18,885 research outputs found
Applicability valuation for evaluation of surface deflection in automotive outer panels
Upon unloading in a forming process there is elastic recovery, which is the release of the elastic strains and the redistribution of the residual stresses through the thickness direction, thus producing surface deflection. It causes changes in shape and dimensions that can create major problem in the external appearance of outer panels. Thus surface deflection prediction is an important issue in sheet metal forming industry. Many factors could affect surface deflection in the process, such as material variations in mechanical properties, sheet thickness, tool geometry, processing parameters and lubricant condition. The shape and dimension problem in press forming is defined as a trouble mainly caused by the elastic recovery of materials during the forming. The use of high strength steel sheets in the manufacturing of automobile outer panels has increased in the automotive industry over the years because of its lightweight and fuel-efficient improvement. But one of the major concerns of stamping is surface deflection in the formed outer panels. Hence, to be cost effective, accurate prediction must be made of its formability. The automotive industry places rigi
Fracture of a viscous liquid
When a viscous liquid hits a pool of liquid of same nature, the impact region
is hollowed by the shock. Its bottom becomes extremely sharp if increasing the
impact velocity, and we report that the curvature at that place increases
exponentially with the flow velocity, in agreement with a theory by Jeong and
Moffatt. Such a law defines a characteristic velocity for the collapse of the
tip, which explains both the cusp-like shape of this region, and the
instability of the cusp if increasing (slightly) the impact velocity. Then, a
film of the upper phase is entrained inside the pool. We characterize the
critical velocity of entrainment of this phase and compare our results with
recent predictions by Eggers
Coherent manipulation of electronic states in a double quantum dot
We investigate coherent time-evolution of charge states (pseudo-spin qubit)
in a semiconductor double quantum dot. This fully-tunable qubit is manipulated
with a high-speed voltage pulse that controls the energy and decoherence of the
system. Coherent oscillations of the qubit are observed for several
combinations of many-body ground and excited states of the quantum dots.
Possible decoherence mechanisms in the present device are also discussed.Comment: RevTe
Fault-tolerant linear optical quantum computing with small-amplitude coherent states
Quantum computing using two optical coherent states as qubit basis states has
been suggested as an interesting alternative to single photon optical quantum
computing with lower physical resource overheads. These proposals have been
questioned as a practical way of performing quantum computing in the short term
due to the requirement of generating fragile diagonal states with large
coherent amplitudes. Here we show that by using a fault-tolerant error
correction scheme, one need only use relatively small coherent state amplitudes
() to achieve universal quantum computing. We study the effects
of small coherent state amplitude and photon loss on fault tolerance within the
error correction scheme using a Monte Carlo simulation and show the quantity of
resources used for the first level of encoding is orders of magnitude lower
than the best known single photon scheme. %We study this reigem using a Monte
Carlo simulation and incorporate %the effects of photon loss in this
simulation
Fermi Velocity Spectrum and Incipient Magnetism in TiBe2
We address the origin of the incipient magnetism in TiBe through precise
first principles calculations, which overestimate the ferromagnetic tendency
and therefore require correction to account for spin fluctuations. TiBe has
sharp fine structure in its electronic density of states, with a van Hove
singularity only 3 meV above the Fermi level. Similarly to the isovalent weak
ferromagnet ZrZn, it is flat bands along the K-W-U lines of hexagonal face
of the fcc Brillouin zone make the system prone to magnetism, and more so if
electrons are added. We find that the Moriya coefficient (multiplying
in the fluctuation susceptibility )
is divergent when the velocity vanishes at a point on the Fermi surface, which
is very close (3 meV) to occurring in TiBe. In exploring how the FM
instability (the =0 Stoner enhancement is ) might be suppressed
by fluctuations in TiBe, we calculate that the Moriya A coefficient (of
) is negative, so =0 is not the primary instability. Explicit
calculation of shows that its maximum occurs at the X point
; TiBe is thus an incipient {\it anti}ferromagnet
rather than ferromagnet as has been supposed. We further show that simple
temperature smearing of the peak accounts for most of the temperature
