37 research outputs found
Numerical model of the ice cover evolution in Arctic Seas for the operational forecasting
Get PDFThe dynamic-thermodynamic model of the ice cover evolution is used for operational 5‑day ice forecasts in the Russian Arctic seas and to obtain some statistical estimates of the ice cover state. The model is a numerical realization of the heat budget and the motion balance equations for sea and ice cover with appropriate boundary conditions. The statistical processing of the data resulted in revealing characteristics of seasonal and spatial variability of the ice compressionin the Barents and Kara Seas
Double-sided fresnel zone plates as high performance optics in X-ray microscopy
Get PDFX-ray microscopy describes a range of analytical techniques, specialized for the characterization of organic and inorganic samples using high energy photons. It takes advantage of the high penetration depth, high resolution and chemical sensitivity of X-rays and allows for the study of extended samples in their native environment without extensive sample preparation. Many of these experimental methods employ diffractive X-ray optics, like Fresnel zone plate lenses to obtain high spatial resolution or the better utilization of the incoming flux. Since improving the efficiency of zone plates can increase the throughput, quality and resolution of measurements, there is a constant demand for high efficiency and high resolution X-ray optics.
Stacking is an established concept for extending the capabilities of zone plate optics. By stacking two zone plates in each other's optical near field, they act as a single zone plate with combined optical transmission profile, that would be infeasible to make as a single optical element. Yet the existing implementations of stacking suffer from issues regarding complexity and stability.
This work presents the development of an alternative solution to conventional zone plate stacking, that circumvents most of its drawbacks. By patterning two zone plates on the front and back sides of a membrane, double-sided zone plates can deliver the advantages of stacked zone plates as inherently monolithic, single-chip optical elements.
Double-sided blazed zone plates with two complementary binary zone plates on the two sides of the membrane were produced to provide an effective four level transmission profile. This allowed to bypass the fundamental limitations of binary zone plates by providing up to 54.7% diffraction efficiency at 6.2 keV while having 200 nm smallest half-pitch and a reasonable working distance.
For high resolution zone plates, structure height is the main limiting factor. Therefore by patterning two identical zone plates on the two sides of the membrane, one can double the effective structure height. This provided us with a significant gain in focusing efficiency at high photon energies, as we have successfully measured 9.9% focusing efficiency at 9 keV with 30 nm smallest half-pitch, while preserving diffraction limited optical performance.
Stacking two complementary zone plates for multiplying their spatial frequencies opens the possibility for ultra-high resolution zone plate optics. We have successfully produced and tested interlaced zone plate optics down to 7 nm smallest half-pitch while still maintaining practical aperture sizes.
This thesis is a comprehensive summary of the work performed for the fabrication and characterization of the high performance zone plates representing each concept and provides possible examples for their future use
Stochastic modeling of sea ice concentration fields for assessment of navigation conditions along the Northern Sea Route
Get PDFArticle describes a probabilistic model (stochastic generator) of spatial-temporal variability of sea ice concentration. Values of the ice concentration are generated at the nodes of the spatial grid with 10 km resolution; the model time step is one day. The change in ice concentration with time (temporal variability) is modeled on the basis of a matrix of transient probabilities (discrete Markov chain), each row of which is a distribution function of the conditional probability of changes in the ice concentration. Spatial variability is determined by empirical probability fields, with which the observed changes in fields of the ice concentration are associated with known conditional probability distribution functions. To identify the parameters of the stochastic generator, satellite data from the OSI SAF project for the period 1987–2019 were used. The generator takes into account seasonal, interannual and climatic variability. Interannual and climatic variability are determined on the basis of a stochastic model of changes in the types of ice coverage. In order to verify the developed stochastic generator, we compared the statistical indicators of observed and calculated ice fields. The results showed that the fieldaverage absolute error of statistical characteristics of the ice concentration (mean and standard deviation) does not exceed 3.3%. The discrepancy between the correlation intervals of ice coverage calculated from the model and measured ice concentration fields does not exceed 2 days. The variograms of the modeled and observed fields have a similar form and close values. As an example, we determined the duration of navigation of Arc4 ice class ships between the Barents and Kara Seas using synthetic fields of the ice concentration reproduced by the stochastic generator
Model-independent particle species disentanglement by X-ray cross-correlation scattering
No full textAbstractMixtures of different particle species are often investigated using the angular averages of the scattered X-ray intensity. The number of species is deduced by singular value decomposition methods. The full disentanglement of the data into per-species contributions requires additional knowledge about the system under investigation. We propose to exploit higher-order angular X-ray intensity correlations with a new computational protocol, which we apply to synchrotron data from two-species mixtures of two-dimensional static test nanoparticles. Without any other information besides the correlations, we demonstrate the assessment of particle species concentrations in the measured data sets, as well as the full ab initio reconstruction of both particle structures. The concept extends straightforwardly to more species and to the three-dimensional case, whereby the practical application will require the measurements to be performed at an X-ray free electron laser.</jats:p
