370 research outputs found
A dip in the UHECR spectrum and the transition from galactic to extragalactic cosmic rays
The dip is a feature in the diffuse spectrum of ultra-high energy (UHE)
protons caused by electron-positron pair production on the cosmic microwave
background (CMB) radiation. For a power-law generation spectrum , the
calculated position and shape of the dip is confirmed with high accuracy by the
spectra observed by the Akeno-AGASA, HiRes, Yakutsk and Fly's Eye detectors.
When the particle energies, measured in these detectors, are calibrated by the
dip, their fluxes agree with a remarkable accuracy. The predicted shape of the
dip is quite robust. The dip is only modified strongly when the fraction of
nuclei heavier than protons is high at injection, which imposes some
restrictions on the mechanisms of acceleration operating in UHECR sources. The
existence of the dip, confirmed by observations, implies that the transition
from galactic to extragalactic cosmic rays occurs at E \lsim 1\times 10^{18}
eV. We show that at energies lower than a characteristic value eV, the spectrum of extragalactic cosmic rays
flattens in all cases of interest, and it provides a natural transition to a
steeper galactic cosmic ray spectrum. This transition occurs at some energy
below , corresponding to the position of the so-called second knee.
We discuss extensively the constraints on this model imposed by current
knowledge of acceleration processes and sources of UHECR and compare it with
the traditional model of transition at the ankle.Comment: Version Accepted for Publication in Astroparticle Physics (minor
changes
Reply to Comment by D. Spemann et al [EPL 98 (2012) 57006, arXiv:1204.2992]
This article is a reply to the Comment by D. Spemann et al (arXiv:1204.2992)
in response to our paper 'Revealing common artifacts due to ferromagnetic
inclusions in highly oriented pyrolytic graphite' (EPL, 97 (2012) 47001).Comment: Reply to arXiv:1204.2992 Comment by D. Spemann et al re
arXiv:1201.6374 by Sepioni et a
Unimpeded permeation of water through helium-leak-tight graphene-based membranes
Permeation through nanometer pores is important in the design of materials
for filtration and separation techniques and because of unusual fundamental
behavior arising at the molecular scale. We found that submicron-thick
membranes made from graphene oxide can be completely impermeable to liquids,
vapors and gases, including helium, but allow unimpeded permeation of water
(H2O permeates through the membranes at least 10^10 times faster than He). We
attribute these seemingly incompatible observations to a low-friction flow of a
monolayer of water through two dimensional capillaries formed by closely spaced
graphene sheets. Diffusion of other molecules is blocked by reversible
narrowing of the capillaries in low humidity and/or by their clogging with
water
Administration of Insurance Rate Regulatory Laws
microRNAs (miRNAs) are key posttranscriptional regulators of gene expression. In the present study, regulation of tumor-suppressor gene D-glucuronyl C5-epimerase (GLCE) by miRNA-218 was investigated. Significant downregulation of miRNA-218 expression was shown in primary breast tumors. Exogenous miRNA-218/anti-miRNA-218 did not affect GLCE mRNA but regulated GLCE protein level in MCF7 breast carcinoma cells in vitro. Comparative analysis showed a positive correlation between miRNA-218 and GLCE mRNA, and negative correlation between miRNA-218 and GLCE protein levels in breast tissues and primary tumors in vivo, supporting a direct involvement of miRNA-218 in posttranscriptional regulation of GLCE in human breast tissue. A common scheme for the regulation of GLCE expression in normal and tumor breast tissues is suggested.Funding Agencies|Russian Foundation for Basic Research|11-04-90400-Ukr_f_a|Ukranian State Foundation of Fundamental Research|F40/146-2011F46/457-2011|Swedish Institute|2011/00888|UICC International Cancer Technology Transfer Fellowship|ICRETT-09-069|FEBS Short-term Fellowship||Karolinska Institute||Swedish Cancer Society||Swedish Research Council||</p
Precise and ultrafast molecular sieving through graphene oxide membranes
There has been intense interest in filtration and separation properties of
graphene-based materials that can have well-defined nanometer pores and exhibit
low frictional water flow inside them. Here we investigate molecular permeation
through graphene oxide laminates. They are vacuum-tight in the dry state but,
if immersed in water, act as molecular sieves blocking all solutes with
hydrated radii larger than 4.5A. Smaller ions permeate through the membranes
with little impedance, many orders of magnitude faster than the diffusion
mechanism can account for. We explain this behavior by a network of
nanocapillaries that open up in the hydrated state and accept only species that
fit in. The ultrafast separation of small salts is attributed to an 'ion
sponge' effect that results in highly concentrated salt solutions inside
graphene capillaries
Superconductivity in Ca-doped graphene
Graphene, a zero-gap semimetal, can be transformed into a metallic,
semiconducting or insulating state by either physical or chemical modification.
