424 research outputs found
Ferroelectricity due to orbital ordering in E-type undoped rare-earth manganites
Aiming at understanding the origin of the electronic contribution to
ferroelectric polarization in undoped manganites, we evaluate the Berry phase
of orbital-polarizable Bloch electrons as an orbital ordering (OO) establishes
in the background of an antiferromagnetic E-type configuration. The onset of OO
is tuned by the Jahn-Teller (JT) interaction in a tight-binding model for
interacting electrons moving along zigzag chains. A finite polarization is
found as soon as the JT coupling is strong enough to induce OO, supporting the
large electronic contribution predicted from first principles.Comment: 4 pages, 2 figures, figure and text substantially improved. Title
change
The best practice for preparation of samples from FTA®cards for diagnosis of blood borne infections using African trypanosomes as a model system
Background: Diagnosis of blood borne infectious diseases relies primarily on the detection of the causative agent
in the blood sample. Molecular techniques offer sensitive and specific tools for this although considerable
difficulties exist when using these approaches in the field environment. In large scale epidemiological studies,
FTA®cards are becoming increasingly popular for the rapid collection and archiving of a large number of samples.
However, there are some difficulties in the downstream processing of these cards which is essential for the
accurate diagnosis of infection. Here we describe recommendations for the best practice approach for sample
processing from FTA®cards for the molecular diagnosis of trypanosomiasis using PCR.
Results: A comparison of five techniques was made. Detection from directly applied whole blood was less
sensitive (35.6%) than whole blood which was subsequently eluted from the cards using Chelex®100 (56.4%).
Better apparent sensitivity was achieved when blood was lysed prior to application on the FTA cards (73.3%)
although this was not significant. This did not improve with subsequent elution using Chelex®100 (73.3%) and was
not significantly different from direct DNA extraction from blood in the field (68.3%).
Conclusions: Based on these results, the degree of effort required for each of these techniques and the difficulty
of DNA extraction under field conditions, we recommend that blood is transferred onto FTA cards whole followed
by elution in Chelex®100 as the best approach
A survey of children's interests from grade IV through grade VIII in the fields of active recreation, entertainment, reading, school subjects, and vocations.
Thesis (Ed.M.)--Boston Universit
Seismic input motion determined from a surface-downhole pair of sensors: a constrained deconvolution approach.
We apply a deconvolution approach to the problem of determining the
input motion at the base of an instrumented borehole using only a pair of recordings,
one at the borehole surface and the other at its bottom. To stabilize the bottom-tosurface
spectral ratio, we apply an iterative regularization algorithm that allows us
to constrain the solution to be positively defined and to have a finite time duration.
Through the analysis of synthetic data, we show that the method is capable of retrieving
reliable input motion, suppressing the effect of the negative interference generated
by the downgoing waves. Results obtained by applying the methodology to weak
earthquakes recorded at the Ataköy (Istanbul) vertical array are also presented and
show that removing the effect of the downgoing waves is remarkable, even considering
the recording at a depth of 140 m
Characterisation of the Trypanosoma brucei rhodesiense isolates from Tanzania using serum resistance associated gene as molecular marker
Serum resistance associated (SRA) gene has been found to confer resistance to the innate trypanolytic factor
(TLF) found in normal human serum; thus allowing Trypanosoma brucei brucei to survive exposure to normal human
serum. This study was carried out to examine the presence of SRA gene and identify the origin of T. b. rhodesiense isolates
from three districts in Tanzania, namely Kibondo, Kasulu and Urambo. Twenty-six T. b. rhodesiense isolates and two
references T. b. rhodesiense isolates from Kenya were examined for SRA gene using simple Polymerase Chain Reaction
technique. The gene was found to be present in all 26 T. b. rhodesiense isolates including the two references isolates from
Kenya. The SRA gene was confirmed to be specific to T. b. rhodesiense since it could not be amplified from all other
Trypanozoon including T. b. gambiense; and gave an amplified fragment of the expected size (3.9kb), confirming that all
these isolates were T. b. rhodesiense of the northern variant. Although the geographic distributions of T. b. gambiense and
T. b. rhodesiense are clearly localized to west/central Africa and eastern Africa, respectively, natural movement of people
and recent influx of large number of refugees into Tanzania from the Democratic Republic of Congo, could have brought
T. b. gambiense in western Tanzania. The overlap in distribution of both of these pathogenic sub-species could result in
erroneous diagnoses since both trypanosome sub-species are morphologically identical, and currently serologic methods
have low specificity. Both the susceptible and resistant T.b. rhodesiense isolates possessed the SRA gene suggesting that
there is no correlation between drug resistance and presence of SRA gene. The use of SRA gene helps to confirm the
identity and diversity of some of the isolates resistant to various drugs. Keywords: Trypanosoma brucei rhodesiense, resistance, SRA gene, PCR, TanzaniaTanzania Health Research Bulletin Vol. 9 (1) 2007: pp.25-3
Magnetism of mixed quaternary Heusler alloys: (Ni,T)MnSn (T=Cu,Pd) as a case study
The electronic properties, exchange interactions, finite-temperature
magnetism, and transport properties of random quaternary Heusler NiMnSn
alloys doped with Cu- and Pd-atoms are studied theoretically by means of {\it
