543 research outputs found
Spatial distribution of ions in a linear octopole radio-frequency ion trap in the space-charge limit
We have explored the spatial distribution of an ion cloud trapped in a linear
octopole radio-frequency (rf) ion trap. The two-dimensional distribution of the
column density of stored silver dimer cations was measured via
photofragment-ion yields as a function of the position of the incident laser
beam over the transverse cross section of the trap. The profile of the ion
distribution was found to be dependent on the number of loaded ions. Under high
ion-loading conditions with a significant space-charge effect, ions form a ring
profile with a maximum at the outer region of the trap, whereas they are
localized near the center axis region at low loading of the ions. These results
are explained quantitatively by a model calculation based on equilibrium
between the space-charge-induced potential and the effective potential of the
multipole rf field. The maximum adiabaticity parameter \eta_max is estimated to
be about 0.13 for the high ion-density condition in the present octopole ion
trap, which is lower than typical values reported for low ion densities; this
is probably due to additional instability caused by the space charge.Comment: 8 pages, 5 figure
Fast-ion-induced secondary ion emission from submicron droplet surfaces studied using a new coincidence technique with forward-scattered projectiles
A mass spectrometric study of secondary ions emitted from droplet surfaces by MeV-energy heavy ion impact was performed to investigate fast-ion-induced molecular reaction processes on liquid surfaces. Herein, a new coincidence technique was developed between secondary ions and scattered projectile ions at a small forward angle. The advantages of this technique were demonstrated by measurement of the collision between 4-MeV C3+ and ethanol droplets. Secondary ion emission probabilities were obtained directly from the coincidence data. Notably, this technique enabled positive fragment ions that had not been identified in previous measurements to be observed by suppressing the strong background originating from gas-phase molecules more than 104-fold. H+, H3O+, C2H5+, and C2H5O+ were found to be produced as major positive fragment ions, in addition to minor fragments H2+, C2H3+, and CH2OH+. Production of these ions suggests that competition between rapid hydrogen ion emission from multiply ionized states and intermolecular proton transfer accompanied by fragmentation through protonated ethanol occurs after fast heavy-ion collisions. Clarification of the positive fragment ions also revealed the characteristic features of negative ions. Negative ions were realized to exhibit higher degrees of fragmentation and reactivity compared with positive ions. Furthermore, the energy loss by forward-scattered ions during droplet penetration was used to evaluate the target thickness at a submicron level. Variations in secondary ion yield, mass distribution, and kinetic energies depending on the penetration length were observed below 1 µm. These results highlight the unknown mechanism of these “submicron effects” observed in secondary ion emission processes as a new phenomenon
Positive and negative ion emission from microdroplets by MeV energy ions
XXIX International Conference on Photonic, Electronic, and Atomic Collisions (ICPEAC2015): 22–28 July 2015, Toledo, SpainWe have developed a new experimental setup that allowed us to study collision interactions between fast ion beams and liquid droplets under a vacuum condition. Droplets of water and ethanol are irradiated with 0.4-1.5 MeV H+ and 2.0 MeV C2+ ions. The droplet diameter is estimated from energy loss measurements of projectile ions penetrating through droplets. Time-of-flight mass spectra of positive and negative secondary ions exhibit a series of cluster ions generated via protonation and deprotonation
A Three-Dimensional Quantum Simulation of Silicon Nanowire Transistors with the Effective-Mass Approximation
The silicon nanowire transistor (SNWT) is a promising device structure for
future integrated circuits, and simulations will be important for understanding
its device physics and assessing its ultimate performance limits. In this work,
we present a three-dimensional quantum mechanical simulation approach to treat
various SNWTs within the effective-mass approximation. We begin by assuming
ballistic transport, which gives the upper performance limit of the devices.
The use of a mode space approach (either coupled or uncoupled) produces high
computational efficiency that makes our 3D quantum simulator practical for
extensive device simulation and design. Scattering in SNWTs is then treated by
a simple model that uses so-called Buttiker probes, which was previously used
in metal-oxide-semiconductor field effect transistor (MOSFET) simulations.
