Preset Depth Research Articles

Rigorous electromagnetic analysis of the common focusing characteristics of a cylindrical microlens with long focal depth and under multiwavelength illumination

The common focusing characteristics of a cylindrical microlens with a long focal depth and under a given multiple-wavelength illumination are analyzed based on the boundary element method (BEM). The surface-relief profile of a finite-substrate-thickness microlens with a long focal depth is presented. Its focusing performances, such as the common extended focal depth (CEFD), the spot size, and the diffraction efficiency, are numerically studied in the case of TE polarization. The results show that the CEFD of the microlens increases initially, reaches a peak value, and then decreases with increasing preset focal depth. Two modified profiles of a finite-substrate-thickness cylindrical microlens are proposed for enlarging the CEFD. The rigorous numerical results indicate that the modified surface-relief structures of a cylindrical microlens can successfully modulate the optical field distribution to achieve longer CEFD, higher transverse resolution, and higher diffraction efficiency simultaneously, compared with the prototypical microlens. These investigations may provide useful information for the design and application of micro-optical elements in various multiwavelength optical systems.

Modified Automated Lamellar Therapeutic Keratoplasty for Keratoconus

To describe a modified automated lamellar therapeutic keratoplasty (ALTK) technique for the treatment of keratoconus. The ALTK procedure was modified to include the use of a Hanna trephine system to control donor and recipient diameters and was performed in 2 stages. The recipient corneal lamellar bed was first prepared by creating a laser in situ keratomileusis (LASIK) flap at a preset depth that was left to heal over. The second stage involved the use of a Hanna trephination system to perform central trephination within the lamellar flap and transplantation of a donor lamellar graft that was fashioned to precisely match the recipient corneal bed, again using the Hanna donor punch to create a central trephination within the lamellar button obtained with the ALTK unit. The modified ALTK procedure effectively treated a patient with moderate keratoconus with a best-corrected visual acuity of 20/80, despite rigid gas-permeable contact lenses. Postoperatively, there was a significant reduction in the irregular astigmatism, and visual acuity improved to 20/25. There were no complications, and the ALTK interface remained clear throughout the 20-month follow-up period. ALTK combined with Hanna trephination enables precise control of both depth and diameter of lamellar dissection during surgery, removes the need for any form of manual dissection, and may therefore improve optical and visual outcomes in lamellar keratoplasty.

Analysis of microlens array with long focal depth and smallf-number by improved first Rayleigh–Sommerfeld method

The improved first Rayleigh?Sommerfeld method (IRSM1) is applied to analyse the focusing performance of dual-?and tri-cylindrical microlens arrays with long focal depth and small f-number for the TE polarization. The real extended focal depth, the diffraction efficiency, the spot size, and the real position of the focal plane of the microlens array with different f-numbers and the preset extended focal depths are calculated by the IRSM1, rigorous boundary element method (BEM), and original Rayleigh?Sommerfeld method (ORSM1), respectively. The accuracies of the IRSM1 and the ORSM1 are evaluated along the longitudinal direction. The results indicate that the IRSM1 can be used for analysing the cylindrical microlens array with long focal depth and small f-number, but the ORSM1 completely fails for those microlens arrays with small f-number. It is expected that this investigation will provide useful information in the design of the micro-optical elements for realizing longitudinal optical field modulation.

Muscle activity onset in the lumbar multifidus muscle recorded simultaneously by ultrasound imaging and intramuscular electromyography

Delayed anticipatory muscle activity response in deep abdominal and back muscles has been observed in patients with low back pain, indicative of a pathological condition. Muscle activity onset is traditionally recorded by intramuscular electromyography, but there is a need for a non-invasive and less cumbersome recording method in large clinical studies. An experimental study was carried out to explore whether high-frame rate m-mode ultrasound could measure anticipatory muscle responses ("onset") in the lumbar multifidus muscle reliably and comparably accurate to intramuscular electromyography. Muscle activity onset was recorded by ultrasound m-mode and intramuscular electromyography. Ultrasound m-mode with a temporal resolution of 500 s(-1) (frames per second) was used to record rapid movements caused by muscle deformations in multifidus. In ultrasound m-mode, the frequency of each echo signal from 0.15 mm incremental depth levels is analysed. The frequency of these signals is proportional to the velocity of the interrogated tissue. The mean amplitude of the high-pass filtered echo signals within a pre-set depth range was plotted against time, and used to indicate onset. The results were compared to muscle activity onset in the multifidus recorded simultaneously by intramuscular electromyography. High inter-rater agreement was found for visual determination of onset within both methods. The smallest detectable difference was 21 and 24 ms for electromyography and the ultrasound methods, respectively. The ultrasound m-mode method recorded muscle activity onset in the deep multifidus on average 16 ms (SD 21) later than intramuscular electromyography. For single trials, large variation and thus unacceptable method agreement was found. Ultrasound m-mode imaging at high time resolution can detect onset of muscle activity comparably accurate to intramuscular electromyography, but with a small systematic delay that should be corrected for in onset determination by m-mode ultrasound. Regardless of recording method, onset estimates should be based on averaged values of repeated trials. Further studies are needed to explore the applicability of the ultrasound method in clinical settings.

