562 research outputs found
Additional Evidence for the Surface Origin of the Peculiar Angular-Dependent Magnetoresistance Oscillations Discovered in a Topological Insulator Bi_{1-x}Sb_{x}
We present detailed data on the unusual angular-dependent magnetoresistance
oscillation phenomenon recently discovered in a topological insulator
Bi_{0.91}Sb_{0.09}. Direct comparison of the data taken before and after
etching the sample surface gives compelling evidence that this phenomenon is
essentially originating from a surface state. The symmetry of the oscillations
suggests that it probably comes from the (111) plane, and obviously a new
mechanism, such as a coupling between the surface and the bulk states, is
responsible for this intriguing phenomenon in topological insulators.Comment: 5 pages, 4 figures, Proceedings manuscript for the 19th International
Conference on the Application of High Magnetic Fields in Semiconductor
Physics and Nanotechnology (HMF-19
Origin of the large thermoelectric power in oxygen-variable RBaCo_{2}O_{5+x} (R=Gd, Nd)
Thermoelectric properties of GdBaCo_{2}O_{5+x} and NdBaCo_{2}O_{5+x} single
crystals have been studied upon continuous doping of CoO_2 planes with either
electrons or holes. The thermoelectric response and the resistivity behavior
reveal a hopping character of the transport in both compounds, providing the
basis for understanding the recently found remarkable divergence of the Seebeck
coefficient at x=0.5. The doping dependence of the thermoelectric power evinces
that the configurational entropy of charge carriers, enhanced by their spin and
orbital degeneracy, plays a key role in the origin of the large thermoelectric
response in these correlated oxides.Comment: 5 pages, 4 figures, accepted for publication in PR
Mobile Broadband Possibilities considering the Arrival of IEEE 802.16m & LTE with an Emphasis on South Asia
This paper intends to look deeper into finding an ideal mobile broadband
solution. Special stress has been put in the South Asian region through some
comparative analysis. Proving their competency in numerous aspects, WiMAX and
LTE already have already made a strong position in telecommunication industry.
Both WiMAX and LTE are 4G technologies designed to move data rather than voice
having IP networks based on OFDM technology. So, they aren't like typical
technological rivals as of GSM and CDMA. But still a gesture of hostility seems
to outburst long before the stable commercial launch of LTE. In this paper
various aspects of WiMAX and LTE for deployment have been analyzed. Again, we
tried to make every possible consideration with respect to south Asia i.e. how
mass people of this region may be benefited. As a result, it might be regarded
as a good source in case of making major BWA deployment decisions in this
region. Besides these, it also opens the path for further research and in depth
thinking in this issue.Comment: IEEE Publication format, ISSN 1947 5500,
http://sites.google.com/site/ijcsis
The effects of leptin on F-actin remodelling in type 1 diabetes
Background: The aim of the current study is to investigate the effect of leptin on cytoskeleton structures in both in vivo and in vitro model of diabetes.
Materials and methods: For in vivo studies, leptin in different doses (240, and 480 mg/kg) was injected to the diabetic rats after 1-week of streptozotocin (STZ, 55 mg/kg) treatment. Leptin levels were analysed in serum, liver, and pancreas samples. Hepatic and pancreatic F- and G-actin expressions were determined by Western blotting. For in vitro studies, hepatic and pancreatic primary cell lines were obtained from the control rats. To these cultures, STZ (15 and 30 mM), leptin (50, 60 and 100 ng/mL), and their combinations were applied for 1, 3, and 4 weeks. After the treatment period, F-actin was visualised by the Alexa-fluor fluorescent dye.
Results: Streptozotocin decreased the G-actin in both tissues in vivo. However, leptin caused a dose-dependent increase in G-actin levels while F-actin decreased in both tissues. Moreover, leptin caused the perimembranous condensation of actin filaments and amelioration of F-actin structures in vivo. A dose-dependent corruption of F-actin filament structures was observed in leptin-treated primary cells in vitro, while STZ also caused corruption of these filaments. Co-exposure of STZ and leptin caused the amelioration of F-actin filaments, while the peri- membranous condensation was also observed as was in vivo study.
