548 research outputs found

    Differential spectrum modeling and sensitivity for keV sterile neutrino search at KATRIN

    Get PDF
    Starting in 2026, the KATRIN experiment will conduct a high-statistics measurement of the differential tritium β\beta-spectrum to energies deep below the kinematic endpoint. This enables the search for keV sterile neutrinos with masses less than the kinematic endpoint energy m4E0=18.6keVm_\mathrm{4} \leq E_0 = 18.6\,\mathrm{keV}, aiming for a statistical sensitivity of Ue42=sin2θ106|U_\mathrm{e4}|^2=\sin^2\theta\sim 10^{-6} for the mixing amplitude. The differential spectrum is obtained by decreasing the retarding potential of KATRIN\u27s main spectrometer, and by determining the β\beta-electron energies by their energy deposition in the new TRISTAN SDD array. In this mode of operation, the existing integral model of the tritium spectrum is insufficient, and a novel differential model is developed in this work. The new model (TRModel) convolves the differential tritium spectrum using responese matrices to predict the energy spectrum of registered events after data acquisition. Each response matrix encodes the spectral spectral distrortion from individual experimental effects, which depend on adjustable systematic parameters. This approach allows to efficiently assess the sensitivity impact of each systematics individually or in combination with others. The response matrices are obtained from monte carlo simulations, numerical convolution, and analytical computation. In this work, the sensitivity impact of 20 systematic parameters is assessed for the TRISTAN Phase-1 measurement for which nine TRISTAN SDD modules are integrated into the KATRIN beamline. Furthermore, it is demonstrated that the sensitivity impact is significantly mitigated with several beamline field adjustments and minimal hardware modifications

