Subterahertz collective dynamics of polar vortices.

The collective dynamics of topological structures1-6 are of interest from both fundamental and applied perspectives. For example, studies of dynamical properties of magnetic vortices and skyrmions3,4 have not only deepened our understanding of many-body physics but also offered potential applications in data processing and storage7. Topological structures constructed from electrical polarization, rather than electron spin, have recently been realized in ferroelectric superlattices5,6, and these are promising for ultrafast electric-field control of topological orders. However, little is known about the dynamics underlying the functionality of such complex extended nanostructures. Here, using terahertz-field excitation and femtosecond X-ray diffraction measurements, we observe ultrafast collective polarization dynamics that are unique to polar vortices, with orders-of-magnitude higher frequencies and smaller lateral size than those of experimentally realized magnetic vortices3. A previously unseen tunable mode, hereafter referred to as a vortexon, emerges in the form of transient arrays of nanoscale circular patterns of atomic displacements, which reverse their vorticity on picosecond timescales. Its frequency is considerably reduced (softened) at a critical strain, indicating a condensation (freezing) of structural dynamics. We use first-principles-based atomistic calculations and phase-field modelling to reveal the microscopic atomic arrangements and corroborate the frequencies of the vortex modes. The discovery of subterahertz collective dynamics in polar vortices opens opportunities for electric-field-driven data processing in topological structures with ultrahigh speed and density.

Terahertz-Range Polar Modes in Domain-Engineered BiFeO_{3}.

The dielectric permittivity and properties of electrically active lattice resonances in nanotwinned BiFeO_{3} crystals have been studied theoretically using an earlier established interatomic potential. The results suggest that an array of 71° domain walls with about 2-5 nm spacing enhances the static permittivity of BiFeO_{3} by more than an order of magnitude. This enhancement is associated with an electrically active excitation, corresponding to a collective vibration of pinned domain walls at a remarkably high frequency of about 0.3 THz.

Tuning of Polar Domain Boundaries in Nonpolar Perovskite.

Domain boundaries in ferroic materials are found to have various physical properties not observed in the surrounding domains. Such differences can be enhanced and bring promising functionalities when centrosymmetric nonpolar materials encounter polar domain boundaries. In this work, a tunable polar domain boundary is discovered in an antiferroelectric single crystal. Under a small stress or electric field, the density, volume, and polarity of the boundaries are successfully controlled.

Disorder in Strontium Barium Niobate: Local Structure, Phonons, and Polarization Dynamics.

The main representative of the tetragonal tungsten bronze family, strontium barium niobate, has been recently studied by the scattering and spectroscopic techniques [diffuse scattering (DS), Raman, infrared, and high-frequency dielectric spectroscopies] to decipher the nature of its ferroelectric-relaxor transformation tuned by composition. DS revealed that mesoscopic range ordered correlations along the polar axis are presented in the crystal, being less organized in the relaxor compositions with higher Sr content. For these compositions, transverse polar correlations are found to be anisotropic. Pair distribution function experiments and first-principle calculations in several compositions showed a concomitant new peak around ~6.5 Å, which develops on cooling and cannot be explained by the current structural models with long-range incommensurate oxygen tilts but with a short-range ordered tilt arrangement. This relates with the development of the macroscopic polarization, tightly linked to the structure, and shows two different contributions related to the two different crystallographic sites for the ferroactive Nb atom, recalling a picture of two independent polarization networks showing disparate dynamics, temperature behavior, and correlation lengths. Cationic substitution in different channels affects mainly the relaxations. Above the MHz range, all members of the solid solutions show three main relaxations, whose temperature dependence is unalike, due to the distinct correlation lengths and nature of the processes. On increasing Sr content, the frequencies are higher, and the contribution to the permittivity of excitations at GHz-THz ranges gets stronger. A soft anharmonic central mode at THz range is the characteristic for all the compositions, together with the slowing down of a relaxation at GHz-MHz ranges, revealing the coexistence of displacive and order-disorder mechanisms of the ferroelectric phase transition in these solid solutions.

