Discrete warehouse problem

A discrete warehouse is a collection of two-dimensional unit-square objects (robot and obstacles), which are allowed to move horizontally and vertically along grid lines. In this paper, we consider motion planning problems in a discrete warehouse with movable obstacles. In such a setup one is allowed to move some of the obstacles in order to:

1. (1) navigate the robot between an initial and a final position of the warehouse, and

2. (2) construct a clearing (path) between two specified points.

The final positions of the obstacles are unimportant for our problems.

We consider two forms of obstacle manipulations:

1. (a) remote, when the obstacles are moved by a remote mechanism, and

2. (b) contact, when the obstacles are moved only by direct contact of the robot.

We present necessary and sufficient conditions for the existence of a motion in both cases, and propose efficient algorithms for constructing feasible motions.     

Langmuir-blodgett films of stilbazole complexes of iridium(I) and rhodium(I)

Complexes of 4-alkoxystilbazoles with iridium and rhodium form stable Langmuir layers at the air-water interface even when the alkoxy chain is relatively short (C₅–C₁₂). The surface pressure-area isotherms indicate that condensed molecular monolayers are obtained. The area per molecule of each compound in its monolayer form is typically 0.60 nm², which agrees well with the cross-sectional area of the [Ir(CO)₂CI] or [Rh(CO)₂CI] head group predicated using molecular models. This suggests that the molecules are oriented with the metal moiety close to the water surface and their alkoxystilbazole ‘rod’ protruding from the plane of the water surface. Such floating monolayers have been transferred on to solid substrates such as glass, aluminium (AI₂O₃/AI/Glass) and silicon (SiO₂/Si) at relatively high speed (10 mm min ^?1) to form Y-type LB assemblies. The UV–Visible absorption properties of these materials in solution and LB film form have been studied. LB films of these complexes yield bathochromically shifted spectra relative to the LB film spectrum of the uncomplexed stilbazole. Additionally, these spectra are often broader and hypsochromically shifted relative to their corresponding solution spectra as a result of the close molecular packing within the LB film and the associated dipole–dipole interactions. The electrically polar nature of the molecules described in this paper suggest that they may be suitable candidates for new pyroelectric materials. Thus the pyroelectric coefficient (the rate of change of electric polarisation with respect to temperature) has been measured for a polar multilayer LB film containing an iridium complex. A pyroelectric coefficient of 3.5 μCm^?2K^?1 (at 30 °C) has been measured, which is one of the highest reported valued for an LB film. Additionally, a low dielectric loss of around 0.01 has been found over the frequency range 50 Hz–1 kHz, indicating that such LB films may be usfeul materials for pyroelectric sensors.     

Effects of doxycycline in actively purging cholera patients: a double-blind clinical trial

In 51 actively purging cholera patients the efficacy of doxycycline, a long-acting tetracycline, was compared with a placebo and tetracycline hydrochloride. Seventeen patients who were given doxycycline at the recommended dose of 2 mg/kg at the beginning of the study, at 12 h, and at the repeated dose once daily purged a mean volume of 5.1 liters of stool and received an average of 5.7 liters of intravenous fluid. Nineteen patients receiving the placebo purged 10.1 liters of stool and received 9.7 liters of fluid. Fifteen patients given tetracycline hydrochloride at 6-h intervals passed 4.8 liters of stool and received 5.5 liters of fluid. The durations of diarrhea calculated in 8-h periods were 3.5, 8.0, and 4.1 h in the respective groups receiving doxycycline, placebo, and tetracycline. The differences between the doxycycline and placebo treatments and the tetracycline and placebo treatments were statistically significant. Those receiving doxycycline became vibrio-free in about 3 days as compared with 2 days for those receiving tetracycline; the group given the placebo were vibrio positive for the duration of their hospitalization. The results show that in the treatment of cholera the administration of doxycycline once daily has effects equal to those when tetracycline is administered at 6-h intervals. This is a distinct advantage because it decreases the demand on nursing personnel in epidemics. Also, doxycycline may be safely administered in cases of suspected renal failure from prolonged shock in cholera.     

Adhesion of ice to a flexible substrate

The adhesion of ice to a flexible substrate, polyurethane elastomer, has been studied using the Andrews-Stevenson test procedure which involves the pressurization to failure of an enclosed interfacial crack. The temperature, rate of pressurization and substrate layer thickness were varied and the failure energy (critical energy release rate) determined. If energy release from the flexible substrate is ignored an apparent failure energy is obtained which first increases and then decreases as the layer thickness rises from zero to 4 mm. This thickness effect results in a large variation in the pressure needed to produce failure, and is thus important in relation to the ice-release properties of the substrate. It is shown that the thickness effect can be explained quantitatively in terms of the energy release from the flexible substrate, which, in turn, depends on its visco-elastic properties. The true failure energy is derived and is also found to correlate with the visco-elastic response of the rubber. Finally, these ideas are used to explain the effects of rate and temperature on the conditions of failure.     

