Large Amplification Research Articles

Quantification of Effects of Ridge and Valley Topography on the Rayleigh Wave Characteristics

The effects of ridge and valley on the characteristics of Rayleigh waves are presented in this paper. The research work carried out has been stimulated by the day by day increase of long-span structures in the hilly areas which are largely affected by the spatial variability in ground motion caused by the high-frequency Rayleigh waves. The Rayleigh wave responses of the considered triangular and elliptical ridge and valley models were computed using a fourth-order accurate staggered-grid viscoelastic P-SV wave finite-difference (FD) program. The simulated results revealed very large amplification of the horizontal component and de-amplification of the vertical component of Rayleigh wave at the top of a triangular ridge and de-amplification of both the components at the base of the triangular valley. The observed amplification of both the components of Rayleigh wave in front of elliptical valley was larger than triangular valley models. A splitting of the Rayleigh wave wavelet was inferred after interaction with ridge and valley. It is concluded that the large-scale topography acts as a natural insulator for the surface waves and the insulating capacity of the valley is more than that of a ridge. This insulation phenomenon is arising due to the reflection, diffraction and splitting of the surface wave while moving across the topography. It is concluded that insulating potential of the topography for the Rayleigh waves largely depends on their shape and shape-ratio.

High resolution flexible 4-PPR U-base planar parallel microstage robotic manipulator

Numerous compliant manipulators, actuated by voice coil, have been developed and are widely used for micro/nano-manipulation. One of the greatest difficulties lies in optimizing the design with consideration of various parameters like high stiffness, large amplification, higher precise tracking, and highly accurate positioning. A modular and compact planar 3PPR+PPR parallel micro positioning platform is presented (3-degrees of freedom) and its symmetric design equips it with various advantages. The parallel-kinematic arrangement of the manipulator with optimum sizes results in high rigidity and greater load carrying capacities. The proposed planar parallel compliant manipulator possesses higher structural rigidity, better amplification, higher accuracy and precision trajectory tracking ability and positioning. The present work is on a flexure-based micro positioning stage with 3 degrees-of-freedom, incorporating compliant double parallelogram mechanism. An innovative idea of multistage compliant compound parallelogram mechanism is proposed here for the development of a three degrees-of-freedom (X-Y- θ) micro-positioning system, with the range of motion larger than 10 mm. The established models and the performance of the proposed stage are verified through finite-element analysis (FEA).

Heat transfer enhancement strategies in a swirl flow minichannel heat sink based on hydrodynamic receptivity

The swirl flow minichannel heat sink has shown to be a promising alternative for thermal management of high heat flux applications, such as electronics and concentrated photovoltaics. Effective heat transfer enhancement strategies for this device are identified by studying the receptivity of temperature disturbances to a momentum forcing input. Steady state laminar flow is calculated numerically and experimental measurements are carried out to validate the results for subcritical Reynolds numbers. Using the framework of nonmodal stability theory, a harmonically driven linear perturbation problem is formulated, and the methodology to apply the local and parallel flow approximations based on order of magnitude arguments is detailed. The input-output response of temperature perturbations to forcing of the radial, azimuthal, and wall-normal momentum components is calculated for a range of wavenumbers, waveangles and temporal frequencies. The largest amplification is presented by streamwise vortices and streaks, followed by axisymmetric inward travelling waves, and then by streamwise propagating waves. Micromachining the channel walls with streamwise spiral grooves is proposed as a heat transfer enhancement technique. Excitation of streamwise independent structures in the wall-normal direction is expected, therefore maximum amplification should be obtained. Due to its simple implementation, we also propose using a pulsating flow rate as a heat transfer enhancement technique. Receptivity results for streamwise propagating waves of radial forcing show a response curve with moderate amplification for a wide range of actuation frequencies. Experimental work is conducted to measure the performance of the swirl flow channel heat sink using flow pulsations at the range of forcing frequencies suggested by the receptivity study. Compared to the unforced case, a lower wall temperature (up to 5°C cooler) was observed with pulsations, at the same imposed heat flux and flow rate. To get the same wall temperature as in the unforced case, a pumping power reduction of up to 26.6% was observed, and using the same pumping power resulted in up to a 10.3% Nusselt enhancement. Hydrodynamic receptivity was successfully used to identify effective heat transfer enhancement strategies, resulting in a significant performance improvement for the swirl flow channel heat sink. This physics based approach can be extended to other techniques, for instance, to select the wavelength of a wavy surface, the periodicity of surface roughness elements, or the frequency of acoustic vibrations.

