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The efficiency of generating electricity from heat using concentrated solar power plants (which use mirrors or lenses to concentrate sunlight in order to drive heat engines, usually involving turbines) may be appreciably increased by operating with higher turbine inlet temperatures, but this would require improved heat exchanger materials. By operating turbines with inlet temperatures above 1,023 kelvin using closed-cycle high-pressure supercritical carbon dioxide (sCO2) recompression cycles, instead of using conventional (such as subcritical steam Rankine) cycles with inlet temperatures below 823 kelvin1-3, the relative heat-to-electricity conversion efficiency may be increased by more than 20 per cent. The resulting reduction in the cost of dispatchable electricity from concentrated solar power plants (coupled with thermal energy storage4-6) would be an important step towards direct competition with fossil-fuel-based plants and a large reduction in greenhouse gas emissions7. However, the inlet temperatures of closed-cycle high-pressure sCO2 turbine systems are limited8 by the thermomechanical performance of the compact, metal-alloy-based, printed-circuit-type heat exchangers used to transfer heat to sCO2. Here we present a robust composite of ceramic (zirconium carbide, ZrC) and the refractory metal tungsten (W) for use in printed-circuit-type heat exchangers at temperatures above 1,023 kelvin9. This composite has attractive high-temperature thermal, mechanical and chemical properties and can be processed in a cost-effective manner. We fabricated ZrC/W-based heat exchanger plates with tunable channel patterns by the shape-and-size-preserving chemical conversion of porous tungsten carbide plates. The dense ZrC/W-based composites exhibited failure strengths of over 350 megapascals at 1,073 kelvin, and thermal conductivity values two to three times greater than those of iron- or nickel-based alloys at this temperature. Corrosion resistance to sCO2 at 1,023 kelvin and 20 megapascals was achieved10 by bonding a copper layer to the composite surface and adding 50 parts per million carbon monoxide to sCO2. Techno-economic analyses indicate that ZrC/W-based heat exchangers can strongly outperform nickel-superalloy-based printed-circuit heat exchangers at lower cost. [ABSTRACT FROM AUTHOR]

This article discusses a case of human bertielliasis in the Amazon region of Brazil. The patient, a 4-year-old girl, experienced abdominal pain, weight loss, and the presence of "white worms" in her stool. After receiving treatment with albendazole and praziquantel, fragments of the worm were expelled from the patient. The taxonomic analysis confirmed the infection as Bertiella, a genus of cestodes that can infect humans. The article highlights the challenges in diagnosing and identifying Bertiella species and emphasizes the importance of molecular biology in complementing morphological analysis. The case is significant as it is the first report of bertielliasis in the Amazon region and underscores the potential for emerging parasitic diseases in areas where human populations interact closely with forests. [Extracted from the article]

The article presents a case study of a four-year-old girl who is who experienced 15 days of nocturnal abdominal pain, weight loss, and the presence of white worms. The patient was prescribed with albendazole for five days at the local hospital in Oriximiná, Brazil. The patient was taken to the Tropical Medicine Nucleus of the Federal University of Pará (UFPA) after the treatment of albendazole, in which cestode infection was confirmed.

This study addresses the product investment decision faced by firms in the rent-to-own industry. In this setting, a customer arrives according to a random process and requests one unit of a product to rent (and eventually own should he/she choose to make all the required payments). At the time of request, if the product is available in inventory, the firm enters into a contractual agreement (by accepting the customer's offer) and rents the merchandise. More interesting and the case considered here, if the requested item is not in inventory, the firm must decide whether to purchase the item in order to rent it out or to simply reject the request. The customer's offer specifies the desired maximum contract length and the payment frequency--from which the firm determines the fixed periodic payment charged. The firm makes its investment decision based on the characteristics of the offer as well as those of the product (eg, initial and resale values, useful life and carrying costs) in essence performing a complicated cost benefit analysis. An extension is also considered whereby instead of simply rejecting the request the firm can adjust the required payment amount. Dynamic programming techniques are used to address the problem and to solve for the firm's optimal decision. [ABSTRACT FROM AUTHOR]

The article presents an analysis of probiotic methods for reducing dental caries. An overview of relevant research is provided, focusing on issues such as the role of Streptococcus mutans in the biofilm commonly referred to as dental plaque, and the effect of specifically targeted anti-microbial peptide applications on the oral biochemical environment. The difficulties of producing commercially viable probiotic products for caries prevention are noted, and the possibility of using synthetic analogs of probiotic proteins is discussed.