Statistical analysis of repeatability in laser percussion drilling

This study investigates the effect of six parameters in the repeatability of drilled holes in laser percussion drilling process by means of statistical techniques. Peak power, pulse width, pulse frequency, number of pulses, gas pressure and focal plane position were considered as independent process parameters. Experiments were designed with the aim of reducing the number of required experiments. The response surface method was used to develop the models for required responses. The significant factors in the process were selected based on the analysis of the variance (ANOVA). The experiments were conducted in mild steel sheet with a thickness of 2 mm. Each experiment was repeated 35 times in order to investigate the repeatability of the process. The equivalent entrance diameter, percentage of standard deviation of entrance diameter (%STD Eq Dia), circularity (ratio of minimum to maximum Feret’s diameter) and its standard deviation (STD circularity) were selected as process characteristics. The %STD Eq Dia and STD circularity, respectively, show the repeatability of equivalent diameter and circularity in the process. The results show that the process of drilling smaller hole diameters is more repeatable than drilling larger holes. Pulse width, gas pressure, focal plane position, peak power and number of pulses, respectively, have significant effect on the repeatability of hole diameter and circularity. Pulse frequency has no significant effect on the repeatability of the process.     

Ten-inch molecular beam epitaxy production system for HgCdTe growth

Growth of Hg_1−xCd_xTe by molecular beam epitaxy (MBE) has been under development since the early 1980s at Rockwell Scientific Company (RSC), formerly the Rockwell Science Center; and we have shown that high-performance and highly reproducible MBE HgCdTe double heterostructure planar p-on-n devices can be produced with high throughput for various single- and multiplecolor infrared applications. In this paper, we present data on Hg_1−xCd_xTe epitaxial layers grown in a ten-inch production MBE system. For growth of HgCdTe, standard effusion cells containing CdTe and Te were used, in addition to a Hg source. The system is equipped with reflection high energy electron diffraction (RHEED) and spectral ellipsometry in addition to other fully automated electrical and optical monitoring systems. The HgCdTe heterostructures grown in our large ten-inch Riber 49 MBE system have outstanding structural characteristics with etch-pit densities (EPDs) in the low 10⁴ cm⁻² range, Hall carrier concentration in low 10¹⁴ cm⁻³, and void density <1000 cm². The epilayers were grown on near lattice-matched (211)B Cd_0.96Zn_0.04Te substrates. High-performance mid wavelength infrared (MWIR) devices were fabricated with R₀A values of 7.2×10⁶ Ω-cm² at 110 K, and the quantum efficiency without an antireflection coating was 71.5% for cutoff wavelength of 5.21 μm at 37 K. For short wavelength infrared (SWIR) devices, an R₀A value of 9.4×10⁵ Ω-cm² at 200 K was obtained and quantum efficiency without an antireflection coating was 64% for cutoff wavelength of 2.61 μm at 37 K. These R₀A values are comparable to our trend line values in this temperature range.     

Microstructure evolution and simulation of copolymerization reaction using a percolation kinetic gelation model

A new kinetic gelation model that incorporates the kinetics of non-linear free radical copolymerization is presented. Copolymerization of bi- and tetrafunctional monomer mixtures is simulated to characterize kinetic effects on polymerization statistics and microstructures. An algorithm for random next step selection in a self-avoiding random walk and efficient mechanisms of component's mobility are introduced to improve the universality of the predictions by removing commonly occurring simulation deficiencies due to early trapping of radicals. The model has the capability to predict the onset of the sol-gel transition, and the effect of chemical composition on the transition point. It is shown that a better understanding of microstructure evolution during polymerization and chemical gelation is attained. Lastly, one important benefit of the simulation method is the ability to simulate very highly packed random chains or microgels within a polymer network.     

Degradation of methotrexate by UV/peroxymonosulfate: Kinetics,effect of operational parameters and mechanism

Methotrexate (MTX) is one of the most consumed anti-cancer drugs in the pharmaceutical market around the world. The widespread occurrence of MTX in aquatic environment through hospital effluent has attracted increasing concern due to its potential to induce water pollution. In the present study, the degradation of MTX in aqueous medium was investigated by UV-activated peroxymonosulfate (PMS). A significant improvement in degradation rate by increasing UV intensity and PMS concentration while the decrease in degradation efficiency with the increase of solution pH and initial concentration of MTX was observed. The proposed UV/PMS process could achieve more than 90% MTX degradation in 30 min with a good mineralization degree (65%). A pseudofirst order kinetic model was employed and successfully predicted the degradation of MTX. The effect of other operational parameters such as the initial concentration of the targeted compound, dosage of oxidant (PMS), solution pH and UV intensity on the degradation rate were investigated. At the last, the main transform intermediates were identified using LC-MS and possible degradation pathways were proposed. The results show that UV/ PMS can be used as an efficient technology to treat pharmaceuticals such as methotrexate containing water and wastewater.     

The structure of crystalline polyethylene sulphide — a laser Raman study

That polyethylene sulphide crystallizes in lamellar units within spherulites, has been presumed. In this paper further evidence for lamellae from Raman spectroscopy is presented and discussed. Thickening of the lamellae betweenT _M-90 andT _M-15 is also demonstrated.     

Interaction of α radiation with iron-doped n-type silicon

Deep-level transient spectroscopy (DLTS) measurements were carried out on low-doped n-silicon before and after irradiation with 5.48 MeV α particles at room temperature with a fluence of 10¹⁰ α particles/cm². The DLTS measurements on the samples identified three electron levels E₁, E₂ and E₃ before irradiation. The deep-levels characteristic studies include emission rate signatures, activation energies, defect concentrations and capture cross sections. It was found that all pre-existing defects decreased their amplitudes during irradiation. The decrease in activation energy of level E₃ and noticeable suppression of level E₁ was also observed after irradiation. It was clearly seen that the composite peak E₃ (combination of E₂ and E₃) was successfully resolved after irradiating with α particles. α-irradiation is seen to lead a significant suppression of the iron interstitial defect, and without causing any change in its room temperature annealing characteristics.