2,135 research outputs found
Differential spectrum modeling and sensitivity for keV sterile neutrino search at KATRIN
Starting in 2026, the KATRIN experiment will conduct a high-statistics measurement of the differential tritium -spectrum to energies deep below the kinematic endpoint. This enables the search for keV sterile neutrinos with masses less than the kinematic endpoint energy , aiming for a statistical sensitivity of for the mixing amplitude. The differential spectrum is obtained by decreasing the retarding potential of KATRIN\u27s main spectrometer, and by determining the -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
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Rapid Neutron-Capture Nucleosynthesis from the Births and Deaths of Neutron Stars
The astrophysical origins of the rapid neutron-capture process (r-process), which gives rise to roughly half of the elements heavier than iron, has remained a mystery for almost 70 years. The likely violent events, which seed the r-process abundances in our solar system and galaxy, remain uncertain to this day. This is in part due to nuclear physics uncertainties associated with the r-process itself, but mainly due to uncertainties in astrophysics modeling. The discovery of the radioactively-powered kilonova emission from the neutron star merger event GW170817 confirmed the violent deaths of neutron stars as one key site of the r-process in the universe. However, other evidence appears to favor an additional r-process channel that more promptly follows star formation in the universe, such as core-collapse supernovae (CCSNe), i.e. the brilliant births of neutron stars.
The two viable sites for the r-process are (1) core-collapse supernovae (CCSNe), which are explosions of massive stars at the end of their lives and (2) compact object mergers, which are violent collisions of stellar remnants formed at the endpoints of stellar evolution.
Chapters 2 and 3 of this dissertation present general relativistic magnetohydrodynamic simulations of one potential r-process site associated with CCSNe: the neutrino-driven wind. These outflows are launched from the hot proto-neutron star (PNS) remnant by neutrino-heating above their surfaces, within seconds after the collapse of a massive star. However, previous work has shown that spherically symmetric winds from non-rotating PNS fail to achieve the requisite conditions for a robust r-process. Chapter 2 explores for the first time the combined effects of rapid rotation and strong gravity of the PNS on the wind properties. Chapter 3 explores the impact of a dynamically strong ordered magnetic field on the properties of non-rotating PNS winds. The wind in both cases is simulated in a controlled environment rather than as a part of a self-consistent global CCSNe simulation, to assess the viability of r-process nucleosynthesis as a function of PNS properties (neutrino energies/luminosities, rotation rate, magnetization).
We find that rapid rotation allows for outflows that are ~10% more neutron-rich in the equatorial region, where the mass loss rate is roughly an order of magnitude higher than that of otherwise equivalent non-rotating models. The birth of very rapidly spinning neutron stars may thus be a site for the production of light r-process nuclei (38 < Z < 47). For PNSs with sufficiently strong magnetic fields (such that magnetic pressure exceeds gas pressure above the PNS surface), we find that equatorial outflows are trapped by the magnetic field in a region near the surface, and therefore receive additional neutrino heating relative to a freely-expanding unmagnetized wind. This allows a modest fraction of the wind material to achieves entropies high enough to synthesize 2nd peak r-process elements via an alpha-rich freeze-out mechanism.
The final chapter explores the interplay between the r-process and the dynamics of compact object merger ejecta. Gravitational wave observatories are expected to detect several additional binary neutron star (BNS) and black hole-neutron star (BHNS) mergers in current and future observing runs, some of which may be accompanied by electromagnetic counterparts such as kilonovae. However, distinguishing more distant BNS from BHNS mergers based on their associated gamma-ray bursts (GRB), has proven tricky.
This chapter presents a calculation of the effects of r-process heating on the dynamics of tidal ejecta from BNS and BHNS mergers. In particular we explore whether late-time fall-back of weakly bound debris created during the merger to the central black hole remnant, can explain the temporally extended X-ray emission observed following several merger GRB on timescales of several seconds to minutes. As a result of the different impact that r-process heating has depending on the composition of the ejecta and the mass of the black hole, a method to differentiate BHNS from BNS mergers, based on their extended X-ray emission, is proposed
Fundamental Study of Photoluminescence-Shape Relationship of Fluorescent Nanodiamonds using Machine Learning Assisted Correlative Transmission Electron Microscopy and Photoluminescence Microscopy Method
Luminescent nanoparticles have shown wide applications ranging from lighting, display, sensors, and biomedical diagnostics and imaging. Among these, fluorescent nanodiamonds (FNDs) containing nitrogen-vacancy (NV) color centers are posed as emerging materials particularly in biomedical and biological imaging applications due to their room-temperature emission, excellent photo- and chemical- stability, high bio-compatibility, and versatile functionalization potentials. The shape variation of nanoparticles has a decisive influence on their fluorescence. However, current relative studies are limited by the lack of reliable statistical analysis of nanoparticle shape and the difficulty of achieving a precise correlation between shape/structure and optical measurements of large numbers of individual nanoparticles. Therefore, new methods are urgently needed to overcome these challenges to assist in nanoparticle synthesis control and fluorescence performance optimization.
