Analysis of DIRAC's behavior using model checking with process algebra

Science.gov (United States)

Remenska, Daniela; Templon, Jeff; Willemse, Tim; Bal, Henri; Verstoep, Kees; Fokkink, Wan; Charpentier, Philippe; Graciani Diaz, Ricardo; Lanciotti, Elisa; Roiser, Stefan; Ciba, Krzysztof

2012-12-01

DIRAC is the grid solution developed to support LHCb production activities as well as user data analysis. It consists of distributed services and agents delivering the workload to the grid resources. Services maintain database back-ends to store dynamic state information of entities such as jobs, queues, staging requests, etc. Agents use polling to check and possibly react to changes in the system state. Each agent's logic is relatively simple; the main complexity lies in their cooperation. Agents run concurrently, and collaborate using the databases as shared memory. The databases can be accessed directly by the agents if running locally or through a DIRAC service interface if necessary. This shared-memory model causes entities to occasionally get into inconsistent states. Tracing and fixing such problems becomes formidable due to the inherent parallelism present. We propose more rigorous methods to cope with this. Model checking is one such technique for analysis of an abstract model of a system. Unlike conventional testing, it allows full control over the parallel processes execution, and supports exhaustive state-space exploration. We used the mCRL2 language and toolset to model the behavior of two related DIRAC subsystems: the workload and storage management system. Based on process algebra, mCRL2 allows defining custom data types as well as functions over these. This makes it suitable for modeling the data manipulations made by DIRAC's agents. By visualizing the state space and replaying scenarios with the toolkit's simulator, we have detected race-conditions and deadlocks in these systems, which, in several cases, were confirmed to occur in the reality. Several properties of interest were formulated and verified with the tool. Our future direction is automating the translation from DIRAC to a formal model.

LHCb: Analysing DIRAC's Behavior using Model Checking with Process Algebra

CERN Multimedia

Remenska, Daniela

2012-01-01

DIRAC is the Grid solution designed to support LHCb production activities as well as user data analysis. Based on a service-oriented architecture, DIRAC consists of many cooperating distributed services and agents delivering the workload to the Grid resources. Services accept requests from agents and running jobs, while agents run as light-weight components, fulfilling specific goals. Services maintain database back-ends to store dynamic state information of entities such as jobs, queues, staging requests, etc. Agents use polling to check for changes in the service states, and react to these accordingly. A characteristic of DIRAC's architecture is the relatively low complexity in the logic of each agent; the main source of complexity lies in their cooperation. These agents run concurrently, and communicate using the services' databases as a shared memory for synchronizing the state transitions. Although much effort is invested in making DIRAC reliable, entities occasionally get into inconsistent states, leadi...

The LHCb Experience on the Grid from the DIRAC Accounting Data

CERN Document Server

Puig, A; Graciani, R; Casajús, A

2011-01-01

DIRAC is the software framework developed by LHCb to manage all its computing operations on the Grid. Since 2003 it has been used for large scale Monte Carlo simulation productions and for user analysis of these data. Since the end of 2009, with the start-up of LHC, DIRAC also takes care of the distribution, reconstruction, selection and analysis of the physics data taken by the detector apparatus. During 2009, DIRAC executed almost 5 million jobs for LHCb. In order to execute this workload slightly over 6 million of pilot jobs were submitted, out of which approximately one third were aborted by the Grid infrastructure. In 2010, thanks to their improved efficiency, DIRAC pilots are able, on average, to match and execute between 2 and 3 LHCb jobs during their lifetime, largely reducing the load on the Grid infrastructure. Given the large amount of submitted jobs and used resources, it becomes essential to store detailed information about their execution to track the behaviour of the system. The DIRAC Accountin...

DIRAC: data production management

International Nuclear Information System (INIS)

Smith, A C; Tsaregorodtsev, A

2008-01-01

The LHCb Computing Model describes the dataflow for all stages in the processing of real and simulated events, and defines the role of LHCb associated Tier-1 and Tier-2 computing centers. The WLCG 'Dress Rehearsal' exercise aims to allow LHC experiments to deploy the full chain of their Computing Models, making use of all underlying WLCG services and resources, in preparation for real data taking. During this exercise simulated RAW physics data, matching the properties of eventual real data, will be uploaded from the LHCb Online storage system to Grid enabled storage. This data will then be replicated to LHCb Tier-1 centers and subsequently processed (reconstructed and stripped). The product of this processing is user analysis data that are distributed to all LHCb Tier-1 centers. DIRAC, LHCbs Workload and Data Management System, supports the implementation of the Computing Model in a data driven, real time and coordinated fashion. In this paper the LHCb Computing Model will be reviewed and the DIRAC components providing the needed functionality to support the Computing Model will be detailed. An evaluation of the preparedness for real data taking will also be given

DIRAC: data production management

Energy Technology Data Exchange (ETDEWEB)

Smith, A C [CERN, CH-1211, Geneva (Switzerland); Tsaregorodtsev, A [CPPM, Marseille (France)], E-mail: a.smith@cern.ch, E-mail: atsareg@in2p3.fr

2008-07-15

The LHCb Computing Model describes the dataflow for all stages in the processing of real and simulated events, and defines the role of LHCb associated Tier-1 and Tier-2 computing centers. The WLCG 'Dress Rehearsal' exercise aims to allow LHC experiments to deploy the full chain of their Computing Models, making use of all underlying WLCG services and resources, in preparation for real data taking. During this exercise simulated RAW physics data, matching the properties of eventual real data, will be uploaded from the LHCb Online storage system to Grid enabled storage. This data will then be replicated to LHCb Tier-1 centers and subsequently processed (reconstructed and stripped). The product of this processing is user analysis data that are distributed to all LHCb Tier-1 centers. DIRAC, LHCbs Workload and Data Management System, supports the implementation of the Computing Model in a data driven, real time and coordinated fashion. In this paper the LHCb Computing Model will be reviewed and the DIRAC components providing the needed functionality to support the Computing Model will be detailed. An evaluation of the preparedness for real data taking will also be given.

LHCb: Pilot Framework and the DIRAC WMS

CERN Multimedia

Graciani, R; Casajus, A

2009-01-01

DIRAC, the LHCb community Grid solution, has pioneered the use of pilot jobs in the Grid. Pilot jobs provide a homogeneous interface to an heterogeneous set of computing resources. At the same time, pilot jobs allow to delay the scheduling decision to the last moment, thus taking into account the precise running conditions at the resource and last moment requests to the system. The DIRAC Workload Management System provides one single scheduling mechanism for jobs with very different profiles. To achieve an overall optimisation, it organizes pending jobs in task queues, both for individual users and production activities. Task queues are created with jobs having similar requirements. Following the VO policy a priority is assigned to each task queue. Pilot submission and subsequent job matching are based on these priorities following a statistical approach. Details of the implementation and the security aspects of this framework will be discussed.

DIRAC data production management

CERN Document Server

Smith, A C

2008-01-01

The LHCb Computing Model describes the dataflow for all stages in the processing of real and simulated events, and defines the role of LHCb associated Tier-1 and Tier-2 computing centers. The WLCG 'Dress Rehearsal' exercise aims to allow LHC experiments to deploy the full chain of their Computing Models, making use of all underlying WLCG services and resources, in preparation for real data taking. During this exercise simulated RAW physics data, matching the properties of eventual real data, will be uploaded from the LHCb Online storage system to Grid enabled storage. This data will then be replicated to LHCb Tier-1 centers and subsequently processed (reconstructed and stripped). The product of this processing is user analysis data that are distributed to all LHCb Tier-1 centers. DIRAC, LHCbs Workload and Data Management System, supports the implementation of the Computing Model in a data driven, real time and coordinated fashion.

Analysis of DIRAC's behavior using model checking with process algebra

CERN Document Server

Remenska, Daniela; Willemse, Tim; Bal, Henri; Verstoep, Kees; Fokkink, Wan; Charpentier, Philippe; Diaz, Ricardo Graciani; Lanciotti, Elisa; Roiser, Stefan; Ciba, Krzysztof

2012-01-01

DIRAC is the grid solution developed to support LHCb production activities as well as user data analysis. It consists of distributed services and agents delivering the workload to the grid resources. Services maintain database back-ends to store dynamic state information of entities such as jobs, queues, staging requests, etc. Agents use polling to check and possibly react to changes in the system state. Each agent's logic is relatively simple, the main complexity lies in their cooperation. Agents run concurrently, and collaborate using the databases as shared memory. The databases can be accessed directly by the agents if running locally or through a DIRAC service interface if necessary. This shared-memory model causes entities to occasionally get into inconsistent states. Tracing and fixing such problems becomes formidable due to the inherent parallelism present. We propose more rigorous methods to cope with this. Model checking is one such technique for analysis of an abstract model of a system. Unlike con...

Dirac materials

OpenAIRE

Wehling, T. O.; Black-Schaffer, A. M.; Balatsky, A. V.

2014-01-01

A wide range of materials, like d-wave superconductors, graphene, and topological insulators, share a fundamental similarity: their low-energy fermionic excitations behave as massless Dirac particles rather than fermions obeying the usual Schrodinger Hamiltonian. This emergent behavior of Dirac fermions in condensed matter systems defines the unifying framework for a class of materials we call "Dirac materials''. In order to establish this class of materials, we illustrate how Dirac fermions ...

Paul Dirac

Science.gov (United States)

Pais, Abraham; Jacob, Maurice; Olive, David I.; Atiyah, Michael F.

2005-09-01

Preface Peter Goddard; Dirac memorial address Stephen Hawking; 1. Paul Dirac: aspects of his life and work Abraham Pais; 2. Antimatter Maurice Jacob; 3. The monopole David Olive; 4. The Dirac equation and geometry Michael F. Atiyah.

Online EEG-Based Workload Adaptation of an Arithmetic Learning Environment.

Science.gov (United States)

Walter, Carina; Rosenstiel, Wolfgang; Bogdan, Martin; Gerjets, Peter; Spüler, Martin

2017-01-01

In this paper, we demonstrate a closed-loop EEG-based learning environment, that adapts instructional learning material online, to improve learning success in students during arithmetic learning. The amount of cognitive workload during learning is crucial for successful learning and should be held in the optimal range for each learner. Based on EEG data from 10 subjects, we created a prediction model that estimates the learner's workload to obtain an unobtrusive workload measure. Furthermore, we developed an interactive learning environment that uses the prediction model to estimate the learner's workload online based on the EEG data and adapt the difficulty of the learning material to keep the learner's workload in an optimal range. The EEG-based learning environment was used by 13 subjects to learn arithmetic addition in the octal number system, leading to a significant learning effect. The results suggest that it is feasible to use EEG as an unobtrusive measure of cognitive workload to adapt the learning content. Further it demonstrates that a promptly workload prediction is possible using a generalized prediction model without the need for a user-specific calibration.

DIRAC Data Management System

CERN Document Server

Smith, A C

2007-01-01

The LHCb experiment being built to utilize CERN’s flagship Large Hadron Collider will generate data to be analysed by a community of over 600 physicists worldwide. DIRAC, LHCb’s Workload and Data Management System, facilitates the use of underlying EGEE Grid resources to generate, process and analyse this data in the distributed environment. The Data Management System, presented here, provides real-time, data-driven distribution in accordance with LHCb’s Computing Model. The data volumes produced by the LHC experiments are unprecedented, rendering individual institutes and even countries, unable to provide the computing and storage resources required to make full use of the produced data. EGEE Grid resources allow the processing of LHCb data possible in a distributed fashion and LHCb’s Computing Model is based on this approach. Data Management in this environment requires reliable and high-throughput transfer of data, homogeneous access to storage resources and the cataloguing of data replicas, all of...

Measuring perceived mental workload in children.

Science.gov (United States)

Laurie-Rose, Cynthia; Frey, Meredith; Ennis, Aristi; Zamary, Amanda

2014-01-01

Little is known about the mental workload, or psychological costs, associated with information processing tasks in children. We adapted the highly regarded NASA Task Load Index (NASA-TLX) multidimensional workload scale (Hart & Staveland, 1988) to test its efficacy for use with elementary school children. We developed 2 types of tasks, each with 2 levels of demand, to draw differentially on resources from the separate subscales of workload. In Experiment 1, our participants were both typical and school-labeled gifted children recruited from 4th and 5th grades. Results revealed that task type elicited different workload profiles, and task demand directly affected the children's experience of workload. In general, gifted children experienced less workload than typical children. Objective response time and accuracy measures provide evidence for the criterion validity of the workload ratings. In Experiment 2, we applied the same method with 1st- and 2nd-grade children. Findings from Experiment 2 paralleled those of Experiment 1 and support the use of NASA-TLX with even the youngest elementary school children. These findings contribute to the fledgling field of educational ergonomics and attest to the innovative application of workload research. Such research may optimize instructional techniques and identify children at risk for experiencing overload.

LHCb: LHCbDirac is a DIRAC extension to support LHCb specific workflows

CERN Multimedia

Stagni, Federico

2012-01-01

We present LHCbDIRAC, an extension of the DIRAC community Grid solution to handle the LHCb specificities. The DIRAC software has been developed for many years within LHCb only. Nowadays it is a generic software, used by many scientific communities worldwide. Each community wanting to take advantage of DIRAC has to develop an extension, containing all the necessary code for handling their specific cases. LHCbDIRAC is an actively developed extension, implementing the LHCb computing model and workflows. LHCbDIRAC extends DIRAC to handle all the distributed computing activities of LHCb. Such activities include real data processing (reconstruction, stripping and streaming), Monte-Carlo simulation and data replication. Other activities are groups and user analysis, data management, resources management and monitoring, data provenance, accounting for user and production jobs. LHCbDIRAC also provides extensions of the DIRAC interfaces, including a secure web client, python APIs and CLIs. While DIRAC and LHCbDIRAC f...

DIRAC distributed secure framework

International Nuclear Information System (INIS)

Casajus, A; Graciani, R

2010-01-01

DIRAC, the LHCb community Grid solution, provides access to a vast amount of computing and storage resources to a large number of users. In DIRAC users are organized in groups with different needs and permissions. In order to ensure that only allowed users can access the resources and to enforce that there are no abuses, security is mandatory. All DIRAC services and clients use secure connections that are authenticated using certificates and grid proxies. Once a client has been authenticated, authorization rules are applied to the requested action based on the presented credentials. These authorization rules and the list of users and groups are centrally managed in the DIRAC Configuration Service. Users submit jobs to DIRAC using their local credentials. From then on, DIRAC has to interact with different Grid services on behalf of this user. DIRAC has a proxy management service where users upload short-lived proxies to be used when DIRAC needs to act on behalf of them. Long duration proxies are uploaded by users to a MyProxy service, and DIRAC retrieves new short delegated proxies when necessary. This contribution discusses the details of the implementation of this security infrastructure in DIRAC.

Strategic workload management and decision biases in aviation

Science.gov (United States)

Raby, Mireille; Wickens, Christopher D.

1994-01-01

Thirty pilots flew three simulated landing approaches under conditions of low, medium, and high workload. Workload conditions were created by varying time pressure and external communications requirements. Our interest was in how the pilots strategically managed or adapted to the increasing workload. We independently assessed the pilot's ranking of the priority of different discrete tasks during the approach and landing. Pilots were found to sacrifice some aspects of primary flight control as workload increased. For discrete tasks, increasing workload increased the amount of time in performing the high priority tasks, decreased the time in performing those of lowest priority, and did not affect duration of performance episodes or optimality of scheduling of tasks of any priority level. Individual differences analysis revealed that high-performing subjects scheduled discrete tasks earlier in the flight and shifted more often between different activities.

The GridPP DIRAC project - DIRAC for non-LHC communities

CERN Document Server

Bauer, D; Currie, R; Fayer, S; Huffman, A; Martyniak, J; Rand, D; Richards, A

2015-01-01

The GridPP consortium in the UK is currently testing a multi-VO DIRAC service aimed at non-LHC VOs. These VOs (Virtual Organisations) are typically small and generally do not have a dedicated computing support post. The majority of these represent particle physics experiments (e.g. NA62 and COMET), although the scope of the DIRAC service is not limited to this field. A few VOs have designed bespoke tools around the EMI-WMS & LFC, while others have so far eschewed distributed resources as they perceive the overhead for accessing them to be too high. The aim of the GridPP DIRAC project is to provide an easily adaptable toolkit for such VOs in order to lower the threshold for access to distributed resources such as Grid and cloud computing. As well as hosting a centrally run DIRAC service, we will also publish our changes and additions to the upstream DIRAC codebase under an open-source license. We report on the current status of this project and show increasing adoption of DIRAC within the non-LHC communiti...

The GridPP DIRAC project - DIRAC for non-LHC communities

Science.gov (United States)

Bauer, D.; Colling, D.; Currie, R.; Fayer, S.; Huffman, A.; Martyniak, J.; Rand, D.; Richards, A.

2015-12-01

The GridPP consortium in the UK is currently testing a multi-VO DIRAC service aimed at non-LHC VOs. These VOs (Virtual Organisations) are typically small and generally do not have a dedicated computing support post. The majority of these represent particle physics experiments (e.g. NA62 and COMET), although the scope of the DIRAC service is not limited to this field. A few VOs have designed bespoke tools around the EMI-WMS & LFC, while others have so far eschewed distributed resources as they perceive the overhead for accessing them to be too high. The aim of the GridPP DIRAC project is to provide an easily adaptable toolkit for such VOs in order to lower the threshold for access to distributed resources such as Grid and cloud computing. As well as hosting a centrally run DIRAC service, we will also publish our changes and additions to the upstream DIRAC codebase under an open-source license. We report on the current status of this project and show increasing adoption of DIRAC within the non-LHC communities.

The impact of crosstalk on three-dimensional laparoscopic performance and workload.

Science.gov (United States)

Sakata, Shinichiro; Grove, Philip M; Watson, Marcus O; Stevenson, Andrew R L

2017-10-01

This is the first study to explore the effects of crosstalk from 3D laparoscopic displays on technical performance and workload. We studied crosstalk at magnitudes that may have been tolerated during laparoscopic surgery. Participants were 36 voluntary doctors. To minimize floor effects, participants completed their surgery rotations, and a laparoscopic suturing course for surgical trainees. We used a counterbalanced, within-subjects design in which participants were randomly assigned to complete laparoscopic tasks in one of six unique testing sequences. In a simulation laboratory, participants were randomly assigned to complete laparoscopic 'navigation in space' and suturing tasks in three viewing conditions: 2D, 3D without ghosting and 3D with ghosting. Participants calibrated their exposure to crosstalk as the maximum level of ghosting that they could tolerate without discomfort. The Randot® Stereotest was used to verify stereoacuity. The study performance metric was time to completion. The NASA TLX was used to measure workload. Normal threshold stereoacuity (40-20 second of arc) was verified in all participants. Comparing optimal 3D with 2D viewing conditions, mean performance times were 2.8 and 1.6 times faster in laparoscopic navigation in space and suturing tasks respectively (p< .001). Comparing optimal 3D with suboptimal 3D viewing conditions, mean performance times were 2.9 times faster in both tasks (p< .001). Mean workload in 2D was 1.5 and 1.3 times greater than in optimal 3D viewing, for navigation in space and suturing tasks respectively (p< .001). Mean workload associated with suboptimal 3D was 1.3 times greater than optimal 3D in both laparoscopic tasks (p< .001). There was no significant relationship between the magnitude of ghosting score, laparoscopic performance and workload. Our findings highlight the advantages of 3D displays when used optimally, and their shortcomings when used sub-optimally, on both laparoscopic performance and workload.

Interlayer magnetoresistance in multilayer Dirac electron systems: motion and merging of Dirac cones

OpenAIRE

Assili, Mohamed; Haddad, Sonia

2013-01-01

We theoretically study the effect of the motion and the merging of Dirac cone on the interlayer magnetoresistance in multilayer graphene like systems. This merging, which could be induced by a uniaxial strain, gives rise in monolayer Dirac electron system to a topological transition from a semi-metallic phase to an insulating phase where Dirac points disappear. Based on a universal Hamiltonian proposed to describe the motion and the merging of Dirac points in two dimensional Dirac electron cr...

Photoconductivity in Dirac materials

International Nuclear Information System (INIS)

Shao, J. M.; Yang, G. W.

2015-01-01

Two-dimensional (2D) Dirac materials including graphene and the surface of a three-dimensional (3D) topological insulator, and 3D Dirac materials including 3D Dirac semimetal and Weyl semimetal have attracted great attention due to their linear Dirac nodes and exotic properties. Here, we use the Fermi’s golden rule and Boltzmann equation within the relaxation time approximation to study and compare the photoconductivity of Dirac materials under different far- or mid-infrared irradiation. Theoretical results show that the photoconductivity exhibits the anisotropic property under the polarized irradiation, but the anisotropic strength is different between 2D and 3D Dirac materials. The photoconductivity depends strongly on the relaxation time for different scattering mechanism, just like the dark conductivity

DIRAC reliable data management for LHCb

CERN Document Server

Smith, A C

2008-01-01

DIRAC, LHCb's Grid Workload and Data Management System, utilizes WLCG resources and middleware components to perform distributed computing tasks satisfying LHCb's Computing Model. The Data Management System (DMS) handles data transfer and data access within LHCb. Its scope ranges from the output of the LHCb Online system to Grid-enabled storage for all data types. It supports metadata for these files in replica and bookkeeping catalogues, allowing dataset selection and localization. The DMS controls the movement of files in a redundant fashion whilst providing utilities for accessing all metadata. To do these tasks effectively the DMS requires complete self integrity between its components and external physical storage. The DMS provides highly redundant management of all LHCb data to leverage available storage resources and to manage transient errors in underlying services. It provides data driven and reliable distribution of files as well as reliable job output upload, utilizing VO Boxes at LHCb Tier1 sites ...

Dirac matter

CERN Document Server

Rivasseau, Vincent; Fuchs, Jean-Nöel

2017-01-01

This fifteenth volume of the Poincare Seminar Series, Dirac Matter, describes the surprising resurgence, as a low-energy effective theory of conducting electrons in many condensed matter systems, including graphene and topological insulators, of the famous equation originally invented by P.A.M. Dirac for relativistic quantum mechanics. In five highly pedagogical articles, as befits their origin in lectures to a broad scientific audience, this book explains why Dirac matters. Highlights include the detailed "Graphene and Relativistic Quantum Physics", written by the experimental pioneer, Philip Kim, and devoted to graphene, a form of carbon crystallized in a two-dimensional hexagonal lattice, from its discovery in 2004-2005 by the future Nobel prize winners Kostya Novoselov and Andre Geim to the so-called relativistic quantum Hall effect; the review entitled "Dirac Fermions in Condensed Matter and Beyond", written by two prominent theoreticians, Mark Goerbig and Gilles Montambaux, who consider many other mater...

A new Dirac cone material: a graphene-like Be3C2 monolayer.

Science.gov (United States)

Wang, Bing; Yuan, Shijun; Li, Yunhai; Shi, Li; Wang, Jinlan

2017-05-04

Two-dimensional (2D) materials with Dirac cones exhibit rich physics and many intriguing properties, but the search for new 2D Dirac materials is still a current hotspot. Using the global particle-swarm optimization method and density functional theory, we predict a new stable graphene-like 2D Dirac material: a Be 3 C 2 monolayer with a hexagonal honeycomb structure. The Dirac point occurs exactly at the Fermi level and arises from the merging of the hybridized p z bands of Be and C atoms. Most interestingly, this monolayer exhibits a high Fermi velocity in the same order of graphene. Moreover, the Dirac cone is very robust and retains even included spin-orbit coupling or external strain. These outstanding properties render the Be 3 C 2 monolayer a promising 2D material for special electronics applications.

LHCb: DIRAC Secure Distributed Platform

CERN Multimedia

Casajus, A

2009-01-01

DIRAC, the LHCb community grid solution, provides access to a vast amount of computing and storage resources to a large number of users. In DIRAC users are organized in groups with different needs and permissions. In order to ensure that only allowed users can access the resources and to enforce that there are no abuses, security is mandatory. All DIRAC services and clients use secure connections that are authenticated using certificates and grid proxies. Once a client has been authenticated, authorization rules are applied to the requested action based on the presented credentials. These authorization rules and the list of users and groups are centrally managed in the DIRAC Configuration Service. Users submit jobs to DIRAC using their local credentials. From then on, DIRAC has to interact with different Grid services on behalf of this user. DIRAC has a proxy management service where users upload short-lived proxies to be used when DIRAC needs to act on behalf of them. Long duration proxies are uploaded by us...

Interlayer magnetoresistance in multilayer Dirac electron systems: motion and merging of Dirac cones

International Nuclear Information System (INIS)

Assili, M; Haddad, S

2013-01-01

We theoretically study the effect of the motion and the merging of Dirac cones on the interlayer magnetoresistance in multilayer graphene-like systems. This merging, which can be induced by a uniaxial strain, gives rise in a monolayer Dirac electron system to a topological transition from a semi-metallic phase to an insulating phase whereby Dirac points disappear. Based on a universal Hamiltonian, proposed to describe the motion and the merging of Dirac points in two-dimensional Dirac electron crystals, we calculate the interlayer conductivity of a stack of deformed graphene-like layers using the Kubo formula in the quantum limit where only the contribution of the n = 0 Landau level is relevant. A crossover from a negative to a positive interlayer magnetoresistance is found to take place as the merging is approached. This sign change of the magnetoresistance can also result from a coupling between the Dirac valleys, which is enhanced as the magnetic field amplitude increases. Our results describe the behavior of the magnetotransport in the organic conductor α-(BEDT) 2 I 3 and in a stack of deformed graphene-like systems. The latter can be simulated by optical lattices or microwave experiments in which the merging of Dirac cones can be observed. (paper)

Interlayer magnetoresistance in multilayer Dirac electron systems: motion and merging of Dirac cones

Science.gov (United States)

Assili, M.; Haddad, S.

2013-09-01

We theoretically study the effect of the motion and the merging of Dirac cones on the interlayer magnetoresistance in multilayer graphene-like systems. This merging, which can be induced by a uniaxial strain, gives rise in a monolayer Dirac electron system to a topological transition from a semi-metallic phase to an insulating phase whereby Dirac points disappear. Based on a universal Hamiltonian, proposed to describe the motion and the merging of Dirac points in two-dimensional Dirac electron crystals, we calculate the interlayer conductivity of a stack of deformed graphene-like layers using the Kubo formula in the quantum limit where only the contribution of the n = 0 Landau level is relevant. A crossover from a negative to a positive interlayer magnetoresistance is found to take place as the merging is approached. This sign change of the magnetoresistance can also result from a coupling between the Dirac valleys, which is enhanced as the magnetic field amplitude increases. Our results describe the behavior of the magnetotransport in the organic conductor α-(BEDT)2I3 and in a stack of deformed graphene-like systems. The latter can be simulated by optical lattices or microwave experiments in which the merging of Dirac cones can be observed.

Interlayer magnetoresistance in multilayer Dirac electron systems: motion and merging of Dirac cones.

Science.gov (United States)

Assili, M; Haddad, S

2013-09-11

We theoretically study the effect of the motion and the merging of Dirac cones on the interlayer magnetoresistance in multilayer graphene-like systems. This merging, which can be induced by a uniaxial strain, gives rise in a monolayer Dirac electron system to a topological transition from a semi-metallic phase to an insulating phase whereby Dirac points disappear. Based on a universal Hamiltonian, proposed to describe the motion and the merging of Dirac points in two-dimensional Dirac electron crystals, we calculate the interlayer conductivity of a stack of deformed graphene-like layers using the Kubo formula in the quantum limit where only the contribution of the n = 0 Landau level is relevant. A crossover from a negative to a positive interlayer magnetoresistance is found to take place as the merging is approached. This sign change of the magnetoresistance can also result from a coupling between the Dirac valleys, which is enhanced as the magnetic field amplitude increases. Our results describe the behavior of the magnetotransport in the organic conductor α-(BEDT)2I3 and in a stack of deformed graphene-like systems. The latter can be simulated by optical lattices or microwave experiments in which the merging of Dirac cones can be observed.

Dirac fermions in blue-phosphorus

International Nuclear Information System (INIS)

Li, Yuanchang; Chen, Xiaobin

2014-01-01

We propose that Dirac cones can be engineered in phosphorene with fourfold-coordinated phosphorus atoms. The key is to separate the energy levels of the in-plane (s, p x , and p y ) and out-of-plane (p z ) oribtals through the sp 2 configuration, yielding respective σ- and π-character Dirac cones, and then quench the latter. As a proof-of-principle study, we create σ-character Dirac cones in hydrogenated and fluorinated phosphorene with a honeycomb lattice. The obtained Dirac cones are at K-points, slightly anisotropic, with Fermi velocities of 0.91 and 1.23 times that of graphene along the ΓK and KM direction, and maintain good linearity up to ∼2 eV for holes. A substantive advantage of a σ-character Dirac cone is its convenience in tuning the Dirac gap via in-plane strain. Our findings pave the way for development of high-performance electronic devices based on Dirac materials. (letter)

Workload Characterization of a Leadership Class Storage Cluster

Energy Technology Data Exchange (ETDEWEB)

Kim, Youngjae [ORNL; Gunasekaran, Raghul [ORNL; Shipman, Galen M [ORNL; Dillow, David A [ORNL; Zhang, Zhe [ORNL; Settlemyer, Bradley W [ORNL

2010-01-01

Understanding workload characteristics is critical for optimizing and improving the performance of current systems and software, and architecting new storage systems based on observed workload patterns. In this paper, we characterize the scientific workloads of the world s fastest HPC (High Performance Computing) storage cluster, Spider, at the Oak Ridge Leadership Computing Facility (OLCF). Spider provides an aggregate bandwidth of over 240 GB/s with over 10 petabytes of RAID 6 formatted capacity. OLCFs flagship petascale simulation platform, Jaguar, and other large HPC clusters, in total over 250 thousands compute cores, depend on Spider for their I/O needs. We characterize the system utilization, the demands of reads and writes, idle time, and the distribution of read requests to write requests for the storage system observed over a period of 6 months. From this study we develop synthesized workloads and we show that the read and write I/O bandwidth usage as well as the inter-arrival time of requests can be modeled as a Pareto distribution.

Three Dimensional Dirac Semimetals

Science.gov (United States)

Zaheer, Saad

2014-03-01

Dirac points on the Fermi surface of two dimensional graphene are responsible for its unique electronic behavior. One can ask whether any three dimensional materials support similar pseudorelativistic physics in their bulk electronic spectra. This possibility has been investigated theoretically and is now supported by two successful experimental demonstrations reported during the last year. In this talk, I will summarize the various ways in which Dirac semimetals can be realized in three dimensions with primary focus on a specific theory developed on the basis of representations of crystal spacegroups. A three dimensional Dirac (Weyl) semimetal can appear in the presence (absence) of inversion symmetry by tuning parameters to the phase boundary separating a bulk insulating and a topological insulating phase. More generally, we find that specific rules governing crystal symmetry representations of electrons with spin lead to robust Dirac points at high symmetry points in the Brillouin zone. Combining these rules with microscopic considerations identifies six candidate Dirac semimetals. Another method towards engineering Dirac semimetals involves combining crystal symmetry and band inversion. Several candidate materials have been proposed utilizing this mechanism and one of the candidates has been successfully demonstrated as a Dirac semimetal in two independent experiments. Work carried out in collaboration with: Julia A. Steinberg, Steve M. Young, J.C.Y. Teo, C.L. Kane, E.J. Mele and Andrew M. Rappe.

First-principles study of Dirac and Dirac-like cones in phononic and photonic crystals

KAUST Repository

Mei, Jun; Wu, Ying; Chan, C. T.; Zhang, Zhao-Qing

2012-01-01

By using the k•p method, we propose a first-principles theory to study the linear dispersions in phononic and photonic crystals. The theory reveals that only those linear dispersions created by doubly degenerate states can be described by a reduced Hamiltonian that can be mapped into the Dirac Hamiltonian and possess a Berry phase of -π. Linear dispersions created by triply degenerate states cannot be mapped into the Dirac Hamiltonian and carry no Berry phase, and, therefore should be called Dirac-like cones. Our theory is capable of predicting accurately the linear slopes of Dirac and Dirac-like cones at various symmetry points in a Brillouin zone, independent of frequency and lattice structure. © 2012 American Physical Society.

First-principles study of Dirac and Dirac-like cones in phononic and photonic crystals

KAUST Repository

Mei, Jun

2012-07-24

By using the k•p method, we propose a first-principles theory to study the linear dispersions in phononic and photonic crystals. The theory reveals that only those linear dispersions created by doubly degenerate states can be described by a reduced Hamiltonian that can be mapped into the Dirac Hamiltonian and possess a Berry phase of -π. Linear dispersions created by triply degenerate states cannot be mapped into the Dirac Hamiltonian and carry no Berry phase, and, therefore should be called Dirac-like cones. Our theory is capable of predicting accurately the linear slopes of Dirac and Dirac-like cones at various symmetry points in a Brillouin zone, independent of frequency and lattice structure. © 2012 American Physical Society.

DIRAC: reliable data management for LHCb

International Nuclear Information System (INIS)

Smith, A C; Tsaregorodtsev, A

2008-01-01

DIRAC, LHCb's Grid Workload and Data Management System, utilizes WLCG resources and middleware components to perform distributed computing tasks satisfying LHCb's Computing Model. The Data Management System (DMS) handles data transfer and data access within LHCb. Its scope ranges from the output of the LHCb Online system to Grid-enabled storage for all data types. It supports metadata for these files in replica and bookkeeping catalogues, allowing dataset selection and localization. The DMS controls the movement of files in a redundant fashion whilst providing utilities for accessing all metadata. To do these tasks effectively the DMS requires complete self integrity between its components and external physical storage. The DMS provides highly redundant management of all LHCb data to leverage available storage resources and to manage transient errors in underlying services. It provides data driven and reliable distribution of files as well as reliable job output upload, utilizing VO Boxes at LHCb Tier1 sites to prevent data loss. This paper presents several examples of mechanisms implemented in the DMS to increase reliability, availability and integrity, highlighting successful design choices and limitations discovered

Fermi–Dirac Statistics

Indian Academy of Sciences (India)

IAS Admin

Pauli exclusion principle, Fermi–. Dirac statistics, identical and in- distinguishable particles, Fermi gas. Fermi–Dirac Statistics. Derivation and Consequences. S Chaturvedi and Shyamal Biswas. (left) Subhash Chaturvedi is at University of. Hyderabad. His current research interests include phase space descriptions.

Dirac, Weyl, Majorana, a review

International Nuclear Information System (INIS)

Uschersohn, J.

1982-05-01

The Dirac equation and the properties of Dirac matrices are presented and discussed. A large number of representations of the Dirac matrices is identified. Special emphasis is put on aspects rarely treated or neglected in textbooks

The Dirac Sea

OpenAIRE

Dimock, J.

2010-01-01

We give an alternate definition of the free Dirac field featuring an explicit construction of the Dirac sea. The treatment employs a semi-infinite wedge product of Hilbert spaces. We also show that the construction is equivalent to the standard Fock space construction.

Graphene based d-character Dirac Systems

Science.gov (United States)

Li, Yuanchang; Zhang, S. B.; Duan, Wenhui

From graphene to topological insulators, Dirac material continues to be the hot topics in condensed matter physics. So far, almost all of the theoretically predicted or experimentally observed Dirac materials are composed of sp -electrons. By using first-principles calculations, we find the new Dirac system of transition-metal intercalated epitaxial graphene on SiC(0001). Intrinsically different from the conventional sp Dirac system, here the Dirac-fermions are dominantly contributed by the transition-metal d-electrons, which paves the way to incorporate correlation effect with Dirac-cone physics. Many intriguing quantum phenomena are proposed based on this system, including quantum spin Hall effect with large spin-orbital gap, quantum anomalous Hall effect, 100% spin-polarized Dirac fermions and ferromagnet-to-topological insulator transition.

Equazione di Dirac

CERN Document Server

Monti, Dalida

1996-01-01

Relativamente poco noto al gran pubblico, il premio Nobel Paul Adrien Maurice Dirac appartiene a quel gruppo di uomini di ingegno che nei primi decenni del secolo contribuirono a dare alla nostra concezione del mondo fisico la sua impronta attuale. Assolutamente cruciali, per una valutazione dell'opera di Dirac, sono gli anni compresi tra il 1925 e il 1931: un periodo in cui il fisico fornisce la prima spiegazione chiara e coerente delle proprietà di spin dell'elettrone (equazione di Dirac) e perviene, in forza della pura deduzione matematica, alla scoperta dell'esistenza dell'elettrone positivo o positrone.

Paul Dirac lectures at CERN

CERN Multimedia

CERN Bulletin

2010-01-01

When a group of physicists entered the Main Auditorium, during the evening of 29 June, they felt they had opened a time portal.   Paul Dirac in front of a blackboard showing his formula. ©Sandra Hoogeboom An attentive audience, dressed in early 1900 costumes, were watching a lecture by the elusive Paul Dirac, presenting for the first time his famous formula on the blackboard. Paul Adrien Maurice Dirac (1902-1984) was a British mathematical physicist at Cambridge, and one of the "fathers" of quantum mechanics. When he first wrote it, in 1928, Dirac was not sure what his formula really meant. As demonstrated by Andersson four year later, what Dirac had written on the blackboard was the first definition of a positron, hence he is credited with having anticipated the existence of antimatter. The actor John Kohl performs as Paul Dirac. ©Sandra Hoogeboom What the group of puzzled physicists were really observing when they entered the CERN Auditorium was the shoo...

A Route to Dirac Liquid Theory: A Fermi Liquid Description for Dirac Materials

Science.gov (United States)

Gochan, Matthew; Bedell, Kevin

Since the pioneering work developed by L.V. Landau sixty years ago, Fermi Liquid Theory has seen great success in describing interacting Fermi systems. While much interest has been generated over the study of non-Fermi Liquid systems, Fermi Liquid theory serves as a formidable model for many systems and offers a rich amount of of results and insight. The recent classification of Dirac Materials, and the lack of a unifying theoretical framework for them, has motivated our study. Dirac materials are a versatile class of materials in which an abundance of unique physical phenomena can be observed. Such materials are found in all dimensions, with the shared property that their low-energy fermionic excitations behave as massless Dirac fermions and are therefore governed by the Dirac equation. The most popular Dirac material, graphene, is the focus of this work. We present our Fermi Liquid description of Graphene. We find many interesting results, specifically in the transport and dynamics of the system. Additionally, we expand on previous work regarding the Virial Theorem and its impact on the Fermi Liquid parameters in graphene. Finally, we remark on viscoelasticity of Dirac Materials and other unusual results that are consequences of AdS-CFT.

A Workload-Adaptive and Reconfigurable Bus Architecture for Multicore Processors

Directory of Open Access Journals (Sweden)

Shoaib Akram

2010-01-01

Full Text Available Interconnection networks for multicore processors are traditionally designed to serve a diversity of workloads. However, different workloads or even different execution phases of the same workload may benefit from different interconnect configurations. In this paper, we first motivate the need for workload-adaptive interconnection networks. Subsequently, we describe an interconnection network framework based on reconfigurable switches for use in medium-scale (up to 32 cores shared memory multicore processors. Our cost-effective reconfigurable interconnection network is implemented on a traditional shared bus interconnect with snoopy-based coherence, and it enables improved multicore performance. The proposed interconnect architecture distributes the cores of the processor into clusters with reconfigurable logic between clusters to support workload-adaptive policies for inter-cluster communication. Our interconnection scheme is complemented by interconnect-aware scheduling and additional interconnect optimizations which help boost the performance of multiprogramming and multithreaded workloads. We provide experimental results that show that the overall throughput of multiprogramming workloads (consisting of two and four programs can be improved by up to 60% with our configurable bus architecture. Similar gains can be achieved also for multithreaded applications as shown by further experiments. Finally, we present the performance sensitivity of the proposed interconnect architecture on shared memory bandwidth availability.

Use of EEG workload indices for diagnostic monitoring of vigilance decrement.

Science.gov (United States)

Kamzanova, Altyngul T; Kustubayeva, Almira M; Matthews, Gerald

2014-09-01

A study was run to test which of five electroencephalographic (EEG) indices was most diagnostic of loss of vigilance at two levels of workload. EEG indices of alertness include conventional spectral power measures as well as indices combining measures from multiple frequency bands, such as the Task Load Index (TLI) and the Engagement Index (El). However, it is unclear which indices are optimal for early detection of loss of vigilance. Ninety-two participants were assigned to one of two experimental conditions, cued (lower workload) and uncued (higher workload), and then performed a 40-min visual vigilance task. Performance on this task is believed to be limited by attentional resource availability. EEG was recorded continuously. Performance, subjective state, and workload were also assessed. The task showed a vigilance decrement in performance; cuing improved performance and reduced subjective workload. Lower-frequency alpha (8 to 10.9 Hz) and TLI were most sensitive to the task parameters. The magnitude of temporal change was larger for lower-frequency alpha. Surprisingly, higher TLI was associated with superior performance. Frontal theta and El were influenced by task workload only in the final period of work. Correlational data also suggested that the indices are distinct from one another. Lower-frequency alpha appears to be the optimal index for monitoring vigilance on the task used here, but further work is needed to test how diagnosticity of EEG indices varies with task demands. Lower-frequency alpha may be used to diagnose loss of operator alertness on tasks requiring vigilance.

Approaching the Type-II Dirac Point and Concomitant Superconductivity in Pt-doping Stabilized Metastable 1T-phase IrTe2

OpenAIRE

Fei, Fucong; Bo, Xiangyan; Wang, Pengdong; Ying, Jianghua; Chen, Bo; Liu, Qianqian; Zhang, Yong; Sun, Zhe; Qu, Fanming; Zhang, Yi; Li, Jian; Song, Fengqi; Wan, Xiangang; Wang, Baigeng; Wang, Guanghou

2017-01-01

Topological semimetal is a topic of general interest in material science. Recently, a new kind of topological semimetal called type-II Dirac semimetal with tilted Dirac cones is discovered in PtSe2 family. However, the further investigation is hindered due to the huge energy difference from Dirac points to Fermi level and the irrelevant conducting pockets at Fermi surface. Here we characterize the optimized type-II Dirac dispersions in a metastable 1T phase of IrTe2. Our strategy of Pt doping...

Stationary solutions of the Maxwell-Dirac and the Klein-Gordon-Dirac equations

International Nuclear Information System (INIS)

Esteban, M.J.; Georgiev, V.; Sere, E.

1995-01-01

The Maxwell-Dirac system describes the interaction of an electron with its own electromagnetic field. We prove the existence of soliton-like solutions of Maxwell-Dirac in (3+1)-Minkowski space-time. The solutions obtained are regular, stationary in time, and localized in space. They are found by a variational method, as critical points of an energy functional. This functional is strongly indefinite and presents a lack of compactness. We also find soliton-like solutions for the Klein-Gordon-Dirac system, arising in the Yukawa model. (author). 32 refs

File-System Workload on a Scientific Multiprocessor

Science.gov (United States)

Kotz, David; Nieuwejaar, Nils

1995-01-01

Many scientific applications have intense computational and I/O requirements. Although multiprocessors have permitted astounding increases in computational performance, the formidable I/O needs of these applications cannot be met by current multiprocessors a their I/O subsystems. To prevent I/O subsystems from forever bottlenecking multiprocessors and limiting the range of feasible applications, new I/O subsystems must be designed. The successful design of computer systems (both hardware and software) depends on a thorough understanding of their intended use. A system designer optimizes the policies and mechanisms for the cases expected to most common in the user's workload. In the case of multiprocessor file systems, however, designers have been forced to build file systems based only on speculation about how they would be used, extrapolating from file-system characterizations of general-purpose workloads on uniprocessor and distributed systems or scientific workloads on vector supercomputers (see sidebar on related work). To help these system designers, in June 1993 we began the Charisma Project, so named because the project sought to characterize 1/0 in scientific multiprocessor applications from a variety of production parallel computing platforms and sites. The Charisma project is unique in recording individual read and write requests-in live, multiprogramming, parallel workloads (rather than from selected or nonparallel applications). In this article, we present the first results from the project: a characterization of the file-system workload an iPSC/860 multiprocessor running production, parallel scientific applications at NASA's Ames Research Center.

Quasi-Dirac neutrino oscillations

Science.gov (United States)

Anamiati, Gaetana; Fonseca, Renato M.; Hirsch, Martin

2018-05-01

Dirac neutrino masses require two distinct neutral Weyl spinors per generation, with a special arrangement of masses and interactions with charged leptons. Once this arrangement is perturbed, lepton number is no longer conserved and neutrinos become Majorana particles. If these lepton number violating perturbations are small compared to the Dirac mass terms, neutrinos are quasi-Dirac particles. Alternatively, this scenario can be characterized by the existence of pairs of neutrinos with almost degenerate masses, and a lepton mixing matrix which has 12 angles and 12 phases. In this work we discuss the phenomenology of quasi-Dirac neutrino oscillations and derive limits on the relevant parameter space from various experiments. In one parameter perturbations of the Dirac limit, very stringent bounds can be derived on the mass splittings between the almost degenerate pairs of neutrinos. However, we also demonstrate that with suitable changes to the lepton mixing matrix, limits on such mass splittings are much weaker, or even completely absent. Finally, we consider the possibility that the mass splittings are too small to be measured and discuss bounds on the new, nonstandard lepton mixing angles from current experiments for this case.

In the Dirac tradition

Energy Technology Data Exchange (ETDEWEB)

Anon.

1988-04-15

It was Paul Dirac who cast quantum mechanics into the form we now use, and many generations of theoreticians openly acknowledge his influence on their thinking. When Dirac died in 1984, St. John's College, Cambridge, his base for most of his lifetime, instituted an annual lecture in his memory at Cambridge. The first lecture, in 1986, attracted two heavyweights - Richard Feynman and Steven Weinberg. Far from using the lectures as a platform for their own work, in the Dirac tradition they presented stimulating material on deep underlying questions.

In the Dirac tradition

International Nuclear Information System (INIS)

Anon.

1988-01-01

It was Paul Dirac who cast quantum mechanics into the form we now use, and many generations of theoreticians openly acknowledge his influence on their thinking. When Dirac died in 1984, St. John's College, Cambridge, his base for most of his lifetime, instituted an annual lecture in his memory at Cambridge. The first lecture, in 1986, attracted two heavyweights - Richard Feynman and Steven Weinberg. Far from using the lectures as a platform for their own work, in the Dirac tradition they presented stimulating material on deep underlying questions

Bohr and Dirac*

Indian Academy of Sciences (India)

IAS Admin

We present an account of the work of Niels Bohr and Paul Dirac, their interactions and personal- ities. 1. Introduction. In this essay I would like to convey to my readers some- thing about the personalities and work of Niels Bohr and Paul Dirac, juxtaposed against one another. Let me hope that the portraits I will paint of these ...

On the Dirac oscillator

International Nuclear Information System (INIS)

Rodrigues, R. de Lima

2007-01-01

In the present work we obtain a new representation for the Dirac oscillator based on the Clifford algebra C 7. The symmetry breaking and the energy eigenvalues for our model of the Dirac oscillator are studied in the non-relativistic limit. (author)

Double Dirac cones in phononic crystals

KAUST Repository

Li, Yan

2014-07-07

A double Dirac cone is realized at the center of the Brillouin zone of a two-dimensional phononic crystal (PC) consisting of a triangular array of core-shell-structure cylinders in water. The double Dirac cone is induced by the accidental degeneracy of two double-degenerate Bloch states. Using a perturbation method, we demonstrate that the double Dirac cone is composed of two identical and overlapping Dirac cones whose linear slopes can also be accurately predicted from the method. Because the double Dirac cone occurs at a relatively low frequency, a slab of the PC can be mapped onto a slab of zero refractive index material by using a standard retrieval method. Total transmission without phase change and energy tunneling at the double Dirac point frequency are unambiguously demonstrated by two examples. Potential applications can be expected in diverse fields such as acoustic wave manipulations and energy flow control.

Double Dirac cones in phononic crystals

KAUST Repository

Li, Yan; Wu, Ying; Mei, Jun

2014-01-01

A double Dirac cone is realized at the center of the Brillouin zone of a two-dimensional phononic crystal (PC) consisting of a triangular array of core-shell-structure cylinders in water. The double Dirac cone is induced by the accidental degeneracy of two double-degenerate Bloch states. Using a perturbation method, we demonstrate that the double Dirac cone is composed of two identical and overlapping Dirac cones whose linear slopes can also be accurately predicted from the method. Because the double Dirac cone occurs at a relatively low frequency, a slab of the PC can be mapped onto a slab of zero refractive index material by using a standard retrieval method. Total transmission without phase change and energy tunneling at the double Dirac point frequency are unambiguously demonstrated by two examples. Potential applications can be expected in diverse fields such as acoustic wave manipulations and energy flow control.

Executor Framework for DIRAC

Science.gov (United States)

Casajus Ramo, A.; Graciani Diaz, R.

2012-12-01

DIRAC framework for distributed computing has been designed as a group of collaborating components, agents and servers, with persistent database back-end. Components communicate with each other using DISET, an in-house protocol that provides Remote Procedure Call (RPC) and file transfer capabilities. This approach has provided DIRAC with a modular and stable design by enforcing stable interfaces across releases. But it made complicated to scale further with commodity hardware. To further scale DIRAC, components needed to send more queries between them. Using RPC to do so requires a lot of processing power just to handle the secure handshake required to establish the connection. DISET now provides a way to keep stable connections and send and receive queries between components. Only one handshake is required to send and receive any number of queries. Using this new communication mechanism DIRAC now provides a new type of component called Executor. Executors process any task (such as resolving the input data of a job) sent to them by a task dispatcher. This task dispatcher takes care of persisting the state of the tasks to the storage backend and distributing them among all the Executors based on the requirements of each task. In case of a high load, several Executors can be started to process the extra load and stop them once the tasks have been processed. This new approach of handling tasks in DIRAC makes Executors easy to replace and replicate, thus enabling DIRAC to further scale beyond the current approach based on polling agents.

Executor Framework for DIRAC

International Nuclear Information System (INIS)

Casajus Ramo, A; Graciani Diaz, R

2012-01-01

DIRAC framework for distributed computing has been designed as a group of collaborating components, agents and servers, with persistent database back-end. Components communicate with each other using DISET, an in-house protocol that provides Remote Procedure Call (RPC) and file transfer capabilities. This approach has provided DIRAC with a modular and stable design by enforcing stable interfaces across releases. But it made complicated to scale further with commodity hardware. To further scale DIRAC, components needed to send more queries between them. Using RPC to do so requires a lot of processing power just to handle the secure handshake required to establish the connection. DISET now provides a way to keep stable connections and send and receive queries between components. Only one handshake is required to send and receive any number of queries. Using this new communication mechanism DIRAC now provides a new type of component called Executor. Executors process any task (such as resolving the input data of a job) sent to them by a task dispatcher. This task dispatcher takes care of persisting the state of the tasks to the storage backend and distributing them among all the Executors based on the requirements of each task. In case of a high load, several Executors can be started to process the extra load and stop them once the tasks have been processed. This new approach of handling tasks in DIRAC makes Executors easy to replace and replicate, thus enabling DIRAC to further scale beyond the current approach based on polling agents.

Alternatives to the Dirac equation

International Nuclear Information System (INIS)

Girvin, S.M.; Brownstein, K.R.

1975-01-01

Recent work by Biedenharn, Han, and van Dam (BHvD) has questioned the uniqueness of the Dirac equation. BHvD have obtained a two-component equation as an alternate to the Dirac equation. Although they later show their alternative to be unitarily equivalent to the Dirac equation, certain physical differences were claimed. BHvD attribute the existence of this alternate equation to the fact that their factorizing matrices were position-dependent. To investigate this, we factor the Klein-Gordon equation in spherical coordinates allowing the factorizing matrices to depend arbitrarily upon theta and phi. It is shown that despite this additional freedom, and without involving any relativistic covariance, the conventional four-component Dirac equation is the only possibility

The DIRAC Data Management System (poster)

CERN Document Server

Haen, Christophe

2015-01-01

The DIRAC Interware provides a development framework and a complete set of components for building distributed computing systems. The DIRAC Data Management System (DMS) offers all the necessary tools to ensure data handling operations for small and large user communities. It supports transparent access to storage resources based on multiple technologies, and is easily expandable. The information on data files and replicas is kept in a File Catalog of which DIRAC offers a powerful and versatile implementation (DFC). Data movement can be performed using third party services including FTS3. Bulk data operations are resilient with respect to failures due to the use of the Request Management System (RMS) that keeps track of ongoing tasks. In this contribution we will present an overview of the DIRAC DMS capabilities and its connection with other DIRAC subsystems such as the Transformation System. The DIRAC DMS is in use by several user communities now. The contribution will present the experience of the LHCb exper...

DIRAC distributed computing services

International Nuclear Information System (INIS)

Tsaregorodtsev, A

2014-01-01

DIRAC Project provides a general-purpose framework for building distributed computing systems. It is used now in several HEP and astrophysics experiments as well as for user communities in other scientific domains. There is a large interest from smaller user communities to have a simple tool like DIRAC for accessing grid and other types of distributed computing resources. However, small experiments cannot afford to install and maintain dedicated services. Therefore, several grid infrastructure projects are providing DIRAC services for their respective user communities. These services are used for user tutorials as well as to help porting the applications to the grid for a practical day-to-day work. The services are giving access typically to several grid infrastructures as well as to standalone computing clusters accessible by the target user communities. In the paper we will present the experience of running DIRAC services provided by the France-Grilles NGI and other national grid infrastructure projects.

