Depth In Medium Research Articles

Statistics of maximum photon penetration depth in a two-layer diffusive medium.

We present numerical results for the probability density function f(z) and for the mean value of photon maximum penetration depth ‹zmax› in a two-layer diffusive medium. Both time domain and continuous wave regime are considered with several combinations of the optical properties (absorption coefficient, reduced scattering coefficient) of the two layers, and with different geometrical configurations (source detector distance, thickness of the upper layer). Practical considerations on the design of time domain and continuous wave systems are derived. The methods and the results are of interest for many research fields such as biomedical optics and advanced microscopy.

A Heat Transfer Problem with a Velocity Slip in Porous Media: A Galerkin Approach

In this paper a steady flow of a viscous fluid of finite depth in a porous medium over a fixed horizontal, impermeable bottom with a velocity slip is studied. A Galerkin Method of solution is considered to solve Momentum and Energy equations as the truncation errors both in general and special cases may result in complex situations to get the analytical form of solutions. Using the obtained velocity profile, the Temperature, Mean velocity, Mean Temperature, and heat transfer rates (Nusselt Number) on the free surface as well as on the bottom plate are obtained. The effect of velocity slip in the obtained fields is studied wherever possible. A special case of low porosity is studied and the results are illustrated graphically.

Compact conformal metasurface antenna for hyperthermia applications

In this paper, the design, analysis and evaluation of a new compact conformal metasurface (MTS)-based bow-tie slot antenna is presented for hyperthermia treatment of cancer. A bow-tie slot antenna in close proximity with tissue designed at 2.45 GHz was used to excite the MTS layer, which is made of a 4 × 4 uniform array of square unit cells. The proposed MTS-based antenna is compact and provides enhanced penetration depth in the tissue medium as compared to the bow-tie antenna only. To verify the design concept, both the proposed MTS-based antenna and bow-tie antenna were fabricated, and the measured results are well anticipated. Finally, the MTS applicator is terminated with water bolus and tissue to characterize its hyperthermia performance in a real scenario. The key features of the proposed MTS applicator include wide impedance bandwidth (stable hyperthermia performance), enhanced penetration depth and effective field size, single-layer structure and ease of fabrication.

Reducing Voluntary Turnover through Career Development: Strategic HRD Research Proposal

Voluntary employee turnover in the United States continues to spiral out of control and is expected to steadily increase in the coming years. Annual cost to American businesses exceeded $630 billion and is expected to exceed $700 billion within the next 24 months. The reasons for the sharp increase in voluntary turnover are not generational by nature as employees of all generations seek a connection with their employer and the ability to share in the firm’s growth. The reasons expressed by employers and employees include lack of training, weak relationships with managers and a general disconnect from company strategy. The primary reason given in recent years is lack of career development. Scheduled, agenda-driven discussions between senior leadership and the employee is needed to focus on employee skills, capacity for learning and enterprise goals has shown promise in reducing voluntary turnover, increasing employee engagement, and increasing talent depth in medium and large businesses. Career planning and development is not necessarily transactional as it includes specific training for a specific purpose to fit the firm’s strategic objectives. This approach can be used for lateral and vertical movement within the company. This proposal seeks to bridge the gap between existing literatures, current human capital management practices and move the discussion to a level that benefits employees and employers alike.

Overcoming the tradeoff between confinement and focal distance using virtual ultrasonic optical waveguides.

A conventional optical lens can be used to focus light into the target medium from outside, without disturbing the medium. The focused spot size is proportional to the focal distance in a conventional lens, resulting in a tradeoff between penetration depth in the target medium and spatial resolution. We have shown that virtual ultrasonically sculpted gradient-index (GRIN) optical waveguides can be formed in the target medium to steer light without disturbing the medium. Here, we demonstrate that such virtual waveguides can relay an externally focused Gaussian beam of light through the medium beyond the focal distance of a single external physical lens, to extend the penetration depth without compromising the spot size. Moreover, the spot size can be tuned by reconfiguring the virtual waveguide. We show that these virtual GRIN waveguides can be formed in transparent and turbid media, to enhance the confinement and contrast ratio of the focused beam of light at the target location. This method can be extended to realize complex optical systems of external physical lenses and in situ virtual waveguides, to extend the reach and flexibility of optical methods.

