Topological representations of matroid maps

The Topological Representation Theorem for (oriented) matroids states that every (oriented) matroid can be realized as the intersection lattice of an arrangement of codimension one homotopy spheres on a homotopy sphere. In this paper, we use a construction of Engstr\"om to show that structure-preserving maps between matroids induce topological mappings between their representations; a result previously known only in the oriented case. Specifically, we show that weak maps induce continuous maps and that the process is a functor from the category of matroids with weak maps to the homotopy category of topological spaces. We also give a new and conceptual proof of a result regarding the Whitney numbers of the first kind of a matroid.Comment: Final version, 21 pages, 8 figures; Journal of Algebraic Combinatorics, 201

Unitarity Restoration in the Presence of Closed Timelike Curves

A proposal is made for a mathematically unambiguous treatment of evolution in the presence of closed timelike curves. In constrast to other proposals for handling the naively nonunitary evolution that is often present in such situations, this proposal is causal, linear in the initial density matrix and preserves probability. It provides a physically reasonable interpretation of invertible nonunitary evolution by redefining the final Hilbert space so that the evolution is unitary or equivalently by removing the nonunitary part of the evolution operator using a polar decomposition.Comment: LaTeX, 17pp, Revisions: Title change, expanded and clarified presentation of original proposal, esp. with regard to Heisenberg picture and remaining in original Hilbert spac

Simulating the dynamics of soil organic matter in long-term rotation plots of Saskatchewan and Alberta

Non-Peer ReviewedThis study used the Century soil organic matter (SOM) model to simulate the dynamics in soil organic carbon, nitrogen, and phosphorus in long-term crop rotation studies established in Saskatchewan and Alberta. Observed losses of organic C, N, and P in the top 30 cm of a Brown Chernozem under fallow-wheat (FW) were 8.2, 1.7, and 1.0 g m-1 y-1. Soil erosion was responsible for 47% of the organic-N losses. The Century model closely mimicked the direction and magnitude of SOM change, within 10% of measured values. Similar SOM declining trends were observed in a thin Black Chernozem under FW and continuous wheat (CW), although soil erosion losses were higher than in the Brown Chernozem. Soil organic matter increased in the Brown Chernozem under CW and in the Black Chernozem under zero-tillage. Under no-till, the organic C, N, and P accumulated at an average rate of 101.7, 5.3, and 2.0 g m-2 y-1. In comparison, the Century model predicted a depletion of organic-C and N in the Brown Chernozem under CW and of organic-C under no-till. Model sensitivity analyses indicated that the rate of erosion and the fixed rate of organic matter decomposition had greater effects than plant biomass production on soil organic matter levels. Under aggrading SOM conditions, the Century model predicted organic carbon accumulation only after the respiration rate for the slow organic matter fraction was reduced by 50%

Are species occurrence data in global online repositories fit for modeling species distributions? The case of the Global Biodiversity Information Facility (GBIF). Final Report of the Task Group on GBIF Data Fitness for Use in Distribution Modelling.

Primary Biodiversity Data (PBD) are defined as the basic attributes of observations or records of the occurrences of species. PBD is a fundamental concept of biodiversity informatics since it is substantial in quantity and provides the links to organize other large and independent bodies of data concerning species (= taxonomic information) and environments. In fact, PBD is at the core of the exploding field of biodiversity informatics, which in some sense now underlies biogeography, macroecology, landscape ecology and several other subdisciplines of biology. A principal - and rapidly growing - class of research that can be performed using PBD is the estimation of a species' environmental requirements and the projection of these in both environmental and geographic spaces to estimate niches or distributional ranges, generally by using models of ecological niches and species' distributions (often called ENMs or SDMs, respectively). The largest point of access to PBD in the world is the Global Biodiversity Information Facility (GBIF), and hundreds of papers have now used GBIF-mediated data to fit and apply ENM/SDM. Experience has shown that GBIF, like other aggregated data research infrastructures, holds a number of potential problems related to incomplete or difficult access to all the fields in its schema, inconsistent information among fields, or simply erroneous or incomplete data. These drawbacks complicate ENM/SDM analyses considerably, and detract from the enormous scientific value of this information storehouse. Three overlapping communities participate in GBIF's data process: providers (museums, herbaria, and observer's networks), users (scientists, analysts working for governments, NGOs or the private sector, the public) and the technical staff managing the huge databases, web services and servers at GBIF. Each can play a different role in fixing data issues of GBIF. Our main recommendations for the GBIF Secretariat are the following: GBIF.org should serve indicators of precision, quality, and uncertainty of data that can be calculated practically, and preferably "on the fly", as well as summaries and metrics of completeness of inventories, at scales and for regions defined by the user. The summaries should display maps and graphs of completeness by region, time-period and taxa. The implementation of the GBIF information resource should go beyond unique identifiers of queries (DOIs for downloads, including the capability to re-run queries, http://www.gbif.org/publishing-data/summary#supporteddatasettypes), and to include identifiers of the individual data that make up the queried data. GBIF.org should include applications or functionalities enabling users to annotate errors or problems, and communicate those changes directly to providers, as it may be practical and appropriate. This point may need to be discussed with providers. A procedure enabling users to make accessible versions of their databases that have been improved and annotated should be supported, but this functionality should not lose the vital tie back to the original data records and the actual data provider. GBIF should partner with and/or support initiatives to do more for training and guiding users on the proper use of the data; such initiatives should incorporate actual expert uses in ENM/SDM to assure that current best practices are followed

