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We propose a novel realization for a topologically superconducting phase hosting Majorana zero-modes on the basis of quantum spin Hall systems. Remarkably, our proposal is completely free of ferromagnets. Instead, we confine helical edge states around a narrow defect line of finite length in a two-dimensional topological insulator. We demonstrate the formation of a new topological regime, hosting protected Majorana modes in the presence of s-wave superconductivity and Zeeman coupling. Interestingly, when the system is weakly tunnel-coupled to helical edge state reservoirs, a particular transport signature is associated with the presence of a non-Abelian Majorana zero-mode., Comment: 8 pages, 7 figures + Supp. Mat

We investigate a class of periodically driven many-body systems that allows us to extend the phenomenon of prethermalization to the vicinity of isolated intermediate-to-low drive frequencies away from the high-frequency limit. We provide numerical evidence for the formation of a parametrically long-lived prethermal plateau, captured by an effective Floquet Hamiltonian computed using the replica inverse-frequency expansion, and demonstrate its stability w.r.t.~random perturbations in the drive period. Considering exclusively nonintegrable Floquet Hamiltonians, we find that heating rates are non-universal: we observe Fermi's Golden Rule scaling, power-law scaling inconsistent with the Golden Rule, and non-power law scaling, depending on the drive. Despite the asymptotic character of the inverse-frequency expansion, we show that it describes the thermostatic properties of the state all along the evolution up to infinite temperature, with higher-order terms improving the accuracy. Our results suggest a dynamical mechanism to gradually increase temperature in isolated quantum simulators, such as ultracold atoms, and open up an alternative possibility to investigate thermal phase transitions and the interplay between thermal and quantum criticality using Floquet drives., More details on the topic are provided in arXiv:2101.04372

Majorana bound states are interesting candidates for applications in topological quantum computation. Low energy models allowing to grasp their properties are hence conceptually important. The usual scenario in these models is that two relevant gapped phases, separated by a gapless point, exist. In one of the phases, topological boundary states are absent, while the other one supports Majorana bound states. We show that a customary model violates this paradigm. The phase that should not host Majorana fermions supports a fractional soliton exponentially localized at only one end. By varying the parameters of the model, we describe analytically the transition between the fractional soliton and two Majorana fermions. Moreover, we provide a possible physical implementation of the model. We further characterize the symmetry of the superconducting pairing, showing that the odd-frequency component is intimately related to the spatial profile of the Majorana wavefunctions., 5 pages, 2 figures

Electrical currents in a quantum spin Hall insulator are confined to the boundary of the system. The charge carriers behave as massless relativistic particles whose spin and momentum are coupled to each other. Although the helical character of those states is already established by experiments, there is an open question regarding how those edge states interact with each other when they are brought into close spatial proximity. We employ an inverted HgTe quantum well to guide edge channels from opposite sides of a device into a quasi-one-dimensional constriction. Our transport measurements show that, apart from the expected quantization in integer steps of 2e2/h, we find an additional plateau at e2/h. We combine band structure calculations and repulsive electron–electron interaction effects captured within the Tomonaga–Luttinger liquid model and Rashba spin–orbit coupling to explain our observation in terms of the opening of a spin gap. These results may have direct implications for the study of one-dimensional helical electron quantum optics, and for understanding Majorana and para fermions. Little is known about how edge states in topological materials interact with each other. Here, a quantum spin Hall insulator is used to show that when edge states are brought close together, additional gaps appear in the spectrum.

The manipulation of the helical edge states of two-dimensional topological insulators is crucial for the development of technological applications. Recently, an important step forward, namely, the experimental realization of a quantum point contact between helical edges, has been accomplished. We theoretically predict that such a quantum point contact, in the presence of a time periodic applied electric field, is characterized by a topological quantum phase transition in the Floquet spectrum. Moreover, we show that it is possible to detect this dynamical topological quantum phase transition by a bare conductance measurements., 5 pages, 3 figures

