8,622 research outputs found
FMR Study of Co/Ti Bilayer Thin Films
. We focused on the interaction between two ferromagnetic cobalt layers
through a non-magnetic titanium layer. The magnetic properties of the structure
were characterized by ferromagnetic resonance technique (FMR). The data were
collected as a function of non-magnetic titanium layer thickness. Co/Ti
multilayer (Ti (50 {\AA})/Co(45 {\AA})/Ti(2-40 {\AA})/Co(40 {\AA})/Ti(100
{\AA}))films were grown onto naturally oxidized p-type single crystal Si (100)
substrate at UHV condition with magnetron sputtering system at room
temperature. The thickness of Ti spacer layer ranges from 2 to 40 {\AA} with 2
{\AA} steps. We did not observe usual optic and acoustic modes; instead we had
two broad overlapped peaks for the films ranged from 6 {\AA} to 40 {\AA}. One
interesting result was the high anisotropic resonance field values for these
films. Exchange coupling between ferromagnetic layers causes shift on resonance
field values but these shifts in our samples were much larger than expected.
This large anisotropic behavior is not clear at the moment. Our theoretical
model was not able to determine a value for the exchange coupling parameter.
One reason can be the close thickness values for Co sublayers. The other reason
can be the Ti non-magnetic layer. If titanium did not grow layer by layer on
cobalt, the cobalt ferromagnetic layers may behave as a single layer. As a
result one cannot observe exchange interaction between ferromagnetic layers
through non-magnetic spacer.Comment: 6 pages, 5 figure
Discrete Cutting Force Model for 5-Axis Milling with Arbitrary Engagement and Feed Direction
5-axis machining operations bring new challenges for predicting cutting forces. Complex tool workpiece engagements and tool orientations make it difficult to adapt 3-axis process models for 5-axis operations. A new model is developed to predict cutting forces with arbitrary tool/workpiece engagement and tool feed direction. A discretization approach is used, in which the tool is composed of multiple cutting elements. Each element is processed to determine its effect on cutting forces, and global forces are determined by combining the elemental effects. Cutting tests are conducted to verify force predictions, where the tool/workpiece engagement is provided through a geometric software application
Homozygosity at variant MLH1 can lead to secondary mutation in NF1, neurofibromatosis type I and early onset leukemia
Cataloged from PDF version of article.Heterozygous germ-line variants of DNA mismatch repair (MMR) genes predispose individuals to hereditary non-polyposis colorectal cancer. Several independent reports have shown that individuals constitutionally homozygous for MMR allelic variants develop early onset hematological malignancies often associated to features of neurofibromatosis type 1 (NF1) syndrome. The genetic mechanism of NF1 associated to MMR gene deficiency is not fully known. We report here that a child with this form of NF1 displays a heterozygous NF1 gene mutation (c.3721C > T), in addition to a homozygous MLH1 gene mutation (c.676C > T) leading to a truncated MLH1 protein (p.R226X). The parents did not display NF1 features nor the NF1 mutation. This new NF1 gene mutation is recurrent and predicts a truncated neurofibromin (p.R1241X) lacking its GTPase activating function, as well as all C-terminally located functional domains. Our findings suggest that NF1 disease observed in individuals homozygous for deleterious MMR variants may be due to a concomitant NF1 gene mutation. The presence of both homozygous MLH1 and heterozygous NF1 mutation in the child studied here also provides a mechanistic explanation for early onset malignancies that are observed in affected individuals. It also provides a model for cooperation between genetic alterations in human carcinogenesis. © 2007 Elsevier B.V. All rights reserved
The central dogma of biological homochirality: How does chiral information propagate in a prebiotic network?
Biological systems are homochiral, raising the question of how a racemic
mixture of prebiotically synthesized biomolecules could attain a homochiral
state at the network level. Based on our recent results, we aim to address a
related question of how chiral information might have flowed in a prebiotic
network. Utilizing the crystallization properties of the central RNA precursor
known as ribose-aminooxazoline (RAO), we showed that its homochiral crystals
can be obtained from its fully racemic solution on a magnetic mineral surface,
due to the chiral-induced spin selectivity (CISS) effect. Moreover, we
uncovered a mechanism facilitated by the CISS effect through which chiral
molecules, like RAO, can uniformly magnetize such surfaces in a variety of
planetary environments in a persistent manner. All this is very tantalizing,
because recent experiments with tRNA analogs demonstrate high stereoselectivity
in the attachment of L-amino acids to D-ribonucleotides, enabling the transfer
of homochirality from RNA to peptides. Therefore the biological homochirality
problem may be reduced to ensuring that a single common RNA precursor (e.g.
