Surface emission determination of selected trace gases from an active municipal solid waste dumpsite under the surface physicochemical heterogeneity.

Karadiyana municipal solid waste (MSW) dumpsite in Colombo, Sri Lanka, has been in operation for over 30 years and was evaluated for its surface Volatile Organic Compounds (VOCs), Ammonia (NH3), and Hydrogen sulfide (H2S) emissions. Based on the surface conditions and waste characters, the dump surface was divided into eight cells, and multiple samplings were done using static flux chamber methods. The study observed that the average flux rates of VOCs, H2S, and NH3 were 137.2 ± 243.8, 6.63 ± 15.9, and 14.2 ± 16.2 mg m-2h-1 throughout the dump site. The highest average VOCs and H2S flux rates (828.6, 24.3 mg m-2h-1) were reported from new organic waste with a considerable fraction (62.5, 35.6 %) from the total emission (61.0, 3.1 Kg d-1). Leachate-flowing trenches produced the highest NH3 flux rate (36.0 mg m-2h-1), while the highest emission fraction (47.5 %) from the total (12.0 Kg d-1) was reported on old mixed waste with vegetation. The moisture content of the organic waste layers is positively correlated with these trace gas flux rates, and the NH3 flux rates depend on the pH of the surface. Results showed that the age of the waste determines the trace gas emission rate, and leachate provides an ideal pathway for landfill trace gas migration to the atmosphere. Gas collection and purification systems are essential for the initial waste dumping area and leachate treatment system. The arrangement of a proper drainage system on the dump would reduce trace gas emissions.

Hot-carrier dynamics in InAs/AlAsSb multiple-quantum wells.

A type-II InAs/AlAs[Formula: see text]Sb[Formula: see text] multiple-quantum well sample is investigated for the photoexcited carrier dynamics as a function of excitation photon energy and lattice temperature. Time-resolved measurements are performed using a near-infrared pump pulse, with photon energies near to and above the band gap, probed with a terahertz probe pulse. The transient terahertz absorption is characterized by a multi-rise, multi-decay function that captures long-lived decay times and a metastable state for an excess-photon energy of [Formula: see text] meV. For sufficient excess-photon energy, excitation of the metastable state is followed by a transition to the long-lived states. Excitation dependence of the long-lived states map onto a nearly-direct band gap ([Formula: see text]) density of states with an Urbach tail below [Formula: see text]. As temperature increases, the long-lived decay times increase [Formula: see text], due to the increased phonon interaction of the unintentional defect states, and by phonon stabilization of the hot carriers [Formula: see text]. Additionally, Auger (and/or trap-assisted Auger) scattering above the onset of the plateau may also contribute to longer hot-carrier lifetimes. Meanwhile, the initial decay component shows strong dependence on excitation energy and temperature, reflecting the complicated initial transfer of energy between valence-band and defect states, indicating methods to further prolong hot carriers for technological applications.

Terahertz generation by optical rectification in chalcopyrite crystals ZnGeP2, CdGeP2 and CdSiP2.

Optical rectification of near-infrared laser pulses generates broadband terahertz radiation in chalcopyrite crystals CdGeP2, ZnGeP2 and CdSiP2. The emission is characterized using linear-polarized excitation from 0.8 eV to 1.55 eV (1550 nm - 800 nm). All three crystals are (110)-cut and polished to 0.5 mm, thinner than the coherence length across most of the excitation photon energy range, such that they all produce a bandwidth ~2.5 THz when excited with ~100 fs pulses. It is found that CdGeP2 produced the strongest emission at telecoms wavelengths, while CdSiP2 is generally the strongest source. Pump-intensity dependence provides the nonlinear coefficients for each crystal.

Enhanced hot electron lifetimes in quantum wells with inhibited phonon coupling.

Hot electrons established by the absorption of high-energy photons typically thermalize on a picosecond time scale in a semiconductor, dissipating energy via various phonon-mediated relaxation pathways. Here it is shown that a strong hot carrier distribution can be produced using a type-II quantum well structure. In such systems it is shown that the dominant hot carrier thermalization process is limited by the radiative recombination lifetime of electrons with reduced wavefunction overlap with holes. It is proposed that the subsequent reabsorption of acoustic and optical phonons is facilitated by a mismatch in phonon dispersions at the InAs-AlAsSb interface and serves to further stabilize hot electrons in this system. This lengthens the time scale for thermalization to nanoseconds and results in a hot electron distribution with a temperature of 490 K for a quantum well structure under steady-state illumination at room temperature.

Interventions to Prevent Cognitive Decline and Dementia in Adults without Cognitive Impairment: A Systematic Review.