ab initio} calculations over the entire range of dopant concentrations. While
the magnetic moments are only weakly dependent on the alloy composition, the
Curie temperatures exhibit strongly non-linear behavior with respect to
Cu-doping in contrast with an almost linear concentration dependence in the
case of Pd-doping. The present parameter-free theory agrees qualitatively and
also reasonably well quantitatively with the available experimental results. An
analysis of exchange interactions is provided for a deeper understanding of the
problem. The dopant atoms perturb electronic structure close to the Fermi
energy only weakly and the residual resistivity thus obeys a simple Nordheim
rule. The dominating contribution to the temperature-dependent resistivity is
due to thermodynamical fluctuations originating from the spin-disorder, which,
according to our calculations, can be described successfully via the disordered
local moments model. Results based on this model agree fairly well with the
measured values of spin-disorder induced resistivity.Comment: 13 pages, 13 figure
Ab-initio electronic and magnetic structure in La_0.66Sr_0.33MnO_3: strain and correlation effects
The effects of tetragonal strain on electronic and magnetic properties of
strontium-doped lanthanum manganite, La_{2/3}Sr_{1/3}MnO_3 (LSMO), are
investigated by means of density-functional methods. As far as the structural
properties are concerned, the comparison between theory and experiments for
LSMO strained on the most commonly used substrates, shows an overall good
agreement: the slight overestimate (at most of 1-1.5 %) for the equilibrium
out-of-plane lattice constants points to possible defects in real samples. The
inclusion of a Hubbard-like contribution on the Mn d states, according to the
so-called "LSDA+U" approach, is rather ineffective from the structural point of
view, but much more important from the electronic and magnetic point of view.
In particular, full half-metallicity, which is missed within a bare
density-functional approach, is recovered within LSDA+U, in agreement with
experiments. Moreover, the half-metallic behavior, particularly relevant for
spin-injection purposes, is independent on the chosen substrate and is achieved
for all the considered in-plane lattice constants. More generally, strain
effects are not seen to crucially affect the electronic structure: within the
considered tetragonalization range, the minority gap is only slightly (i.e. by
about 0.1-0.2 eV) affected by a tensile or compressive strain. Nevertheless, we
show that the growth on a smaller in-plane lattice constant can stabilize the
out-of-plane vs in-plane e_g orbital and significatively change their relative
occupancy. Since e_g orbitals are key quantities for the double-exchange
mechanism, strain effects are confirmed to be crucial for the resulting
magnetic coupling.Comment: 16 pages, 7 figures, to be published on J. Phys.: Condensed Matte
Balanced electron-hole transport in spin-orbit semimetal SrIrO3 heterostructures
Relating the band structure of correlated semimetals to their transport
properties is a complex and often open issue. The partial occupation of
numerous electron and hole bands can result in properties that are seemingly in
contrast with one another, complicating the extraction of the transport
coefficients of different bands. The 5d oxide SrIrO3 hosts parabolic bands of
heavy holes and light electrons in gapped Dirac cones due to the interplay
between electron-electron interactions and spin-orbit coupling. We present a
multifold approach relying on different experimental techniques and theoretical
calculations to disentangle its complex electronic properties. By combining
magnetotransport and thermoelectric measurements in a field-effect geometry
with first-principles calculations, we quantitatively determine the transport
coefficients of different conduction channels. Despite their different
dispersion relationships, electrons and holes are found to have strikingly
similar transport coefficients, yielding a holelike response under field-effect
and thermoelectric measurements and a linear, electronlike Hall effect up to 33
T.Comment: 5 pages, 4 figure
Interpretation of microtremor 2D array data using Rayleigh and Love waves: the case study of Bevagna (central Italy)
In the last decades, geophysicists and seismologists have focused their attention on the inversion of
empirical surface-waves’ dispersion curves from microtremor measurements for estimating the Swaves
velocity structure at a site. This procedure allows a fast and convenient investigation without
strong active sources, which are difficult to deploy especially in urban areas.
In this study we report on a 2D seismic noise array experiment carried out at Bevagna (Central
Italy) near the station BVG of the Italian Accelerometric Network (RAN). The site was investigated
within the DPC-INGV S4 Project (2007-2009). The Rayleigh- and Love- waves dispersion
characteristics were estimated using different methods. The inversion of the dispersion curves was
then performed independently, obtaining two estimations for the S-waves velocity profiles. The
results of cross-hole logging near the seismic station are used for a comparison.
The shear waves velocity profiles estimated by microtremor analyses range up to 150m depth. The
two independent procedures provide consistent shear waves velocity profiles for the shallow part of
the model (20-30 m in depth) in agreement with the results of the cross-hole logging. Some
problems arise between 30 and 40 m in depth in the profile estimated by surface waves. In this
range cross-hole logging evidences an inversion of S-waves velocity. Although the cross-hole
logging stops at 40 m of depth, we are confident about the results provided by the Rayleigh-waves
analysis below 40-50 m. This case study suggests that greater efforts should be devoted to exploit
the potential of a coupled analysis of Rayleigh and Love waves from microtremor array
measurements
- …