Nijmegen Group Research Articles

Onset of the bound states in strange Λ, Ξ-hypernuclei and hyperspherical three-body model calculation for the corresponding double hyperon hypernuclei

In this work, we have explored ground state properties of Be hypernucleus in the light of recent observation of the experiment J-PARC E07 and the onset of stability for Be hypernucleus in the three-body framework using Hyperspherical Harmonics Expansion (HHE) method. An effective core-Y (Y= Λ, Ξ) Woods-Saxon potential with adjustable depth parameter is used to reproduce the observed ground state energy of the two-body subsystem by solving the two-body Schrödinger equation. The core-Y potential so obtained is clubbed with the YY potential model of the Nijmegen group to obtain the observables of the double-hyperon hypernuclei. Computed YY separation energy and YY bond energy are compared with the data available in the literature.

Transport Coefficients of Hyperonic Neutron Star Cores

We consider transport properties of the hypernuclear matter in neutron star cores. In particular, we calculate the thermal conductivity, the shear viscosity, and the momentum transfer rates for npΣ−Λeμ composition of dense matter in β–equilibrium for baryon number densities in the range 0.1–1 fm−3. The calculations are based on baryon interactions treated within the framework of the non-relativistic Brueckner-Hartree-Fock theory. Bare nucleon-nucleon (NN) interactions are described by the Argonne v18 phenomenological potential supplemented with the Urbana IX three-nucleon force. Nucleon-hyperon (NY) and hyperon-hyperon (YY) interactions are based on the NSC97e and NSC97a models of the Nijmegen group. We find that the baryon contribution to transport coefficients is dominated by the neutron one as in the case of neutron star cores containing only nucleons. In particular, we find that neutrons dominate the total thermal conductivity over the whole range of densities explored and that, due to the onset of Σ− which leads to the deleptonization of the neutron star core, they dominate also the shear viscosity in the high density region, in contrast with the pure nucleonic case where the lepton contribution is always the dominant one.

Analytical forms of the deuteron wave function for Nijmegen group potentials and polarization characteristics of A(d,d′)X reactions

Polarization observables of the [Formula: see text] reactions have been calculated according to the received coefficients of the analytical form for deuteron wave function (DWF) in coordinate space for the nucleon–nucleon Nijmegen group potentials (NijmI, NijmII and Nijm93). The obtained values of tensor [Formula: see text] and vector [Formula: see text] analyzing powers have been compared with the published experimental data at [Formula: see text]-scaling for the inelastic scattering of deuterons on hydrogen, carbon and beryllium. Theoretical values of tensor–tensor [Formula: see text] and vector–vector [Formula: see text] polarization transfers have also been evaluated in the plane-wave impulse approximation.

Analytical forms of the wave function and the asymmetry of the polarization characteristics of the deuteron

The basic analytical forms of the deuteron wave function (DWF) in a coordinate representation have been reviewed. The asymptotic behaviour of DWF near the origin of coordinates has been analyzed. New analytical forms of DWF as a product of the exponential function r^n and the sum of the exponential terms Ai*exp(-ai*r3) are applied for the calculation of the polarization characteristics of the deuteron. Numerical calculations have been done for realistic phenomenological potential of Nijmegen groups, Reid93. In the paper, the results of the angular asymmetry for deuteron vector t10, t11 and tensor t20, t21, t22 polarizations are described. Along with the angular asymmetry, the momentum asymmetry for deuteron vector t1i polarizations is described too. The influence of DWF approximation in a coordinate representation on the subsequent results of the calculations of the tensor polarization t20 is investigated. A comparison of values t20 is made at 70 degree if to apply four different DWF approximations to the same NN-potential Reid93. When the received theoretical values t20 are compared with the experimental data of world collaborations and reviews, a good coordination for the area of values momentum p=1-4fm-1 is observed. Using the method of invariant amplitude, spin observables in backward elastic dp-scattering-tensor analyzing power T20 and polarization transfer K0 have been calculated. The values of K0 and correlation K0-T20 are compared with experimental data. In a wide range of momentums p and scattering angles, the asymmetry for the tensor analyzing power T20 and T22 has been presented, which characterizes the photoproduction of negative pi- meson from deuteron in reaction g(d, pi-)pp. A symmetry of values T20 and T22 concerning a 90 angle is observed. The ratio R for the vector Px and tensor Pxz polarizations is characterized by angular asymmetry....

