In this paper, we propose an innovative approach based on the wavelength optimization of a light source for a simple, high-performance surface plasmon resonance (SPR) sensor utilizing comprehensive reflectance analysis in the angular domain. The proposed structure consists of a glass substrate, an adhesion layer of titanium dioxide, a silver plasmonic layer, and a 2D material. Analysis is performed in the Kretschmann configuration for liquid analyte sensing. Sensing parameters such as the refractive index (RI) sensitivity, the reflectance minimum, and the figure of merit (FOM) are investigated in the first step of this study as a function of the thickness of the silver layer together with the RI of a coupling prism. Next, utilizing the results offering a fused silica prism, the thickness of the silver layer and the wavelength of the light source are optimized for the structure with the addition of a 2D material, black phosphorus (BP), which is studied along different principal directions, the zigzag and armchair directions. In addition, a new approach of adjusting the source wavelength using a one-dimensional photonic crystal combined with an LED, is presented. Based on this analysis, for the reference structure at a wavelength of 632.8 nm, the optimized silver layer thickness is 50 nm, and the achieved RI sensitivity ranges from 193.9 to 251.5 degrees per RI unit (deg/RIU), with the highest FOM reaching 52.3 RIU-1. In addition, for the modified structure with BP, the achieved RI sensitivity varies in the range of 269.1-351.2 deg/RIU at the optimized wavelength of 628 nm, with the highest FOM reaching 44.7 RIU-1 for the zigzag direction. Due to the optimization and adjusting the wavelength of the source, the results obtained for the proposed SPR structure could have significant implications for the development of more sensitive and efficient sensors employing a simple plasmonic structure.
- Keywords
- SPR, angular domain, black phosphorus, sensitivity enhancement, silver layer, zigzag and armchair directions,
- Publication type
- Journal Article MeSH
We propose exploiting the superluminal plasma wake for coherent Cherenkov radiation by injecting a relativistic electron beam (REB) into a plasma with a slowly varying density up-ramp. Using three-dimensional particle-in-cell and far-field time-domain radiation simulations, we show that an isolated subcycle pulse is coherently emitted towards the Cherenkov angle by bubble-sheath electrons successively at the rear of the REB-induced superluminal plasma wake. A theoretical model based on a superluminal current dipole has been developed to interpret such coherent radiation, and agrees well with the simulation results. This radiation has ultrashort attosecond-scale duration and high intensity, and exhibits excellent directionality with ultralow angular divergence and stable carrier envelope phase. Its intensity increases with the square of the propagation length and its central frequency can be easily tuned over a wide range, from the far infrared to the ultraviolet.
- Publication type
- Journal Article MeSH
Cytoskeletal structures can be affected by external factors including ultrasound. Our task was to develop a structure analysis method to evaluate these changes quantitatively. We exposed HeLa cells to continuous ultrasound (1 MHz, 1 and 2 W/cm2, 10 min at 37 degrees C). The microtubules were detected by the monoclonal antibody TU-01/SwAM/FITC, observed in a fluorescence microscope and photographed digitally. The images were processed by "FFT magic" software. The structure analysis is based on frequency domain filtering using discrete Fourier transform. The basic idea is to design filters to extract information describing best the structural changes. The properties of the filter can be enhanced by direction filtering, i.e., extraction of a symmetric angular segment in the frequency domain centered on a zero frequency. The final image is a normalized sum of inverse FFT's of such segmented spectra. We needed a method yielding a single number assigned to the structure, e.g., the ratio of the area of microtubules to the total cell area. Assuming that the image background intensity is constant, we can use thresholding to detect areas occupied by the cells. The information about the area of the microtubules is contained in a wide range of higher intensities. Therefore, we use a gamma correction. The area occupied by microtubules is then considered an area with intensities above the selected threshold. There were tested three different filters to extract information about microtubules. The mathematical method chosen seems sensitive enough for quantitative assessment of changes of the microtubular network.
In this work, we deal with general reactive systems involving N species and M elementary reactions under applicability of the mass-action law. Starting from the dynamic variables introduced in two previous works [P. Nicolini and D. Frezzato, J. Chem. Phys. 138(23), 234101 (2013); 138(23), 234102 (2013)], we turn to a new representation in which the system state is specified in a (N × M)(2)-dimensional space by a point whose coordinates have physical dimension of inverse-of-time. By adopting hyper-spherical coordinates (a set of dimensionless "angular" variables and a single "radial" one with physical dimension of inverse-of-time) and by examining the properties of their evolution law both formally and numerically on model kinetic schemes, we show that the system evolves towards the equilibrium as being attracted by a sequence of fixed subspaces (one at a time) each associated with a compact domain of the concentration space. Thus, we point out that also for general non-linear kinetics there exist fixed "objects" on the global scale, although they are conceived in such an abstract and extended space. Moreover, we propose a link between the persistence of the belonging of a trajectory to such subspaces and the closeness to the slow manifold which would be perceived by looking at the bundling of the trajectories in the concentration space.