Exact perturbative solution of the Kondo problem

We explicitly evaluate the infinite series of integrals that appears in the "Anderson-Yuval" reformulation of the anisotropic Kondo problem in terms of a one-dimensional Coulomb gas. We do this by developing a general approach relating the anisotropic Kondo problem of arbitrary spin with the boundary sine-Gordon model, which describes impurity tunneling in a Luttinger liquid and in the fractional quantum Hall effect. The Kondo solution then follows from the exact perturbative solution of the latter model in terms of Jack polynomials.Comment: 4 pages in revtex two-colum

Fourier Analysis of Gapped Time Series: Improved Estimates of Solar and Stellar Oscillation Parameters

Quantitative helio- and asteroseismology require very precise measurements of the frequencies, amplitudes, and lifetimes of the global modes of stellar oscillation. It is common knowledge that the precision of these measurements depends on the total length (T), quality, and completeness of the observations. Except in a few simple cases, the effect of gaps in the data on measurement precision is poorly understood, in particular in Fourier space where the convolution of the observable with the observation window introduces correlations between different frequencies. Here we describe and implement a rather general method to retrieve maximum likelihood estimates of the oscillation parameters, taking into account the proper statistics of the observations. Our fitting method applies in complex Fourier space and exploits the phase information. We consider both solar-like stochastic oscillations and long-lived harmonic oscillations, plus random noise. Using numerical simulations, we demonstrate the existence of cases for which our improved fitting method is less biased and has a greater precision than when the frequency correlations are ignored. This is especially true of low signal-to-noise solar-like oscillations. For example, we discuss a case where the precision on the mode frequency estimate is increased by a factor of five, for a duty cycle of 15%. In the case of long-lived sinusoidal oscillations, a proper treatment of the frequency correlations does not provide any significant improvement; nevertheless we confirm that the mode frequency can be measured from gapped data at a much better precision than the 1/T Rayleigh resolution.Comment: Accepted for publication in Solar Physics Topical Issue "Helioseismology, Asteroseismology, and MHD Connections

An assessment of pulse transit time for detecting heavy blood loss during surgical operation

Copyright @ Wang et al.; Licensee Bentham Open. This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.The main contribution of this paper is the use of non-invasive measurements such as electrocardiogram (ECG) and photoplethysmographic (PPG) pulse oximetry waveforms to develop a new physiological signal analysis technique for detecting blood loss during surgical operation. Urological surgery cases were considered as the control group due to its generality, and cardiac surgery as experimental group since it involves blood loss and water supply. Results show that the control group has the tendency of a reduction of the pulse transient time (PTT), and this indicates an increment in the blood flow velocity changes from slow to fast. While for the experimental group, the PTT indicates high values during blood loss, and low values during water supply. Statistical analysis shows considerable differences (i.e., P <0.05) between both groups leading to the conclusion that PTT could be a good indicator for monitoring patients' blood loss during a surgical operation.The National Science Council (NSC) of Taiwan and the Centre for Dynamical Biomarkers and Translational Medicine, National Central University, Taiwan

Heterotic Compactification, An Algorithmic Approach

We approach string phenomenology from the perspective of computational algebraic geometry, by providing new and efficient techniques for proving stability and calculating particle spectra in heterotic compactifications. This is done in the context of complete intersection Calabi-Yau manifolds in a single projective space where we classify positive monad bundles. Using a combination of analytic methods and computer algebra we prove stability for all such bundles and compute the complete particle spectrum, including gauge singlets. In particular, we find that the number of anti-generations vanishes for all our bundles and that the spectrum is manifestly moduli-dependent.Comment: 36 pages, Late

Path Integral Description of a Semiclassical Su-Schrieffer-Heeger Model

The electron motion along a chain is described by a continuum version of the Su-Schrieffer-Heeger Hamiltonian in which phonon fields and electronic coordinates are mapped onto the time scale. The path integral formalism allows us to derive the non local source action for the particle interacting with the oscillators bath. The method can be applied for any value of the {\it e-ph} coupling. The path integral dependence on the model parameters has been analysed by computing the partition function and some thermodynamical properties from $T= 1K$ up to room temperature. A peculiar upturn in the low temperature {\it heat capacity over temperature} ratio (pointing to a glassy like behavior) has been ascribed to the time dependent electronic hopping along the chain