Probe Size Research Articles

Spectral fiber dosimetry with beryllium oxide for quality assurance in hadron radiation therapy

Using the radioluminescence light of solid state probes coupled to long and flexible fibers for dosimetry in radiotherapy offers many advantages in terms of probe size, robustness and cost efficiency. However, especially in hadron fields, radioluminophores exhibit quenching effects dependent on the linear energy transfer. This work describes the discovery of a spectral shift in the radioluminescence light of beryllium oxide in dependence on the residual range at therapeutic proton energies. A spectrally resolving measurement setup has been developed and tested in scanned proton fields. It is shown that such a system can not only quantitatively reconstruct the dose, but might also give information on the residual proton range at the point of measurement.

Scan-less machine-learning-enabled incoherent microscopy for minimally-invasive deep-brain imaging.

Deep-brain microscopy is strongly limited by the size of the imaging probe, both in terms of achievable resolution and potential trauma due to surgery. Here, we show that a segment of an ultra-thin multi-mode fiber (cannula) can replace the bulky microscope objective inside the brain. By creating a self-consistent deep neural network that is trained to reconstruct anthropocentric images from the raw signal transported by the cannula, we demonstrate a single-cell resolution (< 10μm), depth sectioning resolution of 40 μm, and field of view of 200 μm, all with green-fluorescent-protein labelled neurons imaged at depths as large as 1.4 mm from the brain surface. Since ground-truth images at these depths are challenging to obtain in vivo, we propose a novel ensemble method that averages the reconstructed images from disparate deep-neural-network architectures. Finally, we demonstrate dynamic imaging of moving GCaMp-labelled C. elegans worms. Our approach dramatically simplifies deep-brain microscopy.

Development of single sensor fast response pressure probes

Multi-sensor fast response pressure probes are often used in turbomachinery investigations. However, the size of multi-sensor probes are often larger than is ideal. This paper describes the development of a single sensor pressure probe that has sufficient sensitivity for the measurements of unsteady 3D flow fields in turbomachines. Because there is only one sensor, the probe can be made much smaller than previous designs. Several types of probe were designed and tested using largescale models in a wind tunnel. Both the steady state and the dynamic response have been investigated. The relationship between the shape of the probe and its yaw and pitch sensitivity has been investigated through measurements of the pressure distribution on the large-scale models and through visualizations of the flow. Dambach and Hodson [3] proposed a new method of data reduction for a single sensor pressure probe. In that work, a single sensor pressure probe with the shape of a triangular prism was fabricated and tested with success in a radial flow turbine where the flow field was mainly 2D. The probe was shown to have only yaw sensitivity while pitch sensitivity is also important in the survey of three dimensional turbomachinery flows. In this paper, the model probes were used to assess the pitch sensitivity of single sensor pressure probes. All the probes have the sensing face at the end of a radially mounted stem so that they can be used for inter bladerow measurements. Through the steady state measurements, the dependency of pitch sensitivity on (1) the shape of the probe stem (e.g., Square, Circular, and Triangular) and (2) the angle of the slanted sensing face at the tip of the probe were investigated. Having assessed all the designs based on the steady state experiments, the dynamic behaviour of selected designs was investigated. The results indicate that a slanted face and appropriate probe tip design can be used to increase the pitch sensitivity of the single sensor probe to acceptable levels.

Accuracy requirements of the microarrayed Einzel lens

A microarrayed Einzel lens (MAEL) is adopted in many high throughput applications, such as multibeam lithography, multibeam electron microscope, and multibeam electron beam inspection. The assembly and fabrication errors of mounting an MAEL consist of misalignment, tilt, and ellipticity, which strongly affect the property of the MAEL. In this report, the accuracy requirements of mounting an MAEL are analyzed using Munro’s electron beam software. The results show that the assembly errors of the middle electrode in an MAEL are dominant in spoiling the beam quality. When assembling an MAEL, for a probe size of 10 nm, the requirements on misalignment, tilt, and ellipticity are 2.7 μm, 1 mrad, and 60 nm, respectively, while for a probe size of 1 nm, the assembly accuracy should be controlled to be less than 0.8 μm, 0.7 mrad, and 6 nm, respectively. These calculated results could be able to instruct designing an MAEL. Moreover, a dedicated tool is necessary for assembling the MAEL to ensure that the accuracy requirements of the MAEL are acceptable, to make good quality electron probes.

