Modeling material failure with a vectorized routine

The computational aspects of modelling material failure in structural wood members are presented with particular reference to vector processing aspects. Wood members are considered to be highly orthotropic, inhomogeneous, and discontinuous due to the complex microstructure of wood material and the presence of natural growth characteristics such as knots, cracks and cross grain in wood members. The simulation of strength behavior of wood members is accomplished through the use of a special purpose finite element/fracture mechanics routine, program STARW (Strength Analysis Routine for Wood). Program STARW employs quadratic finite elements combined with singular crack tip elements in a finite element mesh. Vector processing techniques are employed in mesh generation, stiffness matrix formation, simultaneous equation solution, and material failure calculations. The paper addresses these techniques along with the time and effort requirements needed to convert existing finite element code to a vectorized version. Comparisons in execution time between vectorized and nonvectorized routines are provided

Supersonic quantum communication

When locally exciting a quantum lattice model, the excitation will propagate through the lattice. The effect is responsible for a wealth of non-equilibrium phenomena, and has been exploited to transmit quantum information through spin chains. It is a commonly expressed belief that for local Hamiltonians, any such propagation happens at a finite "speed of sound". Indeed, the Lieb-Robinson theorem states that in spin models, all effects caused by a perturbation are limited to a causal cone defined by a constant speed, up to exponentially small corrections. In this work we show that for translationally invariant bosonic models with nearest-neighbor interactions, this belief is incorrect: We prove that one can encounter excitations which accelerate under the natural dynamics of the lattice and allow for reliable transmission of information faster than any finite speed of sound. The effect is only limited by the model's range of validity (eventually by relativity). It also implies that in non-equilibrium dynamics of strongly correlated bosonic models far-away regions may become quickly entangled, suggesting that their simulation may be much harder than that of spin chains even in the low energy sector.Comment: 4+3 pages, 1 figure, some material added, typographic error fixe

Anisotropic valence-->core x-ray fluorescence from a [Rh(en)3][Mn(N)(CN)5]·H2O single crystal: Experimental results and density functional calculations

High resolution x-ray fluorescence spectra have been recorded for emission in different directions from a single crystal of the compound [Rh(en)3][Mn(N)(CN)5]·H2O. The spectra are interpreted by comparison with density functional theory (DFT) electronic structure calculations. The Kbeta[double-prime] line, which is strongly polarized along the Mn–N axis, can be viewed as an N(2s)-->Mn(1s) transition, and the angular dependence is understood within the dipole approximation. The so-called Kbeta2,5 region has numerous contributions but is dominated by Mn(4p) and C(2s)-->Mn(1s) transitions. Transition energy splittings are found in agreement with those of calculated occupied molecular orbitals to within 1 eV. Computed relative transition probabilities reproduce experimentally observed trends

Do mixtures of bosonic and fermionic atoms adiabatically heat up in optical lattices?

Mixtures of bosonic and fermionic atoms in optical lattices provide a promising arena to study strongly correlated systems. In experiments realizing such mixtures in the quantum degenerate regime the temperature is a key parameter. In this work, we investigate the intrinsic heating and cooling effects due to an entropy-preserving raising of the optical lattice potential. We analyze this process, identify the generic behavior valid for a wide range of parameters, and discuss it quantitatively for the recent experiments with 87Rb and 40K atoms. In the absence of a lattice, we treat the bosons in the Hartree-Fock-Bogoliubov-Popov-approximation, including the fermions in a self-consistent mean field interaction. In the presence of the full three-dimensional lattice, we use a strong coupling expansion. As a result of the presence of the fermions, the temperature of the mixture after the lattice ramp-up is always higher than for the pure bosonic case. This sheds light onto a key point in the analysis of recent experiments.Comment: 5 pages, 3 figure

