Increasing Block Length Research Articles

Heptyl mannose decorated glyconanoparticles with tunable morphologies through polymerization induced self-assembly. Synthesis, functionalization and interactions with type 1 piliated E. coli

Mannosylated macro chain transfer agents (MacroCTA) have been used for the RAFT emulsion polymerization of glycidyl methacrylate (GMA) to prepare a series of glyconanoparticles with different morphologies via polymerization-induced self assembly (PISA). Upon increase of PGMA block length and solids content, morphologies progressively evolved from spheres to large vesicles. The epoxide functions located in the core of the nanoparticles were exploited as convenient handles to cross-link the PGMA core and attach red emissive fluorescent tags. Thanks to the presence of multiple n-heptyl α-d-mannose ligands on their shell, the glyconanoparticles strongly interacted with type 1 piliated Escherichia coli leading to the formation of large bacterial clusters.

Effect of Composition and Molecular Structure of Poly(l-lactic acid)/Poly(ethylene oxide) Block Copolymers on Micellar Morphology in Aqueous Solution.

The effect of the hydrophobic block length in diblock (PLLA x- b-PEO113, x = 64, 166, 418) and triblock (PLLA y- b-PEO91- b-PLLA y, y = 30, 52, 120) copolymers of l-lactic acid and ethylene oxide on the structure of micelles prepared by dialysis was studied by wide- and small-angle X-ray scattering in dilute aqueous solution, dynamic light scattering, transmission electron microscopy, atomic force microscopy, and force spectroscopy. It was found that the size of the crystalline PLLA core is weakly dependent on the PLLA block length. In addition to individual micelles, a number of their micellar clusters were detected with characteristic distance between adjacent micelle cores decreasing with an increase in PLLA block length. This effect was explained by the change in the conformation of PEO chains forming the micellar corona because of their overcrowding. Force spectroscopy experiments also reveal a more stretched conformation of the PEO chains for the block copolymers with a shorter PLLA block. A model describing the structure of the individual micelles and their clusters was proposed.

Synthesis and self-assembly of stearic acid-poly (ethylene glycol) block copolymer

Stearic acid-poly(ethylene glycol) (STA-PEG) block copolymers with different hydrophilic segment length were successfully synthesized by the mild esterification. And self-assembly behaviour of the STA-PEGwas followed by fluorescence spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results show that the sphere micelles are formed with the STA block as the core and PEG block as the shell in aqueous solution. In addition, with the increase of PEG block length, the diameters of micelles increase from 148nm to 228nm, and the critical micelle concentration (CMC) decreased from 0.0013mg/ml to 0.0004mg/ml. The very low CMC value indicated that the STA-b-PEG can self-assemble into micelles easily and the formed micelles were stable in very dilute solution

Scaling Laws of Optimal Training Lengths for TDD Massive MIMO Systems

In this study, the scaling laws of optimal training lengths were investigated for time-division duplexing massive multiple-input multiple-output systems. First, the generalized asymptotic achievable rate was derived by taking into account both uplink and downlink training. From the general form, the achievable rates of zero-forcing (ZF) and matched filter (MF) precoders are directly obtained by using the mean and variance of the effective channel. Then, we analyzed the rate gaps of ZF and MF with respect to uplink and downlink training, respectively. According to the analysis of rate gaps, it is shown that the achievable rates are more dominated by the uplink training than downlink training for both ZF and MF. The joint optimization problem for training lengths maximizing the spectral efficiency is formulated as a function of rate gaps. To study the scaling of optimal training lengths with the system parameters, we derived the optimal training lengths as a closed-form expression by using an approximation for the logarithm function. From the analysis, it is shown that the optimal training lengths decrease as the number of antennas increases, and increase as the coherence block length increases. In addition, the optimal training lengths increase as the transmit power increases for ZF, whereas it does not change for MF. Finally, we investigated the superior region for noncoherent detection (which means only statistical information is used for demodulation without downlink training) with the system parameters by comparing the spectral efficiency with and without downlink training.

Moment of inertia for rock blocks subject to bookshelf faulting with geologically plausible density distributions

Moment of Inertia (MOI) for rock blocks that glided smoothly into book-shelf dispositions are deduced considering realistic linear and exponential 3D variations in density along specific axes/directions. Knowing (empirical) algebraic relations of density with depth, which could also be anything other than the exponential and linear variations considered in this work, geoscientists can deduce the MOI by following the same process. MOI for a homogeneous parallelepiped block along any direction is proportional to the length of the block in that direction. However, this simple relation does not hold true for rock blocks with variable densities. Nevertheless, as the block length increases, the MOI along that direction would also increase.

