Variable Block Length Research Articles

Synthesis and Characterization of Four-Arm Star Poly(ϵ-caprolactone)-Block-Poly(cyclic-carbonate methacrylate) Copolymers by Combining Ring-Opening Polymerization With Atom Transfer Radical Polymerization

Well-defined four-arm star poly(ϵ-caprolactone)-block-poly(cyclic carbonate methacrylate) (PCL-b-PCCMA) copolymers were synthesized by combining ring-opening polymerization (ROP) with atom transfer radical polymerization (ATRP). First, a four-arm poly(ϵ-caprolactone) (PCL) macroinitiator [(PCL-Br)4] was prepared by the ROP of ϵ-CL catalyzed by stannous octoate at 110°C in the presence of pentaerythritol as the tetrafunctional initiator followed by esterification with 2-bromoisobutyryl bromide. The sequential ATRP of CCMA monomer was carried out by using the (PCL-Br)4 tetrafunctional macroinitiator (MI) and in the presence of CuBr/2, 2′-bipyridyl system in DMF at 80°C with [(MI)]:[CuBr]:[bipyridyl] = 1:1:3 to yield block polymers with controlled molecular weights (Mn (NMR) = 10700 to 27300 g/mol) by varying block lengths and with moderately narrow polydispersities (Mw/Mn = 1.2–1.4). Block copolymers with different PCL: PCCMA copolymer composition such as 50:50, 70:30 and 74:26 were prepared with good yields (48-74%). All these block copolymers were well characterized by NMR, FTIR and GPC and tested their thermal properties by DSC and TGA.

Ring assembly of silica nanospheres mediated by amphiphilic block copolymers with oxyethylene moieties

Amphiphilic block copolymers poly[(2-ethoxyethyl vinyl ether)-block-(2-methoxyethyl vinyl ether)] (EOVE-b-MOVE) induce the ring assembly of silica nanospheres (SNSs, ca. 15 nm) in the liquid phase. Nanorings form with appropriate polymer concentration, pH and temperature. EOVE-b-MOVEs with varying block lengths successfully induce the ring assembly of SNSs, whereas a random copolymer fails, indicating that polymer’s molecular structure critically affects the assembly mode of SNSs. Interestingly, SNSs of a larger size (ca. 30 nm) one-dimensionally assemble into nanochains with these block copolymers under otherwise identical conditions.

Polybenzimidazole Block Copolymers for Fuel Cell: Synthesis and Studies of Block Length Effects on Nanophase Separation, Mechanical Properties, and Proton Conductivity of PEM

A series of meta-polybenzimidazole-block-para-polybenzimidazole (m-PBI-b-p-PBI), segmented block copolymers of PBI, were synthesized with various structural motifs and block lengths by condensing the diamine terminated meta-PBI (m-PBI-Am) and acid terminated para-PBI (p-PBI-Ac) oligomers. NMR studies and existence of two distinct glass transition temperatures (Tg), obtained from dynamical mechanical analysis (DMA) results, unequivocally confirmed the formation of block copolymer structure through the current polymerization methodology. Appropriate and careful selection of oligomers chain length enabled us to tailor the block length of block copolymers and also to make varieties of structural motifs. Increasingly distinct Tg peaks with higher block length of segmented block structure attributed the decrease in phase mixing between the meta-PBI and para-PBI blocks, which in turn resulted into nanophase segregated domains. The proton conductivities of proton exchange membrane (PEM) developed from phosphoric acid (PA) doped block copolymer membranes were found to be increasing substantially with increasing block length of copolymers even though PA loading of these membranes did not alter appreciably with varying block length. For example when molecular weight (Mn) of blocks were increased from 1000 to 5500 then the proton conductivities at 160 °C of resulting copolymers increased from 0.05 to 0.11 S/cm. Higher block length induced nanophase separation between the blocks by creating less morphological barrier within the block which facilitated the movement of the proton in the block and hence resulting higher proton conductivity of the PEM. The structural varieties also influenced the phase separation and proton conductivity. In comparison to meta-para random copolymers reported earlier, the current meta-para segmented block copolymers were found to be more suitable for PBI-based PEM.

