Hsuan-Chih Lin

Topological insulators are novel materials that manifest spin-polarized Dirac states on their surfaces or at interfaces made with conventional matter. We have measured the electron kinetics of bulk doped TI Bi$_2$Se$_3$ with angle resolved photoemission spectroscopy while depositing cathodic and anodic adatoms on the TI surfaces to add charge carriers of the opposite sign from bulk dopants. These P-N overlayer interfaces create Dirac point transport regimes and larger interface potentials than previous N-N type surface deposition studies, revealing unconventional Rashba-like and surface-bulk electron interactions, and an unusual characteristic distribution of spectral weight near the Dirac point in TI Dirac point interfaces. The electronic structures of P-N doped topological interfaces observed in these experiments are an important step towards the understanding of solid interfaces with topological materials.

© 2015 Taylor & Francis. This analysis compares the climate impacts over North America during winter associated with various El Niño-Southern Oscillation indices, including the Niño 3.4 index, the leading tropical Pacific outgoing longwave radiation and sea surface temperature covariability, and the eastern Pacific and central Pacific types of ENSO identified from both partial-regression-empirical orthogonal function and regression-EOF approaches. The traditional Niño 3.4 SST index is found to be optimal for monitoring the tropical Pacific OLR-SST covariability and for the tropical SST impact on North America. The circulation anomalies associated with the Niño 3.4 index project on both the Pacific/North American and Tropical/Northern Hemisphere patterns. The ENSO associated with the PNA tends to come from both the EP and CP ENSOs, whereas that associated with the TNH comes more from the EP ENSO. The variability of ENSO significantly affects North American temperature and precipitation, as well as temperature and precipitation extremes. For either the EP or CP types of ENSO, qualitatively similar patterns of climate and climate extreme anomalies are apparent associated with the indices identified by the two EOF approaches, with differences mainly in the anomalous amplitude. The anomalous patterns are generally field significant over North America for the EP ENSO but not field significant for the CP ENSO. The circulation anomalies associated with ENSO are reinforced and maintained by synoptic vorticity fluxes in the upper troposphere. The anomalous surface temperature is mainly determined by the anomalies in surface radiative heating in the face of upward surface longwave radiative damping. The precipitation anomalies are supported by the vertically integrated moisture transport. The differences in atmospheric circulation, surface temperature, and precipitation among the various ENSO indices, including the intensity and spatial structure of the fields, can be attributed to the corresponding differences in synoptic eddy vorticity forcing, surface radiative heating, and vertically integrated moisture transport.

Is it possible that there are extended simples—material objects extended in space or spacetime that have no proper parts? The most commonly cited argument for this possibility is based on a version of the Humean principle: namely (and with some qualifications), any pattern of instantiation of a fundamental relation is possible. In this paper, we make the Humean argument fully explicit, and criticise it from three aspects—the Disjunction problem, the Pluralist problem, and the Accidentality problem. First, the original argument only shows a disjunctive thesis: either extended simples are possible, or unextended complexes are possible. In order to reach the desired conclusion, some additional premise is needed. Yet, even though we agree that the Disjunction problem can be met, we argue that the Humean argument fails to establish the possibility of extended simples, for two reasons: the first comes from compositional pluralism, and the second is about the definition of accidental properties. We contend that the latter two problems put the proponents of the Humean argument in serious difficulty. Thus, metaphysicians who hold that there are extended simples should find better arguments for this view.

Consider the following argument, where ‘\’ abbreviates ‘the proposition that p’: It is possible that Socrates does not exist.Necessarily, if Socrates does not exist, then \ is true.Necessarily, if \ is true, then \ exists.Necessarily, if \ exists, then Socrates exists.Therefore, it is possible that Socrates exists and does not exist. How can one respond to this argument? Fine thinks that the argument involves an equivocation concerning the notion of truth for propositions: if we stand inside a possible world to evaluate the truth, in this ‘inner’ sense holds but fails; but if we stand outside, in this ‘outer’ sense holds but fails. In this paper we argue that such an equivocation response is obscure, ad hoc, and unmotivated.