• U-PB Detrital Zircon Geochronology of the Lower Danube and Its Tributaries: Implications for the Geology of the Carpathians

      Ducea, Mihai N.; Giosan, Liviu; Carter, Andrew; Balica, Constantin; Stoica, Adriana M.; Roban, Relu D.; Balintoni, Ion; Filip, Florin; Petrescu, Lucian; Univ Arizona (AMER GEOPHYSICAL UNION, 2018-09)
      We performed a detrital zircon (DZ) U-Pb geochronologic survey of the lower parts of the Danube River approaching its Danube delta, Black Sea sink, and a few large tributaries (Tisza, Jiu, Olt, and Siret) originating in the nearby Carpathian Mountains. Samples are modern sediments. DZ age spectra reflect the geology and specifically the crustal age formation of the source area, which in this case is primarily the Romanian Carpathians and their foreland with contributions from the Balkan Mountains to the south of Danube and the East European Craton. The zircon cargo of these rivers suggests a source area that formed during the latest Proterozoic and mostly into the Cambrian and Ordovician as island arcs and back-arc basins in a Peri-Gondwanan subduction setting (similar to 600-440Ma). The Inner Carpathian units are dominated by a U-Pb DZ peak in the Ordovician (460-470Ma) and little inheritance from the nearby continental masses, whereas the Outer Carpathian units and the foreland have two main peaks, one Ediacaran (570-610 Ma) and one in the earliest Permian (290-300 Ma), corresponding to granitic rocks known regionally. A prominent igneous Variscan peak (320-350 Ma) in the Danube's and tributaries DZ zircon record is difficult to explain and points out to either an extra Carpathian source or major unknown gaps in our understanding of Carpathian geology. Younger peaks corresponding to arc magmatism during the Alpine period make up as much as about 10% of the DZ archive, consistent with the magnitude and surface exposure of Mesozoic and Cenozoic arcs.
    • UAV-Based High Resolution Thermal Imaging for Vegetation Monitoring, and Plant Phenotyping Using ICI 8640 P, FLIR Vue Pro R 640, and thermoMap Cameras

      Sagan, Vasit; Maimaitijiang, Maitiniyazi; Sidike, Paheding; Eblimit, Kevin; Peterson, Kyle; Hartling, Sean; Esposito, Flavio; Khanal, Kapil; Newcomb, Maria; Pauli, Duke; et al. (MDPI, 2019-02-01)
      The growing popularity of Unmanned Aerial Vehicles (UAVs) in recent years, along with decreased cost and greater accessibility of both UAVs and thermal imaging sensors, has led to the widespread use of this technology, especially for precision agriculture and plant phenotyping. There are several thermal camera systems in the market that are available at a low cost. However, their efficacy and accuracy in various applications has not been tested. In this study, three commercially available UAV thermal cameras, including ICI 8640 P-series (Infrared Cameras Inc., USA), FLIR Vue Pro R 640 (FLIR Systems, USA), and thermoMap (senseFly, Switzerland) have been tested and evaluated for their potential for forest monitoring, vegetation stress detection, and plant phenotyping. Mounted on multi-rotor or fixed wing systems, these cameras were simultaneously flown over different experimental sites located in St. Louis, Missouri (forest environment), Columbia, Missouri (plant stress detection and phenotyping), and Maricopa, Arizona (high throughput phenotyping). Thermal imagery was calibrated using procedures that utilize a blackbody, handheld thermal spot imager, ground thermal targets, emissivity and atmospheric correction. A suite of statistical analyses, including analysis of variance (ANOVA), correlation analysis between camera temperature and plant biophysical and biochemical traits, and heritability were utilized in order to examine the sensitivity and utility of the cameras against selected plant phenotypic traits and in the detection of plant water stress. In addition, in reference to quantitative assessment of image quality from different thermal cameras, a non-reference image quality evaluator, which primarily measures image focus that is based on the spatial relationship of pixels in different scales, was developed. Our results show that (1) UAV-based thermal imaging is a viable tool in precision agriculture and (2) the three examined cameras are comparable in terms of their efficacy for plant phenotyping. Overall, accuracy, when compared against field measured ground temperature and estimating power of plant biophysical and biochemical traits, the ICI 8640 P-series performed better than the other two cameras, followed by FLIR Vue Pro R 640 and thermoMap cameras. Our results demonstrated that all three UAV thermal cameras provide useful temperature data for precision agriculture and plant phenotying, with ICI 8640 P-series presenting the best results among the three systems. Cost wise, FLIR Vue Pro R 640 is more affordable than the other two cameras, providing a less expensive option for a wide range of applications.
    • Ubiquitous Fractal Scaling and Filtering Behavior of Hydrologic Fluxes and Storages from A Mountain Headwater Catchment

