Extra Contributions Research Articles

On the dynamic fluid–structure stability response of an innovative airplane configuration

This paper provides, for the first time, a physical explanation of the dynamic fluid–structure stability response of an unconventional aircraft configuration called PrandtlPlane, which has been recently acknowledged as a possible candidate to foster the ambition of a greener aviation. As observed in previous literature efforts on this configuration, flutter onset is significantly different when considering the aircraft being free in the air or fixed in space. Thanks to the formulation adopted in this effort, it is shown how the aerodynamic coupling of elastic and rigid modes has a beneficial effect on dynamic aeroelastic instability (flutter) onset. However, the different modal properties, consequence of the diverse boundary conditions, when switching from fixed-in-space to free-flying aircraft, also play a relevant role in determining the flutter occurrence. Whereas for the longitudinal case both effects are synergistic, contributing to increase flutter speed, for the lateral-directional case the variation in modal properties has a detrimental and dominating effect, leading to a flutter speed well within the flight envelope. Not only effects of rigid and elastic modes interaction have been addressed with respect to the aeroelastic side but the consequent effect on the flexible flight dynamics in terms of deterioration of the flying qualities has been quantified. Within the adopted formulation, unsteady aerodynamic forces are modeled by means of an enhanced Doublet Lattice Method able to take into account terms typically neglected by classic formulations. The work also discusses the relevance of such extra contributions to the dynamic response of the aircraft.

A Strong Kuroshio Intrusion into the South China Sea and Its Accompanying Cold-Core Anticyclonic Eddy in Winter 2020–2021

Multiple remote sensing datasets, combined with in-situ drifter observations, were used to analyze the Kuroshio intrusion through the Luzon Strait (LS). The results showed that a strong Kuroshio Current Loop (KCL) and accompanying anticyclonic eddy (ACE) existed in winter 2020–2021. As quantitatively demonstrated by the Double Index (DI), the Kuroshio Warm Eddy Index (KWI) had low values during a long sustained period compared to those in all other years in the available historical records. Remarkable kinematic properties (i.e., amplitude, diameter, propagated distance, lifespan and propagating speed) of the accompanying ACE were extracted by automatic eddy detection algorithms, showing that the ACE had a maximum diameter of 381 km and a peak amplitude of 50 cm, which significantly exceeded the previous statistics in winter. The orographic negative wind stress curl southwest of Taiwan Island and the westward Ekman transport through the LS during the winter half year of 2020–2021 both had large values beyond their historical maxima. Hence wind forcing is regarded as the primary forcing mechanism during this event. Alternating cyclonic eddies (CEs) and ACEs approaching on the east of the LS were identified, indicating that the interaction between the Kuroshio and the impinging CEs at proper locations made extra contributions to enhancing the KCL. The accompanying ACE had a distinctive feature of a cold-core structure at the surface layer, so as to be categorized as a cold core ACE (CC-ACE), and the temperature difference between the cold core and outer warm ring was maintained for three months. The generation and long duration of the CC-ACE may be due to the sustaining entrainment supported by the warm water from Kuroshio intrusion and the Northwest Luzon Coastal Current (NWLCC) successively.

Impact of an alpha helix and a cysteine–cysteine disulfide bond on the resistance of bacterial adhesion pili to stress

Escherichia coli express adhesion pili that mediate attachment to host cell surfaces and are exposed to body fluids in the urinary and gastrointestinal tracts. Pilin subunits are organized into helical polymers, with a tip adhesin for specific host binding. Pili can elastically unwind when exposed to fluid flow forces, reducing the adhesin load, thereby facilitating sustained attachment. Here we investigate biophysical and structural differences of pili commonly expressed on bacteria that inhabit the urinary and intestinal tracts. Optical tweezers measurements reveal that class 1a pili of uropathogenic E. coli (UPEC), as well as class 1b of enterotoxigenic E. coli (ETEC), undergo an additional conformational change beyond pilus unwinding, providing significantly more elasticity to their structure than ETEC class 5 pili. Examining structural and steered molecular dynamics simulation data, we find that this difference in class 1 pili subunit behavior originates from an α-helical motif that can unfold when exposed to force. A disulfide bond cross-linking β-strands in class 1 pili stabilizes subunits, allowing them to tolerate higher forces than class 5 pili that lack this covalent bond. We suggest that these extra contributions to pilus resiliency are relevant for the UPEC niche, since resident bacteria are exposed to stronger, more transient drag forces compared to those experienced by ETEC bacteria in the mucosa of the intestinal tract. Interestingly, class 1b ETEC pili include the same structural features seen in UPEC pili, while requiring lower unwinding forces that are more similar to those of class 5 ETEC pili.

