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The direct, ultrafast excitation of polar phonons with electromagnetic radiation is a potent strategy for controlling the properties of a wide range of materials, particularly in the context of influencing their magnetic behavior. Here, we show that, contrary to common perception, the origin of phonon-induced magnetic activity does not stem from the Maxwellian fields resulting from the motion of the ions themselves or the effect their motion exerts on the electron subsystem. Through the mechanism of electron–phonon coupling, a coherent state of circularly polarized phonons generates substantial non-Maxwellian fields that disrupt time-reversal symmetry, effectively emulating the behavior of authentic magnetic fields. Notably, the effective fields can reach magnitudes as high as 100 T, surpassing by a factor of α−2≈2×104 the Maxwellian fields resulting from the inverse Faraday effect; α is the fine-structure constant. Because the light-induced nonreciprocal fields depend on the square of the phonon displacements, the chirality the photons transfer to the ions plays no role in magnetophononics.

Diffraction restricts the ability of most electromagnetic devices to image or selectively target objects smaller than the wavelength. We describe planar subwavelength structures capable of focusing well beyond the diffraction limit, operating at arbitrary frequencies. The structure design, related to that of Fresnel plates, forces the input field to converge to a spot on the focal plane. However, unlike the diffraction-limited zone plates, for which focusing results from the interference of traveling waves, the subwavelength plates control the near field and, as such, their superlensing properties originate from a static form of interference. Practical implementations of these plates hold promise for near-field data storage, noncontact sensing, imaging, and nanolithography applications.

CS 2 promises easy access to degradable sulfur-rich polymers and insights into how main-group derivatisation affects polymer formation and properties, though its ring-opening copolymerisation is plagued by low linkage selectivity and small-molecule by-products. We demonstrate that a cooperative Cr(III)/K catalyst selectively delivers poly(dithiocarbonates) from CS 2 and oxetanes while state-of-the-art strategies produce linkage scrambled polymers and heterocyclic by-products. The formal introduction of sulfur centres into the parent polycarbonates results in a net shift of the polymerisation equilibrium towards, and therefore facilitating, depolymerisation. During copolymerisation however, the catalyst enables near quantitative generation of the metastable polymers in high sequence selectivity by limiting the lifetime of alkoxide intermediates. Furthermore, linkage selectivity is key to obtain semi-crystalline materials that can be moulded into self-standing objects as well as to enable chemoselective depolymerisation into cyclic dithiocarbonates which can themselves serve as monomers in ring-opening polymerisation. Our report demonstrates the potential of cooperative catalysis to produce previously inaccessible main-group rich materials with beneficial chemical and physical properties. CS2 promises easy access to degradable sulfur-rich polymers, but ring-opening copolymerisation using CS2 is challenging due to low linkage selectivity and small-molecule by-products. Here, the authors report a cooperative Cr(III)/K catalyst which selectively delivers poly(dithiocarbonates) from CS 2 and oxetanes.

We use coherent midinfrared optical pulses to resonantly excite large-amplitude oscillations of the Si–C stretching mode in silicon carbide. When probing the sample with a second pulse, we observe parametric optical gain at all wavelengths throughout the reststrahlen band. This effect reflects the amplification of light by phonon-mediated four-wave mixing and, by extension, of optical-phonon fluctuations. Density functional theory calculations clarify aspects of the microscopic mechanism for this phenomenon. The high-frequency dielectric permittivity and the phonon oscillator strength depend quadratically on the lattice coordinate; they oscillate at twice the frequency of the optical field and provide a parametric drive for the lattice mode. Parametric gain in phononic four-wave mixing is a generic mechanism that can be extended to all polar modes of solids, as a means to control the kinetics of phase transitions, to amplify many-body interactions or to control phonon-polariton waves.

Microwave annealing technology is gaining importance for processing metal oxides owing to its faster reaction time and volumetric heating. However, the utilization of this technique for producing vanadium oxide has not been explored. This study investigates the impact of both conventional annealing and microwave annealing on the crystal structure, light absorption, defect formation and humidity sensing performance of V 2 O 5 nanoparticles. V 2 O 5 was synthesized using the polyol method, involving the thermolysis of vanadyl ethylene glycol followed by annealing in oxygen atmosphere at 400 °C, 500 °C and 600 °C. The formation of layered, orthorhombic and stable phase of V 2 O 5 nanoparticles was confirmed using X-ray diffraction and Raman spectroscopy analyses. Field emission scanning microscopy showed the development of sheet-like morphology with average particle sizes of 99 ± 40 nm and 104 ± 51 nm for conventional annealing and microwave annealing, respectively. Annealing at elevated temperatures induced grain growth and facilitated oxygen diffusion, leading to the formation of oxygen vacancies. This was confirmed by optical studies, which revealed a reduction in the bandgap and the presence of defect states within the band. Relatively, microwave annealing resulted in fewer oxygen vacancies due to rapid heating, as evidenced by electron paramagnetic resonance studies and X-ray photoelectron spectroscopy. Moreover, the samples were evaluated for humidity sensing capabilities. The superior sensitivity of 48% at a higher relative humidity (97%) was observed for M5 sample that can be attributed to the smaller particle size facilitating more active sites, which makes it suitable for humidity sensing applications. Graphical abstract

Light can be used to directly excite phonon modes in condensed matter. Simultaneously exciting several modes in an antiferromagnetic rare-earth orthoferrite drives behaviour that mimics the application of a magnetic field. Light fields at terahertz and mid-infrared frequencies allow for the direct excitation of collective modes in condensed matter, which can be driven to large amplitudes. For example, excitation of the crystal lattice 1 , 2 has been shown to stimulate insulator–metal transitions 3 , 4 , melt magnetic order 5 , 6 or enhance superconductivity 7 , 8 , 9 . Here, we generalize these ideas and explore the simultaneous excitation of more than one lattice mode, which are driven with controlled relative phases. This nonlinear mode mixing drives rotations as well as displacements of the crystal-field atoms, mimicking the application of a magnetic field and resulting in the excitation of spin precession in the rare-earth orthoferrite ErFeO 3 . Coherent control of lattice rotations may become applicable to other interesting problems in materials research—for example, as a way to affect the topology of electronic phases.

