6,903 research outputs found
Experimental and theoretical investigation of three-dimensional turbulent boundary layers and turbulence characteristics inside an axial flow inducer passage
Analytical and experimental investigations of the characteristics of three dimensional turbulent boundary layers in a rotating helical passage of an inducer rotor are reported. Expressions are developed for the velocity profiles in the inner layer, where the viscous effects dominate, in the outer layer, where the viscous effects are small, and in the interference layer, where the end walls influence the flow. The prediction of boundary layer growth is based on the momentum integral technique. The equations derived are general enough to be valid for all turbomachinery rotors with arbitrary pressure gradients. The experimental investigations are carried out in a flat plate inducer 3 feet in diameter. The mean velocity profiles, turbulence intensities and shear stresses, wall shear stress, and limiting streamline angles are measured at various radial and chordwise locations by using rotating probes. The measurements are in general agreement with the predictions. The radial flows are well represented by an expression which includes the effect of stagger angle and radial pressure gradient. The radial flows in the rotor channel are higher than those on a single blade. The collateral region exists only very near the blade surface. The radial component of turbulence intensity is higher than the streamwise component because of the effect of rotation
Investigations of the effect of nonmagnetic Ca substitution for magnetic Dy on spin-freezing in Dy2Ti2O7
Physical properties of partially Ca substituted hole-doped Dy2Ti2O7 have been
investigated by ac magnetic susceptibility \chi_ac(T), dc magnetic
susceptibility \chi(T), isothermal magnetization M(H) and heat capacity C_p(T)
measurements on Dy1.8Ca0.2Ti2O7. The spin-ice system Dy2Ti2O7 exhibits a
spin-glass type freezing behavior near 16 K. Our frequency dependent \chi_ac(T)
data of Dy1.8Ca0.2Ti2O7 show that the spin-freezing behavior is significantly
influenced by Ca substitution. The effect of partial nonmagnetic Ca2+
substitution for magnetic Dy3+ is similar to the previous study on nonmagnetic
isovalent Y3+ substituted Dy2-xYxTi2O7 (for low levels of dilution), however
the suppression of spin-freezing behavior is substantially stronger for Ca than
Y. The Cole-Cole plot analysis reveals semicircular character and a single
relaxation mode in Dy1.8Ca0.2Ti2O7 as for Dy2Ti2O7. No noticeable change in the
insulating behavior of Dy2Ti2O7 results from the holes produced by 10% Ca2+
substitution for Dy3+ ions.Comment: 9 pages, 7 figures, 1 tabl
Analysis of the Inter-basin Water Transfer Scheme in India: a case study of the Godavari-Krishna link
River basin managementRiver basin developmentDevelopment projectsWater availab ilityWater demandWater transferDamsCanalsCrop management
India’s water supply and demand from 2025-2050: business-as-usual scenario and issues
Water demandEstimationIrrigation waterRiver basinsWater supplySimulation modelsPopulation growthFood productionFood consumptionCrop yieldGroundwater irrigation
India’s water future to 2025-2050: Business-as-usual scenario and deviations
Poverty / Mapping/ Water demand / Water supply / Population growth / Crop production / Crop yield / Groundwater irrigation / Food security
Observation of long range magnetic ordering in pyrohafnate Nd2Hf2O7: A neutron diffraction study
We have investigated the physical properties of a pyrochlore hafnate Nd2Hf2O7
using ac magnetic susceptibility \chi_ac(T), dc magnetic susceptibility
\chi(T), isothermal magnetization M(H) and heat capacity C_p(T) measurements,
and determined the magnetic ground state by neutron powder diffraction study.
