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Polynomial Chaos Expansion: Efficient Evaluation and Estimation of Computational Models
Get PDFWe apply Polynomial chaos expansion (PCE) to surrogate time-consuming repeated model evaluations for different parameter values. PCE represents a random variable, the quantity of interest (QoI), as a series expansion of other random variables, the inputs. Repeated evaluations become inexpensive by treating uncertain parameters of a model as inputs, and an element of a model’s solution, e.g., the policy function, second moments, or the posterior kernel as the QoI. We introduce the theory of PCE and apply it to the standard real business cycle model as an illustrative example. We analyze the convergence behavior of PCE for different QoIs and its efficiency when used for estimation. The results are promising both for local and global solution methods
Spacetime Imaging of Group and Phase Velocities of Terahertz Surface Plasmon Polaritons in Graphene
Get PDFDetecting electromagnetic radiation scattered from
a tip−sample junction has enabled overcoming the diffraction limit
and started the flourishing field of polariton nanoimaging.
However, most techniques only resolve amplitude and relative
phase of the scattered radiation. Here, we utilize field-resolved
detection of ultrashort scattered pulses to map the dynamics of
surface polaritons in both space and time. Plasmon polaritons in
graphene serve as an ideal model system for the study,
demonstrating how propagating modes can be visualized and
modeled in the time domain by a straightforward mathematical
equation and normalization method. This novel approach enables
a direct assessment of the polaritons’ group and phase velocities, as
well as the damping. Additionally, it is particularly powerful in
combination with a pump−probe scheme to trace subcycle changes in the polariton propagation upon photoexcitation. Our method
readily applies to other quantum materials, providing a versatile tool to study ultrafast nonequilibrium spatiotemporal dynamics of
polaritons
Highly Nucleophilic Pyridinamide Anions in Apolar Organic Solvents due to Asymmetric Ion Pair Association
Get PDFFree ions in organic solvents of low polarity would be valuable tools for the activation of low-reactivity substrates. However, the formation of unreactive ion pairs at concentrations relevant for synthesis has prevented the success of this concept so far. On the example of highly nucleophilic pyridinamide phosphonium salts in dichloromethane, we show that asymmetric aggregation offers a solution to this general problem. A combination of conductivity, diffusion-ordered NMR (DOSY), and kinetic measurements utilizing a refined ionic strength-controlled benzhydrylium ion methodology enables unique insight into the aggregation/association state of the ions and the nucleophilicity of the involved anions. This approach reveals that pyridinamide tetraphenylphosphonium salts aggregate in dichloromethane solution asymmetrically to form sandwich-type cations and anions together with their free counterions. The nucleophilicity of free pyridinamide ions exceeds that of the neutral reference nucleophile 9-azajulolidine (TCAP) by up to 2 orders of magnitude. Based on these results, we suggest that asymmetric aggregation in organic solvents of low polarity might be a general pathway to boost the reactivity of anionic nucleophiles
Recommendations for sample selection, collection and preparation for NMR-based metabolomics studies of blood
No full textBackground: Metabolic profiling of blood metabolites, particularly in plasma and serum, is vital for studying human diseases, human conditions, drug interventions and toxicology. The clinical significance of blood arises from its close ties to all human cells and facile accessibility. However, patient-specific variables such as age, sex, diet, lifestyle and health status, along with pre-analytical conditions (sample handling, storage, etc.), can significantly affect metabolomic measurements in whole blood, plasma, or serum studies. These factors, referred to as confounders, must be mitigated to reveal genuine metabolic changes due to illness or intervention onset.
Review objective: This review aims to aid metabolomics researchers in collecting reliable, standardized datasets for NMR-based blood (whole/serum/plasma) metabolomics. The goal is to reduce the impact of confounding factors and enhance inter-laboratory comparability, enabling more meaningful outcomes in metabolomics studies.