Two-Dimensional Infrared Spectroscopy with Local Plasmonic Fields of a Trimer Gap-Antenna Array.

Half-wavelength plasmonic antennas tuned to resonance with molecular vibrational excitations have been demonstrated to enhance 2DIR signals by multiple orders of magnitude. We design doubly degenerate in-plane plasmonic normal modes of the symmetric trimer gap-antenna, which have orthogonal dipole moments excited by light of the appropriate polarization, to localize the enhanced field into the antenna's gap. Vibrational excitations serve as sensitive probes of the plasmonic fields. 2DIR spectroscopy of thin molecular films indicates that molecules emitting enhanced signals experience an electric field with a direction independent of the excitation laser pulse polarization. Our results illustrate the trade-off between the large signal amplification in molecules close to the antenna surface by resonant plasmons, where the direction of the enhanced fields follows metal surface boundary conditions, and the associated limitations for the polarization-selective spectroscopy. The ultrafast quantum dynamics reported by the enhanced signals is not affected by its interaction with plasmonic excitation.

Stability and receptivity of boundary layers in a swirl flow channel

The analysis of the disturbances on a spiraling base flow is relevant for the design, operation, and control of technological devices such as parallel-disk turbines and swirl flow channel heat sinks. Spiraling inflow inside an annular cavity closed at the top and bottom is analyzed in the framework of modal and nonmodal stability theories. Local and parallel flow approximations are applied, and the inhomogeneous direction is discretized using the Chebyshev collocation method. The optimal growth of initial disturbances and the optimal response to external harmonic forcing are characterized by the exponential and the resolvent of the dynamics matrix. As opposed to plane Poiseuille flow, transient growth is small, and consequently, it does not play a role in the transition mechanism. The transition is attributed to a crossflow instability that occurs because of the change in the shape of the velocity profile due to rotational effects. Agreement is found between the critical Reynolds number predicted in this work and the deviation of laminar behavior observed in the experiments conducted by Ruiz and Carey (J Heat Transfer 137(7):071702, 2015). For the harmonically driven problem, an energy amplification of $$\textit{O}(100)$$ is observed for spiral crossflow waves. Transition to turbulence should be avoided to ensure the safe operation of a parallel-disk turbine, whereas large forcing amplification may be sought to promote mixing in a swirl flow channel heat sink. The analysis presented predicts and provides insight into the transition mechanisms. Due to its easy implementation and low computational cost, it is particularly useful for the early stages of engineering design.

Physical process and statistical properties of solar irradiance enhancement observed under clouds

Solar irradiance intensity is usually reduced by cloud shading. However, an enhancement of solar irradiance has rarely been detected. For the detection of irradiance enhancement events, high-speed pyranometers are employed here. The enhancement is detected in almost one-third of days in a month on average in central Japan. From sky-camera observation and meteorological analysis, the enhancement occurs owing to the superimposition of the diffuse irradiance scattered at the edges of cumulus clouds near the sun on the direct irradiance passing through a gap in the clouds, which exist along meteorological fronts. Events of solar irradiance enhancement were detected in a five-month observation period and were analyzed statistically. Some of the events with the largest enhancement are amplified by more than 1.6, and their durations are from 30 s to 4 min. Statistical analyses showed events with either large amplifications or long durations but not events with both large amplifications and long durations.

Carbon Nanotube Film Gate in Vacuum Electronic Devices.