Single-particle spectral function of the Λ hyperon in finite nuclei

The spectral function of the Λ hyperon in finite nuclei is calculated from the corresponding Λ self-energy, which is constructed within a perturbative many-body approach using some of the hyperon–nucleon interactions of the Jülich and Nijmegen groups. Binding energies, wave functions and disoccupation numbers of different single-particle states are obtained for various hypernuclei from HeΛ5 to PbΛ209. The agreement between the calculated binding energies and experimental data is qualitatively good. The small spin–orbit splitting of the p-,d-,f- and g-wave states is confirmed. The discrete and the continuum contributions of the single-Λ spectral function are computed. Their appearance is qualitatively similar to that of the nucleons. The Z-factor, that measures the importance of correlations, is also calculated. Our results show that its value is relatively large, indicating that the Λ hyperon is less correlated than nucleons. This is in agreement with the results obtained by other authors for the correlations of the Λ in infinite nuclear matter. The disoccupation numbers are obtained by integrating the spectral function over the energy. Our results show that the discrete contribution to the disoccupation number decreases when increasing the momentum of the Λ. This indicates that, in the production reactions of hypernuclei, the Λ hyperon is mostly formed in a quasi-free state.

The phase-functions method and scalar amplitude of nucleon–nucleon scattering

A known phase-functions method (PFM) has been considered for calculation of a single-channel nucleon–nucleon scattering. The following partial waves of a nucleon–nucleon scattering have been considered using the phase shifts by PFM: 1S0-, 3P0-, 3P1-, 1D2-, 3F3-states for nn-scattering, 1S0-, 3P0-, 3P1-, 1D2-states for pp-scattering and 1S0-, 1P1-, 3P0-, 3P1-, 1D2-, 3D2-states for np-scattering. The calculations have been carried out using phenomenological nucleon–nucleon Nijmegen group potentials (NijmI, NijmII, Nijm93 and Reid93) and Argonne v18 potential. The scalar scattering amplitude has been calculated using the obtained phase shifts. Our results are not much different from those obtained by using the known phase shifts published in other papers. The difference between calculations depending on a computational method of phase shifts makes: for real (imaginary) parts 0.14–4.36% (0.16–4.05%) for NijmI. 0.02–4.79% (0.08–3.88%) for NijmII. 0.01–5.49% (0.01–4.14%) for Reid93 and 0.01–5.11% (0.01–2.40%) for Argonne v18 potentials.

The phase-functions method and full cross-section of nucleon–nucleon scattering

A known phase-functions method (PFM) has been considered for calculation of a single-channel nucleon–nucleon scattering. The following phase shifts of a nucleon–nucleon scattering have been calculated numerically using the phase-functions method:[Formula: see text]-, [Formula: see text]-, [Formula: see text]-, [Formula: see text]-, [Formula: see text]-states), [Formula: see text]-, [Formula: see text]-, [Formula: see text]-, [Formula: see text]-states) and [Formula: see text]-, [Formula: see text]-, [Formula: see text]-, [Formula: see text]-, [Formula: see text]-, [Formula: see text]-states). The calculations have been carried out using realistic nucleon–nucleon Nijmegen group potentials (NijmI, NijmII and Reid93) and Argonne v18 potential. Numerically calculated phase shifts are in good agreement with the results obtained with the other methods. The full cross-section has been calculated using the obtained phase shifts. Our results are not very different from those obtained by using the known phases published in the literature. The difference between calculations depending on a computational method of scattering phases makes: 0.2–6.3% for [Formula: see text]- and 0.1–5.3% for [Formula: see text]-scatterings (for NijmI, NijmII), 0.1–4.1% for [Formula: see text]- and 0.1–0.4% for [Formula: see text]-scatterings (Reid93), not more than 4.5% (Argonne v18).

The Triton from the Reid93 Potential in the UPA

The unitary pole approximation (UPA) provides an effective means to construct a rank one separable potential for calculations in which one requires a simple representation of the deuteron and/or triton ground-state wave function. By construction the deuteron wave function and the 1S0 anti-bound state wave function of the original potential are reproduced. We report results for the corresponding triton ground state. We choose to utilize the realistic Reid93 potential for this purpose. The Reid93 potential, generated by the Nijmegen group, is a Reid-like, partial-wave local potential that produces a χ2 representation of the nucleon–nucleon (NN) scattering data that is as precise as an NN partial-wave analysis. Results for properties of 2H and 3H from the UPA are compared with those for the original potential. To further illustrate the precision of the method, results for properties of the deuteron and triton from the UPA are also compared with those for the original Reid68 potential.

