees, physical transport processes alone are sufficient to create hysteresis. Therefore, the existence of hysteresis does not necessarily indicate soil respiration is influenced by photosynthetic carbon supply. We also demonstrated how lags can cause errors in Q10 values calculated from regressions of surface flux and soil temperature measured at a single depth. Furthermore, synchronizing surface flux and soil temperature to account for transport-related lags generally does not improve Q10 estimation. In order to calculate the sensitivity of soil respiration to temperature, we suggest using approaches that account for the gradients in temperature and production existing within the soil. We conclude that consideration of heat and CO2 transport processes is a requirement to correctly interpret diel soil respiration patterns.

First-principles study on the electronic structure of dilute magnetic semiconductor Ga1−x Cr x P in zinc-blende phase

[Huang, H. M.; Luo, S. J.] Hubei Univ Automot Technol, Sch Sci, Shiyan 442002, Peoples R China. [Yao, K. L.] Huazhong Univ Sci & Technol, Sch Phys, Wuhan 430074, Peoples R China. [Yao, K. L.] Chinese Acad Sci, Int Ctr Mat Phys, Shenyang 110015, Peoples R China.;Huang, HM (reprint author), Hubei Univ Automot Technol, Sch Sci, Shiyan 442002, Peoples R China;smilehhm@163.com

A first principles calculation of oxygen uptake in the acinus

A first principles calculation of oxygen uptake in the acinus

Phase stability of Ta-W alloys

The characteristic crystal model is applied to the study of phase stability and thermodynamics in substitutional bcc-based Ta-W alloys. The basic principle and method of alloy thermodynamics which is described by the characteristic crystal model is introduced in detail. The Gibbs energy of various phases including both disordered and ordered phases of the Ta-W system are evaluated. The phase diagram of Ta-W alloys is assessed and predicted. The results are in good agreement with experiments and better than that of first principle.

Thermodynamic properties and heat capacity of Ru metal in HCP, FCC, BCC and liquid state

Isometric heat capacity c v and isobar heat capacity c p of Ru metal in HCP, FCC, BCC and liquid state were calculated by using pure element systematic theory. The results are in good agreement with joint army-navy-air force (JANAF) experimental value and the calculation result by first-principle (FP) method. But the results have great differences in contrast to Scientific Group Thermodata Europe (SGTE) database. The cause is found that it cannot neglect the electron devotion to heat capacity to adjust c p in one-atom (OA) method. The disparity between OA method and SGTE database was discussed. The main cause is that OA method adopts the crosspoint with iso- E c -line and iso- a-line in hybritriangle to determine the properties, but SGTE database is obtained by extrapolation from activity measurements and critical assessment of data from a large number of binary system. Thermodynamic properties of Ru metal in HCP, FCC, BCC and liquid state, such as entropy S, enthalpy H and Gibbs energy G were calculated. Therefore, the full description of thermodynamic properties from 0 K to random temperature is implemented.

Protecting research participants with impaired decision-making capacity

Protecting research participants with impaired decision-making capacity

Trapping of multiple hydrogen atoms in a tungsten monovacancy

The configuration of multiple hydrogen atoms trapped in a tungsten monovacancy is investigated using first-principles calculations to determine trapping energy. Unlike previous computational studies, which have reported that hydrogen in BCC metal monovacancies occupies octahedral interstitial sites, it is found that the stable sites shift towards tetrahedral interstitial sites as the number of hydrogen atoms increases. As a result, a maximum of twelve hydrogen atoms can become trapped in a tungsten monovacancy.

The Universe in a solid design

A new material designed from first principles and subsequently synthesized and characterized in the laboratory may shed light on why there is much more matter than antimatter in the Universe.

Relative entropy as a universal metric for multiscale errors

We show that the relative entropy, Srel, suggests a fundamental indicator of the success of multiscale studies, in which coarse-grained (CG) models are linked to first-principles (FP) ones. We demonstrate that Srel inherently measures fluctuations in the differences between CG and FP potential energy landscapes, and develop a theory that tightly and generally links it to errors associated with coarse graining. We consider two simple case studies substantiating these results, and suggest that Srel has important ramifications for evaluating and designing coarse-grained models.

The Effect of Disorder on the Concentration‐Dependence of Stacking Fault Energies in Fe1‐xMnx – a First Principles Study

The stacking fault energy plays a significant role in defining the type of plasticity mechanism which prevails in high-Mn steels. Therefore, a detailed understanding and control over the physical mechanisms that influence the stacking fault energies is crucial for effective design and optimization of such steels. We present results of a first principle study on the influence of the chemical and magnetic ordering on the composition dependence of stacking fault energies in austenitic Fe1-xMnx alloys, which are prototypes for high-Mn steels. Our calculations show that chemical ordering has a significant influence on the intrinsic stacking faults. We have further demonstrated that, although FeMn-alloys have zero net magnetization, the internal magnetic structure significantly changes the properties of the stacking faults. Specifically, we have shown for chemically disordered structures that the dependence of the equilibrium volume and of the SFE on their composition is strongly changed if they are under paramagnetic instead of non-magnetic exposure. These results prove the importance of atomistic simulations for the determination of the SFE and clearly indicate that the magnetic interactions and the chemical ordering in this system must be accurately captured by the theory.

