EXAFS Analysis of Size-Constrained Semiconducting Materials

Semiconducting materials such as CdSe, CdS, PbS and GaP are included in crystalline zeolite Y and mordenite and structurally flexible ethylene-methacrylic acid copolymer solid matrices. EXAFS analysis reveals formation of species with dimensions of molecular size up to ca. 13 A in the crystalline hosts, while the polymer matrices allow agglomeration of larger semiconducting particles. Zeolite anchored structures are distinctively different to small particles with bulk crystal structure as usually found in colloidal systems

University student perceptions of the current and future role of non-carbon emitting energy sources in the world

This article documents university student perceptions of the role and viability of non-carbon emitting energy sources in the short term (1 to 3 years) and medium term (10 to 30 years) for Earth. Consequently, the perceptions of 7,980 students at the University of Idaho (Moscow, ID, USA) about the future of geothermal energy (G), hydropower energy (H), nuclear power (NP), ocean thermal energy conversion (OTEC), solar energy (S) and wind energy (W) were measured between 1993 and 2016. All students were enrolled in the introductory environmental science class. Two survey instruments were used to gather this data. The first survey instrument evaluated six energy sources in 1994, 1998, 2002, 2006, 2010 and 2014. The second instrument focused on questions about nuclear energy. In the first survey a significant portion of the students considered solar, wind and nuclear power to be viable nonemitting carbon energy sources in the medium-term (10 to 30 years) future. Also, students taking the survey in later years (2006, 2010, 2014) were much more likely to consider non-carbon energy sources viable in the near and mid-term than students taking the survey in 1994, 1998 and 2002. In general, 46.7% of students considered nuclear power a serious problem at the beginning of the course; however, at the end of the term less than 36% of students still held their initial negative opinion. In addition, a significant majority of the students changed from indicating that fossil fuels were preferable to nuclear energy, an opinion they held at the beginning of the course, to favoring or at least saying that nuclear power was no worse than fossil fuels at the conclusion of the term. The significant findings of this study were: (1) students considered both solar and wind energy viable alternatives that have the potential to be significant on a world-wide basis within 30 years; (2) students saw only a limited expansion of hydropower and geothermal energy in the next 30 years; and (3) once students were educated in an unbiased way – including both the pros and cons of using nuclear energy – they were more receptive to view the nuclear power option favorably

Fourier's Law from Schroedinger Dynamics

We consider a class of one-dimensional chains of weakly coupled many level systems. We present a theory which predicts energy diffusion within these chains for almost all initial states, if some concrete conditions on their Hamiltonians are met. By numerically solving the time dependent Schroedinger equation, we verify this prediction. Close to equilibrium we analyze this behavior in terms of heat conduction and compute the respective coefficient directly from the theory.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Let

Cavity-induced temperature control of a two-level system

We consider a two-level atom interacting with a single mode of the electromagnetic field in a cavity within the Jaynes-Cummings model. Initially, the atom is thermal while the cavity is in a coherent state. The atom interacts with the cavity field for a fixed time. After removing the atom from the cavity and applying a laser pulse the atom will be in a thermal state again. Depending on the interaction time with the cavity field the final temperature can be varied over a large range. We discuss how this method can be used to cool the internal degrees of freedom of atoms and create heat baths suitable for studying thermodynamics at the nanoscale

Local Versus Global Thermal States: Correlations and the Existence of Local Temperatures

We consider a quantum system consisting of a regular chain of elementary subsystems with nearest neighbor interactions and assume that the total system is in a canonical state with temperature $T$. We analyze under what condition the state factors into a product of canonical density matrices with respect to groups of $n$ subsystems each, and when these groups have the same temperature $T$. While in classical mechanics the validity of this procedure only depends on the size of the groups $n$, in quantum mechanics the minimum group size $n_{min}$ also depends on the temperature $T$! As examples, we apply our analysis to a harmonic chain and different types of Ising spin chains. We discuss various features that show up due to the characteristics of the models considered. For the harmonic chain, which successfully describes thermal properties of insulating solids, our approach gives a first quantitative estimate of the minimal length scale on which temperature can exist: This length scale is found to be constant for temperatures above the Debye temperature and proportional to $T^{-3}$ below.Comment: 12 pages, 5 figures, discussion of results extended, accepted for publication in Phys. Rev.

Existence of temperature on the nanoscale

We consider a regular chain of quantum particles with nearest neighbour interactions in a canonical state with temperature $T$. We analyse the conditions under which the state factors into a product of canonical density matrices with respect to groups of $n$ particles each and under which these groups have the same temperature $T$. In quantum mechanics the minimum group size $n_{min}$ depends on the temperature $T$, contrary to the classical case. We apply our analysis to a harmonic chain and find that $n_{min} = const.$ for temperatures above the Debye temperature and $n_{min} \propto T^{-3}$ below.Comment: Version that appeared in PR