Experimental observation of Berreman modes in an uniaxial anisotropic nanoporous alumina film on aluminum substrate.

In this Letter, we demonstrate experimentally and verify numerically the excitation of Berreman modes that propagate in a dielectric film of uniaxial anisotropic nanoporous alumina grown on an aluminum substrate. It is an air-dielectric-metal asymmetric polaritonic system with a real part of the effective permittivity having a value near zero. The modes are excited at a wavelength lower than the epsilon-near-zero wavelength region. Minimum reflection is observed for the mid-infrared p-polarized light, while maximum reflection is observed for the s-polarized light. The experimental results are numerically reproduced for both p- and s-polarized light and confirm the excitation of Berreman modes in the system. At the exciting wavelength, the field is confined in the dielectric region near the air-dielectric interface. The reported system is straightforward and can be easily fabricated over a large scale and is helpful in a variety of mid-infrared applications such as thermal management systems, sensors, passive radiative cooling devices, nonlinear applications, and terahertz frequency generation.

Dynamics from noisy data with extreme timing uncertainty.

Imperfect knowledge of the times at which 'snapshots' of a system are recorded degrades our ability to recover dynamical information, and can scramble the sequence of events. In X-ray free-electron lasers, for example, the uncertainty--the so-called timing jitter--between the arrival of an optical trigger ('pump') pulse and a probing X-ray pulse can exceed the length of the X-ray pulse by up to two orders of magnitude, marring the otherwise precise time-resolution capabilities of this class of instruments. The widespread notion that little dynamical information is available on timescales shorter than the timing uncertainty has led to various hardware schemes to reduce timing uncertainty. These schemes are expensive, tend to be specific to one experimental approach and cannot be used when the record was created under ill-defined or uncontrolled conditions such as during geological events. Here we present a data-analytical approach, based on singular-value decomposition and nonlinear Laplacian spectral analysis, that can recover the history and dynamics of a system from a dense collection of noisy snapshots spanning a sufficiently large multiple of the timing uncertainty. The power of the algorithm is demonstrated by extracting the underlying dynamics on the few-femtosecond timescale from noisy experimental X-ray free-electron laser data recorded with 300-femtosecond timing uncertainty. Using a noisy dataset from a pump-probe experiment on the Coulomb explosion of nitrogen molecules, our analysis reveals vibrational wave-packets consisting of components with periods as short as 15 femtoseconds, as well as more rapid changes, which have yet to be fully explored. Our approach can potentially be applied whenever dynamical or historical information is tainted by timing uncertainty.

Performance enhancement due to a top dielectric coating on a metamaterial perfect absorber.

A tri-layer metamaterial structure with enhanced absorption is demonstrated at infrared wavelengths by coating the top surface of the metamaterial absorber with an additional thin layer of dielectric material. The metamaterial absorber, which consists of a micrometer-sized metallic circular patch separated from a metal ground plane by a dielectric spacer layer, when coated with a supplementary protective dielectric layer on the top, shows a spectral red shift of the peak absorption along with a change in the absorption amplitude. The increase or decrease in absorption arises basically from an interference phenomenon of light reflected from the surface of the protective dielectric and the surface of metamaterial structures, and is highly dependent on the thickness of the top dielectric layer. The protective dielectric coatings provide an alternative way to modify and optimize the absorption in a metamaterial absorber along with a robustness that protects metamaterial structures from environmental and mechanical degradation.

Unified theory of plasmon-induced resonance energy transfer and hot electron injection processes for enhanced photocurrent efficiency.

Plasmons in metal nanoparticles (MNPs) promise to enhance solar energy conversion in semiconductors. Two essential mechanisms of enhancement in the near-field regime are hot electron injection (HEI) and plasmon-induced resonance energy transfer (PIRET). Individual studies of both mechanisms indicate that the PIRET efficiency is limited by the short lifetime of the plasmon, whereas the hot electrons result from the plasmon decay. The development of a unified theory of the coupled HEI and PIRET processes is fundamentally interesting and necessary for making reliable predictions but is complicated by the multiple interactions between various components that participate in the enhancement process. In this paper, we use the model-Hamiltonian approach to develop a combined theoretical framework including both PIRET and HEI. The coupled dynamics as well as the time evolution of hot electron energy distribution are studied. The theory further predicts an interference-induced asymmetry in the spectral dependence of PIRET, which can be used to distinguish it from HEI. As the relative contributions of PIRET and HEI strongly depend on the size of the MNPs, this presents itself as a simple route to control the strength of their contributions. The results presented here can further guide future applications of plasmonic solar energy harvesting.

