Nijmegen Model Research Articles

Simulation of Bone Mechanical Adaptation Using Different Mathematical Models: A Comparative Numerical Study

The adaptation of bones to mechanical loads or bone remodeling can be simulated using specific mathematical models in conjunction with the finite element method. There are several theories proposed within the literature for the prediction of the bone behavior under mechanical loads and all have been used successfully, within certain limits of prediction details, but no unanimous acceptance have been reported yet. Within this context, it is important to know the differences and similarities between the results which these theories can produce, in order to improve their interpretation. On the basics of the above observation, the paper presents the comparison between density distributions achieved using three different models of bone remodeling: the original strain energy density equation developed at the University of Nijmegen, the principle of cellular accommodation incorporated into the Nijmegen model and the variant developed at the University of Manchester obtained by adding the quadric term which eliminates the density accumulation at physiologically unrealistic high loads. It is shown, using a suggestive test problem, that the three models generate significantly different results.

Performance of IMPACT, CRASH and Nijmegen models in predicting six month outcome of patients with severe or moderate TBI: an external validation study.

BackgroundExternal validation on different TBI populations is important in order to assess the generalizability of prognostic models to different settings. We aimed to externally validate recently developed models for prediction of six month unfavourable outcome and six month mortality.MethodsThe International Neurotrauma Research Organization – Prehospital dataset (INRO-PH) was collected within an observational study between 2009-2012 in Austria and includes 778 patients with TBI of GCS < = 12. Three sets of prognostic models were externally validated: the IMPACT core and extended models, CRASH basic models and the Nijmegen models developed by Jacobs et al – all for prediction of six month unfavourable outcome and six month mortality. The external validity of the models was assessed by discrimination (Area Under the receiver operating characteristic Curve, AUC) and calibration (calibration statistics and plots).ResultsMedian age in the validation cohort was 50 years and 44% had an admission GSC motor score of 1-3. Six-month mortality was 27%. Mortality could better be predicted (AUCs around 0.85) than unfavourable outcome (AUCs around 0.80). Calibration plots showed that the observed outcomes were systematically better than was predicted for all models considered. The best performance was noted for the original Nijmegen model, but refitting led to similar performance for the IMPACT Extended, CRASH Basic, and Nijmegen models.ConclusionsIn conclusion, all the prognostic models we validated in this study possess good discriminative ability for prediction of six month outcome in patients with moderate or severe TBI but outcomes were systemically better than predicted. After adjustment for this under prediction in locally adapted models, these may well be used for recent TBI patients.

EQUATION OF STATE FOR MASSIVE NEUTRON STARS

Using relativistic Hartree-Fock approximation, we investigate the properties of the neutron-star matter in detail. In the present calculation, we consider not only the tensor coupling of vector mesons to octet baryons and the form factors at interaction vertexes but also the internal (quark) structure change of baryons in dense matter. The relativistic Hartree-Fock calculations are performed in two ways: one is the calculation with the coupling constants determined by SU(6) (quark model) symmetry, the other is with the coupling constants based on SU(3) (flavor) symmetry. For the latter case, we use the latest Nijmegen (ESC08) model. Then, it is very remarkable that the particle composition of the core matter in SU(3) symmetry is completely different from that in SU(6) symmetry. In SU(6) symmetry, all octet baryons appear in the density region below $\sim 1.2$ fm$^{-3}$, while, in the ESC08 model, only the \Xi^- hyperon is produced. Furthermore, the medium modification of the internal baryon structure hardens the equation of state for the core matter. Taking all these effects into account, we can obtain the maximum neutron-star mass which is consistent with the recently observed mass, 1.97 \pm 0.04 M_\sun (PSR J1614-2230). We therefore conclude that the extension from SU(6) symmetry to SU(3) symmetry in the meson-baryon couplings and the internal baryon-structure variation in matter certainly enhance the mass of neutron star. Furthermore, the effects of the form factor at vertex and the Fock contribution including the tensor coupling due to the vector mesons are indispensable to describe the core matter. In particular, the Fock term is very vital in reproducing the preferable value of symmetry energy, a_4 (\simeq 30 - 40 MeV), in nuclear matter.

