Neutron reactions in astrophysics Reifarth, R; Lederer, C; Käppeler, F
Journal of physics. G, Nuclear and particle physics,
05/2014, Letnik:
41, Številka:
5
Journal Article
Recenzirano
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The quest for the origin of matter in the Universe had been the subject of philosophical and theological debates over the history of mankind, but quantitative answers could be found only by the ...scientific achievements of the last century. A first important step on this way was the development of spectral analysis by Kirchhoff and Bunsen in the middle of the 19th century, which provided first insight in the chemical composition of the sun and the stars. The energy source of the stars and the related processes of nucleosynthesis, however, could be revealed only with the discoveries of nuclear physics. A final break-through came eventually with the compilation of elemental and isotopic abundances in the solar system, which reflect the various nucleosynthetic processes in detail. This review focuses on the mass region above iron, where the formation of the elements is dominated by neutron capture, mainly in the slow (s) and rapid (r) processes. Following a brief historic account and a sketch of the relevant astrophysical models, emphasis is put on the nuclear physics input, where status and perspectives of experimental approaches are presented in some detail, complemented by the indispensable role of theory.
ABSTRACT
The origin of the proton-rich trans-iron isotopes in the Solar system is still uncertain. Single-degenerate thermonuclear supernovae (SNIa) with n-capture nucleosynthesis seeds assembled in ...the external layers of the progenitor’s rapidly accreting white dwarf (RAWD) phase may produce these isotopes. We calculate the stellar structure of the accretion phase of five white dwarf (WD) models with initial masses ≥ 0.85 $\, \mathrm{M}_\odot$ using the stellar code mesa The near-surface layers of the 1, 1.26, 1.32 and 1.38 $\, \mathrm{M}_\odot$ models are most representative of the regions in which the bulk of the p nuclei are produced during SNIa explosions, and for these models we also calculate the neutron-capture nucleosynthesis in the external layers. Contrary to previous RAWD models at lower mass, we find that the H-shell flashes are the main site of n-capture nucleosynthesis. We find high neutron densities up to several 1015 cm−3 in the most massive WDs. Through the recurrence of the H-shell flashes these intermediate neutron densities can be sustained effectively for a long time leading to high-neutron exposures with a strong production up to Pb. Both the neutron density and the neutron exposure increase with increasing the mass of the accreting WD. Finally, the SNIa nucleosynthesis is calculated using the obtained abundances as seeds. We obtain solar to supersolar abundances for p-nuclei with A > 96. Our models show that SNIa are a viable p-process production site.
Ecological validity implicates in how far clinical assessments refer to real life. Short clinical gait tests up to ten meters and 2- or 6-Minutes Walking Tests (2MWT/6MWT) are used as ...performance-based outcomes in Multiple Sclerosis (MS) studies and considered as moderately associated with real life mobility.
To investigate the ecological validity of 10 Meter Walking Test (10mWT), 2MWT and 6MWT.
Persons with MS performed 10mWT, 6MWT including 2MWT and 7 recorded days by accelerometry. Ecological validity was assumed if walking tests represented a typical walking sequence in real-life and correlations with accelerometry parameters were strong.
In this cohort (n=28, medians: age=45, EDSS=3.2, disease duration=9 years), uninterrupted walking of 2 or 6 minutes occurred not frequent in real life (2.61 and 0.35 sequences/day). 10mWT correlated only with slow walking speed quantiles in real life. 2MWT and 6MWT correlated moderately with most real life walking parameters.
Clinical gait tests over a few meters have a poor ecological validity while validity is moderate for 2MWT and 6MWT. Mobile accelerometry offers the opportunity to control and improve the ecological validity of MS mobility outcomes.
Background:
The multiple sclerosis (MS) clinical course and relapses frequency before progression vary widely.
Objective:
To investigate the influence of age on the MS phenotype.
Methods:
Among 751 ...primary progressive (PP = 217) and secondary progressive (SP = 534) MS patients from the London Ontario database, we assessed the relationship of age on the relapse frequency and on the progressive phase evolution, and the impact of relapses on the age at onset of progression.
Results:
Age at onset did not influence the early attacks frequency, but patients younger at onset had larger number of total attacks before progression (age = 27.4, 31.0 and 32.8 mean years; ⩾4, 2–3 and 1 relapses, respectively) and longer latency to SP. Although frequent early relapses predicted younger age at SP onset, patients with no attacks (primary progressive multiple sclerosis (PPMS)), or 1, 2–3 and ⩾4 relapses during the relapsing-remitting phase started progressing at similar age (38.6, 41.3, 41.4 and 39.2 mean years, respectively). The age at onset of progressive phase did not affect its evolution.
Conclusions:
Age strongly influences the phenotype before progression. Relapsing-remitting patients younger at onset are more likely to display a predominantly inflammatory course, yet relapses number does not affect the age at onset of progression.
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Heart failure (HF) prevalence is rising due to reduced early mortality and demographic change. Relaxin (RLN) mediates protective effects in the cardiovascular system through ...Relaxin-receptor 1 (RXFP1). Cardiac overexpression of RXFP1 with additional RLN supplementation attenuated HF in the pressure-overload transverse aortic constriction (TAC) model. Here, we hypothesized that robust transgenic RXFP1 overexpression in cardiomyocytes (CM) protects from TAC-induced HF even in the absence of RLN.