Depth estimation of the absorbing structure in a slab turbid medium using point spread function

Nowadays, transillumination imaging is more popular used in the medical field with the development of the vein finder and the non-invasive diagnosis applications. Near-infrared light with a wavelength of 700 - 1200 nm has relatively high transmission through biological tissue. Using near-infrared light, we can able to obtain a two dimensional (2D) transillumination image of the internal absorption structure such as blood vessel structure, liver ... in the body noninvasively. Even with a simple system (light-emitting diode (LED)'s array and low-cost camera), we could obtain the blood vessel transillumination image of human arm. However, the image is severely blurred due to the strong scattering in the tissue. We have devised the depth-dependent point spread function (PSF) to suppress the scattering effect in fluorescent imaging. In previous studies, we successfully applied this principle and developed a technique to reconstruct the absorbing structure in a turbid medium without using fluorescent material. The feasibility and effectiveness of the proposed technique were verified in experiments. However, this point spread function (PSF) is depth dependence, so that the depth information is required in practice. In order to make this method more practical, the new techniques for estimating the parameters of absorbing structure (depth and width) in the turbid medium by convolution and de-convolution with the point spread function (PSF) were devised. This paper presents a new technique for the estimation depth of an absorber in 2D transillumination image. This new technique was developed to estimate the depth of the absorber in turbid medium by convolution operation with the point spread function (PSF). By observing images with two-wavelength selected at which the scattering property of the medium is different. The transillumination image at one of the wavelengths is convolved with the PSF of another wavelength. Two images of alternative wavelengths are compared while changing the depth of the PSF. We can obtain the correct depth that gives a minimum difference between the two convoluted images. This technique does not require the repetition of the unstable deconvolution operation. The effectiveness of the proposed technique was verified in simulation and experiment.

Study of the characteristics of train-induced dynamic SIFs of tunnel lining cracks based on the modal superposition approach

Cracks on a tunnel lining are commonly observed during in-site tunnel inspection. The cracks are generated owing to various reasons and can potentially further propagate as they are subjected to repeated dynamic train loads during the entire tunnel service life. The study investigated train-induced dynamic stress intensity factors (SIFs) of tunnel lining cracks by numerical simulations using the modal superposition approach and examined the effects of a wide range of factors. The methodology of the modal superposition approach was adopted and validated to determine dynamic SIFs. Subsequently, the coupled dynamic FE model was established to calculate train-induced SIFs of tunnel lining cracks and radiation damping owing to the infinite surrounding medium was determined. Finally, a parametric analysis was conducted to investigate the effects of crack location, crack depth, wave velocity of the surrounding medium, and material damping on dynamic SIFs of tunnel lining cracks subjected to metro train loads. The results demonstrate that the modal superposition approach can be employed to accurately and effectively calculate the train-induced dynamic SIFs of tunnel lining cracks when radiation damping is considered. The effects of crack location, crack depth, and wave velocity of the surrounding medium are significant, while the effect of material damping is not considerably evident. The maximum dynamic SIF significantly increases with crack depth, while it decreases with the wave velocity of the surrounding medium and material damping ratio. Cracks with greater depth in the poorer medium are more likely to propagate under dynamic train loads.

Estimation of the Corrosion Resistance of the Metal Coatings Formed by Powder Metallurgy

A method is suggested to restore the worn surfaces of the components of food-processing equipment, which operate in an aggressive medium and are subjected to corrosive mechanical wear, by electrocontact welding of metallic powders placed in metallic-network containers. A combined additive, which allows one to exclude the losses of adding powder, is used. The corrosion penetration depth in an aggressive medium for metal coatings with a cast-iron addition is studied experimentally.

