25,958 research outputs found

    Precise characterization of nanometer-scale systems using interferometric scattering microscopy and Bayesian analysis

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    Interferometric scattering microscopy (iSCAT) can image the dynamics of nanometer-scale systems. The typical approach to analyzing interferometric images involves intensive processing, which discards data and limits the precision of measurements. We demonstrate an alternative approach: modeling the interferometric point spread function (iPSF) and fitting this model to data within a Bayesian framework. This approach yields best-fit parameters, including the particle's three-dimensional position and polarizability, as well as uncertainties and correlations between these parameters. Building on recent work, we develop a model that is parameterized for rapid fitting. The model is designed to work with Hamiltonian Monte Carlo techniques that leverage automatic differentiation. We validate this approach by fitting the model to interferometric images of colloidal nanoparticles. We apply the method to track a diffusing particle in three dimensions, to directly infer the diffusion coefficient of a nanoparticle without calculating a mean-square displacement, and to quantify the ejection of DNA from an individual lambda phage virus, demonstrating that the approach can be used to infer both static and dynamic properties of nanoscale systems

    Simulation of metal powder packing behaviour in laser-based powder bed fusion

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    Laser-based powder bed fusion (L-PBF) is a method of additive manufacturing, in which metal powder is fused into solid parts, layer by layer. L-PBF shows high promise for manufacture of functional Tungsten parts, but the development of Tungsten powder feedstock for L-PBF processing is demanding and expensive. Therefore, computer simulation is explored as a possible tool for Tungsten powder feedstock development at EOS Finland Oy, with whom this thesis was made. The aim of this thesis was to develop a simulation model of the recoating process of an EOS M 290 L-PBF system, as well as a validation method for the simulation. The validated simulation model can be used to evaluate the applicability of the used simulation software (FLOW-3D DEM) in powder material development, and possibly use the model as a platform for future application with Tungsten powder. In order to reduce complexity and uncertainties, the irregular Tungsten powder is not yet simulated, and a well-known, spherical EOS IN718 powder feedstock was used instead. The validation experiment is based on building a low, enclosed wall using the M 290 L-PBF system. Recoated powder is trapped inside as the enclosure is being built, making it possible to remove the sampled powder from a known volume. This enables measuring the powder packing density (PD) of the powder bed. The experiment was repeated five times and some sources of error were also quantified. Average PD was found to be 52 % with a standard deviation of 0.2 %. The simulation was modelled after the IN718 powder and corresponding process used in the M 290 system. Material-related input values were found by dynamic image analysis, pycnometry, rheometry, and from literature. PD was measured with six different methods, and the method considered as most analogous to the practical validation experiment yielded a PD of 52 %. Various particle behavior phenomena were also observed and analyzed. Many of the powder bed characterization methods found in literature were not applicable to L-PBF processing or were not representative of the simulated conditions. Many simulation studies were also found to use no validation, or used a validation method which is not based on the investigated phenomena. The validation model developed in this thesis accurately represents the simulated conditions and is found to produce reliable and repeatable results. The simulation model was parametrized with values acquired from practical experiments or literature and closely matched the validation experiment, and could therefore be considered a truthful representation of the powder recoating process of an EOS M 290. The model can be used as a platform for future development of Tungsten powder simulation

    Studies of excited states in the odd-odd nucleus 178Au

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    Atomic nuclei close to the Z = 82 shell closure are well known for exhibiting shape coexistence with one of the earliest examples of this being the neutron-deficient gold (Z = 79) nuclei close to the neutron mid shell gap at N=104. Subsequently, such isotopes have been examined with both laser-spectroscopy and decay studies. The present investigation was motivated by the recent experiments at ISOLDE CERN to study the chain of gold isotopes 176−181 Au. In the odd-odd nucleus, 178 Au (N=99), two α-decaying states were identified, a low spin (I π = 2+ , 3− ) ground state 178 Aug , and a high-spin (I π = 7+ , 8− ) isomer. Laser-spectroscopy measurements have shown both isomers to be deformed with the high-spin state having slightly larger deformation. In this thesis, excited states of 178 Au (Z=79, N=99) have been established for the first time by means of in-beam γ-ray spectroscopy. The previously established sub-microsecond isomers with half-lives of 294-ns and 373-ns were confirmed and their decay schemes to the α-decaying states of 178 Au were established with new multipolarity assignments. The existence of sub-microsecond isomers of 178 Au allowed for isomer decay tagging to be utilised to identify excited states. A total of 3 rotational bands were established. Configuration assignments of these bands has been made on the basis of comparison with similar bands in neighbouring odd-odd Ir isotopes, with the πi13/2 ⊗ νi11/2 and πh11/2 ⊗ ν f7/2 bands observed in 178 Au. The establishment of rotational bands is discussed and may also constrain the the spin-parity of both previously established α-decaying states 178 Aug,m

    The characterization and application of plasma-based photonic crystals for high power Terahertz devices.

