56 research outputs found
Look-ahead in the two-sided reduction to compact band forms for symmetric eigenvalue problems and the SVD
We address the reduction to compact band forms, via unitary similarity
transformations, for the solution of symmetric eigenvalue problems and the computation of the singular value decomposition (SVD). Concretely, in the first case, we
revisit the reduction to symmetric band form, while, for the second case, we propose a similar alternative, which transforms the original matrix to (unsymmetric)
band form, replacing the conventional reduction method that produces a triangular–
band output. In both cases, we describe algorithmic variants of the standard Level
3 Basic Linear Algebra Subroutines (BLAS)-based procedures, enhanced with lookahead, to overcome the performance bottleneck imposed by the panel factorization.
Furthermore, our solutions employ an algorithmic block size that differs from the
target bandwidth, illustrating the important performance benefits of this decision.
Finally, we show that our alternative compact band form for the SVD is key to introduce an effective look-ahead strategy into the corresponding reduction procedure
First modern human settlement recorded in the Iberian hinterland occurred during Heinrich Stadial 2 within harsh environmental conditions
As the south-westernmost region of Europe, the Iberian Peninsula stands as a key area for understanding the process of modern human dispersal into Eurasia. However, the precise timing, ecological setting and cultural context of this process remains controversial concerning its spatiotemporal distribution within the different regions of the peninsula. While traditional models assumed that the whole Iberian hinterland was avoided by modern humans due to ecological factors until the retreat of the Last Glacial Maximum, recent research has demonstrated that hunter-gatherers entered the Iberian interior at least during Solutrean times. We provide a multi-proxy geoarchaeological, chronometric and paleoecological study on human–environment interactions based on the key site of Peña Capón (Guadalajara, Spain). Results show (1) that this site hosts the oldest modern human presence recorded to date in central Iberia, associated to pre-Solutrean cultural traditions around 26, 000 years ago, and (2) that this presence occurred during Heinrich Stadial 2 within harsh environmental conditions. These findings demonstrate that this area of the Iberian hinterland was recurrently occupied regardless of climate and environmental variability, thus challenging the widely accepted hypothesis that ecological risk hampered the human settlement of the Iberian interior highlands since the first arrival of modern humans to Southwest Europe. © 2021, The Author(s)
On-Surface Driven Formal Michael Addition Produces m-Polyaniline Oligomers on Pt(111)
On-surface synthesis is emerging as a highly rational bottom-up methodology for the synthesis of molecular structures that are unattainable or complex to obtain by wet chemistry. Here, oligomers of meta-polyaniline, a known ferromagnetic polymer, were synthesized from para-aminophenol building-blocks via an unexpected and highly specific on-surface formal 1, 4 Michael-type addition at the meta position, driven by the reduction of the aminophenol molecule. We rationalize this dehydrogenation and coupling reaction mechanism with a combination of in situ scanning tunneling and non-contact atomic force microscopies, high-resolution synchrotron-based X-ray photoemission spectroscopy and first-principles calculations. This study demonstrates the capability of surfaces to selectively modify local molecular conditions to redirect well-established synthetic routes, such as Michael coupling, towards the rational synthesis of new covalent nanostructures
SEOM clinical guidelines in hereditary breast and ovarian cancer (2019)
Mutations in BRCA1 and BRCA2 high penetrance genes account for most hereditary breast and ovarian cancer, although other new high-moderate penetrance genes included in multigene panels have increased the genetic diagnosis of hereditary breast and ovarian cancer families by 50%. Multigene cancer panels provide new challenges related to increased frequency of variants of uncertain significance, new gene-specific cancer risk assessments, and clinical recommendations for carriers of mutations of new genes. Although clinical criteria for genetic testing continue to be largely based on personal and family history with around a 10% detection rate, broader criteria are being applied with a lower threshold for detecting mutations when there are therapeutic implications for patients with breast or ovarian cancer. In this regard, new models of genetic counselling and testing are being implemented following the registration of PARP inhibitors for individuals who display BRCA mutations. Massive sequencing techniques in tumor tissue is also driving a paradigm shift in genetic testing and potential identification of germline mutations. In this paper, we review the current clinical criteria for genetic testing, as well as surveillance recommendations in healthy carriers, risk reduction surgical options, and new treatment strategies in breast cancer gene-mutated carriers
First modern human settlement recorded in the Iberian hinterland occurred during Heinrich Stadial 2 within harsh environmental conditions
As the south-westernmost region of Europe, the Iberian Peninsula stands as a key area for understanding the process of modern human dispersal into Eurasia. However, the precise timing, ecological setting and cultural context of this process remains controversial concerning its spatiotemporal distribution within the different regions of the peninsula. While traditional models assumed that the whole Iberian hinterland was avoided by modern humans due to ecological factors until the retreat of the Last Glacial Maximum, recent research has demonstrated that hunter-gatherers entered the Iberian interior at least during Solutrean times. We provide a multi-proxy geoarchaeological, chronometric and paleoecological study on human?environment interactions based on the key site of Peña Capón (Guadalajara, Spain). Results show (1) that this site hosts the oldest modern human presence recorded to date in central Iberia, associated to pre-Solutrean cultural traditions around 26,000 years ago, and (2) that this presence occurred during Heinrich Stadial 2 within harsh environmental conditions. These findings demonstrate that this area of the Iberian hinterland was recurrently occupied regardless of climate and environmental variability, thus challenging the widely accepted hypothesis that ecological risk hampered the human settlement of the Iberian interior highlands since the first arrival of modern humans to Southwest Europe.Tis research was carried out in the context of the ERC MULTIPALEOIBERIA project, funded by the European Research Council (ERC-2018-STG-805478), and the PALEOINTERIOR project, funded by the Spanish Ministry of Science and Innovation (HAR2017-82483-C3-3-P)
Observation of the nonlinear Hall effect under time reversal symmetric conditions
The electrical Hall effect is the production of a transverse voltage under an
out-of-plane magnetic field. Historically, studies of the Hall effect have led
to major breakthroughs including the discoveries of Berry curvature and the
topological Chern invariants. In magnets, the internal magnetization allows
Hall conductivity in the absence of external magnetic field. This anomalous
Hall effect (AHE) has become an important tool to study quantum magnets. In
nonmagnetic materials without external magnetic fields, the electrical Hall
effect is rarely explored because of the constraint by time-reversal symmetry.
