Single-molecule measurements of viral ssRNA packaging.

Genome packaging of double-stranded RNA (dsRNA) phages has been widely studied using biochemical and molecular biology methods. We adapted the existing in vitro packaging system of one such phage for single-molecule experimentation. To our knowledge, this is the first attempt to study the details of viral RNA packaging using optical tweezers. Pseudomonas phage φ6 is a dsRNA virus with a tripartite genome. Positive-sense (+) single-stranded RNA (ssRNA) genome precursors are packaged into a preformed procapsid (PC), where negative strands are synthesized. We present single-molecule measurements of the viral ssRNA packaging by the φ6 PC. Our data show that packaging proceeds intermittently in slow and fast phases, which likely reflects differences in the unfolding of the RNA secondary structures of the ssRNA being packaged. Although the mean packaging velocity was relatively low (0.07-0.54 nm/sec), packaging could reach 4.62 nm/sec during the fast packaging phase.

Saccadic eye movements estimate prolonged time awake.

Prolonged time awake increases the need to sleep. Sleep pressure increases sleepiness, impairs human alertness and performance and increases the probability of human errors and accidents. Human performance and alertness during waking hours are influenced by homeostatic sleep drive and the circadian rhythm. Cognitive functions, especially attentional ones, are vulnerable to circadian rhythm and increasing sleep drive. A reliable, objective and practical metrics for estimating sleepiness could therefore be valuable. Our aim is to study whether saccades measured with electro-oculography (EOG) outside the laboratory could be used to estimate the overall time awake without sleep of a person. The number of executed saccades was measured in 11 participants during an 8-min saccade task. The saccades were recorded outside the laboratory (Naval Academy, Bergen) using EOG every sixth hour until 54 hr of time awake. Measurements were carried out on two occasions separated by 10 weeks. Five participants participated in both measurement weeks. The number of saccades decreased during sustained wakefulness. The data correlated with the three-process model of alertness; performance differed between participants but was stable within individual participants. A mathematically monotonous relation between performance in the saccade task and time awake was seen after removing the circadian rhythm component from measured eye movement data. The results imply that saccades measured with EOG can be used as a time-awake metric outside the laboratory.

Group refractive index quantification using a Fourier domain short coherence Sagnac interferometer.

The group refractive index is important in length calibration of Fourier domain interferometers by transparent transfer standards. We demonstrate accurate group refractive index quantification using a Fourier domain short coherence Sagnac interferometer. Because of a justified linear length calibration function, the calibration constants cancel out in the evaluation of the group refractive index, which is then obtained accurately from two uncalibrated lengths. Measurements of two standard thickness coverslips revealed group indices of 1.5426±0.0042 and 1.5434±0.0046, with accuracies quoted at the 95% confidence level. This agreed with the dispersion data of the coverslip manufacturer and therefore validates our method. Our method provides a sample specific and accurate group refractive index quantification using the same Fourier domain interferometer that is to be calibrated for the length. This reduces significantly the requirements of the calibration transfer standard.

Subsurface metrology using scanning white light interferometry: absolute z coordinates deep inside displays.

Mobile devices with interactive displays are ubiquitous commodities. Efficient quality control (QC) drives competitiveness. Scanning white light interferometry imaging offers a fast and nondestructive tool for QC purposes. Relying on optical compensation and image stitching, one can rapidly and cost-effectively produce sharp 3D images of a display's inner structures with a few nanometers' accuracy along the z direction. As a practical example, 3D images of a mobile device display revealed 0.92±0.02 µm height variation in the top glass assembly. The proposed method improves quality assurance methods of display manufacturing.

System spectrum conversion from white light interferogram.

Capability to simulate the coherence function is important when tuning an interference microscope in an effort to reduce sidelobes in interference signals. The coherence function cannot directly be derived from the light source spectrum since the microscope's effective spectrum is affected by e.g. spatial coherence effects. We show this by comparing the true system spectrum measured using a spectrometer against the effective system spectrum obtained by Fourier analysis of the interference data. The results show that a modulation function that describes the scattering-induced spatial coherence dampening in the system is needed to correct the observed difference between these two spectra. The validity of this modulation function is further verified by quantifying the arithmetic mean roughness of two specified roughness standards. By providing a spectral transfer function for scattering, our method can simulate a sample specific coherence function, and thus shows promise to increase the quality of interference microscope images.

Transfer standard for traceable dynamic calibration of stroboscopic scanning white light interferometer.

