A DC Programming Approach for Solving Multicast Network Design Problems via the Nesterov Smoothing Technique

This paper continues our effort initiated in [9] to study Multicast Communication Networks, modeled as bilevel hierarchical clustering problems, by using mathematical optimization techniques. Given a finite number of nodes, we consider two different models of multicast networks by identifying a certain number of nodes as cluster centers, and at the same time, locating a particular node that serves as a total center so as to minimize the total transportation cost through the network. The fact that the cluster centers and the total center have to be among the given nodes makes this problem a discrete optimization problem. Our approach is to reformulate the discrete problem as a continuous one and to apply Nesterov smoothing approximation technique on the Minkowski gauges that are used as distance measures. This approach enables us to propose two implementable DCA-based algorithms for solving the problems. Numerical results and practical applications are provided to illustrate our approach

Low-frequency electronic noise in superlattice and random-packed thin films of colloidal quantum dots

We report measurements of low-frequency electronic noise in ordered superlattice, weakly-ordered and random-packed thin films of 6.5 nm PbSe quantum dots prepared using several different ligand chemistries. For all samples, the normalized noise spectral density of the dark current revealed a Lorentzian component, reminiscent of the generation-recombination noise, superimposed on the 1/f background (f is the frequency). An activation energy of 0.3 eV was extracted from the temperature dependence of the noise spectra. The noise level in the ordered films was lower than that in the weakly-ordered and random-packed films. A large variation in the magnitude of the noise spectral density was also observed in samples with different ligand treatments. The obtained results are important for application of colloidal quantum dot films in photodetectors.Comment: 24 pages, 6 figures and supplemental inf

Electric Switching of the Charge-Density-Wave and Normal Metallic Phases in Tantalum Disulfide Thin-Film Devices

We report on switching among three charge-density-wave phases - commensurate, nearly commensurate, incommensurate - and the high-temperature normal metallic phase in thin-film 1T-TaS2 devices induced by application of an in-plane electric field. The electric switching among all phases has been achieved over a wide temperature range, from 77 K to 400 K. The low-frequency electronic noise spectroscopy has been used as an effective tool for monitoring the transitions, particularly the switching from the incommensurate charge-density-wave phase to the normal metal phase. The noise spectral density exhibits sharp increases at the phase transition points, which correspond to the step-like changes in resistivity. Assignment of the phases is consistent with low-field resistivity measurements over the temperature range from 77 K to 600 K. Analysis of the experimental data and calculations of heat dissipation suggest that Joule heating plays a dominant role in the electric-field induced transitions in the tested 1T-TaS2 devices on Si/SiO2 substrates. The possibility of electrical switching among four different phases of 1T-TaS2 is a promising step toward nanoscale device applications. The results also demonstrate the potential of noise spectroscopy for investigating and identifying phase transitions in materials.Comment: 32 pages, 7 figure

Thermal Properties of the Binary-Filler Composites with Few-Layer Graphene and Copper Nanoparticles

The thermal properties of an epoxy-based binary composites comprised of graphene and copper nanoparticles are reported. It is found that the "synergistic" filler effect, revealed as a strong enhancement of the thermal conductivity of composites with the size-dissimilar fillers, has a well-defined filler loading threshold. The thermal conductivity of composites with a moderate graphene concentration of ~15 wt% exhibits an abrupt increase as the loading of copper nanoparticles approaches ~40 wt%, followed by saturation. The effect is attributed to intercalation of spherical copper nanoparticles between the large graphene flakes, resulting in formation of the highly thermally conductive percolation network. In contrast, in composites with a high graphene concentration, ~40 wt%, the thermal conductivity increases linearly with addition of copper nanoparticles. The electrical percolation is observed at low graphene loading, less than 7 wt.%, owing to the large aspect ratio of graphene. At all concentrations of the fillers, below and above the electrical percolation threshold, the thermal transport is dominated by phonons. The obtained results shed light on the interaction between graphene fillers and copper nanoparticles in the composites and demonstrate potential of such hybrid epoxy composites for practical applications in thermal interface materials and adhesives.Comment: 25 pages, 4 figure

Households with unimproved water sources in Ethiopia: spatial variation and point-of-use treatment based on 2016 Demographic and Health Survey

Published online: 07 December 2020Background: Improved water sources are not equally available in all geographical regions. Populations dependent on unsafe water sources are recommended to treat their water at point-of-use using adequate methods to reduce associated health problems. In Ethiopia, the spatial distribution of households using unimproved water sources have been incomplete or ignored in most of the studies. Moreover, evidence on the point-of-use water treatment practice of households dependent on such water sources is scarce. Therefore, the current study is intended to analyze the spatial distribution of unimproved water sources by wealth quintiles at country level and point-of-use treatment (POU) practices using nationally representative data. Method: The data of 2016 Ethiopian Demographic and Health Survey (EDHS) conducted on 16650 households from 643 clusters were used for the analysis. For spatial analysis, the raw and spatially smoothed coverage data was joined to the geographic coordinates based on EDHS cluster identification code. Global spatial autocorrelation was performed to analyze whether the pattern of unimproved water coverage is clustered, dispersed, or random across the study areas. Once a positive global autocorrelation was confirmed, a local spatial autocorrelation analysis was applied to detect local clusters. The POU water treatment is analyzed based on reported use of either boiling, chlorine (bleach), filtration, or solar disinfection (SODIS). Results: There were 5005 households using unimproved water sources for drinking purposes. Spatial variation of unimproved water coverage was observed with high coverage observed at Amhara, Afar, Southern Nations Nationalities and People and Somalia regions. Disparity in unimproved water coverage between wealth quintiles was also observed. The reported point-of-use water treatment practice among these households is only 6.24%. The odds of POU water treatment among household heads with higher education status is 2.5 times higher (95% CI = 1.43-4.36) compared to those who did not attend education. Conclusion: An apparent clustering trend with high unimproved water coverage was observed between regions and among wealth quintiles hence indicates priority areas for future resource allocation and the need for regional and national policies to address the issue. Promoting households to treat water prior to drinking is essential to reduce health problems.Yohannes Tefera Damtew and Abraham Gereme

