Deformed Skyrme Crystals

The Skyrme crystal, a solution of the Skyrme model, is the lowest energy-per-charge configuration of skyrmions seen so far. Our numerical investigations show that, as the period in various space directions is changed, one obtains various other configurations, such as a double square wall, and parallel vortex-like solutions. We also show that there is a sudden "phase transition" between a Skyrme crystal and the charge 4 skyrmion with cubic symmetry as the period is gradually increased in all three space directions.Comment: 13 pages, 6 figures. To be published in JHE

Geometrically Induced Gauge Structure on Manifolds Embedded in a Higher Dimensional Space

We explain in a context different from that of Maraner the formalism for describing motion of a particle, under the influence of a confining potential, in a neighbourhood of an n-dimensional curved manifold M^n embedded in a p-dimensional Euclidean space R^p with p >= n+2. The effective Hamiltonian on M^n has a (generally non-Abelian) gauge structure determined by geometry of M^n. Such a gauge term is defined in terms of the vectors normal to M^n, and its connection is called the N-connection. In order to see the global effect of this type of connections, the case of M^1 embedded in R^3 is examined, where the relation of an integral of the gauge potential of the N-connection (i.e., the torsion) along a path in M^1 to the Berry's phase is given through Gauss mapping of the vector tangent to M^1. Through the same mapping in the case of M^1 embedded in R^p, where the normal and the tangent quantities are exchanged, the relation of the N-connection to the induced gauge potential on the (p-1)-dimensional sphere S^{p-1} (p >= 3) found by Ohnuki and Kitakado is concretely established. Further, this latter which has the monopole-like structure is also proved to be gauge-equivalent to the spin-connection of S^{p-1}. Finally, by extending formally the fundamental equations for M^n to infinite dimensional case, the present formalism is applied to the field theory that admits a soliton solution. The resultant expression is in some respects different from that of Gervais and Jevicki.Comment: 52 pages, PHYZZX. To be published in Int. J. Mod. Phys.

First direct observation of the Van Hove singularity in the tunneling spectra of cuprates

In two-dimensional lattices the electronic levels are unevenly spaced, and the density of states (DOS) displays a logarithmic divergence known as the Van Hove singularity (VHS). This is the case in particular for the layered cuprate superconductors. The scanning tunneling microscope (STM) probes the DOS, and is therefore the ideal tool to observe the VHS. No STM study of cuprate superconductors has reported such an observation so far giving rise to a debate about the possibility of observing directly the normal state DOS in the tunneling spectra. In this study, we show for the first time that the VHS is unambiguously observed in STM measurements performed on the cuprate Bi-2201. Beside closing the debate, our analysis proves the presence of the pseudogap in the overdoped side of the phase diagram of Bi-2201 and discredits the scenario of the pseudogap phase crossing the superconducting dome.Comment: 4 pages, 4 figure

In-plane optical spectral weight transfer in optimally doped Bi2_{2}Sr2_{2}Ca2_{2}Cu3_{3}O10_{10}

We examine the redistribution of the in-plane optical spectral weight in the normal and superconducting state in tri-layer \bbb (Bi2223) near optimal doping ($T_c$ = 110 K) on a single crystal via infrared reflectivity and spectroscopic ellipsometry. We report the temperature dependence of the low-frequency integrated spectral weight $W(\Omega_c)$ for different values of the cutoff energy $\Omega_c$. Two different model-independent analyses consistently show that for $\Omega_c$ = 1 eV, which is below the charge transfer gap, $W(\Omega_c)$ increases below $T_c$, implying the lowering of the kinetic energy of the holes. This is opposite to the BCS scenario, but it follows the same trend observed in the bi-layer compound \bb (Bi2212). The size of this effect is larger in Bi2223 than in Bi2212, approximately scaling with the critical temperature. In the normal state, the temperature dependence of $W(\Omega_c)$ is close to $T^2$ up to 300 K

Vortex Imaging in the pi-Band of Magnesium Diboride

We report scanning tunneling spectroscopy imaging of the vortex lattice in single crystalline MgB2. By tunneling parallel to the c-axis, a single superconducting gap (Delta = 2.2 meV) associated with the pi-band is observed. The vortices in the pi-band have a large core size compared to estimates based on Hc2, and show an absence of localized states in the core. Furthermore, superconductivity between the vortices is rapidly suppressed by an applied field. These results suggest that superconductivity in the pi-band is, at least partially, induced by the intrinsically superconducting sigma-band.Comment: 4 pages, 3 figure

