Negative Differential Spin Conductance by Population Switching

An examination of the properties of many-electron conduction through spin-degenerate systems can lead to situations where increasing the bias voltage applied to the system is predicted to decrease the current flowing through it, for the electrons of a particular spin. While this does not necessarily constitute negative differential conductance (NDC) per se, it is an example of negative differential conductance per spin (NDSC) which to our knowledge is discussed here for the first time. Within a many-body master equation approach which accounts for charging effects in the Coulomb Blockade regime, we show how this might occur.Comment: 6 page, 2 figure

Race, Federalism, and Voting Rights

In Shelby County v. Holder, the Court struck down an important provision of the Voting Rights Act, section 4, on federalism grounds. The Court argued that Congress no longer had the power to enact section 4 because of the “federalism costs” imposed by the Act and because the Act violated basic principles of federalism. Unfortunately, the Court failed to articulate the costs to federalism imposed by the Act, much less conduct a cost-benefit analysis in order to determine whether the benefits of the Act outweighed its costs. Moreover, the Court failed to discuss whether the Reconstruction Amendments ought to matter at all to the federalism debate. In this Essay, we ask three basic questions in response to Shelby County. First, what does the Court mean by “federalism costs,” and why have these costs undermined the constitutionality of the VRA? Second, does the failure to discuss Reconstruction and the Reconstruction Amendments undermine the Court’s decision in Shelby County? And third, we ask how should we understand the utility of federalism in the context of race and voting. We suggest that if one purpose of federalism is that it enables minorities to engage in self-rule, we should ask whether federalism enables racial minorities to engage in self-rule

The toxic sheep collar for control of sheep-killing coyotes: A progress report

The toxic sheep collar is the most selective method known for killing coyotes that prey on domestic sheep. The concept dates back to the early 1900's and has been studied at the Denver Wildlife Research Center (DWRC) since 1974. Field tests with sodium cyanide (NaCN) in 1975 were unsuccessful due to repellent properties of the toxicant and to the apparent reluctance of coyotes to attack tethered lambs wearing bulky collars. Coyotes attacked one or more tethered, collared lambs in 7 of the 19 test pastures. In all, 14 collared lambs were attacked. Eight of the collars were punctured but no dead coyotes were recovered. A smaller collar containing diphacinone was field tested in 1976. The diphacinone-filled collars were readily accepted by coyotes and lethal to them, but the slow action (5-16 days between dosing and death) of diphacinone made it difficult to assess the effectiveness of these collars under field conditions. Target flocks containing 1 to 12 collared lambs plus uncollared ewes were placed in 15 fenced pastures from which the larger ranch flocks had been removed after repeated coyote predation. One or more collared lambs were attacked in 11 of the 15 tests. An unknown number of coyotes were killed, and in most tests the subsequent incidence of predation was lower than that before the test. Captive coyotes continued to kill sheep for 4 or 5 days after they received a lethal dose of diphacinone; therefore a faster-acting toxicant is needed. This research has shown that problem coyotes can be killed with toxic collars, but further studies are needed to determine the feasibility of this approach compared with traditional means of control. In most tests to date the frequency of coyote predation has been too low and too irregular to permit effective use of the collar; target flocks were in the field for an average of 10 days before being attacked. The known disadvantages of the method include the need to sacrifice live lambs, the human hazards associated with the use of toxicants under field conditions, and the costs of managing target flocks and other sheep in the problem areas

Interactions between Domestic and Foreign Investment

We present a model of portfolio allocation by noise traders who form incorrect expectations about the variance of the return distribution of a particular asset. We show that for many types of misperceptions, as long as such noise traders do not affect prices, they earn higher expected returns than do rational investors with similar degrees of risk aversion. Moreover, many such noise traders survive and dominate the market in terms of wealth in the long run, in the sense that the probability that noise traders will eventually have a high share of the economy's wealth is arbitrarily close to one. Noise traders come to dominate the market despite the fact that they take excessive risk that skews the distribution of their long run wealth and despite their excessive consumption. We conclude that the theoretical case against the long run viability of noise traders is by no means as clear cut as is commonly supposed.

Altering an extended phenotype reduces intraspecific male aggression and can maintain diversity in cichlid fish

Reduced male aggression towards different phenotypes generating negative frequency-dependent intrasexual selection has been suggested as a mechanism to facilitate the invasion and maintenance of novel phenotypes in a population. To date, the best empirical evidence for the phenomenon has been provided by laboratory studies on cichlid fish with different colour polymorphisms. Here we experimentally tested the hypothesis in a natural population of Lake Malawi cichlid fish, in which males build sand-castles (bowers) to attract females during seasonal leks. We predicted that if bower shape plays an important role in male aggressive interactions, aggression among conspecific males should decrease when their bower shape is altered. Accordingly, we allocated randomly chosen bowers in a Nyassachromis cf. microcephalus lek into three treatments: control, manipulated to a different shape, and simulated manipulation. We then measured male behaviours and bower shape before and after these treatments. We found that once bower shape was altered, males were involved in significantly fewer aggressive interactions with conspecific males than before manipulation. Mating success was not affected. Our results support the idea that an extended phenotype, such as bower shape, can be important in maintaining polymorphic populations. Specifically, reduced male conspecific aggression towards males with different extended phenotypes (here, bower shapes) may cause negative frequency-dependent selection, allowing the invasion and establishment of a new phenotype (bower builder). This could help our understanding of mechanisms of diversification within populations, and in particular, the overall diversification of bower shapes within Lake Malawi cichlids