Micellar structures of PAAc/PAAm block copolymers in the processes of doxorubicin encapsulation

Micelle formation of asymmetric block copolymers PAAc-b-PAAm (DBC) and PAAm-b-PAAc-b-PAAm (TBC) comprised poly(acrylic acid) and polyacrylamide were investigated. A steady increase in the critical micellization concentration and the Gibbs free micellization energy of the block copolymers at PAAm block lengthening was observed in every series, thus implying the growth of micelle stability. The existence of two morphological forms of micelles was found and discussed. The encapsulation capability of DBC and TBC micelles with respect to doxorubicin (Dox) is reduced at the increase in PAAm block length. The decrease in the Dox encapsulation degree at the pH lowering is stipulated by a strong stabilization of micellar structures.

Crystallization Behaviors and Regime Kinetics Analysis of Poly(L-lactide)-poly(butylene adipate)-poly(L-lactide) Based Multiblock Thermoplastic Polyurethanes

Poly(L-lactide)-based (PLLA) poly(ester-urethane)s are particularly relevant and gain significant attention due to their environment-friendly degradability and elastomeric shape memory capability. The tensile properties, resilience and degradation are strongly affected by their crystallization. This work was to investigate crystallization behaviors of the poly(L-lactide)-poly(butylene adipate)-poly(L-lactide) (PLLA-PBAPLLA) based thermoplastic polyurethane elastomers (PLAEUs) we synthesized previously. Dynamic scanning calorimetry (DSC) and polarized optical microscopy (POM) in combination with Avrami, Jezioney and Hoffman-Weeks models were used to analyze the impact of the PLLA block length on the crystallization temperature Tc, degree of crystallinity Xc, nucleation and spherulite growth mode and crystallization regime kinetics of the PLAEUs. The results indicate the low melting point poly(butylene adipate) (PBA) block resides in the amorphous domains while the PLLA block resides in both crystalline and amorphous phases. The Xc of the PLAEUs increase with the increased length of the PLLA block (i.e. higher content of PLLA block). The analyses with Avrami and Jezioney models show the PLAEU copolymers follow a disc-like spherulite growth. The covalently bonded PBA block decreases both nucleation velocity and spherulite growth rate in the isothermal crystallization. Such an impact is lessened as PLLA block length increases. The PLLA homopolymers demonstrate crystallization regime transition from II to III at a certain Tc of isothermal crystallization, while the crystallization regime kinetics of PLLA block in the PLAEUs are explained by a single regime III at low molecular weights of PLLA and the transition is restored as the PLLA block length increases (i.e. regime II to III).

A Tight Upper Bound on the Second-Order Coding Rate of the Parallel Gaussian Channel With Feedback

This paper investigates the asymptotic expansion for the maximum rate of fixed-length codes over a parallel Gaussian channel with feedback under the following setting: a peak power constraint is imposed on every transmitted codeword, and the average error probabilities of decoding the transmitted message are non-vanishing as the blocklength increases. The main contribution of this paper is a self-contained proof of an upper bound on the first- and second-order asymptotics of the parallel Gaussian channel with feedback. The proof techniques involve developing an information spectrum bound followed by using Curtiss’ theorem to show that a sum of dependent random variables associated with the information spectrum bound converges in distribution to a sum of independent random variables, thus facilitating the use of the usual central limit theorem. Combined with existing achievability results, our result implies that the presence of feedback does not improve the first- and second-order asymptotics.

Capturing haplotypes in germplasm core collections using bioinformatics

Genomewide data sets of single nucleotide polymorphisms (SNPs) offer great potential to improve ex situ conservation. Two factors impede their use for producing core collections. First, due to the large number of SNPs, the assembly of collections that maximize diversity may be intractable using existing, serial software algorithms. Second, the effect of the natural partitioning of the genome into linked regions, or haplotype blocks, on the optimization of collections, and the capture of diversity, is unknown. To address the first problem, we report the development of a parallel computer program, M+, for identifying optimized core collections from arbitrarily large genotypic data sets on high performance computing systems. With respect to the second problem, we use three exemplar data sets to show that, as haplotype block length increases, the number of accessions necessary to capture a predetermined proportion of genomewide haplotypic variation also increases. This relationship is asymptotic such that the minimum haplotype block length suitable for assembling core collections can be empirically determined, and the number of accessions necessary to capture a given percentage of the haplotypic diversity present in the entire collection can be estimated, even when true haplotype structure is unknown. Additionally, we test whether simple geographic or environmental information can be used to produce core collections with elevated genomewide haplotypic diversity. We find this opportunity to be limited, and dependent on natural history and improvement status.

