Spectral Characterization of the Hamming Graphs

We show that the Hamming graph H(3; q) with diameter three is uniquely determined by its spectrum for q ¸ 36. Moreover, we show that for given integer D ¸ 2, any graph cospectral with the Hamming graph H(D; q) is locally the disjoint union of D copies of the complete graph of size q ¡ 1, for q large enough.Hamming graphs;distance-regular graphs;eigenvalues of graphs

There are only finitely many distance-regular graphs of fixed valency greater than two

In this paper we prove the Bannai–Ito conjecture, namely that there are only finitely many distance-regular graphs of fixed valency greater than two

Mechanical Properties of Dissimilar A356/SAPH440 Lap Joints by the Friction Stir Spot Welding and Self-Piercing Riveting

Aluminum alloy A356-T6 and automotive steel sheet SAPH440 were joined using friction stir spot welding and self-piercing riveting. The maximum tensile shear strength values in weld joints were approximately 3.5 kN at a rotation speed of 500 rpm and plunge depth of 1.0 mm. It was confirmed that the intermetallic compound layer of weld joints below 9.23 m did not exceed the permissible thickness 10 m of Al–Fe joints. The self-piercing riveting joints exhibited maximum tensile- shear strength of 7.9 kN, which was higher than that of the weld joints. However, during the riveting process, cracking appeared in the joint on the aluminum side, which was caused by lack of ductility of cast aluminum. In addition, it was observed that the cracks on the aluminum side were getting larger, as the radius of the lower mold increased.Алюминиевый сплав А356-Т6 и автомобильную листовую сталь SAPH440 соединяли с помощью точечной ротационной сварки трением и самопробивной клепки. Максимальный предел прочности на сдвиг при растяжении для сварных соединений составлял примерно 3,5 кН при скорости вращения 500 об/мин и глубине проникновения 1,0 мм. Доказано, что слой интерметаллидов сварных соединений толщиной менее 9,23 мкм не превышал допустимый уровень в 10 мкм для соединений Al–Fe. Клепаные соединения имели предел прочности 7,9 кН в отличие от сварных соединений. Однако при клепке на алюминии появлялись трещины ввиду низкой пластичности литого материала, при этом трещины подрастали по мере увеличения радиуса нижней формы

Three-Body Halos. II. from Two- to Three-Body Asymptotics

The large distance behavior of weakly bound three-body systems is investigated. The Schr\"{o}dinger equation and the Faddeev equations are reformulated by an expansion in eigenfunctions of the angular part of a corresponding operator. The resulting coupled set of effective radial equations are then derived. Both two- and three-body asymptotic behavior are possible and their relative importance is studied for systems where subsystems may be bound. The system of two nucleons outside a core is studied numerically in detail and the character of possible halo structure is pointed out and investigated.Comment: 16 pages, compressed and uuencoded PosrScript file, IFA-94/3

Two-proton overlap functions in the Jastrow correlation method and cross section of the 16^{16}O(e,e′pp)14(e,e^{\prime}pp)^{14}Cg.s._{\rm g.s.} reaction

Using the relationship between the two-particle overlap functions (TOF's) and the two-body density matrix (TDM), the TOF's for the $^{16}$O$(e,e^{\prime}pp)^{14}$C$_{\rm g.s.}$ reaction are calculated on the basis of a TDM obtained within the Jastrow correlation method. The main contributions of the removal of $^1S_0$ and $^3P_1$ $pp$ pairs from $^{16}$O are considered in the calculation of the cross section of the $^{16}$O$(e,e^{\prime}pp)^{14}$C$_{\rm g.s.}$ reaction using the Jastrow TOF's which include short-range correlations (SRC). The results are compared with the cross sections calculated with different theoretical treatments of the TOF's.Comment: 10 pages, 8 figures, ReVTeX

Andreev reflections in the pseudogap state of cuprate supercondcutors

We propose that, if the pseudogap state in the cuprate superconductors can be described in terms of the phase-incoherent preformed pairs, there should exist Andreev reflection from these pairs even above the superconducting transition temperature, $T_c$. After giving qualitative arguments for this effect, we present more quantitative calculations based on the Bogoliubov--de Gennes equation. Experimental observations of the effects of Andreev reflections above $T_c$---such as an enhanced tunneling conductance below the gap along the copper oxide plane---could provide unambiguous evidence for the preformed pairs in the pseudogap state.Comment: 5 pages, 1 figur

On the self-consistent spin-wave theory of layered Heisenberg magnets

The versions of the self-consistent spin-wave theories (SSWT) of two-dimensional (2D) Heisenberg ferro- and antiferromagnets with a weak interlayer coupling and/or magnetic anisotropy, that are based on the non-linear Dyson-Maleev, Schwinger, and combined boson-pseudofermion representations, are analyzed. Analytical results for the temperature dependences of (sublattice) magnetization and short-range order parameter, and the critical points are obtained. The influence of external magnetic field is considered. Fluctuation corrections to SSWT are calculated within a random-phase approximation which takes into account correctly leading and next-leading logarithmic singularities. These corrections are demonstrated to improve radically the agreement with experimental data on layered perovskites and other systems. Thus an account of these fluctuations provides a quantitative theory of layered magnets.Comment: 46 pages, RevTeX, 7 figure