30,173 research outputs found
Lathe attachment used to machine elliptical cones
Close-tolerance elliptical cones are fabricated by cutting-tool guide assembly used with conventional tracer cartridge on turret lathe accurately produced in two machine operations
Apparatus for machining geometric cones Patent
Rotary spindle lathe attachments for machining geometrical cone
Witnessing the Growth of the Nearest Galaxy Cluster: Thermodynamics of the Virgo Cluster Outskirts
We present results from Suzaku Key Project observations of the Virgo Cluster,
the nearest galaxy cluster to us, mapping its X-ray properties along four long
`arms' extending beyond the virial radius. The entropy profiles along all four
azimuths increase with radius, then level out beyond , while the
average pressure at large radii exceeds Planck Sunyaev-Zel'dovich measurements.
These results can be explained by enhanced gas density fluctuations (clumping)
in the cluster's outskirts. Using a standard Navarro, Frenk and White (1997)
model, we estimate a virial mass, radius, and concentration parameter of
M, kpc, and , respectively. The inferred cumulative baryon fraction exceeds
the cosmic mean at along the major axis, suggesting enhanced
gas clumping possibly sourced by a candidate large-scale structure filament
along the north-south direction. The Suzaku data reveal a large-scale sloshing
pattern, with two new cold fronts detected at radii of 233 kpc and 280 kpc
along the western and southern arms, respectively. Two high-temperature regions
are also identified 1 Mpc towards the south and 605 kpc towards the west of
M87, likely representing shocks associated with the ongoing cluster growth.
Although systematic uncertainties in measuring the metallicity for low
temperature plasma remain, the data at large radii appear consistent with a
uniform metal distribution on scales of kpc and larger,
providing additional support for the early chemical enrichment scenario driven
by galactic winds at redshifts of 2-3.Comment: submitted to MNRA
A uniform metallicity in the outskirts of massive, nearby galaxy clusters
Suzaku measurements of a homogeneous metal distribution of Solar
in the outskirts of the nearby Perseus cluster suggest that chemical elements
were deposited and mixed into the intergalactic medium before clusters formed,
likely over 10 billion years ago. A key prediction of this early enrichment
scenario is that the intracluster medium in all massive clusters should be
uniformly enriched to a similar level. Here, we confirm this prediction by
determining the iron abundances in the outskirts () of a sample
of ten other nearby galaxy clusters observed with Suzaku for which robust
measurements based on the Fe-K lines can be made. Across our sample the iron
abundances are consistent with a constant value,
Solar ( for 25 degrees of freedom). This is remarkably similar to
the measurements for the Perseus cluster of Solar,
using the Solar abundance scale of Asplund et al. (2009).Comment: accepted for publication in MNRA
BRST quantization of the massless minimally coupled scalar field in de Sitter space (zero modes, euclideanization and quantization)
We consider the massless scalar field on the four-dimensional sphere .
Its classical action is degenerate
under the global invariance . We then quantize
the massless scalar field as a gauge theory by constructing a BRST-invariant
quantum action. The corresponding gauge-breaking term is a non-local one of the
form where
is a gauge parameter and is the volume of . It allows us to
correctly treat the zero mode problem. The quantum theory is invariant under
SO(5), the symmetry group of , and the associated two-point functions have
no infrared divergence. The well-known infrared divergence which appears by
taking the massless limit of the massive scalar field propagator is therefore a
gauge artifact. By contrast, the massless scalar field theory on de Sitter
space - the lorentzian version of - is not invariant under the
symmetry group of that spacetime SO(1,4). Here, the infrared divergence is
real. Therefore, the massless scalar quantum field theories on and
cannot be linked by analytic continuation. In this case, because of zero modes,
the euclidean approach to quantum field theory does not work. Similar
considerations also apply to massive scalar field theories for exceptional
values of the mass parameter (corresponding to the discrete series of the de
Sitter group).Comment: This paper has been published under the title "Zero modes,
euclideanization and quantization" [Phys. Rev. D46, 2553 (1992)
On the universality of the scaling of fluctuations in traffic on complex networks
We study the scaling of fluctuations with the mean of traffic in complex
networks using a model where the arrival and departure of "packets" follow
exponential distributions, and the processing capability of nodes is either
unlimited or finite. The model presents a wide variety of exponents between 1/2
and 1 for this scaling, revealing their dependence on the few parameters
considered, and questioning the existence of universality classes. We also
report the experimental scaling of the fluctuations in the Internet for the
Abilene backbone network. We found scaling exponents between 0.71 and 0.86 that
do not fit with the exponent 1/2 reported in the literature.Comment: 4 pages, 4 figure
A Uniform Contribution of Core-Collapse and Type Ia Supernovae to the Chemical Enrichment Pattern in the Outskirts of the Virgo Cluster
We present the first measurements of the abundances of -elements (Mg,
Si, and S) extending out to beyond the virial radius of a cluster of galaxies.
