5,777 research outputs found
Averaging of the electron effective mass in multicomponent transparent conducting oxides
We find that layered materials composed of various oxides of cations with
electronic configuration, O, =In or Sc, =Ga, Zn, Al, Cd
and/or Mg, exhibit isotropic electron effective mass which can be obtained via
averaging over those of the corresponding single-cation oxide constituents.
This effect is due to a hybrid nature of the conduction band formed from the
s-states of {\it all} cations and the oxygen p-states. Moreover, the observed
insensitivity of the electron effective mass to the oxygen coordination and to
the distortions in the cation-oxygen chains suggests that similar behavior can
be expected in technologically important amorphous state. These findings
significantly broaden the range of materials as efficient transparent conductor
hosts.Comment: Figures with higher resolution include
Unconventional approaches to combine optical transparency with electrical conductivity
Combination of electrical conductivity and optical transparency in the same
material -- known to be a prerogative of only a few oxides of post-transition
metals, such as In, Sn, Zn and Cd -- manifests itself in a distinctive band
structure of the transparent conductor host. While the oxides of other elements
with electronic configuration, for example, Mg, Ca, Sc and Al, also
exhibit the desired optical and electronic features, they have not been
considered as candidates for achieving good electrical conductivity because of
the challenges of efficient carrier generation in these wide-bandgap materials.
Here we demonstrate that alternative approaches to the problem not only allow
attaining the transport and optical properties which compete with those in
currently utilized transparent conducting oxides (TCO), but also significantly
broaden the range of materials with a potential of being developed into novel
functional transparent conductors.Comment: Accepted for publicatio
On the microeconomic problems studied by portfolio theory
In the paper we consider economically motivated problems, which are treated with the help of methods of portfolio theory that goes back to the papers by H. Markowitz [1] and J. Tobin [2]. We show that the portfolio theory initially developed for risky securities (stocks) could be applied to other objects. In the present paper we consider several situations where such an application is reasonable and seems to be fruitful. Namely, we consider the problems of constructing the efficient portfolio of banking services and the portfolio of counteragents of a firm. © 2012 American Institute of Physics
Demographic Transformation and the Future of Museums
In 2009 the Center for the Future of Museums commissioned Betty Farrell to produce a report to explore in more detail the demographic trends in American society and their implications for museums. The report identifies, synthesizes, and interprets existing research on demographics, cultural consumer attitudes, museum diversity practices, and related topics. It is meant to help the museum field explore the future of museums in a "majority minority" society. Topics of inquiry include national demographic projections for the next 25 years with a focus on the shifting racial and ethnic composition of the United States; current patterns of museum attendance (and cultural participation more generally) by race, ethnicity, cultural origin and other relevant factors; culturally/ethnically specific attitudes towards museums, including perceptual and behavioral barriers to museum attendance; ways that museums currently reach out to diverse audiences; specific models and best practices; and larger trends in societal attitudes towards racial and other classifications
Work hardening behavior in a steel with multiple TRIP mechanisms
Transformation induced plasticity (TRIP) behavior was studied in steel with
composition Fe-0.07C-2.85Si-15.3Mn-2.4Al-0.017N that exhibited two TRIP
mechanisms. The initial microstructure consisted of both {\epsilon}- and
{\alpha}-martensites with 27% retained austenite. TRIP behavior in the first 5%
strain was predominately austenite transforming to {\epsilon}-martensite (Stage
I), but upon saturation of Stage I, the {\epsilon}-martensite transformed to
{\alpha}-martensite (Stage II). Alloy segregation also affected the TRIP
behavior with alloy rich regions producing TRIP just prior to necking. This
behavior was explained by first principle calculations that revealed aluminum
significantly affected the stacking fault energy in Fe-Mn-Al-C steels by
decreasing the unstable stacking fault energy and promoting easy nucleation of
{\epsilon}-martensite. The addition of aluminum also raised the intrinsic
stacking fault energy and caused the {\epsilon}-martensite to be unstable and
transform to {\alpha}-martensite under further deformation. The two stage TRIP
behavior produced a high strain hardening exponent of 1.4 and led to ultimate
tensile strength of 1165 MPa and elongation to failure of 35%.Comment: submitted to Met. Mater. Trans. A manuscript E-TP-12-953-
Computer simulation of field ion images of nanoporous structure in the irradiated materials
Computer simulation and interpretation of field ion microscopy images of ion irradiated platinum are discussed. Field ion microscopy technique provides direct precise atomic scale investigation of crystal lattice defects of atomically pure surface of material; at the same time it allows to analyze the structural defects in volume by controlled and sequential removal of surface atoms by electric field. Defects identification includes the following steps: at the first stage the type of crystalline structure and spatial orientation of crystallographic directions were determined. Thus, we obtain the data about exact position of all atoms of the given volume, i.e. the model image of an ideal crystal. At the second stage, the ion image was processed used the program to obtain the data about real arrangement of atoms of the investigated sample. At the third stage the program compares these two data sets, with a split-hair accuracy revealing a site of all defects in a material. Results of the quantitative analysis show that shape of nanopores are spherical or cylindrical, diameter on nanopores was varied from 1 to 5 run, their depth was fond to be from 1 to 9 nm. It was observed that nearly 40% of nanopores are concentrated in the subsurface layer 10 nm thick, the concentration of nanopores decreased linearly with the distance from the irradiated surface
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