471 research outputs found
Cancellation of light-shifts in an N-resonance clock
We demonstrate that first-order light-shifts can be cancelled for an
all-optical, three-photon-absorption resonance ("N-resonance") on the D1
transition of Rb87. This light-shift cancellation enables improved frequency
stability for an N-resonance clock. For example, using a table-top apparatus
designed for N-resonance spectroscopy, we measured a short-term fractional
frequency stability (Allan deviation) 1.5e-11 tau^(-1/2) for observation times
1s< tau < 50s. Further improvements in frequency stability should be possible
with an apparatus designed as a dedicated N-resonance clock.Comment: 4 pages, 4 figure
Synthèse formelle de l’hormaomycine et de la bélactosine A par utilisation d’une réaction de cyclopropanation intramoléculaire catalysée par un complexe de rhodium (II)
Ce mémoire présente trois approches différentes vers la synthèse du 3–(trans–2–nitrocyclopropyl)alanine, un intermédiaire synthétique de la hormaomycine. Cette molécule naturelle démontre d’intéressantes activités biologiques et pharmacologiques. Il est intéressant de souligner que ce dérivé donne facilement accès au 3–(trans–2–aminocyclopropyl)alanine, unité centrale de la bélactosine A. Ce composé naturel possédant lui aussi d’intéressantes propriétés biologiques, plusieurs études relationnelles structures-activités menant à des dérivés plus actifs de cette molécule ont été entreprises, démontrant l’intérêt toujours présent de synthétiser de façon efficace et optimale ces dérivés cyclopropaniques. Une méthodologie développée au sein de notre groupe de recherche et basée sur une réaction de cyclopropanation intramoléculaire diastéréosélective sera mise à profit afin d’élaborer une nouvelle voie de synthèse aussi élégante qu’efficace à la construction du 3–(trans–2–nitrocyclopropyl) alanine.
En utilisant un carbène de rhodium généré soit par la dégradation d’un dérivé diazoïque, soit par la formation d’un réactif de type ylure d’iodonium, une réaction de cyclopropanation diastéréosélective permettra la formation de deux autres centres contigus et ce, sans même utiliser d’auxiliaire ou de catalyseur énantioenrichis. Ensuite, un réarrangement intramoléculaire précédant deux réactions synchronisées d’ouverture de cycle et de décarboxylation permettront l’obtention du composé d’intérêt avec un rendement global convenable et en relativement peu d’étapes. De cette manière, la synthèse formelle de la bélactosine A et de l’hormaomycine a été effectuée. Cette synthèse se démarque des autres par l’utilisation d’une seule transformation catalytique énantiosélective.This master’s thesis presents three different approaches toward the synthesis of 3–(trans–2–nitrocyclopropyl)alanine, a key constituent of the natural product hormaomycin. This unusual compound demonstrates interesting biological and pharmaceutical activity. It is noteworthy that this unique amino acid can be readily converted to the corresponding 3–(trans–2–aminocyclopropyl)alanine, the central core of belactosin A, a natural compound exhibiting interesting biological properties. Efficient syntheses of these aminocyclopropane derivatives are of current interest since several structure-activity relationships in syntheses of belactosin A and hormaomycin analogues are currently under study in an effort to discover enhanced biological activity. A methodology developed in our research group based on a diastereoselective intramolecular cyclopropanation reaction will be used to elaborate a unique and elegant pathway to the synthesis of the 3–(trans–2–nitrocyclopropyl)alanine.
