Weight Of Segment Research Articles

Interpenetration enhancing of Chitosan-PEGLM double network (DN) hydrogel and its properties

A series of polylactic acid-polyethylene glycol-polylactic acid diacrylate macromers (PEGLM) were synthesized, and a novel chitosan-PEGLM double network (DN) hydrogel was further successfully fabricated by the sequential interpenetrating technology with highly cross-linked chitosan as the rigid component and PEGLM as the flexible component. Their structures and components were characterized by 1H NMR, FTIR, and XRD. Their fracture morphology was investigated by SEM. It was interesting to found that the compressive strength of hydrogel wound reach its maximum value when the chitosan content was 10%, no matter what the molecular weight of PEGLM component was. What’s more, we found that the compressive strength of 6KL7 could reach 1.07 MPa at gel state, whose PEG segment molecular weight was 6,000, and polymerization degree of PLA was 7. The effects of glutaraldehyde ratio, polymerization degree of PLA, and molecular weight of PEG segment on the mechanical strength of DN hydrogels were also discussed in this article. To further strengthen DN hydrogels, the double network-linear (DNL) hydrogels were fabricated by introducing linear poly(vinyl alcohol) (PVA) into the DN hydrogels. The DN-L hydrogels exhibited better mechanical properties, with the compressive strength up to 1.45 MPa. These hydrogels may have prospective applications in the fields of wound dressing, artificial cartilage and tissue engineering scaffold materials which require high mechanical properties. Open image in new window

Influence of the degree of polymerisation and of the architecture on the elastic properties of new polyurea elastomers

The elastic properties of new polyurea elastomers have been studied by varying the segmental molecular weight and the chemical nature of the polymer end groups showing up to two plateaus.

Analysis on Segment Floating in the Construction of Large-Diameter Crossing-River Shield Tunnel

Segment floating is a common problem met in the construction of large-diameter crossing-river shield tunnel. The factors affecting segment floating are discussed first and analyzed by numerical simulation, including the properties of grouting material, the speed of shield tunneling, grouting pressure difference, the tunnel longitudinal stiffness, frictional force between segment rings and weight of the supporting system. The simulation results indicate that segment floating will reduce by shortening slurry’s initial solidification time, slowing shielding speed, improving the tunnel longitudinal stiffness as well as increasing the frictional force between segment rings. And some measures are given such as applying new rapid-setting slurries, shear pins, rubber mats with high friction coefficient and pre-stressed bolts

Optimized Prefetching Scheme to Support VCR-Like Operations in P2P VoD Applications with Guided Seeks

In Peer-to-Peer (P2P) Video-on-Demand (VoD) streaming systems, supporting free VCR operations is challenging. Prefetching is a good way to improve user experience of VCR interactivity. But most existing P2P VoD prefetching schemes are proposed aimed at those popular videos with large amount of log data, without considering the situation that the videos are unpopular or the popular videos are in their initial phase of release. In this situation, these schemes cannot support user VCR interactivity very well. To address this issue, we propose a new optimized prefetching scheme, called Hybrid Anchor Scheme (HAS), in which fixed anchors and dynamic anchors are merged together. The dynamic anchors are generated based on association rule and segments popularity. Through combining the way of sequential prefetching according to weight of segments and the way of several rounds prefetching, we implement HAS effectively. Extensive simulations validate the proposed prefetching scheme provide shorter seeking latency compared to other prefetching schemes.

Mechanical, Thermal and Morphology Properties of Thermoplastic Polyurethane Copolymers Incorporating α,ω-Dihydroxy-[poly(propyleneoxide)-poly (dimethylsiloxane)-poly(propyleneoxide)] of Varying Poly(propyleneoxide) Molecular Weight

