7,705 research outputs found
Magnetic Properties of the Novel Low-Dimensional Cuprate Na5RbCu4(AsO4)4Cl2
The magnetic properties of a new compound, Na5RbCu4(AsO4)4Cl2 are reported.
The material has a layered structure comprised of square Cu4O4 tetramers. The
Cu ions are divalent and the system behaves as a low-dimensional S=1/2
antiferromagnet. Spin exchange in Na5RbCu4(AsO4)4Cl2 appears to be
quasi-two-dimensional and non-frustrated. Measurements of the bulk magnetic
susceptibility and heat capacity are consistent with low-dimensional magnetism.
The compound has an interesting, low-entropy, magnetic transition at T = 17 K.Comment: 4 pages, 5 figure
Structural and magnetic study of a dilute magnetic semiconductor: Fe doped CeO2 nanoparticles
This paper reports the effect of Fe doping on the structure and room
temperature ferromagnetism of CeO2 nanoparticles. X-ray diffraction and
selective area electron diffraction measurement reflects that Ce1-xFexO2 (x =
0.0 - 0.07) nanoparticles exhibit single phase nature with cubic structure and
none of the sample showed the presence of any secondary phase. The mean
particle size calculated by using a transmission electron microscopy
measurement was found to increase with increase in Fe content. DC magnetization
measurements performed at room temperature indicates that all the samples
exhibit ferromagnetism. The saturation magnetic moment has been found to
increase with an increase in the Fe content.Comment: 16 Pages, 5 figure, 1 Table, Accepted in JN
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Polyamide Nanocomposites for Selective Laser Sintering
Current polyamide 11 and 12 are lacking in fire retardancy and high strength/high
heat resistance characteristics for a plethora of finished parts that are desired and required
for performance driven applications. It is anticipated that nanomodification of polyamide
11 and 12 will result in enhanced polymer performance, i.e., fire retardancy, high strength
and high heat resistance for polyamide 11 and 12. It is expected that these findings will
expand the market opportunities for polyamide 11 and 12 resin manufacturers.
The objective of this research is to develop improved polyamide 11 and 12 polymers
with enhanced flame retardancy, thermal, and mechanical properties for selective laser
sintering (SLS) rapid manufacturing (RM). A nanophase was introduced into the
polyamide 11 and 12 via twin screw extrusion to provide improved material properties of
the polymer blends. Arkema RILSAN® polyamide 11 molding polymer pellets and
Degussa VESTAMID® L1670 polyamide 12 were examined with three types of
nanoparticles: chemically modified montmorillonite (MMT) organoclays, surface
modified nanosilica, and carbon nanofibers (CNFs) to create polyamide 11 and 12
nanocomposites.
Wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM)
were used to determine the degree of dispersion. Injection molded test specimens were
fabricated for physical, thermal, mechanical properties, and flammability tests. Thermal
stability of these polyamide 11 and 12 nanocomposites was examined by TGA.
Mechanical properties such as tensile, flexural, and elongation at break were measured.
