126 research outputs found
Variational quantum Monte Carlo calculations for solid surfaces
Quantum Monte Carlo methods have proven to predict atomic and bulk properties
of light and non-light elements with high accuracy. Here we report on the first
variational quantum Monte Carlo (VMC) calculations for solid surfaces. Taking
the boundary condition for the simulation from a finite layer geometry, the
Hamiltonian, including a nonlocal pseudopotential, is cast in a layer resolved
form and evaluated with a two-dimensional Ewald summation technique. The exact
cancellation of all Jellium contributions to the Hamiltonian is ensured. The
many-body trial wave function consists of a Slater determinant with
parameterized localized orbitals and a Jastrow factor with a common two-body
term plus a new confinement term representing further variational freedom to
take into account the existence of the surface. We present results for the
ideal (110) surface of Galliumarsenide for different system sizes. With the
optimized trial wave function, we determine some properties related to a solid
surface to illustrate that VMC techniques provide standard results under full
inclusion of many-body effects at solid surfaces.Comment: 9 pages with 2 figures (eps) included, Latex 2.09, uses REVTEX style,
submitted to Phys. Rev.
ALTERNATIVE METHODS OF DESALINATION FOR SUB-SAHARAN AFRICA: A REVIEW OF PREFILTRATION AND MICROBIAL DESALINATION CELL TECHNOLOGY
Gemstone Team NOSALTOur research project has addressed the global need for greater accessibility to
potable drinking water, specifically within the regions of sub-Saharan Africa. Initially,
we planned to design a unique desalination system that was composed of a pre-filtration
unit, a microbial desalination cell (MDC) and a post-desalination treatment unit. When
in-person lab work was no longer feasible due to COVID-19 guidelines, we refocused our
project to review the construction, efficiency, and cost effectiveness of the different
designs of potential prefiltration units and MDC configurations. Our review of potential
prefiltration systems included both chemical and physical separation methods, and the
review of the MDC included the air cathode, biocathode and stacked configurations.
While researching the technical details of the prefiltration and MDC systems, we also
considered the cultural and societal impacts of introducing a technology such as the MDC
into our project region. Our project started as an analysis of an emerging technology, but
as the team has grown, the project has transformed into a comprehensive review of the
emerging microbial desalination technology and the societal impacts of implementing it
into some of the water scarce regions of coastal sub-Saharan Africa
Properties of Saturn Kilometric Radiation measured within its source region
On 17 October 2008, the Cassini spacecraft crossed the southern sources of
Saturn kilometric radiation (SKR), while flying along high-latitude nightside
magnetic field lines. In situ measurements allowed us to characterize for the
first time the source region of an extra-terrestrial auroral radio emission.
Using radio, magnetic field and particle observations, we show that SKR sources
are surrounded by a hot tenuous plasma, in a region of upward field-aligned
currents. Magnetic field lines supporting radio sources map a continuous,
high-latitude and spiral-shaped auroral oval observed on the dawnside,
consistent with enhanced auroral activity. Investigating the Cyclotron Maser
Instability (CMI) as a mechanism responsible for SKR generation, we find that
observed cutoff frequencies are consistent with radio waves amplified
perpendicular to the magnetic field by hot (6 to 9 keV) resonant electrons,
measured locally
MedShapeNet -- A Large-Scale Dataset of 3D Medical Shapes for Computer Vision
Prior to the deep learning era, shape was commonly used to describe the
objects. Nowadays, state-of-the-art (SOTA) algorithms in medical imaging are
predominantly diverging from computer vision, where voxel grids, meshes, point
clouds, and implicit surface models are used. This is seen from numerous
shape-related publications in premier vision conferences as well as the growing
popularity of ShapeNet (about 51,300 models) and Princeton ModelNet (127,915
models). For the medical domain, we present a large collection of anatomical
shapes (e.g., bones, organs, vessels) and 3D models of surgical instrument,
called MedShapeNet, created to facilitate the translation of data-driven vision
algorithms to medical applications and to adapt SOTA vision algorithms to
medical problems. As a unique feature, we directly model the majority of shapes
on the imaging data of real patients. As of today, MedShapeNet includes 23
dataset with more than 100,000 shapes that are paired with annotations (ground
truth). Our data is freely accessible via a web interface and a Python
application programming interface (API) and can be used for discriminative,
reconstructive, and variational benchmarks as well as various applications in
virtual, augmented, or mixed reality, and 3D printing. Exemplary, we present
use cases in the fields of classification of brain tumors, facial and skull
reconstructions, multi-class anatomy completion, education, and 3D printing. In
future, we will extend the data and improve the interfaces. The project pages
are: https://medshapenet.ikim.nrw/ and
https://github.com/Jianningli/medshapenet-feedbackComment: 16 page
Observing many researchers using the same data and hypothesis reveals a hidden universe of uncertainty
This study explores how researchersâ analytical choices affect the reliability of scientific findings. Most discussions of reliability problems in science focus on systematic biases. We broaden the lens to emphasize the idiosyncrasy of conscious and unconscious decisions that researchers make during data analysis. We coordinated 161 researchers in 73 research teams and observed their research decisions as they used the same data to independently test the same prominent social science hypothesis: that greater immigration reduces support for social policies among the public. In this typical case of social science research, research teams reported both widely diverging numerical findings and substantive conclusions despite identical start conditions. Researchersâ expertise, prior beliefs, and expectations barely predict the wide variation in research outcomes. More than 95% of the total variance in numerical results remains unexplained even after qualitative coding of all identifiable decisions in each teamâs workflow. This reveals a universe of uncertainty that remains hidden when considering a single study in isolation. The idiosyncratic nature of how researchersâ results and conclusions varied is a previously underappreciated explanation for why many scientific hypotheses remain contested. These results call for greater epistemic humility and clarity in reporting scientific findings
The Crowdsourced Replication Initiative: Investigating Immigration and Social Policy Preferences. Executive Report.
In an era of mass migration, social scientists, populist parties and social movements raise concerns over the future of immigration-destination societies. What impacts does this have on policy and social solidarity? Comparative cross-national research, relying mostly on secondary data, has findings in different directions. There is a threat of selective model reporting and lack of replicability. The heterogeneity of countries obscures attempts to clearly define data-generating models. P-hacking and HARKing lurk among standard research practices in this area.This project employs crowdsourcing to address these issues. It draws on replication, deliberation, meta-analysis and harnessing the power of many minds at once. The Crowdsourced Replication Initiative carries two main goals, (a) to better investigate the linkage between immigration and social policy preferences across countries, and (b) to develop crowdsourcing as a social science method. The Executive Report provides short reviews of the area of social policy preferences and immigration, and the methods and impetus behind crowdsourcing plus a description of the entire project. Three main areas of findings will appear in three papers, that are registered as PAPs or in process
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