4,340 research outputs found
Bound states and E_8 symmetry effects in perturbed quantum Ising chains
In a recent experiment on CoNb_2O_6, Coldea et al. [Science 327, 177 (2010)]
found for the first time experimental evidence of the exceptional Lie algebra
E_8. The emergence of this symmetry was theoretically predicted long ago for
the transverse quantum Ising chain in the presence of a weak longitudinal
field. We consider an accurate microscopic model of CoNb_2O_6 incorporating
additional couplings and calculate numerically the dynamical structure function
using a recently developed matrix-product-state method. The excitation spectra
show bound states characteristic of the weakly broken E_8 symmetry. We compare
the observed bound state signatures in this model to those found in the
transverse Ising chain in a longitudinal field and to experimental data.Comment: 4 pages, 3 figure
Space station structures and dynamics test program
The design, construction, and operation of a low-Earth orbit space station poses challenges for development and implementation of technology. One specific challenge is the development of a dynamics test program for defining the space station design requirements, and identifying and characterizing phenomena affecting the space station's design and development. The test proposal, as outlined, is a comprehensive structural dynamics program to be launched in support of the space station (SS). Development of a parametric data base and verification of the mathematical models and analytical analysis tools necessary for engineering support of the station's design, construction, and operation provide the impetus for the dynamics test program. The four test phases planned are discussed: testing of SS applicable structural concepts; testing of SS prototypes; testing of actual SS structural hardware; and on-orbit testing of SS construction
Time-evolving a matrix product state with long-ranged interactions
We introduce a numerical algorithm to simulate the time evolution of a matrix
product state under a long-ranged Hamiltonian. In the effectively
one-dimensional representation of a system by matrix product states,
long-ranged interactions are necessary to simulate not just many physical
interactions but also higher-dimensional problems with short-ranged
interactions. Since our method overcomes the restriction to short-ranged
Hamiltonians of most existing methods, it proves particularly useful for
studying the dynamics of both power-law interacting one-dimensional systems,
such as Coulombic and dipolar systems, and quasi two-dimensional systems, such
as strips or cylinders. First, we benchmark the method by verifying a
long-standing theoretical prediction for the dynamical correlation functions of
the Haldane-Shastry model. Second, we simulate the time evolution of an
expanding cloud of particles in the two-dimensional Bose-Hubbard model, a
subject of several recent experiments.Comment: 5 pages + 3 pages appendices, 4 figure
Linear PDEs and numerical methods that preserve a multi-symplectic conservation law
Multisymplectic methods have recently been proposed as a generalization of symplectic ODE methods to the case of Hamiltonian PDEs. Their excellent long time behavior for a variety of Hamiltonian wave equations has been demonstrated in a number of numerical studies. A theoretical investigation and justification of multisymplectic methods is still largely missing. In this paper, we study linear multisymplectic PDEs and their discretization by means of numerical dispersion relations. It is found that multisymplectic methods in the sense of Bridges and Reich Phys. Lett. A, 284 (2001), pp. 184-193] and Reich J. Comput. Phys., 157 (2000), pp. 473-499], such as Gauss-Legendre Runge-Kutta methods, possess a number of desirable properties such as nonexistence of spurious roots and conservation of the sign of the group velocity. A certain CFL-type restriction on might be required for methods higher than second order in time. It is also demonstrated by means of the explicit midpoint method that multistep methods may exhibit spurious roots in the numerical dispersion relation for any value of despite being multisymplectic in the sense of discrete variational mechanics [J. E. Marsden, G. P. Patrick, and S. Shkoller, Commun. Math. Phys., 199 (1999), pp. 351-395]
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Traditional and Model Based Assay of Irregular Geometry Items
The Analytical Development Section (ADS) of SRNL was requested to perform a waste disposal assay of two heater boxes which had been used in the HB Line dissolvers. They had been sent to SRNL for study to make recommendations on how to prevent future failure of the units when they were replaced. The study having been completed, the units needed to be characterized prior to sending to Solid Waste for disposal. An assay station consisting of a turntable, HPGe detector, CANBERRA Inspector, transmission source and a portable computer was set up to do the required assays. The assays indicate the presence of U-235, Pu-239 and Cs-137. No measurable amounts of U-235 or Pu-239 were found. Therefore the Minimum Detectable Activities for U-235 and Pu-239 were calculated. For Heater Box 1, 0.23 grams of U-235 and 0.24 grams of Pu-239. For Heater Box 2, the results were 0.21 grams of U-235 and 0.21 grams of Pu-239. This paper describes and documents the assays employed to determine the amount of U, Pu and Cs contents of the heater boxes. The paper provides results of SNM assays using traditional calibration of the system and on one based on modeling. It also provides the scientific community with data that will assist the user in determining the method of choice for assaying items with irregular geometries
Ground-gamma band mixing and evolution of collectivity in even-even neutron-rich nuclei with 40<Z<50
We propose an extended band mixing formalism capable of describing the
ground-gamma band interaction in a wide range of collective spectra beyond the
regions of well deformed nuclei. On this basis we explain the staggering
effects observed in the gamma bands of Mo, Ru and Pd nuclei providing a
consistent interpretation of new experimental data in the neutron rich region.
