Major research universities are grappling with their response to the deluge of scientific data in its big data and long tail data forms. The latter consist of many diverse and heterogeneous sets, the data are collected via diverse and specialized methods, and are stored in a variety of formats and places. University libraries and their institutional repositories have traditionally been able to handle scientific output. But long-tail scientific data introduce substantial challenges to a traditional document-based repository through its vast heterogeneity, size, and its demands for meaningful discovery and in the case of large data sets, place-based use.
In this presentation we will provide a brief overview of the NSF-funded project "Sustainable Environment - Actionable Data" (SEAD), which addresses the challenges of long-tail scientific data with the focus on sustainability science. We will provide an overview of this project and of its discovery and preservation component, called SEAD Virtual Archive. This component is being developed by the Data to Insight Center team at Indiana University in collaboration with IU and UIUC libraries. We will describe main features and our ongoing work on SEAD Virtual Archive and discuss the value and importance of partnerships between data research centers...
The first mode of access by the community of digital humanities and informatics researchers and educators to the copyrighted content of the HathiTrust digital repository will be to extracted statistical and aggregated information about the copyrighted texts. But can the HathiTrust Research Center support scientific research that allows a researcher to carry out their own analysis and extract their own information?
This question is the focus of a 3-year, $606,000 grant from the Alfred P. Sloan Foundation (Plale, Prakash 2011-2014), which has resulted in a novel experimental framework that permits analytical investigation of a corpus but prohibits data from leaving the capsule. The HTRC Data Capsule is both a system architecture and set of policies that enable computational investigation over the protected content of the HT digital repository that is carried out and controlled directly by a researcher. It leverages the foundational security principles of the Data Capsules of A. Prakash of University of Michigan, which allows privileged access to sensitive data while also restricting the channels through which that data can be released.
Ongoing work extends the HTRC Data Capsule to give researchers more compute power at their fingertips. The new thrust...
Neste trabalho implementamos experimentos para a medida da corrente de tunelamento em amostras de Dupla Barreira de GaAs/AlxGa1-xAs e de GaAs com dopagem planar de Si (d -doping).
Para isto preparamos dois sistemas experimentais: a) "Circuito Ponte de Wheatstone" e b) sistema "Fonte de Corrente e Voltímetro".
O primeiro sistema, "Circuito Ponte de Wheatstone", permite-nos medir diretamente, além da curva característica I vs. V, a primeira e segunda derivada. Sob algumas condições particulares, é também possível obter a curva C vs. V. Entretanto, este sistema está limitado a corrente máxima de 1OmA .
O sistema "Fonte de Corrente e Voltímetro " permite-nos medir apenas a curva I vs. V, mas com correntes de até IA e com resolução melhor que de uma parte em 103 , o que nos possibilita obter a primeira e a segunda derivada numericamente.
Para a análise das estruturas na corrente de tunelamento apresentamos os modelos teóricos utilizados para o estudo de tunelamento de elétrons e de buracos em amostras de dupla barreira. Estes são calculados na aproximação da função envelope e no método da matriz de transferência (tunelamento de elétrons), e mais o Hamiltoniano da massa efetiva de Luttinger e Kohn (tunelamento de buracos). Baseado nestes modelos determinamos: i) as posições dos picos na curva I vs. V através do cálculo da corrente de tunelamento (no caso de elétrons) e ii) as curvas das Posições dos Picos da Probabilidade de Transmissão de buracos em função da Tensão Aplicada...
Recent low-temperature scanning-tunneling microscopy experiments [T. Kumagai
et al., Phys. Rev. B 79, 035423 (2009)] observed the vibrationally induced flip
motion of a hydroxyl dimer (OD)2 on Cu(110). We propose a model to describe
two-level fluctuations and current-voltage characteristics of nanoscale systems
which undergo vibrationally induced switching. The parameters of the model are
based on comprehensive density-functional calculations of the system's
vibrational properties. For the dimer (OD)2 the calculated population of the
high and low conductance states, the I-V, dI/dV, and d2I/dV2 curves are in good
agreement with the experimental results and underlines the different roles
played by the free and shared OD stretch modes of the dimer.; Comment: 5 pages, 4 figures
Formation of electron pairs is essential to superconductivity. For
conventional superconductors, tunnelling spectroscopy has established that
pairing is mediated by bosonic modes (phonons); a peak in the second derivative
of tunnel current d2I/dV2 corresponds to each phonon mode . For
high-transition-temperature (high-Tc) superconductivity, however, no boson
mediating electron pairing has been identified. One explanation could be that
electron pair formation and related electron-boson interactions are
heterogeneous at the atomic scale and therefore challenging to characterize.
