Designing an Adaptive Acoustic Modem for Underwater Sensor Networks

Abstract-There is a growing interest in using underwater networked systems for oceanographic applications. These networks often rely on acoustic communication, which poses a number of challenges for reliable data transmission. The underwater acoustic channel is highly variable; each link can experience a vastly conditions, which change according to environmental factors as well as the locations of the communicating nodes. This makes it difficult to ensure reliable communication. Furthermore, due to the high transmit power, the energy consumed in transmitting data is substantial which is exacerbated at lower data rates. The main challenge that we address in this article is how to build a system that provides reliable and energy efficient communication in underwater sensor networks. To this end, we propose an adaptive underwater acoustic modem which changes its parameters according to the situation. We present the design of such a modem and provide supporting results from simulations and experiments

A New Test Data Compression Scheme for Multi-scan Designs

In this paper we present a new test data compression scheme for multi-scan designs to reduce the test data volume and thus the test cost. The proposed method achieves the target in two steps. First a drive bit matrix with less columns is generated by exploiting the compatibilities between the columns of the initial scan bit matrix, as well as the inverse compatibilities and the logic dependencies between the columns of the mid bit matrices. Then a dictionary bit matrix with limited rows is constructed, having the properties that for each row of the drive bit matrix a compatible row exists or can be generated by an XOR operation on multiple rows in the dictionary bit matrix, and the total numbers of rows in the dictionary bit matrix used to compute all the compatible rows is minimal. The rows in the dictionary matrix are encoded to further reduce the number of ATE channels and the test data volume. The experimental results for the large ISCAS 89 benchmarks show that the proposed method significantly reduces test data volume for multi-scan designs.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000246800400028&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Computer Science, Hardware & ArchitectureEICPCI-S(ISTP)

Improved Production of Aspergillus usamii endo-β-1,4-Xylanase in Pichia pastoris via Combined Strategies

A series of strategies were applied to improve expression level of recombinant endo-β-1,4-xylanase from Aspergillus usamii (A. usamii) in Pichia pastoris (P. pastoris). Firstly, the endo-β-1,4-xylanase (xynB) gene from A. usamii was optimized for P. pastoris and expressed in P. pastoris. The maximum xylanase activity of optimized (xynB-opt) gene was 33500 U/mL after methanol induction for 144 h in 50 L bioreactor, which was 59% higher than that by wild-type (xynB) gene. To further increase the expression of xynB-opt, the Vitreoscilla hemoglobin (VHb) gene was transformed to the recombinant strain containing xynB-opt. The results showed that recombinant strain harboring the xynB-opt and VHb (named X33/xynB-opt-VHb) displayed higher biomass, cell viability, and xylanase activity. The maximum xylanase activity of X33/xynB-opt-VHb in 50 L bioreactor was 45225 U/mL, which was 35% and 115% higher than that by optimized (xynB-opt) gene and wild-type (xynB) gene. Finally, the induction temperature of X33/xynB-opt-VHb was optimized in 50 L bioreactor. The maximum xylanase activity of X33/xynB-opt-VHb reached 58792 U/mL when the induction temperature was 22°C. The results presented here will greatly contribute to improving the production of recombinant proteins in P. pastoris

Cloning and Characterization of Farnesyl Diphosphate Synthase Gene Involved in Triterpenoids Biosynthesis from Poria cocos

Poria cocos (P. cocos) has long been used as traditional Chinese medicine and triterpenoids are the most important pharmacologically active constituents of this fungus. Farnesyl pyrophosphate synthase (FPS) is a key enzyme of triterpenoids biosynthesis. The gene encoding FPS was cloned from P. cocos by degenerate PCR, inverse PCR and cassette PCR. The open reading frame of the gene is 1086 bp in length, corresponding to a predicted polypeptide of 361 amino acid residues with a molecular weight of 41.2 kDa. Comparison of the P. cocos FPS deduced amino acid sequence with other species showed the highest identity with Ganoderma lucidum (74%). The predicted P. cocos FPS shares at least four conserved regions involved in the enzymatic activity with the FPSs of varied species. The recombinant protein was expressed in Pichia pastoris and purified. Gas chromatography analysis showed that the recombinant FPS could catalyze the formation of farnesyl diphosphate (FPP) from geranyl diphosphate (GPP) and isopentenyl diphosphate (IPP). Furthermore, the expression profile of the FPS gene and content of total triterpenoids under different stages of development and methyl jasmonate treatments were determined. The results indicated that there is a positive correlation between the activity of FPS and the amount of total triterpenoids produced in P. cocos

A physics-based analytic solution to the MOSFET surface potential from accumulation to strong-inversion region

A physics-based analytic solution to the surface potential from the accumulation to the strong-inversion region has been derived from the complete MOSFET surface potential equation in this paper without any need for smooth functions or simplification by dropping some second-order related terms. Its high accuracy in predicting the surface potential and the transcapacitance under various bias conditions has also been verified by a comparison with the numerical results. The explicit surface potential solution not only leads to a more clear understanding of MOSFET device physics but also provides a better platform to develop the advanced surface potential-based model for the circuit simulation

An analytic model to account for quantum-mechanical effects of MOSFETs using a parabolic potential well approximation

An analytic model to account for the quantum-mechanical effects (QMEs) of the MOSFETs using a parabolic potential well approximation is presented in this paper. Based on the solution of the coupled Schrbdinger and Poisson equations following the Wentzel-Kramer-Brillouin method, a transcendental equation of the subband energy level has been rigorously derived to obtain an approximate analytic solution for the subband energy levels and the inversion charge centroid. Calculated results from the obtained analytical solution are compared with the previous approximate solutions reported in the literature and the numerically simulated data. A good agreement between the analytical and numerical is obtained, proving the validity of the analytic modeling of QMEs

A new analytic method to design multiple floating field limiting rings of power devices

A new analytical method to design the multiple floating field limiting rings (MFFLRs) system of power devices has been proposed in this paper. This analytic method starts from our previous single field limiting theory, extending to predict the MFFLRs's electric field and voltage distribution between multiple rings. Based on this method result, the effects of the junction depth and ring spacing on the voltage and edge field profile have been analyzed. A new simple procedure to predict the optimal spacing and the maximum breakdown voltage has also been presented. The excellent agreement with experimental and numerical analysis proves the applicability of the method presented in optimization of the MFFLRs of the power devices. (c) 2006 Elsevier Ltd. All rights reserved