Novel segmented thermoplastic polyurethane (TPU) copolymers were synthesized using two-step solventless bulk polymerization. 4,4’-methylenediphenyl diisocyanate (MDI) and 1,4-Butanediol (BDO) were used to form hard segment of TPU and α,ω-dihydroxy-[poly(propyleneoxide)-poly (dimethylsiloxane)-poly(propyleneoxide)] (α,ω-dihydroxy-(PPO-PDMS-PPO)) was used to form soft segment of TPU, where the molar ratio of the –N=C=O/OH was 1.02 and the hard segment weight percentage was 30%. A series of TPUs were characterized by fourier transform infrared spectroscopy (FT-IR). The investigation of triblock oligomer’s PPO molecular weight impact on the derived TPU’s mechanical properties, thermal performance, surface water repellency and morphology performance was carried by Instron material tester, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), water contact angles (WCA), scanning electron microscope and energy dispersive X-ray spectroscopy (SEM-EDX) and wide angle X-ray diffraction (WAXD), respectively. FT-IR confirmed α,ω-dihydroxy-(PPO-PDMS-PPO) well cooperating into urethane structure and analyzed hydrogen bonding between N-H group with hard segment C=O group and N-H group with soft segment C-O-C group. DSC and WAXD results showed α,ω-dihydroxy-(PPO-PDMS-PPO) segments crystallization. SEM-EDX results showed that the presence of a spherulitic morphology, which arose from the crystallization of the PPO segments. The thermal properties measured by TGA and DSC were slightly affected by molecular weight of PPO and microphase separation. The weight loss of TPUs started between 294°C and 300°C, and Tg was in the range of -70°C to -107°C. TPU copolymers’ surface hydrophobicity property was excellent with WCA range of 95° to 112°. TPU-3 with 1000 molecular weight PPO has the optimized mechanical properties with tensile strength 16.4 MPa and the modulus at 100% elongation 6.2 MPa and elongation 398%.

Preparation and characterization of novel electrospun poly(ε-caprolactone)-based nanofibrous scaffolds

Nanofibrous scaffolds have many advantages that make them excellent candidates for tissue engineering applications. The scaffolds with high surface area to volume ratio favor cell adhesion, proliferation, migration and differentiation. In the present study, the preparation of electrospun poly (ε-caprolactone)-polyethylene glycol-poly (ε-caprolactone) (PCL-PEG-PCL) nanofibers is shown for the first time. PCL-PEG-PCL copolymers were synthesized using a ring-opening polymerization method. The polymers were characterized by FT-IR, 1H NMR and DSC. Nanofibers with mean diameters ranging from 60 to 170 nm were obtained by the electrospinning method. Their morphology was evaluated by scanning electron microscopy (SEM). An MTT assay was used to compare the number of cells in the nanofiber scaffold. It was found that the morphology and diameter of the nanofiber depended on the chemical composition and molecular weight of the PEG segment of the copolymer used for electrospinning. Increasing the molecular weight of PEG blocks from 2000 to 6000 led to a decrease of the diameter of the fibers and the formation of beads.

Gross and Histomorphological Studies of the Oviduct of Native Chicken of Bangladesh

The present study was carried out on the oviduct of laying native chicken of Bangladesh at the age range of 8-12 months old. After dissection, morphological parameters such as total length and weight of oviduct, length and weight at the age range of 8-11 months were determined. For the histological study, after preparation and staining with hematoxylin and eosin, histological layer of oviductal tissues were recognized. The mean length and weight of total oviduct of native chicken were 7.18±4.22 cm and 24.45±1.81 gm respectively. The mean length and weight of oviductal segments, infundibulum (7.18±4.22 cm and 7.18±4.22 gm), magnum (18.40±6.75 cm and 18.40±6.75 gm), isthmus (7.68±3.46 cm and 7.68±3.46 gm), uterus (6.10±2.80 cm and 6.10±2.80 gm) and vagina (6.83±2.82 cm and 6.83±2.82 gm) were measured. Both the length and weight of oviductal segment was progressively increasing from 8-10 months and was decreased at 11 months age. Histological features of oviductal segments varied in regards to the distribution of gland, connective tissues arrangement and mucosal folding. Particularly, the distribution of tubular glands among the segments of oviduct was significantly different. In the magnum and isthmus, populations of tubular glands were higher whereas other segments had limited glands.DOI: http://dx.doi.org/10.3329/bjvm.v12i1.20458 Bangl. J. Vet. Med. (2014). 12 (1): 9-15

