Allosteric Recognition of Homomeric and Heteromeric Pairs of Monosaccharides by a Foldamer Capsule

The recognition of either homomeric or heteromeric pairs of pentoses in an aromatic oligoamide double helical foldamer capsule was evidenced by circular dichroism (CD), NMR spectroscopy, and X‐ray crystallography. The cavity of the host was predicted to be large enough to accommodate simultaneously two xylose molecules and to form a 1:2 complex (one container, two saccharides). Solution and solid‐state data revealed the selective recognition of the α‐⁴C₁‐d ‐xylopyranose tautomer, which is bound at two identical sites in the foldamer cavity. A step further was achieved by sequestering a heteromeric pair of pentoses, that is, one molecule of α‐⁴C₁‐d ‐xylopyranose and one molecule of β‐¹C₄‐d ‐arabinopyranose despite the symmetrical nature of the host and despite the similarity of the guests. Subtle induced‐fit and allosteric effects are responsible for the outstanding selectivities observed.     

A study of the thermal properties of bamboo knitted fabrics

In this research, the thermal properties of bamboo single jersey knitted fabrics have been studied in relation to stitch length and yarn linear density in tex. The objective was to determine the influence of fabric factors like stitch length and the constituent yarn linear density on fabric properties, such as air permeability, thermal conductivity, thermal resistance and relative water vapour permeability. Yarns with linear densities of 19.6, 23.6, 29.5 tex and with the same twist level were used to construct the fabrics of single jersey structure with stitch lengths of 0.27, 0.29 and 0.31 cm. The anticipated increase in air permeability and relative water vapour permeability with decrease in yarn linear density and increase in stitch length was observed. The thermal conductivity and thermal resistance tended in general to increase with constituent yarn linear density but decreased with increase in stitch length.     

Synthesis of β‐Peptides with β‐Helices from New C‐Linked Carbo‐β‐Amino Acids: Study on the Impact of Carbohydrate Side Chains

The design and synthesis of β‐peptides from new C‐linked carbo‐β‐amino acids (β‐Caa) presented here, provides an opportunity to understand the impact of carbohydrate side chains on the formation and stability of helical structures. The β‐amino acids, Boc‐(S)‐β‐Caa_(g)‐OMe 1 and Boc‐(R)‐β‐Caa_(g)‐OMe 2 , having a D ‐galactopyranoside side chain were prepared from D ‐galactose. Similarly, the homo C‐linked carbo‐β‐amino acids (β‐hCaa); Boc‐(S)‐β‐hCaa_(x)‐OMe 3 and Boc‐(R)‐β‐hCaa_(x)‐OMe 4 , were prepared from D ‐glucose. The peptides derived from the above monomers were investigated by NMR, CD, and MD studies. The β‐peptides, especially the shorter ones obtained from the epimeric (at the amine stereocenter C_β) 1 and 2 by the concept of alternating chirality, showed a much smaller propensity to form 10/12‐helices. This substantial destabilization of the helix could be attributed to the bulkier D ‐galactopyranoside side chain. Our efforts to prepare peptides with alternating 3 and 4 were unsuccessful. However, the β‐peptides derived from alternating geometrically heterochiral (at C_β) 4 and Boc‐(R)‐β‐Caa_(x)‐OMe 5 (D ‐xylose side chain) display robust right‐handed 10/12‐helices, while the mixed peptides with alternating 4 and Boc‐β‐hGly‐OMe 6 (β‐homoglycine), resulted in left‐handed β‐helices. These observations show a distinct influence of the side chains on helix formation as well as their stability.     

Approximation algorithms for finding and partitioning unit-disk graphs into co-<Emphasis Type="Italic">k</Emphasis>-plexes

This article studies a degree-bounded generalization of independent sets called co-k-plexes. Constant factor approximation algorithms are developed for the maximum co-k-plex problem on unit-disk graphs. The related problem of minimum co-k-plex coloring that generalizes classical vertex coloring is also studied in the context of unit-disk graphs. We extend several classical approximation results for independent sets in UDGs to co-k-plexes, and settle a recent conjecture on the approximability of co-k-plex coloring in UDGs.     

