bluuebunny/crossref_metadata_2025 huggingface dataset:
Missing data in randomized controlled trials of rheumatoid arthritis with radiographic outcomes: A simulation study
Authors: Baron Gabriel , Ravaud Philippe , Samson Adeline , Giraudeau Bruno
Published: December 2007

Objective

To assess the impact, in terms of statistical power and bias of treatment effect, of approaches to dealing with missing data in randomized controlled trials of rheumatoid arthritis with radiographic outcomes.

Methods

We performed a simulation study. The missingness mechanisms we investigated copied the process of withdrawal from trials due to lack of efficacy. We compared 3 methods of managing missing data: all available data (case‐complete), last observation carried forward (LOCF), and multiple imputation. Data were then analyzed by classict‐test (comparing the mean absolute change between baseline and final visit) or F test (estimation of treatment effect with repeated measurements by a linear mixed‐effects model).

Results

With a missing data rate close to 15%, the treatment effect was underestimated by 18% as estimated by a linear mixed‐effects model with a multiple imputation approach to missing data. This bias was lower than that obtained with the case‐complete approach (−25%) or LOCF approach (−35%). This statistical approach (combination of multiple imputation and mixed‐effects analysis) was moreover associated with a power of 70% (for a 90% nominal level), whereas LOCF was associated with a power of 55% and a case‐complete power of 58%. Analysis with thet‐test gave qualitatively equivalent but poorer quality results, except when multiple imputation was applied.

Conclusion

Our simulation study demonstrated multiple imputation, offering the smallest bias in treatment effect and the highest power. These results can help in planning trials, especially in choosing methods of imputation and data analysis.
Physical inactivity in patients with rheumatoid arthritis: Data from twenty‐one countries in a cross‐sectional, international study
Authors: Sokka Tuulikki , Häkkinen Arja , Kautiainen Hannu , Maillefert Jean Francis , Toloza Sergio , MØrk hansen Troels , Calvo‐Alen Jaime , Oding Rolf , Liveborn Margareth , Huisman Margriet , Alten Rieke , Pohl Christof , Cutolo Maurizio , Immonen Kai , Woolf Anthony , Murphy Eithne , Sheehy Claire , Quirke Edel , Celik Selda , Yazici Yusuf , Tlustochowicz Witold , Kapolka Danuta , Skakic Vlado , Rojkovich Bernadette , Müller Raili , Stropuviene Sigita , Andersone Daina , Drosos Alexandros A. , Lazovskis Juris , Pincus Theodore
Published: December 2007

Objective

Regular physical activity is associated with decreased morbidity and mortality. Traditionally, patients with rheumatoid arthritis (RA) have been advised to limit physical exercise. We studied the prevalence of physical activity and associations with demographic and disease‐related variables in patients with RA from 21 countries.

Methods

The Questionnaires in Standard Monitoring of Patients with Rheumatoid Arthritis (QUEST‐RA) is a cross‐sectional study that includes a self‐report questionnaire and clinical assessment of nonselected consecutive outpatients with RA who are receiving usual clinical care. Frequency of physical exercise (≥30 minutes with at least some shortness of breath, sweating) is queried with 4 response options: ≥3 times weekly, 1–2 times weekly, 1–2 times monthly, and no exercise.

Results

Between January 2005 and April 2007, a total of 5,235 patients from 58 sites in 21 countries were enrolled in QUEST‐RA: 79% were women, >90% were white, mean age was 57 years, and mean disease duration was 11.6 years. Only 13.8% of all patients reported physical exercise ≥3 times weekly. The majority of the patients were physically inactive with no regular weekly exercise: >80% in 7 countries, 60–80% in 12 countries, and 45% and 29% in 2 countries, respectively. Physical inactivity was associated with female sex, older age, lower education, obesity, comorbidity, low functional capacity, and higher levels of disease activity, pain, and fatigue.

Conclusion

In many countries, a low proportion of patients with RA exercise. These data may alert rheumatologists to motivate their patients to increase physical activity levels.
Effect of two contrasting types of physical exercise on chronic neck muscle pain
Authors: Andersen Lars L. , KjÆr Michael , SØgaard Karen , Hansen Lone , Kryger Ann I. , SjØgaard Gisela
Published: December 2007

Objective

The prevalence of neck muscle pain has steadily increased and especially pain from the descending part of the trapezius muscle has been associated with monotonous work tasks such as computer work. Physical exercise is generally recommended as treatment, but it is unclear which type of training is most effective. Our objective was to determine the effectiveness of specific strength training of the painful muscle versus general fitness training without direct involvement of the painful muscle (leg bicycling) on work‐related neck muscle pain.

Methods

We conducted a randomized controlled trial and recruited subjects from 7 workplaces characterized by monotonous jobs (e.g., computer‐intensive work). Forty‐eight employed women with chronic neck muscle pain (defined as a clinical diagnosis of trapezius myalgia) were randomly assigned to 10 weeks of specific strength training locally for the affected muscle, general fitness training performed as leg bicycling with relaxed shoulders, or a reference intervention without physical activity. The main outcome measure was an acute and prolonged change in intensity of neck muscle pain (100‐mm visual analog scale [VAS]).

Results

A decrease of 35 mm (∼79%; P < 0.001) in the worst VAS pain score over a 10‐week period was seen with specific strength training, whereas an acute and transient decrease in pain (5 mm; P < 0.05) was found with general fitness training.

