Variable Block Length Research Articles

Construction of Energy Transfer Systems within Nanosized Polymer Micelles and their Fluorescence Modulation Properties

The nanoparticle-based fluorescence resonance energy transfer (FRET) systems have recently attracted considerable attention due to some of their advantages; however, these systems are structurally more complicated than that of small molecule systems, and the energy transfer behavior for particle systems has been seldom investigated. In this study, we synthesized a series of ABC triblock copolymers that contain hydrophilic poly(ethylene oxide) (PEO), hydrophobic poly(styrene) (PS) and photochromic poly(2-(3-(3',3'-dimethyl-6-nitrospiro(indoline-2',2-[2H-1]benzopyran)-1'-yl)propanoylo-xy)ethyl methacrylate) (PSPMA) blocks by using the sequential two-step atom transfer radical polymerization (ATRP). The amphiphilic micelles made from these copolymers can incorporate a hydrophobic fluorescent dye, the nitrobenzoxadiazolyl derivative (NBD), thus forming a water dispersible energy transfer system with the fluorescent dye NBD as the donor and spiropyran moieties as the potential acceptor. The spectral properties of NBD/triblock copolymers with varied PS block lengths and PSPMA block lengths have been investigated; the results indicate that the length of PS block in triblock copolymers can affect the energy transfer efficiency of the micelle-based fluorescence modulation system, the micelles with moderate PS block length are preferable for forming FRET system with higher energy transfer efficiency, and short PSPMA blocks (less than 5 repetition units) are enough for efficient energy transfer.

Unequal Error Protection: An Information-Theoretic Perspective

An information-theoretic framework for unequal error protection is developed in terms of the exponential error bounds. The fundamental difference between the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bit-wise</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">message-wise</i> unequal error protection ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">UEP</i> ) is demonstrated, for fixed-length block codes on discrete memoryless channels (DMCs) without feedback. Effect of feedback is investigated via variable-length block codes. It is shown that, feedback results in a significant improvement in both <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bit-wise</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">message-wise UEPs</i> (except the single message case for missed detection). The distinction between false-alarm and missed-detection formalizations for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">message-wise UEP</i> is also considered. All results presented are at rates close to capacity.

A linear model for determining coordination of two adjacent signalized intersections

PurposeUrban networks are usually divided into several open or closed sub‐networks. Signal coordination has been recognized as one of the most efficient methods of controlling sub‐networks that have independently optimized timing plans. However, coordinating adjacent intersections in a network is a basic prerequisite to optimizing signal‐timing plans for sub‐networks. This paper aims to develop a linear model to support decisions regarding coordination of adjacent signals.Design/methodology/approachThis paper aims to develop a linear model to support decisions regarding coordination of adjacent signals. The tests of this model which using the field data differ from those for calibration from various roadways, indicating that the model has transferability. Evaluations using microscopic simulation show that the model can objectively determine whether or not to interconnect adjacent signals depending on various traffic demands.FindingsThe model was calibrated by stepwise regression analysis with a total of 195 field samples. This model consists of the dependent variable critical block length (CL) between adjacent intersections, and the independent variables original platoon size (OPS) and platoon completeness ratio (PCR). The calibrated model is shown as following: CL = 689.97 + 6.86 OPS−7.15 PCR.Originality/valueThe proposed model appears to be a viable solution for determining whether to coordinate adjacent signals according to various traffic demands for variously configured roadways. The model shows that a larger OPS or a smaller PCR implies a larger CL. The model also indicates that adjacent signals must be interconnected if they are separated by 690 meters or less. The results also suggest that OPS from 10 to 30 fully disperse at about 800 meters downstream of a stop line. The results support the CL for effectively coordinating adjacent signals, similar to that recommended in the Manual on Uniform Traffic Control Devices. These results may be useful for the effective management of traffic signal networks.

A Simple Converse of Burnashev's Reliability Function

In a remarkable paper published in 1976, Burnashev determined the reliability function of variable-length block codes over discrete memoryless channels with feedback. Subsequently, an alternative achievability proof was obtained by Yamamoto and Itoh via a particularly simple and instructive scheme. Their idea is to alternate between a communication and a confirmation phase until the receiver detects the codeword used by the sender to acknowledge that the message is correct. We provide a converse that parallels the Yamamoto-Itoh achievability construction. Besides being simpler than the original, the proposed converse suggests that a communication and a confirmation phase are implicit in any scheme for which the probability of error decreases with the largest possible exponent. The proposed converse also makes it intuitively clear why the terms that appear in Burnashev's exponent are necessary.