      Dwivedi, Ravindra; Knowles, John F.; Eastoe, Christopher; Minor, Rebecca; Abramson, Nathan; Mitra, Bhaskar; Wright, William E.; McIntosh, Jennifer; Meixner, Thomas; “Ty” Ferre, Paul A.; et al. (MDPI, 2020-02-24)
      We used the weighted wavelet method to perform spectral analysis of observed long-term precipitation, streamflow, actual evapotranspiration, and soil water storage at a sub-humid mountain catchment near Tucson, Arizona, USA. Fractal scaling in precipitation and the daily change in soil water storage occurred up to a period of 14 days and corresponded to the typical duration of relatively wet and dry intervals. In contrast, fractal scaling could be observed up to a period of 0.5 years in streamflow and actual evapotranspiration. By considering long-term observations of hydrologic fluxes and storages, we show that, in contrast to previous findings, the phase relationships between water balance components changed with component period and were not perfectly in or out of phase at all periods. Self-averaging behavior was apparent, but the temporal scales over which this behavior was applicable differed among the various water balance components. Conservative tracer analysis showed that this catchment acted as a fractal filter by transforming white noise in the precipitation input signal to a 1/f flicker in the streamflow output signal by means of both spatial and temporal subsurface advection and dispersion processes and soil wetting properties. This study provides an improved understanding of hydrological filtering behavior in mountain critical zones that are critical sources of water and ecosystem services throughout the world.
    • UCHL1, a deubiquitinating enzyme, regulates lung endothelial cell permeability in vitro and in vivo

      Mitra, Sumegha; Epshtein, Yulia; Sammani, Saad; Quijada, Hector; Chen, Weiguo; Bandela, Mounica; Desai, Ankit A; Garcia, Joe G N; Jacobson, Jeffrey R; Department of Medicine, Arizona Health Sciences Center, University of Arizona (American Physiological Society, 2021-01-13)
      Increasing evidence suggests an important role for deubiquitinating enzymes (DUBs) in modulating a variety of biological functions and diseases. We previously identified the upregulation of the DUB ubiquitin carboxyl terminal hydrolase 1 (UCHL1) in murine ventilator-induced lung injury (VILI). However, the role of UCHL1 in modulating vascular permeability, a cardinal feature of acute lung injury (ALI) in general, remains unclear. We investigated the role of UCHL1 in pulmonary endothelial cell (EC) barrier function in vitro and in vivo and examined the effects of UCHL1 on VE-cadherin and claudin-5 regulation, important adherens and tight junctional components, respectively. Measurements of transendothelial electrical resistance confirmed decreased barrier enhancement induced by hepatocyte growth factor (HGF) and increased thrombin-induced permeability in both UCHL1-silenced ECs and in ECs pretreated with LDN-57444 (LDN), a pharmacological UCHL1 inhibitor. In addition, UCHL1 knockdown (siRNA) was associated with decreased expression of VE-cadherin and claudin-5, whereas silencing of the transcription factor FoxO1 restored claudin-5 levels. Finally, UCHL1 inhibition in vivo via LDN was associated with increased VILI in a murine model. These findings support a prominent functional role of UCHL1 in regulating lung vascular permeability via alterations in adherens and tight junctions and implicate UCHL1 as an important mediator of ALI.
    • UHRF1 predicts poor prognosis by triggering cell cycle in lung adenocarcinoma