The H +-electrochemical gradient was originally considered as a driving force for solute transport only across cellular membranes of bacteria, plants and yeast. However, in the mammalian small intestine, a H +-electrochemical gradient is present at the epithelial brush-border membrane in the form of an acid microclimate. Over recent years, a large number of H +-coupled cotransport mechanisms have been identified at the luminal membrane of the mammalian small intestine. These transporters are responsible for the initial stage in absorption of a remarkable variety of essential and non-essential nutrients and micronutrients, including protein digestion products (di/tripeptides and amino acids), vitamins, short-chain fatty acids and divalent metal ions. Proton-coupled cotransporters expressed at the mammalian small intestinal brush-border membrane include: the di/tripeptide transporter PepT1 (SLC15A1); the proton-coupled amino-acid transporter PAT1 (SLC36A1); the divalent metal transporter DMT1 (SLC11A2); the organic anion transporting polypeptide OATP2B1 (SLC02B1); the monocarboxylate transporter MCT1 (SLC16A1); the proton-coupled folate transporter PCFT (SLC46A1); the sodium–glucose linked cotransporter SGLT1 (SLC5A1); and the excitatory amino acid carrier EAAC1 (SLC1A1). Emerging research demonstrates that the optimal intestinal absorptive capacity of certain H +-coupled cotransporters (PepT1 and PAT1) is dependent upon function of the brush-border Na +–H + exchanger NHE3 (SLC9A3). The high oral bioavailability of a large number of pharmaceutical compounds results, in part, from absorptive transport via the same H +-coupled cotransporters. Drugs undergoing H +-coupled cotransport across the intestinal brush-border membrane include those used to treat bacterial infections, hypercholesterolaemia, hypertension, hyperglycaemia, viral infections, allergies, epilepsy, schizophrenia, rheumatoid arthritis and cancer. [ABSTRACT FROM AUTHOR]

OBJECTIVE: To assess whether catheter ablation of fascicular tachycardia can be facilitated by the recording of sharp deflections arising from the mid-septum---inferior apical septum of the left ventricle. PATIENTS AND METHODS: Seven consecutive patients (mean age 29 (range 16-43) years) with ventricular tachycardia originating from the left posterior fascicle underwent electrophysiology study and detailed mapping of endocardial activation. Selection of ablation sites in the last five patients was based on the recording, during left posterior fascicular tachycardia and sinus rhythm, of a discrete potential preceding the earliest ventricular electrogram, which was thought to represent conduction through the posterior fascicle. RESULTS: Patients were treated with low energy direct current or radiofrequency current ablation. The median fluoroscopy and procedure times were 23 (range 6-42) min and 110 (range 50-176) min, respectively. In a follow up period of 4 to 16 months, six patients were asymptomatic and one had minor symptoms. No patient had any change in intraventricular conduction. Similar potentials were also recorded from the left posterobasal septum in three of eight patients who underwent catheter ablation of left free wall accessory pathways. CONCLUSION: Fascicular potentials can be reproducibly recorded in left posterior fascicular tachycardia and may serve as a reliable marker for successful ablation procedures. The relation of these potentials with the substrate of the tachycardia, however, remains obscure. [ABSTRACT FROM PUBLISHER]

Investigations of the etiology and epidemiology of pathogenic diseases can be genetically divided into several stages. Initially, attention is concentrated upon describing and quantifying the disease symptoms themselves, so that new outbreak may be recognized easily by other workers. The second phase focuses attention upon the environmental factors responsible for the optimum spread of the pathogen and for the development of the disease. Initially, a knowledge of these factors is used in order to predict the likelihood of future disease outbreaks. This approach has been used with considerable success on many serious plant diseases.

BACKGROUND--Although heart rate variability has already been studied in survivors of sudden cardiac death secondary to coronary artery disease, an assessment of heart rate variability in survivors of sudden cardiac death not associated with coronary artery disease has not been made. METHODS--10 patients with aborted sudden cardiac death not associated with coronary artery disease (seven patients with primary ventricular fibrillation and three with unclassified mild cardiomyopathy) underwent two channel 24 hour Holter monitoring in a drug free state. All subjects were in sinus rhythm and had normal atrioventricular conduction and normal cardiac function. Spectral heart rate variability was analysed on a Holter analysis system and was expressed as total (0.01-1.00 Hz), low (0.04-0.15 Hz) and high (0.15-0.40 Hz) frequency components for each hour. Heart rate variability index was calculated for the 24 hour periods. 10 age and sex matched healthy subjects were taken as a control group. RESULTS--The spectral heart rate variability over 24 hours was significantly lower in survivors of sudden cardiac death than in controls (total 38(15) v 48(14) ms; low, 25(11) v 32(13) ms; and high, 13(8) v 18(8) ms; p < 0.05 for all comparisons). The differences in the ratio of low/high (2.19(0.76) v 1.98(0.50), p = 0.132), mean heart rate (77(12) v 69(12) beats/min, p = 0.070), and heart rate variability index (38(12) v 44(16), p = 0.287) over 24 hours between survivors of sudden cardiac death and controls did not reach significance. Comparisons of the hourly heart rate variability over the 24 hour period between the two groups showed that the differences in all components of heart rate variability, low/high ratio and mean heart rate were highly significant. Furthermore, there was no significant difference in the maximum hourly heart rate variability over the 24 hour period. The minimum hourly heart rate variability was, however, significantly lower in survivors of sudden cardiac death than in controls (total, 20(8) v 28(4) ms; low, 12(6) v 17(3) ms; high, 6(2) v 8(2) ms; p < 0.05 for all comparisons). CONCLUSIONS--These findings suggest that there is abnormal autonomic influence on the heart in patients without coronary artery disease at risk of sudden cardiac death. Hourly analysis of heart rate variability throughout the 24 hour period may provide additional information important in the identification of high risk patients. [ABSTRACT FROM PUBLISHER]

