bluuebunny/crossref_metadata_2025 huggingface dataset:
Supercritical and subcritical rotating convection in a horizontally periodic box with no-slip walls at the top and bottom
Authors: Mandal Sutapa , Ghosh Manojit , Maity Priyanka , Banerjee Ankan , Pal Pinaki
Published: October 2022

The study of instabilities in the convection of rotating fluids is one of the classical topics of research. However, in spite of more than five decades of research, the instabilities and related transition scenarios near the onset of rotating convection of low Prandtl number fluids are not well understood. Here, we investigate the transition scenario in rotating Rayleigh–Bénard convection with no-slip boundary conditions by performing 3D direct numerical simulations (DNS) and low-dimensional modeling. The governing parameters, namely, the Taylor number (Ta), Rayleigh number (Ra), and Prandtl number (Pr), are varied in the ranges 0<Ta≤8×103, 0<Ra<1×104, and 0<Pr≤0.35, where convection appears as a stationary cellular pattern. In DNS, for Pr<0.31, the supercritical or subcritical onset of convection appears, according as Ta>Tac(Pr) or Ta<Tac(Pr), where Tac(Pr) is a Pr dependent threshold of Ta. On the other hand, only supercritical onset of convection is observed for Pr≥0.31. At the subcritical onset, both finite amplitude stationary and time dependent solutions are manifested. The origin of these solutions are explained using a low dimensional model. DNS show that as Ra is increased beyond the onset of convection, the system becomes time dependent and depending on Pr, standing and traveling wave solutions are observed. For very small Pr (≤0.045), interestingly, finite amplitude time dependent solutions are manifested at the onset for higher Ta.
A modified viscosity approach for shear thinning lubricants
Authors: Ahmed H. , Biancofiore L.
Published: October 2022

Lubrication is essential to minimize wear and friction between contacting surfaces in relative motion. Oil based lubricants are often enhanced via polymer additives to minimize self-degradation due to the shear thinning effect. Therefore, an accurate estimate of the load carrying capacity of the thin lubricating film requires careful modeling of shear thinning. Available models such as the generalized Reynolds equation (GR) and the approximate shear distribution have drawbacks such as large computational time and poor accuracy, respectively. In this work, we present a new approach, i.e., the modified viscosity (MV) model, based on calculating the strain rate only in one point along the vertical direction. We investigate, for both MV and GR, the load, the maximum pressure, and the computational time for (i) sliding (non-cavitating) contacts, (ii) cavitating, and (iii) squeezing contacts. We observe that the computational time is reduced (i) considerably for non-cavitating sliding and rolling contacts and (ii) by several orders of magnitudes for cavitating and squeezing contacts. Furthermore, the accuracy of MV is comparable with the GR model within an appreciable range of bearing numbers. Finally, for each type of boundary motion, we have determined the optimal vertical location to calculate the shear strain rate for MV; while this optimal value is close to half the height of the contact for sliding configurations, for rolling dominated and squeezing contacts it is around one quarter (or three quarter) of their height. We finally provide an analysis to a priori estimate the optimal location of the strain rate.
The effects of submergence depth on energy harvesting from the VIV of a four-cylinder oscillator with rigid connection
Authors: Yang Tao , Luo Zhumei , Yu Fengrong , Li Jun , Gao Suoming
Published: October 2022

Numerical and experimental studies of energy harvesting driven by vortex-induced vibration (VIV) are currently focused on arranging the energy-captured structure in a uniform incoming flow at a certain depth, ignoring the effect of the free surface on VIV. The fluid–structure coupling effect can be enhanced when a column-group structure with rigid connection is arranged under uniform flow, which is helpful for the structure to concentrate hydrokinetic energy from low-velocity water flow. In this paper, a staggered arrangement of a four-cylinder oscillator with rigid connections is proposed as the energy converter, and the fluid–solid interaction numerical method is carried out to simulate the VIV of the four-cylinder structure under single-phase flow and free surfaces. In U* = 2–16 (flow velocity U = 0.16–1.28 m/s), the results of the energy harvesting magnitude, efficiency, and density of the four-cylinder oscillator under the arrangement depth ratios S* = 2, S* = 3, S* = 4, and S* = 5 are compared with the results obtained in the single-phase flow. It was found that the column-group structure has a broader resonance range of VIV in single-phase flows than a single cylinder and can capture more hydrokinetic energy concentratedly from low-velocity flow. The VIV responses of the four-cylinder oscillator are suppressed at low submergence depths with a narrower resonance range, and its captured energy is reduced. In contrast, at high submergence depth ratio S*, the VIV responses are not suppressed obviously by the free surface. The magnitude of captured energy, energy-harvesting efficiency, and density of the four-cylinder structure are basically consistent with the results obtained in single-phase flow at S* = 5.
Koopmans’ theorem and selection rules for one-electron ionization processes in orbitally degenerate systems
Authors: Plakhutin Boris N.
Published: October 2022