      Tu, Zhenbo; Deng, Xinzhou; Hou, Shengqi; Feng, Anlin; Zhang, Qiuping; Univ Arizona, Coll Med Phoenix, Dept Internal Med (WILEY, 2020-06-03)
      Accumulating evidence suggests that ubiquitin-like with plant homeodomain and ring finger domains 1 (UHRF1) is overexpressed in non-small cell lung cancer (NSCLC); however, the expression and function of UHRF1 in the subtype of NSCLC are still unclear. Here, we investigate the expression and prognosis traits of UHRF1 in large NSCLC cohorts and explore the molecular characters during UHRF1 up-regulation. We find that UHRF1 is predominantly overexpressed in lung squamous cell carcinoma (SCC). Surprisingly, the up-regulated UHRF1 is only associated with the overall survival of lung adenocarcinoma (ADC) and knockdown of UHRF1 dramatically attenuates ADC tumorigenesis. Mechanically, we identify a hub gene that includes a total of 55 UHRF1-related genes, which are tightly associated with cell cycle pathway and yield to the poor clinical outcome in ADC patients. What's more, we observe knockdown of UHRF1 only affects ADC cells cycle and induces cell apoptosis. These results suggest that up-regulated UHRF1 only contributes to lung ADC survival by triggering cell cycle pathway, and it may be a prognostic biomarker for lung ADC patients.
    • Ultimate causes of antipredator vocalizations in a nonhibernating squirrel

      Burnett, Alexandra D.; Koprowski, John L.; Univ Arizona, Sch Nat Resources & Environm (ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2020-09-22)
      Communication plays an integral role in facilitating intra- and interspecific interactions. The study of signal function and content reveals the rules that govern such interactions, informing hypotheses in behavioural ecology and evolution. The ubiquitous nature of antipredator vocalizations in ground squirrels provides a useful model for studying the evolution of communication. Conspecifics in many ground squirrel species respond to anti-predator vocalizations, and sociality functions as a strong selective force favouring more informative antipredator vocalizations. However, studies of a single antipredator vocalization system in both social and nonsocial contexts are relatively scarce, preventing diagnosis of selective forces other than sociality. We conducted a 2-year study to test two alternative hypotheses relating to the function of antipredator vocalizations in a nonhibernating squirrel, the Harris' antelope squirrel, Ammospermophilus harristi. We hypothesized that if vocalizations function as a predator deterrent, callers should be of equal sex ratio and vocalize year-round. If vocalizations function primarily as a warning to offspring, callers should be predominantly female and vocalize only when juveniles are above ground. We found that spontaneous callers were predominantly female but vocalized throughout the year. We also found that call bouts varied in trill number, which could hold additional layers of information. Our results suggest that antipredator vocalizations function as both a predator deterrent and a warning to offspring. Antipredator vocalizations with multiple functions or receivers are subject to a greater compilation of selective forces that may induce communicative complexity to arise. (C) 2020 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
    • Ultimate Limits for Multiple Quantum Channel Discrimination

      Zhuang, Quntao; Pirandola, Stefano; Univ Arizona, Dept Elect & Comp Engn; Univ Arizona, James C Wyant Coll Opt Sci (AMER PHYSICAL SOC, 2020-08)
      Quantum hypothesis testing is a central task in the entire field of quantum information theory. Understanding its ultimate limits will give insight into a wide range of quantum protocols and applications, from sensing to communication. Although the limits of hypothesis testing between quantum states have been completely clarified by the pioneering works of Helstrom in the 1970s, the more difficult problem of hypothesis testing with quantum channels, i.e., channel discrimination, is less understood. This is mainly due to the complications coming from the use of input entanglement and the possibility of employing adaptive strategies. In this Letter, we establish a lower limit for the ultimate error probability affecting the discrimination of an arbitrary number of quantum channels. We also show that this lower bound is achievable when the channels have certain symmetries. As an example, we apply our results to the problem of channel position finding, where the goal is to identify the location of a target channel among multiple background channels. In this general setting, we find that the use of entanglement offers a great advantage over strategies without entanglement, with nontrivial implications for data readout, target detection, and quantum spectroscopy.
    • Ultra high performance liquid chromatography tandem mass spectrometry for rapid analysis of trace organic contaminants in water

