[Comparison of the NoSAS score with four different questionnaires as screening tools for obstructive sleep apnea-hypopnea syndrome]

Objective: To evaluate the clinical utility of the NoSAS score in the screening of patients with obstructive sleep apnea-hypopnea syndrome(OSAHS), and to compare the performance of the NoSAS score with other tools including Epworth Sleepiness Scale(ESS), STOP, STOP-Bang(SBQ) and Berlin questionnaires. Methods: A total of 444 consecutive patients(328 males and 116 females) with suspected OSAHS who underwent an overnight polysomnography(PSG) were recruited into this study. Five questionnaires including the NoSAS score, ESS, STOP, SBQ and Berlin were completed. Based on the severity of OSAHS which was determined by apnea-hypopnea index(AHI), the patients were classified into 4 groups: normal(<5 events/h), mild(5-15 events/h), moderate(15-30 events/h) and, severe (≥30 events/h) OSA.Sensitivity, specificity, positive predictive values, negative predictive values and the area under the receiver operating characteristics curve of 5 questionnaires were calculated. Results: With AHI≥5 events/h as the standard diagnosis of OSAHS, the NoSAS score and SBQ questionnaire showed a moderate performance, with the NoSAS score having the largest area under the ROC curve(0.753, P<0.001), followed by the SBQ questionnaire (0.727, P<0.001). The performance of the ESS, Berlin, and the STOP questionnaire was not high. Using mild moderate-severe(≥5 events/h), moderate-severe(≥15 events/h), and severe(≥30 events/h)OSAHS as cutoffs, NoSAS had the highest specificity and positive predictive values(80.2% and 88%, 72% and 69.8%, 66.3% and 50.5%), and the sensitivity and negative predictive values were (51.5% and 36.9%, 56.5% and 59.1%, 66.3% and 74.2%) .SBQ had the highest sensitivity and the negative predictive values(80.2% and 88%, 72% and 69.8%, 66.3% and 50.5%), and the specific and positive predictive values were (45.7% and 81.0%, 39.1% and 61.9%, 34.8% and 44.4%). The NoSAS score ≥ 7 had higher sensitivity and negative predictive value(75.0% and 47.1%, 78.1% and 66.5%, 82.7% and 81.9%)than the NoSAS socre ≥ 8. With AHI≥5 events/h as the standard diagnosis of OSAHS, the NoSAS score and the SBQ questionnaire had a higher accuracy than the other 3 questionnaires as screening questionnaires for diagnosing OSAHS, and the value of DOR were 4.298 and 3.758 respectively. Conclusions: The NoSAS score and the SBQ questionnaire have a moderate performance in diagnosing OSAHS. The NoSAS score is a new screening tool, and it is similar to the SBQ questionnaire, being also simple and effective. While the SBQ questionnaire is more widely used, it is necessary to further evaluate the diagnostic value of NoSAS score.

Density functional theory calculations for magnetic properties of Co3W systems

Cheaper permanent magnetic nanostructures with magnetic properties equivalent to those of noble-metal or rare-earth nanomagnets have been experimentally developed for their potential applications in ultrahigh storage densities in magnetic memory. To date, their intrinsic magnetic properties are not well understood under the micro-level of local atomic arrangements and electronic structures. In this work, we performed theoretical investigations on the Co₃W bulk, the clean surface, nanoclusters, and the Co|Co₃W bilayers and superlattices for their geometrical structures, magnetic moments, and magnetic anisotropy energies (MAEs). We found that the Co₃W nanostructures we constructed are stable and have the local minima in the energetic landscape, whose stabilities increase with increasing proportion of W and cluster size. The Co and W atoms in clusters are antiferromagnetically coupled, and their local magnetic moments decrease with increasing proportion of W. The breakdown of the Hund's third rule in W atoms observed in experiment can be interpreted as the competition between the intra-atomic spin-orbit coupling in W atoms and interatomic Co-W hybridizations. The highest MAE of about a few tens of meV is obtained in small cluster sizes, whereas it is an order of magnitude reduction in large cluster sizes. The magnetic systems of Co₃W clean surface, Co|Co₃W bilayer and superlattice can present large MAEs, and their easy-axes of magnetization are perpendicular to the (001) surface. Our calculated MAEs are of the same order of magnitude as that of the experimental measurements, and the electronic origin is revealed through the second-order perturbation method.

