First evidence of widespread positivity to anticoagulant rodenticides in grey wolves (Canis lupus)

Second-generation Anticoagulant Rodenticides (ARs) can be critical for carnivores, due to their widespread use and impacts. However, although many studies explored the impacts of ARs on small and mesocarnivores, none assessed the extent to which they could contaminate large carnivores in anthropized landscapes. We filled this gap by exploring spatiotemporal trends in grey wolf (Canis lupus) exposure to ARs in central and northern Italy, by subjecting a large sample of dead wolves (n = 186) to the LC-MS/MS method. Most wolves (n = 115/186, 61.8 %) tested positive for ARs (1 compound, n = 36; 2 compounds, n = 47; 3 compounds, n = 16; 4 or more compounds, n = 16). Bromadiolone, brodifacoum and difenacoum, were the most common compounds, with brodifacoum and bromadiolone being the ARs that co-occurred the most (n = 61). Both the probability of testing positive for multiple ARs and the concentration of brodifacoum, and bromadiolone in the liver, systematically increased in wolves that were found at more anthropized sites. Moreover, wolves became more likely to test positive for ARs through time, particularly after 2020. Our results underline that rodent control, based on ARs, increases the risks of unintentional poisoning of non-target wildlife. However, this risk does not only involve small and mesocarnivores, but also large carnivores at the top of the food chain, such as wolves. Therefore, rodent control is adding one further conservation threat to endangered large carnivores in anthropized landscapes of Europe, whose severity could increase over time and be far higher than previously thought. Large-scale monitoring schemes for ARs in European large carnivores should be devised as soon as possible.

In vitro susceptibility of Brachyspira hyodysenteriae strains isolated in pigs in northern Italy between 2005 and 2022

Pleuromutilins (tiamulin and valnemulin) are often used to treat swine dysentery due to recurrent resistance to macrolides and lincosamides. Recently, reduced susceptibility of B. hyodysenteriae to pleuromutilin has been reported. 536 strains of B. hyodysenteriae were isolated from symptomatic pigs weighing 30-150 kg in northern Italy between 2005 and 2022. B. hyodysenteriae was isolated by standard methods and confirmed by PCR. The minimum inhibitory concentration (MIC) to doxycycline, lincomycin, tiamulin, tylosin, tylvalosine and valnemulin was evaluated according to CLSI procedures and MIC data were reported as MIC 50 and MIC 90. The temporal trend of the MIC values was evaluated by dividing the data into two groups (2005-2013 and 2014-2022). Comparison of the distribution in frequency classes in the two periods was performed using Pearson's chi-squared test (p < 0.01). MIC 50 was close to the highest values tested for lincomycin and tylosin, while MIC 90 was close to the highest values tested for all antibiotics. 71.7% of the strains were susceptible to tylvalosin, while 75%-80.4% had reduced susceptibility to valnemulin and tiamulin, respectively. The difference in the distribution of MIC classes was statistically significant in the two periods for doxycycline, tiamulin, tylvalosin and valnemulin, and more MIC classes above the epidemiological cut-off were observed in 2014-2022 compared with 2005-2013. The evaluation of the trends during the period considered shows a decreasing rate of wild-type strains with MIC values below the epidemiological cut-off over time and confirms the presence of resistant strains in northern Italy.

Identification and phylogenetic analysis of Taenia spp. parasites found in wildlife in the Emilia-Romagna region, northern Italy (2017-2022)

The recent expansion of the habitat of several wildlife species, comprising anthropized areas, is a relevant risk factor for many zoonotic diseases and should be considered in national and regional sanitary monitoring systems. We evaluated adult intestinal Taenia spp. parasites isolated from wild carnivores and cystic larval forms isolated from wild mammals analysed at the Istituto Zooprofilattico Sperimentale della Lombardia ed Emilia-Romagna (IZSLER) as part of the regional wildlife sanitary surveillance plan. Then, we assessed parasite species through molecular analysis (multiplex PCR followed by ribosomal 12S subunit gene sequencing) in order to update the epidemiological situation on Taeniids infection in the Emilia-Romagna wildlife, reporting the prevalence of each isolated species. The most commonly isolated species was Taenia serialis, which we detected in both wolves and foxes as definitive hosts and in roe deer as intermediate host. More attention on the distribution of Taeniids in wildlife should be paid, considering their potential zoonotic role: several Taenia spp. (Taenia solium, Taenia multiceps, Taenia serialis, Taenia brauni, Taenia glomerulatus) are known for causing coenurosis in humans, with possible severe or fatal outcomes.