Conclusion

Specific strength training had high clinical relevance and led to marked prolonged relief in neck muscle pain. General fitness training showed only a small yet statistically significant acute pain reduction.
Participation restrictions among older adults with osteoarthritis: A mediated model of physical symptoms, activity limitations, and depression
Authors: Machado Gustavo P. M. , Gignac Monique A. M. , Badley Elizabeth M.
Published: December 2007

Objective

Research emphasizes the negative impact of osteoarthritis (OA) on social participation, yet few studies have examined the roles of symptoms, activity limitations, and depression in this relationship. The present longitudinal study tested a model that hypothesizes that the relationship between physical symptoms and later participation restrictions among older adults with OA is mediated by activity limitations and depressive symptoms.

Methods

Participants were 184 community‐dwelling senior adults (age ≥55 years) with a physician diagnosis of OA who were interviewed at 2 time points 18 months apart. Measures included demographic variables; a derived physical symptoms measure based on severity of pain, stiffness, and fatigue in the previous week; and depressive symptoms measured by the Center for Epidemiologic Studies Depression Scale. Measures of activity limitations and participation restrictions were derived by factor analysis of questions about difficulty in everyday life. Sequential multiple linear regression analyses controlling for demographic and illness‐related variables were used to test for mediation.

Results

Severity of time 1 physical symptoms was associated with difficulties in participation 18 months later. Sequential introduction of variables showed that this relationship was partially mediated by time 1 activity limitations and time 1 depressive symptoms. When both of these variables were included in the model, the effect of symptoms severity was completely mediated.

Conclusion

This study demonstrates the importance of taking into account both the physical (activity limitations) and psychological (depressive symptoms) consequences of OA symptoms and suggests that these factors act as a pathway to subsequent participation restrictions.
Pharmacokinetics of desethylamiodarone in the rat after its administration as the preformed metabolite, and after administration of amiodarone
Authors: Shayeganpour Anooshirvan , Hamdy Dalia A. , Brocks Dion R.
Published: December 2007

The pharmacokinetics of desethylamiodarone (DEA), the active metabolite of amiodarone (AM), were studied in the rat after administration of AM or preformed metabolite. Rats received 10 mg/kg of either intravenous or oral AM HCl or DEA base. Blood samples were obtained via a surgically implanted jugular vein cannula. Plasma concentrations were measured by a validated LC/MS method. In all AM treated rats, AM plasma concentrations greatly exceeded those of the formed DEA. The fraction of AM converted to DEA after i.v. administration was 14%. Amiodarone had a significantly lower (∼50%) clearance than DEA, although the volume of distribution and terminal phase half‐life did not differ significantly. The hepatic extraction ratio of DEA was 0.48, similar to that of AM (0.51). Oral AM demonstrated higher plasma AUC (5.6 fold) and higher Cmax (6.1 fold) than oral DEA and oral bioavailability of AM (46%) was greater than DEA (17%). The estimated fraction of the oral dose of AM converted to DEA was 4.5 fold higher than after i.v. administration, suggesting first‐pass formation of DEA from AM. Amiodarone and DEA differed in their pharmacokinetic characteristics mostly due to a higher CL of DEA. With oral dosing, AM appeared to undergo significant presystemic first‐pass metabolism within the intestinal tract. Copyright © 2007 John Wiley & Sons, Ltd.
Cognitive function and symptoms in adults and adolescents in relation to rf radiation from UMTS base stations
Authors: Riddervold Ingunn S. , Pedersen Gert F. , Andersen Niels T. , Pedersen Anders D. , Andersen Jørgen B. , Zachariae Robert , Mølhave Lars , Sigsgaard Torben , Kjærgaard Søren K.
Published: December 2007

There is widespread public concern about the potential adverse health effects of mobile phones in general and their associated base stations in particular. This study was designed to investigate the acute effects of radio frequency (RF) electromagnetic fields (EMF) emitted by the Universal Mobile Telecommunication System (UMTS) mobile phone base stations on human cognitive function and symptoms. Forty adolescents (15–16 years) and 40 adults (25–40 years) were exposed to four conditions: (1) sham, (2) a Continuous Wave (CW) at 2140 MHz, (3) a signal at 2140 MHz modulated as UMTS and (4) UMTS at 2140 MHz including all control features in a randomized, double blinded cross‐over design. Each exposure lasted 45 min. During exposure the participants performed different cognitive tasks with the Trail Making B (TMB) test as the main outcome and completed a questionnaire measuring self reported subjective symptoms. No statistically significant differences between the UMTS and sham conditions were found for performance on TMB. For the adults, the estimated difference between UMTS and sham was −3.2% (−9.2%; 2.9%) and for the adolescents 5.5% (−1.1%; 12.2%). No significant changes were found in any of the cognitive tasks. An increase in ‘headache rating’ was observed when data from the adolescents and adults were combined (P = 0.027), an effect that may be due to differences at baseline. In conclusion, the primary hypothesis that UMTS radiation reduces general performance in the TMB test was not confirmed. However, we suggest that the hypothesis of subjective symptoms and EMF exposure needs further research. Bioelectromagnetics 29:257–267, 2008. © 2007 Wiley‐Liss, Inc.
Enhanced secretion of prostaglandin E2 from osteoblasts by exposure to a strong static magnetic field
Authors: Sakurai Tomonori , Terashima Shingo , Miyakoshi Junji
Published: December 2007

