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Hoyeong Kwon, Dimitrios Sounas, Andrea Cordaro, Albert Polman, Andrea Alù
Optical analog signal processing has been gaining significant attention as a way to overcome the speed and energy limitations of digital techniques. Metasurfaces offer a promising avenue towards this goal due to their efficient manipulation of optical signals over deeply subwavelength volumes. To date, metasurfaces have been proposed to transform signals in the spatial domain, e.g., for beam steering, focusing, or holography, for which angular-dependent responses, or nonlocality, are unwanted features that must be avoided or mitigated...
October 26, 2018: Physical Review Letters
Adam Mock, Dimitrios Sounas, Andrea Alù
Lasers and light emitters do not typically radiate fields with orbital angular momentum (OAM). Here we show that a suitable scheme of spatiotemporal modulation of a microring cavity laser can impart a synthetic angular momentum, resulting in beams with well-defined OAM. The phenomenon relies on a traveling wave modulation of the refractive index of the microring, which breaks the degeneracy of oppositely oriented whispering gallery modes. In parallel, a static structural grating on the periphery of the microring enables efficient vertical radiation...
September 7, 2018: Physical Review Letters
Abdoul Wahab Alassane Mohamed, Koini Moussa, Souna Badio Seyni, Zirbine Abassa Seyni, Akambi Sanoussi Kasoumou, Konguise Ziberou
Myositis ossificans circumscripta (MOC) is a rare benign condition characterized by heterotopic ossification occurring in the soft tissues. We report the case of a 15-year old patient complaining of mixed hip pain. No trauma has been reported during the interview. The joint had inflammation appearance and a non-mobilizing swelling adhered to the deeper structure with parietal projection over the groin fold. Radiographs of the hip showed a thickening of the soft tissues of the hip and some periarticular calcifications with unclear appearance...
2018: Pan African Medical Journal
Li Quan, Younes Ra'di, Dimitrios L Sounas, Andrea Alù
Willis coupling in acoustic materials defines the cross-coupling between strain and velocity, analogous to bianisotropic phenomena in electromagnetics. While these phenomena have been garnering significant attention in recent years, to date their effects have been considered mostly perturbative. Here, we derive general bounds on the Willis response of acoustic scatterers, show that these bounds can be reached in suitably designed scatterers, and outline a systematic venue for the realistic implementation of maximally bianisotropic acoustic inclusions...
June 22, 2018: Physical Review Letters
Matthew E Coldiron, Ousmane Guindo, Rockyath Makarimi, Issaka Soumana, Amadou Matar Seck, Souna Garba, Emilie Macher, Sheila Isanaka, Rebecca F Grais
BACKGROUND: Rotavirus remains a major cause of diarrhea among children under 5 years of age. The efficacy of RotaSIIL, a pentavalent rotavirus vaccine, was shown in an event-driven trial in Niger. We describe the two-year safety follow-up of this trial. METHODS: Follow-up of safety outcomes began upon administration of the first dose of RotaSIIL or placebo. Adverse events were followed until 28 days after the third dose, and serious adverse events were followed until 2 years of age...
June 14, 2018: Vaccine
Chengzhi Qin, Feng Zhou, Yugui Peng, Dimitrios Sounas, Xuefeng Zhu, Bing Wang, Jianji Dong, Xinliang Zhang, Andrea Alù, Peixiang Lu
By using optical phase modulators in a fiber-optical circuit, we theoretically and experimentally demonstrate large control over the spectrum of an impinging signal, which may evolve analogously to discrete diffraction in spatial waveguide arrays. The modulation phase acts as a photonic gauge potential in the frequency dimension, realizing efficient control of the central frequency and bandwidth of frequency combs. We experimentally achieve a 50 GHz frequency shift and threefold bandwidth expansion of an impinging comb, as well as the frequency analogue of various refraction phenomena, including negative refraction and perfect focusing in the frequency domain, both for discrete and continuous incident spectra...
