21,383 research outputs found
Thermal Analysis of As-received and Clinically Retrieved Copper-Nickel-Titanium Orthodontic Archwires
Objective: To compare as-received copper-nickel-titanium (CuNiTi) archwires to those used in patients by means of differential scanning calorimetry (DSC). Also, the thermal or phase properties of 27°C, 35°C, and 40°C CuNiTi archwires were studied to ascertain if their properties match those indicated by the manufacturer.
Materials and Methods: Six wires of 27°C, 35°C, and 40°C CuNiTi were tested as-received, and six each of the 27°C and 35°C wires were examined after use in patients for an average of approximately 9 and 7 weeks, respectively. Segments of archwire were investigated by DSC over the temperature range from −100°C to 150°C at 10°C per minute.
Results: There were no significant differences between as-received and clinically used 27°C and 35°C wires for all parameters (heating onset, endset, and enthalpy and cooling onset, endset, and enthalpy), except the 27°C wires exhibited a significant decrease in the heating enthalpy associated with the martensite-to-austenite transition after clinical use. The heating endsets (austenite finish temperatures) of the 27°C and 35°C wires were within 2°C of those claimed by the manufacturer, but the 40°C wires were found to be nearer to 36°C than 40°C.
Conclusions: Clinical use of CuNiTi wires resulted in few differences when compared with as-received wires analyzed by DSC. Two temperature varieties of CuNiTi are reasonably within the parameters of those identified by the manufacturer
Are There Any Redshift >8 Gamma-Ray Bursts in the BATSE Catalog?
Several luminosity indicators have been found for Gamma-Ray Bursts (GRBs)
wherein measurable light curve and spectral properties are well-correlated with
the peak luminosity. Several papers have each applied one different luminosity
relation to find redshifts for BATSE GRBs and claim to identify specific bursts
with z>8. The existence of such high redshift events is not surprising, as
BATSE has enough sensitivity to see them and GRBs are expected out to the
redshift of the first star formation. To improve results we used five
luminosity relations with updated calibrations to determine redshifts with
error bars. Combining these relations, we calculated the redshifts of 36 BATSE
GRBs with claimed z>8. Our results include 13 bursts with our derived best
redshift z_best>8, which looks promising at first. But the calculated redshift
uncertainties are significantly large in these selected cases. With only one
exception, all of our bursts have z_1siglow<9. The one exception (BATSE trigger
2035) is likely a short duration burst at z>~4. Our best case for a very high
redshift event is BATSE trigger 3142 with z_best>20 and z_1siglow=8.9, however
we can only say z>4.1 at the two-sigma confidence level. In all, we cannot
point toward any one BATSE burst as confidently having z>8. One implication is
to greatly weaken prior claims that GRBs have a steeply rising rate-density out
to high redshifts.Comment: ApJ in press, 18 page
Late Archean greenstone tectonics: Evidence for thermal and thrust-loading lithospheric subsidence from stratigraphic sections in the Slave Province, Canada
How late Archean tectonics could be seen to have operated in the Slave Province is illustrated. Lithospheric thinning and stretching, with the formation of rifted margins (to continental or island arc fragments), and lithospheric flexural loading of the kind familiar in arcs and mountain belts could be discerned
Explosion of a collapsing Bose-Einstein condensate
We show that elastic collisions between atoms in a Bose-Einstein condensate
with attractive interactions lead to an explosion that ejects a large fraction
of the collapsing condensate. We study variationally the dynamics of this
explosion and find excellent agreement with recent experiments on magnetically
trapped Rubidium-85. We also determine the energy and angular distribution of
the ejected atoms during the collapse.Comment: Four pages of ReVTeX and five postscript figure
Spin domain formation in spinor Bose-Einstein condensation
The spatial structure of the spinor Bose-Einstein condensates with the spin
degrees of freedom is analyzed based on the generalized Gross-Pitaevskii
equation (GP) in the light of the present spin domain experiment on m_F=\pm 1,
and 0 of the hyperfine state F=1 of ^{23}Na atom gases. The GP solutions in
three- and one-spatial dimensional cases reproduce the observed spin domain
structures, revealing the length scale associated with the existence of the
weak interaction of the spin-spin channel, other than the ordinary coherence
length related to the density-density channel. The obtained domain structure in
GP is compared with the result in Thomas-Fermi approximation. The former
solution is found to better describe the observed features than the latter.Comment: 9 pages, 14 figure
Facies Patterns and Conodont Biogeography in Arctic Alaska and the Canadian Arctic Islands: Evidence against Juxtaposition of These Areas during Early Paleozoic Time
Mean field ground state of a spin-1 condensate in a magnetic field
We revisit the topic of the mean field ground state of a spin-1 atomic
condensate inside a uniform magnetic field () under the constraints that
both the total number of atoms () and the magnetization () are
conserved. In the presence of an internal state (spin component) independent
trap, we also investigate the dependence of the so-called single spatial mode
approximation (SMA) on the magnitude of the magnetic field and . Our
result indicate that the quadratic Zeeman effect is an important factor in
balancing the mean field energy from elastic atom-atom collisions that are
known to conserve both and .Comment: 13 pages, 9 figures, to be published in New J. Phys.
(http://www.njp.org/
Double Phase Transitions in Magnetized Spinor Bose-Einstein Condensation
It is investigated theoretically that magnetized Bose-Einstein condensation
(BEC) with the internal (spin) degrees of freedom exhibits a rich variety of
phase transitions, depending on the sign of the interaction in the spin
channel. In the antiferromagnetic interaction case there exist always double
BEC transitions from single component BEC to multiple component BEC. In the
ferromagnetic case BEC becomes always unstable at a lower temperature, leading
to a phase separation. The detailed phase diagram for the temperature vs the
polarization, the spatial spin structure, the distribution of non-condensates
and the excitation spectrum are examined for the harmonically trapped systems.Comment: 6 pages, 7 figures. Submitted to J. Phys. Soc. Jp
Theory of the Ramsey spectroscopy and anomalous segregation in ultra-cold rubidium
The recent anomalous segregation experiment of Lewandowski et al. (PRL, 88,
070403, 2002) shows dramatic, rapid internal state segregation for two
hyperfine levels of rubidium. We simulate an effective one dimensional model of
the system for experimental parameters and find reasonable agreement with the
data. The Ramsey frequency is found to be insensitive to the decoherence of the
superposition, and is only equivalent to the interaction energy shift for a
pure superposition. A Quantum Boltzmann equation describing collisions is
derived using Quantum Kinetic Theory, taking into account the different
scattering lengths of the internal states. As spin-wave experiments are likely
to be attempted at lower temperatures we examine the effect of degeneracy on
decoherence by considering the recent experiment of Lewandowski et al. where
degeneracy is around 10%. We also find that the segregation effect is only
possible when transport terms are included in the equations of motion, and that
the interactions only directly alter the momentum distributions of the states.
The segregation or spin wave effect is thus entirely due to coherent atomic
motion as foreseen in the experimental reportComment: 26 pages, 4 figures, to be published in J. Phys.
Elastic and inelastic collisions of 6Li in magnetic and optical traps
We use a full coupled channels method to calculate collisional properties of
magnetically or optically trapped ultracold 6Li. The magnetic field dependence
of the s-wave scattering lengths of several mixtures of hyperfine states are
determined, as are the decay rates due to exchange collisions. In one case, we
find Feshbach resonances at B=0.08 T and B=1.98 T. We show that the exact
coupled channels calculation is well approximated over the entire range of
magnetic fields by a simple analytical calculation.Comment: 4 pages revtex including 4 figures, submitted to PR
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