Cylindrical Poly Research Articles

Application of a Clapeyron-Type Equation to the Volume Phase Transition of Polymer Gels.

The applicability of the Clapeyron equation to the volume phase transition of cylindrical poly(N-isopropylacrylamide)-based gels under external force is reviewed. Firstly, the equilibrium conditions for the gels under tension are shown, and then we demonstrate that the Clapeyron equation can be applied to the volume phase transition of polymer gels to give the transition entropy or the transition enthalpy. The transition enthalpy at the volume phase transition obtained from the Clapeyron equation is compared with that from the calorimetry. A coefficient of performance, or work efficiency, for a gel actuator driven by the volume phase transition is also defined. How the work efficiency depends on applied force is shown based on a simple mechanical model. It is also shown that the force dependence of transition temperature is closely related to the efficiency curve. Experimental results are compared with the theoretical prediction.

Scaffold vascularization method using an adipose-derived stem cell (ASC)-seeded scaffold prefabricated with a flow-through pedicle

BackgroundVascularization is important for the clinical application of tissue engineered products. Both adipose-derived stem cells (ASCs) and surgical prefabrication can be used to induce angiogenesis in scaffolds. Our aim was to compare the angiogenic potential of ASC-seeded scaffolds combined with scaffold prefabrication with that of non-seeded, non-prefabricated scaffolds.MethodsFor prefabrication, functional blood vessels were introduced into the scaffold using a flow-through pedicle system. ASCs were isolated from rat fat deposits. Three-dimensional-printed cylindrical poly-ε-caprolactone scaffolds were fabricated by fused deposition modelling. Three groups, each containing six rats, were investigated by using non-seeded, ASC-seeded, and osteogenic induced ASC-seeded scaffolds. In each group, one rat was implanted with two scaffolds in the inguinal region. On the right side, a scaffold was implanted subcutaneously around the inferior epigastric vessels (classic prefabrication group). On the left side, the inferior epigastric vessels were placed inside the prefabricated scaffold in the flow-through pedicle system (flow-through prefabrication group). The vessel density and vascular architecture were examined histopathologically and by μCT imaging, respectively, at 2 months after implantation.ResultsThe mean vessel densities were 10- and 5-fold higher in the ASC-seeded and osteogenic induced ASC-seeded scaffolds with flow-through prefabrication, respectively, than in the non-seeded classic prefabricated group (p < 0.001). μCT imaging revealed functional vessels within the scaffold.ConclusionASC-seeded scaffolds with prefabrication showed significantly improved scaffold vasculogenesis and could be useful for application to tissue engineering products in the clinical settings.

Establishment of diagnostic reference levels arising from common CT examinations in Semnan County, Iran

Abstract Objective: The literature has approved that the use of the concept of diagnostic reference level (DRL) as a part of an optimization process could help to reduce patient doses in diagnostic radiology comprising the Computed Tomography (CT) examinations. There are four public/governmental CT centers in the province (Semnan, Iran) and, to our knowledge, after about 12 years since the launch of the first CT scanner in the province there is no dosimetry information on those CT scanners. The aim of this study was to evaluate CT dose indices with the aim of the establishment of the DRL for head, chest, cervical spine, and abdomen-pelvis examinations. Methods: Scan parameters of 381 patients were collected during two months from 4 CT scanners. The CT dose index (CTDI) was measured using a calibrated ionization chamber on two cylindrical poly methyl methacrylate (PMMA) phantoms. For each sequences, weighted CTDI (CTDIw), volumetric CTDI (CTDIv) and dose length product (DLP) were calculated. The 75th percentile was proposed as the criterion for DRL values. Results: Proposed DRL (CTDIw, CTDIv, DLP) for the head, chest, cervical spine, and abdomen-pelvis were (46.1 mGy, 46.1 mGy, 723 mGy × cm), (13.8 mGy, 12.0 mGy, 377 mGy × cm), (40.0 mGy, 40.0 mGy, 572 mGy × cm) and (14.9 mGy, 12.1 mGy, 524 mGy × cm), respectively. Conclusion: Comparison with the others results from the other countries indicates that the head, chest and abdomen-pelvis scans in our region are lower or in the range of the other studies investigated in terms of dose. In the case of cervical spine scanning it’s necessary to review and regulate scan protocols to reach acceptable dose levels.

Regeneration of osteochondral defects in vivo by a cell-free cylindrical poly(lactide-co-glycolide) scaffold with a radially oriented microstructure.