Nasolabial Esthetics in Children With Complete Unilateral Cleft Lip and Palate After 1- Versus 3-Stage Treatment Protocols

Facial esthetics play an important role in social interactions. However, children with a repaired complete unilateral cleft lip and palate usually show some disfigurement of the nasolabial area. To date, few studies have assessed the nasolabial appearance after different treatment protocols. The aim of the present study was to compare the nasolabial esthetics after 1- and 3-stage treatment protocols. Four components of the nasolabial appearance (nasal form, nasal deviation, mucocutaneous junction, and profile view) were assessed by 4 raters in 108 consecutively treated children who had undergone either 1-stage closure (Warsaw group, 41 boys and 19 girls, mean age 10.8 years, SD 2.0) or 3-stage (Nijmegen group, 30 boys and 18 girls, mean age 8.9 years, SD 0.7). A 5-grade esthetic index of Asher-McDade was used, in which grade 1 indicates the most esthetic and grade 5 the least esthetic outcome. The nasal form was judged the least esthetic in both groups and graded 3.1 (SD 1.1) and 3.2 (SD 1.1). The nasal deviation, mucocutaneous junction, and profile view were scored from 2.1 (SD 0.8) to 2.3 (SD 1.0) in both groups. The treatment outcome after the Warsaw and Nijmegen protocols was comparable. Neither overall nor any of the 4 components of the nasolabial appearance showed intercenter differences (P > .1). The nasolabial appearance after the Warsaw (1-stage) and Nijmegen (3-stage) protocols was comparable. The technique of lip repair (triangular flap in Warsaw and Millard rotation advancement in Nijmegen) gave comparable results for the esthetics of the nasolabial area.

Analysis of experimental data on neutron-proton scattering in the energy range between 0 and 150 keV

Experimental data on neutron-proton scattering in the energy range between 0 and 150 keV are analyzed by using various sets of effective-range parameters. It is shown that, in contrast to the parameters corresponding to the phase shifts of a Nijmegen group, the parameters corresponding to the experimental phase shifts reported by a group from George Washington University (GWU group) lead to very good agreement between the calculated cross sections and their experimental counterparts in the energy region under consideration. On the basis of the experimental value of the cross section for neutron—proton scattering at an energy of 2 keV, the total cross section for neutron-proton scattering at zero energy was found to be σ0 = 20.428(16) b, which is in very good agreement with a value of σ0 = 20.423(9) b, which was obtained as the weighted mean of the cross sections presented by Houke and Hurst. It is shown that, in the energy region around several tens of keV units, the effective-range parameters matched with Dilg’s cross-section value of σ0 = 20.491(14) b lead to calculated cross sections whose values are in excess of their experimental counterparts.

Stability of the s- and p-shell α cluster hypernuclei with strangeness S = −2 to −4

The energies of the s- and p-shell hypernuclei in the α cluster model with strangeness content S = −1 to −4 are calculated in a variational Monte Carlo framework. Two types of Λα and Ξ0α potentials and a variety of three-range Gaussian YY potentials simulated from models of the Nijmegen group are used. The Woods–Saxon Ξ0α potential with central depths −24.0 and −14.0 MeV is considered. Unlike the earlier Faddeev–Yakubovsky results, the system He is as strongly bound for the Isle Ξ0α potential as for the Woods–Saxon shape. The hypernuclei of the 8Be core with strange baryons Ξ0 and ΛΛΞ0 are also found to be stable, but the latter one is overbound without dispersive Λαα force. The strong conversion makes S = −3 hypernucleus Be unstable and no definitive conclusion about the stability of He can be drawn. The attractive three-body ααα force is required to fit the ground-state energy and root-mean-square radius of 12C for a αα potential, similar to earlier works. The BΛ of 13ΛC is not consistent with the data without Λαα dispersive force. The system C has been found to be stable.

Meson-exchange description of hadronic systems: Recent developments

I review recent developments in the description of hadronic systems within the conventional meson-exchange picture. In particular, I discuss the new hyperon-nucleon models published recently by the Jülich and Nijmegen groups. I report also results for the πN interaction at intermediate energies, obtained by the Jülich group within a meson-exchange model and in a coupled-channels approach.