Using this simple approach, the effects of scattering on both internal device
characteristics and terminal currents can be examined, which enables our
simulator to be used for the exploration of realistic performance limits of
SNWTs.Comment: 38 pages, 11 figures, submitted to Journal of Applied Physic
The impact of solar radiation on polar mesospheric ice particle formation
Mean temperatures in the polar summer mesopause can drop to 130 K. The low
temperatures in combination with water vapor mixing ratios of a few parts per
million give rise to the formation of ice particles. These ice particles may
be observed as polar mesospheric clouds. Mesospheric ice cloud formation is
believed to initiate heterogeneously on small aerosol particles (r < 2 nm) composed of recondensed meteoric material, so-called meteoric
smoke particles (MSPs). Recently, we investigated the ice activation and
growth behavior of MSP analogues under realistic mesopause conditions. Based
on these measurements we presented a new activation model which largely
reduced the uncertainties in describing ice particle formation. However, this
activation model neglected the possibility that MSPs heat up in the
low-density mesopause due to absorption of solar and terrestrial irradiation.
Radiative heating of the particles may severely reduce their ice formation
ability. In this study we expose MSP analogues (Fe2O3 and
FexSi1 − xO3) to realistic mesopause
temperatures and water vapor concentrations and investigate particle warming
under the influence of variable intensities of visible light (405, 488, and
660 nm). We show that Mie theory calculations using refractive indices of
bulk material from the literature combined with an equilibrium temperature
model presented in this work predict the particle warming very well.
Additionally, we confirm that the absorption efficiency increases with the
iron content of the MSP material. We apply our findings to mesopause
conditions and conclude that the impact of solar and terrestrial radiation on
ice particle formation is significantly lower than previously assumed.</p
Radio-frequency capacitance spectroscopy of metallic nanoparticles
Recent years have seen great progress in our understanding of the electronic properties of nanomaterials in which at least one dimension measures less than 100 nm. However, contacting true nanometer scale materials such as individual molecules or nanoparticles remains a challenge as even state-of-the-art nanofabrication techniques such as electron-beam lithography have a resolution of a few nm at best. Here we present a fabrication and measurement technique that allows high sensitivity and high bandwidth readout of discrete quantum states of metallic nanoparticles which does not require nm resolution or precision. This is achieved by coupling the nanoparticles to resonant electrical circuits and measurement of the phase of a reflected radio-frequency signal. This requires only a single tunnel contact to the nanoparticles thus simplifying device fabrication and improving yield and reliability. The technique is demonstrated by measurements on 2.7 nm thiol coated gold nanoparticles which are shown to be in excellent quantitative agreement with theory
Histological and ultrastructural evaluation of the early healing of the lateral collateral ligament epiligament tissue in a rat knee model
<p>Abstract</p> <p>Background</p> <p>In this study, we evaluated the changes which occurred in the epiligament, an enveloping tissue of the ligament, during the ligament healing. We assessed the association of epiligament elements that could be involved in ligament healing.</p> <p>Methods</p> <p>Thirty-two 8-month old male Wistar rats were used in this study. In twenty-four of them the lateral collateral ligament of the knee joint was surgically transected and was allowed to heal spontaneously. The evaluation of the epiligament healing included light microscopy and transmission electron microscopy.</p> <p>Results</p> <p>At the eight, sixteenth and thirtieth day after injury, the animals were sacrificed and the ligaments were examined. Our results revealed that on the eight and sixteenth day post-injury the epiligament tissue is not completely regenerated. Till the thirtieth day after injury the epiligament is similar to normal, but not fully restored.</p> <p>Conclusion</p> <p>Our study offered a more complete description of the epiligament healing process and defined its important role in ligament healing. Thus, we provided a base for new strategies in ligament treatment.</p
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