A MAC protocol for a wireless LAN based on OFDM-CDMA

Local access encompasses requirements of high throughput, transfer performance, flexibility, and ease of user/terminal mobility at a relatively low cost. While some of these targets can often be met satisfactorily with wired infrastructures, it is getting increasingly popular to resort to wireless access (wireless LAN), mainly because of its simpler deployment, continuous coverage, availability of ad hoc connectivity, and user/terminal mobility support. This article outlines the proposal of a broadband quality-oriented WLAN system. The basic system characteristics are described, with details given on a MAC protocol supporting IP and exploiting an OFDM-CDMA technique     

The IPCS Collaborative Study on Neurobehavioral Screening. I. Background and genesis

Numerous events over several years culminated in recognition of the need to explicitly evaluate the nervous system as a potential target for environmental chemicals. Based on recommendations from several international expert panels, the International Programme on Chemical Safety (IPCS) sponsored the Collaborative Study on Neurobehavioral Screening Methods. A Steering Committee was created to oversee the project, develop the testing protocol, recruit participating laboratories and review and analyze the data. The protocol specified the tests, the chemicals (supplied from a common source) and the exposure conditions (acute and repeated dosing). Test methods were based upon existing practices in toxicological screening as well as recent advances in neurotoxicity screening. Chemicals were selected to produce different profiles of neurobehavioral effects. Considerable latitude was afforded the participating laboratories in the choice of several key variables (e.g., strain of rat, testing device for motor activity assessment) that could potentially affect the results of the experiments. The approach therefore provided a standardized yet flexible protocol for evaluating the reproducibility of neurobehavioral screening data in diverse laboratory settings.     

Influence of autonomic tone on QT interval duration

The autonomic tone has been shown to influence the duration of the QT interval, however the independent contribution of sympathetic and parasympathetic tone is not fully elucidated. The influence of autonomic tone on QT duration was studied in 10 young healthy volunteers by evaluating the changes in QT and RR duration induced by i.v. isoproterenol infusion and by standing before and after i.v. administration of propranolol or atropine. Furthermore, the relationship between RR interval and QT duration was evaluated during nocturnal sinus arrhythmia and submaximal exercise test. Low doses of isoproterenol reduced RR (p < 0.01) but not QT interval duration, while higher doses influenced both RR (p < 0.0001) and QT (p < 0.001) duration. Propranolol did not influence standing-induced shortening of RR and QT intervals; on the contrary, atropine administration abolished standing-induced QT interval shortening, without influencing RR changes. QT duration resulted significantly related to preceding RR interval at peak exercise (r = 0.87, p < 0.001) and during nocturnal sinus arrhythmia (r = 0.73, p < 0.0005), however, the regression lines showing the correlation between QT and preceding RR interval were different. Both sympathetic and parasympathetic tone appear to contribute to heart rate-independent changes in QT duration. In the basal state parasympathetic more than sympathetic tone influences the relation QT-heart rate. Major increases of sympathetic nervous system activity may change the relation QT-heart rate. Thus, in case of abrupt autonomic changes, any proposed formula for heart rate correction of QT may result inappropriate, also in the normal range of heart rate.     

Effects of prenatal exposure to low concentrations of carbon monoxide on sexual behaviour and mesolimbic dopaminergic function in rat offspring

1. Inhalation of low concentrations of carbon monoxide (CO) by pregnant rats (75 and 150 p.p.m. from day 0 to day 20 of gestation) leads to changes in mesolimbic dopaminergic transmission associated with an impairment of sexual behaviour in male offspring. 2. Eighty day old males exposed in utero to CO (150 p.p.m.) exhibited a significant increase in mount/ intromission latency as well as a significant decrease in mount/intromission frequency. A significant decrease in ejaculation frequency was also found in CO (150 p.p.m.)-exposed animals. 3. The acute administration of amphetamine, at a dose (0.5 mg kg(-1) s.c.) stimulating copulatory activity in control rats, failed to reduce mount/intromission latency and did not increase mount frequency in 80-day offspring exposed to CO (150 p.p.m.) during gestation. 4. These behavioural alterations were paralleled by neurochemical changes (in vivo microdialysis) showing that prenatal CO exposure, at concentrations (150 p.p.m.) that did not affect basal extracellular levels of dopamine in the nucleus accumbens, blunted the amphetamine (0.5 mg kg(-1) s.c.)-induced increase in dopamine release in 80-day old male rats. 5. No significant changes in either behavioural or neurochemical parameters were observed in 10-month old rats exposed prenatally to CO. 6. Since the alterations in sexual behaviour and dopaminergic transmission have been produced by prenatal exposure to CO levels resulting in maternal blood carboxyhaemoglobin concentrations equivalent to those maintained by human cigarette smokers, the present data further point out the large risk that the smoking mother poses for her offspring.     