Without preventative strategies, the burden of dementia is likely to increase rapidly worldwide. Primary prevention approaches involve modifying risk factors before symptoms of cognitive impairment develop. This review systematically assesses Randomised Controlled Trials (RCTs) and reviews of RCTs for their effectiveness in primary prevention. We searched Medline, the Cochrane Library, Web of Science and Psych-Info for relevant studies using pre-determined keywords. Both non-pharmacological and pharmacological interventions were considered. Inclusion criteria were sample size greater or equal to 50, at least 6 months of follow-up, and participants with no cognitive impairment at baseline. Outcomes included dementia incidence, cognitive decline and cognitive function. Study quality was rated using the Jadad criteria. Thirty-nine studies, 17 non-pharmacological and 22 pharmacological, were included. Results were heterogeneous across interventions and studies, with few significant effects. Studies investigating physical activity and calcium channel blocker treatment demonstrated significant effects in preventing cognitive decline. There were no conclusive results demonstrating overall capacity of assessed interventions to reduce risk of dementia. The review provides an overview of the current literature, and identifies areas in need of further research.

Prevalence of behavioral and emotional problems among seven to eleven year old children in selected schools in Kandy District, Sri Lanka.

BACKGROUND: Behavioral and emotional problems comprising internalizing, externalizing and mixed disorders consist of psychiatric disorders in childhood and adolescents. Prevalence rates of 8.3% for preschoolers, 12.2% for preadolescents and 15.0% for adolescents have been reported from around the world. This study aimed to measure the prevalence of emotional and behavioral disorders in 7-11 year-old school children studying in Kandy District Sri Lanka which was a first for the geographic area. METHOD: This was a community based study at the primary section of the selected schools. The questionnaire, Child behavior Checklist-Sinhala (CBCL-S) was administered in a group setting to the main caregiver of 562 subjects selected randomly. The questionnaire identified problems in 8 subscales under three main sub categories : internalizing, externalizing and other. Data were analyzed using The Syndrome Scales for Boys and Girls developed for analyzing the questionnaire CBCL. RESULTS: Indicated a prevalence of 13.8% of emotional and behavioral problems in the study population. 8.8% of children showed internalizing problems and 8.8% externalizing problems. These findings are in line with the prevailing rates from previous studies of the world. Children in school types 1AB and 1C had less emotional and behavioral problems compared to type 2 and 3 schools. LIMITATIONS: Only 20 schools in KEZ and Sinhala speaking population of the Kandy were studied. CONCLUSIONS: This study showed the extent of childhood emotional and behavioral problems and also confirms that the schools with advanced level classes have lesser problems amongst primary children.

Spatiotemporal distribution of insecticide resistance in Anopheles culicifacies and Anopheles subpictus in Sri Lanka.

The malaria situation in Sri Lanka worsened during the 1990s with the emergence and spread of resistance to the drugs and insecticides used for control. Chloroquine resistance has increased rapidly over this period, but adverse changes in malaria transmission are more closely associated with insecticide use rather than drug resistance. Insecticide susceptibility tests were routinely carried out in key anopheline vectors across the country for more than a decade. These sentinel data were combined with data collected by other research programmes and used to map the spatial and temporal trends of insecticide resistance in the main vectors, Anopheles culicifacies and A. subpictus, and to examine the relationship between insecticide resistance, changes in national spraying regimens and malaria prevalence. Both species had widespread resistance to malathion, the insecticide of choice in the early 1990s. Both species were initially susceptible to the organophosphate and pyrethroid insecticides used operationally from 1993, but some resistance has now been selected. The levels of malathion and fenitrothion resistance in A. subpictus were higher in some ecological regions than others, which may be related to the distribution of sibling species, agricultural pesticide exposure and/or environmental factors. The study highlights that the emergence and spread of insecticide resistance is a constant threat and that active surveillance systems are vital in identifying key vectors and evidence of resistance.

Neural correlates of dual task interference can be dissociated from those of divided attention: an fMRI study.

When people perform two tasks simultaneously, the tasks are often executed slower and with more errors than when they are carried out as single tasks. This is called dual task interference. With functional magnetic resonance imaging (fMRI), we show that concurrently performed visual and somatosensory reaction time (RT) tasks engage almost identical volumes of cortical and subcortical motor structures. Moreover, dual RT tasks engaged additional cortical regions that are not activated by the component RT tasks had they been performed as single tasks. When the inter-stimulus interval was <300 ms, the first task interfered with the second, and a field in the right inferior frontal gyrus (RIFG) appeared with activity correlated with the increased RT to the second stimulus. This activation was spatially distinct from the cortical activity of the main effect of dual task performance. Thus, the performance of single RT tasks, dual RT tasks and dual RT tasks that interfere differ psychophysically and in the brain structures subserving these tasks. A short occupancy of the common motor structures can explain the interference effect. The increased activity of the RIFG correlated with the interference effect is very likely to be a specific outcome of situations where two concurrent tasks interfere with each other. The brain appears to recruit the RIFG for a subsequent (delayed) response when there is interference between dual tasks.

