2,447 research outputs found
Spin injection from a half-metal at finite temperatures
Spin injection from a half-metallic electrode in the presence of thermal spin
disorder is analyzed using a combination of random matrix theory,
spin-diffusion theory, and explicit simulations for the tight-binding s-d
model. It is shown that efficient spin injection from a half-metal is possible
as long as the effective resistance of the normal metal does not exceed a
characteristic value, which does not depend on the resistance of the
half-metallic electrode, but is rather controlled by spin-flip scattering at
the interface. This condition can be formulated as \alpha<(l/L)/T, where \alpha
is the relative deviation of the magnetization from saturation, l and L the
mean-free path and the spin-diffusion length in the non-magnetic channel, and T
the transparency of the tunnel barrier at the interface (if present). The
general conclusions are confirmed by tight-binding s-d model calculations. A
rough estimate suggests that efficient spin injection from true half-metallic
ferromagnets into silicon or copper may be possible at room temperature across
a transparent interface.Comment: 9 pages, 4 figures, revtex4-1; expanded introduction, added
references, additional comments in Section V, fixed typo
Closed-Form Derivations of ISI and MUI for Time-Reversed Ultra Wideband
Through transmitter pre-filtering, a time reversed UWB system is capable if harnessing a multipath channel to achieve temporal and spatial focusing. Unfortunately, large RMS channel delay spread leads to significant intersymbol and multiuser interference. This paper presents closed-form expressions for self and multi-user interference for a UWB system utilizing a time-reversed approach. The influence of user multiplexing codes is taken to account through incorporation of a ‘separation probability’, which characterizes a family of hopping sequences. The standardized IEEE 802.15.3a channel model is applied, and the derived performances are compared with that of a simulated time hopped time-reversed UWB system
Compactness results in Symplectic Field Theory
This is one in a series of papers devoted to the foundations of
Symplectic Field Theory sketched in [Y Eliashberg, A Givental and H
Hofer, Introduction to Symplectic Field Theory,
Geom. Funct. Anal. Special Volume, Part II (2000) 560--673]. We prove
compactness results for moduli spaces of holomorphic curves arising in
Symplectic Field Theory. The theorems generalize Gromov's compactness theorem
in [M Gromov, Pseudo-holomorphic curves in symplectic manifolds, Invent. Math.
82 (1985) 307--347] as well as compactness theorems in Floer homology theory,
[A Floer, The unregularized gradient flow of the symplectic action, Comm. Pure
Appl. Math. 41 (1988) 775--813 and Morse theory for Lagrangian intersections,
J. Diff. Geom. 28 (1988) 513--547], and in contact geometry, [H Hofer,
Pseudo-holomorphic curves and Weinstein conjecture in dimension three, Invent.
Math. 114 (1993) 307--347 and
H Hofer, K Wysocki and E Zehnder, Foliations of the Tight Three
Sphere, Annals of Mathematics, 157 (2003) 125--255].Comment: Published by Geometry and Topology at
http://www.maths.warwick.ac.uk/gt/GTVol7/paper25.abs.htm
First-principles analysis of spin-disorder resistivity of Fe and Ni
Spin-disorder resistivity of Fe and Ni and its temperature dependence are
analyzed using noncollinear density functional calculations within the
supercell method. Different models of thermal spin disorder are considered,
including the mean-field approximation and the nearest-neighbor Heisenberg
model. Spin-disorder resistivity is found to depend weakly on magnetic
short-range order. If the local moments are kept frozen at their
zero-temperature values, very good agreement with experiment is obtained for
Fe, but for Ni the resistivity at elevated temperatures is significantly
overestimated. Agreement with experiment for Fe is improved if the local
moments are iterated to self-consistency. The overestimation of the resistivity
for paramagnetic Ni is attributed to the reduction of the local moments down to
0.35 Bohr magnetons. Overall, the results suggest that low-energy spin
fluctuations in Fe and Ni are better viewed as classical rotations of local
moments rather than quantized spin fluctuations that would require an (S+1)/S
correction.Comment: 10 pages (RevTeX), 6 eps figure
Field Test of a Remote Multi-Path CLaDS Methane Sensor
Existing technologies for quantifying methane emissions are often limited to single point sensors, making large area environmental observations challenging. We demonstrate the operation of a remote, multi-path system using Chirped Laser Dispersion Spectroscopy (CLaDS) for quantification of atmospheric methane concentrations over extended areas, a technology that shows potential for monitoring emissions from wetlands
Adenoid cystic carcinoma: emerging role of translocations and gene fusions.
