Poster Presentations

Continuous to intermittent flow transition in sandpiles

Alonso Llanes, Laciel (Cuba)

If a granular medium is deposited on a horizontal surface, between two flat and parallel vertical walls, a granular pile is formed due to the flow established on its top. Initially, when the pile is relatively small, this granular flow is smooth and constant, while after a certain critical size (𝑥𝑐 ) it begins to be intermittent, evidenced by the occurrence of avalanches. This phenomenon is known as the continuous to intermittent flow transition [1-3]. By means of experiments, using a specially designed experimental setup to control the distance between the apex of the pile and the container dropping the grains, we have found that 𝑥𝑐 grows linearly with the input flux and with the square root of the dropping height. We also demonstrate that our results allow to predict the values of 𝑥𝑐 and 𝑡𝑐 –elapsed time until the transition occurs– for observations commonly reported in the literature in which the feeding height decreases as the pile increases its size.

Engineering Topological Quantum Dots in Graphene Nanoribbons

Butler, Paul (United States)

The recently established on-surface synthesis methodology has allowed us to engineer atomically precise Graphene Nanoribbons (GNRs). This unprecedented control over atomic geometry allows us to explore topological states in GNRs. We interconnected GNR segments of different topological character to conceive heterostructures hosting topologically protected interface states at the Fermi level. We synthesized structures consisting of Armchair Graphene Nanoribbons (AGNRs) of N = 7 and N = 9 atoms in width to produce these localized states. Neighboring states hybridize to give bonding and antibonding combinations. The emergent quantum dots are characterized using Scanning Tunneling Microscopy and Spectroscopy. Our research provides the preliminary tools for engineering both isolated states and bands. It is predicted that the energy gap can be precisely tuned over an order of magnitude in topological GNR quantum dots and periodic heterostructures—making GNRs a promising candidate for use in future nanoscale electronic applications.

 

A new analytical method of solution of the advection-diffusion equation: Case of study a surface water quality model

Cardenas Pestana, Jorge Alberto (Cuba)

In modeling studies of surface water quality, specifically estuaries, due to their physical – mathematical complexity, few problems are solved with analytical methods. Our main goal was to solve a pollutant transport model of dissolved oxygen applied to estuaries with a certain level of stratification under a microtidal regime. The physical and mathematical considerations were assumed only for cuban estuaries. Here we used the method proposed by which allows to solve a Riemann problem with general initial conditions divided by semiaxes by means of the use of conformal transformations and applying the Cherski’s technique. We solve the model only for the zero index cases, having unique solution and also practical application. This work constitutes a practical contribution to the theory of partial differential equations and hydrodynamic models applied to estuaries with these specific characteristics.

 

Taylor Scale and Magnetic Reynolds Number Estimation via Two-Point Spatial Correlations

Cartagena-Sanchez, Carlos (United States)

The Bryn Mawr Plasma Laboratory (BMPL) is a new facility investigating plasma turbulence. Here, spatial correlation analysis of magnetic fluctuations within the Bryn Mawr Magnetohydrodynamic Experiment (BMX) is used to estimate outer and inner scales of the inertial range of the energy cascade. These measurements are made using an array of magnetic pickup probes aligned parallel to the bulk flow of the plasma.  With these estimates a magnetic Reynolds number is calculated. The spatial correlation scale and the Taylor microscale are used as the outer scale and inner scale respectively. This presentation represents the first BMX results of plasma turbulence properties.

 

Hydrogen adsorption in MOF5: QL-DFT calculations

Cerutti Torres, Joeluis (Cuba)

The study of the adsorption properties of nanomaterials, in particular their abilities to take in molecular hydrogen have attracted a lot of attention in recent years. In particular, the need for the design of efficient lightweight hydrogen storage devices have triggered a large number of theoretical and experimental investigations on the hydrogen uptake of a variety of nanostructured materials [1]. MOFs are nanoporous materials which constitute promising candidates for renewable energy applications, specifically for hydrogen storage [2]. Quantum liquid density functional theory (QL-DFT) [3] is a model that can be used for computing the density profile of guest species adsorbed in porous materials under the influence of an external potential at given thermodynamic conditions. QL-DFT translates the main equations of electronic DFT to a different problem, i.e., the problem of many interacting bosons at finite temperatures. Therefore, Bose Einstein (or Maxwell Boltzmann for high temperatures) instead of Fermi Dirac statistic is used. Also, electronic structure of MOFs and of the Hydrogen molecules are not taken into account explicitly, but they are masked in the guest-host interaction potentials. In this work, QL-DFT calculations are performed for the determination of the Hydrogen adsorbed density in MOF-5 (Fig.1), at varying thermodynamic conditions. Limitations and immediate perspectives for the modelling of adsorption phenomena in these media are also discussed.

 

Photoluminescent properties effects of Erbium-doped glasses from ternary system CdO-V2O5-P2O5

Cervantes Juárez, Erika (Mexico)

