bluuebunny/crossref_metadata_2025 huggingface dataset:
Probiotics and prebiotics in female health
Authors: Smejkal Christopher , Kolida Sofia , Bingham Max , Gibson Glenn , McCartney Anne
Published: August 2004

Functional foods such as probiotics, prebiotics and nutraceuticals are of extreme interest to researchers. There is growing evidence that these food ingredients may improve and in some cases treat certain conditions that are implicated in women's health. The use of probiotics (live, beneficial bacteria) in improving gastrointestinal and non-gastrointestinal tract conditions such as irritable bowel syndrome, candidiasis and other female urogenital tract conditions are reviewed. Emphasis is also given to the importance of prebiotics (non-digestible food ingredients) in osteoporosis management and alleviation of menopausal symptoms and reducing the onset of cancer.
Risk factors for urinary incontinence in women
Authors: Robinson Dudley , Cardozo Linda
Published: August 2004

Urinary incontinence is a common and distressing condition which, whilst not life threatening, is known to cause considerable morbidity. Causation is multifactorial, although many risk factors have been identified. The purpose of this review is to provide a critical overview of the epidemiological evidence when considering risk factors for urinary incontinence in women.
Prophylactic mastectomy: why and when?
Authors: Von Smitten Karl
Published: August 2004

Introduction of BRCA1 and BRCA2 gene mutation analysis has increased interest in prophylactic mastectomy and immediate breast reconstruction as a risk reduction measure for women at increased risk of breast cancer. Prophylactic mastectomy has been suggested to decrease the risk of breast cancer by at least 90%. Because the cosmetic result of immediate breast reconstruction may not be optimal, nipple sensation is lost, and capsule contraction may cause problems when silicon prostheses are used, the patients should be well informed of risks and other preventive methods. Surveillance or chemoprevention are suggested as alternatives to risk reduction mastectomy, but there is lack of prospective randomised trials comparing these options. Because BRCA1 and BRCA2 gene mutations also increase risk of ovarian cancer, management of these patients should be shared by the breast surgeon and gynaecologist.
Prophylactic oophorectomy: why and when?
Authors: Lane Geoffrey
Published: August 2004

Ovarian cancer presents at a late stage and is associated with a very poor chance of cure. Ability to predict women who are at genetic risk has directed our thoughts to the possibility that the timely removal of the ovaries in these women is likely to prevent cancer and save lives. Only approximately 10% of ovarian cancers arise as a result of an inherited condition; it is this group which is most likely to benefit from prophylactic oophorectomy. Women in this group may be identified following referral on the basis of personal or family histories of disease. With continued improvement in genetic screening, the literature regarding prevention of ovarian cancer appears to be moving beyond the appropriateness of prophylactic oophorectomy to a discussion of the technical aspects of the procedure. There is little doubt that this type of surgical prophylaxis will become more popular. Numerous studies have now demonstrated that prophylactic oophorectomy will not only offer a high degree of protection against ovarian cancer but also against breast cancer. It is important for the future that research continues to examine the operative technique and its implications, particularly with regard to Fallopian tube and peritoneal cancer.
Hormone therapy after endometrial cancer
Authors: Mueck Alfred O. , Seeger Harald
Published: August 2004

Endometrial carcinoma is often listed in data sheets as an absolute contraindication to hormone replacement therapy. However, observational studies have not shown an increased rate of recurrence or mortality. Thus, it is often used after stage I or II disease. Alternatives such as progestogens, tibolone, raloxifene, venlafaxine and herbal preparations are examined. The use of progestogens is under discussion because of potential adverse effects on the breast. Generally after treatment for endometrial cancer, current preference should be for low-dose oestrogen monotherapy rather than continuous combined therapy with progestogen addition in view of the increased risk of breast cancer and cardiovascular disease found with the latter regimen. It is important to note that risk factors for endometrial cancer such as hypertension, obesity, polycystic ovary syndrome and diabetes mellitus also increase the risk of cardiovascular disease. However, women must be informed about potential risks and the use of alternatives.
Hand function after the menopause
Authors: Edmonds Sally
Published: August 2004

Hand function declines with age, and therefore, by implication, after the menopause. The simple ageing process clearly affects both women and men, but women may experience more of a decline of hand function in older age. This is not readily explained in terms of straightforward ageing, but women are more likely to be adversely affected by diseases such as osteoarthritis and rheumatoid arthritis. Hormonal influences, particularly in osteoarthritis, may be the reason for women experiencing more severe disease. Both arthritides are multi-factorial in their aetiology, and the same is true of the declining hand function that is seen as part of the ageing process.
'Two week wait' standards for suspected gynaecological malignancy. On target, but missing the point?
Authors: Morrison Joanne
Published: August 2004

Objective: To assess the two-week rapid access referral system for UK general practitioners introduced in April 2000 for women suspected of having a gynaecological cancer.

Study design: An audit of details of women referred between 1st April 2000 and 31st March 2003 via the two-week rapid access system to one gynaecological consultant who performs gynaecological oncology surgery at the John Radcliffe Hospital, Oxford.