    Spintronic Operations Driven by Terahertz Electromagnetic Pulses

    Get PDF
    Spintronic devices, supplementing and surpassing charge-based electronics by including the electron spin, have recently begun to reach the market. Information carriers such as electrons (in field-effect transistors) and photons (in optical fibers) have already reached the terahertz range (THz, 10^12 Hz). To make the electron spin compatible and competitive, spintronic operations need to be pushed to THz frequencies. So far, is is unclear whether fundamental spintronic effects such as spin accumulation or spin-orbit torque can be transferred to THz frequencies. In this respect, it is also important to note that the THz range coincides with many fundamental excitations, for instance phonons, magnons, and the relaxation of electronic currents. Strong THz electromagnetic pulses can be used to study such fundamental excitations, making use of both the electric and magnetic fields of the electromagnetic pulse. In this thesis, strong THz electromagnetic pulses are applied to spintronic thinfilm stacks to drive charge and spin currents, apply torque and manipulate magnetic order. A short optical probe pulse or a resistance probe interrogate the transient magnetic response. First, a measurement strategy is developed to simultaneously detect all components of the vector magnetization of thin film magnets in optical transmission probe experiments at normal incidence, requiring only a variation in the initial probe polarization. To this end, the magnetic circular and linear birefringence (MCB, MLB) effects are measured simultaneously and a calibration strategy for the often neglected MLB effect is presented. Second, using this detection scheme, we study the THz frequency operation of spintronic effects in ferromagnetic(FM)/non-magnetic (NM) heavy metal stacks. We find signatures of THz spin accumulation at the FM/NM interface. The spins injected into a ferromagnet relax within ∼ 100 fs, in line with electron-spin equilibration times measured by ultrafast optically induced demagnetization. Indications of the field-like spin-orbit torque (FL-SOT) are found. Third, an effective method to modulate the relative THz electric and magnetic field amplitudes in thin film samples is presented, enabling one to disentangle effects driven by the electric or the magnetic component of the THz electromagnetic pulse. A nearperfect conductor (THz mirror) quenches the THz electric field in a region close to the mirror, while doubling the THz magnetic field. Measurements with a ferromagnetic thin film confirmed a THz magnetic field increase of 1.97 ± 0.06 and a suppression of the THz electric field in the sample. Finally, we utilize the electric-field suppression effect close to metals to optically gate the THz electric field driven resistance modulation of an antiferromagnet (AFM) grown on a semiconducting substrate. An optically induced transient substrate conductance depletes the THz electric field in the AFM layer, while not perturbing the AFM magnetic order directly. A simple model of parallel conductances is presented, confirming the experimental observations. In conclusion, this thesis is an important contribution to push fundamental spintronic effects such as spin accumulation and spin-orbit torque to the THz range. The developed methodologies are helpful to advance nonlinear THz spectroscopy of magnetic materials.Da die ersten auf spintronischen Prinzipien erbauten Speicher den Markt erreichen und gleichzeitig Informationsträger wie Elektronen (in Feldeffekttransistoren) und Photonen (in Glasfaserkabeln) in den Terahertz-Frequenzbereich (THz, 10^12 Hz) vordringen, stellt sich die Frage, ob die Spintronik, welche die Elektronik um den Elektronenspin erweitert, mit solch hohen Frequenzen kompatibel ist. Gleichzeitig ist der THz-Frequenzbereich, welcher elementare Anregungen wie Phononen und Magnonen enthält, auch fur die Grundlagenforschung interessant. Um diese Anregungen zu untersuchen bieten sich elektromagnetische THz-Pulse mit hohen Feldstärken an, denn sie können direkt an elektrische und magnetische Resonanzen koppeln. Diese Arbeit untersucht mit THz-Lichtpulsen, die in spintronischen Dünnfilmproben Spin- und Ladungsströme induzieren, ob elementare spintronische Effekte, wie die Spin-Akkumulation oder das Spin-Bahn-Drehmoment, auch bei THz-Frequenzen aktiv sind. Die magnetische Antwort wird mit kurzen optischen Pulsen oder mittels elektrischer Messungen zeitaufgelöst abgefragt. Die spintronischen Effekte werden in ferromagnetischen (FM)/nichtmagnetischen (NM) Dunnfilm-Metallmultilagen untersucht, wobei zuerst eine Messmethode erarbeitet ¨ wird, um alle räumlichen Anteile der Probenmagnetisierung gleichzeitig zu bestimmen. Hierzu werden die magnetische zirkuläre Doppelbrechung (MCB) und die, oft vernachlässigte, magnetische lineare Doppelbrechung (MLB), welche der Abfragepuls beim Durchdringen der Probe entlang der Probennormale erfährt, gleichzeitig bestimmt. Ein besonderes Augenmerk liegt auf der Normierung des MLB-Signals. Mithilfe dieser neuartigen Messmethode werden Indizien fur eine THz Spin-Akkumulation und das feldartige Spin- ¨ Bahn-Drehmoment (FL-SOT) an der FM/NM Grenzfläche gefunden, welche auf einen Spinaustausch zwischen dem nichtmagnetischen Schwermetall und dem FM zuruckgeführt ¨ werden. Die in den FM eindringenden Spins relaxieren auf einer Zeitskala von ∼ 100 fs, was mit Ergebnissen aus ultraschnellen optischen Demagnetisierungsstudien ubereinstimmt. ¨ Zusätzlich wird die nichtlineare THz-Spektroskopie dahingehend erweitert, vom elektrischen oder magnetischen THz-Feld getriebene Signale unterscheiden zu können, indem die relativen Stärken der elektromagnetischen Felder im Inneren einer Dunnfilmprobe beeinflusst werden. Hierbei unterdruckt ein elektrisch leitender THz Spiegel das THz elektrische Feld in der Probe, während das THz magnetische Feld um einen Faktor 1.97±0.06 verstärkt wird. Diese Unterdruckung des THz elektrischen Feldes in der Nähe eines Leiters wird genutzt, um die vom THz elektrischen Feld getriebene Widerstandsmodulation in einem, auf einem (optisch angeregten) halbleitenden Substrat gewachsenen, Antiferromagneten (AFM) zu steuern. Dabei wird die Wirkung des THz elektrischen Feldes im AFM unterdruckt ohne den magnetischen Zustand des AFM zu stören. Ein einfaches Modell stutzt die Interpretation der Beobachtungen. Zusammenfassend leistet diese Arbeit einen wichtigen Beitrag, um spintronische Effekte wie die Spin-Akkumulation und das Spin-Bahn-Drehmoment im THz-Frequenzbereich zu etablieren und erweitert zusätzlich die Möglichkeiten der nichtlinearen THz-Spektroskopie an Magneten

