Efficiency of Truthful and Symmetric Mechanisms in One-sided Matching

We study the efficiency (in terms of social welfare) of truthful and symmetric mechanisms in one-sided matching problems with {\em dichotomous preferences} and {\em normalized von Neumann-Morgenstern preferences}. We are particularly interested in the well-known {\em Random Serial Dictatorship} mechanism. For dichotomous preferences, we first show that truthful, symmetric and optimal mechanisms exist if intractable mechanisms are allowed. We then provide a connection to online bipartite matching. Using this connection, it is possible to design truthful, symmetric and tractable mechanisms that extract 0.69 of the maximum social welfare, which works under assumption that agents are not adversarial. Without this assumption, we show that Random Serial Dictatorship always returns an assignment in which the expected social welfare is at least a third of the maximum social welfare. For normalized von Neumann-Morgenstern preferences, we show that Random Serial Dictatorship always returns an assignment in which the expected social welfare is at least \frac{1}{e}\frac{\nu(\opt)^2}{n}, where \nu(\opt) is the maximum social welfare and $n$ is the number of both agents and items. On the hardness side, we show that no truthful mechanism can achieve a social welfare better than \frac{\nu(\opt)^2}{n}.Comment: 13 pages, 1 figur

Social welfare in one-sided matchings: Random priority and beyond

We study the problem of approximate social welfare maximization (without money) in one-sided matching problems when agents have unrestricted cardinal preferences over a finite set of items. Random priority is a very well-known truthful-in-expectation mechanism for the problem. We prove that the approximation ratio of random priority is Theta(n^{-1/2}) while no truthful-in-expectation mechanism can achieve an approximation ratio better than O(n^{-1/2}), where n is the number of agents and items. Furthermore, we prove that the approximation ratio of all ordinal (not necessarily truthful-in-expectation) mechanisms is upper bounded by O(n^{-1/2}), indicating that random priority is asymptotically the best truthful-in-expectation mechanism and the best ordinal mechanism for the problem.Comment: 13 page

Comparison of the Spinels Co3O4 and NiCo2O4 as Bifunctional Oxygen Catalysts in Alkaline Media

Data from experiments with both rotating disc electrodes (RDEs) and gas diffusion electrodes (GDEs) are used to investigate the properties of the spinels, Co3O4 and NiCo2O4, as bifunctional oxygen electrocatalysts. Emphasis is placed on catalyst compositions and electrode structures free of carbon. Oxygen evolution and reduction occur at surfaces where the transition metals are in different oxidation states but the surface can be repeatedly cycled between these two states without significant change. It is shown that carbon-free, NiCo2O4 catalysed GDEs can be fabricated using structures based on stainless steel cloth or nickel foam. Those based on nickel foam can be cycled extensively and allow both O2 evolution and reduction at current densities up to 100 mA cm−2.European Commission (Theme 2010.7.3.1) Energy Storage Systems for Power Distribution NetworksMinistry of National Education, Republic of Turke

Voltammetric studies of the mechanism of the oxygen reduction in alkaline media at the spinels Co3O4and NiCo2O4

The mechanism of O2 reduction at the spinels, Co3O4 and NiCo2O4, in KOH electrolyte is probed using voltammetry at rotating disc and rotating ring-disc electrodes by examination of the rotation rate dependent limiting currents. The analysis shows that the products and mechanisms at the two spinels are quite different. At the cobalt spinel, a substantial amount of the 2e? reduction product, H2O2, is formed while at NiCo2O4 the 4e? reduction strongly predominates. In terms of both the overpotential for reduction and its limiting current density, the mixed spinel is a substantially better electrocatalyst. It is proposed that the differences arise from an enhanced rate of O-O bond cleavage early in the reduction process at NiCo2O4