Characterization of topographic effects on sonic boom reflection by resolution of the Euler equations.

The influence of topography on sonic boom propagation is investigated. The full two-dimensional Euler equations in curvilinear coordinates are solved using high-order finite-difference time-domain techniques. Simple ground profiles, corresponding to a terrain depression, a hill, and a sinusoidal terrain, are examined for two sonic boom waves: a classical N-wave and a low-boom. Ground reflection of the sonic boom is affected by elevation variations: a concave ground profile induces compression, which tends to increase the peak pressure in particular, while the opposite is true for convex elevation variations, which lead to expansion and a reduction in peak pressure. The reflected boom is then strongly altered. Furthermore, a sufficiently concave topography can cause focal zones, which generate extra contributions at ground level in the form of U-waves in addition to the reflected wave. This mechanism has the largest effect on waveforms at ground level. The variations of standard metrics are of a few dBs compared to a flat ground for both sonic boom waves, and they are notably greater for the terrain depression than for the hill. Finally, in the case of a sinusoidal terrain, the pressure waveforms are composed of multiple arrivals due to successive focal zones.

Semiconductor Bloch-equations formalism: Derivation and application to high-harmonic generation from Dirac fermions

We rederive the semiconductor Bloch equations emphasizing the close link to the Berry connection. Our rigorous derivation reveals the existence of two further contributions to the current, in addition to the frequently considered intraband and polarization-related interband terms. The extra contributions become sizable in situations with strong dephasing or when the dipole-matrix elements are strongly wave-number dependent. We apply the formalism to high-harmonic generation for a Dirac metal. The extra terms add to the frequency-dependent emission intensity (high-harmonic spectrum) significantly at certain frequencies changing the total signal up to a factor of 10.

S-processing in AGB Stars Revisited. III. Neutron Captures from MHD Mixing at Different Metallicities and Observational Constraints

Abstract We present post-process neutron-capture computations for Asymptotic Giant Branch (AGB) stars of 1.5–3 M ⊙ and metallicities −1.3 ≤ [Fe/H] ≤ 0.1. The reference stellar models are computed with the FRANEC code, using the Schwarzschild's criterion for convection; our motivations for this choice are outlined. We assume that MHD processes induce the penetration of protons below the convective boundary, when the Third Dredge Up occurs. There, the 13C n-source can subsequently operate, merging its effects with those of the 22Ne(α, n)25Mg reaction, activated at the temperature peaks characterizing AGB stages. This work has three main scopes. (i) We provide a grid of abundance yields, as produced through our MHD mixing scheme, which are uniformly sampled in mass and metallicity. From this, we deduce that the solar s-process distribution, as well as the abundances in recent stellar populations, can be accounted for, without the need of the extra primary-like contributions suggested in the past. (ii) We formulate analytic expressions for the mass of the 13C-pockets generated to allow easy verification of our findings. (iii) We compare our results with observations of evolved stars and with isotopic ratios in presolar SiC grains, also noticing how some flux tubes should survive turbulent disruption, carrying C-rich materials into the winds even when the envelope is O-rich. This wind phase is approximated through the G-component of AGB s-processing. We conclude that MHD-induced mixing is adequate to drive slow n-capture phenomena accounting for observations; our prescriptions should permit its inclusion into current stellar evolutionary codes.

