Strong Mismatch Research Articles

A novel approach to prepare optically active ion doped luminescent materials via electron beam evaporation into ionic liquids.

A novel approach to prepare luminescent materials via electron-beam evaporation into ionic liquids is presented which even allows doping of host lattices with ions that have a strong size mismatch. To prove this, MgF2 nanoparticles doped with Eu(3+) were fabricated. The obtained nanoparticles featured an unusually high luminescence lifetime and the obtained material showed a high potential for application.

Polarity compensation in ultra-thin films of complex oxides: the case of a perovskite nickelate.

We address the fundamental issue of growth of perovskite ultra-thin films under the condition of a strong polar mismatch at the heterointerface exemplified by the growth of a correlated metal LaNiO3 on the band insulator SrTiO3 along the pseudo cubic [111] direction. While in general the metallic LaNiO3 film can effectively screen this polarity mismatch, we establish that in the ultra-thin limit, films are insulating in nature and require additional chemical and structural reconstruction to compensate for such mismatch. A combination of in-situ reflection high-energy electron diffraction recorded during the growth, X-ray diffraction, and synchrotron based resonant X-ray spectroscopy reveal the formation of a chemical phase La2Ni2O5 (Ni2+) for a few unit-cell thick films. First-principles layer-resolved calculations of the potential energy across the nominal LaNiO3/SrTiO3 interface confirm that the oxygen vacancies can efficiently reduce the electric field at the interface.

Fermi-level electronic structure of a topological-insulator/cuprate-superconductor based heterostructure in the superconducting proximity effect regime

Understanding the superconducting proximity effect on the surface of a topological insulator is of critical importance in realizing topological superconductivity and Majorana fermions in solid state settings. We fabricate delicate heterostructure samples between topological insulator (TI) Bi2Se3 thin film and high temperature superconductor Bi2Sr2CaCu2O8+ (Tc ~ 91 K). Using angle-resolved photoemission spectroscopy, we probe the electronic structure and the possible existence of superconducting gap on the top surface of Bi2Se3 thin films. Our systematic data show no significant proximity-induced superconducting gap in the topological surface states with sample temperature down to 10 K (<<91 K) and with a confidence level of sub 5 meV, much smaller than what have been claimed previously, which indicates the near absence of the proximity-induced superconductivity on the TI surface. Our momentum space imaging provides evidence for the coexistence of two crystalline phases in Bi2Se3/Bi2Sr2CaCu2O8+ samples, which we argue to be due to the strong mismatch of lattice crystalline symmetries. Our data identify the major contributors in reducing the proximity-induced superconducting gap below the meV range, including the lack of momentum space overlap between the Bi2Se3 and Bi2Sr2CaCu2O8+ Fermi surfaces, the strong mismatch of lattice crystalline symmetries and superconducting pairing symmetries, as well as the very short superconducting coherence length in Bi2Sr2CaCu2O8+. Our ARPES studies not only provide critical momentum space insights into the Bi2Se3/Bi2Sr2CaCu2O8+ heterostructure, but also set an upper bound on the proximity induced gap for realizing a Majorana fermion condition in this system, which may be further destabilized by the d-wave nodes dominated in a cuprate superconductor.

Thermal transport properties of defective graphene: A molecular dynamics investigation

In this work the thermal transport properties of graphene nanoribbons with randomly distributed vacancy defects are investigated by the reverse non-equilibrium molecular dynamics method. We find that the thermal conductivity of the graphene nanoribbons decreases as the defect coverage increases and is saturated in a high defect ratio range. Further analysis reveals a strong mismatch in the phonon spectrum between the unsaturated carbon atoms in 2-fold coordination around the defects and the saturated carbon atoms in 3-fold coordination, which induces high interfacial thermal resistance in defective graphene and suppresses the thermal conductivity. The defects induce a complicated bonding transform from sp2 to hybrid sp—sp2 network and trigger vibration mode density redistribution, by which the phonon spectrum conversion and strong phonon scattering at defect sites are explained. These results shed new light on the understanding of the thermal transport behavior of graphene-based nanomaterials with new structural configurations and pave the way for future designs of thermal management phononic devices.

Acousto-optic Bragg imaging of biological tissue.

