414 research outputs found
Ladder operators for subtle hidden shape invariant potentials
Ladder operators can be constructed for all potentials that present the
integrability condition known as shape invariance, satisfied by most of the
exactly solvable potentials. Using the superalgebra of supersymmetric quantum
mechanics we construct the ladder operators for two exactly solvable potentials
that present a subtle hidden shape invariance.Comment: 9 pages, based on the talk given at International Conference Progress
in Supersymmetric Quantum Mechanics (PSQM03), Valladolid, Spain, 15-19 July,
2003, to appear in a Special Issue of J. Phys. A: Math. Ge
Generalized Ladder Operators for Shape-invariant Potentials
A general form for ladder operators is used to construct a method to solve
bound-state Schr\"odinger equations. The characteristics of supersymmetry and
shape invariance of the system are the start point of the approach. To show the
elegance and the utility of the method we use it to obtain energy spectra and
eigenfunctions for the one-dimensional harmonic oscillator and Morse potentials
and for the radial harmonic oscillator and Coulomb potentials.Comment: in Revte
Supersymmetric solutions of PT-/non-PT-symmetric and non-Hermitian Screened Coulomb potential via Hamiltonian hierarchy inspired variational method
The supersymmetric solutions of PT-symmetric and Hermitian/non-Hermitian
forms of quantum systems are obtained by solving the Schrodinger equation for
the Exponential-Cosine Screened Coulomb potential. The Hamiltonian hierarchy
inspired variational method is used to obtain the approximate energy
eigenvalues and corresponding wave functions.Comment: 13 page
PROBABILISTIC ASSESSMENT OF THE SEISMIC PERFORMANCE OF STEEL BUILDINGS DESIGNED ACCORDING TO THE LRFD SPECIFICATION
Seismic regulations and building codes experienced major advances in the last decades. Nevertheless, current trends in earthquake engineering are the assessment of the computational procedures provided by such design rules, by using probabilistic techniques, in order to test the anticipated levels of reliability and performance of the structures. While some consideration is given in codes to the uncertainties associated to the seismic action, no probabilistic requirements are posed on the responses, which determine the final design. Consequently, the risk associated to the design formulas remains unknown. The objective of this chapter is to study whether steel buildings designed and constructed according to the Load and Resistance Factor Design (LRFD) specification for Structural Steel Buildings, reasonably meet the probabilistic requirements on structural member safety applying non-linear dynamic analyses and Monte-Carlo techniques. Starting from a specific low-rise braced frame steel building existing in Manizales, Colombia, we also analyze mid-rise and high-rise braced frame buildings. Similar low- mid- and high-rise Moment-resisting frame buildings are also studied. For each building we performed more than ten thousand dynamic simulations, covering a wide range of combinations of demand and strength. In this way, we determine the exceedance probability of the construction capacity and we verify the safety and reliability of the structural members of the buildings. In the analysis of demand, we consider the probabilistic variation of the vertical gravity loads as well as of the seismic horizontal ones. The analyses of the strength of the studied buildings take into account the uncertainties and probability distributions of several parameters as: the yielding strain, the elasticity modulus, the cross-sectional area and their inertia moments. The analysis shows that in the cases here analyzed, but especially in moment-resisting frame buildings, the uncertainties in the input parameters may lead to significant failure probabilities. We conclude that braced frame steel buildings fulfil the seismic safety requirements while moment-resisting frame buildings would require a safety factor of about 2.7 for the column anchorages to the foundations
Deterministic and Probabilistic Earthquake Scenarios for the Seismic Risk Analysis of URM Buildings
