Distributed Channel Assignment in Cognitive Radio Networks: Stable Matching and Walrasian Equilibrium

We consider a set of secondary transmitter-receiver pairs in a cognitive radio setting. Based on channel sensing and access performances, we consider the problem of assigning channels orthogonally to secondary users through distributed coordination and cooperation algorithms. Two economic models are applied for this purpose: matching markets and competitive markets. In the matching market model, secondary users and channels build two agent sets. We implement a stable matching algorithm in which each secondary user, based on his achievable rate, proposes to the coordinator to be matched with desirable channels. The coordinator accepts or rejects the proposals based on the channel preferences which depend on interference from the secondary user. The coordination algorithm is of low complexity and can adapt to network dynamics. In the competitive market model, channels are associated with prices and secondary users are endowed with monetary budget. Each secondary user, based on his utility function and current channel prices, demands a set of channels. A Walrasian equilibrium maximizes the sum utility and equates the channel demand to their supply. We prove the existence of Walrasian equilibrium and propose a cooperative mechanism to reach it. The performance and complexity of the proposed solutions are illustrated by numerical simulations.Comment: submitted to IEEE Transactions on Wireless Communicaitons, 13 pages, 10 figures, 4 table

Novel organic synthesis through ultrafast chemistry

How fast are flashes? The field of flow chemistry has recently received increasing attention owing to the availability of commercial flow equipment. New syntheses with very short-lived intermediates have been enabled by sub-millisecond mixing and reaction regimes in tailor-made flow devices

Neue organische synthesen durch ultraschnelle chemie

Schnell wie der Blitz: Neue Synthesen gelingen dank sehr kurzlebiger Intermediate, die durch Submillisekundenmischen und -reaktionen in speziellen Fluss-Systemen erzeugt werden

330— Public Opinion and Policy Regarding Welfare in the United States

Government spending on social programs is perhaps the most widely debated platform topic in American politics. The American two party system has produced two distinctive camps, defined most obviously by liberal Democrats and Democratic Socialists on one side, and conservative Republicans on the other. The former argues that government should play a stronger role in securing wealth for the lower class than it currently does via social safety nets provided by taxes on richer individuals. The latter claims that the current American welfare state is either doing enough or too much in its legal role to redistribute funds to lower class individuals/households. While these assertions may be accurate, they are extremely broad and do not properly explain the status of our welfare state or how it has attained its current form. In this analysis, I will look at data and historical trends regarding the US budget, public opinion on its own welfare/ social spending, specific programs, and any legislation, movements, or events that are relevant to the current status of our welfare state. I predict that public opinion regarding the social spending programs of the US government have had an effect on actual legislation and budgets passed by congress

In vivo manipulation of interleukin-2 expression by a retroviral tetracycline (tet)-regulated system

We have used the tetracycline (tet)-regulated system as described previously to evaluate the applicability of controlled gene expression in cancer gene therapy. As a model gene, we used the human interleukin-2 (IL-2) gene, which has been placed under the transcriptional control of the tetO/promoter. Human melanoma cells were transduced by two modified retroviral tet vectors containing the transactivator regulatory unit and the IL-2 gene driven by the tetO/promoter, respectively. In the absence of tet, IL-2 expression in the target cells was stable over several months. IL-2 production was in the range of 40 U/106 cells/24 hours. A fine tuning of IL-2 expression could be achieved by culturing the transduced cells with increasing doses of tet, whereby a concentration of 500 ng/mL tet in the culture medium abrogated IL-2 expression. Most importantly for clinical application, IL-2 expression by the transduced melanoma cells could also be regulated in vivo. When nu/nu mice were inoculated with the transduced tumor cells, they failed to develop tumors. Instead, the inhibition of IL-2 expression in the transduced tumor cells by oral administration of tet led to subcutaneous tumor growth; this growth rate was comparable with the growth rate of subcutaneously inoculated untransduced parental cells. The finding demonstrates the applicability of the tet-regulated system in cancer gene therapy

Safe use of nitromethane for aldol reactions in flow

Using a simple flow reactor, the safe use of nitromethane at elevated reaction temperatures was demonstrated in a nitroaldol reaction of different aldehydes. The reaction products were isolated in good yields after a short reaction tim

Frontispiece: stereoselective ketone rearrangements with hypervalent iodine reagents

Stereoselective Rearrangements The first stereoselective version of an iodine(III)-mediated rearrangement of arylketones in the presence of orthoesters is described T. Wirth and F. Malmedy on page 16072 ff. The reaction products, α-arylated esters, are very useful intermediates in the synthesis of bioactive compounds, such as ibuprofen. With chiral lactic acid-based iodine(III) reagents, enantioselectivities of up to 73 % ee have been achieved

Iodoaminations of alkenes

The activation of alkenes and their subsequent functionalization is a frequently used methodology in synthetic chemistry. This review highlights recent iodine-mediated aminations and elaborates on the various strategies to bring about regio- or stereoselective transformations

A simple setup for transfer hydrogenations in flow chemistry

By using a packed-bed reactor with a palladium/charcoal catalyst and ammonium formate or triethylsilane as hydrogen/hydride source, various functional groups including nitro groups, azides and alkenes can be efficiently reduced by a transfer hydrogenation process under mild conditions in a simple flow system