Gaseous Cavities Research Articles

Simulating cross‐modal medical images using multi‐task adversarial learning of a deep convolutional neural network

AbstractComputed tomography (CT) and magnetic resonance imaging (MRI) are widely utilized modalities for primary clinical imaging, providing crucial anatomical and pathological information for diagnosis. CT measures X‐ray attenuation, while MRI captures hydrogen atom density in tissues. Despite their distinct imaging physics principles, the signals obtained from both modalities when imaging the same subject can be represented by modality‐specific parameters and common latent variables related to anatomy and pathology. This paper proposes an adversarial learning approach using deep convolutional neural networks to disentangle these factors. This disentanglement allows us to simulate one modality from the other. Experimental results demonstrate our ability to generate synthetic CT images from MRI inputs using the Gold‐atlas dataset, which consists of paired CT‐MRI volumes. Patch‐based learning techniques and a visual Turing test are employed to model discriminator losses. Our approach achieves a mean absolute error of 36.81 4.46 HU, peak signal to noise ratio of 26.12 0.31 dB, and structural similarity measure of 0.9 0.02. Notably, the synthetic CT images accurately represent bones, gaseous cavities, and soft tissue textures, which can be challenging to visualize in MRI. The proposed model operates at an inference compute cost of 430.68 GFlops/voxel. This method can minimize radiation exposure by reducing the need for pre‐operative CT scans, providing an MR‐only alternative in clinical settings.

Deep-Learning-Based Segmentation of Keyhole in In-Situ X-ray Imaging of Laser Powder Bed Fusion.

In laser powder bed fusion processes, keyholes are the gaseous cavities formed where laser interacts with metal, and their morphologies play an important role in defect formation and the final product quality. The in-situ X-ray imaging technique can monitor the keyhole dynamics from the side and capture keyhole shapes in the X-ray image stream. Keyhole shapes in X-ray images are then often labeled by humans for analysis, which increasingly involves attempting to correlate keyhole shapes with defects using machine learning. However, such labeling is tedious, time-consuming, error-prone, and cannot be scaled to large data sets. To use keyhole shapes more readily as the input to machine learning methods, an automatic tool to identify keyhole regions is desirable. In this paper, a deep-learning-based computer vision tool that can automatically segment keyhole shapes out of X-ray images is presented. The pipeline contains a filtering method and an implementation of the BASNet deep learning model to semantically segment the keyhole morphologies out of X-ray images. The presented tool shows promising average accuracy of 91.24% for keyhole area, and 92.81% for boundary shape, for a range of test dataset conditions in Al6061 (and one AliSi10Mg) alloys, with 300 training images/labels and 100 testing images for each trial. Prospective users may apply the presently trained tool or a retrained version following the approach used here to automatically label keyhole shapes in large image sets.

Construction of High-Active SERS Cavities in a TiO2 Nanochannels-Based Membrane: A Selective Device for Identifying Volatile Aldehyde Biomarkers.

The accurate, sensitive, and selective on-site screening of volatile aldehyde biomarkers for lung cancer is of utmost significance for preclinical cancer diagnosis and treatment. Applying surface-enhanced Raman scattering (SERS) for gas sensing remains difficult due to the small Raman cross section of most gaseous molecules and interference from other components in exhaled breath. Using an Au asymmetrically coated TiO2 nanochannel membrane (Au/TiO2 NM) as the substrate, a ZIF-8-covered Au/TiO2 NM SERS sensing substrate is designed for the detection of exhaled volatile organic compounds (VOCs). Au/TiO2 NM provides uniformly amplified Raman signals for trace measurements in this design. Importantly, the interfacial nanocavities between Au nanoparticles (NPs) and metal-organic frameworks (MOFs) served as gaseous confinement cavities, which is the key to enhancing the capture and adsorption ability toward gaseous analytes. Both ends of the membrane are left open, allowing gas molecules to pass through. This facilitates the diffusion of gaseous molecules and efficient capture of the target analyte. Using benzaldehyde as a typical gas marker model of lung cancer, the Schiff base reaction with a Raman-active probe molecule 4-aminothiophene (4-ATP) pregrafted on Au NPs enabled trace and multicomponent detection. Moreover, the combination of machine learning (ML) and Raman spectroscopy eliminates subjective assessments of gaseous aldehyde species with the use of a single feature peak, allowing for more accurate identification. This membrane sensing device offers a promising design for the development of a desktop SERS analysis system for lung cancer point-of-care testing (POCT).