Acousto-optic Bragg imaging is a technique that uses the interaction of light with ultrasound to optically image obstructions in acoustical fields. Existing reports of acousto-optic Bragg imaging based on transmission of acoustic fields through obstructions exhibit strong acoustic impedance mismatches manifested by poor image quality and missing details of physical structures of obstructions. In this work, the image quality was improved to exhibit detailed physical structures of an object by using an improved Bragg imaging system described in Sec. III below. This paper investigates the possibility of extending an acoustic Bragg imaging technique in transmission mode to image animal or plant tissues; a small azalea leaf is used as an illustration in this case. The Bragg image produced clearly shows the veins of the vascular azalea leaf serving as a proof of concept for cost-effective potential application of acoustic Bragg imaging of biological objects in the medical field. Moreover, acousto-optic Bragg imaging is potentially harmless to biological cells and is sensitive to density and elastic variations in the tissue.

Constraining the origin of magnetar flares

Sudden relaxation of the magnetic field in the core of a magnetar produces mechanical energy primarily in the form of shear waves which propagate to the surface and enter the magnetosphere as relativistic Alfvén waves. Due to a strong impedance mismatch, shear waves excited in the star suffer many reflections before exiting the star. If mechanical energy is deposited in the core and is converted directly to radiation upon propagation to the surface, the rise time of the emission is at least seconds to minutes, and probably minutes to hours for a realistic magnetic field geometry, at odds with observed rise times of ≲10 ms for both small and giant flares. Mechanisms for both small and giant flares that rely on the sudden relaxation of the magnetic field of the core are rendered unviable by the impedance mismatch, requiring the energy that drives these events to be stored in the magnetosphere just before the flare. A corollary to this conclusion is that if the quasi-periodic oscillations seen in giant flares represent stellar oscillations, they must be excited by the magnetosphere, not by mechanical energy released inside the star. Excitation of stellar oscillations by relativistic Alfvén waves in the magnetosphere could be quick enough to excite stellar modes well before a giant flare ends, unless the waves are quickly damped.

The mismatch repair pathway maintains genomic stability in human pluripotent stem cells (735.1)

The mismatch repair (MMR) pathway repairs polymerase errors to help maintain genome stability and prevent tumorigenesis. In addition to repair, MMR is also involved in the induction of cell cycle arrest and apoptosis in response to certain forms of DNA damage. The role of MMR in preserving genome integrity in human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) has not been previously examined. Accumulation of mutation in pluripotent stem cells (PSCs) would be detrimental to the developing organism so we hypothesize that these cells have a robust MMR pathway. We find that ESCs and iPSCs express high levels of MMR proteins and demonstrate strong mismatch repair activity. PSCs are also hypersensitive to DNA damage, showing a high level of apoptosis after treatment with a DNA alkylating agent that is MMR dependent. However, the specific response observed differs from that seen in HeLa or other cancer or primary cells. In these other cells, a permanent G2/M cell cycle arrest is induced in the second cell cycle after damage, however, PSCs directly undergo apoptosis in the first cell cycle. Interestingly, there is no activation of cell cycle checkpoint kinases CHK1 or CHK2, although phosphorylation of H2AX is increased. This more immediate apoptotic response suggests a separate molecular mechanism by which the MMR pathway can induce a response to DNA damage in PSCs.Grant Funding Source: Supported by NIH CA 115783 and CT Stem Cell 13‐SCB‐UCHC‐06

Highly Sensitive Electrochemiluminescence Detection of Mercury(II) Ions Based on DNA‐Linked Luminol‐Au NPs Superstructure

AbstractA novel highly sensitive electrochemiluminescence (ECL) detection protocol for mercury(II) ions was developed. Based on the strong and stable thyminethymine mismatches complexes coordination chemistry, mercury(II) ions can specifically bind to a designed DNA strand, leading to the release of the complimentary DNA strand. The released DNA strand was then captured by magnetic beads modified with specific DNA, and then through the formation of DNA‐linked luminol‐Au nanoparticles (NPs) superstructure, a specific ECL system for mercury(II) ions was developed. Using 3‐aminopropyl‐triethoxysilane as an effective enhancer, the ECL system can detect Hg2+ ion within a linear range from 2.0×10−10 mol L−1 to 2.0×10−8 M, with a detection limit as low as 1.05×10−10 M (3σ). Moreover, this ECL system is highly specific for Hg2+, without interference from other commonly coexisted metal ions, and it can be used for the analysis of real samples.

Spatial mismatch of phylogenetic diversity across three vertebrate groups and protected areas in Europe.