A scaffold with an oriented porous architecture to facilitate cell infiltration and bioactive interflow between neo-host tissues is of great importance for in situ inductive osteochondral regeneration. In this study, a poly(lactide-co-glycolide) (PLGA) scaffold with oriented pores in its radial direction was fabricated via unidirectional cooling of the PLGA solution in the radial direction, following with lyophilization. Micro-computed tomography evaluation and scanning electron microscopy observation confirmed the radially oriented microtubular pores in the scaffold. The scaffold had porosity larger than 90% and a compressive modulus of 4MPa in a dry state. Culture of bone marrow stem cells in vitro revealed faster migration and regular distribution of cells in the poly(lactide-co-glycolide) scaffold with oriented pores compared with the random PLGA scaffold. The cell-free oriented macroporous PLGA scaffold was implanted into rabbit articular osteochondral defect in vivo for 12weeks to evaluate its inductive tissue regeneration function. Histological analysis confirmed obvious tide mark formation and abundant chondrocytes distributed regularly with obvious lacunae in the cartilage layer. Safranin O-fast green staining showed an obvious boundary between the two layers with distinct staining results, indicating the simultaneous regeneration of the cartilage and subchondral bone layers, which is not the case for the random poly(lactide-co-glycolide) scaffold after the same implantation in vivo. The oriented macroporous PLGA scaffold is a promising material for the in situ inductive osteochondral regeneration without the necessity of preseeding cells.

Matching polynomial coefficients and the Hosoya indices of poly(p-phenylene) graphs

ABSTRACTA general approach to determine the matching polynomial (MP) of a graph with two parts connected by an edge is presented in matrix product that is ultimately used in deducing recursion formulas for obtaining the MP coefficients of linear and cylindrical poly(p-phenylene) (PPP) graphs. The Hosoya indices of linear and cylindrical PPPs are derived in terms of that of the two immediately preceding graphs as well as in analytical forms with the use of transfer matrices. Ambient condition density and bulk modulus of linear PPPs with 2–6 phenyl rings have been found to correlate well with the logarithm of their Hosoya indices. Excellent correlations of diameters with the logarithm of Hosoya indices and strain energies with the inverse of the logarithm of Hosoya indices for cylindrical PPPr with r (= 6–16, 18, 20) phenyl rings are obtained. The linear relation between the logarithm of Hosoya indices and diameter and the inverse relation between diameter and strain energy corroborate the fact.

Effect of liquid urea ammonium nitrate application at varying depths on root and shoot growth in wheat (Triticum aestivum)

An experiment was conducted to optimise the desired concentration of urea ammonium nitrate (UAN), a liquid fertilizer, and its suitable depth of application in wheat (Triticum aestivum L.) during 2016-17 in a completely randomized factorial design. The wheat seed germination was affected both on blotting paper and in soil mixed with different UAN:water dilutions. Viability test showed that when soil was mixed with UAN:water dilution ratio of less than 1:20, all the embryos were destroyed. The cultivar HD 2967 was grown in cylindrical poly vinyl chloride tubes where two different dilution ratio of UAN:water, viz. 1:5 (U1) and 1:10 (U2) were used as fertilizer @ 120N kg/ha. The fertilizer was placed at three depths below the seed, i.e. at 1 (D1), 2 (D2) and 3 cm (D3).The shoot and root growth parameters up to 34 days after sowing were recorded. Both fertilizer concentration and depth of its placement significantly affected plant height, root length, root surface area and root tips at 8, 20 and 34 DAS. At higher concentration of UAN (U1), the root growth significantly reduced by about 43% as that of U2 after 8 DAS. However, after 34 DAS, it was reduced to 16% which shows that the plants were able to overcome the initial shock given by high concentration of UAN. Root surface area was maximum at U2D3 (7.04, 18.26 and 40.89 cm2) and minimum at U1D1 (0.91, 7.46 and 15.24 cm2) after 8, 20 and 34 DAS, respectively. Root tip numbers were also affected at 8 DAS. However, it was non-significantly affected by concentration and depths at 34 DAS. Deep placement of fertilizer at 3 cm showed significantly better growth of both root and shoot in plants. Higher fresh root weight at all the growth stages was observed in D3, which was at par to D2 at 8 DAS. Similarly, highest root and shoot growth were observed at U2D2 which was statistically at par to U1D3. The UAN may be applied in 1:10 dilution ratio at 2 cm depth or 1:5 dilution ratio at 3 cm depth below the seed in order to get better growth of seedlings. Hence, sowing machines for wheat shall be developed keeping in mind these application depths of liquid UAN.