Modeling of Cavity Discharges under AC and DC Voltage — Part II: Opportunities of the Dipole-based PD Model

To explain the occurrence of partial discharges (PD) in gaseous cavities embedded in the bulk dielectric of HV equipment, as well as to analyze the associated PD transients, two fundamental approaches have been proposed in the past, which are commonly referred to as network-based and dipole-based PD model. The first one has been reviewed critically in Part I of this publication, while this Part II is addressed to the dipole-based PD model. This alternative approach, which was promoted by Pedersen in the 1980, is based on the fundamentals of the gas discharge physics and adopts the electromagnetic field theory to treat the electromagnetic transients, which are associated with the establishment of an electrical dipole as consequence of a cavity discharge. However, understanding this more sophisticated concept needs a deep knowledge of the electromagnetic field theory based on Maxwell's equations. Presumably, this may be the reason why the dipole-based PD model is rarely adopted in the relevant literature. However, introducing some simplifications, this approach becomes easy understandable and can simply be handled, as highlighted in this paper based on some chosen case studies of practical interest.

Modeling of Cavity Discharges under AC and DC Voltage — Part I: Limitations of the Network-based PD Model

To explain the phenomena of partial discharges (PD) in gaseous cavities embedded in the bulk dielectric of HV equipment and their components as well as to analyze the associated PD transients, two fundamental approaches have been proposed in the past, which are commonly referred to as network-based PD model and dipole-based PD model. This paper is addressed to the first approach, while the second one will be reviewed in the Part II of this publication. Verifying the feasibility of the network-based PD model leads to results, which contradict the expectations from a physical point of view. The reason for that are simplified assumptions, which are inconsistent with the fundamentals of the gas discharge physics. Another shortcoming is the use of the classical network theory, although the field theory must be adopted to treat the PD transients. This leads to the conclusion that the traditional abc-model is only applicable to describe and explain he phenomena of cavity discharges qualitatively, but not to treat the PD transients quantitatively, as will be highlighted in more detail in this paper.

Discharge Development in a Saline Solution at the Above-The-Threshold Voltages

The process of a breakdown in a saline solution in a pin – plane electrode geometry is investigated for the interelectrode gap of 1 cm and a 3% NaCl concentration in the water. Single voltage pulses of about 2 ms duration and amplitude of a few kilovolts are applied to the gap. A current of up to units of kiloamps is passed through the gap. It is shown that a necessary condition for the discharge to form is the availability of gaseous cavities in the electrolyte. The stages of discharge development are investigated at the voltages applied to the gap, which exceed the threshold value (at which plasma forms in the gas cavities). An analysis of the influence of the processes of formation and collapse of gas cavities in the solution and plasma in the cavities on the shape and value of the discharge current is performed.

The hydroelastic response of a surface-piercing hydrofoil in multiphase flows. Part 2. Modal parameters and generalized fluid forces

The fluid–structure interactions (FSI) of compliant lifting surfaces is complicated by free-surface and multiphase flows such as cavitation and ventilation. This paper describes the dynamic FSI response of a flexible surface-piercing hydrofoil in dry, wetted, ventilating and cavitating conditions. Experimental modal analysis is used to quantify the resonant frequencies and damping ratios of the fluid–structure system in each flow regime. The generalized hydrodynamic stiffness, fluid damping and fluid added mass are also determined as ratios to the corresponding structural modal forces. Added mass increases with increasing partial immersion of the hydrofoil and decreases in the presence of gaseous cavities. In particular, modal frequencies were observed to increase significantly in fully ventilated flow compared to fully wetted flow. The modal frequencies varied non-monotonically with speed in fully wetted flow. Gaseous cavities reduced the modal added mass and reduced the fluid disturbing force. Modal damping increases non-monotonically with increasing immersion depth. Forward speed causes the fluid damping force to increase with an approximately quadratic functional behaviour, consistent with a series expansion of the Morison equation, although damping identification became increasingly difficult at high flow speeds. The results indicate that fluid damping is greater than the associated structural damping in a quiescent liquid, and increasingly so with increasing immersion, suggesting viscous dissipation as a dominant mechanism. A preliminary investigation of modal vibration as a means of controlling the size and stability of ventilated cavities indicates that low-order modes encourage the formation of ventilation, while higher-order modes encourage the washout and elimination of ventilation.