Anomalous Diffusion in the Long-Range Haken-Strobl-Reineker Model

We analyze the propagation of excitons in a d-dimensional lattice with power-law hopping ∝1/r^{α} in the presence of dephasing, described by a generalized Haken-Strobl-Reineker model. We show that in the strong dephasing (quantum Zeno) regime the dynamics is described by a classical master equation for an exclusion process with long jumps. In this limit, we analytically compute the spatial distribution, whose shape changes at a critical value of the decay exponent α_{cr}=(d+2)/2. The exciton always diffuses anomalously: a superdiffusive motion is associated to a Lévy stable distribution with long-range algebraic tails for α≤α_{cr}, while for α>α_{cr} the distribution corresponds to a surprising mixed Gaussian profile with long-range algebraic tails, leading to the coexistence of short-range diffusion and long-range Lévy flights. In the many-exciton case, we demonstrate that, starting from a domain-wall exciton profile, algebraic tails appear in the distributions for any α, which affects thermalization: the longer the hopping range, the faster equilibrium is reached. Our results are directly relevant to experiments with cold trapped ions, Rydberg atoms, and supramolecular dye aggregates. They provide a way to realize an exclusion process with long jumps experimentally.

Eleven Years of Health Monitoring in Wild Boars (Sus scrofa) in the Emilia-Romagna Region (Italy)

In recent years, the growth of wild ungulates has increased the focus on their health monitoring. In particular, the health status of wild boars is relevant for the economic impact on the pig industry. The Emilia-Romagna region activated a wildlife monitoring plan to better evaluate the health status of the wild boar population. Between 2011 and 2021, samples of found dead and hunted wild boar have been examined for trichinellosis, tuberculosis, brucellosis, african swine fever, classical swine fever, Aujeszky's disease, swine vesicular disease, and swine influenza A. Trichinella britovi was identified in 0.001% of the examined wild boars; neither M. bovis nor M. tuberculosis were found in M. tuberculosis complex positive samples; 2.3% were positive for Brucella suis; 29.4% of the sera were positive for Aujeszky's disease virus; and 0.9% of the samples were positive for swine influenza A virus. With an uncertain population estimate, the number of animals tested, the number of positives, and the sampling method do not allow us to make many inferences but suggest the need to implement and strengthen the existing surveillance activity, as it seems to be the only viable alternative for safeguarding animal and human health.

Wildlife Hosts of Leishmania infantum in a Re-Emerging Focus of Human Leishmaniasis, in Emilia-Romagna, Northeast Italy

In the last decade, an upsurge of human leishmaniasis has been reported in the Emilia-Romagna region, Northeast Italy. Epidemiologic data have raised doubts about the role of dogs as the main reservoirs for Leishmania infantum. In the present study, a total of 1,077 wild animals were screened for L. infantum DNA in earlobe and spleen samples from 2019 to 2022. The lymph nodes were tested only in 23 animals already positive in the earlobe and/or spleen. A total of 71 (6.6%) animals resulted positive in at least one of the sampled tissues, including 3/18 (16.7%) wolves, 6/39 (15.4%) European hares, 38/309 (12.3%) roe deer, 1/11 (9.1%) red deer, 8/146 (4.9%) wild boars, 13/319 (4.1%) red foxes, 1/54 (1.9%) porcupine, and 1/59 (1.7%) European badger. Most of the infected animals (62/71) tested positive only in the earlobe tissue, only four animals (two roe deer and two wild boars) tested positive only in the spleen, and five animals (three roe deer and two red foxes) resulted positive for both tissues. L. infantum DNA was detected in the lymph nodes of 6/23 animals. L. infantum detection occurred in all seasons associated with low real-time PCR Ct values. Further research is needed in order to clarify the role of wildlife in the re-emerging focus of leishmaniasis in Northeast Italy.

