Synergistic effect of GO/ZnO loading on the performance of cellulose acetate/chitosan blended reverse osmosis membranes for NOM rejection

Declining freshwater resources along with their pollution are threatening the life existence on earth. To meet the freshwater demand, one of the most appropriate and possible ways which has been adopted all over the world is to reuse wastewater by removing its impurities. Among many water pollutants, natural organic matter (NOM) is found to be responsible as major precursor for the formation of other pollutants. Removal of NOM from wastewater is being done by using membrane filtration systems incorporated with certain nanofillers to increase membranes efficiency and permeability. In this study, novel nanocomposite reverse osmosis (RO) membranes were prepared using cellulose acetate and chitosan in N,N-Dimethyl formamide. Graphene oxide (GO) nanosheets and zinc oxide (ZnO) in different concentration were loaded to modify the membranes for tuning their RO performance. The confirmation of the functional groups is demonstrated by Fourier transform infrared spectroscopy which revealed the specific peaks indicating the formation of the nano-composite membranes. The surface morphology was studied by scanning electronic microscopy which shows a gradual transformation of the membrane surface from voids-free to macro-voids filled surface up to threshold concentration of GO and ZnO. The thermal properties of GO based membranes were analyzed using thermogravimetric analysis and differential scanning calorimetry. The uniform interaction of the GO and ZnO with polymers induced the remarkable thermal properties of the synthesized membranes. Permeate flux and contact angle measurements were considered to estimate their water content (96%) capacity and NOM rejection (96%) using 0.1 ppm humic acid solution. The permeate flux, NOM rejection and the water content changed directly with GO and inversely with ZnO wt% in the membranes up to GO5 (GO:0.14: ZnO:0.03) whereas the contact angle exhibited the inverse relationship with GO and ZnO concentration in casting solution of the synthesized membranes. Hence it can be concluded that prepared RO membranes are suitable for NOM rejection and recommended for water treatment.

Novel antibacterial polyurethane and cellulose acetate mixed matrix membrane modified with functionalized TiO2 nanoparticles for water treatment applications

Bacterial contamination is one of the leading causes of water pollution. Antibacterial polyurethane/cellulose acetate membranes modified by functionalized TiO₂ nanoparticles were processed and studied. TiO₂ nanoparticles were prepared and ultraviolet (UV) irradiated to activate their photocatalytic activity against Escherichia coli (E. Coil) and Methicillin-resistant Staphylococcus aureus (MRSA) bacteria. Functionalized TiO₂ nanoparticles were incorporated in flat-sheet mixed matrix membranes (MMMs). These membranes were characterized for their different properties such as morphology, thermal stability, mechanical strength, surface wettability, water retention, salt rejection, water flux, and their antibacterial performance against E. Coil and MRSA was also tested. The activity of nanoparticles against MRSA and E. coli was analyzed using three different concentrations, 0.5 wt%, 1.0 wt% and 1.5 wt% of nanoparticles and 0.5 wt% of TiO₂ nanoparticles showed maximum growth of bacteria. The maximum inhibition was observed in membranes with maximum nanoparticles when compared with other membranes. All these characteristics were strongly affected by increasing the concentration of TiO₂ nanoparticles in the prepared membranes and the duration of their UV exposure. Hence, it was proved from this analysis that these TiO₂ modified membranes exhibit substantial antibacterial properties. The results are supporting the utilization of these materials for water purification purposes.

Alkyl Silica Hybrid Nanowire Assembly in Improved Superhydrophobic Membranes for RO Filtration

Alkyl silica membranes and wires were synthesized by a sol-gel method, which has the capacity to control the size of the particles or membranes by controlling the reactions. Trimethoxyoctylsilane (C₈TMOS) was used as a chemical surfactant; poly(vinylpyrrolidone) (PVP) as an emulsifier, dissolved in butanol for emulsion; and tetraethylorthosilicate (TEOS) as a precursor and a source of silica. An assembly of silica wires was fabricated on glass and cotton substrates by the dip-coating technique. Porous membranes and silica wires were observed using scanning electron microscopy (SEM) images. The contact angles of all of the samples were in the range of 140-154° as measured by ImageJ software, which confirmed the hydrophobic nature of the samples. The contact angle was increased by increasing the amount of the surfactant. Phase changes of silica wires and membranes were investigated by thermogravimetric analysis. Chemical bonds of the sample were studied using Fourier transform infrared (FTIR) spectroscopy. The band gap of silica nanowires was measured to be 3.8-3.4 eV using the UV-visible spectrum and decreased as compared to that of bulk silica. These silica-based porous membranes with enhanced transport properties can be used in filtration and separation techniques. This fabricated hybrid silica membrane showed ∼96% salt rejection within a permeation flux of 3.04 L/m² h.