Our results, based on Suzaku Key Project observations of the Virgo Cluster,
show that the chemical composition of the intra-cluster medium is consistent
with being constant on large scales, with a flat distribution of the Si/Fe,
S/Fe, and Mg/Fe ratios as a function of radius and azimuth out to 1.4 Mpc (1.3
). Chemical enrichment of the intergalactic medium due solely to core
collapse supernovae (SNcc) is excluded with very high significance; instead,
the measured metal abundance ratios are generally consistent with the Solar
value. The uniform metal abundance ratios observed today are likely the result
of an early phase of enrichment and mixing, with both SNcc and type Ia
supernovae (SNIa) contributing to the metal budget during the period of peak
star formation activity at redshifts of 2-3. We estimate the ratio between the
number of SNIa and the total number of supernovae enriching the intergalactic
medium to be between 12-37%, broadly consistent with the metal abundance
patterns in our own Galaxy or with the SNIa contribution estimated for the
cluster cores.Comment: accepted for publication in ApJ
Slow polaritons with orbital angular momentum in atomic gases
Polariton formalism is applied for studying the propagation of a probe field
of light in a cloud of cold atoms influenced by two control laser beams of
larger intensity. The laser beams couple resonantly three hyperfine atomic
ground states to a common excited state thus forming a tripod configuration of
the atomic energy levels involved. The first control beam can have an optical
vortex with the intensity of the beam going to zero at the vortex core. The
second control beam without a vortex ensures the loseless (adiabatic)
propagation of the probe beam at a vortex core of the first control laser. We
investigate the storage of the probe pulse into atomic coherences by switching
off the control beams, as well as its subsequent retrieval by switching the
control beams on. The optical vortex is transferred from the control to the
probe fields during the storage or retrieval of the probe field. We analyze
conditions for the vortex to be transferred efficiently to the regenerated
probe beam and discuss possibilities of experimental implementation of the
proposed scheme using atoms like rubidium or sodium.Comment: 4 figure
Two-gap superconductivity in MgB: clean or dirty?
A large number of experimental facts and theoretical arguments favor a
two-gap model for superconductivity in MgB. However, this model predicts
strong suppression of the critical temperature by interband impurity scattering
and, presumably, a strong correlation between the critical temperature and the
residual resistivity. No such correlation has been observed. We argue that this
fact can be understood if the band disparity of the electronic structure is
taken into account, not only in the superconducting state, but also in normal
transport
Optimal routing on complex networks
We present a novel heuristic algorithm for routing optimization on complex
networks. Previously proposed routing optimization algorithms aim at avoiding
or reducing link overload. Our algorithm balances traffic on a network by
minimizing the maximum node betweenness with as little path lengthening as
possible, thus being useful in cases when networks are jamming due to queuing
overload. By using the resulting routing table, a network can sustain
significantly higher traffic without jamming than in the case of traditional
shortest path routing.Comment: 4 pages, 5 figure
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