Influence Of Variation Research Articles

The influence of laser fluences on surface properties, plasma formation, and microhardness of Mg-alloy

The impact of variation in laser fluence on the surface modifications and plasma parameters of biocompatible, Magnesium (Mg) alloy has been studied. A 1064 nm Nd: YAG laser with, 10 ns pulse duration and a repetition rate of 1 to 10 Hz has been used for this purpose. Mg-alloy targets were subjected to fluences ranging from 1.3 J·cm−2 to 10.47 J·cm−2 in Argon (Ar) ambient. The surface morphology of irradiated targets was analyzed using a Scanning Electron Microscope (SEM). Formation of ripples, ridges, conical structures, pores, and cavities are observed on the surface of the irradiated Mg targets and are shown in the SEM topographical images. A higher initial fluence causes a rise in the size and density of these structures, which subsequently falls off as the fluence increases more to its highest value. Plasma parameters, such as electron temperature (Te) and number density (ne), are measured using Laser-Induced-Breakdown-Spectroscopy (LIBS). It was also found that both Te and ne increase with increasing fluence. XRD analysis is performed to study properties such as phase purity and structural studies were carried out through X-ray diffraction (XRD) technique, aiding in the investigation of material behavior and guiding the development of new materials with specific properties. Using a Vickers Micro hardness tester, we haveinvestigated the hardness of irradiated Mg targets. From the present investigation it is observed that the hardness value of irradiated targets is higher than the pristine Mg target. It is also found that Te and ne play a significant role for the enhancement of hardness as well as for the growth of surface structures on Mg-alloy.

Pharmacogenomic Role in Cytochrome P450 Enzymes-Mediated Metabolism for Drug Therapy

The rapid development of genetic science in recent decades has provided opportunities for clinical implementation. In the field of pharmacology, this opens up hope for the use of more targeted drugs with fewer side effects.Genetic variation's influence on pharmacological response has been well-established in practice. Patients' responses to pharmacological therapies can be varied, ranging from positive effects to serious adverse drug reactions (ADRs). Numerous genetic variations have been found to have a major impact on how people react to routinely prescribed medications over time, according to experts. In order to use this genetic information to inform treatment choices, a pharmacogenomic (PGx) profile can be used. PGx works on identifying and validating genomic variations that affect drug response. The generic approach to healthcare has given way to a more individualized and precise treatment paradigm as it has developed. Keywords: Adverse Drug Reactions - Genetic Variants – Pharmacogenomics - Cytochrome P450

Quantitative photoacoustic tomography with light fluence compensation based on radiance Monte Carlo model

Objective. Photoacoustic tomography (PAT) is a rapidly evolving imaging modality that provides images with high contrast and spatial resolution showing the optical properties of biological tissues. The photoacoustic pressure is proportional to the product of the optical absorption coefficient and the local light fluence. The essential challenge in reconstructing quantitative images representing spatially varying absorption coefficients is the unknown light fluence. In addition, optical attenuation induces spatial variations in the light fluence, and the heterogeneity of the fluence determines the limits of reconstruction quality and depth. Approach. In this work, a reconstruction enhancement scheme is proposed to compensate for the variation in the light fluence in the absorption coefficient recovery. The inverse problem of the radiance Monte Carlo model describing light transport through the tissue is solved by using an alternating optimization strategy. In the iteration, the absorption coefficients and photon weights are alternately updated. Main results. The method provides highly accurate quantitative images of absorption coefficients in simulations, phantoms, and in vivo studies. The results show that the method has great potential for improving the accuracy of absorption coefficient recovery compared to conventional reconstruction methods that ignore light fluence variations. Comparison with state-of-the-art fluence compensation methods shows significant improvements in root mean square error, normalized mean square absolute distance, and structural similarity metrics. Significance. This method achieves high precision quantitative imaging by compensating for nonuniform light fluence without increasing the complexity and operation of the imaging system.