Low-Dose Contrast-Enhanced Breast CT Using Spectral Shaping Filters: An Experimental Study.

Iodinated contrast-enhanced X-ray imaging of the breast has been studied with various modalities, including full-field digital mammography (FFDM), digital breast tomosynthesis (DBT), and dedicated breast CT. Contrast imaging with breast CT has a number of advantages over FFDM and DBT, including the lack of breast compression, and generation of fully isotropic 3-D reconstructions. Nonetheless, for breast CT to be considered as a viable tool for routine clinical use, it would be desirable to reduce radiation dose. One approach for dose reduction in breast CT is spectral shaping using X-ray filters. In this paper, two high atomic number filter materials are studied, namely, gadolinium (Gd) and erbium (Er), and compared with Al and Cu filters currently used in breast CT systems. Task-based performance is assessed by imaging a cylindrical poly(methyl methacrylate) phantom with iodine inserts on a benchtop breast CT system that emulates clinical breast CT. To evaluate detectability, a channelized hoteling observer (CHO) is used with sums of Laguerre-Gauss channels. It was observed that spectral shaping using Er and Gd filters substantially increased the dose efficiency (defined as signal-to-noise ratio of the CHO divided by mean glandular dose) as compared with kilovolt peak and filter settings used in commercial and prototype breast CT systems. These experimental phantom study results are encouraging for reducing dose of breast CT, however, further evaluation involving patients is needed.

Heat conduction in poly(N-isopropylacrylamide) hydrogels

Biological tissues are combination of liquids and fibrous solids, therefore polymer hydrogels can be used as model heat transfer system for soft tissues. The 3D network structure of the polymer prevents the convection and the dominant mechanism becomes heat conduction. The main purpose of the present work is to study the effect of network structure on the thermal conduction behavior of soft gels. Cylindrical poly(N-isopropylacrylamide) gel which shows lower critical solution temperature below which the system is completely miscible, whereas above LCST phase separation accours (LCST, [1]). The LCST temperature of the p(NIPA) gel is denoted by Tph throughout this article and is equal to 35 °C.One dimensional heat transfer through the length of the gel cylinder has been experimentally and theoretically studied. The temperature at the bottom of the gel cylinder was suddenly raised above the phase transition temperature. That part of gel cylinder becomes opaque where the temperature exceeds Tph. This defines a visible front that moves forward in the opposite direction to temperature gradient. It was found that our novel technique can be successfully applied to determine heat conductivity and heat diffusivity of loosely cross-linked hydrogels. The kinetics of the moving turbid front was determined and analyzed on the basis of standard 1-d transient heat equation and Stefan's law [2]. It was found that the presence of network structure increases thermal diffusivity compared to pure water. It was also observed that latent heat influences thermal diffusivity.

Dye sorption and swelling of poly(vinyl alcohol) hydrogels in Congo red aqueous solution

The swelling behavior of cylindrical poly(vinyl alcohol) (PVA) hydrogels, prepared by means of γ-ray irradiation technique with different irradiation doses have been investigated. The cylindrical gels with ca. 0.2 mm diameter were immersed in various concentrations of Congo red (CR) solutions, and the time course of the swelling degree of the gels were microscopically measured. The swelling degree was increased with the increase in polymer content and time course, but decreased with increasing the irradiation dose. The sorption experiment of CR onto PVA hydrogels was also carried out. CR concentrations of the solutions before and after the sorption were determined spectrophotometrically. Higher irradiation dose of hydrogels had higher dye uptakes. This result reveals that the gels were strongly crosslinked, and the CR anions were bound to PVA as bridges between the hydroxyl groups of PVA. The effect of incorporation of dye on the chemical structure of PVA hydrogels was studied by using differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. The results of DSC analysis showed that the melting temperatures of CR-PVA hydrogels are significantly lower than that of PVA hydrogels alone. It is possible to conclude that PVA structure has a significant loss of crystallinity when PVA interacts with CR. FTIR spectra of PVA hydrogels and CR-PVA hydrogels showed the absorption regions of the specific functional groups associated with hydroxyl groups of PVA confirming the formation of cross-links between them. The results showed that the interaction between PVA hydrogels and CR affect the swelling and sorption properties of the hydrogels. Open image in new window

Cardinalities of poly(p-phenylene) graphs

Recurrence relation for the cardinalities of linear and cylindrical poly(p-phenylene) (PPP) compounds has been developed that requires the cardinalities of two of their immediate lower homologues. Such recurrence relation reduces into analytical expressions for the cardinalities under transfer matrix formalism. Ambient condition density and bulk modulus of linear PPPs are found to bear excellent linear correlation with the inverse of logarithm of their cardinalities. Topological bond orders obtained from the cardinalities of such PPPs have been found to have good linear correlations with the respective Hückel bond orders.