An upturn is observed below 6 K in C_p(T)/T, however both C_p(T) and \chi(T) do
not show any clear anomaly down to 2 K. The \chi_ac(T) shows a well pronounced
anomaly indicating an antiferromagnetic transition at T_N = 0.55 K. The long
range antiferromagnetic ordering is confirmed by neutron diffraction. The
refinement of neutron diffraction pattern reveals an all-in/all-out
antiferromagnetic structure, where for successive tetrahedra, the four Nd3+
magnetic moments point alternatively all-into or all-out-of the tetrahedron,
with an ordering wavevector k = (0, 0, 0) and an ordered state magnetic moment
of m = 0.62(1) \mu_B/Nd at 0.1 K. The ordered moment is strongly reduced
reflecting strong quantum fluctuations in ordered state.Comment: 10 pages, 9 figures and 2 tables; to appear in Phys. Rev.
Investigation of the magnetic structure and crystal field states of pyrochlore antiferromagnet Nd2Zr2O7
We present synchrotron x-ray diffraction, neutron powder diffraction and
time-of-flight inelastic neutron scattering measurements on the rare earth
pyrochlore oxide Nd2Zr2O7 to study the ordered state magnetic structure and
cystal field states. The structural characterization by high-resolution
synchrotron x-ray diffraction confirms that the pyrochlore structure has no
detectable O vacancies or Nd/Zr site mixing. The neutron diffraction reveals
long range all-in/all-out antiferromagnetic order below T_N ~ 0.4 K with
propagation vector k = (0 0 0) and an ordered moment of 1.26(2) \mu_B/Nd at 0.1
K. The ordered moment is much smaller than the estimated moment of 2.65
\mu_B/Nd for the local Ising ground state of Nd3+ (J=9/2) suggesting that
the ordering is partially suppressed by quantum fluctuations. The strong Ising
anisotropy is further confirmed by the inelastic neutron scattering data which
reveals a well-isolated dipolar-octupolar type Kramers doublet ground state.
The crystal field level scheme and ground state wavefunction have been
determined.Comment: 12 pages, 15 figures, 2 table
Cost and benefits of intermediate water storage structures: case study of diggies in Rajasthan
Water storageWater deliveryIrrigation schedulingWater controlIrrigation canalsWatercoursesFarmsCrop productionCost benefit analysis
Physical Properties of Metallic Antiferromagnetic CaCo{1.86}As2 Single Crystals
We report studies of CaCo{1.86}As2 single crystals. The electronic structure
is probed by angle-resolved photoemission spectroscopy (ARPES) measurements of
CaCo{1.86}As2 and by full-potential linearized augmented-plane-wave
calculations for the supercell Ca8Co15As16 (CaCo{1.88}As2). Our XRD crystal
structure refinement is consistent with the previous combined refinement of
x-ray and neutron powder diffraction data showing a collapsed-tetragonal
ThCr2Si2-type structure with 7(1)% vacancies on the Co sites corresponding to
the composition CaCo{1.86}As2 [D. G. Quirinale et al., Phys. Rev. B 88, 174420
(2013)]. The anisotropic magnetic susceptibility chi(T) data are consistent
with the magnetic neutron diffraction data of Quirianale et al. that
demonstrate the presence of A-type collinear antiferromagnetic order below the
Neel temperature TN = 52(1) K with the easy axis being the tetragonal c axis.
However, no clear evidence from the resistivity rho(T) and heat capacity Cp(T)
data for a magnetic transition at TN is observed. A metallic ground state is
demonstrated from band calculations and the rho(T), Cp(T) and ARPES data, and
spin-polarized calculations indicate a competition between the A-type AFM and
FM ground states. The Cp(T) data exhibit a large Sommerfield electronic
coefficient reflecting a large density of states at the Fermi energy D(EF),
consistent with the band structure calculations which also indicate a large
D(EF) arising from Co 3d bands. At 1.8 K the M(H) data for H|| c exhibit a
well-defined first-order spin-flop transition at an applied field of 3.5 T. The
small ordered moment of 0.3 muB/Co obtained from the M(H) data at low T, the
large exchange enhancement of chi and the lack of a self-consistent
interpretation of the chi(T) and M(H,T) data in terms of a local moment
Heisenberg model together indicate that the magnetism of CaCo{1.86}As2 is
itinerant.Comment: 18 pages, 15 figures, 4 tables, 61 references; v2: extended the fits
of experimental data by additional electronic structure calculations;
published versio
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