Weak Phase Research Articles

Year‐round sub‐seasonal forecast skill for Atlantic–European weather regimes

AbstractWeather regime forecasts are a prominent use case of sub‐seasonal prediction in the midlatitudes. A systematic evaluation and understanding of year‐round sub‐seasonal regime forecast performance is still missing, however. Here we evaluate the representation of and forecast skill for seven year‐round Atlantic–European weather regimes in sub‐seasonal reforecasts from the European Centre for Medium‐Range Weather Forecasts. Forecast calibration improves regime frequency biases and forecast skill most strongly in summer, but scarcely in winter, due to considerable large‐scale flow biases in summer. The average regime skill horizon in winter is about 5 days longer than in summer and spring, and 3 days longer than in autumn. The Zonal Regime and Greenland Blocking tend to have the longest year‐round skill horizon, which is driven by their high persistence in winter. The year‐round skill is lowest for the European Blocking, which is common for all seasons but most pronounced in winter and spring. For the related, more northern Scandinavian Blocking, the skill is similarly low in winter and spring but higher in summer and autumn. We further show that the winter average regime skill horizon tends to be enhanced following a strong stratospheric polar vortex (SPV), but reduced following a weak SPV. Likewise, the year‐round average regime skill horizon tends to be enhanced following phases 4 and 7 of the Madden–Julian Oscillation (MJO) but reduced following phase 2, driven by winter but also autumn and spring. Our study thus reveals promising potential for year‐round sub‐seasonal regime predictions. Further model improvements can be achieved by reduction of the considerable large‐scale flow biases in summer, better understanding and modeling of blocking in the European region, and better exploitation of the potential predictability provided by weak SPV states and specific MJO phases in winter and the transition seasons.

Impact of systematic and amplitude model correlations within and between systems of combined input: a case study with \u03d52 (\u03b1)

The pursuit of experimental precision in the CP-violating weak phase ϕ2 (α) is not without its challenges, in part due to the need to combine multiple physical observables from various related decay channels, and therein lies a fundamental issue. Similarities in analysis procedures give rise to systematic correlations between the measured inputs constraining ϕ2 that must be taken into account to avoid bias. Specifically, in the case of the irreducible model uncertainty accompanying analyses involving the ρ meson, it is demonstrated that ignoring correlations derived from its pole parameters, or indeed even treating correlations individually contained within each decay channel, can ultimately lead to a bias in ϕ2 of (1°). Correct treatment on the other hand, markedly reduces wandering of its central value as a function of the model uncertainty strength with the added dividend of a further improved overall uncertainty. Bias in the combination of B0 → (ρπ)0 and B → ρρ is also seen to depend on the statistical strength of the former in relation to that of the model uncertainty in the latter. This work can inspire other studies into the points at which systematic correlations beyond those determined in single measurements matter in combinations leading to other CP-violating weak phases such as ϕ1 (β), ϕ3 (γ) and ϕs.

Three-dimensional network model for strong topological insulator transitions

We construct a three-dimensional (3D), time-reversal symmetric generalization of the Chalker-Coddington network model for the integer quantum Hall transition. The novel feature of our network model is that in addition to a weak topological insulator phase already accommodated by the network model framework in the pre-existing literature, it hosts strong topological insulator phases as well. We unambiguously demonstrate that strong topological insulator phases emerge as intermediate phases between a trivial insulator phase and a weak topological phase. Additionally, we found a non-local transformation that relates a trivial insulator phase and a weak topological phase in our network model. Remarkably, strong topological phases are mapped to themselves under this transformation. We show that upon adding sufficiently strong disorder the strong topological insulator phases undergo phase transitions into a metallic phase. We numerically determine the critical exponent of the insulator-metal transition. Our network model explicitly shows how a semi-classical percolation picture of topological phase transitions in 2D can be generalized to 3D and opens up a new venue for studying 3D topological phase transitions.

