6,719 research outputs found
Fracture toughness and crack-resistance curve behavior in metallic glass-matrix composites
Nonlinear-elastic fracture mechanics methods are used to assess the fracture toughness of bulk metallic glass (BMG) composites; results are compared with similar measurements for other monolithic and composite BMG alloys. Mechanistically, plastic shielding gives rise to characteristic resistance-curve behavior where the fracture resistance increases with crack extension. Specifically, confinement of damage by second-phase dendrites is shown to result in enhancement of the toughness by nearly an order of magnitude relative to unreinforced glass
Exploring the Oxygen Order in Hg-1223 and Hg-1201 by 199Hg MAS NMR
We demonstrate the use of a high-resolution solid-state fast (45 kHz) magic
angle spinning (MAS) NMR for mapping the oxygen distribution in Hg-based
cuprate superconductors. We identify observed three peaks in 199Hg spectrum as
belonging to the different chemical environments in the HgO? layer with no
oxygen neighbors, single oxygen neighbor, and two oxygen neighbors. We discuss
observed differences between Hg-1201 and Hg-1223 materials.Comment: 4 pages, 2 figures included. Submitted to NATO Advanced Research
Workshop Proceedings (Miami January 2004
Inhomogeneous Low Frequency Spin Dynamics in La_{1.65}Eu_{0.2}Sr_{0.15}CuO_4
We report Cu and La nuclear magnetic resonance (NMR) measurements in the
title compound that reveal an inhomogeneous glassy behavior of the spin
dynamics. A low temperature peak in the La spin lattice relaxation rate and the
``wipeout'' of Cu intensity both arise from these slow electronic spin
fluctuations that reveal a distribution of activation energies. Inhomogeneous
slowing of spin fluctuations appears to be a general feature of doped lanthanum
cuprate.Comment: 4 pages, 2 figures. Very slight modifications to figure
Spin Dynamics in the LTT Phase of ~1/8 Doped Single Crystal La_{1.67}Eu_{0.2}Sr_{0.13}CuO_4
We present La and Cu NMR relaxation measurements in single crystal
La_{1.67}Eu_{0.2}Sr_{0.13}CuO_4. A strong peak in the La spin-lattice
relaxation rate observed in the spin ordered state is well-described by the BPP
mechanism[1] and arises from continuous slowing of electronic spin fluctuations
with decreasing temperature; these spin fluctuations exhibit XY-like anisotropy
in the ordered state. The spin pseudogap is enhanced by the static
charge-stripe order in the LTT phase.Comment: Four pages, three figure
Strong enhancement of spin fluctuations in the low-temperature-tetragonal phase of antiferromagnetically ordered La_{2-x-y}Eu_ySr_xCuO_4
Measurements of the static magnetization, susceptibility and ESR of Gd spin
probes have been performed to study the properties of antiferromagnetically
ordered La_{2-x-y}Eu_ySr_xCuO_4 (x less or equal 0.02) with the low temperature
tetragonal structure. According to the static magnetic measurements the CuO_2
planes are magnetically decoupled in this structural phase. The ESR study
reveals strong magnetic fluctuations at the ESR frequency which are not present
in the orthorhombic phase. It is argued that this drastic enhancement of the
spin fluctuations is due to a considerable weakening of the interlayer exchange
and a pronounced influence of hole motion on the antiferromagnetic properties
of lightly hole doped La_2CuO_4. No evidence for the stripe phase formation at
small hole doping is obtained in the present study.Comment: 10 pages, LaTeX, 3 EPS figures; to be published in Journal of
Physics: Condensed Matte
Easy on that trigger dad: a study of long term family photo retrieval
We examine the effects of new technologies for digital photography on people's longer term storage and access to collections of personal photos. We report an empirical study of parents' ability to retrieve photos related to salient family events from more than a year ago. Performance was relatively poor with people failing to find almost 40% of pictures. We analyze participants' organizational and access strategies to identify reasons for this poor performance. Possible reasons for retrieval failure include: storing too many pictures, rudimentary organization, use of multiple storage systems, failure to maintain collections and participants' false beliefs about their ability to access photos. We conclude by exploring the technical and theoretical implications of these findings
Analysis of White Dwarfs with Strange-Matter Cores
We summarize masses and radii for a number of white dwarfs as deduced from a
combination of proper motion studies, Hipparcos parallax distances, effective
temperatures, and binary or spectroscopic masses. A puzzling feature of these
data is that some stars appear to have radii which are significantly smaller
than that expected for a standard electron-degenerate white-dwarf equations of
state. We construct a projection of white-dwarf radii for fixed effective mass
and conclude that there is at least marginal evidence for bimodality in the
radius distribution forwhite dwarfs. We argue that if such compact white dwarfs
exist it is unlikely that they contain an iron core. We propose an alternative
of strange-quark matter within the white-dwarf core. We also discuss the impact
of the so-called color-flavor locked (CFL) state in strange-matter core
associated with color superconductivity. We show that the data exhibit several
features consistent with the expected mass-radius relation of strange dwarfs.
We identify eight nearby white dwarfs which are possible candidates for strange
matter cores and suggest observational tests of this hypothesis.Comment: 11 pages, 6 figures, accepted for publication in J. Phys. G: Nucl.
Part. Phy
Putative spin liquid in the triangle-based iridate BaIrTiO
We report on thermodynamic, magnetization, and muon spin relaxation
measurements of the strong spin-orbit coupled iridate BaIrTiO,
which constitutes a new frustration motif made up a mixture of edge- and
corner-sharing triangles. In spite of strong antiferromagnetic exchange
interaction of the order of 100~K, we find no hint for long-range magnetic
order down to 23 mK. The magnetic specific heat data unveil the -linear and
-squared dependences at low temperatures below 1~K. At the respective
temperatures, the zero-field muon spin relaxation features a persistent spin
dynamics, indicative of unconventional low-energy excitations. A comparison to
the isostructural compound BaRuTiO suggests that a concerted
interplay of compass-like magnetic interactions and frustrated geometry
promotes a dynamically fluctuating state in a triangle-based iridate.Comment: Physical Review B accepte
Study of the neutron star structure in strong magnetic fields including the anomalous magnetic moments
We study the effects of strong magnetic fields on the neutron star structure.
If the interior field of a star is on the same order of the surface field
currently observed, the influences of the magnetic field on the star mass and
radius are negligible. If one assumes that the internal magnetic field can be
as large as that estimated from the scalar virial theorem, considerable effects
can be induced. The maximum mass of stars is arisen substantially while the
central density is largely suppressed. For two equal-mass stars the radius of
the magnetic star can be larger by about 10% 20% than the nonmagnetic
star.Comment: 26 pages, 5 postscript figures; replaced by the revised version,
Chin. J. Astron. Astrophys., accepte
Shear stress fluctuations in the granular liquid and solid phases
We report on experimentally observed shear stress fluctuations in both
granular solid and fluid states, showing that they are non-Gaussian at low
shear rates, reflecting the predominance of correlated structures (force
chains) in the solidlike phase, which also exhibit finite rigidity to shear.
Peaks in the rigidity and the stress distribution's skewness indicate that a
change to the force-bearing mechanism occurs at the transition to fluid
behaviour, which, it is shown, can be predicted from the behaviour of the
stress at lower shear rates. In the fluid state stress is Gaussian distributed,
suggesting that the central limit theorem holds. The fibre bundle model with
random load sharing effectively reproduces the stress distribution at the yield
point and also exhibits the exponential stress distribution anticipated from
extant work on stress propagation in granular materials.Comment: 11 pages, 3 figures, latex. Replacement adds journal reference and
addresses referee comment
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