Factorization at subleading power and endpoint divergences in h \u2192 \u03b3\u03b3 decay. Part II. Renormalization and scale evolution

Building on the recent derivation of a bare factorization theorem for the b-quark induced contribution to the h → γγ decay amplitude based on soft-collinear effective theory, we derive the first renormalized factorization theorem for a process described at subleading power in scale ratios, where λ = mb/Mh « 1 in our case. We prove two refactorization conditions for a matching coefficient and an operator matrix element in the endpoint region, where they exhibit singularities giving rise to divergent convolution integrals. The refactorization conditions ensure that the dependence of the decay amplitude on the rapidity regulator, which regularizes the endpoint singularities, cancels out to all orders of perturbation theory. We establish the renormalized form of the factorization formula, proving that extra contributions arising from the fact that “endpoint regularization” does not commute with renormalization can be absorbed, to all orders, by a redefinition of one of the matching coefficients. We derive the renormalization-group evolution equation satisfied by all quantities in the factorization formula and use them to predict the large logarithms of order {alpha alpha}_s^2{L}^k in the three-loop decay amplitude, where L=ln left(-{M}_h^2/{m}_b^2right) and k = 6, 5, 4, 3. We find perfect agreement with existing numerical results for the amplitude and analytical results for the three-loop contributions involving a massless quark loop. On the other hand, we disagree with the results of previous attempts to predict the series of subleading logarithms sim {alpha alpha}_s^n{L}^{2n+1} .

Microstructure and tensile property of a precipitation strengthened high entropy alloy processed by selective laser melting and post heat treatment

The microstructure and tensile property of Al0.2Co1.5CrFeNi1.5Ti0.3 high entropy alloy (HEA) processed by selective laser melting (SLM) have been studied in comparisons to that fabricated by traditional cast & wrought (C&W) route. The C&W samples were annealed and then aged at 750 ℃ for 50 h to promote precipitation strengthening of L12 structured phase in FCC matrix. By contrast, SLM samples were aged directly at 750 ℃ for 50 h from the as-built condition, which possessed sub-micron dendritic segregation, internal stress and nano oxides; the result was a microstructure with not only L12 particles dispersion, but also L21 phase was formed at subgrain boundaries, nano oxides and dislocations were present in the matrix. The tensile properties of this HEA were significantly enhanced by the SLM and direct ageing process; the room temperature yield strength (1235 MPa) and ultimate tensile strength (1550 MPa) achieved in this work are the highest to-date for HEAs subjected to laser additive manufacturing processes. Comparing to those of C&W samples, the SLM samples at room temperature and 500 °C exhibited additional yield strengths of 284 MPa and 229 MPa, and additional ultimate tensile strengths of 240 MPa and 275 MPa, respectively. The degree of L12 phase precipitation strengthening was similar for both SLM and C&W samples subjected to the same ageing treatment, interestingly, the additional microstructure features of SLM sample provided extra strengthening contributions; detailed analysis on microstructure evolution and strengthening factors are presented and discussed in this article.

Development and application of the entropy production diagnostic model to the cavitation flow of a pump-turbine in pump mode

A novel mathematical model, entropy production diagnostic model (EPDM) with phase transition (EPDMS), was developed, which is practical to analyze the irreversible loss for cavitation flow in hydraulic machinery by including mass transfer and slip velocity. To model the corresponding flow, two-fluid model with main interphase forces was employed. Compared with the EPDM in homogeneous model, two extra contributions, diffusion and interface entropy production (DifE, IntE), are added in EPDMS. Then, EPDMS was validated by experiments of a pump-turbine in pump mode at three off-design conditions. The improved numerical model is more accurate in capturing the typical cavitation points, while the original one is obviously lower due to poor consideration of phase interaction. Therefore, the loss predicted by EPDMS is more rational. A detailed comparison among four overlapping items of EPDM and EPDMS was performed. It shows that these items merely interpret the accumulative effect of cavitation on the flow, while as a key part of EPDMS, IntE is closely related to the evolution of cavitation. Moreover, low-frequency excitation that caused by cavitation-induced vortex is captured by the probe at the edge of the cavity, which is consistent with the frequency-domain characteristics of IntE instead of other items.