Hence, transgenic mice with a CM-specific overexpression of human RXFP1 (hRXFP1tg) were generated. Receptor functionality was demonstrated by in vivo hemodynamics, where the administration of RLN induced positive inotropy strictly in hRXFP1tg. An increase in phospholamban-phosphorylation at serine 16 was identified as a molecular correlate. hRXFP1tg were protected from TAC without additional RLN administration, presenting not only less decline in systolic left ventricular (LV) function but also abrogated LV dilation and pulmonary congestion compared to WT mice. Molecularly, transgenic hearts exhibited not only a significantly attenuated fetal and fibrotic gene activation but also demonstrated less fibrotic tissue and CM hypertrophy in histological sections. These protective effects were evident in both sexes. Similar cardioprotective effects of hRXFP1tg were detectable in a RLN-knockout model, suggesting an alternative mechanism of receptor activation through intrinsic activity, alternative endogenous ligands or crosstalk with other receptors.
In summary, CM-specific RXFP1 overexpression provides protection against TAC even in the absence of endogenous RLN. This suggests RXFP1 overexpression as a potential therapeutic approach for HF, offering baseline protection with optional RLN supplementation for specific activation.
Lentiviruses are the vectors of choice for many preclinical studies and clinical applications of gene therapy. Accurate measurement of biological vector titre before treatment is a prerequisite for ...vector dosing, and the calculation of vector integration sites per cell after treatment is as critical to the characterisation of modified cell products as it is to long-term follow-up and the assessment of risk and therapeutic efficiency in patients. These analyses are typically based on quantitative real-time PCR (qPCR), but as yet compromise accuracy and comparability between laboratories and experimental systems, the former by using separate simplex reactions for the detection of endogene and lentiviral sequences and the latter by designing different PCR assays for analyses in human cells and animal disease models. In this study, we validate in human and murine cells a qPCR system for the single-tube assessment of lentiviral vector copy numbers that is suitable for analyses in at least 33 different mammalian species, including human and other primates, mouse, pig, cat and domestic ruminants. The established assay combines the accuracy of single-tube quantitation by duplex qPCR with the convenience of one-off assay optimisation for cross-species analyses and with the direct comparability of lentiviral transduction efficiencies in different species.
Inferences about long-term effects of therapies in multiple sclerosis (MS) have been based on surrogate markers studied in short-term trials. Preventing progressive disability is the key therapeutic ...goal but there remains no validated definition for its measurement in a trial context. Meanwhile, MS trials continue to shorten and to depend on unvalidated surrogates. Since there have been no treatment claims for improving unremitting disability, worsening of disability in the placebo/control arm must occur for effectiveness on this outcome to be shown.
We examined widely-used clinical surrogates of long-term disability progression in individual patients with MS within a unique database from the placebo arms of 31 randomized clinical trials.
Detection of treatment effects in secondary progressive MS trials is undermined by noise in disability measurement. Whereas existing measures can be partially validated in secondary progressive MS, this is not the case in relapsing-remitting MS. Here, examination of widely used definitions of treatment failure demonstrated that disability progression was no more likely than similarly defined improvement. Existing definitions of disease progression in short-term intervention trials in relapsing-remitting patients reflect random variation, measurement error, and remitting relapses.
Clinical surrogates of unremitting disability used in trials of relapsing-remitting multiple sclerosis cannot be validated. Trials have been too short or degrees of disability change too small to measure the key outcomes. These analyses highlight the difficulty in determining effectiveness of therapy in chronic diseases.
•SLCMSR challenged established outcome parameters in MS.•Sustained increase of EDSS appeared to be an invalid outcome for clinical trials.•SLCMSR contributed to the development of new outcomes such ...as real-world walking speed.•A tool was constructed to provide individual prognostic estimates based on a matching algorithm.
The SLCMSR was formed as an international Multiple Sclerosis Trials, Research and Resource Center to identify clinical MRI and other predictors of the course of multiple sclerosis (MS) based on a large database of natural history and clinical trial data. Using an elaborate validation concept several key findings were published, challenging established outcome parameters and their assessment in MS such as disability ratings with Expanded Disability Status Scale (EDSS), relapses and MRI endpoints. Sustained increase of EDSS appeared to be an invalid outcome for 2–3 year clinical trials at least in patients with relapsing-remitting MS. The number of gadolinium-enhancing lesions and T2-lesion load on MRI were shown not to have a meaningful additional predictive value for the disease course. These issues risen some 15 years ago had triggered controversial discussions which have also been noticed by regulatory authorities and they all have not been resolved. In addition the SLCMSR contributed to the development of new outcomes such as real-world walking speed as an attractive, ecologically valid tool based on a wearable device. A so-called evidence-based-decision-support tool was constructed to provide individual prognostic estimates based on a matching algorithm to a given database. This paper condensates the findings of 20 years of critical MS research.
Nine neutron induced reactions on Ge isotopes (
70
Ge(n,2n)
69
Ge,
76
Ge(n,2n)
75
Ge,
73
Ge(n,p)
73
Ga,
72
Ge(n,p)
72
Ga,
73
Ge(n,d/np)
72
Ga,
74
Ge(n,d/np)
73
Ga,
74
Ge(n,α)
71m
Zn,
72
Ge(n,α)
69m
...Zn,
73
Ge(n,nα)
69m
Zn) have been measured in this work at energies 16.4-18.9 MeV. For these reactions, most of the experimental datasets in literature were obtained with a
nat
Ge target. However, the residual nucleus produced by some reaction channels can also be produced from neighboring isotopes, acting as a contamination for the measured reactions. This contribution must be subtracted, based on theoretical calculations, bearing their own uncertainties. The use of enriched targets however, does not suffer from such contaminations, leading to accurate experimental results. In this scope, five highly isotopically enriched Ge samples have been used in this work. The quasi-monoenergetic neutron beams were produced via the
3
H(d,n)
4
He reaction at the 5.5 MV Tandem Van de Graaff accelerator of N.C.S.R. ‘Demokritos’. The cross section of these nine reactions were measured using the activation method, with respect to the
27
Al(n,α)
24
Na reference reaction.
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