5,213 research outputs found
Serological evidence of exposure to Rickettsia felis and Rickettsia typhi in Australian veterinarians
BACKGROUND: Rickettsia felis and Rickettsia typhi are emerging arthropod-borne zoonoses causing fever and flu-like symptoms. Seroprevalence and risk factors associated with exposure to these organisms was explored in Australian veterinarians. METHODS: One hundred and thirty-one veterinarians from across Australia were recruited to participate in a cross-sectional survey. Veterinarians provided a single blood sample and answered a questionnaire on potential risk factors influencing their exposure to R. felis and R. typhi. Indirect microimmunofluorescence antibody testing (IFAT) was used to identify evidence of serological exposure of the participants to R. felis and R. typhi. Results were analyzed and a logistical regression model performed to predict risk factors associated with seropositivity. RESULTS: In total, 16.0% of participants were seropositive to R. felis, 4.6% to R. typhi and 35.1% seropositive to both, where cross-reactivity of the IFAT between R. felis and R. typhi precluded a definitive diagnosis. Veterinarians residing within the south-eastern states of Victoria and Tasmania were at a higher risk of exposure to R. felis or generalised R. felis or R. typhi exposure. Older veterinarians and those that recommended flea treatment to their clients were found to be significantly protected from exposure. CONCLUSIONS: The high exposure to R. felis amongst veterinary professionals suggests that flea-borne spotted fever is an important cause of undifferentiated fever conditions that may not be adequately recognized in Australia
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Polyamide 11-Carbon Nanotubes Nanocomposites: Preliminary Investigation
The objective of this research is to develop an improved polyamide 11 (PA11) polymer with
enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering
(SLS) rapid manufacturing. In the present study, a nanophase was introduced into polyamide 11
via twin screw extrusion. Arkema Rilsan® polyamide 11 molding polymer pellets were used
with 1, 3, 5, and 7 wt% loadings of Arkema’s GraphistrengthTM multi-wall carbon nanotubes
(MWNTs) to create a family of PA11-MWNT nanocomposites.
Transmission electron microscopy and scanning electron microscopy were used to determine
the degree and uniformity of dispersion. Injection molded test specimens were fabricated for
physical, thermal, mechanical properties, and flammability measurements. Thermal stability of
these polyamide 11-MWNT nanocomposites was examined by TGA. Mechanical properties such
as ultimate tensile strength, rupture tensile strength, and elongation at rupture were measured.
Flammability properties were also obtained using the UL 94 test method. All these different
methods and subsequent polymer characteristics are discussed in this paper.Mechanical Engineerin
Luminous Compact Blue Galaxies up to z~1 in the HST Ultra Deep Field: I. Small galaxies, or blue centers of massive disks?
We analyze 26 Luminous Compact Blue Galaxies (LCBGs) in the HST/ACS Ultra
Deep Field (UDF) at z ~ 0.2-1.3, to determine whether these are truly small
galaxies, or rather bright central starbursts within existing or forming large
disk galaxies. Surface brightness profiles from UDF images reach fainter than
rest-frame 26.5 B mag/arcsec^2 even for compact objects at z~1. Most LCBGs show
a smaller, brighter component that is likely star-forming, and an extended,
roughly exponential component with colors suggesting stellar ages >~ 100 Myr to
few Gyr. Scale lengths of the extended components are mostly >~ 2 kpc, >1.5-2
times smaller than those of nearby large disk galaxies like the Milky Way.
