2,935 research outputs found
3D Arbitrary Channel Fabrication for Lab on a Chip Applications using Chemical Decomposition
This article demonstrate a simple method to use of three-dimensionally (3D) printed molds that are chemically decomposable for rapid fabrication of complex and arbitrary microchannel geometries. These complex microchannel are unachievable through existing soft lithography techniques. The molds are printed directly from hand held 3D printing pen that can print in midair, making rapid prototyping of microfluidic devices possible in hours. PLA based copper filament is used to print the arbitrary channels. The printed channels are then placed inside PDMS and PDMS is cured. The cured sample is then immersed in chemical solution (Acetic Acid + Sodium Chloride+ Hydrogen peroxide), which decomposes the PLA based copper channel thus leaving an empty channel inside the PDMS block. This method enable precise control of various device geometries, such as the profile of the channel cross-section and variable channel diameters in a single device
Local Hall effect in hybrid ferromagnetic/semiconductor devices
We have investigated the magnetoresistance of ferromagnet-semiconductor
devices in an InAs two-dimensional electron gas system in which the magnetic
field has a sinusoidal profile. The magnetoresistance of our device is large.
The longitudinal resistance has an additional contribution which is odd in
applied magnetic field. It becomes even negative at low temperature where the
transport is ballistic. Based on the numerical analysis, we confirmed that our
data can be explained in terms of the local Hall effect due to the profile of
negative and positive field regions. This device may be useful for future
spintronic applications.Comment: 4 pages with 4 fugures. Accepted for publication in Applied Physics
Letter
Vertical beaming of wavelength-scale photonic crystal resonators
We report that of the photons generated inside a photonic crystal
slab resonator can be funneled within a small divergence angle of . The far-field radiation properties of a photonic crystal slab
resonant mode are modified by tuning the cavity geometry and by placing a
reflector below the cavity. The former method directly shapes the near-field
distribution so as to achieve directional and linearly-polarized far-field
patterns. The latter modification takes advantage of the interference effect
between the original waves and the reflected waves to enhance the
energy-directionality. We find that, regardless of the slab thickness, the
optimum distance between the slab and the reflector closely equals one
wavelength of the resonance under consideration. We have also discussed an
efficient far-field simulation algorithm based on the finite-difference
time-domain method and the near- to far-field transformation.Comment: 14 pages, 15 figures, submitted to Phys. Rev.
Effect of microstructure on the magnetoresistive properties of NiFe/Co(CoFe)/Al(Ta)?oxide/Co(CoFe) tunnel junctions
科研費報告書収録論文(課題番号:11355001・基盤研究(A)(2)・H11~H13/研究代表者:宮崎, 照宣/ハイブリッド磁性体の微細化プロセスとトンネル再生磁気ヘッドの作製
Implications of Compressed Supersymmetry for Collider and Dark Matter Searches
Martin has proposed a scenario dubbed ``compressed supersymmetry'' (SUSY)
where the MSSM is the effective field theory between energy scales M_{\rm weak}
and M_{\rm GUT}, but with the GUT scale SU(3) gaugino mass M_3<< M_1 or M_2. As
a result, squark and gluino masses are suppressed relative to slepton, chargino
and neutralino masses, leading to a compressed sparticle mass spectrum, and
where the dark matter relic density in the early universe may be dominantly
governed by neutralino annihilation into ttbar pairs via exchange of a light
top squark. We explore the dark matter and collider signals expected from
compressed SUSY for two distinct model lines with differing assumptions about
GUT scale gaugino mass parameters. For dark matter signals, the compressed
squark spectrum leads to an enhancement in direct detection rates compared to
models with unified gaugino masses. Meanwhile, neutralino halo annihilation
rates to gamma rays and anti-matter are also enhanced relative to related
scenarios with unified gaugino masses but, depending on the halo dark matter
distribution, may yet be below the sensitivity of indirect searches underway.
In the case of collider signals, we compare the rates for the potentially
dominant decay modes of the stop_1 which may be expected to be produced in
cascade decay chains at the LHC: \tst_1\to c\tz_1 and \tst_1\to bW\tz_1. We
examine the extent to which multilepton signal rates are reduced when the
two-body decay mode dominates. For the model lines that we examine here, the
multi-lepton signals, though reduced, still remain observable at the LHC.Comment: 22 pages including 24 eps figure
Superconductivity and Pseudogap in Quasi-Two-Dimensional Metals around the Antiferromagnetic Quantum Critical Point
Spin fluctuations (SF) and SF-mediated superconductivity (SC) in
quasi-two-dimensional metals around the antiferrromagnetic (AF) quantum
critical point (QCP) are investigated by using the self-consistent
renormalization theory for SF and the strong coupling theory for SC. We
introduce a parameter y0 as a measure for the distance from the AFQCP which is
approximately proportional to (x-xc), x being the electron (e) or hole (h)
doping concentration to the half-filled band and xc being the value at the
AFQCP. We present phase diagrams in the T-y0 plane including contour maps of
the AF correlation length and AF and SC transition temperatures TN and Tc,
respectively. The Tc curve is dome-shaped with a maximum at around the AFQCP.