Visual recognition: evidence for two distinctive mechanisms from a PET study.

In this study, we examined the hypothesis that two distinct sets of cortical areas subserve two dissociable neurophysiological mechanisms of visual recognition. We posited that one such mechanism uses category specific cues extractable from the viewed pattern for the purpose of recognition. The other mechanism matches the pattern to be recognized with a pre-encoded memory representation of the pattern. In order to distinguish the cortical areas active in these two strategies, we measured changes in regional cerebral blood flow (rCBF) with positron emission tomography (PET) and (15)O Butanol as the radiotracer. Ten subjects performed pattern recognition tasks based on three different short-term memory conditions and a condition based on visual categories of the patterns. When subjects used representations of the patterns held in short-term memory for the purpose of recognition, the precunei were bilaterally activated. Recognition based on visual categories of the patterns activated the right (R) angular gyrus, left (L) inferior temporal gyrus, and L superior parieto-occipital cortex. These findings demonstrate that the R angular gyrus, the L inferior temporal gyrus, and the L superior parieto-occipital cortex are associated with recognition of patterns based on visual categories, whereas recognition of patterns using memory representations is associated with the activity of the precunei. This study is the first to show functional dual dissociation of active cortical fields for different mechanisms of visual pattern recognition.

Insecticide resistance in Anopheles sacharovi Favre in southern Turkey.

We report the resistance to 12 insecticides of specimens of Anopheles sacharovi, both in laboratory cultures and those collected in the malarious areas of Adana, Adiyaman, Antalya, Aydin, and Mugla in southern Turkey. Mortality was higher 24 h after exposure than immediately after exposure but was unaffected by temperature (24 degrees C or 29 degrees C) or the position of the test kit (horizontal or vertical). In Adana, Adiyaman and Antalya, A. sacharovi was susceptible only to malathion and pirimiphos-methyl. In Aydin it was susceptible to both these insecticides as well as to dieldrin, lambda-cyhalothrin, and etofenprox; and in Mugla it was susceptible to dieldrin, fenitrothion, lambda-cyhalothrin, cyfluthrin and etofenprox, as well as to malathion and pirimiphos-methyl.

Method to estimate relative transmission efficiencies of Anopheles species (Diptera: Culicidae) in human malaria transmission.

A mathematical expression was derived to estimate the relative malaria transmission efficiency of an anopheline species with respect to a standard well-characterized species for which all vector parameters can be sufficiently determined. The method is particularly useful in situations where multiple anopheline species contribute to human malaria transmission and requires the estimation of the man-biting rate, the sporozoite rate, and the human malaria incidence. Under stable conditions of vector abundance, the average sporozoite rate in a species during a transmission season would by itself reflect its relative transmission efficiency. This "efficiency" then was used to calculate the "effective human-biting rate"; i.e., the human-biting rate of that species if it were to have ecological properties identical to those of the standard species. The standard well-characterized species then could be used with the effective human-biting rate of all species to quantify transmission, thus overcoming the need to measure vector parameters for all anopheline species contributing to transmission. An expression also was derived to calculate the relative contribution made by each species to malaria transmission. The usefulness of this method was illustrated using entomological and epidemiological data from Kataragama, Sri Lanka.

Clustering of malaria infections within an endemic population: risk of malaria associated with the type of housing construction.

The occurrence of malaria infections due to Plasmodium vivax and P. falciparum was monitored in a population of 3,023 people living in six contiguous villages in Kataragama, an area of endemic malaria in southern Sri Lanka, over a period of 17 months. The annual incidence of malaria in this population during the study period was 25.8%. Malaria attacks were clustered, occurring more frequently than expected in certain individuals and housing groups and less frequently than expected in others. In one of these villages, the distribution of cases was examined in relation to locality and to the type of house construction. There was a strong association between the malaria incidence and house construction, independent of location. The risk of getting malaria was greater for inhabitants of the poorest type of house construction (incomplete, mud, or cadjan (palm) walls, and cadjan thatched roofs) compared to houses with complete brick and plaster walls and tiled roofs. Houses that were better constructed had a significantly lower malaria incidence rate (10.5%) than those that were poorly constructed (21.2%; P less than 0.01, by Student's t-test). There was also a significantly higher number of indoor resting mosquitoes collected from the poorly constructed houses than from those better constructed; the average (geometric mean) of mosquito densities found in houses of better versus poor construction were 0.97 and 1.89 per collection in the dry season, and 1.95 and 3.42 per collection in the wet season, respectively (P less than 0.05 in both seasons). This indicated that the higher malaria risk associated with poorly constructed houses was at least partly due to higher human-mosquito contact among their inhabitants.

