在定点DSP上实现浮点运算

DSP结构可以分为定点型(FXP)和浮点型(FLP).虽然FXP型DSP只能实现整数运算,但是它运算速度快,占用资源少,比FLP型成本低.而FXP型DsP使用FLP算法能够实现更高的精度和动态运算范围.对FXP DSP结构支持下的FLP需求不断增长,这主要有以下原因:第一,实现算法代码通常用C/C (采用浮点数形式)编写,将FLP算法转换成FXP格式是比较麻烦的.而将浮点算法移植到DSP平台所花费的时间较少,因而FLP降低了研发成本.另外,常用的算法得益于浮点运算提供的较大的运算范围.最后,在某些情况下应用FXP算法无法获得期望的精度和动态范围.     

Transmural versus nontransmural in situ electrical impedance spectrum for healthy, ischemic, and healed myocardium

Electrical properties of myocardial tissue are anisotropic due to the complex structure of the myocardial fiber orientation and the distribution of gap junctions. For this reason, measured myocardial impedance may differ depending on the current distribution and direction with respect to myocardial fiber orientation and, consequently, according to the measurement method. The objective of this study is to compare the specific impedance spectra of the myocardium measured using two different methods. One method consisted of transmural measurements using an intracavitary catheter and the other method consisted of nontransmural measurements using a four-needle probe inserted into the epicardium. Using both methods, we provide the in situ specific impedance spectrum (magnitude and phase angle) of normal, ischemic, and infarcted pig myocardium tissue from 1 kHz to 1 MHz. Magnitude spectra showed no significant differences between the measurement techniques. However, the phase angle spectra showed significant differences for normal and ischemic tissues according to the measurement technique. The main difference is encountered after 60 min of acute ischeimia in the phase angle spectrum. Healed myocardial tissue showed a small and flat phase angle spectrum in both methods due tothe low content of cells in the transmural infarct scar. In conclusion, both transmural and nontransmural measurements of phase angle spectrum allow the differentiation among normal, ischemic, and infarcted tissue.     

Cognitive radio resource management exploiting heterogeneous primary users and a radio environment map database

The efficient utilization of radio resources is a fundamental issue in cognitive radio (CR) networks. Thus, a novel cognitive radio resource management (RRM) is proposed to improve the spectrum utilization efficiency. An optimization framework for RRM is developed that makes the following contributions: (i) considering heterogeneous primary users (PUs) with multiple features stored in a radio environment map database, (ii) allowing variable CR demands, (iii) assuring interference protection towards PUs. After showing that the optimal solution is computationally infeasible, a suboptimal solution is consequently proposed. Performance evaluation is conducted in terms of total achieved data rate and satisfaction of CR requirements.     

An implementation of the nudged elastic band algorithm and application to the reaction mechanism of HGXPRTase from Plasmodium falciparum

The understanding of transition processes, such as chemical reactions, is a central topic in theoretical molecular science. A common approach for investigating such processes is to calculate paths between reactant and product structures that are representative of the transition. Many approaches have been proposed to determine such paths but, in this paper, we examine the nudged elastic band algorithm which was recently introduced by Jónsson and co-workers and has been used to study a wide range of transition problems. We describe our implementation of the method in the simulation program Dynamo and some modifications to the original algorithm that we found improve its efficiency. The use of the method is illustrated by an application to the reaction mechanism of the enzyme hypoxanthine-guanine-xanthine phosphoribosyltransferase from Plasmodium falciparum.     

Spurious Frequency Rejection

A major problem of superheterodyne receivers is receiver response to undesired frequencies. The magnitude of the spurious response, or the spurious rejection, is computed by assuming that the mixer characteristic is the theoretical exponential form. It is shown that the spurious rejection increases with increased local oscillator power, decreases with increased desired signal power and increases with larger, harmonically derived, spurious responses.     

Ontogenic variation of biologically active metabolites ofPteridium aquilinum (L. Kuhn) pterosins A and B,and ptaquiloside in a bracken population of the tropical andes

A negative correlation has been found between the amounts of pterosins A and B and ptaquiloside per biomass unit, and the growth stage of the blade of bracken. Their concentration decreased progressively from the crozierto the mature frond, where it attained less than 5% of the initial value. The growth was measured following the total blade length, its height, moisture content, and time of emergence from the soil surface. Quantitation of these compounds was achieved by HPLC using a water extraction, methylene chloride treatment, and silica gel microcolumn cleanup sequence. Pterosins were unevenly distributed in the blade, whereas ptaquiloside maintained a constant concentration throughout. Rhizomes contained only minor amounts of these compounds. Their possible role as semiochemicals in bracken is discussed.     

On the Reduction of Interference Due to Common Mode Voltage in Two-Electrode Biopotential Amplifiers

The circuit parameters contributing to common mode voltage interferences in two-electrode amplifiers, both isolated and nonisolated, are reviewed. For the isolated case, a more complete model than that reported in the literature is described, and a new methodology to analyze the problem is introduced. Next, the usual values of the parameters concerned are considered; and by applying the results obtained with the model and method described, some conclusions about the design of this kind of amplifier are drawn.     

Efficient electromagnetic source imaging with adaptive standardized LORETA/FOCUSS

Functional brain imaging and source localization based on the scalp's potential field require a solution to an ill-posed inverse problem with many solutions. This makes it necessary to incorporate a priori knowledge in order to select a particular solution. A computational challenge for some subject-specific head models is that many inverse algorithms require a comprehensive sampling of the candidate source space at the desired resolution. In this study, we present an algorithm that can accurately reconstruct details of localized source activity from a sparse sampling of the candidate source space. Forward computations are minimized through an adaptive procedure that increases source resolution as the spatial extent is reduced. With this algorithm, we were able to compute inverses using only 6% to 11% of the full resolution lead-field, with a localization accuracy that was not significantly different than an exhaustive search through a fully-sampled source space. The technique is, therefore, applicable for use with anatomically-realistic, subject-specific forward models for applications with spatially concentrated source activity.     

"Parallel" and "antiparallel tail-clamps" increase the efficiency of triplex formation with structured DNA and RNA targets

Sequence-specific triple-helix structures can be formed by parallel and antiparallel DNA clamps interacting with single-stranded DNA or RNA targets. Single-stranded nucleic acid molecules are known to adopt secondary structures that might interfere with intermolecular interactions. We demonstrate the correlation between a secondary structure involving the target--a stable stem predicted by in silico folding and experimentally confirmed by thermal stability and competition analyses--and an inhibitory effect on triplex formation. We overcame structural impediments by designing a new type of clamp: "tail-clamps". A combination of gel-shift, kinetic analysis, UV thermal melting and thermodynamic techniques was used to demonstrate that tail-clamps efficiently form triple helices with a structured target sequence. The performance of parallel and antiparallel tail-clamps was compared: antiparallel tail-clamps had higher binding efficiencies than parallel tail-clamps both with structured DNA and RNA targets. In addition, the reported triplex-stabilizing property of 8-aminopurine residues was confirmed for tail-clamps. Finally, we discuss the possible use of this improved triplex technology as a new tool for applications in molecular biology.