Phase-Shift Depth Migration for Plane-Wave Ultrasound Imaging.

Plane-wave ultrasound imaging is an important modality that enables very high frame rates, which is necessary for adequate characterization of blood flow and tissue motion properties. This work describes a novel Fourier-domain method for plane-wave ultrasound image reconstruction that can be used in situations where the speed of sound varies with depth in a layered propagation medium. Our approach is based on geophysical phase-shift migration technique that has been modified to handle plane-wave ultrasound data processing. Our simulation results show that the proposed method is capable of accurately imaging point targets in a three-layer medium, mimicking tissue-bone-tissue ultrasound propagation.

SEDIGISM: Structure, excitation, and dynamics of the inner Galactic interstellar medium

The origin and life-cycle of molecular clouds are still poorly constrained, despite their importance for understanding the evolution of the interstellar medium. We have carried out a systematic, homogeneous, spectroscopic survey of the inner Galactic plane, in order to complement the many continuum Galactic surveys available with crucial distance and gas-kinematic information. Our aim is to combine this data set with recent infrared to sub-millimetre surveys at similar angular resolutions. The SEDIGISM survey covers 78 deg^2 of the inner Galaxy (-60 deg < l < +18 deg, |b| < 0.5 deg) in the J=2-1 rotational transition of 13CO. This isotopologue of CO is less abundant than 12CO by factors up to 100. Therefore, its emission has low to moderate optical depths, and higher critical density, making it an ideal tracer of the cold, dense interstellar medium. The data have been observed with the SHFI single-pixel instrument at APEX. The observational setup covers the 13CO(2-1) and C18O(2-1) lines, plus several transitions from other molecules. The observations have been completed. Data reduction is in progress, and the final data products will be made available in the near future. Here we give a detailed description of the survey and the dedicated data reduction pipeline. Preliminary results based on a science demonstration field covering -20 deg < l < -18.5 deg are presented. Analysis of the 13CO(2-1) data in this field reveals compact clumps, diffuse clouds, and filamentary structures at a range of heliocentric distances. By combining our data with data in the (1-0) transition of CO isotopologues from the ThrUMMS survey, we are able to compute a 3D realization of the excitation temperature and optical depth in the interstellar medium. Ultimately, this survey will provide a detailed, global view of the inner Galactic interstellar medium at an unprecedented angular resolution of ~30".

Drag law for an intruder in granular sediments.

We investigate the drag experienced by a spherical intruder moving through a medium consisting of granular hydrogels immersed in water as a function of its depth, size, and speed. The medium is observed to display a yield stress with a finite force required to move the intruder in the quasistatic regime at low speeds before rapidly increasing at high speeds. In order to understand the relevant time scales that determine drag, we estimate the inertial number I given by the ratio of the time scales required to rearrange grains due to the overburden pressure and imposed shear and the viscous number J given by the ratio of the time scales required to sediment grains in the interstitial fluid and imposed shear. We find that the effective friction μ_{e} encountered by the intruder can be parametrized by I=sqrt[ρ_{g}/P_{p}]v_{i}, where ρ_{g} is the density of the granular hydrogels, v_{i} is the intruder speed, and P_{p} is the overburden pressure due to the weight of the medium, over a wide range of I where the Stokes number St=I^{2}/J≫1. We then show that μ_{e} can be described by the function μ_{e}(I)=μ_{0}+αI^{β}, where μ_{0}, α, and β are constants that depend on the medium. This formula can be used to predict the drag experienced by an intruder of a different size at a different depth in the same medium as a function of its speed.

