98 research outputs found
Mechanisms limiting the coherence time of spontaneous magnetic oscillations driven by DC spin-polarized currents
The spin-transfer torque from a DC spin-polarized current can generate
highly-coherent magnetic precession in nanoscale magnetic-multilayer devices.
By measuring linewidths of spectra from the resulting resistance oscillations,
we argue that the coherence time can be limited at low temperature by thermal
deflections about the equilibrium magnetic trajectory, and at high temperature
by thermally-activated transitions between dynamical modes. Surprisingly, the
coherence time can be longer than predicted by simple macrospin simulations.Comment: 12 pages, 4 figure
Non universality of entanglement convertibility
Recently, it has been suggested that operational properties connected to
quantum computation can be alternative indicators of quantum phase transitions.
In this work we systematically study these operational properties in 1D systems
that present phase transitions of different orders. For this purpose, we
evaluate the local convertibility between bipartite ground states. Our results
suggest that the operational properties, related to non-analyticities of the
entanglement spectrum, are good detectors of explicit symmetries of the model,
but not necessarily of phase transitions. We also show that thermodynamically
equivalent phases, such as Luttinger liquids, may display different
convertibility properties depending on the underlying microscopic model.Comment: 5 pages + references, 4 figures - improved versio
Radial abundance gradients in the outer Galactic disk as traced by main-sequence OB stars
Using a sample of 31 main-sequence OB stars located between galactocentric
distances 8.4 - 15.6 kpc, we aim to probe the present-day radial abundance
gradients of the Galactic disk. The analysis is based on high-resolution
spectra obtained with the MIKE spectrograph on the Magellan Clay 6.5-m
telescope on Las Campanas. We used a non-NLTE analysis in a self-consistent
semi-automatic routine based on TLUSTY and SYNSPEC to determine atmospheric
parameters and chemical abundances. Stellar parameters (effective temperature,
surface gravity, projected rotational velocity, microturbulence, and
macroturbulence) and silicon and oxygen abundances are presented for 28 stars
located beyond 9 kpc from the Galactic centre plus three stars in the solar
neighborhood. The stars of our sample are mostly on the main-sequence, with
effective temperatures between 20800 - 31300 K, and surface gravities between
3.23 - 4.45 dex. The radial oxygen and silicon abundance gradients are negative
and have slopes of -0.07 dex/kpc and -0.09 dex/kpc, respectively, in the region
\,kpc. The obtained gradients are compatible with the
present-day oxygen and silicon abundances measured in the solar neighborhood
and are consistent with radial metallicity gradients predicted by
chemodynamical models of Galaxy Evolution for a subsample of young stars
located close to the Galactic plane.Comment: Accepted for publication in the A&
Spin-Transfer Effects in Nanoscale Magnetic Tunnel Junctions
We report measurements of magnetic switching and steady-state magnetic
precession driven by spin-polarized currents in nanoscale magnetic tunnel
junctions with low-resistance, < 5 Ohm-micron-squared, barriers. The current
densities required for magnetic switching are similar to values for
all-metallic spin-valve devices. In the tunnel junctions, spin-transfer-driven
switching can occur at voltages that are high enough to quench the tunnel
magnetoresistance, demonstrating that the current remains spin-polarized at
these voltages
Magnetic vortex oscillator driven by dc spin-polarized current
Transfer of angular momentum from a spin-polarized current to a ferromagnet
provides an efficient means to control the dynamics of nanomagnets. A peculiar
consequence of this spin-torque, the ability to induce persistent oscillations
of a nanomagnet by applying a dc current, has previously been reported only for
spatially uniform nanomagnets. Here we demonstrate that a quintessentially
nonuniform magnetic structure, a magnetic vortex, isolated within a nanoscale
spin valve structure, can be excited into persistent microwave-frequency
oscillations by a spin-polarized dc current. Comparison to micromagnetic
simulations leads to identification of the oscillations with a precession of
the vortex core. The oscillations, which can be obtained in essentially zero
magnetic field, exhibit linewidths that can be narrower than 300 kHz, making