Synthesis of new multiblock copolymers via cross-metathesis reaction of polytrimethylsilylnorbornene and polycyclooctene

The cross-metathesis reaction between polytrimethylsilylnorbornene and polycyclooctene is investigated for the first time. Using the Grubbs Ru-carbene complex of the first generation, the synthesis of random multiblock copolymers of trimethylsilylnorbornene and cyclooctene is carried out. The effect of the reaction conditions on the block length and thermal and crystalline properties of new copolymers is studied by NMR, GPC, and DSC methods. With the use of in situ 1Н NMR spectroscopy, the kinetics of the crossmetathesis reaction is investigated. As for unsubstituted polynorbornene (Polym. Sci., Ser. B 58, 292 (2016)), the catalyst interacts initially with polycyclooctene, giving a polymer carbene complex [Ru]=PCO. Further, this complex attacks the polytrimethylsilylnorbornene chain via cross reaction with formation of complex [Ru]=PNB-Si and a diblock copolymer of trimethylsilylnorbornene and cyclooctene as reaction products. The subsequent cross reactions form a multiblock copolymer with gradually increasing block length. Throughout the entire process, the concentration of [Ru]=PCO exceeds the concentration of [Ru]=PNB-Si by more than two orders of magnitude. Simultaneously, the total concentration of carbene complexes decreases in time through their decay. The reaction kinetics is satisfactorily described by a model proposed previously for interaction between polycyclooctene and polynorbornene.

Effect of the block length and the molecular weight on the isothermal crystallization behavior of multi-stereoblock poly(lactic-acid)s

Multi-stereoblock PLAs (multi-sb-PLA)s having the controlled block sequences between PLLA and PDLA were synthesized by the chain-extension of tri-stereoblock PLAs. These multi-sb-PLAs only crystallize into the stereocomplex without forming any traces of homo-chiral crystal. The effects of the block length and the total molecular weight on the isothermal crystallization behavior and the higher order structure of the multi-sb-PLAs were investigated. Observation of isothermal crystallization behavior revealed that the multi-sb-PLA with longer blocks and higher molecular weights started the crystallization at a lower temperature within a shorter period of time in a wider temperature range. The crystallization rate increases with increasing block length and the multi-sb-PLA with a longer blocks achieves higher degree of crystal. The multi-sb-PLA with a higher molecular weight forms more complete structure of the spherulite than that with a low molecular weight. Annealing of the amorphous multi-sb-PLA produced sc with two different lamellar thicknesses. One which melts at a higher temperature is a main sc phase with a lamellar thickness merely determined by the block length and the molecular weight regardless of the thermal history. The chains in the amorphous region only crystallized upon annealing and gradually grew with increasing annealing temperature giving some addition to the lamellar thickness of the samples detected by SAXS.

Crystalline inclusion complexes formed between the drug diflunisal and block copolymers

The solid form of drugs plays a central role in optimizing the physicochemical properties of drugs, and new solid forms will provide more options to achieve the desirable pharmaceutical profiles of drugs. Recently, certain drugs have been found to form crystalline inclusion complexes (ICs) with multiple types of linear polymers, representing a new subcategory of pharmaceutical solids. In this study, we used diflunisal (DIF) as the model drug host and extended the guest of drug/polymer ICs from homopolymers to block copolymers of poly(ethylene glycol) (PEG) and poly(ε-caprolactone) (PCL). The block length in the guest copolymers showed a significant influence on the formation, thermal stability and dissolution behavior of the DIF ICs. Though the PEG block could hardly be included alone, it could indeed be included in the DIF ICs when the PCL block was long enough. The increase of the PCL block length produced IC crystals with improved thermal stability. The dissolution profiles of DIF/block copolymer ICs exhibited gradually decreased aqueous solubility and dissolution rate with the increasing PCL block length. These results demonstrate the possibility of using drug/polymer ICs to modulate the desired pharmaceutical profiles of drugs in a predictable and controllable manner.