Study Objective describe a relationship between actinomycosis and persistent foreign bodies in the female genital tract; emphasize the importance of pre-therapeutic biopsy in genital tract disease. Design Actinomycoses are opportunistic bacteria that can cause invasive, suppurative infections when mucosal barriers are compromised. Most cases are seen in patients with long-term use of intrauterine devices (IUDs). Infections are slow-growing and produce non-specific symptomatology, making initial misdiagnosis of malignancy or other pathologies common. This may lead to avoidable surgery, as most actinomycosis resolves with antibiotics alone. We present a case of isolated vaginal actinomycosis in a 66-year-old female without a history of IUD use, presenting with post-menopausal bleeding. She had a remote history of colpoperineorrhaphy with inorganic mesh placement, and a total abdominal hysterectomy and bilateral salpingectomy. Preoperative biopsy guided a less invasive surgical approach than that considered for malignancy. Setting The patient presented at her outpatient gynecologist. Biopsy revealed actinomycosis. Surgical excision occurred via a posterior approach with the patient in lithotomy position. Patients or Participants 66-year-old post-menopausal female without a history of IUD use, presenting with post-menopausal bleeding. Interventions The rectovaginal septum was dissected and 3.25cm x 1.5cm of tissue/mesh were excised. The healthy vaginal epithelium was reapproximated. The patient was treated with 6 weeks of ceftriaxone followed by 30 days of amoxicillin-clavulanate. Measurements and Main Results Histopathological report demonstrated acute and chronic inflammation, granulation tissue and no evidence of malignancy. The patient recovered well after surgery. Conclusion This case is notable for actinomycosis isolated to the vagina and in a female without concomitant IUD-use, suggesting a relationship between actinomycosis and any foreign body in the lower female genital tract. Actinomycosis should be considered for any slow-growing mass with foreign body presence. Preoperative biopsy or, at a minimum, intraoperative frozen section should be obtained to prevent unnecessary surgery.

Parafermions are generalizations of Majorana fermions that may appear in interacting topological systems. They are known to be powerful building blocks of topological quantum computers. Existing proposals for realizations of parafermions typically rely on strong electronic correlations which are hard to achieve in the laboratory. We identify a novel physical system in which parafermions generically develop. It is based on a quantum constriction formed by the helical edge states of a quantum spin Hall insulator in the vicinity of an ordinary s-wave superconductor. Interestingly, our analysis suggests that Z_{4} parafermions are emerging bound states in this setup in the weakly interacting regime. Furthermore, we identify a situation in which Majorana fermions and parafermions can coexist.

Parafermions are generalizations of Majorana fermions that may appear in interacting topological systems. They are known to be powerful building blocks of topological quantum computers. Existing proposals for realizations of parafermions typically rely on strong electronic correlations which are hard to achieve in the laboratory. We identify a novel physical system in which parafermions generically develop. It is based on a quantum constriction formed by the helical edge states of a quantum spin Hall insulator in the vicinity of an ordinary s-wave superconductor. Interestingly, our analysis suggests that Z_{4} parafermions are emerging bound states in this setup in the weakly interacting regime. Furthermore, we identify a situation in which Majorana fermions and parafermions can coexist.

Topological superconductors give rise to unconventional superconductivity, which is mainly characterized by the symmetry of the superconducting pairing amplitude. However, since the symmetry of the superconducting pairing amplitude is not directly observable, its experimental identification is rather difficult. In our work, we propose a system, composed of a quantum point contact and proximity-induced $s$-wave superconductivity at the helical edge of a two-dimensional topological insulator, for which we demonstrate the presence of odd-frequency pairing and its intimate connection to unambiguous transport signatures. Notably, our proposal requires no time-reversal symmetry breaking terms. We discover the domination of crossed Andreev reflection over electron cotunneling in a wide range of parameter space, which is a quite unusual transport regime.

We propose two experimental setups that allow for the implementation and the detection of fractional solitons of the Goldstone-Wilczek type. The first setup is based on two magnetic barriers at the edge of a quantum spin Hall system for generating the fractional soliton. If then a quantum point contact is created with the other edge, the linear conductance shows evidence of the fractional soliton. The second setup consists of a single magnetic barrier covering both edges and implementing a long quantum point contact. In this case, the fractional soliton can unambiguously be detected as a dip in the conductance without the need to control the magnetization of the barrier., Comment: 6 pages, 4 figures

