8,955 research outputs found
Roll Resonance for a Gravity-gradient Satellite
Roll and attitude stability for gravity gradient satellite
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.
Magnetically suspended flywheel system study
A program to study the application of a graphite/epoxy, magnetically suspended, pierced disk flywheel for the combined function of spacecraft attitude control and energy storage (ACES) is described. Past achievements of the program include design and analysis computer codes for the flywheel rotor, a magnetically suspended flywheel model, and graphite/epoxy rotor rings that were successfully prestressed via interference assembly. All hardware successfully demonstrated operation of the necessary subsystems which form a complete ACES design. Areas of future work include additional rotor design research, system definition and control strategies, prototype development, and design/construction of a UM/GSFC spin test facility. The results of applying design and analysis computer codes to a magnetically suspended interference assembled rotor show specific energy densities of 42 Wh/lb (92.4 Wh/kg) are obtained for a 1.6 kWh system
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
Crystal field states of Kondo lattice heavy fermions CeRuSn3 and CeRhSn3
Inelastic neutron scattering experiments have been carried out to determine
the crystal field states of the Kondo lattice heavy fermions CeRuSn3 and
CeRhSn3. Both the compounds crystallize in LaRuSn3-type cubic structure (space
group Pm-3n) in which the Ce atoms occupy two distinct crystallographic sites
with cubic (m-3) and tetragonal (-4m.2) point symmetries. The INS data of
CeRuSn3 reveal the presence of a broad excitation centered around 6-8 meV which
is accounted by a model based on crystal electric field (CEF) excitations. On
the other hand, the INS data of isostructural CeRhSn3 reveal three CEF
excitations around 7.0, 12.2 and 37.2 meV. The neutron intensity sum rule
indicates that the Ce ions at both cubic and tetragonal Ce sites are in Ce3+
state in both CeRuSn3 and CeRhSn3. The CEF level schemes for both the compounds
are deduced. We estimate the Kondo temperature T_K = 3.1(2) K for CeRuSn3 from
neutron quasielastic linewidth in excellent agreement with that determined from
the scaling of magnetoresistance which gives T_K = 3.2(1) K. For CeRhSn3 the
neutron quasielastic linewidth gives T_K = 4.6 K. For both CeRuSn3 and CeRhSn3,
the ground state of Ce3+ turns out to be a quartet for the cubic site and a
doublet for the tetragonal site.Comment: 12 pages, 13 figures, 2 tables, to appear in Phys. Rev.
Sodium Benzoate is Associated with Salmonella Typhi Resistant to Chloramphenicol
Background: There are many factors that govern growth and resistant of Salmonella typhi. A study had reported that the use of sodium benzoate caused antibiotic resistant. However, no study has directly evaluated the effect of sodium benzoate exposure on S. typhi sensitivity to chloramphenicol. The aim of this study was to evaluate the resistance or sensitivity of S. typhi to chloramphenicol after sodium benzoate exposure. Methods: The study was conducted in seven groups: three treatment groups (sodium benzoate insensitive S. typhi+8 µg/mL, 16 µg/mL, and 32 µg/mL of chloramphenicol), three positive control groups (sodium benzoate sensitive S. typhi+8 µg/mL, 16 µg/mL, and 32 µg/mL of chloramphenicol), and one negative control groups (sodium benzoate sensitive S. typhi+0 µg/mL of chloramphenicol). The effect of sodium benzoate exposure to S. typhi sensitivity to chloramphenicol was measured after 24 hours. Spearman test was used to analyzed this association. Results: In this study, we found that the average S. typhi growth in the treatment groups (A, B, C) was 445 CFU/mL, 385 CFU/mL, and 171 CFU/mL, respectively. While in the positive control group (D, E, F) was not obtained any S. typhi growth. Average S. typhi growth in the negative control group was 430 CFU/mL. Discussion: We found that sodium benzoate exposure inhibited S. typhi growth and affected S. typhi sensitivity to chloramphenicol (p<0.05). In addition, we found that 32 µg/mL chloramphenicol had the highest mean difference value, so this showed that the dose 32 µg/mL of chloramphenicol had the best effectiveness of various treatment groups (p<0.05). Conclusions: Sodium benzoate exposure can inhibit S. typhi growth and cause S. typhi resistant to chloramphenicol. 
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