One-electron ionization processes X→Xi+ in orbitally degenerate systems, such as atoms with the open-shell configuration pN, can be divided into two groups. The first group involves the processes that are allowed in photoelectron spectra. The processes of this group in atoms obey the familiar selection rules (SRs) formulated within the Russell–Saunders L, S coupling. All other ionization processes, for which SRs are not obeyed, belong to the second group. Here, we analyze the validity of Koopmans’ theorem (KT) for the processes of the second group forbidden by SRs. We show that the general formulation of KT in the Hartree–Fock method [Plakhutin, J. Chem. Phys. 148, 094101 (2018)] is implicitly based on the assumption that a X→Xi+ process is allowed by SRs, and this presents a limitation of KT. To overcome the latter, we develop an extension of KT that enables estimating the energies of SR-forbidden processes. We prove that the variational condition underlying KT gives different results for SR-allowed and SR-forbidden processes. For the former processes, this condition gives the familiar KT relationship Ii = −ɛi, while for SR-forbidden processes, the respective relationship between Ii and ɛi takes a more complex form. The practical applicability of the extension of KT is verified by applying it to the totality of ionization processes in the valence 2s and 2p shells of atoms C, N, and O in their ground and excited states, which involves a total of 29 SR-allowed and 34 SR-forbidden processes. For all of these processes, we compare KT estimates of ionization energies (IEs) with the relevant experimental data. For comparison, we also present the respective estimates of IEs derived with a ΔSCF approach. Particular attention is paid to the analysis of the validity of KT in the specific cases of violation of Hund’s rules for cation states.
Ensemble inequivalence and negative extensibility in a strongly stretched wormlike chain with fluctuating bending stiffness
Authors: Benetatos Panayotis
Published: October 2022

Many semiflexible polymers exhibit fluctuations in the local bending stiffness along their contour. This may be due to intrinsic conformational changes (e.g., denaturation bubble formation in double stranded DNA or helix–coil transition in polypeptides) or the reversible adsorption and desorption of molecules from the polymer’s environment (e.g., DNA–protein interactions or hybridization of oligonucleotides). In this article, we analyze the tensile elasticity of a strongly stretched wormlike chain, which consists of N concatenated segments, where each segment can be in one of two states, A or B, which differ in bending stiffness. We call this model the reversible wormlike chain (rWLC) model. In the Gibbs (fixed-force, isotensional) ensemble, we obtain analytic expressions for the force–extension relation and the mean fraction of B segments. We show that, under certain conditions, there is a tension-induced crossover from a mostly A to a mostly B rWLC. In the Helmholtz (fixed-extension, isometric) ensemble, we obtain analytic expressions up to a summation. We show that, for finite N, there is marked ensemble inequivalence. Remarkably, in the Helmholtz ensemble, the rWLC can exhibit negative extensibility and multiple peaks.
Pivot invariance of multiconfiguration perturbation theory via frame vectors
Authors: Szabados Á. , Margócsy Á. , Surján P. R.
Published: October 2022

Multiconfiguration perturbation theory (MCPT) is a general framework for correcting the reference function of arbitrary structures. The variants of MCPT introduced so far differ in the specification of their zero-order Hamiltonian, i.e., the partitioning. A common characteristic of MCPT variants is that no numerical procedure is invoked when handling the overlap of the reference function and determinants spanning the configuration space. This comes at the price of pinpointing a principal term in the determinant expansion of the reference, rendering the PT results dependent on this choice. It is here shown that the pivot dependence of MCPT can be eliminated by using an overcomplete set of projected determinants in the space orthogonal and complementary to the reference. The projected determinants form a so-called frame, a generalization of the notion of basis, allowing for redundancy of the set. The simple structure of the frame overlap matrix facilitates overlap treatment in closed form, a feature shared by previous MCPT variants. In particular, the Moore–Penrose inverse of singular matrices appearing in frame-based MCPT can be constructed without the need for any pivoting algorithm or numerical zero threshold. Pilot numerical studies are performed for the singlet-triplet gap of biradicaloid systems, relying on geminal-based, incomplete model space reference function. Comparison with previous MCPT variants as well as illustration of pivot invariance is provided.
On the development of relativistic distorted wave approximation for the energies and collision dynamics of atoms or ions subjected to the outside plasma
Authors: Chen Zhan-Bin
Published: October 2022