Monte Carlo investigation of electron fluence perturbation in MRI-guided radiotherapy beams using six commercial radiation detectors

With the integration of treatments with MRI-linacs to the clinical workflow, the understanding and characterization of detector response in reference dosimetry in magnetic fields are required. The external magnetic field perturbs the electron fluence. The degree of perturbation depends on the irradiation conditions and on the detector type. The purpose of this study is to evaluate the magnetic field impact on the electron fluence spectra in several detectors to provide a deeper understanding of detector response in these conditions. Monte Carlo calculations of the electron fluence are performed in six detectors (solid-state: PTW60012 and PTW60019, ionization chambers: PTW30013, PTW31010, PTW31021, and PTW31022) in water and irradiated by a 7 MV FFF photon beam with a small and a reference field, at 0 and 1.5 T. Three chamber axis orientations are investigated: parallel or perpendicular (either the Lorentz force pointing towards the stem or the tip) to the magnetic field and always perpendicular to the photon beam. One orientation for the solid-state detector is studied: parallel to the photon beam and perpendicular to the magnetic field. Additionally, electron fluence spectra are calculated in modified detector geometries to identify the underlying physical mechanisms behind the fluence perturbations. The total electron fluence in the Farmer chamber varies up to 1.24% and 5.12% at 1.5 T, in the parallel and perpendicular orientation, respectively. The interplay between the gyration radius and the Farmer chamber cavity length significantly affects the electron fluence in the perpendicular orientation. For the small-cavity chambers, the maximal variation in total electron fluence is 0.19% in the parallel orientation for the reference field. Significant small-field effects occur in these chambers; the magnetic field reduces the total electron fluence (with respect to the no field case) between 9.86% and 14.50%, depending on the orientation. The magnetic field strongly impacted the solid-state detectors in both field sizes, probably due to the high-Z components and cavity density. The maximal reductions of total electron fluence are 15.06 ± 0.09% (silicon) and 16.00 ± 0.07% (microDiamond). This work provides insights into detector response in magnetic fields by illustrating the interplay between several factors causing dosimetric perturbation effects: (1) chamber and magnetic field orientation, (2) cavity size and shape, (3) extracameral components, (4) air gaps and their asymmetry, (5) electron energy. Low-energy electron trajectories are more susceptible to change in magnetic fields, and are associated with detector response perturbation. Detectors with higher density and high-Z extracameral components exhibit more significant perturbations in the presence of a magnetic field, regardless of field size.

Analysis of stability and sensitivity of deterministic and stochastic models for the spread of the new corona virus SARS-CоV-2

Basic reproduction number for deterministic SEIPHAR model and its stochastic counterpart for the spread of SARS-CoV-2 virus are analyzed and compared. For deterministic version of the model, conditions for stability of the disease-free equilibrium are derived and, in addition, conditions for existence of bifurcation state related to endemic equilibrium are established. For stochastic model, conditions for extinction and persistence in mean of the disease are derived. Complete sensitivity analysis of thresholds between the extinction and mean-persistence are performed for both the deterministic and the stochastic version of the model. Influence of variation in parameter values is illustrated for epidemics in Wuhan in early 2020.

Useful island block geometries of a passive intensity modulator used for intensity-modulated bolus electron conformal therapy.

PurposeThis project determined the range of island block geometric configurations useful for the clinical utilization of intensity‐modulated bolus electron conformal therapy (IM‐BECT).MethodsMultiple half‐beam island block geometries were studied for seven electron energies 7‐20 MeV at 100 and 103 cm source‐to‐surface distance (SSD). We studied relative fluence distributions at 0.5 cm and 2.0 cm depths in water, resulting in 28 unique beam conditions. For each beam condition, we studied intensity reduction factor (IRF) values of 0.70, 0.75, 0.80, 0.85, 0.90, and 0.95, and hexagonal packing separations for the island blocks of 0.50, 0.75, 1.00, 1.25, and 1.50 cm, that is, 30 unique IM configurations and 840 unique beam‐IM combinations. A combination was deemed acceptable if the average intensity downstream of the intensity modulator agreed within 2% of that intended and the variation in fluence was less than ±2%.ResultsFor 100 cm SSD, and for 0.5 cm depth, results showed that beam energies above 13 MeV did not exhibit sufficient scatter to produce clinically acceptable fluence (intensity) distributions for all IRF values (0.70–0.95). In particular, 20 MeV fluence distributions were unacceptable for any values, and acceptable 16 MeV fluence distributions were limited to a minimum IRF of 0.85. For the 2.0 cm depth, beam energies up to and including 20 MeV had acceptable fluence distributions. For 103 cm SSD and for 0.5 cm and 2.0 cm depths, results showed that all beam energies (7–20 MeV) had clinically acceptable fluence distributions for all IRF values (0.70–0.95). In general, the more clinically likely 103 cm SSD had acceptable fluence distributions with larger separations (r), which allow larger block diameters.ConclusionThe geometric operating range of island block separations and IRF values (block diameters) producing clinically appropriate IM electron beams has been determined.

