132 research outputs found
Comparison of Bond in Roll-bonded and Adhesively Bonded Aluminums
Lap-shear and peel test measurements of bond strength have been carried out as part of an investigation of roll bonding of 2024 and 7075 aluminum alloys. Shear strengths of the bonded material in the F temper are in the range of 14 to 16 ksi. Corresponding peel strengths are 120 to 130 lb/inch. These values, which are three to five times those reported in the literature for adhesively bonded 2024 and 7075, are a result of the true metallurgical bond achieved. The effects of heat-treating the bonded material are described and the improvements in bond strength discussed relative to the shear strength of the parent material. The significance of the findings for aerospace applications is discussed
Nonnegative Minimum Biased Quadratic Estimation in the Linear Regression Models
AbstractIn the paper the problem of nonnegative estimation of β′Hβ + hσ2 in the linear model E(y) = Xβ, Var(y)= σ2I is discussed. Here H is a nonnegative definite matrix while h is a nonnegative scalar. An iterative procedure for the nonnegative minimum biased quadratic estimator is described. Moreover, in the case that H and X′X commute, an explicit formula for this estimator is given. Admissibility of the estimator is proved. The results are applied to nonnegative estimation of the total mean squared error of a linear biased estimator
Symmetric Teleparallel Gauss-Bonnet Gravity and its Extensions
General Teleparallel theories assume that curvature is vanishing in which
case gravity can be solely represented by torsion and/or nonmetricity. Using
differential form language, we express the Riemannian Gauss-Bonnet invariant
concisely in terms of two General Teleparallel Gauss-Bonnet invariants, a bulk
and a boundary one. Both terms are boundary terms in four dimensions. We also
find that the split is not unique and present two possible alternatives. In the
absence of nonmetricity our expressions coincide with the well-known Metric
Teleparallel Gauss-Bonnet invariants for one of the splits. Next, we focus on
the description where only nonmetricity is present and show some examples in
different spacetimes. We finish our discussion by formulating novel modified
Symmetric Teleparallel theories constructed with our new scalars.Comment: 21 page
Depth-dependent ordering, two-length-scale phenomena and crossover behavior in a crystal featuring a skin-layer with defects
Structural defects in a crystal are responsible for the "two length-scale"
behavior, in which a sharp central peak is superimposed over a broad peak in
critical diffuse X-ray scattering. We have previously measured the scaling
behavior of the central peak by scattering from a near-surface region of a V2H
crystal, which has a first-order transition in the bulk. As the temperature is
lowered toward the critical temperature, a crossover in critical behavior is
seen, with the temperature range nearest to the critical point being
characterized by mean field exponents. Near the transition, a small two-phase
coexistence region is observed. The values of transition and crossover
temperatures decay with depth. An explanation of these experimental results is
here proposed by means of a theory in which edge dislocations in the
near-surface region occur in walls oriented in the two directions normal to the
surface. The strain caused by the dislocation lines causes the ordering in the
crystal to occur as growth of roughly cylindrically shaped regions. After the
regions have reached a certain size, the crossover in the critical behavior
occurs, and mean field behavior prevails. At a still lower temperature, the
rest of the material between the cylindrical regions orders via a weak
first-order transition.Comment: 12 pages, 8 figure
Proton Collimation in TeV Colliders
In high intensity proton colliders with superconducting magnets, quenches induced by beam losses are unavoidable in the absence of a collimation system. We will show that a single stage system cannot suffice at TeV energies. We will discuss a two-stage collimation system at first as an optical system then considering true scattering in collimator jaws. Expected performance at LHC are presented. then finally, we present the preliminary measurements done at 120 GeV/c in the SPS ring with a simplified three stage collimation system
On linear combinations of generalized involutive matrices
Let X(dagger) denotes the Moore-Penrose pseudoinverse of a matrix X. We study a number of situations when (aA + bB)(dagger) = aA + bB provided a, b is an element of C\{0} and A, B are n x n complex matrices such that A(dagger) = A and B(dagger) = B. (C) 2011 Taylor & FrancisLiu, X.; Wu, L.; Benítez López, J. (2011). On linear combinations of generalized involutive matrices. Linear and Multilinear Algebra. 59(11):1221-1236. doi:10.1080/03081087.2010.496111S12211236591
European Multicenter Study for the Evaluation of a Dual-Layer Flow-Diverting Stent for Treatment of Wide-Neck Intracranial Aneurysms: The European Flow-Redirection Intraluminal Device Study
BACKGROUND AND PURPOSE: Endoluminal reconstruction with flow-diverting stents represents a widely accepted technique for the treatment of complex intracranial aneurysms. This European registry study analyzed the initial experience of 15 neurovascular centers with the Flow-Redirection Intraluminal Device (FRED) system. MATERIALS AND METHODS: Consecutive patients with intracranial aneurysms treated with the FRED between February 2012 and March 2015 were retrospectively reviewed. Complications and adverse events, transient and permanent morbidity, mortality, and occlusion rates were evaluated. RESULTS: During the defined study period, 579 aneurysms in 531 patients (median age, 54 years;range, 13-86 years) were treated with the FRED. Seven percent of patients were treated in the acute phase (3 days) of aneurysm rupture. The median aneurysm size was 7.6 mm (range, 1-36.6 mm), and the median neck size 4.5 mm (range, 1-30 mm). Angiographic follow-up of >3 months was available for 516 (89.1%) aneurysms. There was progressive occlusion witnessed with time, with complete occlusion in 18 (20%) aneurysms followed for up to 90 14 days, 141 (82.5%) for 180 +/- 20 days, 116 (91.3%) for 1 year +/- 24 days, and 122 (95.3%) aneurysms followed for >1 year. Transient and permanent morbidity occurred in 3.2% and 0.8% of procedures, respectively. The overall mortality rate was 1.5%. CONCLUSIONS: This retrospective study in real-world patients demonstrated the safety and efficacy of the FRED for the treatment of intracranial aneurysms. In most cases, treatment with a single FRED resulted in complete angiographic occlusion at 1 year
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