Exposure to static magnetic fields (SMFs) has been reported to promote osteoblast differentiation in vitro, and increase bone formation in vivo and in clinical studies. Prostaglandins respond early to exogenous mechanical loading, and play an important role in bone formation. In this study, we investigated whether exposure to a strong SMF affects prostaglandin E2 (PGE2) secretion from a mouse osteoblastic cell line, MC3T3‐E1. We also investigated the PGE2‐synthesizing enzyme, cyclooxygenase 2 (Cox‐2), and translocation of the transcription factor nuclear factor kappa B (NF‐κB), which is involved in the induction of Cox‐2 expression. In the SMF exposures, experiments were performed at the 10 T‐exposure position, at which the magnetic flux density was highest, and at the 6 T‐exposure position, at which the magnetic field gradient was highest (41.7 T/m). PGE2 secretion was not affected by exposure at the 10 T‐exposure position compared to sham‐exposure, but was enhanced at the 6 T‐exposure position (about 1.5‐fold). Similarly, Cox‐2 expression and NF‐κB translocation were not enhanced at the 10 T‐exposure position, but increased at the 6 T‐exposure position (about twofold, two‐ to threefold, respectively). These findings suggested that exposure to a high magnetic field gradient induced secretion of PGE2 and expression of the Cox‐2 protein, which was mediated through increased translocation of NF‐κB. Bioelectromagnetics 29:277–283, 2008. © 2007 Wiley‐Liss, Inc.
Psychomotor performance is not influenced by brief repeated exposures to mobile phones
Authors: Curcio G. , Valentini E. , Moroni F. , Ferrara M. , De Gennaro L. , Bertini M.
Published: December 2007

The present study investigated the presence of a cumulative effect of brief and repeated exposures to a GSM mobile phone (902.40 MHz, 217 Hz modulated; peak power of 2 W; average power of 0.25 W; SAR = 0.5 W/kg) on psychomotor functions. To this end, after each of 3 15‐min exposures, both an acoustic simple reaction time task (SRTT) and a sequential finger tapping task (SFTT) were administered to 24 subjects. The present study was unable to detect the cumulative effects of brief and repeated EMF exposure on human psychomotor performance, although there was a non‐statistical trend to shorter reaction times. In summary, these data show an absence of effects with these particular exposure conditions; however, possible cognitive effects induced by different signal characteristics cannot be excluded. Bioelectromagnetics 29:237–241, 2008. © 2007 Wiley‐Liss, Inc.
Comparison of outcomes of ileal pouch–anal anastomosis for familial adenomatous polyposis with and without previous ileorectal anastomosis
Authors: von Roon A C , Tekkis P P , Lovegrove R E , Neale K F , Phillips R K S , Clark S K
Published: December 2007

Background

It is reported that previous colectomy and ileorectal anastomosis (IRA) has no effect on postoperative complications and functional outcomes of secondary proctectomy and ileal pouch–anal anastomosis (IPAA) in patients with familial adenomatous polyposis (FAP). This retrospective study re-examined the question in a single centre.

Methods

Some 185 patients were grouped by either IPAA as the initial prophylactic surgical procedure (primary IPAA) or IPAA preceded by IRA (secondary IPAA). Data on functional outcomes were available for 104, 83 and 56 patients at years 1, 5 and 10 respectively.

Results

The 78 patients who had secondary IPAA were older at the time of operation than the 107 who underwent primary IPAA (35·7 versus 29·2 years; P < 0·001). Six (8 per cent) of the secondary IPAA procedures could not be completed. Otherwise, apart from more wound infections in the secondary IPAA group (9 versus 0·9 per cent in the primary IPAA group; P = 0·012), there were no significant differences in rates of complications, functional outcomes, desmoid disease or pouch failure.

Conclusion

Conversion from IRA to IPAA may not be possible in patients with FAP. Where conversion is successful, pouch outcomes are similar but wound infections are more frequent.
Management of concomitant hepatic artery injury in patients with iatrogenic major bile duct injury after laparoscopic cholecystectomy
Authors: Li J , Frilling A , Nadalin S , Paul A , Malagò M , Broelsch C E
Published: December 2007

Background

Concomitant hepatic artery injury is a rare but severe complication associated with bile duct injury during laparoscopic cholecystectomy (LC).

Methods

Sixty patients referred with biliary injury after LC between April 1998 and December 2005 were divided into two groups according to the time elapsed between injury and definitive surgical revision; patients in group 1 were referred early (within 4 days) after operation and those in group 2 were referred later. Hepatic rearterialization was performed in addition to biliary reconstruction when technically possible.

Results

Damage to the hepatic artery was detected in ten patients. Hepatic rearterialization was carried out in five patients by end-to-end anastomosis (one), or by using an autologous graft (three) or allogeneic vascular graft (one). Three patients in group 2 underwent right hemihepatectomy without arterial reconstruction owing to liver necrosis or lobar atrophy. Three of ten patients died from postoperative complications.

Conclusion

Combined bile duct and hepatic artery injury during LC led to a complicated clinical course, with a high mortality rate. Reconstruction of the right hepatic artery might be helpful in reducing hepatic ischaemia, but is usually feasible only if the injury is identified early.
Length of follow-up after fistulotomy and fistulectomy associated with endorectal advancement flap repair for fistula in ano
Authors: Ortiz H , Marzo M , de Miguel M , Ciga M A , Oteiza F , Armendariz P
Published: December 2007

Background

The length of follow-up required after surgical repair of cryptoglandular fistula in ano has not been established. This prospective study determined the follow-up time needed to establish that an anal fistula has been cured after elective fistulotomy or fistulectomy associated with endorectal advancement flap (ERAF) repair.