A superaligned carbon nanotube (SACNT) film can act as an ideal gate electrode in vacuum electronics due to its low secondary electron emission, high electron transparency, ultrasmall thickness, highly uniform electric field, high melting point, and high mechanical strength. We used a SACNT film as the gate electrode in a thermionic emission electron tube and field emission display prototype. The SACNT film gate in a thermionic emission electron tube shows a larger amplification factor. A triode tube with the SACNT film gate is used in an audio amplification circuit. The SACNT film gate electrode in field emission devices shows better field uniformity. The field emission display prototype is demonstrated to dynamically display Chinese characters.

Mechanisms for primordial black hole production in string theory

We consider mechanisms for producing a significant population of primordial black holes (PBHs) within string inspired single field models of inflation. The production of PBHs requires a large amplification in the power spectrum of curvature perturbations between scales associated with CMB and PBH formation. In principle, this can be achieved by temporarily breaking the slow-roll conditions during inflation. In this work, we identify two string setups that can realise this process. In string axion models of inflation, subleading non-perturbative effects can superimpose steep cliffs and gentle plateaus onto the leading axion potential. The cliffs can momentarily violate the slow-roll conditions, and the plateaus can lead to phases of ultra slow-roll inflation. We thus achieve a string motivated model which both matches the Planck observations at CMB scales and produces a population of light PBHs, which can account for an order one fraction of dark matter. In DBI models of inflation, a sharp increase in the speed of sound sourced by a steep downward step in the warp factor can drive the amplification. In this scenario, discovery of PBHs could indicate non-trivial dynamics in the bulk, such as flux-antibrane annihilation at the tip of a warped throat.

Abstract 424: Defining prostate cancer subtypes by genomic features associated with defects in DNA repair processes

Abstract Introduction: Prostate cancer (PC) exhibits a spectrum of genomic aberrations, a subset of which associate with responses to specific therapeutics. In particular, mutations in genes involved in DNA repair processes expose therapeutic vulnerabilities that include PARP inhibitors and DNA-damaging chemotherapy for homology-directed repair(HR) defects and immune checkpoint blockade for mismatch repair (MMR) defects. Deploying appropriate therapy is dependent on accurate tumor classification. Experimental Procedures: We evaluated whole-exome sequences derived from localized (n = 465) and metastatic (n = 208) PCs to identify mutations and structural aberrations predicted to disrupt or alter the function of genes involved in DNA repair processes. We annotated all tumors for trinucleotide (COSMIC) mutation signatures by comparing somatic alterations in tumor versus paired normal exomes. We compared the type and frequency of presumed pathogenic mutations, tumor ploidy, copy number aberrations, and mutational signatures between primary and metastatic tumors and evaluated associations between specific DNA repair gene aberrations and mutation signatures. Results: Overall, 54% of localized PCs and 24.5% of metastatic PCs had a component of their somatic mutation burden associated with a mutation signature indicative of a DNA repair defect. Metastatic PCs had significantly higher numbers of somatic mutations (n=223) compared to primary PCs (n=93) (p<0.008). Aneuploid and hypermutated tumors are also more common in metastatic PCs compared to primary PCs. Tumors with high LOH (>0.1) scores were enriched for pathogenic mutations in BRCA1/2 and lowest LOH scores were observed in tumors with mutation/loss of CDK12, which were near-diploid. In addition to relatively frequent aberrations in BRCA2, BRCA1 and ATM, we found CDK12 mutations in ~1% of primary PCs and 5.3% of metastatic PCs. Tumors with BRCA1/2 loss or ATM and RecQ-Helicase pathway aberration exhibited larger amplifications and loss events, whereas PCs with CDK12 aberrations demonstrated a high number (n>73 to 261) of focal (500b-1mb range) amplifications with rare focal losses. Conclusions: 102 individual metastatic cases with some fraction of HR-defect signature and 41 (~40%) of them are without any bona fide HR pathway mutations. DNA repair gene (DRG) aberrations are common in metastatic PC and associate with distinct mutational signatures and structural aberrations that partition PCs into distinct subtypes. Epigenetic processes may contribute to HR signatures in tumors where DRG mutations were not identified. Preclinical and clinical studies are required to determine if mutation signatures are accurate predictors of responses to therapeutics. Thus, with these signatures, we have proposed a few molecular subcategories of prostate tumors and such information can be harnessed for future precision cancer therapies. Citation Format: Navonil De Sarkar, Emily Kohlbrenner, Ilsa Coleman, Peter S. Nelson. Defining prostate cancer subtypes by genomic features associated with defects in DNA repair processes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 424.