Automated chest radiography and mass systematic screening for tuberculosis

BACKGROUND: Systematic screening for TB using automated chest radiography (ACR) with computer-aided detection software (CAD4TB) has been implemented at scale in Karachi, Pakistan. Despite evidence supporting the use of ACR as a pre-screen prior to Xpert^® MTB/RIF diagnostic testing in presumptive TB patients, there has been no data published on its use in mass screening in real-world settings.METHOD: Screening was undertaken using mobile digital X-ray vehicles at hospital facilities and community camps. Chest X-rays were offered to individuals aged ≥15 years, regardless of symptoms. Those with a CAD4TB score of ≥70 were offered Xpert testing. The association between Xpert positivity and CAD4TB scores was examined using data collected between 1 January and 30 June 2018 using a custom-built data collection tool.RESULTS: Of the 127 062 individuals screened, 97.2% had a valid CAD4TB score; 11 184 (9.1%) individuals had a CAD4TB score ≥70. Prevalence of Xpert positivity rose from 0.7% in the <50 category to 23.5% in the >90 category. The strong linear association between CAD4TB score and Xpert positivity was found in both community and hospital settings.CONCLUSION: The strong association between CAD4TB scores and Xpert positivity provide evidence that an ACR-based pre-screening performs well when implemented at scale in a high-burden setting.

Sodium alginate blended membrane with polyurethane: Desalination performance and antimicrobial activity evaluation

A series of polymeric membranes were synthesized by blending polyurethane with sodium alginate (0.2, 0.4, 0.6, 0.8 and 1.0%). The structural, morphological and thermal properties of the membranes were examined by FTIR, SEM, AFM and TGA, respectively. Performance evaluation (salt rejection and flux) was assessed through reverse osmosis technique (RO). The FTIR spectra of membranes confirmed extensive hydrogen bonding (3350 cm^-1). The SEM and AFM analyses supported a progressively rising surface roughness of blended membranes. The hydrophilicity, crosslinking density and thermal stability of the membranes were improved with an increase in alginate content. The capability of salt (NaCl and MgCl₂) rejection was improved with alginate up to 0.8%. In addition, the rejection of divalent ions was better than monovalent ions (94 ± 0.96% for NaCl and 98 ± 0.98% for MgCl₂). The blended membranes ascertained an effective chlorine resistivity. The antibacterial activity was also promising, which enhanced with the alginate content in the membrane. The sodium alginate blended membrane with polyurethane proved to be an efficient approach to develop the blended membranes with tunable properties for water desalination.

Effect of Varying Amount of Polyethylene Glycol (PEG-600) and 3-Aminopropyltriethoxysilane on the Properties of Chitosan based Reverse Osmosis Membranes

Chitosan and polyethylene glycol (PEG-600) membranes were synthesized and crosslinked with 3-aminopropyltriethoxysilane (APTES). The main purpose of this research work is to synthesize RO membranes which can be used to provide desalinated water for drinking, industrial and agricultural purposes. Hydrogen bonding between chitosan and PEG was confirmed by displacement of the hydroxyl absorption peak at 3237 cm-1 in pure chitosan to lower values in crosslinked membranes by using FTIR. Dynamic mechanical analysis revealed that PEG lowers Tg of the modified membranes vs. pure chitosan from 128.5 °C in control to 120 °C in CS-PEG5. SEM results highlighted porous and anisotropic structure of crosslinked membranes. As the amount of PEG was increased, hydrophilicity of membranes was increased and water absorption increased up to a maximum of 67.34%. Permeation data showed that flux and salt rejection value of the modified membranes was increased up to a maximum of 80% and 40.4%, respectively. Modified films have antibacterial properties against Escherichia coli as compared to control membranes.