The presence of a Majorana bound state in condensed matter systems is often associated to a zero bias peak in conductance measurements. Here, we analyze a system were this paradigm is violated. A Majorana bound state is always present at the interface between a quantum spin Hall system that is magnetically gapped and a quantum spin Hall system gapped by proximity induced s-wave superconductivity. However, the linear conductance could be either zero or nonzero and quantized depending on the energy and length scales of the barriers. The transition between the two values is reminiscent of the topological phase transition in proximitized spin-orbit coupled quantum wires in the presence of an applied magnetic field. We interpret the behavior of the conductance in terms of scattering states at both zero and non-zero energy., Comment: submitted to: EPJ ST Special Issue: Topological States of Matter: Theory and Applications

We show that correlated two-particle backscattering can induce fractional charge oscillations in a quantum dot built at the edge of a two-dimensional topological insulator by means of magnetic barriers. The result nicely complements recent works where those fractional oscillations were predicted in the strong-coupling regime. Moreover, since by rotating the magnetization of the barriers a fractional charge can be trapped in the dot via the Jackiw-Rebbi mechanism, the system we analyze offers the opportunity to study the interplay between this noninteracting charge fractionalization and the fractionalization due to two-particle backscattering. We demonstrate that the number of fractional oscillations of the charge density depends on the magnetization angle. In fact, a rotating magnetization can add or subtract fractional charges from the dot continuously. Finally, we address the renormalization induced by two-particle backscattering on the spin density, which is characterized by a dominant oscillation with a length twice as large as the charge-density oscillations.

Motivated by recent experiments, we investigate the excitation energy of a proximitized Rashba wire in the presence of a position dependent pairing. In particular, we focus on the spectroscopic pattern produced by the overlap between two Majorana bound states that appear for values of the Zeeman field smaller than the value necessary for reaching the bulk topological superconducting phase. The two Majorana bound states can arise because locally the wire is in the topological regime. We find three parameter ranges with different spectral properties: crossings, anticrossings and asymptotic reduction of the energy as a function of the applied Zeeman field. Interestingly, all these cases have already been observed experimentally. Moreover, since an increment of the magnetic field implies the increase of the distance between the Majorana bound states, the amplitude of the energy oscillations, when present, gets reduced. The existence of the different Majorana scenarios crucially relies on the fact that the two Majorana bound states have distinct $k$-space structures. We develop analytical models that clearly explain the microscopic origin of the predicted behavior., Comment: 9 pages, 8 figures

The interest in electrophoretic deposition (EPD) of ceramics has widely increased owing to its versatility to combine different materials in unique shapes and structures interesting for several applications (e.g. solid oxide fuel cells, thermal barrier coatings and biomaterials). In this work, an automated robotic EPD set-up was constructed and used to produce tetragonal and cubic zirconia multilayered specimens, which combine the high conductivity of the cubic layer with the high toughness of the tetragonal layer. This automated EPD set-up allowed us to study in detail the very sensitive EPD process, whose success highly depends on a good control of the EPD parameters (e.g. electrode distance, applied tension, deposition time). Tetragonal layers of 20 μm and cubic layers of 10 μm were obtained with high reproducibility. The in situ measurement of the electric current evolution with the deposition time enabled us to analyse the EPD process for each layer.

The weakly interacting helical Luttinger liquid, due to spin momentum locking, is characterized by extremely peculiar local observables: we show that the density-density correlation functions do not exhibit signatures of Friedel and Wigner oscillations, and that spin-spin correlation functions, which are strongly anisotropic, witness the formation of a planar spin wave. Moreover, we demonstrate that the most relevant scattering potentials involving a localized impurity are not able to modify the electron density, while only magnetic impurities can pin the planar spin density wave., Comment: 6 pages, 2 figures

The chiral anomaly is based on a nonconserved chiral charge and can happen in Dirac fermion systems under the influence of external electromagnetic fields. In this case, the spectral flow leads to a transfer of right- to left-moving excitations or vice versa. The corresponding transfer of chiral particles happens in momentum space. Here we describe an intriguing way to introduce the chiral anomaly into real space. Our system consists of two quantum dots that are formed at the helical edges of a quantum spin Hall insulator by means of magnetic barriers. Such a setup gives rise to fractional charges which we show to be sharp quantum numbers for large barrier strengths. Interestingly, it is possible to map the system onto a quantum spin Hall ring in the presence of a flux pierced through the ring, where the relative angle between the magnetization directions takes the role of the flux. The chiral anomaly in this system is then directly related to the excess occupation of particles in the two quantum dots. This analogy allows us to predict an observable consequence of the chiral anomaly in real space, which is connected to the presence of fractional charges in the very same system.