Effect of molecular weight of PEG soft segments on photo-stimulated self-healing performance of coumarin functionalized polyurethanes

Polyurethanes consisting of tri-functional homopolymer of hexamethylene diisocyanate (tri-HDI) and polyethylene glycol (PEG) are synthesized, in which photo-reversible coumarin moieties act as pendant groups. Accordingly, the polyurethanes can be repeatedly self-healed under UV lights at room temperature by taking advantages of the photodimerization and photocleavage habits of coumarin. Molecular weight of the soft segment, PEG, is found to be closely related to the healing performance of the polyurethanes. Lower molecular weight PEG that corresponds to higher initial coumarin concentration in the polymer is critical for obtaining higher healing efficiency in the case of the first healing action. Nevertheless, it does not guarantee high reversibility of the photo-remendability during the repeated healing events. In contrast, the polyurethane with moderate molecular weight PEG has achieved balanced performance. Reaction kinetics is less important for the healing effect.

Coach Evaluation Model Based on the Comprehensive Weights

In this paper, an evaluation model is established to choose the best college coach. Taking times background into consideration, the whole previous century is divided into ten segments. Using the method of coefficient of variation and the subjective weighting method in each segment, objective and subjective weight of each basic evaluating factor are obtained respectively. Then based on modified T-test, we integrate them and get the comprehensive weights, which conduct the selection. Thus, one coach is chosen as a representative of each segment.

SU‐E‐T‐250: New IMRT Sequencing Strategy: Towards Intra‐Fraction Plan Adaptation for the MR‐Linac

Purpose:To develop a new sequencer for IMRT planning that during treatment makes the inclusion of external factors possible and by doing so accounts for intra‐fraction anatomy changes. Given a real‐time imaging modality that will provide the updated patient anatomy during delivery, this sequencer is able to take these changes into account during the calculation of subsequent segments.Methods:Pencil beams are generated for each beam angle of the treatment and a fluence optimization is performed. The pencil beams, together with the patient anatomy and the above optimal fluence form the input of our algorithm. During each iteration the following steps are performed: A fluence optimization is done and each beam's fluence is then split to discrete intensity levels. Deliverable segments are calculated for each one of these. Each segment's area multiplied by its intensity describes its efficiency. The most efficient segment among all beams is then chosen to deliver a part of the calculated fluence and the dose that will be delivered by this segment is calculated. This delivered dose is then subtracted from the remaining dose. This loop is repeated until 90% of the dose has been delivered and a final segment weight optimization is performed to reach full convergence.Results:This algorithm was tested in several prostate cases yielding results that meet all clinical constraints. Quality assurance was performed on Delta4 and film phantoms for one of these prostate cases and received clinical acceptance after passing both gamma analyses with the 3%/3mm criteria.Conclusion:A new sequencing algorithm was developed to facilitate the needs of intensity modulated treatment. The first results on static anatomy confirm that it can calculate clinical plans equivalent to those of the commercially available planning systems. We are now working towards 100% dose convergence which will allow us to handle anatomy deformations.This work is financially supported by Elekta AB, Stockholm, Sweden.

MO‐C‐17A‐06: Online Adaptive Re‐Planning to Account for Independent Motions Between Multiple Targets During Radiotherapy of Lung Cancer

