1,131 research outputs found
Acoustic driving of rotor
Sound waves are utilized to apply torque to a body in an enclosure of square cross section, by driving two transducers located on perpendicular walls of an enclosure, at the same frequency but at a predetermined phase difference such as 90 degrees. The torque is a first order effect, so that large and controlled rotational speeds can be obtained
High resolution Ge/Li/ spectrometer reduces rate-dependent distortions at high counting rates
Modified spectrometer system with a low-noise preamplifier reduces rate-dependent distortions at high counting rates, 25,000 counts per second. Pole-zero cancellation minimizes pulse undershoots due to multiple time constants, baseline restoration improves resolution and prevents spectral shifts
Effects of mechanical strain on thermal denaturation of DNA
As sections of a strand duplexed DNA denature when exposed to high
temperature, the excess linking number is taken up by the undenatured portions
of the molecule. The mechanical energy that arises because of the overwinding
of the undenatured sections can, in principle, alter the nature of the thermal
denaturation process. Assuming that the strains associated with this
overwinding are not relieved, we find that a simple model of strain-altered
melting leads to a suppression of the melting transition when the unaltered
transition is continuous. When the melting transition is first order in the
absence of strain associated with overwinding, the modification is to a third
order phase transition.Comment: 4 pages, 5 figures, RevTe
Radio Galaxy Zoo: Cosmological Alignment of Radio Sources
We study the mutual alignment of radio sources within two surveys, FIRST and
TGSS. This is done by producing two position angle catalogues containing the
preferential directions of respectively and extended
sources distributed over more than and square degrees. The
identification of the sources in the FIRST sample was performed in advance by
volunteers of the Radio Galaxy Zoo project, while for the TGSS sample it is the
result of an automated process presented here. After taking into account
systematic effects, marginal evidence of a local alignment on scales smaller
than is found in the FIRST sample. The probability of this happening
by chance is found to be less than per cent. Further study suggests that on
scales up to the alignment is maximal. For one third of the sources,
the Radio Galaxy Zoo volunteers identified an optical counterpart. Assuming a
flat CDM cosmology with , we
convert the maximum angular scale on which alignment is seen into a physical
scale in the range Mpc . This result supports recent
evidence reported by Taylor and Jagannathan of radio jet alignment in the
deg ELAIS N1 field observed with the Giant Metrewave Radio Telescope. The
TGSS sample is found to be too sparsely populated to manifest a similar signal
Radio Galaxy Zoo: Knowledge Transfer Using Rotationally Invariant Self-Organising Maps
With the advent of large scale surveys the manual analysis and classification
of individual radio source morphologies is rendered impossible as existing
approaches do not scale. The analysis of complex morphological features in the
spatial domain is a particularly important task. Here we discuss the challenges
of transferring crowdsourced labels obtained from the Radio Galaxy Zoo project
and introduce a proper transfer mechanism via quantile random forest
regression. By using parallelized rotation and flipping invariant Kohonen-maps,
image cubes of Radio Galaxy Zoo selected galaxies formed from the FIRST radio
continuum and WISE infrared all sky surveys are first projected down to a
two-dimensional embedding in an unsupervised way. This embedding can be seen as
a discretised space of shapes with the coordinates reflecting morphological
features as expressed by the automatically derived prototypes. We find that
these prototypes have reconstructed physically meaningful processes across two
channel images at radio and infrared wavelengths in an unsupervised manner. In
the second step, images are compared with those prototypes to create a
heat-map, which is the morphological fingerprint of each object and the basis
for transferring the user generated labels. These heat-maps have reduced the
feature space by a factor of 248 and are able to be used as the basis for
subsequent ML methods. Using an ensemble of decision trees we achieve upwards
of 85.7% and 80.7% accuracy when predicting the number of components and peaks
in an image, respectively, using these heat-maps. We also question the
