7,918 research outputs found
Improved precision with Hologic Apex software.
UnlabelledThe precision of Hologic Apex v2.0 analysis software is significantly improved from Hologic Delphi v11.2 software and is comparable to GE Lunar Prodigy v7.5 software. Apex and Delphi precisions were, respectively, 1.0% vs. 1.2% (L1-L4 spine), 1.l % vs. 1.3% (total femur), 1.6% vs. 1.9% (femoral neck), and 0.7% vs. 0.9% (dual total femur).IntroductionPrecision of bone mineral density (BMD) measurements by dual-energy X-ray absorptiometry (DXA) is known to vary by manufacturer, model, and technologist. This study evaluated the precision of three analysis versions: Apex v2.0 and Delphi v11.2 (Hologic, Inc.), and Prodigy v7.5 (GE Healthcare, Inc.) independent of technologist skill.MethodsDuplicate spine and dual hip scans on 90 women were acquired on both Delphi and Prodigy DXA systems at three clinics. BMD measures were converted to standardized BMD (sBMD) units. Precision errors were described as a root-mean-square (RMS) standard deviations and RMS percent coefficients of variation across the population.ResultsApex and Delphi values were highly correlated (r ranged from 0.90 to 0.99). Excluding the right neck, the Apex precision error was found to be 20% to 25% lower than the Delphi (spine: 1.0% versus 1.2% (p < 0.05), total hip: 1.1% versus 1.3% (p < 0.05), right neck: 2.3% versus 2.6% (p > 0.1)). No statistically significant differences were found in the precision error of the Apex and Prodigy (p > 0.05) except for the right neck (2.3% versus 1.8% respectively, p = 0.03).ConclusionThe Apex software has significantly lower precision error compared to Delphi software with similar mean values, and similar precision to that of the Prodigy
One-loop approximation for the Heisenberg antiferromagnet
We use the diagram technique for spin operators to calculate Green's
functions and observables of the spin-1/2 quantum Heisenberg antiferromagnet on
a square lattice. The first corrections to the self-energy and interaction are
taken into account in the chain diagrams. The approximation reproduces main
results of Takahashi's modified spin-wave theory [Phys. Rev. B 40, 2494 (1989)]
and is applicable in a wider temperature range. The energy per spin calculated
in this approximation is in good agreement with the Monte Carlo and
small-cluster exact-diagonalization calculations in the range 0 <= T < 1.2J
where J is the exchange constant. For the static uniform susceptibility the
agreement is good for T < 0.6J and becomes somewhat worse for higher
temperatures. Nevertheless the approximation is able to reproduce the maximum
in the temperature dependence of the susceptibility near T = 0.9J.Comment: 15 pages, 6 ps figure
Temperature behavior of the magnon modes of the square lattice antiferromagnet
A spin-wave theory of short-range order in the square lattice Heisenberg
antiferromagnet is formulated. With growing temperature from T=0 a gapless mode
is shown to arise simultaneously with opening a gap in the conventional
spin-wave mode. The spectral intensity is redistributed from the latter mode to
the former. For low temperatures the theory reproduces results of the modified
spin-wave theory by M.Takahashi, J.E.Hirsch et al. and without fitting
parameters gives values of observables in good agreement with Monte Carlo
results in the temperature range 0 <= T < 0.8J where J is the exchange
constant.Comment: 12 pages, 2 figure
Corticothalamic projections control synchronization in locally coupled bistable thalamic oscillators
Thalamic circuits are able to generate state-dependent oscillations of
different frequencies and degrees of synchronization. However, only little is
known how synchronous oscillations, like spindle oscillations in the thalamus,
are organized in the intact brain. Experimental findings suggest that the
simultaneous occurrence of spindle oscillations over widespread territories of
the thalamus is due to the corticothalamic projections, as the synchrony is
lost in the decorticated thalamus. Here we study the influence of
corticothalamic projections on the synchrony in a thalamic network, and uncover
the underlying control mechanism, leading to a control method which is
applicable in wide range of stochastic driven excitable units.Comment: 4 pages with 4 figures (Color online on p.3-4) include
Cyclotron effect on coherent spin precession of two-dimensional electrons
We investigate the spin dynamics of high-mobility two-dimensional electrons
in GaAs/AlGaAs quantum wells grown along the and directions by
time-resolved Faraday rotation at low temperatures. In measurements on the
-grown structures without external magnetic fields, we observe coherent
oscillations of the electron spin polarization about the effective spin-orbit
field. In non-quantizing magnetic fields applied normal to the sample plane,
the cyclotron motion of the electrons rotates the effective spin-orbit field.
This rotation leads to fast oscillations in the spin polarization about a
non-zero value and a strong increase in the spin dephasing time in our
experiments. These two effects are absent in the -grown structure due to
the different symmetry of its effective spin-orbit field. The measurements are
in excellent agreement with our theoretical model.Comment: 4 pages, 3 figure
Pressure-Induced Magnetic Quantum Phase Transitions from Gapped Ground State in TlCuCl3
Magnetization maesurements under hydrostatic pressure were performed on an
S=1/2 coupled spin system TlCuCl3 with a gapped ground state under magnetic
field H parallel to the [2,0,1] direction. With increasing applied pressure P,
the gap decreases and closes completely at Pc=0.42 kbar. For P>Pc, TlCuCl3
undergoes antiferromagnetic ordering. A spin-flop transition was observed at
Hsf=0.7T. The spin-flop field is approximately independent of pressure,
although the sublattice magnetization increases with pressure. The gap and Neel
temperature are presented as function is attributed to to the relative
enhancement of the interdimer exchange interactions compared with the
intradimer exchange interaction.Comment: 4pages,3figures To be published in J. Phys. Soc. Jpn. Vol.73 No.1
Ehrenfest relations and magnetoelastic effects in field-induced ordered phases
Magnetoelastic properties in field-induced magnetic ordered phases are
studied theoretically based on a Ginzburg-Landau theory. A critical field for
the field-induced ordered phase is obtained as a function of temperature and
pressure, which determine the phase diagram. It is found that magnetic field
dependence of elastic constant decreases discontinuously at the critical field,
Hc, and that it decreases linearly with field in the ordered phase (H>Hc). We
found an Ehrenfest relation between the field dependence of the elastic
constant and the pressure dependence of critical field. Our theory provides the
theoretical form for magnetoelastic properties in field- and pressure-induced
ordered phases.Comment: 7 pages, 3 figure
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