Strategic allocation of inspection stations for a flow assembly line: a hybrid procedure

A hybrid method is presented for the design of inspection stations in serial production systems. The hybrid method combines a constrained bottleneck shortest path algorithm and discrete event simulation. The network method determines the allocation of the inspection stations and the simulation helps the decision maker estimate accurately the possible outcome of the allocation. A computational study with the method is performed based on a practical problem. Other aspects related to the application of the method to real problems are also discussed.     

Microcalorimetric measurement of reaction enthalpies in solutions of uranium and neptunium compounds

The formation of complexes of uranyl and neptunyl (VI) ions with carbonate and hydrogen carbonate has been studied by titration microcalorimetry. The measurements were carried out with a computer-controlled microcalorimeter which is described in detail. Sample volumes are typically in the range of 1.5 to 2.5 ccm, containing about 0.05 millimole of the ionic species to be studied. The small volume renders the calorimeter useful for the measurement of uncommon and strongly radioactive substances.Enthalpies of reaction were obtained for the formation of the dicarbonato and the tricarbonato uranyl ions in a sulfate medium of ionic strength 1.6. The enthalpies are $\text{ΔH}{}_2\text{= ?39.6 ± 1 kJ/mol}$ and $\text{ΔH}{}_3\text{= ?57.5 ± 1.5 kJ/mol}$, for the dicarbonato- and the tricarbonato-uranyl ions, respectively. The titration data for the neptunyl (VI) — carbonate system yield a value of $\text{ΔH}{}_{\mathrm{Np}}\text{?50 ± 2 kJ/mol}$ for the tricarbonato-neptunyl ion when interpreted in analogy to the uranyl system.     

Mechanisms of Photochemical Reactions in Solution. LXXIV. The Photochemistry of 3-Methyl-1-Phenoxybut-2-Ene.,

The photochemical reactions of 3-methyl-1-phenoxybut-2-ene (γ,γ-dimethylallyl phenyl ether), I, were investigated in solution and in the gas phase. Irradiation of I resulted in the formation of phenol, II, 3-methyl-3-phenoxybutene, III, 1-(2-hydroxyphenyl)-3-methylbut-2-ene, IV, 1-(4-hydroxyphenyl)-3-methylbut-2-ene, V, 3-(2-hydroxyphenyl)-3-methylbutene, VI, and 3-(4-hydroxyphenyl)-3-methylbutene, VII. Formation of III - VII in the gas phase was efficiently quenched by nitric oxide. The results suggest that all products were formed by a dissociation - radical recombination mechanism and that none were formed by concerted processes. The absorption spectrum of I and its quantum yields for fluorescence and photochemical reaction were used to estimate the rates of the processes which deactivate its lowest-lying excited singlet state. The results suggest that O? C bond homolysis need not occur via intersystem crossing from an S₁ (π, π*) to a ³σ (C? O) state. Fragmentation to radicals, and perhaps rapid non-radiative decay without chemical reaction, probably involve internal conversion with population of high vibrational levels of the C? O bond. Weak electronic interaction between the aromatic nucleus and the olefinic chromophore may also be important.     

Diagnostic scalene node biopsy in the preoperative evaluation of the surgical cancer patient: Five-year experience with 108 cases and literature review

Records were reviewed of 108 consecutive patients with a variety of surgically approachable malignancies undergoing scalene node biopsy as part of a preoperative staging evaluation. Metastases to the scalene nodes were detected in 12 patients (11.1%). In six patients the scalene nodes were clinically suspicious before biopsy, but in six with nonpalpable nodes the scalene metastases were occult clinically. Four of the patients with clinically benign, but pathologically positive, scalene biopsies were found among the group of 62 patients with epidermoid carcinoma of the cervix. It was concluded that routine scalene biopsies are justified in the properative evaluation of cancer patients only if the nodes are clinically suspicious, except for in patients with advanced pelvic cancers, in whom the incidence of completely occult scalene metastases is 6% or more.     

A fully automated calibration method for an optical see-through head-mounted operating microscope with variable zoom and focus

Ever since the development of the first applications in image-guided therapy (IGT), the use of head-mounted displays (HMDs) was considered an important extension of existing IGT technologies. Several approaches to utilizing HMDs and modified medical devices for augmented reality (AR) visualization were implemented. These approaches include video-see through systems, semitransparent mirrors, modified endoscopes, and modified operating microscopes. Common to all these devices is the fact that a precise calibration between the display and three-dimensional coordinates in the patient's frame of reference is compulsory. In optical see-through devices based on complex optical systems such as operating microscopes or operating binoculars-as in the case of the system presented in this paper-this procedure can become increasingly difficult since precise camera calibration for every focus and zoom position is required. We present a method for fully automatic calibration of the operating binocular Varioscope M5 AR for the full range of zoom and focus settings available. Our method uses a special calibration pattern, a linear guide driven by a stepping motor, and special calibration software. The overlay error in the calibration plane was found to be 0.14-0.91 mm, which is less than 1% of the field of view. Using the motorized calibration rig as presented in the paper, we were also able to assess the dynamic latency when viewing augmentation graphics on a mobile target; spatial displacement due to latency was found to be in the range of 1.1-2.8 mm maximum, the disparity between the true object and its computed overlay represented latency of 0.1 s. We conclude that the automatic calibration method presented in this paper is sufficient in terms of accuracy and time requirements for standard uses of optical see-through systems in a clinical environment.     

A novel local thresholding algorithm for trabecular bone volume fraction mapping in the limited spatial resolution regime of in vivo MRI

Recent advances in micro-magnetic resonance imaging have shown the possibility of in vivo assessment of trabecular bone architecture. However, the small feature size and relatively low signal-to-noise ratio (SNR) achievable in vivo cause the intensity histogram to be unimodal. The critical first step in the processing of these images is the extraction of bone volume fraction for each voxel. Here, we propose a local threshold algorithm (LTA) that determines the marrow intensity value in the neighborhood of each voxel based on nearest-neighbor statistics. Using the local marrow intensities we threshold the image and scale the intensities of voxels partially occupied by bone to produce a marrow volume fraction map of the trabecular bone region. We show that structural parameters derived with the LTA are highly correlated with those obtained with the previously published histogram deconvolution algorithm (HDA) and that the LTA is robust to image noise corruption. The LTA is found to correctly identify trabeculae with a significantly higher reliability than HDA. Finally, we demonstrate that the LTA is superior in preserving connectivity by showing for 75 in vivo images that the genus of the trabecular bone surface is always higher than when processed with the HDA.     

Finite-difference time-domain simulation of a liquid-crystal optical phased array

Accurate modeling of a high-resolution, liquid-crystal-based, optical phased array (OPA) is demonstrated. The modeling method is extendable to cases where the array element size is close to the wavelength of light. This is accomplished through calculating an equilibrium liquid-crystal (LC) director field that takes into account the fringing electric fields in LC OPAs with small array elements and by calculating the light transmission with a finite-difference time-domain method that has been extended for use in birefringent materials. The diffraction efficiency for a test device is calculated and compared with the simulation.