In this thesis a new correlative TEM and photoluminescence (PL) microscopy (TEMPL) method has been developed that combines the measurements of the optical properties and the materials structure at the exact same particle and sample area, so that accurate correlation can be established to statistically study the FND morphology/structure and PL properties, at the single nanoparticle level. Moreover, machine learning based methods have been developed for categorizing the 2D and 3D shapes of a large number of nanoparticles generated in TEMPL method.
This ML-assisted TEMPL method has been applied to understand the PL correlation with the size and shape of FNDs at the single particle level. In this thesis, a strong correlation between particle morphology and NV fluorescence in FND particles has been revealed: thin, flake-like particles produce enhanced fluorescence. The robustness of this trend is proven in FND with different surface oxidation treatments. This finding offers guidance for fluorescence-optimized sensing applications of FND, by controlling the shape of the particles in fabrication.
Overall the TEMPL methodology developed in the thesis provides a versatile and general way to study the shape and fluorescence relationship of various nanoparticles and opens up the possibility of correlation methods between other characterisation techniques
Molecular modeling of drug delivery systems based on carbon nanostructures: structure, function, and potential applications for anticancer complexes of Pt(II)
The medication with Pt(II) drugs (cisplatin, carboplatin, and oxaliplatin) has been an effective
alternative for treating cancers due to their notable inhibition of cancer cells growth and the
prevention of metastasis. Nevertheless, the low selectivity of these metallodrugs for malignant
cells produces severe side effects, which limit this chemotherapy. In this context, carbon
nanohorns (CNHs) have been considered potential nanovectors for drugs, since they present
low toxicity, drug-loading capacity, biodegradation routes, and biocompatibility when
oxidized. However, there is still a lack of studies regarding the molecular behavior of these
nanocarriers on cell membranes. The present work aims to characterize the interactions between
inclusion complexes drug@CNH, which are formed by platinum drugs encapsulated in CNHs,
and plasma membranes by using molecular dynamics simulations. The results demonstrated
that the van der Waals contribution played a primary role (∼74%) for the complex stability,
which explain the confined dynamics of drugs inside the CNHs. The free energy profiles
revealed an endergonic character of the drug release processes from CNHs, in which the energy
barrier for oxaliplatin release (~24 kcal mol–1
) was ~30% larger than those for carboplatin and
cisplatin (~18 kcal mol-1
). The simulations also showed four stages of the interaction
mechanism CNH--membrane: approach, insertion, permeation, and internalization. Despite the
low structural disturbance of the membranes, the free energy barrier of ∼55 kcal mol-1 for the
CNHs translocation indicated that this transport is kinetically unfavorable by passive process.
The in silico experiments evidenced that the most likely mechanism of cisplatin delivery from
CNHs involve the approach and insertion stages, where the nanovector adheres on the surface
of cancer cells, as reported in in vitro studies. After this retention, the drug load may be slowly
released in the tumor site. Finally, simulations of the cellular uptake of Pt(II) drugs also pointed
out significant energy barriers (~30 kcal mol-1
) for this process, which reflects their low
permeability in membranes as discussed in experimental studies. In addition to reinforcing the
potential of CNH as nanovector of Pt(II) drugs, the results presented in this thesis may assist
and drive new experimental studies with CNHs, focusing on the development of less aggressive
formulations for cancer treatments.A medicação com fármacos a base de Pt(II) (cisplatina, carboplatina e oxaliplatina) tem sido
uma alternativa efetiva para tratar cânceres devido à sua notável inibição do crescimento de
células cancerosas e a prevenção de metástases. No entanto, a baixa seletividade dessas
metalodrogas por células cancerosas gera severos efeitos colaterais. Nesse contexto, nanohorns
de carbono (CNHs) têm sido considerados potenciais nanovetores de fármacos, devido a baixa
toxicidade, capacidade de carreamento de fármacos, rotas de biodegradação, e
biocompatibilidade quando oxidados. Porém, existe uma carência de estudos tratando o
comportamento desses nanocarreadores em biomembranas. Esse trabalho tem como objetivo
caracterizar as interações entre complexos de inclusão fármaco@CNH, formados por fármacos
de Pt(II) encapsulados em CNHs, e membranas usando simulações por dinâmica molecular. Os
resultados demonstraram que a contribuição de van der Waals teve um papel primário (∼74%)
na estabilidade dos complexos, o que explica a dinâmica confinada dos fármacos dentro dos
CNHs. Os perfis de energia livre revelaram o caráter endergônico da liberação dos fármacos a
partir de CNHs, nos quais a barreira de energia para a liberação da oxaliplatina (~24 kcal mol–
1
) é ~30% maior do que aquelas para carboplatina e cisplatina. As simulações mostraram quatro
estágios do mecanismo de interação CNH-membrana: aproximação, inserção, permeação e
internalização. Apesar do baixo distúrbio estrutural das membranas, a barreira de energia livre
de ∼55 kcal mol-1 para a translocação de CNHs indicou que esse transporte é desfavorável
cineticamente via o processo passivo. Os experimentos in silico evidenciam que o mecanismo
mais provável de entrega de cisplatina a partir de CNHs envolve a aproximação e inserção,
onde o nanovetor adere na superfície de células cancerosas, como reportado em estudos in vitro.
