General solution for single-layer electromagnetic-wave absorber

A general solution for perfect absorption under normal incidence in a single-layer homogeneous absorber backed by a perfect conductor is derived considering both electric and magnetic losses. Design curves and equations are given for the lowest-order or minimum-thickness solutions, and its possible use in the design and fabrication of practical absorbing materials is also illustrated.     

LANDSAT-4 MSS And Thematic Mapper Data Quality And Information Content Analysis

Landsat-4 Thematic Mapper and Multispectral Scanner data were analyzed to obtain information on data quality and information content. Geometric evaluations were performed to test band-to-band registration accuracy. Thematic Mapper overall system resolution was evaluated using scene objects which demonstrated sharp high contrast edge responses. Radiometric evaluation included detector relative calibration, effects of resampling, and coherent noise effects. Information content evaluation was carried out using clustering, principal components, transformed divergence separability measure, and numerous supervised classifiers on data from Iowa and Illinois. A detailed spectral class analysis (multispectral classification) was carried out on data from the Des Moines, Iowa area to compare the information content of the MSS and TM for a large number of scene classes.     

High performance of V–Ga–O catalysts for oxidehydrogenation of propane

The catalytic performance in the oxidehydrogenation (ODH) of propane of vanadium oxide catalysts supported on gallium oxide, VO_x/Ga₂O₃, with vanadium coverages lower or near the theoretical monolayer has been studied as a function of the vanadium content and compared with those of other known effective V–M–O (M=Mg, Ca) catalysts. Catalyst activity was very high and increased with the increase of vanadium loading in the range studied, while the selectivity trend was similar for the studied catalysts, excepting that with the lower V content. FT-Raman and ⁵¹V solid state NMR spectroscopies show that for coverages below the theoretical monolayer vanadium atoms are in tetrahedral co-ordination either in isolated or polymeric species, while the onset of vanadia formation is detected above that coverage. Interestingly, these catalysts show an one order of magnitude higher area-specific rate, similar initial olefin selectivity and slightly higher selectivity decrease with the increase of conversion than the best VMgO catalyst. This is due to the high intrinsic activity of isolated tetrahedral vanadium species. The combination of these factors produces an enhanced olefin productivity of V–Ga–O catalysts.     

Reproductive health in adolescent students: knowledge, attitudes, and behavior in both sexes, in a community of Santiago

Nine hundred forty eight teenagers (600 females) from a public school of one of the poorest communities of Santiago were surveyed about knowledge and practices on sexuality and reproductive health. Twenty four percent of females and 40% of males did not talk about their problems at home, instead they talked preferentially with their friends. Half of the sample attributed a risk a pregnancy to the first sexual intercourse; 67% did not know the infertile phase of the menstrual cycle and 20% did not identify two sexually transmitted diseases. Sixty percent considered rhythm technique as a safe fertility control method, 60% of males and 50% of females considered masturbation as risky, 57% of males and 49% of females estimated that condoms could be reused and between 5 and 16% of the sample correctly identified AIDS modes of transmission. Fifty percent had a couple and 23% of males and 17% of females had a sexual intercourse in the last six months; of these, 45% of women and 27% of men used a contraceptive method. Four percent of women and 6% of men became involved in a pregnancy and 57% of these terminated in abortions. It is concluded that knowledge about sexuality and reproductive biology among low income teenagers is scanty.     

Measurement and characterization of the temporal behavior of fixed wireless links

We analyze the methodology and present the interpretation of results obtained in the measurement of the temporal Ricean K-factor and the time-autocovariance function of the received power for fixed narrowband wireless links in urban residential environments. Our main observation is that the time-autocovariance function (and thus both the temporal K-factor and the coherence time) fundamentally depends on a combination of the characterization of the transmit-receive path and whether the street-level moving objects are in the field of view of the antennas. In most practical cases the latter refers only to the customer premises antenna, as the base station is typically placed at a much greater distance from moving scatterers. No significant basis was found for the popular conjecture that the K-factor is mainly influenced by the excess path loss. However, a strong correlation between coherence times and temporal K-factor was observed over a wide range of link conditions. We also found that the time-autocovariance function can be quite accurately modeled by the weighted sum of two exponentially decaying functions: one with a time constant on the order of 1 s and the other typically slower by one order of magnitude. The results will be helpful in establishing design criteria for radio systems such as multiple input-multiple output that need to estimate the channel response and its persistence in time and for media access control (MAC) layer transmission protocols whose efficiency is affected by the depth and duration of channel outages.     

