Network connectivity during mergers and growth: optimizing the addition of a module

The principal eigenvalue $\lambda$ of a network's adjacency matrix often determines dynamics on the network (e.g., in synchronization and spreading processes) and some of its structural properties (e.g., robustness against failure or attack) and is therefore a good indicator for how ``strongly'' a network is connected. We study how $\lambda$ is modified by the addition of a module, or community, which has broad applications, ranging from those involving a single modification (e.g., introduction of a drug into a biological process) to those involving repeated additions (e.g., power-grid and transit development). We describe how to optimally connect the module to the network to either maximize or minimize the shift in $\lambda$, noting several applications of directing dynamics on networks.Comment: 7 pages, 5 figure

Sedentary Time Accumulated in Bouts is Positively Associated with Disease Severity in Fibromyalgia: The Al-andalus Project

To examine the associations of prolonged sedentary time (ST) with disease severity in women with fibromyalgia, and to analyse the combined association of total ST and prolonged ST with the disease severity in this population. Women (n = 451; 51.3 +/- 7.6 years old) with fibromyalgia participated. Sedentary time and moderate-to-vigorous physical activity (MVPA) were measured using triaxial accelerometry and ST was processed into 30- and 60-min bouts. Dimensions of fibromyalgia (function, overall, symptoms) and the overall disease impact were assessed with the Revised Fibromyalgia Impact Questionnaire (FIQR). Body fat percentage was assessed using a bio-impedance analyser, and physical fitness was assessed with the Senior Fitness Tests Battery. Greater percentage of ST in 30-min bouts and 60-min bouts were associated with worse function, overall, symptoms and the overall impact of the disease (all, P 60-min bouts) presented lower overall impact compared to participants with high levels of total ST and prolonged ST (mean difference = 6.56; 95% confidence interval (CI) = 1.83 to 11.29, P = 0.002). Greater percentage of ST accumulated in 30- and 60-min bouts and a combination of high levels of total and prolonged ST are related to worse disease severity. Although unable to conclude on causality, results suggest it might be advisable to motivate women with fibromyalgia to break prolonged ST and reduce their total daily ST

Use of Cilostazol for Secondary Stroke Prevention: An Old Dog with New Tricks?

OBJECTIVE: To evaluate the safety and efficacy of cilostazol for secondary prevention of non-cardioembolic ischemic stroke. DATA SOURCES: PubMed and MEDLINE searches were performed (January 1970-September 2011) using the key words cilostazol, antiplatelet, aspirin, acetylsalicylic acid, secondary stroke prevention, ischemic stroke, intracerebral hemorrhage, intracranial, cerebrovascular accident, and transient ischemic attack. Additionally, reference citations from publications identified were reviewed. STUDY SELECTION AND DATA EXTRACTION: Articles published in English and relevant primary literature evaluating the efficacy and safety of cilostazol in the secondary prevention of atherosclerotic ischemic stroke were included. DATA SYNTHESIS: Antiplatelet therapy plays a vital role in the multifaceted approach to secondary stroke prevention. Current American Heart Association/American Stroke Association clinical guidelines for secondary stroke prevention support the use of aspirin, clopidogrel, and combination aspirin/extended-release dipyridamole. The antiplatelet, antithrombotic, and vasodilatory effects of cilostazol make it a potential alternative agent for atherosclerotic stroke prevention. Recent literature has demonstrated superior efficacy of cilostazol 100 mg twice daily for secondary stroke prevention compared to placebo and aspirin. Three clinical trials were reviewed (1 placebo-controlled, 2 aspirin-controlled), all of which were conducted in Japan or China. Cilostazol reduced the primary outcome of recurrence of stroke, with significantly fewer major bleeding events when compared to aspirin. CONCLUSIONS: Available literature suggests that cilostazol may be safer and more effective than aspirin in the secondary prevention of stroke in Asian patients. Further large-scale studies in more heterogeneous study populations are warranted to determine whether cilostazol is a viable therapeutic option for patients with a history of non-cardioembolic ischemic stroke