      Anumol, Tarun; Merel, Sylvain; Clarke, Bradley; Snyder, Shane; Department of Chemical & Environmental Engineering, University of Arizona, 1133 E James E Rogers Way, Harshbarger 108, Tucson, AZ, 85721-0011, USA; School of Applied Sciences, RMIT University, 100 LaTrobe St, Melbourne, 3000, Australia (Chemistry Central, 2013)
      BACKGROUND:The widespread utilization of organic compounds in modern society and their dispersion through wastewater have resulted in extensive contamination of source and drinking waters. The vast majority of these compounds are not regulated in wastewater outfalls or in drinking water while trace amounts of certain compounds can impact aquatic wildlife. Hence it is prudent to monitor these contaminants in water sources until sufficient toxicological data relevant to humans becomes available. A method was developed for the analysis of 36 trace organic contaminants (TOrCs) including pharmaceuticals, pesticides, steroid hormones (androgens, progestins, and glucocorticoids), personal care products and polyfluorinated compounds (PFCs) using a single solid phase extraction (SPE) technique with ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). The method was applied to a variety of water matrices to demonstrate method performance and reliability.RESULTS:UHPLC-MS/MS in both positive and negative electrospray ionization (ESI) modes was employed to achieve optimum sensitivity while reducing sample analysis time (<20min) compared with previously published methods. The detection limits for most compounds was lower than 1.0 picogram on the column while reporting limits in water ranged from 0.1 to 15ng/L based on the extraction of a 1L sample and concentration to 1mL. Recoveries in ultrapure water for most compounds were between 90-110%, while recoveries in surface water and wastewater were in the range of 39-121% and 38-141% respectively. The analytical method was successfully applied to analyze samples across several different water matrices including wastewater, groundwater, surface water and drinking water at different stages of the treatment. Among several compounds detected in wastewater, sucralose and TCPP showed the highest concentrations.CONCLUSION:The proposed method is sensitive, rapid and robust
    • Ultra-compact integrated silicon photonics balanced coherent photodetector

      Meyer, Jason T.; Fallahi, Mahmoud; Univ Arizona, Coll Opt Sci (SPIE-INT SOC OPTICAL ENGINEERING, 2016-02-13)
      In this paper, the performance simulations of a novel ultra-compact balanced coherent photodetector for operation at a wavelength of 1.5 mu m are presented and design proposals for future fabrication processes are provided. It consists of a compact 2x2 MMI that is evanescently coupled into a germanium MSM photodetection layer. The simulations demonstrate dark current less than 10 nA, capacitance less than 20 fF, and optical bandwidth in the 10-30 GHz range. We propose utilizing the simplicity of direct wafer bonding to bond the detection layer to the output waveguides to avoid complicated epitaxial growth issues. This ultra-compact device shows promise as a high-speed, low-cost integrated silicon photonics solution for the telecommunications infrastructure.
    • Ultra-diffuse Galaxies at Ultraviolet Wavelengths

      Singh, Pranjal Rajendra; Zaritsky, Dennis; Donnerstein, Richard; Spekkens, Kristine; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2019-05-06)
      We measure near-ultraviolet (NUV) aperture magnitudes from Galaxy Evolution Explorer images for 258 ultra-diffuse galaxy (UDG) candidates drawn from the initial Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes) survey of similar to 300 square degrees surrounding, and including, the Coma galaxy cluster. For the vast majority, 242 of them, we present flux upper limits due either to a lack of significant flux in the aperture or confusion with other objects projected within the aperture. These limits often place interesting constraints on the UDG candidates, indicating that they are non-star-forming or quiescent. In particular, we identify field, quiescent UDG candidates, which are a challenge for formation models and are, therefore, compelling prospects for spectroscopic follow-up and distance determinations. We present far-ultraviolet (FUV) and NUV magnitudes for 16 detected UDG candidates and compare those galaxies to the local population of galaxies on color-magnitude and specific star formation rate diagrams. The NUV-detected UDG candidates form mostly an extension toward lower stellar masses of the star-forming galaxy sequence, and none of these lie within regions of high local galaxy density. UDG candidates span a range of properties, although almost all are consistent with being quiescent, low surface brightness galaxies, regardless of environment.
    • Ultra-high aspect ratio copper nanowires as transparent conductive electrodes for dye sensitized solar cells