Intra-cavity Photodynamic Therapy for malignant tumors of the paranasal sinuses: An in vivo light dosimetry study.

Photodynamic therapy (PDT) is a promising treatment option for recurrent sinonasal malignancies. However, light administration in this area is challenging given the complex geometry, varying tissue optical properties and difficult accessibility. The goal of this study was to estimate the temporal and spatial variation in fluence and fluence rate during sinonasal mTHPC-mediated PDT. It was investigated whether the predetermined aim to illuminate with a fluence of 20 J⋅cm-2 and fluence rate of 100 mW⋅cm-2 was achieved. In eleven patients the fluence and fluence rates were measured using in vivo light dosimetry at the target location during real-time sinonasal PDT. There was a variance in sinonasal target location and type of light diffuser used. In four patients two isotropic detectors were used within the same cavity. All measurements showed major fluence rate fluctuations within each single isotropic detector probe over time, as well as between probes within the same cavity. The largest fluence rate range measured was 328 mW⋅cm-2. Only one probe showed a mean fluence rate of ∼100 mW⋅cm-2. Taken all probes together, a fluence rate above 80 mW⋅cm-2 was measured in 31 % of the total light exposure; in 22 % it was less than 20 mW⋅cm-2. Thirty-three percent showed a fluence of at least 20 J⋅cm-2. The current dosimetry approach for sinonasal intra-cavity PDT shows major temporal and spatial variations in fluence rate and a large variance in light exposure time. The results emphasize the need for improvement of in vivo light dosimetry and dosimetry planning.

Surface texturing of steel by femtosecond laser and accompanying structure/phase transformations

Topography, structure, and phase composition of surface layers of AISI 321 stainless steel textured by 1030-nm 320-fs-laser pulses were studied by scanning electron microscopy and X-ray diffraction analysis. Variation in single-pulse fluence and the number of pulses was found to change the laser-produced surface texture from one-dimensional quasi-periodic nanograting to microrelief of various roughness. It was shown that the nanograting formed in the spallation regime contained austenite, just as a non-irradiated steel surface, and ferrite. The redeposited oxide layers on the grating surface produced in the phase explosion regime with a thickness increasing versus single-pulse fluence were found to consist of austenite, ferrite, and Fe3O4. In case of high-fluence mode, the two-layer microporous oxide coating, consisting of Fe3O4 and Fe2O3 in addition to conventional phases, was detected. SEM studies showed that the submicrocrystalline structure of nano- and microsized ridges was preserved, except for the high-fluence mode.

A highlight effects generation model for translucent materials perception based on directional subsurface scattering

Usually the highlights can be calculated with the specular term of the bidirectional reflectance distribution functions developed for glossy or matte materials. However, as for the translucent materials, complex appearance could be caused by the scattering of light inside the medium. An efficient highlight generation model is presented to simulate the highlight effects on smooth or rough surfaces or around the boundaries of objects made from translucent materials. The presented model is derived from the directional dipole model approximation of the diffusive part of the bidirectional scattering surface reflectance distribution function. Unlike the previous specular reflection models, the presented model builds a relationship between the highlights and the scattered lights inside the medium by considering the refracted ray of the incident point and the ray toward the emergent point, which could represent the variation in fluence due to the internal scattering at the surface. By integrating a rendering process with the directional dipole model, the resulting highlight effects term could be represented in a similar way by the specular term of a bidirectional reflectance distribution function model. The number and the strength of the generated highlight pixels were compared among typical highlight generation models. It is demonstrated that the presented model could generate highlight effects at the appropriate positions and enhance the perceptual translucency of specific edge areas greatly.