Development of three-port fiber-coupled vapor cell probe and its application in microwave digital communication

The quantum microwave measurement technology based on Rydberg atoms has developed rapidly and received widespread attention. It has shown significant advantages such as probe size independent of wavelength and broad spectrum measurement. Fiber-coupled vapor cell probe is one of the key technologies for portable quantum microwave measurement systems. The existing two-port fiber-coupled probe shares the graded index (GRIN) lens and optical fibers for outputting detection light with inputting coupling light, which limits light transmission efficiency of the detection light to 17%. Under these conditions, the power of the inputting detection light must be increased to ensure sufficient power to output the detection light, causing the electromagnetically-induced transparency (EIT) spectrum to broaden to 11 MHz, ultimately resulting in reduced measurement sensitivity. In this work, we propose a three-port fiber-coupled atomic gas chamber probe with an integrated dichroic mirror. On condition that the detection light and coupling light are transmitted in opposite directions and overlap in the vapor cell, the outgoing detection light is separated into two beams; one goes to an individual GRIN lens and the other to the output fiber, and the detection light transmission efficiency is 40.4%, and the half-height width of the EIT spectrum is reduced to 6 MHz. The probe is used to measure the microwave electric field intensity and phase; its effectiveness is verified by its ability to receive QPSK, 16QAM digitally modulated signals.

Short-term improvements in the body schema can modulate pain perception in fibromyalgia syndrome.

This study aimed to evaluate the pain perception and several aspects of disrupted body schema, in a sample of patients suffering from fibromyalgia (FM) syndrome. Twenty-six patients were organised into two groups: the tactile discrimination group and control group (exposed to tactile stimulation alone). Outcome measures were the pain intensity in body regions commonly described as painful (visual analogue scale) and clinical status, body esteem scale (BES), interoceptive awareness. Tactile acuity was measured by the two-point discrimination test (TPD), hits in the location of the stimulus, the probe size discrimination and the graphesthesia task. The group exposed to tactile discrimination experienced a significant improvement in all tactile acuity outcome measures. The decrease of the Fibromyalgia Impact Questionnaire variable was relevant (81.58, SEM 3.29 vs. 72.91, SEM 6.43; p=0.07). Likewise, pain perception was lower in all of the body regions evaluated (reduction of 12.2% in the stimulated body region (cervical VAS) with a large effect size, a pain reduction of 11.3% in the wrists and 9.2% in the knees. The correlation index showed association between the cervical VAS and TPD (ρ=0.53; p<0.05). There was no improvement in pain scores in the control group but the TPD was decreased also. The BES scores did not show differences between groups. However, interoceptive awareness showed a slight reduction in the group exposed to tactile discrimination (3.68, SEM 0.15 vs. 3.35, SEM 0.19; p=0.01). After short-term tactile discrimination protocol, the group exposed to tactile discrimination experienced a significant improvement in all tactile acuity outcome measures: pain perception, tactile acuity and body perception, compatible with adjustments in the body schema. The tactile stimulation alone group did not show the same improvement.

Polarization fluctuation of BaTiO3 at unit cell level mapped by four-dimensional scanning transmission electron microscopy

Diffraction analysis in four-dimensional scanning transmission electron microscopy now enables the mapping of local structures including symmetry, strain, and polarization of materials. However, measuring the distribution of these configurations at the unit cell level remains a challenge because most analysis methods require the diffraction disks to be separated, limiting the electron probe sizes to be larger than a unit cell. Here, we show improved spatial resolution in mapping the polarization displacement and phases of BaTiO3 sampled at a rate equivalent to the size of the projected unit cells using 4D-STEM. This improvement in spatial resolution is accomplished by masking out the overlapping regions in partially overlapped convergent beam electron diffraction patterns. By reducing the probe size to the order of single projected unit cells in size, the measurement shows local fluctuation within the nanosized rhombohedral domains in tetragonal phased BaTiO3, indicating the origin of phase transition and evolution across different length scales.

Ptychography Reduces Spectral Distortions Intrinsic to Conventional Zone-Plate-Based X-Ray Spectromicroscopy

Abstract Scanning transmission X-ray microscopy is a powerful method for mapping chemical phases in nano-materials. The point spread function (PSF) of a conventional zone-plate-based microscope limits the achievable spatial resolution and also results in spatially resolved spectra that do not accurately reflect the spatial heterogeneity of the samples when the scale of the detail approaches the probe size. X-ray ptychography, a coherent-scattering-based imaging scheme that effectively removes the probe from the image data, returns accurate spectra from regions smaller than the probe size. We show through simulation how the long tails on the PSF of an x-ray optic can cause spectral distortion near a boundary between two spectrally distinct regions. The resulting apparent point spectra can appear mixed, with the species on one side of the boundary seeming to be present on the other even at a distance from the boundary equal to several times the spatial resolution. We further demonstrate the effect experimentally and show that ptychographic microscopy can return the expected spectra from a model system, whereas conventional microscopy does not.