Cellulose acetate based Complexation-NF membranes for the removal of Pb(II) from waste water

This study investigates the removal of Pb(II) using polymer matrix membranes, cellulose acetate/vinyl triethoxysilane modified graphene oxide and gum Arabic (GuA) membranes. These complexation-NF membranes were successfully synthesized via dissolution casting method for better transport phenomenon. The varied concentrations of GuA were induced in the polymer matrix membrane. The prepared membranes M-GuA2–M-GuA10 were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscope and bio-fouling studies. Thermal stability of the membranes was determined by thermogravimetric analysis under nitrogen atmosphere. Dead end nanofiltration was carried out to study the perm- selectivity of all the membranes under varied pressure and concentration of Pb(NO₃)₂. The complexation-NF membrane performances were significantly improved after the addition of GuA in the polymer matrix membrane system. M-GuA8 membrane showed optimum result of permeation flux 8.6 l m⁻² h⁻¹. Rejection of Pb(II) ions was observed to be around 97.6% at pH 9 for all the membranes due to electrostatic interaction between CA and Gum Arabic. Moreover, with the passage of time, the rate of adsorption was also increased up to 15.7 mg g⁻¹ until steady state was attained. Gum Arabic modified CA membranes can open up new possibilities in enhancing the permeability, hydrophilicity and anti-fouling properties.

A Review of Biodegradable Natural Polymer-Based Nanoparticles for Drug Delivery Applications

Biodegradable natural polymers have been investigated extensively as the best choice for encapsulation and delivery of drugs. The research has attracted remarkable attention in the pharmaceutical industry. The shortcomings of conventional dosage systems, along with modified and targeted drug delivery methods, are addressed by using polymers with improved bioavailability, biocompatibility, and lower toxicity. Therefore, nanomedicines are now considered to be an innovative type of medication. This review critically examines the use of natural biodegradable polymers and their drug delivery systems for local or targeted and controlled/sustained drug release against fatal diseases.

Novel Maleic Acid, Crosslinked, Nanofibrous Chitosan/Poly (Vinylpyrrolidone) Membranes for Reverse Osmosis Desalination

Fresh and clean water is consistently depleting and becoming a serious problem with rapid increases in population, so seawater desalination technology has captured global attention. For an efficient desalination process, this work proposes a novel, nanofibrous, thin-film composite membrane (NF-TFC) based on the deposition of the nanofibrous active layer of a blend of chitosan (CS) and poly (vinylpyrrolidone) (PVP) crosslinked with maleic acid on a 3-triethoxysilylpropylamine functionalized cellulose acetate substrate. FTIR analysis demonstrated the development of chemical and physical interactions and confirmed the incorporation of functional groups present in the NF-TFC. Scanning electron microscopy (SEM) micrographs depict the fibrous structure of the active layers. The reverse osmosis (RO) desalination characteristics of NF-TFC membranes are elevated by increasing the concentration of the crosslinker in a CS/PVP blend. Cellulose acetate (CA)-S4 attained an optimal salt rejection of 98.3% and permeation flux of 42.9 L/m2h, suggesting that the NF-TFC membranes could be favorable for seawater desalination.

Novel N-p-carboxy benzyl chitosan/poly (vinyl alcohol/functionalized zeolite mixed matrix membranes for DMFC applications

The novel N-p-carboxy benzyl chitosan (CBC)/ poly (vinyl alcohol) (PVA) based mixed matrix membranes (MMMs) filled with surface-modified zeolite have been prepared using the dissolution casting technique. The applicability of prepared MMMs for direct methanol fuel cell (DMFC) was investigated in terms of water uptake, methanol permeation, and proton conductivity by changing filler content (10-50 wt. %). The zeolite was modified by silane coupling agent, 3-mercaptopropyltrimethoxysilane (MPTMS). The resultant modified zeolite (MZ) was incorporated into CBC/PVA blend to obtain mixed matrix PEMs. The functional group, structural properties, morphological and topographical investigation of MMMs were examined using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Scanning electron microscopy (SEM) respectively. The prepared MMMs exhibited a remarkable decrease in methanol permeability of 2.3 × 10^-7  cm²/s with C-CPMZ50. The maximum value of proton conductivity of 0.0527 Scm^-1, was shown by C-CMPZ10. The prepared PEMs also displayed good stability during long term operating time.