OBJECTIVE--To develop a model to assess the cost-efficacy of the implantable cardioverter defibrillator to prevent sudden death. The model must be sufficiently flexible to allow the use of cost and survival figures derived from different sources. SETTING--The study was conducted in a teaching hospital department of cardiology with experience of 40 implantable cardioverter defibrillator implants and a large database of over 500 survivors of myocardial infarction. PROCEDURE--The basic costs of screening tests, stay in hospital, and purchase of implantable cardioverter defibrillators were derived from St George's Hospital during 1991. To assess the cost-efficacy of various strategies for the use of implantable cardioverter defibrillators, survival data taken from published studies or from our own database. Implications of the national cost of the various strategies were calculated by estimating the number of patients a year requiring implantation of a defibrillator if the strategy was adopted. RESULTS--Use of implantable cardioverter defibrillators in survivors of cardiac arrest costs between 22,400 pounds and 57,000 pounds for each year of life saved. Most of the strategies proposed by the current generation of implantable cardioverter defibrillator trials have cost efficacies in the same range, and adoption of any one of these strategies in the United Kingdom could cost between 2 million pounds and 100 million pounds a year. Future technical and medical developments mean that cost-efficacy may be improved by up to 80%. Due to the limitations of screening tests currently available restriction on the use of implantable cardioverter defibrillators to those groups where it seems highly cost-effective will result in a small impact on overall mortality from sudden cardiac death. CONCLUSION--Present and possible future applications of the implantable cardioverter defibrillator seem expensive when compared with currently accepted treatments. Technical and medical developments are, however, likely to result in a dramatic improvement in cost efficacy over the next few years. [ABSTRACT FROM PUBLISHER]

OBJECTIVE--Preliminary assessment of the efficacy and safety of the low speed rotational angioplasty catheter system (ROTACS). DESIGN--Open prospective trial. SETTING--Department of cardiology in a teaching hospital. PATIENTS--Eleven patients (10 with chronic stable angina and one with acute coronary occlusion after conventional angioplasty) in whom a coronary angiogram showed occlusion or critical stenosis of the coronary artery (right in seven patients, circumflex in two, and left anterior descending in two). The nature or severity of the lesion ruled out conventional coronary angioplasty. INTERVENTIONS--An attempt was made to cross the lesion with a rotating guide wire with a blunt swelling at its tip. Where necessary progress was assessed by simultaneous injection of contrast into both main coronary arteries. MAIN OUTCOME MEASURES--Progress of the ROTACS through the lesion that allowed a guide wire to pass into the distal vessel was regarded as a device specific success. When a guide wire crossed the lesion aided only by the support of the ROTACS without the use of rotation this was counted as a success that was not device specific. Failure to cross the lesion and any associated complications were noted. RESULTS--The ROTACS crossed only two of the 10 chronic lesions (20% device specific success rate); however, the support it provided enabled a guide wire to cross a further two lesions and allowed subsequent successful angioplasty in four of the 10 patients. One of these four patients presented after five months with recurrent angina requiring bypass grafting. The other three were symptom free at follow up seven months after the procedure. In the one patient with acute coronary occlusion the ROTACS was advanced over the guide wire to allow passage of an angioplasty balloon where this had previously proved impossible. An excellent final result was obtained and this patient remains symptom free. Three of the six patients in whom the ROTACS was unsuccessful had coronary artery dissection without sequelae. Three patients required subsequent elective coronary bypass grafting for control of symptoms while the other three remain well on medical treatment. CONCLUSIONS--The ROTACS may extend the range of patients with coronary artery occlusion or critical stenosis who can be treated non-surgically. The low device specific success rate (20%) achieved in this study indicates that it should be compared with other simpler mechanical devices that may be just as effective. [ABSTRACT FROM PUBLISHER]

We discuss the nature of errors which may occur when the spectra of random signals not obeying Gaussian statistics are measured with typical rf spectrum analyzers. These errors depend on both the noise statistics and the process used to detect the random signal after it has been passed through a narrow bandpass filter within the spectrum analyzer. In general, for random signals not obeying Gaussian statistics, the output of the bandpass filter must be measured with a square law detector if the resulting measurement is to be strictly proportional to the power spectrum of the input signal. We compare measurements of the power spectra of non-Gaussian noise using a commerical spectrum analyzer with its resident envelope detector, with measurements by the same analyzer fitted with a square law detector. Differences of about 5% were observed. [ABSTRACT FROM AUTHOR]