Unvailing the spin–phonon coupling in nanocrystalline BiFeO3 by resonant two-phonon Raman active modes

We report on temperature dependence of two-phonon Raman spectra in BiFeO3 nanocrystals, above and below the Néel temperature TN using a resonant laser excitation line (λ=532 nm). Two-phonon modes exhibited anomalous frequency hardening and deviation from the anharmonic decay below TN. Such behavior strongly supported the existence of spin-two-phonon interaction, because these modes are known to be very sensitive to the antiferromagnetic ordering. Within the mean-field theory for the nearest-neighbor interaction, the linear relationship between spin–spin correlation function and observed two-phonon frequency shift below TN was obtained. This approach enabled to quantify the spin–phonon interaction by spin–phonon coupling strength for both two-phonon modes and justified the application of mean-field approach. Magnetic measurements revealed the coexistence of antiferromagnetic and weak ferromagnetic phases below TN, which were found non competitive, additionally supporting the mean-field approach from which we deduced that the two-phonon modes in BiFeO3 are correlated with antiferromagnetic ordering below TN.

A 145 kyr record of upstream changes in Indian monsoon circulation and its link to southern high-latitude climate

The influence of northern high latitude climate variability on the South Asian Summer Monsoon has been extensively studied using both instrumental and proxy based climate data. In comparison, only a few studies have attempted to explore the southern high latitude association of the South Asian Summer Monsoon. Here we present a 145 kyr long new data (oxygen and carbon isotopic abundance of two depth-stratified species of foraminifera viz. Globigerinoides ruber and Globorotalia menardii) from a sediment core on sub-millennial to millennial scale resolution from the southwestern tropical Indian Ocean - a region swept by the southeasterly wind during boreal summer (referred to as ‘summer’ hereafter), which transforms to the southwest monsoon wind after crossing the equator. The available records of past summer monsoon variability are predominantly based on reconstruction of downstream hydrology, which is identifiable with the thermodynamics of the system. The present study is a reconstruction of the dynamics of the summer monsoon circulation from an upstream region which is ideally suited for exploring its link with the southern high-latitude climate. We identified several occurrences of interchanging intense and weak monsoon circulation events during the 145 kyr period. We further find that warm (cold) conditions in Antarctica show a near one-to-one coupling with weak (strong) monsoon phases, suggesting a strong mechanistic link between them during the period.

Interdecadal Linkage Between the Winter Northern Hemisphere Climate and Arctic Sea Ice of Diverse Location and Seasonality

During the past few decades, Arctic sea-ice has declined rapidly in both autumn and winter, which is likely to link extreme weather and climate events across the Northern Hemisphere midlatitudes. Here, we use reanalysis data to investigate the possible linkage between mid–high-latitude atmospheric circulation and Arctic sea-ice loss in different geographical locations and seasons and associated impacts on wintertime climate on interdecadal timescales. Four critical sea-ice subregions are analyzed in this study—namely, the Pan-Arctic, Barents–Kara–Laptev Seas (BKL), East Siberia–Chukchi–Beaufort Seas (EsCB), and Bering Sea (Ber). Results suggest that interdecadal reduction of autumn sea-ice, irrespective of geographical location, is dynamically associated with the negative phase of the North Atlantic Oscillation (NAO) in the subsequent winter via stratospheric pathways. Specifically, autumn sea-ice loss appears to cause a weakened stratospheric polar vortex that propagates to the troposphere in the ensuing months, leading to lower surface air temperature and a deficit in precipitation over Siberia and northeastern North America. Meanwhile, an anomalous cyclone over Europe favors excessive precipitation over southern Europe. For wintertime sea-ice loss in the Pan-Arctic and BKL, a weak positive NAO phase, with a dipole pressure pattern over Greenland–northeastern North America and North Atlantic, and a shrunken Siberian high over Eurasia are observed over mid–high-latitudes. The former results in excessive precipitation over northwestern and southeastern North America, whilst the latter leads to less precipitation and mild winter over Siberia. In contrast, Ber sea-ice loss is associated with a circumglobal wave train downstream of the Bering Sea, leading to extensive warming over Eurasia. The anomalous dipole cyclone and anticyclone over the Bering Sea transport more Pacific and Arctic water vapor to North America, and the anomalous cyclone over the Barents Sea results in abundant precipitation in Siberia. Such midlatitude anomaly is dynamically linked to winter sea-ice loss, mainly through tropospheric rather than stratospheric pathways. These results have important implications for future seasonal and interdecadal forecasts in the context of ongoing sea-ice decline.

