179 research outputs found
Use of threshold parameter variation for tropical cyclone tracking
Assessing the capacity of numerical models to produce viable tropical cyclones, as well as assessing the climatological behavior of simulated tropical cyclones, requires an objective tracking method. These make use of parameter thresholds to determine whether a detected feature, such as a vorticity maximum or a warm core, is strong enough to indicate a tropical cyclone. The choice of parameter thresholds is generally subjective.
This study proposes and assesses the parallel use of many threshold parameter combinations, combining a number of weaker and stronger values. The tracking algorithm succeeds in tracking tropical cyclones within the model data, beginning at their aggregation stage or shortly thereafter and ending when they interact strongly with extratropical flow and transition into extratropical cyclones or when their warm core decays.
The sensitivity of accumulated cyclone energy to tracking errors is assessed. Tracking errors include the faulty initial detection and termination of valid tropical cyclones and systems falsely identified as tropical cyclones. They are found to not significantly impact the accumulated cyclone energy. Thus, the tracking algorithm produces an adequate estimate of the accumulated cyclone energy within the underlying data.</p
Crossover from thermal hopping to quantum tunneling in Mn_{12}Ac
The crossover from thermal hopping to quantum tunneling is studied. We show
that the decay rate with dissipation can accurately be determined near
the crossover temperature. Besides considering the Wentzel-Kramers-Brillouin
(WKB) exponent, we also calculate contribution of the fluctuation modes around
the saddle point and give an extended account of a previous study of crossover
region. We deal with two dangerous fluctuation modes whose contribution can't
be calculated by the steepest descent method and show that higher order
couplings between the two dangerous modes need to be taken into considerations.
At last the crossover from thermal hopping to quantum tunneling in the
molecular magnet Mn_{12}Ac is studied.Comment: 10 pages, 3 figure
Macroscopic Quantum Coherence in a Magnetic Nanoparticle Above the Surface of a Superconductor
We study macroscopic quantum tunneling of the magnetic moment in a
single-domain particle placed above the surface of a superconductor. Such a
setup allows one to manipulate the height of the energy barrier, preserving the
degeneracy of the ground state. The tunneling amplitude and the effect of the
dissipation in the superconductor are computed.Comment: RevTeX, 4 pages, 1 figure. Submitted to Phys. Rev. Let
Berry's phase and Quantum Dynamics of Ferromagnetic Solitons
We study spin parity effects and the quantum propagation of solitons (Bloch
walls) in quasi-one dimensional ferromagnets. Within a coherent state path
integral approach we derive a quantum field theory for nonuniform spin
configurations. The effective action for the soliton position is shown to
contain a gauge potential due to the Berry phase and a damping term caused by
the interaction between soliton and spin waves. For temperatures below the
anisotropy gap this dissipation reduces to a pure soliton mass renormalization.
The gauge potential strongly affects the quantum dynamics of the soliton in a
periodic lattice or pinning potential. For half-integer spin, destructive
interference between soliton states of opposite chirality suppresses nearest
neighbor hopping. Thus the Brillouin zone is halved, and for small mixing of
the chiralities the dispersion reveals a surprising dynamical correlation: Two
subsequent band minima belong to different chirality states of the soliton. For
integer spin, the Berry phase is inoperative and a simple tight-binding
dispersion is obtained. Finally it is shown that external fields can be used to
interpolate continuously between the Bloch wall dispersions for half-integer
and integer spin.Comment: 20 pages, RevTex 3.0 (twocolumn), to appear in Phys. Rev. B 53, 3237
(1996), 4 PS figures available upon reques
Leptogenesis with Heavy Majorana Neutrinos Reexamined
The mass term for Majorana neutrinos explicitly violates lepton number.
