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

The European Cancer Patient’s Bill of Rights: Action Steps for Success

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140050/1/onco0225.pd

Optical microrheology using rotating laser-trapped particles

We demonstrate an optical system that can apply and accurately measure the torque exerted by the trapping beam on a rotating birefringent probe particle. This allows the viscosity and surface effects within liquid media to be measured quantitatively on a micron-size scale using a trapped rotating spherical probe particle. We use the system to measure the viscosity inside a prototype cellular structure.Comment: 5 pages, 4 figures. v2: bibliographic details, minor text correction

Nurse practice environments and outcomes: Implications for oncology nursing

PURPOSE/OBJECTIVES: To examine practice environments and outcomes of nurses working in oncology units or Magnet hospitals and to understand the association between the two. DESIGN: Secondary analysis of survey data collected in 1998. SETTING: Medical and surgical units of 22 hospitals, of which 7 were recognized by the American Nurses Credentialing Center Magnet program. SAMPLE: 1,956 RNs, of whom 305 worked in oncology units. METHODS: Chi-square tests compared nurse-reported outcomes by work setting, analysis of variance tested practice environment differences by setting, and logistic regression estimated the effects of practice environment, specialty, and Magnet status on outcomes. MAIN RESEARCH VARIABLES: Practice environments, emotional exhaustion, job satisfaction, and quality of care. FINDINGS: Oncology nurses had superior outcomes compared with nononcology nurses. Emotional exhaustion was significantly lower among oncology nurses working in Magnet hospitals. Scores on the Collegial Nurse-Physician Relations subscale were highest among oncology nurses. Outcomes were associated with Practice Environment Scale of the Nursing Work Index scores and Magnet status. Oncology nurses with favorable collegial nurse-physician relations were twice as likely to report high-quality care. CONCLUSIONS: Oncology nurses benefit from working in American Nurses Credentialing Center Magnet hospitals. Adequate staffing and resources are necessary to achieve optimal outcomes. Collegial nurse-physician relations appear to be vital to optimal oncology practice settings. IMPLICATIONS FOR NURSING: In addition to pursuing American Nurses Credentialing Center Magnet recognition, nurse managers should assess practice environments and target related interventions to improve job satisfaction and retention. High-priority areas for interventions include ensuring adequate staff and resources, promoting nurse-physician collaboration, and strengthening unit-based leadership.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94160/1/Nurse practice environments and outcomes Implications for oncology nursing.pd

The effects of meson mixing on dilepton spectra

The effect of scalar and vector meson mixing on the dilepton radiation from hot and dense hadronic matter is estimated in different isospin channels. In particular, we study the effect of $\sigma$-$\omega$ and $\rho-a_0$ mixing and calculate the corresponding rates. Effects are found to be significant compared to standard $\pi$-$\pi$ and $K$-${\bar K}$ annihilations. While the mixing in the isoscalar channel mostly gives a contribution in the invariant mass range between the two-pion threshold and the $\omega$ peak, the isovector channel mixing induces an additional peak just below that of the $\phi$. Experimentally, the dilepton signals from $\rho$-$a_0$ mixing seem to be more tractable than those from $\sigma$-$\omega$ mixing.Comment: 10 pages, 9 figure

Disparities in breast cancer care delivery: Solving a complex puzzle

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94110/1/Disparities in breast cancer care delivery Solving a complex puzzle.pd

Theory of Optical Tweezers

We derive a partial-wave (Mie) expansion of the axial force exerted on a transparent sphere by a laser beam focused through a high numerical aperture objective. The results hold throughout the range of interest for practical applications. The ray optics limit is shown to follow from the Mie expansion by size averaging. Numerical plots show large deviations from ray optics near the focal region and oscillatory behavior (explained in terms of a simple interferometer picture) of the force as a function of the size parameter. Available experimental data favor the present model over previous ones.Comment: 4 pages, 3 figure

Optical application and measurement of torque on microparticles of isotropic nonabsorbing material

We show how it is possible to controllably rotate or align microscopic particles of isotropic nonabsorbing material in a TEM00 Gaussian beam trap, with simultaneous measurement of the applied torque using purely optical means. This is a simple and general method of rotation, requiring only that the particle is elongated along one direction. Thus, this method can be used to rotate or align a wide range of naturally occurring particles. The ability to measure the applied torque enables the use of this method as a quantitative tool--the rotational equivalent of optical tweezers based force measurement. As well as being of particular value for the rotation of biological specimens, this method is also suitable for the development of optically-driven micromachines.Comment: 8 pages, 6 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