Remarkable Tuning Research Articles

Trivalent Yb/Ho/Ce tri-doped core/shell NaYF4 nanoparticles for tunable upconversion luminescence from green to red

Three types of β-NaYF4 nanoparticles, uncoated core (NaYF4:Yb/Ho/Ce), single-layer coated core@shell (NaYF4:Yb/Ho/ Ce@NaYF4:Yb) and double-layer coated core@shell@shell (NaYF4:Yb/Ho@NaYF4:Yb@NaYF4:Yb) with Ce3+ doped in core, first and second shell, respectively, were synthesized through solvothermal method to investigate the cross-relaxation between Ho3+ and Ce3+ for the tunable upconversion luminescence. By doping Ce3+ into different layers with different doping concentrations, a systematical investigation on the tunable upconversion luminescence from green to red was conducted. The results showed that a remarkable color tuning could be achieved from green to red when increasing the doping concentration of Ce3+ in the same layer of Ho3+. And if Ce3+ and Ho3+ were separated in different layers, the color tuning would be depressed significantly due to the reduced cross-relaxation between Ho3+ and Ce3+. Moreover, the UC emission intensity of core@shell and core@shell@shell was enhanced significantly compared with that of unmodified core nanoparticles.

The Coupling between Ca2+ Channels and the Exocytotic Ca2+ Sensor at Hair Cell Ribbon Synapses Varies Tonotopically along the Mature Cochlea.

The cochlea processes auditory signals over a wide range of frequencies and intensities. However, the transfer characteristics at hair cell ribbon synapses are still poorly understood at different frequency locations along the cochlea. Using recordings from mature gerbils, we report here a surprisingly strong block of exocytosis by the slow Ca2+ buffer EGTA (10 mM) in basal hair cells tuned to high frequencies (∼30 kHz). In addition, using recordings from gerbil, mouse, and bullfrog auditory organs, we find that the spatial coupling between Ca2+ influx and exocytosis changes from nanodomain in low-frequency tuned hair cells (∼<2 kHz) to progressively more microdomain in high-frequency cells (∼>2 kHz). Hair cell synapses have thus developed remarkable frequency-dependent tuning of exocytosis: accurate low-latency encoding of onset and offset of sound intensity in the cochlea's base and submillisecond encoding of membrane receptor potential fluctuations in the apex for precise phase-locking to sound signals. We also found that synaptic vesicle pool recovery from depletion was sensitive to high concentrations of EGTA, suggesting that intracellular Ca2+ buffers play an important role in vesicle recruitment in both low- and high-frequency hair cells. In conclusion, our results indicate that microdomain coupling is important for exocytosis in high-frequency hair cells, suggesting a novel hypothesis for why these cells are more susceptible to sound-induced damage than low-frequency cells; high-frequency inner hair cells must have a low Ca2+ buffer capacity to sustain exocytosis, thus making them more prone to Ca2+-induced cytotoxicity.SIGNIFICANCE STATEMENT In the inner ear, sensory hair cells signal reception of sound. They do this by converting the sound-induced movement of their hair bundles present at the top of these cells, into an electrical current. This current depolarizes the hair cell and triggers the calcium-induced release of the neurotransmitter glutamate that activates the postsynaptic auditory fibers. The speed and precision of this process enables the brain to perceive the vital components of sound, such as frequency and intensity. We show that the coupling strength between calcium channels and the exocytosis calcium sensor at inner hair cell synapses changes along the mammalian cochlea such that the timing and/or intensity of sound is encoded with high precision.