Using a field probe to study the mechanism of partial discharges in very small air gaps under direct voltage

Due to growing use of high-voltage direct current (HVDC) for power transmission, it is of interest whether diagnostic tools introduced in past for insulation condition assessment of high-voltage alternating current (HVAC) apparatus are also applicable for quality assurance tests of HVDC equipment. This refers in particular to measurement of partial (PD) in compliance with international standard IEC 60270 [1], [2]. As PD events in gaseous cavities embedded in bulk dielectric of HV equipment are most harmful ones, mechanism of such internal should be well known to judge PD severity as well as to specify appropriate procedures and quantities for PD tests under direct voltage. According to Devins cavity can be classified as Townsendlike discharges and streamer-like discharges [3]. Even if this classification seems to be reasonable for cavity under both alternating and direct voltage [4]-[6], this has been rejected by Bartnikas. So, he argued in [7] that the term 'streamer' by itself, when applied to PD in relatively short gaps or small cavity diameters, introduces unnecessarily a misleading term in PD lexicon. PD, when occurring in short gaps, may assume different forms: rapid and slow rise time spark-type pulses. This is also consistent with worldwide established PD model according to Kreuger [8], which is based on hypothesis that virtual cavity capacitance is discharged via a conductive spark channel. Despite simplicity, this concept was rejected by Pedersen and his coworkers [9], [10]. As an alternative, they promoted a more sophisticated field-theoretical approach based on a dipole model. As their concept is not easily understandable, this was presented in a more simplified manner in this Magazine [11], [12] as well as in [13].

Controlled Precipitation Gaseous Cavities in Aluminium Castings

Abstract At thermal junctions of aluminium alloy castings and at points where risering proves to be difficult there appear internal or external shrinkages, which are both functionally and aesthetically inadmissible. Applying the Probat Fluss Mikro 100 agent, which is based on nano-oxides of aluminium, results in the appearance of a large amount of fine microscopic pores, which compensate for the shrinking of metal. Experimental tests with gravity die casting of AlSi8Cu3 and AlSi10Mg alloys have confirmed that the effect of the agent can be of advantage in foundry practice, leading to the production of castings without local concentrations of defects and without the appearance of shrinkages and macroscopic gas pores. Also, beneficial effect on the mechanical properties of the metal has been observed.

(IJCESEN)

This paper studies the electrical constraints within an XLPE insulated cable containing micro-cavities. The purpose of this work is to determine by simulation the distortions caused by micro-cavities on the electric field distribution in the insulating layer of cable. The computation method used to determine the electric field is based on numerical resolution of Laplace equation using the finite element method. The threshold of partial discharges ignition in gaseous cavities contained in XLPE insulation of 30 kV cable is studied. The computation of the critical field by approached formula of Paschen permits us to elucidate the harmfulness caused by a cavity according to its size and its position.

Bovine serum albumin film as a template for controlled nanopancake and nanobubble formation: In situ atomic force microscopy and nanolithography study

Air nanobubbles and nanopancakes were investigated in situ by both tapping mode atomic force microscopy (TM AFM) and atomic force nanolithography techniques employing bovine serum albumin (BSA) film supported by highly oriented pyrolytic graphite (HOPG). The BSA denaturation induced by the water-to-ethanol exchange served for conservation of nanobubble and nanopancake sites appearing as imprints in BSA film left by gaseous cavities formerly present on the interface in the aqueous environment. Once the BSA film was gently removed by the nanoshaving technique applied in ethanol, a clean basal plane HOPG area with well-defined dimensions was regenerated. The subsequent reverse ethanol-to-water exchange led to the re-formation of nanopancakes specifically at the nanoshaved area. Our approach paves the way for the study of gaseous nanostructures with defined dimensions, formed at solid–liquid interface under controlled conditions.

Last Decade of Research in Sonochemistry for Green Organic Synthesis

Ultrasounds, an efficient and virtually innocuous means of activation in synthetic chemistry, have been employed for decades with varied success. This high-energy input enhances not only mechanical effects in heterogeneous processes, but it is also known to induce new reactivities leading to the formation of unexpected chemical species. The remarkable phenomenon of cavitation makes sonochemistry unique. This patent review is aimed at summarizing the status of cavitational chemistry in organic synthesis and to highlight the more recent applications in this field. The use of ultrasound to promote chemical reactions is called sonochemistry. The effects of ultrasound observed during organic reactions are due to cavitation, a physical process that creates, enlarges, and implodes gaseous and vaporous cavities in an irradiated liquid. Cavitation induces very high local temperatures and pressures inside the bubbles (cavities), leading to turbulent flow of the liquid and enhanced mass transfer. Keywords: Ultrasounds, cavitation, heterogeneous catalysis, photocatalysis, phase transfer catalysis, aqueous media, ionic liquids, acid-catalyzed reactions, base-catalyzed reactions, C-C bond formation, oxidation reactions, reduction reactions