We investigate patterns of phylogenetic diversity in relation to species diversity for European birds, mammals and amphibians, to evaluate their congruence and highlight areas of particular evolutionary history. We estimate the extent to which the European network of protected areas (PAs) network retains interesting evolutionary history areas for the three groups separately and simultaneously. Europe. Phylogenetic (QEPD) and species diversity (SD) were estimated using the Rao's quadratic entropy at 10' resolution. We determined the regional relationship between QEPD and SD for each taxa with a spatial regression model and used the tails of the residuals (QERES) distribution to identify areas of higher and lower QEPD than predicted. Spatial congruence of biodiversity between groups was assessed with Pearson's correlation. A simple classification scheme allowed building a convergence map where a convergent pixel equalled to a QERES value of the same sign for the 3 groups. This convergence map was overlaid to the current PAs network to estimate the level of protection in convergent pixels and compared it to a null expectation built on 1000 randomization of PAs over the landscape. QERES patterns across vertebrates show a strong spatial mismatch highlighting different evolutionary histories. Convergent areas represent only 2.7% of the Western Palearctic, with only 8.4% of these areas being covered by the current PAs network while a random distribution would retain 10.4% of them. QERES are unequally represented within PAs: areas with higher QEPD than predicted are better covered than expected, while low QEPD areas are undersampled. Patterns of diversity strongly diverge between groups of vertebrates in Europe. Although Europe has the world's most extensive PAs network, evolutionary history of terrestrial vertebrates is unequally protected. The challenge is now to reconcile effective conservation planning with a contemporary view of biodiversity integrating multiple facets.

Multifunctionalized Microbubbles for Cancer Diagnosis and Therapy

Microbubbles (MBs) are gas-filled hollow microparticles. Under the ultrasound field, the difference of acoustic characteristics between gas and plasma in the blood vessel will cause strong impedance mismatch and echogenicity to enhance ultrasonic grey scale imaging. The linear or nonlinear resonance of MB shell in the ultrasound field would lead to repeated expansion-contraction till destruction. In this case, the pre-loaded drug in the MB shell will be released in an accelerated manner triggered by the ultrasound at a probe–given site. Sonoporation effect of the cell membrane would also help increase the uptake of substances into cells. This paper is dedicated to review recent developments on MBs, especially multifunctionalized MBs, as a potential drug/gene delivery microdevices for both diagnosis and therapy of malignant tumors.

Size control of gold nanoparticles produced by laser ablation of thin films in an aqueous environment

Nanoparticles have been produced by laser ablation of thin gold films on soda lime glass slides that are immersed in distilled and deionized water. The size of the nanoparticles, as determined by fitting the UV–vis absorption spectrum, shows that the average particle radius depends on the thin film thickness in the range of 50–200nm. A heuristic model is developed to explain these results as being strongly dependent on the average temperature that is reached in the thin films, and the subsequent heating of the surrounding medium. The strong thermal mismatch at the film-substrate boundary appears to play a strong role as well.

THz nanocrystal acoustic vibrations from ZrO2 3D supercrystals

We report sharp low-frequency Raman spectral features of supercrystals synthesized via the “benzyl alcohol route” and consisting of either yttrium-stabilized or pure zirconia (ZrO2) nanocrystals. In situ formed benzoate species control the nanocrystal growth and act as organic glue leading to the assembly of the nanocrystals in highly ordered 3D supercrystals. We attribute some Raman peaks to THz acoustic vibrations of individual nanocrystals which are only weakly coupled due to the strong acoustic mismatch between the capping ligands and the nanocrystals. Peak positions are consistent with nanocrystal sizes estimated from transmission electron microscopy and X-ray powder diffraction studies. Narrow size distribution, together with uniform morphological and structural features of the nanocrystals, leads to sharp Raman peaks in the THz spectral region. After removing the ligands by annealing, the acoustic vibrations of the nanocrystals couple resulting in an increase of their frequency. These findings suggest that 3D supercrystals of zirconia nanocrystals can be used for manipulating THz phonons.

Multifunctionalized Microbubbles for Cancer Diagnosis and Therapy

Microbubbles (MBs) are gas-filled hollow microparticles. Under the ultrasound field, the difference of acoustic characteristics between gas and plasma in the blood vessel will cause strong impedance mismatch and echogenicity to enhance ultrasonic grey scale imaging. The linear or nonlinear resonance of MB shell in the ultrasound field would lead to repeated expansion-contraction till destruction. In this case, the pre-loaded drug in the MB shell will be released in an accelerated manner triggered by the ultrasound at a probe-given site. Sonoporation effect of the cell membrane would also help increase the uptake of substances into cells. This paper is dedicated to review recent developments on MBs, especially multifunctionalized MBs, as a potential drug/gene delivery microdevices for both diagnosis and therapy of malignant tumors.