Evaluation of Control Program Against Streptococcus agalactiae Infection in Dairy Herds During 2019–2021 in Emilia-Romagna Region, Northern Italy

Streptococcus agalactiae (group B Streptococcus, GBS) is a causative agent of mastitis in dairy cattle, mainly causing a subclinical disease associated with a high somatic cell count (SCC), and a consequent decrease in production yield and quality of milk. GBS has been almost eradicated in many Northern European countries, but there are warnings of its re-emergence as a zoonotic threat. In Italy, only two regions carry out a GBS control program: Lombardy and Emilia-Romagna. In Emilia-Romagna, the program has been in place since 2019 and provides for the bacteriological culture of bulk-tank milk (BTM) of all dairy farms every 6 months and the voluntary application of herd eradication programs in the case of positive results. To assess the progress of the program in Emilia Romagna, in terms of herd-level prevalence and GBS transmission between herds, we analyzed the results of 17,056 BTM cultures from 2,831 dairy herds, sampled bi-annually in the period 2019–2021 (six rounds total). The impact of GBS infection on SCC and milk production was also evaluated. The results show a decreasing trend in both the incidence rate (from 3.0 to 1.5%) and apparent prevalence (from 8.9 to 5.2%) of GBS over the study period. By using a susceptible-infected-susceptible (SIS) model for the estimation of the transmission parameters, a basic reproductive number R₀ of 1.4 was calculated, indicating an active spread of GBS in the dairy cattle population of the Emilia-Romagna region. GBS infected farms have a consistently higher BTM SCC than negative ones (+77,000 cells/ml), corresponding to a 0.4 kg/cow/day milk loss. Moreover, GBS infected herds resulted in almost three times more likelihood of having non-marketable milk by exceeding the legal SCC limit. This study demonstrates the need to maintain the current control program against GBS to lower its occurrence and prevent significant market losses to farmers.

Influenza A in Wild Boars: Viral Circulation in the Emilia-Romagna Region (Northern Italy) between 2017 and 2022

Simple Summary

Wild boars and feral pigs are underinvestigated hosts for influenza A viruses (IAVs). This study confirmed and evaluated viral circulation in the Emilia-Romagna wild boar population between 2017 and 2022. Samples were collected at post mortems and screened for IAVs; 0.37% of the tested animals provided positive results. Positive samples were subtyped, isolated, and genotyped via full-genome sequencing. The results highlight the co-circulation of the same viral genotypes in overlapping years in both pigs and wild boars in the same geographical area. Considering the role of domestic and wild Sus scrofa species in the IAVs’ ecology, surveillance against these viruses in the wild boar population needs to be implemented.

Abstract

A systematic surveillance against influenza A viruses (IAVs) in the Suidae population is essential, considering their role as IAV mixing vessels. However, the viral circulation in wild Sus scrofa species is poorly investigated in comparison to the knowledge of IAV infection dynamics in domestic pigs. This study investigated the circulation and the genetic diversity of wild boars’ IAVs detected in the Emilia-Romagna region (2017–2022). A total of 4605 lung samples were screened via an M gene real-time RT-PCR for SwIAV; positive samples were subtyped by multiplex RT-PCR, and viral isolation was attempted. Isolated strains (3 out of the 17 positives) were fully sequenced to evaluate viral genotypic diversity. H1N1 was the most frequently detected subtype, with identification of H1pdm09N1 and H1avN1. Whole-genome phylogenetic analysis revealed SwIAVs belonging to different genotypes, with different genetic combinations, and highlighted the simultaneous circulation of the same genotypes in both pigs and wild boars, supporting the hypothesis of SwIAV spillover events at the wildlife–livestock interface. This study represents an update on the wild boar SwIAV Italian situation, and the strains’ complete genome analysis showed an evolving and interesting situation that deserves further investigation.

Preliminary dosimetric analysis of DOTA-folate radiopharmaceutical radiolabelled with 47Sc produced through natV(p,x)47Sc cyclotron irradiation