Test Data Compression Based on Variable-to-Variable Huffman Encoding With Codeword Reusability

A new statistical test data compression method that is suitable for IP cores of an unknown structure with multiple scan chains is proposed in this paper. Huffman, which is a well-known fixed-to-variable code, is used in this paper as a variable-to-variable code. The precomputed test set of a core is partitioned into variable-length blocks, which are, then, compressed by an efficient Huffman-based encoding procedure with a limited number of codewords. To increase the compression ratio, the same codeword can be reused for encoding compatible blocks of different sizes. Further compression improvements can be achieved by using two very simple test set transformations. A simple and low-overhead decompression architecture is also proposed.

Nanocatalysts with Tunable Properties Derived from Polystyrene-b-poly(vinyl pyridine) Block Copolymer Templates for Achieving Controllable Carbon Nanotube Synthesis

Chemical vapor deposition, one of major carbon nanotube synthesis techniques, has demonstrated great promise for substrate-based carbon nanotube device applications. To understand carbon nanotube growth mechanisms for achieving controllable synthesis, thereby producing carbon nanotubes with consistent and predefined behavior for materializing their highly touted properties, it is imperative to develop a methodology to create nanocatalyst systems controllably with great tunability. In this paper, a comparative study of polystyrene-b-poly(4-vinyl pyridine) versus polystyrene-b-poly(2-vinyl pyridine) as templates for creating nanocatalysts is presented. Creating uniform and periodically ordered nanocatalyst arrays with tunable size and spacing is demonstrated. A scaling relationship between nanocatalyst spacing and polystyrene block length for polystyrene-b-poly(2-vinyl pyridine) is elicited. The potential of synthesizing nanocatalysts with adjustable composition is discussed. The ability to tailor nanocatalyst size and spacing by varying block lengths has been demonstrated to promote controllable synthesis of carbon nanotubes with adjustable diameter and density. Finally, an example of using such highly controlled nanocatalysts derived from the block copolymer template approach, to study the effect of substrate on carbon nanotubes synthesis, is described.

Poly(ε-caprolactone)-block-poly(ethyleneoxide) -block-poly(ε-caprolactone): Biodegradable triblock copolymer spread at the air–water interface

Synthesis, characterization and behavior at the air–water interface of A–B–A triblock copolymers are reported. The copolymers consist of a poly(ethylene oxide) central block and poly(ε-caprolactone) lateral blocks. The synthesis was controlled in order to obtain central and lateral blocks of variable length. Copolymer characterization was performed by FTIR and 1H NMR spectroscopy, size exclusion chromatography (SEC), and thermal analysis. Monolayers of the copolymers at the air–water interface were obtained by the Langmuir technique and the respective isotherms were obtained by monolayer compression. The limiting area per repeat unit ( A o) and the critical exponent of the excluded volume ( ν) for spread monolayers were obtained. The static elasticity ( ε 0) of the monolayers was also determined. The obtained results allow proposing a schematic model of the orientation of the different blocks during the compression of the respective monolayers.

Fluorinated Bis(phenoxyketimine)titanium Complexes for the Living, Isoselective Polymerization of Propylene: Multiblock Isotactic Polypropylene Copolymers via Sequential Monomer Addition

A series of bis(phenoxyketimine)titanium dichloride complexes were synthesized and evaluated as catalysts for living, isoselective propylene polymerization upon activation with methylaluminoxane (MAO). Catalysts bearing phenoxyketimine ligands with different substituents at the ortho and para positions of the phenolate ring and substituents at the ketimine carbon were investigated. The identity of the ketimine substituent had the largest effect on the activity and isoselectivity of propylene polymerization. Complex 12/MAO promoted the living, isoselective polymerization of propylene ([m4] = 0.73, alpha = 0.94). This catalyst system was used for the synthesis of a number of block copolymers featuring isotactic polypropylene semicrystalline blocks and poly(ethylene-co-propylene) amorphous blocks. Several triblock samples with varying block lengths, a pentablock, and a heptablock copolymer were synthesized. Mechanical testing has revealed that each is elastomeric with elongations at break between approximately 790-1000%.