By using a rhodium carbene generated either by the degradation of a diazoic derivative or by the formation of the corresponding iodonium ylide, a diastereoselective cyclopropanation reaction can be applied in the concerted elaboration of two chiral centers needed in the desired aminocyclopropanes, avoiding in this way the utilisation of chiral reagents. Following this key sequence, an intramolecular rearrangement followed by synchronous ring–opening/decarboxylation reactions will permit a convenient formation of the desired product in an acceptable overall yield and in few ensuing steps. In this manner, the formal synthesis of the hormaomycin and the belactosin A can be achieved. This synthesis is unique since it involves only one asymmetric step in the whole synthetic process
Measurement of the Blackbody Radiation Shift of the 133Cs Hyperfine Transition in an Atomic Fountain
We used a Cs atomic fountain frequency standard to measure the Stark shift on
the ground state hyperfine transiton frequency in cesium (9.2 GHz) due to the
electric field generated by the blackbody radiation. The measures relative
shift at 300 K is -1.43(11)e-14 and agrees with our theoretical evaluation
-1.49(07)e-14. This value differs from the currently accepted one
-1.69(04)e-14. The difference has a significant implication on the accuracy of
frequency standards, in clocks comparison, and in a variety of high precision
physics tests such as the time stability of fundamental constants.Comment: 4 pages, 2 figures, 2 table
A novel absorption resonance for all-optical atomic clocks
We report an experimental study of an all-optical three-photon-absorption
resonance (known as a "N-resonance") and discuss its potential application as
an alternative to atomic clocks based on coherent population trapping (CPT). We
present measurements of the N-resonance contrast, width and light-shift for the
D1 line of 87Rb with varying buffer gases, and find good agreement with an
analytical model of this novel resonance. The results suggest that N-resonances
are promising for atomic clock applications.Comment: 4 pages, 6 figure
Magnetic field imaging with atomic Rb vapor
We demonstrate the possibility of dynamic imaging of magnetic fields using
electromagnetically induced transparency in an atomic gas. As an experimental
demonstration we employ an atomic Rb gas confined in a glass cell to image the
transverse magnetic field created by a long straight wire. In this arrangement,
which clearly reveals the essential effect, the field of view is about 2 x 2
mm^2 and the field detection uncertainty is 0.14 mG per 10 um x 10 um image
pixel.Comment: 4 pages, 3 figure
Investigation of microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells
Using laser optical pumping, widths and frequency shifts are determined for
microwave transitions between ground-state hyperfine components of Rb
and Rb atoms contained in vapor cells with alkane anti-relaxation
coatings. The results are compared with data on Zeeman relaxation obtained in
nonlinear magneto-optical rotation (NMOR) experiments, a comparison important
for quantitative understanding of spin-relaxation mechanisms in coated cells.
By comparing cells manufactured over a forty-year period we demonstrate the
long-term stability of coated cells, an important property for atomic clocks
and magnetometers
Modulation induced frequency shifts in a CPT-based atomic clock
We investigate systematic errors associated with a common modulation
technique used for phase sensitive detection of a coherent population trapping
(CPT) resonance. In particular, we show that modification of the CPT resonance
lineshape due to the presence of off-resonant fields leads to frequency shifts
which may limit the stability of CPT-based atomic clocks. We also demonstrate
that an alternative demodulation technique greatly reduces these effects.Comment: 14 pages, 7 figure
Alpine Space Prospective Study. Sustainable territorial development in the Alpine Space: Towards long term transnational cooperation
This "Prospective Study" argues that a long term transnational cooperation will be able to pursue the sustainable territorial development in the Alpine Space only at the condition of a substantial improvement of the current experience. This regards an increased awareness of the complexity of issues and challenges currently at stake in the Alpine area but especially, in this light, the capacity of involving all relevant institutional and socioeconomic stakeholders in the building of shared transnational strategie
Pulsed beams as field probes for precision measurement
We describe a technique for mapping the spatial variation of static electric,
static magnetic, and rf magnetic fields using a pulsed atomic or molecular
beam. The method is demonstrated using a beam designed to measure the electric
dipole moment of the electron. We present maps of the interaction region,
showing sensitivity to (i) electric field variation of 1.5 V/cm at 3.3 kV/cm
with a spatial resolution of 15 mm; (ii) magnetic field variation of 5 nT with
25 mm resolution; (iii) radio-frequency magnetic field amplitude with 15 mm
resolution. This new diagnostic technique is very powerful in the context of
high-precision atomic and molecular physics experiments, where pulsed beams
have not hitherto found widespread application.Comment: 6 pages, 12 figures. Figures heavily compressed to comply with
arxiv's antediluvian file-size polic
Comparison of 87Rb N-resonances for D1 and D2 transitions
We report an experimental comparison of three-photon-absorption resonances
(known as "N-resonances") for the D_1 and D_2 optical transitions of thermal
87Rb vapor. We find that the D_2 N-resonance has better contrast, a broader
linewidth, and a more symmetric lineshape than the D_1 N-resonance. Taken
together, these factors imply superior performance for frequency standards
operating on alkali D_2 N-resonances, in contrast to coherent population
trapping (CPT) resonances for which the D_2 transition provides poorer
frequency standard performance than the D_1 transition.Comment: 3 pages, 4 figure
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