currently used discrete classification schema and introduce a continuous scale
that better reflects the uncertainty in transition between two classes, caused
by sensitivity and resolution limits
Theory of monolayers with boundaries: Exact results and Perturbative analysis
Domains and bubbles in tilted phases of Langmuir monolayers contain a class
of textures knows as boojums. The boundaries of such domains and bubbles may
display either cusp-like features or indentations. We derive analytic
expressions for the textures within domains and surrounding bubbles, and for
the shapes of the boundaries of these regions. The derivation is perturbative
in the deviation of the bounding curve from a circle. This method is not
expected to be accurate when the boundary suffers large distortions, but it
does provide important clues with regard to the influence of various energetic
terms on the order-parameter texture and the shape of the domain or bubble
bounding curve. We also look into the effects of thermal fluctuations, which
include a sample-size-dependent effective line tension.Comment: replaced with published version, 21 pages, 16 figures include
Detecting the Cold Spot as a Void with the Non-Diagonal Two-Point Function
The anomaly in the Cosmic Microwave Background known as the "Cold Spot" could
be due to the existence of an anomalously large spherical (few hundreds Mpc/h
radius) underdense region, called a "Void" for short. Such a structure would
have an impact on the CMB also at high multipoles l through Lensing. This would
then represent a unique signature of a Void. Modeling such an underdensity with
an LTB metric, we show that the Lensing effect leads to a large signal in the
non-diagonal two-point function, centered in the direction of the Cold Spot,
such that the Planck satellite will be able to confirm or rule out the Void
explanation for the Cold Spot, for any Void radius with a Signal-to-Noise ratio
of at least O(10).Comment: v1: 6 pages, 2 figures; v2: 6 pages, 2 figures, text improved, to
appear on JCA
HST and Spitzer imaging of red and blue galaxies at z~2.5: A correlation between size and star formation activity from compact quiescent galaxies to extended star forming galaxies
We present HST NICMOS+ACS and Spitzer IRAC+MIPS observations of 41 galaxies
at 2<z<3.5 in the FIRES MS1054 field with red and blue rest-frame optical
colors. About half of the galaxies are very compact (effective radii r_e < 1
kpc) at rest-frame optical wavelengths, the others are extended (1< r_e < 10
kpc). For reference, 1 kpc corresponds to 0.12 arcsec at z=2.5 in the adopted
cosmology. We separate actively star forming galaxies from quiescent galaxies
by modeling their rest-frame UV-NIR SEDs. The star forming galaxies span the
full range of sizes, while the quiescent galaxies all have r_e<2kpc. In the
redshift range where MIPS 24 micron imaging is a sensitive probe of re-radiated
dust emission (z<2.5), the 24 micron fluxes confirm that the light of the small
quiescent galaxies is dominated by old stars, rather than dust-enshrouded star
formation or AGN activity. The inferred surface mass densities and velocity
dispersions for the quiescent galaxies are very high compared to those in local
galaxies. The galaxies follow a Kormendy relation (between surface brightness
and size) with approximately the same slope as locally, but shifted to brighter
surface brightnesses, consistent with a mean stellar formation redshift of
z_f~5. This paper demonstrates a direct relation between star formation
activity and size at z~2.5, and the existence of a significant population of
massive, extremely dense, old stellar systems without readily identifiable
counterparts in the local universe.Comment: Accepted for publication in Ap
Parametric Generation of Second Sound by First Sound in Superfluid Helium
We report the first experimental observation of parametric generation of
second sound (SS) by first sound (FS) in superfluid helium in a narrow
temperature range in the vicinity of . The temperature dependence
of the threshold FS amplitude is found to be in a good quantitative agreement
with the theory suggested long time ago and corrected for a finite geometry.
Strong amplitude fluctuations and two types of the SS spectra are observed
above the bifurcation. The latter effect is quantitatively explained by the
discreteness of the wave vector space and the strong temperature dependence of
the SS dissipation length.Comment: 4 pages, 4 postscript figures, REVTE
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