3,456 research outputs found
Study of young stellar objects and associated filamentary structures in the inner Galaxy
Young Stellar Objects (YSOs) in the inner Galactic region
and are studied using GLIMPSE images and GLIMPSE data
catalogue. A total number of 1107 Class I and 1566 Class II sources are
identified in this Galactic region. With the help of GLIMPSE 5.8 m & 8
m images, we have identified the presence of 10 major star forming sites
in the Galactic midplane, of which 8 of them are filamentary while 2 are
possible clusters of Class I & II sources. The length of the identified
filaments are estimated as 8'-33' ( 9 - 56 pc). Occurrence of
Hub-Filamentary System (HFS) is observed in many filamentary star forming
sites. Most of the Class I sources are found to be aligned along the length of
these filamentary structures, while Class II sources have a random
distribution. Mass and age distribution of 425 Class I and 241 Class II sources
associated with filaments & clusters are studied through their SED analysis.
Most of the Class I sources detected have mass 8M, while Class II
sources have relatively low mass regime. Class I sources have ages 0.5
Myr, while Class II sources have ages in the range 0.1 - 3 Myr. Along
with the help of high mass star forming tracers, we demonstrate that the 10
regions studied here are forming a large number of high-mass stars.Comment: 19 pages, 18 figures. Accepted for publication in MNRA
Ultra-fast escape maneuver of an octopus-inspired robot
We design and test an octopus-inspired flexible hull robot that demonstrates
outstanding fast-starting performance. The robot is hyper-inflated with water,
and then rapidly deflates to expel the fluid so as to power the escape
maneuver. Using this robot we verify for the first time in laboratory testing
that rapid size-change can substantially reduce separation in bluff bodies
traveling several body lengths, and recover fluid energy which can be employed
to improve the propulsive performance. The robot is found to experience speeds
over ten body lengths per second, exceeding that of a similarly propelled
optimally streamlined rigid rocket. The peak net thrust force on the robot is
more than 2.6 times that on an optimal rigid body performing the same maneuver,
experimentally demonstrating large energy recovery and enabling acceleration
greater than 14 body lengths per second squared. Finally, over 53% of the
available energy is converted into payload kinetic energy, a performance that
exceeds the estimated energy conversion efficiency of fast-starting fish. The
Reynolds number based on final speed and robot length is .
We use the experimental data to establish a fundamental deflation scaling
parameter which characterizes the mechanisms of flow control via
shape change. Based on this scaling parameter, we find that the fast-starting
performance improves with increasing size.Comment: Submitted July 10th to Bioinspiration & Biomimetic
Diffractive wave guiding of hot electrons by the Au (111) herringbone reconstruction
The surface potential of the herringbone reconstruction on Au(111) is known
to guide surface-state electrons along the potential channels. Surprisingly, we
find by scanning tunneling spectroscopy that hot electrons with kinetic
energies twenty times larger than the potential amplitude (38 meV) are still
guided. The efficiency even increases with kinetic energy, which is reproduced
by a tight binding calculation taking the known reconstruction potential and
strain into account. The guiding is explained by diffraction at the
inhomogeneous electrostatic potential and strain distribution provided by the
reconstruction.Comment: 10 pages, 9 figure
Molecular beacons: nucleic acid hybridization and emerging applications
Molecular beacons (MBs) are a novel class of nucleic acid probes that become fluorescent when bound to a complementary sequence. Because of this characteristic, coupled with the sequence specificity of nucleic acid hybridization and the sensitivity of fluorescence techniques, MBs are very useful probes for a variety of applications requiring the detection of DNA or RNA. We survey various applications of MBs, including the monitoring of DNA triplex formation, and describe recent developments in MB design that enhance their sensitivity
Enskog kinetic theory for monodisperse gas–solid flows
The Enskog kinetic theory is used as a starting point to model a suspension of solid particles in a viscous gas. Unlike previous efforts for similar suspensions, the gas-phase contribution to the instantaneous particle acceleration appearing in the Enskog equation is modelled using a Langevin equation, which can be applied to a wide parameter space (e.g. high Reynolds number). Attention here is limited to low Reynolds number flow, however, in order to assess the influence of the gas phase on the constitutive relations, which was assumed to be negligible in a previous analytical treatment. The Chapman–Enskog method is used to derive the constitutive relations needed for the conservation of mass, momentum and granular energy. The results indicate that the Langevin model for instantaneous gas–solid force matches the form of the previous analytical treatment, indicating the promise of this method for regions of the parameter space outside of those attainable by analytical methods (e.g. higher Reynolds number). The results also indicate that the effect of the gas phase on the constitutive relations for the solid-phase shear viscosity and Dufour coefficient is non-negligible, particularly in relatively dilute systems. Moreover, unlike their granular (no gas phase) counterparts, the shear viscosity in gas–solid systems is found to be zero in the dilute limit and the Dufour coefficient is found to be non-zero in the elastic limit
Silver Nanoparticle Aggregates as Highly Efficient Plasmonic Antennas for Fluorescence Enhancement
