The Halley multicolour camera

Keller, H. U.; Schmidt, Wolfgang; Wilhelm, K.; Becker, Christopher; Curdt, W.; Engelhardt, W.; Hartwig, H.; Kramm, J.-R.; Meyer, H.J.; Schmidt, R. N.; Gliem, F.; Krahn, E.; Schmidt, Hartmut; Schwarz, G.; Turner, John; Bouyries, Philippe; Cazes, S.; Angrilli, Francesco; Bianchini, G.; Fanti, Giulio; Brunello, Pierfrancesco; Delamere, A.; Reitsema, H. J.; Jamar, C.; Cucchiaro, A

doi:10.1088/0022-3735/20/6/039

Cited by 20 publications

(8 citation statements)

References 3 publications

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“…In principle, Boltzmann distribution allows experimentalists to recover the energetic landscape by measuring the distributions of positions of the trapped Brownian particles using video microscopy. In practice, however, cameras measure a moving average of positions over a shutter time σ, to which a zero-mean random vector ξ resulting from instrumental noise is added [10,37,38,51]:…”

Section: Static and Dynamic Errorsmentioning

confidence: 99%

Errors in Energy Landscapes Measured with Particle Tracking

Bogdan

Savin

2018

Biophysical Journal

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Tracking Brownian particles is often employed to map the energy landscape they explore. Such measurements have been exploited to study many biological processes and interactions in soft materials. Yet video tracking is irremediably contaminated by localization errors originating from two imaging artifacts: the "static" errors come from signal noise, and the "dynamic" errors arise from the motion blur due to finite frame-acquisition time. We show that these errors result in systematic and nontrivial biases in the measured energy landscapes. We derive a relationship between the true and the measured potential that elucidates, among other aberrations, the presence of false double-well minima in the apparent potentials reported in recent studies. We further assess several canonical trapping and pair-interaction potentials by using our analytically derived results and Brownian dynamics simulations. In particular, we show that the apparent spring stiffness of harmonic potentials (such as optical traps) is increased by dynamic errors but decreased by static errors. Our formula allows for the development of efficient corrections schemes, and we also present in this work a provisional method for reconstructing true potentials from the measured ones.

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Section: Static and Dynamic Errorsmentioning

confidence: 99%

Errors in Energy Landscapes Measured with Particle Tracking

Bogdan

Savin

2018

Biophysical Journal

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“…An oscillatory force f (t) = f 0 exp(iωt) is exerted to generate a displacement of the particle, expressed as x (t) = x 0 exp[i(ωt − ϕ)] with a frequencydependent amplitude x 0 (ω) and phase shift ϕ(ω). The viscoelastic modulus G*(ω) can be obtained as [95] ( ) 6 ( ) cos ( ) i sin ( )…”

Section: Magnetic Tweezersmentioning

confidence: 99%

“…Therefore, magnetic tweezers are widely used in complex and heterogeneous environments, including the studies of DNA topology, [105][106][107] cell mechanics, [92,108,109] and polymer networks. [95,110] Despite such advantages, magnetic tweezers also have some shortcomings and limitations. (1) The robust permanent magnets are not flexible in manipulation of the particle as optical tweezers or AFM; (2) the custom-made electromagnetic poles might not be uniform in the shape of tips when couples of poles are usually employed simultaneously; (3) the high current applied to the electromagnetic coils produces local heating nearby the sample chamber; (4) the high inductance in terms of the high frequency input limits its frequency bandwidth; and (5) the video-based detection limits its resolution (higher than tens of nanometer).…”