Potential scattering of Dirac particles

International Nuclear Information System (INIS)

Thaller, B.

1981-01-01

A quantum mechanical interpretation of the Dirac equation for particles in external electromagnetic potentials is discussed. It is shown that a consequent development of the Stueckelberg-Feynman theory into a probabilistic interpretation of the Dirac equation corrects some prejudices concerning negative energy states, Zitterbewegung and bound states in repulsive potentials and yields the connection between propagator theory and scattering theory. Limits of the Dirac equation, considered as a wave mechanical equation, are considered. (U.K.)

Benchmarking transaction and analytical processing systems the creation of a mixed workload benchmark and its application

CERN Document Server

Bog, Anja

2014-01-01

This book introduces a new benchmark for hybrid database systems, gauging the effect of adding OLAP to an OLTP workload and analyzing the impact of commonly used optimizations in historically separate OLTP and OLAP domains in mixed-workload scenarios.

P A M Dirac

Indian Academy of Sciences (India)

Home; Journals; Resonance – Journal of Science Education. P A M Dirac. Articles written in Resonance – Journal of Science Education. Volume 8 Issue 8 August 2003 pp 102-110 Classics. XI. The Relation between Mathematics and Physics · P A M Dirac · More Details Fulltext PDF ...

A Dirac algebraic approach to supersymmetry

International Nuclear Information System (INIS)

Guersey, F.

1984-01-01

The power of the Dirac algebra is illustrated through the Kaehler correspondence between a pair of Dirac spinors and a 16-component bosonic field. The SO(5,1) group acts on both the fermion and boson fields, leading to a supersymmetric equation of the Dirac type involving all these fields. (author)

THE WORKLOAD ANALYSIS OF EMPLOYEE BY USING NATIONAL AERONAUTICS AND SPACE ADMINISTRATION-TASK LOAD INDEX METHOD (NASA-TLX

Directory of Open Access Journals (Sweden)

Nur Azemil

2017-09-01

Full Text Available Development of manufacturing and service institutions can not be separated from the role of human resources. Human resources have an important role in fulfilling vision and mission. University of A is one of the private educational institutions in East Java to achieve the goal must be managed properly that can be utilized optimally, this can be done by analyzing workload and performance or optimizing the number of employees. The purpose this research is measure workload and effect the employee’s performance. Measurement of workload is using National Aeronautics and Space Administration-Task Load Index (NASA-TLX method, NASA-TLX method is rating multidimentional subjective mental workload  that divides the workload based on the average load of 6 dimensions, and the measurement of performance is using questionnaire with 5 scales by likert scale. The results showed that employees who have Medium workload is 8%, High workload is 84% and Very high workload is 8%. The result of the questionnaire showed the category of employee’s performance, simply performance is 24% and satisfactory performance is 76%. From the statistical test by using Chi Square method, it is known that the value = 5,9915 and = 2,2225, the result shows  < , then  is accepted and  is rejected. Thus, there is influence between the workload of employees and the employees’s performance.

Psychophysical workload in the operating room: primary surgeon versus assistant.

Science.gov (United States)

Rieger, Annika; Fenger, Sebastian; Neubert, Sebastian; Weippert, Matthias; Kreuzfeld, Steffi; Stoll, Regina

2015-07-01

Working in the operating room is characterized by high demands and overall workload of the surgical team. Surgeons often report that they feel more stressed when operating as a primary surgeon than in the function as an assistant which has been confirmed in recent studies. In this study, intra-individual workload was assessed in both intraoperative functions using a multidimensional approach that combined objective and subjective measures in a realistic work setting. Surgeons' intraoperative psychophysiologic workload was assessed through a mobile health system. 25 surgeons agreed to take part in the 24-hour monitoring by giving their written informed consent. The mobile health system contained a sensor electronic module integrated in a chest belt and measuring physiological parameters such as heart rate (HR), breathing rate (BR), and skin temperature. Subjective workload was assessed pre- and postoperatively using an electronic version of the NASA-TLX on a smartphone. The smartphone served as a communication unit and transferred objective and subjective measures to a communication server where data were stored and analyzed. Working as a primary surgeon did not result in higher workload. Neither NASA-TLX ratings nor physiological workload indicators were related to intraoperative function. In contrast, length of surgeries had a significant impact on intraoperative physical demands (p NASA-TLX sum score (p < 0.01; η(2) = 0.287). Intra-individual workload differences do not relate to intraoperative role of surgeons when length of surgery is considered as covariate. An intelligent operating management that considers the length of surgeries by implementing short breaks could contribute to the optimization of intraoperative workload and the preservation of surgeons' health, respectively. The value of mobile health systems for continuous psychophysiologic workload assessment was shown.

A fractional Dirac equation and its solution

International Nuclear Information System (INIS)

Muslih, Sami I; Agrawal, Om P; Baleanu, Dumitru

2010-01-01

This paper presents a fractional Dirac equation and its solution. The fractional Dirac equation may be obtained using a fractional variational principle and a fractional Klein-Gordon equation; both methods are considered here. We extend the variational formulations for fractional discrete systems to fractional field systems defined in terms of Caputo derivatives. By applying the variational principle to a fractional action S, we obtain the fractional Euler-Lagrange equations of motion. We present a Lagrangian and a Hamiltonian for the fractional Dirac equation of order α. We also use a fractional Klein-Gordon equation to obtain the fractional Dirac equation which is the same as that obtained using the fractional variational principle. Eigensolutions of this equation are presented which follow the same approach as that for the solution of the standard Dirac equation. We also provide expressions for the path integral quantization for the fractional Dirac field which, in the limit α → 1, approaches to the path integral for the regular Dirac field. It is hoped that the fractional Dirac equation and the path integral quantization of the fractional field will allow further development of fractional relativistic quantum mechanics.

The Dirac medals of the ICTP. 1993

Energy Technology Data Exchange (ETDEWEB)

NONE

1996-12-31

The Dirac Medals of the International Centre for Theoretical Physics (ICTP) were instituted in 1985. These are awarded yearly to outstanding physicists, on Dirac`s birthday - 8th August- for contributions to theoretical physics. The document includes the lectures of the three Dirac Medalists for 1993: Professor Sergio Ferrara, Professor Daniel Z. Freedman, and Professor Peter van Nieuwenhuizen. A separate abstract was prepared for each lecture

Dirac equations for generalised Yang-Mills systems

International Nuclear Information System (INIS)

Lechtenfeld, O.; Nahm, W.; Tchrakian, D.H.

1985-06-01

We present Dirac equations in 4p dimensions for the generalised Yang-Mills (GYM) theories introduced earlier. These Dirac equations are related to the self-duality equations of the GYM and are checked to be elliptic in a 'BPST' background. In this background these Dirac equations are integrated exactly. The possibility of imposing supersymmetry in the GYM-Dirac system is investigated, with negative results. (orig.)

Dirac Fermions in an Antiferromagnetic Semimetal

Science.gov (United States)

Tang, Peizhe; Zhou, Quan; Xu, Gang; Zhang, Shou-Cheng; Shou-Cheng Zhang's Group Team, Prof.

Analogues of the elementary particles have been extensively searched for in condensed matter systems for both scientific interest and technological applications. Recently, massless Dirac fermions were found to emerge as low energy excitations in materials now known as Dirac semimetals. All the currently known Dirac semimetals are nonmagnetic with both time-reversal symmetry  and inversion symmetry "". Here we show that Dirac fermions can exist in one type of antiferromagnetic systems, where both  and "" are broken but their combination "" is respected. We propose orthorhombic antiferromagnet CuMnAs as a candidate, analyze the robustness of the Dirac points under symmetry protections, and demonstrate its distinctive bulk dispersions as well as the corresponding surface states by ab initio calculations. Our results provide a possible platform to study the interplay of Dirac fermion physics and magnetism. We acknowledge the DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under contract DE-AC02-76SF00515, NSF under Grant No.DMR-1305677 and FAME, one of six centers of STARnet.

Physician workload in primary care: what is the optimal size of practices? A cross-sectional study.

NARCIS (Netherlands)

Wensing, M.J.P.; Hombergh, P. van den; Akkermans, R.P.; Doremalen, J.H.M. van; Grol, R.P.T.M.

2006-01-01

OBJECTIVE: To determine the impact of practice size and scope of services on average physician workload in primary care practices in The Netherlands, and to examine the associations between average physician workload, average assistant volume and organisational practice characteristics. METHODS:

The workload of fishermen

DEFF Research Database (Denmark)

Østergaard, Helle; Jepsen, Jørgen Riis; Berg-Beckhoff, Gabriele

2016-01-01

-reported occupational and health data. Questions covering the physical workload were related to seven different work situations and a score summing up the workload was developed for the analysis of the relative impact on different groups of fishermen. Results: Almost all fishermen (96.2%) were familiar to proper...... health. To address the specific areas of fishing with the highest workload, future investments in assistive devices to ease the demanding work and reduce the workload, should particularly address deckhands and less mechanized vessels....

DDM Workload Emulation

CERN Document Server

Vigne, R; The ATLAS collaboration; Garonne, V; Stewart, G; Barisits, M; Beermann, T; Lassnig, M; Serfon, C; Goossens, L; Nairz, A

2013-01-01

Rucio is the successor of the current Don Quijote 2 (DQ2) system for the distributed data management (DDM) system of the ATLAS experiment. The reasons for replacing DQ2 are manifold, but besides high maintenance costs and architectural limitations, scalability concerns are on top of the list. Current expectations are that the amount of data will be three to four times as it is today by the end of 2014. Further is the availability of more powerful computing resources pushing additional pressure on the DDM system as it increases the demands on data provisioning. Although DQ2 is capable of handling the current workload, it is already at its limits. To ensure that Rucio will be up to the expected workload, a way to emulate it is needed. To do so, first the current workload, observed in DQ2, must be understood in order to scale it up to future expectations. The paper discusses how selected core concepts are applied to the workload of the experiment and how knowledge about the current workload is derived from vario...

DDM Workload Emulation

CERN Document Server

Vigne, R; The ATLAS collaboration; Garonne, V; Stewart, G; Barisits, M; Beermann, T; Serfon, C; Goossens, L; Nairz, A

2014-01-01

Rucio is the successor of the current Don Quijote 2 (DQ2) system for the distributed data management (DDM) system of the ATLAS experiment. The reasons for replacing DQ2 are manifold, but besides high maintenance costs and architectural limitations, scalability concerns are on top of the list. Current expectations are that the amount of data will be three to four times as it is today by the end of 2014. Further is the availability of more powerful computing resources pushing additional pressure on the DDM system as it increases the demands on data provisioning. Although DQ2 is capable of handling the current workload, it is already at its limits. To ensure that Rucio will be up to the expected workload, a way to emulate it is needed. To do so, first the current workload, observed in DQ2, must be understood in order to scale it up to future expectations. The paper discusses how selected core concepts are applied to the workload of the experiment and how knowledge about the current workload is derived from vario...

Semi-Dirac points in phononic crystals

KAUST Repository

Zhang, Xiujuan

2014-01-01

A semi-Dirac cone refers to a peculiar type of dispersion relation that is linear along the symmetry line but quadratic in the perpendicular direction. It was originally discovered in electron systems, in which the associated quasi-particles are massless along one direction, like those in graphene, but effective-mass-like along the other. It was reported that a semi-Dirac point is associated with the topological phase transition between a semi-metallic phase and a band insulator. Very recently, the classical analogy of a semi-Dirac cone has been reported in an electromagnetic system. Here, we demonstrate that, by accidental degeneracy, two-dimensional phononic crystals consisting of square arrays of elliptical cylinders embedded in water are also able to produce the particular dispersion relation of a semi-Dirac cone in the center of the Brillouin zone. A perturbation method is used to evaluate the linear slope and to affirm that the dispersion relation is a semi-Dirac type. If the scatterers are made of rubber, in which the acoustic wave velocity is lower than that in water, the semi-Dirac dispersion can be characterized by an effective medium theory. The effective medium parameters link the semi-Dirac point to a topological transition in the iso-frequency surface of the phononic crystal, in which an open hyperbola is changed into a closed ellipse. This topological transition results in drastic change in wave manipulation. On the other hand, the theory also reveals that the phononic crystal is a double-zero-index material along the x-direction and photonic-band-edge material along the perpendicular direction (y-direction). If the scatterers are made of steel, in which the acoustic wave velocity is higher than that in water, the effective medium description fails, even though the semi-Dirac dispersion relation looks similar to that in the previous case. Therefore different wave transport behavior is expected. The semi-Dirac points in phononic crystals described in

Scaling Deep Learning Workloads: NVIDIA DGX-1/Pascal and Intel Knights Landing

Energy Technology Data Exchange (ETDEWEB)

Gawande, Nitin A.; Landwehr, Joshua B.; Daily, Jeffrey A.; Tallent, Nathan R.; Vishnu, Abhinav; Kerbyson, Darren J.

2017-07-03

Deep Learning (DL) algorithms have become ubiquitous in data analytics. As a result, major computing vendors --- including NVIDIA, Intel, AMD and IBM --- have architectural road-maps influenced by DL workloads. Furthermore, several vendors have recently advertised new computing products as accelerating DL workloads. Unfortunately, it is difficult for data scientists to quantify the potential of these different products. This paper provides a performance and power analysis of important DL workloads on two major parallel architectures: NVIDIA DGX-1 (eight Pascal P100 GPUs interconnected with NVLink) and Intel Knights Landing (KNL) CPUs interconnected with Intel Omni-Path. Our evaluation consists of a cross section of convolutional neural net workloads: CifarNet, CaffeNet, AlexNet and GoogleNet topologies using the Cifar10 and ImageNet datasets. The workloads are vendor optimized for each architecture. GPUs provide the highest overall raw performance. Our analysis indicates that although GPUs provide the highest overall performance, the gap can close for some convolutional networks; and KNL can be competitive when considering performance/watt. Furthermore, NVLink is critical to GPU scaling.

Dirac cones in isogonal hexagonal metallic structures

Science.gov (United States)

Wang, Kang

2018-03-01

A honeycomb hexagonal metallic lattice is equivalent to a triangular atomic one and cannot create Dirac cones in its electromagnetic wave spectrum. We study in this work the low-frequency electromagnetic band structures in isogonal hexagonal metallic lattices that are directly related to the honeycomb one and show that such structures can create Dirac cones. The band formation can be described by a tight-binding model that allows investigating, in terms of correlations between local resonance modes, the condition for the Dirac cones and the consequence of the third structure tile sustaining an extra resonance mode in the unit cell that induces band shifts and thus nonlinear deformation of the Dirac cones following the wave vectors departing from the Dirac points. We show further that, under structure deformation, the deformations of the Dirac cones result from two different correlation mechanisms, both reinforced by the lattice's metallic nature, which directly affects the resonance mode correlations. The isogonal structures provide new degrees of freedom for tuning the Dirac cones, allowing adjustment of the cone shape by modulating the structure tiles at the local scale without modifying the lattice periodicity and symmetry.

LHCbDIRAC as Apache Mesos microservices

CERN Multimedia

Couturier, Ben

2016-01-01

The LHCb experiment relies on LHCbDIRAC, an extension of DIRAC, to drive its offline computing. This middleware provides a development framework and a complete set of components for building distributed computing systems. These components are currently installed and ran on virtual machines (VM) or bare metal hardware. Due to the increased load of work, high availability is becoming more and more important for the LHCbDIRAC services, and the current installation model is showing its limitations. Apache Mesos is a cluster manager which aims at abstracting heterogeneous physical resources on which various tasks can be distributed thanks to so called "framework". The Marathon framework is suitable for long running tasks such as the DIRAC services, while the Chronos framework meets the needs of cron-like tasks like the DIRAC agents. A combination of the service discovery tool Consul together with HAProxy allows to expose the running containers to the outside world while hiding their dynamic placements. Such an arc...

Multi-objective efficiency enhancement using workload spreading in an operational data center

International Nuclear Information System (INIS)

Habibi Khalaj, Ali; Scherer, Thomas; Siriwardana, Jayantha; Halgamuge, Saman K.

2015-01-01

Highlights: • Development of the heat-flow reduced order model (HFROM) for the IBM ZRL data center. • Verification of the developed HFROM with the experimentally verified CFD model. • Multi-objective efficiency enhancement of the HFROM using particle swarm optimization. • Improving the COP of the data center’s cooling system by about 17%. • Increasing the total allocated workload of the servers by about 10%. - Abstract: The cooling systems of rapidly growing Data Centers (DCs) consume a considerable amount of energy, which is one of the main concerns in designing and operating DCs. The main source of thermal inefficiency in a typical air-cooled DC is hot air recirculation from outlets of servers into their inlets, causing hot spots and leading to performance reduction of the cooling system. In this study, a thermally aware workload spreading method is proposed for reducing the hot spots while the total allocated server workload is increased. The core of this methodology lies in developing an appropriate thermal DC model for the optimization process. Given the fact that utilizing a high-fidelity thermal model of a DC is highly time consuming in the optimization process, a three dimensional reduced order model of a real DC is developed in this study. This model, whose boundary conditions are determined based on measurement data of an operational DC, is developed based on the potential flow theory updated with the Rankine vortex to account for buoyancy and air recirculation effects inside the DC. Before evaluating the proposed method, this model is verified with a computational fluid dynamic (CFD) model simulated with the same boundary conditions. The efficient load spreading method is achieved by applying a multi-objective particle swarm optimization (MOPSO) algorithm whose objectives are to minimize the hot spot occurrences and to maximize the total workload allocated to servers. In this case study, by applying the proposed method, the Coefficient of

System performance optimization

International Nuclear Information System (INIS)

Bednarz, R.J.

1978-01-01

The System Performance Optimization has become an important and difficult field for large scientific computer centres. Important because the centres must satisfy increasing user demands at the lowest possible cost. Difficult because the System Performance Optimization requires a deep understanding of hardware, software and workload. The optimization is a dynamic process depending on the changes in hardware configuration, current level of the operating system and user generated workload. With the increasing complication of the computer system and software, the field for the optimization manoeuvres broadens. The hardware of two manufacturers IBM and CDC is discussed. Four IBM and two CDC operating systems are described. The description concentrates on the organization of the operating systems, the job scheduling and I/O handling. The performance definitions, workload specification and tools for the system stimulation are given. The measurement tools for the System Performance Optimization are described. The results of the measurement and various methods used for the operating system tuning are discussed. (Auth.)

Data Management System of the DIRAC Project

CERN Multimedia

Haen, Christophe; Tsaregorodtsev, Andrei

2015-01-01

The DIRAC Interware provides a development framework and a complete set of components for building distributed computing systems. The DIRAC Data Management System (DMS) offers all the necessary tools to ensure data handling operations for small and large user communities. It supports transparent access to storage resources based on multiple technologies, and is easily expandable. The information on data files and replicas is kept in a File Catalog of which DIRAC offers a powerful and versatile implementation (DFC). Data movement can be performed using third party services including FTS3. Bulk data operations are resilient with respect to failures due to the use of the Request Management System (RMS) that keeps track of ongoing tasks. In this contribution we will present an overview of the DIRAC DMS capabilities and its connection with other DIRAC subsystems such as the Transformation System. The DIRAC DMS is in use by several user communities now. The contribution will present the experience of the LHCb exper...

The Dirac equation

International Nuclear Information System (INIS)

Thaller, B.

1992-01-01

This monograph treats most of the usual material to be found in texts on the Dirac equation such as the basic formalism of quantum mechanics, representations of Dirac matrices, covariant realization of the Dirac equation, interpretation of negative energies, Foldy-Wouthuysen transformation, Klein's paradox, spherically symmetric interactions and a treatment of the relativistic hydrogen atom, etc., and also provides excellent additional treatments of a variety of other relevant topics. The monograph contains an extensive treatment of the Lorentz and Poincare groups and their representations. The author discusses in depth Lie algebaic and projective representations, covering groups, and Mackey's theory and Wigner's realization of induced representations. A careful classification of external fields with respect to their behavior under Poincare transformations is supplemented by a basic account of self-adjointness and spectral properties of Dirac operators. A state-of-the-art treatment of relativistic scattering theory based on a time-dependent approach originally due to Enss is presented. An excellent introduction to quantum electrodynamics in external fields is provided. Various appendices containing further details, notes on each chapter commenting on the history involved and referring to original research papers and further developments in the literature, and a bibliography covering all relevant monographs and over 500 articles on the subject, complete this text. This book should satisfy the needs of a wide audience, ranging from graduate students in theoretical physics and mathematics to researchers interested in mathematical physics

The DIRAC Web Portal 2.0

Science.gov (United States)

Mathe, Z.; Casajus Ramo, A.; Lazovsky, N.; Stagni, F.

2015-12-01

For many years the DIRAC interware (Distributed Infrastructure with Remote Agent Control) has had a web interface, allowing the users to monitor DIRAC activities and also interact with the system. Since then many new web technologies have emerged, therefore a redesign and a new implementation of the DIRAC Web portal were necessary, taking into account the lessons learnt using the old portal. These new technologies allowed to build a more compact, robust and responsive web interface that enables users to have better control over the whole system while keeping a simple interface. The web framework provides a large set of “applications”, each of which can be used for interacting with various parts of the system. Communities can also create their own set of personalised web applications, and can easily extend already existing ones with a minimal effort. Each user can configure and personalise the view for each application and save it using the DIRAC User Profile service as RESTful state provider, instead of using cookies. The owner of a view can share it with other users or within a user community. Compatibility between different browsers is assured, as well as with mobile versions. In this paper, we present the new DIRAC Web framework as well as the LHCb extension of the DIRAC Web portal.

Dirac equation on a curved surface

Energy Technology Data Exchange (ETDEWEB)

Brandt, F.T., E-mail: fbrandt@usp.br; Sánchez-Monroy, J.A., E-mail: antosan@usp.br

2016-09-07

The dynamics of Dirac particles confined to a curved surface is examined employing the thin-layer method. We perform a perturbative expansion to first-order and split the Dirac field into normal and tangential components to the surface. In contrast to the known behavior of second order equations like Schrödinger, Maxwell and Klein–Gordon, we find that there is no geometric potential for the Dirac equation on a surface. This implies that the non-relativistic limit does not commute with the thin-layer method. Although this problem can be overcome when second-order terms are retained in the perturbative expansion, this would preclude the decoupling of the normal and tangential degrees of freedom. Therefore, we propose to introduce a first-order term which rescues the non-relativistic limit and also clarifies the effect of the intrinsic and extrinsic curvatures on the dynamics of the Dirac particles. - Highlights: • The thin-layer method is employed to derive the Dirac equation on a curved surface. • A geometric potential is absent at least to first-order in the perturbative expansion. • The effects of the extrinsic curvature are included to rescue the non-relativistic limit. • The resulting Dirac equation is consistent with the Heisenberg uncertainty principle.

The Dirac equation for accountants

International Nuclear Information System (INIS)

Ord, G.N.

2006-01-01

In the context of relativistic quantum mechanics, derivations of the Dirac equation usually take the form of plausibility arguments based on experience with the Schroedinger equation. The primary reason for this is that we do not know what wavefunctions physically represent, so derivations have to rely on formal arguments. There is however a context in which the Dirac equation in one dimension is directly related to a classical generating function. In that context, the derivation of the Dirac equation is an exercise in counting. We provide this derivation here and discuss its relationship to quantum mechanics

easyDiracGauginos

International Nuclear Information System (INIS)

Abel, Steven; Goodsell, Mark

2011-02-01

A simple and natural model is presented that gives Dirac gauginos. The configuration is related to ''deconstructed gaugino mediation''. A high energy completion is provided based on existing ISS-like models of deconstructed gaugino mediation. This provides a complete picture of Dirac gauginos that includes the necessary extra adjoint fermions (generated as magnetic quarks of the ISS theory) and supersymmetry breaking (via the ISS mechanism). Moreover the screening of the scalar masses means that they can similar to or less than the gaugino masses, even though the supersymmetry breaking is driven by F-terms. (orig.)

Full utilization of semi-Dirac cones in photonics

Science.gov (United States)

Yasa, Utku G.; Turduev, Mirbek; Giden, Ibrahim H.; Kurt, Hamza

2018-05-01

In this study, realization and applications of anisotropic zero-refractive-index materials are proposed by exposing the unit cells of photonic crystals that exhibit Dirac-like cone dispersion to rotational symmetry reduction. Accidental degeneracy of two Bloch modes in the Brillouin zone center of two-dimensional C2-symmetric photonic crystals gives rise to the semi-Dirac cone dispersion. The proposed C2-symmetric photonic crystals behave as epsilon-and-mu-near-zero materials (ɛeff≈ 0 , μeff≈ 0 ) along one propagation direction, but behave as epsilon-near-zero material (ɛeff≈ 0 , μeff≠ 0 ) for the perpendicular direction at semi-Dirac frequency. By extracting the effective medium parameters of the proposed C4- and C2-symmetric periodic media that exhibit Dirac-like and semi-Dirac cone dispersions, intrinsic differences between isotropic and anisotropic materials are investigated. Furthermore, advantages of utilizing semi-Dirac cone materials instead of Dirac-like cone materials in photonic applications are demonstrated in both frequency and time domains. By using anisotropic transmission behavior of the semi-Dirac materials, photonic application concepts such as beam deflectors, beam splitters, and light focusing are proposed. Furthermore, to the best of our knowledge, semi-Dirac cone dispersion is also experimentally demonstrated for the first time by including negative, zero, and positive refraction states of the given material.

Dirac equation in magnetic-solenoid field

Energy Technology Data Exchange (ETDEWEB)

Gavrilov, S.P. [Dept. Fisica e Quimica, UNESP, Campus de Guaratingueta (Brazil); Gitman, D.M.; Smirnov, A.A. [Instituto de Fisica, Universidade de Sao Paulo (Brazil)

2004-07-01

We consider the Dirac equation in the magnetic-solenoid field (the field of a solenoid and a collinear uniform magnetic field). For the case of Aharonov-Bohm solenoid, we construct self-adjoint extensions of the Dirac Hamiltonian using von Neumann's theory of deficiency indices. We find self-adjoint extensions of the Dirac Hamiltonian and boundary conditions at the AB solenoid. Besides, for the first time, solutions of the Dirac equation in the magnetic-solenoid field with a finite radius solenoid were found. We study the structure of these solutions and their dependence on the behavior of the magnetic field inside the solenoid. Then we exploit the latter solutions to specify boundary conditions for the magnetic-solenoid field with Aharonov-Bohm solenoid. (orig.)

Dirac particle on S2

International Nuclear Information System (INIS)

Ferreira, P.L.; Palladino, B.E.

1985-01-01

The problem of a Dirac particle in stationary motion on S 2 - a two dimensional sphere embedded in Euclidean space E 3 - is discussed. It provides a particularly simple case of an exactly solvable constrained Dirac particle whose properties are here studied, with emphasis on its magnetic moment. (Author) [pt

Understanding I/O workload characteristics of a Peta-scale storage system

Energy Technology Data Exchange (ETDEWEB)

Kim, Youngjae [ORNL; Gunasekaran, Raghul [ORNL

2015-01-01

Understanding workload characteristics is critical for optimizing and improving the performance of current systems and software, and architecting new storage systems based on observed workload patterns. In this paper, we characterize the I/O workloads of scientific applications of one of the world s fastest high performance computing (HPC) storage cluster, Spider, at the Oak Ridge Leadership Computing Facility (OLCF). OLCF flagship petascale simulation platform, Titan, and other large HPC clusters, in total over 250 thousands compute cores, depend on Spider for their I/O needs. We characterize the system utilization, the demands of reads and writes, idle time, storage space utilization, and the distribution of read requests to write requests for the Peta-scale Storage Systems. From this study, we develop synthesized workloads, and we show that the read and write I/O bandwidth usage as well as the inter-arrival time of requests can be modeled as a Pareto distribution. We also study the I/O load imbalance problems using I/O performance data collected from the Spider storage system.

[p,q] {ne} i{Dirac_h}

Energy Technology Data Exchange (ETDEWEB)

Costella, J P

1995-05-22

In this short note, it is argued that [p, q] {ne} i{Dirac_h}, contrary to the oiginal claims of Born and Jordan, and Dirac. Rather, [p, q] is equal to something that is infinitesimally different from i{Dirac_h}. While this difference is usually harmless, it does provide the solution of the Born-Jordan `trace paradox` of [p, q]. More recently, subtleties of a very similar form have been found to be of fundamental importance in quantum field theory. 3 refs.

DIRAC - The Distributed MC Production and Analysis for LHCb

CERN Document Server

Tsaregorodtsev, A

2004-01-01

DIRAC is the LHCb distributed computing grid infrastructure for MC production and analysis. Its architecture is based on a set of distributed collaborating services. The service decomposition broadly follows the ARDA project proposal, allowing for the possibility of interchanging the EGEE/ARDA and DIRAC components in the future. Some components developed outside the DIRAC project are already in use as services, for example the File Catalog developed by the AliEn project. An overview of the DIRAC architecture will be given, in particular the recent developments to support user analysis. The main design choices will be presented. One of the main design goals of DIRAC is the simplicity of installation, configuring and operation of various services. This allows all the DIRAC resources to be easily managed by a single Production Manager. The modular design of the DIRAC components allows its functionality to be easily extended to include new computing and storage elements or to handle new tasks. The DIRAC system al...

easyDiracGauginos

Energy Technology Data Exchange (ETDEWEB)

Abel, Steven [Durham Univ. (United Kingdom). Inst. for Particle Physics Phenomenology; CERN, Geneva (Switzerland); Goodsell, Mark [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

2011-02-15

A simple and natural model is presented that gives Dirac gauginos. The configuration is related to ''deconstructed gaugino mediation''. A high energy completion is provided based on existing ISS-like models of deconstructed gaugino mediation. This provides a complete picture of Dirac gauginos that includes the necessary extra adjoint fermions (generated as magnetic quarks of the ISS theory) and supersymmetry breaking (via the ISS mechanism). Moreover the screening of the scalar masses means that they can similar to or less than the gaugino masses, even though the supersymmetry breaking is driven by F-terms. (orig.)

DDM Workload Emulation

Science.gov (United States)

Vigne, R.; Schikuta, E.; Garonne, V.; Stewart, G.; Barisits, M.; Beermann, T.; Lassnig, M.; Serfon, C.; Goossens, L.; Nairz, A.; Atlas Collaboration

2014-06-01

Rucio is the successor of the current Don Quijote 2 (DQ2) system for the distributed data management (DDM) system of the ATLAS experiment. The reasons for replacing DQ2 are manifold, but besides high maintenance costs and architectural limitations, scalability concerns are on top of the list. Current expectations are that the amount of data will be three to four times as it is today by the end of 2014. Further is the availability of more powerful computing resources pushing additional pressure on the DDM system as it increases the demands on data provisioning. Although DQ2 is capable of handling the current workload, it is already at its limits. To ensure that Rucio will be up to the expected workload, a way to emulate it is needed. To do so, first the current workload, observed in DQ2, must be understood in order to scale it up to future expectations. The paper discusses how selected core concepts are applied to the workload of the experiment and how knowledge about the current workload is derived from various sources (e.g. analysing the central file catalogue logs). Finally a description of the implemented emulation framework, used for stress-testing Rucio, is given.

DDM workload emulation

International Nuclear Information System (INIS)

Vigne, R; Schikuta, E; Garonne, V; Stewart, G; Barisits, M; Beermann, T; Lassnig, M; Serfon, C; Goossens, L; Nairz, A

2014-01-01

Rucio is the successor of the current Don Quijote 2 (DQ2) system for the distributed data management (DDM) system of the ATLAS experiment. The reasons for replacing DQ2 are manifold, but besides high maintenance costs and architectural limitations, scalability concerns are on top of the list. Current expectations are that the amount of data will be three to four times as it is today by the end of 2014. Further is the availability of more powerful computing resources pushing additional pressure on the DDM system as it increases the demands on data provisioning. Although DQ2 is capable of handling the current workload, it is already at its limits. To ensure that Rucio will be up to the expected workload, a way to emulate it is needed. To do so, first the current workload, observed in DQ2, must be understood in order to scale it up to future expectations. The paper discusses how selected core concepts are applied to the workload of the experiment and how knowledge about the current workload is derived from various sources (e.g. analysing the central file catalogue logs). Finally a description of the implemented emulation framework, used for stress-testing Rucio, is given.

Paul Dirac: the purest soul in physics

International Nuclear Information System (INIS)

Berry, M.

1998-01-01

Paul Dirac published the first of his papers on ''The Quantum Theory of the Electron'' seventy years ago this month. Published in the Proceedings of the Royal Society (London) in February and March 1928, the papers contained one of the greatest leaps of imagination in 20th century physics. The Dirac equation, derived in those papers, is one of the most important equations in physics. Dirac showed that the simplest wave satisfying the requirements of quantum mechanics and relativity was not a simple number but had four components. He found that the logic that led to the theory was, although deeply sophisticated, in a sense beautifully simple. Much later, when someone asked him ''How did you find the Dirac equation?'' he is said to have replied: ''I found it beautiful''. In addition to explaining the magnetic and spin properties of the electron, the equation also predicts the existence of antimatter. Because Dirac was a quiet man - famously quiet, indeed - he is not well known outside physics, although this is slowly changing. In 1995 a plaque to Dirac was unveiled at Westminster Abbey in London and last year Institute of Physics Publishing, which is based in Bristol, named its new building Dirac House. In this article the author recalls the achievements of the greatest physicists of the 20th century. (UK)

Clean Energy Use for Cloud Computing Federation Workloads

Directory of Open Access Journals (Sweden)

Yahav Biran

2017-08-01

Full Text Available Cloud providers seek to maximize their market share. Traditionally, they deploy datacenters with sufficient capacity to accommodate their entire computing demand while maintaining geographical affinity to its customers. Achieving these goals by a single cloud provider is increasingly unrealistic from a cost of ownership perspective. Moreover, the carbon emissions from underutilized datacenters place an increasing demand on electricity and is a growing factor in the cost of cloud provider datacenters. Cloud-based systems may be classified into two categories: serving systems and analytical systems. We studied two primary workload types, on-demand video streaming as a serving system and MapReduce jobs as an analytical systems and suggested two unique energy mix usage for processing that workloads. The recognition that on-demand video streaming now constitutes the bulk portion of traffic to Internet consumers provides a path to mitigate rising energy demand. On-demand video is usually served through Content Delivery Networks (CDN, often scheduled in backend and edge datacenters. This publication describes a CDN deployment solution that utilizes green energy to supply on-demand streaming workload. A cross-cloud provider collaboration will allow cloud providers to both operate near their customers and reduce operational costs, primarily by lowering the datacenter deployments per provider ratio. Our approach optimizes cross-datacenters deployment. Specifically, we model an optimized CDN-edge instance allocation system that maximizes, under a set of realistic constraints, green energy utilization. The architecture of this cross-cloud coordinator service is based on Ubernetes, an open source container cluster manager that is a federation of Kubernetes clusters. It is shown how, under reasonable constraints, it can reduce the projected datacenter’s carbon emissions growth by 22% from the currently reported consumption. We also suggest operating

School Nurse Workload.

Science.gov (United States)

Endsley, Patricia

2017-02-01

The purpose of this scoping review was to survey the most recent (5 years) acute care, community health, and mental health nursing workload literature to understand themes and research avenues that may be applicable to school nursing workload research. The search for empirical and nonempirical literature was conducted using search engines such as Google Scholar, PubMed, CINAHL, and Medline. Twenty-nine empirical studies and nine nonempirical articles were selected for inclusion. Themes that emerged consistent with school nurse practice include patient classification systems, environmental factors, assistive personnel, missed nursing care, and nurse satisfaction. School nursing is a public health discipline and population studies are an inherent research priority but may overlook workload variables at the clinical level. School nurses need a consistent method of population assessment, as well as evaluation of appropriate use of assistive personnel and school environment factors. Assessment of tasks not directly related to student care and professional development must also be considered in total workload.

The Dirac equation and its solutions

CERN Document Server

Bagrov, Vladislav G

2014-01-01

Dirac equations are of fundamental importance for relativistic quantum mechanics and quantum electrodynamics. In relativistic quantum mechanics, the Dirac equation is referred to as one-particle wave equation of motion for electron in an external electromagnetic field. In quantum electrodynamics, exact solutions of this equation are needed to treat the interaction between the electron and the external field exactly.In particular, all propagators of a particle, i.e., the various Green's functions, are constructed in a certain way by using exact solutions of the Dirac equation.

The Dirac equation and its solutions

International Nuclear Information System (INIS)

Bagrov, Vladislav G.; Gitman, Dmitry; P.N. Lebedev Physical Institute, Moscow; Tomsk State Univ., Tomsk

2013-01-01

The Dirac equation is of fundamental importance for relativistic quantum mechanics and quantum electrodynamics. In relativistic quantum mechanics, the Dirac equation is referred to as one-particle wave equation of motion for electron in an external electromagnetic field. In quantum electrodynamics, exact solutions of this equation are needed to treat the interaction between the electron and the external field exactly. In particular, all propagators of a particle, i.e., the various Green's functions, are constructed in a certain way by using exact solutions of the Dirac equation.

Superconductivity in doped Dirac semimetals

Science.gov (United States)

Hashimoto, Tatsuki; Kobayashi, Shingo; Tanaka, Yukio; Sato, Masatoshi

2016-07-01

We theoretically study intrinsic superconductivity in doped Dirac semimetals. Dirac semimetals host bulk Dirac points, which are formed by doubly degenerate bands, so the Hamiltonian is described by a 4 ×4 matrix and six types of k -independent pair potentials are allowed by the Fermi-Dirac statistics. We show that the unique spin-orbit coupling leads to characteristic superconducting gap structures and d vectors on the Fermi surface and the electron-electron interaction between intra and interorbitals gives a novel phase diagram of superconductivity. It is found that when the interorbital attraction is dominant, an unconventional superconducting state with point nodes appears. To verify the experimental signature of possible superconducting states, we calculate the temperature dependence of bulk physical properties such as electronic specific heat and spin susceptibility and surface state. In the unconventional superconducting phase, either dispersive or flat Andreev bound states appear between point nodes, which leads to double peaks or a single peak in the surface density of states, respectively. As a result, possible superconducting states can be distinguished by combining bulk and surface measurements.

Wigner function for the Dirac oscillator in spinor space

International Nuclear Information System (INIS)

Ma Kai; Wang Jianhua; Yuan Yi

2011-01-01

The Wigner function for the Dirac oscillator in spinor space is studied in this paper. Firstly, since the Dirac equation is described as a matrix equation in phase space, it is necessary to define the Wigner function as a matrix function in spinor space. Secondly, the matrix form of the Wigner function is proven to support the Dirac equation. Thirdly, by solving the Dirac equation, energy levels and the Wigner function for the Dirac oscillator in spinor space are obtained. (authors)

Designing workload analysis questionnaire to evaluate needs of employees

Science.gov (United States)

Astuti, Rahmaniyah Dwi; Navi, Muhammad Abdu Haq

2018-02-01

Incompatibility between workload with work capacity is one of main problem to make optimal result. In case at the office, there are constraints to determine workload because of non-repetitive works. Employees do work based on the targets set in a working period. At the end of the period is usually performed an evaluation of employees performance to evaluate needs of employees. The aims of this study to design a workload questionnaire tools to evaluate the efficiency level of position as indicator to determine needs of employees based on the Indonesian State Employment Agency Regulation on workload analysis. This research is applied to State-Owned Enterprise PT. X by determining 3 positions as a pilot project. Position A is held by 2 employees, position B is held by 7 employees, and position C is held by 6 employees. From the calculation result, position A has an efficiency level of 1,33 or "very good", position B has an efficiency level of 1.71 or "enough", and position C has an efficiency level of 1.03 or "very good". The application of this tools giving suggestion the needs of employees of position A is 3 people, position B is 5 people, and position C is 6 people. The difference between the number of employees and the calculation result is then analyzed by interviewing the employees to get more data about personal perception. It can be concluded that this workload evaluation tools can be used as an alternative solution to evaluate needs of employees in office.

The Dirac medals of the ICTP. 1993

International Nuclear Information System (INIS)

1995-01-01

The Dirac Medals of the International Centre for Theoretical Physics (ICTP) were instituted in 1985. These are awarded yearly to outstanding physicists, on Dirac's birthday - 8th August- for contributions to theoretical physics. The document includes the lectures of the three Dirac Medalists for 1993: Professor Sergio Ferrara, Professor Daniel Z. Freedman, and Professor Peter van Nieuwenhuizen. A separate abstract was prepared for each lecture

Counter-diabatic driving for Dirac dynamics

Science.gov (United States)

Fan, Qi-Zhen; Cheng, Xiao-Hang; Chen, Xi

2018-03-01

In this paper, we investigate the fast quantum control of Dirac equation dynamics by counter-diabatic driving, sharing the concept of shortcut to adiabaticity. We systematically calculate the counter-diabatic terms in different Dirac systems, like graphene and trapped ions. Specially, the fast and robust population inversion processes are achieved in Dirac system, taking into account the quantum simulation with trapped ions. In addition, the population transfer between two bands can be suppressed by counter-diabatic driving in graphene system, which might have potential applications in opt-electric devices.

The Dirac equation and its solutions

Energy Technology Data Exchange (ETDEWEB)

Bagrov, Vladislav G. [Tomsk State Univ., Tomsk (Russian Federation). Dept. of Quantum Field Theroy; Gitman, Dmitry [Sao Paulo Univ. (Brazil). Inst. de Fisica; P.N. Lebedev Physical Institute, Moscow (Russian Federation); Tomsk State Univ., Tomsk (Russian Federation). Faculty of Physics

2013-07-01

The Dirac equation is of fundamental importance for relativistic quantum mechanics and quantum electrodynamics. In relativistic quantum mechanics, the Dirac equation is referred to as one-particle wave equation of motion for electron in an external electromagnetic field. In quantum electrodynamics, exact solutions of this equation are needed to treat the interaction between the electron and the external field exactly. In particular, all propagators of a particle, i.e., the various Green's functions, are constructed in a certain way by using exact solutions of the Dirac equation.

New exact solutions of the Dirac equation. 8

International Nuclear Information System (INIS)

Bagrov, V.G.; Gitman, D.M.; Zadorozhnyj, V.N.; Sukhomlin, N.B.; Shapovalov, V.N.

1978-01-01

The paper continues the investigation into the exact solutions of the Dirac, Klein-Gordon, and Lorentz equations for a charge in an external electromagnetic field. The fields studied do not allow for separation of variables in the Dirac equation, but solutions to the Dirac equation are obtained

The time-of-flight detector of the DIRAC experiment

International Nuclear Information System (INIS)

Adeva, B.; Gallas, M.V.; Gomez, F.; Lopez-Agueera, A.; Nunez-Pardo, T.; Plo, M.; Rodriguez, A.M.; Rodriguez, X.M.; Saborido, J.J.; Santamarina, C.; Tobar, M.J.; Vazquez, P.

2002-01-01

The construction and performance of a large area time-of-flight detector for the DIRAC experiment at CERN is reported. With an average time resolution of 123 ps per counter at rates up to 1 MHz, it allows excellent separation of pπ - from π + π - pairs up to 4.6 GeV/c momentum, as well as of Coulomb-correlated pion pairs from accidentals. The optimization of scintillator material, photomultiplier performance and readout electronics is described

Shift scheduling model considering workload and worker’s preference for security department

Science.gov (United States)

Herawati, A.; Yuniartha, D. R.; Purnama, I. L. I.; Dewi, LT

2018-04-01

Security department operates for 24 hours and applies shift scheduling to organize its workers as well as in hotel industry. This research has been conducted to develop shift scheduling model considering the workers physical workload using rating of perceived exertion (RPE) Borg’s Scale and workers’ preference to accommodate schedule flexibility. The mathematic model is developed in integer linear programming and results optimal solution for simple problem. Resulting shift schedule of the developed model has equally distribution shift allocation among workers to balance the physical workload and give flexibility for workers in working hours arrangement.

The workload analysis in welding workshop

Science.gov (United States)

Wahyuni, D.; Budiman, I.; Tryana Sembiring, M.; Sitorus, E.; Nasution, H.

2018-03-01

This research was conducted in welding workshop which produces doors, fences, canopies, etc., according to customer’s order. The symptoms of excessive workload were seen from the fact of employees complaint, requisition for additional employees, the lateness of completion time (there were 11 times of lateness from 28 orders, and 7 customers gave complaints). The top management of the workshop assumes that employees’ workload was still a tolerable limit. Therefore, it was required workload analysis to determine the number of employees required. The Workload was measured by using a physiological method and workload analysis. The result of this research can be utilized by the workshop for a better workload management.

Strain engineering of Dirac cones in graphyne

Energy Technology Data Exchange (ETDEWEB)

Wang, Gaoxue; Kumar, Ashok; Pandey, Ravindra, E-mail: pandey@mtu.edu [Department of Physics, Michigan Technological University, Houghton, Michigan 49931 (United States); Si, Mingsu [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China)

2014-05-26

6,6,12-graphyne, one of the two-dimensional carbon allotropes with the rectangular lattice structure, has two kinds of non-equivalent anisotropic Dirac cones in the first Brillouin zone. We show that Dirac cones can be tuned independently by the uniaxial compressive strain applied to graphyne, which induces n-type and p-type self-doping effect, by shifting the energy of the Dirac cones in the opposite directions. On the other hand, application of the tensile strain results into a transition from gapless to finite gap system for the monolayer. For the AB-stacked bilayer, the results predict tunability of Dirac-cones by in-plane strains as well as the strain applied perpendicular to the plane. The group velocities of the Dirac cones show enhancement in the resistance anisotropy for bilayer relative to the case of monolayer. Such tunable and direction-dependent electronic properties predicted for 6,6,12-graphyne make it to be competitive for the next-generation electronic devices at nanoscale.

Semi-Dirac points in phononic crystals

KAUST Repository

Zhang, Xiujuan; Wu, Ying

2014-01-01

of rubber, in which the acoustic wave velocity is lower than that in water, the semi-Dirac dispersion can be characterized by an effective medium theory. The effective medium parameters link the semi-Dirac point to a topological transition in the iso

Dirac experiment

International Nuclear Information System (INIS)

Gomez, F.; Adeva, B.; Afanasev, L.; Benayoun, M.; Brekhovskikh, V.; Caragheorgheopol, G.; Cechak, T.; Chiba, M.; Constantinescu, S.; Doudarev, A.; Dreossi, D.; Drijard, D.; Ferro-Luzzi, M.; Gallas, M.V.; Gerndt, J.; Giacomich, R.; Gianotti, P.; Goldin, D.; Gorin, A.; Gortchakov, O.; Guaraldo, C.; Hansroul, M.; Hosek, R.; Iliescu, M.; Jabitski, M.; Kalinina, N.; Karpoukhine, V.; Kluson, J.; Kobayashi, M.; Kokkas, P.; Komarov, V.; Koulikov, A.; Kouptsov, A.; Krouglov, V.; Krouglova, L.; Kuroda, K.-I.; Lanaro, A.; Lapshine, V.; Lednicky, R.; Leruste, P.; Levisandri, P.; Lopez Aguera, A.; Lucherini, V.; Maki, T.; Manuilov, I.; Montanet, L.; Narjoux, J.-L.; Nemenov, L.; Nikitin, M.; Nunez Pardo, T.; Okada, K.; Olchevskii, V.; Pazos, A.; Pentia, M.; Penzo, A.; Perreau, J.-M.; Petrascu, C.; Plo, M.; Ponta, T.; Pop, D.; Riazantsev, A.; Rodriguez, J.M.; Rodriguez Fernandez, A.; Rykaline, V.; Santamarina, C.; Saborido, J.; Schacher, J.; Sidorov, A.; Smolik, J.; Takeutchi, F.; Tarasov, A.; Tauscher, L.; Tobar, M.J.; Trusov, S.; Vazquez, P.; Vlachos, S.; Yazkov, V.; Yoshimura, Y.; Zrelov, P.

2001-01-01

The main objective of DIRAC experiment is the measurement of the lifetime τ of the exotic hadronic atom consisting of π + and π - mesons. The lifetime of this atom is determined by the decay mode π + π - → π 0 π 0 due to the strong interaction. Through the precise relationship between the lifetime and the S-wave pion-pion scattering length difference |a 0 - a 2 | for isospin 0 and 2 (respectively), a measurement of τ with an accuracy of 10% will allow a determination of |a 0 - a 2 | at a 5% precision level. Pion-pion scattering lengths have been calculated in the framework of chiral perturbation theory with an accuracy below 5%. In this way DIRAC experiment will provide a crucial test of the chiral symmetry breaking scheme in QCD effective theories at low energies

Quantum geometry of the Dirac fermions

International Nuclear Information System (INIS)

Korchemskij, G.P.

1989-01-01

The bosonic path integral formalism is developed for Dirac fermions interacting with a nonabelian gauge field in the D-dimensional Euclidean space-time. The representation for the effective action and correlation functions of interacting fermions as sums over all bosonic paths on the complex projective space CP 2d-1 , (2d=2 [ D 2] is derived where all the spinor structure is absorbed by the one-dimensional Wess-Zumino term. It is the Wess-Zumino term that ensures all necessary properties of Dirac fermions under quantization. i.e., quantized values of the spin, Dirac equation, Fermi statistics. 19 refs

Scalar potentials and the Dirac equation

International Nuclear Information System (INIS)

Bergerhoff, B.; Soff, G.

1994-01-01

The Dirac equation is solved for various types of scalar potentials. Energy eigenvalues and normalized bound-state wave functions are calculated analytically for a scalar 1/r-potential as well as for a mixed scalar and Coulomb 1/r-potential. Also continuum wave functions for positive and negative energies are derived. Similarly, we investigate the solutions of the Dirac equation for a scalar square-well potential. Relativistic wave functions for scalar Yukawa and exponential potentials are determined numerically. Finally, we also discuss solutions of the Dirac equation for scalar linear and quadratic potentials which are frequently used to simulate quark confinement. (orig.)

Identifying Dirac cones in carbon allotropes with square symmetry

Energy Technology Data Exchange (ETDEWEB)

Wang, Jinying [College of Chemistry and Molecular Engineering, Peking University, Beijing 100871 (China); Huang, Huaqing; Duan, Wenhui [Department of Physics, Tsinghua University, Beijing 100084 (China); Liu, Zhirong, E-mail: LiuZhiRong@pku.edu.cn [College of Chemistry and Molecular Engineering, Peking University, Beijing 100871 (China); State Key Laboratory for Structural Chemistry of Unstable and Stable Species and Beijing National Laboratory for Molecular Sciences (BNLMS), Peking University, Beijing 100871 (China)

2013-11-14

A theoretical study is conducted to search for Dirac cones in two-dimensional carbon allotropes with square symmetry. By enumerating the carbon atoms in a unit cell up to 12, an allotrope with octatomic rings is recognized to possess Dirac cones under a simple tight-binding approach. The obtained Dirac cones are accompanied by flat bands at the Fermi level, and the resulting massless Dirac-Weyl fermions are chiral particles with a pseudospin of S = 1, rather than the conventional S = 1/2 of graphene. The spin-1 Dirac cones are also predicted to exist in hexagonal graphene antidot lattices.

Scaling deep learning workloads: NVIDIA DGX-1/Pascal and Intel Knights Landing

Energy Technology Data Exchange (ETDEWEB)

Gawande, Nitin A.; Landwehr, Joshua B.; Daily, Jeffrey A.; Tallent, Nathan R.; Vishnu, Abhinav; Kerbyson, Darren J.

2017-08-24

Deep Learning (DL) algorithms have become ubiquitous in data analytics. As a result, major computing vendors --- including NVIDIA, Intel, AMD, and IBM --- have architectural road-maps influenced by DL workloads. Furthermore, several vendors have recently advertised new computing products as accelerating large DL workloads. Unfortunately, it is difficult for data scientists to quantify the potential of these different products. This paper provides a performance and power analysis of important DL workloads on two major parallel architectures: NVIDIA DGX-1 (eight Pascal P100 GPUs interconnected with NVLink) and Intel Knights Landing (KNL) CPUs interconnected with Intel Omni-Path or Cray Aries. Our evaluation consists of a cross section of convolutional neural net workloads: CifarNet, AlexNet, GoogLeNet, and ResNet50 topologies using the Cifar10 and ImageNet datasets. The workloads are vendor-optimized for each architecture. Our analysis indicates that although GPUs provide the highest overall performance, the gap can close for some convolutional networks; and the KNL can be competitive in performance/watt. We find that NVLink facilitates scaling efficiency on GPUs. However, its importance is heavily dependent on neural network architecture. Furthermore, for weak-scaling --- sometimes encouraged by restricted GPU memory --- NVLink is less important.