Conformal microstrip slot antenna with an AMC reflector for hyperthermia

This paper presents the simulation and experimental studies of a conformal microstrip slot antenna integrated with artificial magnetic conductor (AMC) for hyperthermia application. In the proposed applicator, an AMC consisting of an array of modified ring patches on a grounded dielectric substrate is located at optimized distance (=4 mm) from the microstrip slot antenna for improved performance of the applicator. The feed configuration of the proposed slot antenna consists of tapered microstrip line with curved tuning stub. The slot and feed configurations of the antenna are modified to widen its bandwidth so that changes in dielectric property of biological phantom medium can have minimal effect on its operating frequency and impedance bandwidth. In addition, the applicator with modified slot and feed arrangement provides enhanced heating depth in the phantom muscle medium. Provision for cooling of tissue surface is made by providing air gap between the slot antenna and phantom muscle medium. Moreover, the presence of AMC not only reduces the backfield but also enhances the penetration depth in the medium. Additionally, performance comparison of the proposed antenna–AMC and the antenna–perfect electric conductor(PEC) combinations in terms of input characteristics and specific absorption rate (SAR) parameters is also made. Finally, the effects of change in the radius of curvature of the substrate and bio-model on effective field size (EFS) for both homogeneous and tri-layered bio-models are also investigated. It is demonstrated through thermal simulation that temperature above 41 °C exists in the irregular-shaped tumor, which is embedded in the muscle region of the curved/planar tri-layered bio-model near its surface.

Magneto-Thermosolutal Convection in Couple-Stress Fluid in a Porous Medium

Thermosolutal instability of Veronis(1965) type in a couple-stress fluid in the presence of uniform vertical magnetic field in a porous medium is considered. Following the linearized stability theory and normal mode analysis, the paper mathematically established the condition for characterizing the oscillatory motions which may be neutral or unstable, for any arbitrary combination of free and rigid boundaries at the top and bottom of the fluid. It is proved analytically that all non-decaying slow motions starting from rest, in a couple-stress fluid of infinite horizontal extension and finite vertical depth in a porous medium, which is acted upon by uniform vertical magnetic field opposite to force field of gravity and a constant vertical adverse temperature gradient, are necessarily nonoscillatory, in the regime established, the result is important since the exact solutions of the problem investigated are not obtainable in closed form, for any arbitrary combination of free and rigid boundaries. A similar characterization theorem is also established for Stern (1960) type of configuration.

Extinction depth in a smooth X-ray waveguide

An approximate solution to the dispersion equation for the dynamics of an X-ray beam trapped in a plane waveguide with smooth walls is used to study the dependence of extinction depth on the optical density of wall material and X-ray energy. For angles of incidence of the X-ray beam that are no greater than the Fresnel angle, the extinction depth in nonabsorbing medium depends only on difference N e1–N e1 of electron densities in the wall material and waveguide layer as (πr 0(N e1–N e2))–1/2, where r 0 ~ 2.81794 × 10–13 cm is the classical electron radius. The results are in good agreement with the penetration depth of X-ray radiation into surface that is obtained using the Fresnel formulas in the approximation of plane waves at grazing angles that range from zero to one half of the critical angle of total external reflection.

MHD convective flow through porous medium in a horizontal channel with insulated and impermeable bottom wall in the presence of viscous dissipation and Joule heating

This paper deals with a steady MHD forced convective flow of a viscous fluid of finite depth in a saturated porous medium over a fixed horizontal channel with thermally insulated and impermeable bottom wall in the presence of viscous dissipation and joule heating. The governing equations are solved in the closed form and the exact solutions are obtained for velocity and temperature distributions when the temperatures on the fixed bottom and on the free surface are prescribed. The expressions for flow rate, mean velocity, temperature, mean temperature, mean mixed temperature in the flow region and the Nusselt number on the free surface have been obtained. The cases of large and small values of porosity coefficients have been obtained as limiting cases. Further, the cases of small depth (shallow fluid) and large depth (deep fluid) are also discussed. The results are presented and discussed with the help of graphs.