The open transmission characteristics in wireless environments and scarce energy resources generated many challenging factors in MANET’s. Presently, MANET’s are highly employed in security related applications. Moreover, security problems and energy efficiency are considered as the supreme factors in MANET whereas, the security threats emerges out due to their scare resource characteristics; hence their functionalities are highly degraded with numerous security attacks namely, the cruel black hole attack (BHA). The BHA mainly distresses the data collection and makes an effort to engage in most of the links as possible to increase the resource constrained issues in the network. In order to withstand these issues, we propose a novel trust based energy aware routing (TEAR) mechanism for MANETs. The most important characteristics of TEAR mechanism is that it mitigates BHs through the dynamic generation of multiple detection routes to detect the BHs quickly as possible and provides better data route security by obtaining the nodal trust. More significantly, the TEAR mechanism can effectively handle both the creation and sharing of these multi-detection routes for the detection of BHs. Essentially, these multi-detection routes in TEAR mechanism are generated by wholly utilizing the energy in non-hotspots (i.e. without wasting the energy) to improve the energy efficiency and desired data route security. The theoretical and experimental analysis proved that our TEAR mechanism exhibited better performance than that of the earlier research works. The TEAR mechanism highly optimizes the lifespan of network by avoiding the black hole attacks and drastically increasing the probability of successful data routing.

Light can interact with the electrons in a crystalline solid, which in turn generates lattice vibrations or phonons. A related phenomenon was proposed 40 years ago in which it is the ions in the crystal rather than the electrons that mediate the interaction. This effect, known as ionic Raman scattering, is now observed experimentally. Two types of coupling between electromagnetic radiation and a crystal lattice have so far been identified experimentally. The first is the direct coupling of light to infrared-active vibrations carrying an electric dipole. The second is indirect, involving electron–phonon coupling and occurring through excitation of the electronic system; stimulated Raman scattering 1 , 2 , 3 is one example. A third path, ionic Raman scattering (IRS; refs  4 , 5 ), was proposed 40 years ago. It was posited that excitation of an infrared-active phonon could serve as the intermediate state for Raman scattering, a process that relies on lattice anharmonicities rather than electron–phonon interactions 6 . Here, we report an experimental demonstration of IRS using femtosecond excitation and coherent detection of the lattice response. We show how this mechanism is relevant to ultrafast optical control in solids: a rectified phonon field can exert a directional force onto the crystal, inducing an abrupt displacement of the atoms from their equilibrium positions. IRS opens up a new direction for the optical control of solids in their electronic ground state 7 , 8 , 9 , different from carrier excitation 10 , 11 , 12 , 13 , 14 .

The generation of synchrotron radiation is typically achieved by accelerating charges in large magnetic fields. Synchrotron facilities are usually the realm of large international organizations. Henstridge et al. show that the interaction of a femtosecond light pulse moving in an arc on a specially designed metasurface can also generate synchrotron radiation. In this case, the synchrotron radiation at terahertz frequencies was produced by the nonlinear polarization induced by the light pulse. The results hold promise for the development of powerful on-chip light sources. Science , this issue p. 439 A light pulse moving in an arc on a metasurface produces terahertz synchrotron radiation. Synchrotron radiation—namely, electromagnetic radiation produced by charges moving in a curved path—is regularly generated at large-scale facilities where giga–electron volt electrons move along kilometer-long circular paths. We use a metasurface to bend light and demonstrate synchrotron radiation produced by a subpicosecond pulse, which moves along a circular arc of radius 100 micrometers inside a nonlinear crystal. The emitted radiation, in the terahertz frequency range, results from the nonlinear polarization induced by the pulse. The generation of synchrotron radiation from a pulse revolving about a circular trajectory holds promise for the development of on-chip terahertz sources.

In recent years, the research on abnormal events detection is a significant work in surveillance video. Many researchers have been attracted by this work for the past two decades. As a result, several abnormal event detection approaches have been developed. Though several approaches have been used in the field still many problems remain to get the abnormal events detection accuracy. Moreover, many feature representations have limited capability to describe the content since several research works applied hand craft features, this type of feature can work in limited problems. To overcome this problem, this paper introduced the novel feature descriptor namely STS-D (Spatial and Temporal Saliency - Descriptor), which includes spatial and temporal information of the objects. This feature descriptor efficiently describes the shape and speed of the object. To find the anomaly score, fuzzy representation is modeled to efficiently differentiate the normal and abnormal events using fuzzy membership degree. The benchmark datasets UMN, UCSD Ped1 and Ped2 and real time roadway surveillance dataset are used to evaluate the performance of the proposed approach. Also, several existing abnormal events detection approaches are used to compare with the proposed method to evaluate the effectiveness of the proposed work.