Cyclic homooligomers of furanoid sugar amino acids

Cyclic homooligomers of mannose-derived furanoid sugar amino acid 1 [H-Maa(Bn(2))-OH] were synthesized by using BOP reagent in the presence of DIPEA under dilute conditions that converted the sugar amino acid monomer directly into its cyclic homooligomers 3a and 4a. The glucose-based sugar amino acid 2 [H-Gaa(Bn(2))-OH] under the same reaction conditions gave a bicyclic lactam 5a as the major product. Cyclic homooligomers of 2 were prepared by cyclizing their linear precursors 6 and 7 leading to the formation of cyclic peptides 8a and 9a, respectively. Conformational analysis by NMR and constrained MD studies revealed that all the cyclic products, 3, 4, 8, and 9, had symmetrical structures. The deprotected cyclic trimer of Maa 3b displayed a conformation in which all the C=O and the N-H bonds of the molecule point in opposite directions. In the deprotected cyclic tetramer of Maa 4b, the COs and NHs were in the plane of the ring with the former pointing to outside and the latter inside the ring. The structure of the cyclic Gaa dimer 8b displayed an unusual six-membered intramolecular hydrogen bond between NH(i)() --> C3-O(i)()(-)(1) and a syn orientation between the C2-H and CO. In this molecule, the C2-hydrogens and the COs can be seen on one side of the ring while the NHs point to the other side. Addition of the bicyclic lactam 5b resulted in the influx of Na(+) ions across the lipid bilayer leading to the dissipation of valinomycin-mediated K(+) diffusion potential.     

Widely programmable high-frequency continuous-time filters indigital CMOS technology

We present design considerations for programmable high-frequency continuous-time filters implemented in standard digital CMOS processes. To reduce area, accumulation MOS capacitors are used as integrating elements. The filter design problem is examined from the viewpoint of programmability. To allow frequency scalability without deterioration of noise performance and of the frequency response shape, we employ a technique called “constant-capacitance scaling,” which assures that even parasitic capacitances remain invariant when transconductors are switched in and out of the filter. This technique is applied to the design of a programmable fourth order Butterworth continuous-time filter with a bandwidth programmable from 60 to 350 MHz implemented in a 0.25-μm digital CMOS process. The filter has a dynamic range of 54 dB, dissipates 70 mW from a 3.3-V supply, and occupies an area of 0.15 mm²     

High-spin structure of yrast-band in 78Kr

Lifetime of levels up to 22⁺, have been measured in ⁷⁸Kr and an oblate shape is assigned to the ground state using the CSM and the configuration dependent shell correction calculations. Calculations further show that ⁷⁸Kr is highly γ-soft nucleus. The experimental Q _t values coupled with theoretical calculations indicate an oblate shape for ⁷⁸Kr at low spins and triaxial shape at higher spins     

Diformylhydrazine as analytical reagent for spectrophotometric determination of iron(II) and iron(III)

The bidentate ligand diformylhydrazine (OHC-HN-NH-CHO), DFH, combines with iron(II) and iron(III) in alkaline media in the pH range 7.3-9.3 to form an intensely colored red-purple iron(III) complex with an absorption maximum at 470 nm. Beer's law is obeyed for iron concentrations from 0.25 to 13 microg mL(-1). The molar absorptivity was in the range 0.3258x10(4)-0.3351x10(4) L mol(-1) cm(-1) and Sandell's sensitivity was found to be 0.0168 microg cm(-2). The method has been applied to the determination of iron in industrial waste, ground water, and pharmaceutical samples.     

Concatenated Trellis Coded Modulation for Quasi-Static Fading Channels

In this paper, we present a novel concatenated trellis coded modulation (CTCM) scheme for limited diversity order fading channels. Examples for such channels include those encountered in indoor wireless networks like IEEE 802.11. It is first shown that when the diversity order afforded by the channel is fixed, bit interleaved coded modulation (BICM) is no longer the best way to encode. We then develop CTCM, which is superior to both BICM and conventional TCM of similar complexities. Unlike conventional TCM where convolutional codes are designed over modulated signal sets, CTCM has TCM concatenated to short length inner codes. Each trellis branch in the TCM now corresponds to a short block-code. We discuss design of good inner codes that allow for simple decoders. CTCM design incorporates useful features of both BICM and conventional TCM. Code design is explained with examples. Simulation results and information theoretic supporting the arguments are shown.     