Larger, very low surface brightness disks can be excluded down to faint
rest-frame surface brightnesses (>~ 26 B mag/arcsec^2). However, 1 or 2 of the
LCBGs are large, disk-like galaxies that meet LCBG selection criteria due to a
bright central nucleus, possibly a forming bulge. These results indicate that
>~ 90% of high-z LCBGs are small galaxies that will evolve into small disk
galaxies, and low mass spheroidal or irregular galaxies in the local Universe,
assuming passive evolution and no significant disk growth. The data do not
reveal signs of disk formation around small, HII-galaxy-like LCBGs, and do not
suggest a simple inside-out growth scenario for larger LCBGs with a disk-like
morphology. Irregular blue emission in distant LCBGs is relatively extended,
suggesting that nebular emission lines from star-forming regions sample a major
fraction of an LCBG's velocity field.Comment: 11 pages, 2 figures, AASTeX; accepted for publication in
Astrophysical Journal Letter
Evidences of a consolute critical point in the Phase Separation regime of La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single crystals
We report on DC and pulsed electric field sensitivity of the resistance of
mixed valent Mn oxide based La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single
crystals as a function of temperature. The low temperature regime of the
resistivity is highly current and voltage dependent. An irreversible transition
from high (HR) to a low resistivity (LR) is obtained upon the increase of the
electric field up to a temperature dependent critical value (V_c). The
current-voltage characteristics in the LR regime as well as the lack of a
variation in the magnetization response when V_c is reached indicate the
formation of a non-single connected filamentary conducting path. The
temperature dependence of V_c indicates the existence of a consolute point
where the conducting and insulating phases produce a critical behavior as a
consequence of their separation.Comment: 5 pages, 6 figures, corresponding author: C. Acha ([email protected]
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Flame Retardant Intumescent Polyamide 11 Nanocomposites – Further Study
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). In the present study, a nanophase was introduced into the
polyamide 11 and combine with a conventional intumescent flame retardant (FR) additive via
twin screw extrusion. Arkema Rilsan® polyamide 11 molding polymer pellets were used with
two types of nanoparticles such as: chemically modified montmorillonite (MMT) organoclays
and carbon nanofibers (CNFs). Two types of Clariant’s Exolit® OP 1311 and 1312 intumescent
FR additives were used to generate a family of FR intumescent polyamide 11 nanocomposites
with anticipated synergism.Mechanical Engineerin
The DEEP2 Galaxy Redshift Survey: Discovery of Luminous, Metal-poor, Sta r-forming Galaxies at Redshifts z~0.7
We have discovered a sample of 17 metal-poor, yet luminous, star-forming
galaxies at redshifts z~0.7. They were selected from the initial phase of the
DEEP2 survey of 3900 galaxies and the Team Keck Redshift Survey (TKRS) of 1536
galaxies as those showing the temperature-sensitive [OIII]l4363 auroral line.
These rare galaxies have blue luminosities close to L*, high star formation
rates of 5 to 12 solar masses per year, and oxygen abundances of 1/3 to 1/10
solar. They thus lie significantly off the luminosity-metallicity relation
found previously for field galaxies with strong emission lines at redshifts
z~0.7. The prior surveys relied on indirect, empirical calibrations of the R23
diagnostic and the assumption that luminous galaxies are not metal-poor. Our
discovery suggests that this assumption is sometimes invalid. As a class, these
newly-discovered galaxies are: (1) more metal-poor than common classes of
bright emission-line galaxies at z~0.7 or at the present epoch; (2) comparable
in metallicity to z~3 Lyman Break Galaxies but less luminous; and (3)
comparable in metallicity to local metal-poor eXtreme Blue Compact Galaxies
(XBCGs), but more luminous. Together, the three samples suggest that the
most-luminous, metal-poor, compact galaxies become fainter over time.Comment: This is a .tgz file. It should create the following files: texto.tex,
tab1.tex, f1.eps and f2.eps. The LaTeX style used is emulateapj.cls, version
November 26, 2004. This submission is 5 pages long, one table and two
figures. To appear in ApJ
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Intumescent Flame Retardant Polyamide 11 Nanocomposites
Current polyamide 11 and 12 are lacking in fire retardancy and high strength/high heat
resistance characteristics for a plethora of fabricated parts that are desired and required
for performance driven applications. The introduction of selected nanoparticles such as
surface modified montmorillonite (MMT) clay or carbon nanofibers (CNFs), combined
with a conventional intumescent flame retardant (FR) additive into the polyamide
11/polyamide 12 (PA11/PA12) by melt processing conditions has resulted in the
preparation of a family of intumescent polyamide nanocomposites. These intumescent
polyamide 11 and 12 nanocomposites exhibit enhanced polymer performance
characteristics, i.e., fire retardancy, high strength and high heat resistance and are
expected to expand the market opportunities for polyamide 11 and polyamide 12 polymer
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). In the present study, a nanophase was
introduced into the polyamide 11 and combining it with a conventional intumescent FR
additive via twin screw extrusion. Arkema RILSAN® polyamide 11 molding polymer
pellets were examined with two types of nanoparticles: chemically modified
montmorillonite (MMT) organoclays, and carbon nanofibers (CNFs); and Clairant’s
Exolit® OP 1230 intumescent FR additive were used to create a family of FR
intumescent polyamide 11 nanocomposites.
