Study of young stellar objects and associated filamentary structures in the inner Galaxy

Young Stellar Objects (YSOs) in the inner Galactic region $10^0 < l < 15^0$ and $-1^0 < b < 1^0$ 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 $\mu$m & 8 $\mu$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' ($\sim$ 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$_\odot$, while Class II sources have relatively low mass regime. Class I sources have ages $\le$ 0.5 Myr, while Class II sources have ages in the range $\sim$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 $Re \approx 700,000$. We use the experimental data to establish a fundamental deflation scaling parameter $\sigma^*$ 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

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

Non-HFE haemochromatosis

Non-HFE hereditary haemochromatosis (HH) refers to a genetically heterogeneous group of iron overload disorders that are unlinked to mutations in the HFE gene. The four main types of non-HFE HH are caused by mutations in the hemojuvelin, hepcidin,, transferrin receptor 2 and ferroportin genes. Juvenile haemochromatosis is an autosomal recessive disorder and can be caused by mutations in either hemojuvelin or hepcidin. An adult onset form of HH similar to HFE-HH is caused by homozygosity for mutations in transferrin receptor 2. The autosomal dominant iron overload disorder ferroportin disease is caused by mutations in the iron exporter ferroportin. The clinical characteristics and molecular basis of the various types of non-HFE haemochromatosis are reviewed. The study of these disorders and the molecules involved has been invaluable in improving our understanding of the mechanisms involved in the regulation of iron metabolism