472 research outputs found
Observation of coherent population trapping in a V-type two-electron system
We observe coherent population trapping (CPT) in a two-electron
atom---Yb---using the
transition. CPT is not possible for such a transition according to one-electron
theory because the magnetic sublevels form a V-type system, but in a
two-electron atom like Yb, the interaction of the electrons transforms the
level structure into a -type system, which allows the formation of a
dark state and hence the observation of CPT. Since the two levels involved are
degenerate, we use a magnetic field to lift the degeneracy. The single
fluorescence dip then splits into five dips---the central unshifted one
corresponds to coherent population oscillation, while the outer four are due to
CPT. The linewidth of the CPT resonance is about 300 kHz and is limited by the
natural linewidth of the excited state, which is to be expected because the
excited state is involved in the formation of the dark state.Comment: 5 pages, 5 figures, 2 table
Observation of the nuclear magnetic octupole moment of Yb from precise measurements of hyperfine structure in the state
We measure hyperfine structure in the metastable state of
Yb and extract the nuclear magnetic octupole moment. We populate the
state using dipole-allowed transitions through the and
states. We measure frequencies of hyperfine transitions of the line at 770 nm using a Rb-stabilized ring cavity resonator
with a precision of 200 kHz. Second-order corrections due to perturbations from
the nearby and states are below 30 kHz. We obtain the
hyperfine coefficients as: MHz, MHz, which
represent two orders-of-magnitude improvement in precision, and
MHz. From atomic structure calculations, we obtain the nuclear moments:
quadrupole b and octupole b\,.Comment: 5 pages, 1 figur
Optical frequency metrology with a Rb-stabilized ring-cavity resonator -- Study of cavity-dispersion errors
We have developed a technique to measure the absolute frequencies of optical
transitions by using an evacuated Rb-stabilized ring-cavity resonator as a
transfer cavity. We study possible wavelength-dependent errors due to
dispersion at the cavity mirrors by measuring the frequency of the same
transition in the line of Cs at three cavity lengths. We find no
discernable change in values within our error of 30 kHz. Our values are
consistent with measurements using the frequency-comb technique and have
similar accuracy.Comment: 3 pages, 2 figure
Atomic fountain of laser-cooled Yb atoms for precision measurements
We demonstrate launching of laser-cooled Yb atoms in a cold atomic fountain.
Atoms in a collimated thermal beam are first cooled and captured in a
magneto-optic trap (MOT) operating on the strongly-allowed transition at 399~nm (blue line). They are then transferred to a MOT
on the weakly-allowed transition at 556~nm (green
line). Cold atoms from the green MOT are launched against gravity at a velocity
of around 2.5~m/s using a pair of green beams. We trap more than atoms
in the blue MOT and transfer up to 70\% into the green MOT. The temperature for
the odd isotope, Yb, is 1~mK in the blue MOT, and reduces by a
factor of 40 in the green MOT.Comment: 6 pages, 7 figure
Precise measurement of hyperfine structure in the state of Li using saturated-absorption spectroscopy
We report a precise measurement of the hyperfine interval in the
state of Li. The transition from the ground state ( line) is
accessed using a diode laser and the technique of saturated-absorption
spectroscopy in hot Li vapor. The interval is measured by locking an
acousto-optic modulator to the frequency difference between the two hyperfine
peaks. The measured interval of 92.040(6)~MHz is consistent with an earlier
measurement reported by us using an atomic-beam spectrometer [Das and
Natarajan, J.\ Phys.\ B {\bf 41}, 035001 (2008)]. The interval yields the
magnetic dipole constant in the state as , which is
discrepant from theoretical calculations by ~kHz.Comment: 5 pages, 3 figure
Multi-wavelength Temporal Variability of the Blazar 3C 454.3 during 2014 Activity Phase
We present a multi-wavelength temporal analysis of the blazar 3C 454.3 during
the high -ray active period from May-December, 2014. Except for X-rays,
the period is well sampled at near-infrared (NIR)-optical by the \emph{SMARTS}
facility and the source is detected continuously on daily timescale in the
\emph{Fermi}-LAT -ray band. The source exhibits diverse levels of
variability with many flaring/active states in the continuously sampled
-ray light curve which are also reflected in the NIR-optical light
curves and the sparsely sampled X-ray light curve by the \emph{Swift}-XRT.
Multi-band correlation analysis of this continuous segment during different
activity periods shows a change of state from no lags between IR and
-ray, optical and -ray, and IR and optical to a state where
-ray lags the IR/optical by 3 days. The results are consistent
with the previous studies of the same during various -ray flaring and
active episodes of the source. This consistency, in turn, suggests an extended
localized emission region with almost similar conditions during various
-ray activity states. On the other hand, the delay of -ray with
respect to IR/optical and a trend similar to IR/optical in X-rays along with
strong broadband correlations favor magnetic field related origin with X-ray
and -ray being inverse Comptonized of IR/optical photons and external
radiation field, respectively.Comment: 15 pages, 5 figures, 1 table, MNRAS accepte
Functionality of C-Reactive Protein for Atheroprotection
C-reactive protein (CRP) is a pentameric molecule made up of identical monomers. CRP can be seen in three different forms: native pentameric CRP (native CRP), non-native pentameric CRP (nonnative CRP), and monomeric CRP (mCRP). Both native and nonnative CRP execute ligand-recognition functions for host defense. The fate of any pentameric CRP after binding to a ligand is dissociation into ligand-bound mCRP. If ligand-bound mCRP is proinflammatory, like free mCRP has been shown to be in vitro, then mCRP along with the bound ligand must be cleared from the site of inflammation. Once pentameric CRP is bound to atherogenic low-density lipoprotein (LDL), it reduces both formation of foam cells and proinflammatory effects of atherogenic LDL. A CRP mutant, that is non-native CRP, which readily binds to atherogenic LDL, has been found to be atheroprotective in a murine model of atherosclerosis. Thus, unlike statins, a drug that can lower only cholesterol levels but not CRP levels should be developed. Since non-native CRP has been shown to bind to all kinds of malformed proteins in general, it is possible that non-native CRP would be protective against all inflammatory states in which host proteins become pathogenic. If it is proven through experimentation employing transgenic mice that non-native CRP is beneficial for the host, then using a small-molecule compound to target CRP with the goal of changing the conformation of endogenous native CRP would be preferred over using recombinant non-native CRP as a biologic to treat diseases caused by pathogenic proteins such as oxidized LDL
Component traits influencing seed yield in recombinant inbred lines of lentil (Lens culinaris Medik.)
One hundred and thirty five RILs (Recombinant Inbred Lines) developed from a cross between an indigenous and exotic line of lentil (Lens culinarisMedik.)were evaluated for seed yield and component traits during rabi 2012-13 and 2013-14. Pooled analysis of variance revealed significant differences among the RILsfor all the traits studied. This suggested that there was ample scope for selection of promising RILs for yield improvement in lentil. Phenotypic and genotypic coefficients of variation were high for pods per plant(32.49% and 26.75%) followed by biological yield per plot(24.38% and 21.28%). Genetic advance was highest for 100-seed weight(47.75%)followed by pods per plant(45.39%). Estimation of phenotypic correlation coefficients indicated that seed yield per plot expressed highly significant and positive correlation with biological yield per plot(0.634), harvest index(0.300) and seeds per pod(0.156). Path coefficient analysis revealed that the traits; biological yield per plot , harvest index, number of pods per plant, days to 50% flowering, days to maturity , plant height and primary branches per plant had positive direct effect on seed yield per plot. The selection of these traits would be helpful for further yield improvement in lentil
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