In this work has been proposed the analysis of a novel matrix composed by CdO-V2O5-P2O5 doped with Erbium (Er3+) ions, in order to analyze its photoluminescence properties for potential applications in lasers, solar cells optical communications etc. It is well known that Er3+ possesses several electronic levels in the IR-visible region. Particularly, the 4I13/2, 4I11/2 y 4I9/2 levels are symmetrically spaced in the IR region and match with the emissions of commercial 1534, 980 y 806 nm laser diodes, respectively. Recently, it has been found that the CdO-V2O5 -P2O5 system remains amorphous at large content of CdO (80.0 mol%). Thus, the host composition was 90-5-5 % mol of CdO-V2O5-P2O5, respectively. The Er3+ content was varied from 0.5 to 4.0 mol% regarding the host composition by using Er nitrate as source. The starting precursors were melted at 1200 °C in a high alumina crucible for one hour and poured onto a stainless steel mold at room temperature in order to induce a thermal shock. The structural analysis performed by X-Ray diffraction patterns and Raman Spectroscopy reveals amorphous phases in all cases according with the lack of diffraction peaks and the broad vibrational bands located at 850, 637 and 355 cm-1, related to Cd2V2O7 in amorphous phase [4]. By optical absorption was possible to identify the typical Er3+ transitions (see figure 1) and estimate the band gap energy values (Eg= 2.45-2.58 eV) by the Tauc’s Method, which are reduced as Er3+ is incorporated. Such fact is associated with Non-bonding oxygens [5]. The up-conversion emissions upon 980 nm laser excitation, display the Er3+ emissions located at 521, 541 and 660 nm, attributed to the 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 y 4F9/2 → 4I15/2 transitions, respectively. The down conversion emission spectra show a broad band centered at 1532 nm, related to the 4I13/2 → 4I15/2 transition. Both emissions reach their optimum intensity at 2.5 mol% of Er3+, at higher contents the emission intensity gradually decreases. This behavior is most likely due to cross relaxation processes, which promote non-radiative transitions, as is suggested by the emission decay profiles at 1532 nm.

 

Geometry of Deformations and Bending Energy of Relativistic Extended Objects

Chávez Tovar, Johan Michel (Mexico)

Dynamics of relativistic extended objects concerns to the study of brane mechanics, which is indeed an important tool in the study of the behavior of several physical systems. This kind of objects can emerge as topological defects during phase transitions in the early universe or as fundamental objects in physical theories such as String Theory. In this work is shown a kinematical description of infinitesimal deformations of the world-sheet spanned by branes moving through a curved spacetime of arbitrary dimension, this description is formulated as an extension of the Riemannian Geometry and provides a solid framework to obtain both the equations of motion and the infinitesimal deformation equations of the worldsheet. Under this framework is constructed also a geometrical model of the world-sheet bending energy based upon a Lagrangian description and a general covariant variational principle which is expressed in terms of its intrinsic and extrinsic geometry.

 

Background characterisation for water and scintillator phases of SNO+

Cox, Matthew (Canada)

The SNOPLUS experiment is a multinational collaboration, that has the ultimate aim of detecting the radioactive decay process known as neutrinoless double beta decay. Hence, proving neutrinos are Majorana particles and constraining the Majorana neutrino mass.  SNO+ has been taking data with the detector filled with water since May 2017, and is now transitioning to the scintillator phase. During the water phase, the main physics goals are the search for invisible nucleon decay modes and to study high energy solar neutrinos. The main radioactive background contributions during this phase are from Bi-214 and Tl-208. Rn-222 is largely present in mine air and its ingress into the detector results in backgrounds from the decay of its Bi-214 daughter. Hence, the first year of my PhD focussed on the analysis of Bi-214 in water.  The daily monitoring of Bi-214 (radon) levels within the detector is an important tool that we can use to identify changes in the detector conditions and act promptly. Weekly in-situ analysis has been performed by applying multiple selection cuts such as rejecting reconstructed events with energy above a specified threshold (i.e. 3.5 MeV) or events falling outside a specified fiducial volume (i.e. 4.3 m). This analysis provides an adequate estimate of the purity within the detector and its external UPW shielding. Another important background related to Rn ingress into the detector, is Po-210. This background is particularly important in the detector’s next stage, when liquid scintillator will replace the UPW. Po-210 can interact with the C and O atoms in the scintillator and AV, producing neutrons. The resulting signal, has the same signature of an anti-neutrino (geo/reactor) interaction. Therefore, it is essential to study this source of background for reactor and geoneutrino investigations. The future research direction of this PhD will aim to characterize and minimize this.

 

Signal and Background Selection Using Computer Learning for SNO+

Delay, Dominique (Canada)

The SNO+ experiment is a 780 Tonne liquid scintillator neutrino detector located 2 kilometers underground. The rock provides a 6000-meter water equivalent shielding, significantly reducing cosmic rays. The SNOLAB facility is a state of the art clean lab. There is, never the less, a small amount of radon and other decay sources that can cause background events which mask signals. It is important to separate signal from background properly so that only physics events are selected by the analysis. Machine learning has the potential to have the best event selection, with a high signal efficiency and background rejection. ROOT TMVA, a machine learning environment for the processing and evaluation of multivariate classification, is trained and tested using simulated Bismuth decay events, and neutrino events as examples of background and signal respectively. TMVA uses different multivariate analysis classifiers such as decision trees, likelihood, cuts, and linear discriminant analysis to do so. Each of these classifiers has a different level of accuracy to distinguish background from signal for the specific data set. After evaluating these methods, we will seek to add them to the common SNO+ code.