Communications Privacy in the Military

In the wake of the 1996 case of United States v. Larson, in which the Court of Appeals for the Armed Forces held that a service member held a right to privacy in her workplace e-mail, the Department of Defense issued a DoD-wide policy requiring DoD employees to consent to e-mail monitoring, interception, and seizure for any purpose - including law enforcement. With military members deployed to Iraq and Afghanistan relying exclusively on government information systems to communicate daily with friends and family, the DoD policy arguably violates core Fourth Amendment privacy protections. Proceeding from a discussion of first principles in military privacy to the four seminal military cases involving communications privacy expectations, I address the constitutional implications of the DoD policy, exploring whether it unconstitutionally warrants searches for law enforcement purposes. I conclude with a normative appeal for military courts and the DoD to follow the Supreme Court’s reasoning in O’Connor v. Ortega and distinguish work-related from law enforcement searches.With both civilian and military law in flux over the scope of privacy expectations in workplace electronic communications, my aim is to provide timely, considered guidance to courts, policy makers, and practitioners in determining what service members should expect from a normative perspective as they use government information systems to communicate with family and friends.

Construction of Building Blocks for Highly Functional π-Electron Silicon Nanomaterials by First-Principles Calculations

本総説では、高機能性ケイ素π電子ナノ材料の厳密に本来のπ電子をもつ基本単位の構築に関する我々の第一原理計算による研究を紹介する。ケイ素は炭素と同族であるが、不飽和ケイ素化合物の構造は不飽和炭素化合物と異なりいわゆる非古典的であることが知られている。即ち、ケイ素二重結合および三重結合化合物はトランス折れ曲がり構造をしており、ケイ素六員環は椅子型構造をしている。我々は、最近、従来のアルキル基、アリール基などの置換基のかわりに電子を使うことで、直線型D∞h対称性ケイ素三重化合物やD6h対称性ケイ素六員環など厳密に本来のπ電子をもつ基本単位を理論的に設計することに成功した。主に我々の発見をまとめるとともに、ケイ素π電子系の古典的構造を実現するための鍵となる点について議論する。

Evidence for hydrogen transport in deuteratedLiBH4from low-temperature Raman-scattering measurements and first-principles calculations

Note: Times Cited: 28 Reference EPFL-ARTICLE-205954doi:10.1103/PhysRevB.80.100301View record in Web of Science URL: ://WOS:000270383100002 Record created on 2015-03-03, modified on 2017-05-12

Chemistry from first principles

Part I: A New Look at Old Theories 1. Historical Perspective 2. The Important Concepts 2.1 The Principle of Relativity 2.2 The Old Quantum Theory 2.3 Wave-Particle Duality 2.4 Orbital Angular Momentum 2.5 The Quantum Theory 2.6 Atomic Shape 2.7 Chemical Bonding 3. The Quantum Quandary 3.1 The Classical Background 3.2 The Copenhagen Orthodoxy 3.3 The Schrodinger Interpretation 3.4 The Hydrodynamic Alternative 3.5 Bohmian Mechanics 3.6 Atomic Theory Part II: Alternative Theory 4. The Periodic Laws 4.1 Nuclides and Nuclear Structure 4.2 Chemical Elements and Atomic Structure 4.3 The Golden Ratio 5. Chemical Interaction 5.1 The Valence State 5.2 Electronegativity 5.3 Chemical Cohesion 6. Molecular Structure 6.1 Molecular Shape 6.2 Stereoisomerism 6.3 Molecular Modelling 7. Chemical Change 7.1 The Holistic Molecule 7.2 Molecular Rearrangement 7.3 Reaction Mechanisms 8. Future Outlook

Thermodynamic properties of stable and metastable phases of Pt metal

Isometric heat capacity c v and isobaric heat capacity c p of Pt with stable and metastable phases were calculated by using pure element systematic theory. These results are in excellent agreement with of SGTE (Scientific Group Thermodata Europe) database and JANAF (Joint Army-Navy-Air Force) experimental values. The calculation results of c v and c p of Pt metal in natural state are in good agreement with those calculated by FP(first-principles) method. It is found that the electron devotion to heat capacity is important to adjust in OA(one-atom) method while calculating heat capacity. The full information about thermodynamic properties of Pt metal with stable and metastable phases, such as entropy( S), enthalpy( H) and Gibbs energy( G) were calculated from 0 K to random temperature. The results are in good agreement with JANAF experimental value. In contrast to SGTE database, the thermodynamic properties from 0 K to 298.15 K are implemented.

Injury mechanism and first aid principle of multiple trauma

多发伤最初指累及不同解剖部位的复杂创伤,有多个伤口.现代多发伤是指机体在单一机械致伤因素作用下,同时或相继遭受两个或两个以上解剖部位的创伤,其中至少有一处较严重.所谓解剖部位指按AIS-2005版划分的头颈部、面部、胸部(包括胸椎、膈肌和肋骨架)、腹部(包括腰椎、盆腔)、四肢和体表等6个部位。