Influence of the type of neoplasm and treatment on the survival of patients with malignant spinal tumours.

INTRODUCTION: The skeletal system is the third most frequent (after lungs and liver) seat of metastases, and metastatic tumours are the most common type of bone malignancies. The aim of the study was to evaluate the influence of the type of neoplasm and method of treatment on the survival of patients with malignant spinal tumours. MATERIALS AND METHODS: A retrospective analysis of 452 patients operated on between 2000 and 2004 in the Orthopaedic Surgery Hospital in Piekary Slaskie revealed a group of 203 patients whose histopathologic examination confirmed the presence of neoplastic foci in the spine. Data concerning the type of surgery and tumour location in 139 patients with the most frequent malignant spinal tumors were analyzed. The other information concerning subsequent treatment was analyzed in the Maria Sklodowska-Curie Oncology Centre and Institute in Gliwice. Patient deaths were verified in the Regional Administrative Office in Katowice. RESULTS: The most common types of neoplasms producing spinal metastases (in patients who underwent surgery) were: breast cancer, prostatic adenocarcinoma and kidney cancer. Multiple myeloma was the most frequent diagnosis among primary bone neoplasms. The survival of patients with multiple myeloma was statistically longer than the survival of patients with renal, breast and prostatic cancer metastases. It appears that, in the absence of contraindications, the best treatment for patients with spinal metastases is locally radical surgery combined with radiation therapy (a single teleradiotherapy session of 8 Gy). This treatment resulted in a statistically significant prolongation of life of the patients. CONCLUSIONS: The length of survival of patients with malignant spinal metastases is influenced by the type of neoplasm and locally radical surgery combined with palliative radiation therapy.

Determination of chemical ordering in the complex perovskite Pb(Cd1/3Nb2/3)O3.

Pure-phase Pb(Cd1/3Nb2/3)O3 (PCN) single crystals and ceramics with a complex perovskite structure are synthesized for the first time. The local chemical ordering in PCN has been investigated by X-ray diffraction (including diffuse scattering) and Cs-corrected transmission electron microscopy experiments. It is concluded that the PCN samples have large coherent chemical ordering regions that even extend to the long range, and the ordering model is consistent with ß-type chemical ordered regions. The antiphase domain boundaries were also observed. Two dielectric anomaly peaks were found in these two types of samples, one of which indicates possible relaxor behaviour. The novel structure of the completely ordered regions and its relationship with the electrical properties make PCN a unique material for the fundamental understanding of chemically substituted perovskites.

[Arthroscopy of the knee joint--history and present state]. / Artroskopia stawu kolanowego--historia i terazniejszosc.

This study presents, based on the literature, data and own experience, the history, the development and current trends of the knee joint arthroscopy.

Polarized cluster dynamics at the paraelectric to ferroelectric phase transition in BaTiO3.

The mechanism of the prototype ferroelectric phase transition in BaTiO(3) is a matter of intense debate and to a large extent still wrapped in mystery. Precursor phenomena in the form of polarized clusters in paraelectric BaTiO(3) are by now believed to represent a key step into the ferroelectric phenomenon. The determination of a slower dynamics of cluster polarization flipping along with a faster order-disorder Ti hopping mode among <111> off-center sites suggests coexistence, instead of mutual exclusion, of displacive and order-disorder types, initially proposed as distinct models. However, no clear picture of the transition state has been proposed so far, which is able to provide insight into the coexistence of the paraelectric and ferroelectric phenomena. Here, by means of a dedicated molecular dynamics approach, we provide a detailed atomistic picture of intermediate regions along the transition. Therein, different time and length scales coexist as they characterize different portions of the same material. From an imbalance of dynamically and more statically polarized clusters in this highly inhomogeneous intermediate, a symmetry breaking step naturally results. Further, we find that ferroelectric nanodomains may host antiferroelectric defects, which appear as an intrinsic feature of the growing BaTiO(3) ferroelectric material.

