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376 results on '"Strecker, K."'

3. Molecular Probe of Pairing in the BEC-BCS Crossover

Author

Partridge, G. B., Strecker, K. E., Kamar, R. I., Jack, M. W., and Hulet, R. G.

Subjects
Condensed Matter - Other Condensed Matter
Abstract

We have used optical molecular spectroscopy to probe the many-body state of paired $^6$Li atoms near a broad Feshbach resonance. The optical probe projects pairs of atoms onto a vibrational level of an excited molecule. The rate of excitation enables a precise measurement of the closed-channel contribution to the paired state. This contribution is found to be quite small, supporting the concept of universality for the description of broad Feshbach resonances. The dynamics of the excitation provide clear evidence for pairing across the BEC-BCS crossover, and into the weakly interacting BCS regime., Comment: 11 pages, 5 figures, submitted to Phys. Rev. Lett

Published
2005
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4. Bright soliton trains of trapped Bose-Einstein condensates

Author

Khawaja, U. Al, Stoof, H. T. C., Hulet, R. G., Strecker, K. E., and Partridge, G. B.

Subjects
Condensed Matter
Abstract

We variationally determine the dynamics of bright soliton trains composed of harmonically trapped Bose-Einstein condensates with attractive interatomic interactions. In particular, we obtain the interaction potential between two solitons. We also discuss the formation of soliton trains due to the quantum mechanical phase fluctuations of a one-dimensional condensate., Comment: 4 pages, 2 figures, submitted to PRL

Published
2002

5. Development and characterization of Al2O3-based biocomposites reinforced with 3Y-TZP nanoparticles.

Author

Cossu, C. M. F. A., Alves, M. F. R. P., Gomes, R. M. T., Strecker, K., Magnago, R. O., and Santos, C.

Subjects
FRACTURE toughness, VICKERS hardness, SPECIFIC gravity, BENDING strength, FRACTURE strength, NANOPARTICLES, POWDERS
Abstract

Alumina ceramics were reinforced with different amounts of stabilized-tetragonal zirconia nanoparticles, 3Y-TZP, and their properties were evaluated aiming for future applications in orthopedic medicine. Different amounts of 3Y-TZP (3 to 15 wt%) were mixed with Al2O3 powder, using high-energy milling (400 rpm-24 h). Samples were uniaxially compacted and sintered at 1600 °C-2 h. The samples were characterized by their relative density, microstructure, and crystalline phases. Furthermore, Vickers hardness, fracture toughness, and bending strength were determined. After the high-energy milling process, a considerable amount of monoclinic (m) ZrO2 was detected in the powder mixtures, besides the α -Al2O3 and tetragonal (t) ZrO2 phases. After sintering the samples presented relative densities greater than 98.5%, regardless of the amount of the Y-TZP additions used. Furthermore, the monoclinic phase was reconverted into the tetragonal phase during sintering. The Vickers hardness varied between 1750 and 1690 HV, depending on the amount of Y-TZP added. Bending strength and fracture toughness were also sensitive to the addition of Y-TZP, with values increasing from 351.5 to 701.7 MPa and KIC from 3.5 to 5.6 MPa.m1/2, indicating that the t-ZrO2 grains enable the activation of the transformation toughening mechanisms such as t → m phase transformation and residual stress. The biological responses of the composites, evaluated by their cytotoxicity and chemical solubility, accredit the materials developed for future in vitro and in vivo studies aimed at application as biomaterials. [ABSTRACT FROM AUTHOR]

Published
2023
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6. Mechanical properties of Ce-TZP/Al2O3 ceramic composites as a function of sintering parameters.

Author

Freitas, B. X., Duarte, E. T., Vasconcelos, J. E. A., Magnago, R. O., Strecker, K., and Santos, C.

Subjects
HEAT treatment, PARTICLE size distribution, YOUNG'S modulus, FRACTURE toughness, SPECIFIC gravity, HARDNESS, CERAMICS
Abstract

Ceramic composites based on Ce-TZP/Al2O3/H6A were sintered in order to promote grain growth and to study the effects of ZrO2 grain size on the properties of this material. A mixture of ZrO2-CeO2-Al2O3 powders was sintered at 1450 °C-2 h, following the manufacturer's recommendations. Then, the samples were further treated at 1500 or 1600 °C, for 0, 2, 8, or 24 h. The sintered specimens were characterized by X-ray diffraction, relative density, and grain size distribution. Vickers nanohardness, Young's modulus (E), and fracture toughness were measured. The materials showed complete densification for all sintering conditions studied. t-ZrO2, α -Al2O3, and cerium hexaluminate (H6A) were observed. The alumina and hexaluminate grains had average grain sizes of 0.7 and 4.5 μm (AR>3), respectively, without significant variations during the additional heat treatments. However, significant growth took place for the ZrO2 grains with increasing temperature and holding time, increasing the average grain size from 0.6~1.4 μm, when sintered at 1500 °C-2 h to 1600 °C-24 h, respectively. The materials exhibited Vickers nanohardness of 1800 HV and E=241 ± 15 GPa. On the other hand, the considerable grain growth of the ZrO2 grains as a function of holding time reflected in a reduction of the fracture toughness, which decreased from 8.5 to 5.7 MPa.m1/2 for samples sintered at 1500 °C-2 h to 1600 °C-24 h, respectively. [ABSTRACT FROM AUTHOR]

Published
2023
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17. Zu Erotian

Author

Strecker, K.

Published
1891

44. Atom Skimmers and Atom Lasers Utilizing Them

Author

Hulet, Randall, Tollett, Jeff, Franke, Kurt, Moss, Steve, Sackett, Charles, Gerton, Jordan, Ghaffari, Bita, McAlexander, W, Strecker, K, and Homan, D

Subjects
Lasers And Masers
Abstract

Atom skimmers are devices that act as low-pass velocity filters for atoms in thermal atomic beams. An atom skimmer operating in conjunction with a suitable thermal atomic-beam source (e.g., an oven in which cesium is heated) can serve as a source of slow atoms for a magneto-optical trap or other apparatus in an atomic-physics experiment. Phenomena that are studied in such apparatuses include Bose-Einstein condensation of atomic gases, spectra of trapped atoms, and collisions of slowly moving atoms. An atom skimmer includes a curved, low-thermal-conduction tube that leads from the outlet of a thermal atomic-beam source to the inlet of a magneto-optical trap or other device in which the selected low-velocity atoms are to be used. Permanent rare-earth magnets are placed around the tube in a yoke of high-magnetic-permeability material to establish a quadrupole or octupole magnetic field leading from the source to the trap. The atoms are attracted to the locus of minimum magnetic-field intensity in the middle of the tube, and the gradient of the magnetic field provides centripetal force that guides the atoms around the curve along the axis of the tube. The threshold velocity for guiding is dictated by the gradient of the magnetic field and the radius of curvature of the tube. Atoms moving at lesser velocities are successfully guided; faster atoms strike the tube wall and are lost from the beam.

Published
2005

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