Reliable Multimedia Transmission Over Cognitive Radio Networks Using Fountain Codes

With the explosive growth of wireless multimedia applications over the wireless Internet in recent years, the demand for radio spectral resources has increased significantly. In order to meet the quality of service, delay, and large bandwidth requirements, various techniques such as source and channel coding, distributed streaming, multicast etc. have been considered. In this paper, we propose a technique for distributed multimedia transmission over the secondary user network, which makes use of opportunistic spectrum access with the help of cognitive radios. We use digital fountain codes to distribute the multimedia content over unused spectrum and also to compensate for the loss incurred due to primary user interference. Primary user traffic is modelled as a Poisson process. We develop the techniques to select appropriate channels and study the trade-offs between link reliability, spectral efficiency and coding overhead. Simulation results are presented for the secondary spectrum access model.     

Dynamic spectrum access in open spectrum wireless networks

One of the reasons for the limitation of bandwidth in current generation wireless networks is the spectrum policy of the Federal Communications Commission (FCC). But, with the spectrum policy reform, open spectrum wireless networks, and spectrum agile radios are set to drive next general wireless networks. In this paper, we investigate continuous-time Markov models for dynamic spectrum access in open spectrum wireless networks. Both queueing and no queueing cases are considered. Analytical results are derived based on the Markov models. A random access protocol is proposed that is shown to achieve airtime fairness. A distributed version of this protocol that uses only local information is also proposed based on homo egualis anthropological model. Inequality aversion by the radio systems to achieve fairness is captured by this model. These protocols are then extended to spectrum agile radios. Extensive simulation results are presented to compare the performances of fixed versus agile radios.     

On the formation of protected gold nanoparticles from AuCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> by the reduction using aromatic amines

Amines are used extensively as reductants and subsequent capping agents in the synthesis of metal nanoparticles, especially gold, due to its affinity to nitrogen. Taking 2-methyl aniline as an example, we show that metal reduction is followed by polymerization of the amine, while part of it covers the nanoparticle surface another fraction deposits in the solution. It is found that the oxidative polymerization of the amine goes in step with the formation of gold nanoparticles. The gold nanoparticles thus formed have a mean diameter of 20 nm. The polymerized amine encapsulates the gold nanoparticle forming a robust shell of about 5 nm thickness, making the gold core inert towards mineralizing agents such as chloroform, bromoform, sodium cyanide, benzylchloride, etc. which react with the naked gold nanoparticles. The deposited polymer is largely protonated, taking up protons from the medium during its formation. Similar results have been observed in the case of aniline also. The materials have been fully characterized by spectroscopy and microscopy.This revised version was published online in August 2005 with a corrected issue number.     

Statistical group testing with queueing involved

We consider a queueing model in which items wait to undergo group testing in batches of sizem. However, if fewer thanm items are present at the beginning of a service, items are tested singly. Ifm or more items are waiting at such an epoch, a group of sizem is tested and, if the group passes the test, allm items leave the system. When a group is found to contain at least one defective item, them items in it are retested individually. An algorithm is developed to compute many steady-state probabilities related to this queue. Comparisons of these probabilities are used to assess the effect of the group sizem on the behavior of the queue of items waiting for testing.This research was supported in part by Grant Nr. ECS-8601203 from the National Science Foundation.     

A convenient general method for the synthesis of hydroxy diacids

Olefinic aldehydes and epoxides with terminal double bonds react with Grignard reagents, and the acetates made from the resulting alcohols undergo double bond cleavage on treatment with RuCl₃·xH₂O in the presence of NaIO₄ to give acetoxy diacids. Hydrolysis with LiOH then affords hydroxy diacids.     

Measurement of High Energy Gross Beta and 40K by Cerenkov Counting in Liquid Scintillation Analyser

The Environmental Survey Laboratory is responsible for the monitoring of radioactivity due to natural and artificially produced radionuclides in a variety of samples available around the nuclear facilities at Tarapur. Standard methods of radiochemical separation and counting are followed to determine -emitters in various matrices. To make the measurement simple and detect lower levels of contamination in some of the matrices, a method was developed to measure the high energy gross -activity primarily due to ⁹⁰Y in borehole water and urine samples of occupational workers by Cerenkov counting in a liquid scintillation analyser. Cerenkov counting results of borehole samples were compared with the total gross -activity measured by a low background beta-counter. The combined measurements were used to evaluate ⁹⁰Sr and ¹³⁷Cs levels without chemical separation or gamma-spectrometry. Cerenkov counting technique was also utilised to evaluate ⁴⁰K in drinking water and intercomparison water samples. The paper presents the methodology and results of a few measurements using the technique.