Barcelona, as well as a large number of cities in the Mediterranean basin, has a housing stock composed of a large number of unreinforced brick masonry buildings. Motivated by different factors, the enlargement of the city (Eixample in Catalan) was held from the second half of the 19th century and the beginning of the 20th, a period in which a large number of buildings of this type were built, many of which are still used as dwellings. Although the buildings were built individually, some of them are linked to adjacent buildings by the side walls. This feature leads to the analysis of the buildings as isolated structures and also as an aggregate. Barcelona is located in a seismic region of low to moderate hazard, with macroseismic intensity between the grades VI and VII of the European macroseismic scale EMS'98. Based on the deterministic and probabilistic response spectra for the different types of soils present in Barcelona obtained in the work of Irizarry (2004), the seismic risk of four individual buildings and an aggregate is evaluated. The buildings are modeled and analyzed using the TREMURI program and MATLAB routines under the guidance of RISK-UE project
4He experiments can serve as a database for determining the three-nucleon force
We report on microscopic calculations for the 4He compound system in the
framework of the resonating group model employing realistic nucleon-nucleon and
three nucleon forces. The resulting scattering phase shifts are compared to
those of a comprehensive R-matrix analysis of all data in this system, which
are available in numerical form. The agreement between calculation and analysis
is in most cases very good. Adding three-nucleon forces yields in many cases
large effects. For a few cases the new agreement is striking. We relate some
differencies between calculation and analysis to specific data and discuss
neccessary experiments to clarify the situation. From the results we conclude
that the data of the 4He system might be well suited to determine the structure
of the three-nucleon force.Comment: title changed,note added, format of figures changed, appearance of
figures in black-and-white changed, Phys. Rev. C accepte
Field-induced nematic-like magnetic transition in an iron pnictide superconductor, Ca(PtAs)((FePt)As)
We report a high magnetic field study up to 55 T of the nearly optimally
doped iron-pnictide superconductor Ca(PtAs)
((FePt)As) (x=0.078(6)) with a Tc 10 K using
magnetic torque, tunnel diode oscillator technique and transport measurements.
We determine the superconducting phase diagram, revealing an anisotropy of the
irreversibility field up to a factor of 10 near Tc and signatures of multiband
superconductivity. Unexpectedly, we find a spin-flop like anomaly in magnetic
torque at 22 T, when the magnetic field is applied perpendicular to the ab
planes, which becomes significantly more pronounced as the temperature is
lowered to 0.33 K. As our superconducting sample lies well outside the
antiferromagnetic region of the phase diagram, the observed field-induced
transition in torque indicates a spin-flop transition not of long-range ordered
moments, but of nematic-like antiferromagnetic fluctuations.Comment: Latex, 4 figure
Upper critical magnetic field in K0.83Fe1.83Se2 and Eu0.5K0.5Fe2As2 single crystals
The H-T phase diagrams of single crystalline electron-doped K0.83Fe1.83Se2
(KFS1), K0.8Fe2Se2 (KFS2) and hole-doped Eu0.5K0.5Fe2As2 (EKFA) have been
deduced from tunnel diode oscillator-based contactless measurements in pulsed
magnetic fields up to 57 T for the inter-plane (H//c) and in-plane (H//ab)
directions. The temperature dependence of the upper critical magnetic field
Hc2(T) relevant to EFKA is accounted for by the Pauli model including an
anisotropic Pauli paramagnetic contribution (\mu_BHp=114 T for H//ab and 86 T
for H//c). This is also the case of KFS1 and KFS2 for H//ab whereas a
significant upward curvature, accounted for by a two-gap model, is observed for
H//c. Despite the presence of antiferromagnetic lattice order within the
superconducting state of the studied compounds, no influence of magnetic
ordering on the temperature dependence of Hc2(T) is observed.Comment: 9 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1104.561
Upper critical magnetic field in Ba_0.68K_0.32Fe_2As_2 and Ba(Fe_0.93Co_0.07)_2As_2
We report measurements of the temperature dependence of the radio-frequency
magnetic penetration depth in Ba_0.68K_0.32Fe_2As_2 and
Ba(Fe_0.93Co_0.07)_2As_2 single crystals in pulsed magnetic fields up to 60 T.
From our data, we construct an H-T phase diagram for the inter-plane (H || c)
and in-plane (H || ab) directions for both compounds. For both field
orientations in Ba_0.68K_0.32Fe_2As_2, we find a concave curvature of the
Hc2(T) lines with decreasing anisotropy and saturation towards lower
temperature. Taking into account Pauli spin paramagnetism we can describe
Hc2(T) and its anisotropy. In contrast, we find that Pauli paramagnetic pair
breaking is not essential for Ba(Fe_0.93Co_0.07)_2As_2. For this electron-doped
compound, the data support a Hc2(T) dependence that can be described by the
Werthamer Helfand Hohenberg model for H || ab and a two-gap behavior for H ||
c.Comment: 7 pages, 8 figure
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