3,682 research outputs found
The pitch-heave dynamics of transportation vehicles
The analysis and design of suspensions for vehicles of finite length using pitch-heave models is presented. Dynamic models for the finite length vehicle include the spatial distribution of the guideway input disturbance over the vehicle length, as well as both pitch and heave degrees-of-freedom. Analytical results relate the vehicle front and rear accelerations to the pitch and heave natural frequencies, which are functions of vehicle suspension geometry and mass distribution. The effects of vehicle asymmetry and suspension contact area are evaluated. Design guidelines are presented for the modification of vehicle and suspension parameters to meet alternative ride quality criteria
Database Search Strategies for Proteomic Data Sets Generated by Electron Capture Dissociation Mass Spectrometry
Large data sets of electron capture dissociation (ECD) mass spectra from proteomic experiments are rich in information; however, extracting that information in an optimal manner is not straightforward. Protein database search engines currently available are designed for low resolution CID data, from which Fourier transform ion cyclotron resonance (FT-ICR) ECD data differs significantly. ECD mass spectra contain both z-prime and z-dot fragment ions (and c-prime and c-dot); ECD mass spectra contain abundant peaks derived from neutral losses from charge-reduced precursor ions; FT-ICR ECD spectra are acquired with a larger precursor m/z isolation window than their low-resolution CID counterparts. Here, we consider three distinct stages of postacquisition analysis: (1) processing of ECD mass spectra prior to the database search; (2) the database search step itself and (3) postsearch processing of results. We demonstrate that each of these steps has an effect on the number of peptides identified, with the postsearch processing of results having the largest effect. We compare two commonly used search engines: Mascot and OMSSA. Using an ECD data set of modest size (3341 mass spectra) from a complex sample (mouse whole cell lysate), we demonstrate that search results can be improved from 630 identifications (19% identification success rate) to 1643 identifications (49% identification success rate). We focus in particular on improving identification rates for doubly charged precursors, which are typically low for ECD fragmentation. We compare our presearch processing algorithm with a similar algorithm recently developed for electron transfer dissociation (ETD) data
Evaluation of advanced lift concepts and potential fuel conservation for short-haul aircraft
The effect of different field lengths, cruise requirements, noise level, and engine cycle characteristics on minimizing fuel consumption and minimizing operating cost at high fuel prices were evaluated for some advanced short-haul aircraft. The conceptual aircraft were designed for 148 passengers using the upper surface-internally blown jet flap, the augmentor wing, and the mechanical flap lift systems. Advanced conceptual STOL engines were evaluated as well as a near-term turbofan and turboprop engine. Emphasis was given to designs meeting noise levels equivalent to 95-100 EPNdB at 152 m (500 ft) sideline
Self-Regulation of Solar Coronal Heating Process via Collisionless Reconnection Condition
I propose a new paradigm for solar coronal heating viewed as a
self-regulating process keeping the plasma marginally collisionless. The
mechanism is based on the coupling between two effects. First, coronal density
controls the plasma collisionality and hence the transition between the slow
collisional Sweet-Parker and the fast collisionless reconnection regimes. In
turn, coronal energy release leads to chromospheric evaporation, increasing the
density and thus inhibiting subsequent reconnection of the newly-reconnected
loops. As a result, statistically, the density fluctuates around some critical
level, comparable to that observed in the corona. In the long run, coronal
heating can be represented by repeating cycles of fast reconnection events
(nano-flares), evaporation episodes, and long periods of slow magnetic stress
build-up and radiative cooling of the coronal plasma.Comment: 4 pages; Phys. Rev. Lett., in pres
A Model for Patchy Reconnection in Three Dimensions
We show, theoretically and via MHD simulations, how a short burst of
reconnection localized in three dimensions on a one-dimensional current sheet
creates a pair of reconnected flux tubes. We focus on the post-reconnection
evolution of these flux tubes, studying their velocities and shapes. We find
that slow-mode shocks propagate along these reconnected flux tubes, releasing
magnetic energy as in steady-state Petschek reconnection. The geometry of these
three-dimensional shocks, however, differs dramatically from the classical
two-dimensional geometry. They propagate along the flux tube legs in four
isolated fronts, whereas in the two-dimensional Petschek model, they form a
continuous, stationary pair of V-shaped fronts.
We find that the cross sections of these reconnected flux tubes appear as
teardrop shaped bundles of flux propagating away from the reconnection site.
