Optical alignment and spinning of laser-trapped microscopic particles

Light-induced rotation of absorbing microscopic particles by transfer of angular momentum from light to the material raises the possibility of optically driven micromachines. The phenomenon has been observed using elliptically polarized laser beams or beams with helical phase structure. But it is difficult to develop high power in such experiments because of overheating and unwanted axial forces, limiting the achievable rotation rates to a few hertz. This problem can in principle be overcome by using transparent particles, transferring angular momentum by a mechanism first observed by Beth in 1936, when he reported a tiny torque developed in a quartz waveplate due to the change in polarization of transmitted light. Here we show that an optical torque can be induced on microscopic birefringent particles of calcite held by optical tweezers. Depending on the polarization of the incident beam, the particles either become aligned with the plane of polarization (and thus can be rotated through specified angles) or spin with constant rotation frequency. Because these microscopic particles are transparent, they can be held in three-dimensional optical traps at very high power without heating. We have observed rotation rates in excess of 350 Hz.Comment: 4 pages, 4 figure

Optical angular momentum transfer to trapped absorbing particles

Particle rotation resulting from the absorption of light carrying angular momentum has been measured. When absorbing CuO particles (1-5μm) were trapped in a focused ‘‘donut’’ laser beam, they rotated, due to the helical phase structure of the beam. Changing the polarization of the light from plane to circular caused the rotation frequency to increase or decrease, depending on the sense of the polarization with respect to the helicity of the beam. Rotation frequencies were obtained by Fourier analysis of amplitude fluctuations in the backscattered light from the particles. © 1996 The American Physical Society

Mechanical Effects of Optical Vortices

We concentrate on the forces and torques exerted on transparent and absorbing particles trapped in laser beams containing optical vortices. We review previous theoretical and experimental work and then present new calculations of the effect of vortex beams on absorbing particles

Low autocorrelated multi-phase sequences

The interplay between the ground state energy of the generalized Bernasconi model to multi-phase, and the minimal value of the maximal autocorrelation function, $C_{max}=\max_K{|C_K|}$, $K=1,..N-1$, is examined analytically and the main results are: (a) The minimal value of $\min_N{C_{max}}$ is $0.435\sqrt{N}$ significantly smaller than the typical value for random sequences $O(\sqrt{\log{N}}\sqrt{N})$. (b) $\min_N{C_{max}}$ over all sequences of length N is obtained in an energy which is about 30% above the ground-state energy of the generalized Bernasconi model, independent of the number of phases m. (c) The maximal merit factor $F_{max}$ grows linearly with m. (d) For a given N, $\min_N{C_{max}}\sim\sqrt{N/m}$ indicating that for m=N, $\min_N{C_{max}}=1$, i.e. a Barker code exits. The analytical results are confirmed by simulations.Comment: 4 pages, 4 figure

Interferometry signatures for QCD first-order phase transition in heavy ion collisions at GSI-FAIR energies

Using the technique of quantum transport of the interfering pair we examine the Hanbury-Brown-Twiss (HBT) interferometry signatures for the particle-emitting sources of pions and kaons produced in the heavy ion collisions at GSI-FAIR energies. The evolution of the sources is described by relativistic hydrodynamics with the system equation of state of the first-order phase transition from quark-gluon plasma (QGP) to hadronic matter. We use quantum probability amplitudes in a path-integral formalism to calculate the two-particle correlation functions, where the effects of particle decay and multiple scattering are taken into consideration. We find that the HBT radii of kaons are smaller than those of pions for the same initial conditions. Both the HBT radii of pions and kaons increase with the system initial energy density. The HBT lifetimes of the pion and kaon sources are sensitive to the initial energy density. They are significantly prolonged when the initial energy density is tuned to the phase boundary between the QGP and mixed phase. This prolongations of the HBT lifetimes of pions and kaons may likely be observed in the heavy ion collisions with an incident energy in the GSI-FAIR energy range.Comment: 16 pages, 4 figure

Coherent atomic beam splitter using transients of a chaotic system

A coherent atomic beam splitter can be realized using the transient dynamics of a chaotic system. We have experimentally observed such an effect using ultracold rubidium atoms. Our experimental results are in good agreement with numerical simulations of the Schrödinger equation for the syste

