2,421 research outputs found
Numerical Simulation of Projectile Impact on Mild Steel ArmourPlates using LS-DYNA: Part I: Validation
The paper describes the simulation of impact of jacketed projectiles on steel armour plates usingexplicit finite element analysis as implemented in LS-DYNA. Validation of numerical modelling includesa comprehensive mesh convergence study leading to insights not previously reported in literature,using shell, solid, and axisymmetric elements for representing target plates. It is shown for a numberof cases that with a proper choice of contact algorithm, element size, and strain rate-dependent materialproperties, computed projectile residual velocities can match closely with corresponding test-basedvalues. The modelling requirements are arrived at by correlating against published test residual velocities1for variants of mild steel plates (designated as MS1, MS2 and MS3) of different thicknesses at impactvelocities in the range of ~820-870 m/s. Using the validated numerical procedure, a number of parametricstudies such as the effect of projectile shape and geometric aspect ratios as well as plate thickness onresidual velocity have been carried out and presented in Part II of the current paper
Single-electron quantum dot in Si/SiGe with integrated charge-sensing
Single-electron occupation is an essential component to measurement and
manipulation of spin in quantum dots, capabilities that are important for
quantum information processing. Si/SiGe is of interest for semiconductor spin
qubits, but single-electron quantum dots have not yet been achieved in this
system. We report the fabrication and measurement of a top-gated quantum dot
occupied by a single electron in a Si/SiGe heterostructure. Transport through
the quantum dot is directly correlated with charge-sensing from an integrated
quantum point contact, and this charge-sensing is used to confirm
single-electron occupancy in the quantum dot.Comment: 3 pages, 3 figures, accepted version, to appear in Applied Physics
Letter
Modeling the influence of chain length on secondary organic aerosol (SOA) formation via multiphase reactions of alkanes
Secondary organic aerosol (SOA) from diesel fuel is known to be
significantly sourced from the atmospheric oxidation of aliphatic
hydrocarbons. In this study, the formation of linear alkane SOA was
predicted using the Unified Partitioning Aerosol Phase Reaction (UNIPAR)
model that simulated multiphase reactions of hydrocarbons. In the model, the
formation of oxygenated products from the photooxidation of linear alkanes
was simulated using a nearly explicit gas kinetic mechanism. Autoxidation
paths integrated with alkyl peroxy radicals were added to the Master
Chemical Mechanism v3.3.1 to improve the prediction of low-volatility
products in the gas phase and SOA mass. The resulting gas products were then
lumped into volatility- and reactivity-based groups that are linked to mass-based
stoichiometric coefficients. The SOA mass in the UNIPAR model is produced
via three major pathways: partitioning of gaseous oxidized products onto
both the organic and wet inorganic phases, oligomerization in the organic phase,
and reactions in the wet inorganic phase (acid-catalyzed oligomerization and
organosulfate formation). The model performance was demonstrated for SOA
data that were produced through the photooxidation of a homologous series of
linear alkanes ranging from C9–C15 under varying environments (NOx
levels and inorganic seed conditions) in a large outdoor photochemical smog
chamber. The product distributions of linear alkanes were mathematically
predicted as a function of carbon number using an incremental volatility
coefficient (IVC) to cover a wide range of alkane lengths. The prediction of
alkane SOA using the incremental volatility-based product distributions,
which were obtained with C9–C12 alkanes, was evaluated for C13
and C15 chamber data and further extrapolated to predict the SOA from longer-chain alkanes (≥ C15) that can be found in diesel. The model simulation
of linear alkanes in diesel fuel suggests that SOA mass is mainly produced
by alkanes C15 and higher. Alkane SOA is insignificantly impacted by the
reactions of organic species in the wet inorganic phase due to the
hydrophobicity of products but significantly influenced by gas–particle
partitioning.</p
Pauli spin blockade and lifetime-enhanced transport in a Si/SiGe double quantum dot
We analyze electron transport data through a Si/SiGe double quantum dot in
terms of spin blockade and lifetime-enhanced transport (LET), which is
transport through excited states that is enabled by long spin relaxation times.
We present a series of low-bias voltage measurements showing the sudden
appearance of a strong tail of current that we argue is an unambiguous
signature of LET appearing when the bias voltage becomes greater than the
singlet-triplet splitting for the (2,0) electron state. We present eight
independent data sets, four in the forward bias (spin-blockade) regime and four
in the reverse bias (lifetime-enhanced transport) regime, and show that all
eight data sets can be fit to one consistent set of parameters. We also perform
a detailed analysis of the reverse bias (LET) regime, using transport rate
equations that include both singlet and triplet transport channels. The model
also includes the energy dependent tunneling of electrons across the quantum
barriers, and resonant and inelastic tunneling effects. In this way, we obtain
excellent fits to the experimental data, and we obtain quantitative estimates
for the tunneling rates and transport currents throughout the reverse bias
regime. We provide a physical understanding of the different blockade regimes
and present detailed predictions for the conditions under which LET may be
observed.Comment: published version, 18 page
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