Emergence of Landauer transport from quantum dynamics: A model Hamiltonian approach.

The Landauer expression for computing current-voltage characteristics in nanoscale devices is efficient but not suited to transient phenomena and a time-dependent current because it is applicable only when the charge carriers transition into a steady flux after an external perturbation. In this article, we construct a very general expression for time-dependent current in an electrode-molecule-electrode arrangement. Utilizing a model Hamiltonian (consisting of the subsystem energy levels and their electronic coupling terms), we propagate the Schrödinger wave function equation to numerically compute the time-dependent population in the individual subsystems. The current in each electrode (defined in terms of the rate of change of the corresponding population) has two components, one due to the charges originating from the same electrode and the other due to the charges initially residing at the other electrode. We derive an analytical expression for the first component and illustrate that it agrees reasonably with its numerical counterpart at early times. Exploiting the unitary evolution of a wavefunction, we construct a more general Landauer style formula and illustrate the emergence of Landauer transport from our simulations without the assumption of time-independent charge flow. Our generalized Landauer formula is valid at all times for models beyond the wide-band limit, non-uniform electrode density of states and for time and energy-dependent electronic coupling between the subsystems. Subsequently, we investigate the ingredients in our model that regulate the onset time scale of this steady state. We compare the performance of our general current expression with the Landauer current for time-dependent electronic coupling. Finally, we comment on the applicability of the Landauer formula to compute hot-electron current arising upon plasmon decoherence.

High contrast switchability of VO2 based metamaterial absorbers with ITO ground plane.

A metamaterial consisting of an array of gold micro-disks, separated from a ground plane of indium tin oxide (ITO) by a thin film of vanadium dioxide (VO2), behaves as a perfect absorber at infrared (IR) frequencies at room temperature. This metamaterial, which is transparent to visible light, can be switched to a highly reflecting state for IR light by heating the metamaterial to temperatures larger than the metal-insulator phase transition temperature 68°C of VO2. For a disk diameter of 1.5 µm and VO2 film thickness of 320 nm, two absorption bands are obtained: one, that arises from the metamaterial resonance; and a second peak that arises principally from a Fabry-Pérot resonance. A large change (>78%) occurs in the reflectivity between the low and high temperature phases. IR emittance of the metamaterial was measured with IR cameras and shown to be switchable to result in low emittance at high temperature. Optical readout of the state of VO2 within the metamaterial is demonstrated.

Optical limiting by nonlinear tuning of resonance in metamaterial absorbers.

Metamaterial resonant absorbers (MRA) have intense local field enhancements that can be used to elicit large nonlinear responses. An MRA, composed of gold disks separated by a ZnS thin film from an underlying gold layer, shows optical limiting for the reflectivity of 8 ps pulses at 1064 nm due to the Kerr nonlinearity of gold and ZnS. Fluorescence from multiphoton absorption due to large fields localized in the ZnS layer is measured, and the effective χ(3) of the layer is enhanced by 3 orders of magnitude compared to bare ZnS thin films. Self-consistent nonlinear electromagnetic simulations confirm that the nonlinear absorption is caused by a shift of the resonance with increasing intensity.

Characteristics of surface plasmon-polariton waves excited on 2D periodically patterned columnar thin films of silver.

Periodically patterned thin films of slanted silver nanocolumns were deposited by directing a collimated vapor flux of silver toward square and hexagonal gratings of photoresist on glass substrates. Angle-resolved specular-transmittance measurements in the visible and near-infrared wavelength bands on these periodically patterned columnar thin films (CTFs) were carried out to investigate the excitation of surface plasmon-polariton (SPP) waves bound tightly to either the air/CTF or the photoresist/CTF interfaces. The orientation of the propagation vector of the incident p-polarized plane wave with respect to the morphologically significant plane of the CTFs was varied to reveal asymmetric (unidirectional) coupling of Floquet modes to SPP waves. The asymmetric coupling is maximal when the propagation vector of the incident plane wave lies wholly in the morphologically significant plane. Theoretical understanding based on the Bruggeman formalism to homogenize the silver CTFs into hyperbolic biaxial continua is able to explain the experimental observations very well.

Photobiological hydrogen production and artificial photosynthesis for clean energy: from bio to nanotechnologies.

