182 research outputs found
Substrate-induced band gap opening in epitaxial graphene
Graphene has shown great application potentials as the host material for next
generation electronic devices. However, despite its intriguing properties, one
of the biggest hurdles for graphene to be useful as an electronic material is
its lacking of an energy gap in the electronic spectra. This, for example,
prevents the use of graphene in making transistors. Although several proposals
have been made to open a gap in graphene's electronic spectra, they all require
complex engineering of the graphene layer. Here we show that when graphene is
epitaxially grown on the SiC substrate, a gap of ~ 0.26 is produced. This gap
decreases as the sample thickness increases and eventually approaches zero when
the number of layers exceeds four. We propose that the origin of this gap is
the breaking of sublattice symmetry owing to the graphene-substrate
interaction. We believe our results highlight a promising direction for band
gap engineering of graphene.Comment: 10 pages, 4 figures; updated reference
Origin of the energy bandgap in epitaxial graphene
We studied the effect of quantum confinement on the size of the band gap in
single layer epitaxial graphene. Samples with different graphene terrace sizes
are studied by using low energy electron microscopy (LEEM) and angle-resolved
photoemission spectroscopy (ARPES). The direct correlation between the terrace
size extracted from LEEM and the gap size extracted from ARPES shows that
quantum confinement alone cannot account for the large gap observed in
epitaxial graphene samples
Feedback in laparoscopic skills acquisition: an observational study during a basic skills training course
This study aimed to obtain insight in the effect of expert feedback during a basic laparoscopic skills training course for residents. A questionnaire was held among participants regarding provided feedback and the self-perceived laparoscopic skills improvement. The participants (n = 24) who completed the questionnaire were in their first to fifth postgraduate year. Most feedback was directed at intracorporeal knot tying (47% reported extensive feedback), while camera navigation and body positioning received the least feedback (40% and 43%, respectively, responded to have received no feedback at all). After the course, the self-perceived competence in intracorporeal knot tying and cutting had improved significantly, while camera navigation, body positioning, pointing, and grasping tasks did not improve. In conclusion, most benefit from expert feedback can be obtained at the start of the learning curve. Therefore, the basic laparoscopic skills course should be attended early in residency. Additionally, it is crucial that training objectives are clear prior to a course for both the expert and the trainee, in order to focus the feedback on all training objectives
Estimation of urinary stone composition by automated processing of CT images
The objective of this article was developing an automated tool for routine
clinical practice to estimate urinary stone composition from CT images based on
the density of all constituent voxels. A total of 118 stones for which the
composition had been determined by infrared spectroscopy were placed in a
helical CT scanner. A standard acquisition, low-dose and high-dose acquisitions
were performed. All voxels constituting each stone were automatically selected.
A dissimilarity index evaluating variations of density around each voxel was
created in order to minimize partial volume effects: stone composition was
established on the basis of voxel density of homogeneous zones. Stone
composition was determined in 52% of cases. Sensitivities for each compound
were: uric acid: 65%, struvite: 19%, cystine: 78%, carbapatite: 33.5%, calcium
oxalate dihydrate: 57%, calcium oxalate monohydrate: 66.5%, brushite: 75%.
Low-dose acquisition did not lower the performances (P < 0.05). This entirely
automated approach eliminates manual intervention on the images by the
radiologist while providing identical performances including for low-dose
protocols
Influences of Excluded Volume of Molecules on Signaling Processes on Biomembrane
We investigate the influences of the excluded volume of molecules on
biochemical reaction processes on 2-dimensional surfaces using a model of
signal transduction processes on biomembranes. We perform simulations of the
2-dimensional cell-based model, which describes the reactions and diffusion of
the receptors, signaling proteins, target proteins, and crowders on the cell
membrane. The signaling proteins are activated by receptors, and these
activated signaling proteins activate target proteins that bind autonomously
from the cytoplasm to the membrane, and unbind from the membrane if activated.
If the target proteins bind frequently, the volume fraction of molecules on the
membrane becomes so large that the excluded volume of the molecules for the
reaction and diffusion dynamics cannot be negligible. We find that such
excluded volume effects of the molecules induce non-trivial variations of the
signal flow, defined as the activation frequency of target proteins, as
follows. With an increase in the binding rate of target proteins, the signal
flow varies by i) monotonically increasing; ii) increasing then decreasing in a
bell-shaped curve; or iii) increasing, decreasing, then increasing in an
S-shaped curve. We further demonstrate that the excluded volume of molecules
influences the hierarchical molecular distributions throughout the reaction
processes. In particular, when the system exhibits a large signal flow, the
signaling proteins tend to surround the receptors to form receptor-signaling
protein clusters, and the target proteins tend to become distributed around
such clusters. To explain these phenomena, we analyze the stochastic model of
the local motions of molecules around the receptor.Comment: 31 pages, 10 figure
Alternating electric fields (TTFields) inhibit metastatic spread of solid tumors to the lungs
Tumor treating fields (TTFields) are low intensity, intermediate frequency, alternating electric fields used to treat cancerous tumors. This novel treatment modality effectively inhibits the growth of solid tumors in vivo and has shown promise in pilot clinical trials in patients with advanced stage solid tumors. TTFields were tested for their potential to inhibit metastatic spread of solid tumors to the lungs in two animal models: (1) Mice injected with malignant melanoma cells (B16F10) into the tail vein, (2) New Zealand White rabbits implanted with VX-2 tumors within the kidney capsule. Mice and rabbits were treated using two-directional TTFields at 100–200 kHz. Animals were either monitored for survival, or sacrificed for pathological and histological analysis of the lungs. The total number of lung surface metastases and the absolute weight of the lungs were both significantly lower in TTFields treated mice then in sham control mice. TTFields treated rabbits survived longer than sham control animals. This extension in survival was found to be due to an inhibition of metastatic spread, seeding or growth in the lungs of TTFields treated rabbits compared to controls. Histologically, extensive peri- and intra-tumoral immune cell infiltration was seen in TTFields treated rabbits only. These results raise the possibility that in addition to their proven inhibitory effect on the growth of solid tumors, TTFields may also have clinical benefit in the prevention of metastatic spread from primary tumors
Tumour suppressor microRNA-584 directly targets oncogene Rock-1 and decreases invasion ability in human clear cell renal cell carcinoma
BackgroundThe purpose of this study was to identify new tumour suppressor microRNAs (miRs) in clear cell renal cell carcinoma (ccRCC), carry out functional analysis of their suppressive role and identify their specific target genes.MethodsTo explore suppressor miRs in RCC, miR microarray and real-time PCR were performed using HK-2 and A-498 cells. Cell viability, invasion and wound healing assays were carried out for functional analysis after miR transfection. To determine target genes of miR, we used messenger RNA (mRNA) microarray and target scan algorithms to identify target oncogenes. A 3'UTR luciferase assay was also performed. Protein expression of target genes in ccRCC tissues was confirmed by immunohistochemistry and was compared with miR-584 expression in ccRCC tissues.ResultsExpression of miR-584 in RCC (A-498 and 769-P) cells was downregulated compared with HK-2 cells. Transfection of miR-584 dramatically decreased cell motility. The ROCK-1 mRNA was inhibited by miR-584 and predicted to be target gene. The miR-584 decreased 3'UTR luciferase activity of ROCK-1 and ROCK-1 protein expression. Low expression of miR-584 in ccRCC tissues was correlated with high expression of ROCK-1 protein. The knockdown of ROCK-1 by siRNA inhibited cell motility.ConclusionmiR-584 is a new tumour suppressor miR in ccRCC and inhibits cell motility through downregulation of ROCK-1
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