5,570 research outputs found
Spatial effects of Fano resonance in local tunneling conductivity in vicinity of impurity on semiconductor surface
We present the results of local tunneling conductivity spatial distribution
detailed theoretical investigations in vicinity of impurity atom for a wide
range of applied bias voltage. We observed Fano resonance in tunneling
conductivity resulting from interference between resonant tunneling channel
through impurity energy level and direct tunneling channel between the
tunneling contact leads. We have found that interference between tunneling
channels strongly modifies form of tunneling conductivity measured by the
scanning tunneling microscopy/spectroscopy (STM/STS) depending on the distance
value from the impurity.Comment: 4 pages, 3 figure
Quantum Spin Hall Insulator State in HgTe Quantum Wells
Recent theory predicted that the Quantum Spin Hall Effect, a fundamentally
novel quantum state of matter that exists at zero external magnetic field, may
be realized in HgTe/(Hg,Cd)Te quantum wells. We have fabricated such sample
structures with low density and high mobility in which we can tune, through an
external gate voltage, the carrier conduction from n-type to the p-type,
passing through an insulating regime. For thin quantum wells with well width d
< 6.3 nm, the insulating regime shows the conventional behavior of vanishingly
small conductance at low temperature. However, for thicker quantum wells (d >
6.3 nm), the nominally insulating regime shows a plateau of residual
conductance close to 2e^2/h. The residual conductance is independent of the
sample width, indicating that it is caused by edge states. Furthermore, the
residual conductance is destroyed by a small external magnetic field. The
quantum phase transition at the critical thickness, d = 6.3 nm, is also
independently determined from the magnetic field induced insulator to metal
transition. These observations provide experimental evidence of the quantum
spin Hall effect.Comment: 16 pages, 5 figure
Estimating novel potential drug targets of Plasmodium falciparum by analysing the metabolic network of knock-out strains in silico
Malaria is one of the world’s most common and serious diseases causing death of about 3 million people
each year. Its most severe occurrence is caused by the protozoan Plasmodium falciparum. Biomedical
research could enable treating the disease by effectively and specifically targeting essential enzymes of
this parasite. However, the parasite has developed resistance to existing drugsmaking it indispensable to
discover new drugs. We have established a simple computational tool which analyses the topology of the
metabolic network of P. falciparum to identify essential enzymes as possible drug targets.Weinvestigated
the essentiality of a reaction in the metabolic network by deleting (knocking-out) such a reaction in silico.
The algorithmselected neighbouring compounds of the investigated reaction that had to be produced by
alternative biochemical pathways. Using breadth first searches, we tested qualitatively if these products
could be generated by reactions that serve as potential deviations of the metabolic flux. With this we
identified 70 essential reactions. Our results were compared with a comprehensive list of 38 targets of
approved malaria drugs. When combining our approach with an in silico analysis performed recently
[Yeh, I., Hanekamp, T., Tsoka, S., Karp, P.D., Altman, R.B., 2004. Computational analysis of Plasmodium
falciparum metabolism: organizing genomic information to facilitate drug discovery. Genome Res. 14,
917–924] we could improve the precision of the prediction results. Finally we present a refined list of 22
new potential candidate targets for P. falciparum, half of which have reasonable evidence to be valid
targets against micro-organisms and cancer
Fiber-optical analogue of the event horizon
The physics at the event horizon resembles the behavior of waves in moving
media. Horizons are formed where the local speed of the medium exceeds the wave
velocity. We use ultrashort pulses in microstructured optical fibers to
demonstrate the formation of an artificial event horizon in optics. We observed
a classical optical effect, the blue-shifting of light at a white-hole horizon.