 

Liquid Scintillator Phase of the SNO+ Neutrino Detector

Deluce, Caroline (Canada)

SNO+ is a detector used to study the properties and behaviour of neutrinos. With a radius of approximately 6m, the experiment is composed of a spherical acrylic shell that has been filled with light water, which will then be replaced with linear alkylbenzene (LAB) and poly(p-phenylene oxide) (PPO), and finally with LAB and PPO along with Tellurium. The acrylic vessel (AV) is contained in a cavity filled with light water, and is held in position so that it is centered within a shell of photomultiplier tubes (PMTs) that capture traces of scintillation light produced by particle interactions with LAB. The primary goal of SNO+ is to search for neutrinoless double beta decay, however its secondary goals include the observation of nucleons decaying into neutrinos, to study proton-electron-proton (pep) and carbon-nitrogen-oxygen (CNO) cycles within the sun, to study the release of geoneutrinos, to improve the accuracy of the parameters of neutrino oscillation through the observation of fission daughter products, and it is to be used as a supernova early warning detector. Currently, SNO+ is undergoing the scintillator (LAB & PPO) fill phase and is continuing to record physics data although it contains both light water and LAB in the AV. The scintillator will float above the water in the AV, and since both liquids have different indices of refraction, it will affect the reconstruction of events. The vertical location of the interface between the two liquids in the AV can provide guidance to adjust the method of event reconstruction to account for the two different fluids. The height of the interface between the water and scintillator can be found by rearranging the cylindrical, spherical, and spherical cap volume equations. This method for calculating the location of the interface will be implemented in the RAT software, which is a package that handles simulation and reconstruction of neutrino events in SNO+.

 

Harnessing advanced classical computing techniques including distributed computing with tensor networks and machine learning for discovery in theoretical quantum physics

Edwards, Marcus (Canada)

In 1982, Feynman famously described the exponential scaling issue that is faced by any classical computing method that attempts to simulate a quantum system. This is not only a challenge for simulators, but also for theorists who study quantum many-body system dynamics. For example, exploring multi-qubit entanglement is important for a fundamental understanding of quantum mechanics as well as for building large scale quantum computers. A growing list of analogues between classical computing and quantum computing are being discovered in areas including machine learning [3, 4] and tensor networks [5]. We explore how distributed computing systems can be used to combine simulation approaches based on these analogues and enable more resource-optimized simulations. We contribute a framework for expressively implementing distributed quantum systems simulations in code. Our framework executes simulations using resources traditionally used for distributed cloud machine learning and data processing. We show how it can be used to analyze the performance of different simulation approaches and automatically suggest the best approaches to use for particular problems.

 

Intelligent coupler for a prototype applied  to  civil  protection  and  further space missions

Espinoza, Leonardo (Mexico)

We present the design and development of an intelligent coupler to mount a drone over a rover. Using 3D modeling software (Solidworks) we obtained the first design of the coupler, and 3D printed it. For our first approach we developed a system using Arduino and some basic sensors to control the operating mechanism. We are planning the whole system (rover, coupler and drone) to be used for civil protection purposes and further space exploration missions. The rover and drone were previously acquired in order to test the coupler. We have done successful laboratory tests in which the rover waits for the drone to be placed on it and where the coupler takes the drone autonomously to continue later with another specific task. This work was developed in the specialization degree in Aerospace Industry at the National Institute of Technology of Mexico / Ensenada Institute of Technology as part of a thesis requirement.

 

Detecting seismic activity and testing calibration ropes in SNO+

Felber, Connor (Canada)

SNO+ is the successor to the successful SNO experiment that lead to the construction of SNOLAB. This experiment consists of a large vessel, currently filled with ultrapure water used to detect and study neutrinos. The vessel is a 12-m sphere made of acrylic located 2km underground in VALE’s Creighton mine in Sudbury, Ontario. For SNO+ this vessel will be filled with liquid scintillator allowing to explore lower energy regions due to the higher light output of the scintillator. The neutrinos are detected by photomultiplier tubes (PMTs) which are mounted on an 18-m stainless steel structure surrounding the acrylic sphere. One outstanding project is to design and program a hydrophone to be placed in the surrounding cavity filled with ultrapure water. The hydrophone will detect any seismic activity occurring and communicate with the detector to ignore the next few events that are detected, as vibrations can trigger the PMTs and cause issues. This will be done by using a piezo vibration sensor and programming it with an Arduino board. In addition, calibrations are very important for producing the best physics data possible and therefore it is crucial to understand the location of the calibration sources as they are guided calibration ropes throughout the inner detector volume. The rope stretch/elasticity and positioning accuracy must be thoroughly tested in scintillator and then implemented into the code, before they can be implemented into SNO+.

 

Emissivity Measurements of Aerosol Deposited YAG:Dy and MnFGeO:Mg

Flores Brito, Wendy (United States)

Emissivity is defined as the ratio of the energy radiated from a material’s surface to that radiated from a perfect emitter, known as a blackbody, at the same temperature and wavelength all under the same viewing conditions. In other words, its effectively emitting energy as thermal radiation. Thermographic phosphors (TP) have a temperature dependent emission that is used to measure temperatures. However, emissivity can change depending on the material, and the process to which it has been subjected to. Past work on room temperature coating methods have led to study the use of aerosol deposition (AD), a room temperature coating method that embeds the particles of the seeded powder onto the desired substrate or surface, to create better coated samples of thermographic phosphors for calibration and temperature sensitive applications. AD can potentially substitute our current “painted-on” method of coating; where phosphor is mixed with ethanol and brushed onto the desired surface, the ethanol then evaporates after a short time. The focus of this work is to study and measure the thermal radiation emissivity of Dysprosium doped Yttrium Aluminum-Garnate (YAG:Dy) and Magnesium doped Manganese Fluoro-Germanate (MnFGeO:Mg). Tests were conducted on both an AD and a “painted-on” stainless steel sample. The Sandia LED driver, with a UV LED (365nm), was used as the light source. Samples were submitted to a temperature range of 50-550ᵒC at approximately 50ᵒC steps. The heater was controlled using a FLUKE multifunction process calibrator and a FLIR A655 camera was used for temperature data. The data for both AD samples, compared to the “painted-on” samples, shows a decrease in emissivity; that could be as a result of the darker coating or the difference in thickness between the two coatings. The YAG:Dy temperature vs. emissivity curve is fairly stable around 0.65 for the ”painted-on” sample and 0.4 for the AD sample. On the other hand, for the MnFGeO:Mg, the emissivity decreases with temperature.