dependence of the susceptibility, which previously had been attributed to local
moments (via a Curie-Weiss fit), and that energy dependence of the density of
states also strongly affects the magnetic field variation of
Concurrence of assistance and Mermin inequality on three-qubit pure states
We study a relation between the concurrence of assistance and the Mermin
inequality on three-qubit pure states. We find that if a given three-qubit pure
state has the minimal concurrence of assistance greater than 1/2 then the state
violates some Mermin inequality.Comment: 4 pages, 1 figur
Two Circular-Rotational Eigenmodes in Vortex Gyrotropic Motions in Soft Magnetic Nanodots
We found, by micromagnetic numerical and analytical calculations, that the
clockwise (CW) and counterclockwise (CCW) circular-rotational motions of a
magnetic vortex core in a soft magnetic circular nanodot are the elementary
eigenmodes existing in the gyrotropic motion with respect to the corresponding
CW and CCW circular-rotational-field eigenbasis. Any steady-state vortex
gyrotropic motions driven by a linearly polarized oscillating in-plane magnetic
field in the linear regime can be perfectly understood according to the
superposition of the two circular eigenmodes, which show asymmetric resonance
characteristics reflecting the vortex polarization. The relative magnitudes in
the amplitude and phase between the CCW and CW eigenmodes determine the
elongation and orientation of the orbital trajectories of the vortex core
motions, respectively, which trajectories vary with the polarization and
chirality of the given vortex as well as the field frequency across the
resonance frequency.Comment: 30 pages, 7 figure
Generalized W-Class State and its Monogamy Relation
We generalize the W class of states from qubits to qudits and prove
that their entanglement is fully characterized by their partial entanglements
even for the case of the mixture that consists of a W-class state and a product
state .Comment: 12 pages, 1 figur
Weak spin-orbit interactions induce exponentially flat mini-bands in magnetic metals without inversion symmetry
In metallic magnets like MnSi the interplay of two very weak spin-orbit
coupling effects can strongly modify the Fermi surface. In the absence of
inversion symmetry even a very small Dzyaloshinsky-Moriya interaction of
strength delta<<1 distorts a ferromagnetic state into a chiral helix with a
long pitch of order 1/delta. We show that additional small spin-orbit coupling
terms of order delta in the band structure lead to the formation of
exponentially flat minibands with a bandwidth of order exp(-1/sqrt(delta))
parallel to the direction of the helix. These flat minibands cover a rather
broad belt of width sqrt(delta) on the Fermi surface where electron motion
parallel to the helix practically stops. We argue that these peculiar
band-structure effects lead to pronounced features in the anomalous skin
effect.Comment: 7 pages, minor corrections, references adde
Premarket Safety and Efficacy Studies for ADHD Medications in Children
Background: Attention-deficit hyperactivity disorder (ADHD) is a chronic condition and pharmacotherapy is the mainstay of treatment, with a variety of ADHD medications available to patients. However, it is unclear to what extent the long-term safety and efficacy of ADHD drugs have been evaluated prior to their market authorization. We aimed to quantify the number of participants studied and their length of exposure in ADHD drug trials prior to marketing. Methods: We identified all ADHD medications approved by the Food and Drug Administration (FDA) and extracted data on clinical trials performed by the sponsor and used by the FDA to evaluate the drug’s clinical efficacy and safety. For each ADHD medication, we measured the total number of participants studied and the length of participant exposure and identified any FDA requests for post-marketing trials. Results: A total of 32 clinical trials were conducted for the approval of 20 ADHD drugs. The median number of participants studied per drug was 75 (IQR 0, 419). Eleven drugs (55%) were approved after <100 participants were studied and 14 (70%) after <300 participants. The median trial length prior to approval was 4 weeks (IQR 2, 9), with 5 (38%) drugs approved after participants were studied <4 weeks and 10 (77%) after <6 months. Six drugs were approved with requests for specific additional post-marketing trials, of which 2 were performed. Conclusions: Clinical trials conducted for the approval of many ADHD drugs have not been designed to assess rare adverse events or long-term safety and efficacy. While post-marketing studies can fill in some of the gaps, better assurance is needed that the proper trials are conducted either before or after a new medication is approved
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