Resolutions of Subsets of Finite Sets of Points in Projective Space

Given a finite set, $X$, of points in projective space for which the Hilbert function is known, a standard result says that there exists a subset of this finite set whose Hilbert function is ``as big as possible'' inside $X$. Given a finite set of points in projective space for which the minimal free resolution of its homogeneous ideal is known, what can be said about possible resolutions of ideals of subsets of this finite set? We first give a maximal rank type description of the most generic possible resolution of a subset. Then we show that this generic resolution is not always achieved, by incorporating an example of Eisenbud and Popescu. However, we show that it {\em is} achieved for sets of points in projective two space: given any finite set of points in projective two space for which the minimal free resolution is known, there must exist a subset having the predicted resolution.Comment: 17 page

Magnetic domain state and coercivity predictions for biogenic greigite (Fe_3S_4): A comparison of theory with magnetosome observations

The discovery of bacteria that precipitate greigite within intracellular organelles (magnetosomes) offers new evidence about the origin of greigite in natural environments. Unlike magnetite, only scarce information is available about the magnetic characteristics of greigite. For this reason, and the present inability to grow these microorganisms in pure culture, it is not known whether or not the magnetosomes in the newly discovered greigite-precipitating bacteria are of single-domain (SD) size, as are the magnetosomes from magnetite-precipitating bacteria. The hypothesis of natural selection for magnetotactic behavior predicts that the greigite-bearing magnetosomes should also be single magnetic domains. Using previously reported magnetic properties and crystallographic features for greigite, we have calculated the size and shape boundaries expected for SD and superparamagnetic (SPM) behavior in this mineral. For further characterization of the greigite crystals, we analyzed the domain state at various length/width ratios assuming crystal shapes of parallelepipeds and prolate spheroids. Magnetite was used as control for the current theories supporting these calculations. We also present a simple algorithm to calculate the upper size limit of single-domain grains. Our results show that the crystals of bacterial greigite characterized so far are located in the region close to the single-domain superparamagnetic boundary and should have relatively low coercivity. If these crystals contribute to the magnetization of sediments, remanence produced by bacterial greigite could be mistaken for large, multidomain magnetite in alternating field demagnetization studies

Aβ ion channels. Prospects for treating Alzheimer's disease with Aβ channel blockers

AbstractThe main pathological features in the Alzheimer’s brain are progressive depositions of amyloid protein plaques among nerve cells, and neurofibrillary tangles within the nerve cells. The major components of plaques are Aβ peptides. Numerous reports have provided evidence that Aβ peptides are cytotoxic and may play a role in the pathogenesis of AD. An increasing number of research reports support the concept that the Aβ–membrane interaction event may be followed by the insertion of Aβ into the membrane in a structural configuration which forms an ion channel. This review summarizes experimental procedures which have been designed to test the hypothesis that the interaction of Aβ with a variety of membranes, both artificial and natural, results in the subsequent formation of Aβ ion channels We describe experiments, by ourselves and others, that support the view that Aβ is cytotoxic largely due to the action of Aβ channels in the cell membrane. The interaction of Aβ with the surface of the cell membrane may results in the activation of a chain of processes that, when large enough, become cytotoxic and induce cell death by apoptosis. Remarkably, the blockage of Aβ ion channels at the surface of the cell absolutely prevents the activation of these processes at different intracellular levels, thereby preserving the life of the cells. As a prospect for therapy for Alzheimer’s disease, our findings at cellular level may be testable on AD animal models to elucidate the potential role and the magnitude of the contribution of the Aβ channels for induction of the disease

Whose Data Is It Anyway? Lessons in Data Management and Sharing from Resurrecting and Repurposing Lidar Data for Archaeology Research in Honduras