Synthesis, Characterization and Properties of a Series of Copoly(amide-imide-ether-urethane)s with a New Hard Segment Constituent: Study of the Effect of Hard Segment Content

Two series of thermally modified thermoplastic polyurethane elastomers (TPU)s based on poly(oxytetramethylene glycol) (PTMG) (PT samples), and poly(oxyethylene glycol) (POE) (PO samples) were synthesized from 4,4'-methylene-bis-(4-phenylisocyanate) (MDI) and an aromatic diacid, bis( p-amido benzoic acid)- N-trimellitylimido- L-leucine (BPABTL) (1). The aromatic diacid contains a L-leucine group and a preformed imide ring. The novel diacid was reacted with excess MDI to give an isocyanate terminated oligomer that was subsequently reacted with a polyol to give the poly(amide-imide-ether-urethane)s (PAIEU)s. The properties of the resulting PAIEUs were compared with poly(ether urethane)s without incorporation of BPABTL. The PAIEUs had a constant soft segment (SS) length derived from the polyol (average Mn 1000) but a variable hard block length. Studies were conducted on the effect of hard segment (HS) molar ratio on dynamic mechanical thermal properties, thermal properties, phase separation, crystallinity and solvent resistance of these new PAIEUs.

Efficient Variable Length Block Switching Mechanism

Most popular and widely used packet switch architecture is the crossbar. Its attractive characteristics are simplicity, non-blocking and support for simultaneous multiple packet transmission across the switch. The special version of crossbar switch is Combined Input Crossbar Queue (CICQ) switch. It overcomes the limitations of un-buffered crossbar by employing buffers at each crosspoint in addition to buffering at each input port. Adoption of Crosspoint Buffer (CB) simplifies the scheduling complexity and adapts the distributed nature of scheduling. As a result, matching operation is not needed. Moreover, it supports variable length packets transmission without segmentation. Native switching of variable length packet transmission results in unfairness. To overcome this unfairness, Fixed Length Block Transfer mechanism has been proposed. It has the following drawbacks: (a) Fragmented packets are reassembled at the Crosspoint Buffer (CB). Hence, minimum buffer requirement at each crosspoint is twice the maximum size of the block. When number of ports are more, existence of such a switch is infeasible, due to the restricted memory available in switch core. (b) Reassembly circuit at each crosspoint adds the cost of the switch. (c) Packet is eligible to transfer from CB to output only when the entire packet arrives at the CB, which increases the latency of the fragmented packet in the switch. To overcome these drawbacks, this paper presents Variable Length Block Transfer mechanism. It does not require internal speedup, segmentation and reassembly circuits. Using simulation it is shown that proposed mechanism is superior to Fixed Length Block Transfer mechanism in terms of delay and throughput.

Supramolecular Triblock Copolymers Containing Complementary Nucleobase Molecular Recognition

A novel difunctional alkoxyamine initiator, DEPN2, was synthesized and utilized as an efficient initiator in nitroxide-mediated controlled radical polymerization of triblock copolymers. Complementary hydrogen-bonding triblock copolymers containing adenine (A) and thymine (T) nucleobase-functionalized outer blocks were synthesized. These thermoplastic elastomeric block copolymers contained short nucleobase-functionalized outer blocks (Mn ∼ 1K−4K) and n-butyl acrylate rubber blocks of variable length (Mn ∼ 14K−70K). Hydrogen-bonding interactions were observed for blends of the complementary nucleobase-functionalized block copolymers in terms of increased specific viscosity as well as higher scaling exponents for specific viscosity as a function of solution concentration. In the solid state, the blends exhibited evidence of a complementary A−T hard phase, which formed upon annealing, and dynamic mechanical analysis (DMA) revealed higher softening temperatures. Morphological development of the block copolymer...

A Simulated Annealing Study of Diblock Copolymer Brushes in Selective Solvents

We report a simulated annealing study of the morphology of block copolymer brushes in selective solvents. The investigation is carried out with a lattice model, in which the ends of A-blocks of monodisperse linear AB diblock copolymer flexible chains are grafted regularly on a flat substrate plane with an equal “spacing”. The morphological dependences of the brushes on solvent selectivity, polymer grafting density, and block lengths are investigated systematically. Phase diagrams of the system are constructed. Snapshots, polymer density profiles, and average contact numbers of the blocks are used to provide detailed information about the system. It is observed that multiple morphological transitions can be induced by varying block lengths as well as polymer grafting densities. At very low polymer grafting density, B-pinned or A-legged micelles or “flowerlike” structures are observed when the solvent is selective for the A or the B-blocks, respectively. Morphological transitions as well as size and spacing of the micellar aggregates can be manipulated by varying the block lengths. These predicted phase diagrams are consistent with available experiments and theories.