A Stimulatory Role for Cytokinin in the Arbuscular Mycorrhizal Symbiosis of Pea

The arbuscular mycorrhizal (AM) symbiosis between terrestrial plants and AM fungi is regulated by plant hormones. For most of these, a role has been clearly assigned in this mutualistic interaction; however, there are still contradictory reports for cytokinin (CK). Here, pea plants, the wild type (WT) cv. Sparkle and its mutant E151 (Pssym15), were inoculated with the AM fungus Rhizophagus irregularis. E151 has previously been characterized as possessing high CK levels in non-mycorrhizal (myc-) roots and exhibiting high number of fungal structures in mycorrhizal (myc+) roots. Myc- and myc+ plants were treated 7, 9, and 11 days after inoculation (DAI) with synthetic compounds known to alter CK status. WT plants were treated with a synthetic CK [6-benzylaminopurine (BAP)] or the CK degradation inhibitor INCYDE, whereas E151 plants were treated with the CK receptor antagonist PI-55. At 13 DAI, plant CK content was analyzed by mass spectrometry. The effects of the synthetic compounds on AM colonization were assessed at 28 (WT) or 35 (E151) DAI via a modified magnified intersections method. The only noticeable difference seen between myc- and myc+ plants in terms of CK content was in the levels of nucleotides (NTs). Whereas WT plants responded to fungi by lowering their NT levels, E151 plants did not. Since NTs are thought to be converted into active CK forms, this result suggests that active CKs were synthesized more effectively in WT than in E151. In general, myc+ and myc- WT plants responded similarly to INCYDE by lowering significantly their NT levels and increasing slightly their active CK levels; these responses were less obvious in BAP-treated WT plants. In contrast, the response of E151 plants to PI-55 depended on the plant mycorrhizal status. Whereas treated myc- plants exhibited high NT and low active CK levels, treated myc+ plants displayed low levels of both NTs and active CKs. Moreover, treated WT plants were more colonized than treated E151 plants. We concluded that CKs have a stimulatory role in AM colonization because increased active CK levels were paralleled with increased AM colonization while decreased CK levels corresponded to reduced AM colonization

Solid acids as fuel cell electrolytes

Fuel cells are attractive alternatives to combustion engines for electrical power generation because of their very high efficiencies and low pollution levels. Polymer electrolyte membrane fuel cells are generally considered to be the most viable approach for mobile applications. However, these membranes require humid operating conditions, which limit the temperature of operation to less than 100°C; they are also permeable to methanol and hydrogen, which lowers fuel efficiency. Solid, inorganic, acid compounds (or simply, solid acids) such as CsHSO_4 and Rb_3H(SeO_4)_2 have been widely studied because of their high proton conductivities and phase-transition behaviour. For fuel-cell applications they offer the advantages of anhydrous proton transport and high-temperature stability (up to 250°C). Until now, however, solid acids have not been considered viable fuel-cell electrolyte alternatives owing to their solubility in water and extreme ductility at raised temperatures (above approximately 125°C). Here we show that a cell made of a CsHSO_4 electrolyte membrane (about 1.5 mm thick) operating at 150–160°C in a H_2/O_2 configuration exhibits promising electrochemical performances: open circuit voltages of 1.11 V and current densities of 44 mA cm^-2 at short circuit. Moreover, the solid-acid properties were not affected by exposure to humid atmospheres. Although these initial results show promise for applications, the use of solid acids in fuel cells will require the development of fabrication techniques to reduce electrolyte thickness, and an assessment of possible sulphur reduction following prolonged exposure to hydrogen

Predicting Crystal Structures with Data Mining of Quantum Calculations

Predicting and characterizing the crystal structure of materials is a key problem in materials research and development. It is typically addressed with highly accurate quantum mechanical computations on a small set of candidate structures, or with empirical rules that have been extracted from a large amount of experimental information, but have limited predictive power. In this letter, we transfer the concept of heuristic rule extraction to a large library of ab-initio calculated information, and demonstrate that this can be developed into a tool for crystal structure prediction.Comment: 4 pages, 3 pic