Dirac equation in low dimensions: The factorization method

Energy Technology Data Exchange (ETDEWEB)

Sánchez-Monroy, J.A., E-mail: antosan@if.usp.br [Instituto de Física, Universidade de São Paulo, 05508-090, São Paulo, SP (Brazil); Quimbay, C.J., E-mail: cjquimbayh@unal.edu.co [Departamento de Física, Universidad Nacional de Colombia, Bogotá, D. C. (Colombia); CIF, Bogotá (Colombia)

2014-11-15

We present a general approach to solve the (1+1) and (2+1)-dimensional Dirac equations in the presence of static scalar, pseudoscalar and gauge potentials, for the case in which the potentials have the same functional form and thus the factorization method can be applied. We show that the presence of electric potentials in the Dirac equation leads to two Klein–Gordon equations including an energy-dependent potential. We then generalize the factorization method for the case of energy-dependent Hamiltonians. Additionally, the shape invariance is generalized for a specific class of energy-dependent Hamiltonians. We also present a condition for the absence of the Klein paradox (stability of the Dirac sea), showing how Dirac particles in low dimensions can be confined for a wide family of potentials. - Highlights: • The low-dimensional Dirac equation in the presence of static potentials is solved. • The factorization method is generalized for energy-dependent Hamiltonians. • The shape invariance is generalized for energy-dependent Hamiltonians. • The stability of the Dirac sea is related to the existence of supersymmetric partner Hamiltonians.

Dirac Magnons in Honeycomb Ferromagnets

Directory of Open Access Journals (Sweden)

Sergey S. Pershoguba

2018-01-01

Full Text Available The discovery of the Dirac electron dispersion in graphene [A. H. Castro Neto, et al., The Electronic Properties of Graphene, Rev. Mod. Phys. 81, 109 (2009RMPHAT0034-686110.1103/RevModPhys.81.109] led to the question of the Dirac cone stability with respect to interactions. Coulomb interactions between electrons were shown to induce a logarithmic renormalization of the Dirac dispersion. With a rapid expansion of the list of compounds and quasiparticle bands with linear band touching [T. O. Wehling, et al., Dirac Materials, Adv. Phys. 63, 1 (2014ADPHAH0001-873210.1080/00018732.2014.927109], the concept of bosonic Dirac materials has emerged. We consider a specific case of ferromagnets consisting of van der Waals-bonded stacks of honeycomb layers, e.g., chromium trihalides CrX_{3} (X=F, Cl, Br and I, that display two spin wave modes with energy dispersion similar to that for the electrons in graphene. At the single-particle level, these materials resemble their fermionic counterparts. However, how different particle statistics and interactions affect the stability of Dirac cones has yet to be determined. To address the role of interacting Dirac magnons, we expand the theory of ferromagnets beyond the standard Dyson theory [F. J. Dyson, General Theory of Spin-Wave Interactions, Phys. Rev. 102, 1217 (1956PHRVAO0031-899X10.1103/PhysRev.102.1217, F. J. Dyson, Thermodynamic Behavior of an Ideal Ferromagnet, Phys. Rev. 102, 1230 (1956PHRVAO0031-899X10.1103/PhysRev.102.1230] to the case of non-Bravais honeycomb layers. We demonstrate that magnon-magnon interactions lead to a significant momentum-dependent renormalization of the bare band structure in addition to strongly momentum-dependent magnon lifetimes. We show that our theory qualitatively accounts for hitherto unexplained anomalies in nearly half-century-old magnetic neutron-scattering data for CrBr_{3} [W. B. Yelon and R. Silberglitt, Renormalization of Large-Wave-Vector Magnons in

Dirac Magnons in Honeycomb Ferromagnets

Science.gov (United States)

Pershoguba, Sergey S.; Banerjee, Saikat; Lashley, J. C.; Park, Jihwey; Ågren, Hans; Aeppli, Gabriel; Balatsky, Alexander V.

2018-01-01

The discovery of the Dirac electron dispersion in graphene [A. H. Castro Neto, et al., The Electronic Properties of Graphene, Rev. Mod. Phys. 81, 109 (2009), 10.1103/RevModPhys.81.109] led to the question of the Dirac cone stability with respect to interactions. Coulomb interactions between electrons were shown to induce a logarithmic renormalization of the Dirac dispersion. With a rapid expansion of the list of compounds and quasiparticle bands with linear band touching [T. O. Wehling, et al., Dirac Materials, Adv. Phys. 63, 1 (2014), 10.1080/00018732.2014.927109], the concept of bosonic Dirac materials has emerged. We consider a specific case of ferromagnets consisting of van der Waals-bonded stacks of honeycomb layers, e.g., chromium trihalides CrX3 (X =F , Cl, Br and I), that display two spin wave modes with energy dispersion similar to that for the electrons in graphene. At the single-particle level, these materials resemble their fermionic counterparts. However, how different particle statistics and interactions affect the stability of Dirac cones has yet to be determined. To address the role of interacting Dirac magnons, we expand the theory of ferromagnets beyond the standard Dyson theory [F. J. Dyson, General Theory of Spin-Wave Interactions, Phys. Rev. 102, 1217 (1956), 10.1103/PhysRev.102.1217, F. J. Dyson, Thermodynamic Behavior of an Ideal Ferromagnet, Phys. Rev. 102, 1230 (1956), 10.1103/PhysRev.102.1230] to the case of non-Bravais honeycomb layers. We demonstrate that magnon-magnon interactions lead to a significant momentum-dependent renormalization of the bare band structure in addition to strongly momentum-dependent magnon lifetimes. We show that our theory qualitatively accounts for hitherto unexplained anomalies in nearly half-century-old magnetic neutron-scattering data for CrBr3 [W. B. Yelon and R. Silberglitt, Renormalization of Large-Wave-Vector Magnons in Ferromagnetic CrBr3 Studied by Inelastic Neutron Scattering: Spin-Wave Correlation

Dirac experiment

Energy Technology Data Exchange (ETDEWEB)

Gomez, F.; Adeva, B.; Afanasev, L.; Benayoun, M.; Brekhovskikh, V.; Caragheorgheopol, G.; Cechak, T.; Chiba, M.; Constantinescu, S.; Doudarev, A.; Dreossi, D.; Drijard, D.; Ferro-Luzzi, M.; Gallas, M.V.; Gerndt, J.; Giacomich, R.; Gianotti, P.; Goldin, D.; Gorin, A.; Gortchakov, O.; Guaraldo, C.; Hansroul, M.; Hosek, R.; Iliescu, M.; Jabitski, M.; Kalinina, N.; Karpoukhine, V.; Kluson, J.; Kobayashi, M.; Kokkas, P.; Komarov, V.; Koulikov, A.; Kouptsov, A.; Krouglov, V.; Krouglova, L.; Kuroda, K.-I.; Lanaro, A.; Lapshine, V.; Lednicky, R.; Leruste, P.; Levisandri, P.; Lopez Aguera, A.; Lucherini, V.; Maki, T.; Manuilov, I.; Montanet, L.; Narjoux, J.-L.; Nemenov, L.; Nikitin, M.; Nunez Pardo, T.; Okada, K.; Olchevskii, V.; Pazos, A.; Pentia, M.; Penzo, A.; Perreau, J.-M.; Petrascu, C.; Plo, M.; Ponta, T.; Pop, D.; Riazantsev, A.; Rodriguez, J.M.; Rodriguez Fernandez, A.; Rykaline, V.; Santamarina, C.; Saborido, J.; Schacher, J.; Sidorov, A.; Smolik, J.; Takeutchi, F.; Tarasov, A.; Tauscher, L.; Tobar, M.J.; Trusov, S.; Vazquez, P.; Vlachos, S.; Yazkov, V.; Yoshimura, Y.; Zrelov, P

2001-04-01

The main objective of DIRAC experiment is the measurement of the lifetime {tau} of the exotic hadronic atom consisting of {pi}{sup +} and {pi}{sup -} mesons. The lifetime of this atom is determined by the decay mode {pi}{sup +} {pi}{sup -} {yields} {pi}{sup 0} {pi}{sup 0} due to the strong interaction. Through the precise relationship between the lifetime and the S-wave pion-pion scattering length difference |a{sub 0} - a{sub 2}| for isospin 0 and 2 (respectively), a measurement of {tau} with an accuracy of 10% will allow a determination of |a{sub 0} - a{sub 2}| at a 5% precision level. Pion-pion scattering lengths have been calculated in the framework of chiral perturbation theory with an accuracy below 5%. In this way DIRAC experiment will provide a crucial test of the chiral symmetry breaking scheme in QCD effective theories at low energies.

Quasiparticle dynamics in reshaped helical Dirac cone of topological insulators.

Science.gov (United States)

Miao, Lin; Wang, Z F; Ming, Wenmei; Yao, Meng-Yu; Wang, Meixiao; Yang, Fang; Song, Y R; Zhu, Fengfeng; Fedorov, Alexei V; Sun, Z; Gao, C L; Liu, Canhua; Xue, Qi-Kun; Liu, Chao-Xing; Liu, Feng; Qian, Dong; Jia, Jin-Feng

2013-02-19

Topological insulators and graphene present two unique classes of materials, which are characterized by spin-polarized (helical) and nonpolarized Dirac cone band structures, respectively. The importance of many-body interactions that renormalize the linear bands near Dirac point in graphene has been well recognized and attracted much recent attention. However, renormalization of the helical Dirac point has not been observed in topological insulators. Here, we report the experimental observation of the renormalized quasiparticle spectrum with a skewed Dirac cone in a single Bi bilayer grown on Bi(2)Te(3) substrate from angle-resolved photoemission spectroscopy. First-principles band calculations indicate that the quasiparticle spectra are likely associated with the hybridization between the extrinsic substrate-induced Dirac states of Bi bilayer and the intrinsic surface Dirac states of Bi(2)Te(3) film at close energy proximity. Without such hybridization, only single-particle Dirac spectra are observed in a single Bi bilayer grown on Bi(2)Se(3), where the extrinsic Dirac states Bi bilayer and the intrinsic Dirac states of Bi(2)Se(3) are well separated in energy. The possible origins of many-body interactions are discussed. Our findings provide a means to manipulate topological surface states.

Memory and subjective workload assessment

Science.gov (United States)

Staveland, L.; Hart, S.; Yeh, Y. Y.

1986-01-01

Recent research suggested subjective introspection of workload is not based upon specific retrieval of information from long term memory, and only reflects the average workload that is imposed upon the human operator by a particular task. These findings are based upon global ratings of workload for the overall task, suggesting that subjective ratings are limited in ability to retrieve specific details of a task from long term memory. To clarify the limits memory imposes on subjective workload assessment, the difficulty of task segments was varied and the workload of specified segments was retrospectively rated. The ratings were retrospectively collected on the manipulations of three levels of segment difficulty. Subjects were assigned to one of two memory groups. In the Before group, subjects knew before performing a block of trials which segment to rate. In the After group, subjects did not know which segment to rate until after performing the block of trials. The subjective ratings, RTs (reaction times) and MTs (movement times) were compared within group, and between group differences. Performance measures and subjective evaluations of workload reflected the experimental manipulations. Subjects were sensitive to different difficulty levels, and recalled the average workload of task components. Cueing did not appear to help recall, and memory group differences possibly reflected variations in the groups of subjects, or an additional memory task.

Particles and Dirac-type operators on curved spaces

International Nuclear Information System (INIS)

Visinescu, Mihai

2003-01-01

We review the geodesic motion of pseudo-classical particles in curved spaces. Investigating the generalized Killing equations for spinning spaces, we express the constants of motion in terms of Killing-Yano tensors. Passing from the spinning spaces to the Dirac equation in curved backgrounds we point out the role of the Killing-Yano tensors in the construction of the Dirac-type operators. The general results are applied to the case of the four-dimensional Euclidean Taub-Newman-Unti-Tamburino space. From the covariantly constant Killing-Yano tensors of this space we construct three new Dirac-type operators which are equivalent with the standard Dirac operator. Finally the Runge-Lenz operator for the Dirac equation in this background is expressed in terms of the fourth Killing-Yano tensor which is not covariantly constant. As a rule the covariantly constant Killing-Yano tensors realize certain square roots of the metric tensor. Such a Killing-Yano tensor produces simultaneously a Dirac-type operator and the generator of a one-parameter Lie group connecting this operator with the standard Dirac one. On the other hand, the not covariantly constant Killing-Yano tensors are important in generating hidden symmetries. The presence of not covariantly constant Killing-Yano tensors implies the existence of non-standard supersymmetries in point particle theories on curved background. (author)

All-Metallic Vertical Transistors Based on Stacked Dirac Materials

OpenAIRE

Wang, Yangyang; Ni, Zeyuan; Liu, Qihang; Quhe, Ruge; Zheng, Jiaxin; Ye, Meng; Yu, Dapeng; Shi, Junjie; Yang, Jinbo; Lu, Jing

2014-01-01

It is an ongoing pursuit to use metal as a channel material in a field effect transistor. All metallic transistor can be fabricated from pristine semimetallic Dirac materials (such as graphene, silicene, and germanene), but the on/off current ratio is very low. In a vertical heterostructure composed by two Dirac materials, the Dirac cones of the two materials survive the weak interlayer van der Waals interaction based on density functional theory method, and electron transport from the Dirac ...

Multiplexing Low and High QoS Workloads in Virtual Environments

Science.gov (United States)

Verboven, Sam; Vanmechelen, Kurt; Broeckhove, Jan

Virtualization technology has introduced new ways for managing IT infrastructure. The flexible deployment of applications through self-contained virtual machine images has removed the barriers for multiplexing, suspending and migrating applications with their entire execution environment, allowing for a more efficient use of the infrastructure. These developments have given rise to an important challenge regarding the optimal scheduling of virtual machine workloads. In this paper, we specifically address the VM scheduling problem in which workloads that require guaranteed levels of CPU performance are mixed with workloads that do not require such guarantees. We introduce a framework to analyze this scheduling problem and evaluate to what extent such mixed service delivery is beneficial for a provider of virtualized IT infrastructure. Traditionally providers offer IT resources under a guaranteed and fixed performance profile, which can lead to underutilization. The findings of our simulation study show that through proper tuning of a limited set of parameters, the proposed scheduling algorithm allows for a significant increase in utilization without sacrificing on performance dependability.

Kondo effect in three-dimensional Dirac and Weyl systems

NARCIS (Netherlands)

Mitchell, Andrew K.; Fritz, Lars

2015-01-01

Magnetic impurities in three-dimensional Dirac and Weyl systems are shown to exhibit a fascinatingly diverse range of Kondo physics, with distinctive experimental spectroscopic signatures. When the Fermi level is precisely at the Dirac point, Dirac semimetals are in fact unlikely candidates for a

Dirac's equation and the nature of quantum field theory

International Nuclear Information System (INIS)

Plotnitsky, Arkady

2012-01-01

This paper re-examines the key aspects of Dirac's derivation of his relativistic equation for the electron in order advance our understanding of the nature of quantum field theory. Dirac's derivation, the paper argues, follows the key principles behind Heisenberg's discovery of quantum mechanics, which, the paper also argues, transformed the nature of both theoretical and experimental physics vis-à-vis classical physics and relativity. However, the limit theory (a crucial consideration for both Dirac and Heisenberg) in the case of Dirac's theory was quantum mechanics, specifically, Schrödinger's equation, while in the case of quantum mechanics, in Heisenberg's version, the limit theory was classical mechanics. Dirac had to find a new equation, Dirac's equation, along with a new type of quantum variables, while Heisenberg, to find new theory, was able to use the equations of classical physics, applied to different, quantum-mechanical variables. In this respect, Dirac's task was more similar to that of Schrödinger in his work on his version of quantum mechanics. Dirac's equation reflects a more complex character of quantum electrodynamics or quantum field theory in general and of the corresponding (high-energy) experimental quantum physics vis-à-vis that of quantum mechanics and the (low-energy) experimental quantum physics. The final section examines this greater complexity and its implications for fundamental physics.

Realization of non-symmorphic Dirac cones in PbFCl materials

Science.gov (United States)

Schoop, Leslie

While most 3D Dirac semimetals require two bands with different orbital character to be protected, there is also the possibility to find 3D Dirac semimetals that are guaranteed to exist in certain space groups. Those are resulting from the non-symmoprhic symmetry of the space group, which forces the bands to degenerate at high symmetry points in the Brillouin zone. Non-symmorphic space groups can force three- four, six and eight fold degeneracies which led to the proposal to find 3D Dirac Semimetals as well as new quasiparticles in such space groups. Problematic for realizing this types of Dirac materials is that they require and odd band filling in order to have the Fermi level located at or also near by the band crossing points. Therefore, although the first prediction for using non-symmoprhic symmetry to create a Dirac material was made in 2012, it took almost four years for an experimental verification of this type of Dirac crossing. In this talk I will introduce the material ZrSiS that has, besides other Dirac features, a Dirac cone protected by non-symmorphic symmetry at about 0.5 eV below the Fermi level and was the first material where this type of Dirac cone was imaged with ARPES. I will then proceed to discuss ways to shift this crossing to the Fermi edge and finally show an experimental verification of a fourfold Dirac crossing, protected by non-symmorphic symmetry, at the Fermi energy.

Electronic structure, Dirac points and Fermi arc surface states in three-dimensional Dirac semimetal Na3Bi from angle-resolved photoemission spectroscopy

International Nuclear Information System (INIS)

Liang Aiji; Chen Chaoyu; Wang Zhijun; Shi Youguo; Feng Ya; Yi Hemian; Xie Zhuojin; He Shaolong; He Junfeng; Peng Yingying; Liu Yan; Liu Defa; Hu Cheng; Zhao Lin; Liu Guodong; Dong Xiaoli; Zhang Jun; Nakatake, M; Iwasawa, H; Shimada, K

2016-01-01

The three-dimensional (3D) Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction band and valence band are connected. They have isolated 3D Dirac nodes in the whole Brillouin zone and can be viewed as a 3D counterpart of graphene. Recent theoretical calculations and experimental results indicate that the 3D Dirac semimetal state can be realized in a simple stoichiometric compound A 3 Bi ( A = Na, K, Rb). Here we report comprehensive high-resolution angle-resolved photoemission (ARPES) measurements on the two cleaved surfaces, (001) and (100), of Na 3 Bi. On the (001) surface, by comparison with theoretical calculations, we provide a proper assignment of the observed bands, and in particular, pinpoint the band that is responsible for the formation of the three-dimensional Dirac cones. We observe clear evidence of 3D Dirac cones in the three-dimensional momentum space by directly measuring on the k x – k y plane and by varying the photon energy to get access to different out-of-plane k z s. In addition, we reveal new features around the Brillouin zone corners that may be related with surface reconstruction. On the (100) surface, our ARPES measurements over a large momentum space raise an issue on the selection of the basic Brillouin zone in the (100) plane. We directly observe two isolated 3D Dirac nodes on the (100) surface. We observe the signature of the Fermi-arc surface states connecting the two 3D Dirac nodes that extend to a binding energy of ∼150 meV before merging into the bulk band. Our observations constitute strong evidence on the existence of the Dirac semimetal state in Na 3 Bi that are consistent with previous theoretical and experimental work. In addition, our results provide new information to clarify on the nature of the band that forms the 3D Dirac cones, on the possible formation of surface reconstruction of the (001) surface, and on the issue of basic Brillouin zone selection for the (100) surface. (rapid communication)

Spectrum of the Wilson Dirac operator at finite lattice spacings

DEFF Research Database (Denmark)

Akemann, G.; Damgaard, Poul Henrik; Splittorff, Kim

2011-01-01

We consider the effect of discretization errors on the microscopic spectrum of the Wilson Dirac operator using both chiral Perturbation Theory and chiral Random Matrix Theory. A graded chiral Lagrangian is used to evaluate the microscopic spectral density of the Hermitian Wilson Dirac operator...... as well as the distribution of the chirality over the real eigenvalues of the Wilson Dirac operator. It is shown that a chiral Random Matrix Theory for the Wilson Dirac operator reproduces the leading zero-momentum terms of Wilson chiral Perturbation Theory. All results are obtained for fixed index...... of the Wilson Dirac operator. The low-energy constants of Wilson chiral Perturbation theory are shown to be constrained by the Hermiticity properties of the Wilson Dirac operator....

Graphene Dirac point tuned by ferroelectric polarization field

Science.gov (United States)

Wang, Xudong; Chen, Yan; Wu, Guangjian; Wang, Jianlu; Tian, Bobo; Sun, Shuo; Shen, Hong; Lin, Tie; Hu, Weida; Kang, Tingting; Tang, Minghua; Xiao, Yongguang; Sun, Jinglan; Meng, Xiangjian; Chu, Junhao

2018-04-01

Graphene has received numerous attention for future nanoelectronics and optoelectronics. The Dirac point is a key parameter of graphene that provides information about its carrier properties. There are lots of methods to tune the Dirac point of graphene, such as chemical doping, impurities, defects, and disorder. In this study, we report a different approach to tune the Dirac point of graphene using a ferroelectric polarization field. The Dirac point can be adjusted to near the ferroelectric coercive voltage regardless its original position. We have ensured this phenomenon by temperature-dependent experiments, and analyzed its mechanism with the theory of impurity correlation in graphene. Additionally, with the modulation of ferroelectric polymer, the current on/off ratio and mobility of graphene transistor both have been improved. This work provides an effective method to tune the Dirac point of graphene, which can be readily used to configure functional devices such as p-n junctions and inverters.

Dirac and Weyl semimetals with holographic interactions

NARCIS (Netherlands)

Jacobs, V.P.J.

2015-01-01

Dirac and Weyl semimetals are states of matter exhibiting the relativistic physics of, respectively, the Dirac and Weyl equation in a three-dimensional bulk material. These three-dimensional semimetals have recently been realized experimentally in various crystals. Theoretically, especially the

Patient Safety Incidents and Nursing Workload

Directory of Open Access Journals (Sweden)

Katya Cuadros Carlesi

Full Text Available ABSTRACT Objective: to identify the relationship between the workload of the nursing team and the occurrence of patient safety incidents linked to nursing care in a public hospital in Chile. Method: quantitative, analytical, cross-sectional research through review of medical records. The estimation of workload in Intensive Care Units (ICUs was performed using the Therapeutic Interventions Scoring System (TISS-28 and for the other services, we used the nurse/patient and nursing assistant/patient ratios. Descriptive univariate and multivariate analysis were performed. For the multivariate analysis we used principal component analysis and Pearson correlation. Results: 879 post-discharge clinical records and the workload of 85 nurses and 157 nursing assistants were analyzed. The overall incident rate was 71.1%. It was found a high positive correlation between variables workload (r = 0.9611 to r = 0.9919 and rate of falls (r = 0.8770. The medication error rates, mechanical containment incidents and self-removal of invasive devices were not correlated with the workload. Conclusions: the workload was high in all units except the intermediate care unit. Only the rate of falls was associated with the workload.

New solitons connected to the Dirac equation

International Nuclear Information System (INIS)

Grosse, H.

1984-01-01

Imposing isospectral invariance for the one dimensional Dirac operator leads to systems of nonlinear partial differential equations. By constructing reflectionless potentials of the Dirac equation we obtain a new type of solitons for a system of modified Korteweg-de Vries equations. (Author)

Nonlinear Dirac Equations

Directory of Open Access Journals (Sweden)

Wei Khim Ng

2009-02-01

Full Text Available We construct nonlinear extensions of Dirac's relativistic electron equation that preserve its other desirable properties such as locality, separability, conservation of probability and Poincaré invariance. We determine the constraints that the nonlinear term must obey and classify the resultant non-polynomial nonlinearities in a double expansion in the degree of nonlinearity and number of derivatives. We give explicit examples of such nonlinear equations, studying their discrete symmetries and other properties. Motivated by some previously suggested applications we then consider nonlinear terms that simultaneously violate Lorentz covariance and again study various explicit examples. We contrast our equations and construction procedure with others in the literature and also show that our equations are not gauge equivalent to the linear Dirac equation. Finally we outline various physical applications for these equations.

Mental workload and cognitive task automaticity: an evaluation of subjective and time estimation metrics.

Science.gov (United States)

Liu, Y; Wickens, C D

1994-11-01

The evaluation of mental workload is becoming increasingly important in system design and analysis. The present study examined the structure and assessment of mental workload in performing decision and monitoring tasks by focusing on two mental workload measurements: subjective assessment and time estimation. The task required the assignment of a series of incoming customers to the shortest of three parallel service lines displayed on a computer monitor. The subject was either in charge of the customer assignment (manual mode) or was monitoring an automated system performing the same task (automatic mode). In both cases, the subjects were required to detect the non-optimal assignments that they or the computer had made. Time pressure was manipulated by the experimenter to create fast and slow conditions. The results revealed a multi-dimensional structure of mental workload and a multi-step process of subjective workload assessment. The results also indicated that subjective workload was more influenced by the subject's participatory mode than by the factor of task speed. The time estimation intervals produced while performing the decision and monitoring tasks had significantly greater length and larger variability than those produced while either performing no other tasks or performing a well practised customer assignment task. This result seemed to indicate that time estimation was sensitive to the presence of perceptual/cognitive demands, but not to response related activities to which behavioural automaticity has developed.

On Huygens' principle for Dirac operators associated to electromagnetic fields

Directory of Open Access Journals (Sweden)

CHALUB FABIO A.C.C.

2001-01-01

Full Text Available We study the behavior of massless Dirac particles, i.e., solutions of the Dirac equation with m = 0 in the presence of an electromagnetic field. Our main result (Theorem 1 is that for purely real or imaginary fields any Huygens type (in Hadamard's sense Dirac operators is equivalent to the free Dirac operator, equivalence given by changes of variables and multiplication (right and left by nonzero functions.

Particle creation and Dirac's large number hypothesis; and Reply

International Nuclear Information System (INIS)

Canuto, V.; Adams, P.J.; Hsieh, S.H.; Tsiang, E.; Steigman, G.

1976-01-01

The claim made by Steigman (Nature; 261:479 (1976)), that the creation of matter as postulated by Dirac (Proc. R. Soc.; A338:439 (1974)) is unnecessary, is here shown to be incorrect. It is stated that Steigman's claim that Dirac's large Number Hypothesis (LNH) does not require particle creation is wrong because he has assumed that which he was seeking to prove, that is that rho does not contain matter creation. Steigman's claim that Dirac's LNH leads to nonsensical results in the very early Universe is superficially correct, but this only supports Dirac's contention that the LNH may not be valid in the very early Universe. In a reply Steigman points out that in Dirac's original cosmology R approximately tsup(1/3) and using this model the results and conclusions of the present author's paper do apply but using a variation chosen by Canuto et al (T approximately t) Dirac's LNH cannot apply. Additionally it is observed that a cosmological theory which only predicts the present epoch is of questionable value. (U.K.)

Workload assessment for mental arithmetic tasks using the task-evoked pupillary response

NARCIS (Netherlands)

Marquart, G.; de Winter, J.C.F.

2015-01-01

Pupillometry is a promising method for assessing mental workload and could
be helpful in the optimization of systems that involve human–computer
interaction. The present study focuses on replicating the studies by Ahern
(1978) and Klingner (2010), which found that for three levels of

LHCb : The DIRAC Web Portal 2.0

CERN Multimedia

Mathe, Zoltan; Lazovsky, N; Stagni, Federico

2015-01-01

For many years the DIRAC interware (Distributed Infrastructure with Remote Agent Control) has had a web interface, allowing the users to monitor DIRAC activities and also interact with the system. Since then many new web technologies have emerged, therefore a redesign and a new implementation of the DIRAC Web portal were necessary, taking into account the lessons learnt using the old portal. These new technologies allowed to build a more compact and more responsive web interface that is robust and that enables users to have more control over the whole system while keeping a simple interface. The framework provides a large set of "applications", each of which can be used for interacting with various parts of the system. Communities can also create their own set of personalised web applications, and can easily extend already existing web applications with a minimal effort. Each user can configure and personalise the view for each application and save it using the DIRAC User Profile service as RESTful state prov...

Perceived Time as a Measure of Mental Workload

DEFF Research Database (Denmark)

Hertzum, Morten; Holmegaard, Kristin Due

2013-01-01

The mental workload imposed by systems is important to their operation and usability. Consequently, researchers and practitioners need reliable, valid, and easy-to-administer methods for measuring mental workload. The ratio of perceived time to clock time appears to be such a method, yet mental...... is a performance-related rather than task-related dimension of mental workload. We find a higher perceived time ratio for timed than untimed tasks. According to subjective workload ratings and pupil-diameter measurements the timed tasks impose higher mental workload. This finding contradicts the prospective...... paradigm, which asserts that perceived time decreases with increasing mental workload. We also find a higher perceived time ratio for solved than unsolved tasks, while subjective workload ratings indicate lower mental workload for the solved tasks. This finding shows that the relationship between...

Leptons as systems of Dirac particles

International Nuclear Information System (INIS)

Borstnik, N.M.; Kaluza, M.

1988-03-01

Charged leptons are treated as systems of three equal independent Dirac particles in an external static effective potential which has a vector and a scalar term. The potential is constructed to reproduce the experimental mass spectrum of the charged leptons. The Dirac covariant equation for three interacting particles is discussed in order to comment on the magnetic moment of leptons. (author). 9 refs, 2 figs, 4 tabs

Axial anomaly and index theorem for Dirac-Kaehler fermions

International Nuclear Information System (INIS)

Fonseca Junior, C.A.L. da.

1985-02-01

Some aspects of topological influence on gauge field theory are analysed, considering the geometry and differential topology methods. A review of concepts of differential forms, fibered spaces, connection and curvature, showing an interpretation of gauge theory in this context, is presented. The question of fermions, analysing in details the Dirac-Kaehler which fermionic particle is considered a general differential form, is studied. It is shown how the explicit expressions in function of the Dirac spinor components vary with the Dirac matrix representation. The Dirac-Kahler equation contains 4 times (in 4 dimensions) the Dirac equation, each particle being associated an ideal at left of the algebra of general differential forms. These ideals and the SU(4) symmetry among them are also studied on the point of view of spinors and, the group of reduction to one of the ideals is identified as the Cartan subalgebra of this SU(4). Finally, the axial anomaly is calculated through the functional determinant given by the Dirac-Kaehler operator. The regularization method is the Seeley's coefficients. From that results a comparison of the index theorems for the twisted complexes of signature and spin, which proportionality is given by the number of the algebra ideals contained in the Dirac-Kaehler equation and which also manifests in the respective axial anomaly equations. (L.C.) [pt

Psychological workload and body weight

DEFF Research Database (Denmark)

Overgaard, Dorthe; Gyntelberg, Finn; Heitmann, Berit L

2004-01-01

on the association between obesity and psychological workload. METHOD: We carried out a review of the associations between psychological workload and body weight in men and women. In total, 10 cross-sectional studies were identified. RESULTS: The review showed little evidence of a general association between...... adjustment for education. For women, there was no evidence of a consistent association. CONCLUSION: The reviewed articles were not supportive of any associations between psychological workload and either general or abdominal obesity. Future epidemiological studies in this field should be prospective......BACKGROUND: According to Karasek's Demand/Control Model, workload can be conceptualized as job strain, a combination of psychological job demands and control in the job. High job strain may result from high job demands combined with low job control. Aim To give an overview of the literature...

Three Dirac neutrinos

International Nuclear Information System (INIS)

Joshipura, A.S.; Rindani, S.D.

1991-01-01

The consequences of imposing an exact L e +L τ -L μ symmetry on a 6x6 matrix describing neutrino masses are discussed. The presence of right-handed neutrinos avoids the need of introducing any SU(2) Higgs triplet. Hence the conflict with the CERN LEP data on the Z width found in earlier models with L e +L τ -L μ symmetry is avoided. The L e +L τ -L μ symmetry provides an interesting realization of a recent proposal of Glashow to accommodate the 17-keV Dirac neutrino in the SU(2)xU(1) theory. All the neutrinos in this model are Dirac particles. The solar-neutrino problem can be solved in an extension of the model which generates a large (∼10 -11 μ B ) magnetic moment for the electron neutrino

Preparing the Gaudi framework and the DIRAC WMS for multicore job submission

International Nuclear Information System (INIS)

Rauschmayr, N; Streit, A

2014-01-01

HEP applications need to adapt to the continuously increasing number of cores on modern CPUs. This must be done at different levels: the software must support parallelization, and the scheduling has to differ between multicore and singlecore jobs. The LHCb software framework (GAUDI) provides a parallel prototype (GaudiMP), based on the multiprocessing approach. It allows a reduction of the overall memory footprint and a coordinated access to data via separated reader and writer processes. A comparison between the parallel prototype and multiple independent Gaudi jobs in respect of CPU time and memory consumption will be shown. Furthermore, speedup must be predicted in order to find the limit beyond which the parallel prototype (GaudiMP) does not bring further scaling. This number must be known as it indicates the point, where new technologies must be introduced into the software framework. In order to reach further improvements in the overall throughput, scheduling strategies for mixing parallel jobs can be applied. It allows overcoming limitations in the speedup of the parallel prototype. Those changes require modifications at the level of the Workload Management System (DIRAC).

Dirac cones beyond the honeycomb lattice : a symmetry based approach

NARCIS (Netherlands)

Miert, G. van; de Morais Smith, Cristiane

2016-01-01

Recently, several new materials exhibiting massless Dirac fermions have been proposed. However, many of these do not have the typical graphene honeycomb lattice, which is often associated with Dirac cones. Here, we present a classification of these different two-dimensional Dirac systems based on

Double Dirac Point Semimetal in Two-Dimensional Material: Ta2Se3

OpenAIRE

Ma, Yandong; Jing, Yu; Heine, Thomas

2017-01-01

Here, we report by first-principles calculations one new stable 2D Dirac material, Ta2Se3 monolayer. For this system, stable layered bulk phase exists, and exfoliation should be possible. Ta2Se3 monolayer is demonstrated to support two Dirac points close to the Fermi level, achieving the exotic 2D double Dirac semimetal. And like 2D single Dirac and 2D node-line semimetals, spin-orbit coupling could introduce an insulating state in this new class of 2D Dirac semimetals. Moreover, the Dirac fe...

Effects of work zone configurations and traffic density on performance variables and subjective workload.

Science.gov (United States)

Shakouri, Mahmoud; Ikuma, Laura H; Aghazadeh, Fereydoun; Punniaraj, Karthy; Ishak, Sherif

2014-10-01

This paper investigates the effect of changing work zone configurations and traffic density on performance variables and subjective workload. Data regarding travel time, average speed, maximum percent braking force and location of lane changes were collected by using a full size driving simulator. The NASA-TLX was used to measure self-reported workload ratings during the driving task. Conventional lane merge (CLM) and joint lane merge (JLM) were modeled in a driving simulator, and thirty participants (seven female and 23 male), navigated through the two configurations with two levels of traffic density. The mean maximum braking forces was 34% lower in the JLM configuration, and drivers going through the JLM configuration remained in the closed lane longer. However, no significant differences in speed were found between the two merge configurations. The analysis of self-reported workload ratings show that participants reported 15.3% lower total workload when driving through the JLM. In conclusion, the implemented changes in the JLM make it a more favorable merge configuration in both high and low traffic densities in terms of optimizing traffic flow by increasing the time and distance cars use both lanes, and in terms of improving safety due to lower braking forces and lower reported workload. Copyright © 2014 Elsevier Ltd. All rights reserved.

EEG correlates of task engagement and mental workload in vigilance, learning, and memory tasks.

Science.gov (United States)

Berka, Chris; Levendowski, Daniel J; Lumicao, Michelle N; Yau, Alan; Davis, Gene; Zivkovic, Vladimir T; Olmstead, Richard E; Tremoulet, Patrice D; Craven, Patrick L

2007-05-01

The ability to continuously and unobtrusively monitor levels of task engagement and mental workload in an operational environment could be useful in identifying more accurate and efficient methods for humans to interact with technology. This information could also be used to optimize the design of safer, more efficient work environments that increase motivation and productivity. The present study explored the feasibility of monitoring electroencephalo-graphic (EEG) indices of engagement and workload acquired unobtrusively and quantified during performance of cognitive tests. EEG was acquired from 80 healthy participants with a wireless sensor headset (F3-F4,C3-C4,Cz-POz,F3-Cz,Fz-C3,Fz-POz) during tasks including: multi-level forward/backward-digit-span, grid-recall, trails, mental-addition, 20-min 3-Choice Vigilance, and image-learning and memory tests. EEG metrics for engagement and workload were calculated for each 1 -s of EEG. Across participants, engagement but not workload decreased over the 20-min vigilance test. Engagement and workload were significantly increased during the encoding period of verbal and image-learning and memory tests when compared with the recognition/ recall period. Workload but not engagement increased linearly as level of difficulty increased in forward and backward-digit-span, grid-recall, and mental-addition tests. EEG measures correlated with both subjective and objective performance metrics. These data in combination with previous studies suggest that EEG engagement reflects information-gathering, visual processing, and allocation of attention. EEG workload increases with increasing working memory load and during problem solving, integration of information, analytical reasoning, and may be more reflective of executive functions. Inspection of EEG on a second-by-second timescale revealed associations between workload and engagement levels when aligned with specific task events providing preliminary evidence that second

The DIRAC Data Management System and the Gaudi dataset federation

CERN Document Server

Haen, Christophe; Frank, Markus; Tsaregorodtsev, Andrei

2015-01-01

The DIRAC Interware provides a development framework and a complete set of components for building distributed computing systems. The DIRAC Data Management System (DMS) offers all the necessary tools to ensure data handling operations for small and large user communities. It supports transparent access to storage resources based on multiple technologies, and is easily expandable. The information on data files and replicas is kept in a File Catalog of which DIRAC offers a powerful and versatile implementation (DFC). Data movement can be performed using third party services including FTS3. Bulk data operations are resilient with respect to failures due to the use of the Request Management System (RMS) that keeps track of ongoing tasks.In this contribution we will present an overview of the DIRAC DMS capabilities and its connection with other DIRAC subsystems such as the Transformation System. This paper also focuses on the DIRAC File Catalog, for which a lot of new developments have been carried out, so that LH...

Pilot Workload and Speech Analysis: A Preliminary Investigation

Science.gov (United States)

Bittner, Rachel M.; Begault, Durand R.; Christopher, Bonny R.

2013-01-01

Prior research has questioned the effectiveness of speech analysis to measure the stress, workload, truthfulness, or emotional state of a talker. The question remains regarding the utility of speech analysis for restricted vocabularies such as those used in aviation communications. A part-task experiment was conducted in which participants performed Air Traffic Control read-backs in different workload environments. Participant's subjective workload and the speech qualities of fundamental frequency (F0) and articulation rate were evaluated. A significant increase in subjective workload rating was found for high workload segments. F0 was found to be significantly higher during high workload while articulation rates were found to be significantly slower. No correlation was found to exist between subjective workload and F0 or articulation rate.

Workload modelling for data-intensive systems

CERN Document Server

Lassnig, Mario

This thesis presents a comprehensive study built upon the requirements of a global data-intensive system, built for the ATLAS Experiment at CERN's Large Hadron Collider. First, a scalable method is described to capture distributed data management operations in a non-intrusive way. These operations are collected into a globally synchronised sequence of events, the workload. A comparative analysis of this new data-intensive workload against existing computational workloads is conducted, leading to the discovery of the importance of descriptive attributes in the operations. Existing computational workload models only consider the arrival rates of operations, however, in data-intensive systems the correlations between attributes play a central role. Furthermore, the detrimental effect of rapid correlated arrivals, so called bursts, is assessed. A model is proposed that can learn burst behaviour from captured workload, and in turn forecast potential future bursts. To help with the creation of a full representative...

Effects of acceleration through the Dirac sea

International Nuclear Information System (INIS)

Hacyan, S.

1986-01-01

The effects of acceleration through massive scalar and spin-1/2 fields are investigated. It is shown that the density-of-states factor in a uniformly accelerated frame takes a complicated form, but the energy spectrum exhibits a Bose-Einstein or Fermi-Dirac distribution function. In particular, the Dirac sea shows thermal-like effects

Data acquisition software for DIRAC experiment

International Nuclear Information System (INIS)

Ol'shevskij, V.G.; Trusov, S.V.

2000-01-01

The structure and basic processes of data acquisition software of DIRAC experiment for the measurement of π + π - atom life-time are described. The experiment is running on PS accelerator of CERN. The developed software allows one to accept, record and distribute to consumers up to 3 Mbytes of data in one accelerator supercycle of 14.4 s duration. The described system is used successfully in the DIRAC experiment starting from 1998 year

Time-dependent massless Dirac fermions in graphene

Energy Technology Data Exchange (ETDEWEB)

Khantoul, Boubakeur, E-mail: bobphys@gmail.com [Department of Mathematics, City University London, Northampton Square, London EC1V 0HB (United Kingdom); Department of Physics, University of Jijel, BP 98, Ouled Aissa, 18000 Jijel (Algeria); Fring, Andreas, E-mail: a.fring@city.ac.uk [Department of Mathematics, City University London, Northampton Square, London EC1V 0HB (United Kingdom)

2015-10-30

Using the Lewis–Riesenfeld method of invariants we construct explicit analytical solutions for the massless Dirac equation in 2+1 dimensions describing quasi-particles in graphene. The Hamiltonian of the system considered contains some explicit time-dependence in addition to one resulting from being minimally coupled to a time-dependent vector potential. The eigenvalue equations for the two spinor components of the Lewis–Riesenfeld invariant are found to decouple into a pair of supersymmetric invariants in a similar fashion as the known decoupling for the time-independent Dirac Hamiltonians. - Highlights: • An explicit analytical solution for a massless 2+1 dimensional time-dependent Dirac equation is found. • All steps of the Lewis–Riesenfeld method have been carried out.

Maxwell-Like Equations for Free Dirac Electrons

Science.gov (United States)

Bruce, S. A.

2018-03-01

In this article, we show that the wave equation for a free Dirac electron can be represented in a form that is analogous to Maxwell's electrodynamics. The electron bispinor wavefunction is explicitly expressed in terms of its real and imaginary components. This leads us to incorporate into it appropriate scalar and pseudo-scalar fields in advance, so that a full symmetry may be accomplished. The Dirac equation then takes on a form similar to that of a set of inhomogeneous Maxwell's equations involving a particular self-source. We relate plane wave solutions of these equations to waves corresponding to free Dirac electrons, identifying the longitudinal component of the electron motion, together with the corresponding Zitterbewegung ("trembling motion").

Multi-component bi-Hamiltonian Dirac integrable equations

Energy Technology Data Exchange (ETDEWEB)

Ma Wenxiu [Department of Mathematics and Statistics, University of South Florida, Tampa, FL 33620-5700 (United States)], E-mail: mawx@math.usf.edu

2009-01-15

A specific matrix iso-spectral problem of arbitrary order is introduced and an associated hierarchy of multi-component Dirac integrable equations is constructed within the framework of zero curvature equations. The bi-Hamiltonian structure of the obtained Dirac hierarchy is presented be means of the variational trace identity. Two examples in the cases of lower order are computed.

The Dirac equation in classical statistical mechanics

International Nuclear Information System (INIS)

Ord, G.N.

2002-01-01

The Dirac equation, usually obtained by 'quantizing' a classical stochastic model is here obtained directly within classical statistical mechanics. The special underlying space-time geometry of the random walk replaces the missing analytic continuation, making the model 'self-quantizing'. This provides a new context for the Dirac equation, distinct from its usual context in relativistic quantum mechanics

The Lorentz-Dirac equation in light of quantum theory

International Nuclear Information System (INIS)

Nikishov, A.I.

1996-01-01

To high accuracy, an electron in ultrarelativistic motion 'sees' an external field in its rest frame as a crossed field (E=H, E·H=0). In this case, quantum expressions allow the introduction of a local intensity of the radiation, which determines the radiative term of the force of radiative reaction. For γ=(1-v2)-1/2>> 1 this term is much larger than the mass term, i.e., the term with xd3do. Under these conditions, the reduced Lorentz-Dirac equation, which is obtained from the full Lorentz-Dirac equation by eliminating the terms xd3do and xe on the right side using the equation of motion without taking into account the force of radiative reaction, is equivalent to good accuracy to the original Lorentz-Dirac equation. Exact solutions to the reduced Lorentz-Dirac equation are obtained for a constant field and the field of a plane wave. For γ∼1 a local expression for the radiative term cannot be obtained quantitatively from the quantum expressions. In this case the mass (Lorentz-Dirac) terms in the original and reduced Lorentz-Dirac equations are not small compared to the radiative term. The predictions of these equations, which depend appreciably on the mass terms, are therefore less reliable

Profiling, analisi delle prestazioni e proposte per l'ottimizzazione del RDBMS MySQL utilizzato dal progetto DIRAC/LHCbDIRAC

CERN Document Server

Mesin, Alberto

Il lavoro presentato in questa tesi riguarda lo studio, l'analisi e la formula- zione di proposte per il miglioramento del database di back-end del progetto DIRAC/LHCbDIRAC. LHCbDIRAC, basato su DIRAC, e il sistema di sot- tomissione per l'accesso all'infrastruttura distribuita Grid per l'esperimento LHCb del CERN. Ad esso e adata la gestione dei job di Produzione, Mer- ge, Ricostruzione degli Eventi e Analisi per i dati sperimentali e simulati. Il sistema utilizza un RDBMS MySQL per la gestione di numerosi databa- se. La volonta di passare ad un motore relazionale e transazionale per la denizione schemi e la possibilita che, in un recente futuro, il DBMS possa rappresentare un serio limite alle prestazioni del sistema stesso hanno reso necessario questo studio. Il lavoro svolto si e concentrato sul proling di un singolo schema relazionale per il quale sono stati utilizzati metodi di analisi e fornite soluzioni ai problemi riscontrati il quanto piu possibile generali e per tanto validi per l'intero sistema. L...

Patient Safety Incidents and Nursing Workload 1

Science.gov (United States)

Carlesi, Katya Cuadros; Padilha, Kátia Grillo; Toffoletto, Maria Cecília; Henriquez-Roldán, Carlos; Juan, Monica Andrea Canales

2017-01-01

ABSTRACT Objective: to identify the relationship between the workload of the nursing team and the occurrence of patient safety incidents linked to nursing care in a public hospital in Chile. Method: quantitative, analytical, cross-sectional research through review of medical records. The estimation of workload in Intensive Care Units (ICUs) was performed using the Therapeutic Interventions Scoring System (TISS-28) and for the other services, we used the nurse/patient and nursing assistant/patient ratios. Descriptive univariate and multivariate analysis were performed. For the multivariate analysis we used principal component analysis and Pearson correlation. Results: 879 post-discharge clinical records and the workload of 85 nurses and 157 nursing assistants were analyzed. The overall incident rate was 71.1%. It was found a high positive correlation between variables workload (r = 0.9611 to r = 0.9919) and rate of falls (r = 0.8770). The medication error rates, mechanical containment incidents and self-removal of invasive devices were not correlated with the workload. Conclusions: the workload was high in all units except the intermediate care unit. Only the rate of falls was associated with the workload. PMID:28403334

Wave Functions for Time-Dependent Dirac Equation under GUP

Science.gov (United States)

Zhang, Meng-Yao; Long, Chao-Yun; Long, Zheng-Wen

2018-04-01

In this work, the time-dependent Dirac equation is investigated under generalized uncertainty principle (GUP) framework. It is possible to construct the exact solutions of Dirac equation when the time-dependent potentials satisfied the proper conditions. In (1+1) dimensions, the analytical wave functions of the Dirac equation under GUP have been obtained for the two kinds time-dependent potentials. Supported by the National Natural Science Foundation of China under Grant No. 11565009

Using OSG Computing Resources with (iLC)Dirac

CERN Document Server

AUTHOR|(SzGeCERN)683529; Petric, Marko

2017-01-01

CPU cycles for small experiments and projects can be scarce, thus making use of all available resources, whether dedicated or opportunistic, is mandatory. While enabling uniform access to the LCG computing elements (ARC, CREAM), the DIRAC grid interware was not able to use OSG computing elements (GlobusCE, HTCondor-CE) without dedicated support at the grid site through so called 'SiteDirectors', which directly submit to the local batch system. This in turn requires additional dedicated effort for small experiments on the grid site. Adding interfaces to the OSG CEs through the respective grid middleware is therefore allowing accessing them within the DIRAC software without additional sitespecific infrastructure. This enables greater use of opportunistic resources for experiments and projects without dedicated clusters or an established computing infrastructure with the DIRAC software. To allow sending jobs to HTCondor-CE and legacy Globus computing elements inside DIRAC the required wrapper classes were develo...

Deuteron stripping reactions using dirac phenomenology

Science.gov (United States)

Hawk, E. A.; McNeil, J. A.

2001-04-01

In this work deuteron stripping reactions are studied using the distorted wave born approximation employing dirac phenomenological potentials. In 1982 Shepard and Rost performed zero-range dirac phenomenological stripping calculations and found a dramatic reduction in the predicted cross sections when compared with similar nonrelativistic calculations. We extend the earlier work by including full finite range effects as well as the deuteron's internal D-state. Results will be compared with traditional nonrelativistic approaches and experimental data at low energy.

Lie algebras for the Dirac-Clifford ring

International Nuclear Information System (INIS)

Mignaco, J.A.; Linhares, C.A.

1992-01-01

It is shown in a general way that the Dirac-Clifford ring formed by the Dirac matrices and all their products, for all even and odd spacetime dimensions D, span the cumulation algebras SU(2 D/2 ) for even D and SU(2 (D- 1 )/2 ) + SU(2 (D-1)/2 ) for odd D. Some physical consequences of these results are discussed. (author)

Dirac operator on spaces with conical singularities

International Nuclear Information System (INIS)

Chou, A.W.

1982-01-01

The Dirac operator on compact spaces with conical singularities is studied via the separation of variables formula and the functional calculus of the Dirac Laplacian on the cone. A Bochner type vanishing theorem which gives topological obstructions to the existence of non-negative scalar curvature k greater than or equal to 0 in the singular case is proved. An index formula relating the index of the Dirac operator to the A-genus and Eta-invariant similar to that of Atiyah-Patodi-Singer is obtained. In an appendix, manifolds with boundary with non-negative scalar curvature k greater than or equal to 0 are studied, and several new results on constructing complete metrics with k greater than or equal to on them are obtained

Dirac vacuum: Acceleration and external-field effects

International Nuclear Information System (INIS)

Jauregui, R.; Torres, M.; Hacyan, S.

1991-01-01

The quantization of the massive spin-1/2 field in Rindler coordinates is considered, including the effects of a background magnetic field. We calculate the expectation values of conserved quantities such as the stress-energy tensor, current density, and spin distribution, as detected by an accelerated observer. The ratio of the energy and particle densities is given by a Fermi-Dirac distribution, but the spectrum of these quantities takes in general a complicated form that cannot be simply interpreted as a thermal spectrum. For the free-particle case the spectrum of the energy-stress tensor has a Fermi-Dirac form only in the massless limit. In the presence of the magnetic field the Dirac vacuum is magnetized and exhibits plasmalike properties

Hawking radiation of Dirac particles in the hot NUT-Kerr-Newman spacetime

International Nuclear Information System (INIS)

Ahmed, M.

1991-01-01

The Hawking radiation of charged Dirac particles on the horizons of the hot NUT-Kerr-Newman spacetime is studied in this paper. To this end, we obtain the radial decoupled Dirac equation for the electron in the hot NUT-Kerr-Newman spacetime. Next we solve the Dirac equation near the horizons. Finally, by analytic continuation, the Hawking thermal spectrum formula of Dirac particles is obtained. The problem of the Hawking evaporation of Dirac particles in the hot NUT-Kerr-Newman background is thus solved. (orig.)

Optical analogue of relativistic Dirac solitons in binary waveguide arrays

Energy Technology Data Exchange (ETDEWEB)

Tran, Truong X., E-mail: truong.tran@mpl.mpg.de [Department of Physics, Le Quy Don University, 236 Hoang Quoc Viet str., 10000 Hanoi (Viet Nam); Max Planck Institute for the Science of Light, Günther-Scharowsky str. 1, 91058 Erlangen (Germany); Longhi, Stefano [Department of Physics, Politecnico di Milano and Istituto di Fotonica e Nanotecnologie del Consiglio Nazionale delle Ricerche, Piazza L. da Vinci 32, I-20133 Milano (Italy); Biancalana, Fabio [Max Planck Institute for the Science of Light, Günther-Scharowsky str. 1, 91058 Erlangen (Germany); School of Engineering and Physical Sciences, Heriot-Watt University, EH14 4AS Edinburgh (United Kingdom)

2014-01-15

We study analytically and numerically an optical analogue of Dirac solitons in binary waveguide arrays in the presence of Kerr nonlinearity. Pseudo-relativistic soliton solutions of the coupled-mode equations describing dynamics in the array are analytically derived. We demonstrate that with the found soliton solutions, the coupled mode equations can be converted into the nonlinear relativistic 1D Dirac equation. This paves the way for using binary waveguide arrays as a classical simulator of quantum nonlinear effects arising from the Dirac equation, something that is thought to be impossible to achieve in conventional (i.e. linear) quantum field theory. -- Highlights: •An optical analogue of Dirac solitons in nonlinear binary waveguide arrays is suggested. •Analytical solutions to pseudo-relativistic solitons are presented. •A correspondence of optical coupled-mode equations with the nonlinear relativistic Dirac equation is established.

Workload Control with Continuous Release

NARCIS (Netherlands)

Phan, B. S. Nguyen; Land, M. J.; Gaalman, G. J. C.

2009-01-01

Workload Control (WLC) is a production planning and control concept which is suitable for the needs of make-to-order job shops. Release decisions based on the workload norms form the core of the concept. This paper develops continuous time WLC release variants and investigates their due date

Combining Quick-Turnaround and Batch Workloads at Scale

Science.gov (United States)

Matthews, Gregory A.

