Quantum backflow for many-particle systems

Quantum backflow is the classically-forbidden effect pertaining to the fact that a particle with a positive momentum may exhibit a negative probability current at some space-time point. We investigate how this peculiar phenomenon extends to many-particle systems. We give a general formulation of quantum backflow for systems formed of $N$ free nonrelativistic structureless particles, either identical or distinguishable. Restricting our attention to bosonic systems where the $N$ identical bosons are in the same one-particle state allows us in particular to analytically show that the maximum achievable amount of quantum backflow in this case becomes arbitrarily small for large values of $N$.Comment: 12 pages, 2 figure

Unbounded quantum backflow in two dimensions

Quantum backflow refers to the counterintuitive fact that the probability can flow in the direction opposite to the momentum of a quantum particle. This phenomenon has been seen to be small and fragile for one-dimensional systems, in which the maximal amount of backflow has been found to be bounded. Quantum backflow exhibits dramatically different features in two-dimensional systems that, contrary to the one-dimensional case, allow for degenerate energy eigenstates. Here we investigate the case of a charged particle that is confined to move on a finite disk punctured at the center and that is pierced through the center, and normally to the disk, by a magnetic flux line. We demonstrate that quantum backflow can be unbounded (in a certain sense), which makes this system a promising physical platform regarding the yet-to-be-performed experimental observation of this fundamental quantum phenomenon.Comment: 11 pages, 1 figur

Effect of Inhibition of the Lysophosphatidic Acid Receptor 1 on Metastasis and Metastatic Dormancy in Breast Cancer

Background Previous studies identified the human nonmetastatic gene 23 (NME1, hereafter Nm23-H1) as the first metastasis suppressor gene. An inverse relationship between Nm23-H1 and expression of lysophosphatidic acid receptor 1 gene (LPAR1, also known as EDG2 or hereafter LPA1) has also been reported. However, the effects of LPA1 inhibition on primary tumor size, metastasis, and metastatic dormancy have not been investigated. Methods The LPA1 inhibitor Debio-0719 or LPA1 short hairpinned RNA (shRNA) was used. Primary tumor size and metastasis were investigated using the 4T1 spontaneous metastasis mouse model and the MDA-MB-231T experimental metastasis mouse model (n = 13 mice per group). Proliferation and p38 intracellular signaling in tumors and cell lines were determined by immunohistochemistry and western blot to investigate the effects of LPA1 inhibition on metastatic dormancy. An analysis of variance-based two-tailed t test was used to determine a statistically significant difference between treatment groups. Results In the 4T1 spontaneous metastasis mouse model, Debio-0719 inhibited the metastasis of 4T1 cells to the liver (mean = 25.2 liver metastases per histologic section for vehicle-treated mice vs 6.8 for Debio-0719-treated mice, 73.0% reduction, P < .001) and lungs (mean = 6.37 lesions per histologic section for vehicle-treated mice vs 0.73 for Debio-0719-treated mice, 88.5% reduction, P < .001), with no effect on primary tumor size. Similar results were observed using the MDA-MB-231T experimental pulmonary metastasis mouse model. LPA1 shRNA also inhibited metastasis but did not affect primary tumor size. In 4T1 metastases, but not primary tumors, expression of the proliferative markers Ki67 and pErk was reduced by Debio-0719, and phosphorylation of the p38 stress kinase was increased, indicative of metastatic dormancy. Conclusion The data identify Debio-0719 as a drug candidate with metastasis suppressor activity, inducing dormancy at secondary tumor site

Comparison between two models of absorption of matter waves by a thin time-dependent barrier

We report a quantitative, analytical, and numerical comparison between two models of the interaction of a nonrelativistic quantum particle with a thin time-dependent absorbing barrier. The first model represents the barrier by a set of time-dependent discontinuous matching conditions, which are closely related to Kottler boundary conditions used in stationary-wave optics as a mathematical basis for Kirchhoff diffraction theory. The second model mimics the absorbing barrier with an off-diagonal δ potential with a time-dependent amplitude. We show that the two models of absorption agree in their predictions in a semiclassical regime, the regime readily accessible in modern experiments with ultracold atoms

