1,766 research outputs found
Tunable gigahertz dynamics of low-temperature skyrmion lattice in a chiral magnet
Recently, it has been shown that the chiral magnetic insulator Cu2OSeO3hosts skyrmions in two separated pockets in temperature and magnetic field phase space. It has also been shown that the predominant stabilization mechanism for the low-temperature skyrmion (LTS) phase is via the crystalline anisotropy, opposed to temperature fluctuations that stabilize the well-established high-temperature skyrmion (HTS) phase. Here, we report on a detailed study of LTS generation by field cycling, probed by GHz spin dynamics in Cu2OSeO3. LTSs are populated via a field cycling protocol with the static magnetic field applied parallel to the âš100â© crystalline direction of plate and cuboid-shaped bulk crystals. By analyzing temperature-dependent broadband spectroscopy data, clear evidence of LTS excitations with clockwise (CW), counterclockwise (CCW), and breathing mode (BR) character at temperatures belowT= 40Â K are shown. We find that the mode intensities can be tuned with the number of field-cycles below the saturation field. By tracking the resonance frequencies, we are able to map out the field-cycle-generated LTS phase diagram, from which we conclude that the LTS phase is distinctly separated from the high-temperature counterpart. We also study the mode hybridization between the dark CW and the BR modes as a function of temperature. By using two Cu2OSeO3crystals with different shapes and therefore different demagnetization factors, together with numerical calculations, we unambiguously show that the magnetocrystalline anisotropy plays a central role for the mode hybridization
Manipulation of magnetic skyrmion density in continuous Ir/Co/Pt multilayers
We show that magnetic skyrmions can be stabilised at room temperature in continuous [Ir/Co/Pt]5 multilayers on SiO2/Si substrates without the prior application of electric current or magnetic field. While decreasing the Co thickness, a transition of the magnetic domain patterns from worm-like state to separated stripes is observed. The skyrmions are clearly imaged in both states using magnetic force microscopy. The density of skyrmions can be significantly enhanced after applying the âin-plane field procedureâ. Our results provide means to manipulate magnetic skyrmion density, further allowing for the optimised engineering of skyrmion-based devices
Moral Distress Amongst American Physician Trainees Regarding Futile Treatments at the End of Life: A Qualitative Study.
BACKGROUND: Ethical challenges are common in end of life care; the uncertainty of prognosis and the ethically permissible boundaries of treatment create confusion and conflict about the balance between benefits and burdens experienced by patients. OBJECTIVE: We asked physician trainees in internal medicine how they reacted and responded to ethical challenges arising in the context of perceived futile treatments at the end of life and how these challenges contribute to moral distress. DESIGN: Semi-structured in-depth qualitative interviews. PARTICIPANTS: Twenty-two internal medicine residents and fellows across three American academic medical centers. APPROACH: This study uses systematic qualitative methods of data gathering, analysis and interpretation. KEY RESULTS: Physician trainees experienced significant moral distress when they felt obligated to provide treatments at or near the end of life that they believed to be futile. Some trainees developed detached and dehumanizing attitudes towards patients as a coping mechanism, which may contribute to a loss of empathy. Successful coping strategies included formal and informal conversations with colleagues and superiors about the emotional and ethical challenges of providing care at the end of life. CONCLUSIONS: Moral distress amongst physician trainees may occur when they feel obligated to provide treatments at the end of life that they believe to be futile or harmful.This study was funded by the Health Resources and Service Administration T32 HP10025-20 Training Grant, the Gates Cambridge Scholarship, Society of General Internal Medicine Founders Grant, and the Ho-Chiang Palliative Care Research Fellowship at the Johns Hopkins School of Medicine.This is the author accepted manuscript. The final version is available from Springer via http://dx.doi.org/10.1007/s11606-015-3505-
Switching of magnetization by non-linear resonance studied in single nanoparticles
Magnetization reversal in magnetic particles is one of the fundamental issues
in magnetic data storage. Technological improvements require the understanding
of dynamical magnetization reversal processes at nanosecond time scales. New
strategies are needed to overcome current limitations. For example, the problem
of thermal stability of the magnetization state (superparamagnetic limit) can
be pushed down to smaller particle sizes by increasing the magnetic anisotropy.
High fields are then needed to reverse the magnetization that are difficult to
achieve in current devices. Here we propose a new method to overcome this
limitation. A constant applied field, well below the switching field, combined
with a radio-frequency (RF) field pulse can reverse the magnetization of a
nanoparticle. The efficiency of this method is demonstrated on a 20 nm cobalt
particle by using the micro-SQUID technique. Other applications of this method
might be nucleation or depinning of domain walls.Comment: 11 pages, 5 figure
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First measurement of neutrino oscillation parameters using neutrinos and antineutrinos by NOvA.
