685 research outputs found
Physical-Layer Security: Combining Error Control Coding and Cryptography
In this paper we consider tandem error control coding and cryptography in the
setting of the {\em wiretap channel} due to Wyner. In a typical communications
system a cryptographic application is run at a layer above the physical layer
and assumes the channel is error free. However, in any real application the
channels for friendly users and passive eavesdroppers are not error free and
Wyner's wiretap model addresses this scenario. Using this model, we show the
security of a common cryptographic primitive, i.e. a keystream generator based
on linear feedback shift registers (LFSR), can be strengthened by exploiting
properties of the physical layer. A passive eavesdropper can be made to
experience greater difficulty in cracking an LFSR-based cryptographic system
insomuch that the computational complexity of discovering the secret key
increases by orders of magnitude, or is altogether infeasible. This result is
shown for two fast correlation attacks originally presented by Meier and
Staffelbach, in the context of channel errors due to the wiretap channel model.Comment: 12 pages, 5 figures. Submitted and accepted to the International
Conference on Communications (ICC) 2009. v2: equivalent to the version that
will be published in the conference proceedings. Has some altered notation
from version 1 as well as slight changes in the wording to make the paper
more readable and easier to understan
D=2 N=(2,2) Semi Chiral Vector Multiplet
We describe a new 1+1 dimensional N=(2,2) vector multiplet that naturally
couples to semi chiral superfields in the sense that the gauged supercovariant
derivative algebra is only consistent with imposing covariantly semi chiral
superfield constraints. It has the advantages that its prepotentials shift by
semi chiral superfields under gauge transformations. We also see that the
multiplet relates the chiral vector multiplet with the twisted chiral vector
multiplet by reducing to either multiplet under appropriate limits without
being reducible in terms of the chiral and twisted chiral vector multiplet.
This is explained from the superspace geometrical point of view as the result
of possessing a symmetry under the discrete supercoordinate transformation that
is responsible for mirror copies of supermultiplets. We then describe how to
gauge a non linear sigma model with semi chiral superfields using the
prepotentials of the new multiplet.Comment: 15 page
Extremely Sub-wavelength Planar Magnetic Metamaterials
We present highly sub-wavelength magnetic metamaterials designed for
operation at radio frequencies (RFs). A dual layer design consisting of
independent planar spiral elements enables experimental demonstration of a unit
cell size (a) that is ~ 700 times smaller than the resonant wavelength
({\lambda}0). Simulations indicate that utilization of a conductive via to
connect spiral layers permits further optimization and we achieve a unit cell
that is {\lambda}0/a ~ 2000. Magnetic metamaterials are characterized by a
novel time domain method which permits determination of the complex magnetic
response. Numerical simulations are performed to support experimental data and
we find excellent agreement. These new designs make metamaterial low frequency
experimental investigations practical and suggest their use for study of
magneto-inductive waves, levitation, and further enable potential RF
applications.Comment: 5 pages, 4 figure
Holographic interference lithography for integrated optics
In this paper, some of our recent work in the use of holographic interference lithography and various material removal techniques to corrugate thin-film optical waveguides are reviewed. The specific applications of these periodic thin-film devices in the distributed feedback and distributed Bragg reflector semiconductor laser, and as output grating couplers, are described. Recent results in the use and fabrication of chirped and curved-line gratings are also summarized
DYNAMIC ELUTRIATION MEASUREMENT IN A CONTINUOUSLY OPERATED BUBBLING FLUIDIZED BED
Measurements were performed using a novel thermal mass flow meter. The dynamic behaviour of the total elutriation rate was monitored from start-up until a steady rate was achieved. It was found that the elutriation rate at unsteady conditions can be as much as 5 times that of the steady value and that it can take more than an hour to reach steady state. This is attributed to the dynamic changes of the fines distribution between the fluidized bed and dipleg. It was further shown that a steady dipleg height does not indicate steady elutriation rates. Using the flow meter to confirm steady state measurements, elutriation constants were determined for the glass bead - air system at different superficial velocities
Influence of Simulated Harvest on Iowa Wild Turkey Populations
Computer models were used to simulate autumn harvest of a wild turkey (Meleagris gallopava silvestrus) population in Iowa. Parameters were based on estimates of survival rates, fecundity rates, and age and sex ratios from field studies in mixed forest-farmland from 1977 to 1981. Simulations with average survival and fecundity parameters resulted in a population growth rate of 4% per year. If female survival rates were reduced 4.8% or fecundity was reduced 13.9%, the population became stationary. Interaction of hunting and non-hunting mortality was incorporated according to 3 hypotheses: additive, completely compensatory, and compensatory mortality rates up to a threshold. Estimated allowable autumn harvest rates, based on the goal of a stationary breeding population, ranged from 4.7% to 9.5 % of the females and from 14.8% to 28.4% of the males. At these harvest levels, female survival would have to increase approximately 5% and fecundity 16% to compensate for the harvest and return the population to former growth rates. The time required for the total population to decline by 25% of present levels ranged from more than 100 years at 5% harvest rate under additive mortality to almost 74 years at 10% harvest rate under the threshold theory
Natural functionally-graded composites in hard-to-soft tissue (bone- tendon) junctions
Composite materials are often functionally engineered to imbue desired mechanical properties in materials for structural applications. Nature has long engaged in such composite engineering of biological organisms, which has evolved in both flora and fauna in response to specific mechanical demands. Incorporation of phenolic compounds (like lignin) in stiffening cell assemblies in plant basts, or of silica in plant leaves to resist chomping insect incursions, are good examples in the plant world. Skeletal bone in vertebrates is the classic example in the animal kingdom, a composite of flexible fibrous polymerized organic protein and platy-crystalline inorganic mineral that results in a mechanically strong, hard, tough tissue.