Gravitational wave and collider searches for electroweak symmetry breaking patterns

We study the Electroweak symmetry breaking mechanism with extra Electroweak symmetry breaking contributions (eEWSB) that are bounded by the Fermi constant and limits from the related collider searches. The eEWSB is helpful to build a different zero temperature vacuum structure from the Standard Model (SM), and therefore leads to different Electroweak phase transition patterns at the early Universe. We investigate the collider search prospects and gravitational waves (GW) predictions from the strongly firstly order phase transition (SFOEWPT) in this scenario. The Higgs pair searches at lepton colliders are found to be complementary with the GW searches of the SFOEWPT parameter spaces.

Induced fault reactivation by thermal perturbation in enhanced geothermal systems

Heat extraction by circulating cold water through a geothermal reservoir could potentially induce earthquakes of large magnitudes. In this work, we explore the role of water injection inside a normal fault in triggering seismic slip, under different temperature and rate scenarios of fluid injection into fault damage zones. The resulted non-uniformity of thermal drawdown along the fault damage zones significantly affects the magnitude and timing of induced earthquakes. A non-dimensional expression integrating fault configuration (e.g. length and thickness) and injection condition (e.g. rate and temperature) is used to describe the relationship between the injection schedule and the resulting fault seismic slip event. As the dimensionless parameter QD increases, suggesting a transition from heat conduction to convection, the dimensionless event timing also grows nonlinearly. The perturbation of fault stress field induced from localized thermal cooling process is pronounced, compared to decoupled hydro-mechanical scenarios. The stress field perturbation in the system due to thermal cooling is characterized through a Coulomb friction ratio analysis for evaluating the stress changes along the fault plane and a tensor-based stress perturbation analysis for quantifying the stress changes in the damage zones and host rocks. The thermal influence acting on local patches along the fault strike not only advances the timing of seismic slip, but also increases the magnitude of induced seismic events, by unloading the fault to prompt seismic rupture. The injection temperature has a significant impact on facilitating the onset of seismic slip, i.e. attempting to accelerate the timing and increase the magnitude of fault reactivation. The injection rate variation will affect the timing by changing the pore pressure field and heat transfer manner. Prior to the onset of fault reactivation, the thermal unloading response increases fault permeability by decreasing normal stress, such that more permeable channels in the fault allow fluid to diffuse. Produced plastic shear strain due to fault slip provide extra positive contributions to increased normal aperture through shear dilation, thereby the fault permeability increases significantly by around two orders of magnitude.

ActiveAxADD : Toward non-parametric and orientationally invariant axon diameter distribution mapping using PGSE.

Non-invasive axon diameter distribution (ADD) mapping using diffusion MRI is an ill-posed problem. Current ADD mapping methods require knowledge of axon orientation before performing the acquisition. Instead, ActiveAx uses a 3D sampling scheme to estimate the orientation from the signal, providing orientationally invariant estimates. The mean diameter is estimated instead of the distribution for the solution to be tractable. Here, we propose an extension (ActiveAxADD ) that provides non-parametric and orientationally invariant estimates of the whole distribution. The accelerated microstructure imaging with convex optimization (AMICO) framework accelerates mean diameter estimation using a linear formulation combined with Tikhonov regularization to stabilize the solution. Here, we implement a new formulation (ActiveAxADD ) that uses Laplacian regularization to provide robust estimates of the whole ADD. The performance of ActiveAxADD was evaluated using Monte Carlo simulations on synthetic white matter samples mimicking axon distributions reported in histological studies. ActiveAxADD provided robust ADD reconstructions when considering the isolated intra-axonal signal. However, our formulation inherited some common microstructure imaging limitations. When accounting for the extra axonal compartment, estimated ADDs showed spurious peaks and increased variability because of the difficulty of disentangling intra and extra axonal contributions. Laplacian regularization solves the ill-posedness regarding the intra axonal compartment. ActiveAxADD can potentially provide non-parametric and orientationally invariant ADDs from isolated intra-axonal signals. However, further work is required before ActiveAxADD can be applied to real data containing extra-axonal contributions, as disentangling the 2 compartment appears to be an overlooked challenge that affects microstructure imaging methods in general.

