3,881 research outputs found
Synthesis of strontium ferrite/iron oxide exchange coupled nano-powders with improved energy product for rare earth free permanent magnet applications
We present a simple, scalable synthesis route for producing exchange coupled
soft/hard magnetic composite powder that outperforms pure soft and hard phase
constituents. Importantly, the composites is iron oxide based (SrFe12O19 and
Fe3O4) and contain no rare earth or precious metal. The two step synthesis
process consists of first precipitating, an Iron oxide/hydroxide precursor
directly on top of SrFe12O19 nano-flakes, ensuring a very fine degree of mixing
between the hard and the soft magnetic phases. We then use a second step that
serves to reduce the precursor to create the proper soft magnetic phase and
create the intimate interface necessary for exchange coupling. We establish a
clear processing window; at temperatures below this window the desired soft
phase is not produced, while higher temperatures result in deleterious reaction
at the soft/hard phase interfaces, causing an improper ratio of soft to hard
phases. Improvements of Mr, Ms, and (BH)max are 42%, 29% and 37% respectively
in the SrFe12O19/Fe3O4 composite compared to pure hard phase (SrFe12O19). We
provide evidence of coupling (exchange spring behavior) with hysteresis curves,
first order reversal curve (FORC) analysis and recoil measurements.Comment: in J. Mater. Chem. C, 201
Correlates and Predictors of Employee Turnover Intentions in the Postal Industry! A Case Study of the Omaha Hub of United Parcel Service
The purpose of this study was to identify the correlates and predictors of turnover intentions among manual laborers. The study was exploratory and used a modification of the Rusbult and Farrell (1983) investment model as its theoretical framework. Simple correlation analysis uncovered no significant relationships between the fifteen independent variables and turnover intention, with one exception; there was a significant correlation between intent to retire and turnover intention. Therefore, further analysis was conducted by testing each independent variable against each item of turnover intentions. The independent variables that were found to be significantly correlated with the items of turnover intentions were then entered into a regression analysis to test for predictive potential. Of the independent variables that were included in the regression analysis, three emerged as predictors of various items of turnover intentions at the .05 level of significance: Alternatives, distributive justice, and active pursuit o f degree. Of those, alternatives is the only one that showed a pattern of predictability. The Rusbult and Farrell model posits that job costs and job rewards lead to satisfaction which, along with alternatives and investments, predict commitment, of which turnover is a function. However, the present study found, to the contrary, that among manual laborers, job costs, job rewards, job satisfaction, and investment had no effect on turnover intent. Instead, the variable perception of alternatives was the only one that predicted turnover intentions. One reason these findings differ from those of previous research may be the fact that turnover literature has largely overlooked the category of manual laborers, which is structurally dissimilar from the traditionally studied categories of workers
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Ultrafast laser welding of ceramics.
Welding of ceramics is a key missing component in modern manufacturing. Current methods cannot join ceramics in proximity to temperature-sensitive materials like polymers and electronic components. We introduce an ultrafast pulsed laser welding approach that relies on focusing light on interfaces to ensure an optical interaction volume in ceramics to stimulate nonlinear absorption processes, causing localized melting rather than ablation. The key is the interplay between linear and nonlinear optical properties and laser energy-material coupling. The welded ceramic assemblies hold high vacuum and have shear strengths comparable to metal-to-ceramic diffusion bonds. Laser welding can make ceramics integral components in devices for harsh environments as well as in optoelectronic and/or electronic packages needing visible-radio frequency transparency
Technology transfer and scaling up with partners: The plastic barrier technology for pest control in community-based.Organic Potato Production in the Peruvian Andes
Stability analysis of sonic horizons in Bose-Einstein condensates
We examine the linear stability of various configurations in Bose-Einstein
condensates with sonic horizons. These configurations are chosen in analogy
with gravitational systems with a black hole horizon, a white hole horizon and
a combination of both. We discuss the role of different boundary conditions in
this stability analysis, paying special attention to their meaning in
gravitational terms. We highlight that the stability of a given configuration,
not only depends on its specific geometry, but especially on these boundary
conditions. Under boundary conditions directly extrapolated from those in
standard General Relativity, black hole configurations, white hole
configurations and the combination of both into a black hole--white hole
configuration are shown to be stable. However, we show that under other (less
stringent) boundary conditions, configurations with a single black hole horizon
remain stable, whereas white hole and black hole--white hole configurations
develop instabilities associated to the presence of the sonic horizons.Comment: 14 pages, 7 figures (reduced resolution
Large Solar Neutrino Mixing in an Extended Zee Model
The Zee model, which employs the standard Higgs scalar () with its
duplicate () and a singly charged scalar (), can utilize two
global symmetries associated with the conservation of the numbers of and
, , where coincides
with the hypercharge while () is a new
conserved charge, which is identical to for the left-handed
leptons. Charged leptons turn out to have - and - mixing
masses, which are found to be crucial for the large solar neutrino mixing. In
an extended version of the Zee model with an extra triplet Higgs scalar (s),
neutrino oscillations are described by three steps: 1) the maximal atmospheric
mixing is induced by democratic mass terms supplied by with =2 that can
initiate the type II seesaw mechanism for the smallness of these masses; 2) the
maximal solar neutrino mixing is triggered by the creation of radiative masses
by with = 0; 3) the large solar neutrino mixing is finally induced by
a - mixing arising from the rotation of the radiative mass
terms as a result of the diagonalization that converts - and -
mixing masses into the electron mass.Comment: RevTex, 10 pages including one figure page, to be published in Int.