Efficacy of oseltamivir treatment started within 5 days of symptom onset to reduce influenza illness duration and virus shedding in an urban setting in Bangladesh: a randomised placebo-controlled trial

Influenza causes substantial morbidity and mortality worldwide. Few data exist for the efficacy of neuraminidase inhibitors, which are the only readily available influenza treatment options, especially in low-income settings. We assessed the efficacy of treatment with the neuraminidase inhibitor oseltamivir to reduce patient illness and viral shedding in people with influenza, in whom treatment was started within 5 days of symptom onset, in an urban setting in Bangladesh. We undertook a double-blind, randomised, controlled trial between May, 2008, and December, 2010. Patients with a positive rapid influenza test identified by surveillance of households in Kamalapur, Bangladesh were randomly allocated on a 1:1 basis to receive oseltamivir or placebo twice daily for 5 days. Randomisation lists for individuals enrolled less than 48 h and 48 h or longer since illness onset were generated with permuted blocks of variable length between two and eight. Participants and study staff were masked to treatment group. Participants provided nasal wash specimens at enrolment and 2, 4, and 7 days later, and were visited daily to record symptoms. All specimens were tested for influenza with reverse-transcriptase PCR, and if the result was positive, we isolated the virus. The primary endpoints were duration of clinical illness and viral shedding in patients treated less than and more than 48 h since illness onset and the frequency of oseltamivir resistance during treatment. Analyses were intention to treat unless otherwise specified. This trial is registered with ClinicalTrials.gov, number NCT00707941. Overall, 1190 people with a median age of 5 years (IQR 2-9) were enrolled: 794 (67%) less than 48 h since symptom onset and 396 (33%) 48 h or longer since symptom onset. 592 participants were assigned to placebo and 598 to oseltamivir. The median duration of symptoms was shorter in the oseltamivir group (3 days, IQR 1-5) than in the placebo group (4 days, 1-6; p=0.01). When stratified by timing of treatment initiation, in participants enrolled 48 h or longer since illness onset, the median duration of symptoms was similar in both groups (oseltamivir 3 days [IQR 2-5], placebo 3 days [1-5]; p=0.04). The median duration of symptoms was reduced by 1 day in the group given oseltamivir who were enrolled less than 48 h since symptom onset compared with those given placebo, but this difference was not significant. In those with all swab specimens (n=1134), oseltamivir significantly reduced virus isolation on days 2 (placebo 374 [66%] vs oseltamivir 321 [56%]; difference 15.2%, 95% CI 9.5-20.8, p=0.0004), 4 (241 [43%] vs 174 [30%]; difference 30.2%, 95% CI 24.6-35.8, p<0.0001), and 7 (68 [12%] vs 36 [6%]; difference 47.5%, 95% CI 44.2-50.8, p=0.0009). In participants enrolled 48 h or longer since illness onset, oseltamivir treatment significantly reduced virus isolation on days 2 and 4, but not day 7. In participants enrolled less than 48 h since illness onset, oseltamivir treatment significantly reduced virus isolation on days 2, 4, and 7. The emergency of resistance to oseltamivir during treatment was rare overall (<1%) and in influenza A H1N1pdm09 viruses (3.9%). Oseltamivir treatment resulted in a modest reduction in the duration of symptoms and virus shedding in people with uncomplicated influenza infections, even when treatment was started 48 h or longer after illness onset. Centers for Disease Control and Prevention (in agreement with the International Centre for Diarrhoeal Disease Research, Bangladesh).

Tenside-Free Biodegradable Polymer Nanofiber Nonwovens by “Green Electrospinning”

This work highlights the formation and use of tenside-free biodegradable polyester dispersions in water for making water stable nanofibers in accordance with the method of “Green Electrospinning”. The concept was to use the amphiphilic block copolyesters poly[(hexamethylene adipate)-block-(methoxypolyethylene glycol)] (PHA-b-MPEG) and poly[(ε-caprolactone)-block-(methoxypolyethylene glycol)] (PCL-b-MPEG) for making tenside-free water dispersions. Different copolymers with varied block lengths were synthesized and converted to high-concentration aqueous dispersions by the solvent displacement method followed by dialysis. The dispersions were electrospun with solid contents of up to 28 wt %. Via addition of small amounts of a high-molecular weight poly(ethylene oxide) as a template polymer, the dispersions were processed to nanofiber nonwovens by electrospinning. Water stable PHA-b-MPEG and PCL-b-MPEG nanofibers were obtained by aqueous extraction of the nanofibers.

