In Direct Sequence Code Division Multiple Access (DS-CDMA) systems,the chip wave-form affects the implementation,system bandwidth,envelope uniformity,eye pattern and Multiple user Access Interference (MAI). In this pa...In Direct Sequence Code Division Multiple Access (DS-CDMA) systems,the chip wave-form affects the implementation,system bandwidth,envelope uniformity,eye pattern and Multiple user Access Interference (MAI). In this paper,based on an elementary density function of a second order polynomial,a class of second order continuity pulses is proposed. From this class of pulses,we can find some members having faster decaying rate,bigger eye opening,more uniform envelope and stronger anti-MAI capability than the Nyquist waveform. The normalized-bandwidth-pulse-shape-factor product,the decaying rate of the tail of the time waveform,the opening of the eye diagram,and the envelope uniformity of the second order continuity pulses are addressed in the paper that provide the basic information for the selection of the chip pulse for CDMA systems.展开更多
Peptides/proteins aggregation can give rise to pathological conditions of many human diseases.Small partially ordered oligomers formed in the early stage of aggregation,rather than mature fibrils,are thought to be the...Peptides/proteins aggregation can give rise to pathological conditions of many human diseases.Small partially ordered oligomers formed in the early stage of aggregation,rather than mature fibrils,are thought to be the main toxicity agent for the living cell.Thus,understanding the pathway and the underlying physical mechanism in the early stage of aggregation is very important for prevention and treatment of these protein functional diseases.Herein we use all-atom molecular dynamics simulations to study the aggregation of four NFGAIL hexapeptides(NFGAIL peptide is a core segment of human islet amyloid polypeptide and exhibits similar aggregation kinetics as the full-length polypeptide).We observe that the peptide monomers in water mainly adopt non-structural coil configurations;the four peptides which are randomly placed in water aggregate spontaneously to partially ordered oligomer(β-sheets)through dimerization or trimerization,with the dimerization predominated.Both parallel and anti-parallelβ-sheets are observed.The hydrophobic interactions drive the initial peptides associations,and the subsequent conformational fluctuations promote the formation of more hydrogen bonds between the dangling hydrogen sites in the main chains of peptides.展开更多
基金Supported by University Natural Science Research Pro-ject of Jiangsu (No.03KJB510088)National Natural Science Foundation of China (No.60572130).
文摘In Direct Sequence Code Division Multiple Access (DS-CDMA) systems,the chip wave-form affects the implementation,system bandwidth,envelope uniformity,eye pattern and Multiple user Access Interference (MAI). In this paper,based on an elementary density function of a second order polynomial,a class of second order continuity pulses is proposed. From this class of pulses,we can find some members having faster decaying rate,bigger eye opening,more uniform envelope and stronger anti-MAI capability than the Nyquist waveform. The normalized-bandwidth-pulse-shape-factor product,the decaying rate of the tail of the time waveform,the opening of the eye diagram,and the envelope uniformity of the second order continuity pulses are addressed in the paper that provide the basic information for the selection of the chip pulse for CDMA systems.
基金Supported by the National Natural Science Foundation of China under Grant Nos.30870593 and 11204269the China Postdoctoral Science Foundation under Grant No.2012M511351+2 种基金Zhejiang Provincial Natural Science Foundation of China under Grant No.LY12A04007the Fundamental Research Funds for the Central Universitiesthe KYLIN-I Supercomputer in Institute for Fusion Theory and Simulation,Zhejiang University
文摘Peptides/proteins aggregation can give rise to pathological conditions of many human diseases.Small partially ordered oligomers formed in the early stage of aggregation,rather than mature fibrils,are thought to be the main toxicity agent for the living cell.Thus,understanding the pathway and the underlying physical mechanism in the early stage of aggregation is very important for prevention and treatment of these protein functional diseases.Herein we use all-atom molecular dynamics simulations to study the aggregation of four NFGAIL hexapeptides(NFGAIL peptide is a core segment of human islet amyloid polypeptide and exhibits similar aggregation kinetics as the full-length polypeptide).We observe that the peptide monomers in water mainly adopt non-structural coil configurations;the four peptides which are randomly placed in water aggregate spontaneously to partially ordered oligomer(β-sheets)through dimerization or trimerization,with the dimerization predominated.Both parallel and anti-parallelβ-sheets are observed.The hydrophobic interactions drive the initial peptides associations,and the subsequent conformational fluctuations promote the formation of more hydrogen bonds between the dangling hydrogen sites in the main chains of peptides.
