Dynamics of immersed molecules in superfluids

The dynamics of a molecule immersed in a superfluid medium are considered. Results are derived using a classical hydrodynamic approach followed by canonical quantization. The classical model, a rigid body immersed in incompressible fluid, permits a thorough analysis; its effective Hamiltonian generalizes the usual rigid-rotor Hamiltonian. In contrast to the free rigid rotor, the immersed body is shown to have chaotic dynamics. Quantization of the classical model leads to new and experimentally verifiable features. It is shown, for instance, that chiral molecules can behave as "quantum propellers": the rotational-translational coupling induced by the superfluid leads to a nonzero linear momentum in the ground state. Hydrogen peroxide is a strong candidate for experimental detection of this effect. The signature is a characteristic splitting of rotational absorption lines. The 1_{01} --> 1_{10} line in hydrogen peroxide, for example, is predicted to split into three lines separated by as much as 0.01 cm^{-1}, which is about the experimental linewidth.Comment: 10 pages, 3 figure

Comparison of light transmission and reflection techniques to determine concentrations in flow tank experiments

Transmissive and reflective intensity measurements for visual concentration determinations in 2D flow tank experiments were compared and evaluated for their applicability in the study of flow and transport phenomena. A density-dependent heterogeneous flow experiment was conducted and transmission and reflection images of the dyed saltwater plume were analyzed. A single light source and dark curtains forced the light to pass through the porous media only, thus facilitating the transmission measurements. The reflection images delivered a more homogeneous spatial illumination than the transmission images. Major perturbations of the transmission images were lens flare effects and light dispersion within the bead-water-Plexiglas system which smear the front of the plume. Based on the conducted evaluation of transmissive and reflective intensity measurements, the reflection data delivered more reliable intensity values to derive solute concentrations in intermediate scale flow tank experiment

Rethinking the Mengkom-Mixing Bowl: Salvage Archaeology at the Johannes Luyster House, A Dutch-American Farm

Salvage excavations at the Johannes Luyster Farm (28Mo261) revleade extensive archaeological depostis reflecting three centuries of life on a Dutch-American farm. These deposties, when taken in conjunction with the architecture of the house and surviving primary documents, provide a glimpse of the changing lifestyles of the Jersey Dutch during the 19th century. Although the Luysters maintained some aspects of their ethnic heritage, they also participated in many aspects of the larger society. Case studies of the individual sites such as this one are a first step towards understanding the interrelationships between national trends and their local manifestations. Furthermore, they highlight the importance of studying 19th-century, rural, agrarian sites

Atividades experimentais e computacionais como recursos instrucionais que se complementam : um estudo exploratório no ensino de eletromagnetismo em física geral

Neste trabalho relatamos um estudo exploratório que teve como objetivo o levantamento de proposições norteadoras para embasar um estudo mais amplo, que visa investigar a integração entre atividades computacionais e experimentais no ensino de Eletromagnetismo em Física Geral como meio de propiciar condições favoráveis para uma aprendizagem significativa (Ausubel, 2003) e vivência com atividades práticas que propiciem aos alunos uma visão adequada de modelos teóricos (Bunge, 1974). Trabalhamos com 32 alunos matriculados na disciplina de Física III (Eletromagnetismo) do curso de Física da UFRGS, no 1° semestre de 2008. Os resultados mostram que as atividades integradas tornam os alunos mais ativos e participativos em comparação com as tradicionais aulas de laboratório, principalmente em discussões sobre questões conceituais e no auxílio a seus parceiros de grupo

Changes in species composition in alpine snowbeds with climate change inferred from small-scale spatial patterns

Alpine snowbeds are characterised by a very short growing season. However, the length of the snow-free period is increasingly prolonged due to climate change, so that snowbeds become susceptible to invasions from neighbouring alpine meadow communities. We hypothesised that spatial distribution of species generated by plant interactions may indicate whether snowbed species will coexist with or will be out-competed by invading alpine species – spatial aggregation or segregation will point to coexistence or competitive exclusion, respectively. We tested this hypothesis in snowbeds of the Swiss Alps using the variance ratio statistics. We focused on the relationships between dominant snowbed species, subordinate snowbed species, and potentially invading alpine grassland species. Subordinate snowbed species were generally spatially aggregated with each other, but were segregated from alpine grassland species. <br><br> Competition between alpine grassland and subordinate snowbed species may have caused this segregation. Segregation between these species groups increased with earlier snowmelt, suggesting an increasing importance of competition with climate change. Further, a dominant snowbed species (<i>Alchemilla pentaphyllea</i>) was spatially aggregated with subordinate snowbed species, while two other dominants (<i>Gnaphalium supinum</i> and <i>Salix herbacea</i>) showed aggregated patterns with alpine grassland species. These dominant species are known to show distinct microhabitat preferences suggesting the existence of hidden microhabitats with different susceptibility to invaders. <br><br> These results allow us to suggest that alpine snowbed areas are likely to be reduced as a consequence of climate change and that invading species from nearby alpine grasslands could outcompete subordinate snowbed species. On the other hand, microhabitats dominated by <i>Gnaphalium</i> or <i>Salix</i> seem to be particularly prone to invasions by non-snowbed species

