Avalanches in a Bose-Einstein condensate

Collisional avalanches are identified to be responsible for an 8-fold increase of the initial loss rate of a large 87-Rb condensate. We show that the collisional opacity of an ultra-cold gas exhibits a critical value. When exceeded, losses due to inelastic collisions are substantially enhanced. Under these circumstances, reaching the hydrodynamic regime in conventional BEC experiments is highly questionable.Comment: 4 pages, 2 figures, 1 tabl

Dyadic existential rules

In the field of ontology-based query answering, existential rules (a.k.a. tuple-generating dependencies) form an expressive Datalog-based language to specify implicit knowledge. The presence of existential quantification in rule-heads, however, makes the main reasoning tasks undecidable. To overcome this limitation, in the last two decades, a number of classes of existential rules guaranteeing the decidability of query answering have been proposed. Unfortunately, such classes are typically based on different syntactic conditions imposing the development of different ad hoc reasoners. This paper introduces a novel general condition that allows to define, systematically, from any decidable class C of existential rules, a new class called Dyadic-C that enjoys the following properties: (i) it is decidable; (ii) it generalizes C; (iii) it keeps the same data complexity as C; and (iv) it can exploit any reasoner for query answering over C. Additionally, the paper proposes a simple and elegant syntactic condition that gives rise to the class Ward+ generalizing the well-known decidable classes Shy and Ward, and being included in Dyadic-Shy

Optomechanical deformation and strain in elastic dielectrics

Light forces induced by scattering and absorption in elastic dielectrics lead to local density modulations and deformations. These perturbations in turn modify light propagation in the medium and generate an intricate nonlinear response. We generalise an analytic approach where light propagation in one-dimensional media of inhomogeneous density is modelled as a result of multiple scattering between polarizable slices. Using the Maxwell stress tensor formalism we compute the local optical forces and iteratively approach self-consistent density distributions where the elastic back-action balances gradient- and scattering forces. For an optically trapped dielectric we derive the nonlinear dependence of trap position, stiffness and total deformation on the object's size and field configuration. Generally trapping is enhanced by deformation, which exhibits a periodic change between stretching and compression. This strongly deviates from qualitative expectations based on the change of photon momentum of light crossing the surface of a dielectric. We conclude that optical forces have to be treated as volumetric forces and that a description using the change of photon momentum at the surface of a medium is inappropriate

Band Gaps for Atoms in Light based Waveguides

The energy spectrum for a system of atoms in a periodic potential can exhibit a gap in the band structure. We describe a system in which a laser is used to produce a mechanical potential for the atoms, and a standing wave light field is used to shift the atomic levels using the Autler-Townes effect, which produces a periodic potential. The band structure for atoms guided by a hollow optical fiber waveguide is calculated in three dimensions with quantised external motion. The size of the band gap is controlled by the light guided by the fiber. This variable band structure may allow the construction of devices which can cool atoms. The major limitation on this device would be the spontaneous emission losses.Comment: 7 pages, four postscript figures, uses revtex.sty, available through http://online.anu.edu.au/Physics/papers/atom.htm

Laparoscopic approach to Meckel's diverticulum

Aim.To retrospective review the laparoscopic management of Meckel Diverticulum (MD) in two Italian Pediatric Surgery Centers. METHODS: Between January 2002 and December 2012, 19 trans-umbilical laparoscopic-assisted (TULA) procedures were performed for suspected MD. The children were hospitalized for gastrointestinal bleeding and/or recurrent abdominal pain. Median age at diagnosis was 5.4 years (range 6 mo-15 years). The study included 15 boys and 4 girls. All patients underwent clinical examination, routine laboratory tests, abdominal ultrasound and technetium-99m pertechnetate scan, and patients with bleeding underwent gastrointestinal endoscopy. The abdominal exploration was performed with a 10 mm operative laparoscope. Pneumoperitoneum was established based on the body weight. Systematic overview of the peritoneal cavity allowed the ileum to be grasped with an atraumatic instrument. The complete exploration and surgical treatment of MD were performed extracorporeally, after intestinal exteriorization through the umbilicus. All patients' demographics, main clinical features, diagnostic investigations, operative time, histopathology reports, conversion rate, hospital stay and complications were registered and analyzed. RESULTS: MD was identified in 17 patients, while 1 had an ileal duplication and 1 a jejunal hemangioma. Fifteen patients had painless intestinal bleeding, while 4 had recurrent abdominal pain and exhibited cyst like structures in an ultrasound study. Eleven patients had a positive technetium-99m pertechnetate scan. In the patients with bleeding, gastrointestinal endoscopy did not name the source of hemorrhage. All patients were subjected to a TULA surgical procedure. An intestinal resection/anastomosis was performed in 14 patients, while 4 had a wedge resection of the diverticulum and 1 underwent stapling diverticulectomy. All surgical procedures were performed without conversion to open laparotomy. Mean operative time was 75 min (range 40-115 min). No major surgical complications were recorded. The median hospital stay was 5-7 d (range 4-13 d). All patients are asymptomatic at a median follow up of 4, 5 years (range 10 mo-10 years). CONCLUSION: Trans-umbilical laparoscopic-assisted Meckel's diverticulectomy is safe and effective in the treatment of MD, with excellent results. KEYWORDS: Gastrointestinal bleeding; Ileal duplication; Jejunal hemangioma; Laparoscopy; Meckel’s diverticulum; Minimal invasive surgery; One trocar surger