Flammability properties were also obtained using the Cone Calorimeter at an external
heat flux of 50 kW/m2. TEM micrographs, physical, mechanical, and flammability
properties are included in the paper. Polyamide 11 and 12 nanocomposites properties are
compared with polyamide 11 and 12 baseline polymers. Based on flammability and
mechanical material performance, selective polymers including polyamide 11
nanocomposites and control polyamide 11 were cryogenically ground into fine powders
and fabricated into SLS parts.Mechanical Engineerin
Refined Simulations of the Reaction Front for Diffusion-Limited Two-Species Annihilation in One Dimension
Extensive simulations are performed of the diffusion-limited reaction
AB in one dimension, with initially separated reagents. The reaction
rate profile, and the probability distributions of the separation and midpoint
of the nearest-neighbour pair of A and B particles, are all shown to exhibit
dynamic scaling, independently of the presence of fluctuations in the initial
state and of an exclusion principle in the model. The data is consistent with
all lengthscales behaving as as . Evidence of
multiscaling, found by other authors, is discussed in the light of these
findings.Comment: Resubmitted as TeX rather than Postscript file. RevTeX version 3.0,
10 pages with 16 Encapsulated Postscript figures (need epsf). University of
Geneva preprint UGVA/DPT 1994/10-85
Ideal Bose gas in fractal dimensions and superfluid He in porous media
Physical properties of ideal Bose gas with the fractal dimensionality between
D=2 and D=3 are theoretically investigated. Calculation shows that the
characteristic features of the specific heat and the superfluid density of
ideal Bose gas in fractal dimensions are strikingly similar to those of
superfluid Helium-4 in porous media. This result indicates that the geometrical
factor is dominant over mutual interactions in determining physical properties
of Helium-4 in porous media.Comment: 13 pages, 6 figure
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Innovative Selective Laser Sintering Rapid Manufacturing using Nanotechnology
The objective of this research is to develop an improved nylon 11 (polyamide 11) polymer
with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering
(SLS) rapid manufacturing (RM). A nanophase was introduced into nylon 11 via twin screw
extrusion to provide improved material properties of the polymer blends. Atofina (now known
as Arkema) RILSAN® nylon 11 injection molding polymer pellets was used with three types of
nanoparticles: chemically modified montmorillonite (MMT) organoclays, nanosilica, and carbon
nanofibers (CNF) to create nylon 11 nanocomposites. Wide angle X-ray diffraction (WAXD)
and transmission electron microscopy (TEM) were used to determine the degree of dispersion.
Fifteen nylon 11 nanocomposites and control nylon 11 were fabricated by injection molding.
Flammability properties (using a cone calorimeter with a radiant flux of 50 kW/m2
) and
mechanical properties such as tensile strength and modulus, flexural modulus, elongation at
break were determined for the nylon 11 nanocomposites and compared with the baseline nylon
11. Based on flammability and mechanical material performance, five polymers including four
nylon 11 nanocomposites and a control nylon 11 were cryogenically ground into fine powders
for SLS RM. SLS specimens were fabricated for flammability, mechanical, and thermal
properties characterization. Nylon 11-CNF nanocomposites exhibited the best overall properties
for this study.Mechanical Engineerin
Kpc-scale Properties of Emission-line Galaxies
We perform a detailed study of the resolved properties of emission-line
galaxies at kpc-scale to investigate how small-scale and global properties of
galaxies are related. 119 galaxies with high-resolution Keck/DEIMOS spectra are
selected to cover a wide range in morphologies over the redshift range
0.2<z<1.3. Using the HST/ACS and HST/WFC3 imaging data taken as a part of the
CANDELS project, for each galaxy we perform SED fitting per resolution element,
producing resolved rest-frame U-V color, stellar mass, star formation rate, age
and extinction maps. We develop a technique to identify blue and red "regions"
within individual galaxies, using their rest-frame color maps. As expected, for
any given galaxy, the red regions are found to have higher stellar mass surface
densities and older ages compared to the blue regions. Furthermore, we quantify
the spatial distribution of red and blue regions with respect to both redshift
and stellar mass, finding that the stronger concentration of red regions toward
the centers of galaxies is not a significant function of either redshift or
stellar mass. We find that the "main sequence" of star forming galaxies exists
among both red and blue regions inside galaxies, with the median of blue
regions forming a tighter relation with a slope of 1.1+/-0.1 and a scatter of
~0.2 dex compared to red regions with a slope of 1.3+/-0.1 and a scatter of
~0.6 dex. The blue regions show higher specific Star Formation Rates (sSFR)
than their red counterparts with the sSFR decreasing since z~1, driver
primarily by the stellar mass surface densities rather than the SFRs at a giver
resolution element.Comment: 17 pages, 17 figures, Submitted to the Ap
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