However, with the latest advances in d2I/dV2 spectroscopy using scanning
tunnelling microscopy, it has become possible to study bosonic modes directly
at the atomic scale . Here we report d2I/dV2 imaging studies of the high-Tc
superconductor Bi2Sr2CaCu2O8+d. We find intense disorder of electron-boson
interaction energies at the nanometre scale, along with the expected
modulations in d2I/dV2 (refs 9,10). Changing the density of holes has minimal
effects on both the average mode energies and the modulations, indicating that
the bosonic modes are unrelated to electronic or magnetic structure. Instead,
the modes appear to be local lattice vibrations, as substitution of 18O for 16O
throughout the material reduces the average mode energy by approximately 6 per
cent - the expected effect of this isotope substitution on lattice vibration
We comment on the recent paper "Reconciling results of tunnelling experiments
on (Ga,Mn)As" arXiv:1102.3267v2 by Dietl and Sztenkiel. They claimed that the
oscillations observed in the d2I/dV2-V characteristics in our studies on the
resonant tunneling spectroscopy on GaMnAs, are not attributed to the resonant
levels in the GaMnAs layer but to the two-dimensional interfacial subbands in
the GaAs:Be layer. Here, we show that this interpretation is not able to
explain our experimental results and our conclusions remain unchanged.; Comment: 5 pages, 2 figures
In this paper, we analytically investigate the electronic structure of Bernal
stacking (AB stacking) graphene evolving from monolayer (a zero-gap
semiconductor with a linear Dirac-like spectrum around the Fermi energy) to
multi-layer (semi-metal bulk graphite). We firstly derive a real space
analytical expression for the free Green's function (propagator) of multi-layer
graphene based on the effective-mass approximation. The simulation results
exhibit highly spatial anisotropy with three-fold rotational symmetry. By
combining with the STM measurement of d2I/dV2 (the second derivative of
current), we also provide a clear high-throughput and non-destructive method to
identify graphene layers. Such a method is lacking in the emerging graphene
research.; Comment: 10 pages, 4 figures
We investigate numerically the signatures of collective modes in the
tunneling spectra of superconductors. The larger strength of the signatures
observed in the high-Tc superconductors, as compared to classical low-Tc
materials, is explained by the low dimensionality of these layered compounds.
We also show that the strong-coupling structures are dips (zeros in the d2I/dV2
spectrum) in d-wave superconductors, rather than the steps (peaks in d2I/dV2)
observed in classical s-wave superconductors. Finally we question the
usefulness of effective density of states models for the analysis of tunneling
data in d-wave superconductors.; Comment: 8 pages, 6 figures
Elastic and inelastic tunneling processes are investigated in GaAs–AlAs–GaAs double heterojunctions grown in the  direction by metal–organic chemical vapor deposition (MOCVD). The AlAs quantum barriers in the heterostructures studied are doped p-type with Mg. Theoretical calculations of tunneling currents are performed and compared with experimental I–V data. It is found that for structures with thin AlAs barriers, the dominant current transport mechanism at low temperatures is tunneling through the AlAs band gap at both the Gamma and X points. This is consistent with inelastic processes observable in first (dI/dV) and second (d2I/dV2) derivative spectra obtained with modulation techniques. A simple model, developed for calculating impurity-assisted tunneling currents, shows that the role of barrier impurities becomes more important as the barrier is grown thicker. Implications of some of these results for resonant tunneling heterostructures consisting of two AlAs quantum barriers separated by a GaAs quantum well are discussed. Experimental second derivative spectra showing reproducible features are also presented for these double barrier structures.
We investigate the perturbation in the tunneling current caused by nonadiabatic mechanical motion in a mesoscopic tunnel junction. A theory introduced by Caroli et al. is used to evaluate second-order self-energy corrections for this nonequilibrium situation lacking translational invariance. Inelastic signatures of the mechanical degrees of freedom are found in the current-voltage I(V) characteristics. These give rise to sharp features in the derivative spectrum, d2I/dV2.