Main outcome measures: Information on waiting times, clinical indication (postmenopausal bleeding, suspicious pelvic mass, vulval lesions, or "other" symptoms including postcoital vaginal bleeding, suspicious lesions of the cervix or vagina), and subsequent diagnosis were recorded. Data on all other women in whom a diagnosis of a gynaecological malignancy was made during the same period following referral to the same consultant's routine gynaecological outpatient clinic were also collected.

Results: The target time of two weeks to see a consultant was met for 94% of women referred via the rapid access system. The response time declined slightly with increasing numbers of referrals. However, the majority of women with a gynaecological malignancy were not referred via the rapid access system.

Conclusions: To accommodate the two-week rapid access referrals and achieve UK government targets, there was a reduction in appointments for routine outpatient referrals. However, as the majority of women with gynaecological malignancy presented via traditional referral routes, there is a danger that their diagnoses are being delayed.
The role of HRT: Where are we now? Clinical implications of latest HRT data
Authors: Currie Heather
Published: August 2004

The results of the Women's Health Initiative have highlighted some small but important risks associated with hormone replacement therapy (HRT). Interpretation of these findings by the media has generated considerable adverse publicity. This review discusses the clinical implications of recent data relating to HRT. When used appropriately for the control of menopausal symptoms or for treating or preventing osteoporosis in those at risk, the benefits generally outweigh the risks. For symptom control or bone effects, the type of HRT chosen should be that which achieves its therapeutic goal with as few adverse effects as possible. Currently, there is little rationale for the use of HRT in the prevention of cardiovascular disease. To help ensure the appropriate use of HRT, women and healthcare professionals alike require high quality, up-to-date information on menopause and its management. Notwithstanding issues relating to quality of content, the Internet is a useful source of information with much potential for education. The appropriate use of HRT also depends upon regular review of patients taking HRT and other “at risk” groups (eg, patients at risk of developing osteoporosis). This practice allows re-analysis of risk vs benefit, the balance of which will change with duration of therapy, the development of other medical problems and the publication of new information on HRT.
No increased risk of endometrial hyperplasia with fixed long-cycle oestrogen-progestogen therapy after five years
Authors: Erkkola Risto , Kumento Ulpu , Lehmuskoski Sirpa , Mattila Leena , Mustonen Mika
Published: August 2004

Objective: The aim of this study was to evaluate the long-term endometrial safety of long-cycle sequential oestrogenprogestogen hormone replacement therapy (HRT).

Study design: A prospective, longitudinal, single group study was undertaken in postmenopausal women, aged 45-66 years, treated with up to 21 3-month cycles (five years) of sequential oestrogen-progestogen HRT. Treatment consisted of 70 days of 2 mg/day oestradiol valerate (E2V), followed by 14 days of E2V combined with 20 mg/day medroxyprogesterone acetate (MPA), followed by seven days placebo.

Endometrial biopsies were assessed at baseline, at 12 months in women with an endometrial thickness >6 mm and in all participants at 24, 36, 48 and 60 months. Mammography was performed at baseline and at 24-month intervals thereafter. Adverse events were assessed throughout the study.

Results: Of 132 women enrolled, 94 completed five years of treatment (540 women years). Endometrial changes (oestrogen effect II) were apparent in most women from 24-60 months (95, 83.3% women at 24 months). One case of simple hyperplasia was found (at 60 months), and none of complex hyperplasia or endometrial cancer. The pattern and frequency of adverse events were consistent with other sequential oestrogen-progestogen HRT regimens.

Conclusions: The incidence of hyperplasia over five years (0.19%, upper 95% CI 0.88) was well within the acceptable rates defined by the European Union Committee for Proprietary Medicinal Products (CPMP).
The developmental origins of osteoporotic fracture
Authors: Harvey Nicholas , Cooper Cyrus
Published: August 2004

Undernutrition and other adverse influences arising in fetal life or immediately after birth have a permanent effect on body structure, physiology and metabolism. Evidence is now accumulating from human studies that programming of bone growth might be an important contributor to the later risk of osteoporotic fracture. Body weight in infancy is a determinant of adult bone mineral content, as well as of the basal levels of activity of the GH/IGF-1 and HPA axes, and recent work has suggested a central role for vitamin D. Epidemiological studies have suggested that maternal smoking and nutrition during pregnancy influence intrauterine skeletal mineralization. Finally, childhood growth rates have been directly linked to the risk of hip fracture many decades later. Further work is needed to use this approach to develop novel therapeutic and preventative strategies to reduce the burden of osteoporotic fractures in the population.
Screening for breast cancer
Authors: Litherland Janet
Published: August 2004

Mammographic screening for breast cancer commenced in the UK in 1988 following the recommendations of the Forrest Committee and is now well established. This article reviews the evidence for efficacy of mammographic screening, the mode of delivery of the service including the assessment of mammographic abnormalities and the role of needle biopsy in diagnosis. Despite the established position of breast screening in the UK there are continuing challenges, not least workforce issues and the recent extension of the programme. There is increasing interest in the use of digital mammography and research continues into the possibility of computer-assisted detection (CAD) of mammographic abnormalities.
Hormone replacement therapy and the bladder
Authors: McCully Keri S , Jackson Simon
Published: August 2004

Lower urinary tract symptoms are a common, distressing and embarrassing problem for women of all ages, but become increasingly more common with advancing age. Oestrogen preparations have been used for many years to manage urinary symptoms, but there is still controversy over the efficacy of these preparations. The purpose of this review is to provide a critical overview of the epidemiological evidence when considering hormone replacement therapy for treatment of urinary symptoms in women.