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Computational models of acoustic wave propagation are frequently used in transcranial ultrasound therapy, for example, to calculate the intracranial pressure field or to calculate phase delays to correct for skull distortions. To allow intercomparison between the different modeling tools and techniques used by the community, an international working group was convened to formulate a set of numerical benchmarks. Here, these benchmarks are presented, along with intercomparison results. Nine different benchmarks of increasing geometric complexity are defined. These include a single-layer planar bone immersed in water, a multi-layer bone, and a whole skull. Two transducer configurations are considered (a focused bowl and a plane piston operating at 500 kHz), giving a total of 18 permutations of the benchmarks. Eleven different modeling tools are used to compute the benchmark results. The models span a wide range of numerical techniques, including the finite-difference time-domain method, angular spectrum method, pseudospectral method, boundary-element method, and spectral-element method. Good agreement is found between the models, particularly for the position, size, and magnitude of the acoustic focus within the skull. When comparing results for each model with every other model in a cross-comparison, the median values for each benchmark for the difference in focal pressure and position are less than 10% and 1 mm, respectively. The benchmark definitions, model results, and intercomparison codes are freely available to facilitate further comparisons.
A complex study of the spatial arrangement of different genetic elements (genes, centromeres and chromosomal domains) in the cell nucleus is presented and the principles of this arrangement are discussed. We show that the radial location of genetic elements in the three-dimensional (3D) space between the center of the nucleus and the nuclear membrane is element specific and dependent on the position of the element on the chromosome. In contrast, mutual angular positioning of both homologous and heterologous genetic elements is, in the majority of cases, random. In several cases, tethering of heterologous genetic elements was observed. This close proximity of specific loci may be responsible for their mutual rearrangement and the development of cancer. Comparison of our results with transcriptome maps shows that the nuclear location of chromosomal domains with highly expressed genes is more central when compared with chromosomes with low expression. The higher-order chromatin structure is strikingly similar in various human cell types, which correlates with the fact that the profiles of gene expression are also similar.
- MeSH
- Cell Nucleus genetics metabolism MeSH
- DNA chemistry MeSH
- Gene Expression physiology MeSH
- Genome, Human * MeSH
- In Situ Hybridization, Fluorescence MeSH
- Nucleic Acid Conformation * MeSH
- Humans MeSH
- Imaging, Three-Dimensional MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Names of Substances
- DNA MeSH
Unique 3D tomography apparatus was built and successfully tested in Research Centre Rez. The apparatus allows three-dimensional view into the interior of low-dimension radioactive samples with a diameter up to several tens of millimeters with a betterresolution then 1 mm3 and is designed to detect domains with different levels of radioactivity. Structural inhomogeneities such as cavities, cracks or regions with different chemical composition can be detected using this equipment. The SPECT scanner has been successfully tested on several samples composed of a 3-mm radionuclide source located eccentrically within homogeneous steel bushings. To detect fine cracks inside a small sample, an ultrafine scan of the sample was carried out in the course of 24 hours with a 0.5-mm longitudinal and transverse step and 18° angular step. The exact location and orientation of a fine crack artificially formed inside a sample has been detected.