March 30, 2018: Physical Review Letters
Tolga Dinc, Mykhailo Tymchenko, Aravind Nagulu, Dimitrios Sounas, Andrea Alu, Harish Krishnaswamy
Recent research has explored the spatiotemporal modulation of permittivity to break Lorentz reciprocity in a manner compatible with integrated-circuit fabrication. However, permittivity modulation is inherently weak and accompanied by loss due to carrier injection, particularly at higher frequencies, resulting in large insertion loss, size, and/or narrow operation bandwidths. Here, we show that the presence of absorption in an integrated electronic circuit may be counter-intuitively used to our advantage to realize a new generation of magnet-free non-reciprocal components...
October 6, 2017: Nature Communications
Younes Ra'di, Dimitrios L Sounas, Andrea Alù
Graded metasurfaces exploit the local momentum imparted by an impedance gradient to mold the impinging wave front. This approach suffers from fundamental limits on the overall conversion efficiency, and it is challenged by fabrication limitations on the spatial resolution. Here, we introduce the concept of metagratings, formed by periodic arrays of carefully tailored bianisotropic inclusions and show that they enable wave front engineering with unitary efficiency and significantly lower fabrication demands...
August 11, 2017: Physical Review Letters
Amanda J Souna, John S Bender, John T Fourkas
Solvents for cleaning optics often come into contact with plastic and/or rubber during storage and transfer. To explore the effects that exposure to these materials can have on solvents, we used vibrational sum-frequency-generation spectroscopy to study a silica optic following cleaning with solvents that had come into contact with either low-density polyethylene, high-density polyethylene, or rubber. Our studies show that even brief contact of acetone, methanol, or isopropanol with plastic or rubber can cause otherwise pure solvents to leave a persistent residue...
May 1, 2017: Applied Optics
Dimitrios L Sounas, Andrea Alù
Asymmetric structures support different field distributions and electromagnetic responses when excited from different directions. Here we show that time-reversal symmetry imposes fundamental constraints on their overall response, beyond those dictated by reciprocity. For two-port devices, the asymmetry in field distribution for opposite excitations is shown to be fundamentally bounded by the reflection at the ports, and the fields are identical everywhere in space in the case of full transmission. In multiport and open scenarios, these bounds have implications on radiation and scattering at different ports and towards different directions...
April 14, 2017: Physical Review Letters
Corentin Coulais, Dimitrios Sounas, Andrea Alù
Reciprocity is a general, fundamental principle governing various physical systems, which ensures that the transfer function-the transmission of a physical quantity, say light intensity-between any two points in space is identical, regardless of geometrical or material asymmetries. Breaking this transmission symmetry offers enhanced control over signal transport, isolation and source protection. So far, devices that break reciprocity (and therefore show non-reciprocity) have been mostly considered in dynamic systems involving electromagnetic, acoustic and mechanical wave propagation associated with fields varying in space and time...
February 23, 2017: Nature
Romain Fleury, Dimitrios Sounas, Andrea Alù
Sensing an incoming signal is typically associated with absorbing a portion of its energy, inherently perturbing the measurement and creating reflections and shadows. Here, in contrast, we demonstrate a non-invasive, shadow-free, invisible sensor for airborne sound waves at audible frequencies, which fully absorbs the impinging signal, without at the same time perturbing its own measurement or creating a shadow. This unique sensing device is based on the unusual scattering properties of a parity-time (PT) symmetric metamaterial device formed by a pair of electro-acoustic resonators loaded with suitably tailored non-Foster electrical circuits, constituting the acoustic equivalent of a coherent perfect absorber coupled to a coherent laser...
2015: Nature Communications
Romain Fleury, Dimitrios L Sounas, Andrea Alù
We introduce a new mechanism to realize negative refraction and planar focusing using a pair of parity-time symmetric metasurfaces. In contrast to existing solutions that achieve these effects with negative-index metamaterials or phase conjugating surfaces, the proposed parity-time symmetric lens enables loss-free, all-angle negative refraction and planar focusing in free space, without relying on bulk metamaterials or nonlinear effects. This concept may represent a pivotal step towards loss-free negative refraction and highly efficient planar focusing by exploiting the largely uncharted scattering properties of parity-time symmetric systems...