Synthesis, characterization, biodegradability and biocompatibility of a temperature-sensitive PBLA-PEG-PBLA hydrogel as protein delivery system with low critical gelation concentration

Temperature-sensitive hydrogels were designed using a series of A-B-A triblock copolymers consisting of poly (ethylene glycol) (PEG) with different molecular weights as the hydrophilic block B and poly (β-butyrolactone-co-lactic acid)(PBLA) with varying block lengths and composition as the hydrophobic block A. The triblock copolymers were synthesized by ring-opening polymerization (ROP) of β-BL and LA in bulk using PEG as an initiator and Sn(Oct)2 as the catalyst. Their chemical structure and molecular characteristics were determined by NMR, GPC and DSC, and the relationship between structure and phase behaviors in aqueous solutions was investigated as well. It was found that the phase behaviors in aqueous solutions including critical micelle concentration (CMC), sol-gel-sedimentation phase transition temperature, gel window width and critical gelation concentration (CGC) are largely dependent on the molecular weight and block length ratio of PEG/PBLA. Most importantly, they show a very low CGC ranging from 4 to 8 wt% because of the introduction of β-BL. Furthermore, the biodegradability and biocompatibility of the hydrogels were evaluated. Finally, lysozyme as a model protein was used to evaluate the ability to deliver protein drugs in a sustained release manner and biologically active form. All results demonstrated that the temperature-sensitive in situ forming hydrogel has a promising potential as sustained delivery system for protein drugs.

Amphiphilic Polymer Conetworks Based on End Group Cross-Linked Poly(2-oxazoline) Homo- and Triblock Copolymers

Novel amphiphilic polymer conetworks (APCNs) were prepared via end group cross-linking. To this end, poly(2-methyloxazoline) (PMOx), poly(2-butyloxazoline) (PBuOx), and the triblock copolymers PMOx-b-PBuOx-b-PMOx were synthesized by cationic ring-opening polymerization in varying block lengths and telechelically modified with N,N-bis(2-aminoethyl)ethylendiamine (TREN). First the cross-linking with 1,4-dibromo-2-butene (DBB) was established for the homopolymers. The swelling of those matches the theoretical value for full cross-linking, indicating that in this way “near perfect” networks could be obtained. Mixtures of the homopolymers and the triblock copolymers were cross-linked with DBB to give APCNs with similar polymer segments but different network topology. AFM showed that all formed APCNs are nanophase separated with slight structural differences in the nanostructures when comparing conetworks with similar composition but different cross-linking strategies. The more drastic difference between APCNs ...

Environmentally friendly PBS-based copolyesters containing PEG-like subunit: Effect of block length on solid-state properties and enzymatic degradation

The use of biodegradable polymers could contribute to mitigate the huge environmental problems caused by the massive use of conventional non-biodegradable plastics, especially in the case of time-limited applications. In this framework, in the present study we propose a new class of multiblock eco-friendly copolyesters containing butylene succinate (BS) and triethylene succinate (TES) sequences. In particular, four copolyesters with the same chemical composition but different block lengths – P(BS10TES10), P(BS5TES5), P(BS3TES3), and P(BS2TES2) – were synthesized by reactive blending. For sake of comparison, homopolymer PBS was also considered. Physicochemical characterization (DSC, WAXS, tensile tests, WCA) of the copolymers synthesized demonstrated that it is possible to control polymer crystallinity, thermal and mechanical properties and wettability of the final product by simply varying block length. As a matter of fact, melting point, crystallinity degree, elastic modulus and surface wettability decreased with the block length; on the contrary, elongation to break significantly increased. Enzymatic hydrolysis performed with lipase from Candida cylindracea ([E]=50U/mL, T=30°C and pH=7.0), showed that copolymers biodegradation is much higher than that of PBS homopolymer. Moreover, copolymers displayed a tunable range of degradation rates, related to their crystallinity degree and hydrophilic/hydrophobic ratio, which render them promising for different time-span applications, ranging from long-term (P(BS10TES10) to very short-term (P(BS2TES2)).