    Net effect of environmental fluctuations in multiple global-change drivers across the tree of life

    Get PDF
    Jensen’s inequality predicts that the response of any given system to average constant conditions is different from its average response to varying ones. Environmental fluctuations in abiotic conditions are pervasive on Earth; yet until recently, most ecological research has addressed the effects of multiple environmental drivers by assuming constant conditions. One could thus expect to find significant deviations in the magnitude of their effects on ecosystems when environmental fluctuations are considered. Drawing on experimental studies published during the last 30 years reporting more than 950 response ratios ( n = 5,700), we present a comprehensive analysis of the role that environmental fluctuations play across the tree of life. In contrast to the predominance of interactive effects of global-change drivers reported in the literature, our results show that their cumulative effects were additive (58%), synergistic (26%), and antagonistic (16%) when environmental fluctuations were present. However, the dominant type of interaction varied by trophic level (autotrophs: interactive; heterotrophs: additive) and phylogenetic group (additive in Animalia; additive and positive antagonism in Chromista; negative antagonism and synergism in Plantae). In addition, we identify the need to tackle how complex communities respond to fluctuating environments, widening the phylogenetic and biogeographic ranges considered, and to consider other drivers beyond warming and acidification as well as longer timescales. Environmental fluctuations must be taken into account in experimental and modeling studies as well as conservation plans to better predict the nature, magnitude, and direction of the impacts of global change on organisms and ecosystems.Agencia Estatal de Investigación | Ref. PGC2018-094553B-I00Agencia Estatal de Investigación | Ref. FJCI2017-32318Agencia Estatal de Investigación | Ref. IJC2019-040850-IJunta de Andalucía | Ref. POSTDOC-21-0004

    Probing quantum devices with radio-frequency reflectometry

    Get PDF
    Many important phenomena in quantum devices are dynamic, meaning that they cannot be studied using time-averaged measurements alone. Experiments that measure such transient effects are collectively known as fast readout. One of the most useful techniques in fast electrical readout is radio-frequency reflectometry, which can measure changes in impedance (both resistive and reactive) even when their duration is extremely short, down to a microsecond or less. Examples of reflectometry experiments, some of which have been realized and others so far only proposed, include projective measurements of qubits and Majorana devices for quantum computing, real-time measurements of mechanical motion, and detection of non-equilibrium temperature fluctuations. However, all of these experiments must overcome the central challenge of fast readout: the large mismatch between the typical impedance of quantum devices (set by the resistance quantum) and of transmission lines (set by the impedance of free space). Here, we review the physical principles of radio-frequency reflectometry and its close cousins, measurements of radio-frequency transmission and emission. We explain how to optimize the speed and sensitivity of a radio-frequency measurement and how to incorporate new tools, such as superconducting circuit elements and quantum-limited amplifiers into advanced radio-frequency experiments. Our aim is threefold: to introduce the readers to the technique, to review the advances to date, and to motivate new experiments in fast quantum device dynamics. Our intended audience includes experimentalists in the field of quantum electronics who want to implement radio-frequency experiments or improve them, together with physicists in related fields who want to understand how the most important radio-frequency measurements work

    Advanced Sensing, Fault Diagnostics, and Structural Health Management

    Get PDF
    Advanced sensing, fault diagnosis, and structural health management are important parts of the maintenance strategy of modern industries. With the advancement of science and technology, modern structural and mechanical systems are becoming more and more complex. Due to the continuous nature of operation and utilization, modern systems are heavily susceptible to faults. Hence, the operational reliability and safety of the systems can be greatly enhanced by using the multifaced strategy of designing novel sensing technologies and advanced intelligent algorithms and constructing modern data acquisition systems and structural health monitoring techniques. As a result, this research domain has been receiving a significant amount of attention from researchers in recent years. Furthermore, the research findings have been successfully applied in a wide range of fields such as aerospace, manufacturing, transportation and processes