Global energy demand is increasing rapidly and due to intensive consumption of different forms of fuels, there are increasing concerns over the reduction in readily available conventional energy resources. Because of the deleterious atmospheric effects of fossil fuels and the uncertainties of future energy supplies, there is a surge of interest to find environmentally friendly alternative energy sources. Hydrogen (H2) has attracted worldwide attention as a secondary energy carrier, since it is the lightest carbon-neutral fuel rich in energy per unit mass and easy to store. Several methods and technologies have been developed for H2 production, but none of them are able to replace the traditional combustion fuel used in automobiles so far. Extensively modified and renovated methods and technologies are required to introduce H2 as an alternative efficient, clean, and cost-effective future fuel. Among several emerging renewable energy technologies, photobiological H2 production by oxygenic photosynthetic microbes such as green algae and cyanobacteria or by artificial photosynthesis has attracted significant interest. In this short review, we summarize the recent progress and challenges in H2-based energy production by means of biological and artificial photosynthesis routes.

Anisotropic metamaterial optical fibers.

Internal physical structure can drastically modify the properties of waveguides: photonic crystal fibers are able to confine light inside a hollow air core by Bragg scattering from a periodic array of holes, while metamaterial loaded waveguides for microwaves can support propagation at frequencies well below cutoff. Anisotropic metamaterials assembled into cylindrically symmetric geometries constitute light-guiding structures that support new kinds of exotic modes. A microtube of anodized nanoporous alumina, with nanopores radially emanating from the inner wall to the outer surface, is a manifestation of such an anisotropic metamaterial optical fiber. The nanopores, when filled with a plasmonic metal such as silver or gold, greatly increase the electromagnetic anisotropy. The modal solutions in such anisotropic circular waveguides can be uncommon Bessel functions with imaginary orders.

Reconfiguring gratings of slanted plasmonic nanocolumns by ion beam irradiation.

Gratings with slanted plasmonic nanocolumns of silver (Ag) on top fabricated by physical vapor deposition at large oblique angles on predefined gratings show unique plasmonic properties. These aligned nanocolumns with high-aspect ratios can be uniformly re-oriented to any desired angle of slant by ion beam irradiation. A focused ion beam (FIB) has been used as the ion source here. The plastic deformation of the nanocolumns arises due to defect formation caused by the energetic ions and can enable the complete tuning of the photonic and plasmonic properties of the grating through the slant angle. The reorientation can be uniformly carried over large areas of 0.2 mm(2) with the FIB and the diffraction patterns from the reoriented grating show large changes in the diffraction efficiencies. Electromagnetic simulations of the grating structures reveal large changes in the photonic properties with the slant angle such as diffraction efficiencies and the electromagnetic near fields.

Strong field coherent control of molecular torsions--Analytical models.

We introduce analytical models of torsional alignment by moderately intense laser pulses that are applicable to the limiting cases of the torsional barrier heights. Using these models, we explore in detail the role that the laser intensity and pulse duration play in coherent torsional dynamics, addressing both experimental and theoretical concerns. Our results suggest strategies for minimizing the risk of off-resonant ionization, noting the qualitative differences between the case of torsional alignment subject to a field-free torsional barrier and that of torsional alignment of a barrier-less system (equivalent to a 2D rigid rotor). We also investigate several interesting torsional phenomena, including the onset of impulsive alignment of torsions, field-driven oscillations in quantum number space, and the disappearance of an alignment upper bound observed for a rigid rotor in the impulsive torsional alignment limit.

Use of romiplostim in patients with chronic idiopathic thrombocytopenic purpura during perioperative period.

INTRODUCTION: In patients with chronic idiopathic thrombocytopenic purpura (cITP), the platelet count tends to be quite variable and, in the majority of cases, specific therapy is not warranted on a regular basis. However, patients with low platelet count (<30 nL) or with bleeding complications would require therapy, such as prednisolone, intravenous immunoglobulin infusions, splenectomy and/or immunosuppression. Romiplostim, a thrombopoietin agonist, has also proven to be useful in improving platelet counts. cITP can be associated with bleeding complications perioperatively. As such, a higher platelet count is warranted (approximately 80 nL), particularly for invasive surgeries, such as orthopaedic surgery, cardio-thoracic surgery, head and neck surgery and abdominal surgery, where risk of bleeding is quite high already. AIM: The aim of this study is to evaluate the safety and efficacy of short-term use of romiplostim, perioperatively. METHODS: Patients with chronic ITP requiring major surgical interventions were enrolled in the study. Patients with malignancies or myelodysplastic syndromes, major bleeding disorders, under 18 years of age or pregnancy were excluded. CONCLUSION: This study has shown that the use of romiplostim is safe and effective in improving platelet counts preoperatively and that this could achieve excellent haemostasis, with no associated bleeding complications or rebound thrombocytopenia. A larger study involving multiple centres is required to verify these findings.