Understanding and tuning the self-assembly of polyether-based triblock terpolymers in aqueous solution

The synthesis and self-assembly of well-defined poly(ethylene oxide)-block-poly(allyl glycidyl ether)-block-poly(tert-butyl glycidyl ether) (PEO-b-PAGE-b-PtBGE) triblock terpolymers with varying block lengths of PAGE and PtBGE are reported. The materials were synthesized using sequential living anionic ring-opening polymerization (AROP). The middle block, PAGE, was further modified by post-polymerization addition of 2,3,4,6-tetra-O-acetyl-1-thio-β-D-galactopyranose via thiol–ene chemistry, resulting in PEO-b-PAGEGal-b-PtBGE. Self-assembly of the terpolymers in aqueous media resulted in the predominant formation of core–shell–corona architectures and the aggregates featured a PtBGE core, a PAGE shell, and a PEO corona. The structures were investigated using dynamic light scattering (DLS) and cryogenic transmission electron microscopy (cryo-TEM) measurements. In addition, the presence of a PEO corona rendered the formed micellar structures thermo-responsive, as demonstrated using turbidimetry. Depending on the ratio of hydrophilic to hydrophobic segments and on the thermal history of the samples, several micellar morphologies could be identified, including spheres of different size, worm-like structures, and vesicles. More important, both reversible and irreversible structural rearrangements could be identified during the heating–cooling cycles.

Parallel design for error-resilient entropy coding algorithm on GPU

The error-resilient entropy coding (EREC) algorithm is an effective method for combating error propagation at low cost in many compression methods using variable-length coding (VLC). However, the main drawback of the EREC is its high complexity. In order to overcome this disadvantage, a parallel EREC is implemented on a graphics processing unit (GPU) using the NVIDIA CUDA technology. The original EREC is a finer-grained parallel at each stage which brings additional communication overhead. To achieve high efficiency of parallel EREC, we propose partitioning the EREC (P-EREC) algorithm, which splits variable-length blocks into groups and then every group is coded using the EREC separately. Each GPU thread processes one group so as to make the EREC coarse-grained parallel. In addition, some optimization strategies are discussed in order to obtain higher performance using the GPU. In the case that the variable-length data blocks are divided into 128 groups (256 groups, resp.), experimental results show that the parallel P-EREC achieves 32× to 123× (54× to 350×, resp.) speedup over the original C code of EREC compiled with the O2 optimization option. Higher speedup can even be obtained with more groups. Compared to the EREC, the P-EREC not only achieves a good speedup performance, but it also slightly improves the resilience of the VLC bit-stream against burst or random errors.

Bit-Wise Unequal Error Protection for Variable-Length Block Codes With Feedback

The bit-wise unequal error protection problem, for the case when the number of groups of bits $\ell$ is fixed, is considered for variable length block codes with feedback. An encoding scheme based on fixed length block codes with erasures is used to establish inner bounds to the achievable performance for finite expected decoding time. A new technique for bounding the performance of variable length block codes is used to establish outer bounds to the performance for a given expected decoding time. The inner and the outer bounds match one another asymptotically and characterize the achievable region of rate-exponent vectors, completely. The single message message-wise unequal error protection problem for variable length block codes with feedback is also solved as a necessary step on the way.

Polysiloxane‐Backbone Block Copolymers in a One‐Pot Synthesis: A Silicone Platform for Facile Functionalization

Block copolymers consisting exclusively of a silicon-oxygen backbone are synthesized by sequential anionic ring-opening polymerization of different cyclic siloxane monomers. After formation of a poly(dimethylsiloxane) (PDMS) block by butyllithium-initiated polymerization of D3, a functional second block is generated by subsequent addition of tetramethyl tetravinyl cyclotetrasiloxane (D4(V) ), resulting in diblock copolymers comprised a simple PDMS block and a functional poly(methylvinylsiloxane) (PMVS) block. Polymers of varying block length ratios were obtained and characterized. The vinyl groups of the second block can be easily modified with a variety of side chains using hydrosilylation chemistry to attach compounds with Si-H bond. Conversion of the hydrosilylation used for polymer modification was investigated.