Auditory habituation to simple tones: reduced evidence for habituation in children compared to adults

Habituation—the response decrement to repetitively presented stimulation—is a basic cognitive capability and suited to investigate development and integrity of the human brain. To evaluate the developmental process of auditory habituation, the current study used magnetoencephalography (MEG) to investigate auditory habituation, dishabituation and stimulus specificity in children and adults and compared the results between age groups. Twenty-nine children (Mage = 9.69 years, SD ± 0.47) and 14 adults (Mage = 29.29 years, SD ± 3.47) participated in the study and passively listened to a habituation paradigm consisting of 100 trains of tones which were composed of five 500 Hz tones, one 750 Hz tone (dishabituator) and another two 500 Hz tones, respectively while focusing their attention on a silent movie. Adults showed the expected habituation and stimulus specificity within-trains while no response decrement was found between trains. Sensory adaptation or fatigue as a source for response decrement in adults is unlikely due to the strong reaction to the dishabituator (stimulus specificity) and strong mismatch negativity (MMN) responses. However, in children neither habituation nor dishabituation or stimulus specificity could be found within-trains, response decrement was found across trains. It can be speculated that the differences between children and adults are linked to differences in stimulus processing due to attentional processes. This study shows developmental differences in task-related brain activation and discusses the possible influence of broader concepts such as attention, which should be taken into account when comparing performance in an identical task between age groups.

Ultrafast and Octave-Spanning Optical Nonlinearities from Strongly Phase-Mismatched Quadratic Interactions

Cascaded nonlinearities have attracted much interest, but ultrafast applications have been seriously hampered by the simultaneous requirements of being near phase matching and having ultrafast femtosecond response times. Here we show that in strongly phase-mismatched nonlinear frequency conversion crystals the pump pulse can experience a large and extremely broadband self-defocusing cascaded Kerr-like nonlinearity. The large cascaded nonlinearity is ensured through interaction with the largest quadratic tensor element in the crystal, and the strong phase mismatch ensures an ultrafast nonlinear response with an octave-spanning bandwidth. We verify this experimentally by showing few-cycle soliton compression with noncritical cascaded second-harmonic generation: Energetic 47 fs infrared pulses are compressed in a just 1-mm long bulk lithium niobate crystal to 17 fs (under 4 optical cycles) with 80% efficiency, and upon further propagation an octave-spanning supercontinuum is observed. Such ultrafast cascading is expected to occur for a broad range of pump wavelengths spanning the near- and mid-IR using standard nonlinear crystals.

Spatial characterization of the response of a silica optical fiber to wideband ultrasound

Optical fibers have long been recognized as a promising technology for remote sensing of ultrasound. Nonetheless, very little is known about the characteristics of their spatial response, which is significantly affected by the strong acoustic mismatches between the fiber and surrounding medium. In this Letter, a new method is demonstrated for wideband spatial acoustic characterization of optical fibers. The method is based on the excitation of a point-like acoustic source via the opto-acoustic effect, while a miniature fiber sensor is implemented by a π-phase-shifted fiber Bragg grating. Despite the relative complexity of acoustic wave propagation in the fiber, its spatial sensitivity in the high frequency band (6-30 MHz) exhibited an orderly pattern, which can be described by a simple model. This property reveals new possibilities for high-performance imaging using fiber-based ultrasound sensors, where knowledge of the sensor's spatial sensitivity map is generally required.

Strengths and strain energies of volcanic edifices: implications for eruptions, collapse calderas, and landslides

Abstract. Natural hazards associated with volcanic edifices depend partly on how fracture resistant the edifices are, i.e. on their strengths. Observations worldwide indicate that large fluid-driven extension fractures (dikes, inclined sheets), shear fractures (landslides), and mixed-mode fractures (ring dikes and ring faults) normally propagate more easily in a basaltic edifice (shield volcano) than in a stratovolcano. For example, dike-fed eruptions occur once every few years in many basaltic edifices but once every 102-3 yr in many stratovolcanoes. Large landslides and caldera collapses also appear to be more common in a typical basaltic edifice/shield volcano than in a typical stratovolcano. In contrast to a basaltic edifice, a stratovolcano is composed of mechanically dissimilar rock layers, i.e. layers with mismatching elastic properties (primarily Young's modulus). Elastic mismatch encourages fracture deflection and arrest at contacts and increases the amount of energy needed for a large-scale edifice failure. Fracture-related hazards depend on the potential energy available to propagate the fractures which, in turn, depends on the boundary conditions during fracture propagation. Here there are two possible scenarios: one in which the outer boundary of the volcanic edifice or rift zone does not move during the fracture propagation (constant displacement); the other in which the boundary moves (constant load). In the former, the total potential energy is the strain energy stored in the volcano before fracture formation; in the latter, the total potential energy is the strain energy plus the work done by the forces moving the boundary. Constant-displacement boundary conditions favor small eruptions, landslides, and caldera collapses, whereas constant-load conditions favor comparatively large eruptions, landslides, and collapses. For a typical magma chamber (sill-like with a diameter of 8 km), the strain energy change due to magma-chamber inflation is estimated at the order of 1014 J (0.1 PJ). For comparison, the surface energy needed to form a typical feeder dike is of the same order of magnitude, or 1014 J. There are several processes besides magma-chamber inflation that may increase the strain energy in a volcano before eruption. Thus, during a typical unrest period with magma-chamber inflation, the added strain energy in the volcano is large enough for a typical feeder dike to form. An injected dike, however, only reaches the surface and becomes a feeder if it is able to propagate through the numerous layers and contacts that tend to deflect or arrest dikes. The strong elastic mismatch between layers that constitute stratovolcanoes not only encourages fracture arrest, but also the storage of more strain energy (than in a typical basaltic edifice/shield volcano) before fracture formation and failure. It is thus through producing materials of widely different mechanical properties that stratovolcanoes become strong and resilient.