Transparent Hydrophobic Hybrid Silica Films by Green and Chemical Surfactants

Monodispersed and transparent hybrid silica wires were synthesized by the sol-gel method using the chemical surfactant trimethoxyoctylsilane (C₈TMOS or C₁₁H₂₆O₃Si) and, for the first time, by green surfactants (Nelumbo nucifera/lotus leaf extract). The purpose was to introduce a less toxic, cost-effective, and one-step easy approach to get superhydrophobic silica films. Each of the surfactants was used at two different concentrations to investigate hydrophobicity of the films. Assembly of silica wires was obtained by dip-coating and vacuum filtration methods on glass and cellulose acetate filter paper as substrates, respectively. The water contact angle (CA) up to 154° was measured for hybrid silica films on filter paper, which revealed their superhydrophobicity as compared to hydrophobic behavior of those films coated on a glass substrate with CA up to 135°. Chemical, optical, and structural properties of prepared films were characterized by Fourier transform infrared spectroscopy, UV-vis spectroscopy, scanning electron microscopy, thermogravimetry, and differential scanning calorimetry. The hybrid silica wires prepared displayed good transparency, low surface energy, and superhydrophobicity. These silica assemblies can create outstanding and multifunctional structures with superhydrophobic coatings for waterproof electronic devices, military uniforms, self-cleaning surfaces, etc.

Fractionation of direct dyes using modified vapor grown carbon nanofibers and zirconia in cellulose acetate blend membranes

In the textile industry, membrane technology has been widely employed for the exclusion of direct dyes. In this research paper, firstly vapor grown carbon nanofibers (VGCNFs) were functionalized with carboxylates group via piranha oxidation, and then series of CA/PEO-PPO-PEO triblock copolymers were prepared by blending with varying weight percentages of modified VGCNFs and Zirconia (ZrO₂). The structural morphologies of membranes were visualized by scanning electron microscope (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM), which exhibits the dispersity of dual fillers in polymer matrix thus improving the microstructure of resultant membranes. The experimental data indicates that the modified VGCNF and ZrO₂ nanoparticles were shown increase hydrophilic character. The direct dyes rejection were successfully after filler addition, which were 96% (for Direct Red), 99% (for Direct Blue) and 93% (for Direct Orange). The membranes showed a better antifouling property even after several washing cycles along with improved biofouling property, both of these properties showed a better membrane life. As an outcome, this research could have been a great potential to be used to treat dyes in textile industry.

Are Gap and Cast Indices Predictors of Efficacy of Reduction in Fractures of Both Bones of the Leg? A Cohort Study

Introduction: Non-operative management has successfully been practised for long in diaphyseal fractures of both bones of the leg. This study attempts to establish an acceptability criteria for plaster cast in order to predict future loss of reduction and its adequacy.

Materials and Methods: A total of forty subjects were included as per inclusion-exclusion criteria. Gap and cast indices were calculated in the immediate post reduction phase and at third week follow-up visit.

Results: The mean values of gap and cast indices in the immediate post-reduction phase were 0.35±0.220 and 0.99±0.08 respectively and at the third week follow-up the mean value for both the parameters in those without loss of reduction were 1.11±0.50 and 1.03±0.09 respectively and in those with loss of reduction were 0.84±0.44 and 1.01±0.06 respectively.

Conclusion: Gap and cast indices are not informative in assessing adequacy of reduction in diaphyseal fractures of both bones of the leg.

The effect of Nanocrystalline cellulose/Gum Arabic conjugates in crosslinked membrane for antibacterial, chlorine resistance and boron removal performance

In this work, we developed hybrid membranes integrated with Nanocrystalline cellulose (NCC)/Gum Arabic (GuA) conjugates using crosslinked Poly (vinyl alcohol) (PVA) as a matrix phase with the addition of PEO-PPO-PEO block copolymer that insured pore formation. At first, the NCC was prepared from microcrystalline cellulose via acid hydrolysis process. The performance property of hybrid NCC/GuA was measured using boron removal. The results showed that the rejection capability enhanced as compared to the control membranes, especially at 0.1wt% of NCC the selectivity is up to 92.4% with the flux rate of 21.3L/m².h. Moreover, the GuA in NCC/GuA conjugate significantly enhances the antibacterial activity by hindering the bacterial attachment to the surface as both of them carry the negative charge. Also by providing the active sites responsible for hydrogen bonding thus enhancing the hydrophilic character resulted in increased permeation flux rate. Therefore, the NCC/GuA conjugated membranes have great potentials for boron removal.