Three-Dimension Measurement of Mechanical Parts Based on Structure from Motion(SfM) Algorithm

Background: As an important branch of computer vision, visual measurement is a fast developing cutting-edge technology, which has been widely used in the manufacturing field. In recent years, the visual measurement of feature size of probes through small IC probes has aroused wide concern. Objective: This study aims to take small shaft parts as the research object in order to provide a full set of novel and reliable technical means for the three-dimension measurement of mechanical parts. Methods: Firstly, the trinocular vision measurement system based on the curved cantilever mechanism was designed and constructed. Secondly, the measurement system was used to collect the part images from different angles, and the images derived from the four categories of segmentation algorithms such as threshold-based, region-based segmentation algorithm were compared and analyzed. Lazy Snapping image segmentation algorithm was used to extract the foreground parts of each image. After comparing and analyzing SfM-based algorithm and Visual Hull-based algorithm, the SfM-based algorithm was adopted to reconstruct the 3D morphology of the parts. The measurement of the relevant dimensions was performed. Results: The results shows that Lazy Snapping's human-computer interaction brush function improves the accuracy and stability of image segmentation of different algorithms, such as threshold value method, regional method, Grab Cut, and Dense Cut. The SfM-based 3D reconstruction algorithm is of high robustness and fast speed. Conclusion: This study provides an effective method for measuring small mechanical parts, which will shorten the measurement cycle, improve the measurement speed, and reduce the measurement cost.

Multiscale Characterization of the Mechanical Properties of Fibrin and Polyethylene Glycol (PEG) Hydrogels for Tissue Engineering Applications

AbstractShear rheology and atomic force microscopy (AFM) are used to characterize the stiffness of hydrogels in tissue engineering applications, with several studies reporting differences of several orders of magnitude in the elastic moduli determined by these two methods. This work compares the elastic properties of soft fibrin and polyethylene glycol (PEG) hydrogels used for stem cell applications, determined by AFM indentation with different probe sizes (from nano‐ to micrometer) to shear rheometry data. For all hydrogels, AFM nanoscale probing consistently yields higher elastic modulus (E) values and variability than micrometer‐probe indentation, while the shear modulus (G) values determined are the lowest. Colloidal probe AFM results are closer to rheology data for the stiffest samples, where E/G ratios converge to the theoretical Trouton ratio of 3. The results suggest that high polymer concentration hydrogels are better described by the affine elastic network theory, whereas low polymer concentration hydrogels deviate significantly from the Trouton ratio. Thus, for soft hydrogels relevant for stem cell culture, the assumption E = 3G is often invalid and care should be taken when comparing data from studies where different characterization methods are used in order to discern the impact of material properties on cell behavior.

Multiple criteria optimization of electrostatic electron lenses using multiobjective genetic algorithms

The design of an electrostatic electron optical system with five electrodes and two objective functions is optimized using multiobjective genetic algorithms (MOGAs) optimization. The two objective functions considered are minimum probe size of the primary electron beam in a fixed image plane and maximum secondary electron detection efficiency at an in-lens detector plane. The time-consuming step is the calculation of the system potential. There are two methods to do this. The first is using COMSOL (finite element method) and the second is using the second-order electrode method (SOEM). The former makes the optimization process very slow but accurate, and the latter makes it fast but less accurate. A fully automated optimization strategy is presented, where a SOEM-based MOGA provides input systems for a COMSOL-based MOGA. This boosts the optimization process and reduces the optimization times by at least ∼10 times, from several days to a few hours. A typical optimized system has a probe size of 11.9 nm and a secondary electron detection efficiency of 80%. This new method can be implemented in electrostatic lens design with one or more objective functions and multiple free variables as a very efficient, fully automated optimization technique.

