6,143 research outputs found
Deflection microwave amplifier with field‐emitter arrays
A new class of microwave and millimeter‐wave amplifiers, based on the deflection of collimated microscopic electron beams with high‐current density and low voltage from field‐emitter arrays, was analyzed. The deflection concept may be applied in two ways; as microelectronic amplifiers or as bunched beam cathodes to power conventional amplifier configurations such as klystrodes and traveling wave tubes. We found that the frequency fT, at which the short‐circuit current gain attains unit magnitude, depends only on the electron beam energy, current density, and emittance, and is independent of beamwidth and total current. The results indicate that field‐emitter arrays have the potential of making wideband deflection amplifiers at frequencies up to tens of GHz. © 1994 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69885/2/APPLAB-65-22-2881-1.pd
Unpacking the difference between digital transformation and IT-enabled organizational transformation
Although digital transformation offers a number of opportunities for today’s organizations, information systems scholars and practitioners struggle to grasp what digital transformation really is, particularly in terms of how it differs from the well-established concept of information technology (IT)-enabled organizational transformation. By integrating literature from organization science and information systems research with two longitudinal case studies—one on digital transformation, the other on IT-enabled organizational transformation—we develop an empirically grounded conceptualization that sets these two phenomena apart. We find that there are two distinctive differences: (1) digital transformation activities leverage digital technology in (re)defining an organization’s value proposition, while IT-enabled organizational transformation activities leverage digital technology in supporting the value proposition, and (2) digital transformation involves the emergence of a new organizational identity, whereas IT-enabled organizational transformation involves the enhancement of an existing organizational identity. We synthesize these arguments in a process model to distinguish the different types of transformations and propose directions for future research
Ascorbate depletion increases growth and metastasis of melanoma cells in vitamin C deficient mice
Aim: Our main objective was to determine the effect of ascorbate supplementation in mice unable to synthesize ascorbic acid (gulo KO) when challenged with murine B16FO cancer cells. Methods: Gulo KO female mice 36–40 weeks of age were deprived of or maintained on ascorbate in food and water for 4 weeks prior to subcutaneous injection of 2.5×106 B16FO murine melanoma cells in the right flank of mice. A control group of wild type mice were also injected with the melanoma cells and maintained on a regular murine diet. Mice were continued on their respective diets for another 2 weeks after injection. The mice were then sacrificed, blood was drawn and their tumors were measured, excised and processed for histology. Results: Mean weight of animals decreased significantly (30%, p < 0.0001) in the ascorbate-restricted group but increased slightly, but insignificantly, in the ascorbate-supplemented group. The mean tumor weight in ascorbate supplemented mice was significantly reduced (by 64%, p = 0.004) compared to tumor weight in ascorbate-deprived gulo mice. The mean tumor weight of wild type mice did not differ significantly from the ascorbate-supplemented mice. Gulo KO mice supplemented with ascorbate developed smaller tumors with more collagen encapsulation and fibrous capsule interdigitation, while gulo KO mice deprived of ascorbate hosted large tumors with poorly defined borders, showing more necrosis and mitosis. Ascorbate supplementation of gulo KO mice resulted in profoundly decreased serum inflammatory cytokine IL-6 (90% decrease, p = 0.04) and IL-1β (62% decrease) compared to the levels in gulo KO mice deprived of ascorbate. Conclusion: Ascorbate supplementation modulated tumor growth and inflammatory cytokine secretion as well as enhanced encapsulation of tumors in scorbutic mice
Phase Transitions in the Two-Dimensional XY Model with Random Phases: a Monte Carlo Study
We study the two-dimensional XY model with quenched random phases by Monte
Carlo simulation and finite-size scaling analysis. We determine the phase
diagram of the model and study its critical behavior as a function of disorder
and temperature. If the strength of the randomness is less than a critical
value, , the system has a Kosterlitz-Thouless (KT) phase transition
from the paramagnetic phase to a state with quasi-long-range order. Our data
suggest that the latter exists down to T=0 in contradiction with theories that
predict the appearance of a low-temperature reentrant phase. At the critical
disorder and for there is no
quasi-ordered phase. At zero temperature there is a phase transition between
two different glassy states at . The functional dependence of the
correlation length on suggests that this transition corresponds to the
disorder-driven unbinding of vortex pairs.Comment: LaTex file and 18 figure
Domain regime in two-dimensional disordered vortex matter
A detailed numerical study of the real space configuration of vortices in
disordered superconductors using 2D London-Langevin model is presented. The
magnetic field is varied between 0 and for various pinning
strengths . For weak pinning, an inhomogeneous disordered vortex matter
is observed, in which the topologically ordered vortex lattice survives in
large domains. The majority of the dislocations in this state are confined to
the grain boundaries/domain walls. Such quasi-ordered configurations are
observed in the intermediate fields, and we refer it as the domain regime (DR).
