3,055 research outputs found
Spin-torque switching: Fokker-Planck rate calculation
We describe a new approach to understanding and calculating magnetization
switching rates and noise in the recently observed phenomenon of "spin-torque
switching". In this phenomenon, which has possible applications to information
storage, a large current passing from a pinned ferromagnetic (FM) layer to a
free FM layer switches the free layer. Our main result is that the spin-torque
effect increases the Arrhenius factor in the switching rate, not
by lowering the barrier , but by raising the effective spin temperature .
To calculate this effect quantitatively, we extend Kramers' 1940 treatment of
reaction rates, deriving and solving a Fokker-Planck equation for the energy
distribution including a current-induced spin torque of the Slonczewski type.
This method can be used to calculate slow switching rates without long-time
simulations; in this Letter we calculate rates for telegraph noise that are in
good qualitative agreement with recent experiments. The method also allows the
calculation of current-induced magnetic noise in CPP (current perpendicular to
plane) spin valve read heads.Comment: 11 pages, 8 figures, 1 appendix Original version in Nature format,
replaced by Phys. Rev. Letters format. No substantive change
Virus Sharing, Genetic Sequencing, and Global Health Security
The WHO’s Pandemic Influenza Preparedness (PIP) Framework was a milestone global agreement designed to promote the international sharing of biological samples to develop vaccines, while that ensuring poorer countries would have access to those vaccines. Since the PIP Framework was negotiated, scientists have developed the capacity to use genetic sequencing data (GSD) to develop synthetic viruses rapidly for product development of life-saving technologies in a time-sensitive global emergency—threatening to unravel the Framework. Access to GSD may also have major implications for biosecurity, biosafety, and intellectual property (IP).
By rendering the physical transfer of viruses antiquated, GSD may also undermine the effectiveness of the PIP Framework itself, with disproportionate impacts on poorer countries. We examine the changes that need to be made to the PIP Framework to address the growing likelihood that GSD might be shared instead of physical virus samples. We also propose that the international community harness this opportunity to expand the scope of the PIP Framework beyond only influenza viruses with pandemic potential.
In light of non-influenza pandemic threats such as the Middle East Respiratory Syndrome (MERS) and Ebola, we call for an international agreement on the sharing of the benefits of research – such as vaccines and treatments – for other infectious diseases to ensure not only a more secure and healthy world, but also a more just world, for humanity
Correlation of patterns of anchorage-independent growth with in vivo behavior of cells from a murine fibrosarcoma.
Simulation Studies of Nanomagnet-Based Architecture
We report a simulation study on interacting ensembles of Co nanomagnets that
can perform basic logic operations and propagate logic signals, where the state
variable is the magnetization direction. Dipole field coupling between
individual nanomagnets drives the logic functionality of the ensemble and
coordinated arrangements of the nanomagnets allow for the logic signal to
propagate in a predictable way. Problems with the integrity of the logic signal
arising from instabilities in the constituent magnetizations are solved by
introducing a biaxial anisotropy term to the Gibbs magnetic free energy of each
nanomagnet. The enhanced stability allows for more complex components of a
logic architecture capable of random combinatorial logic, including horizontal
wires, vertical wires, junctions, fanout nodes, and a novel universal logic
gate. Our simulations define the focus of scaling trends in nanomagnet-based
logic and provide estimates of the energy dissipation and time per nanomagnet
reversal
The 2010 Field Demonstration of the Solar Carbothermal Reduction of Regolith to Produce Oxygen
The Moon and other space exploration destinations are comprised of a variety of oxygen-bearing minerals, providing a virtually unlimited quantity of raw material which can be processed to produce oxygen. One attractive method to extract oxygen from the regolith is the carbothermal reduction process, which is not sensitive to variations in the mineral composition of the regolith. It also creates other valuable resources within the processed regolith, such as iron and silicon metals. Using funding from NASA, ORBITEC recently built and tested the Carbothermal Regolith Reduction Module to process lunar regolith simulants using concentrated solar energy. This paper summarizes the experimental test results obtained during a demonstration of the system at a lunar analog test site on the Mauna Kea volcano on Hawaii in February 2010