Insights into the content and spatial distribution of dust from the integrated spectral properties of galaxies

[Abridged] We present a new approach to investigate the content and spatial distribution of dust in structurally unresolved star-forming galaxies from the observed dependence of integrated spectral properties on galaxy inclination. We develop an innovative combination of generic models of radiative transfer (RT) in dusty media with a prescription for the spectral evolution of galaxies, via the association of different geometric components of galaxies with stars in different age ranges. We show that a wide range of RT models all predict a quasi-universal relation between slope of the attenuation curve at any wavelength and V-band attenuation optical depth in the diffuse interstellar medium (ISM), at all galaxy inclinations. This relation predicts steeper (shallower) dust attenuation curves than both the Calzetti and MW curves at small (large) attenuation optical depths, which implies that geometry and orientation effects have a stronger influence on the shape of the attenuation curve than changes in the optical properties of dust grains. We use our combined RT and spectral evolution model to interpret the observed dependence of the H\alpha/H\beta\ ratio and ugrizYJH attenuation curve on inclination in a sample of ~23 000 nearby star-forming galaxies. From a Bayesian MCMC fit, we measure the central face-on B-band optical depth of this sample to be tau_B\perp~1.8\pm0.2. We also quantify the enhanced optical depth towards newly formed stars in their birth clouds, finding this to be significantly larger in galaxies with bulges than in disc-dominated galaxies, while tau_B\perp is roughly similar in both cases. Finally, we show that neglecting the effect of geometry and orientation on attenuation can severely bias the interpretation of galaxy spectral energy distributions, as the impact on broadband colours can reach up to 0.3-0.4 mag at optical wavelengths and 0.1 mag at near-infrared ones.

Performance of Multi-Layer Soil Electric Resistivity Model Comparing with Two-Layer Characterizations in Geotechnical Investigations

This paper shows the performance of multi-layer soil electric resistivity model comparing with two-layer characterizations in geotechnical investigations. In conventional model, there are inter-relationships between soil apparent electrical resistivity (ρ) and several soil physical or chemical properties. These empirical relationships show limitations to obtain specific soil characterizations of different layers with. Multi-layer true resistivity model is the improvement of conventional two-layer earth model including the criteria of four points probe method. Multi-layer soil resistivity profile shows more accuracy to obtain near surface soil characteristics including the types of soil and rocks, and to detect anomalous materials in soil profile. Alternatively, apparent resistivity in two-layer model can be used to obtain deeper profile of soil characteristics. In this multi-layer soil model, the soil resistivity and resistivity ratio corresponding to the depth in soil medium are considered for geotechnical investigations. Two-layer model includes soil apparent resistivity according to probe distances in depth corresponding resistivity profile. This paper is important for including criteria and performance of multi-layer soil resistivity model and conventional two-layer model for geotechnical characterizations.

Impact and intrusion experiments on the deceleration of low-velocity impactors by small-body regolith

Previous laboratory impact experiments into sand and glass beads have enriched our understanding of the cratering process on granular media common on asteroids and planetary regolith. However, less attention has been paid to the fate of the projectile, such as its penetration depth in the granular medium, although this may be important for the regolith mixing process. We conducted laboratory experiments on the deceleration of projectiles with low impact velocities to understand the re-accumulation process of ejecta on small asteroids. Glass beads were used as a model of a granular target. Impact experiments using 6-mm plastic projectiles with velocities of ∼70ms−1 were performed on the Earth’s surface and under microgravity. Measurements of the resistance force of the glass beads against slow intrusion and penetration were also performed. In the impact experiments, the projectiles were decelerated mainly as a result of drag proportional to the square of the velocity. The drag coefficient was 0.9–1.5. Additionally, we found a possible term proportional to the projectile velocity corresponding to the viscous drag with a viscosity up to 2Pas. These forces are consistent with numerical simulations that we carried out. The slow intrusion and penetration measurements showed that the velocity-independent resistance force per unit area on a projectile is roughly 20 times larger than the lithostatic pressure. The penetration depth of re-accumulated ejecta was examined based on the drag parameters obtained in this study. A simple configuration was used to visualize the dependence of penetration depth on the drag parameters. The penetration depth was more sensitive to the drag parameters in the case of small particles impacting a relatively small model asteroid.