 

An Experimental Approach to Particle-Shock Interactions

Freelong, Daniel (United States)

The interaction of a sparse curtain of particles with a shock wave is investigated experimentally. Soda lime particles form the curtain, which is gravity-driven. We measure the instantaneous and average velocities of the particles to show that the particles are nearly in a free-falling state, with their average velocity increasing linearly with vertical distance. The volume fraction of the curtain decreases as it accelerates, ranging between 2 and 9%. The particle-shock interaction is studied for three different Mach numbers: 1.2, 1.45, and 1.7. Experimental data reveals that the shock wave is both transmitted through and partially reflected by the sparse curtain. Time-resolved images show the underlying flow structure of the particle-shock interaction.

 

Meandering around metal inclusions: the tunable inverse current cloak

García Gordillo, Andy Scott (Cuba)

Turning invisible an object in any physics field has important technological and scientific implications. The devices used in this kind of experiments are named ‘invisibility cloaks’ and they are all over the electromagnetic spectra, e.g., the visible light cloak, the magnetic cloak, the current cloak, etc… Electrical current cloaks can be calculated analytically and have, in our opinion, very good opportunities to serve as models to granular and microfluidic cloaks. We suggest that an electrical current cloak can be tuned by, for example, an applied magnetic field. We call this new device the “Tunable Inverse Current Cloak” (TICC). Instead of having a hole in the center of a metallic foil (“repealing” the current lines) surrounded by a washer of a material of larger conductivity (“attracting” the current lines), the TICC consist on a metal immersed in a sea of a magneto-resistant material of smaller conductivity that undergoes an increase of its resistivity in a ring just outside the best conducting material because of the application of an external magnetic field. The setting of the magnetic field is what makes the device tunable, i.e. the cloaking and non-cloaking states are both reachable by varying the value of a DC magnetic field.

 

Transport properties and thermoelectric effects in gated silicene superlattices

Guzmán Ortiz, Eric Jovani (Mexico)

Low-dimensional thermoelectricity opens the possibility of improving the performance and the efficiency of thermoelectric devices by redistributing the electron density of states through the reduction of dimensionality. In this work, we explore this possibility in silicene by reducing its dimensionality through the periodic arrangement of gated electrodes, the socalled gated silicene superlattices. Silicene electrons were described quantum relativistically. The transmission, conductance, and thermoelectric properties were obtained with the transfer matrix method, the Landauer-Büttiker formalism, and the Cutler-Mott formula, respectively. We find that the redistribution of the density of states together with the intrinsic characteristics of silicene, the local bandgap and the large spin-orbit coupling, contribute to the enhancement of the thermoelectric properties. In particular, the Seebeck coefficient and the power factor reach values of a few mV/K and nW/K2 . These findings in conjunction with the low thermal conductivity of silicene indicate that silicene-based nanostructures could be the basis of more efficient thermoelectric devices.

 

Effect of finite size on density of states and Landauer conductance in graphene superlattices

Hernandez Bertran, Michael Alejandro (Cuba)

In order to determine the density of states of a system is necessary to know the dispersion relation. When the effects of disorder or finite crystal size are included, the translational symmetry is broken and the Bloch-Floquet theorem is no longer valid to determine the dispersion relation. We followed the method proposed in and improved in and derived a formula for the density of states ρN(E) of a N-period graphene superlattice (SL), which is given as an integral over the inverse of the absolute value of the group delay velocity along the SL-axis. Using that formula, it was shown that ρN(E) exhibits essentially the same structure for all values of N ≥ 5. Additionally for negative energies, the effects of finite crystal size modify dramatically the density of states of the corresponding infinite SL, whereas for positive energies and N ≥ 5, it is only slightly modified. According to our results, the inverse of the group delay velocity is proportional to the transmission coefficient, which allows us to establish a correlation between the properties of ρN(E) and those of the Landauer conductance GN(E) of the N-period SL. Certainly, GN(E) exhibits a peak structure as a function of E, with local dips located at the same energies as those of ρN(E). The same behavior was observed for the potential dependence of GN(E) with E = 0, which is very similar to that of ρN(0). When N increases, the peak positions of both GN(0) and ρN(0) tend to be located at those values of potential where new Dirac points appear.

 

A Position-time Reconstruction Algorithm for SNO+

Hu, Jie (Canada)

SNO+ is a multi-purpose neutrino experiment aiming to study unknown properties of neutrinos. The main physics goal of SNO+ is to explore whether neutrinos are Majorana-type particles by searching for neutrinoless double beta decay of 130Te. The experiment is divided into three phases: the water phase, the scintillator phase and the tellurium-loaded scintillator phase. The detector was filled with ultrapure water and took water phase physics data from May 2017 to October 2018. It is currently being filled with liquid scintillator. A partially filled detector will be run for about two weeks for understanding the backgrounds of the liquid scintillator. The detector is planned to be fully filled for the scintillator phase by the end of this year. After the scintillator phase, 0.5% tellurium by mass will be loaded into the liquid scintillator. To analyze the SNO+ data, an event position-time reconstruction algorithm has been developed. This algorithm utilizes simplified photon path calculations and can be adjusted to different SNO+ phases. The algorithm has been tested with calibration data during the water phase as well as with Monte Carlos simulations for different phases. By testing the algorithm with 16N calibration source data in the water phase, a 30 cm position resolution is reached. Simulations of electron events in the scintillator phase show a 6 cm position resolution. The algorithm is also tuned for the partially filled detector and will be tested on the partial-fill phase data.