Deriving an optimal threshold of waist circumference for detecting cardiometabolic risk in sub-Saharan Africa

BACKGROUND

Waist circumference (WC) thresholds derived from western populations continue to be used in sub-Saharan Africa (SSA) despite increasing evidence of ethnic variation in the association between adiposity and cardiometabolic disease and availability of data from African populations. We aimed to derive a SSA-specific optimal WC cut-point for identifying individuals at increased cardiometabolic risk.

METHODS

We used individual level cross-sectional data on 24 181 participants aged ⩾15 years from 17 studies conducted between 1990 and 2014 in eight countries in SSA. Receiver operating characteristic curves were used to derive optimal WC cut-points for detecting the presence of at least two components of metabolic syndrome (MS), excluding WC.

RESULTS

The optimal WC cut-point was 81.2 cm (95% CI 78.5-83.8 cm) and 81.0 cm (95% CI 79.2-82.8 cm) for men and women, respectively, with comparable accuracy in men and women. Sensitivity was higher in women (64%, 95% CI 63-65) than in men (53%, 95% CI 51-55), and increased with the prevalence of obesity. Having WC above the derived cut-point was associated with a twofold probability of having at least two components of MS (age-adjusted odds ratio 2.6, 95% CI 2.4-2.9, for men and 2.2, 95% CI 2.0-2.3, for women).

CONCLUSION

The optimal WC cut-point for identifying men at increased cardiometabolic risk is lower (⩾81.2 cm) than current guidelines (⩾94.0 cm) recommend, and similar to that in women in SSA. Prospective studies are needed to confirm these cut-points based on cardiometabolic outcomes.International Journal of Obesity advance online publication, 31 October 2017; doi:10.1038/ijo.2017.240.

Novel reverse osmosis membranes composed of modified PVA/Gum Arabic conjugates: Biofouling mitigation and chlorine resistance enhancement

A novel crosslinked Poly (vinyl alcohol) (PVA) reverse osmosis (RO) thin film membrane conjugated with Gum Arabic (GA) with superb performance and features was synthesized for water desalination. RO membrane desalination parameters, such as hydrophilicity, surface roughness, water permeability, salt rejection, Chlorine resistance and biofouling resistance were evaluated using a dead end RO filtration unit. The incorporation of Pluronic F127 and the conjugation of Gum Arabic improved the overall RO performance of the membranes. This study has shown that the membrane PVA-GA-5 that contains 0.9wt% Gum Arabic provided excellent permeation, salt rejection, Chlorine and biofouling resistance and mechanical strength. The most remarkable result to arise from this research is that the overall RO performance enhancement has been achieved while utilizing PVA/Gum Arabic as a separation layer without the use of a substrate, which eliminates negative effects associated with the use of a substrate like internal concentration polarization.

Fabrication of tethered carbon nanotubes in cellulose acetate/polyethylene glycol-400 composite membranes for reverse osmosis

In this study pristine multi-walled carbon nanotubes (MWCNTs) were surface engineered (SE) in strong acidic medium by oxidation purification method to form SE-MWCNT. Five different amount of SE-MWCNT ranging from 0.1 to 0.5 wt% were thoroughly and uniformly dispersed in cellulose acetate/polyethylene glycol (CA/PEG400) polymer matrix during synthesis of membrane by dissolution casting method. The structural analysis, surface morphology and roughness was carried out by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively, which showed that the dispersed SE-MWCNT was substantially tethered in CA/PEG400 polymer matrix membrane. The thermogravimetric analysis (TGA) of membranes also suggested some improvement in thermal properties with the addition of SE-MWCNT. Finally, the performance of these membranes was assessed for suitability in drinking water treatment. The permeation flux and salt rejection were determined by using indigenously fabricated reverse osmosis pilot plant with 1000 ppm NaCl feed solution. The results showed that the tethered SE-MWCNT/CA/PEG400 polymer matrix membrane, with strong SE-MWCNTs/polymer matrix interaction, improved the salt rejection performance of the membrane with the salt rejection of 99.8% for the highest content of SE-MWCNT.

