Recent soft-core baryon–baryon interactions

Recent results obtained with the extended-soft-core (ESC) interactions are presented. In a unified manner the ESC-model describes nucleon–nucleon (NN), hyperon–nucleon (YN), and hyperon–hyperon (YY), using (broken) SU_F(3)-symmetry. In the ESC approach to baryon–baryon (BB) the dynamics is derived from (i) one-boson-exchanges (OBE), (ii) two-meson-exchanges (TME), and (iii) meson-pair-exchanges (MPE). Special features are the inclusion of the axial-vector meson potentials, and a zero in the scalar-meson form-factors. With these ingredients a rather flexible dynamical framework is constructed. Namely, it appeared feasible to keep the parameters of the model rather close to the predictions of the quark-pair-creation model (QPC). This is the case for the meson–baryon coupling constants and the F/(F+D)-ratios as well. The NN, YN, and YY results for this model are rather promising. Here, we report on a recently obtained version, called ESC04. Also, we present the first results with the next version, called ESC06, where we explore the inclusion of the second nonets for the pseudoscalar, vector, and scalar mesons, which have masses approximately in the interval . In the -picture these mesons are the radially excited states, with principal quantum number N=2, of the low lying meson nonets for M1 GeV. This improves the Σ-well-depth considerably.     

Assessment of Blood Hemodynamics by USPIO-Induced R 1 Changes in MRI of Murine Colon Carcinoma

The objective of this study is to assess whether ultrasmall superparamagnetic iron oxide (USPIO)-induced changes of the water proton longitudinal relaxation rate (R ₁) provide a means to assess blood hemodynamics of tumors. Two types of murine colon tumors (C26a and C38) were investigated prior to and following administration of USPIO blood-pool contrast agent with fast R ₁ measurements. In a subpopulation of mice, R ₁ was measured following administration of hydralazine, a well-known blood hemodynamic modifier. USPIO-induced R ₁ increase in C38 tumors (ΔR ₁ = 0.072 ± 0.0081 s⁻¹) was significantly larger than in C26a tumors (ΔR ₁ = 0.032 ± 0.0018 s⁻¹, N = 9, t test, P < 0.001). This was in agreement with the immunohistochemical data that showed higher values of relative vascular area (RVA) in C38 tumors than in C26a tumors (RVA = 0.059 ± 0.015 vs. 0.020 ± 0.011; P < 0.05). Following administration of hydralazine, a decrease in R ₁ value was observed. This was consistent with the vasoconstriction induced by the steal effect mechanism. In conclusion, R ₁ changes induced by USPIO are sensitive to tumor vascular morphology and to blood hemodynamics. Thus, R ₁ measurements following USPIO administration can give novel insight into the effects of blood hemodynamic modifiers, non-invasively and with a high temporal resolution.     

New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.     

Z4-Kerdock Codes, Orthogonal Spreads, and Extremal Euclidean Line-Sets

When m is odd, spreads in an orthogonal vector space of type⁺(2m + 2,2) are related to binary Kerdock codes and extremalline-sets in 2^{m + 1} with prescribed angles. Spreads in a 2m-dimensionalbinary symplectic vector space are related to Kerdock codesover Z₄ and extremal line-sets in with prescribed angles. These connections involve binary, realand complex geometry associated with extraspecial 2-groups.A geometric map from symplectic to orthogonal spreads is shownto induce the Gray map from a corresponding Z₄-Kerdock codeto its binary image. These geometric considerations lead tothe construction, for any odd composite m, of large numbersof Z₄-Kerdock codes. They also produce new Z₄-linear Kerdockand Preparata codes. 1991 Mathematics Subject Classification:primary 94B60; secondary 51M15, 20C99.