2012-01-01

NAS uses PBS Professional to schedule and manage the workload on Pleiades, an 11,000+ node 1B cluster. At this scale the user experience for quick-turnaround jobs can degrade, which led NAS initially to set up two separate PBS servers, each dedicated to a particular workload. Recently we have employed PBS hooks and scheduler modifications to merge these workloads together under one PBS server, delivering sub-1-minute start times for the quick-turnaround workload, and enabling dynamic management of the resources set aside for that workload.

Dirac Mass Dynamics in Multidimensional Nonlocal Parabolic Equations

KAUST Repository

Lorz, Alexander

2011-01-17

Nonlocal Lotka-Volterra models have the property that solutions concentrate as Dirac masses in the limit of small diffusion. Is it possible to describe the dynamics of the limiting concentration points and of the weights of the Dirac masses? What is the long time asymptotics of these Dirac masses? Can several Dirac masses coexist? We will explain how these questions relate to the so-called "constrained Hamilton-Jacobi equation" and how a form of canonical equation can be established. This equation has been established assuming smoothness. Here we build a framework where smooth solutions exist and thus the full theory can be developed rigorously. We also show that our form of canonical equation comes with a kind of Lyapunov functional. Numerical simulations show that the trajectories can exhibit unexpected dynamics well explained by this equation. Our motivation comes from population adaptive evolution a branch of mathematical ecology which models Darwinian evolution. © Taylor & Francis Group, LLC.

Mental workload during brain-computer interface training.

Science.gov (United States)

Felton, Elizabeth A; Williams, Justin C; Vanderheiden, Gregg C; Radwin, Robert G

2012-01-01

It is not well understood how people perceive the difficulty of performing brain-computer interface (BCI) tasks, which specific aspects of mental workload contribute the most, and whether there is a difference in perceived workload between participants who are able-bodied and disabled. This study evaluated mental workload using the NASA Task Load Index (TLX), a multi-dimensional rating procedure with six subscales: Mental Demands, Physical Demands, Temporal Demands, Performance, Effort, and Frustration. Able-bodied and motor disabled participants completed the survey after performing EEG-based BCI Fitts' law target acquisition and phrase spelling tasks. The NASA-TLX scores were similar for able-bodied and disabled participants. For example, overall workload scores (range 0-100) for 1D horizontal tasks were 48.5 (SD = 17.7) and 46.6 (SD 10.3), respectively. The TLX can be used to inform the design of BCIs that will have greater usability by evaluating subjective workload between BCI tasks, participant groups, and control modalities. Mental workload of brain-computer interfaces (BCI) can be evaluated with the NASA Task Load Index (TLX). The TLX is an effective tool for comparing subjective workload between BCI tasks, participant groups (able-bodied and disabled), and control modalities. The data can inform the design of BCIs that will have greater usability.

LHCb: Monitoring the DIRAC Distribution System

CERN Multimedia

Nandakumar, R; Santinelli, R

2009-01-01

DIRAC is the LHCb gateway to any computing grid infrastructure (currently supporting WLCG) and is intended to reliably run large data mining activities. The DIRAC system consists of various services (which wait to be contacted to perform actions) and agents (which carry out periodic activities) to direct jobs as required. An important part of ensuring the reliability of the infrastructure is the monitoring and logging of these DIRAC distributed systems. The monitoring is done collecting information from two sources - one is from pinging the services or by keeping track of the regular heartbeats of the agents, and the other from the analysis of the error messages generated by both agents and services and collected by the logging system. This allows us to ensure that he components are running properly and to collect useful information regarding their operations. The process status monitoring is displayed using the SLS sensor mechanism which also automatically allows one to plot various quantities and also keep ...

On the confinement of a Dirac particle to a two-dimensional ring

International Nuclear Information System (INIS)

Bakke, K.; Furtado, C.

2012-01-01

In this contribution, we propose a new model for studying the confinement of a spin-half particle to a two-dimensional quantum ring for systems described by the Dirac equation by introducing a new coupling into the Dirac equation. We show that the introduction of this new coupling into the Dirac equation yields a generalization of the two-dimensional quantum ring model proposed by Tan and Inkson [W.-C. Tan, J.C. Inkson, Semicond. Sci. Technol. 11 (1996) 1635] for relativistic spin-half quantum particles. -- Highlights: ► Two-dimensional ring model for condensed matter systems described by the Dirac equation. ► Exact solutions of the Dirac equation. ► Persistent currents for Dirac-like systems confined to a two-dimensional quantum ring.

Kapitza–Dirac effect with traveling waves

International Nuclear Information System (INIS)

Hayrapetyan, Armen G; Götte, Jörg B; Grigoryan, Karen K; Petrosyan, Rubik G

2015-01-01

We report on the possibility of diffracting electrons from light waves traveling inside a dielectric medium. We show that, in the frame of reference which moves with the group velocity of light, the traveling wave acts as a stationary diffraction grating from which electrons can diffract, similar to the conventional Kapitza–Dirac effect. To characterize the Kapitza–Dirac effect with traveling light waves, we make use of the Hamiltonian Analogy between electron optics and quantum mechanics and apply the Helmholtz–Kirchhoff theory of diffraction. (fast track communication)

A Model of Student Workload

Science.gov (United States)

Bowyer, Kyle

2012-01-01

Student workload is a contributing factor to students deciding to withdraw from their study before completion of the course, at significant cost to students, institutions and society. The aim of this paper is to create a basic workload model for a group of undergraduate students studying business law units at Curtin University in Western…

Impact of adding additional providers to resident workload and the resident experience on a medical consultation rotation.

Science.gov (United States)

Fang, Michele; Linson, Eric; Suneja, Manish; Kuperman, Ethan F

2017-02-22

Excellence in Graduate Medical Education requires the right clinical environment with an appropriate workload where residents have enough patients to gain proficiency in medicine with optimal time for reflection. The Accreditation Council for Graduate Medical Education (ACGME) has focused more on work hours rather than workload; however, high resident workload has been associated with lower resident participation in education and fatigue-related errors. Recognizing the potential risks associated with high resident workload and being mindful of the costs of reducing resident workload, we sought to reduce residents' workload by adding an advanced practice provider (APP) to the surgical comanagement service (SCM) and study its effect on resident satisfaction and perceived educational value of the rotation. In Fiscal Year (FY) 2014 and 2015, an additional faculty member was added to the SCM rotation. In FY 2014, the faculty member was a staff physician, and in FY 2015, the faculty member was an APP.. Resident workload was assessed using billing data. We measured residents' perceptions of the rotation using an anonymous electronic survey tool. We compared FY2014-2015 data to the baseline FY2013. The number of patients seen per resident per day decreased from 8.0(SD 3.3) in FY2013 to 5.0(SD 1.9) in FY2014 (p value of the rotation (40.0%, 72.2%, 72.6% in FY2013, 2014, 2015 respectively, p perceived educational value and clinical experience of a medical consultation rotation.

Double Dirac point semimetal in 2D material: Ta2Se3

Science.gov (United States)

Ma, Yandong; Jing, Yu; Heine, Thomas

2017-06-01

Here, we report by first-principles calculations one new stable 2D Dirac material, Ta2Se3 monolayer. For this system, stable layered bulk phase exists, and exfoliation should be possible. Ta2Se3 monolayer is demonstrated to support two Dirac points close to the Fermi level, achieving the exotic 2D double Dirac semimetal. And like 2D single Dirac and 2D node-line semimetals, spin-orbit coupling could introduce an insulating state in this new class of 2D Dirac semimetals. Moreover, the Dirac feature in this system is layer-dependent and a metal-to-insulator transition is identified in Ta2Se3 when reducing the layer-thickness from bilayer to monolayer. These findings are of fundamental interests and of great importance for nanoscale device applications.

Weak cosmic censorship, dyonic Kerr–Newman black holes and Dirac fields

International Nuclear Information System (INIS)

Tóth, Gábor Zsolt

2016-01-01

It was investigated recently, with the aim of testing the weak cosmic censorship conjecture, whether an extremal Kerr black hole can be converted into a naked singularity by interaction with a massless classical Dirac test field, and it was found that this is possible. We generalize this result to electrically and magnetically charged rotating extremal black holes (i.e. extremal dyonic Kerr–Newman black holes) and massive Dirac test fields, allowing magnetically or electrically uncharged or nonrotating black holes and the massless Dirac field as special cases. We show that the possibility of the conversion is a direct consequence of the fact that the Einstein–Hilbert energy-momentum tensor of the classical Dirac field does not satisfy the null energy condition, and is therefore not in contradiction with the weak cosmic censorship conjecture. We give a derivation of the absence of superradiance of the Dirac field without making use of the complete separability of the Dirac equation in the dyonic Kerr–Newman background, and we determine the range of superradiant frequencies of the scalar field. The range of frequencies of the Dirac field that can be used to convert a black hole into a naked singularity partially coincides with the superradiant range of the scalar field. We apply horizon-penetrating coordinates, as our arguments involve calculating quantities at the event horizon. We describe the separation of variables for the Dirac equation in these coordinates, although we mostly avoid using it. (paper)

Mental workload in decision and control

Science.gov (United States)

Sheridan, T. B.

1979-01-01

This paper briefly reviews the problems of defining and measuring the 'mental workload' of aircraft pilots and other human operators of complex dynamic systems. Of the alternative approaches the author indicates a clear preference for the use of subjective scaling. Some recent experiments from MIT and elsewhere are described which utilize subjective mental workload scales in conjunction with human decision and control tasks in the laboratory. Finally a new three-dimensional mental workload rating scale, under current development for use by IFR aircraft pilots, is presented.

A Dirac sea pilot-wave model for quantum field theory

International Nuclear Information System (INIS)

Colin, S; Struyve, W

2007-01-01

We present a pilot-wave model for quantum field theory in which the Dirac sea is taken seriously. The model ascribes particle trajectories to all the fermions, including the fermions filling the Dirac sea. The model is deterministic and applies to the regime in which fermion number is superselected. This work is a further elaboration of work by Colin, in which a Dirac sea pilot-wave model is presented for quantum electrodynamics. We extend his work to non-electromagnetic interactions, we discuss a cut-off regularization of the pilot-wave model and study how it reproduces the standard quantum predictions. The Dirac sea pilot-wave model can be seen as a possible continuum generalization of a lattice model by Bell. It can also be seen as a development and generalization of the ideas by Bohm, Hiley and Kaloyerou, who also suggested the use of the Dirac sea for the development of a pilot-wave model for quantum electrodynamics

DIRAC framework evaluation for the Fermi-LAT and CTA experiments

International Nuclear Information System (INIS)

Arrabito, L; Cohen-Tanugi, J; Piron, F; Renaud, M; Rolland, V; Diaz, R Graciani; Longo, F; Kuss, M; Sapunov, M; Tsaregorodtsev, A; Zimmer, S

2014-01-01

DIRAC (Distributed Infrastructure with Remote Agent Control) is a general framework for the management of tasks over distributed heterogeneous computing environments. It has been originally developed to support the production activities of the LHCb (Large Hadron Collider Beauty) experiment and today is extensively used by several particle physics and biology communities. Current (Fermi Large Area Telescope – LAT) and planned (Cherenkov Telescope Array – CTA) new generation astrophysical/cosmological experiments, with very large processing and storage needs, are currently investigating the usability of DIRAC in this context. Each of these use cases has some peculiarities: Fermi-LAT will interface DIRAC to its own workflow system to allow the access to the grid resources, while CTA is using DIRAC as workflow management system for Monte Carlo production and analysis on the grid. We describe the prototype effort that we lead toward deploying a DIRAC solution for some aspects of Fermi-LAT and CTA needs.

A bio-inspired approach for the reduction of left ventricular workload.

Directory of Open Access Journals (Sweden)

Niema M Pahlevan

Full Text Available Previous studies have demonstrated the existence of optimization criteria in the design and development of mammalians cardiovascular systems. Similarities in mammalian arterial wave reflection suggest there are certain design criteria for the optimization of arterial wave dynamics. Inspired by these natural optimization criteria, we investigated the feasibility of optimizing the aortic waves by modifying wave reflection sites. A hydraulic model that has physical and dynamical properties similar to a human aorta and left ventricle was used for a series of in-vitro experiments. The results indicate that placing an artificial reflection site (a ring at a specific location along the aorta may create a constructive wave dynamic that could reduce LV pulsatile workload. This simple bio-inspired approach may have important implications for the future of treatment strategies for diseased aorta.

Elastic gauge fields and Hall viscosity of Dirac magnons

Science.gov (United States)

Ferreiros, Yago; Vozmediano, María A. H.

2018-02-01

We analyze the coupling of elastic lattice deformations to the magnon degrees of freedom of magnon Dirac materials. For a honeycomb ferromagnet we find that, as happens in the case of graphene, elastic gauge fields appear coupled to the magnon pseudospinors. For deformations that induce constant pseudomagnetic fields, the spectrum around the Dirac nodes splits into pseudo-Landau levels. We show that when a Dzyaloshinskii-Moriya interaction is considered, a topological gap opens in the system and a Chern-Simons effective action for the elastic degrees of freedom is generated. Such a term encodes a phonon Hall viscosity response, entirely generated by quantum fluctuations of magnons living in the vicinity of the Dirac points. The magnon Hall viscosity vanishes at zero temperature, and grows as temperature is raised and the states around the Dirac points are increasingly populated.

Basic quantum mechanics for three Dirac equations in a curved spacetime

International Nuclear Information System (INIS)

Arminjon, Mayeul

2010-01-01

We study the basic quantum mechanics for a fully general set of Dirac matrices in a curved spacetime by extending Pauli's method. We further extend this study to three versions of the Dirac equation: the standard (Dirac-Fock-Weyl or DFW) equation, and two alternative versions, both of which are based on the recently proposed linear tensor representations of the Dirac field (TRD). We begin with the current conservation: we show that the latter applies to any solution of the Dirac equation, if the field of Dirac matrices γμ satisfies a specific PDE. This equation is always satisfied for DFW with its restricted choice for the γμ matrices. It similarly restricts the choice of the γμ matrices for TRD. However, this restriction can be achieved. The frame dependence of a general Hamiltonian operator is studied. We show that in any given reference frame with minor restrictions on the spacetime metric, the axioms of quantum mechanics impose a unique form for the Hilbert space scalar product. Finally, the condition for the general Dirac Hamiltonian operator to be Hermitian is derived in a general curved spacetime. For DFW, the validity of this hermeticity condition depends on the choice of the γμ matrices. (author)

Fermi-Dirac correlation and Q-νKν(Q) distribution

International Nuclear Information System (INIS)

Dai Qirun; Li Jimei; Ma Zhanqing; Zhao Shusong

1996-01-01

The Fermi-Dirac correlation of identical protons is studied. Based on the non-perturbative theory of quantum fields, we put forward a kind of source distribution--the Q -ν K ν (Q) distribution. The Fermi-Dirac correlation of (p +- -p +- )-pairs is calculated from this distribution. The fitted curves agree with experimental data. The Q -ν K ν (Q) distribution has more advantages than the Gauss Source distribution. The radii of the source emitting hadrons and the anomalous dimensions of the Fermi field are calculated from the Fermi-Dirac correlation of identical protons

A strong-topological-metal material with multiple Dirac cones

OpenAIRE

Ji, Huiwen; Pletikosić, I; Gibson, Q. D.; Sahasrabudhe, Girija; Valla, T.; Cava, R. J.

2015-01-01

We report a new, cleavable, strong-topological-metal, Zr2Te2P, which has the same tetradymite-type crystal structure as the topological insulator Bi2Te2Se. Instead of being a semiconductor, however, Zr2Te2P is metallic with a pseudogap between 0.2 and 0.7 eV above the fermi energy (EF). Inside this pseudogap, two Dirac dispersions are predicted: one is a surface-originated Dirac cone protected by time-reversal symmetry (TRS), while the other is a bulk-originated and slightly gapped Dirac cone...

Majorana mass term, Dirac neutrinos and selective neutrino oscillations

International Nuclear Information System (INIS)

Leung, C.N.

1987-01-01

In a theory of neutrino mixing via a Majorana mass term involving only the left-handed neutrinos there exist selection rules for neutrino oscillations if true Dirac and/or exactly zero mass eigenstates are present. In the case of three neutrino flavours no oscillation is allowed if the mass spectrum contains one Dirac and one nondegenerate Majorana massive neutrino. The origin of these selection rules and their implications are discussed and the number of possible CP-violating phases in the lepton mixing matrix when Dirac and Majorana mass eigenstates coexist is given. (orig.)

A framework for unified Dirac gauginos

Directory of Open Access Journals (Sweden)

Benakli Karim

2017-01-01

Full Text Available We identify the Minimal Dirac Gaugino Supersymmetric Standard Model (MDGSSM as the minimal field content with Dirac gauginos allowing unification of gauge coupling. We stress that its parameter space describes also other most popular models as the MSSM, NMSSM and MRSSM. We discuss the generation of trilinear couplings in models of gauge mediation that has been overlooked in the past. We study the different source of Higgs mixings and constraints from the ƿ parameter. Finally, we provide new experimental limits on the masses of the scalar octets.

Relationship between workload and mind-wandering in simulated driving.

Directory of Open Access Journals (Sweden)

Yuyu Zhang

Full Text Available Mental workload and mind-wandering are highly related to driving safety. This study investigated the relationship between mental workload and mind-wandering while driving. Participants (N = 40 were asked to perform a car following task in driving simulator, and report whether they had experienced mind-wandering upon hearing a tone. After driving, participants reported their workload using the NASA-Task Load Index (TLX. Results revealed an interaction between workload and mind-wandering in two different perspectives. First, there was a negative correlation between workload and mind-wandering (r = -0.459, p < 0.01 for different individuals. Second, from temporal perspective workload and mind-wandering frequency increased significantly over task time and were positively correlated. Together, these findings contribute to understanding the roles of workload and mind-wandering in driving.

A comparative study of numerical methods for the overlap Dirac operator--a status report

International Nuclear Information System (INIS)

Eshof, J. van den; Frommer, A.; Lippert, Th.; Schilling, K.; Vorst, H. van der

2002-01-01

Improvements of various methods to compute the sign function of the hermitian Wilson-Dirac matrix within the overlap operator are presented. An optimal partial fraction expansion (PFE) based on a theorem of Zolotarev is given. Benchmarks show that this PFE together with removal of converged systems within a multi-shift CG appears to approximate the sign function times a vector most efficiently. A posteriori error bounds are given

Measuring workload in collaborative contexts: trait versus state perspectives.

Science.gov (United States)

Helton, William S; Funke, Gregory J; Knott, Benjamin A

2014-03-01

In the present study, we explored the state versus trait aspects of measures of task and team workload in a disaster simulation. There is often a need to assess workload in both individual and collaborative settings. Researchers in this field often use the NASATask Load Index (NASA-TLX) as a global measure of workload by aggregating the NASA-TLX's component items. Using this practice, one may overlook the distinction between traits and states. Fifteen dyadic teams (11 inexperienced, 4 experienced) completed five sessions of a tsunami disaster simulator. After every session, individuals completed a modified version of the NASA-TLX that included team workload measures.We then examined the workload items by using a between-subjects and within-subjects perspective. Between-subjects and within-subjects correlations among the items indicated the workload items are more independent within subjects (as states) than between subjects (as traits). Correlations between the workload items and simulation performance were also different at the trait and state levels. Workload may behave differently at trait (between-subjects) and state (within-subjects) levels. Researchers interested in workload measurement as a state should take a within-subjects perspective in their analyses.

A matricial approach for the Dirac-Kahler formalism

International Nuclear Information System (INIS)

Goto, M.

1987-01-01

A matricial approach for the Dirac-Kahler formalism is considered. It is shown that the matrical approach i) brings a great computational simplification compared to the common use of differential forms and that ii) by an appropriate choice of notation, it can be extended to the lattice, including a matrix Dirac-Kahler equation. (author) [pt

Workload-Aware Indexing of Continuously Moving Objects

DEFF Research Database (Denmark)

Tzoumas, Kostas; Yiu, Man Lung; Jensen, Christian Søndergaard

2009-01-01

structures can easily become performance bottlenecks. We address the need for indexing that is adaptive to the workload characteristics, called workload-aware, in order to cover the space in between maintaining an accurate index, and having no index at all. Our proposal, QU-Trade, extends R-tree type...... indexing and achieves workload-awareness by controlling the underlying index’s filtering quality. QU-Trade safely drops index updates, increasing the overlap in the index when the workload is update-intensive, and it restores the filtering capabilities of the index when the workload becomes query......-intensive. This is done in a non-uniform way in space so that the quality of the index remains high in frequently queried regions, while it deteriorates in frequently updated regions. The adaptation occurs online, without the need for a learning phase. We apply QU-Trade to the R-tree and the TPR-tree, and we offer...

Hydrogenated arsenenes as planar magnet and Dirac material

Energy Technology Data Exchange (ETDEWEB)

Zhang, Shengli; Cai, Bo; Zeng, Haibo, E-mail: Huziyu@csrc.ac.cn, E-mail: zeng.haibo@njust.edu.cn [Institute of Optoelectronics and Nanomaterials, Herbert Gleiter Institute of Nanoscience, College of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); Hu, Yonghong [Institute of Optoelectronics and Nanomaterials, Herbert Gleiter Institute of Nanoscience, College of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); School of Nuclear Technology and Chemistry and Biology, Hubei University of Science and Technology, Xianning 437100 (China); Hu, Ziyu, E-mail: Huziyu@csrc.ac.cn, E-mail: zeng.haibo@njust.edu.cn [Beijing Computational Science Research Center, Beijing 100084 (China)

2015-07-13

Arsenene and antimonene are predicted to have 2.49 and 2.28 eV band gaps, which have aroused intense interest in the two-dimensional (2D) semiconductors for nanoelectronic and optoelectronic devices. Here, the hydrogenated arsenenes are reported to be planar magnet and 2D Dirac materials based on comprehensive first-principles calculations. The semi-hydrogenated (SH) arsenene is found to be a quasi-planar magnet, while the fully hydrogenated (FH) arsenene is a planar Dirac material. The buckling height of pristine arsenene is greatly decreased by the hydrogenation, resulting in a planar and relatively low-mass-density sheet. The electronic structures of arsenene are also evidently altered after hydrogenating from wide-band-gap semiconductor to metallic material for SH arsenene, and then to Dirac material for FH arsenene. The SH arsenene has an obvious magnetism, mainly contributed by the p orbital of the unsaturated As atom. Such magnetic and Dirac materials modified by hydrogenation of arsenene may have potential applications in future optoelectronic and spintronic devices.

Hydrogenated arsenenes as planar magnet and Dirac material

International Nuclear Information System (INIS)

Zhang, Shengli; Cai, Bo; Zeng, Haibo; Hu, Yonghong; Hu, Ziyu

2015-01-01

Arsenene and antimonene are predicted to have 2.49 and 2.28 eV band gaps, which have aroused intense interest in the two-dimensional (2D) semiconductors for nanoelectronic and optoelectronic devices. Here, the hydrogenated arsenenes are reported to be planar magnet and 2D Dirac materials based on comprehensive first-principles calculations. The semi-hydrogenated (SH) arsenene is found to be a quasi-planar magnet, while the fully hydrogenated (FH) arsenene is a planar Dirac material. The buckling height of pristine arsenene is greatly decreased by the hydrogenation, resulting in a planar and relatively low-mass-density sheet. The electronic structures of arsenene are also evidently altered after hydrogenating from wide-band-gap semiconductor to metallic material for SH arsenene, and then to Dirac material for FH arsenene. The SH arsenene has an obvious magnetism, mainly contributed by the p orbital of the unsaturated As atom. Such magnetic and Dirac materials modified by hydrogenation of arsenene may have potential applications in future optoelectronic and spintronic devices

Hydrogenated arsenenes as planar magnet and Dirac material

Science.gov (United States)

Zhang, Shengli; Hu, Yonghong; Hu, Ziyu; Cai, Bo; Zeng, Haibo

2015-07-01

Arsenene and antimonene are predicted to have 2.49 and 2.28 eV band gaps, which have aroused intense interest in the two-dimensional (2D) semiconductors for nanoelectronic and optoelectronic devices. Here, the hydrogenated arsenenes are reported to be planar magnet and 2D Dirac materials based on comprehensive first-principles calculations. The semi-hydrogenated (SH) arsenene is found to be a quasi-planar magnet, while the fully hydrogenated (FH) arsenene is a planar Dirac material. The buckling height of pristine arsenene is greatly decreased by the hydrogenation, resulting in a planar and relatively low-mass-density sheet. The electronic structures of arsenene are also evidently altered after hydrogenating from wide-band-gap semiconductor to metallic material for SH arsenene, and then to Dirac material for FH arsenene. The SH arsenene has an obvious magnetism, mainly contributed by the p orbital of the unsaturated As atom. Such magnetic and Dirac materials modified by hydrogenation of arsenene may have potential applications in future optoelectronic and spintronic devices.

Majorana zero modes in Dirac semimetal Josephson junctions

Science.gov (United States)

Li, Chuan; de Boer, Jorrit; de Ronde, Bob; Huang, Yingkai; Golden, Mark; Brinkman, Alexander

We have realized proximity-induced superconductivity in a Dirac semimetal and revealed the topological nature of the superconductivity by the observation of Majorana zero modes. As a Dirac semimetal, Bi0.97Sb0.03 is used, where a three-dimensional Dirac cone exists in the bulk due to an accidental touching between conduction and valence bands. Electronic transport measurements on Hall-bars fabricated out of Bi0.97Sb0.03 flakes consistently show negative magnetoresistance for magnetic fields parallel to the current, which is associated with the chiral anomaly. In perpendicular magnetic fields, we see Shubnikov-de Haas oscillations that indicate very low carrier densities. The low Fermi energy and protection against backscattering in our Dirac semimetal Josephson junctions provide favorable conditions for a large contribution of Majorana zero modes to the supercurrent. In radiofrequency irradiation experiments, we indeed observe these Majorana zero modes in Nb-Bi0.97Sb0.03-Nb Josephson junctions as a 4 π periodic contribution to the current-phase relation.

Radiationless Zitterbewegung of Dirac particles and mass formula

International Nuclear Information System (INIS)

Noboru Hokkyo.

1987-06-01

The Zitterbewegung of the Dirac particle is given a visual representation by solving the two-component difference form of the Dirac equation. It is seen that the space-time trajectory of a Dirac particle can be pictured as a correlated whole of a network of zigzags of left- and right-handed chiral neutrino-like line elements. These zigzags can feel the curl of the external electromagnetic vector potential and give rise to the spin magnetic interaction, confirming Schroedinger's earlier intuitive picture of the spin as the orbital angular momentum of the Zitterbewegung. The network of zigzags associated with an electron splits and reunites in passing through the slits in the electron beam interference experiment. It is proposed to interpret Nambu's empirical mass formula m n =(n/2)137m e =(n/2)((h/2π)/cL), n=integer, as a radiationless condition for the Zitterbewegung of the hadronic Dirac particle of the linear spatial extension of the order of the classical electron radius L=e 2 /m e c 2 . (author). 20 refs, 4 figs

Workload based order acceptance in job shop environments

NARCIS (Netherlands)

Ebben, Mark; Hans, Elias W.; Olde Weghuis, F.M.; Olde Weghuis, F.M.

2005-01-01

In practice, order acceptance and production planning are often functionally separated. As a result, order acceptance decisions are made without considering the actual workload in the production system, or by only regarding the aggregate workload. We investigate the importance of a good workload

Characterization and Architectural Implications of Big Data Workloads

OpenAIRE

Wang, Lei; Zhan, Jianfeng; Jia, Zhen; Han, Rui

2015-01-01

Big data areas are expanding in a fast way in terms of increasing workloads and runtime systems, and this situation imposes a serious challenge to workload characterization, which is the foundation of innovative system and architecture design. The previous major efforts on big data benchmarking either propose a comprehensive but a large amount of workloads, or only select a few workloads according to so-called popularity, which may lead to partial or even biased observations. In this paper, o...

New exact solutions of the Dirac equation

International Nuclear Information System (INIS)

Bagrov, V.G.; Gitman, D.M.; Zadorozhnyj, V.N.; Lavrov, P.M.; Shapovalov, V.N.

1980-01-01

Search for new exact solutions of the Dirac and Klein-Gordon equations are in progress. Considered are general properties of the Dirac equation solutions for an electron in a purely magnetic field, in combination with a longitudinal magnetic and transverse electric fields. New solutions for the equations of charge motion in an electromagnetic field of axial symmetry and in a nonstationary field of a special form have been found for potentials selected concretely

Solvable linear potentials in the Dirac equation

International Nuclear Information System (INIS)

Dominguez-Adame, F.; Gonzalez, M.A.

1990-01-01

The Dirac equation for some linear potentials leading to Schroedinger-like oscillator equations for the upper and lower components of the Dirac spinor have been solved. Energy levels for the bound states appear in pairs, so that both particles and antiparticles may be bound with the same energy. For weak coupling, the spacing between levels is proportional to the coupling constant while in the strong limit those levels are depressed compared to the nonrelativistic ones

Bound-state Dirac eigenvalues for scalar potentials

International Nuclear Information System (INIS)

Ram, B.; Arafah, M.

1981-01-01

The Dirac equation is solved with a linear and a quadratic scalar potential using an approach in which the Dirac equation is first transformed to a one-dimensional Schroedinger equation with an effective potential. The WKB method is used to obtain the energy eigenvalues. The eigenvalues for the quadratic scalar potential are real just as they are for the linear potential. The results with the linear potential agree well with those obtained by Critchfield. (author)

Remarks about singular solutions to the Dirac equation

International Nuclear Information System (INIS)

Uhlir, M.

1975-01-01

In the paper singular solutions of the Dirac equation are investigated. They are derived in the Lorentz-covariant way of functions proportional to static multipole fields of scalar and (or) electromagnetic fields and of regular solutions of the Dirac equations. The regularization procedure excluding divergences of total energy, momentum and angular momentum of the spinor field considered is proposed

Granular superconductor in a honeycomb lattice as a realization of bosonic Dirac material

Science.gov (United States)

Banerjee, S.; Fransson, J.; Black-Schaffer, A. M.; Ågren, H.; Balatsky, A. V.

2016-04-01

We examine the low-energy effective theory of phase oscillations in a two-dimensional granular superconducting sheet where the grains are arranged in a honeycomb lattice structure. Using the example of graphene, we present evidence for the engineered Dirac nodes in the bosonic excitations: the spectra of the collective bosonic modes cross at the K and K' points in the Brillouin zone and form Dirac nodes. We show how two different types of collective phase oscillations are obtained and that they are analogous to the Leggett and the Bogoliubov-Anderson-Gorkov modes in a two-band superconductor. We show that the Dirac node is preserved in the presence of an intergrain interaction, despite induced changes of the qualitative features of the two collective modes. Finally, breaking the sublattice symmetry by choosing different on-site potentials for the two sublattices leads to a gap opening near the Dirac node, in analogy with fermionic Dirac materials. The Dirac node dispersion of bosonic excitations is thus expanding the discussion of the conventional Dirac cone excitations to the case of bosons. We call this case as a representative of bosonic Dirac materials (BDM), similar to the case of Fermionic Dirac materials extensively discussed in the literature.

A new measurement of workload in Web application reliability assessment

Directory of Open Access Journals (Sweden)

CUI Xia

2015-02-01

Full Text Available Web application has been popular in various fields of social life.It becomes more and more important to study the reliability of Web application.In this paper the definition of Web application failure is firstly brought out,and then the definition of Web application reliability.By analyzing data in the IIS server logs and selecting corresponding usage and information delivery failure data,the paper study the feasibility of Web application reliability assessment from the perspective of Web software system based on IIS server logs.Because the usage for a Web site often has certain regularity,a new measurement of workload in Web application reliability assessment is raised.In this method,the unit is removed by weighted average technique;and the weights are assessed by setting objective function and optimization.Finally an experiment was raised for validation.The experiment result shows the assessment of Web application reliability base on the new workload is better.

Do neutron stars disprove multiplicative creation in Dirac's large number hypothesis

International Nuclear Information System (INIS)

Qadir, A.; Mufti, A.A.

1980-07-01

Dirac's cosmology, based on his large number hypothesis, took the gravitational coupling to be decreasing with time and matter to be created as the square of time. Since the effects predicted by Dirac's theory are very small, it is difficult to find a ''clean'' test for it. Here we show that the observed radiation from pulsars is inconsistent with Dirac's multiplicative creation model, in which the matter created is proportional to the density of matter already present. Of course, this discussion makes no comment on the ''additive creation'' model, or on the revised version of Dirac's theory. (author)

Dirac operator, chirality and random matrix theory

International Nuclear Information System (INIS)

Pullirsch, R.

2001-05-01

Quantum Chromodynamics (QCD) is considered to be the correct theory which describes quarks and gluons and, thus, all strong interaction phenomena from the fundamental forces of nature. However, important properties of QCD such as the physical mechanism of color confinement and the spontaneous breaking of chiral symmetry are still not completely understood and under extensive discussion. Analytical calculations are limited, because in the low-energy regime where quarks are confined, application of perturbation theory is restricted due to the large gluon coupling. A powerful tool to investigate numerically and analytically the non-perturbative region is provided by the lattice formulation of QCD. From Monte Carlo simulations of lattice QCD we know that chiral symmetry is restored above a critical temperature. As the chiral condensate is connected to the spectral density of the Dirac operator via the Banks-Casher relation, the QCD Dirac spectrum is an interesting object for detailed studies. In search for an analytical expression of the infrared limit of the Dirac spectrum it has been realized that chiral random-matrix theory (chRMT) is a suitable tool to compare with the distribution and the correlations of the small Dirac eigenvalues. Further, it has been shown that the correlations of eigenvalues on the scale of mean level spacings are universal for complex physical systems and are given by random-matrix theory (Rm). This has been formulated as the Baghouse-Giannoni-Schmit conjecture which states that spectral correlations of a classically chaotic system are given by RMT on the quantum level. The aim of this work is to analyze the relationship between chiral phase transitions and chaos to order transitions in quantum field theories. We study the eigenvalues of the Dirac operator for Quantum Electrodynamics (QED) with compact gauge group U(1) on the lattice. This theory shows chiral symmetry breaking and confinement in the strong coupling region. Although being

Magnetotransport in Layered Dirac Fermion System Coupled with Magnetic Moments

Science.gov (United States)

Iwasaki, Yoshiki; Morinari, Takao

2018-03-01

We theoretically investigate the magnetotransport of Dirac fermions coupled with localized moments to understand the physical properties of the Dirac material EuMnBi2. Using an interlayer hopping form, which simplifies the complicated interaction between the layers of Dirac fermions and the layers of magnetic moments in EuMnBi2, the theory reproduces most of the features observed in this system. The hysteresis observed in EuMnBi2 can be caused by the valley splitting that is induced by the spin-orbit coupling and the external magnetic field with the molecular field created by localized moments. Our theory suggests that the magnetotransport in EuMnBi2 is due to the interplay among Dirac fermions, localized moments, and spin-orbit coupling.

String effects on Fermi-Dirac correlation measurements

International Nuclear Information System (INIS)

Duran Delgado, R.M.; Gustafson, G.; Loennblad, L.

2007-01-01

We investigate some recent measurements of Fermi-Dirac correlations by the LEP collaborations indicating surprisingly small source radii for the production of baryons in e + e - annihilation at the Z 0 peak. In hadronization models there is besides the Fermi-Dirac correlation effect also a strong dynamical (anti-) correlation. We demonstrate that the extraction of the pure FD effect is highly dependent on a realistic Monte Carlo event generator, both for separation of those dynamical correlations that are not related to Fermi-Dirac statistics, and for corrections of the data and background subtractions. Although the model can be tuned to well reproduce single particle distributions, there are large model uncertainties when it comes to correlations between identical baryons. We therefore, unfortunately, have to conclude that it is at present not possible to draw any firm conclusion about the source radii relevant for baryon production at LEP. (orig.)

DIRAC - Distributed Infrastructure with Remote Agent Control

CERN Document Server

Tsaregorodtsev, A; Closier, J; Frank, M; Gaspar, C; van Herwijnen, E; Loverre, F; Ponce, S; Graciani Diaz, R.; Galli, D; Marconi, U; Vagnoni, V; Brook, N; Buckley, A; Harrison, K; Schmelling, M; Egede, U; Bogdanchikov, A; Korolko, I; Washbrook, A; Palacios, J P; Klous, S; Saborido, J J; Khan, A; Pickford, A; Soroko, A; Romanovski, V; Patrick, G N; Kuznetsov, G; Gandelman, M

2003-01-01

This paper describes DIRAC, the LHCb Monte Carlo production system. DIRAC has a client/server architecture based on: Compute elements distributed among the collaborating institutes; Databases for production management, bookkeeping (the metadata catalogue) and software configuration; Monitoring and cataloguing services for updating and accessing the databases. Locally installed software agents implemented in Python monitor the local batch queue, interrogate the production database for any outstanding production requests using the XML-RPC protocol and initiate the job submission. The agent checks and, if necessary, installs any required software automatically. After the job has processed the events, the agent transfers the output data and updates the metadata catalogue. DIRAC has been successfully installed at 18 collaborating institutes, including the DataGRID, and has been used in recent Physics Data Challenges. In the near to medium term future we must use a mixed environment with different types of grid mid...

Dirac particle tunneling from black rings

International Nuclear Information System (INIS)

Jiang Qingquan

2008-01-01

Recent research shows that Hawking radiation can be treated as a quantum tunneling process, and Hawking temperatures of Dirac particles across the horizon of a black hole can be correctly recovered via the fermion tunneling method. In this paper, motivated by the fermion tunneling method, we attempt to apply the analysis to derive Hawking radiation of Dirac particles via tunneling from black ring solutions of 5-dimensional Einstein-Maxwell-dilaton gravity theory. Finally, it is interesting to find that, as in the black hole case, fermion tunneling can also result in correct Hawking temperatures for the rotating neutral, dipole, and charged black rings.

Are Dirac electrons faster than light?

International Nuclear Information System (INIS)

De Angelis, G.F.

1986-01-01

This paper addresses the problem of path integral solutions of the Dirac equation. The path integral construction of the Dirac propagator which extends Fynman's checkerboard rule in more than one space dimension is discussed. A distinguished feature of such extension is the fact that the speed of a relativistic electron is actually greater than the speed of light when the space has more than one dimension. A technique employed in obtaining an extension to higher space dimension is described which consists in comparing continuity equations of quantum mechanical origin with forward Kolmogorov equations for suitable chosen classes of random processes

Managing Teacher Workload: Work-Life Balance and Wellbeing

Science.gov (United States)

Bubb, Sara; Earley, Peter

2004-01-01

This book is divided into three sections. In the First Section, entitled "Wellbeing and Workload", the authors examine teacher workload and how teachers spend their time. Chapter 1 focuses on what the causes and effects of excessive workload are, especially in relation to wellbeing, stress and, crucially, recruitment and retention?…

Workload analyse of assembling process

Science.gov (United States)

Ghenghea, L. D.

2015-11-01

The workload is the most important indicator for managers responsible of industrial technological processes no matter if these are automated, mechanized or simply manual in each case, machines or workers will be in the focus of workload measurements. The paper deals with workload analyses made to a most part manual assembling technology for roller bearings assembling process, executed in a big company, with integrated bearings manufacturing processes. In this analyses the delay sample technique have been used to identify and divide all bearing assemblers activities, to get information about time parts from 480 minutes day work time that workers allow to each activity. The developed study shows some ways to increase the process productivity without supplementary investments and also indicated the process automation could be the solution to gain maximum productivity.

Fermi field and Dirac oscillator in a Som-Raychaudhuri space-time

Science.gov (United States)

de Montigny, Marc; Zare, Soroush; Hassanabadi, Hassan

2018-05-01

We investigate the relativistic dynamics of a Dirac field in the Som-Raychaudhuri space-time, which is described by a Gödel-type metric and a stationary cylindrical symmetric solution of Einstein field equations for a charged dust distribution in rigid rotation. In order to analyze the effect of various physical parameters of this space-time, we solve the Dirac equation in the Som-Raychaudhuri space-time and obtain the energy levels and eigenfunctions of the Dirac operator by using the Nikiforov-Uvarov method. We also examine the behaviour of the Dirac oscillator in the Som-Raychaudhuri space-time, in particular, the effect of its frequency and the vorticity parameter.

Analytical solutions for Dirac and Klein-Gordon equations using Backlund transformations

Energy Technology Data Exchange (ETDEWEB)

Zabadal, Jorge R.; Borges, Volnei, E-mail: jorge.zabadal@ufrgs.br, E-mail: borges@ufrgs.br [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Dept. de Engenharia Mecanica; Ribeiro, Vinicius G., E-mail: vinicius_ribeiro@uniritter.edu.br [Centro Universitario Ritter dos Reis (UNIRITTER), Porto Alegre, RS (Brazil); Santos, Marcio, E-mail: marciophd@gmail.com [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Centro de Estudos Interdisciplinares

2015-07-01

This work presents a new analytical method for solving Klein-Gordon type equations via Backlund transformations. The method consists in mapping the Klein-Gordon model into a first order system of partial differential equations, which contains a generalized velocity field instead of the Dirac matrices. This system is a tensor model for quantum field theory whose space solution is wider than the Dirac model in the original form. Thus, after finding analytical expressions for the wave functions, the Maxwell field can be readily obtained from the Dirac equations, furnishing a self-consistent field solution for the Maxwell-Dirac system. Analytical and numerical results are reported. (author)

Large optical conductivity of Dirac semimetal Fermi arc surface states

Science.gov (United States)

Shi, Li-kun; Song, Justin C. W.

2017-08-01

Fermi arc surface states, a hallmark of topological Dirac semimetals, can host carriers that exhibit unusual dynamics distinct from that of their parent bulk. Here we find that Fermi arc carriers in intrinsic Dirac semimetals possess a strong and anisotropic light-matter interaction. This is characterized by a large Fermi arc optical conductivity when light is polarized transverse to the Fermi arc; when light is polarized along the Fermi arc, Fermi arc optical conductivity is significantly muted. The large surface spectral weight is locked to the wide separation between Dirac nodes and persists as a large Drude weight of Fermi arc carriers when the system is doped. As a result, large and anisotropic Fermi arc conductivity provides a novel means of optically interrogating the topological surfaces states of Dirac semimetals.

Phase diagram and Chiral Magnetic Effect in Dirac Semimetals from Lattice Simulation

Directory of Open Access Journals (Sweden)

Boyda D.L.

2018-01-01

Full Text Available Dirac Semimetals Na3Bi and Cd3As2 are recently discovered materials, which low energy electronic spectrum is described by two flavours of massless 3+1D fermions. In order to study electronic properties of these materials we formulated lattice field theory with rooted staggered fermions on anisotropic lattice. It is shown that in the limit of zero temporal lattice spacing this theory reproduces effective theory of Dirac semimetals. Using the lattice field theory we study the phase diagram of Dirac semimetals in the plane effective coupling constant - Fermi velocity anisotropy. We also measure conductivity of Dirac Semimetals within lattice field theory in external magnetic field. Our results confirm the existence of Chiral Magnetic Effect in Dirac Semimetals.

Monday Morning Workload Reports (FY15 - 17)

Data.gov (United States)

Department of Veterans Affairs — The Monday Morning Workload Report (MMWR) displays a snapshot of the Veterans Benefits Administration’s (VBA) workload as of a specified date, typically the previous...

[Nursing workloads and working conditions: integrative review].

Science.gov (United States)

Schmoeller, Roseli; Trindade, Letícia de Lima; Neis, Márcia Binder; Gelbcke, Francine Lima; de Pires, Denise Elvira Pires

2011-06-01

This study reviews theoretical production concerning workloads and working conditions for nurses. For that, an integrative review was carried out using scientific articles, theses and dissertations indexed in two Brazilian databases, Virtual Health Care Library (Biblioteca Virtual de Saúde) and Digital Database of Dissertations (Banco Digital de Teses), over the last ten years. From 132 identified studies, 27 were selected. Results indicate workloads as responsible for professional weariness, affecting the occurrence of work accidents and health problems. In order to adequate workloads studies indicate some strategies, such as having an adequate numbers of employees, continuing education, and better working conditions. The challenge is to continue research that reveal more precisely the relationships between workloads, working conditions, and health of the nursing team.

Upper-Division Student Difficulties with the Dirac Delta Function

Science.gov (United States)

Wilcox, Bethany R.; Pollock, Steven J.

2015-01-01

The Dirac delta function is a standard mathematical tool that appears repeatedly in the undergraduate physics curriculum in multiple topical areas including electrostatics, and quantum mechanics. While Dirac delta functions are often introduced in order to simplify a problem mathematically, students still struggle to manipulate and interpret them.…

Two-dimensional spin-orbit Dirac point in monolayer HfGeTe

Science.gov (United States)

Guan, Shan; Liu, Ying; Yu, Zhi-Ming; Wang, Shan-Shan; Yao, Yugui; Yang, Shengyuan A.

2017-10-01

Dirac points in two-dimensional (2D) materials have been a fascinating subject of research, with graphene as the most prominent example. However, the Dirac points in existing 2D materials, including graphene, are vulnerable against spin-orbit coupling (SOC). Here, based on first-principles calculations and theoretical analysis, we propose a new family of stable 2D materials, the HfGeTe-family monolayers, which host so-called spin-orbit Dirac points (SDPs) close to the Fermi level. These Dirac points are special in that they are formed only under significant SOC, hence they are intrinsically robust against SOC. We show that the existence of a pair of SDPs are dictated by the nonsymmorphic space group symmetry of the system, which are very robust under various types of lattice strains. The energy, the dispersion, and the valley occupation around the Dirac points can be effectively tuned by strain. We construct a low-energy effective model to characterize the Dirac fermions around the SDPs. Furthermore, we find that the material is simultaneously a 2D Z2 topological metal, which possesses nontrivial Z2 invariant in the bulk and spin-helical edge states on the boundary. From the calculated exfoliation energies and mechanical properties, we show that these materials can be readily obtained in experiment from the existing bulk materials. Our result reveals HfGeTe-family monolayers as a promising platform for exploring spin-orbit Dirac fermions and topological phases in two-dimensions.

The Dirac equation in the Lobachevsky space-time

International Nuclear Information System (INIS)

Paramonov, D.V.; Paramonova, N.N.; Shavokhina, N.S.

2000-01-01

The product of the Lobachevsky space and the time axis is termed the Lobachevsky space-time. The Lobachevsky space is considered as a hyperboloid's sheet in the four-dimensional pseudo-Euclidean space. The Dirac-Fock-Ivanenko equation is reduced to the Dirac equation in two special forms by passing from Lame basis in the Lobachevsky space to the Cartesian basis in the enveloping pseudo-Euclidean space

Dirac equation and optical wave propagation in one dimension

Energy Technology Data Exchange (ETDEWEB)

Gonzalez, Gabriel [Catedras CONACYT, Universidad Autonoma de San Luis Potosi (Mexico); Coordinacion para la Innovacion y la Aplicacion de la Ciencia y la Tecnologia, Universidad Autonoma de San Luis Potosi (Mexico)

2018-02-15

We show that the propagation of transverse electric (TE) polarized waves in one-dimensional inhomogeneous settings can be written in the form of the Dirac equation in one space dimension with a Lorentz scalar potential, and consequently perform photonic simulations of the Dirac equation in optical structures. In particular, we propose how the zero energy state of the Jackiw-Rebbi model can be generated in an optical set-up by controlling the refractive index landscape, where TE-polarized waves mimic the Dirac particles and the soliton field can be tuned by adjusting the refractive index. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Topological transport in Dirac nodal-line semimetals

Science.gov (United States)

Rui, W. B.; Zhao, Y. X.; Schnyder, Andreas P.

2018-04-01

Topological nodal-line semimetals are characterized by one-dimensional Dirac nodal rings that are protected by the combined symmetry of inversion P and time-reversal T . The stability of these Dirac rings is guaranteed by a quantized ±π Berry phase and their low-energy physics is described by a one-parameter family of (2+1)-dimensional quantum field theories exhibiting the parity anomaly. Here we study the Berry-phase supported topological transport of P T -invariant nodal-line semimetals. We find that small inversion breaking allows for an electric-field-induced anomalous transverse current, whose universal component originates from the parity anomaly. Due to this Hall-like current, carriers at opposite sides of the Dirac nodal ring flow to opposite surfaces when an electric field is applied. To detect the topological currents, we propose a dumbbell device, which uses surface states to filter charges based on their momenta. Suggestions for experiments and device applications are discussed.

Quantum transport through 3D Dirac materials

International Nuclear Information System (INIS)

Salehi, M.; Jafari, S.A.

2015-01-01

Bismuth and its alloys provide a paradigm to realize three dimensional materials whose low-energy effective theory is given by Dirac equation in 3+1 dimensions. We study the quantum transport properties of three dimensional Dirac materials within the framework of Landauer–Büttiker formalism. Charge carriers in normal metal satisfying the Schrödinger equation, can be split into four-component with appropriate matching conditions at the boundary with the three dimensional Dirac material (3DDM). We calculate the conductance and the Fano factor of an interface separating 3DDM from a normal metal, as well as the conductance through a slab of 3DDM. Under certain circumstances the 3DDM appears transparent to electrons hitting the 3DDM. We find that electrons hitting the metal-3DDM interface from metallic side can enter 3DDM in a reversed spin state as soon as their angle of incidence deviates from the direction perpendicular to interface. However the presence of a second interface completely cancels this effect

Quantum transport through 3D Dirac materials

Energy Technology Data Exchange (ETDEWEB)

Salehi, M. [Department of Physics, Sharif University of Technology, Tehran 11155-9161 (Iran, Islamic Republic of); Jafari, S.A., E-mail: jafari@physics.sharif.edu [Department of Physics, Sharif University of Technology, Tehran 11155-9161 (Iran, Islamic Republic of); Center of Excellence for Complex Systems and Condensed Matter (CSCM), Sharif University of Technology, Tehran 1458889694 (Iran, Islamic Republic of)

2015-08-15

Bismuth and its alloys provide a paradigm to realize three dimensional materials whose low-energy effective theory is given by Dirac equation in 3+1 dimensions. We study the quantum transport properties of three dimensional Dirac materials within the framework of Landauer–Büttiker formalism. Charge carriers in normal metal satisfying the Schrödinger equation, can be split into four-component with appropriate matching conditions at the boundary with the three dimensional Dirac material (3DDM). We calculate the conductance and the Fano factor of an interface separating 3DDM from a normal metal, as well as the conductance through a slab of 3DDM. Under certain circumstances the 3DDM appears transparent to electrons hitting the 3DDM. We find that electrons hitting the metal-3DDM interface from metallic side can enter 3DDM in a reversed spin state as soon as their angle of incidence deviates from the direction perpendicular to interface. However the presence of a second interface completely cancels this effect.

On oscillations of neutrinos with Dirac and Majorana masses

International Nuclear Information System (INIS)

Bilenky, S.M.; Hosek, J.; Petcov, S.T.; Bylgarska Akademiya na Naukite, Sofia)

1980-01-01

Pontecorvo neutrino beam oscillations are discussed assuming both Dirac and Majorana neutrino mass terms. It is proved that none of possible experiments on neutrino oscillations, including those on effects of CP violation, can distinguish between these two possibilities. Neutrino oscillations with concomitant Dirac and Majorana mass terms are also considered

Dirac in 20th century physics: a centenary assessment

International Nuclear Information System (INIS)

Sanyuk, Valerii I; Sukhanov, Alexander D

2003-01-01

Current views on Dirac's creative heritage and on his role in the formation and development of quantum physics and in shaping the physical picture of the world are discussed. Dirac's fundamental ideas in later life (1948 - 1984) and their current development are given considerable attention. (from the history of physics)

Evaluating stereoscopic displays: both efficiency measures and perceived workload sensitive to manipulations in binocular disparity

Science.gov (United States)

van Beurden, Maurice H. P. H.; Ijsselsteijn, Wijnand A.; de Kort, Yvonne A. W.

2011-03-01

Stereoscopic displays are known to offer a number of key advantages in visualizing complex 3D structures or datasets. The large majority of studies that focus on evaluating stereoscopic displays for professional applications use completion time and/or the percentage of correct answers to measure potential performance advantages. However, completion time and accuracy may not fully reflect all the benefits of stereoscopic displays. In this paper, we argue that perceived workload is an additional valuable indicator reflecting the extent to which users can benefit from using stereoscopic displays. We performed an experiment in which participants were asked to perform a visual path-tracing task within a convoluted 3D wireframe structure, varying in level of complexity of the visualised structure and level of disparity of the visualisation. The results showed that an optimal performance (completion time, accuracy and workload), depend both on task difficulty and disparity level. Stereoscopic disparity revealed a faster and more accurate task performance, whereas we observed a trend that performance on difficult tasks stands to benefit more from higher levels of disparity than performance on easy tasks. Perceived workload (as measured using the NASA-TLX) showed a similar response pattern, providing evidence that perceived workload is sensitive to variations in disparity as well as task difficulty. This suggests that perceived workload could be a useful concept, in addition to standard performance indicators, in characterising and measuring human performance advantages when using stereoscopic displays.

