2,015 research outputs found
Exploring the possibility of enhancing the figure-of-merit ( 2) of NaCoO: A combined experimental and theoretical study
Search of new thermoelectric (TE) materials with high
\textit{figure-of-merit} (ZT) is always inspired the researcher in TE field.
Here, we present a combined experimental and theoretical study of TE properties
of NaCoO compound in high-temperature region. The experimental
Seebeck coefficient (S) is found to vary from 64 to 118 V/K in the
temperature range K. The positive values of S are indicating the
dominating p-type behaviour of the compound. The observed value of thermal
conductivity () is 2.2 W/m-K at 300 K. In the temperature region
K, the value of increases up to 2.6 W/m-K and then
decreases slowly till 620 K with the corresponding value of 2.4 W/m-K.
We have also carried out the theoretical calculations and the best matching
between experimental and calculated values of transport properties are observed
in spin-polarized calculation within DFT+\textit{U} by chosen \textit{U} = 4
eV. The maximum calculated value of ZT is found to be 0.67 at 1200 K for
p-type conduction. Our computational study suggests that the possibility of
n-type behaviour of the compound which can lead to a large value of ZT at
higher temperature region. Electron doping of 5.110
cm is expected to give rise the high ZT value of 2.7 at 1200 K.
Using these temperature-dependent ZT values, we have calculated the maximum
possible values of efficiency () of thermoelectric generator (TEG) made
by p and n-type NaCoO. The present study suggests that one can
get the efficiency of a TE cell as high as 11 when the cold and hot
end temperature are fixed at 300 K and 1200 K, respectively. Such high values
of ZT and efficiency suggest that NaCoO can be used as a
potential candidate for high-temperature TE applications
Suppression of low-frequency noise in two-dimensional electron gas at degenerately doped Si:P \delta-layers
We report low-frequency 1/f noise measurements of degenerately doped Si:P
\delta-layers at 4.2K. The noise was found to be over six orders of magnitude
lower than that of bulk Si:P systems in the metallic regime and is one of the
lowest values reported for doped semiconductors. The noise was found to be
nearly independent of magnetic field at low fields, indicating negligible
contribution from universal conductance fluctuations. Instead interaction of
electrons with very few active structural two-level systems may explain the
observed noise magnitudeComment: 4 pages, 4 figure
Study of bone marrow: dyserythropoiesis for etiological evaluation of anemia
Background: Bone Marrow Aspiration plays a major role in the diagnosis of various hematolgical disorders which are very frequent in various age groups. The aim of this study was to analyze the causes of haematological disorders, and to interpret the bone marrow aspiration findings with various dyserythropoietic changes in it.Methods: This was a study carried out in the department of Pathology of Shri M P Shah Govt. Medical college over a period of two years from June 2008 to June 2010. Bone marrow examination of 100 cases of suspected haematological disorders was carried out. All details of the patients were the recorded in the department of pathology.Results: Out of 100 cases of bone marrow aspiration, erythroid hyperplasia and megaloblastic changes were commonest findings and Megaloblastic anemia was most common diagnosis given on bone marrow examination. Other dyserythropoietic changes were erythroidhypoplasia, micronormoblasts, dimorphic erythropoiesis, megaloblastoid changes and other like – cytoplasmic bleb, multinucleation,nuclear bridging.Conclusions: The sincere blood film examination and keen morphological evaluation of erythroid series for dyserythropiesis and leukopoesis and megakaryopiesis in bone marrow aspiration smear - supported with other investigation can navigate to etiological factors of anaemia and other haematological disorders.
Depositional Environment of Phosphorites of the Sonrai Basin, Lalitpur District, Uttar Pradesh, India
Phosphates are regarded as one of the most important fertilizer minerals used by man. In Sonrai basin of Lalitpur the phosphorites are found to occur as lenticular and detached bodies throughout the Formation of the Bijawar Group. Individual bodies range from a few meters to about 4 km in length, and width varies from thin bands to about 125 meter with P2O5 concentration ranging from 10 to 20%. The Paleoproterozoic Bijawar Group are overlain by the Archaean Bundelkhand Basement Complex and underlain by Vindhyan Supergroup. The occurrence of phosphorites is confined to the Sonrai Formation which consists of massive to brecciated phosphorite within the lower reddish shales, with at least three bands identified. Megascopic study reveals that the brecciated phosphorite is reddish brown in color and fine to medium grained with angular fragments of chert and quartz embedded in a groundmass of iron oxides and secondary silica intercalated with minor veins of chert and iron oxides. The phosphorite horizon in the Lalitpur area is associated with pink to white brecciated massive quartzite, shale, dolomite and limestone of the basal unit. The concentration trends of certain major oxides indicate that the phosphorites are more enriched in CaO, P2O5 and SiO2 than Al2O3, Fe2O3, TiO2, Na2O and K2O. The concentration trends of trace elements reveal that the phosphorites are moderately enriched in Co, Zn, Zr, Pb, U than in Sc, Ba, V, Cr, Ni, , Rb, Sr, Y and Th. The dispersion patter, correlation coefficient and mutual relationship of significant major oxides represented by plotted diagrams, indicate that SiO2, CaO, MgO are antipathetically related with P2O5. The relationship suggests a gradual replacement among these oxides during diagenesis. High values of P2O5 and CaO in the phosphorites indicate more concentration of apatite constituent. The difference in geochemical behavior of CaO and MgO may be due to ionic substitution of Ca+2 by MgO+2 in the apatite crystal lattice during alkaline environment of the basin. The strong negative relationship between P2O5 with Fe2O3 in phosphorites may be due to leaching and/mild weathering of iron from the ores and reprecipitation along with P2O5 in the pore spaces, cavities/voids, veins, etc in highly oxidizing marine environment of the basin. The minimum evidence of organic matter, absence of sulphide minerals and lower concentration of V, Ni, and Cu suggest that the phosphorites were deposited in an oxidizing environment with slightly anaerobic to highly aerobic facies
Experimental and computational approaches to study the high temperature thermoelectric properties of novel topological semimetal CoSi
Here, we study the thermoelectric properties of topological semimetal CoSi in
the temperature range K by using combined experimental and density
functional theory (DFT) based methods. CoSi is synthesized using arc melting
technique and the Rietveld refinement gives the lattice parameters of a = b = c
= 4.445 {\AA}. The measured values of Seebeck coefficient (S) shows the
non-monotonic behaviour in the studied temperature range with the value of
81 V/K at room temperature. The first increases till 560 K
(93 V/K) and then decreases up to 800 K (84 V/K)
indicating the dominating n-type behaviour in the full temperature range. The
electrical conductivity, (thermal conductivity, ) shows the
monotonic decreasing (increasing) behaviour with the values of 5.2 (12.1 W/m-K) and 3.6 (14.2 W/m-K)
at 300 K and 800 K, respectively. The exhibits the
temperature dependency as, . The DFT based Boltzmann
transport theory is used to understand these behaviour. The multi-band electron
and hole pockets appear to be mainly responsible for deciding the temperature
dependent transport behaviour. Specifically, the decrease in the above
560 K and change in the slope of around 450 K are due to the
contribution of thermally generated charge carriers from the hole pockets. The
temperature dependent relaxation time is computed which shows temperature
dependency of . Present study suggests that electronic
band-structure obtained from DFT provides reasonably good estimate of the
transport coefficients of CoSi in the high temperature region of K
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