Engineering the polar magneto-optical Kerr effect in strongly strained L10–MnAl films

We report the engineering of the polar magnetooptical (MO) Kerr effect in perpendicularly magnetized L10–MnAl epitaxial films with remarkably tuned magnetization, strain, and structural disorder by varying substrate temperature (Ts) during molecular-beam epitaxy growth. The Kerr rotation was enhanced by a factor of up to 5 with Ts increasing from 150 to 350 °C as a direct consequence of the improvement of the magnetization. A similar remarkable tuning effect was also observed on the Kerr ellipticity and the magnitude of the complex Kerr angle, while the phase of the complex Kerr angle appears to be independent of the magnetization. The combination of the good semiconductor compatibility, the moderate coercivity of 0.3–8.2 kOe, the tunable polar MO Kerr effect of up to ~0.034°, and giant spin precession frequencies of up to ~180 GHz makes L10–MnAl films a very interesting MO material. Our results give insights into both the microscopic mechanisms of the MO Kerr effect in L10–MnAl alloys and their scientific and technological application potential in the emerging spintronics and ultrafast MO modulators.

Quantum chemical characterization and design of homoleptic Ir(III) complexes employing triphenylamine-featured thiazole-based ligand for efficient phosphors in OLEDs

The electronic structures and photophysical properties of a series of homoleptic Ir(III) complexes with triphenylamine-featured thiazole (1: fac-tris(2-phenylthiazole)iridium(III)) and benzothiazole (2: fac-tris[6-(1-naphthalenylphenylamino)-2-phenylbenzothiazole]iridium(III)) based ligands are investigated using the density functional method. By introducing the diphenylamine unit at 2-, 3- and 4-position of the phenyl ring in (C^N) ligands, 1a–1c (1a: fac-tris[2-(2-(N,N-diphenylamino)phenyl)thiazole]iridium(III); 1b: fac-tris[2-(3-(N,N-diphenylamino)phenyl)thiazole]iridium(III); 1c: fac-tris[2-(4-(N,N-diphenylamino)phenyl)thiazole]iridium(III)) and 2a–2c (2a: fac-tris[6-(1-naphthalenylphenylamino)-2-(2-(N,N-diphenylamino)phenyl)benzothiazole]iridium(III); 2b: fac-tris[6-(1-naphthalenylphenylamino)-2-(3-(N,N-diphenylamino)phenyl)benzothiazole]iridium(III); 2c: fac-tris[6-(1-naphthalenylphenylamino)-2-(4-(N,N-diphenylamino)phenyl)benzothiazole]iridium(III)) are studied to get insight into the influence of different ligation positions of diphenylamine unit on the photophysical properties. The calculated results showed that the incorporation of diphenylamine unit into (C^N) ligands is beneficial to raise the HOMO levels, reducing the barrier height for hole injection and enhancing the balance of charge-transfer process. In addition, a remarkable color tuning could also be realized by altering the ligation positions of the diphenylamine units. A 82–132nm blue shift is found for the thiazole-based 1a–1c compared with 1, while a relatively small red shift (7–35nm) is observed on the emissions of benzothiazole-based 2a and 2c compared with 2. Meanwhile, a qualitative analysis on the parameters that would affect the quantum yields (ΦPL) of the studied complexes has also been presented.

Predicting Input Impedance and Efficiency of Graphene Reconfigurable Dipoles Using a Simple Circuit Model

An analytical circuit model able to predict the input impedance of reconfigurable graphene plasmonic dipoles is presented. A suitable definition of plasmonic characteristic impedance, employing natural currents, is used to for consistent modeling of the antenna-load connection in the circuit. In its purely analytical form, the model shows good agreement with full-wave simulations and explains the remarkable tuning properties of graphene antennas. Furthermore, using a single full-wave simulation and scaling laws, additional parasitic elements can be determined for a vast parametric space, leading to very accurate modeling. Finally, we also show that the modeling approach allows fair estimation of radiation efficiency as well. The approach also applies to thin plasmonic antennas realized using noble metals or semiconductors.