Direct simulation of ion beam induced stressing and amorphization of silicon

Using molecular dynamics (MD) simulation, we investigate the mechanical response of silicon to high dose ion-irradiation. We employ a realistic and efficient model to directly simulate ion beam induced amorphization. Structural properties of the amorphized sample are compared with experimental data and results of other simulation studies. We find the behavior of the irradiated material is related to the rate at which it can relax. Depending upon the ability to deform, we observe either the generation of a high compressive stress and subsequent expansion of the material, or generation of tensile stress and densification. We note that statistical material properties, such as radial distribution functions are not sufficient to differentiate between different densities of amorphous samples. For any reasonable deformation rate, we observe an expansion of the target upon amorphization in agreement with experimental observations. This is in contrast to simulations of quenching which usually result in denser structures relative to crystalline Si. We conclude that although there is substantial agreement between experimental measurements and most simulation results, the amorphous structures being investigated may have fundamental differences; the difference in density can be attributed to local defects within the amorphous network. Finally we show that annealing simulations of our amorphized samples can lead to a reduction of high energy local defects without a large scale rearrangement of the amorphous network. This supports the proposal that defects in amorphous silicon are analogous to those in crystalline silicon.Comment: 13 pages, 12 figure

Parameter identification in a semilinear hyperbolic system

We consider the identification of a nonlinear friction law in a one-dimensional damped wave equation from additional boundary measurements. Well-posedness of the governing semilinear hyperbolic system is established via semigroup theory and contraction arguments. We then investigte the inverse problem of recovering the unknown nonlinear damping law from additional boundary measurements of the pressure drop along the pipe. This coefficient inverse problem is shown to be ill-posed and a variational regularization method is considered for its stable solution. We prove existence of minimizers for the Tikhonov functional and discuss the convergence of the regularized solutions under an approximate source condition. The meaning of this condition and some arguments for its validity are discussed in detail and numerical results are presented for illustration of the theoretical findings

Comparison between a prenatal sonographic scoring system and a clinical grading at delivery for Placenta Accreta Spectrum disorders

OBJECTIVE: Placenta Accreta Spectrum (PAS) disorders have become a major iatrogenic obstetric complication worldwide. Data on the accuracy of ultrasound examination diagnosis are limited by incomplete confirmation and variability in the description of the different grades of PAS at delivery. The aim of this study was to compare our prenatal routine sonographic screening and diagnostic scoring system with a standardized clinical grading system at birth in patient at risk of PAS. STUDY DESIGN: This is a retrospective cohort study of 607 pregnant patients with at least one prior cesarean delivery between December 2013 and December 2018. All patients were assessed for PAS using our institutional prenatal sonographic scoring system and the corresponding ultrasound findings were compared with those of a standardized clinical intra-operative macroscopic grading system of the degree of accreta placentation at vaginal birth or laparotomy. RESULTS: PAS was diagnosed clinically at birth in 50 (8.2%) cases, 17 of which were confirmed by histopathology. A low (score ≤ 5), medium (score 6-7), high (score ≥ 8) probability for PAS was reported in 502, 61 and 44 cases, respectively. The probability score increased significantly (p < .001) in women ≥2 prior cesarean deliveries, with an anterior low-lying/placenta previa, with absent clear space, increased in retroplacental vascularity and with the size and numbers of lacunae. The number of cases classified clinically as grade 1 (non-PAS) and 3 (adherent PAS) was significantly (p < .001) lower in women with a high probability score whereas the rates of the other grades was significantly (p < .001) higher. The widest discrepancy between ultrasound probability score and clinical grade was found for grade 2 which, describes a partial placental adherence and grades 4 and 5 which, refer to placental percreta which describes tissue having invade trough the uterine serosa and beyond. CONCLUSIONS: Both ends of the spectrum of accreta placentation remain difficult to diagnose antenatal and clinically at birth, in particular when no histopathologic confirmation is available. There is a need to develop ultrasound accuracy score systems that can differentiate between the different grades of PAS and which are validated by standardized clinical and pathology protocols

The electronic specific heat in the pairing pseudogap regime

When pairing correlations in a quasi two dimensional electron system induce a pseudogap in the single particle density of states, the specific heat must also contain a sizeable pair contribution. The theoretically calculated specific heat for such a system is compared to the experimental results of Loram and his collaborators for underdoped YBa_2Cu_3O_{6+x} and La_{2-x}Sr_{x}CuO_4 samples. The size and doping dependence of the extracted pseudogap energy scale for both materials is comparable to the values obtained from a variety of other experiments.Comment: 4 pages, 5 eps figure

Accurate mass measurements of 26^{26}Ne, 26−30^{26-30}Na, 29−33^{29-33}Mg performed with the {\sc Mistral} spectrometer

The minuteness of the nuclear binding energy requires that mass measurements be highly precise and accurate. Here we report on new measurements $^{29-33}$Mg and $^{26}$Na performed with the {\sc Mistral} mass spectrometer at {\sc Cern}'s {\sc Isolde} facility. Since mass measurements are prone to systematic errors, considerable effort has been devoted to their evaluation and elimination in order to achieve accuracy and not only precision. We have therefore conducted a campaign of measurements for calibration and error evaluation. As a result, we now have a satisfactory description of the {\sc Mistral} calibration laws and error budget. We have applied our new understanding to previous measurements of $^{26}$Ne, $^{26-30}$Na and $^{29,32}$Mg for which re-evaluated values are reported.Comment: submitted to Nuclear Physics