Combustion and extinction of a ballistite propellant at critical diameter

1977 ◽  
Vol 12 (2) ◽  
pp. 156-161 ◽  
Author(s):  
A. A. Zenin ◽  
O. I. Leipunskii ◽  
S. V. Piskovskii ◽  
V. M. Puchkov
Keyword(s):  
Critical Diameter ◽  
Ballistite Propellant

Determination of Intrinsic Magnetic Parameters of SmCo5 Phase in Sintered Samples

2005 ◽  
Vol 498-499 ◽  
pp. 129-133 ◽  
Author(s):  
Marcos Flavio de Campos ◽  
Fernando José Gomes Landgraf
Keyword(s):  
Powder Metallurgy ◽  
Domain Wall ◽  
Kerr Effect ◽  
Critical Diameter ◽  
Optical Microscope ◽  
Domain Theory ◽  
Magnetic Domains ◽  
Magnetic Parameters ◽  
Intrinsic Parameters

SmCo5 magnets are usually produced by powder metallurgy route, including milling, compaction and orientation under magnetic field, sintering and heat treatment. The samples produced by powder metallurgy, with grain size around 10 μm, are ideal for determination of intrinsic parameters. The first step for determination of intrinsic magnetic parameters is obtaining images of domain structure in demagnetized samples. In the present study, the domain images were produced by means of Kerr effect, in a optical microscope. After the test of several etchings, Nital appears as the most appropriate for observation of magnetic domains by Kerr effect. Applying Stereology and Domain Theory, several intrinsic parameters of SmCo5 phase were determined: domain wall energy 120 erg/cm2, critical diameter for single domain particle size 2 μm and domain wall thickness 60 Å. In the case of SmCo5, and also other phases with high magnetocrystalline anisotropy, Domain Theory presents several advantages when compared with Micromagnetics.

Molecular Dynamics Studies of Nanotube Growth in a Carbon ARC

1994 ◽  
Vol 359 ◽  
Author(s):  
C. J. Brabec ◽  
A. Maiti ◽  
C. Roland ◽  
J. Bernholc
Keyword(s):  
Molecular Dynamics ◽  
Electric Field ◽  
Electric Fields ◽  
Arc Discharge ◽  
Critical Diameter ◽  
Critical Factor ◽  
Carbon Arc ◽  
Dynamics Simulations ◽  
Nanotube Growth ◽  
Brenner Potential

ABSTRACTIt has been shown experimentally that the growth of carbon nanotubes in an arc discharge is open-ended. This is surprising, because dangling bonds at the end of open tubes make the closed tube geometry more favorable energetically. Recently, it has been proposed that the large electric fields present at the tip of tube is the critical factor that keeps the tube open. We have studied the effects of the electric field on the growth of the nanotubes via ab initio molecular dynamics simulations. Surprisingly, it is found that the electric field cannot play a significant role in keeping the tubes open, implying that some other mechanism must be important. Extensive studies of the energetics and simulations of the growth of tubes were performed using a threebody Tersoff-Brenner potential. Our results show that there exists a critical diameter of ∼ 3 nm above which a defect-free growth of a straight tubule is possible. Narrower tubes stabilize configurations with adjacent pentagons that lead to tube-closure and termination of the growth. This explains the absence of tube narrower than 2.2 nm in arc discharge experiments.

scholarly journals Theory of Time-Dependent Freezing. Part II: Scheme for Freezing Raindrops and Simulations by a Cloud Model with Spectral Bin Microphysics

2015 ◽  
Vol 72 (1) ◽  
pp. 262-286 ◽  
Author(s):  
Vaughan T. J. Phillips ◽  
Alexander Khain ◽  
Nir Benmoshe ◽  
Eyal Ilotoviz ◽  
Alexander Ryzhkov
Keyword(s):  
Water Mass ◽  
Cloud Model ◽  
Critical Diameter ◽  
Time Dependent ◽  
Growth Surface ◽  
Mature Stage ◽  
Liquid Drops ◽  
Thermodynamic Effects ◽  
Bin Microphysics ◽  
Cloud Ice