Various studies have demonstrated that oestrogen replacement can improve, or even cure, urinary stress and urge incontinence. High dose oestrogen can reduce the total number of voids in 24 hours, including nocturnal voids. Vaginal oestriol significantly reduces the risk of recurrent infections in postmenopausal women with a history of recurrent urinary tract infections. Data on combining oestrogen with a progestogen are limited, but suggest it may negate the benefit and more research is still required in this area to clarify their role.
Managing the menopause: BMS Council Consensus statement on HRT
Authors: Pitkin Joan
Published: August 2004

The British Menopause Society Council aims to help health professionals to inform and advise women about the menopause. The oestrogen plus progestogen arm of the Women's Health Initiative was stopped in July 2002. This guidance regarding hormone replacement therapy (HRT) use responds to the results and analysis that have been published since then, as well as the Million Women Study published in August 2003. Because there are few effective alternatives to HRT for vasomotor and urogenital symptoms, oestrogen-based treatments still have a major role. HRT is also most effective for the prevention of osteoporosis. Unopposed oestrogens are contraindicated in women with an intact uterus, and hence a range of oestrogen and progestogen combinations, with differing routes of delivery, now exists under the title of "HRT". Treatment choice should be based on up to date information and targeted to individual women's needs. Hormone replacement still offers the potential for benefit to outweigh harm, providing the appropriate regimen has been instigated in terms of dose, route and combination.
Red clover isoflavones and menopausal health
Authors: Ronald Barentsen
Published: August 2004

Menopausal symptoms such as hot flushes and night sweats can be very disrupting. While hormone replacement therapy is an effective therapy, concerns about side effects and breast cancer risk have stimulated interest into alternative therapies such as phytoe-strogens. These are oestrogen-like compounds made by plants. Two major sources of phytoestrogens are soy and red clover. Data on randomised controlled trials of red clover for the control of menopausal symptoms are presented. The conflicting data are encouraging and suggest that phytoestrogens are a treatment modality that needs pursuing.
Shared decision-making, health choices and the menopause
Authors: Salkovskis Paul M , Wroe Abigail L , Rees Margaret CP
Published: August 2004

The growing influence of the mass media on public understanding of health care matters has increased both information and misinformation in patients seeking help with menopausal symptoms. The use of shared decision-making strategies provides the opportunity to engage the patient in taking some responsibility for their own treatment. It also allows the identification and correction of any distortions in the perceived balance of evidence for and against any particular treatment. Shared decision-making balances the need to respect patients’ values and autonomy with the drive towards evidence-based medicine and clinical cost-effectiveness. Although ways of achieving such a balance are much discussed, the current need is for research which can identify effective strategies that allow the principles of “shared decision-making” and “evidence-based patient choice” to be validated and applied in clinical practice. Previous research focused on hormone replacement therapy indicates that the patient's decision is the outcome of the way they balance the pros and cons of taking (or not taking) it, and that their satisfaction with the decision is strongly associated with the perception that they have been given information about the full range of treatment available. It therefore seems likely that patients will respond more positively to consultations which include discussion of hormone replacement therapy alongside alternative strategies such as natural remedies and dietary/lifestyle changes. Psychological factors influencing treatment choice and the decision making process are discussed, and clinical and research implications for clinical practice in the menopause clinic examined.
Mental health and the ageing population
Authors: Dening Tom , Barapatre Charul
Published: August 2004

The ageing population of the world presents major challenges for society and for health services. Mental health issues are extremely important, as mental disorders, notably dementia and depression, are common in old age. Mental ill health can profoundly affect the quality of people's old age and has a significant impact upon the use of health and social services. In this paper, we examine these problems from the point of view of older people as consumers, and discuss the role of health promotion, primary care, social services and specialist mental health services for older people. Certain groups within the population, including women, people from minority ethnic backgrounds, very old people, people with learning disabilities, and gay and lesbian older people face some particular issues, which are briefly discussed. Although this paper takes a mainly UK perspective, the mental health of older people is a huge global public health issue. Good epidemiology is central to understanding the needs of ageing populations and responding to them appropriately. Further research is needed in other areas, especially as to which service interventions are effective and efficient.
Endocrine disrupters and menopausal health
Authors: Holmes Philip , Rumsby Paul , Harrison Paul T.C.
Published: August 2004

