173 research outputs found
Ferroelectrically induced weak-ferromagnetism in a single-phase multiferroic by design
We present a strategy to design structures for which a polar lattice
distortion induces weak ferromagnetism. We identify a large class of
multiferroic oxides as potential realizations and use density-functional theory
to screen several promising candidates. By elucidating the interplay between
the polarization and the Dzyaloshinskii-Moriya vector, we show how the
direction of the magnetization can be switched between 180 symmetry
equivalent states with an applied electric field.Comment: Significantly revised for clarit
Epitaxial-strain-induced multiferroicity in SrMnO from first principles
First-principles density-functional calculations reveal a large spin-phonon
coupling in cubic SrMnO, with ferromagnetic ordering producing a polar
instability. Through combination of this coupling with the strain-polarization
coupling characteristic of perovskites, the bulk antiferromagnetic paraelectric
ground state of SrMnO is shown to be driven to a previously unreported
multiferroic ferroelectric-ferromagnetic state by increasing epitaxial strain,
both tensile and compressive. This state has a computed polarization and
estimated Curie temperature above 54 C/cm and 92 K. Large mixed
magnetic-electric-elastic responses are predicted in the vicinity of the phase
boundaries.Comment: 5 pages, 2 figures, 1 tabl
Frustrated classical Heisenberg model in 1 dimension with added nearest-neighbor biquadratic exchange interactions
The ground state phase diagram is determined for the frustrated classical
Heisenberg chain with added nearest-neighbor biquadratic exchange interactions.
There appear ferromagnetic, incommensurate-spiral, and up-up-down-down phases;
a lock-in transition occurs at the spiral boundary. The model contains an
isotropic version of the ANNNI model; it is also closely related to a model
proposed for some manganites. The Luttinger-Tisza method is not obviously
useful due to the non-linear weak-constraint problem; however the ground state
is obtained analytically by the exact cluster method of Lyons and Kaplan. The
results are compared to the model of Thorpe and Blume, where the Heisenberg
part of the energy is not frustrated.Comment: 4 pages, 3 figure
Strain induced half-metal to semiconductor transition in GdN
We have investigated the electronic structure and magnetic properties of GdN
as a function of unit cell volume. Based on the first-principles calculations
of GdN, we observe that there is a transformation in conduction properties
associated with the volume increase: first from halfmetallic to semi-metallic,
then ultimately to semiconducting. We show that applying stress can alter the
carrier concentration as well as mobility of the holes and electrons in the
majority spin channel. In addition, we found that the exchange parameters
depend strongly on lattice constant, thus the Curie temperature of this system
can be enhanced by applying stress or doping impurities.Comment: 9 pages, 3 figure
Quality of life in restorative versus non-restorative resections for rectal cancer:systematic review
BACKGROUND: Low rectal cancers could be treated using restorative (anterior resection, AR) or non-restorative procedures with an end/permanent stoma (Hartmann’s, HE; or abdominoperineal excision, APE). Although the surgical choice is determined by tumour and patient factors, quality of life (QoL) will also influence the patient's future beyond cancer. This systematic review of the literature compared postoperative QoL between the restorative and non-restorative techniques using validated measurement tools. METHODS: The review was registered on PROSPERO (CRD42020131492). Embase and MEDLINE, along with grey literature and trials websites, were searched comprehensively for papers published since 2012. Inclusion criteria were original research in an adult population with rectal cancer that reported QoL using a validated tool, including the European Organization for Research and Treatment of Cancer QLQ-CR30, QLQ-CR29, and QLQ-CR38. Studies were included if they compared AR with APE (or HE), independent of study design. Risk of bias was assessed using the Risk Of Bias In Non-Randomized Studies of Interventions (ROBINS-I) tool. Outcomes of interest were: QoL, pain, gastrointestinal (GI) symptoms (stool frequency, flatulence, diarrhoea and constipation), and body image. RESULTS: Nineteen studies met the inclusion criteria with a total of 6453 patients; all papers were observational and just four included preoperative evaluations. There was no identifiable difference in global QoL and pain between the two surgical techniques. Reported results regarding GI symptoms and body image documented similar findings. The ROBINS-I tool highlighted a significant risk of bias across the studies. CONCLUSION: Currently, it is not possible to draw a firm conclusion on postoperative QoL, pain, GI symptoms, and body image following restorative or non-restorative surgery. The included studies were generally of poor quality, lacked preoperative evaluations, and showed considerable bias in the data
