4,986 research outputs found
Dynamic and Static Transmission Electron Microscopy Studies on Structural Evaluation of Au nano islands on Si (100) Surface
Transmission electron microscopy (TEM) study on morphological changes in gold
nanostructures deposited on Si (100) upon annealing under different vacuum
conditions has been reported. Au thin films of thickness ~2.0 nm were deposited
under high vacuum condition (with the native oxide at the interface of Au and
Si) using thermal evaporation. In-situ, high temperature (from room temperature
(RT) to 850\degreeC) real time TEM measurements showed the evaluation of gold
nanoparticles into rectangular/square shaped gold silicide structures. This has
been attributed to selective thermal decomposition of native oxide layer.
Ex-situ annealing in low vacuum (10-2 mbar) at 850\degreeC showed no growth of
nano-gold silicide structures. Under low vacuum annealing conditions, the
creation of oxide could be dominating compared to the decomposition of oxide
layers resulting in the formation of barrier layer between Au and Si.Comment: 15 pages, 4 figure
Diamond electro-optomechanical resonators integrated in nanophotonic circuits
Diamond integrated photonic devices are promising candidates for emerging
applications in nanophotonics and quantum optics. Here we demonstrate active
modulation of diamond nanophotonic circuits by exploiting mechanical degrees of
freedom in free-standing diamond electro-optomechanical resonators. We obtain
high quality factors up to 9600, allowing us to read out the driven
nanomechanical response with integrated optical interferometers with high
sensitivity. We are able to excite higher order mechanical modes up to 115 MHz
and observe the nanomechanical response also under ambient conditions.Comment: 15 pages, 4 figure
Evaporative Cooling of a Guided Rubidium Atomic Beam
We report on our recent progress in the manipulation and cooling of a
magnetically guided, high flux beam of atoms. Typically
atoms per second propagate in a magnetic guide providing a
transverse gradient of 800 G/cm, with a temperature K, at an
initial velocity of 90 cm/s. The atoms are subsequently slowed down to cm/s using an upward slope. The relatively high collision rate (5 s)
allows us to start forced evaporative cooling of the beam, leading to a
reduction of the beam temperature by a factor of ~4, and a ten-fold increase of
the on-axis phase-space density.Comment: 10 pages, 8 figure
The effect of parallel static and microwave electric fields on excited hydrogen atoms
Motivated by recent experiments we analyse the classical dynamics of a
hydrogen atom in parallel static and microwave electric fields. Using an
appropriate representation and averaging approximations we show that resonant
ionisation is controlled by a separatrix, and provide necessary conditions for
a dynamical resonance to affect the ionisation probability.
The position of the dynamical resonance is computed using a high-order
perturbation series, and estimate its radius of convergence. We show that the
position of the dynamical resonance does not coincide precisely with the
ionisation maxima, and that the field switch-on time can dramatically affect
the ionisation signal which, for long switch times, reflects the shape of an
incipient homoclinic. Similarly, the resonance ionisation time can reflect the
time-scale of the separatrix motion, which is therefore longer than
conventional static field Stark ionisation. We explain why these effects should
be observed in the quantum dynamics.
PACs: 32.80.Rm, 33.40.+f, 34.10.+x, 05.45.Ac, 05.45.MtComment: 47 pages, 20 figure
Parametrization of dark energy equation of state Revisited
A comparative study of various parametrizations of the dark energy equation
of state is made. Astrophysical constraints from LSS, CMB and BBN are laid down
to test the physical viability and cosmological compatibility of these
parametrizations. A critical evaluation of the 4-index parametrizations reveals
that Hannestad-M\"{o}rtsell as well as Lee parametrizations are simple and
transparent in probing the evolution of the dark energy during the expansion
history of the universe and they satisfy the LSS, CMB and BBN constraints on
the dark energy density parameter for the best fit values.Comment: 11 page
Discrimination, molecular characterisation and phylogenetic comparison of porcine Eimeria spp. in India
Infections with Eimeria spp. are common in pigs worldwide,occasionally affecting animals clinically after weaning or during the fattening period when diarrhoea and weight loss can be observed upon infection with the more pathogenic species. Molecular characterization of pathogens is valuable to accurately delimit species and development novel diagnostics, although sequences which define Eimeria species that infect pigs are scarce. Only three of the eight common species are currently represented in GenBank. In this study we describe the occurrence of Eimeria species in pigs sampled in Punjab, India;going on to use the samples to generate new species-specific 18 S rDNA sequences for all of the previously uncharacterised species. Using these data we report the first phylogenetic analyses to include the eight Eimeria species that commonly infect the domestic pig (Sus scrofa domesticus).Consideration of phylogenetic trees produced using Maximum Likelihood, Neighbour Joining, Maximum Parsimony and Unweighted Pair Group Method with Arithmetic Mean methods indicate that the 18 S rDNA sequences present lower levels of genetic diversity than Eimeria which infect avian species and are insufficient to infer stable phylogenies
High-Q optomechanical circuits made from polished nanocrystalline diamond thin films
We demonstrate integrated optomechanical circuits with high mechanical
quality factors prepared from nanocrystalline diamond thin films. Using
chemomechanical polishing, the RMS surface roughness of as grown
polycrystalline diamond films is reduced below 3nm to allow for the fabrication
of high-quality nanophotonic circuits. By integrating free-standing
nanomechanical resonators into integrated optical devices, efficient read-out
of the thermomechanical motion of diamond resonators is achieved with on-chip
Mach-Zehnder interferometers. Mechanical quality factors up to 28,800 are
measured for four-fold clamped optomechanical resonators coupled to the
evanescent near-field of nanophotonic waveguides. Our platform holds promise
for large-scale integration of optomechanical circuits for on-chip metrology
and sensing applications
Determination of the Kobayashi-Maskawa-Cabibbo matrix element V_{us} under various flavor-symmetry-breaking models in hyperon semileptonic decays
We study the success to describe hyperon semileptonic decays of four models
that incorporate second-order SU(3) symmetry breaking corrections. The criteria
to assess their success is by determining V_{us} in each of the three relevant
hyperon semileptonic decays and comparing the values obtained with one another
and also with the one that comes from K_{l3} decays. A strong dependence on the
particular symmetry breaking model is observed. Values of V_{us} which do not
agree with the one of K_{l3} are generally obtained. However, in the context of
chiral perturbation theory, only the model whose corrections are O(m_s) and
O(m_s^{3/2}) is successful. Using its predictions for the f_1 form factors one
can quote a value of V_{us} from this model, namely, V_{us}=0.2176\pm 0.0026,
which is in excellent agreement with the K_{l3} one.Comment: Final versio
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