Chemicals known to disrupt the endocrine system of animal models are assessed for their potential impact on the health of menopausal and postmenopausal women. These "endocrine disrupters" consist of two groups of compounds – man-made and naturally occurring. There is some evidence to suggest that the naturally occurring phytoestrogens, derived from plant material, may have some beneficial effects on menopausal symptoms and the risk of breast cancer, cardiovascular disease and osteoporosis. Further studies are required to confirm these possibilities. Some man-made environmental pollutants appear to increase the risk of breast cancer, although again the evidence is inconclusive. Mechanistic experiments indicate that these chemicals interact with oestrogen receptors and alter metabolism in a number of different ways, some of which may be important in postmenopausal women. Further investigation of the differences in mode of action between the manmade and the natural endocrine disrupters may lead to important insights into their effects on women's health.
Physical activity and postmenopausal health
Authors: Beitz Roma , Dören Martina
Published: August 2004

Physical activity leads to a 30-50 % reduction in cardiovascular disease in women. Moderate activities such as walking, gardening or light sports appear to have beneficial effects. Additional exercise training may enhance these effects. Moderate-intensity activities constitute a key recommendation for primary prevention. Vigorous intensity activity may render additional benefits. Recent recommendations suggest an increase to at least 60 minutes of cumulative daily physical activity. Practical recommendations for the prevention of osteoporosis are less clear. There is a relative abundance of randomised controlled trials assessing bone mineral density at various sites. Meta-analyses of these studies indicate a beneficial health effect of physical activity on prevention of bone loss. However, the effects seen appear to be relatively small. Two recent end-point studies examining hip and fragility fractures show stronger evidence for the protective potential of physical activity in bone health. Exercise throughout life, particularly weight-bearing, is assumed to be beneficial for bone health. Older people at risk of falling are advised to participate in tailored exercise programmes to improve strength and balance, since physical training might contribute to fracture prophylaxis by increasing mobility and general activity of ageing people. Beyond the promotion of regular physical activity, primary disease prevention requires the adoption of healthy life habits including dietary patterns, weight control, and avoiding smoking. In the light of the failure of postmenopausal hormone use to protect against heart disease, rethinking the role of exercise in maintaining postmenopausal health is of increasing importance.
Non-response to osteoporosis treatment
Authors: Francis Roger M.
Published: August 2004

There are now a number of effective treatments for osteoporosis, which increase bone mineral density (BMD) and decrease the risk of fractures. There is no clear consensus on the optimal method for assessing response to treatment in the individual patient. The goal of osteoporosis treatment is to prevent fractures after minimal trauma, but these are relatively uncommon events and cannot be totally avoided by the use of currently available therapies. Alternative methods of assessing response to treatment include serial measurement of BMD or the biochemical markers of bone turnover, but the observed changes may be misleading if they do not exceed the least significant change. The proportion of patients who fail to respond to osteoporosis treatments is difficult to quantify. Clinical trials show continuing bone loss in up to 15% of participants on hormone replacement therapy or bisphosphonates. Non-response to treatment is probably more common in clinical practice, but may be due to poor adherence to treatment recommendations. Other potential causes of an apparent failure to respond to treatment include the use of a weak antiresorptive agent, differences in bioavailability, low dietary calcium intake, vitamin D insufficiency and underlying causes of secondary osteoporosis. The management of patients who fail to respond to treatment includes confirmation that they are adhering to treatment and have an adequate dietary calcium intake and vitamin D status and excluding causes of secondary osteoporosis. Consideration should also be given to the addition of calcium and vitamin D supplementation and the use of alternative treatments for osteoporosis.
Drug screening: Actual status, pitfalls and suggestions for improvement/Drogenscreening: Gegenwärtiger Stand, Fehlermöglichkeiten und Verbesserungsvorschläge
Authors: Külpmann Wolf R.
Published: August 2004

Abstract Immunoassays for drug screening are often regarded as procedures which are easily performed and interpreted. But in fact, many aspects have to be considered to obtain a meaningful result. Among these are sampling, specificity and sensitivity of assays, and quality assessment. Although the mechanised procedures yield quantitative results, there are good reasons to generally report qualitative findings. The mechanised procedures allow the adjustment of the cut-off concentration to the clinical setting, e.g. in the case of acute intoxication, chronic abuse or drug withdrawal, an important advantage as compared to test strips. Procedures for the detection of amphetamines, barbiturates, benzodiazepines or opiates are hampered by the fact that the analytical signal is in principle not related to the pharmacological effect of the contributing drug. A proposal for adjusting the analytical response to the pharmacodynamic action of a compound is presented, as well as a list of drugs for which immunoassays are required. This may give guidance to manufacturers for improving and developing assays. Procedures for individual compounds should in general specifically detect the pertinent metabolite in urine as a proof of drug uptake. Hydrolysis is mandatory in case of poor cross-reactivity of the antibody with the excreted conjugates.
Therapeutisches Drug Monitoring von Antidepressiva und Antipsychotika/Therapeutic monitoring of antidepressant and antipsychotic drugs
Authors: Hiemke Christoph
Published: August 2004