Purpose:To quantify interfractional independent motions between multiple targets in radiotherapy (RT) of lung cancer, and to study the dosimetric benefits of an online adaptive replanning method to account for these variations.Methods:Ninety five diagnostic‐quality daily CTs acquired for 9 lung cancer patients treated with IGRT using an in‐room CT (CTVision, Siemens) were analyzed. On each daily CT set, contours of the targets (GTV, CTV, or involved nodes) and organs at risk were generated by populating the planning contours using an auto‐segmentation tool (ABAS, Elekta) with manual editing. For each patient, an IMRT plan was generated based on the planning CT with a prescription dose of 60 Gy in 2Gy fractions. Three plans were generated and compared for each daily CT set: an IGRT (repositioning) plan by copying the original plan with the required shifts, an online adaptive plan by rapidly modifying the aperture shapes and segment weights of the original plan to conform to the daily anatomy, and a new fully re‐optimized plan based on the daily CT using a planning system (Panther, Prowess).Results:The daily deviations of the distance between centers of masses of the targets from the plans varied daily from ‐10 to 8 mm with an average −0.9±4.1 mm (one standard deviation). The average CTV V100 are 99.0±0.7%, 97.9±2.8%, 99.0±0.6%, and 99.1±0.6%, and the lung V20 Gy 928±332 cc, 944±315 cc, 917±300 cc, and 891±295 cc for the original, repositioning, adaptive, and re‐optimized plans, respectively. Wilcoxon signed‐rank tests show that the adaptive plans are statistically significantly better than the repositioning plans and comparable with the reoptimized plans.Conclusion:There exist unpredictable, interfractional, relative volume changes and independent motions between multiple targets during lung cancer RT which cannot be accounted for by the current IGRT repositioning but can be corrected by the online adaptive replanning method.

SU‐E‐J‐20: Adaptive Aperture Morphing for Online Correction for Prostate Cancer Radiotherapy

Purpose:Online adaptive aperture morphing is desirable over translational couch shifts to accommodate not only the target position variation but also anatomic changes (rotation, deformation, and relation of target to organ‐atrisks). We proposed quick and reliable method for adapting segment aperture leaves for IMRT treatment of prostate.Methods:The proposed method consists of following steps: (1) delineate the contours of prostate, SV, bladder and rectum on kV‐CBCT; (2) determine prostate displacement from the rigid body registration of the contoured prostate manifested on the reference CT and the CBCT; (3) adapt the MLC segment apertures obtained from the pre‐treatment IMRT planning to accommodate the shifts as well as anatomic changes. The MLC aperture adaptive algorithm involves two steps; first move the whole aperture according to prostate translational/rotational shifts, and secondly fine‐tune the aperture shape to maintain the spatial relationship between the planning target contour and the MLC aperture to the daily target contour. Feasibility of this method was evaluated retrospectively on a seven‐field IMRT treatment of prostate cancer patient by comparing dose volume histograms of the original plan and the aperture‐adjusted plan, with/without additional segments weight optimization (SWO), on two daily treatment CBCTs selected with relative large motion and rotation.Results:For first daily treatment, the prostate rotation was significant (12degree around lateral‐axis). With apertureadjusted plan, the D95 to the target was improved 25% and rectum dose (D30, D40) was reduced 20% relative to original plan on daily volumes. For second treatment‐fraction, (lateral shift = 6.7mm), after adjustment target D95 improved by 3% and bladder dose (D30, maximum dose) was reduced by 1%. For both cases, extra SWO did not provide significant improvement.Conclusion:The proposed method of adapting segment apertures is promising in treatment position correction, including target translational displacement, rotation and deformation. Additional SWO could improve ROIs dose distribution.

Crystallization Behavior of Stereo Diblock Poly(Lactide)s with Relatively Short Poly(D‐Lactide) Segment from Partially Melted State

Stereo diblock poly(lactide)s (SDB‐PLAs) composed of relatively short poly(D‐lactide) (PDLA) and relatively long poly(L‐lactide) (PLLA) segments were synthesized, and the effects of incorporated short PDLA segments on crystallization behavior of SDB‐PLAs were investigated after melting at 200 °C, at which only homo‐crystallites were melted and stereocomplex (SC) crystallites remained un‐melted. During heating of melt‐quenched samples, SC crystallites and homo‐crystallites were contained and formed for D‐lactyl unit contents above 2.3% and below 28.8%, respectively, whereas after slow cooling from 200 °C, SC crystallites and homo‐crystallites were contained and formed for D‐lactyl unit contents above 0.9% and below 16.6%, respectively. By manipulating the overall molecular weight and the molecular weight of the PDLA segment, the SDB‐PLAs can attain accelerated crystallization and higher crystallinity compared to those of PLLAs.

