356 research outputs found
Art & Technology [6th-8th grade]
This unit was designed to meet several needs in the art classroom: a.) to expose students to digital art and design; b.) to reveal instances where technology has altered the path of artists, c.) to integrate technology standards in the art curriculum. The central understandings for this unit are: a.) Art evolves as technology develops; and b.) Technology has provided a venue for the widespread production and mass viewing of art. Essential questions are: a.) In what ways has technology changed art? b.) Has art advanced/improved or declined/deteriorated with the advent of new technology? c.) Is the value of an artwork diminished when it is digitally manipulated? The performance assessment for this unit asks students to create a Portraiture Portfolio, collectively demonstrating how technology has evolved art. The first portrait is drawn on paper with pencil/charcoal; the second portrait is taken on black and white film with a manual camera; the third portrait is taken on a digital camera and then digitally manipulated through software on a computer. The final component of the project is to scan/upload the images to an internet class blog/gallery and comment/critique on the work of classmates. At the conclusion of the unit, students will be prepared to continue with the larger theme of Art & Technology or Digital Media
Synthesis, crystal structure and chemical stability of the superconductor FeSe_{1-x}
We report on a comparative study of the crystal structure and the magnetic
properties of FeSe1-x (x= 0.00 - 0.15) superconducting samples by neutron
powder diffraction and magnetization measurements. The samples were synthesized
by two different methods: a 'low-temperature' one using powders as a starting
material at T =700 C and a "high-temperature' method using solid pieces of Fe
and Se at T= 1070 C. The effect of a starting (nominal) stoichiometry on the
phase purity of the obtained samples, the superconducting transition
temperature Tc, as well as the chemical instability of FeSe1-x at ambient
conditions were investigated. It was found that in the Fe-Se system a stable
phase exhibiting superconductivity at Tc~8K exists in a narrow range of
selenium concentration (FeSe0.974(2)).Comment: 7 pages, 7 figures, 1 tabl
Negative Oxygen Isotope Effect on the Static Spin Stripe Order in La_(2-x)Ba_xCuO_4 (x = 1/8)
Large negative oxygen-isotope (16O/18O) effects (OIE's) on the static
spin-stripe ordering temperature T_so and the magnetic volume fraction V_m were
observed in La_(2-x)Ba_xCuO_4 (x = 1/8) by means of muon spin rotation
experiments. The corresponding OIE exponents were found to be alpha_(T_so) =
-0.57(6) and alpha_(V_m) = -0.71(9), which are sign reversed to alpha_(T_c) =
0.46(6) measured for the superconducting transition temperature T_c. This
indicates that the electron-lattice interaction is involved in the stripe
formation and plays an important role in the competition between bulk
superconductivity and static stripe order in the cuprates.Comment: 5 pages, 4 figure
Intrinsic and structural isotope effects in Fe-based superconductors
The currently available results of the isotope effect on the superconducting
transition temperature T_c in Fe-based high-temperature superconductors (HTS)
are highly controversial. The values of the Fe isotope effect (Fe-IE) exponent
\alpha_Fe for various families of Fe-based HTS were found to be as well
positive, as negative, or even be exceedingly larger than the BCS value
\alpha_BCS=0.5. Here we demonstrate that the Fe isotope substitution causes
small structural modifications which, in turn, affect T_c. Upon correcting the
isotope effect exponent for these structural effects, an almost unique value of
\alpha~0.35-0.4 is observed for at least three different families of Fe-based
HTS.Comment: 4 pages, 2 figure
Evidence for strong lattice effects as revealed from huge unconventional oxygen isotope effects on the pseudogap temperature in LaSrCuO
The oxygen isotope (O/O) effect (OIE) on the pseudogap
(charge-stripe ordering) temperature is investigated for the cuprate
superconductor LaSrCuO as a function of doping by means
of x-ray absorption near edge structure (XANES) studies. A strong dependent
and sign reversed OIE on is observed. The OIE exponent
systematically decreases from for to for ,
corresponding to increasing and decreasing superconducting
transition temperature . Both and
exhibit a linear doping dependence with different
slopes and critical end points (where and
fall to zero) at and
, indicating a large positive OIE of
with an exponent of . The remarkably large and
strongly doping dependent OIE on signals a substantial involvement
of the lattice in the formation of the pseudogap, consistent with a polaronic
approach to cuprate superconductivity and the vibronic character of its ground
state
Evolution of two-gap behavior of the superconductor FeSe_1-x
The superfluid density, \rho_s, of the iron chalcogenide superconductor,
FeSe_1-x, was studied as a function of pressure by means of muon-spin rotation.
