In-plane Moment Research Articles

Global optimum design of externally pressurized isogrid stiffened cylindrical shells with added T-rings

PANDA2 is a code for the minimum-weight design of perfect and imperfect elastic stiffened panels and shells made of composite laminates and subjected to multiple sets of in-plane loads, edge moments, normal pressure, and temperature. The scope of PANDA2 is increased to include global optimization and the capability to handle isogrid stiffening. The enhanced program is used to find global optimum designs of internally T-isogrid and internally T-ring stiffened perfect and imperfect isotropic cylindrical shells under uniform external pressure. For the cases studied, it is found that for the perfect optimized shells the isogrid stiffening is important but the rings are not, whereas the opposite holds for the optimized shells with an initial general buckling modal imperfection of amplitude equal to one per cent of the shell radius

Step-induced in-plane orbital anisotropy in FeNi films on Cu(111) probed by magnetic circular x-ray dichroism

The effects of nanostructured magnetic ${\mathrm{Fe}}_{65}{\mathrm{Ni}}_{35}$ films deposited on a vicinal Cu(111) single-crystal surface on the magnetic anisotropy have been studied using magnetic circular x-ray dichroism (MCXD) at the Fe ${L}_{2,3}$ edges. In the one-dimensional (1D) limit a large dipolar out-of-plane anisotropy is evidenced with in-plane isotropic magnetic moments. After the 1D coalescence the orbital moment shows a more complex behavior depending on the in-plane direction of saturation. We show that MCXD is strongly sensitive to in-plane orbital anisotropy for the 1D stripes. We demonstrate the importance of the step induced in-plane anisotropy by measuring the orbital magnetic moment dependence as a function of the in-plane azimuth angle. In the submonolayer regime an in-plane magnetic anisotropy is observed related to the step decoration growth mode. In the thickness range of 2--4 equivalent monolayers, 2D coalescence induces a strong in-plane magnetic anisotropy of the magnetic orbital moment. The microscopic origin of the strong in-plane variation of ${M}_{L}$ has been attributed to magnetocrystalline effects. Strained films give rise to an in-plane magnetic anisotropy energy up to 2 meV/at., which is larger than those measured out of the plane (0--1 meV/at.).

In-plane magnetic anisotropy of stepped epitaxial Fe(001) thin films probed by x-ray magnetic circular dichroism

X-ray magnetic circular dichroism experiments were performed at the Fe ${L}_{2,3}$ edges on stepped epitaxial Fe thin films structured by the so-called atomic saw method. The measurements highlight a slight in-plane orbital moment anisotropy. The orbital moment is larger along the in-plane uniaxial easy magnetization axis corresponding to the crystallographic direction along which the tensile strain is relieved. This points out the link between the magnetocrystalline or magnetoelastic energy and the orbital moment anisotropy as predicted by Bruno's model. A theoretical approach performed within the tight-binding formalism corroborates the experimental results by evidencing the enhancement of the orbital moment along the more tightly bound direction.

Modified magnetism at a buried Co/Pd interface resolved with X-ray standing waves.

Soft x-ray standing waves produced by a multilayer interference substrate add depth sensitivity to magnetic circular dichroism to resolve changes in Co magnetism across a 1 nm distance from the Co center to the Co-on-Pd interface of a Pd/Co/Pd trilayer with an in-plane magnetization. Large enhancements of the number of Co d holes, and of in-plane orbital and spin magnetic moments, are strongly localized at a thin, chemically modified interface layer. These results provide new insight into magnetic anisotropy at interfaces, and suggest a broad applicability of such standing wave measurements to interface magnetism studies.

Nozzles in the knuckle region of a torispherical head: limit load interaction under combined pressure and piping loads

Limit loads are assessed for a piping nozzle in a Klöpperböden torispherical drumhead. The particular concern is when the nozzle is located in the knuckle region of the head. Individual limit loads for internal pressure and the four nozzle loads are presented. Limit load interaction plots for pressure versus nozzle axial force, in-plane moment, out-of-plane moment and torsion, and for in-plane moment versus out-of-plane moment are also presented. The results are discussed in the light of design code rules for load interaction.