Magnetic moment and magnetic anisotropy of Ge3Mn5 thinfilms on Ge(111) substrate: A density functional study

Magnetism and magnetic anisotropy energy (MAE) of the Ge₃Mn₅ bulk, free-standing surface, and Ge₃Mn₅(001)|Ge(111) thinfilms and superlattice have been systemically investigated by using the relativistic first-principles electronic structure calculations. For Ge₃Mn₅ adlayers on Ge(111) substrates within Mn1 termination, the direction of magnetization undergoes a transition from in-plane at 1 monolayer (ML) thickness (MAE = -0.50 meV/ML) to out-of-plane beginning at 3 ML thickness (nearly invariant MAE = 0.16 meV/ML). The surficial/interfacial MAE is extracted to be 1.23/-0.54 meV for Mn1-termination; the corresponding value is 0.19/1.03 meV for Mn2/Ge-termination; the interior MAE is averaged to be 0.09 meV per ML. For various Ge₃Mn₅ systems, the in-plane lattice expansion and/or interlayer distance contraction would enhance the out-of-plane MAE. Our theoretical magnetic moments and MAEs fit well with the experimental measurements. Finally, the origination of MAE is elucidated under the framework of second-order perturbation with the electronic structure analyses.

Monoxides of small terbium clusters: a density functional theory investigation

To investigate the effect of oxygen atom on the geometrical structures, electronic, and magnetic properties of small terbium clusters, we carried out the first-principles calculations on TbnO (n = 1-14) clusters. The capping of an oxygen atom on one trigonal-facet of Tbn structures is always favored energetically, which can significantly improve the structural stability. The far-infrared vibrational spectroscopies are found to be different from those of corresponding bare clusters, providing a distinct signal to detect the characteristic structures of TbnO clusters. The primary effect of oxygen atom on magnetic properties is to change the magnetic orderings among Tb atoms and to reduce small of local magnetic moments of the O-coordinated Tb atoms, both of which serve as the key reasons for the experimental magnetic evolution of an oscillating behavior. These calculations are consistent with, and help to account for, the experimentally observed magnetic properties of monoxide TbnO clusters [C. N. Van Dijk et al., J. Appl. Phys. 107, 09B526 (2010)].

Emergence of antiferromagnetic ordering in Tbn (n = 2-33) clusters

Using the density functional theory (DFT) under both frameworks of the local density approximation (LDA) and the generalized gradient approximation (GGA), we show that the anomalous magnetic moment of Tbn (n = 2-20, 22, 33) clusters found in recent experiment [J. Appl. Phys. 2010, 107, 09B526] is due to the antiferromagnetic or ferromagnetic couplings between Tb atoms in clusters. The local spin magnetic moment of Tb atoms is in the range 5.1-5.7 μ(B), which is faintly influenced by the cluster sizes, geometrical structures, and spin arrangements. Emphasis is made on the Tb13 cluster to eliminate the large magnetic discrepancy between the experiment and calculation. Geometrical evolution shows that the square-antiprism motif with one centered atom is competitive with the icosahedral motif for small Tb clusters n = 9-12, whereas the close packed icosahedral growth is clearly favored for large clusters n = 13-20, 22, 33. The clusters containing 4, 7, 10, 13, and 19 atoms are found to be more stable than their neighboring sizes, in agreement with the early mass spectral measurements. The electronic properties including the HOMO-LUMO energy gaps, ionization potentials, electron affinities, and electric dipole moments are calculated, and more importantly, the variational trends of the magnetic moment and electric dipole moment qualitatively fit well with the experimental observations.

Electronic structural and magnetic properties of Mn5Ge3 clusters

Theoretical understanding of the stability, ferromagnetism, and spin polarization of Mn5Ge3 clusters has been performed by using the density functional theory with generalized gradient approximation for exchange and correlation. The magnetic moments and magnetic anisotropy energy (MAE) have been calculated for both bulk and clusters, and the enhanced magnetic moment as well as the enlarged MAE have been identified in clusters. The most attractive achievement is that Mn5Ge3 clusters show a fine half-metallic character with large energy scales. The present results may have important implications for potential applications of small Mn5Ge3 clusters as both emerging spintronics and next-generation data-storage technologies.