As a response to Hurricane Mitch and the resulting widespread loss of life and destruction of Honduran infrastructure in 1998, the United States Geological Survey (USGS) conducted the first wide-area airborne lidar topographic mapping project in Central America. The survey was executed by the Bureau of Economic Geology at the University of Texas at Austin (BEG) in 2000, and it was intended to cover 240 square kilometers distributed among 15 flood-prone communities throughout Honduras. The original data processing produced basic digital elevation models at 1.5-meter grid spacing which were used as inputs for hydrological modeling. The USGS published the results in a series of technical reports in 2002. The authors became interested in this dataset in 2013 while searching for geospatial data that would provide additional context and comparative references for an archaeological lidar project conducted in 2012 in the Honduran Mosquitia. After multiple requests to representatives from the USGS and BEG, we found various types of processed data in personal and institutional archives, culminating in the identification of 8-mm magnetic tapes that contained the original point clouds. Point clouds for the 15 communities plus a test area centered on the Maya site of Copán were recovered from the tapes (16 areas totaling 700 km2). These point clouds have been reprocessed by the authors using contemporary software and methods into higher resolution and fidelity products. Within these new products, we have identified and mapped multiple archaeological sites in proximity to modern cities, many of which are not part of the official Honduran site registry. Besides improving our understanding of ancient Honduras, our experiences dealing with issues of data management and access, ethics, and international collaboration have been informative. This paper summarizes our experiences in the hope that they will contribute to the discussion and development of best practices for handling geospatial datasets of archaeological value

Staphylococcus Biofilms

The majority of staphylococci produce biofilm on medical devices, which is the main mechanism to infect humans. Staphylococcal biofilms attach to abiotic or biotic surfaces, forming aggregates and protecting themselves against the immune system and the antimicrobial compounds of the host. Few studies on biofilm formation mechanism in Staphylococcus epidermidis and other coagulase-negative staphylococci (CNS) have been performed; however, there is a great interest in studying and controlling biofilm formation of this genus. This chapter exhibits the state of the art on biofilm formation in S. epidermidis and other staphylococcal species. The main goal of this chapter is to recognize the importance of biofilm formation in Staphylococcus. The participating molecules in staphylococcal biofilm formation are described. Currently, biofilm producer strains of Staphylococcus and mainly CNS have been frequently isolated at hospitals, causing significant economic losses. This chapter includes promising solutions in order to prevent medical device-associated infections, as the development of medical devices possessing anti-biofilm materials or surfaces that act against the adhesion or viability of the microorganisms

Surface Proteins of Staphylococcus aureus

Staphylococcus aureus is a commensal bacterium that causes infections such as sepsis, endocarditis, and pneumonia. S. aureus can express a variety of virulence factors, including surface proteins. Surface proteins are characterized by presence of a Sec‐dependent signal sequence at the amino terminal, and the sorting signal domain. Surface proteins are covalently attached to peptidoglycan and they are commonly known as cell wall–anchored (CWA) proteins. CWA proteins have many functions and participate in the pathogenesis of S. aureus. Furthermore, these proteins have been proposed as therapeutic targets for the generation of vaccines. In this chapter, different topics related to CWA proteins of S. aureus are addressed. The molecular structure of CWA proteins and their role as virulence factors of S. aureus are described. Furthermore, the involvement of CWA proteins in the processes of adhesion, invasion of host cells and tissues, evasion of the immune response, and the formation of biofilm is discussed. In addition, the role of CWA proteins in skin infection and the proposal to use them as potential vaccine antigens are described. The information contained in this chapter will help the readers to understand the biology of CWA proteins and to recognize the importance of surface molecules of S. aureus

A proteomic approach to identify endosomal cargoes controlling cancer invasiveness

We have previously shown that Rab17 - a small GTPase associated with epithelial polarity - is specifically suppressed by ERK2 signalling to promote an invasive phenotype. However, the mechanisms through which Rab17 loss permits invasiveness, and the endosomal cargoes that are responsible for mediating this are not known. Using quantitative mass spectrometry-based proteomics, we have found that knockdown of Rab17 leads to highly selective reduction in the cellular levels of a v-SNARE (Vamp8). Moreover, proteomics and immunofluorescence indicate that Vamp-8 is associated with Rab17 at late endosomes. Reduced levels of Vamp8 promote transition between ductal carcinoma in situ (DCIS) and a more invasive phenotype. We developed an unbiased proteomic approach to elucidate the complement of receptors that redistributes between endosomes and the plasma membrane, and have pin-pointed neuropilin-2 (NRP2) as a key pro-invasive cargo of Rab17/Vamp8-regulated trafficking. Indeed, reduced Rab17 or Vamp8 levels lead to increased mobilisation of NRP2-containing late endosomes and upregulated cell surface expression of NRP2. Finally, we show that NRP2 is required for the basement membrane disruption which accompanies transition between DCIS and a more invasive phenotype