RAO) can be made homochiral. The emergence of homochirality at RAO then allows
for the chiral information to propagate through RNA, then to peptides, and
ultimately, through enantioselective catalysis, to metabolites. This
directionality of the chiral information flow parallels that of the central
dogma of molecular biology--the unidirectional transfer of genetic information
from nucleic acids to proteins.Comment: 8 pages, 4 figure
Application-Specific Heterogeneous Network-on-Chip Design
Cataloged from PDF version of article.As a result of increasing communication demands, application-specific and scalable Network-on-Chips (NoCs) have emerged to connect processing cores and subsystems in Multiprocessor System-on-Chips. A challenge in application-specific NoC design is to find the right balance among different tradeoffs, such as communication latency, power consumption and chip area. We propose a novel approach that generates latency-aware heterogeneous NoC topology. Experimental results show that our approach improves the total communication latency up to 27% with modest power consumption. © 2013 The Author 2013. Published by Oxford University Press on behalf of The British Computer Society
Photoelectron Diffraction Determination of the Structure of Ultrathin Vanadium Films on Cu(001)
X-ray photoelectron diffraction (XPD) and low-energy electron diffraction (LEED) have been used to study the structural properties of V thin films on Cu(001). For room-temperature growth, submonolayer coverages result in (1x1) LEED patterns that evolve to exhibit very diffuse (2x1) structure at approximately 1 monolayer coverage. We do not observe any V forward-focusing enhancements for V films that exhibit either the (1x1) or (2x1) structure, suggesting that these structures are limited to the first 1-2 vanadium layers. At coverages above 1 monolayer, the V films display complex LEED patterns characteristic of four bcc(110) domains. This structure persists to V coverages as high as 100 ML, and the LEED and XPD angular scans suggest that V in these films retain the bulk V lattice constant. These results have important ramifications for predictions of magnetic order in vanadium thin films that typically assume pseudomorphic growth
Work holding assessment of an UV adhesive and fixture design method
Adhesive work holding can be used to minimize clamping distortion and provide greater access to a work piece during machining. This paper proposes shear and tensile strength criteria to evaluate the work holding strength of adhesive grippers and definition of a strength safety coefficient of adhesive grippers. It also demonstrates a case study of work holding design with an UV adhesive for a grinding process based on a strength criteria explained in the paper. A test rig has been designed and manufactured to assess the capability of an adhesive work holding material. Tests include measurement of strength and repeatability of adhesion under different film thicknesses, curing times and pre-cleaning methods. The test shows the strength repeatability is less than ± 20%, which is good enough for many work holding applications. A shear-tensile combined strength can be evaluated by the strength sphere in a fixture design of a specific part geometry for production by the combined safety coefficient. Following the test rig assessment, a fixture has been designed with 3 grippers to demonstrate the adhesive for a grinding process with a simple part geometry. The method has a high potential for application in industry, and is not limited to the given part geometry and machining method. The grinding test shows that the adhesive work holding is strong enough for the application and that similar results can be expected for milling and turning with a good gripper arrangement
Heterogeneous network-on-chip design through evolutionary computing
This article explores the use of biologically inspired evolutionary computational techniques for designing and optimising heterogeneous network-on-chip (NoC) architectures, where the nodes of the NoC-based chip multiprocessor exhibit different properties such as performance, energy, temperature, area and communication bandwidth. Focusing primarily on array-dominated applications and heterogeneous execution environments, the proposed approach tries to optimise the distribution of the nodes for a given NoC area under the constraints present in the environment. This article is the first one, to our knowledge, that explores the possibility of employing evolutionary computational techniques for optimally placing the heterogeneous nodes in an NoC. We also compare our approach with an optimal integer linear programming (ILP) approach using a commercial ILP tool. The results collected so far are very encouraging and indicate that the proposed approach generates close results to the ILP-based approach with minimal execution latencies. © 2010 Taylor & Francis
Reducing Satellite Interference to Radio Telescopes Using Beacons
This paper proposes the transmission of beacon signals to alert potential
interferers of an ongoing or impending passive sensing measurement. We focus on
the interference from Low-Earth Orbiting (LEO) satellites to a radio-telescope.
We compare the beacon approach with two versions of Radio Quiet Zones (RQZs):
fixed quiet zones on the ground and in the sky, and dynamic quiet zones that
vary across satellites. The beacon-assisted approach can potentially exploit
channel reciprocity, which accounts for short-term channel variations between
the satellite and radio telescope. System considerations associated with beacon
design and potential schemes for beacon transmission are discussed. The
probability of excessive Radio Frequency Interference (RFI) at the radio
telescope (outage probability) and the fraction of active links in the
satellite network are used as performance metrics. Numerical simulations
compare the performance of the approaches considered, and show that the beacon
approach enables more active satellite links relative to quiet zones for a
given outage probability
Metalorganic chemical vapor deposition growth and thermal stability of the AllNN/GaN high electron mobility transistor structure
Cataloged from PDF version of article.The AlxIn1-xN barrier high electron mobility transistor (HEMT) structure has been optimized with varied barrier composition and thickness grown by metalorganic chemical vapor deposition. After optimization, a transistor structure comprising a 7 nm thick nearly lattice-matched Al0.83In0.17 N barrier exhibits a sheet electron density of 2.0 x 10(13) cm(-2) with a high electron mobility of 1540 cm(2) V-1 s(-1). AnAl(0.83)In(0.17)N barrier HEMT device with 1 mu m gate length provides a current density of 1.0 A mm(-1) at V-GS = 0 V and an extrinsic transconductance of 242 mS mm(-1), which are remarkably improved compared to that of a conventional Al0.3Ga0.7N barrier HEMT. To investigate the thermal stability of the HEMT epi-structures, post-growth annealing experiments up to 800 degrees C have been applied to Al0.83In0.17N and Al0.3Ga0.7N barrier heterostructures. As expected, the electrical properties of an Al0.83In0.17N barrier HEMT structure showed less stability than that of an Al0.3Ga0.7N barrier HEMT to the thermal annealing. The structural properties of Al0.83In0.17N/GaN also showed more evidence for decomposition than that of the Al0.3Ga0.7N/GaN structure after 800 degrees C post-annealing
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