Mössbauer spectroscopic studies of the moment distribution in Fe73.5Cu1Nb3Si13.5B9

Fe 57 Mössbauer spectroscopy can be used to determine the distribution of moment directions in magnetic materials. Here, we have applied this technique to a study of Fe73.5Cu1Nb3Si13.5B9 (isocompositional with FINEMET). We are particularly interested in establishing the distribution of moment directions in the nanophase material, obtained by devitrification from an amorphous precursor. The nanophase material consists of Fe–Si grains embedded in an amorphous matrix. Current understanding of the resulting magnetic properties, which involves application of the random anisotropy model to these materials, assumes that the magnetization in the grains is exchange coupled to neighbors, giving a long exchange length compared with the nanometer grain size. We present data for the amorphous precursor, the standard nanophase material, and nanophase material devitrified in an external magnetic field. If σu and σv represent the Gaussian widths of the out-of-plane and in-plane moment direction distributions respectively, we have found that σu=14° and σv=68° for the amorphous precursor, σu=14° and σv=92° for the standard nanophase material, and σu=22° and σv=79° for a magnetic field aligned specimen. We interpret these data as demonstrating that standard devitrification does result in grains with a wide spread of moment direct ions over the volume sampled by this technique, even allowing for exchange coupling. These results and the implications for macroscopic magnetic properties such as anisotropy will be discussed.

Biexcitons in unbalanced double layers in quantizing magnetic fields

Correlations of two electrons and two holes are studied in unbalanced double layers in strong magnetic fields using a variational method. The ground state of an electron-hole pair (exciton) in quantized cyclotron orbits possesses an in-plane electric dipole moment, when an electron and a hole are in different Landau orbits with different radii. The resulting attractive interactions between excitons creates the possibility of novel biexciton states.

Phosphorescence and fluorescence characterization of fluorescein derivatives immobilized in various polymer matrices

The phosphorescence quantum yield, zero-time anisotropy, and lifetime are the three factors determining the suitability of a phosphorescent dye for rotational diffusion experiments. Furthermore, knowledge of the absolute orientation of the phosphorescence dipole moment in the molecular frame is a prerequisite for a quantitative analysis of time-resolved phosphorescence anisotropy (TPA) measurements in orientationally anisotropic systems. These factors have been characterized for four dye molecules, consisting of a fluorescein core with two or four substituted heavy-atoms (iodine and bromine). The characterization was performed by a combination of spectral and time-resolved phosphorescence and fluorescence measurements on dye molecules embedded in immobilizing polymer matrices. A quantitative criterion was found for the time-region where to use which dye, as well as for the dye concentrations to be used. For the latter criterion the effect of Forster radiationless energy transfer on the phosphorescence anisotropy was treated explicitly. The phosphorescence dipole moment was found to be tilted somewhat out of the molecular plane, and aligned more towards the in-plane fluorescence dipole moment than to the in-plane S1←S0 absorption dipole moment. The results for the four fluorescein derivatives indicate that the effect of the spin-orbital coupling is to pull the in-plane component of the phosphorescence dipole moment towards the fluorescence dipole moment, causing an increase of the phosphorescence quantum yield. This effect is primarily influenced by the Z-number of the substituted heavy atoms. The number of substituted heavy atoms plays a less important role.

Magnetic ordering of TbFe 4Al 8 studied by neutron diffraction.I

The structure and magnetic ordering of the tetragonal TbFe 4Al 8 compound were studied by neutron diffraction at temperatures between 1.5 and 170 K. The structure refinement in the paramagnetic state confirms the preference of the Fe atoms for the 8(f) positions. Magnetic reflections are only discernable below 110 K. The magnetic ordering is described by two wave vectors: q 1=0 , and q 2=(q x, q x, 0) , the latter having a temperature-dependent length. The ordering associated with these two wave vectors occurs simultaneously below 110 K. In the high-temperature range 40–110 K the best model obtained by refining neutron difference diagrams leads for the ordering associated with q 1=0 to exclusively Tb ferromagnetic contributions with moments in the basal plane. For the ordering associated with q 2=( q x, q x, 0 ) it leads to a cycloid spiral structure comprising Tb and Fe contributions. The moments of both sublattices rotate within the plane of the wave vector (0 0 1). The value of q x below 8 K is 0.125(1) r.l.u. Symmetry analysis shows that the Fe site splits into two independent sets (orbits) under the action of the in-plane wave vector q 2=( q x, q x, 0 ). Various models are discussed. For the cycloid spiral, within the 3 σ limit, the phases of the Fe moments of both orbits are zero. The high-temperature structure is a distorted cycloid with elliptical envelope for the Tb sublattice which below 40 K induces a distortion to the Fe cycloid spiral because of the increasing in-plane magnetic field of the in-plane ferromagnetic Tb moment. Below 40 K the q 1=0 structure comprises ferromagnetic Tb as well as antiferromagnetic Fe contributions in the basal plane.