Analytical eigenspectra of alternant edge-weighted graphs of linear chains and cycles: some applications

Analytical eigenspectra for the graphs of linear chains and cycles with alternant edge weights has been derived with the use of two independent methods, namely, the characteristic polynomial and the graph squaring. In the former method the rotational symmetry and the trigonometric identity have been exploited. These methods along with the expressions of eigenspectra so obtained have been found to be very useful in expressing analytical eigensolutions of some important as well as novel benzenoids, for example, linear p-methylene poly(p-phenylene), cylindrical poly(p-phenylene), zigzag edge graphene, carbon nanotube and carbon nanotori. Some of these eigensolutions have been analysed in exploring some consequences thereof.

MO‐D‐134‐10: Using HVL and KVp to Portray An X‐Ray Source for Dose Calculations in CT

Purpose: To show that the nominal peak tube voltage potential (kVp) and measured half‐value layer (HVL) are sufficient to generate energy spectra and fluence profiles for fast and accurate machine‐specific dose computations in Computed Tomography (CT). Methods: Spatial variation of the x‐ray source spectrum was found by measuring HVL across the internal bowtie filter axis and using the nominal kVp settings and third‐party software Spektr to generate the spectra. The beam fluence was calculated by multiplying in‐air dose measurements along the filter axis with the integral product of the spectra and the in‐air NIST mass‐energy attenuation coefficients. Dose calculations were performed using a previously validated in‐house hybrid deterministic and stochastic kV x‐ray dose computation algorithm (kVDoseCalc). To ensure dose convergence while minimizing calculation time, we examined the sensitivity of kVDoseCalc to the number of photons seeded. We modeled the source of a Philips Brilliance Big Bore CT scanner for 90, 120, and 140 kVp settings. Doses measured using a Farmer‐type Capintec ion chamber (0.6 cc) placed in a cylindrical poly methyl methacrylate (PMMA) phantom were compared to those computed with kVDoseCalc. Results: The number of photons seeded required to keep the average statistical uncertainty in dose less than .1% was found to be 1.25 million. The average percent difference between calculation and measurement pooled over all 12 positions in the phantom was found to be 1.68%, 1.60%, and 1.25% for 90, 120, and 140 kVp, respectively. The maximum percent difference between calculation and measurement was less than 3.64% pooled over all energies and measurement positions. Thirty‐one out of a total of 36 simulation conditions were within the experimental uncertainties associated with measurement reproducibility and chamber volume effects. Conclusion: Our source characterization technique, which derives incident fluence and spectra from measurements of HVL across the bowtie profile, is sufficient for accurate machine‐specific CT dose computations.

Additional imaging dose from kV-cone beam computed tomography

Objectives: The objective of the following study is to provide the quantitative imaging dose dependency on treatment region and scanning settings concerning the additional imaging doses from kV-cone beam computed tomography (CBCT) scans. Materials and Methods: Patient imaging dose measurements were performed using head and body cylindrical poly methyl metha acrylate (PMMA) phantoms, 0.125 cm 3 ionization chamber and electrometer and metal oxide semiconductor field effect transistor dosimeter. Results: The dose values for the pelvis phantom was found vary from 8.6 mGy to 22.2 mGy for 120 kVp, 1040 mAs. For the head phantom, the dose values vary from 0.71 mGy to 1.37 mGy for 100 kVp, 36.1 mAs. For head scanning mode, the peripheral doses are greater than the central axis doses by a magnitude of 1.3-2 with the largest found consistently at 3 o'clock position of the PMMA head phantom. For the pelvis scan, the peripheral doses are greater than the central doses by a magnitude of 2.1-2.6 with the largest found consistently at 9 o'clock position of the PMMA pelvis phantom. Conclusion: One should be aware of the additional imaging dose with daily kV-CBCT when setting up CBCT scanning protocol and should try to reduce the high voltage usage since reduction of the tube voltage can reduce radiation dose to the patient, especially for pediatric patients.