Study on Microphase Separation of Waterborne Polyurethane by the Infrared Spectroscopy Peak Fitting

A series of waterborne polyurethane (WPU) with different soft segment structures were sythesised, and the effects of the structure and molecular weight of the soft segment on the degree of PU microphase separation were evaluated by the infrared spectroscopy (FTIR) computer peak fitting. The experiment results indicated that phase separation between hard and soft segments of poly (ether–urethane) was more significant than poly (ester–urethane), based on the qualitative analysis on the N–H stretching region of the FTIR spectrum. And the qualitative analysis on the carbonyl stretching region showed that PU with lower soft segment molecular weight had a higher relative amount of hard segment, and possesses higher microphase separation degree. The addition of polyether soft segment PEG had an internal plasticization by actuating the PCD molecular chain. Therefore, it becomes easier for PU to conduct structure adjustment and increased the phase separation degree.

Properties and in vitro evaluation of high modulus biodegradable polyurethanes for applications in cardiovascular stents

This study examined the suitability of a family of biodegradable polyurethanes (PUs) NovoSorb developed for the vascular stent application. These segmented PUs are formulated to be biodegradable using degradable polyester and PU blocks. A series of PUs comprising different hard segment weight percentage ranging from 60 to 100 were investigated. The mechanical properties of the PUs were evaluated before and after gamma sterilization to assess their suitability for vascular implants. The real-time (PBS/37°C/pH 7.4) hydrolytic degradation studies were carried out under sterile conditions and PU glass transition temperature, molecular weight, and mass loss at 3, 6, and 9 months were determined. The viability and growth of Human Umbilical Vein Endothelial Cells (HUVEC) on PU surfaces were determined to assess the effect of PU degradation. The effect of coating of extracellular matrix (ECM) components on cell viability was also investigated. The study showed that the PUs possess excellent mechanical properties exhibiting high tensile strength (41-56 MPa) and tensile modulus (897-1496 MPa). The PU films maintained mechanical strength during the early phase of the degradation but lost strength at latter stages. The unmodified polymer surface of each PU promotes endothelial cell growth and proliferation, with a HUVEC retention rate of >70%.

Direct aperture optimization using an inverse form of back-projection.

Direct aperture optimization (DAO) has been used to produce high dosimetric quality intensity‐modulated radiotherapy (IMRT) treatment plans with fast treatment delivery by directly modeling the multileaf collimator segment shapes and weights. To improve plan quality and reduce treatment time for our in‐house treatment planning system, we implemented a new DAO approach without using a global objective function (GFO). An index concept is introduced as an inverse form of back‐projection used in the CT multiplicative algebraic reconstruction technique (MART). The index, introduced for IMRT optimization in this work, is analogous to the multiplicand in MART. The index is defined as the ratio of the optima over the current. It is assigned to each voxel and beamlet to optimize the fluence map. The indices for beamlets and segments are used to optimize multileaf collimator (MLC) segment shapes and segment weights, respectively. Preliminary data show that without sacrificing dosimetric quality, the implementation of the DAO reduced average IMRT treatment time from 13 min to 8 min for the prostate, and from 15 min to 9 min for the head and neck using our in‐house treatment planning system PlanUNC. The DAO approach has also shown promise in optimizing rotational IMRT with burst mode in a head and neck test case.PACS number: 87.55.D‐

A two-phase approach for mining weighted partial periodic patterns

Partial periodic pattern mining has recently become an important issue in the field of data mining due to its wide applications in many businesses. A partial periodic pattern considers part of but not all the events within a specific period length, repeating with high frequency in an event sequence. Traditional partial periodic pattern mining, however, only considered the frequencies of patterns, but did not consider events that might have different importance. The study thus proposes a weighted partial periodic patterns mining algorithm to resolve this problem. To increase the efficiency, the two-phase upper-bound weighted model based on segmental maximum weights is adopted to prune unimportant candidates in early stage. Then the weighted partial periodic patterns are discovered from the candidate patterns. Finally, the experimental results on synthetic datasets and a real oil dataset show that the weighted partial periodic pattern mining is more practical to assist users for decision making.