 

A multimodal interferometry technique for detection and classification of tissue interfaces

Kaiyum, Rohith (Canada)

Advanced medical imaging modalities such as X-ray and Computed tomography (CT) are common in oral care however, X-ray lacks the temporal and spatial resolution needed for early diagnosis. While CT cannot be used in real time surgical treatment procedures. To provide an alternative to such hospital-restricted imaging methods, we introduce a high-resolution optical sensing technique into the patient care plan that will allow for the detection of pre-diseased, inflamed and aging tissue. Optical coherence tomography (OCT) is a non-invasive interferometry technique that allows measurement of the structural integrity and connectivity at the interfaces of soft and hard tissue to be examined as a pre-diagnostic biomarker of oral disease. Based on scattering and refractive index variances, an OCT is developed to identify and classify tissue interfaces, abnormalities at the micron scale, both lateral and axial spatial resolution. Our research seeks to classify various tissue interfaces though well-controlled tissue mimicking optical phantom studies and in vivo characterizations. The discrimination of optical scattering variances between different are being examined through OCT to assess efficacy in its ability to discern pathological lesions from healthy tissue in periodontal multilayer tissue interfaces. We look to compare these model systems with in vivo characterizations of bone structures through small layers of epithelial cells of the gum. In future investigations, we aim to incorporate near-infrared spectroscopic (NIRS) imaging, which allows for complimentary investigation into the microenvironment of oral tissue in situ by observing changes in oxy-/deoxy-hemoglobin absorption and local gradient of pH in inflamed tissues. We aim to spatially co-register data sets from both OCT and NIRS that can be mapped to assess structural-functional correlations of the target tissue and its biochemical microenvironment. Our multi-modal technique presents new opportunities with clinically amenable optical techniques for exploring structure-function relationships towards early detection of biomarkers linked to topical degenerative diseases.

 

External Background for Solar Neutrino Studies in SNO+

Khaghani, Pouya (Canada)

SNO+ is a multi-purpose scintillator based neutrino experiment located 2 km underground at SNOLAB, Sudbury, Ontario. SNO+ reuses the Sudbury Neutrino Observatory (SNO) detector, consisting of a 12 m diameter acrylic vessel that will be filled with 780 tonnes of ultra-pure organic liquid scintillator. The primary goal of the experiment is a search for neutrino-less double beta decay with 130Te loaded into the liquid scintillator. In addition, SNO+ aims to measure low energy solar neutrinos, reactor anti-neutrinos, geo-neutrinos as well as the neutrinos from a supernova event. Measuring low energy solar neutrinos requires a very low background level in the region of interest. SNO+ uses various techniques to identify and reject the background such as applying certain cuts on angular and timing parameters of the recorded events. An inevitable consequence of applying cuts is that a portion of the physics events will also be subject to the conditions of a portion of these cuts. The goal is to minimize the signal loss, known here as sacrifice, while still maintaining a cut that removes nearly all of the background. This poster will present different types of backgrounds for solar studies in SNO+ and furthermore will discuss some of the techniques to identify and reject the background.

 

Characterization of Nanometer-scale Blade-based Field Emission Cathode

Lawler, Gerard (United States)

The effectiveness of nano-fabricated blades as a robust electron source for use in future accelerators is examined. Manufacturing utilizes physical vapor deposition (PVD) of 5 nm of titanium followed by 15 nm of gold on a laser-etched silicon wafer. Long-term storage does not require high vacuum. Peak field enhancements at the tips of the blades from an incident laser fields are 20 GV/m. Initial tests verified the emission of electrons up to keV energies. Beamlet extraction and energy selection ( with subsequent energy spectrum reconstruction) are of foremost consideration. To this end,a modular two-component (einzel lens and hemispherical deflection analyzer) spectrometer was designed. The einzel lens with pinhole mask when operated independently serves as an electron beamlet extractor. Further figures of merit such as mean transverse energy (MTE), emission uniformity, intrinsic emittance, and cathode lifetime are forthcoming.

 

Study of Oxygen adsorption on Co(0001) and Co/Ir(111) surfaces

Leon Valido, Dario Alejandro (Cuba)

In recent years great interest arose for graphene (Gr) layers grown on non-commensurate transition metal (TM) substrates leading to a moire patterning, to be further used as templates for the adsorption of e.g. magnetic molecules. The presence of the graphene interlayer can then result in a partial moleculesubstrate decoupling at the electronic level, while maintaining the magnetic coupling. A practical realization of this structure has been achieved recently by adsorbing TM-phthalocyanine molecules on Gr/Co/Ir. Depending on how many Co layers are intercalated on Gr/Iridium, Gr can be lat- tice matched (multi Co layers) or not (eg when only one Co layer is intercalated it is arranged morphologically to the Ir surface lattice). The magnetic configuration of Co intercalated under graphene can be tuned as a function of Co thickness. Oxygen can play a role similar to Gr for the decoupling. It has been shown experimentally that these systems can adsorb oxygen stably under Gr, as a way to control Co magnetization, but the mechanisms and structural details of the adsorbed oxygen are unclear. On the other hand, the chemisorption of oxygen on transition metal (TM) surfaces, itself, is an interesting topic of high importance in heterogeneous oxidation catalysis. Low oxygen exposures on Co and Co/Ir result in chemisorbed oxygen coupled ferromagnetically with the substrate. As the oxygen exposure increases, cobalt oxide may form in two different stoichiometries: CoO or, in smaller proportion Co3O4. Computationally, the adsorption of O on thick Co (0001) films has been studied. In this work we perform total energy calculations within density functional theory at PBE level to compare the adsorption of O on Co (0001) and Co/Ir(111) with a one monolayer of Co. We have studied a number of different adsorption configurations for O, with coverage ranging from 0.25 and 0.5ML, and including inequivalent O atoms in the unit cell. Our results show that, for all configurations, the strained Co/Ir system absorbs oxygen with binding energies larger (0.25-0.51 eV) than those obtained for O@Co(0001) thick film. Regarding the magnetic coupling, all the ground states are ferromagnetic as was expected from such low oxygen exposures, although we report some metastable antiferromagnetic coupled solutions in case of oxygen adsorbed on Co/ Ir.