Sludge reduction with pulse ozonation

Biyolojik atıksu arıtma tesislerinde atıksuyun arıtılmasının yanı sıra fazla çamurun da uzaklaştırılması önemlidir. Tesis işletme maliyetlerinin yaklaşık yarıdan fazlası çamur bertarafına harcanmaktadır. Bu nedenle uygulanabilir, ekonomik ve yenilikçi yöntemler araştırılmaktadır. Araştırılan süreçler arasında ozon güçlü bir oksidan olarak ön plana çıkmaktadır. Bu çalışmada 15-30 gün gibi uzun süren aerobik çürütmeyi kısaltmak için havalandırmaya ilave olarak ozon kullanılması araştırılmıştır. Benzer çalışmalardan farklı olarak araştırmada ozon sürekli olarak kullanılmamış olup bakterilerin ikileme zamanı dikkate alınarak 24 saatte bir kez pals şeklinde kısa sürelerle tatbik edilmiştir. Böylece ozonun biyolojik parçalanmaya olan etkisi de incelenmiştir. Ankara Tatlar Atıksu Arıtma Tesisi Havalandırma Tankı’ndan alınan numuneler ile yapılan deneyler sırasında günde bir kez erlenlerdeki çamurlara 2, 3, 4 ve 6 dakikalık sürelerle ozonlama yapılmış, daha sonra çamur 24 saat süreyle çalkalayıcıda bekletilmiştir. Dört gün süreyle devam eden deneylerde rutin olarak TKM, UKM, KOİ ve OTH  ölçümleri yapılmıştır. Sonuç olarak bu süre bitiminde UKM indirgenmesi 2, 3, 4 ve 6 dakika ozonlamalar için sırasıyla %22.6, %40, %75 ve %84 olarak tespit edilmiştir. Standart havasal çamur çürütme ile elde edilen çamur azaltımı %40-50 iken kesikli ozonlama ile elde edilen çamur azaltımı % 80 üzerine çıkmıştır. Yine reaksiyon süresi 20-30 günden 4 günlere inmiştir. Ozon destekli çürütülmüş çamurda yapılan koli basili analizleri de çamurdaki koli basillerinin bu süre içersinde tamamen öldürüldüğünü göstermiştir. Yine ozon destekli havasal çürütmede önemli mitarda ortama fosfor salınmadığı görülmüştür. Anahtar Kelimeler: Ozon, çamur degredasyonu, bakteri, ikileme zamanı, pals.Biological treatment is one of the most widely used treatment techniques. Although its high efficiency and easy design make it a preferable option, excess sludge production is a massive burden for the facilities. Approximately, half of the operation cost for domestic wastewater treatment plants is spent for sludge treatment and disposal. Even after treatment it may act as a secondary pollution source at the disposal site due to its heavy metal, pathogen and persistent organic pollutant contents. Therefore, several strategies are considered for excess sludge treatment. Incineration, dewatering, landfilling and use for agricultural purposes are some of them. However, since regulations on the use and disposal of excess sludge are much more stringent than past years, people tend to use methods which reduce the volume of sludge such as thermal, mechanical, chemical and oxidation pretreatment. Ozonation which is a chemical treatment method establishes disintegration by two mechanisms: first one is the destruction of the cell wall of the microorganism and the second one is the mineralization of the intracellular components. According to high degree of disintegration and cost effectiveness of ozonation make it a feasible technique among the other disintegration techniques. Consequently, ozone treatment of sludge gaining popularity and this leads to a new area of study in environmental engineering. The common point of previous studies is the continuous ozonation of the samples. However, ozone is a very expensive chemical to be wasted. Therefore it should be used properly. That led us to consider about pulse ozonation of sludge which would be economically more feasible if it can be as efficient as continuous ozonation. In this study it was planned to use ozone as a substitute to shorten the 15-30 day-long aerobic digestion process. Waste activated sludge samples from Ankara Tatlar Wastewater Treatment Plant were ozonated for 2, 3, 4 and 6 minutes respectively in Erlenmeyer flasks once a day on each of four consecutive days and left for incubation in between on a shaker. In the experiments, ozone was supplied by OSC-Modular 4HC, WEDECO ITT INDUSTRIES (2007) ozone generator. Operating pressure of the generator is 5 bar and the gas flow rate is 10-140 L/hr with a rated capacity of 4 g/hr. Ozone amount that is released to water in time interval was measured by using Standard Methods 8021 (DPD chlorine reagent) and calibration curve was obtained by spectrophoto-metric measurement (for 25 mL sample). The MLVSS, MLSS, COD and OUR parameters were measured routinely during the four days. MLSS measurements were done according to Standard Methods (2540B) (APHA, 1998). Chemical oxygen demand (COD) was measured by Hach Lange kits according to HACH 8000(US EPA approved) method. Volatile Suspended Solids (MLVSS) was measured according to 2540 solids method. Total-P was analyzed by 365.4 EPA Method and ortho-phosphate was analysed with 365.3 EPA Method. Obviously, one of the most important reasons of sludge treatment is sludge disinfection. In order to have an opinion about this concept, it was decided to count E.coli in the sludge. Also considering the possibility of phosphorus release, total phosphorus and ortho-phosphate were checked in the 6' ozonated sample. At the first day, total phosphorus of the sludge was 0.006 g per g biomass and after the first ozonation this amount increased to 0.0082. By these results, it can be concluded that ozonation does not release significant amounts of phosphorus to the medium. At the end of the experiments, MLVSS reductions for 2, 3, 4, and 6 minutes were observed as 22.6%, 40%, 75% and 84% respectively. As a result of the experiments, by the pulse ozonation of the non-digested activated sludge, both stabilization and reduction of the sludge were achieved in such short period as 4 days. Moreover, it can be ascertained that the obtained sludge was both disinfected from E.coli and phosphorus rich. Furthermore, since the COD left in the medium after the experiments was biodegradable, it was concluded that it would be feasible to return to the beginning of the system.  Hence, it became possible to save on both time of contact and the amount of ozone used in comparison with other studies where samples were ozonated on continuous bases. The obtained results show similar values for MLVSS, MLSS and COD for both 4' and 6' ozonation for first 3 days. Nevertheless, since the 6' ozonation is more effective in sludge stabilization, after the 4' ozonation for the first 3 days, 6' ozonation for the 4th day is suggested. Keywords: Ozone, sludge degradation, bacteria, doubling time, pulse