Easily synthesized novel biodegradable copolyesters with adjustable properties for biomedical applications

Current compositions of biodegradable aliphatic polyesters experience a number of limitations associated with the difficulty of customizing mechanical, physicochemical, and biological properties for different biomedical applications. In this study, we propose a new class of multiblock copolyesters made using butylene succinate (BS) and triethylene succinate (TES). In particular, four copolyesters with the same chemical composition but different block lengths – P(BS18TES18), P(BS9TES9), P(BS4TES4), and P(BS2TES2) – were synthesized by reactive blending. Physicochemical characterization (DSC, WAXS, tensile tests, WCA, hydrolysis experiments) demonstrated that, by simply varying block length, it is possible to control polymer crystallinity, thermal and mechanical properties, wettability, and degradation rate. Copolymers displayed different stiffness, depending on the crystallinity degree, a tunable range of degradation rates, and different surface hydrophilicity. In vitro drug release and cell culture experiments were performed to evaluate the potential of these new copolyesters in the biomedical field. In particular, fluorescein isothiocyanate (FITC) was used as a model molecule to study the release profile of small molecules, and polymer cytocompatibility and fibronectin absorption capability were assessed. Depending on comonomer distribution, the polyesters are capable of releasing FITC in a tailorable manner. Moreover, the newly developed biomaterials are not cytotoxic and they are able to absorb proteins and, consequently, to tailor cell adhesion according to their surface hydrophilicity.

An efficient chaotic source coding scheme with variable-length blocks

An efficient chaotic source coding scheme operating on variable-length blocks is proposed. With the source message represented by a trajectory in the state space of a chaotic system, data compression is achieved when the dynamical system is adapted to the probability distribution of the source symbols. For infinite-precision computation, the theoretical compression performance of this chaotic coding approach attains that of optimal entropy coding. In finite-precision implementation, it can be realized by encoding variable-length blocks using a piecewise linear chaotic map within the precision of register length. In the decoding process, the bit shift in the register can track the synchronization of the initial value and the corresponding block. Therefore, all the variable-length blocks are decoded correctly. Simulation results show that the proposed scheme performs well with high efficiency and minor compression loss when compared with traditional entropy coding.

A variable-length block bootstrap method for multi-site synthetic streamflow generation

The complexity of stochastic streamflow generators limits their practical use, highlighting the need for effective but simpler approaches. An attempt to meet this objective is presented using variable-length bootstrapping (VLB) of annual flows, and a weighted method of fragments for disaggregation and perturbing the bootstrapped annual flows. The perturbations enable generation of annual flows different from those present in the historical record, thereby overcoming one of the main limitations of the classical bootstrap method. The VLB replicates adequately nine historical annual statistics of a five-site problem, and reproduces the annual serial and cross-correlations better than STOMSA—a state-of-the-art parametric generator. The VLB achieves reasonable validation using the sum of minimum flows and the reservoir storage size test. Because of the modification of the monthly flow distribution caused by the weighted averaging of fragments, the VLB cannot be safely used for within-year analysis, but is a potentially robust annual streamflow generator. Citation Ndiritu, J. (2011) A variable length block bootstrap for multi-site synthetic streamflow generation. Hydrol. Sci. J. 56(3), 362–379.

Effect of fragment-based perturbations on the disaggregation performance of a VLB streamflow generator

In order to adequately incorporate measures of reliability in water resources planning, synthetically generated streamflow sequences are often applied in addition to historic time series. In spite of decades of research on parametric stochastic generation methods, their practical use has not been prevalent and some practitioners have been applying much simpler non-parametric bootstrap methods. The traditional bootstrap however does not provide any flows other than those in the historic record and consequently obtains synthetic sequences of low variability. This considerably limits its value as an effective stochastic generator. The Variable Length Block (VLB) bootstrap was recently developed to get rid of this limitation and to enable a more realistic replication of multi-annual flow variability by using blocks of variable length. VLB replicates annual and monthly statistics reasonably but over-estimates the minimum monthly flows and also tends to over-estimate the skewness of monthly flows. VLB also has a tendency to under-estimate serial correlation towards the middle of the year and to over-estimate correlation closer to the end and the beginning of the year. This study presents an attempt to remove these deficiencies of the VLB disaggregation scheme. The disaggregation uses a weighted average of historic fragments (monthly flow/annual flow) obtained from historic matching years with perturbations superimposed to counter the smoothing effect of averaging. The perturbations are subjectively obtained from a triangular distribution and perturbations derived to specifically recover the monthly flow structure (after smoothing) are tried out in the new scheme. These perturbations are obtained as weighted difference of pairs of fragments from historic matching years. Disaggregation using these perturbations is tested on a 5-site stochastic data generation problem. Sixty-eight years of naturalized monthly flows are used and 101 synthetic sequences are generated simultaneously at the 5 sites.The fragment-based perturbations are found to result in gross under-estimation of the minimum monthly flows and to obtain matching performance of the triangular distribution-based perturbations in replicating the other statistics. The gross under-estimation of minimum flows is considered to be the result of inadequate matching of the historic years that uses a loose classification of annual flows based on mean annual runoff. Further work will therefore seek to improve the matching of historic years.