In this manuscript, we present the development of a relativistic distorted wave method for determining the energies and collision dynamics of plasma-immersed atoms or ions. The methodology is based on the Dirac–Coulomb Hamiltonian, in which contributions from relativity and higher order effects, such as quantum electrodynamics and Breit interaction, are incorporated. The key element in this method is that a modified Debye–Hückel approximation is employed to represent the effect of plasma screening. In order to correctly describe the (bound and continuous state) wave functions, a self-consistent field calculation incorporating the shielding potential is performed within the fully relativistic framework. The particle interaction within the scattering matrix element of the excitation process is described by the shielded Coulomb interaction. The present technique is illustrated by calculations of energy, line shift, transition probability, electron-impact excitation/ionization cross section, and photoionization cross section of a few-electron system confined in plasma environments. The present model is tested and validated against a number of known cases (simulations are made for the He-like Al11+ ion) in the literatures. Numerical results demonstrate that the modifications to the Coulomb potential proposed in the spatial and temporal criteria of the Debye–Hückel approximation allow us to improve the theoretical description of the plasma shielding and thus the dynamical processes in dense plasmas. Comparisons of our computational predictions and the recent experimental measurements are performed. The current work not only has far-reaching implications for our understanding of the dense plasma screening, but also has potential applications in fusion, laboratory astrophysics, and related disciplines.
Numerical study of pure rotational fs/ps CARS coherence beating at high pressure and for multi-species rotation-vibration non-equilibrium thermometry
Authors: Chen Timothy Y. , Kliewer Christopher J.
Published: October 2022

Coherent anti-Stokes Raman scattering (CARS) has long been the gold standard for non-intrusively measuring gas temperature in reacting flows such as flames and plasmas. Recently, the development of ultrafast hybrid fs/ps CARS has enabled the exploitation of coherence beating between neighboring spectral lines to simultaneously measure rotational and vibrational temperatures from a single pure rotational spectrum. However, the influence of non-Boltzmann vibrational state distributions and limitations due to collisional dephasing at pressures greater than 1 atm remains unclear. In this work, we use spectral simulations to investigate the effects of non-Boltzmann vibrational state distributions and the applicability of coherence beating at pressures up to 10 atm. We show that short probe pulses can be leveraged to quantify non-Boltzmann vibrational state distributions of N2. Furthermore, we demonstrate that fs/ps CARS coherence beating can simultaneously provide sensitive measurements of rotational and vibrational temperatures of both O2 and N2 in air. A sensitivity analysis was conducted to qualitatively explain the accuracy and precision comparisons between probe delays.
Contactless excitation of acoustic resonance in insulating wafers
Authors: Zhai Gan , Xin Yizhou , Kopas Cameron J. , Lachman Ella , Field Mark , Mutus Josh Y. , Cicak Katarina , Aumentado José , Sung Zuhawn , Halperin W. P.
Published: October 2022

Contactless excitation and detection of high harmonic acoustic overtones in a thin insulator single crystal are described using radio frequency spectroscopy techniques. Single crystal [001] silicon wafer samples were investigated, one side covered with a Nb thin film, the common starting point for the fabrication of quantum devices. The coupling between electromagnetic signals and mechanical oscillation is achieved from the Lorentz force generated by an external magnetic field. This method is suitable for any sample with a metallic surface or covered with a thin metal film. High resolution measurements of the temperature dependence of the sound velocity and elastic constants of silicon are reported and compared with known results.
On acoustically modulated jet shear layers and the Nyquist–Shannon sampling theorem
Authors: Nicholls C. J. , Chakravarthy K. , Tang B. M. T. , Williams B. A. O. , Bacic M.
Published: October 2022

The goal of this paper is to present the behavior of a jet shear layer in response to acoustic excitation from a signal processing perspective. The main idea is that the vortices that roll-up in the jet shear layer are similar to the discrete samples of a digital control system, and, hence, that the Nyquist–Shannon sampling theorem should apply. We further hypothesize that the strength of a vortex is determined by the mean amplitude of the excitation waveform during its creation. We also argue that, at least in some cases, demodulation occurs as a result of the vorticity signal generated by the convection of discrete vortices past a point in the shear layer. This vorticity signal is related to the amplitude modulation (AM) excitation waveform by a half-wave rectification operation, a common implementation of an AM demodulator. To investigate these ideas, a free, round jet that is excited upstream of the nozzle is studied using particle image velocimetry. Experiments are conducted that confirm that the sampling theorem applies, and an aliased response is observed when the Nyquist limit is exceeded. Previous authors have attributed demodulation to a vortex merging mechanism, but we demonstrate that merging is not always required for demodulation and suggest that it is one of two mechanisms at play.
Extended coupled-states approximation for full-dimensional quantum treatments of rovibrationally inelastic scattering between atoms and triatomic molecules
Authors: Yang Dongzheng , Xie Daiqian , Guo Hua
Published: October 2022

While the rigorous time-independent close-coupling approach is ideally suited for cold and ultracold rovibrationally inelastic collision, its application beyond atom–diatom systems in full dimensionality is numerically expensive. Coupled-states (CS) approximation and its extensions are good choices to reduce the computational cost and have been successfully applied to diatom–diatom systems. In this work, we introduce the extended CS (ECS) approximation, in which one or a few nearest Coriolis coupled helicity channels are included. Its usefulness in atom–triatom systems is demonstrated for scattering of H2O with rare gas atoms. The results show that the ECS approximation, even when only the nearest neighbors are included, is generally much better than the CS approximation in describing scattering. At low collision energies, the ECS gradually converges to the exact results with the increasing number of Coriolis coupled helicity blocks. We further discuss three major factors that may lead to the failure of the CS approximation, namely, the reduced mass, collision energy, and triatomic rotational quantum number. It is illustrated that these factors could impact the relative importance of off-diagonal matrix elements in the Hamiltonian, thus influencing the coupling between different helicity channels.
Phenomenon and analysis of direct initiation of detonation using multiple turbulent flame jets
Authors: Li Xiang , Lei Qingchun , Zhao Xiaocun , Zheng Jiawei , Zhang Qibin , Fan Wei
Published: October 2022