Prediction of single-cross hybrid performance in maize using haplotype blocks associated with QTL for grain yield

Marker-based prediction of hybrid performance facilitates the identification of untested single-cross hybrids with superior yield performance. Our objectives were to (1) determine the haplotype block structure of experimental germplasm from a hybrid maize breeding program, (2) develop models for hybrid performance prediction based on haplotype blocks, and (3) compare hybrid performance prediction based on haplotype blocks with other approaches, based on single AFLP markers or general combining ability (GCA), under a validation scenario relevant for practical breeding. In total, 270 hybrids were evaluated for grain yield in four Dent x Flint factorial mating experiments. Their parental inbred lines were genotyped with 20 AFLP primer-enzyme combinations. Adjacent marker loci were combined into haplotype blocks. Hybrid performance was predicted on basis of single marker loci and haplotype blocks. Prediction based on variable haplotype block length resulted in an improved prediction of hybrid performance compared with the use of single AFLP markers. Estimates of prediction efficiency (R(2)) ranged from 0.305 to 0.889 for marker-based prediction and from 0.465 to 0.898 for GCA-based prediction. For inter-group hybrids with predominance of general over specific combining ability, the hybrid prediction from GCA effects was efficient in identifying promising hybrids. Considering the advantage of haplotype block approaches over single marker approaches for the prediction of inter-group hybrids, we see a high potential to substantially improve the efficiency of hybrid breeding programs.

Understanding Multicompartment Micelles Using Dissipative Particle Dynamics Simulation

AbstractMulticompartment micelles are a new class of nanomaterials that may find wide applications in the fields of drug delivery, nanotechnology and catalysis. Due to their structural complexity, as well as the wide parameter space to explore, experimental investigations are a difficult task, to which molecular simulation may contribute greatly. In this paper, the application of the dissipative particle dynamics simulation technique to the understanding of multicompartment micelles is introduced, illustrating that DPD is a powerful tool for identifying new morphologies by varying block length, block ratio and solvent quality in a systematic way. The formation process of multicompartment micelles, as well as shear effects and the self‐assembly of nanoparticle mixtures in multicompartment micelles, can also be studied well by DPD simulation. The present work shows that DPD, as well as other simulation techniques and theories, can complement experiments greatly, not only in exploring properties in a wider parameter space, but also by giving a preview of phenomena prior to experiments. DPD, as a mesoscopic dynamic simulation technique, is particularly useful for understanding the dynamic processes of multicompartment micelles at a microscopic level.magnified image

Fast and robust fixed-length packetization algorithm for set partitioning in hierarchical trees bit stream over packet erasure channels

We consider the robust packetization scheme for set par- titioning in hierarchical trees (SPIHT) embedded bit stream over packet erasure channels and propose a fast and robust fixed-length packetization scheme using a two-step process. In the first step, a multiplexer is used to partition the embedded bit stream into multiple variable-length blocks with block sizes close to the fixed packet size. In the second step, a packetized error-resilient entropy code (PEREC) algorithm is proposed to reorganize these variable-length blocks into fixed-size packets to be transmitted over the physical network. Any lost packets have only minor effects on other received packets. Computer simulations show that the proposed method pro- vides both excellent compression performance with fast speed and graceful degradation under serve packet losses. © 2007 SPIE and

Error Exponents for Variable-Length Block Codes With Feedback and Cost Constraints

Variable-length block-coding schemes are investigated for discrete memoryless channels with ideal feedback under cost constraints. Upper and lower bounds are found for the minimum achievable probability of decoding error $P_{e,\min}$ as a function of constraints $R, \AV$, and $\bar \tau$ on the transmission rate, average cost, and average block length respectively. For given $R$ and $\AV$, the lower and upper bounds to the exponent $-(\ln P_{e,\min})/\bar \tau$ are asymptotically equal as $\bar \tau \to \infty$. The resulting reliability function, $\lim_{\bar \tau\to \infty} (-\ln P_{e,\min})/\bar \tau$, as a function of $R$ and $\AV$, is concave in the pair $(R, \AV)$ and generalizes the linear reliability function of Burnashev to include cost constraints. The results are generalized to a class of discrete-time memoryless channels with arbitrary alphabets, including additive Gaussian noise channels with amplitude and power constraints.

