1,298 research outputs found
Метод формирования цифровой тени процесса перемещения человека на основе объединения систем захвата движений
В статье рассматривается задача формирования цифровой тени процесса перемещения человека. Проведен анализ предметной области, который показал необходимость формализации процесса создания цифровых теней для имитации движений человека в виртуальном пространстве, тестировании программно-аппаратных комплексов, функционирующих на основе действий человека, а также в различных системах опорно-двигательной реабилитации. Выявлено, что среди существующих подходов к захвату движений человека нельзя выделить универсальный и стабильно работающий при различных условиях внешней среды. Разработан метод формирования цифровой тени на основе комбинирования и синхронизации данных из трех систем захвата движений (трекеры виртуальной реальности, костюм motion capture и камеры с использованием технологий компьютерного зрения). Объединение перечисленных систем позволяет получить комплексную оценку положения и состояния человека независимо от условий внешней среды (электромагнитные помехи, освещенность). Для реализации предложенного метода проведена формализация цифровой тени процесса перемещения человека, включающая описание механизмов сбора и обработки данных от различных систем захвата движений, а также этапы объединения, фильтрации и синхронизации данных. Научная новизна метода заключается в формализации процесса сбора данных о перемещении человека, объединении и синхронизации аппаратного обеспечения используемых систем захвата движений для создания цифровых теней процесса перемещения человека. Полученные теоретические результаты будут использоваться в качестве основы для программной абстракции цифровой тени в информационных системах для решения задач тестирования, имитации человека и моделирования его реакции на внешние раздражители за счет обобщения собранных массивов данных о его перемещении
Enabling propagation of anisotropic polaritons along forbidden directions via a topological transition
Recent discoveries of polaritons in van der Waals (vdW) crystals with
directional in-plane propagation, ultra-low losses, and broad spectral
tunability have opened the door for unprecedented manipulation of the flow of
light at the nanoscale. However, despite their extraordinary potential for
nano-optics, these unique polaritons also present an important limitation:
their directional propagation is intrinsically determined by the crystal
structure of the host material, which imposes forbidden directions of
propagation and hinders its control. Here, we theoretically predict and
experimentally demonstrate that directional polaritons (in-plane hyperbolic
phonon polaritons) in a vdW biaxial slab (alpha-phase molybdenum trioxide) can
be steered along previously forbidden directions by inducing an optical
topological transition, which naturally emerges when placing the slab on a
substrate with a given negative permittivity (4H-SiC). Importantly, due to the
low-loss nature of this topological transition, we are able to visualize in
real space exotic intermediate polaritonic states between mutually orthogonal
hyperbolic regimes, which permit to unveil the unique topological origin of the
transition. This work provides new insights into the emergence of low-loss
optical topological transitions in vdW crystals, offering a novel route to
efficiently steer the flow of energy at the nanoscale
Focusing of in-plane hyperbolic polaritons in van der Waals crystals with tailored infrared nanoantennas
Phonon polaritons (PhPs),light coupled to lattice vibrations,with in-plane
hyperbolic dispersion exhibit ray-like propagation with large wavevectors and
enhanced density of optical states along certain directions on a surface. As
such, they have raised a surge of interest as they promise unprecedented
possibilities for the manipulation of infrared light with planar circuitry and
at the nanoscale. Here, we demonstrate, for the first time, the focusing of
in-plane hyperbolic PhPs propagating along thin slabs of MoO3. To that end, we
developed metallic nanoantennas of convex geometries for both the efficient
launching and focusing of the polaritons. Remarkably, the foci obtained exhibit
enhanced near-field confinement and absorption compared to foci produced by
in-plane isotropic PhPs. More intriguingly, foci sizes as small as lamdap/5
=lamda0/50 were achieved (lamdap is the polariton wavelength and lamda0 the
photon wavelength). Focusing of in-plane hyperbolic polaritons introduces a
first and most basic building block developing planar polariton optics
utilizing in-plane anisotropic van der Waals materials and metasurfaces
Chiral photonic super-crystals based on helical van der Waals homostructures
Chirality is probably the most mysterious among all symmetry transformations.
Very readily broken in biological systems, it is practically absent in
naturally occurring inorganic materials and is very challenging to create
artificially. Chiral optical wavefronts are often used for the identification,
control and discrimination of left- and right-handed biological and other
molecules. Thus, it is crucially important to create materials capable of
chiral interaction with light, which would allow one to assign arbitrary chiral
properties to a light field. In this paper, we utilized van der Waals
technology to assemble helical homostructures with chiral properties (e. g.