J. Mod. Phys. A (2002
An Expanding HI Photodissociated Region Associated with the Compact HII Region G213.880-11.837 in the GGD 14 Complex
We present high angular and spectral resolution HI 21~cm line observations
toward the cometary-shaped compact HII region G213.880-11.837 in the GGD~14
complex.The kinematics and morphology of the photodissociated region, traced by
the HI line emission, reveal that the neutral gas is part of an expanding flow.
The kinematics of the HI gas along the major axis of G213.880-11.837 shows that
the emission is very extended toward the SE direction, reaching LSR radial
velocities in the tail of about 14 km/s. The ambient LSR radial velocity of the
molecular gas is 11.5 km/s, which suggests a champagne flow of the HI gas. This
is the second (after G111.61+0.37) cometary HII/HI region known.Comment: Accepted for publication in the Astronomical Journal (10 pages, 4
figures, 1 table
Fairness and Efficiency in DAG-based Cryptocurrencies
Bitcoin is a decentralised digital currency that serves as an alternative to
existing transaction systems based on an external central authority for
security. Although Bitcoin has many desirable properties, one of its
fundamental shortcomings is its inability to process transactions at high
rates. To address this challenge, many subsequent protocols either modify the
rules of block acceptance (longest chain rule) and reward, or alter the
graphical structure of the public ledger from a tree to a directed acyclic
graph (DAG). Motivated by these approaches, we introduce a new general
framework that captures ledger growth for a large class of DAG-based
implementations. With this in hand, and by assuming honest miner behaviour, we
(experimentally) explore how different DAG-based protocols perform in terms of
fairness, i.e., if the block reward of a miner is proportional to their hash
power, as well as efficiency, i.e. what proportion of user transactions a
ledger deems valid after a certain length of time. Our results demonstrate
fundamental structural limits on how well DAG-based ledger protocols cope with
a high transaction load. More specifically, we show that even in a scenario
where every miner on the system is honest in terms of when they publish blocks,
what they point to, and what transactions each block contains, fairness and
efficiency of the ledger can break down at specific hash rates if miners have
differing levels of connectivity to the P2P network sustaining the protocol
Probing semiclassical analogue gravity in Bose--Einstein condensates with widely tunable interactions
Bose-Einstein condensates (BEC) have recently been the subject of
considerable study as possible analogue models of general relativity. In
particular it was shown that the propagation of phase perturbations in a BEC
can, under certain conditions, closely mimic the dynamics of scalar quantum
fields in curved spacetimes. In two previous articles [gr-qc/0110036,
gr-qc/0305061] we noted that a varying scattering length in the BEC corresponds
to a varying speed of light in the ``effective metric''. Recent experiments
have indeed achieved a controlled tuning of the scattering length in Rubidium
85. In this article we shall discuss the prospects for the use of this
particular experimental effect to test some of the predictions of semiclassical
quantum gravity, for instance, particle production in an expanding universe. We
stress that these effects are generally much larger than the Hawking radiation
expected from causal horizons, and so there are much better chances for their
detection in the near future.Comment: 18 pages; uses revtex4. V2: Added brief discussion of "Bose-Nova"
phenomenon, and appropriate reference
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