Observations and Modeling of Long‐Period Ground‐Motion Amplification Across Northeast China

AbstractBasin resonances can significantly amplify and prolong ground shaking, and accurate site‐amplification estimates are crucial for mitigating potential seismic hazards within metropolitan basins. In this work, we estimate the site amplification of long‐period (2–10 s) ground motions across northeast China for both surface waves and vertically incident shear waves. The spatial distribution of relatively large site amplifications correlates strongly with known sedimentary basins for both wave types. However, the site response of surface waves is typically twice as high as that of shear waves at most basin sites. We further show that these site‐amplification features can be well explained by predictions based on the local one‐dimensional structure at each site. Our results highlight the importance of accounting for surface‐wave contributions and demonstrate the usefulness of semi‐analytical theory for surface‐wave amplification, which may be broadly applicable in future seismic hazard analysis.

Plasmon-Enhanced Multicarrier Photocatalysis.

Conversion of solar energy into liquid fuel often relies on multielectron redox processes that include highly reactive intermediates, with back reaction routes that hinder the overall efficiency of the process. Here, we reveal that these undesirable reaction pathways can be minimized, rendering the photocatalytic reactions more efficient, when charge carriers are harvested from a multiexcitonic state of a semiconductor photocatalyst. A plasmonic antenna, comprising Au nanoprisms, was employed to accomplish feasible levels of multiple carrier excitations in semiconductor nanocrystal-based photocatalytic systems (CdSe@CdS core-shell quantum dots and CdSe@CdS seeded nanorods). The antenna's near-field amplifies the otherwise inherently weak biexciton generation in the semiconductor. The two-electron photoreduction of Pt and Pd metal precursors served as model reactions. In the presence of the plasmonic antenna, these photocatalyzed two-electron reactions exhibited enhanced yields and kinetics. This work uniquely relies on a nonlinear enhancement that has potential for large amplification of photocatalytic activity in the presence of a plasmonic near-field.

Large amplification of the 1906 Colombia–Ecuador earthquake tsunami in Hilo Bay induced by bay-scale resonance

Large amplification of the 1906 Colombia–Ecuador earthquake tsunami in Hilo Bay induced by bay-scale resonance

Direct Electrochemical Observation of Single Platinum Cluster Electrocatalysis on Ultramicroelectrodes.

We demonstrate a method to electrodeposit and observe the electrocatalysis of small platinum clusters and nanoparticles (NPs) in real time as they form on an ultramicroelectrode (UME). Water droplets ( rdrop ∼ 700 nm), stabilized by sodium dodecyl sulfate (SDS), were suspended in a solution of dichloromethane (DCM) and tetrabutylammonium perchlorate ([TBA][ClO4]), which was used to mitigate charge balance during droplet electrolysis. When droplets collided with an UME biased sufficiently negative to drive water reduction, large blips of current were observed. Droplets were synthesized with varying concentrations of H2PtCl6 (from 24.4 mM to 32 nM), which can be reduced to Pt0 at 0.8 V more positive than water reduction on a Au or C UME. The observation of current blips synthesized with mM amounts of H2PtCl6 indicated water droplets deliver H2PtCl6 to the electrode surface, where a cathodic potential caused Pt NPs to form. The formation of clusters was observed by biasing the electrode potential more negative than water reduction on Pt but more positive than water reduction on Au, giving current blips for droplets containing μM to nM amounts of H2PtCl6. These blips corresponded to the electrocatalysis of thousands to tens of atoms (clusters). Droplet electrolysis allows for a large amplification such that the electrocatalysis of clusters can be observed in real time. Single, isolated clusters were further characterized voltammetrically on carbon fiber UMEs. The isolation step used the amperometric method, which unambiguously depicted cluster formation in real time. Carbon was chosen due to its large potential window and slow kinetics toward many inner-sphere reactions, such as proton reduction, used in this study. Voltammetric characterization of proton reduction in HClO4 and NaClO4 allowed for cluster size analysis using the limiting current. The reduction of proton on the clusters ( E1/2 ∼ -0.6 V vs Ag/AgCl) occurred at ca. 400 mV more negative than bulk, polycrystalline platinum.