SU‐DD‐A1‐04: In Vivo Prostate IMRT Dosimetry With MOSFET Detectors Using Brass Build‐Up Caps

Purpose: To develop a general formalism with various correction factors to predict dmax entrance dose with the new hemispherical brass buildup caps to be used with MOSFET detectors in anterior prostate IMRT fields and thereby integrate in vivo IMRT dose measurement as part of routine QA process in IMRT radiotherapy Method and Materials: We have used the new wide energy hemispherical build‐up caps for this study. Due to its high density and high atomic number it provides the minimal amount of metal needed to achieve full build‐up at Dmax for a range of photon energies. We have developed a general formalism to predict Dmax entrance dose by applying necessary correction factors after studying the response of MOSFET with brass build up caps for energy, dose rate, dose reproducibility, SSD and patient specific IMRT correction factor. Results: In vivo Prostate IMRT dose measurements with MOSFET detectors using brass buildup caps was performed and compared against dose predicted by two different treatment planning systems. We used both 6 MV and 10 MV for this study and compared the in vivo MOSFET detector reading with dose predicted by Philips Pinnacle (6 MV) and CMS XiO (10 MV) treatment planning systems respectively. We achieved a overall accuracy of better than ± 5% on measured patient doses. Conclusion: Routine IMRT QA in most institutions today only involves verifying the optimized fluence map delivered to the patient in a test phantom at a certain preset depth. Based on our work here, we believe adding in vivo IMRT dosimetry with MOSFET detectors using the new brass build up caps along with routine fluence map verification in phantoms and MLC quality assurance offers greater accuracy and confidence in actual dose delivered to the patient.

A Broadband Geoacoustic Inversion Scheme

A geoacoustic inversion scheme, which combines several inversionmethods together to invert for the bottom parameters, has been proposedbased on the fact that the bottom acoustic parameters have differentsensitivities to the different physical parameters of acoustic field.Firstly, the characteristic impedance of the bottom is inverted bymeasuring the vertical bottom reflective coefficients. Secondly, thederived bottom characteristic impedance is used as a constrainedcondition in another inversion procedure, which is very sensitive tothe bottom sound speed but less sensitive to the attenuation, toinverse the bottom sound speed and bottom density. Lastly, the bottomattenuation can be estimated from methods such as transmissionloss data, the vertical correlation of propagation data, and the normalmode attenuation. To obtain the characteristic impedance of the bottomaccurately, vacuum glass spheres (VGS) are used as broadband soundsources, and a special mechanism is designed to trigger the VGSimploded at the preset depth. The inversion scheme has beensuccessfully used for a set of sea experimental data. It shows that theinverted bottom parameters could distinguish the atlas marked bottomtype quite well. The excellent comparison of the numerical results withthe experimental data shows the validity of the inverted parameters.

In situ remediation of soils contaminated with toxic metal ions using microwave energy

Following onto our work on the in situ remediation of soils contaminated with PAH’s, PCB’s and other polychlorinated organic compounds using microwave energy, we now report a preliminary investigation on the in situ remediation of soils contaminated with toxic metal ions: Cd(II), Mn(II), Th(IV), Cr(III) and mainly Cr(VI). The soil is partially vitrified in the process, and extraction with hot (70 °C) 35% nitric acid for 4.5 h leads to the recovery of very small amounts of the metals which had been spiked into the clean soil: Cd, Mn, and Cr(III) are completely immobilized (unextractable), Th is mostly unextractable, and Cr(VI) partially extractable at very high levels of spiking, but almost completely unextractable using the US EPA Toxicity Characteristic Leaching Procedure. This suggests that contaminated soils which are not going to be used for agricultural purposes can be remediated safely to preset depths without fear of the toxic metal ions leaching out for a long time.