Purpose: There is evidence that mesenchymal somatic stem cells isolated from cord blood have the capability to differentiate into different tissues. Strategies to isolate, cryopreserve and differentiate mesenchymal stem cells are of high interest. We examined survival, proliferation and transdifferentiation of human mesenchymal stem cells transplanted into healthy mouse livers. Methods: Mesenchymal stem cells isolated from human cord blood were transplanted into the livers of 12 SCID mice. Liver tissue was stained for stem cells with the fluorescent dye PKH26 7 and 21 days after transplantation. Expression of human albumin, α1-antitrypsin, GATA4, α-fetoprotein, β2 microglobulin and β-actin in stem cells was studied before and after transplantation with immunohistochemistry and RT-PCR. Results: PKH-positive, fluorescent, intact cells were identified in the livers of all 12 transplanted mice. More PKH26-positive cells were seen after 21 than after 7 days. Expression of human albumin in mouse liver tissue was demonstrated immunohisto-chemically with a specific monoclonal antibody and confirmed with RT-PCR. Conclusion: Human mesenchymal stem cells isolated from cord blood can survive, proliferate and transdifferentiate after transplantation into mouse liver tissue. This may have therapeutic applications in the future. It appears that gene expression by the transplanted stem cells adapts to the host tissue. The transplanted stem cells express some, but not all genes typically expressed in liver (for instance albumin but not GATA4). It is not clear whether this is due to an inherent limitation of these stem cells to transdifferentiate or to interspecies incompatibilities between humans and mice.

El interés por la deposición electroforética (EPD) de la cerámica o compuestos de cerámica ha aumentado mucho debido a la posibilidad de crear bloques de cerámica en verde con varias características interesantes para aplicaciones biomédicas, por ejemplo, cerámicas porosas y/o laminadas con un gradiente de funcionalidad. A fin de obtener una buena deposición de cerámica es necesario el uso de electrodos de elevada conductividad. Los metales con alta conductividad se utilizan comúnmente para esta aplicación. En este trabajo se propone el uso de polímeros de bajo coste, no conductores, como electrodos. Para aumentar su conductividad, los electrodos de polímero se recubrieron mediante sputtering con oro o carbono. El aumento de la conductividad obtenido permite la deposición de diversas cerámicas ampliamente utilizadas en la productos dentales y ortopédicos, como son la zirconia estabilizada con ytria (Y-TZP), la alúmina o la hidroxiapatita (HA). The interest in electrophoretic deposition (EPD) of ceramics or ceramic composites has widely increased due to the possibility to create green bodies with several interesting characteristics for biomedical applications, for instance porous and/or laminated functionally graded ceramics. In order to get a good ceramic deposition the use of high conductive electrodes is required. Metals with high conductivity are commonly used for this purpose. In this work, the use of low cost non conductive polymers as electrodes is proposed. To increase their conductivity, these polymer electrodes were sputtered with gold or carbon. The conductivity increase obtained by the sputtering allowed the deposition of different ceramics widely used in the dental and orthopaedic industry, as yttria stabilised tetragonal zirconia particles (Y-TZP), alumina and hydroxyapatite (HA).

Despite remarkable progress made in the fields of antiviral therapy and virological laboratory diagnosis, infections with the human cytomegalovirus (CMV) still pose considerable problems in certain patient groups. The variety of available test methods - mostly not standardised - with their different test characteristics, sample types etc. is often confusing for the clinician. There is often great uncertainty as to whether a given laboratory result is pathognomonic. In addition, not only is the diagnostic repertoire growing constantly - for instance through genome quantification and measurement of virus-specific T lymphocytes - but also the available antiviral therapeutic options with the need for adequate surveillance. This paper gives an up-to-date overview about the available diagnostic means with their specific advantages and disadvantages. Concrete recommendations regarding a rational and comprehensive, yet economic approach to CMV diagnosis have to be targeted at the individual patient group and specific diagnostic problem; this is beyond the scope of this paper and the reader is referred to the pertinent expert groups' publications. This review article deals with general and fundamental aspects.