    Design of a single-particle detection system for strong-field QED experiments

    Get PDF
    One of the most intriguing physics processes that remain untested is the pure photon electron-positron pair production via quantum-vacuum fluctuations described by the nonlinear Breit-Wheeler theory. These fluctuations generate virtual pairs that can be turned into observable particles by applying strong electric fields above the Schwinger critical limit of \num{1.3d18}~V/m~\cite{Schwinger.1951, Ritus.1985}. Despite the advent of high-intense lasers, the critical limit is still far beyond achievable. However, such fields can be achieved on the rest frame of the real particles after the collision of a high-energy γ\gamma-ray photons with the laser beam. To diagnose the created pairs, this thesis describes the design of a particle detection system capable of successfully probing the single leptons created from strong-field quantum electrodynamics (SF-QED) interactions at the upcoming SF-QED experiments E-320 at FACET-II and FOR2783 at CALA. The designed detection system is composed of tracking layers made of LYSO:Ce scintillating screens and a Cherenkov calorimeter that, having their signals combined, can identify a positive event with a confidence level above 99%. At the E-320 experiment, electron beams generated by the FACET-II linear accelerator with an energy of 13~GeV collide with an intense laser beam of \anot \approx 10, and nonlinear Breit-Wheeler pairs are produced in the nonperturbative full quantum regime of SF-QED interaction (\chie > 1 and \anot > 1). About 100 electron-positron pairs per shot are expected to be created. According to Monte-Carlo simulations of the experimental layout, the detection system will be placed on a region permeated by a shower of x-rays and few-MeV γ\gamma-photons, however, a signal-to-noise ratio of \SNRsig \approx 18 on the detectors is achieved

    Computational modeling of biological nanopores

    Full text link
    Throughout our history, we, humans, have sought to better control and understand our environment. To this end, we have extended our natural senses with a host of sensors-tools that enable us to detect both the very large, such as the merging of two black holes at a distance of 1.3 billion light-years from Earth, and the very small, such as the identification of individual viral particles from a complex mixture. This dissertation is devoted to studying the physical mechanisms that govern a tiny, yet highly versatile sensor: the biological nanopore. Biological nanopores are protein molecules that form nanometer-sized apertures in lipid membranes. When an individual molecule passes through this aperture (i.e., "translocates"), the temporary disturbance of the ionic current caused by its passage reveals valuable information on its identity and properties. Despite this seemingly straightforward sensing principle, the complexity of the interactions between the nanopore and the translocating molecule implies that it is often very challenging to unambiguously link the changes in the ionic current with the precise physical phenomena that cause them. It is here that the computational methods employed in this dissertation have the potential to shine, as they are capable of modeling nearly all aspects of the sensing process with near atomistic precision. Beyond familiarizing the reader with the concepts and state-of-the-art of the nanopore field, the primary goals of this dissertation are fourfold: (1) Develop methodologies for accurate modeling of biological nanopores; (2) Investigate the equilibrium electrostatics of biological nanopores; (3) Elucidate the trapping behavior of a protein inside a biological nanopore; and (4) Mapping the transport properties of a biological nanopore. In the first results chapter of this thesis (Chapter 3), we used 3D equilibrium simulations [...]Comment: PhD thesis, 306 pages. Source code available at https://github.com/willemsk/phdthesis-tex

    Pediatric Physiologically Based Pharmacokinetic (PBPK) Modeling to Advance Knowledge of Breastfeeding Infant Exposure to Maternal Medications