This work reports experimental investigations on the direct initiation of detonation using multiple turbulent flame jets, with a special focus on the arrangement schemes and fundamental physics in the initiation processes. Results show that the direct initiation of detonation can be achieved using turbulent jets even when the jet tube diameter is much smaller than the empirical critical tube diameter due to flame–shock–wall interactions. Conspicuous evidence has been shown that the probability of the direct initiation increases significantly near the detonatability limit using multi-jets compared to a single jet. These results are found to be closely related to several new phenomena observed when using multiple jets to initiate the detonation. They are: (1) unexpected rapid promotion of the final-stage flame acceleration in ignition tubes by multiple jets, which is attributed to the fact that the expanding precursor shock waves propagate back into the adjacent tube and interact with the flame; (2) enhancement of hot spot generation by multiple jets due to the precursor shock intersection and the formation of an induction zone; (3) obvious velocity loss of impinging jets initiation as a result of induced hot spots propagation in the burned gases.
Finite-temperature stability of hydrocarbons: Fullerenes vs flakes
Authors: Perez-Mellor Ariel Francis , Parneix Pascal , Calvo Florent , Falvo Cyril
Published: October 2022

The effects of a finite temperature on the equilibrium structures of hydrocarbon molecules are computationally explored as a function of size and relative chemical composition in hydrogen and carbon. Using parallel tempering Monte Carlo simulations employing a reactive force field, we find that in addition to the phases already known for pure carbon, namely, cages, flakes, rings, and branched structures, strong changes due to temperature and the addition of little amounts of hydrogen are reported. Both entropy and the addition of moderate amounts of hydrogen favor planar structures such as nanoribbons over fullerenes. Accurate phase diagrams are proposed, highlighting the possible presence of multiple phase changes at finite size and composition. Astrophysical implications are also discussed.
Albert Einstein. Myth Buster: Relativity
Authors: Kastrup Helge , Mallow Jeffry V.
Published: October 2022

Albert Einstein made several major contributions to physics. The first and foremost were his theories of relativity. His special theory of relativity showed that time and space were observer-dependent and led to the famous E = mc2, the equivalence of matter and energy. His general theory of relativity showed that gravity and acceleration were indistinguishable and that space was curved. While it was not Einstein's goal to produce practical applications of his theories, the special theory of relativity led to nuclear energy and the general theory to the GPS. He was awarded the 1922 Nobel Prize but not for the theory of relativity, which was at that time not generally accepted. In a widespread albeit apocryphal legend, after he discovered general relativity, Einstein purportedly gave an exam to his secretary to prepare. When she noted that these were the same questions as the previous year, he remarked, “Yes, but the answers have changed.”
Erwin Schrödinger. It’s Not Just About the Cat
Authors: Kastrup Helge , Mallow Jeffry V.
Published: October 2022

It had been known for decades that matter, like light, had both wave and particle properties, but there was no quantitative description relating the two. Schrödinger derived it. His equation begins with a wave description and leads to clusters of waves that behave like particles. His first success was to predict the average radii of the orbits of electrons in atoms. These matched the values postulated by Bohr. But there is a hitch, embedded in the word “average.” Different measurements of the same property of an object, such as position, give a variety of answers and not due to experimental error. There is at best a probability associated with each property. The Schrödinger equation has been interpreted to argue that every object actually has a mix of the values of a property until you measure it; hence, it “chooses” one. Schrödinger himself was not happy with this and hence the cat. Is it both alive and dead until you look and force it to choose one? Interpretations still raise controversy. The equation itself ranks as one of the most important in all of physics.
Charles H. Townes. Stimulant
Authors: Kastrup Helge , Mallow Jeffry V.
Published: October 2022

The 1964 Nobel Prize to Charles H. Townes reads in part, “for fundamental work in the field of quantum electronics… based on the… laser principle.” The laser is one of the most important inventions of the 20th century, arguably matched only by the transistor. The original theory was conceived in 1916 by Einstein. He argued that photons of the right incident energy could stimulate electrons in atoms to drop from a higher to a lower state (rather than up to a higher one, as might be expected), emitting photons of the same energy. One incident photon would stimulate many emitted photons. Perhaps counterintuitive, but true. Forty-four years later, Townes and his colleague (and brother-in-law) Arthur Schawlow proved Einstein correct, inventing the laser. Laser is the acronym for “light amplification by stimulated emission of radiation.” One example, which readers are likely to have seen, is the helium–neon laser. Demonstration models are generally weak. However, as we know, there are lasers that cut metal, do surgery, print, catch speeders—applications run at least into the hundreds, with doubtless more to come.
Enrico Fermi. Jack of Both Trades
Authors: Kastrup Helge , Mallow Jeffry V.
Published: October 2022