Статистические особенности экстремального дрейфа льда юго-западной части Карского моря, полученные по результатам модельных расчетов
Get PDFThe aim of the study was to identify the basic characteristics of ice drift in the south-western Kara Sea and to estimate the extreme drift speed of given probability, including its spatial variability and statistical correlation with the main drift-forming factors.In order to obtain the ice drift data, the numerical dynamic-thermodynamic model of ice cover evolution developed in AARI was used. Its basic specific feature is imitation of ice cover with the help of so-called markers (conventional ice floes). Using three variants of the model grid net (25, 12.5 and 5 km), the ice conditions in the Baidara Bay and the adjoining area in January-March 2018 were simulated.The analysis of the simulation results showed that the average ice drift (average ice transport) is directed from the Baidara Bay to the open sea, i.e. northward with slight deviations mostly to the west. A less detailed grid net results in a smoothed ice drift field, while an increase in the spatial resolution of the model increases the spatial contrasts of the ice drift.The maximum values of the extreme ice drift velocity expressed as “once per N years” occur in the northern part of the model area at the directions of the north-western quarter (up to 1.5-1.8 m/s “once per 10 years” - “once per 100 years”, respectively). The frequency of ice drift velocity exceeding 0.3 m/s is about 4-7 %, and that of ice drift velocity exceeding 0.6 m/s is not more than 1 %.At low drift velocity, the role of inertia is very high, but as the drift rate grows, the inertia contribution decreases noticeably. At increasing drift velocity, the statistical correlation between the ice drift (on the one hand) and the wind, current and sea level tilt (on the other hand) becomes evident. This effect is especially evident for the correlation “drift / wind”. The correlation “drift / ice pressure” depends on the drift speed more or less noticeably at low and high drift speeds, when unidirectional changes of the ice drift and ice pressure happen more often than the opposite ones. At the drift velocities within 0.15-0.60 m\s, the correlation between the ice drift and ice pressure is insignificant, i.e. the unidirectional and opposite changes of the ice drift and ice pressure are almost equally likely.Для выявления основных параметров дрейфа льда в юго-западной части Карского моря и получения оценок экстремальных скоростей дрейфа заданной обеспеченности, включая статистическую связь с основными дрейфообразующими факторами, была использована разработанная в ААНИИ численная динамико-термодинамическая модель эволюции ледяного покрова.С помощью модели была воспроизведена эволюция ледяного покрова в юго-западной части Карского моря за 3 месяца 2018 г. для трех вариантов пространственного разрешения: 5 км, 12,5 км и 25 км. Для трех специально выбранных точек были получены статистические оценки дрейфа льда, включая экстремальные значения заданной обеспеченности в терминах «1 раз в N лет». Были вычислены парные коэффициенты корреляции скорости дрейфа льда с основными влияющими на дрейф факторами в разных диапазонах скоростей, что позволило оценить изменение вклада каждого фактора в зависимости от скорости дрейфа. Показано, что, по мере увеличения скорости дрейфа, наиболее сложным образом меняется статистическая связь между дрейфом и сжатием льда. Выявлены основные черты влияния пространственной детализации модели на статистические оценки экстремального дрейфа
Chemical and biochemical sensors based on silicon nanowire field-effect transistor arrays
Get PDFField-effect transistors (FETs) made from semiconducting nanowires have great potential as electronic biochemical sensors if they can be integrated as an array in a CMOS-compatible architecture together with microfluidic channels and interfacing electronics. Such nanoscale electronic transducers based on ion-sensitive field-effect transistors could be mass fabricated at reasonable costs. This, in combination with their small size, makes them ideal for personalized medicine and for future implanted sensing devices.
The sensing principle is based on adsorption of charged species on the sensor surface, leading to a change in surface potential and subsequently a change in current in the FET channel. Thereby, the high-impedance input signal is transformed into a low-impedance output signal, which is an advantage against classic ion-selective electrodes. The potential for downscaling and integration for the simultaneous detection of multiple parameters make silicon nanowire FETs a promising platform to meet the demand for cheap, multifunctional and scalable sensors. Even though many promising results on chemical and biochemical sensing have been achieved so far, a detailed understanding of the electrolyte surface interaction is still missing. Inconsistent outcomes regarding the effect of electrolyte concentrations and electrical noise, suggest that further quantitative studies are needed. The aspect of the size compatibility between the sensor unit and the analyte species is often emphasized to favor nanoscale FETs. Another aspect, often mentioned, is the surface to volume ratio. Hence smaller sensing units should enhance the sensitivity of the sensor, allowing the detection at ultra-low concentrations or a small number of molecules. Furthermore, the capacitances decrease for smaller sensing units, which could lead to faster response times. However, other aspects such as the intrinsic electronic noise, the analyte diffusion time and surface reaction kinetics have to be considered for the development of an applicable sensor.
