745 research outputs found
Localized U(1) Gauge Fields, Millicharged Particles, and Holography
We consider U(1) gauge fields in a slice of AdS_5 with bulk and boundary mass
parameters. The zero mode of a bulk U(1) gauge field can be localized either on
the UV or IR brane. This leads to a simple model of millicharged particles in
which fermions can have arbitrarily small electric charge. In the electroweak
sector we also discuss phenomenological implications of a localized U(1)_Y
gauge boson. Using the AdS/CFT correspondence we present the 4D holographic
interpretation of the 5D model. In particular the photon is shown to be a
composite particle when localized near the IR brane, whereas it is elementary
when localized near the UV brane. In the dual interpretation the
``millicharge'' results from an elementary fermion coupling to a composite
photon via a vector current with large anomalous dimension.Comment: 26 pages, 1 figur
Concentrating light in Cu(In,Ga)Se2 solar cells
Light concentration has proven beneficial for solar cells, most notably for
highly efficient but expensive absorber materials using high concentrations
and large scale optics. Here, we investigate the light concentration for cost-
efficient thin-film solar cells that show nano- or microtextured absorbers.
Our absorber material of choice is Cu(In,Ga)Se2 (CIGSe), which has a proven
stabilized record efficiency of 22.6% and which—despite being a
polycrystalline thin-film material—is very tolerant to environmental
influences. Taking a nanoscale approach, we concentrate light in the CIGSe
absorber layer by integrating photonic nanostructures made from dielectric
materials. The dielectric nanostructures give rise to resonant modes and field
localization in their vicinity. Thus, when inserted inside or adjacent to the
absorber layer, absorption and efficiency enhancement are observed. In
contrast to this internal absorption enhancement, external enhancement is
exploited in the microscaled approach: mm-sized lenses can be used to
concentrate light onto CIGSe solar cells with lateral dimensions reduced down
to the micrometer range. These micro solar cells come with the benefit of
improved heat dissipation compared with the large scale concentrators and
promise compact high-efficiency devices. Both approaches of light
concentration allow for reduction in material consumption by restricting the
absorber dimension either vertically (ultrathin absorbers for dielectric
nanostructures) or horizontally (microabsorbers for concentrating lenses) and
have significant potential for efficiency enhancement
Photoinduced Temperature Gradients in Sub-wavelength Plasmonic Structures: The Thermoplasmonics of Nanocones
Plasmonic structures are renowned for their capability to efficiently convert
light into heat at the nanoscale. However, despite the possibility to generate
deep sub-wavelength electromagnetic hot spots, the formation of extremely
localized thermal hot spots is an open challenge of research, simply because of
the diffusive spread of heat along the whole metallic nanostructure. Here we
tackle this challenge by exploiting single gold nanocones. We theoretically
show how these structures can indeed realize extremely high temperature
gradients within the metal, leading to deep sub-wavelength thermal hot spots,
owing to their capability of concentrating light at the apex under resonant
conditions even under continuous wave illumination. A three-dimensional Finite
Element Method model is employed to study the electromagnetic field in the
structure and subsequent thermoplasmonic behaviour, in terms of the
three-dimensional temperature distribution. We show how the latter is affected
by nanocone size, shape, and composition of the surrounding environment.