The musculo-skeletal system of vertebrates in fact comprises a variety of both hard and soft tissue types (bone, cartilage, tendon, ligament), generative cell types (osteoblasts, chondrocytes, tenocytes, fibroblasts, all of which can derive from multipotent mesenchymal stem cell precursors), and fibrous connective-tissue proteins (chiefly collagen, types I and II) that are susceptible to varying degrees of mineralization. In the case of bone, mineralization is extensive and forms a bi-continuous composite of mineral (chiefly partially-carbonated hydroxyapatite [Ca10(PO4,CO3)6(OH)2] and precursors) and collagen (a triple a-helix polypeptide) that self-assembles into protein fibrils (mostly type I collagen). Bone continually remodels itself and also re-forms as a consequence of injury or around implanted prostheses (such as knee and hip prostheses). High-resolution analytical TEM reveals [1] a mineralization mechanism which entails initial creation, at the mitochondria of bone-forming cells (osteoblasts), of pre-packaged vesicles that fill with a calcium-phosphate hydrogel and thereafter migrate through the cell wall. The vesicle contents subsequently crystallize [2] in the extra-cellular space with the dissolution of the vesicle containment wall, shortly before self-assembling collagen is expressed from the osteoblasts, providing a “just-in-time” ready source of Ca and P for mineralization of collagen fibrils with close to (though not identical with) the Ca/P ratio of hydroxyapatite found in the mature bone composite.
The critical connective junctions between different tissue types in the musculo-skeletal system (bone, cartilage, tendon, muscle, ligament) involve several hard-tissue/soft-tissue interfaces, characterized by gradients in mineralization, cell type, cell morphology, and collagen self-assembly modes. For example, standard procedure for re-attachment of ruptured tendons—by surgically re-locating the tendon proximally to bone—re-establishes the important bone-tendon junction (enthesis) in a period of about one year. The process proceeds through growth, contiguous to the (fully mineralized) bone surface, of a partially-mineralized fibrocartilage layer (comprising collagen, expressed by chondrocyte cells, that self-assembles into principally Type II and Type X collagens). TEM [3] of ovine models shows that mineralization of this cartilaginous layer appears to occur via the identical mechanism established [1,2] for bone mineralization but initiated instead by chondrocyte cells. SEM [3] reveals that the cell-type in the remaining unmineralized cartilage portion gradually morphs into tenocytes, which form more elastic tendon fibers comprising, again, mostly Type I collagen (but also Types III, IV, V and IX self-assembly motifs). The resulting hard-tissue/soft-tissue enthesis junction is thus seen [3] to be a multiply graded interface involving three different cell types, several different collagen self-assembly motifs, and the functional gradation of a composite material paradigm spanning fully-hard tissue (bone) to fully-soft tissue (tendon).
[1] S. Boonrungsiman, E. Gentleman, R. Carzaniga, N.D. Evans, D.W. McComb, A. E. Porter and M.M. Stevens, PNAS 109 (2012) 141.
[2] V. Benezra, L. W. Hobbs and M. Spector, Biomaterials 23 (2001) 725; A. E. Porter, L. W. Hobbs, V. Benezra and M. Spector, Biomaterials 23 (2001) 921.
[3] L. W. Hobbs, H. Wang, W. M. Reese, B. M. Tomerline, T. Y. C. Lim, A. E. Porter, M. Walton and M. J. Cotton, Microscopy & Microanalysis 19 (2013) 182
Pertumbuhan Kacang Hias (Arachis Pintoi) Pada Media Tanah Pasca Penambangan Batubara Yang Diperkaya Mikoriza, Kapur Dan Pupuk Npk
This study aimed to determine the effects of the provision of arbuscular mycorrhizal fungi (AMF), the provision of lime, and the provision of NPK fertilizer, and the interaction effect of the provision of Arbuscular mycorrhizal fungi (AMF), lime and NPK fertilizers in promoting the growth of pinto peanut in the soil media of post-mining land. The research method used was a completely randomized design (CRD) three-factor factorial with the first factor is the type of inoculant FMA (M) = 3 levels, the second factor is the provision of lime (K) = 3 levels, and the third factor is the NPK fertilizer (P) = 3 levels. These results indicated that the interaction between AMF Glomus sp. and NPK fertilizer dose of 1 gram/polybag can increase height increase pinto peanut plants for 34.16 % of the controls. The interaction between AMF Gigaspora sp. The lime dose of 50 % Al-dd and Fertilizers NPK dose of 1 gram/polybag can increase the growth of leaves pinto peanut plants at 108.33 % of the controls. The interaction between AMF Glomus sp. and NPK fertilizer dose of 2 grams/polybag can increase canopy and root biomass pinto peanut plants at 245.21 % of the controls. The interaction between AMF Glomus sp. and NPK fertilizer dose of 2 grams/polybag can increase canopy and root biomass pinto peanut plants at 245.21 % of the controls. Level relative mycorrhizal dependency (RMD) was influenced by the type of AMF plant inoculated host. Highest RMD shown in pinto peanut using AMF Glomus sp. is 31.99% at moderately dependent
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