Robotically assisted laparoscopic repair of anterior vaginal wall and uterine prolapse by lateral suspension with mesh: initial experience and video

Abstract Introduction and hypothesis Sacral colpopexy/hysteropexy is a well-established approach to vaginal apex support and was the first technique used to treat pelvic organ prolapse (POP) with robotic assistance. However, dissection at the level of the promontory may be difficult, especially in obese patients, and associated with rare but potential serious morbidity such as life-threatening vascular injury. In an attempt to avoid this risk, we describe a new robotic approach for POP repair with lateral suspension. Methods From March 2012 through June 2013, ten patients with symptomatic anterior vaginal wall and uterine prolapse were operated by a single surgeon. The video presents the different steps of robotically assisted laparoscopic repair of POP by lateral suspension with mesh and uterine conservation using da Vinci S or Si system. Results POP repair was successfully completed in all ten patients without any perioperative or postoperative complication. Conclusion Robotically assisted laparoscopic repair of POP by lateral suspension with mesh is a novel and feasible technique with promising short-term results. It may have several theoretical advantages over sacral colpopexy/hysteropexy and may represent an alternative in cases of difficult dissection of the promontory. Keywords Pelvic organ prolapse . Sacrocolpopexy . Hysteropexy . Robotic surgery . da Vinci system . Uterine prolapse Aim of the video Sacral colpopexy/hysteropexy is the method of choice for the treatment of apical vaginal and uterine prolapse. It was the first technique described to treat pelvic organ prolapse (POP) with robotic assistance. It offers similar results as abdominal sacrocolpopexy Electronic supplementary material The online version of this articl

Early last glacial maximum in the southern Central Andes reveals northward shift of the westerlies at ~39 ka

The latitudinal position of the southern westerlies has been suggested to be a key parameter for the climate on Earth. According to the general notion, the southern westerlies were shifted equatorward during the global Last Glacial Maximum (LGM: ~24–18 ka), resulting in reduced deep ocean ventilation, accumulation of old dissolved carbon, and low atmospheric CO<sub>2</sub> concentrations. In order to test this notion, we applied surface exposure dating on moraines in the southern Central Andes, where glacial mass balances are particularly sensitive to changes in precipitation, i.e. to the latitudinal position of the westerlies. Our results provide robust evidence that the maximum glaciation occurred already at ~39 ka, significantly predating the global LGM. This questions the role of the westerlies for atmospheric CO<sub>2</sub>, and it highlights our limited understanding of the forcings of atmospheric circulation

Effect of Process Parameters on the Generated Surface Roughness of Down-Facing Surfaces in Selective Laser Melting

Down-facing surfaces are one of the most challenging features in metal parts produced by laser powder bed fusion (LPBF). A combination of reasons, primary of which are residual stresses and overheating cause these features to have the worst surface finish and dimensional accuracy of all LPBF surfaces. In order to examine this phenomenon, a Design of Experiments (DoE) study is conducted for three different inclination angles, namely 45°, 35° and 25° and for two different layer thicknesses of 60 µm and 90 µm. The results from the DoE are used to establish quadratic regression equations that can be used to predict the quality marks of surface roughness and the relative dimensional error.This fundamental investigation helps to explain the reasons for the major defects in down-facing surfaces of parts produced with Ti-6AL-4 V material, namely the dross formation and attempts to improve the predictability of quality within the region. Further to the establishment of the quadratic equations, a discussion is conducted on the thermomechanical processes involved in the mechanism of dross formation and explanations are given on the reasons behind the observed physical phenomena. The trend of the propagation of (Root Mean Square) RMS Surface roughness (Sq) and the relative dimensional error with respect to the Volumetric Energy Density (VED) is discussed in detail. The respective quadratic equations are then tested by a second round of validation prints, and the results confirm the feasibility of the developed quadratic models to accurately predict process outcomes especially when operating near the suggested optimal printing zones. The high roughness of low VED printing is attributed to the formation of ‘inverse mushroom’ structures, and the low roughness of high VED surface is attributed to the formation of large flat regions formed as adjacent meltpools that can fuse together at various locations