Influence of hydrophobic block length and ionic liquid on the performance of multiblock poly (arylene ether) proton exchange membrane

The present article includes the synthesis of nanophase-separated poly (arylene ether) multiblock copolymers. A series of poly (arylene ether sulfone) hydrophobic oligomers consisting of bisphenol-A groups were reacted with a disulfonated poly (arylene ether ketone) hydrophilic oligomer containing 4, 4′- bis (4-hydroxyphenyl) valeric acid moieties to prepare multiblock copolymers. The synthesized oligomers and block copolymers were characterized by using FT-IR, 1H NMR spectra and Gel Permeation Chromatography. The membranes obtained by solution casting method exhibited good dimensional and thermal stability. The increase in hydrophobic block length reduced the water uptake and methanol permeability of the membranes. The complexation of multiblock copolymer with ionic liquid (1-butyl-3-methyl-imidazolium tetrafluoroborate) resulted into novel hybrid membranes. These showed enhanced proton conductivity without affecting the mechanical stability. The Fenton's test revealed that the hybrid multiblock membranes were stable towards radical oxidation. The hydrophobic-hydrophilic phase separation was characterized by using tapping mode Atomic Force Microscopy (AFM). The hybrid membranes showed better fuel cell performance than that of pristine membrane.

States of water in proton exchange membranes: Part A - Influence of chemical structure and composition

Disulfonated poly(arylene ether) and polyimide copolymers can phase separate to form nanoscale hydrophilic and hydrophobic domain morphology. Water in these domains has been assigned to three different states, tightly bound, loosely bound and free water. The states of water were characterized using DSC, NMR relaxation and TGA. The chemical structures of the proton exchange membranes were varied in chemical composition, microstructure (random and block) and also regarding functional sulfonic acid groups fixed to the polymer backbones. A strong dependence of the types of water on the ion content and morphology was observed. For the random copolymers, the formation of free water in the system occurs after reaching a certain ion content. For the multi-blocks, in addition to the ion content, free water also develops with increasing block lengths. The formation of continuous morphology in the copolymers was correlated to the onset of free water. Influences of the states of water on PEM transport properties will be reported separately.

Responsive behavior of polyampholyte brushes in electric fields

We conducted coarse-grained molecular dynamics simulations to study the responsive behaviors of polyampholyte brushes (PABs) under external electric fields. The effects of charge sequence, chain rigidity and electric field strength on the conformational transition and local structures of grafted chains were addressed systematically. Without electric field, the calculations indicate that the thickness of the PABs is smaller compared to polyelectrolyte brushes (PEBs). The presence of electric field leads to inconsistency of densities between negatively and positively charged monomers except for the alternating brush. Counterions from the PABs can diffuse inside or outside the brush. Unlike the PABs, to separate the polyelectrolytes and their counterions the electric field needs to overcome the osmotic pressure of counterions. The critical field which induces the extension of the flexible PABs is much larger than the PEBs. Meanwhile, it was also found that the critical field which induces the collapse of the PABs decreases as the block length increases. In the limit of strong field studied, the chains with longer blocks are in a local extended state. For diblock brushes, once oppositely charged blocks in a single chain are separated, the chain will become straighter due to strong electrostatic repulsion in intrablock.

Small angle neutron scattering study on complex coacervate core micelles formed by oppositely charged poly(ethylene oxide-b-allyl glycidyl ether) block copolymer in water

Structure of complex coacervate core micelles in aqueous solution formed by oppositely charged polyelectrolytes based on poly(ethylene oxide-b-allyl glycidyl ether) (PEOAGE) diblock copolymer was investigated using dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Two PEOAGE diblock copolymers are prepared by anionic ring-opening polymerization to provide PEOAGE-1 (Mn,PEO = 5000 g/mol and Mn,PAGE = 2700 g/mol) and PEOAGE-2 (Mn,PEO = 5000 g/mol and Mn,PAGE = 5500 g/mol). PAGE block in the diblock copolymer was functionalized with either primary amine or sulfonate group by thiol-ene click chemistry to generate two oppositely charged block copolyelectrolytes. In addition, unfunctionalized PAGE block is hydrophobic, and therefore PEOAGE block copolymer in aqueous solution forms hydrophobic driven micelles, which is used as control. Combination of DLS and SANS provides micelle dimension including overall micelle size, core radius, and aggregation number. Based on the results, hydrophobic driven micelles show relatively well-defined cores, and morphology changes from sphere to cylinder as PAGE block length increases. Spherical cores in complex coacervate core micelles are significantly swollen by water, and diffusive in comparison to hydrophobic driven micelles.

