49 research outputs found
Temperature-dependent magnetization in diluted magnetic semiconductors
We calculate magnetization in magnetically doped semiconductors assuming a
local exchange model of carrier-mediated ferromagnetic mechanism and using a
number of complementary theoretical approaches. In general, we find that the
results of our mean-field calculations, particularly the dynamical mean field
theory results, give excellent qualitative agreement with the experimentally
observed magnetization in systems with itinerant charge carriers, such as
Ga_{1-x}Mn_xAs with 0.03 < x < 0.07, whereas our percolation-theory-based
calculations agree well with the existing data in strongly insulating
materials, such as Ge_{1-x}Mn_x. We comment on the issue of non-mean-field like
magnetization curves and on the observed incomplete saturation magnetization
values in diluted magnetic semiconductors from our theoretical perspective. In
agreement with experimental observations, we find the carrier density to be the
crucial parameter determining the magnetization behavior. Our calculated
dependence of magnetization on external magnetic field is also in excellent
agreement with the existing experimental data.Comment: 17 pages, 15 figure
Leadership training to improve adenoma detection rate in screening colonoscopy: A randomised trial
Objective Suboptimal adenoma detection rate (ADR) at colonoscopy is associated with increased risk of interval colorectal cancer. It is uncertain how ADR might be improved. We compared t
Single-Band Model for Diluted Magnetic Semiconductors: Dynamical and Transport Properties and Relevance of Clustered States
Dynamical and transport properties of a simple single-band spin-fermion
lattice model for (III,Mn)V diluted magnetic semiconductors (DMS) is here
discussed using Monte Carlo simulations. This effort is a continuation of
previous work (G. Alvarez, Phys. Rev. Lett. 89, 277202 (2002)) where the static
properties of the model were studied. The present results support the view that
the relevant regime of J/t (standard notation) is that of intermediate
coupling, where carriers are only partially trapped near Mn spins, and locally
ordered regions (clusters) are present above the Curie temperature T_C. This
conclusion is based on the calculation of the resistivity vs. temperature, that
shows a soft metal to insulator transition near T_C, as well on the analysis of
the density-of-states and optical conductivity. In addition, in the clustered
regime a large magnetoresistance is observed in simulations. Formal analogies
between DMS and manganites are also discussed.Comment: Revtex4, 20 figures. References updated, minor changes to figures and
tex
An angle-resolved photoemission spectral function analysis of the electron doped cuprate Nd_1.85Ce_0.15CuO_4
Using methods made possible by recent advances in photoemission technology,
we perform an indepth line-shape analysis of the angle-resolved photoemission
spectra of the electron doped (n-type) cuprate superconductor
Nd_1.85Ce_0.15CuO_4. Unlike for the p-type materials, we only observe weak mass
renormalizations near 50-70 meV. This may be indicative of smaller
electron-phonon coupling or due to the masking effects of other interactions
that make the electron-phonon coupling harder to detect. This latter scenario
may suggest limitations of the spectral function analysis in extracting
electronic self-energies when some of the interactions are highly momentum
dependent.Comment: 8 pages, 5 figure
Interplay of Electron-Phonon Interaction and Electron Correlation in High Temperature Superconductivity
We study the electron-phonon interaction in the strongly correlated
superconducting cuprates. Two types of the electron-phonon interactions are
introduced in the model; the diagonal and off-diagonal interactions which
modify the formation energy of the Zhang-Rice singlet and its transfer
integral, respectively. The characteristic phonon-momentum and
electron-momentum dependence resulted from the off-diagonal coupling
can explain a variety of experiments. The vertex correction for the
electron-phonon interaction is formulated in the SU(2) slave-boson theory by
taking into account the collective modes in the superconducting ground states.
It is shown that the vertex correction enhances the attractive potential for
the d-wave paring mediated by phonon with around
which corresponds to the half-breathing mode of the oxygen
motion.Comment: 14 pages, 13 figure
Increasing incidence of colorectal cancer in young adults in Europe over the last 25 years
Objective The incidence of colorectal cancer (CRC)
declines among subjects aged 50 years and above. An
opposite trend appears among younger adults. In Europe,
data on CRC incidence among younger adults are
lacking. We therefore aimed to analyse European trends
in CRC incidence and mortality in subjects younger than
50 years.
Design Data on age-related CRC incidence and
mortality between 1990 and 2016 were retrieved from
national and regional cancer registries. Trends were
analysed by Joinpoint regression and expressed as
annual percent change.
Results We retrieved data on 143.7million people
aged 20–49 years from 20 European countries. Of
them, 187 918 (0.13%) were diagnosed with CRC. On
average, CRC incidence increased with 7.9% per year
among subjects aged 20–29 years from 2004 to 2016.
The increase in the age group of 30–39 years was 4.9%
per year from 2005 to 2016, the increase in the age
group of 40–49 years was 1.6% per year from 2004
to 2016. This increase started earliest in subjects aged
20–29 years, and 10–20 years later in those aged 30–39
and 40–49 years. This is consistent with an age-cohort
phenomenon. Although in most European countries the
CRC incidence had risen, some heterogeneity was found
between countries. CRC mortality did not significantly
change among the youngest adults, but decreased with
1.1%per year between 1990 and 2016 and 2.4% per
year between 1990 and 2009 among those aged 30–39
years and 40–49 years, respectively.
Conclusion CRC incidence rises among young
adults in Europe. The cause for this trend needs to be
elucidated. Clinicians should be aware of this trend. If
the trend continues, screening guidelines may need to be
reconsidered
Characterization of soil chemical properties of strawberry fields using principal component analysis
The CARMENES search for exoplanets around M dwarfs: Two planets on opposite sides of the radius gap transiting the nearby M dwarf LTT 3780
We present the discovery and characterisation of two transiting planets observed by the Transiting Exoplanet Survey Satellite (TESS) orbiting the nearby (d∗ ≈ 22 pc), bright (J ≈ 9 mag) M3.5 dwarf LTT 3780 (TOI-732). We confirm both planets and their association with LTT 3780 via ground-based photometry and determine their masses using precise radial velocities measured with the CARMENES spectrograph. Precise stellar parameters determined from CARMENES high-resolution spectra confirm that LTT 3780 is a mid-M dwarf with an effective temperature of Teff = 3360 ± 51 K, a surface gravity of log g∗ = 4.81 ± 0.04 (cgs), and an iron abundance of [Fe/H] = 0.09 ± 0.16 dex, with an inferred mass of M∗ = 0.379 ± 0.016M· and a radius of R∗ = 0.382 ± 0.012R·. The ultra-short-period planet LTT 3780 b (Pb = 0.77 d) with a radius of 1.35-0.06+0.06 R·, a mass of 2.34-0.23+0.24 M·, and a bulk density of 5.24-0.81+0.94 g cm-3 joins the population of Earth-size planets with rocky, terrestrial composition. The outer planet, LTT 3780 c, with an orbital period of 12.25 d, radius of 2.42-0.10+0.10 R·, mass of 6.29-0.61+0.63 M·, and mean density of 2.45-0.37+0.44 g cm-3 belongs to the population of dense sub-Neptunes. With the two planets located on opposite sides of the radius gap, this planetary system is anexcellent target for testing planetary formation, evolution, and atmospheric models. In particular, LTT 3780 c is an ideal object for atmospheric studies with the James Webb Space Telescope (JWST)