Nanoantenna‐Sandwiched Graphene with Giant Spectral Tuning in the Visible‐to‐Near‐Infrared Region

Graphene exhibits intriguing electronic and optical properties, making it promising for integrating electronics and optics. Effective light modulation can be achieved by combining graphene with plasmonic metal structures. However, to tune plasmonic response with graphene at visible‐to‐near‐infrared frequencies has remained challenging owing to the weak coupling between plasmonic resonances and graphene optical transitions as well as inefficient gate control of the latter. Here the remarkable tuning of plasmonic scattering is reported by loading graphene into the cavities between Au nanocrystals and a Au film. The graphene‐loaded nanoantennas show dramatic resonance red shifts, which can further be modified by varying graphene dielectric screening effect. Such nanoantennas can therefore not only strengthen light−graphene interactions drastically but also exemplify an electroplasmonic system naturally. This study will open up an avenue for effectively operating graphene photonic devices in the visible‐to‐near‐infrared range and pave a way for electrically controlling light with plasmonic structures.

Effect of pH and Oxygen Atom of the Hydrophobic Chain on the Self-Assembly Property and Morphology of the Pyridyl Boronic Acid Based Amphiphiles

The surface activity and aggregation behavior of two synthesized boronic acid based anionic surfactants, sodium salt of 2-dodecyl pyridine-5-boronic acid (SDDPB) and sodium salt of 2-oxydodecyl pyridine-5-boronic acid (SODDPB), were studied in buffer solution at pH 9 and 13 containing carbohydrates. The self-assembly formation was investigated by use of a number of techniques including surface tension, conductivity, fluorescence spectroscopy, dynamic light scattering, X-ray diffraction, and transmission electron microscopy (TEM). Both of the amphiphiles exhibit a single break in the surface tension vs log(concentration) plots, indicating existence of one critical aggregation concentration. Steady state fluorescence spectroscopy was used to determine the polarity indexes using pyrene and the rigidity of the microenvironments of the aggregates using 1,6-diphenyl-1,3,5-hexatriene (DPH) as fluorescence probe molecules. The pKa's of both amphiphiles were determined in buffer solutions of different pH's. XRD studies were performed to shed light on the morphology of the self-assemblies. TEM micrographs revealed the existence of vesicles for both the amphiphiles in buffer solution of pH 9, but at pH 13, TEM pictures indicate the existence of closed vesicles in SDDPB solution and at concentrated solution the vesicles are fused to form sponge-like micelles. After aging the vesicular solution of pH 13 of SDDPB, the closed vesicles are destroyed. In contrast, for SODDPB at pH 13, TEM pictures suggest the existence of spherical and complex micelles in solution which were further transformed into crystal-like structure upon aging. The average hydrodynamic radii were determined by dynamic light scattering measurement. Therefore, for the first time, we have successfully synthesized two new surfactants containing pyridyl-boronic acid as a headgroup which shows remarkable tuning of morphology in two different pH's and in the presence of two different carbohydrates.

Hippocampal Place Fields Emerge upon Single-Cell Manipulation of Excitability During Behavior

The origin of the spatial receptive fields of hippocampal place cells has not been established. A hippocampal CA1 pyramidal cell receives thousands of synaptic inputs, mostly from other spatially tuned neurons; however, how the postsynaptic neuron's cellular properties determine the response to these inputs during behavior is unknown. We discovered that, contrary to expectations from basic models of place cells and neuronal integration, a small, spatially uniform depolarization of the spatially untuned somatic membrane potential of a silent cell leads to the sudden and reversible emergence of a spatially tuned subthreshold response and place-field spiking. Such gating of inputs by postsynaptic neuronal excitability reveals a cellular mechanism for receptive field origin and may be critical for the formation of hippocampal memory representations.

