Tomography of full sawtooth crashes on the Tokamak Fusion Test Reactor

Full sawtooth crashes in high temperature plasmas have been investigated on the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Fusion 33, 1509 (1991)]. A strong asymmetry in the direction of major radius, a feature of the ballooning mode, and a remaining m=1 region after the crash have been observed with electron cyclotron emission image reconstructions. The TFTR data is not consistent with two-dimensional (2-D) models; it rather suggests a three-dimensional (3-D) localized reconnection arising on the bad curvature side. This process explains the phenomenon of fast heat transfer which keeps the condition q0<1

Thermodynamics and evaporation of the noncommutative black hole

We investigate the thermodynamics of the noncommutative black hole whose static picture is similar to that of the nonsingular black hole known as the de Sitter-Schwarzschild black hole. It turns out that the final remnant of extremal black hole is a thermodynamically stable object. We describe the evaporation process of this black hole by using the noncommutativity-corrected Vaidya metric. It is found that there exists a close relationship between thermodynamic approach and evaporation process.Comment: 16 pages, 6 figures, added references, to appear in JHE

Modular Cosmology, Thermal Inflation, Baryogenesis and Predictions for Particle Accelerators

Modular cosmology is plagued by overproduction of unwanted relics, gravitinos and especially moduli, at relatively low energy scales. Thermal inflation provides a compelling solution to this moduli problem, but invalidates most baryogenesis scenarios. We propose a simple model in which the MSSM plus neutrino mass term $(LH_u)^2$ is supplemented by a minimal flaton sector to drive the thermal inflation, and make two crucial assumptions: the flaton vacuum expectation value generates the $\mu$-term of the MSSM and $m_L^2 + m_{H_u}^2 < 0$. The second assumption is particularly interesting in that it violates a well known constraint, implying that there exists a nearby deep non-MSSM vacuum, and provides a clear signature of our model which can be tested at future particle accelerators. We show that our model leads to thermal inflation followed by Affleck-Dine leptogenensis along the $LH_u$ flat direction. A key feature of our leptogenesis scenario is that the $H_uH_d$ flat direction is also induced to temporarily acquire a large value, playing a crucial role in the leptogenesis, as well as dynamically shielding the field configuration from the deep non-MSSM minimum, ensuring that the fields relax into our MSSM vacuum.Comment: v3; 19 pages, 3 figures; added a reference for section

Lattice instabilities of PbZrO3/PbTiO3 [1:1] superlattices from first principles

Ab initio phonon calculations for the nonpolar reference structures of the (001), (110), and (111) PbZrO_3/PbTiO_3 [1:1] superlattices are presented. The unstable polar modes in the tetragonal (001) and (110) structures are confined in either the Ti- or the Zr-centered layers and display two-mode behavior, while in the cubic (111) case one-mode behavior is observed. Instabilities with pure oxygen character are observed in all three structures. The implications for the ferroelectric behavior and related properties are discussed.Comment: 12 pages, 2 figures, 7 tables, submitted to PR

Electromigration-Induced Flow of Islands and Voids on the Cu(001) Surface

Electromigration-induced flow of islands and voids on the Cu(001) surface is studied at the atomic scale. The basic drift mechanisms are identified using a complete set of energy barriers for adatom hopping on the Cu(001) surface, combined with kinetic Monte Carlo simulations. The energy barriers are calculated by the embedded atom method, and parameterized using a simple model. The dependence of the flow on the temperature, the size of the clusters, and the strength of the applied field is obtained. For both islands and voids it is found that edge diffusion is the dominant mass-transport mechanism. The rate limiting steps are identified. For both islands and voids they involve detachment of atoms from corners into the adjacent edge. The energy barriers for these moves are found to be in good agreement with the activation energy for island/void drift obtained from Arrhenius analysis of the simulation results. The relevance of the results to other FCC(001) metal surfaces and their experimental implications are discussed.Comment: 9 pages, 13 ps figure

Missing data approaches in longitudinal studies of aging: A case example using the National Health and Aging Trends Study