Development of a nanoparticle-based influenza vaccine using the PRINT® technology

Historically it is known that presentation of vaccine antigens in particulate form, for a wide range of pathogens, has clear advantages over the presentation of soluble antigen alone [J.C. Aguilar, E.G. Rodriguez, Vaccine adjuvants revisited. Vaccine 25 (2007) 3752–3762, M. Singh, D. O'Hagan, Advances in vaccine adjuvants. Nature Biotechnology 17 (1999) 1075–1081]. Herein we describe a novel particle-based approach, which independently controls size, shape, and composition to control the delivery and presentation of vaccine antigen to the immune system. Highly uniform particles were produced using a particle molding technology called PRINT® (Particle Replication in Non-wetting Templates) which is an off-shoot of imprint lithography [J Am Chem Soc 127 (2005) 10096–10100, J Am Chem Soc 126 (2004) 2322–2323, Chem Soc Rev 35 (2006) 1095–1104, J Am Chem Soc 130 (2008) 5008–5009, J Am Chem Soc 130 (2008) 5438–5439, Polymer Reviews 47 (2007) 321–327, Acc Chem Res 41 (2008) 1685–1695, Acc Chem Res 44 (10) (2011) 990–998]. Cylindrical (diameter [d]=80nm, height [h]=320nm) poly (lactide-co-glycolide) (PLGA) based PRINT particles were designed to electrostatically bind commercial trivalent injectable influenza vaccine. In a variety of blended PLGA formulations, these particles were safe and showed enhanced responses to influenza hemagglutinin in murine models. From the Clinical EditorShape is one of the determining factors in interactions of nanoparticles with their biologic environment. PRINT technology is able to fabricate nearly uniform nanoparticles and this technology is tested here in murine models to effectively deliver influenza vaccine.

Catalytic Activity of Macroion–Porphyrin Nanoassemblies

A new type of catalytically active self-assembled nanostructures in aqueous solution is presented. Polyelectrolyte-porphyrin nanoscale assemblies consisting of anionic cylindrical poly(styrene sulfonate) brush molecules and cationic tetravalent meso-tetrakis(4-N-methyl-pyridinium)porphyrin (TMPyP) or meso-tetrakis(4-(trimethyl-ammonium)phenyl)-porphyrin (TAPP), respectively, exhibit up to 8-fold higher catalytic activity with regard to light induced iodide oxidation than the corresponding porphyrins without polymeric template. This is particularly interesting because a general concept rather than a specific binding motif is exploited. The approach introduced here hence is attractive due to its facility and versatility and bears potential, for example, in light harvesting and energy conversion.

Packing of Cylindrical Keggin-Type Polyoxometalate Hybrid Micelles as a Function of Aspect Ratio

Abstract The packing of cylindrical Keggin-Type polyoxometalate hybrid micelles and its influence on specific surface area was studied as function of aspect ratio. Core-crosslinked cylindrical poly(butadiene-block-2-vinylpyidine) (PB-b-P2VP) micelles were used as templates for mesostructuring phosphomolybdic acid (H3PMo12O40). Prior to hybrid formation the length of the cylindrical PB-b-P2VP micelles was adjsuted by sonication. Depending on the aspect ratio of the cylinders a remarkable and unexpected evolution of specific surface areas was observed. The changes in the specific surface area could be explained by a series of scanning electron microscopy and transmission electron microscopy images and were related to the packing of the 1D nanoobjects.

Regeneration of Completely Transected Spinal Cord Using Scaffold of Poly(D,L-Lactide-co-Glycolide)/Small Intestinal Submucosa Seeded with Rat Bone Marrow Stem Cells

Using a complete spinal cord transection model, the present study employed a combinatorial strategy comprising rat bone marrow stem cells (rBMSCs) and polymer scaffolds to regenerate neurological function after spinal cord injury (SCI) of different lengths. SCI models with completely transected lesions were prepared by surgical removal of 1 mm (SC1) or 3 mm (SC3) lengths of spinal cord in the eighth-to-ninth spinal vertebrae, a procedure that resulted in bilateral hindlimb paralysis. A cylindrical poly(D,L-lactide-co-glycolide)/small intestinal submucosa scaffold 1 or 3 mm in length with or without rBMSCs was fitted into the completely transected lesion. Rats in SC1 and SC3 groups implanted with rBMSC-containing scaffolds received Basso-Beattie-Bresnahan scores for hindlimb locomotion of 15 and 8, respectively, compared with ∼3 for control rats in SC1-C and SC3-C groups implanted with scaffolds lacking rBMSCs. The amplitude of motor-evoked potentials recorded in the hindlimb area of the sensorimotor cortex after stimulation of the injured spinal cord averaged ∼100 μV in SC1-C and 10-50 μV in SC3-C groups at 4 weeks, and then declined to nearly zero at 8 weeks. In contrast, the amplitude of motor-evoked potentials increased from ∼300 to 350 μV between 4 and 8 weeks in SC1 rats and from ∼200 to ∼250 μV in SC3 rats. These results demonstrate functional recovery in rBMSC-transplanted rats, especially those with smaller defects. Immunohistochemically stained sections of the injury site showed clear evidence for axonal regeneration only in rBMSC-transplanted SC1 and SC3 models. In addition, rBMSCs were detected at the implanted site 4 and 8 weeks after transplantation, indicating cell survival in SCI. Collectively, our results indicate that therapeutic rBMSCs in a poly(D,L-lactide-co-glycolide)/small intestinal submucosa scaffold induced nerve regeneration in a complete spinal cord transection model and showed that functional recovery further depended on defect length.