Finally, we anticipate the use of photoinduced temperature gradients in
nanocones for applications in optofluidics and thermoelectrics or for thermally
induced nanofabrication
Concentrating light in Cu(In,Ga)Se 2
Light concentration has proven beneficial for solar cells, most notably for highly efficient but expensive absorber materials using high concentrations and large scale optics. Here we investigate light concentration for cost efficient thin film solar cells which show nano or microtextured absorbers. Our absorber material of choice is Cu In,Ga Se2 CIGSe which has a proven stabilized record efficiency of 22.6 and which despite being a polycrystalline thin film material is very tolerant to environmental influences. Taking a nanoscale approach, we concentrate light in the CIGSe absorber layer by integrating photonic nanostructures made from dielectric materials. The dielectric nanostructures give rise to resonant modes and field localization in their vicinity. Thus when inserted inside or adjacent to the absorber layer, absorption and efficiency enhancement are observed. In contrast to this internal absorption enhancement, external enhancement is exploited in the microscale approach mm sized lenses can be used to concentrate light onto CIGSe solar cells with lateral dimensions reduced down to the micrometer range. These micro solar cells come with the benefit of improved heat dissipation compared to the large scale concentrators and promise compact high efficiency devices. Both approaches of light concentration allow for reduction in material consumption by restricting the absorber dimension either vertically ultra thin absorbers for dielectric nanostructures or horizontally micro absorbers for concentrating lenses and have significant potential for efficiency enhancemen
Metal nanoparticle plasmons operating within quantum lifetime
We investigate the dynamics of a plasmonic oscillation over a metal
nanoparticle when it is strongly coupled to a quantum emitter (e.g. quantum
dot, molecule). We simulate the density matrix evolution for a simple model;
coupled classical--quantum oscillators system. We show that lifetime of the
plasmonic oscillations can be increased several orders of magnitude, upto the
decay time of the quantum emitter. This effect shows itself as the narrowing of
the plasmon emission band in the spaser (surface plasmon amplification by
stimulated emission of radiation) experiment [{\it Nature}, {\bf 2009}, 460,
1110], where a gold nanoparticle interacts with the surrounding molecules.
Enhancement of the plasmonic excitation lifetime enables stimulated emission to
overcome the spontaneous one. The enhancement occurs due to the emergence of a
phenomenon analogous to electromagnetically induced transparency (EIT). The
effect can find applications in many areas of nanoscale physics, such as in
quantum information with plasmons and in increasing solar cell efficiency.Comment: 9 pages, 7 figure
Overview of bladder heating technology: matching capabilities with clinical requirements.
Moderate temperature hyperthermia (40-45°C for 1 h) is emerging as an effective treatment to enhance best available chemotherapy strategies for bladder cancer. A rapidly increasing number of clinical trials have investigated the feasibility and efficacy of treating bladder cancer with combined intravesical chemotherapy and moderate temperature hyperthermia. To date, most studies have concerned treatment of non-muscle-invasive bladder cancer (NMIBC) limited to the interior wall of the bladder. Following the promising results of initial clinical trials, investigators are now considering protocols for treatment of muscle-invasive bladder cancer (MIBC). This paper provides a brief overview of the devices and techniques used for heating bladder cancer. Systems are described for thermal conduction heating of the bladder wall via circulation of hot fluid, intravesical microwave antenna heating, capacitively coupled radio-frequency current heating, and radiofrequency phased array deep regional heating of the pelvis. Relative heating characteristics of the available technologies are compared based on published feasibility studies, and the systems correlated with clinical requirements for effective treatment of MIBC and NMIBC
Monotonicity and local uniqueness for the Helmholtz equation
This work extends monotonicity-based methods in inverse problems to the case
of the Helmholtz (or stationary Schr\"odinger) equation in a bounded domain for fixed non-resonance frequency and real-valued
scattering coefficient function . We show a monotonicity relation between
the scattering coefficient and the local Neumann-Dirichlet operator that
holds up to finitely many eigenvalues. Combining this with the method of
localized potentials, or Runge approximation, adapted to the case where
finitely many constraints are present, we derive a constructive
monotonicity-based characterization of scatterers from partial boundary data.
We also obtain the local uniqueness result that two coefficient functions
and can be distinguished by partial boundary data if there is a
neighborhood of the boundary where and
Eigenspace Time-Reversal Robust Capon Beamforming for Target Localization in Continuous Random Media
© 2017 IEEE. We propose a novel eigenspace time-reversal robust Capon beamformer (E-TR-RCB) for improved target localization in continuous random media. We also derive the Beamspace-TR-RCB (B-TR-RCB) algorithm and compare their localization performances by varying the medium characteristic and excitation bandwidth. Finite-difference time-domain (FDTD) method is used to numerically obtain the multistatic scattered field data from the continuous random dielectric medium. The results indicate that the E-TR-RCB has superior performance over the B-TR-RCB and outperforms the conventional (elementspace) TR-RCB and decomposition of the time-reversal operator (DORT) imaging techniques
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