Neural Representations of Location Composed of Spatially Periodic Bands

The mammalian hippocampal formation provides neuronal representations of environmental location, but the underlying mechanisms are poorly understood. Here, we report a class of cells whose spatially periodic firing patterns are composed of plane waves (or bands) drawn from a discrete set of orientations and wavelengths. The majority of cells recorded in parasubicular and medial entorhinal cortices of freely moving rats belonged to this class and included grid cells, an important subset that corresponds to three bands at 60° orientations and has the most stable firing pattern. Occasional changes between hexagonal and nonhexagonal patterns imply a common underlying mechanism. Our results indicate a Fourier-like spatial analysis underlying neuronal representations of location, and suggest that path integration is performed by integrating displacement along a restricted set of directions.

High‐Temperature Transport Property of In2−xCexO3 (0 ≤ x ≤ 0.10) Fine Grained Ceramics

Using the spark plasma sintering process In2−xCexO3 (0 ≤ x ≤ 0.10) fine grained ceramics have been synthesized. Our results indicate that all the In2O3‐based ceramic samples show good electrical conductivity and high thermoelectric power factor. In comparison with pure In2O3 bulks or doped samples with grain size above 1 μm, the 100–300 nm fine grain In2O3‐based ceramics exhibit much lower thermal conductivities (1.9–2.5 W·(m·K)−1 at 1173 K), demonstrating a remarkable cooperative tuning effect imposed by grain size reduction and nano‐clusters formation. The maximum figure of merit ZT value is optimized up to ~0.47 at 1223 K for In1.92Ce0.08O3 sample, which makes them promising candidates for thermoelectric applications.

Outer hair cell‐specific prestin‐CreERT2 knockin mouse lines

Outer hair cells (OHCs) in the cochlea are crucial for the remarkable hearing sensitivity and frequency tuning. To understand OHC physiology and pathology, it is imperative to use mouse genetic tools to manipulate gene expression specifically in OHCs. Here, we generated two prestin knockin mouse lines: (1) the prestin-CreERT2 line, with an internal ribosome entry site-CreERT2-FRT-Neo-FRT cassette inserted into the prestin locus after the stop codon, and (2) the prestin-CreERT2-NN line, with the FRT-Neo-FRT removed subsequently. We characterized the inducible Cre activity of both lines by crossing them with the reporter lines CAG-eGFP and Ai6. Cre activity was induced with tamoxifen at various postnatal ages and only detected in OHCs, resembling the endogenous prestin expression pattern. Moreover, prestin-CreERT2+/-(heterozygotes) and +/+(homozygotes) as well as prestin-CreERT2-NN+/-mice displayed normal hearing. These two prestin-CreERT2 mouse lines are therefore useful tools to analyze gene function in OHCs in vivo.

Defect modes tuning of one-dimensional photonic crystals with lithium niobate and silver material defect

In this paper, a novel PCs defect mode is designed by inserting a Ag/LiNbO 3/Ag sandwich structure into periodically stacked TiO 2/MgF 2 dielectric superlattice. The band gap calculation is conducted using transfer matrix method. An emergence of defect mode around 525 nm is demonstrated. By applying an external voltage on this defect mode, remarkable wavelength tuning can be achieved. At normal incidence, a tuning bandwidth up to 70 nm is obtained by moderate change of external voltage from −250 to 250 V. This feature can be employed to fabricate practical tunable filters in visible region.

Photoluminescence properties of silica aerogel/porous silicon nanocomposites

The luminescent properties of nanocomposite pellets based on silica aerogel and porous Si powder are studied depending on the ratio of chemical compounds. The photoluminescence of nanocomposites is characterized by a red–orange band related to silicon nanoparticles and a blue–green band related to silica aerogel with close values of decay time and activation energy. Remarkable tuning of nanocomposites' photoluminescence spectra in the RGB region is established allowing their use as promising phosphor materials for light-emitting diodes. The outgoing spectra of pellet photoluminescence are guided by the chemical composition ratio, porous Si and silica aerogel technology, and the storage time in ambient atmosphere. It was shown that using the silica aerogel as a dielectric matrix considerably increases the stability of photoluminescence yield of silicon nanoparticles.

