5 research outputs found
Transformations between WISE, 2MASS, SDSS and BVRI photometric systems: I. Transformation equations for dwarfs
We present colour transformations for the conversion of the W1 and W2
magnitudes of WISE photometric system to the Johnson-Cousins' BVRI, SDSS (gri),
and 2MASS (JHK_s) photometric systems, for dwarfs. The W3 and W4 magnitudes
were not considered due to their insufficient signal to noise ratio (S/N). The
coordinates of 825 dwarfs along with their BVRI, gri, and JHK_s data, taken
from Bilir et al. (2008) were matched with the coordinates of stars in the
preliminary data release of WISE (Wright et al., 2010) and a homogeneous dwarf
sample with high S/N ratio have been obtained using the following constraints:
1) the data were dereddened, 2) giants were identified and excluded from the
sample, 3) sample stars were selected according to data quality, 4)
transformations were derived for sub samples of different metallicity range,
and 5) transformations are two colour dependent. These colour transformations,
coupled with known absolute magnitudes at shorter wavelenghts, can be used in
space density evaluation for the Galactic (thin and thick) discs, at distances
larger than the ones evaluated with JHK_s photometry.Comment: 16 pages, including 5 figures and 7 tables, accepted for publication
in MNRA
Local stellar kinematics from RAVE data: III. Radial and Vertical Metallicity Gradients based on Red Clump Stars
We investigate radial and vertical metallicity gradients for a sample of red
clump stars from the RAdial Velocity Experiment (RAVE) Data Release 3. We
select a total of 6781 stars, using a selection of colour, surface gravity and
uncertainty in the derived space motion, and calculate for each star a
probabilistic (kinematic) population assignment to a thin or thick disc using
space motion and additionally another (dynamical) assignment using stellar
vertical orbital eccentricity. We derive almost equal metallicity gradients as
a function of Galactocentric distance for the high probability thin disc stars
and for stars with vertical orbital eccentricities consistent with being
dynamically young, e_v<=0.07, i.e. d[M/H]/dR_m = -0.041(0.003) and d[M/H]/dR_m
= -0.041(0.007) dex/kpc. Metallicity gradients as a function of distance from
the Galactic plane for the same populations are steeper, i.e. d[M/H]/dz_{max} =
-0.109(0.008) and d[M/H]/dz_{max} = -0.260(0.031) dex/kpc, respectively. R_m
and z_{max} are the arithmetic mean of the perigalactic and apogalactic
distances, and the maximum distance to the Galactic plane, respectively.
Samples including more thick disc red clump giant stars show systematically
shallower abundance gradients. These findings can be used to distinguish
between different formation scenarios of the thick and thin discs.Comment: 27 pages, including 15 figures and 4 tables, accepted for publication
in MNRA
Analytical approach for entropy generation and heat transfer in CNT-nanofluid dynamics through a ciliated porous medium
The transportation of biological and industrial nanofluids by natural propulsion like cilia movement and self-generated contraction-relaxation of flexible walls has significant applications in numerous emerging technologies. Inspired by multi-disciplinary progress and innovation in this direction, a thermo-fluid mechanical model is proposed to study the entropy generation and convective heat transfer of nanofluids fabricated by the dispersion of single-wall carbon nanotubes (SWCNT) nanoparticles in water as the base fluid. The regime studied comprises heat transfer and steady, viscous, incompressible flow, induced by metachronal wave propulsion due to beating cilia, through a cylindrical tube containing a sparse (i.e. high permeability) homogenous porous medium. The flow is of the creeping type and is restricted under the low Reynolds number and long wavelength approximations. Slip effects at the wall are incorporated and the generalized Darcy drag-force model is utilized to mimic porous media effects. Cilia boundary conditions for velocity components are employed to determine analytical solutions to the resulting non-dimensionalized boundary value problem. The influence of pertinent physical parameters on temperature, axial velocity, pressure rise and pressure gradient, entropy generation function, Bejan number and stream-line distributions are computed numerically. A comparative study between SWCNT nanofluids and pure water is also computed. The computations demonstrate that axial flow is accelerated with increasing slip parameter and Darcy number and is greater for SWCNT- nanofluids than for pure water. Furthermore the size of the bolus for SWCNT-nanofluids is larger than that of the pure water. The study is applicable in designing and fabricating nanoscale and microfluidics devices, artificial cilia and biomimetic micro-pump
Tunnel FET with non-uniform gate capacitance for improved device and circuit level performance
We report the significant improvement obtained by a non-uniform gate capacitance made by appropriate combination of high-k and low-k regions over the tunneling and the channel regions of a heterostucture TFET (called HKLKFFET). In addition to significantly enhanced ION and subthreshold swing, we find that this structure offers great improvements for the dynamic switching energy (66% saving) and propagation delay (similar to 3 x fast operation) compared to a heterostructure TFET (HeTFET) due to the reduction of the Miller effect. We compare and benchmark the proposed device against a 65 nm low stand-by power (LSTP) CMOS technology, and we show that at a supply voltage of V-DD = 0.4 V, TFETs can have smaller propagation delays compared to CMOS operating in the subthreshold region. Higher cut-off frequency (similar to 3x) and bandwidth for analog applications is observed in circuit-level simulations. (C) 2013 Elsevier Ltd. All rights reserved