Microrheology analysis in molecular dynamics simulations: Finite box size correction

In single-particle microrheology, the viscoelastic properties of a complex fluid can be extracted using the generalized Stokes–Einstein (GSE) relation by embedding a micrometer-sized particle and tracking its motion through the fluid. Applying the same analysis to molecular dynamics simulations can result in overestimated G∗ values because of the hydrodynamic interaction between the probe bead and its periodic images. We derive a simple correction to the GSE equation by implementing an analytical solution for Stokes drag on a periodic array of spheres, which allows smaller box sizes to be simulated while still retaining accuracy. Fluid and particle inertia are neglected, although the approach used here might be generalized to include them. The correction is applied to molecular dynamics simulations of a coarse-grained polymer melt. For several bead-to-box-size ratios R/L and two probe sizes, we measure the mean squared displacement and calculate G∗ using both the original GSE and the corrected hydrodynamic Stokes–Einstein (HSE) equations. These results are compared to small amplitude oscillatory non-equilibrium molecular dynamics (NEMD) simulations, which show that the HSE analysis correctly predicts the G∗ values at low frequencies but breaks down when either fluid inertia is important or the bead size is too small to “see” a continuum. For small R/L, the GSE and HSE results are similar, although a small correction is still required for the finite box size and computational cost is significantly larger. The HSE equation allows the use of smaller box sizes, reducing computational costs by more than an order of magnitude.

Laser photo-detachment combined with Langmuir probe in magnetized electronegative plasma: how the probe size affects the plasma dynamic?

Laser photo-detachment combined with a Langmuir probe (LP) is used to diagnose negative ion properties in electronegative plasmas. The technique relies on the combined use of a laser pulse and an LP. The laser pulse converts negative ions into electron–atom pairs, while the LP tracks the temporal evolution of electron current (laser photo-detachment signal) that is analyzed to retrieve the negative ion density. Although an external magnetic field is frequently used to enhance the negative ion production and extraction, the data analysis often neglects the effects of the magnetic field on the probe current. This work investigates the response of an electronegative plasma to a laser pulse in the presence of an external magnetic field through a two-dimensional particle-in-cell/Monte Carlo collision model. The results show that a low electron density region surrounding the probe, called a flux-tube, can form for a probe size comparable with or larger than the electron Larmor radius. The formation of the flux-tube strongly affects the components of the laser photo-detachment signal, leading to an important oscillation of probe current during the plateau phase, i.e. the amplitude of the AC component of the probe current is in the same magnitude order of the DC component of this current, and an important overshoot in comparison to the current rise. Numerical results are qualitatively compared to measurements obtained from the RAID negative ion source.

Dual energy X-ray beam ptycho-fluorescence imaging.

X-ray ptychography and X-ray fluorescence are complementary nanoscale imaging techniques, providing structural and elemental information, respectively. Both methods acquire data by scanning a localized beam across the sample. X-ray ptychography processes the transmission signal of a coherent illumination interacting with the sample, to produce images with a resolution finer than the illumination spot and step size. By enlarging both the spot and the step size, the technique can cover extended regions efficiently. X-ray fluorescence records the emitted spectra as the sample is scanned through the localized beam and its spatial resolution is limited by the spot and step size. The requisites for fast ptychography and high-resolution fluorescence appear incompatible. Here, a novel scheme that mitigates the difference in requirements is proposed. The method makes use of two probes of different sizes at the sample, generated by using two different energies for the probes and chromatic focusing optics. The different probe sizes allow to reduce the number of acquisition steps for the joint fluorescence-ptychography scan compared with a standard single beam scan, while imaging the same field of view. The new method is demonstrated experimentally using two undulator harmonics, a Fresnel zone plate and an energy discriminating photon counting detector.

Multiscale Microrheology Using Fluctuating Filaments as Stealth Probes.

The mechanical properties of soft materials can be probed on small length scales by microrheology. A common approach tracks fluctuations of micrometer-sized beads embedded in the medium to be characterized. This approach yields results that depend on probe size when the medium has structure on comparable length scales. Here, we introduce filament-based microrheology using high-aspect-ratio semiflexible filaments as probes. Such quasi-1D probes are much less invasive than beads due to their small cross sections. Moreover, by imaging transverse bending modes, we simultaneously determine the micromechanical response of the medium on multiple length scales corresponding to the mode wavelengths. We use semiflexible single-walled carbon nanotubes as probes that can be accurately and rapidly imaged based on their stable near-IR fluorescence. We find that the viscoelastic properties of sucrose, polyethylene oxide, and hyaluronic acid solutions measured in this way are in good agreement with those measured by conventional micro- and macrorheology.

Design of a Low-Cost Small-Size Fluxgate Sensor.