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    Thesis (Ph.D.)--University of Washington, 2023Plasma photonic crystals (PPCs) have the potential to significantly expand the capabilities of current submillimeter wave technologies by providing high speed (microsecond time scale) control of energy transmission characteristics in the GHz through low THz range. Furthermore, plasma-based devices can be used in higher power applications than their solid-state counterparts without experiencing significant changes in function or incurring damage. PPC studies on the unique conditions present in high powered applications are few. Furthermore, the construction of THz PPC experimental devices requires lattice sizes on the order of microns, plasma densities exceeding 102210^{22} m−3^{-3}, and high power THz sources, all of which sit at the limit (or outside) of the capabilities of current technology. Analytical and numerical exploration of THz PPCs is therefore strongly motivated, allowing for advancements in understanding as hardware capabilities grow. In support of the use of plasma-based photonic crystals for high power THz wave applications, three complementary lines of research amenable to theoretical or numerical treatment are developed that account for plasma's unique properties. Plasmas do not have discontinuous density profiles; therefore, assumptions used for dielectric PCs are not valid and a new analysis is necessary. In the first line of investigation the effect of smooth versus discontinuous density profiles in PPCs on transmission characteristics is explored using a linear analytical model and group velocity band gap maps. Plasmas can deform in response to large electromagnetic fields. In the second line of investigation a two-dimensional plasma-vacuum photonic crystal is simulated using a high-fidelity plasma model, implemented in the discontinuous Galerkin finite element code WARPXM, and the plasma's response to high amplitude fields is observed. When the plasma in the PPC used for high power applications is partially ionized, changes in plasma density can occur due to energy absorption and ionization. In the final line of investigation, a reacting 5-moment multi-fluid model is implemented and applied to capture collisions and reactions for partially ionized THz plasmas

    Study of neural circuits using multielectrode arrays in movement disorders

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    Treballs Finals de Grau d'Enginyeria Biomèdica. Facultat de Medicina i Ciències de la Salut. Universitat de Barcelona. Curs: 2022-2023. Tutor/Director: Rodríguez Allué, Manuel JoséNeurodegenerative movement-related disorders are characterized by a progressive degeneration and loss of neurons, which lead to motor control impairment. Although the precise mechanisms underlying these conditions are still unknown, an increasing number of studies point towards the analysis of neural networks and functional connectivity to unravel novel insights. The main objective of this work is to understand cellular mechanisms related to dysregulated motor control symptoms in movement disorders, such as Chorea-Acanthocytosis (ChAc), by employing multielectrode arrays to analyze the electrical activity of neuronal networks in mouse models. We found no notable differences in cell viability between neurons with and without VPS13A knockdown, that is the only gene known to be implicated in the disease, suggesting that the absence of VPS13A in neurons may be partially compensated by other proteins. The MEA setup used to capture the electrical activity from neuron primary cultures is described in detail, pointing out its specific characteristics. At last, we present the alternative backup approach implemented to overcome the challenges faced during the research process and to explore the advanced algorithms for signal processing and analysis. In this report, we present a thorough account of the conception and implementation of our research, outlining the multiple limitations that have been encountered all along the course of the project. We provide a detailed analysis on the project’s economical and technical feasibility, as well as a comprehensive overview of the ethical and legal aspects considered during the execution

    Demonstration of a Response Time Based Remaining Useful Life (RUL) Prediction for Software Systems

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    Prognostic and Health Management (PHM) has been widely applied to hardware systems in the electronics and non-electronics domains but has not been explored for software. While software does not decay over time, it can degrade over release cycles. Software health management is confined to diagnostic assessments that identify problems, whereas prognostic assessment potentially indicates when in the future a problem will become detrimental. Relevant research areas such as software defect prediction, software reliability prediction, predictive maintenance of software, software degradation, and software performance prediction, exist, but all of these represent diagnostic models built upon historical data, none of which can predict an RUL for software. This paper addresses the application of PHM concepts to software systems for fault predictions and RUL estimation. Specifically, this paper addresses how PHM can be used to make decisions for software systems such as version update and upgrade, module changes, system reengineering, rejuvenation, maintenance scheduling, budgeting, and total abandonment. This paper presents a method to prognostically and continuously predict the RUL of a software system based on usage parameters (e.g., the numbers and categories of releases) and performance parameters (e.g., response time). The model developed has been validated by comparing actual data, with the results that were generated by predictive models. Statistical validation (regression validation, and k-fold cross validation) has also been carried out. A case study, based on publicly available data for the Bugzilla application is presented. This case study demonstrates that PHM concepts can be applied to software systems and RUL can be calculated to make system management decisions.Comment: This research methodology has opened up new and practical applications in the software domain. In the coming decades, we can expect a significant amount of attention and practical implementation in this area worldwid