Purpose Missing data is a key methodological consideration in longitudinal studies of aging. We described missing data challenges and potential methodological solutions using a case example describing five-year frailty state transitions in a cohort of older adults. Methods We used longitudinal data from the National Health and Aging Trends Study, a nationally-representative cohort of Medicare beneficiaries. We assessed the five components of the Fried frailty phenotype and classified frailty based on their number of components (robust: 0, prefrail: 1–2, frail: 3–5). One-, two-, and five-year frailty state transitions were defined as movements between frailty states or death. Missing frailty components were imputed using hot deck imputation. Inverse probability weights were used to account for potentially informative loss-to-follow-up. We conducted scenario analyses to test a range of assumptions related to missing data. Results Missing data were common for frailty components measured using physical assessments (walking speed, grip strength). At five years, 36% of individuals were lost-to-follow-up, differentially with respect to baseline frailty status. Assumptions for missing data mechanisms impacted inference regarding individuals improving or worsening in frailty. Conclusions Missing data and loss-to-follow-up are common in longitudinal studies of aging. Robust epidemiologic methods can improve the rigor and interpretability of aging-related research

Antiferromagnetic Domains and Superconductivity in UPt3

We explore the response of an unconventional superconductor to spatially inhomogeneous antiferromagnetism (SIAFM). Symmetry allows the superconducting order parameter in the E-representation models for UPt3 to couple directly to the AFM order parameter. The Ginzburg-Landau equations for coupled superconductivity and SIAFM are solved numerically for two possible SIAFM configurations: (I) abutting antiferromagnetic domains of uniform size, and (II) quenched random disorder of `nanodomains' in a uniform AFM background. We discuss the contributions to the free energy, specific heat, and order parameter for these models. Neither model provides a satisfactory account of experiment, but results from the two models differ significantly. Our results demonstrate that the response of an E_{2u} superconductor to SIAFM is strongly dependent on the spatial dependence of AFM order; no conclusion can be drawn regarding the compatibility of E_{2u} superconductivity with UPt3 that is independent of assumptions on the spatial dependence of AFMComment: 12 pages, 13 figures, to appear in Phys. Rev.

Muon anomalous magnetic moment in the standard model with two Higgs doublets

The muon anomalous magnetic moment is investigated in the standard model with two Higgs doublets (S2HDM) motivated from spontaneous CP violation. Thus all the effective Yukawa couplings become complex. As a consequence of the non-zero phase in the couplings, the one loop contribution from the neutral scalar bosons could be positive and negative relying on the CP phases. The interference between one and two loop diagrams can be constructive in a large parameter space of CP-phases. This will result in a significant contribution to muon anomalous magnetic moment even in the flavor conserving process with a heavy neutral scalar boson ($m_h \sim$ 200 GeV) once the effective muon Yukawa coupling is large ($|\xi_\mu|\sim 50$). In general, the one loop contributions from lepton flavor changing scalar interactions become more important. In particular, when all contributions are positive in a reasonable parameter space of CP phases, the recently reported 2.6 sigma experiment vs. theory deviation can be easily explained even for a heavy scalar boson with a relative small Yukawa coupling in the S2HDM.Comment: 8 pages, RevTex file, 5 figures, published version Phys. Rev. D 54 (2001) 11501

Electron Scattering From High-Momentum Neutrons in Deuterium

We report results from an experiment measuring the semi-inclusive reaction $d(e,e'p_s)$ where the proton $p_s$ is moving at a large angle relative to the momentum transfer. If we assume that the proton was a spectator to the reaction taking place on the neutron in deuterium, the initial state of that neutron can be inferred. This method, known as spectator tagging, can be used to study electron scattering from high-momentum (off-shell) neutrons in deuterium. The data were taken with a 5.765 GeV electron beam on a deuterium target in Jefferson Laboratory's Hall B, using the CLAS detector. A reduced cross section was extracted for different values of final-state missing mass $W^{*}$, backward proton momentum $\vec{p}_{s}$ and momentum transfer $Q^{2}$. The data are compared to a simple PWIA spectator model. A strong enhancement in the data observed at transverse kinematics is not reproduced by the PWIA model. This enhancement can likely be associated with the contribution of final state interactions (FSI) that were not incorporated into the model. A ``bound neutron structure function'' $F_{2n}^{eff}$ was extracted as a function of $W^{*}$ and the scaling variable $x^{*}$ at extreme backward kinematics, where effects of FSI appear to be smaller. For $p_{s}>400$ MeV/c, where the neutron is far off-shell, the model overestimates the value of $F_{2n}^{eff}$ in the region of $x^{*}$ between 0.25 and 0.6. A modification of the bound neutron structure function is one of possible effects that can cause the observed deviation.Comment: 33 pages RevTeX, 9 figures, to be submitted to Phys. Rev. C. Fixed 1 Referenc