121 research outputs found
Cold trapped atoms detected with evanescent waves
We demonstrate the in situ detection of cold 87 Rb atoms near a dielectric
surface using the absorption of a weak, resonant evanescent wave. We have used
this technique in time of flight experiments determining the density of atoms
falling on the surface. A quantitative understanding of the measured curve was
obtained using a detailed calculation of the evanescent intensity distribution.
We have also used it to detect atoms trapped near the surface in a
standing-wave optical dipole potential. This trap was loaded by inelastic
bouncing on a strong, repulsive evanescent potential. We estimate that we trap
1.5 x 10 4 atoms at a density 100 times higher than the falling atoms.Comment: 5 pages, 3 figure
Theoretical study of a cold atom beam splitter
A theoretical model is presented for the study of the dynamics of a cold
atomic cloud falling in the gravity field in the presence of two crossing
dipole guides. The cloud is split between the two branches of this laser guide,
and we compare experimental measurements of the splitting efficiency with
semiclassical simulations. We then explore the possibilities of optimization of
this beam splitter. Our numerical study also gives access to detailed
information, such as the atom temperature after the splitting
Treatment of intrahepatic congenital portosystemic shunts in dogs: a systematic review
The aim of this study was to establish the evidence base for the treatment of intrahepatic congenital portosystemic shunts in dogs through a systematic review of the pertinent literature. Studies were filtered for evidence to answer the question “Which of the treatment options for intrahepatic CPSS in dogs offers the best short‐ and long‐term outcome?” Studies were assigned a level of evidence based on a system published by the Oxford Centre for Evidence‐Based Medicine. Thirty‐two studies were included in the review. Twenty‐six provided level 4 evidence and six provided level 5 evidence. There were no level 1, 2 or 3 studies. One study compared surgical treatment with medical management and one study compared suture ligation with ameroid constrictor placement. The remaining studies were case series describing the outcome for one treatment method alone. Methods and timings of assessments of short‐ and long‐term outcomes were highly varied, making direct comparisons challenging. The evidence regarding the treatment of intrahepatic congenital portosystemic shunts in dogs is weak, with only two studies directly comparing treatments. There is a lack of evidence regarding short‐ and long‐term outcomes on which to base clinical decisions
Принцип коеволюції в контексті ноосферної концепції В.Вернадського
Досліджується принцип коеволюції людини та природи в контексті ноосферного вчення В.Вернадського. Аналізуються особливості світогляду суспільства ноосферної цивілізації.Исследуется принцип коэволюции человека и природы в контексте ноосферного учения В.Вернадского. Анализуются особенности мировоззрения общества ноосферной цивилизации.The principle of coevolution of person and nature is investigated in the context of noospherian doctrine of V.Vernadsky. The particularities of world view оf society of noospherian civilization are analyzed
Guiding of cold atoms by a red-detuned laser beam of moderate power
We report measurements on the guiding of cold Rb atoms from a
magneto-optical trap by a continuous light beam over a vertical distance of 6.5
mm. For moderate laser power (85 mW) we are able to capture around 40% of
the cold atoms. Although the guide is red-detuned, the optical scattering rate
at this detuning (70 GHz) is acceptably low. For lower detuning (30
GHz) a larger fraction was guided but radiation pressure starts to push the
atoms upward, effectively lowering the acceleration due to gravity. The
measured guided fraction agrees well with an analytical model.Comment: final version, 6 pages, incl. 6 figure
A rainbow of cold atoms caused by a stochastic process
We report direct observation of a rainbow caustic in the velocity distribution of ^{87}Rb atoms, bouncing inelastically on an evanescent-wave atom mirror. In contrast to known examples, this caustic is caused by a stochastic process, namely a spontaneous Raman transition during the bounce. The results are in good agreement with a classical calculation. We observed that although energy is extracted from the atoms, the phase-space density is in most cases not increased
Creating a low-dimensional quantum gas using dark states in an inelastic evanescent-wave mirror
We discuss an experimental scheme to create a low-dimensional gas of
ultracold atoms, based on inelastic bouncing on an evanescent-wave mirror.
Close to the turning point of the mirror, the atoms are transferred into an
optical dipole trap. This scheme can compress the phase-space density and can
ultimately yield an optically-driven atom laser. An important issue is the
suppression of photon scattering due to ``cross-talk'' between the mirror
potential and the trapping potential. We propose that for alkali atoms the
photon scattering rate can be suppressed by several orders of magnitude if the
atoms are decoupled from the evanescent-wave light. We discuss how such dark
states can be achieved by making use of circularly-polarized evanescent waves.Comment: 8 pages, 4 figure
Comparison of computed tomographic angiography and intraoperative mesenteric portovenography for extrahepatic portosystemic shunts
Objectives
Comparison of intra-operative mesenteric portovenography and computed tomographic angiography for the documentation of the portal vasculature in patients with single extrahepatic portosystemic shunts.
Methods
Retrospective study of patients with extrahepatic portosystemic shunts that underwent preoperative computed tomographic angiography and intra-operative mesenteric portography. Studies were compared for identification of the intra- and extrahepatic portal vasculature.
Results
Computed tomographic angiography demonstrated all four portal vein tributaries and sub-tributaries. Intra-operative mesenteric portography inconsistently demonstrated the cranial mesenteric vein, the gastroduodenal vein (12 of 49 dogs and 0 of 10 cats), splenic vein (46 of 49 dogs and 8 of 10 cats) and caudal mesenteric vein (3 of 49 dogs and 2 of 10 cats). Computed tomographic angiography showed the intrahepatic portal vein with shunts emanating from the left gastric vein, splenocaval shunts or shunts involving the left colic vein. It showed intrahepatic portal branching in 5 of 12 patients with shunts involving the right gastric vein. Intra-operative mesenteric portography showed the intrahepatic portal vein in 29 of 59 patients but was outperformed by computed tomographic angiography in all cases except those patients with a shunt involving the right gastric vein.
Clinical Significance
In cases that have undergone diagnostic preoperative computed tomographic angiography there is no indication for diagnostic intra-operative mesenteric portovenography before ligation. In contrast, portovenography performed “after” temporary full ligation of the shunt provides clinical useful information and might be considered an integral investigation during shunt attenuation surgery
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