Abstract Studies have shown the beneficial effects of Therapeutic Drug Monitoring (TDM) for some antidepressant (tricyclic antidepressants) and antipsychotic drugs (e.g. haloperidol or clozapine). For these drugs, TDM should be used as standard care. Moreover, TDM is useful for a number of specific indications such as control of compliance, drug-drug interactions, comorbidity, nonresponse, or unexpected side effects. In practice, blood should be taken under steady state conditions and analytical methods should be sufficiently sensitive (lower limit of quantification about 5 to 50 ng/ml) and precise (day-to-day variabilities below 20%). Chromatographic methods are suitable, whereas immunoassays for antidepressants and radioreceptor assays for antipsychotics have insufficient reliability. TDM results should be reported with inclusion of a qualified comment as soon as possible after blood withdrawal. The clinical decision must consider not only blood levels but also time under drug therapy, clinical improvement and side effects. Some studies have shown an economical impact of TDM. The potential beneficial effects of TDM in anti-psychotic and anti-depressive drug therapy are not adequately utilized, since psychiatrists order these tests too rarely.
Extraction and separation of Am(III) and Sr(II) by N,N,N´,N´-tetraoctyl-3-oxapentanediamide (TODGA)
Authors: Suzuki H. , Sasaki Y. , Sugo Y. , Apichaibukol A. , Kimura T.
Published: August 2004

By using an extractant, N,N,N´,N´-tetraoctyl-3-oxapentanediamide (TODGA), extraction and separation of Sr(II) from Am(III) were investigated for the partitioning of high level liquid waste (HLLW). Both metal ions, accompanied with the counter anion, NO3
-, and HNO3 without dissociation, were extracted by TODGA. We used two distinct methods for the separation of Am(III) and Sr(II). A mixture of TODGA and monoamide reduced the distribution ratio D of Sr(II) compared to that without monoamide, whereas D(Am) was still high value under the identical condition. After extraction of Am(III) by TODGA and monoamide, Sr(II) remaining in HLLW can be extracted by using enough concentration of TODGA at the next step. In the other method, Sr(II) was coextracted with Am(III) by TODGA. It was observed that D(Sr) decreased with an increase of HNO3 from 3 M to 6 M HNO3 at the same TODGA concentration, while D(Am) increased until 6 M HNO3. By using 6 M HNO3, Am(III) and Sr(II) were separated after coextraction.
Monitoring of metallurgical process plants by using biplots
Authors: Aldrich C. , Gardner S. , Le Roux N. J.
Published: August 2004

Although principal component analysis has been applied widely for monitoring plant performance in a broad range of industrial processes, the use of accompanying biplots has not received similar attention. Moreover, principal component analysis is a linear technique that tends to break down when processes exhibit significant nonlinear behavior. In this paper biplot methodology is introduced. This methodology allows for projecting high‐dimensional data to a low‐dimensional subspace that can be visualized by a human operator. It provides management with sophisticated tools, highly graphical in nature, to extract information regarding variation in process variables, correlations among these variables, as well as class separation, taking into account the multidimensional character of the data. Biplot methodology can also be applied to data sets exhibiting nonlinear behavior. As is shown by way of two case studies, operating regions can be quantitatively explored by superimposing alpha bags on biplots, which facilitates the automatic detection and visualization of process disturbances. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2167–2186, 2004
Comparison of micromixing models for CFD simulation of nanoparticle formation
Authors: Wang Liguang , Fox Rodney O.
Published: August 2004

Reactive precipitation is an important research topic in chemical engineering because of its numerous industrial applications in the formation of nanoparticles. Recently, computational fluid dynamics (CFD) has been successfully coupled with micromixing models and probability density function (PDF) methods to predict the effect of mixing on the particle size distribution. The micromixing model is generally based on the presumed PDF method. The objective of this work is to compare multienvironment‐presumed PDFs and a recently proposed direct‐quadrature‐method‐of‐moments‐interaction‐by‐exchange‐with‐the‐mean (DQMOM‐IEM) micromixing model with transported PDF predictions for the simulation of reactive precipitation, including simultaneous mixing‐limited reaction, nucleation, and growth in a plug‐flow reactor. DQMOM is applied to calculate the turbulent spurious dissipation rate for the multienvironment micromixing models. The results show that the DQMOM‐IEM model agrees well with the transported PDF simulations, even when the number of nodes used in DQMOM is small (such as 2–4). Given the computational efficiency of the DQMOM‐IEM model relative to transported PDF methods, this model offers great promise as a practical CFD tool for simulating plant‐scale reactors. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2217–2232, 2004
Closed‐loop behavior of nonlinear model predictive control
Authors: Tenny Matthew J. , Rawlings James B. , Wright Stephen J.
Published: August 2004