Determination of low-energy parameters of neutron-proton scattering on the basis of modern experimental data from partial-wave analyses

The triplet and singlet low-energy parameters in the effective-range expansion for neutron-proton scattering are determined by using the latest experimental data on respective phase shifts from the SAID nucleon-nucleon database. The results differ markedly from the analogous parameters obtained on the basis of the phase shifts of the Nijmegen group and contradict the parameter values that are presently used as experimental ones. The values found with the aid of the phase shifts from the SAID nucleon-nucleon database for the total cross section for the scattering of zero-energy neutrons by protons, σ 0 = 20.426 b, and the neutron-proton coherent scattering length, f = −3.755 fm, agree perfectly with experimental cross-section values obtained by Houk, σ 0 = 20.436 ± 0.023 b, and experimental scattering-length values obtained by Houk and Wilson, f = −3.756 ± 0.009 fm, but they contradict cross-section values of σ 0 = 20.491 ± 0.014 b according to Dilg and coherent-scattering-length values of f = −3.7409 ± 0.0011 fm according to Koester and Nistler.

Five-year Follow-up of Socket Movements and Loosening After Revision With Impacted Morselized Allograft Bone and Cement: A Radiostereometric and Radiographic Analysis

In 1999, we reported on the 2-year results of a series of 21 first-time socket revisions using impacted morselized allograft bone. Seven still migrated between 1.5 and 2 years. Seventeen remained for the current 5-year follow-up. No socket had been rerevised. Five sockets showed signs of radiographic loosening. These 5 cases also exhibited radiographic signs of allograft resorption as well as high rates of socket migration and rotation as measured by radiostereometric analysis. Of the 6 remaining sockets that had migrated between 1.5 and 2 years, 3 stabilized and 3 were among those with signs of radiographic loosening. Fifteen patients (15 hips) revealed pain reduction at the 5-year follow-up. Three had slight pain on walking that disappeared immediately at rest (pain score 4). All the others revealed either no pain (pain score 6) or slight pain that disappeared with activity (pain score 5). No pattern of early socket migration according to radiostereometric analysis could be identified, predicting later socket migration or loosening. The rate of cases with signs of radiographic loosening (29%, 5/17) was comparable to that reported by the Nijmegen group but the follow-up was shorter in the current study. The rate of cases with signs of radiographic loosening was comparable to both conventionally cemented socket revisions and cementless revisions. The future will show if further sockets loosen and if the loose sockets up to date will end up in rerevisions.

On triplet low-energy parameters of nucleon-nucleon scattering

Triplet low-energy parameters of neutron-proton scattering, including high-order shape parameters, are calculated on the basis of approximating the effective-range function k cot δ t by polynomials and rational functions with the aid of the latest experimental data on phase shifts from the SAID nucleon-nucleon database. With the resulting values of the low-energy parameters, a good description of phase shifts over a broad energy interval is obtained by using the effective-range expansion featuring a small number of terms. The properties of the deuteron that were calculated on the basis of the values found for the triplet low-energy parameters of scattering agree very well with experimental values. The triplet low-energy parameters and the properties of the deuteron that were obtained here by using present-day data from the SAID database differ markedly from the analogous results obtained for data of the Nijmegen group. Possible reasons behind this discrepancy are discussed. Highly precise new approximate formulas for determining the shape parameter v 2 are proposed and are shown to be efficient in calculations. The effective-range expansion for the D wave is considered, and preliminary results of calculations of low-energy scattering parameters for this case are obtained.

Comparison of Facial Morphology in Two Populations with Complete Unilateral Cleft Lip and Palate from Two Different Centers

To identify differences in craniofacial morphology of two populations with a history of complete unilateral cleft lip and palate (UCLP) treated under different protocols. Retrospective longitudinal cohort study. Cleft Center of the University of Nijmegen, The Netherlands, and the Cleft Lip and Palate Program, The Hospital for Sick Children, Toronto, Canada. Nineteen patients (16 male, 3 female) from Nijmegen and 19 patients (16 male, 3 female) from Toronto. Each patient was matched for sex and age with a patient from the other group. The mean ages at which lateral cephalometric radiographs were available for the Nijmegen group were 5.5, 9.9, and 18.3 years, while for the Toronto group these were available at mean ages of 5.3, 10.1, and 18.3 years, respectively. Eighteen patients from the Nijmegen group received an alveolar bone graft at a mean age of 9.5 years (range 8.2 to 13.5 years). None of the patients from Toronto received bone grafts. Eighteen cephalometric variables per radiograph were calculated at each time registration, using Dentofacial Planner cephalometric software. Statistical evaluation was performed with repeated-measures analysis of variance. No differences were seen in the maxillary measurements. The patients in the Toronto group had significantly larger mandibles at all three time registrations. The Nijmegen and Toronto protocols resulted in similar maxillary projections in patients with UCLP. Comparison of data from other studies supports the contention that the larger profile convexity of the Nijmegen group is a reflection of a genetically determined smaller mandibular size in the Dutch population.