Effects of Changes in the Bore Shape and the Labium Position in a Txistu

The Basque txistu is a fipple flute with three finger holes. The sound produced by txistus depends on the physical characteristics of the instrument and the control exerted by the player. Cross fingering and half holing methods are used to play over two octaves. The effect of the horizontal position of the metal labium W, is experimentally measured in this paper. The studied notes are measured with a blowing machine, recording the radiated sound for a known input pressure and also with a musician playing them in mezzo forte dynamic. Data produced by a traditional and a new txistu prototype have been collected, analysed and compared. The internal bore shape of this new txistu is not pure cylindrical as that of the traditional txistu. Moreover the location, size and height of the holes have been changed. The analysis shows remarkable tuning differences between the two txistus.

Remarkable Tuning of the Coordination and Photophysical Properties of Lanthanide Ions in a Series of Tetrazole‐Based Complexes

A series of seven new tetrazole-based ligands (L1, L3-L8) containing terpyridine or bipyridine chromophores suited to the formation of luminescent complexes of lanthanides have been synthesized. All ligands were prepared from the respective carbonitriles by thermal cycloaddition of sodium azide. The crystal structures of the homoleptic terpyridine-tetrazolate complexes [Ln(Li)(2)]NHEt(3) (Ln = Nd, Eu, Tb for i = 1, 2; Ln = Eu for i = 3, 4) and of the monoaquo bypyridine-tetrazolate complex [Eu(H(2)O)(L7)(2)]NHEt(3) were determined. The tetradentate bipyridine-tetrazolate ligand forms nonhelical complexes that can contain a water molecule coordinated to the metal. Conversely, the pentadentate terpyridine-tetrazolate ligands wrap around the metal, thereby preventing solvent coordination and forming chiral double-helical complexes similarly to the analogue terpyridine-carboxylate. Proton NMR spectroscopy studies show that the solid-state structures of these complexes are retained in solution and indicate the kinetic stability of the hydrophobic complexes of terpyridine-tetrazolates. UV spectroscopy results suggest that terpyridine-tetrazolate complexes have a similar stability to their carboxylate analogues, which is sufficient for their isolation in aerobic conditions. The replacement of the carboxylate group with tetrazolate extends the absorption window of the corresponding terpyridine- (approximately 20 nm) and bipyridine-based (25 nm) complexes towards the visible region (up to 440 nm). Moreover, the substitution of the terpyridine-tetrazolate system with different groups in the ligand series L3-L6 has a very important effect on both absorption spectra and luminescence efficiency of their lanthanide complexes. The tetrazole-based ligands L1 and L3-L8 sensitize efficiently the luminescent emission of lanthanide ions in the visible and near-IR regions with quantum yields ranging from 5 to 53% for Eu(III) complexes, 6 to 35% for Tb(III) complexes, and 0.1 to 0.3% for Nd(III) complexes, which is among the highest reported for a neodymium complex. The luminescence efficiency could be related to the energy of the ligand triplet states, which are strongly correlated to the ligand structures.

New Frontiers of Metamaterials: Design and Fabrication

AbstractArtificially engineered metamaterials have emerged with properties and functionalities previously unattainable in natural materials. The scientific breakthroughs made in this new class of electromagnetic materials are closely linked with progress in developing physics-driven design and novel parallel fabrication methods. For example, a smooth superlens has been demonstrated with 30-nm imaging resolution, or 1/12 of the corresponding wavelength, far below the diffraction limit. Similarly, a photoswitchable optical negative-index material has been printed, showing a remarkable tuning range of refractive index in the communication wavelength. New frontiers are being explored as intrinsic limitations challenge the scaling of microwave metamaterial designs to optical frequencies. These novel metamaterials promise an entire new generation of passive and active optical elements, such as paper-thin superlenses and modulators.