The enhanced local fields around plasmonic structures can lead to enhancement of the excitation and modification of the emission quantum yield of fluorophores. So far, high enhancement of fluorescence intensity from dye molecules was demonstrated using bow-tie gap antenna made by e-beam lithography. However, the high manufacturing cost and the fact that currently there are no effective ways to place fluorophores only at the gap prevent the use of these structures for enhancing fluorescence-based biochemical assays. We report on the simultaneous modification of fluorescence intensity and lifetime of dye-labeled DNA in the presence of aggregated silver nanoparticles. The nanoparticle aggregates act as efficient plasmonic antennas, leading to more than 2 orders of magnitude enhancement of the average fluorescence. This is comparable to the best-reported fluorescence enhancement for a single molecule but here applies to the average signal detected from all fluorophores in the system. This highlights the remarkable efficiency of this system for surface-enhanced fluorescence. Moreover, we show that the fluorescence intensity enhancement varies with the plasmon resonance position and measure a significant reduction (300×) of the fluorescence lifetime. Both observations are shown to be in agreement with the electromagnetic model of surface-enhanced fluorescence
On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions
Based on the CCD observations of remote young open clusters NGC 2383, NGC
2384, NGC 4103, NGC 4755, NGC 7510 and Hogg 15, we constructed their observed
luminosity functions (LFs). The observed LFs are corrected for field star
contamination determined with the help of galactic star count model. In the
case of Hogg 15 and NGC 2383 we also considered the additional contamination
from neighbouring clusters NGC 4609 and NGC 2384 respectively. These
corrections provided the realistic pattern of cluster LF in the vicinity of the
MS turn on point and at fainter magnitudes, revealed the so called H-feature
arising due to transition of the Pre-MS phase to MS, which is dependent on the
cluster age. The theoretical LFs were constructed representing a cluster
population model with continuous star formation for a short time scale and a
power law Initial Mass Function (IMF) and these were fitted to the observed LF.
As a result we are able to determine for each cluster a set of parameters,
describing cluster population (the age, duration of star formation, IMF slope
and percentage of field star contamination). It was found that in spite of the
non-monotonic behaviour of observed LFs, cluster IMFs can be described as the
power law functions with slopes similar to Salpeter's value. The present MS
turn on cluster ages are several times lower than those derived from the
fitting of theoretical isochrones to the turn off region of the upper Main
Sequences.Comment: 17 pages, 5 figures, To appear in MNRA
Isobutane/butene alkylation on microporous and mesoporous solid acid catalysts: probing the pore transport effects with liquid and near critical reaction media
This is the published version. Copyright 2008 Royal Society of ChemistryThe alkylation of isobutane with 1-butene was investigated on microporous (β-zeolite) and mesoporous (silica supported heteropolyacids) catalysts in a slurry reactor. The reaction was investigated in the range of 25–100 bar and 15–95 °C in liquid phase and in near critical reaction media with either dense CO2 or dense ethane as diluent, partially replacing the excess isobutane. At 75 °C, the selectivity towards trimethylpentanes (TMP) in the liquid phase is 70%+ initially, but decreases with time on all the catalysts investigated. While near-critical reaction mixtures were employed in order to enhance pore diffusion rates, the conversion and selectivity profiles obtained with such mixtures are comparable to those obtained with liquid phase reaction mixtures in both microporous and mesoporous catalysts. This implies that pore diffusion effects play a limited role at higher temperatures (75–95 °C). In contrast, the liquid phase results at sub-ambient temperatures indicate that the catalyst is deactivated before the TMPs diffuse out of the pores, indicating that pore diffusion effects play an important role in the deactivation process at low temperatures. Our results suggest that novel approaches that enhance the pore-diffusion rates of the TMPs at lower temperatures must be pursued
Damage Assessment in Concrete Structures using PZT patches
Piezoelectric based PZT smart sensors offer significant
potential for continuously monitoring the development and
progression of internal damage in concrete structures.
PZT-based damage sensors consisting of piezo-electric
patches, which are bonded to the surface of a concrete
structure can be developed for assessing the damage
progression of concrete members. The primary challenge
in developing a PZT-based sensor lies in developing a
methodology to infer about the level of damage in the
material from measurement. Changes in the resonant
behavior in the measured electrical conductance obtained
from electro-mechanical (EM) response of a PZT bonded
to a concrete substrate is investigated for increasing
levels of damage. The sensitivity of EM impedance-
based measurements to level of damage in concrete is
reported. Incipient damage in the form of microcracks in
the concrete substrate produces a change in the electrical
conductance signature associated with the resonant
peaks. Changes in the conductance resonant signature
from EM conductance measurement are detected before
visible signs of cracking. The root mean square deviation
of the conductance signature at resonant peaks is shown
to accurately reflect the level of damage in the substrate.
The findings presented here provide a basis for developing
a sensing methodology using PZT patches for continuous
monitoring of concrete structures
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