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We theoretically investigated the structural and thermoelectric properties of Mg2Si with Al and Sb (Na and B) as n-type (p-type) impurities. Supercell calculations involving relaxation of the atomic positions using an ab initio pseudo-potential method were performed. The formation energies, Eform,i, for the i = Mg, Si, and 4b sites, and consequently, the energetically preferred sites occupied by the impurities, were discussed. The calculated Eform,i were used to estimate the impurity-site occupancy probabilities, pi(T), based on the canonical distribution in the equilibrium state, i.e., pi(T) ∝ exp(−Eform,i/kBT) (Boltzmann constant: kB, temperature: T), and the resultant effects on the carrier concentration. Next, an all-electron full-potential linearized augmented-plane-wave calculation was performed based on the optimized structures, and the temperature dependence of the thermoelectromotive force (the Seebeck coefficient) was evaluated using the Boltzmann transport equation. The calculated and experimental results for n-type doped systems were compared.
Continuous deep sedation (CDS) is a way to reduce conscious experience of symptoms of severe suffering in terminally ill cancer patients. However, there is wide variation in the frequency of its reported. So we conducted a retrospective analysis to assess the prevalence and features of CDS in our palliative care unit (PCU).
We performed a systemic retrospective analysis of the medical and nursing records of all 1581 cancer patients who died at the PCU at Higashi Sapporo Hospital between April 2005 and August 2011. Continuous deep sedation can only be administered safely and appropriately when a multidisciplinary team is involved in the decision-making process. Prior to administration of CDS, a multidisciplinary team conference (MDTC) was held with respect to all the patients considered for CDS by an attending physician. The main outcome measures were the frequency and characteristics of CDS (patient background, all target symptoms, medications used for sedation, duration, family's satisfaction, and distress). We mailed anonymous questionnaires to bereaved families in August 2011.
Of 1581 deceased patients, 22 (1.39%) had received CDS. Physical exhaustion 8 (36.4%), dyspnea 7 (31.8%), and pain 5 (22.7%) were the most frequently mentioned indications. Continuous deep sedation had a duration of less than 1 week in 17 (77.3%). Six patients (0.38%) did not meet the appropriate criteria for CDS according to the MDTC and so did not receive it. Although bereaved families were generally comfortable with the practice of CDS, some expressed a high level of emotional distress.
Significance of results:
Our results indicate that the prevalence of CDS will be decreased when it is carried out solely for appropriate indications. Continuity of teamwork, good coordination, exchange of information, and communication between the various care providers are essential. A lack of any of these may lead to inadequate assessment, information discrepancies, and unrest.
We present theoretical calculations of the phonon-drag contribution to the Nernst thermoelectric power Syx in Bismuth nanowires. We investigate the thermopower Syx with diameters L ranging from 22 to 900 nm at low temperatures (0.1 - 4.0 K) and high magnetic fields (up to 16 T). We find that the peak of thermopower Syx around 14.75 T exhibits the size effect in two different ways: for wires with L≥200 nm, the peak height increases with decreasing L; for wires with L<200 nm, on the other hand, the peak height rapidly decreases with decreasing L. The dependence is accounted for by considering the contributions of discrete quantized phonon modes. We also discuss the temperature dependence of Syx.
Mg2Si bulk was fabricated by spark plasma sintering (SPS) nano-powder, and the thermoelectric characteristics of the bulk sample were evaluated at temperatures up to 873 K. A pre-synthesized all-molten commercial polycrystalline Mg2Si source (un-doped n-type semiconductor) was pulverized into powder of 75 μm or less. To obtain nano-sized fine powder, the powder was milled using planetary ball mill equipment under an inert atmosphere. Fine Mg2Si nano-powder with a mean grain size of about 500 nm was obtained. XRD analysis confirmed that no MgO existed in the nano-powder. The fine powder was put in a graphite die to obtain a sintering body of Mg2Si and treated by SPS under vacuum conditions. The resulting Mg2Si bulk had high density and did not crack. However, the XRD analysis revealed a small amount of MgO in it. The thermoelectric properties (electrical conductivity, Seebeck coefficient, and thermal conductivity) were measured from room temperature to 873 K. The microstructure of the sintered body was observed by scanning electron microscopy. The maximum dimensionless figure of merit of a sample made from Mg2Si nano-powder was ZT = 0.67 at 873 K.
The thermoelectrical properties of α and γ phases of NaxCo2O4 having different amounts of Na were evaluated. The γ NaxCo2O4 samples were synthesized by thermal decomposition in a metal-citric acid compound, and the α NaxCo2O4 samples were synthesized by self-flux processing. Dense bulk ceramics were fabricated using spark plasma sintering (SPS), and the sintered samples were of high density and highly oriented. The thermoelectrical properties showed that γ NaxCo2O4 had higher electrical conductivity and lower thermal conductivity compared with α NaxCo2O4 and that α NaxCo2O4 had a larger Seebeck coefficient. These results show that γ NaxCo2O4 has a larger power factor and dimensionless figure of merit, ZT, than α NaxCo2O4.
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