Effects of acculturation, coping strategies, locus of control, and self-efficacy on chronic pain: Study of Chinese immigrant women in Italy - insights from a thematic field analysis

Chronic pain represents a common public health concern worldwide. It is a complex phenomenon, owing to the interaction of different factors, including biological, physiological, psychological, environmental, and social variables. Some groups, such as women and immigrants, are particularly vulnerable. However, little is known about how Chinese women in Italy live with and face chronic pain. The present study aimed at filling this knowledge gap by examining the burden of chronic pain in Chinese immigrants in Italy in terms of acculturation processes, perceived control over disease, social networks, and coping strategies. A qualitative approach was used, performing a thematic field analysis. We interviewed 82 Chinese women from different Italian towns (Genoa, Milan, Turin, Bologna, Florence, and Prato) in depth. The sense of belonging to the host culture was strong in our sample. However, this did not simply reflect or translate into a linear engagement with medical systems, as health care pathways were more complex and dual (both Chinese and Western). Chinese women who felt deeply rooted in the Italian environment did not discontinue the use of traditional Chinese medicine. Chronic pain extensively and adversely affected daily life, particularly interfering with work. Coping strategies were mainly adaptive behaviors, being problem focused or maladaptive, relying upon “cope and avoid” mechanisms. Chinese women preferred to use traditional Chinese remedies rather than conventional medicine, while using the Italian system in emergencies. Perceived control over chronic pain was usually external. Finally, Chinese women with chronic pain benefit from social networks and support, which were mainly composed of Chinese peers. In conclusion, our findings underline the tremendous burden of chronic pain affecting all aspects of Chinese women’s lives. Health care workers and providers should be aware of the complexity of chronic pain Therefore, a holistic approach, involving different stakeholders, should be adopted when managing chronic pain and approaching immigrant patients

Human amniotic fluid glycoproteins expressing sialyl Lewis carbohydrate antigens stimulate progesterone production in human trophoblasts in vitro

Background: Progesterone is thought to mediate immune modulator effects by regulating uterine responsiveness. The aim of the study was to clarify the effect of transferrin and glycodelin A (former name PP14) as sialyl Lewis X-expressing glycoproteins on the release of progesterone by trophoblast cells in vitro. Methods: Cytotrophoblast cells were prepared from human term placentas by standard dispersion of villous tissue followed by a Percoll gradient centrifugation step. Trophoblasts were incubated with varying concentrations (50-300 mug/ml) of human amniotic fluid- and serum-transferrin as well as with glycodelin A. Culture supernatants were assayed for progesterone, human chorionic gonadotropin (hCG) and cortisol by enzyme immunometric methods. Results: The release of progesterone is increased in amniotic fluid transferrin- and glycodelin A-treated trophoblast cell cultures compared to untreated trophoblast cells. There is no relation between transferrin and the hCG or cortisol production of trophoblast cells. Conclusion: The results suggest that sialyl Lewis carbohydrate antigen-expressing amniotic fluid glycoproteins modulate the endocrine function of trophoblasts in culture by upregulating progesterone production. Copyright (C) 2004 S. Karger AG, Basel

Religious beliefs and entrepreneurial behaviours in Africa: a case study of the informal sector in Uganda

Religion plays a major role in Africa’s polity and its influence on the business landscape of the continent has been acknowledged in literature. This study contributes to the discourse by investigating and explaining how religious beliefs shape entrepreneurial behaviours in Uganda’s informal sector. Using a qualitative methodology, we explored how entrepreneurs in the context use or adopt religious beliefs in their entrepreneurial activities. By spanning a diverse set of entrepreneurial activities in the informal sector- food vendors, fabricators, hawkers, and recyclers among others, we conducted 49 in-depth interviews. Our findings reveal that the entrepreneurs relied on their religious beliefs in defining and coping with a penurious context. Further to this, we explain how religious beliefs galvanize business behaviours and calibrate the entrepreneurial identities of respondents in the context. To facilitate future work, the study highlights how knowledge gaps in the cultural and social setup of the informal economy will produce new insights in entrepreneurship research. It concludes by guiding policy makers and educators to engage and involve faith based institutions in the entrepreneurship promotion agenda