The reconstructed image of a moving sample always shows a distorted representation of reality. Therefore, one needs to calibrate, for example, out-of-plane nano-videos for quality control of nano-microelectromechanical systems (N-MEMS). Here we discuss how to calibrate and obtain confidence limits for stroboscopic scanning white light interferometry (SSWLI) data when there are differences in speed and amplitude across the field of view. Many N-MEMS devices rely on oscillating structures; consequently, one must calibrate movie recordings of these structures to have global standards and to allow inter-device comparison. We propose to use a quartz tuning fork driven off-resonance as a transfer standard. This approach allows a broad range of traceable frequencies and out-of-plane amplitudes to be introduced into selected parts of the field of view of the SSWLI device featuring similar optical surface properties to many N-MEMS devices without demanding an additional reference surface.

Microsphere-assisted phase-shifting profilometry.

In the present work, we have investigated the combination of a superresolution microsphere-assisted 2D imaging technique with low-coherence phase-shifting interference microscopy. The imaging performance of this technique is studied by numerical simulation in terms of the magnification and the lateral resolution as a function of the geometrical and optical parameters. The results of simulations are compared with the experimental measurements of reference gratings using a Linnik interference configuration. Additional measurements are also shown on nanostructures. An improvement by a factor of 4.7 in the lateral resolution is demonstrated in air, thus giving a more isotropic nanometric resolution for full-field surface profilometry in the far field.

Beamforming with a volumetric array of massless laser spark sources--Application in reflection tracking.

A volumetric array of laser-induced air breakdown sparks is used to produce a directional and steerable acoustic source. The laser breakdown array element is broadband, point-like, and massless. It produces an impulse-like waveform in midair, thus generating accurate spatio-temporal information for acoustic beamforming. A laser-spark scanning setup and the concept of a massless steerable source are presented and evaluated with a cubic array by using an off-line far field delay-and-sum beamforming method. This virtual acoustic array with minimal source influence can, for instance, produce narrow transmission beams to obtain localized and directional impulse response information by reflection tracking.

Benefits and applications of laser-induced sparks in real scale model measurements.

The characteristics of using a laser-induced spark as a monopole source in scale model measurements were assessed by comparison with an electric spark and a miniature spherical loudspeaker. Room impulse responses of first order directivity sources were synthesized off-line using six spatially distributed sparks. The source steering direction was scanned across the horizontal and vertical plane to assess the origin of early reflections. The results confirm that the characteristics of the laser-induced spark outperform those of typical sources. Its monopole characteristics enable the authors to synthesize room responses of directional sources, e.g., to obtain directional information about reflections inside scale models.

Tailoring the excitation of fundamental flexural guide waves in coated bone by phase-delayed array: two-dimensional simulations.

The fundamental flexural guided wave (FFGW) enables ultrasonic assessment of cortical bone thickness. In vivo, it is challenging to detect this mode, as its power ratio with respect to disturbing ultrasound is reduced by soft tissue covering the bone. A phase-delayed ultrasound source is proposed to tailor the FFGW excitation in order to improve its power ratio. This situation is analyzed by 2D finite-element simulations. The soft tissue coating (7-mm thick) was simulated as a fluid covering an elastic plate (bone, 2-6 mm thick). A six-element array of emitters on top of the coating was excited by 50-kHz tone bursts so that each emitter was appropriately delayed from the previous one. Response was recorded by an array of receivers on top of the coating, 20-50 mm away from the closest emitter. Simulations predicted that such tailored/phase-delayed excitations should improve the power ratio of FFGW by 23 ± 5 dB, independent of the number of emitters (N). On the other hand, the FFGW magnitude should increase by 5.8 ± 0.5 dB for each doubling of N. This suggests that mode tailoring based on phase-delayed excitation may play a key role in the development of an in vivo FFGW assessment.

Optical tweezers reveal force plateau and internal friction in PEG-induced DNA condensation.

The simplified artificial environments in which highly complex biological systems are studied do not represent the crowded, dense, salty, and dynamic environment inside the living cell. Consequently, it is important to investigate the effect of crowding agents on DNA. We used a dual-trap optical tweezers instrument to perform force spectroscopy experiments at pull speeds ranging from 0.3 to 270 µm/s on single dsDNA molecules in the presence of poly(ethylene glycol) (PEG) and monovalent salt. PEG of sizes 1,500 and 4,000 Da condensed DNA, and force-extension data contained a force plateau at approximately 1 pN. The level of the force plateau increased with increasing pull speed. During slow pulling the dissipated work increased linearly with pull speed. The calculated friction coefficient did not depend on amount of DNA incorporated in the condensate, indicating internal friction is independent of the condensate size. PEG300 had no effect on the dsDNA force-extension curve. The force plateau implies that condensation induced by crowding agents resembles condensation induced by multivalent cations.