⁴⁷Sc is one of the most promising theranostic radionuclides, thanks to its low energy γ-ray emission (159 keV), suitable for single photon emission computed tomography imaging and its intense β ^- emission, useful for tumour treatment. Despite promising preclinical results, the translation of ⁴⁷Sc-therapeutic agents to the clinic is hampered by its limited availability. Among different ⁴⁷Sc-production routes currently being investigated, the ^natV(p,x)⁴⁷Sc reaction has proved to be of particular interest, thanks to the low-cost and easy availability on the market of ^natV material and the diffusion of medium energy proton cyclotrons. However, the cross section of this specific nuclear reaction is quite low and small amounts of Sc-contaminants are co-produced at energies E _P ≤ 45 MeV, namely ⁴⁸Sc and ⁴⁶Sc. The main concern with these Sc-contaminants is their contribution to the patient absorbed dose. For such a reason, the absorbed dose contributions to healthy organs and the effective dose contributions by the three radioisotopes, ⁴⁸Sc, ⁴⁷Sc and ⁴⁶Sc, were evaluated using DOTA-folate conjugate (cm10) as an example of radiopharmaceutical product. Considering as acceptable the limits of 99% for the radionuclidic purity and 10% for the contribution of radioactive Sc-contaminants to the total effective dose after ⁴⁷Sc-cm10 injection, it was obtained that proton beam energies below 35 MeV must be used to produce ⁴⁷Sc through irradiation of a ^natV target.

Ultrafast Creation of Overlapping Rydberg Electrons in an Atomic BEC and Mott-Insulator Lattice

We study an array of ultracold atoms in an optical lattice (Mott insulator) excited with a coherent ultrashort laser pulse to a state where single-electron wave functions spatially overlap. Beyond a threshold principal quantum number where Rydberg orbitals of neighboring lattice sites overlap with each other, the atoms efficiently undergo spontaneous Penning ionization resulting in a drastic change of ion-counting statistics, sharp increase of avalanche ionization, and the formation of an ultracold plasma. These observations signal the actual creation of electronic states with overlapping wave functions, which is further confirmed by a significant difference in ionization dynamics between a Bose-Einstein condensate and a Mott insulator. This system is a promising platform for simulating electronic many-body phenomena dominated by Coulomb interactions in the condensed phase.

Ensemble-Induced Strong Light-Matter Coupling of a Single Quantum Emitter

We discuss a technique to strongly couple a single target quantum emitter to a cavity mode, which is enabled by virtual excitations of a nearby mesoscopic ensemble of emitters. A collective coupling of the latter to both the cavity and the target emitter induces strong photon nonlinearities in addition to polariton formation, in contrast to common schemes for ensemble strong coupling. We demonstrate that strong coupling at the level of a single emitter can be engineered via coherent and dissipative dipolar interactions with the ensemble, and provide realistic parameters for a possible implementation with SiV^{-} defects in diamond. Our scheme can find applications, amongst others, in quantum information processing or in the field of cavity-assisted quantum chemistry.

Salmonella Brandenburg in the pork chain in Italy: Genetic comparison with the human isolates

Salmonella Brandenburg ranked 16th among the serovars responsible for human infections in EU in 2015 and it was found to be associated with swine. In Emilia- Romagna and Lombardy regions of northern Italy, S. Brandenburg was isolated from mesenteric lymph nodes, fecal matter, carcasses and conveyor belts at pig slaughterhouses in 2014 and 2015. In the same area, S. Brandenburg was detected in pork salami in 2015. In the present study, 12 isolates of S. Brandenburg recovered from the pork food-chain were typed by XbaI PFGE and their three profiles were compared to all human S. Brandenburg isolates processed by the Surveillance System of Emilia- Romagna region from 2012 to 2017 (105 isolates). The most frequent pulsotype of porcine origin (6/12) was the second most frequent in humans (16/105). Of the other two pulsotypes of porcine origine (3/12 each), one was the most frequent in humans (41/105), the other was undetected among human isolates.

Loops and Strings in a Superconducting Lattice Gauge Simulator

We propose an architecture for an analog quantum simulator of electromagnetism in 2+1 dimensions, based on an array of superconducting fluxonium devices. The encoding is in the integer (spin-1) representation of the quantum link model formulation of compact U(1) lattice gauge theory. We show how to engineer Gauss' law via an ancilla mediated gadget construction, and how to tune between the strongly coupled and intermediately coupled regimes. The witnesses to the existence of the predicted confining phase of the model are provided by nonlocal order parameters from Wilson loops and disorder parameters from 't Hooft strings. We show how to construct such operators in this model and how to measure them nondestructively via dispersive coupling of the fluxonium islands to a microwave cavity mode. Numerical evidence is found for the existence of the confined phase in the ground state of the simulation Hamiltonian on a ladder geometry.