Impact of Block Length and Temperature over Self-Assembling Behavior of Block Copolymers

Self-assembling behavior of block copolymers having water-soluble portion as one of the blocks plays key role in the properties and applications of the copolymers. Therefore, we have synthesized block copolymers of different block length and investigated their self-assembling behavior with reference to concentration and temperature using surface tension and conductance measurement techniques. The results obtained through both techniques concluded that critical micelles concentration (CMC) was decreased from 0.100 to 0.078 g/dL with the increase in length of water insoluble block and 0.100 to 0.068 g/dL for the increased temperature.ΔGmicwas also decreased with the increase in temperature of the system, concluding that the micellization process was encouraged with the increase in temperature and block length. However,ΔHmicvalues were highest for short block length copolymer. The surface excess concentration obtained from surface tension data concluded that it was highest for short block length and vice versa and was increased with the increase in temperature of the system. However, the minimum area per molecule was largest for highest molecular weight copolymers or having longest water insoluble block and decreases with the increase in temperature.

Scaling Exponent of List Decoders With Applications to Polar Codes

Motivated by the significant performance gains which polar codes experience under successive cancellation list decoding, their scaling exponent is studied as a function of the list size. In particular, the error probability is fixed, and the tradeoff between the block length and back-off from capacity is analyzed. A lower bound is provided on the error probability under $\rm MAP$ decoding with list size $L$ for any binary-input memoryless output-symmetric channel and for any class of linear codes such that their minimum distance is unbounded as the block length grows large. Then, it is shown that under $\rm MAP$ decoding, although the introduction of a list can significantly improve the involved constants, the scaling exponent itself, i.e., the speed at which capacity is approached, stays unaffected for any finite list size. In particular, this result applies to polar codes, since their minimum distance tends to infinity as the block length increases. A similar result is proved for genie-aided successive cancellation decoding when transmission takes place over the binary erasure channel, namely, the scaling exponent remains constant for any fixed number of helps from the genie. Note that since genie-aided successive cancellation decoding might be strictly worse than successive cancellation list decoding, the problem of establishing the scaling exponent of the latter remains open.

Entropy-constrained reflected residual vector quantization: A realization of large block vector quantization

Vector quantization (VQ) techniques have been used for a number of years for developing successful data compression and classification algorithms. Vector quantization is inherently an unsupervised data clustering technique that smartly adopts to the given data statistics and is thus used in large variety of tasks. The gains associated with a VQ system are largely linked to the size of the block used. However, the complexity increases exponentially with an increase in block length. In conventional methods, a dimensional reduction pre-processing step is invoked before the VQ system in order to reduce the block length. For some data sources this may be unacceptable approach such as with hyper-spectral data. Therefore, a large block VQ is needed to fully exploit the linear and non-linear correlation in a data source. We propose an entropy-constrained reflected residual VQ (EC-RRVQ) as one alternative for large block vector quantization. The reflected residual VQ, a type of multistage VQ, has constrained structure with multiple stages having small-size code-books. The use of multiple code-books and a reflection constraint makes the computational complexity linearly depend on the number of stages involved. The linear increase in complexity prompted us to pose EC-RRVQ as a contender in the list of options of large block vector quantization implementation algorithms. Experimental results indicate that good image reproduction quality can be accomplished at relatively low bit rates. The performance of a 64-stage 16×16 EC-RRVQ at 0.175 bits per pixel is 23.75dB with 96 vector distortion calculations per source vector, while the number for previously proposed large-dimensional entropy-constrained residual VQ (EC-RVQ) designed under the same specifications is 21.17dB with 1212 vector distortion calculations per source vector.

Structural Analysis of Efficient Error Control Scheme in PLC Environment

Turbo codes are attractive compared with Low Density Parity Check (LDPC) codes for Forward Error Correction (FEC) applications mainly due to their better performance, specially at low Signal-to-Noise Ratio (SNR) as are common in Powerline channels. Turbo Code is patented hence it is costlier for HomePlug device so it cannot be used. For small block length other code like LDPC which gives better performance as Turbo Code but at low SNR. Complexity of LDPC is increased when block length increase and it works well with low code rate. Complexity of Polar code is not increase even though its block length increases. The objective of this paper is to implement Polar code on PLC Channel to reduce the complexity and improve BER using specific Block Length.