SURFACE AND SUBSURFACE SENSORS TO RECORD VARIABLE RUNOFF GENERATION AREAS

Hydrologic processes related to runoff generation during rainfall events are being studied in a small ridge and valley watershed in east-central Pennsylvania. To record the dynamics of the near-surface water table (top 45 cm) and the occurrence and dynamics of surface saturation and runoff generation areas, two types of sensors, subsurface saturation and surface runoff, were designed. These two types of sensors are an improvement over an earlier version of saturation sensor. The newly designed subsurface saturation sensor is a printed circuit board with sensing pins to indicate the depth of water table as it exceeds six different preset depths (1, 5, 10, 20, 30, and 45 cm from the surface). The surface runoff sensor, a miniature V-notch weir, is a “yes-no” sensor that indicates whether or not there is surface runoff. Sixty-three subsurface saturation and 42 surface runoff sensors were installed in a 20 m ×40 m hillslope adjacent to a headwater stream. All sensors were connected to data-loggers for automated continuous data collection. This field application proved that these sensors are easy-to-install and cost effective as compared to shallow wells. The performance of the subsurface saturation sensors compared favorably with local shallow wells. Data from these sensors can be used to identify the process(es), saturation excess or infiltration excess, that leads to the occurrence of surface saturation and runoff generation areas over distributed spatial locations. The time series data from these sensors can be used to identify and define the dynamics of surface saturation and runoff generation areas during rainfall events.

Formula omitted] decomposition of PCBs in soil using microwave energy

The decomposition of individual PCBs and of Aroclors in soil using microwave energy and graphite fibers occurs quantitatively in a machinable ceramic alumina bomb. As a model for in situ remediation, the reactions were then carried out in open vessels equipped with rudimentary condensers, and using either pencil lead (as a cheap graphite rod equivalent) or iron wire. Most of the chlorinated aromatics decomposed (none left in the soil), and a small portion was desorbed, collected, and dechlorinated quantitatively by catalytic hydrogenation. This procedure should allow soil remediation to any preset depth by using the appropriate length of graphite or iron rods. When 14C-2,2′,5,5′-tetrachlorobiphenyl was used (with thinner pencil lead) 27% was desorbed and 1–2.5% of 14CO 2 was evolved. The remaining material could not be extracted from the soil under any conditions, and this suggests that the dechlorinated fragments are very tightly bound, and possibly encapsulated, by the vitrified soil.

Calculation of Gamma-ray Exposure Buildup Factors up to 40mfp using the EGS4 Monte Carlo Code with a Particle Splitting

Gamma-ray exposure buildup factors up to 40 mfp have been calculated using the Monte Carlo code EGS4 for water, iron and lead for point isotropic sources. The new algorithm which applies particle-splitting at each preset depth to simulate almost same number of particles from the preset depth is developed in order to obtain reasonable results with EGS4 at deep-penetrations. Comparisons of these results to the standard data calculated with the moments method or the discrete ordinates code PALLAS show good agreements if the same cross section data and energy absorption coefficients are used. The EGS4 calculations with this new algorithm will be a useful tool for future studies of gamma-ray buildup factors including the review of the standard data.

Damage development in drilling glass fibre reinforced plastics

In the drilling of reinforced plastics the quality of the cut surfaces is strongly dependent on the appropriate choice of drilling parameters. The aim of this work is to clarify the interaction mechanisms between the drilling tool and material. Drilling tests were carried out on glass-polyester composites using standard HSS tools; drilling was interrupted at preset depths to study damage development during drilling. The specimens, polished by a metallographic technique, were examined by optical microscopy to identify any damage. The results obtained are useful in describing the damage history and to help design drill geometries specifically conceived for composite machining. The qualitative agreement of the observed behaviour with the predictions of the model presented in the literature and some of their intrinsic limitations are assessed.

