2,539 research outputs found
Fermi Velocity Spectrum and Incipient Magnetism in TiBe2
We address the origin of the incipient magnetism in TiBe through precise
first principles calculations, which overestimate the ferromagnetic tendency
and therefore require correction to account for spin fluctuations. TiBe has
sharp fine structure in its electronic density of states, with a van Hove
singularity only 3 meV above the Fermi level. Similarly to the isovalent weak
ferromagnet ZrZn, it is flat bands along the K-W-U lines of hexagonal face
of the fcc Brillouin zone make the system prone to magnetism, and more so if
electrons are added. We find that the Moriya coefficient (multiplying
in the fluctuation susceptibility )
is divergent when the velocity vanishes at a point on the Fermi surface, which
is very close (3 meV) to occurring in TiBe. In exploring how the FM
instability (the =0 Stoner enhancement is ) might be suppressed
by fluctuations in TiBe, we calculate that the Moriya A coefficient (of
) is negative, so =0 is not the primary instability. Explicit
calculation of shows that its maximum occurs at the X point
; TiBe is thus an incipient {\it anti}ferromagnet
rather than ferromagnet as has been supposed. We further show that simple
temperature smearing of the peak accounts for most of the temperature
dependence of the susceptibility, which previously had been attributed to local
moments (via a Curie-Weiss fit), and that energy dependence of the density of
states also strongly affects the magnetic field variation of
Spin wave resonances in La_{0.7}Sr_{0.3}MnO_{3} films: measurement of spin wave stiffness and anisotropy field
We studied magnetic field dependent microwave absorption in epitaxial
LaSrMnO films using an X-band Bruker ESR spectrometer. By
analyzing angular and temperature dependence of the ferromagnetic and spin-wave
resonances we determine spin-wave stiffness and anisotropy field. The spin-wave
stiffness as found from the spectrum of the standing spin-wave resonances in
thin films is in fair agreement with the results of inelastic neutron
scattering studies on a single crystal of the same composition [Vasiliu-Doloc
et al., J. Appl. Phys. \textbf{83}, 7343 (1998)].Comment: 15 pages, 7 figures (now figure captions are included
Intrinsic Low Temperature Paramagnetism in B-DNA
We present experimental study of magnetization in -DNA in
conjunction with structural measurements. The results show the surprising
interplay between the molecular structures and their magnetic property. In the
B-DNA state, -DNA exhibits paramagnetic behaviour below 20 K that is
non-linear in applied magnetic field whereas in the A-DNA state, remains
diamagnetic down to 2 K. We propose orbital paramagnetism as the origin of the
observed phenomena and discuss its relation to the existence of long range
coherent transport in B-DNA at low temperature.Comment: 5 pages, 4 figures, submitted to Physical Review Letters October 200
A core genetic module : the Mixed Feedback Loop
The so-called Mixed Feedback Loop (MFL) is a small two-gene network where
protein A regulates the transcription of protein B and the two proteins form a
heterodimer. It has been found to be statistically over-represented in
statistical analyses of gene and protein interaction databases and to lie at
the core of several computer-generated genetic networks. Here, we propose and
mathematically study a model of the MFL and show that, by itself, it can serve
both as a bistable switch and as a clock (an oscillator) depending on kinetic
parameters. The MFL phase diagram as well as a detailed description of the
nonlinear oscillation regime are presented and some biological examples are
discussed. The results emphasize the role of protein interactions in the
function of genetic modules and the usefulness of modelling RNA dynamics
explicitly.Comment: To be published in Physical Review
Socio-Economic Management Theory Related to BPM: A Case Study of Dysfunctions in Digital Transformation Strategy
This research claims that dynamic strategies demanded by todayâs digital environment exacerbate inconsistency between an organizationâs digital transformation efforts and its enterprise architecture (EA) planning process. This phenomenon leads to redundant investments, delayed implementation, and frequent failures in digital transformation projects. In order to investigate this inconsistency, we apply the socioeconomic approach to management (SEAM) theory. Through critical analysis of four case studies in a large manufacturing organization, we clarify the relationship between digital transformation and EA and reveal the dysfunction in strategic implementation from a SEAM and business process management (BPM) perspective. In practice, this research integrates digital transformation and EA to provide a context-specific approach for planning and designing enterprise digital transformation strategies
Signatures of Spin Glass Freezing in NiO Nanoparticles
We present a detailed study of the magnetic properties of sol-gel prepared
nickel oxide nanoparticles of different sizes. We report various measurements
such as frequency, field and temperature dependence of ac susceptibility,
temperature and field dependence of dc magnetization and time decay of
thermoremanent magnetization. Our results and analysis show that the system
behaves as a spin glass.Comment: 8 pages, 9 figure
Validation of an experimental setup to study atmospheric heterogeneous ozonolysis of semi-volatile organic compounds
International audienceThere is currently a need for reliable experimental procedures to follow the heterogeneous processing simulating the atmospheric conditions. This work offers an alternative experimental device to study the behaviour of semi-volatile organic compounds (SVOC) that presumably exhibit extremely slow reactivity (e.g. pesticides) towards the atmospheric oxidants such as ozone and OH. Naphthalene was chosen as a test compound since it was widely studied in the past and hence represents a good reference. Prior to ozone exposure, the gaseous naphthalene was adsorbed via gas-solid equilibrium on silica and XAD-4 particles. Then, the heterogeneous reaction of ozone with adsorbed naphthalene was investigated in specially designed flow tube reactors. After the reaction, the remaining naphthalene (adsorbed on particles surface) was extracted, filtered and analyzed by Gas Chromatography-Flame Ionization Detector (GC-FID). Thus, the kinetics results were obtained following the consumption of naphthalene. Using this procedure, the rate constants of heterogeneous ozonolysis of naphthalene (kO3 silica=2.26 (±0.09)Ă10â17 cm3 molecâ1 sâ1 and kO3 XAD-4=4.29 (±1.06)Ă10â19 cm3 molecâ1 sâ1) were determined for silica and XAD-4 particles, at 25°C and relative humidity <0.7%. The results show that the nature of the particles significantly affects the kinetics and that heterogeneous ozonolysis of naphthalene is faster than its homogeneous ozonolysis in the gas phase
Zeeman effects on the impurity-induced resonances in d-wave superconductors
It is shown how the resonant states induced by a single spinless impurity in
a d-wave superconductor evolve under the effect of an applied Zeeman magnetic
field. Moreover, it is demonstrated that the spin-orbit coupling to the
impurity potential can have important and characteristic effects on the
resonant states and their response to the Zeeman field, especially when the
impurity is close to the unitary limit. For zero or very small spin-orbit
interaction, the resonant states becomes Zeeman splitted by the magnetic field
while when the spin-orbit coupling is important, new low-lying resonances arise
which do not show any Zeeman splitting.Comment: 5 pages with 5 eps figures embedded. To appear on Phys. Rev.
Effect of magnetic and non-magnetic impurities on highly anisotropic superconductivity
We generalize Abrikosov-Gor'kov solution of the problem of weakly coupled
superconductor with impurities on the case of a multiband superconductor with
arbitrary interband order parameter anisotropy, including interband sign
reversal of the order parameter. The solution is given in terms of the
effective (renormalized) coupling matrix and describes not only
suppression but also renormalization of the superconducting gap basically at
all temperatures. In many limiting cases we find analytical solutions for the
critical temperature suppression. We illustrate our results by numerical
calculations for two-band model systems.Comment: 18 pages (12pt) RevTeX, 4 postscript figure
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