High-temperature electrical properties of silane cross-linked chitosan/poly(vinyl alcohol) membrane: thermal, mechanical and surface characterization

Chitosan and poly(vinyl alcohol) were blended and cross-linked with tetraethoxysilane and showed conductive properties. Impedance spectroscopy was used to study the influence of temperature on the electrical properties of the membranes. The conductivity of the membranes was increased with an increase in temperature. Free water was decreased and bound water was increased with an increase in cross-linker contents. The tensile strength improved, whereas elongation at break decreased by increasing the amount of cross-linker contents. The water contact angle of the membranes lowered with time, exhibiting the hydrophilic nature of the membranes. The novel characteristics of biocompatible membranes can be used in biomedical applications including biological schemes that require smaller charge in medicinal apparatus, bioelectrode coatings, etc.

Xenia and metaxenia in grapes: differences in berry and seed characteristics of maternal grape cv. 'Narince' (Vitis vinifera L.) as influenced by different pollen sources

Literature investigations indicate that the grapes have quite complex fertilisation biology. This complexity necessitates extensive investigations to obtain reliable knowledge for both well-organised hybridisation studies and maximising grape yield. Therefore, this study was conducted to investigate the influences of self-, free- and cross-pollination on berry and seed characteristics in grape. Five different pollination treatments were applied to 'Narince', the most widely known and popular white wine grape in Turkey. Pollen tests indicated that all the cultivars had satisfactory in vitro pollen viability percentages. Free-pollination produced a significantly higher percentage berry set. Among the pollinizers, the use of pollen of 'Thompson Seedless' and 'Cardinal' varieties resulted in higher berry set percentage in 'Narince'. The free-pollination was also superior in giving the highest weight, length and width of the berry, as well as number of seeds per berry. These findings revealed that there were strong xenial and metaxenial effects in the studied grape cultivars. Among the pollinizer cultivars, the most effective pollinator was 'Thompson Seedless'. Hence, for better berry set and quality, the use of 'Thompson Seedless' as a pollinizer may be an attractive option in both grape production and breeding studies.

CALCINOSIS CUTIS - A SERIES OF 59 CONSECUTIVE CASES CONFINED AMONG WOMEN

BACKGROUND

Calcinosis cutis is the cutaneous deposition of calcium salts. Tumoral Calcinosis is a condition consisting of massive subcutaneous deposits of calcium salts often overlying large joints in otherwise healthy patients.

OBJECTIVE

To describe the characteristics of a series of patients with Tumoral Calcinosis in the Gurage Zone of Central Ethiopia.

METHODOLOGY

Data was collected from 59 patients who presented with clinical diagnosis of calcinosis cutis around hip region between January 2005 and January 2009.

RESULTS

All cases were females, with a mean (standard deviation) age at diagnosis of 50.7(10.8). The duration of illness ranged from one to eighteen years. The cases were distributed in the different villages of Gurage Zone without any sign of clustering of cases. The lesions were localized around hip region on both sides. The patients did not have any related co-morbidity or any history of similar illness among close family members. None of the patients gave history of evident trauma to the site of the lesions. Significant proportion of the patients (53.4%) confirmed to carry water container and/or other goods on their side. Serum Phosphate and Calcium levels in selected patients were with in normal limit. Histo-pathological examinations of five cases revealed Calcium deposits in collagenous connective tissue.

CONCLUSION

The lesion was found to be relatively common in the study area and specifically confined to females. The probable factor associated with the cases is carrying objects on their side (hip area). Further research with in-depth clinical and laboratory evaluation is of paramount importance.

Computer modeling of the effect of perfusion on heating patterns in radiofrequency tumor ablation

PURPOSE

To use an established computer simulation model of radiofrequency (RF) ablation to further characterize the effect of varied perfusion on RF heating for commonly used RF durations and electrode types, and different tumor sizes.