Phytoplankton responses to freshwater inputs in a small semi-enclosed gulf (Gulf of Trieste, Adriatic Sea)

Phytoplankton variations in response to freshwater inputs and water column structure in a shallow (c25 m) semi-enclosed Mediterranean gulf (Gulf of Trieste, Adriatic Sea) are described. Hydrographic profiles and In situ fluorescence were recorded at high resolution, while nutrients and phytoplankton were analysed at 5 pre-set depths. Analyses of the phytoplankton community structure were completed by determinations of the pigment pool using reverse-phase high-performance liquid chromatography and size-fractionated primary production. The phytoplankton standing crop, community structure and primary production were profoundly influenced by freshwater inputs and water column stratification. The water column was well mixed and supported modest phytoplankton concentrations during winter. A spring diatom bloom (Skeletonema costatum, Nitzschia spp., Chaetoceros spp.) developed in response to major freshwater input to the surface layer; a similar increase in diatoms (Rhizosolenia delicatula, R. fragilissima) followed October-November freshets. A shift from diatomdominated winter-spring phytoplankton to a flora wlth increased numbers of flagellates in the stratified water column during late spring-summer was reflected in the composition of accessory pigments [lower fucoxanthin : 19'-hexanoyloxyfucoxanthin ratio, an increase of chlorophyll b (chl b) and peridinin concentration]. Primary productivity was correlated with chl a biomass and showed surface peaks in April and June. The 2 to 10 pm phytoplankton contributed significantly to the total productivity in January and June, while on an annual basis the most important producers were > l 0 pm. The smallest fraction (<2 pm) seemed to contribute little, except in July. Our data indicate that the new production resulting from land-born nutrient inputs was the main cause of major phytoplankton blooms, while the nutrient supply from the bottom became comparatively more important during dry summer months.

Keratotomy for astigmatism using an arcuate keratome.

We describe a new system for performing transverse arcuate corneal incisions for the correction of astigmatism. The instrument consists of a conical housing with suction and/or friction fixation to the limbus and two micrometric diamond knives mounted on a carrier that can be rotated by a gear mechanism. The depth, length, and location of the incisions can be predetermined. Light microscopy of donor eye corneas documented the achieved incision depth. One sweep at normal speed produced an incision depth 28% less deep than the preset depth. One sweep at low speed achieved depths of approximately 100% of the knife setting. Variability from one incision to another in the same cornea was related to blade sharpness. We report successful use of the instrument in five consecutive eyes with naturally occurring astigmatism.

Electronic diving apparatus

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DEPTH ESTIMATION FROM RESIDUAL BOUGUER ANOMALIES: A PROCEDURE BASED ON THE BACKUS‐GILBERT MINIMUM DISTANCE CRITERION *

AbstractThe minimum distance criterion of Backus and Gilbert is used to determine the depths of line masses approximating the subsurface two dimensional distribution of density differences responsible for the observed residual Bouguer anomaly values. The quantity minimized is the sum of the squared differences between the starting trial depths and the desired final depths of line masses. The search for the desired depths is limited to preset depth ranges.

A velocity profiler based on the principles of geomagnetic induction

Abstract A technique to determine the variations of horizontal velocity between the sea surface and bottom, based on the measurement of electric currents generated by the motion of the seawater through the Earth's magnetic field, has been developed. A freely-falling Electro-Magnetic Velocity Profiler, EMVP, senses the currents as a function of depth. Velocity is inferred as the equivalent velocities required to generate the observed electric currents in the local geomagnetic field. The inferred velocity profile is relative to an unknown, but depth-independent, velocity contribution. Hence, the profiles are of the depth-variable velocity components. The device is released from the surface, falls to a preset depth or to the sea floor and returns to the surface. Both descent and ascent take about 90 min in water 6000 m deep. The r.m.s. velocity errors are about 1 to 2 cm s−1 at the vertical resolution of independent methods, 50 m and larger. Simultaneous profiles by two identical EMVPs have r.m.s. velocity differences of less than 0.7 cm s−1 at a vertical resolution of 10 m. A second electric measurement on the instrument yields a velocity profile within 0.3 cm s−1 r.m.s. of the first electric measurement every 10 m. A performance level of ±1 cm s−1 at a vertical resolution of 10 m is indicated. This level is expected in the absence of strong magnetotelluric currents, which can produce errors as large as 10 cm s−1 during infrequent (10 to 20 times per year) periods of strong temporal fluctuations of the geomagnetic field. Temperature, electrical conductivity, pressure, and other variables are recorded twice each second. The digitally recorded data are processed aboard ship to obtain velocity and density profiles.