Development, validation, and application of a new method for the quantitative determination of monohydrogen-substituted perfluoroalkyl carboxylic acids (H–PFCAs) in surface water

Per- and polyfluoroalkyl substances (PFASs) are a large and diverse class of chemicals. While some have been phased out internationally due to concerns over their human and environmental health risks, novel alternative PFASs continue to be manufactured and detected in environmental samples. The occurrence and fate of these alternatives remain poorly understood. The present study investigated the occurrence of an emerging class of PFAS alternative, the monohydrogen-substituted perfluoroalkyl carboxylic acids (H–PFCAs), in conjunction with the more well-known PFCAs. A weak anion exchange solid phase extraction-liquid chromatography tandem mass spectrometry method for quantitative determination of H–PFCAs in surface water was developed, validated, and applied on samples collected from the Netherlands. To improve chromatography, especially for short-chain (H-)PFCAs, an ion-pairing agent, tetrabutylammonium hydrogen sulphate, was used. The method was validated for linearity (R2 > 0.99), instrumental detection limits (0.01–0.09 ng/mL), method detection limits (0.03–0.75 ng/mL), matrix effects (<20%), percent absolute- and relative recovery (57–121%), trueness (130-80%), repeatability (<20%), and within-lab reproducibility (<20%). Eleven out of fourteen PFASs showed acceptable results. Application of the newly validated method to surface water throughout the Netherlands revealed trace levels of H–PFCAs (including two new H–PFCAs) and high concentrations of PFCAs.

Time-dependent study of KS \u2192 \u03c0+\u03c0\u2212 decays for flavour physics measurements

Nowadays High Energy Physics experiments can accumulate unprecedented statistics of heavy flavour decays that allows to apply new methods, based on the study of very rare phenomena, which used to be just desperate. In this paper we propose a new method to measure composition of K0- overline{K} 0, produced in a decay of heavy hadrons. This composition contains important information, in particular about weak and strong phases between amplitudes of the produced K0 and overline{K} 0. We consider possibility to measure these parameters with time-dependent K0 → π+π− analysis. Due to C P -violation in kaon mixing time-dependent decay rates of K0 and overline{K} 0 differ, and the initial amplitudes revealed in the CP-violating decay pattern. We perform phenomenological study of K0 decay evolution initially produced as a combination aleft.|{K}^0(t)rightrangle +bleft.|{overline{K}}^0(t)rightrangle , where a and b, complex amplitudes, could also be dependent on decay time of heavy mother particle. In particular we consider cases of charmed hadrons decays: D+ → K0π+, {D}_s^{+} → K0K+, Λ → pK0 and with some assumptions D0 → K0π0. This can be used to test the sum rule for charmed mesons and to obtain input for the full constraint of the two body amplitudes of D-mesons.

Phase transition of four-dimensional lattice ϕ4 theory with tensor renormalization group

We investigate the phase transition of the four-dimensional single-component ${\ensuremath{\phi}}^{4}$ theory on the lattice using the tensor renormalization group method. We have examined the hopping parameter dependence of the bond energy and the vacuum condensation of the scalar field $⟨\ensuremath{\phi}⟩$ at a finite quartic coupling $\ensuremath{\lambda}$ on large volumes up to $V=102{4}^{4}$ in order to detect the spontaneous breaking of the ${\mathbb{Z}}_{2}$ symmetry. Our results show that the system undergoes the weak first-order phase transition at a certain critical value of the hopping parameter. We also make a comparative study of the three-dimensional ${\ensuremath{\phi}}^{4}$ theory and find that the properties of the phase transition are consistent with the universality class of the three-dimensional Ising model.

Improving axial localization of weak phase particles in digital in-line holography.

One shortcoming of digital in-line holography (DIH) is the low axial position accuracy due to the elongated particle traces in the reconstruction field. Here, we propose a method that improves the axial localization of DIH when applying it to track the motion of weak phase particles in dense suspensions. The proposed method detects particle positions based on local intensities in the reconstruction field consisting of scattering and incident waves. We perform both numerical and experimental tests and demonstrate that the proposed method has a higher axial position accuracy than the previous method based on the local intensities in the reconstructed scattered field. We show that the proposed method has an axial position error below 1.5 particle diameters for holograms with a particle concentration of 4700particles/mm3. The proposed method is further validated by tracking the Brownian motion of 1µmparticles in dense suspensions.