Diffusion-Limited Reactions In Spherical Cavities

We study a quenching reaction occurring at sinks within a spherical cavity and at the cavity surface. One may think of reactions at these two, distinct locations as two, coupled reactive channels. Reactions of the type D* + A--\u3eD + A are studied in the limit of nondilute A, present at both locations, and dilute D, present within the cavity. We use a Monte Carlo algorithm to compute mean rates, pseudo-first-order rates and branching ratios, and compare with results obtained by assuming that the two reactive channels operate in parallel. The ratio of activities of the two channels are varied; static and moving sinks are studied. We discuss an application to the determination of pore structure by NMR (nuclear magnetic resonance)

SiO2 glass density to lower-mantle pressures

The convection or settling of matter in the deep Earth’s interior is mostly constrained by density variations between the different reservoirs. Knowledge of the density contrast between solid and molten silicates is thus of prime importance to understand and model the dynamic behavior of the past and present Earth. SiO2 is the main constituent of Earth’s mantle and is the reference model system for the behavior of silicate melts at high pressure. Here, we apply our recently developed x-ray absorption technique to the density of SiO2 glass up to 110 GPa, doubling the pressure range for such measurements. Our density data validate recent molecular dynamics simulations and are in good agreement with previous experimental studies conducted at lower pressure. Silica glass rapidly densifies up to 40 GPa, but the density trend then flattens to become asymptotic to the density of SiO2 minerals above 60 GPa. The density data present two discontinuities at ∼17 and ∼60  GPa that can be related to a silicon coordination increase from 4 to a mixed 5/6 coordination and from 5/6 to sixfold, respectively. SiO2 glass becomes denser than MgSiO3 glass at ∼40  GPa, and its density becomes identical to that of MgSiO3 glass above 80 GPa. Our results on SiO2 glass may suggest that a variation of SiO2 content in a basaltic or pyrolitic melt with pressure has at most a minor effect on the final melt density, and iron partitioning between the melts and residual solids is the predominant factor that controls melt buoyancy in the lowermost mantle

Protein Interaction Profiling of the p97 Adaptor UBXD1 Points to a Role for the Complex in Modulating ERGIC-53 Trafficking

UBXD1 is a member of the poorly understood subfamily of p97 adaptors that do not harbor a ubiquitin association domain or bind ubiquitin-modified proteins. Of clinical importance, p97 mutants found in familial neurodegenerative conditions Inclusion Body Myopathy Paget's disease of the bone and/or Frontotemporal Dementia and Amyotrophic Lateral Sclerosis are defective at interacting with UBXD1, indicating that functions regulated by a p97-UBXD1 complex are altered in these diseases. We have performed liquid chromatography-mass spectrometric analysis of UBXD1-interacting proteins to identify pathways in which UBXD1 functions. UBXD1 displays prominent association with ERGIC-53, a hexameric type I integral membrane protein that functions in protein trafficking. The UBXD1-ERGIC-53 interaction requires the N-terminal 10 residues of UBXD1 and the C-terminal cytoplasmic 12 amino acid tail of ERGIC-53. Use of p97 and E1 enzyme inhibitors indicate that complex formation between UBXD1 and ERGIC-53 requires the ATPase activity of p97, but not ubiquitin modification. We also performed SILAC-based quantitative proteomic profiling to identify ERGIC-53 interacting proteins. This analysis identified known (e.g. COPI subunits) and novel (Rab3GAP1/2 complex involved in the fusion of vesicles at the cell membrane) interactions that are also mediated through the C terminus of the protein. Immunoprecipitation and Western blotting analysis confirmed the proteomic interaction data and it also revealed that an UBXD1-Rab3GAP association requires the ERGIC-53 binding domain of UBXD1. Localization studies indicate that UBXD1 modules the sub-cellular trafficking of ERGIC-53, including promoting movement to the cell membrane. We propose that p97-UBXD1 modulates the trafficking of ERGIC-53-containing vesicles by controlling the interaction of transport factors with the cytoplasmic tail of ERGIC-53