Nonthermal Cosmic Rays during Big Bang Nucleosynthesis to Solve the Lithium Problem

Abstract The discrepancy between the theoretical prediction of primordial lithium abundances and astronomical observations is called the Lithium Problem. We assume that during Big Bang Nucleosynthesis (BBN), nucleons can gain energy and deviate from thermal equilibrium, namely BBN cosmic rays (BBNCRs). BBNCR primary spectra are uncertain and the Coulomb energy-loss processes are neglected; however, we suppose a steady state of BBNCR spectra referring to the Galactic cosmic ray spectra observed today, to see constraints on BBNCRs, for example, the amount and energy range, not sticking to the explicit shape of the spectra. Such extra contributions from BBNCRs can explain the discrepancy, for both Li-7 and Li-6, and will change the deuterium abundance by only a little. The allowed parameter space of such an amount of nonthermal particles and the energy range are shown. The hypothesis is stable regardless of the cross-section uncertainty of relevant reactions and the explicit shape of the energy spectrum.

Variation of phase composition of Mo-Si-B alloys induced by boron and their mechanical properties and oxidation resistance

Mo-12Si-xB (x = 5, 8.5, 17 at%) alloys, doped with 0.9 wt% nanometer La2O3, were fabricated via a powder metallurgical process. The distribution of the α-Mo, Mo3Si and Mo5SiB2 phases existed in these alloys was dependent on the volume fractions of the individual phases. The Mo-12Si-5B (~52 vol% of α-Mo) and Mo-12Si-8.5B (~46 vol% of α-Mo) alloys possessed a continuous α-Mo matrix where Mo3Si/Mo5SiB2 particles distributed dispersedly and the former exhibited the highest fracture toughness. Our theoretical analysis demonstrated that the crucial contribution of crack trapping mechanism to the toughness and the α-Mo volume fraction increasing effectively promoted this mechanism. Besides, the α-Mo/intermetallic interface debonding and the formation of intragranular microcracks induced by La2O3 provided extra contributions to toughness. The Mo-12Si-17B alloy (~65 vol% of intermetallic) formed an intermetallic matrix with embedded semi-continuous α-Mo colonies and other isolated α-Mo islands, having the highest compression strengths at 800–1300 °C. Especially at 1200–1300 °C, the intermetallic matrix with low plastic deformation played a significant role in reinforcing alloy. Besides, the intragranular La2O3 particles strengthened alloy by pinning down and accumulating dislocations in the grain interior. The Mo-12Si-17B was also found to have the excellent oxidation resistance at 1000 °C owing to exhibiting the shortest duration and minimal mass loss in the transient oxidation stage. Moreover, higher B content decreased the viscosity of the borosilicate and thereby formed a dense and protective glassy borosilicate scale quickly, which substantially reduced the growth of inner oxide layers in the steady oxidation stage. In addition, the La2O3 as a blocking phase could impede the permeation of MoO3 bubbles/clusters through the flowing SiO2 glass scale.

On elliptic genera of 6d string theories

We study the elliptic genera of 6d strings based on their modular properties. They are weak Jacobi forms of weight 0, whose indices are determined from the 2d chiral anomalies. We propose the ansatz for the elliptic genera which reflects the analytic structure of instanton partition functions. Given a finite amount of initial BPS data, we completely determine the elliptic genera of 6d strings in various 6d SCFTs. We also apply our ansatz to study mathcal{N}=left(2,0right) and (1, 1) little strings as well as mathcal{N}=left(1,0right) heterotic little strings, for which T-duality of little string theories supplies a sufficient number of initial BPS data. The anomaly polynomials of 6d little strings are worked out, which is needed for the elliptic genera bootstrap. In some little string theories, the elliptic genera must have the extra contributions from the Coulomb branch, which correspond to the additional zero modes for the full strings. The modified ansatze for such elliptic genera are also discussed.