Conductivity in organic semiconductors hybridized with the vacuum field

Much effort over the past decades has been focused on improving carrier mobility in organic thin-film transistors by optimizing the organization of the material or the device architecture. Here we take a different path to solving this problem, by injecting carriers into states that are hybridized to the vacuum electromagnetic field. To test this idea, organic semiconductors were strongly coupled to plasmonic modes to form coherent states that can extend over as many as 10(5) molecules and should thereby favour conductivity. Experiments show that indeed the current does increase by an order of magnitude at resonance in the coupled state, reflecting mostly a change in field-effect mobility. A theoretical quantum model confirms the delocalization of the wavefunctions of the hybridized states and its effect on the conductivity. Our findings illustrate the potential of engineering the vacuum electromagnetic environment to modify and to improve properties of materials.

Coherent coupling of molecular resonators with a microcavity mode

The optical hybridization of the electronic states in strongly coupled molecule–cavity systems have revealed unique properties, such as lasing, room temperature polariton condensation and the modification of excited electronic landscapes involved in molecular isomerization. Here we show that molecular vibrational modes of the electronic ground state can also be coherently coupled with a microcavity mode at room temperature, given the low vibrational thermal occupation factors associated with molecular vibrations, and the collective coupling of a large ensemble of molecules immersed within the cavity-mode volume. This enables the enhancement of the collective Rabi-exchange rate with respect to the single-oscillator coupling strength. The possibility of inducing large shifts in the vibrational frequency of selected molecular bonds should have immediate consequences for chemistry.

Coherent coupling of light with electronic transitions has led to phenomena such as polariton lasing and superfluidity. Shalabney et al. now couple the optical modes of micro-cavity to the vibrational modes of a molecule at room temperature and thereby alter the chemical behaviour of the molecule.

Defect-induced supersolidity with soft-core bosons

More than 40 years ago, Andreev, Lifshitz and Chester suggested the possible existence of a peculiar solid phase of matter, the microscopic constituents of which can flow superfluidly without resistance due to the formation of zero-point defects in the ground state of self-assembled crystals. Yet, a physical system where this mechanism is unambiguously established remains to be found, both experimentally and theoretically. Here we investigate the zero-temperature phase diagram of two-dimensional bosons with finite-range soft-core interactions. For low particle densities, the system is shown to feature a solid phase in which zero-point vacancies emerge spontaneously and give rise to superfluid flow of particles through the crystal. This provides the first example of defect-induced, continuous-space supersolidity consistent with the Andreev-Lifshitz-Chester scenario.

Supersolid vortex crystals in Rydberg-dressed Bose-Einstein condensates

We study rotating quasi-two-dimensional Bose-Einstein condensates, in which atoms are dressed to a highly excited Rydberg state. This leads to weak effective interactions that induce a transition to a mesoscopic supersolid state. Considering slow rotation, we determine its superfluidity using quantum Monte Carlo simulations as well as mean field calculations. For rapid rotation, the latter reveal an interesting competition between the supersolid crystal structure and the rotation-induced vortex lattice that gives rise to new phases, including arrays of mesoscopic vortex crystals.

Atomic Rydberg reservoirs for polar molecules

We discuss laser-dressed dipolar and van der Waals interactions between atoms and polar molecules, so that a cold atomic gas with laser admixed Rydberg levels acts as a designed reservoir for both elastic and inelastic collisional processes. The elastic scattering channel is characterized by large elastic scattering cross sections and repulsive shields to protect from close encounter collisions. In addition, we discuss a dissipative (inelastic) collision where a spontaneously emitted photon carries away (kinetic) energy of the collision partners, thus providing a significant energy loss in a single collision. This leads to the scenario of rapid thermalization and cooling of a molecule in the mK down to the μK regime by cold atoms.

Three-body correlation functions and recombination rates for bosons in three dimensions and one dimension

We investigate local three-body correlations for bosonic particles in three dimensions and one dimension as a function of the interaction strength. The three-body correlation function g(3) is determined by measuring the three-body recombination rate in an ultracold gas of Cs atoms. In three dimensions, we measure the dependence of g(3) on the gas parameter in a BEC, finding good agreement with the theoretical prediction accounting for beyond-mean-field effects. In one dimension, we observe a reduction of g(3) by several orders of magnitude upon increasing interactions from the weakly interacting BEC to the strongly interacting Tonks-Girardeau regime, in good agreement with predictions from the Lieb-Liniger model for all strengths of interaction.