Key concepts: This review outlines the main factors affecting blood metabolite levels and offers practical suggestions for what to measure and expect, how to mitigate confounding factors, how to properly prepare, handle and store blood, plasma and serum biosamples and how to report data in targeted NMR-based metabolomics studies of blood, plasma and serum
Deazaflavin‐Catalyzed Arylation of White Phosphorus with Aryl Bromides and Chlorides
Get PDFA substantial improvement in the challenging photocatalytic arylation of white phosphorus (P4) with aryl chlorides and bromides is reported. Using the readily accessible deazaflavin-based photocatalyst o-Me-dFl, valuable triarylphosphines (PAr3) and tetraarylphosphonium salts ([PAr4]X, X = Br, Cl) are synthesized from P4 under near UV-LED (365 nm) irradiation in up to 87% combined yield with drastically reduced reaction times compared to previous protocols. 31P nuclear magnetic resonance spectroscopic monitoring studies and density functional theory calculations provide insights into the reaction pathway. The results represent an important step toward more atom-efficient and economical photocatalytic P4 functionalization reactions
Identification of morphological risk factors for sacroiliac joint syndrome using in vivo computed tomography—A comparative study
Get PDFIntroduction
Sacroiliac joint syndrome (SIJS) is an important cause of lower back pain, constituting a common source of morbidity, especially in today’s ageing population. Underlying pathophysiology is complex and likely multifactorial. Previous studies have suggested characteristic morphologies of the sacroiliac joint (SIJ) shape in pain patients.
Aim
To find morphological markers for SIJS in vivo by evaluating an extensive array of, particularly anatomical, measurements of the SIJ, pelvis and associated musculature using computed tomography (CT) by comparison with non-SIJS control patients.
Methods
CT scans of 754 patients suffering from SIJS and 116 age-matched control patients were analyzed evaluating anatomy and musculoskeletal degeneration. Combined and gender-grouped T-tests, Mann-Whitney-U-tests and chi-square-tests were conducted. Age correlations were tested using linear regressions.
Results
Pelvis and SIJ morphology differed significantly in SIJS patients when compared to the control group. Pelves were narrower and deeper, sacra were narrower and there was less sacroiliac depth. True SIJ were deeper at S1 level and less deep at S2 and S3 levels. There was more sagittal angulation of SIJ at S1, S2 and S3 levels. Furthermore, less psoas muscle volume, higher grades of fatty degeneration of the back musculature as well as increased cutis/subcutis thickness were demonstrated in SIJS patients. Grades of SIJ degeneration were higher in all evaluated portions, although moderate in overall extent.
Discussion and Conclusion
Our data suggest a number of morphological markers associated with SIJS, visible in conventional CT imaging. Further studies are needed to evaluate for causality, prognostic value and potential impact of these factors on individual treatment procedure. In a high-risk population, opportunistic analyses might enable targeted preventive measures
Care in palliative care: a challenging concept with normative issues
No full textPalliative care is an approach for seriously ill patients. Illnesses and knowledge of limited life expectancy often limit self-determination among patients. Along with the concepts of patient autonomy and heteronomy, care is central to the everyday personal and institutional lives of the ill. However, the term ‘care’ has not yet been systematically examined. I argue for a clear distinction between care and paternalism in the discussion about the individual approach to a situation in everyday life, which are two different forms of action in which the patient’s will is considered to varying degrees. The (at least ethical) evaluation, and thus the individual situational need for justification of an action, is different for both forms of action, even if both forms can promote the autonomy of the patient. However, not ‘all’ patient requests are fulfilled through palliative care. There are (justified and perhaps necessary) limitations in the fulfilment of the patient’s goals on the part of those providing care. However, in the context of the discussion on care, these limitations also require a well-founded justification for each individual case
On the Relation between Efficiency, Security, and Practicality of Structured Lattices in Cryptography
No full textThis thesis presents current research on the relations between efficiency and security in the theory and practical constructions of lattice-based cryptography.
