366 research outputs found
Synthetic Frequency Protocol in the Ramsey Spectroscopy of Clock Transitions
We develop an universal method to significantly suppress probe-induced shifts
in any types of atomic clocks using the Ramsey spectroscopy. Our approach is
based on adaptation of the synthetic frequency concept [V. I. Yudin, et al.,
Phys. Rev. Lett. 107, 030801 (2011)] (previously developed for BBR shift
suppression) to the Ramsey spectroscopy with the use of interrogations for
different dark time intervals. Universality of the method consists in
arbitrariness of the possible Ramsey schemes. However, most extremal results
are obtained in combination with so-called hyper-Ramsey spectroscopy [V. I.
Yudin, et al., Phys. Rev. A 82, 011804(R) (2010)]. In the latter case, the
probe-induced frequency shifts can be suppressed considerably below a
fractional level of 10 practically for any optical atomic clocks, where
this shift previously was metrologically significant. The main advantage of our
method in comparison with other radical hyper-Ramsey approaches [R. Hobson, et
al., Phys. Rev. A 93, 010501(R) (2016); T. Zanon-Willette, et al., Phys. Rev. A
93, 042506 (2016)] consist in much greater efficiency and resistibility in the
presence of decoherentization.Comment: 9 pages, 7 figure
Studies of contribution of metals bonded with organic matter of seawater to the fluxes of total dissolved metals across water-sediment interface at Vistula Lagoon of Baltic Sea
© 2004 IEEE. Investigations of fluxes of a dissolved element across the water-sediment interface in Vistula Lagoon (Baltic Sea) were carried out in August 2001 and 2002, using chamber experiments. Oxygen, iron(II), total dissolved iron, manganese, copper and lead fluxes were calculated. For the first time the fluxes of metals bonded with organic matter of sea water were studied. The contribution of metals bonded with organic matter to the total flux was varied depending upon conditions and may reach up to 70 %. It was found that metal fluxes at the coastal zone are larger than at the center of the lagoon by the factor of 2-4
Tissue-Engineered Vascular Graft of Small Diameter Based on Electrospun Polylactide Microfibers
Tubular vascular grafts 1.1 mm in diameter based on poly(L-lactide) microfibers were obtained by electrospinning. X-ray diffraction and scanning electron microscopy data demonstrated that the samples treated at T=70°C for 1 h in the fixed state on a cylindrical mandrel possessed dense fibrous structure; their degree of crystallinity was approximately 44%. Strength and deformation stability of these samples were higher than those of the native blood vessels; thus, it was possible to use them in tissue engineering as bioresorbable vascular grafts. The experiments on including implantation into rat abdominal aorta demonstrated that the obtained vascular grafts did not cause pathological reactions in the rats; in four weeks, inner side of the grafts became completely covered with endothelial cells, and fibroblasts grew throughout the wall. After exposure for 12 weeks, resorption of PLLA fibers started, and this process was completed in 64 weeks. Resorbed synthetic fibers were replaced by collagen and fibroblasts. At that time, the blood vessel was formed; its neointima and neoadventitia were close to those of the native vessel in structure and composition
Theory of nonlinear sub-Doppler laser spectroscopy taking into account atomic-motion-induced density-dependent effects in a gas
We develop a field-nonlinear theory of sub-Doppler spectroscopy in a gas of
two-level atoms, based on a self-consistent solution of the Maxwell-Bloch
equations in the mean field and single-atom density matrix approximations. This
makes it possible to correctly take into account the effects caused by the free
motion of atoms in a gas, which lead to a nonlinear dependence of the
spectroscopic signal on the atomic density even in the absent of a direct
interatomic interaction (e.g., dipole-dipole interaction). Within the framework
of this approach, analytical expressions for the light field were obtained for
an arbitrary number of resonant waves and arbitrary optical thickness of a gas
medium. Sub-Doppler spectroscopy in the transmission signal for two
counterpropagating and co-propagating waves has been studied in detail. A
previously unknown red shift of a narrow sub-Doppler resonance is predicted in
a counterpropagating waves scheme, when the frequency of one wave is fixed and
the frequency of the other wave is varied. The magnitude of this shift depends
on the atomic density and can be more than an order of magnitude greater than
the known shift from the interatomic dipole-dipole interaction (Lorentz-Lorenz
shift). The found effects, caused by the free motion of atoms, require a
significant revision of the existing picture of spectroscopic effects depending
on the density of atoms in a gas. Apart of fundamental aspect, obtained results
are important for precision laser spectroscopy and optical atomic clocks.Comment: 18 pages, 12 figure
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