Methods

Between January 2001 and June 2004, consecutive patients with anal fistula of cryptoglandular aetiology were included provided that they lived within the catchment area of the hospital and agreed to participate in a follow-up programme, which comprised scheduled visits every month until complete wound healing and annually thereafter.

Results

Some 206 of 219 eligible patients were evaluable; fistulotomy was performed in 115 and ERAF repair in 91. Median follow-up was 42 (range 24–65) months. Eighteen patients had recurrence of the fistula during follow-up, with a median time to relapse of 5·0 (range 1·0–11·7) months. There were no recurrences after 1 year.

Conclusion

Recurrence of fistula in ano of cryptoglandular origin treated by means of fistulotomy or ERAF repair occurs within the first year of operation.
Detoxification enzyme polymorphisms are not involved in duodenal adenomatosis in familial adenomatous polyposis
Authors: Berkhout M , Roelofs H M J , te Morsche R H M , Dekker E , van Krieken J H J M , Nagengast F M , Peters W H M
Published: December 2007

Background

Patients with familial adenomatous polyposis (FAP) are at high risk of developing duodenal adenomas and carcinomas. Besides germline mutations in the adenomatous polyposis coli (APC) gene, additional factors may influence the age of onset and number of duodenal adenomas. This study compared the genotype distributions of duodenal detoxification enzyme isoforms in patients with FAP and controls.

Methods

The study included 85 patients with FAP and 218 healthy age- and sex-matched controls. Genotyping of all participants using polymerase chain reaction was performed to detect polymorphisms in isoforms of uridine 5′-diphosphate glucuronosyltransferases (UGTs) and glutathione S-transferases (GSTs): UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A10, UGT2B4, UGT2B7, UGT2B15, GSTA1, GSTP1, GSTM1 and GSTT1.

Results

The variant genotypes of UGT1A3 were less common in patients with FAP than in controls (odds ratio 0·39 (95 per cent confidence interval 0·22 to 0·67)). There were no associations between FAP and the other polymorphic genes. The polymorphisms investigated had no predictive value for the severity of duodenal adenomatosis in patients with FAP.

Conclusion

Although the variant genotypes of UGT1A3 were less common in patients with FAP than in those without, this did not modulate the severity of duodenal adenomatosis.
Carbohydrate antigen 19·9 accurately selects patients for laparoscopic assessment to determine resectability of pancreatic malignancy
Authors: Halloran C M , Ghaneh P , Connor S , Sutton R , Neoptolemos J P , Raraty M G T
Published: December 2007

Background

Laparoscopy with laparoscopic ultrasonography (L–LUS) may be useful in the selection of patients for surgery to resect peripancreatic malignancy in addition to contrast-enhanced computed tomography (CE–CT). The present prospective study assessed the strategy of using carbohydrate antigen 19·9 (CA19·9) levels to select patients for L–LUS.

Methods

Patients with suspected peripancreatic malignancy that appeared resectable on CE–CT were selected for immediate surgery if CA19·9 was low (up to 150 kU/l, or up to 300 kU/l if serum bilirubin was above 35 µmol/l), or to L–LUS if CA19·9 was high (over 150 kU/l, or over 300 kU/l if serum bilirubin was above 35 µmol/l). Data were assessed to determine the clinical utility of this strategy.

Results

A total of 94 patients went straight to surgery, of whom 65 proved resectable: 63 of 80 with a low CA19·9 level but only two of 14 with a high CA19·9 level and gastric outlet obstruction. From 55 patients with high CA19·9 levels, L–LUS correctly identified 26 of 31 resectable tumours and eight of 24 unresectable tumours.

Conclusion

Using CA19·9 levels to help select patients with pancreatic malignancy for immediate surgery or L–LUS for further assessment of resectability effectively increased resection rates and reduced unnecessary laparotomies.
Surgery in immunocompromised patients
Authors: Graeb C , Jauch K-W
Published: December 2007

Aging, immune disease and transplantation are discussed
Oncoplastic surgery for breast cancer
Authors: Baildam A D
Published: December 2007

Higher levels of evidence proving difficult
Letter 1: Functional results after extended myotomy for diffuse oesophageal spasm (Br J Surg 2007; 94: 1113–1118)
Authors: Storr M
Published: December 2007

The Editors welcome topical correspondence from readers relating to articles published in the Journal. Responses should be sent electronically via the BJS website (www.bjs.co.uk). All letters will be reviewed and, if approved, appear on the website. A selection of these will be edited and published in the Journal. Letters must be no more than 250 words in length.
Solubility Calculation of Oil‐Conta‐minated Drill Cuttings in Supercritical Carbon Dioxide Using Statistical Associating Fluid Theory (PC‐SAFT)
Authors: Esmaeilzadeh F. , Goodarznia I. , Daneshi R.
Published: December 2007

Supercritical fluid extraction is a new technology that could be effectively used to treat oil‐contaminated drill cuttings generated during drilling for oil and gas. In this work, the solubility of oil‐contaminated drill cuttings in supercritical carbon dioxide is obtained by an experimental flow type apparatus. The solubility was measured at 200 bar pressure, over a temperature range of 55–79.5 °C. The measured solubility and experimental data for oil in drill cuttings were correlated using the PC‐SAFT, PR and SRK EOS models, without any adjustable parameters. Average absolute derivations of less than 15.1 %, 98.7 %, and 99.3 % are achieved between predicted and experimental values for the PC‐SAFT, PR and SRK EOS models, respectively, over a wide range of temperatures.
Modification of Nafion Membranes by Impregnation with Ionic Liquids
Authors: Schmidt C. , Glück T. , Schmidt‐Naake G.
Published: December 2007