Encapsulation of hydrophobic drugs in polymeric micelles through co-solvent evaporation: The effect of solvent composition on micellar properties and drug loading

This study was designed to develop an optimized co-solvent evaporation procedure for the efficient encapsulation of hydrophobic drugs in polymeric micelles of methoxy poly(ethylene oxide)- block-poly(ɛ-caprolactone) (MePEO- b-PCL). MePEO- b-PCL block copolymers having varied MePEO and PCL molecular weights were synthesized, assembled to polymeric micelles, and used for the encapsulation of cyclosporine A (CyA) by a co-solvent evaporation method. The co-solvent composition was varied by changing the type of organic co-solvent (using acetone, acetonitrile and tetrahydrofuran), the ratio of organic to aqueous phase, and their order of addition. Carrier size, morphology and encapsulated CyA levels were defined by dynamic light scattering (DLS), transmission electron microscopy (TEM) and HPLC, respectively, and the effect of co-solvent composition on micellar properties and loaded CyA levels was evaluated. Application of acetone and acetonitrile as the selective co-solvent for the core-forming block led to a decrease in the average diameter of self-assembled structures. When acetone was added to water, a decrease in the ratio of organic to aqueous phase led to an increase in the loading efficiency of CyA in MePEO- b-PCL micelles. A similar trend in CyA loading was observed for MePEO- b-PCL micelles of varied MePEO and PCL block lengths. The ratio of organic to aqueous phase did not affect CyA loading when water was added to acetone. Irrespective of the order of addition, the decrease in the organic to aqueous phase ratio caused a reduction in the average diameter of the empty and CyA loaded micelles. We conclude that the co-solvent evaporation method may be optimized to improve the efficiency of drug encapsulation in polymeric micelles. For CyA encapsulation in MePEO- b-PCL micelles, addition of acetone to water at lower organic to aqueous phase ratio is shown to be the optimum procedure leading to higher drug encapsulation and smaller average diameter for the self-assembled structures.

Bi-directional error-resilient entropy coding (BEREC)

In this paper, a new bi-directional error-resilient entropy coding (BEREC) technique is proposed which uses the beginnings and ends of fixed-length slots to synchronize variable-length blocks of data in two directions. In BEREC frames, every two variable-length blocks of data are grouped to generate one block-pair and placed in one fixed-length slot back-to-back using the similar searching strategy to that of the error-resilient entropy coding (EREC). Therefore, two blocks in one block-pair can be decoded in forward and backward directions separately. Compared to the EREC, the BEREC shows a significantly better performance of error robustness for noisy channels.

Star-Block Copolymers as Templates for the Preparation of Stable Gold Nanoparticles

Gold nanoparticles of improved stability against aggregation were prepared using poly(ethylene oxide)-block-poly(epsilon-caprolactone) (PEO-b-PCL) star-block copolymers. A five-arm star-shaped macroinitiator (PEO) was utilized for the automated parallel controlled ring-opening polymerization of epsilon-caprolactone to prepare a series of PEO-b-PCL star-block copolymers with a constant PEO core linked to PCL blocks of variable length. The PEO core was swelled with KAuCl4 in N,N-dimethylformamide (DMF), and gold nanoparticles were subsequently obtained by reduction with NaBH4. Since the process was always templated by the same PEO core for all investigated polymers, the average dimension of the formed gold nanoparticles was in the same range for all star-block copolymers. In sharp contrast, the size distribution and long-term stability against aggregation of the gold nanoparticles dispersed in DMF were strongly dependent on the PCL block length, confirming the role of PCL blocks as stabilizing blocks for these nanoparticles.

Nine-coded compression technique for testing embedded cores in SoCs

This paper presents a new test-data compression technique that uses exactly nine codewords. Our technique aims at precomputed data of intellectual property cores in system-on-chips and does not require any structural information of cores. The technique is flexible in utilizing both fixed- and variable-length blocks. In spite of its simplicity, it provides significant reduction in test-data volume and test-application time. The decompression logic is very small and can be implemented fully independent of the precomputed test-data set. Our technique is flexible and can be efficiently adopted for single- or multiple-scan chain designs. Experimental results for ISCAS'89 benchmarks illustrate the flexibility and efficiency of the proposed technique.