circular dichroism). Because of the large range of van der Waals materials
available such helical homostructures can be assigned with very flexible
optical properties. We demonstrate our approach by creating helical
homostructures based on multilayer AsS, which offers the most
pronounced chiral properties even in thin structures due to its strong biaxial
optically anisotropy. Our work showcases that the chirality of an
electromagnetic system may emerge at an intermediate level between the
molecular and the mesoscopic one due to the tailored arrangement of non-chiral
layers of van der Waals crystals and without additional patterning
Multi-particle Production and Thermalization in High-Energy QCD
We argue that multi-particle production in high energy hadron and nuclear
collisions can be considered as proceeding through the production of gluons in
the background classical field. In this approach we derive the gluon spectrum
immediately after the collision and find that at high energies it is
parametrically enhanced by ln(1/x) with respect to the quasi-classical result
(x is the Bjorken variable). We show that the produced gluon spectrum becomes
thermal (in three dimensions) with an effective temperature determined by the
saturation momentum Qs, T= c Qs/2pi during the time ~1/T; we estimate
c=sqrt{2pi}/2 ~ 1.2. Although this result by itself does not imply that the
gluon spectrum will remain thermal at later times, it has an interesting
applications to heavy ion collisions. In particular, we discuss the possibility
of Bose-Einstein condensation of the produced gluon pairs and estimate the
viscosity of the produced gluon system.Comment: 25 pages, 4 figures; typos fixed; discussions expanded; we added a
new section IV in which we argue that at high energies the production
mechanism discussed in the paper is parametrically enhanced by ln(1/x) with
respect to the quasi-classical resul
Planar refraction and lensing of highly confined polaritons in anisotropic media
Refraction between isotropic media is characterized by light bending towards the normal to the boundary when passing from a low- to a high-refractive-index medium. However, refraction between anisotropic media is a more exotic phenomenon which remains barely investigated, particularly at the nanoscale. Here, we visualize and comprehensively study the general case of refraction of electromagnetic waves between two strongly anisotropic (hyperbolic) media, and we do it with the use of nanoscale-confined polaritons in a natural medium: alpha-MoO3. The refracted polaritons exhibit non-intuitive directions of propagation as they traverse planar nanoprisms, enabling to unveil an exotic optical effect: bending-free refraction. Furthermore, we develop an in-plane refractive hyperlens, yielding foci as small as lambdap/6, being lambdap the polariton wavelength (lambda0/50 compared to the wavelength of free-space light). Our results set the grounds for planar nano-optics in strongly anisotropic media, with potential for effective control of the flow of energy at the nanoscale.G.Á.-P. and J.T.-G. acknowledge support through the Severo Ochoa Program from the Government of the Principality of Asturias (nos. PA-20-PF-BP19-053 and PA-18-PF-BP17-126, respectively). S.X. acknowledges the support from Independent Research Fund Denmark (Project No. 9041-00333B). B.C. acknowledges the support from VILLUM FONDEN (No. 00027987). The Center for Nanostructured Graphene is sponsored by the Danish National Research Foundation (Project No. DNRF103.) K.V.V. and V.S.V. gratefully acknowledge the financial support from the Ministry of Science and Higher Education of the Russian Federation (Agreement No. 075-15-2021-606). J.M.-S. acknowledges financial support through the Ramón y Cajal Program from the Government of Spain (RYC2018-026196-I). A.Y.N. and J.I.M. acknowledge the Spanish Ministry of Science, Innovation and Universities (national projects MAT201788358-C3-3-R and PID2019-104604RB/AEI/10.13039/501100011033). R.H. acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (national project RTI2018-094830-B-100 and the project MDM-2016-0618 of the Marie de Maeztu Units of Excellence Program) and the Basque Government (grant No. IT1164-19). A.Y.N. also acknowledges the Basque Department of Education (grant no. PIBA-2020-1-0014). P.A.-G. acknowledges support from the European Research Council under starting grant no. 715496, 2DNANOPTICA and the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation grant number PID2019-111156GB-I00)
Multiple and spectrally robust photonic magic angles in reconfigurable α-MoO3 trilayers
The emergence of a topological transition of the polaritonic dispersion in twisted bilayers of anisotropic van der Waals materials at a given twist angle-the photonic magic angle-results in the diffractionless propagation of polaritons with deep-subwavelength resolution. This type of propagation, generally referred to as canalization, holds promise for the control of light at the nanoscale. However, the existence of a single photonic magic angle hinders such control since the canalization direction in twisted bilayers is unique and fixed for each incident frequency. Here we overcome this limitation by demonstrating multiple spectrally robust photonic magic angles in reconfigurable twisted α-phase molybdenum trioxide (α-MoO3) trilayers. We show that canalization of polaritons can be programmed at will along any desired in-plane direction in a single device with broad spectral ranges. These findings open the door for nanophotonics applications where on-demand control is crucial, such as thermal management, nanoimaging or entanglement of quantum emitters.A.I.F.T.