In physics research, there is a stark divide between theorists and experimentalists. Very occasionally, a person appears who bridges that divide. One such was Enrico Fermi. Born in 1901, at age 22, he made his first breakthrough in theory. He realized that Einstein's E = mc2 predicted that a small decrease in mass from an atomic nucleus could release an enormous amount of energy. Three years later, he made his next. Wolfgang Pauli had propounded his exclusion principle. Fermi had become an expert in the statistical mechanics of Ludwig Boltzmann. He applied this to the analysis of the energy distribution of particles in a gas, with the constraint that they obey the exclusion principle, another theoretical achievement. Over the next decade, he made two more breakthroughs. The first, theoretical, was his analysis of beta decay, the ejection of an electron from a nucleus. The second, the one destined to have a worldwide impact, was experimental: the production of a sustained nuclear reaction. This was the crucial step toward building the atom bomb and peaceful uses of nuclear energy.
Preferences of parents for mental health services to suit children with chronic medical conditions
Authors: Ride Jemimah , Cameron Lachlan , Jones Renee , Dalziel Kim , Wurzel Danielle , Kao Kung-Ting , Freeman Jeremy L. , Hiscock Harriet
Published: October 2022

Objectives To identify features of mental health services that affect the uptake of services among parents of children with chronic medical conditions, to inform the design of pathways into mental health care. Methods A discrete choice experiment in which participants made choices between hypothetical mental health services described in terms of service features: cost, wait time, provider knowledge of chronic medical conditions, recommendations, opening hours, and travel time. Participants were parents of children attending The Royal Children’s Hospital outpatient clinics for the management of a chronic medical condition who completed the online survey between August 2020 and January 2021. The uptake of mental health services with differing features was predicted based on regression models examining the relationship between choice and service features, and accounting for participant characteristics and unobserved heterogeneity. Results The sample comprised 112 parents, of whom 52% reported unmet needs. The most influential service features were wait times, cost, recommendation from medical specialists, and mental health provider knowledge of chronic medical conditions. Predicted uptake of a realistic service showed inequalities across income, parental education, and single parent status. A service comprising preferred features was predicted to eliminate these inequalities. Conclusions Reducing cost and wait time for mental health services could reduce unmet need among children with chronic medical conditions. Specific approaches to tackle the high levels of unmet needs in this group include equipping medical specialists to recommend mental health providers and training mental health providers on the impacts of chronic medical conditions on children. Offering preferred services could increase uptake and reduce inequalities in mental health care.
Nobel and novice: Author prominence affects peer review
Authors: Huber Jürgen , Inoua Sabiou , Kerschbamer Rudolf , König-Kersting Christian , Palan Stefan , Smith Vernon L.
Published: October 2022

Peer review is a well-established cornerstone of the scientific process, yet it is not immune to biases like status bias, which we explore in this paper. Merton described this bias as prominent researchers getting disproportionately great credit for their contribution, while relatively unknown researchers get disproportionately little credit [R. K. Merton,
Science
159, 56–63 (1968)]. We measured the extent of this bias in the peer-review process through a preregistered field experiment. We invited more than 3,300 researchers to review a finance research paper jointly written by a prominent author (a Nobel laureate) and by a relatively unknown author (an early career research associate), varying whether reviewers saw the prominent author’s name, an anonymized version of the paper, or the less-well-known author’s name. We found strong evidence for the status bias: More of the invited researchers accepted to review the paper when the prominent name was shown, and while only 23% recommended “reject” when the prominent researcher was the only author shown, 48% did so when the paper was anonymized, and 65% did when the little-known author was the only author shown. Our findings complement and extend earlier results on double-anonymized vs. single-anonymized review [R. Blank,
Am. Econ. Rev.
81, 1041–1067 (1991); M. A. Ucci, F. D’Antonio, V. Berghella,
Am. J. Obstet. Gynecol. MFM
4, 100645 (2022)].
V. cholerae MakA is a cholesterol-binding pore-forming toxin that induces non-canonical autophagy
Authors: Jia Xiaotong , Knyazeva Anastasia , Zhang Yu , Castro-Gonzalez Sergio , Nakamura Shuhei , Carlson Lars-Anders , Yoshimori Tamotsu , Corkery Dale P. , Wu Yao-Wen
Published: October 2022