 

Violation of an augmented set of Leggett-Garg inequalities using a non-invasive continuous in time velocity measurement

Majidy, Shayan (Canada)

Macroscopic realism (MR) is the view that a system may possess definite properties at any time independent of past or future measurements, and may be tested experimentally using the LeggettGarg inequalities (LGIs). In this work we advance the study of LGIs in two ways using experiments carried out on a nuclear magnetic resonance spectrometer. Firstly, we addresses the fact that the LGIs are only necessary conditions for MR but not sufficient ones. We implement a recently-proposed test of necessary and sufficient conditions for MR which consists of a combination of the original four three-time LGIs augmented with a set of twelve two-time LGIs. We explore different regimes in which the two- and three-time LGIs may each be satisfied or violated. Secondly, we implement a recent proposal for a measurement protocol which determines the temporal correlation functions in an approximately non-invasive manner. It employs a measurement of the velocity of a dichotomic variable Q, continuous in time, from which a possible sign change of Q may be determined in a single measurement of an ancilla coupled to the velocity. This protocol involves a significantly different set of assumptions to the traditional ideal negative measurement protocol and a comparison with the latter is carried out.

 

Superparamagnetic Fe3O4 Nanoparticles: Examination of Their Feasibility for Hyperthermia Treatment for Cancer

Meneses Brassea, Bianca Paola (United States)

Briefly, subjecting iron oxide magnetic nanoparticles (IONPs) to an alternating current (AC) magnetic field the IONPs will convert energy stored into heat exposing tumors to intolerable conditions. In the work at hand, we have synthesized superparamagnetic iron oxide nanoparticles (SPIONs) using supercritical condition of liquids and have been characterized using XRD, SEM, VSM, and D5 hyperthermia. The particles show spherical like shape with size of 63, 128, 91 nm, crystalline Fe3O4 cubic structure with grain size of 65, 43, 55 nm respectively and superparamagnetic behavior with magnetization of 108, 77, 74 emu/g. Moreover, in order to investigate the feasibility of the particles for hyperthermia treatment for cancer (specific absorption rate (SAR)), the particles have been immersed in water solution and subjected under applied AC magnetic field at different frequencies and field strengths. The SAR yields 140 W/g at 304 kHz and 400 Oe which is very promising for hyperthermia treatment of cancer.

 

Graphite Reflector in HALO_1kT

Patel, Divya (Canada)

The Helium and Lead Observatory 1 Kiloton (HALO- 1kT) is a lead-based detector to study electron neutrinos emitted in supernova events. It is proposed to follow the same-purpose lesser sensitive HALO detector located at SNOLAB, Ontario, Canada. The electron neutrinos sensitivity make HALO-1kT (and also the current HALO detector) unique in the sense that all other detectors with capability to detect supernova neutrinos are sensitive to anti-electron neutrinos through charged- current inverse beta-decay such as the SuperKamiokande, LVD, IceCube and KamLAND. HALO-1kT sensitivity to supernova neutrinos is larger than that for HALO due to its proposed 12-fold target-mass increase relative to HALO and a more efficient neutron detection. The detector will consist of 1 kt of lead. Neutrinos from supernova will interact with the lead via inverse betadecay process producing bismuth or lead in high-excited states (the excitation states depend on the income neutrino flauvor). The daughter nuclei emit neutrons during de-excitation, which are then detected by 3He proportional counters. The outer most layer of lead consists of a Graphite reflector to recover neutrons that would other otherwise escape detector. I am currently working on the design of the graphite layer which will work as moderator and reflector to redirect some of the neutrons back into the detector lead block. This will increase the detection efficiency by up to 50% (as an example, it is currently 28% in HALO). Geant4 simulations have been used to tune the thickness and grade of the graphite to be used. I found that the optimal thickness is ~15 cm, and as for the graphite grade, it should, ideally, be of Nuclear-Reactor quality.

 

A Neutrino Disappearance Search for Sterile Neutrinos with the CAPTAIN-Mills Detector at the Los Alamos Neutron Science Center

Hasan Rejoanur Rahman

MiniBooNE (Mini Booster Neutrino Experiment) and LSND (Liquid Scintillator Neutrino Detector) have shown compelling evidence for sterile neutrinos at ∆m 2 ∼1 eV2 in short baseline neutrino oscillations experiments. In these experiments, a pure muon neutrino beam is used to search for electron neutrino appearance, i.e., νµ disappears in νe, but muon neutrino disappearance searches have shown no anomalies. The CAPTAIN-Mills experiment uses a 10-ton liquid argon scintillation detector to leverage the enhanced cross section from coherent elastic neutrino-nucleus scattering (CEνNS) to measure muon neutrino disappearance at the Lujan Center at the Los Alamos Neutron Science Center. Lujan is a 100-kW stopped pion source that nominally delivers a 290-ns wide, 800-MeV proton beam onto a tungsten target at 20 Hz, but the beam width can be significantly narrowed to 30 ns. Fast pulsing is critical for isolating the monoenergetic muon neutrino from the other neutrino flavors and neutron backgrounds. Description of the CAPTAINMills detector, the Lujan neutrino source, the expected sensitivities for sterile neutrinos will be presented along with the results obtained from the summer 2018 neutrino test run and a December engineering run.