Exceptionally strong and robust millimeter-scale graphene-alumina composite membranes.

Graphene has attracted attention as a potential strengthening material and functional component in suspended membranes as utilized in micro and nanosystems. Development of a practical and scalable fabrication process is a necessary step to allow the exceptional material properties of graphene to be fully exploited in composite structures. Using standard and scalable microfabrication processes, we fabricated free-standing chemical vapor deposition monolayer graphene-reinforced Al2O3 composite membranes, 0.5 mm in diameter, that are strong and robust. Bulge tests revealed that the graphene reinforcement increased the membrane fracture strength by a factor of at least three and maximum sustainable strain from 0.28% to at least 0.69%. We show that the graphene-reinforced membranes are even tolerant to significant cracking without loss of membrane integrity. The graphene composite membranes' freestanding area of ∼ 200 000 µm(2) is almost a thousand times larger than suspended graphene membranes reported elsewhere. The presented graphene composite membranes may be seen as representing an interesting new class of durable composite materials warranting further study and having potential for broad applicability in a variety of fields.

Laser-induced acoustic point source for accurate impulse response measurements within the audible bandwidth.

Laser induced air breakdown is proposed as a sound source for accurate impulse response measurements. Within the audible bandwidth, the source is repeatable, broadband, and omnidirectional. The applicability of the source was evaluated by measuring the impulse response of a room. The proposed source provides a more accurate temporal and spatial representation of room reflections than conventional loudspeakers due to its omnidirectionality, negligible size and short pulse duration.

Wireless and battery-operatable IoT platform for cost-effective detection of fouling in industrial equipment.

We present a novel internet of things (IoT) sensing platform that uses helical propagation paths of ultrasonic guided waves (UGWs) for structural health monitoring. This wireless sensor network comprises multiple identical sensor units that communicate with a host PC. The units have dedicated hardware to both generate and receive ultrasonic signals, as well as RF signals for use in triggering the sensors. The system was developed for monitoring and sensing pipelines and similar structures in real-time to facilitate interactive sensing. For accurate sensing with a limited number of arbitrarily scattered sensors, we obtain information from all sensor pairs and analyze helical propagation paths in addition to the commonly used shortest paths. UGWs can propagate long distances along the walls of pipelines, and their propagation velocity depends directly on the thickness of the waveguide, and is affected by energy leakage and mass loading. In this paper, we evaluated the network by utilizing it to detect fouling. The network could be adapted for further ultrasonic measurement tasks, e.g., measuring wall thicknesses or monitoring defects with pulse-echo methods.

Stroboscopic scanning white light interferometry at 2.7 MHz with 1.6 µm coherence length using a non-phosphor LED source.

Stroboscopic scanning white light interferometry (SSWLI) allows precise three dimensional (3D) measurements of oscillating samples. Commercial SSWLI devices feature limited pulsing frequency. To address this issue we built a 400-620 nm wideband 150 mW light source whose 1.6 µm wide interferogram is without side peaks. The source combines a non-phosphor white LED with a cyan LED. We measured a calibration artifact with 10 nm precision and obtained 40 nm precision when measuring the 3D profile of a capacitive micromachined ultrasonic transducer membrane operating at 2.72 MHz. This source is compatible with solid state technology.

High-speed stroboscopic imaging with frequency-doubled supercontinuum.

We present a supercontinuum (SC) light source designed for stroboscopic white light interferometry. The compact, cost-effective SC source is built from off-the-shelf optical components and operates both in the visible and near-IR at arbitrary repetition rates in the 10 kHz-1 MHz frequency range. We estimate that our source allows performing dynamic white-light interferometric characterization of rapidly oscillating objects up to several tens of megahertz. Its current potential is demonstrated by capturing the movement of a microelectromechanical system oscillating at 2.16 MHz with sub-100 nm accuracy.

Algorithm for automatic analysis of electro-oculographic data.