Linearity Distortion Analysis of III–V and Si Quadruple Gate Field Effect Transistor (QG-FET) for Analog Applications

In this work, analog and linearity distortion performance of a III–V AlGaN/GaN quadruple gate field effect transistor (III–V QG-FET) has been analyzed and compared with conventional Si QG-FET having identical physical dimensions. Specifically, we investigate the linearity by numerically computing transconductance (gm1), its second and third order derivatives (gm2 and gm3), along-with linearity metrics comprising of third order intermodulation distortion (IMD3), third order input intercept point (IIP3), and extrapolated input voltages (VIP2 and VIP3). The consequences of variations in physical parameters of III–V QG-FET, i.e., channel length, channel height, the thickness of oxide layer, doping concentration, along-with temperature on the linearity metrics parameters, drain current, and threshold voltage are analyzed and compared with Si QG-FET. The gate capacitance and dynamic power dissipation is calculated numerically and compared by performing small signal AC analysis at 1 MHz frequency for III–V and Si QG-FETs. The influence of variations in above mentioned physical parameters is also analyzed on dynamic power dissipation and gate capacitance considering the effects of quantum capacitance in the nanometer regime. The present analysis reveals that in III–V QG-FET, the dynamic power dissipation is considerably reduced than its contender Si QG-FET due to its reduced threshold voltage, and thus it is a more promising candidate for analog and low power dissipation applications.

Laser—synthesised Ag2S nanoparticles in liquid: effect of laser fluence on structural and optical properties

In this study, we report for the first time the preparation and characterization of silver sulfide nanoparticles (NPs) by one-step laser ablation of the silver target in thiourea aqueous solution without using a catalyst. The effect of laser fluence on the crystal structure, morphology, size and elemental composition of Ag2S NPs was investigated. X-ray diffraction (XRD) results show Ag2S NPs are polycrystalline with monoclinic phase and the variation in laser fluence affects the crystallinity of the synthesized NPs. The optical energy gap decreases from 2.2 eV to 1.6 eV as the laser fluence increases from 2.38 Jcm−2 to 6.77 Jcm−2. Transmission electron microscope (TEM) investigation confirms the formation of spherical Ag2S NPs and nanosheets morphologies and the particle size is found increases from 30 nm to 65 nm when the laser fluence increases from 2.38 Jcm−2 to 6.77 Jcm−2. The Raman spectra of Ag2S NPs show the presence of six active Raman peaks and their intensity increased with laser fluence.

Incubation studies and the threshold for surface damage and cavity formation in the processing of polycarbonate by Nd:YAG laser

Polycarbonate (PC) is highly resistant to laser ablation at 532 nm. For efficient laser ablation of PC at this wavelength, it is required to use absorbing dopants or apply high fluences. This paper reports an experimental study on laser ablation of polycarbonate with a 2nd harmonic of a Q-switched Nd:YAG laser having 6 ns pulse duration at low fluence. The change in surface morphology of laser irradiated polycarbonate surface has been studied as a function of laser fluence per pulse as well as number of laser pulses. At low fluence and fewer number of laser shots, the bubbling of the laser exposed region was observed whereas at larger fluence and repeated exposer of laser for longer duration, a clear formation of the cavity was observed indicating the surface damage. Effects of variation in input laser fluence and number of pulses on ablation depth, width and ablation rate have been studied. Based on the surface morphology of the laser irradiated zone, damage threshold for polycarbonate material was found to be ∼7.35 J/cm2 per pulse with single shot and 4.41 J/cm2 with 15 number of repeated shots of laser, while 29.4 J/cm2 was noted as the ablation threshold. These results can be applied in practice to assess the parameters for laser fabrication of precise micro-cavity and channels on polycarbonate.