Adenoid cystic carcinoma (ACC), the second most common salivary gland malignancy, is notorious for poor prognosis, which reflects the propensity of ACC to progress to clinically advanced metastatic disease. Due to high long-term mortality and lack of effective systemic treatment, the slow-growing but aggressive ACC poses a particular challenge in head and neck oncology. Despite the advancements in cancer genomics, up until recently relatively few genetic alterations critical to the ACC development have been recognized. Although the specific chromosomal translocations resulting in MYB-NFIB fusions provide insight into the ACC pathogenesis and represent attractive diagnostic and therapeutic targets, their clinical significance is unclear, and a substantial subset of ACCs do not harbor the MYB-NFIB translocation. Strategies based on detection of newly described genetic events (such as MYB activating super-enhancer translocations and alterations affecting another member of MYB transcription factor family-MYBL1) offer new hope for improved risk assessment, therapeutic intervention and tumor surveillance. However, the impact of these approaches is still limited by an incomplete understanding of the ACC biology, and the manner by which these alterations initiate and drive ACC remains to be delineated. This manuscript summarizes the current status of gene fusions and other driver genetic alterations in ACC pathogenesis and discusses new therapeutic strategies stemming from the current research
Simulation Supported Estimation of End-to-End Transmission Parameters in Non-Viral Gene Delivery
Communications, in general, involve delivery of information from a source to a sink. At nano-scale, an example of a man-made communications involving interfacing with biological systems at intra-cellular level is non-viral gene delivery. From a telecommunications engineering perspective, important end-to-end parameters of such a system are: the endto- end delay, system capacity, and packet loss rate. There are neither known methods to estimate those parameters theoretically nor they are ready available from standard measurements. The paper provides estimates for those parameters based on the simulation of non-viral gene delivery system based on the queuing theory. The simulator used has been validated through the series of in-vitro laboratory experiments
Identifying Intracellular pDNA Losses From a Model of Nonviral Gene Delivery
Nonviral gene delivery systems are a type of nanocommunication system that transmit plasmid packets (i.e., pDNA packets) that are programmed at the nanoscale to biological systems at the microscopic cellular level. This engineered nanocommunication system suffers large pDNA losses during transmission of the genetically encoded information, preventing its use in biotechnological and medical applications. The pDNA losses largely remain uncharacterized, and the ramifications of reducing pDNA loss from newly designed gene delivery systems remain difficult to predict. Here, the pDNA losses during primary and secondary transmission chains were identified utilizing a MATLAB model employing queuing theory simulating delivery of pEGFPLuc transgene to HeLa cells carried by Lipofectamine 2000 nonviral DNA carrier. Minimizing pDNA loss during endosomal escape of the primary transmission process results in increased number of pDNA in the nucleus with increased transfection, but with increased probability of cell death. The number of pDNA copies in the nucleus and the amount of time the pDNAs are in the nucleus directly correlates to improved transfection efficiency. During secondary transmission, pDNAs are degraded during distribution to daughter cells. Reducing pDNA losses improves transfection, but a balance in quantity of nuclear pDNA, mitosis, and toxicity must be considered in order to achieve therapeutically relevant transfection levels
Calculations of spin-disorder resistivity from first principles
Spin-disorder resistivity of Fe and Ni is studied using the noncollinear
density functional theory. The Landauer conductance is averaged over random
disorder configurations and fitted to Ohm's law. The distribution function is
approximated by the mean-field theory. The dependence of spin-disorder
resistivity on magnetization in Fe is found to be in excellent agreement with
the results for the isotropic s-d model. In the fully disordered state,
spin-disorder resistivity for Fe is close to experiment, while for fcc Ni it
exceeds the experimental value by a factor of 2.3. This result indicates strong
magnetic short-range order in Ni at the Curie temperature.Comment: 3 pages, 3 figure
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