      Zhu, Zhaozhao; Mankowski, Trent; Shikoh, Ali Sehpar; Touati, Farid; Benammar, Mohieddine A.; Mansuripur, Masud; Falco, Charles M.; Univ Arizona, Coll Opt Sci; College of Optical Sciences, The Univ. of Arizona (United States); College of Optical Sciences, The Univ. of Arizona (United States); et al. (SPIE-INT SOC OPTICAL ENGINEERING, 2016-09-23)
      We report the synthesis of ultra-high aspect ratio copper nanowires (CuNW) and fabrication of CuNW-based transparent conductive electrodes (TCE) with high optical transmittance (> 80%) and excellent sheet resistance (R-s < 30 Omega/sq). These CuNW TCEs are subsequently hybridized with aluminum-doped zinc oxide (AZO) thin-film coatings, or platinum thinfilm coatings, or nickel thin-film coatings. Our hybrid transparent electrodes can replace indium tin oxide (ITO) films in dye-sensitized solar cells (DSSCs) as either anodes or cathodes. We highlight the challenges of integrating bare CuNWs into DSSCs, and demonstrate that hybridization renders the solar cell integrations feasible. The CuNW/AZO-based DSSCs have reasonably good open-circuit voltage (V-oc = 720 mV) and short-circuit current-density (J(sc) = 0.96 mA/cm(2)), which are comparable to what is obtained with an ITO-based DSSC fabricated with a similar process. Our CuNW-Ni based DSSCs exhibit a good open-circuit voltage (V-oc = 782 mV) and a decent short-circuit current (J(sc) = 3.96 mA/cm2), with roughly 1.5% optical-to-electrical conversion efficiency.
    • Ultra-strong nonlinear optical processes and trigonal warping in MoS2 layers

      Säynätjoki, Antti; Karvonen, Lasse; Rostami, Habib; Autere, Anton; Mehravar, Soroush; Lombardo, Antonio; Norwood, Robert A.; Hasan, Tawfique; Peyghambarian, Nasser; Lipsanen, Harri; et al. (NATURE PUBLISHING GROUP, 2017-10-12)
      Nonlinear optical processes, such as harmonic generation, are of great interest for various applications, e. g., microscopy, therapy, and frequency conversion. However, high-order harmonic conversion is typically much less efficient than low-order, due to the weak intrinsic response of the higher-order nonlinear processes. Here we report ultra-strong optical nonlinearities in monolayer MoS2 (1L-MoS2): the third harmonic is 30 times stronger than the second, and the fourth is comparable to the second. The third harmonic generation efficiency for 1L-MoS2 is approximately three times higher than that for graphene, which was reported to have a large chi((3)). We explain this by calculating the nonlinear response functions of 1L-MoS2 with a continuum-model Hamiltonian and quantum mechanical diagrammatic perturbation theory, highlighting the role of trigonal warping. A similar effect is expected in all other transition-metal dichalcogenides. Our results pave the way for efficient harmonic generation based on layered materials for applications such as microscopy and imaging.
    • ULTRA: Universal Grammar as a Universal Parser

      Medeiros, David P.; Univ Arizona, Dept Linguist (FRONTIERS MEDIA SA, 2018-02-15)
      A central concern of generative grammar is the relationship between hierarchy and word order, traditionally understood as two dimensions of a single syntactic representation. A related concern is directionality in the grammar. Traditional approaches posit process-neutral grammars, embodying knowledge of language, put to use with infinite facility both for production and comprehension. This has crystallized in the view of Merge as the central property of syntax, perhaps its only novel feature. A growing number of approaches explore grammars with different directionalities, often with more direct connections to performance mechanisms. This paper describes a novel model of universal grammar as a one-directional, universal parser. Mismatch between word order and interpretation order is pervasive in comprehension; in the present model, word order is language-particular and interpretation order (i.e., hierarchy) is universal. These orders are not two dimensions of a unified abstract object (e.g., precedence and dominance in a single tree); rather, both are temporal sequences, and UG is an invariant real-time procedure (based on Knuth's stack-sorting algorithm) transforming word order into hierarchical order. This shift in perspective has several desirable consequences. It collapses linearization, displacement, and composition into a single performance process. The architecture provides a novel source of brackets (labeled unambiguously and without search), which are understood not as part-whole constituency relations, but as storage and retrieval routines in parsing. It also explains why neutral word order within single syntactic cycles avoids 213-like permutations. The model identifies cycles as extended projections of lexical heads, grounding the notion of phase. This is achieved with a universal processor, dispensing with parameters. The empirical focus is word order in noun phrases. This domain provides some of the clearest evidence for 213-avoidance as a cross-linguistic word order generalization. Importantly, recursive phrase structure "bottoms out" in noun phrases, which are typically a single cycle (though further cycles may be embedded, e.g., relative clauses). By contrast, a simple transitive clause plausibly involves two cycles (vP and CP), embedding further nominal cycles. In the present theory, recursion is fundamentally distinct from structure-building within a single cycle, and different word order restrictions might emerge in larger domains like clauses.
    • An ultrabroadband 3D achromatic metalens