DIRAC: Secure web user interface

International Nuclear Information System (INIS)

Casajus Ramo, A; Sapunov, M

2010-01-01

Traditionally the interaction between users and the Grid is done with command line tools. However, these tools are difficult to use by non-expert users providing minimal help and generating outputs not always easy to understand especially in case of errors. Graphical User Interfaces are typically limited to providing access to the monitoring or accounting information and concentrate on some particular aspects failing to cover the full spectrum of grid control tasks. To make the Grid more user friendly more complete graphical interfaces are needed. Within the DIRAC project we have attempted to construct a Web based User Interface that provides means not only for monitoring the system behavior but also allows to steer the main user activities on the grid. Using DIRAC's web interface a user can easily track jobs and data. It provides access to job information and allows performing actions on jobs such as killing or deleting. Data managers can define and monitor file transfer activity as well as check requests set by jobs. Production managers can define and follow large data productions and react if necessary by stopping or starting them. The Web Portal is build following all the grid security standards and using modern Web 2.0 technologies which allow to achieve the user experience similar to the desktop applications. Details of the DIRAC Web Portal architecture and User Interface will be presented and discussed.

Relativistic space-charge-limited current for massive Dirac fermions

Science.gov (United States)

Ang, Y. S.; Zubair, M.; Ang, L. K.

2017-04-01

A theory of relativistic space-charge-limited current (SCLC) is formulated to determine the SCLC scaling, J ∝Vα/Lβ , for a finite band-gap Dirac material of length L biased under a voltage V . In one-dimensional (1D) bulk geometry, our model allows (α ,β ) to vary from (2,3) for the nonrelativistic model in traditional solids to (3/2,2) for the ultrarelativistic model of massless Dirac fermions. For 2D thin-film geometry we obtain α =β , which varies between 2 and 3/2, respectively, at the nonrelativistic and ultrarelativistic limits. We further provide rigorous proof based on a Green's-function approach that for a uniform SCLC model described by carrier-density-dependent mobility, the scaling relations of the 1D bulk model can be directly mapped into the case of 2D thin film for any contact geometries. Our simplified approach provides a convenient tool to obtain the 2D thin-film SCLC scaling relations without the need of explicitly solving the complicated 2D problems. Finally, this work clarifies the inconsistency in using the traditional SCLC models to explain the experimental measurement of a 2D Dirac semiconductor. We conclude that the voltage scaling 3 /2 <α <2 is a distinct signature of massive Dirac fermions in a Dirac semiconductor and is in agreement with experimental SCLC measurements in MoS2.

Split Dirac Supersymmetry: An Ultraviolet Completion of Higgsino Dark Matter

Energy Technology Data Exchange (ETDEWEB)

Fox, Patrick J. [Fermilab; Kribs, Graham D. [Oregon U.; Martin, Adam [Notre Dame U.

2014-10-07

Motivated by the observation that the Higgs quartic coupling runs to zero at an intermediate scale, we propose a new framework for models of split supersymmetry, in which gauginos acquire intermediate scale Dirac masses of $\\sim 10^{8-11}$ GeV. Scalar masses arise from one-loop finite contributions as well as direct gravity-mediated contributions. Like split supersymmetry, one Higgs doublet is fine-tuned to be light. The scale at which the Dirac gauginos are introduced to make the Higgs quartic zero is the same as is necessary for gauge coupling unification. Thus, gauge coupling unification persists (nontrivially, due to adjoint multiplets), though with a somewhat higher unification scale $\\gtrsim 10^{17}$ GeV. The $\\mu$-term is naturally at the weak scale, and provides an opportunity for experimental verification. We present two manifestations of Split Dirac Supersymmetry. In the "Pure Dirac" model, the lightest Higgsino must decay through R-parity violating couplings, leading to an array of interesting signals in colliders. In the "Hypercharge Impure" model, the bino acquires a Majorana mass that is one-loop suppressed compared with the Dirac gluino and wino. This leads to weak scale Higgsino dark matter whose overall mass scale, as well as the mass splitting between the neutral components, is naturally generated from the same UV dynamics. We outline the challenges to discovering pseudo-Dirac Higgsino dark matter in collider and dark matter detection experiments.

Dirac directional emission in anisotropic zero refractive index photonic crystals.

Science.gov (United States)

He, Xin-Tao; Zhong, Yao-Nan; Zhou, You; Zhong, Zhi-Chao; Dong, Jian-Wen

2015-08-14

A certain class of photonic crystals with conical dispersion is known to behave as isotropic zero-refractive-index medium. However, the discrete building blocks in such photonic crystals are limited to construct multidirectional devices, even for high-symmetric photonic crystals. Here, we show multidirectional emission from low-symmetric photonic crystals with semi-Dirac dispersion at the zone center. We demonstrate that such low-symmetric photonic crystal can be considered as an effective anisotropic zero-refractive-index medium, as long as there is only one propagation mode near Dirac frequency. Four kinds of Dirac multidirectional emitters are achieved with the channel numbers of five, seven, eleven, and thirteen, respectively. Spatial power combination for such kind of Dirac directional emitter is also verified even when multiple sources are randomly placed in the anisotropic zero-refractive-index photonic crystal.

First-Principles Prediction of Spin-Polarized Multiple Dirac Rings in Manganese Fluoride

Science.gov (United States)

Jiao, Yalong; Ma, Fengxian; Zhang, Chunmei; Bell, John; Sanvito, Stefano; Du, Aijun

2017-07-01

Spin-polarized materials with Dirac features have sparked great scientific interest due to their potential applications in spintronics. But such a type of structure is very rare and none has been fabricated. Here, we investigate the already experimentally synthesized manganese fluoride (MnF3 ) as a novel spin-polarized Dirac material by using first-principles calculations. MnF3 exhibits multiple Dirac cones in one spin orientation, while it behaves like a large gap semiconductor in the other spin channel. The estimated Fermi velocity for each cone is of the same order of magnitude as that in graphene. The 3D band structure further reveals that MnF3 possesses rings of Dirac nodes in the Brillouin zone. Such a spin-polarized multiple Dirac ring feature is reported for the first time in an experimentally realized material. Moreover, similar band dispersions can be also found in other transition metal fluorides (e.g., CoF3 , CrF3 , and FeF3 ). Our results highlight a new interesting single-spin Dirac material with promising applications in spintronics and information technologies.

First-Principles Prediction of Spin-Polarized Multiple Dirac Rings in Manganese Fluoride.

Science.gov (United States)

Jiao, Yalong; Ma, Fengxian; Zhang, Chunmei; Bell, John; Sanvito, Stefano; Du, Aijun

2017-07-07

Spin-polarized materials with Dirac features have sparked great scientific interest due to their potential applications in spintronics. But such a type of structure is very rare and none has been fabricated. Here, we investigate the already experimentally synthesized manganese fluoride (MnF_{3}) as a novel spin-polarized Dirac material by using first-principles calculations. MnF_{3} exhibits multiple Dirac cones in one spin orientation, while it behaves like a large gap semiconductor in the other spin channel. The estimated Fermi velocity for each cone is of the same order of magnitude as that in graphene. The 3D band structure further reveals that MnF_{3} possesses rings of Dirac nodes in the Brillouin zone. Such a spin-polarized multiple Dirac ring feature is reported for the first time in an experimentally realized material. Moreover, similar band dispersions can be also found in other transition metal fluorides (e.g., CoF_{3}, CrF_{3}, and FeF_{3}). Our results highlight a new interesting single-spin Dirac material with promising applications in spintronics and information technologies.

Strangest man the hidden life of Paul Dirac, quantum genius

CERN Document Server

Farmelo, Graham

2009-01-01

Paul Dirac was among the great scientific geniuses of the modern age. One of the discoverers of quantum mechanics, the most revolutionary theory of the past century, his contributions had a unique insight, eloquence, clarity, and mathematical power. His prediction of antimatter was one of the greatest triumphs in the history of physics. One of Einstein's most admired colleagues, Dirac was in 1933 the youngest theoretician ever to win the Nobel Prize in physics. Dirac's personality is legendary. He was an extraordinarily reserved loner, relentlessly literal-minded and appeared to have no empath

impact of workload induced stress on the professional effectiveness

African Journals Online (AJOL)

PROF EKWUEME

aids, evaluation of students, learning motivation, classroom management, supervision of co-curricular activities and ... of workload. KEYWORDS; Stress, Workload, Professional effectiveness, Teachers, Cross River State .... determining the relationship between workload ..... adapted to cope with the stress that could have.

Halogenated arsenenes as Dirac materials

International Nuclear Information System (INIS)

Tang, Wencheng; Sun, Minglei; Ren, Qingqiang; Wang, Sake; Yu, Jin

2016-01-01

Highlights: • We have revealed the presence of Dirac cone in fully-halogenated arsenene compounds. • All fully-halogenated arsenene except As_2I_2 would spontaneously form and stable in defending the thermal fluctuation in room temperature. - Abstract: Arsenene is the graphene-like arsenic nanosheet, which has been predicted very recently [S. Zhang, Z. Yan, Y. Li, Z. Chen, and H. Zeng, Angewandte Chemie, 127 (2015) 3155–3158]. Using first-principles calculations, we systematically investigate the structures and electronic properties of fully-halogenated arsenenes. Formation energy analysis reveals that all the fully-halogenated arsenenes except iodinated arsenene are energetically favorable and could be synthesized. We have revealed the presence of Dirac cone in fully-halogenated arsenene compounds. They may have great potential applications in next generation of high-performance devices.

The algebraic manipulation program DIRAC on IBM personal computers

International Nuclear Information System (INIS)

Grozin, A.G.; Perlt, H.

1989-01-01

The version DIRAC (2.2) for IBM compatible personal computers is described. It is designed to manipulate algebraically with polynomials and tensors. After a short introduction concerning implementation and usage on personal computers an example program is given. It contains a detailed user's guide to DIRAC (2.2) and, additionally some useful applications. 4 refs

School Nurse Workload: A Scoping Review of Acute Care, Community Health, and Mental Health Nursing Workload Literature

Science.gov (United States)

Endsley, Patricia

2017-01-01

The purpose of this scoping review was to survey the most recent (5 years) acute care, community health, and mental health nursing workload literature to understand themes and research avenues that may be applicable to school nursing workload research. The search for empirical and nonempirical literature was conducted using search engines such as…

Dirac fermions in nontrivial topology black hole backgrounds

International Nuclear Information System (INIS)

Gozdz, Marek; Nakonieczny, Lukasz; Rogatko, Marek

2010-01-01

We discuss the behavior of the Dirac fermions in a general spherically symmetric black hole background with a nontrivial topology of the event horizon. Both massive and massless cases are taken into account. We will conduct an analytical study of intermediate and late-time behavior of massive Dirac hair in the background of a black hole with a global monopole and dilaton black hole pierced by a cosmic string. In the case of a global monopole swallowed by a static black hole, the intermediate late-time behavior depends on the mass of the Dirac field, the multiple number of the wave mode, and the global monopole parameter. The late-time behavior is quite independent of these factors and has a decay rate proportional to t -5/6 . As far as the black hole pierced by a cosmic string is concerned, the intermediate late-time behavior depends only on the hair mass and the multipole number of the wave mode, while the late-time behavior dependence is the same as in the previous case. The main modification stems from the topology of the S 2 sphere pierced by a cosmic string. This factor modifies the eigenvalues of the Dirac operator acting on the transverse manifold.

Optimizing Preseason Training Loads in Australian Football.

Science.gov (United States)

Carey, David L; Crow, Justin; Ong, Kok-Leong; Blanch, Peter; Morris, Meg E; Dascombe, Ben J; Crossley, Kay M

2018-02-01

To investigate whether preseason training plans for Australian football can be computer generated using current training-load guidelines to optimize injury-risk reduction and performance improvement. A constrained optimization problem was defined for daily total and sprint distance, using the preseason schedule of an elite Australian football team as a template. Maximizing total training volume and maximizing Banister-model-projected performance were both considered optimization objectives. Cumulative workload and acute:chronic workload-ratio constraints were placed on training programs to reflect current guidelines on relative and absolute training loads for injury-risk reduction. Optimization software was then used to generate preseason training plans. The optimization framework was able to generate training plans that satisfied relative and absolute workload constraints. Increasing the off-season chronic training loads enabled the optimization algorithm to prescribe higher amounts of "safe" training and attain higher projected performance levels. Simulations showed that using a Banister-model objective led to plans that included a taper in training load prior to competition to minimize fatigue and maximize projected performance. In contrast, when the objective was to maximize total training volume, more frequent training was prescribed to accumulate as much load as possible. Feasible training plans that maximize projected performance and satisfy injury-risk constraints can be automatically generated by an optimization problem for Australian football. The optimization methods allow for individualized training-plan design and the ability to adapt to changing training objectives and different training-load metrics.

Shot noise in systems with semi-Dirac points

International Nuclear Information System (INIS)

Zhai, Feng; Wang, Juan

2014-01-01

We calculate the ballistic conductance and shot noise of electrons through a two-dimensional stripe system (width W ≫ length L) with semi-Dirac band-touching points. We find that the ratio between zero-temperature noise power and mean current (the Fano factor) is highly anisotropic. When the transport is along the linear-dispersion direction and the Fermi energy is fixed at the semi-Dirac point, the Fano factor has a universal value F = 0.179 while a minimum conductivity exists and scales with L 1∕2 . Along the parabolic dispersion direction, the Fano factor at the semi-Dirac point has a contact-independent limit exceeding 0.9, which varies weakly with L due to the common-path interference of evanescent waves. Our findings suggest a way to discern the type of band-touching points

Dirac charge dynamics in graphene by infrared spectroscopy

International Nuclear Information System (INIS)

Martin, Michael C; Li, Z.Q.; Henriksen, E.A.; Jiang, Z.; Hao, Z.; Martin, Michael C; Kim, P.; Stormer, H.L.; Basov, Dimitri N.

2008-01-01

A remarkable manifestation of the quantum character of electrons in matter is offered by graphene, a single atomic layer of graphite. Unlike conventional solids where electrons are described with the Schroedinger equation, electronic excitations in graphene are governed by the Dirac hamiltonian. Some of the intriguing electronic properties of graphene, such as massless Dirac quasiparticles with linear energy-momentum dispersion, have been confirmed by recent observations. Here, we report an infrared spectromicroscopy study of charge dynamics in graphene integrated in gated devices. Our measurements verify the expected characteristics of graphene and, owing to the previously unattainable accuracy of infrared experiments, also uncover significant departures of the quasiparticle dynamics from predictions made for Dirac fermions in idealized, free-standing graphene. Several observations reported here indicate the relevance of many-body interactions to the electromagnetic response of graphene

A self-analysis of the NASA-TLX workload measure.

Science.gov (United States)

Noyes, Jan M; Bruneau, Daniel P J

2007-04-01

Computer use and, more specifically, the administration of tests and materials online continue to proliferate. A number of subjective, self-report workload measures exist, but the National Aeronautics and Space Administration-Task Load Index (NASA-TLX) is probably the most well known and used. The aim of this paper is to consider the workload costs associated with the computer-based and paper versions of the NASA-TLX measure. It was found that there is a significant difference between the workload scores for the two media, with the computer version of the NASA-TLX incurring more workload. This has implications for the practical use of the NASA-TLX as well as for other computer-based workload measures.

Special function solutions of the free particle Dirac equation

International Nuclear Information System (INIS)

Strange, P

2012-01-01

The Dirac equation is one of the fundamental equations in physics. Here we present and discuss two novel solutions of the free particle Dirac equation. These solutions have an exact analytical form in terms of Airy or Mathieu functions and exhibit unexpected properties including an enhanced Doppler effect, accelerating wavefronts and solutions with a degree of localization. (paper)

Workload Measurement in Human Autonomy Teaming: How and Why?

Science.gov (United States)

Shively, Jay

2016-01-01

This is an invited talk on autonomy and workload for an AFRL Blue Sky workshop sponsored by the Florida Institute for Human Machine Studies. The presentation reviews various metrics of workload and how to move forward with measuring workload in a human-autonomy teaming environment.

Mental workload measurement in operator control room using NASA-TLX

Science.gov (United States)

Sugarindra, M.; Suryoputro, M. R.; Permana, A. I.

2017-12-01

The workload, encountered a combination of physical workload and mental workload, is a consequence of the activities for workers. Central control room is one department in the oil processing company, employees tasked with monitoring the processing unit for 24 hours nonstop with a combination of 3 shifts in 8 hours. NASA-TLX (NASA Task Load Index) is one of the subjective mental workload measurement using six factors, namely the Mental demand (MD), Physical demand (PD), Temporal demand (TD), Performance (OP), Effort (EF), frustration levels (FR). Measurement of a subjective mental workload most widely used because it has a high degree of validity. Based on the calculation of the mental workload, there at 5 units (DTU, NPU, HTU, DIST and OPS) at the control chamber (94; 83.33; 94.67; 81, 33 and 94.67 respectively) that categorize as very high mental workload. The high level of mental workload on the operator in the Central Control Room is a requirement to have high accuracy, alertness and can make decisions quickly

Einstein-Cartan-Dirac theory in (1+2)-dimensions

Energy Technology Data Exchange (ETDEWEB)

Dereli, Tekin [Koc University, Department of Physics, Istanbul (Turkey); Oezdemir, Nese [Istanbul Technical University, Department of Physics Engineering, Istanbul (Turkey); Sert, Oezcan [Pamukkale University, Department of Physics, Denizli (Turkey)

2013-01-15

Einstein-Cartan theory is formulated in (1+2) dimensions using the algebra of exterior differential forms. A Dirac spinor is coupled to gravity and the field equations are obtained by a variational principle. The space-time torsion is found to be given algebraically in terms of a quadratic spinor condensate field. Circularly symmetric, exact solutions that collapse to AdS{sub 3} geometry in the absence of the Dirac condensate are found. (orig.)

Nonlinear Excitations in Strongly-Coupled Fermi-Dirac Plasmas

OpenAIRE

Akbari-Moghanjoughi, M.

2012-01-01

In this paper we use the conventional quantum hydrodynamics (QHD) model in combination with the Sagdeev pseudopotential method to explore the effects of Thomas-Fermi nonuniform electron distribution, Coulomb interactions, electron exchange and ion correlation on the large-amplitude nonlinear soliton dynamics in Fermi-Dirac plasmas. It is found that in the presence of strong interactions significant differences in nonlinear wave dynamics of Fermi-Dirac plasmas in the two distinct regimes of no...

Front-line ordering clinicians: matching workforce to workload.

Science.gov (United States)

Fieldston, Evan S; Zaoutis, Lisa B; Hicks, Patricia J; Kolb, Susan; Sladek, Erin; Geiger, Debra; Agosto, Paula M; Boswinkel, Jan P; Bell, Louis M

2014-07-01

Matching workforce to workload is particularly important in healthcare delivery, where an excess of workload for the available workforce may negatively impact processes and outcomes of patient care and resident learning. Hospitals currently lack a means to measure and match dynamic workload and workforce factors. This article describes our work to develop and obtain consensus for use of an objective tool to dynamically match the front-line ordering clinician (FLOC) workforce to clinical workload in a variety of inpatient settings. We undertook development of a tool to represent hospital workload and workforce based on literature reviews, discussions with clinical leadership, and repeated validation sessions. We met with physicians and nurses from every clinical care area of our large, urban children's hospital at least twice. We successfully created a tool in a matrix format that is objective and flexible and can be applied to a variety of settings. We presented the tool in 14 hospital divisions and received widespread acceptance among physician, nursing, and administrative leadership. The hospital uses the tool to identify gaps in FLOC coverage and guide staffing decisions. Hospitals can better match workload to workforce if they can define and measure these elements. The Care Model Matrix is a flexible, objective tool that quantifies the multidimensional aspects of workload and workforce. The tool, which uses multiple variables that are easily modifiable, can be adapted to a variety of settings. © 2014 Society of Hospital Medicine.

Avoid the tsunami of the Dirac sea in the imaginary time step method

International Nuclear Information System (INIS)

Zhang, Ying; Liang, Haozhao; Meng, Jie

2010-01-01

The discrete single-particle spectra in both the Fermi and Dirac sea have been calculated by the imaginary time step (ITS) method for the Schroedinger-like equation after avoiding the "tsunami" of the Dirac sea, i.e. the diving behavior of the single-particle level into the Dirac sea in the direct application of the ITS method for the Dirac equation. It is found that by the transform from the Dirac equation to the Schroedinger-like equation, the single-particle spectra, which extend from the positive to the negative infinity, can be separately obtained by the ITS evolution in either the Fermi sea or the Dirac sea. Identical results with those in the conventional shooting method have been obtained via the ITS evolution for the equivalent Schroedinger-like equation, which demonstrates the feasibility, practicality and reliability of the present algorithm and dispels the doubts on the ITS method in the relativistic system. (author)

Self-Assembled Si(111) Surface States: 2D Dirac Material for THz Plasmonics

Science.gov (United States)

Wang, Z. F.; Liu, Feng

2015-07-01

Graphene, the first discovered 2D Dirac material, has had a profound impact on science and technology. In the last decade, we have witnessed huge advances in graphene related fundamental and applied research. Here, based on first-principles calculations, we propose a new 2D Dirac band on the Si(111) surface with 1 /3 monolayer halogen coverage. The s p3 dangling bonds form a honeycomb superstructure on the Si(111) surface that results in an anisotropic Dirac band with a group velocity (˜106 m /s ) comparable to that in graphene. Most remarkably, the Si-based surface Dirac band can be used to excite a tunable THz plasmon through electron-hole doping. Our results demonstrate a new way to design Dirac states on a traditional semiconductor surface, so as to make them directly compatible with Si technology. We envision this new type of Dirac material to be generalized to other semiconductor surfaces with broad applications.

Self-Assembled Si(111) Surface States: 2D Dirac Material for THz Plasmonics.

Science.gov (United States)

Wang, Z F; Liu, Feng

2015-07-10

Graphene, the first discovered 2D Dirac material, has had a profound impact on science and technology. In the last decade, we have witnessed huge advances in graphene related fundamental and applied research. Here, based on first-principles calculations, we propose a new 2D Dirac band on the Si(111) surface with 1/3 monolayer halogen coverage. The sp(3) dangling bonds form a honeycomb superstructure on the Si(111) surface that results in an anisotropic Dirac band with a group velocity (∼10(6)  m/s) comparable to that in graphene. Most remarkably, the Si-based surface Dirac band can be used to excite a tunable THz plasmon through electron-hole doping. Our results demonstrate a new way to design Dirac states on a traditional semiconductor surface, so as to make them directly compatible with Si technology. We envision this new type of Dirac material to be generalized to other semiconductor surfaces with broad applications.

A comparison of policies on nurse faculty workload in the United States.

Science.gov (United States)

Ellis, Peggy A

2013-01-01

This article describes nurse faculty workload policies from across the nation in order to assess current practice. There is a well-documented shortage of nursing faculty leading to an increase in workload demands. Increases in faculty workload results in difficulties with work-life balance and dissatisfaction threatening to make nursing education less attractive to young faculty. In order to begin an examination of faculty workload in nursing, existing workloads must be known. Faculty workload data were solicited from nursing programs nationwide and analyzed to determine the current workloads. The most common faculty teaching workload reported overall for nursing is 12 credit hours per semester; however, some variations exist. Consideration should be given to the multiple components of the faculty workload. Research is needed to address the most effective and efficient workload allocation for nursing faculty.

Dirac Material Graphene

OpenAIRE

Sheka, Elena F.

2016-01-01

The paper presents the author view on spin-rooted properties of graphene supported by numerous experimental and calculation evidences. Dirac fermions of crystalline graphene and local spins of graphene molecules are suggested to meet a strict demand - different orbitals for different spins- which leads to a large spectrum of effects caused by spin polarization of electronic states. The consequent topological non-triviality, making graphene topological insulator, and local spins, imaging graph...

Dirac particle in a box, and relativistic quantum Zeno dynamics

International Nuclear Information System (INIS)

Menon, Govind; Belyi, Sergey

2004-01-01

After developing a complete set of eigenfunctions for a Dirac particle restricted to a box, the quantum Zeno dynamics of a relativistic system is considered. The evolution of a continuously observed quantum mechanical system is governed by the theorem put forth by Misra and Sudarshan. One of the conditions for quantum Zeno dynamics to be manifest is that the Hamiltonian is semi-bounded. This Letter analyzes the effects of continuous observation of a particle whose time evolution is generated by the Dirac Hamiltonian. The theorem by Misra and Sudarshan is not applicable here since the Dirac operator is not semi-bounded

Excitation spectrum of correlated Dirac fermions

Science.gov (United States)

Jalali, Z.; Jafari, S. A.

2015-04-01

Motivated by the puzzling optical conductivity measurements in graphene, we speculate on the possible role of strong electronic correlations on the two-dimensional Dirac fermions. In this work we employ the slave-particle method to study the excitations of the Hubbard model on honeycomb lattice, away from half-filling. Since the ratio U/t ≈ 3.3 in graphene is not infinite, double occupancy is not entirely prohibited and hence a finite density of doublonscan be generated. We therefore extend the Ioff-Larkin composition rule to include a finite density of doublons. We then investigate the role played by each of these auxiliary particles in the optical absorption of strongly correlated Dirac fermions.

Dirac equation in Kerr space-time

Energy Technology Data Exchange (ETDEWEB)

Iyer, B R; Kumar, Arvind [Bombay Univ. (India). Dept. of Physics

1976-06-01

The weak-field low-velocity approximation of Dirac equation in Kerr space-time is investigated. The interaction terms admit of an interpretation in terms of a 'dipole-dipole' interaction in addition to coupling of spin with the angular momentum of the rotating source. The gravitational gyro-factor for spin is identified. The charged case (Kerr-Newman) is studied using minimal prescription for electromagnetic coupling in the locally intertial frame and to the leading order the standard electromagnetic gyro-factor is retrieved. A first order perturbation calculation of the shift of the Schwarzchild energy level yields the main interesting result of this work: the anomalous Zeeman splitting of the energy level of a Dirac particle in Kerr metric.

A model for pseudo-Dirac neutrinos: leptogenesis and ultra-high energy neutrinos

Energy Technology Data Exchange (ETDEWEB)

Ahn, Y.H. [Center for Theoretical Physics of the Universe, Institute for Basic Science (IBS),Daejeon, 34051 (Korea, Republic of); Kang, Sin Kyu [Insitute for Convergence Fundamental Study, School of Liberal Arts, Seoul-Tech.,Seoul, 01811 (Korea, Republic of); Kim, C.S. [Dept. of Physics and IPAP, Yonsei University,Seoul, 120-749 (Korea, Republic of)

2016-10-18

We propose a model where sterile neutrinos are introduced to make light neutrinos to be pseudo-Dirac particles. It is shown how tiny mass splitting necessary for realizing pseudo-Dirac neutrinos can be achieved. Within the model, we show how leptogenesis can be successfully generated. Motivated by the recent observation of very high energy neutrino events at IceCube, we study a possibility to observe the effects of the pseudo-Dirac property of neutrinos by performing astronomical-scale baseline experiments to uncover the oscillation effects of very tiny mass splitting. We also discuss future prospect to observe the effects of the pseudo-Dirac property of neutrinos at high energy neutrino experiments.

Electron mean-free-path filtering in Dirac material for improved thermoelectric performance.

Science.gov (United States)

Liu, Te-Huan; Zhou, Jiawei; Li, Mingda; Ding, Zhiwei; Song, Qichen; Liao, Bolin; Fu, Liang; Chen, Gang

2018-01-30

Recent advancements in thermoelectric materials have largely benefited from various approaches, including band engineering and defect optimization, among which the nanostructuring technique presents a promising way to improve the thermoelectric figure of merit ( zT ) by means of reducing the characteristic length of the nanostructure, which relies on the belief that phonons' mean free paths (MFPs) are typically much longer than electrons'. Pushing the nanostructure sizes down to the length scale dictated by electron MFPs, however, has hitherto been overlooked as it inevitably sacrifices electrical conduction. Here we report through ab initio simulations that Dirac material can overcome this limitation. The monotonically decreasing trend of the electron MFP allows filtering of long-MFP electrons that are detrimental to the Seebeck coefficient, leading to a dramatically enhanced power factor. Using SnTe as a material platform, we uncover this MFP filtering effect as arising from its unique nonparabolic Dirac band dispersion. Room-temperature zT can be enhanced by nearly a factor of 3 if one designs nanostructures with grain sizes of ∼10 nm. Our work broadens the scope of the nanostructuring approach for improving the thermoelectric performance, especially for materials with topologically nontrivial electronic dynamics.

Mental workload and motor performance dynamics during practice of reaching movements under various levels of task difficulty.

Science.gov (United States)

Shuggi, Isabelle M; Oh, Hyuk; Shewokis, Patricia A; Gentili, Rodolphe J

2017-09-30

The assessment of mental workload can inform attentional resource allocation during task performance that is essential for understanding the underlying principles of human cognitive-motor behavior. While many studies have focused on mental workload in relation to human performance, a modest body of work has examined it in a motor practice/learning context without considering individual variability. Thus, this work aimed to examine mental workload by employing the NASA TLX as well as the changes in motor performance resulting from the practice of a novel reaching task. Two groups of participants practiced a reaching task at a high and low nominal difficulty during which a group-level analysis assessed the mental workload, motor performance and motor improvement dynamics. A secondary cluster analysis was also conducted to identify specific individual patterns of cognitive-motor responses. Overall, both group- and cluster-level analyses revealed that: (i) all participants improved their performance throughout motor practice, and (ii) an increase in mental workload was associated with a reduction of the quality of motor performance along with a slower rate of motor improvement. The results are discussed in the context of the optimal challenge point framework and in particular it is proposed that under the experimental conditions employed here, functional task difficulty: (i) would possibly depend on an individuals' information processing capabilities, and (ii) could be indexed by the level of mental workload which, when excessively heightened can decrease the quality of performance and more generally result in delayed motor improvements. Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.

Procedures of grasp92 code to calculate accurate Dirac-Coulomb energy for the ground sate of helium atom

International Nuclear Information System (INIS)

Utsumi, Takayuki; Sasaki, Akira

2000-02-01

The procedures of grasp92 code to calculate accurate (relative error nearly equal 10 -7 ) eigenvalue for the ground sate of helium atom of the Dirac-Coulomb Hamiltonian are presented. The grasp92 code, based on the multi-configuration Dirac-Fock method, is widely used to calculate the atomic properties. However, the main part of the accurate calculations, extended optimal level calculation (EOL), suffer frequently numerical instabilities due to the lack of the confident procedures. The purpose of this report is to illustrate the guideline for stable EOL calculations by calculating the most fundamental atomic system, i.e. the ground sate of helium atom ls 2 1 S 2 . This procedure could be extended for the high-precise eigenfunction calculation of more complex atomic systems, for example highly ionized atoms and high-Z atoms. (author)

Considerations concering the generalization of the Dirac equations to unstable fermions

International Nuclear Information System (INIS)

Kniehl, Bernd A.; Sirlin, Alberto

2014-08-01

We discuss the generalization of the Dirac equations and spinors in momentum space to free unstable spin-1/2 fermions taking into account the fundamental requirement of Lorentz covariance. We derive the generalized adjoint Dirac equations and spinors, and explain the very simple relation that exists, in our formulation, between the unstable and stable cases. As an application of the generalized spinors, we evaluate the probability density. We also discuss the behavior of the generalized Dirac equations under time reversal.

Assessing Clinical Trial-Associated Workload in Community-Based Research Programs Using the ASCO Clinical Trial Workload Assessment Tool.

Science.gov (United States)

Good, Marjorie J; Hurley, Patricia; Woo, Kaitlin M; Szczepanek, Connie; Stewart, Teresa; Robert, Nicholas; Lyss, Alan; Gönen, Mithat; Lilenbaum, Rogerio

2016-05-01

Clinical research program managers are regularly faced with the quandary of determining how much of a workload research staff members can manage while they balance clinical practice and still achieve clinical trial accrual goals, maintain data quality and protocol compliance, and stay within budget. A tool was developed to measure clinical trial-associated workload, to apply objective metrics toward documentation of work, and to provide clearer insight to better meet clinical research program challenges and aid in balancing staff workloads. A project was conducted to assess the feasibility and utility of using this tool in diverse research settings. Community-based research programs were recruited to collect and enter clinical trial-associated monthly workload data into a web-based tool for 6 consecutive months. Descriptive statistics were computed for self-reported program characteristics and workload data, including staff acuity scores and number of patient encounters. Fifty-one research programs that represented 30 states participated. Median staff acuity scores were highest for staff with patients enrolled in studies and receiving treatment, relative to staff with patients in follow-up status. Treatment trials typically resulted in higher median staff acuity, relative to cancer control, observational/registry, and prevention trials. Industry trials exhibited higher median staff acuity scores than trials sponsored by the National Institutes of Health/National Cancer Institute, academic institutions, or others. The results from this project demonstrate that trial-specific acuity measurement is a better measure of workload than simply counting the number of patients. The tool was shown to be feasible and useable in diverse community-based research settings. Copyright © 2016 by American Society of Clinical Oncology.

Kinks and the Dirac equation

International Nuclear Information System (INIS)

Skyrme, T.H.R.

1994-01-01

In a model quantum theory of interacting mesons, the motion of certain conserved particle-like structures is discussed. It is shown how collective coordinates may be introduced to describe them, leading, in lowest approximation, to a Dirac equation. (author)

Relativistic Photoionization Computations with the Time Dependent Dirac Equation

Science.gov (United States)

2016-10-12

Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/6795--16-9698 Relativistic Photoionization Computations with the Time Dependent Dirac... Photoionization Computations with the Time Dependent Dirac Equation Daniel F. Gordon and Bahman Hafizi Naval Research Laboratory 4555 Overlook Avenue, SW...Unclassified Unlimited Unclassified Unlimited 22 Daniel Gordon (202) 767-5036 Tunneling Photoionization Ionization of inner shell electrons by laser

Equivalence of Dirac quantization and Schwinger's action principle quantization

International Nuclear Information System (INIS)

Das, A.; Scherer, W.

1987-01-01

We show that the method of Dirac quantization is equivalent to Schwinger's action principle quantization. The relation between the Lagrange undetermined multipliers in Schwinger's method and Dirac's constraint bracket matrix is established and it is explicitly shown that the two methods yield identical (anti)commutators. This is demonstrated in the non-trivial example of supersymmetric quantum mechanics in superspace. (orig.)

Dark matter scenarios in a constrained model with Dirac gauginos

CERN Document Server

Goodsell, Mark D.; Müller, Tobias; Porod, Werner; Staub, Florian

2015-01-01

We perform the first analysis of Dark Matter scenarios in a constrained model with Dirac Gauginos. The model under investigation is the Constrained Minimal Dirac Gaugino Supersymmetric Standard model (CMDGSSM) where the Majorana mass terms of gauginos vanish. However, $R$-symmetry is broken in the Higgs sector by an explicit and/or effective $B_\\mu$-term. This causes a mass splitting between Dirac states in the fermion sector and the neutralinos, which provide the dark matter candidate, become pseudo-Dirac states. We discuss two scenarios: the universal case with all scalar masses unified at the GUT scale, and the case with non-universal Higgs soft-terms. We identify different regions in the parameter space which fullfil all constraints from the dark matter abundance, the limits from SUSY and direct dark matter searches and the Higgs mass. Most of these points can be tested with the next generation of direct dark matter detection experiments.

Dirac Magnon Nodal Loops in Quasi-2D Quantum Magnets.

Science.gov (United States)

Owerre, S A

2017-07-31

In this report, we propose a new concept of one-dimensional (1D) closed lines of Dirac magnon nodes in two-dimensional (2D) momentum space of quasi-2D quantum magnetic systems. They are termed "2D Dirac magnon nodal-line loops". We utilize the bilayer honeycomb ferromagnets with intralayer coupling J and interlayer coupling J L , which is realizable in the honeycomb chromium compounds CrX 3 (X ≡ Br, Cl, and I). However, our results can also exist in other layered quasi-2D quantum magnetic systems. Here, we show that the magnon bands of the bilayer honeycomb ferromagnets overlap for J L  ≠ 0 and form 1D closed lines of Dirac magnon nodes in 2D momentum space. The 2D Dirac magnon nodal-line loops are topologically protected by inversion and time-reversal symmetry. Furthermore, we show that they are robust against weak Dzyaloshinskii-Moriya interaction Δ DM  magnon edge modes.

The Emergence of Dirac points in Photonic Crystals with Mirror Symmetry

Science.gov (United States)

He, Wen-Yu; Chan, C. T.

2015-01-01

We show that Dirac points can emerge in photonic crystals possessing mirror symmetry when band gap closes. The mechanism of generating Dirac points is discussed in a two-dimensional photonic square lattice, in which four Dirac points split out naturally after the touching of two bands with different parity. The emergence of such nodal points, characterized by vortex structure in momentum space, is attributed to the unavoidable band crossing protected by mirror symmetry. The Dirac nodes can be unbuckled through breaking the mirror symmetry and a photonic analog of Chern insulator can be achieved through time reversal symmetry breaking. Breaking time reversal symmetry can lead to unidirectional helical edge states and breaking mirror symmetry can reduce the band gap to amplify the finite size effect, providing ways to engineer helical edge states. PMID:25640993

Evaluation of Mental Workload among ICU Ward's Nurses.

Science.gov (United States)

Mohammadi, Mohsen; Mazloumi, Adel; Kazemi, Zeinab; Zeraati, Hojat

2015-01-01

High level of workload has been identified among stressors of nurses in intensive care units (ICUs). The present study investigated nursing workload and identified its influencing perfor-mance obstacles in ICUs. This cross-sectional study was conducted, in 2013, on 81 nurses working in ICUs in Imam Khomeini Hospital in Tehran, Iran. NASA-TLX was applied for assessment of workload. Moreover, ICUs Performance Obstacles Questionnaire was used to identify performance obstacles associated with ICU nursing. Physical demand (mean=84.17) was perceived as the most important dimensions of workload by nurses. The most critical performance obstacles affecting workload included: difficulty in finding a place to sit down, hectic workplace, disorganized workplace, poor-conditioned equipment, waiting for using a piece of equipment, spending much time seeking for supplies in the central stock, poor quality of medical materials, delay in getting medications, unpredicted problems, disorganized central stock, outpatient surgery, spending much time dealing with family needs, late, inadequate, and useless help from nurse assistants, and ineffective morning rounds (P-value<0.05). Various performance obstacles are correlated with nurses' workload, affirms the significance of nursing work system characteristics. Interventions are recommended based on the results of this study in the work settings of nurses in ICUs.

Assessing physician job satisfaction and mental workload.

Science.gov (United States)

Boultinghouse, Oscar W; Hammack, Glenn G; Vo, Alexander H; Dittmar, Mary Lynne

2007-12-01

Physician job satisfaction and mental workload were evaluated in a pilot study of five physicians engaged in a telemedicine practice at The University of Texas Medical Branch at Galveston Electronic Health Network. Several previous studies have examined physician satisfaction with specific telemedicine applications; however, few have attempted to identify the underlying factors that contribute to physician satisfaction or lack thereof. One factor that has been found to affect well-being and functionality in the workplace-particularly with regard to human interaction with complex systems and tasks as seen in telemedicine-is mental workload. Workload is generally defined as the "cost" to a person for performing a complex task or tasks; however, prior to this study, it was unexplored as a variable that influences physician satisfaction. Two measures of job satisfaction were used: The Job Descriptive Index and the Job In General scales. Mental workload was evaluated by means of the National Aeronautics and Space Administration Task Load Index. The measures were administered by means of Web-based surveys and were given twice over a 6-month period. Nonparametric statistical analyses revealed that physician job satisfaction was generally high relative to that of the general population and other professionals. Mental workload scores associated with the practice of telemedicine in this environment are also high, and appeared stable over time. In addition, they are commensurate with scores found in individuals practicing tasks with elevated information-processing demands, such as quality control engineers and air traffic controllers. No relationship was found between the measures of job satisfaction and mental workload.

Activity-based differentiation of pathologists' workload in surgical pathology.

Science.gov (United States)

Meijer, G A; Oudejans, J J; Koevoets, J J M; Meijer, C J L M

2009-06-01

Adequate budget control in pathology practice requires accurate allocation of resources. Any changes in types and numbers of specimens handled or protocols used will directly affect the pathologists' workload and consequently the allocation of resources. The aim of the present study was to develop a model for measuring the pathologists' workload that can take into account the changes mentioned above. The diagnostic process was analyzed and broken up into separate activities. The time needed to perform these activities was measured. Based on linear regression analysis, for each activity, the time needed was calculated as a function of the number of slides or blocks involved. The total pathologists' time required for a range of specimens was calculated based on standard protocols and validated by comparing to actually measured workload. Cutting up, microscopic procedures and dictating turned out to be highly correlated to number of blocks and/or slides per specimen. Calculated workload per type of specimen was significantly correlated to the actually measured workload. Modeling pathologists' workload based on formulas that calculate workload per type of specimen as a function of the number of blocks and slides provides a basis for a comprehensive, yet flexible, activity-based costing system for pathology.

Crew workload-management strategies - A critical factor in system performance

Science.gov (United States)

Hart, Sandra G.

1989-01-01

This paper reviews the philosophy and goals of the NASA/USAF Strategic Behavior/Workload Management Program. The philosophical foundation of the program is based on the assumption that an improved understanding of pilot strategies will clarify the complex and inconsistent relationships observed among objective task demands and measures of system performance and pilot workload. The goals are to: (1) develop operationally relevant figures of merit for performance, (2) quantify the effects of strategic behaviors on system performance and pilot workload, (3) identify evaluation criteria for workload measures, and (4) develop methods of improving pilots' abilities to manage workload extremes.

Workload Characterization of CFD Applications Using Partial Differential Equation Solvers

Science.gov (United States)

Waheed, Abdul; Yan, Jerry; Saini, Subhash (Technical Monitor)

1998-01-01

Workload characterization is used for modeling and evaluating of computing systems at different levels of detail. We present workload characterization for a class of Computational Fluid Dynamics (CFD) applications that solve Partial Differential Equations (PDEs). This workload characterization focuses on three high performance computing platforms: SGI Origin2000, EBM SP-2, a cluster of Intel Pentium Pro bases PCs. We execute extensive measurement-based experiments on these platforms to gather statistics of system resource usage, which results in workload characterization. Our workload characterization approach yields a coarse-grain resource utilization behavior that is being applied for performance modeling and evaluation of distributed high performance metacomputing systems. In addition, this study enhances our understanding of interactions between PDE solver workloads and high performance computing platforms and is useful for tuning these applications.

State of science: mental workload in ergonomics.

Science.gov (United States)

Young, Mark S; Brookhuis, Karel A; Wickens, Christopher D; Hancock, Peter A

2015-01-01

Mental workload (MWL) is one of the most widely used concepts in ergonomics and human factors and represents a topic of increasing importance. Since modern technology in many working environments imposes ever more cognitive demands upon operators while physical demands diminish, understanding how MWL impinges on performance is increasingly critical. Yet, MWL is also one of the most nebulous concepts, with numerous definitions and dimensions associated with it. Moreover, MWL research has had a tendency to focus on complex, often safety-critical systems (e.g. transport, process control). Here we provide a general overview of the current state of affairs regarding the understanding, measurement and application of MWL in the design of complex systems over the last three decades. We conclude by discussing contemporary challenges for applied research, such as the interaction between cognitive workload and physical workload, and the quantification of workload 'redlines' which specify when operators are approaching or exceeding their performance tolerances.

[P.A.M. Dirac and antimatter applied to medicine].

Science.gov (United States)

Kulenović, Fahrudin; Vobornik, Slavenka; Dalagija, Faruk

2003-01-01

Regarding to the hundredth anniversary of P. Dirac birth, it was made review on life and work of this genius in the history of physics and science generally. His ingenious scientific work, that significantly marked contemporary time, was presented in the simplest way with aim to approach more number of readers. Special accent was put on application of Dirac's ideas about antiparticles in medical practice.

Zero-energy eigenstates for the Dirac boundary problem

International Nuclear Information System (INIS)

Hortacsu, M.; Rothe, K.D.; Schroer, B.

1980-01-01

As an alternative to the method of spherical compactification for the Dirac operator in instanton background fields we study the correct method of 'box-quantization': the Atiyah-Patodi-Singer spectral boundary condition. This is the only self-adjoint boundary condition which respects the charge conjugation property and the γ 5 symmetry, apart form the usual breaking due to zero modes. We point out the relevance of this approach to the computation of instanton determinants and other problems involving Dirac spinors. (orig.)

Levinson theorem for Dirac particles in n dimensions

International Nuclear Information System (INIS)

Jiang Yu

2005-01-01

We study the Levinson theorem for a Dirac particle in an n-dimensional central field by use of the Green function approach, based on an analysis of the n-dimensional radial Dirac equation obtained through a simple algebraic derivation. We show that the zero-momentum phase shifts are related to the number of bound states with |E|< m plus the number of half-bound states of zero momenta--i.e., |E|=m--which are denoted by finite, but not square-integrable, wave functions

The Dirac equation in external fields: Variable separation in Cartesian coordinates

International Nuclear Information System (INIS)

Shishkin, G.V.; Cabos, W.D.

1991-01-01

The method of separation of variables in the Dirac equation proposed in an earlier work by one of the present authors [J. Math. Phys. 30, 2132 (1989)] is developed for the complete set of interactions of the Dirac particle. The essence of the method consists of the separation of the first-order matrix differential operators that define the dependence of the Dirac bispinor on the related variables, but commutation of such operators with or between the operator of the equation is not assumed. This approach, which is perfectly justified in the presence of gravitational [Theor. Math. Phys. 70, 204 (1987)] or vector fields [J. Math. Phys. 30, 2132 (1989)], permits one to find all the possibilities of separation of variables in the Dirac equation in the case of the most general set of external fields. The complete set of interactions of the Dirac particle is determined by the symmetry group of equations, namely, viz. the SU(4) group. The interactions are scalar, vector, tensor, pseudovector and pseudoscalar. The analysis in this article is limited to Cartesian coordinates. The corresponding results for the general curvilinear coordinates will be presented in a future paper

New position of Dirac points in the strained graphene reciprocal lattice

Directory of Open Access Journals (Sweden)

Cui-Lian Li

2014-08-01

Full Text Available In the strained graphene, Fermi velocity shows space-dependent and it changes as the position of Dirac point shifts. In this paper, we apply the tight-binding approach within linear elasticity theory to investigate the shifting of Dirac points in the strained graphene reciprocal lattice space. Based on this, we derive the analytical expression on the new positions of the Dirac points as the strain parameter varies. Comparing the data from our analytical expression, ones from Eq. (20 in Phys. Rev. B 80, 045401 (2009, and those from numerical calculation, we find that our analytical expression raises the effective prediction range of the strain parameter from 3% to 15%. i.e., our analytical expression is practicable until the strain parameter is larger than 15%. This almost includes the whole range where the Dirac points present and the energy gap is zero. Moreover, we further calculate the energy gap by numerical method when the shear strain parameter varies from 0 to 20%, and find that the energy gap can not open until the strain parameter is larger than 16%. After this, the energy gap open and the Dirac points disappear.

Dirac spinors for doubly special relativity and κ-Minkowski noncommutative spacetime

International Nuclear Information System (INIS)

Agostini, Alessandra; Amelino-Camelia, Giovanni; Arzano, Michele

2004-01-01

We construct a Dirac equation that is consistent with one of the recently-proposed schemes for a 'doubly special relativity', a relativity with both an observer-independent velocity scale (still naturally identified with the speed-of-light constant) and an observer-independent length/momentum scale (possibly given by the Planck length/momentum). We find that the introduction of the second observer-independent scale only induces a mild deformation of the structure of Dirac spinors. We also show that our modified Dirac equation naturally arises in constructing a Dirac equation in the κ-Minkowski noncommutative spacetime. Previous, more heuristic studies had already argued for a possible role of doubly special relativity in κ-Minkowski, but remained vague on the nature of the consistency requirements that should be implemented in order to assure the observer-independence of the two scales. We find that a key role is played by the choice of a differential calculus in κ-Minkowski. A much-studied choice of the differential calculus does lead to our doubly special relativity Dirac equation, but a different scenario is encountered for another popular choice of differential calculus

PREFACE: International Workshop on Dirac Electrons in Solids 2015

Science.gov (United States)

Ogata, M.; Suzumura, Y.; Fuseya, Y.; Matsuura, H.

2015-04-01

It is our pleasure to publish the Proceedings of the International Workshop on Dirac Electrons in Solids held in University of Tokyo, Japan, for January 14-15, 2015. The workshop was organized by the entitled project which lasted from April 2012 to March 2015 with 10 theorists. It has been supported by a Grand-in-Aid for Scientific Research (A) from the Ministry of Education, Culture, Sports, Science, and Technology, Japan. The subjects discussed in the workshop include bismuth, organic conductors, graphene, topological insulators, new materials including Ca3PbO, and new directions in theory (superconductivity, orbital susceptibility, etc). The number of participants was about 70 and the papers presented in the workshop include four invited talks, 16 oral presentations, and 23 poster presentations. Dirac electron systems appear in various systems, such as graphene, quasi-two-dimensional organic conductors, bismuth, surface states in topological insulators, new materials like Ca3PbO. In these systems, characteristic transport properties caused by the linear dispersion of Dirac electrons and topological properties, have been extensively discussed. In addition to these, there are many interesting research fields such as Spin-Hall effect, orbital diamagnetism due to interband effects, Landau levels characteristic to Dirac dispersion, anomalous interlayer transport phenomena and magnetoresistance, the effects of spin-orbit interaction, and electron correlation. The workshop focused on recent developments of theory and experiment of Dirac electron systems in the above materials. We note that all papers published in this volume of Journal of Physics: Conference Series were peer reviewed. Reviews were performed by expert referees with professional knowledge and high scientific standards in this field. Editors made efforts so that the papers may satisfy the criterion of a proceedings journal published by IOP Publishing. We hope that all the participants of the workshop

Floquet-Engineered Valleytronics in Dirac Systems.

Science.gov (United States)

Kundu, Arijit; Fertig, H A; Seradjeh, Babak

2016-01-08

Valley degrees of freedom offer a potential resource for quantum information processing if they can be effectively controlled. We discuss an optical approach to this problem in which intense light breaks electronic symmetries of a two-dimensional Dirac material. The resulting quasienergy structures may then differ for different valleys, so that the Floquet physics of the system can be exploited to produce highly polarized valley currents. This physics can be utilized to realize a valley valve whose behavior is determined optically. We propose a concrete way to achieve such valleytronics in graphene as well as in a simple model of an inversion-symmetry broken Dirac material. We study the effect numerically and demonstrate its robustness against moderate disorder and small deviations in optical parameters.

Spin-1 Dirac-Weyl fermions protected by bipartite symmetry

Energy Technology Data Exchange (ETDEWEB)

Lin, Zeren [College of Chemistry and Molecular Engineering, Peking University, Beijing 100871 (China); School of Physics, Peking University, Beijing 100871 (China); Liu, Zhirong, E-mail: LiuZhiRong@pku.edu.cn [College of Chemistry and Molecular Engineering, Peking University, Beijing 100871 (China); Center for Nanochemistry, Beijing National Laboratory for Molecular Sciences (BNLMS), Peking University, Beijing 100871 (China)

2015-12-07

We propose that bipartite symmetry allows spin-1 Dirac-Weyl points, a generalization of the spin-1/2 Dirac points in graphene, to appear as topologically protected at the Fermi level. In this spirit, we provide methodology to construct spin-1 Dirac-Weyl points of this kind in a given 2D space group and get the classification of the known spin-1 systems in the literature. We also apply the workflow to predict two new systems, P3m1-9 and P31m-15, to possess spin-1 at K/K′ in the Brillouin zone of hexagonal lattice. Their stability under various strains is investigated and compared with that of T{sub 3}, an extensively studied model of ultracold atoms trapped in optical lattice with spin-1 also at K/K′.

Issues for resolving adverse effects on the safety culture of human work underload and workload transitions in complex human-machine systems

International Nuclear Information System (INIS)

Ryan, T.G.

1996-01-01

A workshop was conducted whose specific purpose was to build on earlier work of the US National Research Council, US federal government agencies, and the larger human factors community to: (1) clarify human factors issues pertaining to degraded safety performance in advanced human-machine systems(e.g., nuclear production, transportation, aerospace) due to human work underload and workload transition, and (2) develop strategies for resolving these issues. The workshop affirmed that: (1) work underload and workload transition are issues that will have to be addressed by designers of advanced human-machine systems, especially those relying on automation, if cost, performance, safety, and operator acceptability are to be optimized, (2) human machine allocation models, standards and guidelines which go beyond simple capability approaches will be needed to preclude or seriously diminish the work underload and workload transition problems, and (3) the 16 workload definition, measurement, situational awareness, and trust issues identified during the workshop, need resolution if these models, standards, and guidelines are to be achieved

A compact expression for bilinear combination of Dirac spinors via world tensors

International Nuclear Information System (INIS)

Rogalev, R.N.

1994-01-01

A compact expression for a product of two Dirac spinors is obtained as a linear combination of 16 Dirac γ-matrices. The result is presented in a convenient from, which can give rise to using it for analytical calculations of multiparticle amplitudes. It has been shown that a bilinear combination of Dirac spinors can be expressed by momentum and spin vectors of the corresponding particles up to a phase factor. 8 refs

A semi-Dirac point and an electromagnetic topological transition in a dielectric photonic crystal

KAUST Repository

Wu, Ying

2014-01-01

Accidental degeneracy in a photonic crystal consisting of a square array of elliptical dielectric cylinders leads to both a semi-Dirac point at the center of the Brillouin zone and an electromagnetic topological transition (ETT). A perturbation method is deduced to affirm the peculiar linear-parabolic dispersion near the semi-Dirac point. An effective medium theory is developed to explain the simultaneous semi-Dirac point and ETT and to show that the photonic crystal is either a zero-refractive-index material or an epsilon-near-zero material at the semi-Dirac point. Drastic changes in the wave manipulation properties at the semi-Dirac point, resulting from ETT, are described.©2014 Optical Society of America.