    Thermo-Optical Measurements and Simulation in a Fibre-Optic Circuit Using an Extrinsic Fabry–Pérot Interferometer under Pulsed Laser Heating

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    Advantages of using an external Fabry–Pérot interferometer (EFPI) as a high-speed local temperature deformation sensor are demonstrated for the fibre-optic circuit combining a powerful laser beam for surface heating with a low-power probing radiation. The difference in the formation of the heating and probing radiation provides a simple basis for varying the gap between the fibre end and the surface in order to change the ratio between the heating and EFPI measuring areas. Using an example of modelling the laser heating by radiation from a standard single-mode fibre, we demonstrate the possibility of employing the EFPI to measure the temperature deformation of the surface on a quasi-isothermal area with the temperature close to the maximum at gap values of more than 100 μm. With the condition of preliminary calibration, the proposed scheme can be used to evaluate the heat treatment of the surface with the speed of the applied photodetector. The practical possibilities of the method are demonstrated on examples of heating some metal and semiconductor samples by laser pulses of microsecond duration

    Simulating substrate binding sites in the S. aureus Type II NADH Dehydrogenase

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    "Type II NADH Oxidoreductase (NDH-2) from Staphylococcus aureus was established as a therapeutic target against the virulency of this bacterium and an alternative to treat Complex I-derived diseases. To accurately model interactions of NDH-2 with its substrates such as menaquinones and NADH, Coarse-Grain (CG) simulations were employed. "N/

    Modulation of the substrate specificity of the kinase PDK1 by distinct conformations of the full-length protein

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    The activation of at least 23 different mammalian kinases requires the phosphorylation of their hydrophobic motifs by the kinase PDK1. A linker connects the phosphoinositide-binding PH domain to the catalytic domain, which contains a docking site for substrates called the PIF pocket. Here, we used a chemical biology approach to show that PDK1 existed in equilibrium between at least three distinct conformations with differing substrate specificities. The inositol polyphosphate derivative HYG8 bound to the PH domain and disrupted PDK1 dimerization by stabilizing a monomeric conformation in which the PH domain associated with the catalytic domain and the PIF pocket was accessible. In the absence of lipids, HYG8 potently inhibited the phosphorylation of Akt (also termed PKB) but did not affect the intrinsic activity of PDK1 or the phosphorylation of SGK, which requires docking to the PIF pocket. In contrast, the small molecule valsartan bound to the PIF pocket and stabilized a second distinct monomeric conformation. Our study reveals dynamic conformations of full-length PDK1 in which the location of the linker and the PH domain relative to the catalytic domain determines the selective phosphorylation of PDK1 substrates. The study further suggests new approaches for the design of drugs to selectively modulate signaling downstream of PDK1

    NetClone: Fast, Scalable, and Dynamic Request Cloning for Microsecond-Scale RPCs

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    Spawning duplicate requests, called cloning, is a powerful technique to reduce tail latency by masking service-time variability. However, traditional client-based cloning is static and harmful to performance under high load, while a recent coordinator-based approach is slow and not scalable. Both approaches are insufficient to serve modern microsecond-scale Remote Procedure Calls (RPCs). To this end, we present NetClone, a request cloning system that performs cloning decisions dynamically within nanoseconds at scale. Rather than the client or the coordinator, NetClone performs request cloning in the network switch by leveraging the capability of programmable switch ASICs. Specifically, NetClone replicates requests based on server states and blocks redundant responses using request fingerprints in the switch data plane. To realize the idea while satisfying the strict hardware constraints, we address several technical challenges when designing a custom switch data plane. NetClone can be integrated with emerging in-network request schedulers like RackSched. We implement a NetClone prototype with an Intel Tofino switch and a cluster of commodity servers. Our experimental results show that NetClone can improve the tail latency of microsecond-scale RPCs for synthetic and real-world application workloads and is robust to various system conditions.Comment: 13 pages, ACM SIGCOMM 202
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