1,985 research outputs found
Carbon Nanotubes in Helically Modulated Potentials
We calculate effects of an applied helically symmetric potential on the low
energy electronic spectrum of a carbon nanotube in the continuum approximation.
The spectrum depends on the strength of this potential and on a dimensionless
geometrical parameter, P, which is the ratio of the circumference of the
nanotube to the pitch of the helix. We find that the minimum band gap of a
semiconducting nanotube is reduced by an arbitrarily weak helical potential,
and for a given field strength there is an optimal P which produces the biggest
change in the band gap. For metallic nanotubes the Fermi velocity is reduced by
this potential and for strong fields two small gaps appear at the Fermi surface
in addition to the gapless Dirac point. A simple model is developed to estimate
the magnitude of the field strength and its effect on DNA-CNT complexes in an
aqueous solution. We find that under typical experimental conditions the
predicted effects of a helical potential are likely to be small and we discuss
several methods for increasing the size of these effects.Comment: 12 pages, 10 figures. Accepted for publication in Physical Review B.
Image quality reduced to comply with arxiv size limitation
The 2PI finite temperature effective potential of the O(N) linear sigma model in 1+1 dimensions, at next-to-leading order in 1/N
We study the O(N) linear sigma model in 1+1 dimensions. We use the 2PI
formalism of Cornwall, Jackiw and Tomboulis in order to evaluate the effective
potential at finite temperature. At next-to-leading order in a 1/N expansion
one has to include the sums over "necklace" and generalized "sunset" diagrams.
We find that - in contrast to the Hartree approximation - there is no
spontaneous symmetry breaking in this approximation, as to be expected for the
exact theory. The effective potential becomes convex throughout for all
parameter sets which include N=4,10,100, couplings lambda=0.1 and 0.5, and
temperatures between 0.2 and 1. The Green's functions obtained by solving the
Schwinger-Dyson equations are enhanced in the infrared region. We also compare
the effective potential as function of the external field phi with those
obtained in various other approximations.Comment: 19 pages, 9 figures; v2: references added, some changes in the tex
Experimental Evidence for Weathering and Martian Sulfate Formation Under Extremely Cold Weather-Limited Environments
High resolution photography and spectroscopy of the martian surface (MOC, HiRISE) from orbit has revolutionized our view of Mars with one of the most important discoveries being wide-spread layered sedimentary deposits associated with sulfate minerals across the low to mid latitude regions of Mars [1, 2]. The mechanism for sulfate formation on Mars has been frequently attributed to playa-like evaporative environments under prolonged warm conditions [3]. However, there are several problems with the presence of prolonged surface temperatures on Mars above 273 K during the Noachian including the faint young Sun [4] and the presence of suitable greenhouse gases [5]. The geomorphic evidence for early warm conditions may instead be explained by periodic episodes of warming rather than long term prolonged warm temperatures [6]. An alternate view of the ancient martian climate contends that prolonged warm temperatures were never present and that the atmosphere and climate has been similar to modern conditions throughout most of its history [6]. This view is more consistent with the climate models, but has had a difficult time explaining the sedimentary history of Mars and in particular the presence of sulfate minerals. We suggest here that mixtures of atmospheric aerosols, ice, and dust have the potential for creating small films of cryo-concentrated acidic solutions that may represent an important unexamined environment for understanding weathering processes on Mars [7, 8]. This study seeks to test whether sulfate formation may be possible at temperatures well below 0 C in water limited environments removing the need for prolonged warm periods to form sulfates on early Mars
Seeds Buffering for Information Spreading Processes
Seeding strategies for influence maximization in social networks have been
studied for more than a decade. They have mainly relied on the activation of
all resources (seeds) simultaneously in the beginning; yet, it has been shown
that sequential seeding strategies are commonly better. This research focuses
on studying sequential seeding with buffering, which is an extension to basic
sequential seeding concept. The proposed method avoids choosing nodes that will
be activated through the natural diffusion process, which is leading to better
use of the budget for activating seed nodes in the social influence process.