-M. and G.Á.-P. acknowledge support from the Severo Ochoa program of the Government of the Principality of Asturias (nos. PA-21-PF-BP20-117 and PA-20-PF-BP19-053, respectively). J.M.-S. acknowledges financial support from the Ramón y Cajal Program of the Government of Spain and FSE (RYC2018-026196-I) and the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation grant no. PID2019-110308GA-I00). P.A.-G. acknowledges support from the European Research Council under starting grant no. 715496, 2DNANOPTICA and the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation grant no. PID2019-111156GB-I00). A.Y.N. acknowledges the Spanish Ministry of Science and Innovation (grant PID2020-115221GB-C42) and the Basque Department of Education (grant PIBA-2020-1-0014). This project has also been supported by Asturias FICYT under grant AYUD/2021/51185 with the support of FEDER funds. These results also received support from a fellowship from ‘la Caixa’ Foundation (ID 100010434). The fellowship code is LCF/BQ/DI21/11860026. In addition, this work was supported by a 2022 Leonardo Grant for Researchers in Physics, BBVA Foundation.Peer reviewe
Twist-tunable polaritonic nanoresonators in a van der Waals crystal
Optical nanoresonators are key building blocks in various nanotechnological applications (e.g., spectroscopy) due to their ability to effectively confine light at the nanoscale. Recently, nanoresonators based on phonon polaritons (PhPs)—light coupled to lattice vibrations—in polar crystals (e.g., SiC, or h-BN) have attracted much attention due to their strong field confinement, high quality factors, and their potential to enhance the photonic density of states at mid-infrared (mid-IR) frequencies, where numerous molecular vibrations reside. Here, we introduce a new class of mid-IR nanoresonators that not only exhibit the extraordinary properties previously reported, but also incorporate a new degree of freedom: twist tuning, i.e., the possibility of controlling their spectral response by simply rotating the constituent material. To achieve this result, we place a pristine slab of the van der Waals (vdW) α-MoO3 crystal, which supports in-plane hyperbolic PhPs, on an array of metallic ribbons. This sample design based on electromagnetic engineering, not only allows the definition of α-MoO3 nanoresonators with low losses (quality factors, Q, up to 200), but also enables a broad spectral tuning of the polaritonic resonances (up to 32 cm−1, i.e., up to ~6 times their full width at half maximum, FWHM ~5 cm−1) by a simple in-plane rotation of the same slab (from 0 to 45°). These results open the door to the development of tunable and low-loss IR nanotechnologies, fundamental requirements for their implementation in molecular sensing, emission or photodetection applications.A.I.F.T.-M. and J.T.-G. acknowledge support through the Severo Ochoa program from the Government of the Principality of Asturias (nos. PA-21-PF-BP20-117 and PA-18-PF-BP17-126, respectively). J.M.-S. acknowledges financial support from the Ramón y Cajal Program of the Government of Spain and FSE (RYC2018-026196-I), and the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation grant number PID2019-110308GA-I00/AEI/10.13039/501100011033). P.A.-G. acknowledges support from the European Research Council under starting grant no. 715496, 2DNANOPTICA and the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation grant number PID2019-111156GB-I00). A.Y.N. acknowledges the Spanish Ministry of Science and Innovation (grants MAT201788358-C3-3-R and PID2020-115221GB-C42) and the Basque Department of Education (grant PIBA-2020-1-0014). This project has been supported by Asturias FICYT under grant AYUD/2021/51185 with the support of FEDER funds. This work is produced with the support of a 2022 Leonardo Grant for Researchers in Physics, BBVA Foundation.Peer reviewe
van der Waals materials for overcoming fundamental limitations in photonic integrated circuitry
With the advance of on-chip nanophotonics, there is a high demand for high-refractive-index and low-loss materials. Currently, this technology is dominated by silicon, but van der Waals (vdW) materials with a high refractive index can offer a very advanced alternative. Still, up to now, it was not clear if the optical anisotropy perpendicular to the layers might be a hindering factor for the development of vdW nanophotonics. Here, we studied WS2-based waveguides in terms of their optical properties and, particularly, in terms of possible crosstalk distance. Surprisingly, we discovered that the low refractive index in the direction perpendicular to the atomic layers improves the characteristics of such devices, mainly due to expanding the range of parameters at which single-mode propagation can be achieved. Thus, using anisotropic materials offers new opportunities and novel control knobs when designing nanophotonic devices.L.M.M. acknowledges Project PID2020-115221GB-C41, financed by MCIN/AEI/10.13039/501100011033, and the Aragon Government through Project Q-MAD. A.A.V., I.K., and D.I.Y. gratefully acknowledge the financial support from the Ministry of Science and Higher Education (Agreement No. 075-15-2021-606). I.A.K. gratefully acknowledges the financial support from the RSF (No. 22-19-00738) for first-principle calculations. K.S.N. is grateful to the Ministry of Education, Singapore (Research Centre of Excellence award to the Institute for Functional Intelligent Materials, I-FIM, project No. EDUNC-33-18-279-V12) and to the Royal Society (UK, grant number RSRP\R\190000) for support.Peer reviewe
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