1,255 research outputs found
The localization transition in SU(3) gauge theory
We study the Anderson-like localization transition in the spectrum of the
Dirac operator of quenched QCD. Above the deconfining transition we determine
the temperature dependence of the mobility edge separating localized and
delocalized eigenmodes in the spectrum. We show that the temperature where the
mobility edge vanishes and localized modes disappear from the spectrum,
coincides with the critical temperature of the deconfining transition. We also
identify topological charge related close to zero modes in the Dirac spectrum
and show that they account for only a small fraction of localized modes, a
fraction that is rapidly falling as the temperature increases.Comment: 7 pages, 5 figures, v3: additional data on finer lattice; final,
published versio
On the measurement of frequency and of its sample variance with high-resolution counters
A frequency counter measures the input frequency averaged over a
suitable time , versus the reference clock. High resolution is achieved
by interpolating the clock signal. Further increased resolution is obtained by
averaging multiple frequency measurements highly overlapped. In the presence of
additive white noise or white phase noise, the square uncertainty improves from
to .
Surprisingly, when a file of contiguous data is fed into the formula of the
two-sample (Allan) variance
of
the fractional frequency fluctuation , the result is the \emph{modified}
Allan variance mod . But if a sufficient number of contiguous
measures are averaged in order to get a longer and the data are fed into
the same formula, the results is the (non-modified) Allan variance. Of course
interpretation mistakes are around the corner if the counter internal process
is not well understood.Comment: 14 pages, 5 figures, 1 table, 18 reference
Probing the massive star forming environment - a multiwavelength investigation of the filamentary IRDC G333.73+0.37
We present a multiwavelength study of the filamentary infrared dark cloud
(IRDC) G333.73+0.37. The region contains two distinct mid-infrared sources S1
and S2 connected by dark lanes of gas and dust. Cold dust emission from the
IRDC is detected at seven wavelength bands and we have identified 10 high
density clumps in the region. The physical properties of the clumps such as
temperature: 14.3-22.3 K and mass: 87-1530 M_sun are determined by fitting a
modified blackbody to the spectral energy distribution of each clump between
160 micron and 1.2 mm. The total mass of the IRDC is estimated to be $~4700
M_sun. The molecular line emission towards S1 reveals signatures of
protostellar activity. Low frequency radio emission at 1300 and 610 MHz is
detected towards S1 (shell-like) and S2 (compact morphology), confirming the
presence of newly formed massive stars in the IRDC. Photometric analysis of
near and mid-infrared point sources unveil the young stellar object population
associated with the cloud. Fragmentation analysis indicates that the filament
is supercritical. We observe a velocity gradient along the filament, that is
likely to be associated with accretion flows within the filament rather than
rotation. Based on various age estimates obtained for objects in different
evolutionary stages, we attempt to set a limit to the current age of this
cloud.Comment: 26 pages, 20 figures, accepted by Ap
Radio and infrared study of the star forming region IRAS 20286+4105
A multi-wavelength investigation of the star forming complex IRAS 20286+4105,
located in the Cygnus-X region, is presented here. Near-infrared K-band data is
used to revisit the cluster / stellar group identified in previous studies. The
radio continuum observations, at 610 and 1280 MHz show the presence of a HII
region possibly powered by a star of spectral type B0 - B0.5. The cometary
morphology of the ionized region is explained by invoking the bow-shock model
where the likely association with a nearby supernova remnant is also explored.
A compact radio knot with non-thermal spectral index is detected towards the
centre of the cloud. Mid-infrared data from the Spitzer Legacy Survey of the
Cygnus-X region show the presence of six Class I YSOs inside the cloud. Thermal
dust emission in this complex is modelled using Herschel far-infrared data to
generate dust temperature and column density maps. Herschel images also show
the presence of two clumps in this region, the masses of which are estimated to
be {\sim} 175 M{\sun} and 30 M{\sun}. The mass-radius relation and the surface
density of the clumps do not qualify them as massive star forming sites. An
overall picture of a runaway star ionizing the cloud and a triggered population
of intermediate-mass, Class I sources located toward the cloud centre emerges
from this multiwavelength study. Variation in the dust emissivity spectral
index is shown to exist in this region and is seen to have an inverse relation
with the dust temperature.Comment: 20 pages, 16 figures, accepted for publication in MNRA
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