Section: Magnetic Tweezersmentioning

confidence: 99%

Rheological Study of Soft Matters: A Review of Microrheology and Microrheometers

Liu

2017

Macro Chemistry & Physics

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To overcome these shortcomings of macrorheology, a number of novel microrheological methods have emerged during the last few decades, [2] often involving a small tracking or probing particle (micrometer size) dispersed in a softmatter medium. By tracking the fluctuation due to thermal energy or applying an external force, usually in the form of magnetic force or optical trap, one can measure local mechanical responses. The local disturbance in a micrometer scale avoids reconstruction of local viscoelastic response, an inevitable problem in bulk rheology, especially when the probe particle size is smaller than the characteristic length of a soft matter. Depending on whether the probe is manipulated by an external force instead of a random walk due to thermal fluctuation, microrheometers can be generally characterized as active or passive ones. For an equilibrium system, the fluctuationdissipation theorem (FDT) guarantees that these two methods are equivalent. [3] In this review, we will detail these two classes of microrheometers, including their basic principles and typical setups as well as some recently developed hybrid microrheometers, [4][5][6] often used in characterizing polymer solutions and biological materials. Passive MicrorheologyIn a passive microrheometry method, the fluctuation of probes dispersed in a soft-matter medium is detected and analyzed by calculating the mean-square displacement (MSD) often from their video-based trajectories or scattered light intensities. Since the fluctuation of probes in space is driven by an extremely small thermal energy (k B T), the results from a passive method are always fallen inside the linear range of viscoelasticity. Generally, the elastic modulus is estimated within an upper limit of hundreds of Pa, which means that passive microrheometers are more suitable for measuring "soft" materials with a low viscosity and elasticity. Otherwise, the probes would be trapped without a measurable movement. Even newly developed super-resolution microscopes can provide a sub-nanometer resolution, [7] they are still not widely available methods and have a limited frequency range (up to 100 Hz). Mechanical properties of a soft matter can be obtained from MSD by using the generalized Stokes-Einstein relation (GSER). [8,9] In two extreme cases, (1) the probe is dispersed in a Newtonian viscous fluid and undergoes a Brownian motion with an MSD of 〈Δr 2 (t)〉. The viscosity η is related to the translational diffusion coefficient D as Microrheological TechniquesRheological properties of soft matter like polymer solutions/gels, colloidal dispersions, and biological materials have been extensively studied by macroscopic methods. Recently, a set of microrheometers has emerged as powerful tools to investigate the dynamics and structures of homogeneous or heterogeneous soft matter at the micro-or nanoscale. In this review, these microrheometers, including some novel hybrid microrheometers are summarized and compared.

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“…This difficulty may be obviated by taking into account the heavy absorption of the branch 2 wavefields which have a strong overlap with the core-level atomic wave functions dominating the absorption: hence, a solution may be to cut the plate thick enough so that only the branch 1 wavefields survive to the back. This is unfortunately not simple because the a-or n-polarization components also exhibit unequal attenuation so that it may be preferable for silicon single crystals to substitute 3/4-wave plates for 1/4-wave plates (Hart, 1978;Golovchenko, Kincaid, Levesque, Meixner & Kaplan, 1986;Keller & Stern, 1986). As pointed out first by Skalicky & Malgrange (1972), there is another strategy, which is to exploit the limited overlap in space of the branch 1 and 2 wavefields off Bragg angle [AO = (0 -Oa) :/= 0] when the crystal is thick enough and the incident beam very well collimated.…”

Section: X-ray Phase Platesmentioning

confidence: 99%

“…As pointed out first by Skalicky & Malgrange (1972), there is another strategy, which is to exploit the limited overlap in space of the branch 1 and 2 wavefields off Bragg angle [AO = (0 -Oa) :/= 0] when the crystal is thick enough and the incident beam very well collimated. This led some people to explore the use of phase plates rather far from the Bragg condition (Keller & Stern, 1986;Mills, 1988). Note that birefringence will affect the forward-diffracted beam as well as the beam diffracted in the 20B direction: this was exploited by Mills (1988) who proposed a compact design combining the phase plate and the collimator.…”

Section: X-ray Phase Platesmentioning

confidence: 99%

Energy-dispersive phase plate for magnetic circular dichroism experiments in the X-ray range

Giles¹,

Malgrange²,

Goulon³

et al. 1994

J Appl Cryst

105

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A 220 diamond phase plate was combined with an energy‐dispersive absorption spectrometer to convert linearly polarized X‐rays into circularly polarized photons and to detect circular magnetic X‐ray dichroism (CMXD) from ferromagnetic samples. In these experiments, carried out at LURE, the energy‐dispersive spectrometer was equipped with a bent Si (311) polychromator and vertically collimating slits accepting essentially a linearly polarized incident beam. The quarter‐wave plate was operated in the Bragg geometry but well outside the range of quasi total reflection, with the consequence that the forward‐diffracted beam was circularly polarized with a polarization rate approaching 80% over the whole energy bandpass of the polychromator. CMXD spectra of GdFe2 and GdCo2 intermetallic compounds were recorded at ca 7.2 keV near the Gd LIII absorption edge: they are essentially identical to the spectra commonly recorded with elliptically polarized X‐ray photons collected out of the orbit plane of the storage ring. It is suggested that the energy‐dispersive phase plate will be very useful to detect CMXD spectra with energy‐dispersive spectrometers exploiting the well collimated linearly polarized emission of standard undulators installed on the storage rings of the third generation.

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The Halley multicolour camera

Cited by 20 publications

References 3 publications

Errors in Energy Landscapes Measured with Particle Tracking

Errors in Energy Landscapes Measured with Particle Tracking

Rheological Study of Soft Matters: A Review of Microrheology and Microrheometers

Energy-dispersive phase plate for magnetic circular dichroism experiments in the X-ray range

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