A Hybrid Grey Wolf Optimizer for Process Planning Optimization with Precedence Constraints.

Process planning optimization is a well-known NP-hard combinatorial problem extensively studied in the scientific community. Its main components include operation sequencing, selection of manufacturing resources and determination of appropriate setup plans. These problems require metaheuristic-based approaches in order to be effectively and efficiently solved. Therefore, to optimize the complex process planning problem, a novel hybrid grey wolf optimizer (HGWO) is proposed. The traditional grey wolf optimizer (GWO) is improved by employing genetic strategies such as selection, crossover and mutation which enhance global search abilities and convergence of the traditional GWO. Precedence relationships among machining operations are taken into account and precedence constraints are modeled using operation precedence graphs and adjacency matrices. Constraint handling heuristic procedure is adopted to move infeasible solutions to a feasible domain. Minimization of the total weighted machining cost of a process plan is adopted as the objective and three experimental studies that consider three different prismatic parts are conducted. Comparative analysis of the obtained cost values, as well as the convergence analysis, are performed and the HGWO approach demonstrated effectiveness and flexibility in finding optimal and near-optimal process plans. On the other side, comparative analysis of computational times and execution times of certain MATLAB functions showed that the HGWO have good time efficiency but limited since it requires more time compared to considered hybrid and traditional algorithms. Potential directions to improving efficiency and performances of the proposed approach are given in conclusions.

Occupational radiation dose of personnel involved in sentinel node biopsy procedure.

INTRODUCTION: Sentinel node biopsy is a procedure used for axillary nodal staging in breast cancer surgery. The process uses radioactive 99mTc isotope for mapping the sentinel node(s) and all the staff involved in the procedure is potentially exposed to ionizing radiation. The colloid for radiolabelling (antimone-sulphide) with 99mTc isotope (half-life 6 h) is injected into the patient breast. The injection has activity of 18.5 MBq. The surgeon removes the primary tumor and detects active lymph nodes with gamma detection unit. The tumor as well as the active nodal tissue is transferred to pathologist for the definitive findings. The aim of the study was to measure dose equivalents to extremities and whole body for all staff and suggest practice improvement in order to minimize exposure risk. MATERIALS AND METHODS: The measurements of the following operational quantities were performed: Hp(10) personal dose equivalent to whole body and Hp(0.07) to extremities for staff as well as ambiental dose for operating theatre and during injection. Hp(0.07) were measured at surgeon's finger by ring thermoluminescent dosimeter (TLD) type MTS-N, and reader RADOS RE2000. Surgeon and nurse were wearing TLD personal dosimeter at the chest level. Anesthesiologist and anesthetist were wearing electronic personal dosimeters, while pathologist was wearing ring TLD while manipulating tissue samples. Electronic dosimeters used were manufactured by Polimaster, type PM1610. All TLD and electronic dosimeters data were reported, including background radiation. Background radiation was also monitored separately. Personal TLDs are standard for this type of personal monitoring, provided by accredited laboratory. Measurements of ambiental dose in workplaces of other staff involved around the patient was performed before the surgery took place, by calibrated survey meters manufactured by Atomtex, type 1667. The study involved two surgeons and one pathologist, two anesthesiologists and three anesthetists during two months period. RESULTS AND DISCUSSION: The doses received by all staff are evaluated using passive and active personal dosimeters and ambiental dose monitors and practice was improved based on results collected. Average annual whole body dose for all staff involved in the procedure was less than 0.8 mSv. Extremity dose equivalents to surgeon and pathologist were far below the limits set for professionally exposed (surgeon) and for public (pathologist). CONCLUSIONS: Although has proven to be very safe for all staff, additional measures for radiation protection, in accordance to ALARA principle (As Low As Reasonably Achievable) should be conducted. The recommendations for practice improvement with respect to radiation protection were issued.

Oral continuous positive airway pressure for sleep apnea: effectiveness, patient preference, and adherence.

BACKGROUND: Nasal continuous positive airway pressure (CPAP) is the most definitive medical therapy for obstructive sleep apnea (OSA). Many patients have difficulty tolerating nasal CPAP due to nasal airway problems, mouth leak, and general discomfort from the mask and headgear. These limitations may be overcome by an oral mask (Oracle; Fisher & Paykel Healthcare; Languna Hills, CA) that does not require headgear. We performed a study to compare the Oracle mask to conventional nasal and oronasal masks in the effectiveness of CPAP delivery and patient satisfaction and adherence. METHODS: Ninety-eight, consecutive CPAP-naïve patients with OSA diagnosed by overnight polysomnography (apnea-hypopnea index [AHI] > 5) were referred for CPAP therapy. All patients were presented with a variety of CPAP masks, including nasal, oronasal, and Oracle, and reasons for mask choice were documented. After 3 weeks of acclimatization to the mask of their choice, patients had a CPAP titration sleep study to determine their optimal CPAP level. Further follow-up was obtained 2 months and 6 months later with a subjective patient assessment of CPAP use and efficacy, mask comfort, and upper airway dryness. RESULTS: Patients were predominantly male (70%), middle aged (50.6 +/- 11.7 years), and moderately obese (body mass index, 32.5 +/- 9.0) with severe OSA (AHI, 40.6 +/- 25.8/h) [mean +/- SD]. Patients were classified into three groups based on their choice of mask: nasal (66%), Oracle (27%), and oronasal (7%). Baseline characteristics did not differ significantly between groups. Optimal CPAP was not significantly different between mask groups (nasal, 7.7 +/- 2.1 cm H(2)O; Oracle, 8.0 +/- 2.0 cm H(2)O; oronasal, 9.7 +/- 3.2 cm H(2)O; p = 0.267). Subjective ratings of adherence, efficacy, and mask comfort were also similar between groups. However, the Oracle group had more complaints of upper airway dryness and "rain-out." The oronasal group had a disproportionately greater number of dropouts from CPAP therapy than the Oracle group (57% vs 19%, p = 0.046). Nine patients changed from the Oracle mask to a nasal mask during the study, whereas no patients changed from their nasal or oronasal masks. CONCLUSIONS: The Oracle mask is an efficacious interface for long-term CPAP therapy in patients with OSA. The main limitations of the mask are upper airway dryness and rain-out associated with heated humidification, which may be improved by further technical modifications. Oracle may be more acceptable than oronasal masks for patients who cannot rely exclusively on the nasal airway for CPAP therapy.