Applications of aerospace technology to petroleum extraction and reservoir engineering

Through contacts with the petroleum industry, the petroleum service industry, universities and government agencies, important petroleum extraction problems were identified. For each problem, areas of aerospace technology that might aid in its solution were also identified, where possible. Some of the problems were selected for further consideration. Work on these problems led to the formulation of specific concepts as candidate for development. Each concept is addressed to the solution of specific extraction problems and makes use of specific areas of aerospace technology

Wave Packet Echoes in the Motion of Trapped Atoms

We experimentally demonstrate and systematically study the stimulated revival (echo) of motional wave packet oscillations. For this purpose, we prepare wave packets in an optical lattice by non-adiabatically shifting the potential and stimulate their reoccurence by a second shift after a variable time delay. This technique, analogous to spin echoes, enables one even in the presence of strong dephasing to determine the coherence time of the wave packets. We find that for strongly bound atoms it is comparable to the cooling time and much longer than the inverse of the photon scattering rate

What do I want to be? Predictors of communal occupational aspirations in early to middle childhood

Research investigating occupational aspirations in childhood is scarce. In addition, most research on occupational aspirations has focused on increasing the number of women in agentic jobs. In the present work, we investigate factors associated with communal occupational aspirations in two studies with young children (Study 1: 159 children [84 boys, 75 girls], Mage = 5.51 years, SD = 0.37; Study 2: 96 children [48 boys, 48 girls]; Mage = 9.44 years, SD = 1.91). We found gender differences in communal aspirations only among the older children. In both samples, as well as when combining the two samples, the stronger the communal occupational gender stereotypes children reported, the less boys (and the more girls) aspired toward communal occupations. In the combined sample, communal self-perceptions mediated the relationship between child gender and occupational aspirations. Finally, the perceived status of the occupations was positively associated with communal aspirations among older children

What do I want to be? Predictors of communal occupational aspirations in early to middle childhood

Research investigating occupational aspirations in childhood is scarce. In addition, most research on occupational aspirations has focused on increasing the number of women in agentic jobs. In the present work, we investigate factors associated with communal occupational aspirations in two studies with young children (Study 1: 159 children [84 boys, 75 girls], Mage = 5.51 years, SD = 0.37; Study 2: 96 children [48 boys, 48 girls]; Mage = 9.44 years, SD = 1.91). We found gender differences in communal aspirations only among the older children. In both samples, as well as when combining the two samples, the stronger the communal occupational gender stereotypes children reported, the less boys (and the more girls) aspired toward communal occupations. In the combined sample, communal self-perceptions mediated the relationship between child gender and occupational aspirations. Finally, the perceived status of the occupations was positively associated with communal aspirations among older children.publishedVersio

Psychiatric Comorbidity, Social Aspects and Quality of Life in a Population-Based Cohort of Expecting Fathers with Epilepsy

Objectives. To investigate psychiatric disorders, adverse social aspects and quality of life in men with epilepsy during partner’s pregnancy. Method. We used data from the Norwegian Mother and Child Cohort Study, including 76,335 men with pregnant partners. Men with epilepsy were compared to men without epilepsy, and to men with non-neurological chronic diseases. Results. Expecting fathers in 658 pregnancies (mean age 31.8 years) reported a history of epilepsy, 36.9% using antiepileptic drugs (AEDs) at the onset of pregnancy. Symptoms of anxiety or depression were increased in epilepsy (7.0% and 3.9%, respectively) vs. non-epilepsy (4.6% and 2.5%, respectively, p = 0.004 and 0.023), and so were new onset symptoms of depression (2.0% vs. 1.0%, p < 0.031) and anxiety (4.3% vs. 2.3%, p = 0.023). Low self-esteem (2.5%) and low satisfaction with life (1.7%) were more frequent among fathers with epilepsy compared to fathers without epilepsy (1.3% and 0.7%, respectively, p = 0.01 and 0.010). Adverse social aspects and life events were associated with epilepsy vs. both reference groups. Self-reported diagnoses of ADHD (2.2%) and bipolar disorder (1.8%) were more common in epilepsy vs. non-epilepsy (0.4% and 0.3%, respectively, p = 0.002 and 0.003) and non-neurological chronic disorders (0.5% and 0.5%, respectively, p = 0.004 and 0.018). A screening tool for ADHD symptoms revealed a higher rate compared to self-reported ADHD (9.5% vs. 2.2%, p < 0.001). Conclusion. Expecting fathers with epilepsy are at high risk of depression and anxiety, adverse socioeconomic aspects, low self-esteem, and low satisfaction with life. Focus on mental health in fathers with epilepsy during and after pregnancy is important. The use of screening tools can be particularly useful to identify those at risk.publishedVersio