Design of two-dimensional zero reference codes with cross-entropy method.

We present a cross-entropy (CE)-based method for the design of optimum two-dimensional (2D) zero reference codes (ZRCs) in order to generate a zero reference signal for a grating measurement system and achieve absolute position, a coordinate origin, or a machine home position. In the absence of diffraction effects, the 2D ZRC design problem is known as the autocorrelation approximation. Based on the properties of the autocorrelation function, the design of the 2D ZRC is first formulated as a particular combination optimization problem. The CE method is then applied to search for an optimal 2D ZRC and thus obtain the desirable zero reference signal. Computer simulation results indicate that there are 15.38% and 14.29% reductions in the second maxima value for the 16x16 grating system with n(1)=64 and the 100x100 grating system with n(1)=300, respectively, where n(1) is the number of transparent pixels, compared with those of the conventional genetic algorithm.

Design of zero reference codes using cross-entropy method.

This paper considers the use of autocorrelation properties to design zero reference codes (ZRCs) for optical applications. Based on the properties of the autocorrelation function, the design of an optimum ZRC problem is transformed into a minimization problem with binary variables, and the objective is to minimize the second maximum of the autocorrelation signal sigma. However, the considerable computational complexity for an exhaustive search through all combinations of (nn (1)l) different code patterns is a potential problem especially for large codes, where n and n1 are the length of the ZRC and the number of transparent slits, respectively. To minimize sigma while reducing the computational complexity at the same time, we introduce the Cross-Entropy (CE) method, an effective algorithm that solves various combinatorial optimization problems to obtain a good code. The computer simulation results show that compared with the conventional genetic algorithm (GA), the proposed CE obtains the better sigma with low computational complexity.

Totally laparoscopic radical BII gastrectomy for the treatment of gastric cancer: a comparison with open surgery.

BACKGROUND: Laparoscopically assisted distal gastrectomy has been used for distal part early gastric cancer resection. However, use of totally laparoscopic gastric cancer resection remains limited because of technical problems, especially when standard D2 nodal dissection was applied. We had reported the first totally laparoscopic Billroth II (BII) subtotal gastrectomy with lymphadenectomy for early gastric cancer in the year 1998. The aim of this study is to determine whether this procedure is superior to conventional open technique. METHODS: The clinical course of 34 consecutive patients who underwent totally laparoscopic BII gastrectomy using an upper to lower, right to left, and clockwise quadrant-to-quadrant technique was compared with 34 sex-matched and age-matched patients who underwent open gastrectomy. Main outcome measures included operative time, blood loss, length of stay, morbidity and mortality, adequacy of lymphadenectomy, and long-term outcome. RESULTS: In the laparoscopic group, all the operations were completed by laparoscopic technique, but 1 patient required secondary laparotomy for total gastrectomy owing to inadequate resection margin. There was no operation mortality in this study. The postoperative complication rates were similar in these 2 groups. The mean operative time for laparoscopic group was 283+/-122 minutes (range: 186 to 480 min), significantly longer than the 195+/-26 minutes in the conventional group (P<0.001). Laparoscopic group was associated with less intraoperative blood loss (74 vs. 190 mL; P<0.01), early flatus passage (2.9 vs. 4.9 d; P<0.01), less usage of analgesics (3.5 vs. 5.8 doses; P<0.05), and a shorter postoperative hospital stay (8.5 vs. 12.1 d; P<0.01). There was no significant difference between laparoscopic and conventional open radical gastrectomy with regard to ratio of free margin, number of harvested lymph nodes, and survival. CONCLUSION: Although totally laparoscopic BII gastrectomy using the upper to lower technique required a longer surgical time and was technically more demanding than conventional open surgery, it resulted in shorter recovery time, less analgesic use, and less severe physical discomfort without compromising the operative curability and oncologic outcomes.