Magnetic properties of (FeCo)B alloys and the effect of doping by 5 elements
We have explored, computationally and experimentally, the magnetic properties
of \fecob{} alloys. Calculations provide a good agreement with experiment in
terms of the saturation magnetization and the magnetocrystalline anisotropy
energy with some difficulty in describing CoB, for which it is found that
both full potential effects and electron correlations treated within dynamical
mean field theory are of importance for a correct description. The material
exhibits a uniaxial magnetic anisotropy for a range of cobalt concentrations
between and . A simple model for the temperature dependence of
magnetic anisotropy suggests that the complicated non-monotonous temperature
behaviour is mainly due to variations in the band structure as the exchange
splitting is reduced by temperature. Using density functional theory based
calculations we have explored the effect of substitutional doping the
transition metal sublattice by the whole range of 5 transition metals and
found that doping by Re or W elements should significantly enhance the
magnetocrystalline anisotropy energy. Experimentally, W doping did not succeed
in enhancing the magnetic anisotropy due to formation of other phases. On the
other hand, doping by Ir and Re was successful and resulted in magnetic
anisotropies that are in agreement with theoretical predictions. In particular,
doping by 2.5~at.\% of Re on the Fe/Co site shows a magnetocrystalline
anisotropy energy which is increased by 50\% compared to its parent
(FeCo)B compound, making this system interesting, for
example, in the context of permanent magnet replacement materials or in other
areas where a large magnetic anisotropy is of importance.Comment: 15 pages 17 figure
Ultrafast intramolecular electronic energy transfer in rigidly linked aminopyrenyl-aminobenzanthronyl dyads-a femtosecond study.
A randomised feasibility trial of an intervention to support sharing of HIV status for 18-25-year olds living with perinatally acquired HIV compared with standard care: HIV Empowering Adults' Decisions to Share-UK/Uganda Project (HEADS-UP)
Abstract: Background: Young adults with perinatally acquired HIV (PAH) face several challenges, including adhering to antiretroviral therapy (ART), managing the risk of onward HIV transmission and maintaining positive well-being. Sharing one's HIV status with others (onward HIV disclosure) may assist with these challenges by facilitating emotional and practical support. Rates of HIV status sharing are, however, low in this population. There are no existing interventions focused on sharing one's HIV status for young adults living with PAH. The HEADS-UP study is designed to develop and test the feasibility of an intervention to help the sharing of HIV status for young adults with PAH. Methods: The study is a 30-month multi-site randomised feasibility study across both a high-income/low-HIV prevalence country (UK) and a low-income/high-HIV prevalence country (Uganda). Phase 1 (12 months) will involve developing the intervention using qualitative interviews with 20 young people living with PAH (ten in the UK-18 to 29 years; ten in Uganda-18 to 25 years), 20 of their social network (friends, family, sexual partners as defined by the young person; ten in the UK, ten in Uganda) and ten professionals with experience working with young adults with PAH (five in the UK, five in Uganda). Phase 2 (18 months) involves conducting a randomised feasibility parallel group trial of the intervention alongside current standard of care condition in each country (main study) with 18- to 25-year olds with PAH. A sample size of 94 participants per condition (intervention or standard of care; 188 participants in total: 47 in each condition in each country) with data at both the baseline and 6-month follow-up time points, across UK and Ugandan sites will be recruited. Participants in the intervention condition will also complete measures immediately post-intervention. Face-to-face interviews will be conducted with ten participants in both countries immediately post-intervention and at 6-month follow-up (sub-study). Discussion: This study will be the first trial that we are aware of to address important gaps in understanding acceptable and feasible ways of delivering HIV status sharing support for young people living with PAH. Trial registration: ISRCTN Registry, ISRCTN31852047, Registered on 21 January, 2019. Study sponsor: Royal Holloway University of London. Sponsor contact: [email protected]. Date and version: April 2020. Protocol version 3.5
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