Contaminants standards

Contaminant and toxic hazards during manned space flight

Quantum phases of atomic boson-fermion mixtures in optical lattices

The zero-temperature phase diagram of a binary mixture of bosonic and fermionic atoms in an one-dimensional optical lattice is studied in the framework of the Bose-Fermi-Hubbard model. By exact numerical solution of the associated eigenvalue problems, ground state observables and the response to an external phase twist are evaluated. The stiffnesses under phase variations provide measures for the boson superfluid fraction and the fermionic Drude weight. Several distinct quantum phases are identified as function of the strength of the repulsive boson-boson and the boson-fermion interaction. Besides the bosonic Mott-insulator phase, two other insulating phases are found, where both the bosonic superfluid fraction and the fermionic Drude weight vanish simultaneously. One of these double-insulator phases exhibits a crystalline diagonal long-range order, while the other is characterized by spatial separation of the two species.Comment: 4 pages, 3 figures, using REVTEX

Phase Transitions in Hexane Monolayers Physisorbed onto Graphite

We report the results of molecular dynamics (MD) simulations of a complete monolayer of hexane physisorbed onto the basal plane of graphite. At low temperatures the system forms a herringbone solid. With increasing temperature, a solid to nematic liquid crystal transition takes place at $T_1 = 138 \pm 2$K followed by another transition at $T_2 = 176 \pm 3$K into an isotropic fluid. We characterize the different phases by calculating various order parameters, coordinate distributions, energetics, spreading pressure and correlation functions, most of which are in reasonable agreement with available experimental evidence. In addition, we perform simulations where the Lennard-Jones interaction strength, corrugation potential strength and dihedral rigidity are varied in order to better characterize the nature of the two transitions through. We find that both phase transitions are facilitated by a ``footprint reduction'' of the molecules via tilting, and to a lesser degree via creation of gauche defects in the molecules.Comment: 18 pages, eps figures embedded, submitted to Phys. Rev.

Improving science education for sustainable development

In recent issues of noteworthy journals, natural scientists have argued for the improvement of science education [1–4]. Such pleas reflect the growing awareness that high-quality science education is required not only for sustaining a lively scientific community that is able to address global problems like global warming and pandemics, but also to bring about and maintain a high level of scientific literacy in the general population. There is no doubt that effective education can serve as a vehicle for solving global problems. The problem centers on how to achieve more effective education. We believe that science education would greatly benefit from incorporating the lessons of cognitive science and contemporary ethology to provide a framework for explaining human behavior grounded in evolutionary theory. According to such a perspective, humans collectively produce and reproduce their environment through their actions and are therefore capable of acting responsibly for a sustainable future. In order to design education that will effectively contribute to a sustainable future, we argue for a learning framework that is consistent with contemporary ethology and represents human beings as self-determined yet integral parts of their environment. Such an epistemology is more holistic than traditional and often reductionistic frameworks in education and draws on the central paradigm of the life sciences—evolution. Furthermore, this framework approaches collective human activity as the pivotal unit of analysis in which individuals transact with the social and natural world. Drawing on data from an environmental education project, we demonstrate how this epistemology allows us to contribute both to the improvement of education and to a sustainable future of life on earth

Fluctuation spectra in the NASA Lewis bumpy-torus plasma

The electrostatic potential fluctuation spectrum in the NASA Lewis bumpy-torus plasma was studied with capacitive probes in the low pressure (high impedance) mode and in the high pressure (low impedance) mode. Under different operating conditions, the plasma exhibited electrostatic potential fluctuations (1) at a set of discrete frequencies, (2) at a continuum of frequencies, and (3) as incoherent high-frequency turbulence. The frequencies and azimuthal wave numbers were determined from digitally implemented autopower and cross-power spectra. The azimuthal dispersion characteristics of the unstable waves were examined by varying the electrode voltage, the polarity of the voltage, and the neutral background density at a constant magnetic field strength

Improving science education for sustainable development

In recent issues of noteworthy journals, natural scientists have argued for the improvement of science education [1–4]. Such pleas reflect the growing awareness that high-quality science education is required not only for sustaining a lively scientific community that is able to address global problems like global warming and pandemics, but also to bring about and maintain a high level of scientific literacy in the general population. There is no doubt that effective education can serve as a vehicle for solving global problems. The problem centers on how to achieve more effective education. We believe that science education would greatly benefit from incorporating the lessons of cognitive science and contemporary ethology to provide a framework for explaining human behavior grounded in evolutionary theory. According to such a perspective, humans collectively produce and reproduce their environment through their actions and are therefore capable of acting responsibly for a sustainable future. In order to design education that will effectively contribute to a sustainable future, we argue for a learning framework that is consistent with contemporary ethology and represents human beings as self-determined yet integral parts of their environment. Such an epistemology is more holistic than traditional and often reductionistic frameworks in education and draws on the central paradigm of the life sciences—evolution. Furthermore, this framework approaches collective human activity as the pivotal unit of analysis in which individuals transact with the social and natural world. Drawing on data from an environmental education project, we demonstrate how this epistemology allows us to contribute both to the improvement of education and to a sustainable future of life on earth

Magnetic-field induced resistivity minimum with in-plane linear magnetoresistance of the Fermi liquid in SrTiO3-x single crystals

We report novel magnetotransport properties of the low temperature Fermi liquid in SrTiO3-x single crystals. The classical limit dominates the magnetotransport properties for a magnetic field perpendicular to the sample surface and consequently a magnetic-field induced resistivity minimum emerges. While for the field applied in plane and normal to the current, the linear magnetoresistance (MR) starting from small fields (< 0.5 T) appears. The large anisotropy in the transverse MRs reveals the strong surface interlayer scattering due to the large gradient of oxygen vacancy concentration from the surface to the interior of SrTiO3-x single crystals. Moreover, the linear MR in our case was likely due to the inhomogeneity of oxygen vacancies and oxygen vacancy clusters, which could provide experimental evidences for the unusual quantum linear MR proposed by Abrikosov [A. A. Abrikosov, Phys. Rev. B 58, 2788 (1998)].Comment: 5 pages, 4 figure