Upper Bounds on the Multiplicative Complexity of Symmetric Boolean Functions

A special metric of interest about Boolean functions is multiplicative complexity (MC): the minimum number of AND gates sufficient to implement a function with a Boolean circuit over the basis {XOR, AND, NOT}. In this paper we study the MC of symmetric Boolean functions, whose output is invariant upon reordering of the input variables. Based on the Hamming weight method from Muller and Preparata (1975), we introduce new techniques that yield circuits with fewer AND gates than upper bounded by Boyar et al. in 2000 and by Boyar and Peralta in 2008. We generate circuits for all such functions with up to 25 variables. As a special focus, we report concrete upper bounds for the MC of elementary symmetric functions $\Sigma^n_k$ and counting functions $E^n_k$ with up to n = 25 input variables. In particular, this allows us to answer two questions posed in 2008: both the elementary symmetric $\Sigma^8_4$ and the counting $E^8_4$ functions have MC 6. Furthermore, we show upper bounds for the maximum MC in the class of n-variable symmetric Boolean functions, for each n up to 132

Effect of exogenous GnRH at the time of artificial insemination on reproductive performance of awassi ewes synchronized with progestagen-PMSG-PGF2α combination

This study was carried out to investigate the efficacy of PGF2a for oestrus synchronization (ES) in Awassi ewes to which were administered the progestagen–PMSG combination, and to evaluate the effect of the exogenous GnRH administration immediately after the artificial insemination (AI) on their pregnancy rate and lambing performance during the breeding season. The ewes (n ¼ 33) were treated with an intravaginal sponge impregnated with 30 mg fluorogestane acetate for 12 days and were injected with 500 IU PMSG at the time of removal of the sponge. The ewes were then divided into three equal groups of 11 ewes each. One millilitre of physiological saline (0.9% NaCl; placebo) was administered to each ewe in Group 1 at the time of second AI. Approximately 4 lg GnRH (busereline) was injected to each ewe in Group 2 immediately after second AI. A total of 150 lg PGF2a (cloprostenole) was injected at the time of sponge removal on day 12 and 4 lg GnRH immediately after the second AI was also treated to each ewe in Group 3. Intracervical AI with diluted fresh semen was performed twice at 12 and 24 h following the onset of oestrus. The injection-oestrus onset and injection-oestrus-end interval in Group 3 was significantly (p < 0.001) shorter than both Groups 1 and 2. Although the pregnancy rates of Groups 2 and 3 (81.8%; 9/11) were numerically higher than of Group 1 (63.6%; 7/11), the difference among the groups was statistically insignificant. The multiple birth rate of Group 3 was found higher than Groups 1 and 2. However, the number of single lambs of Group 1 was also higher than Groups 2 and 3 (p < 0.05). Despite the litter sizes of Groups 2 (1.27; 14/11) and 3 (1.55; 17/11) being numerically higher than Group 1 (0.73; 8/11), the differences among all the groups were statistically insignificant. In conclusion, the administration of PGF2a at the time of removal of the sponge shortens the injection oestrus-onset and oestrus-end interval in Awassi ewes treated with progestagen–PMSG. Additionally, exogenous GnRH treatment immediately after the AI increases the multiple birth rate of Awassi ewes synchronized with progestagen– PMSG–PGF2a combination

A novel approach for rapid screening of mitochondrial D310 polymorphism

BACKGROUND: Mutations in the mitochondrial DNA (mtDNA) have been reported in a wide variety of human neoplasms. A polynucleotide tract extending from 303 to 315 nucleotide positions (D310) within the non-coding region of mtDNA has been identified as a mutational hotspot of primary tumors. This region consists of two polycytosine stretches interrupted by a thymidine nucleotide. The number of cytosines at the first and second stretches are 7 and 5 respectively, according to the GeneBank sequence. The first stretch exhibits a polymorphic length variation (6-C to 9-C) among individuals and has been investigated in many cancer types. Large-scale studies are needed to clarify the relationship between cytosine number and cancer development/progression. However, time and money consuming methods such as radioactivity-based gel electrophoresis and sequencing, are not appropriate for the determination of this polymorphism for large case-control studies. In this study, we conducted a rapid RFLP analysis using a restriction enzyme, BsaXI, for the single step simple determination of 7-C carriers at the first stretch in D310 region. METHODS: 25 colorectal cancer patients, 25 breast cancer patients and 41 healthy individuals were enrolled into the study. PCR amplification followed by restriction enzyme digestion of D310 region was performed for RFLP analysis. Digestion products were analysed by agarose gel electrophoresis. Sequencing was also applied to samples in order to confirm the RFLP data. RESULTS: Samples containing 7-C at first stretch of D310 region were successfully determined by the BsaXI RFLP method. Heteroplasmy and homoplasmy for 7-C content was also determined as evidenced by direct sequencing. Forty-one percent of the studied samples were found to be BsaXI positive. Furthermore, BsaXI status of colorectal cancer samples were significantly different from that of healthy individuals. CONCLUSION: In conclusion, BsaXI RFLP analysis is a simple and rapid approach for the single step determination of D310 polymorphism of mitochondrial DNA. This method allows the evaluation of a significant proportion of samples without the need for sequencing- and/or radioactivity-based techniques