1,099 research outputs found
Observation of sub-natural linewidths for cold atoms in a magneto-optic trap
We have studied the absorption of a weak probe beam through cold rubidium
atoms in a magneto-optic trap. The absorption spectrum shows two peaks with the
smaller peak having linewidth as small as 28% of the natural linewidth. The
modification happens because the laser beams used for trapping also drive the
atoms coherently between the ground and excited states. This creates
``dressed'' states whose energies are shifted depending on the strength of the
drive. Linewidth narrowing occurs due to quantum coherence between the dressed
states. The separation of the states increases with laser intensity and
detuning, as expected from this model.Comment: 8 pages, 4 figure
Meeting the challenges related to material issues in chemical industries
Reliable performance and profitability are two important requirements for any chemical industry. In order to achieve high level of reliability and excellent performance, several issues related to design, materials selection, fabrication, quality assurance, transport, storage, inputs from condition monitoring, failure analysis etc. have to be adequately addressed and implemented. Technology related to nondestructive testing and monitoring of the plant is also essential for precise identification of defect sites and to take appropriate remedial decision regarding repair, replacement or modification of process conditions. The interdisciplinary holistic approach enhances the life of critical engineering components in chemical plants. Further, understanding the failure modes of the components through the analysis of failed components throws light on the choice of appropriate preventive measures to be taken well in advance, to have a control over the overall health of the plant. The failure analysis also leads to better design modification and condition monitoring methodologies, for the next generation components and plants. At the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam, a unique combination of the expertise in design, materials selection, fabrication, NDT development, condition monitoring, life prediction and failure analysis exists to obtain desired results for achieving high levels of reliability and performance assessment of critical engineering components in chemical industries. Case studies related to design, materials selection and fabrication aspects of critical components in nuclear fuel reprocessing plants, NDT development and condition monitoring of various components of nuclear power plants, and important failure investigations on critical engineering components in chemical and allied industries are discussed in this paper. Future directions are identified and planned approaches are briefly described
Protein targets in Mycobacterium tuberculosis and their inhibitors for therapeutic implications: A narrative review
Advancement in the area of anti-tubercular drug development has been full-fledged, yet, a very less number of drug molecules have reached phase II clinical trials, and therefore "End-TB" is still a global challenge. Inhibitors to specific metabolic pathways of Mycobacterium tuberculosis (Mtb) gain importance in strategizing anti-tuberculosis drug discovery. The lead compounds that target DNA replication, protein synthesis, cell wall biosynthesis, bacterial virulence and energy metabolism are emerging as potential chemotherapeutic options against Mtb growth and survival within the host. In recent times, the in silico approaches have become most promising tools in the identification of suitable inhibitors for specific protein targets of Mtb. An update in the fundamental understanding of these inhibitors and the mechanism of interaction may bring hope to future perspectives in novel drug development and delivery approaches. This review provides a collective impression of the small molecules with potential antimycobacterial activities and their target pathways in Mtb such as cell wall biosynthesis, DNA replication, transcription and translation, efflux pumps, antivirulence pathways and general metabolism. The mechanism of interaction of specific inhibitor with their respective protein targets has been discussed. The comprehensive knowledge of such an impactful area of research would essentially reflect in the discovery of novel drug molecules and effective delivery approaches. This narrative review encompasses the knowledge of emerging targets and promising chemical inhibitors that could potentially translate in to the anti-TB-drug discovery
Precise measurements of UV atomic lines: Hyperfine structure and isotope shifts in the 398.8 nm line of Yb
We demonstrate a technique for frequency measurements of UV transitions with
sub-MHz precision. The frequency is measured using a ring-cavity resonator
whose length is calibrated against a reference laser locked to the line
of Rb. We have used this to measure the 398.8 nm line of atomic Yb. We report isotope shifts of all the
seven stable isotopes, including the rarest isotope Yb. We have been
able to resolve the overlapping Yb() and Yb
transitions for the first time. We also obtain high-precision measurements of
excited-state hyperfine structure in the odd isotopes, Yb and
Yb. The measurements resolve several discrepancies among earlier
measurements.Comment: 7 pages, 6 figure
Solvent Extraction Studies of Gadolinium in Tri-Butyl Phosphate
AbstractFast reactor spent fuel reprocessing plants should be designed for inherent criticality safety due to high plutonium content. Addition of soluble neutron poison is one way to do that. Gadolinium is the best choice based on neutron absorption cross section and chemical compatibility. In this work, using classical thermodynamic approach, the distribution coefficient of gadolinium in tributyl phosphate has been calculated and compared with the experimental data. The influence of acidity and uranium at equilibrium on gadolinium distribution in tributyl phosphate has been investigated. The result establishes the feasibility of employing gadolinium as soluble neutron poison in fast fuel reprocessing
HST/STIS Imaging of the Host Galaxy of GRB980425/SN1998bw
We present HST/STIS observations of ESO 184-G82, the host galaxy of the
gamma-ray burst GRB 980425 associated with the peculiar Type Ic supernova
SN1998bw. ESO 184-G82 is found to be an actively star forming SBc sub-luminous
galaxy. We detect an object consistent with being a point source within the
astrometric uncertainty of 0.018 arcseconds of the position of the supernova.
The object is located inside a star-forming region and is at least one
magnitude brighter than expected for the supernova based on a simple
radioactive decay model. This implies either a significant flattening of the
light curve or a contribution from an underlying star cluster.Comment: 12 pages, 2 figures, AASTeX v5.02 accepted for publication in ApJ
Letter
Atom focusing by far-detuned and resonant standing wave fields: Thin lens regime
The focusing of atoms interacting with both far-detuned and resonant standing
wave fields in the thin lens regime is considered. The thin lens approximation
is discussed quantitatively from a quantum perspective. Exact quantum
expressions for the Fourier components of the density (that include all
spherical aberration) are used to study the focusing numerically. The following
lens parameters and density profiles are calculated as functions of the pulsed
field area : the position of the focal plane, peak atomic density,
atomic density pattern at the focus, focal spot size, depth of focus, and
background density. The lens parameters are compared to asymptotic, analytical
results derived from a scalar diffraction theory for which spherical aberration
is small but non-negligible (). Within the diffraction theory
analytical expressions show that the focused atoms in the far detuned case have
an approximately constant background density
while the peak density behaves as , the focal distance or
time as , the focal spot size as
, and the depth of focus as .
Focusing by the resonant standing wave field leads to a new effect, a Rabi-
like oscillation of the atom density. For the far-detuned lens, chromatic
aberration is studied with the exact Fourier results. Similarly, the
degradation of the focus that results from angular divergence in beams or
thermal velocity distributions in traps is studied quantitatively with the
exact Fourier method and understood analytically using the asymptotic results.
Overall, we show that strong thin lens focusing is possible with modest laser
powers and with currently achievable atomic beam characteristics.Comment: 21 pages, 11 figure
- …