METHODS

Computer simulation of RF heating using 2-D and 3-D finite element analysis (Etherm) was performed. Simulated RF application was systematically modeled on clinically relevant application parameters for a range of inner tumor perfusion (0-5 kg/m3-s) and outer normal surrounding tissue perfusion (0-5 kg/m3-s) for internally cooled 3-cm single and 2.5-cm cluster electrodes over a range of tumor diameters (2-5 cm), and RF application times (5-60 min; n = 4618 simulations). Tissue heating patterns and the time required to heat the entire tumor +/- a 5-mm margin to > 50 degrees C were assessed. Three-dimensional surface response contours were generated, and linear and higher order curve-fitting was performed.

RESULTS

For both electrodes, increasing overall tissue perfusion exponentially decreased the overall distance of the 50 degrees C isotherm (R2 = 0.94). Simultaneously, increasing overall perfusion exponentially decreased the time required to achieve thermal equilibrium (R2 = 0.94). Furthermore, the relative effect of inner and outer perfusion varied with increasing tumor size. For smaller tumors (2 cm diameter, 3-cm single; 2-3 cm diameter, cluster), the ability and time to achieve tumor ablation was largely determined by the outer tissue perfusion value. However, for larger tumors (4-5 cm diameter single; 5 cm diameter cluster), inner tumor perfusion had the predominant effect.

CONCLUSION

Computer modeling demonstrates that perfusion reduces both RF coagulation and the time to achieve thermal equilibrium. These results further show the importance of considering not only tumor perfusion, but also size (in addition to background tissue perfusion) when attempting to predict the effect of perfusion on RF heating and ablation times.

Formulation and process optimization to eliminate picking from market image tablets

A tablet formulation when compressed using market image tooling may cause picking of powder. A D-optimal statistical experiment was designed to optimize the direct compression formulation and the process to alleviate picking of powder. The effects of levels of magnesium stearate, colloidal silicon dioxide (CSD), and lubrication time on picking were investigated using original compression tooling. These optimization results provided a small robust manufacturing region, hence a change in the cut angles of embossed letters and numbers from 70 degrees to 90 degrees in the modified compression tooling was evaluated. A statistical analysis of the data identified a robust manufacturing region that included formulations containing magnesium stearate 1-1.25% w/w, CSD 0.1-0.3% w/w, with a lubrication time of 5-10 min when compressed using modified compression tooling. The results indicate a significant reduction in picking by increasing the cut angles of embossed letters and numbers in the modified compression tooling. By evaluating interactions between various variables, we demonstrate a concentration dependent effect of CSD on the lubrication efficiency of magnesium stearate and compactability of microcrystalline cellulose containing formulation. In addition, the lubrication efficiency of magnesium stearate is maintained by blending CSD with powder blend prior to lubrication with magnesium stearate.

The albedo effect on neutron transmission probability

The aim of this study is to evaluate the albedo effect on the neutron transmission probability through slab shields. For this reason we have considered an infinite homogeneous slab having a fixed thickness equal to 20 lambda (lambda is the mean free path of the neutron in the slab). This slab is characterized by the factor Ps (scattering probability) and contains a vacuum channel which is formed by two horizontal parts and an inclined one (David, M. C. (1962) Duc and Voids in shields. In Reactor Handbook, Vol. III, Part B, p. 166). The thickness of the vacuum channel is taken equal to 2 lambda. An infinite plane source of neutrons is placed on the first of the slab (left face) and detectors, having windows equal to 2 lambda, are placed on the second face of the slab (right face). Neutron histories are sampled by the Monte Carlo method (Booth, T. E. and Hendricks, J. S. (1994) Nuclear Technology 5) using exponential biasing in order to increase the Monte Carlo calculation efficiency (Levitt, L. B. (1968) Nuclear Science and Engineering 31, 500-504; Jehouani, A., Ghassoun, J. and Abouker, A. (1994) In Proceedings of the 6th International Symposium on Radiation Physics, Rabat, Morocco) and we have applied the statistical weight method which supposes that the neutron is born at the source with a unit statistical weight and after each collision this weight is corrected. For different values of the scattering probability and for different slopes of the inclined part of the channel we have calculated the neutron transmission probability for different positions of the detectors versus the albedo at the vacuum channel-medium interface. Some analytical representations are also presented for these transmission probabilities.