Abstract The time-dependent process of raindrop freezing is described in a general form, including thermodynamic effects from the accretion of cloud liquid and cloud ice. Freezing drops (FDs) larger than 80 μm (and their water mass) are represented explicitly in a cloud model with spectral bin microphysics. FDs consist of interior water covered by ice initially. Possibilities of both dry (icy surface) and wet growth (surface covered by liquid) of FDs are accounted for. Schemes of time-dependent freezing for rain (discussed in this paper) and wet growth of hail and graupel (discussed in Part I) were implemented in a spectral bin microphysics cloud model. The model predicted that accretion of liquid produces giant FDs of 0.5–2 cm in diameter, far larger than purely liquid drops can become. This growth of FDs is promoted by recirculation from the downdraft back into the updraft and by cessation of internal freezing from some accreted liquid remaining unfrozen (wet growth of FDs). Significant contents of FDs reach a height level of 7 km (−29°C) in the simulated storm. After FDs finish freezing and become hailstones, wet growth may resume. The critical diameter separating wet- and dry-growth regimes is predicted to increase with height for FDs and is more vertically uniform for hail. A sensitivity test shows that time-dependent freezing initially delays the formation of hail but later in the mature stage of the storm boosts it. Convection is invigorated. Hail and freezing drops are upwelled to higher levels, causing hail to grow to sizes up to 100% larger than without time-dependent freezing.

scholarly journals ZnTiO3 ceramic nanopowder microstructure changes during compaction

2013 ◽  
Vol 45 (2) ◽  
pp. 209-221
Author(s):  
N. Labus ◽  
J. Krstic ◽  
S. Markovic ◽  
D. Vasiljevic-Radovic ◽  
M.V. Nikolic ◽  
...  
Keyword(s):  
Particle Size ◽  
Pore Size ◽  
Size Distribution ◽  
Mercury Porosimetry ◽  
Critical Diameter ◽  
Nitrogen Adsorption ◽  
Powder Particle Size ◽  
Scanning Electron Micrographs ◽  
Force Microscopy ◽  
Scanning Electron

ZnTiO3 nanopowder as a constitutive component in compact production was primarily characterized. Scanning electron micrographs of as received powder were recorded. Mercury porosimetry and nitrogen adsorption were also performed on loose powder. Particle size distribution in a water powder suspension was determined with a laser particle size analyser. Compaction was performed on different pressures in a range from 100 to 400 MPa using the uniaxial double sided compaction technique without binder and lubricant. Micrographs of compacted specimens were obtained using scanning electron microscopy and atomic force microscopy. Pore size distribution was also determined by mercury porosimetry and nitrogen adsorption. Results revealed that with increasing pressure during compaction interagglomerate pores diminish in size until they reach some critical diameter related to the intra-agglomerate pore size.

Characterizing the High Reynolds Number Regime for Deterministic Lateral Displacement (DLD) Devices

2017 ◽  
Author(s):  
Brian Dincau ◽  
Arian Aghilinejad ◽  
Jong-Hoon Kim ◽  
Xiaolin Chen
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Soft Lithography ◽  
Lateral Displacement ◽  
Flow Characteristics ◽  
Critical Diameter ◽  
Flow Rates ◽  
Deterministic Lateral Displacement ◽  
Array Configuration ◽  
High Reynolds

Deterministic lateral displacement (DLD) is a common name given to a class of continuous microfluidic separation devices that use a repeating array of pillars to selectively displace particles having a mean diameter greater than the critical diameter (Dc). This Dc is an emergent property influenced by pillar shape, size, and spacing, in addition to the suspending fluid and target particle properties. The majority of previous research in DLD applications has focused on the utilization of laminar flow in low Reynolds number (Re) regimes. While laminar flow exhibits uniform streamlines and predictable separation characteristics, this low-Re regime is dependent on relatively low fluid velocities, and may not hold true at higher processing speeds. Through numerical modeling and experimentation, we investigated high-Re flow characteristics and potential separation enhancements resulting from vortex generation within a DLD array. We used an analytical model and computational software to simulate DLD performance spanning a Re range of 1–100 at flow rates of 2–170 μL/s (0.15–10 mL/min). Each simulated DLD array configuration was composed of 60 μm cylindrical pillars with a 45 μm gap size. The experimental DLD device was fabricated using conventional soft lithography, and injected with 20 μm particles at varying flow rates to observe particle trajectories. The simulated results predict a shift in Dc at Re > 50, while the experimental results indicate a breakdown of typical DLD operation at Re > 70.