Interfacial mixing in as-deposited Si/Ni/Si layers analyzed by x-ray and polarized neutron reflectometry

Interdiffusion occurring across the interfaces in a Si/Ni/Si layered system during deposition at room temperature was probed using x-ray reflectivity (XRR) and polarized neutron reflectivity (PNR). Exploiting the complementarity of these techniques, both structural and magnetic characterization with nanometer depth resolution could be achieved. Suitable model fitting of the reflectivity profiles identified the formation of Ni–Si mixed alloy layers at the Si/Ni and Ni/Si interfaces. The physical parameters of the layered structure, including quantitative assessment of the stoichiometry of interfacial alloys, were obtained from the analyses of XRR and PNR patterns. In addition, PNR provided magnetic moment density profile as a function of depth in the stratified medium.

Dosimetry of 125I and 103Pd COMS eye plaques for intraocular tumors: Report of Task Group 129 by the AAPM and ABS

Dosimetry of eye plaques for ocular tumors presents unique challenges in brachytherapy. The challenges in accurate dosimetry are in part related to the steep dose gradient in the tumor and critical structures that are within millimeters of radioactive sources. In most clinical applications, calculations of dose distributions around eye plaques assume a homogenous water medium and full scatter conditions. Recent Monte Carlo (MC)-based eye-plaque dosimetry simulations have demonstrated that the perturbation effects of heterogeneous materials in eye plaques, including the gold-alloy backing and Silastic insert, can be calculated with reasonable accuracy. Even additional levels of complexity introduced through the use of gold foil "seed-guides" and custom-designed plaques can be calculated accurately using modern MC techniques. Simulations accounting for the aforementioned complexities indicate dose discrepancies exceeding a factor of ten to selected critical structures compared to conventional dose calculations. Task Group 129 was formed to review the literature; re-examine the current dosimetry calculation formalism; and make recommendations for eye-plaque dosimetry, including evaluation of brachytherapy source dosimetry parameters and heterogeneity correction factors. A literature review identified modern assessments of dose calculations for Collaborative Ocular Melanoma Study (COMS) design plaques, including MC analyses and an intercomparison of treatment planning systems (TPS) detailing differences between homogeneous and heterogeneous plaque calculations using the American Association of Physicists in Medicine (AAPM) TG-43U1 brachytherapy dosimetry formalism and MC techniques. This review identified that a commonly used prescription dose of 85 Gy at 5 mm depth in homogeneous medium delivers about 75 Gy and 69 Gy at the same 5 mm depth for specific (125)I and (103)Pd sources, respectively, when accounting for COMS plaque heterogeneities. Thus, the adoption of heterogeneous dose calculation methods in clinical practice would result in dose differences >10% and warrant a careful evaluation of the corresponding changes in prescription doses. Doses to normal ocular structures vary with choice of radionuclide, plaque location, and prescription depth, such that further dosimetric evaluations of the adoption of MC-based dosimetry methods are needed. The AAPM and American Brachytherapy Society (ABS) recommend that clinical medical physicists should make concurrent estimates of heterogeneity-corrected delivered dose using the information in this report's tables to prepare for brachytherapy TPS that can account for material heterogeneities and for a transition to heterogeneity-corrected prescriptive goals. It is recommended that brachytherapy TPS vendors include material heterogeneity corrections in their systems and take steps to integrate planned plaque localization and image guidance. In the interim, before the availability of commercial MC-based brachytherapy TPS, it is recommended that clinical medical physicists use the line-source approximation in homogeneous water medium and the 2D AAPM TG-43U1 dosimetry formalism and brachytherapy source dosimetry parameter datasets for treatment planning calculations. Furthermore, this report includes quality management program recommendations for eye-plaque brachytherapy.