    Get PDF
    While there are benefits of breastfeeding to the maternal-infant pair, mothers taking medication may decide not to breastfeed amid unclear risks of exposing the infant to the drug through milk. Uncertainty arises mainly due to the fact that lactating mothers and breastfeeding infants are excluded in the drug development process. In lieu of necessary data for decision making, existing resources include metrics to help estimate risk to the breastfed infant and informational resources that aim to gather all sparsely available information in databases to increase accessibility and empower healthcare providers with knowledge. Current metrics such as the relative infant dose, solely estimate the dose the infant would intake. Before better understanding the potential adverse events an infant might experience (response), a step further to understand exposure is paramount. Yet, the availability of exposure information is difficult to ascertain due to the lack of critical information on the pharmacokinetics (PK; movement of drugs in the body describing dose to exposure) of drug secretion into breast milk, and the resultant levels or exposure of the drug in infant plasma. Physiologically based pharmacokinetic (PBPK) modeling is a promising tool to fill in the gap of scant maternal medication exposure information in breastfeeding infants. PBPK models use a simulation-based approach to model drug kinetics in an organism using knowledge of anatomy and physiology and the physicochemical properties of the drug. Pediatric PBPK models can be developed with minimal a priori data in children because these models rely on a mechanistic understanding of the disposition of the drug typically learned from rich adult data. Thus, despite the lack of available data on drug PK in infants, pediatric PBPK modeling can be used to simulate virtual breastfeeding infant populations to predict exposure given proper estimated doses. The aim of this thesis is to use PBPK modeling to produce a novel risk metric that advances the knowledge of breastfeeding infant exposure to maternal medications. The objectives are to (1) create and apply a workflow incorporating pediatric PBPK modeling to develop the novel metric with infants breastfed from mothers taking lamotrigine, cannabidiol (CBD), and ezetimibe, (2) identify potential maternal factors that may impact concentrations of drugs in milk for incorporation into the workflow established in objective 1 for CBD, and (3) optimize the utility of the novel metric for use in clinical practice. To arrive at the first objective, a literature review was used to develop a model to describe the weight-normalized volume of intake infants typically receive. The model was then used in combination with literature (lamotrigine) or collaborator collected (CBD and ezetimibe) drug concentrations in breast milk to estimate infant daily doses. The doses were then given to virtual breastfeeding infants created through developed and evaluated pediatric PBPK models. For the second objective, linear regression was used to identify influential maternal factors on CBD milk concentrations and breastfeeding exposure predictions. Finally, qualitative interviews were conducted with healthcare providers to ascertain perspectives on the novel metric for use in practice. Through this work, a milk intake model described weight-normalized milk intake with a maximum of 152.6 mg/kg/day at 19.7 days postnatal age. The greatest risk for breastfeeding infant exposure to maternal medications occurred during the 2-4 week postnatal age window. Pediatric PBPK models were developed for lamotrigine, CBD, and ezetimibe. For CBD, literature in vitro data informed the identity and percent contributions of metabolizing enzymes to clearance. These contributions were ascertained as UGT1A7 4%, UGT1A9 16%, UGT2B7 10%, CYP3A4 38%, CYP2C19 21%, and CYP2C9 11%. This information was used to populate the CBD pediatric PBPK model. Results from the linear regression analysis with maternal factors, including administration type, dose-frequency of use, and time after last dose of CBD, revealed that oil or pipe and joint/blunt or edible administrations produced the highest and lowest CBD concentrations in milk, respectively. Overall, the three PBPK models were able to adequately predict exposures of the drug administered in children. A novel risk metric termed the upper area under the curve ratio (UAR) was developed to describe the 95th percentile of breastfed infant AUC divided by the median therapeutic AUC of adults or children for approved indications. Across all ages (0-1 years old), the UAR ranged from 0.18-0.44, 0.00022-0.0044, and 0.0015-0.0026 for lamotrigine, CBD, and ezetimibe, respectively. From the qualitative interviews with 28 healthcare providers, six main themes emerged: (1) Current Practice Approaches, (2) Advantages of Existing Resources, (3) Disadvantages of Existing Resources, (4) Advantages of the UAR, (5) Disadvantages of the UAR, and (6) Strategies to Improve the UAR. Multiple strategies to improve the UAR, such as combining the UAR with another resource and providing guidance to interpret the UAR were attained. The work in this thesis developed the UAR to account for the relative exposure of breastfeeding infants to maternal medications and identify potential outliers who may be most vulnerable. Through healthcare provider interviews, it was evident that the UAR confers benefits over existing metrics and can be optimized for use in practice. With the workflow applied to further drugs, the UAR has the potential to improve our understanding of drug exposures in breastfeeding infants and be used by healthcare providers in their advising