New CP-violation and preferred-frame tests with polarized electrons

We used a torsion pendulum containing $\sim 9 \times 10^{22}$ polarized electrons to search for CP-violating interactions between the pendulum's electrons and unpolarized matter in the laboratory's surroundings or the sun, and to test for preferred-frame effects that would precess the electrons about a direction fixed in inertial space. We find $|g_{\rm P}^e g_{\rm S}^N|/(\hbar c)< 1.7 \times 10^{-36}$ and $|g_{\rm A}^e g_{\rm V}^N|/(\hbar c) < 4.8 \times 10^{-56}$ for $\lambda > 1$AU. Our preferred-frame constraints, interpreted in the Kosteleck\'y framework, set an upper limit on the parameter $|\bm{\tilde {b}}^e| \leq 5.0 \times 10^{-21}$ eV that should be compared to the benchmark value $m_e^2/M_{\rm Planck}= 2 \times 10^{-17}$ eV.Comment: 4 figures, accepted for publication in Physical Review Letter

Model for Stress Analysis and Strength Prediction of Lumber

A mathematical model has been developed that can predict the elastic and strength behavior of a section of a structural lumber member containing a knot and cross grain. The model, embodied in the computer program KMESHI, accounts for the presence of a knot, the associated grain deviations, and global cross grain, and can define localized stresses and displacements anywhere within the member. These capabilities are illustrated here through an examination of maximum stress concentrations for varying knot locations. The results point out the severe stress concentration that can be caused by an edge knot as opposed to a similar size center knot.An "effective section technique" is presented as a strength prediction procedure that uses Program KMESHI and a maximum stress failure theory. Unlike other strength prediction methods, this procedure recognizes that a progressive failure sequence leads to the ultimate member load. Through calculation of stresses and strains, and a predicted progressive failure sequence, the effective section technique was shown to be quite accurate in predicting the strength for two example pieces of lumber

Parametric instabilities in magnetized multicomponent plasmas

This paper investigates the excitation of various natural modes in a magnetized bi-ion or dusty plasma. The excitation is provided by parametrically pumping the magnetic field. Here two ion-like species are allowed to be fully mobile. This generalizes our previous work where the second heavy species was taken to be stationary. Their collection of charge from the background neutral plasma modifies the dispersion properties of the pump and excited waves. The introduction of an extra mobile species adds extra modes to both these types of waves. We firstly investigate the pump wave in detail, in the case where the background magnetic field is perpendicular to the direction of propagation of the pump wave. Then we derive the dispersion equation relating the pump to the excited wave for modes propagating parallel to the background magnetic field. It is found that there are a total of twelve resonant interactions allowed, whose various growth rates are calculated and discussed.Comment: Published in May 2004; this is a late submission to the archive. 14 pages, 8 figure

Structure and function of the initially transcribing RNA polymerase II–TFIIB complex

The general transcription factor (TF) IIB is required for RNA polymerase (Pol) II initiation and extends with its B-reader element into the Pol II active centre cleft. Low-resolution structures of the Pol II– TFIIB complex1,2 indicated how TFIIB functions in DNA recruitment, but they lacked nucleic acids and half of the B-reader, leaving other TFIIB functions3,4 enigmatic. Here we report crystal structures of the Pol II–TFIIB complex from the yeast Saccharomyces cerevisiae at 3.4A˚ resolution and of an initially transcribing complex that additionally contains theDNAtemplate and a 6-nucleotide RNAproduct.The structures reveal the entire B-reader and protein– nucleic acid interactions, and together with functional data lead to a more complete understanding of transcription initiation. TFIIB partially closes the polymerase cleft to position DNA and assist in its opening. The B-reader does not reach the active site but binds the DNA template strand upstream to assist in the recognition of the initiator sequence and in positioning the transcription start site. TFIIB rearranges active-site residues, induces binding of the catalytic metal ion B, and stimulates initial RNA synthesis allosterically. TFIIB then prevents the emergingDNA–RNAhybrid duplex from tilting, which would impair RNA synthesis. When the RNA grows beyond 6 nucleotides, it is separated from DNA and is directed to its exit tunnel by the B-reader loop. Once the RNA grows to 12–13 nucleotides, it clashes with TFIIB, triggering TFIIB displacement and elongation complex formation. Similar mechanisms may underlie all cellular transcription because all eukaryotic and archaeal RNA polymerases use TFIIB-like factors5, and the bacterial initiation factor sigma has TFIIB-like topology1,2 and contains the loop region 3.2 that resembles the B-reader loop in location, charge and function6–8. TFIIB and its counterparts may thus account for the two fundamental properties that distinguish RNA from DNA polymerases: primer-independent chain initiation and product separation from the template