Enhanced gene disruption by programmable nucleases delivered by a minicircle vector.

Targeted genetic modification using programmable nucleases such as zinc finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs) is of great value in biomedical research, medicine and biotechnology. Minicircle vectors, which lack extraneous bacterial sequences, have several advantages over conventional plasmids for transgene delivery. Here, for the first time, we delivered programmable nucleases into human cells using transient transfection of a minicircle vector and compared the results with those obtained using a conventional plasmid. Surrogate reporter assays and T7 endonuclease analyses revealed that cells in the minicircle vector group displayed significantly higher mutation frequencies at the target sites than those in the conventional plasmid group. Quantitative PCR and reverse transcription-PCR showed higher vector copy number and programmable nuclease transcript levels, respectively, in 293T cells after minicircle versus conventional plasmid vector transfection. In addition, tryphan blue staining and flow cytometry after annexin V and propidium iodide staining showed that cell viability was also significantly higher in the minicircle group than in the conventional plasmid group. Taken together, our results show that gene disruption using minicircle vector-mediated delivery of ZFNs and TALENs is a more efficient, safer and less toxic method than using a conventional plasmid, and indicate that the minicircle vector could serve as an advanced delivery method for programmable nucleases.

Broadband infrared metamaterial absorber with visible transparency using ITO as ground plane.

Metamaterials that have broadband absorption at MIR frequencies, and yet, are transmitive at visible frequencies are fabricated using a semi-conducting Indium Tin Oxide (ITO) film as ground plane. The metamaterial absorber consists of an array of uniform aluminum disks separated by a Zinc Sulphide (ZnS) dielectric spacer layer from the ITO ground plane. The metamaterial was fabricated by a simple, cost-effective vapor deposition through a shadow mask. Compared with the usual metal/dielectric/metal tri-layer absorbers, the metal/dielectric/ITO absorber shows a peak absorbance of 98% and >70% over the mid-infrared regime from 4 to 7 µm. The broadband nature arises due to smaller dispersion in the dielectric permittivity of ITO compared to that of plasmonic metals at mid-infrared frequencies.

Synthesis of a terphenyl substituted 4-aza-2,3-didehydropodophyllotoxin analogues as inhibitors of tubulin polymerization and apoptosis inducers.

A series of terphenyl based 4-aza-2,3-didehydropodophyllotoxin conjugates (8a-r) were synthesized by a straightforward one-step multicomponent synthesis that demonstrated anticancer activity against five human cancer cell lines (lung, colon, renal, prostate and cervical). All the tested compounds showed potent anticancer activity with IC50 values ranging from 0.87 to 16.59 µM. Among them compounds 8n and 8p showed significant anticancer activity in lung cancer cells with IC50 values 0.91 and 0.87 µM, respectively. Flow cytometric analysis revealed that these compounds induced cell cycle arrest in G2/M phase in A549 cell line leading to caspase-3 dependent apoptotic cell death. The tubulin polymerization assay and immunofluorescence analysis showed that these compounds effectively inhibit microtubule assembly at both molecular and cellular levels in A549 cells. Further, Hoechst staining, DNA fragmentation analysis also suggested that these compounds induced cell death by apoptosis. Overall, the current study demonstrated that the synthesis of terphenyl based 4-aza-2,3-didehydropodophyllotoxin conjugates as promising anticancer agents with G2/M cell cycle arrest and apoptotic-inducing activities via targeting tubulin.

Theory of ultrafast photoinduced electron transfer from a bulk semiconductor to a quantum dot.

This paper describes analytical and numerical results from a model Hamiltonian method applied to electron transfer (ET) from a quasicontinuum (QC) of states to a set of discrete states, with and without a mediating bridge. Analysis of the factors that determine ET dynamics yields guidelines for achieving high-yield electron transfer in these systems, desired for instance for applications in heterogeneous catalysis. These include the choice of parameters of the laser pulse that excites the initial state into a continuum electronic wavepacket and the design of the coupling between the bridge molecule and the donor and acceptor. The vibrational mode on a bridging molecule between donor and acceptor has an influence on the yield of electron transfer via Franck-Condon factors, even in cases where excited vibrational states are only transiently populated. Laser-induced coherence of the initial state as well as energetic overlap is crucial in determining the ET yield from a QC to a discrete state, whereas the ET time is influenced by competing factors from the coupling strength and the coherence properties of the electronic wavepacket.

