2,962 research outputs found
Speciation and spectrophotometric determination of uranium in seawater
A series of ion-exchange and extraction procedures for the separation of uranium from seawater samples and subsequent spectrophotometric determination of uranium in seawater by means of arsenazo(III) is described. According to the measurements performed by means of traced samples at every stage of separation, the yield of the pre-analytical procedures is generally over 90% and the separation of uranium very selective. The mean uranium concentration in seawater samples collected from five different coastal areas in Cyprus was found to be 3.2 ± 0.2 & micro; g L-1. Uranium in seawater is stable in its hexavalent oxidation state and UO2 (CO3)34- is the predominant species under normal coastal conditions (pH ≥ 8, EH ≥ 0.35 mV, 1 atm and 0.03% CO2)
Tetrahedron maps, Yang-Baxter maps, and partial linearisations
We study tetrahedron maps, which are set-theoretical solutions to the
Zamolodchikov tetrahedron equation, and Yang-Baxter maps, which are
set-theoretical solutions to the quantum Yang-Baxter equation.
In particular, we clarify the structure of the nonlinear algebraic relations
which define linear (parametric) tetrahedron maps (with nonlinear dependence on
parameters), and we present several transformations which allow one to obtain
new such maps from known ones. Furthermore, we prove that the differential of a
(nonlinear) tetrahedron map on a manifold is a tetrahedron map as well. Similar
results on the differentials of Yang-Baxter and entwining Yang-Baxter maps are
also presented.
Using the obtained general results, we construct new examples of (parametric)
Yang-Baxter and tetrahedron maps. The considered examples include maps
associated with integrable systems and matrix groups. In particular, we obtain
a parametric family of new linear tetrahedron maps, which are linear
approximations for the nonlinear tetrahedron map constructed by Dimakis and
M\"uller-Hoissen [arXiv:1708.05694] in a study of soliton solutions of vector
Kadomtsev-Petviashvili (KP) equations. Also, we present invariants for this
nonlinear tetrahedron map.Comment: 23 pages; v2: new results and references added, minor corrections
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Clinical diagnostic model for sciatica developed in primary care patients with low back-related leg pain
Background
Identification of sciatica may assist timely management but can be challenging in clinical practice. Diagnostic models to identify sciatica have mainly been developed in secondary care settings with conflicting reference standard selection. This study explores the challenges of reference standard selection and aims to ascertain which combination of clinical assessment items best identify sciatica in people seeking primary healthcare.
Methods
Data on 394 low back-related leg pain consulters were analysed. Potential sciatica indicators were seven clinical assessment items. Two reference standards were used: (i) high confidence sciatica clinical diagnosis; (ii) high confidence sciatica clinical diagnosis with confirmatory magnetic resonance imaging findings. Multivariable logistic regression models were produced for both reference standards. A tool predicting sciatica diagnosis in low back-related leg pain was derived. Latent class modelling explored the validity of the reference standard.
Results
Model (i) retained five items; model (ii) retained six items. Four items remained in both models: below knee pain, leg pain worse than back pain, positive neural tension tests and neurological deficit. Model (i) was well calibrated (p = 0.18), discrimination was area under the receiver operating characteristic curve (AUC) 0.95 (95% CI 0.93, 0.98). Model (ii) showed good discrimination (AUC 0.82; 0.78, 0.86) but poor calibration (p = 0.004). Bootstrapping revealed minimal overfitting in both models. Agreement between the two latent classes and clinical diagnosis groups defined by model (i) was substantial, and fair for model (ii).
Conclusion
Four clinical assessment items were common in both reference standard definitions of sciatica. A simple scoring tool for identifying sciatica was developed. These criteria could be used clinically and in research to improve accuracy of identification of this subgroup of back pain patients
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