Mechanical response of linear viscoelastic composite laminates incorporating non-isothermal physical aging effects

This paper presents a method of predicting the mechanical response of composite laminates including the effects of linear viscoelasticity and physical aging. Effective-time theory has been used to characterize the physical aging behavior of each linear viscoelastic lamina. In accordance with experimental findings, the aging behavior of each lamina is allowed to differ in the shear and transverse directions. The mechanical loading is restricted to the linear range, which decouples the aging and load behavior. A recursive algorithm has been used to solve the hereditary convolution integral that governs the response of each ply. Classical thin-laminate theory is then used to assemble the individual ply response equations and determine the overall laminate response to general in-plane force and moment loading. The method automatically recovers the ply-level stresses and strains, which are often critical to strength and durability predictions. The model can use either lamina compliance or modulus properties as its basis. Several illustrative examples of long-term laminate response to variable loading are presented and the impact of physical aging is explored. It is shown that for multidirectional laminates, the stiffness of the lamina in the fiber directions can allow simplifications of the model.

Molecular dynamics simulation of domain formation in Langmuir monolayers of molecules with dipole moments

A two-dimensional molecular dynamics model of dimers and monomers with in-plane and off-plane dipole moments is set up in order to test the importance of different anisotropic forces on the creations of pinned labyrinthine-like domains, observed in monolayers. The model is designed especially in such a way as to simulate the domain growth in Langmuir monolayers of diglycerides or phospholipids. The simulations show that in-plane dipole moments only have a minor impact on the domain growth, whereas the off-plane dipole moments inhibit the domain formation. The dimers align for big values of the off-plane dipole moment and maintain in a pinned, non-equilibrium conformation. For smaller values of the off-plane dipole moments the mean size of the phases grow algebraically, R(t) = at n ; but slower than in the case of no dipole moment. This behaviour is explained by that the created interfaces constitute a strong and repulsive field which slows down the phase separation.

Reorientation of Spin Density Waves in Cr(001) Films Induced by Fe(001) Cap Layers

Proximity effects of 20 \AA{} Fe layers on the spin density waves (SDWs) in epitaxial Cr(001) films are revealed by neutron scattering. Unlike in bulk Cr we observe a SDW with its wave vector $\mathbf{Q}$ pointing along only one ${100}$ direction which depends dramatically on the film thickness ${t}_{\mathrm{Cr}}$. For ${t}_{\mathrm{Cr}}<250\AA{}$ the SDW propagates out of plane with the spins in the film plane. For ${t}_{\mathrm{Cr}}>1000\AA{}$ the SDW propagates in the film plane with the spins out of plane perpendicular to the in-plane Fe moments. This reorientation transition is explained by frustration effects in the antiferromagnetic interaction between Fe and Cr across the Fe/Cr interface due to steps at the interface.

Ordering of a Functional Molecules on a Flat Surface as Evidenced by Scanning Probe Microscopies: The Case of a Di-Alkyl Amino Group

Abstract Our group is interested in exploring how functional molecules (e.g. those composed of organic functional groups that do not necessarily lend themselves to an ordered 2D packing arrangement) can form well-ordered adlayers with functional properties. To this end. we have studied the formation of self assembled structures of 5-(N,N-didecyl-amino)-2.4- pentadienal (DAPDA, Figure 1) deposited on a highly ordered pyrolytic graphite (HOPG) surface. This molecule has two distinctive features that should dramatically affect its ordering on a surface. Neither of these have been systematically explored in ordered adlayers. First, the extended conjugation of the molecule gives it a large in-plane dipole moment as well as a high polarizability. Second, it contains two hydrocarbon tails, only one of which can lie coplanar with the conjugated moiety. Both molecularly resolved monolayer and bilayer structures were found using a combination of scanning tunneling microscopy and tapping mode atomic force microscopies.