Pore-forming toxins (PFTs) are important virulence factors produced by many pathogenic bacteria. Here, we show that the Vibrio cholerae toxin MakA is a novel cholesterol-binding PFT that induces non-canonical autophagy in a pH-dependent manner. MakA specifically binds to cholesterol on the membrane at pH < 7. Cholesterol-binding leads to oligomerization of MakA on the membrane and pore formation at pH 5.5. Unlike other cholesterol-dependent cytolysins (CDCs) which bind cholesterol through a conserved cholesterol-binding motif (Thr-Leu pair), MakA contains an Ile-Ile pair that is essential for MakA-cholesterol interaction. Following internalization, endosomal acidification triggers MakA pore-assembly followed by ESCRT-mediated membrane repair and V-ATPase-dependent unconventional LC3 lipidation on the damaged endolysosomal membranes. These findings characterize a new cholesterol-binding toxin that forms pores in a pH-dependent manner and reveals the molecular mechanism of host autophagy manipulation.
Low budget gamma spectroscopy
Authors: Hoeling Barbara , Siegel P B
Published: October 2022

We describe gamma spectroscopy experiments with an NaI-detector for the student laboratory that can be carried out with moderate expense and without licensed radioactive sources. For calibration, thoriated welding rods and potassium chloride are used, both of which are freely available for purchase. In addition, lead shielding, a costly and hard to handle part of the equipment in radiation lab experiments, is not required. The students analyze the gamma radiation from bulk soil samples they collect themselves, making this a meaningful measurement and a radiation physics experiment accessible to everyone without the usual safety restrictions.
The mechanics of a cat landing from a drop
Authors: Challis John H
Published: October 2022

Cats have a remarkable ability to survive drops from great heights. This ability is examined by considering the aerodynamics of the cat during a drop, and by examining the mechanics of the landing. For the landing the spring-like properties of the cat’s legs and the compliance of the landing surface are all modeled. The analysis shows that a combination of the reduction of landing velocity due to aerodynamics, the spring like properties of the cat’s legs, and the relationship between cat mass and bone diameter give cat’s the ability to survive drops from great heights. The analysis highlights how simple models exploiting mechanical principles can explain the survivability of falling cats.
Mean-field theory of the spin-1/2 transverse field Ising model with a negative thermal expansion
Authors: Rončík M , Balcerzak T , Szałowski K , Jaščur M
Published: October 2022

A generalized spin-1/2 transverse field Ising model with a negative thermal expansion of the lattice is introduced and investigated using standard methods of statistical mechanics. Besides the volume-dependent magnetic energy, the static lattice energy, and anharmonic Einstein phonon energy are also considered in calculations. Analytic relations for the Gibbs free energy, magnetic moments, and equations of state are obtained, taking into account a simple volume dependence of all energy contributions. The ground-state and finite-temperature phase diagrams are discussed in detail for the strong and weak magneto-elastic coupling. It is clearly demonstrated that the generalized spin-1/2 transverse field Ising model exhibits a novel critical behavior, due to the strong negative expansion of the lattice, which is controlled by the strength of magneto-elastic coupling. The presented approach can be easily modified to study also other magnetic and non-magnetic crystalline models of solids.
Possible realization of three-dimensional quantum spin liquid behavior in HoVO4
Authors: Ranaut Dheeraj , Shastri Shivprasad S , Pandey Sudhir K , Mukherjee K
Published: October 2022

The study of geometrically frustrated magnetic systems with unusual crystal field ground states offers a possibility of realizing the new aspects of physics of disordered systems. In this study, we report our results of structural, magnetic susceptibility, heat capacity measurements, along with density functional theory (DFT) calculations on HoVO4; a compound in which the presence of a distorted kind of HoO8 polyhedral leads to multiple magnetic interaction paths. The observed broad maximum below 10 K in the temperature response of DC susceptibility curves implies the presence of short-range correlations. AC susceptibility rules out the possibility of any kind of spin freezing. Temperature dependent heat capacity measurement at zero field indicate towards the absence of long-range ordering, along with the presence of a broad maximum centered around 14 K. The residual heat capacity exhibits a characteristic power-law (Tα
) behavior with the exponent α nearly equal to 2, which is analogous to that observed for other three-dimensional (3D) quantum spin liquid (QSL) systems. The DFT calculations signify the presence of dominant second and third nearest neighbor interactions, which in turn lead to magnetic frustration in our system. Our investigations suggest that HoVO4 can be a candidate for realizing a 3D QSL state.
Number of trials and data structure affect the number and components of muscle synergies in upper-limb reaching movements
Authors: Zhao Kunkun , Zhang Zhisheng , Wen Haiying , Scano Alessandro
Published: October 2022