these highly compact spin-torque vortex oscillator devices potential candidates
for microwave signal-processing applications, and a powerful new tool for
fundamental studies of vortex dynamics in magnetic nanostructures.Comment: 14 pages, 4 figure
Prediction of continuous and discrete kinetic parameters in horses from inertial measurement units data using recurrent artificial neural networks
Vertical ground reaction force (GRFz) measurements are the best tool for assessing horses' weight-bearing lameness. However, collection of these data is often impractical for clinical use. This study evaluates GRFz predicted using data from body-mounted IMUs and long short-term memory recurrent neural networks (LSTM-RNN). Twenty-four clinically sound horses, equipped with IMUs on the upper-body (UB) and each limb, walked and trotted on a GRFz measuring treadmill (TiF). Both systems were time-synchronised. Data from randomly selected 16, 4, and 4 horses formed training, validation, and test datasets, respectively. LSTM-RNN with different input sets (All, Limbs, UB, Sacrum, or Withers) were trained to predict GRFz curves or peak-GRFz. Our models could predict GRFz shapes at both gaits with RMSE below 0.40 N.kg−1. The best peak-GRFz values were obtained when extracted from the predicted curves by the all dataset. For both GRFz curves and peak-GRFz values, predictions made with the All or UB datasets were systematically better than with the Limbs dataset, showing the importance of including upper-body kinematic information for kinetic parameters predictions. More data should be gathered to confirm the usability of LSTM-RNN for GRFz predictions, as they highly depend on factors like speed, gait, and the presence of weight-bearing lameness
The increasing threat to European forests from the invasive foliar pine pathogen, Lecanosticta acicola
European forests are threatened by increasing numbers of invasive pests and pathogens. Over the past century, Lecanosticta acicola, a foliar pathogen predominantly of Pinus spp., has expanded its range globally, and is increasing in impact. Lecanosticta acicola causes brown spot needle blight, resulting in premature defoliation, reduced growth, and mortality in some hosts. Originating from southern regions of North American, it devastated forests in the USA's southern states in the early twentieth century, and in 1942 was discovered in Spain.Derived from Euphresco project 'Brownspotrisk,' this study aimed to establish the current distribution of Lecanosticta species, and assess the risks of L. acicola to European forests. Pathogen reports from the literature, and new/ unpublished survey data were combined into an open-access geo-database (http://www.portaloff orestpathology.com), and used to visualise the pathogen's range, infer its climatic tolerance, and update its host range. Lecanosticta species have now been recorded in 44 countries, mostly in the northern hemisphere. The type species, L. acicola, has increased its range in recent years, and is present in 24 out of the 26 European countries where data were available. Other species of Lecanosticta are largely restricted to Mexico and Central America, and recently Colombia.The geo-database records demonstrate that L. acicola tolerates a wide range of climates across the northern hemisphere, and indicate its potential to colonise Pinus spp. forests across large swathes of the Europe. Pre-liminary analyses suggest L. acicola could affect 62% of global Pinus species area by the end of this century, under climate change predictions.Although its host range appears slightly narrower than the similar Dothistroma species, Lecanosticta species were recorded on 70 host taxa, mostly Pinus spp., but including, Cedrus and Picea spp. Twenty-three, including species of critical ecological, environmental and economic significance in Europe, are highly susceptible to L. acicola, suffering heavy defoliation and sometimes mortality. Variation in apparent susceptibility between reports could reflect variation between regions in the hosts' genetic make-up, but could also reflect the signif-icant variation in L. acicola populations and lineages found across Europe. This study served to highlight sig-nificant gaps in our understanding of the pathogen's behaviour.Lecanosticta acicola has recently been downgraded from an A1 quarantine pest to a regulated non quarantine pathogen, and is now widely distributed across Europe. With a need to consider disease management, this study also explored global BSNB strategies, and used Case Studies to summarise the tactics employed to date in Europe