Field-induced transverse spin ordering inFeBr2

Weak first-order phase transitions from axial to oblique spin ordering in FeBr2 are evidenced by SQUID magnetometry in axial fields H1(T) above the multicritical point, Hm = 2.4 MA/m, Tm = 4.6 K, and below the antiferro-to-paramagnetic phase line, Hc(T), in agreement with recent specific heat data (Aruga Katori et al., 1996). The ordering of the in-plane moments is probably due to non-diagonal coupling to the longitudinal ones, both of which increase dis-continuously at H1(T) only under an additional symmetry-breaking transverse field.

Stress Concentration Factors in Tubular K-Joints under In-Plane Moment Loading

An extensive parametric study is presented of the distributions of stress concentration factors in tubular K-joints commonly found in offshore platforms. The study covers a comprehensive range of geometric joint parameters for balanced in-plane moment loading. The results of the study were first used to assess two sets of widely used parametric equations, which predict the maximum stress concentration factors on the outer surfaces of the chord and the brace. The new database of finite-element results was then used to develop parametric equations for predicting stress concentration factors at key locations around the intersection on the outer as well as the inner surfaces of the chord. The reliability of the proposed and existing parametric equations was then assessed using an acrylic test joint database and some published test data measured from a steel model. Fracture mechanics fatigue calculations were also performed to demonstrate that the information provided from the proposed equations could be utilized to obtain accurate, and safe, fatigue life estimates.

Neutron diffraction study of the La 1− xY xMn 2Si 2 solid solution (0≤ x≤1)

The La 1− x Y x Mn 2Si 2 compounds (0< x≤1) have been investigated by powder neutron diffraction. For x<0.5, the low temperature magnetic structures are characterized by mixed planes where both ferro- and antiferromagnetic components coexist while for x≥0.5, ferromagnetic Mn planes prevail. The in-plane ferromagnetic component couples ferromagnetically with those of adjacent planes for x<0.2 and antiferromagnetically for x>0.2. The La 0.8Y 0.2Mn 2Si 2 compound displays a F–AF transition as a function of the temperature. The in-plane antiferromagnetic Mn moment components are smaller than those measured in the corresponding germanides. These results are discussed and compared with previous results of the La 1− x Y x Mn 2Ge 2 compounds. The Mn magnetic behaviour is consistent with bibliographic data on NMR experiments and Mössbauer spectroscopy.

Standardized sign conventions and notation for generally loaded foundations

There has recently been increasing research on the classical geotechnical problem of the load-displacement response of rigid shallow foundations under general loading conditions. Most of the published experimental data and mathematical models relate to the problem's two-dimensional version, where a footing of given breadth supports given vertical and horizontal loads and given in-plane moment. Unfortunately, different authors have used different, often conflicting, sign conventions and notations. This note proposes adopting a specific right-handed coordinate system, with the clockwise positive convention, which can be applied consistently to all such problems, and a comprehensive notation for load and displacement components and their normalised dimensionless counterparts. Six other specific recommendations are made.

The vibrational spectrum of acenaphthylene: linear dichroism and ab initio model calculations

Complete infrared linear dichroism spectra were recorded between 50 and 3200 cm −1 of acenaphthylene aligned in stretched polyethylene and polyethylene-d 4 as well as Raman solution spectra. The information obtained from the infrared spectra made it possible to separate the electric dipole allowed transitions into three groups, corresponding to three different excited state symmetries. The separation is possible for the C 2 v symmetric molecule, since the three groups of transitions correspond to three mutually perpendicular transition moment directions, which in the stretched polymer obtain different average alignments. This information makes a safe assignment of all allowed fundamental vibrational transitions, belonging to three of the four C 2 v symmetry classes, possible. Similarly, the Raman spectra permitted an assignment of vibrations belonging to the fourth symmetry class. The assignments were supported by ab initio quantum mechanical modelling calculations at various levels. A comparison of the present assignments with those from recent linear dichroism studies of acenaphthylene aligned in a nematic liquid crystal matrix confirmed most assignments, but also led to new assignments and reassignment of several transitions. This was possible because of the additional information that becomes available in the stretched polyethylene method, which provide an excellent separation of the excited state symmetries corresponding to the two in-plane transition moment directions.