The neutron channeling phenomenon

Shields, used for protection against radiation, are often pierced with vacuum channels for passing cables and other instruments for measurements. The neutron transmission through these shields is an unavoidable phenomenon. In this work we study and discuss the effect of channels on neutron transmission through shields. We consider an infinite homogeneous slab, with a fixed thickness (20 lambda, with lambda the mean free path of the neutron in the slab), which contains a vacuum channel. This slab is irradiated with an infinite source of neutrons on the left side and on the other side (right side) many detectors with windows equal to 2 lambda are placed in order to evaluate the neutron transmission probabilities (Khanouchi, A., Aboubekr, A., Ghassoun, J. and Jehouani, A. (1994) Rencontre Nationale des Jeunes Chercheurs en Physique. Casa Blanca Maroc; Khanouchi, A., Sabir, A., Ghassoun, J. and Jehouani, A. (1995) Premier Congré International des Intéractions Rayonnements Matière. Eljadida Maroc). The neutron history within the slab is simulated by the Monte Carlo method (Booth, T. E. and Hendricks, J. S. (1994) Nuclear Technology 5) and using the exponential biasing technique in order to improve the Monte Carlo calculation (Levitt, L. B. (1968) Nuclear Science and Engineering 31, 500-504; Jehouani, A., Ghassoun, J. and Aboubker, A. (1994) In Proceedings of the 6th International Symposium on Radiation Physics, Rabat, Morocco). Then different geometries of the vacuum channel have been studied. For each geometry we have determined the detector response and calculated the neutron transmission probability for different detector positions. This neutron transmission probability presents a peak for the detectors placed in front of the vacuum channel. This study allowed us to clearly identify the neutron channeling phenomenon. One application of our study is to detect vacuum defects in materials.

The vacuum geometry effect on neutron transmission and spatial resolution of neutron transmission

Frequently, shields used against radiation contain some vacuum channels. We have therefore considered an infinite slab with a fixed thickness (thickness 20 lambda with lambda the mean free path of the neutron in the slab) and an infinite plane source of neutrons which arrived on the left side of the slab; transmitted neutrons through the slab to its right side are detected by finite detectors having windows equal to 2 lambda. This slab contains a vacuum channel. This channel has many legs with several horizontal parts. We used the Monte Carlo method for sampling the neutron history in the slab with a spatial biasing technique in order to accelerate the calculation convergence (Levitt, L. B. (1968) Nuclear Science and Engineering 31, 500-504; Jehouani, A., Ghassoun, J. and Aboubker, A. (1994) In Proceedings of 6th International Symposium on Radiation Physics, Rabat, Morocco). We studied the effects of the angle position and the number of horizontal parts of the channel on the neutron transmission. We have studied the effect of the vacuum channel opening (Artigas, R. and Hungerford, H. E. (1969) Nuclear Science and Engineering 36, 295-303) on the neutron transmission; for several values of this opening we have calculated the neutron transmission probability for each detector position. This study allowed us to determine the optimal conditions of vacuum geometries to improve protection against neutrons. In the second part we considered a shield which consists of a slab and a two-legged vacuum channel with two horizontal parts. The spatial distribution of neutrons transmitted through the protection screen was determined. This distribution shows two peaks. The study was made for different distances between the two horizontal parts. We have determined the smallest distance between the two horizontal parts for which the two peaks can be resolved.

Determination of genetic stability using isozymes and RFLPs in beet plants regenerated in vitro

Sugar, fodder and garden beet (Beta vulgaris L.) plants have been regenerated in culture from a range of expiant material. Of the regenerants 764 were subjected to isozyme analysis using eight enzyme-specific stains, and 60 were subjected to RFLP analysis using three cDNA probes. Both molecular techniques allowed the identification of somaclonal variant plants. Assessment of the numbers of variant isozymes and restriction fragments has allowed the calculation of the approximate percentage of variant alleles occurring in any one somaclonal regenerant, namely between 0.05% and 0.1%.

Parathyroid hormone acutely increases polyphosphoinositides of the rabbit kidney cortex by a cycloheximide-sensitive process

Parathyroid hormone(PTH) rapidly increases the concentrations of diphosphoinositide and triphosphoinositide in rabbit kidney cortex. Cycloheximide pretreatment abolishes these effects of PTH. These findings are similar to those reported for adrenocorticotropin and cyclic AMP action in the adrenal cortex, and suggest a common mechanism. Cycloheximide-sensitive effects of PTH, e.g., phosphaturia, may require polyphosphoinositides and/or other phospholipids.