Model predictive control (MPC) relies on real‐time optimization to determine open‐loop control profiles and state estimates given process measurements. When the underlying process model is nonlinear, the MPC system exhibits unique behavior not seen in linear MPC. Some of the characteristics are highlighted of nonlinear models in the context of closed‐loop performance. The effects are examined of disturbance models on closed‐loop performance and necessary conditions are shown for how and where steady states of the closed‐loop system may be found. These conditions are demonstrated on a simple example to show that the input disturbance model can lead to failure of the control system, and that linear MPC is inadequate for controlling this class of systems. Additionally, due to nonconvexity, the optimization problems solved in nonlinear MPC may have local optima. These local minima may lead to undesirable performance, particularly in the state estimator. The existence is studied of these optima in the regulator and estimator and their potential effects are examined on the performance of the closed‐loop system. To avoid unwanted local minima, the use is advocated of constraints in the estimator and regulator formulations and it is shown how a shorter prediction horizon in the regulator leads to better control profiles for some nonlinear models. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2142–2154, 2004
Modeling ethane oxy‐dehydrogenation over monolithic combustion catalysts
Authors: Caputo Francesco Donsfi Tiziana , Russo Gennaro , Di Benedetto Almerinda , Pirone Raffaele
Published: August 2004

A numerical approach is used to investigate the role of a combustion catalyst in the oxidative dehydrogenation of ethane at short contact times for ethylene production. A two‐dimensional (2‐D) model, with mass and energy equations coupled with the Navier‐Stokes equations, is applied to show that an oxidation catalyst can beneficially affect the formation of ethylene, by optimizing the sacrifice of ethane for producing heat with a larger selectivity to CO2 than a purely homogeneous process. Simulations also showed that for exceedingly high catalyst activity hot spots are formed on the catalyst walls, as the characteristic times of heat production become comparable with those of heat transfer. This may result into the formation of byproducts that reduce ethylene selectivity. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2233–2245, 2004
Helical flows and chaotic mixing in curved micro channels
Authors: Jiang F. , Drese K. S. , Hardt S. , Küpper M. , Schönfeld F.
Published: August 2004

The mixing due to helical flows in curved micro channels is investigated. A new chaotic mixing mechanism is presented relying on alternately switching between different flow patterns exhibiting four Dean vortices. Flow patterns and interfacial stretching factors are numerically computed for various Dean numbers. For experimental studies a prototype of a chaotic mixer with curved channels was fabricated. The experimental evaluation of the mixing performance corroborates the numerical prediction: the mixing performance found for Dean numbers above 140 is qualitatively different from that at lower Dean numbers; the periodic switching between different vortex patterns leads to efficient mixing, manifesting itself in an exponential growth of interfacial area. In addition to the studies on mixing, residence‐time distributions in the mixing channel are computed numerically. These investigations indicate that due to mass‐transfer enhancement originating from the transversal redistribution of matter in the chaotic flow, hydrodynamic dispersion is substantially reduced relative to a straight channel. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2297–2305, 2004
Temperature control of heterogeneous reactive distillation
Authors: Huang Shih‐Ger , Kuo Chien‐Lin , Hung Shih‐Bo , Chen Yi‐Wei , Yu Cheng‐Ching
Published: August 2004

In this work, we explore the temperature control of heterogeneous reactive distillation. By heterogeneous reactive distillation, we mean a two‐liquid phase exists in the reflux drum and a decanter is used to separate the aqueous product from the organic reflux. Process characteristics of n‐butyl propionate are explored and a systematic procedure is proposed for the design of butyl propionate reactive distillation. The control structure design procedure consists of the following steps: (1) setting the control objective, (2) selection of manipulated variables, (3) determination of temperature‐control trays, (4) finding controller settings for regulatory control, and (5) providing feedforward compensation for production rate variation. Because specifications on the bottoms product have to be met and stoichiometric balance has to be maintained, we have a 2 × 2 control problem with two obvious inputs: reboiler duty and feed ratio. The reactive distillation exhibits unique temperature sensitivities and the nonsquare relative gain successfully identifies temperature‐control trays, which results in an almost one‐way decoupled system. Therefore, decentralized PI controllers are used at the regulatory level. As a result of the unique feature of a kinetically controlled distillation column, maintaining constant tray temperatures does not imply the same quality specification. Feedforward temperature compensation is necessary to maintain the desired product composition. The proposed design procedure is further extended to butyl acetate reactive distillation, where a similar process behavior is observed, and good control performance can be achieved using simple temperature control. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2203–2216, 2004
The social and discursive construction of computing skills
Authors: Talja Sanna
Published: August 2004

In this article a social constructionist approach to information technology (IT) literacy is introduced. This approach contributes to the literature on IT literacy by introducing the concept of IT self as a description of the momentary, context‐dependent, and multilayered nature of interpretations of IT competencies. In the research literature, IT literacy is often defined as sets of basic skills to be learned, and competencies to be demonstrated. In line with this approach, research on IT competencies conventionally develops models for explaining user acceptance, and for measuring computer‐related attitudes and skills. The assumption is that computer‐related attitudes and self‐efficacy impact IT adoption and success in computer use. Computer self‐efficacy measures are, however, often based on self‐assessments that measure interpretations of skills rather than performance in practice. An analysis of empirical interview data in which academic researchers discuss their relationships with computers and IT competence shows how a self‐assessment such as “computer anxiety” presented in one discussion context can in another discussion context be consigned to the past in favor of a different and more positive version. Here it is argued that descriptions of IT competencies and computer‐related attitudes are dialogic social constructs and closely tied with more general implicit understandings of the nature of technical artifacts and technical knowledge. These implicit theories and assumptions are rarely taken under scrutiny in discussions of IT literacy yet they have profound implications for the aims and methods in teaching computer skills.
Stem cells as probabilistic self‐producing entities
Authors: Ramalho‐Santos Miguel
Published: August 2004