Low-Frequency Noise Spectroscopy of Charge-Density-Wave Phase Transitions in Vertical Quasi-2D Devices

We report results regarding the electron transport in vertical quasi-2D layered 1T-TaS2 charge-density-wave devices. The low-frequency noise spectroscopy was used as a tool to study changes in the cross-plane electrical characteristics of the quasi-2D material below room temperature. The noise spectral density revealed strong peaks - changing by more than an order-of-magnitude - at the temperatures closely matching the electrical resistance steps. Some of the noise peaks appeared below the temperature of the commensurate to nearly-commensurate charge-density-wave transition, possibly indicating the presence of the debated "hidden" phase transitions. These results confirm the potential of the noise spectroscopy for investigations of electron transport and phase transitions in novel materials.Comment: 16 pages; 5 figure

Teachers and Sanitation Promotion: An Assessment of Community-Led Total Sanitation in Ethiopia

Community-led total sanitation (CLTS) is a participatory approach to addressing open defecation that has demonstrated success in previous studies, yet there is no research on how implementation arrangements and context change effectiveness. We used a quasi-experimental study design to compare two interventions in Ethiopia: conventional CLTS in which health workers and local leaders provided facilitation and an alternative approach in which teachers provided facilitation. In 2012, Plan International Ethiopia trained teachers from 111 villages and health workers and leaders from 54 villages in CLTS facilitation. The trained facilitators then implemented CLTS in their respective villages for a year. Latrine ownership, use, and quality were measured with household surveys. Differences between interventions were explored using surveys and interviews. The decrease in open defecation associated with teacher-facilitated CLTS was 8.2 percentage points smaller than for conventional CLTS (p = 0.048). Teachers had competing responsibilities and initially lacked support from local leaders, which may have lessened their success. Teachers may be more appropriate for a supporting rather than leading role in sanitation promotion because they did demonstrate ability and engagement. Open defecation decreased by 15.3 percentage points overall but did not change where baseline open defecation was below 30%. Ownership of a latrine with stable flooring increased by 8.7 percentage points overall. Improved latrine ownership did not change during the intervention. CLTS is most appropriate where open defecation is high because there were no significant changes in sanitation practices or latrine upgrades where baseline open defecation was low

Mycoflora of grain maize (Zea mays L.) Stored in traditional storage containers (Gombisa and sacks) in selected woredas of Jimma zone, Ethiopia

Mycoflora of maize (Zea mays L.) grain (Variety: Bako Hybrid-660) stored in two traditional storage containers (Gombisa and Sacks) for 180 days was studied for mycoflora in two agro-ecologies, that is Intermediate and Lowland, with altitude ranges of 1500-2500 meters above sea level, and 1000-1500 meters above sea level, respectively, in Jimma zone, Ethiopia. The temperature and relative humidity were observed for identifying fungi species which can flourish and cause maximum deterioration to maize grains. Significant (P<0.05) decreases in germination rate of the grains were observed with time under each storage method for both the low and intermediate altitude ranges. Germination percentage reduced from 98% and 97.5% to 68.5% and 80.5% for grains stored in Gombisa and Sacks, respectively. Storage type significantly (p<0.05) affected seed germination under intermediate agro-ecology whereas no significant (p>0.05) effect was observed under lowland agro-ecology due to storage container type. One sterile white mycelium and a total number of eight species of fungi viz., Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger, Aspergillus tereus, Cladosporium cladosporioides, Drechslera halodes, Fusarium oxysporum and Penicillium chrysogenum were identified from maize grain at the beginning and during storage. The most common fungi recorded from both agro-ecologies in the two storage structures were A. flavus, A. niger, D. halodes and F. oxysporum. These fungi were recorded from 90, 51, 72 and 44 percentage of the seed samples, respectively. In the districts of both intermediate and lowland agro-ecology these fungi were consistently recorded throughout 180 days, during storage. A. fumigatus was detected in3.6% of samples while C. cladosporioides observed in 15% of the samples. Fungal species A. tereus and Penicillium were recorded in 0.5% of samples in selected districts of Jimma. These fungal species were known to cause deterioration of maize and are a health risk to humans and animals due to the toxins they potentially produce.Key words: Agro ecologies, Fungi, Maize, Storag

Household water treatment using adequate methods in sub-saharan countries: evidence from 2013-2016 demographic and health surveys

In sub-Saharan countries, where a large number of populations depend on unsafe water, household water treatment is the recommended means to reduce diarrhea. However, the practice in the region is very low. The current study is intended to assess the households’ water treatment using adequate methods, boiling, adding bleach, filtration and solar disinfection, and associated factors in the region which will be an input to design and implement intervention strategies. The Demographic and Health Survey (DHS) data conducted from 2013 to 2016 in 23 sub-Saharan countries were obtained from the DHS program and weighted using the ‘svy’ command for analysis. The households’ reported use of treatment methods and associated factors were analyzed using log-binomial regression. In total, 357,979 households were included in the analysis of which 29% used unimproved water for drinking purposes. Households reportedly treating water in the region were 22% and those who used adequate treatment methods were 18%. The households’ reported use of adequate treatment methods was statistically associated with household head education, owning a radio and wealth quintiles. The treatment methods’ use is low in the region therefore intervention on wide-scale use should be designed and implemented.Abraham Geremew and Yohannes Tefera Damte