EREC-Based Length Coding of Variable-Length Data Blocks

This paper investigates error-resilient transmission of variable-length-coding bitstream. We propose a method for coding the lengths of variable-length data blocks based on the error-resilient entropy coding (EREC). The idea is converting the problem of coding VLB lengths into the problem of coding the number of blank bits in fixed-length EREC slots. We give the upper bound of side information (SI) cost. To combat error propagation in SI bits, we rearrange SI bits into EREC structure. Detailed decoder design is given, which reveals that the proposed algorithm simplifies EREC decoder design by decomposing the decoder into three serially concatenated components. Experimental results show that the proposed method is economical and robust.

Spiking Neurons With ASNN Based-Methods for the Neural Block Cipher

Problem statement: This paper examines Artificial Spiking Neural Network (ASNN) which inter-connects group of artificial neurons that uses a mathematical model with the aid of block cipher. The aim of undertaken this research is to come up with a block cipher where by the keys are randomly generated by ASNN which can then have any variable block length. This will show the private key is kept and do not have to be exchange to the other side of the communication channel so it present a more secure procedure of key scheduling. The process enables for a faster change in encryption keys and a network level encryption to be implemented at a high speed without the headache of factorization. Approach: The block cipher is converted in public cryptosystem and had a low level of vulnerability to attack from brute, and moreover can able to defend against linear attacks since the Artificial Neural Networks (ANN) architecture convey non-linearity to the encryption/decryption procedures. Result: In this paper is present to use the Spiking Neural Networks (SNNs) with spiking neurons as its basic unit. The timing for the SNNs is considered and the output is encoded in 1’s and 0’s depending on the occurrence or not occurrence of spikes as well as the spiking neural networks use a sign function as activation function, and present the weights and the filter coefficients to be adjust, having more degrees of freedom than the classical neural networks. Conclusion: In conclusion therefore, encryption algorithm can be deployed in communication and security applications where data transfers are most crucial. So this paper, the neural block cipher proposed where the keys are generated by the SNN and the seed is considered the public key which generates the both keys on both sides In future therefore a new research will be conducted on the Spiking Neural Network (SNN) impacts on communication.

The Impact of Antidepressant Treatment on Cognitive Functioning in Depressed Patients with Parkinson's Disease

The Impact of Antidepressant Treatment on Cognitive Functioning in Depressed Patients with Parkinson's Disease

Formation of Nanostructured Poly(dicyclopentadiene) Thermosets Using Reactive Block Polymers

Nanostructured thermosets were prepared by reaction-induced phase separation (RIPS) using a metathesis-cross-linkable monomer in the presence of a metathesis-reactive block polymer. Mixtures of poly(norbornenylethylstyrene-s-styrene)-b-poly(lactide) (PNS−PLA) and dicyclopentadiene (DCPD) in tetrahydrofuran were cross-linked using the second generation Grubbs catalyst. Small-angle X-ray scattering analysis of a series of cured films containing PNS−PLA with varied PLA block lengths and 0−83 wt % DCPD indicated the presence of nanophase-separated disordered morphologies postcuring in most cases. Scanning electron microscopy of cured films after removal of the PLA phase revealed that a majority of the films exhibited a bicontinuous structure. Mechanistic investigations demonstrated that cross-linking the PNS block into the matrix was vital in preventing macrophase separation, and the morphologies observed were relatively unaffected by variations in the concentration of the catalyst. We propose a general mecha...