Nafion 117 membranes were impregnated with various imidazolium (1‐hexyl‐3‐methyl‐imidazolium/HMI, 1‐butyl‐3‐methyl‐imidazolium/BMI) and pyrrolidinium (1‐butyl‐1‐methyl‐pyrrolidinium/BMPyr) based ionic liquids bearing hydrophobic (tris(pentafluoroethyl)trifluorophosphate/FAP, bis(trifluoromethylsulfonyl)imide/BTSI, hexafluorophosphate/PF6) and more hydrophilic (tetrafluoroborate/BF4) anions. The modified membranes were characterized in terms of uptake behavior, washing out of the ionic liquids by water, swelling in humidified environment, thermal stability, mechanical properties, ion exchange capacity and ion conductivity. Upon this treatment, the ionic liquids' cations partially replace the protons of the sulfonic acid groups in Nafion. While the ionic liquids act as potent plasticizers in the polymer matrix, thermal stability of these systems remains unchanged and swelling by water of the dried ionomer membranes is reduced. Ion conductivities at 120 °C under dry conditions have been found to be up to 100 times higher than for dry Nafion 117. In particular, modification of Nafion by ionic liquids bearing the bulky hydrophobic FAP anion seems promising.
Factors Affecting Scale Formation in Sea Water Environments – An Experimental Approach
Authors: Alahmad M.
Published: December 2007

Sea water is a complex aqueous environment with a large tendency for scale formation, which is usually ascribed to scaling from dissolved salts and suspended particles. Scale formation is causing many problems in thermal processes such as desalination and steam generation plants. In a typical desalination plant, ca. 40 % of the heat transfer area is provided to allow for scale formation problems, which is equivalent to a ca. 10 % increase of the whole capital cost of the plant. The main constituents forming scale in sea water environments, i.e., calcium carbonate, calcium sulfate and magnesium hydroxide, are extensively investigated in the present work. In order to obtain a better understanding of the scaling tendency of the seawater environment, an experimental unit was precisely designed and coupled with a data acquisition system for continuous monitoring of the investigated parameters. Significant factors affecting scale formation such as concentration of salts, flow velocity, water temperature and pH of the environments were studied at length using mild steel and stainless steel (smooth and rough). Hydrodynamic parameters such as Reynolds number and shear stress were used in the analysis of the collected data and revealed the role of shear stress in the effective removal of scale. The Kern‐Seaton scale model was used to calculate the fouling resistance in each case and the values obtained were compared with the experimental results. A modification of this model was also undertaken to provide better agreement with experimental findings.
Study of the Characteristics of Methanol Synthesis in a Recirculation Slurry Reactor – A Novel Three‐Phase Synthesis Reactor
Authors: Hu L. H. , Wang X. J. , Yu G. S. , Wang F. C. , Yu Z. H.
Published: December 2007

A process feasibility analysis on the liquid phase methanol synthesis (LPMeOHTM) process was performed in a recirculation slurry reactor (RSR). In the three‐phase RSR system, a fine catalyst is slurried in the paraffin and this catalyst slurry is continuously recirculated through the nozzle from the slurry sector to the entrained sector by a pump. The syngas is fed concurrently with the downward flow of slurry to form the methanol product. A laboratory scale mini‐pilot plant version of a recirculation slurry reactor system was successfully designed and built to carry out process engineering research, and in addition, an identical cold model was built to measure the mass transfer coefficient in the recirculation slurry reactor. The effects of operating conditions, including temperature, pressure, gas flow rate and catalyst slurry recirculation flow rate on the productivity of methanol were studied. This experimental data helps the scale‐up and commercialization of the methanol synthesis process in recirculation slurry reactors.
Measuring Average Particle Size for Fluidized Bed Reactors by Employing Acoustic Emission Signals and Neural Networks
Authors: Chen X. M. , Chen D. Z.
Published: December 2007

Average particle size is one of the key parameters of fluidized bed reactors. A novel method to measure the average particle size in fluidized bed reactors by acoustic emission (AE) signal is proposed. The measurement of the average particle size by AE is superior to other methods since it is inherently safe to use and it is also a non‐invasive method. AE signals originating from different particle sizes were 8‐level decomposed by a Daubechies wavelet of order 3 after being denoised with a sym8 wavelet filter combined with the rigrsure threshold method. Principal component analysis (PCA) was applied to overcome the complex collinearity and reduce the number of input variables of the neural network. A feed‐forward back propagation neural network with two hidden layers was used to predict the average particle size according to the principal components. The results show that this soft‐measuring model is suitable for measuring the average particle size in the fluidized bed reactors by online AE. It achieved high accuracy when applied to a model‐scale fluidized bed.
Particle Shape and Purity in Membrane Based Crystallization
Authors: Weckesser D. , König A.
Published: December 2007

Well‐controlled crystallization is the best method for preparing materials that are uniform in shape, size, structure and purity. The driving forces for crystallization are local gradients of supersaturation as the source and desupersaturation as the drain. Very high local supersaturation causes a high growth rate and represents a limiting factor for unstable modifications and product impurities. Hybrid membrane technology provides an interesting tool for controlling and limiting the maximum level of supersaturation due to defined mass transfer across the membrane. In this paper, the level of crystal growth rate in the system NaCl/KCl/water is varied by using different crystallization techniques. Vacuum evaporation crystallization (high growth rate) is compared to membrane based evaporation crystallization (low growth rate) and the results are interpreted in terms of product purity, particle shape and size. Membrane based crystallization in combination with effective solid/liquid separation as well as high performance analytics is suggested as a significant ultrapurification methodology.
Numerical Investigation of Hydrocarbon Enrichment of Process Gas Mixtures by Permeation through Polymeric Membranes
Authors: Kawachale N. , Kumar A. , Kirpalani D. M.
Published: December 2007

