156 research outputs found
First principles design of Ohmic spin diodes based on quaternary Heusler compounds
The Ohmic spin diode (OSD) is a recent concept in spintronics, which is based
on half-metallic magnets (HMMs) and spin-gapless semiconductors (SGSs).
Quaternary Heusler compounds offer a unique platform to realize the OSD for
room temperature applications as these materials possess very high Curie
temperatures as well as half-metallic and spin-gapless semiconducting behavior
within the same family. Using state-of-the-art first-principles calculations
combined with the non-equilibrium Green's function method we design four
different OSDs based on half-metallic and spin-gapless semiconducting
quaternary Heusler compounds. All four OSDs exhibit linear current-voltage
() characteristics with zero threshold voltage . We show that these
OSDs possess a small leakage current, which stems from the overlap of the
conduction and valence band edges of opposite spin channels around the Fermi
level in the SGS electrodes. The obtained on/off current ratios vary between
and . Our results can pave the way for the experimental fabrication
of the OSDs within the family of ordered quaternary Heusler compounds.Comment: 7 pages, 5 figure
Study of Magnetic Tunnel Junctions Based on Half-Metallic and Spin-Gapless Semiconducting Heusler Compounds: Reconfigurable Diode and Inverse Tunnel-Magnetoresistance Effect
Magnetic tunnel junctions (MTJs) have attracted strong research interest
within the last decades due to their potential use as nonvolatile memory such
as MRAM as well as for magnetic logic applications. Half-metallic magnets
(HMMs) have been suggested as ideal electrode materials for MTJs to achieve an
extremely large tunnel-magnetoresistance (TMR) effect. Despite their high TMR
ratios, MTJs based on HMMs do not exhibit current rectification, i.e., a diode
effect, which was achieved in a magnetic tunnel junction concept based on HMMs
and type-II spin-gapless semiconductors (SGSs). The proposed concept has
recently been experimentally demonstrated using Heusler compounds. In the
present work, we investigate from first-principles MTJs based on type-II SGS
and HMM quaternary Heusler compounds FeVTaAl, FeVTiSi, MnVTiAl, and CoVTiSb.
Our quantum transport calculations based on a nonequilibrium
Green's function method have demonstrated that the MTJs under consideration
exhibit current rectification with relatively high on:off ratios. We show that,
in contrast to conventional semiconductor diodes, the rectification bias
voltage window (or breakdown voltage) of the MTJs is limited by the spin gap of
the HMM and SGS Heusler compounds. A unique feature of the present MTJs is that
the diode effect can be configured dynamically, i.e., depending on the relative
orientation of the magnetization of the electrodes, the MTJ allows the
electrical current to pass either in one or the other direction, which leads to
an inverse TMR effect. The combination of nonvolatility, reconfigurable diode
functionality, tunable rectification voltage window, and high Curie temperature
of the electrode materials makes the proposed MTJs very promising for
room-temperature spintronic applications and opens ways to magnetic memory and
logic concepts as well as logic-in-memory computing.Comment: 14+7 pages, 7+10 figure
Foundations of character: methodological aspects of a study of character development in three- to six-year-old children with a focus on sharing behaviours
This article focuses on methodological issues arising in a study of character development, using illustrations of ‘sharing behaviours.’ Based primarily in six early years settings in southeast England the research records naturalistic observations of peer interactions for 55 children aged three to six years. Applying grounded theory to the processes of observing, analysing and interpreting evidence required a cautious and collectively reflective approach. The methodology sought to moderate the influence of the researchers' prior knowledge of ‘grand theories’ of moral development and assumptions about relevance to the observation records. The study's originality lay in the exploration of moral development without reference to any particular grand theory as an explanatory framework; and in the reluctance to be drawn to potentially simplistic rationalisations of the children's intentions on the basis of their observed behaviours. Exploring young children's subjective experiences, this research provides insights into the intricacy of this process, steering away from ‘neat’ findings and attempting to reflect the sophistication of the children's skilful and sometimes surprising negotiations of moral dilemmas. Implications for practice relate to the complexities involved in attempts to unravel the developing moral characters of young children and the practice through which this may be nurtured
Ab initio design of quaternary Heusler compounds for reconfigurable magnetic tunnel diodes and transistors
Reconfigurable magnetic tunnel diodes and transistors are a new concept in
spintronics. The realization of such a device requires the use of materials