Pilot experience with the use of an ambulatory geriatric assessment instrument

BACKGROUND: Ten percent of the Chilean population is over 60 years old and general practitioners need an instrument to assess the degree of disability and multiple ailments of elders. AIM: To develop and use an instrument to assess elders consulting in primary care outpatient clinics. PATIENTS AND METHODS: An instrument to be used by general practitioners, aimed to assess bio-psico-social risk of elders was devised by the Geriatrics Program at the Faculty of Medicine of the Catholic University of Chile. The instrument was used in 100 elders (82 female) aged 71 +/- 8 years old consulting in a primary care outpatient clinic. RESULTS: The instrument took less than 5 minutes to be used. The most frequent risk factors found were living alone in 62% of subjects, falls in the last year in 47%, memory disturbances in 62%, overweight in 76%, visual impairment in 76%, urinary incontinence in 26% and depression in 76%. Thirty percent had difficulties to climb stairs and 4% had no support in case of severe disability. CONCLUSIONS: The applied instrument is fast to apply, easily understood by patients and detects problems associated with old age, that will help to plan primary care health programs.     

Intraarterial urokinase for acute native arterial occlusion of the limbs

Since 1988, 49 limbs of 47 patients underwent intraarterial urokinase infusion for acute native artery occlusion. The time from the onset of ischemic symptoms ranged from 1 to 45 days (mean = 17.5). The arterial sectors involved were femoropopliteal in 32 cases, followed by aortoiliac in 13 cases, distal in three cases, and subclavian in one case. Treatment consisted of placing a catheter in the clot and the infusion of 4400 U/kg in 20', followed by a series of 4400 U/kg weight/hour during 6 hours. Clinical evaluation, hemodynamic and coagulation parameters, and angiographical changes were assessed periodically. Infusion time ranged from 6 to 24 hours (mean = 13.2 hours). Improvement of ischemic was achieved in 43 (87.75%) patients. In five patients (12.25%) there was no improvement. Total immediate lysis was achieved in 35 cases (71.5%), and among them, 13 patients (26%) required no associated treatment, 16 (48%) underwent PTA, and four (12%) had surgery of underlying peripheral aneurysms revealed after thrombolysis. Partial lysis was achieved in 13 cases (26.5%), that was enough in four of them, but the remaining nine required further treatment (four PTA, and five arterial surgery). In one case no lysis was achieved, and arterial surgery was carried out. No mortality was recorded, and major complications included one upper gastrointestinal bleeding, and one cerebral hematoma. Late follow-up of successfully treated patients who did not require further surgery shows a cumulative patency rate of 81% at 24 months.     

General and oral manifestations of human immunodeficiency virus infection: a general overview with guidelines for infection control in the dental practice

The human immunodeficiency virus (HIV-1), responsible for the acquired immunodeficiency syndrome, has in the span of a decade become an epidemic of global proportions. Oral lesions, head and neck diseases are often the first manifestations of HIV-1 infection and AIDS. It is essential for all dentists to familiarize themselves with the oral manifestations of HIV-infection as well as the dental management of such manifestations. In addition to all health care, professionals should become acquainted with the "universal precautions" recommended by the Centers for Disease Control, in order to protect themselves, their staff, and their patients to minimize, if not totally eliminate, any risk of infectious disease transmission in the health care setting. This paper presents a general overview of the human immunodeficiency virus; oral manifestations of HIV-infection; "universal precautions" and guidelines for the control of infection in the dental practice.