In membrane‐based gaseous separations, a consensus on the distribution of the components of the permeate stream in the immediate membrane vicinity has yet to be reached and the possibility of an underestimation of selective gas permeance due to lack of gas mixing on the permeate side exists. In this work, a numerical study of the permeation of ethylene and propylene in their binary mixtures with nitrogen through a composite poly(dimethylsiloxane) coated polysulfone membrane was performed. Continuity and momentum equations, along with gas compressibility and permeance properties for individual species of the gas mixture, were introduced into a comprehensive computational fluid dynamics (CFD) model. Simulation results showed that irrespective of the stage‐cut, gases with higher selectivity were well mixed in the vicinity of the membrane on the permeate side.
Co‐current and Countercurrent Configurations for a Membrane Dual Type Methanol Reactor
Authors: Rahimpour M. R. , Lotfinejad M.
Published: December 2007

A dynamic model for a membrane dual‐type methanol reactor was developed in the presence of catalyst deactivation. This reactor is a shell and tube type where the first reactor is cooled with cooling water and the second one with feed synthesis gas. In this reactor system, the wall of the tubes in the gas‐cooled reactor is covered with a palladium‐silver membrane which is only permeable to hydrogen. Hydrogen can penetrate from the feed synthesis gas side into the reaction side due to the hydrogen partial pressure driving force. Hydrogen permeation through the membrane shifts the reaction towards the product side according to the thermodynamic equilibrium. Moreover, the performance of the reactor was investigated when the reaction gas side and feed gas side streams are continuously either co‐current or countercurrent. Comparison between co‐current and countercurrent mode in terms of temperature, activity, methanol production rate as well as permeation rate of hydrogen through the membrane shows that the reactor in co‐current configuration operates with lower conversion and also lower permeation rate of hydrogen but with longer catalyst life than does the reactor in countercurrent configuration.
Flue Gas Desulfurization by a Powder‐Particle Spouted Bed
Authors: Moeini M. , Hatamipour M. S.
Published: December 2007

The powder‐particle spouted bed process is one of the semi‐dry processes that have been developed for flue gas desulfurization. In this study, which is designed for SO2 removal by a powder‐particle spouted bed, the reaction term is included in one‐dimensional and streamtube models that were presented previously for spouted beds. Hydrated lime is used as the sorbent in this process. The predictions of the models are compared with some published experimental data and it is found that the developed models are valid. The results of two models are compared with each other and their various properties are evaluated. The effects of different operating conditions on SO2 removal efficiency are also investigated and preferred operating conditions are discussed.
The Effect of Oxygen Concentration on the Reaction of NOx with Soot Over BaAl2O4
Authors: Li Y. J. , Lin H. , Shangguan W. F. , Huang Z.
Published: December 2007

The effect of oxygen concentration on the catalytic reaction of NOx with soot over BaAl2O4 has been studied by Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS). The introduction of O2 into the NO flow can result in a reactant mixture of NO/NO2/O2. Increasing the O2 concentration from 2 % to 5 % in the NO‐containing flow promotes the formation of NO2 from the gas phase oxidation of NO. The reactant mixture with high O2/NO flow, allows for the formation of greater amounts of nitrate species than that with low O2/NO flow, which further promotes the reaction of soot with NOx and leads to a high conversion efficiency of NOx into N2 and N2O. In the absence of O2, N2O is not observed since the N2O produced at high temperatures has reacted with soot before it can be detected.
Temperature‐Programmed Oxidation of Soot in a Hybrid Catalysis‐Plasma System
Authors: Lin H. , Huang Z. , Shangguan W. F.
Published: December 2007

Non‐thermal plasma (NTP) technology was applied to promote the temperature‐programmed oxidation (TPO) of soot over a perovskites type of La0.8K0.2MnO3 catalyst. The O radicals originating from the decomposition of O2, as well as NO dissociation if nitrogen oxide were involved, reduce the ignition temperatures of soot. In NO‐O2‐He, for example, the ignition temperature decreased to 240 °C from 290 °C as the voltage increased from 0 kV to 15 kV. The higher voltage also benefited the adsorption of NO molecules onto the catalyst surface (NOad). As a result, the maximum N2/NO ratio (conversion ratio of NO into N2) rose from 23 % to 53 %. Some of the NO molecules were dissociated into N and O radicals in plasma, and hence, the N2/NO ratio was further enhanced due to the combination of N atoms. In any case, the redox process between NOx and soot proved to be important in soot oxidation.
Preparative Purification of Solanesol from Tobacco Leaf Extracts by Macroporous Resins
Authors: Du X. L. , Yuan Q. P. , Li Y. , Zhou H. H.
Published: December 2007