The(π−,K+)reaction onSi28and theΣ-nucleus potential

We calculate in the impulse approximation the kaon spectrum from the ({pi}{sup -},K{sup +}) reaction on {sup 28}Si. The strength V{sub {sigma}} of the real part of the single particle potential of the {sigma} hyperons produced in the reaction is obtained from the Nijmegen model F of the baryon-baryon interaction, and the strength W{sub {sigma}} of the imaginary (absorptive) part is determined by the {sigma}N cross sections for the {sigma}{lambda} conversion and also for the elastic {sigma}N scattering (this elastic scattering introduces a strong dependence of W{sub {sigma}} on the {sigma} momentum). The momentum dependence of V{sub {sigma}} is also considered. Our calculated inclusive kaon spectrum agrees reasonably with the spectrum measured at KEK. The strengths of the real and absorptive {sigma} potentials used in the present calculation are compatible with these strengths determined in the analyses of {sigma} atoms and of the strangeness exchange reactions.

Σ ATOMS AND NUCLEON DENSITY DISTRIBUTIONS

It is shown that the measured cross section for the Σ production reactions, the observed properties of Σ atoms, and the two-body hyperon-nucleon data indicate that the ΣN interaction is well represented by the Nijmegen model F of the hyperon-nucleon interaction. It is demonstrated how the strong-interaction shifts and widths measured in Σ- Pb atoms may be used to obtain information on the nucleon density distributions in Pb .

Does - - Form a Quasi-Bound State?

We have investigated the possible existence of a quasi-bound state for the Σ-Σ-α system in the framework of Faddeev calculations. We are particularly interested in the state of total iso-spin T = 2, since for an inert α particle there is no strong conversion to Ξ-N-α or Λ-Λ-α possible. A Σ-α optical potential based on Nijmegen model D and original Σ-Σ interactions of the series of Nijmegen potentials NSC97 as well a simulated Gaussian type versions thereof are used. Our investigation of the Σ-Σ-α system leads to a quasi bound state where, depending on the potential parameters, the energy ranges between −1.4 and −2.4 MeV and the level width is less than 0.4 MeV.

Full-coupled channel approach to [formula omitted]s-shell hypernuclear systems

We describe full-coupled-channel ab initio calculations among the octet baryons for S = − 2 s-shell hypernuclei, 4 ΛΛ H, 5 ΛΛ H and 6 ΛΛ He. The wave function includes ΛΛ, ΛΣ, NΞ and ΣΣ channels. Minnesota NN, D 2 ′ YN and Nijmegen model D simulated YY interactions are used. This is the first attempt to explore the few-body problem of the full-coupled channel scheme for A = 4 – 6 , S = − 2 multistrangeness hypernuclear systems. Bound state solutions of the ΛΛ hypernuclei, 4 ΛΛ H, 5 ΛΛ H and 6 ΛΛ He, are obtained.

Implementing clinical ethics in health care institutions: The Nijmegen model

Implementing clinical ethics in health care institutions: The Nijmegen model

Λ-Λ interaction andΛΛ6He

A one-boson exchange (OBE) potential model, based on the Nijmegen model D potential, for the ${}^{1}{S}_{0},$ $S=\ensuremath{-}2$ interaction is analyzed with emphasis on the role of coupling between the \ensuremath{\Lambda}\ensuremath{\Lambda}, $N\ensuremath{\Xi},$ and \ensuremath{\Sigma}\ensuremath{\Sigma} channels. Singlet scalar exchange, an approximation to two-pion exchange, is significant in all channels; surprisingly, the one-pion exchange component is almost negligible. The size of the channel coupling as a function of the overall strength of the OBE model potential is examined. Implications of the analysis for the binding energy of ${}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{6}\mathrm{He}$ are considered; the new experimental datum may suggest a consistency between the extracted \ensuremath{\Lambda}\ensuremath{\Lambda} matrix element and the relation implied by SU(3) among OBE baryon-baryon interactions.