Traditional fluxgate sensors used in geomagnetic field observations are large, costly, power-consuming and often limited in their use. Although the size of the micro-fluxgate sensors has been significantly reduced, their performance, including indicators such as accuracy and signal-to-noise, does not meet observational requirements. To address these problems, a new race-track type probe is designed based on a magnetic core made of a Co-based amorphous ribbon. The size of this single-component probe is only Φ10 mm × 30 mm. The signal processing circuit is also optimized. The whole size of the sensor integrated with probes and data acquisition module is Φ70 mm × 100 mm. Compared with traditional fluxgate and micro-fluxgate sensors, the designed sensor is compact and provides excellent performance equal to traditional fluxgate sensors with good linearity and RMS noise of less than 0.1 nT. From operational tests, the results are in good agreement with those from a standard fluxgate magnetometer. Being more suitable for modern dense deployment of geomagnetic observations, this small-size fluxgate sensor offers promising research applications at lower costs.

Probing size variations of molecular aggregates inside chlorosomes using single-object spectroscopy.

We theoretically investigate the possibility to use single-object spectroscopy to probe size variations of the bacteriochlorophyll aggregates inside chlorosomes. Chlorosomes are the light-harvesting organelles of green sulfur and non-sulfur bacteria. They are known to be the most efficient light-harvesting systems in nature. Key to this efficiency is the organization of bacteriochlorophyll molecules in large self-assembled aggregates that define the secondary structure inside the chlorosomes. Many studies have been reported to elucidate the morphology of these aggregates and the molecular packing inside them. It is widely believed that tubular aggregates play an important role. Because the size (radius and length) of these aggregates affects the optical and excitation energy transport properties, it is of interest to be able to probe these quantities inside chlorosomes. We show that a combination of single-chlorosome linear polarization resolved spectroscopy and single-chlorosome circular dichroism spectroscopy may be used to access the typical size of the tubular aggregates within a chlorosome and, thus, probe possible variations between individual chlorosomes that may result, for instance, from different stages in growth or different growth conditions.

Environmentally Sensitive Luminescence Reveals Spatial Confinement, Dynamics, and Their Molecular Weight Dependence in a Polymer Glass.

Polymer glasses have an irregular structure. Among the causes for such complexity are the chemically distinct chain end groups that are the most abundant irregularities in any linear polymer. In this work, we demonstrate that chain end induced defects allow polymer glasses to create confined environments capable of hosting small emissive molecules. Using environmentally sensitive luminescent complexes, we show that the size of these confinements depends on molecular weight and can dramatically affect the photoluminescence of free or covalently bound emissive complexes. We confirm the impact of chain end confinement on the bulk glass transition in poly(methyl acrylate) (pMA) and show that commonly observed Tg changes induced by the chain ends should have a structural origin. Finally, we demonstrate that the size and placement of luminescent molecular probes in pMA can dramatically affect the probe luminescence and its temperature dependence, suggesting that polymer glass is a highly irregular and complex environment, marking its difference with conventional small molecule solvents. Considering the ubiquity of luminescent glassy materials, our work lays down a blueprint for designing them with structural considerations in mind, ones where packing density and chain end size are key factors.

Mechanical Deconvolution of Elastic Moduli by Indentation of Mechanically Heterogeneous Materials

Most materials are mechanically heterogeneous on a certain length scale. In many applications, this heterogeneity is crucial for the material’s function, and exploiting mechanical heterogeneity could lead to new materials with interesting features, which require accurate understanding of the local mechanical properties. Generally used techniques to probe local mechanics in mechanically heterogeneous materials include indentation and atomic force microscopy. However, these techniques probe stresses at a region of finite size, so that experiments on a mechanically heterogeneous material lead to blurring or convolution of the measured stress signal. In this study, finite element method simulations are performed to find the length scale over which this mechanical blurring occurs. This length is shown to be a function of the probe size and indentation depth, and independent of the elastic modulus variations in the heterogeneous material, for both 1D and 2D modulus profiles. Making use of these findings, we then propose two deconvolution methods to approximate the actual modulus profile from the apparent, blurred measurements, paving the way for an accurate determination of the local mechanical properties of heterogeneous materials.

500 μm field-of-view probe-based confocal microendoscope for large-area visualization in the gastrointestinal tract

Rapid large-area tissue imaging at the cellular resolution is important for clinical diagnosis. We present a probe-based confocal microendoscope (pCM) with a field-of-view (FOV) diameter over 500 μm, lateral resolution of 1.95 μm, and outer diameter of 2.6 mm, compatible with the biopsy channel of conventional gastroscopes. Compared to a conventional pCM, our system’s FOV increased by a factor of 4 while maintaining the probe size and cellular resolution—comparable to the FOV of Zeiss Axio Observer’s 20 × / 0.8 numerical aperture objective lens. Ex vivo imaging of wide areas in healthy and diseased rat gastrointestinal tract tissues demonstrates the system’s practicality.