Large spin-phonon coupling and magnetically induced phonon anisotropy in SrMO3 perovskites (M = V,Cr,Mn,Fe,Co)
First-principles calculations reveal large zone-center spin-phonon coupling and magnetically-driven phonon anisotropy in cubic perovskites SrMO3 (M = V,Cr,Mn,Fe,Co). In particular, the frequency and splitting of the polar Slater mode is found to depend strongly upon magnetic ordering. The coupling is parameterized in a crystalstructure-dependent Heisenberg model, and its main features seen to arise from the Goodenough-Kanamori rules. This coupling can be expected to produce distinct low-energy alternative phases, resulting in a rich variety of coupled magnetic, structural, and electronic phase transitions driven by temperature, stress, electric field, and cation substitutionclose1
Biological conversion assay using Clostridium phytofermentans to estimate plant feedstock quality
BACKGROUND: There is currently considerable interest in developing renewable sources of energy. One strategy is the biological conversion of plant biomass to liquid transportation fuel. Several technical hurdles impinge upon the economic feasibility of this strategy, including the development of energy crops amenable to facile deconstruction. Reliable assays to characterize feedstock quality are needed to measure the effects of pre-treatment and processing and of the plant and microbial genetic diversity that influence bioconversion efficiency. RESULTS: We used the anaerobic bacterium Clostridium phytofermentans to develop a robust assay for biomass digestibility and conversion to biofuels. The assay utilizes the ability of the microbe to convert biomass directly into ethanol with little or no pre-treatment. Plant samples were added to an anaerobic minimal medium and inoculated with C. phytofermentans, incubated for 3 days, after which the culture supernatant was analyzed for ethanol concentration. The assay detected significant differences in the supernatant ethanol from wildtype sorghum compared with brown midrib sorghum mutants previously shown to be highly digestible. Compositional analysis of the biomass before and after inoculation suggested that differences in xylan metabolism were partly responsible for the differences in ethanol yields. Additionally, we characterized the natural genetic variation for conversion efficiency in Brachypodium distachyon and shrub willow (Salix spp.). CONCLUSION: Our results agree with those from previous studies of lignin mutants using enzymatic saccharification-based approaches. However, the use of C. phytofermentans takes into consideration specific organismal interactions, which will be crucial for simultaneous saccharification fermentation or consolidated bioprocessing. The ability to detect such phenotypic variation facilitates the genetic analysis of mechanisms underlying plant feedstock quality
HETDEX pilot survey for emission-line galaxies - I. Survey design, performance, and catalog
We present a catalog of emission-line galaxies selected solely by their
emission-line fluxes using a wide-field integral field spectrograph. This work
is partially motivated as a pilot survey for the upcoming Hobby-Eberly
Telescope Dark Energy Experiment (HETDEX). We describe the observations,
reductions, detections, redshift classifications, line fluxes, and counterpart
information for 397 emission-line galaxies detected over 169 sq.arcmin with a
3500-5800 Ang. bandpass under 5 Ang. full-width-half-maximum (FWHM) spectral
resolution. The survey's best sensitivity for unresolved objects under
photometric conditions is between 4-20 E-17 erg/s/sq.cm depending on the
wavelength, and Ly-alpha luminosities between 3-6 E42 erg/s are detectable.
This survey method complements narrowband and color-selection techniques in the
search for high redshift galaxies with its different selection properties and
large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS,
and XMM-LSS areas are rich with existing, complementary data. We find 104
galaxies via their high redshift Ly-alpha emission at 1.9<z<3.8, and the
majority of the remainder objects are low redshift [OII]3727 emitters at
z<0.56. The classification between low and high redshift objects depends on
rest frame equivalent width, as well as other indicators, where available.
Based on matches to X-ray catalogs, the active galactic nuclei (AGN) fraction
amongst the Ly-alpha emitters (LAEs) is 6%. We also analyze the survey's
completeness and contamination properties through simulations. We find five
high-z, highly-significant, resolved objects with full-width-half-maximum sizes
>44 sq.arcsec which appear to be extended Ly-alpha nebulae. We also find three
high-z objects with rest frame Ly-alpha equivalent widths above the level
believed to be achievable with normal star formation, EW(rest)>240 Ang.Comment: 45 pages, 36 figures, 5 tables, submitted to ApJ
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