316 research outputs found
Magnetic induction mapping of magnetite chains in magnetotactic bacteria at room temperature and close to the Verwey transition using electron holography
Off-axis electron holography in the transmission electron microscope is used to record magnetic induction maps of closely spaced magnetite crystals in magnetotactic bacteria at room temperature and after cooling the sample using liquid nitrogen. The magnetic microstructure is related to the morphology and crystallography of the particles, and to interparticle interactions. At room temperature, the magnetic signal is dominated by interactions and shape anisotropy, with highly parallel and straight field lines following the axis of each chain of crystals closely. In contrast, at low temperature the magnetic induction undulates along the length of the chain. This behaviour may result from a competition between interparticle interactions and an easy axis of magnetisation that is no longer parallel to the chain axis. The quantitative nature of electron holography also allows the change in magnetisation in the crystals with temperature to be measured
Spectral properties of a two-orbital Anderson impurity model across a non-Fermi liquid fixed point
We study by NRG the spectral properties of a two-orbital Anderson impurity
model in the presence of an exchange splitting which follows either regular or
inverted Hund's rules. The phase diagram contains a non-Fermi liquid fixed
point separating a screened phase, where conventional Kondo effect occurs, from
an unscreened one, where the exchange-splitting takes care of quenching the
impurity degrees of freedom. On the Kondo screened side close to this fixed
point the impurity density of states shows a narrow Kondo-peak on top of a
broader resonance. This narrow peak transforms in the unscreened phase into a
narrow pseudo-gap inside the broad resonance. Right at the fixed point only the
latter survives. The fixed point is therefore identified by a jump of the
density of states at the chemical potential. We also show that particle-hole
perturbations which simply shift the orbital energies do not wash out the fixed
point, unlike those perturbations which hybridize the two orbitals.
Consequently the density-of-state jump at the chemical potential remains finite
even away from particle-hole symmetry, and the pseudo-gap stays pinned at the
chemical potential, although it is partially filled in. We also discuss the
relevance of these results for lattice models which map onto this Anderson
impurity model in the limit of large lattice-coordination. Upon approaching the
Mott metal-insulator transition, these lattice models necessarily enter a
region with a local criticality which reflects the impurity non-Fermi liquid
fixed point. However, unlike the impurity, the lattice can get rid of the
single-impurity fixed-point instability by spontaneously developing
bulk-coherent symmetry-broken phases, which we identify for different lattice
models.Comment: 43 pages, 11 figures. Minor corrections in the Appendi
Relativistic general-order coupled-cluster method for high-precision calculations: Application to Al+ atomic clock
We report the implementation of a general-order relativistic coupled-cluster
method for performing high-precision calculations of atomic and molecular
properties. As a first application, the static dipole polarizabilities of the
ground and first excited states of Al+ have been determined to precisely
estimate the uncertainty associated with the BBR shift of its clock frequency
measurement. The obtained relative BBR shift is -3.66+-0.44 for the 3s^2
^1S_0^0 --> 3s3p ^3P_0^0 transition in Al+ in contrast to the value obtained in
the latest clock frequency measurement, -9+-3 [Phys. Rev. Lett. 104, 070802
(2010)]. The method developed in the present work can be employed to study a
variety of subtle effects such as fundamental symmetry violations in atoms.Comment: 4 pages, 3 tables, submitte
Complement factor h-antibody-associated hemolytic uremic syndrome: pathogenesis, clinical presentation, and treatment.
The presence of circulating autoantibodies, primarily to complement factor H antibodies (CFH-Abs) in plasma characterizes the autoimmune form of atypical hemolytic uremic syndrome (aHUS). This acquired form of aHUS defines a distinct subgroup of aHUS patients, which requires diagnostic and treatment approaches in part different from those of the genetically defined forms. The mechanisms leading to CFH-Ab production and disease onset are not completely understood, but CFH-Ab HUS seems to be secondary to a combination of genetic predisposition and environmental factors. Early diagnosis of this specific aHUS entity is important, as prompt induction of plasma exchange and concomitant immunosuppression leads to a favorable outcome. Nevertheless, information on clinical features and outcome in children is limited. Here, we review the literature on the biological and clinical features of CFH-Ab HUS and discuss therapeutic options
Nanoscale spin-polarization in dilute magnetic semiconductor (In,Mn)Sb
Results of point contact Andreev reflection (PCAR) experiments on (In,Mn)Sb
are presented and analyzed in terms of current models of charge conversion at a
superconductor-ferromagnet interface. We investigate the influence of surface
transparency, and study the crossover from ballistic to diffusive transport
regime as contact size is varied. Application of a Nb tip to a (In,Mn)Sb sample
with Curie temperature Tc of 5.4 K allowed the determination of
spin-polarization when the ferromagnetic phase transition temperature is
crossed. We find a striking difference between the temperature dependence of
the local spin polarization and of the macroscopic magnetization, and
demonstrate that nanoscale clusters with magnetization close to the saturated
value are present even well above the magnetic phase transition temperature.Comment: 4 page
Establishment and Early Operations of the State Audit Office of Hungary
Re-established in 1867 by the Austro-Hungarian Compromise, parliamentarism institutionalised the powers of the legis-lature to exercise control over the government in Hungary as well, and Parliament established the State Audit Office to carry out the duty of economic control. However, Act XVIII of 1870 codifying the State Audit Office contained ambiguous provisions on its legal status, specifying only arithmetic control as its task, as a result of which the operations of the Office, from the beginning to its dis-continuation, were described in contradictory terms
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