with unique spin-dependent electronic properties such as half-metallic magnets
(HMMs) and spin-gapless semiconductors (SGSs). Quaternary Heusler compounds
offer a unique platform to design within the same family of compounds HMMs and
SGSs with similar lattice constants to make coherent growth of the consecutive
spacers of the device possible. Employing state-of-the-art first-principles
calculations, we scan the quaternary Heusler compounds and identify suitable
candidates for these spintronic devices combining the desirable properties: (i)
HMMs with sizable energy gap or SGSs with spin gaps both below and above the
Fermi level, (ii) high Curie temperature, (iii) convex hull energy distance
less than 0.20 eV, and (iv) negative formation energies. Our results pave the
way for the experimental realization of the proposed magnetic tunnel diodes and
transistors.Comment: 13 pages, 9 figure
A proposed quantitative methodology for the evaluation of the effectiveness of Human Element, Leadership and Management (HELM) training in the UK
In 2006, a review of maritime accidents found that non-technical skills (NTSs) are the single largest contributing factor towards such incidents. NTSs are composed of both interpersonal and cognitive elements. These include things such as situational awareness, teamwork, decision making, leadership, management and communication skills. In a crisis situation, good NTSs allow a deck officer to quickly recognise that a problem exists and then harness the resources that are at their disposal to safely and efficiently bring the situation back under control. This paper has two aims. The first is to develop a methodology which will enable educators to quantitatively assess the impact of Maritime and Coastguard Agency (MCA)-approved Human Element, Leadership and Management (HELM) training on deck officer’s NTSs with a view to identifying further training requirements. The second is to determine whether the HELM training provided to develop the NTSs of trainee deck officers is fit for purpose. To achieve these aims, a three-phase approach was adopted. Initially, a taxonomy for deck officer’s NTSs is established, behavioural markers are identified and the relative importance of each attribute is calculated using the analytical hierarchy process (AHP). Subsequently, a set of scenarios were identified for the assessment of deck officer’s NTSs in a ship bridge simulator environment. A random selection of students that have completed the Chief Mate (CM) programme was performed, and data regarding their NTS-related performance in the scenarios was collected. Finally, the collected data was fed into the evidential reasoning (ER) algorithm, utility values were produced and, having established these values, the effectiveness of the HELM training that the students have received was then evaluated
Flux pinning characteristics in cylindrical ingot niobium used in superconducting radio frequency cavity fabrication
We present the results of from DC magnetization and penetration depth
measurements of cylindrical bulk large-grain (LG) and fine-grain (FG) niobium
samples used for the fabrication of superconducting radio frequency (SRF)
cavities. The surface treatment consisted of electropolishing and low
temperature baking as they are typically applied to SRF cavities. The
magnetization data were fitted using a modified critical state model. The
critical current density Jc and pinning force Fp are calculated from the
magnetization data and their temperature dependence and field dependence are
presented. The LG samples have lower critical current density and pinning force
density compared to FG samples which implies a lower flux trapping efficiency.
This effect may explain the lower values of residual resistance often observed
in LG cavities than FG cavities
Genomic diversity of bacteriophages infecting Microbacterium spp
The bacteriophage population is vast, dynamic, old, and genetically diverse. The genomics of phages that infect bacterial hosts in the phylum Actinobacteria show them to not only be diverse but also pervasively mosaic, and replete with genes of unknown function. To further explore this broad group of bacteriophages, we describe here the isolation and genomic characterization of 116 phages that infect Microbacterium spp. Most of the phages are lytic, and can be grouped into twelve clusters according to their overall relatedness; seven of the phages are singletons with no close relatives. Genome sizes vary from 17.3 kbp to 97.7 kbp, and their G+C% content ranges from 51.4% to 71.4%, compared to ~67% for their Microbacterium hosts. The phages were isolated on five different Microbacterium species, but typically do not efficiently infect strains beyond the one on which they were isolated. These Microbacterium phages contain many novel features, including very large viral genes (13.5 kbp) and unusual fusions of structural proteins, including a fusion of VIP2 toxin and a MuF-like protein into a single gene. These phages and their genetic components such as integration systems, recombineering tools, and phage-mediated delivery systems, will be useful resources for advancing Microbacterium genetics
- …