Glutathione S-transferase T1 null polymorphism and the risk for head and neck cancer

Conclusions. Inter-regional differences in the distribution of genetic polymorphisms in glutathione S-transferases (GSTs) exist, which may have significant effect on the outcome of other GST polymorphism studies. The GSTT1 null genotype appears to be involved in modulation of the risk for head and neck squamous cell carcinoma (HNSCC). Background. The risk of HNSCC is strongly associated with smoking of cigarettes and consumption of alcohol, resulting in a load of toxins/carcinogens. Detoxification of such exogenous harmful compounds often occurs by phase II enzymes such as GSTs. Proper functioning of these enzymes may be deficient due to the presence of particular genetic polymorphisms in these GSTs, and this may increase the risk for HNSCC. We compared the GSTT1, GSTM1 and GSTP1 genotype frequencies in two groups of healthy blood donors, collected from different but adjacent regions in the Netherlands, with those of a group of patients with HNSCC. Subjects and methods. The GSTM1,GSTT1 and GSTP1 genotype frequencies in two Dutch Caucasian control populations (n=207 and n=285) from different but adjacent geographical regions (Maastricht and Nijmegen; distance, 125 km) and 185 patients with HNSCC from the Maastricht region were determined by PCR-related methods. Results. For the occurrence of the GSTT1 null genotype we found a significant difference (p=0.003) between the two control groups (20.3% vs 33.0% null genotype in the Nijmegen and Maastricht control groups, respectively). Since the HNSCC patients were collected from the Maastricht area, comparison with the Maastricht controls reveals a significant difference for GSTT1 null rates, which are lower in patients vs controls (OR = 0.49, CI = 0.32–0.76).

Formula omitted] elastic scattering cross sections in the region of [formula omitted] with a scintillating fiber active target

A hyperon–nucleon scattering experiment, KEK-PS E289, was carried out at the K2 beam line in KEK. We adopted a scintillating fiber active target as a hydrogen target for hyperon production and subsequent hyperon–nucleon scattering. We collected more data than in a previous experiment, KEK-PS E251. In this paper, the differential cross sections for Σ + p elastic scattering in the incident momentum range from 350 to 750 MeV/ c are presented and compared with theoretical predictions from the Nijmegen group (Nijmegen Soft Core 97) and the Kyoto–Niigata group (RGM-FSS and fss2).

Effectiveness of effective field theory in peripheral nucleon-nucleon scattering

Peripheral nucleon-nucleon scattering is analyzed in the framework of an effective field theory. Distorted-wave methods are used to remove the effects of one-pion exchange. Two-pion exchange and recoil corrections to one-pion exchange are then subtracted pertubatively. This removes all contributions up to order ${Q}^{3}$ in the chiral expansion. We have applied this to the $^{1}D_{2}$, $^{1}F_{3}$, and $^{1}G_{4}$ waves, using phase shifts from various partial-wave analyses by the Nijmegen group. In regions where these analyses agree we find no evidence for a breakdown of the chiral expansion. One of the terms in the effective short-range potential, the leading one in the $^{1}D_{2}$ channel, is larger than might be expected, but in general these terms have momentum scales of about $300--400\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. We also see hints of isospin breaking in the $\ensuremath{\pi}N$ couplings.

Superfluidity ofΣ−hyperons inβ-stable neutron star matter

In this work we evaluate the $^1S_0$ energy gap of $\Sigma^-$ hyperons in $\beta$-stable neutron star matter. We solve the BCS gap equation for an effective $\Sigma^-\Sigma^-$ pairing interaction derived from the most recent parametrization of the hyperon-hyperon interaction constructed by the Nijmegen group. We find that the $\Sigma^-$ hyperons are in a $^1S_0$ superfluid state in the density region $\sim 0.27-0.7$ fm$^{-3}$, with a maximum energy gap of order 8 MeV at a total baryon number density of $\sim 0.37$ fm$^{-3}$ and a $\Sigma^-$ fraction of about 8%. We examine the implications on neutron star cooling.