Transmission electron microscopy (TEM) was used to determine the degree of
nanoparticles dispersion. Injection molded specimens were fabricated for physical,
thermal, and flammability measurements. Thermal stability of these intumescent
polyamide 11 nanocomposites was examined by TGA. Flammability properties were
obtained using the Cone Calorimeter at an external heat flux of 35 kW/m
2
and UL 94
Test Method. Heat deflection temperatures (HDT) were also measured. TEM
micrographs, physical, thermal, and flammability properties are presented. FR
intumescent polyamide 11 nanocomposites properties are compared with polyamide 11
baseline polymer. Based on flammability and mechanical material performance, selective
polymers including polyamide 11 nanocomposites and control polyamide 11 will be
cryogenically ground into fine powders for SLS RM processing. SLS specimens will be
fabricated for thermal, flammability, and mechanical properties characterization.Mechanical Engineerin
The Magnitude-Size Relation of Galaxies out to z ~ 1
As part of the Deep Extragalactic Evolutionary Probe (DEEP) survey, a sample
of 190 field galaxies (I_{814} <= 23.5) in the ``Groth Survey Strip'' has been
used to analyze the magnitude-size relation over the range 0.1 < z < 1.1. The
survey is statistically complete to this magnitude limit. All galaxies have
photometric structural parameters, including bulge fractions (B/T), from Hubble
Space Telescope images, and spectroscopic redshifts from the Keck Telescope.
The analysis includes a determination of the survey selection function in the
magnitude-size plane as a function of redshift, which mainly drops faint
galaxies at large distances. Our results suggest that selection effects play a
very important role. A first analysis treats disk-dominated galaxies with B/T <
0.5. If selection effects are ignored, the mean disk surface brightness
(averaged over all galaxies) increases by ~1.3 mag from z = 0.1 to 0.9.
However, most of this change is plausibly due to comparing low luminosity
galaxies in nearby redshift bins to high luminosity galaxies in distant bins.
If this effect is allowed for, no discernible evolution remains in the disk
surface brightness of bright (M_B < -19) disk-dominated galaxies. A second
analysis treats all galaxies by substituting half-light radius for disk scale
length, with similar conclusions. Indeed, at all redshifts, the bulk of
galaxies is consistent with the magnitude-size envelope of local galaxies,
i.e., with little or no evolution in surface brightness. In the two highest
redshift bins (z > 0.7), a handful of luminous, high surface brightness
galaxies appears that occupies a region of the magnitude-size plane rarely
populated by local galaxies. Their wide range of colors and bulge fractions
points to a variety of possible origins.Comment: 19 pages, 12 figures. Accepted for publication in the Astrophysical
Journa
Dynamics of axialized laser-cooled ions in a Penning trap
We report the experimental characterization of axialization - a method of
reducing the magnetron motion of a small number of ions stored in a Penning
trap. This is an important step in the investigation of the suitability of
Penning traps for quantum information processing. The magnetron motion was
coupled to the laser-cooled modified cyclotron motion by the application of a
near-resonant oscillating quadrupole potential (the "axialization drive").
Measurement of cooling rates of the radial motions of the ions showed an
order-of-magnitude increase in the damping rate of the magnetron motion with
the axialization drive applied. The experimental results are in good
qualitative agreement with a recent theoretical study. In particular, a
classical avoided crossing was observed in the motional frequencies as the
axialization drive frequency was swept through the optimum value, proving that
axialization is indeed a resonant effect.Comment: 8 pages, 9 figure
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