Achieving nonlinear optical modulation via four-wave mixing in a four-level atomic system

We propose an accessible scheme for implementing tunable nonlinear optical amplification and attenuation via a synergetic mechanism of four-wave mixing (FWM) and optical interference in a four-level ladder-type atomic system. By constructing a cyclic atom-field interaction, we show that two reverse FWM processes can coexist via optical transitions in different branches. In the suitable input-field conditions, strong interference effects between the input fields and the generated FWM fields can be induced and result in large amplification and deep attenuation of the output fields. Moreover, such an optical modulation from enhancement to suppression can be controlled by tuning the relative phase. The quantum system can be served as a switchable optical modulator with potential applications in quantum nonlinear optics.

Design of a New Piezoelectric Energy Harvester Based on Compound Two-Stage Force Amplification Frame

This paper presents the design and verification of a piezoelectric energy harvester with compound two-stage force amplification frame and compact footprint size to achieve high power output for a piezoelectric stack. An improved design of the conventional bridge-type force amplification frame is proposed with compound beam, which is able to maintain the large force amplification ratio while bearing a large loading force. Analytical model is developed based on Euler-Bernoulli beam theory to predict the force amplification ratio of the compound two-stage force amplifier. The architectural parameters are optimally tuned to achieve the largest force amplification ratio, so as to obtain the maximum power output for the piezoelectric stack under other constraints. Simulation study is carried out by finite element analysis to demonstrate the advantage of the proposed compound two-stage force amplifier over conventional design. Moreover, a prototype harvester is fabricated for experimental testing. Results indicate that the proposed harvester features high safety factor, large amplification ratio, and compact size, which can be adopted in practical application for scavenging energy induced by human footstep during walking.

Seismic hazard in Buenos Aires, Argentina: A preliminary study on the effects of long‐distance earthquakes on tall buildings

SummaryThe 2015 Illapel earthquake produced self‐evacuation of tall buildings in the city of Buenos Aires, Argentina, located 1280 km away from the epicenter. The ground motions in Buenos Aires due to the main event (Mw 8.3) and its aftershocks were registered by a new seismometer. The data collected allowed to estimate the maximum story drift ratios and top floor accelerations for tall buildings in Buenos Aires. The similarities between the response spectra and the Fourier amplitude spectra for the mainshock and its aftershocks show the influence that the dynamic properties of the 300‐m soil deposit have on the large acceleration amplification produced in these groups of buildings.

Role of Shape and Numbers of Ridges and Valleys in the Insulating Effects of Topography on the Rayleigh Wave Characteristics

This research work is inspired by the recently accepted concept that high frequency Rayleigh waves are generated in the epicentral zone of shallow earthquakes. Such high frequency Rayleigh waves with large amplitude may develop much of spatial variability in ground motion which in turn may cause unexpected damage to long-span structures like bridges, underground pipelines, dams, etc., in the hilly regions. Further, it has been reported that topography acts as an insulator for the Rayleigh waves (Ma et al. BSSA 97:2066–2079, 2007). The above mentioned scientific developments stimulated to quantify the role of shape and number of ridges and valleys falling in the path of Rayleigh wave in the insulating effect of topography on the Rayleigh waves. The simulated results reveals very large amplification of the horizontal component of Rayleigh wave near the top of a triangular ridge which may cause intensive landslides under favorable condition. The computed snapshots of the wave-field of Rayleigh wave reveals that the interaction of Rayleigh wave with the topography causes reflection, splitting, and diffraction of Rayleigh wave in the form of body waves which in turn provides the insulating capacity to the topography. Insulating effects of single valley is more than that of single ridge. Further this effect was more in case of elliptical ridge/valley than triangular ridge/valley. The insulating effect of topography was proportional to the frequency of Rayleigh wave and the number of ridges and valleys in the string. The obtained level of insulation effects of topography on the Rayleigh wave (energy of Rayleigh wave reduced to less than 4% after crossing a topography of span 4.5 km) calls for the consideration of role of hills and valleys in seismic hazard prediction, particularly in case of shallow earthquakes.