Faddeev–Yakubovsky calculations for light ΛΛ hypernuclei

New Faddeev–Yakubovsky calculations are reported for 6 ΛΛ He and 10 ΛΛ Be in terms of clusters of α's and Λ's, using ΛΛ s-wave potentials motivated by several of the Nijmegen model interactions. The self consistency of the ΛΛ hypernuclear world data for these species is discussed. The newly reported 6 ΛΛ He event is found to be compatible with ΛΛ interaction strengths provided by the Nijmegen soft-core one-boson-exchange model NSC97. Faddeev calculations for 5 ΛΛ H and 5 ΛΛ He suggest that these ΛΛ hypernuclei are stable against emitting Λ's for any (essentially attractive) ΛΛ interaction, whereas calcualtions for 4 ΛΛ H do not allow a clear-cut conclusion whether or not it is particle stable.

Four-body calculation of Λ4H and Λ4He with realistic YN and NN interactions

We carried out four-body calculations of Λ 4H and Λ 4He taking both the 3 N + Λ and 3 N + Σ channels explicity with the use of realistic NN and YN interactions. The Σ-channel component plays an important role in binding energies of the A = 4 hypernuclei though the admixture is approximately 1%. The ΛN - ΣN coupling is found to be of central-force type in the Nijmegen model D and of tensor-force type in the model F.

Widths of Ξ Hypernuclear States

The $\Lambda$ and neutron decay widths of $\Xi$ hypernuclear states, based on calculated $\Xi N \to \lala$ mixing amplitudes, are estimated. The widths which result from using the Nijmegen Model D interaction are sufficiently small, of order 1.5 MeV, that experiments to observe $\Xi$ hypernuclear states using the $(K^-,K^+)$ reaction may be feasible.

A quark-model approach to ΛN and ΣN LS forces with flavor symmetry breaking

The ΛN and ΣN spin-orbit potentials are studied in a quark model which employs the full Fermi-Breit interaction with explicit flavor symmetry breaking through the mass difference of the strange and up-down quarks. Both LS and antisymmetric LS potentials predicted with the quark model are compared to those of the Nijmegen hard-core models and found to be in reasonable agreement with Nijmegen Model F in the intermediate-range region.

G-matrix calculations in finite hypernuclei.

g-matrix calculations have been performed for $_{\mathrm{\ensuremath{\Lambda}}}^{5}\mathrm{He}$, $_{\mathrm{\ensuremath{\Lambda}}}^{17}\mathrm{O}$, and $_{\mathrm{\ensuremath{\Lambda}}}^{41}\mathrm{Ca}$ by solving the \ensuremath{\Lambda}-\ensuremath{\Sigma} coupled channels Bethe-Goldstone equation. The potentials employed were the Nijmegen model D and Nijmegen soft core. Calculations were performed with various choices for the Pauli-forbidden space and the energy denominator. The Nijmegen model D does a reasonable job of reproducing most experimental single-particle energies, but the calculated ground-state binding energies vary smoothly from being underbound in the $_{\mathrm{\ensuremath{\Lambda}}}^{5}\mathrm{He}$ to overbound in $_{\mathrm{\ensuremath{\Lambda}}}^{41}\mathrm{Ca}$. The Nijmegen soft core underbinds all single \ensuremath{\Lambda} states, but gives level spacings which agree with experimental values.

Binding Energies of Double- Hypernuclei and G-Matrix

Binding energies of double-Λ hypernuclei 10ΛΛBe, 13ΛΛB and 6ΛΛHe are calculated on the basis of G-matrix theory in finite nuclei. The core + Λ+ Λ three-body model is adopted and the G-matrix for ΛΛ interaction is treated consistently with the model space. As the bare interaction the Nijmegen model D and model F are used. It is discussed that the consistency of the interaction with the model space is very important to calculate reliably the binding energies. It is shown that if the new event of double-Λ hypernuclei is interpreted as 13ΛΛB, model D reproduces the experimental data very well, whereas model F does not.

Structures of Λ18O and Λ42Ca based on a realistic effective ΛN interaction

The shell model without the nuclear center-of-mass spurious effect is applied to Λ 16,17,18O isotopes, predicting the bunched and dense hypernuclear energy levels. The 42Ca structure is also treated within a simplified model. The (K −, π −) and ( π +, K +) reaction cross sections are calculated at several angles. The realistic ΛN effective interaction derived on the basis of the Nijmegen Model −D is employed and the ΛN J=0 + pairing correlation is found to be repulsive, which should be tested in the study of (K −, π −) and ( π +, K +) excitation spectra leading to, e.g., Λ 18O (or Λ 42Ca).