In the present study, the preparative purification of solanesol by macroporous resins was studied. The adsorption and desorption properties of solanesol on macroporous resins including SP207, SP700, SP825, SP850 and HP20 were compared. SP850 resin offered the best adsorption and desorption capacities based on the research results. Both Langmuir and Freundlich isotherms were used to describe the interactions between the solutes and resin at different temperatures, and the experimental data fits best to the Freundlich isotherms. Adsorption and desorption kinetic curves were obtained for solanesol adsorption on SP850 resin in the temperature range of 298–303 K. The results showed that the mobility of solanesol adsorption increased and the proportion of adsorbed solanesol decreased with increasing temperature. The adsorption kinetic curve can be classified into three portions, i.e., instantaneous adsorption stage, intraparticle diffusion stage and the final equilibrium stage. Dynamic adsorption and desorption experiments were carried out with the column packed by SP850 resin to optimize the separation process. The isocratic and stepwise operations were designed for the separation of solanesol. The use of stepwise elution allowed a reduction in the process time and solvent consumption, but also led to some loss in purity. The corresponding optimal parameters for adsorption and desorption were determined. According to the research results, it can be concluded that SP850 resin possesses a good ability to separate solanesol and the results in this study may provide scientific references for large‐scale solanesol production from tobacco leaf extracts.
Heterogeneous Catalysis in Supercritical Media: 1. Carbon Dioxide
Authors: Kruse A. , Vogel H.
Published: December 2007

Over the past few years, supercritical fluids have received considerable interest as reaction media. Supercritical fluids combine properties of gases and liquids. Densities are lower than in the liquid phase, but significantly higher than in the gas phase. This makes supercritical fluids excellent solvents for a variety of substances. The good dissolution capacity exists only in or near the supercritical range. Reaction products can be separated, for instance, simply by decreasing temperature and pressure. This may be used to intensify the process as complex separation processes, like distillation, are avoided.
Extension of a Method for the Design of Divided Wall Columns
Authors: Sotudeh N. , Shahraki B. H.
Published: December 2007

For most separations, a fully thermally coupled distillation column or divided wall columns are thermodynamically more efficient than conventional columns. This paper develops a method for the design of divided wall columns consisting of multi‐component mixtures (more than three components) with constant relative volatilities and a relatively sharp separation between the key components.
Degradation of Pentoses and Hexouronic Acids in Subcritical Water
Authors: Usuki C. , Kimura Y. , Adachi S.
Published: December 2007

The degradation of arabinose, xylose, ribose and lyxose in subcritical water was measured at 200, 220 and 240 °C. Ribose was the most rapidly degraded among the pentoses tested. The degradation of the glucuronic and galacturonic acids proceeded at lower temperatures than that of the pentoses, and was measured at 140, 150 and 160 °C. The degradation processes of the pentoses and hexouronic acids could be expressed by the Weibull model, and the kinetic parameters were then estimated. The activation energy and frequency factor for the degradation of each substrate were estimated from the temperature dependence of the rate constant. The enthalpy‐entropy compensation held for the degradation of the pentoses as well as the hexoses, which suggests that the degradation of the hexouronic acids proceeded through a mechanism different from that for the pentoses and hexoses. The molar yield of a pentose to furfural was ca. 0.3 at any temperature, irrespective of the pentose type. Acidic compounds were also formed from the pentoses in proportion to the amount of consumed substrates. The formation of acidic compounds resulted in a rapid decrease in pH.
Folding Control in Cyclic Peptides through N‐Methylation Pattern Selection: Formation of Antiparallel β‐Sheet Dimers, Double Reverse Turns and Supramolecular Helices by 3α,γ Cyclic Peptides
Authors: Amorín Manuel , Castedo Luis , Granja Juan R.
Published: December 2007

Peptide foldamers constitute a growing class of nanomaterials with potential applications in a wide variety of chemical, medical and technological fields. Here we describe the preparation and structural characteristics of a new class of cyclic peptide foldamers (3α,γ‐CPs) that, depending on their backbone N‐methylation patterns and the medium, can either remain as flat rings that dimerize through arrays of hydrogen bonds of antiparallel β‐sheet type, or can fold into twisted double reverse turns that, in the case of double γ‐turns, associate in nonpolar solvents to form helical supramolecular structures. A 3α,γ‐CP consists of a number of multiples of a repeat unit made up of four amino acid residues of alternating chirality: three corresponding to α‐amino acids and one to a γ‐amino acid (acis‐3‐aminocycloalkanecarboxylic acid).
Towards a Fully Conjugated, Double‐Stranded Cycle: A Mass Spectrometric and Theoretical Study
Authors: Denekamp Chagit , Etinger Alexander , Amrein Walter , Stanger Amnon , Stuparu Mihaiela , Schlüter A. Dieter
Published: December 2007

The two compounds, 1 and 5, are investigated by means of collision‐induced dissociation experiments by using ion cyclotron resonance mass spectrometry and other mass spectrometric techniques as to their ability to act as precursors for the fully unsaturated double‐stranded target compound 2. These experiments are complemented by flask‐type pyrolyses of 5, the products of which are analyzed by mass spectrometry. For 1, no conditions were found under which the expected molecular ion of 2 at m/z 932 appeared, however, for its derivative 5 this was possible. This interesting finding is not in contradiction with the chemical structure of the long sought for compound 2 but calculations suggest that this compound may have isomerized into one where the conjugation is interrupted by hydrogen shift from the solubilizing alkyl chains into the cycle's perimeter. The key driving force for such an isomerization would be the considerable relief of strain energy.
Delicate Crystal Structure Changes Govern the Magnetic Properties of 1D Coordination Polymers Based on 3d Metal Carboxylates
Authors: Gavrilenko Konstantin S. , Cador Olivier , Bernot Kevin , Rosa Patrick , Sessoli Roberta , Golhen Stéphane , Pavlishchuk Vitaly V. , Ouahab Lahcène
Published: December 2007