      Balli, Fatih; Sultan, Mansoor A.; Ozdemir, Aytekin; Hastings, Jeffrey Todd; College of Optical Sciences, University of Arizona (De Gruyter Open Ltd, 2021-01-25)
      We design and fabricate ultra-broadband achromatic metalenses operating from the visible into the short-wave infrared, 450-1700 nm, with diffraction-limited performance. A hybrid 3D architecture, which combines nanoholes with a phase plate, allows realization in low refractive index materials. As a result, two-photon lithography can be used for prototyping while molding can be used for mass production. Experimentally, a 0.27 numerical aperture (NA) metalens exhibits 60% average focusing efficiency and 6% maximum focal length error over the entire bandwidth. In addition, a 200 μm diameter, 0.04 NA metalens was used to demonstrate achromatic imaging over the same broad spectral range. These results show that 3D metalens architectures yield excellent performance even using low-refractive index materials, and that two-photon lithography can produce metalenses operating at visible wavelengths.
    • Ultrafast band-gap renormalization and build-up of optical gain in monolayer MoTe2

      Meckbach, L.; Hader, J.; Huttner, U.; Neuhaus, J.; Steiner, J. T.; Stroucken, T.; Moloney, J. V.; Koch, S. W.; Univ Arizona, Wyant Coll Opt Sci (AMER PHYSICAL SOC, 2020-02-03)
      The dynamics of band-gap renormalization and gain build-up in monolayer MoTe2 -H is investigated by evaluating the nonequilibrium Dirac-Bloch equations with the incoherent carrier-carrier and carrier-phonon scattering treated via quantum-Boltzmann type scattering equations. For the case where an approximately 300-fs-long high-intensity optical pulse generates charge-carrier densities in the gain regime, the strong Coulomb coupling leads to a relaxation of excited carriers on a few-femtosecond timescale. The pump-pulse generation of excited carriers induces a large band-gap renormalization during the timescale of the pulse. Efficient phonon coupling leads to a subsequent carrier thermalization within a few picoseconds, which defines the timescale for the optical gain build-up energetically close to the low-density exciton resonance.
    • Ultrafast magmatic buildup and diversification to produce continental crust during subduction

      Ducea, Mihai N.; Bergantz, George W.; Crowley, James L.; Otamendi, Juan; Department of Geosciences, University of Arizona (GEOLOGICAL SOC AMER, INC, 2017-03)
      The processes and fluxes that produce the distinct compositional structure of Earth's continental crust by subduction remain controversial. The rates of oceanic crust production, in contrast, are well quantified and are generally believed to be faster than those responsible for building magmatic systems in subduction settings. Here we show that a recently recognized crustal section, the 30-km-thick Ordovician Sierra Valle Fertil-Sierra Famatina complex in Argentina, was built magmatically within only similar to 4 m.y. More than half of the crustal section represents additions from the mantle, and is preserved as mafic igneous rocks and maficultramafic cumulates; the remainder is tonalite to granodiorite with evidence for widespread assimilation from highly melted metasedimentary units. U-Pb zircon geochronology reveals that the construction of the arc was not a simple bottom-up construction process. This continuous exposure of the arc crust allows the quantification of field constrained magmatic addition rates of 300-400 km(3) km(-1) m.y.(-1). These rates are similar to those determined for modern slow-spreading mid-ocean ridges and are of the same magnitude as magmatic addition rates required to build certain large segments of the continental masses such as the Arabian-Nubian shield, among others. The implication is that significant convective removal of arc roots is required over time in order to build the modern continental crust via subduction-related magmatism.
    • Ultrafast mid-infrared high harmonic and supercontinuum generation with n characterization in zinc selenide

