653 research outputs found
Phase Field Crystal model for particles with n-fold rotational symmetry in two dimensions
We introduce a Phase Field Crystal (PFC) model for particles with n-fold
rotational symmetry in two dimensions. Our approach is based on a free energy
functional that depends on the reduced one-particle density, the strength of
the orientation, and the direction of the orientation, where all these order
parameters depend on the position. The functional is constructed such that for
particles with axial symmetry (i. e. n = 2) the PFC model for liquid crystals
as introduced by H. L\"owen [J. Phys.: Condens. Matter 22, 364105 (2010)] is
recovered. We discuss the stability of the functional and explore phases that
occur for . In addition to isotropic, nematic, stripe, and
triangular order, we also observe cluster crystals with square, rhombic,
honeycomb, and even quasicrystalline symmetry. The n-fold symmetry of the
particles corresponds to the one that can be realized for colloids with
symmetrically arranged patches. We explain how both, repulsive as well as
attractive patches, are described in our model.Comment: 20 pages, 12 figure
Millimeter-Wave and Terahertz Transceivers in SiGe BiCMOS Technologies
This invited paper reviews the progress of silicon–germanium (SiGe) bipolar-complementary metal–oxide–semiconductor (BiCMOS) technology-based integrated circuits (ICs) during the last two decades. Focus is set on various transceiver (TRX) realizations in the millimeter-wave range from 60 GHz and at terahertz (THz) frequencies above 300 GHz. This article discusses the development of SiGe technologies and ICs with the latter focusing on the commercially most important applications of radar and beyond 5G wireless communications. A variety of examples ranging from 77-GHz automotive radar to THz sensing as well as the beginnings of 60-GHz wireless communication up to THz chipsets for 100-Gb/s data transmission are recapitulated. This article closes with an outlook on emerging fields of research for future advancement of SiGe TRX performance
Crop diversity and stability of revenue on farms in Central Europe : an analysis of big data from a comprehensive agricultural census in Bavaria
<div><p>Diversity of agricultural landscapes is important to maintain the provision of ecosystem services. In face of decreasing support measures for agricultural markets in the European Union, diversified crop portfolios could also offer a possibility to stabilize revenue at farm level (portfolio effect). We hypothesize that (i) diversity of crop portfolios changes along spatial gradients in the study area (Bavaria, Germany), (ii) the composition of portfolios depends on farm parameters, and (iii) more diverse portfolios on arable land provide higher revenue stability. We analysed agricultural census data comprising all farms (<i>N</i> = 105 314) in the study area and identified 26 typical crop portfolios. We show that portfolio composition is related to farm characteristics (whole farm revenue, farm type, farm size) and location. Currently, diversification of crop portfolios fails to promote stability of portfolio revenue in the study area, where policy still indirectly influences market prices of energy crops. We conclude that the portfolio effect as a natural insurance was less important in recent years due to high market prices for specific crops. This low need for natural insurances probably favoured simplified portfolios leading to decreased agricultural diversity.</p></div
Climate Impact and GIS Education Using Realistic Applications of Data.gov Thematic Datasets in a Structured Lesson-Based Workbook
This project created a workbook which teaches Earth Science to undergraduate and graduate students through guided in-class activities and take-home assignments organized around climate topics which use GIS to teach key geospatial analysis techniques and cartography skills. The workbook is structured to the White House's Data.gov climate change themes, which include Coastal Flooding, Ecosystem Vulnerability, Energy Infrastructure, Arctic, Food Resilience, Human Health, Transportation, Tribal Nations, and Water. Each theme provides access to framing questions, associated data, interactive tools, and further reading (e.g. The US Climate Resilience Toolkit and National Climate Assessment). Lessons make use of the respective theme's available resources. The structured thematic approach is designed to encourage independent exploration. The goal is to teach climate concepts and concerns, GIS techniques and approaches, and effective cartographic representation and communication results; and foster a greater awareness of publicly available resources and datasets. To reach more audiences more effectively, a two level approach was used. Level 1 serves as an introductory study and relies on only freely available interactive tools to reach audiences with fewer resources and less familiarity. Level 2 presents a more advanced case study, and focuses on supporting common commercially available tool use and real-world analysis techniques
Diquarks and Exotic Spectroscopy
We propose that the recently discovered \Theta baryon is a bound state of
four quarks and an antiquark, containing two highly correlated ud-pairs. If so,
the \Theta baryon has positive parity, and it lies in an near-ideally mixed
SU(3)_{f} \mathbf{\bar{10}}_{f} oplus \mathbf{8}_{f}. The Roper resonance and
the P_{11}(1710) fit naturally into this classification. We predict an isospin
3/2 multiplet of \Xi's (S=-2) with J^{\Pi}=\half^{+} around 1750 MeV. A search
for manifestly exotic \Xi^{+} and \Xi^{--} in this mass range could provide a
sharp test of our proposal. We predict that charm and bottom analogues of the
\Theta baryon are stable against strong decays.Comment: 5 pages, 2 figures, revtex 4, minor corrections and revisions for
journal publicatio
- …