Stem cells have the capacity both to self‐renew and to give rise to differentiated progeny, and are vital to the organization of multicellular organisms. Stem cells raise a number of fundamental questions regarding lineage restriction and cellular differentiation, and they hold enormous promise for cell‐based therapies. Here I propose a theoretical framework for stem cell biology based on the concepts of autopoiesis (self‐production) and complementarity. I argue that stem cells are pivotal in the self‐production of the organism and that we need complementary approaches to understand their probabilistic behavior. I discuss how this framework generates testable hypotheses regarding stem‐cell functions. BioEssays 26:1013‐1016, 2004. © 2004 Wiley Periodicals, Inc.
Bile ducts as a source of pancreatic β cells
Authors: Burke Zoë D. , Shen Chia‐Ning , Tosh David
Published: August 2004

In recent years, there have been a number of well‐documented examples demonstrating that one cell type can be converted to another. Two such examples are the appearance of ectopic pancreas in the liver and formation of hepatic tissue in the pancreas. The conversion of liver to pancreas raises the intriguing possibility of generating insulin‐producing β cells for therapeutic transplantation into diabetics. There is now a striking addition to the growing list of pancreatic conversions: the formation of pancreatic tissue in the developing biliary system.1 BioEssays 26:932–937, 2004. © 2004 Wiley Periodicals, Inc.
Adding to the ends: what makes telomerase processive and how important is it?
Authors: Lue Neal F.
Published: August 2004

Telomerase is a cellular reverse transcriptase responsible for telomere maintenance in most organisms. It does so by adding telomere repeats onto pre‐existing ends using an integral RNA component as template. Compared to “prototypical” reverse transcriptases, telomerase is unique in being able to repetitively copy a short templating RNA segment, thus adding multiple copies of the repeat to the DNA substrate following a single binding event. This uniquely processive property hints at the intricate conformational alterations that the enzyme must choreograph during its reaction cycles. Recent studies have identified distinct structural elements within both the RNA and protein components of telomerase that modulate enzyme processivity. Pharmacological and genetic analysis suggest that telomerase processivity is a significant determinant of telomere length. Because telomere maintenance and the lack thereof have been linked to tumor progression and aging, further investigation of telomerase processivity may lead to novel medical intervention strategies. BioEssays 26:955–962, 2004. © 2004 Wiley Periodicals, Inc.
Superconductivity in Copper, Silver, and Gold Compounds
Authors: Larsson Sven
Published: August 2004

High‐temperature superconductivity exists in layered, square‐planar cuprates, but is almost absent in most other CuII compounds and in most AgII and AuII compounds. Valence state II is quite unusual in silver and gold and often disproportionates to valence states I and III (“negative‐U compounds”). The two‐electron difference in oxidation state is suggestive of electron pairing, a prerequisite for superconductivity. In the present paper the connection between disproportionation and geometrical structure on one hand and superconductivity on the other is discussed by using the accepted theory for mixed valence complexes. It is concluded that absence of superconductivity in gold and silver compounds can be connected to the instability of oxidation state II and the large difference in equilibrium geometry between oxidation states I and III.
Facile Access to Redox‐Active C2‐Bridged Complexes with Half‐Sandwich Manganese End Groups
Authors: Kheradmandan Sohrab , Venkatesan Koushik , Blacque Olivier , Schmalle Helmut W. , Berke Heinz
Published: August 2004

The dinuclear mixed‐valent complex [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)]+[(η2‐MeC5H4)3Mn]− [1]+[2]− (dmpe=1,2‐bis(dimethylphosphanyl)ethane) was prepared by the reaction of [Mn(MeC5H4)2] with dmpe and Me3SnCCSnMe3. The reactions of [1]+[2]− with K[PF6] and Na[BPh4] yielded the corresponding anion metathesis products [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)][PF6] ([1][PF6]) and [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)][BPh4] ([1][BPh4]). These mixed‐valent species can be reduced to the neutral form by reaction with Na/Hg. The obtained complex [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)] (1) displays a triplet/singlet spin equilibrium in solution and in the solid state, which was additionally studied by DFT calculations. The diamagnetic dicationic species [(MeC5H4)(dmpe)MnC2Mn(dmpe)(C5H4Me)][PF6]2 ([1][PF6]2) was obtained by oxidizing the mixed‐valent complex [1][PF6] with one equivalent of [Fe(C5H5)2][PF6]. Both redox processes are fully reversible. The dinuclear compounds were characterized by NMR, IR, UV‐visible, and Raman spectroscopy, cyclic voltammetry, and magnetic susceptibility measurements. X‐ray diffraction studies were performed on [1][2], [1][PF6], [1][BPh4], and [1][PF6]2.
Boron–Diindomethene (BDI) Dyes and Their Tetrahydrobicyclo Precursors—en Route to a New Class of Highly Emissive Fluorophores for the Red Spectral Range
Authors: Shen Zhen , Röhr Holger , Rurack Knut , Uno Hidemitsu , Spieles Monika , Schulz Burkhard , Reck Günter , Ono Noboru
Published: August 2004

