The thermal Hall effect of spin excitations in a Kagome magnet

At low temperatures, the thermal conductivity of spin excitations in a magnetic insulator can exceed that of phonons. However, because they are charge neutral, the spin waves are not expected to display a thermal Hall effect in a magnetic field. Recently, this semiclassical notion has been upended in quantum magnets in which the spin texture has a finite chirality. In the Kagome lattice, the chiral term generates a Berry curvature. This results in a thermal Hall conductivity $\kappa_{xy}$ that is topological in origin. Here we report observation of a large $\kappa_{xy}$ in the Kagome magnet Cu(1-3, bdc) which orders magnetically at 1.8 K. The observed $\kappa_{xy}$ undergoes a remarkable sign-reversal with changes in temperature or magnetic field, associated with sign alternation of the Chern flux between magnon bands. We show that thermal Hall experiments probe incisively the effect of Berry curvature on heat transport.Comment: 6 pages, 3 figure

Is health insurance competition good for consumers?

Less insurer competition can lower hospital prices, but savings may not reach consumers, write Kate Ho and Robin S. Le

Subsidizing Creativity Through Network Design: Zero Pricing and Net Neutrality

Today, through historical practice, there exists a de facto ban on termination fees – also referred to as a “zero-price” rule (Hemphill, 2008) – which forbids an Internet service provider from charging an additional fee to a content provider who wishes to reach that ISP’s customers. The question is whether this zero-pricing structure should be preserved, or whether carriers should be allowed to charge termination fees and engage in other practices that have the effect of requiring payment to reach users. This paper begins with a defense of the de facto zero-price rule currently in existence. We point out that the Internet, as an intermediary between users and content providers, exhibits pricing dynamics similar to other intermediaries in “two-sided markets.” In particular, we posit that the Internet’s absence of payments from content creators to users’ ISPs facilitates the entry of content creators. In that respect, the rule provides an alternative implementation of the policy goals provided by the intellectual property system and achieves functions similar to copyright and patent law. The rule also helps avoid the problems of Internet fragmentation, in which content providers who do not reach agreements with ISPs cannot access all customers, and consumers on a single ISP are foreclosed from proccessing their content

Signalling Preferences in Interviewing Markets

The process of match formation in matching markets can be divided into three parts: information sharing, investments in information acquisition, and the formation of matches based on available information. The last stage where agents are assumed to know their preferences has been studied in seminal work of Gale and Shapley (1962), and a model of second stage costly information acquisition is introduced and studied in Lee and Schwarz (2007). This paper focuses on the first stage -- information sharing -- and examines mechanisms which allow workers to signal their preferences over matching partners prior to the assignment of interviews. The incentives of firms and workers vis-a-vis information revelation are partially aligned -- all other things being equal, a worker prefers to have an interview with a firm that is high in his preference ranking and a firm prefers to invest in interviewing a worker who ranks a firm highly because such worker is more likely to accept a job if offered. However, the incentives are far from being perfectly aligned. For instance, if firms pay the full cost of interviewing, each worker would prefer to have as many interviews as possible, and in a world with bilateral communication no information is revealed as each workers would want to tell each firm that it is his first choice. But if communication is moderated through an intermediary or there is a restriction on the number of messages a worker can send, then cheap talk becomes informative. Currently existing market institutions that facilitate information exchange prior to interviewing are discussed

Friction Stir Processing of SSM356 Aluminium Alloy

AbstractThe aim of this experiment was to improve the mechanical properties of SSM 356 aluminum alloys by friction stir processing, a solid-state technique for microstructural modification using the heat from a friction and stirring. The parameters of friction stir processing for SSM 356 aluminum alloys were studied at three different travelling speeds: 80, 120 and 160mm/min under three different rotation speeds 1320, 1480 and 1750rpm. The hardness and tensile strength properties were increased by friction stir processing. The hardness of friction stir processing was 64.55 HV which was higher than the base metal (40.58 HV). The tensile strengths of friction stir processing were increased about 11.8% compared to the base metal. The optimal processing parameter was rotation speed at 1750rpm with the travelling speed at 160mm/min. Consequently, the application of the friction stir processing is a very effective method for the mechanical improvement of semi-solid metal aluminum alloys

Excitation Spectrum of the Holstein Model

In this paper the polaron problem for the Holstein model is studied in the weak coupling limit. We use second order perturbation theory to construct renormalized electron and phonons. Eigenstates of the Hamiltonian are labelled and the excitation spectrum is constructed.Comment: 4 pages, revtex, 1 figures, more stuff at http://www.mpipks-dresden.mpg.de/~robin/robin.htm

Mindfulness Meditation Improves Visual Short-Term Memory

Research into the effects of mindfulness meditation on behavioral outcomes has received much interest in recent years, with benefits for both short-term memory and working memory identified. However, little research has considered the potential effects of brief mindfulness meditation interventions or the nature of any benefits for visual short-term memory. Here, we investigate the effect of a single, 8-minute mindfulness meditation intervention, presented via audio recording, on a short-term memory task for faces. In comparison with two control groups (listening to an audiobook or simply passing the time however they wished), our mindfulness meditation participants showed greater increases in visual short-term memory capacity from pre- to post-intervention. In addition, only mindfulness meditation resulted in significant increases in performance. In conclusion, a single, brief mindfulness meditation intervention led to improvements in visual short-term memory capacity for faces, with important implications regarding the minimum intervention necessary to produce measurable changes in short-term memory tasks

Vertical Integration and Exclusivity in Platform and Two-Sided Markets

This paper develops techniques to analyze the adoption decisions of both consumers and firms for competing platform intermediaries in two-sided markets, and applies the methodology to empirically measure the impact of vertical integration and exclusive contracting in the sixth-generation of the U.S. videogame industry (2000-2005). I first introduce a framework to structurally estimate consumer demand in these types of hardware-software markets which (i) simultaneously analyzes both hardware and software adoption decisions; (ii) accounts for dynamic issues including the selection of heterogenous consumers across platforms, durability of goods, and agents' timing of purchases; and (iii) explicitly provides the marginal contribution of an individual software title to each platform's installed base of users. Demand results show the gains obtained by a platform provider from exclusive access to certain software titles can be large, and failure to account for dynamics, consumer heterogeneity, and multiple hardware purchases significantly biases estimates. I next specify dynamic network formation game to model the adoption decision of hardware platforms by software providers. Counterfactual experiments indicate that vertical integration and exclusivity benefited the smaller entrant platforms and not the dominant incumbent, which stands contrary to the interpretation of exclusivity as primarily a means of foreclosure and entry deterrence