This approach was compared with sequential seeding without buffering and single
stage seeding. The results on both real and artificial social networks confirm
that the buffer-based consecutive seeding is a good trade-off between the final
coverage and the time to reach it. It performs significantly better than its
rivals for a fixed budget. The gain is obtained by dynamic rankings and the
ability to detect network areas with nodes that are not yet activated and have
high potential of activating their neighbours.Comment: Jankowski, J., Br\'odka, P., Michalski, R., & Kazienko, P. (2017,
September). Seeds Buffering for Information Spreading Processes. In
International Conference on Social Informatics (pp. 628-641). Springe
Olivine Weathering aud Sulfate Formation Under Cryogenic Conditions
High resolution photography and spectroscopy of the martian surface (MOC, HiRISE) from orbit has revolutionized our view of Mars with one of the most important discoveries being widespread layered sedimentary deposits associated with sulfate minerals across the low to mid latitude regions of Mars. The mechanism for sulfate formation on Mars has been frequently attributed to playalike evaporative environments under prolonged warm conditions. An alternate view of the ancient martian climate contends that prolonged warm temperatures were never present and that the atmosphere and climate has been similar to modern conditions throughout most of its history. This view has had a difficult time explaining the sedimentary history of Mars and in particular the presence of sulfate minerals which seemingly need more water. We suggest here that mixtures of atmospheric aerosols, ice, and dust have the potential for creating small films of cryoconcentrated acidic solutions that may represent an important unexamined environment for understanding weathering processes on Mars. This study seeks to test whether sulfate formation may be possible at temperatures well below 0degC in water limited environments removing the need for prolonged warm periods to form sulfates on early Mars. To test this idea we performed laboratory experiments to simulate weathering of mafic minerals under Marslike conditions. The weathering rates measured in this study suggest that fine grained olivine on Mars would weather into sulfate minerals in short time periods if they are exposed to H2SO4 aerosols at temperatures at or above 40degC. In this system, the strength of the acidic solution is maximized through eutectic freezing in an environment where the silicate minerals are extremely fine grained and have high surface areas. This provides an ideal environment despite the very low temperatures. On Mars the presence of large deposits of mixed ice and dust is undisputed. The presence of substantial sulfurrich volcanism, and sulfurrich surface deposits also makes it very likely that sulfate aerosols have also been an important component of the martian atmosphere. Thus mixtures of ice, dust, and sulfate aerosols are likely to have been common on the martian surface. Given the fact that it is not difficult to achieve surface temperatures above 40degC on Mars throughout its history, it seems likely that sulfate formation on Mars is controlled by the availability of sulfate aerosols and not by the martian climate. The current polar regions of Mars and Earth provide interesting analogs. Large regions of sulfaterich material have been detected on and around the modern north polar region of Mars. The prevalence of icedust mixtures in this region and the existence of sulfates within the ice cap itself are strong evidence for the origin of the sulfates from inside the ice deposits. In addition sulfates have been found in ice deposits in Greenland and Mount Fuji on Earth that have been attributed to forming within the ice deposit. These sulfates can form either through interaction with dust particles in the atmosphere or through weathering inside the ice itself
Update on perineuronal net staining with Wisteria floribunda agglutinin (WFA)
As chemically specialized forms of the extracellular matrix in the central nervous system, polyanionic perineuronal nets (PNs) contain diverse constituents, including chondroitin sulfate proteoglycans (CSPGs), hyaluronic acid, and tenascins. They are detectable by various histological approaches such as colloidal iron binding and immunohistochemical staining to reveal, for instance, the CSPGs aggrecan, neurocan, phosphacan, and versican. Moreover, biotin, peroxidase, or fluorescein conjugates of the lectins Vicia villosa agglutinin and soybean agglutinin enable the visualization of PNs. At present, the N-acetylgalactosamine-binding Wisteria floribunda agglutinin (WFA) is the most widely applied marker for PNs. Therefore, this article is largely focused on methodological aspects of WFA staining. Notably, fluorescent WFA labeling allows, after its conversion into electron-dense adducts, electron microscopic analyses. Furthermore, the usefulness of WFA conjugates for the oftentimes neglected in vivo and in vitro labeling of PNs is emphasized. Subsequently, we discuss impaired WFA-staining sites after long-lasting experiments in vitro, especially in autoptic brain samples with long postmortem delay and partial enzymatic degradation, while immunolabeling of aggrecan and CSPG link proteins under such conditions has proven more robust. In some hippocampal regions from perfusion-fixed mice, more PNs are aggrecan immunoreactive than WFA positive, whereas the retrosplenial cortex displays many WFA-binding PNs devoid of visible aggrecan immunoreactivity. Additional multiple fluorescence labeling exemplarily revealed in ischemic tissue diminished staining of WFA-binding sites and aquaporin 4 and concomitantly upregulated immunolabeling of neurofilament, light chains, and collagen IV. Finally, we briefly discuss possible future staining approaches based on nanobodies to facilitate novel technologies revealing details of net morphology
Zorganizowana skrzeplina w lewej komorze powstała po zabiegu przezskórnej angioplastyki wieńcowej mimo stosowanej podwójnej terapii przeciwpłytkowej
Myocardial infarction is an acute condition which can lead to many complications in a postinfarct period (MI, myocardial
infarction). Left ventricular thrombus formation after successful primary percutaneous coronary intervention (PCI)
with stenting and treating with dual antiplatelet therapy nowadays is a less common finding especially in absence of
severe left ventricular dysfunction associated with MI. Case of 70-year-old male who was admitted to the Emergency
Department with severe MI treating with successful primary PCI with stenting and dual antiplatelet therapy with a new
unexpected finding of thrombus in the left ventricular apex observed in control of the echocardiography examination
during hospitalisation despite dual antiplatelet therapy.Zawał serca jest stanem ostrym, który może prowadzić do licznych powikłań we wczesnym okresie pozawałowym.Występowanie skrzepliny w lewej komorze u pacjentów po skutecznej pierwotnej przezskórnej angioplastyce (PCI) z implantacją stentu i zastosowaniu podwójnej terapii przeciwpłytkowej (DAPT) w obecnych czasach jest mniej powszechnym zjawiskiem, zwłaszcza u osób bez ciężkiej pozawałowej dysfunkcji mięśnia lewej komory. Zaprezentowano przypadek 70-letniego mężczyzny, przyjętego do kliniki z prezentacją ostrego zespołu wieńcowego leczonego skuteczną pierwotną PCI z implantacją stentu i zastosowaniem DAPT, u którego, mimo zastosowanej terapii, w kolejnych badaniach echokardiograficznych podczas hospitalizacji obserwowano skrzeplinę w koniuszku lewej komory
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