17,460 research outputs found
Theory of Optical Nonlocality in Polar Dielectrics
Sub-wavelength confinement of mid-infrared light can be achieved exploiting
the metal-like optical response of polar dielectric crystals in their
Reststrahlen spectral region, where they support evanescent modes termed
surface phonon polaritons. In the past few years the investigation of phonon
polaritons localised in nanoresonators and layered heterostructures has enjoyed
remarkable success, highlighting them as a promising platform for mid-infrared
nanophotonic applications. Here we prove that the standard local dielectric
description of phonon polaritons in nanometric objects fails due to the
nonlocal nature of the phonon response and we develop the corresponding
nonlocal theory. Application of our general theory to both dielectric
nanospheres and thin films demonstrates that polar dielectrics exhibit a rich
nonlocal phenomenology, qualitatively different from the one of plasmonic
systems, due to the negative dispersion of phononic optical modes.Comment: 13 pages, 6 figure
Theory of four-wave-mixing in phonon polaritons
Third order anharmonic scattering in light-matter systems can drive a wide
variety of practical and physically interesting processes from lasing to
polariton condensation. Motivated by recent experimental results in the
nonlinear optics of localised phonon polaritons, in this Letter we develop a
quantum theory capable of describing four-wave mixing in arbitrarily
inhomogeneous photonic environments. Using it we investigate Kerr
self-interaction and parametric scattering of surface and localised phonon
polaritons, showing both processes to be within experimental reach.Comment: 20 pages, 3 figure
Real-space Hopfield diagonalization of inhomogeneous dispersive media
We introduce a real-space technique able to extend the standard Hopfield
approach commonly used in quantum polaritonics to the case of inhomogeneous
lossless materials interacting with the electromagnetic field. We derive the
creation and annihilation polaritonic operators for the system normal modes as
linear, space-dependent superpositions of the microscopic light and matter
fields, and we invert the Hopfield transformation expressing the microscopic
fields as functions of the polaritonic operators. As an example, we apply our
approach to the case of a planar interface between vacuum and a polar
dielectric, showing how we can consistently treat both propagative and surface
modes, and express their nonlinear interactions, arising from phonon
anharmonicity, as polaritonic scattering terms. We also show that our theory
can be naturally extended to the case of dissipative materials
Theoretical Investigation of Phonon Polaritons in SiC Micropillar Resonators
Of late there has been a surge of interest in localised phonon polariton
resonators which allow for sub-diffraction confinement of light in the
mid-infrared spectral region by coupling to optical phonons at the surface of
polar dielectrics. Resonators are generally etched on deep substrates which
support propagative surface phonon polariton resonances. Recent experimental
work has shown that understanding the coupling between localised and
propagative surface phonon polaritons in these systems is vital to correctly
describe the system resonances. In this paper we comprehensively investigate
resonators composed of arrays of cylindrical SiC resonators on SiC substrates.
Our bottom-up approach, starting from the resonances of single, free standing
cylinders and isolated substrates, and exploiting both numerical and analytical
techniques, allows us to develop a consistent understanding of the parameter
space of those resonators, putting on firmer ground this blossoming technology.Comment: 10 Pages, 8 Figure
Atmospheric monitoring in the mm and sub-mm bands for cosmological observations: CASPER2
Cosmological observations from ground at millimetre and sub-millimetre
wavelengths are affected by atmospheric absorption and consequent emission. The
low and high frequency (sky noise) fluctuations of atmospheric performance
imply careful observational strategies and/or instrument technical solutions.
Measurements of atmospheric emission spectra are necessary for accurate
calibration procedures as well as for site testing statistics. CASPER2, an
instrument to explore the 90-450 GHz (3-15 1/cm) spectral region, was developed
and verified its operation in the Alps. A Martin-Puplett Interferometer (MPI)
operates comparing sky radiation, coming from a field of view (fov) of 28
arcminutes (FWHM) collected by a 62-cm in diameter Pressman-Camichel telescope,
with a reference source. The two output ports of the interferometer are
detected by two bolometers cooled down to 300 mK inside a wet cryostat. Three
different and complementary interferometric techniques can be performed with
CASPER2: Amplitude Modulation (AM), Fast-Scan (FS) and Phase Modulation (PM).
An altazimuthal mount allows the sky pointing, possibly co-alligned to the
optical axis of the 2.6-m in diameter telescope of MITO (Millimetre and
Infrared Testagrigia Observatory, Italy). Optimal timescale to average acquired
spectra is inferred by Allan variance analysis at 5 fiducial frequencies. We
present the motivation for and design of the atmospheric spectrometer CASPER2.