Modeling of breakdown voltage of White Minilex Paper in the presence of voids under ac and dc conditions using fuzzy logic techniques

Occluded gaseous cavities within the insulating materials are potential sources of electrical trees which can lead to continuous deterioration and breakdown of materials. To determine the suitability of use and to acquire the data for the dimensioning of electrical insulation systems breakdown voltage of insulators should be determined. In this paper, fuzzy logic (FL) method is used to model breakdown voltages of White Minilex Paper samples based on experimental data generated in the laboratory. Different models are proposed with different shapes of the membership functions for the FL under both dc and ac voltage conditions. The cavities are created artificially with different dimensions. Low values of mean absolute errors of the estimated breakdown voltage of the test data show the effectiveness of such models.

Xenon in and at the End of the Tunnel of Bifunctional Carbon Monoxide Dehydrogenase/Acetyl-CoA Synthase,

A fascinating feature of some bifunctional enzymes is the presence of an internal channel or tunnel to connect the multiple active sites. A channel can allow for a reaction intermediate generated at one active site to be used as a substrate at a second active site, without the need for the intermediate to leave the safety of the protein matrix. One such bifunctional enzyme is carbon monoxide dehydrogenase/acetyl-CoA synthase from Moorella thermoacetica (mtCODH/ACS). A key player in the global carbon cycle, CODH/ACS uses a Ni-Fe-S center called the C-cluster to reduce carbon dioxide to carbon monoxide and uses a second Ni-Fe-S center, called the A-cluster, to assemble acetyl-CoA from a methyl group, coenzyme A, and C-cluster-generated CO. mtCODH/ACS has been proposed to contain one of the longest enzyme channels (138 A long) to allow for intermolecular CO transport. Here, we report a 2.5 A resolution structure of xenon-pressurized mtCODH/ACS and examine the nature of gaseous cavities within this enzyme. We find that the cavity calculation program CAVENV accurately predicts the channels connecting the C- and A-clusters, with 17 of 19 xenon binding sites within the predicted regions. Using this X-ray data, we analyze the amino acid composition surrounding the 19 Xe sites and consider how the protein fold is utilized to carve out such an impressive interior passageway. Finally, structural comparisons of Xe-pressurized mtCODH/ACS with related enzyme structures allow us to study channel design principles, as well as consider the conformational flexibility of an enzyme that contains a cavity through its center.

MR guided cancer treatment system for an elevated therapeutic index – A macroscopic approach

Adjuvant therapy for cancer usually refers to surgery followed by chemotherapy and/or radiation treatment to decrease the risk of recurrence. But still, the absolute benefit for survival obtained with adjuvant therapy compared with control is only approximately 6%. The objective of this analysis is to formulate a non-invasive multimodal cancer treatment system related to cancer stem cells and hypoxic fractions of solid tumors, emphasizing MRI monitoring and guidance, to elevate the therapeutic index. Tumor hypoxia is a therapeutic concern since it can reduce the effectiveness of drugs and radiotherapy, where well oxygenated cells requiring one third of the dose of hypoxic cells to achieve a given level of cell killing. Cancer stem cells might be the cause of tumor recurrence, sometimes many years after the appearance of the successful treatment of a primary tumor. Thus, the primary objective of such a treatment system will be to provide sufficient selective toxicity to both kill cancer stem cells and cells of hypoxic fractions of the tumor. Active tumor targeting with the use of liposomally encapsulated drugs is the starting point of the treatment procedure. The system facilitates quality assurance means by MR monitoring of drug accumulation and drug release, in real time. Cavitation involves the nucleation, growth and oscillation of gaseous cavities. Selective drug release and/or hyperthermia are achieved by ultrasound induced cavitation well defined to the tumor region. Hyperthermic effects, increased vascularization and subsequent increase in pO2 levels to hypoxic regions, can be monitored by MRI. MRI monitoring of key physiological parameters facilitates optimization related to approximate real time concomitant treatments, including correct timing and various combinations of drug therapy, hyperthermia, ionizing radiation, ablation, other treatment options, before or after surgery. The likelihood of an improved therapeutic index with the use of such a system seems compelling. Further research related to optimal timing, combinations of responses between liposomally encapsulated drug dosage, ultrasound exposure, hyperthermia, pO2 response time, ionizing radiation fractionation and treatment time, have to be conducted.

