50 words for snow

Scientists and philosophers routinely talk about phenomena, and the ways in which they relate to explanation, theory and practice in science. However, there are very few definitions of the term, which is often used synonymously with "data'', "model'' and in older literature, "hypothesis''. In this paper I will attempt to clarify how phenomena are recognized, categorized and the role they play in scientific epistemology. I conclude that phenomena are not necessarily theory-based commitments, but that they are what explanations are called to account for, which are not presently explained

Accurate Ab-initio Predictions of III-V Direct-Indirect Band Gap Crossovers

We report the compositional dependence of the electronic band structure for a range of III-V alloys. Density functional theory with the PBE functional is insufficient to mimic the electronic gap energies at different symmetry points of the Brillouin zone. The HSE hybrid functional with screened exchange accurately reproduces the experimental band gaps and, more importantly, the alloy concentration of the direct-indirect gap crossovers for the III-V alloys studied here: AlGaAs, InAlAs, AlInP, InGaP, and GaAsP.Comment: 3 pages, 2 figure

Negative dynamic conductance from photon-assisted tunneling in superconducting junctions

We show that a superconductor-insulator-superconductor (SIS) junction may exhibit regions of negative dynamic conductance if it is irradiated by a time-varying signal source which deviates from the conventionally treated constant ac voltage limit. This phenomenon reflects the strong dependence of the junction absorption cross section upon dc bias voltage. Analytic estimates for the magnitude of the negative conductance and its impact upon the frequency down conversion process are obtained in the constant ac current limit

Irrigation and drainage in the new millennium

Presented at the 2000 USCID international conference, Challenges facing irrigation and drainage in the new millennium on June 20-24 in Fort Collins, Colorado.Includes bibliographical references.One of the more important business practices over the years in larger multipurpose water districts has been the delivery of untreated water for lawns and gardens. This is generally in addition to traditional irrigation water deliveries. With rapid urbanization occurring in many rural agricultural counties, even smaller irrigation districts and canal companies are beginning to provide such service to small acreage subdivisions and a variety of other non-agricultural water users (golf courses, parks, etc.). It is a business innovation stemming from urbanization in traditional and, for the most part, prime irrigated lands throughout the West. This paper presents two case studies of untreated water delivery for lawns and gardens by such enterprises. It discusses some of the issues surrounding the development of this practice, the costs and benefits of engaging in this kind of water service, and what opportunities and constraints lay ahead for this business practice in the future

Magnetic states and optical properties of single-layer carbon-doped hexagonal boron nitride

We show that carbon-doped hexagonal boron nitride (h-BN) has extraordinary properties with many possible applications. We demonstrate that the substitution-induced impurity states, associated with carbon atoms, and their interactions dictate the electronic structure and properties of C-doped h-BN. Furthermore, we show that stacking of localized impurity states in small C clusters embedded in h-BN forms a set of discrete energy levels in the wide gap of h-BN. The electronic structures of these C clusters have a plethora of applications in optics, magneto-optics, and opto-electronics