- MeSH
- Algorithms MeSH
- Diffusion MeSH
- Geology MeSH
- Tomography, Emission-Computed, Single-Photon * MeSH
- Silicon Dioxide MeSH
- Image Processing, Computer-Assisted methods MeSH
- Porosity MeSH
- Cobalt Radioisotopes MeSH
- Radiometry instrumentation methods MeSH
- Radon MeSH
- Scintillation Counting MeSH
- Software MeSH
- Models, Theoretical MeSH
- Tungsten MeSH
- Gamma Rays MeSH
- Imaging, Three-Dimensional * MeSH
- Publication type
- Journal Article MeSH
- Names of Substances
- granite MeSH Browser
- Silicon Dioxide MeSH
- Cobalt Radioisotopes MeSH
- Radon MeSH
- Tungsten MeSH
BACKGROUND: Cognitive impairment in Parkinson's disease (PD) is associated with altered connectivity of the resting state networks (RSNs). Longitudinal studies in well cognitively characterized PD subgroups are missing. OBJECTIVES: To assess changes of the whole-brain connectivity and between-network connectivity (BNC) of large-scale functional networks related to cognition in well characterized PD patients using a longitudinal study design and various analytical methods. METHODS: We explored the whole-brain connectivity and BNC of the frontoparietal control network (FPCN) and the default mode, dorsal attention, and visual networks in PD with normal cognition (PD-NC, n = 17) and mild cognitive impairment (PD-MCI, n = 22) as compared to 51 healthy controls (HC). We applied regions of interest-based, partial least squares, and graph theory based network analyses. The differences among groups were analyzed at baseline and at the one-year follow-up visit (37 HC, 23 PD all). RESULTS: The BNC of the FPCN and other RSNs was reduced, and the whole-brain analysis revealed increased characteristic path length and decreased average node strength, clustering coefficient, and global efficiency in PD-NC compared to HC. Values of all measures in PD-MCI were between that of HC and PD-NC. After one year, the BNC was further increased in the PD-all group; no changes were detected in HC. No cognitive domain z-scores deteriorated in either group. CONCLUSION: As compared to HC, PD-NC patients display a less efficient transfer of information globally and reduced BNC of the visual and frontoparietal control network. The BNC increases with time and MCI status, reflecting compensatory efforts.
- Keywords
- Between-network connectivity, Parkinson’s disease, cognitive resting state brain networks, functional MRI, graph measures, longitudinal, mild cognitive impairment, partial least squares analysis,
- MeSH
- Adult MeSH
- Cognitive Dysfunction etiology pathology psychology MeSH
- Middle Aged MeSH
- Humans MeSH
- Longitudinal Studies MeSH
- Magnetic Resonance Imaging MeSH
- Brain diagnostic imaging pathology MeSH
- Nerve Net diagnostic imaging pathology MeSH
- Neuroimaging MeSH
- Parkinson Disease complications pathology psychology MeSH
- Prefrontal Cortex pathology MeSH
- Aged, 80 and over MeSH
- Aged MeSH
- Case-Control Studies MeSH
- Parietal Lobe pathology MeSH
- Mental Status and Dementia Tests MeSH
- Visual Cortex pathology MeSH
- Check Tag
- Adult MeSH
- Middle Aged MeSH
- Humans MeSH
- Male MeSH
- Aged, 80 and over MeSH
- Aged MeSH
- Female MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Commercial magnetic memories rely on the bistability of ordered spins in ferromagnetic materials. Recently, experimental bistable memories have been realized using fully compensated antiferromagnetic metals. Here we demonstrate a multiple-stable memory device in epitaxial MnTe, an antiferromagnetic counterpart of common II-VI semiconductors. Favourable micromagnetic characteristics of MnTe allow us to demonstrate a smoothly varying zero-field antiferromagnetic anisotropic magnetoresistance (AMR) with a harmonic angular dependence on the writing magnetic field angle, analogous to ferromagnets. The continuously varying AMR provides means for the electrical read-out of multiple-stable antiferromagnetic memory states, which we set by heat-assisted magneto-recording and by changing the writing field direction. The multiple stability in our memory is ascribed to different distributions of domains with the Néel vector aligned along one of the three magnetic easy axes. The robustness against strong magnetic field perturbations combined with the multiple stability of the magnetic memory states are unique properties of antiferromagnets.
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
The spontaneous formation of chiral structures offers a variety of liquid crystals (LC) phases that could be further tailored for practical applications. In our work, the characteristic features of spiral ordering in the cholesteric phase of EZL10/10 LC were evaluated. To disclose resonant reflections related to a nanoscale helix pitch, resonant soft X-ray scattering at the carbon K edge was employed. The angular positions of the observed element-specific scattering peaks reveal a half-pitch of the spiral ordering p/2 ≈ 52 nm indicating the full pitch of about 104 nm at room temperature. The broadening of the peaks points to a presence of coherently scattering finite-size domains formed by cholesteric spirals with lengths of about five pitches. No scattering peaks were detectable in the EZL10/10 isotropic phase at higher temperatures. The characteristic lengths extracted from the resonant soft X-ray scattering experiment agree well with the periodicity of the surface "fingerprint" pattern observed in the EZL10/10 cholesteric phase by means of atomic force microscopy. The stability of LC molecules under the incident beam was proven by X-ray absorption spectroscopy in transmission geometry.
- Publication type
- Journal Article MeSH
