10,288 research outputs found
An optical fibre dynamic instrumented palpation sensor for the characterisation of biological tissue
AbstractThe diagnosis of prostate cancer using invasive techniques (such as biopsy and blood tests for prostate-specific antigen) and non-invasive techniques (such as digital rectal examination and trans-rectal ultrasonography) may be enhanced by using an additional dynamic instrumented palpation approach to prostate tissue classification. A dynamically actuated membrane sensor/actuator has been developed that incorporates an optical fibre Fabry–Pérot interferometer to record the displacement of the membrane when it is pressed on to different tissue samples. The membrane sensor was tested on a silicon elastomer prostate model with enlarged and stiffer material on one side to simulate early stage prostate cancer. The interferometer measurement was found to have high dynamic range and accuracy, with a minimum displacement resolution of ±0.4μm over a 721μm measurement range. The dynamic response of the membrane sensor when applied to different tissue types changed depending on the stiffness of the tissue being measured. This demonstrates the feasibility of an optically tracked dynamic palpation technique for classifying tissue type based on the dynamic response of the sensor/actuator
Trapped Ion Imaging with a High Numerical Aperture Spherical Mirror
Efficient collection and analysis of trapped ion qubit fluorescence is
essential for robust qubit state detection in trapped ion quantum computing
schemes. We discuss simple techniques of improving photon collection efficiency
using high numerical aperture (N.A.) reflective optics. To test these
techniques we placed a spherical mirror with an effective N.A. of about 0.9
inside a vacuum chamber in the vicinity of a linear Paul trap. We demonstrate
stable and reliable trapping of single barium ions, in excellent agreement with
our simulations of the electric field in this setup. While a large N.A.
spherical mirror introduces significant spherical aberration, the ion image
quality can be greatly improved by a specially designed aspheric corrector lens
located outside the vacuum system. Our simulations show that the spherical
mirror/corrector design is an easy and cost-effective way to achieve high
photon collection rates when compared to a more sophisticated parabolic mirror
setup.Comment: 5 figure
Second Core Formation and High Speed Jets: Resistive MHD Nested Grid Simulations
The stellar core formation and high speed jets driven by the formed core are
studied by using three-dimensional resistive MHD nested grid simulations.
Starting with a Bonnor-Ebert isothermal cloud rotating in a uniform magnetic
field, we calculate the cloud evolution from the molecular cloud core (n = 10^6
cm^-3, r_c = 4.6 times 10^4 AU) to the stellar core (n \simeq 10^23 cm^-3, r_c
\simeq 1 solar radius). We resolve cloud structure over 7 orders of magnitude
in spatial extent and over 17 orders of magnitude in density contrast. For
comparison, we calculate two models: resistive and ideal MHD models. Both
models have the same initial condition, but the former includes dissipation
process of magnetic field while the latter does not. The magnetic fluxes in
resistive MHD model are extracted from the first core during 10^12 cm^-3 < n <
10^16 cm^-3 by Ohmic dissipation. Magnetic flux density of the formed stellar
core (n \simeq 10^20 cm^-3) in resistive MHD model is two orders of magnitude
smaller than that in ideal MHD model. Since magnetic braking is less effective
in resistive MHD model, rapidly rotating stellar core (the second core) is
formed. After stellar core formation, the magnetic field of the core is largely
amplified both by magneto-rotational instability and the shearing motion
between the stellar core and ambient medium. As a consequence, high speed
(simeq 45 km,s^-1) jets are driven by the second core, which results in strong
mass ejection. A cocoon-like structure around the second core also forms with
clear bow shocks.Comment: 12 pages, 3 figures, Submitted to ApJL, For high resolution figures
see
http://www2.scphys.kyoto-u.ac.jp/~machidam/diffusion/doc_diff/MS20545v1.pd
Tidal Barrier and the Asymptotic Mass of Proto Gas-Giant Planets
Extrasolar planets found with radial velocity surveys have masses ranging
from several Earth to several Jupiter masses. While mass accretion onto
protoplanetary cores in weak-line T-Tauri disks may eventually be quenched by a
global depletion of gas, such a mechanism is unlikely to have stalled the
growth of some known planetary systems which contain relatively low-mass and
close-in planets along with more massive and longer period companions. Here, we
suggest a potential solution for this conundrum. In general, supersonic infall
of surrounding gas onto a protoplanet is only possible interior to both of its
Bondi and Roche radii. At a critical mass, a protoplanet's Bondi and Roche
radii are equal to the disk thickness. Above this mass, the protoplanets' tidal
perturbation induces the formation of a gap. Although the disk gas may continue
to diffuse into the gap, the azimuthal flux across the protoplanets' Roche lobe
is quenched. Using two different schemes, we present the results of numerical
simulations and analysis to show that the accretion rate increases rapidly with
the ratio of the protoplanet's Roche to Bondi radii or equivalently to the disk
thickness. In regions with low geometric aspect ratios, gas accretion is
quenched with relatively low protoplanetary masses. This effect is important
for determining the gas-giant planets' mass function, the distribution of their
masses within multiple planet systems around solar type stars, and for
suppressing the emergence of gas-giants around low mass stars
Galaxy Morphology - Halo Gas Connections
We studied a sample of 38 intermediate redshift MgII absorption-selected
galaxies using (1) Keck/HIRES and VLT/UVES quasar spectra to measure the halo
gas kinematics from MgII absorption profiles and (2) HST/WFPC-2 images to study
the absorbing galaxy morphologies. We have searched for correlations between
quantified gas absorption properties, and host galaxy impact parameters,
inclinations, position angles, and quantified morphological parameters. We
report a 3.2-sigma correlation between asymmetric perturbations in the host
galaxy morphology and the MgII absorption equivalent width. We suggest that
this correlation may indicate a connection between past merging and/or
interaction events in MgII absorption-selected galaxies and the velocity
dispersion and quantity of gas surrounding these galaxies.Comment: 6 pages; 3 figures; contributed talk for IAU 199: Probing Galaxies
through Quasar Absorption Line
Magneto-Hydrodynamics of Population III Star Formation
Jet driving and fragmentation process in collapsing primordial cloud are
studied using three-dimensional MHD nested grid simulations. Starting from a
rotating magnetized spherical cloud with the number density of n=10^3 cm^-3, we
follow the evolution of the cloud up to the stellar density n=10^22 cm^-3. We
calculate 36 models parameterizing the initial magnetic and rotational energies
(\gamma_0, \beta_0). In the collapsing primordial clouds, the cloud evolutions
are characterized by the ratio of the initial rotational to magnetic energy,
\gamma_0/\beta_0. The Lorentz force significantly affects the cloud evolution
when \gamma_0 > \beta_0, while the centrifugal force is more dominant than the
Lorentz force when \beta_0 > \gamma_0. When the cloud rotates rapidly with
angular velocity of \Omega_0 > 10^-17 (n/10^3 cm^-3)^2/3 s^-1 and \beta_0 >
\gamma_0, fragmentation occurs before the protostar is formed, but no jet
appears after the protostar formation. On the other hand, a strong jet appears
after the protostar formation without fragmentation when the initial cloud has
the magnetic field of B_0 > 10^-9 (n/10^3 cm^-3)^2/3 G and \gamma_0 > \beta_0.