Crystallographic evolution of microstructure in thin film processing: Part I. grain size distribution

Processing parameters and the resulting properties of a material are linked by the relationship between processing and microstructure. Characterizing the effect of processing variations on microstructure and determining its origin are essential to advanced material development. In this and a companion article, some readily applied techniques for producing quantitative data on grain size and shape, as well as grain and boundary crystallography, are described. The method described in Part I utilizes transmission electron microscopy and image analysis to measure grain size in large quantities (2000 to 3000 grains per sample), differentiated into orientation class subpopulation distributions. On application to Ni thin films produced by ion assisted deposition, the results have identified an orientation subpopulation that is predominantly responsible for the larger grain sizes observed in films grown under high ion flux. Larger grain size and the development of a preferred orientation have both been associated with increasing ion flux during growth, however, these results give the first experimental evidence connecting grain size and texture in these films.     

Influence of atmospheric nitric oxide concentration on the measurement of nitric oxide in exhaled air

BACKGROUND: Measurement of nitric oxide (NO) in exhaled air shows promise as a non-invasive method of detecting lung inflammation. However, variable concentrations of NO are measured in environmental air. The aim of this study was to verify a possible relationship between exhaled NO and atmospheric NO values during high atmospheric NO days. METHOD: Exhaled air from 78 healthy non-smokers of mean age 35.3 years was examined for the presence of NO using a chemiluminescence NO analyser and NO levels were expressed as part per billion (ppb). The exhaled air from all the subjects was collected into a single bag and into two sequential bags. Before each test atmospheric NO was measured. RESULTS: The mean (SE) concentration of exhaled NO collected into the single bag was 17.1 (0.6) ppb while the mean values of exhaled NO in bags 1 and 2 were 16.7 (1.3) ppb and 13.8 (1.2) ppb, respectively. The atmospheric NO concentrations registered before each test varied from 0.4 to 71 ppb. There was a significant correlation between exhaled NO in the single bag and atmospheric NO (r = 0.38, p = 0.001). The atmospheric NO concentration also correlated with exhaled NO both in bag 1 (r = 0.44, p = 0.0001) and in bag 2 (r = 0.42, p = 0.0001). These correlations disappeared with atmospheric NO concentrations lower than 35 ppb. CONCLUSIONS: These results indicate a relationship between atmospheric NO and NO levels measured in exhaled air, therefore exhaled NO should not be measured on very high atmospheric NO days.     

Oxidation processes using ion beams

Recent work demonstrates that reactive ion beams can be used to grow compound layers on metal and semiconductor surfaces. Ion beams are characterized by easily controlled ion flux and energy, with a narrow energy spread. Also, the ion species are delivered to the sample in a low pressure environment. These advantages allow greater control and simpler analysis of compound formation processes than other techniques do. Ion beam oxidation is reviewed and compared with thermal, plasma and r.f. oxidation and with oxidation by ion implantation. The ion energy range of several electronvolts to hundreds of electronvolts is suitable for depositing the oxidizing species in the metal in an active state, and simultaneous sputtering can produce a self-limiting oxide thickness when the sputtering yield and oxidation rate are in proper balance. The process of ion beam oxidation is also discussed in light of the etching behavior of metals under combined inert gas and oxygen ion bombardment and of the related technique of reactive ion beam sputter deposition using ion bombardment of a growing film. Additional examples are drawn from the use of other reactive ion beam species, including nitrogen and hydrogen.     

The IPCS Collaborative Study on Neurobehavioral Screening Methods: II. Protocol design and testing procedures

This paper describes the development of the protocol for the International Programme on Chemical Safety (IPCS)-sponsored Collaborative Study on Neurobehavioral Screening Methods, including background on the methods and chemicals selected, as well as details concerning the conduct of the collaborative study, including proficiency testing, range-finding and main study. Participating laboratories in the collaborative study received training in the conduct and scoring of the behavioral tests and each laboratory received a video training film to train additional personnel as needed. Each of the eight laboratories that chose to participate in the study completed proficiency testing and assessed seven representative chemicals using a functional observational battery and automated motor activity assessment. The seven chemicals studied were acrylamide, bis-acrylamide, p,p'-DDT, lead acetate, parathion, toluene, and triethyl tin. Participants received coded samples of the chemicals from a common source. Each laboratory derived doses for single and repeated administration based on the determination of a within-laboratory acute "top dose." Animal strains were not standardized and laboratory conditions were standardized to a limited degree in order to judge the general utility and robustness of these procedures in a diversity of testing situations.