BEACON: an adaptive set-membership filtering technique with sparseupdates

This paper deals with adaptive solutions to the so-called set-membership filtering (SMF) problem. The SMF methodology involves designing filters by imposing a deterministic constraint on the output error sequence. A set-membership decision feedback equalizer (SM-DFE) for equalization of a communications channel is derived, and connections with the minimum mean square error (MMSE) DFE are established. Further, an adaptive solution to the general SMF problem via a novel optimal bounding ellipsoid (OBE) algorithm called BEACON is presented. This algorithm features sparse updating, wherein it uses about 5-10% of the data to update the parameter estimates without any loss in mean-squared error performance, in comparison with the conventional recursive least-squares (RLS) algorithm. It is shown that the BEACON algorithm can also be derived as a solution to a certain constrained least-squares problem. Simulation results are presented for various adaptive signal processing examples, including estimation of a real communication channel. Further, it is shown that the algorithm can accurately track fast time variations in a nonstationary environment. This improvement is a result of incorporating an explicit test to check if an update is needed at every time instant as well as an optimal data-dependent assignment to the updating weights whenever an update is required     

2/sup 1///sub 2/ step flash A/D convertor

A simple technique for obtaining an extra bit of resolution from a multistep flash A/D convertor is described. It is shown that when used with a conventional multistep convertor, this technique can give significant savings in chip area and power at the expense of a very small increase in conversion time.<>     

Comments on `The impact of NRZ data asymmetry on the performance ofa space telemetry system' by T.M. Nguyen

The commenters point out an error in the continuous power density spectrum given by the terms indicated in the above-titled paper (see ibid., vol.33, no.4, p.343-50, 1991). The continuous component of the spectrum computed directly from an equation given in the paper is shown and differs substantially from that shown in the original figure. Some repercussions as regards other results in the paper are indicated     

A 250-mW, 8-b, 52-Msamples/s parallel-pipelined A/D converter withreduced number of amplifiers

A parallel-pipelined A/D converter with an area and power efficient architecture is described. By sharing amplifiers along the pipeline and also completely eliminating the amplifier from the last stage, an 8-b pipeline is realized using just three amplifiers (instead of seven amplifiers with a conventional pipeline architecture). By using two such pipelines in parallel, a 52 Msamples/s prototype A/D converter that is Intended for a switched digital video application has been implemented in a 0.9-μm CMOS technology. The device occupies 15 mm ² and dissipates 250 mW from a 5 V supply     

Adaptive multiuser detection and beamforming for interferencesuppression in CDMA mobile radio systems

This paper considers the problem of interference suppression in direct-sequence code-division multiple-access (DS-CDMA) systems over fading channels. An adaptive array receiver is presented which integrates multiuser detection, beamforming, and RAKE reception to mitigate cochannel interference and fading. The adaptive multiuser detector is formulated using a blind constrained energy minimization criterion and adaptation is carried out using a novel algorithm based on set-membership parameter estimation theory. The proposed detector overcomes the shortcomings of conventional LMS- and RLS-type algorithms, namely, that of slow convergence and large computational load, respectively. This is especially the case when strong interferers are present or when the number of adaptive weights is relatively large. DS-CDMA systems can have a relatively large number of spatially distributed interferers. Thus beamforming is based on direction-of-arrival (DOA) estimates provided by an approximate maximum-likelihood estimator (DOA-MLE). Unlike previous approaches, the DOA-MLE exploits the structure of the DS-CDMA signaling scheme resulting in robust performance and simple implementation in the presence of angle spreading. The overall method is suitable for real-time implementation and can substantially improve the interference suppression capabilities of a CDMA system