Our results indicate that proto-Population III stars frequently show
fragmentation and protostellar jet. Population III stars are therefore born as
binary or multiple stellar systems, and they can drive strong jets, which
disturb the interstellar medium significantly, as well as in the present-day
star formation, and thus they may induce the formation of next generation
stars.Comment: 37 pages, 10 figures, Submitted to ApJ, For high resolution figures,
see http://astro3.sci.hokudai.ac.jp/~machida/astro-ph.pd
The CJT calculation in studying nuclear matter beyond mean field approximation
We have introduced a CJT calculation in studying nuclear matter beyond mean
field approximation. Based on the CJT formalism and using Walecka model, we
have derived a set of coupled Dyson equations of nucleons and mesons.
Neglecting the medium effects of the mesons, the usual MFT results could be
reproduced. The beyond MFT calculations have been performed by thermodynamic
consistently determining the meson effective masses and solving the coupled gap
equations for nucleons and mesons. The numerical results for the nucleon and
meson effective masses at finite temperature and chemical potential in nuclear
matter are discussed.Comment: 8 pages, 8 figure
Realistic Magnetohydrodynamical Simulation of Solar Local Supergranulation
Three-dimensional numerical simulations of solar surface magnetoconvection
using realistic model physics are conducted. The thermal structure of
convective motions into the upper radiative layers of the photosphere, the main
scales of convective cells and the penetration depths of convection are
investigated. We take part of the solar photosphere with size of 60x60 Mm in
horizontal direction and by depth 20 Mm from level of the visible solar
surface. We use a realistic initial model of the Sun and apply equation of
state and opacities of stellar matter. The equations of fully compressible
radiation magnetohydrodynamics with dynamical viscosity and gravity are solved.
We apply: 1) conservative TVD difference scheme for the magnetohydrodynamics,
2) the diffusion approximation for the radiative transfer, 3) dynamical
viscosity from subgrid scale modeling. In simulation we take uniform
two-dimesional grid in gorizontal plane and nonuniform grid in vertical
direction with number of cells 600x600x204. We use 512 processors with
distributed memory multiprocessors on supercomputer MVS-100k in the Joint
Computational Centre of the Russian Academy of Sciences.Comment: 6 pages, 5 figures, submitted to the proceedings of the GONG 2008 /
SOHO XXI conferenc
Formation Scenario for Wide and Close Binary Systems
Fragmentation and binary formation processes are studied using
three-dimensional resistive MHD nested grid simulations. Starting with a
Bonnor-Ebert isothermal cloud rotating in a uniform magnetic field, we
calculate the cloud evolution from the molecular cloud core (n=10^4 cm^-3) to
the stellar core (n \simeq 10^22 cm^-3). We calculated 147 models with
different initial magnetic, rotational, and thermal energies, and the
amplitudes of the non-axisymmetric perturbation. In a collapsing cloud,
fragmentation is mainly controlled by the initial ratio of the rotational to
the magnetic energy, regardless of the initial thermal energy and amplitude of
the non-axisymmetric perturbation. When the clouds have large rotational
energies in relation to magnetic energies, fragmentation occurs in the
low-density evolution phase (10^12 cm^-3 < n < 10^15 cm^-3) with separations of
3-300 AU. Fragments that appeared in this phase are expected to evolve into
wide binary systems. On the other hand, fragmentation does not occur in the
low-density evolution phase, when initial clouds have large magnetic energies
in relation to the rotational energies. In these clouds, fragmentation only
occurs in the high-density evolution phase (n > 10^17 cm^-3) after the clouds
experience significant reduction of the magnetic field owing to Ohmic
dissipation in the period of 10^12 cm^-3 < n < 10^15 cm^-3. Fragments appearing
in this phase have separations of < 0.3 AU, and are expected to evolve into
close binary systems. As a result, we found two typical fragmentation epochs,
which cause different stellar separations. Although these typical separations
are disturbed in the subsequent gas accretion phase, we might be able to
observe two peaks of binary separations in extremely young stellar groups.Comment: 45 pages,12 figures, Submitted to ApJ, For high resolution figures
see
http://www2.scphys.kyoto-u.ac.jp/~machidam/protostar/proto/main-astroph.pd
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