[Realloplasty of the acetabular component of the hip joint endoprosthesis without mechanical support systems]. / Realloplastyka komponentu panewkowego endoprotezy stawu biodrowego bez uzycia mechanicznych systemów wzmacniajacych.

This work presents the tactics of surgical procedures in 40 patients who underwent revision of the hip joint due to isolated loosening of the acetabular component of the endoprosthesis. The studied group were operated between 2004 to 2006 without the use of mechanical support systems. Realloplasty of the acetabular component involved the evaluation of: etiology of acetabular loosening, concomitant diseases in the operated patients, and the grade of acetabular defects according to Paprosky's classification. In this work we analyze the type of both the loosened acetabulum and that used in revision, and discuss complications. Finally, we present a clinical evaluation of the operated patients according to Harris scale before revision surgery and six and twelve months after, with good early results.

[Early clinical and radiological results following cervical disc arthroplasty]. / Wczesne wyniki kliniczne i radiologiczne protezoplastyki krazka miedzykregowego w odcinku szyjnym.

The aim of this study was to assess early results of anterior cervical decompression and arthroplasty for cervical disc disease. The results of operations of 32 patients (43 instrumented levels) were examined to assess clinical outcome, the restoration of disc height, postoperative lordosis, mobility of instrumented segment and complication rate. Clinical outcome evaluated with VAS score improved from 7.5 preoperatively to 2.7 post operation. There was improvement in disc height measured by Tureyen method of 48%, 5 degree restoration of lordosis per segment and average 5 degree mobility of operated segment. In two cases spontaneous fusion occurred. There were no loosening of prosthesis observed. Overall the study shows that early results of arthroplasty are clinically efficient and safe as fusion. Assessment of biomechanical advantages of arthroplasty demands further observation to compare if long-term results are superior to fusion.

[Assessment of radiological results of anterior cervical discectomy with different fusion cages]. / Ocena radiologicznych wyników leczenia operacyjnego dyskopatii szyjnej z zastosowaniem róznych typów wszczepów miedzytrzonowych.

The purpouse of this study was to compare results of anterior cervical decompression and fusion for cervical disc disease with 2 different interbody devices: titanium cylinder-design cage and carbon box-design cage. The results of operations of 46 patients (60 instrumented levels) divided in to groups according to implant type were examined to asses the restoration of disc height, clinical outcome, bony fusion and complication rate. In the cylinder-design cage group average postoperative restoration of disc height was 72% but with narrowing rate of 26% in follow up. In the carbon box group postoperative disc height restoration was 51% with narrowing in follow up to 6%. Clinical outcome was comparable in both groups and loss of disc height in cylinder-design cage group had no effect on clinical outcome. There were 2 cases of pseudoarthrosis in cylinder cage group. Overall the study shows better radiological outcome of carbon box-design cages in comparison to cylinder design cages with no influence on clinical effect.

[Frequency of neurological complications connected with transpedicular spine fixation]. / Czestosc wystepowania powiklan neurologicznych zwiazanych z transpedikularna stabilizacja kregoslupa.

To asses a frequency of neurological complications concerned with transpedicular spine fixation 1127 inserted transpedicular screws were reviewed. Penetration of pedicle was found in 5.5% of inserted screws. Radicular symptoms accompanied 0.8% of screw insertions. Complications were concerned only to medial or subpedicular penetrations. Highest number of potentially hazardous medial wall penetrations was found in lower lumbar spine. Treatment consisted of removal and repositioning of screws but with direct visualisation in cases with self tapping screws systems. The results shows that rate of neurological complications during transpedicular fixation is small and procedure is relatively safe.

[Operative treatment of sacral tumors]. / Leczenie chirurgiczne guzów kosci krzyzowej.

The paper presents posterior access to sacrum according to Gennari used for resection of sacral tumors. Technique was compared with other operative techniques described in literature. The advantage of this method is the low risk of postoperative infection and limited operative technique.