Are cocaine-seeking “habits” necessary for the development of addiction-like behavior in rats?

Drug self-administration models of addiction typically require animals to make the same response (e.g., a lever-press or nose-poke) over and over to procure and take drugs. By their design, such procedures often produce behavior controlled by stimulus-response (S-R) habits. This has supported the notion of addiction as a “drug habit”, and has led to considerable advances in our understanding of the neurobiological basis of such behavior. However, for addicts to procure drugs, like cocaine, often requires considerable ingenuity and flexibility in seeking behavior, which, by definition, precludes the development of habits. To better model drug-seeking behavior in addicts we first developed a novel cocaine self-administration procedure (the Puzzle Self-Administration Procedure; PSAP) that required rats to solve a new puzzle every day to gain access to cocaine, which they then self-administered on an Intermittent Access (IntA) schedule. Such daily problem-solving precluded the development of S-R seeking habits. We then asked whether prolonged PSAP/IntA experience would nevertheless produce ‘symptoms of addiction’. It did, including escalation of intake, sensitized motivation for drug, continued drug use in the face of adverse consequences and very robust cue-induced reinstatement of drug-seeking, especially in a subset of ‘addiction-prone’ rats. Furthermore, drug-seeking behavior continued to require dopamine neurotransmission in the core of the nucleus accumbens (but not the dorsolateral striatum). We conclude that the development of S-R seeking habits is not necessary for the development of cocaine addiction-like behavior in rats

The strong-CP question in SU(3)_c X SU(3)_L X U(1)_N models

We analyze two recent models based on the gauge group SU(3)$_c\times$SU(3)$_L\times$U(1)$_N$ where each generation is not anomaly-free, but anomaly cancels when three generations are taken into account. We show that the most general Yukawa couplings of these models admit of a Peccei-Quinn symmetry. This symmetry can be extended to the entire Lagrangian by using extra fields in a very elegant way so that the resulting axion can be made invisible.Comment: Latex, 8 pages, no figure

Symmetry breaking and phase coexistence in a driven diffusive two-channel system

We consider classical hard-core particles moving on two parallel chains in the same direction. An interaction between the channels is included via the hopping rates. For a ring, the stationary state has a product form. For the case of coupling to two reservoirs, it is investigated analytically and numerically. In addition to the known one-channel phases, two new regions are found, in particular the one, where the total density is fixed, but the filling of the individual chains changes back and forth, with a preference for strongly different densities. The corresponding probability distribution is determined and shown to have an universal form. The phase diagram and general aspects of the problem are discussed.Comment: 12 pages, 10 figures, to appear in Phys.Rev.

Polarized light emission from individual incandescent carbon nanotubes

We fabricate nanoscale lamps which have a filament consisting of a single multiwalled carbon nanotube. After determining the nanotube geometry with a transmission electron microscope, we use Joule heating to bring the filament to incandescence, with peak temperatures in excess of 2000 K. We image the thermal light in both polarizations simultaneously as a function of wavelength and input electrical power. The observed degree of polarization is typically of the order of 75%, a magnitude predicted by a Mie model of the filament that assigns graphene's optical conductance $\pi e^2/2 h$ to each nanotube wall.Comment: 5 pages, 4 figure

Mutual assessment in the social programmer ecosystem: an empirical investigation of developer profile aggregators

The multitude of social media channels that programmers can use to participate in software development has given rise to online developer profiles that aggregate activity across many services. Studying members of such developer profile aggregators, we found an ecosystem that revolves around the social programmer. Developers are assessing each other to evaluate whether other developers are interesting, worth following, or worth collaborating with. They are self-conscious about being assessed, and thus manage their public images. They value passion for software development, new technologies, and learning. Some recruiters participate in the ecosystem and use it to find candidates for hiring; other recruiters struggle with the interpretation of signals and issues of trust. This mutual assessment is changing how software engineers collaborate and how they advance their skills.Leif Singer, Fernando Figueira Filho, Brendan Cleary, Christoph Treude, Margaret-Anne Storey, Kurt Schneide

Are animal models of addiction useful?

Background: Preclinical research involving non-human animals has made important contributions to our understanding of risk-factors for addiction, neuroadaptations that follow chronic drug exposure, and to the development of some efficacious pharmacotherapies for addiction. Despite these contributions, we argue that animal models of addiction have impeded progress in our understanding of addiction and its treatment in humans. Argument: First of all, the majority of pharmacological treatments that were initially developed using animal models have failed to prove effective for the treatment of addiction in humans, resulting in a huge waste of resources. Secondly, we demonstrate that prevailing animal models that portray addiction as a disorder of compulsion and habit cannot be reconciled with observations that psychoactive drug use in humans is a goal-directed operant behaviour that remains under the control of its consequences, even in people who are addicted. Thirdly, addiction may be a uniquely human phenomenon that is dependent on language, which necessarily limits the validity of animal models. Finally, we argue that addicted brains must be understood as one component of broader networks of symptoms and environmental and social factors that are impossible to model in laboratory animals. Conclusions: A case can be made that animal models of addiction have not served us well in understanding and treating addiction in humans. It is important to reconsider some widely-held beliefs about the nature of addictive behaviour in humans that have arisen from the zeal to translate observations of laboratory animals

The Higgs Sector of the Minimal 3 3 1 Model Revisited

The mass spectrum and the eigenstates of the Higgs sector of the minimal 3 3 1 model are revisited in detail. There are discrepancies between our results and previous results by another author.Comment: 20 pages, latex, two figures. One note and one reference are adde