Após essa retenção, a carga de fármaco deve ser ligeiramente liberada no tumor. As simulações
de captação celular de fármacos de Pt(II) também apontaram barreiras de energia significativas
(∼30 kcal mol-1
) para esse processo, o que reflete a baixa permeabilidade deles em membranas
como discutido em estudos experimentais. Além de reforçar o potencial de CNHs como
nanovetores de fármacos de Pt(II), os resultados apresentados nessa tese podem auxiliar e
impulsionar novos estudos com CNHs, focando no desenvolvimento de formulações menos
agressivas para tratamentos de câncer.FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerai
LIPIcs, Volume 261, ICALP 2023, Complete Volume
LIPIcs, Volume 261, ICALP 2023, Complete Volum
MULTISCALE MOLECULAR MODELING STUDIES OF THE DYNAMICS AND CATALYTIC MECHANISMS OF IRON(II)- AND ZINC(II)-DEPENDENT METALLOENZYMES
Enzymes are biological systems that aid in specific biochemical reactions. They lower the reaction barrier, thus speeding up the reaction rate. A detailed knowledge of enzymes will not be achievable without computational modeling as it offers insight into atomistic details and catalytic species, which are crucial to designing enzyme-specific inhibitors and impossible to gain experimentally. This dissertation employs advanced multiscale computational approaches to study the dynamics and reaction mechanisms of non-heme Fe(II) and 2-oxoglutarate (2OG) dependent oxygenases, including AlkB, AlkBH2, TET2, and KDM4E, involved in DNA and histone demethylation. It also focuses on Zn(II) dependent matrix metalloproteinase-1 (MMP-1), which helps collagen degradation. Chapter 2 investigates the substrate selectivity and dynamics on the enzyme-substrate complexes of DNA repair enzymes, AlkB and FTO. Chapter 3 unravels the mechanisms and effects of dynamics on the demethylation of 3-methylcytosine substrate by AlkB and AlkBH2 enzymes. The results imply that the nature of DNA and conformational dynamics influence the electronic structure of the iron center during demethylation. Chapter 4 delineates how second-coordination and long-range residue mutations affect the oxidation of 5-methylcytosine substrate to 5-hydroxymethylcytosine by TET2 enzyme. The results reveal that mutations affect DNA binding/interactions and the energetic contributions of residues stabilizing key catalytic species. Chapter 5 describes the reparation of unnatural alkylated substrates by TET2, their effects on second-coordination interactions and long-range correlated motions in TET2. The study reveals that post-hydroxylation reactions occur in aqueous solution outside the enzyme environment. Chapter 6 establishes how applying external electric fields (EEFs) enhances specificity of KDM4E for C—H over N—H activation during dimethylated arginine substrate demethylation. The results reveal that applying positive EEFs parallel to Fe=O bond enhances C—H activation rate, while inhibiting the N—H one. Chapter 7 addresses the formation of catalytically competent MMP-1·THP complex of MMP-1. The studies reveal the role of MMP-1’s catalytic domain a-helices, the linker, and changes in coordination states of catalytic Zn(II) during the transition. Overall, the presented results contribute to the in-depth understanding of the fundamental mechanisms of the studied enzymes and provide a background for developing enzyme-specific inhibitors against the associated disorders and diseases
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