The zero-temperature value of \rho_s increases with increasing transition
temperature T_c (increasing pressure) following the tendency observed for
various Fe-based and cuprate superconductors. The analysis of \rho_s(T) within
the two-gap scheme reveals that the effect on both, T_c and \rho_s(0), is
entirely determined by the band(s) where the large superconducting gap
develops, while the band(s) with the small gap become practically unaffected.Comment: 5 pages, 3 figure
Pressure Induced Static Magnetic Order in Superconducting FeSe_1-x
We report on a detailed investigation of the electronic phase diagram of
FeSe_1-x under pressures up to 1.4GPa by means of AC magnetization and
muon-spin rotation. At a pressure \simeq0.8GPa the non-magnetic and
superconducting FeSe_1-x enters a region where long range static magnetic order
is realized above T_c and bulk superconductivity coexists and competes on short
length scales with the magnetic order below T_c. For even higher pressures an
enhancement of both the magnetic and the superconducting transition
temperatures as well as of the corresponding order parameters is observed.
These exceptional properties make FeSe1-x to be one of the most interesting
superconducting systems investigated extensively at present.Comment: 5 pages, 3 figure
Coherency of the superconducting state: the muon spin rotation and ARPES studies of (BiPb)_2(SrLa)_2CuO_{6+\delta}
The superfluid density \rho_s in underdoped (T_c\simeq23K), optimally doped
(T_c\simeq35K) and overdoped (T_c\simeq29K) single crystalline
(BiPb)_2(SrLa)_2CuO_{6+\delta} samples was studied by means of muon-spin
rotation (\muSR). By combining the \muSR data with the results of ARPES
measurements on similar samples [Nature 457, 296 (2009)] good self-consistent
agreement is obtained between two techniques concerning the temperature and the
doping evolution of \rho_s.Comment: 4 pages, 3 figures
Static and dynamic Jahn-Teller effect in the alkali metal fulleride salts A4C60 (A = K, Rb, Cs)
We report the temperature dependent mid- and near-infrared spectra of K4C60,
Rb4C60 and Cs4C60. The splitting of the vibrational and electronic transitions
indicates a molecular symmetry change of C604- which brings the fulleride anion
from D2h to either a D3d or a D5d distortion. In contrast to Cs4C60, low
temperature neutron diffraction measurements did not reveal a structural phase
transition in either K4C60 and Rb4C60. This proves that the molecular
transition is driven by the molecular Jahn-Teller effect, which overrides the
distorting potential field of the surrounding cations at high temperature. In
K4C60 and Rb4C60 we suggest a transition from a static to a dynamic Jahn-Teller
state without changing the average structure. We studied the librations of
these two fullerides by temperature dependent inelastic neutron scattering and
conclude that both pseudorotation and jump reorientation are present in the
dynamic Jahn-Teller state.Comment: 13 pages, 10 figures, to be published in Phys. Rev.
Tuning the superconducting and magnetic properties in Fe_ySe_0.25Te_0.75 by varying the Fe-content
The superconducting and magnetic properties of FeSeTe
single crystals () were studied by means of x-ray
diffraction, SQUID magnetometry, muon spin rotation, and elastic neutron
diffraction. The samples with exhibit coexistence of bulk
superconductivity and incommensurate magnetism. The magnetic order remains
incommensurate for , but with increasing Fe content superconductivity
is suppressed and the magnetic correlation length increases. The results show
that the superconducting and the magnetic properties of the
FeSeTe can be tuned not only by varying the Se/Te ratio but
also by changing the Fe content
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