The adopted procedure to calibrate the instrument and preliminary performance
of the instrument are described. Instrument capabilities were checked during
the summer observational campaign at MITO in July 2010 by measuring atmospheric
emission spectra with the three different procedures.Comment: 11 pages, 9 figures, 2 tables, Accepted for publication in MNRA
Coherent coupling between localised and propagating phonon polaritons
Following the recent observation of localised phonon polaritons in
user-defined silicon carbide nano-resonators, here we demonstrate coherent
coupling between those localised modes and propagating phonon polaritons bound
to the surface of the nano-resonator's substrate. In order to obtain
phase-matching, the nano-resonators have been fabricated to serve the double
function of hosting the localised modes, while also acting as grating for the
propagating ones. The coherent coupling between long lived, optically
accessible localised modes, and low-loss propagative ones, opens the way to the
design and realisation of phonon-polariton based quantum circuits
Strengthening measurements from the edges: application-level packet loss rate estimation
Network users know much less than ISPs, Internet exchanges and content providers about what happens inside the network. Consequently users cannot either easily detect network neutrality violations or readily exercise their market power by knowledgeably switching ISPs. This paper contributes to the ongoing efforts to empower users by proposing two models to estimate -- via application-level measurements -- a key network indicator, i.e., the packet loss rate (PLR) experienced by FTP-like TCP downloads. Controlled, testbed, and large-scale experiments show that the Inverse Mathis model is simpler and more consistent across the whole PLR range, but less accurate than the more advanced Likely Rexmit model for landline connections and moderate PL
Electrical Generation of Surface Phonon Polaritons
Efficient electrical generation of mid-infrared light is challenging because
of the dearth of materials with natural dipole-active electronic transitions in
this spectral region. One approach to solve this problem is through
quantum-engineering of the electron dispersion to create artificial
transitions, as in quantum cascade devices. In this work we propose an
alternative method to generate mid-infrared light, utilizing the coupling
between longitudinal and transverse degrees of freedom due to the nonlocal
optical response of nanoscopic polar dielectric crystals. Polar crystals
support transverse sub-diffraction photonic modes in the mid-infrared. They
also support longitudinal phonons, which couple efficiently with electrical
currents through the Fr\"ohlich interaction. As we have shown in previous
theoretical and experimental works, these two degrees of freedom can hybridize
forming longitudinal-transverse polaritons. Here we theoretically demonstrate
that longitudinal-transverse polaritons can be efficiently generated by
electrical currents, leading to resonant narrowband photonic emission. This
approach can therefore be utilised to electrically generate far-field
mid-infrared photons in the absence of dipole-active electronic transitions,
potentially underpinning a novel generation of mid-infrared optoelectronic
devices.Comment: 14 pages, 6 figure
Insufficient control of blood pressure and incident diabetes
OBJECTIVE:
Incidence of type 2 diabetes might be associated with preexisting hypertension. There is no information on whether incident diabetes is predicted by blood pressure control. We evaluated the hazard of diabetes in relation to blood pressure control in treated hypertensive patients.
RESEARCH DESIGN AND METHODS:
Nondiabetic, otherwise healthy, hypertensive patients (N = 1,754, mean +/- SD age 52 +/- 11 years, 43% women) participated in a network over 3.4 +/- 1 years of follow-up. Blood pressure was considered uncontrolled if systolic was >or=140 mmHg and/or diastolic was >or=90 mmHg at the last outpatient visit. Diabetes was defined according to American Diabetes Association guidelines.
RESULTS:
Uncontrolled blood pressure despite antihypertensive treatment was found in 712 patients (41%). At baseline, patients with uncontrolledblood pressure were slightly younger than patients with controlled blood pressure (51 +/- 11 vs. 53 +/- 12 years, P < 0.001), with no differences in sex distribution, BMI, duration of hypertension, baseline blood pressure, fasting glucose, serum creatinine and potassium, lipid profile, or prevalence of metabolic syndrome. During follow-up, 109 subjects developed diabetes. Incidence of diabetes was significantly higher in patients with uncontrolled (8%) than in those with controlled blood pressure (4%, odds ratio 2.08, P < 0.0001). In Cox regression analysis controlling for baseline systolic blood pressure and BMI, family history of diabetes, and physical activity, uncontrolled blood pressure doubled the risk of incident diabetes (hazard ratio [HR] 2.10, P < 0.001), independently of significant effects of age (HR 1.02 per year, P = 0.03) and baseline fasting glucose (HR 1.10 per mg/dl, P < 0.001).
CONCLUSIONS:
In a large sample of treated nondiabetic hypertensive subjects, uncontrolled blood pressure is associated with twofold increased risk of incident diabetes independently of age, BMI, baseline blood pressure, or fasting glucose
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