Homo‐ and heterometallic 1D coordination polymers of transition metals (CoII, MnII, ZnII) have been synthesized by an in‐situ ligand generation route. Carboxylato‐based complexes [Co(PhCOO)2]n (1 a, 1 b), [Co(p‐MePhCOO)2]n (2), [ZnMn(PhCOO)4]n (3), and [CoZn(PhCOO)4]n (4) (PhCOOH=benzoic acid, p‐MePhCOOH=p‐methylbenzoic acid) have been characterized by chemical analysis, single‐crystal X‐ray diffraction, and magnetization measurements. The new complexes 2 and 3 crystallize in orthorhombic space groups Pnab and Pcab respectively. Their crystal structures consist of zigzag chains, with alternating MII centers in octahedral and tetrahedral positions, which are similar to those of 1 a and 1 b. Compound 4 crystallizes in monoclinic space group P21/c and comprises zigzag chains of MII ions in a tetrahedral coordination environment. Magnetic investigations reveal the existence of antiferromagnetic interactions between magnetic centers in the heterometallic complexes 3 and 4, while ferromagnetic interactions operate in homometallic compounds (1 a, 1 b, and 2). Compound 1 b orders ferromagnetically at TC=3.7 K whereas 1 a does not show any magnetic ordering down to 330 mK and displays typical single‐chain magnet (SCM) behavior with slowing down of magnetization relaxation below 0.6 K. Single‐crystal measurements reveal that the system is easily magnetized in the chain direction for 1 a whereas the chain direction coincides with the hard magnetic axis in 1 b. Despite important similarities, small differences in the molecular and crystal structures of these two compounds lead to this dramatic change in properties.
(Me3Si)3SiH: Twenty Years After Its Discovery as a Radical‐Based Reducing Agent
Authors: Chatgilialoglu Chryssostomos
Published: December 2007

This Concept shows the flexibility and applicability of (Me3Si)3SiH in several synthetic transformations, such as radical reductions, consecutive radical reactions and hydrosilylation. The reactivity of (Me3Si)3SiH combines the multidisciplinary aspects of physical organic chemistry and organic synthesis, extending to polymers and materials science, as in the functionalization of flat silicon surfaces.
The Total Synthesis of (+)‐Tedanolide—A Macrocyclic Polyketide from Marine Sponge Tedania ignis
Authors: Ehrlich Gunnar , Hassfeld Jorma , Eggert Ulrike , Kalesse Markus
Published: December 2007

Tedanolide, which was isolated by Schmitz in 1984 from the marine sponge Tedania ignis, is a highly cytotoxic macrolide leading to strong growth inhibition of P338 tumor cells in bioassays. A unique structural feature of the known tedanolides is the primary hydroxyl group incorporated in the macrolactone. This unusual motif for macrolactones originated from PKS biosynthesis might arise through lactonizations others than those derived by the thioesterase reaction. First experimental data that support this hypothesis and reflect the inherent preference of PKS‐induced macrolactonization were obtained during this synthesis. The inherent preference for the formation of a 14‐membered macrocyclization is discussed together with the pivotal steps in the synthesis.
Synthesis, Characterization, Molecular Structure and Theoretical Studies of Axially Fluoro‐Substituted Subazaporphyrins
Authors: Rodríguez‐Morgade M. Salomé , Claessens Christian G. , Medina Anaïs , González‐Rodríguez David , Gutiérrez‐Puebla Enrique , Monge Angeles , Alkorta Ibon , Elguero José , Torres Tomás
Published: December 2007

A new and general synthetic method for the preparation of fluoro‐substituted subazaporphyrins is reported that involves the treatment of the corresponding chloro‐ or aryloxy‐substituted subazaporphyrins (SubAPs) with BF3⋅OEt2. The strategy has been applied to both subphthalocyanines (SubPcs) and subporphyrazines (SubPzs). The yields were high for the latter, although low yields were obtained for the benzo derivatives. In contrast to the corresponding chloro derivatives, fluorosubazaporphyrins are quite robust towards hydrolysis. All of the new compounds were characterized by several spectroscopic techniques, which included1H,13C,19F,15N, and11B NMR spectroscopy, IR spectroscopy, UV/Vis spectrophotometry, and mass spectrometry (both high and low resolution). In addition, DFT calculations provided theoretical NMR spectroscopy values that are in good agreement with the experimental ones. The high dipole moments exhibited by the fluorosubazaporphyrins as a result of the presence of a fluorine atom in an axial position are responsible for the spontaneous and singular supramolecular aggregation of the macrocycles in the crystalline state. The molecular and crystal structures of two one‐dimensional fluorine SubAPs, namely, a SubPc and a SubPz, are discussed. Molecules of the same class stack in alternating configurations along thecaxis, which gives rise to columns that contain large numbers of monomers. SubPz3 cforms aggregates with the macrocycles arranged in a parallel fashion with the BF bonds perfectly aligned within a column, whereas with SubPc3 bthe neighboring columns cause a commensurate sinusoidal distortion along the columns in thecdirection, which prevents the alignment of the BF bonds. However, the most remarkable feature, common to both crystalline architectures, is the extremely short and unusual intermolecular F⋅⋅⋅N distances of the contiguous molecules, which are shorter than the sum of the corresponding van der Waals radii. Theoretical calculations have shown that these short distances can be explained by the existence of a cooperativity effect as the number of monomers included in the cluster increases.