Modelling of solid particle aggregation dynamics in non-wetting liquid medium

The aim of this work is to re-examine and, if need be, to discuss or modify several of the elements of the classical aggregation dynamics models and to adapt them to the case of aggregation in non-wetting media and particularly alumina inclusions aggregation in a turbulent flow of liquid steel. As proved by several experiments and models, solid particles in contact in non-wetting media are linked by gaseous bridges which may pre-exist prior to the aggregate formation. In this paper, the role of these gaseous cavities in the aggregation process is considered. In particular, a complete calculation of the interaction force between hydrophobic surfaces (Bjerkness–Ruckenstein model) is performed. Main aspects of the aggregation dynamics are envisaged in the particular conditions which result from non-wetting. Hydrodynamic interactions between particles are modified by non-wetting, thus the collision efficiency coefficient and the aggregation kernel. The fragmentation kernel of the aggregates, however, is modified to a larger extent and is equal to zero in most cases. Numerical applications are presented in the reference case (alumina particles in liquid steel). A general procedure of use of this model in other non-wetting situations is given too.

Hollow rhombohedral calcite crystals encompassing CO 2 microcavities nucleated in solution

A new way for heterogeneous nucleation of crystals from the solution is described: 3D crystalline structure can nucleate and grow encompassing gaseous cavities, formed on solid substrates in the aqueous solution, so giving rise to crystal bubbles. The double surface of a crystal bubble is made, in this case, by the faces of the cleavage calcite rhombohedron separating the solution from the enclosed gas cavity. The faces thickness and the edges length amount to a few nanometers and to about 5 μm, respectively. Then, the surface-to-volume ratio is the highest obtained for 3D crystals, amidst the consulted literature. Bubbles’ shape is explained through the equilibrium properties of crystal–cavity and crystal–solution interfaces and in terms of growth mechanisms operating on the separate interfaces. The nucleation of the crystals around gas cavities can provide new insight on those mineralization phenomena where the gas phase participate in crystal growth. Potential applications are also envisaged concerning the nucleation of the gas cavities on peculiar templates which impose 1D (or 2D) periodicity to crystal bubbles, in order to obtain 1D and/or 2D photonic crystals.

Investigations of the role of cavitation in low‐frequency sonophoresis using acoustic spectroscopy

Application of low‐frequency ultrasound significantly enhances skin permeability. The enhancement of skin permeability is mediated by cavitation, oscillation, and collapse of gaseous cavities. In this article, we report detailed investigations of the occurrence of cavitation during low‐frequency sonophoresis. Cavitation was monitored by recording pressure amplitudes of subharmonic emission and broadband noise at four different ultrasound frequencies in the range of 20–100 kHz and at various intensities in the range of 0–2.6 W/cm2. Enhancement of skin conductivity, in the presence of sodium lauryl sulfate (SLS), was also measured under the same ultrasound conditions. Enhancement of skin conductivity correlated well with the amplitude of broadband noise, which suggests the role of transient cavitation in low‐frequency sonophoresis. No correlation was found between the subharmonic pressure amplitude and conductivity enhancement.

Picosecond and nanosecond polychromatic pump–probe studies of bubble growth in carbon-nanotube suspensions

Optical limiting in carbon-nanotube suspensions, whose origin lies in a strong nonlinear scattering due to solvent vapor bubbles and sublimation of the nanotubes, is investigated in the picosecond and nanosecond regimes by polychromatic pump–probe experiments. Samples were pumped either with 532-nm or 1064-nm pulses, and probed from 400 nm to 650 nm. Using a model based on Mie theory, we determine the time evolution of the radius and the concentration of the scattering centers for both temporal regimes. We compare the transmission signals for single-wall carbon nanotubes suspended in water and in chloroform and for multiwall carbon nanotubes in water. Several conclusions can be drawn. First, coalescence of gaseous cavities is more effective in water than in chloroform, leading to nonlinear scattering by a smaller number of larger bubbles. Second, in spite of the smaller size of the scattering centers, the limiting efficiency of chloroform suspensions is better than that of water suspensions, due to a larger volume fraction of the gaseous phase. However, the characteristic times for the growth of laser-induced bubbles are too long to allow efficient limiting of subnanosecond laser pulses.

Mass Transfer of Lead Coolant Vapors in a BREST-OD-300 Reactor

The goal of the work reflected in this paper is to investigate the mass transfer of lead from the coolant surface in the gaseous cavities of the cooling loop of a BREST-OD-300 reactor. The theoretical and experimental investigations show that the amount of lead evaporating from the free surfaces of the first loop of the reactor is negligible.