Engineering of high-temperature ferromagnetic Si1–xMnx (x ≈ 0.5) alloyed films by pulsed laser deposition: Effect of laser fluence

Thin films of Si1−xMnx were deposited on Al2O3 substrate using pulsed laser deposition(PLD)technique employing time-of-flight separation of the ejected particles with different laser fluence (E = 3.8–7.6 J/cm2). Magnetic properties of these films reveal that the variation in the laser fluence has engineered several magnetic phases in Si1−xMnx films: high temperature (HT) ferromagnetic (FM) phase Si1−xMnx(x = 0.51–0.52) with uniformly distributed Si vacancies, and the low-temperature (LT) FM phases MnSi and Mn4Si7 with Curie temperature ≤40 K. At small fluence, the mesoscopic size MnSi and Mn4Si7 crystallites are formed in the upper layer of Si1−xMnx films with Si excess (x ≈ 0.4–0.5), yielding to inhomogeneous magnetic phase distribution along the film growth direction, while the high and optimal fluence has resulted in uniform distribution of the HT FM phase during the film growth. The XPS, magnetotransport and ferromagnetic resonance (FMR) measurements confirm the presence of several FM phases in the samples and the amplifying role of LT FM for films grown at E ≤ 4.4 J/cm2.

Fuzz growth in the gaps of castellated W in PISCES-A: experiment and modeling

A castellated W target with gaps of width 0.5, 1.0, and 1.5 mm is exposed at 1120 K to He ions in the PISCES-A linear plasma device. The average ion impact energy was 70 eV and the accumulated ion fluence 3.6 × 1026 m−2 over the top surface, which is exposed normal to the plasma flow. A layer of W fuzz of 3.4 ± 0.4 μm thick developed on the top surface. In addition, fuzz morphology is found to develop on the side walls of the gaps. Particle in cell modeling of the plasma-target sheath using the SPICE2 code predicts the plasma penetration into the gaps. The He ion flux to gap side walls falls off quasi-exponentially with depth with a decay rate dependent on the gap width. When the variation in He ion wall fluence is used in conjunction with the fluence dependent growth expression of Petty et al (2015 Nucl. Fusion 55 093033), modeling correctly predicts the observed maximum depth of formation, and measured variation of layer thickness, for fuzz found on the gap walls.

Nano-pits on GaAs (1 0 0) surface: Preferential sputtering and diffusion

Self organized nano-structure array on the surfaces of semiconductors have potential applications in photonics, magnetic devices, photovoltaics, and surface-wetting tailoring etc. Therefore, the control over their dimensions is gaining scientific interest in last couple of decades. In this work, fabrication of pits of nano-dimensions is carried out on the GaAs (100) surface using 50keV Ar+ at normal incidence. Variation in fluence from 3×1017ions/cm2 to 5×1018ions/cm2 does not make a remarkable variation in the dimension of pits such as size and depth, which is confirmed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). However the simultaneous dots formation is observed along with the pits at higher fluences. Average size of pits is found to be of 22nm with depth of 1–5nm for the used fluences. The importance of preferential sputtering of ‘As’ as compared to ‘Ga’ is estimated using energy dispersive X-ray analysis (EDX). The observed alteration in near surface composition shows the Ga enrichment of surface, which is not being much affected by variation in fluence. The growth evolution of pits and dots for the used experimental conditions is explained on the basis of ion beam induced preferential sputtering and surface diffusion.

High-speed video study of laser-induced forward transfer of silver nano-suspensions

High-speed video (100 000 fps) is used to examine the behavior of silver nanoparticle suspensions ejected from a donor substrate during laser-induced forward transfer (LIFT) as a function of viscosity, donor film thickness, and voxel area. Both high-speed video and inspection of the post-transferred material indicate dramatic changes in the behavior of the fluid as the viscosity of the nano-suspensions increases from that of inks (∼0.01 Pa·s) to pastes (>100 Pa·s). Over a specific range of viscosities (90–150 Pa·s) and laser fluences (35–65 mJ/cm2), the ejected voxels precisely reproduce the size and shape of the laser spot. This LIFT regime is known as laser decal transfer or LDT. Analysis of the high-speed video indicates that the speeds of the voxels released by the LDT process do not exceed 1 m/s. Such transfer speeds are at least an order of magnitude lower than those associated with other LIFT processes, thus minimizing voxel deformation during flight and upon impact with the receiving substrate. Variation in the threshold fluence for initiating the LDT process is measured as a function of donor film thickness and transfer spot size. Overall, the congruent nature of the silver nanopaste voxels deposited by LDT is unique among non-contact digital printing techniques given its control of the voxel's size and shape, thus allowing partial parallelization of the direct-write process.