Superconductivity is conspicuously missing among these states despite
considerable experimental efforts as well as many theoretical proposals. Here,
we report superconductivity in calcium-decorated graphene achieved by
intercalation of graphene laminates that consist of well separated and
electronically decoupled graphene crystals. In contrast to intercalated
graphite, we find that Ca is the only dopant that induces superconductivity in
graphene laminates above 1.8 K among intercalants used in our experiments such
as potassium, caesium and lithium. Ca-decorated graphene becomes
superconducting at ~ 6 K and the transition temperature is found to be strongly
dependent on the confinement of the Ca layer and the induced charge carrier
concentration. In addition to the first evidence for superconducting graphene,
our work shows a possibility of inducing and studying superconductivity in
other 2D materials using their laminates
Revealing common artifacts due to ferromagnetic inclusions in highly-oriented pyrolytic graphite
We report on an extensive investigation to figure out the origin of
room-temperature ferromagnetism that is commonly observed by SQUID magnetometry
in highly-oriented pyrolytic graphite (HOPG). Electron backscattering and X-ray
microanalysis revealed the presence of micron-size magnetic clusters
(predominantly Fe) that are rare and would be difficult to detect without
careful search in a scanning electron microscope in the backscattering mode.
The clusters pin to crystal boundaries and their quantities match the amplitude
of typical ferromagnetic signals. No ferromagnetic response is detected in
samples where we could not find such magnetic inclusions. Our experiments show
that the frequently reported ferromagnetism in pristine HOPG is most likely to
originate from contamination with Fe-rich inclusions introduced presumably
during crystal growth.Comment: 8 pages, 7 figure
Vortex patterns in a superconducting-ferromagnetic rod
A superconducting rod with a magnetic moment on top develops vortices
obtained here through 3D calculations of the Ginzburg-Landau theory. The
inhomogeneity of the applied field brings new properties to the vortex patterns
that vary according to the rod thickness. We find that for thin rods (disks)
the vortex patterns are similar to those obtained in presence of a homogeneous
magnetic field instead because they consist of giant vortex states. For thick
rods novel patterns are obtained as vortices are curve lines in space that exit
through the lateral surface.Comment: 4 pages, 4 figues, Proceeding of the Sixth International Conference
in School Format on Vortex Matter in Nanostructured Superconductors (VORTEX
VI
On resonant scatterers as a factor limiting carrier mobility in graphene
We show that graphene deposited on a substrate has a non-negligible density
of atomic scale defects. This is evidenced by a previously unnoticed D peak in
the Raman spectra with intensity of about 1% with respect to the G peak. We
evaluated the effect of such impurities on electron transport by mimicking them
with hydrogen adsorbates and measuring the induced changes in both mobility and
Raman intensity. If the intervalley scatterers responsible for the D peak are
monovalent, their concentration is sufficient to account for the limited
mobilities achievable in graphene on a substrate.Comment: version 2: several comments are taken into account and refs adde
Formation of Professional Language Competence of Foreign Students in the Process of Teaching Architectural and Urban Terminology in the Lessons of Russian Language
Techniques and methods of teaching architectural and town-planning terminology at the lessons of Russian as a foreign language is presented. The authors believe that, despite the large number of works devoted to the problem of terminology, the field of architectural terminology and the language of architecture is not sufficiently studied. The article summarizes the experience of teachers of Russian Language Department of Novosibirsk state University of Architecture and Construction (sibstrin), where pedagogical techniques have been developed for many years, and textbooks and teaching materials on the formation of communicative competences in the field of professional communication for foreign students of different levels of education are published. This article examines and analyzes the complex terminological system of sub-language of architecture and urban planning. Methods of teaching foreign students of architectural direction of special vocabulary of the studied disciplines is proposed. Proposed is the model of education, which involves the acquaintance of foreign students with architectural and urban planning terms, taking into account their form, semantics and peculiarities of functioning in the scientific text. Classification of architectural and urban planning terms is presented. Productive types of tasks for independent work of foreign students are considered. The expediency of drawing up educational thematic mini-dictionaries of basic terms on the main studied disciplines is proved
- …