    Two techniques to enhance particle reconstruction in JUNO: Liquid Scintillator purification and Waveform analysis

    Get PDF
    This thesis describes two techniques to enhance the particle reconstruction in large antineutrino experiments where large target masses are pivotal to compensate for neutrinos’ extremely elusive nature. The main obstacle for the correct characterization of the antineutrino crossing the experiment is the radioactive background. In the first section of this thesis, It is described the design, construction principles and operations of a distillation and a stripping plant for the purification of Liquid Scintillator. The main goal of these plants is to remove radio impurities from the liquid scintillator while increasing its optical attenuation length. Such a combined system will aim at obtaining a total attenuation length greater than 20 m @430 nm, and a bulk radiopurity for 238U and 232Th in the 10−15 ÷ 10−17 g/g range. In order to better understand the purification capability of these techniques two pilot plant were built and operated at the Daya Bay laboratories. Depending on the detector light yield, several scintillation photons stemming from the same neutrino interaction are likely to hit a single Photo Multiplier Tube in a few tens/hundreds of nanoseconds, resulting in several photoelectrons (pes) to pile-up at the anode. In such scenario, the signal generated by each pe is entangled to the others, and an accurate charge reconstruction becomes challenging. Thus, leads to a degradation of the resolution of the antineutrino energy spectrum. In the second part of this manuscript, it is described an experimental method able to address the charge reconstruction in the case of large pe pile-up, providing an unbiased charge estimator at the permille level up to 15 detected pes. The method is based on a signal filtering technique (Wiener filter) which suppresses the noise due to both pmt and readout electronics, and on a Fourier-based deconvolution able to minimize the influence of signal distortions — such as an overshoot.Questa tesi descrive due tecniche che possono essere utilizzate per migliorare la ricostruzione delle caratteristiche delle particelle interagenti all’interno di esperimenti per la rivelazione di antineutrini, in cui le grandi masse bersaglio sono fondamentali per compensare la natura estremamente sfuggente di queste particelle. L'ostacolo principale per la corretta caratterizzazione dell'antineutrino è il fondo radioattivo. Nella prima sezione di questa tesi, viene descritto la progettazione, i principi costruttivi e le operazioni di un impianto di distillazione e strippaggio per la purificazione si Scintillatore Liquido. L'obiettivo principale di questi impianti è rimuovere le radio-impurità dallo scintillatore liquido aumentandone contemporaneamente la lunghezza di attenuazione ottica. Tale sistema combinato mirerà ad ottenere una lunghezza di attenuazione totale maggiore di 20 m @430 nm, e una radiopurezza, espressa in concentrazione massica, per 238U e 232Th nell'intervallo 10−15 ÷ 10−17 g/g. Per comprendere meglio la capacità di purificazione di queste tecniche sono stati costruiti e messi in funzione due impianti pilota presso i laboratori di Daya Bay. A seconda della resa luminosa del rivelatore, è probabile che diversi fotoni di scintillazione derivanti dalla stessa interazione di neutrini colpiscano un singolo tubo fotomoltiplicatore in poche decine/centinaia di nanosecondi, con il risultato che diversi fotoelettroni (pes) si accumulino all'anodo. In tale scenario, il segnale generato da ciascun pe è sovrapposto agli altri, e una ricostruzione accurata della carica diventa impegnativa, comportando quindi un degrado della risoluzione dello spettro energetico dell'antineutrino. Nella seconda parte di questo manoscritto, viene descritto un metodo sperimentale in grado ricostruire la carica generata da multipli foto-elettroni incidenti sul PMT nel caso di pile-up, fornendo uno stimatore della carica con una precisione a livello del permille. Il metodo si basa su una tecnica di filtraggio del segnale (filtro Wiener) che sopprime il rumore dovuto sia al PMT che all'elettronica di lettura del segnale, e su una deconvoluzione basata sull’analisi di Fourier in grado di minimizzare l'influenza delle distorsioni del segnale
    corecore