As a result the systematic behavior of the odd-even staggering effect and some
general characteristics of the spectrum such as the mutual disposition of the
bands, the interaction strength and the band structures is explained as the
manifestation of respective changes in collective dynamics of the system.Comment: 17 pages, 6 figures, 4 table
Outcomes After Bidirectional Cavopulmonary Shunt in Infants Less Than 6 Months Old
AbstractObjectives. We sought to assess the results after bidirectional cavopulmonary shunt (BCPS) in infants <6 months old and to identify risk factors for poor outcome.Background. Although BCPS is a well established procedure for the palliation of patients with a single-ventricle heart, there have been very few reports of outcomes after BCPS in young infants.Methods. Since 1990, 42 infants between 0.8 and 6.0 months of age (mean [±SD] 3.7 ± 1.4) have undergone BCPS for primary (n = 16) or secondary (n = 26) palliation of tricuspid atresia (n = 13), hypoplastic left heart syndrome (n = 10) or other forms of functional single-ventricle heart (n = 19). Accessory pulmonary blood flow was included in 18 patients. Preoperative and perioperative data were gathered on retrospective review of patient records, and follow-up was conducted by means of direct physician contact or record review.Results. The overall hospital mortality rate, including that associated with reoperations, was 4.8% (2 of 42 patients). Seven patients (17%) required reoperation related to the BCPS or pulmonary blood flow in the early postoperative period: Procedures included take-down of the BCPS in four patients, with one early death, and procedures to decrease pulmonary blood flow in three patients. Age <1 month correlated significantly with early death and with early failure of the BCPS (death or take-down). Follow-up of the 37 patients discharged with intact BCPS was obtained at a mean ± SD of 14.3 ± 11.3 months postoperatively, during which time three patients died (at 6.5 ± 2.5 months). The 2-year actuarial survival rate for patients undergoing BCPS at <6 months of age was 86%. Overall freedom from death or take-down (including early and late events) was significantly lower in patients <2 months old than in those >2 months old. Four patients have undergone successful Fontan completion (18.3 ± 2.9 months postoperatively), and one patient whose BCPS was taken down subsequently underwent successful restoration of a BCPS.Conclusions. Outcomes after BCPS in young infants are comparable to those in older infants and children. However, our current preference is to defer this procedure until after 2 months of age.(J Am Coll Cardiol 1997;29:1365–70
Young adult carers: the impact of caring on health and education
Research has shown that young people who care for parents and relatives (young carers and young adult carers) are at greater risk of mental and emotional difficulties and are more likely to do badly at school or college. To explore the difficulties faced by young adult carers (aged 14 to 25) in the UK, an online survey was conducted. Almost half (45%) of the 295 respondents reported having a mental health problem. The relationship between the extent of caring and perceived mental health problems, and the impact of caring responsibilities on work and education were investigated
Electromagnetic modes of Maxwell fisheye lens
We provide an analysis of the radial structure of TE and TM modes of the
Maxwell fisheye lens, by means of Maxwell equations as applied to the fisheye
case. Choosing a lens of size R = 1 cm, we plot some of the modes in the
infrared range.Comment: 2+6 pages in Latex, 3 figures to be found in the published referenc
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