Dynamics of matter wave packets in the presence of time-dependent absorption

Atom-laser interaction is at the heart of the vibrant field of quantum optics. The dynamical properties of a moving atom submitted to a laser radiation are strongly influenced by the position- and time-dependence of the latter. The full physical state of the atom must include information about the centre-of-mass motion and the internal structure of the atom. It is challenging to obtain a complete description of the full state of the atom. However, there exists an alternative approach to the dynamics of an atom in the presence of a laser, which is based on the concept of matter-wave absorption. In this thesis, we theoretically study the nonrelativistic one-dimensional motion of an electrically neutral quantum particle in the presence of a thin time-dependent absorber, representing the laser radiation. Our aim is to better understand the precise connection between time-dependent matter-wave absorption and the interaction between an atom and a localised time-dependent laser. Our analysis is based on two different approaches to the problem. The first one describes the moving atom by a two-level system, and represents the laser radiation by an off-diagonal δ-potential. The second model treats the atom as a structureless particle, and describes the laser by a time-dependent absorbing barrier. While the former model can be derived from first principles, the treatment of the absorbing barrier in the latter model lacks a rigorous quantum mechanical justification. The main outcome of our work is to provide a solid physical ground for the absorber model, by explicitly connecting it to the δ-potential model. We have thus extended the range of theoretical tools useful for investigating the effects of time-dependent laser radiation on quantum matter

Synthèse et substitution d'oligosaccharides de nature pectique

L'objectif de ce travail était la préparation de dérivés d'acides oligogalacturoniques potentiellement actifs au niveau biologique. Deux voies ont été étudiées, la première par synthèse chimique d'un unique motif monosaccharidique, pouvant servir de donneur ou d'accepteur de glycosyle lors des réactions de glycosylations. La deuxième voie consistait à modifier chimiquement des acides oligogalacturoniques libres, obtenus par dégradation de pectines issues du végétal. Ces deux voies de synthèse ont pu être réalisées, elles offrent de nombreux débouchés et perspectives. Lors de ces recherches, d'autres domaines ont pu être explorés : des études sur des oxydations sélectives au TEMPO regénéré de façon chimique ou électrochimique ont été menées, ainsi que des études de conductimétrie pour déterminer et doser les modifications chimiques réalisées sur les acides oligogalacturoniques libres.The aim of this work was the synthesis of oligogalacturonic acid derivatives with potential biological activity. Two approaches have been studied, the first one by chemical synthesis of a unique monosaccharide precursor, to be used either as a donor or as an acceptor in glycosylation reactions. The second approach was the chemical modification of free oligogalacturonic acids, obtained by degradation of plant pectins. These two strategies could be achieved, offering a wide spectrum of future studies. In addition, during this research, other areas have been explored : the selective oxidation of carbohydrate derivatives using TEMPO regenerated chemically or electrochemically, and conductimetric titrations for accurate evaluation of chemical modifications performed on free oligogalacturonic acids.AMIENS-BU Sciences (800212103) / SudocSudocFranceF

Ways of preventing surgeon burnout.

In surgical practice, numerous sources of stress (stressors) are unpredictable, two examples being daily workload and postoperative complications. They may help to explain surgeon burnout, of which the prevalence (34 to 53%) has been the subject of many studies. That said, even though assessments are legion, recommended solutions have been few and far between, especially insofar as by nature and training, surgeons are disinclined to interest themselves in burnout, which they are prone to consider as something experienced by "others". The objective of this attempt at clarification is to identify in the literature the strategies put forward in view of avoiding surgeon burnout, and to assess the impact of this phenomenon not only on the surgeon's professional and personal entourage, but also on patient safety. Prevention-based strategies, many of them focused on modifiable stressors, will be detailed

Selective TEMPO‐Catalyzed Chemicals vs. Electrochemical Oxidation of Carbohydrate Derivatives

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