• Bulletin of the Korean Mathematical Society
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• v.56 no.4
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• pp.1077-1097
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• 2019

Let M be a finitely generated module over a regular local ring (R, n). We will fix an n-stable filtration for M and show that the minimal free resolution of M can be obtained from any filtered free resolution of M by zero and negative consecutive cancellations. This result is analogous to [10, Theorem 3.1] in the more general context of filtered free resolutions. Taking advantage of this generality, we will study resolutions obtained by the mapping cone technique and find a sufficient condition for the minimality of such resolutions. Next, we give another application in the graded setting. We show that for a monomial order ${\sigma}$, Betti numbers of I are obtained from those of $LT_{\sigma}(I)$ by so-called zero ${\sigma}$-consecutive cancellations. This provides a stronger version of the well-known cancellation "cancellation principle" between the resolution of a graded ideal and that of its leading term ideal, in terms of filtrations defined by monomial orders.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.239-242
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• 2003

Transmit diversity using STBC(Space Time Block Code) provides the same diversity gain as MRRC(Maximal Ratio Receiver Combining), when the fading channel is constant across two consecutive symbols. But, when the channel condition is changed for the two consecutive symbols, the transmit diversity using STBC does not offer good performance due to the large doppler shift. In this paper, we have proposed a interference cancellation scheme for performance enhancement in transmit diversity using STBC over time selective fading channel. Simulation results for various doppler shift rates are presented for the transmit diversity using the proposed scheme.

• Journal of the Korea Society of Computer and Information
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• v.17 no.7
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• pp.77-86
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• 2012

Using OFDM(Orthogonal Frequency Division Multiplexing) provides the same diversity order as MRRC(Maximal Ratio Receiver Combining). It is assumed that fading channel is constant across two consecutive symbols. Unfortunately, when the channel condition is changed for the two consecutive symbols, the OFDM using STBC(Space Time Block Code) does not offer good performance due to the large doppler shift. In this paper, we have proposed a performance enhancement scheme for OFDM using STBC over time-selective fading channel. Simulation results for various doppler shift rates are presented to robust system performance of OFDM due to using our proposed scheme over time-selective fading channel.

• Clinical and Experimental Reproductive Medicine
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• v.25 no.3
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• pp.239-244
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• 1998

The purpose of this study is compare IVF cycle outcome in poor responders between clomiphene citrate (CC) stimulated and controlled ovarian hyperstimulation (COH) protocol. A total of 94 patients responding poorly in previous IVF cycles (estradiol<600 pg/ml or less than 3 oocytes retrieved) subsequently underwent either COH (COH group: 122 cycles, 68 patients) or CC-stimulated cycles (CC group: 43 cycles, 26 patients). CC was administered for five consecutive days starting on cycle day 3 at a dose of 100 mg daily. Serial transvaginal ultrasound examination was done from cycle day 8. Urine was collected $3\sim4$ times before hCG injection for the detection of LH surge. The hCG was administered when serum estradiol reached greater than 150 pg/ml and mean follicle diameter>16 mm. In COH group, ovarian stimulation was done using short protocol (GnRH-a/FSH/HMG/hCG). No difference in age or number of transferred embryos was found between CC group and COH group. COH group had significantly (p<0.05) higher mean peak level of $E_2$ ($810{\pm}112$ vs $412{\pm}55$ pg/ml) and greater number of retrieved oocytes ($3.0{\pm}0.2$ vs $2.0{\pm}0.2$) than CC group. CC group had transferred embryos $(1.8{\pm}0.2)$ compared with $(2.1{\pm}0.2)$ in COH group. However, CC group had higher pregnancy rate than COH group per retrieval [26.9% (7/26) vs 6.2% (6/97)], or per transfer [31.8% (7/22) vs 7% (6/86)]. Although cycle cancellation rate in CC group (48.8%) was higher than that of COH group (21.3%), the pregnancy rate per cycle in CC group was still higher (16.3%) than COH group (4.9%). In addition, implantation rate in CC group was 17.5% (7/40), which was significantly (p<0.01) higher than 3.9% (7/180) in COH group. These data suggest that oocyte and embryo quality are lower in COH cycles of poor responders than CC cycles. We suggest that clomiphene citrate stimulated IVF cycle may be more efficient than COH IVF cycle in poor responders in terms of lower costs and higher pregnancy performance.