Study on hydrophilic 5-fluorouracil release from hydrophobic poly(ϵ-caprolactone) cylindrical implants

Hydrophilic 5-fluorouracil (5-FU) loaded cylindrical poly(ϵ-caprolactone) (PCL) implants with different implant diameters (2, 4 and 8 mm), different drug loadings (25% and 50%) and end-capping were fabricated and characterized. The implant structure, drug content and molecular weight of PCL after 120 days drug release were investigated. The in vitro release results showed that, when the drug loading was the same, drug release was fastest for the implant with a diameter of 2 mm and slowest for the implant with a diameter of 8 mm; for the implants with the same diameters, the release of drug from the implants with 50% drug loading was faster than that from the implants with 25% drug loading; however, this effect of drug loading decreased with the increase of implant diameter; in addition, 5-FU was released slightly slower from the end-capped implants than from the corresponding uncapped implants; the drug release data for all the uncapped implants were best fit with the Ritger-Peppas model. Drug release from the hydrophobic implants was found to be dominated by diffusion mechanism. Scanning electron microscopy images and drug content measurements revealed that 5-FU release took place gradually from the exterior region to the interior region of the implants.

Practical patient dosimetry for partial rotation cone beam CT.

This work investigates the validity of estimating effective dose for cone beam CT (CBCT) exposures from the weighted CT dose index (CTDIW) and irradiated length. Measurements were made within cylindrical poly(methyl methacrylate) (PMMA) phantoms measuring 14 cm and 28 cm in length and 32 cm in diameter for the 200° DynaCT acquisition on the Siemens Artis zee fluoroscopy unit (Siemens Medical Solutions, Erlangen, Germany). An interpolated average dose was calculated to account for the partial rotation. Organ and effective doses were estimated by modelling projections in the Monte Carlo software programme PCXMC (STUK, Helsinki, Finland). The CTDIW was found to closely approximate the interpolated average dose if the positions of the measured doses reflected the X-ray beam rotation. The average dose was found to increase by 8% when the phantom length was increased from 14 to 28 cm. Using the interpolated average dose and the irradiated length for effective dose calculations gave similar values to PCXMC when a double-length (28-cm) CT dose index phantom was irradiated. Simplifying the estimation of effective dose with PCXMC by modelling just 4 projections around the abdomen gave effective doses that were only 7% different to those given when 41 projections were modelled. Calculated doses to key organs within the beam varied by as much as 27%. Estimating effective dose from the CTDIW and the irradiated length is sufficiently accurate for CBCT if the chamber positions are considered carefully. A conversion factor can be used only if a single CT dose index phantom is available. The estimation of organ doses requires a large number of modelled projections in PCXMC.

Association of a Cylindrical Polyelectrolyte Brush with Tetravalent Counterions

Cylindrical poly(styrene sulfonate) brushes were combined with a tetravalent double-DABCO based counterion. With increasing addition of counterion, hydrodynamic radius and radius of gyration decrease and AFMreveals a conformation change from wormlike to curled structures. Rg/Rh changes from 1.3 to 0.9. Above charge stoichiometry, brushes become interconnected into finite size assemblies, which are stable in aqueous solution for charge ratios (ratio of the molar concentration of charged counterion groups to the molar concentration of charged monomer units of the polymer brush) 1 < l < 1.2. They are compact and consist of the brushes in curled (bent) conformation, which is in difference to network-like aggregates from cylindrical poly(styrene sulfonate) brushes with tetravalent porphyrin counterions (Gröhn et al. Macromolecules 2009) and to a wormlike - bent conformation - helix transition found for another brush counterion system (Müller et al. Soft Matter 2009).