A mathematical model for Plasmodium vivax malaria transmission: estimation of the impact of transmission-blocking immunity in an endemic area.

We have developed a multi-state mathematical model to describe the transmission of Plasmodium vivax malaria; the model accommodates variable transmission-blocking/enhancing immunity during the course of a blood infection, a short memory for boosting immunity, and relapses. Using the model, we simulated the incidence of human malaria, sporozoite rates in the vector population, and the level of transmission-blocking immunity for the infected population over a period of time. Field data from an epidemiological study conducted in Kataragama in the south of Sri Lanka were used to test the results obtained. The incidence of malaria during the study period was simulated satisfactorily. The impact of naturally-acquired transmission-blocking immunity on malaria transmission under different vectorial capacities was also simulated. The results show that at low vectorial capacities, e.g., just above the threshold for transmission, the effect of transmission-blocking immunity is very significant; however, the effect is lower at higher vectorial capacities.

Characteristics of malaria transmission in Kataragama, Sri Lanka: a focus for immuno-epidemiological studies.

Parasitological and entomological parameters of malaria transmission were monitored for 17 months in 3,625 residents in a Plasmodium vivax malaria endemic region in southern Sri Lanka; the study area consisted of 7 contiguous villages where routine national malaria control operations were being conducted. Malaria was monitored in every resident; fever patients were screened and 4 periodical mass blood surveys were conducted. An annual malaria incidence rate of 23.1% was reported during the period: 9.3% was due to P. vivax and 13.8% was due to P. falciparum; there had been a recent epidemic of the latter in this region, whereas the P. falciparum incidence rate in the previous 10 years had been negligible. There was a wide seasonal fluctuation in the malaria incidence, with the peak incidence closely following the monsoon rains. The prevalence of malaria due to both species detected at the 4 mass blood surveys ranged from 0.98% (at low transmission) to 2.35% (at peak transmission periods). Adults and children developed acute clinical manifestations of malaria. Entomological measurements confirmed a low degree of endemicity with estimated inoculation rates of 0.0029 and 0.0109 (infectious bites/man/night) for P. vivax and P. falciparum, respectively. Several anopheline species contributed to the transmission, and the overall man biting rates (MBR) showed a marked seasonal variation. Malaria at Kataragama, typical of endemic areas of Sri Lanka, thus presents characteristics of "unstable" transmission. Malaria was clustered in the population. There was a low clinical tolerance to P. falciparum malaria, to which most had only been at risk, compared to P. vivax, to which most had had a life-long exposure.

Pesticide selection pressure on Anopheles subpictus in Sri Lanka: comparison with two other Sri Lankan anophelines.

Adult Anopheles subpictus from Sri Lanka show a broad spectrum of resistance towards organophosphate insecticides but not to carbamates in contrast to the broad resistance to organophosphates and carbamates reported earlier for An. nigerrimus. In both species the frequency of resistance to malathion and fenitrothion increased between 1980 and 1987, despite the ban on agricultural use of these two compounds and the restriction of malathion to indoor residual spraying in malaria control since 1977. In contrast, An. culicifacies shows only low level specific resistance to malathion at a very low frequency. As An. subpictus breeds to a large extent in paddy fields which are highly contaminated by agricultural pesticides, and is highly endophilic, selection for resistance theoretically could occur through both agricultural and anti-malarial pesticide use. However, the anti-malarial use of malathion may have been less important, taking into consideration the low level of resistance of An. culicifacies which is also highly endophilic but breeds to a negligible extent in paddy fields.

Modulation of human malaria transmission by anti-gamete transmission blocking immunity.

Natural Plasmodium vivax malaria infections in man evoke anti-gamete transmission blocking antibodies which influence the infectivity of malaria patients to the vector mosquito. In this study, entomological, immunological and parasitological data obtained through the monitoring of an epidemic of human vivax malaria in Sri Lanka were used in a mathematical simulation to assess the effect of naturally induced transmission blocking immunity on malaria transmission. A mathematical model to describe malaria transmission accounting for transmission blocking immunity was developed from the basic differential equations originally stated by R. Ross and the epidemic was simulated using the available data. An attempt was made to predict the monthly malaria incidence by means of the mathematical simulation, with and without accounting for transmission blocking immunity. A plausible mathematical solution of the epidemic could be obtained when transmission blocking immunity was accounted for, and it was not possible to obtain such a plausible solution in the absence of immunity. Thus, the postulated occurrence of transmission blocking immunity was essential to describe adequately this malaria epidemic, indicating that, at least in epidemic situations, naturally occurring transmission blocking immunity has a controlling influence on malaria incidence.