The NOvA experiment has seen a 4.4Ï signal of Îœ[over ÂŻ]_{e} appearance in a 2 GeV Îœ[over ÂŻ]_{ÎŒ} beam at a distance of 810 km. Using 12.33Ă10^{20} protons on target delivered to the Fermilab NuMI neutrino beamline, the experiment recorded 27 Îœ[over ÂŻ]_{ÎŒ}âÎœ[over ÂŻ]_{e} candidates with a background of 10.3 and 102 Îœ[over ÂŻ]_{ÎŒ}âÎœ[over ÂŻ]_{ÎŒ} candidates. This new antineutrino data are combined with neutrino data to measure the parameters |Îm_{32}^{2}|=2.48_{-0.06}^{+0.11}Ă10^{-3}ââeV^{2}/c^{4} and sin^{2}Ξ_{23} in the ranges from (0.53-0.60) and (0.45-0.48) in the normal neutrino mass hierarchy. The data exclude most values near ÎŽ_{CP}=Ï/2 for the inverted mass hierarchy by more than 3Ï and favor the normal neutrino mass hierarchy by 1.9Ï and Ξ_{23} values in the upper octant by 1.6Ï
A Study of Time-Dependent CP-Violating Asymmetries and Flavor Oscillations in Neutral B Decays at the Upsilon(4S)
We present a measurement of time-dependent CP-violating asymmetries in
neutral B meson decays collected with the BABAR detector at the PEP-II
asymmetric-energy B Factory at the Stanford Linear Accelerator Center. The data
sample consists of 29.7 recorded at the
resonance and 3.9 off-resonance. One of the neutral B mesons,
which are produced in pairs at the , is fully reconstructed in
the CP decay modes , , , () and , or in flavor-eigenstate
modes involving and (). The flavor of the other neutral B meson is tagged at the time of
its decay, mainly with the charge of identified leptons and kaons. The proper
time elapsed between the decays is determined by measuring the distance between
the decay vertices. A maximum-likelihood fit to this flavor eigenstate sample
finds . The value of the asymmetry amplitude is determined from
a simultaneous maximum-likelihood fit to the time-difference distribution of
the flavor-eigenstate sample and about 642 tagged decays in the
CP-eigenstate modes. We find , demonstrating that CP violation exists in the neutral B meson
system. (abridged)Comment: 58 pages, 35 figures, submitted to Physical Review
Measurement of the Branching Fraction for B- --> D0 K*-
We present a measurement of the branching fraction for the decay B- --> D0
K*- using a sample of approximately 86 million BBbar pairs collected by the
BaBar detector from e+e- collisions near the Y(4S) resonance. The D0 is
detected through its decays to K- pi+, K- pi+ pi0 and K- pi+ pi- pi+, and the
K*- through its decay to K0S pi-. We measure the branching fraction to be
B.F.(B- --> D0 K*-)= (6.3 +/- 0.7(stat.) +/- 0.5(syst.)) x 10^{-4}.Comment: 7 pages, 1 postscript figure, submitted to Phys. Rev. D (Rapid
Communications
Measurement of Branching Fraction and Dalitz Distribution for B0->D(*)+/- K0 pi-/+ Decays
We present measurements of the branching fractions for the three-body decays
B0 -> D(*)-/+ K0 pi^+/-B0 -> D(*)-/+ K*+/- using
a sample of approximately 88 million BBbar pairs collected by the BABAR
detector at the PEP-II asymmetric energy storage ring.
We measure:
B(B0->D-/+ K0 pi+/-)=(4.9 +/- 0.7(stat) +/- 0.5 (syst)) 10^{-4}
B(B0->D*-/+ K0 pi+/-)=(3.0 +/- 0.7(stat) +/- 0.3 (syst)) 10^{-4}
B(B0->D-/+ K*+/-)=(4.6 +/- 0.6(stat) +/- 0.5 (syst)) 10^{-4}
B(B0->D*-/+ K*+/-)=(3.2 +/- 0.6(stat) +/- 0.3 (syst)) 10^{-4}
From these measurements we determine the fractions of resonant events to be :
f(B0-> D-/+ K*+/-) = 0.63 +/- 0.08(stat) +/- 0.04(syst) f(B0-> D*-/+ K*+/-) =
0.72 +/- 0.14(stat) +/- 0.05(syst)Comment: 7 pages, 3 figures submitted to Phys. Rev. Let
Evidence for the Rare Decay B -> K*ll and Measurement of the B -> Kll Branching Fraction
We present evidence for the flavor-changing neutral current decay and a measurement of the branching fraction for the related
process , where is either an or
pair. These decays are highly suppressed in the Standard Model,
and they are sensitive to contributions from new particles in the intermediate
state. The data sample comprises
decays collected with the Babar detector at the PEP-II storage ring.
Averaging over isospin and lepton flavor, we obtain the branching
fractions and , where the
uncertainties are statistical and systematic, respectively. The significance of
the signal is over , while for it is .Comment: 7 pages, 2 postscript figues, submitted to Phys. Rev. Let
Differential branching fraction and angular analysis of the decay B0âKâ0ÎŒ+ÎŒâ
The angular distribution and differential branching fraction of the decay B 0â K â0 ÎŒ + ÎŒ â are studied using a data sample, collected by the LHCb experiment in pp collisions at sâ=7 TeV, corresponding to an integrated luminosity of 1.0 fbâ1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
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