Subtle influence of the Atlantic Meridional Overturning Circulation (AMOC) on seasonal sea surface temperature (SST) hindcast skill in the North Atlantic

Abstract. We investigate the impact of the strength of the Atlantic Meridional Overturning Circulation (AMOC) at 26∘ N on the prediction of North Atlantic sea surface temperature anomalies (SSTAs) a season ahead. We test the dependence of sea surface temperate (SST) predictive skill in initialised hindcasts on the phase of the AMOC at 26∘N, invoking a seesaw mechanism driven by AMOC fluctuations, with positive SSTAs north of 26∘ N and negative SSTAs south of 26∘ N after a strong AMOC and vice versa. We use initialised simulations with the MPI-ESM-MR (where MR is mixed resolution) seasonal prediction system. First, we use an assimilation experiment between 1979–2014 to confirm that the AMOC leads a SSTA dipole pattern in the tropical and subtropical North Atlantic, with the strongest AMOC fingerprints after 2–4 months. Going beyond previous studies, we find that the AMOC fingerprint has a seasonal dependence and is sensitive to the length of the observational window used, i.e. stronger over the last decade than for the entire time series back to 1979. We then use a set of ensemble hindcast simulations with 30 members, starting each February, May, August and November between 1982 and 2014. We compare the changes in skill between composites based on the AMOC phase a month prior to each start date to simulations without considering the AMOC phase and find subtle influence of the AMOC mechanism on seasonal SST prediction skill. We find higher subtropical SST hindcast skill at a 2–4-month lead time for June–July–August (JJA) SSTA composites based on the AMOC phase at May start dates than for the full time period. In other regions and seasons, we find a negligible impact of the AMOC seesaw mechanism on seasonal SST predictions due to atmospheric influence, calling for caution when considering such a mechanism. Our method shows that, for May start dates following strong AMOC phases, summer SST hindcast skill over the subtropics increases significantly compared to that of weak AMOC phases. This suggests that in the assessment of SST skill for a season ahead an eye should be kept on the initial AMOC state.

Global analysis of hadronic two-body B decays in the perturbative QCD approach

Based on the flavor structure of four-quark effective operators, we develop an automatic computation program to calculate hadronic two-body $B$ meson decay amplitudes, and apply it to their global analysis in the perturbative QCD (PQCD) approach. Fitting the PQCD factorization formulas for $B\to PP,VP$ decays at leading order in the strong coupling $\alpha_s$ to measured branching ratios and direct CP asymmetries, we determine the Gegenbauer moments in light meson light-cone distribution amplitudes (LCDAs). It is found that most of the fitted Gegenbauer moments of the twist-2 and twist-3 LCDAs for the pseudoscalar meson $P$ ($P=\pi$, $K$) and vector meson $V$ ($V=\rho$, $K^*$) agree with those derived in QCD sum rules. The shape parameter for the $B_s$ meson distribution amplitude and the weak phase $\phi_3(\gamma)=(75.1\pm2.9)^\circ$ consistent with the value in Particle Data Group are also obtained. It is straightforward to extend our analysis to higher orders and higher powers in the PQCD approach, and to the global determination of LCDAs for other hadrons.

Research on weak signal detection of integral average digital lock-in amplifier

In the process of detecting the amplitude and phase of the weak signal based on digital lock-in amplifier (DLIA), a low-pass filter (LPF) with an extremely low cut-off frequency is required. Even so, the effect is often not good. The detection results of amplitude and phase of weak signal are distorted and fluctuate sharply. To eliminate the difficulty of LPF design, and to reduce the distortion and output fluctuation of detection results of DLIA, this paper proposes a weak signal detection method based on integral average digital lock-in amplifier (IADLIA), which can be used for weak signal detection under strong noise. This method optimizes the structure of the traditional DLIA based on the principle of cross-correlation detection. And then this paper analyzes the influence of the cut-off frequency and signal-to-noise ratio of the LPF on the detection accuracy and output stability of the weak signal amplitude and phase. Finally, the corresponding weak-signal amplitude at the bearing rotating frequency is accurately detected by the proposed method, and the accurate identification of bearing faults is realized. The experimental results show that the IADLIA is characterized by stable output, strong anti-interference ability and high output accuracy. The proposed method can accurately detect the amplitude and phase information of the weak signal in a strong noise environment, get rid of the structure of LPF, and the overall performance is better than the traditional DLIA.