However, strictly speaking, only the Hall effect in the linear response regime,
i.e., the Hall voltage linearly proportional to the external electric field,
identically vanishes due to time-reversal symmetry. The Hall effect in the
nonlinear response regime, on the other hand, may not be subject to such
symmetry constraints. Here, we report the observation of the nonlinear Hall
effect (NLHE) in the electrical transport of the nonmagnetic 2D quantum
material, bilayer WTe2. Specifically, flowing an electrical current in bilayer
WTe2 leads to a nonlinear Hall voltage in the absence of magnetic field. The
NLHE exhibits unusual properties sharply distinct from the AHE in metals: The
NLHE shows a quadratic I-V characteristic; It strongly dominates the nonlinear
longitudinal response, leading to a Hall angle of about 90 degree. We further
show that the NLHE directly measures the "dipole moment" of the Berry
curvature, which arises from layer-polarized Dirac fermions in bilayer WTe2.
Our results demonstrate a new Hall effect and provide a powerful methodology to
detect Berry curvature in a wide range of nonmagnetic quantum materials in an
energy-resolved way
The Sunrise Mission
The first science flight of the balloon-borne \Sunrise telescope took place
in June 2009 from ESRANGE (near Kiruna/Sweden) to Somerset Island in northern
Canada. We describe the scientific aims and mission concept of the project and
give an overview and a description of the various hardware components: the 1-m
main telescope with its postfocus science instruments (the UV filter imager
SuFI and the imaging vector magnetograph IMaX) and support instruments (image
stabilizing and light distribution system ISLiD and correlating wavefront
sensor CWS), the optomechanical support structure and the instrument mounting
concept, the gondola structure and the power, pointing, and telemetry systems,
and the general electronics architecture. We also explain the optimization of
the structural and thermal design of the complete payload. The preparations for
the science flight are described, including AIV and ground calibration of the
instruments. The course of events during the science flight is outlined, up to
the recovery activities. Finally, the in-flight performance of the
instrumentation is briefly summarized.Comment: 35 pages, 17 figure
Nut production in Bertholletia excelsa across a logged forest mosaic: implications for multiple forest use
Although many examples of multiple-use forest management may be found in tropical smallholder systems, few studies provide empirical support for the integration of selective timber harvesting with non-timber forest product (NTFP) extraction. Brazil nut (Bertholletia excelsa, Lecythidaceae) is one of the world’s most economically-important NTFP species extracted almost entirely from natural forests across the Amazon Basin. An obligate out-crosser, Brazil nut flowers are pollinated by large-bodied bees, a process resulting in a hard round fruit that takes up to 14 months to mature. As many smallholders turn to the financial security provided by timber, Brazil nut fruits are increasingly being harvested in logged forests. We tested the influence of tree and stand-level covariates (distance to nearest cut stump and local logging intensity) on total nut production at the individual tree level in five recently logged Brazil nut concessions covering about 4000 ha of forest in Madre de Dios, Peru. Our field team accompanied Brazil nut harvesters during the traditional harvest period (January-April 2012 and January-April 2013) in order to collect data on fruit production. Three hundred and ninety-nine (approximately 80%) of the 499 trees included in this study were at least 100 m from the nearest cut stump, suggesting that concessionaires avoid logging near adult Brazil nut trees. Yet even for those trees on the edge of logging gaps, distance to nearest cut stump and local logging intensity did not have a statistically significant influence on Brazil nut production at the applied logging intensities (typically 1–2 timber trees removed per ha). In one concession where at least 4 trees ha-1 were removed, however, the logging intensity covariate resulted in a marginally significant (0.09) P value, highlighting a potential risk for a drop in nut production at higher intensities. While we do not suggest that logging activities should be completely avoided in Brazil nut rich forests, when a buffer zone cannot be observed, low logging intensities should be implemented. The sustainability of this integrated management system will ultimately depend on a complex series of socioeconomic and ecological interactions. Yet we submit that our study provides an important initial step in understanding the compatibility of timber harvesting with a high value NTFP, potentially allowing for diversification of forest use strategies in Amazonian Perù
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