Three-dimensional infinite order sudden quantum theory for indirect photodissociation processes. Application to the photofragment yield spectrum of NOCl in the region of the T1(13A″) ←S(11A′) transition. Fragment rotational distributions and thermal averages

The analytical infinite order sudden (IOS) quantum theory of triatomic photodissociation, developed in paper I, is applied to study the indirect photodissociation of NOCl through a real or virtual intermediate state. The theory uses the IOS approximation for the dynamics in the final dissociative channels and an Airy function approximation for the continuum functions. The transition is taken as polarized in the plane of the molecule; symmetric top wave functions are used for both the initial and intermediate bound states; and simple semiempirical model potentials are employed for each state. The theory provides analytical expressions for the photofragment yield spectrum for producing particular final fragment ro-vibrational states as a function of the photon excitation energy. Computations are made of the photofragment excitation spectrum of NOCl in the region of the T1(13A″) ←S0(11A′) transition for producing the NO fragment in the vibrational states nNO=0, 1, and 2. The computed spectra for the unexcited nNO==0 and excited nNO=2 states are in reasonable agreement with experiment. However, some discrepancies are observed for the singly excited nNO=1 vibrational state, indicating deficiencies in the semiempirical potential energy surface. Computations for two different orientations of the in-plane transition dipole moment produce very similar excitation spectra. Calculations of fragment rotational distributions are performed for high values of the total angular momentum J, a feature that would be very difficult to perform with close-coupled methods. Computations are also made of the thermally averaged rotational energy distributions to simulate the conditions in actual supersonic jet experiments.

Conformational Study of Phospholipids in Crystalline State and Hydrated Bilayers by 13C and 31P CP-MAS NMR

Crystalline forms of the racemic and enantiomerically pure saturated zwitterionic phospholipids, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidyl-N-methylethanolamine (PEM1), and phosphatidyl-N,N-dimethylethanolamine (PEM2) have been investigated using 13C and 31P cross-polarization magic angle spinning (CP-MAS) NMR. The observed spectra indicate two types of packing behavior depending on the optical purity of phospholipids and the structure of a head group. The crystalline lattices of the enantiomerically pure PC, PE, PEM1, and PEM2 contained two conformations, whereas the corresponding racemic phospholipids contained only a single conformational species. On the basis of the known crystal structures of phospholipids, these results can be explained in terms of different ways the various zwitterionic phospholipids achieve packing into lattices with a minimal residual dipole moment. In enantiomerically pure PC and PE, the presence of two conformations, combining one configurational isomer of the diacyl glycerol moiety with two conformational mirror images of the head group, is necessary to eliminate the residual in-plane dipole moment of head groups and still achieve tight packing of the chiral diacylglycerol residue. In racemates, the in-plane dipole moment is eliminated by packing a single conformation into a true centrosymmetric lattice. The hydration of the crystalline phospholipid samples produced significant spectral alterations such as changes in the 13C chemical shifts of the diacylglycerol C2 carbon and carbonyl groups, and 31P NMR signals, suggesting conformational changes. The hydrated bilayers of both racemic and enantiomerically pure dipalmitoyl PC (DPPC) gave rise to identical 13C NMR spectra regardless the phase state, except for the most rigid Lc subgel phase. The invariance of chemical shifts in these gel phases indicated that no major conformational changes occurred during phase transitions of hydrated bilayers of PC. The NMR data presented in this work provide evidence that conformations of phospholipids in the crystalline state are strongly affected by packing forces and the tendency of the head groups to pack in true- or quasi-centrosymmetric lattices. On the other hand, conformations in hydrated bilayers are largely governed by the intrinsic conformational properties of monomeric molecules. The data presented address the problem of the relevance of the X-ray structures of crystalline phospholipids for evaluation of the conformations in the less ordered hydrated bilayers.