A secreted kinase from the parasitic protozoan, Toxoplasma gondii, is shown to cooperate with a phylogenetically related pseudokinase to phosphorylate and inactivate a mouse resistance protein of the IRG system., The ability of mice to resist infection with the protozoan parasite, Toxoplasma gondii, depends in large part on the function of members of a complex family of atypical large GTPases, the interferon-gamma-inducible immunity-related GTPases (IRG proteins). Nevertheless, some strains of T. gondii are highly virulent for mice because, as recently shown, they secrete a polymorphic protein kinase, ROP18, from the rhoptries into the host cell cytosol at the moment of cell invasion. Depending on the allele, ROP18 can act as a virulence factor for T. gondii by phosphorylating and thereby inactivating mouse IRG proteins. In this article we show that IRG proteins interact not only with ROP18, but also strongly with the products of another polymorphic locus, ROP5, already implicated as a major virulence factor from genetic crosses, but whose function has previously been a complete mystery. ROP5 proteins are members of the same protein family as ROP18 kinases but are pseudokinases by sequence, structure, and function. We show by a combination of genetic and biochemical approaches that ROP5 proteins act as essential co-factors for ROP18 and present evidence that they work by enforcing an inactive GDP-dependent conformation on the IRG target protein. By doing so they prevent GTP-dependent activation and simultaneously expose the target threonines on the switch I loop for phosphorylation by ROP18, resulting in permanent inactivation of the protein. This represents a novel mechanism in which a pseudokinase facilitates the phosphorylation of a target by a partner kinase by preparing the substrate for phosphorylation, rather than by upregulation of the activity of the kinase itself., Author Summary Toxoplasma gondii is an intracellular parasitic protozoan infecting about a third of humankind. Humans, however, are unlikely to be important hosts in terms of the evolution of the parasite because, for completion of the parasite sexual cycle, the infected animal must be eaten by a cat. Therefore, important intermediate hosts for Toxoplasma are species like mice that are often preyed on by cats. Mice use an intracellular resistance mechanism, the IRG proteins, against Toxoplasma. In turn, Toxoplasma appears to have evolved a virulence factor, a protein kinase called ROP18, that inactivates IRG proteins. We show that ROP18 does not act alone. It needs help from the ROP5 pseudokinases, proteins related to ROP18 but without enzymatic activity. ROP5 pseudokinases assist ROP18 by binding to the IRG proteins, holding them inactive, and laying them open to enzymatic attack and likely permanent inactivation by the ROP18 kinase. This mechanism illustrates the principle that members of an enzyme family can lose their enzymatic activity and evolve into regulators or co-factors for the active members.

The insulation of domestic markets through standards-related activities, while not new, has become newsworthy as attempts are made to achieve economic balances among nations. Governmental negotiations addressing reasons for trade imbalances have included such technical barriers to trade as standards, testing, and certification systems. The discussions of these non-tariff barriers illustrate the effectiveness of standards and their implementation in protecting the position of domestic products from imports. Elimination of these insulators and related systems on a country-by-country basis provides opportunities for increasing exports to each country. Pressure to do so demonstrates that today's markets are worldwide in scope.

We study the dynamics of periodically kicked many-body systems away from the high-frequency regime, and discuss a family of Floquet systems where the notion of prethermalization can be naturally extended to intermediate and low driving frequencies. We investigate numerically the dynamics of both integrable and nonintegrable systems, and report on the formation of a long-lived prethermal plateau, akin to the high-frequency limit, where the system thermalizes with respect to an effective Hamiltonian captured by the inverse-frequency expansion (IFE). Unlike the high-frequency regime, we find that the relevant heating times are model dependent: we analyze the stability of the prethermal plateau to small perturbations in the drive period and show that, in a spin chain whose IFE is intractable, the plateau duration is insensitive to the perturbation strength, in contrast to a chain where the IFE admits the resummation of an entire subseries. Infinitesimal perturbations are enough to restore the ergodic properties of the system, and decrease residual finite-size effects. Although the regime where the Floquet system leaves the prethermal plateau and starts heating up to infinite temperature is not captured by the IFE, we provide evidence that the evolved subsystem is described well by a thermal state with respect to the IFE Hamiltonian, with a gradually changing temperature, in accord with the eigenstate thermalization hypothesis.