The calculated one-electron spectral density shows a pseudogap in the
high-density-of-states region near (pi,0) below around a certain temperature T*
and gives a contour map at the Fermi energy reminiscent of the Fermi arc. These
results are discussed in comparison with e- and h-doped high-Tc cuprates.Comment: 5 pages, 3 figure
Ginzburg-Landau Equations for Coexistent States of Superconductivity and Antiferromagnetism in t-J model
Ginzburg-Landau (GL) equations for the coexistent state of superconductivity
and antiferromagnetism are derived microscopically from the t-J model with
extended transfer integrals. GL equations and the GL free energy, which are
obtained based on the slave-boson mean-field approximation, reflect the
electronic structure of the microscopic model, especially the evolution of the
Fermi surface due to the change of the doping rate. Thus they are suitable for
studying the material dependence of the coexistent states in high- cuprate
superconductors.Comment: 12 page
Spin correlations in the electron-doped high-transition-temperature superconductor Nd{2-x}Ce{x}CuO{4+/-delta}
High-transition-temperature (high-Tc) superconductivity develops near
antiferromagnetic phases, and it is possible that magnetic excitations
contribute to the superconducting pairing mechanism. To assess the role of
antiferromagnetism, it is essential to understand the doping and temperature
dependence of the two-dimensional antiferromagnetic spin correlations. The
phase diagram is asymmetric with respect to electron and hole doping, and for
the comparatively less-studied electron-doped materials, the antiferromagnetic
phase extends much further with doping [1, 2] and appears to overlap with the
superconducting phase. The archetypical electron-doped compound
Nd{2-x}Ce{x}CuO{4\pm\delta} (NCCO) shows bulk superconductivity above x \approx
0.13 [3, 4], while evidence for antiferromagnetic order has been found up to x
\approx 0.17 [2, 5, 6]. Here we report inelastic magnetic neutron-scattering
measurements that point to the distinct possibility that genuine long-range
antiferromagnetism and superconductivity do not coexist. The data reveal a
magnetic quantum critical point where superconductivity first appears,
consistent with an exotic quantum phase transition between the two phases [7].
We also demonstrate that the pseudogap phenomenon in the electron-doped
materials, which is associated with pronounced charge anomalies [8-11], arises
from a build-up of spin correlations, in agreement with recent theoretical
proposals [12, 13].Comment: 5 pages, 4 figure
Collider and Dark Matter Phenomenology of Models with Mirage Unification
We examine supersymmetric models with mixed modulus-anomaly mediated SUSY
breaking (MM-AMSB) soft terms which get comparable contributions to SUSY
breaking from moduli-mediation and anomaly-mediation. The apparent (mirage)
unification of soft SUSY breaking terms at Q=mu_mir not associated with any
physical threshold is the hallmark of this scenario. The MM-AMSB structure of
soft terms arises in models of string compactification with fluxes, where the
addition of an anti-brane leads to an uplifting potential and a de Sitter
universe, as first constructed by Kachru {\it et al.}. The phenomenology mainly
depends on the relative strength of moduli- and anomaly-mediated SUSY breaking
contributions, and on the Higgs and matter field modular weights, which are
determined by the location of these fields in the extra dimensions. We
delineate the allowed parameter space for a low and high value of tan(beta),
for a wide range of modular weight choices. We calculate the neutralino relic
density and display the WMAP-allowed regions. We show the reach of the CERN LHC
and of the International Linear Collider. We discuss aspects of MM-AMSB models
for Tevatron, LHC and ILC searches, muon g-2 and b->s \gamma branching
fraction. We also calculate direct and indirect dark matter detection rates,
and show that almost all WMAP-allowed models should be accessible to a
ton-scale noble gas detector. Finally, we comment on the potential of colliders
to measure the mirage unification scale and modular weights in the difficult
case where mu_mir>>M_GUT.Comment: 34 pages plus 42 EPS figures; version with high resolution figures is
at http://www.hep.fsu.edu/~bae
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