Vacuum state of the Dirac field in de Sitter space and entanglement entropy

Energy Technology Data Exchange (ETDEWEB)

Kanno, Sugumi [Department of Theoretical Physics and History of Science,University of the Basque Country,48080 Bilbao (Spain); IKERBASQUE, Basque Foundation for Science,Maria Diaz de Haro 3, 48013, Bilbao (Spain); Sasaki, Misao [Center for Gravitational Physics,Yukawa Institute for Theoretical Physics, Kyoto University,Kyoto 606-8502 (Japan); Tanaka, Takahiro [Department of Physics, Kyoto University,Kyoto 606-8502 (Japan); Center for Gravitational Physics,Yukawa Institute for Theoretical Physics, Kyoto University,Kyoto 606-8502 (Japan)

2017-03-13

We compute the entanglement entropy of a free massive Dirac field between two causally disconnected open charts in de Sitter space. We first derive the Bunch-Davies vacuum mode functions of the Dirac field. We find there exists no supercurvature mode for the Dirac field. We then give the Bogoliubov transformation between the Bunch-Davies vacuum and the open chart vacua that makes the reduced density matrix diagonal. We find that the Dirac field becomes more entangled than a scalar field as m{sup 2}/H{sup 2} becomes small, and the difference is maximal in the massless limit.

Academic context and perceived mental workload of psychology students.

Science.gov (United States)

Rubio-Valdehita, Susana; López-Higes, Ramón; Díaz-Ramiro, Eva

2014-01-01

The excessive workload of university students is an academic stressor. Consequently, it is necessary to evaluate and control the workload in education. This research applies the NASA-TLX scale, as a measure of the workload. The objectives of this study were: (a) to measure the workload levels of a sample of 367 psychology students, (b) to group students according to their positive or negative perception of academic context (AC) and c) to analyze the effects of AC on workload. To assess the perceived AC, we used an ad hoc questionnaire designed according to Demand-Control-Social Support and Effort-Reward Imbalance models. Using cluster analysis, participants were classified into two groups (positive versus negative context). The differences between groups show that a positive AC improves performance (p student autonomy and result satisfaction were relevant dimensions of the AC (p < .001 in all cases).

P A M Dirac meets M G Krein: matrix orthogonal polynomials and Dirac's equation

International Nuclear Information System (INIS)

Duran, Antonio J; Gruenbaum, F Alberto

2006-01-01

The solution of several instances of the Schroedinger equation (1926) is made possible by using the well-known orthogonal polynomials associated with the names of Hermite, Legendre and Laguerre. A relativistic alternative to this equation was proposed by Dirac (1928) involving differential operators with matrix coefficients. In 1949 Krein developed a theory of matrix-valued orthogonal polynomials without any reference to differential equations. In Duran A J (1997 Matrix inner product having a matrix symmetric second order differential operator Rocky Mt. J. Math. 27 585-600), one of us raised the question of determining instances of these matrix-valued polynomials going along with second order differential operators with matrix coefficients. In Duran A J and Gruenbaum F A (2004 Orthogonal matrix polynomials satisfying second order differential equations Int. Math. Res. Not. 10 461-84), we developed a method to produce such examples and observed that in certain cases there is a connection with the instance of Dirac's equation with a central potential. We observe that the case of the central Coulomb potential discussed in the physics literature in Darwin C G (1928 Proc. R. Soc. A 118 654), Nikiforov A F and Uvarov V B (1988 Special Functions of Mathematical Physics (Basle: Birkhauser) and Rose M E 1961 Relativistic Electron Theory (New York: Wiley)), and its solution, gives rise to a matrix weight function whose orthogonal polynomials solve a second order differential equation. To the best of our knowledge this is the first instance of a connection between the solution of the first order matrix equation of Dirac and the theory of matrix-valued orthogonal polynomials initiated by M G Krein

Rework the workload.

Science.gov (United States)

O'Bryan, Linda; Krueger, Janelle; Lusk, Ruth

2002-03-01

Kindred Healthcare, Inc., the nation's largest full-service network of long-term acute care hospitals, initiated a 3-year strategic plan to re-evaluate its workload management system. Here, follow the project's most important and difficult phase--designing and implementing the patient classification system.

Tilted Dirac Cone Effect on Interlayer Magnetoresistance in α-(BEDT-TTF)2I3

Science.gov (United States)

Tajima, Naoya; Morinari, Takao

2018-04-01

We report the effect of Dirac cone tilting on interlayer magnetoresistance in α-(BEDT-TTF)2I3, which is a Dirac semimetal under pressure. Fitting of the experimental data by the theoretical formula suggests that the system is close to a type-II Dirac semimetal.

Chiral Tricritical Point: A New Universality Class in Dirac Systems

Science.gov (United States)

Yin, Shuai; Jian, Shao-Kai; Yao, Hong

2018-05-01

Tricriticality, as a sister of criticality, is a fundamental and absorbing issue in condensed-matter physics. It has been verified that the bosonic Wilson-Fisher universality class can be changed by gapless fermionic modes at criticality. However, the counterpart phenomena at tricriticality have rarely been explored. In this Letter, we study a model in which a tricritical Ising model is coupled to massless Dirac fermions. We find that the massless Dirac fermions result in the emergence of a new tricritical point, which we refer to as the chiral tricritical point (CTP), at the phase boundary between the Dirac semimetal and the charge-density wave insulator. From functional renormalization group analysis of the effective action, we obtain the critical behaviors of the CTP, which are qualitatively distinct from both the tricritical Ising universality and the chiral Ising universality. We further extend the calculations of the chiral tricritical behaviors of Ising spins to the case of Heisenberg spins. The experimental relevance of the CTP in two-dimensional Dirac semimetals is also discussed.

Dirac mechanics and Landau two-fluid model in /sup 4/HeII

Energy Technology Data Exchange (ETDEWEB)

Rodriguez-Gomez, J [Instituto Universitario Pedagogico de Caracas (Venezuela). Dept. de Matematica y Fisica

1980-07-01

This paper is devoted to the development of the Dirac formalism for singular systems when applied to the Landau two-fluid model in superfluid helium. Notably, the Hamiltonian density is weakly zero (in the sense of Dirac). We obtain the physical and gauge variables and show that all the constraints are of first class and hence that the Dirac bracket coincides with the Poisson bracket. The quantization of this system is left for a future paper.

Inverse scattering scheme for the Dirac equation at fixed energy

International Nuclear Information System (INIS)

Leeb, H.; Lehninger, H.; Schilder, C.

2001-01-01

Full text: Based on the concept of generalized transformation operators a new hierarchy of Dirac equations with spherical symmetric scalar and fourth component vector potentials is presented. Within this hierarchy closed form expressions for the solutions, the potentials and the S-matrix can be given in terms of solutions of the original Dirac equation. Using these transformations an inverse scattering scheme has been constructed for the Dirac equation which is the analog to the rational scheme in the non-relativistic case. The given method provides for the first time an inversion scheme with closed form expressions for the S-matrix for non-relativistic scattering problems with central and spin-orbit potentials. (author)

Expressing Solutions of the Dirac Equation in Terms of Feynman Path Integral

CERN Document Server

Hose, R D

2006-01-01

Using the separation of the variables technique, the free particle solutions of the Dirac equation in the momentum space are shown to be actually providing the definition of Delta function for the Schr dinger picture. Further, the said solution is shown to be derivable on the sole strength of geometrical argument that the Dirac equation for free particle is an equation of a plane in momentum space. During the evolution of time in the Schr dinger picture, the normal to the said Dirac equation plane is shown to be constantly changing in direction due to the uncertainty principle and thereby, leading to a zigzag path for the Dirac particle in the momentum space. Further, the time evolution of the said Delta function solutions of the Dirac equation is shown to provide Feynman integral of all such zigzag paths in the momentum space. Towards the end of the paper, Feynman path integral between two fixed spatial points in the co-ordinate space during a certain time interv! al is shown to be composed, in time sequence...

about the Dirac Delta Function(?)

Indian Academy of Sciences (India)

V Balakrishnan is in the. Department of ... and sweet as befits this impatient age. It said (in its en- ... to get down to real work by shutting down the system and reverting to ... the Dirac delta function" - but do note the all-important question mark in ...

Spin symmetry in the Dirac sea derived from the bare nucleon-nucleon interaction

Science.gov (United States)

Shen, Shihang; Liang, Haozhao; Meng, Jie; Ring, Peter; Zhang, Shuangquan

2018-06-01

The spin symmetry in the Dirac sea has been investigated with relativistic Brueckner-Hartree-Fock theory using the bare nucleon-nucleon interaction. Taking the nucleus 16O as an example and comparing the theoretical results with the data, the definition of the single-particle potential in the Dirac sea is studied in detail. It is found that if the single-particle states in the Dirac sea are treated as occupied states, the ground state properties are in better agreement with experimental data. Moreover, in this case, the spin symmetry in the Dirac sea is better conserved and it is more consistent with the findings using phenomenological relativistic density functionals.

New approaches for searching for the Dirac magnetic monopole

International Nuclear Information System (INIS)

Kukhtin, V.V.; Krivokhizhin, V.G.; Stetsenko, S.G.; Cheplakov, A.P.

2012-01-01

Three new approaches, not applied earlier, are proposed to search for the Dirac monopole - an object whose existence was proposed by P.Dirac more than 80 years ago to explain the electrical charge quantization. The first approach assumes that the monopole must be accelerated by a magnetic field, and such acceleration is constant in the magnetic field which is homogeneous and constant. The conclusion about the object movement nature can be drawn by measuring the time marks for equidistant registering planes. The second approach is supposed to reconstruct the movement trajectory in the homogeneous and permanent electrical field, which is the circle or its part for the magnetic monopole. The third approach is based on the constancy of energy losses by Dirac monopole due to medium ionization in the multilayer passive dielectric tracking detectors placed in the homogeneous and permanent electrical field

Mental workload and its relation with fatigue among urban bus drivers

Directory of Open Access Journals (Sweden)

Narmin Hassanzadeh-Rangi

2017-06-01

Full Text Available Introduction: Driving crash is one of major concerns in all countries. Mental workload reflects the level of attention resources required to meet both objec­tive and subjective performance criteria, which may be affected by task demand, external support, and past experience. Mental workload has been commonly cited as a major cause of workplace and transportation accidents. The objective of this study was assessment of mental workload and its relation with fatigue among urban bus drivers in Tehran, Iran. Methods: In this descriptive and analytical study, the NASA-TLX workload scale and the Samn-Perelli fatigue scale were completed by 194 professional bus drivers. Descriptive statistics as well as correlation and regression analysis were performed for data processing. Results: The total mental workload had highest correlation with the physical demand(r=0.73, p<0.001, the mental demand (r=0.68, p<0.001 and the time pressure (r=0.58, p<0.001. The total fatigue perceived by bus driver had highest correlation with the frustration level (r=0.42, p<0.001, the time pressure (r=0.24, p<0.001 and the mental workload (r=0.21, p<0.001. Conclusion: Mental workload, physical workload and time pressure are important determinants of the total mental workload and fatigue perceived by urban bus drivers. A comprehensive intervention program, include work turnover, trip and work-rest scheduling as well as smoking cessation, was recommended to improve mental workload and fatigue. 

Antecedents of basic psychological need satisfaction of pharmacy students: The role of peers, family, lecturers and workload.

Science.gov (United States)

Basson, Mariëtta J; Rothmann, Sebastiaan

2018-04-01

Self-determination theory (SDT) provides a model to improve pharmacy students' well-being or functioning in their study context. According to SDT, students need a context that satisfies their needs for autonomy, relatedness and competence in order to function optimally. Contextual factors that could have an impact on a student's functioning are lecturers, family, peers and workload. To investigate whether there is a difference between the contributions family, lecturers, peers and workload make towards the satisfaction of pharmacy students' basic psychological needs within a university context. An electronic survey was administered amongst students registered with the North-West University's School of Pharmacy. Registered pharmacy students, 779, completed said electronic survey comprised of a questionnaire on demographics, BMPN (Balanced Measure of Psychological Needs) and self-developed ANPNS (Antecedents of Psychological Need-satisfaction Scale). Data derived from the afore-going was analysed with the aid of structural equation modelling (SEM). Structural equation modelling explained 46%, 25% and 30% respectively of the total group's variances in autonomy, competence and relatedness satisfaction, and 26% of the variance in psychological need frustration. Peers and family played a significant role in the satisfaction of students' need for autonomy, relatedness and competence, whilst workload seemingly hampered satisfaction with regards to relatedness and autonomy. Workload contributed towards frustration with regards to psychological need satisfaction. The role played by lecturers in satisfying pharmacy students' need for autonomy, relatedness and competence will also be highlighted. This study added to the body of knowledge regarding contextual factors and the impact those factors have on pharmacy students' need satisfaction by illustrating that not all factors (family, lecturers, peers and workload) can be considered equal. Lecturers ought to recognise the

Dirac phenomenology and hyperon-nucleus interactions

Energy Technology Data Exchange (ETDEWEB)

Mares, J; Jennings, B K [TRIUMF, Vancouver, British Columbia (Canada); Cooper, E D [Fraser Valley Univ. College, Chilliwack, British Columbia (Canada). Dept. of Physics

1993-05-01

We discuss various aspects of hyperon-nucleus interactions in the relativistic mean field theory. First, characteristics of {Lambda}, {Sigma} and {identical_to} hypernuclei, as well as multi strange baryonic objects, are investigated. The spin-orbit splittings and magnetic moments are shown to be very sensitive to the value of the tensor coupling f{omega}y. Second, optical potentials for {Lambda} and {Sigma} scattering off nuclei are developed based on a global nucleon-nucleon Dirac optical potential and SU(3) symmetry. The tensor coupling has a large effect on the predictions for the analyzing power. Third, the Dirac approach is used in the calculations of the non-mesonic decay of {Lambda} hypernuclei. The large discrepancy between the decay rates and data suggests the need for additional meson exchanges. (authors). 62 refs.,7 figs., 6 tabs.

Dirac and Weyl fermion dynamics on two-dimensional surface

International Nuclear Information System (INIS)

Kavalov, A.R.; Sedrakyan, A.G.; Kostov, I.K.

1986-01-01

Fermions on 2-dimensional surface, embedded into a 3-dimensional space are investigated. The determinant of induced Dirac operator for the Dirac and Weyl fermions is calculated. The reparametrization-invariant effective action is determined by conformal anomaly (giving Liouville action) and also by Lorentz anomaly leading to Wess-Zumino term, the structure of which at d=3 is determined by the Hopf topological invariant of the S 3 → S 2 map

From a world-sheet supersymmetry to the Dirac equation

International Nuclear Information System (INIS)

Mankoc Borstnik, N.

1991-10-01

Starting from a classical action for a point particle with a local world-sheet supersymmetry, the Dirac equation follows with operators α-vector, β-vector γ-vector being defined in the Grassmann space as differential operators and having all the properties of the corresponding Dirac matrices except that α-vector and β-vector are anti-Hermitian rather than Hermitian. Such a particle interacts with an external field as expected. (author). 7 refs

Revivals of zitterbewegung of a bound localized Dirac particle

International Nuclear Information System (INIS)

Romera, Elvira

2011-01-01

In this paper a bound localized Dirac particle is shown to exhibit a revival of the zitterbewegung (ZB) oscillation amplitude. These revivals go beyond the known quasiclassical regenerations in which the ZB oscillation amplitude is decreasing from period to period. This phenomenon is studied in a Dirac oscillator and it is shown that it is possible to set up wave packets in which there is a regeneration of the initial ZB amplitude.

Topological Crystalline Insulators and Dirac Octets in Anti-perovskites

OpenAIRE

Hsieh, Timothy H.; Liu, Junwei; Fu, Liang

2014-01-01

We predict a new class of topological crystalline insulators (TCI) in the anti-perovskite material family with the chemical formula A$_3$BX. Here the nontrivial topology arises from band inversion between two $J=3/2$ quartets, which is described by a generalized Dirac equation for a "Dirac octet". Our work suggests that anti-perovskites are a promising new venue for exploring the cooperative interplay between band topology, crystal symmetry and electron correlation.

Effect of time span and task load on pilot mental workload

Science.gov (United States)

Berg, S. L.; Sheridan, T. B.

1986-01-01

Two sets of simulations designed to examine how a pilot's mental workload is affected by continuous manual-control activity versus discrete mental tasks that included the length of time between receiving an assignment and executing it are described. The first experiment evaluated two types of measures: objective performance indicators and subjective ratings. Subjective ratings for the two missions were different, but the objective performance measures were similar. In the second experiments, workload levels were increased and a second performance measure was taken. Mental workload had no influence on either performance-based workload measure. Subjective ratings discriminated among the scenarios and correlated with performance measures for high-workload flights. The number of mental tasks performed did not influence error rates, although high manual workloads did increase errors.

Analytical Expressions of Matrix Elements of Physical Quantities for Dirac Oscillator

Institute of Scientific and Technical Information of China (English)

LI Ning; JU Guo-Xing; REN Zhong-Zhou

2004-01-01

The analytical expressions of the matrix elements for physical quantities are obtained for the Dirac oscillator in two and three spatial dimensions. Their behaviour for the case of operator's square is discussed in details. The twodimensional Dirac oscillator has similar behavior to that for three-dimensional one.

Giant Planar Hall Effect in the Dirac Semimetal ZrTe5

KAUST Repository

Li, Peng

2018-03-03

Exploration and understanding of exotic topics in quantum physics such as Dirac and Weyl semimetals have become highly popular in the area of condensed matter. It has recently been predicted that a theoretical giant planar Hall effect can be induced by a chiral anomaly in Dirac and Weyl semimetals. ZrTe5 is considered an intriguing Dirac semimetal at the boundary of weak and strong topological insulators, though this claim is still controversial. In this study, we report the observation in ZrTe5 of giant planar Hall resistivity. We have also noted three different dependences of this resistivity on the magnetic field, as predicted by theory, maximum planar Hall resistivity occurs at the Lifshitz transition temperature. In addition, we have discovered a nontrivial Berry phase, as well as a chiral-anomaly-induced negative longitudinal and a giant in-plane anisotropic magnetoresistance. All these experimental observations coherently demonstrate that ZrTe5 is a Dirac semimetal.

Dirac Equation in (1 +1 )-Dimensional Curved Spacetime and the Multiphoton Quantum Rabi Model

Science.gov (United States)

Pedernales, J. S.; Beau, M.; Pittman, S. M.; Egusquiza, I. L.; Lamata, L.; Solano, E.; del Campo, A.

2018-04-01

We introduce an exact mapping between the Dirac equation in (1 +1 )-dimensional curved spacetime (DCS) and a multiphoton quantum Rabi model (QRM). A background of a (1 +1 )-dimensional black hole requires a QRM with one- and two-photon terms that can be implemented in a trapped ion for the quantum simulation of Dirac particles in curved spacetime. We illustrate our proposal with a numerical analysis of the free fall of a Dirac particle into a (1 +1 )-dimensional black hole, and find that the Zitterbewegung effect, measurable via the oscillatory trajectory of the Dirac particle, persists in the presence of gravity. From the duality between the squeezing term in the multiphoton QRM and the metric coupling in the DCS, we show that gravity generates squeezing of the Dirac particle wave function.

Relativistic Spinning Particle without Grassmann Variables and the Dirac Equation

Directory of Open Access Journals (Sweden)

A. A. Deriglazov

2011-01-01

Full Text Available We present the relativistic particle model without Grassmann variables which, being canonically quantized, leads to the Dirac equation. Classical dynamics of the model is in correspondence with the dynamics of mean values of the corresponding operators in the Dirac theory. Classical equations for the spin tensor are the same as those of the Barut-Zanghi model of spinning particle.

The spectral density of the QCD Dirac operator and patterns of chiral symmetry breaking

International Nuclear Information System (INIS)

Toublan, D.; Verbaarschot, J.J.M.

1999-01-01

We study the spectrum of the QCD Dirac operator for two colors with fermions in the fundamental representation and for two or more colors with adjoint fermions. For N f flavors, the chiral flavor symmetry of these theories is spontaneously broken according to SU (2N f → Sp (2N f ) and SU (N f → O (N f ), respectively, rather than the symmetry breaking pattern SU (N f ) x SU (N f ) → SU (N f ) for QCD with three or more colors and fundamental fermions. In this paper we study the Dirac spectrum for the first two symmetry breaking patterns. Following previous work for the third case we find the Dirac spectrum in the domain λ QCD by means of partially quenched chiral perturbation theory. In particular, this result allows us to calculate the slope of the Dirac spectrum at λ = 0. We also show that for λ 2 Λ QCD (wing L the linear size of the system) the Dirac spectrum is given by a chiral Random Matrix Theory with the symmetries of the Dirac operator

Three dimensional Dirac point at k=0 in photonic and phononic systems

OpenAIRE

Huang, Xueqin; Liu, Fengming; Chan, C. T.

2012-01-01

While "Dirac cone" dispersions can only be meaningfully defined in two dimensional (2D) systems, the notion of a Dirac point can be extended to three dimensional (3D) classical wave systems. We show that a simple cubic photonic crystal composing of core-shell spheres exhibits a 3D Dirac point at the center of the Brillouin zone at a finite frequency. Using effective medium theory, we can map our structure to a zero refractive index material in which the effective permittivity and permeability...

Individual differences and subjective workload assessment - Comparing pilots to nonpilots

Science.gov (United States)

Vidulich, Michael A.; Pandit, Parimal

1987-01-01

Results by two groups of subjects, pilots and nonpilots, for two subjective workload assessment techniques (the SWAT and NASA-TLX tests) intended to evaluate individual differences in the perception and reporting of subjective workload are compared with results obtained for several traditional personality tests. The personality tests were found to discriminate between the groups while the workload tests did not. It is concluded that although the workload tests may provide useful information with respect to the interaction between tasks and personality, they are not effective as pure tests of individual differences.

Luciano Maiani and Jean Iliopoulos awarded the Dirac Medal

CERN Multimedia

2007-01-01

Luciano Maiani, when he was Director-General of CERN. Jean Iliopoulos in 1999. (©CNRS Photothèque - Julien Quideau)On 8 August, the 2007 Dirac Medal, one of the most prestigious prizes in the fields of theoretical physics and mathematics, was awarded to Luciano Maiani, professor at Rome’s La Sapienza University and former Director-General of CERN, and to Jean Iliopoulos, emeritus Director of Research at the CNRS Laboratory of Theoretical Physics. The medal was awarded to both physicists for their joint "work on the physics of the charm quark, a major contribution to the birth of the Standard Model, the modern theory of Elementary Particles." Founded by the Abdus Salam International Centre for Theoretical Physics (ICTP) in 1985, the Dirac Medal is awarded annually on 8 August, the birthday of the famous physicist Paul Dirac, winner of the 1933 Nobel Prize for Physics. It is awarded to ...

Quantitative assessment of workload and stressors in clinical radiation oncology.

Science.gov (United States)

Mazur, Lukasz M; Mosaly, Prithima R; Jackson, Marianne; Chang, Sha X; Burkhardt, Katharin Deschesne; Adams, Robert D; Jones, Ellen L; Hoyle, Lesley; Xu, Jing; Rockwell, John; Marks, Lawrence B

2012-08-01

Workload level and sources of stressors have been implicated as sources of error in multiple settings. We assessed workload levels and sources of stressors among radiation oncology professionals. Furthermore, we explored the potential association between workload and the frequency of reported radiotherapy incidents by the World Health Organization (WHO). Data collection was aimed at various tasks performed by 21 study participants from different radiation oncology professional subgroups (simulation therapists, radiation therapists, physicists, dosimetrists, and physicians). Workload was assessed using National Aeronautics and Space Administration Task-Load Index (NASA TLX). Sources of stressors were quantified using observational methods and segregated using a standard taxonomy. Comparisons between professional subgroups and tasks were made using analysis of variance ANOVA, multivariate ANOVA, and Duncan test. An association between workload levels (NASA TLX) and the frequency of radiotherapy incidents (WHO incidents) was explored (Pearson correlation test). A total of 173 workload assessments were obtained. Overall, simulation therapists had relatively low workloads (NASA TLX range, 30-36), and physicists had relatively high workloads (NASA TLX range, 51-63). NASA TLX scores for physicians, radiation therapists, and dosimetrists ranged from 40-52. There was marked intertask/professional subgroup variation (P<.0001). Mental demand (P<.001), physical demand (P=.001), and effort (P=.006) significantly differed among professional subgroups. Typically, there were 3-5 stressors per cycle of analyzed tasks with the following distribution: interruptions (41.4%), time factors (17%), technical factors (13.6%), teamwork issues (11.6%), patient factors (9.0%), and environmental factors (7.4%). A positive association between workload and frequency of reported radiotherapy incidents by the WHO was found (r = 0.87, P value=.045). Workload level and sources of stressors vary

Quantitative Assessment of Workload and Stressors in Clinical Radiation Oncology

International Nuclear Information System (INIS)

Mazur, Lukasz M.; Mosaly, Prithima R.; Jackson, Marianne; Chang, Sha X.; Burkhardt, Katharin Deschesne; Adams, Robert D.; Jones, Ellen L.; Hoyle, Lesley; Xu, Jing; Rockwell, John; Marks, Lawrence B.

2012-01-01

Purpose: Workload level and sources of stressors have been implicated as sources of error in multiple settings. We assessed workload levels and sources of stressors among radiation oncology professionals. Furthermore, we explored the potential association between workload and the frequency of reported radiotherapy incidents by the World Health Organization (WHO). Methods and Materials: Data collection was aimed at various tasks performed by 21 study participants from different radiation oncology professional subgroups (simulation therapists, radiation therapists, physicists, dosimetrists, and physicians). Workload was assessed using National Aeronautics and Space Administration Task-Load Index (NASA TLX). Sources of stressors were quantified using observational methods and segregated using a standard taxonomy. Comparisons between professional subgroups and tasks were made using analysis of variance ANOVA, multivariate ANOVA, and Duncan test. An association between workload levels (NASA TLX) and the frequency of radiotherapy incidents (WHO incidents) was explored (Pearson correlation test). Results: A total of 173 workload assessments were obtained. Overall, simulation therapists had relatively low workloads (NASA TLX range, 30-36), and physicists had relatively high workloads (NASA TLX range, 51-63). NASA TLX scores for physicians, radiation therapists, and dosimetrists ranged from 40-52. There was marked intertask/professional subgroup variation (P<.0001). Mental demand (P<.001), physical demand (P=.001), and effort (P=.006) significantly differed among professional subgroups. Typically, there were 3-5 stressors per cycle of analyzed tasks with the following distribution: interruptions (41.4%), time factors (17%), technical factors (13.6%), teamwork issues (11.6%), patient factors (9.0%), and environmental factors (7.4%). A positive association between workload and frequency of reported radiotherapy incidents by the WHO was found (r = 0.87, P value=.045

Quantitative Assessment of Workload and Stressors in Clinical Radiation Oncology

Energy Technology Data Exchange (ETDEWEB)

Mazur, Lukasz M., E-mail: lukasz_mazur@ncsu.edu [Department of Radiation Oncology, University of North Carolina, Chapel Hill, North Carolina (United States); Industrial Extension Service, North Carolina State University, Raleigh, North Carolina (United States); Biomedical Engineering, North Carolina State University, Raleigh, North Carolina (United States); Mosaly, Prithima R. [Industrial Extension Service, North Carolina State University, Raleigh, North Carolina (United States); Jackson, Marianne; Chang, Sha X.; Burkhardt, Katharin Deschesne; Adams, Robert D.; Jones, Ellen L.; Hoyle, Lesley [Department of Radiation Oncology, University of North Carolina, Chapel Hill, North Carolina (United States); Xu, Jing [Industrial Extension Service, North Carolina State University, Raleigh, North Carolina (United States); Rockwell, John; Marks, Lawrence B. [Department of Radiation Oncology, University of North Carolina, Chapel Hill, North Carolina (United States)

2012-08-01

Purpose: Workload level and sources of stressors have been implicated as sources of error in multiple settings. We assessed workload levels and sources of stressors among radiation oncology professionals. Furthermore, we explored the potential association between workload and the frequency of reported radiotherapy incidents by the World Health Organization (WHO). Methods and Materials: Data collection was aimed at various tasks performed by 21 study participants from different radiation oncology professional subgroups (simulation therapists, radiation therapists, physicists, dosimetrists, and physicians). Workload was assessed using National Aeronautics and Space Administration Task-Load Index (NASA TLX). Sources of stressors were quantified using observational methods and segregated using a standard taxonomy. Comparisons between professional subgroups and tasks were made using analysis of variance ANOVA, multivariate ANOVA, and Duncan test. An association between workload levels (NASA TLX) and the frequency of radiotherapy incidents (WHO incidents) was explored (Pearson correlation test). Results: A total of 173 workload assessments were obtained. Overall, simulation therapists had relatively low workloads (NASA TLX range, 30-36), and physicists had relatively high workloads (NASA TLX range, 51-63). NASA TLX scores for physicians, radiation therapists, and dosimetrists ranged from 40-52. There was marked intertask/professional subgroup variation (P<.0001). Mental demand (P<.001), physical demand (P=.001), and effort (P=.006) significantly differed among professional subgroups. Typically, there were 3-5 stressors per cycle of analyzed tasks with the following distribution: interruptions (41.4%), time factors (17%), technical factors (13.6%), teamwork issues (11.6%), patient factors (9.0%), and environmental factors (7.4%). A positive association between workload and frequency of reported radiotherapy incidents by the WHO was found (r = 0.87, P value=.045

A sequence of Clifford algebras and three replicas of Dirac particle

International Nuclear Information System (INIS)

Krolikowski, W.; Warsaw Univ.

1990-01-01

The embedding of Dirac algebra into a sequence N=1, 2, 3,... of Clifford algebras is discussed, leading to Dirac equations with N=1 additional, electromagnetically ''hidden'' spins 1/2. It is shown that there are three and only three replicas N=1, 3, 5 of Dirac particle if the theory of relativity together with the probability interpretation of wave function is applied both to the ''visible'' spin and ''hidden'' spins, and a new ''hidden exclusion principle''is imposed on the wave function (then ''hidden'' spins add up to zero). It is appealing to explore this idea in order to explain the puzzle of three generations of lepton and quarks. (author)

Large linear magnetoresistance in a new Dirac material BaMnBi2

International Nuclear Information System (INIS)

Wang Yi-Yan; Yu Qiao-He; Xia Tian-Long

2016-01-01

Dirac semimetal is a class of materials that host Dirac fermions as emergent quasi-particles. Dirac cone-type band structure can bring interesting properties such as quantum linear magnetoresistance and large mobility in the materials. In this paper, we report the synthesis of high quality single crystals of BaMnBi 2 and investigate the transport properties of the samples. BaMnBi 2 is a metal with an antiferromagnetic transition at T N = 288 K. The temperature dependence of magnetization displays different behavior from CaMnBi 2 and SrMnBi 2 , which suggests the possible different magnetic structure of BaMnBi 2 . The Hall data reveals electron-type carriers and a mobility μ (5 K) = 1500 cm 2 /V·s. Angle-dependent magnetoresistance reveals the quasi-two-dimensional (2D) Fermi surface in BaMnBi 2 . A crossover from semiclassical MR ∼ H 2 dependence in low field to MR ∼ H dependence in high field, which is attributed to the quantum limit of Dirac fermions, has been observed in magnetoresistance. Our results indicate the existence of Dirac fermions in BaMnBi 2 . (rapid communication)

Covariant Conservation Laws and the Spin Hall Effect in Dirac-Rashba Systems

Science.gov (United States)

Milletarı, Mirco; Offidani, Manuel; Ferreira, Aires; Raimondi, Roberto

2017-12-01

We present a theoretical analysis of two-dimensional Dirac-Rashba systems in the presence of disorder and external perturbations. We unveil a set of exact symmetry relations (Ward identities) that impose strong constraints on the spin dynamics of Dirac fermions subject to proximity-induced interactions. This allows us to demonstrate that an arbitrary dilute concentration of scalar impurities results in the total suppression of nonequilibrium spin Hall currents when only Rashba spin-orbit coupling is present. Remarkably, a finite spin Hall conductivity is restored when the minimal Dirac-Rashba model is supplemented with a spin-valley interaction. The Ward identities provide a systematic way to predict the emergence of the spin Hall effect in a wider class of Dirac-Rashba systems of experimental relevance and represent an important benchmark for testing the validity of numerical methodologies.

Imaginary Time Step Method to Solve the Dirac Equation with Nonlocal Potential

International Nuclear Information System (INIS)

Zhang Ying; Liang Haozhao; Meng Jie

2009-01-01

The imaginary time step (ITS) method is applied to solve the Dirac equation with nonlocal potentials in coordinate space. Taking the nucleus 12 C as an example, even with nonlocal potentials, the direct ITS evolution for the Dirac equation still meets the disaster of the Dirac sea. However, following the recipe in our former investigation, the disaster can be avoided by the ITS evolution for the corresponding Schroedinger-like equation without localization, which gives the convergent results exactly the same with those obtained iteratively by the shooting method with localized effective potentials.

Crucial test of the Dirac cosmologies

International Nuclear Information System (INIS)

Steigman, G.

1978-01-01

In a cosmology consistent with the Cosmological Principle (large scale, statistical isotropy and homogeneity of the universe), a Planck spectrum is not preserved as the universe evolves unless the number of photons in a comoving volume is conserved. It is shown that a large class of cosmological models based on Dirac's Large Numbers Hypothesis (LNH) violate this constraint. The observed isotropy and spectral distribution of the microwave background radiation thus provide a crucial test of such cosmologies. After reviewing the LNH, the general evolution of radiation spectra in cosmologies consistent with the cosmological principle is outlined. It is shown that the predicted deviations from a Planck spectrum for Dirac cosmologies (as well as for ''tired-light'' cosmologies) are enormous. The Planckian (or near-Planckian) spectral form for the microwave radiation provides a crucial test, failed by such cosmologies

Evaluation of mental workload on digital maintenance systems in nuclear power plants

International Nuclear Information System (INIS)

Hwang, S. L.; Huang, F. H.; Lin, J. C.; Liang, G. F.; Yenn, T. C.; Hsu, C. C.

2006-01-01

The purpose of this study is to evaluate operators' mental workload dealing with digital maintenance systems in Nuclear Power Plants. First of all, according to the factors affected the mental workload, a questionnaire was designed to evaluate the mental workload of maintenance operators at the second Nuclear Power (NPP) in Taiwan. Then, sixteen maintenance engineers of the Second NPP participated in the questionnaire survey. The results indicated that the mental workload was lower in digital systems than that in analog systems. Finally, a mental workload model based on Neural Network technique was developed to predict the workload of maintenance operators in digital maintenance systems. (authors)

Out-of-Bounds Hydrodynamics in Anisotropic Dirac Fluids

Science.gov (United States)

Link, Julia M.; Narozhny, Boris N.; Kiselev, Egor I.; Schmalian, Jörg

2018-05-01

We study hydrodynamic transport in two-dimensional, interacting electronic systems with merging Dirac points at charge neutrality. The dispersion along one crystallographic direction is Dirac-like, while it is Newtonian-like in the orthogonal direction. As a result, the electrical conductivity is metallic in one and insulating in the other direction. The shear viscosity tensor contains six independent components, which can be probed by measuring an anisotropic thermal flow. One of the viscosity components vanishes at zero temperature leading to a generalization of the previously conjectured lower bound for the shear viscosity to entropy density ratio.

Radiative heat transfer in 2D Dirac materials

International Nuclear Information System (INIS)

Rodriguez-López, Pablo; Tse, Wang-Kong; Dalvit, Diego A R

2015-01-01

We compute the radiative heat transfer between two sheets of 2D Dirac materials, including topological Chern insulators and graphene, within the framework of the local approximation for the optical response of these materials. In this approximation, which neglects spatial dispersion, we derive both numerically and analytically the short-distance asymptotic of the near-field heat transfer in these systems, and show that it scales as the inverse of the distance between the two sheets. Finally, we discuss the limitations to the validity of this scaling law imposed by spatial dispersion in 2D Dirac materials. (paper)

Dirac neutrinos and hybrid inflation from string theory

International Nuclear Information System (INIS)

Antusch, Stefan; Eyton-Williams, Oliver J.; King, Steve F.

2005-01-01

We consider a possible scenario for the generation of Dirac neutrino masses motivated by type-I string theory. The smallness of the neutrino Yukawa couplings is explained by an anisotropic compactification with one compactification radius larger than the others. In addition to this we utilise small Yukawa couplings to develop strong links between the origin of neutrino masses and the physics driving inflation. We construct a minimal model which simultaneously accommodates small Dirac neutrino masses leading to bi-large lepton mixing as well as an inflationary solution to the strong CP and to the μ problem

New symmetries for the Dirac equation

International Nuclear Information System (INIS)

Linhares, C.A.; Mignaco, J.A.

1990-01-01

The Dirac equation in four dimension is studied describing fermions, both as 4 x 4 matrices and differential forms. It is discussed in both formalisms its properties under transformations of the group SU(4). (A.C.A.S.) [pt

CHROMagar Orientation Medium Reduces Urine Culture Workload

Science.gov (United States)

Manickam, Kanchana; Karlowsky, James A.; Adam, Heather; Lagacé-Wiens, Philippe R. S.; Rendina, Assunta; Pang, Paulette; Murray, Brenda-Lee

2013-01-01

Microbiology laboratories continually strive to streamline and improve their urine culture algorithms because of the high volumes of urine specimens they receive and the modest numbers of those specimens that are ultimately considered clinically significant. In the current study, we quantitatively measured the impact of the introduction of CHROMagar Orientation (CO) medium into routine use in two hospital laboratories and compared it to conventional culture on blood and MacConkey agars. Based on data extracted from our Laboratory Information System from 2006 to 2011, the use of CO medium resulted in a 28% reduction in workload for additional procedures such as Gram stains, subcultures, identification panels, agglutination tests, and biochemical tests. The average number of workload units (one workload unit equals 1 min of hands-on labor) per urine specimen was significantly reduced (P < 0.0001; 95% confidence interval [CI], 0.5326 to 1.047) from 2.67 in 2006 (preimplementation of CO medium) to 1.88 in 2011 (postimplementation of CO medium). We conclude that the use of CO medium streamlined the urine culture process and increased bench throughput by reducing both workload and turnaround time in our laboratories. PMID:23363839

Dirac, Prof. Paul Adrien Maurice

Indian Academy of Sciences (India)

Home; Fellowship. Fellow Profile. Elected: 1935 Honorary. Dirac, Prof. Paul Adrien Maurice Nobel Laureate (Physics) - 1933. Date of birth: 8 August 1902. Date of death: 20 October 1984. YouTube; Twitter; Facebook; Blog. Academy News. IAS Logo. 29th Mid-year meeting. Posted on 19 January 2018. The 29th Mid-year ...

CMS readiness for multi-core workload scheduling

Science.gov (United States)

Perez-Calero Yzquierdo, A.; Balcas, J.; Hernandez, J.; Aftab Khan, F.; Letts, J.; Mason, D.; Verguilov, V.

2017-10-01

In the present run of the LHC, CMS data reconstruction and simulation algorithms benefit greatly from being executed as multiple threads running on several processor cores. The complexity of the Run 2 events requires parallelization of the code to reduce the memory-per- core footprint constraining serial execution programs, thus optimizing the exploitation of present multi-core processor architectures. The allocation of computing resources for multi-core tasks, however, becomes a complex problem in itself. The CMS workload submission infrastructure employs multi-slot partitionable pilots, built on HTCondor and GlideinWMS native features, to enable scheduling of single and multi-core jobs simultaneously. This provides a solution for the scheduling problem in a uniform way across grid sites running a diversity of gateways to compute resources and batch system technologies. This paper presents this strategy and the tools on which it has been implemented. The experience of managing multi-core resources at the Tier-0 and Tier-1 sites during 2015, along with the deployment phase to Tier-2 sites during early 2016 is reported. The process of performance monitoring and optimization to achieve efficient and flexible use of the resources is also described.

CMS Readiness for Multi-Core Workload Scheduling

Energy Technology Data Exchange (ETDEWEB)

Perez-Calero Yzquierdo, A. [Madrid, CIEMAT; Balcas, J. [Caltech; Hernandez, J. [Madrid, CIEMAT; Aftab Khan, F. [NCP, Islamabad; Letts, J. [UC, San Diego; Mason, D. [Fermilab; Verguilov, V. [CLMI, Sofia

2017-11-22

In the present run of the LHC, CMS data reconstruction and simulation algorithms benefit greatly from being executed as multiple threads running on several processor cores. The complexity of the Run 2 events requires parallelization of the code to reduce the memory-per- core footprint constraining serial execution programs, thus optimizing the exploitation of present multi-core processor architectures. The allocation of computing resources for multi-core tasks, however, becomes a complex problem in itself. The CMS workload submission infrastructure employs multi-slot partitionable pilots, built on HTCondor and GlideinWMS native features, to enable scheduling of single and multi-core jobs simultaneously. This provides a solution for the scheduling problem in a uniform way across grid sites running a diversity of gateways to compute resources and batch system technologies. This paper presents this strategy and the tools on which it has been implemented. The experience of managing multi-core resources at the Tier-0 and Tier-1 sites during 2015, along with the deployment phase to Tier-2 sites during early 2016 is reported. The process of performance monitoring and optimization to achieve efficient and flexible use of the resources is also described.

Accidental degeneracy of double Dirac cones in a phononic crystal

KAUST Repository

Chen, Ze-Guo; Ni, Xu; Wu, Ying; He, Cheng; Sun, Xiao-Chen; Zheng, Li-Yang; Lu, Ming-Hui; Chen, Yan-Feng

2014-01-01

Artificial honeycomb lattices with Dirac cone dispersion provide a macroscopic platform to study the massless Dirac quasiparticles and their novel geometric phases. In this paper, a quadruple-degenerate state is achieved at the center of the Brillouin zone in a two-dimensional honeycomb lattice phononic crystal, which is a result of accidental degeneracy of two double-degenerate states. In the vicinity of the quadruple-degenerate state, the dispersion relation is linear. Such quadruple degeneracy is analyzed by rigorous representation theory of groups. Using method, a reduced Hamiltonian is obtained to describe the linear Dirac dispersion relations of this quadruple-degenerate state, which is well consistent with the simulation results. Near such accidental degeneracy, we observe some unique properties in wave propagating, such as defect-insensitive propagating character and the Talbot effect.

Accidental degeneracy of double Dirac cones in a phononic crystal

KAUST Repository

Chen, Ze-Guo

2014-04-09

Artificial honeycomb lattices with Dirac cone dispersion provide a macroscopic platform to study the massless Dirac quasiparticles and their novel geometric phases. In this paper, a quadruple-degenerate state is achieved at the center of the Brillouin zone in a two-dimensional honeycomb lattice phononic crystal, which is a result of accidental degeneracy of two double-degenerate states. In the vicinity of the quadruple-degenerate state, the dispersion relation is linear. Such quadruple degeneracy is analyzed by rigorous representation theory of groups. Using method, a reduced Hamiltonian is obtained to describe the linear Dirac dispersion relations of this quadruple-degenerate state, which is well consistent with the simulation results. Near such accidental degeneracy, we observe some unique properties in wave propagating, such as defect-insensitive propagating character and the Talbot effect.

Using Psychophysiological Sensors to Assess Mental Workload During Web Browsing.

Science.gov (United States)

Jimenez-Molina, Angel; Retamal, Cristian; Lira, Hernan

2018-02-03

Knowledge of the mental workload induced by a Web page is essential for improving users' browsing experience. However, continuously assessing the mental workload during a browsing task is challenging. To address this issue, this paper leverages the correlation between stimuli and physiological responses, which are measured with high-frequency, non-invasive psychophysiological sensors during very short span windows. An experiment was conducted to identify levels of mental workload through the analysis of pupil dilation measured by an eye-tracking sensor. In addition, a method was developed to classify mental workload by appropriately combining different signals (electrodermal activity (EDA), electrocardiogram, photoplethysmo-graphy (PPG), electroencephalogram (EEG), temperature and pupil dilation) obtained with non-invasive psychophysiological sensors. The results show that the Web browsing task involves four levels of mental workload. Also, by combining all the sensors, the efficiency of the classification reaches 93.7%.

A computerized multidimensional measurement of mental workload via handwriting analysis.

Science.gov (United States)

Luria, Gil; Rosenblum, Sara

2012-06-01

The goal of this study was to test the effect of mental workload on handwriting behavior and to identify characteristics of low versus high mental workload in handwriting. We hypothesized differences between handwriting under three different load conditions and tried to establish a profile that integrated these indicators. Fifty-six participants wrote three numerical progressions of varying difficulty on a digitizer attached to a computer so that we could evaluate their handwriting behavior. Differences were found in temporal, spatial, and angular velocity handwriting measures, but no significant differences were found for pressure measures. Using data reduction, we identified three clusters of handwriting, two of which differentiated well according to the three mental workload conditions. We concluded that handwriting behavior is affected by mental workload and that each measure provides distinct information, so that they present a comprehensive indicator of mental workload.

Manipulation of Dirac cones in metal-intercalated epitaxial graphene

Science.gov (United States)

Wang, Cai-Zhuang; Kim, Minsung; Tringides, Michael; Ho, Kai-Ming

Graphene is one of the most attractive materials from both fundamental and practical points of view due to its characteristic Dirac cones. The electronic property of graphene can be modified through the interaction with substrate or another graphene layer as illustrated in few-layer epitaxial graphene. Recently, metal intercalation became an effective method to manipulate the electronic structure of graphene by modifying the coupling between the constituent layers. In this work, we show that the Dirac cones of epitaxial graphene can be manipulated by intercalating rare-earth metals. We demonstrate that rare-earth metal intercalated epitaxial graphene has tunable band structures and the energy levels of Dirac cones as well as the linear or quadratic band dispersion can be controlled depending on the location of the intercalation layer and density. Our results could be important for applications and characterizations of the intercalated epitaxial graphene. Supported by the U.S. DOE-BES under Contract No. DE-AC02-07CH11358.

Pilots 2.0: DIRAC pilots for all the skies

CERN Document Server

Stagni, F; McNab, A; Luzzi, C

2015-01-01

In the last few years, new types of computing infrastructures, such as IAAS (Infrastructure as a Service) and IAAC (Infrastructure as a Client), gained popularity. New resources may come as part of pledged resources, while others are opportunistic. Most of these new infrastructures are based on virtualization techniques. Meanwhile, some concepts, such as distributed queues, lost appeal, while still supporting a vast amount of resources. Virtual Organizations are therefore facing heterogeneity of the available resources and the use of an Interware software like DIRAC to hide the diversity of underlying resources has become essential. The DIRAC WMS is based on the concept of pilot jobs that was introduced back in 2004. A pilot is what creates the possibility to run jobs on a worker node. Within DIRAC, we developed a new generation of pilot jobs, that we dubbed Pilots 2.0. Pilots 2.0 are not tied to a specific infrastructure; rather they are generic, fully configurable and extendible pilots. A Pilot 2.0 can be s...

Multi-symplectic Runge-Kutta methods for nonlinear Dirac equations

International Nuclear Information System (INIS)

Hong Jialin; Li Chun

2006-01-01

In this paper, we consider the multi-symplectic Runge-Kutta (MSRK) methods applied to the nonlinear Dirac equation in relativistic quantum physics, based on a discovery of the multi-symplecticity of the equation. In particular, the conservation of energy, momentum and charge under MSRK discretizations is investigated by means of numerical experiments and numerical comparisons with non-MSRK methods. Numerical experiments presented reveal that MSRK methods applied to the nonlinear Dirac equation preserve exactly conservation laws of charge and momentum, and conserve the energy conservation in the corresponding numerical accuracy to the method utilized. It is verified numerically that MSRK methods are stable and convergent with respect to the conservation laws of energy, momentum and charge, and MSRK methods preserve not only the inner geometric structure of the equation, but also some crucial conservative properties in quantum physics. A remarkable advantage of MSRK methods applied to the nonlinear Dirac equation is the precise preservation of charge conservation law

Situation awareness and workload in complex tactical environments

NARCIS (Netherlands)

Veltman, J.A.

1999-01-01

The paper provides an example of a method to get insight into workload changes over time, executed tasks and situation awareness (SA) in complex task environments. The method is applied to measure the workload of a helicopter crew. The method has three components: 1) task analysis, 2) video

Integrating out the Dirac sea

International Nuclear Information System (INIS)

Karbstein, Felix

2009-01-01

We introduce a new method for dealing with fermionic quantum field theories amenable to a mean-field-type approximation. In this work we focus on the relativistic Hartree approximation. Our aim is to integrate out the Dirac sea and derive a no-sea effective theory'' with positive energy single particle states only. As the derivation of the no-sea effective theory involves only standard Feynman diagrams, our approach is quite general and not restricted to particular space-time dimensions. We develop and illustrate the approach in the ''large N'' limit of the Gross-Neveu model family in 1+1 dimensions. As the Gross-Neveu model has been intensely studied and several analytical solutions are known for this model, it is an ideal testing ground for our no-sea effective theory approach. The chiral Gross-Neveu model, also referred to as 1+1 dimensional Nambu-Jona-Lasinio model, turns out to be of particular interest. In this case, we explicitly derive a consistent effective theory featuring both elementary ''π meson'' fields and (positive energy) ''quark'' fields, starting from a purely fermionic quantum field theory. In the second part of this work, we apply our approach to the Walecka model in 1+1 and 3+1 dimensions. As the Dirac sea caused considerable difficulties in attempts to base nuclear physics on field theoretic models like the Walecka model, mean-field calculations were typically done without the sea. We confront several of these mean-field theory results with our no-sea effective theory approach. The potential of our approach is twofold. While the no-sea effective theory can be utilized to provide new analytical insights in particular parameter regimes, it also sheds new light on more fundamental issues as the explicit emergence of effective, Dirac-sea induced multi-fermion interactions in an effective theory with positive energy states only. (orig.)

Decay Rates and Probability Estimatesfor Massive Dirac Particlesin the Kerr-Newman Black Hole Geometry

Science.gov (United States)

Finster, F.; Kamran, N.; Smoller, J.; Yau, S.-T.

The Cauchy problem is considered for the massive Dirac equation in the non-extreme Kerr-Newman geometry, for smooth initial data with compact support outside the event horizon and bounded angular momentum. We prove that the Dirac wave function decays in L∞ {loc} at least at the rate t-5/6. For generic initial data, this rate of decay is sharp. We derive a formula for the probability p that the Dirac particle escapes to infinity. For various conditions on the initial data, we show that p = 0, 1 or 0 < p < 1. The proofs are based on a refined analysis of the Dirac propagator constructed in [4].

Development of an EEG-based workload measurement method in nuclear power plants

International Nuclear Information System (INIS)

Choi, Moon Kyoung; Lee, Seung Min; Ha, Jun Su; Seong, Poong Hyun

2018-01-01

Highlights: •A human operator’s workload in nuclear power plants(NPPs) usually has been evaluated by using subjective ratings. •Subjective rating techniques have several weaknesses such as dependence on the operator’s memory as well as bias. •We suggested an electroencephalogram (EEG)-based workload index for measuring the workload of human operators. •The suggested index was applied to evaluate the effects of operating support systems. -- Abstract: The environment of main control rooms of large scale process control systems such as nuclear power plants (NPPs) has been changed from the conventional analog type to the digital type. In digitalized advanced main control rooms, human operators conduct highly cognitive work rather than physical work compared to the case of the original control rooms in NPPs. Various operating support systems (OSSs) have been developed to reduce an operator’s workload. Most representative techniques to evaluate the workload are based on subjective ratings. However, there are some limitations including the possibility of skewed results due to self-assessment of the workload and the impossibility of continuously measuring the workload due to freezing simulation for workload assessment. As opposed to subjective ratings techniques, physiological techniques can be used for objective and continuous measurements of a human operator’s mental status by sensing the physiological changes of the autonomic or central nervous system. In this study, electroencephalogram (EEG) was used to measure the operator’s mental workload because it had been proven to be sensitive to variations of mental workload in other studies, and it allows various types of analysis. Based on various research reviews on the characteristics of brainwaves, EEG-based Workload Index (EWI) was suggested and validated through experiments. As a result, EWI is concluded to be valid for measuring an operator’s mental workload and preferable to subjective techniques

Academic workload management towards learning, components of academic work

OpenAIRE

Ocvirk, Aleksandra; Trunk Širca, Nada

2013-01-01

This paper deals with attributing time value to academic workload from the point of view of an HEI, management of teaching and an individual. We have conducted a qualitative study aimed at analysing documents on academic workload in terms of its definition, and at analysing the attribution of time value to components of academic work in relation to the proportion of workload devoted to teaching in the sense of ensuring quality and effectiveness of learning, and in relation to financial implic...

