arXiv Physics @arxiv_physics@qoto.org

Long range flight by fixed-wing aircraft without propulsion systems can be accomplished by "soaring" -- exploiting randomly located updrafts to gain altitude which is expended in gliding flight. As the location of updrafts is uncertain and cannot be determined except through in situ observation, aircraft exploiting this energy source are at risk of failing to find a subsequent updraft. Determining when an updraft must be exploited to continue flight is essential to managing risk and optimizing speed. Graph percolation offers a theoretical explanation for this risk, and a framework for evaluating it using information available to the operator of a soaring aircraft in flight. The utility of graph percolation as a risk measure is examined by analyzing flight logs from human soaring pilots. This analysis indicates that in sport soaring pilots rarely operate in a condition which does not satisfy graph percolation, identifies an apparent desired minimum node degree, and shows that pilots accept reduced climb rates in order to maintain percolation.

The MORA experimental setup is designed to measure the triple-correlation D parameter in nuclear beta decay. The D coefficient is sensitive to possible violations of time-reversal invariance. The experimental configuration consists of a transparent Paul trap surrounded by a detection setup with alternating beta and recoil-ion detectors. The octagonal symmetry of the detection setup optimizes the sensitivity of positron-recoil-ion coincidence rates to the D correlation, while reducing systematic effects. MORA utilizes an innovative in-trap laser polarization technique. The design and performance of the ion trap, associated beamline elements, lasers and beta and recoil-ion detectors, are presented. Recent progress towards the polarization proof-of-principle is described.

This work frames the first three publications around the development of the Flight Physics Concept Inventory (FliP-CoIn), and elaborates on many aspects in more detail. FliP-CoIn is a multiple-choice conceptual assessment instrument for improving fluid dynamics learning and teaching. I give insights into why and how FliP-CoIn was developed and how it is best used for improving conceptual learning. Further, this work presents evidence for several dimensions of FliP-CoIn's validity and reliability. Finally, I discuss key insights from the development process, the data analysis, and give recommendations for future research. This is a pre print version of the following book: Florian Genz, The Flight Physics Concept Inventory, 2025, Springer Spektrum, published with permission of Springer Fachmedien Wiesbaden GmbH. The final authenticated version is available online at: http://doi.org/10.1007/978-3-658-47515-4 and https://link.springer.com/book/9783658475147

In 1950, Chien-Shiung Wu and her student published a coincidence experiment on entangled photon pairs that were created in electron-positron annihilation. This experiment precisely verified the prediction of quantum electrodynamics. Additionally, it was also the first instance of a precisely controlled quantum entangled state of spatially separated particles, although Wu did not know about this at the time. In 1956, Wu initiated and led the so-called Wu experiment, which discovered parity nonconservation, becoming one of the greatest experiments of the 20th century. As Chen Ning Yang said, Wu's experiments were well known for their precision and accuracy. Experimental precision and accuracy manifested Wu's scientific spirit, which we investigate here in some detail. This paper is the translated transcript of the speech the author made at the International Symposium Commemorating the 110th Anniversary of the Birth of Chien-Shiung Wu, on May 31, 2022. The above abstract is the translation of the original abstract of the speech.

Applications such as augmented and virtual reality (AR/VR), optical atomic clocks, and quantum computing require photonic integration of (near-)visible laser sources to enable commercialization at scale. The heterogeneous integration of III-V optical gain materials with low-loss silicon nitride waveguides enables complex photonic circuits with low-noise lasers on a single chip. Previous such demonstrations are mostly geared towards telecommunication wavelengths. At shorter wavelengths, limited options exist for efficient light coupling between III-V and silicon nitride waveguides. Recent advances in wafer-bonded devices at these wavelengths require complex coupling structures and suffer from poor heat dissipation. Here, we overcome these challenges and demonstrate a wafer-scale micro-transfer printing method integrating functional III-V devices directly onto the silicon substrate of a commercial silicon nitride platform. We show butt-coupling of efficient GaAs-based amplifiers operating at 800 nm with integrated saturable absorbers to silicon nitride cavities. This resulted in extended-cavity continuous-wave and mode-locked lasers generating pulse trains with repetition rates ranging from 3.2 to 9.2 GHz and excellent passive stability with a fundamental radio-frequency linewidth of 519 Hz. These results show the potential to build complex, high-performance fully-integrated laser systems at 800 nm using scalable manufacturing, promising advances for AR/VR, nonlinear photonics, timekeeping, quantum computing, and beyond.