Based on this, we argue that the descending coronal voids seen by Yohkoh SXT,
LASCO, and TRACE are reconnected flux tubes descending from a flare site in the
high corona, for example after a coronal mass ejection. In this model, these
flux tubes would then settle into equilibrium in the low corona, forming an
arcade of post-flare coronal loops.Comment: 27 pages plus 16 figure
Scanning a photonic crystal slab nanocavity by condensation of xenon
Allowing xenon or nitrogen gas to condense onto a photonic crystal slab nanocavity maintained at 10–20 K results in shifts of the nanocavity mode wavelength by as much as 5 nm (~=4 meV). This occurs in spite of the fact that the mode defect is achieved by omitting three holes to form the spacer. This technique should be useful in changing the detuning between a single quantum dot transition and the nanocavity mode for cavity quantum electrodynamics experiments, such as mapping out a strong coupling anticrossing curve. Compared with temperature scanning, it has a much larger scan range and avoids phonon broadening
Thermal performance of two heat exchangers for thermoelectric generators
Thermal performance of heat exchanger is important for potential application in integrated solar cell/module and
thermoelectric generator (TEG) system. Usually, thermal performance of a heat exchanger for TEGs is analysed
by using a 1D heat conduction theory which ignores the detailed phenomena associated with thermo-hydraulics.
In this paper, thermal and mass transports in two different exchangers are simulated by means of a steady-state,
3D turbulent flow k -e model with a heat conduction module under various flow rates. In order to simulate an
actual working situation of the heat exchangers, hot block with an electric heater is included in the model. TEG
model is simplified by using a 1D heat conduction theory, so its thermal performance is equivalent to a real TEG.
Natural convection effect on the outside surfaces of the computational model is considered. Computational
models and methods used are validated under transient thermal and electrical experimental conditions of a TEG.
It is turned out that the two heat exchangers designed have a better thermal performance compared with an
existing heat exchanger for TEGs, and more importantly, the fin heat exchanger is more compact and has nearly
half temperature rise compared with the tube heat exchanger
Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms?
It is known that there must be some weak form of transport (called cool
bottom processing, or CBP) acting in low mass RGB and AGB stars, adding nuclei,
newly produced near the hydrogen-burning shell, to the convective envelope. We
assume that this extra-mixing originates in a stellar dynamo operated by the
differential rotation below the envelope, maintaining toroidal magnetic fields
near the hydrogen-burning shell. We use a phenomenological approach to the
buoyancy of magnetic flux tubes, assuming that they induce matter circulation
as needed by CBP models. This establishes requirements on the fields necessary
to transport material from zones where some nuclear burning takes place,
through the radiative layer, and into the convective envelope. Magnetic field
strengths are determined by the transport rates needed by CBP for the model
stellar structure of a star of initially 1.5 solar mass, in both the AGB and
RGB phases. The field required for the AGB star in the processing zone is B_0 ~
5x10^6 G; at the base of the convective envelope this yields an intensity B_E <
10^4 G (approximately). For the RGB case, B_0 ~ 5x10^4 to 4x10^5 G, and the
corresponding B_E are ~ 450 to 3500 G. These results are consistent with
existing observations on AGB stars. They also hint at the basis for high field
sources in some planetary nebulae and the very large fields found in some white
dwarfs. It is concluded that transport by magnetic buoyancy should be
considered as a possible mechanism for extra mixing through the radiative zone,
as is required by both stellar observations and the extensive isotopic data on
circumstellar condensates found in meteorites.Comment: 26 pages, 4 figures, accepted by Astrophysical Journa
Fast and slow two-fluid magnetic reconnection
We present a two-fluid magnetohydrodynamics (MHD) model of quasi-stationary,
two-dimensional magnetic reconnection in an incompressible plasma composed of
electrons and ions. We find two distinct regimes of slow and fast reconnection.
The presence of these two regimes can provide a possible explanation for the
initial slow build up and subsequent rapid release of magnetic energy
frequently observed in cosmic and laboratory plasmas.Comment: 16 pages, 2 figures, 1 tabl
Targeted online liquid chromatography electron capture dissociation mass spectrometry for the localization of sites of in vivo phosphorylation in human Sprouty2
We demonstrate a strategy employing collision-induced dissociation for phosphopeptide discovery, followed by targeted electron capture dissociation (ECD) for site localization. The high mass accuracy and low background noise of the ECD mass spectra allow facile sequencing of coeluting isobaric phosphopeptides, with up to two isobaric phosphopeptides sequenced from a single mass spectrum. In contrast to the previously described neutral loss of dependent ECD method, targeted ECD allows analysis of both phosphotyrosine peptides and lower abundance phosphopeptides. The approach was applied to phosphorylation analysis of human Sprouty2, a regulator of receptor tyrosine kinase signaling. Fifteen sites of phosphorylation were identified, 11 of which are novel
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