Equilibrium current in a Weyl semimetal–superconductor heterostructure

A heterostructure consisting of a magnetic Weyl semimetal and a conventional superconductor exhibits an equilibrium current parallel to the superconductor interface and perpendicular to the magnetization. Analyzing a minimal model, which as a function of parameters may be in a trivial magnetic insulator phase, a Weyl semimetal phase, or a three-dimensional weak Chern insulator phase, we find that the equilibrium current is sensitive to the presence of surface states, such as the topological Fermi-arc states of the Weyl semimetal or the chiral surface states of the weak Chern insulator. While there is a nonzero equilibrium current in all three phases, the appearance of the surface states in the topological regime leads to a reversal of the direction of the current, compared to the current direction for the trivial magnetic insulator phase. We discuss the interpretation of the surface-state contribution to the equilibrium current as a real-space realization of the superconductivity-enabled equilibrium chiral magnetic effect of a single chirality, predicted to occur in bulk Weyl superconductors.

Unitary matrix models and random partitions: Universality and multi-criticality

The generating functions for the gauge theory observables are often represented in terms of the unitary matrix integrals. In this work, the perturbative and non-perturbative aspects of the generic multi-critical unitary matrix models are studied by adopting the integrable operator formalism, and the multi-critical generalization of the Tracy-Widom distribution in the context of random partitions. We obtain the universal results for the multi-critical model in the weak and strong coupling phases. The free energy of the instanton sector in the weak coupling regime, and the genus expansion of the free energy in the strong coupling regime are explicitly computed and the universal multi-critical phase structure of the model is explored. Finally, we apply our results in concrete examples of supersymmetric indices of gauge theories in the large N limit.

Negative Polarity Items, DPs and Phase Sliding

A negative polarity item (henceforth, NPI) needs a licensor and it may be an overt negation, question force, or a conditional clause (Benmamoun, 1997; Kelepir, 2001; Kumar, 2006; Kural, 1997; Laka, 2013; Mahajan, 1990; Vasishth, 1999). Studies on NPI literature abound and various studies have suggested various licensing conditions of NPIs. However, literature on the licensing conditions of NPIs can be grouped under two major titles. One of them is clausemateness (Choe, 1988; Kelepir, 2001; Muraki, 1978), which basically requires that NPIs and negation be in the same clausal domain. On the other side of the coin stands a more recent account, i.e. phasemateness (Kayabaşı &amp; Özgen 2018; Yamashita, 2003), which states that NPIs must be spelt out within the same domain in which negation exists. Given the two accounts, only phasemateness can predict the behaviors of NPIs in full finite CPs, whereas none of those accounts can predict the grammaticality of nominal DP domains in Turkish with a negative licensor outside of the spell-out domain of the same DP. I attempted to discuss this problem at length, and show that the structural hierarchy within Turkish DPs is somewhat tricky. I will follow Gallego (2010) and Chomsky (2001) and assume that there is phase sliding within DPs, thus NPIs are also licensed within the same domain on the grounds of weak phase impenetrability condition ‘PIC’ (a.k.a. PIC2). The system I will propose here is also borne out by other independent factors such as binding and embedding in Turkish.

Symmetry of diffraction patterns of two-dimensional crystal structures

Conventionally, theoretical considerations in electron microscopy employ the weak phase approximation (WPA), which is only valid for weak scattering atomic elements (C, B, N) but not for transition metal dichalcogenide (TMD) materials. This leads to many exciting phenomena being overlooked. The present theoretical study goes beyond the weak phase approximation and thus the obtained results can be applied for two-dimensional (2D) crystals made of weakly as well of strongly scattering atoms, including the TMD materials. We show that the symmetry of an electron diffraction pattern, characterized by the Friedel’s pairs, is governed by the symmetry of the exit wave distribution. For an infinite periodic crystal, the exit wave is an infinite and periodic 2D distribution which can be assigned an exit wave unit cell. The latter is determined by both the chemical composition of the crystallographic unit cell and the distance between the atomic layers. For 2D crystals of identical atoms, such as graphene, the exit wave unit cell is symmetrical and, thus, a symmetrical diffraction pattern is expected. For TMD materials, the exit wave unit cell is not symmetrical and a non-symmetrical diffraction pattern is expected for both monolayer and bilayer. Conventionally asymmetry in diffraction patterns has been explained by presence of dynamical (multiple) scattering effects. Our study shows that the asymmetry of a diffraction pattern can be explained solely by the asymmetry of the exit wave unit cell. The exit wave unit cell can be asymmetrical even in kinematic (single) scattering model. Therefore, conclusions about dynamical (multiple) scattering effects in 2D materials cannot be made based solely on asymmetry of a diffraction pattern. We also show that for hexagonally arranged atoms the second-order diffraction peaks show perfectly symmetrical intensities independently on the symmetry of the exit wave unit cell distribution.