      Werner, Kevin; Hastings, Michael G; Schweinsberg, Aaron; Wilmer, Brian L; Austin, Drake; Wolfe, Christopher M; Kolesik, Miroslav; Ensley, Trenton R; Vanderhoef, Laura; Valenzuela, Anthony; et al. (OPTICAL SOC AMER, 2019-02-04)
      Polycrystalline ZnSe is an exciting source of broadband supercontinuum and high-harmonic generation via random quasi phase matching, exhibiting broad transparency in the mid-infrared (0.5-20 μm). In this work, the effects of wavelength, pulse power, intensity, propagation length, and crystallinity on supercontinuum and high harmonic generation are investigated experimentally using ultrafast mid-infrared pulses. Observed harmonic conversion efficiency scales linearly in propagation length, reaching as high as 36%. For the first time to our knowledge, n2 is measured for mid-infrared wavelengths in ZnSe: n2(λ=3.9 μm)=(1.2±0.3)×10-14 cm2/W. Measured n2 is applied to simulations modeling high-harmonic generation in polycrystalline ZnSe as an effective medium.
    • Ultrafast relaxation of hot phonons in graphene-hBN heterostructures

      Golla, Dheeraj; Brasington, Alexandra; LeRoy, Brian J.; Sandhu, Arvinder; Univ Arizona, Dept Phys; Department of Physics, University of Arizona, Tucson, Arizona 85721, USA; Department of Physics, University of Arizona, Tucson, Arizona 85721, USA; Department of Physics, University of Arizona, Tucson, Arizona 85721, USA; Department of Physics, University of Arizona, Tucson, Arizona 85721, USA (AMER INST PHYSICS, 2017-05-01)
      Fast carrier cooling is important for high power graphene based devices. Strongly coupled optical phonons play a major role in the relaxation of photo-excited carriers in graphene. Heterostructures of graphene and hexagonal boron nitride (hBN) have shown exceptional mobility and high saturation current, which makes them ideal for applications, but the effect of the hBN substrate on carrier cooling mechanisms is not understood. We track the cooling of hot photo-excited carriers in graphene-hBN heterostructures using ultrafast pump-probe spectroscopy. We find that the carriers cool down four times faster in the case of graphene on hBN than on a silicon oxide substrate thus overcoming the hot phonon bottleneck that plagues cooling in graphene devices. (C) 2017 Author(s).
    • Ultrafast Rydberg-state dissociation in oxygen: Identifying the role of multielectron excitations

      Plunkett, Alexander; Harkema, Nathan; Lucchese, Robert R.; McCurdy, C. William; Sandhu, Arvinder; Univ Arizona, Dept Phys (AMER PHYSICAL SOC, 2019-06-06)
      We investigated the fragmentation dynamics of highly excited states of molecular oxygen using femtosecond transient photoelectron spectroscopy. An extreme ultraviolet (XUV) pulse populates the autoionizing Rydberg series converging to O-2(+) c(4)Sigma(-)(u), and a femtosecond near-infrared (IR) pulse was used to photoionize these states as they dissociate. Monitoring the differential photoelectron spectra as a function of time delay allowed us to obtain the relaxation lifetimes of these Rydberg states. We observed a photoelectron signal corresponding to the formation of a 4p excited atomic oxygen fragment, which is not an expected dissociation product of the (O-2(+) c(4)Sigma(-)(u))nl sigma(g) Rydberg series. Analysis of the time-dependent photoelectron spectra and photoionization calculations indicate that this fragment results from a previously unexplored (O-2(+) (4)Pi(g))4p repulsive state and that, contrary to expectations, this multielectron excitation pathway presents a substantial cross section. Our study demonstrates that two-color time-resolved differential photoelectron spectroscopy is an excellent tool to study the fragmentation dynamics of such multielectron excited states, which are not easily probed by other means.
    • Ultrafast-timing lifetime measurements in Ru 94 and Pd 96 : Breakdown of the seniority scheme in N = 50 isotones

      Mach, H.; Korgul, A.; Górska, M.; Grawe, H.; Matea, I.; Stănoiu, M.; Fraile, L. M.; Penionzkevich, Yu. E.; Santos, F. De Oliviera; Verney, D.; et al. (AMER PHYSICAL SOC, 2017-01-13)
      The advanced time-delayed gamma gamma(t) method has been applied to determine half-lives of low-lying states in the N = 50 isotones Ru-94 and Pd-96. The inferred experimental E2 strengths for the 4(+) -> 2(+) transitions in the two nuclei show a dramatic deviation with respect to the shell model predictions in the (f(5/2), p, g(9/2)) proton hole space in Sn-100. The anomalous behavior can be ascribed to a breakdown of the seniority quantum number in the pi g(9/2)(n) configuration due to particle-hole excitations across the N = Z = 50 shell as confirmed by large-scale shell model calculations.