Lattice-based cryptography is the most established family of post-quantum cryptography and has an almost 30-year history.
Its very nature allows for many constructions which are simultaneously efficient and rely on trustworthy hardness
assumptions on lattices.
In this thesis, we contribute to the area of lattice-based cryptography in three directions.
First, the efficiency of lattice-based cryptography stems to a great extent from algebraic structures attached to the
lattices used in practice.
Structures can spawn risks that adversaries may exploit.
Therefore, having a good understanding of lattice problems in the presence of structures is crucial to guarantee
security.
Here, we approach this question in terms of a mathematical framework to expand the set of techniques that can be used to
analyze structured lattices and computational problems on those.
Second, cryptographic protocols are used ubiquitously in modern network infrastructures.
Therefore, it is important to ensure that in all use cases, the security is guaranteed.
However, cryptographic primitives can expose vulnerabilities even though they are secure with respect to standard
security models.
Such vulnerabilities can be caused through misuse on the protocol level.
We develop several notions for digital signatures that go beyond standard assumptions and have real-world
use cases.
Further, we analyze concrete schemes regarding their security with respect to these notions and conclude with a deeper
relational understanding of these additional security features.
Third, we provide new constructions based on lattice assumptions in two cases.
On the one hand, the basic functionality of identification becomes interesting in the context of side-channel security on resource-constrained devices.
We present an efficient and secure identification protocol that is, by design, easy to harden against physical attacks.
On the other hand, we analyze many constructions of sanitizable signature schemes and present a systemized account of their potential to be instantiated with lattices.
We explain various cryptographic building blocks and whether these can be built from lattices.
A particular focus lies on the construction of chameleon hash functions from lattices that provide collision
resistance in the presence of collision oracles, thus, giving a strong security guarantee.
Our results lead to new research questions:
First, the framework in which we analyze structured lattices has the potential to be used to further increase our understanding of lattice problems.
Second, new advanced security notions are being introduced in recent works that give additional security guarantees.
Corresponding schemes need to be analyzed regarding those notions.
Moreover, a formal method to ensure security with respect to such new notions may be developed, as has been done in
the case of signatures.
Finally, while lattices provide the most versatile tools to develop cryptographic applications, many constructions have
not yet been instantiated with lattices and are open to further research
A high-precision continuum limit study of the HVP short-distance window
No full textPrecision tests are an essential tool in probing the Standard Model (SM) of particle physics. By pushing theoretical and experimental uncertainties to ever-smaller margins, one can either strengthen confidence in the SM or reveal tensions that could signal new physics. One quantity that has received significant attention in recent years is the anomalous magnetic moment of the muon which has been measured to a remarkable precision of 0.19 ppm, with even greater precision expected in the near future. It is therefore of utmost importance that theoretical calculations match this precision. The dominant source of theoretical uncertainty arises from hadronic contributions, in particular from the leading-order hadronic vacuum polarization (HVP). While the current theory prediction relies on a dispersive approach using experimental scattering data, lattice quantum chromodynamics (QCD) has seen major advances in recent years, making sub-percent level calculations increasingly feasible. At the same time, concerns have emerged regarding the reliability of the experimental data. Therefore, independent, high-precision lattice studies are essential to further scrutinize the SM prediction of . This thesis represents an important step towards re-establishing a robust, high-precision SM prediction.
The separation of the HVP contribution into Euclidean windows allows for a tailored approach to address the different dominant challenges encountered at short, intermediate, and long distances. In this thesis, a novel lattice approach is presented to determine the short-distance contribution to the leading-order HVP without relying on input from perturbative QCD. The method combines a continuum extrapolation in the quenched approximation across 18 lattice spacings () with a separate continuum extrapolation of the dynamical theory, including sea-quark effects. This separation enables the computationally expensive sea-quark contributions to be estimated using only four ensembles at coarser lattice spacings (), while largely confining the logarithmic dependency of the continuum extrapolation to the quenched component