Preparation of Electrospun Fibers of Polyethylene Glycol Monomethyl Ether-Co-Polyaniline Blended with Polycaprolactone: Effect of Low Molecular Weight Copolymer on Obtained Fibers

Polyethylene glycol monomethyl ether (mPEG)-co-polyaniline(PANI) is presented and the effect of this low molecular weight copolymer on properties of electrospun fibers obtained from its blends with polycaprolactone (PCL) was investigated. MPEG-co-PANI was synthesized by esterification of mPEG with 4-amino benzoic acid and polymerization of aniline from amine-capped mPEG. Molecular weight of polyaniline segment was determined by 1H NMR spectroscopy. Electroactivity of blend was confirmed by cyclic voltammetry. Field Emission Microscope showed that presence of low molecular weight copolymer with PANI segment resulted in fibers without any beads and average size of micrometer. This novel system offers new possibilities in biomedical applications.

Effects of Oregano Essential Oil Supplementation to Diets of Broiler Chicks with Delayed Feeding After Hatching. Morphological Development of Small Intestine Segments

The study aimed to investigate the effects of dietary supplementation of oregano essential oil (OEO) on the morphological development of small intestine of broilers with different feeding times (immediate, 24, 48 or 72 h posthatching delayed feeding) from d 0 to 14. The diets were supplemented with: no, 250 or 500 mg/kg of the OEO (OEO250 and OEO500, respectively). Fasting for 72 h significantly increased the weight and length of small intestine segments of broilers on d 14. The OEO250 and OEO500 significantly increased the jejunum villus height of chickens fed immediately and the duodenum villus height of broilers fasted for 48 h. The duodenum villus surface area of chickens fasted for 48 h and the ileum villus surface area of broilers fasted for 24 h were significantly increased by the OEO250. The OEO500 significantly enhanced the duodenum villus surface area of broilers fasted for 24 h and their ileum villus surface area fasted for 48 h. The crypt depths of small intestine segments of broilers fasted for 72 h were significantly reduced by OEO250 and OEO500. In conclusion, the dose of phenolic compounds in OEO reaching the small intestine might be enough for protecting the intestinal epithelial cells from damages of toxins and for removing the negative effects of delayed feeding on the morphological development of all the small intestine segments of broiler chicks on d 14.

Mesoporous silicas templated by symmetrical multiblock copolymers through evaporation-induced self-assembly

In this study, we synthesized long-range-ordered mesoporous silicas through evaporation-induced self-assembly (EISA), templated by the ABA-type triblock copolymer PEO-PPO-PEO (F127), and found that the morphologies of the mesostructures could be controlled from a hexagonal cylinder structure to a body-centered cubic (bcc) structure by varying the amount of added tetraethyl orthosilicate (TEOS). In addition, we synthesized the multiblock ABCBA-type copolymer PCL-PEO-PPO-PEO-PCL (PCL-F127-PCL) through ring-opening polymerization (using F127 as the macro-initiator) and then examined the effect of its PCL segments on the morphology of the resulting mesoporous silica. We employed small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and N2 adsorption/desorption isotherms to investigate the mesophase transformations of these mesoporous nanostructures containing various TEOS contents. Upon increasing the molecular weight of the PCL segments, the d-spacing decreased initially, but then increased thereafter. The PCL-F127-PCL multiblock copolymer assembled into an “m”-shaped structure, with the hydrophilic PEO segments folded outside and the hydrophobic PCL and PPO segments aggregated inside. In addition to the relatively strong interactions with the PCL segments, the hydrophilic PPO segments also interacted relatively strongly with the silica matrix, such that some of the PPO segments could enter within it. Using this approach with ABA-type triblock and ABCBA-type multiblock copolymers as templates, we can prepare highly ordered mesoporous silicas having narrow pore size distributions and various mesoporous structures.