The X‐ray crystallographic, optical spectroscopic, and electrochemical properties of a newly synthesized class of boron–diindomethene (BDI) dyes and their tetrahydrobicyclo precursors (bc‐BDP) are presented. The BDI chromophore was designed to show intensive absorption and strong fluorescence in an applicationary advantageous spectral range. Its modular architecture permits fusion of a second subunit, for example, a receptor moiety to the dye's core to yield directly linked yet perpendicularly prearranged composite systems. The synthesis was developed to allow facile tuning of the chromophore platform and to thus adjust its redox properties. X‐ray analysis revealed a pronounced planarity of the chromophore in the case of the BDIs, which led to a remarkable close packing in the crystal of the simplest derivative. On the other hand, deviation from planarity was found for the diester‐substituted bc‐BDP benzocrown that exhibits a “butterfly”‐like conformation in the crystal. Both families of dyes show charge‐ or electron‐transfer‐type fluorescence‐quenching characteristics in polar solvents when equipped with a strong donor in the meso‐position of the core. These processes can be utilized for signaling purposes if an appropriate receptor is introduced. Further modification of the chromophore can invoke such a guest‐responsive intramolecular quenching process, also for receptor groups of low electron density, for example, benzocrowns. In addition to the design of various prototype molecules, a promising fluoroionophore for Na+ was obtained that absorbs and emits in the 650 nm region and shows a strong fluorescence enhancement upon analyte binding. Furthermore, investigation of the remarkable solvatokinetic fluorescence properties of the “butterfly”‐like bc‐BDP derivatives suggested that a second intrinsic nonradiative deactivation channel can play a role in the photophysics of boron–dipyrromethene dyes.
Revealing the Configuration and Crystal Packing of Organic Compounds by Solid‐State NMR Spectroscopy: Methoxycarbonylurea, a Case Study
Authors: Macholl Sven , Börner Frank , Buntkowsky Gerd
Published: August 2004

The molecular configuration and intermolecular arrangement of polycrystalline methoxycarbonylurea (MCU) has been studied by a combination of chemical editing, rotational echo double resonance (REDOR) spectroscopy and ab initio calculations. From the multispin ISnREDOR experiments several dipolar couplings were determined and converted into distance constraints. Intra‐ and intermolecular dipolar couplings were distinguished by isotope dilution. The configuration of the MCU molecule can be determined from three torsion anglesΨ1,Ψ2, andΨ3. Ab initio calculations showed that these angles are either 0° or 180° (ZorE). From the REDOR experiments, theEconfiguration was found forΨ1andΨ2and theZconfiguration forΨ3. Thus the configuration of MCU in the solid state was determined to beEEZ. Distance constraints for the intermolecular arrangement of MCU were obtained by performing REDOR experiments on13C15N2MCU with different degrees of isotope dilution and on a cocrystallized 1:1 mixture of13C(urea) MCU and15N(amide) MCU. By combining these distance constraints with molecular modeling, three different possible packing motifs for MCU molecules were found. The molecules in these motifs are arranged as linear chains with methoxy groups at the borders of the chains. All the intermolecular hydrogen bond donors and acceptors in the interior of the chain are saturated.
Theory and Experiment in Concert: Templated Synthesis of Amide Rotaxanes, Catenanes, and Knots
Authors: Schalley Christoph A. , Reckien Werner , Peyerimhoff Sigrid , Baytekin Bilge , Vögtle Fritz
Published: August 2004

The synthesis of amide rotaxanes, amide catenanes, and trefoil amide knots is based on template effects mediated by hydrogen bonds. While a large body of experimental data is available, in‐depth theoretical studies of these template syntheses are virtually unavailable, although they would provide a more profound insight into the exact details of the hydrogen‐bonding patterns involved in the formation of these mechanically interlocked species. In this article we present a density functional study of the conformational properties of tetralactam macrocycles and the threading mechanism that produces the immediate precursor for rotaxane and catenane formation. Predictions of the geometries and relative energies made on the basis of semi‐empirical AM1 calculations are compared with these results in order to judge the reliability of the simpler approach. Since these calculations yield good agreement with the structural features, they have been used to extend the calculations in order to understand the mechanism of formation of a trefoil dodecaamide knot that has recently been synthesized. The inherent topological chirality of the knot is reflected in the intermediates generated during its formation; these involve helical loops. These loops parallel the rotaxane and catenane wheels with respect to the arrangement of the functional groups that mediate the template effect and may well serve as wheel analogues through which one of the precursor molecules can be threaded. This threading step finally results in the knotted structure. Good agreement between the results of the calculations presented here and experimental findings is achieved.