Efficacy of Water Chamber Type Seawall to Dissipate Incident Wave and Its Performance to Extract Wave Power

This study examined performance a water chamber type of seawall to dissipate incident wave and also extract wave power. The model of water chamber is consists of two water chamber type. The low reflection wave resulted by flow separation in lower end of vertical wall and it occurs after wave resonant condition. This structure is appropriate for short and long wave condition. A horizontal plate was setup in the end of vertical wall in order to improve performance of water chamber type seawall. This trial test taken to dissipate much longer waves condition and it’s related to utilize the wave energy inside the water chamber. Additional trial of the cross section, such as an adoption of a bevel edge instead of a right angle edge was also examined. It was seen that the seawall of a water chamber type with a horizontal plate is very effective to reduce reflected waves for both short and long waves. Also it was confirmed that large amplifications of pumping mode wave motions in the two water chambers appear for comparatively wide range of wave frequency

Oxygen Vacancy Engineering in Europia Clusters/Graphite-Like Carbon Nitride Nanostructures Induced Signal Amplification for Highly Efficient Electrochemiluminesce Aptasensing.

Oxygen vacancy is an intrinsic defect in metal oxide semiconductors and has a crucial influence on their physicochemical and electronic properties. To boost the electrochemiluminescence (ECL) efficiency of the graphite-like carbon nitride (g-C3N4), the wet-chemical-calcination method was developed to introduce an oxygen vacancy in Eu-doped g-C3N4 nanostructures for the first time. The morphology and structure characterization suggest that the Eu element was present in the matrix of the europia (Eu2O3) clusters. Because of the effect of oxygen vacancy promoting catalytic activity, the doping of Eu caused a great positive shift of onset potential and large signal amplification in cathodic ECL signals compared with pure g-C3N4. Furthermore, a novel and ultrasensitive ECL aptasensor was realized with 17β-estradiol (E2) as a prototype target by adsorption of E2 aptamer onto the Eu2O3-doped g-C3N4 (Eu2O3- g-C3N4) surface via van der Waals force. Given the specific recognition between aptamer and E2, the ECL signal decreased with the increasing concentration of E2, because the formation of E2-aptamer complex impeded the diffusion of luminophor molecules and the electrons approaching the surface of the electrode. Under the optimal cases, the as-prepared ECL aptasensor showed superior performances and also manifested outstanding selectivity toward E2. The present conceptual strategy offers a novel methodology to boost the sensitivity of the ECL sensor and promote the activity of ECL reagents.

Experimental Evaluation of Structural Intensity in Two-Dimensional Plate-Type Locally Resonant Elastic Metamaterials

Elastic metamaterials utilize locally resonant mechanical elements to onset band gap characteristics that are typically exploited in vibration suppression and isolation applications. The present work employs a comprehensive structural intensity analysis (SIA) to depict the structural power distribution and variations associated with band gap frequency ranges, as well as outside them along both dimensions of a two-dimensional (2D) metamaterial. Following a brief theoretical dispersion analysis, the actual mechanics of a finite metamaterial plate undergoing flexural loading and consisting of a square array of 100 cells is examined experimentally using a fabricated prototype. Scanning laser Doppler vibrometer (SLDV) tests are carried out to experimentally measure the deformations of the metamaterial in response to base excitations within a broad frequency range. In addition to confirming the attenuation and blocked propagation of elastic waves throughout the elastic medium via graphical visualizations of power flow maps, the SIA reveals interesting observations, which give additional insights into energy flow and transmission in elastic metamaterials as a result of the local resonance effects. A drastic reduction in power flow magnitudes to the bulk regions of the plate within a band gap is noticeably met with a large amplification of structural intensity around and in the neighborhood of the excitation source as a compensatory effect. Finally, the theoretical and experimentally measured streamlines of power flow are presented as an alternative tool to predict the structural power patterns and track vortices as well as confined regions of energy concentrations.