Several authors have used this fact to create a lepton asymmetry in the
universe by considering CP violating effects in the one loop self-energy
correction for the decaying heavy Majorana neutrino. We compare and comment on
the different approaches used to calculate the lepton asymmetry including those
using an effective Hamiltonian and resummed propagators. We also recalculate
the asymmetry in the small mass difference limit.Comment: 16 pages, LaTex, 1 figure included. 2 footnotes and 1 reference adde
Quantum-Classical Transition of the Escape Rate of a Uniaxial Spin System in an Arbitrarily Directed Field
The escape rate \Gamma of the large-spin model described by the Hamiltonian H
= -DS_z^2 - H_zS_z - H_xS_x is investigated with the help of the mapping onto a
particle moving in a double-well potential U(x). The transition-state method
yields in the moderate-damping case as a Boltzmann average of the
quantum transition probabilities. We have shown that the transition from the
classical to quantum regimes with lowering temperature is of the first order
(d\Gamma/dT discontinuous at the transition temperature T_0) for h_x below the
phase boundary line h_x=h_{xc}(h_z), where h_{x,z}\equiv H_{x,z}/(2SD), and of
the second order above this line. In the unbiased case (H_z=0) the result is
h_{xc}(0)=1/4, i.e., one fourth of the metastability boundary h_{xm}=1, at
which the barrier disappears. In the strongly biased limit \delta\equiv 1-h_z
<< 1, one has h_{xc} \cong (2/3)^{3/4}(\sqrt{3}-\sqrt{2})\delta^{3/2}\cong
0.2345 \delta^{3/2}, which is about one half of the boundary value h_{xm} \cong
(2\delta/3)^{3/2} \cong 0.5443 \delta^{3/2}.The latter case is relevant for
experiments on small magnetic particles, where the barrier should be lowered to
achieve measurable quantum escape rates.Comment: 17 PR pages, 16 figures; published versio
A systematic review of attitudes, anxiety, acceptance, and trust towards social robots
As social robots become more common, there is a need to understand how people perceive and interact with such technology. This systematic review seeks to estimate people’s attitudes toward, trust in, anxiety associated with, and acceptance of social robots; as well as factors that are associated with these beliefs. Ninety-seven studies were identified with a combined sample of over 13,000 participants and a standardized score was computed for each in order to represent the valence (positive, negative, or neutral) and magnitude (on a scale from 1 to − 1) of people’s beliefs about robots. Potential moderating factors such as the robots’ domain of application and design, the type of exposure to the robot, and the characteristics of potential users were also investigated. The findings suggest that people generally have positive attitudes towards social robots and are willing to interact with them. This finding may challenge some of the existing doubt surrounding the adoption of robotics in social domains of application but more research is needed to fully understand the factors that influence attitudes
The FANCM:p.Arg658* truncating variant is associated with risk of triple-negative breast cancer
Breast cancer is a common disease partially caused by genetic risk factors. Germline pathogenic variants in DNA repair genes BRCA1, BRCA2, PALB2, ATM, and CHEK2 are associated with breast cancer risk. FANCM, which encodes for a DNA translocase, has been proposed as a breast cancer predisposition gene, with greater effects for the ER-negative and triple-negative breast cancer (TNBC) subtypes. We tested the three recurrent protein-truncating variants FANCM:p.Arg658*, p.Gln1701*, and p.Arg1931* for association with breast cancer risk in 67,112 cases, 53,766 controls, and 26,662 carriers of pathogenic variants of BRCA1 or BRCA2. These three variants were also studied functionally by measuring survival and chromosome fragility in FANCM (-/-) patient-derived immortalized fibroblasts treated with diepoxybutane or olaparib. We observed that FANCM:p.Arg658* was associated with increased risk of ER-negative disease and TNBC (OR = 2.44, P = 0.034 and OR = 3.79; P = 0.009, respectively). In a country-restricted analysis, we confirmed the associations detected for FANCM:p.Arg658* and found that also FANCM:p.Arg1931* was associated with ER-negative breast cancer risk (OR = 1.96; P = 0.006). The functional results indicated that all three variants were deleterious affecting cell survival and chromosome stability with FANCM:p.Arg658* causing more severe phenotypes. In conclusion, we confirmed that the two rare FANCM deleterious variants p.Arg658* and p.Arg1931* are risk factors for ER-negative and TNBC subtypes. Overall our data suggest that the effect of truncating variants on breast cancer risk may depend on their position in the gene. Cell sensitivity to olaparib exposure, identifies a possible therapeutic option to treat FANCM-associated tumors
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