24,128 research outputs found
On modifying properties of polymeric melts by nanoscopic particles
We study geometric and energetic factors that partake in modifying properties
of polymeric melts via inserting well-dispersed nanoscopic particles (NP).
Model systems are polybutadiene melts including 10-150 atom atomic clusters
(0.1-1.5% v/v). We tune interactions between chains and particle by van der
Waals terms. Using molecular dynamics we study equilibrium fluctuations and
dynamical properties at the interface. Effect of bead size and interaction
strength both on volume and volumetric fluctuations is manifested in mechanical
properties, quantified here by bulk modulus, K. Tuning NP size and non-bonded
interactions results in ~15% enhancement in K by addition of a maximum of 1.5%
v/v NP.Comment: 25 pages, 7 figure
Discovery of a Peculiar Dip from GX 301-2
We present temporal and spectral properties of a unique X-ray dip in GX 301-2
as seen with Rossi X-ray Timing Explorer in May 2010. The X-ray pulsation from
the source gradually declined prior to the dip, disappears for one spin cycle
during the dip and is abruptly restored in the spin cycle immediately after the
dip. Moreover, the phase-integrated spectrum of the source becomes softer
before and during the dip and it quickly hardens again following the dip. Our
findings indicate the fact that the mechanism for pulsations gradually turned
off briefly and underlying dim and softer emission likely from the accretion
column became observable in the brief absence of high level emission due to
wind accretion.Comment: Accepted for publication in A&A Letter
Estimation based control of flexible systems-sensorless wave based technique
This paper presents an algorithm for parameters
and positions estimation of lumped flexible systems. As soon as
the parameters and the positions are estimated they can be used
to design virtual sensors that can be moved along the system
to estimate the position of any lumped mass keeping the system
free from any attached sensors. The virtual sensors are nothing
but a chain of estimators that are connected at the end of each
other, starting with two actuator’s measurements and ending up
with system parameters and all the system lumped positions.
An estimation Based PID controller is presented based on the
feedback of the virtual sensor’s estimates instead of the actual
measurement
Hyper-parameter selection in non-quadratic regularization-based radar image formation
We consider the problem of automatic parameter selection in regularization-based radar image formation techniques. It
has previously been shown that non-quadratic regularization produces feature-enhanced radar images; can yield
superresolution; is robust to uncertain or limited data; and can generate enhanced images in non-conventional data
collection scenarios such as sparse aperture imaging. However, this regularized imaging framework involves some
hyper-parameters, whose choice is crucial because that directly affects the characteristics of the reconstruction. Hence
there is interest in developing methods for automatic parameter choice. We investigate Stein’s unbiased risk estimator
(SURE) and generalized cross-validation (GCV) for automatic selection of hyper-parameters in regularized radar
imaging. We present experimental results based on the Air Force Research Laboratory (AFRL) “Backhoe Data Dome,”
to demonstrate and discuss the effectiveness of these methods
Phosphorus-containing sulfonated polyimides for proton exchange membranes
Synthesis and characterization of the novel sulfonated BAPPO monomer and its use in the synthesis of a new phosphine oxide-based sulfonated polyimide are described. BTDA, 6FDA, and DDS were used as monomers in the polyimide synthesis. Sulfonated polyimide membranes were obtained by a solution thermal imidization method. The thermal behavior of the polymers was investigated by DSC and TGA. The morphological structure of the membranes was investigated by tapping-mode AFM. The proton conductivities of the sulfonated polyimide increased regularly as a function of sulfonated diamine content. The conductivities are good compared to typical proton exchange membranes
Nitrogen front evolution in purged polymer electrolyte membrane fuel cell with dead-ended anode
In this paper, we model and experimentally verify the evolution of liquid water and nitrogen fronts along the length of the anode channel in a proton exchange membrane fuel cell operating with a dead-ended anode that is fed by dry hydrogen. The accumulation of inert nitrogen and liquid water in the anode causes a voltage drop, which is recoverable by purging the anode. Experiments were designed to clarify the effect of N-2 blanketing, water plugging of the channels, and flooding of the gas diffusion layer. The observation of each phenomenon is facilitated by simultaneous gas chromatography measurements on samples extracted from the anode channel to measure the nitrogen content and neutron imaging to measure the liquid water distribution. A model of the accumulation is presented, which describes the dynamic evolution of a N-2 blanketing front in the anode channel leading to the development of a hydrogen starved region. The prediction of the voltage drop between purge cycles during nonwater plugging channel conditions is shown. The model is capable of describing both the two-sloped behavior of the voltage decay and the time at which the steeper slope begins by capturing the effect of H-2 concentration loss and the area of the H-2 starved region along the anode channel
SPH with the multiple boundary tangent method
In this article, we present an improved solid boundary treatment formulation for the smoothed particle hydrodynamics (SPH) method. Benchmark simulations using previously reported boundary treatments can suffer from particle penetration and may produce results that numerically blow up near solid boundaries. As well, current SPH boundary approaches do not properly treat curved boundaries in complicated flow domains. These drawbacks have been remedied in a new boundary treatment method presented in this article, called the multiple boundary tangent (MBT) approach. In this article we present two important benchmark problems to validate the developed algorithm and show that the multiple boundary tangent
treatment produces results that agree with known numerical and experimental solutions. The two benchmark problems chosen are the lid-driven cavity problem, and flow over a cylinder. The SPH solutions using the MBT approach and the results from literature are in very good agreement. These solutions involved
solid boundaries, but the approach presented herein should be extendable to time-evolving, free-surface boundaries
Parametric, Secure and Compact Implementation of RSA on FPGA
We present a fast, efficient, and parameterized modular multiplier and a secure exponentiation circuit especially intended for FPGAs on the low end of the price range. The design utilizes dedicated block multipliers as the main functional unit and Block-RAM as storage unit for the operands. The adopted design methodology allows adjusting the number of multipliers, the radix used in the multipliers, and number of words to meet the system requirements such as
available resources, precision and timing constraints. The architecture, based on the Montgomery modular multiplication algorithm, utilizes a pipelining technique that allows concurrent operation of hardwired multipliers. Our
design completes 1020-bit and 2040-bit modular multiplications in 7.62 μs and 27.0 μs, respectively. The multiplier uses a moderate amount of system resources while achieving the best area-time product in literature. 2040-bit modular exponentiation engine can easily fit into Xilinx Spartan-3E 500; moreover the exponentiation circuit withstands known side channel attacks
Copper and nickel supported FSM-16 molecular sieves for carbon nanotube production
FSM-16, Cu-FSM-16 and Ni-FSM-16 type folded sheet mesoporous materials has been synthesized by using kanemite and hexadecyltrimethylammonium bromide as a template. 1, 5, 10 wt % Cu and Ni were loaded by simple impregnation method. The X-ray diffraction and N2 sorption characteristics show that the resultant materials has uniform pore structure with hexagonal well ordered arrangement.
BET surface area, pore volume nd pore diameters were decreased as the metal loading increased. Carbon nanotubes (CNTs) have been synthesized within the metal trapped channels of the FSM-16 via chemical vapor deposition using acetylene as the hydrocarbon source. The resultant nanotubes were compared under similar reaction conditions and they were characterized by scanning electron microscopy (SEM), Raman Spectroscopy, AFM and TGA
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