Multisource least‐squares migration of marine streamer and land data with frequency‐division encoding

ABSTRACTMultisource migration of phase‐encoded supergathers has shown great promise in reducing the computational cost of conventional migration. The accompanying crosstalk noise, in addition to the migration footprint, can be reduced by least‐squares inversion. But the application of this approach to marine streamer data is hampered by the mismatch between the limited number of live traces/shot recorded in the field and the pervasive number of traces generated by the finite‐difference modelling method. This leads to a strong mismatch in the misfit function and results in strong artefacts (crosstalk) in the multisource least‐squares migration image. To eliminate this noise, we present a frequency‐division multiplexing (FDM) strategy with iterative least‐squares migration (ILSM) of supergathers. The key idea is, at each ILSM iteration, to assign a unique frequency band to each shot gather. In this case there is no overlap in the crosstalk spectrum of each migrated shot gather m(x, ωi), so the spectral crosstalk product m(x, ωi)m(x, ωj) =δi, j is zero, unless i=j. Our results in applying this method to 2D marine data for a SEG/EAGE salt model show better resolved images than standard migration computed at about 1/10th of the cost. Similar results are achieved after applying this method to synthetic data for a 3D SEG/EAGE salt model, except the acquisition geometry is similar to that of a marine OBS survey. Here, the speedup of this method over conventional migration is more than 10. We conclude that multisource migration for a marine geometry can be successfully achieved by a frequency‐division encoding strategy, as long as crosstalk‐prone sources are segregated in their spectral content. This is both the strength and the potential limitation of this method.

Evolutionary demography of iteroparous plants: incorporating non-lethal costs of reproduction into integral projection models.

Understanding the selective forces that shape reproductive strategies is a central goal of evolutionary ecology. Selection on the timing of reproduction is well studied in semelparous organisms because the cost of reproduction (death) can be easily incorporated into demographic models. Iteroparous organisms also exhibit delayed reproduction and experience reproductive costs, although these are not necessarily lethal. How non-lethal costs shape iteroparous life histories remains unresolved. We analysed long-term demographic data for the iteroparous orchid Orchis purpurea from two habitat types (light and shade). In both the habitats, flowering plants had lower growth rates and this cost was greater for smaller plants. We detected an additional growth cost of fruit production in the light habitat. We incorporated these non-lethal costs into integral projection models to identify the flowering size that maximizes fitness. In both habitats, observed flowering sizes were well predicted by the models. We also estimated optimal parameters for size-dependent flowering effort, but found a strong mismatch with the observed flower production. Our study highlights the role of context-dependent non-lethal reproductive costs as selective forces in the evolution of iteroparous life histories, and provides a novel and broadly applicable approach to studying the evolutionary demography of iteroparous organisms.

Terahertz photonic states in semiconductor–graphene cylinder structures

We propose a semiconductor-graphene cylinder that can serve as a terahertz (THz) photonic crystal. In such a structure, graphene plays a role in achieving a strong mismatch of the dielectric constant at the semiconductor-graphene interface due to its two-dimensional nature and relatively low value of the dielectric constant. We find that when the radius of the outer semiconductor layer is about ρ(1)~100 μm, the frequencies of the photonic modes are within the THz bandwidth and they can be efficiently tuned via varying ρ(1). Furthermore, the dispersion relation of the photonic modes shows that a semiconductor-graphene cylinder is of excellent light transport properties, which can be utilized for the THz waveguide. This study is pertinent to the application of graphene as THz photonic devices.