Chalcogenic orbital density waves in the weak- and strong-coupling limit

Stimulated by recent works highlighting the indispensable role of Coulomb interactions in the formation of helical chains and chiral electronic order in the elemental chalcogens, we explore the p-orbital Hubbard model on a one-dimensional helical chain. By solving it in the Hartree approximation we find a stable ground state with a period-three orbital density wave. We establish that the precise form of the emerging order strongly depends on the Hubbard interaction strength. In the strong coupling limit, the Coulomb interactions support an orbital density wave that is qualitatively different from that in the weak-coupling regime. We identify the phase transition separating these two orbital ordered phases, and show that realistic values for the inter-orbital Coulomb repulsion in elemental chalcogens place them in the weak coupling phase, in agreement with observations of the order in the elemental chalcogens.

Magnetic and electronic ordering phenomena in the Ru2O6 -layer honeycomb lattice compound AgRuO3

The silver ruthenium oxide AgRuO$_3$ consists of honeycomb [Ru$_2^{5+}$O$_6^{2-}$] layers, and can be considered an analogue of SrRu$_2$O$_6$ with a different intercalation stage. We present measurements of magnetic susceptibility and specific heat on AgRuO$_3$ single crystals which reveal a sharp antiferromagnetic transition at 342(3)K. The electrical transport in single crystals of AgRuO$_3$ is determined by a combination of activated conduction over an intrinsic semiconducting gap of $\approx$ 100 meV and carriers trapped and thermally released from defects. From powder neutron diffraction data a N\'eel-type antiferromagnetic structure with the Ru moments along the $c$ axis is derived. Raman and muon spin rotation spectroscopy measurements on AgRuO$_3$ powder samples indicate a further weak phase transition or a crossover in the temperature range 125-200 K. The transition does not show up in magnetic susceptibility and its origin is argued to be related to defects but cannot be fully clarified. The experimental findings are complemented by DFT-based electronic structure calculations. It is found that the magnetism in AgRuO$_3$ is similar to that of SrRu$_2$O$_6$, however with stronger intralayer and weaker interlayer magnetic exchange interactions.

Fatigue mechanism of medium-carbon steel welded joint: Competitive impacts of various defects

Fatigue of welded joint is a scientific issue of great significance, because welding process always causes the loss of fatigue strength up to 40–60% for welded joint of the key components, resulting in a relatively poor reliability in service. In the present work, the fatigue behavior and damage mechanism of a medium-carbon steel welded joint were systematically investigated by microstructure observation and fatigue tests. It was found that, for the medium-carbon steel welded joint, fatigue crack mainly initiated at the welding defects, e.g., welding porosity, slag inclusion and heterogeneous microstructure with a poor mechanical property (i.e., the network-block proeutectoid ferrite). The competitive impact of various defects on the fatigue damage behaviors of welded joint was discussed, i.e., the competition between the volume defects (e.g., porosity and inclusions) and the heterogeneous structure. It is revealed that the smaller surface defects are more susceptible to fatigue damage due to the low constraint of plane stress state and higher stress intensity factor at high stress amplitude, while the larger internal defects easily cause fatigue damage at low stress amplitude because the driving force for crack propagation is larger than that of the damage case from the sample surface. Generally, the fatigue lives of samples with fatigue crack initiating from the weak phase are relatively longer, about 10 times as long as those of the samples with fatigue crack starting from the sample surface. In addition, the residual fatigue crack growth life, Nf, and the initial stress intensity factor (SIF), ΔK1 at the volume defect tip exhibit a linear relation in the double logarithmic coordinate system. The present findings can provide a theoretical basis for the anti-fatigue design and fatigue life extension technology for the metallic component with welded structures.