Designing free-form photonic devices is fundamentally challenging due to the vast number of possible geometries and the complex requirements of fabrication constraints. Traditional inverse-design approaches--whether driven by human intuition, global optimization, or adjoint-based gradient methods--often involve intricate binarization and filtering steps, while recent deep learning strategies demand prohibitively large numbers of simulations (10^5 to 10^6). To overcome these limitations, we present AdjointDiffusion, a physics-guided framework that integrates adjoint sensitivity gradients into the sampling process of diffusion models. AdjointDiffusion begins by training a diffusion network on a synthetic, fabrication-aware dataset of binary masks. During inference, we compute the adjoint gradient of a candidate structure and inject this physics-based guidance at each denoising step, steering the generative process toward high figure-of-merit (FoM) solutions without additional post-processing. We demonstrate our method on two canonical photonic design problems--a bent waveguide and a CMOS image sensor color router--and show that our method consistently outperforms state-of-the-art nonlinear optimizers (such as MMA and SLSQP) in both efficiency and manufacturability, while using orders of magnitude fewer simulations (approximately 2 x 10^2) than pure deep learning approaches (approximately 10^5 to 10^6). By eliminating complex binarization schedules and minimizing simulation overhead, AdjointDiffusion offers a streamlined, simulation-efficient, and fabrication-aware pipeline for next-generation photonic device design. Our open-source implementation is available at https://github.com/dongjin-seo2020/AdjointDiffusion.

Criminal activities are predominantly due to males, with females exhibiting a significantly lower involvement, especially in serious offenses. This pattern extends to organized crime, where females are often perceived as less tolerant to illegal practices. However, the roles of males and females within corruption networks are less understood. Here, we analyze data from political scandals in Brazil and Spain to shed light on gender differences in corruption networks. Our findings reveal that females constitute 10% and 20% of all agents in the Brazilian and Spanish corruption networks, respectively, with these proportions remaining stable over time and across different scandal sizes. Despite this disparity in representation, centrality measures are comparable between genders, except among highly central individuals, for which males are further overrepresented. Additionally, gender has no significant impact on network resilience, whether through random dismantling or targeted attacks on the largest component. Males are more likely to be involved in multiple scandals than females, and scandals predominantly involving females are rare, though these differences are explained by a null network model in which gender is randomly assigned while maintaining gender proportions. Our results further reveal that the underrepresentation of females partially explains gender homophily in network associations, although in the Spanish network, male-to-male connections exceed expectations derived from a null model.

Quantum and molecular mechanics based electronic energy studies of weak H-bonded ammonium dimer show distinctive feature in energy profile when computed by different QM methods contrast to MM methods. MM based MMFF and SYBYL methods show smoothly varying dihedral energy profile for torsion angle variation around weak N1-H5 held by H-bond strength of around 13 KJ/mol. All the QM based methods HF, B3LYP and MP2 show noisy and unstable torsion dependent electronic energy profile for H-bonded ammonium dimer. Exploring energy surface beyond bond length shows singularities and discontinuities. QM-based computation of dipole moment shows several discreet values with jumps and discontinuities with torsion angle variation for ammonium dimer. Also repeated computations and reverse torsion energy profile show persistent singularity feature observed in all standard QM techniques. KEY WORDS: ammonium dimer, H-bond, quantum signature, anisotropic energy singularities

Computational physics is integrated throughout the current undergraduate physics curriculum, though there are surprisingly few resources for computational physics in the advanced lab courses. This is despite the fact that a comparison of numerical simulations to experimental results is common practice in modern physics research. In this paper we present a simple experiment in thermal diffusion in metal rods. An analytical solution exists for the transient heat conduction in an infinite rod with a delta function heat input, but no analytical solution exists for short rods or for long duration heat inputs. Our apparatus is a copper rod with a heater and thermometers attached to the rod. The temperature difference on the metal rods due to transient heat conduction can be modeled using a simple numerical simulation using the finite centered difference method. Using a 22 cm long copper rod with the ends thermally sunk in aluminum blocks, we show poor agreement between the experimental results and the infinite-rod analytical model, but excellent agreement between the experimental results and our numerical simulation. Repeating the experiment with only one end of the rod sunk into an aluminum block (the other floating), we get good qualitative agreement between the experimental results and the numerical model. This experiment shows the power of a numerical simulation but also the limitations of the chosen model, which can be used as motivation for further exploration.

This work presents new Gaussian single- and double-zeta basis sets optimized for stochastic density functional theory (sDFT) using real-space auxiliary grids. Previous studies showed standard basis sets like STO-3G and 6-31G are sub-optimal for this approach. Our basis-set's Gaussian-type orbitals (GTOs) resemble norm-conserving pseudo-orbitals for H, C, N, O, F, and Si, but minimize real-space and momentum-space support. These basis sets achieve accuracy comparable to established sets while offering improved efficiency for sDFT calculations with auxiliary grids.