Trimer liquids and crystals of polar molecules in coupled wires

We investigate pairing and crystalline instabilities of bosonic and fermionic polar molecules confined to a ladder geometry. Combining analytical and numerical techniques, we show that gases of composite molecular dimers as well as trimers can be stabilized as a function of the density difference between the wires. A shallow optical lattice can pin both liquids, realizing crystals of composite bosons and fermions. We show that these exotic quantum phases are robust against conditions of confinement of the molecular gas to harmonic finite-size potentials.

One-dimensional quantum liquids with power-law interactions: the Luttinger staircase

We study one-dimensional fermionic and bosonic gases with repulsive power-law interactions 1/|x|(β), with β>1, in the framework of Tomonaga-Luttinger liquid (TLL) theory. We obtain an accurate analytical expression linking the TLL parameter to the microscopic Hamiltonian, for arbitrary β and strength of the interactions. In the presence of a small periodic potential, power-law interactions make the TLL unstable towards the formation of a cascade of lattice solids with fractional filling, a "Luttinger staircase." Several of these quantum phases and phase transitions are realized with ground state polar molecules and weakly bound magnetic Feshbach molecules.

Supersolid droplet crystal in a dipole-blockaded gas

A novel supersolid phase is predicted for an ensemble of Rydberg atoms in the dipole-blockade regime, interacting via a repulsive dipolar potential softened at short distances. Using exact numerical techniques, we study the low-temperature phase diagram of this system, and observe an intriguing phase consisting of a crystal of mesoscopic superfluid droplets. At low temperature, phase coherence throughout the whole system, and the ensuing bulk superfluidity, are established through tunnelling of identical particles between neighboring droplets.

Strongly correlated gases of Rydberg-dressed atoms: quantum and classical dynamics

We discuss techniques to generate long-range interactions in a gas of ground state alkali atoms, by weakly admixing excited Rydberg states with laser light. This provides a tool to engineer strongly correlated phases with reduced decoherence from inelastic collisions and spontaneous emission. As an illustration, we discuss the quantum phases of dressed atoms with dipole-dipole interactions confined in a harmonic potential, as relevant to experiments. We show that residual spontaneous emission from the Rydberg state acts as a heating mechanism, leading to a quantum-classical crossover.

Quantum phases of cold polar molecules in 2D optical lattices

We study the quantum phases of hard-core bosonic polar molecules on a two-dimensional square lattice interacting via repulsive dipole-dipole interactions. In the limit of small tunneling, we find evidence for a devil's staircase, where Mott solids appear at rational fillings of the lattice. For finite tunneling, we establish the existence of extended regions of parameters where the ground state is a supersolid, obtained by doping the solids either with particles or vacancies. We discuss the effects of finite temperature and finite-size confining potentials as relevant to experiments.

Suppression of inelastic collisions between polar molecules with a repulsive shield

We propose and analyze a technique that allows one to suppress inelastic collisions and simultaneously enhance elastic interactions between cold polar molecules. The main idea is to cancel the leading dipole-dipole interaction with a suitable combination of static electric and microwave fields in such a way that the remaining van der Waals-type potential forms a three-dimensional repulsive shield. We analyze the elastic and inelastic scattering cross sections relevant for evaporative cooling of polar molecules and discuss the prospect for the creation of stable crystalline structures.

Cold atoms and molecules in self-assembled dipolar lattices

We study the realization of lattice models, where cold atoms and molecules move as extra particles in a dipolar crystal of trapped polar molecules. The crystal is a self-assembled floating mesoscopic lattice structure with quantum dynamics given by phonons. We show that within an experimentally accessible parameter regime extended Hubbard models with tunable long-range phonon-mediated interactions describe the effective dynamics of dressed particles.

Strongly correlated 2D quantum phases with cold polar molecules: controlling the shape of the interaction potential

We discuss techniques to tune and shape the long-range part of the interaction potentials in quantum gases of bosonic polar molecules by dressing rotational excitations with static and microwave fields. This provides a novel tool towards engineering strongly correlated quantum phases in combination with low-dimensional trapping geometries. As an illustration, we discuss the 2D superfluid-crystal quantum phase transition for polar molecules interacting via an electric-field-induced dipole-dipole potential.