Remarkable Tuning of the Photophysical Properties of Bifunctional Lanthanide tris(Dipicolinates) and its Consequence on the Design of Bioprobes

Derivatives of dipicolinic acid with a polyoxyethylene pendant arm at the pyridine 4-position have been functionalized for potential grafting with biological material. Four ligands with different terminal functions (alcohol, methoxy, phtalimide and amine) have been synthesized, which react with trivalent lanthanide ions Ln (III) to yield triple helical [Ln(L) 3] (3-) complexes, as shown by NMR and UV-vis titrations. The tris chelates display large thermodynamic stability with log beta 13 approximately 19-20 for all Eu (III) complexes for instance. Photophysical measurements reveal adequate sensitization of the metal-centered luminescence in the europium (eta sens = 33-72%) and terbium complexes, which is modulated by the nature of the terminal function. The lifetimes of the metal-centered excited states are long, up to 1.4 ms for [Eu(L) 3] (3-) and 1.6 ms for [Tb(L) 3] (3-) at room temperature, in line with hydration numbers essentially equal to zero. Quantum yields are as high as 29% for the [Eu( L ( NH2 )) 3] (3-) and 18% for the [Tb( L ( OH )) 3] (3-) tris chelates in water at physiological pH. These series of complexes demonstrate the extent of fine-tuning achievable for lanthanide luminescent probes and are simple models for investigating the effect of binding to biological molecules on the metal-centered luminescent properties.

Large-scale modulation of thermodynamic protein folding barriers linked to electrostatics

Protein folding barriers, which range from zero to the tens of RT that result in classical two-state kinetics, are primarily determined by protein size and structural topology [Plaxco KW, Simons KT, Baker D (1998) J Mol Biol 277:985-994]. Here, we investigate the thermodynamic folding barriers of two relatively large proteins of the same size and topology: bovine alpha-lactalbumin (BLA) and hen-egg-white lysozyme (HEWL). From the analysis of differential scanning calorimetry experiments with the variable-barrier model [Muñoz V, Sanchez-Ruiz JM (2004) Proc Natl Acad Sci USA 101:17646-17651] we obtain a high barrier for HEWL and a marginal folding barrier for BLA. These results demonstrate a remarkable tuning range of at least 30 kJ/mol (i.e., five to six orders of magnitude in population) within a unique protein scaffold. Experimental and theoretical analyses on these proteins indicate that the surprisingly small thermodynamic folding barrier of BLA arises from the stabilization of partially unfolded conformations by electrostatic interactions. Interestingly, there is clear reciprocity between the barrier height and the biological function of the two proteins, suggesting that the marginal barrier of BLA is a product of natural selection. Electrostatic surface interactions thus emerge as a mechanism for the modulation of folding barriers in response to special functional requirements within a given structural fold.

Defect modes and wavelength tuning of one-dimensional photonic crystal with lithium niobate

The defect state of the one-dimensional photonic crystals consisting of lithium niobate and air is theoretically investigated. By applying an external voltage on the defect layer, remarkable wavelength tuning can be achieved. The relation between the wavelength peak and the external voltage is a straight line and the tuning rate is 1.358 nm/kV. The dependence of the wavelength peak on the angle of incidence was also observed at each applied voltage. This feature can be employed to fabricate tunable filters.

Small-signal analysis and particle-in-cell simulations of planar dielectric Cherenkov masers for use as high-frequency, moderate-power broadband amplifiers

A small-signal gain analysis of the planar dielectric Cherenkov maser is presented. The analysis results in a Pierce gain solution, with three traveling-wave modes. The analysis shows that the dielectric Cherenkov maser has a remarkable broadband tuning ability near cutoff, while maintaining reasonable gain rates. Numerical simulations verifying the small-signal gain results are presented, using a particle-in-cell code adapted specifically for planar traveling-wave tubes. An instantaneous bandwidth is numerically shown to be very large, and saturated efficiency for a nominal high-power design is shown to be in the range of standard untapered traveling-wave tubes.