BACKGROUND: Large amounts of electro-oculographic (EOG) data, recorded during electroencephalographic (EEG) measurements, go underutilized. We present an automatic, auto-calibrating algorithm that allows efficient analysis of such data sets. METHODS: The auto-calibration is based on automatic threshold value estimation. Amplitude threshold values for saccades and blinks are determined based on features in the recorded signal. The performance of the developed algorithm was tested by analyzing 4854 saccades and 213 blinks recorded in two different conditions: a task where the eye movements were controlled (saccade task) and a task with free viewing (multitask). The results were compared with results from a video-oculography (VOG) device and manually scored blinks. RESULTS: The algorithm achieved 93% detection sensitivity for blinks with 4% false positive rate. The detection sensitivity for horizontal saccades was between 98% and 100%, and for oblique saccades between 95% and 100%. The classification sensitivity for horizontal and large oblique saccades (10 deg) was larger than 89%, and for vertical saccades larger than 82%. The duration and peak velocities of the detected horizontal saccades were similar to those in the literature. In the multitask measurement the detection sensitivity for saccades was 97% with a 6% false positive rate. CONCLUSION: The developed algorithm enables reliable analysis of EOG data recorded both during EEG and as a separate metrics.

An optoacoustic point source for acoustic scale model measurements.

A massless acoustic source is proposed for scale model work. This source is generated by focusing a pulsed laser beam to rapidly heat the air at the focal point. This produces an expanding small plasma ball which generates a sonic impulse that may be used as an acoustic point source. Repeatability, frequency response, and directivity of the source were measured to show that it can serve as a massless point source. The impulse response of a rectangular space was determined using this type of source. A good match was found between the predicted and the measured impulse responses of the space.

UV-visible absorption spectroscopy for in-line API concentration measurement in nanoparticle production process using controlled expansion of supercritical solutions (CESS®).

Most new small drug molecules in pharmaceutical development require improvement of solubility. The controlled expansion of supercritical solutions (CESS®) process is a nanoparticle production technology, dedicated to enhancing the dissolution rate of active pharmaceutical ingredients (APIs) suffering from poor solubility and enabling novel drug delivery opportunities. In this process, the API is dissolved in supercritical carbon dioxide (scCO2) and nanoparticles are formed through controlled pressure reduction. To improve process visibility and control, ultraviolet-visible (UV-Vis) spectroscopy was incorporated into CESS® process as a process analytical technology (PAT) tool. The tool quantifies the amount of API dissolved in scCO2 during the solubilization phase of the process. Sample interfacing of the UV-Vis spectrometer was done with a custom-made pressure and temperature rated transmission flow-through cell. In-process calibration was developed to correlate the UV-Vis absorption spectra to the API concentration. Due to the density-dependent molar absorption coefficient of API in scCO2, the calibration was done for each combination of temperature and pressure. The developed PAT tool provides insight into the process enabling real-time API quantity estimation. It also facilitates process development through Quality by Design (QbD) and offers a system for enhanced process control and troubleshooting. For instance, the in-line API concentration data allows one to study the solubilization behavior of the API in the process and to optimize the process parameters in order to maximize throughput.

Evaluation of bone growth around bioactive glass S53P4 by scanning acoustic microscopy co-registered with optical interferometry and elemental analysis.

Bioactive glass (BAG) is a bone substitute that can be used in orthopaedic surgery. Following implantation, the BAG is expected to be replaced by bone via bone growth and gradual degradation of the BAG. However, the hydroxyapatite mineral forming on BAG resembles bone mineral, not providing sufficient contrast to distinguish the two in X-ray images. In this study, we co-registered coded-excitation scanning acoustic microscopy (CESAM), scanning white light interferometry (SWLI), and scanning electron microscopy with elemental analysis (Energy Dispersive X-ray Spectroscopy) (SEM-EDX) to investigate the bone growth and BAG reactions on a micron scale in a rabbit bone ex vivo. The acoustic impedance map recorded by the CESAM provides high elasticity-associated contrast to study materials and their combinations, while simultaneously producing a topography map of the sample. The acoustic impedance map correlated with the elemental analysis from SEM-EDX. SWLI also produces a topography map, but with higher resolution than CESAM. The two topography maps (CESAM and SWLI) were in good agreement. Furthermore, using information from both maps simultaneously produced by the CESAM (acoustic impedance and topography) allowed determining regions-of-interest related to bone formation around the BAG with greater ease than from either map alone. CESAM is therefore a promising tool for evaluating the degradation of bone substitutes and the bone healing process ex vivo.