 

In-situ laser sensitization of ZnO nanorods for emerging solar cells

Rodríguez Martínez, Yerila (Cuba)

Since the inception of the development of emerging solar technologies, the application of simples and scalable techniques have been a challenge for their production and commercialization. The present work proposes an in-situ, low cost, easy to implement and scalable method with interesting applications for emerging solar cells. The technique, including a Nd:YAG pulsed laser, was used in previous work as energy source to activate a ZnO seed layer before the growth of ZnO nanorods (seeding process) [2]. In this case, applying the laser to ZnO nanorods previously submerged in an aqueous precursor solution, CdS nanoparticles were obtained covering the nanorods surface [3]. Different laser parameters like fluence and number of shots were changed and it was possible to obtain structures with different morphologies. In particular, SEM images shown a whole and in depth covering of ZnO nanorods with a highly homogeneous film of CdS nanoparticles for around 40 mJ/cm2 and 2 laser shots, and structures like CdS nanorods for laser fluence values around and higher than 60 mJ/cm2 . Passivation of characteristic surface defects in ZnO material after CdS growth, was also observed.

 

Analysis by Principal Components of SNO+ Burst Data

Rost, Philip (Canada)

SNO+ is a kilo-tonne scale neutrino detector utilizing much of the same hardware that was used during the SNO experiment. The experiment will be conducted with several different phases to explore various aspects of neutrino physics. Through all phases the detector will be sensitive to a large neutrino burst from a nearby supernova. Measures have been implemented in order to capture the data from these bursts. Bursts can be caused by physics processes of interest or other physical phenomena such as electronic pickup, static discharge, equipment malfunctions and unintended light injection. A study was conducted with bursts which occurred during the light water phase commissioning of detector operation using a principal component analysis. This study found the bursts in general manifested in a uniform nature with an overwhelming background of events caused by not yet optimized detector tuning. A repetition of the study through the different phases of the experiment is recommended.

 

A Supernova Calibration Source for SNO+

Rumleskie, Janet (Canada)

Only one supernova neutrino burst has ever been detected, and the detection of additional neutrinos from galactic core-collapse supernovae are expected to provide insight on the supernova explosion mechanism. One candidate for detecting supernova neutrinos is SNO+, a multipurpose ultra-low background particle detector. Within SNO+, a galactic supernova neutrino burst is expected to generate an unprecedented rate. Thus, it is necessary to stress-test and optimize the SNO+ data acquisition and electronics so that a supernova signal can be reliably read out. For this purpose, a Supernova Calibration Source is under development to mimic the light expected from supernova neutrino interactions [1]. Using one-dimensional simulated supernova neutrino datasets [2, 3], light profiles representing neutrino interactions are calculated and realised using a laser diode light source delivered into the detector via fibre optics and a deployed light diffuser. Here I focus on the software conversion of neutrino datasets to light profiles, which define the light intensity and timing in the calibration source.

 

Preliminary Synthesis of Ruthenium Doped Oxyfluorides and Exploration of Polar and Magnetic Oxides

Shah, Michael (United States)

Layered perovskites are intergrowth structures of anionic perovskite blocks interleaved with metal cations and their rich chemistry makes them amenable to ion-exchange and exfoliation reactions. Layered oxide materials are used in diverse applications such as superconductors, semiconductors, ferroelectrics and photovoltaics. Late transition metal perovskites are particularly interesting due to their correlated electronic properties but cannot be exfoliated into nanosheets. This study sought to create ruthenium-doped layered oxyfluoride perovskites due to ruthenium’s dn electrons which may give rise to metallic phases and can also be exfoliated. Ruthenium-doped oxyfluoride perovskites were synthesized via two step methods by first preparing a titano-niobate phase (LaNbTiO6) followed by intercalation of rubidium fluoride (RbF). Samples were characterized using X-ray diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy to give information about the phase and chemical compositions. The precursor phase LaNbTiO6 was produced during the heating process as well as a small impurity of LaNbO4. The conditions for intercalation of RbF were optimized and could be intercalated to form the layered structure. Ruthenium doping was shown to have increased the occurrence of the impurity phase.

 

Investigating Excited State and Ground State Dynamics of Provitamin D analogs in DPPC lipid Bilayers

Sofferman, Danielle (United States)

Ultrafast photochemical transformations of 7-Dehydrocholesterol (DHC, Provitamin D3), DHC-Acetate and Ergosterol (Ergo, Provitamin D2) to previtamin D3, D3-acetate and D2 occurs upon a ring-opening reaction in the excited state where a cyclohexadiene (CHD) chromophore embedded within the molecules opens to form a hexatriene previtamin D species. The initial ring opening of isolated CHD in the excited state occurs on a sub-picosecond time scale, whereas conformer relaxation on the ground state happens on the time scale of picoseconds. In order to capture the dynamics of the molecule, ultrafast techniques such as transient absorption is used.  Here we are studying excited state ring openings and ground state relaxation dynamics of DHC and its analogs in liposomes as a simple model for biologically relevant skin membranes. The excited state of DHC has been studied extensively in isotropic solvents where the molecule ring opens to form a previtamin D species with decay dynamics that are best modeled as a biexponential containing a fast 500fs and slow 1-2ps component. On the ground state conformer relaxation occurs within 6ps to form a stable previtamin D3 species.  However, in the cell membrane the molecule is hypothesized to be locked in an unstable previtamin D3 conformation that thermally relaxes down to form Vitamin D3. When DHC is incorporated into the lipid bilayer, the longest time constant observed in solution is significantly slowed down to 11ps and 25ps in the excited and ground state respectively.  To understand excited and ground state dynamics that takes place in biological membranes, we investigate structural influences such as hydrogen bonding and van der waals interactions between the molecule and its environment by extending our studies to incorporate DHC analogs, DHC-Acetate and Ergosterol into the bilayer and in isotropic solvents.