Effect of Br+6 ions on the structural, morphological and luminescent properties of ZnO/Si thin films

ZnO/Si thin films were synthesized by radio frequency (RF) magnetron sputtering. The films were irradiated by 80meV Br+6 ions at various ion fluencies. X-ray diffraction (XRD) indicated that hexagonal wurtzite crystal structured thin films were obtained. X-ray photoelectron spectroscopy (XPS) indicated that the O1s peak consist of two components: O1 (ZnO) and O3 (adsorbed species). The roughness of the films changed from 34 to 24nm with a variation in the ion fluence. The observation of the various phonon modes in the Raman spectra of the ZnO confirmed that the ZnO on Si films have wurtzite structures according to the selection rules. Defect level emission (DLE) was obtained in the luminescence spectra of the irradiated ZnO/Si sample. The thermal spikes model was used to explain the swift heavy ions (SHI) induced modifications in the structural, morphological and luminescent properties of the ZnO/Si films.

Swift heavy ion induced topography changes of Tin oxide thin films

Monodisperse tin oxide nanocrystalline thin films are grown on silicon substrates by electron beam evaporation method followed by 100MeV silver ion bombardment with varying ion fluence from 5×1011 ionscm−2 to 1×1013 ionscm−2 at constant ion flux. Enhancement of crystallinity of thin films with fluence is observed from glancing angle X-ray diffraction studies. Morphological studies by atomic force microscopy reveal the changes in grain size from 25nm to 44nm with variation in ion fluence. The effect of initial surface roughness and adatom mobility on topography is reported. In this work correlation between ion beam induced defect concentration with topography and grain size distribution is emphasized.

HETEROGENEOUS ISOTOPIC ANOMALIES OF SM AND GD IN THE NORTON COUNTY METEORITE: EVIDENCE FOR IRRADIATION FROM THE ACTIVE EARLY SUN

Large and heterogeneous isotopic variations of 150Sm/149Sm and 158Gd/157Gd due to neutron capture reactions caused by cosmic-ray irradiation were found in chemical and mineral separates from the Norton County meteorite. The light-colored separates, consisting mainly of enstatite (Mg2Si2O6), have a very large neutron fluence of 1.98?? 1017?n?cm?2, which is 10 times higher than that of the whole rock. Furthermore, four chemical separates showed a large variation in neutron fluences, ranging from 1.82?? 1016 to 1.87?? 1017?n?cm?2. The variable amounts of neutron fluences from a small single fragment of the Norton County meteorite cannot be simply explained by single-stage cosmic-ray irradiation in space. Rare earth element (REE) analyses revealed that the fractions with high neutron fluences have similar chemical properties to those in the early condensates in the solar system, showing depletions of Eu and Yb in their REE abundance patterns. The data provide evidence for an activity of the early Sun (T Tauri), suggesting the migration of early and intense irradiation materials into the Norton County meteorite's parent body.

SU‐E‐T‐231: Exit Fluence Analysis in RapidArc Using EPID

Purpose: In measuring the exit fluences, there are several sources of deviations which include the changes in the entrance fluence, changes in the detector response and patient orientation or geometry. The purpose of this work is to quantify these sources of the errors. Methods: The quantification of the errors caused by the machine delivery is done by comparing arc picket fence test for a period of 30 days. To quantify the sources of error due leaf and gantry positions and positioning of the patient a RapidArc plan created for the pelvis site was delivered with and without rando phantom and the exit portal images were measured. The day to day exit fluence variation in the patient anatomy were analysed by comparing the daily exit dose images during the course of treatment. For comparison, the first fraction image is used as the reference image. Standard deviation and the gamma analysis were used to quantify the errors between fractions. The gamma criterion used for analysis is 3% Dose Difference and 3 mm Distance to Agreement. Results: The maximum gamma value and Standard deviation for the picket fence test fields was 3.3 and 1.35 respectively. The area failing the gamma criteria was less than 0.1%. The delivery of the RapidArc plans without phantom shows a maximum standard deviation of 1.85 and the maximum gamma value of 0.59. The maximum gamma value for the RapidArc plan delivered with the phantom was found to be 1.2. The largest observed fluence deviation during the delivery for patient was 5.7% and the maximum standard deviation was 4.1%. Conclusions: From this study, it is found that the variation in exit fluence due to patient interfraction organ motion found to be significant than the deviations caused by the machine and detectors.