Objective. Due to the variability of human movements, muscle activations vary among trials and subjects. However, few studies investigated how data organization methods for addressing variability impact the extracted muscle synergies. Approach. Fifteen healthy subjects performed a large set of upper limb multi-directional point-to-point reaching movements. Then, the study extracted muscle synergies under different data settings and investigated how data structure prior to synergy extraction, namely concatenation, averaging, and single trial, the number of considered trials, and the number of reaching directions affected the number and components of muscle synergies. Main results. The results showed that the number and components of synergies were significantly affected by the data structure. The concatenation method identified the highest number of synergies, and the averaging method usually found a smaller number of synergies. When the concatenated trials or reaching directions was lower than a minimum value, the number of synergies increased with the increase of the number of trials or reaching directions; however, when the number of trials or reaching directions reached a threshold, the number of synergies was usually constant or with less variation even when novel directions and trials were added. Similarity analysis also showed a slight increase when the number of trials or reaching directions was lower than a threshold. This study recommends that at least five trials and four reaching directions and the concatenation method are considered in muscle synergies analysis during upper limb tasks. Significance. This study makes the researchers focus on the variability analysis induced by the diseases rather than the techniques applied for synergies analysis and promotes applications of muscle synergies in clinical scenarios.
Domain boundaries in ScAlMgO4 single crystal observed by synchrotron radiation x-ray topography and reticulography
Authors: Yao Yongzhao , Hirano Keiichi , Sugawara Yoshihiro , Ishikawa Yukari
Published: October 2022

We performed synchrotron radiation x-ray topography (XRT) and reticulography to observe dislocations and crystal misorientation at domain boundaries (DBs) in a scandium magnesium aluminate single-crystal substrate grown via the Czochralski method. By inserting a fine-scale x-ray-absorbing mesh between the sample and the topograph-recording medium, reticulography was clearly observed allowing for direct measurement of twist and tile domain misorientation >5 × 10−5 rad. The results show that the angular resolution can be further improved to better than 2 × 10−5 rad by applying a different mesh-to-film distance M and then comparing the relative displacement in their reticulographs. The character of dislocations aligning at the DBs revealed by XRT analysis is consistent with the reticulography results. Finally, we demonstrate a method that combines reticulography and XRT into a single reticulographic XRT image, from which dislocation observation and misorientation measurement can be performed simultaneously.
Magnetar hard X-ray emission from axion-like particle conversion
Authors: Fortin Jean-François , Gratton Marianne
Published: October 2022

We explore the possibility that axion-like-particles (ALPs), which would be produced in the core of magnetars and would then convert in the magnetosphere into photons, can explain magnetar hard X-ray spectra. We remark that this scenario would also provide answers to some questions related to magnetar heating. Indeed, considering that magnetars have: 1) hard X-ray spectra that are difficult to explain with known mechanisms; 2) large photon luminosities that force high core temperatures; 3) high core temperatures that imply large neutrino emissivities; 4) and large neutrino emissivities that lead to small magnetar lifetimes in contradiction to observations — explaining the hard X-ray spectra with ALPs could decrease the core temperatures and thus the neutrino emissivities, allowing for longer magnetar lifetimes as expected from observations. In this work, we initiate the study of this scenario for three magnetars with extreme luminosities, and conclude that the general idea is likely worth investigating in more detail.
The Electromagnetic Compatibility between FAST and Public Mobile Communication Stations and its Cognitive Using Frequency Strategy
Authors: Wang Jian , Zhao Yi-Bo , Shi Ya-Fei , Yang Cheng , Hao Yu-Long , Sun Jian-Min
Published: October 2022

To master the electromagnetic environment characteristics around the Five-hundred-meter Aperture Spherical radio Telescope (FAST) and ensure a better ecological environment in the radio-quiet zone of FAST, we analyzed the radiation characteristics of the public communication stations around FAST. By comparing the FAST received signal power from the communication stations and the interference protection threshold of the radio astronomy applications, we found that the total proportion of the communication stations exceeding the radio astronomy protection threshold is 69.01%. Furthermore, to fully protect the regular operation of FAST, we proposed four interference avoidance and frequency coordination strategies based on the cognitive theory. Namely: (1) increasing the operating frequency of the communication station; (2) adjusting the direction of the transmitter antennas; (3) reducing the height of the transmitter antennas; (4) decreasing the transmitting power of the communication station. As a result, the impact on FAST can effectively be reduced, and the FAST's received power from the communication stations will be lower than the radio astronomy protection threshold by using the above mentioned four strategies. Through the analysis of the experiment, the prediction is consistent with the overall trend of the measurement, and using frequency strategies can significantly reduce the signal power at the receiving locations. Furthermore, we construct a quality evaluation system for frequency coordination and analyze the satisfaction of the four strategies under the four criteria. The results show that adjusting the direction of the transmitter antennas has better satisfaction, and the maximum satisfaction is 0.85. The above research results can be further expanded to potentially improve the electromagnetic ecological environment around FAST and support the regular operation of FAST.
Testing the Coincidence Problem with Strong Gravitational Lens, Type Ia Supernovae and Hubble Parameter Observational Data
Authors: Diao Jingwang , Pan Yu , Xu Wenxiao
Published: October 2022

In this paper, we use three different kinds of observational data, including 130 strong gravitational lensing (SGL) systems, type Ia supernovae (SNeIa: Pantheon and Union2.1) and 31 Hubble parameter data points (H(z)) from cosmic chronometers to constrain the phenomenological model (ρ

x
∝ ρ

m

a

ξ
). By combining these three kinds of data (Union2.1+SGL+H(z)), we get the parameter value at the confidence interval of 2σ, Ω
X,0 = 0.69 ± 0.34, ω

x
= −1.24 ± 0.61, ξ = 3.8 ± 3.9 and H
0 = 70.22 ± 0.86 kms−1 Mpc−1. According to our results, we find that the ΛCDM model is still the model which is in best agreement with the observational data at present, and the coincidence problem is not alleviated. In addition, the Ω
X
and Ω
m
have the same order of magnitude in 0 < z < 1.26. Finally, we obtain the transition redshift z