The DR is distinct from the low-field and the high-fields amorphous regimes
which are characterized by a homogeneous distribution of defects over the
entire system. Analysis of the real space configuration suggests domain wall
roughening as a possible mechanism for the crossover from the DR to the
high-field amorphous regime. The DR also shows a sharp crossover to the high
temperature vortex liquid phase. The domain size distribution and the roughness
exponent of the lattice in the DR are also calculated. The results are compared
with some of the recent Bitter decoration experiments.Comment: 9 pages, 9 figure
Spin Bose Glass Phase in Bilayer Quantum Hall Systems at
We develop an effective spin theory to describe magnetic properties of the
Quantum Hall bilayer systems. In the absence of disorder this theory
gives quantitative agreement with the results of microscopic Hartree-Fock
calculations, and for finite disorder it predicts the existence of a novel spin
Bose glass phase. The Bose glass is characterized by the presence of domains of
canted antiferromagnetic phase with zero average antiferromagnetic order and
short range mean antiferromagnetic correlations. It has infinite
antiferromagnetic transverse susceptibility, finite longitudinal spin
susceptibility and specific heat linear in temperature. Transition from the
canted antiferromagnet phase to the spin Bose glass phase is characterized by a
universal value of the longitudinal spin conductance.Comment: 4 pages, 4 eps figure
Moving Wigner Glasses and Smectics: Dynamics of Disordered Wigner Crystals
We examine the dynamics of driven classical Wigner solids interacting with
quenched disorder from charged impurities. For strong disorder, the initial
motion is plastic -- in the form of crossing winding channels. For increasing
drive, the disordered Wigner glass can reorder to a moving Wigner smectic --
with the electrons moving in non-crossing 1D channels. These different dynamic
phases can be related to the conduction noise and I(V) curves. For strong
disorder, we show criticality in the voltage onset just above depinning. We
also obtain the dynamic phase diagram for driven Wigner solids and prove that
there is a finite threshold for transverse sliding, recently found
experimentally.Comment: 4 pages, 4 postscript figure
Light-color-induced Changes in Fatty Acid Biosynthesis in Chlorella SP. Strain Ks-ma2 in Early Stationary Growth Phase
Optimization of light supply remains a critical issue in microalgae biotechnology. The impacts of light color on fatty acid production and biosynthesis in microalgae are poorly understood. The aim of this study was to determine the effect of light color on growth and fatty acid content in Chlorella strain KS-MA2. Cells were cultured on F/2 medium and incubated under blue, green, red or white light. The cells' growth, fatty acid composition and the expression levels of the ketoacyl synthase 1 (KAS-1), omega-6 desaturase (ω-6 FAD) and omega-3 desaturase (ω-3 FAD) genes were measured at the early stationary growth phase. Results of this study indicated that light color affected cell density and fatty acid profile produced by Chlorella sp. strain KS-MA2. Cells cultured under blue, red and white light had higher cell density than those cultured under green light. Palmitic acid (38.62 ± 3.29% of biomass dry weight) and linolenic acid (7.96 ± 0.88% of biomass dry weight) were highly accumulated under white light. Stearic acid was dominant under blue light (11.11 ± 0.14% of biomass dry weight), whereas oleic acid was dominant under red light (30.50 ± 0.14% of biomass dry weight). Linoleic acid was highly produced under green and blue light (28.63 ± 1.36% and 26.00 ± 0.81 % of biomass dry weight, respectively). KAS-1 and ω-6 FAD were highly expressed under blue light, whereas ω-3 FAD was highly expressed under green light. The production of particular fatty acids of interest from Chlorella could be achieved by shifting color of light used during the incubation of the cell cultures. Blue-light is the most suitable light color for producing biomass and stearic acid by Chlorellastrain KS-MA2
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