This thesis was part of a research project aimed at developing a modular, scalable and integrateable sensor platform for the electronic detection of analytes in solution. The main focus lies on the sensor-solution interface and thus the thesis quantitatively compares the experimental data with analytical models.
In this work we have established a versatile sensor platform based on silicon nanowire arrays. The sensor functionality was changed by surface modification for the detection of various analytes such as pH, alkaline ions and even FimH proteins. We achieved an ideal pH sensor with a response close to the Nernst limit. Full surface passivation for protons was accomplished for the implementation of a nanoscale reference electrode. Using the differential signal from differently functionalized silicon nanowires we could detect sodium and potassium ions selectively. Ultimately we present the detection of protein-ligand interactions of the physiologically relevant protein FimH. An extended site binding model was derived to calculate the theoretical limits and assess the properties of the surface groups by evaluating the experimental results
RCSB Protein Data Bank: Biological macromolecular structures enabling research and education in fundamental biology, biomedicine, biotechnology and energy
No full textThe Research Collaboratory for Structural Bioinformatics Protein Data Bank (RCSB PDB, rcsb.org), the US data center for the global PDB archive, serves thousands of Data Depositors in the Americas and Oceania and makes 3D macromolecular structure data available at no charge and without usage restrictions to more than 1 million rcsb.org Users worldwide and 600 000 pdb101.rcsb.org education-focused Users around the globe. PDB Data Depositors include structural biologists using macromolecular crystallography, nuclear magnetic resonance spectroscopy and 3D electron microscopy. PDB Data Consumers include researchers, educators and students studying Fundamental Biology, Biomedicine, Biotechnology and Energy. Recent reorganization of RCSB PDB activities into four integrated, interdependent services is described in detail, together with tools and resources added over the past 2 years to RCSB PDB web portals in support of a 'Structural View of Biology.
Two-dimensional structure from random multiparticle X-ray scattering images using cross-correlations
No full textKnowledge of the structure of biological macromolecules, especially in their native environment, is crucial because of the close structure–function relationship. X-ray small-angle scattering is used to determine the shape of particles in solution, but the achievable resolution is limited owing to averaging over particle orientations. In 1977, Kam proposed to obtain additional structural information from the cross-correlation of the scattering intensities. Here we develop the method in two dimensions, and give a procedure by which the single-particle diffraction pattern is extracted in a model-independent way from the correlations. We demonstrate its application to a large set of synchrotron X-ray scattering images on ensembles of identical, randomly oriented particles of 350 or 200 nm in size. The obtained 15 nm resolution in the reconstructed shape is independent of the number of scatterers. The results are discussed in view of proposed ‘snapshot’ scattering by molecules in the liquid phase at X-ray free-electron lasers
Interlaced zone plate optics for hard X-ray imaging in the 10 nm range
No full textMulti-keV X-ray microscopy has been particularly successful in bridging the resolution gap between optical and electron microscopy. However, resolutions below 20 nm are still considered challenging, as high throughput direct imaging methods are limited by the availability of suitable optical elements. In order to bridge this gap, we present a new type of Fresnel zone plate lenses aimed at the sub-20 and the sub-10 nm resolution range. By extending the concept of double-sided zone plate stacking, we demonstrate the doubling of the effective line density and thus the resolution and provide large aperture, singlechip optical devices with 15 and 7 nm smallest zone widths. The detailed characterization of these lenses shows excellent optical properties with focal spots down to 7.8 nm. Beyond wave front characterization, the zone plates also excel in typical imaging scenarios, verifying their resolution close to their diffraction limited optical performance
Epitaxial Growth of Fe on GaN(0001): Strucural and Magnetic Properties
No full textWe report results on growth studies of Fe on GaN, in particular with respect to structural and magnetic properties. The growth of GaN has been carried out by molecular beam epitaxy (MBE) and metal organic vapour phase epitaxy (MOVPE) on Si(111) and Al2O3 substrates, respectively. Fe depositions of different thicknesses were performed in ultra high vacuum (UHV) at room temperature using an electron-beam evaporation set-up. X-ray diffraction analysis shows that the iron films are crystalline and indications of a (110) bee orientation of the film are observed. By means of scanning tunneling microscopy (STM) epitaxial islands of Fe on the GaN(0001) surface, on a scale of 500 x 500 nm(2), have been observed. The experimentally determined magnetic hysteresis loops, with the magnetic field applied parallel to the sample surface, show a coercive field that decreases as the temperature increases; at 300 K and 50 K we measure a coercive field of 12 G and 36 G, respectively. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