T
= 0.645. If the transition occurs in z > 0.645, it is necessary to introduce the dark energy interacting with dark matter.
The Dependence of Stellar Activity Cycles on Effective Temperature
Authors: Kitchatinov Leonid
Published: October 2022

This paper proposes the idea that the observed dependence of stellar activity cycles on rotation rate can be a manifestation of a stronger dependence on the effective temperature. Observational evidence is recalled and theoretical arguments are given for the presence of cyclic activity in the case of sufficiently slow rotation only. Slow rotation means proximity to the observed upper bound on the rotation period of solar-type stars. This maximum rotation period depends on temperature and shortens for hotter stars. The maximum rotation period is interpreted as the minimum rotation rate for operation of a large-scale dynamo. A combined model for differential rotation and the dynamo is applied to stars of different mass rotating with a rate slightly above the threshold rate for the dynamo. Computations show shorter dynamo cycles for hotter stars. As the hotter stars rotate faster, the computed cycles are also shorter for faster rotation. The observed smaller upper bound for rotation period of hotter stars can be explained by the larger threshold amplitude of the α-effect for onset of their dynamos: a larger α demands faster rotation. The amplitude of the (cycling) magnetic energy in the computations is proportional to the difference between the rotation period and its upper bound for the dynamo. Stars with moderately different rotation rates can differ significantly in super-criticality of their dynamos and therefore in their magnetic activity, as observed.
Brain electrical microstate features as biomarkers of a stable motor output
Authors: Croce Pierpaolo , Tecchio Franca , Tamburro Gabriella , Fiedler Patrique , Comani Silvia , Zappasodi Filippo
Published: October 2022

Objective. The aim of the present study was to elucidate the brain dynamics underlying the maintenance of a constant force level exerted during a visually guided isometric contraction task by optimizing a predictive multivariate model based on global and spectral brain dynamics features. Approach. Electroencephalography (EEG) was acquired in 18 subjects who were asked to press a bulb and maintain a constant force level, indicated by a bar on a screen. For intervals of 500 ms, we calculated an index of force stability as well as indices of brain dynamics: microstate metrics (duration, occurrence, global explained variance, directional predominance) and EEG spectral amplitudes in the theta, low alpha, high alpha and beta bands. We optimized a multivariate regression model (partial least square (PLS)) where the microstate features and the spectral amplitudes were the input variables and the indexes of force stability were the output variables. The issues related to the collinearity among the input variables and to the generalizability of the model were addressed using PLS in a nested cross-validation approach. Main results. The optimized PLS regression model reached a good generalizability and succeeded to show the predictive value of microstates and spectral features in inferring the stability of the exerted force. Longer duration and higher occurrence of microstates, associated with visual and executive control networks, corresponded to better contraction performances, in agreement with the role played by the visual system and executive control network for visuo-motor integration. Significance. A combination of microstate metrics and brain rhythm amplitudes could be considered as biomarkers of a stable visually guided motor output not only at a group level, but also at an individual level. Our results may play an important role for a better understanding of the motor control in single trials or in real-time applications as well as in the study of motor control.
Online control of the gain drift with temperature of SiPM arrays used for the readout of LaBr3:Ce crystals
Authors: Bonesini M. , Bertoni R. , Prata M. , Rossella M.
Published: October 2022

LaBr3:Ce crystals have been introduced for radiation imaging in medical physics, with photomultiplier or single SiPM readout. An R&D was pursued with 1/2″ and 1″ LaBr3:Ce crystals, from different producers, to realize compact large area detectors (up to some cm2 area) with SiPM array readout, aiming at high light yields, good energy resolution, good detector linearity and fast time response for low-energy X-rays. A natural application was found inside the FAMU project at RIKEN-RAL muon facility, that aims at a precise measure of the proton Zemach radius to solve the so-called “proton radius puzzle”, triggered by the recent measure of the proton charge radius at PSI. The goal is the detection of characteristic X-rays around 130 keV. Other applications may be foreseen in medical physics, such as PET, and gamma-ray astronomy. A limiting factor is the gain drift of SiPM arrays with temperature, that give a deterioration of the detector’s FWHM energy resolution. To solve this problem, a custom NIM module, based on CAEN A7585 digital power supply, was developed. Test results of the correction of gain drift with temperature for SiPM arrays from Advansid, Sensl, Hamamatsu will be presented. At the 137Cs peak, an energy resolution better than 3% was obtained for a typical LaBr3:Ce crystal, using Hamamatsu S13461 arrays. This compares well with best available results obtained with a PMTs.