The Impact of Heavy Perceived Nurse Workloads on Patient and Nurse Outcomes

Directory of Open Access Journals (Sweden)

Maura MacPhee

2017-03-01

Full Text Available This study investigated the relationships between seven workload factors and patient and nurse outcomes. (1 Background: Health systems researchers are beginning to address nurses’ workload demands at different unit, job and task levels; and the types of administrative interventions needed for specific workload demands. (2 Methods: This was a cross-sectional correlational study of 472 acute care nurses from British Columbia, Canada. The workload factors included nurse reports of unit-level RN staffing levels and patient acuity and patient dependency; job-level nurse perceptions of heavy workloads, nursing tasks left undone and compromised standards; and task-level interruptions to work flow. Patient outcomes were nurse-reported frequencies of medication errors, patient falls and urinary tract infections; and nurse outcomes were emotional exhaustion and job satisfaction. (3 Results: Job-level perceptions of heavy workloads and task-level interruptions had significant direct effects on patient and nurse outcomes. Tasks left undone mediated the relationships between heavy workloads and nurse and patient outcomes; and between interruptions and nurse and patient outcomes. Compromised professional nursing standards mediated the relationships between heavy workloads and nurse outcomes; and between interruptions and nurse outcomes. (4 Conclusion: Administrators should work collaboratively with nurses to identify work environment strategies that ameliorate workload demands at different levels.

The Dirac field in the electromagnetic potential of a charged string; Das Dirac-Feld im elektromagnetischen Potential eines geladenen Strings

Energy Technology Data Exchange (ETDEWEB)

Anaguano, L.

2005-07-01

According to the theory of Quantum Electrodynamics (QED) the vacuum state will change in the presence of very strong electromagnetic fields. If the external field (in the simplest case purely electrostatic) exceeds a certain critical value the creation of electron-positron pairs will ensue, resulting the the formation of a charged vacuum. This process is characterized by the emergence of electron states with a binding energy larger than twice the electron rest mass. The effect up to now usually was studied for spherically symmetric systems, in particular for the Coulomb potential of a heavy nucleus. In the present thesis we investigate, how this phenomenon changes when passing from spherical to cylindrical geometry. For this, we derive the solutions of the Dirac equation for electrons in the electrostatic potential of a long, thin charged cylinder (a ''charged string'') and study the ensuing supercritical effects. Since the logarithmic potential of an infinitely long string rises indefinitely with growing distance, all electron states should be supercritical (i.e., electrons should be able to tunnel through the particle-antiparticle gap of the Dirac equation). Therefore on may expect that the central charge will surround itself with an oppositely charged sheath of vacuum electrons, leading to neutralization of the string. To develop a quantitative description of this process, we investigate the solutions of the Poisson equation and the Dirac equation in cylindrical symmetry. In the first step a series expansion of the electrostatic potential in the central plane of a homogeneously charge cylinder of finite length and finite radius is derived. Subsequently, we employ the tetrad (vierbein) formalism to separate the Dirac equation in cylindrical coordinates. The resulting radial Dirac equation is transformed to Schroedinger type. The bound states are evaluated using the method of uniform approximation (a version of the WKB approximation). We study

Dirac gauginos in low scale supersymmetry breaking

International Nuclear Information System (INIS)

Goodsell, Mark D.; Tziveloglou, Pantelis

2014-01-01

It has been claimed that Dirac gaugino masses are necessary for realistic models of low-scale supersymmetry breaking, and yet very little attention has been paid to the phenomenology of a light gravitino when gauginos have Dirac masses. We begin to address this deficit by investigating the couplings and phenomenology of the gravitino in the effective Lagrangian approach. We pay particular attention to the phenomenology of the scalar octets, where new decay channels open up. This leads us to propose a new simplified effective scenario including only light gluinos, sgluons and gravitinos, allowing the squarks to be heavy – with the possible exception of the third generation. Finally, we comment on the application of our results to Fake Split Supersymmetry

Classical electromagnetic radiation of the Dirac electron

Science.gov (United States)

Lanyi, G.

1973-01-01

A wave-function-dependent four-vector potential is added to the Dirac equation in order to achieve conservation of energy and momentum for a Dirac electron and its emitted electromagnetic field. The resultant equation contains solutions which describe transitions between different energy states of the electron. As a consequence it is possible to follow the space-time evolution of such a process. This evolution is shown in the case of the spontaneous emission of an electromagnetic field by an electron bound in a hydrogen-like atom. The intensity of the radiation and the spectral distribution are calculated for transitions between two eigenstates. The theory gives a self-consistent deterministic description of some simple radiation processes without using quantum electrodynamics or the correspondence principle.

Renormalization group evolution of Dirac neutrino masses

International Nuclear Information System (INIS)

Lindner, Manfred; Ratz, Michael; Schmidt, Michael Andreas

2005-01-01

There are good reasons why neutrinos could be Majorana particles, but there exist also a number of very good reasons why neutrinos could have Dirac masses. The latter option deserves more attention and we derive therefore analytic expressions describing the renormalization group evolution of mixing angles and of the CP phase for Dirac neutrinos. Radiative corrections to leptonic mixings are in this case enhanced compared to the quark mixings because the hierarchy of neutrino masses is milder and because the mixing angles are larger. The renormalization group effects are compared to the precision of current and future neutrino experiments. We find that, in the MSSM framework, radiative corrections of the mixing angles are for large tan β comparable to the precision of future experiments

Particlelike solutions of the Einstein-Dirac equations

Science.gov (United States)

Finster, Felix; Smoller, Joel; Yau, Shing-Tung

1999-05-01

The coupled Einstein-Dirac equations for a static, spherically symmetric system of two fermions in a singlet spinor state are derived. Using numerical methods, we construct an infinite number of solitonlike solutions of these equations. The stability of the solutions is analyzed. For weak coupling (i.e., small rest mass of the fermions), all the solutions are linearly stable (with respect to spherically symmetric perturbations), whereas for stronger coupling, both stable and unstable solutions exist. For the physical interpretation, we discuss how the energy of the fermions and the (ADM) mass behave as functions of the rest mass of the fermions. Although gravitation is not renormalizable, our solutions of the Einstein-Dirac equations are regular and well behaved even for strong coupling.

Probabilistic solution of the Dirac equation

International Nuclear Information System (INIS)

Blanchard, P.; Combe, P.

1985-01-01

Various probabilistic representations of the 2, 3 and 4 dimensional Dirac equation are given in terms of expectation with respect to stochastic jump processes and are used to derive the nonrelativistic limit even in the presence of an external electromagnetic field. (orig.)

GPs' perceptions of workload in England: a qualitative interview study.

Science.gov (United States)

Croxson, Caroline Hd; Ashdown, Helen F; Hobbs, Fd Richard

2017-02-01

GPs report the lowest levels of morale among doctors, job satisfaction is low, and the GP workforce is diminishing. Workload is frequently cited as negatively impacting on commitment to a career in general practice, and many GPs report that their workload is unmanageable. To gather an in-depth understanding of GPs' perceptions and attitudes towards workload. All GPs working within NHS England were eligible. Advertisements were circulated via regional GP e-mail lists and national social media networks in June 2015. Of those GPs who responded, a maximum-variation sample was selected until data saturation was reached. Semi-structured, qualitative interviews were conducted. Data were analysed thematically. In total, 171 GPs responded, and 34 were included in this study. GPs described an increase in workload over recent years, with current working days being long and intense, raising concerns over the wellbeing of GPs and patients. Full-time partnership was generally not considered to be possible, and many participants felt workload was unsustainable, particularly given the diminishing workforce. Four major themes emerged to explain increased workload: increased patient needs and expectations; a changing relationship between primary and secondary care; bureaucracy and resources; and the balance of workload within a practice. Continuity of care was perceived as being eroded by changes in contracts and working patterns to deal with workload. This study highlights the urgent need to address perceived lack of investment and clinical capacity in general practice, and suggests that managing patient expectations around what primary care can deliver, and reducing bureaucracy, have become key issues, at least until capacity issues are resolved. © British Journal of General Practice 2017.

Selection rule for Dirac-like points in two-dimensional dielectric photonic crystals

KAUST Repository

Li, Yan

2013-01-01

We developed a selection rule for Dirac-like points in two-dimensional dielectric photonic crystals. The rule is derived from a perturbation theory and states that a non-zero, mode-coupling integral between the degenerate Bloch states guarantees a Dirac-like point, regardless of the type of the degeneracy. In fact, the selection rule can also be determined from the symmetry of the Bloch states even without computing the integral. Thus, the existence of Dirac-like points can be quickly and conclusively predicted for various photonic crystals independent of wave polarization, lattice structure, and composition. © 2013 Optical Society of America.

Light trapping and circularly polarization at a Dirac point in 2D plasma photonic crystals

Science.gov (United States)

Li, Qian; Hu, Lei; Mao, Qiuping; Jiang, Haiming; Hu, Zhijia; Xie, Kang; Wei, Zhang

2018-03-01

Light trapping at the Dirac point in 2D plasma photonic crystal has been obtained. The new localized mode, Dirac mode, is attributable to neither photonic bandgap nor total internal reflection. It exhibits a unique algebraic profile and possesses a high-Q factor resonator of about 105. The Dirac point could be modulated by tuning the filling factor, plasma frequency and plasma cyclotron frequency, respectively. When a magnetic field parallel to the wave vector is applied, Dirac modes for right circularly polarized and left circularly polarized waves could be obtained at different frequencies, and the Q factor could be tuned. This property will add more controllability and flexibility to the design and modulation of novel photonic devices. It is also valuable for the possibilities of Dirac modes in photonic crystal containing other kinds of metamaterials.

How the workload impacts on cognitive cooperation: A pilot study.

Science.gov (United States)

Sciaraffa, Nicolina; Borghini, Gianluca; Arico, Pietro; Di Flumeri, Gianluca; Toppi, Jlenia; Colosimo, Alfredo; Bezerianos, Anastatios; Thakor, Nitish V; Babiloni, Fabio

2017-07-01

Cooperation degradation can be seen as one of the main causes of human errors. Poor cooperation could arise from aberrant mental processes, such as mental overload, that negatively affect the user's performance. Using different levels of difficulty in a cooperative task, we combined behavioural, subjective and neurophysiological data with the aim to i) quantify the mental workload under which the crew was operating, ii) evaluate the degree of their cooperation, and iii) assess the impact of the workload demands on the cooperation levels. The combination of such data showed that high workload demand impacted significantly on the performance, workload perception, and degree of cooperation.

Common origin of neutrino mass, dark matter and Dirac leptogenesis

Energy Technology Data Exchange (ETDEWEB)

Borah, Debasish [Department of Physics, Indian Institute of Technology Guwahati, Assam 781039 (India); Dasgupta, Arnab, E-mail: dborah@iitg.ernet.in, E-mail: arnab.d@iopb.res.in [Institute of Physics, HBNI, Sachivalaya Marg, Bhubaneshwar 751005 (India)

2016-12-01

We study the possibility of generating tiny Dirac neutrino masses at one loop level through the scotogenic mechanism such that one of the particles going inside the loop can be a stable cold dark matter (DM) candidate. Majorana mass terms of singlet fermions as well as tree level Dirac neutrino masses are prevented by incorporating the presence of additional discrete symmetries in a minimal fashion, which also guarantee the stability of the dark matter candidate. Due to the absence of total lepton number violation, the observed baryon asymmetry of the Universe is generated through the mechanism of Dirac leptogenesis where an equal and opposite amount of leptonic asymmetry is generated in the left and right handed sectors which are prevented from equilibration due to tiny Dirac Yukawa couplings. Dark matter relic abundance is generated through its usual freeze-out at a temperature much below the scale of leptogenesis. We constrain the relevant parameter space from neutrino mass, baryon asymmetry, Planck bound on dark matter relic abundance, and latest LUX bound on spin independent DM-nucleon scattering cross section. We also discuss the charged lepton flavour violation (μ → e γ) and electric dipole moment of electron in this model in the light of the latest experimental data and constrain the parameter space of the model.

Evidence for $\\pi K$ -atoms with DIRAC-II

CERN Document Server

Allkofer, Yves

2008-01-01

DIRAC-II is a fixed-target experiment at the CERN Proton Synchroton (PS) which has been designed to search for piK atoms, a bound state of a pi±K± pair, and measure their lifetime. These atoms are observed through an excess of low energetic piK pairs over the background, detected in the two spectrometer arms. This excess comes from the ionization of piK atoms in the target and can be related to their mean life. The piK S-wave scattering length combination |a1/2 - a3/2| (for isospin 1/2 and 3/2) can be related to the latter. The aim of the upgraded DIRAC-II experiment is a measurement of the scattering length combination |a1/2 - a3/2| with a precision of 5%. piK atoms have not been observed so far. The original DIRAC experiment was designed to measure the scattering lengths of pipi atoms. So far, close to 15 000 atoms have been detected, leading to a precision on |a0 - a2| which is better than 10%. In chiral perturbation theories (ChPT) the pipi scattering lengths have been calculated with 2% precision a...

Training and testing ERP-BCIs under different mental workload conditions

Science.gov (United States)

Ke, Yufeng; Wang, Peiyuan; Chen, Yuqian; Gu, Bin; Qi, Hongzhi; Zhou, Peng; Ming, Dong

2016-02-01

Objective. As one of the most popular and extensively studied paradigms of brain-computer interfaces (BCIs), event-related potential-based BCIs (ERP-BCIs) are usually built and tested in ideal laboratory settings in most existing studies, with subjects concentrating on stimuli and intentionally avoiding possible distractors. This study is aimed at examining the effect of simultaneous mental activities on ERP-BCIs by manipulating various levels of mental workload during the training and/or testing of an ERP-BCI. Approach. Mental workload was manipulated during the training or testing of a row-column P300-speller to investigate how and to what extent the spelling performance and the ERPs evoked by the oddball stimuli are affected by simultaneous mental workload. Main results. Responses of certain ERP components, temporal-occipital N200 and the late reorienting negativity evoked by the oddball stimuli and the classifiability of ERP features between targets and non-targets decreased with the increase of mental workload encountered by the subject. However, the effect of mental workload on the performance of ERP-BCI was not always negative but depended on the conditions where the ERP-BCI was built and applied. The performance of ERP-BCI built under an ideal lab setting without any irrelevant mental activities declined with the increasing mental workload of the testing data. However, the performance was significantly improved when an ERP-BCI was built under an appropriate mental workload level, compared to that built under speller-only conditions. Significance. The adverse effect of concurrent mental activities may present a challenge for ERP-BCIs trained in ideal lab settings but which are to be used in daily work, especially when users are performing demanding mental processing. On the other hand, the positive effects of the mental workload of the training data suggest that introducing appropriate mental workload during training ERP-BCIs is of potential benefit to the

WBDOC Weekly Workload Status Report

Data.gov (United States)

Social Security Administration — Weekly reports of workloads processed in the Wilkes Barre Data Operation Center. Reports on quantities of work received, processed, pending and average processing...

The reactive content of the proton-nucleus impulse - approximation Dirac optical potential

International Nuclear Information System (INIS)

Carlson, B.V.; Isidro Filho, M.P.; Hussein, M.S.

1984-01-01

The total reaction cross sections for intermediate energy proton scattering on 40 Ca and 208 Pb are calculated within the Dirac-Eikonal formalism. Comparison with data indicate that the recently proposed impulse-approximation Dirac optical potential for nucleon-nucleus scattering, is not absorptive enough. (Author) [pt

Dirac and non-Dirac conditions in the two-potential theory of magnetic charge

Science.gov (United States)

Scott, John; Evans, Timothy J.; Singleton, Douglas; Dzhunushaliev, Vladimir; Folomeev, Vladimir

2018-05-01

We investigate the Cabbibo-Ferrari, two-potential approach to magnetic charge coupled to two different complex scalar fields, Φ _1 and Φ _2, each having different electric and magnetic charges. The scalar field, Φ _1, is assumed to have a spontaneous symmetry breaking self-interaction potential which gives a mass to the "magnetic" gauge potential and "magnetic" photon, while the other "electric" gauge potential and "electric" photon remain massless. The magnetic photon is hidden until one reaches energies of the order of the magnetic photon rest mass. The second scalar field, Φ _2, is required in order to make the theory non-trivial. With only one field one can always use a duality rotation to rotate away either the electric or magnetic charge, and thus decouple either the associated electric or magnetic photon. In analyzing this system of two scalar fields in the Cabbibo-Ferrari approach we perform several duality and gauge transformations, which require introducing non-Dirac conditions on the initial electric and magnetic charges. We also find that due to the symmetry breaking the usual Dirac condition is altered to include the mass of the magnetic photon. We discuss the implications of these various conditions on the charges.

Twisting dirac fermions: circular dichroism in bilayer graphene

Science.gov (United States)

Suárez Morell, E.; Chico, Leonor; Brey, Luis

2017-09-01

Twisted bilayer graphene is a chiral system which has been recently shown to present circular dichroism. In this work we show that the origin of this optical activity is the rotation of the Dirac fermions’ helicities in the top and bottom layer. Starting from the Kubo formula, we obtain a compact expression for the Hall conductivity that takes into account the dephasing of the electromagnetic field between the top and bottom layers and gathers all the symmetries of the system. Our results are based in both a continuum and a tight-binding model, and they can be generalized to any two-dimensional Dirac material with a chiral stacking between layers.

Hydrogenated and halogenated blue phosphorene as Dirac materials: A first principles study

International Nuclear Information System (INIS)

Sun, Minglei; Wang, Sake; Yu, Jin; Tang, Wencheng

2017-01-01

Highlights: • The fully hydrogenated and halogenated blue phosphorenes are 2D Dirac materials. • The Dirac cone in fluorinated and iodinated blue phosphorenes lies exactly at the Fermi level. • The mass density of hydrogenated and fluorinated blue phosphorenes is rather small. - Abstract: Using first-principles calculations, we systematically investigate the structures and electronic properties of fully hydrogenated and halogenated blue phosphorene (P_2X_2). All these systems possess Dirac cone at high-symmetry K point, which are mainly contributed by P s p_x p_y orbitals. The Dirac cone in P_2F_2 and P_2I_2 systems lies exactly at the Fermi level. Formation energy analysis denotes that all the systems are energetically stable except P_2I_2. The mass density for P_2H_2 and P_2F_2 systems is rather small. Our calculations proposed that these systems, especially P_2F_2 system, have great potential applications in future nanoelectronics.

P A M Dirac meets M G Krein: matrix orthogonal polynomials and Dirac's equation

Energy Technology Data Exchange (ETDEWEB)

Duran, Antonio J [Departamento de Analisis Matematico, Universidad de Sevilla, Apdo (PO BOX) 1160, 41080 Sevilla (Spain); Gruenbaum, F Alberto [Department of Mathematics, University of California, Berkeley, CA 94720 (United States)

2006-04-07

The solution of several instances of the Schroedinger equation (1926) is made possible by using the well-known orthogonal polynomials associated with the names of Hermite, Legendre and Laguerre. A relativistic alternative to this equation was proposed by Dirac (1928) involving differential operators with matrix coefficients. In 1949 Krein developed a theory of matrix-valued orthogonal polynomials without any reference to differential equations. In Duran A J (1997 Matrix inner product having a matrix symmetric second order differential operator Rocky Mt. J. Math. 27 585-600), one of us raised the question of determining instances of these matrix-valued polynomials going along with second order differential operators with matrix coefficients. In Duran A J and Gruenbaum F A (2004 Orthogonal matrix polynomials satisfying second order differential equations Int. Math. Res. Not. 10 461-84), we developed a method to produce such examples and observed that in certain cases there is a connection with the instance of Dirac's equation with a central potential. We observe that the case of the central Coulomb potential discussed in the physics literature in Darwin C G (1928 Proc. R. Soc. A 118 654), Nikiforov A F and Uvarov V B (1988 Special Functions of Mathematical Physics (Basle: Birkhauser) and Rose M E 1961 Relativistic Electron Theory (New York: Wiley)), and its solution, gives rise to a matrix weight function whose orthogonal polynomials solve a second order differential equation. To the best of our knowledge this is the first instance of a connection between the solution of the first order matrix equation of Dirac and the theory of matrix-valued orthogonal polynomials initiated by M G Krein.

Dirac's aether in relativistic quantum mechanics

International Nuclear Information System (INIS)

Petroni, N.C.; Bari Univ.; Vigier, J.P.

1984-01-01

The paper concerns Dirac's aether model, based on a stochastic covariant distribution of subquantum motions. Stochastic derivation of the relativistic quantum equations; deterministic nonlocal interpretation of the Aspect-Rapisarda experiments on the EPR paradox; and photon interference with itself; are all discussed. (U.K.)

Poisson geometry from a Dirac perspective

Science.gov (United States)

Meinrenken, Eckhard

2018-03-01

We present proofs of classical results in Poisson geometry using techniques from Dirac geometry. This article is based on mini-courses at the Poisson summer school in Geneva, June 2016, and at the workshop Quantum Groups and Gravity at the University of Waterloo, April 2016.

Non-Existence of Black Hole Solutionsfor a Spherically Symmetric, Static Einstein-Dirac-Maxwell System

Science.gov (United States)

Finster, Felix; Smoller, Joel; Yau, Shing-Tung

We consider for j=1/2, 3/2,... a spherically symmetric, static system of (2j+1) Dirac particles, each having total angular momentum j. The Dirac particles interact via a classical gravitational and electromagnetic field. The Einstein-Dirac-Maxwell equations for this system are derived. It is shown that, under weak regularity conditions on the form of the horizon, the only black hole solutions of the EDM equations are the Reissner-Nordstrom solutions. In other words, the spinors must vanish identically. Applied to the gravitational collapse of a "cloud" of spin-1/2-particles to a black hole, our result indicates that the Dirac particles must eventually disappear inside the event horizon.

Nursing workloads in family health: implications for universal access.

Science.gov (United States)

de Pires, Denise Elvira Pires; Machado, Rosani Ramos; Soratto, Jacks; Scherer, Magda dos Anjos; Gonçalves, Ana Sofia Resque; Trindade, Letícia Lima

2016-01-01

to identify the workloads of nursing professionals of the Family Health Strategy, considering its implications for the effectiveness of universal access. qualitative study with nursing professionals of the Family Health Strategy of the South, Central West and North regions of Brazil, using methodological triangulation. For the analysis, resources of the Atlas.ti software and Thematic Content Analysis were associated; and the data were interpreted based on the labor process and workloads as theorical approaches. the way of working in the Family Health Strategy has predominantly resulted in an increase in the workloads of the nursing professionals, with emphasis on the work overload, excess of demand, problems in the physical infrastructure of the units and failures in the care network, which hinders its effectiveness as a preferred strategy to achieve universal access to health. On the other hand, teamwork, affinity for the work performed, bond with the user, and effectiveness of the assistance contributed to reduce their workloads. investments on elements that reduce the nursing workloads, such as changes in working conditions and management, can contribute to the effectiveness of the Family Health Strategy and achieving the goal of universal access to health.

Rigid particle revisited: Extrinsic curvature yields the Dirac equation

Energy Technology Data Exchange (ETDEWEB)

Deriglazov, Alexei, E-mail: alexei.deriglazov@ufjf.edu.br [Depto. de Matemática, ICE, Universidade Federal de Juiz de Fora, MG (Brazil); Laboratory of Mathematical Physics, Tomsk Polytechnic University, 634050 Tomsk, Lenin Ave. 30 (Russian Federation); Nersessian, Armen, E-mail: arnerses@ysu.am [Yerevan State University, 1 Alex Manoogian St., Yerevan 0025 (Armenia); Laboratory of Mathematical Physics, Tomsk Polytechnic University, 634050 Tomsk, Lenin Ave. 30 (Russian Federation)

2014-03-01

We reexamine the model of relativistic particle with higher-derivative linear term on the first extrinsic curvature (rigidity). The passage from classical to quantum theory requires a number of rather unexpected steps which we report here. We found that, contrary to common opinion, quantization of the model in terms of so(3.2)-algebra yields massive Dirac equation. -- Highlights: •New way of canonical quantization of relativistic rigid particle is proposed. •Quantization made in terms of so(3.2) angular momentum algebra. •Quantization yields massive Dirac equation.

Geometric interpretation for the Dirac field in curved space

International Nuclear Information System (INIS)

Ranganathan, D.

1987-01-01

The imposition of the condition of length invariance on a Weyl manifold that does not lead uniquely to general relativity is shown. Rather, in this limit, the Weyl vector field can be interpreted as a Dirac current. The action is also the same as the Einstein Dirac one, if and only if, the spinor field is anticommuting. The allowed interactions are greatly restricted. They are only minimal gauge couplings and Yukawa interactions with a scalar field transforming according to the rules of Utiyama [Prog. Theor. Phys. 53, 565 (1975)

Adaptive Multigrid Algorithm for the Lattice Wilson-Dirac Operator

International Nuclear Information System (INIS)

Babich, R.; Brower, R. C.; Rebbi, C.; Brannick, J.; Clark, M. A.; Manteuffel, T. A.; McCormick, S. F.; Osborn, J. C.

2010-01-01

We present an adaptive multigrid solver for application to the non-Hermitian Wilson-Dirac system of QCD. The key components leading to the success of our proposed algorithm are the use of an adaptive projection onto coarse grids that preserves the near null space of the system matrix together with a simplified form of the correction based on the so-called γ 5 -Hermitian symmetry of the Dirac operator. We demonstrate that the algorithm nearly eliminates critical slowing down in the chiral limit and that it has weak dependence on the lattice volume.

Particle-like solutions of the Einstein-Dirac-Maxwell equations

Science.gov (United States)

Finster, Felix; Smoller, Joel; Yau, Shing-Tung

1999-08-01

We consider the coupled Einstein-Dirac-Maxwell equations for a static, spherically symmetric system of two fermions in a singlet spinor state. Soliton-like solutions are constructed numerically. The stability and the properties of the ground state solutions are discussed for different values of the electromagnetic coupling constant. We find solutions even when the electromagnetic coupling is so strong that the total interaction is repulsive in the Newtonian limit. Our solutions are regular and well-behaved; this shows that the combined electromagnetic and gravitational self-interaction of the Dirac particles is finite.

[Effects of mental workload on work ability in primary and secondary school teachers].

Science.gov (United States)

Xiao, Yuanmei; Li, Weijuan; Ren, Qingfeng; Ren, Xiaohui; Wang, Zhiming; Wang, Mianzhen; Lan, Yajia

2015-02-01

To investigate the change pattern of primary and secondary school teachers' work ability with the changes in their mental workload. A total of 901 primary and secondary school teachers were selected by random cluster sampling, and then their mental workload and work ability were assessed by National Aeronautics and Space Administration-Task Load Index (NASA-TLX) and Work Ability Index (WAI) questionnaires, whose reliability and validity had been tested. The effects of their mental workload on the work ability were analyzed. Primary and secondary school teachers' work ability reached the highest level at a certain level of mental workload (55.73work ability had a positive correlation with the mental workload. Their work ability increased or maintained stable with the increasing mental workload. Moreover, the percentage of teachers with good work ability increased, while that of teachers with moderate work ability decreased. But when their mental workload was higher than the level, their work ability had a negative correlation with the mental workload. Their work ability significantly decreased with the increasing mental workload (P work ability decreased, while that of teachers with moderate work ability increased (P work ability. Moderate mental workload (55.73∼64.10) will benefit the maintaining and stabilization of their work ability.

Surface states of a system of Dirac fermions: A minimal model

International Nuclear Information System (INIS)

Volkov, V. A.; Enaldiev, V. V.

2016-01-01

A brief survey is given of theoretical works on surface states (SSs) in Dirac materials. Within the formalism of envelope wave functions and boundary conditions for these functions, a minimal model is formulated that analytically describes surface and edge states of various (topological and nontopological) types in several systems with Dirac fermions (DFs). The applicability conditions of this model are discussed.

An integrodifferential Dirac equation with quantized charge in one space dimension

International Nuclear Information System (INIS)

Ranada, A.F.

1985-01-01

An integrodifferential Dirac equation in one space dimension is proposed, such that there is a close correspondence between its solutions and a subset of those of the sine-Gordon equation. It has solitonic solutions, quantized charge and positive definite energy density, so that it can be considered a spinorial version of sine-Gordon. Accordingly, it could be named the sine-Dirac equation. (orig.)

Surface states of a system of Dirac fermions: A minimal model

Energy Technology Data Exchange (ETDEWEB)

Volkov, V. A., E-mail: volkov.v.a@gmail.com; Enaldiev, V. V. [Russian Academy of Sciences, Kotel’nikov Institute of Radio Engineering and Electronics (Russian Federation)

2016-03-15

A brief survey is given of theoretical works on surface states (SSs) in Dirac materials. Within the formalism of envelope wave functions and boundary conditions for these functions, a minimal model is formulated that analytically describes surface and edge states of various (topological and nontopological) types in several systems with Dirac fermions (DFs). The applicability conditions of this model are discussed.

Chaos in Dirac Electron Optics: Emergence of a Relativistic Quantum Chimera.

Science.gov (United States)

Xu, Hong-Ya; Wang, Guang-Lei; Huang, Liang; Lai, Ying-Cheng

2018-03-23

We uncover a remarkable quantum scattering phenomenon in two-dimensional Dirac material systems where the manifestations of both classically integrable and chaotic dynamics emerge simultaneously and are electrically controllable. The distinct relativistic quantum fingerprints associated with different electron spin states are due to a physical mechanism analogous to a chiroptical effect in the presence of degeneracy breaking. The phenomenon mimics a chimera state in classical complex dynamical systems but here in a relativistic quantum setting-henceforth the term "Dirac quantum chimera," associated with which are physical phenomena with potentially significant applications such as enhancement of spin polarization, unusual coexisting quasibound states for distinct spin configurations, and spin selective caustics. Experimental observations of these phenomena are possible through, e.g., optical realizations of ballistic Dirac fermion systems.

Chaos in Dirac Electron Optics: Emergence of a Relativistic Quantum Chimera

Science.gov (United States)

Xu, Hong-Ya; Wang, Guang-Lei; Huang, Liang; Lai, Ying-Cheng

2018-03-01

We uncover a remarkable quantum scattering phenomenon in two-dimensional Dirac material systems where the manifestations of both classically integrable and chaotic dynamics emerge simultaneously and are electrically controllable. The distinct relativistic quantum fingerprints associated with different electron spin states are due to a physical mechanism analogous to a chiroptical effect in the presence of degeneracy breaking. The phenomenon mimics a chimera state in classical complex dynamical systems but here in a relativistic quantum setting—henceforth the term "Dirac quantum chimera," associated with which are physical phenomena with potentially significant applications such as enhancement of spin polarization, unusual coexisting quasibound states for distinct spin configurations, and spin selective caustics. Experimental observations of these phenomena are possible through, e.g., optical realizations of ballistic Dirac fermion systems.

Operator Workload: Comprehensive Review and Evaluation of Operator Workload Methodologies

Science.gov (United States)

1989-06-01

E. A (1979), Measurement end scaing of workload In oornple performance. Aviation, Space and Environmental Medicine , 50, 376-381. Ctoow, S. L... Medicine , 53, 1087-1072. Harris, R. M., Glenn, F., laveocchia, H. P., & 7ak"d, A, (1986). Human Operndor Simulator. In W. Karwoski (Ed.), Trends in...McGiothlin, W. (1974). Effects of marihuana on auditory signal detection. Psychopharmacologia, 40, 137-145. Mulder, I. J. M., & Mulder, G. (1987

Measuring pilot workload in a moving-base simulator. I Asynchronous secondary choice-reaction task

Science.gov (United States)

Kantowitz, B. H.; Hart, S. G.; Bortolussi, M. R.

1983-01-01

The de facto method for measuring airplane pilot workload is based upon subjective ratings. While researchers agree that such subjective data should be bolstered by using objective behavioral measures, results to date have been mixed. No clear objective technique has surfaced as the metric of choice. It is believed that this difficulty is in part due to neglect of theoretical work in psychology that predicts some of the difficulties that are inherent in a futile search for 'the one and only' best secondary task to measure workload. An initial study that used both subjective ratings and an asynchronous choice-reaction secondary task was conducted to determine if such a secondary task could indeed meet the methodological constraints imposed by current theories of attention. Two variants of a flight scenario were combined with two levels of the secondary task. Appropriate single-task control conditions were also included. Results give grounds for cautious optimism but indicate that future research should use synchronous secondary tasks where possible.

Dirac neutrino masses from generalized supersymmetry breaking

International Nuclear Information System (INIS)

Demir, D.A.; Everett, L.L.; Langacker, P.

2007-12-01

We demonstrate that Dirac neutrino masses in the experimentally preferred range are generated within supersymmetric gauge extensions of the Standard Model with a generalized supersymmetry breaking sector. If the usual superpotential Yukawa couplings are forbidden by the additional gauge symmetry (such as a U(1) ' ), effective Dirac mass terms involving the ''wrong Higgs'' field can arise either at tree level due to hard supersymmetry breaking fermion Yukawa couplings, or at one-loop due to nonanalytic or ''nonholomorphic'' soft supersymmetry breaking trilinear scalar couplings. As both of these operators are naturally suppressed in generic models of supersymmetry breaking, the resulting neutrino masses are naturally in the sub-eV range. The neutrino magnetic and electric dipole moments resulting from the radiative mechanism also vanish at one-loop order. (orig.)

EFFECTIVE INDICES FOR MONITORING MENTAL WORKLOAD WHILE PERFORMING MULTIPLE TASKS.

Science.gov (United States)

Hsu, Bin-Wei; Wang, Mao-Jiun J; Chen, Chi-Yuan; Chen, Fang

2015-08-01

This study identified several physiological indices that can accurately monitor mental workload while participants performed multiple tasks with the strategy of maintaining stable performance and maximizing accuracy. Thirty male participants completed three 10-min. simulated multitasks: MATB (Multi-Attribute Task Battery) with three workload levels. Twenty-five commonly used mental workload measures were collected, including heart rate, 12 HRV (heart rate variability), 10 EEG (electroencephalography) indices (α, β, θ, α/θ, θ/β from O1-O2 and F4-C4), and two subjective measures. Analyses of index sensitivity showed that two EEG indices, θ and α/θ (F4-C4), one time-domain HRV-SDNN (standard deviation of inter-beat intervals), and four frequency-domain HRV: VLF (very low frequency), LF (low frequency), %HF (percentage of high frequency), and LF/HF were sensitive to differentiate high workload. EEG α/θ (F4-C4) and LF/HF were most effective for monitoring high mental workload. LF/HF showed the highest correlations with other physiological indices. EEG α/θ (F4-C4) showed strong correlations with subjective measures across different mental workload levels. Operation strategy would affect the sensitivity of EEG α (F4-C4) and HF.

The confluent supersymmetry algorithm for Dirac equations with pseudoscalar potentials

International Nuclear Information System (INIS)

Contreras-Astorga, Alonso; Schulze-Halberg, Axel

2014-01-01

We introduce the confluent version of the quantum-mechanical supersymmetry formalism for the Dirac equation with a pseudoscalar potential. Application of the formalism to spectral problems is discussed, regularity conditions for the transformed potentials are derived, and normalizability of the transformed solutions is established. Our findings extend and complement former results [L. M. Nieto, A. A. Pecheritsin, and B. F. Samsonov, “Intertwining technique for the one-dimensional stationary Dirac equation,” Ann. Phys. 305, 151–189 (2003)

Simulation of Zitterbewegung by modelling the Dirac equation in Metamaterials

OpenAIRE

Ahrens, Sven; Jiang, Jun; Sun, Yong; Zhu, Shi-Yao

2015-01-01

We develop a dynamic description of an effective Dirac theory in metamaterials, in which the wavefunction is modeled by the corresponding electric and magnetic field in the metamaterial. This electro-magnetic field can be probed in the experimental setup, which means that the wavefunction of the effective theory is directly accessible by measurement. Our model is based on a plane wave expansion, which ravels the identification of Dirac spinors with single-frequency excitations of the electro-...

The confluent supersymmetry algorithm for Dirac equations with pseudoscalar potentials

Energy Technology Data Exchange (ETDEWEB)

Contreras-Astorga, Alonso, E-mail: aloncont@iun.edu; Schulze-Halberg, Axel, E-mail: axgeschu@iun.edu, E-mail: xbataxel@gmail.com [Department of Mathematics and Actuarial Science and Department of Physics, Indiana University Northwest, 3400 Broadway, Gary, Indiana 46408 (United States)

2014-10-15

We introduce the confluent version of the quantum-mechanical supersymmetry formalism for the Dirac equation with a pseudoscalar potential. Application of the formalism to spectral problems is discussed, regularity conditions for the transformed potentials are derived, and normalizability of the transformed solutions is established. Our findings extend and complement former results [L. M. Nieto, A. A. Pecheritsin, and B. F. Samsonov, “Intertwining technique for the one-dimensional stationary Dirac equation,” Ann. Phys. 305, 151–189 (2003)].

Neural network real time event selection for the DIRAC experiment

CERN Document Server

Kokkas, P; Tauscher, Ludwig; Vlachos, S

2001-01-01

The neural network first level trigger for the DIRAC experiment at CERN is presented. Both the neural network algorithm used and its actual hardware implementation are described. The system uses the fast plastic scintillator information of the DIRAC spectrometer. In 210 ns it selects events with two particles having low relative momentum. Such events are selected with an efficiency of more than 0.94. The corresponding rate reduction for background events is a factor of 2.5. (10 refs).

Few layer epitaxial germanene: a novel two-dimensional Dirac material

OpenAIRE

María Eugenia Dávila; Guy Le Lay

2016-01-01

Monolayer germanene, a novel graphene-like germanium allotrope akin to silicene has been recently grown on metallic substrates. Lying directly on the metal surfaces the reconstructed atom-thin sheets are prone to lose the massless Dirac fermion character and unique associated physical properties of free standing germanene. Here, we show that few layer germanene, which we create by dry epitaxy on a gold template, possesses Dirac cones thanks to a reduced interaction. This finding established o...

Transversal Dirac families in Riemannian foliations

International Nuclear Information System (INIS)

Glazebrook, J.F.; Kamber, F.W.

1991-01-01

We describe a family of differential operators parametrized by the transversal vector potentials of a Riemannian foliation relative to the Clifford algebra of the foliation. This family is non-elliptic but in certain ways behaves like a standard Dirac family in the absolute case as a result of its elliptic-like regularity properties. The analytic and topological indices of this family are defined as elements of K-theory in the parameter space. We indicate how the cohomology of the parameter space is described via suitable maps to Fredholm operators. We outline the proof of a theorem of Vafa-Witten type on uniform bounds for the eigenvalues of this family using a spectral flow argument. A determinant operator is also defined with the appropriate zeta function regularization dependent on the codimension of the foliation. With respect to a generalized coupled Dirac-Yang-Mills system, we indicate how chiral anomalies are located relative to the foliation. (orig.)

Dirac, Jordan and quantum fields

International Nuclear Information System (INIS)

Darrigol, O.

1985-01-01

The case of two principal physicists of quantum mechanics is specially chose: Paul Dirac and Pascual Jordan. They gave a signification and an importance very different to the notion of quantum field, and in particular to the quantized matter wave one. Through their formation and motivation differences, such as they are expressed in their writings, this deep difference is tentatively understood [fr

Dirac gap-induced graphene quantum dot in an electrostatic potential

Science.gov (United States)

Giavaras, G.; Nori, Franco

2011-04-01

A spatially modulated Dirac gap in a graphene sheet leads to charge confinement, thus enabling a graphene quantum dot to be formed without the application of external electric and magnetic fields [G. Giavaras and F. Nori, Appl. Phys. Lett. 97, 243106 (2010)]. This can be achieved provided the Dirac gap has a local minimum in which the states become localized. In this work, the physics of such a gap-induced dot is investigated in the continuum limit by solving the Dirac equation. It is shown that gap-induced confined states couple to the states introduced by an electrostatic quantum well potential. Hence the region in which the resulting hybridized states are localized can be tuned with the potential strength, an effect which involves Klein tunneling. The proposed quantum dot may be used to probe quasirelativistic effects in graphene, while the induced confined states may be useful for graphene-based nanostructures.

Electronic structure of a graphene superlattice with massive Dirac fermions

International Nuclear Information System (INIS)

Lima, Jonas R. F.

2015-01-01

We study the electronic and transport properties of a graphene-based superlattice theoretically by using an effective Dirac equation. The superlattice consists of a periodic potential applied on a single-layer graphene deposited on a substrate that opens an energy gap of 2Δ in its electronic structure. We find that extra Dirac points appear in the electronic band structure under certain conditions, so it is possible to close the gap between the conduction and valence minibands. We show that the energy gap E g can be tuned in the range 0 ≤ E g  ≤ 2Δ by changing the periodic potential. We analyze the low energy electronic structure around the contact points and find that the effective Fermi velocity in very anisotropic and depends on the energy gap. We show that the extra Dirac points obtained here behave differently compared to previously studied systems

Using the NASA Task Load Index to Assess Workload in Electronic Medical Records.

Science.gov (United States)

Hudson, Darren; Kushniruk, Andre W; Borycki, Elizabeth M

2015-01-01

Electronic medical records (EMRs) has been expected to decrease health professional workload. The NASA Task Load Index has become an important tool for assessing workload in many domains. However, its application in assessing the impact of an EMR on nurse's workload has remained to be explored. In this paper we report the results of a study of workload and we explore the utility of applying the NASA Task Load Index to assess impact of an EMR at the end of its lifecycle on nurses' workload. It was found that mental and temporal demands were the most responsible for the workload. Further work along these lines is recommended.

Planar Dirac diffusion

International Nuclear Information System (INIS)

Leo, Stefano de; Rotelli, Pietro

2009-01-01

We present the results of the planar diffusion of a Dirac particle by step and barrier potentials, when the incoming wave impinges at an arbitrary angle with the potential. Except for right-angle incidence this process is characterized by the appearance of spin flip terms. For the step potential, spin flip occurs for both transmitted and reflected waves. However, we find no spin flip in the transmitted barrier result. This is surprising because the barrier result may be derived directly from a two-step calculation. We demonstrate that the spin flip cancellation indeed occurs for each ''particle'' (wave packet) contribution. (orig.)

The Dirac operator on a finite domain and the R-matrix method

International Nuclear Information System (INIS)

Grant, I P

2008-01-01

Relativistic effects in electron-atom collisions and photo-excitation and -ionization processes increase in importance as the atomic number of the target atom grows and spin-dependent effects increase. A relativistic treatment in which electron motion is described using the Dirac Hamiltonian is then desirable. A version of the popular nonrelativistic R-matrix package incorporating terms from the Breit-Pauli Hamiltonian has been used for modelling such processes for some years. The fully relativistic Dirac R-matrix method has been less popular, but is becoming increasingly relevant for applications to heavy ion targets, where the need to use relativistic wavefunctions is more obvious. The Dirac R-matrix method has been controversial ever since it was first proposed by Goertzel (1948 Phys. Rev. 73 1463-6), and it is therefore important to confirm that recent elaborate and costly applications of the method, such as, Badnell et al (2004 J. Phys. B: At. Mol. Phys. 37 4589) and Ballance and Griffin (2007 J. Phys. B: At. Mol. Opt. Phys. 40 247-58), rest on secure foundations. The first part of this paper analyses the structure of the two-point boundary-value problem for the Dirac operator on a finite domain, from which we construct a unified derivation of the Schroedinger (nonrelativistic) and Dirac (relativistic) R-matrix methods. Suggestions that the usual relativistic theory is not well founded are shown to be without foundation

Large linear magnetoresistance in a new Dirac material BaMnBi2

Science.gov (United States)

Wang, Yi-Yan; Yu, Qiao-He; Xia, Tian-Long

2016-10-01

Dirac semimetal is a class of materials that host Dirac fermions as emergent quasi-particles. Dirac cone-type band structure can bring interesting properties such as quantum linear magnetoresistance and large mobility in the materials. In this paper, we report the synthesis of high quality single crystals of BaMnBi2 and investigate the transport properties of the samples. BaMnBi2 is a metal with an antiferromagnetic transition at T N = 288 K. The temperature dependence of magnetization displays different behavior from CaMnBi2 and SrMnBi2, which suggests the possible different magnetic structure of BaMnBi2. The Hall data reveals electron-type carriers and a mobility μ(5 K) = 1500 cm2/V·s. Angle-dependent magnetoresistance reveals the quasi-two-dimensional (2D) Fermi surface in BaMnBi2. A crossover from semiclassical MR ˜ H 2 dependence in low field to MR ˜ H dependence in high field, which is attributed to the quantum limit of Dirac fermions, has been observed in magnetoresistance. Our results indicate the existence of Dirac fermions in BaMnBi2. Project supported by the National Natural Science Foundation of China (Grant No. 11574391), the Fundamental Research Funds for the Central Universities, and the Research Funds of Renmin University of China (Grant No. 14XNLQ07).

Dirac or Majorana nature and mass effects on the neutrino behaviour; Effets de la nature de Dirac ou de Majorana, ainsi que de la masse, sur le comportement du neutrino

Energy Technology Data Exchange (ETDEWEB)

Campagne, J E

1995-04-01

This work deals with the Dirac or Majorana nature and mass effects on the neutrino behaviour. In the first part of this study are given the Dirac equation properties and the Majorana neutrino definition. As the difference between a Dirac and a Majorana neutrino has only a sense if their masses are not equal to zero, the second part presents a generalization of the Dirac mass term and the different ways to generate a neutrino mass. Several comparisons are made in the third part between quarks and leptons families mixtures which are linked intimately to masses generation. The fourth part gives an example of masses possible values and neutrinos particles mixtures matrix elements predicting. The neutrino electromagnetic and weak interactions are then considered as well as the neutrinos production by the neutral currents. The charged currents are however better to discriminate the Dirac or Majorana nature. The neutrinos propagation in the matter and in the vacuum are analyzed (the case of neutrino oscillations more particularly) under the result of recent experimental observations. At last, are presented the evaluation of neutrino mass (if it exists) through the analysis of double beta decay and the sensibility of future experiments. (O.L.). 164 refs., 73 figs., 20 tabs.

Spectral correlations of the massive QCD Dirac operator at finite temperature

International Nuclear Information System (INIS)

Seif, Burkhard; Wettig, Tilo; Guhr, Thomas

1999-01-01

We use the graded eigenvalue method, a variant of the supersymmetry technique, to compute the universal spectral correlations of the QCD Dirac operator in the presence of massive dynamical quarks. The calculation is done for the chiral Gaussian unitary ensemble of random matrix theory with an arbitrary Hermitian matrix added to the Dirac matrix. This case is of interest for schematic models of OCD at finite temperature

The psychometrics of mental workload: multiple measures are sensitive but divergent.

Science.gov (United States)

Matthews, Gerald; Reinerman-Jones, Lauren E; Barber, Daniel J; Abich, Julian

2015-02-01

A study was run to test the sensitivity of multiple workload indices to the differing cognitive demands of four military monitoring task scenarios and to investigate relationships between indices. Various psychophysiological indices of mental workload exhibit sensitivity to task factors. However, the psychometric properties of multiple indices, including the extent to which they intercorrelate, have not been adequately investigated. One hundred fifty participants performed in four task scenarios based on a simulation of unmanned ground vehicle operation. Scenarios required threat detection and/or change detection. Both single- and dual-task scenarios were used. Workload metrics for each scenario were derived from the electroencephalogram (EEG), electrocardiogram, transcranial Doppler sonography, functional near infrared, and eye tracking. Subjective workload was also assessed. Several metrics showed sensitivity to the differing demands of the four scenarios. Eye fixation duration and the Task Load Index metric derived from EEG were diagnostic of single-versus dual-task performance. Several other metrics differentiated the two single tasks but were less effective in differentiating single- from dual-task performance. Psychometric analyses confirmed the reliability of individual metrics but failed to identify any general workload factor. An analysis of difference scores between low- and high-workload conditions suggested an effort factor defined by heart rate variability and frontal cortex oxygenation. General workload is not well defined psychometrically, although various individual metrics may satisfy conventional criteria for workload assessment. Practitioners should exercise caution in using multiple metrics that may not correspond well, especially at the level of the individual operator.

Pythagoras's theorem on a two-dimensional lattice from a `natural' Dirac operator and Connes's distance formula

Science.gov (United States)

Dai, Jian; Song, Xing-Chang

2001-07-01

One of the key ingredients of Connes's noncommutative geometry is a generalized Dirac operator which induces a metric (Connes's distance) on the pure state space. We generalize such a Dirac operator devised by Dimakis et al, whose Connes distance recovers the linear distance on an one-dimensional lattice, to the two-dimensional case. This Dirac operator has the local eigenvalue property and induces a Euclidean distance on this two-dimensional lattice, which is referred to as `natural'. This kind of Dirac operator can be easily generalized into any higher-dimensional lattices.

Correlated Dirac semimetallic state with unusual positive magnetoresistance in strain-free perovskite SrIrO3

Science.gov (United States)

Fujioka, J.; Okawa, T.; Yamamoto, A.; Tokura, Y.

2017-03-01

We investigated magnetotransport properties and charge dynamics of strain-free perovskite SrIrO3. Both the longitudinal and transverse magnetoresistivity (MR) are significantly enhanced with decreasing temperature, in accord with the evolution of the Dirac semimetallic state. The electron correlation effect in the Dirac state shows up as a dramatic change in charge dynamics with temperature and as an enhanced paramagnetic susceptibility. We propose that the field-induced topological transition of the Dirac node coupled to the enhanced paramagnetism causes the unique MR of correlated Dirac electrons.

A spatially homogeneous and isotropic Einstein-Dirac cosmology

Science.gov (United States)

Finster, Felix; Hainzl, Christian

2011-04-01

We consider a spatially homogeneous and isotropic cosmological model where Dirac spinors are coupled to classical gravity. For the Dirac spinors we choose a Hartree-Fock ansatz where all one-particle wave functions are coherent and have the same momentum. If the scale function is large, the universe behaves like the classical Friedmann dust solution. If however the scale function is small, quantum effects lead to oscillations of the energy-momentum tensor. It is shown numerically and proven analytically that these quantum oscillations can prevent the formation of a big bang or big crunch singularity. The energy conditions are analyzed. We prove the existence of time-periodic solutions which go through an infinite number of expansion and contraction cycles.

Local moment formation in Dirac electrons

International Nuclear Information System (INIS)

Mashkoori, M; Mahyaeh, I; Jafari, S A

2015-01-01

Elemental bismuth and its compounds host strong spin-orbit interaction which is at the heart of topologically non-trivial alloys based on bismuth. These class of materials are described in terms of 4x4 matrices at each v point where spin and orbital labels of the underlying electrons are mixed. In this work we investigate the single impurity Anderson model (SIAM) within a mean field approximation to address the nature of local magnetic moment formation in a generic Dirac Hamiltonian. Despite the spin-mixing in the Hamiltonian, within the Hartree approximation it turns out that the impuritys Green function is diagonal in spin label. In the three dimensional Dirac materials defined over a bandwidth D and spin-orbit parameter γ, that hybridizes with impurity through V, a natural dimensionless parameter V 2 D/2πγ 3 emerges. So neither the hybridization strength, V, nor the spin-orbit coupling γ, but a combination thereof governs the phase diagram. By tuning chemical potential and the impurity level, we present phase diagram for various values of Hubbard U. Numerical results suggest that strong spin-orbit coupling enhances the local moment formation both in terms of its strength and the area of the local moment region. In the case that we tune the chemical potential in a similar way as normal metal we find that magnetic region is confined to μ ≥ ε 0 , in sharp contrast to 2D Dirac fermions. If one fixes the chemical potential and tunes the impurity level, phase diagram has two magnetic regions which corresponds to hybridization of impurity level with lower and upper bands. (paper)

Classification Systems for Individual Differences in Multiple-task Performance and Subjective Estimates of Workload

Science.gov (United States)

Damos, D. L.

1984-01-01

Human factors practitioners often are concerned with mental workload in multiple-task situations. Investigations of these situations have demonstrated repeatedly that individuals differ in their subjective estimates of workload. These differences may be attributed in part to individual differences in definitions of workload. However, after allowing for differences in the definition of workload, there are still unexplained individual differences in workload ratings. The relation between individual differences in multiple-task performance, subjective estimates of workload, information processing abilities, and the Type A personality trait were examined.

The half-filled Landau level: The case for Dirac composite fermions

Science.gov (United States)

Geraedts, Scott D.; Zaletel, Michael P.; Mong, Roger S. K.; Metlitski, Max A.; Vishwanath, Ashvin; Motrunich, Olexei I.

2016-04-01

In a two-dimensional electron gas under a strong magnetic field, correlations generate emergent excitations distinct from electrons. It has been predicted that “composite fermions”—bound states of an electron with two magnetic flux quanta—can experience zero net magnetic field and form a Fermi sea. Using infinite-cylinder density matrix renormalization group numerical simulations, we verify the existence of this exotic Fermi sea, but find that the phase exhibits particle-hole symmetry. This is self-consistent only if composite fermions are massless Dirac particles, similar to the surface of a topological insulator. Exploiting this analogy, we observe the suppression of 2kF backscattering, a characteristic of Dirac particles. Thus, the phenomenology of Dirac fermions is also relevant to two-dimensional electron gases in the quantum Hall regime.

AEMnSb2 (AE=Sr, Ba): a new class of Dirac materials

International Nuclear Information System (INIS)

Farhan, M Arshad; Lee, Geunsik; Shim, Ji Hoon

2014-01-01

The Dirac fermions of Sb square net in AEMnSb 2 (AE=Sr, Ba) are investigated by using first-principles calculation. BaMnSb 2 contains Sb square net layers with a coincident stacking of Ba atoms, exhibiting Dirac fermion behavior. On the other hand, SrMnSb 2 has a staggered stacking of Sr atoms with distorted zig-zag chains of Sb atoms. Application of hydrostatic pressure on the latter induces a structural change from a staggered to a coincident arrangement of AE ions accompanying a transition from insulator to a metal containing Dirac fermions. The structural investigations show that the stacking type of cation and orthorhombic distortion of Sb layers are the main factors to decide the crystal symmetry of the material. We propose that the Dirac fermions can be obtained by controlling the size of cation and the volume of AEMnSb 2 compounds. (fast track communication)

Creating stable Floquet-Weyl semimetals by laser-driving of 3D Dirac materials.