Alignment limit in 2HDM: robustness put to test

In a two-Higgs-doublet model (2HDM), at the vicinity of the alignment limit, the extra contributions to the couplings of the SM-like Higgs with other particles can be subdominant to the same coming from the six dimensional operators. In this context, we revisit the alignment limit itself. It is investigated to what extent these operators can mask the actual alignment in a 2HDM. The bosonic operators which rescale the Higgs kinetic terms can lead to substantial change in the parameter space of the model. We find that some other bosonic operators, which are severely constrained from the electroweak precision tests, can also modify the parameter space of 2HDM due to their anomalous momentum structures. A particular kind of Little Higgs model is explored as an example of 2HDM effective field theory in connection with 2HDM alignment. Choosing a suitable benchmark point in a Type-II 2HDM, we highlight the possibility that the exact alignment limit is ruled out at 95% CL in presence of such operators.

Intrinsic spin-orbit torque in an antiferromagnet with a weakly noncollinear spin configuration

An antiferromagnet is a promising material for spin-orbit torque generation. Earlier studies of the spin-orbit torque in an antiferromagnet are limited to collinear spin configurations. We calculate the spin-orbit torque in an antiferromagnet whose spin ordering is weakly noncollinear. Such noncollinearity may be induced spontaneously during the magnetization dynamics even when the equilibrium spin configuration is perfectly collinear. It is shown that deviation from perfect collinearity can modify properties of the spin-orbit torque since noncollinearity generates extra Berry phase contributions to the spin-orbit torque, which are forbidden for collinear spin configurations. In sufficiently clean antiferromagnets, this modification can be significant. We estimate this effect to be of relevance for fast antiferromagnetic domain wall motion.

Study of the AdS$_2$/CFT$_1$ correspondence with the contribution from the Weyl anomaly

In this paper we will consider the Almheiri-Polchinski model of the AdS$_2$ back reaction coupled with Liouville field, which is necessary for quantum consistency. In this model, the Liouville field is determined classically by a bulk conformal transformation. The boundary time is also reparametrized by this transformation. It is shown that the on-shell action on the boundary for the gravity sector is given by a bulk integral containing the Liouville field. This integral stems from Weyl anomaly and is SL(2,R) invariant. A prescription is given for computing correlation functions of the operators dual to massless scalars. The generating function of the correlation functions of these operators is given by a sum of matter action and the bulk integral containing the Liouville field. The latter integral leads to extra contributions to $n(\geq 6)$ point functions.

Instantons from perturbation theory

In quantum mechanics and quantum field theory perturbation theory generically requires the inclusion of extra contributions non-perturbative in the coupling, such as instantons, to reproduce exact results. We show how full non-perturbative results can be encoded in a suitable modified perturbative series in a class of quantum mechanical problems. We illustrate this explicitly in examples which are known to contain non-perturbative effects, such as the (supersymmetric) double-well potential, the pure anharmonic oscillator, and the perturbative expansion around a false vacuum.

Self-assembling graphene-anthraquinone-2-sulphonate supramolecular nanostructures with enhanced energy density for supercapacitors

Boosting the energy density of capacitive energy storage devices remains a crucial issue for facilitating applications. Herein, we report a graphene-anthraquinone supramolecular nanostructure by self-assembly for supercapacitors. The sulfonated anthraquinone exhibits high water solubility, a π-conjugated structure and redox active features, which not only serve as a spacer to interact with and stabilize graphene but also introduce extra pseudocapacitance contributions. The formed nest-like three-dimensional (3D) nanostructure with further hydrothermal treatment enhances the accessibility of ion transfer and exposes the redox-active quinone groups in the electrolytes. A fabricated all-solid-state flexible symmetric device delivers a high specific capacitance of 398.5 F g−1 at 1 A g−1 (1.5 times higher than graphene), superior energy density (52.24 Wh kg−1 at about 1 kW kg−1) and good stability (82% capacitance retention after 10 000 cycles).