We also show by theoretical calculations that such a system is capable of
probing the quantum effects of horizons, in particular Hawking radiation.Comment: MEDIA EMBARGO. This paper is subject to the media embargo of Scienc
Enzyme-immobilized hydrogels to create hypoxia for in vitro cancer cell culture
Hypoxia is a critical condition governing many aspects of cellular fate processes. The most common practice in hypoxic cell culture is to maintain cells in an incubator with controlled gas inlet (i.e., hypoxic chamber). Here, we describe the design and characterization of enzyme-immobilized hydrogels to create solution hypoxia under ambient conditions for in vitro cancer cell culture. Specifically, glucose oxidase (GOX) was acrylated and co-polymerized with poly(ethylene glycol)-diacrylate (PEGDA) through photopolymerization to form GOX-immobilized PEG-based hydrogels. We first evaluated the effect of soluble GOX on inducing solution hypoxia (O2 < 5%) and found that both unmodified and acrylated GOX could sustain hypoxia for at least 24 h even under ambient air condition with constant oxygen diffusion from the air-liquid interface. However, soluble GOX gradually lost its ability to sustain hypoxia after 24 h due to the loss of enzyme activity over time. On the other hand, GOX-immobilized hydrogels were able to create hypoxia within the hydrogel for at least 120 h, potentially due to enhanced protein stabilization by enzyme ‘PEGylation’ and immobilization. As a proof-of-concept, this GOX-immobilized hydrogel system was used to create hypoxia for in vitro culture of Molm14 (acute myeloid leukemia (AML) cell line) and Huh7 (hepatocellular carcinoma (HCC) cell line). Cells cultured in the presence of GOX-immobilized hydrogels remained viable for at least 24 h. The expression of hypoxia associated genes, including carbonic anhydrase 9 (CA9) and lysyl oxidase (LOX), were significantly upregulated in cells cultured with GOX-immobilized hydrogels. These results have demonstrated the potential of using enzyme-immobilized hydrogels to create hypoxic environment for in vitro cancer cell culture
A new approach for improving coronary plaque component analysis based on intravascular ultrasound images
Virtual histology intravascular ultrasound (VH-IVUS) is a clinically available technique for atherosclerosis plaque characterization. It, however, suffers from a poor longitudinal resolution due to electrocardiogram (ECG)-gated acquisition. This article presents an effective algorithm for IVUS image-based histology to overcome this limitation. After plaque area extraction within an input IVUS image, a textural analysis procedure consisting of feature extraction and classification steps is proposed. The pixels of the extracted plaque area excluding the shadow region were classified into one of the three plaque components of fibro-fatty (FF), calcification (CA) or necrotic core (NC) tissues. The average classification accuracy for pixel and region based validations is 75% and 87% respectively. Sensitivities (specificities) were 79% (85%) for CA, 81% (90%) for FF and 52% (82%) for NC. The kappa (kappa) = 0.61 and p value = 0.02 indicate good agreement of the proposed method with VH images. Finally, the enhancement in the longitudinal resolution was evaluated by reconstructing the IVUS images between the two sequential IVUS-VH images
Conductance plateau in quantum spin transport through an interacting quantum dot
Quantum spin transport is studied in an interacting quantum dot. It is found
that a conductance "plateau" emerges in the non-linear charge conductance by a
spin bias in the Kondo regime. The conductance plateau, as a complementary to
the Kondo peak, originates from the strong electron correlation and exchange
processes in the quantum dot, and can be regarded as one of the characteristics
in quantum spin transport.Comment: 5 pages, 5 figure
An in silico Approach to Detect Efficient Malaria Drug Targets to Combat the Malaria Resistance Problem
Resistance to malaria drugs is a major challenging problem in most parts of the world especially in the African continent where about ninety per cent of malaria cases occur. As a response to this alarming problem, the World Health Organisation (W.H.O) recommends that all countries experiencing resistance to conventional monotherapies, such as chloroquine, amodiaquine or sulfadoxine–pyrimethamine, should use combination therapies [1]. Therefore there is a need to discover new drug targets that are able to target the malarial parasite at distinct pathways for an efficient malaria drug. In this paper, we presented a machine-learning tool which is able to identify novel drug targets from the metabolic network of Plasmodium falciparum. With our tool we identified among others 19 drug targets confirmed from literature which we analyzed further with a sophisticated gene expression analysis tool. Our data was clustered using common distance similarity measurements and hierarchical clustering to propose a profound combination of drug targets. Our result suggests that two or more enzymatic reactions from the list of our drug targets which span across about ten pathways (Table 2) could be combined to target at distinct time points in the parasite's intraerythrocytic developmental cycle to detect efficient malaria drug target combination
Exploring the environment, magnetic fields, and feedback effects of massive high-redshift galaxies with [CII]
Massive galaxies are expected to grow through different transformative
evolutionary phases where high-redshift starburst galaxies and quasars are
examples of such phases. The physical mechanisms driving these phases include
companion galaxy interactions, active galactic nuclei feedback, and magnetic
fields. Our aim is to characterize the physical properties and the environment
of the submillimeter galaxy AzTEC-3 at z = 5.3 and the lensed quasar BRI
0952-0115 at z = 4.4, to set a limit on the polarization properties, as well as
placing both in the broader context of galaxy evolution. We used full
polarization, sub-arcsecond-resolution, ALMA band-7 observations of both BRI
0952-0115 and AzTEC-3 and detect [CII] line emission towards both galaxies,
along with companions in each field. We present an updated gravitational
lensing model for BRI 0952-0115. We present infrared luminosities,
star-formation rates, and [CII] line to infrared luminosity ratios for each
source. The [CII] emission line profile for both BRI 0952-0115 and AzTEC-3
exhibit a broad, complex morphology, indicating the possible presence of
outflows. We present evidence of a 'gas bridge' between AzTEC-3 and a companion
source. Using a simple dynamical mass estimate for the sources, we suggest that
both systems are undergoing minor or major mergers. No polarization is detected
for the [CII], placing an upper limit below that of theoretical predictions.
Our results show that high-velocity wings are detected, indicating possible
signs of massive outflows; however, the presence of companion galaxies can
affect the final interpretation. Furthermore, the results provide additional
evidence in support of the hypothesis that massive galaxies form in overdense
regions, growing through interactions. Finally, strong, ordered magnetic fields
are unlikely to exist at the kiloparsec scale in the two studied sources
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