Cause-Specific Mortality Among Adults Aged ≥65 Years in the United States, 1999 Through 2020.

OBJECTIVE: Reports on recent mortality trends among adults aged ≥65 years are lacking. We examined trends in the leading causes of death from 1999 through 2020 among US adults aged ≥65 years. METHODS: We used data from the National Vital Statistics System mortality files to identify the 10 leading causes of death among adults aged ≥65 years. We calculated overall and cause-specific age-adjusted death rates and then calculated the average annual percentage change (AAPC) in death rates from 1999 through 2020. RESULTS: The overall age-adjusted death rate decreased on average by 0.5% (95% CI, -1.0% to -0.1%) per year from 1999 through 2020. Although rates for 7 of the top 10 causes of death decreased significantly, the rates of death from Alzheimer disease (AAPC = 3.0%; 95% CI, 1.5% to 4.5%) and from unintentional injuries (AAPC = 1.2%; 95% CI, 1.0% to 1.4%), notably falls (AAPC = 4.1%; 95% CI, 3.9% to 4.3%) and poisoning (AAPC = 6.6%; 95% CI, 6.0% to 7.2%), increased significantly. CONCLUSION: Public health prevention strategies and improved chronic disease management may have contributed to decreased rates in the leading causes of death. However, longer survival with comorbidities may have contributed to increased rates of death from Alzheimer disease and unintentional falls.

Appropriate analysis on properties of various compositions on fluids with and without additives for liquid insulation in power system transformer applications.

Transformer is a well-known power system apparatus utilized in conjunction with solid insulations such as paper and press board, as well as liquid insulations like mineral oil, a petroleum-based fluid. Despite the notable drawbacks associated with mineral oil, such as limited resources for future generations and its non-eco-friendly nature, its usage remains ubiquitous. There is a growing imperative to explore alternative fluids that surpass mineral oil in terms of environmental impact and performance. Amidst the global shift towards green energy, this study focuses on vegetable seed oils such as corn oil, soybean oil, mustard oil, and rice bran oil as potential substitutes. The research evaluates these oils based on key transformer properties including breakdown voltage, water content, interfacial tension, viscosity, acidity, flash point, and fire point. Interestingly, rice bran oil and soybean oil exhibit promising characteristics that suggest they could effectively replace petroleum-based fluids in transformers. Furthermore, the study extends to blending mineral oil with vegetable seed oils in various compositions, incorporating natural and synthetic antioxidant additives ranging from 0 to 1%. Comparative analyses between samples with and without additives reveal that the inclusion of 1% propyl gallate yields outstanding performance improvements. For instance, a blend comprising 25 ml of mineral oil and 25 ml of soybean oil, supplemented with 1% propyl gallate, demonstrates 90% higher effectiveness compared to other blends and additives tested. Moreover, the research employs statistical regression analysis to establish relationships between different parameter variables, providing deeper insights into the performance and compatibility of these blended oils in transformer applications. This comprehensive investigation underscores the potential of vegetable seed oils as viable alternatives to mineral oil, contributing to the advancement of eco-friendly solutions in power systems.

Design and implementation of single DC-link based three-phase multilevel inverter with CB-PWM techniques.

Simulation and implementation of a single DC-link-based three-phase inverter are investigated in this article. The primary focus is on designing a single DC-link three-phase inverter for high power applications. Unlike conventional inverters that require 600 V to generate 400 V (RMS) at the output, the proposed system achieves this with only 330 V, facilitated by a 12-terminal 1:1 transformer. The system employs Proportional Integral (PI) and Neural Network (NN) controllers to optimize performance. Various Carrier-Based Pulse Width Modulation (CB-PWM) techniques, including Phase Disposition (PD), Phase Opposition Disposition (POD), and Alternative Phase Opposition Disposition (APOD), are implemented and evaluated based on Total Harmonics Distortion (THD) concerning the Modulation Index (MI) of the inverter. The proposed inverter achieves a THD reduction to 4.8%, demonstrating superior performance compared to recent studies. The system's performance is validated through extensive MATLAB/Simulink simulations and practical implementation using XILINX FPGA software, confirming the efficacy of the proposed design.