Cavitation Behavior of Coarse-Grained Al-4.5Mg Alloy Exhibiting Superplastic-Like Elongation

1999 ◽  
Vol 601 ◽  
Author(s):  
H. Iwasaki ◽  
T. Mori ◽  
H. Hosokawa ◽  
T. Tagata ◽  
M. Mabuchi ◽  
...  
Keyword(s):  
Strain Rate ◽  
Diffusion Length ◽  
Critical Diameter ◽  
Coarse Grained ◽  
Primary Crystal ◽  
Tensile Direction ◽  
Elongation To Failure ◽  
Fe Alloys ◽  
Cavitation Behavior ◽  
Primary Crystals

AbstractCavitation behaviors related to ferrous primary crystals have been investigated at a temperature of 653 K and a strain rate of 10−3/s for Al-4.5%Mg-0.05%Fe and Al-4.5%Mg-0.2%Fe alloys which have a grain size of 50;Lm. The alloys constantly exhibited a large elongation-to-failure above 300% at the temperature of 653 K and strain rate of 10−3/s. Cavitation was increased by increasing the iron content. Most cavities were nucleated at the interface between the ferrous primary crystal and matrix and elongated parallel to the tensile direction. The experimental critical diameter of the primary crystal, above which cavity is nucleated, was 1.5 µm at the grain boundary and 0.5µm at grain interior, which were very close to double the critical diffusion length.

Acoustic Radiation, Cavitation Collapses, and Dryout in a Capillary Oscillating Heat Pipe

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Steve Q. Cai
Keyword(s):  
Heat Pipe ◽  
Temperature Difference ◽  
Two Phase Flow ◽  
Acoustic Radiation ◽  
Operating Temperature ◽  
Critical Diameter ◽  
Phase Flow ◽  
Vapor Bubbles ◽  
Temperature Zone ◽  
Two Phase

Abstract In an oscillation heat pipe (OHP), when two-phase flow oscillates to the condensation region, saturated vapor bubbles/slugs are subjected to a sudden temperature reduction or immediate subcooling. Rapid condensation ruptures vapor bubbles and generates cavitation erosions on the tube interior surface. In this article, a thorough study is performed to understand discrepancy of variation tendency between acoustic radiation and OHP temperature difference that both are operating temperature-dependent. On this basis, three temperature zones were identified: (1) low operating temperature zone with strong cavitation collapse and acoustic radiations, (2) optimal temperature zone with the minimum temperature difference and weakening cavitation collapses, and, (3) high-temperature zone where dryout and oscillation failures develop. At the optimal operating temperature, high-frequent oscillations reduce subcooling of two-phase flow, alleviating the impact of cavitation collapses and ceasing acoustic radiations. At high operating temperature, liquid surface tension dramatically reduces and dynamic contact angle significantly increases. Both the factors tend to lower the critical diameter necessary to maintain pressure difference and oscillating two-phase slug flow. When the critical diameter reduces to be less than the OHP tube diameter, liquid slugs are not able to seal the OHP capillary tubes, leading to dryout or insufficient heat and mass transfer.

Towards the Prediction and Minimization of Device Failure for Endolvascular Grafts in Abdominal Aortic Aneurysms

2007 ◽  
Author(s):  
Ron Layman ◽  
Samy Missoum ◽  
Jonathan Vande Geest
Keyword(s):  
United States ◽  
Abdominal Aortic Aneurysm ◽  
Critical Diameter ◽  
Abdominal Aortic Aneurysms ◽  
The United States ◽  
Aortic Aneurysms ◽  
Infrarenal Aorta ◽  
Device Failure ◽  
Clinical Challenge ◽  
Abdominal Aortic

The local dilation of the infrarenal aorta, termed an abdominal aortic aneurysm (AAA), occurs over several years and may eventually lead to rupture, an event currently ranked the 15th leading cause of death in the United States [1, 2]. AAA can often remain quiescent and asymptomatic, making the diagnosis and treatment of AAA patients a clinical challenge. For patients whose AAAs dilate to a critical diameter there are two standard treatments: open surgical resection and endovascular repair (EVAR). EVAR involves inserting an endovascular graft into the aneurysm to prevent pressurization of the AAA cavity.

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