Science.gov (United States)

Hübener, Hannes; Sentef, Michael A; De Giovannini, Umberto; Kemper, Alexander F; Rubio, Angel

2017-01-17

Tuning and stabilizing topological states, such as Weyl semimetals, Dirac semimetals or topological insulators, is emerging as one of the major topics in materials science. Periodic driving of many-body systems offers a platform to design Floquet states of matter with tunable electronic properties on ultrafast timescales. Here we show by first principles calculations how femtosecond laser pulses with circularly polarized light can be used to switch between Weyl semimetal, Dirac semimetal and topological insulator states in a prototypical three-dimensional (3D) Dirac material, Na 3 Bi. Our findings are general and apply to any 3D Dirac semimetal. We discuss the concept of time-dependent bands and steering of Floquet-Weyl points and demonstrate how light can enhance topological protection against lattice perturbations. This work has potential practical implications for the ultrafast switching of materials properties, such as optical band gaps or anomalous magnetoresistance.

Creating stable Floquet-Weyl semimetals by laser-driving of 3D Dirac materials

Science.gov (United States)

Hübener, Hannes; Sentef, Michael A.; de Giovannini, Umberto; Kemper, Alexander F.; Rubio, Angel

2017-01-01

Tuning and stabilizing topological states, such as Weyl semimetals, Dirac semimetals or topological insulators, is emerging as one of the major topics in materials science. Periodic driving of many-body systems offers a platform to design Floquet states of matter with tunable electronic properties on ultrafast timescales. Here we show by first principles calculations how femtosecond laser pulses with circularly polarized light can be used to switch between Weyl semimetal, Dirac semimetal and topological insulator states in a prototypical three-dimensional (3D) Dirac material, Na3Bi. Our findings are general and apply to any 3D Dirac semimetal. We discuss the concept of time-dependent bands and steering of Floquet-Weyl points and demonstrate how light can enhance topological protection against lattice perturbations. This work has potential practical implications for the ultrafast switching of materials properties, such as optical band gaps or anomalous magnetoresistance.

Dirac State in the FeB2 Monolayer with Graphene-Like Boron Sheet.

Science.gov (United States)

Zhang, Haijun; Li, Yafei; Hou, Jianhou; Du, Aijun; Chen, Zhongfang

2016-10-12

By introducing the commonly utilized Fe atoms into a two-dimensional (2D) honeycomb boron network, we theoretically designed a new Dirac material of FeB 2 monolayer with a Fermi velocity in the same order of graphene. The electron transfer from Fe atoms to B networks not only effectively stabilizes the FeB 2 networks but also leads to the strong interaction between the Fe and B atoms. The Dirac state in FeB 2 system primarily arises from the Fe d orbitals and hybridized orbital from Fe-d and B-p states. The newly predicted FeB 2 monolayer has excellent dynamic and thermal stabilities and is also the global minimum of 2D FeB 2 system, implying its experimental feasibility. Our results are beneficial to further uncovering the mechanism of the Dirac cones and providing a feasible strategy for Dirac materials design.

Creating stable Floquet–Weyl semimetals by laser-driving of 3D Dirac materials

Science.gov (United States)

Hübener, Hannes; Sentef, Michael A.; De Giovannini, Umberto; Kemper, Alexander F.; Rubio, Angel

2017-01-01

Tuning and stabilizing topological states, such as Weyl semimetals, Dirac semimetals or topological insulators, is emerging as one of the major topics in materials science. Periodic driving of many-body systems offers a platform to design Floquet states of matter with tunable electronic properties on ultrafast timescales. Here we show by first principles calculations how femtosecond laser pulses with circularly polarized light can be used to switch between Weyl semimetal, Dirac semimetal and topological insulator states in a prototypical three-dimensional (3D) Dirac material, Na3Bi. Our findings are general and apply to any 3D Dirac semimetal. We discuss the concept of time-dependent bands and steering of Floquet–Weyl points and demonstrate how light can enhance topological protection against lattice perturbations. This work has potential practical implications for the ultrafast switching of materials properties, such as optical band gaps or anomalous magnetoresistance. PMID:28094286

Relationship between workload and low back pain in assembly line workers

Directory of Open Access Journals (Sweden)

Reza Kalantari

2016-06-01

Full Text Available Introduction: Work pressure and excessive workload can jeopardize and impair the people’s health. One of these impairments is musculoskeletal disorders. Among these disorders, low back pain is the most common and most costly problem. The purpose of this study was to investigate the relationship between workload and prevalence of low back pain in assembly line workers of a car manufacturing factory. Methods: This cross-sectional study was conducted on 69 workers working in the assembly line of a factory. Data collection tools included three questionnaires: demographic questionnaire, NASA Task Load Index (NASA-TLX and Cornell Musculoskeletal Discomfort Questionnaire (CMDQ. Data were analyzed by descriptive and inferential (T-test and One-way ANOVA statistics. Results: Of the workers, 72.5% were female. The average total workload was 71.42% and the prevalence of musculoskeletal disorders in low back was 43.37%. The results of the analysis of relationship between workload and the prevalence of low back pain showed a significant relationship between physical/ mental workload and the incidence of low back pain (P<0.05. Conclusion: The more is the workload on the person, the greater is the risk of low back pain. Measures such as increasing the number of workers to distribute the workload, slowing the work pace, having work-rest periods for workers, improving psychological conditions of work, etc. can be useful in this regard.

Hydrogenated and halogenated blue phosphorene as Dirac materials: A first principles study

Energy Technology Data Exchange (ETDEWEB)

Sun, Minglei [School of Mechanical Engineering, Southeast University, Nanjing, Jiangsu 211189 (China); Wang, Sake [Department of Physics, Southeast University, Nanjing, Jiangsu 210096 (China); Yu, Jin [School of Materials Science and Engineering, Southeast University, Nanjing, Jiangsu 211189 (China); Tang, Wencheng, E-mail: 101000185@seu.edu.cn [School of Mechanical Engineering, Southeast University, Nanjing, Jiangsu 211189 (China)

2017-01-15

Highlights: • The fully hydrogenated and halogenated blue phosphorenes are 2D Dirac materials. • The Dirac cone in fluorinated and iodinated blue phosphorenes lies exactly at the Fermi level. • The mass density of hydrogenated and fluorinated blue phosphorenes is rather small. - Abstract: Using first-principles calculations, we systematically investigate the structures and electronic properties of fully hydrogenated and halogenated blue phosphorene (P{sub 2}X{sub 2}). All these systems possess Dirac cone at high-symmetry K point, which are mainly contributed by P s p{sub x} p{sub y} orbitals. The Dirac cone in P{sub 2}F{sub 2} and P{sub 2}I{sub 2} systems lies exactly at the Fermi level. Formation energy analysis denotes that all the systems are energetically stable except P{sub 2}I{sub 2}. The mass density for P{sub 2}H{sub 2} and P{sub 2}F{sub 2} systems is rather small. Our calculations proposed that these systems, especially P{sub 2}F{sub 2} system, have great potential applications in future nanoelectronics.

Quantifying the Workload of Subject Bibliographers in Collection Development.

Science.gov (United States)

Metz, Paul

1991-01-01

Discussion of the role of subject bibliographers in collection development activities focuses on an approach developed at Virginia Polytechnic and State Institute to provide a formula for estimating the collection development workload of subject bibliographers. Workload standards and matrix models of organizational structures are discussed, and…

Respiratory sinus arrhythmia as a measure of cognitive workload.

Science.gov (United States)

Muth, Eric R; Moss, Jason D; Rosopa, Patrick J; Salley, James N; Walker, Alexander D

2012-01-01

The current standard for measuring cognitive workload is the NASA Task-load Index (TLX) questionnaire. Although this measure has a high degree of reliability, diagnosticity, and sensitivity, a reliable physiological measure of cognitive workload could provide a non-invasive, objective measure of workload that could be tracked in real or near real-time without interrupting the task. This study investigated changes in respiratory sinus arrhythmia (RSA) during seven different sub-sections of a proposed selection test for Navy aviation and compared them to changes reported on the NASA-TLX. 201 healthy participants performed the seven tasks of the Navy's Performance Based Measure. RSA was measured during each task and the NASA-TLX was administered after each task. Multi-level modeling revealed that RSA significantly predicted NASA-TLX scores. A moderate within-subject correlation was also found between RSA and NASA TLX scores. The findings support the potential development of RSA as a real-time measure of cognitive workload. Copyright © 2011. Published by Elsevier B.V.

Electrodynamic properties of the semimetallic Dirac material SrMnB i2 : Two-carrier-model analysis

Science.gov (United States)

Park, H. J.; Park, Byung Cheol; Lee, Min-Cheol; Jeong, D. W.; Park, Joonbum; Kim, Jun Sung; Ji, Hyo Seok; Shim, J. H.; Kim, K. W.; Moon, S. J.; Kim, Hyeong-Do; Cho, Deok-Yong; Noh, T. W.

2017-10-01

The electrodynamics of free carriers in the semimetallic Dirac material SrMnB i2 was investigated using optical spectroscopy and first-principles calculations. Using a two-carrier-model analysis, the total free-carrier response was successfully decomposed into individual contributions from Dirac fermions and non-Dirac free carriers. Possible roles of chiral pseudospin, spin-orbit interaction (SOI), antiferromagnetism, and electron-phonon (e -p h ) coupling in the Dirac fermion transport were also addressed. The Dirac fermions possess a low scattering rate of ˜10 meV at low temperature and thereby experience coherent transport. However, at high temperatures, we observed that the Dirac fermion transport becomes significantly incoherent, possibly due to strong e -p h interactions. The SOI-induced gap and antiferromagnetism play minor roles in the electrodynamics of the free carriers in SrMnB i2 . We also observed a seemingly optical-gap-like feature near 120 meV, which emerges at low temperatures but becomes filled in with increasing temperature. This gap-filling phenomenon is ascribed to phonon-assisted indirect transitions promoted at high temperatures.

Voltage-induced switching of an antiferromagnetically ordered topological Dirac semimetal

Science.gov (United States)

Kim, Youngseok; Kang, Kisung; Schleife, André; Gilbert, Matthew J.

2018-04-01

An antiferromagnetic semimetal has been recently identified as a new member of topological semimetals that may host three-dimensional symmetry-protected Dirac fermions. A reorientation of the Néel vector may break the underlying symmetry and open a gap in the quasiparticle spectrum, inducing the (semi)metal-insulator transition. Here, we predict that such a transition may be controlled by manipulating the chemical potential location of the material. We perform both analytical and numerical analysis on the thermodynamic potential of the model Hamiltonian and find that the gapped spectrum is preferred when the chemical potential is located at the Dirac point. As the chemical potential deviates from the Dirac point, the system shows a possible transition from the gapped to the gapless phase and switches the corresponding Néel vector configuration. We perform density functional theory calculations to verify our analysis using a realistic material and discuss a two terminal transport measurement as a possible route to identify the voltage-induced switching of the Néel vector.

Supersymmetric Dirac-Born-Infeld action with self-dual mass term

International Nuclear Information System (INIS)

Nishino, Hitoshi; Rajpoot, Subhash; Reed, Kevin

2005-01-01

We introduce a Dirac-Born-Infeld action to a self-dual N = 1 supersymmetric vector multiplet in three dimensions. This action is based on the supersymmetric generalized self-duality in odd dimensions developed originally by Townsend, Pilch and van Nieuwenhuizen. Even though such a self-duality had been supposed to be very difficult to generalize to a supersymmetrically interacting system, we show that the Dirac-Born-Infeld action is actually compatible with supersymmetry and self-duality in three dimensions, even though the original self-duality receives corrections by the Dirac-Born-Infeld action. The interactions can be further generalized to arbitrary (non)polynomial interactions. As a by-product, we also show that a third-rank field strength leads to a more natural formulation of self-duality in 3D. We also show an interesting role played by the third-rank field strength leading to supersymmetry breaking, in addition to accommodating a Chern-Simons form

Few layer epitaxial germanene: a novel two-dimensional Dirac material

Science.gov (United States)

Dávila, María Eugenia; Le Lay, Guy

2016-02-01

Monolayer germanene, a novel graphene-like germanium allotrope akin to silicene has been recently grown on metallic substrates. Lying directly on the metal surfaces the reconstructed atom-thin sheets are prone to lose the massless Dirac fermion character and unique associated physical properties of free standing germanene. Here, we show that few layer germanene, which we create by dry epitaxy on a gold template, possesses Dirac cones thanks to a reduced interaction. This finding established on synchrotron-radiation-based photoemission, scanning tunneling microscopy imaging and surface electron diffraction places few layer germanene among the rare two-dimensional Dirac materials. Since germanium is currently used in the mainstream Si-based electronics, perspectives of using germanene for scaling down beyond the 5 nm node appear very promising. Other fascinating properties seem at hand, typically the robust quantum spin Hall effect for applications in spintronics and the engineering of Floquet Majorana fermions by light for quantum computing.

Few layer epitaxial germanene: a novel two-dimensional Dirac material.

Science.gov (United States)

Dávila, María Eugenia; Le Lay, Guy

2016-02-10

Monolayer germanene, a novel graphene-like germanium allotrope akin to silicene has been recently grown on metallic substrates. Lying directly on the metal surfaces the reconstructed atom-thin sheets are prone to lose the massless Dirac fermion character and unique associated physical properties of free standing germanene. Here, we show that few layer germanene, which we create by dry epitaxy on a gold template, possesses Dirac cones thanks to a reduced interaction. This finding established on synchrotron-radiation-based photoemission, scanning tunneling microscopy imaging and surface electron diffraction places few layer germanene among the rare two-dimensional Dirac materials. Since germanium is currently used in the mainstream Si-based electronics, perspectives of using germanene for scaling down beyond the 5 nm node appear very promising. Other fascinating properties seem at hand, typically the robust quantum spin Hall effect for applications in spintronics and the engineering of Floquet Majorana fermions by light for quantum computing.

Operator ordering in quantum optics theory and the development of Dirac's symbolic method

International Nuclear Information System (INIS)

Fan Hongyi

2003-01-01

We present a general unified approach for arranging quantum operators of optical fields into ordered products (normal ordering, antinormal ordering, Weyl ordering (or symmetric ordering)) by fashioning Dirac's symbolic method and representation theory. We propose the technique of integration within an ordered product (IWOP) of operators to realize our goal. The IWOP makes Dirac's representation theory and the symbolic method more transparent and consequently more easily understood. The beauty of Dirac's symbolic method is further revealed. Various applications of the IWOP technique, such as in developing the entangled state representation theory, nonlinear coherent state theory, Wigner function theory, etc, are presented. (review article)

Darboux partners of pseudoscalar Dirac potentials associated with exceptional orthogonal polynomials

International Nuclear Information System (INIS)

Schulze-Halberg, Axel; Roy, Barnana

2014-01-01

We introduce a method for constructing Darboux (or supersymmetric) pairs of pseudoscalar and scalar Dirac potentials that are associated with exceptional orthogonal polynomials. Properties of the transformed potentials and regularity conditions are discussed. As an application, we consider a pseudoscalar Dirac potential related to the Schrödinger model for the rationally extended radial oscillator. The pseudoscalar partner potentials are constructed under the first- and second-order Darboux transformations

Darboux partners of pseudoscalar Dirac potentials associated with exceptional orthogonal polynomials

Energy Technology Data Exchange (ETDEWEB)

Schulze-Halberg, Axel, E-mail: xbataxel@gmail.com [Department of Mathematics and Actuarial Science, Indiana University Northwest, 3400 Broadway, Gary, IN 46408 (United States); Department of Physics, Indiana University Northwest, 3400 Broadway, Gary, IN 46408 (United States); Roy, Barnana, E-mail: barnana@isical.ac.in [Physics and Applied Mathematics Unit, Indian Statistical Institute, Kolkata 700108 (India)

2014-10-15

We introduce a method for constructing Darboux (or supersymmetric) pairs of pseudoscalar and scalar Dirac potentials that are associated with exceptional orthogonal polynomials. Properties of the transformed potentials and regularity conditions are discussed. As an application, we consider a pseudoscalar Dirac potential related to the Schrödinger model for the rationally extended radial oscillator. The pseudoscalar partner potentials are constructed under the first- and second-order Darboux transformations.

Workload and job satisfaction among general practitioners: a review of the literature.

NARCIS (Netherlands)

Groenewegen, P.P.; Hutten, J.B.F.

1991-01-01

The workload of general practitioners (GPs) is an important issue in health care systems with capitation payment for GPs services. This article reviews the literature on determinants and consequences of workload and job satisfaction of GPs. Determinants of workload are located on the demand side

Continuous measures of situation awareness and workload

International Nuclear Information System (INIS)

Droeivoldsmo, Asgeir; Skraaning, Gyrd jr.; Sverrbo, Mona; Dalen, Joergen; Grimstad, Tone; Andresen, Gisle

1998-03-01

This report presents methods for continuous measures for Situation Awareness and Workload. The objective has been to identify, develop and test the new measures, and compare them to instruments that require interruptions of scenarios. The new measures are: (1) the Visual Indicator of Situation Awareness (VISA); where Situation Awareness is scored from predefined areas of visual interest critical for solving scenarios. Visual monitoring of areas was recorded by eye-movement tracking. (2) Workload scores reflected by Extended Dwell Time (EDT) and the operator Activity Level. EDT was calculated from eye-movement data files, and the activity level was estimated from simulator logs. Using experimental data from the 1996 CASH NRC Alarm study and the 1997 Human Error Analysis Project/ Human-Centred Automation study, the new measurement techniques have been tested and evaluated on a preliminary basis. The results showed promising relationships between the new continuous measures of situation awareness and workload, and established instruments based upon scenario interruptions. (author)

Integrating out the Dirac sea

Energy Technology Data Exchange (ETDEWEB)

Karbstein, Felix

2009-07-08

We introduce a new method for dealing with fermionic quantum field theories amenable to a mean-field-type approximation. In this work we focus on the relativistic Hartree approximation. Our aim is to integrate out the Dirac sea and derive a no-sea effective theory'' with positive energy single particle states only. As the derivation of the no-sea effective theory involves only standard Feynman diagrams, our approach is quite general and not restricted to particular space-time dimensions. We develop and illustrate the approach in the ''large N'' limit of the Gross-Neveu model family in 1+1 dimensions. As the Gross-Neveu model has been intensely studied and several analytical solutions are known for this model, it is an ideal testing ground for our no-sea effective theory approach. The chiral Gross-Neveu model, also referred to as 1+1 dimensional Nambu-Jona-Lasinio model, turns out to be of particular interest. In this case, we explicitly derive a consistent effective theory featuring both elementary ''{pi} meson'' fields and (positive energy) ''quark'' fields, starting from a purely fermionic quantum field theory. In the second part of this work, we apply our approach to the Walecka model in 1+1 and 3+1 dimensions. As the Dirac sea caused considerable difficulties in attempts to base nuclear physics on field theoretic models like the Walecka model, mean-field calculations were typically done without the sea. We confront several of these mean-field theory results with our no-sea effective theory approach. The potential of our approach is twofold. While the no-sea effective theory can be utilized to provide new analytical insights in particular parameter regimes, it also sheds new light on more fundamental issues as the explicit emergence of effective, Dirac-sea induced multi-fermion interactions in an effective theory with positive energy states only. (orig.)

On the level order for Dirac operators

International Nuclear Information System (INIS)

Grosse, H.

1987-01-01

We start from the Dirac operator for the Coulomb potential and prove within first order perturbation theory that degenerate levels split in a definite way depending on the sign of the Laplacian of the perturbing potential. 9 refs. (Author)

Remuneration, workload, and allocation of time in general practice.

NARCIS (Netherlands)

Berg, M.J. van den; Westert, G.P.; Groenewegen, P.P.; Bakker, D.H. de; Zee, J. van der

2006-01-01

Background: General Practitioners (GPs) can cope with workload by, among others, spending more hours in patient care or by spending less time per patient. The way GPs are paid might affect the way they cope with workload. From an economical point of view, capitation payment is an incentive to

Workload demand in police officers during mountain bike patrols

NARCIS (Netherlands)

Takken, T.; Ribbink, A.; Heneweer, H.; Moolenaar, H.; Wittink, H.

2009-01-01

To the authors' knowledge this is the first paper that has used the training impulse (TRIMP) 'methodology' to calculate workload demand. It is believed that this is a promising method to calculate workload in a range of professions in order to understand the relationship between work demands and

All Things Being Equal: Observing Australian Individual Academic Workloads

Science.gov (United States)

Dobele, Angela; Rundle-Thiele, Sharyn; Kopanidis, Foula; Steel, Marion

2010-01-01

The achievement of greater gender equity within Australian universities is a significant issue for both the quality and the strength of Australian higher education. This paper contributes to our knowledge of academic workloads, observing individual workloads in business faculties. A multiple case study method was employed to observe individual…

Modest associations between self-reported physical workload and neck trouble

DEFF Research Database (Denmark)

Holm, Jonas Winkel; Hartvigsen, Jan; Lings, Svend

2013-01-01

-based, cross-sectional questionnaire study using 3,208 monozygotic (MZ) and same-sexed dizygotic (DZ) twins aged 19-70. Twin pairs discordant for self-reported NT during the past year ("Any NT") were included. Self-reported physical workload in four categories was used as exposure ("sitting," "sitting......OBJECTIVES: To investigate the relationship between self-reported physical workload and neck trouble (NT) in twins. Additionally, to explore whether the relationship between physical workload and NT is influenced by genetic factors. METHODS: A twin control study was performed within a population...... and walking," "light physical," and "heavy physical" work). Paired analyses including conditional logistic regression were made for all participants and for each sex, and MZ and DZ pairs separately. RESULTS: No marked associations between physical workload and NT were seen. A moderate risk elevation in "heavy...

Training improves laparoscopic tasks performance and decreases operator workload.

Science.gov (United States)

Hu, Jesse S L; Lu, Jirong; Tan, Wee Boon; Lomanto, Davide

2016-05-01

It has been postulated that increased operator workload during task performance may increase fatigue and surgical errors. The National Aeronautics and Space Administration-Task Load Index (NASA-TLX) is a validated tool for self-assessment for workload. Our study aims to assess the relationship of workload and performance of novices in simulated laparoscopic tasks of different complexity levels before and after training. Forty-seven novices without prior laparoscopic experience were recruited in a trial to investigate whether training improves task performance as well as mental workload. The participants were tested on three standard tasks (ring transfer, precision cutting and intracorporeal suturing) in increasing complexity based on the Fundamentals of Laparoscopic Surgery (FLS) curriculum. Following a period of training and rest, participants were tested again. Test scores were computed from time taken and time penalties for precision errors. Test scores and NASA-TLX scores were recorded pre- and post-training and analysed using paired t tests. One-way repeated measures ANOVA was used to analyse differences in NASA-TLX scores between the three tasks. NASA-TLX score was lowest with ring transfer and highest with intracorporeal suturing. This was statistically significant in both pre-training (p NASA-TLX scores mirror the changes in test scores for the three tasks. Workload scores decreased significantly after training for all three tasks (ring transfer = 2.93, p NASA-TLX score is an accurate reflection of the complexity of simulated laparoscopic tasks in the FLS curriculum. This also correlates with the relationship of test scores between the three tasks. Simulation training improves both performance score and workload score across the tasks.

The square root of the Dirac operator on superspace and the Maxwell equations

Science.gov (United States)

Bzdak, Adam; Hadasz, Leszek

2004-02-01

We re-consider the procedure of "taking a square root of the Dirac equation" on superspace and show that it leads to the well-known superfield Wα and to the proper equations of motion for the components, i.e., the Maxwell equations and the massless Dirac equation.

Generating {mu} and B{mu} in models with Dirac gauginos

Energy Technology Data Exchange (ETDEWEB)

Benakli, Karim [CNRS, UPMC Univ. Paris 06 (France). Lab. de Physique Theorique et Hautes Energies; Goodsell, Mark D. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Maier, Ann-Kathrin [SB-EPFL, Lausanne (Switzerland). Laboratoire de Physique de la Matiere Complexe

2011-04-15

We consider the extension of the Minimal Supersymmetric Standard Model by Dirac masses for the gauginos. We study the possibility that the same singlet S that pairs up with the bino, to form a Dirac fermion, is used to generate {mu} and B{mu} terms through its vacuum expectation value. For this purpose, we assume that, in the Higgs potential, the necessary R-symmetry breaking originates entirely from a superpotential term ({kappa})/(3)S{sup 3} and discuss the implications for the spectrum of the model. (orig.)

Approximate entropy: a new evaluation approach of mental workload under multitask conditions

Science.gov (United States)

Yao, Lei; Li, Xiaoling; Wang, Wei; Dong, Yuanzhe; Jiang, Ying

2014-04-01

There are numerous instruments and an abundance of complex information in the traditional cockpit display-control system, and pilots require a long time to familiarize themselves with the cockpit interface. This can cause accidents when they cope with emergency events, suggesting that it is necessary to evaluate pilot cognitive workload. In order to establish a simplified method to evaluate cognitive workload under a multitask condition. We designed a series of experiments involving different instrument panels and collected electroencephalograms (EEG) from 10 healthy volunteers. The data were classified and analyzed with an approximate entropy (ApEn) signal processing. ApEn increased with increasing experiment difficulty, suggesting that it can be used to evaluate cognitive workload. Our results demonstrate that ApEn can be used as an evaluation criteria of cognitive workload and has good specificity and sensitivity. Moreover, we determined an empirical formula to assess the cognitive workload interval, which can simplify cognitive workload evaluation under multitask conditions.

Drive the Dirac electrons into Cooper pairs in SrxBi2Se3

Science.gov (United States)

Du, Guan; Shao, Jifeng; Yang, Xiong; Du, Zengyi; Fang, Delong; Wang, Jinghui; Ran, Kejing; Wen, Jinsheng; Zhang, Changjin; Yang, Huan; Zhang, Yuheng; Wen, Hai-Hu

2017-01-01

Topological superconductors are a very interesting and frontier topic in condensed matter physics. Despite the tremendous efforts in exploring topological superconductivity, its presence is however still under heavy debate. The Dirac electrons have been proven to exist on the surface of a topological insulator. It remains unclear whether and how the Dirac electrons fall into Cooper pairing in an intrinsic superconductor with the topological surface states. Here we show the systematic study of scanning tunnelling microscope/spectroscopy on the possible topological superconductor SrxBi2Se3. We first demonstrate that only the intercalated Sr atoms can induce superconductivity. Then we show the full superconducting gaps without any in-gap density of states as expected theoretically for a bulk topological superconductor. Finally, we find that the surface Dirac electrons will simultaneously condense into the superconducting state within the superconducting gap. This vividly demonstrates how the surface Dirac electrons are driven into Cooper pairs. PMID:28198378

Face centered cubic SnSe as a Z2 trivial Dirac nodal line material

OpenAIRE

Tateishi, Ikuma; Matsuura, Hiroyasu

2018-01-01

The presence of Dirac nodal line in the time-reversal and inversion symmetric system is dictated by Z2 index when spin-orbit interaction is absent. With the first principles calculation, we show that the Dirac nodal line can emerge in Z2 trivial material by calculating the band structure of SnSe of face centered cubic lattice as an example and it becomes a topological crystalline insulator when spin-orbit interaction is taken into account. We clarify the origin of the Dirac nodal line by obta...

Balancing nurses' workload in hospital wards: study protocol of developing a method to manage workload.

Science.gov (United States)

van den Oetelaar, W F J M; van Stel, H F; van Rhenen, W; Stellato, R K; Grolman, W

2016-11-10

Hospitals pursue different goals at the same time: excellent service to their patients, good quality care, operational excellence, retaining employees. This requires a good balance between patient needs and nursing staff. One way to ensure a proper fit between patient needs and nursing staff is to work with a workload management method. In our view, a nursing workload management method needs to have the following characteristics: easy to interpret; limited additional registration; applicable to different types of hospital wards; supported by nurses; covers all activities of nurses and suitable for prospective planning of nursing staff. At present, no such method is available. The research follows several steps to come to a workload management method for staff nurses. First, a list of patient characteristics relevant to care time will be composed by performing a Delphi study among staff nurses. Next, a time study of nurses' activities will be carried out. The 2 can be combined to estimate care time per patient group and estimate the time nurses spend on non-patient-related activities. These 2 estimates can be combined and compared with available nursing resources: this gives an estimate of nurses' workload. The research will take place in an academic hospital in the Netherlands. 6 surgical wards will be included, capacity 15-30 beds. The study protocol was submitted to the Medical Ethical Review Board of the University Medical Center (UMC) Utrecht and received a positive advice, protocol number 14-165/C. This method will be developed in close cooperation with staff nurses and ward management. The strong involvement of the end users will contribute to a broader support of the results. The method we will develop may also be useful for planning purposes; this is a strong advantage compared with existing methods, which tend to focus on retrospective analysis. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence

Tensile strained gray tin: Dirac semimetal for observing negative magnetoresistance with Shubnikov-de Haas oscillations

Science.gov (United States)

Huang, Huaqing; Liu, Feng

2017-05-01

The extremely stringent requirement on material quality has hindered the investigation and potential applications of exotic chiral magnetic effect in Dirac semimetals. Here, we propose that gray tin is a perfect candidate for observing the chiral anomaly effect and Shubnikov-de-Haas (SdH) oscillation at relatively low magnetic field. Based on effective k .p analysis and first-principles calculations, we discover that gray tin becomes a Dirac semimetal under tensile uniaxial strain, in contrast to a topological insulator under compressive uniaxial strain as known before. In this newly found Dirac semimetal state, two Dirac points which are tunable by tensile [001] strains lie in the kz axis and Fermi arcs appear in the (010) surface. Due to the low carrier concentration and high mobility of gray tin, a large chiral anomaly induced negative magnetoresistance and a strong SdH oscillation are anticipated in this half of the strain spectrum. Comparing to other Dirac semimetals, the proposed Dirac semimetal state in the nontoxic elemental gray tin can be more easily manipulated and accurately controlled. We envision that gray tin provides a perfect platform for strain engineering of chiral magnetic effects by sweeping through the strain spectrum from positive to negative and vice versa.

A new formalism for Dirac-like theories with curved space-time

International Nuclear Information System (INIS)

Halliday, D.W.

1992-01-01

This paper develops a formalism for Dirac-like equations (linear complex differential equations, linear in all derivatives), allowing for general coordinate and open-quotes spin-spaceclose quotes (internal space) transformations. A correspondence principle is also developed by requiring solutions to the Dirac-like equations to be solutions to a Klein-Gordon equation that is likewise generally invariant. Through this treatment, previous generalizations of the Dirac equation are incorporated, and various aspects of these methods are analyzed. Furthermore, the Yang-Mills-like gauge fields allowed, or required, by the formalism are expressed, and found to be associated with much larger symmetries than most would desire, suggesting either there has been much greater symmetry breaking than expected, or else few of the particles accepted as fundamental really are. It is also found that unless the space-time is open-quotes parallelizableclose quotes (so there exist fields that are everywhere parallel transported into themselves, which is not generally the case), or some of the wave function components (and separately some of the Yang-Mills fields) are interdependent, one cannot have the Dirac gamma operators commuting with the momentum operators, while simultaneously having a spin-space metric that is compatible with the Yang-Mills fields

SU(4) properties of the Dirac equation

International Nuclear Information System (INIS)

Linhares, C.A.; Mignaco, J.A.

1988-01-01

The Dirac equation in four dimensions has an intimate connection with the representations of the group SU(4). This connection is shown in detail and subsequente properties are displayed in the continuum as well as in the lattice description. (author) [pt

The Dirac operator on the Fuzzy sphere

International Nuclear Information System (INIS)

Grosse, H.

1994-01-01

We introduce the Fuzzy analog of spinor bundles over the sphere on which the non-commutative analog of the Dirac operator acts. We construct the complete set of eigenstates including zero modes. In the commutative limit we recover known results. (authors)

SU(4) proprerties of the Dirac equation

International Nuclear Information System (INIS)

Linhares, C.A.; Mignaco, J.A.

1985-09-01

The Dirac equation in four dimensions has an intimate connection with the representations of the group SU(4). This connection is shown in detail and subsequent properties are displayed in the continuum as well as in the lattice description [pt

First level trigger of the DIRAC experiment

International Nuclear Information System (INIS)

Afanas'ev, L.G.; Karpukhin, V.V.; Kulikov, A.V.; Gallas, M.

2001-01-01

The logic of the first level trigger of the DIRAC experiment at CERN is described. A parallel running of different trigger modes with tagging of events and optional independent prescaling is realized. A CAMAC-based trigger system is completely computer controlled

Dirac operators and Killing spinors with torsion; Dirac-Operatoren und Killing-Spinoren mit Torsion

Energy Technology Data Exchange (ETDEWEB)

Becker-Bender, Julia

2012-12-17

On a Riemannian spin manifold with parallel skew torsion, we use the twistor operator to obtain an eigenvalue estimate for the Dirac operator with torsion. We consider the equality case in dimensions four and six. In odd dimensions we describe Sasaki manifolds on which equality in the estimate is realized by Killing spinors with torsion. In dimension five we characterize all Killing spinors with torsion and obtain certain naturally reductive spaces as exceptional cases.

Subjective workload and individual differences in information processing abilities

Science.gov (United States)

Damos, D. L.

1984-01-01

This paper describes several experiments examining the source of individual differences in the experience of mental workload. Three sources of such differences were examined: information processing abilities, timesharing abilities, and personality traits/behavior patterns. On the whole, there was little evidence that individual differences in information processing abilities or timesharing abilities are related to perceived differences in mental workload. However, individuals with strong Type A coronary prone behavior patterns differed in both single- and multiple-task performance from individuals who showed little evidence of such a pattern. Additionally, individuals with a strong Type A pattern showed some dissociation between objective performance and the experience of mental workload.

Smartphone form factors: Effects of width and bottom bezel on touch performance, workload, and physical demand.

Science.gov (United States)

Lee, Seul Chan; Cha, Min Chul; Hwangbo, Hwan; Mo, Sookhee; Ji, Yong Gu

2018-02-01

This study aimed at investigating the effect of two smartphone form factors (width and bottom bezel) on touch behaviors with one-handed interaction. User experiments on tapping tasks were conducted for four widths (67, 70, 72, and 74 mm) and five bottom bezel levels (2.5, 5, 7.5, 10, and 12.5 mm). Task performance, electromyography, and subjective workload data were collected to examine the touch behavior. The success rate and task completion time were collected as task performance measures. The NASA-TLX method was used to observe the subjective workload. The electromyogram signals of two thumb muscles, namely the first dorsal interosseous and abductor pollicis brevis, were observed. The task performances deteriorated with increasing width level. The subjective workload and electromyography data showed similar patterns with the task performances. The task performances of the bottom bezel devices were analyzed by using three different evaluation criteria. The results from these criteria indicated that tasks became increasingly difficult as the bottom bezel level decreased. The results of this study provide insights into the optimal range of smartphone form factors for one-handed interaction, which could contribute to the design of new smartphones. Copyright © 2017. Published by Elsevier Ltd.

Observable lepton number violation with predominantly Dirac nature of active neutrinos

Energy Technology Data Exchange (ETDEWEB)

Borah, Debasish [Department of Physics, Indian Institute of Technology Guwahati,Assam-781039 (India); Dasgupta, Arnab [Institute of Physics, HBNI,Sachivalaya Marg, Bhubaneshwar-751005 (India)

2017-01-17

We study a specific version of SU(2){sub R}×SU(2){sub L}×U(1){sub B−L} models extended by discrete symmetries where the new physics sector responsible for tiny neutrino masses at leading order remains decoupled from the new physics sector that can give rise to observable signatures of lepton number violation such as neutrinoless double beta decay. More specifically, the dominant contribution to light neutrino masses comes from a one-loop Dirac mass. At higher loop level, a tiny Majorana mass also appears which remains suppressed by many order of magnitudes in comparison to the Dirac mass. Such a model where the active neutrinos are predominantly of Dirac type, also predicts observable charged lepton flavour violation like μ→3e,μ→eγ and multi-component dark matter.

An Aggregated Optimization Model for Multi-Head SMD Placements

NARCIS (Netherlands)

Ashayeri, J.; Ma, N.; Sotirov, R.

2010-01-01

In this article we propose an aggregate optimization approach by formulating the multi-head SMD placement optimization problem into a mixed integer program (MIP) with the variables based on batches of components. This MIP is tractable and effective in balancing workload among placement heads,

An aggregated optimization model for multi-head SMD placements

NARCIS (Netherlands)

Ashayeri, J.; Ma, N.; Sotirov, R.

2011-01-01

In this article we propose an aggregate optimization approach by formulating the multi-head SMD placement optimization problem into a mixed integer program (MIP) with the variables based on batches of components. This MIP is tractable and effective in balancing workload among placement heads,

Investigation on the relationship between mental workload and musculoskeletal disorders among nursing staff

Directory of Open Access Journals (Sweden)

Yousef Mahmoudifar

2018-01-01

Full Text Available Aims: High prevalence of musculoskeletal disorders owing to the work is one of the popular discomforts between nursing staff. High level of workload is considered as a serious problem and identified as a stressor in the nursing. This study intends to recognize the relationship between musculoskeletal disorders and mental workload in nursing personnel reside at southern part of West Azerbaijan province Iran in 2017. Materials and Methods: In this analytical-descriptive study, 100 nurses working in West Azerbaijan hospitals have been randomly selected. Nordic and National Aeronautics and Space Administration-Task Load Index workload questionnaires have been simultaneously utilized as data collection tools. Data analysis has also carried out using SPSS, variance analysis tests, multiple linear regression, and Pearson's correlation coefficient. Results: Results suggest that the most frequent complaints of musculoskeletal problems are associated to the back area. Investigation on sextet scales of mental workload indicates that each of the six scales of workload was at the high-risk level and the average of total workload was 72.45 ± 19.45 which confirms a high-risk level. Pearson's correlation coefficient also indicates mental workload elements have a significant relationship with musculoskeletal disorders (P < 0.05. Conclusion: The results suggest there is a relationship between musculoskeletal disorders and mental workload and the majority of personnel had mental workload with high-risk level. The best way of management planning to mitigate the risk of musculoskeletal disorders arising of mental workload is, therefore, managing-controlling approach such as staff training, job rotation, and time management.

Neutron beam irradiation study of workload dependence of SER in a microprocessor

Energy Technology Data Exchange (ETDEWEB)

Michalak, Sarah E [Los Alamos National Laboratory; Graves, Todd L [Los Alamos National Laboratory; Hong, Ted [STANFORD; Ackaret, Jerry [IBM; Sonny, Rao [IBM; Subhasish, Mitra [STANFORD; Pia, Sanda [IBM

2009-01-01

It is known that workloads are an important factor in soft error rates (SER), but it is proving difficult to find differentiating workloads for microprocessors. We have performed neutron beam irradiation studies of a commercial microprocessor under a wide variety of workload conditions from idle, performing no operations, to very busy workloads resembling real HPC, graphics, and business applications. There is evidence that the mean times to first indication of failure, MTFIF defined in Section II, may be different for some of the applications.

Photon-Assisted Spectroscopy of Dirac Electrons in Graphene

Directory of Open Access Journals (Sweden)

Abdelrazek A. S.

2012-01-01

Full Text Available The quantum Goos-Hanchen effect in graphene is investigated. The Goos-Hanchen phase shift is derived by solving the Dirac eigenvalue differential equation. This phase shift varies with the angle of incidence of the quasiparticle Dirac fermions on the bar- rier. Calculations show that the dependence of the phase shift on the angle of incidence is sensitive to the variation of the energy gap of graphene, the applied magnetic field and the frequency of the electromagnetic waves. The present results show that the con- ducting states in the sidebands is very effective in the phase shift for frequencies of the applied electromagnetic field. This investigation is very important for the application of graphene in nanoelectronics and nanophotonics.

New correct solutions of the Dirac equation. 5

International Nuclear Information System (INIS)

Bagrov, V.G.; Byzov, N.N.; Gitman, D.M.; Klimenko, Yu.I.; Meshkov, A.G.; Shapovalov, V.N.; Shakhmatov, V.M.

1975-01-01

Some exact solutions for the Dirac equation, Klein-Gordon equation and classical relativistic equations of motion of an electron in external electromagnetic fields of a special type are considered. When fields E vector and H vector are related by the expression H vector=[n vector E vector]+n vector H 3 , where n vector is a constant unit vector, it turns out that among fields permitting the separation of variables in the Klein-Gordon equation more than half satisfy this relationship. For such fields the solution of the Dirac equation may be simplified considerably. Four specific kinds of fields are examined. The character of electron motion in such fields is peculiar but in the mathematical aspect, part of the problem is reduced to those considered previously

The square root of the Dirac operator on superspace and the Maxwell equations

International Nuclear Information System (INIS)

Bzdak, Adam; Hadasz, Leszek

2004-01-01

We re-consider the procedure of 'taking a square root of the Dirac equation' on superspace and show that it leads to the well-known superfield W α and to the proper equations of motion for the components, i.e., the Maxwell equations and the massless Dirac equation

Can neutrino-electron scattering tell us whether neutrinos are Dirac or Majorana particles?

International Nuclear Information System (INIS)

Kayser, B.

1988-04-01

There has recently been interest in the possibility that neutrino-electron scattering experiments could determine whether neutrinos are Dirac or Majorana particles by providing information on their electromagnetic structure. We try to explain why studies of neutrino electromagnetic structure actually cannot distinguish between Dirac and Majorana neutrinos. 9 refs

Upper-division student difficulties with the Dirac delta function

Directory of Open Access Journals (Sweden)

Bethany R. Wilcox

2015-03-01

Full Text Available The Dirac delta function is a standard mathematical tool that appears repeatedly in the undergraduate physics curriculum in multiple topical areas including electrostatics, and quantum mechanics. While Dirac delta functions are often introduced in order to simplify a problem mathematically, students still struggle to manipulate and interpret them. To characterize student difficulties with the delta function at the upper-division level, we examined students’ responses to traditional exam questions and a standardized conceptual assessment, and conducted think-aloud interviews. Our analysis was guided by an analytical framework that focuses on how students activate, construct, execute, and reflect on the Dirac delta function in the context of problem solving in physics. Here, we focus on student difficulties using the delta function to express charge distributions in the context of junior-level electrostatics. Common challenges included invoking the delta function spontaneously, translating a description of a charge distribution into a mathematical expression using delta functions, integrating 3D or non-Cartesian delta function expressions, and recognizing that the delta function can have units. We also briefly discuss implications of these difficulties for instruction.

Nursing workload for cancer patients under palliative care

OpenAIRE

Fuly, Patrícia dos Santos Claro; Pires, Livia Márcia Vidal; Souza, Claudia Quinto Santos de; Oliveira, Beatriz Guitton Renaud Baptista de; Padilha, Katia Grillo

2016-01-01

Abstract OBJECTIVE To verify the nursing workload required by cancer patients undergoing palliative care and possible associations between the demographic and clinical characteristics of the patients and the nursing workload. METHOD This is a quantitative, cross-sectional, prospective study developed in the Connective Bone Tissue (TOC) clinics of Unit II of the Brazilian National Cancer Institute José Alencar Gomes da Silva with patients undergoing palliative care. RESULTS Analysis of 197 ...

Mental workload measurement for emergency operating procedures in digital nuclear power plants.

Science.gov (United States)

Gao, Qin; Wang, Yang; Song, Fei; Li, Zhizhong; Dong, Xiaolu

2013-01-01

Mental workload is a major consideration for the design of emergency operation procedures (EOPs) in nuclear power plants. Continuous and objective measures are desired. This paper compares seven mental workload measurement methods (pupil size, blink rate, blink duration, heart rate variability, parasympathetic/sympathetic ratio, total power and (Goals, Operations, Methods, and Section Rules)-(Keystroke Level Model) GOMS-KLM-based workload index) with regard to sensitivity, validity and intrusiveness. Eighteen participants performed two computerised EOPs of different complexity levels, and mental workload measures were collected during the experiment. The results show that the blink rate is sensitive to both the difference in the overall task complexity and changes in peak complexity within EOPs, that the error rate is sensitive to the level of arousal and correlate to the step error rate and that blink duration increases over the task period in both low and high complexity EOPs. Cardiac measures were able to distinguish tasks with different overall complexity. The intrusiveness of the physiological instruments is acceptable. Finally, the six physiological measures were integrated using group method of data handling to predict perceived overall mental workload. The study compared seven measures for evaluating the mental workload with emergency operation procedure in nuclear power plants. An experiment with simulated procedures was carried out, and the results show that eye response measures are useful for assessing temporal changes of workload whereas cardiac measures are useful for evaluating the overall workload.

Quantitative application of Fermi-Dirac functions of two- and three-dimensional systems

International Nuclear Information System (INIS)

Grimmer, D.P.; Luszczynski, K.; Salibi, N.

1981-01-01

Expressions for the various physical parameters of the ideal Fermi-Dirac gas in two dimensions are derived and compared to the corresponding three-dimensional expressions. These derivations show that the Fermi-Dirac functions most applicable to the two-dimensional problem are F/sub o/(eta), F 1 (eta), and F' 0 (eta). Analogous to the work of McDougall and Stoner in three dimensions, these functions and parameters derived from them are tabulated over the range of the argument, -4 3 He monolayer and bulk liquid 3 He nuclear magnetic susceptibilities, respectively, are considered. Calculational procedures of fitting data to theoretical parameters and criteria for judging the quality of fit of data to both two- and three-dimensional Fermi-Dirac values are discussed

Relativistic two-body equation for one Dirac and one Duffin-Kemmer particle

International Nuclear Information System (INIS)

Krolikowski, W.

1983-01-01

A new relativistic two-body wave equation is proposed for one spin-1/2 and one spin-0 or spin-1 particle which, if isolated from each other, are described by the Dirac and the Duffin-Kemmer equation, respectively. For a static mutual interaction this equation splits into two equations: a two-body wave equation for one Dirac and one Klein-Gordon particle (which was introduced by the author previously) and a new two-body wave equation for one Dirac and one Proca particle. The proposed equation may be applied in particular to the quark-diquark system. In Appendix, however, an alternative approach is sketched, where the diquark is described as the point limit of a very close Breit system rather than a Duffin-Kemmer particle. (Author)

On Kaehler's geometric description of dirac fields

International Nuclear Information System (INIS)

Goeckeler, M.; Joos, H.

1983-12-01

A differential geometric generalization of the Dirac equation due to E. Kaehler seems to be an appropriate starting point for the lattice approximation of matter fields. It is the purpose of this lecture to illustrate several aspects of this approach. (orig./HSI)

Chirality correlation within Dirac eigenvectors from domain wall fermions

International Nuclear Information System (INIS)

Blum, T.; Christ, N.; Cristian, C.; Liao, X.; Liu, G.; Mawhinney, R.; Wu, L.; Zhestkov, Y.; Dawson, C.

2002-01-01

In the dilute instanton gas model of the QCD vacuum, one expects a strong spatial correlation between chirality and the maxima of the Dirac eigenvectors with small eigenvalues. Following Horvath et al. we examine this question using lattice gauge theory within the quenched approximation. We extend the work of those authors by using weaker coupling, β=6.0, larger lattices, 16 4 , and an improved fermion formulation, domain wall fermions. In contrast with this earlier work, we find a striking correlation between the magnitudes of the chirality density, |ψ † (x)γ 5 ψ(x)|, and the normal density, ψ † (x)ψ(x), for the low-lying Dirac eigenvectors

Dispersive estimates for massive Dirac operators in dimension two

Science.gov (United States)

Erdoğan, M. Burak; Green, William R.; Toprak, Ebru

2018-05-01

We study the massive two dimensional Dirac operator with an electric potential. In particular, we show that the t-1 decay rate holds in the L1 →L∞ setting if the threshold energies are regular. We also show these bounds hold in the presence of s-wave resonances at the threshold. We further show that, if the threshold energies are regular then a faster decay rate of t-1(log ⁡ t) - 2 is attained for large t, at the cost of logarithmic spatial weights. The free Dirac equation does not satisfy this bound due to the s-wave resonances at the threshold energies.

Dirac potentials in a coupled channel approach to inelastic scattering

International Nuclear Information System (INIS)

Mishra, V.K.; Clark, B.C.; Cooper, E.D.; Mercer, R.L.

1990-01-01

It has been shown that there exist transformations that can be used to change the Lorentz transformation character of potentials, which appear in the Dirac equation for elastic scattering. We consider the situation for inelastic scattering described by coupled channel Dirac equations. We examine a two-level problem where both the ground and excited states are assumed to have zero spin. Even in this simple case we have not found an appropriate transformation. However, if the excited state has zero excitation energy it is possible to find a transformation

Diagnostic throughput factor analysis for en-route airspace and optimal aircraft trajectory generation based on capacity prediction and controller workload

Science.gov (United States)

Shin, Sanghyun

workload while optimally utilizing limited resources, various aircraft rerouting strategies for Air Traffic Management (ATM) have been proposed. However, the number of rerouting tools available to address these issues for the center-level and the National Airspace System (NAS) are relatively less compared with the tools for the sector-level and terminal airspace. Additionally, previous works consider the airspace containing the weather as no-fly zones instead of reduced-traffic zones and do not explicitly consider controller workload when generating aircraft trajectories to avoid the weather-affected airspace, thereby reducing the overall performance of the airspace. In this thesis, a new rerouting algorithm for the center-level airspace is proposed to address these problems by introducing a feedback loop connecting a tactical rerouting algorithm with a strategic rerouting algorithm using dynamic programming and a modified A* algorithm respectively. This helps reduce the computational cost significantly while safely handling a large number of aircraft. In summary, this thesis suggests the ways in which the NAS's performance can be further improved, thereby supporting various concepts envisioned by the Next Generation Air Transportation System (NextGen) and providing vital information which can be used for suitable economic and environmental advantages.

The square root of the Dirac operator on superspace and the Maxwell equations

Energy Technology Data Exchange (ETDEWEB)

Bzdak, Adam; Hadasz, Leszek

2004-02-26

We re-consider the procedure of 'taking a square root of the Dirac equation' on superspace and show that it leads to the well-known superfield W{sub {alpha}} and to the proper equations of motion for the components, i.e., the Maxwell equations and the massless Dirac equation.

An interpolation between the wave and diffusion equations through the fractional evolution equations Dirac like

International Nuclear Information System (INIS)

Pierantozzi, T.; Vazquez, L.

2005-01-01

Through fractional calculus and following the method used by Dirac to obtain his well-known equation from the Klein-Gordon equation, we analyze a possible interpolation between the Dirac and the diffusion equations in one space dimension. We study the transition between the hyperbolic and parabolic behaviors by means of the generalization of the D'Alembert formula for the classical wave equation and the invariance under space and time inversions of the interpolating fractional evolution equations Dirac like. Such invariance depends on the values of the fractional index and is related to the nonlocal property of the time fractional differential operator. For this system of fractional evolution equations, we also find an associated conserved quantity analogous to the Hamiltonian for the classical Dirac case

A convergent 2D finite-difference scheme for the Dirac-Poisson system and the simulation of graphene

KAUST Repository

Brinkman, Daniel; Heitzinger, Clemens Heitzinger; Markowich, Peter A.

2014-01-01

We present a convergent finite-difference scheme of second order in both space and time for the 2D electromagnetic Dirac equation. We apply this method in the self-consistent Dirac-Poisson system to the simulation of graphene. The model is justified for low energies, where the particles have wave vectors sufficiently close to the Dirac points. In particular, we demonstrate that our method can be used to calculate solutions of the Dirac-Poisson system where potentials act as beam splitters or Veselago lenses. © 2013 Elsevier Inc.

Design and investigation of potential Sn-Te-P and Zr-Te-P class of Dirac materials

Science.gov (United States)

Sarswat, Prashant; Sarkar, Sayan; Free, Michael

A motivation of new Dirac materials design and synthesis by perturbing the symmetry, was explored by substitution of a Sn vacancy by P that maintains the intrinsic band inversion at the L point but also the direct bandgap shrinkage upon the incorporation of spin-orbit coupling. In a similar line of investigation, Zr-Te-P was also systematically studied. The synthesis of both Sn-Te-P and Zr-Te-P system of compounds resulted in the formation of long needles type crystals and the bulk porous deposits. The exotic morphology of the P-doped SnTe needles possesses the pierced surface throughout its extension. First principle based calculations were also carried out for these sets of compounds using General Gradient Approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. In order to ensure structural optimization, a limited memory Broyden-Fletcher-Goldfarb-Shanno (LBFGS) algorithm was employed and the total energy in PBE exchange-correlation functional was considered for the calculation of the formation energy per atom. The new modifications have a potential to establish the new class of Dirac materials ushering upon new frontiers of interest.

Landau quantization and quasiparticle interference in the three-dimensional Dirac semimetal Cd₃As₂.

Science.gov (United States)

Jeon, Sangjun; Zhou, Brian B; Gyenis, Andras; Feldman, Benjamin E; Kimchi, Itamar; Potter, Andrew C; Gibson, Quinn D; Cava, Robert J; Vishwanath, Ashvin; Yazdani, Ali