July 11, 2014: Physical Review Letters
Dimitrios L Sounas, Andrea Alù
Using Lorentz reciprocity and power conservation, we prove that the extinction cross section of an arbitrarily shaped scatterer is always the same when illuminated from opposite directions and with the same polarization. For lossless and passive objects, this finding implies identical scattering cross sections for opposite excitations, with relevant implications on cloaking designs and scattering suppression schemes. This scattering symmetry can be broken by introducing absorption into the system, providing a path toward large scattering asymmetries when combined with Fano interference...
July 1, 2014: Optics Letters
D Souna, A S Amir, S N Bekhoucha, M Berrazeg, M Drissi
OBJECTIVES: Enterobacter cloacae is a major nosocomial bacterium causing severe infections. A multicenter retrospective cohort study was conducted to collect baseline information on the molecular characteristics of β-lactamase producing Enterobacter cloacae in the west of Algeria. MATERIALS AND METHODS: We report a series of 42 extended-spectrum β-lactamase (ESBL) producing non-repetitive Enterobacter cloacae strains, collected in 3 university hospital (Tlemcen, Oran, and Sidi Bel Abbes)...
April 2014: Médecine et Maladies Infectieuses
Romain Fleury, Dimitrios L Sounas, Caleb F Sieck, Michael R Haberman, Andrea Alù
Acoustic isolation and nonreciprocal sound transmission are highly desirable in many practical scenarios. They may be realized with nonlinear or magneto-acoustic effects, but only at the price of high power levels and impractically large volumes. In contrast, nonreciprocal electromagnetic propagation is commonly achieved based on the Zeeman effect, or modal splitting in ferromagnetic atoms induced by a magnetic bias. Here, we introduce the acoustic analog of this phenomenon in a subwavelength meta-atom consisting of a resonant ring cavity biased by a circulating fluid...
January 31, 2014: Science
Nima Chamanara, Dimitrios Sounas, Thomas Szkopek, Christophe Caloz
Terahertz plasmons and magnetoplasmons propagating along electrically and chemically doped graphene p-n junctions are investigated. It is shown that such junctions support non-reciprocal magnetoplasmonic modes which get concentrated at the middle of the junction in one direction and split away from the middle of the junction in the other direction under the application of an external static magnetic field. This phenomenon follows from the combined effects of circular birefringence and carrier density non-uniformity...
October 21, 2013: Optics Express
Christopher A Rivera, Amanda J Souna, John S Bender, Katherine Manfred, John T Fourkas
There is a growing appreciation that dynamic processes play an important role in determining the line shape in surface-selective, nonlinear spectroscopies such as vibrational sum-frequency-generation (VSFG). Here we analyze the influence that reorientation can have on VSFG spectra when the vibrational transition frequency is a function of orientation. Under these circumstances, reorientation-induced spectral diffusion (RISD) causes the underlying spectral line shape to become time dependent. Unlike previously reported mechanisms through which reorientation can contribute to the VSFG signal, RISD influences the line shape regardless of the degree of polarization of the Raman transition that is probed...
December 12, 2013: Journal of Physical Chemistry. B
Dimitrios L Sounas, Christophe Caloz, Andrea Alù
Breaking time-reversal symmetry enables the realization of non-reciprocal devices, such as isolators and circulators, of fundamental importance in microwave and photonic communication systems. This effect is almost exclusively achieved today through magneto-optical phenomena, which are incompatible with integrated technology because of the required large magnetic bias. However, this is not the only option to break reciprocity. The Onsager-Casimir principle states that any odd vector under time reversal, such as electric current and linear momentum, can also produce a non-reciprocal response...
2013: Nature Communications
Nima Chamanara, Dimitrios Sounas, Christophe Caloz
The non-reciprocity of the edge magnetoplasmon modes of a graphene strip is leveraged to design a non-reciprocal magnetoplasmon graphene coupler, coupling only in one direction. The proposed coupler consists of two coplanar parallel magnetically biased graphene strips. In the forward direction, the modes along the adjacent strip edges of the strips have the same wavenumber and therefore couple to each other. In the backward direction, the modes along the adjacent strip edges have different wavenumbers and therefore no coupling occurs...
May 6, 2013: Optics Express
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