The threat of the COVID-19 pandemic on reversing global life-saving gains in the survival of childhood cancer: A call for collaborative action from SIOP, IPSO, PROS, WCC, CCI, st jude global, UICC and WHPCA
The COVID-19 pandemic poses an unprecedented health crisis in all socio-economic regions across the globe. While the pandemic has had a profound impact on access to and delivery of health care by all services, it has been particularly disruptive for the care of patients with life-threatening noncommunicable diseases (NCDs) such as the treatment of children and young people with cancer. The reduction in child mortality from preventable causes over the last 50 years has seen childhood cancer emerge as a major unmet health care need. Whilst survival rates of 85% have been achieved in high income countries, this has not yet been translated into similar outcomes for children with cancer in resource-limited settings where survival averages 30%. Launched in 2018, by the World Health Organization (WHO), the Global Initiative for Childhood Cancer (GICC) is a pivotal effort by the international community to achieve at least 60% survival for children with cancer by 2030. The WHO GICC is already making an impact in many countries but the disruption of cancer care during the COVID-19 pandemic threatens to set back this global effort to improve the outcome for children with cancer, wherever they may live. As representatives of the global community committed to fostering the goals of the GICC, we applaud the WHO response to the COVID-19 pandemic, in particular we support the WHO's call to ensure the needs of patients with life threatening NCDs including cancer are not compromised during the pandemic. Here, as collaborative partners in the GICC, we highlight specific areas of focus that need to be addressed to ensure the immediate care of children and adolescents with cancer is not disrupted during the pandemic; and measures to sustain the development of cancer care so the long-term goals of the GICC are not lost during this global health crisis.Fil: Pritchard Jones, Kathy. University College London; Estados UnidosFil: de Abib, Simone C.V.. International Society Of Paediatric Surgical Oncology; Surinam. Universidade Federal de Sao Paulo; BrasilFil: Esiashvili, Natia. University of Emory; Estados UnidosFil: Kaspers, Gertjan J.L.. Princess Máxima Center for Pediatric Oncology; Países BajosFil: Rosser, Jon. No especifíca;Fil: van Doorninck, John A.. Rocky Mountain Hospital for Children; Estados UnidosFil: Braganca, João M.L.. No especifíca;Fil: Hoffman, Ruth I.. No especifíca;Fil: Rodriguez Galindo, Carlos. St Jude Children’s Research Hospital; Estados UnidosFil: Adams, Cary. Union for International Cancer Control; SuizaFil: Connor, Stephen R.. Worldwide Hospice Palliative Care Alliance; Estados UnidosFil: Abdelhafeez, Abdelhafeez H.. International Society of Paediatric Surgical Oncology; Suiza. St. Jude Children’s Research Hospital; Estados UnidosFil: Bouffet, Eric. University Of Toronto. Hospital For Sick Children; Canadá. International Society of Paediatric Surgical Oncology; SuizaFil: Howard, Scott C.. International Society of Paediatric Surgical Oncology; Suiza. University of Tennessee; Estados UnidosFil: Challinor, Julia M.. International Society of Paediatric Surgical Oncology; Suiza. University of California; Estados UnidosFil: Hessissen, Laila. Children Hospital of Rabat; Marruecos. International Society of Paediatric Surgical Oncology; SuizaFil: Dalvi, Rashmi B.. Bombay Hospital Institute of Medical Sciences; India. International Society of Paediatric Surgical Oncology; SuizaFil: Kearns, Pamela. International Society of Paediatric Surgical Oncology; SuizaFil: Chantada, Guillermo Luis. International Society of Paediatric Surgical Oncology; Suiza. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Frazier, Lindsay A.. International Society of Paediatric Surgical Oncology; Suiza. Dana-Farber Cancer Institute; Estados UnidosFil: Sullivan, Michael J.. University of Melbourne; Australia. International Society of Paediatric Surgical Oncology; SuizaFil: Schulte, Fiona S.M.. University of Calgary; Canadá. International Society of Paediatric Surgical Oncology; SuizaFil: Morrissey, Lisa K.. Boston Children’s Hospital; Estados Unidos. International Society of Paediatric Surgical Oncology; SuizaFil: Kozhaeva, Olga. European Society for Paediatric Oncology; BélgicaFil: Luna Fineman, Sandra. Children’s Hospital Colorado; Estados Unidos. International Society of Paediatric Oncology; SuizaFil: Khan, Muhammad S.. Tawam Hospital; Emiratos Arabes Unido
- …