Conclusions: Leptin therapy could be a candidate for diabetes, but it should not be ruled out as being important the severity of diabetes and leptin doses.
Room-temperature ferromagnetism in Sr_(1-x)Y_xCoO_(3-delta) (0.2 < x < 0.25)
We have measured magnetic susceptibility and resistivity of
SrYCoO ( 0.1, 0.15, 0.2, 0.215, 0.225, 0.25, 0.3,
and 0.4), and have found that SrYCoO is a room
temperature ferromagnet with a Curie temperature of 335 K in a narrow
compositional range of 0.2 0.25. This is the highest transition
temperature among perovskite Co oxides. The saturation magnetization for
0.225 is 0.25 /Co at 10 K, which implies that the observed
ferromagnetism is a bulk effect. We attribute this ferromagnetism to a peculiar
Sr/Y ordering.Comment: 5 pages, 4 figure
Revealing puddles of electrons and holes in compensated topological insulators
Three-dimensional topological insulators harbour metallic surface states with
exotic properties. In transport or optics, these properties are typically
masked by defect-induced bulk carriers. Compensation of donors and acceptors
reduces the carrier density, but the bulk resistivity remains disappointingly
small. We show that measurements of the optical conductivity in BiSbTeSe
pinpoint the presence of electron-hole puddles in the bulk at low temperatures,
which is essential for understanding DC bulk transport. The puddles arise from
large fluctuations of the Coulomb potential of donors and acceptors, even in
the case of full compensation. Surprisingly, the number of carriers appearing
within puddles drops rapidly with increasing temperature and almost vanishes
around 40 K. Monte Carlo simulations show that a highly non-linear screening
effect arising from thermally activated carriers destroys the puddles at a
temperature scale set by the Coulomb interaction between neighbouring dopants,
explaining the experimental observation semi-quantitatively. This mechanism
remains valid if donors and acceptors do not compensate perfectly.Comment: 11 pages with 7 figures plus supplemental material (3 pages
Improved Approximation Algorithms for Segment Minimization in Intensity Modulated Radiation Therapy
he segment minimization problem consists of finding the smallest set of
integer matrices that sum to a given intensity matrix, such that each summand
has only one non-zero value, and the non-zeroes in each row are consecutive.
This has direct applications in intensity-modulated radiation therapy, an
effective form of cancer treatment. We develop three approximation algorithms
for matrices with arbitrarily many rows. Our first two algorithms improve the
approximation factor from the previous best of to (roughly) and , respectively, where is
the largest entry in the intensity matrix. We illustrate the limitations of the
specific approach used to obtain these two algorithms by proving a lower bound
of on the approximation
guarantee. Our third algorithm improves the approximation factor from to , where is (roughly) the largest
difference between consecutive elements of a row of the intensity matrix.
Finally, experimentation with these algorithms shows that they perform well
with respect to the optimum and outperform other approximation algorithms on
77% of the 122 test cases we consider, which include both real world and
synthetic data.Comment: 18 page
Observations of two-dimensional quantum oscillations and ambipolar transport in the topological insulator Bi2Se3 achieved by Cd doping
We present a defect-engineering strategy to optimize the transport properties
of the topological insulator Bi2Se3 to show a high bulk resistivity and clear
quantum oscillations. Starting with a p-type Bi2Se3 obtained by combining Cd
doping and a Se-rich crystal-growth condition, we were able to observe a
p-to-n-type conversion upon gradually increasing the Se vacancies by post
annealing. With the optimal annealing condition where a high level of
compensation is achieved, the resistivity exceeds 0.5 Ohmcm at 1.8 K and we
observed two-dimensional Shubnikov-de Haas oscillations composed of multiple
frequencies in magnetic fields below 14 T.Comment: 7 pages, 6 figure
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