 

KvN Mechanics for the time-dependent frequency harmonic oscillator

Urzua, Alejandro (Mexico)

The use of Koopman-von Neumann formulation of mechanics is a turnaround for solve problems where time dependence of parameters is explicitly given. Using Ermakov-Lewis invariants and the Operational Dynamical Modelling, we shown that dynamics from classical and quantum mechanical systems can be inferred, arriving at the conclusion that the mathematical structure governing is the same in both scenarios when a time-dependent frequency harmonic oscillator is analyzed.

 

Characterization of PVA based CNT nanofibers for electrochemical sensing

Vilchis León, Paloma Alejandra (Mexico)

Polyvinyl alcohol (PVA) is a material that present a high level of compatibility with biological environment. We modify the electric properties of PVA with Multiwall CNT and doped with nitrogen, this were obtained by CVD from Nanotechnology Lab of the Iberoamericana University, after the functionalization of the CNT, were mixed with the PVA Solution in a different concentrations to obtained the nanofibers by electrospinning process. For the characterization, XRD, FTIR and Raman spectroscopy techniques were used. Finally we try out the mats of nanofibers in a potenciostat to demonstrate that nanofibers increase the sensitivity in an electrochemical analysis.

 

Time-correlated single-photon counting technique to measure lifetime of the Na$_2$ $6^1\Sigma_g^+(7,31)$ state

Wagle, Dinesh (United States)

We report on the lifetime measurement of the $6\,^1\Sigma_g^+ (7,31)$ state of sodium molecules using a time-resolved spectroscopic technique [1]. The $6\,^1\Sigma_g^+ (7,31)$ state was populated by double-resonance excitation via the intermediate $A\,^1\Sigma_u^+ (8,30)$ state. This was accomplished by a two synchronized pulsed lasers pumped by a Nd:YAG laser operating at the second harmonics. The molecular fluorescence emitted from the final state was collected and the lifetime was measured from the $v$=6 doublet using a time-correlated photon counting technique, as a function of argon pressure. From this, the radiative lifetime was extracted by extrapolating the plot to collision-free zero pressure. We compared our results with the calculated radiative lifetimes in the range of $v$=0-200 with $J$=1 and $J$=31. The results also reveal the importance of the bound-free transitions and the rotational quantum number dependence on the lifetime calculations. The measured and calculated radiative lifetimes are found to be 39.56~($\pm$ 2.23) ns and 42.8 ns, respectively.  Financial support from the National Science Foundation (Grant No. NSF-PHY-1607601) is gratefully acknowledged. Ref.[1] Saaranen \textit{et al.}, JCP 149, 204302 (2018).

 

Reconstruction of RNA Structure Using Solvent Accessibility

Xie, Jingru (United States)

To understand RNA function, it is vital to construct RNA structure. While experiments can determine RNA structure in single snapshot, less is known about the highly dynamical conformational landscape of RNA. Molecular dynamics (MD) simulation can in principle fill this gap by producing trajectories that describe the temporal properties of each atom in the system. However, due to the usually large size of RNA, all-atom MD simulations are often limited by computational cost. One way to handle this is coarse-grained (CG) simulation, that with a subset of atoms or a few pseudoatoms per nucleotide, the essential physical properties of the system can be simulated. Unfortunately, the simplified representation used in CG simulations often produces biased dynamical ensembles and leads to wrong results. One solution to this challenge is to use specially designed sampling methods that map the dynamical ensembles to their conformational landscape with the guidance of experimental data. Here, we present a new pipeline to resample RNA conformational landscape from CG simulations with the guidance of C8-solvent accessibility (SA). On the one hand, C8-SA is derived from LASER-reactivities in experiments. LASER (Light Activated Structural Examination of RNA) is a sensitive chemical probing method, in which the chemical reactivity directly maps to the C8-SA in purine residues. On the other hand, we parameterized a fast statistical model that calculates C8-SA from pair-wise distances between CG particles. By matching the ensemble average of computed C8-SA to the LASER-derived C8-SA in experiments, we will then be able to correctly reweight the dynamical ensemble generated by CG simulations. We anticipate this new framework will be useful to the RNA modelling community.

 

SNOLAB Covergas Bag

Zarichney, Jazmyn (Canada)

SNO+ is a current experiment at SNOLAB with the purpose of detecting neutrinos from various sources: The Earth, the Sun, and a galactic supernova to learn more about the Universe. The active volume is currently filled with ultrapure water, which will shortly be replaced with liquid scintillator which eventually will be loaded with tellurium to search for neutrinoless double beta decay. A small part of this experiment’s calibration hardware is the Umbilical Retrieval Mechanism otherwise known as the URM which lowers sources into the acrylic vessel. Since most physics goals are rare event searches, it is extremely important to keep radioactive backgrounds out of the inner detector volume, which is protected by a sealed covergas system. This means that the URM also needs to be sealed and protected by a covergas system in the form of a bag. This bag will ensure that any pressure fluctuations that occur underground can be accounted for. This poster will show a detailed analysis of the pressure swings in the underground environment and the plans to design, test and utilize a covergas bag for the URM.